PRINTABLE PAPER COATING COMPOSITION

Abstract: A printable paper coating composition containing inorganic particulate such as calcium carbonate particles, an aqueous latex binder such as carboxylated styrenebutadiene copolymer and, optionally, one or more conventional additives further contains a water-insoluble, liquid aromatic compound possessing at least one hydroxyl, ether and/or ester substituent, e.g., 4-allyl-2-methoxyphenol (eugenol) and/or 1,2-dimethoxybenzene (veratrole), to improve the wet rub, dry pick and/or wet pick of the composition as applied to paper.

Description: PRINTABLE PAPER COATING COMPOSITION BACKGROUND OF THE INVENTION This invention relates to a printable aqueous latex paper coating composition and, in particular, to such a composition containing a component which enhances one or more of the functional properties of the composition as applied to paper, e.g., wet rub, dry pick and/or wet pick. Printable paper coating compositions are generally manufactured from pigments, binders (adhesives) and various additives incorporated therein for a variety of purposes. The pigment, e.g., clay or calcium carbonate particles, is dispersed with water and the binder, e.g., an aqueous latex based on styrene-butadiene copolymer and perhaps one or more other ethylenically unsaturated monomers such as itaconic acid. The pigment particles fill the spaces between the surface fibers of the paper substrate providing a smooth surface for printing while the binder causes the pigment particles to adhere to each other and to the fibers. Additives incorporated into the paper coating composition during the manufacture or during the coating operation may include such materials as defoaming agents, reticulation agents, lubricants, plasticizers, binding agents, colorants, and the like. Illustrative of the many known types of latex paper coating compositions are those described in U.S. Patent Nos. 3,575,913; 3,714,107; 3,793,244; 3,985,932; 4,010,307; 4,154,899; and, 4,284,546, the contents of which are incorporated by reference herein. SUMMARY OF THE INVENTION In accordance with the present invention, a printable paper coating composition is provided which comprises inorganic particulate, aqueous latex binder and a water-insoluble, liquid aromatic compound possessing at least one substituent selected from the group consisting of hydroxyl, ether and ester, the aromatic compound being present in an amount sufficient to improve the wet rub, dry pick and/or wet pick of paper coated with the composition compared with that of paper coated with the same composition but lacking the aromatic compound. The term "paper" is used herein iii its broadest sense and includes paper per se as well as paperboard and other types of porous webs. The term "latex" is used in its conventional sense as designating a dispersion of solid polymer particles in water which is capable of forming a film upon drying. The term "liquid" as applied to the aromatic compound component of the paper coating composition herein is intended to designate such compounds which are generally liquid at ambient temperature and pressure conditions, e.g., from about 15-25°C at atmospheric pressure. The expressions "wet rub", "dry pick" and "wet pick" refer to industry accepted testing standards for evaluating certain functional properties of a paper coating composition as applied to paper. DESCRIPTION OF THE PREFERRED EMBODIMENTS The printable paper coating composition herein contemplates the use of known and conventional pigments in the customary amounts. Suitable pigment materials include plate-shaped pigments such as mica, Kaolin clays and hydrated alumina and pigments having a very small particle size such as high quality coating clay, titanium dioxide, hydrated alumina, precipitated calcium carbonate, talc, precipitated barium sulfate, and so forth. These pigments are generally formed into an aqueous dispersion, generally at an alkaline pH, and in the presence of such dispersing agents as tetrasodium pyrophosphate, sodium hexametaphosphate and polyacrylates of low molecular weight in an amount of from 0.2 to 0.5 weight percent of total pigment(s) . The average particle size of the pigment can vary over relatively wide limits and combinations of pigments of different size, e.g., relatively coarse particles of one type of pigment admixed with relatively fine particles of another type of pigment, can be used. In general, average particle size can vary from less than about 1 micron for the finer materials to over 2 microns for the coarse materials. The total amount of pigment(s) employed will often be in the range of from about 60 to about 90 weight percent of the entire coating composition with from 70 to about 85 weight percent total pigment(s) being more usual. The binder component of the paper coating composition includes any of the aqueous latex resins which are known to be useful as pigment binders. Representative binders include the following lattices commonly employed in paper coating compositions: copolymers of butadiene such as styrene-butadiene and butadiene-acrylonitrile, styrene copolymers, isoprene copolymers, acrylo-nitrile copolymers, polyvinyl chloride, polyvinyl acetate, polyvinyl acetate copolymers, cellulose derivatives such as ethyl cellulose and cellulose acetate, acrylic polymers such as ethyl- methacrylate, butyl methylcrylate and other polyacrylates, vinylidene chloride, vinylidene chloride copolymers, maleic anhydride, ester copolymers and polyurethane. The amount of binder for a specific coating composition is determined by a variety of factors such as the relative amounts of finely divided and coarse pigment where both are present, the chemical composition of the pigmen (s), the bonding strength of the particular binder or binders being employed, the total solids of the coating composition and the coating strength required by the printing process for which the paper is intended. The selection, of an appropriate binder to satisfy a particular requirement is well known in the art. In general, an amount of aqueous latex binder should be used which will provide a coating composition possessing a viscosity of between 100 and 50,000 centipoises, and preferably between 100 and 30,000 centipoises, in order to facilitate its smooth application. Often, such viscosities will be achieved by the use of from about 7 to about 30 weight percent latex binder. The additive employed in the paper coating composition of this invention to improve the wet rub, dry pick and/or wet pick of the paper substrate coated therewith is a water-insoluble liquid aromatic compound, e.g., one possessing a benzene ring, which is substituted with at least one oxygen-containing polar substituent selected from the group consisting of hydroxyl, ether and ester, preferably not exceeding about 12 carbon atoms and more preferably not exceeding about 6 carbon atoms, and, optionally, at least one aliphatic group, preferably not exceeding about 12 carbon atoms and more preferably not exceeding about 6 carbon atoms. A preferred group of water- insoluble liquid aromatic compounds are benzene derivatives substituted with one or more alkoxy and/or hydroxyl groups and, optionally, an alkenyl group. Of this group, a more preferred group of benzene derivatives corresponds to the general formula wherein R 1 is an alkyl group of up to 12 carbon atoms, R 2 is an alkenyl group of up to 12 carbon atoms, a -COOR 3 group in which R 3 is an alkyl group of up to 12 carbon atoms or a 5 -COOROR 5 group in which R 4 is an alkylene group, R 5 is an alkyl group and the total number of carbon atoms in R 4 and R 5 does not exceed 12, and x, y and z each is the same or different and is 0, 1 or 2, with the proviso that the sum of x, y and z is at least 2. In the most preferred group of 0 benzene derivatives, R 1 is methyl or ethyl, R 2 is allyl (isopropenyl) , propenyl or -COO(CH 2 ) 2 0(CH 2 ) 3 CH 3 , x is 0 or 1, y is 0, 1 or 2 and z is 0, 1 or 2, again, with the proviso that the sum of x, y and z is at least 2. Specific benzene derivatives, including those of ς the aforementioned more preferred group, which are useful herein include the following: 2-allyl-4-methoxyphenol, 2- allyl-4-ethoxyphenol, 2-allyl-4-butoxyphenol, 2-allyl-4- dodecyloxy-phenol, 4-allyl-phenol (chavicol) , 4- propenylphenol (isochavicol) , 4-allyl-methoxybenzene (methyl Q chavicol), 4-allyl-2-methoxyphenol (eugenol), 3,4-dimethoxy- 4-allyl benzene (eugenol methyl ether), 2,4-dimethoxy-allyl benzene, eugenol benzoate, l-methoxy-4-propenyl benzene, dibutoxyethylphthalate, and the like and their combinations. Of these benzene derivatives, 4-allyl-2-methoxyphenol (eugenol) and 1,2-dimethoxy-benzene (veratrole) are preferred. The amounts of aromatic compound employed can vary from over fairly wide limits and in general will constitute from about 5 to about 25, and preferably from about 10 to about 20, weight percent of the latex binder component of the paper coating composition. In addition to the aromatic compound, the paper coating compositions of the present invention can contain one or more other additives commonly employed in paper coating compositions. Representative additives include dyes, anti-foaming agents, dispersants, lubricants and the like, present in art-recognized amounts. The paper coating composition is prepared by first combining the latex binder and aromatic compound, together with any optional components, and thereafter adding the pigment, preferably in the form of an aqueous dispersion as mentioned above, to provide a substantially homogeneous fluid mass. The coating compositions of the invention can be applied to paper or similar substrate employing machinery and techniques which are well known in the art. Thus, e.g., the coating device can be a flexible blade coater, size press. Champion coater, Massey coater, trailing blade, or the like. The paper coating composition is applied to at least one side of a paper web and the coated paper is then dried and finished in a conventional manner. The aqueous coating composition is ordinarily applied in an amount sufficient to provide from about 4 to 15 pounds of coating per ream (500 - 25 x 38 inch sheets - 3300 square feet) dry weight per side and preferably at a rate of from about 6 to about 12 pounds per ream. The paper coating composition can be applied to a paper web traveling at speeds of up to about 4000 feet per minute. The application of the coating composition can be carried out "in line" on a conventional paper machine or, in an alternative procedure, the paper can be coated on an off-machine coater. Following the application of the coating composition to the paper web, the coating is dried by any suitable means such as air drying, radiant heat, high velocity dryers, or the like. The coated web is dried until it possesses an acceptable residual water content, e.g., from about 3 to 8 percent by weight. The dried paper is then finished by conventional finishing techniques such as supercalendering, gloss calendering, brushing or any combination thereof. In the following examples which are illustrative of the printable coating composition of this invention and paper coated therewith, the materials employed in the preparation of the paper coating composition are as follows: Hydrogloss 90 (J.M. Huber Corp.) - kaolin clay, pigment Omya 65 (Omya Inc.) - fine ground natural calcium carbonate pigment Dispex N40 (Allied Colloids-Canada) - sodium salt of polyacrylic acid employed in making a stable dispersion of the Kaolin clay and calcium carbonate pigments Hercules 7L2 (Hercules, Inc.) - viscosity modifier and water-retention aid Nopco C104 (Henkel Corp.) - 50% solids dispersion of calcium stearate used as a lubricant Polysar Latex 465 (BASF Canada Inc.) - 50 wt.% aqueous latex binder based on carboxylated styrene butadiene The paper coating compositions illustrated in the examples were applied to 63 lb./ream paper (Rolland RS obtained from the Rolland Paper Company, Ontario, Canada) at a level of about 9g/m 2 and, following drying of the coatings, the properties of the coated papers were measured by the following standard procedures: Gloss - measure of reflectance of the coated paper at an angle of 75 degrees; used to judge the appearance of the sheet. Brightness - measure of whiteness of the coated paper; used to judge the appearance of the sheet. Wet-rub: measure of resistance of the coated paper to abrasion when wetted; also related to suitability for offset printing processes. Dry-pick (I.G.T. No. 3) - measure of how tenaciously the pigments are bound to the paper fiber; used to judge suitability for printing. Wet-pick (I.G.T. Wet) - same as dry pick but related to offset printing processes where the sheet is wetted several time during printing. K & N - measure of ink absorption by the coated paper; related to the ink gloss of the printed coated paper. EXAMPLE 1 The following formulation was prepared: Component Parts Hydrogloss 90 - kaolin clay Omya 65 - calcium carbonate Dispex N40 - polyacrylic acid sodium salt Hercules 7L2 - viscosity modifier Nopco C104 - calcium stearate Polysar Latex 465 - 50% carboxylated styrene-butadiene latex Total 117.6 The total solids content of this formulation was adjusted to 60 weight percent by the addition of water to provide a paper coating composition which was used as the base (control) paper coating composition in this example and each of the examples which follow. Varying amounts of additive compounds, some within and others outside the scope of the invention, were incorporated into the above base coating composition to provide differe: compositions each of which was applied to paper to provide a coating. Following drying of the coating composition, the properties of each coated paper were evaluated in accordance with the above-identified standard measurement tests. The results of the tests, in which the indicated parts of each additive is given on a basis of 100 parts of dry latex, were as follows: At 4 M/S EXAMPLE 2 Example 1 was repeated but with lower binder levels with the following results: EXAMPLE 3 Example 1 was substantially repeated with the following results: Vera rol" Dodecyl Alcohol, Tolu Control 7.5 parts IS parts 15 parts 15 .heated. 15 p Vise, *3 at 100 centipoises 417 414 478 440 735 45 pH 7.9 8.0 8.1 8.3 8.1 8. Gloss 74.7 64.6 57.6 61.6 56.0 61. Brightness 84.0 84.0 84.5 84.0 84.0 83. Wet Rub 22 53.5 83.5 62 68.5 58. K £ N 24.9 13.2 9.7 20.7 23.0 11. I.G.T. No. 3 at M/S 97 168 208 127 161 171 Wet Pick 6 3 2 4 5 1 Porosity (sees) 70 498 1025 172 108 421

Claims: WHAT IS CLAIMED IS: 1. In a printable paper coating composition containing inorganic particulate and aqueous latex binder, the improvement which comprises the presence therein of a water-insoluble aromatic compound possessing at least one substituent selected from the group consisting of hydroxyl, ether and ester, the aromatic compound being present in the paper coating composition in an amount sufficient to improve the wet rub, dry pick and/or wet pick of paper coated with the composition compared with that of paper coated with the same composition but lacking the aromatic compound. 2. The paper coating composition of Claim 1 wherein the aromatic compound possesses a benzene ring. 3. The paper coating composition of Claim 1 wherein the aromatic compound possesses a benzene ring additionally substituted with at least one aliphatic group. 4. The paper coating composition of Claim 1 wherein the aromatic compound possesses a benzene ring additionally substituted with at least one allyl group. 5. The paper coating composition of Claim 1 wherein the aromatic compound possesses the general formula wherein R 1 is an alkyl group of up to 12 carbon atoms, R 2 is an alkenyl group of up to 12 carbon atoms, a -C00R 3 group in which R 3 is an alkyl group of up to 12 carbon atoms or a -COOR 4 OR 5 group in which R 4 is an alkylene group, R 5 is an alkyl group and the total number of carbon atoms in R 4 and R 5 does not exceed 12 and x, y and z each is the same or different and is 0, 1 or 2 with the proviso that the sum of x, y and z is at least 2. 6. The paper coating composition of Claim 5 wherein R 1 is methyl or ethyl, R 2 is allyl, propenyl or -COO(CH 2 ) 2 0(CH 2 ) 3 CH 3 , x is 0 or 1, y is 0, 1 or 2 and z is 0, 1 or 2. 7. The paper coating composition of Claim 1 wherein the aromatic compound is a member of the group consisting of 2-allyl-4-methoxy-phenol, 2-allyl-4- exthoxyphenol, 2-allyl-4-butoxyphenol, 2-allyl-4- dodecyloxyphenol, 4-allyl-methoxybenzene, 4-allyl-2- methoxyphenol , 3,4-dimethoxy-4-allyl benzene, 2,4- dimethoxy-allyl benzene, eugenol benzoate, l-methoxy-4- propenyl benzene, 1,2-dimethoxybenzene and dibutoxyethylphthalate. 8. In a paper coated with a paper coating composition containing inorganic particulate and aqueous latex binder, the improvement which comprises the addition thereto of a water-insoluble aromatic compound possessing at least one substituent selected from the group consisting of hydroxyl, ether and ester, the aromatic compound being present in the paper coating composition in an amount sufficient to improve the wet rub, dry pick and/or wet pick of paper coated with the composition compared with that of paper coated with the same composition but lacking the aromatic compound. 9. The paper of Claim 8 wherein the aromatic compound possesses a benzene ring. 10. The paper of Claim 8 wherein the aromatic compound possesses a benzene ring substituted with at least one aliphatic group. 11. The paper of Claim 8 wherein the aromatic compound possesses a benzene ring with at least one allyl group. 12. The paper of Claim 6 wherein the aromatic compound possesses the general formula wherein R 1 is an alkyl group of up to 12 carbon atoms, R 2 is an alkenyl group of up to 12 carbon atoms, a -COOR 3 group in which R 3 is an alkyl group of up to 12 carbon atoms or a -COOR 4 OR 5 group in which R 4 is an alkylene group, R 5 is an alkyl group and the total number of carbon atoms in R 4 and R 5 does not exceed 12 and x, y and z each is the same or different and is 0, 1 or 2 with the proviso that the sum of x, y and z is at least 2. 13. The paper of Claim 12 wherein R 1 is methyl or ethyl, R 2 is allyl, propenyl or -COO(CH 2 ) 2 0(CH 2 ) 3 CH 3 , x is 0 or 1, y is 0, 1 or 2 and z is 0, 1 or 2. or propenyl, x is 0 or 1, y is 0, 1 or 2 and z is 0 or 1. 14. The paper of Claim 8 wherein the aromatic compound is a member of the group consisting of 2-allyl-4- methoxy-phenol, 2-allyl-4-exthoxyphenol, 2-allyl-4- butoxyphenol, 2-allyl-4-dodecyloxyphenol, 4-allyl- methoxybenzene, 4-allyl-2-methoxyphenol, 3,4-dimethoxy-4- allyl benzene, 2, 4-dimethoxy-allyl benzene, eugenol benzoate, l-methoxy-4-propenyl benzene, 1,2- dimethoxybenzene and dibutoxyethylphthalate.

Inventors: HOBBS DONALD G, SPITZER JAN J, HOBBS, DONALD, G., SPITZER, JAN, J.
Applicants: BASF CORP, BASF CORPORATION
Application year: 1991
Main classification: B32B29
IPC codes: B41M5, D21H19