 |
Description  |
|
|
This is a division of application Ser. No. 394,601, filed Sept. 5, 1973,
now U.S. Pat. No. 3,901,240, and a continuation-in-part application of
Ser. No. 354,062, filed Apr. 24, 1973, now U.S. Pat. No. 3,887,408.
This invention relates to an absorbent article having a top layer of a
crushed polymer latex foam bonded to either a non-woven which is bonded to
an absorbent layer or bonded directly to the absorbent layer, and which in
turn is bonded to either a flexible, liquid impermeable bottom layer such
as polyethylene or to a woven or non-woven gauze. The laminate of the foam
and the non-woven layer or absorbent layer is self-bonded; i.e., no
extraneous adhesive is needed. The liquid impermeable bottom layer such as
polyethylene or the gauze bottom layer may be wider than the absorbent
material but is generally of a width such that the absorbent layer and
foam self-bond.
In the past, similar laminates have been made with a permeable top layer
such as adhesively bonded fibers, and even a fully expanded foam such as
polyurethane foam. However, the foam is either of such light weight or low
density that a fabric-like hand could not be obtained. Alternatively, if a
dense foam is applied by controlling the amount of foaming agent or the
extent of expansion, the product is relatively rubbery and non-fabric-like
or stiff and inflexible and does not have the hand of a soft fabric, or
the desired porosity.
Examples of such prior art of polyurethane foams are shown in U.S. Pat.
Nos. 3,431,911; 3,461,872; 3,463,745; 3,512,530, and 3,563,243. It should
be noted in those patents that illustrate the foams that the open cells
defined by the ribs or struts are essentially symmetrical and
three-dimensional. Thus, when the foam is stretched, for example, when an
attempt is made to flush the absorbent lining covered with a fully
expanded open-celled foam layer, the foam layer is succeptible to
extensive elongation before reaching the limits of its tear strength. Such
polyurethane foams tend to ball up or form ropes and clog the plumbing.
The present invention, by using foams with mainly two dimensional flat open
cells, permits tearing of the crushed foam under moderate elongation, but
provides good integrity at the low elongations (<50 percent) encountered
in normal use.
In general, the invention relates to a flexible absorbent pad comprising a
top layer of polymer foam material which is permeable to liquids, an
underlying layer of liquid-absorbent material and a bottom film of
flexible, moisture-impervious material, the improvement in which said
polymeric foam material is crushed foam of an addition polymer derived
from an aqueous latex, the thickness of the crushed layer being from about
1 mil to about 10 mils preferably the horizontal face of the dry, crushed
foam has a pore size which is less than about 10 mils with approximately
100,000 to 1,000,000 pores per square inch and in which the laminate has
good wet strength and dry strength at a low elongation but which when held
by the film, placed in a body of water and pulled, the crushed foam splits
and tears and the absorbent material breaks up thus providing a flushable
product.
The addition polymer employed is preferably a cross-linked thermoset foam
and the absorbent material is fibrous, which permits intimate intertwining
of the fiber and the foam at their juncture but with a substantial
thickness of the absorbent material free of foam and with a substantial
thickness of the foam free of fiber.
This invention also comprises having a non-woven layer between the crushed
foam layer and absorbent layer. This type of pad is more comfortable than
one in which the non-woven comes in direct contact with the skin.
Also, the invention comprises having the moisture impervious layer replaced
with a gauze. This type of pad would be employed when it is desirable to
allow air to circulate through the pad, such as in a wound dressing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the basic absorbent pad having a crushed foam upper
layer which is bonded to a moisture impermeable layer thereby
encapsulating an absorbent layer.
FIG. 2 illustrates a pad in which a non-woven layer is coated with a
crushed foam which layers are bonded to a moisture impermeable layer
thereby encapsulating an absorbent layer.
FIGS. 3 and 4 illustrate the pads of FIGS. 1 and 2, respectively, having a
woven or non-woven gauze in place of a moisture impermeable layer.
The term "non-woven" as employed herein means those fabrics produced from
staple fibers or continuous filaments without the use of conventional
weaving or knitting operations. For a further description of the type of
non-woven which may be employed, reference is made to U.S. Pat. Nos.
2,931,749; 2,982,682; 3,074,834; 3,101,292 and 3,521,638. These references
insofar as they define the term non-wovens are herein incorporated by
reference.
In a specific preferred embodiment, a crosslinkable or thermosettable
acrylic latex foam is deposited onto release paper coated with a silicone
release coating, and the foam is dried without thermosetting. The latex is
foamed, preferably mechanically by using air and employing a foam
stabilizer. The foam is applied to the release surface and dried without
causing crosslinking. The foamed layer and the absorbent material are then
juxtaposed, the foam is crushed by pressure, with or without embossing a
design in the laminate, and then heated to a temperature sufficiently high
to crosslink and thermoset the polymers.
The absorbent medium may be bonded to the water-proof film but is
preferably incapsulated between the water-proof film and the crushed foam
layer or the non-woven containing a crushed foam surface. When a flushable
composite is dipped in water, the crushed foam surface or crushed foam
top-coated non-woven and the absorbent medium pull away from the film
generally leaving a small residue of adhesive on the water-impervious film
at the glue line.
In another specific preferred embodiment when crushed foam is to be used as
an aesthetically appealing surface over a conventionally bonded non-woven,
the wet foam can be cast on a release medium as previously described and
subsequently adhered to the non-woven by laminating and simultaneously
crushing the foam against the non-woven as described in the case of
combining the crushed foam to an absorbent wadding. Alternately, the wet
foam can be cast directly onto the non-woven so that the foamed non-woven
can then be passed through nip rollers to crush the foam. As opposed to
non-wovens which generally contain between 25 to 40% resin solids and
75-60% fiber in order to provide sufficient strength, the lamination of a
crushable foam to a non-woven permits the use of reduced amounts of resin
applied to the non-woven via saturation, print bonding or beater
deposition. The crushed foam treated non-woven can be cured after the
composite has been made to achieve more complete crosslinking of the foam.
This procedure affords an improved flexible absorbent pad which comprises a
top layer of a non-woven over a liquid absorbent material and a bottom
film of flexible moisture impervious material wherein the improvement
comprises having a crushed foam layer having a thickness of from 1-10 mils
of an addition polymer derived from an aqueous polymeric latex on the top
of the non-woven layer. This is preferred absorbent pad because it
provides a soft, dry velvet-like texture to the surface of the non-woven
which is much more comfortable when used in contact with the skin. When it
is desired to use the crushed foam coated material as a wound dressing the
outer layer of the moisture impervious film is replaced with a woven or
non-woven gauze.
The foam initially has a wet foam density of from about 0.05 to 0.5 grams
per cubic centimeter and is applied in a thickness of from about 4 to
about 45 mils, and preferably at a thickness of no more than 30 mils. The
density, of course, will vary with the presence or absence of pigments and
fillers and their identity. The foam is then dried without causing
thermosetting, crosslinking or vulcanization to a sensibly dry condition,
for example, to an air-dry or sensibly dry state, for example, by heating
at a temperature below that which causes thermosetting, crosslinking, or
vulcanization. For example, by drying for a period of time of from 1 to
10 minutes at an oven temperature in the range of from about 200.degree.
to 350.degree. F., followed by placing the absorbent material and the
surface of the foam together and then crushing the foam to a thickness of
from 5 percent to 35 percent of its original dry thickness to afford a
foam with a density of from about 0.2 to about 3 g./cc., followed by
curing of the crushed foam. In general, the thickness of the dried foam
prior to crushing may be less than that of the wet foam, due to shrinkage.
This shrinkage may be up to 30 percent of the thickness of the wet foam.
Suitable moisture contents range from 5 percent to 20 percent in order to
qualify as air dry or sensibly dry materials. The criteria as to moisture
content is that the foam must be stable enough to be self-bonded to the
absorbent material. In some cases crosslinking may be accomplished by
catalysis rather than primarily by the application of heat. Of course, the
foam may be crushed before it is self-bonded to the absorbent material,
but in this case a crushing roll having a release coating such as a
silicone or Teflon is desirable. Normally no adhesive is needed between
the foam and the absorbent layer, since preferably a thermosettable foam
is used, and the final curing of the foam causes a firm bond between the
layers.
The crushed foam composite is designed so that it disintegrates upon
flushing in a sewage system when used as an absorbent diaper or as a
sanitary napkin. Crushed foam composites can also be used for wound
dressing which do not adhere to human tissue because of the complete lack
of fiber on the exposed surface and porosity allowing wound exudate to
penetrate the foam into the adsorbent medium. The cohesive strength of the
crushed foam lining is low so that any of the lining which becomes
permanently entrained during scab formation of a wound will separate away
from the remainder of the composite without damaging the wound. In
addition, to enhance the comfort of non-woven linings, crushed foam can be
used as a topcoat on the non-woven where it is self-adhering as previously
described. The crushed foam imparts a velvet-like texture to the surface
of the non-woven and prevents fibers from coming in contact with the user.
In addition, the crushed foam enhances the surface dryness of the
composite. The crushed foam surface can also serve as part of the binding
system for the non-woven permitting reduced usage of conventional binders
normally applied by saturation, printing or beater deposition. Beneficial
additives can be incorporated into the foaming mix before casting, such as
germicidal additives, deodorants, reodorants, fillers to enhance comfort
such as talc or fire resistance such as aluminum hydrate and dissipate
static electricity for use in operating rooms.
Of course, a thermoplastic foam may be used. Crushed foam is essential,
since if the initial foam is formed to the final density by control of the
amount of foaming agent or by means such as using a chemical blowing agent
and restraining the expansion in order to get the final density, the walls
or struts connecting the air spaces are relatively thick. A crushed foam,
on the other hand, initially having expanded to a number of times its
final thickness, has thin connective walls or struts. The result is that
the crushed foam is much more flexible and fabric-like than a foam
initially expanded to the density noted above. These foams are inherently
opaque. The opacity can be compared with the opacity of whipped egg
whites; the liquid egg white is substantially transparent and the gas
cells incorporated therein confer opacity of whipped egg whites.
When pigmented compositions are contemplated, examples of the pigments that
may be employed include clays, especially of the kaolin type, calcium
carbonate, blanc fixe, talc, titanium dioxide, colored lakes and toners,
ochre, carbon black, graphite, aluminum powder or flakes, chrome yellow,
molybdate orange, toluidine red, copper phthalocyanines, such as the
"Monastral" blue and green lakes. If dyed compositions are used, examples
of dyes for acrylic film and foam include basic and dispersed dyes. Other
composites could be made dyeable, if not inherently so, through the use of
additives such as methyl cellulose, polyvinyl pyrollidone, hydroxyl ethyl
cellulose, and the like. Other dyes which could be used include acid dyes,
vat dyes, direct dyes, and fiber reactive dyes.
An important advantage in utilizing a dried but uncured foam of a
crosslinkable polymer and an absorbent layer such as opened cellulose is
that the two elements can be passed through the nip of a pair of rollers,
the distance between which is small enough to "marry" the two but
insufficient to crush the dried foam, all without using an adhesive to
bond the foam. Of course, bonding of the dry foam and the absorbent
material can be done at a pressure sufficient to crush the foam with or
without embossing the same. Even after crushing, the foam has sufficient
resilience to be embossed with a patterned roller. If desired, the
embossing roller may be heated to the curing temperature of the foam.
For a description of suitable conventional foaming procedures and foam
stabilizers and foaming agents, reference is made to Mage, E. W., "Latex
Foam Rubber," John Wiley and Sons, New York (1962) and Rogers, T. H.,
"Plastic Foams," Paper, Reg. Tech. Conf., Palisades Sect., Soc. Plastics
Engrs., New York, November, 1964. Most common are the alkali metal,
ammonia, and amine soaps of saturated or unsaturated acids having, for
example, from about 12 to about 22 carbon atoms. Examples of suitable
soaps include tallow soaps and coconut oil soaps, preferably the volatile
amine or ammonia soaps, so that the volatile portion is vaporized from the
foam. Other useful foaming-foam-stabilizing agents include lauryl
sulfate-lauryl alcohol, lauryl sulfate-lauric acid, sodium lauryl sulfate,
and other commonly used foamed stabilizers or foaming agents.
The latex, when formulated with the foam stabilizer and optionally,
suitable pigments, is readily convertible into the foamed state. The
polymer composition is such that excessive thickening of the formulation
is not encountered under the acid or alkaline conditions employed to
assure the most efficient operation of the foam stabilizing agent. In
addition the copolymer is such that the crushed foam retains its softness
and its flexibility at low temperatures at least to a temperature as low
as 10.degree. F., and after curing is non-tacky.
Important properties of the copolymer are its toughness and flexibility and
the minimum film-forming temperature (MFT) of the formulated coating
composition, both dependent in large part upon the influence of its
monomer composition. The glass transition temperature (Tg) of the
copolymer depends upon the selection of monomers and proportions thereof
because of their influence on the Tg. "Tg" is a conventional criterion of
polymer hardness and is described by Flory, "Principles of Polymer
Chemistry," pp. 56 and 57, (1953), Cornell University Press. While actual
measurement of the Tg of copolymers may be made, it may be calculated as
described by Fox, Bull. Am. Physics Soc. 1, p. 123 (1956). Examples of the
Tg of high molecular weight homopolymers and the inherent Tg thereof which
permits such calculations are as follows:
______________________________________
Homopolymer of Tg
______________________________________
n-octyl acrylate -80.degree. C.
n-decyl methacrylate
-60.degree. C.
2-ethylhexyl acrylate
-70.degree. C.
octyl methacrylate -20.degree. C.
methyl acrylate -9.degree. C.
n-tetradecyl acrylate
20.degree. C.
methyl methacrylate 105.degree. C.
acrylic acid 106.degree. C.
______________________________________
These or other monomers are blended to give the desired Tg of the
copolymer. As is known, for a given number of carbon atoms in the alcohol
moiety, the extent and type of branching markedly influences the Tg, the
straight chain products giving the lower Tg.
One of the monomers utilized to prepare the water-insoluble addition
copolymer is a flexibilizing or "soft" monomer which may be represented by
the following formula:
##STR1##
wherein R is H or alkyl having 1 to 4 carbon atoms and R.sup.1 is the
straight chain or branched chain radical of a primary or secondary
alkanol, alkoxyalkanol or alkylthiaalkanol, the alkanol having from 2 to
about 14 carbon atoms, the chain length depending upon the identity of R,
examples being ethyl, methylpropyl, n-butyl, 2-ethylhexyl, heptyl, hexyl,
octyl, propyl, 2-methylbutyl, 1-methylbutyl, butoxybutyl, 2-methylpentyl,
methoxymethyl, ethoxyethyl, cyclohexyl, n-hexyl, isobutyl, ethylthiaethyl,
methylthiaethyl, ethylthiapropyl, n-cotyl, 6-methylnonyl, decyl, dodecyl,
and the like. When R is alkyl and R.sup.1 is alkyl, R.sup.1 should have
from about 6 to about 14 carbon atoms and when R is H and R.sup.1 is
alkyl, R.sup.1 should have from 2 to about 12 carbon atoms, in order to
qualify as a soft monomer. Also, butadiene may be employed. In addition,
copolymers such as those prepared from ethylene or propylene and vinyl
acetate or vinyl chloride may be employed.
In addition to the flexibilizing monomer, the other essential monomers are
the "toughening" or "hard" monomers, discussed in greater detail below and
including, for example, monovinyl aromatic monomers, certain acrylic acid
and/or methacrylic acid esters, vinyl halides, vinyl nitriles, and, if
used, the monomers having hydroxyl, carboxyl, amino, amido epoxy, or other
functionality described below. The hardness or softness of the acid and
other functional monomers is not critical because of the small amounts
used. Styrene and vinyltoluene are examples of the monovinyl aromatics.
The unsaturated carboxylic acid, the preferred functional monomer, may be a
simple monocarboxylic acid, or may be a half ester or half amide of an
.alpha.,.beta.-unsaturated dicarboxylic acid, and salts thereof with a
volatile base such as ammonia, or with a volatile water-soluble amine such
as dimethylamine, triethylamine, triethanolamine, morpholine, N-methyl
morpholine, picoline, and the like. Examples of copolymerizable
ethylenically unsaturated monocarboxylic or polycarboxylic acids are
sorbic, cinnamic, vinyl furoic, .alpha.-chlorosorbic, p-vinylbenzoic,
acrylic, methacrylic, maleic, fumaric, aconitic, atropic, crotonic, and
itaconic acid, or mixtures thereof, with itaconic acid and the
.alpha.,.beta.-unsaturated monocarboxylic acids, particularly methacrylic
acid and acrylic acid, being preferred. Other copolymerizable acid
monomers include the alkyl half esters a partial esters of unsaturated
polycarboxylic acids such as of itaconic acid, maleic acid, and fumaric
acid, or the partial amides thereof. Preferred half esters are the lower
alkyl (C.sub.1 to C.sub.6) esters such as methyl acid itaconate, butyl
acid itaconate, methyl acid fumarate, butyl acid fumarate, methyl acid
maleate, and butyl acid maleate. Such partial esters and partial amides
are considered to be ".alpha.,.beta.-unsaturated monocarboxylic acids,"
and the term as used herein includes such esters and amides.
In addition to or in place of the acids, amides such as acrylamide and
methacrylamide, 2-sulfoethyl methacrylate, the materials disclosed in U.S.
Pat. Nos. 3,446,777 to W. D. Emmons, 3,150,118 to D. H. Clemens, and
3,266,930 to W. D. Emmons and E. Hankins Owens, and various other
functional, polar, or monomers having groups which remain reactive after
the polymer is formed, for example, falling within the definitions of
Formulas II, III, IV, V, and VI, are also useful, as follows:
##STR2##
wherein R.degree. is selected from the group consisting of H and alkyl
groups having 1 to 4 carbon atoms, and
n is an integer having a value of 1 to 4,
CH.sub.2 =C(R)AYNR.sup.1 R.sup.2 III.
wherein R is selected from the group consisting of H and CH.sub.3,
A is selected from the group consisting of O, S,
##STR3##
Y is an alkylene group having 2 to 4 carbon atoms,
R.sup.1 is selected from the group consisting of H and an alkyl group
having 1 to 4 carbon atoms, and
R.sup.2 is selected from the group consisting of H and an alkyl group
having 1 to 4 carbon atoms,
##STR4##
wherein R is the same as above, and
Z is an alkylene group having 2 to 3 carbon atoms.
Examples of compounds of Formula II include:
2-vinylpyridine; 4-vinylpyridine; 2-methyl-5-vinylpyridine;
5-methyl-2-vinylpyridine; 4-methyl-2-vinylpyridine;
2-ethyl-5-vinylpyridine; 2,3,4-trimethyl-5-vinylpyridine;
3,4,5,6-tetramethyl-2-vinylpyridine; 3-ethyl-5-vinylpyridine;
2,6-diethyl-4-vinylpyridine.
Examples of compounds of Formula III include:
dimethylaminoethyl acrylate and methacrylate; diethylaminoethyl acrylate
and methacrylate; dimethylaminopropyl acrylate and methacrylate;
diethylaminopropyl acrylate and methacrylate; dipropylaminoethyl acrylate
and methacrylate; di-n-butylaminoethyl acrylate and methacrylate;
di-sec-butylaminoethyl acrylate and methacrylate; di-t-butylaminoethyl
acrylate and methacrylate; dimethylaminoethyl vinyl ether and sulfide;
diethylaminoethyl vinyl ether and sulfide; aminoethyl vinyl ether and
sulfide; monomethylaminoethyl vinyl ether and sulfide;
N,N-dimethylaminoethyl acrylamide and methacrylamid; N,N-diethylaminoethyl
acrylamide and methacrylamide.
Examples of compounds of Formula IV include:
N-[.beta.-(.alpha.-methacryloxyacetamido)ethyl]-N,N'-ethyleneurea;
N-[.beta.-(.alpha.-acryloxyacetamido)ethyl]-N,N'-ethyleneurea;
N-[.beta.-(.alpha.-acryloxyacetamido)ethyl]-N,N'-trimethyleneurea;
N-[.beta.-(.alpha.-acryloxyacetamido)ethyl]-N,N'-trimethyleneurea;
N-[.beta.-(.alpha.-methacryloxyacetamido)ethyl]-N,N'-trimethyleneurea.
##STR5##
wherein R and Z are as defined above, of which an example is
N-[.beta.-(methacrylamido)ethyl]-N,N'-ethyleneurea.
##STR6##
wherein
A is an alkylene group having 2 to 10 carbon atoms, preferably 2 to 3
carbon atoms, of which at least 2 extend in a chain between the adjoining
oxygen atoms,
Y is selected from the group consisting of
--CH.sub.2 --CH.sub.2 --, --CH=CH--
and ortho-phenylene, and
n is an integer having a value of 1 to 2.
Examples of compounds of Formula VI include methacryloxyisopropyl acid
maleate, methacryloxyethyl acid phthalate, methacryloxypropyl acid
succinate, methacryloxydecyl acid succinate, and metharyloxyoctyl and
phthalate.
While the preferred polymers are thermoplastic, crosslinkable or
thermosetting polymers, those subject to latent crosslinking are also
useful.
There are essentially two types of latent crosslinking which can be used.
These are (1) crosslinking subsequent to polymerization by including
monomers in the polymer recipe which have functional groups capable of
crosslinking by various mechanisms including self-crosslinking, or mutual
crosslinking by different functional groups, both in the polymer chains,
and (2) latent crosslinking by means of an external separately added
chemical compound. Combinations can be used.
Where addition polymers are involved, monomers which are suitable for
latent crosslinking include certain acrylics having crosslinkable
functionality exemplified below.
Examples of the crosslinking reactions which are possible using heat,
aging, and/or catalysis are:
##STR7##
In the above, R is H or CH.sub.3. Addition polymerizable unsaturated
monomers containing such groups are well known in the art, examples being
isocyanates such as isocyanatoethyl methacrylate, epoxy compounds such as
glycidyl methacrylate, aminoalkyl compounds such as methylaminoethyl
methacrylate, and t-butylaminoethyl methacrylate, amides such as
methacrylamide, guanamines such as 4-pentenoguanamine, hydroxyalkyl esters
such as hydroxypropyl methacrylate and hydroxyethyl methacrylate, nitriles
such as methacrylonitrile, N-alkoxyalkyl amides such as methoxymethyl
methacrylamide, hydroxyalkyl amides such as N-methylol methacrylamide, the
analogs of the above methacrylic acid derivatives with other unsaturated
acids such as acrylic acid and itaconic acid, such acids themselves,
dicarboxylic acids such as maleic acid and half esters and half amides
thereof, vinyl ethers of glycols such as ethylene glycol, and so forth.
The crosslinkable addition polymerizable unsaturate monomers have reactive
polar groups selected from these including -OH, -SH, >NH,
##STR8##
--N=C=O, >CHCN, >CHC=O, --COOH,
##STR9##
Such groups may be included as are mutually or self-crosslinkable, or
separate crosslinking compounds such as a triazine-formaldehyde resin may
be added.
Of course, water sensitive materials such as isocyanates should not be used
in aqueous systems unless they are blocked by groups such as phenol groups
which protect the isocyanate groups until subsequent heating or the use of
other reaction mechanisms such as the use of calcium, zinc, or tin
compound catalyst conventional in the art.
The separate added crosslinker, when used, is useful with or without the
use of mutual crosslinking groups and self-crosslinking groups. Among the
external crosslinking methods or compounds is the use of organic peroxides
such as benzoyl peroxide; the use of epoxy resins such as that obtained
from bis-phenol A and epichlorohydrin; esterification, by means of
dicarboxylic acids reacting with hydroxyl groups in the polymers, or by
reacting diols or polyols such as neopentyl glycol, trimethylol propane,
trimethylol ethane, or ethylene glycol with carboxyl groups in the
polymer; use of aminoplasts such as melamine formaldehyde, urea
formaldehyde, or butylated melamine formaldehyde; diamines and polyamines
such as hexamethylene diamine, ethylene diamine, and the Versamids;
polyisocyanates such as toluylene diisocyanate; compounds with mixed
functionality such as ethanolamine, and other well-known external
crosslinkers.
Other ethylenically unsaturated copolymerizable monomers present are the
"hard" or toughening monomers. These may be represented by the formula:
##STR10##
wherein R is as above. R.sup.2 is preferably alkyl and is methyl or alkyl
having from about 13 to about 20 carbon atoms when R is H, and is alkyl of
from 1 to about 5 carbon atoms or alkyl of from about 15 to about 20
carbon atoms when R is methyl. It can be seen from above that for alkyl
acrylates and alkyl methacrylates the Tg at first decreases with an
increased chain length of the alkyl group and then the Tg again increases;
i.e., both hard and soft monomers are known to occur in each group of
esters. Examples of these hard monomers and other hard monomers include:
methyl acrylate, vinyl acetate, tetradecyl acrylate, pentadecyl acrylate,
methyl methacrylate, ethyl methacrylate, t-butyl acrylate, styrene,
vinyltoluene, butyl methacrylate, and pentadecyl methacrylate.
The coating compositions are useful as clear coatings or they may be
pigmented with a variety of pigments as set forth hereinafter.
Minimal amounts of the functional monomers discussed heretofore having
hydroxyl, carboxyl, amino, amido, or epoxy groups and the like, when used,
are beneficial in promoting adhesion and in some cases providing
thermosettability. The maximum proportion of such monomers based on total
monomers is 10 percent, preferably a maximum of about 5 percent. Excessive
amounts of some of these monomers contribute to hydrophilicity of the
polymer; if the polymer is excessively hydrophobic or hydrophilic,
coatings therefrom may be undesirable properties.
If it is desired to increase the viscosity of these latices, they may be
readily thickened with various thickeners such as the water-soluble gums.
Thus, the ammonium or lower amine salts of polycarboxylic acids are
suitable, and typical examples are ammonium polyacrylate, ammonium
polymethacrylate, the salts of polyacrylic and polymethacrylic acids with
mono-, di-, and trimethylamine, the salts of polyacrylic and
polymethacrylic acids with mono-, di-, and triethylamine, etc.
The preferred emulsion copolymers for the foam have a molecular weight of
between about 70,000 and 2,000,000, and preferably between about 250,000
and 1,000,000 and are made by the emulsion copolymerization of the several
monomers in the proper proportions. Conventional emulsion polymerization
techniques are described in U.S. Pat. Nos. 2,754,280 and 2,795,564. Thus,
the monomers may be emulsified with an anionic, a cationic, or a nonionic
dispersing agent, about 0.05 percent to 10 percent thereof ordinarily
being used on the weight of the total monomers. The acid monomer and many
of the other functional or polar monomers may be soluble in water so that
the dispersing agent serves to emulsify the other monomer or monomers. A
polymerization initiator of the free-radical type, such as ammonium or
potassium persulfate, may be used alone or in conjunction with an
accelerator, such as potassium metabisulfite, or sodium thiosulfate.
Organic peroxides, such as benzyl peroxide and t-butyl hydroperoxide are
also useful initiators. The initiator and accelerator, commonly referred
to as catalyst, may be used in proportions of 0.1 percent to 10 percent
each based on the weight of monomers to be copolymerized. The amount, as
indicated above, may be adjusted to control the intrinsic viscosity of the
polymer. The temperature may be from room temperature to 60.degree. C. or
more as is conventional.
Suitable dispersing agents useful in emulsion polymerization include
anionic types such as the sodium salts of the higher fatty acid sulfates,
such as that of lauryl alcohol, the higher fatty acid salts, such as the
oleates or stearates or morpholine, 2-pyrrolidone, triethanolamine or
mixed ethanolamines, or any of the nonionic types, such as ethylene
oxide-modified alkyl phenols, of which tert-octyl phenol modified by 20 to
40 ethylene oxide units is representative, ethylene oxide-modified higher
fatty alcohols such as lauryl alcohol, containing 20 to 50 ethylene oxide
units, similarly modified long-chain mercaptans, fatty acids, amines, or
the like. Mixtures of nonionic and anionic dispersing agents are also
useful.
The elements of the pad, in addition to the crushed foam, are the
liquid-impermeable film and the absorbent material.
Suitable flexible liquid-impermeable films include polyolefins such as
polyethylene and polypropylene, saran, and the like.
Among useful absorbent materials, preferably nontextile materials, held
between the impermeable film and the crushed foam; are cellulosic waddings
made from wood pulp, cotton or rayon; carded, garnetted or other open
wood, cotton or rayon fibers, crepe paper or tissue paper layers and even
hydrophobic fibers which give a capillary effect, such as polyolefins,
polyesters, acrylics, polyvinyls and the like, spongy materials, etc.
EXAMPLE 1
An emulsion copolymer dispersion prepared from 2574 parts deionized water,
87 parts sodium lauryl sulfate, 90 parts acrylic acid, 315 parts
acrylamide, 900 parts acrylonitrile, and 7695 parts n-butyl acrylate is
compounded in the following formulation:
______________________________________
Product Solids
Dispersion 200 100
Titanium Dioxide
(Titanox RA-45) 25 25
Clay (Acme WW) 30 30
Melamine-Formaldehyde
(Resin Aerotex MW)
4.6 3.7
Ammonium Stearate
14 4.6
Water 70 --
Ammonia (28%) 4 --
347.6 163.3
Solids - 47.0%
______________________________________
All parts and percentages are by weight unless otherwise stated.
Foam is made by whipping air into the formulation using a Kitchen-Aid Mixer
(Model C) to a wet density of about 0.16 g./cc. The foam is then cast at
40 mils onto release paper and dried for 1.75 minutes at 280.degree. F.
This is then placed with the foam side adjacent an opened (fluffed)
absorbent wood pulp laying loosely on a polyethylene film of about the
same width as the foam. The laminate is then passed between rollers heated
to 250.degree.-300.degree. F. This crushes the dry foam to about 8 mils
thick, and firmly bonds the foam to the wadding. The release paper is then
peeled off. To achieve more complete crosslinking of the foam, the
composite is heated in an oven for 2 minutes at 300.degree. F. The crushed
foam has a coldflex temperature of -15.degree. F.
By following substantially the same procedure as above but by placing the
foam on a non-woven layer and then placing on the absorbent layer with the
non-woven side adjacent the absorbent layer, there is produced a surface
with extremely soft hand which when bonded to a liquid impermeable layer
or a woven or non-woven gauze affords a comfortable absorbent pad.
EXAMPLE 2
Example 1 is repeated except that 135 parts of itaconic acid, 315 parts of
acrylamide, 5850 parts of ethyl acrylate, 405 parts of acrylonitrile and
2305 parts of n-butyl acrylate are used as the monomers for the foam.
The wet foam is placed directly on the non-woven. The coated material is
dried at 280.degree. F. for 1.5 minutes and then passed through nip
rollers to crush the foam. The crushed foam coated non-woven is then cured
by heating at 300.degree. F. for 2 minutes.
EXAMPLE 3
Example 1 is repeated except that for the foam 90 parts acrylic acid, 315
parts acrylamide, 675 parts of acrylonitrile and 8920 parts of n-butyl
acrylate are used. The resultant crushed foam has a cold flex temperature
of 15.degree. F.
EXAMPLE 4
Example 1 is repeated except that 180 parts of acrylic acid, 315 parts of
acrylamide, 900 parts of acrylonitrile and 7605 parts of n-butyl acrylate
are used as the monomers, for the foam.
EXAMPLE 5
Example 1 is repeated except that 45 parts of acrylic acid, 315 parts of
acrylamide, 1800 parts of acrylonitrile and 6840 parts of n-butyl acrylate
are used as the monomers, for the foam.
EXAMPLE 6
Example 1 is repeated but the monomers for the foam consist of 270 parts
methacrylic acid, 180 parts acrylamide, 375 parts acrylonitrile, 2250
parts butyl acrylate, and 5925 parts ethyl acrylate.
EXAMPLE 7
The procedure described in Example 6 is repeated except the methacrylic
acid is replaced with 45 parts of itaconic acid and the amount of butyl
acrylate is changed to 2475 parts.
EXAMPLE 8
The procedure described in Example 1 followed with an emulsion polymer of
170 parts itaconic acid, 200 parts methacrylic acid, 135 parts acrylamide,
450 parts acrylonitrile, 2700 parts butyl acrylate, and 3485 parts ethyl
acrylate, to prepare the foam.
EXAMPLE 9
The procedure described in Example 1 is carried out with an emulsion
polymer of 135 parts methacrylic acid, 180 parts acrylamide, 630 parts
acrylonitrile, 5400 parts butyl acrylate, and 3655 parts isopropyl
acrylate.
EXAMPLE 10
Example 1 is repeated with an emulsion polymer of 135 parts itaconic acid,
270 parts acrylamide, 630 parts acrylonitrile, 5400 parts butyl acrylate,
1285 parts ethyl acrylate, and 1285 parts methyl acrylate, as the foam.
Similar results are obtained when isobutyl acrylate or 2-ethylhexyl
acrylate are used in place of butyl acrylate or ethyl acrylate.
EXAMPLE 11
Example 1 is repeated with latices of polymers having the composition:
a. 86EA/10AN/2MIAM/2AM
b. 65EA/25.5BA/4.5AN/3.5AM/1.5IA
c. 96EA/2MIAM/2AM
d. 48EA/48BA/3MIAM/1IA with the wet density of between about 0.1 to 0.5
g./cc. at wet thicknesses between about 4 mils and 45 mils. Polymer (a) is
relatively hydrophophilic, (b) and (c) moderately so, and (d) relatively
hydrophobic.
All quickly absorbed pipetted water. The lower thicknesses tend to provide
a textile-like feel whereas the higher thicknesses give a plastic-like
feel.
At a wet density of about 0.18 g./cc. (about 11 lb./ft.sup.3) the crushed
density is about 20-40 lbs./ft..sup.3 (but variabl | | |
