JPS6143374B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an organic aqueous dispersion white pigment composition having excellent whiteness and hiding power. Pigments are widely used in coating materials such as paints, paper processing agents, and fiber treatment agents, and many inorganic and organic pigments are known. However, there are far more organic pigments than inorganic pigments, but the ones currently used as white pigments are titanium oxide, lithopone,
There are no organic pigments useful as white pigments, only inorganic pigments such as antimony white, zinc white, and zinc sulfide. However, since inorganic pigments have a high specific gravity, they have the disadvantage that coated articles coated with inorganic pigments are heavy. In particular, when covering lightweight paper, fibers, etc., it is preferable to use a lightweight covering material. Since the weight of the coating material is mainly due to the pigment, in order to reduce the weight of the coating material, a lightweight pigment, especially a lightweight white pigment, is necessary. As long as the white pigment could be obtained from an organic substance, the problem of reducing the weight of the coating material could be easily solved.
The present inventors have conducted numerous studies on organic substances that can be used as organic white pigments, and have found that only synthetic resins are useful for such applications. In particular, fine particle synthetic resin can be easily obtained by emulsion polymerization, and when the obtained synthetic resin emulsion is dried at a temperature below the glass transition point of the synthetic resin, the synthetic resin particles do not form a film and remain in a particle state. It was discovered that the particles can appear white due to diffuse reflection of light on the surface of the particles. However, since the synthetic resin itself is colorless and transparent, the whiteness and hiding power are insufficient due to the diffuse reflection of light on the surface alone, and it cannot be used as a white pigment as it is. Therefore,
As a result of further intensive research in order to obtain an excellent organic white pigment, the present inventors discovered that an optical brightener is dissolved in a monomer whose glass transition point is 40°C or higher. An aqueous dispersion organic white pigment composition used at a temperature below the glass transition point and containing as a main ingredient fluorescent whitening vinyl resin particles obtained by emulsifying or dispersing a uniformly dispersed monomer composition in water and polymerizing it. The present invention was completed based on the discovery of a new fact that the following various remarkable effects can be achieved. Thus, when the aqueous dispersed organic white pigment composition of the present invention is used as a pigment, it must be dried at a temperature below the glass transition point.
If drying is carried out at a temperature above the glass transition point,
The resin particles fuse together and form a transparent film, which does not exhibit the effect of exhibiting a white color due to diffused reflection of light. That is, since the aqueous dispersed organic white pigment composition of the present invention is an organic substance, its weight is less than half that of an inorganic pigment, and if this aqueous dispersed organic white pigment composition is used, a lightweight coating layer can be formed. It is possible to easily produce a coating material that can obtain Furthermore, the difference between inorganic pigments and the aqueous dispersed organic white pigment composition of the present invention lies in their whiteness. In the aqueous dispersion organic white pigment composition of the present invention,
By changing the type and amount of fluorescent brightener used, the degree of whiteness can be adjusted freely, and the whiteness brightened by the fluorescent brightener cannot be achieved with inorganic white pigments. Furthermore, since the aqueous dispersion organic white pigment composition of the present invention is obtained in the form of fine particles dispersed in water, it has excellent applicability to aqueous coating compositions. In other words, in order to obtain an aqueous coating composition, it is necessary to uniformly disperse a pigment in an aqueous solution of a water-soluble resin or an aqueous dispersion of a water-insoluble resin as a binder. Since the substances are already dispersed in water in a stable state, they can be dispersed and mixed extremely uniformly by simply adding them to the binder and stirring. The fluorescent whitening agent used in the present invention is a substance that can radiate a part of the absorbed light energy again in the form of blue-violet fluorescence. -Diaminostilbene-2,2'-disulfonic acid derivatives, distyrylbenzene derivatives, imidazole, thiazole and oxazole derivatives, imizolone derivatives, triazole derivatives, coumarin derivatives, carbostyril derivatives, piphenyl compounds, naphthalimide derivatives, oxacyanine compounds, pyridine derivative,
Examples include pyrazoline derivatives, but are not limited to these. However, the use of optical brighteners which have the effect of inhibiting the polymerization of monomers should be avoided. Examples of vinyl monomers whose glass transition point is 40°C or higher in the resin obtained by polymerization include styrene, methylstyrene, vinyl chloride, acrylonitrile,
It is preferable to use one or more selected from methyl methacrylate, ethyl methacrylate, and isobutyl methacrylate. These vinyl monomers can also be used in combination with other vinyl monomers in an amount that does not lower the glass transition point of the copolymer resin to 41° C. or lower. Examples of other vinyl monomers include vinyl esters, acrylic esters, methacrylic esters other than those mentioned above, olefins, and dienes. Furthermore, monomers having functional groups other than vinyl groups may also be used in combination. Examples of such monomers include unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, unsaturated acid amides, N-methylolated products of unsaturated amides, and N- These include alkoxymethyl unsaturated acid amides, glycidyl unsaturated acid esters, allyl acrylate, diethylene glycol methacrylate, dipinylbenzene, and vinylpyrrolidone. In addition, the glass transition point of the resin obtained by polymerization is
Monomers below 40°C cannot be used in the present invention. This is because, in the present invention, when a synthetic resin emulsion is dried at a temperature below the glass transition point of the synthetic resin, the synthetic resin particles do not form a film and are obtained in a particle state, which takes on a white color due to the diffuse reflection of light on the particle surface. It is effective. However, if the glass transition point of the resin obtained by polymerization is below 40°C, the resulting resin particles will fuse during drying and lose their transparency when used under normal usage conditions, that is, natural drying conditions. This is because since it forms a film, it has neither whiteness nor hiding power, and does not exhibit the effect as a white pigment. For example, a synthetic resin emulsion with a glass transition point of 18°C becomes a transparent film when dried at 20°C (room temperature), and a synthetic resin emulsion with a glass transition point of 30°C becomes a transparent film when dried at 35°C (room temperature in summer). , it is still a transparent film with almost no whiteness or hiding power. In order to obtain the aqueous dispersed organic white pigment composition of the present invention, first, a fluorescent brightener is dissolved or uniformly added to a vinyl monomer whose glass transition point is 40°C or higher. It can be obtained by dispersing to obtain a monomer composition, and then subjecting this monomer composition to emulsion polymerization using a conventional emulsion polymerization method. A particularly preferred emulsion polymerization method is an emulsion polymerization method in which a monomer composition is emulsified in advance in water, and the emulsion of this monomer composition is dropped into a polymerization system for polymerization. If the optical brightener is poorly soluble in vinyl monomers or has a slow dissolution rate, dissolve or disperse the optical brightener in an organic solvent and/or surfactant before applying to the vinyl monomer. By adding the optical brightener to the vinyl monomer, or by dissolving the organic solvent and/or surfactant in the vinyl monomer in advance and then adding the optical brightener, the optical brightener can be easily converted into vinyl. It can be dissolved or dispersed in the system monomer. The amount of optical brightener used is not particularly limited, but
The amount of optical brightener to vinyl monomer is 0.001
% (weight %, hereinafter the same) or more is preferable. Emulsifiers, emulsion polymerization solvents, and the like used in emulsion polymerization are those commonly used. The aqueous dispersed organic white pigment composition of the present invention includes:
A non-white pigment and an inorganic extender pigment can also be used in combination depending on the purpose. In addition, colored inorganic pigments, organic pigments, dyes, etc. can also be used in combination for coloring. When coloring, since the color tone differs when wet and dry, it is necessary to adjust the color so that the desired color tone is obtained when dry. Next, the aqueous dispersion organic white pigment composition of the present invention will be explained with reference to Examples and Test Examples. In addition, in the examples, parts simply refer to parts by weight. Example 1 425 parts of styrene and 13 parts of methacrylic acid were mixed, and HOSTALUX KCB was added.
(trade name, benzoxazole optical brightener manufactured by Hoechst, West Germany) was dissolved to obtain a monomer composition. Next, 88 parts of a 25% aqueous solution of anionic surfactant and 22 parts of nonionic surfactant were dissolved in 265 parts of water, and 438 parts of the monomer composition was added thereto, followed by stirring to dissolve the monomer composition in water. The mixture was emulsified to obtain a monomer composition emulsion. Next, in a polymerization reaction vessel equipped with a stirrer, a reflux condenser, and a dropping funnel, 145 parts of water, 22 parts of a 25% aqueous solution of an anionic surfactant, 7 parts of a nonionic surfactant, and the emulsion of the monomer composition were added. Add 80 parts of ammonium persulfate and 4 parts of 10% aqueous solution and stir while stirring.
Initial polymerization was carried out at 85°C for 1 hour, and then 733 parts of the monomer composition emulsion and 9 parts of 10% ammonium persulfate aqueous solution were added dropwise over 3 hours to carry out emulsion polymerization to form an aqueous dispersion. An organic white pigment composition was obtained. The glass transition temperature of the resin thus obtained was approximately 100°C. Example 2 300 parts of styrene and 90 parts of acrylonitrile were mixed, and HOSTALUX
A monomer composition was obtained by dissolving 20 parts of PN (l) (trade name, 10% solvent dispersion of birazoline optical brightener manufactured by Hoechst, West Germany). Next, 7 parts of anionic surfactant and 3 parts of nonionic surfactant were dissolved in 270 parts of water, and 410 parts of the monomer composition was added thereto, and the monomer composition was emulsified in water by stirring. A monomer composition emulsion was obtained. Next, in a polymerization reaction vessel equipped with a stirrer, a reflux condenser, and a dropping funnel, 260 parts of water, 1 part of nonionic surfactant, 70 parts of the monomer composition emulsion, and 12 parts of 4% potassium persulfate aqueous solution were added. and 2.5 parts of Rongarit 10% aqueous solution were charged and heated to 75-80°C with stirring to carry out initial polymerization for 30 minutes, followed by 620 parts of the monomer composition emulsion and 4% potassium persulfate aqueous solution.
Emulsion polymerization was carried out while adding 29 parts and 5.5 parts of a 10% Rongarit aqueous solution dropwise over 3 hours and 30 minutes. An aqueous dispersed organic white pigment composition was obtained. The glass transition temperature of the resin thus obtained was approximately 100°C. Example 3 420 parts of methyl methacrylate, butyl acrylate
A monomer composition was obtained by mixing 75 parts of acrylic acid and 15 parts of acrylic acid, and further dissolving 15 parts of HOSTALUX SN (trade name, pyrazoline optical brightener manufactured by Hoechst AG, West Germany). Next, in a polymerization reaction vessel equipped with a stirrer, a reflux condenser, and a dropping funnel, 445 parts of water, 16 parts of anionic surfactant, 3 parts of nonionic surfactant, and 1 part of sodium acetate were added.
and 3 parts of a 10% ammonium persulfate aqueous solution were charged, heated to 80 to 85°C while stirring, and 525 parts of the monomer composition and 7 parts of a 10% ammonium persulfate aqueous solution were added dropwise over 3 hours. Emulsion polymerization was carried out to obtain an aqueous dispersion of an organic white pigment composition. The glass transition temperature of the resin thus obtained was approximately 80°C. Comparative Example 1 (using the composition of Example 1, Hostalax was dispersed in water in advance and the monomer was polymerized) In 410 parts of water, 0.3 part of Hostalax was mixed with 27 parts of nonionic surfactant. Add a mixture mixed with a small amount of water. Next, 25% aqueous solution of anionic surfactant
110 parts, 425 parts of styrene, 13 parts of methacrylic acid and
Add 13 parts of 10% ammonium persulfate. 90% of the mixture at a low temperature of not less than 70-80%
℃, 80% of the remaining liquid was gradually added over 2 to 3 hours, and the polymerization reaction was completed by reacting at 80 to 85℃ for 2 hours, resulting in an aqueous dispersed organic white pigment composition. I got it. The glass transition temperature of the resin thus obtained was approximately 100°C. Test Example 1 Paint A as shown in Table 1 was produced using a combination of the aqueous dispersed organic white pigment composition obtained in Example 1 and an inorganic pigment. Pigment B as shown in Table 1 was prepared. and compared them. Paint film whiteness and gloss are higher with paint A than with paint B.
It was better. The concealing power was the same in both cases. In particular, although Paint A uses the same volume of pigment as Paint B (both use 12.3 parts by volume of pigment), in addition to the inorganic pigment, it also contains the aqueous dispersion of the organic white pigment composition of the present invention. Since the material was used, the coating film was extremely lightweight.

[Table] Test Example 2 Using the aqueous dispersed organic white pigment composition obtained in Example 2, coating composition C for coated paper as shown in Table 2 was produced, and for comparison, coating composition C for coated paper was prepared using an inorganic pigment. Coating composition D for coated paper was prepared as shown in the table.
And compared these. Coating composition C for coated paper was superior to coating composition D for coated paper in terms of whiteness and gloss of the coating film. Furthermore, the concealing power was at the same level in both cases. In particular, coating composition C for coated paper uses the same volume of pigment as coating composition D for coated paper, but since it uses the aqueous dispersion organic white pigment composition of the present invention, the amount of pigment is The weight was less than 1/2 of that of coating composition D for coated paper, and an extremely lightweight coated paper could be obtained.

【table】

[Table] Test Example 3 The emulsions of Example 1 and Comparative Example 1 were applied to a glass plate at a coating weight of 100 g/m ² , dried at room temperature for 24 hours, and then tested for whiteness using a weatherometer for 200 hours. As a result, the sample of Example 1 was shining white with almost no change compared to before being subjected to the Weather-Ometer, but the sample of Comparative Example 1 was shining white before being subjected to the Weather-Ometer, but After that, it lost all its luster.

Claims (1)

[Claims] 1 The glass transition point of the resin obtained by polymerization is 40℃
Glass transition consisting of fluorescent whitening vinyl resin particles obtained by polymerizing and emulsifying or dispersing in water a monomer obtained by dissolving or uniformly dispersing a fluorescent brightener in the above vinyl monomer. An aqueous dispersion organic white pigment composition for use below.