Sealing material

Abstract

Provided is a sealing material having abrasion resistance usable for even construction machinery operated under severe conditions while keeping mechanical strength thereof. The sealing material includes a fluorinated resin composition containing the following materials (1) and (2), and further containing the following material (3) or (4). The materials are: (1) fluorinated resin, (2) bronze, (3) tricobalt tetraoxide, (4) a composite metal oxide containing cobalt and aluminum, and further containing at least one of metals selected from the group of chromium, titanium, magnesium, calcium, and lithium. Preferably, the fluorinated resin is polytetrafluoroethylene. Further, the sealing material is usable for construction machinery.

Claims

1. A sealing material comprised of a fluorinated resin composition containing the following materials (1), (2), and (3), (1) fluorinated resin, (2) bronze, (3) tricobalt tetraoxide, wherein the tricobalt tetraoxide has a mean particle diameter of from 0.1 μm to 10 μm both inclusive.

2. The sealing material described in claim 1, wherein the fluorinated resin is polytetrafluoroethylene.

3. The sealing material described in claim 1, wherein the sealing material is usable for construction machinery.

4. A sealing material comprised of a fluorinated resin composition containing the following materials (1), (2), and (3), (1) fluorinated resin, (2) bronze, (3) a composite metal oxide containing cobalt and aluminum, and further containing at least one of metals selected from the group of chromium, titanium, magnesium, calcium, and lithium, wherein the composite metal oxide has a mean particle diameter of from 0.1 μm to 10 μm both inclusive, and wherein the composite metal oxide is added to the fluorinated resin at from 0.1 to 1.0 mass % both inclusive.

5. The sealing material described in claim 4, wherein the fluorinated resin is polytetrafluoroethylene.

6. The sealing material described in claim 4, wherein the sealing material is usable for construction machinery.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view showing a hydraulic shovel attached with a hydraulic breaker.

(2) FIG. 2 is a schematic diagram of an internal structure of the hydraulic breaker.

(3) FIG. 3 is a graphic diagram showing abrasion losses of Examples and Comparative Examples.

EMBODIMENTS FOR CARRYING OUT INVENTION

(4) Hereinafter, embodiments of the present invention will be described in detail. However, the scope of the present invention is not limited to the embodiments described below.

(5) A sealing material of the present invention includes fluorinated resin as base resin, and further contains bronze, and tricobalt tetraoxide or a cobalt-aluminum based composite metal oxide.

(6) The fluorinated resin is excellent in heat resistance, abrasion resistance, self-lubrication and mechanical strength, and has basic properties needed as a sealing material. The fluorinated resin includes, for example, polytetrafluoroethylene (PTFE), tetafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychloro-trifluoroethylene (PCTFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE) or the like. Among those materials, preferable ones are polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer from the viewpoint of better heat resistance and self-lubrication, and the most preferable one is polytetrafluoroethylene.

(7) Bronze is an alloy of copper and tin, and referred to as “seido” in Japanese. Excellent malleability of bronze allows fluorinated resin to have abrasion resistance, sliding properties and heat resistance when fine particles of bronze are added to the fluorinated resin. Preferably bronze is added to fluorinated resin at 10-70 mass %, more preferably 30-50 mass %. Here, bronze is added as fine particles. The fine particles of bronze have a mean particle diameter of preferably 5-80 μm, more preferably 20-60 μm. Note, the mean particle diameter may be measured by a laser diffraction particle distribution analyzer.

(8) The present inventors have developed investigation focusing on an additive made of metal oxide based fine particles which enable improvement in the abrasion resistance while keeping the mechanical strength of a composition of fluorinated resin and bronze when those fine particles are added to the composition. As a result, the inventors found out that tricobalt tetraoxide and a cobalt-aluminum based composite metal oxide exert an excellent effect of improving the abrasion resistance. Herein, tricobalt tetraoxide and the cobalt-aluminum based composite metal oxide may be added to the composition individually, or in combination.

(9) Tricobalt tetraoxide is a mixed valence compound including both bivalent cobalt (II) and trivalent cobalt (III). It is assumed that dispersion of tricobalt tetraoxide fine particles together with bronze fine particles in the fluorinated resin contributes to improvement in the abrasion resistance and sliding properties. Tricobalt tetraoxide is preferably added to the fluorinated resin at 0.1-5.0 mass %, more preferably 0.5-2.0 mass %. Herein, tricobalt tetraoxide is added as fine particles. The fine particles of tricobalt tetraoxide preferably have a mean particle diameter of 0.1-10 μm.

(10) The cobalt-aluminum based composite metal oxide is a composite metal oxide containing cobalt and aluminum as essential metal elements, and further containing at least one of metal elements selected from the group of chromium, titanium, magnesium, calcium and lithium. It is assumed that dispersion of the metal oxide fine particles together with the bronze fine particles in the fluorinated resin contributes to improvement in the abrasion resistance and sliding properties. Herein, the cobalt-aluminum based composite metal oxide is preferably added to the fluorinated resin at 0.1-5.0 mass %, more preferably 0.5-2.0 mass %. Here, the cobalt-aluminum based composite metal oxide is added as fine particles. The fine particles of the cobalt-aluminum based composite metal oxide preferably have a mean particle diameter of 0.1-10 μm.

(11) A method for preparing a fluorinated resin composition performed through addition of bronze fine particles and tricobalt tetraoxide fine particles to the fluorinated resin, or through addition of bronze fine particles and fine particles of the cobalt-aluminum based composite metal oxide to the fluorinated resin is not specifically limited. A known mixing method may be applied to the preparation method. Further, various types of conventionally known additives may be appropriately blended to the fluorinated resin composition as necessary, in which the additives include an inorganic filler, an organic filler, a dispersing agent, an antioxidant, and a heat stabilizer, in the range without damaging the object of the present invention.

(12) A method for molding the fluorinated resin composition containing bronze and tricobalt tetraoxide, or bronze and the cobalt-aluminum based composite metal oxide in a seal shape is not specifically limited. A known molding method may be applied to the fluorinated resin composition.

EXAMPLES

(13) Hereinafter, the present invention will be described more specifically referring to Examples. However, the present invention is not limited to those Examples. Raw materials used in Examples and Comparative Examples are described as follows.

(14) (1) Polytetrafluoroethylene: AGC Chemicals Co., Ltd., Fuluon G-163.

(15) (2) Bronze: Fukuda Metal Foil & Powder Co., Ltd., Bro-At-200, mean particle diameter: 35 μm.

(16) (3) Additives: (i) Tricobalt Tetraoxide: ISE CHEMICALS CORPORATION, tricobalt tetraoxide. (ii) CoAl.sub.2O.sub.4/Co (Al, Cr).sub.2O.sub.4: Ferro Corporation, PS22-5095PK, containing a small amount of Ti, Mg and Ca. (iii) CoAl.sub.2O.sub.4/Li.sub.2O/TiO.sub.2: Tokan Material Technology Co., Ltd., 42-211A. (iv) Co (Al, Cr).sub.2O.sub.4: Tokan Material Technology Co., Ltd., 42-204A. (v) CoAl.sub.2O.sub.4: Tokan Material Technology Co., Ltd., 42-250A. (vi) CoCO.sub.3: NIHON KAGAKU SANGYO CO., LTD., cobalt carbonate. (vii) Al.sub.2O.sub.3: Sumitomo Chemical Co., Ltd., AL-41-01 (viii) Carbon Black: Mitsubishi Chemical Corporation, #20.

Examples 1-4 and Comparative Examples 1-4

(17) Various types of powdery mixtures were prepared by mixing various types of powdery components listed in Table 1 via using a Henschel mixer at the rate (mass %) of polytetrafluoroethylene/bronze/additive=59.5/40.0/0.5. The resulting powdery mixtures thus obtained were compression-molded by a 100t press machine (i.e., a pressure of 69 Mpa, a holding time of 135 sec). Then, the compressed mixtures were fired at 375° C. for 3.0 hr, thereby to produce sheets (i.e., a thickness of 2 mm) of the various types of fluorinated resin compositions.

(18) The sheets of fluorinated resin compositions thus produced were evaluated about the following items below.

(19) (Tensile Strength and Breaking Elongation)

(20) The tensile strength and the breaking elongation of each sheet were measured following JIS K 6891: 1995.

(21) (Abrasion Loss)

(22) The abrasion loss of each sheet was measured following JIS K 7218: 1986.

(23) Surface Pressure: 6 Mpa, circumferential speed: 2 m/s, temperature: R. T., test time: 8 hr, opposite material: carbon steel S45C (ten-points average roughness of the surface Rz: 1.5 μm)+chromium plating, non-lubrication.

(24) TABLE-US-00001 TABLE 1 Material Composition Physical Properties Additive Tensile Breaking Abrasion Base Contained Mean Particle Strength Elongation Loss Polymer Filler Compound Metal Element Diameter (.Math.m) (Mpa) (%) (g) Example 1 Polytetrafluoroethylene Bronze Co3O4 Co 0.9 26 260 0.03 Example 2 CoAl2O4/Co Co, Al, Cr, Ti, 1.4 26 280 0.11 (Al, Cr)2O4 Mg, Ca Example 3 CoAl2O4/Li2O/TiO2 Co, Al, Li, Ti 3.3 26 270 0.16 Example 4 Co(Al, Cr)2O4 Co, Al, Cr 0.8 26 270 0.14 Comparative CoAl2O4 Co, Al 0.8 20 180 0.14 Example 1 Comparative CoCO3 Co 1 18 160 0.17 Example 2 Comparative Al2O3 Al 1.5 26 260 0.19 Example 3 Comparative Carbon Black None 0.05 25 270 0.27 Example 4

(25) Table 1 shows results of the evaluation. FIG. 3 is a graphic diagram showing abrasion losses of Examples 1-4 and Comparative Examples 1-4 listed in Table 1.

(26) In Comparative Example 4, the fluorinated resin composition corresponded to a sealing material actually used for construction machinery. Results of Examples 1-4 and Comparative Examples 1-4 showed that addition of metal compounds tended to decrease an abrasion loss and improve abrasion resistance. When comparing results among the metal compounds, as shown in Comparative Example 3, addition of the metal oxide of aluminum alone indicated a slightly inferior improvement effect of the abrasion resistance.

(27) Further, as shown in Comparative Example 2, although a cobalt metal was used, addition of cobalt carbonate decreased the mechanical strength. Herein, it was construed that decomposition/decarboxylation of cobalt carbonate generated a lot of voids inside the material, thereby insufficiently contributing to maintenance of the mechanical strength. Moreover, addition of CoAl.sub.2O.sub.4 in Comparative Example 1 showed improvement in the abrasion resistance, but it also showed a decrease in the mechanical strength.

(28) On the contrary, it was confirmed that in Examples 2-4, addition of cobalt-aluminum based composite metal oxides enables improvement in the abrasion resistance while keeping the mechanical strength. Further, as shown in Example 1, it was confirmed that addition of tricobalt tetraoxide exerts the specifically great improvement effect of the abrasion resistance while keeping the mechanical strength.

DESCRIPTION OF REFERENCE NUMERALS

(29) 1: Hydraulic Shovel 2: Hydraulic Breaker