JP3455362B2 - Automotive intermediate coating composition - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an intermediate coating composition for automobiles, and more particularly to an intermediate coating composition for automobiles which is excellent in chipping resistance and appearance.

[0002]

2. Description of the Related Art Conventionally, in the field of automobile industry, it has been strongly desired to prevent the durability of coating, especially the peeling of coating film due to impact. Especially in the cold regions of Europe and America, gravel and the like mixed with a large amount of rock salt is often laid in order to prevent freezing of the motorway in winter. On the outer surface of automobiles running on this kind of road, rock salt particles and pebbles that are splashed up by wheels collide with the surface of the coating film, and the impact locally peels the coating film from the substrate. Cause Due to this phenomenon, the metal surface is exposed at the impacted part,
Corrosion progresses with rapid rusting.

In order to prevent chipping and the progress of corrosion due to this, various studies have been made on chemical conversion treatment, electrodeposition, a primer, an intermediate coating composition and a top coating composition. Especially for intermediate coatings, the impact force is reduced,
Many studies have been conducted to prevent the coating film from peeling off from the metal surface, which causes rusting. For example, Japanese Patent Publication Sho 52
-43657 discloses an intermediate coating composition for automobiles containing sericite in an amount of 10 to 75% by weight based on the total solid content of the coating.

In Japanese Patent Laid-Open No. 55-56165, an acid resin having an acid value of 10 to 50 is added to talc powder 20 to 50.
An intermediate coating composition for an automobile, which contains 10 parts by weight and 10 to 50 parts by weight of an antirust pigment as essential components is disclosed.
At present, the film thickness of the intermediate coating film after baking, which is applied in the field of automobile industry, is 30 to 40 μm, and the quality such as chipping resistance and appearance is good.

[0005]

Recently, from the viewpoint of resource saving and cost reduction, there has been an idea to reduce the thickness of the intermediate coating film to a range of 20 to 30 .mu.m. However,
When the conventional intermediate coating material is applied in the thickness range of 20 to 30 μm, the chipping resistance and the appearance quality of the coating film are deteriorated as compared with the case of coating in the thickness range of 30 μm to 40 μm. .

The decrease in chipping resistance when the thickness of the intermediate coating film is reduced to the range of 20 to 30 .mu.m is due to the reduction in thickness, and the impact force is lower than that of the conventional intermediate coating film of 30 to 40 .mu.m. This is because the peeled area has increased due to the fact that it is easy to reach the electrodeposition and the object to be coated. The deterioration of the appearance when the thickness of the intermediate coating film is reduced to 20 to 30 μm is because the smoothness is impaired due to the insufficient wettability of the intermediate coating film on the electrodeposition of the lower layer. is there.

Therefore, an object of the present invention is to provide an intermediate coating composition for automobiles which is excellent in chipping resistance and appearance.

[0008]

In order to improve the chipping resistance, the present inventors intend to strengthen the intermediate coating film,
As a result of earnestly studying the design design of the polyester resin,
Regarding the ratio between the weight average molecular weight and the number average molecular weight, it is conventionally 3 to
By changing the polyester resin of 4 to a polyester resin of 2 to 2.5 and sharpening the molecular weight distribution,
Regarding the improvement of appearance, as a result of diligent study on the monomer species of the polyester resin in order to improve the wettability of the undercoat of the intermediate coating, by introducing a specific acid anhydride having an alkyl group or an alkenyl group, chipping resistance can be improved. The present invention has been accomplished by finding that the problems of deterioration in the appearance and appearance are solved.

The above object of the present invention is a polyester resin using a polyhydric alcohol and a polycarboxylic acid as a resin raw material, wherein an acid anhydride represented by the following chemical formula 2 is added to the resin raw material.
In the range of 20 to 20% by weight, the ratio of the weight average molecular weight to the number average molecular weight is 2 to 2.5, and the number average molecular weight is 1500 to
2500, a hydroxyl value of 80-120, an acid value of 5-20, a polyester resin of 80-60 parts by weight, and a resin having a reactive group capable of reacting with a hydroxyl group of 20-40 parts by weight. Achieved with an intermediate coating composition.

[Chemical 2] In the formula, R is an alkyl group or alkenyl group having 8 to 20 carbon atoms.

In the present invention, as the resin having a reactive group capable of reacting with a hydroxyl group, at least one selected from the group consisting of alkyl etherified amino resin, blocked polyisocyanate resin and epoxy resin is used. preferable.

The acid anhydride used in the present invention may be linear or branched as the structure of its alkyl group or alkenyl group, and has 8 to 8 carbon atoms.
20, preferably 10-18. When the carbon number is less than 8, the surface activity is poor and the effect of the present invention cannot be obtained.
When it exceeds 20, the carbon chain is excessively long and there is no advantage due to it, and it is difficult to obtain industrially, so that it is not suitable for practical use.

Examples of such an acid anhydride having an alkyl group include succinic anhydrides such as octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl and octadecyl. , Having an alkenyl group, for example, octenyl, nonenyl,
Examples thereof include succinic anhydrides such as decenyl, undecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl and octadecenyl.

The acid anhydride used in the present invention is added to the resin raw material in the polyester resin in an amount of 5 to 20% by weight. Less than 5% and 20% by weight
If it exceeds, the effect of the present invention cannot be obtained.

The polyester resin in the present invention has a weight average molecular weight to number average molecular weight ratio of 2 to 2.5, a number average molecular weight of 1500 to 2500 and a hydroxyl value of 80 to 12.
0 and an acid value of 5 to 20.

The ratio of the weight average molecular weight to the number average molecular weight is 2
When it is less than 2.5, resin synthesis becomes difficult, and when it exceeds 2.5, the chipping resistance is deteriorated. If the number average molecular weight is less than 1500, the chipping resistance is lowered,
On the contrary, when it exceeds 2500, the appearance is deteriorated. further,
When the number of hydroxyl groups is less than 80 or more than 120, the chipping resistance is lowered. If the acid value is less than 5, the crosslinking reactivity is poor, and if it exceeds 20, the water resistance of the coating film is lowered.

The polyester resin in the present invention contains, as a resin raw material, the above-mentioned acid anhydride as an essential component, and the acid anhydride and a polyhydric alcohol or a polybasic acid constituting a normal polyester resin are esterified by a known method. It can be obtained by reaction.

Examples of the above polyhydric alcohols include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butanediol and 1,6-.
Hexanediol, diethylene glycol, dipropylene glycol, cyclohexane-1,4-dimethylol, neopentyl glycol, triethylene glycol, hydrogenated bisphenol A, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, etc. Can be mentioned.

Examples of the polybasic acid include phthalic anhydride, isophthalic acid, terephthalic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, maleic anhydride,
Examples include fumaric acid, itaconic acid, trimellitic anhydride, and the like.

The intermediate coating composition for automobiles of the present invention contains the polyester resin thus obtained and a resin having a reactive group capable of reacting with a hydroxyl group.

Examples of the resin having a reactive group capable of reacting with a hydroxyl group include an alkyl etherified amino resin, a blocked polyisocyanate resin in which all or some of the isocyanate groups are blocked, and an epoxy resin. In the present invention, at least one selected from the group consisting of alkyl etherified amino resins, blocked polyisocyanate resins and epoxy resins can be mentioned.

In the present invention, the weight ratio of the polyester resin to the resin having a reactive group capable of reacting with a hydroxyl group is preferably 80:20 to 60:40. When the ratio with the resin having a reactive group capable of reacting with a hydroxyl group is less than 20, the coating film is insufficiently crosslinked and water resistance, chemical resistance and solvent resistance are poor. On the other hand, if the ratio of the two exceeds 40, the chipping resistance of the coating film decreases.

In addition to the above components, the intermediate coating composition for automobiles of the present invention contains titanium oxide, zinc oxide, carbon black, precipitated barium sulfate, calcium carbonate, talc,
Pigments such as red iron oxide and mapico yellow can be contained. These pigments are not particularly limited, but it is usually preferable to mix them in a weight ratio of 0.2 to 1.4 with respect to the organic binder component.

In addition to the above, an organic solvent and various additives conventionally used in the field of coating materials can be used in the intermediate coating composition for automobiles of the present invention. As the organic solvent, aromatics, alcohols, esters, ketones and ethers can be used, and as the additive, for example, a surface tension adjusting agent, a leveling agent, an anti-sagging agent, a defoaming agent, an anti-settling agent. , Pigments, dispersants and the like can be used.

The automotive intermediate 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 the coating method, any of the methods usually used for coating intermediate 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 intermediate coating composition for automobiles of the present invention is applied to an automobile body which has been previously undercoated with electrodeposition or a primer.
After coating so that the film thickness after curing is 20 to 30 μm, it is cured by heating and drying at a temperature of 120 to 180 ° C. for 1 hour to 10 minutes, and has good chipping resistance and good appearance. Is obtained.

[0026]

EXAMPLES The present invention will now be described in more detail by way of examples, which should not be construed as limiting the invention. Unless otherwise specified, the parts,%, and ratios in each example represent parts by weight,% by weight, and weight ratio, respectively.

(I) Production of Polyester Resin Production Example 1 A polyester resin was produced in the following manner with the ingredients shown in Table 1. A reactor equipped with a heating device, a stirrer, a reflux condenser equipped with a thermometer and a water separator, and a nitrogen gas inlet pipe was charged with hexadecenyl succinic anhydride, neopentyl glycol, cyclohexane-1,4-dimethylol, isophthalic acid. Then, adipic acid was added and heated. When the temperature reached 120 ° C., the nitrogen gas introduction pipe was opened and nitrogen gas was introduced to start stirring.

Further, it was gradually heated to 200 ° C. over 3 hours, and the reaction was continued at a temperature of 200 ° C. for 30 minutes. After 30 minutes, cooling was started and when the temperature reached 150 ° C, trimethylolpropane and phthalic anhydride were added to the contents. After that, gradually heat up to 230 ℃ over 3 hours, 230 ℃
The reaction was continued at the temperature of 1 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 and xylene were azeotropically distilled to promote desorption. The acid value was measured 1 hour after the addition of xylene, and when the acid value was 12 or less, the reaction was terminated and the reaction mixture was cooled and xylene: Solvesso 150 was added.
(Product name of Exxon Chemical Company product): ratio of cyclohexanone: normal butyl alcohol is 20: 30: 4
The mixture was diluted with a mixed solvent of 0:10 so that the non-volatile component was 60%.

Production Example 2 A polyester resin having the composition shown in Table 1 was produced as follows. Hexadecenylsuccinic anhydride, neopentyl glycol,
Cyclohexane-1,4-dimethylol, isophthalic acid and adipic acid were added and heated. When the temperature reached 120 ° C., the nitrogen gas introduction pipe was opened and nitrogen gas was introduced to start stirring. Further, it was gradually heated to 200 ° C. over 3 hours, and the reaction was continued at a temperature of 200 ° C. for 30 minutes. Three
After 0 minutes, cooling was started and when the temperature reached 150 ° C., trimethylolpropane and phthalic anhydride were added to the contents.

Thereafter, the mixture was gradually heated to 230 ° C. over 3 hours, and the reaction was continued at 230 ° C. for 1 hour. After 1 hour, 3 parts of xylene was added to the contents, and the water separator was also filled with xylene so that water and xylene were azeotropically distilled to promote desorption. One hour after the addition of xylene, the acid value was measured, and when the acid value became 17 or less, the reaction was terminated and the mixture was cooled and diluted in the same manner as in the resin of Production Example 1.

Production Example 3 A polyester resin having the composition shown in Table 1 was produced as follows. Dodecyl succinic anhydride, cyclohexane-1,4-dimethylol, neopentyl glycol, isophthalic acid and adipic acid were placed in the same reactor as in Production Example 1 and heated. When the temperature reached 120 ° C., the nitrogen gas introduction pipe was opened and nitrogen gas was introduced to start stirring. Further, it was gradually heated to 200 ° C. over 3 hours, and the reaction was continued at a temperature of 200 ° C. for 30 minutes. After 30 minutes, cooling was started and when the temperature reached 150 ° C., trimethylolpropane and phthalic anhydride were added to the contents.

Thereafter, the mixture was gradually heated to 230 ° C. over 3 hours, and the reaction was continued at 230 ° C. for 1 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 and xylene were azeotropically distilled to promote desorption. One hour after the addition of xylene, the acid value was measured, and when the acid value was 10 or less, the reaction was terminated and the mixture was cooled and diluted exactly as in Production Example 1.

Production Example 4 A polyester resin having the composition shown in Table 1 was produced as follows. Cyclohexane-1,4-dimethylol, neopentyl glycol, isophthalic acid, phthalic anhydride and adipic acid were placed in the same reactor as in Production Example 1 and heated. When the temperature reached 120 ° C., the nitrogen gas introduction pipe was opened and nitrogen gas was introduced to start stirring.

Further, the mixture was gradually heated to 230 ° C. over 3 hours, and the reaction was continued at 230 ° C. for 1 hour. After 1 hour, 3 parts of xylene was added to the contents, and the water separator was also filled with xylene so that water and xylene were azeotroped to promote desorption. One hour after the addition of xylene, the acid value was measured, and when the acid value was 12 or less, the reaction was terminated and cooled, and the resin was diluted exactly as in Production Example 1.

Production Examples 5 to 8 Polyester resins having the formulations shown in Table 1 were produced in the same reaction steps using the same reactor as in Production Example 1.

Production Example 9 A polyester resin having the composition shown in Table 1 was used in the same reactor as in Production Example 1, and the reaction was terminated and cooled when the acid value became less than 5 through the same reaction steps. The resin was diluted in the same manner as the resin of Production Example 1.

Production Example 10 A polyester resin having the composition shown in Table 1 was used in the same reactor as in Production Example 1, and the acid value was 32 after the same reaction steps.
When the temperature became the following, the reaction was terminated and cooled, and then Production Example 1
It was diluted in the same manner as the resin of.

[0039]

[Table 1]

(II) Preparation of paint The following components were put in a vessel of a ball mill disperser and dispersed using a ceramic ball for 48 hours. Polyester resin varnish produced in (1) (solid content 60%) 21.8 parts rutile type titanium oxide 23.6〃 mapico yellow 0.8〃 carbon black 0.2〃 xylene 3.3〃 normal butyl alcohol 3.3〃 After the dispersion, the ceramic balls were separated by a sieve and the following components were added to prepare a paint. Polyester resin varnish manufactured in (1) 19.9 parts U-VAN 21R 21.4〃 (50% solid content of melamine resin varnish manufactured by Mitsui Toatsu Chemicals Inc.) Sumijour BL-3175 1.4〃 (Sumitomo Bayer Co., Ltd. Blocked polyisocyanate resin varnish solids made of 75%) Epoxy resin varnish (Epicoat 828 1.9〃 (60% diluted product of Yuka Shell Epoxy Co., Ltd.) Dibutyltin daurilate 0.2〃 (Dissociation of blocking agent Catalyst) Xylene 2.2 〃 The produced paint has a solid content of 62.5%, a ratio of polyester resin to melamine resin of 70/30, and a ratio of pigment to organic binder of 0.6.

(III) Coating and coating film performance test The intermediate coating prepared in (II) was applied to Solvesso 150 (supra): a thinner having a composition of 95: 5 normal butyl alcohol using Ford Cup No. 4. It was diluted so that the viscosity was 25 seconds when measured at 20 ° C.

An automobile steel sheet (JIS-G-3141) having a thickness of 0.8 mm, a length of 150 mm and a width of 70 mm is treated with Bonderite No. 3004 (trade name of zinc phosphate coating treatment manufactured by Nippon Parkerizing Co., Ltd.). Then, apply Power Top U-100 (trade name of cationic paint for automobiles manufactured by Nippon Paint Co., Ltd.) to 15 to 20 μm.
Test plate coated to a thickness of 10 .mu.m by air spray coating so that the film thickness after baking the diluted intermediate coating composition is 20 to 30 .mu.m and 30 to 40 .mu.m, set at room temperature for 10 minutes, and then set at 140 for 30 minutes. It was baked and cured at a temperature of ° C.

Next, melami No. 1500 red enamel (a product name of automotive top coat paint manufactured by NOF CORPORATION) was similarly baked on this test plate as a top coat so that the film thickness would be 35 to 40 μm. After air spray coating and setting at room temperature for 10 minutes, baking was performed at a temperature of 140 ° C. for 30 minutes to cure. The appearance of the coating film was visually evaluated on the test plate prepared in this way, and
A coating performance test was carried out based on the coating film general rules for automobile parts of IS-D-0202, and a chipping resistance test of the following test method using a gravelometer was carried out to evaluate the chipping resistance.

Test method for chipping resistance: ASTM-D-
3170 "Standard Method of Test for Chip Resista
In accordance with the "nce of Coatings", the chipping resistance test and evaluation are performed as follows. (1) Test equipment; Q-G-R Graperometer (Q-
Panel company product) (2) Chip material; Marble particles with a diameter of about 10 to 15 mm (3) Amount of chip material: About 250 pieces (4) Spraying air pressure; About 4.8 kg / cm ² (5) Test temperature; 20 ℃ (6) Evaluation method; test piece is covered with gum tape leaving 40 mm x 40 mm at the center and attached to the test plate holder, and the chip material is sprayed at a pressure of about 4.8 kg / cm ² and caused by collision 40mm x 4 by measuring the number of scratches and the area of scratches
Record the number of peels and the average peel area in the 0 mm area. Then, a salt spray test is performed for 48 hours according to JIS-Z-2371, and the number of rusts in the non-impacted portion is recorded. The above results are summarized in Table 2.

[0045]

[Table 2]

As is clear from Examples 1, 3, and 5 shown in Table 2, the chipping resistance and the appearance are significantly improved as compared with the conventional ones even when the film thickness after curing is 20 to 30 μm. There is. On the other hand, the conventional intermediate coating for automobiles shown in Comparative Example 8 has a cured film thickness of 20 to 30.
In the case of μm, there is a problem that chipping resistance and appearance are poor. Further, in the case of Comparative Example 9 in which the number average molecular weight of the polyester resin is less than 1500, the chipping resistance is insufficient and the number average molecular weight of the polyester resin is 2,500.
In the case of Comparative Example 10 exceeding 10%, the coatability was poor and the appearance after topcoating was poor, and it was unsuitable as an intermediate coating for automobiles. Comparative Example 1 in which the hydroxyl value of the polyester resin is less than 80
1 and the hydroxyl value of the polyester resin is 120
In the case of Comparative Example 12 in which the acid value of the polyester resin exceeds 20, the cross-linking reactivity is poor, and in the case of Comparative Example 14 in which the acid value of the polyester resin exceeds 20, the water resistance of the coating film decreases.

[0047]

As is clear from the above results, the intermediate coating composition for automobiles of the present invention is a polyester resin containing a polyhydric alcohol and a polycarboxylic acid as a resin raw material, and the alkyl group according to claim 1. Alternatively, the resin raw material contains 5 to 20% by weight of a specific acid anhydride having an alkenyl group, and the ratio of the weight average molecular weight to the number average molecular weight is 2 to 2.5.
Number average molecular weight of 1500 to 2500, hydroxyl value of 80 to
By designing the acid value to be 120 and the acid value to be 5 to 20, the intermediate coating film is toughened and the wettability to the base during coating is improved, so that excellent chipping resistance and appearance can be obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michiaki Wake 4-20-3 Ebisu, Shibuya-ku, Tokyo Within NOF CORPORATION (72) Inventor Ken Nomoto 2 Takara-cho, Kanagawa-ku, Yokohama-shi Kanagawa Nissan Motor Co., Ltd. Incorporated (72) Inventor Katsuya Yamamoto 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Hideki Nakasuji 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A-5-86324 (JP, A) JP-A-3-181575 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C09D 167 / 00,175 / 06 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] 1. A polyester resin comprising a polyhydric alcohol and a polycarboxylic acid as a resin raw material, wherein the resin raw material contains an acid anhydride represented by the following chemical formula 1 in a range of 5 to 20% by weight. The ratio between the molecular weight and the number average molecular weight is 2 to
2.5, polyester resin 8 having a number average molecular weight of 1500 to 2500, a hydroxyl value of 80 to 120, and an acid value of 5 to 20
An intermediate coating composition for an automobile, comprising 0 to 60 parts by weight and 20 to 40 parts by weight of a resin having a reactive group capable of reacting with a hydroxyl group. [Chemical 1] In the formula, R is an alkyl group or alkenyl group having 8 to 20 carbon atoms. 2. The resin having a reactive group capable of reacting with a hydroxyl group is at least one selected from the group consisting of an alkyl etherified amino resin, a blocked polyisocyanate resin, and an epoxy resin. Intermediate coating composition for automobiles.