Note: Descriptions are shown in the official language in which they were submitted.
~1~6~48
TITLE OF THE INVENTION:
Process for the Preparation of Gel for Use
as Cooling Medium
BACKGROUND OF THE INVENTION:
Field of the Invention;
The present invention relates to a process for
the preparation of a gel which is used as a cooling medium,
and more particularly to a process for the preparation
of a gel having superior properties over those of the
known similar gel materials when used as a cooling medium.
Prior Art;
A variety of gel compositions have hitherto been
proposed to be used as cooling media and some of them
are applied for practical uses. Such a gel is referred
to as a cooling gel, chilling gel, coldness-keeping
gel, coldness-keeping heat transfer medium, colloidal
coolant, coldness-keeping means, coolant composition or
Ice-non (Trade Name), i.e. ice pillow. However,
these known coolant gels are not satisfactory in properties
or involves troublesome or difficult steps in preparation,
as will be summarized in items (1) to (9) below.
(1) The easiest and well-known process for the
preparation of a water-containing coolant gel is the
~,~
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lh'7~
preparation of ayar gel. This process comprises the
step of dissolving agax in boiling water or hot water of
80 to 94C to obtain a solution containing not less than
0.1 wt~, for example 1 to 10 wt~ of agar and the step of
allowing the solution to be cooled to the room temperature,
whereby a water-containing gel (hydrogel) having a water
content of about 90 to 99 wt% is easily prepared. However,
when the thus prepared agar gel is used as a substituting
material for ice contained in an ice pillow or an ice
bag after being cooled in an ice box of a refrigerator,
the agar gel is poor in elesticity and too crum~ly to
provide a user with a comfortable touch or feeling but to
give strange and uncomfortable feeling with additional
disadvantage of collapse.
(2) Although ~-carrageenan including a structure
similar to agar, such as D-galactose type structure, 3,6-
anhydrogalactose type structure or a partial sulfuric
ester type structure of polygalactose, forms readily
a hydrogel containing about 90 to 97 wt% of water, this
gel is too soft and crumbly. It has been found and
emphasized that the mechanical strength of this gel may
be improved by immersing the same into an aqueous solution
of potassium chloride or calcium chloride by many personsO
However, the product obtained by such an after-treatment
is too crumbly for practical use, as well as the agar
gel.
~7~J~
It is also well-known in the art to combine the
carrageenan with a Locust Bean Gum. However, not much
effect can be expected by this combination.
(3) It has also been well-known that another
type hydrogel having a water content of 97 to 98 wt% can be
obtained from an aqueous solution of a sodium salt of
alginic acid including a D-manuronic acid type structure
or an L-gluronic acid type structure by dropwisely adding
to or immersing in an aqueous solution of a water-soluble
salt of calcium, barium, zinc, copper, iron, aluminium
or nickel or another acidic solution having a pH value
of 2.5 to 5. However, such a hydrogel isl as is well-
known, easily to be broken and crumbly with additional
disadvantage of displeased odor.
(4) The known gelatine gel merely exhibits a
soft jelly-like appearance at a concentration of gelatine of
2 to 15 wt%. However, although a gel obtainable by using
a solution containing more than 15 wt%, particularly more
than 30 wt%, of gelatine forms a strong mass, this gel is
rigid and lacks elasticity with additional disadvantages
that the water-content thereof is low and that it generates
glue-like odor.
(5) KONNYAKU (devil's tongue) including a
D-mannose structure and a D-glucose structure is the
most advantageous amongst a number of natural gels,
including gelatine, bean-curd, starch paste, agar, alginic
3 --
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acid, curdlan, carrageenan, furcellaran and pectin,
in that it resists deformation and has sufficient
elasticity and resiliency and in that a gel having very
high water content of up to 97 wt% may be prepared
therefrom. However, a gel prepared therefrom tends to
be disintegrated rapidly after being repeatedly used
as a coolant gel. In detail, although KONNYAKU is
relatively stable and excellent in heat resistant
property as far as it is immersed into an aqueous
alkaline solution containing calcium ions, the gel is
changed to a pasty form as the separation and
maldistribution of lime are accelerated during the
repeated cycles of cooling (freezing) and melting.
(6) It has been proposed to use an iron salt,
chromium salt, aluminium salt, lead salt, barium salt or
tin salt of carboxymethyl cellulose (sodium cellulose
glycolate, hereinafter referred to as CMC). However,
a gel obtainable from any of these materials is a soft
and weak paste-like gel having a structure which is
susceptible to disintegration (In this connection,
reference should be made to Japanese Patent Publication
No. 11210/1970). Although the gel obtained by the
reaction between borax (sodium tetraborate decahydrate)
and starch or CMC has been widely known, this gel is
soft and weak, as well.
(7) It has been already well-known that
~ P'`~6~348
gelation occurs instantaneously when boric acid (or an
aqueous solution of boric acid~ or borax (or an aqueous
solution of borax) is added to an aqueous solution of
polyvinyl alcohol. However, the gel thus obtained
is so soft and weak that it is readily torn to pieces
only by pinching by fingers. Another disadvantage of
this gel is the syneresis phenomenon, i.e. separation
of contained water, during the repeated uses (See
Japanese Patent Publication No. 11210/1970).
In order to avoid hardening of a gel of polyvinyl
alcohol-borax system due to congeal of water content
in the gel when the gel is cooled in an ice-box of a
cooling box or refrigerator, it has been proposed a method
in which an aqueous solution of polyvinyl alcohol is added
with any of monohydric alcohols, polyhydric alcohols,
glucose or sucrose followed by the addition of borax to
be gelatinized. However, a gel prepared in accordance with
this proposal becomes weaker with additional disadvantage
that syneresis appears during the repeated uses (See
Japanese Patent Publication No. 19602/1971).
(8) Other various proposals have been made to
form gels from polyvinyl alcohol, including gelation by
the use of phenolic compounds, such as phenol, naphtol or
Congo Red, amino compounds or metals, such as titanium,
chromium or zirconium. However, all of the gels obtained
according to the prior proposals have disadvantages similar
~7~
to those of the aforementioned polyvinyl alcohol-borax
system gel (See Journal of the Chemical Society of
Japan, 72, 1058 (1951) and Japanese Patent Publication
Nos. 9523/1965 and 23204~1965).
(9) Also, gelation of polyvinyl alcohol
by the use of a cross-linking agent or copolymerizable
additive, such as aldehydes, dialdehydes, unsaturated
nitriles, diisocyanates, trimethylolmelamine~
epichlorohydrin, bis(~-hydroxyethyl)sulfone, polyacrylic
acid, dimethylol urea or maleic acid anhydride,
has been well-known in the art. However, notwithstanding
the additional treatment using an additional chemical
agent, it was difficult to obtain a strong gel having
high water content (In this connection, reference
should be made to Textile Res. J., (3)~ 189 (1962)
and the specification of British Patent No. 742,gO0 (1958)).
Many proposals have been previously made in
connection with the method of processing or treating
a gel obtained from polyvinyl alcohol. However,
these previously-made proposals have disadvantages
in operation or in properties of the resultant product,
as will be summarized in items (1) to (4) below.
(1) Although a wet or dried membrane may be
obtained by drying an aqueous solution of polyvinyl
alcohol in air, such a membrane is inferior in water-proof
1~L'7~ 8
property to form a soft and weak film having no integrity
when immerse~ in water. Accordingly, such a membrane may
be used for only limited applications (See Japanese
Patent Publication No. 9523/1965).
(2) The properties of a membrane obtained by
a method comprising the steps of adding an acid to an
aqueous suspension containing polyvinyl alcohol and
tetraethyl silicate and then drying in air, are
similar to those of the membrane obtained by the method
set forth in (1) above. As a modification of the ~ethod~
there has been proposed a method wherein an aqueous
suspension added with an acid is freeze-dried~ Howevert
the membrane prepared by the modified method becomes
weaker to such an extent that it becomes scarcely possible
to mold the same (In this connection, reference should be
made to Japanese Patent Publication Nos. 11311/1980 and
30358/1980).
(3) A gelation method wherein an aqueous
solution of polyvinyl alcohol is exposed to irradiation
of Cobalt 60 (gamma-ray), is also well-known. A special
equipment, i.e. an equipment for irradiating radioactive
rays, is required in practice of this known method, and
additionally the cost for such an irradiation is expensiveO
Yet, a gel obtained in accordance with this method is
often so weak that a further hardening treatment or a
secondary hardening step is indispensable. Accordingly, a
~7~
gel obtained by this method cannot be applied for general
uses other than special use in which a highly viscous
liquid or soft gel is desired, for example, for use as
an artificial vitreous body for filling an intraocular
cavity ~In this connection, reference should be made to
J. Material Sci., 1974, 1815 and Japanese Patnet Provisional
Publication No. 55647/1975).
t4) It has been well-known since a long time ago
that a gel is formed after an aqueous solution of
polyvinyl alcohol is stored for one day to one weekO
However, such a gel is as weak as the agar gel, and
may be dissolved again merely by agitating vigorously,
by agitating after adding with water or by heating at
some extent.
OBJECTS AND SUMMARY OF THE INVENTION-
A primary object of this invention is to providea process for the preparation of a gel for use as a
cooling medium which is strong and highly elastic, free
of unpleasant odor and which resists disintegration and
provides a comfortable touch.
Another object of this invention is to provide a
process for the preparation of a gel for use as a
cooling medium and having excellent insolubility in water.
A further object of this invention is to
provide a process for the preparation of an inexpensive
and yet stable gel for use as a cooling medium so that the
~ 7G~
gel structure is not disintegrated or broken even by the
attack of a freezing point depressing agent, such as
ethylene glycol.
A further object of this invention is to provide
a process for the preparation of a gel of high water
content for use as a cooling medium.
A still further object of this invention i5 to
provide a process for the preparation of a gel for use as
a cooling medium, which resists freezing even when it is
placed in an ice-box of a cooling box Qr freezing box~
Additional object of this invention is to
provide a process for the preparation of a gel for use
as a cooling mediumt which may be molded to have desired
shape and dimensions and immediately used as a final
product without the need of shaping operation, or may be
molded into a block and then shaped, for example by cutting,
to have desired shape and dimensions.
The above and other objects of this invention
will become apparent from the following description of
the invention.
The process for the preparation of a gel for
use as a cooling medium, according to this invention,
comprises the steps of casting an aqueous solution or
suspension containing a polyvinyl alcohol having a degree
of hydrolysis of not less than 95 mol% and a viscosity
average pol~merization degree of not less than 1500 into
~76~
a mold having desired shape and dimensions, cooling the
cast aqueous solution to a temperature of not higher
than - (minus) 6C, and then dehydrating without thawing
the cooled mass of the cast aqueous solution in vacuum
until the percentage dehydration rate reaches not less
than 5 wt~.
DESCRIPTION OF THE INVENTION:
The present invention will now be described more
in detail hereinafter.
According to the invention, an aqueous solution
of polyvinyl alcohol is cooled followed by dehydration
to prepare a gel excellent in mechanical strengths and high
in water content. The process of this invention does
not involve any additional pre-treatment or after-treatment,
i _ secondary hardening step, and the use of an acid,
alkali, radical sources, irradiation of radioactive rays,
organic solvents, chemical reagents or inorganic solvents
other than water, otherwise essential in the gelation step
of prior art process for making a gel of synthetic high
polymer, is not essential at the gelation or pre-treatment
step. Yet, the gel obtainable by the process of this
invention may contain water at high content and has rubber-
like elasticity and satisfactory mechanical strengths
required for a material suited for use as a cooling medium
or coolant gel.
As has been described hereinbefore, it has been
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well-known in the art that an aqueous solution of polyvinyl
alcohol forms a gel after being stored at a temperature
of from 0 to 30C for one day to one week. However, the
resultant gel is crumbly similarly to a gel of agar,
and yet unstable such that it is dissolved again merely
by agitating vigorously, by agitating after adding with
additional water or by heating at some extent. On
the contrary, the gel obtianed by the process of this
invention is insoluble in water or warm water to be
distinctive from the known gel as aforementioned. This
means that the gel provided by the process of this invention
is novel and distinguishable from the known gel prepared
from an aqueous solution of polyvinyl alcohol, and the
gel obtained according to this invention must be formed
by a different mechanism and exhibits a patentably
different flmction.
The polyvinyl alcohol used in the process of
this invention should have a degree of hydrolysis of not
less than 95 mol%, preferably not less than 97 mol%. If
a polyvinyl alcohol having a degree of hydrolysis of
from 80 to 88 mol~, particularly lower than 85 mol~, is
used, only a weak gel is formed to fail to attain the
objects of this invention.
The polyvinyl alcohol used in the process of
this invention should have a viscosity average polymeri~ation
degree of not less than 1500. If not, only a weak gel
~7~
is formed. In the presen~ invention, a polyvinyl alcohol
having a polymerization degree of from about 1500 to
3300 may be used, and it is recommended that a commercially
available polyvinyl alcohol haivng a high polymerization
degree (for instance, having a polymerization degree of
from 1500 to 2600) be used without any treatment.
The initial step of the process of this invention
is the preparation of an aqueous solution of a polyvinyl
alcohol. Although the concentration of polyvinyl alcohol
is not critical, when the aqueous solution contains only
the polyvinyl alcohol the concentration may range within,
for example, 3 to 20 wt%, preferably 7 to 15 wt%.
Although the concentration may be raised, for example, up
to about 90 wt%, the viscosity of aqueous solution obtained
thereby exceeds 10,000 cP. at ambient temperature with
frequent increase in viscosity, resulting in gelation of
the solution. For this reason, the concentration of
polyvinyl alcohol in the solution should not be so
high to avoid difficulties in handling. On the other hand,
if the concentration of polyvinyl alcohol is lower
than 3 wt%, nevertheless a lower concentration may be
allowable, the time required for the subsequent drying step
which will be described hereinafter is prolonged, leading
to an increase in expense for the drying operation.
In the process of this invention, an aqueous
solution may contain solely a plyvinyl alcohol, as
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mentioned hereinabove. However, as will be described
hereinafter, an aqueous suspension containing, in addition
to the polyvinyl alcohol, a laminate structure clay
mineral including a fundamental module of a tri-strata
type (2:1 type) composite layer in an amount of not more
than five times as much as the weight of the polyvinyl
alcohol may be used. It should be noted here that a
certain combined effect obtained by the combined use of a
polyvinyl alcohol and a clay mineral has been already
known but this known combined effect is distinctive from
the effect of the present invention. More specifically~
it has been well-known that a gel is formed by adding
a very small amount, for instance 0.1 to 0.2 wt%, of a
polyvinyl alcohol to kaolin (kaolinite) or bentoniteO
~ased~on ~his principle, it has been tried to change the
ground of a track to have a character of avoiding the
tendency of becoming dusty by sprinkling a dilute
agueous solution of a polyvinyl alcohol on the surface
of the ground, or to improve the water-permeability or
water-retention property of the soil by sprinkling a
small amount of polyvinyl alcohol (dilute aqueous solution)
over the fields. It has been further known in the art to
accerelate the settling by coagulation of a clay present
in the form of colloidal particles by adding a small
amount of polyvinyl alcohol to muddy water. However, the
gels obtained in these known techniques are very crumbly
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such that they can be hardly distinguishable from the
common soil by appearance, and they are easily
disintegrated not only in water but also in the form of
dried powder (Reference should be made to J. Agr. Scio ~
47, 117 (1956)~. Although the distribution of soil or clay
particles or the size of soil lumps may be changed by
the addition of a polyvinyl alcohol, the resultant mass
is not distinguishable from the common soil or extremely
crumbly mud at least from the appearance thereof.
It has also been well-known that a hard membrane
can be formed by adding a clay to an aqueous solution of
polyvinyl alcohol followed by heating to be dried. However~
the thus formed membrane is hard and inferior in water-
absorptivity.
In contrast thereto, the gel containing a clay
mineral and prepared according to the process of this
invention is quite different from any of the known gels
mentioned above in that it is insoluble in water or warm
water. This means that a novel gel having an utterly
distinctive function or effect from those obtainable
by the gels prepared by the known combination of
polyvinyl alcohol and clay mineral by the process
according to this invention.
The gel containing a clay mineral and prepared
by the process of this invention includes a polyvinyl
alcohol in an amount of more than one fifth of the
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quantity of the used clay mineral. In other words, the
quantity of the clay mineral should be not more than 5
times of the amount of polyvinyl alcohol, preferably not
more than 3 times. If the ratio of the used polyvinyl
alcohol is less than one fifth as that of the clay mineral,
for instance the ratio is one tenth, the mechanical
strengths of the formed gel are reduced. On the other
hand, in the aforementioned techniques of improving the
ground or soils, the mixing ratio of a polyvinyl alcohol
to a clay mineral ranges from about L/1000 to 1/100.
The gel obtainable by the process of this invention cannot
be formed under such a condition. Although the
concentration of polyvinyl alcohol is not critical,
when the aqueous suspension contains the clay minerals,
the concentration of the polyvinyl alcohol may range
for example, 1 to 18 wt%, preferably 5 to 12 wt%o
The clay minerals used in the present invention
are laminate structure clay mineraLs, each including a
fundamental module of a tri-strata (2:1 type) composite
layer, the representative examples including
montmorillonite, vermiculite, illite, pyrophyllite and
talc. Another example is bentonite which is known
as a clay for common use and easily available
at low cost. This type of clay is an aggregate
of colloidal particles mainly composed of
montmorillonite formed by weathering of tuff, rhyolite
~7~
or similar rocks and may be found at various places in
Japan, for example, ~okkaido, Akita, Yamagata, Niigata,
Gunma and Shimane. Montmorillonite, the main component
of bentonite, is sometimes referred to as smectite,
and has a laminated structure including a fundamental ...
module made of a tri-strata (2:1 type) composite layer
which includes a layer of silica having a tetrahedron
structure, a layer of alumina or gibbsite having an
octahedron structure and a layer of silica having
a tetrahedron structure. Aluminium included in the
compos:ite layer is partially substituted by magnesium~
and water and a cation, such as sodium, potassium, calcium~
lithium, strontium, barium, aluminium, cesium, magnesi~n~
ammonium or hydrogen ion, are present in-between the
adjacent layers. A typical or approximate structure
of montmorillonite may be represented by the formula
5/3 gl/2)Si410(OH)2XH2 (K, Na~ Ca, H~ NH ,
Mg, Al, Li, Cs, Sr, Ba)y.
The ]homologues of montmorillonite obtained by
substituting t:he main constituting elements, i.e. aluminium
and silicon, of the composite layer by other elements are
well-known as nontronite (substituted by iron), hectorite
(substituted by magnesium), saponite (substituted by
magnesium), beidellite (substituted by aluminium),
sauconite (substituted by iron, magnesium and zinc) and
volkonskoite (substituted by chromiun). These are
- 16 -
referred to as montmorillonite minerals and frequently
found in said bentonite.
Bentonite contains about 50 to 85% of said
montmorillonite group minerals including montmorillonite~
and is mixed with other constituents, such as quartz,
feldspar, zeolite, kaolin, illite or mica, and
cristobalite. The composition of bentonite is varied~
but generally composed of about 42 to 65 wt~ of SiO2,
about 14 to 28 wt% of A12O3, about 11 to 23 wt% of
~2' abcut 1 to 25 wt% of MgO, up to 4 wt% of Fe2O3, up
to 3.5 wt% of Na2O, up to 3 wt% of CaO, about 0.1 to 0~7
wt% of K2O, up to 0.7 wt% of TiO2, up to 0.3 wt% of FeO
and up to 0.04 wt% of P2O5.
Although the Japanese Pharmacopeia stipulates
test methods and standards for the swelling property and
- the gel-forming capacity of bentonite, namely the capacity
for forming a pasty composite gel of magnesium oxide
and bentonite, the commercially available bentonite
- products (reagent grade) does not pass the standards
generally. However~ such a commercially available
bentonite product may be used in this invention without
any trouble. In order to improve the swelling property,
dispersibility or specific surface area of bentonite, it
is a common practice to treat raw bentonite with an
aqueous solution of sodium chloride, sodium hydroxide,
sodium carbonate, sodium nitrate, ammonium hydroxide,
~L~7~P~
sodium pyrophosphate, sodium hexamethaphosphate (i Oe D
an oligomer of sodium methaphosphoric acid), hydrochloric
acid, sulfuric acid or citric acid. Although it is not
essential to treat bentonite prior to use in the
present invention, the bentonite treated by any of the
aforementioned solutions may be conv~niently used in the
present invention.
In the present invention, nontmorillonite base
clay minerals other than bentonite may be used, the
examples being acidic clay (e.g. Kambara earth), activated
clay, Fuller's earth, Florida earth and Georgia earthO
Although each of these minerals contains a relatively
large amount of kaolinite and other amorphous clay minerals~
such as allophane, which are not included in the tri-
strata composite layer clay minerals analcgous tomontmorillonite, the main components thereof are
montmorillonite group minerals. The analogues of
montmorillonite will be described in detail hereinafter.
The clay minerals used in this invention include~
other than the montmorillonite group minerals, those having
tri-strata (2:1 type; structures analogous to the
structure of montmorillonite. A specific example of
such clay minerals is Toseki (pottery stone) mainly
composed of pyrophyllite and found at Go-to Mine in
Nagasaki, Mltsuishi Mine in Okayama and Honami and
Maiko Mines in Nagano. Such Toseki is distinguishable
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~7g~
from the montmoxillonite group clays in -that the content
of magnesium is extremely low and in that it exhibits little
swelling property. However, it resembles montmorillonite
in that the basic structure thereof includes modules
of silica/alumina/silica tri-strata (2:1 type)
composite layers.
The talc products found in Hyogo, Okayama,
Hiroshima, Yamaguchi and Nagasaki areas are differentiated
from montmorillonite in that the content of aluminium
therein is low and the content of magnesium therein is
considerably high. However, these talc products have
the laminated structures each including a fundamental
module of silica/alumina/silica tri-strata (2:1 type)
composite layers.
A variety of illite group clays are found in
Kumamoto and Niigata areas. These illite group clays
may be specifically classified depending on the contents
of iron, fluorine, magnesium or other elements, and may
be referred to as hydromica, glauconite, muscovite, micat
illite or other names. These clay minerals are
differentiated from montmorillonite in that the content
of potassium is high. Howeverl these clay minerals
have the silica/alumina/silica tri~strata (2:1 type)
modules.
Vermiculite which is widely spread in Brazil,
United States of America, particularly in Pennsylvania,
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and India has attracted public attention from long
time ago and referred to as ~IRIJISHI or HIRUZUNA in
Japan. The vermiculite is differentiated from
montmorillonite in that the content of magnesium is
particularly higher. However, this mineral resembles
montmorillonite in that it has a laminated structure
including a fundamental module made of silica (tetrahedron
structure)/alumina and magnesia (octahedron structure)/
silica (tetrahedron structure~ tri-strata composite layer.
Other than the aforementioned tri-strata
composite layer type clay minerals, artificially
synthesized tri~strata composite layer type clay
minerals may be also used in the present invention.
For example, taeniolite found in South Greenland belongs
to the illite group minerals which are enriched in
potassium, fluorine and magnesium, and may be synthesized
by mixing sodium fluoride, lithium fluoride, magnesium
oxide and silicon dioxide followed by fusing. The thu~
synthesized taeniolite may be used in this invention.
It is recommended that any of the aforementioned
tri-strata composite layer type clay minerals be used in
the form of powders having grain size of not more than
0.15 mm (100 meshes). Said bentonite is an advantageous
material, since almost all portion thereof, e.g. about
50 to 95%, is occupied by fine particles ha~ing diameter
of 74 microns (200 meshes) or smaller and particularly
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~7~D~
it is enriched in coarse clay particle of 0.2 to 2
microns in size and also enriched in fine clay particles
of less than 0.2 microns in size. A powdered talc - --
product having a particle size of 150 to 270 meshes
(O.1 to 0.05 mm) is commercially available as a material
for cosmetic goods. When a coarse particle product
having a particle size of 30 to 100 meshes (0~59 to
0.15 mm) and made of acidic terva abla, activated
clay, Fuller's earth, pyrophyllite, illite or
vermiculite is used in the present invention, the
mechanical strength of the formed gel tends to become
uneven. In order to obviate this undesirable tendency,
it is preferred that these materials be pulverized to have
a particle size of not less than 100 meshes, more
preferably not less than 150 meshes.
In the process of this invention, powders of
the aforementioned clay minerals or the clays
containing the aforementioned minerals are added to
an aqueous solution of a polyvinyl alcohol to be dispersed
in the latter, or an aqueous suspension of a certain
clay mineral is prepared and then the suspension is
mixed with said aqueous solution of a polyvinyl
alcohol. Alternatively, a polyvinyl alcohol may
be added to an aqueous suspension of clay minerals to
be dissolved therein.
Anyway, the ratio, by wei~ht, of polyvinyl
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alcohol to the clay minerals contained ln an aqueous
solution or suspension of polyvinyl alcohol and clay
minerals should be such that the weight of the clay
minerals be not more than 5 times as that of the
polyvinyl alcohol, as has been described above. If an
excessive amount of clay minerals is used, the mechanical
strength of the formRd gel tends to be lowered, ~nd this
tendency is promoted when the added amount of clay
minerals exceeds more than 10 times as much as that
of the polyvinyl alcohol. The addition of a tri-strata
composite layer type clay mineral, according to this
invention, contributes to the compatibility of high
water content of the resultant gel and increases in
mechanical strength as far as the added amount is not
excessive. The compatibility of high water content
and high mechanical strength has hitherfore been considered
to be a difficult problem in the course of development
of high polymers for medical uses and selective permeation
membranes. The clay minerals used in the present invention
exert remarkably distinctive and unexpected effects in
this respect. The contribution by these clay minerals
appears particularly remarkable when a tri~strata
composite layer type clay mineral is used in an amount
of from 1/5 to 1/15 as much as the quantity of the
polyvinyl alcohol. In other words, the ratio in
concentration of polyvinyl alcohol to the clay mineral
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~L7~P~3
ranges from 5/1 to 15/1.
According to the present invention, said aqueous
solution of a polyvinyl alcohol or said aqueous suspension
of a polyvinyl alcohol and clay minerals may be further
added with a water-soluble organic compound. In such an
embodiment, the concentration of the polyvinyl alcohol
should be adjusted to 2.5 to 10 wt%, and the concentration
of the additional organic compound should be adjusted to
20 to 80 wt%. According to this embodiment of this
invention, a gel improved in elasticity and flexibility
and being not frozen even in an ice-box of a refrigerator
can be obtained. The gelation and pre-treatment steps of
the process of this invention do not essentially involve
the use of an acid, alkali, radical sources, irradiation
of radioactive rays, organic solvents or chemical reagents,
otherwise widely used inthe gelation step of synthetic high
polymer and any secondary hardening treatment or an
after-treatment for depressing the freezing point of
temperature is not required. Yet, the gel obtained by
the process of the present invention has a rubber-like
elasticity required for a soft type coolant gel, i.e.
non-frozen hardening type coolant gel, and also has
satisfactory flexibility and mechanical strengths~
The most important water-soluble organic
compound added to said aqueous solution of a polyvinyl
alcohol or said aqueous suspension of a polyvinyl
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~17~
alcohol and clay minerals prior to the formation of a gel,
is a freezing prevention agent, namely a so-called freezing
point depressing agent. A representative example of the
freezing prevention agent is ethylene glycol. The
freezing point of pure ethylene glycol is - (mlnus) 16C,
and the freezing points of 38 vol% and 58 vol% (60 wt%)
aqueous solutions thereof are, respectively, -23C and
-49C. Accordingly, it is not always necessary that
the aqueous solution of polyvinyl alcohol contains
a particularly high content, for example 58 vol%, of
ethylene glycol. The object of the addition of ethylene
glycol can be attained by adjusting the concentration of
ethylene glycol at about 35 to 40 vol% to depress the
freezing point to about -20C. The freezing prevention
agent is not limited only to ethylene glycol. Another
water-soluble polyhydric alcohol having the freezing
prevention effect, such as propylene glycol (Freezing
Point: -20C at 40 wt% substitution), 1,3-propylene glycol
(Freezing Point: -24C at 50 wt% substitution), glycerin
(Freezing poin-t: -21C at 49 wt~ substitution) and
2-methyl-2,4-pentanediol (Freezing Point: -20C at 71 wt%
substitution), may be used. By the addition of such a
compound, the temperature at which the gel becomes
hard can be depressed lower than -20C so that the
gel retains satisfactory elasticity and flexibility
suited for use as an ice pillow and is kept unhardened
- 24 -
~7~ 8
to have a touch rese~bling a living tissue even when
it is placed in an ice-box normally maintained at -10
to -20C of a cooling box or refrigerator for general
household uses.
The polyhydric alcohol contributes not only
for a freezing point depressing agentr as aforementioned,
but also for the improvement in mechanical strengths of
the coolant gel of the invention. In detail, when
compared to the gel obtained from an aqueous solution
containing a polyvinyl alcohol only, a gel obtained from
a composition containing any of said polyhydric alcohols
is further increased in strength. As a result, a coolant
gel suited for substitution for an ice pillow and having
sufficient mechanical strength can be prepared by allowing
one or more of said polyhydric alcohols to co-exist. The
concentration of co-existing polyhydric alcohol may be
within the range of from 20 to 80 wt%, preferably from
35 to 75 wt%. If the concentration of co-existing
polyhydric alcohol is less than 20 wt%, it becomes
difficult to lower the freezing or solidification point
to a temperature of lower than -10C. Onthe contrary, if
the concentration of co-existing polyhydric alcohol is
higher than 80 wt%, the freezing point is depressed
excessively in some cases or conversely the freezing or
solidification point is raised, with unnecessary increase
in cost. The effect of depressing the freezing or
- 25 -
~l~7~
solidiflcation temperature of a gel is provided also
by the addition of a water-soluble monohydric alcohol,
such as methyl alcohol (Freezing Point: -20C at
25 wt% substitution), ethyl alcohol (Freezing pointO
~20C at 30 wt% substitution), isopropyl alcohol
(Freezing Point: -19C at 40 wt% substitution), ethoxyethyl
alcohol (Freezing Point: -21C at 40 wt% substitution)
and ethoxyisopropyl alcohol (~reezing Point: -30C at 62 wt%
substitution) or derivatives thereof, and further by the
addition of a general water-soluble organic compound,
such as acetone (Freezing Point: -20C at 36wt%
substitution), dimethyl sulfoxide (Freezing Point:
-25C at 37 wt% substitution), methyl sulfonic acid
(Freezing Point: -28C at 32 wt% substitution), ethyl
sulfonic acid (Freezing Point: -24C at 37 wt%
substitution), dimethylamine (Freezing Point: -20C at
33 wt% substitution), methylamine (Freezing Point: -20C
at 20 wt% substitution) and formic acid (Freezing Point-
-20C at 35 wt% substitution). However, ethylene
glycol, propylene glycol and glycerin are particularly
preferred for the reasons that they are odorless and
poor in volatility, that the cbject of depressing the
freezing point can be attained at relatively low
substituion rate by using one or a mi~ture of them
and that the gel obtained by the addition of them is
greatly improved in mechanical strengths. Trimethylene
- 26 -
~7~
glycol (1,3-propylene glycol) and 2,4-pentanediol are
inferior to ethylene glycol and propylene glycol in that
light almond-like ordor is generated therefrom.
In the present invention, an aqueous solution
containing both of a polyvinyl alcohol and a variety
of water-soluble organic compounds can be used, as
described hereinabove. Other than the aforementioned
polyhydric alcohols including ethylene glycol, propylene
glycol, glycerin and sorbitol, any of the monosaccharides
and polysaccharides may be used as the water-soluble
organic compound. Also, two or more of the aforementioned
organic compounds may be selected arbitrarily and used
in combination.
When any one or more of the aforementioned
polyhydric alcohols, e.g. a water-soluble polyhydric
alcohol having 2 to 6 carbon atoms and 2 to 6
intramolecular hydroxide groups, is used as the water-
soluble organic compound, the polyhydric alcohol i5
capsulated by the gel formed through the process of
the invention, as will be described in detail hereinafter,
to offer a charming and tasteful touch to the skin of
a user if the gel is used in the manner so that it
contacts directly with the skin of the user.
On the other hand, another highly viscous
2~ water-soluble high polymer, such as propylene glycol
alginate, carrageenan or Karaya Gum, may be used in
- 27 -
~7~
addition to the polyhydric alcohol to depress the
moistened touch of the formed gel at some extent.
Therefore, the moistened touch offered by the gel of
the invention can be controlled by the addition of the
highly viscous water-soluble high polymer to comply
with the user's preferance. The highly viscous water-
soluble high polymers suited for this purpose are
those each having a viscosity of a 2 wt~ aqueous
solution thereof of not less than 300 cP,(at 25C), the
polyvinyl alcohoI being exceptionally excluded from
this group of high polymers. The mechanism of this
advantageous effect in controlling the moistened touch
of the resultant gel has not been made clear. However, it
is presumable, from the fact that no such action is
offered by the addition of a water-soluble low molecular
weight compound, that the polyhydric alcohol is firmly
captured or coated by the highly viscous high polymer
solution in the course of formation of the gel
according to this invention and that the highly viscous
water-soluble high polymers, excluding polyvinyl alcohols,
have generally relatively strong effect of inhibiting
permeation of water therethrough.
Almost all of the well-known highly viscous
water-soluble high polymers may be used in this
invention for controlling the moistened touch of the
resultant gel, the only exception being polyvinyl alcohols
28 -
~7~
which are defective in water-retention property or
insufficient in inhibiting permeation of water. Any
natural or synthetic water-soluble high polymers may
be used for this purpose, provided that the viscosity
of a 2 wtQ~ aqueous sc1,1ution thereof is not less than
300 cP. (at 25C). Examples of such high polymers are
propylene glycol alginate, tragacanth gum, pullulan,
gum arabi, gatti gum, karaya gum, dextrin, starch, yama
(Dioscorea japonica) mucilage, Hibiscus Manihot,
furcellaran, curdlan, methyl cellulose, guar gum, Locust
Bean Gum, xanthane gumr agar, carrageenan, fucoidin,
alginic acid, triethanolamine alginate, pectin, agarose,
carboxymethyl cellulose, tamarind gum, gelatine,
polyacrylic acid, sodium polyacrylate, polymethacrylic acid,
polyvinyl sulfonic acid, polyvinyl pyridine, - -
polyethyleneimine, vinylimidazole/itaconic acid copolymer,
poly-(2,4-pentadiene-1-ol) and poly(N-vinyl-2-pyrrolidone)O
All of the high polymers referred to above have high
molecular wei~hts and form viscous aqueous solutions
to be preferably used in this invention. Fox the
purpose of illustration, the viscosities of aqueous
solutions thereof will be set forth as follows:
Sodium Alginate: 1.5 wt% sol. = 1,100 cP.; 2 wt~ sol.
= 3730 cP.; 3 wt% sol.=29,400 cP.(at 25C)
Carrageenan: 2 wt% sol. = 370 cP.; 3 wt% sol.
- 4,400cp.; 4 wt% sol. = 25,356 cp.
(at: 25C)
-- 29 --
1~7~
Guar Gum: 0.5 wt% sol. = 1,350 cP.,
1 wt% sol. = 3,000 cP.~
5 wt% 501. = 510,000 cP.(at 25C)
Locust sean Gum: 2 wt~ sol. = 1,100 cP.;
3 wt% sol. = g,200 cP.;
5 wt% sol. = 120,000 cP.(at 25C)
Propylene Glycol Alginate: 1 wt% sol. =400 cPO
(at 25C)
Xanthane Gum: 1 wt% sol. = 1,100 cP. (at 25C)
i-Carrageenan: 1~4 wt% sol. = 4,000 cP. ~at 25C)
As will be apparent from the foregoing that
the viscosities of the aqueous solutions of these high
polymers are considerably higher than those of
aqueous solutions of polyhydric a].cohols. For the
compaxison purpose, the viscosities of aqueous
solutions of glycerin will be set forth below:
40 wt% Solution: 4.7 cP. at 20C
50 wt~ Solution: 6 cP. at 20C
60 wt% Solution: 7.3 cP. at 30C
85 wt% Solution: 112 cP. at 20C
90 wt% Solution: 160 cP. at 25C
As has been described hereinbefore, other than
the polyhydric alcohols, disaccharides, trisaccharides and
polysaccharides, well-known highly viscous water-soluble
high polymers referred to above may be used in combina~ion
in the present invention. In order to prepare a gel
- 30 -
~ ~7~
offering comfortable touch or well moistened feeling,
it is preferred, in accordance with this inventi.on, to
use one or more of pullulan, xanthane gum, tragacanth
gum, carboxymethyl cellulose, polyacrylie aeid,
i-carrageenan, A-carrageenan, K-carrageenan and propylene
glycol alginate.
The content of the highly viscous water-soluble
high polymer ranges generally not more than 50 wt~,
preferably l to 30 wt~, based on the weight of the
aforementioned polyhydric aleohol.
In preparation of an aqueous solution or
suspension containing any of the aforementioned water-
soluble organic compounds, the selected water-soluble
organic eompound may be added to and dissolved in
water simultaneously with a polyvinyl aleohol or a
polyvinyl aleohol together with ealy minerals; a
polyvinyl aleohol may be dissolved in water and
then the selected water-soluble organie eompound or
an aqueous solution thereof with or without elay
minerals is admixed to the solution of polyvinyl
aleohol, or the seleeted water-soluble organic compound
or an aqueous solution thereof may be added with an
aqueous solution or suspension containing the polyvinyl
aleohol with or without clay minerals or the powders of
the polyvinyl alcohol with or without powdered clay
minerals followed by dissolvation and suspending the
- 31 -
~74j(~ L~
same. Anyway, the order and measures for mixing and
dissolving or suspending respective components
are not critical, provided that the content of polyvinyl
alcohol in the final mixture ranges within 2.5 to
10 wt% and the concentration of the water-soluble organic
compound ranges within 20 to 80 wt% and that the amount
of the clay minerals added is not more than five times as
much as the weight of the polyvinyl alcohol. Since
polyvinyl alcohols are scarcely soluble in a solvent
other than water, they are changed to often become
transparent and fine particles of micro-gels dispersed
in the final mixture containing said water-soluble
organic compound to form a transparent suspension.
However, no problem arises by the use of such a mixture
of an aqueous solution suspended with fine particles.
According to the present invention, an aqueous
solution of any of the said polyvinyl alcohol or an
aqueous solution or suspension containing any of said
clay minerals with or without a water-solubel organic
compound is cast into a mold or container having
desired shape and dimensions, and then the content in
the mold is cooled to a temperature of not higher
than - (minus) 6C. Any known casting molds may be
used for this purpose.
For the cooling agent, a cryogen (or freezing
mixture) such as common salt/ice (23:77) system (-21C),
~7~
calcium chloride/ice (30:70) system (-55C) or solid
carbon dioxide/methyl alcohol system (-72C), or liquid
nitrogen (-196C) may be used to cool the solution or
suspension to a temperature of lower than -6C. In the
present invention, it is desirous that the solution or
suspension be cooled sufficiently. If not, the shape
and dimensions of the final product gel obtained through
the vacuum drying step, as will be described below, do
not take the expected shape and dimensions, in other
words, is not agreed with the cavity of the used mold,
with attendant disadvantage that the mechanical strengths
of the final product gel are deteriorated. Although
the temperature of the solution or suspension may be
lowered to -269C using liquid helium as the cooling agent,
the properties of the resultant gel cannot be improved by
cooling to such a low temperature. Accordingly, the
use of liquid helium is not recommended for economical
standpoint of view, and it is better to use a freon
refrigerator to cool the solution or suspension to
a temperature of from ~20C to -80C, for practical
application. Of course, the solution or suspension may
be placed and cooled in an ice-box maintained at ~10
to -20C of a cooling box or refrigerator for houshold
use. The cooling temperature affects the strength
of a gel obtained through the subsequent vacuum drying
step. It is preferred that the solution or suspension be
- 33 -
~7~8
cooled to a temperature of not higher than -20C, for
example from -20 to -55C, and the strength of the
resultant gel is somewhat lowered when the solution or
suspension is cooled to a temperature of from -6 to -20C.
An aqueous solution of polyvinyl alcohol or
an aqueous suspension of polyvinyl alcohol and clay
minerals is frozen and solidified at the aforementioned
cooling step to form a frozen gel. If the solution or
suspension contains a water-soluble organic compound
acting as a cryogen, the solution or suspension is
actually not frozen but forms a gel having elastic
property.
In contrast thereto,in the cooling step of the
process according to this invention, the aqueous solution
or suspension containing a polyvinyl alcohol is cooled and
molded in a casting mold, and then the upside and/or
downside cover or covers may be removed to dehydrate
the molded composition in vacuum while retaining the shape
and dimensions of the molded body. A further advantage
of the vacuum dehydration method resides in that the
molded body can be substantially evenly and rapidly
dried including the deep internal portions~ For this
reason, the cooling and molding step of the process of
this invention is very important. Moreover, the inclusion
ofthe cooling and molding step in the process according
to this invention is significant in view of the fact that
- 34 -
~7~8
surprisingly unexpected effect of improvement in
mechanical strength is partly attributed to the cold
molding at a low temperature.
The cooling rate at the cold molding step may
S be slow as a rate of 0.1 to 7C per minute, or may be
rapid or high as a rate of 7 to lOOO C per minute.
The mechanical strength of the resultant gel is affected
by the cooling time at some extent so that the gel cooled
for 4 hours or for 10 hours is slightly improved in
mechanical strength and elasticity as compared to the
gel cooled for l hour. However, satisfactory properties
for use as a substitution for an ice pillow can be obtained
by cooling the gel for 1 hour.
According to the present invention, an aqueous
solution of a polyvinyl alcohol or an aqueous suspension
of a polyvinyl alcohol added with one or more clay
minerals, i.e. not containing water-soluble organic
compounds is :initially frozen. After checking the
completion of freezing, the frozen solution or suspension
is subjected to dehydration in vacuum or dehydration
under reduced pressure without thawing. The degree of
vacuum at the vacuum dehydration step may be determined
so that a predetermined percentage of water content is
dehydrated, and the pressure at the vacuum dehydration
step generally ranges not higher than 10 mmHg, preEerably
not higher than l mmHg, and more preferably not higher than
- 35 -
~7~
0~1 m~Hg. ~t this step, any external cooling is not
necessary for preventing the frozen molded body from
thawing, but the frozen molded body is discharged from
a refrigerating chamber and transferred into a vacuum
dehydrating chamber to be dehydrated by sucking
immediately. No external cooling is required, since
the thus dehydrated body is spontaneously cooled as
the water contained therein is removed by sublimation.
Conversely, the frozen molded body may be heated to
an extent not to cause melting of the frozen body,
whereby the dehydration rate may be accelerated. In
brief, the temperature at the dehydration step is not
critical provided that the frozen molded body is not
melted. The temperature of the dehydration step does
not significantly affect the properties of the product gel.
The percentage dehydration rate at this dehydration step
should be not less than 5 wt% to obtain a gel having
a water content of 60 to 95 wt%, based on the weight
of the swelled body. More preferably, the water
content of the gel should be within the range of from
60 to 90 wt%. Although the water content of the
gel may be lowered below 60 wt~, it is not necessary to
lower the water content of the product gel to such a low
level in consideration of the aimed uses, for instance
for coolant gels or cooling media. As a modified process,
the water content of the gel has been once lowered to
- 36 -
~::L7qii6~
a level below 60 wt~, and then the gel is immersed in
water to recover the water content within the range of
60 to 95 wt%.
Meantime, the term "percentage dehydration rate"
used throughout this specification and appended claims
means the ratio of water removed at the dehydration step
relative to the total weight of the frozen gel body or
mass prior to dehydration. This "percentage dehydration
rate" is simply calculated by dividing the weight loss
during the dehydration step, the weight loss being caused
by removal of water and thus equal to the weight of
removed or dehydrated water, by the weight of the cooled gel
prior to dehydration. For example, supposing now that 41
grams of an 8% aqueous solution of a polyvinyl alcohol is
cast in a mold and cooled. The cooled mass is subjected
to vacuum dehydration followed by thawing to obtain 8
grams of a rubber-like gel having a water content of 58%.
The weight loss due to removal of water at the dehydration
step amounts to 41 - 8 = 33 grams. Simply by dividing
33 by 41 followed by multiplcation by 100, I obtain
the percentage dehydration rate in this example of about
80%. It is noted here that the "percentage dehydration
rate" in this invention is defined as the percentage of
weight loss due to water removal relative to the total
25` weight of the agueous solution or suspension prior to
dehydration, and does not mean the percentage of water
:~7~
removed at the dehydration step relative to the weight
of water contained in the aqueous solution or suspensionO
As mentioned above, according to the present
invention, where an aqueous solution of a polyvinyl
alcohol or an aqueous suspension of a polyvinyl alcohol
added with one or more of clay minerals is used,
irrespective of the concentration of polyvinyl alcohol
contained therein, the cast or molded body is subjected
to the dehydration step after being frozen. The
percentage dehydration rate, i.e. the weight reduction
rate as described in detail hereinabove, should be
not less than 5 wt~, preferably not less than 15 wt~o The
maximum percentage dehydration rate is not particularly
limited, and the percentage dehydration rate may be
so high as about 98 wt~. The actual percentage
dehydration rate may be selected depending on the desired
strength of the product gel, because the strength of
the gel is increasingly improved as the dehydration
proceeds.
The body or mass formed by freezing, molding
and drying is then allowed to stand at ambient
temperature for thawing to obtain an elastic gel. The
gel may thaw slowly or rapidly by raising the temperature
thereof at a rate of 1 to 3C~min for slow thawing
or at a rate of 3 to 1000C/min for rapid thawing. The
melting point of the gel obtianed by allowing an
- 38 -
~17~L8
aqueous solution of polyvinyl alcohol to stand or to be
stored at a temperature of about 0 to 30C ranges from
about 15 to 29C. In contrast thereto, the melting point
of the gel obtained by the process of this invention
is so high as higher than 100C, and hence the gel
obtianed according to this ,inven,tion may be subjected
to rapid thawing by warm water or warm air. However,
it is desirous that thawing be effected at a temperature
of lower than 40 to 50C while avoiding the melting of
gel at a higehr temperature, a hard membraneous
surface layer is formed promptly since when the gel
according tot~is invention is dried by hot air of higher
than 60C and even the gel according to this invention
is apt to melt in hot water.
After the thawing operation, the gel can be
easily removed from the cavity of a casting container
or mold. This gel absorbs water when immersed in
water to reach the water content of 80 to 95 wt% (based
on the weight of the swelling body), and the swelling
gel is kept as a tough elastic mass.
On the other hand, when an aqueous solution or
suspension further added with any of the afore~entioned
organic compounds is used in the process of this invention,
the cast mass is cooled to be a little solidified
but not to be frozen and then subjected to vacuum
dehydration. Although the mechanical strength of the gel
- 39 -
66~L8
is further improved as the percentage dehydration rate,
i.e. the weight reduction rate of the cooled gel,
increases, it is not necessary to increase the percentage
dehydration rate too high to obtain strong but hard gel.
In order to obtain a soft gel, the percentage dehydration
rate should be not less than 5 wt%, preferably within
the range of from 5 wt~ to 60 wt%, and more preferably
within the range of from 5 wt% to 55 wt%.
The degree of vacuum at the dehydration step of
drying the gel in vacuum may be such that the gel is
dehydrated to have a predetermined water content, for
example at the level of below 10 mmHg, preferably below
1 mmHg, and more preferably below 0.1 mmHg. A gel obtained
by dehydrating a composition containing a polyvinyl
alcohol and an additional water-soluble organic compound
with or without caly materials in vacuum is a milky and
opague gel forming a solid mass which is insoluble in
water at ambient temperature and which does not become
hard or rigid even in an ice-box of a household ice
box or refrigerator.
It is supposed from the result of observation
conducted using a scanning type electron microscope that
the gel forms an exceedingly porous mass internally
thereof having solid phase of water-insoluble polyvinyl
alcohol and liquld phases of water entangled compricately
to form a labyrinth-like network of tangled water paths.
- 40 -
~L17~ 8
The width of the water paths is varied from 1/2 to 100
microns, and the paths meander to form a complicatedly
continued network. As should be apparent from the high
water content, the major portion of the internal area
of the gel are void filled with water. The water content
of the gel is less than that of KONNYAKU (Water Content:
about 97 wt%, a swelling gel of polysaccharide), but is
comparable with the water content ~70 to 90 wt~) of a
living cell or a living tissue of human being or animals.
In addition, the gel obtainable by this invention is
exceedingly superior over a variety of gels of
polysaccharides, such as KONNYAKU, agar, aliginic acid,
carrageenan, guar gum, ~x~st Bean Gum or agarose, in
strength and elasticity. The strength and elasticity of
the gel obtained according to this invention are comparable
with those of the living tissues of human being and animalsO
Nevertheless, the gel obtained according to this invention
contains a large quantity of water, it exhbiits tough
elasticity and resists deformation so that it is deformed
transiently when squeezed tightly by hand but it restores
the original shape immediately after it is left free.
It has hitherto been considered that the concurrent
provision of high water content and high mechanical
strnength involves a difficult and incompatible problem in
the course of developing a high polymer for medical
uses or developing a membrane having selective permeability.
- 41 -
1~7~8
The gel prepared by the process of this invention is
quite different from the membrane of prior art technique
obtained by drying an aqueous solution of a conventional
polyvinyl alcohol in air or the aforementioned water-
soluble gel formed by merely storing an aqueous solution
of a polyvinyl alcohol at a temperature of from 0 to
30C, and has a high water content and high mechanical
strength, as described in detail hereinbefore.
Water contained in the gel according to this
invention is scarcely exuded even when pressure is
applied thereto, for example, only 1 to 2% of the
contained water is exuded or effused even when a
compressive force of 2 kg/cm2 is applied to the gel
according to this invention having a water content of 90
wt%. As should be understood -from the fact that the gel
retians a large amount of water persistently, the
apparent specific density of the gel is substantially
equal to that of water so that the gel is scarcely settled
in water.
The gel prepared ih accordance with the process
of this invention is not adhesive. Even when about lOg
each of gels respectively molded to have a plate form
(8 mm x 8 mm x 2 mm), a cyclindrical shape (having an
inner diameter of 3 mm, an outer diameter of 6 mm and a
length of 6 mm) and a spherical shape (having a diameter
of 4 mm), were immersed in 50 ml of water while continuing
- 42 -
agitation for 10 days, no mutual adhesion or deformation
was observed. The gel was immersed in city water for one
year, it was not dissolved in water and the elasticity
and the strength thereof were not changed. This is in
-5 striking contrast to the case of KONNYAKU which has been
deformed seriously when it is immersed in city water for
a few days.
In the present invention, the used polyvinyl
alcohol is the sole material or component acting as the
gelation agent, or acting as the gel forming agent.
However, the presence of one or more inorganic or organic
materials which do not participate in the gel forming
reaction of the used polyvinyl alcohol, does not affect
adversely on the properties of the formed gel. The
allowable amount of such a co-existing material may be
less than 1/2 as much as the quantity of the contained
polyvinyl alcohol when the gel forming liquid is an
aqueous solution containing solely the polyvinyl alcohol,
and may be less than 1/2 as much as the total quantity
of the contained polyvinyl alcohol and the clay minerals
and/or the additional water-soluble organic compound when
the gel forming compositions contains the clay minerals
and/or the additional organic compound. On the contrary,
a material which reacts with polyvinyl alcohol (or
polyvinyl acetal, polyvinyl butylal or other similar
compounds which may be construed as an equivalency
- 43 -
or modification of polyvinyl alcohol) to form a
cornposite gel or a material which reacts with polyvinyl
alcohol or a homologue to modify the same, should not be
present because the gel formins capacity attained
solely by the used polyvinyl alcohol is often adversely
affected by the presence of even a small amount of such
a material to make it difficult to form a gel having
improved mechanical properties and high water contnet.
Examples of such materials which affect adversely on the
gel formation according to this invention are those
recognized to have interaction between polyvinyl alcohols
or homologues, the specific examples being colloidal
alkali silicate (See the specification of United States
Patent No. 2,833r661 (1958)), colloidal silica (See
the specification of United States Patent No. 2,833,661
(1958)), alkaline colloidal silica (See Japanese Patent
Provisional Publication No. 153779/1979), organic silica
compounds (see "Vinyl Acetate Resin", page 93, published
by Nikkan Kogyo Shinbun-sha (1962)), tetraalkyl silicates
20- (See Japanese Patent Publication Nos. 30358/1980 and
11311/1980), boron and borate (See French Patent
No. 743,942 (1933)), phenol, naphthol, meta-cresol,
pyrogallol, salicylanilide, disalicylbenzidine, resolcinol
and polyamines (See kobunshi Kagaku (Chemistry of
Polymer), 11, (105)23, (1954)), and kaolin (Nature,
1 , 461 (1955)). All of these materials form composite
- 44 -
gels with a polyvinyl alcohol depending on the
co-existing quantities thereof to lower the inherent
mechanical strength and rubber-like elasticity of the
gel prepared by the present invention, and hence the
presence thereof should be rather avoided.
The gels prepared in accordance with the process
of the invention while using an aqueous solution of a
polyvinyl alcohol or an aqueous solution containing a
polyvinyl alcohol and an additional water-soluble organic
compound are always opaque gels of white color. The
appearance or hue thereof resembles a slice of raw cuttle-
fish, rice cake, white UIRO (a kind of paste product
made of powdered rice), a boiled fishplate or a white meat
portion of raw fish. The touch of the gel resembles a
flesh of human being or an animal, a slice of raw cuttle-
fish, a fish meat, rice cake CHIKUWA (roasted fish paste),
HAMPEN (fish minced and steamed), a chao-mai, KONNYAKU or
sausage. On the other hand, the gel prepared from an
aqueous suspension containing one or more clay minerals
has a hue which is differentiated by the hue of the used
clay mineral. A white gel is obtained when an activated
clay, white bentonite, talc or white illite is used.
The hue of the resultant gels are changed depending on
the hues of the clay minerals when colored materials, such
as light brown bentonite or light yellow acidic terra
abla, are used. In practice of the present inveniton, a
- 45 -
~7~ 8
gel having desired hue can be prepared by dissolving or
suspensidng fine powders of a coloring agent, such as Congo
Red~red color), alkaline phenolphthalein (Red color),
neutral methyl orange (yellow color), phthalonitrile
(lightly rdddish brown, commercially available),
phthalocyanine Blue or Phthalocyanine Green, in an aqueous
suspension containing one or more of clay minerls.
In the process of this invention, an aqueous
solution or suspension containing at least a polyvinyl
alcohol may be cast in a container or mold having desired
shape and dimensions to obtain a swelling gel having
desired form, for instance in the form of particles,
membrane, lump, plate cylindrical or other shape. A
gel having a contour in registry with the final product
may be molded, or alternatively a final product
of desired shape and dimensions may be cut out from a
block of gel through subsequent machining step.
There has not been clarified the mechanism of the
formation of a gel, which is quite different from the
conventionally-known gel of polyvinyl alcohol and is formed
by cooling, molding and drying an aqueous solution for
suspension according to the process of this invention.
However, it is presumable that a numerous hydrogen
bonds are formed intramolecularly and intermolecularly
of polyvinyl alchol molecules at the cooling, molding
or casting and drying steps.
- 46 -
Anyway, it is believed that the gel and the
process according to this invention as defined in
the appended claims are firstly found by the inventor of
the presnet invention.
Nevertheless, the gel prepared in accordance with
the present invention does exude only little water
contained therein even when it is compressed or squeezed
extensively.
The rubber-like gel having high water content
and prepared according to the process of this invention
retains the initial fresh-looking and soft-touch by
sealingly filling the same in a txansparent or opaque
bag made of a soft material, such as polyvinyl chloride,
polyethylene or polypropylene.
The gel obtained by the process of this invention
has a touch resembling a living tissue by itself, and
may be used, as an elastic or resilient material, as a
substitution material for an ice pillow or an ice bag.
The gel prepared from a composition containing an
additional water-soluble organic compound is not frozen
to be rigid or solidified even if it is placed in an
ice-bo~ of a houshold cooling box or refrigerator to
exhibit always a fresh touch and elasticity similar to
KONNYAKU. On the other hand, the gel obtained from the
solution or suspension which does not contain an additional
water-soluble organic compound becomes hard or solidifid
- 47 -
1~7~Q4B
in its entirety when it is cooled in an ixe-box of a
cooling box due to freezing of the water included in
the cooled gel. As a result, the desired fresh touch and
rubber-like elasticity inherent to the gel according
to the present invention cannot be exhibited occationally
to become unsuited for use as an ice pillow until the
frozen water at the surface of the initially frozen gel
thows. However, according to the present invention, a
process for the preparation of non-hardening gel is - -
provided, as will be described in detail hereinbelow.
Namely, in accordance with a further aspect
of the present invention, a gel containing a polyvinyl
alcohol with or without a clay mineral is dipped in a
water-soluble orgnaic compound or an aqueous solution
thereof, for instance in ethylene glycol to substitute at
least a portion of water contained in the gel for ethylene
glycol, whereby a coolant gel similar to the aforementioned
gel obtained from a composition containing an additional
water-soluble organic compound which is not frozen to
become hard in a general ice-room, can be easily prepared.
The freezing point of pure ethylene glycol is -16C (Specifc
Heat at 20C: 0.56 cal/g deg.) The freezing points of 38
vol% and 58 vol% (60 wt%) aqueous solutions of ethylene
glycol are, respectively, -23C (Specific Heat at 20C:
0.85, Specific Heat at -4C: 0.91) and -49C (Specific
Heat at 20C: 0.76). Accordingly, it is not necessary to
- 48 -
~7~
replace all water content in the gel by ethylene glycol,
and desired freezing point depressing effect or
hardening prevention effect can be attained by replacing
about 35 to 40 vol~ of water by ethylene glycol
while avoiding sharp depression in specific heat or
cooling heat capacity of the aqueous solution confined in
the gel. All of the water-soluble orgnic compounds referred
to hereinbefore as the materials to be mixed to the
aqueous solution or suspension for depressing the freezing
point thereof may be used at this step of replacing a
portion of water contained in the gel.
A non-hardening type coolant gel may also
be prepared by allowing the gel to contact with an
aqueous solution of an inorganic salt, suchas aqueous
solution of magnesium chloride, aqueous solution
of sodium chloride or aqueous solution of calcium chloride~
to replace a portion of water in the gel by the aqueous
solution of such an inorganic salt, For example, the
freezing points of 17 to 22 wt% aqueous solution of
magnesium chloride, 23 to 24 wt% aqueous solution of
sodium chloride and 19 to 30 wt~ aqueous solution of
calcium chloride are, respectively -20 to -33C, -17
to -20C and -16 to -51C. The freezing point of
water contained in the gel may be, therefore, depressed
by allowing said water-contained gel with any of
said aqueous solutions of inorganic salts. Similar
- 49 -
~ ~L7~ ~P~'~
effects may be obtained by the addition of various
water-soluble inorganic compounds including bromides
of iron, manganese, barium and sodium, chlorides of iron,
cobalt, nickel, ammonium and copper, nitrates of iron,
cobalt, nickel, magnesium, calcium, sodium,copper, zinc
and ammonium, sulfates of lithium, potassium, ammonium
and cadmium, pyroselenite of ammonium, selenate of
potassium, antimony sulfides of potassium and lithium,
and hydrosulfide of barium. Amongst these water-soluble
inorganic comp~unds, magnesium chloride, calcium
chloride, sodium chloride, ammonium chloride, magnesium
nitrate and zinc nitrate are particularly preferred,
because they are odorless, harmless and inexpensive
and additionally the gel can be prevented from freezing
or solidifying by the replacement of a relatively
small amount of contained water by the aqueous solution
of such an inorganic salt.
In order to replace at least a portion of water
contained in a gel prepared from an aqueous solution of
a polyvinyl alcohol or an aqueous suspensi~n further
added with one or more clay minerals, it is convenient
to adopt a direct contact method in which a water-
containing gel is allowed to contact with an inorganic
salt directly.
When said gel is immersed in a water-soluble
organic compound or a water-soluble inorganic salts or
- 50 -
an aqueous solution thereof, the freezing point of water
at the surface area of the gel has been depressed after
the lapse of 2 to 3 n~nutes. The freezing point depressing
effect extends deeply in the internal portion of the gel
for additional 30 minutes to 10 hours so that the freezing
point of the portions of 1 to 10 cm from the surface
is depressed enough for satisfying the object of this
invention. The liquid, in which the gel is immersed,
may be agitated or circulated at this step with attendant
advantage that the time required for immersion is
shortened.
After a water-soluble organic compound or water
soluble inorganic salt has been once impregnated into
a gel, the aqueous solution thus confined in the gel is
scarcely pressed out even by applying high compression.
After the operation of cooling the gel to -25C to be
used as a coolant is cyclicly repeated, the aqueous
solution in the gel and the gel structure are stable and
no problem arises by such a repeated cycle.
According tu a still further aspect of the
invention, a process for the preparation of composite
coolant gel structure i5 provided, said composite gel
including a first layer (A) containing said polyvinyl
alcohol and one or more of said additional water-soluble
organic compounds and a second layer (B) containing solely
said polyvinyl alcohol. The process provided in
- 51 -
~7~ 8
accordance with this aspect of the invention is a
process for the preparation of a gel for use as a cooling
medium and having a composite layer structure including
a first gel layer (A) and a second gel layer (B) of
higher water content; wherein said first gel layer
(A)is prepared by the steps of casting an aqueous
solution or suspension containing a polyvinyl alcohol
having a degree of hydrolysis of not less than 95 mol%
and a viscosity average polymerization degree of not
less than 1500 and further containing an additional
water-soluble orgnaic compound into a mold having
desired shape and dimensions, the concentration of
said polyvinyl alcohol in said aqueous solution or
suspension being within the range of from 2.5 to 10 wt~
and the concentration of said additional water-soluble
organic compound in said aqueous solution or suspension
being within the range of from 20 to 80 wt~, cooling the
cast aqueous solution or suspension to a temperature of
not higher than - (minus) 6C, and then dehydrating
without thawing the cooled mass of the cast aqueous
solution or suspension in vacuum until the percentage
dehydration rate reaches not less than 5 wt%; and
wherein said second gel layer (B) is prepared by the
steps of casting an aqueous solution of a polyvinyl alcohol
having a degree of hydrolysis of not less than 95 mol%
and a viscosity average polymerization degree of not
1~7~ B
less than 1500 into a mold having desired shape and
dimensions, cooling the cast aqueous solution to a
temperature of not higher than - (minus)6C to freeze
the same to form a mass of desired shape and dimensions,
thereafter dehydrating without thawing the frozen mass
of the cast aqueous solution in vacuum until the
percentage dehydration rate reaches not less than 5 wt%,
and then, if necessary, swelling the once dehydrated
mass with water to have a water-content, based on the
weight of the swelled mass, of from 60 to 95 wt~.
In this embodiment of the invention, as the
gel layer at the side for contacting with a human body
portion provided is the first gel layer (A) obtained by
cooling an aqueous solution or suspension containing both
of a polyvinyl alcohol and an additional water-soluble
organic compound and having sufficient soft touch,
flexibility and elasticity and yet having no tendency
of becoming hard even if it is placed in an ice-making
chamber of a cooling box or refrigerator, and the
second gel layer (B) which is to be frozen to become
hard is provided at the side which does not contact
with any portion of a human body. With this construction,
the hardening gel layer (B) is interposed between the
non-hardening gel layer (A), which does not contact the
body portion of a user. For example, by the provision
of about 1 ~o 1.5 cm thick soft layer made of said first
- 53 -
:~7~
non-hardening gel layer (A), -the product having
a composite layer structure may be comfortably used as
a substitution for an ice pillow with the touch as if
the user contacts with a cooled mass through a layer
made of KONNYAKU.
A composite layer structure may be made by
preparing a plate-shaped gel layer (B) of freezing or
hardening type (high water content gel) and a
plate-shaped gel layer ~A) of non-freezing type (non-
hardening type) and then laminating these gel layersto form a piled product of A/B or A/B/A. The thus
formed product may be applied for use while being
contained in a bag made of an approprite soft film.
Since the gels constituting the composite layer structure
of this embodiment are rubber-like solids at ambient
temperature, the composite layer gel may be ready for
use by wrapping with a polyethylene bag or another suitable
material if the bag initially wrapping the composite layer
gel is accidentally broken. In contrast to the
conventional coolant gel product made of a porridge-like
gel composition which is exposed to the risk of loss
due to flowing-out of the porridge-like gel when a
container or bag containing the same is broken or even
through a fine pinhole or crack, the coolant gel
according to this invention is not susceptible to such
a risk. The gel layers (A) and (B) may be molded to
- 54 -
have the shapes and dimensions coincident with the final
used forms, or alternatively they may be cut out from
larger blocks followed by subsequent shaping.
The non-freezing type gel (layer (A)) has been
incorporated in a composite layer type coolant gel
structure by the inventor in the first place in order
to improve the touch of the coolant product, and no
such trial or proposal has been made by others until now.
According to another advantageous feature of this
invention, a freezing type gel (layer (B)) having a
high water content is combined with the aforementioned
layer (A) with the aim to improving and prolonging the
cooling capacity of the product.
As another application, the aqueous solution
or suspension containing the polyvinyl alcohol and the
additional water-soluble organic compound, may be used
as a cooling medium for cooling the head of a patient.
For this purpose, the aforementioned solution or
suspension prepared according to this invention is cast
into a mold for molding a helmet having a shape and
dimensions for completely surrounding the areas of
the head covered with hairs or eyebrows, and then
cooled and vacuum-dehydrated in accordance with
the procedure described above and defined in the
appended claims.
More particularly, a gel prepared according
to the process of this invention and including a
polyvinyl alcohol added with a relatively large quantity
of glycerin, propylene glycol or ethylene glycol may be
used as a compensation agent for compensating the harmful
secondary effect of the chemotherapy for curing cancer,
as will be described in detail hereinafter. In the
chemotherapy for curing cancer wherein a variety of
antibiotics is administered to a patient, if the
patient suffers harmful secondary effect to lose his
hairs, falling-off of hair can be prevented by cooling the
head by a helmet provided with a lining made of the gel
prepared by the process of this invention. The falling-
off of hair of the patient due to admlnistration of
antibiotics and the prevention effect attainable by
the use of a helmet provided with the coolant gel
according to this invention are most appreciable when
Adriamycin is used as the antibiotics for the therapy of
cancer.
Adriamycin (1,4-hydroxydaunorbicin; doxorubicin)
was separated from Streptomyces peucetius var. caesius,
a mutant of Streptomyces peucetius, at the Fermitalia
Research Laboratories in Italy in 1967, and was well-known
as an antibiotic having an anthracycline type chemical
structure resembling Daunorubicin (Daunomycin). Details
thereof will be apprent by referriny to, for example,
"Biochemistry Data Book", I, page L415 (1979), edited
by Bio-chemical Society of Japan and published by Tokyo
- 56 -
Kagaku Dojln; Kazuo Ghta, "Status Quo and Trend of New
~ledicines", the last ~olume page 168 (1972), edited by,
Kyosuke Tsuda e~ al. and published by Chijin Shoken; A.
Dimarco et al., "Cancer Chemother. Rep., (1)", 53, page 33
(1969); and F. Arcamone, "Chim, Ind. (Milano)", 51, page
835 (1969). The antitumor activity thereof exhibits in
wide range and is applied, singly or in combination of other
chemotherapeutics in a combination chemotherapy, for the
therapy of various diseases including gastric cancer, pul-
monary cancer, ovarian tumor, embryonal carcinoma, infantile
carcinoma, infantile sacrosis, mammary cancer, Wilm's tumor,
lymphatic leukemia, non-lymphoid leukemia, Hodgkin's disease,
mouse sarcoma 180, mouse lymphatic leukamia P388 and mouse
leukemia L1210. In this connection, reference should be
made to the following references: A. Dimarco et al., "Cancer
Chemother., Rep. (1)", page 33 (1969); Kazuo Ohta, "Status
Quo and Trend of New Medicines", the last volume, page 168
(1972), edited by Kyosuke Tsuda et al. and published by
Chijin Shokan; Takeo Fujimoto "HAKKETSU-BYO NO SUBETE"
(General Report on Leukemia), page 412 tl981), edited by
Yoshihisa Nakao and published by NANKODO Co., Ltd.; and
"Handbook of Medicines", page 1014 (1981), edited by
OSAKA-FU BYOIN YAKUZAISHI KAI (Association of
~'
- 57 -
~'7~
Phaxmacists Belonging to Hospitals in Osaka) and
published by Yakugyo jiho-sha. It has been reported that
it has a medicial efficacies superior over the well-known
carcinostatics, such as Daunomycin and Daunorubicin (See
"Handbook of Medicines", page 1014 (1981), edited by
OSAKA-FU BYOIN YAKUZAISHI KAI, and published by Yakugyo
Jiho-sha; and Kazuo Ohta, "Status Quo and Trend of
New Medicines", the last volume, page 168 (1972), edited
by Kyosuke Tsuda et al. and published by Chijin Shokan).
However, the toxicity thereof is intense (see Kazuo Ohta,
"Status Quo and Trend of New Medicines", the last
volume, page 168, edited by Kyosuke Tsuda et al.
and published by Chijin Shokan), and it was reported that
Adriamycin showed frequently more harmful seco~dary
effect than Daunorubicin (See "Handbook of Medicines",
page 1014 (1981) r edited by OSAKA-FU BYOIN YAKIZAISHI
KAI, and published by Yakugyo Jiho-sha, and Takeo
Fujimoto, "HAKKETSU-BYO NO SUBETE", page 412 (1981),
edited by Yoshihisa Nakao and published by NANKODO
CO., Ltd.).
As the harm~ul symptoms caused by the
administration of this medicine, there may be mentioned
stomatitis, nausea, vomitus, pyrexia, mycocardiopathy,
nephropathy, hypohepatia, anorexia, oligoerythrocythemia,
hypoleukocytosis, thrombocytopenia and alopecia.
Particularly, the alopecia is known as a serious
- 58 -
348
harmful secondary effect which is fre~uerltly observed
(See Shigeyuki Osamura et al., "~AKKETSU-BYO NO SUBETE",
page 189 (1981), edited by Yoshihisa Nakao and
published by NANKODO Co., Ltd.; "Hand~ook of ~edicines",
page 1014 (1981), edited by OSAKA-FU BYOIN YAKUZAISHI
KAI and published by Yakugyo Jiho-sha; and Kazuo Ohta,
"Status Quo and Trend of New ~edicines", the last
volume, page 168 (1972), edited by Kyosuke Tsuda
et al. and published by Chijin Shokan ). In order to
alleviate the harmful secondary action, it has been
tried to ameliorate the administration method or to
develop the combination chemotherapy. However, the
alopecia cannot be avoided generally, and regeneration
of hair by the later recuperation is not expected
(See Kazuo Ohta, "Status Quo and Trend of New Medicines",
the last volume, page 168 (1972), edited by Kyosuke
Tsuda et al. and published by Chijin Shokan). For
instance, Adrlamycin is administered by intravenous
drip at every 25-day-interval, more than 90%
of the patients suffer depilatory symptom and the
loss of hairs caused thereby gives considerable
mental pains to the patients. In addition, this
harmful action might raised a serious problem that some
patients who are unfamiliar with the modern medical thera~y
have suspicion or distruct to the treatment or
administration.
- 59 -
~ 7~8
The cause for this alopecia considered is that
the antibiotics administered intc the organism is absorbed
by the cells of hair. In order to suppress the absorption
rate, it has been tried to cool the cells of hair to
a temperature of about 25C at which the metabolism of
living cells is remarkably ceased. The antibiotics
administered by intravenous drip reaches the head of
the patient after about several minutes and is
discharged therefrom after about 30 to 40 minutes,
and is not left inthe blood flows circulated in the
head after then. In view of the result of observation
set forth above, it has been investigated to develope a
practically applicable method of cooling the head of a
patient for abo~t 40 minutes after the antibiotic is
administered by intravenous drip. Prior-made trials
include the method in which an ice-bag is wound around
the head, the method in which a helmet made of sponge
is impregnated with a large amount of cold water and
fitted on the head, and the method in which the inner
cavities of a cap molded from a bag made of, for example
polyvinyl chloride and having cavities are filled with
a jelly, agar, a polyvinyl alcohol or a borax gel.
~Iowever, the method using the ice-bag i5 inconvenient
in that water and ice contained in the bag flow downards
in the wound bag to be dislocated unevenly to make it
difficult to cool the entire head portion ~lniformly.
-- 60 -
The helmet made of sponge is inferior in water-retention
capacity, resulting in that a large quantity of cold
water is oozed out and dropped from the sponge.
For this reason, this method is not practical, as wellO
In the method of using a cap molded from a bag of
polyvinyl chloride and having inner cavities in which
a high water content gel is filled as the cooling medium~
it is difficult to hold the original shape of the cap
or helmet, because the conventionally-known high water
content hydrogels are either fluidal, for example a
polyvinyl alcohol gel, a borax gel and carboxymethyl
cellulose gel, or soft and crumbly solids, for example
gels made of agar, jelly, carrageenan and alginic acidO
A further disadvantage of the known gels is that they
are poor in elasticity not to fit intimately over the
head of a patient.
Many proposals have been made to prevent the
cooling mediurn from deformation or uneven dislocation,
including a method of sawing the helmet over the whole
area in the longitudinal and transverse direction to
form a number of partitioned regions, thereby to
prevent the fillers contained in separate regions from
moving, and a method of providing a number of closed
chambers or small cellular cavities into which cooling
medium is filled~ However, a gap or space is left
between the head and the helmet, since the helmet per se
- 61 -
¢~
lacks elasticity required for intimate contact.
The gel prepared in accordance with the process
of this invention and including a water-soluble organic
compound, such as glycerin, propylene glycol or ethylene
glycol, is improved in water-retention property so that
the water retained thereby scarcely evaporates. Even
if some portions of water evaporate, disadvantageous
drying and hardening of the gel are avoided since the
gel is improved in water-retention property due to the
contained organic compound, such as a polyhydric alcohol.
As a result, the gel does not lose its inherent flexibility
and elasticity without suffering deformation, and
maintains high mechanical strength and comfortable touch
According to this invention, a gel forming composition
containing a polyvinyl alcohol added with an aqueous
solution of a water-soluble organic compound, such
as a polyhydric alcohol, may be cast in a helmet
molding mold followed by cooling, solidification and
shaping, and then partially dehydrated without thawing
to obtain a helmet. ~his helmet can be immediately used
as a head cooling helmet without the need of being wrapped
by a bag made of, for example polyvinyl chloride or
similar material. Since the gel prepared in accordance
with the process of this invention is highly elastic and
extensible, a helmet made of the gel of this invention is
well fitted on the heads of many patients having different
- 62 -
shape and dimensions.
The shape of a helmet used for this purpose is
somewhat different from the shapes of the helmets
conventionally used for safty helmets at the job sites
or used by batters in the baseball game, and the helmet
suited for this medical therapy purpose sho.uld extend to
cover not only the entire portion of the head on which
hairs grow but also the side wishers, i.e. hairs at left
and right sides of the head, preferably to cover
the portions of the face on which eyebrows grow. The
helmet according to this invention for use in medical
therapy may be easily produced by using a mold prepared
by modifying the molds used for the production of
helmets for the operators of motorcycles or the players
of ice hockey game.
EXAMPLES OF THE INVENTION:
The present invention will now be described
more specifically with reference to examples thereof.
However, it is noted here that the invention should
not be limited only to the following examples,
but it is interpreted that the spirit and scope
of this invention is defined only by the appended
claims.
Example l
86g of a commercially available powder (Water
Content: 7 wt~) of a polyvinyl alcohol haivng a degree
- 63 -
a~
of hydrolysis of 97 mol%, a viscosity average
polymerization degree of 1700 and a viscosity at 20C
of a 4~ aqueous solution thereof of 26 cP. was dissolved
in 914g of water to obtain an 8.0 wt% aqueous solution
of polyvinyl alcohol.
41g of the aqueous solution was poured into a
polyethylene beaker having a bottom of 8 cm in diameter,
subjected to cooling operation of -50C x 0.7 hr. to be
frozen for molding, and then subjected to vacuum dehydration
for 6 hours. After thawing, 8g of a white transparent
rubber-like gel having a water content of 58 wt% was
obtained. The percentage dehydration rate calculated
according to the definition as described hereinbefore
to learn that the weight reduction rate of the frozen
body after drying was 80 wt%. The gel was immersed in
10 ml of city water for 6 hours to allow the gel to
absorb water. As the result of immersion, the wegiht of
the gel reached 14g which corresponded to a water content
of 76 wt%. A loading of 2 ]cg/cm was applied on the gel,
to find that no deformation and exudation of water was
observed. The water-retention rate of the swelled gel
was 99%.
The swelled gel was allowed for standing in an
ice chamber (maintained at -15C) of a cooling box for
3 hours to harden the gel to obtain an ice block. lOg of
the gel of ice block form was immersed in 10 ml of warm
- 64 -
water maintained at 40C to be slowly softened to obtain
a gel which was restored to the original rubber-like gel
high in elasticity. In view the result of this simple
test, it was ascertained that the gel could be used as a
substitution material for ice and as a coolant or cooling
medium.
Comparative Example l
4lg of the aqueous solution of polyvinyl
alcohol as prepared in Example l was poured into a square
container having a bottom of 8 cm x 8 cm sqllare and then
allowed to stand at room temperature for 2 days. The
thus obtained material was a colorless, transparent and
soft swelled membrane. The membrane was immersed in
city water for 6 hours to reveal that a portion thereof
was dissolved in water and the membrane exhibited an
adhesive property in itself. A rubber-like gel obtained
by Example l could not be formed in this Comparative
Example.
_mparative Example 2
A commercially available polyvinyl alcohol
having a degree of hydrolysis of 78.5 mol%, a viscosity
average polymerization degree of 1700 and a viscosity
at 20C of a 4% aqueous solution thereof of 30 cP. was
used in place of the polyvinyl alcohol used in Example l.
The operation sequence was the same as in Example l. 7.4g
of a froz~n, molded and dried body having a water content
- 65 -
~7~
of 55 wt% was obtained. This body was softened at 5C
after thawing, and it was observed that a large
quantity of a concentrated aqueous solution of polyvinyl
alcohol was phased-out although a small amount of a gel
layer or phase was present.
Comparative Example 3
Using a commercially available polyvinyl alcohol
having a degree of hydrolysis of 99.2 mol%, a viscosity
average polymerization degree of 500 and a viscosity at
20C of a 4% aqueous solution thereof ~f 5.6 cP. in
place of the polyvinyl alcohol as used in Example 1,
an 18 wt% aqueous solution was prepared and 20g of the
solution was frozen, molded and dried. The result was
that 13g of a crumbly gel resembling an agar gel and
having a water content of 72 wt% was obtained, and that
the resultant gel had only little elasticity.
Example 2
65g of a commercially available powder
(Water Content: 8 wt%) of a polyvinyl alcohol
having a degree of hydrolysis of 99.4 mol%, a
viscosity average polymerization degree of 2600 and a
viscosity at 20C of a 4% aqueous solution thereof of 66
cP. was dissolved in 935g of water to obtain a 6 wt%
aqueous solution. Generally in accordance with the
procedure as described in Example 1, 170g of the
solution was frozen and molded, and then the frozen
- 66 -
body was subjected to dehydration in vacuum for
10 hours. After thawing, 97g of white, opaque and highly
resilient gel (Water Content: 89 wt%, Percentage
Dehydration Rate: 43 wt%) was obtained. The gel having a
thickness of about 2 cm was immersed in 100 ml of city
water for 6 hours, whereby the gel absorbed water and the
weight of the gel reached 143g (Water Content: 93 wt%).
The volume of water squeezed from the gel by applying a
loading of 2 kg/cm was only 3 ml. This water loss
corresponded to about 2% of the contained water. This
gel was subjected to a cooling and heating cycle similar
to Example 1 to ascertain that the gel could be well
suited for use as a coolant similar to the gel obtained
in Example 1.
Comparative Example 4
Using the same polyvinyl alcohol having a
polymerization degree of 500 as used in Comparative
Example 3, an aqueous solution of polyvinyl alcohol
having a raised concentration of polyvinyl alcohol of
. 30 wt% was prepared. 120g of the aqueous solution
was molded by freezing the same under a condition of
-73C x 1 hr, and then the molded body was subjected
to dehydration in vacuum for 6 hours. After allowing
106g (Water Content: 66 wt%) of the frozen,
molded and thendried body to thaw, the body was
immersed in water for 8 hours, whereby it absorbed water
- 67 -
to have a weight of 120g (Water Content: 70 wt%) to
become extremely soft with a portion thereof being
deformed to be dissolved in water.
Example 3
lO.9g of the same powder (Water content: 8.5 wt%)
of the polyvinyl alcohol as used in Example 2 was dissolved
in 89g of water to obtain 90g of a 10 wt% aqueous solution,
which was poured into a polyethylene container having a
bottom of 10 cm x 10 cm and then cooled at -42C for
one hour to freeze and mold the same followed by
dehydration in vacuum for 4 hours.
After allowing to stand for thawing, 53g of a
gel (Water Conte~t: 83 wt%, Percentage Dehydration
Rate: 41 wt%) was obtained. A compressive force of
2 kg/cm was applied to a piece cut out from the gel
and having a size of 1 cm x 10 cm x 0.9 cm. The shape
and dimensions of this elastic gel was restored to the
original states immediately after the compressive
force was removed. The gel was subjected to repeated 50
times cycle of cooling at -15C followed by softening at
40C to ascer-tain that the gel retained the original state
and was suitable for use as a useful coolant.
Example 4
13g of the same powder (Water Content: 8.5 wt%)
of the polyvinyl alcohol as used in Example 3 was
dissolved in 89g of water to obtain 90g of an 11.6 wt%
- 68 -
aqueous solution, which was cast into a mold for molding
18 pieces of a plate-shape mass of l cm x 1 cm x 5 cm.
After cooling the pieces to freeze and to mold
the same at -53C for one hour, the mold ~as disassembled
to remove the molded masses, which were immediately
dehydrated in vacuum for 6 hours to obtain 48g of gel
pieces (Water Content: 78 wt%, Percentage Dehydration
Rate: 47 wt%). The gel piece was subjected to
a tensile test to reveal that the test piece was not
broken until the applied tensile strength reached
5 kg/cm . Also, the gel was subjected to a cooling
and heating test cycles similar to the test conducted
in Example 3 to ascertain that the gel had excellent
properties similar to those of the gel obtained in
lS Example 3.
Example 5
Using the same powder of the polyvinyl alcohol
as used in Example 3, 170g of a 6 wt% aqueous solution
thereof was prepared. The solution was divided into
five equal parts, each of which was poured into a
polyethylene beaker (Volume: 50 ml) followed by cooling
at -50C for one hour to freeze and mold the same. The
molded masses were subjected to dehydration in vacuum,
respectively, for l to 4 hours~ The thus dried masses
were immersed in water for 6 hours, and the weight of
each mass was measured. The results are shown in the
- 69 -
7~P~
following Table.
Drying Dried Gel Swelled Gel
Time
(hr.) weight Water Percentage Weight Water
Content Dehydration (g) (wt%)
twt%) Rate
(wt%)
1 27 92 21 29 93
2 26 92 24 29 93
4 19 89 44 23 91
.. _ ..... . _ _ _ . .. _
The tensile strengths of the swelled gels were
tested to obtain the following results~
Drying Time (h~ Tensile Strength (Broken kg/cm )
2 2
.. . . . _ .
The gels were immersed in city water at room
temperature for a period of more than 90 days, and it was
ascertained tha-t no mutual adhesion or deformation
occurred and the strengths of the gels were not changed
substantially. The result of cyclic cooling and heating
test was comparable to that obtained in Example 3.
- 70 -
S!L~7~
omparative Example 5
lOg of agar powder was dissolved in 90g of
warm water of 96C to prepare a 10% aqueous solution. The
aqueous solution was allowed to stand at room temperature.
When the temperatllre of the solution was lowered to 47C,
it was solidified to form a gel. The gel was not elastic,
and was broken to pieces very easily by picking by fingers.
A cut piece (1 cm x 10 cm x 1 cm) was subjected to a
tensile test to learn that the tensile strength thereof
was far lower than 1 kg/cm .
Comparative Example 6
lOg of ~-Carrageenan was dissolved in 90g of
warm water of 92C to obtain a 10~ aqueous solution,
which was allowed to stand for cooling. When the
temperature of the solution reached 47C, the solution
was solidified to form a gel. The gel was immersed in a
3~ aqueous solution of potassium chloride (hardener),
but the gel was not grown to be left in the form
resembling bo:iled rice particles. The gel was collapsed
~y picking by fingers to be changed to a paste form.
Example 6
lOg of the swelled gel obtained in Example 1 was
immersed in llg of ethylene glycol for 16 hours. As the
specific gravity of the liquid containing the gel was
changed from the initial value of 1.11 (20C) to a
constant value of 1.07 (20C), the concentration of
- 71 -
~7~
ethyiene glycol in the water phase contained
in the gel reached 50 wt%. The gel was cooled to -29C,
but it did not become hard by freezing to be held in
the form of initial elastic gel of white color. The
gel was su~jected to repeated 30 cycles of cooling to
-25C and heating to 40C to ascertain that the touch
of the gel was not changed to retain the initial
elasticity and strength resembling a living tissue so
that it was well suited for use as a coolant gel.
Example 7
140g of the gel (Water content: 93 wt~) obtained
in Example 2 was immersed in 50g of glycerin for one
night. The specific gravity at 20C of the liquid
containing the gel was lowered from the initial value
of 1.27 to 1.10, and the viscosity thereof at 20C was
changed from the initial value of 1500 cP. to 4 cP
From this fact, it was learned that the concentration
of glycerin in the aqueous solution in the gel
re*ched 40 wt%. The gel was cooled to -15C,
but the gel d:id not become hard to retain the initial
fresh appearance and the gel was well suited
for use as a coolant gel similar to that obtained in
Example 6.
Example 8
-
50g of the gel (Water content: 83 wt%) obtained
in Example 3 was immersed in 20g of propylene glycol for
- 72 -
~'7~48
8 hours. By ascertailling that the specific gravity of
the liquid containing the gel reached a constant value of
1.02, it was learned that ~he aqueous solution in the
gel contained 30~ of propylene glycol. The specific heat
of the liquid containing the gel was 0.92 cal/g deg.
at -1C and 1.92 cal/g deg. at -15C. The gel was
cooled to -15C to ascertain that it did not become
hard by freezing and had a form of rubber containing
water and resembling a living tissue. The gel was
well suited for use as a coolant gel similar to that
obtained in Example 6.
Example 9
40g of the gel (Water Content: 78 wt~) obtained
in Example 4 was immersed in 50 ml of an aqueous
solution of calcium chloride (Specific Gravity: 1.29 at
20C, 30 wt~) to ascertain that the specific
gravity of the liquid containing the gel reached a constant
value of 1.18 (at 20C). This fact revealed that the
concentration of calcium chloride in the aqueous solution
contained in the gel reached 20 wt%. The gel was
cooled to -15C, but the gel did not become hard to
find that the gel was well suited for use as a coolant
gel similar to that obtained in Example 6.
Example 10
40g of the gel obtained in Example 4 was immersed
in 100 ml of an aqueo.us solution of ammonium chloride
- 73 -
~7~
(Specific Gravity: 1.076 at 20C, 27 wt%) for 8 hours~
By ascertaining that the specific gravity of the liquid
containing the gel reached 1.05 (at 20C~, it was learned
that the concentration of ammonium chloride in the aqueous
phase contained in the gel reached 20 wt%. The gel did
not become hard even when cooled to -15C, and the gel
was well suited for use as a coolant gel similar to that
obtained in Example 6.
Comparative Example 7
A polyvinyl alcohol/borax gel commonly presented
for practical use as a coolant gel was synthesized in
accordance with the ordinary method. In detail, by
referring to the literatures, for example, H. Thiele et al.,
Kolloid Z., 173, 63 (1960), H Deuel and H. Neukon,
Makromolekulare Chemie., 3, 13 (1949), and I.G.
Farbenindustrie Akt., Fr. 743942 (1933), lOg of a
polyvinyl alcohol powder (Water Content: 7 wt~) having
a degree of hydrolysis of 97.5 mol% and a viscosity
average polymerization degree of 2000 was dissolved in
90g of water to prepare lOOg of a 9.3 wt% aqueous
solution, which was poured into 100 ml of an aqueous
solution ~2.5 wt%, 0.12M Na2B4O7~ pH 9-65) of borax
anhydrate (sodium tetraborate) at 20C. The pH value
of the borax solution was changed to pH 9.45, and it
was recognized that a large amount of a gel was separated
instantaneously. About 60 ml of the water phase was
- 74 -
1 ~7~3~
separated to obtain a gel block, and
the surface of the gel block was softly rinsed with a
small quantity (50 ml) of water to obtain 142g of a
crumbly gel of putty form. The gel was white and
translucent and readily to be deformed by picking by
fingers. The gel was fluidal at some extent and
could be filled in a container of desired shape to
obtain a mass sealingly enclosed in the container.
The soft and weak gel was allowed to stand in
an ice-chamber maintained at -15C of a household
refrigerator for 4 hours to freeze the gel in its
entirety. The gel become hard and rigid similarly to
ice .
Onthe other hand, 10g of the soft and weak
gel immersed in 10g of ethylene glycol, but the gel
was deformed after one hour immersion to become softer.
After being immersed in 10g of glycerin for half an hour,
the gel was collapsed to become pasty. Similarly, the
gel was immersed in 10 ml of methyl alcohol to find that
the liquid phase become viscous and the gel was broken
to a number of crumbly small pieces. It had already
been pointed out by the piror references, for example,
by I. Nick~rson (J. Appl. Polym. Sci., 15, 111 (1971))
that the formation of a polyvinyl alcohol/borax system
gel was hindered by the presence of the co-existing
glycerin or the like materials.
- 75 -
48
The water content (determined by evaporating
at 100C for 16 hours) of the soft and weak gel was
92 wt%.
As will be apparent from the foregoing, although
polyvinyl alcohol/borax system gels are well-known as
coolant gels and many investigations and researches have
been made as applied for patent, for example, by
Japanese Patent Publn. Nos. 21858/1968, 11210/1970,
36572/1970 and 19601/1971 and as reported, for example,
by C. S ~arvel (J. Am Chem. Soc., 60, 1045 (1938)), by
S. Saito (Kolloid ~., 144, 41 (1955)) and by H. Ochiai
(polymer (G.B.R.), 21, (5) 485 (1980)) other than
the aforementioned I. G. F. ~1933), it was found
that the gels were crumbly, soft, weak and inferior
in elasticity to have the pasty, putty-like,
jelly-like or custered pudding-like appearance and
have disadvantages that they are corroded by the
alcohols which are useful as the freezing point
depressing agents.
Example 11
86g of a commercially available polyvinyl
alcohol powder (Water Content: 7 wt%) having a degree of
hydrolysis of 97 mol%, a viscosity average polymerization
degree of 1700 and a viscosity at 20C of a 4%
aqueous solution thereof of 26 cP. was dissolved in
914g of water to obtain an 8.0 wt% aqueous solution.
- 76
~ 3L7~
On the other hand, 104g of a commercially
available bentonite (Reagent grade powder, Water
Content: 15 wt%) was dispersed in 1500g of water to
obtain a 5.5 wt% aqueous suspension of bentonite.
35g of the aforementioned aqueous solution
of polyvinyl alcohol and 10g of the aforementioned
aqueous suspension of bentonite was mixed together to
adjust the concentration of polyvinyl alcohol to 6.2
wt% and to adjust the concentration of bentonite to 1.3 wt%.
In the meantime, the used bentonite was subjected to
analytical tests including an X-ray diffratometry,
differential thermal analysis, an identification using
an electron microscope, a dehydration test by heating,
a test to learn the interlayer expansion by glycerin,
a cation exchange test 89 meq/lOOg and an ultimate
analysis. The result of the ultimate analysis
revealed that the bentonite contained 66.7 wt% of
SiO2, 8.7 wt% of A12O3, 3.1 wt% of Fe2O3, 0.3 wt% of
CaO, 0.16 wt~ of MgO, 3.2 wt% of Na2O, 0.3 wt% of K2O,
0.0 wt% of Tio2, 0.0 wt of MnO, 0.0 wt% of P2O5
and 15 wt% of H2O. From the results of the tests, the
dried clay mineral composition thereof, in % by weight,
included 64% of montmorillonite group minerals, 1% of
illites, 3% of talc, 18% of pyrophyllite and 1% of
vermiculite. Accordingly, the content of -the tri-strate
composite layer clay minera] contained in the afore-
77 -
~L~ 7~ 4~
mentioned aqueous suspension was calculated to be 1.1 wt%,
and the ratio of the used tri-strata composite layer
clay mineral was amounted to 1/6 of the polyvinyl alcohol.
45g of the thus obtained aqueous suspension was poured into
a polyethylene beaker having a bottom of 8 cm in diameter,
and cooled at -50C for 0.5 hours to be frozen and molded,
followed by dehydration in vacuum for 4 hours. After
thawing, 9.8g of a rubber-like gel (Percentage
Dehydration Rate: 78 wt%, Water Content : 65 wt%) was
obtained. The gel was immersed in 10 ml of city water for
6 hours to absorb water until the weight thereof reached
lSg (Water Content: 77 wt%). The gel was applied with
a loading of 4 kg/cm2 to ascertain that no appreciable
deformation and exudation of water observed (93% of
contained water was retained).
After allowing the gel to stand in an ice chamber
of a cooling box at -15C for 3 hours, the gel became
hard to form a rigid ice like mass. lOg of the rigid
ice-like mass was immersed in 10 ml of warm water of
40C. As a result, the mass was gradually softened
and recovered to the original state of rubber-like
elastic gel. The water-containing gel thus obtained
could be used for the substitution for ice as a coolant
or cooling medium.
The used bentonite powder (2.0g) was subjected
to the test stipulated by Japan Pharmacopoeia to learn
- 78 -
1~7~
the swelling capacity. In detail, 100 ml of water was
contained in a mess cylinder, to which the aforementioned
2g of powder was added dividedly for 10 times. Each
divided sample was added in such a way that it was
added after almost all of the sample added previously
was settled. After the completion of adding all of
the sample bentonite, the mess cylinder was held
stationarily for 24 hours. The result was that the
volume of settled bentonite was far lower than ~he
stipulated standard (higher than 20 ml),
the settled volume being only 8 ml.
Similarly, in accordance with the test method
stipulated by Japan Pharmacopoeia, the gel forming
capacity of the bentonite powder was tested using 6g of the
sample. In detail, the powder was mixed with 0.30g of
maanesium oxide, and the mixture was added to 200 ml of
water dividedly for several times. After shaking
for one hour, 100 ml of the obtained suspension was
picked up and allowed to stand for 24 hours. The
transparent supernatant layer separated at the
upper portion exceeded the standard (less than 2ml)
and amounted to 12 ml. As should be clear from the
foregoing, the commercially available bentonite used
in this Example did not satisfy the standard
stipulated by Japan Pharmacopoeia. However, as has
been described hereinbefore, such bentonite may be
~ 79 -
satisfactorily used in the present invention without any
lnconvenlence .
Example 12
In accordance with the general procedure as
described in Example 11, 300g of an 8 wt% aqueous
solution of a polyvinyl alcohol and 130g of an aqueous
suspension of bentonite were prepared and then mixed
together to obtain a mixture containing 5.6 wt% of
polyvinyl alcohol and 1.7 wt% of bentonite. 430g of
the thus obtianed aqueous suspension was poured into a
pillow-shaped bag made of a polyethylene film, and
the opening of the bag was sealingly closed using a metal
fitting followed by cooling at -50C for 2 hours
to be frozen and molded. Then,the polyethylen film
was peeled off, and the thus bared content was
subjected to dehydration in vacuum for 8 hours to obtain
204g of freeze-dried body (Percentage Dehydration Rate:
53 wt%, Water Content: 85 wt%) was obtained. After
allowing the body to stand at room temperature for 8 hours
to thaw, it was immersed in 200 ml of city water for 6
hours. As the result of immersion, the weight of the
molded body was increased to 220g (Water Content: 86 wt%)o
The resultant molded body was a swelling mass
excellent in elasticity, and was not deformed with no
appreciable exudated water even when it was squeezed
by ~hands of an adult having ordinary power. The
- 80 -
7~8
water-~etention rate was 99%.
After storing the molded body while being
contained in a transparent bag made of polyvinyl chloride
for one month, the appearance and the touch felt by
fingers (elasticity or resiliency and flesh-like feeling)
were not changed.
In view of the fact mentioned above, it should
be apparent that a large quantity, about 85 wt%, of
water was contained in the originally molded gel, and
the water content was firmly held internally of the gel.
The gel was allowed to stand in an ice-chamber
(maintained at -20C) of a refrigerator for 3 hours to
become hard by freezing. The gel could be used as a
cooling medium in place of ice.
Example 13
85g of a powder (Water Content: 6 wt%) of a
commercially available polyvinyl alcohol having a
degree of hydrolysis of 97 mol%, a viscosity average
polymerization degree of 2200 and a viscosity at
20C of a 4% aqueous solution of 54 cP. was dissolved
in 915g of water to obtain an 8% aqueous solution.
106g of a commercially available bentonite
(Reagent grade powder, Water Content: 17 wt%) was
dispersed in 1490g of water to obtain a 5.5% bentonite
suspension.
lOOg of the aforementioned aqueous solution of
- 81 -
~7~
polyvinyl alcohol was mixed with 4g of the aforementioned
bentonite suspension to prepare an aqueous suspension
containing 7.6 wt% of polyvinyl alcohol and 0.2 wt% of
bentonite. On the other hand, the bentonite of powder
form used in this Example was subjected to X-ray
diffractiometry, differential thermal analysis,
identification using an electron microscope, dehydration
by heating, interlayer expansion by glycerin and
cation exchange tests, (78 meq/lOOg). From the
results of the tests in view of the result of
ultimate analysis showing that the bentonite
contained 67.2 wt% of SiO2., 6.8 wt% of A12O3, 4.1 wt~
of Fe2O3, 0.3 wt% of CaO, 1.6 wt% of MgO, 0.4 wt%
of TiO2,0.1 wt% of MnO, 0.1 wt% of P2O5, 3.2 wt% of Na2O
and 0.4 wt% of K2O. It was estimated that the dried
clay mineral composition included 58% of montmorillonite
group minerals, 1% of illites, 1% of talc, 11% of pyrophyllite
and 1% of vermiculite. Accordingly, the concentration of
tri-strata composite clay mineral in the aqueous suspension
was 0.14 wt% which corresponded to 1/54 of the concentration
of polyvinyl alcohol. 104g of the aqueous suspension
was poured into a polyethylene beaker having a
bottom of 8 cm in diameter, followed by cooling at -63C
for 0.5 hours to be frozen and molded, and then subjected
to dehydration in vacuum for 6 hours to obtain
22g of a gel having a percentage dehydration rate of
82 -
~7~
79 wt% and a water content of 60 wt%. The gel was
immersed in 20 ml of city water for 6 hours. As a result
of immersion in water, the weight of the gel was
increased to 25g (Water Content: 70 wt%). No appreciable
deformation or exudation of water was observed even when
a loading of 3 kg/cm2 was applied to the gel, and the
result of this loading test revealed that the water-
retention rate was 9~%. The gel was then frozen in
an ice-box maintained at -15C to become an ice-like
block.
The gel was subjected to repeated cycle of
cooling at -15C and softening at 40C for 50 times to
ascertain that the gel retained the initial integrity
so that it could be well suited for use as a coolant.
2.0g of the commercially available bentonite
powder used in this Example was tested in accordance
with the test method stipulated in Japan Pharmacopoeia
to reveal that the apparent volume of precipita~t was
9 ml which was far below the standard (more than 20 ml).
Similarly, the gel forming capacity thereof was
tested in accordance with the test method stipulated
in Japan Pharmacopoeia to obtain the result that the
height of the supernatant transparent layer separated
at the upper portion passed the standard (less than
2 ml) with slight allowance.
- 83 -
Example 14
87g of a powder (Water Content: 7 wt%) of a
commercially available polyvinyl alcohol having a degree
of hydrolysis of 97 mol%, a viscosity average
polymerization degree of 1700 and a viscosity at 20C
of a 4% aqueous solution thereof of 26 cP. was
dissolved in 919g of water to prepare an 8 wt% aqueous
solution.
120g of a commercially available vermiculite
powder (Water Content: 9 wt%) was dispersed in 1200g of
water to prepare an 8 wt% aqueous suspension.
120g of the aforementioned aqueous solution of
polyvinyl alcohol was mixed with 40g of vermiculite
suspension to prepare a mixed suspension containing
6 wt% of polyvinyl alcohol and 2 wt% of vermiculite.
on ~le other hand, from the results of tests, it was
determined that the dried clay mineral composition
(in wt%) contained 4% of montmorillonite group minerals !
2% of illites, 3% of talc, 2% of pyrophyllite,85~ of
vermiculite. The composition contained 42% of SiO2, 19%
of A12O3, 2% of Tio2, 8% of Fe2O3, 2% of FeO, 1% of
CaO, 22% of MgO, 1% of K2O and 1% of Na2O. In view
of the aforementioned test results, it was revealed
that the concentration of the tri-strata composite
layer clay minerals was 1.9 wt% which corresponded
to 1/3 of the concentration of the contained polyvinyl
-- 84 --
~L17~
alcohol. 160g of the aqueous suspension was poured into
a polyethylene bea]cer having a bottom of 8 cm in diameter
followed by cooling at -80C for 0.5 hours to be frozen
and molded, and 54g of a gel having a percentage
dehydration rate of 66 wt% and a water content of 76 wt%
was obtained after being dehydrated in vacuum for 6 hours.
By immersing the gel in 50 ml of city water for 6 hours,
the weight of the gel was increased to 74g (Water Content:
83 wt%). The gel was not deformed even when a loading
of 53 g/mm was applied to the gel, and the original
shape of the gel is restored immediately after the
loading is removed. The gel was frozen in an ice-
chamber of a cooling box to be used as a substituent
for ice.
Example 15
_ . _
An 8 wt% aqueous solution of polyvinyl alcohol
was prepared generally in accordance with the procedures
as described in Example 11.
30g of the bentonite powder same as that used
in Example 11 was dispersed in 560g of an aqueous
solution of sodium pyrophosphate containing 10.7 wt% of
Na4P2O7~10H2O to prepare a 4.5 wt% aqueous suspension,
llOg of the aqueous solution of polyvinyl
alcohol was mixed with 125g of the aqleous suspension of
bentonite to prepare a mixed suspension containing 3.7
wt% of polyvinyl alcohol and 2O3 wt% of bentonite. The
- 85 -
concentration of the suspended tri-strata composite
layer clay minerals was 2.0 wt%, i.e r 1/2 times of the
concentration of polyvinyl alcohol.
235g of the mixed a~ueous suspension was poured
into a polyethylene beaker having a diameter of 8 cm,
followed by cooling at -63C for 0.5 hours, and 75g of a
gel having percentage dehydration rate of 68 wt% and a
water content of 81 wt% was obtained after thawing.
The gel was not deformed even when a loading of 4 kg/cm2
was applied thereto with no appreciable exudation of
water. The gel was frozen at -15C to become hard and
could be used as a substituent for ice.
Example 16
15g of the aqueous solution of polyvinyl alcohol
which was the same as used in Example 11 was mixed with
lOOg of the aqueous suspension of bentonite which was the
same as used in Example 7 to prepare a mixed aqueous
suspension containing 1 wt% of polyvinyl alcohol and
4 wt% of bentonite. The concentration of the tri-
strata composite layer clay minerals in the mixedaqueous suspension was 3.4 wt%, i~e~ 1/3 times
of the concentration of polyvinyl alcohol.
115g of the suspension was poured into a cylinder
having a bottom of 2 cm in diameter, followed by
cooling at -74C for 0.5 hours to be frozen and molded,
and then subjected to dehydration in vacuum for 6 hours
- 86 -
to obtain 27g of a gel having a percen~age dehydration
rate of 76 wt% and a water content of 79 wt% after thawingO
No appreciable deformation or exudation of water
was observed even when a loading of 1 kg/cm applied to
the gel. The gel was frozen at -20C to become
hard and suited to be used as a sustituent for ice.
Example 17
87g of a powder (Water Content: 7 wt%) of a
commercially available polyvinyl alcohol having a degree
of hydrolysis of 97 mol%, a viscosity average
polymerization degree of 1700 and a viscosity at 20C of
a 4% aqueous solution thereof of 26 cP. was dissolved
in 920g of water to prepare an 8 wt% aqueous solution.
120g of a commercially available talc (Water
Content: 14 wt%) was dispersed in 1190g of water to
prepare an 8 wt% aqueous suspension.
265g of the aforementioned aqueous solution
of polyvinyl alcohol was mixed with 250g of the
aforementionecl aqueous suspension of talc to prepare
a mixed suspension containing 4 wt% of polyvinyl
alcohol and 3.8 wt% of talc.
On the other hand, the used talc was subjected
to analytical tests to reveal that the dried clay mineral
composition, in % by weight, contained 6% of montmorillonite
group minerals, 2% of illites, 87% of talc, 2% of
pyrophllite and 1% of vermiculite. The composition
- 87 -
?'~3
contained 32% of MgO, G4% of SiO2, 1% of A1203,
0.3% of CaO, 0.3% of K20, 0.7% of Na20 and 0.5% of
Fe203. Accordingly, the concentration of the tri-strata
composite layer clay minerals contained in the
aforementioned mixed aqueous suspension was 3.7 wt%,
which was substantially the same as that of polyvinyl
alcohol.
515g of the mixed aqueous suspension was poured
into two cylindrical casting molds, each having a
diameter of 8 cm and a height of 4 cm, followed by
cooling at -76C for 1.5 hours to be frozen. Then,
the molded masses were discharged from the casting
molds, followed by dehydration in vacuum for 6 hours,
and then the masses were allowed to thaw, whereby two
cylindrical masses were obtained. The percenta~e
dehydration rate was 72 wt%, and the water content
was 70 wt%. No appreciable deformation or exudation
of water was observed even when a loading of 3 kg/cm
was applied on each of the cylindrical masses such
that the loading was applied in the longitudinal
direction, in other words in the direction of height.
The water-retention rate at this loading test was 98%.
The gel was packed in a bag made of polyvinyl
chloride followed by cooling at -15C to obtain a
solidified mass which could be used as an excellent
coolant.
- 88 -
P~8
Example 18
lOg of the gel prepared in Example 11 was immersed
in 8g of ethylene glycol for 16 hours. The initial index
of refraction n20 (1.430) of the liquid containing
the gel was lowered to a constant value of 1.385. As a
result of immersion, the concentration of ethylene
glycol in the water phase contained in the gel reached 50
wt%. No hardening or freezing phenomenon was observed
even by cooling the gel to -29C, and the gel retained
the initial rubber-like elasticity. After subjecting
the gel 33 times cyclic operations of cooling the same
to -25C and then heating again to 40C, the touch
of the gel was not changed to have the initial living
tissue like elasticity and satisfactory strength,
so that it could be satisfactorily used as a coolant.
~xample 19
140g of the gel (Water Content: 86wt%) which
was the same as that used in Example 12 was immersed in
68g of glycerin. As a result of immersion, the initial
specific gravlty (1.27 at 20C) of the liquid
containing the gel was lowered to 1.10 at 20C and the
initial viscosity (1500cP. at 20C) was also lowered to
4 cP., to learn that the concentration of glycerin in the
aqueous phase contained in the gel reached 40 wt%. The
gel was not hardened even by cooling to -15C to retain
the initial fresh looking and touch, so that it could be
- 89 -
~7~ 8
satisfactorily used as a coolant.
Example 20
20g of the gel (Water Content: 70 wt%) prepared
in Example 13 was immersed in 7g of propylene glycol for
8 hours. As the index of refraction (nD ) of the liquid
containing the gel reached a constant value of 1.3660, the
aqueous solution contained in the gel reached the state
containing 30% of propylene glycol. The specific heat at
-1C was 0.92 cal/g-deg, and the specific heat at -15C
was 1.92 cal/g deg. The gel was not frozen or hardened
even when cooled at -15C, and retained its inherent
rubber-like properties resembling a living tissue.
Example 21
40g of the gei (Water Content: 83 wt%) prepared
in Example 14 was immersed in 50 ml of a 30 wt%
aqueous solution of calcium chloride having a specific
gravit~ at 20C of 1.29 for 8 hours. After the 8 hour
immersion, -the specific gravity of the aqueous solution
containing the gel reached a constant value of 1.].8
at 20C. At that time, the concentration of calcium
chloride in the aqueous solution contained in the gel
reached 20 wt%. The gel was not hardened even by
cooling the same to -15C to retain i-ts flexibility,
and hence the gel could be used as a soft coolant.
~5 Example 22
40g of the gel as prepared in Example 14 was
- 90 -
immersed in lOOml of a 27 wt% aqueous solution (Specific
gravity: 1.076 at 20C) of ammonium chloride for
8 hours. By ascertaining that the specific gravity of
the liquid containing the gel reached a constant value of
1.05 at 20C, it was recognized that the concentration of
ammonium chloirde in the aqueous solution contained
in the gel reached 20 wt%. The gel was not hardened
even by cooling the same to -15C, and thus could
be used satisfactorily as a soft coolant.
Example 23
500g of a 9.4% aqueous solution of a polyvinyl
alcohol having a degree of hydrolysis of 99.5 mol%,
a viscosity average polymerization degree of 2600 and a
viscosity of a 4% aqueous solution thereof at 20C of
67 cP. was mixed with 500g of ethylene glycol. The
mixture was poured into a polyethylene container
having a bottom of 21 cm x 25 cm, followed by cooling
at -50C for 8 hours, and then directly subjected
to dehydration in vacuum to remove 40g of water.
The percentage dehydration rate, i.e. the weight
reduction rate of the cooled mass, was 4 wt%. The
resultant gel had elasticity and flexibility resembling
KONNYAKU, and yet had a mechanical strength superior
to that of KONNYAKU and a compressive strength
of more than 10 kg/cm2.
The gel was not hardened or solidified after
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~L~.7~P48
being allowed to stand in an ice-making chamber of a
household refrigerator, and also withstood cylic cooling
and subsequent heating to room temperature to find that
it was excellent when used as a soft eoolant.
Example 24
630g of a polyvinyl alcohol (Water Content: 7 wt%)
having a degree of hydrolysis of 97.5 mol%, a viscosity
average polymerization degree of 2200 and a viscosity of
a 4% aqueous solution thereof at 20C of 56 cP. was
dissolved in 4800g of water to prepare an 11.4 wt%
aqueous solution.
4536g of the thus prepared aqueous solution
was mixed with 2443g of polypropylene glycol, and 4536g of
the mixture was poured into a polyethylene container
having a bottom of 90 cm x 90 cm and a depth of 1 cm,
followed by allowing to stand at -50C for 6 hours, and
then directly subjected to dehydration in vacuum to
reach the percentage dehydration rate to 15 wt~, the
weight of the removed water to 680g and the liquid
content to 91 wt%.
In order to make a vest for an adult man from
the thus obtalned gel of 5 mm thick sheet form, one for
each of the left front-body, rear-body and right front-
body was cut from the gel sheet so that three cut-pieces
for a vest having a length of 48 cm and a chest (including
slack) of 97 cm were eut oEf. Then, said three cut-
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~ ~76~48
pieces were sewn together by sewing the left and right
shoulder portions.
The thus made cooling vest was placed in a
large-scale cooling box for industrial use maintained
at -20C for 8 hours. No hardening or solidification
was observed so that the cooled vest could be fitted
over the working clothes by an adult man who could
comfortably be working at a high temperature working
site.
Example 25
30g of a polyvinyl alcohol powder having a
degree of hydrolysis of 99.5 mol~, a viscosity average
polymerization degree of 2600 and a viscosity of a 4%
aqueous solution thereof at 20C of 66 cP., 158g of
propylene glycol and 292g of water were mixed together
to prepare a mixture which was agitated at 90C for 2
hours. Then, 471g of the mixture was poured into a
polyethylene container having a diameter of 20 cm and
a depth of 2 cm, followed by cooling at -45C for 5 hours,
and then subjected to dehydration in vacuum to reach
the percentage dehydration rate of 13 wt~ (Weight
of Removed Water: 61g, Liquid Content: 93 wt~).
The thus molded disk-shaped gel (Diameter: 19.5 cm
Thickness: 1.4 cm) was cut along a radial line, i.e.
along a line from the center of the disk to a selected
point on the circumference. Desired segme.ntal areas of the
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disk were overlapped to form a cone made of a gel sheet
and having no bottom. The thus obtained cone-shaped cap
was not hardened even after being allowed to stand for
one night in a household refrigerator, and could be
conveniently used as a cap-shaped collant only by wrapping
with qauze and applied on a breast of a patient
suffering mammary phlegmasia in maternity or other
hospitals.
Example 26
From two sheets of disk-shaped gel prepared in
accordance with the method as described in Example 25,
four sectors or segmental pieces each subtending a
center angle of 50 degrees and eight rectangular
plates of 7 cm x 5 cm were cut out. These pieces
were arranged on the external faces of the left and
right cups of a brassiere (Size: 95D) sold under the
Registered Trade Mark "Lovable R", and sewn to
the cups using a polyester string (O.lmm in diameter).
The brassiere attached with the cut gel pieces were
placed in household refrigerator for 6 hours, and it
was ascertained that the gel-pieces were not hardened to
be held as the coolant gels having fresh appearance
and soft touch. The brassiere was tried to be
used as a substituent for the triangle bundage
conventionally used in maternity or other hospitals
for cooling expanded breasts due to inflammation,
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and favorable result could be obtained thereby.
Example 27
500g of a 9.4 wt% aqueous solution of polyvinyl
alcohol prepared by dissolving 50.5g of a powder (Water
Content: 7 wt~) of a commercially available polyvinyl
alcohol having a degree of hydrolysis of 99.5 mol%, a
viscosity average polymerization degree of 2600 and a
viscosity of a 4% aqueous solution thereof at 20C of
67 cP~ in 450g of water was mixed with 500g of ethylene
glycol to obtian a mixture. The mixture was poured into
a polyethylene container having a bottom of 21 cm x 15 cm,
followed by cooling at -50C for 6 hours, and then
directly subjected to dehydration in vacuum to remove
48g of water (Percentage Dehydration Rate: 5 wt%). The
thus obtained gel had an elasticity and flexibility
resembling those of KON~YAKU, and yet was superior
in mechanical strength. The compressive strength of
the gel was 10 kg/cm2. The gel having the dimensions
of 20 cm x 15 cm x 3 cm was used as the first gel
layer (A).
On theother hand, 1500g of a 9.4 wt% aqueous
solution of polyvinyl alcohol prepared as described above
was poured into a polyethylene container having the same
shape and dimensions as set forth above, followed by
cooling at -50C for 6 hours, and then subjected directly
to dehydration in vacuum for 6 hours. After thawing,
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1200g (Water Content: 88 wt%, Percentage Dehydration
Rate: 20 wt%) of rubber-like gel was obtained. The
gel was immersed in 1 liter of city water for 6 hours,
whereupon the gel absorbed water and the weight
thereof was increased to 1370g (Water Content: 90 wt~).
The gel was not deformed with no appreciable
exudation of water therefrom even when it was applied
with a loading of 10 kg/cm . The gel was changed to
ice-like form by placing for 8 hours the gel absorbing
water in an ice-chamber of a cooling box, the ice-chamber
being maintained at -15C. The gel was immersed in
1 liter of warm water of 40C, whereupon the gel was
restored to its original resilient gel resembling a
rubber. The gel having the dimensions of 20 cm x
15 cm x 4.6 cm was used as the second gel layer
(B).
The gel layer (A) was overlaid on the gel
layer (B), and the composite layers were wrapped with
a polyethylene bag and allowed to stand an ice-making
chamber of a household refrigerator for one night,
whereby the gel layer (B) was frozen to become hard
and the gel layer (A) exhibited cold KONNYAKU-like
appearance and retained its inherent flexibility and
resiliency.
The thus produced composite coolant gel could
withstand repeated cooling and heating operation so
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~7~
that it was well suited for use as a substituent for an
ice-pillow.
Example_28
30g of a powder of a polyvinyl alcohol having
a degree of hydrolysis of 99.5 mol%, a viscosity average
polymerization degree of 2600 and a viscosity of a 4%
aqueous solution thereof at 20C of 66 cP., 158g of
propylene glycol and 292g of water were mixed together
and then agitated at 93C for 2 hours to prepare a
mixture. 470g of the mixture was poured into a
polyethylene container having a diameter of 20 cm and
a depth of 2 cm, followed by cooling at -50C for 6
hours, and then sub~ected directly to dehydration in
vacuum to reach teh percentage dehydration
rate to 13 wt% (Weight of Removed Water: 60g, Liquid
Content: 93 wt%).
The thus molded disk-like gel (Diameter; 19.5 cm,
Thickness: 1.4 cm) was cut along a radial line, i.e.
along a line from the center of the disk to a selected
point o~ the circumference. Then, desired segmental
areas of the disk were overlapped to form a cone made
of the gel layer (A) and having no bottom.
On the other hand, 500g of the aforementioned
10 wt% aqueous solution of polyvinyl alcohol was poured
into a polyethylene container having a diameter of
20 cm and a depth of 2 cm, followed by allowing to stand
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1~7~ 8
at -47C for 6 hours, and then subjected directly to
dehydration in vacuum to reach the percentage dehydration
rate to 17 wt% (Weight of Removed Water: 85g, Water
Content: 88.0 wt~.
The gel was immersed in 1 liter of city water
for 6 hours, whereupon the gel absorbed water and the
weight thereof was increased to 430g (water Content:
88.4 wt%).
The thus molded disk-like gel (Diameter:
19.5 cm, Thickness: 1.5 cm) was out along a radial
line, l.e. along a line from the center of the disk
to a selected point on the circumference. Then,
desired segmental areas of the disk were overlapped
to form a cone made of the gel layer (B) and having
no bottom.
These two conical gel layers were overlaid such
that the gel layer (A) was placed internally of the gel
layer (B), followed by sewing to unite them. The thus
united cap-shaped combination was allowed to stand in
an ice-making chamber of a household refrigerator
for one night, whereby the inside gel layer (A) did
not become hard although the gel layer (B) was frozen
to become hard. The conical united gel layers (A)
and (B) was conveniently used as a cap-shaped coolant
by wrapping with gauge and applied on a breast of
a patient suffering mamary phlegmasia, since the side
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~7$~8
contacting with the skin of the patient was continuously
held to have a soft touch~
Example 29
Two sheets for each of the disk-shaped gels of
different systems (one being a polyvinyl alcohol/
propylene glycol/water system and the other being
a polyvinyl alcohol/water system) obtained as described in
Example 28 were prepared~
Four sectors or segmental pieces each
subtending.a center angle of 50 degrees and eight
rectangular plates of 7 cm x 5 cm were cut out from the
two sheets of the polyvinyl alcohol/water system gel.
These cut-pieces were arranged on the external faces
of the left and right cups of a brassiere
(Size: C70, Bust: 85, Underbust: 70) produced and
sold by Wacoal Co., Ltd. and sewn to the cups.
Similarly, four sectors or segmental pieces each
subtending a center angle of 50 degrees and eight
rectangular plates of 7 cm x 5 cm were cut out from the
two sheets of the polyvinyl alcohol/polypropylene glycol/
water system gel. These cut-pieces were arranged on the
internal sides of the cups, and sewed thereto. A rubber
ball having a diameter of 10 cm was contained in each of
the cups of the brassiere. Then, the brassiere was
allowed to stand in a household refrigerator for 6 hours.
Although the gel-pieces onthe external faces of the
r`
_ 99 _
~3L7~Q48
cups were hardened, the gel-pieces fitted inside of the
cups were left unhardened to retain a soft touch due to
inherent flexibility and resiliency. After removing
two rubber balls from the respective cups, and then the
brassiere provided with the gels prepared in accordance
with the present invention was subjected trial use for
cooling expanded breasts due to inflammation in place
of the conventionally used triangle bundage. The result
of trial uses in maternity or other hospitals were
satisfactory.
Example 30
1 kg of a 10.0 wt~ aqueous solution of a
polyvinyl alcohol having a degree of hydrolysis of
99.5 mol~, a viscosity average polymerization degree
lS of 2600 and a viscosity of a 4% aqueous solution thereof
at 20C of 67 cP. and 500g of ethylene glycol
were mixed to prepare an aqueous solution containing
6.7 wt% of polyvinyl alcohol and 33 wt% of ethylene
glycol. The thus prepared aqueous solution was cast
into a heLmet moldinq mold, followed by cooling
at -40C for 8 hours, and then subjected to dehydration
in vacuum directly to remove 200g of water (Percentage
dehydration rate 13 wt%). Then the dehydrated
mass was allowed to stand at room temperature for
thawing.
The thus molded gel of helmet shape was allowed
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~7~8
to stand in an ice-making chamber maintained at -10C of
a refrigerator for 8 hours. The inherent flexibility of
the gel was not impaired, and the helmet thus produced
could be conveniently used as a cooling cap in the
medical therepy for alleviating the harmful secondary
action caused by chemotherapy for curing cancer
diseases.
Example 31
Generally in accordance with the procedures
as in Example 30, except in that 440g of propylene
glycol and 60g of ~-carrageenan were used in place
of 500g of propylene glycol, a molded gel of helmet
shape was prepared. The color of the helmet-shaped gel
was light brown and different from the white color
of the gel prepared by the precedir.g Example 30.
However, the gel prepared by this Example was
excellent in resiliency and elasticity and had a
sufficient mechanical strength for use as a helmet
which might be subjected to frequent put-on and put-
off operations~ The helmet-shaped gel was allowed
to stand for one night in an ice box of a refrigerator
maintained at -20C to reveal that it was not frozen
or hardened to retain its initial elasticity and
resiliency. The helmet-shaped gel is allowed to
stand at ambient temperature until the temperature
thereof reached 0C, whereupon it was put on the head
101
~ 7~)'4~
of an adult, who lay in the horizontal supine position.
After the lapse of 8 minutes, the temperature of the
head skin reached 20 ~ 22C, and the temperature of the
head skin was maintained within 20C to 25C for
33 minutes. The helmet-shaped gel was composed of
7.5 wt% of polyvinyl alcohol, 33.4 wt% of propylene
glycol, 4.6 wt% of ~-carrageenan and 54 wt% of water.
Although the present invention has been
described with reference to specific examples thereof,
it should be understood that various modifications and
variations may be easily made by those skilled in the art
without departing from the spirit of the invention. It
is, thus, intended to include all such modifications and
variations within the wide scope of the invention as
defined in the appended claims.
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