JPS6254556B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an anticorrosive coating method for a metal surface having a rust layer, and more specifically, it involves applying an epoxy resin paint containing a ketimine compound as a hardening agent to a metal surface on which a rust layer remains to fix the rust layer. The present invention relates to a method for anticorrosive coating of metal surfaces. Traditionally, epoxy resin paints, polyurethane paints, chlorinated rubber paints, vinyl chloride resin paints, and zinc dust-containing paints that use epoxy resins or ethyl silicate as binders have been widely used for long-term corrosion protection of steel materials and steel structures. has been done. Among these paints, epoxy resin paints are used as anticorrosive paints for metals in a wide range of fields due to their excellent anticorrosion performance. However, in order for this epoxy resin paint to exhibit excellent anti-corrosion performance over a long period of time, it is necessary to completely remove the rust existing on the metal surface using a power tool, power brush, or by blasting. It is necessary to perform sufficient treatment, and if this surface treatment is not performed, the adhesion of the epoxy resin paint to the metal substrate will be poor, and the anticorrosion performance will be significantly reduced. On the other hand, when applying the above-mentioned surface treatment to the metal to be coated, the generation of dust, noise, etc. is unavoidable, which is undesirable from the viewpoint of pollution and hygiene. If a coating method, that is, an anti-corrosion coating method that can be applied directly to a metal surface with a rust layer and provides excellent adhesion and anti-corrosion performance, could be developed, it would not only reduce pollution and hygiene, but also save the painting process. It has a great advantage in that it can be used, and its development is strongly desired. However, in the past, various methods have been proposed in which corrosion prevention is achieved by applying paint directly to a metal surface having a rust layer. For example, there is a method of using a paint made by using processed drying oil, alkyd resin, phenolic resin, etc. alone or in an arbitrary mixture as the main coating film-forming element, and adding a rust-preventing pigment to this. has insufficient water resistance and anti-corrosion properties, as well as poor solvent resistance, making it impossible to apply top coats with excellent anti-corrosion properties such as epoxy resin-based, urethane resin-based, and vinyl resin-based paints that contain solvents with strong dissolving power. There is a drawback. Another method is to apply a paint using moisture-curing isocyanate-based resin to the rusted surface, but this paint generates carbon dioxide gas during the curing reaction, resulting in the formation of many pinholes in the paint film, resulting in long-term corrosion resistance. It has the disadvantage of lacking in Furthermore, recently it has been proposed to use a coating material consisting of a precondensate of an epoxy resin and a phenol resin, a polyamine, and a polyamide curing agent (see Japanese Patent Laid-Open No. 149466/1983). However, when this paint is used, the moisture contained in the rust layer is sealed by the paint film and remains as it is, so rust continues to grow under the paint film, eventually leading to blistering rust and spot rust. There are drawbacks to forming a Therefore, the present inventor developed an anti-corrosion coating method that uses an epoxy resin with excellent anti-corrosion properties and can be applied directly to a metal surface with a rust layer without any pretreatment, and that does not have the drawbacks of the conventional methods described above. As a result of intensive research to develop this, we found that by using a ketimine compound as a curing agent for epoxy resin paint, it can be made without the need for metal surface treatment.
It was discovered that an excellent anticorrosion coating film can be formed, and the present invention was completed. Thus, according to the present invention, an epoxy resin paint using a ketimine compound as a hardening agent is applied to a metal surface having a rust layer, and then the epoxy resin paint is cured by moisture in the rust layer, and the rust layer is fixed. Provided is a method for anticorrosive coating of a metal surface having a rust layer, which is characterized by: The reason why it is possible to apply the epoxy resin paint directly to the rusted surface without any pretreatment as in the present invention is due to the use of a ketimine compound as a hardening agent. It is gradually hydrolyzed by the moisture contained in it and the moisture in the air, reproducing amino groups, and slowly reacting with the epoxy resin, so that the epoxy resin paint can fully penetrate and adsorb into the rust layer. Adhesion to the rust layer is also very good. In addition, since the ketones generated during the curing reaction process volatilize out of the coating film together with the organic solvent, they do not cause pinholes and there is no risk of impairing the anticorrosion properties of the coating film. Furthermore, as the water contained in the rust layer is consumed in the curing reaction of the epoxy resin paint as described above, the rust layer becomes firmly fixed inside by the cured paint film in the absence of water. The growth of rust has been completely stopped. The cured coating film thus formed completely blocks out external corrosive substances, thereby preventing corrosive action, and furthermore, has excellent solvent resistance, so it can be coated with various top coatings. In other words, the above-mentioned features of the present invention are achieved by using an epoxy resin paint that uses a ketimine compound as a curing agent, in particular in epoxy resin paints that were conventionally unthinkable to be applied directly to metal surfaces with rust layers. This was achieved for the first time, and cannot be obtained by using conventional epoxy resin paints that use polyamine compounds or polyamide resins as curing agents. The metals to which the method of the present invention is preferably applied are:
It is usually applied to steel, but it can also be applied to non-ferrous metals. The ketimine compound-curable epoxy resin paint used in the present invention will be explained below. Examples of epoxy resins used in the paint include the known epoxy resins described in Chapter 2 of "Epoxy Resins" by Kuniyuki Hashimoto, published by Nikkan Kogyo Shimbun in 1969;
At least 2 or more, preferably 2 to 5 per molecule
Epoxy groups, which are bonded by carbon chains of organic residues containing these epoxy groups or carbon chains interrupted by oxygen atoms, are preferably used, and in particular, those having an average molecular weight of about 350 to about 3000. , those having an epoxy equivalent weight of about 80 to about 1000 are preferred. Examples of suitable epoxy resins include polyhydric alcohols,
Examples include epoxy resins obtained by reacting polyhydric phenols with excess epichlorohydrin or alkylene oxide. Examples of polyhydric alcohols include ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, glycerin, neopentyl glycol, butylene glycol, hexanediol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerol, sorbitol, etc. Polyvalent phenols include 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), halogenated bisphenol A, 4,4-dihydroxyphenylmethane (bisphenol F), and tris(4-hydroxyphenyl). -hydroxyphenyl)bropane, resorcinol, tetrahydroxyphenylethane, novolak-type polyhydric phenol, cresol-type polyhydric phenol, and the like. Other examples of epoxy resins that can be used in the present invention include 1,2,3-tris(2,3-epoxypropoxy)propane, glycidyl adducts of aniline or aniline derivatives (e.g. orthotoluidine, etc.), phthalic acid These include glycidyl esters such as diglycidyl ester, hexahydrophthalic acid diglycidyl ester, and tetrahydrophthalic acid diglycidyl ester, and epoxidized soybean oil. The ketimyl compound used as a curing agent for the above-mentioned epoxy resin is a polyamine compound having at least one primary amino group blocked with a carbonyl compound in one molecule. This “primary amino group blocked with a carbonyl compound”
is a protected amino group that can be easily hydrolyzed into a free primary amino group in the presence of moisture, and is typically represented by the following formula: In the formula, R ₁ represents a hydrogen atom or a monovalent hydrocarbon group such as an alkyl group or a sialoalkyl group, and R ₂
represents a monovalent hydrocarbon group such as an alkyl group or a cycloalkyl group. It is a temporarily protected primary amino group that can be represented by: The polyamine compound may be either aliphatic (including alicyclic) or aromatic. The polyamine compound needs to have a primary amino group that undergoes a curing reaction with the epoxy resin, and generally has a primary amino group equivalent weight of about 2000 or less, preferably within the range of about 30 to about 1000. That is advantageous. It is also advantageous that the polyamine compound generally has a number average molecular weight within the range of about 5000 or less, preferably about 3000 or less. Therefore, polyamine compounds that can be suitably used include aliphatic polyamines such as ethylene diamine, propylene diamine, butylene diamine, hexamethylene diamine, diethylene triamine, triethylene tetramine, and pentaethylene hexamine; xylylene diamine, diaminodiphenylmethane, Examples include aromatic polyamines such as phenylene diamine; alicyclic polyamines such as isophorone diamine and cyclohexylaminopropylamine; and polyamides having at least one primary amino group at the end of the molecule. Among the polyamine compounds mentioned above, polyamine compounds that do not contain a secondary amino group in their molecules, that is, have only ketiminated primary amino groups, are slow to cure and penetrate into the rust layer, allowing them to absorb more moisture during the curing reaction process. This is particularly suitable since it consumes and removes a large amount. Therefore, when using a ketimine compound having a secondary amino group in the molecule, it is desirable to use it as an adduct obtained by reacting the secondary amino group with the above-mentioned epoxy resin. The carbonyl compound that can be used to ketimine the polyamine compound described above includes any commonly used ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, and the like. In addition, the ketimine compound in the present invention includes those obtained by aldiminating a polyamine compound with an aldehyde such as acetaldehyde or benzaldehyde. The reaction between the polyamine compound and these ketones can be carried out by a method known per se, with the quantitative ratio and proportion being such that substantially all of the primary amino groups present react with the ketone. It is generally advantageous to use ketones with poor water solubility and low steric hindrance, such as methyl isobutyl ketone and methyl ethyl ketone, in order to facilitate the reaction (dehydration reaction). The epoxy resin paint used in the present invention is prepared by adding a ketimine compound to the epoxy resin described above, and the ratio of active hydrogen in the ketimine compound to 1 equivalent of epoxy group in the epoxy resin is It is preferable to use it in a proportion of 0.5 to 5.0 equivalents, preferably 0.6 to 3.0 equivalents. If the amount is less than 0.5 equivalent, curing will be insufficient, and if it is more than 5.0 equivalent, stickiness may remain in the cured coating film, which may cause problems in anticorrosion properties. Solvents used in epoxy resin paints include aromatic hydrocarbons such as toluene and xylene; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; ethyl acetate, n-butyl acetate, isobutyl acetate, Common solvents for paints include esters such as cellosolve and cellosolve acetate. The amount used is the total amount of epoxy resin and ketimine compound 100
It is not more than 200 parts by weight. Epoxy resin paints can be easily prepared by simultaneously mixing the above components by any known means, but in some cases, a two-part type may be used in which a ketimine compound is mixed immediately before use of the paint. . In addition to the above-mentioned components, the epoxy resin paint may also contain conventionally used pigments, as desired.
Additives, plasticizers, etc. may be added as appropriate in a range of 200 parts by weight or less based on 100 parts by weight of the total amount of the epoxy resin and ketimine compound. The epoxy resin paint can be applied by conventionally known painting means such as spray painting and brush painting. Although the metal surface of the object to be coated has a rust layer for the purpose of the present invention, it is necessary to remove floating rust during coating. If floating rust is not removed, there is a drawback that the adhesion of the anticorrosive coating is reduced. The amount of epoxy resin paint applied is not particularly limited, but generally the dry film thickness is about 30μ to about
300μ, preferably about 60 to about 150μ. Therefore, in the applied epoxy resin paint, the ketimine compound of the hardening agent is gradually hydrolyzed by the rust layer and moisture in the air, reproduces the primary amino group, and reacts with the epoxy group in the epoxy resin. It hardens and exhibits excellent anti-corrosion performance. Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that parts indicate "parts by weight." The types and properties of the epoxy resin and ketimine curing agent used in each Example and Comparative Example are shown in Tables 1 and 2 below.

【table】

[Table] Example 1 1 mol of epoxy resin and 0.25 ketimine curing agent
For 100 parts of resin solids mixed in molar ratio,
An epoxy resin paint was prepared by adding 26 parts of Bengara, 79 parts of talc, 8 parts of an anti-sagging agent, and 50 parts of a 1:1 mixed solvent of xylene and methisobutyl ketone. This paint was air-sprayed onto shotplast steel plates and shotplast steel plates that had been previously exposed outdoors for two months to generate rust, and any floating rust removed, to a dry film thickness of about 100 microns. The results of the coating film performance test of the obtained coated plate are shown in Section 4 below.
Shown in the table. Examples 2 to 4 Epoxy resin paints were prepared and applied in exactly the same manner as in Example 1, except that the epoxy resin and ketimine curing agent were used in the compositions shown in Table 3. The coating film performance test of the obtained coated plate is shown in Table 4 below.

[Table] Comparative Example 1 A paint was prepared in exactly the same manner as in Example 2, except that 1 mole of Sanmide HB230 (polyamide manufactured by Sanwa Kagaku Co., Ltd.) was used instead of 1 mole of the ketimine curing agent, and the paint was used for painting. did. The results of the coating film performance test of the obtained coated plate are shown in Table 4 below. Comparative Example 2 A paint was prepared and applied in the same manner as in Example 3, except that 0.5 mol of hexamethylene diamine was used instead of 0.5 mol of the ketimine curing agent. The results of the coating film performance test of the obtained coated plate are shown in Table 4 below.

【table】

[Table] As is clear from the above test results, the anti-corrosion coating method according to the present invention cures the epoxy resin paint slowly and reacts with the moisture in the rust, so it can penetrate and adsorb into the rust layer well. The cured coating exhibits the excellent anti-corrosion properties inherent to epoxy resin coatings on rusted surfaces.

Claims (1)

[Claims] 1. A rust layer characterized by applying an epoxy resin paint using a ketimine compound as a hardening agent to a metal surface having a rust layer, and then hardening the epoxy resin paint with moisture in the rust layer and fixing the rust layer. A method for anticorrosive coating of metal surfaces.