JP3499525B2 - Photocatalytic coating composition - Google Patents

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention can be applied to the coating of interior and exterior wall materials, road materials such as tunnel insertion boards and soundproof walls, home appliances such as range hoods and ovens, and office equipment exterior plates such as cabinets. It relates to a photocatalyst coating composition.

[0002]

2. Description of the Related Art A coating composition or paint for forming a coating film having photocatalytic activity has been studied and several compositions have been proposed. As the base coating film, an inorganic material is generally used in which the coating film does not peel off due to chalking due to decomposition by active oxygen generated by light irradiation. For example, in WO96 / 29375,
A composition in which an aqueous dispersion sol of TiO ₂ and an alkoxide such as tetraethoxysilane dissolved in a water / ethanol mixed solvent are mixed is disclosed, and JP-A-8-67835 is disclosed.
Discloses a composition in which TiO ₂ powder is dispersed in a solution prepared by dissolving an organosilica sol in an organic solvent.

[0003]

Silicon tetraethoxide, which is used as a binder for photocatalysts such as titanium oxide, undergoes cross-linking and curing due to hydrolysis and condensation reactions, and therefore has a large volume shrinkage during curing, resulting in a very large shrinkage. Since stress is generated and is not relieved, when the dry coating film thickness of 5 μm or more is applied, the coating film is cracked by its own stress. Thin film coating is required to avoid the stress cracking described above. However, it is very difficult to apply a coating film evenly to a large area of the object to be coated, and a slight film unevenness or distortion may cause a thick film portion to partially cause cracking. Even when the surface having a more complicated shape is coated, a thick film portion is generated in accordance with the uneven portion and cracks occur. Further, in the case of a thin film, the efficiency of purifying the atmosphere of NO _x , SO _x, etc. is low, and the photocatalytic activity becomes insufficient.

Further, when a coating film is prepared by using a composition in which TiO ₂ powder is dispersed in a solution in which an organosilica sol is dissolved in an organic solvent, the dispersion of TiO ₂ is insufficient and powder agglomeration easily occurs. The obtained coating film has poor uniformity and it is difficult to form a thick film. The present invention has been devised to solve such a problem, and an object thereof is to provide a photocatalyst coating composition capable of thick film coating, which has good dispersibility of TiO ₂ and has excellent photocatalytic activity. To do.

[0005]

The photocatalyst coating composition of the present invention is prepared by mixing a photocatalyst-dispersed toner with an inorganic binder. The photocatalyst-dispersed toner is TiO ₂
Particles, mixed solvent of alcohol / ethylene glycol monoethyl ether or ethylene glycol monobutyl ether, isoelectric point of zeta potential is pH 1-3 or 6.5-1
It consists of a metal alkoxide or an organo metal alkoxide as a dispersant which becomes the oxide of 2. The inorganic binder is silica 40 to 70% by mass, organohydroxysilane and a partial condensate of organohydroxysilane 30 to 6
It consists of a solid content of 0 mass% and a mixed solvent of water / alcohol / ethylene glycol monoethyl ether or ethylene glycol monobutyl ether. As the photocatalyst particles, anatase type TiO ₂ having a particle diameter of 5 to 200 nm is used.
Particles are preferred. The metal alkoxide or organometal alkoxide used as the dispersant is an alkoxysilane, an aluminum alkoxide, or a part of an alkoxide which is hydrolyzed into an oxide having an isoelectric point of zeta potential of pH 1-3 or pH 6.5-12. There are organometal alkoxides and the like substituted with.

The silica that constitutes the inorganic binder is colloidal silica, and an aqueous colloidal silica dispersion is mainly used. In addition, organohydroxysilane is
General formula (I): R ¹ Si (OH) ₃ (wherein R ¹ is a carbon number 1
To 3 alkyl groups, vinyl groups, 3,4-epoxycyclohexylethyl groups, γ-glycidoxypropyl groups, γ-mercaptopropyl groups and γ-chloropropyl groups). The pH of the inorganic binder is adjusted to 3 to 6.5.

[0007]

The inorganic binder, which enables the thickening of the silica film, keeps the storage stable by adjusting the pH to 3 to 6.5. When a toner in which anatase type titanium oxide is dispersed in an organic solvent is mixed with the binder to form a paint, titanium oxide particles are aggregated and precipitated at the same time as mixing. It is considered that this is because the isoelectric point of the zeta potential of titanium oxide is 4.5 to 6.0, so that when it is mixed with the binder, aggregation occurs. Therefore, it was found that by adding organoalkoxysilane, which is a binder component, as a dispersant in advance to a toner prepared by dispersing titanium oxide in a solvent, it is possible to obtain a paint having no titanium oxide aggregates even when mixed with a binder. It was this is,
When titanium oxide covered with organoalkoxysilane comes into contact with the binder composition, the organoalkoxysilane hydrolyzes to form silica, which covers the surface of titanium oxide, so that the isoelectric point of the powder surface deviates from the pH range of the binder. It was thought that it was because it changed to pH. That is, it is considered that the isoelectric point of silica is pH 1-2, and by covering the surface of titanium oxide to some extent, it shifts to the low pH side where the titanium oxide has a low isoelectric point.

When aluminum alkoxide was added as a dispersant, a coating material free of titanium oxide aggregates was obtained even when it was mixed with a binder in the same manner. this is,
Aluminum alkoxide hydrolyzes and has an isoelectric point of pH
It is considered that the alumina, which is 8.5 to 9.5, covers the surface of the titanium oxide to some extent, so that the isoelectric point of the titanium oxide surface shifts to the higher pH side. Thus, it was revealed that the dispersibility of titanium oxide in the paint can be improved by making the isoelectric point of titanium oxide deviate from the pH of the binder.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The photocatalyst coating composition of the present invention comprises TiO ₂
Silica 4 is added to a photocatalyst-dispersed toner consisting of particles, a mixed solvent of alcohol / ethylene glycol monoethyl ether or ethylene glycol monobutyl ether, and a metal alkoxide or an organometal alkoxide as a dispersant.
0 to 70% by mass, organohydrohysisilane, a solid content composed of 30 to 60% by mass of organohydrohysisilane partial condensate, and a mixed solvent of water / alcohol / ethylene glycol monoethyl ether or ethylene glycol monobutyl ether. Inorganic binder is mixed. The photocatalyst-dispersed toner is made of Ti having a particle diameter of 5 to 200 nm.
It is prepared by adding O ₂ powder to a mixed solvent of alcohol / ethylene glycol monoethyl ether or ethylene glycol monobutyl ether to which a metal alkoxide or an organometal alkoxide is added as a dispersant, and thoroughly mixing with a bead mill or a ball mill. The mixing ratio of alcohol / ethylene glycol monoethyl ether or ethylene glycol monobutyl ether is 40
When the amount of the dispersant added is 1 to 10% by mass, the dispersibility of fine particles of TiO ₂ is good. As a dispersant, unlike a general dispersant, one of alkoxysilane, aluminum alkoxide, and alkoxide, which is hydrolyzed and whose final form is an oxide whose isoelectric point of the zeta potential deviates from the pH of the inorganic binder. For example, an organoalkoxysilane in which a part is substituted with an organic group is used. The organoalkoxysilane contained in the component of the inorganic binder is also effective.

When the amount of the dispersant added is less than 1% by mass, the effect of improving the dispersibility is not recognized. On the contrary, when it exceeds 10% by mass, the coating rate of the surface of TiO ₂ becomes too high and the coating rate is increased. The photocatalytic activity after film formation is extremely reduced. The inorganic binder is composed of a solid content composed of silica, organohydroxysilane and a partial condensate of organohydroxysilane, and a solvent composed of water, alcohol and ethylene glycol monobutyl ether.
Colloidal silica is used as the silica.
The colloidal silica dispersion is roughly classified into an aqueous colloidal silica dispersion in which high molecular weight silicic acid anhydride is dispersed in water and a non-aqueous colloidal silica dispersion in which an alcoholic solvent is dispersed. In the above, an aqueous colloidal silica dispersion is mainly used. A part of the aqueous colloidal silica dispersion may be replaced with a non-aqueous colloidal silica dispersion. The average particle size of silica in the colloidal silica dispersion is preferably 150 μm or less, more preferably 30 μm or less. The pH of the colloidal silica is preferably acidic, because the basicity of the inorganic binder decreases the storage stability of the obtained inorganic binder.

The organohydroxysilane and the partial condensate of the organohydroxysilane used as the inorganic binder are obtained by hydrolyzing the organoalkoxysilane. A typical example of the organoalkoxysilane is represented by the general formula (II): R ¹ Si (OR ² ).
₃ (wherein R ¹ is an alkyl group having 1 to 3 carbon atoms, a vinyl group,
A group selected from the group consisting of 3,4-epoxycyclohexylethyl group, γ-glycidoxypropyl group and γ-mercaptopropyl group, R ² is an alkyl group having 1 to 4 carbon atoms,
A group selected from the group consisting of an alkoxyethyl group having 1 to 4 carbon atoms and an aryl group). It is the same as that added as a dispersant for the photocatalyst-dispersed toner. Typical examples of the organohydroxysilane obtained by hydrolyzing the above organoalkoxysilane include those represented by the general formula (I): R ¹ Si (OH) ₃ (wherein R ¹ is the same as above). To be Examples of the organohydroxysilane partial condensate include oligomers obtained by partially condensing the organohydroxysilane represented by the general formula (I).

The solvent is (a) water in the aqueous colloidal silica dispersion, condensed water of organohydroxysilane,
(B) Alcohol produced by hydrolysis of organoalkoxysilane, and (c) ethylene glycol monoethyl ether or ethylene glycol monobutyl ether. When at least 20% by mass of ethylene glycol monoethyl ether or ethylene glycol monobutyl ether is contained as a solvent for the inorganic binder, the storage stability of the inorganic binder is dramatically improved,
Moreover, it has excellent coating workability and film forming properties. Usually, when the water content is 20% by mass or more in the same inorganic binder, the storage stability is poor, but when 20% by mass or more of ethylene glycol monobutyl ether is contained in the solvent, the water content is 20% by mass or more. However, sufficient storage stability can be maintained. The pH of the inorganic binder is adjusted to 3 to 6.5 (preferably 4 to 5) from the viewpoint of storage stability, for example, aqueous ammonia, triethanolamine,
It is adjusted with dimethylamino ether or the like.

The TiO ₂ -dispersed toner obtained as described above and an inorganic binder are mixed at a predetermined ratio to prepare a coating material. The mixing ratio of TiO ₂ as solid content is 5 to 80% by mass. Try to be. If the content of TiO ₂ is less than 5% by mass, sufficient photocatalytic activity cannot be obtained. However, if the content of TiO ₂ exceeds 80% by mass, the adhesiveness of the coating film decreases.

The method for producing the coating material of the present invention will be described below. The dispersed toner was prepared by adding TiO ₂ powder to a mixed solvent of alcohol / ethylene glycol monoethyl ether or ethylene glycol monobutyl ether containing a dispersant, stirring the mixture with a stirrer, and then stirring the beads using a horizontal mill filled with beads. In this state, the mixed product was made to flow at a flow rate of 1 liter / min. If desired, colorants such as pigments and dyes, and additives such as thickeners can be added.

As the inorganic binder, (a) an organoalkoxysilane is added to a colloidal silica dispersion and hydrolyzed to form an organohydroxysilane and a partial condensate of the organohydroxysilane, and the reaction product is diluted with a solvent. The method, (b) a method in which the colloidal silica dispersion liquid is diluted with a solvent, and then an organoalkoxysilane is added to the solution for hydrolysis, is exemplified. When the organoalkoxysilane is added to the colloidal silica dispersion liquid and is hydrolyzed, the liquid temperature is kept at 10 to 80 ° C. and the reaction is carried out under normal pressure for about 1 to 24 hours with stirring. Incidentally, a part of the non-aqueous colloidal silica may be added after the reaction is completed. When hydrolyzing the organoalkoxysilane, a small amount of a hydrolysis catalyst such as an inorganic acid or an organic acid may be added.

To mix the dispersed toner and the inorganic binder produced in the above, the inorganic binder was gradually added to the sufficiently stirred dispersed toner, and the mixture was further stirred to form a coating material. As a method for forming a coating film, a well-known method such as a spray coating method, a dipping method, a flow coating method, a roll coating method, a screen printing method, and an electrostatic coating method can be used. A coating having excellent adhesion to the base material can be obtained by applying a coating material after pretreating the base material and heating the base material at 80 to 300 ° C. for 1 to 120 minutes. The thickness of the coating cannot be unconditionally determined because it varies depending on the type and application of the substrate on which the coating is formed, but it is usually 1 to 100 μm. The substrate to which the photocatalyst coating composition of the present invention can be applied includes, for example, ordinary steel, plated steel plate, stainless steel plate, aluminum, copper, metal such as brass, cement, concrete,
Tile, slate board, glass, stone, etc. can be used. Depending on the heating temperature, it is possible to paint on organic materials such as plastics.

[0017]

EXAMPLES Preparation of TiO ₂ dispersed toner: A dispersant was added to a mixed solvent of 50% by mass of isopropanol and 50% by mass of ethylene glycol monobutyl ether, and TiO ₂ powder having a particle diameter of 20 nm was adjusted to 40% by mass of the entire coating material. To the solvent. This mixture was dispersed using a bead mill to prepare a dispersed toner.

Preparation of Inorganic Binder: 184 parts of an aqueous colloidal silica dispersion liquid (silica content: 30% by mass, particle size: 5 to 20 nm, pH 3.0) and 100 parts of methyltrimethoxysilane are mixed, and 30 ° C. In 5
The hydrolysis was completed by stirring for a period of time. Next, a mixed solvent of 33% by mass of isopropanol-67% by mass of ethylene glycol monobutyl ether was added to the obtained hydrolyzate, and ammonia water was further added to adjust the pH to 4.5. The TiO ₂ dispersed toner and the inorganic binder are
The mixture was mixed and stirred so that the TiO ₂ content in the solid content was 40% by mass, and filtered using a 50 μm mesh to obtain a coating material. This coating material was spray-coated on a pretreated SUS304 substrate, and heat-treated at 200 ° C. for 20 minutes to obtain a coating film having a film thickness of 10 μm.

Comparative Example A coating material and a coating film were prepared in the same manner as in Example 1 except that the dispersant was not added to the TiO ₂ -dispersed toner.

The dispersibility of the obtained photocatalyst coating composition and the characteristics of the coating film were evaluated by the following methods. (1) Evaluation of paint dispersibility After mixing a TiO ₂ dispersion toner and an inorganic binder to form a paint, one day later, the degree of aggregation of TiO ₂ particles was examined by a tube gauge. When there is no rib of 10 μm or more, ○: When there is rib of 10 μm or more
It was evaluated. (2) Evaluation of characteristics of coating film 1) Appearance of coating film: The appearance was observed, and a case where a uniform film was formed was evaluated as ◯, and a case where the surface condition was rough and a bump was observed was evaluated as x. 2) Photocatalytic activity: Salad oil was attached to the surface of the test piece at an adhesion amount of 0.2 mg / cm ² , and after irradiation with 5 mW / cm ² of ultraviolet light for 24 hours, the weight reduction rate of the salad oil remaining on the test piece was measured. The photocatalytic activity was determined using the weight reduction rate as the oil decomposition rate, and the oil decomposition rate of 40% or more was evaluated as ◯, and the oil decomposition rate of less than 40% was evaluated as x.

The above test results are summarized in Table 1. As is clear from Table 1, when a coating composition containing no dispersant added to the TiO ₂ dispersed toner was used, TiO ₂ aggregated significantly and a uniform coating film could not be obtained. On the other hand, the photocatalyst coating composition according to the present invention has a T
The agglomeration of the iO ₂ particles was suppressed, and the appearance of the coating film obtained using the particles was good, and a relatively thick film could be formed.

[0021]

[0022]

As described above, the photocatalyst coating composition of the present invention is used as an inorganic binder capable of forming a thick film by adding a metal alkoxide or an organometal alkoxide as a dispersant to a TiO ₂ dispersed toner. Even if mixed, the TiO ₂ powder is dispersed uniformly without agglomeration.
A coating film coated with this photocatalyst coating composition has a uniform film and a good appearance, and a thick film can be formed, and the photocatalytic activity is excellent. As long as it is a material that can withstand heating of 80 ° C or more, a coating film with good adhesion is formed on any substrate, so it is applied to a wide range of applications such as metal panels, concrete walls, tiles, glass windows, translucent plates, etc. It becomes a photocatalyst coating composition.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Ban, 18-8 Katayama-cho, Kashiwara-shi, Osaka Within Osaka Organic Chemical Industry Co., Ltd. (56) Reference JP-A 2000-95969 (JP, A) JP-A 2000- 192021 (JP, A) JP 8-67835 (JP, A) JP 10-195379 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C09D 1/00-10 / 00 C09D 101/00-201/10

Claims (4)

(57) [Claims] 1. TiO ₂ particles, alcohol / ethylene glycol
Recall monoethyl ether or ethylene glycol
The mixed solvent of nobutyl ether and the isoelectric point of the zeta potential are p
As a dispersant that becomes an oxide of H1 to 3 or 6.5 to 12
Of metal alkoxides or organometal alkoxides
It becomes photocatalyst dispersion toner, silica 40-70% by weight, organo hydroxy silane及
And organohydroxysilane partial condensate 30-60 quality
Solid content consisting of amount%, water / alcohol / ethylene glycol
Recall monoethyl ether or ethylene glycol
Inorganic binder consisting of mixed solvent of nobutyl ether
A photocatalyst coating composition, which is prepared by mixing 2. Anatase type Ti having a particle size of 5 to 200 nm.
The photocatalyst coating composition according to claim 1, wherein O ₂ particles are used . 3. General formula (I): R ¹ Si (OH) ₃ (wherein
R ¹ : C 1-3 alkyl group, vinyl group, 3,4-epo
Xycyclohexylethyl group, γ-glycidoxypropyi
Group, γ-mercaptopropyl group or γ-chloropropyl
Contracts using organohydroxysilane represented by
The photocatalyst coating composition according to claim 1. 4. The pH of the inorganic binder is 3 to 6.5.
The photocatalyst coating composition according to claim 1 .