Toothed belt and method for manufacturing the same

Abstract

To provide a toothed belt which achieves rigidity and flexibility of tooth parts and is excellent in resistance to chipping of teeth.SOLUTION: A toothed belt 1 includes: a back part in which a core wire 5 extending in a circumferential direction of a belt is embedded; and a plurality of tooth parts formed on an inner peripheral surface of the back part at intervals in the belt circumferential direction. The toothed belt 1 further includes: a back rubber layer 6 formed at the belt outer periphery side relative to the core wire 5; and a first rubber layer 3 and a second rubber layer 4 formed at the belt inner periphery side relative to the core wire 5. The back part includes the back rubber layer 6. The tooth part is formed by the first rubber layer 3 and the second rubber layer 4 disposed between the first rubber layer 3 and the core wire 5. An elastic modulus of the first rubber layer 3 is adjusted so as to be larger than an elastic modulus of the second rubber layer 4, and a tensile modulus of elasticity in a belt width direction of the second rubber layer 4 is adjusted to 1.0 to 4.5 MPa. The first rubber layer 3 is formed by a first cross-linked rubber composition including a first rubber component of 100 mass part and first short fiber 3a of 5 to 60 mass parts. The first short fibers 3a are aligned in a belt longitudinal direction along a contour of each tooth part.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a rubber toothed belt (or a toothed rubber toothed belt covered with tooth cloth) that is useful for synchronously transmitting power in general industrial machinery and the like under high load conditions when meshed with a toothed pulley, and a method for manufacturing the same. [Background technology]

[0002] Power transmission belts are broadly classified into friction belts and meshing belts. Examples of friction belts include flat belts, V-belts, and V-ribbed belts, while an example of a meshing belt is a toothed belt. A toothed belt has a back portion with a core wire embedded approximately parallel to the belt's circumference, teeth arranged at predetermined intervals in the belt's circumference, and a toothed fabric covering the surface of the teeth. The teeth of a toothed belt transmit power by engaging with a pulley that has grooves opposite to the teeth. Toothed belts do not slip with the pulley and can reliably transmit power even under high loads. In recent years, their use has increased in industrial machinery, internal combustion engines of automobiles, and rear-wheel drive systems of motorcycles. In particular, with the miniaturization of machinery, there is a demand for toothed belts that can accommodate smaller sizes (compatible with smaller diameter pulleys and narrower widths). When a miniaturized toothed belt is used in the same environment as a conventional large toothed belt, a higher load is applied to the toothed belt. Therefore, while miniaturization is possible, there is a need for highly durable toothed belts that can withstand use under conditions where higher loads are applied.

[0003] An important factor in the durability of toothed belts is the rigidity (deformation resistance) of the teeth. During the process of meshing with a toothed pulley, repeated deformation of the teeth due to contact with the pulley can lead to malfunctions such as tooth skipping (jumping) and tooth chipping due to cracks in the tooth root. Tooth chipping is a type of failure in which a tooth falls off the belt body. It is thought that this occurs when repeated deformation of the teeth concentrates stress on the tooth root, causing a microscopic crack to form at the tooth root, and then that crack to grow. In particular, when toothed belts are used under conditions of high load, the stress concentrated on the tooth root becomes especially large, making it easy for cracks to form from the tooth root and lead to tooth chipping. More specifically, microscopic cracks that mainly occur on or near the surface of the tooth root often propagate (grow) into the tooth rubber that forms the tooth, causing tooth chipping.

[0004] Therefore, increasing the rigidity of the teeth is necessary to suppress deformation of the teeth. On the other hand, increasing the rigidity of the teeth also increases the bending rigidity of the belt, reducing its flexibility. As machines become smaller, toothed pulleys also become smaller (smaller in diameter), requiring high flexibility (suppleness) to wrap around the small-diameter pulley and provide good meshing. Furthermore, in running layouts that involve "reverse bending," that is, when an idler pulley or tensioner is pressed against the back side of the toothed belt, causing the toothed belt to run in a bent state where the back side becomes the inner circumference, durability against reverse bending is also required. However, increasing the rigidity of the teeth is not a suitable method for increasing flexibility. On the other hand, even if a minute crack occurs, if it is possible to prevent the minute crack from growing and leading to tooth breakage, tooth breakage can be prevented.

[0005] In other words, in toothed belts, the rigidity (deformation resistance) and flexibility (suppleness) of the teeth are inversely related and difficult to achieve simultaneously. Therefore, a balanced formula is needed to achieve both, and if minute cracks occur due to prolonged use, it is necessary to suppress the growth of these cracks.

[0006] Japanese Patent Publication No. 2023-18654 (Patent Document 1) discloses a toothed belt having teeth formed from a toothed cloth, a first rubber layer formed along the toothed cloth, and a second rubber layer formed between the first rubber layer and the core wire, wherein the elastic modulus of the first rubber layer is adjusted to be greater than that of the second rubber layer. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-18654 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, the toothed belt described in Patent Document 1 did not have sufficient resistance to tooth breakage, nor did it have sufficient flexibility, and in particular, it did not have sufficient durability against reverse bending.

[0009] Therefore, the object of the present invention is to provide a toothed belt and a method for manufacturing the same that can achieve both rigidity (deformation resistance) and flexibility (flexibility) of the teeth, and also have excellent resistance to tooth chipping (durability).

[0010] Another object of the present invention is to provide a toothed belt and a method for manufacturing the same, which can also improve durability against reverse bending. [Means for solving the problem]

[0011] To achieve the above objectives, the inventors focused on the layer structure (distribution of mechanical properties) of the rubber layer constituting the teeth, and diligently studied a balanced configuration that could achieve both rigidity (deformation resistance) and flexibility (flexibility) of the teeth, which are inversely related, while ensuring the rigidity of the teeth that can withstand use under conditions where higher loads are applied. They also studied the compounding components of the rubber layer in order to improve tooth chipping resistance. As a result, they found that by forming the teeth of a toothed belt with a first rubber layer and a second rubber layer formed between the first rubber layer and the core wire, and by making the elastic modulus of the first rubber layer greater than that of the second rubber layer, and adjusting the tensile modulus of the second rubber layer in the belt width direction to 1.0 to 4.5 MPa, and by compounding short fibers in the first rubber layer oriented in the belt longitudinal direction along the contour of the teeth, it is possible to achieve both rigidity and flexibility of the teeth, as well as improve tooth chipping resistance, and thus completed the present invention.

[0012] In other words, a toothed belt as an embodiment of the present invention [1] is The back portion has a core wire embedded in it that extends along the circumference of the belt, The inner circumferential surface of the back portion is provided with a plurality of teeth formed at intervals in the circumferential direction of the belt, A toothed belt comprising a back rubber layer formed on the outer circumference side of the belt relative to the core wire, and a first rubber layer and a second rubber layer formed on the inner circumference side of the belt relative to the core wire, The back portion includes the back rubber layer, The modulus of elasticity of the first rubber layer is greater than that of the second rubber layer. The tensile modulus of the second rubber layer in the belt width direction is 1.0 to 4.5 MPa. The first rubber layer is formed of a first crosslinked rubber composition comprising a first rubber component and first short fibers. The proportion of the first short fibers is 5 to 60 parts by mass per 100 parts by mass of the first rubber component. The first short fibers are oriented along the contour of the teeth in the longitudinal direction of the belt, and The tooth portion includes the first rubber layer and the second rubber layer interposed between the first rubber layer and the core wire.

[0013] Aspect [2] of the present invention is an aspect in which, in the above aspect [1], the area ratio of the first rubber layer is 10 to 80 area% with respect to the total area of the first rubber layer and the second rubber layer in a cross-sectional view in the belt circumferential direction.

[0014] Aspect [3] of the present invention is an aspect in which, in the above aspect [1] or [2], the tensile strength of the first rubber layer in the belt circumferential direction is 40 to 90 MPa, the tensile elastic modulus of the first rubber layer in the belt width direction is 4 to 25 MPa, and the tensile strength of the second rubber layer in the belt circumferential direction is 10 to 50 MPa.

[0015] Aspect [4] of the present invention is an aspect in which, in any of the above aspects [1] to [3], the tensile elastic modulus of the first rubber layer in the belt width direction is 1.1 to 10 times that of the second rubber layer in the belt width direction.

[0016] Aspect [5] of the present invention is an aspect in which, in any of the above aspects [1] to [4], the first short fiber is a polyamide fiber.

[0017] Aspect [6] of the present invention is an aspect in which, in any of the above aspects [1] to [5], the first crosslinked rubber composition further contains a first crosslinking agent and a first co-crosslinking agent, the second rubber layer is formed of a second crosslinked rubber composition containing a second rubber component, a second crosslinking agent, and a second co-crosslinking agent, the first rubber component contains a first composite polymer containing a hydrogenated nitrile rubber and a metal salt of an unsaturated carboxylic acid, the second rubber component contains a second composite polymer containing a hydrogenated nitrile rubber and a metal salt of an unsaturated carboxylic acid, the ratio of the first co-crosslinking agent is 1 to 40 parts by mass with respect to 100 parts by mass of the first rubber component, and the ratio of the second co-crosslinking agent is 0.2 to 25 parts by mass with respect to 100 parts by mass of the second rubber component.

[0018] Aspect [7] of the present invention is the aspect in which, in aspect [6], the second crosslinked rubber composition further comprises second short fibers, wherein the proportion of the second short fibers in the second crosslinked rubber composition is 5 parts by mass or less per 100 parts by mass of the second rubber component.

[0019] Aspect [8] of the present invention is, in aspect [6] or [7], The first crosslinked rubber composition further comprises a first reinforcing inorganic filler, The second crosslinked rubber composition further comprises a second reinforcing inorganic filler, The proportion of the first composite polymer is 80% by mass or more in the first rubber component. The proportion of the second composite polymer is 30% by mass or more in the second rubber component. The first crosslinking agent contains a first organic peroxide, and the proportion of the first organic peroxide is 1 to 20 parts by mass per 100 parts by mass of the first rubber component. The second crosslinking agent contains a second organic peroxide, and the proportion of the second organic peroxide is 0.5 to 5 parts by mass per 100 parts by mass of the second rubber component. The proportion of the first reinforcing inorganic filler is 10 parts by mass or less per 100 parts by mass of the first rubber component, and This embodiment involves a ratio of the second reinforcing inorganic filler of 10 parts by mass or less per 100 parts by mass of the second rubber component.

[0020] Aspect [9] of the present invention is an aspect of any of the above aspects [1] to [8] in which the tooth shear index, which is the slope of an approximate straight line showing the relationship between tooth load and displacement, is 300 to 600 N / mm.

[0021] Aspect

[10] of the present invention is a toothed belt transmission mechanism comprising a toothed belt according to any of the above aspects [1] to [9] and a pulley, wherein the toothed belt is mounted on the pulley in a running layout that bends in the reverse direction.

[0022] The present invention also includes, as an embodiment

[11] , a method for manufacturing a toothed belt according to any embodiment [1] to

[10] , which includes a first rubber layer precursor preparation step of preparing an uncrosslinked rubber sheet in which first short fibers are oriented in one direction on the sheet surface as a first rubber layer precursor for forming a first rubber layer, and a pre-forming step of laminating the first rubber layer precursor and a second rubber layer precursor, which is an uncrosslinked rubber sheet for forming a second rubber layer, in an arrangement in which the first short fibers are oriented in the longitudinal direction of the belt, to produce a semi-crosslinked pre-molded body.

[0023] In this application, the numerical range represented by "A~B" means "A or greater and B or less," and is used to include the values ​​A and B at both ends of that range. [Effects of the Invention]

[0024] In this invention, the teeth of a toothed belt are formed from a first rubber layer and a second rubber layer formed between the first rubber layer and the core wire, the elastic modulus of the first rubber layer is greater than that of the second rubber layer and is adjusted to a specific tensile modulus, and the first rubber layer is formed from a first crosslinked rubber composition containing 100 parts by mass of a first rubber component and 5 to 60 parts by mass of first short fibers, and the first short fibers are oriented in the longitudinal direction of the belt along the contour of the teeth (contour of the first rubber layer or tooth surface). As a result, the rigidity of the teeth can be ensured to withstand use under conditions where higher loads are applied, while simultaneously achieving both the rigidity and flexibility of the teeth, which are in a conflicting relationship, and improving resistance to tooth chipping. Therefore, this invention provides a toothed belt that can suppress jumping (tooth skipping) during belt operation and also improve belt durability. In this toothed belt, tooth loss (tooth chipping) due to the growth of microcracks that occur during operation can also be suppressed, enabling a longer lifespan during high-load operation. In particular, the toothed belt of the present invention has a tooth shear index of 300-600 N / mm, which is the slope of the approximate straight line showing the relationship between tooth load and displacement, thus improving its resistance to reverse bending. [Brief explanation of the drawing]

[0025] [Figure 1] Figure 1 is a partial cross-sectional perspective view showing an example of a toothed belt according to the present invention. [Figure 2] Figure 2 is a schematic cross-sectional view of the toothed belt shown in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view illustrating the function of the teeth of the toothed belt shown in Figure 1. [Figure 4] Figure 4 is a schematic cross-sectional view illustrating the orientation of the short fibers in the toothed belt shown in Figure 1. [Figure 5] Figure 5 is a schematic cross-sectional view illustrating the condition in which a crack has occurred in a toothed belt. [Figure 6] Figure 6 is a schematic diagram illustrating the measurement method for tooth stiffness testing in the embodiment. [Figure 7] This graph shows an example of measurement data to explain the measurement method for tooth stiffness testing in the embodiment. [Figure 8] Figure 8 is a schematic cross-sectional view of the teeth of the toothed belt obtained in the embodiment. [Figure 9] Figure 9 is a graph showing an example of measurement data to illustrate the measurement method for tooth stiffness testing in the embodiment. [Figure 10] Figure 10 is a graph illustrating how to determine the slope of the approximate line from the graph in Figure 9. [Figure 11] Figure 11 is a bar graph comparing the tooth shear index, which is the slope of the approximate line obtained in Figure 10. [Figure 12] Figure 12 is a schematic diagram showing the running layout in the reverse bending durability test of the embodiment. [Modes for carrying out the invention]

[0026] <Toothed belt> Below, an example of a toothed belt of the present invention will be described in detail, with reference to the attached drawings as necessary.

[0027] Figure 1 is a partial cross-sectional perspective view showing an example of a toothed belt of the present invention, and Figure 2 is a schematic cross-sectional view of the toothed belt of Figure 1. The toothed belt 1 in this example is an endless interlocking transmission belt, and comprises a back portion 1c in which a core wire 5 extending in the belt circumferential direction (longitudinal direction) is embedded, and a plurality of teeth 1a provided at predetermined intervals on the inner circumferential surface of the back portion 1c and extending in the belt width direction, and the belt surface (inner circumferential surface) on the tooth portion side is made of tooth fabric 2. The back portion 1c has a back rubber layer 6 disposed on the belt outer circumferential surface side of the core wire 5, and this back rubber layer 6 forms the belt outer circumferential surface. Furthermore, the toothed belt 1 of the present invention has a first rubber layer (surface rubber layer) 3 and a second rubber layer (internal rubber layer) 4 between the tooth fabric 2 and the core wire 5 on the belt inner circumferential surface side of the core wire 5. The first rubber layer 3 is disposed on the inner circumferential surface of the belt along the contour of the tooth fabric 2 (in contact with the tooth fabric 2), and the second rubber layer 4 is interposed or disposed between the first rubber layer 3 and the core wire 5 (in contact with the core wire 5). The first rubber layer 3 has a higher modulus of elasticity (particularly tensile modulus) than the second rubber layer 4.

[0028] Between adjacent tooth portions 1a, there is a flat tooth root portion 1b, and the tooth portions 1a and tooth root portions 1b are alternately formed along the circumferential direction (belt longitudinal direction) on the inner surface of the belt. That is, the surface of the tooth portion 1a and the inner surface of the back portion 1c (i.e., the surface of the tooth root portion 1b) are composed of a single continuous tooth fabric 2.

[0029] In the embodiment shown in Figure 1, the tooth fabric constituting the surface of the tooth portion is a constituent element of the tooth portion, while the tooth fabric constituting the surface of the tooth root portion is a constituent element of the back portion. Furthermore, each tooth fabric constituting the tooth portion is part of a continuous tooth fabric (part of tooth fabric 2 in Figure 2).

[0030] In this example, the tooth portion 1a has a substantially trapezoidal cross-sectional shape in the circumferential direction of the belt. The circumferential surface of the tooth portion 1a, which has a substantially trapezoidal cross-section, is made of the tooth fabric 2, and is formed of a first rubber layer 3 formed along the tooth fabric 2 and a second rubber layer 4 formed between the first rubber layer 3 and the core wire 5. That is, in the tooth portion 1a, the first rubber layer 3 is layered and formed along the tooth fabric 2, and the second rubber layer 4 is layered and formed between the first rubber layer 3 and the core wire 5.

[0031] Furthermore, in the tooth root portion 1b, a first rubber layer acting as a surface rubber layer and a second rubber layer acting as an internal rubber layer are interposed between the tooth fabric 2 and the core wire 5 (not shown). The thickness of the first and second rubber layers in the tooth root portion is extremely thin compared to the thickness of the first rubber layer 3 and the second rubber layer 4 in the tooth portion 1a.

[0032] The core wires 5 extend in the longitudinal direction (circumferential direction) of the belt and are arranged at intervals in the width direction of the belt. The gaps between adjacent core wires 5 may be formed by the cross-linked rubber composition that constitutes the back rubber layer 6 and / or the second rubber layer (in particular, the cross-linked rubber composition that constitutes the back rubber layer 6).

[0033] Toothed belts are used in high-load power transmission applications such as industrial machinery, internal combustion engines in automobiles, and rear-wheel drives in motorcycles. For example, when a toothed belt is wrapped between a drive pulley (toothed pulley) and a driven pulley (toothed pulley), the rotation of the drive pulley transmits power from the drive pulley side to the driven pulley side.

[0034] It should be noted that the toothed belt of the present invention is not limited to the form and structure shown in Figures 1 and 2. For example, the multiple teeth only need to be able to mesh with a toothed pulley, and the cross-sectional shape of the teeth (the cross-sectional shape of the toothed belt in the circumferential direction) is not limited to a substantially trapezoidal shape, but may be, for example, semicircular, semielliptical, polygonal [triangle, quadrilateral (rectangle, trapezoid, etc.)], etc. Of these, a trapezoidal or substantially trapezoidal shape is preferred from the viewpoint of meshing and power transmission.

[0035] In the toothed belt (inner circumference side of the core wire) of the present invention, the area ratio of the first rubber layer is, for example, 10 to 80 area%, preferably 20 to 70 area%, more preferably 30 to 60 area%, and more preferably 35 to 50 area%, of the total area of ​​the first and second rubber layers in a cross-sectional view in the circumferential direction (longitudinal direction of the belt). If this area ratio is too small, the rigidity (deformation resistance) of the teeth may be insufficient, and conversely, if it is too large, the bending rigidity of the belt may become too high, resulting in insufficient flexibility (flexibility).

[0036] In the toothed belt of the present invention, the average distance between the centers of adjacent teeth in the circumferential direction (tooth pitch, see Figure 2) may be, for example, 2 to 25 mm, depending on the shape of the toothed pulley. The tooth pitch value corresponds to the size of the tooth scale (length of the tooth in the belt circumferential direction, and tooth height). That is, the larger the tooth pitch, the larger the tooth scale becomes. In particular, in applications where high loads are applied, teeth with a large scale are required, and the tooth pitch may be 5 mm or more, preferably 8 mm or more, and more preferably 14 mm or more.

[0037] Furthermore, the average tooth height of the teeth is preferably 40-70%, and more preferably 50-65%, of the average thickness of the entire belt.

[0038] In this application, as shown in Figure 2, the average tooth height of the teeth refers to the average height of the teeth protruding from the inner surface of the belt (the average height of the teeth protruding from the tooth root).

[0039] [Dental Department] The teeth portion includes a first rubber layer positioned on the surface side (inner surface side) and a second rubber layer positioned on the inner side in contact with the first rubber layer. The first and second rubber layers are formed from cross-linked rubber compositions with different compositions, the first rubber layer having a relatively high modulus and the second rubber layer having a relatively low modulus. In the toothed belt of the present invention, the cross-linked rubber composition forming the teeth has such a two-layer structure, thereby achieving both rigidity and flexibility in the teeth. This mechanism will be explained with reference to Figure 3. In this application, the rubber layer forming the teeth refers to the rubber layer interposed between the core wire and the tooth cloth when the teeth portion includes a tooth cloth, and to the rubber layer interposed on the inner circumferential surface side relative to the core wire when the teeth portion does not include a tooth cloth. Furthermore, the first rubber layer and the second rubber layer, which form the teeth, are collectively referred to as the tooth rubber layer. In the tooth rubber layer, the first rubber layer is a single-phase layer formed from the first crosslinked rubber composition, and the second rubber layer is a single-phase layer formed from the second crosslinked rubber composition.

[0040] The tooth portion may further include a tooth cloth that constitutes the surface. If the tooth portion does not include a tooth cloth, the surface of the first rubber layer forms the inner circumferential surface of the belt; however, if the tooth portion includes a tooth cloth, the surface of the tooth rubber layer is covered with the tooth cloth, and the inner circumferential surface of the belt is composed of the tooth cloth. That is, if the tooth portion includes a tooth cloth, the tooth portion includes a first rubber layer whose surface is composed of the tooth cloth and which is arranged along the contour of the tooth portion on the surface side in contact with the tooth cloth, and a second rubber layer which is arranged on the interior side in contact with the first rubber layer.

[0041] The inventors have found that within the tooth portion, the part that affects flexibility is the part of the tooth portion corresponding to the second rubber layer, particularly part C located below the core wire 5. In other words, they found that if the rubber layer inside the tooth portion, particularly part C, is highly rigid (high modulus of elasticity), flexibility decreases. Therefore, in the toothed belt of the present invention, in order to ensure high flexibility, the second rubber layer located inside the tooth portion, particularly the second rubber layer 4 containing part C, is adjusted to be relatively low rigidity (low modulus of elasticity). Furthermore, they found that by adjusting the tensile modulus of elasticity in the belt width direction of the second rubber layer 4 containing part C to a specific range, the durability against reverse bending, among other flexibility characteristics, can be effectively improved.

[0042] Furthermore, the inventors have found that within the tooth portion, the areas that affect deformation resistance are the vicinity of the tooth fabric (or inner circumferential surface) corresponding to the first rubber layer, particularly area A located on the side of the tooth and area B located near the tooth root. In other words, they found that if areas A and B are rubber layers with low rigidity (low modulus of elasticity), deformation resistance decreases. Specifically, area A, which is the side of the tooth, is the part that comes into contact with the pulley and receives the most load (impact), so it is effective for the cross-linked rubber composition of area A to have high rigidity (high modulus of elasticity). On the other hand, area B, which is the root near the tooth root, is the part where minute cracks first occur due to repeated deformation (the starting point that leads to tooth chipping), so it is effective for the cross-linked rubber composition of area B to have high rigidity (high modulus of elasticity). Therefore, in the toothed belt of the present invention, in order to ensure deformation resistance, the first rubber layer 3 containing areas A and B is adjusted to have relatively high rigidity (high modulus of elasticity).

[0043] From the viewpoint of deformation resistance, it is sufficient that at least parts A and B of the tooth portion are formed of high-rigidity rubber, and the top of the tooth portion (the tip of the tooth) does not need to be made of high-rigidity rubber. In contrast, in the toothed belt of the present invention, the first rubber layer, including the top, is made of high-rigidity rubber in order to achieve high productivity and high deformation resistance.

[0044] The tensile strength of the first rubber layer is, for example, 40 to 90 MPa, preferably 45 to 85 MPa, more preferably 50 to 83 MPa, more preferably 55 to 80 MPa, and most preferably 60 to 70 MPa in the circumferential direction of the belt. If the tensile strength is too low, the rigidity of the teeth may decrease and the deformation resistance may decrease, and conversely, if it is too high, the flexibility of the belt, in particular, the ability to wrap around (engage with) small diameter pulleys may decrease.

[0045] The tensile strength of the second rubber layer is, for example, 10 to 50 MPa, preferably 20 to 45 MPa, more preferably 25 to 40 MPa, more preferably 25 to 35 MPa, and most preferably 30 to 34 MPa in the circumferential direction of the belt. If the tensile strength is too low, the deformation resistance may decrease, and conversely, if it is too high, the flexibility of the belt, in particular, the ability to wrap around (engage with) small diameter pulleys may decrease.

[0046] In the circumferential direction of the belt, the tensile strength of the first rubber layer is greater than that of the second rubber layer, and the ratio of the tensile strength of the first rubber layer to the tensile strength of the second rubber layer (tensile strength of the first rubber layer / tensile strength of the second rubber layer) may be 1.3 to 3.5, preferably 1.4 to 3.0, more preferably 1.5 to 2.5, more preferably 1.6 to 2.0, and most preferably 1.7 to 1.9. By setting the ratio of the tensile strengths of the two layers within this range, a balance can be achieved between the rigidity (deformation resistance) and flexibility (flexibility) of the teeth, which are in a conflicting relationship, allowing both to be achieved.

[0047] In this application, the tensile strength of the first and second rubber layers is measured using the "tensile strength T" value of each rubber layer, which can be measured by a method compliant with JIS K 6251 (2017), and used as an index value for tensile strength. In detail, it can be measured by the method described in the examples below.

[0048] The tensile modulus of the first rubber layer can be selected in the belt width direction from a range of approximately 4 to 25 MPa, for example, 5 to 20 MPa, preferably 6 to 18 MPa, more preferably 8 to 16 MPa, more preferably 10 to 15 MPa, and most preferably 12 to 15 MPa. If the tensile modulus is too low, the rigidity of the teeth may decrease and the deformation resistance may decrease. Conversely, if it is too high, the flexibility of the belt, in particular, the ability to wrap around (engage with) small diameter pulleys may decrease.

[0049] The tensile modulus of the second rubber layer is, for example, 1.0 to 4.5 MPa, preferably 1.5 to 3.0 MPa, more preferably 1.6 to 2.5 MPa, more preferably 1.8 to 2.3 MPa, and most preferably 2.0 to 2.2 MPa in the belt width direction. If the tensile modulus is too low, the deformation resistance will decrease, which may cause tooth skipping (jumping) or reduce the durability of the belt. Conversely, if it is too high, the flexibility of the belt, especially its resistance to reverse bending, may decrease.

[0050] In the belt width direction, the tensile modulus of the first rubber layer is greater than that of the second rubber layer, and the ratio of the tensile modulus of the first rubber layer to that of the second rubber layer (tensile modulus of the first rubber layer / tensile modulus of the second rubber layer) may be 1.1 to 15.0, for example, 1.1 to 10.0, preferably 2.0 to 10.0, more preferably 4.0 to 9.5, more preferably 5.0 to 9.0 (for example 5.5 to 8.5), even more preferably 6.0 to 8.0, and most preferably 6.0 to 7.5. By setting the ratio of the tensile moduli of both layers within this range, a balance can be achieved between the rigidity (deformation resistance) and flexibility (flexibility) of the teeth, which are in a conflicting relationship.

[0051] In this application, the tensile modulus of the first and second rubber layers is determined by the "tensile stress at 2% elongation" of each rubber layer, which can be measured using a method compliant with JIS K 6251 (2017). This can be measured in detail using the method described in the examples below.

[0052] Furthermore, in the tooth portion, the first rubber layer is formed of a first crosslinked rubber composition containing a first rubber component and first short fibers, and the first short fibers are oriented in the longitudinal direction (circumferential direction) of the belt along the contour of the tooth portion. In the toothed belt of the present invention, by adjusting the tooth portion to the two-layer structure described above, both rigidity and flexibility can be achieved, and minute cracks that mainly occur at the tooth root can be suppressed. Even if minute cracks occur due to long-term use, the orientation of the first short fibers in the first rubber layer in the aforementioned direction can suppress the tooth breakage of the toothed belt, thereby improving the tooth breakage resistance (durability) of the belt. The mechanism by which tooth breakage resistance is improved will be explained with reference to Figures 4 and 5.

[0053] Figure 4 is a schematic cross-sectional view illustrating the orientation of the short fibers in the toothed belt shown in Figure 1, and Figure 5 is a schematic cross-sectional view illustrating the state in which cracks have occurred in the toothed belt.

[0054] As shown in Figure 5, the toothed belt 11 is formed of a tooth cloth 12, a tooth rubber layer 13 covered with the tooth cloth 12, a back rubber layer 16, and a core wire 15 interposed between the tooth rubber layer 13 and the back rubber layer 16. However, minute cracks tend to occur on or near the surface of the tooth rubber layer 13 at the base of the teeth. The minute cracks that occur propagate inward from the rubber surface of the tooth rubber layer 13 in a direction approximately perpendicular to the rubber surface (direction of arrow A in Figure 5), growing into cracks 13a and eventually leading to tooth breakage.

[0055] In contrast, as shown in Figure 4, in the toothed belt 1 of the present invention, the first rubber layer 3 located on the tooth fabric 2 side contains first short fibers 3a. Figure 4 is a schematic diagram showing the dispersion state of the first short fibers 3a in the first rubber layer 3 for understanding the orientation direction. Inside the first rubber layer 3, the first short fibers 3a are oriented in the longitudinal direction of the belt along the contour of the tooth fabric 2 (the surface direction of the tooth fabric). That is, inside the first rubber layer 3, the first short fibers 3a are oriented substantially parallel to the surface direction of the tooth fabric. The orientation direction of these first short fibers 3a is intersecting (particularly approximately perpendicular to) the direction in which minute cracks propagate (the direction extending inward from the tooth surface, such as arrow A in Figure 5, or a direction approximately perpendicular to the tooth surface). Therefore, when the first rubber layer 3 contains first short fibers 3a in a predetermined proportion, first short fibers 3a in a form intersecting or approximately perpendicular to the direction of propagation of minute cracks generated on the surface or inside the first rubber layer 3 are always present. For this reason, in the first rubber layer 3 of the toothed belt 1 of the present invention, the first short fibers 3a have the function of preventing (guarding) the propagation of minute cracks, and even if minute cracks occur due to repeated deformation, the propagation of the cracks can be prevented, improving the tooth breakage resistance of the toothed belt. The proportion of first short fibers required to exhibit this function is approximately 5 to 60 parts by mass, particularly 10 to 60 parts by mass, per 100 parts by mass of the first rubber component. In contrast, toothed belts that contain a small proportion of short fibers in the tooth rubber layer cannot effectively prevent crack progression and improve tooth chipping resistance. Furthermore, the modulus between the tooth rubber layer and the adhesive rubber layer is not adjusted, making them prone to the occurrence of minute cracks.

[0056] In this application, the state in which the first short fibers are oriented along the contour of the tooth means not only the state in which the first short fibers are oriented substantially parallel to the contour of the tooth, but also the state in which the first short fibers are oriented substantially parallel to the contour of the tooth fabric (or inner surface). The same applies to the state in which the first short fibers are oriented in the longitudinal direction of the belt.

[0057] Furthermore, in this application, the "tooth contour" may be the contour of the first rubber layer, or if the tooth includes a tooth cloth, it may be the tooth cloth surface or the interface between the tooth cloth and the first rubber layer, or it may be the interface between the first rubber layer and the second rubber layer. In particular, whether or not the first short fibers are oriented along the contour of the tooth may be determined based on the interface between the first rubber layer and the second rubber layer. For example, if the first short fibers are substantially parallel to the corresponding interface (the corresponding part of the interface at the shortest distance from the first short fibers), it may be determined that they are oriented along the contour of the tooth.

[0058] The shape of the first rubber layer is not particularly limited as long as it is layered along the tooth fabric, and is not limited to the layered shape with uneven thickness shown in Figures 1 to 3 (i.e., in a cross-sectional view of the tooth portion in the longitudinal direction of the belt, the thickness of the layer is maximum at the top or middle of the tooth portion and decreases toward the bottom of the tooth portion), but may also be a layered shape with uniform thickness. Of these, a layered shape with uneven thickness (particularly, in a cross-sectional view of the tooth portion in the longitudinal direction of the belt, the thickness of the layer is maximum at the top or middle of the tooth portion and decreases toward the bottom of the tooth portion) is preferred from the viewpoint of productivity, etc.

[0059] In the teeth, the area ratio of the first rubber layer can be selected from a range of approximately 5 to 85 area % of the total area of ​​the first and second rubber layers in a cross-sectional view in the longitudinal direction (circumferential direction) of the belt, for example, 10 to 80 area %; preferably 20 to 70 area %; more preferably 30 to 60 area %; and more preferably 35 to 50 area %. If this area ratio is too small, the rigidity (deformation resistance) of the teeth may be insufficient, potentially reducing the belt's running performance and durability. Conversely, if it is too large, the bending rigidity of the belt may be too high, resulting in insufficient flexibility (suppleness) and potentially reducing the belt's durability. In applications where belt durability is important, the area ratio is preferably 15 to 65 area %; more preferably 20 to 60 area %.

[0060] The shape of the second rubber layer is not limited to a substantially trapezoidal shape formed between the first rubber layer and the core wire in a cross-sectional view of the tooth portion in the longitudinal direction of the belt, but may also be a layered shape formed along the first rubber layer, or a substantially trapezoidal shape formed between another rubber layer formed along the first rubber layer and the core wire. Of these, a shape that is in contact with the core wire, i.e., a substantially trapezoidal shape formed between the first rubber layer and the core wire, or a substantially trapezoidal shape formed between the other rubber layer and the core wire is preferred from the viewpoint of improving the flexibility of the tooth portion, and a substantially trapezoidal shape formed between the first rubber layer and the core wire is particularly preferred.

[0061] The rubber hardness Hs of the first rubber layer (the first crosslinked rubber composition constituting the first rubber layer) is a type D hardness of, for example, 65 to 80 degrees, preferably 68 to 78 degrees, more preferably 70 to 76 degrees, and most preferably 72 to 74 degrees. If the hardness is too low, the rigidity of the teeth may decrease and the deformation resistance may decrease, and conversely, if it is too high, the flexibility of the belt, in particular, the ability to wrap around (engage with) small diameter pulleys may decrease.

[0062] The rubber hardness Hs of the second rubber layer (the second crosslinked rubber composition constituting the second rubber layer) is a type D hardness of, for example, 50 to 66 degrees, preferably 55 to 65 degrees, more preferably 56 to 60 degrees, more preferably 56 to 59 degrees, and most preferably 57 to 59 degrees. If the hardness is too low, the deformation resistance may decrease, and conversely, if it is too high, the flexibility of the belt, in particular, the durability against reverse bending may decrease.

[0063] In this application, the Type D hardness of the first and second rubber layers refers to the value Hs (Type D) measured using a Type D durometer in accordance with the spring durometer hardness test specified in JIS K 6253 (2012) (Vulcanized rubber and thermoplastic rubber - Method for determining hardness), and may simply be referred to as rubber hardness. In detail, it can be measured by the method described in the examples below, and can be measured as the hardness of a rubber sheet obtained by crosslinking a rubber composition for forming a belt.

[0064] Typically, the rubber hardness of rubber compositions is often measured using Type A hardness (a value measured using a Type A durometer). However, if the value measured using a Type A durometer exceeds 90 degrees, it is considered preferable to use a Type D durometer. In the toothed belt of the present invention, the hardness of the rubber layer constituting the teeth is higher than that of the back rubber layer described later, and the Type A hardness exceeds 90 degrees. Therefore, the hardness of the rubber layer constituting the teeth is evaluated using Type D hardness.

[0065] The tooth portion may further include other rubber layers in addition to the first and second rubber layers, as long as the effects of the present invention are not impaired. Examples of other rubber layers include an adhesive rubber layer interposed between the tooth cloth and the first rubber layer, and an intermediate rubber layer interposed between the first and second rubber layers. The adhesive rubber layer may be a layer for improving the adhesion between the tooth cloth and the first rubber layer. The intermediate rubber layer may be a layer having a smaller tensile modulus than the first rubber layer and a larger tensile modulus than the second rubber layer. Of these, the adhesive rubber layer (third rubber layer) is preferred. The thickness of the adhesive rubber layer should be such that it can improve the adhesion between the tooth cloth and the first rubber layer. Specifically, the thickness of the third rubber layer (adhesive rubber layer) at the top of the tooth portion is preferably 0.5 mm or less, and more preferably 0.3 mm or less. If the thickness of the third rubber layer is too thick, the rigidity of the tooth portion may decrease.

[0066] As for the structure of the teeth, a structure in which the tooth rubber layer includes only an adhesive rubber layer as another layer is preferred, and a structure that does not include any other layers, that is, a structure consisting of a first rubber layer and a second rubber layer formed between the first rubber layer and the core wire, or a structure consisting of a tooth cloth that covers the surface in the circumferential direction of the belt, a first rubber layer formed along this tooth cloth, and a second rubber layer formed between the first rubber layer and the core wire is particularly preferred.

[0067] The toothed belt of the present invention, having such teeth, possesses flexibility (suppleness) that allows it to exhibit resistance to reverse bending. In this application, this flexibility is expressed by the tooth shear index, which is the slope of the approximate straight line showing the relationship between tooth load and displacement. The toothed belt of the present invention has a tooth shear index of 300 to 600 N / mm, preferably 320 to 450 N / mm, more preferably 330 to 400 N / mm, more preferably 340 to 380 N / mm, even more preferably 345 to 375 N / mm, and most preferably 350 to 370 N / mm. If the tooth shear index is too low, tooth skipping (jumping) is more likely to occur and the durability of the belt will decrease, while if it is too high, the durability against reverse bending will decrease.

[0068] In this application, the tooth shear index of the toothed belt can be measured by the method described in the examples below.

[0069] (Crosslinked rubber composition) The toothed belt of the present invention is characterized in that the first rubber layer is formed of a first crosslinked rubber composition containing first short fibers as an essential component, but both the first and second rubber layers may be formed of crosslinked rubber compositions that are conventionally used as rubber compositions for toothed belts. The crosslinked rubber composition may be a crosslinked rubber composition containing rubber components, and by appropriately adjusting the composition, the mechanical properties such as the modulus of each layer constituting the rubber layer, particularly the first and second rubber layers, can be adjusted. The method for adjusting the modulus, etc., is not particularly limited, and it may be adjusted by changing the composition and / or type of components constituting the composition, but from the viewpoint of simplicity, it is preferable to adjust by changing the ratio and / or type of crosslinking compounding agent, short fibers, and filler.

[0070] (A) Rubber component Examples of rubber components (first rubber component and second rubber component) of the crosslinked rubber composition forming the first and second rubber layers include diene rubbers [natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), chloroprene rubber (CR), butyl rubber (IIR), styrene-butadiene rubber (SBR), vinylpyridine-styrene-butadiene rubber, acrylonitrile-butadiene rubber (nitrile rubber: NBR), acrylonitrile-chloroprene rubber, hydrogenated nitrile rubber (HNBR), etc.], ethylene-α-olefin elastomers (ethylene-propylene copolymer (EPM), ethylene-propylene-diene ternary copolymer (EPDM), etc.), chlorosulfonated polyethylene rubber (CSM), alkylated chlorosulfonated polyethylene rubber (ACSM), epichlorohydrin rubber, acrylic rubber, silicone rubber, urethane rubber, fluororubber, etc. These rubber components may be carboxylated, such as carboxylated SBR and carboxylated NBR. These rubber components can be used individually or in combination of two or more types.

[0071] Particularly preferred rubber components are hydrogenated nitrile rubber (HNBR), chloroprene rubber (CR), and ethylene-propylene-diene terpolymer (EPDM). Particularly preferred rubber components for applications subjected to high loads are rubbers with high heat aging resistance, especially hydrogenated nitrile rubber (HNBR) which may be carboxylated (hereinafter, including carboxylated hydrogenated nitrile rubber, it may simply be referred to as hydrogenated nitrile rubber). The proportion of the above preferred rubber components in the rubber components is preferably 50% by mass or more (for example, about 80-100% by mass), and particularly preferably 100% by mass. The hydrogenated nitrile rubber which may be carboxylated may be partially hydrogenated nitrile rubber or fully hydrogenated nitrile rubber. The hydrogenation rate of the hydrogenated nitrile rubber which may be carboxylated can be selected from a range of about 50-100%, and may be 70-100%.

[0072] In this application, HNBR refers to a rubber that maintains the oil resistance, which is an advantage of conventional nitrile rubber, while preventing the deterioration of rubber elasticity due to sulfur recombination reactions during thermal aging. This is achieved by chemically hydrogenating the unsaturated bonds (carbon-carbon double bonds) present in conventional nitrile rubber, thereby making recombination reactions during thermal aging less likely to occur and improving heat resistance.

[0073] The iodine value (unit: mg / 100 mg) of HNBR is, for example, 5 to 60 (for example, 7 to 50), preferably 8 to 40 (for example, 8 to 35), and more preferably 10 to 30.

[0074] In this application, the iodine value is an indicator of the amount of unsaturated bonds; a higher iodine value indicates a greater amount of unsaturated bonds in the polymer molecular chain. The iodine value is determined by adding an excess of iodine to the sample and allowing it to react completely (reacting with unsaturated bonds), then quantifying the remaining amount of iodine by redox titration. If the iodine value of HNBR is low, the crosslinking reaction between HNBRs is insufficient, resulting in lower rigidity of the crosslinked rubber, which may reduce deformation resistance during belt operation. On the other hand, if the iodine value of HNBR is high, the amount of unsaturated bonds becomes excessively high, which may lead to thermal and oxidative degradation of the crosslinked rubber, shortening the belt life.

[0075] The rubber component preferably contains at least hydrogenated nitrile rubber, which may be carboxylated. The proportion of such hydrogenated nitrile rubber may be 80 to 100% by mass of the rubber component, preferably 90 to 100% by mass, and more preferably 100% by mass.

[0076] The rubber component preferably contains a composite polymer (hereinafter referred to as "HNBR / unsaturated carboxylate metal salt composite polymer") comprising hydrogenated nitrile rubber and an unsaturated carboxylate metal salt. This composite polymer may also be a polymer alloy. In this application, the composite polymer contained in the first rubber component is referred to as the first composite polymer, and the composite polymer contained in the second rubber component is referred to as the second composite polymer. This polymer can increase the modulus and hardness of the tooth portion, suppress rubber deformation, and inhibit crack growth.

[0077] An unsaturated carboxylate metal salt may be a compound in which an unsaturated carboxylic acid having one or more carboxyl groups is ionically bonded to a metal.

[0078] Examples of unsaturated carboxylic acids in metal salts of unsaturated carboxylic acids include monocarboxylic acids such as (meth)acrylic acid and crotonic acid, dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid, and monoalkyl esters of these dicarboxylic acids. These unsaturated carboxylic acids can be used alone or in combination of two or more. A preferred unsaturated carboxylic acid is (meth)acrylic acid.

[0079] Examples of metals used in unsaturated carboxylate metal salts include polyvalent metals, such as Group 2 elements of the periodic table (magnesium, calcium, etc.), Group 4 elements (titanium, zirconium, etc.), and Groups 8 to 14 elements of the periodic table (e.g., iron, cobalt, nickel, copper, zinc, aluminum, tin, lead, etc.). These metals can be used individually or in combination of two or more. Preferred metals include Group 2 elements of the periodic table (magnesium, etc.) and Group 12 elements of the periodic table (zinc, etc.).

[0080] Preferred unsaturated carboxylate metal salts include zinc (meth)acrylate and magnesium (meth)acrylate. Unsaturated carboxylate metal salts can be used alone or in combination of two or more.

[0081] Furthermore, commercially available HNBR / unsaturated carboxylate metal salt composite polymers may be used. For example, a product in which zinc methacrylate is highly finely dispersed as an unsaturated carboxylate metal salt in HNBR can be used (e.g., Zeon Corporation's product name "Zeoforte (ZSC)").

[0082] Furthermore, the HNBR / unsaturated carboxylate metal salt composite polymer may be a mixture of a composite polymer in which an unsaturated carboxylate metal salt is finely dispersed in HNBR and hydrogenated nitrile rubber (HNBR) that does not contain an unsaturated carboxylate metal salt. That is, in the HNBR / unsaturated carboxylate metal salt composite polymer, the mass ratio of hydrogenated nitrile rubber to unsaturated carboxylate metal salt may be adjusted by mixing commercially available HNBR containing an unsaturated carboxylate metal salt with commercially available hydrogenated nitrile rubber. The modulus and hardness may be adjusted by changing the mixing ratio of the two.

[0083] In the HNBR / unsaturated carboxylic acid metal salt composite polymer, the mass ratio of hydrogenated nitrile rubber to unsaturated carboxylic acid metal salt can be selected from a range of approximately 100 / 70 to 100 / 180, preferably 100 / 80 to 100 / 175, and more preferably 100 / 90 to 100 / 175. In the first rubber layer, this mass ratio is 100 / 90 to 100 / 170, preferably 100 / 95 to 100 / 150, and more preferably 100 / 100 to 100 / 120, and in the second rubber layer, it is 100 / 70 to 100 / 110, preferably 100 / 75 to 100 / 100, and more preferably 100 / 80 to 100 / 90. If the proportion of unsaturated carboxylate metal salts is too low, the modulus and hardness of the crosslinked rubber composition (or teeth) may decrease. Conversely, if it is too high, the processability and flexibility of the belt will decrease.

[0084] The proportion of HNBR / unsaturated carboxylate metal salt composite polymer may be 10% by mass or more in the rubber component, preferably 30% by mass or more, more preferably 50% by mass or more, more preferably 80% by mass or more, most preferably 90% by mass or more, and may also be 100% by mass. In particular, the proportion of HNBR / unsaturated carboxylate metal salt composite polymer is preferably 80% by mass or more (particularly 100% by mass) in the rubber component (first rubber component) in the first rubber layer, and preferably 30% by mass or more (particularly 100% by mass) in the rubber component (second rubber component) in the second rubber layer. These proportions may be those used in the product "Zeoforte (ZSC)".

[0085] As other rubber components to be combined with the HNBR / unsaturated carboxylic acid metal salt composite polymer, at least one selected from the group consisting of EPDM and CR is preferred. The proportion of other rubber components is, for example, 70% by mass or less, preferably 50% by mass or less, more preferably 30% by mass or less, and most preferably 10% by mass or less, of the total rubber component.

[0086] To ensure adhesion between layers, the first rubber layer and the second rubber layer preferably contain the same series or type of rubber component, more preferably the same type of rubber component, and even more preferably the same rubber component.

[0087] (B) Short fibers As mentioned above, the first crosslinked rubber composition contains the first short fibers as an essential component, but the second crosslinked rubber composition forming the second rubber layer may also contain the second short fibers.

[0088] Examples of short fibers (first short fibers and second short fibers) include polyolefin fibers (polyethylene fibers, polypropylene fibers, etc.), polyamide fibers [aliphatic polyamide fibers such as polyamide 6 fibers, polyamide 66 fibers, polyamide 46 fibers (nylon fibers), aramid fibers, etc.], polyester fibers [polyalkylene arylate fibers (e.g., polyethylene terephthalate (PET) fibers, polytrimethylene terephthalate (PTT) fibers, polybutylene terephthalate (PBT) fibers, polyethylene naphthalate (PEN) fibers, etc.)]. 2-4 Alkilen C 8-14 Examples of staple fibers include: arylate fibers; polyarylate fibers, fully aromatic polyester fibers such as liquid crystal polyester fibers, etc.; synthetic fibers such as vinylon fibers, polyvinyl alcohol fibers, and poly(p-phenylenebenzobisoxazole) (PBO) fibers; natural fibers such as cotton, linen, and wool; regenerated cellulose fibers such as rayon; cellulose ester fibers, etc.; and inorganic fibers such as carbon fibers and glass fibers. These staple fibers can be used individually or in combination of two or more types. In particular, fibers with high modulus, such as polyamide fibers, PBO fibers, glass fibers, and carbon fibers, can be suitably used, with polyamide fibers such as aliphatic polyamide fibers (nylon fibers) and aramid fibers, and PBO fibers being more preferred. Aliphatic polyamide fibers are most preferred as the first staple fiber, and aramid fibers are most preferred as the second staple fiber.

[0089] The average fiber diameter of the short fibers is, for example, 1 to 100 μm (e.g., 3 to 70 μm), preferably 5 to 50 μm (e.g., 7 to 30 μm), and more preferably 10 to 25 μm (particularly 12 to 20 μm). The average fiber length of the short fibers is, for example, 0.3 to 10 mm (e.g., 0.5 to 7 mm), preferably 1 to 5 mm (particularly 2 to 4 mm). If the average fiber diameter of the short fibers is too small or the average fiber length is too long, it may become difficult to uniformly disperse the short fibers or to orient them in a predetermined direction. If the average fiber diameter is too large or the average fiber length is too short, the mechanical properties of each rubber layer may deteriorate.

[0090] Furthermore, it is preferable to apply a conventional adhesive treatment (or surface treatment) to the short fibers to adhere an adhesive component to at least a portion of the surface of the short fibers. Such an adhesive treatment improves the adhesion between the short fibers and the rubber component and suppresses the generation of microcracks originating from the interface between the short fibers and the rubber component. Examples of adhesive treatments include treatment with adhesive components such as epoxy compounds (or epoxy resins), polyisocyanates, silane coupling agents, and resorcinol-formaldehyde-latex (RFL).

[0091] In the first crosslinked rubber composition, the proportion of the first short fibers may be 5 to 60 parts by mass (particularly 10 to 60 parts by mass) per 100 parts by mass of the first rubber component, preferably 8 to 55 parts by mass (for example, 10 to 50 parts by mass), more preferably 15 to 45 parts by mass, more preferably 20 to 40 parts by mass, and most preferably 25 to 35 parts by mass. If the proportion of the first short fibers is too low, the resistance to tooth chipping decreases, and conversely, if it is too high, the effect of the short fibers is reduced, and the mechanical properties of the first rubber layer deteriorate.

[0092] The second crosslinked rubber composition does not necessarily have to contain second short fibers, but it is preferable to include second short fibers in order to improve the mechanical properties of the second rubber layer.

[0093] The ratio of the second short fibers to the second rubber component is preferably smaller than the ratio of the first short fibers to the first rubber component in order to improve tooth chipping resistance. The ratio of the second short fibers may be 10 parts by mass or less (0 to 10 parts by mass), particularly 5 parts by mass or less (for example, 3 parts by mass or less) per 100 parts by mass of the second rubber component, preferably 0.1 to 5 parts by mass (for example, 0.3 to 4 parts by mass), more preferably 0.5 to 3.5 parts by mass, more preferably 1 to 3 parts by mass, and most preferably 1.5 to 2.5 parts by mass. If the ratio of the second short fibers is too high, the modulus and hardness of the second crosslinked rubber composition can be increased, but on the other hand, minute cracks are more likely to occur at the interface between the second rubber component and the second short fibers, which may reduce tooth chipping resistance.

[0094] When the second crosslinked rubber composition contains second short fibers, the orientation direction of the second short fibers is not particularly limited, but it is preferable that they be arranged in the longitudinal direction of the belt, similar to the first short fibers. Furthermore, when the second crosslinked rubber composition contains second short fibers, it is preferable that the second short fibers are oriented along the contour of the teeth on the side closer to the tooth fabric, and as they approach the core wire, the second short fibers are oriented so that they are approximately parallel to the core wire.

[0095] (C) Filling compound The crosslinked rubber composition (first crosslinked rubber composition and second crosslinked rubber composition) may further contain fillers. Examples of fillers (first filler and second filler) include reinforcing inorganic fillers and non-reinforcing fillers.

[0096] Examples of reinforcing inorganic fillers (first reinforcing inorganic filler and second reinforcing inorganic filler) include carbon black and silica. These reinforcing inorganic fillers can be used individually or in combination of two or more. The reinforcing inorganic fillers may also be in powder form.

[0097] The average particle size (average primary particle size) of carbon black is, for example, 5 to 200 nm, preferably 10 to 150 nm, more preferably 20 to 100 nm, and more preferably 30 to 80 nm. The amount of iodine adsorbed by carbon black is, for example, 5 to 200 mg / g, preferably 10 to 150 mg / g, more preferably 15 to 100 mg / g, and more preferably 20 to 80 mg / g.

[0098] Silica includes dry silica, wet silica, and surface-treated silica. Furthermore, silica can be classified by manufacturing method into categories such as dry-processed white carbon, wet-processed white carbon, colloidal silica, and precipitated silica. These silicas can be used individually or in combination of two or more types. Among these silicas, silica with surface silanol groups (anhydrous silicic acid, hydrated silicic acid) is preferred, and hydrated silicic acid with a high number of surface silanol groups exhibits strong chemical bonding with rubber components.

[0099] The average particle diameter (average primary particle diameter) of silica is, for example, 1 to 500 nm, preferably 3 to 300 nm, more preferably 5 to 100 nm, and more preferably 10 to 50 nm.

[0100] Furthermore, the specific surface area for nitrogen adsorption of silica by the BET method is, for example, 50 to 400 m². 2 / g, preferably 100-300m 2 / g, more preferably 150-200m 2 It is / g.

[0101] In this application, the average particle size of the reinforcing inorganic filler can be calculated as the arithmetic mean particle size of an appropriate number of samples (e.g., 50 samples) by image analysis of electron microscope images, including scanning electron microscope images.

[0102] The proportion of the reinforcing inorganic filler may be 10 parts by mass or less per 100 parts by mass of the rubber component, preferably 5 parts by mass or less, more preferably 1 part by mass or less, and more preferably 0 parts by mass. If a reinforcing inorganic filler is used as needed, the proportion of the reinforcing inorganic filler may be, for example, 0.1 to 8 parts by mass, preferably 0.5 to 5 parts by mass, and more preferably 1 to 3 parts by mass per 100 parts by mass of the rubber component. If the proportion of the reinforcing inorganic filler is too high, the heat generation of the rubber composition will increase and the heat resistance will decrease, which may cause cracks or chipping due to thermal degradation.

[0103] Examples of non-reinforcing fillers (first non-reinforcing filler and second non-reinforcing filler) include polyvalent metal carbonates (calcium carbonate, magnesium carbonate, etc.), polyvalent metal hydroxides (aluminum hydroxide, etc.), polyvalent metal sulfates (barium sulfate, etc.), silicates (natural or synthetic silicates in which some of the silicon is replaced by polyvalent metal atoms, such as aluminum silicate, magnesium silicate, and aluminum magnesium silicate; minerals mainly composed of silicates, such as clay containing aluminum silicate, and silicate minerals such as talc and mica containing magnesium silicate), lithopone, and silica sand. These non-reinforcing fillers can be used individually or in combination of two or more.

[0104] Preferred non-reinforcing fillers are at least one selected from calcium carbonate, magnesium carbonate, aluminum hydroxide, barium sulfate, and silicates [silicates such as aluminum silicate, magnesium silicate, and aluminum magnesium silicate; silicate minerals (talc, clay, mica, etc.)]. Furthermore, non-reinforcing fillers are preferable to include at least one selected from calcium carbonate, magnesium silicate or talc containing magnesium silicate, aluminum silicate or clay containing aluminum silicate, as they greatly improve the processability of the belt and the dispersibility of the compounding agents, and are less likely to cause poor dispersion of the compounding agents. In particular, they are preferable to include calcium carbonate. As non-reinforcing fillers, commercially available powdered fillers used as rubber fillers can be used.

[0105] The average particle size (average primary particle size) of the non-reinforcing filler can be selected from a range of approximately 0.01 to 25 μm (e.g., 0.2 to 20 μm), preferably 0.5 to 17 μm (e.g., 1 to 15 μm). The average particle size (average primary particle size) of the non-reinforcing filler may also be, for example, 0.01 to 3 μm (e.g., 0.02 to 2 μm), preferably 0.05 to 1.5 μm (particularly 0.1 to 1 μm), and may be relatively large. Furthermore, the average particle size (average primary particle size) of the non-reinforcing filler may also be, for example, 0.2 to 5 μm (e.g., 0.3 to 3 μm), preferably 0.5 to 2.5 μm (particularly 1 to 2 μm). Depending on the type of non-reinforcing filler, such as magnesium silicate or its minerals, the non-reinforcing filler may be crushed or broken during the mixing process with rubber components. The average particle size of such a non-reinforcing filler having crushability or fragility may be the average particle size before mixing with rubber components, etc. The non-reinforcing filler in each crosslinked rubber composition may typically have an average particle size within the above range (for example, 0.1 to 10 μm, preferably 0.5 to 5 μm, and more preferably 1 to 3 μm).

[0106] In this application, the average particle size of the non-reinforcing filler can be measured as the volume-average particle size using a laser diffraction particle size distribution analyzer. Furthermore, the average particle size of nanometer-sized fillers can be calculated as the arithmetic mean particle size of an appropriate number of samples (e.g., 50 samples) by image analysis of electron microscope images, including scanning electron microscope images.

[0107] The proportion of non-reinforcing filler is, for example, 70 parts by mass or less, preferably 40 parts by mass or less, and more preferably 30 parts by mass or less, per 100 parts by mass of rubber component. If non-reinforcing filler is used as needed, the proportion of non-reinforcing filler may be, for example, 3 to 70 parts by mass, preferably 5 to 40 parts by mass, and more preferably 10 to 30 parts by mass, per 100 parts by mass of rubber component. If the proportion of non-reinforcing filler is too high, the dispersibility of the compounding agent may be poor.

[0108] The proportion of the filler compound is, for example, 3 to 70 parts by mass, preferably 5 to 50 parts by mass, more preferably 10 to 40 parts by mass, and more preferably 20 to 30 parts by mass, per 100 parts by mass of the rubber component.

[0109] (D) Crosslinking compound The rubber composition contains a crosslinking agent (vulcanizing agent) for crosslinking the rubber components, and optionally contains co-crosslinking agents, crosslinking aids (vulcanization aids), crosslinking accelerators (vulcanization accelerators), crosslinking retarders (vulcanization retarders), etc. Of these, the crosslinking compounding agents (first crosslinking compounding agent and second crosslinking compounding agent) preferably contain at least a crosslinking agent and a co-crosslinking agent (crosslinking aid), and a combination of a crosslinking agent and a co-crosslinking agent is particularly preferred.

[0110] Conventional crosslinking agents (first crosslinking agent and second crosslinking agent) can be used depending on the type of rubber component, and examples include organic peroxides, sulfur-based crosslinking agents, and metal oxides.

[0111] Examples of organic peroxides (first organic peroxide and second organic peroxide) include di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, 1,1-t-butylperoxy-3,3,5-trimethylcyclohexane, 1,3-bis(t-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyn-3, 1,3-bis(t-butylperoxy-di-isopropyl)benzene, 2,5-di-methyl-2,5-di(benzoylperoxy)hexane, t-butylperoxybenzoate, and t-butylperoxy-2-ethyl-hexyl carbonate. These organic peroxides can be used individually or in combination of two or more.

[0112] Examples of sulfur-based crosslinking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and sulfur chloride (sulfur monochloride, sulfur dichloride, etc.). These sulfur-based crosslinking agents can be used individually or in combination of two or more.

[0113] Examples of metal oxides include magnesium oxide, zinc oxide, and lead oxide. These metal oxides can be used individually or in combination of two or more.

[0114] The crosslinking agent can be appropriately selected depending on the type of rubber component, with organic peroxides and metal oxides being preferred, and organic peroxides being particularly preferred. The crosslinking agent may also be a combination of organic peroxides and metal oxides.

[0115] The proportion of the crosslinking agent is, for example, 1 to 20 parts by mass, preferably 3 to 15 parts by mass, and more preferably 5 to 10 parts by mass, per 100 parts by mass of the rubber component. If the proportion of the crosslinking agent is too low, the modulus and hardness of the rubber composition will decrease, while if it is too high, the flexibility of the belt will decrease.

[0116] The proportion of the organic peroxide can be selected from a range of approximately 0.5 to 20 parts by mass (for example, 1 to 10 parts by mass) per 100 parts by mass of the rubber component, and is usually 1 to 5 parts by mass (for example, 1.2 to 4.5 parts by mass), preferably 1.5 to 4 parts by mass, and more preferably 2 to 3 parts by mass. In the first rubber layer, the proportion of the first organic peroxide is, for example, 1 to 20 parts by mass, preferably 1.5 to 10 parts by mass, and more preferably 1.5 to 4 parts by mass, per 100 parts by mass of the first rubber component. In the second rubber layer, the proportion of the second organic peroxide is, for example, 0.5 to 5 parts by mass, preferably 0.8 to 4 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of the second rubber component.

[0117] The proportion of metal oxide is, for example, 0.1 to 30 parts by mass, preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, more preferably 2 to 10 parts by mass, and most preferably 3 to 7 parts by mass, per 100 parts by mass of rubber component.

[0118] Co-crosslinking agents (crosslinking aids or co-vulcanizing agents) include known crosslinking aids, such as polyfunctional (iso)cyanurates [e.g., triallyl isocyanurate (TAIC), triallyl cyanurate (TAC), etc.], polydienes (e.g., 1,2-polybutadiene, etc.), metal salts of unsaturated carboxylic acids [e.g., polyvalent metal salts of (meth)acrylic acids such as zinc (meth)acrylate and magnesium (meth)acrylate], oximes (e.g., quinone dioxime, etc.), guanidines (e.g., diphenylguanidine, etc.), polyfunctional (meth)acrylates [e.g., ethylene glycol di(meth)acrylate, alkanediol di(meth)acrylate such as butanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetrapropyl acrylate, etc.]. Examples include alkane polyol poly(meth)acrylates such as la(meth)acrylate, bismaleimides (aliphatic bismaleimides, e.g., alkylene bismaleimides such as N,N'-1,2-ethylenedimaleimide, N,N'-hexamethylenebismaleimide, 1,6'-bismaleimide-(2,2,4-trimethyl)cyclohexane; arene bismaleimides or aromatic bismaleimides, e.g., N,N'-m-phenylenedimaleimide, 4-methyl-1,3-phenylenedimaleimide, 4,4'-diphenylmethanedimaleimide, 2,2-bis[4-(4-maleimoidphenoxy)phenyl]propane, 4,4'-diphenyletherdimaleimide, 4,4'-diphenylsulfonedimaleimide, 1,3-bis(3-maleimoidphenoxy)benzene, etc.). These cocrosslinking agents can be used alone or in combination of two or more. Among these co-crosslinking agents, polyfunctional (iso)cyanurates, polyfunctional (meth)acrylates, and bismaleimides (arene bismaleimides such as N,N'-m-phenylenedimaleimide or aromatic bismaleimides) are preferred, with bismaleimides being particularly preferred. The degree of crosslinking and the modulus of elasticity can be improved by adding a co-crosslinking agent (e.g., bismaleimides).

[0119] The proportion of co-crosslinking agents (crosslinking aids) such as bismaleimides is, in terms of solid content, for example, 0.2 to 40 parts by mass, preferably 0.5 to 30 parts by mass, more preferably 0.8 to 20 parts by mass, and more preferably 1 to 15 parts by mass, per 100 parts by mass of rubber component. In the first rubber layer, the proportion of co-crosslinking agents (first co-crosslinking agents) is, for example, 1 to 40 parts by mass, preferably 2 to 30 parts by mass (for example 5 to 20 parts by mass), more preferably 2.5 to 18 parts by mass (for example 8 to 15 parts by mass), more preferably 3 to 14 parts by mass (for example 4 to 12 parts by mass), and most preferably 5 to 11 parts by mass (for example 5 to 7 parts by mass), per 100 parts by mass of the first rubber component. In the second rubber layer, the proportion of the co-crosslinking agent (second co-crosslinking agent) can be selected from a range of about 0.2 to 25 parts by mass per 100 parts by mass of the second rubber component, for example, 0.3 to 20 parts by mass (for example, 0.5 to 10 parts by mass), preferably 0.5 to 7 parts by mass (for example, 0.5 to 6 parts by mass), more preferably 0.8 to 5 parts by mass, more preferably 0.8 to 3 parts by mass, and most preferably 0.8 to 2 parts by mass. In particular, by adjusting the proportion of the first co-crosslinking agent in the first rubber component to 3 parts by mass or more (especially 5 parts by mass or more), the tooth-breaking resistance of the toothed belt can be greatly improved by the effect of the combination with the first short fibers oriented in a predetermined direction.

[0120] The proportion of the crosslinking compound is, in terms of solid content, for example, 0.2 to 50 parts by mass, preferably 0.5 to 40 parts by mass, more preferably 1 to 30 parts by mass, and more preferably 2 to 20 parts by mass, per 100 parts by mass of the rubber component. In the first rubber layer, the proportion of the crosslinking compound (first crosslinking compound) is, for example, 1 to 40 parts by mass, preferably 5 to 20 parts by mass, and more preferably 10 to 15 parts by mass, per 100 parts by mass of the first rubber component. In the second rubber layer, the proportion of the crosslinking compound (second crosslinking compound) is, for example, 0.3 to 25 parts by mass, preferably 0.5 to 10 parts by mass, and more preferably 1 to 8 parts by mass, per 100 parts by mass of the second rubber component.

[0121] (E) Other combination agents The crosslinked rubber composition may further contain conventional additives used in rubber compositions for toothed belts. Commonly used additives include, for example, metal oxides (calcium oxide, barium oxide, iron oxide, copper oxide, titanium oxide, aluminum oxide, etc.), softeners (oils such as paraffin oil and naphthenic oils), processing agents or processing aids (stearic acid or its metal salts, waxes, paraffin, fatty acid amides, etc.), plasticizers [aliphatic carboxylic acid plasticizers (adipate ester plasticizers, sebacate ester plasticizers, etc.), aromatic carboxylic acid ester plasticizers (phthalate ester plasticizers, trimellitic acid ester plasticizers, etc.), oxycarboxylic acid ester plasticizers, phosphate ester plasticizers, ether plasticizers, ether ester plasticizers, etc.], antioxidants (antioxidants, heat aging inhibitors, flex crack inhibitors, ozone degradation inhibitors, etc.), colorants, tackifiers, plasticizers, coupling agents (silane coupling agents, etc.), stabilizers (ultraviolet absorbers, heat stabilizers, etc.), flame retardants, and antistatic agents. Furthermore, the crosslinked rubber composition may optionally contain adhesion improvers (such as resorcinol-formaldehyde cocondensates or amino resins). These additives can be used individually or in combination of two or more.

[0122] In particular, the proportion of processing agent or processing aid can be selected from a range of approximately 0.1 to 10 parts by mass per 100 parts by mass of rubber component, and may be 0.3 to 3 parts by mass (especially 0.5 to 1.5 parts by mass) in the first rubber layer, and 0.1 to 2 parts by mass (especially 0.3 to 1 part by mass) in the second rubber layer.

[0123] The proportion of the anti-aging agent is, for example, 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of the rubber component.

[0124] (Preferred formulations of the first and second rubber layers) The modulus of the first and second rubber layers can be adjusted by changing the quantitative ratio of predetermined components that affect the modulus of the rubber layers. For example, the modulus can be adjusted by increasing the content of at least one component selected from short fibers, filler compounds, and crosslinking compounds [crosslinking agents, co-crosslinking agents (such as bismaleimides)] in the first rubber layer compared to the second rubber layer. In particular, in the toothed belt of the present invention, since the first rubber layer contains a predetermined amount of first short fibers as an essential component, the modulus can be easily adjusted by adjusting the proportion of second short fibers in the second rubber layer. Furthermore, by making the proportion of second short fibers in the second rubber layer smaller than the proportion of first short fibers in the first rubber layer, the occurrence of minute cracks in the second rubber layer can also be suppressed, thereby improving resistance to tooth chipping. Furthermore, by adjusting the proportion of short fibers as well as the content of co-crosslinking agents (especially bismaleimides), the elastic modulus (tensile modulus) of the first and second rubber layers can be appropriately balanced, enabling a balance between the inherently conflicting rigidity (deformation resistance) and flexibility (flexibility) of the tooth portion, while also significantly improving tooth chipping resistance.

[0125] Furthermore, in the toothed belt of the present invention, in order to obtain a high modulus of elasticity to obtain the rigidity of the teeth that can withstand use under conditions in which higher loads are applied, and to achieve both the rigidity (deformation resistance) and flexibility (flexibility) of the teeth, which are inversely related, the following formulation is preferred.

[0126] In a preferred embodiment, the first rubber layer contains 80% by mass or more of HNBR containing an unsaturated carboxylic acid metal salt as the first rubber component, with a ratio of 5 to 60 parts by mass of first short fibers, a ratio of 10 parts by mass or less of first reinforcing inorganic filler, a ratio of 1 to 40 parts by mass of bismaleimides as the first co-crosslinking agent, and a ratio of 1 to 20 parts by mass of organic peroxides as the first crosslinking agent, and the second rubber layer contains 30% by mass or more of HNBR containing an unsaturated carboxylic acid metal salt as the second rubber component, with a ratio of 5 parts by mass or less of second short fibers, a ratio of 10 parts by mass or less of second reinforcing inorganic filler, a ratio of 0.2 to 25 parts by mass of bismaleimides as the second co-crosslinking agent, and a ratio of 0.5 to 5 parts by mass of organic peroxides as the second crosslinking agent to 5 parts by mass of second short fibers, a ratio of 10 parts by mass or less of second reinforcing inorganic filler, with a ratio of 0.2 to 25 parts by mass of bismaleimides as the second co-crosslinking agent.

[0127] (Tooth cloth) If the teeth include a tooth fabric, the tooth fabric constituting the inner circumferential surface of the belt (the surface of the teeth and tooth base) may be made of a fabric such as a woven fabric, knitted fabric, or nonwoven fabric. Conventionally, it is often a woven fabric (canvas), and is composed of a fabric woven from warp threads extending in the belt width direction and weft threads extending in the belt circumference direction. The weave structure of the woven fabric is not particularly limited as long as the warp and weft threads intersect regularly in the vertical and horizontal directions, and may be any of plain weave, twill weave (or diagonal weave), satin weave, or a weave structure that combines these structures. Preferred woven fabrics have a twill weave and a satin weave structure.

[0128] As fibers forming the weft and warp threads of the tooth fabric, examples include polyphenylene ether fibers, polyether ether ketone fibers, polyether sulfone fibers, and polyurethane fibers, in addition to the same fibers as the short fibers mentioned above. These fibers can be used individually or in combination of two or more. Among these fibers, organic fibers are commonly used, and preferred are cellulose fibers such as cotton and rayon, polyester fibers (such as PET fibers), polyamide fibers (aliphatic polyamide fibers such as polyamide 66 fibers, aramid fibers, etc.), PBO fibers, and fluororesin fibers [such as polytetrafluoroethylene (PTFE) fibers]. Furthermore, composite yarns of these fibers and elastic yarns with elasticity (for example, polyurethane elastic yarns with elasticity such as spandex made of polyurethane, and processed yarns that have undergone stretch processing (for example, woolly processing, crimping processing, etc.)) are also preferred.

[0129] The form of the warp and weft threads is not particularly limited and may be monofilament yarn, which is a single long fiber; multifilament yarn, which is made by aligning or twisting filaments (long fibers); or spun yarn, which is made by twisting short fibers. The multifilament yarn or spun yarn may be a blended yarn or blended yarn using multiple types of fibers. The weft threads preferably contain elastic yarn, while the warp threads usually do not contain elastic yarn from the viewpoint of weaving. In order to ensure the elasticity of the tooth fabric in the circumferential direction of the belt, the weft threads containing elastic yarn extend in the circumferential direction of the belt, and the warp threads extend in the width direction of the belt.

[0130] The average diameter of the fibers (or yarn) is, for example, 1 to 100 μm (e.g., 3 to 50 μm), preferably 5 to 30 μm, and more preferably 7 to 25 μm. Regarding the average fiber diameter (thickness) of the yarn (twisted yarn), the weft may be, for example, around 100 to 1000 dtex (particularly 300 to 700 dtex), and the warp may be, for example, around 50 to 500 dtex (particularly 100 to 300 dtex). The density of the weft (threads / cm) may be, for example, around 5 to 50 (particularly 10 to 30), and the density of the warp (threads / cm) may be, for example, around 10 to 300 (particularly 20 to 100).

[0131] The woven fabric may have a multi-layered structure (such as a double-layered structure), and in a woven structure comprising warp and weft threads, at least some of the weft threads may be made of low-friction fibers (or low-friction fibers) such as fluororesin-containing fibers (such as composite yarns containing fibers formed from fluororesins such as PTFE). For example, the warp threads may be made of polyamide fibers such as nylon 66, polyester fibers, etc., and the weft threads may be made of fluororesin-formed fibers alone; composite yarns of fluororesin-formed fibers and second fibers such as polyamide fibers or polyurethane fibers (elastic yarns); or composite yarns of this composite yarn and a second composite yarn formed from a plurality of the second fibers.

[0132] In this embodiment, it is preferable to use a fluorine-based fiber (e.g., PTFE fiber) with a low coefficient of friction as the weft thread located on the surface side of the tooth fabric (the side that engages with the toothed pulley) (exposed) in order to reduce friction between the tooth fabric and the toothed pulley. On the other hand, by using a fiber other than a fluorine-based fiber for the weft thread located on the back side of the tooth fabric (the side that adheres to the first rubber layer), it is possible to increase the adhesive force between the tooth fabric and the rubber constituting the teeth. In this embodiment of the tooth fabric, friction in the engagement between the tooth fabric and the toothed pulley can be reduced, and sound can be suppressed.

[0133] Furthermore, when using fluorine-based fibers, it is preferable that low-melting-point fibers having a melting point that melts at the crosslinking (vulcanization) temperature of the teeth and back, which are based on rubber, are arranged around the fluorine-based fibers. Specifically, the form of the composite yarn containing fluorine-based fibers includes forms in which fluorine-based fibers and low-melting-point fibers are mixed and twisted together, or forms in which fluorine-based fibers are covered by low-melting-point fibers. The crosslinking (vulcanization) conditions of the teeth and back are not particularly limited, but generally, the crosslinking (vulcanization) temperature is 100 to 200°C and the crosslinking (vulcanization) time is about 1 minute to 5 hours.

[0134] In an embodiment in which low-melting-point fibers are arranged around fluorine-based fibers, the low-melting-point fibers melt during crosslinking (vulcanization) of the teeth and back of the belt, flow into the spaces between the fibers constituting the tooth fabric, and then crystallize when cooled to below their melting point. Therefore, the cutting and scattering of fluorine-based fibers due to impact and abrasion on the surface of the tooth fabric during engagement with or disengagement from a toothed pulley is suppressed. When the weft of the above embodiment is used as the tooth fabric of a toothed belt, the teeth and back are protected for a longer period of time due to the above effect, preventing chipping of the belt teeth and enabling a longer lifespan during high-load operation.

[0135] The average thickness of the tooth fabric (the tooth fabric in the toothed belt) is, for example, 0.1 to 2 mm, preferably 0.2 to 1.5 mm. The average thickness of the tooth fabric as raw material (the tooth fabric before molding) is, for example, 0.5 to 3 mm, preferably 0.75 to 2.5 mm.

[0136] To improve adhesion with the first rubber layer, the fabric forming the tooth cloth may be subjected to an adhesive treatment. Examples of adhesive treatments include immersing the fabric in an RFL treatment solution followed by heat drying; treating with an epoxy compound or isocyanate compound; dissolving a rubber composition in an organic solvent to make rubber glue, immersing the fabric in this rubber glue, and then heat drying; and combining these treatment methods. These methods can be performed individually or in combination, and the order and number of treatments are not limited. For example, after immersing in the RFL treatment solution, the fabric may be further immersed in rubber glue and then heat dried.

[0137] Furthermore, in order to improve the adhesion between the tooth cloth and the first rubber layer, an uncrosslinked rubber sheet, formed by rolling a rubber composition, may be laminated on the back surface (the side that adheres to the first rubber layer) of the fabric forming the tooth cloth. This rubber composition (third crosslinked rubber composition) can be appropriately selected from the crosslinked rubber compositions exemplified above as crosslinked rubber compositions forming the first and second rubber layers, and may also be a conventional adhesive rubber composition. In addition, the uncrosslinked rubber sheet made of this rubber composition may form a third rubber layer (adhesive rubber layer) interposed between the tooth cloth and the first rubber layer in a toothed belt. The fabric subjected to the above adhesive treatment will be referred to as the tooth cloth precursor.

[0138] [Tooth root] When the tooth portion includes a tooth cloth, the tooth cloth constitutes the surface of the tooth portion, as well as the surface on the tooth side of the back (the surface of the tooth root).

[0139] When the tooth portion includes a tooth cloth, in the dorsal portion corresponding to the tooth root, a first rubber layer and a second rubber layer may be interposed between the tooth cloth and the core wire, but only the first rubber layer may be interposed, or the tooth cloth and the core wire may be in contact without the first and second rubber layers interposed. In the dorsal portion corresponding to the tooth root, whether the first rubber layer is interposed or both the first and second rubber layers are interposed, the thickness of the first rubber layer, and the thickness of the first and second rubber layers, are always formed to be thinner than that of the tooth portion.

[0140] If the tooth portion does not include tooth cloth, the dorsal portion corresponding to the tooth root may be formed of a first rubber layer and a second rubber layer, or it may be formed of the first rubber layer alone. In the dorsal portion corresponding to the tooth root, the thickness of the first rubber layer, and the thicknesses of the first and second rubber layers are formed to be thinner than those of the tooth portion in all cases.

[0141] [Back rubber layer] The back portion has the teeth and tooth roots formed on its inner circumferential surface, and on its outer circumferential surface, it has a back rubber layer that forms the outer circumferential surface of the belt. Furthermore, the back rubber layer is made of a crosslinked rubber composition (fourth crosslinked rubber composition). In the embodiments shown in Figures 1 to 3, the other surface (back of the belt) on the side where the teeth are not formed is not covered with a fabric (woven fabric, knitted fabric, nonwoven fabric, etc.), but it may be covered if necessary. This fabric can be selected from the fabrics exemplified as tooth fabrics, including in preferred embodiments.

[0142] (Fourth crosslinked rubber composition) The hardness of the fourth crosslinked rubber composition is preferably lower than that of the first and second crosslinked rubber compositions that constitute the teeth, in order to reduce the bending rigidity of the belt and ensure flexibility (ease of wrapping around the pulley) and bending fatigue resistance.

[0143] Specifically, the rubber hardness Hs of the fourth crosslinked rubber composition is a type A hardness of, for example, 80 to 89 degrees. Alternatively, it may be a type D hardness of about 20 to 30 degrees. By adjusting the hardness of the back rubber layer to the above range, the bending rigidity of the back is reduced, and excellent bending fatigue resistance is obtained. If the type A hardness of the fourth crosslinked rubber composition is too low, there is a risk of cracks occurring in the back due to impact of foreign objects, etc. Conversely, if it is too high, the bending fatigue resistance will decrease, and there is a risk of cracks occurring in the back.

[0144] In this application, Type A hardness refers to the hardness of the surface of the back rubber layer, and can be measured using a Type A durometer in accordance with the spring-type durometer hardness test specified in JIS K 6253 (2012).

[0145] The fourth crosslinked rubber composition is not particularly limited as long as the adhesion between the back rubber layer and the tooth portion is not impaired, and can be selected from, for example, the crosslinked rubber compositions exemplified as the crosslinked rubber compositions for the first and second rubber layers, and can be appropriately adjusted so that the rubber hardness falls within the aforementioned range.

[0146] In the fourth crosslinked rubber composition, the rubber component (fourth rubber component) preferably contains the same series or type of rubber component as the second rubber layer (internal rubber layer), and more preferably the same type of rubber component, in order to improve the adhesion between the back rubber layer and the teeth.

[0147] The fourth rubber component preferably contains an HNBR / unsaturated carboxylate metal salt composite polymer. The proportion of the HNBR / unsaturated carboxylate metal salt composite polymer may be 5% by mass or more of the fourth rubber component, for example, 5 to 50% by mass, preferably 10 to 30% by mass, and more preferably 15 to 25% by mass.

[0148] The filling compound may be a reinforcing inorganic filler (fourth reinforcing inorganic filler), and a combination of carbon black and silica is preferred. The proportion of carbon black is, for example, 1 to 50 parts by mass, preferably 2 to 30 parts by mass, and more preferably 3 to 10 parts by mass, per 100 parts by mass of silica. The proportion of the fourth reinforcing inorganic filler is, for example, 10 to 100 parts by mass, preferably 20 to 80 parts by mass, and more preferably 30 to 50 parts by mass, per 100 parts by mass of the fourth rubber component.

[0149] The crosslinking agent (fourth crosslinking agent) may be a combination of an organic peroxide (fourth organic peroxide) and a metal oxide (fourth metal oxide). The proportion of the fourth organic peroxide is, for example, 0.5 to 5 parts by mass, preferably 0.8 to 4 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of the fourth rubber component. The proportion of the fourth metal oxide is, for example, 1 to 15 parts by mass, preferably 2 to 10 parts by mass, and more preferably 2 to 8 parts by mass, per 100 parts by mass of the fourth rubber component.

[0150] The cocrosslinking agent (fourth cocrosslinking agent) may be a bismaleimide. The proportion of the fourth cocrosslinking agent is, for example, 0.2 to 10 parts by mass, preferably 0.5 to 5 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of the fourth rubber component.

[0151] The fourth crosslinked rubber composition may contain a plasticizer. The plasticizer can be selected from the plasticizers exemplified in the first and second rubber layers. The plasticizer can be used alone or in combination of two or more. Among the plasticizers, ether ester plasticizers are preferred.

[0152] The proportion of the plasticizer is, for example, 1 to 50 parts by mass, preferably 2 to 30 parts by mass, more preferably 3 to 20 parts by mass, and more preferably 5 to 15 parts by mass, per 100 parts by mass of the fourth rubber component.

[0153] The average thickness of the back rubber layer is, for example, 0.3 to 3 mm, preferably 0.5 to 2 mm. The average thickness of the back portion (average thickness of the back portion at the tooth root) is, for example, 1 to 5 mm, preferably 1.5 to 4 mm.

[0154] [Heart wire] On the back of the belt, a core wire extending along the belt circumferential direction is embedded on the inner circumference side of the back rubber layer. This core wire acts as a tensile body, improving the running stability and strength of the toothed belt. Furthermore, on the back, the core wire, which is usually a twisted cord extending along the belt circumferential direction, is embedded at predetermined intervals in the belt width direction. Multiple core wires parallel to the longitudinal direction may be arranged, but from the viewpoint of productivity, they are usually embedded in a spiral shape. When arranged in a spiral shape, the angle of the core wire with respect to the longitudinal direction of the belt may be, for example, 5° or less, and from the viewpoint of belt running performance, it is preferable that it is as close to 0° as possible.

[0155] More specifically, the core wires may be embedded at predetermined intervals (or pitches) (or at equal intervals) from one end to the other in the belt width direction on the back, as shown in Figure 1. The spacing (spinning pitch), which is the distance between the centers of adjacent core wires, should be greater than the core wire diameter, and depending on the core wire diameter, it is, for example, 0.5 to 3.5 mm, preferably 0.8 to 3 mm, and more preferably 0.9 to 2.8 mm.

[0156] The core wire may be formed from a twisted cord made by twisting together multiple strands or multifilament threads. Of these, a twisted cord of strands is preferred, and one strand may be formed by bundling filaments (long fibers). There are no particular limitations on the thickness of the filaments forming the twisted cord, the number of filaments converged, the number of strands, and the twist configuration.

[0157] The twisted cord forming the core wire may be a single-strand, double-strand, or Lang-strand cord. By using a Lang-strand core wire, where the twist direction of the lower twist and the twist direction of the upper twist are the same, the bending stiffness is lower compared to double-strand or single-strand cords, resulting in excellent bending fatigue resistance.

[0158] The fibers forming the core are not particularly limited, and examples include synthetic fibers such as polyester fibers (polyalkylelelate fibers, poly(p-phenylene naphthalate) fibers), polybenzoxazole fibers, acrylic fibers, and polyamide fibers (aliphatic polyamide fibers, aramid fibers, etc.), as well as inorganic fibers such as glass fibers, carbon fibers, and metal fibers (steel fibers). These fibers can be used individually or in combination of two or more types. From the viewpoint of low elongation and high strength, synthetic fibers such as polyester fibers and polyamide fibers, and inorganic fibers such as glass fibers and carbon fibers are commonly used as fibers forming the core.

[0159] In applications involving particularly high loads, multifilament carbon fiber yarns are preferably used. Examples of carbon fibers used include those manufactured by Toray Industries, Inc., under the trade name "Torayca".

[0160] Carbon fiber multifilament yarns can be selected from multifilament yarns with different filament counts, such as 6K and 12K. 6K refers to a multifilament yarn with 6,000 filaments, and 12K refers to a multifilament yarn with 12,000 filaments. The fineness of 6K multifilament yarn is approximately 400 tex, and the fineness of 12K multifilament yarn is approximately 800 tex.

[0161] If the fineness of carbon fiber multifilament yarn is greater than 1000 tex, there is a risk that its flexural fatigue resistance will decrease. Conversely, if the fineness of carbon fiber multifilament yarn is less than 300 tex, the material cost will increase, and the number of under-twisted yarns required to produce a core wire with sufficient tensile strength will increase, leading to an increase in labor costs.

[0162] In one embodiment of the toothed belt of the present invention, the core wire is a carbon fiber cord (12K-1 / 0) made by single-twisting one 12K multifilament yarn (fineness approximately 800 tex). Alternatively, the core wire may be a Lang-twisted carbon fiber cord (12K-1 / 4) made by first twisting one 12K multifilament yarn (fineness approximately 800 tex) to create a pre-twisted yarn, and then combining four of these pre-twisted yarns and twisting them together. Note that "12K-1 / 0" indicates a twisted cord made by single-twisting one 12K multifilament yarn, and "12K-1 / 4" indicates a twisted cord made by first twisting one 12K multifilament yarn to create a pre-twisted yarn, and then combining four of these pre-twisted yarns and twisting them together. Similarly, for example, "12K-1 / 3" indicates a twisted cord made by first twisting one 12K multifilament yarn to create a base twist, then combining three of these base twists and twisting them together. "12K-4 / 0" indicates a twisted cord made by combining four 12K multifilament yarns and twisting them together in a single-ply manner.

[0163] The core wire may be subjected to an adhesive treatment to enhance its adhesion to the fourth crosslinked rubber composition. For example, the adhesive treatment may involve immersing the stranded cord in a resorcinol-formaldehyde-latex treatment solution (RFL treatment solution), followed by heating and drying to form a uniform adhesive layer on the surface of the stranded cord. The RFL treatment solution is a mixture of latex and an initial condensate of resorcinol and formalin. The latex may be, for example, chloroprene rubber, styrene-butadiene-vinylpyridine terpolymer (VP latex), nitrile rubber, or hydrogenated nitrile rubber. Furthermore, the adhesive treatment may involve pre-treating with an epoxy compound or isocyanate compound before treatment with the RFL treatment solution.

[0164] The average diameter (average wire diameter) of the stranded cord (or core wire) is, for example, 0.2 to 2.5 mm, preferably 0.5 to 2.3 mm, more preferably 0.7 to 2.2 mm, and 0.8 to 2.1 mm is preferred for applications where particularly high loads are applied. If the core wire diameter is too thin, the elongation of the core wire will increase, which may cause tooth breakage (loss of teeth). If the core wire diameter is too thick, the fatigue resistance of the core wire will decrease, which may cause core wire breakage. In one embodiment of the present invention, the core wire diameter is adjusted to 1.1 mm.

[0165] <Method for manufacturing toothed belts> The toothed belt of the present invention may be manufactured, for example, by the following method (pre-forming method).

[0166] [Preparation process for the first rubber layer precursor] If the tooth portion includes a tooth cloth, first, a tooth cloth precursor is prepared to form the tooth cloth, and uncrosslinked rubber sheets are prepared to form multiple rubber layers, such as a first rubber layer precursor which is an uncrosslinked rubber sheet that forms the first rubber layer (surface rubber layer), a second rubber layer precursor which is an uncrosslinked rubber sheet that forms the second rubber layer (internal rubber layer), and a back rubber layer precursor which is an unvulcanized rubber sheet that forms the back rubber layer.

[0167] In particular, the first rubber layer precursor is preferably subjected to the first rubber layer precursor preparation process described below in order to orient the first short fibers in a predetermined direction.

[0168] In the first rubber layer precursor preparation step, the first short fibers can be oriented (arranged) in a predetermined direction during the process of preparing an uncrosslinked rubber sheet by rolling the rubber composition, which has been kneaded in a Banbury mixer or the like, using rolls or a calender. Specifically, a conventional method for oriented the first short fibers in a predetermined direction (one direction on the sheet surface) is to pass the rubber between a pair of calender rolls with a predetermined gap between them and roll it into a sheet, thereby obtaining a rolled sheet in which the first short fibers are oriented in the rolling direction.

[0169] The same method can be used to orient the short fibers when the second rubber layer and the back rubber layer contain short fibers (especially when the second rubber layer contains second short fibers).

[0170] [Pre-molding process] Next, a tooth cloth precursor is wound around the outer surface of a cylindrical mold having multiple grooves (recesses) corresponding to the teeth of a toothed belt. Subsequently, a laminate is formed by sequentially winding a first rubber precursor, which is an uncrosslinked rubber sheet for forming the first rubber layer (surface rubber layer), and a second rubber layer precursor, which is an uncrosslinked rubber sheet for forming the second rubber layer (internal rubber layer), on the outer surface, with the orientation direction of the first short fibers of the first rubber precursor oriented in the direction of the belt's longitudinal direction. The laminate is then heated in a predetermined apparatus to a temperature (for example, about 70-90°C) at which the rubber composition softens, and pressure is applied to the laminate from the outer surface to press the rubber composition of the uncrosslinked rubber sheet and the tooth cloth precursor into the grooves (recesses) of the cylindrical mold, thereby forming the teeth and obtaining a semi-crosslinked pre-molded body. In this press-fitting process to form the teeth, the tooth cloth stretches to conform to the contour of the teeth and is positioned on the outermost surface. Inside it, the first rubber layer is positioned along the contour of the teeth, and the first short fibers are also arranged in the direction of the contour of the teeth while remaining aligned in the longitudinal direction of the belt. Furthermore, a second rubber layer is positioned inside, forming a layered structure. If the teeth do not contain tooth cloth, the first rubber precursor is wrapped around the outer surface of the cylindrical mold instead of the tooth cloth precursor.

[0171] Alternatively, instead of using a cylindrical mold, a flat press mold (flat mold) having multiple grooves (recesses) corresponding to the teeth may be used to form the teeth by press-fitting the rubber composition of the uncrosslinked rubber sheet and the tooth fabric precursor into the grooves (recesses) of the flat mold using the above procedure. In this method, after demolding the preform from the flat mold, the preform is wrapped around and attached to a cylindrical mold having multiple grooves (recesses) corresponding to the teeth (fitting the teeth and grooves), and the process moves to the next step.

[0172] [Crosslinking molding process] The twisted cord constituting the core wire is wound spirally around the outer surface of the obtained pre-molded body at a predetermined pitch (so that the pitch is predetermined in the axial direction of the cylindrical mold). Furthermore, a back rubber layer precursor, which is an uncrosslinked rubber sheet that forms the back rubber layer, is wound around the outer surface to form an uncrosslinked belt molded body (uncrosslinked laminate).

[0173] Next, with the uncrosslinked belt molded body positioned on the outer circumference of the cylindrical mold, a rubber jacket, which acts as a vapor barrier, is placed over it. Subsequently, the jacketed belt molded body and the cylindrical mold are housed inside a crosslinking molding device such as a vulcanizing can. When the belt molded body is heated and pressurized inside the crosslinking molding device, the desired shape is formed, and the crosslinking reaction of the uncrosslinked and semi-crosslinked rubber components contained in the belt molded body causes each component to join together and harden integrally, forming a sleeve-shaped crosslinked molded body (crosslinked belt sleeve).

[0174] [Cutting process] Finally, multiple toothed belts are obtained by cutting the bridging belt sleeve, which has been demolded from the cylindrical mold, to a predetermined width. [Examples]

[0175] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0176] [Rubber composition]

[0177] [Table 1]

[0178] [Table 2]

[0179] [Table 3]

[0180] [Materials used in rubber compositions] HNBR: Zetpol2010, manufactured by Nippon Zeon Co., Ltd., iodine value 11mg / 100mg HNBR containing unsaturated metal carboxylate: Zeon Corporation's "Zeoforte ZSC2295CX," base HNBR:unsaturated metal carboxylate (mass ratio) = 100:110, iodine value of base HNBR 28 mg / 100 mg Nylon staple fibers: "Leona" manufactured by Asahi Kasei Corporation, polyamide 66, average fiber length 3 mm, average fiber diameter 27 μm Aramid short fiber 1: "Conex" manufactured by Teijin Limited, average fiber length 3 mm, average fiber diameter 14 μm Aramid short fiber 2: "Twaron®" manufactured by Teijin Limited, average fiber length 3 mm, average fiber diameter 12 μm PBO short fibers: "Zylon" manufactured by Toyobo Co., Ltd., average fiber length 3 mm, average fiber diameter 12 μm Stearic acid: "Stearic acid Tsubaki" manufactured by NOF Corporation. Carbon black SRF: "Seas S" manufactured by Tokai Carbon Co., Ltd., average particle size 66 nm, iodine adsorption capacity 26 mg / g Silica: "UltraSil VN-3" manufactured by Evonik Degussa Japan Co., Ltd., specific surface area 155-195 m² 2 / g Calcium carbonate: Maruo Calcium Co., Ltd. "Super #1500", average particle size 1.5 μm Zinc oxide: "Zinc Oxide Type 2" manufactured by Sakai Chemical Industry Co., Ltd., average particle size 0.55 μm Anti-aging agent: p,p'-dioctyldiphenylamine, manufactured by Seiko Chemical Co., Ltd. ("Nonflex OD3") Organic peroxide: 1,3-bis(t-butylperoxyisopropyl)benzene, theoretical reactive oxygen species content 9.45% Co-crosslinking agent: N,N'-m-phenylenedimaleimide, manufactured by Ouchi Shinko Chemical Co., Ltd. ("Balnock PM") Plasticizer: ADEKA Corporation's "ADEKA Sizer RS700".

[0181] [Heart wire] A carbon fiber cord (12K-1 / 0, tensile modulus 230 GPa) was prepared by twisting one strand of 12K multifilament yarn [Toray Industries, Inc.'s "Torayca T700SC-12000", single filament fineness 0.67 dtex, total fineness 800 tex] into a single strand. This cord was then bonded with an HNBR-based overcoat to obtain a core wire with a diameter of 1.1 mm.

[0182] [Tooth cloth and tooth cloth processing] The woven fabrics shown in Table 4 were immersed in RFL treatment solution and rubber glue to produce tooth cloth precursors. Specifically, for the RFL treatment, two types of RFL treatment solutions (RFL1 and RFL2) shown in Table 5 were used, and the immersion treatment was performed in the order of RFL1 followed by RFL2. Furthermore, for the rubber glue treatment, two types of rubber glue (rubber glue 1 and rubber glue 2) shown in Table 6 were used, and the immersion treatment was performed in the order of rubber glue 1 followed by rubber glue 2.

[0183] [Table 4]

[0184] *1: PTFE fiber [Toray Industries, Inc.'s "Toyoflon 1330dtex"] *2: Polyester fiber [Unitika Ltd.'s "Cornetta," a core-sheath type composite fiber with a core melting point of 256°C and a sheath melting point of 160°C]

[0185] [Table 5]

[0186] [Table 6]

[0187] [Preparation of uncrosslinked rubber sheets] For forming the teeth and back (back rubber layer), each rubber composition shown in Tables 1-3 was kneaded using a Banbury mixer, and the resulting kneaded rubber was rolled to a predetermined thickness using a calender roll to produce an uncrosslinked rubber sheet. The short fibers contained in the uncrosslinked rubber sheet were oriented in the rolling direction. In this application, each rubber composition is denoted by R1 to R34.

[0188] [Hardness (Type D)] A cross-linked rubber sheet (100 mm x 100 mm x 2 mm thick) was prepared by press-heating an uncrosslinked rubber sheet at 165°C for 30 minutes. A laminate of three cross-linked rubber sheets was used as a sample, and the hardness (Type D) of the cross-linked rubber sheet was measured using a Type D durometer in accordance with the spring-type durometer hardness test specified in JIS K 6253 (2012) (Vulcanized rubber and thermoplastic rubber - Method for determining hardness -).

[0189] [Tensile strength] Uncrosslinked rubber sheets were press-heated at 165°C for 30 minutes to produce crosslinked rubber sheets (100mm x 100mm x 2mm thickness), and test specimens were punched out in a dumbbell shape (Type 5) according to JIS K 6251 (2017). For samples containing short fibers, dumbbell-shaped test specimens were taken so that the direction of the short fiber arrangement (parallel to the arrangement) was the tensile direction. Then, both ends of the test specimen were grasped with a chuck (gripping device), and the test specimen was pulled at a speed of 50 mm / min until it broke. The tensile strength was defined as the value obtained by dividing the maximum tensile force recorded by the initial cross-sectional area of ​​the test specimen (tensile strength T). The tensile strengths of each rubber composition are shown in Tables 1 to 3.

[0190] [Tensile modulus of elasticity] Using the same method as described above for tensile strength, dumbbell-shaped test specimens (Type 5) conforming to JIS K 6251 (2017) were prepared. For samples containing short fibers, dumbbell-shaped test specimens were taken so that the direction perpendicular to the arrangement direction of the short fibers (parallel to the arrangement direction) was the tensile direction. Then, both ends of the test specimen were grasped with a chuck (gripping device), and the test specimen was pulled at a speed of 50 mm / min. The tensile force when a predetermined elongation (2%) was applied was divided by the initial cross-sectional area of ​​the test specimen (tensile stress at 2% elongation), and this value was defined as the tensile modulus. The tensile moduli of each rubber composition are shown in Tables 1 to 3.

[0191] [Manufacturing of toothed belts] In the examples and comparative examples, as shown below, toothed belts with a total thickness of 5.6 mm, tooth profile G8M, tooth height (including tooth cloth) of 3.5 mm, tooth pitch of 8 mm, number of teeth of 140, circumference of 1120 mm, and width of 12 mm were manufactured using the pre-forming method described in this embodiment.

[0192] <Examples 1-30 and Comparative Examples 1-10> Tables 8 to 12 show the tooth structure (layer structure) and the rubber composition used in each rubber layer of the toothed belts produced in Examples 1 to 30 and Comparative Examples 1 to 10.

[0193] (Comparative Example 1) A press mold (flat type) having multiple grooves (recesses) corresponding to the teeth of a toothed belt was used to laminate a tooth fabric precursor for forming the tooth fabric, an uncrosslinked rubber sheet (R3, sheet thickness 0.70 mm) for forming the first rubber layer, and an uncrosslinked rubber sheet (R2, sheet thickness 1.00 mm) for forming the second rubber layer in that order. The laminated material was then pressed for 160 seconds at a temperature of 90°C and a press pressure (surface pressure) of 20.2 MPa to produce a semi-crosslinked pre-molded body.

[0194] Next, a pre-molded body was wrapped around a cylindrical mold having multiple grooves (recesses) corresponding to the teeth (fitting the teeth and grooves together), and a stranded cord constituting the core wire was spun spirally around the outer surface of the pre-molded body (tension: 150-250 N / strand, spinning pitch: 1.25 mm, spinning speed: 1.5 m / s). Furthermore, an uncrosslinked rubber sheet (R34, sheet thickness 0.90 mm) that forms the back rubber layer was wrapped around the outer surface to form an uncrosslinked belt molded body (uncrosslinked laminate). The uncrosslinked rubber sheet was wrapped so that the orientation direction of the short fibers contained in the sheet was in the direction of the longitudinal direction of the belt.

[0195] Next, using a vulcanizing vessel, cross-linking molding was performed for 40 minutes under conditions of a heating temperature of 179°C and a steam pressure of 0.83 MPa to produce a cross-linked molded body (cross-linked belt sleeve).

[0196] Finally, a toothed belt was obtained by cutting the bridging belt sleeve, which had been demolded from the cylindrical mold, to a width of 12 mm.

[0197] (Comparative Examples 2-5) Except for using R4 in Comparative Example 2, R5 in Comparative Example 3, R6 in Comparative Example 4, and R7 in Comparative Example 5 as the uncrosslinked rubber sheet forming the first rubber layer, toothed belts were manufactured in the same manner as in Comparative Example 1.

[0198] (Examples 1-6) A toothed belt was manufactured in the same manner as in Comparative Example 1, except that R8 was used as the uncrosslinked rubber sheet for forming the first rubber layer in Example 1, R9 in Example 2, R10 in Example 3, R11 in Example 4, R12 in Example 5, and R13 in Example 6.

[0199] (Comparative Example 6) A toothed belt was manufactured in the same manner as in Comparative Example 1, except that only one type of uncrosslinked rubber sheet, R2 (sheet thickness 1.70 mm), was used to form the teeth.

[0200] (Comparative Example 7) A toothed belt was manufactured in the same manner as in Comparative Example 1, except that only one type of uncrosslinked rubber sheet, R10 (sheet thickness 1.70 mm), was used to form the teeth.

[0201] (Comparative Example 8) A toothed belt was manufactured in the same manner as in Example 3, except that the uncrosslinked rubber sheet forming the first rubber layer was R2 (sheet thickness 0.85 mm) and the uncrosslinked rubber sheet forming the second rubber layer was R10 (sheet thickness 0.85 mm).

[0202] (Example 7) A toothed belt was manufactured in the same manner as in Example 3, except that the thickness of the uncrosslinked rubber sheet forming the first rubber layer was 0.20 mm and the thickness of the uncrosslinked rubber sheet forming the second rubber layer was 1.50 mm.

[0203] (Example 8) A toothed belt was manufactured in the same manner as in Example 3, except that the thickness of the uncrosslinked rubber sheet forming the first rubber layer was 0.35 mm and the thickness of the uncrosslinked rubber sheet forming the second rubber layer was 1.35 mm.

[0204] (Example 9) A toothed belt was manufactured in the same manner as in Example 3, except that the thickness of the uncrosslinked rubber sheet forming the first rubber layer was 1.00 mm and the thickness of the uncrosslinked rubber sheet forming the second rubber layer was 0.70 mm.

[0205] (Example 10) A toothed belt was manufactured in the same manner as in Example 3, except that the thickness of the uncrosslinked rubber sheet forming the first rubber layer was 1.35 mm and the thickness of the uncrosslinked rubber sheet forming the second rubber layer was 0.35 mm.

[0206] (Examples 11-15) A toothed belt was manufactured in the same manner as in Example 3, except that R14 was used as the uncrosslinked rubber sheet forming the first rubber layer in Example 11, R15 in Example 12, R16 in Example 13, R17 in Example 14, and R18 in Example 15.

[0207] (Examples 16-21) A toothed belt was manufactured in the same manner as in Example 3, except that R20 was used as the uncrosslinked rubber sheet forming the first rubber layer in Example 16, R21 in Example 17, R22 in Example 18, R23 in Example 19, R24 in Example 20, and R25 in Example 21.

[0208] (Example 22) A toothed belt was manufactured in the same manner as in Example 3, except that the uncrosslinked rubber sheet forming the first rubber layer was R14 (sheet thickness 0.20 mm) and the uncrosslinked rubber sheet forming the second rubber layer was R2 (sheet thickness 1.50 mm).

[0209] (Example 23) A toothed belt was manufactured in the same manner as in Example 3, except that the uncrosslinked rubber sheet forming the first rubber layer was R17 (sheet thickness 1.00 mm) and the uncrosslinked rubber sheet forming the second rubber layer was R2 (sheet thickness 0.70 mm).

[0210] (Example 24) A toothed belt was manufactured in the same manner as in Example 3, except that the uncrosslinked rubber sheet forming the first rubber layer was R17 (sheet thickness 1.35 mm) and the uncrosslinked rubber sheet forming the second rubber layer was R2 (sheet thickness 0.35 mm).

[0211] (Example 25, Comparative Example 9) A toothed belt was manufactured in the same manner as in Example 3, except that R1 was used as the uncrosslinked rubber sheet forming the second rubber layer in Example 25, and R7 in Comparative Example 9.

[0212] (Examples 26, 27) A toothed belt was manufactured in the same manner as in Example 25, except that R8 was used as the uncrosslinked rubber sheet forming the first rubber layer in Example 26, and R13 in Example 27.

[0213] (Comparative Example 10) An endless belt with teeth was produced in the same manner as in Comparative Example 9, except that the unvulcanized rubber sheet forming the first rubber layer was designated as R8.

[0214] (Example 28) An endless belt with teeth was produced in the same manner as in Example 3, except that the unvulcanized rubber sheet forming the first rubber layer was designated as R27 and the unvulcanized rubber sheet forming the second rubber layer was designated as R26.

[0215] (Examples 29 and 30) In Examples 29 and 30, endless belts with teeth were produced in the same manner as in Examples 3 and 14, respectively, except that preforms were produced without using precursors for the tooth fabric. These endless belts with teeth were configured such that no tooth fabric was provided on the surfaces of the tooth portions and the bottom portions of the teeth of the belt, and had a tooth height of 3.5 mm (excluding the tooth fabric).

[0216] [Flexural rigidity test] (Flexural rigidity test conditions) For the endless belt with teeth, the flexural strength E of the endless belt with teeth was determined by a flexural test using an Olsen-type flexural tester in accordance with JIS K 7106 (1995). r The second moment of area I of the endless belt with teeth calculated from the obtained Er using the following formula (1) was multiplied by the flexural rigidity E of the endless belt with teeth calculated from the following formula (2). Here, the size of the endless belt test piece was set to a length of 80 mm, a width of 12 mm, and a back thickness of 2.1 mm, the distance S between the supports was set to 25.4 mm, and the moment M of the pendulum at a load scale of 100% was set to 0.343 N·m. The test was also conducted under conditions of a temperature of 23 ± 2°C and a humidity of 65 ± 5%. A smaller value of the flexural rigidity indicates better flexibility. The criteria for judging the flexural rigidity are shown below. r r I r was calculated.

[0217] I r =b×h 3 / 12 (1) [where, I r : Second moment of area of the test piece (mm 4 ​[b: width of the test specimen (mm), h: thickness of the back of the test specimen (mm)]

[0218] E r I r =[(S×M) / 300]×[N / (D×0.01745)] (2)[In the formula, E r : Bending stiffness of the test specimen (N / mm 2 ), Ir: Second moment of area of ​​the test specimen (mm 4 ), S: distance between support points (mm), M: pendulum moment (N·m), D: bending angle (degrees) (1 degree = π / 180 = 0.01745 radians), N: reading on the load scale plate corresponding to the bending angle (degrees) (%).

[0219] (Criteria for determining bending stiffness) a: Bending rigidity is less than 700 MPa (pass) b: Bending stiffness of 700 MPa or more, but less than 800 MPa (pass) c: Bending rigidity is 800 MPa or higher (failed)

[0220] The test results for the toothed belts of Examples 1-30 and Comparative Examples 1-10 are shown in Tables 8-12.

[0221] [Tooth stiffness test] (Tooth stiffness test conditions) As shown in Figure 6, the teeth of the toothed belt 1 were hooked onto the projection 21a of a tooth shearing jig (a rigid body simulating the tooth shape of a toothed pulley) 21, and one tooth was pressed down with a constant pressure (tightening torque of 0.98 cN·m per 1 mm width). When the belt was pulled at a speed of 1 mm / min using an autograph, the tooth load per 12 mm width relative to the displacement was defined as the tooth stiffness and evaluated. The value of the tooth load relative to the displacement was obtained by linear approximation in the range of tooth load from 50 to 400 N, using the third cycle where the numerical value stabilizes, as shown in Figure 7. A larger tooth stiffness value indicates better tooth stiffness (deformation resistance). The criteria for determining tooth stiffness are shown below.

[0222] (Criteria for determining tooth rigidity) a: Tooth rigidity of 1300 N / mm or more b: Tooth rigidity of 1100 N / mm or more, and less than 1300 N / mm c: Tooth stiffness less than 1100 N / mm

[0223] The test results for the toothed belts of Examples 1-30 and Comparative Examples 1-10 are shown in Tables 8-12.

[0224] [Jumping Test] (Driving test conditions) Using a two-axis torque measurement test machine, a toothed belt was wrapped between a drive pulley (22 teeth) and a driven pulley (22 teeth), and the distance between the pulleys was adjusted so that the belt tension was 230N. Then, the drive pulley was rotated at 1,800 rpm, and the load on the driven pulley was continuously increased while the belt was running. The load torque applied to the driven pulley when jumping (tooth skipping) occurred was measured as the jumping torque. The jumping torque value was used as an indicator of jumping resistance, and a higher jumping torque value indicates a superior toothed belt that is less prone to tooth skipping.

[0225] Regarding the jumping torque value, the jumping torque value (112 N·m) of Comparative Example 2, which has a small proportion of short fibers in the first rubber layer (2 parts by mass) and exhibits the best durability running performance among the comparative examples, is set to 1.00, and the jumping torque values ​​of each example and comparative example are shown converted to relative values. If this value is 1.00 or less, it indicates that no reinforcing effect is observed on the toothed belt of Comparative Example 2, and if it exceeds 1.00, it indicates that the rigidity (deformation resistance) of the teeth has improved due to the reinforcing effect. The larger this value, the higher the degree of the reinforcing effect.

[0226] (Jumping test evaluation criteria) a: Jumping torque exceeds 1.00 (passed) b: Jumping torque is 1.00 (pass) c: Jumping torque is 0.95 or higher and less than 1.00 (pass) d: Jumping torque is less than 0.95 (failed)

[0227] [Endurance Running Test] (Running Test Conditions) A toothed belt was attached to a two - axis running test machine equipped with a driving pulley (tooth number: 22) and a driven pulley (tooth number: 22), and the running time until a failure (tooth part loss) occurred in the toothed belt was measured as the running life. The attachment tension of the toothed belt was 230 N, the rotational speed of the driving pulley was 1800 rpm, the load of the driven pulley was 9.0 kW, and the ambient temperature was 25 °C (room temperature).

[0228] Regarding the running time until this failure (hereinafter referred to as running time), the proportion of short fibers contained in the first rubber layer was small (2 parts by mass), and taking the running time (159 hours) of Comparative Example 2, which has the best endurance running performance among the comparative examples, as 1.00, the running times of each example and comparative example are shown after conversion into relative values. If this value is less than or equal to 1.00, it indicates that the reinforcing effect on the toothed belt of Comparative Example 2 does not appear. If it exceeds 1.00, it indicates that the endurance running performance has been improved by the reinforcing effect, and it can be said that the greater this value, the more highly the reinforcing effect is exerted.

[0229] (Judgment Criteria for Endurance Running Test) a: The running time until failure is 1.25 or more (with reinforcing effect) b: The running time until failure is 1.10 or more and less than 1.25 (with reinforcing effect) c: The running time until failure exceeds 1.00 and is less than 1.10 (with reinforcing effect) d: The running time until failure is 1.00 or less (without reinforcing effect)

[0230] [Overall Judgment] Considering the level of the reinforcing effect in both jumping torque and endurance running performance with respect to Comparative Example 2 as the reference, a comprehensive evaluation was made according to the judgment criteria shown in Table 7.

[0231]

Table 7

[0232] For the toothed belts of Examples 1 to 30 and Comparative Examples 1 to 10, the test results are shown in Tables 8 to 12. Further, cross-sectional views of the tooth portions of the toothed belts in Examples 3, 8, 9 and Comparative Examples 6 to 8 are shown in FIG. 8.

[0233] [Table 8]

[0234] [Table 9]

[0235] [Table 10]

[0236] [Table 11]

[0237] [Table 12]​​​​​​​​​​​​Comparative Examples 2 to 5 are examples in which the amount of the first co-crosslinking agent in the first rubber layer of Comparative Example 1 was increased to increase the tensile modulus. With the increase in amount, the tensile modulus increased to 9.4 MPa in Comparative Example 2, 10.9 MPa in Comparative Example 3, 13.7 MPa in Comparative Example 4, and 16.8 MPa in Comparative Example 5.

[0240] As a result, the bending stiffness was 602 N / mm (Comparative Example 1: grade a), 652 N / mm (Comparative Example 2: grade a), 660 N / mm (Comparative Example 3: grade a), 676 N / mm (Comparative Example 4: grade a), and 724 N / mm (Comparative Example 5: grade b), all of which were within the acceptable range.

[0241] Furthermore, the tooth rigidity was also within the acceptable range in all cases: 1,185 MPa (Comparative Example 1: grade b), 1,362 MPa (Comparative Example 2: grade a), 1,410 MPa (Comparative Example 3: grade a), 1,454 MPa (Comparative Example 4: grade a), and 1,527 MPa (Comparative Example 5: grade a).

[0242] Furthermore, regarding dynamic performance, the jumping torque (relative value) was 0.95 (Comparative Example 1: grade c), 1.00 (Comparative Example 2: grade b), 1.03 (Comparative Example 3: grade a), 1.06 (Comparative Example 4: grade a), and 1.07 (Comparative Example 5: grade a), all of which were within the acceptable level. Similar to tooth stiffness, it increased as the tensile modulus of the first rubber layer increased.

[0243] However, the endurance test (running time until failure (relative value)) was 0.53 (Comparative Example 1: D rating), 1.00 (Comparative Example 2: D rating), 0.80 (Comparative Example 3: D rating), 0.86 (Comparative Example 4: D rating), and 0.69 (Comparative Example 5: D rating), resulting in an overall failing grade (D rank). In these cases, it can be inferred that minute cracks that developed due to long-term running grew, leading to tooth chipping.

[0244] (Examples 1-6) Example 1 is an example in which the content of the co-crosslinking agent in the first rubber layer of Comparative Example 1 is as low as 1 part by mass (the same amount as the second rubber layer), but the amount of the first short fiber is increased to 20 parts by mass. That is, the first rubber layer is formed of R8 (crosslinked rubber) with a tensile elastic modulus of 5.3 MPa, and the second rubber layer is formed of R2 (crosslinked rubber) with a tensile elastic modulus of 3.8 MPa. The ratio of the tensile elastic moduli of the two layers is 1.4.

[0245] Regarding the dynamic performance, the jumping torque (relative value) was at the same level as that of Comparative Example 1, which was 0.95 (c judgment), but the endurance running (running time until failure (relative value)) was improved to 1.43 (a judgment) compared with Comparative Example 1, which was 0.53 (c judgment), and it passed the comprehensive judgment (C rank).

[0246] Example 2 is an example in which the amount of the first short fiber is increased to 20 parts by mass while the content of the co-crosslinking agent in the first rubber layer of Comparative Example 1 remains the same (3 parts by mass). That is, the first rubber layer is formed of R9 (crosslinked rubber) with a tensile elastic modulus of 9.0 MPa, and the second rubber layer is formed of R2 (crosslinked rubber) with a tensile elastic modulus of 3.8 MPa. The ratio of the tensile elastic moduli of the two layers is 2.4.

[0247] Example 3 is an example in which the amount of the first short fiber is increased to 20 parts by mass while the content of the co-crosslinking agent in the first rubber layer of Comparative Example 2 remains the same (6 parts by mass). That is, the first rubber layer is formed of R10 (crosslinked rubber) with a tensile elastic modulus of 14 MPa, and the second rubber layer is formed of R2 (crosslinked rubber) with a tensile elastic modulus of 3.8 MPa. The ratio of the tensile elastic moduli of the two layers is 3.7.

[0248] Example 4 is an example in which the amount of the first short fiber is increased to 20 parts by mass while the content of the co-crosslinking agent in the first rubber layer of Comparative Example 3 remains the same (8 parts by mass). That is, the first rubber layer is formed of R11 (crosslinked rubber) with a tensile elastic modulus of 14.3 MPa, and the second rubber layer is formed of R2 (crosslinked rubber) with a tensile elastic modulus of 3.8 MPa. The ratio of the tensile elastic moduli of the two layers is 3.8.

[0249] Example 5 is an example in which the amount of the first short fiber was increased to 20 parts by mass in the first rubber layer of Comparative Example 4 while keeping the co-crosslinking agent content the same (11 parts by mass). Specifically, the first rubber layer was formed with R12 (crosslinked rubber) with a tensile modulus of 19.2 MPa, and the second rubber layer was formed with R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa, so the ratio of the tensile moduli of the two layers is 5.1.

[0250] Example 6 is an example in which the amount of the first short fiber was increased to 20 parts by mass while keeping the content of the first co-crosslinking agent the same as in Comparative Example 5 (14 parts by mass) in the first rubber layer. Specifically, the first rubber layer was formed with R13 (crosslinked rubber) with a tensile modulus of 23.5 MPa, and the second rubber layer was formed with R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa, and the ratio of the tensile moduli of the two layers was 6.2.

[0251] When Examples 2-6 were compared with the corresponding comparative examples (comparisons where the amount of the first co-crosslinking agent was the same but the amount of the first short fibers was increased), in all comparisons the jumping torque (relative value) was equal to or better than the comparative examples and received an "a" rating. In terms of endurance running (running time until failure (relative value)), the values ​​improved compared to the comparative examples, which were at a failing level, to 1.64 (Example 2; a rating), 2.08 (Example 3; a rating), 1.50 (Example 4; a rating), 1.55 (Example 5; a rating), and 1.54 (Example 6; a rating), resulting in an overall passing grade (A rank).

[0252] In particular, Example 3 (R10, 6 parts by mass of the first co-crosslinking agent) showed excellent results in both jumping torque and endurance running, suggesting that further increasing the amount of the first co-crosslinking agent did not improve the running life. From these results, it was confirmed that increasing the amount of the first short fibers is effective in improving durability (extending lifespan).

[0253] (Comparative Examples 6-8) Comparative Example 6 is an example of a toothed belt in which the entire rubber layer forming the teeth is made solely of R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa (relatively low modulus), which was used to form the second rubber layer in Examples 1 to 6. The bending stiffness was 553 MPa (grade a), which was better than the examples, but the tooth stiffness was 1,092 N / mm (grade c), which was unacceptable. In terms of dynamic performance, the jumping torque (relative value) was 0.90 (grade d), and the endurance run (running time until failure (relative value)) was also 0.33 (grade d), resulting in an overall unacceptable rating (rank D).

[0254] Comparative Example 7 is an example of a toothed belt in which the entire rubber layer forming the teeth is made solely of R10 (crosslinked rubber) with a tensile modulus of 14 MPa (relatively high modulus), the same material used to form the first rubber layer in Example 3. The tooth stiffness was 1,750 N / mm (grade a), which was better than in Example 3, but the bending stiffness was 825 MPa (grade c), which was unacceptable. In terms of dynamic performance, the jumping torque (relative value) was 1.35 (grade a), but the endurance run (running time until failure (relative value)) was 0.43 (grade d), resulting in an overall unacceptable rating (rank D).

[0255] Comparative Example 8, like the example, has a two-layer structure for the teeth, consisting of a first rubber layer and a second rubber layer, but with the elastic moduli of the first and second rubber layers reversed. Specifically, the first rubber layer used R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa (relatively low modulus), and the second rubber layer used R10 (crosslinked rubber) with a tensile modulus of 14 MPa (relatively high modulus). In the cross-sectional view of the teeth, the area occupied by the first rubber layer relative to the total area of ​​all rubber layers constituting the teeth was set to 50%. As a result, the tooth stiffness was 1,275 N / mm (grade b), which was acceptable, but the bending stiffness was 820 MPa (grade c), which was unacceptable. In terms of dynamic performance, the jumping torque (relative value) was 1.07 (grade a), but the endurance run (running time until failure (relative value)) was 0.75 (grade d), resulting in an overall unacceptable rating (rank D).

[0256] As in Comparative Example 6, forming the entire tooth portion with a low modulus rubber layer results in insufficient rigidity (deformation resistance) of the tooth portion, while forming the entire tooth portion with a high modulus rubber layer results in insufficient flexibility (low bending rigidity). Furthermore, as in Comparative Example 8, even when the tooth portion is made of two layers, forming the interior with a high modulus rubber layer more than the surface layer results in insufficient flexibility (low bending rigidity) and a decrease in the level of rigidity (deformation resistance) of the tooth portion. Moreover, since it does not have a first rubber layer with a predetermined amount of oriented short fibers, its durability is low.

[0257] In contrast, the embodiment of this product has a tooth structure with high rigidity (high modulus of elasticity) that can withstand use under conditions where higher loads are applied, and it is a well-balanced embodiment that can achieve both the conflicting relationship between tooth structure rigidity (resistance to deformation) and flexibility (low bending rigidity: flexibility), and it also has excellent durability.

[0258] (Examples 7-10) In contrast to Example 3, in which the first rubber layer was formed from R10 (crosslinked rubber) with a tensile modulus of 14 MPa and the second rubber layer from R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa, Examples 7 to 10 are examples of toothed belts in which the ratio of the area occupied by the first rubber layer to the total area of ​​the rubber layers constituting the teeth is varied in a cross-sectional view of the teeth.

[0259] In Examples 7-10 and Example 3, the ratio of the area occupied by the first rubber layer to the total rubber layer constituting the tooth in a cross-sectional view of the tooth is 10% (Example 7), 20% (Example 8), 40% (Example 3), 60% (Example 9), and 80% (Example 10).

[0260] As a result, the tooth rigidity was 1,275 N / mm (Example 7: grade b), 1,347 N / mm (Example 8: grade a), 1,442 N / mm (Example 3: grade a), 1,527 N / mm (Example 9: grade a), and 1,561 N / mm (Example 10: grade a), all of which were within the acceptable range, and improved as the proportion of the area of ​​the first rubber layer increased.

[0261] On the other hand, the bending stiffness was 601 MPa (Example 7: grade a), 633 MPa (Example 8: grade a), 671 MPa (Example 3: grade a), 692 MPa (Example 9: grade a), and 743 MPa (Example 10: grade b), all of which were within the acceptable range, and increased as the proportion of the area of ​​the first rubber layer increased.

[0262] Furthermore, regarding dynamic performance, the jumping torque (relative value) was 1.00 (Example 7: grade b), 1.10 (Example 8: grade a), 1.11 (Example 3: grade a), 1.26 (Example 9: grade a), and 1.31 (Example 10: grade a), all of which were within the acceptable range. Similar to tooth rigidity, the jumping torque increased as the proportion of the area of ​​the first rubber layer increased.

[0263] Furthermore, the endurance test (running time until failure (relative value)) was 1.41 (Example 7: a rating), 1.82 (Example 8: a rating), 2.08 (Example 3: a rating), 1.69 (Example 9: a rating), and 1.07 (Example 10: c rating), all of which were within the acceptable range, and the proportion of the area of ​​the first rubber layer increased particularly in the range of 20-60%.

[0264] Based on the overall assessment, the toothed belts in Examples 7-10 met the passing standard (A-C rank).

[0265] (Examples 11-15) Among Examples 1 to 6, Example 3 (20 parts by mass of first short fibers, 6 parts by mass of first co-crosslinking agent, and in a cross-sectional view of the teeth, the area occupied by the first rubber layer relative to the total rubber layer constituting the teeth was 40%) had the best durability and running performance. In contrast, Examples 11 to 15 are examples of toothed belts using rubber compositions in which the amount of first short fibers contained in the first rubber layer was varied. In Example 11, R14 (5 parts by mass of short fibers, tensile modulus 10.8 MPa) was used to form the first rubber layer; in Example 12, R15 (10 parts by mass of short fibers, tensile modulus 12.6 MPa) was used; in Example 3, R10 (20 parts by mass of short fibers, tensile modulus 14 MPa) was used; in Example 13, R16 (30 parts by mass of short fibers, tensile modulus 13.7 MPa) was used; in Example 14, R17 (50 parts by mass of short fibers, tensile modulus 14.0 MPa) was used; and in Example 15, R18 (60 parts by mass of short fibers, tensile modulus 13.9 MPa) was used to form the first rubber layer. Note that the rubber composition of R19 (65 parts by mass of short fibers) could not be mixed, so a toothed belt could not be manufactured.

[0266] As a result, the tooth rigidity was 1,271 N / mm (Example 11: grade b), 1,367 N / mm (Example 12: grade a), 1,442 N / mm (Example 3: grade a), 1,430 N / mm (Example 13: grade a), 1,432 N / mm (Example 14: grade a), and 1,425 N / mm (Example 15: grade a), all of which were within the acceptable range.

[0267] On the other hand, the bending stiffness increased as the elastic modulus of the first rubber layer increased: 648 MPa (Example 11: a rating), 662 MPa (Example 12: a rating), 671 MPa (Example 3: a rating), 687 MPa (Example 13: a rating), 706 MPa (Example 14: b rating), and 713 MPa (Example 15: b rating).

[0268] Furthermore, regarding dynamic performance, the jumping torque (relative value) was 1.03 (Example 11: a rating), 1.05 (Example 12: a rating), 1.11 (Example 3: a rating), 1.07 (Example 13: a rating), 1.07 (Example 14: a rating), and 1.06 (Example 15: a rating), all of which were within the acceptable level and showed the same trend as tooth rigidity.

[0269] On the other hand, the endurance test (running time until failure (relative value)) was 1.24 (Example 11: grade b), 1.86 (Example 12: grade a), 2.08 (Example 3: grade a), 1.30 (Example 13: grade a), 1.25 (Example 14: grade a), and 1.21 (Example 15: grade b), all of which were within the acceptable range.

[0270] Based on the overall assessment, the toothed belts of Examples 3 and 11-15 achieved a high level of passability (A or B rank) in that they demonstrated a reinforcing effect in both jumping torque and durability. In particular, Examples 12 (10 parts by mass of short fibers, tensile modulus 12.6 MPa) and 3 (20 parts by mass of short fibers, tensile modulus 14.0 MPa) showed excellent jumping torque and a significant effect on durability (extended lifespan). In particular, Example 3 can be said to be an embodiment in which the tensile strength of the rubber composition (R10) was remarkably high, resulting in a large reinforcing effect. On the other hand, Examples 13-15, in which the amount of first short fibers was further increased, did not show the same effect of extending lifespan as Examples 12 and 3. Therefore, it can be said that the most suitable range for the reinforcing effect of the first short fibers is an amount of 10-30 parts by mass, with a peak of around 20 parts by mass.

[0271] Based on the above results, the physical properties of the first rubber layer can be said to be preferably in the range of 4 to 25 MPa (particularly 10 to 15 MPa) in the belt width (anti-reaction direction) direction in terms of tensile modulus. Furthermore, the proportion of short fibers contained in the first rubber layer can be said to be preferably in the range of 5 to 60 parts by mass (particularly 10 to 30 parts by mass).

[0272] (Example 16) Compared to Example 1 (R8: 20 parts by mass of first short fibers, 1 part by mass of first co-crosslinking agent), Example 16 is an example of a toothed belt in which the amount of first short fibers contained in the first rubber layer was reduced to 10 parts by mass. This is an example in which the content of first short fibers and first co-crosslinking agent, which affect the elastic modulus (reinforcement) of the first rubber layer, was verified at a level near the lower limit of the reinforcement effect. Specifically, the first rubber layer was formed with R20 (crosslinked rubber) with a tensile modulus of 4.3 MPa, and the second rubber layer was formed with R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa, and the ratio of the tensile moduli of the two layers was 1.1. In terms of dynamic performance, the jumping torque (relative value) was at the same level as Comparative Example 1, which was 0.95 (C rating), but the endurance run (running time until failure (relative value)) reached the passing level of 1.24 (B rating), and the overall judgment was a passing grade (C rank), confirming the reinforcement effect.

[0273] (Examples 17, 18) Compared to Example 1 (R8: 20 parts by mass of first short fibers, 1 part by mass of first co-crosslinking agent), Example 17 is an example of a toothed belt in which the amount of first short fibers contained in the first rubber layer is increased to 50 parts by mass. Specifically, the first rubber layer is formed of R21 (crosslinked rubber) with a tensile modulus of 9.5 MPa, and the second rubber layer is formed of R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa, with a ratio of tensile moduli of the two layers being 2.5. In terms of dynamic performance, the jumping torque (relative value) was 1.00 (grade b), and the endurance run (running time until failure (relative value)) reached a passing level of 1.30 (grade a), resulting in an overall passing grade (rank B).

[0274] Furthermore, Example 18 is an example of a toothed belt in which the type of first short fiber in Example 17 is changed to a meta-aramid fiber. Specifically, the first rubber layer is formed of R22 (crosslinked rubber) with a tensile modulus of 10 MPa, and the second rubber layer is formed of R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa, with a ratio of tensile moduli of the two layers of 2.6. In terms of dynamic performance, the jumping torque (relative value) reached a passing level of 1.00 (grade b), and the endurance run (running time until failure (relative value)) reached a passing level of 1.51 (grade a), resulting in an overall passing grade (rank B). It can be said that there is no significant difference in the reinforcing effect even when the type of short fiber is changed.

[0275] (Examples 19-21) Compared to Example 3 (R10: 20 parts by mass of nylon short fibers, 6 parts by mass of the first co-crosslinking agent), which had the best durability and running performance, Example 19 is an example of a toothed belt in which the type of first short fiber is changed to meta-aramid fiber. Specifically, the first rubber layer is formed of R23 (crosslinked rubber) with a tensile modulus of 14 MPa, and the second rubber layer is formed of R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa, with a ratio of tensile moduli of 3.7 between the two layers. In terms of dynamic performance, the jumping torque (relative value) reached an acceptable level of 1.12 (a rating), and the running durability (running time to failure (relative value)) reached an acceptable level of 2.11 (a rating), resulting in an overall rating of A, the same level as Example 3.

[0276] Example 20 is an example of a toothed belt in which the type of the first short fiber is changed to para-aramid fiber. Specifically, the first rubber layer is formed of R24 (crosslinked rubber) with a tensile modulus of 14.8 MPa, and the second rubber layer is formed of R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa, with a ratio of tensile moduli of 3.9 between the two layers. In terms of dynamic performance, the jumping torque (relative value) reached an acceptable level of 1.15 (a rating), and the endurance run (running time until failure (relative value)) reached an acceptable level of 1.39 (a rating), resulting in an overall passing grade (A rank).

[0277] Example 21 is an example of a toothed belt in which the type of first short fiber is changed to PBO fiber. Specifically, the first rubber layer is made of R25 (crosslinked rubber) with a tensile modulus of 13 MPa, and the second rubber layer is made of R2 (crosslinked rubber) with a tensile modulus of 3.8 MPa, with a ratio of tensile moduli of 3.4 between the two layers. In terms of dynamic performance, the jumping torque (relative value) reached an acceptable level of 1.12 (a rating), and the endurance run (running time until failure (relative value)) reached an acceptable level of 1.85 (a rating), resulting in an overall passing rating (A rank).

[0278] It was confirmed that changing the type of short fiber provides a reinforcing effect in both jumping torque and durability (extended lifespan).

[0279] (Examples 22-24) This is an example of verifying the relationship between the area ratio of the first rubber layer to the total area of ​​the rubber layer constituting the tooth (hereinafter referred to as the area ratio) and the elastic modulus of the first rubber layer (the proportion of first short fibers contained in the first rubber layer) in a cross-sectional view of the tooth. Example 22 is an example near the lower limit of the reinforcing effect (when the area ratio is small and the proportion of first short fibers is also small), with an area ratio of 10% and 5 parts by mass of first short fibers (tensile modulus of elasticity 10.8 MPa). Conversely, Examples 23 and 24 are examples near the upper limit of the reinforcing effect (when the area ratio is large and the proportion of first short fibers is also large), with an area ratio of 60% and 50 parts by mass of first short fibers (tensile modulus of elasticity 14 MPa) in Example 23, and an area ratio of 80% and 50 parts by mass of first short fibers (tensile modulus of elasticity 14 MPa) in Example 24.

[0280] Regarding dynamic performance, the jumping torque (relative value) was 1.00 (Example 22: grade b), 1.28 (Example 23: grade a), and 1.35 (Example 24: grade a), all of which were within the acceptable range.

[0281] On the other hand, the endurance test (running time until failure (relative value)) was 1.13 (Example 22: grade b), 1.28 (Example 23: grade a), and 1.05 (Example 24: grade c), all of which were within the acceptable range, indicating that the reinforcement effect was present.

[0282] Based on the overall assessment, the toothed belts in Examples 22-24 met the passing standard (A-C rank).

[0283] (Example 25, Comparative Example 9) This is an example of a toothed belt in which the second rubber layer uses a rubber composition with a different tensile modulus, compared to the configuration of Example 3, which had the best durability among Examples 1 to 6. Specifically, while Example 3 used R2 (tensile modulus 3.8 MPa, ratio of tensile modulus of the two layers 3.7), Example 25 used R1 (tensile modulus 2.4 MPa, ratio of tensile modulus of the two layers 5.8), and Comparative Example 9 used R7 (tensile modulus 16.8 MPa, ratio of tensile modulus of the two layers 0.8) to form the second rubber layer.

[0284] Regarding dynamic performance, the jumping torque (relative value) was 1.09 (Example 25: grade a) and 1.37 (Comparative Example 9: grade a), both of which were within acceptable limits, indicating that the reinforcement effect was present.

[0285] The endurance test (running time until failure (relative value)) was 1.88 (Example 25: grade a) and 0.42 (Comparative Example 9: grade d). Example 25 met the passing standard, indicating a reinforcement effect. On the other hand, Comparative Example 9 failed.

[0286] Based on the overall assessment, the toothed belt in Example 25 met a high level of compliance (Rank A). On the other hand, in Comparative Example 9, where the tensile modulus of the second rubber layer was increased to be greater than that of the first rubber layer, the running life was short and it failed (Rank D).

[0287] (Examples 26, 27) Examples 26 and 27 are examples of toothed belts in which the rubber composition of the first rubber layer is changed, compared to Example 25 (R1: tensile modulus 2.4 MPa), in which the tensile modulus of the second rubber layer is relatively small. In Example 26, the first rubber layer is R8 (crosslinked rubber) with a tensile modulus of 5.3 MPa. The resulting toothed belt has a tensile modulus ratio of 2.2 between its two layers. The jumping torque (relative value) reached 1.02 (grade A), and the endurance run (running time until failure (relative value)) reached 1.23 (grade B), achieving an overall passing grade (rank B).

[0288] Furthermore, Example 27 is a toothed belt with a 2-layer tensile modulus ratio of 9.8, in which the first rubber layer is formed of R13 (cross-linked rubber) with a tensile modulus of 23.5 MPa. The jumping torque (relative value) was 1.16 (grade a), and the endurance run (running time until failure (relative value)) was 1.24 (grade b), resulting in an overall passing grade (rank B).

[0289] (Comparative Example 10) Comparative Example 10 is an example of a toothed belt in which the rubber composition of the first rubber layer is changed, compared to Comparative Example 9 (R7: tensile modulus 16.8 MPa, ratio of tensile modulus of the two layers 0.8), in which the tensile modulus of the second rubber layer is relatively large. Comparative Example 10 is a toothed belt in which the first rubber layer is formed of R8 (crosslinked rubber) with a tensile modulus of 5.3 MPa, and the ratio of tensile modulus of the two layers is 0.3. The jumping torque (relative value) was 1.19 (grade a), but the endurance run (running time until failure (relative value)) was 0.74 (grade d), which was a failure. Similar to Comparative Example 9, the tensile modulus of the second rubber layer was greater than that of the first rubber layer, resulting in an overall failure (rank D).

[0290] (Example 28) Example 28 is an example of a toothed belt that does not use a reinforcing inorganic filler (carbon black), unlike Example 3, which had the best durability among Examples 1 to 27 (first rubber layer is R10, second rubber layer is R2). Specifically, the first rubber layer is R27 (tensile modulus of elasticity 13.9 MPa), which is the composition obtained by removing carbon black from R10, and the second rubber layer is R26 (tensile modulus of elasticity 3.8 MPa), which is the composition obtained by removing carbon black from R2, and the crosslinked rubber composition is used to form the toothed belt. The jumping torque (relative value) was 1.10 (grade A), and the durability (running time until failure (relative value)) was 2.07 (grade A), and the overall evaluation was at a passing level (rank A), equivalent to Example 3.

[0291] (Examples 29, 30) Examples 29 and 30 are examples of toothed belts in which tooth cloth is not provided on the surface of the teeth and tooth roots of the belt, compared to Example 3 (20 parts by mass of the first short fiber) and Example 14 (50 parts by mass of the first short fiber), respectively. In Example 29, the jumping torque (relative value) was 1.15 (grade A), and the endurance run (running time until failure (relative value)) was 2.03 (grade A), resulting in an overall passing level (A rank) equivalent to Example 3. In Example 30, the jumping torque (relative value) was 1.10 (grade A), and the endurance run (running time until failure (relative value)) was 1.29 (grade A), resulting in an overall passing level (A rank) equivalent to Example 14.

[0292] From the above results, it was confirmed that by forming a first rubber layer along the tooth fabric and a second rubber layer formed between the first rubber layer and the core wire, and by adjusting the elastic modulus of the first rubber layer to be greater than that of the second rubber layer, and by incorporating short fibers into the first rubber layer oriented in the longitudinal direction of the belt along the contour of the teeth, the inherently conflicting rigidity and flexibility of the teeth can be reconciled, thereby suppressing jumping (tooth skipping) during belt operation and preventing tooth loss (tooth chipping), making it suitable for extending the lifespan during high-load operation.

[0293] <Examples 31-40 and Comparative Examples 11-13> Table 14 shows the tooth structure (layer structure) and the rubber composition used in each rubber layer of the toothed belts produced in Examples 31-40 and Comparative Examples 11-13.

[0294] (Comparative Example 11) Except for using R16 as the uncrosslinked rubber sheet forming the first rubber layer and R8 as the uncrosslinked rubber sheet forming the second rubber layer, toothed belts were manufactured in the same manner as in Comparative Example 1.

[0295] (Examples 31-36 and Comparative Example 12) In Examples 31-36 and Comparative Example 12, toothed belts were manufactured in the same manner as in Comparative Example 11, except that R20 and R28-R33 were used as the uncrosslinked rubber sheets forming the second rubber layer, respectively.

[0296] (Example 37) A toothed belt was manufactured in the same manner as in Example 7, except that the uncrosslinked rubber sheet forming the first rubber layer was R16 and the uncrosslinked rubber sheet forming the second rubber layer was R28.

[0297] (Example 38) A toothed belt was manufactured in the same manner as in Example 37, except that R32 was used as the uncrosslinked rubber sheet forming the second rubber layer.

[0298] (Example 39) A toothed belt was manufactured in the same manner as in Example 10, except that the uncrosslinked rubber sheet forming the first rubber layer was R16 and the uncrosslinked rubber sheet forming the second rubber layer was R28.

[0299] (Example 40) A toothed belt was manufactured in the same manner as in Example 39, except that R32 was used as the uncrosslinked rubber sheet forming the second rubber layer.

[0300] (Comparative Example 13) A toothed belt was manufactured in the same manner as in Comparative Example 1, except that only one type of uncrosslinked rubber sheet, R28 (sheet thickness 1.70 mm), was used to form the teeth.

[0301] [Bending stiffness test] Bending stiffness was evaluated using the same method as in Examples 1-30 and Comparative Examples 1-10.

[0302] [Tooth stiffness (shear) test] (Tooth stiffness test conditions) Similar to the tooth stiffness tests in Examples 1-30 and Comparative Examples 1-10, as shown in Figure 6, the teeth of the toothed belt 1 were hooked onto the projection 21a of a tooth shearing jig (a rigid body simulating the tooth shape of a toothed pulley) 21. With one tooth held down with constant pressure (tightening torque of 0.98 cN·m per 1 mm width), the belt was pulled at a speed of 1 mm / min using an autograph to apply a tooth load until the fracture (tooth loss) peak. The slope of the approximate straight line (N / mm) obtained by linear approximation from the relationship between the tooth load (N) per 12 mm width and the displacement (mm) was defined as the tooth shear index. The measurement data for Examples 32-33, 36 and Comparative Example 13 are shown in Figure 9. The results of calculating the slope of the approximate straight line to the fracture peak in Figure 9 using the approximation formula settings of commercially available spreadsheet software (Microsoft Excel) are shown in Figure 10 and Table 13. In the graph of Figure 10, the following are the relationships (relationships that can be read from the graph) where the displacement (mm) is on the x-axis and the tooth load (N) is on the y-axis.

[0303] Example 32: y = 505.11x + 64.82 Example 33: y = 378.87x + 178.21 Example 36: y = 338.06x - 62.93 Comparative Example 13: y = 619.01x - 147.95

[0304] [Table 13]

[0305] Furthermore, Figure 11 shows a bar graph comparing the tooth shear index, which is the slope of the approximate straight line obtained in Figure 10. A larger tooth shear index indicates greater rigidity (deformation resistance) of the tooth portion. The shape of the projection 21a was manufactured to fit with the tooth portion 1a and tooth root portion 1b of the toothed belt 1. The criteria for determining tooth rigidity are shown below.

[0306] (Criteria for determining tooth rigidity) a: Tooth shear index of 400 N / mm or less b: Tooth shear index greater than 400 N / mm and less than or equal to 600 N / mm c: Tooth shear index exceeds 600 N / mm

[0307] [Jumping Test] The jumping torque was measured using the same method as in Examples 1-30 and Comparative Examples 1-10, and evaluated as a relative value with the jumping torque value of Comparative Example 2 (112 N·m) set to 1.00.

[0308] [Endurance driving test] The running life was measured using the same method as in Examples 1-30 and Comparative Examples 1-10, and evaluated as a relative value with the running time of Comparative Example 2 (159 hours) set to 1.00.

[0309] [Reverse bending durability test] (Driving test conditions) As shown in Figure 12, a toothed belt was mounted on a running test machine equipped with a drive pulley DR (24 teeth), a driven pulley DN (24 teeth), a tension pulley Ten (24 teeth), and a bending idler pulley ID (70 mm diameter). The running time until failure (loss of teeth) occurred in the toothed belt was measured as the running life. The toothed belt was mounted with a tension of 260 N, the drive pulley rotated at 4900 rpm, the driven pulley was loaded at 10.0 kW, and the ambient temperature was 25 °C (room temperature). The machine was run for 48 hours. The tensile strength of the toothed belt after running was measured, and the strength retention rate (retention rate) was calculated relative to the tensile strength of the unrunned toothed belt. A higher retention rate indicated a belt with superior durability against reverse bending (flexural fatigue resistance).

[0310] (Criteria for determining reverse bending durability) a: Tensile strength retention rate of 90% or more (pass) b: Tensile strength retention rate of 70% or more (pass) c: Tensile strength retention rate is 50% or more (pass) d: Tensile strength retention rate is less than 50% (failure)

[0311] [Measurement of belt tensile strength] The method for measuring the tensile strength of a toothed belt in a reverse bending durability test is as follows: A strip-shaped test piece measuring 12 mm in width and 300 mm in length was taken from the toothed belt, and the tensile strength of each test piece was measured using a tensile testing machine (Autograph AG-1). In the test, both ends of the test piece were gripped with a chuck, and the test piece was pulled at a tensile speed of 50 mm / min at an ambient temperature of 23°C. The tensile strength at which the belt broke was defined as the tensile strength of the belt.

[0312] [Overall assessment] Considering the level of reinforcement effect in terms of jumping torque in jumping tests, endurance in endurance driving tests, and reverse bending endurance in reverse bending endurance tests, the overall superiority or inferiority was determined (ranked) according to the following criteria. Then, from the perspective of product practicality, ranks A, B, and C were considered acceptable, and rank D was considered unacceptable.

[0313] Rank A: All three of the above tests received an A grade. Rank B: Includes a B grade in the three tests listed above (but does not include C or D grades). Rank C: Includes a C grade in the above three tests (but does not include a D grade). Rank D: Includes a D rating in any of the three tests listed above.

[0314] Table 14 shows the verification results for the toothed belts in the examples and comparative examples.

[0315] [Table 14]

[0316] (Comparative Example 13) Comparative Example 13 is an example where the entire rubber layer of the tooth is a single-layer structure and the tooth shear index is 619 N / mm. However, it had low jumping torque, durability during driving, and reverse bending durability during driving, and the overall rating was D.

[0317] (Comparative Example 11) Comparative Example 11 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 5.3 MPa and the tooth shear index is 610 N / mm. Compared to Comparative Example 13, although the jumping torque and endurance running performance were improved, the bending stiffness was 800 MPa (grade c), which was unacceptable, and the reverse bending endurance running performance was low, similar to Comparative Example 13, resulting in an overall grade of D.

[0318] (Examples 31-36) Example 31 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 4.3 MPa and the tooth shear index is 580 N / mm. Compared to Comparative Example 11, the bending rigidity and reverse bending endurance during running were improved, and the overall evaluation was rank C.

[0319] Example 32 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 3.8 MPa and the tooth shear index is 505 N / mm. Compared to Comparative Example 11, the bending rigidity and reverse bending endurance during running were improved, and the overall evaluation was rank C.

[0320] Example 33 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 2.6 MPa and the tooth shear index is 378 N / mm. Compared to Example 32, the bending rigidity and reverse bending endurance during running were improved, and the overall evaluation was rank B.

[0321] Example 34 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 2.1 MPa and the tooth shear index is 365 N / mm. Compared to Example 33, the reverse bending endurance during running was further improved, and the overall evaluation was A rank.

[0322] Example 35 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 1.9 MPa and the tooth shear index is 355 N / mm. Compared to Example 33, the reverse bending endurance during running was further improved, and the overall evaluation was A rank.

[0323] Example 36 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 1.4 MPa and the tooth shear index is 338 N / mm. Compared to Comparative Example 11, the bending rigidity and reverse bending endurance during running were improved, and the overall evaluation was rank C. (Comparative Example 12) Comparative Example 12 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 0.8 MPa and the tooth shear index is 320 N / mm. However, the jumping torque was lower compared to Example 36, and the overall evaluation was rank D.

[0324] (Examples 37, 38) Examples 37 and 38 are examples in which the area ratio of the second rubber layer is larger compared to Examples 31-36.

[0325] Example 37 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 3.8 MPa and the tooth shear index is 400 N / mm. Compared to Example 32, which has the same tensile modulus, the bending stiffness was improved, but the overall evaluation was C rank, similar to Example 32.

[0326] Example 38 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 1.4 MPa and the tooth shear index is 330 N / mm. However, similar to Example 36, which had the same tensile modulus, the overall evaluation was rank C.

[0327] The results from Examples 37 and 38 showed that when the area ratio of the second rubber layer is large, the overall flexibility of the teeth increases. However, both Example 37, which had a relatively large tensile modulus of elasticity in the belt width direction of the second rubber layer, and Example 38, which had a relatively small tensile modulus, were still classified as a C grade, which is an acceptable level.

[0328] (Examples 39, 40) Examples 39 and 40 are examples in which the area ratio of the second rubber layer is smaller compared to Examples 31-36.

[0329] Example 39 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 3.8 MPa and the tooth shear index is 595 N / mm. Compared to Example 32, which has the same tensile modulus, the durability of the running performance was reduced, but the overall evaluation was the same as Example 32, with a rank of C.

[0330] Example 40 is an example in which the tensile modulus of the second rubber layer in the belt width direction is 1.4 MPa and the tooth shear index is 560 N / mm. Compared to Example 36, which has the same tensile modulus, the jumping torque improved, but the durability running and reverse bending durability running decreased, and the overall rating was C, similar to Example 36.

[0331] The results from Examples 39 and 40 showed that when the area ratio of the second rubber layer is small, the overall rigidity of the teeth increases. However, even in Example 39, where the tensile modulus of elasticity in the belt width direction of the second rubber layer is relatively large, and in Example 40, where it is relatively small, the results were still at an acceptable level of C.

[0332] The results from Examples 31 to 40 confirmed that the effects of the present invention can be obtained over a wide range of area ratios between the first rubber layer and the second rubber layer. [Industrial applicability]

[0333] The toothed belt (meshing transmission belt or toothed transmission belt) of the present invention, when combined with a toothed pulley, can be used in various fields where synchronization between input and output is required, such as power transmission mechanisms in vehicles such as automobiles and motorcycles, power transmission mechanisms in industrial machinery such as motors and pumps, machinery such as automatic doors and automated machines, photocopiers and printers. In particular, it can be used as a power transmission belt (timing belt or cogged belt) for rear-wheel drive in industrial machinery for high-load (high-horsepower) applications and motorcycles. [Explanation of symbols]

[0334] 1…Toothed belt 1a...teeth part 1b...Root of the tooth 1c...back 2… Toothcloth 3…First rubber layer 3a...First short fiber 4…Second rubber layer 5… Core wire 6... Back rubber layer

Claims

1. The back portion has a core wire embedded in it that extends along the circumference of the belt, The inner circumferential surface of the back portion is provided with a plurality of teeth formed at intervals in the circumferential direction of the belt, A toothed belt comprising a back rubber layer formed on the outer circumference side of the belt relative to the core wire, and a first rubber layer and a second rubber layer formed on the inner circumference side of the belt relative to the core wire, The back portion includes the back rubber layer, The modulus of elasticity of the first rubber layer is greater than that of the second rubber layer. The tensile modulus of the second rubber layer in the belt width direction is 1.0 to 4.5 MPa. The first rubber layer is formed of a first crosslinked rubber composition comprising a first rubber component and first short fibers. The proportion of the first short fibers is 5 to 60 parts by mass per 100 parts by mass of the first rubber component. The first short fibers are oriented along the contour of the teeth in the longitudinal direction of the belt, and A toothed belt in which the teeth portion includes the first rubber layer and the second rubber layer interposed between the first rubber layer and the core wire.

2. The toothed belt according to claim 1, wherein the area ratio of the first rubber layer is 10 to 80 area % of the total area of ​​the first rubber layer and the second rubber layer in a cross-sectional view in the circumferential direction of the belt.

3. The tensile strength of the first rubber layer in the belt circumferential direction is 40 to 90 MPa. The tensile modulus of the first rubber layer in the belt width direction is 4 to 25 MPa, and The toothed belt according to claim 1 or 2, wherein the tensile strength of the second rubber layer in the belt circumferential direction is 10 to 50 MPa.

4. The toothed belt according to claim 1 or 2, wherein the tensile modulus of the first rubber layer in the belt width direction is 1.1 to 10 times that of the second rubber layer in the belt width direction.

5. The toothed belt according to claim 1 or 2, wherein the first short fiber is a polyamide fiber.

6. The first crosslinked rubber composition further comprises a first crosslinking agent and a first co-crosslinking agent, The second rubber layer is formed of a second crosslinked rubber composition comprising a second rubber component, a second crosslinking agent, and a second co-crosslinking agent. The first rubber component comprises a first composite polymer containing hydrogenated nitrile rubber and an unsaturated carboxylic acid metal salt. The second rubber component comprises a second composite polymer containing hydrogenated nitrile rubber and an unsaturated carboxylic acid metal salt. The proportion of the first co-crosslinking agent is 1 to 40 parts by mass per 100 parts by mass of the first rubber component, and The toothed belt according to claim 1 or 2, wherein the proportion of the second co-crosslinking agent is 0.2 to 25 parts by mass per 100 parts by mass of the second rubber component.

7. The toothed belt according to claim 6, wherein the second crosslinked rubber composition further comprises second short fibers, and in the second crosslinked rubber composition, the proportion of the second short fibers is 5 parts by mass or less per 100 parts by mass of the second rubber component.

8. The first crosslinked rubber composition further comprises a first reinforcing inorganic filler, The second crosslinked rubber composition further comprises a second reinforcing inorganic filler, The proportion of the first composite polymer is 80% by mass or more in the first rubber component. The proportion of the second composite polymer is 30% by mass or more in the second rubber component. The first crosslinking agent contains a first organic peroxide, and the proportion of the first organic peroxide is 1 to 20 parts by mass per 100 parts by mass of the first rubber component. The second crosslinking agent contains a second organic peroxide, and the proportion of the second organic peroxide is 0.5 to 5 parts by mass per 100 parts by mass of the second rubber component. The proportion of the first reinforcing inorganic filler is 10 parts by mass or less per 100 parts by mass of the first rubber component, and The toothed belt according to claim 6, wherein the proportion of the second reinforcing inorganic filler is 10 parts by mass or less per 100 parts by mass of the second rubber component.

9. A toothed belt according to claim 1 or 2, wherein the tooth shear index, which is the slope of an approximate straight line showing the relationship between tooth load and displacement, is 300 to 600 N / mm.

10. A toothed belt transmission mechanism comprising a toothed belt according to claim 1 or 2 and a pulley, wherein the toothed belt is mounted on the pulley in a running layout that bends in the reverse direction.

11. A method for manufacturing a toothed belt according to claim 1 or 2, comprising: a first rubber layer precursor preparation step of preparing an uncrosslinked rubber sheet in which first short fibers are oriented in one direction on the sheet surface as a first rubber layer precursor for forming a first rubber layer; and a pre-forming step of laminating the first rubber layer precursor and a second rubber layer precursor, which is an uncrosslinked rubber sheet for forming a second rubber layer, in an arrangement in which the first short fibers are oriented in the longitudinal direction of the belt, to produce a semi-crosslinked pre-molded body.

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