JPH04239076A - Heat-resistant coating composition - Google Patents

Abstract

PURPOSE:To improve heat resistance and adhesion to a substrate by dissolving or dispersing polyborosiloxane, a silicone resin, an inorg. particulate filler, and an inorg. short-fiber filler in an org. solvent. CONSTITUTION:100 pts.wt. polyborosiloxane having a number-average mol.wt. of 500-10,000, 10-900 pts.wt. silicone resin, and 10-900 pts.wt. inorg. filler comprising 95-25wt.% inorg. particulate filler having a mean particle diameter of 2-20mum and 5-75wt.% inorg. short-fiber filler having a diameter of 0.1-100mum and an aspect ratio of 5-100 are dissolved or dispersed in an org. solvent to give the title compsn., which is applied to a substrate in a coating wt. of 20-100g/m<2>, dried, and baked at 150 deg.C or higher.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant paint that can withstand use at high temperatures.

0002

[Prior art and its problems] Japanese Patent Application Laid-Open No. 57-20046
Publication No. 2 discloses a heat-resistant paint in which polyborosiloxane, a silicone resin, and an inorganic filler are dispersed or dissolved in an organic solvent. The heat-resistant paint described in this publication can be baked in air, and the coating film obtained therefrom has the advantage of not only excellent heat resistance but also good corrosion resistance and impact resistance.

One of the functions of the inorganic filler, which is a component of the paint described in the above publication, is to improve the adhesion of the resulting paint film to the substrate. However, when the coating film obtained from this paint is exposed to high temperatures, for example, 800 to 1000° C. for a long time, the coating film may peel off in the form of pinholes, which is a problem that needs to be solved.

0004

[Technical means for explaining the problem] The present invention provides a heat-resistant paint that has excellent heat resistance and can provide a coating film with better adhesion to a substrate. According to the present invention, a heat-resistant paint is provided in which polyborosiloxane, silicone resin, granular inorganic filler, and short fibrous inorganic filler are dispersed or dissolved in an organic solvent.

The polyborosiloxane used in the present invention is a known organosilicon polymer, for example, as disclosed in Japanese Patent Publication No. 58-473.
It can be prepared according to the method described in Publication No. 2. The number average molecular weight of polyborosiloxane is usually 500 to 10
000, preferably 1000-5000.

Specific examples of silicone resins used in the present invention include pure silicone resins such as dimethylpolysiloxane, methylphenylpolysiloxane, and diphenylpolysiloxane, and modified pure silicone resins such as alkyd resins, polyester resins, acrylic resins, and epoxy resins. For example, modified silicone reacted with a commercially available resin.

The blending ratio of silicone resin is preferably 10 to 900 parts by weight, particularly 50 to 500 parts by weight, per 100 parts by weight of polyborosiloxane. If the blending ratio of silicone resin is too small, the flexibility of the baked coating will decrease, and if the proportion is too high, the heat resistance and corrosion resistance of the baked coating will decrease.

The granular inorganic fillers used in the present invention include oxides, borides, phosphates, silicates, silicides,
At least one selected from borides, nitrides, and carbides is used. Examples include magnesium, calcium, barium, titanium, zirconium, chromium, manganese, iron, cobalt, nickel, copper, zinc, boron,
Mention may be made of aluminum, silicon oxides, carbides, nitrides, silicides, borides, lithium, sodium, potassium, magnesium, calcium or zinc borates, phosphates and silicates. The average diameter of the granular inorganic filler is usually 2 to 20 μm.

Short fiber inorganic fillers used in combination with particulate inorganic fillers include both whiskers and chopped fibers. As short fibrous inorganic fillers, all known per se can be used, examples include potassium titanate, silicon carbide, silicon nitride, alumina, alumina boria, zinc oxide, magnesium oxyhydroxide. Examples include whiskers or chopped fibers such as. The diameter of the short fibrous inorganic filler is usually 0.1 to 10 μm, and the length/diameter (l/d) is usually 5 to 100.

The total blending ratio of granular and short fibrous inorganic fillers is 10 parts by weight per 100 parts by weight of polyborosiloxane.
It is preferably from 50 to 500 parts by weight, particularly from 50 to 500 parts by weight. If the total blending ratio of the inorganic fillers is too small, the adhesion of the coating film will be reduced, and if the ratio is too high, the flexibility of the coating film will be reduced. In order to form a coating film that exhibits no or very little peeling of the coating film at high temperatures, it is essential to use a granular inorganic filler and a short fibrous inorganic filler in combination. The blending ratio of the short fibrous inorganic filler is 5 to 75 parts by weight per 100 parts by weight of the total amount of inorganic filler. If the blending ratio of the short fibrous inorganic filler is too small, the coating film will easily peel off at high temperatures, and if the ratio is too high, the fluidity of the paint itself will be impaired.

[0011] Although it is possible to use only short fibrous inorganic fillers as the inorganic filler, the short fibrous inorganic fillers become entangled in the paint, resulting in a decrease in the fluidity of the paint. Difficult to apply or spray paint.

As the organic solvent in the present invention, any solvent can be used as long as it is capable of dissolving polymetallocarbosilane and silicone resin. Specific examples include toluene, xylene, n-butanol, isobutanol, butyl acetate, mineral spirit, solvent naphtha, ethyl cellosolve, and cellosolve acetate. The proportion of the organic solvent to be used varies depending on the type and blending proportion of the film-forming components, and can be appropriately determined by those skilled in the art in accordance with the disclosure of the present invention.

The heat-resistant paint of the present invention is applied to metal substrates, electric wires, or non-metallic substrates such as ceramics and refractory bricks by means known per se such as brush coating, roll coating, spraying, and dipping, and then dried and baked.

[0014] The amount of heat-resistant paint applied is 20 to 100 g/m.
It is preferable that it is 2. If the coating amount is too small, pinholes are likely to occur in the coating film, resulting in decreased corrosion resistance. On the other hand, if the coating amount is excessively large, cracks are likely to occur in the coating film when the coating film is exposed to high temperatures or to cooling/heating cycles.

[0015] The baking temperature is 150°C or higher, especially 200°C.
It is preferable that it is above. If the baking temperature is too low, polymetallocarbosilane, which is one of the paint components, will not be sufficiently cured, resulting in lower strength and impact resistance of the paint film. In addition, the temperature of the object to be coated after painting is 150℃.
When placed in the above usage environment, the baking step can be omitted.

[0016]

[Example] Examples and comparative examples are shown below. Unless otherwise specified below, "%" and "parts" refer to "% by weight" and "parts by weight," respectively.

The heat resistance of the coating film was evaluated as follows. The object to be painted was kept in an air oven at 1000°C for 200 hours, then taken out of the oven and cooled slowly in the air. Then, crosscuts with a pitch of 1 mm were made in the coating film using a cutter knife, and adhesive cellophane tape was applied to these areas. The presence or absence of peeling of the coating film was examined after the coating was applied and then rapidly peeled off. Heat resistance is "good" if no peeling of the paint film is observed.
If peeling is observed even in some areas, the heat resistance is "poor".
And so.

The presence or absence of pinhole-like peeling portions in the coating film was evaluated as follows. The object to be coated is heated to 1000℃ for 20 minutes.
After being kept in an air oven for 0 hours, it was removed from the oven and slowly cooled, and then sprayed with salt water for 200 hours.
The coating film was observed under a 50x microscope to see if corrosion had formed. Rust formation and blistering of the paint film were observed on those with pinhole-like peeling.

Example 1 Polybolysiloxane with a number average molecular weight of 1500 prepared according to the method described in Japanese Patent Publication No. 58-4732.
% xylene solution, 50% xylene solution of methylphenylpolysiloxane (manufactured by Toshiba Silicone Co., Ltd., TSR
-116) 100 parts of granular silicon carbide powder with an average diameter of 3 μm, 20 parts of potassium titanate whiskers with a diameter of 1 μm and a length of 50 μm, and 50 parts of xylene were mixed in a mixer to prepare a heat-resistant paint. Apart from this, a stainless steel plate (SUS 31) with a thickness of 0.6 mm was used as a base material.
6L) was degreased with acetone and air-dried.

[0020] The heat-resistant paint was applied to the base material to a thickness of about 30 μm using a spray gun, and then heated in an air oven for 300 μm.
After baking at ℃ for 25 minutes, it was slowly cooled. The heat resistance of the resulting coating film was "good" and no pinhole-like peeling was observed.

Example 2 Instead of potassium titanate whiskers, a diameter of 0.5 μm,
Example 1 was repeated except that silicon nitride whiskers with a length of 30 μm were used. The heat resistance of the resulting coating film was "good" and no pinhole-like peeling was observed.

Comparative Example 1 Example 1 was repeated except that potassium titanate whiskers were included. Although the heat resistance of the resulting coating film was "good", pinhole-like peeling was observed.

Claims (1)

[Claims] 1. A heat-resistant paint comprising a polyborosiloxane, a silicone resin, a granular inorganic filler, and a short fibrous inorganic filler dispersed or dissolved in an organic solvent.