JPH0626709B2 - Powder coating method for steel materials - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coating method for forming an epoxy powder coating film having excellent physical properties such as substrate adhesion, corrosion resistance, and cathode peeling resistance on the surface of a steel material in a safe and hygienic manner with high productivity. .

Recently, for steel products exposed to severe corrosive environment for a long time, such as buried pipelines, steel pipe piles, steel sheet piles, etc., epoxy powder coatings with excellent corrosion resistance, durability, mechanical properties, and high productivity have been applied. I have been painting a lot.
The powder coating method of these steel materials is usually surface blast cleaning of steel materials → preheating of steel materials → hot electrostatic coating of powder coating materials →
It is carried out through the steps of curing the powder coating film in the cooling process, water cooling, and inspection.

The epoxy powder coating film formed by such a process has excellent corrosion resistance, durability, and mechanical properties, but when exposed to a wet environment, especially a hot and humid environment, the so-called secondary adhesion with the material Has a drawback in that it is liable to be deteriorated, and blisters, peeling, and corrosion under the coating film easily occur. In particular, if the coating film has a defect such as a pinhole at the time of coating, or if the coating film is damaged by an external force received during transportation and laying work, the above-mentioned performance deterioration is remarkable. If cathodic protection measures are taken with an external power source to protect against damaged areas in such a case, the coating film due to the electrochemical action of the coating film defects is often more likely to come off. .

It has been conventionally known that the insufficient secondary adhesion of the epoxy powder coating film is compensated and improved by the chromate treatment of the steel base material. For example, in the above-mentioned powder coating process for steel materials, by applying a coating type chromic acid surface treatment agent thinly and uniformly after the surface blast cleaning and before the preheating process, water-resistant secondary adhesion and corrosion protection of the epoxy powder coating film are obtained. And the resistance to cathode peeling are dramatically improved. However, such a chromic acid treatment process has a problem in terms of worker's safety and health, and a problem of environmental pollution due to waste and drainage, and there is a problem that the cost for the countermeasure is added to the coating cost.

Therefore, the present inventor performed a simple surface treatment of a steel material with a material having no problem in occupational safety and health without using a pollution-generating substance such as chromic acid, which was superior to chromic acid treatment. As a result of earnest research on a method of forming a high performance epoxy powder coating film on steel,
This time, they have found that the object can be achieved by applying a cationic aqueous primer instead of the chromic acid treatment, and completed the present invention.

Therefore, according to the present invention, a cationic aqueous primer mainly composed of a water-soluble or water-dispersible resin obtained by neutralizing an active amino hydrogen-containing reaction product of an epoxy resin and a basic amino compound with an acid is used as a steel material. A powder coating method for a steel material is provided, which comprises coating a powder coating containing an epoxy resin as a main component while the active amino hydrogen is present in the coating film to be formed. It

The feature of the present invention resides in that the above-mentioned specific cationic aqueous primer coating is applied in place of the chromic acid treatment in the conventional method. Therefore, according to the method of the present invention, simply adding a simple primer coating equipment to the existing coating line,
The chromic acid treatment step is not required, safety and health problems are eliminated, the risk of pollution is eliminated, and the performance of the formed epoxy powder coating such as corrosion resistance and adhesion can be improved. There are enormous advantages.

The coating method of the present invention will be described in more detail below.

Steel material: A base material (object to be coated) coated with an epoxy powder according to the present invention, and the shape, structure, size, etc. of the steel product are not particularly limited as long as they are steel products requiring anticorrosion treatment.
Examples include cast iron pipes, deformed pipes, steel sheet piles, shaped steels, steel plates, steel bars, and steel structures. The coated surface of these steel materials is preferably preliminarily subjected to pretreatment such as degreasing, sand blasting, and chemical conversion treatment at the time of pickling prior to applying a cationic aqueous primer described below.

Cationic water-based primer: A paint to be applied on the surface of steel material, whose main component is a water-soluble or water-dispersible resin obtained by neutralizing an active amino hydrogen-containing reaction product of an epoxy resin and a basic amino compound with an acid. It is a water-based paint.

In the present invention, the “active amino hydrogen” in the cationic aqueous primer is hydrogen bonded to the primary amino group and / or the secondary amino group, and the active amino hydrogen is the epoxy resin and the basic amino group. It is essential that it be present in the reaction product with the compound.

The epoxy resin is preferably a polyepoxide having two or more epoxy groups per molecule, and for example, one or more polyhydric phenols selected from bisphenol A, bisphenol F, bisphenol AD and epichlorohydrin or β-methylepichlorohydrin. Examples thereof include those obtained by the reaction, and among these, particularly preferable is an epoxy resin obtained from bisphenol A and epichlorohydrin.

On the other hand, as the basic amino compound which is reacted with the epoxy resin, a compound having a primary and / or secondary amino group is used, and preferably a water-soluble aliphatic amino compound as exemplified below is used. It For example, (a) mono- and dialkylamines such as propylamine, butylamine, diethylamine, dipropylamine; (b) mono- and dialkanolamines such as ethanolamine, propanolamine, diethanolamine, dipropanolamine; (c) cyclohexylamine, pyrrolidine. Alicyclic monoamines such as morpholine; (d) ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine,
Examples thereof include polyamines such as tetraethylenepentamine, propylenediamine, dipropylenetriamine, butylenediamine, diethylethylenediamine, diethylaminopropylamine, piperazine, N-methylpiperazine and N-aminoethylpiperazine. Ammonia can also be used.

As the basic amination compound, a polyamidoamine obtained by a condensation reaction between an excess amount of these amines and an aliphatic or aromatic polycarboxylic acid can also be used.
Examples of such polycarboxylic acids include succinic acid and
Adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid, tetrahydrophthalic acid, hexahydrophthalic acid, phthalic acid, trimellitic acid, pyromellitic acid and their anhydrides can be used.

Reaction of the epoxy resin with a basic amino compound opens the epoxy group to form a product having a primary and / or secondary or even a tertiary amino group. This ring-opening reaction is an exothermic reaction and occurs only by mixing at room temperature, but it is preferable to heat it to 50 to 150 ° C, particularly 70 to 130 ° C. The amount of the basic amino compound reacted to the effect of epoxy is such that the active amino hydrogen content in the reaction product is at least 0.1 equivalent or more per 1 kg of the reaction product, and the reaction product is neutralized with an acid. It may be higher than the minimum amount required to render it water soluble or water dispersible, and generally it is desirable that the amount be in the range of 0.5 to 30 equivalents per kg of reaction product.

The acid that can be used to neutralize the reaction product of the epoxy resin thus obtained and the basic amino compound is
For example, water-soluble organic or inorganic acids such as formic acid, acetic acid, propionic acid, butyric acid, lactic acid, hydroxyacetic acid, phosphoric acid, hydrochloric acid and the like. Further, the amount of acid required for neutralization is preferably at least the amount required to dissolve or disperse the reaction product in water and is equal to or less than the equivalent amount of the amine group in the reaction product. The amount is such that the pH of the subsequent cationic aqueous primer is in the range of 3 to 8, preferably 5 to 7.

The cationic aqueous primer used in the present invention is mainly composed of the above-mentioned neutralized water-soluble or water-dispersible resin to improve the physical properties of the coating film formed using the primer. In addition, a water-soluble or water-dispersible cross-linking agent can be blended as necessary. Specific examples of the cross-linking agent that can be blended are a reaction product of urea, benzogamine or melamine and an aldehyde, or an amino resin obtained by etherifying these with a monohydric alcohol having 1 to 5 carbon atoms; a phenol and an aldehyde. Initial condensate; a polyisocyanate having two or more isocyanate groups in one molecule (for example, phenylene diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, etc.) and a blocking agent (for example, methanol). ,ethanol,
Butanol, ethylene glycol monoethyl ether,
Blocked isocyanate compounds in which isocyanate groups are blocked by the addition of volatile low molecular weight active hydrogen compounds such as dimethylaminoethanol, acetoxime phenol, and cresol are listed. The amount of these cross-linking agents blended is 100 parts by weight of the neutralized aqueous resin,
Generally, a range of 5 to 50 parts by weight, particularly 15 to 30 parts by weight is preferable.

When a blocked isocyanate compound is used as the cross-linking agent, a partially blocked isocyanate compound having an average of one free isocyanate group or less left is previously reacted with the reaction product of the epoxy resin and the basic amino compound. You can leave it.

If necessary, a surfactant, a hydrophilic organic solvent, a curing accelerator, a coloring pigment, an extender pigment, an anticorrosive pigment, etc. can be added to the cationic aqueous primer.

The cationic water-based primer can be applied by spray coating, ironing, brush coating, dip coating, cationic electrodeposition coating, etc.
It can be appropriately selected according to the size, for example, spray coating, brush coating, etc. are suitable for large steel materials, while dip coating, cationic electrodeposition coating, etc. are preferable for medium and small steel materials. There is almost no change in performance due to the difference in The solid content of the water-based primer can be arbitrarily adjusted within the range usually used according to the coating method.

The coating film of the cationic aqueous primer can be dried at room temperature or by heating to evaporate water, a neutralizing agent and the like in the coating film, in which case the coating film has a primary or secondary amino group. It is important that the hydrogen (active amino hydrogen) therein is generally held in an amount of 0.1 equivalent or more, preferably 0.5 to 30 equivalent, per 1 kg of the resin.

Epoxy resin powder coating: A fine powder coating that can be coated on steel, heat-melted, and then three-dimensionally crosslinked to form a coating with excellent corrosion resistance, durability, and mechanical properties. Usually, it consists essentially of an epoxy resin and a curing agent. The epoxy resin which is the main component of this paint usually has an average molecular weight of 700 to 4000.
In this case, a polyfunctional epoxy resin having an epoxy equivalent in the range of 150 to 3300 and solid at room temperature is suitable, for example, condensation of a polyhydric phenol such as bisphenol A, bisphenol F, novolac phenol, novolac cresol with epihalohydrin. Things can be given. Examples of the curing agent used for crosslinking and curing these resins include dicyandiamide and its derivatives, aromatic polyamines (such as diphenylmethanediamine), polycarboxylic acids and their anhydrides (such as trimellitic anhydride), and poly Examples thereof include carboxylic acid hydrazides (for example, adipic acid dihydrazide), phenol resins, blocked polyisocyanates, BF ₃ complex compounds, imidazoles, imidazolines and the like. Further, the powder coating includes coloring pigments such as titanium white, red iron oxide, and chromium oxide; extenders such as tantalum, barita, mica, talc, clay, and silica; lead oxides, phosphates, chromates, and the like. The rust preventive pigment may be appropriately blended according to each purpose. The above-mentioned epoxy resin powder paint can be applied by a method known per se, such as a cold or hot electrostatic electrostatic spraying method or a fluidized dipping method. Which coating method should be selected? Can be determined according to the size and shape of the article to be coated, the target coating thickness, and the like.

Method of forming coating film: First, depending on the purpose, degreasing, sandblasting treatment, pickling or chemical conversion treatment (which can be used even if treated with chromic acid type) steel material is spray-coated with the above cationic aqueous primer, Apply by brushing, dipping, ironing, or cationic electrodeposition. These coating methods can be arbitrarily selected according to the size, shape, purpose of coating, etc. of the steel material to be coated, and each coating method can be performed by a method known per se. Therefore, the viscosity and the non-volatile content of the water-based primer may be adjusted within a range suitable for each coating method, and the coating method hardly affects the performance of the coating. The coating thickness of the water-based primer is generally 0.1 to 30 μm, preferably 0.1 based on the dry coating film.
The range of 5 μm is preferable, and after coating, leave at room temperature,
Alternatively, it is dried by heating.

Subsequently, an epoxy resin-based powder coating material is applied to the surface of the cationic water-based primer, and in order to improve the interlayer adhesion between the two coating films and further improve the secondary adhesion in a high temperature and high humidity environment, It is essential that a primary amino group and / or a secondary amino group remain in the coating film of the cationic aqueous primer when the powder coating material is applied,
For that purpose, specifically, after the volatile components such as the neutralizing agent and water in the cationic aqueous primer coating film are substantially removed by drying, and after being regenerated by the volatilization of the neutralizing agent, etc. It is preferable that the epoxy resin powder paint is applied and heat-cured before the active hydrogen of the primary and / or secondary amino group is substantially disappeared by the reaction with the curing agent. However, from the viewpoint of energy saving in the coating process, it is desirable that the preheating for applying the powder coating material is also used as the heating for drying the water-based primer, or both coating films are simultaneously heat-cured. Such a coating process is desirable for improving the adhesion between both coatings. However, if the cationic water-based primer is not sufficiently dried and a large amount of the neutralizing agent, water, solvent, etc. still remain in the coating film, if powder coating is repeatedly applied, there will be a feeling of popping between the coating films. The reaction between the amino hydrogen contained in the cationic aqueous primer and the epoxy resin contained in the powder coating is suppressed by the neutralizing agent, and the adhesion between the two layers is reduced. When a powder coating is applied after the dry curing has completely progressed in the case of containing a cross-linking agent, the compatibility and penetration of the powder coating to the cationic aqueous primer cured film becomes poor, and it is contained in the cationic aqueous primer. The active amino hydrogen that was used is substantially consumed by the reaction with the cross-linking agent contained in the primer, and is no longer used in the reaction with the epoxy resin contained in the powder coating. Adhesion between drops. Therefore, it is important to apply the powder coating material after the coating of the cationic primer is dried and before curing, while the active amino hydrogen remains in the coating.

The coating film thickness of the powder coating material can be usually in the range of 50 to 1000 μm, and its suitable film thickness can be appropriately selected according to the use environment, the handling conditions, the expected useful life, and the like. In addition, the coating method of the powder coating material is related to the coating film thickness. For example, when a coating film thickness of 200 μm or more is desired, a coating method such as a hot electrostatic coating method or a fluidized dipping method is applied before the object to be coated. A method including a heating step is desirable.

Next, the present invention will be further described based on Examples and Comparative Examples. In addition, "part" and "%" are based on weight.

I. Production Example of Cationic Aqueous Primer (A) Epoxy Bis Epoxy Resin with Epoxy Equivalent of 475 (Epicote 1001)
0 part was dissolved in 1293 parts of methyl isobutyl ketone, 210 parts of diethanolamine was added and reacted at 80 ° C. for 1 hour, 146 parts of triethylenetetramine was added, and further reacted at 100 ° C. for 30 minutes to react with epoxy-amine. An adduct was obtained.

On the other hand, 2 parts to 500 parts of diphenylmethane diisocyanate
-260 parts of ethylhexyl alcohol was added dropwise at 60 ° C over 30 minutes, and the mixture was further reacted at 90 ° C for 1 hour. Then, this was added to the above-mentioned epoxy-amine adduct and added at 60 ° C for 3 hours.
The reaction was carried out for 0 minutes to obtain a varnish having a solid content of 70% and an amine value of 74. After 120 parts of acetic acid was added to the varnish for neutralization, it was diluted with 5624 parts of deionized water to obtain a cationic aqueous primer A having a solid content of 30%.

(B) Epibis type epoxy resin having an epoxy equivalent of 950 (Mitsui Petrochemical Co., Ltd., Epomic R-304) 190
0 part was dissolved in 1036 parts of ethyl cellosolve, 73 parts of diethylamine was added and reacted at 60 ° C. for 30 minutes, and to this was added 450 parts of dimer acid polyamide with an amine value of 300 (Fuji Kasei Co., Ltd., Tomeide 225X), and further 10 parts.
The reaction was carried out at 0 ° C for 2 hours to obtain an epoxy-amide adduct.

On the other hand, diethylene glycol monoethyl ether (402 parts) was added to metaxylylene diisocyanate (282 parts), and the mixture was reacted at 50 ° C. for 30 minutes and further at 80 ° C. for 1 hour. This was added to the epoxy-amide adduct to give a solid content of 75%.
% And an amine value of 46 was obtained. Acetic acid 1 in this varnish
After neutralizing by adding 20 parts, it was diluted with 3523 parts of deionized water to obtain a cationic aqueous primer B having a solid content of 40%.

II. Example (1) A cationic aqueous primer A was spray-coated on a sandblasted mild steel plate so that the average film thickness was 1 μ,
After heating in a hot air drying oven at 250 ° C and confirming that the material temperature has risen to 220 ° C, immediately take out Napguard mark X7-2500 (Kishisai Amide-based curing epoxy powder coating made by Kansai Paint). 2 at -8KV
The sample was subjected to hot electrostatic coating to a thickness of 400 μm, and was further heated and cured in the same drying furnace for 3 minutes as above to obtain a test piece A ₀ .

(2) The pickled mild steel plate is immersed in an electrodeposition bath of a cationic aqueous primer B diluted with deionized water so that the solid content is 10%, and electrodeposited at a voltage of 250 V using the mild steel plate as a cathode. It was painted, washed with water and dried at 80 ° C. for 15 minutes. The dry film thickness of the primer obtained at this time was 3 μm. Then, this coated steel sheet was heated to 200 ° C. and immediately thereafter immersed in a fluid tank of EVACLAD No. 3250 (Kansai Paint Co., Ltd., hydrazide-based curable epoxy powder coating material) to a thickness of 300.
After applying a coating film of μ, the film was baked and cured at 200 ° C. for 20 minutes to obtain a test piece B ₀ .

III. Comparative Example (1) A test piece A ₁ was obtained in exactly the same manner as in Example 1, except that the cationic aqueous primer A was not applied.

(2) In exactly the same manner as in Example 1, but substituting the cationic aqueous primer, Cosmer 100 (manufactured by Kansai Paint,
Coating type chromate treatment agent) was coated to a solid 1.5 g / m ^2, to obtain a test piece A _2.

(3) A test piece B ₁ was obtained in exactly the same manner as in Example 2 except that the cationic aqueous primer B was not electrodeposited.

(4) in the same manner as in Example 2, except the cationic aqueous primer instead of the electrodeposition coating of B, and applying the Kosuma 100 so that the solid content 0.5 g / m ^2, to obtain a test piece B ₂ It was

(5) Test piece A ₃ was obtained in the same manner as in Example 1 except that the coating film of cationic aqueous primer A was baked at 170 ° C. for 30 minutes and then the epoxy powder coating material was applied.

(6), except that for coating epoxy powder coating after baking 30 minutes at 170 ° C. The coating film of the cationic aqueous primer B in Example 2 was carried out in the same manner as in Example 2 to obtain a test piece B _3.

IV. Performance test results [Test method] * Water resistance to boiling: Make a cut in the coating film until it reaches the substrate, immerse it in boiling water for 24 hours, pull it up, and then put a knife in the cut portion to peel off the coating film. The degree of ease of peeling after immersion is evaluated as compared to before immersion.

** Cathode peeling resistance: -1.5V, 3% according to the method described in ASTMG-8
The test is carried out for 30 days under the condition of saline and 20 ° C., and the progress of peeling from the initial holiday is evaluated.

As is clear from the above results, according to the method of the present invention, the adhesion to the substrate which is equal to or higher than that of the chromic acid treatment was exhibited. Moreover, it has been confirmed that the method of the present invention does not deteriorate the physical properties of the coating film such as bending resistance and impact resistance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C09D 163/00 PJM 8830-4J

Claims (1)

[Claims] 1. A steel material is coated with a cationic aqueous primer mainly composed of a water-soluble or water-dispersible resin obtained by neutralizing an active amino hydrogen-containing reaction product of an epoxy resin and a basic amino compound with an acid, Then, a powder coating method for a steel material, characterized in that a powder coating material containing an epoxy resin as a main component is coated while active amino hydrogen is substantially left in the primer coating film formed.