CA1120641A - Acrylic thickener for publication gravure inks, method of preparing said thickener, ink containing the same and method of printing - Google Patents

Abstract

Abstract of the Disclosure A thickened organic solvent based system, particularly an aliphatic hydrocarbon-based liquid composition, such as an ink, the polymeric thickener therefore, a method of making the thickener by emulsion polymerization, and methods of using the thickener are disclosed. The preferred novel thickener is an addition polymer of hydrophobic monomers and hydrophilic monomers, specific preferred copolymers being of isobutyl methacrylate as the hydrophobic monomer, and one or more acids selected from acrylic acid, methacrylic acid, and itaconic acid as the hydrophilic monomer, in weight ratios of between about 99.920.1 and 90:10. The preferred acid is methacrylic acid.
Exemplified are ratios of for instance 99:1 and 98:2. The novel aliphatic hydrocarbon-based liquid composition contains an organic solvent, in most cases a pigment, a polymeri-resin binder such as limed rosin, and an acrylic thickener, preferably the novel thickener noted above. The organic solvent is preferably at least predominantly an aliphatic hydrocarbon. Mixtures thereof with an aromatic hydrocarbon are also useful. The molecular weight range of the polymer (Mw 100,000 - 2,000,000), the solubility thereof in certain solvents, the T (? 30°C). and the like are critical for use of the materials in nonpolar or weak solvent-based inks.

Description

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SPECIFICATION
BRIEF DESCRIPTION OF THE INVENTION:
This invention relates to a weak organic solvent-based liquid system, particularly an aliphatic hydrocarbon based liquid such as a colored ink, the thickener therefor, a method of making the thickener pre-ferably by emulsion polymerization, and a method of using the thickensr. The novel thickener is an acrylic copolymer of hydrophobic and hydrophilic monomers, specific preferred copolymers being of isobutyl msthacrylate and one or more acids selected from acrylic acid, methacrylic acid and itaconic acid in weight ratios of between about 99.9:0.1 and 90:10 with narrower ranges being praferred. The pre-ferred acid is methacrylic acid. Other eth~lenically un-saturated addition-polymerizable hydrophobic and hydrophilic monomers are useful in place of or with the preferred monomers, as long as the thickensr is soluble in aliphatic hydrocarbons and has molecular weight limits which cause it to function as a thickener in such a system. The organic solvent is preferably at least predominantly an aliphatic - hydrocarbon, for example a mixture thereof with a minor amount of an aromatic hydrocarbon. Particularly beneficial is the use of this thickener in gravure inks.
The uses of these weak solvent-soluble thickener polymers include:
l) Thickeners for Type A and Type B gravure inks, a preferred use.

2) In sealants and caulks for masonry ~) Textile pigment printing inks or paste

3 auxiliary.

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4) Toughening modifier for powder coatings.

5) Binder/molifier for wet and dry toner systems - Electrofax, Xerography, and related electrophotographic techniques.

6) Anti-sag additive for hot melt adhesives.
i 7) Thickeners for aliphatic hydrocarbon ! systems in general.
The thickener polymer is uncrosslin ed. That is, èssèntially no polyunsaturated addition-polymerizable monomers are used. Any inc;dental crosslinl~ing of the polymer prior to its application to a substrate. as in the ~orm of an ink, i9 such as not to destroy the compatibility of the polymer with the solvent~ binder, etc.

BACKGROUND OF '1'~ INVENTION:
Metallated rosin inks for gravure printing commonly contain ethyl cellulose or ethyl hydroxyethyl cellulose as a thickener. However, the prices of ethyl cellulose and of other cellulose derivatives has escalated to an extent that a substitute (partial or complete) is neeaed.
As is know~, limed rosin has long been used in similar inks as is noted in U.S. patent No. ~,409,449, which gives suitable dyes and pigments for use in such inks.
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U. S. patent No. 2,886,549 is concernsd with aliphatic hydrocarbon (benzine) soluble acrylic polymers for use as lacquers, inks, and textile impregnants. The polymer is solution polymerized at 90C. and 120C. which would give a low molecular weight polymer, and molecular weight (not specified) can be controlled with conventional polymerization regulators. The polymers have at least two - componsnts, with a third optional component. The first -- 2 _ i component (50-90 parts) is a cycloalkyl ester of an unsat-urated acid such as acrylic acid, methacrylic acid or fumaric acid, etc; the preferred alcohol moiety is, for example, cyclohexanol, mono-, di, or trimethyl cyclohexanol, or other substituted cyclohexanol. The second cornponent (10-50 parts) is an ester of (meth)acrylic acid with an alcohol of at least eight carbon atoms, preferably 10-18 carbons. The third and optional component (1-20 parts) is a different polymerizable compound such as vinyl acetate, styrene, etc., or one having a reactive aldehyde, epoxy, carboxy, etc. group. Of the examples, Example 1 (80 cyclo-hexyl methacrylate (C~A)~ 20 dodecyl methacrylate (~[A)) gives a polymer with the highest calculated Tg of the examples -- just below 30C. At 90 C~A and 10 DMA, the calculated (not actual) Tg would be about 45C. As else-where herein, unless specified otherwise, the Tg is the calculated value using the method of Fox (infra). At 50 CHMA and 50 ~A, this value would be -15C. Being solution polymerized at high temperature~, the polymer would have a quite low molecular weight.
A similar disclosure of alkane (ligroine or benzine) soluble acrylic polymers appears in British patent No. 772,746, which, based on CAo 51, 10925f, involves a co-polymer of 20-40~ of a higher alkyl ester such as dodecyl methacrylate or cyclohexyl methacrylate, with styrene and the like. An example is given of a polymer in parts by weight of 680 styrene, 320 dodecyl methacrylate, and 200 methyl methacrylate. This would have a calculated Tg of about 36C. and, because of the polymerization method, a very low molecular weight. If it is assumed the polymer .

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is 20 CHMA and 80 styrene, the calculated Tg is about 90C.
whereas with 20 ~MA and 80 St the figure is about 50C.
The polymer may be combined with other coating materials such as drying oils, phthalic acid resins, etc.
A condensation polymer, of a copoly~.er of acrylic acid-butyl methacrylate-methyl methacrylate with rosin modified by glycerol, fumaric acid and pentarythritol, for use as an additive in rosin inks, is the subject of Japanese patent publication No. 73/18,332 June 5, 1973.
This is reported in Chemical Abstracts 80:97528r.
Experimental use has also been made of solution-polymerized polymers of 97~ isobutyl methacrylate and 3% of a methacrylate, these were not wholly satisfactory, because solution-pclymerized polymers inherently have low molecular weights, and are comparatively inefficient thickeners.
- CA 84:46321T discloses a gravure ink of a low Tg alkane soluble acrylic resin and an alkane insoluble acrylic resin.
Another reference of possible interest is U.S.
patent No. 2,803,611, concerned with an adhesive which contains a blend of a copolymer of lauryl and hexyl meth-- acrylates with limed rosin, a wax-naphthalene condensate and a solvent, particularly a hydrocarbon solvent. These higher methacrylic acid esters give very soft (Tg ~-5C) polymers which normally cannot be produced as a powder. In addition, they have a plasticizing effect upon the hard binder and are not shown by the reference to have any ~$206~1 effect in thickening the composition, particularly so in view of the fact that clay is included in the composition to give thickening.
A Canadian patent application related to the present application is that of Swift et al, Ser. No. 295,526,~ 4~2,1S'Q 'i filed January 24, 1978; it concerns lithographic inks in which the binder is a co-polymer, having a ~n of 1,000 to 15,000, of up to 40~
isobornyl methacrylates (iBO~A) with, for example, isobutyl msthacrylate and an unsaturated acid. The ink contains an aliphatic hydrocarbon solvent.
Another patent con~erned with isobornyl meth-acrylate is U.S. patent No. 3,485,775. It discloses polymsrs containing 25-75% isobornyl methacrylate and substantial amounts of msthyl methacrylate mers, which detract from hydrocarbon solubility oE the polymer. Small amounts of styrane, ethyl acrylate, or butyl acrylate are permitted. Th~ di~closed molecular weight ran~e of the polymers of t:~is reference i3 between lO,G30 to 2,0~0,000.
No unsaturated acid monomers are suggested.
U. S. Patent No. 3681,298 discloses polymers h~ving a molscul~r weight range of l,000 to 8,500, con-taining 40-60~ 13~bornyl metha_rylats and 40-60~ of methyl methacrylate, ~tyrene, s-but~l m~thacrylate, or n-butyl methacrylate, and up to 5~ 01 an unsaturat3d acid, and the use of solvents compri~ing or consi~ting oL paraffins, e.g~, octane. Amount~ of monomers 3u^h as methyl ~eth-acrylate for such low molecular wsight polymer~ do not appear to be particu'arly critical' thus abou' 50% meth~l ~o methacrylate is useful. In the present invention, in-vo?vin~ high molecular weight pol~mers, ~uch qu~ntities of . , .

.

methyl methacrylate would resu't in i~soluble polym~rs.
The pending Canadian application S.N. 295 ,526 and the latter two patents are as3igned ~o ~he assignee of the instant applicationO
Other acrylic copo'ym rs for ink3 are also known, as sho~n for axampl3 in U.S. paLent No~ 3,764,587 (Zun'~er)0 The inhsrant viscosity of the polymer of the latter patent, a measure of molecular wsight, is betwaen 0 2 and 0.35 msasured at 25C. using 25 milligram~ of polymer in 5 cc. of chloroform, which suggest a Mw of 100,~00 or greaterO Tns monomers in the polymer are such as would yield a very rubbsry, soft product, having a very low calculated Tg as .efined herein.
The Aronof~ et al polymsr (U.S. Patsnt No.
3,271,3)l7), in one embodiment is primarily of vinyliden3 chloride, with acrylic acid, methacrylic acid, or itaconic acid, an1 with the o~tion~l inclusion of othsr monomsrs.
The vinylldene chloride copolymers have molscul~r wsights . in the range of 3,000 to 5,000. Arono~f et al also m3ntion all-acrylic copolymers, ths invention being in the inclusion of polyoxethylens ethers in m~terials su_h as inks. No method of prep~ring the acrylic polymer is disclosed nor are molecular weights. The specific acrylics disclosed ~ have extrsinely lo~ calculated Tg's. Aronoff et al disclose 25 - so'vsnts. including aliphatic hydrocarbons, aromatic hydro-carbons, ketones, alcohols, etc.
- Hoshi et al U.S. patent No. ~,912,675 concerns flexographic inks containing a filler, 5-35% by weight of an acrylic resin, 5-20% of ons or more natural resins 30 selected from copal, dammar an~ shellac, and a solvent ~lZV641 containing at lea~t two of an aromati hydroc~rbon, an al~ohol, an ester, and a glycol ethsr. The acryli~
polynsr allegedly has a molecular weight of 30,030-300,000J
a ~g of 20-105C., ~nd may be of isobutyl methacrylate and methacrylic acid (raJios nol being given). Oddly, the intrinsic vi~cosities given in the examp'es define polymers having moLecul~r weights no higher than a few hundred --no-~here near 30,000. One or the other appear3 to be in error. At column 5, line3 35-50, the d-ynamic vi3cositigs at 25C (n~ solvent specified) are given as 210-43v~ ce~ti-poises for Examples 1-6 and 240-350 centipoises for corn~rative Examples 1-5. Some of the copolymers are impractical; in order to ge'~ a Tg of > 20 with lauryl meth~crylate and acrylic acid at least 65~ acid would be 1~ needed. Such a polymer woull not be soluble in aliphatic hydrocarbons, nor w3uld it be compatible with limed rosin.
U.S. patent No. 4,005,022 to Vijayendran dis-closes a liquid toner, for developing electro3tatic images, containin~ (A) 9-9~ parts of a saturated aliphatic hydro-carbon having a Kauri-butanol number of 25-35, (B) 1-10 parts of an intsnsifier. The intensifier (B) contains (1) 1-10 parts soap, 80-97 parts aliphatic hydrocarbon, and - (3) 3-20 parts of a concentrate. The c~ncentrate (3) contains (a) 8-14 parts pigment, (b) 120-200 parts of an acrylic or other polymer, (c) 1~0-240 parts saturated hydrocarbon and (d) 0.03-6 parts pigment. The acrylic polymer "Neocryl B-707!' ~ent~oned by Vijayendran ("a ter-polymer compo~ed of vinyl toluene, i-butyl methacrylate and lauryl or stearyl methacrylate") appears to be similar to the acid-free isobutyl methacrylate-vinyl toluene co-polJmers of Brown et al U.S. patent No. 3,417,041 * Trademark '~ ' ~, (prepared by susp~nsion polymerization l~ing a chain transfer agent to give a low molecul~r weight). The u~3ful polymer3 had visco~itie~ in~-Varso ~o. 3 of from 37 to 1~0 centipoises. Similar waxy po'ymers made with higher alkyl meth~crylates and ~cid~ are shown by Finn et al U.S. patent No. 3,532,654 for floor polish emul3ions.
DETAILED DESCRIPTION OF THE I~ENTION:
According to the present invention, by utilizing a relatively specific po'ym3r compo3ition, preferably obtained by emulsion polymerization, followed by spray drying, freeze drying, etc., a solid, high molecular weigh highly efficient thickener for organic solvent syste!ns, particularly aliphatic hydrocarbon solvents, is obtained. Ths emulsion polymeriza.ion ~ives the desired high molecular weight and the monomsr proportion3 an~ sel-ection gives compatibility and efficient thicksning pxop3rties.with ~olvent~ rich in aliphatic hydrocarbon~.
In particular the thickener~ ar~ efficient thickeners for Lactol spirits (which is a trademark for solvent n~phtha, an aliphatic "naphth~" which vaporizes in the toluene evaporation range and is a blen~ of alipnatic hydrocarbons and a minor amount of aro;natic hydrocarbon3) especially when used in gravure inl~s containin~ metallated rosin as a binder. Predominantly aliphatic hydro_arbon compositions containing a high proportion o~ aromatic hydrocarbo~s such as tolu3ne are also efficiently thickened by the compositions of the invention. The thickeners of the invention are efficient in thickening non-polar solvent systems containing - other hydrocarbon3, such as toluene an~ other aromatics, as well as for oLvher non-polar solvents for example perchloro-ethylen3, and although effective, are les~ efficient ~.

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thickeners for sy3tems containing polar solvents, such as oxy~;enated solvents including acetons, isopropanol, ethyl-acetate, or ethylene glycol monobutyl ether. Preferably ths solvent contains at least 50~, mora preferably at least 70~, of a liquid alkane (sometimes referred to as an aliphatic hydrocarbon).
In the drawing, the visco3ity profiles, on a logarith:nic scale, versus solids content of copolymers of isobutyl methacrylate and methacrylic acid con~aining various amounts of acid, are sho~n to be co!nparable to T-lO ethyl cellulose, a commonly used co;nmercial thickener.
The viscosities in centipoises of the conpositions were determined by measuring th3 visco3ity of a 15~ solution of the polymer in toluene and then diluting to 10%, 7.5~, and 5% with Lactol spirits. The viscosity profile is compared to a reference curve for T-lO ethyl cellulose.
Gravure ink vehicles are known which are based on metallated rosin resins rnodified with T-10 g*rade ethyl cellulose or by ethylhydroxyethyl cellulose, as has been noted hQretofore. These inks are colnmonly used in high volums publication ~ravure printing of Sunday newspaper supplements, quality magazines, and mail order catalogues.
The thickeners of the invention nave viscosity profiles quite si~ilar to "T-lO"*ethyl celluloss (sold by Hercules, Inc.), and are co~patible with metallated rosin, e.g., limed ro3in binders, maleated rosin, etc. The conventionally used ethyl cellulose as well as the thic~eners of the in-vention have the advantages of being soluble in non-polar solvents such as a blend of Lactol spirits and toluen3 in ~o the ratios of 92:8. The high viscosity provided by the thickeners at a low solids content of the thickener in the ; .
* Trademark - 8 -solvent, o~ between about l~ and 15~ solids o~ ths thickeners on tota~ composition, gives co~patibility with metallated rosins such as limed rosin, and contributes to hold-out, gloss, adhesion, and rub and scratch resistance to the ink film. In place of limed rosin, other conven-tion31 ink binders are useful, inclu~ing rosin metallated -with other polyvalent metal conpounds, maleated rosin and other rosin esters, terpene resins, and ths like. The weight ratios of resinous binder:solvent:thickener are between O and ~0 parts binder,preferably at least l part binder:4 and 100 parts solvent: l part thickener, by weig'nt.
Usu~lly, in an ink at least 1 part binder per 1 part of thickener is used. Preferably the ratios are 5-35 binler:
5-80 solvent: 1 thickener. The total thicksner comprises 50~-10~% of the addition polymerized thickener of the invsntion, optionally with ~50~ of the prior art thickeners ethyl cellulose an~/or ethy] hydroxyethyl cellulose.
Ths amoun' of dye or pigment is varied as needed. Other conventional additives may be used.
The thickener i5 an addition polymer of ethyl-enically unsaturated (A) hydrophobic monomers being within : the hydrogen bon~ing class (defined hereinbelow) of from moderate to poor and (B) hydrophilic mono~ers being in the strong hydrogen bonding class in a ratio of between 90 (A):
10 (B) and 99.9 (A):O.l (B), at least about 60% of the those who3e homopolymer3 have hydrophobic monomer(s) (A) are ~ a solubility parameter of ~ 8.8, any oth~r hydrophobic monomer(s) being such as to not destroy the organic solvsnt solubility of the thickener polymer. The hydrophilic mononer(s) (B) preferably compriss 3 at least a predoninant proportion of monomers containing at least one of a.carboxylic acid group and a sulfonic _ g _ .~ , r -~206~

acid group, although other hydrophilic monomers are useful.
Preferably the hydrophobic monomer is selested from at least one of a C~-C20 straight or branched chain alkyl or cycloalkyl ester of methacrylic acid or p~oviding homopolymers acrylic acid, each/having a solubility parameter of ~8.8, hydrophobic styrene and vinyl toluene. Particularly preferred/monomers (A) are ~inyl boluene and ~tyrene and especially those whose polymers have hom~ a solubility parameter of ~8.8 selected from . _-butyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, t-butyl acrylate, i-bornyl methacrylate i-bornyl acrylate, _-propyl methacrylate, dicyclopentenyl methacrylate, - dicyclopentenyl acrylate.
Most highly preferred is i_butyl methacrylate.
Preferably the hydrophilic monomer is selected from acrylic acid, methacrylic acid, itaconic acid, and vinyl sulfonic acid. Methacrylic acid is most highly preferred, ône reason being its particularly high efficiency in this use; for example, the acrylic and analog i9 much~less efficient. The unsaturated carboxylic acid may be a simple monocarboxylic acid, a polycarboxylic acid, or may be a partial ester or half amide of such a,~-unsaturated polycarboxylic acids, and salts thereof with a volatile base such as ammonia, or with a volatile water-soluble amine such as dimethylamine, triethylamine, tri-~0 ethanolamine, morpholine, N-methyl morpholine, picoline, 1~

and the like. ExampLes of copolymerizable ethylenically ` unsaturated monocarboxylic or polyca.rboxylic acids are sorbic, : acryloxyacetic, acryloxypropionic. cLnnamic, vinyl furoic, a-chlorosorbic, methacryloxypropionic, methacryloxyacetic,; 5 p-vinylbenzoic, acrylic, methacrylic, maleic, fumaric, ~ aconitic, atropic, crotonic, and itaconic acid, or mixtures.~. thereof, with itaconic acid and the ~-~-unsaturated mono-f. carboxy.ic acids, particularly methacrylic acid an~ acrylicacid, being preferred. Other copolym~rizab~e acid monomers include the alkyl half esters or partial esters of unsat-urated polycarboxylic acids such as of itaconic acid, maleic acid, and fumaric acid~ or th3 partial amides thereof with C2-C4 amines. Preferred half esters ara th3 lower alkyL
. (Cl to C8) esters such as methyl acid itaconate, butyl aciditaconate, methyl acid funarate, butyl acid fumarate, methyl acid maleate, and butyl acid maleate. Such partial esters ~` and partial amides are considered to be "a-~-unsaturated monocarboxylic acids," and the term as used herein includes such esters and amides. Typical hydrophilic monomers, in addition to or even in place of those containing a sulfonic acid or -COOH group, are one or more of the ethylenically unsaturated acrylamides or hydroxyacry'.amides,including acrylamide, methacrylamide, methylolacrylamide, methyloL-methacrylainide, hydroxyethyl acrylate, hydroxyethyl meth-acrylate, hydroxypropyl methacrylate, and hydroxypropyl acrylate.
The novel preferrsd dried emulsion copolymer of the invention is at least predominantly of l) isobutyl methacrylate an1 2) at least on3 acid selected froln the group ^onsisting of acrylic acid, msthacrylic acid and itaconic acid in the weight ratios of 1):2) of between 99.9:0.1 and gO:lO, preferabLy in a ratio between about 99.5:0.5 and 96:4 and still more preferably in a ratio between about 99.5:0.5 an~ 97.5:2.5. As noted e1sewhsre herein, ths preferred acid is methacrylic acid. Conventional emulsion polymerization is utilized and the resulting latex is processed to recover a dry solid material soluble in the organic solvent.
The viscosity of a solution of the thickener at a concentration of 15~ in toluene ranges from about ~00 to about 200,000 cps. preferably from about 500 to about 75,000 cps., more preferably about from about 750 to 10,000 cps. The weight average molecular weight (Mw) of the thickener, ~s determined by gel permeation chromatography using polymethylmethacrylate for calibration, is between about 100,000 and 2,000,000, preferably 200,000 to 2,000,000 and more preferably ~00,000 to 1,500,000. While high temperature solution polymerization cannot be utilized to prepare the polymers of the invention because low molecular weight polymers are produced, other useful routes, less preferred than emulsion polymerization, are bulk polymer-ization and suspension polymerization.
The molecular weight of typical thickener polymers, determined by gel permeation chromatography (G.P.C.) is of the order of ~w = lx106 + 0.5 x 106. Com-parison of G.P.C. molecular weight and solution viscosity (15% in toluene) of typical replacements for T-10 ethyl cellulose (98~ i~/2~ MAA) is as follows:
~w x 106 ~n x 105 Viscosity - cps.
(15~ in toluene) 1.02 2.6 1600 1.24 2.4 4800 1.40 2.25 4500 ~0 As noted above, the preferred concentration of unsaturated acid in the polymer is between 0.5~ and 2.5~.

1 ~ ~ 6~ 1 One reason for this is that at the lower solids contents in the Lactol spirits~toluene solvent noted above, below about 5 or 6~ solids, the higher acid content materials become less compatible. Another reason the acid level is found to be critical is that at higher acid levels, the thickener becomes less compatible with non-polar solvents and with limed rosin.
The metallated rosin binder or other resinous binde~ useful in the invention are well known in the ink industry as shown by the art cited above, and further des-cription thereof is not considered necessary in the present instance. Also well known are pigments, dyes and other conventional additives for inks, particularly solvent-based gravure inks.
The copolymer of the thickener is preferably made by the emulsion copolymerization of the several monomers in the proper proportions. Conventional emulsion polymer-ization techniques are described in United States patents 2,75~,280 and 2,795,564. Thus, the monomers may be emul-sified with an anionic, a cationic, or a nonionic disper-sing agent, about 0.1~ to lO~ thereof being used on the weight of total monomers. When water-soluble monomers are used, the dispersing agent serves to emulsify the other monomers. A polymerization initiator of the free radical type, such as ammonium or potassium persulfate, t-butyl hydroperoxide, cumene hydroperoxide, etc. may be used alone or in conjunction with an accelerator, such as potassium metabisulfite, or sodium thiosulfite. The initiator and accelerator, commonly referred to as catalyst, may be used in proportions of l/2 to 2~, each based on the weight of monomers to be copolymerized. The polymerization temperature may be from room temperature to 90C or more as is conventional. This polymsr ;s esssntially uncrosslinl~sl.
Examples of emulsifiers or soaps suited to the polymerization process of the present invention include alkali metal and ammonium salts of alkyl, aryl, alkaryl, and aralkyl sulfonates, sulfates, and polyether ~ulfates/
ethoxylated fatty acids, esters, alcohols, amines, amides and alkyl phenols; and complex organo-phosphoric acids, and their alkali metal and ammonium salts.
One way of describing and defining the monomers of this invention is by use of the solubility parameter concept. "Polymer Handbook", 2nd Edition, J. Brandrup and E. H. Immergut, editors (John Wiley and Sons, New York 1975) Section IV Part 15 entitled "Solubility Parameter Values" by H. Burrell, on pages IV-337 to IV-368, defines solubility parameter, : describes how it is determined or calculated, contains tables of solubility parameters and gives further references to the scientific literature on solubility parameters.
The solubility parameter is the square root of the cohesive energy density which in turn is the numerical value of the potential energy of 1 cc. of material, the potential resulting from the van der Waals attraction forces between the molecule~ in a liquid or solid. Burrell describes a number of wayq of calculating solubility parameters from experimentally determined physical constants and two ways of calculating them from the structural formula of a molecule. The structural formula methods are normally used when the data for the calculation from physical con-stants are not available or are c-,nsidered particularly unreliable. Calculation from the structural fornula B

'~ ~12V6~1 utilizes tables of group molar attraction constants such as those given on page IV-339 of the Handbook. The table of Small is preferred. See also J. L. Gardon, J. Paint Technology, 38, 43 (1966), and "Cohesive Energy Density"
in "Encyclopedia of Poly. Sci. & Tech" H. Mark et al, editors.
The solubility parameter concept may be con-sidered an extension of the old rule "like dissolves like"
recognized from the early days of chemistry. A noncross-linked polymer will normally dissolve in a solvent of similar solubility parameter and a crosslinked polymer will normally be swollen by a solvent of similar solubility parameter. Conversely, solvents with solubility pa ameters far from those of the polymers will neither dissolve nor swell the polymer. As given by Burrell the solubility parameter of polymers may be determined, among other ways, by measuring the swelling of the polymer in a series of solvents. Solubility parameter for polymers may also be estimated by calculation from the group molar attraction constants as mentioned above. In the usual situation, it is found that solvents with a range of solubility parameters around that of the polymer will dissolve the uncrosslinked polymer. Those skilled in the art have added the further-refinement of classifying solvents as poorly, moderately and strongly hydrogen bonded solvents used to dissolve a large number o~ polymers. In Iable 5 starting on page IV-345, there is given solubility parameters of a number of polymers determined by calculation and by other methods.
The following table contains a list of monomers ~o along with values (where the values were in readily avail-able sources) of their solubility parameters, the solubility ~2~6~

parameter of homopolymers of given monomers, and the hydrogen bonding class appropriate for the monomer. The solubility parameter values and hydrogen bonding class of most of these monomers are those given in Table 1 cf Burrell. Values for monomers not in Burrell's table are determined or computed following the teachings in Burrell~s writings v.s. Dimensions for the solubility parameters given in the table are the usual ones, square root of (calories per cubic centimeter). The hydrogen bonding class strong, moderate or poor is ascertained by using the method of C. M. Hansen, Journal of Paint Technology, Vol.
39, p . 104-117 and 505-514 (1967) .
High MW
Monom~r-~ Homopolymer*Hydrogen Homo-Solubility Solubility Bonding Polymer Monomer Parameter Parameter- Class T C Abbre _g Acrolein 9. 8 -- S-- Acr.
Acrylamide --- -- --165 A~
Acrylic Acid12.0 -- S~100 AA
Acrylonitrile 10. 5 13 __ 106 AN
o-Bromostyrene 9.8 -- P~- BrSt 1,3-Butadiene 7. 8 8. 2 P~ -44 Bd i-Bornyl meth-~ acrylate --- 8.2 --144 i_BOMA
i-Bornyl acrylate--- 8.2 --94 i_BOA
i_Butyl acrylate 8.5 8.7 M-24 i`-BA
n-Butyl acrylate 8.6 9.0 M-56 BA
t-Butyl acrylate --- 8.7 ---22 t-BA
n-ButyL meth-acrylate 8.2 8.8 M22 BMA
i-Butyl meth-acrylate --- 8.6 --48 _-BMA
s-Butyl meth-~ acrylate --- 8.7 --60 s-BMA

~1206~1 High MW
Monomer* Homopolymer*Hydrogen Homo-Solubility Solubility Bonding Polymer MonomerParameter Parameter Class T C Abbre.
t-Butyl meth-~ acrylate --- 8.6 -- 107 t-BMA
t-Butylaminoethyl methacrylate --- -- -- 33 t-BAEMA
o-Chlorostyrene 9.6 -- P 119 ClSt' Cyclohexyl meth-acrylate --- -- -- 66 CHMA
_-Decyl acrylate 8.2 -- M -- i-DA
Dicyclopentenyl methacrylate ~ - -- -- DCPMA
Dimethylamino ethyl methacrylate 7.0 -- S -- DMAEMA
Ethyl acrylate 9.6 9.4 M -22 EA
Ethyl meth-acrylate 8.~ 9.0 -- 65 EMA
Dihydroxypropyl methacrylate 9.0 -- S -- DHPMA
- Ethylhexyl acrylate 7.8 __ M v~-70 EHA
Fumaric acid --- -- S -- Fu~A
Fumaric half esters and half amides --- -- S
l-Hexene 7.4 -- P -- hex 2-Hydroxyethyl methacrylate 8.0 __ S 55 HEMA
! 30Hydroxypropyl methacrylate --- -- S 73 HPMA
Isoprene 7.4 -- p _7~ Ipn Isopropyl meth-acrylate --- 8.8 -- 81 i-PMA
35ItacGnic acid --- -- S -- IA
Maleic anhydride 13.6 -- S -- MAn Maleic anhydride half esters and half amides --- -- S -- --L

High MW
Monomer* Homopolymer*Hydrogen Homo-Solubility Solubility Bonding Polymer MonomerParameter Parameter Clas3 T C AbbreO
g Methacrylic acid 11.2 -- S ~ 106 MAA
Methyl acrylate 8.910.1 M 9 MA
Methyl methacrylate 8.9 9.3 M 105 M~A
Methylolacrylamide --- -- S -- MOA-100 ~ - Methylstyrene 8.5 -- P 155 MeSt Phenyl methacrylate -~ M ~ 105 PhMA
n-Propyl meth-- acrylate --- 8.8 -- 35 n-PMA
Styrene 9.3 -- P 100 St Tetradecyl acrylate --- -- -- 20 TDA
Vinyl acetate 9.0 9.4 M 3Q VAc Vinyl chloride 7.8 9.7 M 82 VCl Vinyl sulfonic acid --- -- S -- VS acid Vinyl toluene 9.1 -- P -- VTol *K. L. Hoy, J. Paint Technology 42, 76-118 (1970) and other sources.
S - Strong P = Poor M = Moderate The thickener polymers of the invention are sol-uble in C6-C10 normal alkanes at 20-25C; such solubiLity is meant wherever reference is made to solubility in aliphatic hydrocarbons. The solubility parameters of homopolymers of the main proportions o~ the monomers used are ~ 8.8, of course with the proviso that the monomer identity and quantities thereof are such as to not prevent solubility of the thickener in aliphatic hydrocarbons. For example, substantial quan-3 tities of methyl methacrylate are not used for the reason that, although the solubi1ity parameter of the monomer is about 8.8 and the hydrogen bonding class is medium, the homopolymer solubility parameter of this monomer is about 9.3 and in copolymers it may adversely ~2~

affect solubiLity of the polymeric thickener in aliphatic hydrocarbon solvents.
The Tg of the polymeric thickener is ~0C, preferably ~40C. As a practical limit, 100C. may be attained.
Molecular weight i~ determined by gel permeat-ion chromatography, utilizing polymethylmethacrylate for calibrationr further details being given below.
Second order transition temperature or glass transition temperature (Tg) is the temperature at which the polymer changes from a glassy state to a rubbery state, calculated as noted above. The calculated Tg of the polymer is determined by calculation based upon the Tg of homopolymers of individual monomers as described by Fox, Bull. Am. PhysicalSoc. 1, ~, page 123 (1956). Tables of the Tg of homopolymers are given in ~'Polymer Handboo~"
Section III, Part 2 by W. A. Lee and R. A. Rutherford.
~f course, the actual Tg may be measured by known methods.
In drying the latex to give a particulate product, any suitable method may be used, preferably involving spray-drying, but freeze-drying or other methods may also be used.
If bulk or suspension polymerization is used, suitable grinding means are used to produce granules or powders.
A gravure ink formulation useful with thickener polymers of the following examples is:
Nonvolat les Volatiles TiO2 (R-900 grade) 21.7 21.7 ~~
Limed rosin vehicle (60~
solids in Lactol spirits) 45.7 27.4 18.3 30Lactol spirits 21-7 ~~ 21.7 Thickener polymer (15~
solids in toluene) 10.9 1.6 9.3 - 100.0 50.7 49.

llZ(~41 This formulation may ~erve as a substitute for conventional Type A and Type B gravure publication inks, which are suitably formulated as follows:
Type A Type B
Material pbw pbw ~aterial pbw Pigment (organic type) 7 10 Pigment (inorganic type;
e.g., TiO2) 3 Pigment extender (e.g., limestone or clay) 20 10 , Limed rosin 38 Limed rosin 20 20 Lactol spir1ts si 40 Lactol spirits 30 Ethyl cellulo~e2 3 Ethyl hydroxyethyl cellulose 2 Toluene 0 17 Similar typical formulations are given in the publication "Printing Ink, A Multiclient Market Survey"
Hull & Co., 77 Randfield Road, Bronxville, N.Y. 10708, Augu~t 1973.
A Type A gravure ink formula i~ given in which 30 parts of limed rosin containing small amounts of wax and plasticizer are blended with 15 parts pigment and clay, containing for example 4-8% organic pigment or about 10% black pigment, with 55 part~ aliphatics such as 1actol spirits or heptane. The solvent typically contains appre-ciable amounts of aromatic solvents as impurities. Such a formulation is as shipped to the printer, who may add up to 1 part of additional solvent for each part of ink.
A practical test for suitability as a thickener for solvent sy~tem~, including gravure inks, is one in which the pigment is omitted, as in the examples herein below.
A procedure for preparing an emulsion polymer useful in the invention is as fallows:

_ 20 -., , Substance _ Parts by Weight Water 60.33 Surfactant (sodium lauryl sulfate) 0.02 IBMA (isobutyl methacrylate)38.71 MAA (methacrylic acid) 0.79 Sodium dithionite 0.02 Ammonium persulf'ate 0.13 100 . 00 Procedure:
1. Charge about 50 parts of the water to stirred reaction flas~: and heat contents.
, - ~ 2. Prepare monomer emulsion in separate vessel as listed below:
a. Charge remaining water b. Add surfactant c. Mix the monomer (98 iBMA/2 MAA) into the surfactant solution d. Stir well to form a stable monomeric emulsion.
3. Gradually add emulsion to the reactor and initiate polymerization at 80-85C. using peroxy disulfate. Maintain temperature at 80-85C. until all of the monomer has been added.
4. Hold at 80-85C. for 30 minutes.
5~ Cool the batch and pack.
Properties:
Total Solids: 40-42%
pH : 2-5 A similar procedure noted in the examples, using .

.! .

using sodium dodecyl benzene sulfonate in place of sodium lauryl sulfate is also useful. It may be important from -~ an odor standpoint to eliminate residual monomer as nearly as possible. This may be accomplished by means of reduced i 5 pressure, introducing additional initiator at the end of the reaction, adsorption of monomer by solid adsorbents, ',3 etc. Total solids content may be from about 30~ to 50~ or more. Particle size is not critical and may be from 0.05 ., to 1 in the usual case. The resulting latex is spray dried ~; 10 or freeze dried, preferably spray dried, to a powder. The latex usually has an acid pH as made, but may be neutralized or made alkaline with conventional bases, including ammonia, amines, etc. but this is not necessaryO For instance, the latex of Example 9 was neutralized with ammonia before drying whereas the others were not.
To determine compatibility of the thickener ~3 with limed rosin and solvent, the test method utilized is to determine the solution clarity and dried film clarity initially, and after 24 hours at room temperature, of ~ 20 solutions made up as follows:
{~ Solution Nonvolatiles Thickener (45~ in toluene) 8 g 3.6 g !''Limed rosin (60~ in lactol spirits) 43 g 2508 g~
Hexane/heptane 1/1 by weight 490 g 0.0 g r , .

:;

~ ' As soLvents for the thickeners of the invention, suitable aliphatic hydrocarbons (alkanes), which are the `~ preferred solvents, include ligroine (benzine, petroleum ether, coal tar light oil, petroleum naphtha), cycloalkanes such as cyclohexane and ethylcyclohexane, C5-C10 alkanes, etc., generally b~iling in the range of ~0C-175C. These !~ "weak" solvents are those which are conventional in the ~ printing ink industry.
:s Strong aromatic solvents such as xylene, benzene and toluene are not normally used in the present invention in quantities greater than about 10~ of the total solvent being thickened. The term "aliphatic hydrocarbon solvent" as used herein permits of the inclusion of such small amounts of aromatics. In some cases, a small proportion of a solvent such as toluene is inherently present in the aliphatic hydrocarbon as an impurity or may be - deliberately added. For example, some "aliphatic" hydro-~ carbons contain an aromatic impurity. Such strong solvents `i 20 are sometimes necessary, as in the case of "T-10" ethyl cellulose, which is not soluble in pure lactol spirits in the absence of small amounts of toluene. Of course, the thickener must be compatible with the binder as well as the solvent.
As may be noted from the following examples, the polymerization conditions, and those conditions in relation ! .
to proportions of monomers, are important in obtaining products having usable viscosities. Comparative Example B used a chain terminator which gave a low molecu'ar ~0 weight polymer as did Examples C and D. One distinction between comparative Example F and Example 1 is in the - 2~ _ ..

` ` ~
'` 112()64~

leve' of acid. A~ may be noted, the criteria for a u~eful product includs the vi~co~ity and molecular weight, ~olvent an~ binder compatibility, etc. Ths fol~owing Table I give~ the polymerization variable~ and monomer variable~
of example~ in accordance with the invention, and com-parative example~ o~ material~ out~ide of the invention.
_ _ .. _ .. _ . . . .. . .. . ...

t ~ .

, o ~ o ~, o o ~ ~ ~ o ;i o E~ o o I I,, ,, I Io ~ ~\
~13 o ~ ~ cu o o u~ O r~ o o ~Q o ~ o o o o o o o o o . ~

.~ o ~ oo o ~ o ~ o o o o O ~ ~ ~ C~ ~ ~ ~ C~l o O o ~3 C) ~4 o o o o o o o o o o m ~ ~. o~ co co ~
E¢~ ~E~

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o o ~3 a~a~ o ~a~
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.~ ~ O ~ ~ g ~ O
H~1 ~ O~ O ~O
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0~ ~ ~ ~¢ ~ O
8 o ~ mv~ ~o o o ~ ~ ~ co oo o~ c~ ~ c~

~ ~ c~ ~ ~ oo ~ O ,~
x Ll~ O Ll~ O

3~12~)6~ `

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~, C) ~ ~ ~ o ~ o a) a) a) ~ i o a :` ~ ~ ~
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V ~ ~ ~ ~ I
o ~
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.i ~ ~ ~ ~ r~
C) O O O L~ i o o o . ~ . . . .
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0~ ~
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o ~
c~P~ ~ ~ P~ td a) 0 r~ ~ ~ ~ V O ~
~ ~ ; ~ O I td rl ~ O ~ I ~ ~ ~
H H ~ E O ' N CU C~l O bO
O O O 0~ o~ om o~
cC I ~ ~ ¢
~ ~ ~ ~ ~ 'C ~ cC
~ ~ ~ ~ ~ ~ ~ ~ o ~ o~
o c~

~1 \\ \ ~ \ ~ \ \ ~ EO
E ~m; I ~ ~ m .~ r~ ~0 a O 0~~ ~D ~ ~ I ~ ~ c~
~ ~ ~ o~ ~ ~ , ~ ~ ~ ~ ~o ~
~ ~ ~ o ~ O
~ ~ l ~
E C~l ~ ~ ~ ! ~ ~ ~
~ v ¢ m v ~ o i~
I ~ o U~
_ 26 --t.~

~L~,Z~

AA: acrylic acid n-BA: normal butyl acrylate iBMA: isobutyl methacrylate ~` n-BMA: normal butyl methacrylate MAA: methacrylic acid ~ NaBS: sodium bisulfite } NaPS: sodium persulfate NH4PS: ammonium persulfate BTM: bistribromomethane Lykopon: sodium dithionite - FormQpon: sodium formaldehyde sulfoxylate t-B~P: tertiary butyl hydroperoxide DIBHP: diisobutyl hydroperoxide St: styrene ~ 15 CHP: cumene hydroperoxide ~ NOTE: Examples B, C, and D had imPractiall~ low -~ viscosities. As is known, the quantity of initiator, po~ymerization temperature and method, chain transfer agent, etc., influence molecular weight.
.- The viscosity properties of the polymers in solvent and of the formulated inks are given in table II.
In all cases the molecular weights (~w) of the addition-polymerized-polymeric thickeners of the invéntion as determined by gel permeation chromatography, are within the range of 100,000-2,000,000, and for the most part are within the range ~00,000-1,500,000. The products of the Comparative Examples are outside of these ranges or are unsatisfactory for other reasons.

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.
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* ~ ~ CU C~J ~ oo o ~
o ~ C~ ~

~ ~ l o o L~ o o o o o o o o o o o ~ D~ L~ U~ ~ O O O O C~ O O O O O O
* ~ F~ C~ ~ N 1~ ~ O ~ ~D O i~ O C~ O O
~r~ ?~ .
L~ O ~ ~ 1~\ ~ ~1 0 -=t O ~U ~ O C~
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o ~i ~;

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~: C) * 0 LO ~ ~ ~ U
~* ~ ~0 ~o ~ ~o P" ~ ~
* rJ~ ~ ~ r~ N ~ N ~1 P. ~'f O N ~q ~ . ~1 0~ C) ~ O ~ O o O 1~5 a) ~ ~ 0~1 0 ~ O
r. ~ ~ E~! o g~ o ~ ~ =
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L(~ o rl I

B

~Z~6fll Gel perm~ation chromatogram~ for use in e~tima-ting molecuLar weights are run on squipment co~mercially ~- marketed by Water3 Associates of Marlboro, Mas3. !'Styragel" *
column~ are availab e p~epacked in a variety of poro3ites.
A column set i~ normally compo~ed of four or five four-foot (1.22 m) section~ cho~en to cover the molecular weight range i. to be mea~ured. With column ~ets o~ thi~ length sufficient -~ resolution is obtained 90 that axial di~per3ion can bs dis-s regarded. The colu~n ~et mu~t be calibrated for ths polymsr typ9 the molecular weight of which is to be determined.
Narrow molecular weight 3tandards are availabLe for p~'y-~tyrene. Calibration curve~ for othar polymers ~uch as polymethyl methacrylate are con~tructed from the chromato-grams of broad ~amples u ing either an approximate distri-bution techniq~eL or a universal calibration curve technique2.
~i To calcu'ate the molecular weights of unknown samples a table i~ prepared of the value Wi, of ths GPC curve above bassline at equal volume incremsnts and the molecular weight Mi, read from the calibration curva at thsse volumes.
Ths weight average molec~lar weight ~w, and the number average molecuLar weight Mn, can be calculated from the~s valuss with the equation~

~w = ~WiMi ~n = Wi Wi ~-- ~Wih~i ' . ~ Wi = 1 ;,~ 25 It i9 to be realized that the molecular weight number~
given are approximate and not precise, but are valid'y used for comparative purpo~es, particularly with polymers of ~imilar compo~ition~, and u~ing the same ca'ibration ~tandard.

' * Trademark ~

2~ 6 ~1 Calibration of Gel-Permeation Column with Unfractionated Po(ymers, A. Weiss9 E. Ginsberg, J. Poly, Sci., Pt.-A-2, A note on the Universal Calibration Curve ~or Gel Permea-tion Chromatogra~hy - A Weiss, E. Ginsberg Poly Letters ~\ Unless otherwi~e stated, all parts and per- .
. centages given herein are by weight.

s:

~ , .

.~, .

`

Claims (34)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A thickened organic solvent composition containing dissolved therein a thickening amount of an addition polymer of at least one ethylenically unsaturated (A) hydrophobic monomer selected from at least one C3-C20 alkyl, cycloalkyl, or aryl ester of acrylic acid or methacrylic acid, each providing homopolymers having a solubility parameter of 8.8, vinyl acetate, vinyl chloride, styrene, alkyl-and halo-substituted styrenes and vinyl toluene, and (B) at least one unsaturated hydrophilic monomer which is selected from unsaturated monocarboxylic acids, ?.beta.- unsaturated polycarboxylic acids, partial esters of said ?,.beta. -unsaturated polycarboxylic acids, half amides of said ?.beta. -unsaturated polycarboxylic acids, and salts thereof with ammonia or with a volatile water-soluble amine, unsaturated organic sulfonic acids, acrylamides, and alkylolacrylamides, and hydroxyalkyl acrylates and methacrylates; in a ratio of between 90(A):10(B) and 99.9(A):0.1(B), at least about 60%
of the hydrophobic monomer or monomers being one whose homopolymers have a solubility parameter of 8.8, any other hydrophobic monomer(s) as defined above and all of said hydrophilic monomers being such, in quantity and nature, as to not destroy the aliphatic hydrocarbon solvent solubility of the addition polymer, the Tg of the polymer being 30°C., and the weight average molecular weight of the polymer being from about 100,000 to 2,000,000.

2. The composition of claim 1 in which said solvent contains at least 50% of a liquid saturated aliphatic hydrocarbon, said molecular weight is from 200,000 to 2,000,000, at least 60% of said hydrophobic monomer (A) is selected from at least one C3-C20 alkyl, cycloalkyl or aryl ester of acrylic acid or methacrylic acid, each providing homopolymers having a solubility parameter of 8.8, and styrene and vinyl toluene, the ethylenically unsaturated hydrophilic monomer or monomers (B) comprising at least a predominant proportion of monomers containing at least one of a carboxylic acid group and a sulfonic acid group, and said addition polymer is prepared by emulsion polymerization.

3. The composition of claim 2 in which the viscosity of a solution of 15 parts of the polymer in 85 parts of toluene is between about 300 and about 200,000 cps.

and said hydrophilic monomer (B) at least in part is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, vinylsulfonic acid, maleic anhydride, maleic acid and fumaric acid half esters with C1-C6 alcohols, and half amides with C2-C4 amines, any additional hydrophilic monomer being selected from at least one of acrylamide, methacrylamide, methylolacrylamide, methylolmethacrylamide, hydroxyethyl methacrylate or acrylate, and hydroxypropyl acrylate or methacrylate.

4. The composition of Claim 2 in which said monomer (A) is selected from i-butyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, t-butyl acrylate, i-bornyl methacrylate, i-bornyl acrylate, i-propyl-methacrylate, dicyclopsntenyl methacrylate, dicyclopentenyl acrylate, styrene, and vinyl toluene, said solvent is composed of at least about 70% of a liquid alkane, said molecular weight is from 300,000 to 1,500,000,said viscosity is from about 500 to about 75,000 cps ., and said Tg is 40°C.

5. The composition of Claim 4 in which said monomers consist essentially of said hydrophobic monomer (A) whose hompolymers have a solubility parameter of 8.8, and said hydro-philic monomer (B) is at least one of acrylic acid, meth-acrylic acid, itaconic acid and vinylsulfonic acid, present in an amount of between about 0.5% and 4% of the total monomers.

6. The composition of Claim 5 in which said monomer (A) is isobutyl methacrylate, and monomer (B) is methacrylic acid present in an amount between about 0.5%
and 2.5% of the total monomers.

7. The composition of claim 1 in the form of a printing ink containing an alkane-soluble resinous binder dissolved therein, the ratios of binder:solvent:
thickener being between 1 and 40 parts binder:4 and 100 parts solvent:1 part thickener.

8. The composition of claim 2 in the form of a printing ink containing an alkane-soluble resinous binder dissolved therein, the ratio of binder:solvent:thickener being between 1 and 40 parts binder:4 and 100 parts solvent:1 part thickener.

9. The composition of claim 3 in the form of a printing ink containing an alkane-soluble resinous binder dissolved therein, the ratio of binder:solvent:
thickener being between 1 and 40 parts binder:4 and 100 parts solvent:1 part thickener.

10. The composition of claim 4 in the form of a printing ink containing an alkane-soluble resinous binder dissolved therein, the ratio of binder:solvent:
thickener being between 1 and 40 parts binder:4 and 100 parts solvent: 1 part thickener.

11. The composition of claim 5 in the form of a printing ink containing an alkane-soluble resinous binder dissolved therein, the ratio of binder:solvent:
thickener being between 1 and 40 parts binder: 4 and 100 parts solvent:1 part thickener.

12. The composition of claim 6 in the form of a printing ink containing an alkane-soluble resinous binder dissolved therein, the ratio of binder:solvent:
thickener being between 1 and 40 parts binder:4 and 100 parts solvent: 1 part thickener.

13. The composition of claim 7 in which the binder is metallated rosin.

14. The composition of claim 8 in which the binder is metallated rosin.

15. The composition of claim 9 in which the binder is metallated rosin.

16. The composition of claim 10 in which the binder is metallated rosin.

17. The composition of claim 11 in which the binder is metallated rosin.

18. The composition of claim 12 in which the binder is metallated rosin.

19. A copolymer of isobutyl methacrylate and at least one acid selected from the group consisting of acrylic acid, methacrylic acid and itaconic acid, having a methacrylate to acid weight ratio of between about 0.1 and 90:10, the weight average molecular weight of the polymer being from 100,000 to 2,000,000, and the polymer being soluble in aliphatic hydrocarbon solvents.

20. The composition of claim 19 in which the copolymer is an emulsion polymerized polymer in dry form, said ratio is between about 99.5:0.5 and 96:4, and said molecular weight is from about 200,000 to 2,000,000.

21. The composition of claim 20 in which the acid is methacrylic acid.

22. The composition of claim 21 in which said ratio is between 99.5:0.5 and 97.5:2.5 and said molecular weight is between about 250,000 and 1,500,000.

23. A pigmented ink containing a resinous binder, a pigment or dye, an organic solvent and a thickener, said thickener being the polymer of claim 19.

24. The ink of claim 23 in which said ratio is between 99.5:0.5 and 96:4, the weight ratios of binder:
solvent:thickener being from 1 to 40 parts binder:4 to 100 parts solvent:1 part thickener.

25. The ink of claim 24 in which said ratio is between 99.5:0.5 and 97.5:2.5.

26. The ink of claim 25 in which the acid is methacrylic acid.

27, The ink of claim 23 which is gravure ink, the binder is limed rosin and the solvent is at least pre-dominantly one or more liquid aliphatic hydrocarbons.

28. The ink of claim 24 which is gravure ink, the binder is limed rosin and the solvent is at least pre-dominantly one or more liquid aliphatic hydrocarbons.

29. The ink of claim 25 which is gravure ink, the binder is limed rosin and the solvent is at least pre-dominantly one or more liquid aliphatic hydrocarbons.

30. The ink of claim 26 which is gravure ink, the binder is limed rosin and the solvent at least pre-dominantly is one or more liquid aliphatic hydrocarbons.

31. A method of preparing a thickener for non-polar solvent systems comprising emulsion polymerizing isobutyl methacrylate with at least one acid selected from the group consisting of acrylic acid, methacrylic acid and itaconic acid in a weight ratio of methacrylate to acid of between 99.9:0.1 and 90:10, under conditions to obtain a polymer having a Mw of 100,000 to 2,000,000 and then drying the resulting emulsion polymer.

32. The method of claim 31 in which the ratio is between about. 99.5:0.5 and 96:4, said conditions being such as to give a Mw of 200,000 to 2,000,000.

33. The method of claim 32 in which said acid is methacrylic acid.

34; The method of claim 33 in which said ratio is between 99.5:0.5 and 97.5:2.5, said conditions being such as to result in a Mw of from 300,000 to 1,500,000.