JP2000178505A - One-pack thermosetting coating material and coating process therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating material which can be baked at a low temperature, has an excellent storage stability, and gives a good appearance in the coated film, and provide a coating process therefor. SOLUTION: This one-pack thermosetting coating material comprising (A) an active hydrogen group-containing resin, (B) a blocked isocyanate consisting of (B1) a polyisocyanate and (B2) a blocking agent, and (C) a catalyst, is characterized in that the component (B1) contains a moiety of (b1) an aliphatic diisocyanate, a moiety of (b2) a glycol having a side chain and a mol.wt. of 500 or less, an isocyanurate group and a urethane group, and the component (B1) has a (b2) content of 0.5-15.0 mass %, the component (B2) contains 3,5- dimethyl pyrazole; a mole ratio of an active hydrogen group (AH) of (B2) to an isocyanate group (NCO) of (B1) is as follows: 1.15<=AH/NCO<=4.00, and the adding amount of the component (C) is 2.0 mass % or less relative to the total amount of (A) and (B). In addition, a coating process comprises baking the one-pack thermosetting coating material at 90-140 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-part thermosetting paint and a coating method using the paint.

[0002]

2. Description of the Related Art Blocked isocyanates are obtained by reacting a free isocyanate group of a polyisocyanate with a compound containing an active hydrogen group (blocking agent) so as to be inactive at room temperature. When heated, the blocking agent is dissociated. It has the property that isocyanate groups are regenerated. For this reason, it has become possible to mix the main agent having an active hydrogen group and the curing agent in the paint in advance, and automatic coating such as electrodeposition coating has become possible. Coatings containing blocked isocyanates are widely used as baking coatings for metal parts of automobiles, aircraft, home appliances and the like, electrodeposition coatings, and the like.

[0003] As a study of blocked isocyanates having a lower dissociation temperature, there are JP-A-7-304843, JP-A-8-104726 and JP-A-8-225509. In JP-A-7-304843,
A pyrazole-based compound is used as a blocking agent, and the maximum amount of the excess blocking agent is 10% based on isocyanate groups. Japanese Patent Application Laid-Open No. 8-104726 describes a paint which is cured on a acrylic resin with a polyisocyanate partially and temporarily blocked with a pyrazole compound. In JP-A-8-225509, a pyrazole-based compound is used as a blocking agent, and the maximum amount of excess blocking agent is 5% based on isocyanate groups.

[0004] However, the reaction between the blocked isocyanate and the active hydrogen group in the main component progresses little by little even at room temperature, so that the viscosity increases and finally gels.
This tendency is remarkable in a paint containing a low-temperature dissociated blocked isocyanate. JP-A-8-104726, JP-A-8-225509, and the like do not take this point into account, and thus cause concerns about long-term preservation of a paint containing a main agent and a curing agent.

[0005] Japanese Patent Application Laid-Open No. 7-258598 discloses a study of the storage stability of a paint containing a main agent and a curing agent.
An oxime-based blocking agent is preferred for this,
There is no description about 3,5-dimethylpyrazole, and there is a description that the curing temperature is 130 ° C. and the temperature is low. However, JP-A-7-258598 does not consider the compatibility between the main agent and the curing agent, especially when an acrylic resin is used as the main agent, so that the coating film may be fogged or the gloss may be insufficient. There is. Further, a coating using a blocked isocyanate blocked with an oxime-based compound tends to have a problem that the degree of yellowing is slightly large during baking.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a paint and a coating method which can be baked at a low temperature, have excellent storage stability, and have good coating appearance.

[0007]

As a result of diligent studies by the present inventors, it has been found that a one-part thermosetting paint containing a specific blocked isocyanate and a catalyst can solve the above-mentioned problems, and to complete the present invention. Reached.

That is, the present invention provides (1) a blocked isocyanate (B) comprising an active hydrogen group-containing resin (A), a polyisocyanate (B1) and a blocking agent (B2);
In the one-component thermosetting paint containing the catalyst (C), (B
1) contains an aliphatic diisocyanate (b1) residue, a glycol (b2) residue having a side chain having a molecular weight of 500 or less, an isocyanurate group, and a urethane group, and (b2) in (B1) ) Is 0.5
(B2) contains 3,5-dimethylpyrazole, and the molar ratio of the active hydrogen group (AH) of (B2) to the isocyanate group (NCO) of (B1) is , 1.15 ≦ AH / NCO ≦ 4.00,
The one-component thermosetting paint, wherein the amount of (C) added is 2.0% by mass or less based on the total amount of (A) and (B).

Further, the present invention is (2) a coating method, characterized in that the one-part thermosetting paint of (1) or (2) is baked at 90 to 140 ° C.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The one-part thermosetting paint of the present invention contains the active hydrogen group-containing resin (A), the blocked isocyanate (B), and the catalyst (C) as essential components. Active hydrogen group-containing resin (A)
Is not particularly limited as long as it has an active hydrogen group, polyurethane resin, polyamide resin, saturated or unsaturated polyester resin, alkyd resin modified with saturated fatty acid or unsaturated fatty acid, acrylic resin, fluororesin, epoxy resin, Cellulose resins and the like can be mentioned. In the present invention, in consideration of the coating performance and cost such as gloss, texture, hardness, durability, flexibility, and drying property, saturated or unsaturated polyester resin, alkyd resin modified with saturated fatty acid or unsaturated fatty acid And an acrylic resin.

The blocked isocyanate (B) used in the present invention includes an aliphatic diisocyanate (b1) residue, a glycol (b2) residue having a side chain and a molecular weight of 500 or less,
It comprises a polyisocyanate (B1) containing an isocyanurate group and a urethane group and a blocking agent (B2).

The polyisocyanate (B1) is preferably obtained by the following production methods (a) to (c). (A): A method of further reacting (b1) an aliphatic diisocyanate with (b2) a glycol having a side chain and having a molecular weight of 500 or less to obtain an isocyanate group-terminated prepolymer. (B): A method in which (b1) an aliphatic diisocyanate is reacted with (b2) a glycol having a side chain and a molecular weight of 500 or less, and simultaneously with isocyanuration. (C): (b1) an isocyanurate-forming reaction of an aliphatic diisocyanate, (b2) a molecular weight of 5 having a side chain
A method of reacting a glycol of 00 or less. In the present invention, the polyisocyanate obtained by the method (a) is preferable in consideration of the production time and the complexity of the production process.

(B1) As the aliphatic diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, decamethylene diisocyanate, 2
-Methylpentane-1,5-diisocyanate, lysine diisocyanate, and the like. These diisocyanates may be used in combination of two or more.

In the present invention, an organic diisocyanate other than (b1) can be used as required, for example, for improving the strength of the coating film. As organic diisocyanates other than (b1), 2,4-tolylene diisocyanate, 2,6-
Tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2, 2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-
4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-
1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,
Aromatic diisocyanates such as 4'-diisocyanate,
Xylylene-1,4-diisocyanate, xylylene-
1,3-diisocyanate, tetramethylxylylene-
1,4-diisocyanate, tetramethylxylylene-
Alicyclic diisocyanates such as araliphatic diisocyanates such as 1,3-diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogenated tetramethylxylylene diisocyanate. These (b)
When using an organic diisocyanate other than 1),
It is less than 10 mol% with respect to (b1). This is (b
This is because if the amount of the organic diisocyanate other than 1) is too large, the weather resistance, flexibility, and the like of the coating film are likely to decrease.

(B2) Examples of the glycol having a side chain having a molecular weight of 500 or less include 1,2-propanediol,
2-butanediol, 1,3-butanediol, 2-methyl-1,5-pentanediol, 3-methyl-1,5
-Pentanediol, neopentyl glycol, 2,2
-Diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2,
4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2-n-hexadecane-1,2-ethylene glycol, 2-n-eicosan-
1,2-ethylene glycol, 2-n-octacosan-
1,2-ethylene glycol, hydrogenated bisphenol A, dipropylene glycol, 3-hydroxy-2,2
-Dimethylpropyl-3-hydroxy-2,2-dimethylpropionate and the like. These glycols may be used in combination of two or more.

In the present invention, if necessary, an active hydrogen group-containing compound other than (b2) may be used in combination for the purpose of further improving the strength of the coating film and the compatibility with the (A) active hydrogen group-containing resin. Can be. Active hydrogen group-containing compounds other than (b2) include so-called long-chain polyols such as polyester polyols, polyether polyols and polycarbonate polyols, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5 -Low molecular weight glycols having no side chains such as -pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-dencandiol, Examples include trifunctional or higher functional low molecular weight polyols such as glycerin, trimethylolpropane, and pentaerythritol. These (b2)
When using an active hydrogen group-containing compound other than (b)
Less than 10 mol% with respect to 2). If the amount of the long-chain polyol is too large, the effective isocyanate group content of the blocked isocyanate (= the isocyanate group content generated by the dissociation of the blocking agent) becomes small, the crosslink density decreases, and the coating film strength decreases. Cheap. If the amount of the low-molecular glycol having no side chain is too large, the compatibility between the obtained (B) blocked isocyanate and (A) the resin containing an active hydrogen group is likely to be reduced. If the amount of the low-molecular polyol is too large, gelation tends to occur during the production of (B1) polyisocyanate.

The above (b2) has a hydrocarbon group as a side chain, and by introducing (b2) into the molecular skeleton of the polyisocyanate, (B) a blocked isocyanate and (A) an active hydrogen group Since the compatibility with the contained resin, particularly the acrylic resin, is improved, gloss and sharpness when formed into a coating film are improved. In addition, since (b2) is bifunctional, (B1) is introduced not at the end of the polyisocyanate molecule but at (close to) the center of the molecular chain, and from this aspect also contributes to the improvement of compatibility. I do.

The (B1) polyisocyanate of the present invention comprises
Since it has an isocyanurate ring structure, it has a sufficient average number of functional groups, heat resistance, weather resistance, and the like.

In the present invention, the content of the glycol having a side chain (b1) in the polyisocyanate (B1) is 0.5 to 15.0% by mass, preferably 0.6 to 1% by mass.
3.0% by mass. When the content of (b2) is too small, the compatibility with (A) the active hydrogen group-containing resin becomes poor, and the gloss and sharpness of the coating film are liable to decrease. Also, (b
If the content of 2) is too large, the effective isocyanate group content of the blocked isocyanate (B) becomes small, so that the crosslink density of the coating film becomes insufficient and the coating film strength tends to decrease.

(B1) The isocyanate group content of the polyisocyanate is preferably from 10.0 to 30.0% by mass, more preferably from 12.0 to 28.0%. When the isocyanate group content is less than the lower limit, the strength of the coating film tends to decrease.
If it exceeds the upper limit, the coating film tends to be brittle.

(B1) The average number of functional groups in the polyisocyanate is preferably 2.0 to 10.0, more preferably 2.
2 to 8.0. If the average number of functional groups is out of the range, the crosslinking efficiency tends to decrease. The average number of functional groups is calculated from the isocyanate group content and the number average molecular weight.

The viscosity of the polyisocyanate (B1) is preferably not more than 10,000 mPa · s at 25 ° C. and more preferably 8,000 mPa · s at a solid content of 100% by mass. If the viscosity is too high, the workability tends to deteriorate.

The blocking agent used in the present invention is 3,5-
It contains dimethylpyrazole, and preferably 90 mol% or more of the blocking agent (B2) is 3,5-dimethylpyrazole. (B2) By using 3,5-dimethylpyrazole as the blocking agent, baking at a low temperature of 90 to 140 ° C. becomes possible.

In the present invention, if necessary, other than 3,5-dimethylpyrazole can be used in combination with the blocking agent (B2). Specifically, phenol, cresol, ethylphenol, butylphenol, 2-hydroxypyridine, dimethyl malonate, diethyl malonate,
Methyl acetoacetate, acetylacetone, butyl mercaptan, dodecyl mercaptan, acetanilide, acetate amide, ε-caprolactam, δ-valerolactam, γ-
Butyrolactam, succinimide, maleic imide,
Examples thereof include imidazole, 2-methylimidazole, urea, thiourea, ethylene urea, formaldoxime, acetoaldoxime, acetone oxime methyl ethyl ketoxime, cyclohexanone oxime, carbazole, and triazole.

In the present invention, for the purpose of further improving the compatibility between (A) a resin containing an active hydrogen group, particularly an acrylic resin, and (B) a blocked isocyanate, if necessary, other than the above (B2) The monofunctional active hydrogen group-containing compound of the formula (1) can be used. (B2) Functional active hydrogen group-containing compounds other than the blocking agent include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, pentanol, hexanol, heptanol, octanol, 2
-Monools such as ethylhexanol, benzyl alcohol, cyclohexanol, alkylene glycol monoalkyl alcohol, ethylamine, butylamine,
Monoamines such as aniline, diethylamine, dibutylamine, and methylaniline; hydroxy fatty acids and their alkyl esters; polyesters having one active hydrogen group in the molecule; polyethers; polycarbonates; When a monofunctional active hydrogen group-containing compound other than (B2) is used, the amount used is less than 0.1 equivalent to the isocyanate group of (B1) polyisocyanate. If the amount of the monofunctional active hydrogen group-containing compound other than (B2) is too large, the effective isocyanate group content in (B) blocked isocyanate becomes small, and the coating density tends to decrease due to the decrease in crosslinking density. Is likely to occur.

In the present invention, the molar ratio of (B2) the active hydrogen group (AH) of the blocking agent to (B1) the isocyanate group (NCO) in the polyisocyanate is 1.15 ≦
AH / NCO ≦ 4.00, preferably 1.20 ≦
AH / NCO ≦ 3.80. When the content of (B2) is too small, the viscosity tends to increase when a paint containing (A) an active hydrogen group-containing resin and (B) a blocked isocyanate is stored for a long time. When the amount of (B2) is too large, the amount of the (B2) blocking agent remaining in the coating film becomes unnecessarily large, and the coating film strength tends to decrease, and the effect of suppressing the viscosity increase of the coating material is different from that in the case where the amount is within the appropriate range. It is also uneconomic because it is not.

The blocked isocyanate (B) used in the present invention can be used by dissolving or dispersing it in an inert solvent or a liquid plasticizer commonly used in the polyurethane industry.
Examples of the inert solvent include aromatic hydrocarbon solvents such as toluene and xylene, aliphatic hydrocarbon solvents such as n-hexane, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ethyl acetate, and butyl acetate. And ether solvents such as diethyl ether, tetrahydrofuran and 1,4-dioxane, and glycol ether ester solvents such as ethylene glycol monomethyl ether acetate. Examples of the liquid plasticizer include dioctyl phthalate.

The effective isocyanate group content of the blocked isocyanate (B) used in the present invention is from 5.0 to 20.0.
% By mass, more preferably 7.0 to 18.0% by mass. If the effective isocyanate group content is outside this range, the strength of the coating film tends to decrease.

In the present invention, the preferred mixing ratio of (A) the active hydrogen group-containing resin and (B) the blocked isocyanate is (A) the active hydrogen group of the active hydrogen group-containing resin / (B) the effective isocyanate group of the blocked isocyanate. = 1/9
９9/1 (molar ratio), preferably 2/8 to 8/2.
(Molar ratio). If the ratio is out of this range, it becomes easy to form a coating film.

In the present invention, (B) a dissociation reaction of a blocked isocyanate group in a blocked isocyanate,
A catalyst (C) is used to promote the reaction between the generated isocyanate groups and the active hydrogen groups in the (A) active hydrogen group-containing resin. Examples of the (C) catalyst include organotin-based catalysts such as dibutyltin dilaurate, dioctyltin dilaurate and stannas octoate, triethylenediamine, triethylamine, N, N, N ', N'-tetramethylpropylenediamine, N, N , N ', N'-tetrakis (2-hydroxypropyl) ethylenediamine, N-methylmorpholine, 1,2-dimethylimidazole,
5-diaza-bicyclo (4,3,0) nonene-5,1,
8-diaza-bicyclo (5,4,0) -undecene-7
Amine catalysts such as borane salts, phenol salts, octylates and carbonates of these amine catalysts; metal carboxylate catalysts such as magnesium naphthenate, lead naphthenate and potassium acetate; triethyl Examples thereof include phosphorus-based catalysts such as phosphine and tribenzylphosphine, and alkoxide-based catalysts such as sodium methoxide.

The amount of the catalyst (C) added is 2.0% by mass or less, preferably 0.001% or less, based on the total amount of the (A) resin containing an active hydrogen group and the (B) blocked isocyanate.
It is at most 1.8 mass%. (C) If the added amount of the catalyst is too large, it tends to increase the viscosity of the paint and cause discoloration of the coating film at the time of painting. The timing of blending the catalyst (C) in the production of the paint is not particularly limited, but is preferably at the end of the production process.

In the one-part thermosetting paint of the present invention, if necessary, a solvent, a pigment, a dye, a dispersion stabilizer, a viscosity modifier, a leveling agent, an anti-gelling agent, a light stabilizer, an antioxidant, and an ultraviolet absorber Various additives such as an agent, a heat resistance improver, an inorganic or organic filler, a plasticizer, a lubricant, an antistatic agent and a reinforcing agent can be added.

The one-part thermosetting coating composition of the present invention is generally prepared by mixing (A) an active hydrogen group-containing resin solution with various additives, dispersing and mixing, and then (B) blocking isocyanate. (C) It is obtained by blending a catalyst and mixing uniformly. As the paint blending device, known devices such as a grind mill and a ball mill can be used.

Next, a preferred method for producing the (B) blocked isocyanate used in the present invention will be described. The (B) blocked isocyanate used in the present invention comprises (B1)
The (B2) polyisocyanate is obtained by reacting the polyisocyanate with a blocking agent. The (B1) polyisocyanate is preferably produced by: (a) an isocyanate group-terminated prepolymer obtained by reacting an organic isocyanate with an active hydrogen group-containing compound. Is further reacted with an isocyanurate. (B) A method in which an organic isocyanate is reacted with an active hydrogen group-containing compound and simultaneously with an isocyanuration reaction. Is mentioned. If, for example, (A) the viscosity of the active hydrogen group-containing resin (solution) is low and (B) the viscosity of the blocked isocyanate is high, the mixing property deteriorates and the workability in the production of paint is adversely affected, (A) The method is more preferable because the viscosity is reduced.

The reaction for obtaining the isocyanate group-terminated prepolymer can be carried out under the conditions of a usual urethane reaction. The reaction temperature is suitably in the range of 20 to 120 ° C.

In the isocyanuration reaction, for example, tertiary amines, alkyl-substituted ethyleneimines, trialkylphosphines, metal salts of acetylacetone, metal salts of various organic acids, etc., which are isocyanuration catalysts, are used alone or in combination. Used as necessary, a co-catalyst,
For example, phenolic hydroxyl group-containing compounds, alcoholic hydroxyl group-containing compounds, etc.
The reaction is carried out at a reaction temperature of 0 ° C. in the absence of solvents or in the presence of inert solvents or liquid plasticizers customary in the polyurethane industry mentioned above. Termination of the isocyanuration reaction is performed by phosphoric acid,
It becomes possible by inactivating the isocyanuration catalyst by adding a terminator such as paratoluenesulfonic acid, paratoluenesulfonic acid ester, and sulfur. Thereafter, it is preferable to remove free isocyanate monomer in terms of odor.

Next, the obtained (B1) polyisocyanate is reacted with the (B2) blocking agent. This reaction can be performed under the conditions of a usual urethanization reaction. The reaction temperature is suitably in the range of 20 to 120 ° C. (B1) The charge ratio of the polyisocyanate and the (B2) blocking agent is as follows:
(B1) The amount is 1.15 to 4.00 mol, preferably 1.20 to 3.80 mol, per 1 mol of free isocyanate groups of the polyisocyanate.

In the coating method of the present invention, the coating material described
Baking at 140 ° C, preferably 90 to 115 ° C, is an essential condition. The baking time is about 15 to 60 minutes. If the baking temperature is too low, the baking time tends to be longer than necessary. On the other hand, if the baking temperature is too high, the coating film tends to be discolored. Examples of the coating machine include an airless spray machine, an air spray machine, an electrostatic coating machine, a dip coating machine, a roll coating machine, and a brush.

[0039]

The coating composition of the present invention contains 3,5-
Since dimethylpyrazole is used and the blocking agent is present in excess of the effective isocyanate groups, the paint containing the active hydrogen group-containing resin has excellent long-term storage stability and low baking temperature. Further, since a glycol having a side chain is introduced into the base polyisocyanate skeleton in the blocked isocyanate, the coating film is excellent in gloss and sharpness. Further, the coating method of the present invention is economical and has a small burden on the environment because the baking temperature is low.

[0040]

EXAMPLES The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In Examples and Comparative Examples, “parts” were used.
Means “parts by mass”, and “%” means “% by mass”.

[Synthesis of Polyisocyanate] Synthesis Example 1 In a reactor equipped with a stirrer, a thermometer, a nitrogen seal tube, and a cooler, 300.0 parts of HDI and 2,3-BD of 1,3-BD were added.
After charging 8 parts, the inside of the reactor was purged with nitrogen, heated to 80 ° C. while stirring, and reacted at the same temperature for 2 hours. The isocyanate group content of this reaction solution was 48.6%. Next, 0.06 parts of potassium caprate and pheno-
Then, isocyanurate-forming reaction was performed at 60 ° C. for 6 hours. 0.042 parts of phosphoric acid was added to the reaction solution, and the mixture was stirred at the reaction temperature for 1 hour.
It was removed by thin-film distillation under the condition of 1.3 kPa to obtain polyisocyanate P-1. The resulting polyisocyanate P-1 was a pale yellow transparent liquid having an isocyanate group content of 2
0.8%, glycol content 2.6%, viscosity 2,000
mPa · s (25 ° C), average number of functional groups 3.8, free HD
I content 0.3%, FT-IR and ¹³ C-NMR
As a result, the presence of an isocyanate group and an isocyanurate group was confirmed. The yield was 35%.

Synthesis Examples 2, 3, 5 Polyisocyanates P-2, 3, 5 in the same reactor as in Synthesis Example 1 and using the starting materials shown in Table 1.
Was synthesized. Table 1 shows the synthesis results.

Synthesis Example 4 300.0 parts of HDI was charged into the same reactor as in Synthesis Example 1, and the inside of the reactor was replaced with nitrogen to obtain 0.06 part of potassium caprate and 0.3 part of phenol. Add 6 parts at 60 ° C
A time isocyanuration reaction was performed. 0.042 parts of phosphoric acid was added to the reaction solution, and after stirring at the reaction temperature for 1 hour, free HDI was removed by thin-film distillation at 120 ° C. and 1.3 kPa to obtain polyisocyanate P-4. The obtained polyisocyanate P-4 was a pale yellow transparent liquid, an isocyanate group content of 23.5%, and a glycol content of 0.1.
0%, viscosity 1,500 mPa · s (25 ° C.), average number of functional groups 3.7, free HDI content 0.2%, FT-
IR and ¹³ C-NMR confirmed the presence of isocyanate groups and isocyanurate groups. The yield was 37%.

[0044]

[Table 1]

In Synthesis Examples 1 to 5 and Table 1, HDI: hexamethylene diisocyanate 1,3-BD: 1,3-butanediol NPG: neopentyl glycol 1,4-BD: 1,4-butanediol

[Calculation Method of Average Functional Group Number of Polyisocyanate] 1) The number average molecular weight (a) per isocyanate group is determined from the isocyanate group content. 2) GPC (gel permeation chromatography)
To determine the number average molecular weight (b) of the polyisocyanate. The measurement was performed using a polystyrene calibration curve. 3) The value of b / a is the average number of functional groups.

[Synthesis of Blocked Isocyanate] Synthesis Examples 6 to 17 The starting materials shown in Tables 2 and 3 were reacted in the same reactor as in Synthesis Example 1 at 80 ° C. for 2 hours to obtain blocked isocyanates BI-1 to BI-12. I got The synthesis results are shown in Tables 2 and 3.

[0048]

[Table 2]

[0049]

[Table 3]

In Synthesis Examples 6 to 17 and Tables 2 and 3, DMP: 3,5-dimethylpyrazole ε-CL: ε-caprolactam MEKO: methyl ethyl ketoxime PMA: propylene glycol monomethyl ether acetate B2 / B1: active hydrogen in blocking agent Group / isocyanate group in polyisocyanate (molar ratio)

[Method of Measuring Effective Isocyanate Group Content] (1) Approximately 1.0-2.
0 g is precisely weighed into an Erlenmeyer flask (300 ml in internal volume) having a “grinding” opening. (2) 25 ml of a 0.5 mol / l dibutylamine-monochlorobenzene solution was added to the Erlenmeyer flask, and a solvent having a boiling point of 170 ° C. or more and zeolite were added. Install a tube cooler. (3) Place the Erlenmeyer flask on a heating plate prepared in advance and wait 3 seconds after the solvent in the flask starts boiling.
Incubate for 0 minutes. (4) After that, the Erlenmeyer flask is removed from the heating plate and cooled to room temperature.
Pour 30 ml of methanol and flush the inner wall of the cooler with the methanol. (5) After removing the condenser from the Erlenmeyer flask, 100 ml of methanol and one drop of bromophenol blue indicator were put into the Erlenmeyer flask, and a 0.5 mol / l hydrochloric acid standard solution was added to the contents of the flask. Perform a back titration with. At this time, the titer of the hydrochloric acid standard solution required for titration of the sample is defined as A (ml). (6) Except that the above-mentioned heating is not performed, the above (1) to
Perform the same operation as in (4) to obtain a “blank” sample. The blank is titrated as in (5) above. At this time, the titer of the hydrochloric acid standard solution required for the blank titration is defined as B (ml). (7) The endpoint of the titration is the point at which the blue color of the bromophenol blue indicator changes to yellow. (8) The effective isocyanate group content is calculated using the following formula.

[0052]

(Equation 1)

In the above formula, A: titration of 0.5 mol / l hydrochloric acid standard solution required for sample titration (ml) B: titration of 0.5 mol / l hydrochloric acid standard solution required for blank titration (Ml) S: Sampling amount (g)

[Formulation of Clear Coating] Examples 1 to 5, Comparative Examples 1 to 10 An acrylic resin, a blocked isocyanate, a catalyst and methyl ethyl ketone were mixed to prepare a coating having a total solid content of 50%. ~ 15. In addition, acrylic resin is Acridic (registered trademark) A-801 (hydroxyl-containing acrylic resin, hydroxyl value of resin = 100 mg)
KOH / g, solid content = 50%, manufactured by Dainippon Ink and Chemicals, Inc.), and dibutyltin dilaurate was used as a catalyst. The mixing ratio of the acrylic resin and the blocked isocyanate is such that the hydroxyl groups in the acrylic resin and the effective isocyanate groups in the blocked isocyanate are equivalent.
The catalyst addition amount is a ratio to the total amount of the solid content of the acrylic resin and the solid content of the blocked isocyanate.
Tables 4 to 6 show the blocked isocyanates used in the paints and the amounts of catalysts added.

[Evaluation of paint] Stability of the obtained paint over time at 40 ° C., curing temperature, curing temperature over time at 40 ° C., storage stability at 0 ° C., yellowing degree (Δb) and gloss of the coating film・ Haze ・
The solvent resistance was tested. The results are shown in Tables 4 to 6.

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

[Table 6]

[Aging stability test] The obtained clear coating was stored at 40 ° C for one week and evaluated by the thickening ratio represented by the following formula. As this value is smaller, the stability over time is better, and 10% or less is a pass level.

[0060]

(Equation 2)

When the active hydrogen group of the blocking agent in the blocked isocyanate / isocyanate group of the polyisocyanate is less than the lower limit (Comparative Examples 1 and 9) and when the amount of the catalyst added exceeds the upper limit (Comparative Example 8), the thickening ratio is increased. Especially big. On the other hand, in all the examples, such a thing was not recognized.

[Measurement of Curing Temperature] The clear paint immediately after blending and the clear paint stored at 40 ° C. for one week were applied to a bond steel plate so as to have a thickness of about 100 μm (wet).
After heating for 0 minutes and cooling to room temperature, the coated surface was rubbed with absorbent cotton impregnated with methyl ethyl ketone, and the lowest temperature at which the coating film did not fall was defined as the curing temperature. The heating temperature is
80 ° C, 90 ° C ... 160 ° C, 170 ° C, and 10 levels in 10 ° C increments.

When the blocking agent of the blocked isocyanate did not contain 3,5-dimethylpyrazole (Comparative Examples 3 and 10) and when no catalyst was added (Comparative Example 7),
Curing temperature increased. On the other hand, in all the examples, such a thing was not recognized.

[Low-temperature storage stability test] The appearance of the obtained clear coating after storage at 0 ° C for 1 month was observed and evaluated. The acceptable level is that no sediment or suspended matter can be confirmed. ：: No precipitate, suspended matter, etc. could be confirmed. ×: Precipitates, suspended matters, etc. can be confirmed.

When the active hydrogen group of the blocking agent in the blocked isocyanate / the isocyanate group of the polyisocyanate exceeds the upper limit (Comparative Example 2) and when the content of the side chain glycol in the polyisocyanate is less than the lower limit (Comparative Example 5) Had poor low-temperature storage stability. On the other hand, in all the examples, such a thing was not recognized.

[Measurement of Yellowing Degree (Δb)] Each clear paint was applied to a bond steel plate so as to have a thickness of about 100 μm (wet), and baked at the curing temperature determined by the above-mentioned curing temperature measurement for 30 minutes. Was measured for color difference. Thereafter, the coated sample was further baked at 200 ° C. for 30 minutes, the color difference of the coating film was measured, and the yellowing degree (Δb) was obtained. The smaller this value is, the better the heat resistance is, and 1.0 or less is a pass level.

When the active hydrogen group of the blocking agent in the blocked isocyanate / isocyanate group of the polyisocyanate exceeds the upper limit (Comparative Example 2) and when the amount of the catalyst exceeds the upper limit (Comparative Example 8), Δb is 1.0. Crossed. On the other hand, in all the examples, such a thing was not recognized.

[Measurement of Gloss and Haze] Each clear paint was applied to a bond steel plate so as to have a thickness of about 100 μm (wet), baked at the curing temperature determined by the above curing temperature measurement for 30 minutes, and then the gloss of the painted surface was measured. Haze was measured. 60 °
The specular gloss was measured according to JIS K5660-1995. The larger this value is, the better it is, and 80 or more is a pass level. Haze was measured according to the method prescribed in the measuring instrument handling method. The measuring method is substantially the same as the method for measuring the specular glossiness at 60 °. The smaller this value is, the better it is, and 60 or less is a pass level.・ Measuring machine: Haze-Gloss Reflectometer (by Big-Gardner)

When the content of the glycol having a side chain in the polyisocyanate is less than the lower limit (Comparative Example 5) and when the glycol has no side chain (Comparative Example 6), the gloss is low and the haze is large. there were. On the other hand, in all the examples, such a thing was not recognized.

[Solvent Resistance Test] Each clear coating was applied to a bond steel plate so as to have a thickness of about 100 μm (wet), baked at the curing temperature determined by the above curing temperature measurement for 30 minutes, and methyl ethyl ketone was applied to the painted surface. The impregnated cotton wool was rubbed 100 times and the state of the coating film was observed. The pass level is that no change is observed in the appearance of the coating film. ：: No change in the appearance of the coating film was observed. X: "Rough", "cloudy", etc. are recognized in the coating film appearance.

When the active hydrogen group of the blocking agent in the blocked isocyanate / isocyanate group of the polyisocyanate exceeds the upper limit (Comparative Example 2), and when the content of the side chain glycol in the polyisocyanate exceeds the upper limit (Comparative Example 4). ) Had poor solvent resistance.
On the other hand, in all the examples, such a thing was not recognized.

As shown in Tables 4 to 6, the one-part thermosetting paint of the present invention has a low curing temperature, good gloss and sharpness of the coating film, and excellent stability over time. there were. The one-part heat-curing paint of the present invention is used for top coating of automobiles, anti-chipping paint, electrodeposition paint, paint for automotive parts, pre-coated metal for metal parts such as home appliances and office equipment, rust preventive paint, and building materials. Can be used for paints and plastic paints. Further, since the coating method of the present invention is lower than the conventional baking temperature, the energy cost required for coating can be reduced.

Continued on the front page F term (reference) 4J034 BA03 CA04 CB03 CB07 CC03 CC08 CC09 CC15 CC23 CC26 CC52 CC61 CC67 CD04 CD06 DA01 DB03 DB07 DF01 DF29 DK01 DL01 DN03 DP15 DP18 EA08 HA01 HA02 HA07 HA08 HA09 HA11 HB05 HB07 HC03 HC46 HC26 HC61 HC71 HD15 KC17 KD01 KD02 KD04 KD12 KD17 KE02 QA03 QB12 QC05 RA07 4J038 DG101 DG111 DG161 DG171 DG191 DG221 DG291 DG301 GA03 JA23 JA45 JA49 JA64 JB01 JB32 JC21 JC38 JC39 KA04 MA14 NA01

Claims (2)

[Claims] 1. A one-pack thermosetting coating material containing an active hydrogen group-containing resin (A), a blocked isocyanate (B) comprising a polyisocyanate (B1) and a blocking agent (B2), and a catalyst (C), wherein (B1) Contains an aliphatic diisocyanate (b1) residue, a glycol (b2) residue having a side chain having a molecular weight of 500 or less, an isocyanurate group, and a urethane group, and (B2) in (B1) (B2) contains 3,5-dimethylpyrazole, the active hydrogen group (AH) in (B2) and the isocyanate group (B1) in (B1). NCO) is 1.15 ≦ AH / NCO
≦ 4.00, and the addition amount of (C) is 2.0% by mass or less based on the total amount of (A) and (B). 2. A coating method, characterized in that the one-component thermosetting paint according to claim 1 or 2 is baked at 90 to 140 ° C.