Method for improving the stiffness of textile fibers

Battery separators are thin porous substances impregnated with a latex binder and dried in an oven to remove water. In the battery, closely spaced metal electrode plates are connected in series and immersed in a strongly acidic electrolyte solution. The battery separator is placed between the metal electrode plates, on the one hand to prevent the metal electrode plates from coming into contact with each other; on the other hand to prevent metal salts Hydrogen or other conductive substances from forming bridges between the metal electrode plates. Both of these issues eventually lead to the battery shorting out. The battery separator must maintain sufficient porosity to allow the electrolyte solution to flow freely between the metal electrode plates for efficient ion exchange.

When the battery separator is placed between metal electrode plates that are close to each other, the flexibility of the separator material will cause problems, soThis means that the separator cannot be inserted smoothly between the metal electrode plates, resulting in Difficulty in assembly work. This problem is exacerbated at high temperatures and high relative humidity.

In industry, battery separators are made of various fibers (e.g., cellulose, glass, polyolefin, polyester, etc.) and fillers (e.g., diatomaceous earth, various clays, silica, quartz, hydrocarbon polymer powder, etc.) are manufactured by bonding them together with an organic binder, which comes as a latex or aqueous dispersion. Battery separators made with conventional latex binders have some stiffness, but this decreases with increasing temperature and relative humidity. Reduced stiffness can cause problems when mounting the battery.

Many relate to the need for improved battery separators. For example, US No. 4,529,677 disclosesa new and improved battery separation material that is particularly suitable for use in maintenance-free batteries. This battery separator contains a diatomaceous earth filler, an acrylate copolymer binder (containing a silane coupling agent attached to the polymer backbone), and a variety of fiber materials (including polyolefin, polyester, and fiberglass). The acrylate copolymer adhesive used contained about 80 weight percent C1 to C8 alkyl acrylate monomers and to a lesser extent about 80 to about 30 weight percent. Such copolymers have a glass transition temperature of about 30°C to about 60°C. In addition, US No. 4,363,856 discloses organic binders for battery separators. The binder is a commercial polymer capable of forming a film and the constituent monomers are, for example, methacrylic acid, acrylic acid, ethyl acrylate, methyl acrylate and the like. These monomers form hydrophilic, flexible adhesivesn.

One approach to achieving stiffer battery separators is to design monomer-based single-phase latex binders that produce stiffer, more hydrophobic polymers. To achieve this idea, if a common latex used as a binder for battery separation is added to a monomer such as styrene, alkyl-substituted styrene or isobornyl methacrylate to replace the latex. Methyl methacrylate in the compound; the complex factors that the coagulation temperature of the formulated latex adhesive on the non-woven substrate is disturbed, and coagulation cannot take place at the required temperature (the temperature should be about 30 ° C to about 60 ° C, which is an industrially acceptable solidification temperature range, at preferably from about 40°C to about 45°C).

When adjusting the composition of the latex binder to obtain a stiffer battery separator, it is possible that the new samsetting does not cure in the desired temperature range. Battery separators are made from a fleece substrate of fibers and fillers, which is then impregnated with a latex binder. The whole mass is then dried at a high temperature to cross-link the latex binder and evaporate the water in the latex binder to form the battery separator. During drying, the latex binder migrates to the surface of the battery separator as the water evaporates, resulting in an uneven distribution of the latex binder. To avoid this problem, the latex binder is carefully formulated so that it remains stable when impregnated onto a non-woven substrate and when oven dried at a lower, narrower temperature range before most of the water evaporates. non-woven background. Formulations have been developed for latex binders currently used commercially in battery separatorscladding which allow the binder to set at temperatures of about 30°C to about 60°C, preferably about 40°C to 45°C.

Heterophasic polymers have also been used in textiles to improve low temperature properties such as softness. For example, US No. 4,107,120 reports latex compositions in core/shell form and their use for textile materials to improve the low temperature properties of the materials. US No. US 4,277,384 further improves on the above invention by providing a latex composition in core/shell form and its use for textile materials which not only improves low temperature properties but also improves the softness and seam tear resistance of textile materials tears. US Nos. 4,181,769 and 4,351,875 respectively describe finished products of the above core/shell compositions. However, none of these methods mention the use of meerfasige latex binder compositions in which one phase improves the stiffness of the textile fibers and the other phase controls the curing temperature of the latex binder. The invention not only satisfies the requirement of stiffer textile materials at high temperature and high relative humidity (particularly in an acidic environment), but also satisfies the requirement of controllable solidification temperature of latex adhesive. It is therefore an object of the present invention to provide improved textile fibers containing an acid-resistant, curable heterogeneous latex binder.

Another object of the present invention is to provide a method for improving the stiffness of textile materials.

Other objects and advantages of the present invention will become apparent from the following description and claims.

The present invention provides improved fibrous materials that contain acid-resistant, curable heterogeneous lacontain tex binders deposited on textile fibres. The acid-resistant, curable heterogeneous latex binder comprises a first-stage copolymer, which improves the stiffness of textile fibers, and at least one other-stage copolymer, which controls the curing temperature of the latex binder. This latex glue is especially useful for battery separators.

The term \"textile\" as used herein means a material composed of natural or synthetic fibers, woven or non-woven, characterized by their flexibility, fineness and high length to thickness ratio. The term \"latex\" as used herein refers to a water-insoluble polymer prepared by conventional polymerization methods (e.g., emulsion polymerization). \"Glass transition temperature\" or \"Tg\" as used herein refers to the glass transition temperature of the polymer calculated by the Fox method (see Bulletin of the American Physical Society 1.3, page 123 (1956)]: 1Tg=W1Tg(1 )+W2Tg (2)]]> For copolymers, W1 and W2 refer to the weight fraction of the two comonomers and Tg(1) and Tg(2) refer to the glass transition temperature of the two corresponding homopolymers. </p

The latex adhesive composition of the present invention is the heterophasic latex particle composed of at least two mutually incompatible copolymers. These mutually incompatible copolymers can exist following the shape configuration, e.g. core/shell, shell non* encapsulation of core/shell particles, multinuclear core/shell particles, interpenetrating lattice particles, etc. In all these cases, the majority of the particle surface consists of at least one outer phase is occupied, while the interior of the particle is occupied by at least one internal phase.

The mutual incompatibility of two polymer compositions can be determined using various methods known in the art, e.g. Scaning electron microscopy analysis using staining to emphasize differences in appearance between phases or stages is one such method.

The multi-phase latex binder compositions of the present invention will be described as containing a \"*phase\" and a \"second stage\". The term \"second phase\" as used herein is not intended to exclude the possibility that one or more polymers may be intercalated, or may precede the copolymer of the second phase, in the * One or more polymers are formed on the phase copolymer The the present invention requires that the copolymer of the first stage contribute to the stiffness characteristics, and requires that the other copolymer (referred to herein as \"second stage\") can control the curing of the latex adhesive.

The \"*stage\" of the latex binder comprises a hydrophobic, acid stable copolymer having a glass transition temperature in the dry state above about 80°C.For example, various * monomers or monomer mixtures can be used as the compound, such as methyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, phenyl methacrylate, isobornyl methacrylate, styrene, 3-Methylstyrene, 4-methylstyrene, 4-tert-butylstyrene, 2-chlorostyrene, 2,4-dichlorostyrene, 2,5-dichlorostyrene, 2,6-dichlorostyrene Chlorostyrene, 4-chloro-2-methylstyrene, 4-chloro-3-fluorostyrene, etc. In addition to at least one of the above monomers, the copolymer must be composed of at least one polyfunctional monomer (as defined below) This copolymer is formed from at least one *monomer and a monomer having a multifunctional group. The amount of monomer is about 95% to about 99.9%, preferably about 97% to about 99%, about 98, 5%; The amount of group monomer is about 0.1% to about 5%, preferably about 1% to about 3%, about 1.5%.

The term \"multifunctional monomer\", as used herein, refjst to a monomer with at least two functional groups, where at least one functional group is copolymerized, and at least one other functional group left to react after polymerization. with the same or similar functional groups on other monomer units to crosslink the polymer. Examples of these polyfunctional monomers are: amides or N-hydroxylamides of α,β-olefinically unsaturated carboxylic acids with 4 to 10 carbon atoms (such as acrylamide, methacrylamide, N-methylolacrylamide, N-ethanolacrylamide, N-propanolacrylamide, N-Methylol Methacrylamide, N- Ethanol Methacrylamide, N-Methylol Maleimide, N-Methylol Maleimide Amide, N-Methylol Maleamic Acid, N-Methylol Maleamic Acid Ester), N-Alkylamide of Vinylaromatic Acid (such as N-Methylol-p-Vinylbenzamide, etc.). Preferred N-hydroxyalkylamide-type polyfunctional monomers are N-hydroxyalkylamides of α,β-mono-olefinically unsaturated monocarboxylic acids, such as N-methylolacrylamideand N-methylolmethyl acrylamide. Another preferred multifunctional monomer system is a nearly equimolar mixture of acrylamide and N-methylol acrylamide, or a nearly equimolar mixture of methacrylamide and N-methylol methacrylamide. Multifunctional monomers impart their self-curing properties to compositions containing them. Cure can be improved by reaction with resins containing active hydrogen, such as triazine formaldehyde and urea formaldehyde resins, added to the formulation containing the biphasic monomer mixture or resulting polymer. In both cases, the composition undergoes *curing by *drying on the textile material treated as described above.

When the glue is applied to the textile material, the higher Tg of the * phase increases the stiffness of the textile material, and the cross-linking properties formed by this phase lead to chemical resistance and reducedrun high temperatures Thermoplastic when applied; and when the glue is applied to the textile fibers and heated, it bonds the fibers of the textile material together.

The \"second phase\" of the latex binder is a copolymer that can maintain stability in an acidic environment. Coagulation occurs when heated within a narrow temperature range in the presence of surfactants. In addition, \"*phase\" copolymers may also contain multifunctional monomers. The \"second phase\" copolymer, excluding the multifunctional monomer, comprises about 95 to about 100 weight percent, preferably about 97 to about 99 weight percent, based on the total weight of the second stage, and about 98 .5%; Based on the total weight of the second phase, the weight of the multifunctional monomer represents about 0% to about 5%, preferably about 1% to about 3%, about 1.5%.

To have at least two mutually incompatiblecopolymers. Based on the total weight of the latex particles, the * phase comprises from about 1 to about 85 weight percent. Preferably, the * phase comprises about 70% to about 80% by weight, based on the total weight of the latex particles. The second phase comprises from about 15 to about 99 weight percent, based on the total weight of the latex particles comprising at least two mutually incompatible copolymers. Preferably, the second phase comprises about 20% to about 30% by weight, based on the total weight of the latex particles. Latex polymers can be prepared by conventional emulsion polymerization methods known in the art, such as the continuous emulsion polymerization methods described in U.S. Nos. 4,325,856, 4,654,397, and 4,814,373, which are incorporated herein as part of the description .

It is sometimes desirable to have chain transfer agents, such as mercaptans, polymer captanes and halides, present in the respective polymerization mixtures of the two phases to moderate the molecular weight of the latex polymer. Typically, about 0.1 to about 3 weight percent chain transfer agent, based on the weight of the total monomer mixture, can be used. The weight average molecular weight of the * phase is from about 400,000 to about 2,000,000. The weight average molecular weight of the second phase is also about 400,000 to about 2,000,000. The particle size of the latex polymer should be relatively small, preferably about 80 nm to about 225 nm, preferably about 160 nm to about 190 nm. As is known, the particle size for the same polymer backbone mainly depends on the type and amount of emulsifier used in each stage of continuous emulsion polymerization.

Emulsion polymerization uses anionic or cationic surfactants to emulsify the reactants, and it also keeps the emulsion stable during the subsequentsubsequent storage. This surfactant is hereinafter referred to as \"stabilizing surfactant\". A nonionic surfactant and a counterion of the stabilizing surfactant are then added to the stabilized emulsion. For anion-stabilized emulsions, polyvalent metal salts (such as magnesium sulfate) may hinder the stabilization of anionic surfactants, while non-ionic surfactants may continue to stabilize the emulsion. But when the mixture is heated, when the temperature is higher than the cloud point of the nonionic surfactant added later, but still does not exceed the Tg of the binder, the latex emulsion becomes unstable and causes coagulation. Careful selection of surfactants, stabilizing surfactant counterions and temperature are therefore required to ensure that the latex binder operates at a controlledcoagulates in the first way. Emulsions are better stabilized with anions.

Examples of suitable anion stabilizing surfactants are: fatty alcohol sulfates (such as sodium lauryl sulfate, etc.); or sodium or potassium isopropyl naphthalene sulfonate, etc.); alkali metal salts of alkyl sulfosuccinates (such as sodium octyl sulfosuccinate, sodium N-methyl-N-palmitamidethane sulfonate, iso-sodium oleyl thiocarbonate (sodium oleyl, sothionate, etc.), alkali metal salts of alkylaryl polyethoxyethanol sulfuric acid or sulfonic acid (such as tert-octylphenoxy polyethylene having 1 to 5 oxyethylene units sodium oxyethyl sulfate, etc.) .Examples of suitable cationic stabilizing surfactants include: alkylamine salts, quaternary ammonium salts, polyoxyethylene alkylamines, and the like.

Suitable post-added nonionic surfactants include alkylphenoxy polyethoxylates having alkyl groups of from about 7 to 18 carbon atoms and about 6up to about 60 oxyethylene units Ethanol (such as heptylphenoxypolyethoxyethanol, methyloctylphenoxypolyethoxyethanol, etc.); polyethoxyethanol derivatives of methylene-linked alkylphenols; sulfuric materials (such as about 6 to about 60 moles of ethylene oxide condensed with nonyl mercaptan, dodecyl mercaptan, etc., or with alkyl thiophenols having 6 to 16 carbon atoms in the alkyl group); long chain ethylene oxide derivatives of carboxylic acids (such as lauric acid, myristic acid, palmitic acid, oleic acid, etc.), or as present in tall oil having 6 to 60 ethylene oxide units per molecule, mixtures of polyols; vinyloid condensates of long chain alcohols such as octanol, decyl alcohol, lauryl alcohol or cetyl alcohol; ethylene oxide derivatization of etherified or esterified polyols containing hydrophobic hydrocarbon chains (such as sorbitan monostearate having 6 to 60 oxyethylene units) and ethylene oxide segments combined with one or more hydrophobic 1,2-unit propylene oxide segmentsgrafting. Mixtures of alkyl phenyl sulfonates and ethoxylated alkyl phenols can also be used.

Opposites for stabilizing surfactants include polyvalent metal ions (if the emulsion is anionically stable) and halogens and other anionites (if the emulsion is cationically stable).

Applicable polyvalent metal ions, such as calcium, magnesium, zinc, barium, strontium, etc., can be used in the coagulation process. Complexes of polyvalent metal ions (such as zinc hexaamine, etc.) and salts of polyvalent metal ions and counterions (such as chlorides, acetates, bicarbonates, etc.) can be used. Magnesium sulfate is a preferred polyvalent metal ion salt for use in battery separator binders. The specific types and amounts of multivalent metal ions used will depend on the particular anionic surfactant, but are in practice limited to those which do notadversely affect the performance or battery life.

Appropriate anions such as chloride, acetate, bicarbonate, sulfate, carbonate, etc. can be used. The specific types and amounts of multivalent metal ions used will depend on the particular anionic surfactant, but are in practice limited to those that do not adversely affect battery performance or life.

Preferred multi-phase emulsion polymers for use in the present invention are two-phase emulsion polymers stabilized with a suitable anionic surfactant (such as sodium lauryl sulfate), where the second phase is a copolymer of 98.5% (by weight) methyl methacrylate and 1.5% (by weight) methylolacrylamide, with the addition of magnesium (II) as a polyvalent metal ion and branched mono(octylphenyl) In the case of ethers as non-ionic surfactants, the cop coagulatespolymer between 40°C and 50°C.

The two-phase latex of the present invention can be applied to any fabric to produce a variety of useful products. This biphasic latex is especially suitable as a binder in applications that require a high temperature and a higher phase. Textile fibers that are relatively stiff in acidic environments under humid conditions, for example for laminates in the manufacture of printed circuit boards and battery separators.

Latex binders may contain additives that can improve various properties of textile materials, such as dyes, surfactants, coalescing agents, wetting agents, drying retarders, defoamers, preservatives, heat stabilizers, UV stabilizers, etc.

Methods for applying latex adhesives to textile materials include direct application, transfer film application, lamination, saturation, spraying, etc.

The followingthe examples are intended to illustrate the present invention, and they do not limit the present invention, as other applications of the present invention will be apparent to those skilled in the art.

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