JPH06329744A - Aqueous polyurethane resin dispersion for coating material - Google Patents

Abstract

PURPOSE:To obtain the title dispersion used for a metal coating material and excelling in heat and yellowing resistance. CONSTITUTION:The dispersion is prepared by chain-extending a product of the neutralization of an isocyanato urethane prepolymer obtained by reacting aliphatic and/or alicyclic diisocyanates with a polymer polyol, an alpha,alpha- dimethylolmonocarboxylic acid and optionally a low-molecular polyol with a volatile base with a dibasic acid dihydrazide in water.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an aqueous dispersion of polyurethane resin for paint. More specifically, the present invention relates to a polyurethane resin aqueous dispersion for metal coatings which is resistant to thermal yellowing when used in a mixture with an amino resin curing type coating material or when it is overcoated with an amino resin curing type coating film and baked.

[0002]

2. Description of the Related Art Heretofore, as an aqueous dispersion of a polyurethane resin, one using water, diamine, hydrazine or the like as a chain extender is known (for example, Japanese Patent Publication No. 58-25085 and Japanese Patent Publication No. 63-8141). And JP-A-63-275662).

[0003]

However, the aqueous polyurethane resin dispersion for paints obtained by using these extenders is an amino resin curable paint such as melamine formaldehyde resin (acrylic / melamine paint, alkyd / melamine paint). (A paint, etc.) and subjected to a thermosetting reaction at 100 to 200 ° C., or when a thermosetting reaction is carried out by repeatedly coating with the coating film of the amino resin curing type coating, There is a problem that the coating film turns yellow due to the influence of a small amount of formalin contained.

[0004]

The present inventors have arrived at the present invention as a result of intensive studies to obtain a polyurethane resin aqueous dispersion for metal paints which solves the above problems. That is, in the present invention, an aliphatic and / or alicyclic diisocyanate (a), a high molecular weight polyol (b), an α, α-dimethylol monocarboxylic acid (c) and, if necessary, a low molecular weight polyol (d) are reacted. A polyurethane resin aqueous dispersion for paint obtained by chain elongation of a volatile base (B) neutralized product of the obtained urethane prepolymer (A) with dibasic acid dihydrazide (C) in water.

In the present invention, the aliphatic and / or alicyclic diisocyanate (a) constituting the urethane prepolymer (A) is an aliphatic diisocyanate having 2 to 12 carbon atoms such as hexamethylene diisocyanate.
(HDI), 2,2,4-trimethylhexane diisocyanate, lysine diisocyanate; alicyclic diisocyanate having 4 to 18 carbon atoms, such as 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (I
PDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI); aromatic ring Having aliphatic diisocyanates, such as xylylene diisocyanate (XDI), tetramethyl xylylene diisocyanate (TMXD
I); modified products of these diisocyanates (carbodiimide, uretdione, uretoimine, burette and / or isocyanurate modified products); and mixtures of two or more thereof. Preferred among these are HDI, IPDI, hydrogenated MDI and TMXDI.

The high molecular weight polyol (b) is a polyether polyol, for example, one obtained by polymerizing or copolymerizing alkylene oxides (ethylene oxide, propylene oxide, butylene oxide, etc.) and / or heterocyclic ethers (tetrahydrofuran, etc.). , Specifically polyethylene glycol, polypropylene glycol, polyethylene / propylene (block or random) glycol, polyethylene / tetramethylene glycol (block or random), polytetramethylene ether glycol; polyester polyols such as aliphatic dicarboxylic acids (succinic acid, Adipic acid, sebacic acid, glutaric acid, azelaic acid, etc.) and / or aromatic dicarboxylic acids (isophthalic acid, terephthalic acid, etc.) and low-molecular glycol (ethylene glycol Recall, propylene glycol, 1,4-butanediol, 1,6-hexanediol,
Polymethyl adipate diol, polybutylene adipate diol, polyhexamethylene adipate diol, such as 3-methyl-1,5-pentanediol, neopentyl glycol, 1,4-dihydroxymethylcyclohexane) , Polyneopentyl adipate diol, polyethylene / butylene adipate diol, polyneopentyl / hexyl adipate diol, poly-3-methylpentane adipate diol, polybutylene 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 hydrogenated products thereof; and mixtures of two or more thereof. Among the above-exemplified ones, preferable ones are those exemplified below, and a mixture with at least one of the following. The number average molecular weight of (b) is usually 500 to 5000, preferably 1000 to 4000.

Α, α-Dimethylolmonocarboxylic acid (c)
Is a component for introducing an anionic hydrophilic group for stably dispersing a polyurethane resin in water, and specific examples include α, α-dimethylolacetic acid, α, α-dimethylolpropionic acid, α, α- Examples include dimethylol butyric acid,
Of these, preferred is α, α-dimethylolpropionic acid.

As a constituent component of (A), a low molecular weight polyol (d) can be used if necessary. The (d)
Examples of the low molecular weight glycols and their alkylene oxide low molar adducts (number average molecular weight less than 500) listed as the raw materials for the above polyester polyols; bisphenol alkylene oxide low molar adducts (number average molecular weight)
(Less than 500); trihydric alcohols such as glycerin, trimethylolethane, trimethylolpropane and the like and low molar adducts of alkylene oxides (number average molecular weight less than 500); and mixtures of two or more thereof.

Examples of the volatile base (B) used for neutralizing the carboxyl group in (A) include tertiary alkylamines such as trimethylamine, triethylamine and triethylamine.
-n-propylamine, tri-iso-propylamine, tri-n
-Butylamine and tri-iso-butylamine. Of these, preferred are trimethylamine and triethylamine.

Examples of the dibasic acid dihydrazide (C) used as a chain extender include adipic acid dihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, sebacic acid dihydrazide, phthalic acid dihydrazide, glutaric acid dihydrazide, maleic acid dihydrazide. And mixtures of two or more of these. Of these, particularly preferred is adipic acid dihydrazide.

The urethane prepolymer (A) in the present invention comprises (a), (b), (c) and optionally (d) in an NCO / OH equivalent ratio of usually 1.1 to 2.0, preferably 1.2 to. Obtained by reacting in the range of 1.6.

The amount of (c) in (A) is usually 0.3 to 5% by weight as a carboxyl group (--COOH), preferably 0.1.
It is 5 to 4% by weight. If the amount of (c) is less than 0.3% by weight, it is difficult to obtain a stable aqueous dispersion, and if it exceeds 5% by weight, the hydrophilicity of the polymer becomes high, so that the water resistance when formed into a coating film is lowered.

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

The amount of dibasic acid dihydrazide (C) used for chain extension in the present invention is usually 0.4 to 1.1 equivalents, preferably 0.7 to 1.05 equivalents to the isocyanate groups in the urethane prepolymer (A). . The amount of (C) is 0.4
If it is less than the equivalent, heat-resistant yellowing becomes insufficient, and if 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 aqueous dispersion of the present invention is not particularly limited, but for example, in the presence of a hydrophilic organic solvent having no active hydrogen group in the molecule (eg, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, etc.) or In the absence of (a), (b), (c) and optionally (d), one-shot method or multi-step method,
Usually, the reaction is carried out at 20 to 150 ° C., preferably 60 to 110 ° C. for 2 to 10 hours to form a urethane prepolymer containing a terminal NCO group (A), and then the (A) is neutralized with a volatile base (B). After or while neutralizing, usually 10-60 ° C, preferably
A specific example is a method of mixing with an aqueous solution containing a predetermined amount of a dibasic acid dihydrazide chain extender (C) at 20 to 40 ° C. to carry out an emulsion elongation reaction, and distilling off the solvent if necessary.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Further, in the following, "part" means part by weight and "%" means% by weight.

<Production of White Plate> The white plate used for the evaluation of heat-resistant yellowing in Examples and Comparative Examples was prepared by the following method. White plate: A commercially available white acrylic lacquer (without melamine) spray-coated on a tin plate degreased with toluene, acetone, etc., and dried at 80 ° C for 20 minutes. White plate: A melamine-curing white acrylic paint spray-painted, set at room temperature for 20 minutes, and then baked at 120 ° C for 20 minutes.

Example 1 Polycaprolactone diol [number average molecular weight (hereinafter abbreviated as Mn) 2000] 113.2 parts, poly-3-methylpentane adipate diol (Mn2000) 113.2 parts, 1,4-butanediol 1.3 parts, trimethylol 8.6 parts of propane, 17.2 parts of α, α-dimethylolpropionic acid, 101.6 parts of IPDI and 175.1 parts of acetone were charged into a pressure reaction vessel and reacted under stirring and closed pressure at 85 ° C. for 8.5 hours to give an NCO content of 1.7%. An acetone solution of urethane prepolymer was obtained. Then the solution
After cooling to 40 ° C, 11.7 parts of triethylamine was added and stirred and mixed for 30 minutes, and 454.6 parts was added to ion exchanged water 666.7 at 20 ° C.
Adipic acid dihydrazide (hereinafter abbreviated as ADH) 1
5.4 parts (0.9 equivalents of NCO group) was added to a dissolved aqueous solution with stirring and mixing to emulsify, and an extension reaction was carried out at 40 ° C. until the remaining NCO groups were consumed. After distilling off acetone under reduced pressure from this emulsion, 3.9 parts of triethylamine was added to adjust the pH to 10.3 to obtain a polyurethane resin aqueous dispersion (D-1) having a solid content of 34.3% and a viscosity of 40 cps / 25 ° C. Obtained. A coating film was prepared using the obtained (D-1) by the following method, and each Δb value (heat resistant yellowing) was measured. The results are shown in Table 1. <Coating conditions> (Coating-1): (D-1) is ion-exchanged water to obtain a solid content of about 30.
% And applied to a white plate using a 7 mil applicator. This was left standing on a horizontal plate for 30 minutes, preheated at 80 ° C. for 10 minutes, and then baked at 160 ° C. for 60 minutes to form a coating film (film thickness of about 20 μm). (Coating film-2): (D-1) was mixed with water-soluble melamine in the following ratio, diluted with ion-exchanged water to a solid content of 30%, and then applied to a white plate using a 7 mil applicator. This was left still on the horizontal part for about 30 minutes, preheated at 80 ° C for 10 minutes, and then baked at 160 ° C for 60 minutes to form a coating film. Water-based urethane resin dispersion (solid content) 100 parts Cymel 303 (solid content) 5 parts (manufactured by Mitsui Cyanamid KK) (Coating film-3): Coating and baking on a white plate in the same manner as (Coating film-1) It became a film. (Coating film-4): A white plate was blended, coated and baked in the same manner as (Coating film-2) to form a coating film.

Example 2 260.6 parts of polycarbonate diol (Mn2000), α, α-
Dimethylolpropionic acid (18.7 parts) and HDI (84.2 parts) were charged into a pressure reaction vessel, and the reaction was carried out at 80 ° C for 2 hours under closed pressure while stirring. After cooling to 40 ° C, 2 mol of ethylene oxide adduct of bisphenol A (Mn330 ) 21.2 parts and 146 parts of acetone are charged, and the mixture is stirred at 80 ° C. under a closed pressure for 3 times.
By reacting for a time, an acetone solution of a urethane prepolymer having an NCO content of 2.3% was obtained. Then, the solution was cooled to 40 ° C., 12.7 parts of triethylamine was added, and the mixture was stirred and mixed for 30 minutes.
440 parts was added to an aqueous solution prepared by dissolving 18.7 parts of ADH in 700 parts of ion-exchanged water at 20 ° C while stirring and mixing to emulsify it at 40 ° C.
The extension reaction was carried out until the residual NCO group was exhausted. After distilling off acetone under reduced pressure from this emulsion, 4.2 parts of triethylamine was added to adjust the pH to 9.8, and the solid content was 34.2%.
%, Viscosity 55 cps / 25 ° C polyurethane resin aqueous dispersion (D
-2) was obtained. The obtained (D-2) was used to prepare (Coating film-1) to (Coating film-4) in the same manner as in Example 1. Table 1 shows each Δb measurement value.

Example 3 Poly-3-methylpentane adipate diol (Mn3950) 2
48.5 parts, 1,4-butanediol 6.9 parts, trimethylolpropane 3.9 parts, α, α-dimethylolpropionic acid 16.6
Parts, 95.3 parts of IPDI and 158 parts of acetone were charged into a pressure reaction vessel and reacted under stirring and closed pressure at 85 ° C. for 6 hours to obtain an acetone solution of urethane prepolymer having an NCO content of 1.8%. Then, the solution was cooled to 40 ° C., 11.3 parts of triethylamine was added, and 456 parts obtained by stirring and mixing for 30 minutes were added to 2 parts.
ADH 15.2 parts was dissolved in an aqueous solution prepared by dissolving 560 parts of ion-exchanged water at 0 ° C. with stirring and mixing to emulsify, and an extension reaction was carried out at 40 ° C. until there were no remaining NCO groups. After distilling off acetone under reduced pressure from this emulsion, 3.2 parts of triethylamine was added to adjust the pH to 10.0, and the solid content was 34.0% and the viscosity was 37 cps.
A polyurethane resin aqueous dispersion (D-3) at / 25 ° C was obtained. The obtained (D-3) was used to prepare (Coating film-1) to (Coating film-4) in the same manner as in Example 1. Table 1 shows each Δb measurement value.

Comparative Example 1 117.3 parts of polycaprolactone diol (Mn2000), poly-
3-Methylpentane adipate diol (Mn2000) 117.3
Parts, 3.3 parts of 1,4-butanediol, 6.4 parts of trimethylolpropane, 18.7 parts of α, α-dimethylolpropionic acid, I
121.7 parts of PDI and 146 parts of acetone were charged into a pressure reaction vessel and reacted under stirring and pressure at 85 ° C. for 6 hours while stirring to obtain NCO.
An acetone solution of urethane prepolymer having a content of 2.5% was obtained. Then, the solution was cooled to 40 ° C, 12.7 parts of triethylamine was added, and the mixture was stirred and mixed for 30 minutes.
It was added to the aqueous solution prepared by dissolving 6.9 parts of ethylenediamine in 570 parts of ion-exchanged water while stirring and mixing to emulsify, and the elongation reaction was carried out at 40 ° C. until the residual NCO groups were exhausted. After distilling off acetone under reduced pressure from this emulsion, 3.5 parts of triethylamine was added to adjust the pH to 10.9, and a solid content of 35.1% and a viscosity of 48 cps / 25 ° C. of a comparative polyurethane resin aqueous dispersion (D
-4) was obtained. Using the obtained (D-4), (Coating film-1) to (Coating film-4) were prepared in the same manner as in Example 1. Table 1 shows each Δb measurement value.

Comparative Example 2 117.3 parts of polycaprolactone diol (Mn2000), poly-
3-Methylpentane adipate diol (Mn2000) 117.3
Parts, 3.3 parts of 1,4-butanediol, 6.4 parts of trimethylolpropane, 18.7 parts of α, α-dimethylolpropionic acid, I
121.7 parts of PDI and 146 parts of acetone were charged into a pressure reaction vessel and reacted under stirring and pressure at 85 ° C. for 6 hours while stirring to obtain NCO.
An acetone solution of urethane prepolymer having a content of 2.5% was obtained. Then the solution was cooled to 40 ° C. before triethylamine
12.7 parts were added and stirred and mixed for 30 minutes, and 440 parts were added to 560 parts of ion-exchanged water at 20 ° C. with stirring to emulsify.
The extension reaction was carried out at 0 ° C until the remaining NCO groups were exhausted. From this emulsion, acetone was distilled off under reduced pressure, 3.5 parts of triethylamine was added to adjust the pH to 10.7, and the solid content was 34.3.
%, And a viscosity of 42 cps / 25 ° C., a comparative polyurethane resin aqueous dispersion (D-5) was obtained. Using the obtained (D-5), (Coating film-1) to (Coating film-4) were prepared in the same manner as in Example 1. Table 1 shows each Δb measurement value.

[0023]

[Table 1] <Evaluation method> Heat-resistant yellowing: The degree of yellowing of (Coating film-1) to (Coating film-4) was evaluated by a Δb value measured by a multi-source spectrophotometer manufactured by Suga Test Instruments Co., Ltd. The smaller the Δb value, the better the heat-resistant yellowing.

[0024]

EFFECT OF THE INVENTION The aqueous polyurethane resin dispersion for coating material of the present invention is mixed with an amino resin curing agent or an amino resin curing type coating material and subjected to a heat curing reaction, or is overlaid with a coating film of the amino resin curing type coating material. When applied and subjected to a thermosetting reaction, compared to conventional polyurethane resin aqueous dispersions,
Excellent heat yellowing resistance. From the above effect, the polyurethane resin aqueous dispersion is particularly preferably 100 to 200.
It is useful as a material for amino resin curable coatings, such as metal coatings, which is cured by heating at a high temperature of ℃.

Claims (4)

[Claims] 1. An aliphatic and / or alicyclic diisocyanate (a), a high molecular weight polyol (b), an α, α-dimethylol monocarboxylic acid (c), and optionally a low molecular weight polyol (d) are reacted. An aqueous dispersion of a polyurethane resin for paints, obtained by chain extending a volatile base (B) neutralized product of the obtained urethane prepolymer (A) with dibasic acid dihydrazide (C) in water. 2. The aqueous dispersion according to claim 1, wherein (C) is adipic acid dihydrazide. 3. The aqueous dispersion according to claim 1, wherein the amount of (C) is 0.4 to 1.1 equivalents based on the isocyanate groups in (A). 4. The aqueous dispersion according to claim 1, which is used as a baking paint for metals.