Coating agent composition

Abstract

Disclosed is a coating agent composition comprising (A) a polytetrafluoroethylene resin emulsion, (B) an urethane resin emulsion, and (C) a hydrogenated NBR emulsion, and preferably further comprising (D) an acrylic resin emulsion and/or an ethylene-vinyl acetate copolymer resin emulsion. When this coating agent composition is used as a surface coating agent for general vulcanized rubber-molded products, evaluation of adhesion to rubber by an adhesion test is hardly impaired, and bleeding evaluation, evaluation of the flexibility of the coating agent by a bending test, and evaluation of the reduction in adhesion to rubber due to bloom from the rubber by a high-temperature and high-humidity test are all satisfied.

Claims

1. A coating agent composition comprising: (A) a polytetrafluoroethylene resin emulsion in an amount of 20 to 80 wt. %; (B) an urethane resin emulsion in an amount of 10 to 50 wt. %; and (C) a hydrogenated NBR emulsion in an amount of 3 to 40 wt. %, wherein the only NBR used in the composition is hydrogenated NBR.

2. The coating agent composition according to claim 1, further comprising: (D) an acrylic resin emulsion and/or an ethylene-vinyl acetate copolymer resin emulsion.

3. The coating agent composition according to claim 2, wherein component (D) is present in an amount of greater than 0 to 50 wt. %.

4. The coating agent composition according to claim 2, wherein each component is contained as a resin solid matter at the following ratio: component (A): 30 to 70 wt. %; component (B): 15 to 40 wt. %; component (C): 5 to 40 wt. %; and component (D): 5 to 30 wt. %.

5. The coating agent composition according to claim 2, wherein polytetrafluoroethylene resin particles having a number average molecular weight Mn of 2×10.sup.4 to 1×10.sup.7 and an average particle diameter of 200 to 500 nm are used to form the emulsion as component (A).

6. The coating agent composition according to claim 2, which is used as a surface coating agent for a vulcanized rubber-molded product.

7. The coating agent composition according to claim 6, which is used as a surface coating agent for a vulcanized rubber-molded product of NBR, hydrogenated NBR, acrylic rubber, or fluororubber.

8. A vulcanized rubber-molded product having a surface coated with the coating agent composition according to claim 6.

9. The coating agent composition according to claim 1, wherein polytetrafluoroethylene resin particles having a number average molecular weight Mn of 2×10.sup.4 to 1×10.sup.7 and an average particle diameter of 200 to 500 nm are used to form the emulsion as component (A).

10. The coating agent composition according to claim 1, which is used as a surface coating agent for a vulcanized rubber-molded product.

11. The coating agent composition according to claim 10, which is used as a surface coating agent for a vulcanized rubber-molded product of NBR, hydrogenated NBR, acrylic rubber, or fluororubber.

12. A vulcanized rubber-molded product having a surface coated with the coating agent composition according to claim 10.

Description

EXAMPLES

(1) The following describes the present invention with reference to Examples.

Examples 1 to 5 and Comparative Examples 1 to 5

(2) (1) In a container equipped with a stirrer, such as a rotor or propeller, the following components were supplied in this order:

(3) (i) an ethylene-vinyl acetate copolymer resin [EVA] emulsion;

(4) (ii) water;

(5) (iii) a hydrogenated NBR emulsion, an acrylic resin emulsion;

(6) (iv) an urethane resin emulsion; and

(7) (v) a PTFE emulsion.

(8) The resulting mixture was stirred until it was homogeneous, thereby preparing a coating agent having a solid matters content of 30 wt. %.

(9) Here, the following commercial products were used as the respective blending components: PTFE emulsion: Polyflon Dispersion D-1 E, produced by Daikin Industries, Ltd.; solid matters content: 61 wt. %, Mn: 6,000,000, average particle diameter: 220 nm Urethane resin emulsion: UW-1005E, produced by Ube Industries, Ltd.; solid matters content: 27.4 wt. % Hydrogenated NBR emulsion: ZLxB, produced by Zeon Corporation; solid matters content: 40.5 wt. % Acrylic resin emulsion: Nikasol FX-329, produced by Nippon Carbide Industries Co., Inc.; solid matters content: 45 wt. % Ethylene-vinyl acetate copolymer resin emulsion [EVA emulsion]: Nikasol ME-702XT, produced by Nippon Carbide Industries Co., Inc.; solid matters content: 56 wt. % NBR emulsion: Nipol 1562, produced by Zeon Corporation; solid matters content: 41 wt. %

(10) TABLE-US-00001 (2) NBR (JSR N220S, produced by JSR) 100 parts by weight  Carbon black (HTC#S-S, produced 40 parts by weight  by NSCC Carbon Co., Ltd.) Zinc white No. 3 (produced by 5 parts by weight Seido Chemical Industry Co., Ltd.) Stearic acid (produced by 2 parts by weight Miyoshi Oil & Fat Co., Ltd.) Antioxidant (Santaito R, produced by 3 parts by weight Seiko Chemical Co., Ltd.) Antioxidant (6C, produced by Ouchi Shinko 2 parts by weight Chemical Industrial Co., Ltd.) Plasticizer (RS-107, produced by ADEKA) 15 parts by weight  Sulfur (produced by Hosoi 1.2 parts by weight.sup.  Chemical Industry Co., Ltd.) Vulcanization accelerator 2 parts by weight (Nocceler TT, produced by Ouchi Shinko Chemical Industrial Co., Ltd.) Vulcanization accelerator 2.5 parts by weight.sup.  (Nocceler CZ, produced by Ouchi Shinko Chemical Industrial Co., Ltd.)
The above components were kneaded by a roll, and then subjected to press vulcanization at 180° C. for 6 minutes, thereby vulcanization-molding a 2-mm-thick sheet and an O ring.

(11) (3) The surface of the press-vulcanized products was wiped with methyl ethyl ketone applied to a Kimwipe, and was spray-coated with the coating agent with a coating thickness of 5 to 10 μm, followed by heat treatment at 140° C. for 30 minutes. The vulcanizates after coating treatment were measured for the following items:

(12) Dynamic Friction Coefficient: Measured according to ASTM D-1894 (-11el), JIS K7125 (1999), JIS P8147 (2010), ISO 8295 (1995) A surface property tester Heidon Tribogear (produced by Shinto Scientific Co., Ltd.) was used The dynamic friction coefficient of the coated rubber sheet surface was measured under the following test conditions: Mating material: SUS304 steel ball having a diameter of 10 mm Moving rate: 50 mm/min Load: 0.49 N Amplitude: 50 mm

(13) Bending Test: Measured according to JIS K5600-5-1 (1999), ISO 1519 (1973) The rubber sheet after coating treatment was bent around a mandrel having a diameter of 6 mm, and tape peeling same as that of a multi-crossed cut test was performed on the rubber sheet in a bent state. Then, whether the coating agent was removed, that is, the flexibility of the coating agent, was evaluated according to the following evaluation criteria: ◯: No removal in the bent portion and no transfer to the tape X: Removal in the bent portion and transfer to the tape occurred

(14) Adhesion Test: The rubber sheet after coating treatment was punched into a disc having a diameter of 13 mm, and left at room temperature for one week. Then, the rubber sheet disc and a mating material SUS430 were held at a compression ratio of 33.3% so that their coating layers faced each other. After heating at 100° C. for 60 minutes, they were left at room temperature for 1 hour. After the compression mold was removed, the transfer of the coating agent to the metal due to the adhesion of the coating agent to the SUS430 was evaluated as a test of adhesion to metal according to the following evaluation criteria: ◯: No transfer of the coating agent to SUS430 Δ: Partial transfer of the coating agent to SUS430 ×: Transfer of the coating agent to the entire compression surface of SUS430 after removing the mold Notes: The coating agent is transferred to the mating material metal side, for example, when the adhesion between the vulcanized rubber and the coating agent is weak, when the adhesion is reduced due to bloom from the vulcanized rubber, or when the coating agent is sticky

(15) High-Temperature and High-Humidity Test: A test of adhesion to vulcanized rubber and a water resistance test according to JIS K6262 (2006) corresponding to ASTM D395 Coating was applied to the vulcanization-molded O rings (inner diameter: 34.7 mm, thickness: 3.5 mm) in the same manner as described above. The two O rings were piled together and compressed under conditions in which the compression ratio was 20%, the temperature was 60° C., the humidity was 90% RH, and the time was 70 hours. After the compression test, the removal state of the coating agent between the O rings was evaluated according to the following criteria: ◯: No removal of the coating agent Δ: Removal of part of the coating agent occurred on the O ring compression surface ×: Removal of the coating agent occurred on the almost entire O ring compression surface Notes: The removal of the coating agent occurs due to, for example, water present in the compression surface edges of the O rings, adhesion between the O rings, hydrolysis of the urethane resin, or reduced adhesion between the urethane resin and the vulcanized rubber

(16) Bleeding Evaluation: A heat test was performed on the sheets at 70° C. for 30 days. Then, whether bloom components from the vulcanized rubber were deposited on the coating surface was visually observed. The results were evaluated according to the following criteria: ◯: No deposition of solid matters on the surface recognized ×: Deposition of solid matters on the surface recognized

(17) Evaluation of O Ring Conveying Properties: Coating was applied to the vulcanization-molded O rings (inner diameter: 7.8 mm, thickness: 1.9 mm; bearing number: JIS B2401-4 Type D P8 corresponding to ASTM D2240 and D1414) in the same manner as described above, and the conveying properties of the O rings by a parts feeder were evaluated according to the following criteria: ◯: No O rings were conveyed in a piled state, and the conveying speed was faster than that of silicone oil-applied O rings without coating treatment Δ: Although the conveying speed was faster than that of silicone oil-applied O rings without coating treatment, some O rings were conveyed in a state in which two or more O rings were piled together ×: The conveying speed was equal to or slower than that of silicone oil-applied O rings without coating treatment Notes: When uncoated vulcanized rubber to which silicone oil has been applied is conveyed, the stickiness of the silicone oil causes a slow conveying speed, and the blocked O rings remain on the parts feeder Without stickiness and at a lower dynamic friction coefficient, the conveying speed is faster

(18) O Ring Leak Test: Coating was applied to the vulcanization-molded O rings (inner diameter: 119.6 mm, thickness: 7 mm; bearing number: P120) in the same manner as described above, and the O rings were compressed 5%. Helium gas was introduced, and the amount of helium leaked at the time of 3 minutes after the introduction was measured using a helium leak detector. The results were evaluated according to the following criteria: ◯: Low leak ×: High leak

(19) (4) Table 1 (Examples) and Table 2 (Comparative Examples) below show the measurement and evaluation results obtained in the above Examples and Comparative Examples, together with the amounts of the coating agent components (unit: part by weight; numerical values in parentheses indicate the weight percent of each component based on the total solid matters content).

(20) TABLE-US-00002 TABLE 1 (Examples) 1 2 3 4 5 [Coating agent component] PTFE emulsion 98.3 108.2 108.2 98.4 65.6 (60%) (66%) (66%) (60%) (40%) Urethane resin emulsion 87.6 73.0 73.0 69.3 109.5 (24%) (20%) (20%) (19%) (30%) Hydrogenated NBR 39.5 17.3 17.1 17.3 29.6 emulsion (16%) (7%) (7%) (7%) (12%) Acrylic resin emulsion — 15.6 — 15.5 40.0 (7%) (7%) (18%) EVA emulsion — — 12.5 12.5 — (7%) (7%) Distilled water 101.1 119.3 119.6 117.5 88.6 [Measurement and evaluation result] Dynamic friction  0.5  0.3  0.3  0.3  0.5 coefficient Bending test ◯ ◯ ◯ ◯ ◯ Adhesion test Δ ◯ Δ ◯ Δ High-temperature and Δ Δ ◯ ◯ ◯ high-humidity test Bleeding evaluation ◯ ◯ ◯ ◯ ◯ Evaluation of O ring Δ ◯ ◯ ◯ ◯ conveying properties O ring leak test ◯ ◯ ◯ ◯ ◯

(21) TABLE-US-00003 TABLE 2 (Comparative Examples) 1 2 3 4 5 [Coating agent component] PTFE emulsion 108.2 108.2 — — 98.3 (60%) (66%) (60%) Urethane resin emulsion — 146.0 273.7 182.5 87.6 (40%) (75%) (50%) (24%) Hydrogenated NBR — — 61.7 — 39.5 emulsion (25%) (16%) NBR emulsion — — — — 39.5 (16%) Acrylic resin emulsion 37.8 — — 111.1 — (17%) (50%) EVA emulsion 30.3 — — — — (17%) Distilled water 150.4 99.1 — 39.7 101.1 [Measurement and evaluation result] Dynamic friction  0.5  0.4 1.0  0.5  0.7 coefficient Bending test ◯ ◯ ◯ X ◯ Adhesion test X Δ X Δ X High-temperature and X X X X X high-humidity test Bleeding evaluation ◯ ◯ X X ◯ Evaluation of O ring ◯ ◯ X ◯ ◯ conveying properties O ring leak test ◯ ◯ ◯ ◯ ◯