CN120303367A - Aqueous polymer dispersions for pressure-sensitive adhesives having broad temperature properties - Google Patents

Abstract

Disclosed herein are aqueous polymer dispersions, methods for their preparation, and their use in pressure-sensitive adhesives.

Description

Aqueous polymer dispersions for pressure sensitive adhesives with broad temperature properties

Technical Field

The present invention relates to Pressure Sensitive Adhesives (PSAs), and more particularly, to aqueous polymer dispersions, their use in PSAs, and methods of making them.

Background

Pressure Sensitive Adhesives (PSAs) based on aqueous polymer dispersions obtainable by emulsion polymerization are long-term forming techniques. The polymers in question are in particular poly (meth) acrylates. These are typically copolymers in which at least one of the monomers is an acrylate ester that forms a polymer having a relatively low glass transition temperature, such as, for example, n-butyl acrylate or 2-ethylhexyl acrylate. The known acrylate copolymers based on n-butyl acrylate have adhesive properties at room temperature sufficient to produce self-adhesive labels. However, the temperature dependence of the surface tackiness means that the surface tackiness decreases significantly at lower temperatures. This can be particularly challenging when the adhesive is applied to a hydrophobic surface, such as, for example, polyethylene. Lowering the glass transition temperature of the adhesive improves the surface tack at low temperatures, but generally compromises the adhesive peel strength in a hot environment. A particular problem arises if the adhesive must have a wide application and use temperature range. In such applications, polyacrylate-based PSAs often exhibit inadequate adhesion.

There is therefore a need for pressure sensitive adhesive polymers that maintain good surface tack, peel and static shear over a wide temperature range.

Disclosure of Invention

The present invention is based on the discovery that polymer dispersions having low gel content and high molecular weight can be used to form continuous adhesive films having superior characteristics compared to prior dispersion techniques. Provided herein are aqueous dispersions of these polymers and methods of their preparation such that the resulting pressure sensitive adhesives provide good tack, peel, and static shear over a wide temperature range.

In one form thereof, the present disclosure provides a pressure sensitive adhesive composition in the form of an aqueous polymer dispersion comprising at least one copolymer comprising (i) 50 to 95 wt% of at least one soft (meth) acrylate monomer having a glass transition temperature of less than 0 ℃ when polymerized as a homopolymer, (ii) 0to 25 wt% of at least one monomer selected from C1 to C20 alkyl (meth) acrylates, (iii) 0.5 to 20 wt% of styrene, (iv) 0.1 to 5 wt% of at least one ethylenically unsaturated acid or at least one ethylenically unsaturated anhydride, (v) 0to 10 wt% of other ethylenically unsaturated compounds other than monomers (i) to (iv), wherein the amount of monomers is each relative to the total amount of monomers, and wherein the copolymer has a gel content of less than 35 wt% and a weight average molecular weight of greater than 200kDa based on the total weight of the composition.

In its second form, the present disclosure provides a process for preparing an aqueous polymer dispersion comprising polymerizing a monomer mixture comprising (i) 50 to 95 weight percent of at least one soft (meth) acrylate monomer having a glass transition temperature of less than 0 ℃ when polymerized as a homopolymer, (ii) 0 to 25 weight percent of at least one monomer selected from the group consisting of C1 to C20 alkyl (meth) acrylates, (iii) 0.5 to 20 weight percent styrene, (iv) 0.1 to 5 weight percent of at least one ethylenically unsaturated acid or at least one ethylenically unsaturated anhydride, (v) 0 to 10 weight percent of other ethylenically unsaturated compounds other than monomers (i) to (iv), wherein the amounts of monomers are each relative to the total amount of monomers, and producing a copolymer having a polymer gel content of less than 35 weight percent and a weight average molecular weight of greater than 200kDa based on the total weight of the composition.

Detailed Description

I. definition of the definition

As used herein and unless otherwise indicated, the weight% values are based in each case on the sum of all monomers used for polymerization.

The pressure sensitive adhesive is a viscoelastic adhesive that maintains permanent tack and adhesion in a dry state of a cured film at room temperature (20 ℃). Bonding to the substrate is accomplished immediately under mildly applied pressure.

As used herein, the name "(meth) acryl" and similar names are occasionally used as abbreviations for "acryl. In the notation Cx alkyl (meth) acrylate and similar names, x represents the number of carbon atoms in the alkyl group.

As used herein, when describing monomers, the term "soft" refers to monomers that have a glass transition temperature of less than 0 ℃ when polymerized as homopolymers. Likewise, a "hard" monomer is a monomer that has a glass transition temperature greater than 0 ℃ when polymerized as a homopolymer.

A cold surface is a surface having a surface temperature, in particular at least 10 ℃ lower than the ambient temperature. A hot surface is a surface having a surface temperature, in particular at least 10 ℃ higher than the ambient temperature.

As used herein, the phrase "within any range encompassed by any two aforementioned values as endpoints means literally that any range can be selected from any two values listed before the phrase, regardless of whether the values are at the lower or upper part of the list. For example, a pair of values may be selected from two lower values, two higher values, or one lower value and one higher value.

Aqueous polymer dispersions for pressure sensitive adhesives

The present disclosure provides a pressure sensitive adhesive composition in the form of an aqueous polymer dispersion comprising at least one copolymer comprising:

(i) 50 to 95% by weight of at least one soft (meth) acrylate monomer having a glass transition temperature of less than 0 ℃ when polymerized as a homopolymer,

(Ii) 0 to 25% by weight of at least one monomer selected from the group consisting of C1 to C20 alkyl (meth) acrylates,

(Iii) From 0.5 to 20% by weight of styrene,

(Iv) 0.1 to 5% by weight of at least one ethylenically unsaturated acid or at least one ethylenically unsaturated anhydride,

(V) 0 to 10% by weight of other ethylenically unsaturated compounds than the monomers (i) to (iv),

Wherein the amounts of the monomers are each relative to the total amount of the monomers, and

Wherein the copolymer has a gel content of less than 35 wt% based on the total weight of the composition and a weight average molecular weight of greater than 200 kDa.

The primary monomer (i) may be a soft (meth) acrylate monomer present in an amount of 50 to 90 wt%, or more preferably 50 to 70 wt%. The soft monomers (i) are preferably selected from acrylic esters, in particular from C2 to C10 alkyl acrylates, or from C4 to C10 alkyl acrylates or from C4 to C8 alkyl acrylates. Suitable examples are ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate and mixtures of these monomers. Ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate and mixtures thereof are preferred, with n-butyl acrylate and 2-ethylhexyl acrylate and mixtures thereof being particularly preferred.

Soft monomers may have certain characteristics that make them desirable as copolymer emulsions. When polymerized as a homopolymer, the soft (meth) acrylate monomer may, for example, have a glass transition temperature of less than 10 ℃, less than 5 ℃, less than 0 ℃, less than-5 ℃, less than-10 ℃, less than-15 ℃, less than-20 ℃, less than-25 ℃, less than-30 ℃, less than-35 ℃, less than-40 ℃, less than-45 ℃, less than-50 ℃, less than-55 ℃, or less than-60 ℃.

The monomer (ii) may be selected from C1-C20 alkyl (meth) acrylates and be present in an amount of 0 to 25% by weight. C1-C20 alkyl (meth) acrylates are, for example, methyl acrylate, methyl methacrylate and hydroxypropyl acrylate, and mixtures of these monomers.

The monomer (iii) may be styrene, which is present in an amount of 0.5 to 20% by weight.

The monomer (iv) may be at least one ethylenically unsaturated acid or at least one ethylenically unsaturated anhydride. Suitable examples are monomers having carboxylic, sulphonic or phosphonic acid groups. Preferred are carboxylic acid groups. For example, acrylic acid, methacrylic acid, itaconic acid, maleic acid or fumaric acid may be mentioned. The acid groups may be present in the form of their salts. Acrylic acid and methacrylic acid are particularly preferred.

The monomer (v) includes other ethylenically unsaturated compounds different from the monomers (i) to (iv). The other monomer (v) than the monomers (i) to (iv) may be a copolymerizable ethylenically unsaturated compound. They may be used in amounts of from 0% to 10% by weight, preferably from 0.1% to 8% by weight. The other monomers (v) are preferably selected from the group consisting of C1-C20-alkyl (meth) acrylates, hydroxyl-containing monomers, vinyl esters of carboxylic acids having up to 20 carbon atoms, vinylaromatic compounds having up to 20 carbon atoms other than styrene, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols having from 1 to 10 carbon atoms, aliphatic hydrocarbons having from 2 to 8 carbon atoms and one or two double bonds, monomers comprising hydroxyl groups, in particular C1-C10-hydroxyalkyl (meth) acrylates, (meth) acrylamides or mixtures of these monomers. In addition, other monomers which may be mentioned are phenoxyethyl ethylene glycol mono (meth) acrylate, glycidyl (meth) acrylate, aminoalkyl (meth) acrylates such as, for example, 2-aminoethyl (meth) acrylate. The alkyl group preferably has 1 to 20C atoms. The C1-C20 alkyl (meth) acrylate has 1 to 20C atoms in the alkyl group. C1-C10 hydroxyalkyl (meth) acrylates have 1 to 10C atoms in the hydroxyalkyl group. Other monomers which may be mentioned also include crosslinking monomers.

Suitable monomers are, for example, alkyl (meth) acrylates having C3-C10-alkyl groups. Particularly suitable are mixtures of alkyl (meth) acrylates. Vinyl carboxylates having 1 to 20C atoms are, for example, vinyl acetate, vinyl laurate, vinyl stearate, vinyl propionate and vinyl versatate. Contemplated vinyl aromatic compounds include vinyl toluene, alpha-methyl styrene and para-methyl styrene, alpha-butyl styrene, 4-n-decyl styrene. Examples of nitriles are acrylonitrile and methacrylonitrile. Vinyl halides are ethylenically unsaturated compounds substituted with chlorine, fluorine or bromine, preferably vinyl chloride and vinylidene chloride. Vinyl ethers include, for example, vinyl methyl ether or vinyl isobutyl ether. Preferred vinyl ethers are those containing alcohols of 1 to 4 carbon atoms. Suitable hydrocarbons having 4 to 8C atoms and two olefinic double bonds are, for example, butadiene, isoprene and chloroprene.

The other monomers (v) may also comprise crosslinkable monomers. Preferred crosslinkable monomers include diacetone (meth) acrylamide, acetoacetoxyethyl methacrylate, N-methacryloyl (meth) acrylamide, and glycidyl methacrylate.

Other monomers (v) which are generally preferred are C3 to C10 alkyl acrylates and C3 to C10 alkyl methacrylates, more particularly C3 to C8 alkyl acrylates and C3 to C8 alkyl methacrylates, and vinyl esters, especially vinyl acetate, and mixtures thereof, and also C2 to C10 hydroxyalkyl (meth) acrylates. Particularly preferred are n-hexyl acrylate, octyl acrylate, vinyl acetate and hydroxypropyl acrylate, and mixtures thereof.

The other monomers are generally used in small amounts, their total proportion preferably being less than 10% by weight, more particularly less than 8% by weight.

The copolymer of the aqueous polymer dispersion may be a single phase particle.

The copolymer of the aqueous polymer dispersion may have a gel content of less than 35 wt%, less than 30 wt%, less than 25 wt%, less than 20 wt%, less than 15 wt%, less than 10 wt%, less than 5 wt%, less than 1 wt%, less than 0.001 wt%, or less than 0.00001 wt%, based on the total weight of the composition.

The copolymer of the aqueous polymer dispersion may have a weight average molecular weight of greater than 200kDa, such as 300kDa or greater, 400kDa or greater, 500kDa or greater, 600kDa or greater, 700kDa or greater, 800kDa or greater, 900kDa or greater, 1000kDa or greater, 1100kDa or greater, 1200kDa or greater, 1300kDa or greater, 1400kDa or greater, 1500kDa or greater, 1600kDa or greater, 1700kDa or greater, 1800kDa or greater, 1900kDa or greater, 2000kDa or greater, 2500kDa or greater, 3000kDa or greater, 3500kDa or greater, 4000kDa or greater, 4500kDa or greater, 5000kDa or greater, 5500kDa or greater, 6000kDa or greater, 6500kDa or greater, 7000kDa or greater, 7500kDa or greater, 8000kDa or greater, 9000kDa or greater, 9500kDa or greater, or 10,000kDa or greater.

The copolymer of the aqueous polymer dispersion may have a glass transition temperature as low as-75 ℃, -70 ℃, -65 ℃, -60 ℃, -55 ℃, -50 ℃, -45 ℃, -40 ℃, -35 ℃, -30 ℃, -25 ℃, -20 ℃, -15 ℃, or as high as-10 ℃, -5 ℃, -0 ℃,5 ℃,10 ℃,15 ℃, 20 ℃, or in any range encompassed by any two of the foregoing values as endpoints. For example, the copolymer of the aqueous dispersion may have a glass transition temperature of from-65 ℃ to 0 ℃. The glass transition temperature may be determined using differential scanning calorimetry (e.g., ASTM 3418/82, midpoint temperature).

The copolymer of the aqueous polymer dispersion may have a unimodal, bimodal or multimodal dispersion particle size distribution. The number average size represents the d50 of the particle size distribution, meaning that 50% by weight of the total mass of all particles has a particle size less than d 50. The particle size distribution can be determined in a known manner using analytical ultracentrifuge (W.Makromolekulare Chemie 185 (1984), pages 1025 to 1039). The number average particle size of the aqueous polymer dispersion may be 2000nm or less, 1900nm or less, 1800nm or less, 1700nm or less, 1600nm or less, 1500nm or less, 1400nm or less, 1300nm or less, 1200nm or less, 1100nm or less, 1000nm or less, 900nm or less, 800nm or less, 700nm or less, 600nm or less, 500nm or less, 400nm or less, 300nm or less, 200nm or less, 100nm or less, 50nm or less, 25nm or less, 10nm or less, or 5nm or less.

The aqueous polymer dispersion may have a pH of 4.5, more preferably a pH between 5 and 8.

Method for producing aqueous polymer dispersions for pressure-sensitive adhesives

The adhesive polymer of the present invention can be obtained by radical polymerization of an ethylenically unsaturated compound (monomer). The polymer is preferably prepared by emulsion polymerization and is therefore preferably an emulsion polymer. Accordingly, the present invention also provides a pressure sensitive adhesive dispersion comprising the pressure sensitive adhesive polymer of the present invention prepared by emulsion polymerization dispersed in water.

In emulsion polymerization, ethylenically unsaturated monomers are polymerized in water, wherein ionic and/or nonionic emulsifiers and/or protective colloids or stabilizers are used as surface-active compounds to stabilize the monomer droplets and subsequently the polymer particles formed from the monomers. The surface-active substances are used in amounts of from 0.1 to 10 parts by weight, preferably from 0.2 to 5 parts by weight, based on 100 parts by weight of the monomers to be polymerized.

A comprehensive description of suitable protective colloids is found in Houben-Weyl, methoden der organischen Chemie, volume XIV/1, makromolekulare Stoffe [ macromolecular compounds ], georg-Thieme-Verlag, stuttgart,1961, pages 411 to 420. Contemplated emulsifiers include anionic emulsifiers, cationic emulsifiers, and nonionic emulsifiers. The surface-active substances used are preferably emulsifiers whose molecular weights are generally 2000g/mol lower than those of the protective colloids. When mixtures of surface-active substances are used, the components must of course be compatible with one another, which can be checked in case of doubt using several preliminary tests. The surface-active substances used are preferably anionic emulsifiers and nonionic emulsifiers. Common accompanying emulsifiers are, for example, ethoxylated fatty alcohols (EO degree: 3 to 50, alkyl radical: C8 to C36), ethoxylated monoalkylphenols, ethoxylated dialkylphenols and ethoxylated trialkylphenols (EO degree: 3 to 50, alkyl radical: C4 to C9), alkali metal and ammonium salts of dialkyl esters of sulfosuccinic acid, and alkali metal and ammonium salts of alkyl sulfates (alkyl radical: C8 to C12), ethoxylated alkanols (EO degree: 4 to 30, alkyl radical: C12 to C18), ethoxylated alkylphenols (EO degree: 3 to 50, alkyl radical: C4 to C9), alkali metal and ammonium salts of alkylsulfonic acids (alkyl radical: C12 to C18), and alkali metal and ammonium salts of alkylaryl sulfonic acids (alkyl radical: C9 to C18).

Other suitable emulsifiers are compounds of the general formula provided by the following formula 1.

1 (1)

In formula 1, R5 and R6 are hydrogen or C4 to C14 alkyl and are not simultaneously hydrogen, and X and Y may be alkali metal ions and/or ammonium ions. Preferably, R5 and R6 are linear or branched alkyl groups having 6 to 18C atoms or hydrogen, and in particular having 6, 12 and 16C atoms, wherein R5 and R6 are not simultaneously hydrogen. X and Y are preferably sodium, potassium or ammonium ions, sodium being particularly preferred. Particularly advantageous compounds are those in which X and Y are sodium, R5 is a branched alkyl group having 12C atoms and R6 is hydrogen or R5. Commercial mixtures having a monoalkylated product fraction of 50 to 90 wt.% are frequently used. Commercially available products of suitable emulsifiers are, for exampleA1、NP 50、OC 50、Emulgator 825、Emulgator825S、OG、NSO、904S、I-RA、E 3065、FES 77、AT 18、VSL、NPS25. For the purposes of the present invention, ionic emulsifiers or protective colloids are preferred. Particularly preferably, they are ionic emulsifiers, more particularly salts and acids, such as carboxylic acids, sulphonic acids and sulphates, sulphonates or carboxylates. In particular, mixtures of ionic and nonionic emulsifiers can also be used.

Emulsion polymerization may be started using a water-soluble initiator. The water-soluble initiator is, for example, an ammonium salt and an alkali metal salt of peroxodisulfuric acid (for example, sodium peroxodisulfate), hydrogen peroxide or an organic peroxide (for example, tert-butyl hydroperoxide). Other suitable initiators include those known as reduction-oxidation (redox) initiator systems. The redox initiator system consists of at least one, usually inorganic, reducing agent and an organic or inorganic oxidizing agent. The oxidizing component includes an initiator such as has been described above for emulsion polymerization. The reducing component includes, for example, an alkali metal salt of sulfurous acid such as sodium sulfite, sodium bisulfite, an alkali metal salt of metabisulfite such as sodium metabisulfite, an addition compound of bisulfite with fatty aldehydes and ketones such as acetone bisulfite, or a reducing agent such as hydroxymethane sulfinic acid and salts thereof, or ascorbic acid. Redox initiator systems can be used with soluble metal compounds whose metal components can exist in a variety of valence states. Examples of conventional redox initiator systems include ascorbic acid/iron (II) sulfate/sodium peroxodisulfate, t-butyl hydroperoxide/sodium metabisulfite, t-butyl hydroperoxide/sodium hydroxymethanesulfinate. The individual components, for example the reducing component, may also be mixtures, an example being a mixture of sodium salts of hydroxymethanesulfinic acid with sodium metabisulfite.

The initiator is generally used in the form of an aqueous solution, with the lower concentration being determined by the amount of water acceptable in the dispersion and the higher concentration being determined by the solubility of the corresponding compound in water. In general, the concentration of initiator is from 0.1% to 30% by weight, preferably from 0.2% to 20% by weight, more preferably from 0.4% to 2% by weight, based on the monomers to be polymerized. A variety of different initiators may also be used in the emulsion polymerization.

In the polymerization, the chain transfer agent is used in an amount of at least 0.01 parts by weight of the chain transfer agent per 100 parts by weight of the monomer, for example, 0.01 to 0.8 parts by weight, or 0.01 to 0.1 parts by weight per 100 parts by weight of the monomer to be polymerized. With these reagents, the molar mass of the emulsion polymer can be controlled or reduced by chain termination reactions. These agents are bonded to the polymer in this process, typically at the ends of the chain.

Suitable chain transfer agents are, for example, organic compounds containing sulfur in bonded form (e.g. compounds having thiol groups), aliphatic and/or araliphatic halogen compounds, aliphatic and/or aromatic aldehydes, unsaturated fatty acids (e.g. oleic acid), dienes having non-conjugated double bonds (such as, for example, divinyl methane, terpineol or vinylcyclohexene), hydrocarbons having readily extractable hydrogen atoms (such as, for example, toluene), organic acids and/or salts thereof (such as, for example, formic acid, sodium formate, ammonium formate), alcohols (such as, for example, isopropanol), and phosphorus compounds (such as, for example, sodium hypophosphite). However, mixtures of mutually non-interfering chain transfer agents as described above may also be used. Chain transfer agents are generally low molecular weight compounds having a molecular weight of less than 2000g/mol, more particularly less than 1000 g/mol. It may be advantageous to provide some or all of the chain transfer agent to the aqueous reaction medium prior to initiating the free radical polymerization. In addition, during the polymerization, it may also be advantageous to supply part or all of the radical chain transfer compound together with the monomers to the aqueous reaction medium.

Organic compounds having a thiol group are, for example, primary aliphatic thiol, secondary aliphatic thiol or tertiary aliphatic thiol, such as, for example, ethanethiol, n-propanethiol, 2-propanethiol, n-butanethiol, 2-methyl-2-propanethiol, n-pentanethiol, 2-pentanethiol, 3-pentanethiol, 2-methyl-2-butanethiol, n-hexanethiol, 2-hexanethiol, 3-hexanethiol, 2-methyl-2-pentanethiol, 3-methyl-2-pentanethiol, 4-methyl-2-pentanethiol, 2-methyl-3-pentanethiol, 3-methyl-3-pentanethiol, 2-ethylbutanethiol, 2-ethyl-2-butanethiol, n-heptanethiol and their isomer compounds, n-octanol and their isomer compounds, n-decanol and their isomer compounds, n-undecanol and their isomer compounds, n-dodecanol and their isomer compounds, n-triol and their isomer compounds; substituted thiols such as, for example, 2-hydroxyethanethiol; aromatic mercaptans such as, for example, benzenethiol, o-methylbenzene thiol, m-methylbenzene thiol or p-methylbenzene thiol; such as mercaptoalkyl esters of C2 to C4 carboxylic acids, having 1 to 18C atoms on the alkyl group, such as, for example, 2-mercaptoethyl propionate; and all other sulfur compounds described in Polymer Handbook, 3 rd edition, 1989, J.Brandrep and E.H.Immergout, john Wiley & Sons, section II, pages 133-141. Preferred organic compounds comprising sulfur in bonded form are in particular tert-butylmercaptan, ethyl thioglycolate, mercaptoethanol, mercaptopropyl trimethoxysilane, tert-dodecylmercaptan, thiodiglycol, ethylmercaptoethanol, di-n-butylsulfide, di-n-octylsulfide, diphenyl sulfide, diisopropyl disulfide, 2-mercaptoethanol, 1, 3-mercaptopropanol, 3-mercaptopropane-1, 2-diol, 1, 4-mercaptobutanol, mercaptoacetic acid, 3-mercaptopropionic acid, mercaptosuccinic acid, thioacetic acid and thiourea. Particularly preferred sulfur compounds are t-butyl mercaptan, ethyl thioglycolate, mercaptoethanol, mercaptopropyl trimethoxysilane or t-dodecyl mercaptan.

Aliphatic and/or araliphatic halogen compounds are, for example, n-butyl chloride, n-butyl bromide, n-butyl iodide, methylene chloride, dichloroethane, chloroform, bromoform, bromotrichloromethane, dibromomethylene chloride, carbon tetrachloride, carbon tetrabromide, benzyl chloride, benzyl bromide. Aliphatic and/or aromatic aldehydes are, for example, formaldehyde, acetaldehyde, propionaldehyde and/or benzaldehyde.

In the polymerization, an oxidizing agent may be added to help promote low gel content and high molecular weight of the resulting copolymer. The oxidizing agent may be an inorganic oxidizing agent. Particularly preferred examples are sodium persulfate, ammonium persulfate, and potassium persulfate. In a particularly preferred embodiment, the oxidizing agent is free of t-butyl hydroperoxide.

The selected oxidizing agent may be present in an amount as low as 0.00001 wt%, 0.001 wt%, 0.1 wt%, 0.2wt%, 0.3 wt%, or as high as 0.4 wt%, 0.5wt%, 1 wt%, 2wt%, 3 wt%, or 5wt%, based on the total weight of the monomers.

The emulsion polymerization is generally carried out at 50 to 110 ℃, preferably 50 to 90 ℃. The polymerization medium may consist of water alone or in addition of a mixture of water and a water-miscible liquid such as methanol. Preferably, only water is used. The emulsion polymerization may be carried out as a batch operation or as a feed process, including a fractionation procedure or a gradient scheme. Preference is given to a feed process in which a portion of the polymerization batch is introduced as an initial charge, heated to the polymerization temperature and polymerization is started, and the remainder of the polymerization batch is then fed to the polymerization zone, usually via a plurality of spatially separated feeds, wherein one or more of the feeds comprises the monomers in pure form or in emulsified form, this feed being carried out continuously, in stages or subjected to a concentration gradient, the polymerization being maintained. In the polymerization, polymer seeds may also be included in the initial charge, for example, in order to set the particle size more effectively.

The manner in which the initiator is added to the polymerization vessel during the free radical aqueous emulsion polymerization is known to those of ordinary skill in the art. It may be contained entirely in the initial charge to the polymerization vessel or it may be introduced continuously or in stages at the rate of consumption during the free radical aqueous emulsion polymerization. This depends on the chemical nature of the initiator system and also on the polymerization temperature, respectively. Preferably, a portion thereof is included in the initial charge and the remainder is supplied to the polymerization zone at the rate at which it is consumed. To remove residual monomers, it is customary to add the initiator also after the end of the actual emulsion polymerization, i.e. after a monomer conversion of at least 95%. With respect to the feed process, the individual components can be added to the reactor from above, laterally or from below through the bottom of the reactor.

The emulsion polymerization may also optionally be followed by a drying step to remove moisture. The drying step may also be combined with an additional optional crosslinking step, which may be performed during or after the drying step. The crosslinking step may include activating the crosslinking agent by a drying process. Suitable crosslinking agents include dihydrazides, diamines, polyisocyanates, melamine-formaldehyde resins and metal ion salts. The crosslinking step may also include the use of Ultraviolet (UV) light, increasing temperature, or adding a catalyst.

In emulsion polymerization, aqueous polymer dispersions are obtained having a solids content of generally from 15% to 75% by weight, preferably from 40% to 75% by weight. For a high space-time yield of the reactor, dispersions with very high solids contents are preferred. In order to be able to achieve a solids content of >60 wt.%, bimodal or multimodal particle sizes should be established, since otherwise the viscosity becomes too high and dispersion can no longer be controlled. The generation of new generation particles can be achieved, for example, by adding seeds (EP 81083), by adding an excess of emulsifier or by adding a miniemulsion. Another advantage associated with the combination of low viscosity and high solids content is improved coating characteristics at high solids content. The generation of one or more new generations of particles is a matter that can be done at any point in time. This time is guided by the desired particle size distribution for low viscosity.

Pressure sensitive adhesive composition

The pressure sensitive adhesive composition of the present invention comprises a pressure sensitive adhesive polymer obtainable or obtained by emulsion polymerization as described above, preferably in the form of an aqueous polymer dispersion. The pressure sensitive adhesive composition may consist of the polymer alone or of an aqueous dispersion of the polymer. Alternatively, the PSA may also contain other adjuvants, exemplified by fillers, dyes, flow control agents, thickeners (preferably associative thickeners), defoamers, crosslinkers, plasticizers, pigments, wetting agents or tackifiers (tackifying resins). Tackifiers are known, for example, from ADHESIVE AGE, month 7 of 1987, pages 19 to 23, or Polym. Mater. Sci. Eng.61 (1989), pages 588 to 592. In order to more effectively wet the surface, the PSA may in particular comprise wetting aids (wetting agents), exemplified by fatty alcohol ethoxylates, alkylphenol ethoxylates, nonylphenol ethoxylates, polyoxyethylene/propylene or sodium dodecyl sulfonate. The amount of auxiliary is generally from 0.05 to 5 parts by weight, more particularly from 0.1 to 3 parts by weight (solids), per 100 parts by weight of polymer.

Tackifiers are polymeric or oligomeric auxiliaries for adhesive polymers or generally for elastomers, which increase their self-adhesion (tack, intrinsic adhesion, self-adhesion), which means that they adhere firmly to surfaces after a short, gentle application of pressure. Tackifiers are, for example, natural resins such as rosin and its derivatives or terpene resins formed by disproportionation or isomerization, polymerization, dimerization or hydrogenation. These may be present in their salt form (with, for example, monovalent or multivalent counterions (cations)), or preferably in their esterified form. The alcohol used for esterification may be a monohydric or polyhydric alcohol. Examples are methanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,2, 3-glycerol, and pentaerythritol. Also useful are hydrocarbon resins, exemplified by coumarone-indene resins, polyterpene resins, hydrocarbon resins based on unsaturated CH compounds, such as butadiene, pentene, methylbutene, isoprene, piperylene, divinyl methane, pentadiene, cyclopentene, cyclopentadiene, cyclohexadiene, styrene, alpha-methylstyrene and vinyl toluene.

Polyacrylates with low molar weights are also increasingly used as tackifiers. These polyacrylates preferably have a weight average molecular weight Mw of less than 50,000, more particularly less than 30,000. The polyacrylate preferably consists of at least 60% by weight, in particular at least 80% by weight, of C1-C8-alkyl (meth) acrylates. For example, the low molecular mass polymers and oligomers described in WO 2013/117428 have applicability, have a weight average molecular weight of less than 50,000, and a glass transition temperature of greater than or equal to-40 ℃ to less than or equal to 0 ℃, preferably greater than or equal to-35 ℃ to less than or equal to 0 ℃, can be prepared by emulsion polymerization in the presence of at least one chain transfer agent, and can be prepared from a monomer mixture containing at least 40 weight percent of at least one C1 to C20 alkyl (meth) acrylate.

Preferred tackifiers are natural or chemically modified rosins. Rosin consists essentially of abietic acid or derivatives of abietic acid. The tackifier may simply be added to the polymer dispersion. In this case, the tackifier itself is preferably in the form of an aqueous dispersion. The amount of tackifier is preferably 5 to 100 parts by weight, more preferably 10 to 50 parts by weight (solid/solid) based on 100 parts by weight of the polymer.

The pressure sensitive adhesive polymer and pressure sensitive adhesive dispersion can be used to prepare self-adhesive articles. The article is at least partially coated with PSA. After bonding, the self-adhesive article is preferably removable. The self-adhesive article may be, for example, a sheet, tape or label. Suitable backing materials are, for example, paper, polymeric films and metal foils. The self-adhesive tape of the present invention may be a single-sided coated or double-sided coated tape comprising the above-mentioned substances. Particularly preferred are self-adhesive labels. The self-adhesive labels of the present invention may be labels of paper or thermoplastic film. Contemplated thermoplastic films include films of, for example, polyolefin (e.g., polyethylene, polypropylene), polyolefin copolymers, polyester (e.g., polyethylene terephthalate) or polyacetate. The surface of the thermoplastic polymer film is preferably corona treated. The labels are coated on one side with an adhesive.

Preferred substrates for self-adhesive articles are paper and polymeric films. A particularly preferred self-adhesive article is a paper label.

The self-adhesive article is at least partially coated on at least one surface with the PSA of the invention. The adhesive dispersion can be applied by a variety of common coating methods used in various markets, including roll labels, tapes and specialized tapes, graphics and flexible packaging. These include meyer rod (Mayer rod), slot die (slot die), direct gravure, reverse gravure, single and dual chamber reverse gravure, disc or nip roll coating, knife-over-roll coating, curtain coating, and slide curtain coating. The choice of coating method will generally depend on the desired line speed, coating thickness and the required accuracy in the cross-machine direction and machine direction of the web in coating.

The adhesive dispersion is typically applied directly to facestock material (face stock material) (which may be paper, film, fabric) or more commonly to a release coated film or paper substrate (release liner) pre-coated with a specially formulated organosilicon chemical material (solvent-based, water-based, 100% solids technology) that is cured by a thermal drying process, UV light, or Electron Beam (EB). The release coating may be applied in-line during the adhesive dispersion coating application, or the method may use a pre-release coated liner.

The coated adhesive dispersion requires a heat source to remove water from the dispersion and to cause the dispersion to coalesce into a continuous strong film. This is typically accomplished by passing the coated adhesive dispersion through a gas furnace that may employ multiple zones set at different temperatures (e.g., 50 ℃ to 150 ℃) and air velocities to slowly but effectively drive off moisture. In some cases, the drying step may also use an Infrared (IR) heat source to aid in drying. The moisture content is reduced to a level such that an optimal balance of adhesive flow, adhesion and cohesion is obtained, typically at a moisture content of <3% relative to the weight of the dry dispersion, but depending on the desired product properties. More preferably, the moisture content is 2% or less.

The coating weight is preferably 0.1g to 175g, more preferably 2g to 20g solids per m ². The dry adhesive coating will be laminated to a suitable substrate by passing through a pressure jaw laminator. For example, if coated onto a release liner, the coated release liner will be laminated to a facestock, which may be of the paper or film type. In the case of self-wound tape, the release liner may have release coatings on both sides, with different release forces for unwinding, and in this case no facestock is included.

The coated substrates thus obtained are used, for example, as self-adhesive articles, such as labels, linerless labels, tapes or sheets. To this end, the backing may be slit to form a tape, label or sheet, either before or after the adhesive is applied. For subsequent use, the PSA-coated side of the substrate may be lined with a release paper, such as, for example, siliconized paper.

Substrates to which the self-adhesive article may advantageously be applied may include, for example, metal, wood, glass, paper or plastic. The self-adhesive articles are particularly suitable for bonding to packaging surfaces, cartons, plastic packages, books, windows, motor vehicle bodies or body parts. Preferred substrates are self-adhesive labels, more particularly self-adhesive paper labels and self-adhesive film labels. The backing material is paper or a polymeric film and has a first surface and a second surface, wherein the first surface is self-adhesive and at least partially coated with the PSA of the present invention, while the second surface may be printed, or the second surface or label may be at least partially colored. The coloration may be produced, for example, by coloring the coating with pigments or dyes, by color printing or in thermal paper by exposure to heat.

Examples

Example 1

Example 1 was prepared according to the following procedure. 168g of deionized ("DI") water and 4.5g of polystyrene seeds (32%) were fed to a two liter reactor equipped with a condenser, mechanical stirrer, temperature controlled thermocouple, and inlet for initiator and monomer, and heated to 85 ℃. A monomer emulsion was prepared in a separate vessel by mixing 184g DI water, 31g Disponil FES 77, 7g Calfax DB-45, and 660g of a monomer mixture comprising 95.3 wt.% 2-ethylhexyl acrylate ("2-EHA"), 4 wt.% styrene ("STY"), 0.5 wt.% methacrylic acid ("MAA"), and 0.2 wt.% diacetone acrylamide ("DAAM"). Next, a solution of a mixture of 2.3g sodium persulfate ("NaPS") in 73g DI water was added to the reactor. Immediately after the addition of the NaPS solution, the monomer emulsion was fed into the reactor. The feed was carried out for 200 minutes. After the monomer emulsion addition was complete, the reaction mixture was cooled to 80 ℃ and then a solution of 0.65g NaPS in 8.6g DI water and a solution of 1g sodium metabisulfite in 8.2g DI water was gradually added over 60 minutes via two separate feeds. After the feed was complete, the reaction was cooled to room temperature and 4.7gAerosol OT 70PG and 12g DI water were then added. The dispersion obtained was then filtered through a 150 μm mesh filter cloth and then subjected to subsequent evaluation. The glass transition temperature of the obtained dispersion was-58 ℃, the gel content was 2 wt.%, and the weight average molecular weight was 603kDa. The pH of the polymer dispersion was adjusted to 7 or more by adding ammonia water, and then a solution of 0.46g adipic Acid Dihydrazide (ADH) and 46g DI water was added to the dispersion.

Example 2

Example 2 was prepared according to the same procedure as example 1, but using 2.0g sodium persulfate as initiator. The gel content of the obtained dispersion was 4% by weight and the weight average molecular weight was 548kDa. The pH of the polymer dispersion was adjusted to 7 or more by adding ammonia water, and then a solution of 0.46g adipic Acid Dihydrazide (ADH) and 46g DI water was added to the dispersion.

Example 3

Example 3 was prepared according to the same procedure as example 1, but with 3 wt% styrene ("STY") and 1.5 wt% methacrylic acid ("MAA") in the monomer feed. The gel content of the obtained dispersion was 33% by weight and the weight average molecular weight was 354kDa. The pH of the polymer dispersion was adjusted to 7 or more by adding ammonia water, and then a solution of 0.46g adipic Acid Dihydrazide (ADH) and 46g DI water was added to the dispersion.

Example 4

Example 4 was prepared according to the same procedure as example 1, but with 3 wt.% styrene ("STY") and 1.5 wt.% 2-hydroxypropyl acrylate ("HPA") in the monomer feed. The gel content of the obtained dispersion was 1% by weight and the weight average molecular weight was 317kDa. The pH of the polymer dispersion was adjusted to 7 or more by adding ammonia water, and then a solution of 0.46g adipic Acid Dihydrazide (ADH) and 46g DI water was added to the dispersion.

Comparative example 1

Comparative example 1 was prepared according to the same procedure as example 1, but with 3 wt% styrene ("STY") and 1.5 wt% acrylamide ("AM") in the monomer feed. The gel content of the obtained dispersion was 77% by weight and the weight average molecular weight was 314kDa.

Comparative example 2

The acrylic emulsion used as comparative example 1 was available under the trade name from BASF CorporationNX 2160 is commercially available. The glass transition temperature of comparative example emulsion 1 was-58 ℃, the gel content was 54 wt.%, and the weight average molecular weight was 250kDa.

Characterization of the Dispersion

Emulsion polymerization is characterized by a non-volatile content (NV%) and Brookfield viscosity. NV% was measured gravimetrically using a CEM intelligent system 5 microwave moisture analyzer. The viscosity was measured with a Brookfield RV viscometer at 60RPM (spindle 63). Particle size was determined using DLS Microtrac with 180 ° reverse scatter angle.

The molecular weight distribution is characterized by Gel Permeation Chromatography (GPC) against a polystyrene calibration curve. 30mg of the sample was dissolved in 10mL of THF, and 100. Mu.l of the solution was filtered and injected into a column operated at a flow rate of 1.0 mL/min. The column set consisted of a series of guard columns (AGILENT PL1110-1120 PLgel 10 μm guard, 50X 7.5 mm) and two analytical columns (AGILENT PL1110-6100 PLgel Mixed-B, 300X 7.5 mm).

The gel percentage is a measure of the insoluble gel remaining after soaking. The weighed dry polymer film was placed in a 100 mesh (149 μm) gold "harris" cage and allowed to stand in excess Tetrahydrofuran (THF) for 48 hours. After 48 hours of extraction, the cages were removed from the solvent and the polymer films were dried and reweighed. This weight was divided by the original weight to give the gel percentage. Samples were run in duplicate and the results averaged.

Characterization of adhesion Properties (A-F)

(A) Formulation of the adhesive:

the pH of the polymer dispersion is adjusted to 7 or more by adding ammonia. In some cases, crosslinking of the adhesive after coating and drying is achieved by adding adipic Acid Dihydrazide (ADH) to the pH adjusted dispersion so that the ADH can react with the polymerized DAAM monomer after evaporation of water and ammonia.

(B) Laboratory coating of adhesives:

the formulated adhesive was coated on 1.5 mil PET film at 18g/m2 to 22g/m2 on a dry weight basis and dried at 115 ℃ for 4 minutes before lamination with a release liner. Adhesive performance testing was performed after conditioning the adhesive laminate overnight in a Controlled Temperature and Humidity (CTH) environment (23±2 ℃ and 50±5% relative humidity) test laboratory.

(C) Adhesion/peel test:

Samples were tested according to the F deration INternationaledes fabricants et transformateurs d' adhe sifs et Thermocollants ("FINAT") test method 1 ("FTM 1") on stainless steel, high density polyethylene ("HDPE") and B-slot corrugated board test panels. Testing under frozen (-20 ℃) and hot (50 ℃) conditions was accomplished by conditioning in a freezer or oven, respectively, after application of the adhesive strips to the test panel under CTH, and peel testing was performed immediately after removal from temperature conditioning so that the test panel remained within 3 ℃ of the conditioned temperature. The test panels may be insulated with foam bushings to further reduce their temperature drift during testing.

(D) Adhesion/tack test:

FINAT test method 9 ("FTM 9") was used for the "loop tack" initial adhesion test on stainless steel, high density polyethylene ("HDPE") and B-groove corrugated board test panels.

(E) Cohesion/shear test:

Shear resistance testing was performed on stainless steel plates using FINAT test method 8 ("FTM 8"). Qualitative failure mode: "AF" means adhesion failure for each test record. "AT" means adhesive failure from the facestock, i.e., PET film. "CF" means cohesive failure, i.e., adhesive residue on the test panel and facestock. "SF" indicates substrate failure, i.e., tearing of the substrate panel.

(F) Spindle retention test:

The FINAT test method 24 ("FTM 24") was adapted for "mandrel-hold" adhesion testing on HDPE rods of 0.5 "diameter. Here we report "lift" as the shortest distance between the lifting tab edge and the bar surface, rather than the length of the tab no longer in contact with the bar. The results of this test are highly dependent on facestock stiffness, 50# (3300 ft ² wet strength) paper was laminated to the back of each sample to provide high uniform stiffness.

TABLE 1

Peel force, lb/in, average of 5 tests

TABLE 2

Ring tack, lb/in, average of 5 tests

Sample of	Steel plate	HDPE panel	Corrugated board panel
				E1	2.79AT	1.41AF	1.99AT
E2	2.54AT	1.47AF	1.77AT
				E3	3.06AT	1.26AF	1.83AF
E4	4.15AF	2.13AF	2.09AF
				CE1	2.12AT	1.35AF	1.88AT
CE2	2.12AF	1.59AF	1.90AF

TABLE 3 Table 3

Average of static shear, hour, 5 tests

Sample of	Steel plate
		E1	9CF
E2	5.5CF
		E3	>120
E4	7.5CF
		CE1	>120
CE2	81CF

TABLE 4 Table 4

Mandrel lift, mm, average of 4 angles

Claims (37)

1. A pressure sensitive adhesive composition in the form of an aqueous polymer dispersion comprising at least one copolymer comprising:

(i) 50 to 95% by weight of at least one soft (meth) acrylate monomer having a glass transition temperature of less than 0 ℃ when polymerized as a homopolymer,

(Ii) 0 to 25% by weight of at least one monomer selected from the group consisting of C1 to C20 alkyl (meth) acrylates,

(Iii) From 0.5 to 20% by weight of styrene,

(Iv) 0.1 to 5% by weight of at least one ethylenically unsaturated acid or at least one ethylenically unsaturated anhydride,

(V) 0 to 10% by weight of other ethylenically unsaturated compounds than the monomers (i) to (iv),

Wherein the amounts of the monomers are each relative to the total amount of monomers, and

Wherein the copolymer has a gel content of less than 35 wt% based on the total weight of the composition and a weight average molecular weight of greater than 200 kDa.

2. The pressure sensitive adhesive composition of claim 1, wherein the copolymer comprises 50 to 70 weight percent of at least one soft (meth) acrylate monomer having a glass transition temperature of less than 0 ℃ when polymerized as a homopolymer, based on the total weight of the monomers.

3. The pressure sensitive adhesive composition of claim 1 wherein the soft (meth) acrylate monomer is selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, and ethyl acrylate.

4. The pressure sensitive adhesive composition according to any of the preceding claims, wherein the further ethylenically unsaturated compound (v) is selected from the group consisting of C1-C20 alkyl (meth) acrylates, hydroxyl containing monomers, vinyl esters of carboxylic acids having up to 20 carbon atoms, vinyl aromatic compounds having up to 20 carbon atoms other than styrene, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols having from 1 to 10 carbon atoms, aliphatic hydrocarbons having from 2 to 8 carbon atoms and one or two double bonds.

5. The pressure sensitive adhesive according to any one of the preceding claims, wherein the copolymer has a gel content of 0.0001 to 20 wt% based on the total weight of the composition.

6. The pressure sensitive adhesive according to any one of the preceding claims, wherein the copolymer has a gel content of 0.0001 to 10 wt% based on the total weight of the composition.

7. The pressure sensitive adhesive according to any one of the preceding claims, wherein the copolymer has a weight average molecular weight of 400kDa to 10,000 kDa.

8. The pressure sensitive adhesive according to any one of the preceding claims, wherein the copolymer has a weight average molecular weight of 1,000kda to 10,000 kda.

9. The pressure sensitive adhesive according to any of the preceding claims, wherein the copolymer has a glass transition temperature of from-65 ℃ to 0 ℃.

10. The pressure sensitive adhesive according to any of the preceding claims, wherein the copolymer is an emulsion polymer.

11. The pressure sensitive adhesive according to any of the preceding claims, wherein the copolymer further comprises a crosslinkable monomer.

12. The pressure sensitive adhesive of claim 11 wherein the crosslinkable monomer is selected from the group consisting of diacetone (meth) acrylamide, acetoacetoxyethyl methacrylate, N-methacryloyl (meth) acrylamide, and glycidyl methacrylate.

13. The pressure sensitive adhesive according to any of the preceding claims, wherein the copolymer is a single phase particle.

14. The pressure sensitive adhesive according to any one of the preceding claims, wherein the copolymer has a number average particle size of 1000nm or less.

15. A self-adhesive article comprising the pressure sensitive adhesive according to any one of the preceding claims.

16. The self-adhesive article of claim 15, wherein the self-adhesive article is a label, linerless label, tape, or adhesive sheet.

17. The self-adhesive article of claim 15 or 16, having a peel force of 0.5lb/in to 10lb/in on a steel plate at 50 ℃ according to FTM 1 test method.

18. The self-adhesive article of claim 15 or 16, having a peel force of 1.5lb/in to 10lb/in on HDPE board at 23 ℃ according to the FTM 1 test method.

19. The self-adhesive article of claim 15 or 16, having a peel force of 0.25lb/in to 10lb/in on HDPE board at 50 ℃ according to the FTM 1 test method.

20. The self-adhesive article of claim 15 or 16, having a peel force of 0.8lb/in to 10lb/in on corrugated board at 50 ℃ according to the FTM 1 test method.

21. The self-adhesive article of claim 15 or 16, having a tack adhesion of 2.0lb/in to 10lb/in on a steel plate according to FTM 9 test method.

22. The self-adhesive article of claim 15 or 16, wherein after 1 day there is a mandrel lift of 0.01mm to 0.7mm on a 0.5"hdpe rod according to FTM 24 test method.

23. The self-adhesive article of claim 15 or 16, wherein after 7 days there is a mandrel lift of 0.01mm to 0.95mm on a 0.5"hdpe rod according to the FTM 24 test method.

24. A process for preparing an aqueous polymer dispersion, the process comprising:

polymerizing a monomer mixture comprising:

(i) 50 to 95% by weight of at least one soft (meth) acrylate monomer having a glass transition temperature of less than 0 ℃ when polymerized as a homopolymer,

(Ii) 0 to 25% by weight of at least one monomer selected from the group consisting of C1 to C20 alkyl (meth) acrylates,

(Iii) From 0.5 to 20% by weight of styrene,

(Iv) 0.1 to 5% by weight of at least one ethylenically unsaturated acid or at least one ethylenically unsaturated anhydride,

(V) 0 to 10% by weight of other ethylenically unsaturated compounds than the monomers (i) to (iv),

Wherein the amounts of the monomers are each relative to the total amount of monomers,

Copolymers having a polymer gel content of less than 35 wt% and a weight average molecular weight of greater than 200kDa based on the total weight of the composition are prepared.

25. The method of claim 24, wherein the copolymer comprises 50 wt% to 70 wt% of at least one soft (meth) acrylate monomer based on the total weight of the monomers, wherein the soft (meth) acrylate monomer has a glass transition temperature of less than 0 ℃ when polymerized as a homopolymer.

26. The method of claim 24 or claim 25, further comprising adding an oxidizing agent during polymerization.

27. The method of claim 26, wherein the oxidizing agent is an inorganic oxidizing agent.

28. The method of claim 26, wherein the oxidizing agent is selected from the group consisting of sodium persulfate, ammonium persulfate, and potassium persulfate.

29. The method of claim 27, wherein the oxidizing agent is free of t-butyl hydroperoxide.

30. The method of any one of claims 26 to 29, wherein the oxidizing agent is present in an amount of 0.001 wt% to 0.5 wt%, based on the total weight of the monomers.

31. The method of any one of claims 24 to 30, wherein the polymerizing step is performed at a temperature of 50 ℃ to 110 ℃.

32. The method of any one of claims 24 to 31, wherein the polymerizing step is followed by a drying step.

33. The method of any one of claims 24 to 32, wherein the drying step further comprises a crosslinking step.

34. The method of claim 33, wherein the step of crosslinking comprises adding a crosslinking agent selected from the group consisting of dihydrazide, diamine, polyisocyanate, melamine-formaldehyde resin, and metal ion salt.

35. The method of claim 33, wherein the step of crosslinking comprises using UV light, increasing temperature, or adding a catalyst.

36. The method of any one of claims 33 to 35, wherein the drying step and crosslinking step are performed simultaneously.

37. The method of any one of claims 33 to 36, wherein the drying step is performed prior to the crosslinking step.