JPH0422953B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of forming an inorganic coating film, and more particularly to a method of forming a coating film using a coating material containing an inorganic binder containing silicon as a film-forming component. Conventionally, many paints using silicate as a binder have been proposed, including corrosion-resistant paints such as alkyl silicate-based zinc-rich paints and alkali-silicate-based zinc-rich paints, and organosilicon-based heat-resistant paints such as polydimethylsiloxane. well known. The general formula for alkyl silicate zinc-rich paint is as follows: (where R represents a hydrocarbon group having 1 to 8 carbon atoms) or (and) a low condensate is used as a starting material, hydrolyzed in the presence of an acid catalyst such as hydrochloric acid, and partially The condensed product is used as a binder, and a large amount of zinc powder is added to this.
This binder has many silanol groups at its terminals due to acid hydrolysis, and these silanol groups are metastable in the acidic region. This paint is mixed with zinc dust before painting, and this zinc dust consumes the acid catalyst and also reacts with the binder, resulting in crosslinking and curing. Although the degree of progress of the condensation reaction of the above hydrolyzate varies depending on the amount of reaction water and reaction conditions, high condensation products are not produced in the acid-catalyzed reaction (in the acidic region). Even when no zinc powder is added, the stability of this product usually decreases after 3 to 6 months, and it tends to thicken and gel. In addition, the pot life of a paint containing this binder as a film-forming component after adding zinc dust is about 5 to 10 hours, and the curing reaction is based on the reaction between the zinc dust and the silanol group of the binder. If a non-reactive general pigment is used instead of zinc powder, a coating film with a thickness of 1 μm or more cannot be formed, and the coating performance is extremely poor, making it impractical. On the other hand, JP-A-56-116761 discloses a one-component zinc-rich paint using a low condensed alkyl silicate and adding alkyl titanate or alkyl zirconate as a moisture curing aid. During the reaction, a large amount of alcohol is produced as a by-product due to moisture curing, and its volatilization causes a large volumetric contraction. Therefore, it is difficult to use this product for anything other than a zinc-rich paint containing a large amount of zinc powder, and it cannot be used as a clear paint or a paint for forming thick films. Moisture-curable clear paints and inorganic paints such as zinc-free enamels have also been developed that use organosilicon resins such as polydimethylsiloxane as binders, but these binder components contain many alkyl groups. Because of this, it does not have a high degree of heat resistance, and the cohesive force of the paint film is small, and in addition, it is difficult to apply another paint on top of the formed paint film. It is only used for more limited purposes. It is also known to use highly hard organosilicon resins for surface modification of plastics, but in both cases the crosslinking functional group is silanol. The present inventor has been conducting research to solve the problems of paints using this type of silicon-containing compound, and in this research, the organosilicon compound represented by the above general formula [A] and/or A low condensate thereof and an organosilicon compound represented by the following general formula [B] and/or a low condensate thereof

[Formula] (where R' is a hydrocarbon group having 1 to 12 carbon atoms, R is the same as above) is hydrolyzed in the presence of an acid catalyst, and then condensed at a pH of 7 or higher. The condensate produced is a high condensate that does not have silanol groups, and when a coating containing this as a film-forming component is applied to an object, it is cured by moisture in the air, producing a coating film with excellent physical properties and The inventors have discovered that the above-mentioned difficulties can be overcome, and have finally completed the present invention. That is, the present invention relates to an organosilicon compound represented by the following general formula [A] and/or a lower condensate thereof, and

[Formula] ...[A] (where R is a hydrocarbon group having 1 to 8 carbon atoms) An organosilicon compound represented by the following general formula [B] and/or a lower condensate thereof

[Formula] ... [B] (where R is a hydrocarbon group having 1 to 12 carbon atoms, R is the same as above) is hydrolyzed in the presence of an acid catalyst, and then condensed at a pH of 7 or higher. A method for forming an inorganic coating film, which comprises applying a coating material containing a high condensate having no silanol groups as a film-forming component to an object to be coated, and curing the coating film with moisture. It is. The above-mentioned high condensate used in the method of the present invention has good storage stability since it does not have a silanol group at the molecular end, and does not gel for a long period of time even when zinc dust is added, for example. In addition, since the high condensate is formed by a combination of tetraalkoxysilane and trialkoxysilane, the crosslinking density can be adjusted appropriately by changing the blending ratio, resulting in improved curability and thick coating. It is possible to form an excellent inorganic coating film with a good balance of properties, that is, no cracking or peeling during curing, and a high thickness of 50 to 100 μm even with clear coating. Furthermore, since the main skeleton of the cured coating film is -Si-O-Si- bonds, it has excellent properties such as heat resistance, corrosion resistance, chemical resistance, and weather resistance. R in the organosilicon compound represented by the above general formula [A] used as a raw material in the present invention is the same or different hydrocarbon group having 1 to 8 carbon atoms, and the hydrocarbon group in this case is These include alkyl groups such as methyl, ethyl, propyl, and hexyl, aryl groups such as phenyl, tolyl, and xylyl, and cycloalkyl groups such as cyclohexyl, cyclobutyl, and cyclopentyl. Specific examples of the compound include tetramethoxysilane, tetraethoxysilane, tetrapropioxysilane, tetrabutoxysilane, and tetraphenoxysilane. Moreover, the low condensate means an oligomer having a degree of polymerization of 10 or less. Further, R in the organosilicon compound represented by the above general formula [B] is the same as in the case of the above general formula [A]. On the other hand, R' is a hydrocarbon group having 1 to 12 carbon atoms bonded to silicon through a carbon-silicon bond, and examples of hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, hexyl, and octyl, phenyl, tolyl, xylyl, These include aryl groups such as naphthyl, and cycloalkyl groups such as cyclohexyl, cyclobutyl, and cyclopentyl. Specific examples of the compound include methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, and phenyltriethoxysilane. In the method of the present invention, when obtaining a high condensate using the general formulas [A] and [B], it is appropriate to mix both components in the following proportions based on weight. Compound of general formula [A]: 5 to 95% by weight, preferably 20 to 80% by weight Compound of general formula [B]: 5 to 95% by weight, preferably 20 to 80% by weight In the above formulation, the amount of compound [A] is 5% by weight. If it is less than 95% by weight, that is, [B] compound is 95% by weight.
If it exceeds the above, the curability of the inorganic coating film formed using this condensate will be poor, and the overcoatability will be poor. In addition, if the amount of the [B] compound is less than 5% by weight, that is, the amount of the [A] compound is 95% by weight.
If it exceeds 100%, there is a drawback that if thick coating is applied using this condensate, the coating film is likely to cause cracking or peeling. When condensing a mixture of the organosilicon compounds represented by the above general formulas [A] and [B] and/or their low condensates, the compounds and/or
The mixture of low condensates is added to a water-soluble solvent such as an alcohol solvent, a cellosolve solvent, a cellosolve acetate solvent, or a glyme solvent. In the presence of Si, add water at a ratio of 0.2 to 2 mol per 1 mol of RO group bonded to Si,
The reaction is allowed to take place with stirring at approximately 100°C for approximately 30 minutes to 10 hours, and then inorganic bases such as sodium hydroxide and potassium hydroxide, aliphatic amines such as monoethylamine, diethylamine, and triethylamine, ammonia, etc. are added to form a system. The condensation reaction is allowed to proceed by adjusting the pH of the mixture to 7 or higher. After the reaction is completed, the desired high condensate can be easily obtained by removing remaining water by distillation, azeotropy, or the like. The high condensate thus obtained is a three-dimensional condensate with a degree of condensation of at least 20 and a molecular weight of approximately 3,000 or more, and has a sufficient function as an inorganic binder for paints. A coating film with a thickness of about 50 to 100μ can be formed.
It hardens due to moisture in the air within 10 minutes to 10 hours after application, and rapidly hardens within a few minutes when brought into active contact with water after application. At this time, the curability can be further improved by adding a strong base catalyst or a metal alkoxide such as titanium or aluminum. In the present invention, metal powder such as zinc dust can be added to produce a one-component rust-preventing paint, and enamel can also be produced by adding only ordinary extender pigments or coloring pigments. In addition, if a large amount of pigment is added at this time, thick coating of 100 microns or more is possible without causing drawdown or peeling. The inorganic coating film formed by the present invention has superior coating performance compared to conventional silicate coatings, and is especially excellent in corrosion resistance, solvent resistance, heat resistance, and weather resistance. EXAMPLES The present invention will be specifically described below with reference to Examples. Example 1 62 g of tetraethoxysilane, 125 g of methyltriethoxysilane and 187 g of ethyl alcohol were added to a reaction vessel, and the contents were heated while stirring.
After the temperature reached 80℃, add 30g of 0.2N hydrochloric acid and heat to 80℃.
The mixture was allowed to react for 10 hours. Next, 30 g of triethylamine was added to this reaction product to raise the pH to 7 or higher, and a condensation reaction was carried out at 80°C for 2 hours. After that, 100 g of benzene was added to reduce the nonvolatile content to 40% (wt%).
The same applies below). The reaction product (varnish) thus obtained was transparent, had a viscosity of 5.8 centipoise, and exhibited excellent storage stability without thickening or gelling even after being stored at 30°C for two months. Next, polish the above varnish onto a mild steel plate to a film thickness of 50μ.
The panels were painted and placed in a room with a temperature of 20°C and humidity of 75% for 7 days. No abnormalities such as cracks were observed in the coating film thus formed, and no spot rust was observed even after 7 days of the salt spray resistance test (JIS Z 2371). Example 2 132 g of tetrabutoxysilane, 138 g of phenyltributoxysilane and 270 g of butyl alcohol were added to a reaction vessel, and the contents were heated to 100°C with stirring, after which 66 g of a 5% formic acid aqueous solution was added and the mixture was heated to 100°C. The mixture was reacted for 1 hour. Then, 30 g of N-methylmorpholine was added to this reaction product.
Raise the pH to 7 or higher and conduct the condensation reaction at 90℃ for 22 hours, then add 100g of toluene to reduce the non-volatile content to 40%.
% (weight %, hereinafter the same). The reaction product (varnish) thus obtained was transparent, had a viscosity of 28.0 centipoise, and showed excellent storage stability without thickening or gelling even after being stored at 30°C for two months. Next, the above varnish was coated with a paint containing titanium oxide dispersed at a ratio of 100PHR, and a film thickness of 100μ was applied to the mild steel plate.
The panels were painted and placed in a room with a temperature of 20°C and humidity of 75% for 7 days. No abnormalities such as cracks were observed in the coating film thus formed, and no spot rust was observed even after 15 days of the salt spray resistance test (JIS Z 2371). Example 3 In a reaction vessel, 427 g of ES-40 (tetraethoxysilane low condensate manufactured by Nippon Colcoat Co., Ltd.), 58 g of ethyltriethoxysilane, and 300 g of ethyl alcohol were added.
was added, and the contents were heated with stirring until the temperature reached 80°C, after which 142 g of 0.2N hydrochloric acid was added and reacted at 80°C for 30 minutes. Next, 5 g of potassium hydroxide was added to this reaction product to raise the pH to 7 or more, and a condensation reaction was carried out at 80°C for 2 hours, and then 200 g of benzene was added.
The solvent was removed until the nonvolatile content became 30% (by weight, the same applies hereinafter). The reaction product (varnish) thus obtained was transparent, had a viscosity of 11.2 centipoise, and showed excellent storage stability without thickening or gelling even after being stored at 30°C for two months. Next, a paint made by adding zinc powder to the above varnish at a rate of 300 PHR was applied to a sandblasted steel plate to create a film thickness.
Painted 100μ and placed in a room with a temperature of 20℃ and humidity of 75%.
It was set for several days. The thus formed coating showed no abnormalities such as cracks, and no red rust was observed even after being immersed in 40°C seawater for three months. Also, the paint containing zinc dust did not gel even after being stored at 50°C for 7 days. Comparative Example 1 208g of tetraethyl silicate was added to the reaction vessel.
208 g of ethyl alcohol and 72 g of 0.2N hydrochloric acid were added, and the contents were then reacted at 40° C. for 2 hours with stirring. Next, 50 g of triethylamine was added to raise the pH to 7 or more to perform a condensation reaction, and then 50 g of benzene was added to remove the solvent until the nonvolatile content became 22%. The reaction product thus obtained did not change at all even after being stored at 30°C for 2 months, demonstrating excellent storage stability. When this reaction product was applied to a polished mild steel plate to a thickness of 50 μm and set in a room at a temperature of 20°C and a humidity of 75% for 7 days, small cracks appeared. On the other hand, a coating coated with this reaction product to a thickness of 10 μm showed no cracking and no rusting even after 2 days of the salt spray resistance test. Comparative Example 2 In Example 2, when a paint prepared by dispersing titanium oxide at a ratio of 100PHR into the reaction product before adding N-methylmorpholine was applied to a polished mild steel plate to a thickness of 100μ, large cracks were observed after 10 minutes. Occurred. Moreover, this reaction product gelled after 15 days at 50°C. Comparative Example 3 In Example 3, 300 PHR of zinc powder was added to the reaction product before adding potassium hydroxide, and the mixture was applied to a sandblasted steel plate to a thickness of 100μ, and kept at 20℃ and humidity.
Although it was set in a 75% room for 7 days, no abnormalities were observed in the paint film, and no red rust was observed after being immersed in seawater at 40°C for 3 months. However, the varnish to which zinc dust had been added gelled at 20°C for 6 hours, and the varnish to which no zinc dust had been added thickened and gelled at 50°C for 5 days.

Claims (1)

[Claims] 1. An organosilicon compound represented by the following general formula [A] and/or a low condensate thereof, and [Formula] (where R is a hydrocarbon group having 1 to 8 carbon atoms)
... [A] Organosilicon compound and/or its low condensate represented by the following general formula [B] [Formula] (where R' is a hydrocarbon group having 1 to 12 carbon atoms, and R is the same as above) ... ...[B] After hydrolyzing a mixture consisting of in the presence of an acid catalyst and then condensing the mixture to a pH of 7 or more, the coating is coated with a film-forming component containing a high condensate that does not have silanol groups. A method for forming an inorganic coating film, which is characterized by applying the coating to an object and curing the coating film with moisture.