JP2003138208A - Aqueous coating material composition and fuel tank coated therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous coating material composition having excellent anticorrosion even though it does not contain heavy metals such as lead and hexavalent chromium. SOLUTION: The aqueous coating material composition comprises an aqueous epoxy modified alkyd resin, a blocked isocyanate, an anticorrosive pigment composed of an amorphous magnesium silicate compound having an atomic ratio of Mg to Si of 0.025-1.0, and has a ratio (OH group/NCO group) of the hydroxyl group of the aqueous epoxy modified alkyd resin to the isocyanate group of the blocked isocyanate resin of 1/0.1 to 1/2 and a pigment weight concentration (PWC) of the anticorrosive pigment of 20-80 wt.%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aqueous coating composition and a fuel tank coated with the same.

[0002]

2. Description of the Related Art Conventionally, a so-called turn sheet (lead-tin alloy plated steel sheet) has been used as a fuel tank, but since it contains lead, the turn sheet is not used. It is being considered to replace it with an aluminum plated steel sheet.

In order to improve corrosion resistance, such an aluminum-plated steel sheet is formed into a fuel tank after applying a paint containing a rust preventive pigment on it. Conventionally, as a rust preventive paint, a paint containing a chromate-based rust preventive pigment has been used. However, since it contains hexavalent chromium, a rust preventive paint to replace it is required.

An object of the present invention is to provide an aqueous coating composition having excellent anticorrosion properties without containing heavy metals such as lead and hexavalent chromium, a coating method using the same, and a fuel tank.

[0005]

The aqueous coating composition of the present invention comprises an aqueous epoxy-modified alkyd resin, a blocked isocyanate, and an amorphous magnesium silicate compound having a Mg / Si atomic ratio of 0.025 to 1.0. The ratio of the hydroxyl group of the water-based epoxy modified alkyd resin to the isocyanate group of the blocked isocyanate (OH
(Group / NCO group) is 1 / 0.1 to 1/2, and the pigment weight concentration (PWC) of the anticorrosion pigment is 20 to 80% by weight.

The water-based epoxy-modified alkyd resin, blocked isocyanate, and rust preventive pigment used in the present invention will be described in detail below. <Aqueous Epoxy-Modified Alkyd Resin> The aqueous epoxy-modified alkyd resin used in the present invention is a carboxyl of an alkyd resin obtained by an esterification reaction of a polycarboxylic acid and / or acid anhydride, a polyhydric alcohol, and a fatty acid. An epoxy-modified alkyd resin obtained by reacting an epoxy resin with the base is hydrophilized. That is, it is a film-forming resin in which the carboxyl group of the epoxy-modified alkyd resin thus obtained is neutralized with a basic compound, dispersed in an aqueous medium, and stably dissolved or dispersed in water. In the present invention, "aqueous"
Means water-soluble or water-dispersible.

The polyvalent carboxylic acid and / or acid anhydride is not particularly limited, and examples thereof include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride and methyl. Tetrahydrophthalic acid, methyltetrahydrophthalic anhydride, hymic acid anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid Adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, dodecenyl succinic acid, dodecenyl succinic anhydride and the like. Furthermore, as acid components, benzoic acid, crotonic acid, p
A monobasic acid such as -t-butylbenzoic acid can be used together for the purpose of adjusting the molecular weight. These acid components may be used alone or in admixture of two or more.

The polyhydric alcohol is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3. -Butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 2,2-dimethyl-3-hydroxypropyl- 2,2-Dimethyl-3-hydroxypropionate, 2,2,4-trimethyl-1,3-pentanediol, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylol Ruetan, trimethylol propane, trimethylol butane, hexanetriol,
Examples include pentaerythritol and dipentaerythritol.

These polyhydric alcohols can be used alone or in admixture of two or more. Further, a part of the above acid component and alcohol component may be replaced with an oxy acid component such as dimethylolpropionic acid, oxypivalic acid, paraoxybenzoic acid; a lower alkyl ester of these acids; a lactone such as ε-caprolactone. .

Examples of the above fatty acids include coconut oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, safflower oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, and tung oil fatty acid. Oil length of alkyd resin is 3
It is preferably 0% or less, particularly preferably about 5 to 20%.

The esterification reaction (including transesterification reaction) of these components can be carried out by a method known per se. Examples of components other than those described above as components constituting the ester include monoepoxide compounds such as Cardura E (manufactured by Shell Chemical Co.) and lactones. The lactones are those capable of ring-opening addition to a polyester of polyvalent carboxylic acid and polyhydric alcohol to form a graft chain, and include, for example, β-propiolactone, dimethylpropiolactone, butyllactone, γ- Examples thereof include valerolactone, ε-caprolactone, γ-caprolactone, γ-caprylolactone, crotlactone, δ-valerolactone, δ-caprolactone, and among them, ε-caprolactone is most preferable.

The molecular weight of the alkyd resin obtained by esterifying the above-mentioned polyhydric carboxylic acid and / or acid anhydride, polyhydric alcohol and fatty acid is not particularly limited, but is usually a number average molecular weight. It is preferably in the range of 1,000 to 10,000.

Next, as described above, the epoxy group is reacted with the carboxyl group of the alkyd resin thus obtained. Examples of the epoxy resin include bisphenol type epoxy resin and novolac type epoxy resin. The bisphenol-type epoxy resin is, for example, (1) a resin obtained by condensing epichlorohydrin and bisphenol up to a high molecular weight in the presence of a catalyst such as an alkali catalyst, and (2) epichlorohydrin and bisphenol, if necessary. In the presence of a catalyst such as an alkali catalyst, a low molecular weight epoxy resin may be condensed to give a low molecular weight epoxy resin, and the resin obtained by polyaddition reaction of the low molecular weight epoxy resin may be used.

As the bisphenol, bis (4-
Hydroxyphenyl) methane [bisphenol F],
1,1-bis (4-hydroxyphenyl) ethane, 2,
2-bis (4-hydroxyphenyl) propane [bisphenol A], 2,2-bis (4-hydroxyphenyl) butane [bisphenol B], bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-) Hydroxy-tert-butyl-phenyl) 2,2-propane, p- (4-hydroxyphenyl) phenol, oxybis (4-hydroxyphenyl), sulfonylbis (4-hydroxyphenyl), 4,4'-dihydroxybenzophenone, bis (2-hydroxynaphthyl) methane and the like can be mentioned, among which bisphenol A,
Bisphenol F is preferably used. The bisphenols may be used alone or as a mixture of two or more.

As the novolac type epoxy resin which can be used as the epoxy resin, for example, various novolac types such as phenol novolac type epoxy resin, cresol novolac type epoxy resin and phenol glyoxal type epoxy resin having many epoxy groups in the molecule are used. A type epoxy resin may be mentioned.

<Blocked Isocyanate> Blocked isocyanate is obtained by adding a blocking agent having active hydrogen to polyisocyanate, the blocking agent is dissociated by heating to generate an isocyanate group, and the blocked isocyanate is contained in the epoxy-modified alkyd resin. Those that react with a functional group and cure are mentioned.

The blocked isocyanate is not particularly limited, and typical polyisocyanates include aliphatic isocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate and trimethylhexamethylene diisocyanate, 1, Aliphatic cyclic isocyanate such as 3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclosaxane diisocyanate, xylylene diisocyanate, 2,4-tolylene diisocyanate,
Aromatic isocyanates such as 2,6-tolylene diisocyanate, isophorone diisocyanate, alicyclic isocyanates such as norbornane diisocyanate methyl, and multimers and mixtures of these nurates can be used.

Examples of the blocking agent include halogenated hydrocarbons, methanol, ethanol, n-propanol, isopropanol, furfuryl alcohol, alkyl group-substituted furfuryl alcohol, benzyl alcohol and other aliphatic, aromatic or heterocyclic compounds. Examples include oximes such as alcohol, methyl ethyl ketone oxime, methyl isobutyl ketone oxime, acetone oxime, and cyclohexane oxime, as well as caprolactam.

Of these, preferred are oximes,
They are alcohols. Furthermore, a catalyst for dissociating the blocking agent can be used. The amount of the blocked isocyanate compounded is such that the ratio of the hydroxyl groups of the aqueous epoxy-modified alkyd resin to the isocyanate groups of the blocked isocyanate (OH group / NCO group) is 1 / 0.1 / 1 /.
It is preferable to mix them in a ratio of 2. More preferable ratio of OH group / NCO group is 1 / 0.5
~ 1 / 1.5. If the ratio of OH groups / NCO groups is out of the above range, the coating film may be insufficiently cured.

<Antirust Pigment> The antirust pigment used in the present invention contains at least an amorphous magnesium silicate compound having an Mg / Si atomic ratio of 0.025 to 1.0. Mg in this amorphous magnesium silicate compound
A more preferable range of the / Si atomic ratio is 0.025 to
It is 0.8.

The above amorphous magnesium silicate compound is
For example, an aqueous solution of an alkali metal silicate such as potassium silicate or sodium silicate (water glass) and an aqueous solution of a water-soluble magnesium salt such as magnesium sulfate, magnesium chloride or magnesium nitrate are prepared in advance, and Can be produced by mixing the above so as to have the above-mentioned Mg / Si atomic ratio, agitating the resulting precipitate to separate it, washing it with water, drying and pulverizing. Specifically, Japanese Patent Laid-Open No. 2000-273363.
It can be manufactured by the method disclosed in Japanese Patent Publication No.

The anticorrosive pigment used in the present invention may contain titanium oxide. For example, the amorphous magnesium silicate compound and titanium oxide may be mixed, or a mixture in which the amorphous magnesium silicate compound is attached to the surface of titanium oxide may be used.

In the water-based coating composition of the present invention, the content of the rust preventive pigment is preferably 20 to 80% by weight in pigment weight concentration (PWC), more preferably 35 to 7%.
It is 0% by weight.

The coating method of the present invention is characterized in that the water-based coating composition of the present invention is applied to an aluminum-plated steel sheet by a shower coat method and then the coating film is baked.

The shower coat method is a method of spraying a paint in a shower state to apply the paint to an object to be coated. According to such a method, the paint can be easily applied to both surfaces of the aluminum-plated steel plate. After applying the paint, the coating film is baked, but the baking temperature is 80-
Temperatures within the range of 130 ° C. are preferred.

The fuel tank of the present invention is characterized in that it is formed by coating the above-mentioned aqueous coating composition of the present invention on an aluminum-plated steel sheet to form a coating film, and then forming the coating film. The fuel tank of the present invention can be used as a fuel tank for vehicles such as automobiles.

According to the present invention, it is possible to obtain an aqueous coating composition which is excellent in rust prevention even without containing heavy metals such as lead and hexavalent chromium. Further, the fuel tank of the present invention can be made into a fuel tank which does not contain heavy metals such as lead and hexavalent chromium and has excellent corrosion resistance by using the above-mentioned aqueous coating composition of the present invention.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and may be appropriately modified within the scope of the invention. It is possible to carry out.

(Examples 1 to 3) The aqueous coating compositions of Examples 1 to 3 were prepared according to the formulations shown in Table 1 (the unit of the formulation ratio is parts by weight). The raw materials shown in the formulation of Table 1 are specifically as follows.

Aqueous epoxy-modified alkyd resin: trade name "Watersol BC-3010", manufactured by Dainippon Ink and Chemical Co., Ltd., non-volatile content 59% by weight, property dispersion, acid value 30 to 35, hydroxyl value 60 to 65, number average. Molecular weight 250
0, weight average molecular weight 42000 ・ Blocked isocyanate: trade name "Baicijour L"
S2186 ", manufactured by Sumitomo Bayer, hexamethylene diisocyanate (HMDI) -based blocked isocyanate,
Non-volatile content 67% by weight-Mg / Si-based rust preventive pigment: trade name "K White TC-7
20 ", manufactured by Teika, amorphous magnesium silicate compound containing titanium oxide, weight concentration of contained element Mg: 1.5
8% by weight, Al: 1.21% by weight, Si: 38.50% by weight, Ti: 58.71% by weight, Mg / Si atomic ratio =
0.04 ・ Carbon black: trade name "MA-100", manufactured by Mitsubishi Carbon Co., Ltd. ・ Talc: trade name "LMR100", manufactured by Fuji Talc Co., Ltd. ・ Viscosity imparting agent: trade name "Thixozole K-502", polycarboxylic acid type Viscosity-imparting agent, manufactured by Kyoeisha Chemical Co., Ltd., nonvolatile content 20% by weight. In the formulation shown in Table 1, the ratio of OH groups of the aqueous epoxy-modified alkyd resin to NCO groups of the blocked isocyanate (OH groups / NCO groups) is 1 / 1.35. is there.

[0031]

[Table 1]

(Comparative Example 1) Mg-Si in Example 2
As shown in Table 2, an aqueous paint composition was prepared in the same manner except that an aluminum phosphate-based rust preventive pigment was used instead of the rust preventive pigment. The following were used as the aluminum phosphate-based rust preventive pigment.

Aluminum phosphate anticorrosion pigment: trade name "LF Bosei", aluminum tripolyphosphate, manufactured by Kikuchi Color Co., Ltd.

[0034]

[Table 2]

Comparative Example 2 An aqueous coating composition was prepared in the same manner as in Example 2 except that water-soluble melamine was used instead of the blocked isocyanate as shown in Table 3. The following were used as the water-soluble melamine.

Water-soluble melamine: trade name "Watersol S-695", manufactured by Dainippon Ink and Co., Ltd., nonvolatile content 80% by weight

[0037]

[Table 3]

(Comparative Example 3) As a conventional rust-preventive water-based paint, a trade name "Odeshine KS Black KM" (manufactured by Nippon Paint Co., Ltd.) was used. In this paint, an acrylic modified epoxy resin is used as a binder and an aluminum phosphate-based rust preventive pigment is used as a rust preventive pigment.

(Evaluation of Anticorrosion Property) The aqueous coating compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were applied by a shower coat method.
It was applied to both sides of an aluminum plated steel plate. The coating amount is
The coating was applied so that the dry film thickness was 10 to 20 μm. After coating, a baked coating film was formed at 120 ° C.

Next, the test piece with the coating film formed was subjected to a salt spray test for 960 hours in accordance with JIS Z-2371. Rust width from the edge of the test piece (m
m) was measured and evaluated according to the following criteria.

1: Rust width is 10 mm or more 2: Rust width is less than 10 mm and 7 mm or more 3: Rust width is less than 7 mm and 5 mm or more 4: Rust width is less than 5 mm and 3 mm or more 5: Rust width is less than 3 mm The evaluation results are shown in Table 4.

(Evaluation of Workability of Coating Composition) Nozzle clogging, skin burr, and wall adhesion were evaluated for each coating composition as follows.

Nozzle clogging: About 20 to 30 cc of paint is poured into the nozzle once each in the morning and afternoon of the day, and this is continuously performed for 5 days, and the poured paint is discharged from the nozzle. Whether or not it was observed was evaluated according to the following criteria. ○: Paint is normally discharged. ×: Nozzle is clogged and the paint does not come out.

Skin burr: After the lid of a 1/5 liter can containing the paint was opened and left for one day and night, the surface of the paint in the can was observed and evaluated according to the following criteria. ◯: No film is formed on the surface of the paint. X: A film is formed on the surface of the paint, and this film does not dissolve in the paint.

Adhesion to wall surface: The aluminum-plated steel sheet to be coated is immersed in the paint once for a fixed time each in the morning and afternoon of the day, and this is continuously performed for 5 days. The amount of the coating material deposited on was measured gravimetrically and evaluated according to the following criteria.

◯: A slight increase in weight is recognized. X: The weight is remarkably increased. Wall adhesion is not preferable, especially when coating by the shower coat method, because if paint easily adheres to the wall in the coating booth, the paint will collapse from the wall when a certain amount adheres and this will adhere to the object to be coated. , The workability evaluation item.

Table 4 shows the above evaluation results.

[0048]

[Table 4]

As is clear from Table 4, the coating compositions of Examples 1 to 3 according to the present invention are excellent in rust prevention and workability. On the other hand, the coating compositions of Comparative Examples 1 and 2 have good workability, but are inferior in rust prevention. Further, it can be seen that Comparative Example 3, which is a conventional rust preventive coating composition, has good rust preventive properties, but is significantly inferior in workability.

[0050]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide an aqueous coating composition having excellent anticorrosion properties even without containing heavy metals such as lead and hexavalent chromium.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeru Ishida             19-17 Ikedanaka-cho, Neyagawa-shi, Osaka Japan             Into Inc. (72) Inventor Yasutaka Horiuchi             19-17 Ikedanaka-cho, Neyagawa-shi, Osaka Japan             Into Inc. (72) Inventor Shoji Ogiwara             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Hideki Hara             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Hirakko             2-26 Kounosu-cho, Toyota-shi, Aichi Horie             Metal Industry Co., Ltd. (72) Inventor Noriaki Kamiya             2-26 Kounosu-cho, Toyota-shi, Aichi Horie             Metal Industry Co., Ltd. F-term (reference) 4D075 AA01 BB26Z CA33 DA23                       DB07 DC41 EA06 EA10 EB33                       EB36 EB38 EC02 EC54                 4J038 DB062 DB072 DD121 DG111                       DG301 GA03 GA07 HA216                       HA456 KA05 MA08 MA10                       MA14 NA03 PA19 PB06 PC02

Claims (5)

[Claims] 1. An aqueous epoxy-modified alkyd resin, a blocked isocyanate, and a Mg / Si atomic ratio of 0.025.
The ratio of the hydroxyl group of the water-based epoxy-modified alkyd resin to the isocyanate group of the blocked isocyanate (OH group / NCO is included).
The base composition is 1 / 0.1 to 1/2, and the pigment weight concentration (PWC) of the anticorrosion pigment is 20 to 80% by weight. 2. The water-based coating composition according to claim 1, wherein the anticorrosive pigment contains titanium oxide. 3. A coating method comprising coating an aluminum-plated steel sheet with the aqueous coating composition according to claim 1 or 2 by a shower coat method and then baking the coating film. 4. The coating method according to claim 4, wherein the baking temperature is 80 to 150 ° C. 5. The aluminum-plated steel sheet according to claim 1,
Alternatively, a fuel tank is obtained by applying the coating composition according to 2 to form a coating film, and then forming the coating film.