Classifications

• • 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
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B23/00—Methine or polymethine dyes, e.g. cyanine dyes
  • C09B23/14—Styryl dyes
  • C09B23/148—Stilbene dyes containing the moiety -C6H5-CH=CH-C6H5
• • 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
  • D21H21/18—Reinforcing 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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments

Definitions

• the instant invention relates to aqueous coating compositions comprising derivatives of diaminostilbene optical brightener, shading dyes, white pigments, primary binders, and optionally secondary binders which can be used to provide coated substrates of high whiteness and brightness.
• WO 0218705 A1 however teaches that the use of shading dyes, while having a positive effect on whiteness, has a negative impact on brightness.
• the solution to this problem is to add additional optical brightener, the advantage claimed in WO 0218705 A1 being characterized by the use of a mixture comprising at least one direct dye (exemplified by C.I. Direct Violet 35) and at least one optical brightener.
• shading dyes which have a strongly positive effect on whiteness while having little or no effect on brightness, and which can be used in coating compositions comprising optical brighteners, white pigments, primary binders, and optionally secondary binders in order to enable the papermaker to reach high levels of whiteness and brightness.
• the goal of the present invention is to provide aqueous coated compositions containing derivatives of diaminostilbene optical brightener, certain shading dyes, white pigments, primary binders, and optionally secondary binders, which afford enhanced high whiteness levels while avoiding the disadvantages characterized by the use of shading dyes (loss of brightness) or pigments (lower whiteness build) recognized as being state-of-the-art.
• the present invention therefore provides aqueous coating compositions for optical brightening and shading of substrates, preferably paper, comprising
• the CO 2 ⁇ group is preferably in the 2 or 4-position of the phenyl ring.
• Preferred compounds of formula (I) are those in which
• the anionic charge on the brightener is balanced by a cationic charge composed of one or more identical or different cations selected from the group consisting of hydrogen, an alkali metal cation, alkaline earth metal, ammonium which is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4 linear or branched hydroxyalkyl radical, ammonium which is, di-, tri- or tetrasubstituted by a mixture of C 1 -C 4 linear or branched alkylradical and linear or branched hydroxyalkyl radical or mixtures of said compounds,
• the anionic charge on the brightener is balanced by a cationic charge composed of one or more identical or different cations selected from the group consisting of Li + , Na + , K + , Ca 2+ , Mg 2+ , ammonium which is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4 linear or branched hydroxyalkyl radical, ammonium which is, di-, tri- or tetrasubstituted by a mixture of C 1 -C 4 linear or branched alkylradical and linear or branched hydroxyalkyl radical or mixtures of said compounds,
• the anionic charge on the brightener is balanced by a cationic charge composed of one or more identical or different cations selected from the group consisting of Na + , K + , triethanolammonium, N-hydroxyethyl-N,N-dimethylammonium, N-hydroxyethyl-N,N-diethylammonium or mixtures of said compounds,
• Compound of formula (I) is used in an amount typically of from 0.01 to 5% by weight, preferably in the range of from 0.05 to 3% by weight, the % by weight being based on the total weight of dry white pigment.
• Preferred compounds of formula (II) are those in which
• Compound of formula (II) is used in an amount typically of from 0.00001 to 0.05% by weight, preferably in the range of form 0.00005 to 0.02% by weight, the % by weight being based on the total weight of dry white pigment.
• the best white substrates for printing are made using opaque coating compositions comprise from 10 to 70% by weight of white pigments, preferably of from 40 to 60% by weight of white pigments, the % by weight being based on the total weight of the coating composition.
• white pigments are generally inorganic pigments, e.g., aluminium silicates (kaolin, otherwise known as china clay), calcium carbonate (chalk), titanium dioxide, aluminium hydroxide, barium carbonate, barium sulphate, or calcium sulphate (gypsum).
• a mixture of from 10 to 20% by weight of clay and of from 30 to 40% by weight of chalk is used as white pigments, the % by weight being based on the total weight of the coating composition.
• the binders may be any of those commonly used in the paper industry for the production of coating compositions and may consist of a single binder or of a mixture of primary and secondary binders.
• the sole or primary binder is preferably a synthetic latex, typically a styrene-butadiene, vinyl acetate, styrene acrylic, vinyl acrylic or ethylene vinyl acetate polymer.
• the preferred primary binder is a latex binder.
• the sole or primary binder is used in an amount typically in the range of form 2 to 25% by weight, preferably of from 4 to 20% by weight, the % by weight being based on the total weight of white pigment.
• the secondary binder which may be optionally used may be, e.g., starch, carboxymethylcellulose, casein, soy polymers, polyvinyl alcohol or a mixture of any of the above.
• the preferred secondary binder which may be optionally used is a polyvinyl alcohol binder.
• the polyvinyl alcohol which may be optionally used in the coating composition as secondary binder has preferably a degree of hydrolysis greater than or equal to 60% and a Brookfield viscosity of from 2 to 80 mPa ⁇ s (4% aqueous solution at 20° C.). More preferably, the polyvinyl alcohol has a degree of hydrolysis greater than or equal to 80% and a Brookfield viscosity of from 2 to 40 mPa ⁇ s (4% aqueous solution at 20° C.).
• the secondary binder is used in an amount typically in the range of form 0.1 to 20% by weight, preferably of from 0.2 to 8% by weight, more preferably of from 0.3 to 6% by weight, the % by weight being based on the total weight of white pigment.
• the pH value of the coating composition is typically in the range of from 5 to 13, preferably of from 6 to 11, more preferably of from 7 to 10.
• acids or bases may be employed.
• acids which may be employed include but are not restricted to hydrochloric acid, sulphuric acid, formic acid and acetic acid.
• bases which may be employed include but are not restricted to alkali metal and alkaline earth metal hydroxide or carbonates, ammonia or amines.
• the coating composition may contain by-products formed during the preparation of compounds of formula (I) and compounds of formula (II) as well as other conventional paper additives.
• additives are for example antifreezers, dispersing agents, synthetic or natural thickeners, carriers (e.g. polyethylene glycols), defoamers, wax emulsions, dyes, inorganic salts, solubilizing aids, preservatives, complexing agents, biocides, cross-linkers, pigments, special resins etc.
• the coating composition may be prepared by adding one or more compounds of formula (I) and one or more compounds of formula (II), to a preformed aqueous dispersion of one or more binders, optionally one or more secondary binders and one or more white pigments.
• One or more compounds of formula (I) and one or more compounds of formula (II) can be added in any order or at the same time to the preformed aqueous dispersion of one or more binders, optionally one or more secondary binders and one or more white pigments.
• One or more compounds of formula (I), one or more compounds of formula (II) and optionally one or more secondary binders can be added as solids or as preformed aqueous solutions to the preformed aqueous dispersion of one or more white pigments.
• the present invention further provides a process for the optical brightening and tinting of paper substrates characterized in that an aqueous coating composition containing at least one optical brightener, at least one certain shading dye, at least one white pigment, at least one binder and optionally at least one secondary binder is used.
• the concentration of compound of formula (I) in water is preferably of from 1 to 80% by weight, more preferably of from 2 to 50% by weight, even more preferably from 10 to 30% by weight, the % by weight being based on the total weight of the preformed aqueous solution containing the compound of formula (I).
• the concentration of compound of formula (II) in water is preferably of from 0.001 to 30% by weight, more preferably of from 0.01 to 25% by weight, even more preferably from 0.02 to 20% by weight, the % by weight being based on the total weight of the preformed aqueous solution containing the compound of formula (II).
• the concentration of secondary binders in water is preferably of from 1 to 50% by weight, more preferably of from 2 to 40% by weight, even more preferably from 5 to 30% by weight, the % by weight being based on the total weight of the preformed aqueous solution containing the secondary binders.
• An aqueous solution (S1) is prepared by slowly adding 157 parts of water to 843 parts of a preformed aqueous mixture containing 0.210 mol per kg of compound of formula (1) (synthesized according to example 1 in WO 2011/033064-A2 with the sole difference that the final solution was ultra-filtered to remove salts and concentrated to 0.210 mol per kg of compound of formula (1)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S1) containing 0.177 mol per kg of compound of formula (1).
• the resulting aqueous solution (S1) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S1a) is prepared by slowly adding 2 parts of compound of formula (a) and 155 parts of water to 843 parts of a preformed aqueous mixture containing 0.210 mol per kg of compound of formula (1) (synthesized according to example 1 in WO 2011/033064-A2 with the sole difference that the final solution was ultra-filtered to remove salts and concentrated to 0.210 mol per kg of compound of formula (1)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous formulation (S1a) containing compound of formula (a) at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous formulation (S1a) and 0.177 mol per kg of compound of formula (1).
• the resulting aqueous formulation (S1a) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S1 b) is prepared by slowly adding 2 parts of compound of formula (b) and 155 parts of water to 843 parts of a preformed aqueous mixture containing 0.210 mol per kg of compound of formula (1) (synthesized according to example 1 in WO 2011/033064-A2 with the sole difference that the final solution was ultra-filtered to remove salts and concentrated to 0.210 mol per kg of compound of formula (1)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S1b) containing compound of formula (b) at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S1b) and 0.177 mol per kg of compound of formula (1).
• the resulting aqueous solution (S1b) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S1c) is prepared by slowly adding 18.2 parts of a preformed aqueous solution containing 11 weight % of C.I. Direct Violet 35, the weight being based on the total weight of the aqueous C.I. Direct Violet 35 preformed solution and 138.8 parts of water to 843 parts of a preformed aqueous mixture containing 0.210 mol per kg of compound of formula (1) (synthesized according to example 1 in WO 2011/033064-A2 with the sole difference that the final solution was ultra-filtered to remove salts and concentrated to 0.210 mol per kg of compound of formula (1)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S1c) containing C.I. Direct Violet 35 at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S1c) and 0.177 mol per kg of compound of formula (1).
• the resulting aqueous solution (S1c) has a pH in the range of from 8.0 to 9.0.
• a coating composition is prepared containing 70 parts chalk (commercially available under the trade name Hydrocarb 90 from OMYA), 30 parts clay (commercially available under the trade name Kaolin SPS from IMERYS), 42.8 parts water, 0.6 parts dispersing agent (a sodium salt of a polyacrylic acid commercially available under the trade name Polysalz S from BASF), 20 parts of 50% latex (a styrene butadiene copolymer commercially available under the trade name DL 921 from Dow) and 0.8 parts of a polyvinyl alcohol having a degree of hydrolysis of 98-99% and Brookfield viscosity of 4.0-5.0 mPa ⁇ s (4% aqueous solution at 20° C.).
• the solids content of the coating composition is adjusted to approx. 65% by the addition of water, and the pH is adjusted to 8-9 with sodium hydroxide.
• Aqueous solutions (S1), (S1a), (S1b) and (S1c) prepared according to preparative example 1, 1a and 1b and comparative example 1c respectively are added to the stirred coating composition at a range of concentrations of from 0 to 2 weight % (from 0 to 0.4% by weight of compound of formula (1) based on dry solid), the % by weight being based on the total weight of the dry pigment.
• the coating composition is then applied to a commercial 75 gsm neutral-sized white paper base sheet using an automatic wire-wound bar applicator with a standard speed setting and a standard load on the bar.
• the coated paper is then dried for 5 minutes in a hot air flow. Afterwards the paper is allowed to condition and measured then for CIE Whiteness and brightness on a calibrated Elrepho spectrophotometer. Results are depicted in table 1a and 1b respectively and clearly shows the significant improvement in whiteness while avoiding the disadvantages characterized by the use of shading dyes (loss of brightness).
• An aqueous solution (S2) is prepared by slowly adding 157 parts of water to 843 parts of a preformed aqueous mixture containing 0.210 mol per kg of compound of formula (2) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that iminodiacetic acid is used instead of diethanolamine and the final solution is concentrated to 0.210 mol per kg of compound of formula (2)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S2) containing 0.177 mol per kg of compound of formula (2).
• the resulting aqueous solution (S2) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S2a) is prepared by slowly adding 2 parts of compound of formula (a) and 155 parts of water to 843 parts of a preformed aqueous mixture containing 0.210 mol per kg of compound of formula (2) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that iminodiacetic acid is used instead of diethanolamine and the final solution is concentrated to 0.210 mol per kg of compound of formula (2)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S2a) containing compound of formula (a) at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S2a) and 0.177 mol per kg of compound of formula (2).
• the resulting aqueous solution (S2a) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S2b) is prepared by slowly adding 2 parts of compound of formula (b) and 155 parts of water to 843 parts of a preformed aqueous mixture containing 0.210 mol per kg of compound of formula (2) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that iminodiacetic acid is used instead of diethanolamine and the final solution is concentrated to 0.210 mol per kg of compound of formula (2)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S2b) containing compound of formula (b) at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S2b) and 0.177 mol per kg of compound of formula (2).
• the resulting aqueous solution (S2b) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S2c) is prepared by slowly adding 18.2 parts of a preformed aqueous solution containing 11 weight % of C.I. Direct Violet 35, the weight % being based on the total weight of the aqueous C.I. Direct Violet 35 preformed solution and 138.8 parts of water to 843 parts of a preformed aqueous mixture containing 0.210 mol per kg of compound of formula (2) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that iminodiacetic acid is used instead of diethanolamine and the final solution is concentrated to 0.210 mol per kg of compound of formula (2)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S2c) containing C.I. Direct Violet 35 at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S2c) and 0.177 mol per kg of compound of formula (2).
• the resulting aqueous solution (S2c) has a pH in the range of from 8.0 to 9.0.
• a coating composition is prepared containing 70 parts chalk (commercially available under the trade name Hydrocarb 90 from OMYA), 30 parts clay (commercially available under the trade name Kaolin SPS from IMERYS), 42.8 parts water, 0.6 parts dispersing agent (a sodium salt of a polyacrylic acid commercially available under the trade name Polysalz S from BASF), 20 parts of 50% latex (a styrene butadiene copolymer commercially available under the trade name DL 921 from Dow) and 0.8 parts of a polyvinyl alcohol having a degree of hydrolysis of 98-99% and Brookfield viscosity of 4.0-5.0 mPa ⁇ s (4% aqueous solution at 20° C.).
• the solids content of the coating composition is adjusted to approx. 65% by the addition of water, and the pH is adjusted to 8-9 with sodium hydroxide.
• Aqueous solutions (S2), (S2a), (S2b) and (S2c) prepared according to preparative example 2, 2a and 2b and comparative example 2c respectively are added to the stirred coating composition at a range of concentrations of from 0 to 2 weight % (from 0 to 0.4% by weight of compound of formula (2) based on dry solid), the % by weight being based on the total weight of the dry pigment.
• the coating composition is then applied to a commercial 75 gsm neutral-sized white paper base sheet using an automatic wire-wound bar applicator with a standard speed setting and a standard load on the bar.
• the coated paper is then dried for 5 minutes in a hot air flow. Afterwards the paper is allowed to condition and measured then for CIE Whiteness and brightness on a calibrated Elrepho spectrophotometer. Results are depicted in table 2a and 2b respectively and clearly shows the significant improvement in whiteness while avoiding the disadvantages characterized by the use of shading dyes (loss of brightness).
• An aqueous solution (S3) is prepared by slowly adding 222.2 parts of water to 777.8 parts of a preformed aqueous mixture containing 0.157 mol per kg of compound of formula (3) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that aspartic acid is used instead of diethanolamine and the final solution is concentrated to 0.157 mol per kg of compound of formula (3)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S3) containing 0.122 mol per kg of compound of formula (3).
• the resulting aqueous solution (S3) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S3a) is prepared by slowly adding 2 parts of compound of formula (a) and 220.2 parts of water to 777.8 parts of a preformed aqueous mixture containing 0.157 mol per kg of compound of formula (3) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that aspartic acid is used instead of diethanolamine and the final solution is concentrated to 0.157 mol per kg of compound of formula (3)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S3a) containing compound of formula (a) at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S3a) and 0.122 mol per kg of compound of formula (3).
• the resulting aqueous solution (S3a) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S3b) is prepared by slowly adding 2 parts of compound of formula (b) and 220.2 parts of water to 777.8 parts of a preformed aqueous mixture containing 0.157 mol per kg of compound of formula (3) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that aspartic acid is used instead of diethanolamine and the final solution is concentrated to 0.157 mol per kg of compound of formula (3)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S3b) containing compound of formula (b) at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S3b) and 0.122 mol per kg of compound of formula (3).
• the resulting aqueous solution (S3b) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S3c) is prepared by slowly adding 18.2 parts of a preformed aqueous solution containing 11 weight % of C.I. Direct Violet 35, the weight % being based on the total weight of the aqueous C.I. Direct Violet 35 preformed solution and 204.0 parts of water to 777.8 parts of a preformed aqueous mixture containing 0.157 mol per kg of compound of formula (3) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that aspartic acid is used instead of diethanolamine and the final solution is concentrated to 0.157 mol per kg of compound of formula (3)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S3c) containing C.I. Direct Violet 35 at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S3c) and 0.122 mol per kg of compound of formula (3).
• the resulting aqueous solution (S3c) has a pH in the range of from 8.0 to 9.0.
• a coating composition is prepared containing 70 parts chalk (commercially available under the trade name Hydrocarb 90 from OMYA), 30 parts clay (commercially available under the trade name Kaolin SPS from IMERYS), 42.8 parts water, 0.6 parts dispersing agent (a sodium salt of a polyacrylic acid commercially available under the trade name Polysalz S from BASF), 20 parts of 50% latex (a styrene butadiene copolymer commercially available under the trade name DL 921 from Dow) and 0.8 parts of a polyvinyl alcohol having a degree of hydrolysis of 98-99% and Brookfield viscosity of 4.0-5.0 mPa ⁇ s (4% aqueous solution at 20° C.).
• the solids content of the coating composition is adjusted to approx. 65% by the addition of water, and the pH is adjusted to 8-9 with sodium hydroxide.
• Aqueous solutions (S3), (S3a), (S3b) and (S3c) prepared according to preparative example 3, 3a and 3b and comparative example 3c respectively are added to the stirred coating composition at a range of concentrations of from 0 to 2 weight % (from 0 to 0.4% by weight of compound of formula (3) based on dry solid), the % by weight being based on the total weight of the dry pigment.
• the coating composition is then applied to a commercial 75 gsm neutral-sized white paper base sheet using an automatic wire-wound bar applicator with a standard speed setting and a standard load on the bar.
• the coated paper is then dried for 5 minutes in a hot air flow. Afterwards the paper is allowed to condition and measured then for CIE Whiteness and brightness on a calibrated Elrepho spectrophotometer. Results are depicted in table 3a and 3b respectively and clearly shows the significant improvement in whiteness while avoiding the disadvantages characterized by the use of shading dyes (loss of brightness).
• An aqueous solution (S4) is prepared by slowly adding 222.2 parts of water to 777.8 parts of a preformed aqueous mixture containing 0.157 mol per kg of compound of formula (4) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that diisopropanolamine is used instead of diethanolamine and the final solution is concentrated to 0.157 mol per kg of compound of formula (4)) at room temperature with efficient stirring. The obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S4) containing 0.122 mol per kg of compound of formula (4).
• the resulting aqueous solution (S4) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S4a) is prepared by slowly adding 2 parts of compound of formula (a) and 220.2 parts of water to 777.8 parts of a preformed aqueous mixture containing 0.157 mol per kg of compound of formula (4) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that diisopropanolamine is used instead of diethanolamine and the final solution is concentrated to 0.157 mol per kg of compound of formula (4)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S4a) containing compound of formula (a) at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S4a) and 0.122 mol per kg of compound of formula (4).
• the resulting aqueous solution (S4a) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S4b) is prepared by slowly adding 2 parts of compound of formula (b) and 220.2 parts of water to 777.8 parts of a preformed aqueous mixture containing 0.157 mol per kg of compound of formula (4) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that diisopropanolamine is used instead of diethanolamine and the final solution is concentrated to 0.157 mol per kg of compound of formula (4)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S4b) containing compound of formula (b) at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S4b) and 0.122 mol per kg of compound of formula (4).
• the resulting aqueous solution (S4b) has a pH in the range of from 8.0 to 9.0.
• An aqueous solution (S4c) is prepared by slowly adding 18.2 parts of a preformed aqueous solution containing 11 weight % of C.I. Direct Violet 35, the weight % being based on the total weight of the aqueous C.I. Direct Violet 35 preformed solution and 204.0 parts of water to 777.8 parts of a preformed aqueous mixture containing 0.157 mol per kg of compound of formula (4) (synthesized according to example 1 in WO 2011/033064-A2 with the sole differences that diisopropanolamine is used instead of diethanolamine and the final solution is concentrated to 0.157 mol per kg of compound of formula (4)) at room temperature with efficient stirring.
• the obtained mixture is stirred for 1 hour at room temperature to afford 1000 parts of an aqueous solution (S4c) containing C.I. Direct Violet 35 at a concentration of 0.2 weight %, the weight % being based on the total weight of the final aqueous solution (S4c) and 0.122 mol per kg of compound of formula (4).
• the resulting aqueous solution (S4c) has a pH in the range of from 8.0 to 9.0.
• a coating composition is prepared containing 70 parts chalk (commercially available under the trade name Hydrocarb 90 from OMYA), 30 parts clay (commercially available under the trade name Kaolin SPS from IMERYS), 42.8 parts water, 0.6 parts dispersing agent (a sodium salt of a polyacrylic acid commercially available under the trade name Polysalz S from BASF), 20 parts of 50% latex (a styrene butadiene copolymer commercially available under the trade name DL 921 from Dow) and 0.8 parts of a polyvinyl alcohol having a degree of hydrolysis of 98-99% and Brookfield viscosity of 4.0-5.0 mPa ⁇ s (4% aqueous solution at 20° C.).
• the solids content of the coating composition is adjusted to approx. 65% by the addition of water, and the pH is adjusted to 8-9 with sodium hydroxide.
• Aqueous solutions (S4), (S4a), (S4b) and (S4c) prepared according to preparative example 4, 4a and 4b and comparative example 4c respectively are added to the stirred coating composition at a range of concentrations of from 0 to 2 weight % (from 0 to 0.4% by weight of compound of formula (4) based on dry solid), the % by weight being based on the total weight of the dry pigment.
• the coating composition is then applied to a commercial 75 gsm neutral-sized white paper base sheet using an automatic wire-wound bar applicator with a standard speed setting and a standard load on the bar.
• the coated paper is then dried for 5 minutes in a hot air flow. Afterwards the paper is allowed to condition and measured then for CIE Whiteness and brightness on a calibrated Elrepho spectrophotometer. Results are depicted in table 4a and 4b respectively and clearly shows the significant improvement in whiteness while avoiding the disadvantages characterized by the use of shading dyes (loss of brightness).

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