JP3541044B2 - Interlayer chipping paint for automobiles - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to chipping, which is a phenomenon in which a coating film peels off when pebbles or the like on a road surface flipped up by wheels or the like collides with a vehicle body, and to an interlayer chipping-resistant paint for automobiles for preventing rusting of the vehicle body due to the chipping. More specifically, the present invention relates to an automotive chipping-resistant paint capable of forming a high-hardness coating film by heating and drying at a lower temperature than conventionally.
[0002]
[Prior art]
Conventionally, as an interlayer chipping-resistant coating applied between the undercoat layer and the intermediate coating layer to prevent chipping, a blocked urethane prepolymer, a polyamine, One-component heat-curable urethane coatings to which a curing agent component having active hydrogen such as a polyol has been added have been used (see JP-A-64-43573).
[0003]
The one-component heat-curable urethane paint is spray-coated on a vehicle body and then heated in a drying furnace to form a hard coating. If the heating is insufficient, the reaction between the NCO group and the active hydrogen does not proceed completely even if the block is dissociated, and the paint does not cure as a coating film or the solvent component in the coating film does not volatilize. In such a case, there remains a problem that the coating film is adversely affected and the coating film is adversely affected. On the other hand, if the hardness of the coating film is not sufficient, the surface of the coating film will be greatly damaged when chipped by road pebbles or the like, which is not preferable in terms of appearance and rust prevention measures. Therefore, the heat curing of the one-component heat-curable urethane paint has been conventionally performed at least at 140 to 150 ° C. for 30 minutes or more.
[0004]
[Problems to be solved by the invention]
However, recently, it has been required to lower the temperature of the coating film drying furnace in the automobile coating line from the above-mentioned conventional temperature for reasons such as adoption of plastic parts, energy saving and improvement of production efficiency. If the temperature of the drying furnace is lowered, it is not possible to form a coating film exhibiting the same chipping resistance as before with a conventional chipping-resistant coating material without increasing the drying time.
[0005]
Therefore, the problem to be solved by the present invention is that even if the required low-temperature coating film drying at 120 ° C. for about 30 minutes is performed, for example, the “paint general test method” in which the hardness of the coating film is sufficiently specified in JIS K 5400, for example. The present invention is to provide a chipping-resistant paint which is cured to a pencil scratch value F or more and exhibits a chipping resistance equivalent to or higher than the conventional one.
[0006]
[Means for Solving the Problems]
The automotive interlayer chipping resistant coating composition of the present invention is an automotive interlayer chipping resistant coating composition comprising a block polyisocyanate compound and a polyol as main coating components and a curing accelerator, wherein the block polyisocyanate compound is MDI (diphenylmethane diisocyanate) and And / or a nitrogen-containing polyol (amine-based polyol ) having a number average molecular weight of 500 to 10000 and an NCO% of 5 to 10 derived from TDI (tolylene diisocyanate) and a polyol having a number average molecular weight of 400 or less. ) , And the curing promoting catalyst is at least one catalyst selected from the group consisting of lead-based, zinc-based, and tin-based catalysts.
[0007]
The present invention relates to the use of a specific blocked polyisocyanate compound and a specific polyol as the main components of the chipping-resistant paint, and the use of a specific curing acceleration catalyst. Hydrogen completely reacts to obtain a coating that produces a coating film having good physical properties. That is, according to such a coating film, a coating film having sufficiently high hardness is formed even in a low-temperature coating drying oven, and excellent coating resistance is obtained. It has been found out that it exhibits chipping properties.
[0008]
The polyol having a number average molecular weight of 400 or less used in the paint of the present invention is a nitrogen-containing polyol (amine-based polyol) .
[0009]
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 deteriorates.
[0010]
Since a hydroxyl-bonded carbon chain synthesized from an amine-based material as a starting material and having a hydroxyl-bonded carbon chain branched from nitrogen, a so-called nitrogen-containing polyol (amine-based polyol) itself has a catalytic action, Used as a polyol component of the paint of the present invention.
[0011]
As described above, the blocked polyisocyanate compound used in the present invention needs to have a number average molecular weight of 500 to 10,000 and an NCO% of 5 to 10.
[0012]
The reason for limiting the number-average molecular weight of the blocked polyisocyanate compound used in the present invention is that a coating having satisfactory physical properties as a chipping-resistant coating is less likely to be produced as the number-average molecular weight is less than 500, and conversely, This is because the coating operation becomes more difficult as the average molecular weight exceeds 10,000.
[0013]
The reason for limiting the numerical value of NCO% in the blocked polyisocyanate compound used in the present invention is that the reactivity with active hydrogen decreases as NCO% is less than 5, and conversely, as NCO% exceeds 10, This is because the storage stability tends to decrease.
[0014]
As a block polyisocyanate compound that can be used, a compound having a hydroxyl group, polyester, polyether, acryl, epoxy, or the like, which is previously reacted with a part of the isocyanate group of MDI or TDI, and a compound having active hydrogen in the remaining isocyanate group, for example, Methanol, aliphatic primary and secondary alcohols such as ethanol, phenol, benzyl alcohol, cresol, cyclic alcohols such as cyclohexanol, ethylene glycol monomethyl ether, hydroxyl-containing ethers such as ethylene glycol monobutyl ether, methyl lactate, ethyl lactate, Hydroxyl-containing esters such as amyl lactate and butyl lactate, ketones having hydroxyl group such as diacetone alcohol, acetoxime, ketoxime, methyl ethyl ketone oxime, methyl isobutyl ketone Oximes such as shim, ε-caprolactam, lactams such as β-propiolactam, active methylenes such as diethyl malonate and methyl acetoacetate, mercaptans such as butyl mercaptan, hexyl mercaptan, t-butyl mercaptan, acetanilide, Acid amides such as acrylamide and acetic acid amide; imides such as succinimide and phthalic imide; amines such as diphenylamine and phenylnaphthylamine; imidazoles such as imidazole and 2-ethylimidazole; and other ureas, imines and sulfites. And inactivated. By blocking and inactivating, it can be mixed with the polyol to form one liquid.
[0015]
In order to improve the coating workability in the coating line, one or more solvents can be usually added to the interlayer anti-chipping coating of the present invention. Such solvents include, for example, aromatic, aliphatic, alcohol, and ketone solvents. The solvent may be selected in consideration of the compatibility with the blocked polyisocyanate compound and the polyol.
[0016]
The chipping-resistant paint of the present invention includes other conventional additives, for example, pigments such as talc, calcium carbonate, clay, alumina, silica, leech, terra alba, barium sulfate, titanium oxide, carbon black, red iron oxide, oxide yellow, Compounding coloring pigments such as phthalocyanine blue and phthalocyanine green, repelling inhibitors, leveling improvers, defoamers, surfactants, curing accelerators, antistatic agents, pigment dispersants, anti-sagging agents, thickeners, etc. Is also good.
[0017]
The paint 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 promote the dissociation of the blocked polyisocyanate compound. Organometallic catalysts such as zinc octylate, tin octylate, and lead octylate are exemplified. 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 sufficiently high coating film hardness may not be obtained.
[0018]
In order to prepare the automotive interlayer chipping resistant paint of the present invention, each component is dispersed together with a solvent, a three-roller, a ball mill, a pot mill, a steel mill, a pebble mill, an attritor, a sand mill, a sand grinder, a roll mill, a high-speed stirrer with blades, and the like. And then uniformly mixed and dispersed.
[0019]
The coating on the automobile body is performed on a desired portion of the steel plate surface which has been subjected to a chemical conversion treatment and electrodeposited with a primer. As a coating method, a spraying method such as ordinary air spray, electrostatic air spray, airless spray, and hot airless spray can be adopted. In order to cure the chipping-resistant paint of the present invention sprayed on the vehicle body, baking and drying at a temperature of 100 to 120 ° C for about 5 to 15 minutes is sufficient. The dry film thickness is preferably about 50 to 200 μ. If it is less than 50 μm, the chipping resistance required for the coating film cannot be obtained, and if it exceeds 200 μm, problems such as sagging of the coated surface after coating and baking during baking and drying may occur.
[0020]
[Action]
Reducing the molecular weights of the blocked polyisocyanate compound and the polyol to some extent increases their reactivity and crosslink density. The reactivity is also increased by increasing the NCO% of the blocked polyisocyanate compound and by using a specific metal catalyst. Therefore, the paint having the above-mentioned structure produces a coating film having sufficient properties such as chip resistance and hardness even at a low temperature baking and drying at about 120 ° C.
[0021]
【Example】
Examples will be described below to facilitate understanding of the present invention. The blocked polyisocyanate compound used in the following examples and comparative examples is obtained by reacting a polyester having a hydroxyl group with a part of 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 following examples.
[0022]
Example 1
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, based on 100 parts by weight of a block polyisocyanate compound (TDI prepolymer) having a number-average molecular weight of 3000 and NCO% = 6.5. 31 parts by weight of calcium carbonate, 25 parts by weight of sedimentable barium sulfate, and 20 parts by weight of talc are blended, mixed and dispersed by a three-roll mill, and then an aromatic solvent is added to obtain a viscosity that enables the coating with an airless coating machine. Thus, a chipping-resistant paint 1 was obtained.
[0023]
Example 2
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, based on 100 parts by weight of a block polyisocyanate compound (TDI prepolymer) having a number average molecular weight of 4500 and NCO% = 7.0. 31 parts by weight of calcium carbonate, 25 parts by weight of sedimentable barium sulfate, and 20 parts by weight of talc are blended, mixed and dispersed by a three-roll mill, and then an aromatic solvent is added to obtain a viscosity that enables the coating with an airless coating machine. Thus, an anti-chipping paint 2 was obtained.
[0024]
Comparative Example 14 100 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 based on 100 parts by weight of a blocked polyisocyanate compound (TDI prepolymer) having a number average molecular weight of 10500 and NCO% = 12.0. And 20 parts by weight of talc, and after mixing and dispersion, the viscosity was adjusted with an aromatic solvent to obtain a chipping-resistant paint 3.
[0025]
Test example 1
Each of the anti-chipping paints 1 to 3 of Examples 1 and 2 and the comparative example was airless coated on an electrodeposited plate, that is, a steel plate having an undercoat layer (electrodeposited layer of a primer), and baked and dried at 110 ° C. for 10 minutes. After forming a 90 μm-thick chipping-resistant layer, an intermediate coating and a top coating were then applied thereon in a conventional manner. The drying conditions of the intermediate coat layer and the overcoat layer were each 120 ° C. for 20 minutes, and the dry film thickness was 30 μm. The three kinds of test panels coated in this manner were subjected to a “pencil scratch value” test in the paint general test method specified in JIS K 5400, and the maximum value of the hardness of the pencil without scratches was examined.
As a result, it was found that the coating films using the chipping-resistant paints 1 and 2 had a pencil scratch value of F and had sufficient hardness. The pencil scratch value of the coating film of the chipping-resistant coating material 3 of the comparative example was 2B.
[0026]
Test example 2
After each of the anti-chipping paints 1 to 3 of Examples 1 and 2 and the comparative example was applied airless to an electrodeposited plate, and baked and dried at 110 ° C. for 10 minutes to provide a 90 μm-thick anti-chipping layer. Then, a middle coat and then a top coat were applied thereon in a conventional manner. The drying conditions of the intermediate coat layer and the overcoat layer were each 120 ° C. for 20 minutes, and the dry film thickness was 30 μm. A hexagonal nut made of brass of three types M4 according to JIS B 1181 standard is dropped from a height of 2 m in order from a small weight on the three types of test plates coated in this manner, and the resulting coating film is formed. The weight of the drop nut until the scratch reached the electrodeposition painted surface was examined.
As a result, the weight of the nut reached 12 kg in the coating film in which the chipping-resistant paints 1 and 2 were used. From this, it became clear that the anti-chipping paints 1 and 2 exhibited an excellent anti-chipping effect. In addition, in the coating film of the chipping-resistant paint 3 of the comparative example, the nut weight was 9 kg.
[0027]
Test example 3
The same three types of painted test plates as those tested in Test Example 2 were vertically attached to a sample holder of a stepping stone tester (JA-400 type, manufactured by Suga Test Instruments Co., Ltd.), and turned toward the test plates. 500 g of No. 6 crushed stone was injected with a pressure gauge of a testing machine at an air pressure of 4 kg / cm ² , and the crushed stone was caused to collide with the test plate at right angles. Next, the test plate was washed with water, dried, and the coating film lifted by chipping was removed with an adhesive tape. Then, the coated surface was evaluated in five stages from good (◎) to poor (×) by the degree of peeling.
As a result, the coating film using the anti-chipping paints 1 and 2 was ◎, and it was clear that an excellent anti-chipping effect was exhibited. The coating film of the anti-chipping paint 3 was ○ and slightly inferior.
[0028]
【The invention's effect】
The chipping-resistant paint of the present invention reacts at a much lower temperature than in the prior art because a specific paint component and a catalyst are used, and produces a chip-resistant coating film. Therefore, by using the anti-chipping paint of the present invention, the heating temperature of the coating film drying furnace in the automobile coating line can be reduced from the conventional 160 ° C. to about 120 ° C., and the heat influence on the plastic parts of the automobile is reduced, Energy saving and improvement of production efficiency can be achieved. Further, since the chip-resistant coating film formed by the coating material of the present invention has better chipping resistance and higher hardness than the conventional coating film, the generation of rust on the vehicle subjected to chipping can be further extended. And maintain a smooth painted surface.

Claims (1)

In an automotive interlayer chipping resistant coating composition comprising a block polyisocyanate compound and a polyol as a main coating component and a curing acceleration catalyst, the block polyisocyanate compound has a number average molecular weight of 500 to 10,000 derived from MDI and / or TDI, and NCO. % = 5 to 10 at least one prepolymer, the polyol is a nitrogen-containing polyol (amine-based polyol) having a number average molecular weight of 400 or less, and the curing promoting catalyst is a lead-based, zinc-based, or tin-based catalyst. An interlayer chipping resistant paint for automobiles, which is at least one selected catalyst.