POLYACETAL RESIN COMPOSITION AND SLIDING MEMBER

Abstract

A polyoxymethylene (POM) resin composition which is used for a resin molded article having a superior sliding characteristic. The POM resin composition contains: (A) 100 parts by mass of a POM resin; (B) 0.01-1 parts by mass of a hindered phenolic antioxidant; (C) 0.05-1 parts by mass of a nitrogen-containing compound; (D) 0.5-10 parts by mass of a modified olefin polymer; (E) 0.01-5 parts by mass of an alkylene glycol polymer; (F) 0.1-20 parts by mass of calcium carbonate; (G) 0.1-10 parts by mass of a partial ester of a polyhydric alcohol; and (H) 0.1-10 parts by mass of an a-olefin oligomer. An ISO tensile test piece, which is obtained by injection molding at a die temperature of 90° C. and a cylinder temperature of 200° C., is crushed, Soxhlet extraction is performed for 3 hours at 70° C. using methanol, and the alkylene glycol polymer is measured. The weight of the alkylene glycol polymer is 0.001 wt % or less relative to 100 wt % of the test piece.

Claims

1. A polyacetal resin composition, comprising: (A) 100 parts by mass of a polyacetal resin; (B) from 0.01 parts by mass to 1 part by mass of a hindered phenol-based antioxidizing agents; (C) from 0.05 parts by mass to 1 part by mass of a nitrogen-containing compound; (D) from 0.5 parts by mass to 10 parts by mass of a modified olefin-based polymer; (E) from 0.01 parts by mass to 5 parts by mass of an alkylene glycol-based polymer; (F) from 0.1 parts by mass to 20 parts by mass of calcium carbonate; (G) from 0.1 parts by mass to 10 parts by mass of a partial ester of a polyhydric alcohol; and (H) from 0.1 parts by mass to 10 parts by mass of an alpha olefin oligomer, wherein the weight of the alkylene glycol-based polymer is 0.001% by weight or less relative to 100% by weight of an ISO tensile test piece as measured after the test piece is pulverized and subjected to Soxhlet extraction with methanol at 70° C. for 3 hours, the test piece being obtained by performing injection molding at a mold temperature of 90° C. and a cylinder temperature of 200° C.

2. The polyacetal resin composition according to claim 1, wherein particles with a three-dimensional network structure comprising (D) the modified olefin-based polymer are observed when the center of a sample is observed under a scanning electron microscope, the sample being obtained by cutting a cross section between marked lines of the test piece with a trimming diamond blade so as to obtain a mirror surface, and immersed in xylene at 90° C. for 3 hours, and the maximum particle size of the particles from the observation is 10 μm or less.

3. A sliding member, comprising a resin molded body including the polyacetal resin composition according to claim 1.

4. A sliding member, comprising a resin molded body including the polyacetal resin composition according to claim 2.

Description

EXAMPLES

[0067] Below, the present invention will be specifically described with reference to Examples, but the present invention shall not be limited to these.

[Preparation of Polyacetal Resin Composition]

[0068]

TABLE-US-00001 TABLE 1 Comparative Example Example 1 2 3 4 5 1 2 A Polyacetal 100 100 100 100 100 100 100 resin B Hindered 0.3 0.3 0.3 0.3 0.3 0.3 0.3 phenol-based antioxidizing agent C Nitrogen- 0.07 0.07 0.07 0.07 0.07 0.07 0.07 containing compound D Modified olefin-based polymer D-1 Maleic 5 5 5 4 5 anhydride- modified LDPE D-2 Maleic 5 1 anhydride- modified EEA D′-1 LDPE 5 E Alkylene glycol-based polymer E-1 PEG with both 0.3 0.3 1 0.3 0.3 0.3 ends modified with amine (Molecular weight 4000) E-2 PEG 0.3 F Calcium 0.5 0.5 0.5 0.5 0.5 0.5 0.5 carbonate G Partial ester 1 1 1 1 1 1 1 of polyhydric alcohol H Alpha olefin 1 1 1 2 1 1 0 oligomer Extrac- Extraction 0 0 0 0 0 0.25 0.25 tion amount of alkylene glycol-based polymer (wt %) (Units are parts by mass.)
Materials shown in Table 1 are as follows. [0069] (A) Polyacetal resin

[0070] A polyacetal copolymer obtained by copolymerizing 96.7% by weight of trioxane and 3.3% by weight of 1,3-dioxolane (Melt index (as measured at 190° C. under a load of 2160 g): 27 g/10 min.) [0071] (B) Hindered phenol-based antioxidizing agent

[0072] tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (Product name: Irganox 1010, BASF Japan) [0073] (C) Nitrogen-containing compound

[0074] Melamine (Mitsui Chemicals, Inc.) [0075] (D) Modified olefin-based polymer

[0076] (D-1) Maleic anhydride-modified low-density polyethylene (LDPE) (Product name: TAFMER MM6850, Mitsui Chemicals, Inc.)

[0077] (D-2) Maleic anhydride-modified ethylene-ethyl acrylate copolymer (EEA) (Product name: HPR AR2011, Du Pont-Mitsui Polychemicals Co., Ltd.) [0078] (D′) Unmodified olefin-based polymer

[0079] (D′-1) Low density polyethylene (LDPE) (Product name: NOVATEC LD LJ802, Japan Polyethylene Corporation) [0080] (E) Alkylene glycol-based polymer

[0081] (E-1) Polyethylene glycol (PEG) having the both ends modified with amine (Product name: CHEMISTAT Y-400, Number average molecular weight: 4,000, Sanyo Chemical Industries, Ltd.)

[0082] (E-2) Polyethylene glycol (PEG) (Product name: PEG 6000S, Number average molecular weight: 6,000, Sanyo Chemical Industries, Ltd.) [0083] (F) Calcium carbonate

[0084] Calcium carbonate (Product name: Brilliant 1500. A surface-untreated, substantially cube-shaped, and colloidal calcium carbonate having a BET specific surface area of 11.5 m.sup.2/g and a mean particle size of 150 nm. Shiraishi Kogyo Kaisha Ltd.) [0085] (G) Partial ester of polyhydric alcohol

[0086] Glycerin monostearate (Product name: RIKEMAL S100, Riken Vitamin Co., Ltd.) [0087] (H) Alpha olefin oligomer

[0088] Alpha olefin oligomer (Product name: LUCANT HC600, Mitsui Chemicals, Inc.)

[0089] Materials shown in Table 1 were pre-blended at ratios as shown in Table 1 (units were parts by mass), and then fed to the main feeding inlet of a 30 mm-diameter twin screw extruder having one inlet to perform melt mixing (extrusion conditions: L/D=35, extrusion temperature=200° C., screw rotation speed=120 rpm, degree of vent vacuum =-700 mmHg, discharge amount=15 kg/hr), thereby preparing a pellet-like composition. [Extraction of alkylene glycol-based polymer]

[0090] ISO tensile test pieces obtained by injection-molding the polyacetal resin compositions from Examples and Comparative Examples at a mold temperature of 90° C. and a cylinder temperature of 200° C. were pulverized and then subjected to Soxhlet extraction with methanol at 70° C. for 3 hours, and the weight of the alkylene glycol-based polymer was measured for each. Results are shown in Table 1.

<Evaluation>

[Evaluation of Peeling Resistance]

[0091] The above pellet-like composition was molded into a pin gate molded article with dimensions of 50×50×1 mmt and φ1 mm at a cylinder temperature of 200° C., a mold temperature of 40° C., and an injection speed of 4.0 m/min. Then, the above pin gate molded article was bent immediately after the above pin gate molded article was molded, and peeling conditions were observed. A case where neither peeling nor whitening was observed was evaluated as “Good=◯”, and a case where no peeling was observed, but partial whitening was observed was evaluated as “Fair=Δ”, and a case where peeling or extensive whitening was observed was evaluated as “Poor==×”. Results are shown in Table 2.

[Evaluation of Friction Coefficient and Specific Abrasion Amount]

[0092] The above pellet-like composition was subjected to injection molding at a mold temperature of 80° C. and a cylinder temperature of 200° C. to obtain a test piece. This test piece was tested in accordance with the Suzuki friction abrasion test under conditions of a load of 0.06 MPa, a velocity of 15 cm/s, a counterpart member of a polyacetal-resin molded article, and a running time of 24 hours to evaluate dynamic friction coefficient and specific abrasion amount. Results are shown in Table 2. Note that the counterpart member is the polyacetal-resin molded body used in Examples and Comparative Examples which was obtained by injection-molding a resin composition including (A) 100 parts by mass of a polyacetal resin (B) 0.25 parts by mass of a hindered phenol-based antioxidizing agent and (C) 0.07 parts by mass of a nitrogen-containing compound at a mold temperature of 80° C. and a cylinder temperature of 200° C.

[Evaluation of Slidability Against Resin]

[0093] A case where the friction coefficient a test piece was less than 0.3, and the specific abrasion amount of the test piece was 1.0×10.sup.−2 mm.sup.3/(N.Math.km) or less was evaluated as “Good=◯”, and otherwise evaluated as “Poor=×”. Results are shown in Table 2.

[Observation of Test Piece]

[0094] Each of the polyacetal resin compositions from Example 1 and Comparative Example 1 was injection-molded at a mold temperature of 90° C. and a cylinder temperature of 200° C. to obtain an ISO tensile test piece. A cross section between marked lines of the ISO tensile test piece was cut with a trimming diamond blade so as to obtain a mirror surface, and immersed in xylene at 90° C. for 3 hours to obtain a sample. The center of the sample was observed under a scanning electron microscope. Results are shown in Table 2. Further, the maximum particle size of observed particles was measured. Results are shown in Table 2.

TABLE-US-00002 TABLE 2 Comparative Example Example 1 2 3 4 5 1 2 Peeling resistance ∘ ∘ ∘ ∘ ∘ x x Slidability against ∘ ∘ ∘ ∘ ∘ x x resin Friction 0.29 0.29 0.27 0.23 0.27 0.33 0.31 coefficient Specific abrasion 6.6 7.2 4.8 3.6 4.7 18 16 amount (×10.sup.−3 mm.sup.2/(N .Math. km)) Magnified Dispersion Net- Net- Net- Net- Net- Sea- Sea- observation form work work work work work island island of test Maximum 3 3 3 3 3 12 12 piece particle size (μm)

[0095] The polyacetal resin compositions including the (A) to (H) components were shown to be suitable for preparing a resin molded article having superior sliding properties (Examples). Further, the polyacetal resin compositions including the (A) to (H) components were shown to be suitable for preparing a resin molded article having excellent sliding properties as well as superior peeling resistance (Examples). In particular, comparison of Example 1 with Example 2 reveals that inclusion of the (D) component including maleic anhydride-modified polyethylene (Example 1) is preferred in that the peeling resistance and slidability of a resin molded body including the polyacetal resin composition is increased. Further, comparison of Example 1 with Example 3 reveals that a blending amount of the (E) component of 1 part by mass or more (Example 3) is preferred in that the slidability of a resin molded body including the polyacetal resin composition can significantly be improved as compared with a case where the blending amount of the (E) component is 0.3 parts by mass (Example 1). Further, comparison of Example 1 with Example 4 reveals that a blending amount of the (H) component of 2 parts by mass or more (Example 4) is preferred in that the slidability of a resin molded body including the polyacetal resin composition can significantly be improved as compared with a case where the blending amount of the (H) component is 1 part by mass (Example 1).

[0096] Meanwhile, for the polyacetal resin compositions from Examples, particles with a three-dimensional network structure including the (D) component are observed when the center of a sample is observed under a scanning electron microscope, the sample being obtained by cutting a cross section between marked lines of an ISO tensile test piece with a trimming diamond blade so as to obtain a mirror surface and immersed in xylene at 90° C. for 3 hours, the ISO tensile test piece being obtained by performing injection molding at a mold temperature of 90° C. and a cylinder temperature of 200° C.

[0097] The network-like structure is presumably a reaction product between (D) the modified olefin-based polymer and (E) the alkylene glycol-based polymer. Further, the network-like structure presumably makes some kind of contribution to sliding properties and peeling resistance.

[0098] Meanwhile, with regard to the modified olefin-based polymer as the (D) component, the results revealed that even though a polyacetal resin composition included an olefin-based polymer, the peeling resistance and slidability of a resin molded body prepared from the polyacetal resin composition were poor if the above olefin-based polymer was not a modified olefin-based polymer (Comparative Example 1). Further, with regard to the alkylene glycol-based polymer as the (E) component, the results revealed that effects for improving the slidability of a resin molded body were not sufficiently obtained when the weight of the alkylene glycol-based polymer was 0.001% by weight or more relative to an ISO tensile test piece as measured after the test piece was pulverized and subjected to Soxhlet extraction with methanol at 70° C. for 3 hours (Comparative Example 2).

[0099] When the center of the sample from Comparative Example 1 was observed under a scanning electron microscope, only a sea island-like structure was observed, but a network-like structure was not observed. This may likely be responsible for inferior sliding properties and peeling resistance as compared with those from Examples.