Nonwoven fabric with an acrylate interpolymer binder and a process of making the nonwoven fabric

Abstract

 Fibers treated with a novel latex containing a polymeric material of the present invention have an exceptional balance of physical properties. The novel latex is prepared by polymerizing an unsaturated dicarboxylic acid contained 4 to 10 carbon atoms with a copolymerizable monomer(s) and, optionally, a crosslinking monomer in the presence of an effective amount of a surfactant and initiator. In an preferred embodiment of the process, all of the unsaturated dicarboxylic acid is initially placed in the reactor, and a premix containing the copolymerizable monomer(s) and the crosslinking monomer is metered into the reactor. The unsaturated dicarboxylic acid is used an amount from about 1 to about 20 weight parts, the amount of the copolymerizable monomer is from about 70 to 98 weight parts, and the amount of the crosslinking monomer, which is optional is from about 0.52 to about 10 weight parts. The novel polymers have a Tg from about -20°C to about -60°C, a percent hysteresis loss of less than about 20% and exhibit a tensile strength of at least 300 psi and an elongation of at least 350%. When the novel latex is applied to the fibers, a nonwoven fabric having unique balance of properties is created.

Description

BACKGROUND OF THE INVENTION

1) Field of the Invention

[0001] 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 flexibility and good dry, wet, and solvent properties.

2) Prior Art

[0002] 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 upon the resilience of the binder and the strength of interaction between the fibers.

[0003] 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.

[0004] 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.

[0005] 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 resiliency. The present invention relative to entangled nonwovens can provided a balance of resiliency and soft "hand".

[0006] 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

[0007] 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.

[0008] 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 tensile strength and elongation properties common in some "harder" acrylic polymers. The glass transition temperature (Tg) of the novel polymers is from about -20°C. to about -60°C.

[0009] 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.

[0010] 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.

[0011] 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 -20°C. to about -60°C.; 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%.

[0012] 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 -20°C to about -60°C; 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 or less than about 20%.

DETAILED DESCRIPTION OF THE INVENTION

[0013] 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 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.

[0014] 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.

[0015] 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.

[0016] The amount of the unsaturated dicarboxylic acid employed is from about 1 part to about 20 parts 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.

[0017] 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 contain interpolymerized units of more than two monomers.

[0018] 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 equals 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.

[0019] Examples of the copolymerizable monomers are alkyl, alkoxyalkyl, alkylthioalkyl, and cyanoalkyl acrylates and methacrylates containing 1 to about 20 carbon atoms in the alkyl group; diacrylates and dimethacrylates such as ethyleneglycol dimethacrylate, diethylene glycol diacrylate, and the like; monolefins containing 2 to about 10 carbon atoms such as ethylene, propylene, isobutylene, 1-hexene, 1-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, α-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.

[0020] The two conditions on the selection of the copolymerizable monomer(s) are (1) that the glass transition temperature (Tg) of the polymer made is from about -20°C. to about -60°C., and more preferably from about -25°C., to about -50°C. and (2) that the copolymerizable monomer(s) contains a major portion of an acrylate monomer(s).

[0021] The acrylate monomer empolyed is an alkyl, alkoxyalkyl, alkylthioalkyl, or cyanoalkyl acrylate of the formula

wherein R₁ is hydrogen or methyl, and R² 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 α and β-cyanoethyl acrylate, α, β and α-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.

[0022] 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 monomer(s) are those wherein Ra is hydrogen and R¹ 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.

[0023] 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.

[0024] 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.

[0025] 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 +80°C. 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, α-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.

[0026] 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 of the addition of a crosslinking agent to the novel polymer.

[0027] The crosslinking monomers used herein can be any monomer or oligomer polymerizable with the unsaturated dicarboxylic acid and copolymerizable 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 C₁ 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.

[0028] 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.

[0029] 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 weight based on 100 parts by weight total of all monomers.

[0030] 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.

[0031] 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.

[0032] 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-1-sulfonic acid and octadiene-1-sulfonic acid; aralkyl sulfonates such as sodium isopropyl benzene sulfonate, sodium dodecyl benzene sulfonate 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.

[0033] 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.

[0034] The polymerization of the monomers may be conducted at temperatures from about 0°C up to about 100°C 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 1-hydroxycyclohexyl hydroperoxide; azo compounds such as azodiisobutyronitrile and 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.

[0035] 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.

[0036] 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.

[0037] 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 then metered into the reactor and the monomers are polymerized.

[0038] 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.

[0039] 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 polymerizd 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 1.5 weight parts of a suitable initiator such as sodium persulfate.

[0040] The unsaturated carboxylic acid can be added all initially into the reactor before metering of the premix is commenced, or part of 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 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.

[0041] 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 30°C. to about 90°C.

[0042] 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%.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The novel latexes disclosed herein have typically 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 exhibit good mechanical stability when their pH is raised above neutral.

[0047] 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.

[0048] 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 300°F. 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/minutes. The 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 (E_A). 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 (E_B). A perfectly resilient polymer which exhibits no heat or other energy losses would have a hysteresis curve wherein E_A would equal E_B, 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.

[0049] The percent hysteresis loss of the polymers was determined by the following formula:

[0050] 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.

[0051] The novel polymers have other properties which make them unique. They are soft, yet rubbery and tough. Their ultimate raw polymer tensile 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 300°F. 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.

[0052] 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

[0053] 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 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 70°C. to 80°C.

[0054] 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 75°C. and was then cooled to 40°C. At this point, the latex was stripped, cooled to 30°C., its pH was adjusted with ammonia to about 4.5 pH, and it was filtered through cheesecloth and stored.

[0055] Following the above general procedures, three variations of reaction conditions were actually employed. In Variation A, the reaction temperature was 80°C., 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 75°C. In Variation C, the reaction temperature was 70°C., 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 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.

[0056] 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 5 minutes at 300°F (149°C). 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

[0057] 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 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:

[0058] 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

[0059] 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:

[0060] 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

[0061] 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.

[0062] 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.

[0063] 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 -44°C. 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

[0064] 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%.

[0065] 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 both. 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

[0066] 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 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.

[0067] 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

[0068] 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:

[0069] 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.

[0070] 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

[0071] This example demonstrates the use of other copolymerizable monomers in the preparation of the novel latexes and polymers of this invention. The 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:

[0072] 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 -20°C. and about -60°C., 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.

[0073] 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 -65.5°C. 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

[0074] 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:

[0075] The first column of data in Table G shows data from a latex polymerization wherein N-methylol acrylamide (NMA) 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, elongation was 1055%, and an exceptionally high TxE Product was obtained.

[0076] From Table G, it is readily seen that a broad range of crosslinking monomers are suitable for use in this invention.

EXAMPLE 9

[0077] 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.

[0078] 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

[0079] 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 212°F and then cured at 300°F 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 72°F. The results of the test are set forth in Table I.

[0080] 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.

[0081] 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

[0082] 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 212°F and then cured for 3 minutes at 300°F. Two 3˝ × 3˝ squares were cut from the nonwoven fabric and tested using the Thwing-Albert Digital Handle-O-Meter, which measures the force 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 72°F. 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.

[0083] 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

[0084] 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˝ × 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 212°F on a photoprint dryer and then cured for 3 minutes at 300°F. For the wet and solvent strength tests, the strips of paper were soaked for 20 minutes and tested wet. All testing was conducted at 50% relative humidity and 72°F 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.

[0085] 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

[0086] 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˝ × 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.

[0087] 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

[0088] 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 1-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.

[0089] 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.

[0090] 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 -60°C).

[0091] The three Hycar latexes were selected because 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.

EXAMPLE 15

[0092] 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 308°F-312°F. 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 275°F 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 72°F. The results are set forth below in Table N.

[0093] 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

[0094] 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 212°F on a photoprint dryer and cured for 3 minutes at 300°F 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.

[0095] 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.

[0096] These tests show that the latex treated Sontara nonwoven of this invention was durable to the wash and dry clean tests used.

EXAMPLE 17

[0097] 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˝ × 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:

[0098] The results are set forth in Tables Q and R.

[0099] 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.

[0100] 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

[0101] 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.

[0102] 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 300°F 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.

[0103] 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.

[0104] 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.

Claims

1. The combination of a web of fibers and a latex having a polymer with a Tg of from about -20°C. to about -60°C., a percent hysteresis loss of less than about 20%, and a raw polymer tensile strength of at least 300 psi and an elongation of at least 350 percent, said polymer comprising interpolymerized units of from about 1 to about 20 weight parts of at least one unsaturated dicarboxylic acid containing 4 to 10 carbon atoms and from about 70 to about 99 weight parts of at least one copolymerizable monomer a majority of which is at least one acrylate monomer all weights based on 100 weight parts of all monomers.

2. The combination of claim 1, wherein said dicarboxylic acid contains 4 to 6 carbon atoms and is used in an amount from about 2 to about 8 weight parts per 100 parts by weight total of all monomers.

3. The combination of claim 2, wherein said polymer also contains interpolymerized units of from about 0.1 to about 10 weight parts of a crosslinking monomer per 100 parts by weight total of all monomers.

4. The combination of claim 3, wherein said unsaturated dicarboxylic acid is selected from the group consisting of itaconic acid, citraconic acid, glutaconic acid, fumaric acid, maleic acid, and mixtures thereof.

5. The combination of claim 1, wherein said polymer has a Tg of from about -25°C. to about -50°C. and contains interpolymerized units of copolymerizable monomers where at least 40% by weight of such monomers are acrylates of the following formula

where R₁ is hydrogen or methyl, and R₂ is an alkyl radical containing 1 to about 20 carbon atoms, an alkoxyalkyl or alkylthioalkyl radical containing 2 to about 12 carbon atoms, a cyanoalkyl radical containing 2 to about 12 carbon atoms, or a mixture thereof.

6. The combination of claim 5, wherein the unsaturated dicarboxylic acid is itaconic acid.

7. The combination of claim 6, wherein the copolymerizable monomer is n-butyl acrylate.

8. The combination of claim 7, wherein the crosslinking monomer is N-methylol acrylamide.

9. A process for making a nonwoven fabric comprising: Obtaining a web of fibers; and binding the fibers with a latex having a polymer with a Tg of from about -20°C. to about -60°C., a percent hysteresis loss of less than about 20%, and a raw polymer tensile strength of at least 300 psi and an elongation of at least 350 percent, said polymer comprising interpolymerized units of from about 1 to about 20 weight parts of at least one unsaturated dicarboxylic acid containing 4 to 10 carbon atoms per molecule, and from about 70 to about 99 weight parts of at least one copolymerizable monomer a majority of which is at least one acrylate monomer, all weights based on 100 weight parts of all monomers.

10. The process of claim 9, wherein said step of binding includes the steps of drying and curing the latex on said fibers.

11. The process of claim 9, wherein said dicarboxylic acid contains 4 to 6 carbon atoms and is used in an amount from about 2 to about 8 weight parts per 100 weight parts of all monomers.

12. The process of claim 11, wherein said polymer also contains interpolymerized units of from about 0.1 to about 10 weight parts of a crosslinking monomer per 100 weight parts of all monomers.

13. The process of claim 12, wherein said unsaturated dicarboxylic acid is selected from the group consisting of itaconic acid, citraconic acid, glutaconic acid, fumaric acid, maleic acid, and mixtures thereof.

14. The process of claim 9, wherein said polymer has a Tg of from about -25°C. to about -50°C. and contains interpolymerized units of copolymerizable monomers where at least 40% by weight of such monomers are acrylates of the following formula

where R₁ is hydrogen or methyl, and R₂ is an alkyl radical containing 1 to about 20 carbon atoms, an alkoxyalkyl or alkylthioalkyl radical containing 2 to about 12 carbon atoms, a cyanoalkyl radical containing 2 to about 12 carbon atoms, or a mixture thereof.

15. The process of claim 14, wherein said unsaturated dicarboxylic acid is itaconic acid.

16. The process of claim 15, wherein said copolymerizable monomer is N-butyl acrylate.

17. The process of claim 16, wherein said crosslinking monomer is N-methylol acrylamide.

18. The process of making a nonwoven fabric comprising: assembling a loose web of fibers; preparing a latex having a polymer with a Tg of from about -20°C. to about -60°C., a percent hysteresis loss of less than about 20%, and a raw polymer tensile strength of at least 300 psi and an elongation of at least 350 percent, said polymer comprising interpolymerized units of from about 1 to about 20 weight parts of at least one unsaturated dicarboxylic acid containing 4 to 10 carbon atoms per molecule, and from about 70 to about 99 weight parts of at least one copolymerizable monomer a majority of which is at least one acrylate monomer; and coating said fibers with said latex to form a nonwoven fabric.

19. The process of claim 18, wherein said step of preparing the latex includes the step of metering into a reactor a premix which comprises said copolymerizable monomer and up to one-half of said dicarboxylic acid, wherein said reactor contains at least one-half of said dicarboxylic acid, and subsequently conducting polymerization in the reactor at a temperature from about 0°C to about 100°C.

20. The process of claim 19, wherein all of said unsaturated dicarboxylic acid is added initially to the reactor, and said premix is devoid of the unsaturated dicarboxylic acid.