JPS6216144B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for preventing foaming of a rust-preventing coating, and more specifically, a method for preventing foaming that occurs when a top coat is applied to an inorganic high-concentration zinc dust coating. It is related to. BACKGROUND ART Conventionally, inorganic high-concentration zinc powder paints have been recommended and widely used as long-term rust-preventing paints for steel structures such as marine structures and ships because of their extremely excellent performance. Inorganic high-concentration zinc dust paints for rust prevention use alkali-based silicate or alkyl-based silicate as a vehicle and contain zinc dust in high concentration as a rust-preventing pigment, and can be painted with a dry film thickness of 70 to 100μ. It is designed to. When applying this paint to steel materials, the painting process is as follows: Steel plate → (Short primer coating) → Rust removal (blasting treatment, power tool treatment) → Inorganic high concentration zinc powder coating →
A process consisting of a top coat is generally used. The top coating carried out in the final step is carried out in order to impart further corrosion resistance to the object to be coated over a long period of time or to impart a desired color to the object to be coated. However, when this top coat is applied, a foaming phenomenon occurs, and the formed top coat has a major drawback that defects such as bubbles, pinholes, craters, and roughness occur in the top coat. This paint film defect occurs because the surface of the inorganic high-concentration zinc dust paint film is bare, forming voids in the paint film layer. It is presumed that this causes a foaming phenomenon, resulting in the above-mentioned defects in the topcoat film. There are various methods to prevent this defect, but the most common method currently in use is to apply a top coat diluted with a solvent over a layer of inorganic high-concentration zinc dust paint several times. The so-called paint mist coating method is used to obtain the required film thickness of the top coat (usually about 100 to 200 microns) by applying multiple coats. However, even if this method is used, the phenomenon of foaming cannot be completely prevented, and furthermore, the method of applying the top coat many times takes time and effort, and is not satisfactory in terms of workability and productivity. However, it also had the disadvantage of causing various problems in the painting process. Therefore, in order to solve the above-mentioned defects, the present inventors have developed an inorganic high-concentration zinc powder paint that exhibits excellent adhesion even when applied to the surface of the porous coating, and forms a dense film that eliminates voids. As a result of extensive research and exploration into a coating composition that can prevent air from moving into the top coat and further improve long-term corrosion protection, we have discovered that polyvinyl, a reaction product of organic and inorganic substances, has been developed. The present inventors have discovered that a silica composite solution of acetals and alkyl, allyl, or aryl silicate satisfies the above performance, and have completed the present invention. That is, in the present invention, when a top coat is applied to an inorganic high-concentration zinc dust paint film to form a rust-preventive film,
Prior to applying the top coat, a mixture of polyvinyl acetals, alkyl, allyl or aryl silicate, and water is heated to a temperature of 50°C or higher and lower than the boiling point of the mixture in the presence of a solvent and an acid catalyst to cause a reaction. The present invention provides a method for preventing foaming of a rust-preventing coating film, which comprises applying a solution of 5 to 30% by weight solids of a silica composite obtained by the method. In the present invention, the process of applying the inorganic high-concentration zinc dust paint as a rust-preventing paint is no different from the conventional painting process, that is, the base material, such as steel, is subjected to blasting or power tool treatment. After removing rust, apply a temporary rust-preventing shot primer, and before applying an inorganic high-concentration zinc powder paint, remove the rust again by blasting or power tool treatment, or apply a shop primer. A commonly used method is to apply an inorganic high-concentration zinc powder paint after rust removal without painting. Inorganic high-concentration zinc dust paints used as anti-corrosion paints require a dry film thickness of approximately 70 to 100 microns in order to maintain long-term anti-corrosion performance. As a coating method, airless spray, air spray, or brush coating can be used. The inorganic high-concentration zinc dust paint used in the present invention is generally known, and is a vehicle prepared by dissolving an alkyl silicate (e.g., ethyl silicate, propyl silicate, etc.) in an alcoholic solvent, or an alkali silicate (e.g., ethyl silicate, propyl silicate, etc.) dissolved in an alcoholic solvent. for example,
The basic composition is a solution of sodium silicate, potassium silicate, lithium silicate, etc.) dissolved in water, and a high concentration of zinc dust pigment (70 to 95% by weight in the coating film). be. According to the present invention, an inorganic high-concentration zinc dust paint is applied to the required film thickness, and the drying time is approximately 1 to 2 minutes.
A reaction product obtained by heating polyvinyl acetals and an alkyl, allyl or aryl silicate under an acid aqueous solution catalyst to a temperature of 50°C or higher and lower than the boiling point of the mixture (hereinafter referred to as ``reaction product'') Apply a solution of 5 to 30% by weight solids of silica composite to 3 to 40μ by airless spray, air spray, or brush painting.
Paint to a dry film thickness of approximately If the dry film thickness is less than 3 μm, the pores in the inorganic high-concentration zinc-dust paint film will not be completely filled, and the foaming phenomenon of the top coat film cannot be completely prevented. On the other hand, if the dry film thickness is greater than 40 μm, the adhesion becomes poor, which is not preferable. The silica composite used in the present invention is described in Japanese Patent Application Laid-Open No. 53-92847 by the present applicant, and the silica composite is composed of polyvinyl acetals and alkyl, allyl or aryl silicate (hereinafter referred to as "organosilicate"). (abbreviated as ")" and reacting the mixture at a temperature of 50°C or higher and lower than the boiling point under the catalyst of a water-soluble inorganic acid with a dissociation constant (pka) of 7 or less and an aqueous organic acid solution. It will be done. The polyvinyl acetals used in the production of the silica composite are polyvinyl formal, polyvinyl acetal, and polyvinyl obtained by acetalizing the hydrolyzate of polyvinyl esters (e.g., polyvinyl acetate, polyvinyl propionate, etc.). It is a general term for vinyl resins such as butyral, and polyvinyl esters having a number average degree of polymerization of 250 to 1500 are preferably used. The degree of acetalization is preferably 55 to 88 mol%, and the hydroxyl group content is preferably 10 to 45 mol%.
There is no problem even if the vinyl ester portion remains. These polyvinyl acetals can be dissolved in organic solvents such as dioxane, chlorinated hydrocarbons, lower alcohols, ketones, lower esters, or mixtures thereof that have a solubility for the respective polyvinyl acetals. and use as a solution. The organic silicate that reacts with polyvinyl acetals has the general formula (In the formula, R represents an alkyl group, aryl group, or allyl group having 1 to 8 carbon atoms, and n represents 0 or an integer of 11 or less, respectively.) Tetraalkyl, tetraaryl, tetraallyl orthosilicate, or poly It is a silicate. Specifically, for example, methyl orthosilicate, ethyl orthosilicate, n-propyl orthosilicate, n-butyl orthosilicate, n
-Octyl orthosilicate, phenyl orthosilicate, benzyl orthosilicate, phenethyl orthosilicate, allyl orthosilicate, methalyl orthosilicate, and polysilicates produced by dehydration condensation of these orthosilicates. used. In order to produce a silica composite from a polyvinyl acetal and an organic silicate, the organic silicate is added to a solution of the polyvinyl acetal and then heated in an acidic state by adding an acid as a hydrolysis catalyst. The appropriate proportion of the organic silicate to the polyvinyl acetals is 11 to 100 parts by weight of the latter as silica to 100 parts by weight of the former. If the amount of organic silicate used is less than 11 parts by weight, when formed into a film, adhesion will be poor. On the other hand, if you use more than 100 parts by weight,
There is a risk that the foaming phenomenon of the top coat cannot be completely prevented, and at the same time, the storage stability of the silica composite in a solution state may become poor. The total content of polyvinyl acetals and organic silicates in the reaction system is preferably 3 to 30% by weight. If this content is less than 3% by weight, not only will the reaction be too slow, but the solid content will be too low, making it difficult to form the required film thickness, resulting in poor practicality.
If it exceeds % by weight, gel may be formed during the reaction. As the acid component as a hydrolysis catalyst for organic silicate, water-soluble inorganic acids and organic acids having a dissociation constant (pka) of 7 or less are used. Specifically, for example,
Mono- or polycarboxylic acids such as hydrochloric acid, phosphoric acid, hydrofluoric acid, sulfuric acid, nitric acid, propionic acid, lactic acid, monochloroacetic acid, oxalic acid, tartaric acid, citric acid, L-aspartic acid, iminodiacetic acid, oxycarboxylic acid, amino Examples include carboxylic acids. The amount of these acids added is usually 1 to 30 parts by weight per 100 parts by weight of the organic silicate expressed in terms of silica. When forming a silica complex between polyvinyl acetals and organic silicates under acidic conditions, in order to precede the hydrolysis reaction of the organic silicate,
It is necessary to have water present in the reaction system. Although the effect of the proportion of water in the reaction conditions on the reaction rate is generally not particularly significant, the preferred amount added is 0.1 to 20% by weight. In order to form the above formulation into a silica composite, it is necessary to heat the reaction system. Specifically, the reaction is carried out by heating the reaction system to a temperature of 50°C or higher and lower than its boiling point. If the heating temperature is lower than 50°C, only the hydrolyzate of organic silicate is accumulated, and a complex with polyvinyl acetals is not substantially formed. Therefore, when formed into a film, the water resistance becomes poor. The duration of heating required to form the silica complex is 30 minutes to 10 hours. Pigments, additives, etc. commonly used in the coating industry may be added to the silica composite solution thus obtained, if necessary. After drying the silica composite solution synthesized in this way for 1 to 2 days after coating as described above,
Various conventionally used top coat paints such as epoxy and tar epoxy are applied thereon to form a rust-preventive coating. The required film thickness of this top coat is usually 100 to 200 microns, but according to the present invention, even if this required film thickness is applied in one coat, no foaming phenomenon occurs during the top coat. As described above, the present invention aims to reduce the foaming phenomenon of the top coat that occurs when applying a thick coat of inorganic high concentration zinc dust paint and then applying a top coat on top of the thick coating. By coating a silica composite solution on top, a dense film is formed on the paint film in the bare pore state to prevent corrosion.The inorganic high concentration zinc dust paint film is a long-term anti-rust film. It has great industrial significance as it has extremely excellent performance as a metal. Moreover, the silica composite solution forms a coating film that has excellent adhesion to both the inorganic high-concentration zinc dust coating coating and the top coating coating. This is considered to be due to the following reasons. In the silica composite, there are reactive silanol groups derived from colloidal silica produced by the hydrolysis reaction of alkyl silicate, and the silica component having these silanol groups is used to coat the inorganic high-concentration zinc powder coating. By selectively oriented on the surface to form a layer mainly composed of silica on the surface of the zinc dust paint film and creating a strong bond between the zinc dust paint film and the zinc dust paint film. It is thought that it exhibits excellent adhesion to. Furthermore, a dense film mainly composed of polyvinyl acetal bonded to silica is formed on the surface of this silica-based layer, and this film prevents the top coat from foaming, and also prevents the top coat from foaming. It is presumed that this also improves the adhesion. The present invention will be further explained below with reference to Examples and Comparative Examples. These Examples are intended to explain the present invention in more detail, and are not intended to limit the present invention in any way. Note that in the middle part of the example and % indicate parts by weight and % by weight. Example of synthesis of silica composite 1 Into a flask equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet tube and dropping funnel, add polyvinyl butyral (trade name, Denka Butyral #2000L).
20% ethanol solution 880 manufactured by Denki Kagaku Kogyo Co., Ltd.
Prepare g. After nitrogen substitution, 20g of 0.1N hydrochloric acid aqueous solution was added dropwise over about 5 minutes while stirring, and the mixture was heated to 80℃.
Heat to. After raising the temperature, add ethyl polysilicate (trade name, ethyl silicate) through the dropping funnel.
40, SiO ₂ min 40% Nippon Colcoat Chemical Co., Ltd. product) 100
g was added dropwise over a period of 15 minutes. After further stirring at 80° C. for 2 hours, 200 g of butyl cellosolve was added to obtain a transparent silica composite solution 1 with a solid content of about 20%. Synthesis Example 2 of Silica Complex 900 g of polyvinyl butyral solution (consisting of 72 g of Denka Butyral #2000L, 300 g of ethyl alcohol, and 528 g of ethyl cellosolve) and 40 ethyl silicate (same as in Synthesis Example 1 of Silica Complex) were prepared using the same method as in Synthesis Example 1. Using 20 g of 40% phosphoric acid, 80 g of the silica composite solution was reacted for 3 hours to obtain a silica composite solution 2 with a solid content of about 12%. Example 1 Mill scale, red rust, etc. on the surface of a steel plate were removed by shot blasting (the treatment level was at least Sa21/2 of the Swedish standard). Inorganic high concentration zinc powder paint (product name, SD Zinc Primer) on shot blasted board
ZE1500 (product of Kansai Paint Co., Ltd.) was applied using airless spray coating to a dry film thickness of 75μ. After being left at room temperature for one day, the silica composite solution 1 obtained in Synthesis Example 1 of Silica Composite was coated with varying film thickness by air spray coating. After leaving this product at room temperature for 1 day, apply tar epoxy paint (product name: Eposeal 600, manufactured by Kansai Paint Co., Ltd.) as a top coat.
was applied to a dry film thickness of 100μ by airless spray painting, and the performance of various paint films was investigated. The test results are shown in Table 1 below. Example 2 In Example 1, silica composite solution 2 obtained in Silica composite synthesis example 2 was used instead of silica composite solution 1, and the film thickness was set to 15μ, and the other conditions were as in Example 1. I did the same thing. The test results are shown in Table 1 below. Synthesis example of exfoliant for comparison 1 50 parts of ethyl polysilicate used in Synthesis example 1 of silica composite, 5 parts of water, 0.1 part of concentrated hydrochloric acid, 20 parts of isopropyl alcohol, 24.9 parts of ethyl cellosolve
Comparative Exhibitor 1 was obtained by reacting the mixture composition at 40° C. for 2 hours. Synthesis example of comparative vehicle 2 100 parts of comparative vehicle 1, 440 parts of the 20% ethanol solution of polyvinyl butyral used in silica composite synthesis example 1, and 60 parts of butyl cellosolve were mixed with thorough stirring at room temperature to prepare a comparative vehicle. Expanding agent 2 was obtained. Comparative Example 1 In Example 1, Comparative Exhibitor 1 was used instead of Silica Composite Solution 1, the film thickness was set to 15μ, and the other conditions were the same as in Example 1. The test results are shown in Table 1 below. Comparative Example 2 In Example 1, the film thickness was determined by using a 10% ethanol solution of polyvinyl butyral used in Synthesis Example 1 of Silica Composite instead of Silica Composite Solution 1.
15μ, and the other conditions were the same as in Example 1. The test results are shown in Table 1 below. Comparative Example 3 In Example 1, Comparative Exhibitor 2 was used instead of Silica Complex Solution 1, the film thickness was set to 15 μm, and the other conditions were the same as in Example 1. The test results are shown in Table 1 below. Comparative Example 4 In Example 1, the tar epoxy paint was immediately applied without applying the silica composite solution.
Other conditions were the same as in Example 1. The test results are shown in Table 1 below. 【table】

Claims (1)

[Claims] 1. When a top coat is applied to an inorganic high-concentration zinc dust paint film to form a rust-preventing film, a mixture of polyvinyl acetals, alkyl, allyl or aryl silicate, and water is used prior to application of the top coat. The solid content of the silica composite obtained by heating and reacting in the presence of a solvent and an acid catalyst to a temperature of 50°C or higher and lower than the boiling point of the mixture
A method for preventing foaming of a rust-preventing coating film, which is characterized by applying a 30% solution by weight.