JPH0559328A - Interlaminar chipping-resistant paint for automobile - Google Patents

Abstract

PURPOSE:To provide the subject paint composed of specific prepolymer, polyol and cure-acceleration catalyst, curable at a low baking temperature and having excellent rust-proofing property, coating film properties, energy-saving performance and productivity. CONSTITUTION:The objective paint is composed of (A) one or more prepolymers of a blocked polyisocyanate compound derived from MDI and/or TDI and having a number-average molecular weight of 500-10,000 and an NCO% of 5-10, (B) a polyol such as polyether polyol having a number average molecular weight of <=400 and (C) one or more cure-acceleration catalysts selected from lead- based, zinc-based and tin-based catalysts (e.g. zinc octylate).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to prevent chipping, which is a phenomenon in which a coating film is peeled off when a small stone or the like on the road surface repelled by a wheel or the like collides with the vehicle body, and rusting of the vehicle body due to the chipping. Regarding interlayer anti-chipping paint for automobiles,
More specifically, it relates to an interlayer anti-chipping paint for automobiles, which can form a coating film having a high hardness by heating and drying at a lower temperature than before.

[0002]

2. Description of the Related Art Conventionally, as an interlayer chipping-resistant paint applied between an undercoat layer and an intermediate coat layer as a countermeasure against chipping, a blocked urethane precoat has been used because of its excellent physical properties and coating workability. Polymer, polyamine,
A curing agent component having active hydrogen such as polyol was added 1
Liquid heat-curable urethane coatings have been used (Japanese Patent Laid-Open No. Sho 6).
4-43573).

The above-mentioned one-component heat-curable urethane coating composition is spray-coated on the vehicle body and then heated in a drying furnace to form a hard coating film. If the heating is insufficient, the reaction between the NCO group and active hydrogen does not proceed completely even if the block dissociates, the paint does not cure as a coating film, and the solvent component in the coating film does not volatilize. It remains inside and the coating film is adversely affected. Further, if the hardness of the coating film is not sufficient, the surface of the coating film will be greatly damaged when chipped by pebbles on the road, which is not preferable in terms of appearance and rust prevention measures. Therefore, the heat curing of the above-mentioned one-component heat-curable urethane coating has been conventionally performed at least 140
It has been carried out under the condition of ~ 150 ° C for 30 minutes or longer.

[0004]

However, recently, the temperature of the coating film drying furnace of an automobile coating line is made lower than the above-mentioned conventional temperature because of the use of plastic parts, energy saving, and improvement of production efficiency. Has been requested. When the temperature of the drying oven is lowered, it is not possible to form a coating film exhibiting the same chipping resistance performance as before with the conventional chipping resistance paint without prolonging the drying time.

Therefore, the problem to be solved by the present invention is that the hardness of the coating film is sufficiently high, for example, even if the coating film is dried at a low temperature of 120 ° C. for about 30 minutes.
It is an object of the present invention to provide a chipping-resistant paint which becomes a paint film which is hardened to a pencil scratching value F or more in the "paint general test method" defined by 0 and exhibits chipping resistance performance equal to or higher than conventional ones.

[0006]

An interlayer chipping-resistant paint for automobiles according to the present invention is an interlayer chipping-resistant paint for automobiles comprising a block polyisocyanate compound and a polyol as main coating components and a curing-accelerating catalyst. The number average molecular weight of the isocyanate compound derived from MDI (diphenylmethane diisocyanate) and / or TDI (tolylene diisocyanate) is from 500 to
It is at least one prepolymer having an NCO% of 5 to 10 at 10,000, the polyol is a polyol having a number average molecular weight of 400 or less, and the curing accelerating catalyst is at least selected from lead-based, zinc-based and tin-based catalysts. It is characterized by being one kind of catalyst.

According to the present invention, when a specific block polyisocyanate compound and a specific polyol are combined as the main component of a chipping resistant coating and a specific curing accelerating catalyst is used, the NCO of the urethane prepolymer is heated even at a heating and drying temperature lower than before. The group completely reacts with active hydrogen to obtain a coating that produces a coating having good physical properties, that is, such a coating forms a coating having a sufficiently high hardness even in a coating drying oven at a low temperature, It was completed by discovering that it exhibits excellent chipping resistance.

Examples of the polyol having a number average molecular weight of 400 or less used in the coating material of the present invention include polyester polyol, polyether polyol, polyurethane polyol, acrylic polyol, nitrogen-containing polyol (amine polyol), castor oil derivative, tall oil. Derivative,
Examples thereof include polybutadiene polyol, butyral resin, alkyd resin, and epoxy resin. That is, a normal NCO
Examples include resins containing active hydrogen that reacts with the groups,
Among them, polyether polyol, polyester polyol and particularly nitrogen-containing polyol are preferable. It is important that the number average molecular weight of the polyol is 400 or less, because if it exceeds 400, the reactivity with the NCO group becomes poor.

As the polyester polyol, adipic acid, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic acid, succinic acid, azelaic acid, pimelic acid, sebacic acid, fumaric acid, hexahydrophthalic acid, methylhexahexyl A compound having a polybasic acid such as hydrophthalic acid, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, or dimer acid, and a compound having at least two or more hydroxyl groups in one molecule, for example, ethylene glycol, diethylene glycol, polyethylene glycol,
Polypropylene glycol, polytetramethylene ether glycol, propylene glycol, butylene glycol, neopentyl glycol, hydrogenated bisphenol A, glycerin, butanediol, 1,3-pentanediol, hexanediol, trimethylpentanediol, hexanetriol, trimethylolethane, Examples thereof include those synthesized from trimethylolpropane, pentaerythritol and the like by a conventional method.

As the polyether polyol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol, polyoxypropylene triol, polyoxypropylene quadrol and the like can be used. The hydroxyl-bonded carbon chain synthesized using an amine-based raw material as a starting material is a type of polyol branched from nitrogen, a so-called nitrogen-containing polyol (amine-based polyol) itself has a catalytic action. Particularly preferred as the polyol component of the coating composition of the present invention.

As the polyurethane polyol, a compound having a terminal hydroxy group obtained from a polyhydroxy compound and a polyvalent isocyanate compound is used.

The acrylic polyols include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, trimethylolpropane acrylic acid monoesters, their corresponding methacrylic acid derivatives, and hydroxyl groups such as polyhydroxyalkyl maleate and fumarate. Contained monomers and acrylic monomers such as acrylic acid or methacrylic acid methyl, ethyl, butyl, propyl, hexyl, 2-ethylhexyl, hydroxyethyl ester, etc., or α, β-ethylenic monomers such as styrene, vinyltoluene, vinyl acetate, etc. Examples thereof include those obtained by copolymerization with a monomer having a saturated double bond.

The blocked polyisocyanate compound used in the present invention has a number average molecular weight of 5 as described above.
It is necessary to have NCO% of 5 to 10 in the range of 00 to 10,000, but the reason for limiting these numerical values is that a coating film having satisfactory physical properties as a chipping-resistant coating film having a number average molecular weight of less than 500 is obtained. If the number average molecular weight exceeds 10,000, the coating work becomes difficult, and if the NCO% is less than 5, the reactivity with active hydrogen becomes low. Conversely, if the NCO% exceeds 10, the coating becomes difficult. This is because the storage stability tends to decrease.

As the block polyisocyanate compound that can be used, polyesters, polyethers having a hydroxyl group in a part of the isocyanate groups of MDI or TDI,
Acrylics, epoxies, etc. are reacted in advance and the remaining isocyanate groups have active hydrogen, for example, aliphatic primary and secondary alcohols such as methanol and ethanol, phenols, benzyl alcohol, cresol, cycloalcohols such as cyclohexanol. , Ethylene glycol monomethyl ether, hydroxyl group-containing ethers such as ethylene glycol monobutyl ether, methyl lactate, ethyl lactate, amyl lactate, hydroxyl group-containing esters such as butyl lactate, hydroxyl group-containing ketones such as diacetone alcohol,
Acetoximes, ketoxime, methyl ethyl ketone oxime, oximes such as methyl isobutyl ketone oxime, ε-caprolactam, lactams such as β-propiolactam, diethyl malonate, active methylenes such as methyl acetoacetate, butyl mercaptan, hexyl mercaptan, Mercaptans such as t-butyl mercaptan, acid amides such as acetanilide, acrylamide and acetic acid amide, imides such as succinimide and phthalic acid imide,
Examples thereof include amines such as diphenylamine and phenylnaphthylamine, imidazoles such as imidazole and 2-ethylimidazole, and ureas, imines and sulfites which are blocked and inactivated. By blocking and deactivating, it can be mixed with the above-mentioned polyol to form one liquid.

In order to improve the coating workability in the coating line, one or more solvents may be added to the interlayer chipping-resistant coating composition of the present invention. As such a solvent, for example, an aromatic solvent, an aliphatic solvent, an alcohol solvent,
Examples include ketone-based solvents. The solvent may be selected in consideration of compatibility with the block polyisocyanate compound and the polyol.

In the chipping-resistant paint of the present invention, other conventional additives such as talc, calcium carbonate, clay, alumina, silica, hirulite, clay, barium sulfate and other pigments, titanium oxide, carbon black, red iron oxide, Coloring pigments such as oxide yellow, phthalocyanine blue, phthalocyanine green, cissing inhibitor, leveling improver, defoaming agent, surfactant, curing accelerator, antistatic agent, pigment dispersant, anti-sagging agent, thickener, etc. You may mix.

The coating composition of the present invention requires the use of one or more catalysts selected from zinc-based catalysts, tin-based catalysts and lead-based catalysts in order to accelerate the dissociation of the blocked polyisocyanate compound. Examples thereof include organometallic catalysts such as zinc octylate, tin octylate and lead octylate. When a commonly used catalyst such as a tertiary amine compound such as triethylenediamine or triethylamine is used, there is a possibility that a coating film having a sufficiently hard coating film cannot be obtained.

To prepare the interlayer anti-chipping paint for automobiles of the present invention, each component together with a solvent is dispersed by three rolls, a ball mill, a pot mill, a steel mill, a pebble mill, an attritor, a sand mill, a sand grinder, a roll mill and a blade. It suffices to charge the mixture in a mixing and dispersing machine such as a high-speed stirrer to uniformly mix and disperse it.

The coating of the car body is performed on a desired portion of the steel plate surface which has been subjected to chemical conversion treatment and electrodeposited with a primer. As a coating method, a spraying method such as a normal air spray, an electrostatic air spray, an airless spray, a hot airless spray can be adopted. Baking and drying at a temperature of 100 to 120 ° C. for about 5 to 15 minutes is sufficient to cure the chipping-resistant paint of the present invention sprayed on the vehicle body. The dry film thickness is preferably about 50 to 200 μm. 50μ
If it is less than the required chipping resistance for the coating film cannot be obtained,
If it exceeds 200 μ, problems such as sagging of the coated surface after coating and generation of cracks during baking and drying may occur.

[0020]

By reducing the molecular weights of the blocked polyisocyanate compound and the polyol to some extent, their reactivity and crosslink density are increased. The reactivity is also increased by increasing the NCO% of the blocked polyisocyanate compound and by using a specific metal-based catalyst.
Therefore, the coating material having the above-mentioned constitution produces a coating film having sufficient physical properties such as chip resistance and hardness even by baking at a low temperature of about 120 ° C.

[0021]

EXAMPLES In order to understand the present invention, examples will be described below. The blocked polyisocyanate compounds used in the following Examples and Comparative Examples are those obtained by reacting a polyester having a hydroxyl group with a part of the isocyanate groups of tolylene diisocyanate (TDI) and blocking the remaining isocyanate groups with ketoxime. Needless to say, the present invention is not limited to the examples below.

Example 1 100 block polyisocyanate compound (TDI prepolymer) having a number average molecular weight of 3000 and an NCO% of 6.5.
14 parts by weight of an amine-based polyol having a number average molecular weight of 380, 0.5 parts by weight of a lead-based metal catalyst, 31 parts by weight of calcium carbonate, 25 parts by weight of precipitated barium sulfate, and 20 parts by weight of talc are blended with respect to parts by weight. After mixing and dispersing with a three-roll mill, an aromatic solvent was further added to adjust the viscosity so that coating with an airless coating machine was possible to obtain a chipping resistant coating 1.

Example 2 100 block polyisocyanate compound (TDI prepolymer) having a number average molecular weight of 4500 and an NCO% of 7.0
14 parts by weight of an amine-based polyol having a number average molecular weight of 390, 0.5 parts by weight of a lead-based metal catalyst, 31 parts by weight of calcium carbonate, 25 parts by weight of precipitated barium sulfate and 20 parts by weight of talc are blended with respect to parts by weight. After mixing and dispersing with a three-roll mill, an aromatic solvent was further added to adjust the viscosity so that it could be coated with an airless coating machine, and a chipping resistant coating 2 was obtained.

Comparative Example Block polyisocyanate compound (TDI prepolymer) 1 having a number average molecular weight of 10500 and NCO% = 12.0
14 parts by weight of a polyester polyol having a molecular weight of 430, 31 parts by weight of calcium carbonate, 25 parts by weight of barium sulfate, and 20 parts by weight of talc were mixed with 00 parts by weight, and the viscosity was adjusted by an aromatic solvent after mixing and dispersing, Chipping paint 3 was obtained.

Test Example 1 Chipping-resistant paints 1-3 of Examples 1 and 2 and Comparative Example above
After airless coating of each of the above on an electrodeposition plate, that is, a steel plate having an undercoat layer (electrodeposition layer of primer) and baking and drying at 110 ° C. for 10 minutes to provide a chipping-resistant layer having a thickness of 90 μm, An intermediate coating and then a top coating were applied according to a conventional method. The drying conditions of the intermediate coating layer and the top coating layer were 120 ° C. × 20 minutes, and the dry film thickness was 30 μm. Regarding the three types of test plates coated in this way, JIS
The "pencil scratch value" in the general paint test method specified in K 5400 was tested to examine the maximum hardness of a pencil without scratches. As a result, it was revealed that the coating films using the anti-chipping paints 1 and 2 had a pencil scratching value of F and had sufficient hardness. The pencil scratching value of the coating of the chipping-resistant paint 3 of Comparative Example was 2B.

Test Example 2 Chipping-resistant paints 1 to 3 of Examples 1 and 2 and Comparative Example above.
Each of them was airless coated on an electrodeposited plate, baked and dried at 110 ° C. for 10 minutes to provide a chipping resistant layer having a film thickness of 90 μm, and then an intermediate coating and then a top coating were applied according to a conventional method. did. The drying conditions of the intermediate coating layer and the top coating layer were 120 ° C. × 20 minutes, and the dry film thickness was 30 μm. JIS on the three kinds of test plates coated in this way
B 1181 standard type 3 M4 shape brass hex nuts are dropped from a height of 2 m in order from the smallest weight, and the scratches of the coating film at that time reach the electrodeposition coated surface. I checked the weight. As a result, the weight of the nut reached 12 kg in the coating film using the chipping resistant coatings 1 and 2. From this, it was clarified that the chipping-resistant paints 1 and 2 have an excellent chipping-resistant effect. In the coating film of the chipping-resistant paint 3 of the comparative example, the nut weight was 9 kg.

Test Example 3 The same three kinds of coating test plates as those used in Test Example 2 were vertically attached to a sample holder of a stepping stone tester [JA-400 type manufactured by Suga Tester Co., Ltd.], 5 towards this test plate
00g of No. 6 crushed stone is 4kg / cm ² with the pressure gauge of the tester.
The crushed stone was made to collide with the test plate at a right angle. Next, the test plate was washed with water, dried, and after the coating film that had been lifted up by chipping was removed with an adhesive tape, the degree of peeling damage was evaluated on a five-grade scale from good (⊚) to poor (x). As a result, the coating films using the anti-chipping paints 1 and 2 were ⊚, and it was revealed that the anti-chipping effect was excellent. The coating film of the chipping-resistant paint 3 was ◯ and was inferior.

[0028]

EFFECTS OF THE INVENTION Since the chipping-resistant coating material of the present invention uses specific coating components and catalysts, it reacts at a much lower temperature than in the prior art and produces a chip-resistant coating film. Therefore, by using the chipping-resistant paint of the present invention, the heating temperature of the coating film drying furnace in the automobile coating line can be lowered from the conventional 160 ° C. to about 120 ° C., and the thermal effect on the plastic parts of the automobile can be reduced, It is possible to save energy and improve production efficiency. Further, since the chip-resistant coating film formed from the coating material of the present invention has superior chipping resistance performance and higher hardness as compared with the conventional ones, the generation of rust on a car subject to chipping is further prolonged. Can be prevented and a smooth painted surface can be maintained.

Claims (1)

[Claims] 1. An interlayer chipping resistant coating for automobiles, comprising a blocked polyisocyanate compound and a polyol as main coating components and a curing-accelerating catalyst, wherein the blocked polyisocyanate compound is a number average molecular weight derived from MDI and / or TDI. NCO at 500 to 10,000
% = 5-10 of at least one prepolymer,
An interlayer chipping-resistant coating material for automobiles, wherein the polyol is a polyol having a number average molecular weight of 400 or less, and the curing-accelerating catalyst is at least one catalyst selected from lead-based, zinc-based and tin-based catalysts.