EP4791939A1

EP4791939A1 - Impregnated fabric for use in battery cells

Info

Publication number: EP4791939A1
Application number: EP23818235.6A
Authority: EP
Inventors: Bo TONG; John Collinson; Cheng Shen; Ling Zhong; Bing Liang; Xinhong Wang
Original assignee: Dow Global Technologies LLC; Dow Silicones Corp
Current assignee: Dow Global Technologies LLC; Dow Silicones Corp
Priority date: 2023-10-13
Filing date: 2023-10-13
Publication date: 2026-08-19
Also published as: KR20260087591A; CN121969802A; WO2025076807A1

Abstract

A cured fabric that is useful in batteries can be made by impregnating a PET fabric with a binder emulsion that contains a self-crosslinking acrylic polymer binder and an anionic surfactant, which contains (1) a lipophilic moiety and (2) an anionic hydrophilic moiety that is linked to the lipophilic moiety by an oxygenated organic moiety. The combination of the binder and anionic surfactant provides fast wetting of the fabric. The impregnated fabric is cured by heating to crosslink the acrylic polymer. The resulting cured fabric has high tensile strength and good wetting ability with acid solutions used in batteries.

Description

IMPREGNATED FABRIC FOR USE IN BATTERY CELLS

FIELD

This invention relates to the field of fabrics used in batteries.
INTRODUCTION
Electrical batteries contain: (1) a corrosive liquid or paste such as sulfuric acid; (2) a negative active material exposed to the corrosive liquid or paste which generates excess electrons by reaction with the corrosive liquid or paste; (3) a negative electrode electrically connected to the negative active material; (4) a positive active material exposed to the corrosive liquid or paste which consumes electrons by reaction with the corrosive liquid or paste; and (5) a positive electrode electrically connected to the positive active material. Reaction of the positive active material and the negative active material with the corrosive liquid or paste creates a positive charge on the positive electrode and a negative charge on the negative electrode.
Corrosion-resistant fabrics can be used to perform at least two different functions in the electrical battery.
● First, fabric such as a fabric sheet can act as a separator to prevent contact between the negative active material and the positive active material. See for example, US Patents 5,158,844 and 10,396,327 B2 and US Patent Publication US 2015/0372269 A1. Such contact can short circuit the battery.
● Second, fabric gauntlets sometimes cover the positive active material and/or negative active material in a battery, and particularly a rechargeable battery. The gauntlet supports the active material and prevents oxidized portions from flaking off before the battery can be recharged, See for example US Patent 10,957,913 B2.
Fabrics used in the battery must meet several different performance criteria. They must endure years in the corrosive environment of the battery while maintaining enough physical strength that they do not fail. They must be sufficiently wettable so that they can maintain contact between the corrosive liquid or paste and the positive and/or negative active materials. In some cases, they should be thin enough to support use in small batteries. They are desirably inexpensive.
To improve their properties, the fabrics are often impregnated with thermoplastic or thermosetting polymers, which are hardened after impregnation. It is desired to find new combinations of fabric and impregnating materials that can provide improved properties.

SUMMARY

One aspect of this invention is an impregnated fabric comprising:
a. A fabric that contains polyalkylene terephthalate (PAT) fibers; and
b. A binder emulsion impregnating the fabric, which binder emulsion contains:
i. A binder that contains a self-crosslinking acrylic polymer and is present in an amount sufficient to stabilize the fabric after curing; and
ii. An anionic surfactant, which contains (1) a lipophilic moiety and (2) an anionic hydrophilic moiety that is linked to the lipophilic moiety by an oxygenated organic moiety, and which is present in an amount sufficient to promote wetting of the fabric by the binder emulsion; and
iii. An aqueous solvent.
A second aspect of this invention is a process to make a cured fabric comprising the steps of
a. Impregnating a fabric that contains PAT fibers with a binder emulsion that contains:
i. A binder that contains a self-crosslinking acrylic polymer and is present in an amount sufficient to stabilize the fabric after curing;
ii. An anionic surfactant, which contains (1) a lipophilic moiety and (2) an anionic hydrophilic moiety that is linked to the lipophilic moiety by an oxygenated organic moiety, and which is present in an amount sufficient to promote wetting of the fabric by the binder emulsion; and
iii. An aqueous solvent
b. Subjecting the impregnated fabric from Step (a) to raised temperatures that are sufficient to substantially drive off the aqueous solvent and to cause crosslinking reactions in the self-crosslinking acrylic polymer.
A third aspect of this invention is a cured fabric comprising:
a. A fabric that contains PAT fibers; and
b. A cured acrylic binder impregnating the fabric, which acrylic binder contains the reaction product of a self-crosslinking acrylic polymer and is present in an amount sufficient to stabilize the fabric; and
c. An anionic surfactant, which contains (1) a lipophilic moiety and (2) an anionic hydrophilic moiety that is linked to the lipophilic moiety by an oxygenated organic moiety, blended with the cured binder.
A fourth embodiment of this invention is a battery containing a cured fabric of the third aspect.
In some embodiments, the cured acrylic binder provides improved physical properties and improved wetting with acid to the PAT fabric, as compared with some other impregnating polymers. Further, the anionic surfactant improves wetting of the PAT fabric by the binder emulsion that contains the self-crosslinking acrylic polymer, so that impregnation happens more quickly and completely as compared to other surfactants.

DETAILED DESCRIPTION

Some embodiments of the present invention use a fabric that contains polyalkylene terephthalate fibers ( “PAT fabric” ) that is impregnated with a binder emulsion which contains (a) a binder containing self-crosslinking acrylic polymer and (b) an anionic surfactant, which contains (1) a lipophilic moiety and (2) an anionic hydrophilic moiety that is linked to the lipophilic moiety by an oxygenated organic moiety.
Fabric
Polyalkylene terephthalate (PAT) fabrics are well known and commercially available. PAT polymer is made by a condensation reaction of terephthalic acid or dimethyl terephthalate with an alkylene glycol. See, for example, M. Ramya et al., Manufacture of Polyethylene Terephthalate, a Project Report, published by SRM University (May 2017) . It contains repeating units that meet Formula 1.
wherein R¹ comprises primarily a 1, 4-phenylene or substituted 1, 4-phenylene group, and R² comprises an alkylene or substituted alkylene group; and “n” is a number of repeating units. In many embodiments, R¹ comprises a 1, 4-phenylene group or a methyl or dimethyl-substituted 1, 4 phenylene group. In some embodiments, R² comprises at least 2 carbon atoms. In some embodiments, R² comprises at most 8 carbon atoms or at most 6 carbon atoms or at most 4 carbon atoms or at most 3 carbon atoms or 2 carbon atoms. In some embodiments, the fabric contains polyethylene terephthalate (PET) fibers, alone or in combination with polybutylene terephthalate (PBT) fibers. PAT fabrics are known for use in battery separators and gauntlets. Examples of suitable fabrics are described in US Patent 9,508,974 B2, US Patent Publications 2015/0372269 A1 and US 2016/0315327 A1, and PCT Publication WO2006/0117320 A1.
In some embodiments, at least 80 percent of repeating units in the PAT polymer meet Formula 1, or at least 85 percent or at least 90 percent or at least 95 percent. In some embodiments, essentially 100 percent of repeating units in the PAT polymer meet Formula 1.
PAT polymer is spun to make fibers using conventional melt-spinning techniques. See, for example, “6.9.5.1 Polyester Fiber Process Description” in Organic Chemical Process Industry (1990) published by the US Environmental Protection Agency at https: //www3. epa. gov/ttn/chief/old/ap42/ch06/s09/final/c06s09_1995. pdf.
In some embodiments, fabrics used in this invention contain PAT fibers having an average diameter of at least 0.3 microns or at least 0.5 microns or at least 0.6 microns. In some embodiments, fabrics used in this invention contain PAT fibers having an average diameter of at most 40 microns or at most 20 microns or at most 14 microns.
In some embodiments, PAT fabrics used in this invention are woven fabrics. In some embodiments, PAT fabrics used in this invention are non-woven fabrics. In some embodiments, the fabric is a spun-bond nonwoven fabric. In some embodiments, the PAT fabrics used in this invention are multi-layered fabrics. For example, one layer may be designed to provide strength and another layer may be designed to control permeability.
In some embodiments, the PAT fabric consists essentially of PET fibers (up to 100 weight percent) . In some embodiments, the PAT fabric comprises PET fibers blended with other fibers. Other fibers blended with the PET should be stable in the conditions commonly found in a battery. Examples of fibers that can be blended with PET fibers include PBT fibers, glass fibers, polyethylene fibers and polypropylene fibers. In some embodiments, the PAT fabric contains at least 50 weight percent PET fibers (based on the total weight of fibers) or at least 70 weight percent or at least 80 weight percent or at least 90 weight percent or at least 95 weight percent.
In some embodiments, the PAT fabric has an average thickness of at least 0.3 mm or at least 0.5 mm or at least 0.6 mm or at least 0.7 mm. In some embodiments, the PAT fabric has an average thickness of at most 2 mm or at most 1.5 mm or at most 1.2 mm or at most 1 mm or at most 0.9 mm.
In some embodiments, the PAT fabric has a weight of at least 75 g/m² or at least 100 g/m² or at least 120 g/m² or at least 140 g/m². In some embodiments, the PAT fabric has a weight of at most 300 g/m² or at most 200 g/m² or at most 175 g/m² or at most 150 g/m².
In some embodiments, the PAT fabric has air permeability (at a pressure of 200 Pa) of at least 500 L/m²-sor at least 700 L/m²-sor at least 900 L/m²-sor at least 1000 L/m²-s. In some embodiments, the PAT fabric has an average thickness of at most 3000 L/m²-sor at most 2000 L/m²-sor at most 1500 L/m²-sor at most 1200 L/m²-s.
In some embodiments, fabrics used in gauntlets can shrink when heat is applied, to fit the gauntlet more closely to the active material that it covers. See, for example, PCT Publication WO2006/0117320 A1.
Binder
The binder emulsion that impregnates the fabric contains a self-crosslinking acrylic polymer binder in a concentration effective to stabilize and strengthen the fabric. Acrylic polymers, self-crosslinking acrylic polymers and aqueous dispersions that contain self-crosslinking acrylic polymer binders are known, andare commercially available.
An acrylic polymer is a polymer or copolymer that contains repeating units derived from acrylic monomers. Acrylic monomers include acrylic acid, methacrylic acid, and their esters. Exemplary esters used in acrylic monomers include alkyl esters, such as alkyl groups containing from 1 to 8 carbon atoms or from 1 to 4 carbon atoms or in some cases methyl groups or ethyl groups. Examples of useful acrylic monomers are acrylic acid, methacrylic acid, butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate.
Exemplary self-crosslinking acrylic polymers that may be used as binders in this invention ( “acrylic binders” ) may contain at least 70 weight percent repeating units derived from acrylic monomers, or at least 80 weight percent or at least 90 weight percent. Exemplary acrylic binders may contain up to 99 percent repeating units derived from acrylic monomers. Some exemplary acrylic polymer binders are copolymers containing units derived from two or more acrylic monomers, such as copolymers of butyl acrylate with methyl methacrylate and/or methacrylic acid.
The acrylic binders used in this invention further contain repeating units derived from a crosslinking acrylic monomer, such as acetoacetoxyethyl methacrylate (AAEM) or an n- (hydroxyalkyl) acrylamide, such as n- (hydroxymethyl) acrylamide. The crosslinking monomer enables the acrylic binder to crosslink as it sets when applied as a coating. In some embodiments, at most 20 weight percent of repeating units in the acrylic binder are derived from crosslinking acrylic monomers or at most 15weight percent or at most 10 weight percent or at most 8 weight percent or at most 6 weight percent. In some embodiments, at least 0.5 weight percent of repeating units in the acrylic binder are derived from crosslinking acrylic monomers or at least 1 weight percent or at least 2 weight percent or at least 3 weight percent.
Some exemplary acrylic binders may contain repeating units derived from non-acrylic ethylenically unsaturated comonomers, such as ethylene, vinyl esters (such as vinyl acetate) or styrene.
Increasing content of certain monomers, such as methyl methacrylate, is known to increase glass transition temperature (Tg) and melting point of the resulting polymer, and increasing content of other monomers, such as butyl acrylate, is known to reduce Tg and melting point of the resulting polymer. In some embodiments, the acrylic binder may be selected to have a glass-transition temperature (Tg) before curing of at least 0℃ or 10℃ or 15℃ or 20℃ or 25℃. In some embodiments, the acrylic binder may be selected to have a glass-transition temperature (Tg) before curing of at most 100℃ or 80℃ or 60℃ or 50℃ or 45℃ or 40℃.
In many embodiments, the acrylic binder is film-forming under the conditions at which the binder emulsion is applied to the fabric. “Film-forming” means that a substance is capable of forming a film upon application to a solid surface. The ability of polymers and their emulsions to be film-forming is known and described in publications such as: P. A. Steward et al., “An Overview of Polymer Latex Film Formation and Properties” , 86 Advances in Colloid and Interface Science at 195-267 (2000) . Commonly, the film-forming ability of polymers increases with lower molecular weight and/or lower Tg and decreases with higher molecular weight and/or higher Tg.
Increasing content of acidic monomers, such as acrylic and methacrylic acid, is known to increase the acidity of an acrylic polymer; and increasing the content of non-acidic monomers, such as butyl acrylate, is known to decrease acidity. In some embodiments, the acrylic binder has a pH of at least 1 or at least 1.5 or at least 1.8 or at least 2, when measured as described in the Test Methods section below. In some embodiments, the acrylic binder has a pH of at most 6 or at most 5 or at least most 4 or at most 3.5, when measured as described in the Test Methods section below.
Lower polymer molecular weight can in some embodiments, reduce the viscosity of the binder emulsion, making it easier to impregnate the cloth quickly. On the other hand, higher molecular weight can increase the strength of the cured acrylic binder. In some embodiments, the acrylic binder has a weight average molecular weight of at least 20,000 Da or at least 30,000 Da or at least 40,000 Da or at least 50,000 Da. In some embodiments, the acrylic binder has a weight average molecular weight of at most 5,000,000 Da or at most 3,000,000 Da or at most 2,000,000 Da or at most 1,000,000 Da or at most 500,000 Da or at most 250,000 Da.
Acrylic binders useful in this invention are commercially available as an emulsion from the Dow Chemical Company under the PRIMAL^TM and RHOPLEX^TM trademarks. Other acrylic binders can be made by emulsion polymerization of suitable monomers in the presence of suitable emulsifiers. Emulsion polymerization processes are well-known and described in numerous publications, such as Emulsion Polymerization of Acrylic Monomers, published by Rohm and Haas Company (1966) and available at https: //ia600709. us. archive. org/35/items/emulsionpolymeri00rohm/emulsionpolymeri00rohm. pdf; US Patent 2,289,540 and Zahran et al., “Poly Acrylic Acid: Synthesis, Aqueous Properties and their Applications as Scale Inhibitor” , published by KGK Rubberpoint at https: //www. kgk-rubberpoint. de/wp-content/uploads/2016/08/KGK_7-8_2016_53-58. pdf.
The acrylic binder is suspended in an aqueous solvent to form a binder emulsion. The binder emulsions used in this invention contain the acrylic binder in a concentration high enough to effectively strengthen and stabilize the fabric when cured, and low enough to wet the fabric quickly and efficiently. In some embodiments, the binder emulsions contain at least 1 weight percent acrylic binder, based on all ingredients including water, or at least 3 weight percent or at least 5 weight percent or at least 7 weight percent or at least 8 weight percent. In some embodiments, the binder emulsions contain at most 25 weight percent acrylic binder, based on all ingredients including water, or at most 20 weight percent or at most 15 weight percent or at most 12 weight percent or at most 10 weight percent. For example, the binder emulsion may contain from 3 to 20 weight percent acrylic binder, based on all ingredients including water, or from 5 to 15 weight percent or from 7 to 12 weight percent or from 8 to 10 weight percent. It should be noted that acrylic binders are often produced and sold in emulsions that have a higher solids content than the binder emulsions of this invention, so that it may be desirable to further dilute the acrylic binder to make binder emulsions of this invention.
Surfactant
The binder emulsions used in this invention contain an anionic surfactant in a concentration suitable to promote wetting and adhesion of the binder on the fabric. The anionic surfactants contain a lipophilic moiety. The anionic surfactants further contain an anionic hydrophilic moiety that is linked to the lipophilic moiety by an oxygenated organic moiety.
Examples of lipophilic moieties include fatty aliphatic groups and fatty aliphatic-aromatic groups that contain on average at least 8 carbon atoms or at least 10 carbon atoms or at least 12 carbon atoms. In some embodiments, the fatty aliphatic groups and fatty aliphatic-aromatic groups contain on average at most 20 carbon atoms or at most 18 carbon atoms or at most 16 carbon atoms or at most 14 carbon atoms. In some embodiments, the lipophilic moiety is an alkyl group. The alkyl chain in fatty aliphatic group or fatty aliphatic-aromatic group may be linear or branched and saturated or unsaturated. Other examples of lipophilic moieties include lipophilic polymers such as polypropylene oxide, polybutylene oxide, polytetrahydrofuran and mixtures thereof. In some embodiments, the anionic surfactant contains on average one lipophilic moiety linked to the oxygenated organic moiety. In some embodiments, the anionic surfactant contains on average more than one lipophilic moiety linked to the oxygenated organic moiety, such as 2 lipophilic moieties.
Examples of anionic hydrophilic moieties include carboxylic acid groups, sulfonic acid groups, and their salts and phosphoric acid esters. In some embodiments, the salt is a salt of an alkaline or alkaline earth metal. In some embodiments, the salt is an ammonium salt. For example, the anionic surfactant may comprise one or more sodium sulfonate or potassium sulfonate or ammonium sulfonate groups, or it may comprise one or more sodium carbonate or potassium carbonate or ammonium carbonate groups. In some embodiments, the anionic surfactant contains on average one anionic hydrophilic moiety linked to the oxygenated organic moiety. In some embodiments, the anionic surfactant contains on average more than one anionic hydrophilic moiety linked to the oxygenated organic moiety, such as 2 anionic hydrophilic moieties.
The anionic hydrophilic moieties are linked to the lipophilic moieties by oxygenated organic moieties. Oxygenated organic moieties contain organic groups and ether or ester linkages. The organic groups in the oxygenated organic moiety may be aliphatic, such as alkyl, or they may be aromatic, or they may be aliphatic-aromatic.
In some embodiments, the oxygenated organic moiety may contain polyalkylene glycol oligomer, such as polyethylene glycol oligomer or polypropylene glycol oligomer. For example, the anionic surfactant may meet Formula 2:
wherein A is an anionic hydrophilic moiety as previously described, R is a lipophilic moiety as previously described, each R³ is independently hydrogen or an alkyl group, and n is a number of repeating units. In some embodiments, each R³ independently contains at most 6 carbon atoms or at most 4 carbon atoms or at most 2 carbon atoms or at most 1 carbon atom. In some embodiments, the oligomer contains ethylene oxide [-CH₂-CH₂-O-] units, propylene oxide [-CH₂-CH (CH₃) -O-] units, butylene oxide units or a mixture thereof in block or random order. In some embodiments, the oligomer contains on average at least 1 repeating unit or at least 2 repeating units. In some embodiments, the oligomer contains on average at most 50 repeating units or at most 40 repeating units or at most 30 repeating units.
Examples of surfactants that contain polyalkylene glycol oligomer include alkyl alkoxylate sulfate and alkyl alkoxylate carbonate. Examples of anionic surfactants containing alkyl alkoxylate sulfate are sold under the DOWFAX^TM trademark from The Dow Chemical Company. Others can be made by known process such as those described in Kosswig, “Surfactants” , 35 Ullman’s Encyclopedia of Industrial Chemistry at 464 (2012) .
In some embodiments, the oxygenated organic moiety may contain a dicarboxylic acid ester. For example, the anionic surfactant may meet the Formula 3:
wherein A is an anionic hydrophilic moiety as previously described, R⁴ is a non-reactive organic moiety, and at least one of R⁵ and R⁶ is a lipophilic moiety as previously described.
● In some embodiments, R⁴ contains at least 1 carbon atom or at least 2 carbon atoms. In some embodiments, R⁴ contains at most 6 carbon atoms or at most 4 carbon atoms or at most 3 carbon atoms or at most 2 carbon atoms.
● In some embodiments, each of R⁵ and R⁶ independently comprises a lipophilic moiety. In some embodiments, only one of R⁵ and R⁶ comprises a lipophilic moiety, and the other comprises a lower alkyl (C₁ to C₆) group. In some embodiments, one or more of R⁵ and R⁶ may further comprise from 0 to 10 ethylene oxide units, propylene oxide units, butylene oxide units or a mixture thereof that link the carboxylate group to the lipophilic moiety.
In some embodiments, the oxygenated organic moiety comprises a succinate (R⁴ is -C₂H₄-) or glutarate (R⁴ is -C₃H₆-) or adipate (R⁴ is -C₄H₈-) moiety. Examples of surfactants that contain sulfosuccinate diester are sold commercially by The Dow Chemical Company under the TRITON^TM trademark and and by Solvay under the Aerosol name. Others can be made by known processes such as those described in Kosswig, “Surfactants” , 35 Ullman’s Encyclopedia of Industrial Chemistry at 463 (2012) .
In some embodiments, the oxygenated organic moiety may contain a diphenyl oxide moiety. For example, the anionic surfactant may meet the Formula 4:
wherein at least one A is an anionic hydrophilic moiety as previously described and at least one of R⁷ and R⁸ is a lipophilic moiety as previously described. In some embodiments, only one A is an anionic hydrophilic moiety; in some embodiments, each A is an anionic hydrophilic moieties. In some embodiments, only one of R⁷ and R⁸ is independently a lipophilic moiety; in some embodiments, each of R⁷ and R⁸ is independently a lipophilic moiety. In some embodiments, the phenyl rings may contain one or more pendant lower alkyl groups, and in some embodiments the phenyl rings are unsubstituted. Examples of surfactants that contain diphenyl oxide moieties are sold commercially by The Dow Chemical Company under the DOWFAX^TM trademarks. Others can be made by known processes such as those described in US Patent 6,743,764 B1.
The binder emulsions contain the anionic surfactant in a concentration high enough to promote wetting and adhesion of the binder on the fabric. In some embodiments, the binder emulsions contain at least 0.1 weight percent anionic surfactant, based on all ingredients including water, or at least 0.2 weight percent or at least 0.3 weight percent or at least 0.4 weight percent or at least 0.5 weight percent. In some embodiments, the binder emulsions contain at most 5 weight percent anionic surfactant, based on all ingredients including water, or at most 3 weight percent or at most 2 weight percent or at most 1 weight percent or at most 0.8 weight percent or at most 0.6 weight percent. For example, the binder emulsion may contain from 0.1 to 1 weight percent anionic surfactant, based on all ingredients including water, or from 0.2 to 0.8 weight percent or from 0.3 to 0.6 weight percent.
For clarity, quantities of anionic surfactant listed in this application refer to the quantity of surfactant with an oxygenated organic moiety as described above that is added to the binder emulsion. The acrylic binder may contain emulsifiers, which are surfactants, when it is produced or sold to emulsify the acrylic binder. The emulsifiers may be anionic, cationic or non-ionic. The emulsifiers may meet the definition of anionic surfactants for this invention, or they may be outside the definition. In any case, the quantities of anionic surfactant listed in this application may exclude the emulsifiers contained in the acrylic binder when it is made or sold.
In some embodiments, the weight ratio of anionic surfactant to acrylic binder in the binder emulsion is at least 1 weight percent or at least 2 weight percent or at least 3 weight percent or at least 4 weight percent or at least 5 weight percent or at least 6 weight percent, based on the weight of solid components excluding water. In some embodiments, the weight ratio of anionic surfactant to acrylic binder in the binder emulsion is at most 15 weight percent or at most 12 weight percent or at most 10 weight percent or at most 8 weight percent or at most 7 weight percent or at most 3 weight percent, based on the weight of solid components excluding water. For example, the weight ratio of acrylic binder to anionic surfactant may be from 1 to 15 weight percent or from 3 to 10 weight percent or from 5 to 8 weight percent, based on the weight of solid components excluding water.
In some embodiments, the binder emulsion further contains nonionic surfactants. Nonionic surfactants contain a lipophilic tail bonded to a hydrophilic head that does not dissociate in water. Examples of lipophilic moieties are as previously discussed Examples of nonionic hydrophilic moieties include alkylene oxide groups, and oligomers and glucose-derived groups.
Major types of nonionic surfactants include fatty alcohol ethoxylates, fatty alcohol alkoxylates, alkyl phenol ethoxylates, fatty acid alkoxylates and fatty alkyl polyglucoside derivatives. Examples of commonly used nonionic surfactants include alkyl polyglucosides such as octyl, decyl and lauryl glucoside, Polysorbate 20, Polysorbate 80 and Isolaureth-10.
In some embodiments, the nonionic surfactant comprises a fatty alcohol derivative in which the hydroxyl group has been substituted with a hydrophilic group containing one or more ethylene oxide or propylene oxide groups, or the mixture thereof in block or random structure. In some embodiments, the fatty alcohol derivative is aliphatic or alkyl. The number of carbon atoms in the fatty alcohol derivative is previously described. In some embodiments, the hydrophilic group contains on average at least one ethylene oxide or propylene oxide group. In some embodiments, the hydrophilic group contains on average at most six ethylene oxide or propylene oxide groups or at most four ethylene oxide or propylene oxide groups or at most three ethylene oxide or propylene oxide groups or at most two ethylene oxide or propylene oxide groups. In some embodiments, the hydrophilic group contains on average a single ethylene oxide or propylene oxide group. Examples of appropriate surfactants are sold by The Dow Chemical Company under the ECOSURF^TM, TERGITOL^TM and TRITON^TM trademarks.
Concentrations of nonionic surfactants may be as previously described for anionic surfactants.
Solvent
The binder emulsion contains an aqueous solvent. The aqueous solvent contains primarily water, but may contain a minor amount of a cosolvent that is miscible with water such as a lower alkanol, acetone or acetic acid. In some embodiments, the solvent contains at least 70 weight percent water, or at least 80 weight percent water or at least 90 weight percent water or at least 95 weight percent water. In some embodiments, the solvent contains up to 100 weight percent water.
The ratio of solid components (acrylic binder, surfactants and other solid materials) to solvent in the binder emulsion is desirably low enough so that the binder emulsion can effectively impregnate the fabric. If the solid content is too high, the binder emulsion may have too high a viscosity or may be unstable. On the other hand, the ratio of solid components to solvent in the binder emulsion is desirably high enough that the impregnated fabric contains the desired level of acrylic binder and surfactant and dries readily.
In some embodiment, the binder emulsion contains at least 5 weight percent solid components or at least 6 weight percent or at least 7 weight percent or at least 8 weight percent. In some embodiments, the binder emulsion contains at most 20 weight percent solid components or at most 18 weight percent or at most 16 weight percent or at most 14 weight percent or at most 12 weight percent or at most 10 weight percent. For example, the binder emulsion may contain from 5 to 20 weight percent solid components or from 6 to 16 weight percent or from 7 to 12 weight percent or from 8 to 10 weight percent.
In some embodiments, the binder emulsion has a viscosity at 25℃ of at least 20 cP or at least 30 cP or at least 50 cP. In some embodiments, the binder emulsion has a viscosity at 25℃ of at most 400 cP or at most 300 cP or at most 200 cP.
In some embodiments, the binder emulsion has a contact angle with the fabric of at most 54° or at most 52° or at most 50° or at most 40° or at most 30° or at most 20° or at most 10°. In some embodiments, the binder emulsion has a contact angle with the fabric that is essentially 0°.
Process
The PAT fabric is impregnated with the binder emulsion. Then the impregnated fabric is subjected to high temperature conditions that substantially drive off the aqueous solvent and cause cross-linking reactions in the self-crosslinking acrylic binder so that it cures.
Impregnation can be accomplished by known means such as spraying, dipping or pouring. The binder emulsion may further be physically worked into the fabric to provide substantially homogeneous impregnation by known means such as pressing, rolling or calendaring. In some embodiments, the impregnation is substantially homogeneous, without thin or dry spots.
In some embodiments, the amount of binder emulsion impregnated into the fabric is sufficient so that the cured binder and surfactant add at least 5 weight percent to the weight of the initial fabric weight, before impregnation, or at least 10 weight percent or at least 12 weight percent or at least 15 weight percent. In some embodiments, the amount of binder emulsion impregnated into the fabric is sufficient so that the cured binder and surfactant add at most 40 weight percent to the weight of the initial fabric, before impregnation, or at most 30 weight percent or at most 25 weight percent or at most 20 weight percent or at most 18 weight percent.
Of course, the quantity of binder emulsion needed to achieve this weight gain varies depending on the content of solid components in the binder emulsion. In some embodiments, the quantity of binder emulsion impregnated into the fabric is at least 50 weight percent of the weight of the fabric, or at least 60 weight percent or at least 70 weight percent or at least 80 weight percent or at least 90 weight percent or at least 100 weight percent. In some embodiments, the quantity of binder emulsion impregnated into the fabric is at most 400 weight percent of the weight of the fabric, or at most 350 weight percent or at most 300 weight percent or at most 250 weight percent.
The impregnated fabric is cured at high temperature conditions that drive off the water and cause the self-crosslinking acrylic binder to cure. For purposes of efficiency, it is desirable for the curing to happen quickly and at low temperature. In some embodiments, the curing step takes place at a temperature of at least 120℃ or at least 130℃ or at least 140℃ or at least 150℃. In some embodiments, the curing step takes place at a temperature of at most 220℃ or at most 210℃ or at most 200℃ or at most 190℃ or at most 180℃ or at most 170℃ or at most 160℃ or at most 150℃.
In some embodiments, the curing step takes place in air. In some embodiments, the curing step takes place in an inert atmosphere such as nitrogen. In some embodiments, the curing step takes place in the presence of airflow to carry away water released during the curing.
In some embodiments, the curing step is carried out for at least 30 seconds or at least 1 minute or at least 2 minutes or at least 3 minutes. In some embodiments, the curing step is carried out for at most 15 minutes or at most 10 minutes or at most 8 minutes or at most 6 minutes or at most 4 minutes.
In some embodiments, the fabric is held firmly during the curing process to maintain the desired shape. For example, gauntlets may optionally be clamped, drawn or pressed over a form. Separators may be stretched over a roller or tentered.
Cured Fabric
The cured fabric contains:
a. A fabric that contains PAT fibers; and
b. A cured acrylic binder impregnating the fabric, which binder contains the reaction product of a self-crosslinking acrylic polymer and is present in an amount sufficient to stabilize the fabric; and
c. An anionic surfactant, which contains (1) a lipophilic moiety and (2) an anionic hydrophilic moiety that is linked to the lipophilic moiety by an oxygenated organic moiety, blended with the cured binder.
The content and proportions of fabric, binder and surfactant correspond to the content and proportions that were previously discussed.
In some embodiments, water has a contact angle with the cured fabric of at most 54° or at most 52° or at most 50° or at most 40° or at most 30° or at most 20° or at most 10°. In some embodiments, the contact angle of water with the cured fabric is essentially 0°, meaning that the water spreads over and through the fabric in just a few seconds. The contact angle shows that the cured fabric can readily be wetted by the binder emulsion.
In some embodiments, the cured fabric has a tensile strength in the machine direction of at least 6.0 Mpa when cured at a temperature of at most 140℃, or at least 6.5 Mpa or at least 6.75 Mpa or at least 6.95 Mpa or at least 7.0 Mpa or at least 7.2 Mpa or at least 7.3 Mpa or at least 7.4 Mpa. In some embodiments, the cured fabric has a tensile strength in the machine direction of at least 7.0 N/mm² when cured at a temperature of at most 200℃, or at least 7.4 Mpa or at least 7.6 Mpa or at least 7.8 Mpa or at least 8.0 Mpa or at least 8.2 Mpa or at least 8.4 Mpa. There is no maximum desired tensile strength, but tensile strength over 10 Mpa may be unnecessary.
The cured fabric can be used for ordinary purposes in batteries. In some embodiments, the cured fabric serves as the separator between negative active materials in a battery and positive active materials in the battery. In some embodiments, the cured fabric serves as a gauntlet surrounding positive active material or negative active material in a battery. Both of these uses are described in references in the Background.
TEST METHODS
When this document states that a property is measured, it is measured using the following test methods, unless it is clear from the context that a different method is intended.
EXAMPLES
The following Examples illustrate some embodiments of the invention. The Examples do not limit the broad scope of the invention.
The materials in Table 1 are used for these examples:
Table 1
TDCC = The Dow Chemical Company
The nonwoven PET mat is cut into samples of A3 size, and each sample is weighed.
The binders and surfactants are mixed together with water to form binder emulsions with the contents shown in Table 2. The contact angle of each binder emulsion on the mat is tested according to the method described in the Test Methods section above, and the results are recorded in Table 2.
Each binder emulsion is impregnated onto a sample of nonwoven PET mat using a Mathis Foulard calendering device. Both rolls apply a pressure of 3 bar against each other at a speed of 1.2 m/min. Conditions are selected so that the solid content of the binder emulsion impregnated on the nonwoven PET mat (after heating) is about 15 weight percent of the weight of the nonwoven PET mat.
The impregnated PET mats are fixed on a tenter frame to prevent curling. The tentered mats are cured by heating in a preheated oven for 3 minutes at 200℃ or 140℃ as shown in Table 2. After heating, the cured samples are removed from the tenter frame and cooled.
After cooling, the cured samples are weighed to confirm how much binder has been added to the mat. For samples used in testing the added binder is about 15 weight percent of the weight of the mat. Each mat is tested for tensile properties and contact angle with water as set out in the Test Methods section above, and the results are recorded in Table 2
Table 2
All quantities are parts by weight unless otherwise noted.

Claims

A process to make a cured fabric comprising the steps of:

a) impregnating a fabric that contains polyalkylene terephthalate fibers with a binder emulsion that contains:

i) a binder that contains a self-crosslinking acrylic polymer and is present in an amount sufficient to stabilize the fabric after curing;

ii) an anionic surfactant, which contains (1) a lipophilic moiety and (2) an anionic hydrophilic moiety that is linked to the lipophilic moiety by an oxygenated organic moiety, and which is present in an amount sufficient to promote wetting of the fabric by the binder emulsion; and

iii) an aqueous solvent; and

b) subjecting the impregnated fabric from Step (a) to raised temperatures that are sufficient to substantially drive off the aqueous solvent and to cause crosslinking reactions in the self-crosslinking acrylic polymer.
The process of Claim 1 wherein the self-crosslinking acrylic polymer has a pH of 1.5 to 5.
The process of Claim 1 wherein the self-crosslinking acrylic polymer has a glass transition temperature from 10℃ to 50℃.
The process of Claim 1 wherein the self-crosslinking acrylic polymer contains from 80 to 99 weight percent repeating units derived from acrylic or methacrylic acid and from 1 to 20 weight percent repeating units derived from a crosslinking monomer.
The process of Claim 1 wherein the oxygenated organic moiety in the anionic surfactant contains a polyalkylene glycol oligomer, a dicarboxylic acid ester, or a diphenyl oxide moiety.
The process of Claim 1 wherein the oxygenated organic moiety of the anionic surfactant comprises a polyalkylene glycol oligomer.
The process of Claim 1 wherein the oxygenated organic moiety of the anionic surfactant comprises a succinate, glutarate or adipate moiety.
The process of Claim 1 wherein the oxygenated organic moiety of the anionic surfactant comprises a diphenyl oxide moiety.
The process of Claim 1 wherein the weight ratio of anionic surfactant to acrylic binder in the binder emulsion is from 3 to 10 weight percent, based solely on the weight of anionic surfactant and acrylic binder and excluding water.
The process of Claim 1 wherein the binder emulsion has a viscosity from 20 cP to 400 cP.
The process of Claim 1 wherein the binder emulsion has a contact angle with the fabric of at most 50°.
The process of Claim 1 wherein:

a) the fibers in the fabric contain at least 75 weight percent of polyethylene terephthalate fibers or polybutylene terephthalate fibers or both; and

b) the acrylic binder has a glass transition temperature from 10℃ to 50℃ and has a pH of 1.5 to 5, and is present in a concentration of 5 to 20 weight percent in the binder emulsion; and

c) the oxygenated organic moiety of the anionic surfactant contains a polyalkylene glycol oligomer, a succinate, glutarate or adipate moiety, or a diphenyl oxide moiety;

d) the hydrophilic moiety of the anionic surfactant contains a sulfonic acid group or its salt.

e) the weight ratio of anionic surfactant to acrylic binder in the binder emulsion is from 3 to 10 weight percent, based solely on the weight of anionic surfactant and acrylic binder and excluding water; and

f) the binder emulsion has a viscosity of 20 cP to 400 cP and has a contact angle with the with the fabric of at most 50°.
A cured fabric made by the process of any one of Claims 1 to 12.
A cured fabric comprising:

a) a fabric that contains polyalkylene terephthalate fibers; and

b) a cured binder impregnating the fabric, which binder contains the reaction product of a self-crosslinking acrylic polymer and is present in an amount sufficient to stabilize the fabric; and

c) an anionic surfactant which contains a lipophilic moiety and an anionic hydrophilic moiety that is linked to the lipophilic moiety by an oxygenated organic moiety, blended with the cured binder.
The cured fabric of Claim 14 which has a contact angle with distilled water of at most 20°.