JPH0739560B2 - Top coating composition for automobiles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a topcoat paint for automobiles having improved scratch resistance.

(Prior Art) The characteristics required for top coating films for automobiles are durability against chemical factors such as sunlight, acid rain, and gasoline (hereinafter referred to as durability) and causes such as adhesion of dust and oil during coating. There is durability against physical factors such as polishing for the purpose of partially repairing the problems caused by the above, waxing performed by the user after purchasing the vehicle, car washing, etc. (hereinafter referred to as scratch resistance). In order to meet this demand and improve durability and scratch resistance, it is known that increasing the crosslink density of the coating film and ensuring the hardness of the coating film is effective.

On the other hand, the characteristics required for a top coating material for automobiles have workability corresponding to various constraints in automobile manufacturing. Among them, a particularly important characteristic is the adhesiveness (hereinafter referred to as recoat adhesiveness) when the topcoat is applied again for defects such as dust, spots, and color unevenness that occur during the coating process.

In conventional automotive top coatings, the amount of hydroxyl groups, which is thought to be deeply related to recoat adhesion, is controlled by adjusting the number of branches of the polyester resin to control the amount of hydroxyl groups attached to the ends. And a method of controlling the reactivity and the compounding ratio of a resin such as a melamine resin which is cured by reacting with a hydroxyl group.

(Problems to be solved by the invention) However, as a result of the present inventors' research on recoat adhesion, the recoat adhesion is determined by the amount of hydroxyl groups when the recoated coating film (hereinafter referred to as the second coating film) is baked. It became clear that it depends on the ease of penetration into the existing coating film (hereinafter referred to as the first coating film), and it was found that it was difficult to achieve both scratch resistance and recoat adhesion by the conventional method. did. That is,
If the reactivity or the compounding ratio of a resin such as the melamine resin is increased in order to secure the hardness, the recoat adhesion cannot be obtained because the residual amount of hydroxyl groups is insufficient. In addition, if the number of hydroxyl groups is increased by increasing the number of polyester branches to compensate for this, the network structure becomes overcrowded, impeding the penetration of the molecular chains of the recoated coating film,
After all, there was a problem that the recoat adhesion could not be obtained.

(Means for Solving Problems) As a result of intensive research to solve the above problems, the present inventors have found that
Using a polyester obtained by dehydration condensation of the main component polyester with a polyvalent carboxylic acid containing an aromatic polyvalent carboxylic acid as an essential component and a polyhydric alcohol other than the cycloaliphatic polyhydric alcohol, the polyester resin itself is rigid. In addition, the crystallinity due to the intermolecular force can be increased, and the hardness sufficient to secure the scratch resistance can be obtained without depending on the highly branched structure of the polyester resin or the crosslinking degree of the resin such as the melamine resin.

In fact, the cross-linking structure of the coating film is roughened by limiting the branched structure of the polyester, that is, the number of hydroxyl groups is 2.1 to 2.8 on average per molecule, and the first coating film at the time of baking the second coating film is The inventors have found that the penetration and diffusion into the coating film can be facilitated and the recoat adhesion can be obtained at the same time, and the present invention has been accomplished.

The automotive topcoat coating composition of the present invention thus achieved is a dehydration condensation product of a polyhydric carboxylic acid containing an aromatic polyhydric carboxylic acid and a polyhydric alcohol other than the cycloaliphatic polyhydric alcohol. With a number average molecular weight of 2,000 to 10,00
A polyester resin having an average of 2.1 to 2.8 hydroxyl groups in one molecule at 0 and a resin capable of reacting with the hydroxyl groups is 90: 1 in a weight ratio.
It is characterized in that it was contained at a ratio of 0 to 60:40.

Hereinafter, the present invention will be described in detail according to the configuration.

The number average molecular weight of the polyester resin and the amount of hydroxyl groups (hereinafter referred to as OH) per molecule defined in the present invention are parameters that are related to each other and determine the crosslink density as a coating film. That is, when the number average molecular weight is less than 2,000, the absolute amount of OH is large and the crosslink density is increased to prevent sufficient penetration of the second coating film.
When the number average molecular weight exceeds 10,000, the absolute amount of OH becomes insufficient, and the resin viscosity increases, which makes it difficult to penetrate into the first coating film. Similar to the reason for the molecular weight, if the OH content per molecule is less than 2.1 / molecule, not only the recoat adhesion but also the water resistance and solvent resistance will be insufficient.
If it exceeds 2.8, the bridge will be overcrowded and the performance will not be obtained.

Next, the design of the amount of OH in the polyester molecule will be described.

Trifunctional alcohols are usually used for branching polyester. Therefore, the degree of branching can be controlled by how much trifunctional alcohol is added.

Then, the polyester Since the structure is, the relations of the following expressions, and are established.

_{N OH = M 3 +2 ...... M} A = M 2 + M 3 -1 ...... n p = (M 3 × nM 3) + (M 2 × nM 2) + (M A × nM A) - (2 × 18 × M _A ) …… Note) De-H ₂ O reaction amount Therefore, when the type of monomer, molecular weight and OH number are given, the required amount of charged monomer can be determined.

For example, the following monomers allow the following molecular design.

In the actual synthesis, the amount of the dibasic acid is often used in excess of the above amount, and is often left as an acid value in the resin. In that case, an acid can be charged in excess based on the following relationship, and the reaction end point can be determined by measuring the acid value to design a desired molecule.

Acid value (KOH amount to neutralize 1 g of resin (mg): A _V excess acid amount (mol): M _A ′ For example, if the acid value is 5 in the above example, M _A ′ is 0.09 mol, and the total amount of phthalic anhydride charged is 8.03 + 0.
It is necessary to set 09 = 8.12 mol.

The resin capable of reacting with the hydroxyl group used in the present invention serves as a curing agent component for reacting and curing with the polyester resin, and thus the resin serving as the curing agent has a weight ratio with the polyester serving as the main component. It is mixed with 90:10 to 60:40 (main agent: curing agent). If the ratio of the curing agent is less than 10, the chemical cross-linking is insufficient and the water resistance and solvent resistance are poor. If it exceeds 40, the cross-linking becomes too dense and the recoat adhesion cannot be obtained.

Next, the monomer composition will be described. The polyvalent carboxylic acid constituting the polyester used in the present invention has an aromatic polyvalent carboxylic acid as an essential component, and the polyvalent carboxylic acid is 30 to 60% by weight of aromatic polyvalent carboxylic acid in all monomers. It consists of acid and 0 to 20% by weight of aliphatic polycarboxylic acid. And the proportion of polyhydric alcohols other than polyhydric carboxylic acids and cycloaliphatic polyhydric alcohols is usually 40 to 50 wt% for polyhydric alcohols other than cycloaliphatic polyhydric alcohols relative to 50 to 60 wt% polyhydric carboxylic acids. %. The aromatic polyvalent carboxylic acid content of 30 to 60% by weight in all the monomers means that the rigidity and cross-linking of the molecular chain necessary to secure scratch resistance and durability in the so-called upper glass region at room temperature. The crystallinity is given by the intermolecular force equivalent to. On the other hand, when the second coating film is applied and baked, the first coating film also reaches a high temperature, and as the thermal motion of the molecular chains becomes active, the bond due to intermolecular force disappears and the so-called rubber-like region is reached. .
Therefore, the network structure of the first coating film is in a rough state sufficient to permeate and diffuse the unreacted molecules of the second coating film, and sufficient adhesiveness is obtained after the second coating film is cured. . Therefore, in the monomer composition of the present invention, the aromatic polyvalent carboxylic acid accounts for 30 to 60% by weight of all the monomers of the polyester resin, whereby the scratch resistance is remarkably improved. Incidentally, the surface hardness of the current topcoat paint is a pencil hardness value in the range of HB to H, whereas the coating film of the present invention has a hardness of H or more. However, as described above, when the second coating film is baked, it is necessary that the first coating film is in the rubber-like region at the baking temperature. That is, in the present invention, it is an essential condition that the glass transition temperature (Tg) of the completed coating film is always lower than the baking temperature of the second coating film. Desirably, the bond due to intermolecular force is generated at that temperature. No state at all, ie
In the viscoelastic behavior, it is preferable that the elastic modulus reaches a region where it stabilizes as a high temperature elastic modulus.

Therefore, the compounding ratio of the curing agent used in the present invention to the polyester should not exceed 60:40 by weight. Also 90:
If it is less than 10, the chemical crosslinking is insufficient,
Poor water resistance and solvent resistance.

Next, the present invention will be described with reference to specific examples.

The polyester resin used in the present invention is a method conventionally used in the production of polyester resins for paints, that is, 16
It is produced by a method of heating to 0 ° C. to 250 ° C. and separating water generated by the reaction out of the system.

Polyhydric alcohols other than the cycloaliphatic polyhydric alcohols that can be used here include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol,
2,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, 1,10 -Decanediol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbit and the like, and one or more of these may be used in combination.

Next, as the aliphatic polycarboxylic acid, there are succinic acid, adipic acid, 1,10-decanedicarboxylic acid, fumaric acid, maleic anhydride and methyl esters thereof, and one or more of them may be combined. Can be used.

Further, the aromatic polyvalent carboxylic acid which is an essential component includes phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, pyromellitic anhydride and their methyl esters, and one or two of these may be used. The above can be used in combination.

Further, as a result of further examination, a part of the aromatic polyvalent carboxylic acid components listed up to now is replaced with a saturated alicyclic polyvalent carboxylic acid, and the cyclic structural component includes the aromatic polyvalent carboxylic acid described above. It was found that the same effect can be obtained by adjusting the amount to 30 to 60% by weight. Here, hexahydrophthalic acid, hexahydrotrimellitic acid, hexahydro-2-methyltrimellitic acid and their acid anhydrides can be used as the saturated alicyclic polycarboxylic acid.

In the production of the above polyester resin, a monohydric alcohol, a monovalent carboxylic acid, a monoepoxy compound or the like may be used for the purpose of controlling the molecular weight and improving the solubility, but the amount thereof is within a range not impairing the object of the present invention. And should be about 10% by weight or less in the polyester resin. Examples of the monohydric alcohol that can be used include normal octyl alcohol, 2-ethylhexyl alcohol, lauryl call,
Stearyl alcohol and the like. Examples of the monocarboxylic acid include caproic acid, caprylic acid, pelargonic acid, isononanoic acid, lauric acid, stearic acid, oleic acid, benzoic acid, tert-butylbenzoic acid, and various animal and vegetable oil fatty acids such as soybean oil. Fatty acids, flaxseed oil fatty acids, safflower oil fatty acids, rapeseed oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, tall oil fatty acids, rice bran oil fatty acids and the like. As the monoepoxy compound, phenyl glycidyl ether, normal butyl glycidyl ether,
There is glycidyl ester of versatic acid available under the trade name of Cardura E from Shell Chemical Company.

The polyester resin thus obtained is used by diluting it with an organic solvent to an appropriate concentration, preferably 30 to 70% by weight. Examples of organic solvents used include aromatic organic solvents such as benzene, toluene, xylene, Solvesso 100 and Solvesso 150 (both are trade names) commercially available from Exxon Chemical Company; methyl alcohol, ethyl alcohol, isopropyl alcohol. Alcohols such as normal butyl alcohol, isobutyl alcohol, sec-butyl alcohol, amyl alcohol, and cyclohexyl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, acetic acid Glycol-based solvents such as ethylene glycol monoethyl ether; acetone, methyl ethyl ketone, methyl isobutyl ketone, Ketone-based solvents such as luamyl ketone and cyclohexanone; ester-based solvents such as ethyl acetate, butyl acetate, isobutyl acetate, amyl acetate, methyl propionate and ethyl propionate, dioxane, isophorone, 2-nitropropane, N-methylpyrrolidone, etc. And these can be used alone or in combination of two or more.

The coating composition of the present invention comprises the polyester resin obtained as described above and a resin having a reactive group capable of reacting with a hydroxyl group. The resin having a reactive group capable of reacting with a hydroxyl group serves as a curing agent component for reacting and curing the polyester resin as described above, and is a reactive group capable of reacting with a hydroxyl group of the polyester resin. There is no limitation as long as the resin has it.

As the resin having a reactive group capable of reacting with a hydroxyl group, an amino resin, a phenol resin, a ketone resin, a xylene resin,
There are furfural resin, polyisocyanate resin, blocked polyisocyanate resin in which all or some of the isocyanate groups are sealed, epoxy resin and the like. In the present invention, amino resin, polyisocyanate resin and blocked polyisocyanate are used. 1 selected from resin
It is preferable to use one or more kinds. Examples of the amino resin include urea resin, melamine resin, acetoguanamine resin, benzoguanamine resin, and phthaloguanamine resin. Examples of the polyisocyanate resin include Desmodur-L and Desmodur-N available from Bayer, Coronate-EH available from Nippon Polyurethane Industry Co., Ltd., and IPDI-available from Hüls.
There is T-1890 (both are trade names). Further, as the blocked polyisocyanate resin, all or a part of the isocyanate groups of these polyisocyanate resins are used.
A monohydric alcohol such as ethylhexyl alcohol, phenol, oximes such as ε-caprolactam and methylethylketone oxime, and a blocker with a blocking agent such as diethyl malonate and methyl acetoacetate can be used.

In the present invention, in addition to the above components, a pigment for the purpose of coloring and picking is blended. There is no particular limitation on the amount to be blended, but it is usually in the range of 0.08 to 1.4 by weight ratio with respect to the resin component. Examples of the pigment used for the topcoat include inorganic pigments such as titanium oxide, carbon black, yellow lead, iron oxide yellow, navy blue, molybdenum red, phthalocyanine blue, phthalocyanine green, fast yellow, permanent red, and kunacridone red. There are organic pigments.

In the coating composition of the present invention, various other additives commonly used in the field of coating materials, such as an ultraviolet absorber, a light stabilizer, a surface tension adjusting agent, a leveling agent, an anti-sagging agent, and an erasing agent are used. A foaming agent, an anti-settling agent, a pigment dispersant, etc. can be used.

The coating composition of the present invention is produced by an apparatus and method conventionally used for producing an automobile top coating pigment.
In this case, the polyester resin and the resin having a reactive group capable of reacting with a hydroxyl group may be mixed in advance in one liquid, or the two liquids may be separately mixed and mixed during coating. When a polyisocyanate resin is used as a resin having a reactive group capable of reacting with a hydroxyl group, 2
Liquid type is preferable.

The coating composition of the present invention is provided for coating as it is or after being diluted with a thinner to an appropriate viscosity. As a coating method, any of the methods usually used for coating top coatings in the automobile industry, such as air spray coating, airless spray coating, air atomization type electrostatic coating, bell rotary atomization type electrostatic coating, etc., can be applied. it can.

The coating composition of the present invention has a film thickness after curing of 10 to 70 μm on an automobile body to which an undercoat paint such as an electrodeposition primer is previously applied.
If the polyisocyanate resin is blended after being coated to a m of 10 m, the temperature should be between room temperature and 150 ° C for 10 minutes to 2 minutes.
When amino resin or blocked polyisocyanate resin is blended for 4 hours, it is cured by heating and drying at a temperature of 100 to 200 ° C for 5 minutes to 1 hour, and it has excellent scratch resistance, recoat adhesion and water resistance. A coating film having good chemical resistance and solvent resistance can be obtained.

(Example) Hereinafter, the structure, action, and effect of the present invention will be described in more detail with reference to Examples. Unless otherwise specified, the parts,%, and ratios in each example represent parts by weight,% by weight, and weight ratio, respectively.

Examples 1 to 4 and Comparative Examples 1 to 5 (I) Production of Polyester Resin With the formulations shown in Table 1, polyester resins having different number average molecular weights were produced as follows.

That is, a reactor equipped with a heating device, a stirrer, a thermometer, a reflux condenser equipped with a water separator, and a nitrogen gas introduction pipe was used, and neopentyl glycol, trimethylolpropane, cyclohexane-1, with the composition shown in Table 1, 4-Dimethylol, isophthalic acid, phthalic anhydride and adipic acid were added and heated. When the temperature reached 120 ° C., the nitrogen gas introduction pipe was opened and nitrogen gas was passed through to start stirring. Heat gradually to 230 ° C over a further 3 hours and
The reaction continued for an hour. After 1 hour, 3 parts of xylene was added to the content, and the water separator was also filled with xylene so that water was azeotroped with xylene to promote desorption. The acid value was measured 1 hour after the addition of xylene, and when the acid value became 7 or less, the reaction was terminated and cooled, and xylene: Solvesso 150
(Product name of Exxon Chemical Co. product): cyclohexanone: normal butyl alcohol 20: 30: 40: 10 in a mixed solvent with a non-volatile content of 60%.

(II) Preparation of paint The following ingredients were placed in the vessel of a ball mill disperser and dispersed using a ceramic ball for 48 hours.

After the dispersion, the ceramic balls were sifted through a sieve, and the following components were added and mixed with a dissolver to produce a paint.

The paint produced has a nonvolatile content of 65.2%, a polyester resin to melamine resin ratio of 70:30, and a pigment to organic binder component ratio of 0.8.

Examples 5 to 7 Comparative Examples 6 and 7 After dispersing the pigment in the same manner as in Examples 1 to 4 and Comparative Examples 1 to 5, as a curing agent, as shown in Table 2-1 and Table 2-2. Example 5, by changing the ratio of the melamine resin of
6, the paints of Comparative Examples 6 and 7 were produced. Further, in Example 7, a coating was produced by changing the curing agent to polyisocyanate (manufactured by Bayer, trade name: Desmodur-N-70, nonvolatile content = 70%).

Test Examples Coating and Coating Performance Tests The topcoat paints produced in Examples 1-7 and Comparative Examples 1-7 were
Solvesso 150 (existing): 9 normal butyl alcohol
A thinner with a composition of 5: 5, using a Ford Cup No. 4 20
It was diluted so that the viscosity when measured at 25 ° C was 25 seconds.

0.8 mm thick, 150 mm long, 70 mm wide automotive steel plate (JIS-
G-3141) treated with Bonderite No. 3004 (trade name of zinc phosphate coating manufactured by Nippon Parker Rising Co., Ltd.), and then Power Top U-100 (cationic type for automobiles manufactured by Nippon Paint Co., Ltd.) Electrolyzed primer (trade name) is applied to a test plate with a thickness of 15 to 20 μm, and diluted intermediate paint, Epico No. 1500CP sealer (trade name of NOF Corporation's automotive intermediate paint) Apply air spray coating so that the film thickness after baking will be 35-40 μm, set for 10 minutes at room temperature, and then for 30 minutes at 140 ° C.
It was baked and cured at the temperature of. Then, the above-mentioned top coating composition was applied to the test plate, and the film thickness after baking was 35 to 40.
After air spray coating so as to have a thickness of 10 μm and setting at room temperature for 10 minutes, baking was performed at a temperature of 140 ° C. for 30 minutes to cure.

The test plate thus prepared was subjected to a coating film performance test based on JIS-D-0202 general rules for coating automotive parts, and the following test for scratch resistance and recoat adhesion was carried out. It is shown in 3-1 and Table 3-2. For comparison, the performance of the topcoat paint currently used as a reference example is also shown.

(B) Scratch resistance test method This test method is performed when partially repairing defects such as dust and lumps in the coating film, and in the polishing step, the coating film is excessively damaged,
There is a phenomenon that the polished portion is easily soiled, and this development is assumed to occur remarkably in a light solid color.

First, the surface of the test plate is rough-polished, and a fine alumina powder (trade name A-50K manufactured by Showa Light Metal Co., Ltd.) with a small amount of water is applied to a flannel cloth for polishing. After that, as a finishing polish, ultrafine alumina powder (Showa Light Metal Co., Ltd.)
Carbon black manufactured by Tokai Carbon Co., Ltd. under the trade name of UA-5105) manufactured by Tokai Carbon Co., Ltd. ) Rub it with flannel cloth,
After removing excess carbon black, wipe it off thoroughly with a clean flannel cloth. The center of the thus-prepared test plate was visually compared with the Munsell brightness standard plate to determine the Munsell brightness. Incidentally, the untreated brightness was 9.7.

(B) Recoat adhesion test method This test method assumes an actual automobile coating film baking furnace. The paint baking oven is usually set so that the standard value of the paint baking temperature is maintained for a certain period of time or more, but it is not always constant due to the presence or absence of the object to be coated and changes in the external temperature, etc. There is a possibility that it will be baked in the so-called overbaked. If the first coating film is overbaked, crosslinking will proceed excessively, and recoat adhesion will be more difficult to obtain due to the reasons described above.

Therefore, in this test, in addition to the standard test plate obtained by the above method, the first coating film was applied by the above method and then overbaked at a temperature of 170 ° C. for 30 minutes. The so-called non-sand recoating is performed on the two types of test plates thus obtained, without applying a polishing step, by directly applying the second top coating composition and performing standard baking at 140 ° C. for 30 minutes. The test plate obtained in this way is JIS-D-0
This is an eye adhesion test based on 202 general rules for automobile coatings.

(Effects of the Invention) In the above Examples and Comparative Examples, 30% of all monomer components were used.
-60% by weight of aromatic polycarboxylic acid, and the total amount of polycarboxylic acid including this aromatic polycarboxylic acid is 50-60
%, Polyhydric alcohols other than cycloaliphatic polyhydric alcohol 40 to 50% by weight, number average molecular weight 2,000 to 10,000
Example 1 in which a curing agent having a functional group capable of reacting with OH is mixed with a polyester resin having an average of 2.1 to 2.8 OH in one molecule in a ratio of 90/10 to 60/40 The top coating composition for automobiles of No. 7 has extremely good scratch resistance and recoat adhesion as shown in Test Examples.

On the other hand, the coating material of Comparative Example 1 lacks chemical cross-linking due to insufficient amount of OH, and lacks not only scratch resistance and recoat adhesion but also various other properties. The paint of Comparative Example 2 is OH
Therefore, the adhesion of the overbaked coat is poor. Since the coating material of Comparative Example 3 has a small molecular weight, the cross-linking is still dense and the recoat adhesion is also poor. The coating material of Comparative Example 4 has a large molecular weight, a low OH density, and lacks recoat adhesion. Further, since the resin viscosity is high, the leveling is insufficient and the skin becomes poor. The coating material of Comparative Example 5 lacks the aromatic polyvalent carboxylic acid and thus has insufficient hardness and lacks scratch resistance. The coating material of Comparative Example 6 lacks the curing agent and therefore lacks in chemical cross-linking and lacks hardness and moisture resistance. Since the coating material of Comparative Example 7 contains an excessive amount of curing agent, recoat adhesion cannot be obtained, and the surface shrinkage is large, resulting in poor appearance. As a reference example, the performance of the overcoat paint currently used is additionally noted, but the hardness is insufficient and the scratch resistance is insufficient. Thus, the coating composition of the present invention, the specific polyester resin, a resin capable of reacting with a hydroxyl group, in a weight ratio of 9
By containing it in a ratio of 0:10 to 60:40, the effect of having both scratch resistance and recoat adhesion can be obtained.

Claims (1)

[Claims] 1. 50 to 60% by weight of a polyvalent carboxylic acid containing 30 to 60% by weight of the total monomer components, and an aromatic polyvalent carboxylic acid.
40-50 polyhydric alcohols other than cycloaliphatic polyhydric alcohols
It is a dehydrated condensate with a weight average molecular weight of 2,000 to 1
The weight ratio of the polyester resin having an average of 2.1 to 2.8 hydroxyl groups in one molecule at 0,000 to the resin capable of reacting with hydroxyl groups
A top coating composition for automobiles, which is contained in a ratio of 90:10 to 60:40.