WO1997019992A1

WO1997019992A1 - Acrylic emulsions useful in printing inks

Info

Publication number: WO1997019992A1
Application number: PCT/US1996/017782
Authority: WO
Inventors: George A. Smith; Shruti Singhal; Michael D. Mcdermott
Original assignee: Henkel Corporation
Priority date: 1995-11-30
Filing date: 1996-11-19
Publication date: 1997-06-05
Also published as: AU1116797A

Abstract

An aqueous polymer emulsion composition comprising a polymer having repeating units derived from at least one monomer selected from the group consisting of alkyl acrylates and alkyl methacrylates and at least one monomer having the formula: R?1O-(C(R2)CH¿2O)m-R3-[(OCH¿2?C(R?4)H)¿n(OC(O)C(R5)=CH2)]a, wherein: R1 is an alkyl group having 1 to 6 carbon atoms, R?2 and R4¿ are independently hydrogen, methyl or ethyl, R3 is an aliphatic, aromatic or cycloaliphatic organic (preferably a hydrocarbon) radical having (e.g. from 2 to 20 carbon atoms) and a valence of 'a' plus 1, R5 is hydrogen or methyl, a is 1, 2, or 3, m is 0 to 6, and n is 0 to 6, provided that the sum of m plus n is from 1-6, is provided. Also provided are printing inks comprising a colorant and a binder for said colorant comprising an aqueous emulsion polymer of this invention.

Description

ACRYLIC EMULSIONS USEFUL IN PRINTING INKS

Field of the Invention

The present invention relates to acrylic emulsions useful in printing inks, said acrylic emulsions being prepared by emulsion polymerization of acrylic monomers.

Background of the Invention

Flexible packaging printing inks are typically printed by rotary letterpress printing using flexible rubber plates or by gravure printing using engraved chrome-plated cylinders on a wide variety of substrates, e.g. plastic films such as cellulose acetate, polyethylene, polyethylene terephthalate, polyesters, polystyrene, cellophane, glassine, tissue, aluminum foils, liners, bags, paper labels, box coverings, gift wrappings, etc.

Flexible packaging printing inks are widely used in the graphic arts industry. They offer economy, versatility, quality and simplicity and permit a roll of material to be multi-color printed in a continuous web at speeds of over 300 meters per minute and feed it directly to converting machines for slitting, forming or laminating. However, these inks must be carefully formulated so as to avoid the problems indigenous to these types of inks, e.g. chemical pinholing (failure of the ink to properly wet a plastic film surface), mechanical pinholing (the appearance of the pattern of the etched ink form roller), feathering (the appearance of stringy or ragged edges), mottle (ridged or speckled patterns), precipitation of part of the vehicle, blocking (a sticking or transfer of the image to the underside of the web), adhesion of the ink to the substrate, etc.

U.S. Patent No. 5,338,785 (Catena et al.) discloses a flexible packaging printing ink is formulated from a copolymer of polyethylene glycol methacrylate and a polyamide resin, pigment, solvent and cellulose acetate butyrate. The polyamide resin is prepared by condensing a dibasic acid mixture with a diamine mixture. The dibasic acid mixture comprises about 0.5 to 0.8 equivalents of a C_jo-C^, dibasic acid mixture comprised of about 60 to 100% dimers, 0 to 40% trimers and 0 to 5% monomers, and about 0.2-0.7 equivalents of at least one C₆-C₁₂ dibasic acid such as azelaic acid and adipic acid, while the diamine mixture comprises about 0.5-0.8 equivalents of piperazine or a substituted piperazine and the balance comprises at least one C₂-C₁₂ alkyl diamine such as ethylene diamine.

The use of acrylate ester polymers as printing ink vehicles is generally discussed in "Printing Ink Vehicles", Encyclopedia of Polymer Science and Engineering, vol. 13, pp. 368-398 (John Wiley & Sons, Inc. N.Y., N.Y., 1988). For example, at page 393, it is stated that while acrylic and methacrylic ester resins are used in water-based systems, several problems still exist, for example balancing water solubility in the ink and water resistance in the end product. U. S. Patent No. 5,075,364 (Phan et. al.) discloses a blend of a water- dissipatable polyester material, an acrylic polymer and a water-dissipatable vinyl polymer. It is stated that the acrylic polymer and the vinyl polymer must be compatible with the polyester which has a particular composition. It is stated that the polymer blends are useful for preparing ink compositions having improved block resistance, water resistance, and alcohol resistance.

U.S. Patent No. 4,921 ,899 discloses an ink composition containing a blend of a polyester, an acrylic polymer and a vinyl polymer. The water-based inks containing the blend of these polymers as a binder can significantly improve ink film properties such as alcohol resistance, block resistance and water resistance as compared to use of water-dispersible polyester alone. The polymer blends were also employed to prepare ink primers and overprint varnishes. It is stated that these polymer blends were prepared by mixing an aqueous polyester dispersion with an acrylic emulsion which contains surfactants and other additives and that the presence of surfactants in the ink formulations creates several problems related to ink stability, printing process and print quality of the ink film. A number of patent documents disclose surfactants which are polymerizable, degradable or otherwise reactive during or after use. Examples of Japanese patent documents describing reactive anionic surfactants are Iisted as follows: Patent Application Nos. 46-12472, 46-34894, 49-46291 , 56-29657, and Laid Open Application 51-30285, 54-14431 , and 56-127697. Examples of Japanese patent documents describing reactive nonionic surfactants include Laid Open Applications Nos. 50-98484 and 56-28208.

U.S. Patent No. 4,814,515 (Yokota et al.) discloses compounds prepared by the reaction of a glycidyl (meth)acrylate with a hydroxyalkylated polyalkyleneoxy fatty alcohol followed by reaction with an alkylene oxide and the use of these compounds as an emulsifier in the emulsion or dispersion polymerization of ethylenically unsaturated monomers.

U.S. Patent No. 4,390,401 (Costanza) discloses the use of acrylate or methacrylate esters of polyalkylene oxide derivatives of alkyl/aryl phenols as wetting agents and adhesion promoters in ultraviolet curable coating systems. A technical bulletin entitled "TREM LF-40: Reactive Anionic Surfactant for

Emulsion Polymerization", Henkel Coφoration, Ambler, Pennsylvania, states that TREM LF-40 is a sodium alkyl allyl sulfosuccinate with a reactive group in its molecule that will copolymerize with monomers via free radical polymerization. It is stated that the product, when used as a primary or secondary emulsifier, provides low foaming emulsions with improved water resistance. Summary of the Invention

This invention relates to an aqueous polymer emulsion composition comprising a polymer having repeating units derived from at least one monomer selected from the group consisting of alkyl acrylates and alkyl methacrylates and at least one monomer having the formula:

R¹O-(C(R²)CH₂O)_m-R³-[(OCH₂C(R⁴)H)_n(OC(O)C(R⁵)=CH₂)]_a

wherein: R¹ is an alkyl group having 1 to 6 carbon atoms,

R² and R⁴ are independently hydrogen, methyl or ethyl,

R³ is an aliphatic, aromatic or cycloaliphatic organic (preferably a hydrocarbon) radical (e.g. having from 2 to 20 carbon atoms) and having a valence of "a" plus

1 , R⁵ is hydrogen or methyl, a is 1 , 2, or 3, m is 0 to 6, and n is 0 to 6, provided that the sum of m plus n is from 1-6.

The present invention also relates to printing inks comprising a colorant and a binder for said colorant comprising an aqueous emulsion polymer of this invention.

This invention also relates to a method of coating a substrate comprising

(i) contacting a surface of a substrate with a composition comprising an ink as defined above, and (ii) drying said surface to form a film of the solids of said ink in contact with said surface. In certain embodiments, this coating process is a printing process.

Detailed Description of the Invention

The compounds of the above formula can be characterized as alkoxylated polyols that have both alkyl ether groups and (meth)acrylate ester groups, i.e.

(meth)acrylates of lower alkyl ethers of alkoxylated polyols. In the above formulas, R³ is straight, branched, or cyclic and for example can be derived from glycerol, neopentyl glycol, 1 ,6- hexanediol, trimethylolethane, trimethylolpropane and pentaerythritol, R¹ is straight or branched and for example can be methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl or n-hexyl.

Examples of monomers falling within the foregoing formula are:

mono-methoxy, ethoxylated trimethylol propane diacrylate having an average of three moles of ethylene oxide

mono-methoxy, propoxylated trimethylol propane diacrylate having an average of three moles of propylene oxide

mono-methoxy, propoxylated pentaerythritol triacrylate having an average of four moles of propylene oxide

mono-methoxy, ethoxylated neopentyl glycol monoacrylate having an average of two moles of ethylene oxide

mono-methoxy, propoxylated neopentyl glycol monoacrylate having an average of two moles of propylene oxide

mono-methoxy propoxylated glycerol diacrylate having an average of three moles of propylene oxide

mono-methoxy propoxylated hexane glycol monoacrylate having an average of two moles of propylene oxide

mono-methoxy ethoxylated 2,2-bis(p-hydroxyphenyl)propane monoacrylate having an average of four moles of ethylene oxide

mono-methoxy, ethoxylated trimethylol propane dimethacrylate having an average of three moles of ethylene oxide mono-methoxy, propoxylated trimethylol propane dimethacrylate having an average of three moles of propylene oxide

mono-methoxy, propoxylated pentaerythritol trimethacrylate having an average of four moles of propylene oxide

mono-methoxy, ethoxylated neopentyl glycol monomethacrylate having an average of two moles of ethylene oxide

mono-methoxy, propoxylated neopentyl glycol monomethacrylate having an average of two moles of propylene oxide

mono-methoxy propoxylated glycerol dimethacrylate having an average of three moles of propylene oxide

mono-methoxy propoxylated hexane glycol monomethacrylate having an average of two moles of propylene oxide

mono-methoxy ethoxylated 2,2-bis(p-hydroxyphenyl)propane monomethacrylate having an average of four moles of ethylene oxide

mono-n-butoxy ethylene glycol monoacrylate

mono-methoxy diethylene glycol monoacrylate

mono-ethoxy diethylene glycol monoacrylate

mono-n-butoxy diethylene glycol monoacrylate

mono-methoxy triethylene glycol monoacrylate

mono-methoxy tripropylene glycol monoacrylate mono-methoxy diethylene glycol monomethacrylate

mono-ethoxy diethylene glycol monomethacrylate

mono-n-butoxy diethylene glycol monomethacrylate

mono-methoxy triethylene glycol monomethacrylate

mono-methoxy tripropylene glycol monomethacrylate.

The preparation of mono-lower alkyl ethers of alkoxylated polyols can be accomplished as follows. A pressure reactor is charged with alkoxylated polyol and about one-half of the formula weight of sodium hydroxide and pressured with nitrogen. Full vacuum is applied for about one-half hour and reactor repressurized with nitrogen. Then one-half of the formula weight of a lower alkyl chloride such as methyl chloride, ethyl chloride, propyl chloride or n-butyl chloride is added slowly. Reaction is allowed to continue until pressure remains constant. Evacuation with nitrogen is carried out and the reactor is charged with the remainder of the sodium hydroxide. The reactor is evacuated, pressured with nitrogen and the remainder of the lower alkyl chloride introduced slowly. After addition, reaction continues until pressure remains constant. Then, the resulting product is washed, stripped to dryness and filtered using standard procedures.

The preparation of acrylates or methacrylates of mono-lower alkyl ethers of alkoxylated polyols can be accomplished as follows. The ether compound and acrylic or methacrylic acid are added to a reactor equipped with a stirrer, thermometer, sparge tube and azeotropic collecting equipment. The reaction is carried out in the presence of a low boiling point reflux solvent such as benzene, toluene or other aromatic and aliphatic solvents at temperatures ranging from 50°-150°C, preferably from 90°-100°C. Direct esterification is carried out with an excess of acrylic acid or slight excess of methacrylic acid being present.

Water of reaction is collected as the reaction progresses. An esterification catalyst may be employed in the esterification reaction. Examples include p-toluene sulfonic acid, methane sulfonic acid and generally any of the sulfonic or carboxylic acids or an ion exchange esterification catalyst such as divinyl benzene-styrene sulfonic acid reaction products.

Acrylation and methacrylation may also be carried out by transesterification or by utilizing a Schotten-Baumann procedure using acryloyi chloride. Procedures, inhibitors and catalysts for these alternate procedures are well known in the art and need not be repeated here.

When carrying out the esterification, transesterification or acid chloride acrylations, methacrylations, a polymerization inhibitor may be utilized. Examples of such materials include quinones, such as hydroquinone, toluhydroquinone, hydroquinone monomethyl ether (p-methoxyphenol), the various phenols, p-tert-butyl-catechol, 2,4-dicholoro-6-nitrophenol, n-propyl gallate, di-tert-butyl-p-cresol, 2,2'-methylenebis(4-methyl-6-tert-butylphenol),

1-amino-7-naphthol, p-benzoquinone, 2,6-dichloro-p-benzoquinone, 2-amino-1 ,4-naphthoquinone, 3-aminoanthraquinone, diphenylamine, p-nitrosodimethylaniline, alpha and beta-naphthylamine, nitrobenzene, phenothiazine, N-nitrosodimethylamine, hexamethylphosphoramide, n-dodecyl mercaptan, benzenethiol, 2,2-diphenyl-1-picryl-hydrazyl(phenyl hydrazine), divinylacetylene and various antimony and copper salts. Most preferred among the inhibitors are paramethoxyphenol, hydroquinone, phenothiazine, and nitrobenzene. The inhibitors should be added to the reaction mixture in the range of about 50-1000 parts per million (ppm), preferably about 100-400 ppm per 100 parts of final product (ester). Following esterification, transesterification, etc., the products may be purified by standard purification methods, including solvent extraction, washing, drying, evaporation and distillation.

It must be appreciated that when preparing alkoxylated polyol, the addition of alkylene oxide to polyol is random and the total number of moles of added alkylene oxide may be distributed equally or unequally among the hydroxyl groups of the polyol and the foregoing structures are intended to encompass such structures. Further, when a mono-lower alkyl ether is prepared from an alkoxylated polyol, the alkyl group is very likely attached to an alkoxylated hydroxyl group of the alkoxylated polyol and the foregoing structures are intended to encompass compounds prepared in this manner.

Although less preferred, if desired in the case of mono-lower alkyl ether acrylates and methacrylates of alkoxylated polyols, the mono-ether of the polyol can be prepared prior to alkoxylation and the foregoing structures are intended to encompass compounds prepared in this alternative manner.

The group (C(R²)CH₂O) where used herein is derived from alkylene oxide which can be ethylene oxide, propylene oxide, butylene oxide or mixtures of the same. Where mixtures of alkylene oxide are added to polyol, the alkoxylated polyol is referred to as heteric. Where two or more of these alkylene oxides are added to polyol sequentially, the alkoxylated polyol is referred to as block. The foregoing structures are intended to encompass such structures.

The amount of the monomer of (meth)acrylates of lower alkyl ethers of alkoxylated polyols will, in relation to the total monomers, typically be a minor amount, i.e. less than 50% by weight of the total monomers. Typically, the amount of the monomer of (meth)acrylates of lower alkyl ethers of alkoxylated polyols will range from about 0.1% to about 30% by weight, more typically from about 1% to about 20% by weight, and even more typically from about 5% to about 15% by weight of the total monomers. The aqueous polymer emulsion of this invention also contains repeating units derived from alkyl esters of acrylic acid or methacrylic acid. Such esters are described in "Acrylic and Methacrylic Ester Polymers", Enc^yclopedia of Polymer Science and Engineering, vol. 1 , pp. 234-299 (John Wiley & Sons, Inc., N.Y., N.Y., 1985), the disclosure of which is incorporated herein by reference. The polymer may also have repeating units derived from other monomers including, without limitation, ethylenically unsaturated carboxylic acids and vinyl aromatic monomers. Vinyl aromatic compounds are discussed in "Styrene Polymers" Encyclopedia of Polymer Science and Engineering, vol. 16, pp. 1-21 (John Wiley & Sons, Inc., N.Y., N.Y., 1989) and examples of such acids are described in "Acrylic and Methacrylic Acid Polymers", Encyclopedia of Polymer

Science and Engineering, vol. 1 , pp. 211-234 (John Wiley & Sons, Inc., N.Y., N.Y., 1985), the disclosures of which are incorporated herein by reference. Examples of acrylates and methacrylates that should be useful include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-amyl, isoamyl, t-amyl, n-hexyl, 2-ethylbutyl, cyclohexyl, 2-heptyi, n-octyl, 2-ethylhexyl, n-decyl, and n-undecyl. A potential utility of such monomers is the ability of one of ordinary skill, in possession of this disclosure, to use such monomers to optimize the softness of the polymer. Thus, one measure of their utility will depend upon the desired degree of softness of the polymer which, in turn, depends at least in part, on the identity and amounts of the other monomeric units. A measure of the softening or plasticizing effect of a monomer can be found by examining the glass transition temperature of a homopolymer of the monomer. Generally, a plasticizing monomer will be such that a homopolymer of the monomer will exhibit a glass transition temperature (T_g) of less than about -30°C. Thus, acrylates of a straight chain alkyl having from 3 to 11 carbon atoms or a branched chain alkyl having from 5 to 11 carbon atoms may generally be useful for plasticizing the polymer. Because of the relatively high T_g of poly(t-butyl acrylate), the use of a monomer t-butyl acrylate is unlikely to be advantageous.

Vinyl aromatic compounds comprise monovinyl aromatic hydrocarbons containing from 8 to 12 carbon atoms and halogenated derivatives thereof having halo-substituted aromatic moieties. Examples include styrene, alpha-methylstyrene, vinyl toluene (e.g. a 60/40 mixture by weight of meta- methylstyrene and para-methylstyrene), meta-methylstyrene, para- methylstyrene, para-ethylstyrene, para-n-propylstyrene, para-isopropylstyrene, para-tert-butylstyrene, ortho-chlorostyrene, para-chlorostyrene, alpha-methyl- meta-methylstyrene, alpha-methyl-para-methylstyrene, tert-butyl styrene, alpha- methyl-ortho-chlorostyrene, and alpha-methyl-para-chlorostyrene.

Further, while the preferred alkyl acrylates and methacrylates described above are preferably employed without additional comonomers for preparing ink vehicles of this invention, other monoethylenically unsaturated polymerizable monomers useful in minor proportion (e.g. less than 10% by weight of the total monomer composition) as comonomers with acrylic monomers may be useful in preparing the polymers of this invention, particularly for uses other than in ink vehicles. These monomers include the vinylidene halides, vinyl halides, acrylonitrile, methacrylonitrile, vinyl esters such as vinyl formate, vinyl acetate and vinyl propionate, and mixtures of ethylene and such vinyl esters, acrylic and methacrylic acid esters of alcohol ethers such as diethylene glycol monoethyl or monobutyl ether methacrylate, C C₁₀alkyl esters of beta- acryloxypropionic acid and higher oligomers of acrylic acid, styrene and alkyl substituted styrenes and vinyl aromatics including alpha-methyl styrene, mixtures of ethylene and other alkylolefins such as propylene, butylene, pentene and the like, vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, vinyl 2-methoxyethyl ether, vinyl 2-chloroethyl ether and the like. Additional monoethylenically unsaturated polymerizable comonomers that may be useful in preparing the polymer of the invention include hydroxy functional vinyl monomers such as 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl methacrylate, butanediol acrylate,

3-chloro-2-hydroxypropyl acrylate, 2-hydroxy propyl acrylate, and 2-hydroxypropyl methacrylate. Further examples of useful monomers include the partial esters of unsaturated aliphatic dicarboxylic acids and particularly the alkyl half esters of such acids. Examples of such partial esters are the alkyl half esters of itaconic acid, fumaric acid and maleic acid wherein the alkyl group contains 1 to 6 carbon atoms. Representative members of this group of compounds include methyl acid itaconic, butyl acid itaconic, ethyl acid fumarate, butyl acid fumarate, and methyl acid maleate. Minor amounts of other comonomers, such as adhesion promoting comonomers, may also be used. These monomers may be copolymerized with acrylic monomers to yield the polymer. Examples of alpha, beta-ethylenically unsaturated carboxylic acids which may also be useful as comonomers to prepare the polymer of the invention include acrylic acid, beta- acryloxypropionic acid and higher oligomers of acrylic acid and mixtures thereof, methacrylic acid, itaconic acid, aconitic acid, crotonic acid, citraconic acid, maleic acid, fumaric acid, alpha-chloroacrylic acid, cinnamic acid, mesaconic acid and mixtures thereof.

The preparation of aqueous dispersions of polymers by emulsion polymerization for use in coatings applications is well known in the art. The practice of emulsion polymerization is discussed in detaii in G Poehlem, "Emulsion Polymerization", Encyclopedia of Polymer Science and Technology, vol 6, pp. 1-51 (John Wiley & Sons, Inc. N Y , N Y , 1986), the disclosure of which is incoφorated herein by reference. Conventional emulsion polymerization techniques may be used to prepare the aqueous dispersion of polymers of this invention

Thus, monomers may be emulsified with an anionic, cationic or nonionic dispersing agent, using for example from about 0.05% to 10% by weight of dispersing agent on the weight of total monomers. Combinations of anionic and nonionic emulsifiers may also be used. High molecular weight polymers such as hydroxy ethyl cellulose, methyl cellulose and polyvinyl alcohol may be used as emulsion stabilizers and protective colloids, as may polyelectrolytes such as polyacrylic acid. Cationic dispersion agents include lauryl-pyridinium chlorides, cetyldimethyl amine acetate, and alkyldimethylbenzylammonium chlorides in which the alkyl group has from 8 to 18 carbon atoms. Anionic dispersing agents include, for example, the higher fatty alcohol sulfates, such as sodium lauryl sulfate, and the like; alkylaryl sulfonates such as sodium or potassium isopropylbenzene sulfonates or isopropyl naphthalene sulfonates, and the like; alkali metal higher alkyl sulfosuccinates, such as sodium octyl sulfosuccinate, sodium N-methyl-N-palmitoyltaurate, sodium oleyl isothionate, and the like; and alkali metal salts of alkylarylpolyethoxyethanol sulfates or sulfonates, such as sodium tert-octylphenoxypolyethoxyethyl sulfate having 1 to 5 oxyethylene units, and the like.

Suitable non-ionic dispersing agents include alkylphenoxy- polyethoxyethanols having alkyl groups of from about 7 to 18 carbon atoms and from about 6 to about 60 oxyethylene units, such as heptylphenoxypolyethoxyethanols, methyloctyiphenoxypolyethoxyethanols, and the like; polyethoxyethanol derivatives of methylene-linked alkyl phenols, sulfur-containing agents such as those made by condensing from about 6 to about 60 moles of ethylene oxide with nonyl mercaptan, dodecyl mercaptan, and the like, or with alkylthiophenols wherein the alkyl groups contain from 6 to 16 carbon atoms, ethylene oxide derivatives of long-chained carboxylic acids, such as lauric acid, myristic acid, palmitic acid, oleic acid, and the like, or mixtures of acids such as those found in tall oil containing from 6 to 60 oxethyiene units per molecule; analogous ethylene oxide condensates of long-chained alcohols such as octyl, decyl, lauryl, or cetyl alcohols, ethylene oxide derivative of etherified or esterified polyhydroxy compounds having a hydrophobic hydrocarbon chain, such as sorbitan monostearate containing from 6 to 60 oxethylene units; also, ethylene oxide condensates of long-chain or branched chain amines, such as dodecyl amine, hexadecyl amine, and octadecyl amine, containing from 6 to 60 oxyethylene units; block copolymers of ethylene oxide sections combined with one or more hydrophobic propylene oxide sections; and alkyl polyglycosides. Mixtures of alkyl benzenesulfonates and ethoxylated alkylphenols may be employed.

In addition to the emulsifiers set forth above, the emulsion may contain one or more suspending aids. Preferred compositions contain an acrylic resin having a substantial acid number as a suspending aid. Such resins become and contribute to the polymer film prepared from the emulsion, but do not have acceptable properties by themselves.

Preferred carboxylate polymers are vinyl aromatic/acrylic copolymers (e.g. styrene/acrylic copolymers) having a substantial acid number (typically 150-250, and preferably 180-220) and a moderate molecular weight (e.g. 6,000 to 10,000). Vinyl aromatic compounds are discussed in "Styrene Polymers" Encyclopedia of Polymer Science and Engineering, vol. 16, pp. 1-21 (John Wiley & Sons, Inc., N.Y., N.Y., 1989), the disclosure of which is incorporated herein by reference. The vinyl aromatic compounds comprise monovinyl aromatic hydrocarbons containing from 8 to 12 carbon atoms and halogenated derivatives thereof having halo-substituted aromatic moieties. Examples include styrene, alpha-methylstyrene, vinyl toluene (e.g. a 60/40 mixture by weight of meta- methylstyrene and para-methylstyrene), meta-methylstyrene, para- methylstyrene, para-ethylstyrene, para-n-propylstyrene, para-isopropylstyrene, para-tert-butylstyrene, ortho-chlorostyrene, para-chlorostyrene, alpha-methyl- meta-methylstyrene, alpha-methyl-para-methylstyrene, tert-butyl styrene, alpha- methyl-ortho-chlorostyrene, and alpha-methyl-para-chlorostyrene. At least a portion of the acrylic units of the polymer will bear free carboxyl or carboxylate groups (the carboxyl or carboxylate form depending upon the pH of the aqueous emulsion). This carboxylate functionality is solvated by the aqueous polymerization medium and, thus, contributes to the stability of the polymer suspension. The aqueous composition should be essentially free of species which can react with or form a complex with such carboxylate functionality. Such freedom will ensure that the carboxylate functionality remains solvated by the aqueous polymerization medium and/or that the carboxylate polymer will not engage in measurable crosslinking, either in the aqueous polymerization medium or the films prepared therewith. Also, emulsion stabilizers, i.e. water soluble polymers such as water-soluble polyalkylene oxides, may be useful. A preferred emulsion stabilizer is a polypropylene glycol having a molecular weight in the range of 1 ,000 to 1 ,500.

A polymerization initiator of the free radical type, such as ammonium or potassium persulfate, may be used alone or as the oxidizing component of a redox system, which also includes a reducing component such as potassium metabisulfite, sodium thiosulfate or sodium formaldehyde sulfoxylate. The reducing component is frequently referred to as an accelerator. The initiator and accelerator, commonly referred to as catalyst, catalyst system or redox system, may be used in proportion from about 0.01 % or less to 3% each, based on the weight of monomers to be copolymerized. Examples of redox catalyst systems include t-butyl hydroperoxide/sodium formaldehyde sulfoxylate/Fe(ll), and ammonium persulfate/sodium bisulfite/sodium hydrosulfite/Fe(II). The polymerization temperature may be from room temperature to 90°C, or more, and may be optimized for the catalyst system employed, as is conventional.

Emulsion polymerization may be seeded or unseeded. Seeded polymerization is preferred and tends to yield aqueous dispersions of latex polymer having more uniform physical properties than unseeded polymerization.

Chain transfer agents including mercaptans, polymercaptans and polyhalogen compounds are sometimes desirable in the polymerization mixture to moderate polymer molecular weight. Examples of chain transfer agents which may be used include long chain alkyl mercaptans such as t-dodecyl mercaptans, alcohols such as isopropanol, isobutanol, lauryl alcohol or t-octyl alcohol, carbon tetrachloride, tetrachloroethylene and trichlorobromoethane. Generally from about 0 to 3% by weight, based on the weight of the monomer mixture, may be used. The polymerization process may be a thermal or redox type; that is, free radicals may be generated solely by the thermal dissociation of an initiator species or a redox system may be used. A monomer emulsion containing all or some portion of the monomers to be polymerized may be prepared using the monomers, water and emulsifiers. A catalyst solution containing catalyst in water may be separately prepared. The monomer emulsion and catalyst solution may be co-fed into the polymerization vessel over the course of the emulsion polymerization. The reaction vessel itself may initially contain water. The reaction vessel may also additionally contain seed emulsion and further may additionally contain an initial charge of polymerization catalyst. The temperature of the reaction vessel during the emulsion polymerization may be controlled by cooling to remove heat generated by the polymerization reaction or by heating the reaction vessel. Several monomer emulsions may be simultaneously co-fed into the reaction vessel. When multiple monomer emulsions are co-fed, they may be of different monomer composition. The sequence and rates at which the diverse monomer emulsions are co-fed may be altered during the emulsion polymerization process. After addition of the monomer emulsion or emulsions has been completed, the polymerization reaction mixture may be chased (e.g. with t-butyl hydroperoxide and sodium ascorbate) to minimize the concentrations of unreacted monomer and unreacted polymerization catalyst species. The pH of the contents of the reaction vessel may also be altered during the course of the emulsion polymerization process. Both thermal and redox polymerization processes may be employed.

The inks, overprints, and primers of this invention can be prepared, for example, as disclosed in U.S. Pat. No. 4,148,779, which is incorporated herein by reference in its entirety. For example, the printing ink, overprint, or primer may be prepared as follows. The colorant is added to the binder resin or a solution or dispersion thereof and, at a properly adjusted viscosity, dispersed thereinto with ball mill, sand mill, high-shear fluid flow mill, Cowles Dissolver, Katy Mill or the like. The colorants also may be dispersed directly in the polymer by milling on a heated two-roll mill at about 220°F to 360°F. (104.44°C to 182.22 °C.) and using processing aids as desired, such as solvents or plasticizers. The viscosity and printing characteristics of the ink composition may be modified further by addition of water, solvents, plasticizers, sequestered wax, surfactants and the like to suit the particular printing needs.

The ink compositions of the present invention are not limited to any type of dye, pigment, filler, or the like, all of which are hereinafter included in the term "colorant," and can accommodate any colorant which can be dispersed, milled, mixed, blended or dissolved in any manner in either the polymer blend, water or aqueous polymer system.

The printing processes most advantageously used with the inks or varnishes are the flexographic and/or gravure printing processes. One characteristic of such printing processes, is that the aqueous dispersion of ink or varnish is supplied to said surface by a hydrophilic cylindrical transfer roll. Printing processes are described by T. Sulzberg et al., "Printing Ink Vehicles", Encyclopedia of Polvmer Science and Engineering, vol. 13, pp. 368-398 (John Wiley & Sons, Inc., N.Y., N.Y., 1988), the disclosure of which is incorporated herein by reference. Thus, this invention relates to a method of printing comprising applying a first portion of an aqueous dispersion comprised of the polymer of this invention to a first essentially impervious printing surface, said surface having recesses therein which define a resolvable image, contacting said surface with a printable substrate, and repeating said applying and said contacting with a second portion of said aqueous dispersion and a second printable surface. This method may be a letterpress printing method (wherein said recesses define raised portions of the surface which carry the aqueous dispersion to the substrate, e.g. flexography) or a gravure printing method (wherein said recesses carry the aqueous dispersion to the substrate). In flexographic printing in particular, an aqueous dispersion comprised of the polymer of this invention is applied to a flexible plate mounted on a plate cylinder. The flexible plate is then contacted with a printable substrate by rotation of the plate cylinder. In preferred embodiments, the aqueous dispersion is applied to the flexible plate with a cylindrical transfer roll which is rotated to successively take up and then apply successive portions of the aqueous dispersion.

Also provided by this invention is a printing ink comprising an polymer of this invention as a binder and a colorant distributed through the composition in an effective amount sufficient to impart a predetermined color to the resulting composition.

Thus, another ingredient of the printing ink of this invention is the colorant. The generic term colorant is specifically used in this specification in that it is intended to refer to both pigments and dyes which impart a distinct color to the composition. The purpose of any colorant is to provide contrast between the color of the substrate and the color of ink in order to provide a visually identifiable indicia on the substrate.

The colorant may be any of those which are typically used in flexographic inks such as monoazo yellows (e.g. Cl Pigment Yellows 3, 5, 98); diarylide yellows (e.g. Cl Pigment Yellows 12, 13, 14); Pyrazolone Orange, Permanent Red 2G, Lithol Rubine 4B, Rubine 2B, Red Lake C, Lithol Red, Permanent Red R, Phthalocyanine Green, Phthalo-cyanine Blue, Permanent Violet, titanium dioxide, carbon black, etc. The colorant is typically employed in amounts of about 10-45 wt. %, preferably 15-40 wt. %, based on the weight of the ink.

Typical substrates to which the coating or printing compositions of this invention may be applied include a wide variety of flexible materials. Thus, typical substrates include films of polyethylene and polypropylene generally treated for adhesion promotion; also polyester such as polyethylene terephthalate, cellophane and polyamide which may or may not be coated with

PVDC for improved barrier properties. Also contemplated within the present invention are substrates of woven and non-woven fabrics where the fibers are of cotton, polyester, polyolefin, polyamide, polyimide and the like; metallic foils such as aluminum foil; metallized films; paper and paperboard; and cellular flexible sheet material such as polyethylene foam, polyurethane foam and sponge and foam rubber. In coating the substrates, conventional techniques known per se are employed to apply the composition to the substrate. Thus, these compositions may be applied by use of any mechanical coating process such as air knife, trailing blade, knife coater, reverse roll or gravure coating technique. Most commonly, the composition is coated on the substrate and allowed to dry.

The following examples will serve to further illustrate the invention, but should not be construed to limit the invention, unless expressly set forth in the appended claims. All parts, percentages, and ratios are by weight unless otherwise indicated in context.

EXAMPLES

A polymer can be prepared as set forth below from starting materials premixed as six separate charges in the amounts set forth below.

The polymer can be prepared by the following steps. Blanket the reactor with nitrogen and add Charge 1. Heat Charge 1 in the reactor to 77° C. Pump 17.3 parts of Charge 2 from monomer tank into the reactor and add Charge 3 to the reactor and continue mixing. Meter the remaining Charge 2 from the monomer tank into the reactor over a 70 minute period at 81 °C and mix for 1.5 hour at about 80°C . Add Charge 4 to the reactor and one-third of Charge 5 and mix for 5 minutes at 80°C. Add another one-third of Charge 5 and mix for 10 minutes at 80 °C . Add remaining one-third of Charge 5 and mix for about 1 hour. Allow to cool to ambient temperature.

The latex from above 1 was used to prepare white inks by blending with an aqueous titanium dioxide dispersion. The titanium dioxide dispersion was prepared by charging the following to a high speed Waring blender for 30 minutes:

- 150 parts titanium dioxide (Unitane R-960);

- 50 parts styrenated acrylic resin at 30 wt.% solids in water, acid value: 255, M.W.: 8000; and

- 30 parts deionized water.

The resulting dispersion gave a particle size < 20 micrometers on a fineness of grind gauge. Equal parts of latex and pigment dispersion were mixed and the viscosity of the sample adjusted with deionized water to 20 seconds on a #2 shell cup. The ink was applied to the corona treated side of 1 mil polypropylene film using a hand proofer and dried using forced air gun. As a second example, this procedure was repeated using Unitane R-900 titanium dioxide pigment. The printed inks were tested for adhesion to polypropylene film using both dry and wet tape tests. Gloss measurements were determined from 60° reflectance measurements. Ten separate measurements were made on each print and the results averaged. Tape adhesion was determined using Scotch 610 tape. The tape was placed on the print in the cross direction and removed. The amount of ink removed from the print was determined for each sample and ranked (1-10, 10 = best). Both dry tape and wet tape tests (overnight in ice- water) were determined for each print. Compared to a standard latex polymer (G-CRYL 1200, Henkel Corp.), the latex prepared with the above monomer showed improved adhesion to plastic.

SAMPLE PIGMENT GLOSS DRY TAPE WET TAPE

G-CRYL 1200 R-900 41.1 4 4

G-CRYL 1200 R-960 13.4 5 2

Example 1 R-900 40.0 8 7

Example 2 R-960 21.5 7 9

Claims

WHAT IS CLAIMED IS:

1. An aqueous polymer emulsion composition comprising a polymer having repeating units derived from at least one monomer selected from the group consisting of alkyl acrylates and alkyl methacrylates and at least one monomer having the formula:

R^,O-(C(R²)CH₂O)_m-R³-[(OCH₂C(R⁴)H)_n(OC(O)C(R⁵)=CH₂)]_a

wherein:

R¹ is an alkyl group having 1 to 6 carbon atoms,

R² and R⁴ are independently hydrogen, methyl or ethyl,

R³ is an aliphatic, aromatic or cycloaliphatic organic radical having a valence of

"a" plus 1 ,

R⁵ is hydrogen or methyl, a is 1 , 2, or 3, m is 0 to 6, and n is 0 to 6, provided that the sum of m plus n is from 1-6.

2. The aqueous polymer emulsion of claim 1 wherein R³ is a hydrocarbon radical having from 2 to 20 carbon atoms.

3. The aqueous polymer emulsion of claim 1 wherein R³ derived from a member selected from the group consisting of glycerol, neopentyl glycol, 1 ,6- hexanediol, trimethylolethane, trimethylolpropane and pentaerythritol.

4. The aqueous polymer emulsion of claim 1 wherein R is methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl or n-hexyl.

5. The aqueous polymer emulsion of claim 1 wherein R⁴ is methyl.

6. The aqueous polymer emulsion of claim 1 wherein R¹ is methyl.

7. The aqueous polymer emulsion of claim 1 wherein R⁵ is methyl.

8. The aqueous polymer emulsion of claim 1 wherein said monomer having the formula is mono-methoxy propoxylated neopentyl glycol mono-acrylate having an average of 2 mole propylene oxide.

9. The aqueous polymer emulsion of claim 1 wherein said monomer selected from the group consisting of alkyl acrylates and alkyl methacrylates is 2- ethylhexyl acrylate.

10. The aqueous polymer emulsion of claim 1 wherein said monomer selected from the group consisting of alkyl acrylates and alkyl methacrylates is methyl methacrylate.

11. The aqueous polymer emulsion of claim 1 wherein said repeating units derived from at least two monomers selected from the group consisting of alkyl acrylates and alkyl methacrylates.

12. The aqueous polymer emulsion of claim 11 wherein said at least two monomers are 2-ethylhexyl acrylate and methyl methacrylate.

13. The aqueous polymer emulsion of claim 1 wherein said monomer having the formula is from about 0.1% to about 30% by weight of the total monomers.

14. The aqueous polymer emulsion of claim 1 wherein said monomer having the formula is from about 5% to about 15% by weight of the total monomers.

15. An aqueous polymer emulsion composition comprising a polymer having repeating units derived from 2-ethylhexyl acrylate, methyl methacrylate, and mono-methoxy propoxylated neopentyl glycol mono-acrylate having an average of 2 mole propylene oxide, wherein said mono-methoxy propoxylated neopentyl glycol mono-acrylate having an average of 2 mole propylene oxide is present at about 5% to about 15% of the total monomers.

16. A printing ink comprising a colorant and a binder for said colorant comprising an aqueous emulsion polymer as claimed in claim 1.

17. A method of coating a substrate comprising (i) contacting a surface of a substrate with a composition comprising a printing ink as claimed in claim 2 and (ii) drying said surface to form a film of the solids of said ink in contact with said surface.