JPH0826269B2 - Coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a coating composition, and in particular, when applied to a substrate such as a metal material, heat resistance, non-adhesiveness, scratch resistance, corrosion resistance, etc. And coating compositions useful in protecting those substrates.

[Conventional technology and problems] Fluorine resin, especially tetrafluoroethylene resin (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer hexafluoroethylene resin (FEP) are heat resistant and non-adhesive. It has excellent properties and is used mainly for coating the inner surface of cookers in the electric appliance industry and gas appliance industry. However, these so-called fluororesin processing have the following problems.

First, the workability of the fluororesin processing process is poor. That is, the adhesion of the fluororesin to a metal substrate such as iron or aluminum is improved, the corrosion of the substrate from the pinholes of the fluororesin film is prevented, and the wear resistance and scratch resistance of the fluororesin film are improved. For the purpose of improving, etc., it is usually necessary to pretreat the base material such as primer treatment and ceramics thermal spraying treatment, and a high temperature of about 400 ° C. is required to form the fluororesin film, which consumes a lot of energy. What you are doing.

Further, in terms of the performance of the fluororesin coating, the hardness of the coating is low and there is a problem that it is easily scratched. The fact that the coating is easily scratched impairs the aesthetics and non-adhesiveness of the coating, and makes it difficult to process fluororesin on a base material such as iron that is liable to rust due to the scratch. .

[Means for Solving Problems] An object of the present invention is to solve the above problems in processing a fluororesin and to provide a coating composition having heat resistance, non-adhesiveness, scratch resistance and corrosion resistance. is there.

That is, the present invention provides (A) fluororesin fine particles (B)
R ¹ Si (OR ² ) ₃ (where R is the formula, where R ¹ Si (OR ² ) ₃ is dispersed in a vehicle composed of silica fine particles having an average particle size of 5 to 150 mμ, a partial hydrolysis-condensation product of trialkoxysilane represented by the following general formula, and a solvent. ¹ is an alkyl group having 1 to 3 carbon atoms, vinyl group, phenyl group, 3,4 epoxycyclohexylethyl group, γ-glycidoxypropyl group, γ-methacryloxypropyl group, γ-mercaptopropyl group, γ- A chloropropyl group or a 3,3,3-trifluoropropyl group, and R ² represents an alkyl group having 1 to 3 carbon atoms or an aryl group.) In component (B) Solid content composition is silica fine particles 30-70
The content of the partial hydrolysis-condensation product of trialkoxysilane is 70 to 30% by weight, and the addition amount of the fluorine resin fine particles of the component (A) is 5 to 500 relative to 100 parts by weight of the solid content of the component (B). And a coating composition.

The coating composition of the present invention is obtained by hydrolyzing a trialkoxysilane or a mixture of trialkoxysilanes in a silica fine particle dispersion liquid, or by adding silica fine particles to a hydrolyzate of a trialkoxysilane or a mixture of trialkoxysilanes. It is prepared by dispersing and mixing fine particles of fluororesin into the resulting vehicle.

The trialkoxysilane used in the present invention is represented by the following general formula: R ¹ Si (OR ² ) ₃ (wherein R ¹ is an alkyl group having 1 to 3 carbon atoms, a vinyl group, a phenyl group, 3,4- Selected from the group consisting of epoxycyclohexylethyl group, γ-glycidoxypropyl group, γ-methacryloxyropyl group, γ-mercaptopropyl group, γ-chloropropyl group, 3,3,3-trifluoropropyl group And R ² represents an alkyl group or an aryl group having 1 to 3 carbon atoms.) The fluororesin fine particles of the component (A) used in the present invention include tetrafluoroethylene resin and tetrafluoride. Copolymers of ethylene tetrafluoride such as ethylene-hexafluoropropylene copolymer; vinylidene fluoride resin, trifluoroethylene chloride resin and modified fluorine resin are preferred, and tetrafluoroethylene resin is more preferred. . Also, the average particle size of the fluorine resin particles is 0.1 to 20μ.
Is preferable, and more preferably 0.1 to 5 μ. As such fluororesin fine particles, commercially available fluororesin fine powder, fluororesin dispersion and the like can be used.

The amount of the fluorine resin fine particles as the component (A) added is 5 to 500 parts by weight, preferably 25 parts by weight, based on 100 parts by weight of the solid content of the component (B).
If it is less than 5 parts by weight, which is up to 250 parts by weight, a non-adhesive coating cannot be obtained, and if it exceeds 500 parts by weight, a coating having scratch resistance cannot be obtained.

The average particle diameter of the silica fine particles as the component (B) is 5 to 150 mμ, preferably 5 to 30 mμ. As such silica fine particles, a colloidal silica dispersion in which high molecular weight silicic acid anhydride is dispersed in an organic solvent such as water and / or alcohol is preferable, but hydrophilic or hydrophobic produced by burning purified silicon tetrachloride. Powders, silica fine particles whose surface is treated or coated with various organic substances for the purpose of improving dispersibility, and a hydrolysis product of tetraalkoxysilanes, etc. can be included therein.

The partially hydrolyzed condensate of the trialkoxysilane as the component (B) is produced by adding pure water or an acidic aqueous solution of an inorganic acid or an organic acid or a colloidal silica dispersion and stirring. The trialkoxysilane is most preferably methyltrialkoxysilane from the viewpoint of heat resistance, hardness and economy of the coating, but other trialkoxysilane may be mixed in a small amount.

The present invention is to hydrolyze the above-mentioned trialkoxysilane in a colloidal silica dispersion, or to disperse and mix fluororesin fine particles in a vehicle obtained by adding silica fine particles to a hydrolyzate of trialkoxysilane. A method for obtaining a coating composition, and a method for obtaining the coating composition of the present invention will be described in more detail.

First, the vehicle of the coating composition is prepared as follows. Charge the trialkoxysilane and colloidal silica dispersion into a reaction vessel equipped with a stirrer and keep the temperature of the mixture at 10 ~.
It is kept at 80 ° C for about 1 to 24 hours and reacted under stirring or charged with trialkoxysilane in a reaction vessel, and pure water or an acidic aqueous solution of an inorganic acid, an organic acid or the like is added and reacted in the same manner as above. After that, by adding silica fine particles such as colloidal silica, a mixed dispersion liquid of a partial hydrolysis-condensation product of trialkoxysilane and silica fine particles is obtained.

This dispersion contains trialkoxysilane and silica fine particles as a solid content, but its composition is 30 to 70% by weight of partial hydrolysis-condensation product of trialkoxysilane,
Silica fine particles are 30 to 70% by weight. 30 fine silica particles
If it is less than 70% by weight, a heat-resistant coating cannot be obtained, and if it exceeds 70% by weight, the coating properties deteriorate.

Next, at least one selected from the group consisting of lower aliphatic alcohols and glycol derivatives is added to the obtained dispersion, and the solid content is adjusted to 10 to 50% by weight to obtain a vehicle. Then 5 to 500 per 100 parts by weight of solids of vehicle
A coating composition is obtained by adding parts by weight of fluororesin fine particles to a vehicle and dispersing and mixing.

As a method for dispersing the fine particles of the fluororesin in the vehicle, an ordinary method such as mill dispersion can be adopted. An additive such as a dispersant may be added at the time of dispersion. The pH of the obtained coating composition is preferably 3 to 6 and more preferably 4 to 5 in view of storage stability.
Is.

The coating composition of the present invention further comprises a smoothing agent, if necessary.
It is possible to add additives such as thickeners and defoamers, and colorants such as pigments and dyes. In particular, the addition of an inorganic substance such as a coloring pigment, an extender pigment, and a ceramic fine powder is effective in obtaining a coating film that is hard and is not easily scratched.

Then, as a method for coating and curing the coating composition of the present invention on a substrate, a usual coating method such as spray coating, dipping or flow coating can be adopted. The film thickness is preferably 2 to 60 μ, more preferably 5 to 30 μ. Then 10
By heating at 0 to 180 ° C. for 10 to 30 minutes, a coating having a fluororesin coating appearance that has good adhesion to the substrate can be obtained.

As described above, the coating composition of the present invention has very good coating workability, and has a low curing temperature of 100 to 180 ° C., which is lower than about 400 ° C. of fluororesin processing, and is energy saving.

Examples of the base material to which the coating composition of the present invention can be applied include iron, stainless steel, metal materials such as aluminum, and the like,
Inorganic materials such as glass and ceramics are optimal, and the adhesion to these base materials is extremely good, and pretreatment such as primer treatment of the base material necessary for the fluororesin processing is unnecessary. Further, the coating composition of the present invention can be applied to organic materials such as plastics, and the range of applicable substrates is extremely wide.

[Effects of the Invention] As is clear from the examples shown below, the coating composition of the present invention forms a film having good adhesion to a substrate at low temperatures, and the film has a heat resistance characteristic of a fluororesin. In addition to non-adhesiveness, it has so-called scratch resistance, which is an improvement in the drawback of being easily scratched, which is a problem in processing with a fluororesin. Further, the coating film is also excellent in corrosion resistance, solvent resistance, weather resistance and the like, and is suitable for surface protection of substrates made of various materials. In particular, the coating composition of the present invention is useful for protecting the surface of a cooker in which scratches are a problem.

[Examples] In order to make the actual understanding of the present invention more concretely understood, examples will be shown below as examples. The following examples do not limit the present invention described in the claims.

Example 1 500 g of acidic aqueous colloidal silica dispersion (average particle size 10
~ 20 mμ, solid content 20%) and methanolic colloidal silica dispersion 666 g (average particle size 10-20 mμ, solid content 30%) were mixed, then methyltrimethoxysilane 290 g was added and stirred at room temperature for about 5 hours. Hydrolysis was completed. Isopropyl alcohol was added to the obtained product to obtain a vehicle NO.1 having a solid content of 20%. Then, 50 g of tetrafluoroethylene resin fine powder (average particle size 5 μ) was added to 1000 g of vehicle NO.1 and sufficiently dispersed and mixed by a ball mill to obtain coating composition NO.1 having pH 5.

Example 2 1000 g of vehicle NO.1 and 100 g of tetrafluoroethylene resin fine powder
A coating composition No. 2 having a pH of 5 was obtained in the same manner as in Example 1 except that (average particle diameter 5 μm) was added.

Example 3 Vehicle No. 1 1000 g, tetrafluoroethylene resin fine powder 200 g
A coating composition No. 3 having a pH of 5 was obtained in the same manner as in Example 1 except that (average particle size 5 μm) was added.

Example 4 300 g of tetrafluoroethylene resin fine powder to 1000 g of vehicle NO.1
A coating composition No. 4 having a pH of 5 was obtained in the same manner as in Example 1 except that (average particle size 5 μm) was added.

Example 5 100 g of vehicle NO.1 and 100 g of tetrafluoroethylene resin fine powder
A coating composition No. 5 having a pH of 5 was obtained in the same manner as in Example 1 except that (average particle size 5 μ) and 300 g of titanium oxide were added.

Example 6 Vehicle NO.2 was obtained in the same manner as in Example 1 except that 300 g of the acidic aqueous colloidal silica dispersion, 300 g of the methanolic colloidal silica dispersion, and 435 g of methyltrimethoxysilane were used. Next, 200 g of tetrafluoroethiene resin fine powder (average particle size: 5 μ) was added to 1000 g of vehicle NO.2, and the mixture was sufficiently dispersed and mixed in a ball mill to obtain coating composition NO.6 having a pH of 5.

Example 7 To 600 g of an acidic aqueous colloidal silica dispersion liquid (average particle size: about 15 mμ, solid content: 34%) added with 0.6 g of glacial acetic acid, 414 g of methylmethoxysilane was added and stirred for about 1 hour. Isopropyl alcohol was added to the obtained product to obtain a solid content of 20%, which was aged for 4 days to obtain a vehicle NO.3. Next, add 200g of tetrafluoroethylene resin fine powder (average particle size 5μ) to 1000g of vehicle NO.3 and mix well by ball mill.
A coating composition No. 7 having a pH of 4.5 was obtained.

Example 8 To 300 g of methyltrialkoxysilane, 100 g of a 0.05N hydrochloric acid aqueous solution is gradually added dropwise with stirring while maintaining the liquid temperature at 10 ° C. After completion of dropping, cooling was stopped to obtain a hydrolyzate of methyltrialkoxy sila. Next, a methanolic colloidal silica dispersion liquid was added to the hydrolyzate of methyltrialkoxysilane.
691 g (average particle size 10 to 20 mμ, solid content 30%) and isopropyl alcohol were added, and the pH was adjusted to 5 with sodium acetate to obtain a vehicle NO.4 having a solid content of 20%. Next, add 200 g of tetrafluoroethylene resin fine powder (average particle size 5μ) to 1000 g of vehicle NO.4, and sufficiently disperse and mix with a ball mill.
A coating composition No. 8 with pH 5 was obtained.

Comparative Example 1 Vehicle NO.1 obtained in Example 1 was added to coating composition NO.9 at pH 5.
And

Comparative Example 2 500 g of acidic aqueous colloidal silica dispersion (average particle size 10
~ 20mμ, solid content 20%) Methyltrimethoxysilane 578
Carry out the same operation as in Example 1 except that g was added, and vehicle NO.
Got 5. Next, 200 g of tetrafluoroethylene resin fine powder (average particle size 5 μm) was added to 1000 g of vehicle NO.5, and the mixture was sufficiently dispersed and mixed by a ball mill to obtain coating composition NO.10 having pH 5.

<Preparation of test piece for evaluation> An aluminum plate was spray-coated with the coating composition,
It was heated at 0 ° C. for 20 minutes to obtain a test piece having a coating with a film thickness of about 20 μ.

<Evaluation method> (1) Adhesion 100 mm 1 mm wide cross-cuts are made on the film, cellophane adhesive tape is attached on the cross-cut surface, and this is pulled strongly in the direction perpendicular to the film to remove the film. Was observed and displayed with the number of remaining coatings / 100.

(2) Surface hardness A pencil scratching test was conducted to examine the breaking of the coating when the hardness of the pencil shin was changed.

(3) Scratch resistance The coating was rubbed with steel wool and the degree of scratching was observed.

(4) Non-adhesiveness The following evaluation was performed on the coating film after heating the test piece at 300 ° C for 48 hours and before heating.

Contact Angle to Water The contact angle of water droplets on the film was measured with a contact angle measuring device.

30 pieces of test pieces with soy sauce and sauce applied on the film
After heating at 0 ° C for 1 hour, the stain removal property was observed by wiping off the stain with a cloth.

(5) Heat resistance The test piece was allowed to stand under the conditions of 300 ° C and 400 ° C and the appearance change of the coating film after 1000 hours was observed.

(6) Thermal shock resistance The appearance change of the coating film after 10 cycles was observed by setting the test piece to stand at 300 ° C for 24 hours and then putting it in water at 20 ° C as one cycle.

(7) Storage stability After spray-coating the coating composition closed and stored at 25 ° C on an aluminum plate every 10 days and heating at 160 ° C for 20 minutes,
The film forming property was examined.

The evaluation results of Examples 1 to 8 and Comparative Examples 1 and 2 are as shown in Table 1. The results of the coating film performance tests (JIS K 5400 etc.) of Examples 3 and 5 are shown in Table 2.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-49-5434 (JP, A) JP-A-54-77635 (JP, A) JP-A-60-203679 (JP, A) JP-A-62- 116673 (JP, A) JP 58-53671 (JP, B2) JP 58-33266 (JP, B2) JP Hei 6-55922 (JP, B2)

Claims (1)

[Claims] 1. A fluororesin fine particle (A) is dispersed and mixed in a vehicle comprising (B) a silica fine particle having an average particle size of 5 to 150 mμ, a partial hydrolysis-condensation product of a trialkoxysilane represented by the following general formula, and a solvent. R ¹ Si (OR ² ) ₃ (wherein R ¹ is an alkyl group having 1 to 3 carbon atoms, vinyl group, phenyl group, 3,4 epoxycyclohexylethyl group, γ-glycidoxypropyl group, represents a group selected from the group consisting of γ-methacryloxypropyl group, γ-mercaptopropyl group, γ-chloropropyl group and 3,3,3-trifluoropropyl group, and R ² represents 1 to 3 carbon atoms. Of the silica fine particles 30 to 70.
The content of the partial hydrolysis-condensation product of trialkoxysilane is 70 to 30% by weight, and the addition amount of the fluorine resin fine particles of the component (A) is 5 to 500 relative to 100 parts by weight of the solid content of the component (B). A coating composition, characterized in that it is part by weight.