JPH02242867A - Thermosetting coating composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition, consisting essentially of a hydroxyl group-containing resin, amino resin and blocked isocyanate compound, having a specific reaction starting temperature and excellent in acid and scuff resistance of films. CONSTITUTION:The objective composition, consisting of (A) 50-90wt.% hydroxyl group-containing resin (e.g. an acrylic resin), (B) 10-50wt.% amino resin (e.g. methylolated amino resin) and (C) 1-40wt.% blocked polyisocyanate compound (e.g. m- or p-xylylene diisocyanate), having a reaction starting temperature of the components (A) and (C) within the range of -20 to +50 deg.C of that of the components (A) and (B) and capable of eliminating hydroxyl groups in cured films and simultaneously forming the films with a high crosslinking density.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermosetting coating composition, and more particularly, to a thermosetting coating composition that provides a coating film with excellent acid resistance and scratch resistance. .

(Conventional technology and its problems) Conventionally, for painting exterior panels of automobiles, etc., which require a highly finished appearance such as smoothness, gloss, and sharpness, heat treatment, which mainly consists of a hydroxyl group-containing resin and an amino resin, has been used. Curable paints are widely used.

However, in recent years, damage caused by acid rain (generally referred to as rain with a pH of 4 or less) has become a serious social problem, as air pollution has progressed and forests wither. Etching, bleaching, stains, etc. can be seen due to rain, and the surface of the top coat on the exterior of the car is prone to scratches due to collisions with sand and dust while driving or friction from car wash brushes. It has defects and causes a deterioration in the appearance of the painted finish.
It is strongly desired that these deficiencies be resolved.

(Means for Solving the Problems) The present inventor has achieved dramatic improvements in acid resistance and scratch resistance without impairing the weather resistance, solvent resistance, mechanical properties, and appearance of the paint film. We conducted intensive research with the aim of As a result, when (C) a blocked polyisocyanate compound is added to a thermosetting paint whose main components are (A) a hydroxyl group-containing resin and (B) an amino acid resin, it is found that no residue remains in the curing reaction with the (B) component. 8) By reacting the hydroxyl groups in the component with the polyisocyanate-1 compound from which the blocking agent has been dissociated, (also, the unreacted methylol groups or imino groups in the component (B) may also react with the polyisocyanate compound. By reacting), all (or most) of the hydroxyl groups in the cured coating film can be eliminated, and a coating film with high crosslinking density can be formed, and as a result, all of the above-mentioned defects can be eliminated, and the present invention has been made. I was able to complete it.

In addition, in order to obtain a coating film with such a high crosslinking density, the temperature at which the reaction starts with active hydrogen for the above-mentioned component (C) etc. is (
It has also been found that the reaction temperature needs to be between -20°C and +50°C based on the reaction initiation temperature between component A) and component (B).

That is, the present invention comprises (A) a hydroxyl group-containing resin, (B) an amino resin, and a blocked polyisocyanate compound (
C) is the main component, and the reaction initiation temperature between the (C) component and (A) component is -20 to +50% based on the reaction initiation temperature between the (A) component and (B) component. The present invention relates to a thermosetting coating composition characterized in that the temperature is within the range of ℃.

Next, the components (A)=(C) in the composition of the present invention will be specifically explained.

Component (A): Hydroxyl group-containing resin The hydroxyl group-containing resin is a resin having two or more hydroxyl groups in at least one molecule, and examples thereof include acrylic resins, polyester resins, and alkyd resins. Among these, acrylic resins are preferred because they provide coating films with excellent weather resistance.

Among these, the acrylic resin can be a copolymer of a hydroxyl group-containing vinyl monomer and another vinyl monomer. Examples of hydroxyl group-containing monomers include 02-C24 hydroxyalkyl esters of acrylic acid or methacrylic acid, such as 2-hydroxyethyl acrylic 1/-1 to 2-hydroxytoethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl acrylate, etc. N-methylol acrylamide, N
-Methylolmethacrylamide, N-hydroxyethylacrylamide, N-hydroxyethylmethacrylamide, N,N-dihydroxyethylacrylamide, N,
Acrylic acid or methacrylic acid mono- or di-01 such as N-dihydroxyethyl methacrylamide etc.
~CI2hydroxyalkylamide; and the like. Examples of other vinyl monomers include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 1so-butyl acrylate, 3-pentyl acrylate, hexyl acrylate, 2-hebutyl acrylate, octyl acrylate, 2-octyl acrylate, C of acrylic acids such as nonyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-ethyl butyl acrylate
.

~24 alkyl ester; methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, 1so-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-
C3-24 alkyl esters of methacrylic acid such as ethylhexyl methacrylate, decyl methacrylate, lauryl methacrylate, and stearyl methacrylate; carboxyl group-containing and nyl monomers such as acrylic acid and methacrylic acid; styrene, vinyltoluene, gnosidyl methacrylate, etc. can give.

The hydroxyl group-containing acrylic resin can be made into a solution type or a dispersion type by a polymerization method. Further, the hydroxyl group-containing acrylic resin has a hydroxyl value of 20 to 150, preferably 30 to 80. Acid value is 0-50, preferably 5-20
．． It is desirable that the weight average molecular weight is in the range of 3,000-100,000, preferably 5,000-30,000.

Hydroxyl group-containing polyester resins include phthalic acid and its acid anhydride, isophthalic acid, terephthalic acid, trimellitic acid and its acid anhydride, hexahydrophthalic acid and its acid anhydride, succinic acid, adipic acid, pimelic acid, and sebacin. acids, polybasic acid components such as brassylic acid, and polyols such as ethylene glycol, -diethylene glycol, propylene glycol, neopentyl glycol, 1,6-hexanediol, trimethylolpropane, glycerin, pentaerythritol, and tricyclodecane dimetatool. It can be produced by condensation polymerization of the components according to a conventional method. At this time, the molecular weight may be adjusted by using, for example, benzoic acid, pt-butylbenzoic acid, etc. as an end-capping agent. Furthermore, fatty acids such as coconut oil fatty acids, tall oil fatty acids, and castor oil fatty acids may be used as a part of the acid component and may be oil-modified.

Further, a polyester resin modified by chain extension with an aliphatic polyisocyanate such as 1,6-hexamethylene diisocyanate or ε-caprolactone may also be used.

These polyester resins must have a hydroxyl value in order to be crosslinked and cured, and based on the hydroxyl value, the
150, preferably in the range of 30 to 130, and the acid value is 50 or less, preferably 5 to 130.
30 is preferred.

(B) Component Niamino resin Specifically, melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine,
Examples include methylolated amino resins obtained by reacting an amino component such as dicyandiamide with an aldehyde. Examples of the aldehyde include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

Furthermore, etherification of this methylolated amino resin with a suitable alcohol can also be used. Examples of alcohols used for denaturation include methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, Examples include i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol, and the like. When using hexamethoxymethyl melamine or a melamine resin in which a part of its methoxy group is substituted with an alcohol of 04 or higher as an amino resin, for example, a commonly used melamine resin such as para-toluenesulfonic acid, dodecylbenzenesulfonic acid, or their amine neutralized products is used. It is preferable to add a curing catalyst of.

(C) Component diblocked polyisocyanate compound This is a polyisocyanate compound having a small number (average of two isocyanate groups) per molecule, and the isocyanate groups are blocked with a blocking agent.

Examples of the polyisocyanate compound include m- or p-xylylene diisocyanate, 2,4- or 2-
．． 6-tolylene diisocyanate, m-mata is p-phenylene diisocyanate, aromatic diisocyanate compounds such as 4,4'-diphenylmethane diisocyanate,
4.4'-Methylenebis(cyclohexyl isocyanate), methylcyclohexane 2.4 (2,6) diisocyanate, 1,3-(inocyanate methyl)cyclohexane, hexamethylene diisocyanate, isophorone diisocyanate, dimer acid diisocyanate, and other aliphatic ring group) diisocyanate compound; the diisocyanate compound and polyol (ethylene glycol,
(trimethylolpropane, etc.); polymers of the above diisocyanate compounds, billet-type polyisocyanate compounds, and the like.

Volatile low-molecular active hydrogen compounds are used as blocking agents for polyisocyanates, examples of which include methanol, ethanol, propatool, butanol, hexanol, cyclohexanol, benzyl alcohol,
Aliphatic or aromatic monoalcohols such as ethylene glycol monoethyl ether (hereinafter abbreviated as cellosolve), ethylene glycol monobutyl ether (hereinafter abbreviated as butyl cellosolve), hydroxy tertiary amines such as dimethyl- or diethylaminoethanol,
Examples include oximes such as acetoxime and methyl ethyl ketone oxime, active methylene compounds such as acetylacetone, acetoacetate, and malonic acid ester, lactams such as C-caprolactam, and phenol. Among these, aliphatic monoalcohols, oximes, and caprolactam are particularly preferred.

The composition of the present invention can be obtained by dissolving or dispersing the components (A) to (C) in an organic solvent.

In the present invention, the "reaction initiation temperature" is measured using a group pendulum type viscoelasticity meter (manufactured by Orientic Co., Ltd.).
The inflection point of the vibration period according to MODEL DDV 0PA) is the reaction start temperature, and specifically, the size is 25X
Paint for measurement was applied to a 50XO, 5mm tin plate by air spraying to a dry film thickness of approximately 50μ, and the temperature was raised from room temperature to 200℃ at a rate of 3℃/min, and measurements were taken at 30 second intervals. did.

The reaction initiation temperature ■ of component (C) with respect to component (A) is (
Based on the reaction initiation temperature (■) between component A) and component (B), when the temperature is lower than -20°C, the curing reaction between component (A) and component (C) precedes the reaction between component (A) and component (B). The curing reaction with the components is inhibited and the physical performance of the coating decreases, while the +5
When the temperature is higher than 0°C, the reaction between component (A) and component (B) precedes, and the blocking agent of component (C) tends to remain in the coating film without dissociating. Both are unfavorable because the performance will be insufficient.

In the present invention, regarding the constituent proportions of the above-mentioned components (A) to (C), based on the total solid weight percent of components (A) and (B), component (A) is 50 to 90%, and component (B) is 50 to 90%. ) ingredients are 5
A range of 0 to 10% by weight is preferred. Similarly, the amount of component (C) is 1 for the total amount of component (A) and component (B).
~40% by weight, especially 5-20% by weight are suitable.

Examples of the organic solvent for dissolving or dispersing components (A) to (C) include aromatic hydrocarbons such as xylene and toluene; esters such as ethyl acetate, propyl acetate, and butyl acetate; and ketones such as acetone and methyl ethyl ketone. Types: Ether types such as ethylene glycol, cellosolve, butyl cellosolve, cellosolve acetate, etc. can be mentioned. These organic solvents can be used alone or in combination of two or more. Further, from the viewpoint of curability, those having a boiling point of about 150° C. or lower are preferable, but are not limited thereto.

It can be blended so that the amount is %.

The composition of the present invention includes, for example, organic pigments (e.g., quinacridone-based pigments such as quinacridone-based pigments, azo-based pigmentlets such as pigmentlets, phthalocyanine-based materials such as phthalocyanine blue and phthalocyanine green, etc.), inorganic pigments (e.g., titanium oxide,
barium sulfate, calcium carbonate, barida, clay silica, etc.), carbon-based pigments (carbon black), scaly metallic powders (e.g. aluminum, mica-like iron oxide, stainless steel, etc.), anti-rust pigments (e.g. red iron oxide, strontium chromate, etc.) can be used.

In addition to the pigments described above, additives such as ultraviolet absorbers, coating surface conditioners, curing catalysts, and pigment dispersants can be used in the composition of the present invention.

The composition of the present invention can be applied to metals (e.g. steel plates, surface-treated steel plates, etc.)
It can be applied directly to the material to be coated, such as plastic, or to the coated surface of the material to be coated with a primer or primer/intermediate coat. In addition, when used as a top coat for automobile paint, for example, solid color paint or metallic paint for base coat such as 2 coat 1 bake method, 2 coat 2 bake method, etc. and clear paint for top coat; 1 coat It can be used as a solid color paint such as l beta method. Furthermore, the composition of the present invention can also be applied to a clear coated surface that has been finished by a two-coat, one-bake method or a two-coat, two-bake method.

To exemplify the coating method when used as an automobile top coat, for example, the coating composition of the present invention
After adjusting the coating viscosity to a temperature of about 4.20°C for a Ford Cup boat, the dry film thickness is 10 to 60°C by electrostatic coating (bell type, REA type, etc.), air spray coating, etc.
This can be done by painting approximately μ.

The baking conditions for the paint are approximately 120-180°C.
It takes about 10 to 30 minutes.

(Actions and Effects of the Invention) The coating composition of the present invention is an organic solvent-based coating containing components (A) and (B) as vehicle components, and a blocked polyisocyanate compound as a component (C) as an auxiliary crosslinking agent. There is a characteristic in where it is used, and as a result, the hydroxyl group in component (A) that was left behind in the reaction with component (B) is converted into (C).
By reacting with the components and reducing the hydroxyl groups, a coating film with excellent water resistance and acid resistance is formed. In addition, the urethane bond produced by the reaction between the hydroxyl group and the blocked polyisocyanate compound is chemically stable and has excellent chemical resistance and water resistance, as well as mechanical properties and coating surface condition (sag, flow).
An excellent coating film is formed. Furthermore, crosslinking with the blocked polyisocyanate compound forms a cured coating film with a high crosslinking density, making it possible to exhibit excellent solvent resistance and scratch resistance.

(Example) The present invention will be described in more detail with reference to Examples. "Parts" and "%" in Examples and Comparative Examples are based on weight.

1. Example of producing component (A) (A-1): 30 parts of styrene, 40 parts of n-butyl methacrylate, in an organic solvent of 85 parts of xylene and 15 parts of n-butanol.
Monomers of 810 parts of 2-ethylhexyl acrylate, 18 parts of 2-hydroxyethyl acrylate, and 2 parts of acrylic acid were reacted to produce a hydroxyl group-containing product with a weight average molecular weight of 112,000, a hydroxyl value of 87, a resin solid content of 50%, and a Gardner foam viscosity of J. An acrylic resin solution (A-1) was obtained.

(A-2): Monomers of 30 parts of styrene, 30 parts of n-butyl methacrylate, 15 parts of 2-ethylhexyl acrylate, and 25 parts of 2-hydroxyethyl acrylate in an organic solvent of 85 parts of xylol and 15 parts of n-butanol. A hydroxyl-based acrylic resin solution (A-2) having a weight average molecular weight of 10,000, a hydroxyl value of 121, a resin solid content of 50%, and a Gardner foam viscosity of B was obtained.

(A-3): 0.29 mol of isophthalic acid, 0.23 mol of phthalic acid, 0.43 mol of hexahydrophthalic acid, 0.4 mol of trimethylolpropane, 0.6 mol of neopentyl glycol,
Add 0.1 mol of coconut oil fatty acid to the reaction vessel and add 200 to 23
A coconut oil-modified polyester resin having an acid value of 8 and a hydroxyl value of 72 was obtained by condensation polymerization at 0°C. The polyester resin 100
43 parts of xylene was added to this part to prepare a 60% solution (A-3). The viscosity was Y- (25°C, Gardner bubble viscosity).

II, Examples and Comparative Examples Flaming Myu (A-1) 70 parts, 60% knee pants 20SE (Note 2) 3
After stirring a mixture of 0 parts, 80% Coronate #2513 (Note 3), 15 parts, and 1% Raybor #3 (Note 4) 0.01 parts, Tsurupetz 100 was added and the mixture was mixed with four-docup N.
A coating composition was obtained by adjusting the viscosity to 25 seconds using α4.

(Note 2) Manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name, butylated melamine resin (Note 3) Manufactured by Nippon Polyurethane Industries, Ltd., trade name, non-yellowing type blocked isocyanate (low temperature dissociation type).

(Note 4) 70 parts of 1 Weihong λ (A-3), 70 parts of 60% Knee Pan 20 SE, 7
5% desmodule BL-3175*8) 15 parts and 1
After stirring a mixture of 0.01 parts of % Raybor #3, Tsurupez 100 was added and Ford Cup N [L4 was used for 2
The viscosity was adjusted to 5 seconds to obtain a coating composition.

Yuyu Oiwata (A-2) 70 copies, 100% Cymeru 303 (Note 5)
30 copies, 80% Coronate 251,315 copies, NACUR
E5225 (Note 6) 1 part and 1% Raybo 130.0
After stirring 1 part of the mixture, Tsurpez 100 was added, and the viscosity was adjusted to 25 seconds with Ford cup boiling 4 to obtain a coating composition.

(Note 5) Manufactured by Mitsui Cyanamid Co., Ltd., trade name, hexamethoxymethylolmelamine (Note 6) KING INDUSTRIES -INC
Co., Ltd., trade name, amine neutralized product of dodecylbenzenesulfonic acid, 25% active ingredient, 70 parts of Yu (A-1), 30 parts of 60% Kneepan 20SE, and 1% Raybow #30. After stirring the Oi part mixture,
A comparative paint was obtained by adding Tsurpez 100 and adjusting the viscosity to 25 seconds using Ford Cup No. 4.

After stirring a mixture of ratio 1t2J, 70 parts of Tsuki λ (A-3), 30 parts of 60% Kneepan 20SE, and 30.01 parts of 1% Raybow #,
A comparative paint was obtained by adding Tsurpez 100 and adjusting the viscosity to 25 seconds using Ford Cup #4.

(Takumi 1 (A-2) 70 copies, 100% resin Cymes 303 30
part, NACt] RE5225 1 part and 1% Raybo #
After stirring 30.01 parts of the mixture,
was added and the viscosity was adjusted to 25 seconds using a Ford cup #4 to obtain a comparative material.

Kojibori Yo A (A-1) 70 parts, 60% knee pants 203E 30 parts, 8
After stirring a mixture of 15 parts of 0% Coronate 2515*7) and 0.01 parts of 1% Raybor #3,
A comparison use material was obtained by adding Ford Cup N (14 to adjust the viscosity to 25 seconds).

*7) Manufactured by Nippon Polyurethane Kogyo Co., Ltd., trade name, non-yellowing type blocked isocyanate *8) Manufactured by Sumitomo Bayer Urethane Co., Ltd., trade name, non-yellowing type blocked isocyanate The resin blending ratios in the above examples and comparative examples are based on the solid content. This is the converted amount (parts).

(Coating Film Creation Conditions) Painting and cured coating films were created using the paints obtained in the Examples and Comparative Examples.

Dry 20 liters of epoxy cationic electrodeposition paint on a dull steel plate with a thickness of 0 to 8 mm that has been subjected to zinc phosphate chemical conversion treatment.
It was electrodeposited to a color of t, baked at 170°C for 20 minutes, polished with #400 sand vapor, and wiped with petroleum benzene. Next, air spray paint was applied to the car with an intermediate coating of Surf Acer to a dry film thickness of approximately 25 μm.
After baking at 0°C for 30 minutes, it was wet-sanded with #400 sand vapor, drained and dried, and then degreased with petroleum benzene to obtain a test material.

Magiklon Metallic Base Coat HM- on this material
22 (manufactured by Kansai Paint Co., Ltd., trade name) using an air spray gun F5 (manufactured by Meiji Kikai Seisaku Shin, trade name) to a cured film thickness of about 15μ, and after leaving it at room temperature for about 3 minutes,
The coating compositions of Examples 1 to 3 and Comparative Examples 1 to 4 (
Clear coat) was applied to a cured film thickness of approximately 40μ using the air spray gun F5, and then
It was left to set at room temperature for about 10 minutes. Next, this product was heated in an electric hot air dryer at 140° C. for 30 minutes to cure both coating films.

Table 1 summarizes the performance test results of coating films using these coated plates.

Appearance of the second coating film The finished appearance of the second coating film was evaluated based on the following criteria based on gloss and texture.

0: Very good ■：Good condition X: Bad 60° gloss: Specular reflectance was measured at 60°.

Pencil hardness: Measured according to JIS K5400.

Acid resistance: A test coated plate was immersed in a 40% sulfuric acid solution for 172 hours, left at 50°C for 5 hours, washed with water, the coated surface was observed, and evaluated based on the following criteria.

0: No change at all ○: There is no abnormality on the painted surface, but there is a slight difference in level between the immersed and non-soaked areas ×: The painted surface has turned white Water resistance = 40°C warm water After soaking for 240 hours,
After washing with water, the painted surface was observed and evaluated using the following criteria.

0: No change at all ■: Slight loss of gloss Solvent resistance: After wiping the painted surface 10 times with gauze impregnated with xylene, the painted surface was observed and evaluated according to the following criteria.

○: There is almost no change ■: There are noticeable scratches on the painted surface △: The painted surface has swelled 1 and has a tendency to whiten Scratch resistance: A car with a test coating plate attached to the roof was placed in a car wash The condition of the painted surface of the coated plate was observed after the car was washed five times. The car wash machine used was "rPO20FWR C" manufactured by Yasui Sangyo. The evaluation criteria are as follows.

0: Almost no scratches can be seen by visual observation. I passed without getting it.

O: There are some scratches, but The extent of this is extremely slight.

△: Scratches are noticeable by visual observation. failure.

X Two-eye observation clearly shows a noticeable spot. Failed due to scratches.

Molecular weight between crosslinks: Measured by xylene swelling method.

[Method for measuring molecular weight between crosslinks] ■ Clear paint is applied using the same method as the original painting process, except that the object to be coated is a tin plate, and then heated and cured.

(2) Peel off the clear coating film using a tin plate using the mercury amalgam method to obtain a free clear coating film of approximately 4 cm x 4 cm in size.

■ Fill a desicake with xylene, place a film on top of the liquid, and gently swell it with xylene vapor.

■ The film was then immersed in xylene and heated at 25°C for 2 hours.
Soak for 4 hours to reach swelling equilibrium.

■ Remove the film from the xylene and place it between filter papers to quickly remove the xylene from the film surface.

■ Place the film in a weighing bottle that has been weighed in advance and weigh it (the weight of the swollen film is Ws).

■ Remove the lid from the weighing bottle and place it in a vacuum dryer to weigh 10 mg.
[(The weight of the dried coating film is Wd).

If the film is easily broken in the xylene solution, it is recommended that the film be placed in a stainless steel wire mesh, a polyester net, or a porous paper bag and immersed therein.

(2) Calculate the molecular weight between crosslinks (Mc) using the following formula (Flory-Riner formula).

However, here, vR is the volume fraction of the resin in the swollen coating film, and is calculated by the following formula.

W.

Here, ψR is the density of the clear coating fg/cm3), ψ
S is the density of xylene (0,8637 g/cm3) (25
°C).

V3' is the molar volume of xylene (123cc/mole
). X is Fl between xylene and clear coating resin
ory-Huggins interaction constant, which is assumed here to be 0.4.

Gel fraction: Prepare a free clear film using the above methods ① and ②, place it in a 300-mesh stainless steel mesh container, and extract with a Soxhlet extractor using acetone/methanol = 1/1 solvent for 6 hours. After that, the gel fraction was calculated according to the following formula.

Claims (1)

[Claims] (A) a hydroxyl group-containing resin, (B) an amino resin, and a blocked polyisocyanate compound (C) are the main components, and the reaction initiation temperature of the (C) component and (A) component is such that the (A) component A thermosetting coating composition characterized in that the temperature is within the range of -20 to +50°C based on the reaction initiation temperature of component (B).