MXPA06006571A - Optical brightener and method of preparing it - Google Patents

Abstract

The present invention relates generally to an improved method of preparing aqueous coating compositions including an optical brightener and a polyvinyl alcohol resin, the improvement being directed to cooking a slurry to dissolve the polyvinyl alcohol resin subsequent to the addition of optical brightener and polyvinyl alcohol resin to the slurry at a temperature above about 160°F for at least about 5 minutes. The invention enables preparation with lower water content without compromising brightness and color. Particularly preferred is the addition of dry resin and/or dry brightener to provide high solids mixtures. Another aspect of the invention is a dry, particulate blend of brightener and PVOH resin. Disclosed is a method of preparing an optical brightener/PVOH aqueous concentrate comprising the sequential steps of:(a) providing an aqueous brightener composition including water and optical brightener active ingredient, wherein the optical brightener active ingredient is typically present in the aqueous brightenercomposition in an amount of from about 10%to about 25%;(b) admixing a polyvinyl alcohol resin with said aqueous optical brightener composition in an amount of about 1 part of dry polyvinyl alcohol resin per 0.5 to 10 wet parts of aqueous brightener composition to provide a nascent aqueous concentrate of polyvinyl alcohol resin and optical brightener;and (c) cooking the aqueous concentrate to dissolve the solids typically at a temperature of from about 175°F to about 210°F for a time of from about 10 minutes to about 120 minutes to provide a conked brightener/polyvinyl alcohol concentrate.

Description

OPTICAL POLISHER AND METHOD FOR PREPARING IT CROSS REFERENCE TO THE RELATED APPLICATION This non-provisional application is a partial continuation of the US Patent Application Serial No. 10/731, 495 entitled "Polyvinyl Alcohol and Optical Brightener Concentrate", filed December 9, 2003, whose priority is claimed.

TECHNICAL FIELD OF THE INVENTION The present invention relates to a novel methodology and products for preparing polyvinyl alcohol blends (PVOH) and optical brighteners having high solids for faster production rates and easier drying. The coatings made with the compositions are especially suitable for high quality coated papers.

BACKGROUND OF THE INVENTION Paper coating compositions or coating colors are used in the paper industry to impart the desired moisture resistance, physical properties and appearance to certain grades of finished paper. In general, the coating composition is an aqueous dispersion consisting basically of mineral pigments such as clay, calcium carbonate or titanium dioxide, as well as binders of natural protein pigments, starch or synthetic polymer emulsions. Styrene-butadienes and polyvinyl acetates are examples of said synthetic emulsion binders. The coating compositions may also contain additives, such as thickeners, wetting agents and lubricants. The coating compositions are generally applied to a continuous network of material by high speed coating machines, such as knife coaters, air knife coaters, rod coaters and roller coaters. It is advantageous to use faster coaters to increase productivity and use higher solids coating compositions to reduce drying costs and improve binder distribution. Highly glossy coated paper grades typically include optical brighteners (OBs). Optical brighteners generally operate by means of the absorption of ultraviolet radiation and subsequently the immediate readmission on the visible blue-white scale. Examples of optical brighteners include UVITEX® and TINOPAL® from Ciba Specialty Chemicals, BLANKOPHOR® from Bayer, as well as HOSTALUX® and LEUCOPHOR® from Clariant. Most OBs have active ingredients corresponding to the class of stilbene compounds, as shown in Structures A, B and C: A where M can be H, an alkali metal, ammonium or magnesium and Ri represents the hydrogen, C1-C5 alkyl, C1-C5 alkoxy or halogen. Said compounds also include those of Structure B, which is indicated below: U.S. Patent No. 5,057,570 for Air Products and Chemicals of October 15, 1991, discloses a process for producing paper coating compositions using partially hydrolyzed, low molecular weight polyvinyl alcohol. The advantage of using this polymer is that no external heating is required and that it can be added as a dry solid to the aqueous pigment dispersion. This can be achieved under high friction stirring agitation, typically at speeds of 1500 rpm for 5 minutes at room temperature. U.S. Patent No. 5,830,241 to Ciba Specialty Chemicals, dated November 3, 1998, describes a liquid preparation of a fluorescent whitening agent, low MW polyethylene glycol, water and auxiliary compounds. Polyethylene glycol is in liquid form and functions as the non-volatile solvent to stabilize liquid preparations of the agent when stored at elevated temperatures (50 ° C). Low MW polyethylene glycol has a low viscosity, which produces a pumpable solution. A typical structure of the fluorescent whitening agent is: C wherein M is H, an alkali metal, ammonium or magnesium and polyvinyl alcohol (PVOH) is a preferred vehicle. U.S. Patent No. 6,521,701 to Coatex S.A.S., dated February 18, 2003, discloses a stable aqueous liquid polymer composition containing polyvinyl alcohol combined with a homopolymer or carboxylic acid copolymer in fully acidic form. It has been found that this combination of polymers optimizes the function of water retention, which activates the optical brighteners and controls the viscosity of the coating colors. This is achieved without degrading the property of water retention.

U.S. Patent No. 6,620,294 to Ciba Specialty Chemicals, dated September 16, 2003, discloses stable aqueous solutions of fluorescent whitening agents containing polyvinyl alcohol. The solutions can be prepared by mixing a wet press filter cake or dry powder of a fluorescent whitening agent with an aqueous solution of a modified or unmodified polyvinyl alcohol, with or without optional additives, as well as heating and mixing until a distribution is obtained. homogeneous Although OBs by themselves work well, the inclusion of PVOH improves their performance. In some cases, papermakers use standard PVOH grades purchased in dry form, which are then prepared to be used by cooking in conventional batch vats.

A disadvantage of this methodology is that the water used in the cooking of PVOH dilutes the coating formulation in a significant amount, which can have a negative impact on production rates. In addition, there is a cost to the mill for cooking the PVOH; and, in many cases, this cost is associated with problems, due to inadequate equipment or poorly trained operators. In general, PVOH is supplied to paper manufacturers in a variety of ways: 1) dry resin that is fired in water by the customer with solids of 20% to 30%, the advantage being that less expensive grades of PVOH, the disadvantages being those indicated above; 2) the PVOH that has been previously cooked and supplied to the customer with solids from 15% to 25%, which is costly for the paper manufacturer since it involves transporting mostly water; and 3) partially hydrolyzed grades with fine particle size that are added dry to the pigmented formulations. These latter products are relatively expensive shredded materials, but they are convenient if cooking is not an option. See U.S. Patent No. 5,057,570. See also U.S. Patent No. 6,620,294, which discloses PVOH solutions and optical brighteners prepared by thoroughly mixing the wet press cake or the dry powder of a fluorescent whitening agent with an aqueous solution of PVOH and heating. U.S. Patent 4,879,336 describes the production of aqueous pigment suspensions containing a pigment, a dispersing agent, a binder and a collagen polymer. The colligating polymer is added to the pigment dispersion in dry form. U.S. Patent 4,645,736 to Felix Schoeller Jr. GmbH & Co. Describes the production of a barrier layer for a photographic paper support. The barrier layer can be applied as an aqueous solution of a film-forming polymer such as a polyvinyl alcohol. The aqueous solution of the polymer may also include an optical brightener. French Patent Application 2,213,371 to Rhone-Poulenc describes the production of sizing solutions for paper products. The sizing solution can be prepared as a mixture of a polyvinyl alcohol and a protective colloidal agent as a starch product. The sizing solution may also contain an optical agent such as a stilbene compound. US Patent 3,759,736 to Sandoz AG discloses binding solutions for use with non-woven fabrics. The fabric is impregnated with a solution of a binder, a polyvinyl alcohol and other components. It is said that the coated fabrics are suitable for dyeing with reactive dyes, including optical brighteners. U.S. Patent 3,324,057 to Kurashiki Rayon Co. discloses paper coating compositions, including starches, dyes and polyvinyl alcohols. The compositions are prepared by mixing aqueous solutions of the starches, a pigment and an aqueous solution of the desired polyvinyl alcohol. It has been found that, in accordance with the present invention, both the optical brighteners and the relatively inexpensive PVOH grades can be incorporated directly into the water, to form a paste, followed by the cooking of the mixture to solubilize the materials and produce a Aqueous polishing composition, providing manufacturing and product options not previously possible. It is possible to use dry mixtures of PVOH resin and powdered optical brightener, or use any of the components in dry form.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, there is provided a method for preparing an aqueous concentrate of PVOH / optical brightener by means of the sequential steps of: (a) providing an aqueous brightening composition consisting basically of including water and active ingredient of optical brightener, wherein the active ingredient of optical brightener is present in the aqueous polishing composition typically in an amount of about 10% to about 25%; (b) mixing a polyvinyl alcohol resin with said aqueous optical brightening composition in an amount of about 1 part of dry polyvinyl alcohol resin per 0.50.25 to 10 wet portions of aqueous polishing composition, to provide a nascent aqueous resin concentrate. polyvinyl alcohol and optical brightener; and (c) baking the aqueous concentrate to dissolve the solids of substantially all of the PVOH resin, generally at a temperature of about 79.4 ° C to about 98.8 ° C generally for a time of about 10 minutes to about 120 minutes to provide a concentrate of polyvinyl alcohol / cooked brightener consisting basically of water, polyvinyl alcohol resin and active ingredient of optical brightener. Typically, the polyvinyl alcohol resin is mixed in an amount of about 1 part of dry polyvinyl alcohol resin by 0.5 to 10 wet portions of aqueous polish composition. The active ingredient of optical brightener is generally present in the aqueous polishing composition in an amount of about 12% to about 20% and the aqueous PVOH / optical brightener concentrate typically has a solids content of about 20% to about 75%, Based on the water content, polyvinyl alcohol and active ingredient of optical brightener of the concentrate. More typically, the polyvinyl alcohol is mixed with the aqueous optical brightener composition in an amount of about 15% to about 55% PVOH based on the combined weight of the water, the active ingredient of optical brightener and the polyvinyl alcohol resin, the concentrate having a solids content of about 30 to about 60%. Similarly, the aqueous concentrate is generally cooked to dissolve the solids at a temperature from about 85 ° C to about 96.1 ° C for a time from about 20 minutes to about 60 minutes. Suitable polyvinyl alcohol resins have viscosities of about 2 or 3 cps at about 30 or 40 cps; more preferably, in some cases, the polyvinyl alcohol resin has a viscosity of about 2 or 3 cps at about 5 7 or 8 cps, or about 3 cps at about 4 cps. The polyvinyl alcohol resin is generally hydrolyzed based on a mole percentage of about 85 80 to about 99.5 percent; typically, the polyvinyl alcohol resin is hydrolyzed based on a mole percentage of about 85 percent to about 90 percent and has a degree of polymerization of about 50 to about 25002000. A degree of polymerization of about 50 to about 1700 is more preferred because it is a degree of polymerization of about 50 to about 300. Most preferably, the polyvinyl alcohol resin is added to the aqueous polyvinyl alcohol polishing composition in substantially dry form; and, on occasions, the step of diluting the aqueous concentrate is convenient, depending on the processing characteristics sought. So, in addition, the concentrate can be applied directly to a paper substrate in a size press, if desired. The method may additionally include the step of adding polyethylene glycol to the aqueous concentrate and wherein the polyethylene glycol is added to the aqueous brightening composition or to the nascent or cooked aqueous concentrate in an amount of about 0.5 to about 2 parts by weight per dry part of polyvinyl alcohol resin. A preferred method for preparing a color layer composition includes the sequential steps of: (a) providing an aqueous brightening composition consisting essentially of water and active ingredient of optical brightener, wherein the active ingredient of optical brightener is present in the aqueous polishing composition in an amount of about 10 to about 25%; (b) mixing a polyvinyl alcohol resin with said aqueous optical brightening composition in an amount of about 1 part of dry polyvinyl alcohol resin by 0.25 to 10 wet portions of aqueous polishing composition, to provide a nascent aqueous polyvinyl alcohol resin concentrate and optical brightener; (c) cooking the aqueous concentrate to dissolve the solids at a temperature from about 79.4 ° C to about 98.8 ° C for a time from about 10 minutes to about 120 minutes, to provide a polyvinyl alcohol / cooked brightener concentrate consisting basically of water, polyvinyl alcohol resin and optical brightener compounds; and (d) mixing the cooked concentrate with an aqueous dispersion comprising color pigment and a binder resin, to produce the color layer composition. Typically, the polyvinyl alcohol resin is mixed in an amount of about 1 part of dry polyvinyl alcohol resin by 0.5 to 10 wet portions of aqueous polish composition. The method further comprises the step of applying the color layer to the paper. An aqueous concentrate of optical brightener basically consists of water, an active ingredient of optical brightener and a polyvinyl alcohol resin having a viscosity of about 3 2 cps to about 5 4 cps, wherein the aqueous concentrate has from about 20 to about 75 % solids, while the polyvinyl alcohol resin is hydrolyzed from about 85 80 to about 90 percent on a molar basis. The concentrate optionally includes auxiliaries such as dispersing agents, protective colloids, solvents for colloids and / or antifreezes, sequestering agents and the like, none of which changes the basic and novel characteristics of the concentrates. When referring to the aqueous PVOH / optical brightener concentrate, the auxiliaries also include minor amounts of binder, plasticizer, filler, water retention aids, such as carboxymethylcellulose, and the like. Typically, the polyvinyl alcohol resin has a viscosity of 3 cps at 4 cps and the aqueous concentrate has from about 25 to about 65 percent solids. The optical brightener concentrate additionally comprises polyethylene glycol in some cases, while the active ingredient of optical brightener comprises a stilbene compound. The stilbene compound can be a sulphonated stilbene compound with the formula: where X and Y are selected independently of the portions of the following table: Therefore, the active ingredient of the brightener can be disulfonated, tetrasulfonated or hexasulfonated in different modalities. In yet another aspect of the invention, an aqueous concentrate of optical brightener basically consists of water, an active ingredient of optical brightener, polyethylene glycol and a polyvinyl alcohol resin has a viscosity of about 2 cps to about 4 cps, wherein the aqueous concentrate it has from about 20 to about 75% solids and wherein the polyvinyl alcohol resin is hydrolyzed from about 80 to about 90 percent on a molar basis. The present invention additionally relates in general to improved methods for preparing aqueous compositions, including an optical brightener and a polyvinyl alcohol resin, the improvement of which is directed to bake a PVOH containing paste to dissolve the polyvinyl alcohol resin subsequent to the addition of optical brightener and polyvinyl alcohol resin at a temperature above about 71.1 ° C for at least about 5 minutes. The invention allows the preparation of formulations with low water content without compromising brilliance or color. Particularly preferred is the addition of dry resin and / or dry brightener to provide blends with high solids. Another aspect of the invention is a method that provides PVOH and optical brightener to a color layer composition without external heating. Yet another aspect of the invention is a dry blend of polish and PVOH resin particles, the details of which are described hereinafter.

BRIEF DESCRIPTION OF THE FIGURES The invention is illustrated in relation to the various figures, in which: Figures 1 to 4 are histograms showing the Hunter Color data of the coatings of examples 11, 12, as well as the comparative examples F, G; and Figures 5 to 8 are histograms showing the Hunter Color data of the coatings of examples 17, 18, as well as the comparative examples H to M.

DETAILED DESCRIPTION OF THE INVENTION The present invention is described in detail below with reference to numerous embodiments for illustrative purposes only. Modifications within the spirit and scope of the invention, set forth in the appended claims, will be readily apparent to the person skilled in the art. In some cases, the optical brightener is added to an aqueous composition as a PVOH paste in a basically dry form. In other embodiments, the polyvinyl alcohol resin is added to an aqueous optical brightener solution in a basically dry form while, in other embodiments, both the optical brightener and the polyvinyl alcohol resin are added to the water in substantially dry form, to form a pasta. In some preferred applications of the inventive process, the pasta is cooked at a temperature of at least about 79.4 ° C for at least 10 minutes subsequent to the addition of optical brightener and polyvinyl alcohol resin. Typically, the dough is cooked at a temperature greater than about 71.1 ° C for at least about 10 minutes subsequent to the addition of polyvinyl alcohol resin and optical brightener and polyvinyl alcohol resin. Generally the pulp is cooked at a temperature greater than about 71.1 ° C for at least about 20 minutes subsequent to the addition of polyvinyl alcohol resin and optical brightener and polyvinyl alcohol resin. In many cases, the pasta is cooked at a temperature of about 79.4 ° C to about 98.8 ° C for a time of about 10 minutes to about 120 minutes subsequent to the addition of polyvinyl alcohol resin and optical brightener. Probably more preferred, the aqueous composition is baked at a temperature from about 85 ° C to about 96.1 ° C for a time from about 20 minutes to about 60 minutes subsequent to the addition of polyvinyl alcohol resin and optical brightener. Suitable resins of polyvinyl alcohol have a viscosity of about 2 cps at about 40 cps. Typically, the polyvinyl alcohol resin has a viscosity of about 2 cps to about 8 cps. More generally, the polyvinyl alcohol resin has a viscosity of about 3 cps at about 30 cps. From about 3 cps to about 8 cps is a preferred scale, since it is a viscosity of about 3 cps at about 7 cps. Preferably, the polyvinyl alcohol resins are hydrolyzed based on a mole percentage of about 80 to about 99.5 percent. Typically, the polyvinyl alcohol resin is hydrolyzed based on a mole percentage of about 85 percent to about 90 percent and has a degree of polymerization of about 50 to about 2000. Typically, the polyvinyl alcohol resin has a degree of polymerization of about 50 to about 300. In some preferred embodiments, the active ingredient of optical brightener comprises a stilbene compound and could be a sulfonate stilbene compound, such as a sulfonated stilbene tetracompound or a sulfonated stilbene hexacompound. A preferred class is one in which the active ingredient of optical brightener comprises a stilbene compound with the formula: where X and Y are selected independently from the portions indicated below: In another aspect of the invention there is provided a method for preparing an aqueous PVOH / optical brightener concentrate comprising the sequential steps of: preparing an aqueous PVOH slurry; add a particulate dry optical brightener to the aqueous PVOH paste; and cooking the paste containing PVOH and optical brightener to dissolve the PVOH resin for at least 5 minutes at a temperature greater than about 71.1 ° C. In still another aspect of the invention there is provided a method for preparing an aqueous PVOH / optical brightener concentrate comprising the sequential steps of: providing a dry powder optical brightener; provide a dry polyvinyl alcohol resin; dry blending said polyvinyl alcohol resin with said optical brightener in an amount of about 1 part of dry polyvinyl alcohol resin per 0.05 to 1 part of optical brightener; mixing said dry mix with water to provide a nascent aqueous polyvinyl alcohol resin concentrate and optical brightener; and cooking the aqueous concentrate to dissolve the solids at an elevated temperature for a sufficient time to basically dissolve the entire polyvinyl alcohol resin and optical brightener, in order to provide a concentrated polyvinyl alcohol / fused brightener including water, resin of polyvinyl alcohol, optical brightener and, optionally, minor amounts of auxiliaries. Yet another feature is a dry particulate blend of a polyvinyl alcohol resin and an optical brightener, wherein the polyvinyl alcohol resin is hydrolyzed at a mole% of 85-90 and has a degree of polymerization ranging from about 50 to 50%. about 600. Preferably, the polyvinyl alcohol resin is hydrolyzed at a mol% of 85-90 and has a degree of polymerization ranging from about 185 to about 235. Even more preferably, the polyvinyl alcohol resin is hydrolyzed to a % mol of 87-89 and has a viscosity of about 2 cps at about 8 cps. A preferred "non-cooking" process for preparing a colored layer composition includes: (a) preparing a pigment dispersion; (b) preparing a dry blend of polyvinyl alcohol resin and optical brightener, wherein the polyvinyl alcohol resin is hydrolyzed at a mol% of about 85 to about mol% of about 90 and has a fine particle size, so that at least about 99% of the particles pass through a sieve with 80 mesh; (c) adding the dry mixture of polyvinyl alcohol resin and optical brightener to the pigment dispersion; and (d) applying friction stress to the pigment dispersion containing the polyvinyl alcohol and optical brightener, so that the dispersion is mixed and both the optical brightener and the polyvinyl alcohol resin are dissolved without external heating. A method is further provided for preparing an aqueous PVOH / optical brightener concentrate by means of the sequential steps of: (a) providing an aqueous brightening composition that includes water and optical brightener active ingredient, wherein the active ingredient of optical brightener is it is present in the aqueous polishing composition typically in an amount of about 10% to about 25%; (b) mixing a polyvinyl alcohol resin with said aqueous optical brightening composition in an amount of about 1 part of dry polyvinyl alcohol resin by 0.25 to 10 wet portions of aqueous polishing composition to provide a nascent aqueous polyvinyl alcohol resin concentrate and optical brightener; and (c) firing the aqueous concentrate to dissolve substantially all of the PVOH resin, generally at a temperature of about 79.4 ° C to about 98.8 ° C., generally for a time from about 10 minutes to about 120 minutes to provide a concentrated polyvinyl alcohol / brightener concentrate consisting basically of water, polyvinyl alcohol resin and active ingredient of optical brightener. Typically, the polyvinyl alcohol resin is mixed in an amount of about 1 part of dry polyvinyl alcohol resin by 0.5 to 10 wet portions of aqueous polish composition. The active ingredient of optical brightener is generally present in the aqueous polish composition in an amount of about 12% to about 20% and the aqueous PVOH / optical brightener concentrate typically has a solids content of about 20% to about 75% with based on the water content, polyvinyl alcohol and active ingredient of optical brightener of the concentrate. More typically, the polyvinyl alcohol is mixed with the aqueous optical brightener composition in an amount of about 15% to about 55% PVOH based on the combined weight of the water, the active ingredient of optical brightener and the polyvinyl alcohol resin, the concentrate having a solids content of about 30 to about 60%. Similarly, the aqueous concentrate is generally cooked to dissolve the solids at a temperature from about 85 ° C to about 96.1 ° C for a time from about 20 minutes to about 60 minutes. Suitable polyvinyl alcohol resins have viscosities of about 2 or 3 cps at about 30 or 40cps; more preferably, in some cases, the polyvinyl alcohol resin has a viscosity of about 2 or 3 cps at about 7 or 8 cps or about 3 cps at about 4 cps. The polyvinyl alcohol resin is generally hydrolyzed based on a mole percentage of about 80 to about 99.5 percent. Typically, the polyvinyl alcohol resin is hydrolyzed based on a mole percentage of about 85 percent to about 90 percent and has a degree of polymerization of about 50 to about 2000. A degree of polymerization of about 50 to about 1700 is more preferred, since it is a degree of polymerization of about 50 to about 300.

More preferably, the polyvinyl alcohol resin is added to the aqueous polishing composition in a basically dry form and, on occasions, the step of diluting the aqueous concentrate is convenient, depending on the processing characteristics sought. So, in addition, the concentrate can be applied directly to a paper substrate in a size press, if desired. The method may further include the step of adding polyethylene glycol to the aqueous concentrate, wherein the polyethylene glycol is added to the aqueous polish composition or to the nascent or cooked concentrate in an amount of about 0.5 to about 2 parts by weight per dry part of alcohol resin poly. A preferred method for preparing a color layer composition includes the sequential steps of: (a) providing an aqueous brightening composition consisting essentially of water and optical brightener active ingredient, wherein the active ingredient of optical brightener is present in the aqueous brightening composition in an amount of about 10 to about 25%; (b) mixing a polyvinyl alcohol resin with said aqueous optical brightening composition in an amount of about 1 part of dry polyvinyl alcohol resin by 0.25 to 10 wet portions of aqueous polishing composition to provide a nascent aqueous polyvinyl alcohol resin concentrate and optical brightener; (c) cooking the aqueous concentrate to dissolve the solids at a temperature from about 79.4 ° C to about 98.8 ° C for a time from about 10 minutes to about 120 minutes to provide a concentrated polyvinyl alcohol / cooked brightener consisting essentially of water , polyvinyl alcohol resin and optical brightener compounds; and (d) mixing the cooked concentrate with an aqueous dispersion comprising color pigment and a binder resin to produce the color layer composition. Typically, the polyvinyl alcohol resin is mixed in an amount of about 1 part of dry polyvinyl alcohol resin by 0.5 to 10 wet portions of aqueous polish composition. The method may additionally include the step of applying the color layer to the paper. An aqueous concentrate of optical brightener basically consists of water, an active ingredient of optical brightener and a polyvinyl alcohol resin having a viscosity of about 2 cps to about 4 cps, wherein the aqueous concentrate has from about 20 to about 75%. solids and the polyvinyl alcohol resin is hydrolyzed from about 80 to about 90 percent on a molar basis. The concentrate optionally includes auxiliaries such as dispersing agents, protective colloids, solvents for colloids and / or antifreezes, sequestering agents and the like, none of which changes the basic and novel characteristics of the concentrates. By reference to the aqueous PVOH / optical brightener concentrate, the auxiliaries also include minor amounts of binder, plasticizer, filler, water retention aids such as carboxymethylcellulose, and the like. Typically, the polyvinyl alcohol resin has a viscosity of 3 cps at 4 cps and the aqueous concentrate has about 25 to about 65 percent solids. The optical brightener concentrate additionally comprises polyethylene glycol in some cases and the active ingredient of optical brightener comprises a stilbene compound. The stilbene compound may be a stilbene sulfonate compound, as indicated above. In yet another aspect of the invention, an aqueous concentrate of optical brightener basically consists of water, an active ingredient of optical brightener, polyethylene glycol and a polyvinyl alcohol resin has a viscosity of about 2 cps to about 4 cps., wherein the aqueous concentrate has from about 20 to about 75% solids and wherein the polyvinyl alcohol resin is hydrolyzed from about 80 to about 90 percent on a molar basis. As used herein, terminology has its ordinary meaning, unless it is given a more specific or more general meaning later or becomes clear from the context. %, percentage or percent means the percentage by weight, unless the percentage of moles is specified. "Cps" means centipoise.

"Lesser amount" means less than 50% by weight exclusive of the water content. "PVOH" means polyvinyl alcohol resins which are typically prepared from polyvinyl acetate resins by saponification thereof, which is well known in the art. The PVOH resins are derived from wine acetate homopolymers, as well as copolymers of vinyl acetate with other ethylenically unsaturated monomers and may include cationic sites if desired. Preferably, the resins are derived in a mole percentage of 95 or more of the vinyl acetate. The suitable resins available from Celanese, Inc. include: TABLE 1 Polyvinyl alcohol resins 1 4% aqueous solution, 20 ° C When specifying the viscosity of a polyvinyl alcohol resin, the viscosity is the viscosity of a 4% (w / w) aqueous solution of PVOH, at 20 ° C. , CIÉ L *, a *, b * and brightness values are used to characterize the coated products prepared with coating formulations of the invention. The values of L *, a * and b * can be adequately measured using test methods such as TAPPI T 524 om-02, TAPPI T 527 om-02 or similar methods. TAPPI T 524 incorporates a perpendicular observation geometry (0 °) t and directional lighting of 45 °. TAPPI T 527 incorporates diffuse lighting and 0 ° observation geometry. L * is a measure of clarity that increases from 0 for black to 100 for perfect white; a * indicates red when it is positive and green when it is negative; b * indicates yellow when it is positive and blue when it is negative. Note that the brightness (GE) is measured in accordance with TAPPI T 452om-02. TAPPI 452 incorporates 45 ° illumination and 0 ° observation geometry. Unless indicated otherwise, brightness values are reported with ultraviolet (UV) radiation. To calculate the brightness without UV, the UV component is subtracted from the UV brightness. "Paste" refers to an aqueous composition that includes undissolved solids. A "color layer composition" includes aqueous pigment dispersion and, optionally, a synthetic binder resin. Typical binder resins are styrene-butadiene latexes or polyvinyl acetate emulsions. Polyvinyl alcohol resins are binding resins, preferably used as a colligant. The aqueous pigment dispersion with which the concentrates of the invention are combined, typically consists of clay or calcium carbonate, or of mixtures of both with solids levels ranging between about 70 and 76%. In general, at least a portion of the pigment comprises calcium carbonate and, for the clay portion, any of the clays that are customarily used for paper coating, such as the hydrous aluminum silicates of the kaolin clays group can be used. , hydrated silica clays and other similar. In addition to calcium carbonate and clay, other paper pigments may be added, such as, for example, titanium dioxide, synthetic barite ("barium sulfate"), lithopone, zinc sulphide or other coating pigments, including plastics, for example , polystyrene, in various proportions, for example up to 50% by weight, preferably up to 35% by weight based on calcium carbonate and clay. Additionally, the composition may also contain other additives, such as zinc oxide and / or a small amount of dispersing or stabilizing agent, such as tetrasodium pyrophosphate. Suitable polyvinyl alcohols of low molecular weight, partially or largely hydrolyzed for the practice of this invention can be hydrolyzed at a mol% of 70 to 99.5%, preferably 85 to 90, and most preferably 87 to 89 , and have a degree of polymerization (DP) ranging between 50 and 600, preferably between 185 and 255. Another means to evaluate the DP of polyvinyl alcohol is its viscosity as a 4% aqueous solution in weight at 20 ° C. Suitable polyvinyl alcohols have a viscosity ranging from about 2 to 30 cps, preferably 3 to 4 cp. Said polyvinyl alcohols can be prepared by means of synthesis and saponification techniques well known to the person skilled in the art for manufacturing polyvinyl alcohol. A preferred polyvinyl alcohol having a viscosity of about 4 cp and hydrolysis in mol% of 87 to 89 is marketed by Celanese under the trademark CELVOL® 203. Another preferred polyvinyl alcohol is CELVOL® 502, which has a viscosity of approximately 3 cp. Polyvinyl alcohol is incorporated as a dry powder with dry OB. The active ingredients of optical brightener are of the stilbene class indicated above and have the general structure of structures A, B and C. Suitable stilbenes are described in U.S. Patent No. 6,620,294 and U.S. Patent No. 5,830,241, whose descriptions are incorporated by reference. Commercially available optical brighteners include UVITEX® and TINOPAL® from Ciba Specialty Chemicals, BLANKOPHOR® from Bayer and HOSTALUX®, LEUCOPHOR® from Clariant and PARAWHITE® from Paramount. The dispersion of aqueous pigment with high solids containing the polyvinyl alcohol as a colligant can then be used to prepare the paper coating compositions comprising (parts by weight): 100 parts of pigment with content of clay and / or calcium carbonate and of 0 to 35 parts of secondary pigment; from 0.01 to 0.5 parts of dispersing or stabilizing agent; from 1 to 30 parts of polymeric binder emulsion (solid basis); from 0.1 to 10 parts, preferably from 0.5 to 2 parts, of polyvinyl alcohol collator; from 0.1 to 20 parts of other colligants; from 0 to 0.2 parts of defoamer, as well as enough water to provide the desired level of solids, generally from about 45 to 70% by weight, preferably from 60 to 70% by weight or more for the paper coating compositions with solids high The coating compositions produced can be applied to fiber paper webs using any of the conventional coating devices, including exit knife coaters, air knife coaters, roller coaters and the like. It is possible to cook the PVOH in the presence of OB as supplied with -17% solids, without the addition of water, as described hereinafter. The appearance of the resulting cooked mixture, except for the viscosity, does not change. Due to viscosity, dilutions are sometimes desirable. However, with mixed solids of 27%, the paper manufacturer has the benefit of a solution with relatively high solids. For all the formulations described below, the pigments are primarily calcium carbonate and clay, but titanium dioxide could be included. Optionally there are other ingredients such as carboxymethylcellulose, lubricants, dyes, defoamers, as is well known in the art. The units are expressed as dry / 100 pigment parts, except for the OB. In terms of raw materials, the pigments are supplied dry or in the form of pre-dispersed water which may have from about 70% to 76% solids. The styrene-butadiene latexes are supplied with solids of approximately 50%. The PVOH can be supplied in solid form to be fired in the solution before use, or in liquid form having from 15% to 30% solids. The OBs for the coating are supplied in liquid form with approximately 17% active ingredient and are, most preferably, of the tetra or hexasulfonate variety. Mixtures and coatings include 1/1, 2/1, 3.75 / 1 and 5/1 wet OB (TINOPAL® PT from Ciba, a tetrasulfonated form) dry PVOH (CELVOL® 203). Normal operations in paper mills require the addition of PVOH and OBs, each as liquids, in the formulation tank. However, the invention exploits the water in the OB through the addition of dry PVOH to 100 parts of OB paste in a beaker, while stirring sufficiently to disperse the PVOH particles in a uniform manner. The content is then heated to a temperature between 85 ° C and 96.1 ° C, depending on the degree of PVOH used, preferably by means of a water bath heated to steam. The temperature of the mixture is maintained at 30 minutes, at which time the PVOH will be completely solubilized and the mixture could either be cooled or used hot. The levels of previous solids are considered as maximums, since no dilution has occurred. As shown below, in the various examples, the method of this invention produces paper coating formulations with total coating solids greater than what can be achieved by conventional methods. Using the current methodology, for the proportions of OB / PVOH indicated and using dispersion of standard pigments with solids of either 70% or 76%, the maximum coating solids that can be achieved, adding the OB and the PVOH (solids at 25 ° C). %), each as liquid, range between 64.4% and 70.0%, as well as between 69.0% and 70.2% (using PVOH with 30% solids). In contrast, the method of this invention adds dry PVOH to an OB Solution. After the dry PVOH is added, the formulation is heated for 30 minutes at temperatures ranging from 85 ° C to approximately 96.1 ° C, to completely solubilize the PVOH. This solution is then added to the pigment dispersion with solids either 70% or 76%, to achieve the final coating solids shown below. The color layer formulations are sometimes expressed in dry parts and wet parts per 100 parts of dry pigment. A typical or "standard" coating formulation is as follows: 100 parts of dry pigment with 70% solids = 142. 9 wet parts 14 dry parts of latex with 50% solids = 28 wet parts 0.34 dry parts with Ingredient Active at 17% = 2 wet parts 1 dry part of PVOH with 25% solids = 4 wet parts Table 2 below shows the solids content for a standard formulation with a ratio of 2/1 wet / dry parts of OB / PVOH per 100 parts of pigment by means of conventional formulation techniques.

TABLE 2 Sample calculation With the invention, the vehicle water of the PVOH resin composition is removed and the same "dry" formulation (wet 2/1 OB / dry PVOH) has the composition shown in Table 3, with a solids advantage of 1.1. % in general.

TABLE 3 Sample calculation * The above uses the solids solution at 44.7% shown in Example Series 2 with the 70% pigment dispersion.

The following are numerous additional examples and examples comparatives showing the advantages of solids achieved with the invention, as opposed to conventional formulation techniques. These examples use the standard components specified above, varying the proportions of wet OB / dry PVOH and pigment solids content. 1/1 wet optical brightener / dry polyvinyl alcohol Comparative example series A The color layer is formulated with pigment dispersion either with 70% or 76% solids, as well as 25% or 30% PVOH solution.

Using the standard methodology of mixing the liquid OB (usually 17% solids) with liquid PVOH, and adding to the pigment dispersion, the solids that can be achieved are shown below in Table 4: TABLE 4 1/1 wet optical brightener / dry polyvinyl alcohol Example Series 1 In contrast to the above, the invention uses a solution prepared by adding dry PVOH to a 17% OB solution, to achieve the following concentrations. In this case, the OB / PVOH solution is prepared as follows: 83 parts of water and 17 parts of active ingredient OB + 100 parts of dry PVOH. Dry solids = (100 + 17V200 = 58.5%), cooked as indicated above, this solution is subsequently added to the pigment dispersion to achieve the results shown in Table 5: TABLE 5 1/1 wet optical brightener / dry polyvinyl alcohol As can be seen from the previous table, there is a clear advantage of solids in relation to the current practice. 2/1 wet optical brightener / dry polyvinyl alcohol Comparative example B series After the procedures described above, the maximum solids that can be achieved using conventional procedures are shown in Table 6: TABLE 6 2/1 wet optical brightener / dry polyvinyl alcohol Example Series 2 The dry PVOH is mixed with OB at 17% according to the following formula: 83 parts of water and 17 parts of active ingredient OB + 50 parts of dry PVOH. Dry solid = (50 +17) / 150 = 44.7%; followed by cocido. This is added to the pigment dispersion, to achieve the results and solids advantage shown in Table 7: TABLE 7 2/1 wet optical brightener / dry polyvinyl alcohol 3. 75 of wet optical brightener / dry polyvinyl alcohol Comparative example of series C After the above, the following maximum solids are achieved: TABLE 8 3.75 / 1 wet optical brightener / dry polyvinyl alcohol Example Series 3 The PVOH / OB mixture follows the following formula: 83 parts of water and 17 parts of active ingredient OB + 26.7 parts of dry PVOH. Dry solids = (26.7 + 17) /126.7 = 34.5; followed by cocido. The results are shown in Table 9: TABLE 9 3.75 / 1 wet optical brightener / dry polyvinyl alcohol /1 Wet Optical Brightener / Dry Polyvinyl Alcohol Comparative Example Series D Similarly, current practice produces the following% maximum solids: TABLE 10 5/1 wet optical brightener / dry polyvinyl alcohol Example Series 4 The OB / PVOH solution is prepared as follows: 83 parts of water and 17 parts of active ingredient OB + 20 parts of dry PVOH. Dry solid = (20 + 17) / 120 = 30.8%; followed by cocido. The results are shown in Table 11: JCUADRO 11 5/1 wet optical brightener / dry polyvinyl alcohol The results of the previous examples are summarized in Table 12 below: TABLE 12 Example Series 5 The above formulations of this invention do not indicate any dilution in the mixture. The viscosities in the proportion of 3.75 / 1 were -10,000 cps and in 2/1, higher than 73,000 cps, due to the increasing solids. Mixtures with the 5/1 ratio had -4,000 - 5,000 cps initially through 3 days with 30.8% solids. It is desirable, in some cases, to achieve a standard target of total solids of 27% by dilution of the formulations of the invention. At this level, the viscosity of all the PVOH / OB concentrates ranged between 2,000-4,000 cps and a solids advantage continued to be presented in comparison with conventional practice, as shown in the following Table 13.

TABLE 13 Examples 6 to 10, comparative example series E These examples show that the novel process of this invention does not detract from the performance of the optical brightener. The formulation for the paper coatings was as follows: 75/25 dry parts of CaCO3 / Pigment of Clay No. 1 14 dry parts of styrene-butadiene latex binder 0.3 dry parts of water retention aid of carboxymethylcellulose x parts wet (OB NOPAL® PT) and dry PVOH (CELVOL® 203 or 502) Solids -62% The formulations were then coated on the paper using a cylindrical coater. The results of the brightness tests are shown in the following Table 14. The control is the basic liquid-liquid addition sequence of PVOH and OB, while examples 6 to 10 are the pre-cooked OB / PVOH mixtures indicated previously. Both Example 6 and the control are formulated with 3.75 / 1 wet OB / dry PVOH. The base paper has a brightness of 84.3 (standard - without UV). After coating, the brightness values of the paper (again - without UV) improve to 85.3 and 85.6. UV brightness measurements show a very significant additional improvement at 89.0 and 88.9 - comparable to each other. The value of a * indicates the shading color either red or green and these would be considered equal to each other.

The value of b * is important because it indicates desirable blue-white with negative values and undesirable yellow with positive values. Negative values are desirable and not significant in their differences. Examples 7 and 8 are formulated at 2/1 with dry OB / PVOH and compare the performance of two PVOH samples with different viscosity values. Both are precooked with OB according to the invention. The significance here is that C-502 performs as well as C-203 and, since its viscosity is lower, will allow higher solids in the blend from 27% to 30% in the optical brightener concentrate for greater color solid benefits. Coating. Following the same procedures, examples 9 and 10 were formulated with 2/1/1 wet OB / dry PVOH / polyethylene glycol 400, except that Example 10 had 2 less parts of SBR.

TABLE 14 3. 75/1 wet parts of OB / dry parts of C-203 to 25% by separate additions Examples 11, 12 and Comparative Examples F, G Following the procedures indicated above, color layer compositions were prepared with about 3/1 and 1/1 wet OB / dry PVOH. The comparative examples had slightly lower solids and were prepared in a conventional manner.

In Table 15, 0.51 / 1 and 0.17 / 1 refer to the dry ratios of optical brightener with respect to polyvinyl alcohol, while comparative examples F and G use a typical optical brightener as TINOPAL® PT optical brightener with polyvinyl alcohol CELVOL ® 203. As can be seen from Table 15 below, the concentrates of the invention show equality or improvement in the critical optical measurements of UV brightness, blue-white "b" value and CIÉ whiteness.

TABLE 15 The results are also presented graphically in Figures 1 to 4. Examples 13 to 16 Additional concentrates of 3/1 and 1/1 of wet OB / dry PVOH were prepared and mixed with a masterbatch of 75% clay / carbonate clay of calcium at 25%, as indicated in the following Tables 16 to 19.

TABLE 16 Formulation of example 13 TABLE 17 Sample formulation 14 TABLE 18 Formulation of example 15 TABLE 19 Sample formulation 16 The results of the optical tests of the paper coatings are shown in the following Tables 20 and 21.

TABLE 20 Coating properties TABLE 21 Coating properties EXAMPLES 17, 18, Comparative Examples HM Following generally the procedures indicated above, color layer compositions were prepared by basically conventional techniques (HM examples) and by adding dry OB powder, followed by in-situ cooking according to the invention (examples 17,18). The results are shown in the following Table 22, as well as in Figures 5 to 8.

TABLE 22 Optical properties Examples 19, 20 The following are dry mixtures and solutions produced according to the invention.

Aqueous polyvinyl alcohol concentrate / optical brightener with wet / dry ratio of 3: 1 The dry PVOH (10 grams) is added to the dry OB (5.1 grams) and the resulting mixture is dry mixed to produce a uniform mixture of both ingredients. The dry mixture is then slowly added to 40 ml of water. The resulting paste is heated to a temperature of 93.3 to 98.8 ° C, with stirring, for a period of 30 minutes, to completely dissolve the dry ingredients. The resulting solution is cooled to room temperature to produce PVOH / OB concentrate with solids at 27.4%. This example has a ratio of OB / PVOH equivalent to a solution of 3 wet portions of optical brightener with solids at 17% with respect to 1 dry part of polyvinyl alcohol resin.

Aqueous polyvinyl alcohol concentrate / optical brightener with wet / dry ratio of 1: 1 The dry PVOH (20 grams) is added to the dry OB (3.4 grams) and the resulting mixture is dry mixed to produce a uniform mixture of both ingredients. The dry mixture is then slowly added to 50 ml of water. The resulting paste is heated to a temperature of 93.3 to 98.8 ° C, with stirring, for a period of 30 minutes, to completely dissolve the dry ingredients. The resulting solution is cooled to room temperature to produce a concentrate of PVOH / OB with solids at 31.9%. This example has a ratio of OB / PVOH equivalent to a 1 part wet solution of optical brightener with 17% solids with respect to 1 dry part of polyvinyl alcohol resin. A dry blend of PVOH / optical brightener can be added directly to a pigment dispersion, while a color layer composition is prepared, if desired. A preferred embodiment uses PVOH resin having a particle size of less than about 200 microns, ie 99% by weight of the resin particles traverse an 80 mesh sieve. This composition can be easily dissolved in the coating paste during mixing with friction stress applied in the absence of external heating. Although the invention has been described in connection with several examples, modifications to those examples within the spirit and scope of the invention will be readily apparent to one skilled in the art. In view of the foregoing description, the relevant knowledge of the art and the references including the copending applications described above in relation to the Background and the Detailed Description, the descriptions of which are incorporated herein by reference, it is considered that an additional description results unnecessary

Claims (29)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for preparing an aqueous concentrate of

PVOH / optical brightener comprising the sequential steps of: a) providing an aqueous brightening composition that includes water and active ingredient of optical brightener; b) mixing a polyvinyl alcohol resin with said aqueous optical brightening composition in an amount of about 1 part of dry polyvinyl alcohol resin by 0.25 to 10 wet portions of aqueous polish composition to provide a nascent aqueous polyvinyl alcohol resin concentrate and brightener optical; and c) cooking the aqueous concentrate to dissolve the solids at an elevated temperature for a sufficient time to substantially dissolve the entire polyvinyl alcohol resin, so as to provide a polyvinyl alcohol / cooked brightener concentrate including water, alcohol resin poly, optical brightener and, optionally, minor amounts of auxiliaries. 2. The method according to claim 1, further characterized in that the active ingredient of optical brightener is present in the aqueous polishing composition in an amount of about 10% to about 25%.

3. - The method according to any of the preceding claims, further characterized in that the aqueous concentrate of PVOH / optical brightener has a solids content of about 20% to about 75% based on the content of water, polyvinyl alcohol and active ingredient of Concentrated optical brightener.

4. The method according to any of the preceding claims, further characterized in that said polyvinyl alcohol is mixed with said aqueous optical brightener composition in an amount of about 15% to about 55% PVOH based on the combined weight of said water, said active ingredient of optical brightener and said polyvinyl alcohol resin, the concentrate having a solids content of about 30 to about 60%.

5. The method according to any of the preceding claims, further characterized in that the aqueous concentrate is cooked to dissolve the solids at a temperature between about 79.4 ° C and about 98.8 ° C for a time between about 10 minutes and about 120 minutes .

6. The method according to any of the preceding claims, further characterized in that the polyvinyl alcohol resin has a viscosity of about 2 cps to about 40 cps.

7. - The method according to any of the preceding claims, further characterized in that the polyvinyl alcohol resin is hydrolyzed based on a percentage of moles of about 80 to about 99.5 percent.

8. The method according to any of the preceding claims, further characterized in that the polyvinyl alcohol resin is added to the aqueous polishing composition in a basically dry form.

9. The method according to any of the preceding claims, further characterized in that it further comprises the step of diluting the aqueous concentrate.

10. The method according to any of the preceding claims, further characterized in that it further comprises the step of adding polyethylene glycol to said aqueous brightening composition or said nascent or cooked aqueous concentrate.

11. The method according to claim 10, further characterized in that said polyethylene glycol is added to said aqueous brightening composition or said nascent or cooked aqueous concentrate in an amount of about 0.5 to about 2 parts by weight per dry part of alcohol resin poly.

12. The method according to any of the preceding claims, further characterized in that the concentrate of optical brightener / PVOH includes a minor amount of at least one auxiliary selected from dispersing agents., productive colloids, solvents for colloids, antifreezes, sequestering agents, binders, plasticizers, fillers and water retention aids.

13. The method according to any of the preceding claims, further characterized by additionally comprising the step of applying the concentrate of optical brightener / PVOH directly to a paper substrate.

14. A method for preparing a color layer composition comprising mixing the aqueous concentrate of optical brightener / PVOH prepared by the methods according to claim 1 to 12 with an aqueous dispersion comprising color pigment and a binder resin to produce the color layer composition.

15. The method according to claim 14, further characterized in that it further comprises the step of applying the color layer to the paper.

16. The method according to claim 14, further characterized in that the polyvinyl alcohol resin is added to the optical brightener composition in a basically dry form.

17. The method according to any of the preceding claims, further characterized in that the active ingredient of optical brightener comprises a stilbene compound.

18. - The method according to claim 17, further characterized in that the stilbene compound is a stilbene sulfonate compound.

19. The method according to claim 18, further characterized in that the sulfonate stilbene compound is a sulfonated stilbene tetracompound.

20. The method according to claim 18, further characterized in that the sulfonate stilbene compound is a sulphonated stilbene hexacompound.

21. The method according to any of the preceding claims, further characterized in that the active ingredient of optical brightener comprises a stilbene compound with the formula: where X and Y are selected independently of the portions indicated below:

22. - In a method for preparing an aqueous composition including an optical brightener and a polyvinyl alcohol resin, an improvement comprising baking a slurry to dissolve the polyvinyl alcohol resin subsequent to the addition of optical brightener and polyvinyl alcohol resin to the dough at a temperature greater than about 71.1 ° C for at least about 5 minutes.

23. The improvement according to claim 22, further characterized in that the optical brightener is added to the paste in a basically dry form.

24. The improvement according to claim 22, further characterized in that the polyvinyl alcohol resin is added to an optical brightener solution in a basically dry form in order to form the paste.

25. A method for preparing an aqueous concentrate of PVOH / optical brightener comprising the sequential steps of: a) preparing a PVOH paste; b) adding a particulate dry optical brightener to the PVOH paste; and c) cooking the PVOH-containing paste and optical brightener to dissolve the PVOH resin for at least 5 minutes at a temperature greater than about 71.1 ° C. A method for preparing an aqueous PVOH / optical brightener concentrate comprising the sequential steps of: a) providing an optical brightener in dry powder; b) provide a dry polyvinyl alcohol resin; c) dry blending said polyvinyl alcohol resin with said optical brightener in an amount of about 1 part dry polyvinyl alcohol resin per 0.05 with 1 dry part of optical brightener; d) mixing said dry mix with water to provide a nascent aqueous polyvinyl alcohol resin concentrate and optical brightener; and e) cooking the aqueous concentrate to dissolve the solids at an elevated temperature for a sufficient time to substantially dissolve the entire polyvinyl alcohol resin and optical brightener, so as to provide a concentrated polyvinyl alcohol / brightener including water, polyvinyl alcohol resin, optical brightener and, optionally, minor amounts of auxiliaries. 27. A method for preparing a color layer composition comprising: a) preparing an aqueous pigment dispersion; b) preparing a dry blend of polyvinyl alcohol resin and optical brightener, wherein the polyvinyl alcohol resin is hydrolysed in a mole% of 85 mole to about a mole% of 90 and has a fine particle size, so that at least approximately 99% of the particles pass through a sieve with 80 mesh; c) adding the dry mixture of polyvinyl alcohol resin and optical brightener to the pigment dispersion; and d) applying friction stress to the pigment dispersion containing the polyvinyl alcohol and optical brightener, so that the dispersion is mixed and both the optical brightener and the polyvinyl alcohol resin are dissolved without external heating. 28. The method according to claim 27, further characterized in that it comprises adding a latex binder to the pigment dispersion. 29. The method according to claim 28, further characterized in that the pigment dispersion contains a mineral pigment selected from clay, calcium carbonate, titanium dioxide and mixtures thereof. SUMMARY OF THE INVENTION The present invention relates in general to an improved method for preparing aqueous coating compositions including an optical brightener and a polyvinyl alcohol resin, the improvement being directed to bake a paste to dissolve the polyvinyl alcohol resin subsequent to the addition of optical brightener and polyvinyl alcohol resin to the pulp at a temperature greater than about 71.1 ° C for at least about 5 minutes; the invention allows to achieve a preparation with a lower water content without compromising brightness and color; the addition of dry resin and / or dry rinse aid to provide mixtures with high solids is particularly preferred; Another aspect of the invention is a dry particulate mixture of polish and PVOH resin; A method for preparing an aqueous PVOH / optical brightener concentrate comprising the sequential steps of: (a) providing an aqueous brightening composition comprising water and active ingredient of optical brightener, wherein the active ingredient of optical brightener is typically found present in the aqueous brightening composition in an amount of about 10% to about 25%; (b) mixing a polyvinyl alcohol resin with said aqueous optical brightening composition in an amount of about 1 part of dry polyvinyl alcohol resin by 0.5 to 10 wet portions of aqueous polishing composition to provide a nascent aqueous polyvinyl alcohol resin concentrate and optical brightener; and (c) baking the aqueous concentrate to dissolve the solids typically at a temperature from about 79.4 ° C to about 98.8 ° C for a time from about 10 minutes to about 120 minutes, to provide a concentrated polyvinyl alcohol / cooked optical brightener. 11 B P06 / 818F