JP2005315415A - Power transmission belt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power transmission belt capable of preventing a belt from cracking from an outer side of the power transmission belt in a use state in which a lubricant of high temperature is attached, and being used for a long time. <P>SOLUTION: This power transmission belt 10 has a main body rubber layer 12 on one face, and a back rubber layer 14 of fluorine rubber on the other face. A resin adhesive is added to the back rubber layer 14 to be adhered to the main body rubber layer 12. The fluorine rubber has high heat resistance and oil resistance, and can keep processivity for a long time even when the lubricant is attached to an engine which is heated to high temperatures. Thus the generation of cracking on a back face can be prevented for the long time. Further as the expensive fluorine rubber is used only on the back face, its manufacturing cost can be reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power transmission belt used in, for example, an internal combustion engine.

  Along with the downsizing of the internal combustion engine, the power transmission belt is used in an environment where the lubricating oil leaking from the internal combustion engine is attached at a high temperature, and thus performance such as heat resistance and oil resistance is required. As a belt having such a function, a belt having a heat treatment and an oil resistance improved by blending fluororubber with a rubber component subjected to a certain treatment has been known (see Patent Document 1). .

However, the heat resistance and oil resistance required for the power transmission belt are even higher. As a failure phenomenon of the power transmission belt, there are those caused by cracks, peeling, wear, and the like. When used in an environment where high temperature and lubricating oil adheres, there is a problem that the crack on the outer side of the belt first occurs in these failure phenomena and the power transmission belt cannot run.
JP-A-1-223139

  Accordingly, an object of the present invention is to provide a power transmission belt to which lubricating oil adheres and prevents cracks from the outside in use conditions at high temperatures and enables long-term use.

  A first power transmission belt according to the present invention includes a main rubber layer provided on one surface and a back rubber layer which is a fluoro rubber provided on the other surface and bonded to the main rubber layer. Yes.

  The back rubber layer and the main rubber layer are preferably bonded by adding an internally added adhesive to one or both. The internally added adhesive is at least one of resin-based maleic anhydride modified liquid polybutadiene, maleic acid modified liquid polybutadiene, acrylic acid modified liquid polybutadiene, urethane modified liquid polybutadiene, carboxylic modified liquid polybutadiene, and maleic acid modified liquid polyisoprene. Is preferably used as a component.

  When a core wire extending in the longitudinal direction of the power transmission belt is provided, an adhesive rubber layer is provided between the main rubber layer and the back rubber layer, and the core wire is embedded in the adhesive rubber layer so that one entire surface of the adhesive rubber layer is It is preferable to adhere to the back rubber layer. Further, it is preferable to add an internal adhesive to one or both of the adhesive rubber layer and the back rubber layer for adhesion.

  When the power transmission belt is a toothed belt in which tooth portions and tooth bottom portions are alternately formed along the longitudinal direction, the tooth portions are preferably preformed in the main rubber layer. The second power transmission belt according to the present invention includes a main rubber layer provided on one surface and a back rubber layer made of fluoro rubber provided on the other surface. Further, the third power transmission belt according to the present invention is characterized in that at least the back side is formed of fluororubber.

  As described above, according to the present invention, it is possible to prevent the cracks from the outside of the power transmission belt in a use situation under high temperature with the lubricant attached, and to use for a long time.

  The endless power transmission belt to which the first embodiment of the present invention is applied is mounted on a crankshaft pulley and a camshaft pulley by an engine, and transmits the rotational motion of the crankshaft pulley to the camshaft pulley.

  Since the oil pump provided in the engine supplies the lubricating oil stored in the engine to various parts of the engine, the lubricating oil may leak from an oil seal or the like, and the lubricating oil will also adhere to the power transmission belt.

  FIG. 1 is a diagram illustrating an extended state of the power transmission belt 10 fitted to the crankshaft pulley 50. The power transmission belt 10 is an endless toothed belt that is fitted to the crankshaft pulley 50 and deforms into an arc shape. In this arc shape, the power transmission belt 10 is applied with the greatest tension in the longitudinal direction of the power transmission belt 10 on the outer peripheral portion 11, and the extension of the outer peripheral portion 11 is maximized.

  On the other hand, the power transmission belt 10 is deteriorated due to adhesion of lubricating oil in a high temperature engine. The power transmission belt 10 loses stretchability due to deterioration, and breaks when a certain level of tension is applied. Therefore, the deteriorated power transmission belt 10 is cracked from the outside where the tension is maximum.

  2 and 3 show the power transmission belt 10. The power transmission belt 10 is formed by bonding a main rubber layer 12, an adhesive rubber layer 13, and a back rubber layer 14 to each other. The main rubber layer 12 and the adhesive rubber layer 13 are mainly composed of vulcanized rubber whose rubber component is H-NBR, for example. The back rubber layer 14 is mainly composed of fluoro rubber.

  On one surface of the power transmission belt 10, there is provided a main rubber layer 12 in which tooth portions 15 and tooth bottom portions 16 are alternately and integrally formed along the longitudinal direction. The canvas 17 covers the outer surface of the tooth portion 15 and the tooth bottom portion 16 of the main rubber layer 12.

  A back rubber layer 14 is provided on the other surface of the power transmission belt 10. An adhesive rubber layer 13 is provided between the main rubber layer 12 and the back rubber layer 14. The thickness W of the power transmission belt 10 of the adhesive rubber layer 13 is larger than the other portions in the cross section in the vicinity of the tooth tip portion 18 of the tooth portion 15. On the other hand, the thickness W is substantially equal except in the cross section near the tooth tip 18.

  A core wire 19 extending in the longitudinal direction is embedded in the adhesive rubber layer 13 so as to be separated from each other. The main rubber layer 12 is provided with a tooth portion 15 and a tooth bottom portion 16 by pre-molding.

  An internally added adhesive is added to the back rubber layer 14. The internally added adhesive is, for example, a resin-based adhesive, preferably maleic acid-modified liquid polybutadiene. In the case of maleic acid-modified liquid polybutadiene, the amount of the internally added adhesive is preferably 3 to 8 parts by weight with respect to 100 parts by weight of the fluororubber component of the back rubber layer 14.

  The adhesion between the back rubber layer and the main rubber layer or the adhesive rubber layer needs to have an adhesive strength proportional to the tension applied to the power transmission belt. The adhesive strength between fluororubbers and other rubbers using adhesive rubbers mainly composed of H-NBR, which is conventionally used, is lower than the adhesive strength between rubbers other than fluororubbers and other rubbers. Therefore, the adhesive strength of the power transmission belt in which fluororubber is bonded with an adhesive rubber containing H-NBR as a main component may be insufficient for practical use under use conditions where a large tension is applied.

  However, by using an internally added adhesive mainly composed of maleic acid-modified liquid polybutadiene, the adhesive strength is sufficient to cause a cohesive failure in a part of the adhesive surface T with respect to the force for peeling the adhesive surface T. It becomes possible to prepare. This is sufficient strength for use in an engine that is assumed to be used in the power transmission belt of this embodiment.

  The amount of the internally added adhesive is 3 parts by weight or more with respect to 100 parts by weight of the fluororubber component of the back rubber layer 14, and sufficient adhesive strength is provided at 8 parts by weight or less without causing vulcanization trouble. Is possible.

  By embedding the core wire 19 in the adhesive rubber layer 13, the adhesiveness between the core wire 19 and the back rubber layer 14 is enhanced, and the core wire 19 is prevented from peeling off from the back rubber layer 14. That is, only the adhesive rubber layer 13 forms an interface with the back rubber layer 14 mainly composed of fluororubber, and the entire one surface of the adhesive rubber layer 13 is bonded to the back rubber layer 14. Therefore, the core wire 19 is prevented from peeling from the back rubber layer 14 regardless of the type of the material of the core wire 19.

  The power transmission belt 10 is provided in the engine, and the lubricating oil leaked from the engine adheres to the power transmission belt 10. Fluororubber, which is the main component of the back rubber layer 14, has high heat resistance and oil resistance, and can maintain stretchability for a long period of time when the lubricating oil adheres to a high temperature engine. Therefore, compared with the conventional power transmission belt 10, it is possible to suppress the occurrence of cracks on the back surface for a long period of time in a usage situation where the lubricating oil adheres to a high temperature engine.

  Further, the tooth portion 15 is required to have strength against tooth missing. Therefore, the main rubber layer 12 is required to have a higher tensile strength than the back rubber layer 14. Accordingly, the main rubber layer 12 is formed of H-NBR, which is a material having a higher tensile strength than fluororubber, and the main rubber layer 12 is preformed. As a result, the adhesive surface T of the back rubber layer 14 can be kept substantially flat to prevent the back rubber layer made of fluororubber from flowing into the tooth portion 15 and have a strength against tooth chipping.

  Next, the power transmission belt 10 ′ (see FIG. 4) obtained without going through the pre-molding process is compared as an example, and the technical significance of the power transmission belt 10 obtained by using the pre-molded main rubber layer 12 is compared. explain.

  Without pre-molding, directly into the toothed belt molding drum, the canvas material that becomes the canvas 17 ', the core cord that becomes the core wire 19', the blended rubber sheet that becomes the main rubber layer 12 ', and the blend that becomes the adhesive rubber layer 13' When the rubber sheet and the compounded rubber sheet to be the back rubber layer 14 'are sequentially wound and vulcanized, a power transmission belt 10' as shown in FIG. 4 is obtained.

  In the power transmission belt 10 ′, the main rubber layer 12 ′, the adhesive rubber layer 13 ′, and the back rubber layer 14 ′ flow into the teeth during the vulcanization process (reference S). Therefore, when the back rubber layer 14 ′ flows into the tooth portion 15 ′, the back rubber layer 14 ′ and the core wire 19 ′ are joined. Therefore, depending on the material of the core wire 19 ′, there is a possibility that the adhesive strength that prevents the back rubber layer 14 ′ from peeling from the core wire 19 ′ cannot be maintained. Moreover, it may not be possible to provide sufficient strength against missing teeth.

  On the other hand, in the power transmission belt 10 obtained by using the pre-molded main rubber layer 12, the back rubber layer 14 does not flow into the tooth portion 15 as shown in FIG. It is possible to embed in Therefore, the core wire 19 can be prevented from peeling from the back rubber layer 14, and the power transmission belt 10 can have sufficient strength against tooth chipping.

  As described above, according to the power transmission belt 10 of the present embodiment, the engine can be used for a long period of time in a usage situation where high-temperature lubricating oil adheres to the engine. In addition, since high-cost fluororubber is used only on the back surface, the power transmission belt 10 having high heat resistance and oil resistance as described above and reduced in manufacturing cost can be obtained.

  Next, with reference to FIGS. 5-7, the process of manufacturing the power transmission belt 10 through the preforming of the main rubber layer 12 will be described. First, as shown in FIG. 5, a pre-formed toothed drum 30 is prepared, and a tooth portion 31 is provided around the drum 30. Further, the toothed roller 32 is engaged with the pre-formed toothed drum 30, and the toothed roller 32 is provided with a tooth portion 33 that cooperates with the tooth portion 31 of the pre-formed toothed drum 30. Pre-formed toothed drum 30 and toothed roller 32 rotate in the directions indicated by arrows R1 and R2, respectively.

  The canvas material 20 is supplied to the pre-formed toothed drum 30 so as to surround a part of the periphery of the pre-formed toothed drum 30, and is introduced into the engagement region with the toothed roller 32. The tooth portions 31 and 33 are molded into a waveform by the cooperative action. The canvas material 20 finally becomes the canvas 17 of the power transmission belt 10.

  As shown in FIG. 6, the steel belt 34 is driven at a part of the periphery of the pre-formed toothed drum 30 with an appropriate pressing force at the same speed as the peripheral speed of the pre-formed toothed drum 30. The compounded rubber sheet 21 is supplied between the pre-formed toothed drum 30 and the steel belt 34, whereby the pre-molded canvas material 20 and the compounded rubber sheet 21 are integrated.

  That is, the compounded rubber sheet 21 is pressed by the steel belt 34 and preformed according to the shape of the canvas material 20 after preforming. In short, an intermediate product in which the pre-molded canvas material 20 and the compounded rubber sheet 21 pre-formed according to the pre-molding are integrated is obtained. In this intermediate product, a groove 22 is formed on the surface where the compounded rubber sheet 21 is exposed and in the vicinity of the tip of the tooth.

  After the above-mentioned intermediate product is cut into a predetermined length, the cut intermediate product is wound around the toothed belt molding drum 35 as shown in FIG. A core cord 23 to be 19, a blended rubber sheet 24 to be the adhesive rubber layer 13 of the finishing power transmission belt 10, and a blended rubber sheet 25 to be the back rubber layer 14 of the finishing power transmission belt 10 are wound.

  Thereafter, the belt component drum material 35, the compound rubber sheet 21, the cord cord 23, the compound rubber sheet 24, and the toothed belt molding drum 35 around which the compound rubber sheet 25 is wound are placed in a vulcanizing oven (not shown). Therefore, it is subjected to vulcanization treatment at a predetermined temperature and a predetermined pressure.

  There are a large number of gaps between the canvas material 20, the blended rubber sheet 21, the cord cord 23, the blended rubber sheet 24, and the blended rubber sheet 25, which are belt components, but these gaps are removed by vulcanization. . The compounded rubber sheet 25 does not flow into the groove, but the compounded rubber sheet 24 flows. The power transmission belt 10 is obtained by cutting the cylindrical intermediate product thus obtained into an appropriate width.

  FIG. 8 shows a power transmission belt to which the second embodiment of the present invention is applied. In the second embodiment, the back rubber layer 14 has an inner rubber layer 14a and an outer rubber layer 14b. The inner rubber layer 14a is mainly composed of vulcanized rubber whose rubber component is H-NBR, for example. The outer rubber layer 14b is mainly composed of fluoro rubber. That is, the outermost layer forming the surface opposite to the main rubber layer of the back rubber layer 14 is fluororubber. Other configurations are the same as those of the first embodiment. According to the present embodiment, since the back surface of the power transmission belt 10 is provided with fluororubber, the occurrence of cracks on the back surface can be suppressed for a long period of time.

  In addition, although the power transmission belt which is a toothed belt was demonstrated as 1st and 2nd embodiment of this invention, this is applicable also to a V belt, a V ribbed belt, or a flat belt.

  In the above-described embodiment, the internally added adhesive is added to the back rubber layer 14, but the same effect as this embodiment can be obtained by adding the adhesive to the adhesive rubber layer 13. In the above embodiment, maleic acid-modified liquid polybutadiene is added as an adhesive, but maleic anhydride-modified liquid polybutadiene, maleic acid-modified liquid polybutadiene, acrylic acid-modified liquid polybutadiene, urethane-modified liquid polybutadiene, and carboxylic-modified liquid polybutadiene. The effect similar to that of the present embodiment can also be obtained by using at least one of maleic acid-modified liquid polyisoprene.

  Further, in the above-described embodiment, even if the main rubber layer or the adhesive rubber layer is mainly composed of NBR, EPDM, CR, SBR, ACSM, polyurethane, or fluorine rubber, the occurrence of cracks on the back surface is suppressed for a long period of time. be able to. The main component of the main rubber layer or the adhesive rubber layer is not limited to these rubbers. The present invention is also applicable to a power transmission belt that is integrally molded from only fluoro rubber without being separated into a main rubber layer and a back rubber layer. That is, in this case, it is not necessary to use an adhesive as in the above embodiments.

  Hereinafter, the present invention will be described with reference to FIGS. In addition, this invention is not limited at all by these Examples.

  [Composition of compounded rubber] As shown in Tables 1 and 2 below, eight kinds of compounded rubbers A to H to be used for preparation of a sample piece for an adhesive strength test and manufacture of a toothed belt are prepared.

In Table 1 above, * 1 and * 2 indicate the following items.
* 1 Product name of Nippon Zeon Co., Ltd., an ethylenically unsaturated nitrile-conjugated diene-based highly saturated polymerized rubber.
* 2 The weight of the compounding material relative to 100 parts by weight of the compounding material and the rubber component (unit: phr).
Moreover, --- in a table | surface shows unblending.

In Table 2 above, * 1 to * 3 indicate the following items.
* 1 Du Pont's trade name, vinylidene fluoride-4 fluoroethylene-perfluoromethyl vinyl ether copolymer rubber.
* 2 Ricobond1731HS, trade name of RICON RESINS, maleic acid-modified liquid polybutadiene.
* 3 Type of compounding material and parts by weight of compounding material with respect to 100 parts by weight of rubber component (unit: phr).
Moreover, --- in a table | surface shows unblending.

  Next, a sample piece for an adhesive strength test is prepared from one of the above-described compounded rubber A which is H-NBR and compounded rubber sheet C to H which is a fluororubber, and each sample piece is used to create a H -Adhesive strength test between NBR and fluororubber is performed.

  [Sample Piece for Adhesive Strength Test] As an example of producing the sample piece, a method for producing the example sample piece 1 will be described. Prepare a compound rubber sheet A with a thickness of over 2 mm whose main component of the rubber component is H-NBR, and overlay a compound rubber sheet D with a thickness of over 2 mm whose main component of the rubber component is fluoro rubber on this, Press vulcanize. Press vulcanization is performed at a temperature of 170 ° C. for 20 minutes under a pressure of 14.7 MPa. Here, a part of one end is sandwiched with a tape before pressing in order to prevent vulcanization adhesion. The rubber plate thus bonded is cut out to a width of 25 mm and a length of 105 mm, thereby obtaining a sample piece, that is, the example sample piece 1.

  The configuration and processing of the example sample piece 2 are the same as those of the example sample piece 1 except that the compounded rubber sheet E is used instead of the compounded rubber sheet D.

  The configuration and processing of the example sample piece 3 are the same as those of the example sample piece 1 except that the compounded rubber sheet F is used instead of the compounded rubber sheet D.

  The configuration and processing of the example sample piece 4 are the same as those of the example sample piece 1 except that the compounded rubber sheet G is used instead of the compounded rubber sheet D.

  The configuration and processing of the example sample piece 5 are the same as those of the example sample piece 1 except that the compounded rubber sheet H is used instead of the compounded rubber sheet D.

  The configuration and processing of the comparative example sample piece are the same as those of the example sample piece 1 except that the compounded rubber sheet C is used instead of the compounded rubber sheet D.

  [Adhesive Strength Test and Evaluation] FIG. 9 shows a state in which the sample piece 26 is attached to a tensile tester (manufactured by Shimadzu Corporation, trade name: Shimadzu Autograph AGS-500D). The test method will be described with reference to FIG. The end portion of the rubber sheet 27 and the end portion of the rubber sheet 28, which are prevented from being vulcanized and bonded by tape at one end of the sample piece 26, are respectively attached to the chuck 36 and pulled by a tensile tester at a pulling speed of 50 mm per minute. Other experimental conditions are the same as JIS (K6256). The adhesive force is evaluated by measuring the peeling force between the rubber sheet 27 that is H-NBR and the rubber sheet 28 that is fluororubber. Table 3 shows the measurement results.

In Table 3 above, * 1 indicates the following items.
* 1 Ratio B / A of the adhesive strength of each sample piece to the adhesive strength of the comparative sample piece (A: adhesive strength of the comparative sample piece, B: adhesive strength of each sample piece).

  As is apparent from Table 3, the adhesive strength of the example sample piece 2 to the example sample piece 5 is larger than that of the comparative example sample piece, and the adhesive strength exceeds about 5 times. Conventionally used belts, such as a belt whose main rubber layer and back rubber layer are mainly composed of H-NBR, are approximately five times as strong as the main rubber layer in comparison with the adhesive strength of the comparative sample piece. The back rubber layer is bonded. From this result, in order to obtain an adhesive strength equal to or higher than that of a conventionally used belt, it is understood that a preferable result is obtained by adding 3 parts by weight or more of an adhesive to 100 parts by weight of the fluororubber component. .

  Next, the main rubber layer and the adhesive rubber layer are driven by the above-mentioned compounded rubber A which is H-NBR, and the back rubber layer is driven by one of the compounded rubber B which is H-NBR or the compounded rubber F which is fluororubber. A toothed belt for testing is manufactured, and a running test is performed using each toothed belt.

  [Toothed belt for running test] The toothed belt was manufactured in accordance with the above-described toothed belt manufacturing method. Table 4 shows compounded rubbers used as raw materials for Examples and Comparative Examples.

In Table 4 above, * 1 indicates the following items.
* 1 Ratio of travel time of toothed belt of each example to travel time of toothed belt of comparative example B / A (A: travel time of toothed belt of comparative example, B: travel of toothed belt of example time).

  FIG. 10 is a diagram showing a schematic configuration of a running test in a usage situation where oil adheres using an engine. The traveling test apparatus 37 includes a box-shaped housing 38 and a heater (not shown). In the housing 38, a toothed pulley 39, a toothed pulley 40, and a tensioner 41 are provided between these pulleys. The heater is outside the housing 38 and close to the front wall portion facing the toothed pulley 39 and the toothed pulley 40.

  A shaft hole 44 is formed on the rear wall 38 a of the housing 38, and a shaft hole 45 is formed on the lower side. The toothed pulley 39 and the toothed pulley 40 are supported by a shaft shaft 44 and a camshaft 42 inserted into the shaft hole 45 and a crankshaft 43, respectively, and are rotatable. A tensioner 41 is provided obliquely below the toothed pulley 39.

  The to-be-tested belt 47 is laid over the toothed pulley 39, the toothed pulley 40, and the tensioner 41. The crankshaft 43 is connected to a motor (not shown) provided on the back side of the rear wall portion 38 a of the housing 38.

  Lubricating oil is supplied to the camshaft 42 and the crankshaft 43 from an oil pump attached to the engine. The lubricating oil flows through the camshaft 42 and the crankshaft 43 and flows into the housing 38 from the shaft holes 44 and 45.

  A running test was performed by keeping the inside of the housing 38 at 120 ° C. with a heater and rotating the crankshaft 43 at 6000 rpm. The running time until the belt 47 with the tooth under test failed and the belt became unable to run was measured as a test result. Table 4 shows the measurement results.

  The toothed belt of the comparative example was not able to run because a crack occurred on the back surface, that is, the outer surface of the toothed belt after a lapse of a certain time. The running test of the toothed belt of the example was performed until 1.5 times the time of the running time of the toothed belt of the comparative example passed. At this time, no crack occurred on the outer surface of the toothed belt of the example. Thus, according to the toothed belt of the example, it can be understood that the occurrence of cracks on the back surface can be suppressed longer than that of the toothed belt of the comparative example.

It is a side view which shows the fitting state of the power transmission belt and pulley which applied the 1st Embodiment of this invention. The side sectional view of the power transmission belt to which the 1st embodiment of the present invention is applied is shown. Sectional drawing which follows the IV-IV line in FIG. 2 is shown. For comparison with the power transmission belt to which the first embodiment of the present invention is applied, a side sectional view of the power transmission belt deviating from the application of the first embodiment of the present invention is shown. It is a general | schematic process figure which shows the pre-molding process of a tooth rubber sheet among the manufacturing processes of the main body rubber layer which is a structure part of the power transmission belt to which the 1st Embodiment of this invention is applied. It is a general | schematic process figure which shows the pre-molding process of the tooth rubber sheet among the manufacturing processes of the main body rubber layer which is a structure part of the power transmission belt to which the 1st Embodiment of this invention is applied. It is a schematic process drawing which shows the manufacturing process of the power transmission belt to which the 1st Embodiment of this invention is applied. The side sectional view of the power transmission belt to which the 2nd embodiment of the present invention is applied is shown. The schematic diagram of an adhesive strength test is shown. A schematic diagram of a running test is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Power transmission belt 12 Main body rubber layer 13 Adhesive rubber layer 14 Back rubber layer 15 Tooth part 18 Tooth part 19 Core wire

Claims (13)

  A power transmission belt comprising a main rubber layer provided on one surface and a back rubber layer made of fluororubber provided on the other surface and bonded to the main rubber layer.   The power transmission belt according to claim 1, wherein an adhesive rubber layer is provided between the main rubber layer and the back rubber layer.   The power transmission belt according to claim 2, wherein a core wire extending in a longitudinal direction is embedded in the adhesive rubber layer, and one whole surface of the adhesive rubber layer is bonded to the back rubber layer.   The power transmission belt according to claim 2, wherein an internal-added adhesive is added to the adhesive rubber layer for adhesion.   The power transmission belt according to claim 1, wherein an internal additive adhesive is added to the back rubber layer and adhered thereto.   The power transmission belt according to claim 1, wherein an internal additive adhesive is added to and adhered to the main rubber layer.   The power transmission belt according to any one of claims 4 to 6, wherein the adhesive is a resin-based adhesive.   The resin adhesive comprises at least one of maleic anhydride-modified liquid polybutadiene, maleic acid-modified liquid polybutadiene, acrylic acid-modified liquid polybutadiene, urethane-modified liquid polybutadiene, carboxylic-modified liquid polybutadiene, and maleic acid-modified liquid polyisoprene. The power transmission belt according to claim 7.   The back rubber layer includes at least one of maleic anhydride-modified liquid polybutadiene, maleic acid-modified liquid polybutadiene, acrylic acid-modified liquid polybutadiene, urethane-modified liquid polybutadiene, carboxylic acid-modified liquid polybutadiene, and maleic acid-modified liquid polyisoprene. The power transmission belt according to claim 5, wherein 3 to 8 parts by weight of a resin adhesive is added to 100 parts by weight of the fluororubber of the back rubber layer.   The power transmission belt according to claim 1, wherein tooth portions and tooth bottom portions are alternately formed along the longitudinal direction on the inner surface of the main rubber layer, and the tooth portions are pre-molded.   A main rubber layer provided on one surface and a back rubber layer provided on the other surface and bonded to the main rubber layer, the back rubber layer forming a surface opposite to the main rubber layer A power transmission belt having an outermost layer that is fluororubber.   A power transmission belt comprising a main rubber layer provided on one surface and a back rubber layer made of fluoro rubber provided on the other surface. A power transmission belt molded with fluoro rubber at least on the back side.

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