JPH0696681B2 - Method for producing heat resistant coated pigment - Google Patents

Description

Description: TECHNICAL FIELD The present invention provides chemical and thermal stability and weather resistance by providing a coating of a metal oxide or silica (hereinafter referred to as a metal oxide) on the surface of a hydrophilic inorganic pigment. , A method for producing a pigment having excellent heat resistance.

[Conventional technology and problems]

Generally, a pigment exposed to a high temperature is provided with a heat resistant coating on the surface of the pigment in order to improve heat resistance. For example, in the case of cadmium pigments, the main component of cadmium sulfide is 700 ° C.
When it is exposed to high temperature, it produces cadmium oxide or cadmium sulfate, so that it is discolored and a clear color tone cannot be exhibited. Therefore, there is a problem that the cadmium-based pigment cannot be used for things such as porcelain tiles that are baked at high temperature. In addition, yellow lead or molybdenum red containing lead chromate as a main component is easily reduced when kneaded with a resin at 200 ° C. or higher, and decomposes and discolors, so that it cannot be used for engineering plastics. Therefore, the heat resistance is increased by coating the surface of these pigments with silicic acid or a silicate insoluble in water. Conventionally, the following methods have been known as surface treatment methods for improving the heat resistance of pigments.

(A) A method of forming a coating by adding a silicate at the time of generating a precipitate which is a raw material of a pigment, dispersing fine silica powder, and adhering it to the surface of the precipitate.

(B) A method of preventing oxidative decomposition or the like of a pigment by mixing a pigment with a stable substance such as zirconium silicate which is not affected by glaze and firing the mixture.

(C) Insoluble in silicic acid or water by adding a water-soluble silicate to an aqueous dispersion of the calcined pigment and further adding a water-soluble salt of an acid or an alkaline earth metal, zinc, aluminum, zirconium, etc. A method of forming a film by precipitating the silicate of the above to adhere to the surface of the pigment.

However, it is difficult to apply the surface of the primary particles of the pigment uniformly and densely by the conventional coating method, and the satisfactory effect is not achieved.

[Knowledge on problem solving]

In order to overcome the problems of the above-mentioned conventional methods, the present inventors have proceeded with a study on a method for forming a coating film by depositing a metal oxide, and as a result, a hydrophilic pigment was treated with a metal alkoxide such as an alkyl silicate or a metal alkoxide and a solvent thereof. It was found that a uniform and dense coating can be formed at a relatively low temperature when immersed in a mixed solution, and the invention based on this finding was previously filed as "a method for producing a heat-resistant coated pigment" (Japanese Patent Application No.
61-142808, 61-142809, 61-142810, 61-1428
11). According to the above method, compared with the conventional film forming method,
It is possible to produce a coated pigment having remarkably excellent chemical and thermal stability.

The present inventors have further improved the above-mentioned prior application method, by adding a metal alkoxide or a mixed solution of a metal alkoxide and a solvent to a hydrophilic pigment and performing wet pulverization, a more uniform and dense coating film is formed, and a solvent is used. It was also found that the amount used can be significantly reduced.

[Structure of Invention]

According to the present invention, a hydrophilic inorganic pigment is added with a metal alkoxide or a mixed solution of a metal alkoxide and a solvent and wet-milled, and a metal oxide film is formed on the surface of the pigment by hydrolysis of the metal alkoxide. A manufacturing method is provided.

As a preferred embodiment thereof, a production method in which water is added to accelerate hydrolysis of the metal alkoxide simultaneously with or after the wet pulverization, or as the metal alkoxide, silicon, aluminum, zirconium, titanium, or boron is used. There are provided manufacturing methods using alkoxides containing metal elements of zinc, zinc, and tin, respectively.

The hydrophilic inorganic pigment used in the present invention, cadmium pigment, yellow lead, iron hydroxide, iron oxide, color pigments such as ultramarine,
Further, white pigments such as titanium oxide and zinc oxide, extender pigments such as calcium carbonate and barium sulfate, and most other inorganic pigments are included.

The metal alkoxide used in the present invention is an alkoxide containing silicon in addition to each metal element. For example, each metal or silicon of aluminum, zirconium, titanium, boron, zinc, tin and an alkoxy group such as ethoxy, methoxy, and propoxy. Specifically, alkyl silicates such as methyl silicate (silicon tetramethoxide) and ethyl silicate (silicon tetraethoxide), and zirconium tetrabutoxide, titanium tetrapropoxide, aluminum triisopropoxide, boron triethoxy. Do and the like. These alkoxide solutions may be used as a mixture of two or more kinds. In this case, various characteristics can be added in addition to heat resistance by combining those having different properties.

Besides using the metal alkoxide alone, a mixed solution of the metal alkoxide and a solvent is also used. A solvent having a good compatibility with the metal alkoxide is used, and specifically, methyl alcohol, ethyl alcohol, propyl alcohol, acetylacetone, ethyl acetate, ethylene glycol and the like are preferable. Addition of these solvents enhances the dispersibility of the pigment and accelerates the pulverization of the pigment.

In the method of the present invention, the metal alkoxide or a mixed solution of the metal alkoxide and a solvent is added to the pigment, and wet grinding is performed. The crushing may be performed using a commonly used crusher such as a ball mill, a liquor mill, and a sand mill. In addition, it is preferable to use a closed type mixing and crushing machine in order to prevent the solvent from volatilizing.

The mixing ratio of pigment and metal alkoxide is
With respect to 100 parts by weight, the metal alkoxide is 0.1 to 100 parts by weight, preferably 1.0 to 40 parts by weight.If it is less than 0.1 parts by weight, the coating effect is poor, and if it exceeds 100 parts by weight, the coloring power and the coloring property are poor. . If necessary, the solvent is mixed with 60 parts by weight or less of the metal alkoxide, and 35 to 100 parts by weight of the metal alkoxide or the metal alkoxide mixed solution is added to 100 parts by weight of the pigment, and wet grinding is performed. When the amount of the mixed solution added is less than 35 parts by weight or more than 100 parts by weight, the pulverizing effect is small. The amount of water added is not particularly limited, but the amount required for hydrolysis is 20 parts by weight or less.

By adding the metal alkoxide or a mixed solution thereof to the hydrophilic inorganic pigment and stirring and mixing, the metal alkoxide, for example, tetraethyl silicate, is bonded to the hydrophilic group of the pigment surface such as diazo group, hydroxyl group, halogen group, amino group and the like. Then, hydrolysis occurs and a metal oxide coating is formed on the surface of the pigment. When the metal oxide coating is, for example, an alkyl silicate [Si (OR) ₄ , R is an alkyl group], it mainly consists of —SiO— bonds, and a part of —SiOR is polymerized. Incidentally, a part of metal hydroxides, for example, those present as -SiOH, are converted into oxides by firing after coating formation.

In the present invention, the pulverization of the pigment and the mixing with the metal alkoxide are simultaneously performed, and the pulverization of the pigment is performed in the presence of the metal alkoxide. Therefore, the pulverization of the pigment always causes a new surface to appear, and the hydrolysis continuously proceeds on the surface,
Further, a uniform and dense metal oxide coating is firmly formed on the pigment surface by a mechanochemical action due to the heat at the time of pulverization.

The degree of pulverization of the pigment may be primary particles, and for example, 24 hours are sufficient in a ball mill. Rather, the grinding time depends on the hydrolysis time of the metal alkoxide. For example, in the case of silicon tetraethoxide, pulverization in the case where water is not added requires 200 hours or more, but in the present invention, the pigment surface is activated by the pulverization, and the hydrolysis proceeds due to the hydrophilic group on the pigment surface. A mixing and grinding time of 24 hours is sufficient.

In order to accelerate the hydrolysis of the metal alkoxide, water may be added at the same time as the wet pulverization or after the pulverization.
By adding water during milling, the hydrolysis proceeds rapidly on the new surface of the pigment produced by milling. Further, by adding water after the pulverization, the metal oxide generated by the hydrolysis of the metal alkoxide deposited on the surface of the pigment through the pulverization and mixing step is laminated, and a more dense metal oxide film is strongly formed.

The amount of water added is usually 17.3 parts by weight when almost 100 parts by weight of a metal alkoxide, eg, silicon tetraethoxide, is hydrolyzed. If you react for a long time (100 hours or more), the amount of water added may be 8.6 parts by weight.
Also, even if water is added up to 500 parts by weight, if ammonia water is added to adjust the pH to 5 to 7, gelation is promoted, the pigment paste is solidified, and the coated pigment dried by crushing it is chemically,
Excellent thermal stability. When water is added, if methyl alcohol, ethyl alcohol, propyl alcohol, acetylacetone, ethyl acetate, ethylene glycol or the like is added, the miscibility with the metal alkoxide is improved. Furthermore, the addition of an acid catalyst accelerates the hydrolysis reaction.

When water or the like is added to promote the hydrolysis of the metal alkoxide, it is advisable to add an inert liquid organic fluorine compound in order to adjust the progress of the hydrolysis so that rapid hydrolysis does not proceed at one time. . As the inert organic fluorine compound, a perfluoroalkane, for example, "Inert Liquid EF-L100" manufactured by Mitsubishi Metals Co., Ltd. (perfluorooctane); a perfluoro cyclic ether, for example, "Inert Liquid EF-L102" manufactured by Mitsubishi Metals Co., Ltd. Triperfluoroalkylamines such as "EF-L174" (triperfluorobutylamine) manufactured by Mitsubishi Metals Co., Ltd., perfluoropolyether oils such as "Demnum" manufactured by Daikin Industries, Ltd., and the like can be used.

〔The invention's effect〕

The coated pigment according to the present invention is excellent in chemical and thermal stability and weather resistance, and particularly as a coloring material for engineering plastics and engineering plastics that require heat resistance, exhibits a clear color even at high temperatures. For example, the cadmium pigment is 11
It can withstand baking at a high temperature of 50 ° C or higher, and can obtain clear colors without discoloration or decolorization. In addition, yellow lead and molybdenum red can withstand a temperature of 280 ° C and can be used as a coloring material for engineering plastics. Further, when it is applied to titanium oxide, it is less likely to be decomposed by light or ultraviolet rays, and weather resistance and light resistance are improved.

Further, in the production method of the present invention, the pigment dispersion and the coating reaction are carried out under high viscosity. Therefore, when a solvent is used in addition to the metal alkoxide, the addition amount of the solvent such as ethyl alcohol is reduced to 1/20 of the conventional amount. Even if the amount is reduced to 1/30, the sufficient coating effect can be enhanced.

When the pigment and the metal alkoxide are mixed, if the pulverization is not performed, a large amount of a solvent such as ethyl alcohol is required in order to uniformly coat the primary particle surface of the pigment with the metal alkoxide. Therefore, in industrial production, there is a problem that it is necessary to recover the solvent, and a waste gas treatment must be performed when drying the remaining solvent.

In the production method of the present invention, since the amount of solvent used is greatly reduced, such a problem does not occur.

〔Example〕

 The present invention will be specifically described below according to examples.

Examples 1 to 5 Cadmium pigments and metal alkoxides were mixed in a ball mill for 12 hours or more in accordance with the formulations shown in Table 1 and mixed with a predetermined amount of water.
After adding 1N hydrochloric acid and ethyl alcohol, the mixture was further mixed in a ball mill for 24 hours or more, and the ethyl alcohol was removed under reduced pressure, followed by drying at 100 ° C. for 10 hours and 200 ° C. for 3 hours. The coated pigment obtained here was used as a medium-degree frit glaze (SK4-6).
Was added to 5% by weight, and appropriate water was added to form a slurry, which was mixed in a ball mill for 2 hours and then glazed on a porcelain tile.
After fully drying at room temperature and 300 ° C for 3 hours, 4 ~
The temperature was raised at 1100 to 1200 ° C. for 5 hours and baking was carried out for 5 to 30 minutes to examine the change in color tone. The results are shown in Table 1.

Examples 6 and 7 After performing the coating reaction under the same conditions and methods as in Examples 1 to 5 according to Table 1, the pigment paste was transferred from the ball mill, and 1N ammonia water was added while stirring with a high-viscosity stirrer to adjust the pH to 5 It was adjusted to ~ 7 to promote gelation, solidified, then pulverized, and dried at 100 ° C for 10 hours and 200 ° C for 3 hours. The coated pigment obtained here was glazed on a porcelain tile under the same conditions as in Examples 1 to 5 and baked to examine the change in color tone. The results are shown in Table 1.

Examples 8 to 11 According to the formulations shown in Table 1, a coating reaction was carried out on the yellow lead and molybdenum pigments under the same conditions and methods as in Examples. Thereafter, as in Examples 6 and 7, 1N ammonia water was added to the mixture while stirring with a high-viscosity stirrer to adjust the pH to 5 to 7, promote gelation, solidify, then pulverize, and dry at 100 ° C. for 10 hours. . 0.5% of the coated pigment obtained here was added to polypropylene resin, and after thorough mixing, 200 ° C, 250 ° C, 28 ° C in an injection molding machine.
After kneading at 0 ℃ for 10 minutes to form a thickness of 1 mm, JISZ 8722,
Calculate L, a, b according to 8730 I checked. The results are shown in Table 1.

Comparative Example 1 2 parts by weight of sodium metasilicate was added to 100 parts by weight of water,
After the dissolution, 10 parts by weight of cadmium red was added, and after sufficiently mixing for 2 hours, 1N sulfuric acid was dropped little by little to adjust the pH to 6.5 to 7.5, and after the dropping was completed, the mixture was sufficiently stirred at 40 ° C. for 5 hours, The mixture was stirred at room temperature for 20 hours or more, filtered, washed with water, air-dried at room temperature, then dried at 100 ° C for 10 hours and at 200 ° C for 3 hours. The coated pigment obtained here was added to the frit glaze in the same manner as in the example, and a suitable water was added to form a slurry, which was mixed in a ball mill and then glazed on a porcelain tile and baked under the same conditions as the example. , And examined the change in color tone.

Comparative Example 2 100 parts by weight of cadmium red, 30 parts by weight of ethyl silicate and 20 parts by weight of ethyl alcohol were mixed with a stirrer for 2 hours, and a mixed solution of 7 parts by weight of water, 5 parts by weight of ethyl alcohol and 0.5 part by weight of 1N hydrochloric acid was added, After stirring for 5 hours, 1N ammonia water was added to adjust the pH to 5 to 7, promote gelation, solidify, and then crushed, and dried at 100 ° C. for 10 hours and 200 ° C. for 3 hours. The coated pigment obtained here was glazed on a porcelain tile under the same conditions and methods as in Example and baked to examine the change in color tone.

Regarding the above Examples 1 to 7 and Comparative Examples 1 and 2, the change in the color tone was examined at 1100 to 1200 ° C. with the medium-glaze frit glaze, and it was found that the coated pigment obtained by the present invention and the coated pigment of Comparative Example 2 were Has excellent heat resistance with no change in color tone even when baked at 1100 ° C. On the other hand, the coated pigment of Comparative Example 1 was blackish and was extremely decolorized. Further, at a temperature of 1200 ° C. or higher, the discoloration and decolorization of the coated pigment of Comparative Example 2 is remarkable, whereas the coated pigment obtained by the present invention causes less discoloration and decolorization, and the difference from the coated pigment of Comparative Example is further improved. It was remarkable. Also with respect to the yellow lead and molybdenum red shown in Examples 8 to 11, the coated pigment according to the present invention has a color difference ΔE of 1 or less even when the temperature is heated to 250 ° C., and discoloration occurs even when heated to 280 ° C. It was confirmed that the coated pigment according to the present invention was small and was excellent in heat resistance and chemical stability.

Claims (3)

[Claims] 1. A heat-resistant coated pigment comprising a hydrophilic inorganic pigment to which a metal alkoxide or a mixed solution of a metal alkoxide and a solvent is added, wet-milled, and a metal oxide film is formed on the surface of the pigment by hydrolysis of the metal alkoxide. Production method. 2. The method according to claim 1, wherein water is added to accelerate the hydrolysis of the metal alkoxide simultaneously with or after the wet pulverization. 3. The method according to claim 1, wherein an alkoxide containing each metal element of silicon, aluminum, zirconium, titanium, boron, zinc and tin is used as the metal alkoxide.