Toothed belt fabric and toothed belt

Abstract: A toothed belt (10) has a back portion in which cords (14) are embedded, and a front portion defining a plurality of teeth (12) arranged in the longitudinal direction thereof. A facing fabric (18) is adhered to the teeth which comprises a base cloth treated with latex. The solid deposition of latex on the base cloth is adjusted to between 50 and 200 wt% with respect to the weight of the base cloth.

Description: The present invention relates to a toothed belt which is usable for a carriage feed of a copier or printer, positioning of an industrial robot, and so on. Conventionally, teeth of a toothed belt are covered by a fabric which is treated in a manufacturing process with an RFL (resorcinol-formaldehyde-latex) solution, to enable it to strongly bond with the teeth, and is then rubberised. However, with this type of toothed belt, a rise in the frictional coefficient between the surface of the fabric and pulley can occur either because of adhering of the rubber coating or because the tooth rubber exudes and is deposited on the fabric. This rise produces an increase in noise to occur, and rubber dust to be dispersed because of increased friction with the pulley when the belt is run. Since the tooth rubber includes carbon, which has a good electroconductivity, such rubber dust can cause electrical disturbances in office automation equipment and the like. A toothed belt intended to reduce the exudation of the tooth rubber through the fabric is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 7-190150, for example. In this toothed belt, the fabric is treated with an RFL solution, and a solid deposition of RFL, having 30 to 50 wt% with respect to the weight of the base cloth, is generated on the fabric. However, it has been found that even if the solid deposition of the RFL solution is from 30 to 50 wt%, exudation of the tooth rubber is still not adequately prevented. If the solid deposition is increased, although this does reduce the exudation of the tooth rubber, the elasticity of the fabric is impaired. Thus, it becomes difficult to form the teeth of the belt into the desired shape, especially in a toothed belt requiring a small pitch, such as one used for office automation equipment. US-A-4501771 discloses a method of manufacturing elastomer coated bias fabric, which fabric comprises first and second surfaces, said first and second surfaces being coated with an amount of latex. EP-A-0345367 discloses a method of manufacturing a toothed belt fabric comprising the steps of (a) coating at least one surface of a base cloth with a non-rubber elastomeric material, and (b) treating the treated base cloth further with an RFL solution. An object of the present invention is to provide a toothed belt which is not impaired in elasticity and which has a reduced exudation of the tooth rubber in comparison with the prior art. According to the present invention there is provided a toothed belt having a plurality of teeth along the longitudinal direction thereof, said toothed belt comprising a fabric covering said teeth, said fabric having first and second surfaces, said first surface being adhered to said teeth, said second surface being opposite to said first surface, at least one of said first and second surfaces being coated with an amount of latex, wherein the amount of latex is in the range of substantially 50 to 200 wt% with respect to a weight of a base cloth forming said fabric. In this way, the exudation of rubber from the teeth formed on the tooth belt is reduced thereby avoiding an increase in friction with a running pulley so that there is no increase in noise or dispersion of electroconductive rubber dust. Latex deposition in the range of substantially 50 to 200 wt% with respect to a weight of a base cloth forming said fabric has been found to provide an optimal prevention of exudation of rubber whilst maintaining a good elasticity for the fabric. An example of the present invention will now be described with reference to the accompanying drawings, in which:- Fig. 1 is a perspective view showing an embodiment of a toothed belt, cut away in the longitudinal and transverse direction, of the present invention; and Fig. 2 is a cross-sectional view showing the toothed belt shown in Fig. 1 along the longitudinal direction. A toothed belt 10 has a back portion 16, in which cords 14 are embedded, and a front portion defining a plurality of teeth 12 are formed along the longitudinal direction of the belt 10. A fabric 18 is adhered to the surface of the teeth 12. The shape of the teeth 12, when viewed from the side may take many forms, for example, rounded, utilizing partial arcs, or trapezoidal or other suitable shape. Note that, in Fig. 2, Lp indicates the pitch, and PLD the pitch line differential. The rubber stock used for forming the teeth 12 and the back portion 16 can be hydrogenated nitrile rubber, chlorosulfonated polyethylene, or other such rubbers having improved heat and/or aging resistance, such as chloroprene rubber, natural rubber, styrene-butadiene rubber, etc. Blending agents such as zinc white, stearic acid, a plasticizer, an antioxidant, and so on are added to these rubbers. Sulfur, organic peroxides, and so on can be used as the vulcanizing agent. These are examples only of the blending agents and vulcanizing agents usable. Preferably, the cords 14 are twisted cords in which glass fibers, para-aromatic polyamide fibers, and/or other filaments are twisted together and treated with an adhesive, such as an RFL solution, although other forms of twisted cords can be employed. For the facing fabric 18, nylon 6, nylon 66, and so on, may be used alone or mixed. The weft, which extends in the belt width direction of the facing fabric, and the warp, which extends in the belt length direction, are made of filaments or spun yarns of the above-mentioned fibers. The weave may be a plain weave, twill weave, satin weave, etc. Note that the weft need not be elastic, while the warp should have elasticity. The fabric is first treated with latex. The type of latex is not particularly limited, but a self-cross-linking latex, which forms a flexible film, thereby not impairing the elasticity of the fabric, and which has a high film strength when forming the teeth, is preferable. The latex may be untreated latex, or may require the addition of a vulcanizing agent, vulcanizing accelerator, antioxidant, and so on, according to necessity. In the manufacturing process, the base cloth is first immersed in a latex solution, passed between a pair of rollers to wring it out, and is then dried. The solid deposition of latex is preferably 50 to 200 wt% with respect to the weight of the base cloth. The fabric treated with the latex is further treated with an RFL solution. The treatment step is similar to that in which the base cloth is treated with the latex, and therefore is not described in detail here. The RFL solution comprises an initial mixture (RF solution) of resorcinol and formaldehyde which is mixed with the latex. The above-mentioned treated fabric is wrapped around the outer surface of a cylindrical mold, which has a predetermined toothed shape such that the circumferential direction corresponds to the elastic warp. Then, the cords are spirally wound over the fabric, and further, an unvulcanized rubber sheet, which forms the teeth and the back portion, is wrapped around the mold to cover the fabric and spirally wound cord. A vulcanizing sleeve is fitted over this to cover the entire assembly, and then this is vulcanized and pressed by a steam vulcanizer. When vulcanized and pressed, the rubber sheet enters between the cords and into the depressions of the mold, which causes the fabric to be stretched. Thus, teeth covered with a fabric are formed. This cylindrical belt material is then cut into a predetermined width so that the toothed belt, shown in Fig. 1, is obtained. Below, the present invention will be explained with reference to examples and comparative examples, but the present invention is not limited by these examples. The inventors manufactured the toothed belts of Examples 1 to 3 and Comparative Examples 1 and 2, and compared visually for exudation of rubber. The configurations of the toothed belts are shown in Table 1. Rubber A Blending agent Parts by weight Chloroprene rubber 100.0 Stearic acid 0.5 Magnesium oxide 4.0 Zinc oxide 5.0 Plasticizer 10.0 Carbon black 45.0 Antioxidant 2.0 Accelerator 0.5 Total 167.0 Composition of RFL Solution Name of chemical Parts by weight RFL solution Resorcinol 17.3 Formaldehyde (35%) 13.2 Water 340.5 NaOH aqueous solution (10%) 3.7 Latex 370.7 Ammonia water (28%) 30.0 Water 187.0 Total 962.4 (1) Example 1 For the fabric, a cloth comprising a nylon 66 weft and warp, which were plain woven to a thickness of the base cloth of 0.31 mm, was used. The fabric was treated with only latex. The solid deposition of latex on the fabric was 100 wt% with respect to the weight of the base cloth. The thickness of the treated fabric was 0.35 mm. For the latex, a self-cross-linking latex containing a carboxyl group (CROSLENE (phonetic) NA-15 (name of product of Takeda Chemical Industries), for example) was used. The rubber stock forming the teeth and the back portion of the toothed belt of Example 1 was chloroprene rubber. The rubber compound shown in Table 2 was used as the rubber stock. The tooth shape of the belt was trapezoidal. The tooth pitch was 2.032 mm. (2) Example 2 The fabric was treated with latex and then treated with an RFL solution. The RFL solution used is described in Table 3. The solid deposition of latex on the fabric was 100 wt% with respect to the weight of the base cloth. The solid deposition of RFL was 35 wt% with respect to the weight of the base cloth. The rest of the configuration was the same as that of Example 1. (3) Example 3 For the fabric, a cloth comprising a nylon 66 weft and warp, which were given a 2-2 twill weave to form a base cloth with a thickness of 0.78 mm, was used. This cloth was treated with both latex and RFL solutions. The solid deposition of latex on the fabric was 85 wt% with respect to the weight of the base cloth, while the solid deposition of RFL was 25 wt% with respect to the weight of the base cloth. The finished thickness of the fabric was 0.84 mm. The tooth shape was round, while the tooth pitch was 8.00 mm. The rest of the configuration was the same as Example 2. (4) Comparative Example 1 For the fabric, a cloth having a thickness of base cloth of 0.31 mm was used. This cloth was not treated with latex, and was treated with only an RFL solution. The finished thickness of the fabric was 0.33 mm. The rest of the configuration was the same as Example 2. (5) Comparative Example 2 For the fabric, a cloth having a thickness of base cloth of 0.78 mm was used. This cloth was not treated with latex, and was treated with only an RFL solution. The finished thickness of the fabric was 0.81 mm. The rest of the configuration was the same as Example 3. Referring to Table 4, when using a fabric coated with latex, that is, in each of Examples 1 to 3, no exudation of the rubber on the surface of the fabric was observed. Conversely, in Comparative Examples 1 and 2 using fabrics not coated with latex, exudation of rubber was recognized. Note that in Example 1, the fabric was coated with only latex, and thus, the bond between the fabric and belt teeth was weaker than in Comparative Example 1. In the fabric of Example 2 treated with both latex and RFL solutions, despite the finished thickness of the fabric being substantially the same as that of Example 1, it was found that the bond with the belt teeth was good, even compared with Comparative Example 1. The belts of Examples 1 to 3 and Comparative Examples 1 and 2 were used for running tests to evaluate their performance. The evaluation was performed to evaluate three properties during running of the belt, those being, the amount of dispersion of the rubber dust, noise and durability. The running conditions differed for the trapezoidal tooth belts (Example 1, Example 2, and Comparative Example 1) and the round tooth belts (Example 3 and Comparative Example 2). Note, that the results of the running tests are shown in Table 4. Note also, that the "-" marks in Table 4 show that no running test was performed. Dispersion of Rubber Dust Test and Evaluation The belts of Examples 1 to 3 and Comparative Examples 1 and 2 were used to conduct first and second running tests. The degree of dispersion of rubber dust was evaluated visually. A first running test was performed using the trapezoidal belts of Example 1, Example 2, and Comparative Example 1. The belts were used in a carriage feed of a commercially available printer (Japanese language serial printer PC-PR201/63 made by NEC) and run for 24 hours. A second running test was performed using the round tooth belts of Example 3 and Comparative Example 2. A twin-shaft running tester, which was provided with a driving pulley having 22 teeth and a driven pulley having 22 teeth, was used and the belts ran for 24 hours under conditions of 2300 rpm for a speed of the drive pulley and a load of 23 N·m. The results of the first and second running tests are shown in Table 4. Regarding the degree of dispersion of rubber dust, rubber dust was observed in the comparative examples in both the trapezoidal and round tooth belts, but was not observed in the examples. This result corresponds to the presence of exudation of the rubber. Thus, it is apparent that the belts of Example 1 and Example 2, were free from exudation of rubber, i.e. the belts with latex coated on the fabric prevent dispersion of rubber dust. Noise Test and Evaluation Third and fourth running tests were performed using the belts of Examples 1 to 3 and Comparative Examples 1 and 2 to evaluate the noise based on the noise level generated from the belts. The noise level was measured using the A scale of a noise meter, that is, a scale close to human hearing, and was indicated in dBA. The third running test was performed using the trapezoidal tooth belts of Example 1, Example 2, and Comparative Example 1. A twin-shaft running tester, which was provided with a driving pulley having 30 teeth and a driven pulley having 30 teeth, was used, and the belts run under conditions of 1 to 3000 rpm for a speed of the drive pulley and no load. A microphone was placed at a position 100 mm from the belt at the center of the span between the two shafts to measure the noise level of the belt. The fourth running test was performed using the round tooth belts of Example 3 and Comparative Example 2. A twin-shaft running tester, which is provided with a driving pulley having 22 teeth and a driven pulley having 22 teeth, was used, and the belts run under conditions of 1 to 3000 rpm for a speed of the drive pulley and no load. A microphone was placed at a position 100 mm from the belt, at the center of the span between the two shafts, to measure the noise level of the belt. The results of the third and fourth running tests are shown in Table 4. The results of the two running tests for the comparative examples correspond to the presence of exudation of rubber. Compared with the belts of the comparative examples, it was found that the belts of the examples were less noisy. This is because, in the belts of the examples, there is no exudation of rubber on the surface of the fabric so the friction with the pulley at the time of being driven is reduced, and smooth transmission of power is possible. Durability Test and Evaluation The belts of Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to fifth and sixth running tests. The time of running from the start of running to when the belt teeth broke at the bases and running was no longer possible was measured to evaluate the durability. The fifth running test was performed using the trapezoidal tooth belts of Example 1, Example 2, and Comparative Example 1. The belts were run using a twin-shaft running tester, which was provided with a driving pulley having 14 teeth and a driven pulley having 14 teeth, under conditions of 9000 rpm for a speed of the driving pulley and a load of 0.1 N·m. The sixth running test was performed using the round tooth belts of Example 3 and Comparative Example 2. The belts were run using a twin-shaft running tester, which was provided with a driving pulley having 22 teeth and a driven pulley having 22 teeth, under conditions of 2300 rpm for a speed of the driving pulley and a load of 23 N·m. The results of the fifth and sixth driving tests are shown in Table 4. The durability of the belt corresponds to the degree of bonding with the belt teeth. The belt of Example 1, in which the bonding with the belt teeth was poor, was found to be inferior in durability to the belts of Example 2 and Comparative Example 1. Further, negligible difference was observed in the durability between the belt of Example 3 and the belt of Comparative Example 2. That is, a toothed belt using a fabric, which was treated not only with a latex solution, but also with an RFL solution, is still as good in bonding with the belt teeth, and has a long service life. In the toothed belt of the embodiment of the present invention which is described, since the facing fabric is treated with latex, the spaces in the weave of the facing fabric are covered with latex and exudation of rubber can be prevented. Thus, when running the belt, it was found that no rubber dust was generated and hence, due to lower friction with the pulley, the noise was reduced. Note that, although, in the examples described above, the base cloth is immersed in a latex solution so that both of the surfaces of the base cloth are treated with latex, only one of the surfaces may require treating with latex. In addition, although the specific embodiment describes immersing the base cloth in a latex solution, it is possible to provide a fabric having the advantages described above by treating the fabric with latex by a means which coats the fibres from which the cloth is made prior to weaving, instead of coating the woven fabric with latex. Furthermore, whilst latex is particularly advantageous with the present invention, other non rubber elastic materials can be used to coat the fibres of the base cloth or for coating the base cloth.

Claims: A toothed belt (10) having a plurality of teeth (12) along the longitudinal direction thereof, said toothed belt comprising:- a fabric (18) covering said teeth, said fabric having first and second surfaces, said first surface being adhered to said teeth, said second surface being opposite to said first surface, at least one of said first and second surfaces being coated with an amount of latex, wherein the amount of latex is in the range of substantially 50 to 200 wt% with respect to a weight of a base cloth forming said fabric. A toothed belt according to claim 1 wherein said amount is in the range of substantially 85 to 100 wt% with respect to a weight of a base cloth forming said fabric. A toothed belt according to either preceding claim wherein said latex is a self-cross-linking latex containing a carboxyl group. A toothed belt according to any preceding claim wherein said fabric is treated with resorcinol-formaldehyde-latex after being coated with said latex. A toothed belt according to claim 4 wherein the amount of solid deposition of said resorcinol-formaldehyde-latex is in the range of substantially 25 to 35 wt% with respect to a weight of a base cloth forming said fabric.

Inventors: TAMAKI TOSHITAKA, YOKOI JUNJI, TAMAKI, TOSHITAKA, YOKOI, JUNJI, Tamaki, Toshitaka, c/o Nara Factory, Yokoi, Junji, c/o Nara Factory
Applicants: UNITTA CO LTD, UNITTA COMPANY
Application year: 1997
Main classification: F16G1
IPC codes: F16G1