Toothed belt and method for manufacturing toothed belt

Abstract

Provided is a toothed belt having: a belt body comprising a base part and a plurality of tooth parts integrated on the inner peripheral side of the base part; and a core wire embedded in the base part. The tooth pitch is 8-14 mm. The distance L from a tooth bottom line to a core wire center varies along the belt length direction. The absolute value X of the difference between the distance LA from the tooth bottom line to the core wire center in a tooth bottom and the distance LB from the tooth bottom line to the core wire center in a belt tooth is 0.20 mm or more. The tooth parts have a hardness of 46 to 52 as measured by a type D durometer, and the diameter of the core wire is 1.0-2.4 mm.

Description

Toothed belt and method for manufacturing the toothed belt

[0001] The present invention relates to a toothed belt and a method for manufacturing the toothed belt. This application claims priority based on Japanese Patent Application No. 2025-003429 filed on January 9, 2025, and incorporates all the descriptions described in the above Japanese application.

[0002] Toothed belts are suitable for applications that require synchronous rotation and are widely used in automotive applications and general industrial applications. In recent years, the number of cases where they are used in injection molding machines and industrial robots that are subject to high loads has been increasing (for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2007-147025

[0004] For toothed belts, it is required to increase the skip torque (also called jumping torque) so that tooth skipping does not occur during use. [[ID=I4]]

[0005] In view of such circumstances, the present disclosure has been made, and an object thereof is to provide a toothed belt in which tooth skipping is unlikely to occur.

[0006] A toothed belt according to one aspect of the present invention is a toothed belt having a belt body including a base portion and a plurality of tooth portions integrated on the inner peripheral side of the base portion, and a core wire embedded in the base portion, The tooth pitch is 8 mm or more and 14 mm or less, The distance L from the tooth bottom line to the center of the core wire varies along the belt length direction, The absolute value X of the difference between the distance LA from the tooth bottom line to the center of the core wire at the tooth bottom and the distance LB from the tooth bottom line to the center of the core wire at the belt tooth is 0.20 mm or more, The hardness of the tooth portion measured with a Type D durometer is 46 or more and 52 or less, The diameter of the core wire is 1.0 mm or more and 2.4 mm or less.

[0007] A method for manufacturing a toothed belt according to one aspect of the present invention is a method for manufacturing a toothed belt having a belt body comprising a base portion and a plurality of teeth integrated on the inner circumference side of the base portion, and a core wire embedded in the base portion, comprising: (A) winding a core wire around the outer circumference of a cylindrical mold having a cross-sectional shape corresponding to the belt teeth, with axially extending recesses and axially extending protrusions provided between adjacent recesses on its outer circumference; (B) winding at least one layer of uncrosslinked rubber sheet around the mold around which the core wire is wound; and (C) covering the mold around which the core wire and at least one layer of uncrosslinked rubber sheet are wound with a rubber sleeve, and then heating while pressing the uncrosslinked rubber sheet toward the mold to integrally mold the base portion and the teeth portion, wherein the Mooney viscosity of the uncrosslinked rubber sheet is 45 MS (1 + 4) 100°C or more and 60 MS (1 + 4) 100°C or less.

[0008] According to an aspect of the present invention, a toothed belt that is less prone to tooth skipping can be provided.

[0009] Figure 1 is a perspective view showing an example of a toothed belt. Figure 2 is a cross-sectional view taken along line A-A in Figure 1. Figure 3 is a cross-sectional view taken along line B-B in Figure 1. Figure 4 is an end view taken along line C-C in Figure 1. Figure 5 is a diagram illustrating the manufacturing method of a toothed belt. Figure 6 is a diagram illustrating the manufacturing method of a toothed belt. Figure 7 is a diagram illustrating the manufacturing method of a toothed belt. Figure 8 is a diagram illustrating the dimensions of the toothed belts manufactured in the examples and comparative examples. Figure 9 is a diagram illustrating the manufacturing method of the toothed belt of Comparative Example 5. Figure 10 is a diagram illustrating the manufacturing method of the toothed belt of Comparative Example 5. Figure 11 is a diagram illustrating the manufacturing method of the toothed belt of Comparative Example 5. Figure 12 is a diagram illustrating the manufacturing method of the toothed belt of Comparative Example 5. Figure 13 is a diagram illustrating the manufacturing method of the toothed belt of Comparative Example 5. Figure 14 is a diagram showing the pulley layout of the transmission system used in the running tests in the examples and comparative examples.

[0010] The embodiments of the present invention will be outlined below. [1] A toothed belt having a belt body comprising a base and a plurality of teeth integrated on the inner circumference side of the base, and a core wire embedded in the base, wherein the tooth pitch is 8 mm or more and 14 mm or less, the distance L from the root line to the center of the core wire varies along the length direction of the belt, the absolute value X of the difference between the distance LA from the root line to the center of the core wire at the root of the tooth and the distance LB from the root line to the center of the core wire at the belt tooth is 0.20 mm or more, the hardness of the teeth measured with a Type D durometer is 46 or more and 52 or less, and the diameter of the core wire is 1.0 mm or more and 2.4 mm or less.

[0011] The toothed belt described above has sufficiently high tooth hardness and a core wire diameter that allows for optimal meshing with the toothed pulley, resulting in high skip torque and reduced likelihood of tooth skipping.

[0012] [2] The toothed belt described in [1] above preferably has the core wires embedded in such a way that they form a spiral with a pitch in the belt width direction, and the gap between adjacent core wires is 0.1 mm or more and 0.5 mm or less.

[0013] [3] In the toothed belt described in [1] or [2] above, it is preferable that the belt body is made of a crosslinked molded product of an uncrosslinked rubber sheet having a Mooney viscosity before molding of 45 MS (1 + 4) 100°C or more and 60 MS (1 + 4) 100°C or less.

[0014] [4] A method for manufacturing a toothed belt having a belt body comprising a base and a plurality of teeth integrated on the inner circumference of the base, and a core wire embedded in the base, comprising: (A) winding a core wire around the outer circumference of a cylindrical mold having a cross-sectional shape corresponding to the belt teeth, with axially extending recesses and axially extending protrusions provided between adjacent recesses on its outer circumference; (B) winding at least one layer of uncrosslinked rubber sheet around the mold around which the core wire is wound; (C) covering the mold around which the core wire and at least one layer of uncrosslinked rubber sheet are wound with a rubber sleeve, and then heating while pressing the uncrosslinked rubber sheet toward the mold to integrally mold the base and the teeth, wherein the Mooney viscosity of the uncrosslinked rubber sheet is 45 MS (1 + 4) 100°C or more and 60 MS (1 + 4) 100°C or less.

[0015] The above method for manufacturing a toothed belt uses an uncrosslinked rubber sheet having a specific Mooney viscosity and is suitable for manufacturing toothed belts with high rubber hardness, such as the toothed belt described in [1] above.

[0016] [5] The method for manufacturing a toothed belt according to [4] above preferably involves winding the core wires to form a spiral having a pitch in the axial direction, the diameter of the core wires being 1.0 mm or more and 2.4 mm or less, the gap between adjacent core wires being 0.1 mm or more and 0.5 mm or less, and manufacturing a toothed belt with a tooth pitch of 8 mm or more and 14 mm or less. In this case, it is suitable for manufacturing the toothed belt according to [2] above.

[0017] The embodiments of the present invention will be described in detail below with reference to the drawings.

[0018] (Toothed Belt) Figure 1 is a perspective view showing a part of a toothed belt 1 according to an embodiment of the present invention. Figure 2 is a cross-sectional view taken along line A-A in Figure 1. Figure 3 is a cross-sectional view taken along line B-B in Figure 1. Figure 4 is an end view taken along line C-C in Figure 1. Figure 1 shows a part of a toothed belt 1. The toothed belt 1 is an endless interlocking transmission belt. The toothed belt 1 is a single-sided toothed belt. The toothed belt 1 according to this embodiment is used in general industrial applications such as machine tools, printing machines, textile machinery, and injection molding machines, as well as in automobiles and motorcycles. Particularly preferred applications are industrial robots where repeatable positioning accuracy is required.

[0019] In Figure 1, the direction indicated by the double-headed arrow X is the belt width direction of the toothed belt 1. The direction indicated by the double-headed arrow Y is the belt length direction of the toothed belt 1. The belt length direction is also the belt circumference direction of the toothed belt 1. The direction indicated by the double-headed arrow Z is the belt thickness direction of the toothed belt 1. The upper side of each plane is the outer circumference side of the toothed belt 1, and the lower side is the inner circumference side.

[0020] The belt length of the toothed belt 1 (belt length along the belt pitch line) is, for example, 225 mm or more and 6000 mm or less. The belt width Wb of the toothed belt 1 is, for example, 5 mm or more and 120 mm or less. The belt thickness Tb of the toothed belt 1 is, for example, 3.5 mm or more and 9.0 mm or less. The belt thickness Tb of the toothed belt 1 is the thickness of the thickest part of the toothed belt 1. The dimensions (belt length, belt width Wb, and belt thickness Tb) of the toothed belt according to the embodiment of the present invention are not limited to this range.

[0021] The toothed belt 1 has a back portion 11 and a plurality of belt teeth 12. The back portion 11 extends in the circumferential direction of the belt. The back portion 11 is an endless strip. In a cross-section perpendicular to the circumferential direction of the toothed belt 1, the cross-sectional shape of the back portion 11 is rectangular. The plurality of belt teeth 12 are provided on the inner circumferential side of the back portion 11. The plurality of belt teeth 12 are arranged at equal intervals in the circumferential direction of the belt. Each belt tooth 12 extends in the belt width direction. The portion sandwiched between adjacent belt teeth 12 is the tooth root 24. The tooth pitch Pb of the belt teeth 12 is 8 mm or more and 14 mm or less. The tooth profile of the belt teeth 12 is, for example, an arc tooth profile.

[0022] (Structure of a toothed belt) The toothed belt 1 comprises a belt body 2, a core wire 3, and a reinforcing fabric 4. The belt body 2, core wire 3, and reinforcing fabric 4 are described below.

[0023] (Belt body) The belt body 2 has a strip shape. The belt body 2 comprises a base portion 21 and a plurality of teeth 22. The base portion 21 extends in the circumferential direction of the belt. A core wire 3 is embedded in the base portion 21. The plurality of teeth 22 are provided on the inner circumferential side of the base portion 21. The plurality of teeth 22 are integral with the base portion 21. The plurality of teeth 22 are arranged at equal intervals in the circumferential direction of the belt. The surface of the teeth 22 is covered with reinforcing cloth 4.

[0024] The belt body 2 is made of a rubber composition (hereinafter also referred to as a crosslinked rubber composition) which is formed by crosslinking an uncrosslinked rubber composition containing a rubber component and a rubber compounding agent by heating and pressurizing. The base portion 21 and the teeth portion 22 of the belt body 2 are each made of the crosslinked rubber composition. In the toothed belt 1 shown in Figure 1, the base portion 21 and the teeth portion 22 are made of the same crosslinked rubber composition. In other words, the belt body 2 is made of one type of crosslinked rubber composition. The belt body 2 may be made of two or more types of crosslinked rubber compositions.

[0025] As described above, the belt body 2 is composed of a crosslinked rubber composition in which an uncrosslinked rubber composition containing, for example, a rubber component and a rubber compounding agent is crosslinked. Examples of the rubber component include hydrogenated nitrile rubber (HNBR), an alloy in which at least one of metal acrylate salts, metal methacrylate salts, metal polyacrylate salts, and metal polymethacrylate salts is finely dispersed in hydrogenated nitrile rubber (HNBR), ethylene-α-olefin elastomers such as chloroprene rubber (CR) and ethylene-propylene-diene rubber (EPDM), chlorosulfonated polyethylene rubber, styrene-butadiene rubber, and epichlorohydrin rubber. These may be used individually or in combination of two or more.

[0026] Preferred rubber components include hydrogenated nitrile rubber and an alloy in which at least one of zinc acrylate, zinc methacrylate, polyzinc acrylate, and polyzinc methacrylate is finely dispersed in hydrogenated nitrile rubber. In this specification, hydrogenated nitrile rubber (HNBR) and an alloy in which at least one of metal acrylate, metal methacrylate, metal polyacrylate, and metal polymethacrylate is finely dispersed in hydrogenated nitrile rubber (HNBR) are collectively referred to as "HNBR-based rubber components."

[0027] As the above HNBR-based rubber component, a low viscosity type is preferred. For example, an HNBR-based rubber component having a Mooney viscosity of 50 ml (1 + 4) 100°C or higher and 72 ml (1 + 4) 100°C or lower is preferred. Commercially available products can also be used as the above HNBR-based rubber component. Examples of commercially available HNBR-based rubber components include Zetpol 2000L, Zetpol 2010L, Zetpol 2011L, Zetpol 2020L, Zetpol 2030L, Zeoforte 2195LCX, Zeoforte 2295L, and Zeoforte 2395 (all manufactured by ZEON Corporation). These may be used individually or in combination of two or more types.

[0028] Examples of the rubber compounding agents mentioned above include, for example, short fibers, vulcanization accelerators, antioxidants, reinforcing agents, plasticizers, co-crosslinking agents, crosslinking agents, and processing aids. Examples of the short fibers include aramid short fibers, nylon short fibers, and polyester short fibers. Para-aramid short fibers are preferred among the aramid short fibers. Only one type of these short fibers may be used, or two or more types may be used in combination.

[0029] The length of the short fibers is, for example, 0.5 mm to 3.5 mm. The diameter of the short fibers is, for example, 5 μm to 50 μm. The preferred content of the short fibers is 1 part by mass to 7 parts by mass per 100 parts by mass of the rubber component.

[0030] Examples of the above-mentioned vulcanization accelerators include metal oxides, metal carbonates, fatty acids and their derivatives. Examples of the above-mentioned metal oxides include zinc oxide (zinc oxide) and magnesium oxide. Only one type of these vulcanization accelerator may be used, or two or more types may be used in combination. The content of the above-mentioned vulcanization accelerator is, for example, 3 parts by mass or more and 20 parts by mass per 100 parts by mass of the rubber component.

[0031] Examples of the above-mentioned antioxidants include benzimidazole-based antioxidants, aromatic secondary amine-based antioxidants, and amine-ketone-based antioxidants. These antioxidants may be used individually or in combination of two or more. The content of the above-mentioned antioxidants is, for example, 1.5 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the rubber component.

[0032] Examples of the reinforcing material include carbon black and silica. The reinforcing material may be carbon black and silica in combination. Examples of the carbon black include channel black, furnace black, thermal black, and acetylene black. Examples of furnace black include SAF, ISAF, N-339, HAF, N-351, MAF, FEF, SRF, GPF, ECF, and N-234. Examples of thermal black include FT and MT. Only one type of carbon black may be used, or two or more types may be used in combination.

[0033] When carbon black is used, its content is, for example, 5 to 50 parts by mass per 100 parts by mass of rubber component. When silica is used, its content is, for example, 10 to 30 parts by mass per 100 parts by mass of rubber component.

[0034] Examples of the above plasticizers include dialkyl sebacate, dialkyl phthalate, and dialkyl adipate. Examples of dialkyl sebacate include polyether ester and dioctyl sebacate (DOS). Examples of dialkyl phthalate include dibutyl phthalate (DBP) and dioctyl phthalate (DOP). Examples of dialkyl adipate include dioctyl adipate (DOA). Only one type of these plasticizer may be used, or two or more types may be used in combination. The content of the above plasticizer is, for example, 5 parts by mass or more and 20 parts by mass per 100 parts by mass of rubber component.

[0035] Examples of the above-mentioned co-crosslinking agents include trimethylolpropane trimethacrylate, m-phenylenedimaleimide, zinc dimethacrylate, and triallyl isocyanurate. These co-crosslinking agents may be used individually or in combination of two or more. The content of the above-mentioned co-crosslinking agent is, for example, 3 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the rubber component.

[0036] Examples of the crosslinking agents mentioned above include sulfur and organic peroxides. Sulfur and organic peroxides may be used in combination. Of course, either one may be used alone. When sulfur and organic peroxides are used in combination as the crosslinking agents, it is preferable that the total amount of the crosslinking agents is, for example, 0.1 parts by mass or more and 3 parts by mass or less of sulfur and 1 part by mass or more and 5 parts by mass or less of organic peroxide per 100 parts by mass of rubber component.

[0037] Examples of the processing aids mentioned above include stearic acid, polyethylene wax, and metal salts of fatty acids. These processing aids may be used individually or in combination of two or more. The content of the processing aids is, for example, 0.5 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the rubber component.

[0038] The belt body 2 is composed of a crosslinked rubber composition in which such an uncrosslinked rubber composition is crosslinked. The hardness of the teeth 22 of the belt body 2, as measured by a Type D durometer (hereinafter also referred to as Duro-D hardness), is between 46 and 52. Therefore, the toothed belt 1 has high hardness of the teeth 22, making tooth skipping less likely. On the other hand, if the Duro-D hardness of the teeth 22 is less than 46, the skip torque is small, and tooth skipping cannot be sufficiently suppressed. Furthermore, a toothed belt 1 with a Duro-D hardness of the teeth 22 exceeding 52 is difficult to manufacture in a single-stage process.

[0039] In this invention, the reason why the hardness of the tooth portion is defined by a measurement using a Type D durometer is that if the hardness of the tooth portion 22 is measured using a Type A durometer, the measurement value will be 90 or higher, making it difficult to accurately measure the hardness of the tooth portion 22.

[0040] The hardness of the teeth 22 is measured by pressing a Type D durometer, as specified in JIS-K6253-3 (2012), against the side surface of the teeth 22 of the belt body 2 (the end face of the teeth 22 in the belt width direction). The ambient temperature during measurement shall be the standard test temperature of 23±2℃ as specified in JIS-K6250.

[0041] In the belt body 2, it is preferable that the hardness of the base portion 21 is the same as or lower than the hardness of the teeth portion 22. A toothed belt 1 in which the hardness of the base portion 21 is lower than the hardness of the teeth portion 22 has the effect of being less prone to cracking on the back surface.

[0042] (Core wire) The core wire 3 is embedded in the base 21. Examples of core wire 3 include glass core wire, aramid core wire, carbon core wire, and steel core wire. These core wires are preferably made of twisted yarn. Carbon core wire and steel core wire are preferred for core wire 3. Carbon and steel are materials with high elastic modulus. Therefore, in toothed belts equipped with carbon core wire or steel core wire, the length does not change easily when a load is applied, and the change in tooth pitch is small. Therefore, toothed belts equipped with carbon core wire or steel core wire can easily maintain a good meshing state with toothed pulleys.

[0043] The diameter of the core wire 3 is 1.0 mm or more and 2.4 mm or less. Here, the diameter of the core wire 3 is the outer diameter φW of the core wire 3 in the belt width direction at the tooth root 24 of the toothed belt 1. In a toothed belt 1 with a tooth pitch Pb of 8 mm or more and 14 mm or less, if the diameter of the core wire 3 is within this range, tooth skipping is less likely to occur. The outer diameter φW of the core wire 3 can be measured in the cross section at the tooth root 24 of the toothed belt 1 (see Figure 2).

[0044] Increasing the diameter of the core wire embedded in the toothed belt increases the longitudinal elastic modulus of the toothed belt, thereby tending to enhance the performance of suppressing tooth skipping in the toothed belt (hereinafter also referred to as tooth skipping suppression performance). However, if the diameter of the core wire is made too large, meshing interference between the toothed belt and the toothed pulley will occur, and as a result, the tooth skipping suppression performance will decrease. On the other hand, when the diameter of the core wire embedded in the toothed belt is small, even if the core wire is embedded with the gap dimension between adjacent core wires being the same as in the case of using a core wire with a larger diameter, compared with the case of using a core wire with a larger diameter, it tends to be inferior in tooth skipping suppression performance. This is because when the diameter of the core wire is small, the ratio of the total cross-sectional area of the core wire in the cross-section perpendicular to the length direction of the toothed belt is small compared with the case of using a thick core wire, and the longitudinal elastic modulus of the toothed belt is low. From such a perspective, the toothed belt 1 has an excellent tooth skipping suppression performance while maintaining proper meshing with the toothed pulley by setting the diameter of the core wire 3 to be 1.0 mm or more and 2.4 mm or less. The preferred diameter of the core wire 3 is 1.0 mm or more and 2.0 mm or less.

[0045] From the perspective of maintaining proper meshing with the toothed pulley and ensuring excellent tooth skipping suppression performance, the ratio (φW / Pb) of the diameter of the core wire 3 to the tooth pitch Pb of the toothed belt 1 is preferably 0.100 or more and 0.175 or less. In the meshing of the toothed belt and the toothed pulley, PLD (PITCH LINE DIFFERENTIAL) has an impact, and the diameter of the core wire is important as a factor for determining PLD. In the case of the toothed belt 1 with a core wire diameter of 1.0 mm or more and 2.4 mm or less and a tooth pitch Pb of 8 mm or more and 14 mm or less, when the ratio (φW / Pb) is within the above range, it is easy to maintain a proper meshing state with the toothed pulley, and it is easy to ensure the tooth skipping suppression performance.

[0046] Also, in the toothed belt 1, as will be described later, the distance L from the bottom line BL of the teeth to the center of the core wire 3 (hereinafter also referred to as the core wire center) of the core wire 3 varies along the belt length direction. Specifically, as will be described later, the absolute value X of the difference between the distance LA and the distance LB is 0.20 mm or more. Therefore, the toothed belt 1 has a varying PLD along the belt length direction. In such a toothed belt 1, in order to maintain proper meshing with the toothed pulley and ensure excellent tooth skipping suppression performance, it is suitable to set the above ratio (φW / Pb) to 0.100 or more and 0.175 or less.

[0047] The core wire 3 has a pitch in the belt width direction and is provided so as to form a helix. For example, a core wire pair composed of an S-twisted core wire 3 and a Z-twisted core wire 3 may be provided with a pitch in the belt width direction and so as to form a helix.

[0048] The core wires 3 are arranged at intervals in the belt width direction and extend in parallel. Apparently, a plurality of core wires 3 are arranged side by side in the belt width direction. The gap dimension between adjacent core wires 3 is preferably 0.1 mm or more and 0.5 mm or less. If this gap dimension is less than 0.1 mm, molding defects in the tooth portion are likely to occur when manufacturing the toothed belt by the method described later, and if it exceeds 0.5 mm, it is difficult to increase the skip torque.

[0049] The distance L from the bottom line BL of the teeth to the center (core wire center) of the core wire 3 of the core wire 3 varies along the belt length direction. In other words, the distance L from the bottom line BL to the core wire center is not constant along the belt length direction.

[0050] The preferred range for the distance L from the tooth root line BL to the core wire center is, for example, 0.65 mm to 0.86 mm when the nominal pitch of the belt teeth 12 is 8 mm, and 1.40 mm to 1.60 mm when the nominal pitch of the belt teeth 12 is 14 mm. Therefore, it is preferable that the distance L of the toothed belt 1 varies within this range. In this specification, "nominal pitch" has the same meaning as "nominal pitch" used in JIS B 1857-1, etc. In embodiments of the present invention, the range of the tooth pitch Pb of the toothed belt 1 is 8 ± 0.03 mm when the nominal pitch is 8 mm, and 14 ± 0.03 mm when the nominal pitch is 14 mm.

[0051] It is preferable that the distance L of the core wire 3 fluctuates periodically along the length of the belt. Here, the periodic fluctuation of the distance L means that when the distance L at each position along the length of the belt of the core wire 3 is plotted on a graph with any one point on the core wire 3 as the origin, the distance from the origin as the horizontal axis, and the distance L as the vertical axis, the resulting graph will show local minimums appearing at approximately constant intervals along the horizontal axis. Here, "approximately constant intervals" means that all intervals are between 0.95 and 1.05 times the median value.

[0052] A toothed belt in which the above-mentioned distance L fluctuates periodically along the belt length can be manufactured by the toothed belt manufacturing method (one-stage method) described later. In other words, a toothed belt manufactured by the toothed belt manufacturing method (one-stage method) described later has the above-mentioned distance L fluctuating periodically along the belt length.

[0053] In the toothed belt 1, the absolute value X of the difference between the distance LA (see Figure 4) from the root line BL to the center of the core wire at the tooth root 24 and the distance LB (see Figure 4) from the root line BL to the center of the core wire at the belt tooth 12 is 0.20 mm or more. When the toothed belt 1 is manufactured using a one-stage process, the absolute value X is usually 0.20 mm or more. In the toothed belt 1, the above X is 0.60 mm or less. If the above X exceeds 0.60 mm, the core wire 3 is significantly wavy along the length of the belt. As a result, the elongation when tension is applied to the toothed belt 1 increases, the belt tension decreases significantly, and the tooth skipping suppression performance is impaired.

[0054] (Method for calculating X) Distance LA and distance LB for calculating the above X are obtained at adjacent parts. That is, when distance LA is obtained at one tooth root, distance LB is obtained at the belt tooth adjacent to this tooth root, and the difference is calculated based on the obtained LA and LB. Furthermore, in this invention, the difference between distance LA and distance LB is obtained at three locations along the belt length direction, and the average of the absolute values ​​of these differences is calculated as the evaluation value X. Here, distance LA and distance LB are obtained at three locations that are spaced approximately equally apart. In this invention, the three locations that are spaced approximately equally apart on the toothed belt 1 refer to three locations selected such that the difference in the number of belt teeth between the selected locations is one or less.

[0055] Distances LA and LB are measured by acquiring images of a cross-section of the toothed belt 1 perpendicular to the belt length direction (see Figures 2 and 3). Specifically, the following method is used: First, the toothed belt 1 is cut perpendicular to the belt length direction so as to pass through the center of the tooth root 24 in the belt length direction, and a cross-sectional image as shown in Figure 2 is acquired. Next, based on this cross-sectional image, the distance LA from the tooth root line BL to the center of the core wire is measured. At this time, the core wire cross-section to be measured is selected to be the cross-section of the core wire closest to the center in the belt width direction.

[0056] Next, the toothed belt 1 is cut perpendicular to the length of the belt so as to pass through the center of the belt teeth 12 in the length direction of the belt, and a cross-sectional image as shown in Figure 3 is obtained. At this time, the belt tooth 12 to be cut is selected to be adjacent to the tooth root 24 that was cut in order to obtain the distance LA. Next, based on this cross-sectional image, the distance LB from the tooth root line BL to the center of the core wire is measured. At this time, the core wire cross-section to be measured is selected to be close in the length direction of the core wire to the core wire cross-section selected to obtain the distance LA. In measuring the distance LB, first, a virtual tooth root line VBL is set as shown in Figure 3. The virtual tooth root line VBL is a virtual line at a distance LC from the back surface 11a of the toothed belt 1. This distance LC is obtained based on the cross-sectional image (see Figure 2) obtained to measure the distance LA. After that, the distance LB from the set virtual tooth root line VBL to the center of the core wire is measured.

[0057] The core wire 3 may be a core wire that has been treated with an adhesive to enhance its adhesion to the belt body 2. A toothed belt 1 equipped with an adhesive-treated core wire 3 can be manufactured in the toothed belt manufacturing method described later by using a core wire that has been treated with the adhesive described below as the core wire before it is wound onto the mold. Examples of adhesive treatments applied to the core wire before it is wound onto the mold include RFL treatment, which involves immersing it in an aqueous solution (also called RFL aqueous solution) containing an initial condensate of resorcinol and formaldehyde and latex, and then drying it, and rubber glue treatment, which involves immersing it in rubber glue and then drying it. These adhesive treatments may be applied individually or in combination. The core wire before it is wound onto the mold may be subjected to a surface treatment before the above adhesive treatment. Examples of the above surface treatments include immersion in an epoxy solution or an isocyanate solution and then drying it.

[0058] Furthermore, the following bonding treatments may be applied to the core wire before it is wound onto the mold. For example, each filament contained in the core wire may be coated with a converging agent and then dried to form a film, or a twisted set of multiple filaments may be coated with an adhesive and then dried to form a film. In this case, the converging agent and adhesive may be, for example, an aqueous solution containing RFL liquid, resorcinol and an initial condensate of formaldehyde (also called an RF aqueous solution), an emulsion in which an epoxy group-containing compound and a curing agent are dispersed in water. In addition, as the converging agent and adhesive, a composition containing an uncrosslinked rubber such as chlorosulfonated polyethylene or hydrogenated nitrile rubber (HNBR) and a crosslinking agent whose crosslinking progresses by heat treatment, such as a diisocyanate compound, an aromatic nitroso compound, or a maleimide-based crosslinking agent may also be used.

[0059] (Reinforcement Fabric) The reinforcement fabric 4 covers the surface of the teeth 22. The reinforcement fabric 4 constitutes the inner circumferential surface of the toothed belt 1. The inner circumferential surface of the toothed belt 1 includes the reinforcement fabric 4. The reinforcement fabric 4 is a woven fabric. Examples of fibers that make up the reinforcement fabric 4 include polyamide fibers (nylon fibers), polyester fibers, aramid fibers, poly(p-phenylenebenzobisoxazole) (PBO) fibers, cotton, etc. For example, a woven fabric of polyamide fibers is preferred for the reinforcement fabric 4. The thickness of the reinforcement fabric 4 is, for example, 0.5 mm or more and 2.0 mm or less. It is preferable that the reinforcement fabric 4 has elasticity, for example, a woven fabric in which the weft yarn has been treated with a woolly finish. The value of X can be adjusted by adjusting the thickness of the reinforcement fabric 4.

[0060] The reinforcing fabric 4 may be subjected to an adhesive treatment to enhance its adhesion to the belt body 2. Examples of such adhesive treatments include RFL treatment, which involves immersing the fabric in an RFL aqueous solution and then heating it; soaking treatment, which involves immersing the fabric in a low-viscosity rubber adhesive and then drying it; and coating treatment, which involves applying a high-viscosity rubber adhesive to the surface of the belt body and then drying it. One of these treatments may be performed, or two or more may be performed. The reinforcing fabric 4 may also be subjected to a pre-treatment before the adhesive treatment, which involves immersing it in an epoxy solution or isocyanate solution and then heating it. These adhesive treatments and pre-treatments are performed before winding the reinforcing fabric 4 onto the mold in the toothed belt manufacturing method described later.

[0061] (Method for manufacturing a toothed belt) Next, the method for manufacturing the toothed belt 1 will be described. The toothed belt 1 is manufactured, for example, by the method for manufacturing a toothed belt according to an embodiment of the present invention.

[0062] A method for manufacturing a toothed belt according to an embodiment of the present invention includes: (A) winding a core wire around the outer circumference of a cylindrical mold having a cross-sectional shape corresponding to the belt teeth, with axially extending recesses and axially extending protrusions provided between adjacent recesses on its outer circumference; (B) winding at least one layer of uncrosslinked rubber sheet around the mold on which the core wire is wound; and (C) covering the mold on which the core wire and at least one layer of uncrosslinked rubber sheet are wound with a rubber sleeve, and then heating the uncrosslinked rubber sheet while pressing it toward the mold to integrally mold the base and the teeth, wherein the Mooney viscosity of the uncrosslinked rubber sheet is 45 MS (1 + 4) 100°C or higher and 60 MS (1 + 4) 100°C or lower.

[0063] In this method of manufacturing toothed belts, an uncrosslinked rubber sheet with a Mooney viscosity within a predetermined range is used. Therefore, the formability of the teeth is good, and teeth with a predetermined Duro-D hardness can be formed. In this method of manufacturing toothed belts, the base and teeth of the belt body are integrally molded. In this manufacturing method, the base and teeth are molded simultaneously in a single process.

[0064] Two methods are known for manufacturing toothed belts: one in which the base and teeth are integrally molded (referred to as a one-stage method in this specification), and another in which only the teeth are partially molded first, and then the base is molded and the base and teeth are integrated (referred to as a two-stage method in this specification). Comparing the two manufacturing methods, the one-stage method is more economically advantageous because it has fewer steps and can be manufactured in a shorter time. On the other hand, the one-stage method may have inferior moldability of the teeth compared to the two-stage method.

[0065] The method for manufacturing a toothed belt according to an embodiment of the present invention uses an uncrosslinked rubber sheet with a Mooney viscosity within a predetermined range, and therefore, while being a one-step manufacturing process, the moldability of the teeth is good. According to this method for manufacturing a toothed belt, a toothed belt 1 can be manufactured at low cost and in a short time. Figures 5 to 7 are diagrams illustrating the method for manufacturing a toothed belt 1. Figures 5 to 7 show only a part of the mold 5 for belt molding and the belt (including the belt material). The method for manufacturing a toothed belt 1, which will be described with reference to Figures 5 to 7, is a one-step manufacturing process in which the teeth and the base are integrally molded in a single step.

[0066] In the manufacture of the toothed belt 1, a belt forming die 5 is used. The die 5 is cylindrical. The outer circumference of the die 5 is provided with recesses 51 extending in the axial direction and protrusions 52 extending in the axial direction. The recesses 51 have a cross-sectional shape corresponding to the belt teeth 12 and are grooves extending in the axial direction (the direction perpendicular to the plane of the paper in Figure 5). The recesses 51 are provided at regular intervals in the circumferential direction. The protrusions 52 are provided between adjacent recesses 51.

[0067] (1) Prepare the materials. The rubber components are kneaded, and then a rubber compounding agent is added and kneaded to obtain an uncrosslinked rubber composition. The obtained uncrosslinked rubber composition is molded to produce an uncrosslinked rubber sheet 23. At this time, a method such as calendering can be used to mold the uncrosslinked rubber sheet 23.

[0068] Prepare the core wire 3 and reinforcing fabric 4, and apply adhesive treatment and surface treatment to each as needed. Furthermore, shape the reinforcing fabric 4 into a cylindrical shape.

[0069] The uncrosslinked rubber sheet 23 used in the embodiments of the present invention has a Mooney viscosity of 45 MS (1 + 4) 100°C or higher and 60 MS (1 + 4) 100°C or lower. A Mooney viscosity within this range is suitable for molding teeth with a Duro-D hardness within the above range. In contrast, if the Mooney viscosity is 45 MS (1 + 4) 100°C or lower, it is not easy to increase the Duro-D hardness to the above range. On the other hand, if the Mooney viscosity exceeds 60, molding defects in the teeth are likely to occur when manufacturing toothed belts. The Mooney viscosity is measured by a method in accordance with JIS K6300-1 (2013).

[0070] (2) As shown in Figure 5, first, a cylindrical reinforcing cloth 4 is placed over the outer surface of the mold 5. The core wire 3 is then wound spirally over the reinforcing cloth 4. At this time, it is preferable to wind the core wire 3 while applying a tension of 98 N to 490 N.

[0071] After winding the core wire 3, an uncrosslinked rubber sheet 23 is further wound around it. Multiple sheets of uncrosslinked rubber sheet 23 (two in Figure 5) are wound around it. As a result, an uncrosslinked molded body 13 is formed on the outer circumference of the mold 5, with the reinforcing fabric 4, core wire 3, and uncrosslinked rubber sheet 23 laminated together. At this time, it is preferable to laminate the uncrosslinked rubber sheet 23 so that the direction of the fibers corresponds to the direction of the belt length. In particular, if the uncrosslinked rubber sheet 23 contains short fibers, it is preferable to laminate the uncrosslinked rubber sheet 23 so that the direction of the fibers corresponds to the direction of the belt length. When multiple sheets of uncrosslinked rubber sheet 23 are wound around it, each uncrosslinked rubber sheet may have the same composition or a different composition. Here, when uncrosslinked rubber sheets with different compositions are wound around it, the Mooney viscosity of each uncrosslinked rubber sheet is 45 MS (1 + 4) 100°C or higher and 60 MS (1 + 4) 100°C or lower. When multiple uncrosslinked rubber sheets 23 are wrapped around the belt, for example, the uncrosslinked rubber sheet wrapped around the inner circumference (the uncrosslinked rubber sheet that mainly forms the teeth after molding) can be an uncrosslinked rubber sheet containing short fibers, while the uncrosslinked rubber sheet wrapped around the outer circumference (the uncrosslinked rubber sheet that mainly forms the base after molding) can be an uncrosslinked rubber sheet that does not contain short fibers. In this case, flexibility on the back side is ensured, and a toothed belt that is less prone to cracking on the back side can be manufactured.

[0072] (3) As shown in Figure 6, the rubber sleeve 6 is placed over the uncrosslinked molded body 13 on the mold 5. The uncrosslinked molded body 13 with the rubber sleeve 6 is placed inside a vulcanizing can (not shown) together with the mold 5, and the vulcanizing can is sealed. High-temperature and high-pressure steam is filled into the vulcanizing can. This state is maintained for a predetermined time. As a result, the uncrosslinked molded body 13 is pressed towards the mold 5 and heated. The uncrosslinked rubber sheet 23 flows through the cavity formed between the mold 5 and the rubber sleeve 6. The uncrosslinked rubber sheet 23 passes between the core wires 3. The uncrosslinked rubber sheet 23 flows into each of the multiple recesses 51 provided in the mold 5 while pressing against the reinforcing fabric 4. As the uncrosslinked rubber sheet 23 flows through the cavity in this way, it integrates with the core wires 3 and the reinforcing fabric 4 and is crosslinked. As a result, a cylindrical belt slab 14 is formed as shown in Figure 7. In this process, the base and the teeth are vulcanized simultaneously. In this process, the base and the teeth are integrally molded to obtain the belt body.

[0073] (4) The inside of the vulcanizing can is depressurized to release the seal. The belt slab 14 formed between the mold 5 and the rubber sleeve 6 is demolded. The demolded belt slab 14 is cut into slices. The toothed belt 1 is obtained by going through these steps.

[0074] The method for manufacturing a toothed belt according to the embodiment of the present invention is a one-step process in which the base and the teeth are integrally molded in a single step. Therefore, the method for manufacturing a toothed belt according to the embodiment of the present invention allows for the manufacture of toothed belts in a shorter time and at a lower cost compared to a two-step process.

[0075] The embodiments of the present invention will be described in more detail below with reference to examples, but the embodiments of the present invention are not limited to the following examples. Here, several toothed belts were manufactured and their performance was evaluated.

[0076] (Belt raw materials) (1) Uncrosslinked rubber sheets Uncrosslinked rubber compositions A to H were prepared according to the compound compositions shown in Table 1. The uncrosslinked rubber compositions were prepared by kneading the rubber components and then adding and kneading the rubber compounding agent. Using each of the uncrosslinked rubber compositions A to H, uncrosslinked rubber sheets A to H with a thickness of 1.0 mm were produced by calendering.

[0077] The Mooney viscosity of each of the uncrosslinked rubber sheets A to H was measured using a method compliant with JIS K6300-1 (2013). An S rotor was used as the rotor. The sample dimensions were as follows: six 1 mm thick uncrosslinked rubber sheets were stacked and punched out to a diameter of approximately 50 mm, with two disc-shaped pieces forming a pair.

[0078]

[0079] In Table 1, HNBR(1) is Zetpol 2010 (manufactured by Nippon Zeon Co., Ltd.), HNBR(2) is Zeoforte ZSC2195CX (manufactured by Nippon Zeon Co., Ltd.), HNBR(3) is Zetpol 2010L (manufactured by Nippon Zeon Co., Ltd.), and HNBR(4) is Zeoforte ZSC2195LCX (manufactured by Nippon Zeon Co., Ltd.). Also in Table 1, the aramid short fibers are para-aramid short fibers with a fiber length of 1 mm and a wire diameter of 12 μm, and the organic peroxide is peroximone F40 (manufactured by NOF Corporation).

[0080] (2) Carbon core wires with a diameter of 1.0 mm and carbon core wires with a diameter of 2.0 mm were used, which had been bonded with a core wire converging agent and an adhesive. As the converging agent and adhesive, a composition containing HNBR and a maleimide-based crosslinking agent that is crosslinked by heat treatment was used.

[0081] (3) Reinforcement fabric The following bonding treatments were applied to a fabric in which the warp and weft threads were made of polyamide fibers. The bonding treatments included a soaking treatment in which the fabric was immersed in a low-viscosity rubber paste and then dried, and a coating treatment in which a high-viscosity rubber paste was applied to the side of the fabric that would be the belt body and then dried. The thickness of the reinforcement fabric before molding was 1.2 mm, 1.4 mm, 1.7 mm, or 1.8 mm. The thickness of each reinforcement fabric was prepared to match the thickness of the fabric before bonding treatment.

[0082] (Dimensions of toothed belts) Two types of toothed belts were manufactured: one called S8M and the other called S14M. The dimensions of the toothed belt called S8M are as follows, indicated by the symbols in Figure 8: Pb = 8.00 mm, Tb = 5.00 mm, h1 = 1.95 mm, h2 = 3.05 mm, R = 5.20 mm, W = 5.20 mm, a = 0.686 mm, r1 = 0.80 mm, r2 = 0.80 mm, PLD (PITCH LINE DIFFERENTIAL) = 0.686 mm. This toothed belt has a length of 840 mm and a width of 10 mm.

[0083] The dimensions of the toothed belt called S14M are as follows, corresponding to the symbols shown in Figure 8: Pb = 14.00 mm, Tb = 10.20 mm, h1 = 4.90 mm, h2 = 5.30 mm, R = 9.10 mm, W = 9.10 mm, a = 1.397 mm, r1 = 1.40 mm, r2 = 1.40 mm, PLD = 1.397 mm. This toothed belt has a length of 1400 mm and a width of 14 mm.

[0084] [Examples 1-5, Comparative Examples 1-4, and 6-7] Toothed belts were manufactured using the toothed belt manufacturing method (one-step method) described above. The uncrosslinked rubber sheet, core wire, and reinforcing fabric were as described above. The selected uncrosslinked rubber composition, the tooth pitch of the belt teeth, the core wire pitch (gap dimension of the core wires), and the tension when winding the core wires are as shown in Table 2. The vulcanization conditions (steam temperature and holding time in step (3) of the toothed belt manufacturing method described above) were held at 120°C for 5 minutes, followed by holding at 170°C for 15 minutes. The diameter of the core wire (outer diameter φW of the core wire in the belt width direction at the tooth root) was calculated as the average value of three locations using cross-sectional images obtained by calculating the absolute value X as described later, and it was found to be the same as or slightly larger than the diameter of the core wire before winding.

[0085] [Comparative Example 5] Using the belt material combinations shown in Table 2, a toothed belt was manufactured by the following manufacturing method (two-stage method). Figures 9 to 13 show the manufacturing method of the toothed belt in this comparative example.

[0086] (1) Uncrosslinked rubber sheets 23 (uncrosslinked rubber sheets 23A, 23B), core wires 3, and reinforcing fabric 4 were prepared in the same manner as in the one-stage manufacturing method. Furthermore, the reinforcing fabric 4 was formed into a cylindrical shape.

[0087] (2) As shown in Figure 9, first, a cylindrical reinforcing cloth 4 was placed over the outer surface of the mold 5. Next, an uncrosslinked rubber sheet 23A was wrapped around the reinforcing cloth 4. The uncrosslinked rubber sheet 23A is a sheet made of an uncrosslinked rubber composition A (see Table 2).

[0088] Subsequently, as shown in Figure 10, a rubber sleeve 6 was placed over the first uncrosslinked molded body 13A on the mold 5, and this was placed inside the vulcanizing can and sealed. Next, high-temperature (120°C) and high-pressure steam was filled into the vulcanizing can and held in this state for 5 minutes. As a result, the first uncrosslinked molded body 13A was pressed towards the mold 5 and heated. As a result, the uncrosslinked rubber sheet 23A flowed into each of the multiple recesses 51 of the mold 5 while pressing against the reinforcing cloth 4 and was crosslinked. At this time, the uncrosslinked rubber sheet 23A was heated to a semi-crosslinked state. As a result, as shown in Figure 11, multiple semi-crosslinked teeth 122 were formed.

[0089] (3) Next, as shown in Figure 12, the core wire 3 was spirally wound around the outer circumference of the molded tooth portion 122. Furthermore, one uncrosslinked rubber sheet 23B was wound on top of that as a rubber sheet to form the base. As a result, a second uncrosslinked molded body 13B was formed on the mold 5 (on the tooth portion 122) in which the core wire 3 and the uncrosslinked rubber sheet 23B were laminated. As shown in Table 2, the uncrosslinked rubber sheet 23B is a sheet made of uncrosslinked rubber composition B.

[0090] (4) As shown in Figure 13, a rubber sleeve 6 was placed over the second uncrosslinked molded body 13B on the mold 5, and this was placed in a vulcanizing can and sealed. Next, high-temperature (170°C) and high-pressure steam was filled into the vulcanizing can. Furthermore, this state was maintained for 15 minutes. As a result, the second uncrosslinked molded body 13B was pressed towards the mold 5 and heated. At this time, the uncrosslinked rubber sheet 23B passed between the core wires 3 and was crosslinked while being pressed against the multiple semi-crosslinked teeth 122 formed in the multiple recesses 51. As a result, a cylindrical belt slab 14 having integrated and completely crosslinked teeth 22 and base 21 was formed.

[0091] (5) The inside of the vulcanizing can was depressurized to release the seal, and then the belt slab 14 formed between the mold 5 and the rubber sleeve 6 was demolded. After that, as in the embodiment, the demolded belt slab 14 was cut into sections to obtain a toothed belt. The diameter of the core wire of the obtained toothed belt was the same as the diameter of the core wire before winding.

[0092]

[0093] (Evaluation) The toothed belts manufactured in the examples and comparative examples were evaluated as follows. The results are shown in Table 3.

[0094] (1) The judgment was made based on whether the tooth height of the belt-formable belt teeth (tooth portion) was within the tolerance range. If it was within the tolerance range, it was evaluated as "○", and if it was not within the tolerance range, it was evaluated as "×". The tooth height of the above belt teeth was obtained by selecting three belt teeth at approximately equal intervals from the circumference of the belt, obtaining a sample piece of belt with a width of 5 mm including the selected belt teeth, magnifying and projecting the belt tooth shape at 10 to 20 times, and obtaining the distance between the tooth tip and tooth root line of the resulting projection.

[0095] (2) Absolute value X of the difference between distance LA and distance LB As described above, an image of the cross section perpendicular to the belt length direction of the toothed belt 1 was obtained, and the absolute value X was calculated using the obtained image. The average value of three locations was calculated. The results are shown in Table 3. In Comparative Example 1, the belt formability was "×", and the absolute value X could not be calculated. Here, the obtained cross section image was used to calculate the diameter of the core wire.

[0096] (3) Hardness of the belt teeth The hardness of the crosslinked rubber composition constituting the belt teeth was measured using the following method. A commercially available Type D durometer was used for the measurement. Here, the rubber hardness tester was pressed perpendicularly to the side surface of the teeth of the belt body (the end surface of the teeth in the belt width direction) for the measurement. The ambient temperature during measurement was 23 ± 2°C. Measurements were taken on three belt teeth, and the average value was used as the result. The results are shown in Table 3.

[0097] (4) Measurement of skip torque (durability evaluation) Using the transmission system 90 with the pulley layout shown in Figure 14, a belt running test was performed according to the following procedures [1] to [7], and the skip torque was measured. Here, the belt running test for the toothed belt called S8M was performed using a 24-tooth drive pulley and a 48-tooth driven pulley. The belt running test for the toothed belt called S14M was performed using a 28-tooth drive pulley and a 45-tooth driven pulley.

[0098] [1] Place the belt on the two pulleys (drive pulley 91 and driven pulley 92), and while keeping the drive shaft fixed, slide the driven shaft (see arrow in the figure) to tension the belt to a predetermined level. [2] Then rotate the belt several times to allow it to settle. [3] Check with a tension meter whether the belt has reached the predetermined tension. Repeat [1] and [2] until the predetermined tension is reached (350 N for S8M, 400 N for S14M). [4] Once the predetermined tension is reached, fix the driven shaft. [5] Rotate the belt at a constant speed up to a predetermined rotational speed. [6] While rotating at a constant speed, gradually increase the load on the driven pulley 92. [7] As the load is increased, measure the torque (skip torque) when the belt skips teeth using a torque meter (not shown). The results are shown in Table 3. In this evaluation, for toothed belts called S8M, a skip torque of 90N or more indicates that the skip torque is sufficiently high, and for toothed belts called S14M, a skip torque of 250N or more indicates that the skip torque is sufficiently high.

[0099]

[0100] As shown in Table 3, the toothed belt according to the embodiment of the present invention was found to have high skip torque and be less prone to tooth skipping. Comparative Example 5 also has sufficiently high skip torque, but because it is manufactured using a two-stage process, the manufacturing time is longer and the manufacturing cost is higher.

[0101] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims and is intended to include all modifications in the meaning and scope equivalent to the claims.

[0102] 1 Toothed belt 2 Belt body 3 Core wire 4 Reinforcement fabric 5 Mold 6 Rubber sleeve 11 Back part 12 Belt teeth 13, 13A, 13B Uncrosslinked molded body 14 Belt slab 21 Base part 22, 122 Tooth part 23, 23A, 23B Uncrosslinked rubber sheet 24 Tooth root 51 Recess 52 Protrusion 90 Transmission system 91 Drive pulley 92 Driven pulley

Claims

1. A toothed belt comprising a belt body having a base and a plurality of teeth integrated on the inner circumference of the base, and a core wire embedded in the base, wherein the tooth pitch is 8 mm or more and 14 mm or less, the distance L from the root line to the center of the core wire varies along the length of the belt, the absolute value X of the difference between the distance LA from the root line to the center of the core wire at the root of the tooth and the distance LB from the root line to the center of the core wire at the belt tooth is 0.20 mm or more, the hardness of the teeth measured with a Type D durometer is 46 or more and 52 or less, and the diameter of the core wire is 1.0 mm or more and 2.4 mm or less.

2. The toothed belt according to claim 1, wherein the core wires are embedded so as to form a spiral having a pitch in the belt width direction, and the gap between adjacent core wires is 0.1 mm or more and 0.5 mm or less.

3. The toothed belt according to claim 1 or 2, wherein the belt body is composed of a crosslinked molded product of an uncrosslinked rubber sheet having a Mooney viscosity of 45 MS (1 + 4) 100°C or higher and 60 MS (1 + 4) 100°C or lower before molding.

4. A method for manufacturing a toothed belt having a belt body comprising a base and a plurality of teeth integrated on the inner circumference of the base, and a core wire embedded in the base, comprising: (A) winding a core wire around the outer circumference of a cylindrical mold having a cross-sectional shape corresponding to the belt teeth, with axially extending recesses and axially extending protrusions provided between adjacent recesses on its outer circumference; (B) winding at least one layer of uncrosslinked rubber sheet around the mold around which the core wire is wound; (C) covering the mold around which the core wire and at least one layer of uncrosslinked rubber sheet are wound with a rubber sleeve, and then heating while pressing the uncrosslinked rubber sheet toward the mold to integrally mold the base and the teeth, wherein the Mooney viscosity of the uncrosslinked rubber sheet is 45 MS (1 + 4) 100°C or more and 60 MS (1 + 4) 100°C or less.

5. The method for manufacturing a toothed belt according to claim 4, wherein the core wire is wound so as to form a spiral having a pitch in the axial direction, the diameter of the core wire is 1.0 mm or more and 2.4 mm or less, the gap between adjacent core wires is 0.1 mm or more and 0.5 mm or less, and the tooth pitch is 8 mm or more and 14 mm or less.

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