JPH06313148A - Coating composition for stainless steel - Google Patents

Abstract

PURPOSE:To obtain a fluorine-containing coating composition which does not rust a stainless steel substrate when applied thereto. CONSTITUTION:This coating composition comprises a fluorocopolymer having hydroxyl groups and carboxyl groups in the molecule, a curing agent, an ultraviolet absorber and a hindered amine light stabilizer and has a chloride ion concentration of 20ppm or below based on the weight of the resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition for a stainless steel substrate, and more specifically, a clear or long-term durable clear composition having a metallic luster by adding a small amount of pigment. The present invention relates to a coating composition for obtaining a color clear coated stainless steel article.

[0002]

2. Description of the Related Art In recent years, stainless steel has been used in all industrial fields by taking advantage of its rust-resistant property and long-lasting metallic mirror gloss. That is, the fields of use of chemical plants such as tanks and pipes, panels for building exteriors, interiors, exteriors, kitchen products, electrical appliances, automobile parts, etc. are numerous.

[0003] In particular, it is becoming increasingly used in the field of construction, from large parts such as exterior panels of buildings to small parts such as handrails, gates and parts of aluminum sashes.
In addition, with the spread of applications, those with a more fashionable surface are also required.For example, various patterns are applied to the surface of stainless steel, or transparent or nearly transparent paint is applied to achieve a visual effect. Panels are also becoming widespread.

Another aim of painting on this surface is to prevent rusting of stainless steel. As its name implies, stainless steel is known to be extremely resistant to rust under normal conditions, but to rust considerably rapidly under special conditions. That is, when a stainless steel product is used on the beach, etc., chlorination may occur in a short time due to the influence of chlorine ions in the sea salt particles. For this reason, there is a product in which the influence of chlorine ions is minimized and durability is improved by further coating the surface of stainless steel with acrylic, urethane resin or the like. However, since the resin layer itself such as acrylic and urethane is not sufficient from the viewpoint of long-term durability, coating with a more durable resin has been demanded.

[0005]

Problems to be Solved by the Invention From this point of view, vinylidene fluoride resin coating has been put into practical use at present. Painted with a pigmented paint using vinylidene fluoride resin on a galvanized steel sheet,
With over 20 years of experience, it has become a representative of long-term durable paint steel sheets. Therefore, the same effect is expected when stainless steel is coated with vinylidene fluoride resin. A mixture of clear pigments and a small amount of clear pigment was used to bring out the metallic luster of stainless steel to some extent. , Various kinds of products such as color clear are sold, and the demand is increasing. However, when vinylidene fluoride resin is used for clear or color clear, the vinylidene fluoride resin itself is somewhat less transparent, so it will not be as transparent as that of acrylic or urethane coated products. It was

[0006]

[Means for Solving Problems] Therefore, a solvent-soluble type fluororesin for paint, which has the same degree of transparency as acrylic and urethane and has excellent long-term durability, is used instead of the vinylidene fluoride paint. Attempts have been made to make clear and color-clear stainless steel-coated articles, and some construction is being carried out. However, satisfactory results have not always been obtained. That is, the occurrence of rust is often observed. It is considered that this is because many solvent-soluble fluororesins for paints originally use chlorotrifluoroethylene as a fluorine source. That is, as described above, since stainless steel is relatively susceptible to chlorine ions, it is presumed that chlorine in the resin decomposes by some action to generate ions and reacts with iron in stainless steel to generate rust. It Possible processes of generating chlorine ions include firing when the curing reaction is performed and when the coating film is exposed outdoors. It is conceivable that chlorine ions are desorbed by applying heat to the coating film during firing, and similar desorption may be caused by light irradiation during exposure. Therefore, in order to suppress the generation of rust, how to minimize the decomposition of chlorine in both processes is a big problem.

Another method of suppressing the generation of rust is to coat acrylic or urethane as a primer,
A two-layer structure coated with a fluororesin for solvent-soluble paint from above can be considered as a method of preventing the reaction between generated chlorine ions and stainless steel, but the manufacturing process becomes complicated and the cost is reduced. It is hard to say that this is the preferred method because it will also improve.

[0008] Therefore, as a result of intensive studies on the method of suppressing the decomposition of chlorine in the resin on the premise of the further coating, the present inventors have added a specific additive, and
It has been found that a clear or color clear stainless steel article which does not cause rust for a long period of time and has a good appearance can be obtained by using a coating material having a low chlorine ion concentration, and has completed the present invention.

That is, in the present invention, a fluorine-containing copolymer having a hydroxyl group and / or a carboxyl group in the molecule, a curing agent compatible with the copolymer, an ultraviolet absorber and a hindered amine light stabilizer are essential components. The coating composition has a chlorine ion concentration of 20 ppm with respect to the copolymer.
The following is a coating composition for stainless steel. The fluorine resin for solvent-soluble paints used in the present invention is a fluorine-containing copolymer containing a hydroxyl group and / or a carboxyl group in the molecule, such as chlorotrifluoroethylene, carboxylic acid vinyl ester and hydroxyl group. Examples of the polymer include the contained allyl ether as an essential component. This polymer is chlorotrifluoroethylene,
The content of units based on carboxylic acid vinyl ester, hydroxyl group-containing allyl ether and other monomers is
25-75 mol%, 10-70 mol%, 3-40 mol% and 0-2
0 mol%, other comonomers include vinyl acetic acid, undecylenic acid, allyloxyacetic acid, acrylic acid,
Methacrylic acid, crotonic acid, carboxyl group-containing monomers such as itaconic acid, hydroxyethyl acrylate, methyl methacrylate, glycidyl methacrylate,
Acrylic acid such as hydroxyethyl crotonic acid, methacrylic acid, esters such as crotonic acid, acrylamide,
Examples thereof include acrylamides such as N-methylol acrylamide and vinyl ethers such as ethyl vinyl ether, butyl vinyl ether and hydroxyalkyl vinyl ether.

The preferred carboxylic acid vinyl ester is a linear or branched vinyl ester having a carboxylic acid having 2 to 12 carbon atoms, and specific examples thereof include vinyl acetate, vinyl lactate, vinyl butyrate and iso-vinyl ester. Examples thereof include vinyl butyrate, vinyl pivalate, vinyl caproate, vinyl isocaproate, vinyl caprylate, vinyl caprylic acid, vinyl caproic acid, Veova-9, Veova-10 (Showa Shell Sekiyu KK). Further, as the hydroxyl group-containing allyl ether, ethylene glycol monoallyl ether, diethylene glycol monoallyl ether,
Examples thereof include triethylene glycol monoallyl ether, hydroxybutyl allyl ether, and monomers obtained by modifying ethylene glycol monoallyl ether with ε-caprolactone.

The above-mentioned polymers are emulsion-polymerized, suspension-polymerized, in the presence of a polymerization initiator or under the action of ionizing radiation.
It can be produced by a polymerization method such as solution polymerization or bulk polymerization. The method for reducing the chlorine ion concentration in the coating material of the present invention does not need to be particularly limited, and the reducing operation can be performed in the state of the coating material, but it is preferable to remove the chlorine ion in the fluorine-containing copolymer in advance. . For example, a reprecipitation method in which a fluorine-containing copolymer is once dissolved in a solvent, and then a poor solvent is added to cause precipitation to be repeated, or the ability to react with chlorine ions or adsorb chlorine ions after being dissolved in a solvent It is possible to employ a method of purifying by contact with a certain material, and further a washing method.

The stainless steel coating composition of the present invention has a chlorine ion concentration of 20 relative to the weight of the fluorocopolymer.
It must be below ppm. That is, as clearly shown in the examples, when it exceeds 20 ppm, the phenomenon that the occurrence of rust becomes extremely remarkable appears although the cause is not clear. The concentration of chlorine ions in the present invention can be measured in the state of a varnish in which the copolymer is dissolved in a solvent, but a curing agent, an ultraviolet absorber, a light stabilizer and / or other additives are added. It is also possible to measure in the state of the paint that has been made. The measuring method is not particularly limited, and examples thereof include measurement of an aqueous extract by ion chromatography and chemical analysis by a neutralization method.

Since the fluorine-containing copolymer used in the present invention has a hydroxyl group as a curing site, it can cause a curing reaction when combined with a curing agent. As the curing agent, polyisocyanurate, which is a two-pack type paint, blocked isocyanate, which is a one-pack type paint, or melamine can be used, but a blocked isocyanate that can be cured in a short time in view of productivity and economy. And melamine are more preferred.

In the case of blocked isocyanate, the NCO / OH ratio is preferably in the range of 0.5 to 1.5.
When it is less than 0.5, it is not preferable in terms of chemical resistance, and when it is more than 1.5, it is not preferable in terms of weather resistance.
In the case of melamine, the fluorine-containing copolymer solid content / melamine solid content ratio is preferably in the range of 10/1 to 6/4,
Even if it is more or less than the above range, the chemical resistance or weather resistance is inferior like the blocked isocyanate.

Further, in order to accelerate the reaction with these curing agents, it is useful to add a catalyst. As a usable catalyst, an organic tin compound such as dibutyltin dilaurate is particularly suitable when the curing agent is a blocked isocyanate. In addition to the catalytic action of isocyanate, organotin compounds
It is known that it also acts as a heat stabilizer, so it is preferable to add it as long as it does not affect storage stability, and the addition amount is 10 ppm with respect to the total weight of the paint.
It can be arbitrarily selected in the range of 5 wt%. Addition amount is 10pp
When it is m or less, the action as a catalyst is poor, and when it is 5 wt% or more, there is a problem in storage stability, which is not preferable. In the case of melamine, organic acids such as paratoluenesulfonic acid and dodecylbenzenesulfonic acid are useful. The amount of organic acid added is 0.05 to the total paint weight.
It can be changed within the range of 1.0 wt%, but if it is too small, the action as a catalyst is poor, and if it is too large, there is a problem in storage stability, which is not preferable.

In order to suppress chlorine ions produced during firing and during outdoor exposure, it is essential to add an ultraviolet absorber (UVA) and a light stabilizer. As is well known, UV absorbers have a function of efficiently absorbing light in the ultraviolet region and converting it into another harmless energy (heat energy, etc.) to protect the weakly bonded portion in the molecule. . Structurally, they are roughly classified into benzophenone-based, salicylate-based, and benzotriazole-based, but all have non-conjugated electron pairs such as oxygen and nitrogen atoms near the hydroxyl group in the molecule,
The absorption of light energy causes a ring formation between them via a hydrogen bond to effectively consume the light energy.
The ultraviolet absorber that can be used is not particularly limited, but commercially available biosorb 80, 90, 100,
110, 130, 520, 550, 580, 582, 5
83, 591, 910 (above Kyodo Yakuhin brand name), Tinuvin 900, 234, 320, 326, 327, 328.
(Above Ciba Geigy product name), Mark LA-32, L
Examples include A-36, LA-31, 1413, LA-51 (all trade names of Asahi Denka Co., Ltd.).

On the other hand, the light stabilizer has a function of trapping and stabilizing various free radicals generated by heating or irradiation of light, and in particular, a hindered amine light stabilizer (HALS).
Is effective. Usable stabilizers include, but are not limited to, commercially available Sanol LS-770,
LS-765, LS-292, LS-2626, LS-
1114, LS-744 (above Sankyosha brand name), Tinuvin 123, 440, 144, 622LD, Cimasorb 9
44LD, 944FL, 119FL (above Ciba Geigy brand name), Mark LA-57, LA-77, LA-6
2, LA-67, LA-63, LA-68, LA-8
2, LA-87 (all trade names of Asahi Denka Co., Ltd.) and the like can be exemplified, but when an organic acid is used as a curing catalyst,
A block type that does not react with an acid is preferable.

With respect to 100 parts by weight of the resin, the ultraviolet absorber is preferably 1 to 15 parts, and the light stabilizer is preferably 0.3 to 5 parts.
More preferably, the ultraviolet absorber is 2 to 10 parts and the light stabilizer is 0.5 to 3 parts. Further, it is not preferable that the total amount of these additives becomes excessively large, and the combination ratio of the ultraviolet absorber / light stabilizer is preferably in the range of 1/1 to 5/1 by weight. If either one exceeds this ratio and is too much, the other cannot be added in an amount sufficient to exert the effect, which is not preferable. In the ultraviolet absorber or light stabilizer,
In any case, when the amount is less than the specified amount, the effect is not sufficient, and when the amount is excessive, not only is it economically disadvantageous, but also the stability of the coating is impaired and bleeding on the surface is not preferable.

Thus, a clear or color clear paint for stainless steel can be obtained by adding a curing agent, an ultraviolet absorber, a light stabilizer, etc. to the fluororesin varnish for solvent-soluble paint. In order to ensure sufficient adhesiveness, it is preferable that the stainless steel article is surface-treated in advance. The method of surface treatment is not particularly limited, and for example, both a reaction type chemical conversion treatment and a coating type chromate treatment can be used, but the coating type chromate treatment is more preferable in order to secure sufficient adhesion.

The color or color clear paint prepared as described above is applied to the surface-treated stainless article, and the application can be carried out by using a spray, a flow coater, a roll coater or the like. . Also, the painted article should be
By baking in the temperature range of 120 to 240 ° C, a clear or color clear coated article which has a transparent feeling and does not cause rust for a long period of time can be obtained. If the temperature is lower than 120 ° C, it takes a long time to cure and sufficient hardness cannot be obtained.
In the above cases, the coating film may be colored, which is not preferable.

The coating composition for stainless steel of the present invention is suitable for coating other than stainless steel, but is particularly suitable for coating stainless steel. In this case, the article, which is a molded product made of stainless steel, may have any shape, but a preferable example is one having a mirror-finished surface or one having a pattern. The type of stainless steel is not particularly limited, and it can be applied to austenitic, ferritic, martensitic, and precipitation hardening type stainless steels, and there are a wide variety of specific standards. For example, commonly used SUS302, SU
S304, SUS316, SUS316L, SUS43
0, SUS416, etc. can be illustrated.

Details will be described below with reference to examples, but the present invention is not limited thereto. In the following examples and comparative examples, all "parts" refer to "parts by weight".

[0023]

【Example】

[Synthesis Example A of Resin] Vinyl pivalate (VP) was added to a stainless steel autoclave with an internal capacity of 1.4 L equipped with an electromagnetic stirrer.
v) 92.3 g, Veova-9 (V-9) 132.5 g, ethylene glycol monoallyl ether (EGMAE) 37.9 g, undecylenic acid (UA) 7.6 g, perbutyl PV (NOF brand name) 3.8 g, butyl acetate (BuAc) ) 320 g and sodium carbonate 1.6 g were charged, and the autoclave was replaced by degassing three times with nitrogen gas. Then, after introducing 263.8 g of chlorotrifluoroethylene (CTFE) into the autoclave,
The temperature was gradually raised. After polymerizing at 55 ° C. for 17 hours, unreacted CTFE was removed and the autoclave was opened. Then, the polymerization liquid was transferred to an eggplant-shaped flask, concentrated by an evaporator, and at the same time, unreacted monomers other than CTFE were removed, and then diluted with BuAc to a solid content concentration of about 55 wt%, filtered,
Purified to obtain a varnish. The yield was 82% based on the charged monomer based on the solid content when the autoclave was opened. The OH value of the obtained resin is 45 mgKOH /
g (measured by acetylation method with acetic anhydride), acid value 6.9 mgKOH / g (measured according to JIS K 5400), molecular weight (M
n) was 15,300 (polystyrene-equivalent number average molecular weight).

10 g of the obtained varnish was collected in a 100 cc separatory funnel, 50 g of pure water was added, and the mixture was shaken and allowed to stand, and the upper aqueous layer was separated and collected. The same extraction operation was repeated for the separated varnish, and extraction was performed a total of 3 times. When the chlorine ion concentration of each water layer was measured using an ion chromatograph (eluent: sodium carbonate / sodium hydrogencarbonate aqueous solution), the chlorine ion concentration at the third time was 0.1 ppm or less. 1,2
The chloride ion concentration in this varnish was determined to be 35 ppm based on the weight of the resin from the measured value of the second time.

Further, 500 g of n-hexane was poured into 500 g of the obtained varnish with stirring to precipitate the resin component, the solvent was removed, and the product was dried. The same operation was repeated twice more, and a varnish of a butyl acetate solvent having a solid content concentration of 55 wt% was prepared again. When chlorine ions of this varnish were measured by the above-mentioned method, it was 8
It was ppm.

[Synthesis Examples B and C of Resin] By the same method as in Synthesis Example A of resin, copolymerization composition shown in Table 1 (however, the amount of perbutyl PV charged is 0.5 wt% with respect to the amount of monomer).
Polymerization was carried out and the yield, OH value, acid value, molecular weight and chloride ion concentration were measured. Further, the chlorine ion concentration in the varnish after the same chlorine ion removing operation as in Synthesis Example A was performed was measured. The results are shown in Table 1.

[0027]

[Table 1]

Example 1 100 parts of resin solids in the varnish (18% as varnish) was added to the purified varnish of Synthesis Example A.
Biosorb 5 as an ultraviolet absorber against 1.8 parts)
91 (manufactured by Kyodo Pharmaceutical Co., Ltd.) 5 parts, Tinuvin 4 as light stabilizer
1 part of 40 (manufactured by Ciba Geigy), 20 parts of Cymel 303 (manufactured by Mitsui Cyanamid) as a curing agent, and 0.2 parts of paratoluenesulfonic acid as a catalyst were added to prepare a one-pack type clear paint. Then, a coating type chromate-treated hairline finished SUS304 plate (70 mm x
After spray coating (150 mm × 0.2 mm) (dry film thickness: about 20 μm) and setting for about 10 minutes, the plate temperature was maintained at 170 ° C. for 1 minute to cure and dry the test plate. The gloss (60 degrees) of the obtained coated plate was 139 in the hairline direction and 100 in the perpendicular direction. The scratch hardness of the coating film was H, and the rubbing test with methyl ethyl ketone was 100 times or more. Furthermore, this coated plate,
Put it in the dew panel light control weather meter (DPWL), which is an accelerated weathering tester manufactured by Suga Test Machine,
The test was carried out for 00 hours, but no rust was found. The cross-cut cellophane tape test of this coating film was 100/100.

Immediately after preparing the one-pack type clear paint, the same chlorine ion analysis as in Synthesis Example A was carried out. As a result, the chlorine ion concentration was 8 ppm based on the resin weight, which was the same as the value in the varnish. [Examples 2 to 6] In the same manner as in Example 1, a series of tests were performed in which the types and amounts of the varnish, the curing agent, the catalyst, the ultraviolet absorber, the light stabilizer and the other additives after purification were changed. The results obtained are shown in Table 2. In each case, no rust was generated for a long period of time, a good appearance was shown, and the cross-cut Erichsen test was 100/100 and the adhesion was also good.

[0030]

[Table 2]

[Comparative Examples 1 to 3] Using the unpurified varnishes obtained in Synthesis Examples A, B and C, in the same manner as in Example 1,
Table 2 shows the results of a series of tests in which the types and amounts of the curing agent, the catalyst, the ultraviolet absorber, the light stabilizer, and the other additives were changed. Rust generation was observed in a shorter time than in the case of using the purified varnish.

[Comparative Example 4] In a coated plate prepared in the same manner as in Example 1 except that only the ultraviolet absorber was added, rust was observed after 1000 hours even though the purified varnish was used. It was [Comparative Example 5] In the coated plate prepared in the same manner as in Example 1 except that only the light stabilizer was added, rust was observed after 300 hours even though the purified varnish was used.

The manufacturers of the additives used in the above test are as follows. -Tinuvin 900, 384, 123, 440: manufactured by Ciba Geigy. SB-1400, T-501 (dibutyltin-based ester): manufactured by Tokyo Fine Chemical Co., Ltd. -Santhiol N-1 (triazine thiol): manufactured by Sankyo Kasei Co., Ltd. Further, evaluation of various physical properties was performed according to the following methods. Gloss (JISK5400): Gloss at an incident angle of 60 degrees was measured in the hairline direction and the direction perpendicular thereto. MEK rubbing test: the number of rubbing until rubbing the coating film surface with a gauze impregnated with methyl ethyl ketone and visually observing the occurrence of abnormality of the coating film was performed.
6 and Comparative Examples 1 to 5 were 100 times or more. -Hardness (JISK5400): It is indicated by pencil hardness in a scratched state.・ Checkerboard cellophane tape test: JISK5400 on the coating film
Based on the adhesion test method described in 1., make cuts to make 100 cells. Then, a piece of cellophane tape is attached to the cut and peeled off momentarily, and the number of remaining squares is used for the judgment. The coated plates of Examples 1 to 6 and Comparative Examples 1 to 5 were 100/100. Flexibility: The coated plate is bent 180 degrees with the coating film facing upward, and the state of the coating film at the bent portion is visually observed. The coated plates of Examples 1 to 6 and Comparative Examples 1 to 5 were all 0T. -Presence or absence of rust: The coating film after the test was visually observed.

[0034]

The clear or color clear stainless steel sheet coated with the coating composition of the present invention has the effects of maintaining the luster peculiar to stainless steel for a long period of time and not generating rust.

Claims (4)

[Claims] 1. A coating comprising a fluorine-containing copolymer having a hydroxyl group and / or a carboxyl group in the molecule, a curing agent compatible with the copolymer, an ultraviolet absorber and a hindered amine light stabilizer as essential components. A coating composition for stainless steel having a chlorine ion concentration of 20 ppm or less based on the weight of the copolymer. 2. The fluorine-containing copolymer having a hydroxyl group in the molecule has a chlorotrifluoroethylene, carboxylic acid vinyl ester, hydroxy group-containing allyl ether, and other comonomer-based unit content of 25 to 75, respectively.
Mol%, 10-70 mol%, 3-40 mol% and 0
The coating composition for stainless steel according to claim 1, which is 20 mol%. 3. The coating composition for stainless steel according to claim 1, wherein the combination ratio of the ultraviolet absorber and the hindered amine light stabilizer is 1/1 to 5/1. 4. A molded stainless steel obtained by coating a film obtained by applying, curing and drying the coating composition for stainless steel according to claim 1.