JP3157278B2 - Thermosetting polyester resin coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paint used for coating automotive resin parts such as bumpers.

[0002]

2. Description of the Related Art Various coatings ranging from hard to soft are used for coating automotive resin parts depending on the type of resin. For the bumper made of polypropylene resin, a soft and stretchable paint is used in order to prevent cracking of the paint film at the time of collision. However, since the coating film is soft, contamination by dirt substances easily occurs, and particularly, contamination by volcanic ash is remarkable. In addition, since poor appearance due to contamination is remarkable in a white paint color, it is necessary to improve the stainability.

[0003] First, as a result of a test of volcanic ash contamination in white color (exposure to Sakurajima for 6 months), polyester resin /
Resin bumper paints such as melamine resin, acrylic resin / melamine resin, polyester resin / isocyanate resin (two-component paint), and acrylic resin / isocyanate resin (two-component paint) have poor resistance to volcanic ash contamination. Was.

[0004] In the resin bumper coating, since the material of the bumper, such as polypropylene resin, is soft, the coating film is required to have softness corresponding to the softness.
It was presumed that the softness of the coating caused contamination to penetrate into the coating and cause contamination. Therefore, regarding the contamination by volcanic ash, we examined what kind of substances were invading the coating film. In the paint film contaminated by exposure to Sakurajima, it was found that the volcanic ash itself did not penetrate into the paint film, but the dissolved material of the volcanic ash did. A possible solution of volcanic ash upon exposure to Sakurajima is a solution of volcanic ash in water. A water extract of volcanic ash was prepared, applied to the coating film and exposed outdoors, and contamination by volcanic ash was confirmed.

[0005] Therefore, in order to improve the stain resistance due to volcanic ash, it is considered that the coating film should be as hard as possible. As a result of exposing Sakurajima to a polyester resin / melamine resin paint for steel sheets, there is no contamination by volcanic ash. It was good. However, it was found that when a coating material for steel plate was applied to a resin bumper, the coating film was not flexible, so that material destruction was likely to occur in a low-temperature impact test, and was not suitable as a coating material for a resin bumper.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a coating composition which has good contamination resistance to volcanic ash and the like and low-temperature impact resistance at a practical level.

[0007]

As a result of examining the fatty acid modification of the polyester resin, the fatty acid suitable for the present invention is a tall oil fatty acid having a moderate flexibility, and by using the tall oil fatty acid-modified polyester resin, A coating composition having good resistance to contamination by volcanic ash, good low-temperature properties and other various properties was able to be produced.

[0008] The coating composition of the present invention contains tall oil fatty acid
A thermosetting polyester resin coating composition comprising a fatty acid-modified polyester resin having a hydroxyl value of 40 to 150 containing 0 to 40% by weight and a melamine resin, applied to a 0.3 mm tin plate to a thickness of 30 ± 5 μm. , Material temperature 12
The coating film hardness when baked for 30 minutes at 0 ± 10 ° C.
A coating composition having a Knoop hardness of 4.0 to 6.0 when measured at 20 ± 2 ° C.

The fatty acid-modified polyester resin of the present invention has a hydroxyl value of 40 to 150 containing 20 to 40% of tall oil fatty acid in the resin, and may be used in combination with a small amount of a fatty acid or oil other than tall oil fatty acid. Good, but the main component may be tall oil fatty acid. If the tall oil fatty acid is less than 20%, the softening effect is small, and if it exceeds 40%, the weather resistance is reduced. If the hydroxyl value is less than 40, the curability will be insufficient, and if it exceeds 150, the water resistance will decrease, and both will degrade the stain resistance. Further, the fatty acid-modified polyester resin or polyester resin other than the tall oil-fatty acid-modified polyester resin may be contained in an amount equal to or less than the equivalent amount of the tall oil-fatty acid-modified polyester resin, and the content thereof may be less than that of the tall oil fatty acid-modified polyester resin. As the number increases, the flexibility effect decreases.

The fatty acid-modified polyester resin in the present invention is synthesized from tall oil fatty acids and other monocarboxylic acids, polybasic acids and polyhydric alcohols. As the monocarboxylic acid other than the tall oil fatty acid, a saturated or unsaturated fatty acid having 6 to 18 carbon atoms or glyceride, benzoic acid, methylbenzoic acid, pt-butylbenzoic acid and the like can be used. In addition, various natural oils or fatty acids thereof, for example, coconut oil, cottonseed oil, rice bran oil, fish oil, soybean oil, linseed oil, tung oil, rapeseed oil, castor oil, dehydrated castor oil and the like, or those fatty acids are also monocarboxylic acids Can be used as Further, when a monoepoxy compound such as Kajura E (a product of Ciel Chemical Co., Ltd.) is used as a dihydric alcohol, if the monoepoxy compound contains a fatty acid residue having 6 to 18 carbon atoms, Fatty acids can also be included in the monocarboxylic acids of the present invention.

Examples of the polybasic acid include phthalic acid and its anhydride, isophthalic acid, terephthalic acid, methyl terephthalate, tetrahydrophthalic acid and its anhydride, hexahydrophthalic acid and its anhydride, 1,2,5 , 6-tetrahydrophthalic acid and its anhydride, succinic acid and its anhydride, maleic anhydride, fumaric acid, adipic acid, azelaic acid, sebacic acid, trimellitic acid and its anhydride, pyromellitic acid and its anhydride, etc. There is. These monocarboxylic acids and polybasic acids can be used alone or in combination of two or more.

Examples of the polyhydric alcohol include those having a valence of 3 or more, such as glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, and pentaerythritol. Glycol, propylene glycol, 1,4-butanediol, 1,2-pentanediol, 3-methyl-1,2-butanediol, trimethylene glycol, 1,5-pentanediol, 2,4-
Pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 1,4-pentanediol, 3-methyl-4,5-pentanediol,
There are 1,4-hexanediol, 2,5-hexanediol, 1,5-hexanediol, 1,6-hexanediol and the like. These polyhydric alcohols can be used alone or in combination of two or more. Further, a monoepoxy compound such as Kadura E (a product of Ciel Chemical Co., Ltd.) can also be used as the dihydric alcohol.

As a method for synthesizing the resin, the synthesis is carried out using an ordinary polyester resin manufacturing apparatus equipped with a heating device, a stirrer reflux device, a water separator, a rectification tower, a thermometer and the like. First, an acid containing tall oil fatty acid and an alcohol are charged into a reaction tank and heated. When the raw materials are melted and stirring becomes possible, stirring is started, and the temperature of the reactor is raised to 230 ° C. However, the temperature is raised from 160 ° C. to 230 ° C. at a constant rate over 3 hours. The condensed water generated is distilled out of the system through the rectification column. When the temperature reaches 230 ° C., the temperature is kept constant and stirring is continued for 2 hours. After that, add xylol to the reaction tank, switch to the solvent condensation method and continue the reaction,
When a predetermined acid value is reached, the reaction is terminated and cooling is performed. After cooling, xylol is added to a predetermined solid content. For adjusting the Knoop hardness of the coating film, a soft polyester can be added in a range up to the same amount as the tall oil fatty acid polyester resin. When the amount of the soft polyester is equal to or more than that of the tall oil fatty acid polyester resin, the effect of the tall oil fatty acid decreases.

The coating composition of the present invention contains 40 to 20 parts of a melamine resin for 60 to 80 parts of a resin having a hydroxyl group. As the melamine resin, an alkyl etherified melamine resin is used. When the amount of the melamine resin is less than 20 parts, the curing is insufficient, and when the amount is more than 40 parts, the flexibility of the coating film is reduced. Examples of the alkyl etherified melamine resin include butoxymethyl melamine resin (Mitsui Toatsu Co., Ltd. products Uban 20SE60, Uvan 225, Dainippon Ink Co., Ltd. products Super Beckamine G840, Super Beckamine G-821-60, etc.), methoxymethyl Melamine resin (Mitsui Toatsu's products Cymel 300, Cymel 303,
Sumitomo Chemical products Sumimar M-100, Sumimar M
-405 etc.), methoxybutoxy mixed etherified methyl melamine resin (Mitsui Toatsu's product Cymel 1130,
Alkyl etherified melamine resins commonly used in conventional thermosetting polyester resin coatings, such as Sumitomo Chemical's product Sumimar M-66B, can be used.

The coating composition of the present invention may contain a coloring component, if necessary, and may contain any conventionally known auxiliary additives such as a curing accelerator, a pigment settling inhibitor, a leveling agent, and an ultraviolet absorbing agent. Agents, antioxidants, light stabilizers and the like. The Knoop hardness of the coating composition according to the present invention is measured on a 0.3 mm tin plate with a coating applied to a thickness of 30 ± 5 μm and baked at 120 ± 10 ° C. (material temperature) for 30 minutes. The Knoop hardness range of the coating composition of the present invention was measured at 20 ± 2 ° C. with a microhardness tester (DMH-2 type product of Matsuzawa Seiki Co., Ltd.) under the conditions of a load of 25 g and a load loading time of 20 seconds, and a Knoop hardness of 4 was obtained. .0
~ 6.0. When the Knoop hardness is lower than 4, the pollution resistance due to volcanic ash deteriorates, and when the Knoop hardness is higher than 6, the low-temperature impact resistance is not at a practical level.

As a practical evaluation of the low-temperature impact resistance in the present invention, a DuPont impact test method was used. The test piece was left to cool in an atmosphere of -30 ° C for 2 hours or more, and then placed on a pedestal of a DuPont impact tester with the coated surface facing upward in an atmosphere of -30 ° C, and a hemisphere with a radius of 6.35 mm. A shooting pin having a shape tip is placed on the painted surface, and a 500 g weight is dropped on the shooting pin. At this time, the low-temperature impact resistance is determined based on the height of the weight at the time when cracks occur in and around the dent formed in the test piece.

[0017]

The coating composition of the present invention is a thermosetting polyester resin coating composition comprising a fatty acid modified polyester resin having a hydroxyl value of 40 to 150 containing 20 to 40% by weight of tall oil fatty acid and a melamine resin. 3 on 3mm tin plate
It is coated so as to be 0 ± 5μ and baked at 120 ° C. ± 10 ° C. (material temperature) for 30 minutes to obtain a Knoop hardness of 4.
0 to 6.0 (measured at 20 ± 2 ° C) to prevent paint film contamination due to volcanic ash, etc., avoid paint film cracking upon collision, and improve gloss retention performance due to outdoor exposure be able to.

[0018]

EXAMPLES A-1 to A-5 and B-1 in Table 1 were synthesized by the above-mentioned resin synthesis method. For the preparation of the paint, predetermined resins and additives were added using the pigment-dispersed pastes in Table 2, and the viscosity was adjusted with xylol. Then, 30 ± on a 0.3 mm tin plate and a primer-coated polypropylene resin plate
The coating was applied to a thickness of 5 μm, and baked at 120 ° C. ± 2 ° C. (material temperature) for 30 minutes. The praprimer-coated polypropylene resin plate was prepared by subjecting a 3.2 mm thick polypropylene NX-280AK (manufactured by Mitsubishi Yuka Co., Ltd.) to trichloroethane vapor degreasing for 1 minute and then heating at 80 ° C. for 10 minutes.
And dried as a primer. 25
00 primer (manufactured by Kansai Paint Co., Ltd.)
Painted 5 μm and dried at 20 ° C. for 10 minutes or more. The coating film hardness was tested on the painted tin plate, and the coating resin performance was tested on the coated resin plate, such as resistance to volcanic ash contamination.

The results are shown in Table 3. In Table 3, the evaluation of volcanic ash pollution was based on a six-month exposure in Kagoshima.
Indicates that the yellowing due to the volcanic ash is hardly noticeable, も の indicates that the yellowing due to the volcanic ash is slightly conspicuous, and x indicates that the yellowing due to the volcanic ash is clear. The gloss retention was measured at an initial 60 ° gross value (a gloss meter manufactured by Suga Test Instruments Co., Ltd.) after 1000 hours of SWOM (Sunshine Weather Meter manufactured by Suga Test Machine Co., Ltd .; spraying water for 12 minutes per 60 minutes), and then washing the water-washed portion at 60 °. Gross value multiplied by 100, 60
The above is necessary. In the evaluation of low-temperature impact resistance, ○ indicates that a height of 300 m or more is necessary for cracking, and Δ indicates that a height of 250 m or more and less than 350 m is necessary for cracking. , × indicate that cracks occur at a height of less than 250 m.

(Examples 1 to 5) From Table 3, the Knoop hardness was determined using A-1 to A-3 resins which are fatty acid-modified polyester resins containing 20 to 40% of tall oil fatty acids and having a hydroxyl value of 40 to 150. When adjusted to 4 to 6, the volcanic ash contamination resistance is good and the low-temperature impact resistance can be obtained at a practical level.

(Comparative Examples 1 to 15) Even when a tall oil fatty acid-modified polyester resin is used, if the Knoop hardness is more than 6, low-temperature impact resistance is poor, and if it is less than 4, volcanic ash contamination resistance is at a practical level. No. The coconut oil fatty acid-modified polyester resin system has volcanic ash contamination, while the soybean oil fatty acid-modified polyester resin system has not reached the practical level of weather resistance.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

Continuation of the front page (72) Inventor Hiroshi Ueda 33-1, Kanzakicho, Amagasaki-shi, Hyogo Kansai-Paint Co., Ltd. (56) References JP-A-4-28780 (JP, A) Japanese Patent Publication No. 46-3394 (Showa 46-3394) JP, B1) Edited by the Chemical Dictionary Editor's Committee, "Chemical Dictionary, 32nd Edition," Vol. 6 (1989), published by Kyoritsu Publishing Co., Ltd., page 559, "Tall Oil". Introduction to Synthetic Resins "(1974) Published by Kobunshi Kanko-kai, pp. 108-109, pp. 116-119 (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 1/00-201 / Ten

Claims (1)

(57) [Claims] 1. A thermosetting polyester resin coating composition comprising a fatty acid-modified polyester resin having a hydroxyl value of 40 to 150 and a melamine resin containing 20 to 40% by weight of tall oil fatty acid, and having a thickness of 0.3 mm on a tin plate. Painted to 30 ± 5μm and set the material temperature to 120 ℃ ± 10 ℃.
A coating composition having a Knoop hardness of 4.0 to 6.0 as measured at 20 ± 2 ° C. when baked for minutes.