Note: Descriptions are shown in the official language in which they were submitted.
1860~72
1332~Ql
--1--
NONWOVEN FABRIC WITH AN ACRYLATE INTERPOLYMER BINDER
AND A PROCESS OF MAKING THE NONWOVEN FABRIC
BACRGROUND OF THE INv~wlION
1) Field of the Invention
The present invention concerns nonwoven
fabrics, i.e., those fabrics composed of loosely
assembled fibers either bound chemically, thermally,
or through fiber entanglements, forming an
interlocking web of fibers to make a fabric. In
particular, the present invention concerns loosely
assembled fibers saturated, coated, sprayed, or
otherwise treated with an acrylate interpolymer,
which gives a unique balance of physical properties
including, but not limited to, a ~soft hand", high
resilience, low temperature flesibility and good dry,
wet, and solvent properties.
2) Prior Art
Non-woven fabrics have distinct features and
advantages over woven fabrics and can be prepared
using anyone of a variety of processes. For example,
chemically bonded nonwoven fabrics can be formed by
impregnating, printing, or otherwise coating a
loosely assembled web of fibers with a binder such as
an acrylate interpolymer. Thermally bonded nonwovens
can be bound by choosing fibers that will fuse onto
other fibers in the web when the web is subjected to
heat and/or pressure and/or sonic energy. Nonwovens
produced by entangling the fibers can have strength
and integrity without any thermal or chemical
bonding. Entangling techniques include hydraulic
methods, needle punching methods, and arrangement of
spun filaments. Generally thermally bonded or
entangled nonwovens will have strength and integrity
but will lack resiliency. Chemically bonded
nonwovens will have a degree of resilience dependent
13329~1
upon the resilience of the binder and the strength of
interaction between the fibers.
The length and type of fibers employed
depend upon the end use. For example, cotton or
cellulose fibers useful in paper applications are
typically less than 1 millimeter to 10 millimeters in
length. Nonwoven textile fibers are generally from
about 10 millimeters to 75 millimeters in length.
Also a continuous filament fiber can be employed.
They may be composed of synthetic fibers such as
polyester, rayon, dacron, nylon, etc., or natural
fibers such as cotton, wool, or the like. The
nonwoven fabric can be manufactured by conventional
techniques such as spinning, carding, garnetting, air
laying, wet laying, or other known process.
In many end use nonwoven applications, it is
desirable to produce soft fabrics having good wet,
dry, and solvent properties. In chemically bonded
nonwovens, the binder and the fiber type(s) are
important factors in producing the soft fabric
characteristics, the durability, and the wet, dry,
and solvent strength properties. In some end use
applications, resiliency of the nonwoven fabric is
desired along with the above mentioned properties. A
clothing interliner is an example of a chemically
bonded nonwoven application where the balance of soft
hand, durability, resilience, and strength properties
is highly desirable.
Thermally bonded nonwovens, although
possessing strength and durability due to the fusion
of fibers in a web, will generally lack resiliency.
The present invention relative to thermally bonded
nonwovens can impart resiliency while maintaining or
improving the "hand" characteristics of the finished
material. Similarly, untreated, entangled materials
will have strength and durability but lack
13329~1
resiliency. The present invention relative to
entangled nonwovens can provided a balance of
resiliency and soft "hand".
In other applications, especially those
pertaining to paper or cellulose fibers, resiliency
is less important, while strength, tear resistance
and fold endurance are generally more important.
Strongly interacting fibers, such as cellulose, limit
resiliency. The present invention relative to such
chemically bonded nonwovens demonstrates a balance of
properties not found in the prior art.
SUMMARY OF THE INVENTION
The present invention relates to the
combination of a unique acrylic latex binder and
fibers thus forming a nonwoven fabric. In
particular, the latex of the present invention may be
applied to fibers as a coating, binder or impregnant,
or otherwise deposited on the fibers. The present
invention also relates to a process of making this
combination of the unique latex and fibers.
The latexes are prepared by
interpolymerizing (a) from about 1 to about 20 weight
parts of at least one unsaturated dicarboxylic acid
containing 4 to about 10 carbon atoms, with (b) about
70 to about 99 weight parts of at least one
copolymerizable monomer, wherein a major portion of
such copolymerizable monomer is an acrylate
monomer(s), and (c) optionally, about 0.1 to about 10
weight parts of a crosslinking monomer, in the
presence of conventional initiators and surfactants.
The polymers in these latexes have a unique and
improved balance of properties. The novel polymers
are low Tg, soft acrylic polymers that have a good
balance of tensile strength and elongation and
excellent hysteresis characteristics. They are
rubbery, tough, and highly resilient, and exhibit
133~901
tensile strength and elongation properties common in
some "harder" acrylic polymers. The glass transition
temperature (Tg) of the novel polymers is from about
-20C. to about -60C.
The novel latexes can be prepared by
polymerizing the monomers and other ingredients using
a premix of the monomers which is metered into a
reactor containing initiator. However, a preferred
process is to prepare a premix in the usual manner
but devoid of all or a substantial part of the
unsaturated dicarboxylic acid, and add the
unsaturated dicarboxylic acid initially to the
reactor before metering the premix into the reactor.
When using the acrylic latex of the present
invention with a web of fibers, a unique nonwoven is
produced. In thermally bonded nonwovens or entangled
nonwovens treated according to the present invention,
the latex can impart durable resilience, while
maintaining or improving the hand. In loosely
assembled fibers bonded with the latex of the present
invention, the latex can impart a unique balance of
properties such as good wet, dry, and solvent
strength properties, flexibility, softness, and
resiliency.
In the broadest sense, the present invention
relates to the combination of fibers and a latex, the
latex having a Tg in the range of from about -20C.
to about -60C.; about 1 to about 20 weight parts of
at least one unsaturated dicarboxylic acid containing
4 to 10 carbon atoms per molecule; about 70 to about
99 weight parts of at least one copolymerizable
monomer, a majority of which is an acrylate
monomer(s), the raw polymer of the latex having a
tensile strength of at least 300 psi, an elongation
of at least 350% and a percent hysteresis loss of
less than about 20%.
13329G 1
In the broadest sense, the present invention
also relates to a process of forming a nonwoven
fabric, including the steps of assembling a loose web
of fibers and treating the fibers with a latex having
a Tg of from about -20C to about -60C.; about 1 to
20 weight parts of at least one unsaturated
dicarboxylic acid containing 4 to 10 carbon atoms per
molecule; about 70 to 99 weight parts of at least one
copolymerizable monomer, a majority of which is an
acrylate monomer(s), the raw polymer of the latex
having a tensile strength of at least 300 psi, an
elongation of at least 350%, and a percent hysteresis
loss of less than about 20%.
DETAILED DESCRIPTION OF THE INV~N 1 ION
The novel latexes disclosed herein can be
used in conjunction with fibers to yield nonwoven
articles that have unique properties. The novel
polymers exhibit a unique and improved balance of
properties. They have excellent low temperature
flexibility and yet exhibit a good balance of tensile
strength and elongation and excellent hysteresis
characteristics. More specifically, the novel
polymers have an improved balance of high resilience,
rubberyness, toughness, low surface tack considering
their softness, heat and light stability, dry and wet
and solvent strength, and low temperature
flexibility. Certain properties of the novel
polymers are comparable to those of some much harder
acrylate polymers. For example, the novel polymers
exhibit abrasion resistance comparable to harder
acrylate polymers. Moreover, the novel polymers
exhibit rubbery behavior when compared to the more
plastic behavior observed with harder acrylate
polymers. Prior to this invention, low Tg, soft
acrylic polymers basically exhibited a poor balance
of tensile strength and elongation properties
~ 332301
--6--
and inadequate hysteresis characteristics. The
polymers of this invention exhibit a much improved
balance of properties in this regard. Particularly,
the novel polymers of this invention are low Tg, soft
acrylic polymers that have a good balance of tensile
strength and elongation and excellent hysteresis
characteristics as shown by a low percent hysteresis
loss.
The novel latexes disclosed herein are
prepared by polymerizing at least one unsaturated
dicarboxylic acid containing 4 to about 10 carbon
atoms, with at least one copolymerizable monomer in
the presence of an initiator and a surfactant.
Optionally, a crosslinking monomer can be
interpolymerized with the unsaturated dicarboxylic
acid(s) and the copolymerizable monomer(s). The
total amount of all of the monomers charged to the
reactor, whether batchwise, incrementally, and/or
metered in, equals 100 parts by weight.
The use of unsaturated dicarboxylic acids is
critical to the invention. The use of monocarboxylic
acids such as acrylic acid or methacrylic acid does
not produce the unique balance of properties in the
polymer. The unsaturated dicarboxylic acids used in
the invention contain 4 to about 10 carbon atoms per
molecule. Especially suitable dicarboxylic acids are
those containing 4 to 6 carbon atoms such as itaconic
acid, citraconic acid, mesaconic acid, glutaconic
acid, fumaric acid and maleic acid. The anhydrides
of such acids are also useful, such as maleic
anhydride. The more preferred unsaturated
dicarboxylic acids are itaconic acid and fumaric
acid. The most preferred unsaturated dicarboxylic
acid in terms of performance is itaconic acid.
The amount of the unsaturated dicarboxylic
acid employed is from about 1 part to about 20 parts
1332~1
by weight, and more preferably from about 2 parts to
about 8 parts by weight. The use of the unsaturated
dicarboxylic acids in amounts above about 8 parts by
weight necessitates suitable adjustments in
polymerization ingredients due to a destabilizing
effect of the acid and some retardation of the
polymerization. For example, in an experiment where
8 weight parts of itaconic acid was charged initially
into the reactor using the same amount of surfactant
and initiator that gave good results when 4 weight
parts of itaconic acid was used, the resulting latex
had a high residual monomer content which caused some
difficulty in forming an even or level film. When 20
weight parts of itaconic acid was charged initially
into the reactor, a latex was formed but the residual
monomer level was quite high. In such cases the
polymerization conditions and ingredients can be
readily adjusted to obtain latexes with acceptable
amounts of residual monomers. This can be done by
increasing the amounts of surfactant and/or initiator
used, by increasing the temperature of
polymerization, by metering in part of the
unsaturated dicarboxylic acid, by stripping the
latex, or combinations of the above. Excellent
results have been obtained using about 3 to about 6
parts by weight of the unsaturated dicarboxylic acid.
The novel polymers of this invention are
interpolymers of (a) at least one of the
above-described unsaturated dicarboxylic acids with
(b) at least one copolymerizable monomer and (c)
optionally, a crosslinking monomer(s). Hence, a
novel polymer of the invention may be an interpolymer
as simple in structure as a copolymer of 95% by
weight n-butyl acrylate and 5% by weight itaconic
acid. However, the novel polymers are more likely to
-8- ~ 01
contain interpolymerized units of more than two
monomers.
The copolymerizable monomer(s) used in this
invention can be any unsaturated monomer capable of
interpolymerizing with the unsaturated dicarboxylic
acid. The amount of copolymerizable monomer employed
is such that the weight parts of the unsaturated
dicarboxylic acid(s), and the crosslinking
monomer(s), if used, together with the weight parts
of the copolymerizable monomer(s) used total up to
one hundred (100) weight parts. For example, a novel
copolymer of the invention containing 4 parts by
weight of an unsaturated dicarboxylic acid and 2
parts by weight of a crosslinking monomer would then
contain 94 parts by weight of a copolymerizable
monomer(s). Since all the monomers are charged on a
100 weight parts total basis, and the conversions in
the latex reaction typically reach substantial
completion, the weight parts of monomer charged
substantially eguals the weight percent of the
interpolymerized monomer in the final polymer. If
this is not the case, the use of conventional
analytical techniques readily establishes the weight
percent of any interpolymerized monomer in the
polymer. Typically, the total amount of
copolymerizable monomer(s) charged into the reactor
is at least 70 parts by weight, and more typically at
least 90 parts by weight of the total weight of all
monomers.
Examples of the copolymerizable monomers are
alkyl, alkoxyalkyl, alkylthioalkyl, and cyanoalkyl
acrylates and methacrylates containing 1 to about 20
carbon atoms in the alkyl ~roup; diacrylates and
dimethacrylates such as ethyleneglycol
dimethacrylate, diethylene glycol diacrylate, and the
like; monolefins containing 2 to about 10 carbon
133~90~
g
atoms such as ethylene, propylene, isobutylene,
l-hexene, l-octene, and the like; vinyl and allyl
acetates containing 4 to about 20 carbon atoms such
as vinyl acetate, vinyl propionate, allyl acetate,
and the like; vinyl ketones containing 4 to about 20
carbon atoms such as methyl vinyl ketone; vinyl and
allyl ethers containing 4 to about 20 carbon atoms
such as vinyl methyl ether, vinyl ethyl ether,
vinyl-n-butyl ether, allyl methyl ether, and the
like; vinyl aromatics containing 8 to about 20 carbon
atoms such as styrene, a-methyl styrene, p-n-butyl
styrene, p-n-octyl styrene, vinyl toluene, and the
like; vinyl nitriles containing 3 to about 6 carbon
atoms such as acrylonitrile and methacrylonitrile;
vinyl amides containing 4 to about 20 carbon atoms
such as acrylamide, methacrylamide, N-methyl
methacrylamide, and the like; and dienes and divinyls
containing 4 to about 20 carbon atoms such as
butadiene, isoprene, divinyl benzene, divinyl ether,
and the like; monomers of 2 to about 20 carbon atoms
containing a halogen group such as vinyl chloride,
vinyl bromide, vinylidene chloride, vinyl benzyl
chloride, vinyl benzyl bromide, vinyl chloroacetate,
allyl chloroacetate, 2-chloroethyl acrylate,
chloroprene, and the like; unsaturated sulfonate
monomers such as sodium styrene sulfonate, vinyl
sulfonate, and the like; unsaturated carboxylic ester
and amide monomers containing 4 to about 20 carbon
atoms such as dimethyl fumarate, dibutyl itaconate,
the half-ethyl ester of itaconic acid, and the like;
and unsaturated monocarboxylic acids containing 3 to
about 5 carbon atoms such as acrylic acid,
methacrylic acid, and the like.
The two conditions on the selection of the
copolymerizable monomer(s) are (1) that the glass
transition temperature (Tg) of the polymer made is
1332~01
--10--
from about -20C. to about -60C., and more
preferably from about -25C., to about -50C. and (2)
that the copolymerizable monomer(s) contains a major
portion of an acrylate monomer(s).
The acrylate monomer empolyed is an alkyl,
alkoxyalkyl, alkylthioalkyl, or cyanoalkyl acrylate
of the formula
Rl O
CH2= ~ - C - O - R2 2
wherein Rl is hydrogen or methyl, and R is an
alkyl radical containing 1 to about 20 carbon atoms,
an alkoxyalkyl or alkylthioalkyl radical containing a
total of 2 to about 12 carbon atoms, or a cyanoalkyl
radical containing 2 to about 12 carbon atoms. The
alkyl structure can contain primary, secondary, or
tertiary carbon configurations. Examples of such
acrylates are methyl acrylate, ethyl acrylate, propyl
acrylate, n-butyl acrylate, isobutyl acrylate,
n-pentyl acrylate, isoamyl acrylate, n-hexyl
acrylate, 2-methyl pentyl acrylate, n-octyl acrylate,
2-ethylhexyl acrylate, n-decyl acrylate, n-dodecyl
acrylate, n-octadecyl acrylate, and the like;
methoxymethyl acrylate, methoxyethyl acrylate,
ethoxyethyl acrylate, butoxyethyl acrylate,
ethoxypropyl acrylate, methylthioethyl acrylate,
hexylthioethylacrylate, and the like; and a and
B-cyanoethyl acrylate, , B and -cyanopropyl
cyanobutyl, cyanohexyl, and cyanooctyl acrylate, and
the like; n-butyl methacrylate, 2-ethylhexyl
methacrylate, isodecyl methacrylate, octadecyl
methacrylate, and the like. Mixtures of two or more
acrylate monomers are readily employed.
Preferably, the copolymerizable monomer(s)
used contains from about forty percent (40%) up to
one hundred percent (100%) by weight of acrylates of
the above formula. The most preferred alkylate
l 332901
--11--
monomer(s) are those wherein Ra is hydrogen and Rl
is an alkyl radical containing 4 to about 10 carbon
atoms or an alkoxyalkyl radical containing 2 to about
8 carbon atoms. Examples of the most preferred
acrylates are n-butyl acrylate, hexyl acrylate,
2-ethylhexyl acrylate, and the like, and methoxyethyl
acrylate, ethoxyethyl acrylate and the like. Both an
alkyl acrylate and an alkoxyalkyl acrylate can be
used. Excellent results have been obtained when the
acrylate monomer(s) employed is the most preferred
acrylate monomer(s) and such monomer(s) comprises
about seventy-five percent (75%) to one hundred
percent (100%) of the copolymerizable monomer.
The two criteria on the selection of the
copolymerizable monomer such that the novel polymer
has a low Tg and contains a major portion of
interpolymerized acrylate monomer(s) are somewhat
complementary in that the use of a high level of the
preferred acrylate monomer(s) as the copolymerizable
monomer readily yields a novel polymer having the
required Tg value. It is understood that the novel
polymers of this invention can have more than one Tg
value within the prescribed Tg range.
The Tg of a polymer can be easily determined
using differential thermal analysis. Further, the Tg
of a polymer is predictable from the interpolymerized
monomers using known formulas and readily obtainable
data following the procedure and teachings given in
many publications. One such publication is the book
Mechanical Properties of PolYmers by L. E. Nielsen,
Reinhold Publishing Corp. (1967) Library of Congress
catalog card no. 62-18939. Chapter 2 is devoted to
transitions in polymers, and the tables given on
pages 16 to 24 list out the Tg values of many
polymers, including acrylate polymers, based on the
monomers employed.
133~Ql
-12-
Hence, the Tg of the novel polymers can be
determined through knowledge of the types and amounts
of copolymerizable monomers employed. However, from
the aforementioned list of copolymerizable monomers,
it is apparent that some of the monomers cannot be
used in large amounts and yet make a polymer meeting
the necessary criteria. For example, the "hard"
copolymerizable monomers; i.e. those which would
yield a homopolymer Tg value of +80C. or above,
would typically be used in amounts of from 0 percent
to about 25 percent by weight of the total weight of
the copolymerizable monomers. Examples of such hard
monomers are the vinyl aromatics such as styrene,
a-methyl styrene, vinyl toluene; vinyl nitriles such
as acrylonitrile and methacrylonitrile; and monomers
containing a halogen group such as vinyl chloride,
vinylidene chloride, vinyl benzyl chloride. Further,
certain of the copolymerizable monomers have an
activity which, if the monomers were present in large
amounts, could overshadow the features of the
polymers of this invention. Hence, copolymerizable
monomers such as the vinyl amides, the diacrylates
and dimethacrylates, the unsaturated sulfonate
monomers, and the unsaturated monocarboxylic acids
would typically be used in amounts of from 0 percent
to about 5 percent by weight of the total weight of
the copolymerizable monomers.
The novel polymers do not require the
presence of a crosslinking monomer to achieve their
unique properties. However, many uses of the novel
polymers benefit from the presence of a crosslinking
monomer in the polymer or the addition of a
crosslinking agent to the novel polymer.
The crosslinking monomers used herein can be
any monomer or oligomer polymerizable with the
unsaturated dicarboxylic acid and copolymerizable
1 3 3h ~ ~ ~
--13--
monomer which exhibits crosslinking or which can be
converted into a crosslinking site. An example of a
crosslinking monomer which can be interpolymerized
with the unsaturated dicarboxylic acid and
copolymerizable monomer, and then converted to yield
a crosslinking site is acrylamide, which, when
treated with formaldehyde, forms a methylol group.
The more preferred crosslinking monomers are
monoethylenically unsaturated monomers containing
N-methylol groups such as N-methylol acrylamide, or
N-methylol derivatives of allyl carbamate which may
contain one or two N-methylol groups. The N-methylol
groups may be left unreacted or they may be
etherized, as with Cl to C4 carbon alcohols. The
alcohol is released on curing to regenerate the
N-methylol group for cure. Alcohol etherifying
agents are illustrated by methyl alcohol, ethyl
alcohol, isopropyl alcohol, isobutyl alcohol,
2-ethoxyethanol, and 2-butoxy ethanol.
More particularly, the preferred
crosslinking monomers are selected from N-alkylol
acrylamides that contain from about 4 to about 18,
preferably 4 to 12 carbon atoms in the alkyl group,
and lower alkyl acrylamidoglycolate lower alkyl
ethers containing from about 7 to about 20 carbon
atoms. Specific examples of the particularly
preferred crosslinking monomers include N-methylol
acrylamide, N-methylol methacrylamide, N-butoxymethyl
acrylamide, iso-butoxymethyl acrylamide and methyl
acrylamidoglycolate methyl ether. Especially good
results have been obtained using N-methylol
acrylamide as the crosslinking monomer.
The crosslinking monomer is used in the
range from about 0.1 to about 10 parts by weight, and
more preferably from about 0.5 to about 5 parts by
1332~01
-14-
weight based on 100 parts by weight total of all
monomers.
If a crosslinking monomer is not
interpolymerized with the unsaturated dicarboxylic
acid and the copolymerizable monomer, the novel
polymer can still be crosslinked by the
post-polymerization addition of a crosslinking agent
to the latex or the polymer. Examples of such
crosslinking agents are urea-formaldehyde resins,
melamine-formaldehyde resins and partially
methylolated melamine-formaldehyde resins, glyoxal
resins, and the like. These crosslinking agents can
be used in levels of from about 0.1 part to about 20
parts, and more preferably from about 0.5 part to
about 2 parts, by weight, based on 100 parts by
weight of polymer.
The novel polymers are prepared as latexes.
As the novel polymers have great utility used in the
form of a latex, the latexes themselves are unique
and novel.
The aqueous medium in which the novel
polymers are prepared may be free of traditional
emulsifiers, or it may contain traditional
emulsifiers. When traditional emulsifiers are used
to prepare the unique latexes of this invention, the
standard types of anionic and nonionic emulsifiers
can be employed. Useful emulsifiers include alkali
metal or ammonium salts of the sulfates of alcohols
having from 8 to 18 carbon atoms such as sodium
lauryl sulfate, ethanolamine lauryl sulfate, and
ethylamine lauryl sulfate; alkali metal and ammonium
salts of sulfonated petroleum and paraffin oils;
sodium salts of sulfonic acids such as
dodecane-l-sulfonic acid and octadiene-l-sulfonic
acid; aralkyl sulfonates such as sodium isopropyl
benzene sulfonate, sodium dodecyl benzene sulfonate
1332.~1)1
-15-
and sodium isobutyl naphthalene sulfonate; alkali
metal and ammonium salts of sulfonated dicarboxylic
acid esters such as sodium dioctyl sulfosuccinate and
disodium-N-octadecyl sulfosuccinate; alkali metal or
ammonium salts of the free acid of complex organic
amon-and diphosphate esters; copolymerizable
surfactants such as vinyl sulfonate and the like.
Nonionic emulsifiers such as octyl- or nonylphenyl
polyethoxyethanol may also be used. Latexes of the
invention having excellent stability are obtained
using the alkali metal and ammonium salts of aromatic
sulfonic acids, aralkyl sulfonates, long chain alkyl
sulfonates and poly(oxyalkylene) sulfonates as
emulsifiers.
The emulsifier or a mixture thereof may be
added entirely at the outset of the polymerization or
it may be added incrementally or metered throughout
the run. Typically, some of the emulsifier is added
to the reactor at the outset of the polymerization
and the remainder is charged incrementally or
proportionately to the reactor as the monomers are
proportioned.
The polymerization of the monomers may be
conducted at temperatures from about 0C up to about
100C in the presence of a compound capable of
initiating the polymerizations. Initiating compounds
and mixtures thereof are chosen, often in conjunction
with oxidation-reduction catalysts, in an amount and
type which results in a suitable initiation rate at a
chosen polymerization temperature profile. Commonly
used initiators include the free radical initiators
like the various peroxygen compounds such as
persulfates, benzoyl peroxide, t-butyl
diperphtahlate, pelargonyl peroxide and
l-hydroxycyclohexyl hydroperoxide; azo compounds such
as azodiisobutyronitrile and
13~2~01
-16-
dimethylazodiisobutyrate; and the like. Particularly
useful initiators are the water-soluble peroxygen
compounds such as hydrogen peroxide and sodium,
potassium and ammonium persulfates used by themselves
or in activated systems. Typical oxidation-reduction
systems include alkali metal persulfates in
combination with a reducing substance such as
polyhydroxyphenols, oxidizable sulfur compounds such
as sodium sulfite or sodium bisulfite, reducing
sugars, dimethylamino propionitrile, diazomercapto
compounds, water-soluble ferricyanide compounds, or
the like. Heavy metal ions may also be used to
activate persulfate catalyzed polymerizations.
The amount of surfactant used is from about
0.01 to about 10 parts by weight, and the amount of
initiator is used from about 0.01 to about 1.5 parts
by weight, both based on 100 weight parts of the
total amount of monomers.
Polymer latexes of the invention having
excellent stability are obtained using an alkali
metal and ammonium persulfate as the initiator. The
initiator may be charged completely into the reactor
at the outset of the polymerization, or incremental
addition or metering of the initiator throughout the
polymerization may also be employed. Addition of the
initiator throughout the polymerization is often
advantageous in providing a suitable rate throughout
the polymerization.
The novel acrylic latexes can be made in
different ways. In a one process, a premix is
prepared by mixing the monomers, optionally with
water, a surfactant or a mixture thereof, buffering
agents, modifiers and the like. If water is used,
the aqueous premix is agitated to form an emulsion.
Separately added to a reactor are more water, the
initiator, and optional ingredients. The premix is
1332~01
-17-
then metered into the reactor and the monomers are
polymerized.
In a variation on the above process, part of
the premix can be added to the reactor, the initiator
is then added and polymerization of the initial
monomers in the reactor thereto is allowed to form
seed polymer particles. Thereafter, the remainder of
the premix or another premix is metered into the
reactor and the polymerization reaction is concluded
in the usual way. In yet another variation, the
premix can be fed to the reactor incrementally rather
than continuously. Finally, in yet another variation
of the process, all of the monomers and other
ingredients can be added directly to the reactor and
polymerization conducted in a known manner. This
last variation is typically called a batch process.
Monomers can also be added to the reactor in separate
streams other than in the premix.
In a preferred embodiment of the process for
preparing a latex of the invention, about 2 to about
8 weight parts of the unsaturated dicarboxylic acid
such as itaconic acid is polymerized in water with 90
to 98 weight parts of an alkyl acrylate monomer such
as n-butyl acrylate and 0.5 to 5 weight parts of a
crosslinking monomer such as N-methylol acrylamide,
in the presence of 0.1 to 5 weight part of a suitable
surfactant such as sodium lauryl sulfate and 0.01 to
l.S weight parts of a suitable initiator such as
sodium persulfate.
The unsaturated dicarboxylic acid can be
added all initially into the reactor before metering
of the premix is commenced, or part or all of the
said acid can be metered into the reactor during
polymerization. In a preferred embodiment of the
process, the unsaturated dicarboxylic acid is all
initially added to the reactor, and the premix
1~3~9~
-18-
containing the copolymerizable monomer(s) and
crosslinking monomer(s) is metered into the reactor.
The best balance of polymer physical properties was
obtained when all of the unsaturated dicarboxylic
acid was added initially to the reactor. However, as
compared to similar polymers made using
monocarboxylic acids only, polymers having an
improved balance of properties are also obtained when
some or all of unsaturated dicarboxylic acid is added
to the premix.
As already noted, processes for preparing
acrylic latexes usually involve a number of stages.
A premix is typically prepared containing one or more
monomers, optionally surfactant, water and
ingredients such as buffering agents, chain
modifiers, and the like. The premix is vigorously
agitated to form an emulsion at ambient temperature.
The reactor is also prepared for polymerization by
addition of water, initiator, monomer (if added to
the reactor), optionally buffering agents, and other
ingredients. The reactor and its contents can be
preheated. The premix is metered to the reactor over
a period of about 0.5 to about 10 or more hours,
preferably 1 to 4 hours. As soon as the
polymerization starts, the temperature of the reactor
increases. A cold water or other type of cooling
jacket around the reactor can be used to control the
polymerization temperature, preferably at about 30C.
to about 90C.
The latex obtained is typically treated or
processed to reduce residual monomers and the pH is
adjusted to whatever value is desired. The latex is
then often filtered through a cheesecloth or filter
sock and stored. The stored latex has a total solids
content of from about 10 to about 68%, and more
typically from about 40% to 60%.
133290~
--19--
It should be understood that although the
best results were obtained when all or at least
one-half or more of the unsaturated dicarboxyclic
acid was placed in the reactor initially, an
unexpected improvement in the balance of the physical
properties of the novel polymers was also obtained
when over one-half or all of the acid is placed in
the premix, as long as the acid used is the
unsaturated dicarboxylic acid described herein. The
use of unsaturated monocarboxylic acids, such as
acrylic acid and methacrylic acid, did not work to
produce the unique balance of properties in the novel
polymer. Further, when acrylic acid or methacrylic
acid was placed initially all in the reactor, the
reaction mixture gelled or coagulated, despite
attempts to prevent this by adding water during the
polymerization.
As already described, in a preferred process
of this invention, the unsaturated dicarboxylic acid
is all added initially to the reactor, unlike prior
art processes in which all of the monocarboxylic acid
is typically added to the premix. Addition of large
amounts of the unsaturated dicarboxylic acid to the
reactor initially requires adjustments in the
polymerization recipe in order to obtain a latex with
optimum properties. For example, placing all of the
unsaturated dicarboxylic acid into the reactor
without making any other changes in the
polymerization recipe or process can result in a
larger particle size latex. The reason for this is
believed to be that the dicarboxylic acid reduces the
efficiency of the initiator in the reactor and/or
causes destabilization of forming particles in the
reactor, which, in turn, can affect the particle size
of the latex polymer.
13~29~1
-20-
It is known in acrylic latex technology that
the amount of the surfactant in the reactor can
substantially affect the particle size of the latex.
Hence, by increasing the amount of surfactant used,
the particle size of the latex can be reduced.
Since the presence of the unsaturated dicarboxylic
acid in the reactor can have the affect of increasing
the particle size, an upward adjustment in the amount
of surfactant (and/or initiator) used can compensate
for this effect.
The novel latexes disclosed herein have
typical colloidal properties. They are anionically
stabilized, have a pH of from about 1 to about 6 as
prepared, have a particle size in the range of about
1000 to 5000 angstroms, and e~h;bit good mechanical
stability when their pH is raised above neutral.
One of the most unique properties of the
polymers of this invention is their excellent
hysteresis characteristics. The novel polymers
prepared herein have very tight hysteresis curves.
The tighter a hysteresis curve, the more resilient
the polymer. Also, the tighter the hysteresis curve,
the less heat will be generated on stretching or
working of the polymer.
The percent hysteresis loss of polymers were
determined from the polymer's hysteresis curve using
the following procedure. Dumbell samples of the raw
polymer having about 7 to 10 mils thickness were
prepared from the latex using a draw bar. The cast
films were air-dried then heated at 300F. for 5
minutes. By raw polymer is it meant that no
compounding ingredients such as fillers, pigments,
plasticizers and the like were added, and no curative
ingredients were added. The samples were placed in
an Instron*tensile testing machine and elongated to
200% elongation at a speed of 20 inches/minute. The
Trade Mark
9 0 1
-21-
sample was then retracted at 20 inches/minute to its
original position (making one cycle), and then
elongated and retracted again until five cycles were
completed. The tensile/elongation (i.e. hysteresis)
curves for each cycle were recorded. The percent
hysteresis loss measurements were performed in each
case on the recorded data for the second cycle. The
area of the figure described by the initial stretch
of the polymer to 200% elongation represents the
amount of work energy needed to produce the
elongation (EA). The area of the figure described
when the polymer is retracted in the cycle represents
the work energy exerted by the polymer in returning
to its original position (EB). A perfectly
resilient polymer which exhibits no heat or other
energy losses would have a hysteresis curve wherein
EA would equal EB, i.e. the two curves would lie
on top of each other. The deviation from this ideal
condition is a measure of the polymer's hysteresis
loss. A gummy polymer would have a very high percent
hysteresis loss.
The percent hysteresis loss of the polymers
was determined by the following formula:
EA ~ EB
Percent Hysteresis Loss = EA x 100%.
The polymers of this invention exhibit a
percent hysteresis loss of less than about 20% as
calculated from their hysteresis curves. The
polymers prepared from the most preferred unsaturated
dicarboxylic acids, copolymerizable monomers, and
crosslinking monomers and prepared by the preferred
process exhibit a percent hysteresis loss of below 15
percent.
The novel polymers have other properties
which make them unique. They are soft, yet rubbery
and tough. Their ultimate raw polymer tensile
133~!~0~L
-22-
strength is at least 300 psi and ultimate percent
elongation is at least 350%, as measured on raw
polymer films cast with a draw bar, air-dried and
heated for 5 minutes at 300F. A way of observing
the good balance of tensile strength and elongation
exhibited by the polymers of this invention is to
calculate their "TxE Product", which is simply the
figure obtained by multiplying the polymer's ultimate
tensile strength by its percent elongation at break.
The figure is reported to the nearest 1000. The TxE
Product a measure of the overall strength of the
polymer. The TxE Product of the novel polymers is at
least about 140,000, and more preferably at least
about 200,000. The TxE Product for the novel
polymers made from the most preferred monomers using
the most preferred process is at least about 250,000.
The following examples are presented for the
purpose of illustrating the invention. The examples
are not to be construed as limiting the invention in
any manner, the scope of which is defined by the
appended claims.
EXAMPLES
In the following experiments, except as
stated otherwise, the latex was prepared by
polymerizing a monomer mix of 93 to 97 parts by
weight parts of the copolymerizable monomer, 2 to 4.5
weight parts of the stated acid, and 1 to 3 weight
parts of the crosslinking monomer. In comparative
experiments where no acid was used, the amount of
copolymerizable monomer was increased accordingly.
The premix was prepared in a separate tank by mixing
demineralized water, sodium lauryl sulfate as the
surfactant, the crosslinking monomer, and the
copolymerizable monomer(s). All or part of the acid
was placed in the premix or the reactor, as
1332~
-23-
indicated. The reactor initially contained
demineralized water, sodium lauryl sulfate, and
sodium persulfate. The premix was metered into the
reactor over a period of about 1.5 to about 2.5
hours, during which time the temperature in the
reactor was controlled at 70C. to 80C.
After commencement of the metering of the
premix to the reactor, in some cases a second
initiator system was added to the reactor. The
second initiator system consisted of sodium
persulfate, sodium lauryl sulfate, and ammonium
carbonate in demineralized water. The second
initiator was metered into the reactor over a period
of 3.5 hours. At times, an initiator booster was
merely slugged into the reactor rather than metered
in. When the reaction was completed, the latex in
the reactor was allowed to stand for about 1.5 hours
at 75C. and was then cooled to 40C. At this point,
the latex was stripped, cooled to 30C., its pH was
adjusted with ammonia to about 4.5 pH, and it was
filtered through cheesecloth and stored.
Following the above general procedures,
three variations of reaction conditions were actually
employed. In Variation A, the reaction temperature
was 80C., the premix metering time was 2 hours, an
initiator booster containing 0.05 weight part of
sodium persulfate was added after 2 hours, and the
amount of sodium lauryl sulfate used was 0.05 weight
part in the reactor and 0.95 weight part in the
premix. Variation B was like Variation A except that
the reaction temperature was 75C. In Variation C,
the reaction temperature was 70C., 0.35 weight part
of sodium persulfate initiator was in the reactor, a
second initiator of 0.15 part of sodium persulfate
and 0.05 part of sodium lauryl sulfate was metered in
~3~0li
-24-
over 3.5 hours, and the amount of sodium lauryl
sulfate in the reactor was 0.4 weight part and in the
premix was 0.6 weight part.
The raw polymer films were prepared in the
following manner. First, the latex was neutralized
by adjusting the pH of the latex to between 7 and 8
with ammonia. Thickener was added to the latex, as
necessary, to raise its viscosity to about 500 cps so
that a level film could be obtained. A latex film
was deposited on a polyethylene backing using a draw
bar so as to yield a dry film of 7 to 10 mils
thickness, and the latex film was dried at room
temperature for about 24 hours. The polymer film was
then peeled from the backing, dusted with talc if
necessary for easier handling, and heated for S
minutes at 300F (149C). The test specimens were
prepared and tested using the following procedure. A
dumbell shaped test specimen was prepared from the
polymer film and placed in an Instron tensile tester
at a 1" jaw spacing. The jaws were separated at a
speed of 20 inches/minute. Elongation was measured
using a 0.5 inch benchmark. Each data point given in
the examples represents an average of three separate
measurements.
EXAMPLE 1
This example demonstrates the preparation of
a novel latex of the invention, the preparation of a
novel polymer of the invention from the latex, and
shows a comparison of the properties of the novel
polymer with those of polymers containing no acid,
acrylic acid, or methacrylic acid in the polymer.
Only the polymer prepared from the latex containing
polymerized itaconic acid is representative of the
invention. The other samples were prepared and are
presented for comparison purposes only. All of the
1 3 ~
-25-
latexes were prepared with 2 parts by weight of
N-methylol acrylamide as the crosslinking monomer,
and using the process described above as Variation
B. The acid, if used, was placed all in the premix
and the premix was metered into the reactor. All
reaction conditions and procedures were identical in
these tests except for the particular acid used, if
any. Ultimate tensile strength and percent
elongation tests were performed on film samples of
the raw polymers, which samples were prepared as
described above. The results are given in Table A
below:
Table A
No Acrylic Methacrylic Itaconic
Acid Acid Acid Acid
Tensile StrenBth, psi 207 350 330 693
Elongation, % 260 343 390 380
TxE Product 54000 120000 129000 263000
Percent Hysteresis12.2 18.1 22.9 18.9
Loss
1332~û~
-27-
It is apparent from the above data that the
novel polymer of the invention made using itaconic
acid (IA) has a superior balance of tensile strength
and elongation and percent hysteresis loss. The
polymer containing polymerized itaconic acid (IA) had
a tensile strength of 693 psi an ultimate elongation
of 380%, and a TxE Product of 263000, whereas the
corresponding results for acrylic acid (AA) were 350
psi, 390%, and 120000, and for methacrylic acid (MAA)
were 330 psi, and 390%, and 129000 respectively. For
the polymer prepared containing no acid at all, the
tensile strength was only 207 psi, elongation was
260%, and the TxE Product was only 53800. The data
shows that the polymer of the invention has a good
balance of tensile strength and elongation and low
hysteresis loss.
EXAMPLE 2
For purposes of further comparison, the
properties of a novel polymer of the invention were
compared to properties of some commercial polymers.
The novel polymer used herein is similar to the
polymer prepared in Example 1 above except that, in
this case, all of the itaconic acid was placed
initially into the reactor (no itaconic acid was in
the premix). The commercial polymers are Hycar~
2671 (Acrylic A), Hycar~ 2673 (Acrylic B), and an
acrylic polymer known as Rhoplex TR934 sold by Rohm
and Haas (Acrylic C). Results are given in Table B
below:
13329Cl
-28-
Table B
Novel Acrylic Acrylic Acrylic
Polymer A B C
Tensile, psi755 665 407 617
Elongation,%608 610 1483 433
TXE Product459000406000 636000 267000
Percent
Hysteresis
Loss 12.8 22.0 36.4 12.5
Tg, C -44 -11 -15 -28
The data shows that the novel polymer of the
invention gives a unique balance of good tensile
strength and elongation and low hysteresis loss. The
balance of tensile and elongation properties and
hysteresis loss of the novel polymer were actually
better than most of those properties of the "harder"
acrylic polymers, yet the Tg of the novel polymer was
considerably lower than such polymers.
EXAMPLE 3
This example shows the preparation and
testing of polymers of the invention wherein the
latexes were prepared using Variation A and all of
the unsaturated dicarboxylic acid was placed in the
premix. The following monomers were charged on the
following weight basis: 4.5 parts of the stated
acid, 1.0 part N-methylol acrylamide, and 94.5 parts
n-butyl acrylate.
The film samples were prepared from the
polymers and tested as described above. As a
comparison, a polymer was also prepared using the
monocarboxylic acid, acrylic acid, in place of
itaconic acid. The acrylic acid was also placed all
in the premix. Results of the tests are given in
Table C below.
1~3~
-29-
Table C
AA all IA all
in in
Premix Premix
Tensile, psi 310 546
Elongation % 493 553
TxE Product 153000 317000
Percent
Hysteresis
Loss 23.1 19.6
The tensile strength, elongation, TxE
Product, and hysteresis loss for the polymer made
with acrylic acid (AA) in the premix was 310 psi,
493%, 153000, and 23.1% respectively. When itaconic
acid (IA) was used all in the premix, thereby making
a polymer of this invention, the tensile strength,
elongation, TxE Product, and hysteresis loss was 546
psi, 553%, 317000, and 19.6% respectively. When the
experiment with the itaconic acid all placed in the
premix was repeated, the results were even better,
with a tensile strength of 670 psi, and elongation of
573%, a TxE Product of 366000, and a percent
hysteresis loss of 17.5%. All of the polymers had a
Tg of about -44C. It is apparent that the use of
itaconic acid (IA) in place of acrylic acid (AA)
results in a polymer having a superior balance of
tensile strength and elongation properties and low
percent hysteresis loss at a low Tg.
EXAMPLE 4
An experiment was performed wherein the
itaconic acid was placed all initially in the
reactor. This experiment used the same monomers and
parts by weight, and same polymerization and test
conditions given in Example 3 above. This novel
polymer had a tensile strength of 507 psi, and
elongation of 753%, a TxE Product of 382000, and a
percent hysteresis loss of 19.8%.
1 3 ~
-30-
With no buffers, the latex prepared in this
Example 3 had a pH of about 1.9. As mentioned
before, it is believed that the use of all of the
unsaturated dicarboxylic acid initially in the
reactor has the effect of reducing initiation
efficiency of the polymerization and/or destabilizing
the forming particles, which can result in a latex
which has a larger particle size than when the acid
is placed in the premix. The reduction in initiation
efficiency can be overcome by increasing the amount
of the surfactant or initiator, or ~oth. This was
demonstrated by conducting an experiment in which the
level of the surfactant used in the reactor was
increased from 0.05 weight part to 0.5 weight part,
with all other conditions remaining the same. By
increasing the amount of surfactant, the preparation
of the novel latex was more nearly optimized. The
data obtained on the film of the novel polymer
prepared in this manner shows that the tensile
strength of the polymer increased to 773 psi, the
elongation dropped to 647%, the TxE Product increased
to 500000, and the percent hysteresis loss dropped to
14.9~. This indicates a different balance of
properties than obtained using the lesser amount of
surfactant. This balance of properties may be
preferred in some uses.
EXAMPLE 5
This example demonstrates the superior
results that can be obtained by preparing the novel
latexes by the preferred process wherein all or at
least one-half of the unsaturated dicarboxylic acid
is placed initially in the reactor. The data in
Table D gives properties for films made from latexes
wherein the amount of itaconic acid (IA) placed in
the reactor ranged from all placed into the reactor
1332~0~
-31-
initially to all of the itaconic acid placed in the
premix. The latexes were prepared with 2 parts by
weight of N-methylol acrylamide as the crosslinking
monomers, and using process procedure Variation A.
Results are given in Table D below.
1 3 ~
--32--
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r O g~
1~32~01
-33-
When all 4 weight parts of the itaconic acid
are placed initially in the reactor, tensile
strength, elongation, TXE Product, and hysteresis
loss were 792 psi, 688%, 45900, and 12.8%
respectively. As more of the itaconic acid was
placed in the premix, the polymer properties changed,
especially in the percent elongation and percent
hysteresis loss. However, no matter how the novel
polymers were prepared, i.e. by the process wherein
all of the itaconic acid was placed in the reactor,
in the premix, or the itaconic acid was split between
the two, the polymers still show a superior balance
of properties as compared to similar polymers made
using acrylic acid or methacrylic acid. See Table A
for a comparison.
EXAMPLE 6
The suitability of using unsaturated
dicarboxylic acids other than itaconic acid is
demonstrated in this Example. The polymers were
prepared using 2 parts by weight of N-methylol
acrylamide as the crosslinking monomer, and using the
process procedure Variation B where all 4.0 weight
parts of the defined acid was placed initially into
the reactor. The unsaturated dicarboxylic acids
employed were itaconic acid (IA), fumaric acid (FA),
maleic acid (MA), and citraconic acid (CA). An
attempt was also made to prepare comparative latexes
and polymers which would contain no acid, acrylic
acid (AA) or methacrylic acid (MAA) in place of the
unsaturated dicarboxylic acid. Results are given in
Table E below:
Table E
Itaconic Fumaric Maleic Citraconic Acrylic Methacrylic
Acid Acid Acid Acid Acid Acid No Acid
Tensile, psi755 454 440 327 gelledgelled 207
Elongation, %603 427 467 637 260
TXE Product4590002330002050000 208000 54000 w
Percent
Hysteresis
Loss 12.8 18.4 18.0 19.9 12.2
~3
1332~0~
-35-
Both experiments wherein acrylic acid (AA)
or methacrylic acid (MAA) was placed all in the
reactor resulted in a gelled latex during
polymerization, even though an attempt was made to
prevent this by adding water to the reactor during
polymerization. With itaconic acid (IA) in the
reactor, the tensile strength of the novel polymer
was 755 psi, elongation was 603%, the TxE Product was
459000, and the percent hysteresis loss was a low
12.8%. The use of fumaric acid (FA) in the process
produced a polymer having a somewhat lower tensile
strength and elongation and higher percent hysteresis
low. The use of maleic acid (MA) or citraconic acid
(CA) as the unsaturated dicarboxylic acid yielded
polymers having lower tensile strengths and good
elongations. The TxE Products and percent hysteresis
loss of these polymers was good. With no acid, the
tensile strength of the polymer was only 207 psi, its
elongation was only 260%, and the TxE Product was a
very low 5400.
Certain of the above experiments were
repeated wherein the unsaturated dicarboxylic acid
was placed all in the premix (none initially in the
reactor). The polymer prepared using maleic acid in
the premix had a tensile strength of 351 psi, an
elongation of 357%, and a TxE Product of 12600. The
polymer prepared using citraconic acid in the premix
had a tensile strength of 321 psi, an elongation of
553%, and a TxE Product of 17800. Both of these
results are better than those obtained when using
acrylic acid in the reactor (as above) or in the
premix (see Table A).
EXAMPLE 7
This example demonstrates the use of other
copolymerizable monomers in the preparation of the
novel latexes and polymers of this invention. The
~ 3 ~
-36-
procedures used were the same as those used in
Example 6 wherein the itaconic acid was placed all
initially into the reactor. A portion of the n-butyl
acrylate in the premix was replaced with one or more
of the indicated higher Tg yielding copolymerizable
monomers in the amounts shown. Results are given in
Table F below:
Table F
5 PHR ST 10 PHR 10 PHR
5 PHR AN VAC MMA
Tensile, psi 838 678 943
Elongation, % 670 630 560
TxE Product 562000 427000 529000
Percent Hysteresis17.8 13.8 14.5
Loss
Estimated Tg, C -25 -36 -29
The above results demonstrate that the novel
latexes and polymers of this invention can be readily
prepared using a large range of copolymerizable
monomers, as long as the Tg of the final polymer is
between about -20C. and about -60C., and an
acrylate monomer is present as the major
copolymerizable monomer. Of course, the presence of
one or more other copolymerizable monomers,
particularly "harder" monomers, can affect the
physical properties of the polymers made from the
corresponding latexes. For example, with 5 weight
parts of styrene (ST) and 5 weight parts of
acrylonitrile (AN) used in place of a corresponding
amount of n-butyl acrylate, the tensile strength of
the polymer was 838 psi and elongation was 670%.
Using 10 weight parts of vinyl acetate (VAC), the
polymer tensile strength was 678 psi and elongation
was 630%. With 10 weight parts of methyl
methacrylate (MMA), polymer tensile strength was 943
psi and elongation was 560%. In all three cases, the
TxE Products were very high and the percent
hysteresis loss was within the stated range.
~ 33~
-37-
A very low Tg polymer was prepared using the
same procedure as given above using 94 weight parts
of 2-ethyl hexyl acrylate (2-EHA) as the sole
copolymerizable monomer. The polymer was weak,
having a tensile strength of 230 psi, an elongation
of 980%, and a Tg of -65.5C. This polymer did not
meet the necessary criteria of the novel polymers of
this invention. This Example shows that a choice of
copolymerizable monomer(s) which takes the Tg of the
polymer outside of the stated Tg range, results in a
polymer that does not have the unique balance of
properties described herein.
EXAMPLE 8
This example demonstrates the use of other
crosslinking monomers in the preparation of the novel
latexes and polymers of the invention. The
crosslinking monomer is used in each experiment at
2.0 weight parts in the premix. The itaconic acid
was used at 4 parts by weight and was placed all
initially in the reactor. The process procedure used
was Variation B. Results are given in Table G below:
TABLE G
NMA NMMA MAGME
Tensile, psi 830 937 910
Elongation, % 773 360 1055
TsE Product 642000 337000 960000
Percent Hysteresis15.4 13.9 14.2
Loss
The first column of data in Table G shows
data from a latex polymerization wherein N-methylol
acrylamide (~A) was used as the crosslinking
monomer. The polymer prepared using N-methylol
methacrylamide (NMMA) as the crosslinking monomer had
a higher tensile strength (937 psi) but lower
elongation (360%). When methyl acrylamidoglycolate
methyl ether (MAGME) was used as the crosslinking
monomer, the polymer tensile strength was 910 psi,
1~32~1
-38-
elongation was 1055%, and an exceptionally high TxE
Product was obtained.
From Table G, it is readily seen that a
broad range of crosslinking monomers are suitable for
use in this invention.
EXAMPLE 9
A series of latexes were prepared in which
the amount of itaconic acid (IA) and the amount of
N-methylol acrylamide (NMA) were varied. The
copolymerizable monomer used was n-butyl acrylate at
93 to 97 parts by weight. The itaconic acid was
placed all initially in the reactor. The initiator
used was sodium persulfate. Process procedure C was
employed. The results of the tests on the polymers
are given in Table H below.
13329~1
--39--
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H 0 ~ ~ ~ ~ ~ ~ ~J (~
1 ~ 3~
-40-
The above data shows that the novel polymers
of this invention can be readily prepared using
various amounts of the unsaturated dicarboxylic acid
and the crosslinking monomer.
EXAMPLE 10
The MIT fold test was conducted in this
example by saturating 5 mil flat paper with 40~
add-on. Forty percent add-on means 40 weight parts
of dry polymer has been added to each 100 weight
parts of fibers. The saturated paper was dried on a
photoprint drier at approximately 212F and then
cured at 300F for 3 minutes. The cured paper was
cut into 15 millimeter widths in the machine
direction and mounted in a MIT tester with a load of
1 kilogram applied to the ends of the strip of
paper. The paper was then flexed by the MIT tester
at a 180 angle to first one side and then the other
side. The number of folds necessary to break the
paper was measured to indicate the fold endurance of
the latex and paper. All testing was conducted at a
relative humidity of 50% at a temperature of 72F.
The results of the test are set forth in Table I.
Table I
MIT DOUBLE FOLDS
LATEX TYPE1 KILOGRAM LOAD
HYCAR~ 2600 X 322
(A commercially available latex
manufactured by BFG having a Tg
of -15C used commonly in paper
saturation) 240
HYCAR~ 26083
(Another commercially available
latex manufactured by BFG specific-
ally made for use in paper appli-
cations having a Tg of -15C) 1,400
133~Q~
-41-
HYCAR ~ 1562
(A commercially available
nitrile latex manufactured by BFG
for paper saturation having a
Tg of -26C) 200
Latex A of the present invention
having a Tg of -29C. 3,500
Latex B of the present invention
having a Tg of -43C. 1,725
Latex A included 86 weight parts of N-butyl
acrylate, 6 weight parts acrylonitrile, 4 weight
parts itaconic acid, 2 weight parts ethyl acrylate
and 2 weight parts N-methylol acrylamide. Latex B
included 92 weight parts n-butyl acrylate, 4 weight
parts itaconic acid, 2 weight parts ethyl acrylate
and 2 weight parts N-methylol acrylamide.
This example demonstrates that a latex of
the present invention having a low Tg performs better
than the indicated commercially available soft
latexes employed in paper applications. Latex B
performed better than the above noted commercially
available latexes. Latex A was far superior to any
of the above noted commercially available latexes.
In fact, the number of folds achieved when using
Latex A is more than double the best of the above
latexes.
EXAMPLE 11
In this experiment, a Handle-O-Meter test
was conducted on 1.1 ounce per square yard chemically
bound saturated polyester nonwoven fabric to measure
softness. In the procedure, a latex was applied to
an unbound carded polyester fiber web at about 30%
add-on. The fabric was dried on a photoprint dryer
at approximately 212F and then cured for 3 minutes
at 300F. Two 3" x 3" squares were cut from the
nonwoven fabric and tested using the Thwing-Albert
Digital Handle-O-Meter, which measures the force
* Trade Mark
133290~
-42-
necessary to advance a sample through a measured open
slit width. The polyester nonwoven fabric was tested
in the machine direction, cross-direction, then
flipped over and again tested in the machine
direction and the cross direction. All testing was
conducted at 50% relative humidity and 72F. The
results of this experiment are set forth in Table J.
The lower numbers indicate a softer hand. The
averages of 8 readings are also shown.
Table J
Handle-O-Meter
Latex TYPe M.D. C.D. F.M.D. F.C.D. Avg.
Rhoplex TR934,
Rohm and 30.4 35.0 24.8 36.2 29.0
Haas (Tg-28) 22.4 30.6 22.7 29.6
HYCAR~ 2671 25.0 40.8 25.9 38.4 32.0
(Tg-ll) 29.1 38.3 24.6 33.3
Latex B 20.2 27.9 18.9 28.1 26.0
(Tg-43) 24.3 34.6 23.6 30.1
The results indicate that the nonwoven web
produced from Latex B of the present invention has a
softer hand than the other soft acrylic latexes
designed to be employed in such nonwovens.
EXAMPLE 12
In this example, the dry, solvent and wet
tensile strengths of 5 mil flat paper saturated with
40% add-on are demonstrated. In these tests, a 1" x
3" piece of saturated paper was tested in the machine
direction using the Thwing-Albert Intellect II
tensile tester. Prior to testing, the samples were
dried at 212F on a photoprint dryer and then cured
for 3 minutes at 300F. For the wet and solvent
strength tests, the strips of paper were soaked for
20 minutes and tested wet. All testing was conducted
133~
-43-
at 50% relative humidity and 72F to eliminate
temperature and air moisture as variables. Jaw
separation was 2~ and jaw speed was 1" per minute.
The tensile strength indicated is the peak or maximum
value in pounds. The elongation indicated is the
elongation at peak tensile strength. The tensile
energy absorption is the TEA at the peak tensile
strength.The results of the test are set forth below
in Table K.
l332sal
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Table K (continued)
Latex TYPe DrY Wet Solvent 2 3
as above, except all
parts of itaconic
acid are in the
premix. 19.6 5.7 0.663 11.7 8.0 0.483 12.1 3.5 0.228
Latex B 20.5 5.6 0.704 14.2 7.9 0.617 14.1 3.7 0.283
1 Peak Load in lbs.
2 Percent Elongation at Peak Load
3 Tensile Energy Absorption at Peak Load
nBA is n-butyl acrylate
NMA is n-methylol acrylamide
e~
.
o
1332~1
-47-
The latex of the present invention having
all weight parts of itaconic acid in the reactor
produced the highest wet, dry, and solvent
strengths. In particular, the last five experiments
indicate that all the latexes of the present
invention using a dicarboxylic acid are an
improvement over the commercially available acrylic
latexes having the same Tg, and similar composition
except with respect to the acid used.
EXAMPLE 13
The same dry, wet, and solvent strength
tests as in Example 12 were conducted on chemically
bonded polyester nonwoven fabric having 30% add-on.
The untreated fiber mat having an unbonded density of
1.1 oz. per sq. yd. was cut into 1" x 3" rectangles
and tested in the cross machine direction using the
Thwing-Albert Intellect II tensile tester. Drying,
curing, and testing were identical to those in
Example 11. The results for the polyester nonwoven
fabric are set forth in Table L.
Table L
DrY Wet Solvent
Latex TYDe PKLGl X Elon~.2 TEA.3 PKLGl % Elon~.2 TEA 3 PKLGl % Elon~.2 TEA 3
Hycar 26171 Tg of
44 168 28 35.3 132 35 38.9 35 19 5.3
Hycar 26171 Tg of
-44 (laboratory made) 170 38 34.9 147 29 34.3 31 32 6.6
Present invention;
Tg of -444.5 weight
parts itaconic acid in
premix, with 93.5 nBA
and 2 weight parts NMA. 319 54 128.3 228 43 77.4 67 17 7.6
Present invention; 4.5
weight parts itaconic
acid in reactor, 93.5
weight parts nBA and
2 weights NMA. 263 58 156.6 184 54 64.6 71 23 12.0
Present invention; 4.5 ~
weight parts itaconic ~3
acid in reactor, 93.5
weight parts nBA, and
2 weight parts NMA
(smaller particle
size). 277 57 123.6 135 48 54.6 49 21 7.5
~33~
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13~01
-51-
The first five tests indicate again that the
latex made with the itaconic acid in the reactor
gives the best dry strength while the latex with the
itaconic acid in the premix gives the best wet
strengths and again the latex made with itaconic acid
in the reactor gives the best solvent strengths.
Each of the examples of the present invention perform
better than the commercially available acrylate latex
(Hycar~ 26171) having the same Tg. With respect to
the balance of properties, it is shown that the
latexes made with the itaconic acid produce the best
balance of properties. The last five latexes
sampled, again indicate that the best dry properties
are obtained with all the itaconic acid being in the
reactor while the best wet properties are obtained
with all the itaconic acid in the premix. The
solvent strength data in the last five examples
indicates that the best solvent strengths were
obtained with the itaconic acid in the reactor.
Thus, again the balance of properties is best
achieved when all weight parts of itaconic acid are
introduced in the reactor.
EXAMPLE 14
This example demonstrates the tear strength
of a 40% add-on saturated 5 mil flat paper. In this
example, 2-1/2~ square samples of l-ply paper were
tested on the Thwing-Albert Elmendorf tear tester.
The paper was dried and cured under the same
conditions set forth in Example 7.
The paper was tested first in the machine
direction and then in the cross direction for its
tear strength. The results are set forth below in
Table M.
1~329~1
-52-
Table M
Machine Cross
Latex TypeDirection Direction
Latex B 88 88
Latex A 72 96
Latex C 112 128
Hycar 26083 BFG commercially
available latex Tg -15. 84 84
Hycar 26000 x 322 (commercially
available BFG manufactured
acrylic latex) Tg -18 76 84
Hycar 1562 (commercially
available BFG nitrile latex)
Tg -25. 116 140
Latexes A and B are set forth in Example
10. Latex C comprises 82 weight parts 2 ethylhexyl
acrylate, 10 weight parts n-butyl acrylate, 2 weight
parts ethyl acrylate, 4 weight parts itaconic acid
and 2 weight parts N-methylol acrylamide (Tg of
-60C)-
The three Hycar latexes were selectedbecause they are recommended for use in paper
saturations. The nitrile latex was developed
specifically to give good tear strength. As the
results indicate, the Elmendorf tear of the present
invention (Latexes A, B, and C) are about as good or
better than the commercially available acrylic
latexes. Though the nitrile latex product has
excellent tear strength, it has several shortcomings
such as poor wet strength and poor resistance to
oxidation. The latexes of the present invention do
not have these draw backs.
_53_ 133~9~
EXAMPLE 15
This example demonstrates the delamination
resistance or internal bond of 40% add-on saturated 5
mil flat paper (the same paper used in Example 10).
A sheet of 20 cm long saturated paper (20 cm long in
machine direction) was sandwiched between 2 sheets of
heat sensitive tape. The sandwich was heated and
pressurized at 308F-312F. with a hand iron.
Samples were cut into 1.5 cm by 20 cm. After
ironing, the samples are positioned in a delamination
press for 30 seconds at 275F and 27 psig. The
samples were then tested on the Thwing-Albert
Intellect II. Jaw separation was one inch and jaw
speed was 25 cm/min. The test conditions were at 50%
relative humidity and 72F. The results are set
forth below in Table N.
Table N
Mean
Machine Cross Delamination
Latex TYDeDirection Direction Resistance (oz.
Latex B 88 88 9.32
Latex A 72 96 13.23
Latex C 112 128 10.92
Hycar 26083 (BFG commercially
available latex) Tg -15. 84 84 13.23
Hycar 26000 x 322 (commercially
available BFG manufactured
acrylic latex) Tg -18 76 84 10.56
Hycar 1562 (commercially
available BFG nitrile latex)
Tg -25. 116 140 10.31
G~
æ~
1~2~01
-55-
As this data indicates, the delamination
resistance of the three samples of the present
invention are very comparable to the Hycar latexes
designed for paper use.
EXAMPLE 16
This example demonstrates the durability to
dry cleaning and washing of a nonwoven fabric treated
with the latex of the present invention. All the
samples were saturated with different levels of latex
add-on and dried at approximately 212F on a
photoprint dryer and cured for 3 minutes at 300F in
an air circulating oven. The washability test was a
modified AATCC #61-1980-II-A test using a
Launder-O-Meter*for 1 cycle (1 cycle represents
approximately 5 machine washings). The entangled
nonwoven fabric chosen was DuPont's Sontara~ 8103
fabric. The results are reported in Table O.
Table O
% Latex Add-On Comments
Control - 0% All samples OK - no fabric
damage, treated samples were
4% still resilient indicating
minimal or no loss of polymer.
All samples, including control
10% sample, had a slightly softer
hand after testing.
18%
The dry cleaning test was a modified AATCC
#86-1761 test on a Launder-O-Meter for one 30 minute
cycle. The results of this test is set forth in
Table P.
* Trde Mark
~ 3~2901
-56-
Table P
% Latex Add-On Comments
Control - 0~ All samples OK - no fabric
damage, treated samples were
3.9~ still resilient. All samples
including control had a slightly
9.0% softer hand.
17%
These tests show that the latex treated
Sontara~ nonwoven of this invention was durable to
the wash and dry clean tests used.
EXAMPLE 17
This example demonstrates the resiliency of
latex treated Sontara~ nonwoven fabric of this
invention at different levels of latex add-on after
20% elongation and 30% elongation. In the resiliency
testing 1" x 6~ samples were cut in cross machine
direction and (6" is the cross machine direction) and
the samples were stretched to the indicated
elongation and released. Each sample was measured
after five minutes. The permanent deformation is
calculated as:
(length after stretch and relaxation - original
lenqth)
Original Length
The results are set forth in Tables Q and R.
Table Q
20% Elon~ation
Permanent
Change
Perm. Def. Between 1 h
Add On Permanent Deformation (1 cYcle) (2 cYcles) 2 cYcle~
0% 6.3% 10.4X 4.1%
4% 3.1% 4.2% 1.1%
10% 2.1% 3.1% 1.0X
18% 2.1% 2.1% 0%
e~
~3
Table R
30% Elon~ation
Permanent
Change
Perm. Def. Between 1 &
Add On Permanent Deformation (1 cYcle) ~2 cYcles) 2 cycles
o% 15.6% 17.7% 2.1%
4% 6.3X 8.3% 2.0%
10% 5.2% 6.3X 1.1%
18% 5.2% 6.3% 1.1%
C~
~ 3~2~0~
sg
This example shows that a significant level
of resiliency can be imparted to an entangled
synthetic fiber nonwoven fabric using the latex of
this invention.
Furthermore, when the 10% pick-up sample was
stretched to 20% of its elongation 10 times and each
stretch was held for 10 seconds and then relaxed 5
minutes between stretches, the permanent deformation
after one stretch was 2.1%, after two stretches 3.1%,
and after ten stretches 4.2%. This shows that the
change in permanent deformation after 10 stretches is
smaller than that after 1 or 2 stretches.
EXAMPLE 18
This example demonstrates the resistance to
heat aging which can cause latex treated nonwoven
fabrics to discolor. Yellowing or other
discoloration is not desirable in many end use
applications of nonwoven fabrics.
Samples of polyester nonwoven fabric having
an unbounded density of 1.1 oz per sq. yd. with about
30% add-on with latex A, latex B (see Example 6),
Hycar~ 2671 and RHOPLEX~ Tr 934 (made by Rohm &
Haas Co.) were tested. Each sample was air dried and
cured at 300F for 3 minutes before testing. The
results of the example are set forth in Table S as
precent reflectance of incident light passed through
a 1" by 1" nonwoven samples and reflected back from
the standard reference. The samples were heated for
the time indicated. The standard reference white
ceramic plaque was calibrated to 78% reflectance.
The lower values indicate a lower reflectance.
1~329~1
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-61-
The results of this experiment indicate that
the novel latex saturated nonwoven fabric possesses
comparable resistance to discoloration after heat
aging with commercially available latexes designed
for use with nonwoven fabrics. It has thus been
demonstrated that the products of the present
invention resulting from the treatment of fibers used
in the examples with the novel latexes have a
superior balance of properties which is unique. This
balance of properties is demonstrated by high fold
endurance, soft hand, good dry, wet, and solvent
tensile properties, good tear resistance, good
delamination resistance, a high degree of permanent
deformation resistance and good color aging
properties. None of conventional latex polymers
tested demonstrated this unique balance.
Thus it is apparent that there has been
provided in accordance with the invention a nonwoven
fabric treated with a latex composition that fully
satisfies the objects, aims, and advantages set forth
above. While the invention has been described in
conjunction with specific embodiments thereof, it is
evident that many alternatives, modifications, and
variations will be apparent to those skilled in the
art in light of the foregoing description.
Accordingly, this invention is intended to embrace
all such alternatives, modifications, and variations
which fall within the spirit and scope of the
invention.
