Synchronous belt

Abstract: [Purpose] To improve a facing fabric for belt by enhancement of heat resistance, the strength maintaining ratio of the facing fabric, the adhesive property to rubber and the abrasion resistance to rubber, to increase in belt life due to cracks. [Constitution] A facing fabric covering tooth faces of tooth rubber layers of a belt body is treated with a rubber composition in which hydrogenated acrylonitrile-butadiene rubber is mixed with N, N'-m-phenylenedimaleimide.

Description: A synchronous belt as a power transmission belt generally has a belt body composed of a backing rubber layer in which a plurality of cords are embedded in a longitudinal direction of the belt; and a large number of tooth rubber layers integrally provided on the backing rubber layer at regular intervals in the longitudinal direction of the belt. The tooth rubber layers of the belt body are covered with a facing fabric. In recent years, such a synchronous belt has been employed in various kinds of fields and is often used under severe conditions such as high-speed rotation, high load and high temperature. The use of the synchronous belt under such severe conditions progresses deterioration of materials forming the belt. This frequently causes, at an early stage, the tooth rubber layers to shatter or the cords to break, thereby shortening belt life. It is therefore desired to enhance the durability of the synchronous belt. To meet the above requirement, improvements of the belt body have now increasingly been performed. For example, a rubber having a good heat resistance has been used as the rubber forming the belt body. Out of such improvements, special attention is focused on a synchronous belt containing hydrogenated acrylonitrile-butadient rubber (hereinafter, also referred to as "H-NBR") in the rubber portion forming the belt body, since H-NBR has excellent heat resistance. Meanwhile, since the facing fabric has also a significant effect on the belt life, researches on the facing fabric have been done parallel with the researches on the belt body. For example, it has been proposed to subject the facing fabric to adhesive treatment with a rubber composition in which H-NBR is mixed with silica, a methylene donor, and resorcin or a denatured product thereof (see Japanese Utility-Model Application Laid Open No. 63-64948). Further, it has been proposed to subject the facing fabric to an adhesive treatment with a rubber composition in which e.g. H-NBR is mixed with a nickel compound (See Japanese Patent Application Laid Open No. 2-99667). EP-A-547880 discloses the impregnation of the fabric with a rubber paste made of an organic peroxide crosslinked hydrogenated nitrile rubber composition containing at least one crosslinking agent selected from the group consisting of a higher ester of an organic acid, a metal salt of acrylic acid and a metal salt of methacrylic acid, and N,N'-m-phenylenedimaleimide as the other crosslinking agent. However, while each of the facing fabrics subjected to adhesive treatment with the above rubber compositions has excellent heat resistance resulting from the characteristics of H-NBR and the nickel compound, and has a large strength maintaining ratio even after being heat-aged, its adhesive properties and abrasion resistance are insufficient. In particular, since a synchronous belt receives intensive stresses at the tooth roots thereof, it may be broken at an early stage due to cracks generated at the tooth roots, if its adhesive properties and abrasion resistance are not sufficiently secured. This invention has been made in view of the foregoing problem. Thus, it is the object of the present invention to enhance not only the heat resistance and the strength maintaining ratio of the facing fabric, but also its abrasion resistance and its adhesive properties to the rubber forming the belt body and to the rubber for treating tension members such as cords, by subjecting the facing fabric to a treatment with a rubber composition in which H-NBR is mixed with a specific additive, thereby preventing the belt from breaking at an early stage due to cracks generated at its tooth root to increase the belt life. To attain this object, the present invention provides a synchronous belt comprising a belt body having a backing rubber layer in which a plurality of cords are embedded in a longitudinal direction of the belt and a large number of teeth made of tooth rubber layers integrally provided on the backing rubber layer at regular intervals in the longitudinal direction of the belt; and a facing fabric covering the tooth faces of the tooth rubber layers of the belt body, charactenzed in that the facing fabric is treated with a rubber composition in which hydrogenated acrylonitrile-butadiene rubber is mixed with sulfur and N,N'-m-phenylenedimaleimide, the amount of the N,N'-m-phenylenedimaleimide being 0.5 to 10 parts by weight per 100 parts by weight of the hydrogenated acrylonitrile-butadiene rubber. The amount of N,N'-m-phenylenedimaleimide is 0.5 to 10 parts by weight, based on 100 parts by weight of the hydrogenated acrylonitrile-butadiene rubber (H-NBR). Further, it is preferred that at least one of the tooth rubber layers contains as a main ingredient hydrogenated acrylonitrile-butadiene rubber (H-NBR). According to one embodiment of the invention the cords are subjected to an adhesive treatment with a treatment liquid containing a chlorosulfonated polyethylene rubber. According to another embodiment of the invention the cords are subjected to an adhesive treatment with a treatment liquid containing a hydrogenated acrylonitrile-butadiene rubber (H-NBR). The H-NBR contained in the rubber composition as a treatment liquid for a facing fabric enhances the heat resistance of the facing fabric and the strength maintaining ratio of the facing fabric after being heat-aged. Further, the combination of H-NBR with sulfur and N,N'-m-phenylenedimaleimide presents, in addition to the above effects, an increase in adhesive properties and abrasion resistance of the facing fabric, so that a sufficient strength maintaining ratio can be obtained even after the belt is used over a long term under high temperature conditions. Due to the characteristics of the facing fabric treated as above-mentioned, the synchronous belt sufficiently endures stress focused on the tooth roots so that is does not break at the tooth roots. Further, since crosslinking is accelerated in the rubber forming the tooth rubber layer and in the rubber contained as an ingredient in the treatment liquid for subjecting the cords to an adhesive treatment, the belt life is extensively increased. In particular, crosslinking is distinctively performed in the case of a synchronous belt according to claims 2 to 4. Fig. 1 is a cross-sectional diagram of a synchronous belt. Fig. 2 is a graph which illustrates data showing the relationship between the adhesive strength of a facing fabric to rubber and the ratio of N,N'-m-phenylenedimaleimide to H-NBR in a rubber composition forming the treatment liquid for a facing fabric, and data showing the relationship between the abrasion resistance (abrasion loss) of the facing fabric and the ratio of N,N'-m-phenylenedimaleimide to H-NBR in the same rubber composition. Fig. 3 is an explanatory diagram of an abrasion test. Description is made below about preferred embodiments of this invention with reference to the drawings. Fig. 1 shows a synchronous belt A according to an embodiment of this invention. The synchronous belt A has a belt body 1. The belt body 1 is composed of a backing rubber layer 3 in which a plurality of cords 2 as tension members are embedded in a longitudinal direction of the belt, and a large number of tooth rubber layers 4 provided integrally on one face of the backing rubber layer 3 at regular intervals in the longitudinal direction of belt. Further, tooth faces of the tooth rubber layers 4 of the belt body 1 are covered with a facing fabric 5. The backing rubber layer 3 and the tooth rubber layers 4 are formed of hydrogenated acrylonitrile-butadiene rubber (H-NBR) in which hydrogen is added to acrylonitrile-butadiene rubber (NBR) having double bonds to saturate the double bonds thereby restraining recombination reactions based on double bonds. In the case of using H-NBR, H-NBR is mixed with each necessary amount of vulcanizing agent, vulcanization accelerator, reinforcer, plasticizer and, as needed, various kinds of other additives. The cord 2 is used in the form of, as needed, yarn formed of one kind of fibers, blended yarn formed by mixed fiber spinning or twisted yarn formed of blended fibers. The material of the cord 2 is, for example, selected from glass fibers, aromatic polyamide fibers, polyester fibers, whisker fibers and metallic fibers according to the purpose. Further, the cords 2 are subjected to an adhesive treatment in order to be adhered to the rubber forming the belt body 1. A treatment liquid used for the adhesive treatment is rubber cement so formed that rubber, such as natural rubber (NR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), chlorosulfonated polyethylene rubber (CSM) and hydrogenated acrylonitrile-butadiene rubber (H-NBR), is dissolved in an organic solvent, such as methylethylketone (MEK) and toluene. One of the treatment liquids, respectively, containing the above various kinds of rubber ingredients is selectively used according to the purpose. In particular, chlorosulfonated polyethylene rubber (CSM) and hydrogenated acrylonitrile-butadiene rubber (H-NBR) are preferable because they are distinctively crosslinked by N,N'-m-phenylenedimaleimide present in the below-mentioned treatment liquid for the facing fabric 5. The facing fabric 5 is formed of a material, such as aliphatic polyamide fibers, aromatic polyamide fibers and polyester fibers. Its weave design is selected according to the purpose. The facing fabric 5 is treated with a rubber composition in which H-NBR is mixed with sulfur and N,N'-m-phenylenedimaleimide. The mixing ratio is set to 0.5 to 10 parts by weight of N,N'-m-phenylenedimaleimide per 100 parts by weight of H-NBR. The reason for such a setting is that while N,N'-m-phenylenedimaleimide of less than 0.5 parts by weight has little adhesive effect, N,N'-m-phenylenedimaleimide of more than 10 parts by weight causes decrease in heat resistance and decrease in belt life due to generated cracks. When the rubber composition is used for treating the facing fabric 5, it is mixed with each necessary amount of vulcanizing agent, vulcanization accelerator, reinforcer, plasticizer and, as needed, various kinds of other additives. The above treatment for the facing fabric 5 can be conducted by various kinds of methods commonly used, for example, a method of applying on the facing fabric 5, with an applying device such as a roller coater, a rubber cement formed in such a manner that the rubber composition is dissolved by a suitable organic solvent, or a method of dipping the facing fabric 5 in the rubber cement. Further, if necessary, the facing fabric 5 may be preliminarily treated with a treatment liquid including a composition of RFL (resorcin-formaldehyde condensation product and latex) or other treatment liquids. Shown in Table 1 and Fig. 2 are test results of synchronous belts according to embodiments of this invention and test results of synchronous belts according to comparative examples. The conditions with which the test results are obtained will be described next. <Rubber composition for belt body> Both the embodiments of this invention and the comparative examples used rubber compositions in which N,N'-m-phenylenedimaleimide was excepted from respective rubber compositions shown in upper sections of Table 1. <Material of facing fabric> Both the embodiments of this invention and the comparative examples used 6,6-nylon fibers. <Material of cord> Both the embodiments of this invention and the comparative examples used glass fiber cords. <Treatment of facing fabric> Both the embodiments of this invention and the comparative examples were subjected to a preliminary treatment with an RFL liquid and an adhesive treatment with respective treatment liquids composed of rubber compositions shown in Table 1. The application amount of the rubber was 260 g/m 2 . <Treatment of cords> Both the embodiments of this invention and the comparative examples were each subjected to an adhesion treatment with a RFL liquid commonly used, and thereafter were each subjected to an adhesive treatment with a treatment liquid of rubber cement composed of a rubber composition containing chlorosulfonated polyethylene rubber (CSM). <Measurement details of the adhesive strength between the rubber and the treated facing fabric> Prepared were test pieces in each of which a facing fabric was integrally interposed in each of the rubber members composed of rubber compositions shown in upper sections of Table 1. Then, the interface between the rubber composition and the facing fabric in each test piece was peeled at a peeling speed of 50 mm/min. <Details of abrasion test> As shown in Fig. 3, prepared were test pieces 11 as treated facing fabric complexes in each of which a facing fabric 5 was adhesively bonded to each of rubber members 1' composed of rubber compositions shown in upper sections of Table 1. Then, each of the test pieces 11 was set on a slide table 12 of an abrasion test machine at the state that the facing fabric 5 was faced upward, and an abrasion jig 13 was set on the facing fabric 5 of the test piece 11. Under the conditions that a load of 20 kg was applied from above to the test piece 11 with the abrasion jig 13 at a temperature of 25°C, a driving motor (not shown) was rotated at a rotation speed of 800 rpm so that rotational torque thus generated was converted to a horizontally linear movement, thereby horizontally sliding the slide table 12. <Calculation of the strength maintaining ratio of the facing fabric after being heat-aged> Each of the facing fabrics treated in the above-mentioned manner was punched in dimensions of 3 × 20 cm to form a test piece. The test piece was entered into a thermostat wherein the inner temperature was maintained at 120 °C. Then, the test piece was retrieved therefrom after 72 hours and subsequently was aged for 24 hours at a room temperature. Thereafter, the test piece was subjected to a tensile test at a tension speed of 300 m/min so that a strength maintaining ratio (%) was obtained according to the following formula. Strength maintaining ratio (%) = (Strength after aged/Strength before aged) × 100 <Conditions of measurement of belt life due to cracks> A synchronous belt was wound between a driving pulley having 18 teeth and a driven pulley having 18 teeth. Under conditions that a load of 2.94 kW (4PS) was applied to the driven pulley and a tension of 20 kg was applied to the synchronous belt, the driving pulley was rotated at 1000 rpm at a temperature of 100°C. As is evident from the test results, it will be appreciated that examples 1 to 3 of this invention are more excellent in almost all evaluation items than the comparative examples 1 to 4. In comparative example 1 in which the rubber composition did not include N,N'-m-phenylenedimaleimide, the adhesive strength between the rubber and the facing fabric was low. In comparative example 2 in which the content of N,N'-m-phenylenedimaleimide was 15 parts by weight, though the adhesive strength between the rubber and the facing fabric was better, the strength maintaining ratio of facing fabric after being heat-aged was lower and the belt life due to cracks was shorter. In comparative example 3, since H-NBR was not used in the rubber composition forming the treatment liquid for the facing fabric, evaluations were worse in all the evaluation items. In comparative example 4, though the strength between the rubber and the facing fabric was slightly higher than in comparative example 3, it was lower than in examples 1 to 3 of this invention and the other evaluation items were as bad as in comparative example 3. It will be appreciated from the above test results that the differences of the examples of this invention and the comparative examples depend on whether or not the treatment liquid for the facing fabric contained H-NBR and N,N'-m-phenylenedimaleimide at a suitable mixing ratio.

Claims: A synchronous belt comprising a belt body having a backing rubber layer in which a plurality of cords are embedded in a longitudinal direction of the belt and a large number of teeth made of tooth rubber layers integrally provided on the backing rubber layer at regular intervals in the longitudinal direction of the belt; and a facing fabric covering the tooth faces of the tooth rubber layers of the belt body, characterized in that the facing fabric is treated with a rubber composition in which hydrogenated acrylonitrile-butadiene rubber is mixed with sulfur and N,N'-m-phenylenedimaleimide, the amount of the N,N'-m-phenylenedimaleimide being 0.5 to 10 parts by weight per 100 parts by weight of the hydrogenated acrylonitrile-butadiene rubber. The synchronous belt according to claim 1, wherein at least one of the tooth rubber layers contains as a main ingredient hydrogenated acrylonitrile-butadiene rubber. The synchronous belt according to claim 2, wherein the cords are subjected to an adhesive treatment with a treatment liquid containing a chlorosulfonated polyethylene rubber. The synchronous belt according to claim 2, wherein the cords are subjected to an adhesive treatment with a treatment liquid containing a hydrogenated acrylonitrile-butadiene rubber.

Inventors: KASADA MITUMORI, OHNO KIMICHIKA, TACHIBANA HIROYUKI, KASADA, MITUMORI, OHNO, KIMICHIKA, TACHIBANA, HIROYUKI, KASADA, MITUMORI, BANDO CHEMICAL IND.LTD., OHNO, KIMICHIKA, BANDO CHEMICAL IND.LTD., TACHIBANA, HIROYUKI, BANDO CHEMICAL IND.LTD.
Applicants: BANDO CHEMICAL IND, BANDO CHEMICAL INDUSTRIES, LIMITED
Application year: 1995
Main classification: F16G1
IPC codes: D06N3, D06M101, F16G1, C08K5, D06M13, D06M15