Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D129/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Coating compositions based on hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Coating compositions based on derivatives of such polymers
  • C09D129/02—Homopolymers or copolymers of unsaturated alcohols
  • C09D129/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L29/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical; Compositions of hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Compositions of derivatives of such polymers
  • C08L29/02—Homopolymers or copolymers of unsaturated alcohols
  • C08L29/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/71—Mixtures of material ; Pulp or paper comprising several different materials not incorporated by special processes
  • D21H17/72—Mixtures of material ; Pulp or paper comprising several different materials not incorporated by special processes of organic material
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/56—Macromolecular organic compounds or oligomers thereof obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H19/60—Polyalkenylalcohols; Polyalkenylethers; Polyalkenylesters
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/66—Coatings characterised by a special visual effect, e.g. patterned, textured
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/28—Colorants ; Pigments or opacifying agents
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/30—Luminescent or fluorescent substances, e.g. for optical bleaching
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/32—Bleaching agents
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
  • C08K5/0041—Optical brightening agents, organic pigments
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds
  • C08K5/41—Compounds containing sulfur bound to oxygen
  • C08K5/42—Sulfonic acids; Derivatives thereof

Definitions

• the present invention relates to a novel methodology and products for preparing mixtures of polyvinyl alcohol (PVOH) and optical brighteners having high solids for easier drying and faster production rates.
• the coatings made with the compositions are especially suited for high quality coated papers.
• Paper coating compositions are used by the paper industry to impart the desired moisture resistance, physical properties and appearance to certain grades of finished paper.
• the coating composition is an aqueous dispersion consisting mainly of mineral pigments like clay, calcium carbonate or titanium dioxide, and pigment binders of natural protein, starch or synthetic polymer emulsions. Styrene-butadienes and polyvinyl acetates are examples of such synthetic emulsion binders.
• Coating compositions may also contain additives, such as thickeners, humectants and lubricants. Coating compositions are usually applied to a continuous web of material by high speed coating machines, such as blade coaters, air knife coaters, rod coaters and roll coaters.
• High brightness coated grades of paper typically include optical brighteners (OBs).
• OBs optical brighteners
• Optical brighteners generally operate by way of absorbing ultra-violet radiation and then immediately re-admitting in the visible blue-white range.
• Examples of optical brighteners include UVITEX ® and TINOPAL ® from Ciba Specialty Chemicals, BLANKOPHOR ® from Bayer and HOSTALUX ® and LEUCOPHOR ® from Clariant.
• Most OBs have active ingredients that belong to the stilbene class of compounds as shown in Structures A, B, and C: A
• M can be H, an alkali metal, ammonium or magnesium and K ⁇ represents hydrogen, Ci- C 5 alkyl, C t -Cs alkoxy or halogen.
• 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 accomplished under high shear stirring, typically at speeds of 1500 rpm for 5 minutes at room temperature.
• the 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).
• the low MW of the polyethylene glycol has a low viscosity, which results in a pumpable solution.
• a typical structure of the fluorescent whitening agent is:
• PVOH is supplied to papermakers in a variety of forms: 1) dry resin that is cooked in water by the customer at 20% to 30% solids, the advantage being that less costly grades of PVOH can be used, the drawbacks being noted above; 2) PVOH that has been pre-cooked and delivered to the customer at 15% to 25% solids, which is costly to the papermaker as it involves shipping mostly water; and 3) dry, fine particle size partially hydrolyzed grades that are added dry to the pigmented formulations. These latter products are relatively expensive ground material, but are convenient if cooking is not an option. See United States Patent No. 5,057,570.
• an optical brightener/PVOH aqueous concentrate by way of the sequential steps of: (a) providing an aqueous brightener composition consisting essentially ofincluding water and optical brightener active ingredient, wherein the optical brightener active ingredient is present in the aqueous brightener composition typically 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 0.50.25 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 solidssubstantially all of the PVOH resin, usually at a temperature of from about 175°F to about 210°F generally for a time of from about 10 minutes to about 120 minutes to provide a cooked bright
• the polyvinyl alcohol resin is admixed in an amount of about 1 part of dry polyvinyl alcohol resin per 0.5 to 10 wet parts of aqueous brightener composition.
• the optical brightener active ingredient is generally usually present in the aqueous brightener composition in an amount of from about 12%o to about 20% and the optical brightener/PVOH aqueous concentrate typically has a solids content of from about 20% to about 75%) based on the water, polyvinyl alcohol and optical brightener active ingredient content of the concentrate.
• the polyvinyl alcohol is admixed with the aqueous optical brightener composition in an amount of from about 15% to about 55% PVOH based on the combined weight of the water, the optical brightener active ingredient and polyvinyl alcohol resin, the concentrate having a solids content of from about 30 to about 60%.
• the aqueous concentrate is usually cooked to dissolve the solids at a temperature of from about 185°F to about 205°F for a time of from about 20 minutes to about 60 minutes.
• Suitable polyvinyl alcohol resins have viscosities of from about 2 or 3 cps to about 30 or 40 cps; most preferably in some cases the polyvinyl alcohol resin has a viscosity of from about 2 or 3 cps to about 5 7 or 8 cps or from about 3 cps to about 4 cps.
• the polyvinyl alcohol resin is generally hydrolyzed on a mole percent basis of from about 85 80 to about 99.5 percent; typically, the polyvinyl alcohol resin is hydrolyzed on a mole percent basis of from about 85 percent to about 90 percent and has a degree of polymerization of from about 50 to about 25002000.
• a degree of polymerization of from about 50 to about 1700 is more preferred as is a degree of polymerization of from about 50 to about 300.
• the polyvinyl alcohol resin is added to the aqueous polyvinyl alcoholbrightener composition in substantially dry form; and sometimes the step of diluting the aqueous concentrate is expedient, depending on processing characteristics sought. So also, the concentrate can be directly applied to a paper substrate in a size press, if so desired.
• the method may further include the step of adding polyethylene glycol to the aqueous concentrate and wherein the polyethylene glycol is added to the aqueous brightener composition or to the nascent or cooked aqueous concentrate in an amount of from about 0.5 to about 2 parts by weight per dry part of polyvinyl alcohol resin.
• a preferred method of preparing a color coat composition includes the sequential steps of:
• aqueous brightener composition consisting essentially of water and optical brightener active ingredient, wherein the optical brightener active ingredient is present in the aqueous brightener composition in an amount of from about 10 to about 25%;
• the polyvinyl alcohol resin is admixed in an amount of about 1 part of dry polyvinyl alcohol resin per 0.5 to 10 wet parts of aqueous brightener composition.
• the method further comprises the step of applying the color coat to paper.
• An optical brightener aqueous concentrate consists essentially of water, an optical brightener active ingredient and a polyvinyl alcohol resin having a viscosity of from about 3 2 cps to about 5 4 cps, wherein the aqueous concentrate is from about 20 to about 75% solids, and 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 the colloids, and/or antifreezes, sequestering agents and the like, none of which change the basic and novel characteristics of the concentrates.
• auxiliaries also include minor amounts of binder, plasticizer, filler, water retention aids such as carboxymethyl cellulose and so forth.
• the polyvinyl alcohol resin has a viscosity of from 3 cps to 4 cps and the aqueous concentrate is from about 25 to about 65 percent solids.
• the optical brightener concentrate further comprises polyethylene glycol in some cases and the optical brightener active ingredient comprises a stilbene compound.
• the stilbene compound may be a sulfonated stilbene compound of the formula:
• an optical brightener aqueous concentrate consists essentially of water, an optical brightener active ingredient, polyethylene glycol and a polyvinyl alcohol resin has a viscosity of from about 2 cps to about 4 cps, wherein the aqueous concentrate is 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 further relates generally to improved methods of preparing aqueous compositions including an optical brightener and a polyvinyl alcohol resin, the improvement being directed to cooking a PVOH containing slurry to dissolve the polyvinyl alcohol resin subsequent to the addition of optical brightener and polyvinyl alcohol resin at a temperature above about 160°F for at least about 5 minutes.
• the invention enables preparation of lower water content formulations 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 metliod of providing PVOH and optical brightener to a color coat composition without external heating.
• Still another aspect of the invention is a dry, particulate blend of brightener and PVOH resin, the details of which are described hereinafter.
• Figures 1-4 are histograms presenting the Hunter Color data of the coatings of Examples 11, 12 and Comparative Examples F, G; and Figures 5-8 are histograms presenting the Hunter Color data of the coatings of Examples 17, 18 and Comparative Examples H-M.
• the optical brightener is added to an aqueous composition such as a PVOH slurry in substantially dry form; in other embodiments, the polyvinyl alcohol resin is added to an aqueous optical brightener solution in substantially dry form; while in still other embodiments both the optical brightener and the polyvinyl alcohol resin are added to water in substantially dry form, to form a slurry.
• an aqueous composition such as a PVOH slurry in substantially dry form
• the polyvinyl alcohol resin is added to an aqueous optical brightener solution in substantially dry form
• both the optical brightener and the polyvinyl alcohol resin are added to water in substantially dry form, to form a slurry.
• the slurry is cooked at a temperature of at least about 175°F for at least 10 minutes subsequent to the addition of optical brightener and polyvinyl alcohol resin.
• the slurry is cooked at a temperature above about 160°F for at least bout 10 minutes subsequent to the addition of polyvinyl alcohol resin and optical brightener and polyvinyl alcohol resin; usually the slurry is cooked at a temperature above about 160°F for at least bout 20 minutes subsequent to the addition of polyvinyl alcohol resin and optical brightener and polyvinyl alcohol resin.
• the slurry is cooked at a temperature of from about 175°F to about 210°F for a time of from about 10 minutes to about 120 minutes subsequent to the addition of polyvinyl alcohol resin and optical brightener.
• the aqueous composition is cooked at a temperature of from about 185°F to about 205°F for a time of from about 20 minutes to about 60 minutes subsequent to the addition of polyvinyl alcohol resin and optical brightener.
• Suitable polyvinyl alcohol resins have a viscosity of from about 2 cps to about 40 cps; typically, the polyvinyl alcohol resin has a viscosity of from about 2 cps to about 8 cps; more generally, the polyvinyl alcohol resin has a viscosity of from about 3 cps to about 30 cps. From about 3 cps to about 8 cps is one preferred range as is a viscosity of from about 3 cps to about 7 cps.
• the polyvinyl alcohol resins are hydrolyzed on a mole percent basis of from about 80 to about 99.5 percent; typically, the polyvinyl alcohol resin is hydrolyzed on a mole percent basis of from about 85 percent to about 90 percent and has a degree of polymerization of from about 50 to about 2000. Typically, the polyvinyl alcohol resin has a degree of polymerization of from about 50 to about 300.
• the optical brightener active ingredient comprises a stilbene compound and may be a sulfonated stilbene compound, such as a tetrasulfonated stilbene compound or a hexasulfonated stilbene compound.
• the optical brightener active ingredient comprises a stilbene compound of the formula:
• a method of preparing an optical brightener/PVOH aqueous concentrate comprising the sequential steps of: preparing an aqueous PVOH slurry; adding a dry, particulate optical brightener to the aqueous PVOH slurry; and cooking the slurry containing PVOH and optical brightener to dissolve the PVOH resin for at least 5 minutes at a temperature of above about 160°F.
• a method of preparing an optical brightener/PVOH aqueous concentrate comprising the sequential steps of: providing a dry powder optical brightener; providing 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; admixing said dry blend with water to provide a nascent aqueous concentrate of polyvinyl alcohol resin and optical brightener; and cooking the aqueous concentrate to dissolve the solids at an elevated temperature for a time sufficient to dissolve substantially all of the polyvinyl alcohol resin and optical brightener so as to provide a cooked brightener/polyvinyl alcohol concentrate including water, polyvinyl alcohol resin, optical brightener, and optionally minor amounts of auxiliaries.
• Still another feature is a dry, particulate blend of a polyvinyl alcohol resin and an optical brightener wherein the polyvinyl alcohol resin is 85-90 mol% hydrolyzed and has a degree of polymerization ranging from about 50 to about 600.
• the polyvinyl alcohol resin is preferably 85-90 mol% hydrolyzed and has a degree of polymerization ranging from about 185 to about 235.
• the polyvinyl alcohol resin is 87-89 mole% hydrolyzed and has a viscosity of from about 2 cps to about 8 cps.
• a preferred "no cook" process for making a color coat 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 from about 85 mol% to about 90 mol% hydrolyzed and has a fine particle size, such that at least about 99% of the particles pass an 80 mesh sieve; (c) adding the dry blend of polyvinyl alcohol resin and optical brightener to the pigment dispersion; and (d) applying shear to the pigment dispersion containing the polyvinyl alcohol and optical brightener so as to mix the dispersion and dissolve both the optical brightener and polyvinyl alcohol resin without external heating.
• an optical brightener/PVOH aqueous concentrate by way of the sequential steps of: (a) providing an aqueous brightener composition including water and optical brightener active ingredient, wherein the optical brightener active ingredient is present in the aqueous brightener composition typically 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 0.25 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 substantially all of the PVOH resin, usually at a temperature of from about 175°F to about 210°F generally for a time of from about 10 minutes to about 120 minutes to provide a cooked brightener/polyvinyl alcohol concentrate consisting essentially of water, polyvinyl alcohol
• the polyvinyl alcohol resin is admixed in an amount of about 1 part of dry polyvinyl alcohol resin per 0.5 to 10 wet parts of aqueous brightener composition.
• the optical brightener active ingredient is usually present in the aqueous brightener composition in an amount of from about 12% to about 20%> and the optical brightener/PVOH aqueous concentrate typically has a solids content of from about 20% to about 75% based on the water, polyvinyl alcohol and optical brightener active ingredient content of the concentrate.
• the polyvinyl alcohol is admixed with the aqueous optical brightener composition in an amount of from about 15% to about 55% PVOH based on the combined weight of the water, the optical brightener active ingredient and polyvinyl alcohol resin, the concentrate having a solids content of from about 30 to about 60%.
• the aqueous concentrate is usually cooked to dissolve the solids at a temperature of from about 185°F to about 205°F for a time of from about 20 minutes to about 60 minutes.
• Suitable polyvinyl alcohol resins have viscosities of from about 2 or 3 cps to about 30 or 40 cps; most preferably in some cases the polyvinyl alcohol resin has a viscosity of from about 2 or 3 cps to about 7 or 8 cps or from about 3 cps to about 4 cps.
• the polyvinyl alcohol resin is generally hydrolyzed on a mole percent basis of from about 80 to about 99.5 percent; typically, the polyvinyl alcohol resin is hydrolyzed on a mole percent basis of from about 85 percent to about 90 percent and has a degree of polymerization of from about 50 to about 2000.
• a degree of polymerization of from about 50 to about 1700 is more preferred as is a degree of polymerization of from about 50 to about 300.
• the polyvinyl alcohol resin is added to the aqueous brightener composition in substantially dry form; and sometimes the step of diluting the aqueous concentrate is expedient, depending on processing characteristics sought. So also, the concentrate can be directly applied to a paper substrate in a size press, if so desired.
• the method may further include the step of adding polyethylene glycol to the aqueous concentrate and wherein the polyethylene glycol is added to the aqueous brightener composition or to the nascent or cooked aqueous concentrate in an amount of from about 0.5 to about 2 parts by weight per dry part of polyvinyl alcohol resin.
• One preferred method of preparing a color coat composition includes the sequential steps of:
• aqueous brightener composition consisting essentially of water and optical brightener active ingredient, wherein the optical brightener active ingredient is present in the aqueous brightener composition in an amount of from about 10 to about 25%;
• a polyvinyl alcohol resin with said aqueous optical brightener composition in an amount of about 1 part of dry polyvinyl alcohol resin per 0.25 to 10 wet parts of aqueous brightener comlposition to provide a nascent aqueous concentrate of polyvinyl alcohol resin and optical brightener; (c) cooking the aqueous concentrate to dissolve the solids 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 cooked brightener/polyvinyl alcohol concentrate consisting essentially of water, polyvinyl alcohol resin and optical brightener compounds; and (d) admixing the cooked concentrate with an aqueous dispersion comprising color pigment and a binder resin to produce the color coat composition.
• the polyvinyl alcohol resin is admixed in an amount of about 1 part of dry polyvinyl alcohol resin per 0.5 to 10 wet parts of aqueous brightener composition.
• the method may further include the step of applying the color coat to paper.
• An optical brightener aqueous concentrate consists essentially of water, an optical brightener active ingredient and a polyvinyl alcohol resin having a viscosity of from about 2 cps to about 4 cps, wherein the aqueous concentrate is 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 the colloids, and/or antifreezes, sequestering agents and the like, none of which change the basic and novel characteristics of the concentrates.
• auxiliaries also include minor amounts of binder, plasticizer, filler, water retention aids such as carboxymethyl cellulose and so forth.
• the polyvinyl alcohol resin has a viscosity of from 3 cps to 4 cps and the aqueous concentrate is from about 25 to about 65 percent solids.
• the optical brightener concentrate further comprises polyethylene glycol in some cases and the optical brightener active ingredient comprises a stilbene compound.
• the stilbene compound may be a sulfonated stilbene compound as noted above.
• an optical brightener aqueous concentrate consists essentially of water, an optical brightener active ingredient, polyethylene glycol and a polyvinyl alcohol resin has a viscosity of from about 2 cps to about 4 cps, wherein the aqueous concentrate is 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.
• %, percent or per cent means weight percent unless mole percent is specified. "Cps" means centipoise.
• “Minor amount” means less than 50% by weight exclusive of 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. PVOH resins are derived from homopolymers of vinyl acetate as well as copolymers of vinyl acetate with other ethylenically unsaturated monomers and may include cationic sites if so desired. Preferably, the resins are 95 mole percent or more vinyl acetate derived. Suitable resins, available from Celanese, Inc. include:
• the viscosity is the viscosity of a 4% aqueous (wt/wt) solution of the PVOH, at 20°C.
• CIE L*, a*, b* and brightness values are used to characterize coated products prepared with coating formulations of the invention. L*, a*, and b* values may be suitably measured using test methods such as TAPPI T 524 om-02, TAPPI T 527 om-02, or similar methods.
• TAPPI T 524 incorporates 45° directional illumination and perpendicular (0°) 1 observation geometry.
• TAPPI T 527 incorporates diffuse illumination and 0° observation geometry.
• L* is a measure of lightness increasing from 0 for black to 100 for perfect white; a* indicates redness when positive and green when negative; b* indicates yellowness when positive and blueness when negative.
• (GE) brightness is measured in accordance with TAPPI T 452 om-02.
• TAPPI 452 incorporates 45° illumination and 0° observation geometry. Unless otherwise indicated, Brightness values are reported with ultra-violet (UV) radiation. To calculate Brightness without UV, the UV component is subtracted from the UV Brightness.
• Slurry refers to an aqueous composition including undissolved solids.
• a "color coat 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 binder resins, preferably used as a co-binder.
• the aqueous pigment dispersion with which the inventive concentrates are combined typically consists of clay or calcium carbonate or mixtures of the two at solids levels ranging from about 70 to 76%>.
• at least a portion of the pigment comprises calcium carbonate and for the clay portion, any of the clays customarily used for the paper coating, such as the hydrous aluminum silicates of the kaolin group clays, hydrated silica clays and the like can be used.
• the calcium carbonate and clay there may be added other paper pigments, such as, for example titanium dioxide, blanc fixe ("barium sulfate"), lithopone, zinc sulfide, or other coating pigments, including plastics, for example, polystyrene, in various ratios, for example, up to 50 wt.%., preferably up to 35 wt.% based on calcium carbonate and clay.
• the composition may also contain other additives, such as zinc oxide and/or a small amount of a dispersing or stabilizing agent, such as tetra-sodium pyrophosphate.
• Suitable low molecular weight, partially or mostly hydrolyzed polyvinyl alcohols for the practice of this invention can be 70-99.5%), preferably 85-90, and most preferably 87-89, mole% hydrolyzed and have a degree of polymerization (DP) ranging from 50-600, preferably 185 to 255.
• Another means for assessing the DP of the polyvinyl alcohol is its viscosity as a 4 wt.% aqueous solution at 20°C.
• Suitable polyvinyl alcohols have a viscosity ranging from about 2 to 30 cps, preferably 3-4 cp.
• Such polyvinyl alcohols can be prepared by synthesis and saponification techniques well known to those skilled in the art of manufacturing polyvinyl alcohol.
• a preferred polyvinyl alcohol having a viscosity of about 4 cp and an 87-89 mole% hydrolysis is marketed by Celanese under the trademark CELVOL ® 203.
• Another preferred polyvinyl alcohol is CELVOL ® 502, which has a viscosity of about 3 cp.
• the polyvinyl alcohol is incorporated as a dry powder with the dry OB.
• the optical brightener active ingredients are of the stilbene class noted above and have the general structure of structures A, B and C. Suitable stilbenes are disclosed in United States Patent No. 6,620,294 and United States Patent No.
• optical brighteners include UVITEX ® and TINOPAL ® from Ciba Specialty Chemicals, BLANKOPHOR ® from Bayer and HOSTALUX ® , LEUCOPHOR ® from Clariant and PARAWHITE ® from Paramount.
• the high solids aqueous pigment dispersion containing the polyvinyl alcohol as a co- binder can then be used to prepare paper coating compositions comprising (parts by wt): 100 parts pigment containing clay and/or calcium carbonate and 0 to 35 parts secondary pigment; 0.01 to 0.5 parts dispersing or stabilizing agent; 1 to 30 parts polymer binder emulsion (solids basis); 0.1 to 10 parts, preferably 0.5 to 2 parts, polyvinyl alcohol co-binder; 0.1 to 20 parts other co-binders; 0 to 0.2 parts defoamer, and sufficient water to provide the desired level of solids, usually about 45 to 70 wt.%, preferably 60 to 70 wt.%> or more for high solids paper coating compositions.
• the coating compositions produced may be applied to fibrous paper webs using any of the conventional coating devices, including trailing blade coaters, air-knife coaters roll coaters, and the like. It is possible to cook the PVOH in the presence of OB as delivered at ⁇ 17% solids without the addition of water as hereinafter described. The appearance of the resulting cooked blend, other than viscosity, does not change. Because of the viscosity, sometimes dilutions are desirable. However, at 27% blends solids, the papermaker has the benefit of a relatively high solids solution. For all the formulations discussed below, pigments are primarily calcium carbonate and clay, but may include titanium dioxide.
• pigments are delivered in dry or in water pre-dispersed form that may range from about 70% to 76% solids.
• Styrene butadiene latexes are delivered at about 50% solids.
• PVOH may be delivered in solid form to be cooked into solution prior to using, or in liquid form at 15%o to 30% solids.
• OBs for coating are delivered in liquid form at about 17% active ingredient, and are most preferably of the tetra or hexa sulfonated variety.
• Blends and coatings include 1/1, 2/1, 3.75/1 and 5/1 wet OB (Ciba's TINOPAL ® PT, a tetrasulfonated formVdry PVOH (CELVOL ® 203).
• Normal operations in paper mills call for PVOH and OBs to be added each as liquids into the formulating tank.
• the invention takes advantage of the water in the OB through the addition of dry PVOH to 100 pts of OB slurry in a vessel while stirring sufficiently to disperse the PVOH particles in a uniform fashion.
• the contents are then heated to 185°F to 205°F, depending upon the grade of PVOH used, preferably by steam heated water bath.
• the temperature of the blend is held at temperature for 30 minutes, at which time the PVOH will be totally solubilized and the blend may be either cooled or used hot.
• the solids levels above are considered maximum since no dilutions have taken place.
• the method of this invention results in paper coating formulations with higher total coating solids than can be achieved by conventional methods.
• the maximum coating solids that can be achieved, by adding the OB and PVOH (25% solids) each as liquids range from 64.4% to 70.0% and 69.0% to 70.2% (using 30% solids PVOH).
• 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 185°F to about 205°F to completely solubilize the PVOH. This solution is then added to either a 70% or 16% solids pigment dispersion to achieve the final coating solids shown below. Color coat formulations are sometimes expressed in dry parts and wet parts per 100 parts dry pigment.
• Table 2 below shows solids content for a standard formulation with 2/1 wet parts/dry parts OB/PVOH ratio per 100 parts of pigment by way of conventional formulation techniques.
• COMPARATIVE EXAMPLE Series A The color coat is formulated with either 70% or 76% solids pigment dispersions and 25% or 30% PVOH solution. Using the standard methodology of mixing liquid OB (usually 17% solids) with liquid PVOH, and adding to the pigment dispersion, the solids that can be achieved is shown below in Table 4:
• EXAMPLE Series 1 utilizes a solution prepared by adding dry PVOH to a 17% solution of OB to achieve the following concentrations.
• the OB/PVOH solution is prepared as follows:
• the control is the basic liquid-liquid addition sequence of PVOH and OB, whereas Examples 6-10 are in-situ pre-cooked PVOH/OB blends as noted above.
• Example 6 and the control are both formulated with a 3.75/1 wet OB/dry PVOH.
• the base paper has a brightness of 84.3 (standard - no UV). After coating, brightness values of the paper (again - no UV) improve to 85.3 and 85.6.
• the UV brightness measurements show a very significant further improvement to 89.0 and 88.9 - comparable to each other.
• the a* value indicates color shading to either red or green and these would be considered equal to each other.
• the b* value is important because it indicates the desirable blue-white with negative values and undesirable yellow with positive values.
• Examples 7 and 8 are formulated at 2/1 with OB/dry PVOH and compare the performance of two PVOH samples with different viscosity values. Both are pre-cooked with OB as per the invention. The significance here is that C-502 performs as well as C-203 and, since it is lower in viscosity, will allow for higher blend solids from 27% to 30% in the optical brightener concentrate for higher coating color solids benefits.
• Examples 9 and 10 were formulated at 2/1/1 wet OB/dry PVOH/polyethylene glycol 400; except that Example 10 had 2 parts less SBR.
• This example has an OB/PVOH ratio equivalent to a solution of 3 wet parts of optical brightener at 17% solids to 1 dry part polyvinyl alcohol resin.
• This example has an OB/PVOH ratio equivalent to a solution of 1 wet part of optical brightener at 17%) solids to 1 dry part of polyvinyl alcohol resin.
• a dry mixture of PVOH/optical Brightener powder can be added directly to a pigment dispersion while preparing a color coat composition if so desired.
• a preferred embodiment utilizes PVOH resin having a particle size of less than about 200 microns, that is, 99'% by weight of the resin particles pass through an 80 mesh sieve. This composition can be readily dissolved in the coating slurry during mixing with applied shear in the absence of external heating.

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• 2004
  • 2004-12-08 EP EP04813296A patent/EP1694759A1/de not_active Withdrawn
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