JP2700290B2 - Paint composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating composition and a composite coating. More specifically, the present invention relates to a coating composition which is less likely to be heated yellowing when baked after being overcoated with an amino resin-curable coating film and a composite coating film comprising the same.

[0002]

2. Description of the Related Art Conventionally, aqueous polyurethane resin dispersions using water, diamine, hydrazine or the like as a chain extender are known (for example, JP-B-58-250).
No. 85, JP-B-63-8141 and JP-A-63-275662.

[0003]

However, a coating comprising a polyurethane resin water-thread dispersion obtained by using these elongating agents is an amino resin-curable coating such as a melamine formaldehyde resin (acryl / melamine-based coating, alkyd). / Melamine paint etc.)
When heated at 0 to 200 ° C. to form a composite coating film, there is a problem that the coating film turns yellow due to the influence of a small amount of formalin contained in the amino resin-curable coating film.

[0004]

Means for Solving the Problems The present inventors have intensively studied to obtain a paint comprising a polyurethane resin aqueous dispersion which solves the above-mentioned problems, and as a result, have reached the present invention. That is, the present invention comprises reacting an aliphatic and / or alicyclic diisocyanate (a), a high molecular polyol (b), α, α-dimethylolmonocarboxylic acid (c) and, if necessary, a low molecular polyol (d). An amino resin-cured coating film comprising a polyurethane resin aqueous dispersion obtained by chain-extending a volatile base (B) neutralized product of the obtained urethane prepolymer (A) with dibasic acid dihydrazide (C) in water. The present invention relates to a composite coating film comprising a coating composition to be overcoated; a cured amino resin coating film; and a cured coating film of the coating composition overcoated on the cured coating film.

In the present invention, the aliphatic and / or alicyclic diisocyanate (a) constituting the urethane prepolymer (A) includes an aliphatic diisocyanate having 2 to 12 carbon atoms, for example, hexamethylene diisocyanate (HDI), Alicyclic diisocyanates having 4 to 18 carbon atoms, such as 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (water MDI), methylcyclohexanediisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI); aliphatic diisocyate having an aromatic ring , For example, xylylene diisocyanate (XDI), tetramethyl xylylene diisocyanate (TMXDI); modified products of these diisocyanates (carbodiimide, uretdione, uretimine, buret and / or isocyanurate modified products); Mixtures are mentioned. Preferred among these are HDI, IPDI, hydrogenated MDI
And TMXDI.

Examples of the high molecular polyol (b) include polyether polyols, for example, those obtained by polymerizing or copolymerizing an alkylene oxide (ethylene oxide, propylene oxide, butylene oxide, etc.) and / or a heterocyclic ether (tetrahydrofuran, etc.). Specifically, polyethylene glycol, polypropylene glycol, polyethylene / propylene (block or random) glycol, polyethylene / tetramethylene (block or random) glycol, polytetramethylene ether glycol; polyester polyol such as aliphatic dicarboxylic acid (succinic acid, Adipic acid, sebacic acid, glutaric acid, azelaic acid, etc.) and / or aromatic dicarboxylic acid (isophthalic acid, terephthalic acid, etc.) and low molecular weight glycol (ethylene glycol) Coal, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,4-dihydroxymethylcyclohexane, etc.) Specifically, polyethylene adipate diol, polybutylene adipate diol, polyhexamethylene adipate diol, polyneopentyl adipate diol, polyethylene / butylene adipate diol, polyneopentyl / hexyl adipate diol, poly-3-methylpentane adipate diol, poly Butylene isophthalate diol;
Polylactone polyols such as polycaprolactone diol or triol, poly-3-methylvalerolactone diol; polycarbonate polyols such as polyhexamethylene carbonate diol; polyolefin polyols such as polybutadiene glycol,
Polyisoprene glycol or a hydride thereof; and a mixture of two or more thereof. Preferred among the above examples are those exemplified above and mixtures with at least one of the above.
The number average molecular weight of (b) is usually from 500 to 5,000, preferably from 1,000 to 4,000.

Α, α-dimethylol monocarboxylic acid (c) is a component for introducing an anionic hydrophilic group for stably dispersing a polyurethane resin in water,
Specific examples include α, α-dimethylolacetic acid, α, α-dimethylolpropionic acid, α, α-dimethylolbutyric acid, and among them, α, α-dimethylolpropionic acid is preferred.

[0008] As a component of (A), a low molecular polyol (d) can be used if necessary. (D)
Examples of the low-molecular-weight glycol and its alkylene oxide low-molar adduct (number-average molecular weight less than 500); low-molecular-weight alkylene oxide adduct of bisphenol (number-average molecular weight less than 500); trivalent Alcohols such as glycerin, trimethylolethane, trimethylolpropane, and the like, and low-molecular-weight alkylene oxide adducts (number average molecular weight of less than 500); and mixtures of two or more thereof.

The volatile base (B) used for neutralizing the carboxyl group in (A) includes a tertiary alkylamine such as trimethylamine, triethylamine, tri-n-propylamine, tri-iso-propylamine, Tri-n-butylamine and tri-iso-butylamine. Preferred among these are trimethylamine and triethylamine.

The dibasic dihydrazide (C) used as a chain extender includes, for example, adipic dihydrazide, oxalic dihydrazide, malonic dihydrazide, succinic dihydrazide, sebacic dihydrazide, phthalic dihydrazide, glutaric dihydrazide, maleic dihydrazide. And mixtures of two or more of these. Of these, particularly preferred is adipic dihydrazide.

The urethane prepolymer (A) of the present invention comprises (a), (b), (c) and, if necessary, (d), having an NCO / OH equivalent ratio of usually 1.1 to 2.
0, preferably 1.2 to 1.6.

The amount of (c) in (A) is usually 0.3 to 5% by weight, preferably 0.5 to 4% by weight as carboxyl group (-COOH). 0.3% by weight of (c)
If it is less than 5 wt%, it is difficult to obtain a stable aqueous dispersion, and if it exceeds 5 wt%, the hydrophilicity of the polymer increases, and the water resistance of the coating film decreases.

The amount of the volatile base (B) is usually 0.5 to 1.5 equivalents, preferably 0.7 to 1.3 equivalents to the carboxyl group in (A).

The amount of the dibasic dihydrazide (C) used as a chain extender in the present invention is usually from 0.4 to 1. 1 based on the isocyanate groups in the urethane prepolymer (A).
One equivalent, preferably 0.7 to 1.05 equivalent.
When the amount of (C) is less than 0.4 equivalent, heat yellowing becomes insufficient, and when it exceeds 1.1 equivalent, a high molecular weight resin cannot be obtained and the physical properties of the coating film deteriorate.

The method for producing the polyurethane resin water thread dispersion in the present invention is not particularly limited. For example, a hydrophilic organic solvent containing no active hydrogen group in the molecule (for example, acetone,
(A), (b), (c) and, if necessary, (d) in the presence or absence of methyl ethyl ketone, tetrapidrofuran, dioxane, etc., usually at 20 to 150 ° C. by a one-shot method or a multistage method. , Preferably 60 to 110 ° C
For 2 to 10 hours to form a urethane prepolymer (A) having a terminal NCO group, and then neutralizing (A) with or after neutralizing the (A) with a volatile base (B).
A specific example is a method in which the mixture is mixed with an aqueous solution containing a predetermined amount of a dibasic acid dihydrazide chain extender (C) at 0 to 60 ° C., preferably 20 to 40 ° C. to carry out an emulsification elongation reaction and, if necessary, distill off the solvent. No.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.
In the following, "parts" indicates parts by weight and "%" indicates% by weight.

<Preparation of White Plate> The white plates used in the evaluation of heat-resistant yellowing in Examples and Comparative Examples were prepared by the following method. White plate: A commercially available melamine-curable white acrylic paint is spray-coated on a tin plate degreased with toluene and acetone, set at room temperature for 20 minutes, and baked at 120 ° C. for 20 minutes (dry film thickness: about 40 μm) ).

<Method of Evaluating Heat-Resistant Yellowing> The degree of yellowing of the composite coating films obtained in Examples and Comparative Examples was evaluated by a Δb value measured by a multi-light source spectrocolorimeter manufactured by Suga Test Co., Ltd. The smaller the Δb value, the better the heat-resistant yellowing.

Example 1 Polycaprolactone diol [number average molecular weight (hereinafter referred to as Mn)
2000] 113.2 parts, poly-3-methylpentane adipate diol (Mn2000) 11
3.2 parts, 1.3 parts of 1,4-butanediol, 8.6 parts of trimethylolpropane, 17.2 parts of α, α-dimethylolpropionic acid, 101.6 parts of IPDI and 175.1 parts of acetone The mixture was charged into a reaction vessel, and reacted at 85 ° C. for 8.5 hours under tightly closed pressure with stirring to obtain an NCO content of 1.
A 7% urethane prepolymer in acetone solution was obtained. Then the solution was cooled to 40 ° C. and triethylamine 1
1.74.6 parts were stirred and mixed for 30 minutes, and 454.6 parts were added to 666.7 parts of 20 ° C. ion-exchanged water and 15.4 parts of adipic dihydrazide (hereinafter abbreviated as ADH) (to N).
(Equivalent of CO group: 0.9 equivalent) was added to the dissolved aqueous solution while stirring and mixing, and emulsified, and an elongation reaction was carried out at 40 ° C. until there was no remaining NCO group. After acetone was distilled off from this emulsion under reduced pressure, 3.9 parts of triethylamine was added to adjust the pH to 10.3, and the solid content was 34.3% and the viscosity was 40%.
cps / 25 ° C polyurethane resin aqueous dispersion (D-
1) was obtained. The obtained (D-1) was diluted with ion-exchanged water to a solid content of about 30%, and applied to a white plate using a 7 mil applicator (film thickness: about 20 μm). This is left standing on a horizontal plate for 30 minutes, preheated at 80 ° C. for 10 minutes, and then
Baking at 60 ° C. for 60 minutes to form a composite coating, Δ of the coating
The b value (heat-resistant yellowing) was measured. Table 1 shows the results.

Comparative Example 1 A water-soluble melamine (methoxylated methylol melamine) was added to (D-1) obtained in Example 1 in the following ratio, diluted with ion-exchanged water to a solid content of 30%, and then diluted to 7 mil. It was applied to a white plate using an applicator. This is left standing on a horizontal part for about 30 minutes, preheated at 80 ° C. for 10 minutes, and then 160 ° C.
For 60 minutes to form a composite coating film, and the Δb value of the coating film was measured. Table 1 shows the results. Aqueous urethane resin dispersion (D-1) (solid content) 100 parts "Symel 303" (solid content) 5 parts (Mitsui Cyanamid KK)

Example 2 Polycarbonate diol (Mn2000) 260.6
Parts, 18.7 parts of α, α-dimethylolpropionic acid, H
84.2 parts of DI was charged into a pressurized reaction vessel, and the mixture was reacted at 80 ° C. for 2 hours under stirring and closed pressure while stirring. After cooling to 40 ° C., 21.2 parts of ethylene oxide 2 mol adduct (Mn330) of bisphenol A and acetone were further added. 146 parts were charged and reacted at 80 ° C. for 3 hours under tightly closed pressure with stirring to obtain an acetone solution of a urethane prepolymer having an NCO content of 2.3%. Next, the solution was cooled to 40 ° C., 12.7 parts of triethylamine was added, and the mixture was stirred and mixed for 30 minutes.
H. 18.7 parts was dissolved in an aqueous solution in which the mixture was dissolved while stirring and emulsified, and an elongation reaction was carried out at 40 ° C. until no residual NCO groups were present. After acetone was distilled off from the emulsion under reduced pressure, 4.2 parts of triethylamine was added thereto to adjust the pH.
Adjusted to 9.8, 34.2% solids, 55 cps viscosity
/ 25 ° C. to obtain a polyurethane resin aqueous dispersion (D-2). Using (D-2) obtained, a composite coating film was prepared in the same manner as in Example 1, and the Δb value was measured. Table 1 shows the results.

Comparative Example 2 A composite coating film was prepared in the same manner as in Comparative Example 1 except that (D-2) obtained in Example 2 was used instead of (D-1). The Δb value was measured. Table 1 shows the results.

Example 3 Poly-3-methylpentane adipate diol (Mn3
950) 248.5 parts, 1,4-butanediol 6.9
Parts, 3.9 parts of trimethylolpropane, 16.6 parts of α, α-dimethylolpropionic acid, 95.3 parts of IPDI and 158 parts of acetone are charged into a pressurized reaction vessel, and the mixture is sealed and pressurized at 85 ° C. for 6 hours while stirring. The reaction was performed to obtain an acetone solution of a urethane prepolymer having an NCO content of 1.8%. Then, the solution was cooled to 40 ° C., and 11.3 parts of triethylamine was added and stirred and mixed for 30 minutes. 456 parts of a mixture obtained by dissolving 15.2 parts of ADH in 560 parts of ion-exchanged water at 20 ° C. was stirred and mixed. In addition, emulsify,
The elongation reaction was performed at 40 ° C. until no residual NCO groups were found. After distilling off acetone under reduced pressure from this emulsion,
The pH was adjusted to 10.0 by adding 3.2 parts of triethylamine to obtain a polyurethane resin aqueous dispersion (D-3) having a solid content of 34.0% and a viscosity of 37 cps / 25 ° C. Using (D-3) obtained, a composite coating film was prepared in the same manner as in Example 1, and the Δb value was measured. Table 1 shows the results.

Comparative Example 3 A composite coating film was prepared in the same manner as in Comparative Example 1 except that (D-3) obtained in Example 3 was used instead of (D-1). The Δb value was measured. Table 1 shows the results.

Comparative Example 4 Polycaprolactone diol (Mn2000)
3 parts, 117.3 parts of poly-3-methylpentane adipate diol (Mn2000), 3.3 parts of 1,4-butanediol, 6.4 parts of trimethylolpropane, α, α
-18.7 parts of dimethylolpropionic acid, IPDI12
1.7 parts and 146 parts of acetone were charged into a pressurized reaction vessel, and the mixture was reacted at 85 ° C. for 6 hours under tightly closed pressure with stirring.
An acetone solution of a urethane prepolymer having a CO content of 2.5% was obtained. Next, the solution was cooled to 40 ° C., and 12.7 parts of triethylamine was added, and the mixture was stirred and mixed for 30 minutes. 440 parts of the mixture was stirred and mixed with an aqueous solution obtained by dissolving 6.9 parts of ethylenediamine in 570 parts of ion-exchanged water at 20 ° C. Then, the mixture was emulsified while adding, and an elongation reaction was carried out at 40 ° C. until there was no residual NCO group. From this emulsion, acetone was distilled off under reduced pressure, and then 3.5 parts of triethylamine was added to adjust the pH.
Adjusted to 10.9, 35.1% solids, 48 cp viscosity
s / 25 ° C comparative polyurethane resin aqueous dispersion (D-
4) was obtained. Using (D-4) obtained, a composite coating film was prepared in the same manner as in Example 1, and the Δb value was measured.
Table 1 shows the results.

Comparative Example 5 A composite coating film was prepared in the same manner as in Comparative Example 1, except that (D-4) obtained in Comparative Example 4 was used instead of (D-1). The Δb value was measured. Table 1 shows the results.

Comparative Example 6 Polycaprolactone diol (Mn2000)
3 parts, 117.3 parts of poly-3-methylpentane adipate diol (Mn2000), 3.3 parts of 1,4-butanediol, 6.4 parts of trimethylolpropane, α, α
-18.7 parts of dimethylolpropionic acid, IPDI12
1.7 parts and 146 parts of acetone were charged into a pressurized reaction vessel, and the mixture was reacted at 85 ° C. for 6 hours under tightly closed pressure with stirring.
An acetone solution of a urethane prepolymer having a CO content of 2.5% was obtained. Next, the solution was cooled to 40 ° C., and 12.7 parts of triethylamine was added, followed by stirring and mixing for 30 minutes.
Forty parts were added to 560 parts of 20 ° C. ion-exchanged water while stirring and mixing to emulsify, and an elongation reaction was carried out at 40 ° C. until there was no residual NCO group. After acetone was distilled off from the emulsion under reduced pressure, the pH was adjusted to 10.7 by adding 3.5 parts of triethylamine, and the solid content was 34.3% and the viscosity was 42.
A comparative polyurethane resin water thread dispersion (D-5) having a cps / 25 ° C. was obtained. Using (D-5) obtained, a composite coating film was prepared in the same manner as in Example 1, and the Δb value was measured. Table 1 shows the results.

Comparative Example 7 A composite coating film was prepared in the same manner as in Comparative Example 1 except that (D-5) obtained in Comparative Example 4 was used instead of (D-1). The Δb value was measured. Table 1 shows the results.

[0028]

[Table 1]

[0029]

The coating composition comprising the aqueous polyurethane resin dispersion of the present invention, when subjected to a thermosetting reaction by overcoating with a coating film of an amino resin-curable coating, can be used as a conventional polyurethane resin aqueous dispersion. A composite coating film having extremely excellent heat-resistant yellowing is formed as compared with that used. The coating composition comprising the aqueous polyurethane resin dispersion of the present invention, which exhibits the above-mentioned effects, is particularly useful for forming a composite coating film with a coating film of an amino resin-curable coating material which is cured by heating at a high temperature of 100 to 200 ° C. Useful as a coating material.

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication // C08G 18/00 C08G 18/00 C 18/10 18/10 18/65 18/65 B C08L 75:08

Claims (4)

(57) [Claims] 1. An aliphatic and / or alicyclic diisocyanate (a), a high molecular polyol (b), an α, α-dimethylolmonocarboxylic acid (c) and, if necessary, a low molecular polyol (d) are reacted. Resin cured coating consisting of an aqueous polyurethane resin dispersion obtained by chain-extending a neutralized volatile base (B) of a urethane prepolymer (A) obtained with a dibasic acid dihydrazide (C) in water Paint composition overlaid on top . 2. The coating composition according to claim 1, wherein (C) is adipic dihydrazide. 3. The method according to claim 1, wherein the amount of (C) is 0.4 to 1.1 equivalents based on the isocyanate groups in (A).
The coating composition according to any one of the preceding claims. 4. A amino resin cured coating film, a composite coating film comprising a cured film of the coating composition according to any one of claims 1 to 3 which is recoated on <br/> top of the cured coating film .