JP2004136649A - Method for producing double-layer rubber sheet for power transmission belt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a rough surface of a rubber surface from being generated by laminating a rubber in which a short fiber corresponding to a compressed rubber layer is oriented in a predetermined direction and an adhesive rubber containing no short fiber, and thereby preventing the roughening of the rubber surface, and reducing the number of manufacturing steps Provided is a method for manufacturing a two-layer rubber sheet that can be used for a power transmission belt that can be formed at a low cost at a minimum.
SOLUTION: This is a method for manufacturing a two-layer rubber sheet 20 corresponding to a compression rubber and an adhesive rubber of a power transmission belt, and a two-layer cylinder in which short fiber-containing rubber 15 is laminated on an inner peripheral side and adhesive rubber 16 is laminated on an outer peripheral side. A short fiber orientation obtained by extruding a cylindrical molded body 17 from an expansion die 5 having a diameter gradually increased from an inlet to a discharge port, cutting the cylindrical molded body 17 straight, and laminating an adhesive rubber 16 thereon. A two-layer rubber sheet 20 of rubber 15 is formed.
[Selection diagram] FIG.

Description

The present invention relates to a method for manufacturing a two-layer rubber sheet for a power transmission belt, and more particularly to a method for manufacturing a two-layer rubber sheet for a power transmission belt that can be formed at low cost with a reduced number of manufacturing steps.

Conventionally, as a method for orienting the short fibers in a certain direction in the unvulcanized rubber, as in a rolled sheet manufacturing process, the unvulcanized rubber containing the short fibers is put into a pair of calender rolls at different rotation speeds, and then rolled. The short fibers in the rubber sheet were oriented in the rolling direction of the sheet, and were cut in accordance with the belt width to be formed. Then, several cut rolled sheets are laminated and laminated to a predetermined thickness, and then a laminate in which short fibers are oriented in the width direction is wound around a forming drum to be used in the production of a power transmission belt as in a winding step. Was.

That is, in a method of manufacturing a V-ribbed belt or a low-edge V-belt transmission belt, one or more sheets of cover canvas and an adhesive rubber layer are wound around the peripheral surface of a cylindrical forming drum, and a cord made of a cord is placed thereon. Was spirally spun, and a compressed rubber layer was sequentially wound thereon to obtain a laminate, which was then vulcanized to form a belt sleeve. The compressed rubber layer used here had a thickness of three to four rolled sheets stacked on each other, and was wound around a forming drum in which short fibers were oriented in the sheet width direction.

However, since the rolled sheet cannot sufficiently orient the short fibers in the sheet rolling direction unless the thickness is reduced, it is inevitable that the sheets are stacked to have a desired thickness. Man-hours were required.

As a method of improving this, for example, using an extruder equipped with an expansion die, orienting the short fibers in the circumferential direction of the extrusion cylindrical body, the intermediate space, from the predetermined flow path width of the inlet space to the outlet space An enlarged space portion in which the flow path width changes to a predetermined flow path width is provided, the cross-sectional area of the outlet space of the expansion die is formed to be larger than the cross-sectional area of the inlet space by a predetermined amount, and the flow path width of the inlet portion is an intermediate portion. And the outlet width is set to be smaller than or equal to the intermediate passage width. (For example, see Patent Document 1)

Further, a cutting device for axially cutting the cylindrical elastomer in which the extruded short fibers are oriented in the circumferential direction, and a device for developing the cut elastomer into a flat plate are provided. A guide device is provided between the cylinder and the air, and air is blown out from the cylinder to cool while suppressing the shrinkage of the cylindrical elastomer in the circumferential direction, and the disorder of the short fiber orientation caused by uneven shrinkage is reduced. A manufacturing apparatus is shown in which the inclination of the unfolding mechanism can be adjusted so that the distance between the both ends and the center of the sheet becomes equal, thereby preventing the occurrence of flare. (For example, see Patent Document 2)
Japanese Patent Publication No. 6-9847 JP-A-6-106602

However, when a conventional adhesive die is used and a highly adhesive material such as chloroprene is used, the surface layer, especially the outer peripheral layer, generates a large frictional force with the inner peripheral surface of the die and smoothly. Because the rubber did not flow, the rubber surface became rough. For this reason, the adhesion between the matrix rubber and the fibers is poor, and the orientation is also poor. In practice, it has sometimes been difficult to use the matrix for the compressed rubber layer of the power transmission belt.

The present invention has been made in view of the above-described situation in view of the above, and is intended to cope with this. Laminating a rubber in which short fibers corresponding to a compressed rubber layer are oriented in a predetermined direction and an adhesive rubber containing no short fibers, and extruding smoothly. A method for producing a two-layer rubber sheet which can be used for a power transmission belt such as a V-ribbed belt, a double-ribbed belt, a low-edge V-belt or the like, which can prevent roughening of the rubber surface and can be formed at low cost with a reduced number of manufacturing steps. The purpose is to provide.

That is, the invention according to claim 1 of the present application relates to a method for manufacturing a two-layer rubber sheet corresponding to the compression rubber and the adhesive rubber of the power transmission belt, wherein the short fiber-containing rubber is laminated on the inner peripheral side and the adhesive rubber is laminated on the outer peripheral side. The layered cylindrical molded body is extruded from an expansion die whose diameter is gradually increased from the inlet to the discharge port, and the cylindrical molded body is cut straight to form a short fiber oriented rubber in which an adhesive rubber is laminated. There is a method for manufacturing a two-layer rubber sheet for a power transmission belt to be a sheet, and extruding a two-layer cylindrical molded body in which the adhesive rubber is laminated so as to be on the outer peripheral side of the short fiber-containing rubber, By making a short fiber oriented two-layer rubber sheet that is cut straight and laminated with adhesive rubber, it enables smooth extrusion, prevents roughening of the rubber surface, and laminates the adhesive rubber and the compressed rubber layer in advance. Transmission with low manufacturing cost It is possible to mold the belt.

According to the invention of claim 2 of the present application, the extruded short fiber-containing rubber whose outer peripheral surface is coated with adhesive rubber is simultaneously extruded from the entrance of the expansion die, and the adhesive rubber is surrounded on the outer peripheral surface of short fiber-containing rubber. The method for producing a two-layer rubber sheet for a power transmission belt according to claim 1, wherein the rubber sheet is molded into a cylindrical molded body.

According to the invention of claim 3 of the present application, the short fiber-containing rubber is made to enter from the entrance of the expansion die, and the adhesive rubber is made to enter at a position between the entrance of the extension die and the discharge port, so that the adhesive rubber is formed on the outer periphery of the short fiber-containing rubber. The present invention is directed to a method for manufacturing a two-layer rubber sheet for a power transmission belt, which is extruded into a cylindrical molded body surrounded by a surface, and the thickness of the adhesive rubber can be extruded more uniformly.

The invention according to claim 4 of the present application is characterized in that the intrusion position of the adhesive rubber is between the entrance of the expansion die and the discharge port, and the width of the rubber passage is laminated from the intrusion position of the adhesive rubber to the discharge port. In the method of manufacturing a two-layer rubber sheet for a power transmission belt, which has only become larger, it reduces the penetration resistance of the adhesive rubber into the rubber passage, makes it easy to smoothly surround the outer surface of the short fiber-containing rubber, and the thickness of the adhesive rubber Can be made uniform.

The invention according to claim 5 is directed to a method for manufacturing a two-layer rubber sheet for a power transmission belt in which the position where the adhesive rubber enters is near the discharge port of the expansion die, and the short fiber-containing rubber is harder than the adhesive rubber. If the rubber sheet is extruded while being expanded in a laminated state, the adhesive rubber layer is affected by the short fiber-containing rubber layer, and the resulting rubber sheet is likely to undulate. There is an effect that the distance over which the layer is affected by the short fiber-containing rubber layer is shortened, and the waving is hardly generated.

The invention according to claim 6 is a method for producing a two-layer rubber sheet for a power transmission belt, in which short fiber-containing rubber kneaded by an extrusion screw is passed through a gear pump, and then guided to an expansion die and extruded. By feeding the short-fiber-mixed rubber to the expansion die at a low pressure, it is possible to obtain a short-fiber-containing rubber sheet with less internal heat generation.

According to the present invention, there is provided a method for producing a two-layer rubber sheet corresponding to a compression rubber and an adhesive rubber of a power transmission belt, wherein the short-fiber-containing rubber layer is laminated on an inner peripheral side, and the adhesive rubber is laminated on an outer peripheral side. A compact is extruded from an expansion die whose diameter is gradually increased from an inlet to a discharge port, and the tubular compact is cut straight into a short fiber oriented rubber sheet laminated with adhesive rubber. In the method for manufacturing a two-layer rubber sheet for a belt, a two-layer cylindrical molded body in which the adhesive rubber is laminated so as to be on the outer peripheral side of the short fiber-containing rubber is extruded, and the cylindrical molded body is linearly cut. Short-fiber-oriented two-layer rubber sheet laminated with adhesive rubber to enable smooth extrusion and prevent the occurrence of rough surface on the rubber surface. Power transmission belt at low cost There is an effect that can.

In addition, cylindrical molding in which the short fiber-containing rubber is made to enter from the entrance of the extension die, and the adhesive rubber is made to enter at a position between the entrance of the extension die and the discharge port to surround the adhesive rubber on the outer peripheral surface of the short fiber-containing rubber. By extruding on the body, the thickness of the adhesive rubber can be extruded more uniformly, and the adhesive rubber intrusion position should be between the entrance of the expansion die and the discharge port, and from the adhesive rubber intrusion position to the discharge port By increasing the width of the rubber passage by the thickness of the adhesive rubber to be laminated, the penetration resistance of the adhesive rubber into the rubber passage is reduced, and it is easy to smoothly surround the outer surface of the short fiber-containing rubber. There is an effect that the thickness can be made uniform.

Furthermore, by setting the position where the adhesive rubber enters the vicinity of the discharge port of the expansion die, it is possible to prevent the sheet from hitting and to obtain a high quality two-layer rubber sheet. Also, by guiding the short-fiber-containing rubber to the expansion die via a gear pump, it becomes possible to send a large amount of short-fiber-containing rubber to the expansion die at a low pressure, thereby obtaining a short-fiber-containing rubber sheet with less internal heat generation. Can be.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic view of a process of forming a short fiber oriented rubber sheet in which an adhesive rubber is laminated while cutting an extruded cylindrical molded body into a straight line. In this step, the manufacturing apparatus 1 is used. In the present apparatus 1, the first extruder 2a for kneading the short fiber-containing rubber by rotation of the extrusion screw 4a in the cylinder 3a and the second extruder 2 for kneading the rubber containing no short fiber by rotation of the extrusion screw 4b in the cylinder 3b. The extruder 2 b connects the extruded rubber to the back of the expansion die 5 and introduces the rubber into the rubber passage 8 formed by the shaft 6 and the cylinder 7.

In the expansion die 5, the inner die 10 mounted on the shaft portion 6 is combined with the outer die 13 connected to the cylindrical portion 7 to form an expanded rubber passage 8. The inner die 10 is a conical body whose diameter is gradually increased from the inlet 11 to the discharge port 12. In the vicinity of the entrance 11 of the outer die 13, the thickness of the extruded rubber can be made uniform by combining the alignment block 14.

The second extruder 2b for kneading and extruding the adhesive rubber 16 containing no short fibers is disposed closer to the inlet 11 than the first extruder 2a, and the outer peripheral portion of the short fiber-containing rubber 15 extruded earlier. Then, the adhesive rubber 16 is made to flow and extruded into a two-layered cylindrical molded body 17 which is surrounded. The adhesive rubber 16 has good fluidity of the rubber and can completely surround the outer periphery of the short fiber-containing rubber 15. The extruded cylindrical molded body 17 is cut off by the cutting means 19 and then wound up.

In the first extruder 2a and the second extruder 2b, the extruding screws 4a and 4b are rotatably accommodated in the cylinders 3a and 3b, and the rubber compound is introduced from the raw material inlet and the extruding screws 4a and 4b are rotated. Knead with rubber. At this time, the air and the gas generated from the rubber compound in the cylinders 3a and 3b are discharged from an exhaust port (not shown). The temperature of the cylinders 3a and 3b is changed according to the type of rubber, but is usually adjusted to 40 to 100 ° C., and the short fibers and rubber are heated to a temperature at which mixing is easy, and are thermoplasticized so that they can be easily extruded. . Further, the kneading time in this case is adjusted to such an extent that the vulcanization of the rubber does not proceed.

The expansion die 5 gradually expands the diameter of the inner die 10 toward the discharge port 12 to form a conical shape. The expansion die 5 is accommodated in the outer die 13, and a gap having a predetermined thickness is provided between the inner die 10 and the outer die 13. ing. The short fiber-mixed rubber 15 is gradually stretched in the circumferential direction toward the discharge port 12 while orienting the short fibers in the circumferential direction, and at the same time, the adhesive rubber 16 is extruded into the cylindrical molded body 17 surrounded by the outer layer. Mold.

The expansion die 5 is arranged vertically with respect to the horizontally arranged first extruder 2a and second extruder 2b, and the cylindrical molded body 17 is extruded from the discharge port 12 so as to resist gravity. In addition, the cylindrical molded body 17 does not deform due to gravity, and the dimensional change is relatively small. Further, the expansion die 5 arranged in the vertical direction is hardly bent by the weight of the inner die 10, the gap between the inner die 10 and the outer die 13 is kept constant, and the cylindrical die 17 having a small thickness deformation can be finished. it can.

In addition, the rubber passage 8 formed by the inner die 10 and the outer die 13 has a substantially uniform gap from the inlet 11 to the discharge port 12, so that the extrusion of the cylindrical molded body 17 can be smoothly performed in the longitudinal direction without applying a brake. It is finished into a cylindrical molded body 17 having a uniform thickness without flowing and without internal distortion.

形状 The shape of the inner die 10 is a factor that affects the magnitude of the shearing force. The taper angle at which the diameter gradually expands from the inlet 11 toward the outlet 12 is 30 ° or more and less than 90 °, the inlet has a diameter of 20 to 60 mm, the outlet has a diameter of 100 to 440 mm, and an expansion ratio which is a ratio thereof. (Discharge port / entrance) is set to 1.5 to 12.5. If it is less than the set range, the circumferential stretching around the discharge port 12 of the inner die 10 is small, and the short fibers are less likely to be circumferentially oriented in the inner and outer layers of the thick cylindrical molded body 17. On the other hand, if it exceeds this setting range, the stretching in the circumferential direction becomes too large, and when the extrusion pressure is inferior, the tubular molded body 17 is easily torn.

冷却 A cooling device (not shown) for circulating cooling water inside the inner die 10 may be provided in order to suppress internal heat generation of the rubber existing in the rubber passage 8 between the inner die 10 and the outer die 13. In the cooling device, cooling water is put into the inner die 10 and the outer die 13, and is discharged from each die through a passage provided in each die by a pump and circulated.

The cutting means 19 cuts the cylindrical molded body 17 as shown in FIG. 5 along the extrusion direction to form a two-layer rubber sheet 20 as shown in FIG. Consists of a sonic vibration cutter. The two-layer rubber sheet 20 is fed at a constant speed by a driving roll via a guide roll, and is wound by laminating a liner such as canvas on a winding roll.

In another apparatus 1 shown in FIG. 2, which is a short fiber oriented rubber sheet in which an adhesive rubber is laminated, a first extruder 2a for kneading the short fiber-containing rubber 15 by rotating an extrusion screw 4a in a cylinder 3a, and a cylinder 3b. The second extruder 2b kneading the adhesive rubber 16 containing no short fibers by the rotation of the extrusion screw 4b introduces the extruded rubber into the rubber passage 8 provided at the back of the expansion die 5.

The first extruder 2a is directly connected to the expansion die 5 in the axial direction of the extrusion screw 4a, and the second extruder 2b is arranged at right angles to the first extruder 2a. Then, when the adhesive rubber 16 extruded from the second extruder 2b collides with a rectifying projection provided at a position away from the tip end portion 25 of the extrusion screw 4a of the first extruder 2a, the adhesive rubber 16 wraps around the short fiber-containing rubber 15. It becomes easier to siege.

The expansion die 5 accommodates the inner die 10 having a conical shape by gradually expanding the diameter toward the discharge port 12 in the outer die 13, and forms a gap having a predetermined thickness between the inner die 10 and the outer die 13. Provided. The conical fluid splitting 27 attached and fixed to the inner die 10 divides the flow of the rubber uniformly to 360 degrees and pushes out the rubber passage 8 between the inner die 10 and the outer die 13.

The short-fiber-containing rubber 15 gradually orients the short fibers in the circumferential direction while being gradually stretched in the circumferential direction toward the discharge port 12, and at the same time, as shown in FIG. Extrusion molding into a shaped body 17. Then, as shown in FIG. 6, the tubular molded body 17 immediately after being extruded is cut into two-layer rubber sheets 20 by the cutting means 19 along the extrusion direction.
The thickness of the short fiber mixed rubber 15 is 1.5 to 10 mm, and the thickness of the adhesive rubber 16 is 0.1 to 1.0 mm.

As described above, the apparatus 1 shown in FIG. 2 simultaneously extrudes the short fiber-containing rubber 15 extruded with the adhesive rubber 16 on the outer peripheral surface thereof from the inlet 11 of the expansion die 5 to remove the adhesive rubber 16. The apparatus 1 shown in FIG. 3 is to form the short-fiber-containing rubber 15 from the inlet 11 of the expansion die 5 and to form the other adhesive rubber. The adhesive rubber 16 is made to intrude at a position P between the inlet 11 and the discharge port 12 of the expansion die 5 to extrude the adhesive rubber 16 into a cylindrical molded body 17 surrounded by the outer peripheral surface of the short fiber-containing rubber 15.

That is, in the apparatus 1 shown in FIG. 3, the first extruder 2a for kneading the short fiber-containing rubber 15 by rotating the extrusion screw 4a in the cylinder 3a extrudes the rubber from the inlet 11 of the expansion die 5 to the discharge port 12. On the other hand, a second extruder 2b for kneading the adhesive rubber 16 containing no short fibers is arranged in a state of intersecting with the first extruder 2a, and a rubber passage 36 is provided from a rubber reservoir 35 in which the adhesive rubber 16 is arranged in a circumferential direction. At a position P between the inlet 11 and the discharge port 12 of the expansion die 5 via a cylinder.

At the intrusion position P, a clear step is provided in the rubber passage 8 as shown in FIG. 4, and the width of the rubber passage 8 from the intrusion position P to the discharge port 12 is equal to the thickness of the laminated adhesive rubber 16. It is large and reduces the penetration resistance of the adhesive rubber 16 into the rubber passage 8 so that it is easy to smoothly surround the outer peripheral surface of the short fiber-containing rubber 15 and makes the thickness of the adhesive rubber 16 uniform. There is no problem if the intrusion position P is between the inlet 11 and the discharge port 12, but it is preferable to be near the discharge port 12.

In the device 1 shown in FIG. 7, a gear pump 40 is interposed between the cylinder 3a and the expansion die 5, and the short fiber-containing rubber 15 kneaded by the rotation of the extrusion screw 4a in the cylinder 3a in the first extruder 2a is engaged. It is forcibly fed into the expanding die 5 through the space between the rotating drive gear 41 and the driven gear 42 and extruded from the inlet 11 to the discharge port 12. On the other hand, a second extruder 2b for kneading the adhesive rubber 16 containing no short fibers is arranged in a state of intersecting with the first extruder 2a, and a rubber passage 36 is provided from a rubber reservoir 35 in which the adhesive rubber 16 is arranged in a circumferential direction. At a position P near the discharge port 12 of the extension die 5 through the cylindrical shape.

There is no problem if the intrusion position P is between the inlet 11 and the discharge port 12, but in detail, as shown in FIG. When the intrusion position P is arranged up to 12, a rubber sheet having a small thickness variation can be obtained.
The present inventor has found that, since the short fiber-containing rubber is harder than the adhesive rubber, when extruding while expanding in a laminated state, the adhesive rubber layer is affected by the short fiber-containing rubber layer, and the obtained rubber is obtained. Wavy sheet is likely to occur. However, when the intrusion position P is located near the discharge port 12, the distance that the adhesive rubber layer is affected by the short-fiber-containing rubber layer is shortened, so that there is a feature that the waving hardly occurs.
It should be noted that the combination of setting the intrusion position P near the discharge port 12 and interposing the gear pump 40 between the cylinder 3a and the expansion die 5 is not essential, and these can be implemented independently.

The rubber of the short fiber-containing rubber 15 includes natural rubber, butyl rubber, styrene-butadiene rubber, chloroprene rubber, ethylene-propylene rubber, alkylated chlorosulfanated polyethylene, hydrogenated nitrile rubber, hydrogenated nitrile rubber, and unsaturated carboxylic acid. A mixed polymer with a metal salt, a rubber material such as an ethylene-α-olefin elastomer composed of ethylene-propylene rubber (EPR) or an ethylene-propylene-diene monomer (EPDM) alone, or a mixture thereof is used. Examples of diene monomers include dicyclopentadiene, methylene norbornene, ethylidene norbornene, 1,4-hexadiene, cyclooctadiene, and the like.

The rubber is made of fibers such as aramid fiber, polyamide fiber, polyester fiber, and cotton, and the length of the fiber varies depending on the type of fiber, but short fibers of about 1 to 10 mm are used. About 7 mm, and about 5 to 10 mm for polyamide fiber, polyester fiber, and cotton are used. The addition amount is 10 to 40 parts by mass based on 100 parts by mass of the rubber. Further, a softener, a reinforcing agent composed of carbon black, a filler, an antioxidant, a vulcanization accelerator, a vulcanizing agent and the like are added to the rubber of the present invention.

Examples of the softener include plasticizers for general rubbers, for example, phthalates such as dibutyl phthalate (DBP) and dioctyl phthalate (DOP), adipates such as dioctyl adipate (DOA), and dioctyl sebacate (DOS). It includes sebacate-based phosphates such as tricresyl phosphate, and general petroleum-based softeners.

According to the present invention, a master batch can be prepared by previously kneading at least rubber short fibers with an open roll or a kneader. In this method, 10 to 40 parts by mass of short fibers are put into 100 parts by mass of a polymer by an open roll and kneaded, and then the kneaded master batch is once released and cooled to 20 to 50 ° C. This is to prevent rubber scorch.

1-10 parts by mass of a softening agent can be added together with the short fibers. This improves the familiarity between the short fibers and the rubber and improves the dispersion in the rubber, and also has the effect of preventing the short fibers themselves from becoming entangled and becoming flocculent. In other words, the softener penetrates into the short fibers and acts as a lubricant to loosen the entanglement between the elementary fibers, prevents the short fibers from becoming cotton-like, and reduces the familiarity between the short fibers and the rubber. It becomes better and the dispersion of short fibers becomes better.

On the other hand, the adhesive rubber 16 is the same as the rubber used for the short fiber-containing rubber. When the rubber composition of the ethylene-alpha-olefin elastomer is used, a rubber composition which can be crosslinked with sulfur is used. And, if necessary, carbon black, a reinforcing agent such as silica, a filler such as calcium carbonate and talc, a plasticizer, a stabilizer, a processing aid, and a normal rubber compound such as a coloring agent are used. Things are used.

二 The obtained two-layer rubber sheet can be applied to transmission belts such as a V-ribbed belt, a double-ribbed belt, and a low-edge V-belt.

It is the schematic which shows the process used as a 1st Example which makes a short fiber orientation rubber sheet, while incising linearly the extruded cylindrical molded object. It is the schematic which shows the process used as a 2nd Example of making a short fiber orientation rubber sheet, while incising the extruded cylindrical molded body linearly. It is the schematic which shows the process used as a 3rd Example of making a short fiber orientation rubber sheet, while incising linearly the extruded cylindrical molded object. FIG. 4 is an enlarged view of a portion C in FIG. 3. It is sectional drawing of the AA direction of FIG. It is a perspective view of the two-layer rubber sheet which cut out the short fiber orientation rubber sheet with adhesive rubber. It is the schematic which shows the process used as a 3rd Example of making a short fiber orientation rubber sheet, while incising linearly the extruded cylindrical molded object. FIG. 8 is an enlarged view of a portion C in FIG. 7.

Explanation of reference numerals

Reference Signs List 2a First extruder 2b Second extruder 5 Expansion die 8 Rubber passage 10 Inner die 11 Inlet 12 Discharge port 13 Outer die 15 Short fiber-containing rubber 16 Adhesive rubber 17 Cylindrical molded body 19 Cutting means 20 Double-layer rubber sheet 40 Gear pump P Intrusion position

Claims (6)

In the method for producing a two-layer rubber sheet corresponding to the compression rubber and the adhesive rubber of the power transmission belt, a two-layer cylindrical molded body in which short fiber-containing rubber is laminated on the inner peripheral side and adhesive rubber is laminated on the outer peripheral side is discharged from the inlet. Extrusion molding from an expansion die whose diameter is gradually increased toward the outlet, and the cylindrical molded body is cut straight to form a short fiber oriented rubber sheet laminated with adhesive rubber, for a power transmission belt. A method for producing a two-layer rubber sheet. A method in which the outer peripheral surface of the previously extruded short fiber-containing rubber coated with adhesive rubber is simultaneously extruded from the entrance of the expansion die to form the adhesive rubber into a cylindrical molded body surrounded by the outer peripheral surface of the short fiber-containing rubber. Item 2. A method for producing a two-layer rubber sheet for a power transmission belt according to Item 1. The short-fiber-containing rubber is made to enter from the entrance of the expansion die, and the adhesive rubber is made to enter at a position between the entrance of the extension die and the discharge port, so that the adhesive rubber is formed into a tubular molded body surrounded by the outer peripheral surface of the short-fiber-containing rubber. The method for producing a two-layer rubber sheet for a power transmission belt according to claim 1, which is extruded. 4. The intrusion position of the adhesive rubber is between the entrance of the expansion die and the discharge port, and the width of the rubber passage from the intrusion position of the adhesive rubber to the discharge port is increased by the thickness of the laminated adhesive rubber. Of producing a two-layer rubber sheet for a power transmission belt. The method for producing a two-layer rubber sheet for a power transmission belt according to claim 3 or 4, wherein the intrusion position of the adhesive rubber is near the discharge port of the extension die. The method for producing a two-layer rubber sheet for a power transmission belt according to any one of claims 1 to 5, wherein the short fiber-containing rubber kneaded with an extrusion screw is passed through a gear pump, and then guided through an expansion die and extruded.

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