JPH05179156A - Method of forming coating film - Google Patents

Abstract

PURPOSE:To form a coating film excellent in hardness, decorativeness and solvent resistance and having good acid resistance, marring resistance and thermal yellowing resistance. CONSTITUTION:A composition which consists of the following components is heated in the atmosphere of an inert gas to harden through cross-linking: 50-100 pts.wt. component (a) comprising an aliphatic and/or alicyclic urethane (meth)acrylate containing at least two (meth)acryloyl groups in the molecule; 0-50 pts.wt. radical-polymerizable compound (b) which contains at least two (meth)acryloyl groups and no urethane linkage in the molecule and has a molecular weight of 300 or higher; and a radical polymerization initiator (c) in an amount of 0.1-10.0 pts.wt. based on 100 pts.wt. total of components (a) and (b).

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coating film which is excellent in hardness, beauty and solvent resistance, and has good acid resistance, scratch resistance and heat yellowing resistance.

[0002]

2. Description of the Related Art It is generally known that radical-polymerizable unsaturated group-containing oligomers are cured by heating using a radical polymerization initiator. Was considered insufficient and did not have good solvent resistance, weather resistance, etc. Therefore, it has been essential to use a photosensitizer and UV irradiation together in the polymerizable oligomer curing system.

The inventors of the present invention have previously described the Japanese Patent Laid-Open No. 2-5055.
In No. 4, by using a radical-polymerizable oligomer having a specific bond and having a certain molecular weight or more, even if it is heat-cured, the hardness and weather resistance as seen in acrylic resins can be exhibited. It was proposed that a good coating performance can be obtained with respect to acid resistance and scratch resistance, which were low in the melamine crosslinking system.

However, when the curing temperature exceeds 150 ° C. and the heating is excessively advanced, the yellowing is remarkable, and it is particularly low in comparison with the melamine crosslinking system. this is,
It is considered that oxygen molecules in the air enter the curing reaction system to form a kind of chromophore, and therefore it is presumed that there is no heat yellowing under the condition where oxygen is not present. Here, the inventors of the present invention, when the radical-polymerizable oligomer is heat-cured, proceed with the crosslinking reaction under an inert gas atmosphere, that is, under the condition that the oxygen concentration is low. It was suppressed to yellowing by heating and, in hardness, solvent resistance, acid resistance, and scratch resistance, it was possible to obtain extremely good performance as compared with heat curing in air.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a coating film which is excellent in hardness, beauty and solvent resistance and has good acid resistance, scratch resistance and heat yellowing resistance. It is in.

[0006]

The gist of the present invention is that (a) 50 or more aliphatic and / or alicyclic urethane (meth) acrylates containing two or more (meth) acryloyl groups in one molecule. To 100 parts by weight, (b) 0 to 50 parts by weight of a radically polymerizable compound having two or more (meth) acryloyl groups in one molecule and no urethane bond, and a molecular weight of 300 or more, and (c) a radical. A composition comprising 0.1 to 10.0 parts by weight of a polymerizable initiator based on 100 parts by weight of the total of the components (a) and (b) is crosslinked and cured under an inert gas atmosphere. There is a method for forming a coating film.

The present invention will be described in detail below. The aliphatic and / or alicyclic urethane (meth) acrylate (a) containing two or more (meth) acryloyl groups in one molecule which is the first component is a diisocyanate, triisocyanate simple substance, diisocyanate or triisocyanate view. It can be synthesized by reacting a polyisocyanate such as a lett, a multimer or an adduct with a polyol with a monomer having a hydroxyl group. The compound (a) is contained in an amount of 50 to 100 parts by weight based on 100 parts by weight of the total amount of the components (a) and (b) in the composition of the present invention. It deteriorates and is not preferable.

Specific examples of polyisocyanates include ethylene diisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, lysine isocyanate, 4,4. ′ -Methylenebis (cyclohexyl) isocyanate, methylcyclohexane 2,4-diisocyanate, methylcyclohexane 2,6-diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, isophorone diisocyanate, trimethylhexamethylene diisocyanate, tetramethylene diisocyanate, dimer acid Diisocyanates such as diisocyanates, simple substances of triisocyanates, burettes and their multimers and their adducts with polyols, etc. It can gel.

Specific examples of the polyol used in the adduct include ethylene glycol, propylene glycol, butylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, polytetramethylene glycol, trimethylolpropane, polytrimethylolpropane and pentaerythritol. , Polyventaerythritol, sorbitol, mannitol,
Examples include alcohols such as glycerin and polyglycerin, polyether polyols, polyester polyols synthesized from polyhydric alcohols and polybasic acids, and polyester polyols such as polycaprolactone polyols.

As the hydroxyl group-containing vinyl monomer, 2-
Hydroxyethyl (meth) acryl, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth)
Hydroxyalkyl (meth) acrylates such as acrylates, 2-hydroxyethyl (meth) acrylate and ethylene oxide adducts, 2-hydroxyethyl (meth) acrylate and propylene oxide adducts, 2-
Examples thereof include adducts of 2-hydroxyethyl (meth) acrylate and organic lactones such as adducts of hydroxyethyl (meth) acrylate and ε-caprolactone.

The reaction between the polyisocyanate and the hydroxyl group-containing monomer is completed by heating at 60 to 70 ° C. for several hours using a tin-based catalyst such as dibutyltin dilaurate so that the isocyanate and the hydroxyl group are in substantially equal amounts. ..

The second component, the radically polymerizable compound (b), contains two or more (meth) acryloyl groups in one molecule, has a molecular weight of 300 or more, and has no urethane bond. 0 to 50 parts by weight, preferably 10 to 40 parts by weight, is added to 100 parts by weight of the total amount of the components (a) and (b), and if it exceeds 50 parts by weight, the weather resistance is lowered, Absent.

Specifically, polyester poly (meth) acrylates and epoxies obtained by reacting polybasic acids such as phthalic acid and adipic acid with polyhydric alcohols such as ethylene glycol and butanediol and (meth) acrylic acid compounds. Epoxy poly (meth) acrylate obtained by reaction of resin with (meth) acrylic acid compound, polysiloxane poly (meth) acrylate obtained by reaction of polysiloxane with (meth) acrylic acid compound, polyamide and (meth) acrylic Examples thereof include polyamide poly (meth) acrylate obtained by the reaction with an acid compound.

The radical polymerization initiator (c) is added to the composition of the present invention in an amount of 0.1 to 10.0 parts by weight based on 100 parts by weight of the total amount of the components (a) and (b). If the amount is less than 1 part by weight, sufficient coating film hardness cannot be obtained, and 10.0
If it exceeds 5 parts by weight, the stability of the coating composition is deteriorated, which is not preferable.

Examples of the polymerization initiator used here include benzoyl peroxide, cumene hydroperoxide, di-t-butyl hydroperoxide, dicumyl peroxide, t-butyl peracetate and t-.
Butyl perbenzoate, peroxides such as t-butyl hydroperoxide, azobisisobutyronitrile,
2,2-azobis (2-methylbutyronitrile), 1,
Examples thereof include azo compounds such as 1-azobis (cyclohexane-1-carbonitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), and 2,2-azobis (2-methylpropane). It is not something that will be done.

In the present invention, good heat-resistant yellowing can be exhibited by subjecting the composition to a crosslinking curing reaction in an inert gas atmosphere. Crosslinking reaction in an inert gas atmosphere is considered to have a good effect of inhibiting the radical polymerization reaction due to oxygen, and to prevent the formation of a yellowing chromophore, resulting in better coating performance than heat curing in air. Be done.
Further, if it is a small amount of oxygen, even if it exists, it has no influence, and it is preferable to adjust the inert gas concentration so that the oxygen concentration becomes 2000 ppm or less. Specific examples of the inert gas include, but are not limited to, nitrogen, carbon dioxide, helium, neon, argon, krypton, and xenon.

The coating film forming method of the present invention can be realized under curing conditions of 100 ° C. or higher for 15 to 45 minutes.
Further, the cured product of the composition of the present invention is excellent in hardness, cosmetic properties, solvent properties, and has good acid resistance, scratch resistance, and heat yellowing resistance, so that it is an inorganic substance (iron plate, tin plate, galvanized sheet, It is useful as a paint and coating agent for the surface of aluminum plates, zinc steel plates, roof tiles, etc. and organic substances (wood, paper, plastics, coating films of organic paints, etc.).

Further, a surface conditioner, a cissing inhibitor, an ultraviolet absorber, an antioxidant, an organic solvent, and other additives may be added to the composition, if necessary.

[0019]

EXAMPLES The present invention will be described below with reference to examples. <Production Example of Urethane (meth) acrylate (a) -1>
1 mol of hexamethylene diisocyanate burette and 0.002 mol of dibutyltin dilaurate were added to the reaction vessel, and the temperature was raised to 70 ° C., and then 3 mol of 2-hydroxypropyl methacrylate was added dropwise for 1 hour, and after addition 5
Urethane (meth) acrylate (a)-
Got 1.

<Urethane (meth) acrylate (a)-
Preparation Example 2> Hexamethylene diisocyanate in place of hexamethylene diisocyanate burette, 0.001 mol in place of 0.002 mol of dibutyltin dilaurate, and 2-hydroxybutyl acrylate 2 in place of 3 mol of 2-hydroxypropyl methacrylate 2 Urethane (meth) acrylate (a) -2 was synthesized in the same manner as in the production example of (a) -1 except that the mole was used.

<Urethane (meth) acrylate (a)-
Production Example 3> Urethane (meth) acrylate (a) in the same manner as in Production Example (a) -1 except that isophorone diisocyanate buret and 0.001 mol of dibutyltin dilaurate are used instead of hexamethylene diisocyanate buret. -3 was synthesized.

<Production Example of Acrylic Resin Varnish> Stirrer,
Solvesso in a container equipped with a temperature controller and condenser
53.3 parts by weight of ^# 100 was added. Then, the temperature was raised to 120 ° C. with stirring, and then 100 parts by weight of the following monomer mixture was added and mixed with 2 parts by weight of azobisisobutyronitrile and 2 parts by weight of t-butylperoxyisopropyl carbonate in 3 hours. Dropped. Then
While stirring this, azobisisobutyronitrile 0.1
Parts by weight were added 4 times at 30 minute intervals. 2 hours 12
After heating and stirring at 0 ° C. to increase the reaction rate, 13.3 parts by weight of n-butyl acetate was added to terminate the reaction to obtain an acrylic resin varnish.

(Monomer mixture) Styrene 25 parts by weight Methacrylic acid 3 parts by weight n-Butyl methacrylate 20 parts by weight t-Butyl methacrylate 5 parts by weight 2-Ethylhexyl methacrylate 29 parts by weight 2-Hydroxyethyl methacrylate 18 parts by weight

<Examples 1 to 5 and Comparative Examples 1 to 7> After degreasing the steel sheet, various compositions shown in Table 1 were coated on the steel sheet so as to have a dry film thickness of 35 .mu. In 1
After leaving it for 0 minutes, it was baked under the curing conditions shown in Table 1.
The coating film performance evaluation results of the obtained coating film are as shown in Table 2, and those of the examples have hardness, cosmetic properties, solvent resistance, acid resistance, scratch resistance and heat resistance yellow that those of the comparative examples. All were excellent in denaturation.

[0025]

[Table 1]

* 1 (b) -1: glycerin propylene oxide adduct triacrylate * 2 (b) -2: trimethylolpropane propylene oxide adduct triacrylate * 3 (b) -3: neoventil glycol diacrylate / Polyethylene glycol diacrylate = 1/1 * 4 (c) -1: t-butyl hydroperoxide * 5 (c) -2: 2,2'-asobisisobutyronitrile * 6 Uban 20SE: Mitsui Toatsu Chemical ( Co., Ltd. melamine resin * 7 Curing conditions (1): In a nitrogen atmosphere (oxygen concentration 0.2
%) 140 ° C. 25 minutes Curing condition (2): Nitrogen atmosphere (oxygen concentration 0.5%) 1
40 ° C. 25 minutes Curing condition (3): In nitrogen atmosphere (oxygen concentration 2%) 140
℃ 25 minutes curing conditions (4): 140 ℃ in air 25 minutes

[0027]

[Table 2] * 1 Visual appearance judgment (judgment criteria: ◎ very good ◯ good △ bad × extremely poor) * 2 Visual evaluation after 30 reciprocations of xylene rubbing * 3 Visual judgment after 2 hours at 50 ° C after spotting 10% sulfuric acid aqueous solution * 4 Cleanser Wetnel test: Load 500g 1
Visual evaluation after 0 reciprocation * 5 ΔE measurement value of coating film at 160 ° C 1H heat curing (measured by color difference meter Z-1001DP type manufactured by Nippon Denshoku Co., Ltd.)

[0028]

As described above in detail, the composition of the present invention can be cured by heat, and the cured coating film obtained has hardness, cosmetic properties, solvent resistance, weather resistance, acid resistance, It has excellent scratch resistance and heat yellowing resistance, and its industrial significance is extremely high.

Claims (1)

[Claims] 1. (a) 50 to 100 parts by weight of an aliphatic and / or alicyclic urethane (meth) acrylate containing two or more (meth) acryloyl groups in one molecule, and (b) (in one molecule) 0 to 50 parts by weight of a radically polymerizable compound having two or more (meth) acryloyl groups and no urethane bond and having a molecular weight of 300 or more, and (c) a radically polymerizable initiator (a) component and (b) A method for forming a coating film, which comprises cross-linking and curing a composition comprising 0.1 to 10.0 parts by weight with respect to 100 parts by weight of the total amount of components in an inert gas atmosphere. [0001]