JPH10245546A - Production of water-repellent powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-repellent powder easily within a short time without using any organic solvent by coating the surface of an inorganic powder with an emulsion prepared by emulsifying an alkyltrialkoxysilane in an aqueous medium and drying the powder. SOLUTION: An inorganic powder (e.g. calcium carbonate powder) having a particle diameter of desirably 0.01 to several mm, more desirably 1-100μm is surface-coated with an emulsion prepared by emulsifying an alkoxytrialkoxysilane or a mixture thereof with an oligomer thereof (e.g. Aquaproof 40J, a product of Toa Gosei K.K.) and dried. A desirable example of the method for coating the inorganic powder with the emulsion consists of spraying the emulsion having a concentration of e.g. 30-40wt.% onto the powder or kneading a slurry comprising the powder and the emulsion having a concentration of e.g. 3-4wt.% by means of e.g. a mixer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a water-repellent inorganic powder suitable as an additive to paints and the like.

[0002]

2. Description of the Related Art Water-repellent inorganic particles such as silica particles, alumina particles and titanium oxide particles are known as water-repellent inorganic powders. Such a water-repellent inorganic powder, a method of coating the inorganic powder with a conventional organic solvent solution of a water-repellent organic polymer compound such as dimethyl silicone oil, or after coating the inorganic powder with a hydrolyzable silane monomer having a water-repellent group, It has been produced by a method of heating and condensing the monomer. However, inorganic powders obtained by a water-repellent method using a water-repellent organic polymer compound are limited in application because the polymer compound is dissolved and removed by an organic solvent or the like.

On the other hand, according to a water repellent method using a hydrolyzable silane monomer such as an alkyl trialkoxysilane, the silanol and hydrolyzable silane monomer, which are usually contained in inorganic powder, are chemically bonded to the surface of the powder while forming a chemical bond. To form an aqueous coating, the water repellent coating is integrated with the inorganic powder. Therefore, the water-repellent powder obtained by this method has no particular restriction on the application. Specific examples of the water-repellent method using a hydrolyzable silane monomer include spraying an alkyltrialkoxysilane or an alkyltrichlorosilane in a solvent-free state on inorganic powder, and attaching a silane compound in the presence of water vapor. A method of heating the powder (Japanese Patent Publication No. 53-28399) and a method of using a water repellent such as hexamethyldisilazane in combination with a silane coupling agent having an amino group to make the inorganic powder water repellent in the presence of an organic solvent. (Japanese Patent Laid-Open No. 58-185405)
Etc. However, Japanese Patent Publication No. 53-28399
In the method described in JP-A-58-185405, a relatively large amount of non-water-repellent powder, that is, raw material powder, is easily contained in the obtained water-repellent inorganic powder. There is a problem in that a large amount of organic solvent is released into the atmosphere.

On the other hand, as for the hydrolyzable silane monomer, an aqueous silane emulsion in which it is emulsified and dispersed in an aqueous medium is known (for example, Japanese Patent Application Laid-Open No. 1-2920).
No. 89), the silane-based emulsion is used for making the surfaces of concrete blocks, bricks, porous stones and the like water-repellent. However, when the inorganic molded body is coated with the aqueous silane-based emulsion, there is a problem that it takes a long period of time, usually 5 to 3 months, for the coated surface to exhibit water repellency.

[0005]

The present inventors have conducted intensive studies to obtain a method for making the surface of an inorganic powder water-repellent in a short time without releasing a large amount of an organic solvent into the atmosphere. The present inventors have obtained the unexpected finding that, when an aqueous silane-based emulsion is applied to an inorganic powder, a water-repellent inorganic powder can be obtained in a short time of only about 24 hours at room temperature, and have completed the present invention. That is, in the present invention, the surface of an inorganic powder is coated with an emulsion obtained by emulsifying and dispersing an alkyltrialkoxysilane or a mixture of the alkoxysilane and an oligomer thereof in an aqueous medium (hereinafter, referred to as an aqueous silane-based emulsion) and then dried. This is a method for producing a water-repellent powder. Hereinafter, the present invention will be described in more detail.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous silane emulsion according to the present invention is an emulsion obtained by emulsifying and dispersing an alkyl trialkoxy silane or a mixture of the alkoxy silane and an oligomer thereof in an aqueous medium as described above.
The alkyltrialkoxysilane preferably used as a component of the aqueous silane-based emulsion includes methyltrimethoxysilane, methyltriethoxysilane, methyl-tri-n-propoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, and ethyl-trimethoxysilane. Bird
n-propoxysilane, propyltriethoxysilane,
Propyl-tri-n-propoxysilane, butyltrimethoxysilane, butyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane,
n-hexyltrimethoxysilane, n-hexyltriethoxysilane, cyclohexyltrimethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, octyltriisopropoxysilane, 2-ethylhexyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxy Examples include silane, tetradecyltriethoxysilane, hexadecyltriethoxysilane, and octadecyltriethoxysilane. A mixture of an alkyl trialkoxy silane and an oligomer of the alkoxy silane, that is, a low condensate, can also be used in the same manner as the above alkyl trialkoxy silane.

In emulsifying and dispersing the above alkyltrialkoxysilane or a mixture of the alkoxysilane and its oligomer (hereinafter sometimes collectively referred to as a hydrolyzable silane) in an aqueous medium, specific examples are given below. It is preferable to use a nonionic emulsifier and an anionic emulsifier. As nonionic emulsifiers, glycerol monooleate, glycerol monostearate,
Sorbitan monolaurate, sorbitan monopalmate, sorbitan monostearate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene Examples include sorbitol tetraoleate, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyl phenyl ether, and polyoxyethylene nonyl phenyl ether.

Examples of the anionic emulsifier include sodium lauryl sulfate, triethanolamine lauryl sulfate, sodium dodecylbenzenesulfonate, sodium alkylnaphthalenesulfonate, sodium dialkylsuccinate, sodium polyoxyethylene alkyl ether sulfate, and polyoxyethylene alkyl ether sulfate. And sodium salts of triethanolamine, sodium polyoxyethylene alkylphenyl ether sulfate, sodium alkane sulfone sulfate, sodium stearate, potassium oleate, sodium higher alcohol sulfate and β-naphthalenesulfonic acid formalin condensate. The amount of the emulsifier used is preferably 0.5 to 20 parts by weight per 100 parts by weight of the hydrolyzable silane. The preferred concentration of the hydrolyzable silane in the aqueous silane-based emulsion varies depending on the method of coating the inorganic powder with the emulsion, but is usually 5 to 50% by weight.

The inorganic powder that can be used in the present invention includes inorganic compound powders classified into the following (a) to (e). Preferred particle size of the inorganic powder,
0.01 to several mm, more preferably 1 to 100 μm
m. (A) silicon dioxide, aluminum oxide, titanium oxide, zirconium oxide, zinc oxide, calcium oxide, iron oxide,
Oxides such as lead oxide, bismuth oxide and antimony trioxide (b) Hydrous oxides such as aluminum hydroxide, hydrous titanium oxide, white carbon, colloidal silica, hydrous bismuth, hydrous antimony pentoxide and slaked lime (c) Complex of oxides such as mullite, fly ash, metakaolin, aluminum silicate and diatomaceous earth (d) Hydrous of complex oxides such as zeolite, activated clay, acid clay, bentonite and talc (e) Oxidation of calcium carbonate and lithopone Inorganic compound not belonging to a substance The preferred amount of the hydrolyzable silane used for coating the inorganic powder is 1 to 5 parts by weight of the hydrolyzable silane per 100 parts by weight of the inorganic powder.

As a method for applying the above-mentioned inorganic powder with an aqueous silane-based emulsion, the following method is preferable, but other methods can also be adopted. (A) Method of spraying an aqueous silane-based emulsion on inorganic powder Specifically, the concentration of the hydrolyzable silane is 30 to 40% by weight.
It is preferable to use the aqueous silane-based emulsion described above. (B) A method of kneading a slurry composed of an inorganic powder and an aqueous silane-based emulsion with a mixer or the like Specifically, 50 weight-percent of an aqueous silane-based emulsion having a hydrolyzable silane concentration of 3 to 4% by weight per 100 parts by weight of the inorganic powder. It is preferable to knead the slurry obtained by adding about parts.

The inorganic powder coated with the hydrolyzable silane by the above method or the like is then dried to exhibit water repellency. In the drying step, it is considered that the condensation reaction of the hydrolyzable silane in the present invention proceeds, and an alkylpolysiloxane film is formed on the surface of the inorganic powder. Then, it is determined that water repellency appears when the alkyl side chain in the alkyl polysiloxane film takes a steric configuration toward the atmosphere. The drying temperature is suitably from 20 to 80 ° C., and the preferable drying time is, for example, a drying temperature of 2 to 80 ° C.
At about 0 ° C, it takes 16 to 24 hours, and the drying temperature is 80 ° C.
About 4 to 8 hours. As described above, in the present invention, water repellency is exerted on the surface of the inorganic powder by drying from 4 hours to at most 24 hours. On the other hand, as is apparent from the comparative examples described later, the water repellency hardly appears in a molded body such as a silica silicate plate or a gypsum board made of calcium silicate when dried for about 24 hours.

In order to shorten the drying time required for exhibiting the water repellency of the inorganic powder, a catalyst that promotes the hydrolysis and condensation reaction of the hydrolyzable silane can be used. As the catalyst, inorganic or organic acids such as hydrochloric acid, acetic acid, sulfuric acid, paratoluenesulfonic acid, benzoic acid, phthalic acid and maleic acid; potassium hydroxide, sodium hydroxide, ammonia,
Inorganic or organic bases such as sodium carbonate, diethylamine and diethanolamine; and organic tin compounds such as dibutyltin dilaurate, dibutyltin octylate and dibutyltin diacetate. The catalyst can be used in the form of an aqueous solution or an organic solvent solution. The inorganic powder before being coated with the aqueous silane-based emulsion is sprayed with an aqueous solution of the catalyst or an organic solvent solution or the powder is sprayed with the aqueous solution or the organic solution of the catalyst. The catalyst is preferably supported by a method of immersion in a solvent solution or the like.

The water-repellent powder obtained by the present invention can be used as an additive for concrete, mortar, brick or ceramic board, and can be added to materials such as paints, inks, plastics, rubber and cosmetics.
Properties such as water resistance, heat resistance, electrical insulation, anti-blocking, printability, improved fluidity, and anti-corrosion properties can be imparted to the above materials. Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The “parts” in each example is “parts by weight”, and the particle diameter of the inorganic powder used is 5 to 6 μm.

[0014]

Example 1 Calcium carbonate powder 100 in a plastic bag
After spraying 5 parts of an aqueous silane-based emulsion [Toagosei Co., Ltd., trade name Aquaproof 40J, aqueous emulsion having a higher alkyl trialkoxysilane concentration of 40% by weight] onto the part, the bag is shaken and the powder in the bag is sufficiently washed. Was mixed. The calcium carbonate powder was taken out of the bag and dried at 80 ° C. for 8 hours to produce a water-repellent powder. The degree of water repellency of the obtained water repellent powder was evaluated by the following method. As a result, the water sprayed on the plane formed by the water-repellent powder,
It became water droplets and flowed down without wetting the plane.

Evaluation of Water Repellency A powder to be evaluated is densely filled in a cylinder with a bottom plate (material: polymethyl methacrylate) having an inner diameter of 60 mm and a height of 30 mm. At the time of filling, a vibrator was applied to the side surface of the cylinder. By this operation, a filled cylinder having the filled powder exposed on the surface was obtained. Fix the filling cylinder in a state where the powder surface is inclined 45 degrees from horizontal,
Water was sprayed on the powder surface, and the water-repellent state was visually observed.

[0016]

Examples 2 to 13 Instead of calcium carbonate, lithopone, silica powder, white carbon powder, titanium oxide powder, hydrous titanium oxide powder, mullite, fly ash,
A water-repellent powder was produced in the same manner as in Example 1 except that calcium silicate powder, diatomaceous earth, talc, titanium dihydrogen phosphate powder or gypsum were used. Each of the obtained water repellent powders had the same excellent water repellency as in Example 1.

[0017]

[Comparative Example 1-2] silicofluoride cull plate 70 mm × 70 mm × 10 mm (Comparative Example 1), or using the gypsum board of the same size (Comparative Example 2), the aqueous silane at a coverage of 150 g / m ² on their one side System emulsion [Toagosei Co., Ltd., trade name Aquaproof 40J], and then apply each test plate to 8
Dry at 0 ° C. for 24 hours. The obtained water-repellent treated surface was sprayed with water to evaluate the water repellency. In both Comparative Examples 1 and 2, the sprayed water did not form water droplets but spread and wet the substrate surface. It became.

[0018]

According to the present invention, the surface of the inorganic powder can be easily made water-repellent in a short time by an aqueous water-repellent agent having no problem such as environmental pollution.

Claims (1)

[Claims] 1. A water-repellent powder, characterized in that the surface of an inorganic powder is coated with an emulsion obtained by emulsifying and dispersing an alkyltrialkoxysilane or a mixture of the alkoxysilane and its oligomer in an aqueous medium, and then dried. Production method.