JPH04283249A - Coating composition and method for preventing surface fouling of silicone elastomer - Google Patents

Abstract

PURPOSE:To provide a coating compsn. which forms a weather-resistant antifouling coating film on the surface of a silicone elastomer by compounding an NCO-reactive fluororesin sol. in an org. solvent, an isocyanate compd., a specific organosilicon compd., and a specific org. solvent. CONSTITUTION:A coating comps. which comprises 100 pts.wt. NCO-reactive fluororesin sol. in an org. solvent, 0.1-30 pts.wt. isocyanate compd. having at least two NCO groups in the molecule, 0.1-30 pts.wt. organosilicon compd. of formula I (wherein Q is a divalent hydrocarbon group; R<1> is a monovalent hydrocarbon group; X is a hydrolyzable group such as a 1-6C alkoxy group; and a is 2 or 3) or hydrolyzate thereof, and 10-5000 pts.wt. mixed solvent consisting of 5-95wt.% volatile organosilicon compd. of formula II, III, IV, or V (wherein R<2> is alkyl; m>=0; and n>=3) having a b.p. under ordinary pressure of 70-250 deg.C and 95-5wt.% org. solvent contg. no active hydrogen, and in which the number of SH groups in the organosilicon compd. is 90% or lower of the number of NCO groups in the isocyanate compd.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD OF THE INVENTION The present invention relates to a composition for forming a coating film and a method for preventing staining, and more particularly, the present invention relates to a composition for forming a coating film and a method for preventing staining. The present invention relates to a method that makes it possible to prevent staining over a long period of time.

0002

Technical background of the invention and its problems Silicone compositions that cure into rubber-like elastic bodies include heat-curable silicone rubber compositions that use organic peroxide as a vulcanization accelerator, and silicone rubber compositions that use a platinum-based catalyst. Si-H and Si-CH=C
Addition reaction-curable silicone rubber compositions that utilize an addition reaction with H2 groups, and condensation reaction-curable silicone rubber compositions that cure under the action of moisture in the air at room temperature are known. These silicone elastomers are heat resistant, cold resistant,
Because it has excellent weather resistance, electrical insulation properties, and non-toxic properties, it is used in a wide range of fields, including the construction field, the electrical machinery industry, and the food and medical industry. However, although such silicone elastomers have the excellent properties mentioned above, they remain slightly sticky even after the curing reaction, and because their main component, polydiorganosiloxane, is a dielectric, they are susceptible to dust. Easy to attract. In particular, when non-reactive polydiorganosiloxane is added to obtain a flexible silicone elastomer while maintaining workability, polysiloxane that does not participate in such crosslinking oozes out from the inside of the elastomer to the surface. Since the dust is covered with water to make it water-repellent, the dust is not washed away by rainwater, and the appearance is seriously spoiled due to staining.

As described above, silicone elastomers have problems, especially in terms of maintaining the appearance required as a building material.
There are restrictions on usage. In addition, there are many uses for industrial materials other than construction, where dust adhesion can affect the appearance and use. Therefore, the establishment of a technique for preventing dust from adhering to the surface of a silicone elastic body has been desired by various industries including the construction industry. In order to solve these problems, Japanese Patent Application Laid-Open No. 56-157464 and Japanese Patent Application Laid-Open No. 57-1023
No. 43 discloses a method of forming a film containing silicone resin as a main component on the surface of a silicone elastic body. However, in this method, the antifouling effect was insufficient because the coating was made of silicone resin. Also, JP-A-59-10
5057, JP 59-126470, and JP 59-227955 disclose a method of forming a coating of alkyd resin or acrylic resin mixed or modified with a curable silicone compound on the surface of a silicone elastomer. It is shown. However, these methods have a problem in that the films formed have insufficient long-term weather resistance.

0004

[Structure of the Invention] As a result of studying methods for solving the above-mentioned problems, the present inventors have discovered that an organic solvent-soluble fluororesin having a group capable of reacting with an isocyanate group, an isocyanate compound,
By applying a coating film forming composition consisting of a silicon compound having a thiol group and a hydrolyzable group and a mixed solvent of a volatile organosilicon compound and an organic solvent to the surface of a silicone elastomer, it is possible to prevent deterioration over a long period of time. discovered that it is possible to form an antifouling film on its surface,
The present invention has now been completed. That is, the present invention provides (A
) 100 parts by weight of a fluororesin having a group capable of reacting with an isocyanate group and soluble in an organic solvent (B) 0.1 to 30 parts by weight of a compound having two or more isocyanate groups in the molecule

[0005]

[Case 2]

(wherein, Q is a divalent hydrocarbon group, R1 is a monovalent hydrocarbon group, X is a hydrolyzable group selected from an alkoxy group having 1 to 6 carbon atoms and an alkoxyalkoxy group, and a is 2 or 3) Organosilicon compound and its hydrolyzate 0.1 to 30 parts by weight (D) (a) General formula; R24Si, R23SiO (
R22SiO)mSiR23, R2Si(OSiR
23) 3 or (R22SiO)n (wherein R2 is the same or different alkyl group, m is 0 or a positive integer, n is a positive integer of 3 or more), and has a boiling point under normal pressure It consists of a volatile organosilicon compound in the range of 70 to 250°C and (b) an organic solvent that does not have active hydrogen, and the blending amount of (a) is 5% of the total amount of (a) and (b).
A composition for forming a coating film, comprising 10 to 5,000 parts by weight of a mixed solvent of 95% by weight, and the number of thiol groups in (C) is 90% or less of the number of isocyanate groups in (B). The present invention relates to a method for preventing staining of the surface of a silicone elastomer, which comprises applying a composition to the surface of the silicone elastomer and drying and curing the composition.

The fluororesin (A) has a group that reacts with an isocyanate group and is soluble in an organic solvent. Various types of these fluororesins are commercially available, and any of these commercially available fluororesins can be used in the present invention. Examples of suitable fluororesins include those capable of reacting with fluorine-containing olefin monomers such as tetrafluoroethylene and trifluorochloroethylene and isocyanate groups such as hydroxyl groups, carboxyl groups, amino groups, acid anhydride groups, epoxy groups, and thiol groups. It may be a copolymer with a monomer having a functional group, or it may be one to which these reactive groups are added after copolymerization. Typical examples of these copolymerizable monomers include vinyl acetate, vinyl ester,
Examples include (meth)acrylic acid and various esters thereof. Of course, during copolymerization, a third monomer having no reactivity may be blended and copolymerized. The copolymerization ratio of the fluorine-containing monomer and other monomers is within the range in which the resulting copolymer is soluble in the organic solvent, and varies depending on the type of the fluorine-containing monomer and other monomers, but generally the amount of the fluorine-containing monomer is preferably 30 to 90 mol%.

The isocyanate compound (B) is (A
) is a component that reacts with the reactive groups of the fluororesin (C) and the thiol groups of (C) to form an insoluble and infusible crosslinked structure. It is necessary to have These isocyanate compounds include:

[0009]

[Chemical formula 3]

0010

[C4]

[0011]

[C5]

0012

[C6]

[0013] etc. can be exemplified.

The amount of (B) used is in the range of 0.1 to 30 parts by weight per 100 parts by weight of (A). (B)
If the amount used is less than 0.1 part by weight, a sufficient crosslinked structure will not be formed, resulting in not only a decrease in the strength of the formed film but also a decrease in weather resistance. On the other hand, if the amount is more than 30 parts by weight, the crosslink density becomes too high and the film becomes brittle.

The organosilicon compound (C) is an essential component for imparting strong adhesion to the silicone elastomer of the cured film. The divalent hydrocarbon group for Q is preferably an ethylene group, a trimethylene group, or a tetramethylene group from the viewpoint of ease of synthesis and availability of raw materials, and a trimethylene group is particularly recommended. Examples of the monovalent hydrocarbon group for R1 include ethyl group, propyl group, butyl group, pentyl group, hexyl group, vinyl group, allyl group, phenyl group, β-phenylethyl group, etc. In particular, methyl group is recommended from the viewpoint of raw material availability. Hydrolyzable group
has good hydrolyzability, and therefore has 1 to 6 carbon atoms.
is selected from alkoxy groups and alkoxyalkoxy groups, and methyl or ethyl groups are particularly recommended because they have an appropriate rate of hydrolysis. The number a of hydrolyzable groups is 2
or 3, and if the number is 1, the adhesion of the coating to the silicone elastomer will be insufficient. These (C) include HS(CH2)3Si(OCH3)
3, HS(CH2)3Si(OC2H5)3, HS(
CH2)2Si(OCH3)2, HS(CH2)2Si
(OC2H5)3, HS(CH2)2Si(CH3)
Examples include silanes such as (OCH3)2 and hydrolyzed condensates thereof. These may be used alone or in combination. The amount of (C) used is based on 100 parts by weight of (A).
The range is from 0.1 to 30 parts by weight. and the number of thiol groups in (C) is 90 the number of isocyanate groups in (B)
% or less. If the amount of (C) is less than 0.1 parts by weight, the adhesion of the cured coating to the silicone elastomer will be insufficient, while if it is more than 30 parts by weight, the coating will become brittle. Furthermore, if the number of thiol groups in (C) exceeds 90% of the number of isocyanate groups in (B), the number of isocyanate groups that can react with the reactive groups in (A) will decrease, resulting in an insufficient crosslinked structure. As a result, the adhesiveness of the cured film to the silicone elastomer decreases, and the weather resistance decreases.

The mixed solvent (D) is a component for uniformly applying the coating film forming agent composition of the present invention to the surface of the silicone elastomer without repelling it to form a uniform film, and is a component for forming a uniform film on the surface of the silicone elastomer. It also functions to appropriately adjust the viscosity of the product and provide good coating workability. The volatile organosilicon compound (A) constituting (D) needs to have appropriate volatility, in other words, it needs to have a boiling point in the range of 70 to 250°C. If the boiling point is lower than this, it will volatilize early during application and will not work effectively, while if it is too high, drying properties will be poor and the formation of a film will be delayed. Here, R2 is a monovalent alkyl group, and examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, and the like. Specific examples of such include silanes such as triethylsilane, dimethyldiethylsilane, and trimethylbutylsilane; linear siloxanes such as hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, and dodecamethylpentasiloxane; -branched siloxanes such as trimethylsiloxy-1,1,1,3,7,7,7-heptamethyltrisiloxane, hexamethylcyclotetrasiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, 1- Examples include cyclic siloxanes such as ethyl-3,3,5,5,7,7-hexamethylcyclotetrasiloxane,
Methyl-based siloxane is preferred because of its ease of synthesis, and octamethylcyclotetrasiloxane is particularly preferred in view of appropriate volatility. The organic solvent (b) needs to be free of active hydrogen in order not to affect the reaction of the isocyanate group. These organic solvents include aromatic solvents such as benzene, toluene, and xylene; aliphatic solvents such as n-hexane, n-heptane, cyclohexane, and gasoline; ester solvents such as ethyl acetate and butyl acetate; acetone and dimethyl Ketones such as ketones, methyl ethyl ketone, diethyl ketone;
Examples include ethers such as diethyl ether and tetrahydrofuran. (D) The blending amount of (a) in (a) must be within the range of 5 to 95% by weight based on the total amount of (a) and (b), and must be within the range of 10 to 80 wt%. It is preferable that When the amount of (A) is less than 5% by weight, the wettability of the coating film forming agent to the silicone elastomer decreases, resulting in repellency and uneven coating.On the other hand, when it is more than 95% by weight, component (A) separates. It is not preferable because it precipitates. In addition, the usage amount of the mixed solvent (D) is (A) 1
It is in the range of 10 to 5000 parts by weight based on 0.00 parts by weight. If the amount of (D) is less than this range, the viscosity of the film-forming agent composition will become high and the workability will be significantly reduced.On the other hand, if it is more than this range, it will be necessary to repeat the coating many times, resulting in work efficiency. decreases significantly.

[0017] The coating film forming agent composition used in the present invention may also contain a catalyst such as an organic tin compound or a tertiary amine in order to speed up the curing rate of the coating. In addition, the film forming agent composition also contains ultraviolet absorbers, antioxidants,
Modifiers such as viscosity and flow modifiers, fillers such as fumed silica, ground quartz, calcium carbonate, titanium oxide,
Pigments such as iron oxide and carbon black can also be blended.

The film forming agent composition used in the present invention is:
A component usually consisting of (A), (D) and others,
It is used as a two-component type, in which the two components (B) and (C) are blended together as needed, are stored separately, and both components are mixed at the time of use.

[0019] In the present invention, (A
) to (D) and other components is applied and dried and cured. The method of application is not particularly limited, and any method such as brush, spray, or roller may be used. Dry curing may be accelerated at room temperature or by heating.

[0020]

[Effects of the Invention] According to the present invention, an antifouling film with excellent weather resistance can be formed on the surface of a silicone elastomer.
Contamination can be prevented for a long period of time.

[0021]

[Examples] The present invention will be explained below with reference to Examples. still,
In the examples, parts indicate parts by weight.

Examples 1 to 6, Comparative Examples 1 to 4 100 parts of fluoroethylene-vinyl ether copolymer resin (solid content 60%, solvent: ethyl acetate, hydrogen value 32 mg KOH/g, manufactured by Asahi Glass) were added with the following ingredients as shown in Table 1. A composition for forming a coating film was prepared by adding an isocyanate group-containing compound, an organosilicon compound, a volatile organosilicon compound, an organic solvent, and others as shown. These paint film-forming compositions were applied to a test piece on which the silicone sealant shown in Figure 1 was cast (using Toshiba Silicone's aminoxy-curing silicone sealant ``Tosseal 361'' as the sealant, for 14 hours at room temperature.
It was applied with a brush to the surface of the silicone sealant (hardened for one day), and after observing the paintability, it was cured at room temperature for 7 days. Next, after irradiating the film-forming agent-coated surfaces of these test specimens with ultraviolet rays for 1000 hours in a weatherometer, the condition was observed, and the appearance and degree of staining of the paint films were evaluated 6 months and 1 year after exposure outdoors. observed. The results are also shown in Table 1. Comparative Example 1 is a comparative example that does not use the organosilicon compound of the present invention, Comparative Example 2 is a comparative example that does not use a volatile organosilicon compound as a solvent, and Comparative Examples 3 and 4 are comparative examples that do not use a volatile organosilicon compound as a solvent. This is a comparative example.

[0023]

[Table 1]

Examples 7 to 12, Comparative Examples 5 to 8 Trifluorochloroethylene-vinyl ether copolymer resin solution (solid content 60
%, hydroxyl value 25 mg KOH/g, manufactured by Central Glass), and add an isocyanate group-containing compound, an organosilicon compound, a volatile organosilicon compound, an organic solvent, and others as shown in Table 2 to form a coating film forming agent composition. was prepared. These film-forming agent compositions were applied to a test piece coated with the silicone elastic coating material shown in Figure 2 (the coating material was Toshiba Silicone's oxime-curable silicone elastic coating material "Toscoat 30", and the coating was cured at room temperature for 14 days. Examples 1 to 6 were applied using a brush to the surface of the silicone coating material.
And tests similar to Comparative Examples 1 to 4 were conducted. The results are also shown in Table 2. Comparative Example 5 is a comparative example that does not use the organosilicon compound of the present invention, Comparative Example 6 is a comparative example that does not use a volatile organosilicon compound as a solvent, and Comparative Examples 7 and 8 are comparative examples that do not use a volatile organosilicon compound as a solvent. This is a comparative example.

[0025]

[Table 2]

[Brief explanation of the drawing]

FIG. 1 shows test specimens used in outdoor exposure tests in Examples 1 to 6 and Comparative Examples 1 to 4.

FIG. 2 shows test specimens used in outdoor exposure tests in Examples 7 to 12 and Comparative Examples 5 to 8.

[Explanation of symbols]

1...Coating film forming agent 2...Silicone sealant 3...Enamel board 4...Silicone elastic coating material 5...Zinc steel plate

Claims (2)

[Claims] Claims 1: (A) 100 parts by weight of a fluororesin having a group capable of reacting with an isocyanate group and soluble in an organic solvent; (B) a compound having two or more isocyanate groups in the molecule; 0.1 to 100 parts by weight; 30 parts by weight [Formula 1] (wherein, Q is a divalent hydrocarbon group, R1 is a monovalent hydrocarbon group, and X is a hydrolyzable group selected from an alkoxy group having 1 to 6 carbon atoms and an alkoxyalkoxy group , a is 2 or 3) Organosilicon compound and its hydrolyzate 0.1 to 30 parts by weight (D) (a) General formula;
R24Si, R23SiO(R22SiO)mSi
R23 , R2Si(OSiR23)3 or (R2
2SiO)n (wherein R2 is the same or different alkyl group, m is 0 or a positive integer, n is a positive integer of 3 or more), and has a boiling point under normal pressure of 70 to 25
It consists of a volatile organosilicon compound in the range of 0°C and (b) an organic solvent that does not have active hydrogen, and the blending amount of (a) is 5 to 95% by weight of the total amount of (a) and (b). 10 to 5,000 parts by weight of a mixed solvent, and the number of thiol groups in (C) is 9 as the number of isocyanate groups in (B)
A composition for forming a coating film, characterized in that the content thereof is 0% or less. 2. A method for preventing staining of the surface of a silicone elastomer, comprising applying the composition of claim 1 to the surface of the silicone elastomer and drying and curing the composition.