Note: Descriptions are shown in the official language in which they were submitted.
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This inventiou relates to hardenable sheet materials and
more particularly to sheet materials which harden on contact
with water. ~ater-hardenable sheet materials have a variety
of applications, for example, in orthopaedic surgery they are
widely used as splinting materials. Traditionally, bandages
comprising plaster-of-Paris are soaked in water and then applied
to the affected limb. The plaster-of-Paris hardens within a
- few minutes to form a rigid casing. Although plaster-of-Paris
casts are adequate for some applications, they are heavy, not
wholly resistant to water, and partially opaque to x-rays. In
addition, plaster-of-Paris casts usually take at least twenty four
hours to develop their maximum strength, and thi~ time may be
considerably longer in high humidity environments. If a
plaster-of-Paris cast is stressed whilst in the "green" state,
that is to say before it has reached its maximum strength, it i9
liable to delaminate, leading to incipient failure of the cast.
In some applications these disadvantages can be quite serious,
and for this reason many attempts to find an alternative to
plaster-of-Paris have been tried. For example, it has been
suggested to use a polymerisable resin system which i~ polymsrised
by ultraviolet light. ~owever, this requires the use of
specialised techniques, and of course involves the expense of
a suitable ultraviolet light source. For many surgical
applications there i~ a need for a splinting material which is
simple to u~e, hardens at room temperature without the evolution
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of substantial amounts of heat, has a high green strength, develops
its maximum strength as rapidly as possible, is non-toxic, resistant
to hot and cold water, and transparent to x-rays.
In recent years, a range of dental cements have been developed
known as the poly(carboxylate) cements and these are described and
claimed in British Patent~ Nos. 1,139,430 and 1,316,129. The~e materials
normally comprise an ion-leachable powder and an a~ueous soluti-Dn of a
poly(carboxylic acid) which when mixed together form a cement of great
mechanical strength and water resistance.
The present invention provides a water-hardenable sheet material in
which the hardening reaction involves the formation of a poly(carboxylate)
cement~
According to the present invention, a water-hardenable sheet material
comprises a flexible web having deposited thereon an intimate mixture of a
water soluble poly(carboxylic acid) or a precursor thereof and an
ion-leachable inorganic particulate material.
The term "sheet" is used in the sense of a body whose breadth
i8 large in comparison with its thickness. The flexible web
may be woven, laid down as a non-woven fabric, cast, or extruded.
It is preferred that the web be permeable in order to aid the
deposition thereon of the water soluble poly(carboxylic acid)
or precursor thereof and the ion-leachable inorganic particulate
material. For surgical applications, a permeable web has
the further advantage that it can allow access of air to the
encased limb. The web most preferably has a porous structure,
and in the case of woven or non-woven fabrics, the poro~ity
of the web-may be conditioned by the method of manufacture, so
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that this particular characteristic may be predetermined to suit anyspecial requirements.
; The flexible web may ccmprise an or~anic natural or synthetic
polymeric material, and particularly a cellulosic fibrous material such -`
as cotton or other vegetable fibres, animal fibres such as wool, and
synthetic polymeric fibrous material such as polyamides, polyesters, and
cellulose acetates. The flexible web desirably has sufficient mechanical
strength to enable it to act as a reinforcement for the sheet material.
For surgical aPplications very good results have been obtained using a
cotton bandage fabric, for example of leno weave. The cotton fibres may
be reinforced with glass fibre if desired. Although less preferred, the
flexible web may also be in the form of an impermeable film or foil of
plastic or other suitable material.
me preferred poly(carboxylic acids) are those prepared by
the homopolymerisation and copolymerisation of unsaturated aliphatic
carboxylic acids for example acrylic acid, itaconic acid, mesaconic acid,
citraconic acid, and aconitic acid, and copoly~meris~tion of these acids
with other unsaturated aliphatic monomers, for example, acrylamide and
acrylonitrile. Particularly preferred are the homopolymers of acrylic
acid, and its copolymers, particularly with itaconic acid for example as
described and claimed in ~ritish Patent Specification No. 1,~84,454.
Good results have also been obtained using a copolymer of vinyl methyl
ether and maleic acid. Any suitable route may be used for the preparation
of the poly(carboxylic acid) and for example, polyacrylic acid may be
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prepared by hydrolysis of polyacrylonitrile. It is also possible to use
a precursor of a poly(carboxylic acid) which will be transformed into
the poly(carboxylic acid) on contact with water, for example, a poly(car-
boxylic acid anhydride) or other suitable polymer. The poly(carboxylic
acid anhydride) may be a hcmopolymer of an unsaturated carboxylic acid
anhydride, or a copolymer with a vinyl monomer, and particularly a vinyl
hydrocarbon m~nomer. Particularly good results may be obtained using
; homopolymers of maleic anhydride, and copolymers thereof with ethylene,
propene, butene and styrene.
The poly(carboxylic acid) or precursor thereof is preferably
linear, although branched polymers may also be used, and preferably has
an average molecular weight of from 1,000 to 1,000,000 and most preferably
from 10,000 to 100,000. In this specification the average molecular
weight is defined as being that measured by gel permeation chromatography.
The poly(carboxylic acid) is preferably in fine particulate
form, and most preferably with a degree of fineness such that it will
pass through a 150 BS mesh sieve.
The ion-leachable inorganic particulate material may for
example comprise a di- or polyvalent metal oxide, preferably one that has
been deactivated, for example by heat treatment as described in Eritish
Patent No. 1,139,430, or by partially coating the surface of the metal
oxide particles with an organic acid such as stearic acid.
A preferred metal oxide is zinc oxide, to which there may be
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added up to about 10% by weight of other metal oxides such as, for
example magnesium oxide. The di- or polyvalent metal oxide may
if desired be replaced by a salt of the di- or polyvalent metal
with a weak acid,the weak acid being capable of an exchange reaction
with the poly(carboxylic acid) used, for example zinc oxide may be
wholly or partially replaced by zinc borate. Alternatively, the
ion-leachable inorganic particulate material may comprise a fused
oxide made by heating a mixture of simple oxides to fusion
temperature or an oxide glass, for example a glass comprising
calcium or sodium oxide with alumina and silica. The preferred
ion-leachable inorganic materials for use in the present invention
are aluminosilicate glasses, wherein the ratio by weight of acidic
to basic oxides in the glass is such that the glass will react
with a poly(carboxylic acid) in the presence o$ wàter to produce
a poly(carboxylate) cement. It has been found that the rate of
reaction increases with increasing basicity of the aluminosilicate
gla~s and thus the ratio of the oxides in the glass composition can
be chosen in order to allow adequate working time to form the
water-hardenable sheet material into a desired shape before it has
set. For many applications it is preferable to attain a working
time of about 5 minutes, or less, and then to have the shortest
possible setting time in which the sheet material hardens and
attains an appreciable rigidity and mechanical strength. Suitable
aluminosilicate glasses may, for example, be prepared by fusing
mixtures of alumina, silica, and calcium oxide in the appropriate
proportions, together with, if necessary, up to 30% by weight,
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based on the total weight of the composition, of a flux which may be a
fluoride, a borate, a phosphate, or a carbonate. Many suitable alumino- -
silicate glasses are available. Most prefera~ly, however, the ion-leachable
inorganic partic~ate material comprises a fluoroaluninosilicate glass,
for example as described and claimed in British Patent No. 1,316,129,
wherein the ratio by weight of silica to alumina is from 1.5 to 2.0 and
the ratio by weight of fluorine to alumina is from o.6 to 2.5 or wherein
; the ratio by weight of silica to alumina is from 0.5 to 1.5 and the ratio
by weight of fluorine to alumina is from 0.25 to 2Ø The fluoroalumino-
silicate glasses may be prepared by fusing mixtures of silica, alumina,
cryolite, and fluorite in the appropriate proportions at a temperature -
above 950 C. Suitable methods for preparing the glasses are described in
the aforementioned British Patent.
me degree of fineness of the ion-leachable inorganic particulate
material should preferably be such that when the water-hardenable sheet
material is contacted with water it sets in the desired shape within an
, acceptable period. Preferably the degree of fineness of the ion-leachable
} inorganic particulate material is such that it will pass through a 150
mesh B.S. sieve and most preferably such that it will pass through a 350
mesh B.S. sieve. Where the ion-leachable inorganic material comprises
an aluminosilicate glass, this may be used in the form of glass fibres
if desired.
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In a preferred method of preparing the water-hardenable sheet
materials of this invention, the ion-leachable inorganic particulate
material is slurried in a dispersion or solution of the
poly(carboxylic acid) or precursor thereof in a suitable organic
solvent, Ifor example methyl ethyl ketone, cyclohexanone or
methylene dichloride. The flexible web is then impregnated with
the slurry by a coating technique, and the organic solvent removed,
for example by evaporation. m e amount of slurry deposited on the
flexible web may be varied within wide limits, but preferably the
depo~ited ion-leachable inorganic particulate material and
poly(carboxylic acid) or precursor thereof comprise from ahout 5 to
about 95% by weight, preferably from 60 to 90% by weight, of the
total weight of the water-hardenable sheet material. m e acid
and the ion-leachable inorganic particulate material are preferably
present in the ratio of 1 to 100 parts by weight of ion-leachable
inorganic particulate material for each 10 parts by weight of the
poly(carboxylic acid) or precursor thereof.
Preferably, the ~lurry comprises a binder to assist the
adherence of the ion-leachable inorganic particulate material to
the flexible web. Suitable binders include polyvinyl alcohol,
polyvinyl acetate and partially hydrolysed polyvinylacetate.
Usually only small quantities of the binder are required, for
example up to about 5% by weight based on the combined weight
of the acid and the inorganic material, and preferably from
0.1 to 1%.
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The water-hardenable sheet m~terial may comprise additional
components, for example chemically unreactive particulate fillers may be
included, to effectively eliminate any slight contraction which may take
place on hardening of the hardenable sheet material. It is also often
found advantageous to add a water soluble chelating agent such as tartaric
; acid, as described and claimed in British Patent Specification No. 1,422,3~7,
to the water-hardenable sheet material as this has been found to decrease
the setting time of poly(carboxylate) cements and increase the strength
of the set cement.
In low humidity environments, poly(carboxylate) cements tend
to lose water and this may have a slight detrimental effect upon the
strength of the hardened sheet material. This effect may be substantially
overcome by including in the slurry to be applied to the flexible web a
water insoluble polymer. Such a polymer may, for example, be dissolved
or emulsified in the organic solvent so that after removal of the solvent
the water insoluble polymer is in particulate form, intimately mixed with
the other components. The water insoluble polymer preferably comprises
pendant carboxylic acid groups which can take part in the hardening
reaction, and for example it may comprise a copolymer of an unsaturated
allphatic carboxylic acid for example acrylic acid, methacrylic acid and
itaconic acid, and an unsaturated aliphatic ester, for example an acrylic
ester such as methyl methacrylate, ethyl acrylate and ethyl methacrylate.
Good results E3y be obtained using a
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copolymer of methacrylic acid and ethyl acrylate. Alternatively the
water insoluble polymer may be applied to the water-hardenable sheet ~ -
material as an aqueous emulsion at the time of use.
When used as splinting materlal-s~ the water-hardenable sheet
materials of this invention are designed to be used by the practitioner
in the same manner as the conventional plaster-of-Paris splinting materials.
m us the water-hardenable sheet material in the form of a roll may be
contacted with water by, for example, dipping or spraying, and then wound
around the limb which it is desired to encase, overlapping ad~acent turns
as required. me sheet material is ~nitially flexible enabling it to be
formed into a desired shape prior to hardening. Within a relatively short
time, usually a few minutes, however, the hardening has proceeded to an
extent sufficient to produce a hard tough cast. me hardening reaction
may be accelerated by the use of warm water.
The water-hardenable sheet materials of the present invention
may also find applications outside conventional surgical use, for ex~mple
they may be used in forestry to repair damaged branches of young ~rees,
¦ and may find application as m~delling materials for children.
e inventlon is illustrated by the following Example:
EXAMPLE
This Example describes the production of a water-hardenable
sheet material according to the present invention and its application to
the manufacture of surglcal splints.
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80.0 gms. of a fluroaluminosilicate glass powder prepared
as described in Example 2 of British Patent No. 1,316,129 and
having a particle size of 350 B.S. mesh are intimately mixed with
24.4 gms. of finely powdered polyacrylic acid of average molecular
weight 90000 and water content 8% by weight. This mixture is
slurried in methylethyl ketone to give a suspension of about 40X
solids, and 0.5 gm. of poly(vinyl acetate) binder added. With
the suspension in agitation, 50 mm width leno gauze bandage is
passed through and the pick-up of solids controlled with a doctor
blade. The methylethylketone is removed by drying under a hot
air blower whereupon the gauze can be rolled up in the manner of
a conventional bandage.
m e coated gauze is then sprayed with water, and wound around
a cylindrical mandrel, smoothing the turns by hand. m e turns
of the gauze are allowed to overlap so that on hardening, after
30 minutes, the gauze can be removed from the mandrel as a hollow
cylindrical cast. After 48 hours the cast i8 cut up into rings,
mounted in an Instron machine and subjected to compression at a
rate of 5 mm.min 1 The stresses for strains of 5%, 10% and 12.5%
are calculated. For the purposes of comparison, a pla~ter-of-Paris
ca~t i~ prepared in the same manner and similarly tested for
compressive strength. The results are given below:
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TABLE 1:
Specimen Rin~ Dimensions Poly(carboxylate) Plaster-of-Paris
Length (mm) 15 15
Internal Diameter (mm) 14 14
External Diameter (mm) 15. 5 18
Weight of material (Kgm ) 0.183 0.398
Length of gauze bandage (mm) 225 225
TABLE 2:
. _
Strain (%) Average Stress (N)
Poly(carboxylate) Plaster-of-Paris
.
16.3 21.1
22.4 26.4
12.5 24.2 28.8
These results show that the water-hardenable sheet materials of
the present invention have excellent compressive strength combined
with a considerable reduction in weight. Although the
poly(carboxylate) cast iY half the weight of the plaster-of-Paris
5 cast, its compressive strength is only slightly less. In addition,
the poly(carboxylate) cast is not attacked by hot or cold water,
is non-toxic and non-irritational, and is transparent to x-rays.
The average time taken for a poly(carboxylate) cast to reach its
maximum strength is about 8 hours, in comparison with 2~ hours for
a plaster-of-Paris cast.
Further tensile stress tests carried out on samples of comparable
size show that a poly(carboxylate) cast i9 almost twice as strong
as a cast made from plaster-of-Paris.
