JPH0598206A - Water-based coating composition curable at low temperature - Google Patents

Abstract

PURPOSE:To improve low-temp. curability and coating film appearance by incorporating a carboxylated and hydroxylated acrylic resin, an amino resin, and a hydroxylated halogenoresin. CONSTITUTION:40-80 pts.wt. acrylic resin which has been carboxylated and hydroxylated and has an acid value of 20-150, a hydroxyl value of 20-200, and a number-average mol.wt. of 10,000-100,000 is mixed with 60-20 pts.wt. amino resin. Into 100 pts.wt. this mixture is incorporated 5-30 pts.wt. hydroxylated halogenoresin in which hydroxyl groups and halogen atoms are bonded to the polymer backbone and which has a number-average mol.wt. of 1,000-100,000 and a hydroxyl value of 10-300. A neutralizing agent is further added in an amount of 0.2-1.5 neutralization equivalents to the carboxyl groups of the resin. The resulting mixture is dispersed into water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low temperature curable aqueous coating composition, and more particularly to a coating composition capable of forming a coating film excellent in low temperature curability by electrodeposition coating on anodized aluminum or aluminum alloy material. Regarding

[0002]

2. Description of the Related Art Conventionally, as an electrodeposition paint used for coating aluminum materials, acrylic copolymers obtained by copolymerizing hydroxyl group-containing acrylic monomers, (meth) acrylic acid and other acrylic monomers A water dispersion is used in which a mixed resin of a neutralized resin and an amino resin obtained by neutralizing the combined product with an amine is dispersed in water.

However, curing of a coating film formed from the coating material requires baking at a high temperature of about 170 ° C. or more, so that it is difficult to apply to a material having a large heat capacity, and economical loss is also caused. It has the drawback of being large.

However, conventionally, as the monomer component of the acrylic copolymer, a monomer component containing a halogen atom such as vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride, and trichloroethylene is further used. A low temperature baking type electrodeposition coating composition containing a copolymer and a melamine resin as film forming components has been proposed. However, since the monomer component containing a halogen atom used in the electrodeposition coating is not sufficiently copolymerizable with the acrylic monomer component, an unreacted monomer component remains in the resin, resulting in abnormal electrodeposition during electrodeposition coating. There is a drawback that the appearance of the coating film tends to deteriorate. Further, even in the case of a polymerized product, there are many homopolymers of the monomer component, the homopolymer itself is soft, and it does not crosslink with the melamine resin to form a three-dimensional structure. Therefore, there is a problem that the surface hardness and curability of the coating film become poor.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve the above-mentioned problems, and as a result, acrylic resin containing carboxyl group and hydroxyl group, amino resin, halogen-containing resin containing hydroxyl group. It was found that an aqueous coating composition containing as a curable resin component can provide a coating film having excellent appearance and performance, and completed the present invention.

That is, the present invention relates to a low temperature curable aqueous coating composition containing a carboxyl group- and hydroxyl group-containing acrylic resin, an amino resin, and a hydroxyl group-containing halogen-containing resin as a curable resin component.

As the carboxyl group- and hydroxyl group-containing acrylic resin used in the composition of the present invention, a conventionally known water-soluble acrylic resin containing an amino resin as a crosslinking agent can be used.

The acrylic resin preferably has a carboxyl group in an acid value of about 20 to 150 and a hydroxyl group in a hydroxyl value of about 20 to 200. The molecular weight of the acrylic resin is about 1 in terms of number average molecular weight.
It is desirable to have in the range of 10,000 to 100,000.

The acrylic resin is, for example, a hydroxyl group-containing (meth) acrylic monomer (hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, etc.), a carboxyl group-containing polymerizable unsaturated monomer ((meth) acrylic acid, (Anhydrous) maleic acid and the like and other polymerizable unsaturated monomers (methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl ( meth) acrylate, stearyl (meth) alkyl esters of (meth) _1-24 units C of acrylic acid such as acrylates, styrene, vinyl aromatic monomers such as vinyl toluene, N- methylol acrylamide, N- butoxymethyl acryl Copolymers are included for the acrylamide-based monomers) such as bromide and monomer components.

The amino resin used in the composition of the present invention is a curing agent for curing the acrylic resin and the halogen-containing resin described below, and specifically, melamine, benzoguanamine, triazine compounds, urea and formaldehyde. Those obtained by condensate or co-condensation with are included. Among these, a melamine formaldehyde resin and a resin obtained by alkoxylating this resin with alcohol are preferable.

The halogen-based resin used in the composition of the present invention is
It accelerates the curing of the acrylic resin and the amino resin and is itself cured by the amino resin.

The halogen-based resin includes a resin having a hydroxyl group and a halogen atom bonded to the resin skeleton, and preferably having a number average molecular weight of about 1,000 to 100,000. When the resin does not have a hydroxyl group, the curability of the coating film decreases, and the adhesion to the substrate, the surface hardness of the coating film, the processability, the durability, etc. deteriorate. The content of the hydroxyl group is about 10 to 300, preferably about 2 in terms of the hydroxyl value of the resin.
The range of 0-280 is good. The halogen atom is preferably chlorine or fluorine atom. When the number average molecular weight is less than about 1,000, the halogen-based resin component is phase-separated from the acrylic resin during baking and a large amount of the halogen-based resin component is present in the surface layer of the coating film to accelerate the curing of the acrylic resin and the amino resin. This is not preferable, because the effect of reducing the effect becomes smaller and the surface hardness, workability, durability, etc. of the coating film decrease. On the other hand, when the number average molecular weight exceeds about 100,000, the melt viscosity at the time of baking becomes high, the miscibility with the acrylic resin and the amino resin deteriorates, and the curability of the coating film decreases, which is not preferable.

The halogen-based resin may have an acid group (preferably a carboxyl group) in the resin skeleton.

The above-mentioned halogen-based resin is a monomer (a) containing one radical-polymerizable unsaturated group and a halogen atom in one molecule, a linear, branched or aliphatic resin having about 2 to 8 carbon atoms. Alkyl vinyl ethers (b) having a cyclic hydroxyl group-containing alkyl group and, if necessary, 2 to 8 carbon atoms
A copolymer containing, as a monomer component, an alkyl vinyl ether (c), an olefin (d), a carboxylic acid vinyl ester (e) or the like having a linear, branched, or alicyclic alkyl group of a certain degree is used. Included. Examples of the “monomers (a)” include vinyl fluoride, vinylidene fluoride,
Examples thereof include trifluorochloroethylene, tetrafluoroethylene and vinyl chloride. Examples of the “hydroxyl-containing alkyl vinyl ethers (b)” include 2-hydroxyethyl vinyl ether and 4-hydroxybutyl vinyl ether. "Alkyl vinyl ethers (c)"
Examples thereof include ethyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether and the like.
Examples of the "olefins (d)" include ethylene, propylene, butylene and the like. Examples of the “carboxylic acid vinyl ester (e)” include vinyl acetate and vinyl butyrate.

To introduce a carboxyl group into the halogen-based resin, for example, some of the hydroxyl groups of the halogen-based resin are acid anhydrides (maleic anhydride, succinic anhydride, 1,2-anhydride).
Cyclohexanedicarboxylic acid, etc.) or as a monomer component, a carboxyl group-containing vinyl monomer (for example, a monomer obtained by reacting the above vinyl ethers (b) with the above acid anhydride) can be used.

The content of each monomer in the halogen-based resin is 20 to 80 mol% of the monomer (a), 20 to 80 mol% of the hydroxyl group-containing alkyl vinyl ether (b) and other monomers (c) to (e). ) A range of 0-40 mol% is preferable.

The content of each resin component used in the composition of the present invention is 40 to 80% by weight, preferably 50 to 70% by weight of the acrylic resin and the amino resin based on the total weight (solid content) of both. %, Amino resin 60 to 2
The range is 0% by weight, preferably 50 to 30% by weight.
If the acrylic resin and the amino resin are out of the above ranges, the curability is lowered and the hardness of the coating film, the adhesion to the substrate, the mechanical properties, the weather resistance and the like tend to be deteriorated, which is not preferable. Further, in the halogen-based resin, the range of about 5 to 30 parts by weight, preferably about 5 to 20 parts by weight is good with respect to 100 parts by weight of the total amount (solid content) of the acrylic resin and the amino resin. When the amount of the halogen-based resin is less than about 5 parts by weight, the low temperature curability is not sufficiently exhibited, while the content of the resin is 30
If the amount is more than parts by weight, the effect on the low temperature curability becomes small, the bath stability is lowered, and the coating becomes expensive, which is not preferable.

The composition of the present invention can be produced by dispersing a mixture of an acrylic resin, an amino resin, a halogen resin and a neutralizing agent in water. Examples of the neutralizing agent include triethylamine, dimethylethanolamine and ammonia. The neutralizing agent is usually about 0.2 to 1.5, preferably about 0.3 to the carboxyl group in the resin.
1.2 Neutralization equivalent is added.

In addition to the above, organic solvents, fluidity modifiers, coloring pigments and extender pigments can be used in the composition of the present invention.

The composition of the present invention can be applied to a material such as various plastics, various metals, various types of surface treatments of the metals, coated materials, inorganic materials and the like, and then baked to form a cured coating film. The coating can be performed by conventionally known means such as brush coating, spray coating, dip coating, roller coating, and electrodeposition coating. The coating film thickness (dry) is usually considered to be sufficient in the range of about 5 to 60 μm. The baking may be performed at a baking temperature of 140 ° C. for about 30 minutes or more, and at a baking temperature of 170 ° C. for about 20 minutes or more.

Next, an example in which the composition of the present invention is applied as an electrodeposition coating composition will be described.

The above composition was adjusted to a concentration of about 4 to 15% by weight, and this composition was used as an electrodeposition paint bath, and the bath temperature was 15 ° C to 35 ° C.
With the coating voltage of 80 to 350 V, a coating film can be formed on the object to be coated by the anion electrodeposition coating method. In the present invention, as the article to be coated, particularly effective is an aluminum material, and examples thereof include anodized aluminum plates, rods, tubes, sashes, and other various shaped articles.

[0023]

In the composition of the present invention, the halogen hydride generated by decomposition of the halogen-based resin during baking accelerates the reaction between the acrylic resin as the base resin and the amino resin as the cross-linking agent, and the temperature can be lowered. It has become.

The composition of the present invention can form a coating film having good appearance and performance by separating the halogen-based resin and the acrylic resin (there is no need to react those having poor copolymerization reactivity).

In the composition of the present invention, the surface hardness of the halogen-based resin itself reacts with the amino resin to form a cured film.
Excellent effects such as solvent resistance, processability, and durability.

[0026]

EXAMPLES The present invention will be described in detail below with reference to examples. "Parts" and "%" are based on weight.

Preparation Example of Acrylic Resin Solution 55 parts of isopropyl alcohol were charged into a reaction vessel 8
While maintaining at 0 ° C., 15 parts of styrene, 32 parts of methyl methacrylate, 19 parts of n-butyl acrylate, 10 parts of ethyl acrylate, 1 part of hydroxyethyl acrylate
A mixture of 5 parts, 7 parts of acrylic acid, and 1.0 part of azobisdimethylvaleronitrile was added dropwise over 3 hours, and this temperature was maintained for 1 hour after the completion of the addition, and then 1 part of azobisdimethylvaleronitrile and butylcellosolve were added. 13 parts was dropped and the reaction was continued at 80 ° C. for 4 hours to give a resin solid content of 63
%, Resin average molecular weight 30,000, resin hydroxyl value 72,
An acrylic resin solution having a resin acid value of 53 was obtained.

Example 1 111 parts of the acrylic resin solution, Nicalac MX-4
0 (manufactured by Sanwa Chemical Co., trade name, butoxymethoxymethylolmelamine) 30 parts, triethylamine (1.0 equivalent to the carboxyl group), halogen-containing resin (* 1)
23 parts of the solution was stirred and mixed with a despar, and deionized water was then added to obtain an aqueous coating material of Example 1 having a solid content of 10%.

(* 1) Halogen-containing resin solution: chlorotrifluoroethylene / 4-hydroxybutyl vinyl ether (47/53, molar ratio) diglyme / isopropanol (50/50, weight ratio) 43% solid content of organic solvent .. The resin has a hydroxyl value of 256 and an average molecular weight of 20,000.
Is.

Example 2 In Example 1, a halogen-containing resin solution (* 2) (chlorotrifluoroethylene / cyclohexyl vinyl ether / ethyl vinyl ether / 4-hydroxybutyl vinyl ether = 50) was used instead of the halogen-containing resin (* 1) solution.
/ 10/10/30/10 (molar ratio), 43 g solid solution of diglyme / isopropanol (50/50 weight ratio), resin hydroxyl value 48, average molecular weight 10,000) except that the same amount was used. Similarly, an aqueous paint of Example 2 was obtained.

Example 3 In Example 1, instead of the halogen-containing resin (* 1) solution, a halogen-containing resin solution (* 3) (halogen-containing resin (*
1) A resin solution obtained by reacting 229 parts of the solution with 1.4 parts of 1,2-cyclohexanedicarboxylic acid anhydride in the presence of a zirconium naphthenate catalyst, resin solid content 43%, resin hydroxyl value 246, and resin acid value 5 Water-based coating material of Example 3 was obtained in the same manner as in Example 1 except that the same amount was used.

Comparative Example 1 An aqueous paint of Comparative Example 1 was obtained with the same formulation as in Example 1 except that the halogen-containing resin (* 1) solution was not used at all.

Comparative Example 2 The same composition as in Example 1 was used, except that the halogen-containing resin (* 1) solution in Example 1 was changed to Kainer V500 (polyvinylidene fluoride resin, trade name, manufactured by Penwort, USA). An aqueous paint of Comparative Example 2 was obtained.

The results of the performance of coating films formed by the water-based paints of Examples and Comparative Examples are shown below.

Preparation of Test Plate 1 The water-based paints of the above Examples and Comparative Examples were diluted to a spray coating viscosity and then applied to a tin plate (dry film thickness 4
0 μm) to form a coating film, and then heated at 140 ° C. for 30 minutes to prepare a test plate.

The coating performance and appearance are shown in Table 1.

The test methods and evaluations of the coating film performance and appearance in Table 1 are as follows.

(* 1) Appearance of coating film: The presence or absence of abnormalities on the coating film surface (luster, smoothness, armpits) was visually observed and evaluated.

◯ (no abnormality, good), Δ (abnormality is recognized), × (abnormality is significantly recognized) (* 2) Coating film hardness: JISK-5400 (* 3) Solvent resistance: Soaked in acetone solvent After rubbing vigorously 10 times with wet gauze, the gloss of the coating film was observed and the curability was evaluated. ○ (Good), △ (Glossy), × (Remarkable glossy) Preparation of test plate 2 Aqueous paint was placed in the electrodeposition tester as an anion electrodeposition coating bath, and the 6063S aluminum alloy plate was anodized. The coated film (anodized film thickness 9 μm) was used as an object to be coated (anode) and the film thickness (dry) was about 10 at a bath temperature of 22 ° C.
A coating film was formed by applying electricity for 3 minutes at a coating voltage of μm, and then heated at 140 ° C. for 30 minutes to prepare a test plate.

The coating performance and appearance are shown in Table 2.

In Table 2, (* 1) to (* 3) are the same test methods and evaluations as described above, and (* 4) is as follows.

(* 4) Adhesion: 100 pieces of 1 × 1 mm goggles were formed on the coating film with a sharp blade so as to reach the substrate, and cellophane tape was adhered to the surface and strongly pulled The number of streaks in the remaining coating film was examined.

[0043]

[Table 1]

[0044]

[Table 2]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location C09D 161/20 PHK 8215-4J (72) Inventor Shigeki Matsubara 4-17-1 Higashihachiman, Hiratsuka-shi, Kanagawa No. Kansai Paint Co., Ltd.

Claims (2)

[Claims] 1. A low-temperature curable aqueous coating composition comprising a carboxyl group- and hydroxyl group-containing acrylic resin, an amino resin, and a hydroxyl group-containing halogen-containing resin as a curable resin component. 2. A coating composition comprising the composition according to claim 1 as an anionic electrocoating composition.