JPH0711188A - Resin composition for water-based coating material - Google Patents

Abstract

PURPOSE:To obtain the subject composition which can form a coating film excellent in hardness, weather resistance, pigment dispersion and flexibility by mixing a specified polyester resin with an amino resin. CONSTITUTION:This resin composition comprises a polyester resin (A) comprising an alkylene oxide adduct (a-1) to a compound having at least two hydroxyl groups and a polycarboxylic acid (a-2) and an amino resin (B). As the compound (a-1), a dihydric to tetrahydric aliphatic polyalcohol or a dihydric phenol is desirable. As the alkylene oxide, ethylene oxide and/or propylene oxide are desirable. Propylene oxide or a combination of ethylene oxide with propylene oxide is particularly desirable. As amino resin B, hexamthylolated melamine or an alkylated benzoguanamine is desirable. When this composition further contains an acrylic resin (C) in addition to resins A and B, the hardness of the baked coating film can further be increased.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a resin for water-based paint. More specifically, it relates to a resin composition for homogeneous water-based coatings, which forms a coating film having excellent hardness, weather resistance, pigment dispersibility and flexibility.

[0002]

2. Description of the Related Art A resin mixture obtained by combining an acrylic resin or a polyester resin as a base resin with a curing agent and dissolving or dispersing it in water can reduce the volatilization of an organic solvent at the time of forming a coating film. It is being widely used as a pollution-based water-based thermosetting paint for home appliances, pre-coated metal, automobiles, cans and the like.

Acrylic resin-based products can provide coating films excellent in hardness, weather resistance, stain resistance, and chemical resistance, and therefore are required for home appliances and cans, etc. Used in the coating composition of JP-A-1-10466.
No. 5).

On the other hand, a polyester resin-based resin gives a coating film excellent in pigment dispersibility and flexibility, and therefore can coatings, intermediate coatings for automobiles, which require these characteristics. It is used for top-coating of home electric appliances and the like (for example, JP-A-64-60670).

In addition, as an attempt to combine the properties of both resins, a resin (Japanese Patent Laid-Open No. 1-129072) in which a hydrophilic acrylic resin and a hydrophobic polyester resin are reacted with each other by a transesterification reaction has been proposed. There is.

[0006]

However, acrylic resins have the drawbacks of poor flexibility and poor impact resistance due to low flexibility, and polyester resins have poor hardness and water resistance. Further, when these are used in combination, the acrylic resin and the polyester resin have poor compatibility with each other. Therefore, when they are simply blended and used, phase separation occurs, and a uniform resin solution cannot be obtained, which cannot be put to practical use as a coating material.
Furthermore, the one that made both resins react with each other to form a composite,
There was a problem that a gel was generated during the complexation.

[0007]

SUMMARY OF THE INVENTION The inventors of the present invention have developed a base for each of a polyester resin and another resin used as an aqueous thermosetting paint by simply blending a specific polyester resin with another resin. The present invention has been achieved as a result of extensive studies to obtain a water-based composite resin that can be homogenized and can utilize the excellent characteristics of each of the coating materials used as the resin.

That is, the present invention comprises a polyester resin (A) and an amino resin (B) comprising an alkylene oxide adduct (a-1) of a compound having two or more active hydrogens and a polycarboxylic acid (a-2). It is a resin composition for water-based paints characterized by being

The compound having at least two hydroxyl groups in the molecule (a-1) constituting the polyester resin (A) of the present invention is a divalent alcohol (ethylene glycol, propylene glycol). , Neopentyl glycol, etc.), trivalent or higher alcohols (glycerin, butanol, trimethylolpropane, triethanolamine, sorbitan monooleate, pentaerythritol).
, Sorbitol, diglycerin, tripentaerythritol, etc.), divalent phenols (hydroquinone, catechol, bisphenol A, etc.), trivalent or higher pheno
Examples thereof include tris (hydroxyphenyl) methane and the like. Of these, preferred are 2- to 4-valent aliphatic polyhydric alcohols and / or divalent phenols.

(A-1) is one in which one or more kinds of alkylene oxides (ethylene oxide, propylene oxide, butylene oxide, etc.) are added to the above hydroxyl group, and the number of moles of alkylene oxide added is usually 1 to 50 moles, preferably It is 3 to 20 mol. If the added mole number of alkylene oxide is less than 1 mole, the compatibility with other resins such as amino resin and acrylic resin becomes insufficient, and if it exceeds 50 moles, the water resistance of the coating film is lowered.

As the alkylene oxide, ethylene oxide and / or propylene oxide is preferable, and propylene oxide alone or a combination of ethylene oxide and propylene oxide (block or random) is particularly preferable.

Polyvalent carboxylic acids (a) constituting the (A)
Examples of -2) include divalent to tetravalent carboxylic acids. Specific examples of (a-2) include divalent carboxylic acids (oxalic acid, succinic acid, alkylsuccinic acid, adipic acid, sebacic acid, maleic acid fumarate, phthalic acid, terephthalic acid, hymic acid, etc.); 3 Divalent carboxylic acids (propanetricarboxylic acid, butanetricarboxylic acid, trimellitic acid, etc.); tetravalent carboxylic acids (butanetetracarboxylic acid, pyromellitic acid); dicarboxylic acid ester-forming derivatives thereof (anhydrides) , Acid halides, methyl esters, glycerides, etc.); and mixtures of two or more thereof. Among these, preferred are divalent or trivalent carboxylic acids and their ester-forming derivatives, and particularly preferred are divalent or trivalent aromatic carboxylic acids and their ester-forming derivatives.

As the hydroxyl group-containing compound constituting the (A), in addition to the above-mentioned (a-1), a part of the polyvalent alcohol (a-3), for example, a divalent alcohol ( Ethylene glycol, propylene glycol, neopentyl glycol, etc.), trivalent or higher alcohols (glycerin,
Butantriol, trimethylolpropane, triethanolamine, sorbitan monooleate, pentaerythritol, sorbitol, diglycerin, tripentaerythritol, etc.) may be used in combination.

Polyester resin (A) in the present invention
Can be obtained by subjecting the above (a-1) and (a-2) and, if necessary, (a-3) to an esterification reaction by a usual method.

The hydroxyl value of the (A) is usually 10 to 800.
mgKOH / g, preferably 100-500 mgKOH
/ G. If the hydroxyl value is less than 10 mgKOH / g, the reaction with the amino resin will be insufficient, resulting in 800 mgKOH / g.
If it exceeds g, the gel tends to be partially generated.

(A) is usually a water-soluble polyester. The polyester resin composed of an ethylene oxide adduct as (a-1) exhibits water solubility, but other (a-
When 1) is used, the acid groups present in the polyester are volatile bases (ammonia, aliphatic amines,
The hydrophilicity of the resin with respect to water can be increased by neutralizing with an alkanolamine or the like). The acid value of the (A) is usually 5
~ 100 mgKOH / g, preferably 10-30 mgK
OH / g. When the acid value is less than 10 mgKOH / g, the affinity for water is poor and it may be difficult to dissolve in water. When the acid value exceeds 100 mgKOH / g, the water resistance of the coating film decreases.

The amino resin (B) in the present invention is a resin synthesized from at least one kind of melamine, urea, benzoguanamine, glycoluril, etc. and formaldehyde, including methanol, ethanol and propanol. , Isopropanol, butanol, isobutanol and the like, and those in which a part or all of the methylol group is alkyl etherified with a lower alcohol. Among these, preferred are hexamethylolated melamine and alkylated benzoguanamine.

The (B) is a curing agent component which reacts with the hydroxyl groups or carboxyl groups in the polyester resin (A) and the acrylic resin (C) to form a crosslinked coating film.

In the present invention, by adding an acrylic resin (C) in addition to (A) and (B), the coating film hardness after baking can be further increased.

As the acrylic resin (C) to be further blended in the present invention, an ordinary acrylic resin for water-based paint having a hydroxyl group and an acid group in the molecule and reacting with an amino resin can be used. The hydroxyl value of the (C) is usually 10 to 300 mg.
KOH / g, preferably 50-300 mg KOH / g,
More preferably, it is 50 to 200 mgKOH / g. When the hydroxyl value is less than 10 mgKOH / g, the reaction with the amino resin does not proceed sufficiently, and the hardness of the obtained coating film becomes low, and 3
If it exceeds 00 mgKOH / g, a gel tends to be partially generated.

The (C) is preferably a water-soluble acrylic resin. Therefore, as in the case of (A), the acid group present in the acrylic resin is neutralized with a volatile base (ammonia, aliphatic amine, alkanolamine, etc.) as necessary to enhance the hydrophilicity of the resin with respect to water. be able to. The acid value of the (C) is usually 10 to 300 mgKOH / g, preferably 50 to 300 mgKOH / g, more preferably 5
It is 0 to 150 mg KOH / g. Acid value is 10mgKO
If it is less than H / g, the affinity for water is poor and it may be difficult to dissolve it in water. If it exceeds 300 mgKOH / g, the water resistance of the coating film is lowered.

Examples of the polymerizable monomer constituting (C) include methyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate and isobutyl (meth) acrylate. G, tert-butyl (meth)
Acrylate, 2-ethylhexyl (meth) acrylate
, Stearyl (meth) acrylate, tridecyl (meth) acrylate, cyclohexyl (meth) acrylate
G, benzyl (meth) acrylate, phenyl (meth)
Acrylate, glycidyl (meth) acrylate, α-
Ester of acrylic acid and / or methacrylic acid such as methylglycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylamino (meth) acrylate Is mentioned.

As the hydroxyl group-containing monomer, hydroxyethyl (meth) acrylate and hydroxypropyl (meth)
Acrylate, hydroxybutyl (meth) acrylate
And 1,4-butanediol mono (meth) acrylate.

The acid group-containing monomer is a lower alcohol such as (meth) acrylic acid, itaconic acid, maleic acid or fumaric acid.
And a modified monoalkyl ester.

If necessary, other copolymerizable monomers (styrene, α-methylstyrene,
Vinyltoluene, acrylonitrile, vinyl acetate, vinyl propionate, acrylamide, methacrylamide,
Methylol acrylamide, methylol methacrylamide, vinyl chloride, propylene, ethylene, α-olefin, etc.) can be used.

The production method of (C) is not particularly limited, and it can be produced by any known polymerization method such as solution polymerization method, suspension polymerization method, bulk polymerization method and emulsion polymerization method. At that time, as a polymerization initiator, azobisisobutyronitrile, 4,
4'-azobis (4-cyanopentanoic acid), benzoylper-oxide, t-butylperoxy-2-ethylhexanoate, cumene hydroperoxide, potassium persulfate, hydrogen peroxide, 2,2'-azobis (2-Methyl-N- (2-hydroxyethyl) propioamide or the like can be used, and a chain transfer agent (dodecyl mercaptan, mercaptoethanol or the like) can be used if necessary.

The number average molecular weight of (C) by GPC is usually 500 to 50,000, preferably 1,000 to 2.
It is 10,000.

In the present invention, the weight ratio of (A) to (C) is usually (10-100) :( 90-0), preferably (20-100) :( 80-0). If the ratio of (C) exceeds 90, the flexibility decreases. The blending of (A) and (C) usually requires only mixing, but (A)
Part or all of (C) and (C) may be reacted with each other.

The amount of (B) in the present invention is 5 to 70 relative to the weight of (A) alone or the total weight of (A) and (C).
%, Preferably 10 to 60% by weight. If the amount of (B) is less than 5% by weight, the hardness and water resistance of the obtained coating film will be insufficient, and the flexibility of the coating film exceeding 70% by weight will decrease.

In the resin composition for water-based paints of the present invention, various additives (coloring pigments, natural resins, synthetic resins, leveling agents, anti-sagging agents, etc.) that are generally used in paints are optionally added.
Defoaming agent, surfactant, curing accelerator, etc.) may be blended.

The resin composition of the present invention or a coating material using the same can be prepared by uniformly mixing and dispersing by a known method.

The coating composition comprising the resin of the present invention can be applied by a known coating method such as spray coating, brush coating or roll coating, and can be heat-cured to form a coating film. The heat curing conditions are not particularly limited, but the curing temperature is usually 100 to 250 ° C., and the curing time is usually 1 to 30 minutes.

[0033]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited thereto. In the following, "part" means "part by weight" and "%" means "% by weight".

Production Example 1 (Synthesis of Polyester Resin) 48 parts of a propylene oxide adduct of trimethylolpropane (number average molecular weight 700) was placed in a four-necked flask equipped with a thermometer, a stirrer, a water separation tube, and a nitrogen gas blowing tube. Charge 5 parts of ethylene oxide adduct of bisphenol A (number average molecular weight 400), 9 parts of trimethylolpropane, 11 parts of pentaerythritol, 7 parts of stearic acid, 15 parts of phthalic anhydride, 5 parts of trimellitic anhydride. Esterification was carried out at a temperature of 160 ° C. with stirring while introducing nitrogen gas to obtain a transparent viscous liquid polyester resin (resin A1) having a hydroxyl value of 260 and an acid value of 15.

Production Example 2 (Synthesis of Polyester Resin) By the same operation as in Production Example 1, a propylene oxide adduct of trimethylo-propane (number average molecular weight 700) was obtained.
3 parts, 12 parts of ethylene oxide adduct of bisphenol A (number average molecular weight 400), pentaerythritol 7
Parts, 12 parts of trimethylolpropane and 16 parts of trimellitic anhydride were charged and esterified at 190 ° C. to obtain a transparent viscous liquid polyester resin (resin A2) having a hydroxyl value of 280 and an acid value of 10.

Production Example 3 (Synthesis of Polyester Resin) By the same operation as in Production Example 1, 30 parts of propylene oxide adduct of bisphenol A (number average molecular weight 500),
16 parts of trimethylolpropane, 16 parts of pentaerythritol, 19 parts of phthalic anhydride and 19 parts of adipic acid were charged and esterification was carried out at 180 ° C. to give a hydroxyl value of 280,
A viscous liquid polyester resin (resin A3) having an acid value of 30 was obtained.

Production Example 4 (Synthesis of Polyester Resin) By the same procedure as in Production Example 1, 40 parts of neopentyl glycol, 10 parts of pentaerythritol, 20 parts of trimethylolpropane and 30 parts of trimellitic anhydride were charged. ,
Esterification was performed at 190 ° C., and a transparent viscous liquid polyester resin having a hydroxyl value of 600 and an acid value of 20 (Comparative Resin A
4) was obtained.

Production Example 5 (Production of acrylic resin solution) 67 parts of butyl cellosolve was placed in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank, and a nitrogen gas blowing tube, and the mixture was stirred while introducing nitrogen gas. While maintaining the temperature at 105 ° C., a mixture of 8 parts of acrylic acid, 22 parts of butyl acrylate, 20 parts of styrene, 50 parts of hydroxyethyl methacrylate and 3.8 parts of benzoyl peroxide was added from a dropping tank over 3 hours. Dropped. One hour after the completion of the dropping, 0.4 part of benzoyl peroxide was added, and after aging for one hour, cooling was started. When the liquid temperature became 30 ° C or less, 9 parts of dimethylethanolamine was added to the solid content of 60%.
%, A hydroxyl value of 210 mgKOH / g (based on solid content, the same applies hereinafter), and an acid value of 60 mgKOH / g (based on solid content, apply the same below), a transparent viscous liquid water-soluble acrylic resin solution (resin solution C) was obtained.

Examples 1 to 4 and Comparative Example 1 Polyester resin solutions A1 to A obtained in Production Examples 1 to 4
4. Acrylic resin C obtained in Production Example 5, amino resin B [Cymel 327 (manufactured by Mitsui Cytec Co.)] butyl cellosolve and deionized water were mixed at a ratio shown in Table 1 to obtain a solid content of 50.
% Compounded resin solution was obtained. This was applied on an aluminum plate with a bar coater so that the film thickness was 9 μm, and heated at 230 ° C. for 2 minutes to obtain a test plate. The coating film performance measurement results of the test plate are shown in Table 1.

[0040]

[Table 1]

Appearance of coating film: The finish of the coating film was visually observed, and a smooth and uniform coating film was marked with ⊚, and a coating film with poor uniformity was marked with x. Pencil hardness: The pencil hardness was evaluated by the pencil hardness test method according to JIS. Impact resistance: DuPont type 1/2 inch, evaluated with a load of 500 g. Adhesiveness: Cross-cutting was performed with a test plate immersed in boiling water for 30 minutes. Water resistance: A test plate immersed in boiling water for 1 hour was visually observed.

[0042]

INDUSTRIAL APPLICABILITY The resin composition for water-based paint of the present invention can be made into a uniform solution by simply mixing the polyester resin with other resins such as amino resin and acrylic resin, and by heat curing Since it gives excellent gloss and coating hardness, it is useful as an aqueous baking paint for metals, especially as a top coat for food cans.

Claims (8)

[Claims] 1. A polyester resin (A) comprising an alkylene oxide adduct (a-1) of a compound having at least two hydroxyl groups and a polycarboxylic acid (a-2), and an amino resin (B). A resin composition for a water-based coating, which is characterized. 2. (A) is 100 to 800 mg KOH /
The resin composition according to claim 1, which has a hydroxyl value of g and an acid value of 5 to 100 mgKOH / g. 3. The resin composition according to claim 1 or 2, wherein (a-1) is an ethylene oxide and / or propylene oxide adduct of a divalent to tetravalent alcohol. 4. The resin composition according to claim 1, further comprising an acrylic resin (C). 5. (C) is 10 to 300 mg KOH / g
The resin composition according to claim 4, which has a hydroxyl value of 10 and an acid value of 10 to 300 mgKOH / g. 6. A weight ratio of (A) :( C) is (10 to 10).
0): (90-0), The resin composition according to claim 4 or 5. 7. The resin composition according to claim 4, wherein the amount of (B) is 5 to 70% by weight based on the total weight of (A) and (C). 8. The resin composition according to claim 1, which is used as a top coat for a metal can.