Note: Descriptions are shown in the official language in which they were submitted.
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1
TEMPERATURE SENSITIVE ADHESIVE
COMPOSITION
TECHNICAL FIELD
The present invention relates to a flushable adhesive
composition that may be disposed of by flushing in a conventional
toilet. More particularly, the present invention relates to a
temperature-triggerable water soluble adhesive composition
comprising a poly (vinyl alkyl ether), preferably poly (vinyl methyl
ether) and a hydrophobic polymer) preferably a hydrophobic
polystyrene resin or an acrylate. The adhesive composition of the
present invention retains its integrity at fluid temperatures above
approximately 33~ C., but is water soluble at fluid temperatures
0
below approximately 22 C.
BACKGROUND OF THE INVENTION
The term "adhesive" as used herein encompasses the
term adhesive and its art accepted usages. For example, the term
adhesive includes, but is not limited to, the material that causes one
surface to adhere to another like or unlike surface.
The term "flushable" as used herein means capable of
being flushed in a conventional toilet and being introduced into a
conventional sewage system such as a municipal sewage system, an
industrial septic tank system and a residential septic tank system,
without causing an obstruction or blockage in the conventional toilet
or conventional sewage system.
The term "flushable adhesive" as used herein means the
temperature-triggerable water soluble adhesive of the present
invention.
The term "flushable product" as used herein refers to
products comprising or containing the flushable adhesive of the
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present invention and includes, but is not limited to) adhesives, tapes,
labels, sheets, papers, tissues, structural members, nonwoven fabric
articles, wo v en fabric articles and combinations thereof. Flushable
articles include, but are not limited to, infant care articles such as
diapers, protectors, bibs and wipes; child care articles such as
training pants) protectors, bibs and wipes; adult care articles such as
diapers and incontinence pads; feminine care articles such as pads and
tampons; medical care articles such as bed coverings, wound
dressings, ostomy bags. wipes and gowns; surgical care articles such
as table coverings, drapes, wound dressings and gowns; household
articles such as wipes; insulation; and packaging materials.
The term "water dispersible" as used herein means an
adhesive film which, when exposed to a fluid at a temperature of
approximately 22~ C. for approximately 2 minutes, dissolves or
fragments into pieces all of which pass through a 20 mesh screen.
The term "water disintegratable" as used herein means
an adhesive film which, when exposed to a fluid at a temperature of
approximately 22~ C. for approximately 2 minutes, disintegrates or
fragments into pieces some of which will pass through a 20 mesh
screen.
The term "water weakened" as used herein means an
adhesive film which, when exposed to a fluid at a temperature of
approximately 22~ C. for approximately 5 minutes, loses rigidity and
will bend without the application of an external force when the film
is held horizontally by one corner.
The term "water stable" as used herein means an
adhesive film which, when exposed to a fluid at a temperature of
approximately 22~ C. for approximately 5 minutes, is not water
dispersible, water disintegratable or water weakened.
The term "water soluble" as used herein means an
adhesive which is water dispersible or water disintegratable in the
0
presence of fluid having a temperature of approximately 22 C., such
as the temperature of tap water normally present in a conventional
toilet bowl.
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The term "water insoluble" as used herein means an
adhesive which is water stable in the presence of fluid having a
temperature of approximately 33~ C., such as the temperature of
body waste fluids.
The term "temperature-triggerable" as used herein
means that the water solubility of an adhesive is temperature
dependent. More particularly, the term "temperature-triggerable"
means that the flushable adhesive of the present invention is water
0
insoluble at or above a temperature of approximately 33 C. and is
l0 water soluble at or below a temperature of approximately 22 C .
The term approximate as used herein with respect to temperature
includes temperatures within two degrees of the stated temperature.
Disposable products which are easy to use, relatively
inexpensive and sanitary are a great convenience. However, as the
15 closing of solid waste landfills preclude dumping and as clean air
standards preclude incineration, disposal of these products has
become a problem. An alternative to dumping and incineration is the
use of flushable products which can be disposed of by flushing down
a conventional toilet into a conventional sewage system. To be
20 flushable, a product must meet two criteria. First, it must have
sufficient wet strength for its intended use. Second, it must be water
soluble on contact with toilet bowl water.
One approach to producing a flushable product is to
limit the size of the product so that it will pass through plumbing
25 without causing blockages. Such products have high wet strength,
but do not disintegrate on contact with tap water in a toilet bowl. A
second approach to producing a flushable product is to produce a
product which is not itself water soluble but which disintegrates on
contact with acidic or alkaline aqueous solutions or in the presence of
30 specific enzymes. Such products have high wet strength, but require
the addition of acidic, alkaline or enzymatic material to enable their
disposal in a conventional sewage system. A third approach to
producing a flushable product is to adhere a product together with a
salt sensitive adhesive. However, some salt-sensitive adhesives
35 precipitate in the presence of high calcium ion concentrations. As
*rB
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the calcium content of normal tap water varies tremendously among
geographic locales (1982-1983 Analysis of Metropolitan Water
Supplies), in locales having high calcium containing water, products
produced using calcium adhesives may not, in fact, be flushable. For
a useful flushable adhesive, the adhesive used should be flushable in
the tap water of any geographic locale so that the flushable product
disperses or disintegrates on contact with the tap water.
However, even if a flushable adhesive and a flushable
product containing the flushable adhesive are water soluble in any
geographic locale, to be useful the flushable product must also have
sufficient wet strength for its intended use. Sufficient wet strength
for its intended use and dispersion or disintegration on contact with
toilet bowl water is particularly difficult to achieve for adhesives in
disposable products designed to contact body fluids. This difficulty
results from the similarity in composition of body fluids and of tap
water. This is illustrated in Table 1. which compares the pH and
ionic composition of the body fluid urine and of tap water.
Parameter Infant Urine Ta Water
5.8-8.5 5.0 10.5
Calcium 4-182 m 0-145 m
Ma esium 6-333 m 0-120 m
Sodium 12-6,200 m 1-198 m
Chloride 190-10,320 m 0-540 m
Sulfate 23-3,514 m 0-572 m
There is, however, a distinct difference between the
temperature of body fluids and of tap water. For example, the skin
temperature within the area covered by a disposable diaper averages
approximately 34.3 C. (Jordan, W.E. and Bailey T.L. 1982.
"Factors influencing infant diaper dermatitis" in Neonatal Skin, H.
Maibach and K. Boisitis, Eds. Marcel Dekker, Inc. New York),
0
whereas the temperature of toilet bowl water is approximately 20 C.
- 25~ C. This temperature difference between body waste fluids and
toilet bowl water provides an opportunity to exploit temperature as a
trigger wherein the adhesive is water insoluble at one temperature
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and water soluble at another temperature. Such a temperature-
triggerable water soluble adhesive can be used alone or as a mesas to
adhere one substrate to another like or unlike substrate. Such a
flushable adhesive would enable a flushable product to disperse or
5 disintegrate into it component parts each of which can be disposed of
in the most environmentally efficient and cost effective manner.
Therefore, what is needed is a non-toxic, temperature-
triggerable water soluble adhesive which has sufficient wet strength
for its intended use at one temperature and which is water soluble at
another temperature. That is a flushable adhesive which is water
insoluble at the temperature of body waste fluids, but is water soluble
at the temperature of normal tap water and, therefore, is flushable
into conventional sewage systems.
SUMMARY OF THE INVENTION
The flushable adhesive of the present invention
comprises a temperature-triggerable water soluble polymer, wherein
the polymer is a poly (vinyl alkyl ether), preferably a poly (vinyl
methyl ether) {PVME) obtained as Amobond (Amoco Chemical Co.)
and a means for altering the temperature at which the PVME is
water soluble, the means comprising a hydrophobic polymer,
preferably a polystyrene resin or an acrylate, admixed with the
PVME in an amount sufficient to render the admixed PVME and the
hydrophobic polymer water insoluble in the presence of fluid having
a temperature above approximately 33~ C., but water soluble in the
0
presence of fluid having a temperature below approximately 22 C.
The flushable adhesive composition of the present invention is used
alone and to adhere one substrate to another like or unlike substrate.
Accordingly, it is an object of the present invention to
provide a flushable adhesive which is water insoluble in fluid having
a temperature above approximately 33~ C., but is water soluble in
0
fluid having a temperature below approximately 22 C.
It is another object of the present invention to provide a
flushable adhesive that disintegrates in tap water regardless of
geographic variations in tap water salt concentration.
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It is another object of the present invention to provide a
flushable adhesive that is non-toxic and that is non-irritating to the
skin.
It is another object of the present invention to provide a
permanent adhesive that is converted to a removable adhesive by a
change in the temperature of the fluid to which the adhesive is
exposed.
It is another object of the present invention to provide
an adhesive which retains satisfactory adhesion properties in the
presence of changes in ambient humidity.
It is another object of the present invention to provide a
flushable adhesive as a part of a disposable product that can be
flushed down a toilet.
It is another object of the present invention to provide a
flushable adhesive as a part of a disposable product that can be
flushed down a toilet without the addition of dissolving chemicals.
It is another object of the present invention to provide a
flushable adhesive for use in infant care articles.
It is another object of the present invention to provide a
flushable adhesive for use in child care articles.
It is another object of the present invention to provide a
flushable adhesive for use in adult care articles.
It is another object of the present invention to provide a
flushable adhesive for use in feminine care articles.
It is another object of the present invention to provide a
flushable adhesive for use in medical care articles.
It is another object of the present invention to provide a
flushable adhesive for use in surgical care articles.
It is another object of the present invention to provide a
flushable adhesive for use in household articles,.
It is another object of the present invention to provide a
flushable adhesive for use in insulation.
It is another object of the present invention to provide a
flushable adhesive for use in packaging material.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 depicts the water-uptake of films prepared from
100% PVME) from 75% PVME + 25% Piccotex-100 and from 50%
PVME + 50% Piccotex after 1, 4) 9 and 16 minutes exposure to
0
water at 20 C.
Fig. 2 depicts the water-uptake of films prepared from
100% PVME, from 75% PVME + 25% Piccotex-100 and from 50%
PVME + 50% Piccotex after l, 4, 9 and 16 minutes exposure to
0
synthetic urine at 35 C.
lp Fig. 3 depicts the water-uptake of films prepared from
75% PVME + 25% Kristalex 5140 after 1, 4, 9 and 16 minutes
exposure to water at 20~ C., to water at 35~ C. and to synthetic urine
at 35oC.
Fig. 4 depicts the water-uptake of films prepared from
100% PVME after 1, 4, 9 and I6 minutes exposure to water at
20~ C.; to water at 35~ C. and to synthetic urine at 35~ C.
DETAILED DESCRIPTION OF THE INVENTION
The temperature-triggerable water soluble adhesive of
the present invention comprises two components. The first
component is a polyvinyl alkyl ether), preferably a poly (vinyl
methyl ether) (PVME). The second component is a hydrophobic
polymer, preferably a hydrophobic polystyrene resin or an acrylate.
The PVME for use in this invention is a polymer which
is soluble in water below 33~-35~ C. and insoluble in water above
33~-35~ C., which is the cloud point temperature (T~CST) for
PVME. The closeness of the TLCST of PVME to the temperature of
body waste fluids makes PVME unsuitable for use as an adhesive in
flushable products designed to contact the body of a human or
animal. In addition, PVME is characterized by a low glass-
transition temperature (Tg) of -21 ~ C. and, therefore, a pronounced
tendency to "cold flow". That is, PVME tends to flow away from
the bonding site on storage at or below room temperature. This
"cold flow" tendency makes PVME unsuitable for use as an adhesive
in products which must be stored for a length of time.
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g
To use PVME as a temperature-triggerable water
soluble adhesive either alone or in flushable products intended to
contact the body of a human or animal, it is necessary to reduce its
solubility in fluid at temperatures of 33~-35~ C. without significantly
0
decreasing its solubility in fluids at 22 C.
The hydrophobic polymers for use in this invention are
more water insensitive than PVME and are characterized by positive
0 0
Tgs of preferably between approximately 50 C. and 95 C., more
0 0
preferably between approximately 55 C. and 92 C., and most
a o
1o preferably between approximately 60 C. and 91 C. As expected,
when a hydrophobic polymer is blended with PVME, the
0
composition is less sensitive to water above 33 C. than is PVME
alone. However, totally unexpectedly, when a hydrophobic polymer
is blended with PVME, the composition is more sensitive to water
below 22~ C. than is PVME alone. That is, blends of PVME and a
0
hydrophobic polymer are more inert to fluids at 33 C. than PVME
alone and therefore provide more wet strength than PVME alone.
Even more importantly, blends of PVME and a hydrophobic
0
polymer absorb water faster at 22 C. than PVME alone and
therefore provide a more flushable adhesive than PVME alone.
Moreover, the flushable adhesive of the present invention comprising
PVME and a hydrophobic polymer is characterized by an increase in
Tg over that of PVME alone and a decrease in the "cold flow" over
that of PVME alone. This increase in Tg and decrease in "cold flow"
make the PVME-hydrophobic polymer flushable adhesive of the
present invention an unexpectedly superior flushable adhesive.
The PVME for use in the present invention can be
amorphous or isotatic. The PVME preferably has a number average
molecular weight of 40,000 to 300,000 Daltons, more preferably a
number average molecular weight of $0,000 to 200,000 Daltons and
most preferably a number average molecular weight of 120,000 to
160,000 Daltons. Preferably, the PVME comprises between
approximately 10% and 90% by weight (grams/100 grams), more
preferably, between approximately 25% and 80% by weight and
most preferably between approximately 50% and 75% by weight of
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9
the temperature-triggerable water soluble adhesive composition of
the present invention.
The hydrophobic polymers for use in the present
invention include, but are not limited to, polystyrene copolymers and
acrylates. Polystyrene copolymers include, but are not limited to, a
polystyrene oligomer such as Piccolastic D 150 (Hercules Inc.), an
alpha-methyl styrene such as Kristalex 3100 (Hercules Inc.) or
Amoco Resin 18-290 (Amoco Chemical Co.)) an aromatic copolymer
such as Kristalex 5140 (Hercules Inc.), a terpene phenol such a
Piccofyn A 135 (Hercules Inc.), a poly (vinyl toluene-co-alpha methyl
styrene) copolymer such as Piccotex 100 (Hercules Inc.), and a
pentaerythritol ester of polymerized resin such as Pentalyn C.
(Hercules Inc.). Preferably, the hydrophobic polystyrene resin
comprises between approximately 10% and 90% by weight
(grams/100 grams), more preferably between approximately 20%
and 75 % by weight and most preferably between approximately 25 %
and 50% by weight of the flushable adhesive of the present invention.
Acrylates include, but are not limited to, a poly (ethyl acrylate-co-
methacrylic acid) copolymer such as ASE-75 (Rohm & Haas) and a
cross-linked poly (ethyl acrylate-co-methacrylic acid) copolymer
such as ASE-b0 (Rohm & Haas). Preferably, the acrylate comprises
between approximately 20% and b5% by weight (grams/100 grams),
more preferably between approximately 25% and 55% by weight
and most preferably between approximately 40% and 50% by weight
of the flushable adhesive of the present invention.
The flushable adhesive of the present invention can
contain optional non-hydrophilic additives including, but not limited
to, anti-oxidants, pigments, and colorants.
The flushabie adhesive of the present invention can be
used alone or can be applied to a substrate including, but not limited
to, tape, film, paper, structural elements, woven fabric, nonwoven
fabric and combinations thereof. Methods of applying the flushable
adhesive of the present invention to a substrate include, but are not
limited to, rolling, dipping, dotting, printing, extruding, spraying
and other methods known to those skilled in the art.
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The flushable adhesive of the present invention is
prepared by blending PVME and a hydrophobic polymer until a
homogeneous mixture is obtained using any of the various methods
known in the art. Such methods include, but are not limited to,
5 mixing a solution of PVME and a solution of a hydrophobic polymer
in a common solvent and evaporating the solvent or hot melt mixing
the PVME and the hydrophobic polymer. The hot melt method used
may be any of the methods known to those skilled in the art. It is to
be understood that the precise temperature to be used in the hot melt
10 method will depend on the melting point of the PVME and of the
hydrophobic polymer.
The following examples illustrate a variety of the
flushable adhesives that can be made within the scope of the present
invention.
EXAMPLE 1- FLUID UPTAKE
Fluid uptake is used to evaluate the performance of the
flushable adhesive of the present invention. Fluid uptake is
important because the flushable adhesive of the present invention
must be water insoluble in the presence of fluid having a temperature
a
above approximately 33 C., but water soluble in the presence of
0
fluid having a temperature below approximately 22 C.
To measure fluid uptake one-half inch squares of
0
adhesive film are weighed and are immersed in water at 22 C. and
35~ C. and in synthetic urine at 35~ C. for 1, 4, 9 and 16 minutes.
Weight gain is measured and fluid uptake is def ned as [final weight -
initial weight]/initial weight.
PVME - Adhesive film is prepared by dissolving 100%
by weight of PVME having a number average molecular weight of
122,000 Daltons in ethyl acetate. The dissolved PVME is poured
into a silicone rubber mold, the solvent is allowed to evaporate for 3
0
days at room temperature and the film pressed at 150 F. for 5
minutes. The resulting film is a 0.43 cm, bubble-free, uniform,
smooth film.
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PVME+PICCOTEX 100 BLENDS - Adhesive films are
prepared by dissolving 75% by weight of PVME having a number
average molecular weight of 122,000 Daltons in ethyl acetate and
25% by weight of Piccotex 100 in ethyl acetate and by dissolving
50% by weight of PVME having a number average molecular weight
of 122,000 Daltons in ethyl acetate and 50% by weight of Piccotex
100 in ethyl acetate. The dissolved PVME and the dissolved Piccotex
100 are blended to homogeneity. The PVME-Piccotex 100 blends
are poured into a silicone rubber mold, the solvent is allowed to
evaporate for 3 days at room temperature and the films are pressed
at 150° F. for 5 minutes. The resulting films are 0.43 mm in
thickness, bubble-free, uniform and smooth.
Figure 1. shows the water uptake of a 100% PVME
film, a 75% PVME+25% Piccotex 100 film and a 50% PVME+50%
Piccotex 100 film after l, 4, 9 and 16 minutes of immersion in water
at 22° C.
Figure 2. shows the fluid uptake of a 100% PVME film,
a 75% PVME+25% Piccotex 100 film and a 50% PVME+50%
Piccotex-100 film after 1, 4, 9 and 16 minutes of immersion in
0
synthetic urine at 35 C.
These data show that adhesive films prepared from
blends of 25% and 50% of the hydrophobic polystyrene resin
Piccotex 100 with 50% and 75% PVME show an increase in fluid
uptake at 22° C. and reduction in fluid uptake at 35~ C. over that of
100% PVME alone.
PVME+KRISTALEX 5140 BLENDS - An adhesive film
is prepared by dissolving 75% by weight of PVME in ethyl acetate
and 25% by weight of Kristalex 5140 in ethyl acetate. The dissolved
PVME and the dissolved Kristalex 5140 are blended to homogeneity.
The PVME+Kristalex 5140 blend is poured into a silicone rubber
mold, the solvent is allowed to evaporate for 3 days at room
temperature and the films are pressed at 1500 F for 5 minutes. The
resulting films are 0.43 mm in thickness, bubble-free, uniform and
smooth.
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Figure 3 shows the fluid uptake of a 100% PVME
adhesive film after 1, 4, 9 and 16 minutes of immersion in water at
20o C. and after 1, 4, 9 and 16 minutes of immersion in water or in
0
synthetic urine at 35 C.
Figure 4 shows the fluid uptake of the 75% PVME+25%
Kristalex 5140 adhesive film after 1, 4, 9 and 16 minutes of
immersion in water at 22~ C. and after 1, 4) 9 and 16 minutes of
0
immersion in water or in synthetic urine at 35 C.
These data show that blending 25% of the hydrophobic
polystyrene resin Kristalex 5140 with 75% PVME increases fluid
uptake at 20~ C.-22~ C. and reduces fluid uptake at 35~ C. over that
of 100% PVME alone.
EXAMPLE 2 - FLUID UPTAKE
Adhesive films are prepared by mixing from 5090 to
100% by weight of PVME and from 25% to 50% by weight of the
hydrophobic polystyrene resins Piccotex 100) Piccolastic D 150 and
Amoco Resin 18-290 and heating the mixture in a Haake Rheomix
0
600 to a temperature at which it is a flowable fluid (200 C. to
350 C.). Each PVME-hydrophobic polystyrene resin hot blend is
mixed for approximately 10 minutes until homogeneous, filtered if
needed, cooled and pressed with a 0.13 mm shim in a Dake press to
o,
form a film. Each film is tested for water sensitivity at 22 C. and at
35~ C. and for urine sensitivity at 35~ C.
Table 2 compares the percent fluid uptake of the 100%
PVME adhesive film with the fluid uptake of the PVME
hydrophobic polystyrene resin adhesive films after 9 minutes of
immersion in water at 22~ C. and at 35~ C. and in synthetic urine at
0
C.
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Table 2
% UPTAKE (9 minute immersion)
BLEND PVME 259oP-1005096P-1002596 5096 2596 6090
Amoco Amoco PS PS
7596 0~ PVME 75~ PVME5096 7596 60%a
PVME PVME
PVME PVME
wale .3896 .9296 .4396 .8396 .52% .55% .39%
22 C.
water .3596 .2496 .089'0 .24% .03% .2390 .069c
@
35o
C.
synthetic.29~ .2790 .02% .13% .04% .17% .t29o
twine
~
35 C.
P-100 = Piccotex 100
PS = Piccolastic D 150
Amoco = Amoco Resin 18-290
These data show that adhesive films prepared by
blending 25% to 50% of the hydrophobic polystyrene resins Piccotex
100, Piccolastic D 150 and Amoco Resin 18-290 with 50% to 75 %
PVME show reduced fluid uptake at 35~ C. and increased fluid
uptake at 22~ C. over that of adhesive films prepared from 100%
PVME.
Examples 1 and 2 demonstrate that flushable adhesives of the
present invention comprising PVME and a hydrophobic polystyrene
resin take up less fluid at 35~ C. than PVME alone and absorb more
fluid at 22~ C. than PVME alone. These unexpected results show that
the adhesive composition of the present invention has both greater
wet strength at 35~ C. than PVME alone and greater water solubility
at 22~ C. than PVME alone.
EXAMPLE 3 - GLASS TRANSITION TEMPERATURE
Glass transition temperature (Tg) is the temperature at
which a polymer changes from its glass-like state to a rubber-like
state due to increased molecular motion. The Tg of a polymer blend
is an indicator of the miscibility of the polymers in the blend. Tg is
determined by the step change in heat capacity versus temperature
measured using a TA instruments 2910 Differential Scanning
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14
Calorimeter. The Tg is chosen as the midpoint of the change in heat
capacity at a heating rate of 20 degrees per minute.
Table 3A shows the Tg of PVME, the Tgs of the
hydrophobic polystyrene resins Piccolastic D 150, Kristalex 5140,
Piccotex 100 and the Tg of the acrylate ASE-60 Figure 3B shows
the Tgs of blends of 50% and 75% PVME with 25% and 50% of
Piccolastic D150) Kristalex 5140, Piccotex 100, Pentalyn C and ASE-
60.
Table 3A
Tg of Starting Material T g
.
PVME -21
Piccolastic D 150 69
Kristalex 5140 91
Piccotex 100 60
ASE-60 76
Table 3B
Tg of Blends Tg (C.)*
75% PVME + 25% Piccolastic D-150 -19
50% PVME + 50% Piccolastic D-150 -14
25% PVME + ?5% Kristalex 5140 -18
75 % PVME + 25 % Piccotex-100 -16
50% PVME + 50% Piccotex-100 -7
75% PVME + 25% Pentac n C -7
75% PVME + 25% ASE-60 -15
50% PVME + 50% ASE-60 3
*Tgs are ~ to C.
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Table 3A and in Table 3B show that blending PVME
with the representative hydrophobic polystyrene resins Piccolastic
D 150, Kristalex 5140, Piccotex 100 and the Tg of with the
representative acrylate ASE-60 raises the Tg of the PVME and
5 lowers the Tgs of the representative hydrophobic polystyrene resins
and of the representative acrylic to a single Tg value in-between that
of the representative hydrophobic polystyrene resins and of the
representative acrylic used. Moreover, the increase in the Tgs of the
PVME+hydrophobic polystyrene resin blends and of the
10 PVME+acrylate blends over that of 100% PVME indicates that the
blends have less of a tendency to "cold flow" than does the PVME
alone.
EXAMPLE 4 - DIFFUSIVITY
15 Diffusivity testing is used to determine the effect of
water vapor on the flushable adhesive of the present invention. This
is important because the flushable adhesive and products containing
the flushable adhesive must be stored, shipped and worn in various
humidities.
To measure diffusivity, half inch squares of a film of the
flushable adhesive of the present invention are put in a desiccator at
high humidity for 7 days. The humidity is created by placing a
slurry of K2S04 in the desiccator which gives a relative humidity of
97% at room temperature. The weight gain is measured periodically
and R(t) is calculated, plotted versus the square root of time and the
slope K is found through a regression. The diffusivity coefficient D
is calculated using the equation D = ~r,/16*K2*82, where b is film
thickness.
Adhesive films are prepared from 100% PVME and
from blends of 50% and 75% PVME with 25% and 50% of a
representative hydrophobic polystyrene resin according to the
methods of Examples 1 and Example 2. PVME+acrylate adhesives
films are prepared by dissolving 50% by weight of PVME . in
tetrahydrofluran (THF) and by dissolving 50% by weight of the
representative acrylates ASE-60 and ASE-75 in THF. The dissolved
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16
PVME and the dissolved ASE-60 or ASE-75 are blended to
homogeneity. The PVME-ASE-60 and PVME ASE-75 blends are
poured into silicone rubber molds, the solvent is allowed to
evaporate for 3 days at room temperature and the films are pressed
at 150 C. for 5 minutes and at room temperature for an additional
12 hours.
Table 3 compares the diffusivity of 100% PVME films
to films prepared from blends of from 50% to 75% PVME and from
25% to 50% of representative hydrophobic polystyrene resins and
acrylates.
TABLE 4
Diffusivity Data
Blend Thickness D
(mm)
25% Piccolastic 0.45 2.50E-06
50% Piccolastic 0.54 4.66E-06
25% Kristalex 5140 0.41 2.18E-06
25% Piccotex 100 0.43 2.76E-06
50% Piccotex 100 0.34 1.91 E-06
25 % Pental n C 0.45 4.41 E-06
25 % Amoco 18-290 0.42 6.66E-06
50% Amoco 18-290 0.37 3.13E-06
50% ASE-75 0.41 7.84E-06
50% ASE-60 0.26 2.97E-06
100% PVME* 0.81 3.72E-05
*PVME is probably not accurate because it became a gel after
3 days.
These data show that adhesive films prepared from
blends of.25% and 50% PVME and 25% and 50% of a representative
hydrophobic polystyrene resin and of a representative acrylate show
reduced diffusivity over adhesive films prepared from 100% PVME
after 7 days at 97% humidity.
CA 02275200 1999-06-11
WO 98129517 PCTIUS97I22877
17
The flushable adhesives of the present invention provide
sufficient wet strength for their intended at the temperature of body
fluids) yet disintegrate and disperse at the temperature of normal tap
water. The flushable adhesives of the present invention have Tgs at
which "cold flow" will not result in the adhesive tending to flow
away from the bonding site on storage. The flushable adhesives of
the present invention have diffusivity coefficients which enable them
to maintain their integrity at high humidifies and which allow them
to be stored, shipped and worn in different humidifies.
The flushable adhesives of the present invention may be used
alone, in products composed entirely of flushable components and in
products composed of flushable and nonflushable components. In the
former case the entire product disintegrates or disperses in normal
tap water, whereas in the later case the flushable components
disintegrate disperse in normal tap water and the flushable article
falls apart into pieces small enough to be flushed into a conventional
sewage system without causing obstruction.
It is to be understood that in light of the disclosure of
the present invention, modifications and improvements thereon will
become readily apparent to those skilled in the art and all such
obvious variations are contemplated within the scope of the appended
claims.
