JPS6328942B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a primary antirust coating composition for steel.
More specifically, the present invention relates to a coating composition that is effective as a primary antirust coating for large steel structures and that can maintain a healthy coating film on the back surface during heating for welding, strain relief, etc. BACKGROUND OF THE INVENTION Conventionally, primary rust-preventing paints have been applied to large steel structures such as ships and bridges in order to temporarily prevent rust from forming during construction. Typical examples of such paints include wash primers made of polyvinyl butyral resin, phosphoric acid, and chromate, organic zinc-rich paints made of epoxy resin-zinc dust, inorganic zinc-rich paints made of ethyl silicate-zinc dust, and organic resins. Examples include new inorganic zinc-rich paints made of ethyl silicate and zinc powder. The desired rust prevention properties are obtained for the general parts of the structure, but for parts heated to high temperatures such as the back side of welding and strain relief, the paint film may be burnt off or the paint film components may be lost. Due to deterioration, etc., the purpose of preventing rusting has not been achieved. Large structures have many welding points and strain relief points, and as a result, even though they are coated with a primary anti-corrosion paint, it takes a lot of effort to prevent rust before applying the top coat. is the current situation. For this reason, those involved have desired the development of a primary rust-preventing paint that provides a healthy coating film even on the heated portions of the backside of welding and the backside of strain relief. Among conventional primary rust-preventing paints, inorganic zinc-rich paints mainly composed of inorganic substances have less paint film burnout during heating, and have good adhesion and anti-corrosion properties after heating. However, most of the inorganic zinc-rich paint is made of zinc powder, and it is not sanitary due to the generation of zinc fume during welding and fusing, and it is selective in overcoating because it cannot be overcoated with alkyd paint.
There is a strong desire to reduce the amount of zinc dust.
However, as the amount of zinc dust is reduced, the coating film becomes hard and brittle due to the characteristics of the binder, making it more likely to crack, making it difficult to form a coating film. Therefore, in order to reduce the amount of zinc dust, it is necessary to mix in an organic resin such as a new inorganic zinc-rich paint. However, in the new inorganic zinc-rich paint, the organic resin in the heated part decomposes, leaving no paint film. As a result of intensive research, the inventors of the present invention have developed a rust-preventing paint composition that can form a good film even when the amount of zinc dust is reduced by specifying the composition of the silicate binder. The present inventors have found that a healthy coating film can be obtained even in the high-temperature heated portion corresponding to the welded back surface or the strain relief back surface, and that the corrosion resistance is less deteriorated, leading to the completion of the present invention. That is, in a primary rust preventive paint composition for steel that is heat resistant at 600°C and contains a rust preventive agent, tetraalkoxysilane (alkyl group has 1 to 5 carbon atoms) is hydrated under acidic conditions as a binder. Decomposition initial condensate
A composition characterized in that (a) 100 parts by weight is blended with an initial condensate of alkyltrialkoxysilane (the alkyl group has 1 to 5 carbon atoms) hydrolyzed under acidic conditions (b) 10 to 250 parts by weight. exists in Specifically, the tetraalkoxysilane that is a raw material for component (a) used in the present invention includes tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane,
Examples include tetrabutoxysilane. The initial condensate (a) hydrolyzed under acidic conditions is a known agent used in inorganic zinc-rich paints and the like. However, as mentioned above, when using only zinc dust as a binder, there is a drawback that a good coating film cannot be provided if the amount of zinc dust is reduced. In addition, specific examples of the alkyltrialkoxysilane that is a raw material for component (b) include methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, and butyltrimethoxysilane. , amyltriethoxysilane, and the like. The initial condensate (b) hydrolyzed under acidic conditions is a known agent used as a modifier for plastic surfaces. In both of the above silane compounds, the alkyl group constituting the alkoxy group produces alcohol through hydrolysis and is dispersed from the coating film, but when the number of carbon atoms exceeds 6, the dispersibility decreases and the coating film becomes This is not preferable because the drying of the membrane becomes slow. Therefore, the alkyl group desirably has 1 to 5 carbon atoms, and is preferably an alkyl group having 2 to 3 carbon atoms (i.e., ethyl group, propyl group, or isopropyl group) from the viewpoint of the harmlessness and drying properties of the paint. It's advantageous. In addition, alkyl groups that bond directly to silicon atoms remain even in the final cured coating film and decompose at high temperatures of 600 to 700°C, but when the number of carbon atoms exceeds 6, the amount of the coating film burned out increases. Coating film adhesion decreases after high temperature heating. Furthermore, when the alkyl group has 1 to 5 carbon atoms, the heat resistance of the coating film is better than that of tetraalkoxysilane, even though the alkyl group remains in the coating film. On the other hand, the drying properties of alkyltrialkoxysilanes were found to be inferior to those of tetraalkoxysilanes. Therefore, the present invention is characterized by the discovery that the drying properties, film-forming properties, and heat resistance of a coating material can be improved by using a specific tetraalkoxysilane component and an alkyltrialkoxysilane component in combination. The active ingredients (a) and (b) as binders of the composition of the present invention can be obtained by hydrolyzing the above-mentioned tetraalkoxysilane and alkyltrialkoxysilane under acidic conditions according to a conventional method. That is, it can be obtained by hydrolysis under an acid catalyst as shown in Reference Examples below. In the present invention, the reaction system containing the active ingredient (a) or (b) obtained by hydrolysis is
It may be used as is to produce the desired composition. Alternatively, the desired composition may be produced by separately obtaining the active ingredients (a) and (b), or the active ingredient (a) obtained by subjecting a mixture of tetraalkoxysilane and alkyltrialkoxysilicate to hydrolysis. and
The target composition may be manufactured using the mixture system (b). In the composition of the present invention, 100% of the above active ingredient (a)
10 to 10 parts (parts by weight, same hereinafter) of active ingredient (b)
It is preferable to mix it in a proportion of 250 parts, preferably 40 to 100 parts. If the amount of active ingredient (b) is too small, film forming properties tend to deteriorate, and as a result, coating film adhesion tends to deteriorate. On the other hand, if it is in excess, drying properties tend to be poor and corrosion resistance tends to decrease. In the composition of the present invention, in addition to the above-mentioned active ingredients (a) and (b) as binders, various rust preventive agents, pigments, solvents, additives, etc. may be added as necessary, as in ordinary rust preventive paints. may be blended. Rust preventive agents include rust preventive metal powders (e.g. zinc powder, iron phosphide, etc.) and general rust preventive pigments (e.g.
Zinc phosphate, aluminum phosphate, barium metaborate, zinc molybdate, aluminum molybdate, etc.). Examples of extender pigments include talc, mica, barium sulfate, clay, and calcium carbonate; examples of coloring pigments include zinc white, titanium white, and Bengara. Zinc dust has good corrosion resistance in areas other than heated areas, but it is oxidized and loses its corrosion resistance in heated areas, so it is reduced to 50% by weight in the dry coating film.
It is desirable to mix them as follows. Although it is not impossible to achieve the purpose of the present invention even if the amount is 50% by weight or more, as mentioned above, as the content of zinc dust increases, the generation of zinc fume increases and the adhesion of the top coat becomes poor. . Pigments other than those mentioned above can also be used, but they must not significantly change color or change in quality when heated. Examples of solvent components include common isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, butyl cellosolve, ethyl cellosolve, etc., and may be blended in an appropriate amount so as to optimize coating workability and coating drying properties. As additive components, agents normally used in anti-rust paints such as anti-sagging agents, wetting agents, reaction accelerators, adhesion agents, anti-color separation agents, and anti-settling agents are mixed in appropriate amounts depending on the purpose. good. The composition of the present invention can be prepared according to conventional methods. For example, a liquid component containing a binder and a system containing other powder components may be stored in separate containers, and the two may be mixed immediately before use. Alternatively, part or all of the powder components other than the components that react with the binder (eg, zinc dust) may be dispersed together with the liquid component containing the binder, and the mixture and the remaining components may be mixed immediately before use. For dispersing the liquid component and the powder component, a conventional dispersing machine such as a row mill, sand grind mill, or ball mill may be used. In the compositions thus obtained, the binder concentration is generally from 5 to 15% by weight.
It may be applied to the steel structure by ordinary means such as air spray, airless spray, roll coater, brush, etc., and then dried by air drying or hot air drying. The composition of the present invention having the above-mentioned structure can fully exhibit its function as a rust-preventing paint, and can also leave a healthy coating film on heated parts such as the back side of welding and the back side of strain relief. It is possible to maintain corrosion resistance. As described above, the present invention is characterized in that the initial condensate of tetraalkoxysilane hydrolyzed under acidic conditions (a) and the initial condensate of alkyltrialkoxysilane hydrolyzed under acidic conditions (b) are blended as binders. be. It is conceivable to use a high condensate obtained by further condensing the above components (a) and (b) under alkaline conditions as a binder, but in this case,
When the system is converted to alkaline conditions, the binder component may precipitate and the system may gel, making it impossible to prepare a uniform paint. In addition, the primary anticorrosive paint that reduces the film thickness is required to have strong bonding properties with the steel plate, and the silanol groups remaining in the initial condensate of hydrolysis under acidic conditions are effective in increasing the bonding property with the steel plate. It is. However, when the initial condensate is then converted to alkalinity, the silanol groups are significantly reduced, and the resulting paint film has poor adhesion to the steel plate. There is a problem in that the heated part causes cracking and peeling of the paint film. Next, the present invention will be specifically explained with reference to Reference Examples, Examples, and Comparative Examples. Note that parts refer to parts by weight. Reference example 1 Manufacture of binder (A) Hydrolyzed initial condensation product of tetraalkoxysilane Tetraethoxysilane (Nippon Colcoat Co., Ltd. "Ethylsilicate 28") 100 parts Isobutyl alcohol 50 Isopropyl alcohol 24.7 Water 16.6 0.1N Hydrochloric acid 0.7 192.0 parts ( B) Hydrolysis initial condensate of alkyltrialkoxysilane Methyltriethoxysilane (reagent) 100 parts Isobutyl alcohol 60 Isopropyl alcohol 75.6 Water 14.4 0.1N Hydrochloric acid 0.7 250.7 parts (C) Hydration of a mixture of tetraalkoxysilane and alkyltrialkoxysilane Decomposition initial condensate tetraethoxysilane (Ethylsilicate 28 manufactured by Nippon Colcoat) 208.3 parts Methyltriethoxysilane (reagent) 106.4 Isobutyl alcohol 130 Isopropyl alcohol 169.9 Water 49.9 0.1N Hydrochloric acid 2.2 666.7 parts Remaining water and hydrochloric acid removed The ingredients are placed in a reaction vessel, and water and hydrochloric acid are added dropwise over 1 hour while maintaining the temperature at 40°C and stirring. After the completion of the dropwise addition, stirring was continued for 1 hour to obtain binders A, B, and C. Binders D and E are obtained by similar treatment with tetraheptoxysilane or ethyltriisopropoxysilane. The amount of active ingredient in each binder A, B, C, D, E is 15% by weight. Examples 1 to 9 and Comparative Examples 1 to 4 Even with the formulations shown in Table 1, the binder component was mixed with the pigment component mixture immediately before use, thoroughly stirred, and if necessary, isopropyl alcohol was added to adjust the viscosity. , and then subjected to painting. Each of the resulting coating compositions was subjected to the following tests. (1) Drying test Apply the paint composition to a degreased polished steel plate (70 x 150 x 0.8 mm) using air spray, leave it indoors, and measure the time until semi-hardening as specified in JIS-K-5400. . (2) Paint film adhesion test The paint composition was applied to a sandblasted steel plate (70 x 150 x 1.6 mm) with a film thickness of 15 to 20 μ by air spray, and after drying at 20°C and 75% relative humidity for 7 days, or Furthermore, after heating for 10 minutes in an electric furnace and cooling, the state of peeling of the coating film was measured using adhesive tape. 〇: Almost no peeling of the paint film △: Slight peeling of the paint film ×: Most of the paint film peels off (3) Rust prevention test Test piece obtained by method (2) above (peel test before)
Subjected to JIS-K-5400 salt water spray test for 240 hours, and the state of rusting determined by ASTM (D610). The above test results are shown in Table 2. As is clear from the table, the coating composition prepared by combining the active ingredients of tetraalkoxysilane and alkyltrialkoxysilane has drying properties and heat resistance within a practical range, and has excellent corrosion resistance after heating. A membrane can be provided.

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Claims (1)

[Scope of Claims] 1. A primary rust preventive paint composition for steel that is heat resistant at 600°C and contains a rust preventive agent, wherein the binder is a tetraalkoxysilane (the number of carbon atoms in the alkyl group is 1 to 5). Initial condensate (a) hydrolyzed under acidic conditions of
1. A composition comprising 10 to 250 parts by weight of an initial condensate (b) of an alkyltrialkoxysilane (alkyl group having 1 to 5 carbon atoms) hydrolyzed under acidic conditions to 100 parts by weight. 2. The composition of item 1 above, which contains 40 to 100 parts by weight of component (b).