JPS6078672A - Corrosion-proof painting method of metal surface having rust layer - Google Patents

Abstract

PURPOSE:To apply corrosion-proof coating to the surface of a metal by fixing a rust layer, by applying an epoxy resin paint containing a ketimine compound as a curing agent to the surface of a metal on which a rust layer remains. CONSTITUTION:An epoxy resin containing a ketimine compound as a curing agent is applied to the surface of a metal having a rust layer. Whereupon, the moisture in the rust layer cures the epoxy resin paint and fixes the rust layer. As mentioned above, the epoxy resin paint can be directly applied to a rust surface without applying under-coat treatment and corrosion-proof coating is applied to a metal surface.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for anti-corrosion coating of a metal surface having a rust layer, and more specifically, to a method of coating a metal surface with a rust layer remaining on the surface using a ketimine compound as a hardening agent. This relates to a method of anticorrosive coating on metal surfaces, which involves applying paint and fixing the rust layer.

Conventionally, epoxy resin paints, polyurethane paints, chlorinated rubber paints, vinyl chloride resin paints, and zinc dust-containing paints that use epoxy resin Yanityl silicate as a binder 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 to achieve long-term development of excellent anti-corrosion performance using this epoxy resin paint, it is necessary to use a power tool, a power brush, or a blasting process to completely remove the rust present on the metal surface. If this surface treatment is not performed, the adhesion of the epoxy resin paint to the metal base 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 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 eliminate the painting process. It also has the great advantage of being measurable, 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 that uses processed drying oil, alkyd resin, phenol resin, etc. alone or in any combination thereof as the main film-forming element, and to which anti-corrosion pigments are added. has insufficient water resistance, corrosion resistance, and poor solvent resistance, so it is necessary to apply a top coat with excellent corrosion resistance such as epoxy resin, urethane resin, or vinyl resin that contains a strong solvent. The drawback is that it cannot be done. Another method is to apply a paint using a moisture-curable incyanate resin to the rusted surface, but this paint generates coal gas during the curing reaction, resulting in the formation of many pinholes in the paint film and long-term use. It has the disadvantage of lacking corrosion resistance. 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 (Japanese Unexamined Patent Publication No. 1983-1999-1).
(See Publication No. 149466). 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 forming blistering rust or black rust. There are drawbacks to doing so.

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 aimed at developing the epoxy resin paint, it was discovered that by using a ketimine compound as a hardening agent for epoxy resin paint, an excellent anti-corrosion coating film could be formed without the need for metal surface treatment, and the present invention was developed. I was able to complete it.

Thus, according to the present invention, on a metal surface having a rust layer,
A method for anticorrosive coating of a metal surface having a rust layer, characterized by applying an epoxy resin paint using a ketimine compound as a hardening agent, and then hardening the epoxy resin paint with moisture in the rust layer, and fixing the rust layer. is provided.

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 to reproduce amino groups,
Since it reacts slowly with the epoxy resin, the epoxy resin paint sufficiently penetrates and adsorbs into the rust layer, and has very good adhesion to the rust layer. In addition, since the ketones generated during the curing reaction process volatilize out of the coating film together with the organic solvent, there is no risk of impairing the anticorrosion properties of the coating film, which would otherwise cause pinholes. Furthermore, as the moisture contained in the rust layer is consumed in the curing reaction of the epoxy resin paint as mentioned above, the interior of the rust layer is firmly fixed by the cured paint film in the absence of moisture. 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 can be achieved by using an epoxy resin paint that uses a ketimine compound as a curing agent, especially in an epoxy resin paint that could not be applied directly to a metal surface with a rust layer. This is something that could not be achieved by using conventional epoxy resin paints that use polyamine compounds or polyamide resins as curing agents.

The metal to which the method of the present invention is preferably applied is usually steel, but it can also be applied to non-ferrous metals.

Hereinafter, the ketimine compound-curable epoxy paint used in the present invention will be explained.

Examples of the epoxy resin used in the paint include the known epoxy resins described in Chapter 2 of "Epoxy Resins" by Kuniyuki Hashimoto, published by Nikkan Kogyo Shimbun, 1969, among which 1 Those having at least 2 or more, preferably 2 to 5, epoxy groups per molecule and bonded by carbon chains of organic residues containing these epoxy groups or carbon chains interrupted by oxygen atoms are preferably used. In particular, those having an average molecular weight of about 350 to about 3,000 and an epoxy equivalent of about 80 to about 1,000 are preferred.

Good: i! Examples of i-type epoxy resins include epoxy resins obtained by reacting polyhydric alcohols, polyhydric phenols, etc. with excess epichlorohydrin or alkylene oxide. Examples of polyhydric alcohols include ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, glycerin, neopentyl glycol, phethylene gelicol, hexanediol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, diglycidyl, nlubitol, etc. Yes, as polyhydric phenols,
2,2-bis(4-hydroxyphenyl)furopane (bisphenol A), halogenated bisphenol A, 4.
4-dihydroxyphenylmethane (bisphenol F)
,l-! Examples of epoxy resins that can be used in the present invention other than these include 4-hydroxyphenyl propane, resorcinol, tetrahydroxyphenyletha/, novolac type polyhydric phenol, and cresol type polyhydric phenol. .2.3-) glycidyl adducts of lith(2°3-epoxypropoxy)propane, aniline or aniline barrier conductors (such as orthotoluidine);
These include glycidyl esters such as phthalate diglycidyl ester, hexahydrofucleate diglycidyl ester, and tetrahydrophthalic acid diglycidyl ester, and epoxidized soybean oil.

The ketimine 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 and converted into a free primary amino group in the presence of moisture. , represents a monovalent hydrocarbon group such as a cycloalkyl group, and the island 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 above polyamide/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, but generally about 2
It is advantageous to have a primary amine group equivalent weight of less than 1,000, preferably within the range of about 30 to about 1,000. It is also advantageous that the polyamine compound generally has a number average molecular weight within the range of about 5'000 or less, preferably about 3000 or less.

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, and Examples include aromatic polyamines such as ethylene diamine; alicyclic polyamines such as isophorone diamine and cyclohexylaminoprobylamine; and polyamides having at least one primary amino group at the end of the molecule.

Among the above-mentioned polyamine compounds, polyamine compounds that do not contain secondary amino groups in their molecules, that is, have only ketiminated primary amino groups, are slow to cure and penetrate into the rust layer, releasing moisture during the curing reaction process. It is particularly suitable because it consumes and removes a large amount of water. Therefore, when using a ketimine compound having a secondary amino group in the molecule,
It is preferable to use an adduct obtained by reacting a class 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, main butyl 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, using quantitative proportions and reaction conditions such that substantially all of the primary amine 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. It is preferable to use it in a proportion such that it is 0.5 to 5.0 equivalents, preferably 0.6 to 3.0 equivalents. If the amount is less than 0.5 equivalents, curing will be insufficient, and if it is more than 5.0 equivalents, adhesive may remain in the cured coating, which may cause problems in anticorrosion.

Solvents used in epoxy resin paints include aromatic hydrocarbons such as toluene and xylene; ketones such as acetate, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; ethyl acetate, n-butyl acetate, and isobutyl acetate. Common solvents for paints include esters such as cellosolve, cellosolve acetate, etc. The amount used is 200 parts by weight or less per 100 parts by weight of the total amount of the epoxy resin and ketimine compound.

The epoxy resin paint can be easily prepared by simultaneously mixing the above-mentioned components by any known means, but in some cases it may be of a two-component type in which a ketimine compound is mixed immediately before use of the paint. In addition to the above components, the epoxy resin paint may contain conventionally used pigments, additives, plasticizers, etc., as desired, in an amount of 200 parts by weight or less per 100 parts by weight of the total amount of the epoxy resin and ketimine compound. It can be added as appropriate within the range.

The epoxy resin paint can be applied by conventionally known painting means such as spray painting and brush painting. Although the metal optical surface of the object to be coated has a rust layer for the purpose of the present invention, it is necessary to remove the 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 the epoxy resin paint to be applied is not particularly limited, but is generally about 30 to about 300 microns in dry film thickness, preferably about 60 to about 150 microns.

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.

EXAMPLES 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 2 Ketimine Curing Agent In the table, MIBK indicates methyl isobutyl ketone and MEK indicates methyl ethyl ketone.

Example 1 Bengara 2 was added to 100 parts of resin solids mixed in a ratio of 1 mole of epoxy resin and 25 moles of ketimine curing agent [F].
An epoxy resin paint was prepared by adding 6 parts of talc, 79 parts of talc, 8 parts of an anti-sagging agent, and 50 parts of a 1:1 mixed solvent of xylene and methyl isobutyl ketone.

Shot-blasted steel plates and shot-blasted steel plates are exposed to this paint outdoors for two months in advance to generate rust.
After removing the floating rust, air spray painting was applied so that the dry film thickness was approximately 100 μm. The results of the coating film performance test of the obtained coated plate are shown in Table 4 below.

Examples 2 to 4 Epoxy resin paints were prepared and applied in 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 3 Comparative Examples In Example 2, Sanmide HB230 (polyamide manufactured by Sanwa Kagaku Co., Ltd.) was used instead of 1 mol of ketimine curing agent [F].
A paint was prepared in exactly the same manner as in Example 2, except that 0.5 mol was used, and it was applied. The results of the coating film performance test of the obtained coated plate are shown in Table 4 below.

Note 1: Exposed outdoors for 6 months in a beach area.

Note 2: ◎No rust at all. ○Black rust develops on less than 1% of the area of the painted plate. Black rust develops in an area of Δ6 inches or less.

Note 3: Subjected to cross-cut tape test.

◎There is no peeling at all. ○Peeling occurs on an area of 5% or less of the painted plate. 6
Peeling to an area of 30% or less.

As is clear from the above test results, the anticorrosive coating method according to the present invention cures the epoxy resin paint slowly and reacts with the moisture in the rust layer, so it penetrates and adsorbs well into the rust layer and does not adhere to the rust surface. The cured coating exhibits the excellent corrosion resistance inherent to epoxy resin coatings on rusted surfaces.

(hereafter

Claims (1)

[Claims] ■ 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.