POLYACETAL RESIN COMPOSITION AND SLIDING MEMBER

Abstract

A polyacetal resin composition and a sliding member, the polyacetal resin composition having excellent performance with respect to friction/abrasion characteristics while maintaining good appearance of a molded article thereof or low occurrence of mold contamination during molding. The polyacetal resin composition contains at least (A) 100 parts by mass of a polyacetal resin, (B) 0.01 part by mass to 1 part by mass of a hindered-phenol-based antioxidant, (C) 0.3 part by mass to 5 parts by mass of silicone oil, (D) 0.1 part by mass to 1.0 part by mass of calcium carbonate, and (E) 0.02 part by mass to 0.2 part by mass of a fatty acid, the calcium carbonate (D) is precipitated calcium carbonate which is not surface-treated and which has an average particle diameter of 1μm or less, and the fatty acid (E) is a C12-30 fatty acid.

Claims

1. A polyacetal resin composition comprising at least: 100 parts by mass of (A) a polyacetal resin; 0.01 parts by mass or more and 1 part by mass or less of (B) a hindered phenol antioxidant; 0.3 parts by mass or more and 5 parts by mass or less of (C) a silicone oil; 0.1 parts by mass or more and 1.0 parts by mass or less of (D) calcium carbonate; and 0.02 parts by mass or more and 0.2 parts by mass or less of (E) a fatty acid, wherein the (D) calcium carbonate is a non-surface treated precipitated calcium carbonate having an average particle diameter of 1 μm or less, and the (E) fatty acid has 12 or more and 30 or less carbon atoms.

2. A sliding member comprising the polyacetal resin composition according to claim 1.

Description

EXAMPLES

[0050] Hereinafter, embodiments of the present invention will be specifically described with reference to Examples, which are not intended to limit the present invention.

Examples and Comparative Examples

<Preparation of Polyacetal Resin Composition>

[0051] Components shown in Tables 1 and 2 were formulated at proportions shown in Tables 1 and 2 and melt-kneaded with a twin-screw extruder at 210° C. to thereby prepare polyacetal resin compositions according to Examples and Comparative Examples in pellet form. Note that, the components shown in Tables 1 and 2 and used in Examples according to an embodiment of the present invention and Comparative Examples are as follows.

(A) Polyacetal Resin

[0052] (A-1) Polyacetal copolymer formed by copolymerizing 96.7% by mass of trioxane and 3.3% by mass of 1,3-dioxolane (Melt index as measured at 190° C. and under a load of 2160 g): 9 g/10 min)

(B) Hindered Phenol Antioxidant

[0053] (B-1) Irganox 245 (manufactured by BASF) Triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate]

(C) Silicone Oil

[0054] (C-1) SH200-60000CS (manufactured by Dow Toray Co., Ltd.) Dynamic viscosity at 25° C.: 60,000 cSt (600 cm.sup.2/s)

(D) Calcium Carbonate

[0055] (D-1) Brilliant-1500 (manufactured by Shiraishi Kogyo Kaisha, Ltd.),

[0056] Non-surface treated Precipitated calcium carbonate having an average particle diameter of 150 nm

[0057] (D-2) Whiton P-30 (manufactured by Toyo Fine Chemical Kaisha, Ltd.)

[0058] Heavy calcium carbonate having an average particle diameter of 4.4 μm

[0059] (D-3) Vigot-15 (manufactured by Shiraishi Kogyo Kaisha, Ltd.) Precipitated calcium carbonate having an average particle diameter of 150 nm and surface-treated with a fatty acid

(E) Fatty Acid

[0060] (E-1) Stearic acid (number of carbon atoms: 18)

[0061] (E-2) Oleic acid (number of carbon atoms: 18)

[0062] (E-3) Lauric acid (number of carbon atoms: 12)

[0063] (E-4) Caprylic acid (number of carbon atoms: 8)

TABLE-US-00001 TABLE 1 Example Component 1 2 3 4 5 6 7 8 9 Polyacetal resin A-1 100 100 100 100 100 100 100 100 100 Antioxidant B-1 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Silicone oil C-1 1.5 1.5 1.5 0.5 4.5 1.5 1.5 1.5 1.5 Calcium carbonate D-1 0.5 0.5 0.5 0.5 0.5 0.2 0.9 0.5 0.5 D-2 D-3 Fatty acid E-1 0.1 0.1 0.1 0.1 0.1 0.03 0.15 E-2 0.1 E-3 0.1 E-4

TABLE-US-00002 TABLE 2 Comparative Example Component 1 2 3 4 5 6 7 8 9 10 11 12 Polyacetal resin A-1 100 100 100 100 100 100 100 100 100 100 100 100 Antioxidant B-1 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Silicone oil C-1 1.5 1.5 1.5 1.5 1.5 0.1 10 1.5 1.5 1.5 1.5 Calcium carbonate D-1 0.5 0.5 0.5 0.5 0.5 0.05 1.5 0.5 0.5 D-2 0.5 D-3 0.5 Fatty acid E-1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.01 0.3 E-2 E-3 E-4 0.1

<Evaluation>

[0064] In order to evaluate the polyacetal resin compositions according to Examples and Comparative Examples in pellet form, friction and wear properties, appearance of a molded article, and an amount of a mold deposit upon molding were evaluated. The results are shown in Tables 3 to 4.

«Friction and wear properties«

[0065] Cylindrical test pieces (outer diameter: 25.6 mm, inner diameter: 20 mm, height: 15 mm) were molded using the polyacetal resin compositions according to Examples and Comparative Examples in pellet form under the conditions mentioned below. The test pieces were used to evaluate the friction and wear properties under the conditions mentioned below and measured for a coefficient of dynamic friction and a specific wear amount at the end of tests. The tests were performed under an atmosphere at 23° C. and 50 RH %.

[Evaluation Method]

[0066] Test method: Suzuki friction/wear test

[0067] Tester: EFM-3-EN (manufactured by ORIENTEC CO., LTD.)

[0068] Test conditions: counterpart material: the above-mentioned cylindrical test piece made of the polyacetal resin

[0069] (Product name: DURACON (registered trademark) M90-44, manufactured by Polyplastics Co., Ltd)

[0070] Contact pressure: 0.06 MPa

[0071] Rate: 15 cm/s

[0072] Test time: 24 hours

[Condition A for Molding Test Piece]

[0073] Molding device: FANUC ROBOSHOT α-S50iA (manufactured by FANUC CORPORATION)

[0074] Molding condition: cylinder temperature (° C.): nozzle-C1-C2-C3

[0075] 200-200-180-170° C.

[0076] Injection pressure: 60 (MPa)

[0077] Injection rate: 0.4 (m/min)

[0078] Mold temperature: 80 (° C.)

«Appearance of Molded Article»

[0079] Test pieces (80 mm×80 mm×1 mmt; side gate: 2 mm×1 mm) were molded in the same manner using the polyacetal resin compositions according to Examples and Comparative Examples in pellet form under Condition A for molding test piece.

[Evaluation Method]

[0080] Surfaces of the resultant 10 molded pieces were visually observed. Appearance was evaluated according to the criteria mentioned below based on the number of the molded pieces on which surfaces roughness or delamination was observed.

[0081] 0: No molded piece had surface roughness or delamination.

[0082] 1: Two or less pieces had surface roughness or delamination.

[0083] 2: Three or more pieces had surface roughness or delamination.

«Mold Contamination Upon Molding»

[0084] Test pieces for mold deposit (33 mm×23 mm×1 mmt) were molded using the polyacetal resin compositions according to Examples and Comparative Examples in pellet form under Condition B mentioned below.

[Evaluation Method]

[0085] After continuously molding for 5000 shots, a surface of a cavity portion on a mold was visually observed and visually determined for a deposit amount according to the following criteria:

[0086] 0: No deposit was observed.

[0087] 1: Slight deposit was observed.

[0088] 2: Deposit was observed overall.

[Condition B for Molding Test Piece]

[0089] *Molding device: FANUC ROBOSHOT S-2000i 50B (manufactured FANUC CORPORATION)

[0090] *Molding condition: cylinder temperature (° C.): nozzle-C1-C2-C3

[0091] 205 215 205 185° C.

[0092] Injection pressure: 40 (MPa)

[0093] Injection rate: 1.5 (m/min)

[0094] Mold temperature: 80 (° C.)

[0095] Evaluation results are shown below.

TABLE-US-00003 TABLE 3 Example Evaluation 1 2 3 4 5 6 7 8 9 Coefficient of dynamic friction 0.21 0.21 0.25 0.29 0.25 0.27 0.29 0.28 0.23 Specific wear amount Material 3.9 4.6 5.5 9.2 10.1 11.5 12.8 5.0 4.6 (×10.sup.−3 mm.sup.3/(N .Math. km)) itself Counterpart 3.3 1.8 3.8 6.9 5.0 2.3 10.1 6.9 3.7 material Appearance of molded article 0 0 0 0 1 1 0 1 0 Mold deposit upon molding 0 0 0 0 1 1 0 1 0

TABLE-US-00004 TABLE 4 Comparative Example Evaluation 1 2 3 4 5 6 7 8 9 10 11 12 Coefficient of dynamic friction 0.34 0.34 0.3 0.33 0.31 0.3 0.33 0.33 0.33 0.33 0.29 0.29 Specific wear amount Material 50.4 13.3 4.1 13.7 14.2 11.5 36.6 24.3 14.7 27.5 4.6 6.0 (×10.sup.−3 mm.sup.3/(N .Math. km)) itself Counterpart 10.1 6.9 2.8 18.3 6.9 4.6 7.8 8.2 5.0 13.7 5.0 4.6 material Appearance of molded article 0 2 2 0 2 1 0 2 2 0 2 2 Mold deposit upon molding 0 2 2 0 0 2 0 2 2 0 2 2

[0096] As shown above, it is apparent that the polyacetal resin compositions according to an embodiment of the present invention have good performance regarding not only excellent friction and wear properties but also appearance of a molded article or mold contamination upon molding.