Toothed belt and method for manufacturing the same

Abstract

The present application relates to a toothed belt having a back portion in which a core wire extending in the belt circumferential direction is embedded, and two or more tooth portions formed at intervals in the belt circumferential direction on the inner peripheral surface of the back portion, comprising a back rubber layer formed on the outer peripheral side of the belt with respect to the core wire, and a first rubber layer and a second rubber layer formed on the inner peripheral side of the belt with respect to the core wire, and the inner peripheral surface of the belt is composed of a tooth cloth, in which the back portion comprises the back rubber layer, the elastic modulus of the first rubber layer is greater than the elastic modulus of the second rubber layer, the tooth portion comprises the tooth cloth, the first rubber layer formed along the tooth cloth, and the second rubber layer sandwiched between the first rubber layer and the core wire.

Description

Technical Field

[0001] This invention relates to a rubber toothed belt (or a rubber toothed belt covered with toothed cloth) that is useful for synchronously transmitting power under high load conditions in general industrial machinery and the like when meshing with a toothed pulley. 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 multi-ribbed belts, while examples of meshing belts include toothed belts. Toothed belts have: a back with core wires embedded approximately parallel to the belt's circumference; teeth spaced at predetermined intervals along the belt's circumference; and a toothed cloth covering the teeth. Power is transmitted by the teeth of the toothed belt engaging with pulleys that have grooves corresponding to the teeth. Because there is no slippage between the toothed belt and the pulley, it can reliably transmit power even under high loads. In recent years, its use in industrial machinery, automotive internal combustion engines, and rear-wheel drive systems for motorcycles has increased, especially with the miniaturization of machinery, requiring toothed belts that correspond to miniaturization (smaller diameter pulleys and narrower widths). If miniaturized toothed belts are used in the same environment as conventional large toothed belts, the load on the belt is higher. Therefore, there is a need for highly durable toothed belts that can withstand higher loads while still being miniaturized.

[0003] Among the key factors for the durability of toothed belts is the rigidity (resistance to deformation) of the teeth. During meshing with a toothed pulley, if the teeth repeatedly deform due to contact with the pulley, it can lead to problems such as poor meshing due to tooth slippage (tooth skipping) and missing teeth due to cracking at the tooth root. The mechanism of missing teeth is believed to be that, in the failure mode where the teeth detach from the belt body, the stress concentrated at the tooth root due to repeated deformation first forms tiny cracks at the root, which then grow. Especially when toothed belts are used under high loads, the stress concentrated at the tooth root is particularly high, making it easy for cracks to originate at the root and lead to missing teeth.

[0004] Therefore, to suppress tooth deformation, it is necessary to increase rigidity. On the other hand, if the rigidity of the teeth is increased, the bending rigidity of the belt also increases, and the flexibility decreases. If the toothed pulleys are miniaturized (smaller diameter) along with the miniaturization of machinery, then high flexibility (softness) is also required to achieve good meshing by winding around the small-diameter pulleys. The treatment method of increasing tooth rigidity to improve flexibility is not suitable.

[0005] That is, in toothed belts, the rigidity (resistance to deformation) and flexibility (flexibility) of the teeth are inversely related and difficult to balance. Therefore, a treatment method is needed to achieve a balance between the two.

[0006] Japanese Patent Application Publication No. 2011-85160 (Patent Document 1) discloses a toothed belt in which a toothed belt with an intermediate canvas having an elastic modulus of 100 GPa or more in the width direction is embedded inside a belt body having teeth and tooth bases alternately arranged on one side along the length direction. The tooth is described as being formed by a core rubber layer constituting the inside of the tooth and a toothed rubber layer arranged along the outer periphery of the tooth and stacked on one side of the core rubber layer, and the modulus of the core rubber layer is higher than the modulus of the toothed rubber layer.

[0007] In addition, International Publication No. 2011 / 045984 (Patent Document 2) discloses a toothed belt that has a belt body having teeth and tooth bases alternately arranged on one surface along the length direction. As the belt body, the belt body has a toothed rubber layer arranged along the outer periphery of the teeth and a core rubber layer constituting the interior of the teeth, and the modulus of the core rubber layer is higher than that of the toothed rubber layer.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2011-85160

[0011] Patent Document 2: International Publication No. 2011 / 045984 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, for the toothed belts in Patent Documents 1 and 2, it is difficult to balance the rigidity and flexibility of the teeth.

[0014] Therefore, the object of the present invention is to provide a toothed belt and a method thereof that can take into account both the rigidity (resistance to deformation) and the flexibility (flexibility) of the teeth.

[0015] Methods for solving problems

[0016] To achieve the aforementioned objectives, the inventors focused on the layer structure (distribution of mechanical properties) within the rubber layer constituting the teeth, and conducted in-depth research on methods to achieve a balance between the rigidity (resistance to deformation) and flexibility (flexibility) of the teeth, which are inversely related, while ensuring the rigidity of the teeth under conditions of higher load tolerance. The results showed that by forming a toothed band from a toothed fabric, a first rubber layer formed along the toothed 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, both the rigidity and flexibility of the teeth can be balanced, thus completing the present invention.

[0017] That is, the toothed belt [1] of the present invention has a back portion with a core wire embedded therein extending along the belt circumferential direction and two or more teeth spaced apart in the belt circumferential direction on the inner circumferential surface of the back portion, comprising a back rubber layer formed on the outer circumferential side of the belt relative to the core wire and a first rubber layer and a second rubber layer formed on the inner circumferential side of the belt relative to the core wire, and the inner circumferential surface of the belt is made of toothed cloth, wherein,

[0018] The aforementioned back includes the aforementioned back rubber layer.

[0019] The elastic modulus of the first rubber layer is greater than that of the second rubber layer.

[0020] The aforementioned toothed portion includes the aforementioned toothed cloth, the aforementioned first rubber layer formed along the aforementioned toothed cloth, and the aforementioned second rubber layer sandwiched between the aforementioned first rubber layer and the aforementioned core wire.

[0021] The present invention [2] is as follows: the area ratio of the first rubber layer in the circumferential cross-sectional view is 10 to 80% of the total area of ​​the first rubber layer and the second rubber layer.

[0022] The present invention [3] is as follows: in the above-mentioned method [1] or [2], the tensile elastic modulus of the first rubber layer is 0.6 to 20 MPa, and the tensile elastic modulus of the second rubber layer is 0.5 to 5 MPa.

[0023] The present invention [4] is as follows: in any one of the above methods [1] to [3], the tensile elastic modulus of the first rubber layer is 1.2 to 4 times that of the tensile elastic modulus of the second rubber layer.

[0024] The present invention [5] is as follows: In any one of the above methods [1] to [4], the first rubber layer is formed from a first crosslinked rubber composition comprising a first rubber component, a first crosslinking agent, and a first co-crosslinking agent.

[0025] The second rubber layer is formed from a second crosslinked rubber composition comprising a second rubber component, a second crosslinking agent, and a second co-crosslinking agent.

[0026] The aforementioned first rubber component contains a first composite polymer comprising hydrogenated nitrile butadiene rubber and an unsaturated carboxylic acid metal salt.

[0027] The aforementioned second rubber component contains a second composite polymer comprising hydrogenated nitrile butadiene rubber and an unsaturated carboxylic acid metal salt.

[0028] The proportion of the first co-crosslinking agent is 1 to 40 parts by mass relative to 100 parts by mass of the first rubber component, and

[0029] The proportion of the second co-crosslinking agent is 0.2 to 25 parts by mass relative to 100 parts by mass of the second rubber component.

[0030] The present invention [6] is as follows: In the above-described [5],

[0031] The aforementioned first crosslinked rubber composition further comprises a first reinforcing inorganic filler.

[0032] The aforementioned second crosslinked rubber composition further comprises a second reinforcing inorganic filler.

[0033] The proportion of the first composite polymer in the first rubber component is 80% by mass or more.

[0034] The proportion of the second composite polymer in the second rubber component is 30% by mass or more.

[0035] The first crosslinking agent mentioned above comprises a first organic peroxide, wherein the proportion of the first organic peroxide is 1 to 20 parts by mass relative to 100 parts by mass of the first rubber component.

[0036] The second crosslinking agent mentioned above comprises a second organic peroxide, wherein the proportion of the second organic peroxide is 0.5 to 5 parts by mass relative to 100 parts by mass of the second rubber component.

[0037] The proportion of the first reinforcing inorganic filler is less than 10 parts by mass relative to 100 parts by mass of the first rubber component, and

[0038] The proportion of the second reinforcing inorganic filler is 10 parts by mass or less relative to 100 parts by mass of the second rubber component.

[0039] In this invention, as a method [7], a method for manufacturing a toothed belt according to any one of the methods [1] to [6] above is also included, which includes a preforming step of making a preform, the preform being formed by stacking a toothed cloth precursor for forming a toothed cloth, an uncrosslinked rubber sheet for forming a first rubber layer and an uncrosslinked rubber sheet for forming a second rubber layer.

[0040] Invention Effects

[0041] In this invention, the teeth of the toothed belt are formed by a toothed cloth constituting the inner circumferential surface of the belt, a first rubber layer formed along the toothed cloth, and a second rubber layer formed between the first rubber layer and the core wire. The elastic modulus of the first rubber layer is adjusted to be greater than that of the second rubber layer. Therefore, while ensuring the rigidity of the teeth under conditions of higher loads, the rigidity and flexibility of the teeth in a contradictory relationship can be considered. Thus, this invention provides a toothed belt that can suppress tooth slippage during belt operation while also improving belt durability. This toothed belt can also suppress tooth defects (missing teeth) caused by tooth slippage, achieving a long service life under high loads. Attached Figure Description

[0042] Figure 1 This is a partial cross-sectional perspective view showing an example of the toothed belt of the present invention.

[0043] Figure 2 yes Figure 1 A schematic cross-sectional view of the toothed band.

[0044] Figure 3 It is used for explanation Figure 1 A schematic cross-sectional view illustrating the function of the teeth in the toothed belt.

[0045] Figure 4 This is a schematic diagram illustrating the method for determining tooth rigidity in an embodiment.

[0046] Figure 5 This is a graph illustrating an example of measurement data from the tooth rigidity test method used to illustrate the embodiments.

[0047] Figure 6 This is a schematic cross-sectional view of the teeth of the toothed belt obtained in the embodiment. Detailed Implementation

[0048] <toothed band>

[0049] Hereinafter, an example of the toothed belt of the present invention will be described in detail with reference to the accompanying drawings, as needed.

[0050] Figure 1 This is a partial cross-sectional perspective view showing an example of the toothed band of the present invention. Figure 2 yes Figure 1A schematic cross-sectional view of a toothed belt. The toothed belt 1 in this example is an annular meshing transmission belt, comprising a back surface 1c with a core wire 5 embedded therein extending in the belt circumferential direction, and two or more teeth 1a arranged at predetermined intervals on the inner circumferential surface of the back surface 1c and extending in the belt width direction. The belt surface (inner circumferential surface) on the tooth side is formed by toothed cloth 2. The back surface 1c has a back rubber layer 6 disposed on the outer circumferential surface side of the core wire 5, forming the outer circumferential surface of the belt. Furthermore, the toothed belt 1 of the present invention has a first rubber layer (surface rubber layer) 3 and a second rubber layer (inner rubber layer) 4 on the inner circumferential surface side of the core wire 5, between the toothed cloth 2 and the core wire 5. The first rubber layer 3 is disposed along the contour of the toothed cloth 2 on the inner circumferential surface of the belt (in contact with the toothed cloth 2), and the second rubber layer 4 is sandwiched 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 elastic modulus (especially tensile elastic modulus) than the second rubber layer 4.

[0051] Between adjacent tooth portions 1a, there is a flat tooth base 1b, and the tooth portions 1a and the tooth bases 1b are formed alternately along the inner circumferential direction of the belt. That is, the surface of the tooth portion 1a and the inner circumferential surface of the back 1c (i.e., the surface of the tooth base 1b) are composed of a continuous sheet of toothed cloth 2.

[0052] It should be noted that, in this application, the toothed fabric forming the surface of the tooth is a structural element of the tooth, while the toothed fabric forming the surface of the tooth base is a structural element of the back. Furthermore, each toothed fabric forming the tooth is a portion of a continuous toothed fabric. Figure 2 (part of the toothed cloth 2).

[0053] In this example, the circumferential cross-sectional shape of the tooth portion 1a is approximately trapezoidal. Furthermore, the circumferential surface of the tooth portion 1a, with its approximately trapezoidal cross-section, is formed by the aforementioned toothed fabric 2, consisting of a first rubber layer 3 formed along the toothed fabric 2 and a second rubber layer 4 formed between the first rubber layer 3 and the core wire 5. It should be noted that at the tooth bottom 1b, a first rubber layer serving as an outer rubber layer and a second rubber layer serving as an inner rubber layer (not shown) are also sandwiched between the toothed fabric 2 and the core wire 5. Compared to the thickness of the first rubber layer 3 and the second rubber layer 4 in the tooth portion 1a, the thickness of the first rubber layer and the second rubber layer at the tooth bottom is extremely thin.

[0054] The aforementioned core wires 5 extend in the length direction (circumferential direction) of the belt and are spaced apart in the width direction of the belt. The gaps between adjacent core wires 5 can be formed by a cross-linked rubber composition constituting the back rubber layer 6 and / or the second rubber layer (especially the cross-linked rubber composition constituting the back rubber layer 6).

[0055] Toothed belts are used in high-load transmission applications such as industrial machinery, automotive internal combustion engines, and rear-wheel drive systems for motorcycles. For example, when a toothed belt is wound between a drive pulley (toothed pulley) and a driven pulley (toothed belt pulley), power is transmitted from the drive pulley side to the driven pulley side by the rotation of the drive pulley.

[0056] It should be noted that the toothed belt of the present invention is not limited to... Figure 1 and 2 The method and structure are shown. For example, two or more teeth are sufficient as long as they can mesh with the toothed pulley. The cross-sectional shape of the teeth (the circumferential cross-sectional shape of the toothed belt) is not limited to an approximate trapezoid; for example, it can also be a semi-circle, a semi-ellipse, or a polygon (triangle, quadrilateral (rectangle, trapezoid, etc.)). Among these, from the viewpoint of meshing transmission performance, a trapezoidal or approximate trapezoidal shape is preferred.

[0057] In the toothed belt (inner circumferential side of the core wire) of the present invention, the area ratio of the first rubber layer in a cross-sectional view along the belt circumferential direction (belt length direction) relative to the total area of ​​the first rubber layer and the second rubber layer is, for example, 10 to 80% area, preferably 20 to 70% area, and more preferably 30 to 60% area. If this area ratio is too small, the rigidity (deformation resistance) of the teeth may be insufficient; conversely, if it is too large, the bending rigidity of the belt may be high and the flexibility (flexibility) may be insufficient.

[0058] In the toothed belt of the present invention, the average distance between the centers of adjacent teeth in the circumferential direction (tooth pitch, reference) Figure 2 The tooth pitch can range from 2 to 25 mm, depending on the shape of the toothed pulley. The value of the tooth pitch also corresponds to the size of the tooth section (the circumferential length of the tooth section and the tooth height). That is, the larger the tooth pitch, the larger the size of the tooth section. Especially in applications involving high loads, large tooth sections are required; the tooth pitch can be 5 mm or more, preferably 8 mm or more, and even more preferably 14 mm or more.

[0059] Furthermore, the average tooth height of the teeth is preferably 40-70% and more preferably 50-65% of the average thickness of the belt as a whole.

[0060] It should be noted that, in this application, if Figure 2 As shown, the average tooth height refers to the average height of the teeth protruding from the inner circumference of the belt (the average height of the teeth protruding from the bottom of the tooth).

[0061] [Teeth]

[0062] The surface of the teeth is made of toothed fabric, comprising a first rubber layer disposed along the contour of the teeth on the surface side (inner surface side) in contact with the toothed fabric, and a second rubber layer disposed on the inner side in contact with the first rubber layer. The first and second rubber layers are formed of different cross-linked rubber compositions, with the first rubber layer having a relatively large elastic modulus and the second rubber layer having a relatively small elastic modulus. In the toothed belt of the present invention, by giving the cross-linked rubber composition forming the teeth such a two-layer structure, both the rigidity and flexibility of the teeth can be balanced. For its mechanism, see [reference needed]. Figure 3 This will be explained. It should be noted that, in this application, the rubber layer forming the teeth refers to the rubber layer sandwiched between the core wire and the toothed fabric. Furthermore, the first and second rubber layers, which form the teeth, are collectively referred to as the toothed rubber layer.

[0063] The inventors have discovered that within the toothed section, the portion affecting flexibility (flexibility) is the interior of the second rubber layer, particularly section C located at the lower part of the core wire 5. Specifically, it was found that if the interior of the toothed section, particularly section C, is a high-rigidity (high elastic modulus) rubber layer, flexibility (flexibility) decreases. Therefore, in the toothed belt of the present invention, to ensure high flexibility, the second rubber layer located within the toothed section, particularly the second rubber layer 4 containing section C, is adjusted to have relatively low rigidity (low elastic modulus).

[0064] Furthermore, the inventors discovered that within the toothed section, the areas affecting deformation resistance are the vicinity of the toothed fabric corresponding to the first rubber layer, particularly section A located on the side of the tooth and section B located near the tooth base. Specifically, it was found that if sections A and B are rubber layers with low rigidity (low elastic modulus), deformation resistance decreases. More specifically, section A, being the side of the tooth, is the part that contacts the pulley and bears the maximum load (impact), therefore, it is effective for the crosslinked rubber composition in section A to have high rigidity (high elastic modulus). On the other hand, section B, being the root near the tooth base, is the part that first develops micro-cracks due to repeated deformation (the starting point of missing teeth), therefore, it is effective for the crosslinked rubber composition in section B to have high rigidity (high elastic modulus). Therefore, in the toothed belt of the present invention, to ensure deformation resistance, the first rubber layer 3, containing sections A and B, is adjusted to have relatively high rigidity (high elastic modulus).

[0065] From the viewpoint of resistance to deformation, as long as at least parts A and B are formed of high-rigidity rubber, the top of the tooth (the part at the tooth tip) does not need to be formed of high-rigidity rubber. In contrast, in the toothed belt of the present invention, from the viewpoint of high productivity and the ability to achieve high resistance to deformation, the first rubber layer at the top is also formed of high-rigidity rubber.

[0066] The tensile modulus of elasticity of the first rubber layer can be selected in the circumferential direction from about 0.6 MPa to about 20 MPa, for example, 2 to 15 MPa (e.g., 3 to 12 MPa), preferably 2 to 10 MPa (e.g., 2 to 8 MPa), further preferably 3 to 8 MPa (e.g., 3 to 7 MPa), more preferably 4 to 7 MPa, and most preferably 4 to 6 MPa. If the tensile modulus of elasticity is too small, the rigidity of the teeth may decrease and the resistance to deformation may decrease; conversely, if it is too large, the flexibility of the belt, especially the winding (meshing) property towards the smaller diameter pulley, may decrease.

[0067] The tensile modulus of elasticity of the second rubber layer is, for example, 0.5 to 5 MPa in the circumferential direction, preferably 1 to 4 MPa, more preferably 1.5 to 3.5 MPa, and even more preferably 1.5 to 3 MPa. If the tensile modulus of elasticity is too small, the resistance to deformation may be reduced; conversely, if it is too large, the flexibility of the belt, especially its winding (engagement) with the smaller diameter pulley, may be reduced.

[0068] The tensile modulus of elasticity of the first rubber layer is greater than that of the second rubber layer. The ratio of the tensile modulus of elasticity of the first rubber layer to that of the second rubber layer (tensile modulus of elasticity of the first rubber layer / tensile modulus of elasticity of the second rubber layer) can be 1.2 to 4, preferably 1.5 to 3.5, more preferably 1.5 to 3 (e.g., 2 to 3), more preferably 1.6 to 2.7, and most preferably 1.7 to 2.5. By making the ratio of the tensile modulus of elasticity of the two layers within this range, a balance can be achieved between the rigidity (resistance to deformation) and the bending (flexibility) of the tooth portion, which are in a reverse relationship, thus achieving a balance.

[0069] It should be noted that, in this application, the tensile modulus of elasticity (modulus) of the first and second rubber layers is measured using the value of the "tensile stress at 1% elongation" of each rubber layer, which can be determined according to the method of JIS K6251 (2017). Specifically, it can be measured using the method described in the embodiments described later.

[0070] The compressive modulus of the first rubber layer can be selected from the range of about 0.5 MPa to about 2 MPa, for example, 0.8 to 1.6 MPa, preferably 1 to 1.5 MPa, more preferably 1.2 to 1.48 MPa, more preferably 1.3 to 1.45 MPa, and most preferably 1.3 to 1.4 MPa. If the compressive modulus is too small, the rigidity of the teeth may decrease and the resistance to deformation may decrease; conversely, if it is too large, the flexibility of the belt, especially the winding (meshing) property towards the small-diameter pulley, may decrease.

[0071] The compressive modulus of the second rubber layer is, for example, 0.3 to 1.5 MPa, preferably 0.5 to 1.3 MPa, more preferably 0.7 to 1.25 MPa, and even more preferably 0.8 to 1.2 MPa. If the compressive modulus is too small, the resistance to deformation may decrease; conversely, if it is too large, the belt's flexibility, especially its winding (engagement) with smaller diameter pulleys, may decrease.

[0072] The compressive elastic modulus of the first rubber layer is greater than that of the second rubber layer. The ratio of the compressive elastic modulus of the first rubber layer to that of the second rubber layer (compressive elastic modulus of the first rubber layer / compressive elastic modulus of the second rubber layer) can be 1.05 to 1.7 (e.g., 1.2 to 1.7), preferably 1.1 to 1.65 (e.g., 1.25 to 1.65), more preferably 1.15 to 1.6 (e.g., 1.3 to 1.6, more preferably 1.4 to 1.58, and most preferably 1.42 to 1.5). By making the ratio of the compressive elastic modulus of the two layers within this range, a balance can be achieved between the rigidity (resistance to deformation) and the bending (flexibility) of the tooth portion, which is in a reverse relationship, thus achieving a balance.

[0073] It should be noted that, in this application, the compressive modulus of the first and second rubber layers is measured using the value of the "compressive stress at 2% compressive strain" of each rubber layer, which can be determined according to the method of JIS K6254 (2016). Specifically, it can be measured using the method described in the embodiments below.

[0074] The shape of the first rubber layer is not particularly limited as long as it follows the layered structure formed along the toothed fabric; it is not limited to... Figures 1-3 The layer shape with uneven thickness shown (i.e., a shape in which the layer thickness is greatest at the top or center of the tooth and decreases towards the bottom of the tooth in a cross-sectional view along the length of the tooth) can be a layer shape with uniform thickness. Among these, from the viewpoint of productivity, a layer shape with uneven thickness (especially a shape in which the layer thickness is greatest at the top or center of the tooth and decreases towards the bottom of the tooth in a cross-sectional view along the length of the tooth) is preferred.

[0075] In the tooth section, the area percentage of the first rubber layer relative to the combined area of ​​the first and second rubber layers in a cross-sectional view along the belt length (circumferential direction) is selected from approximately 5% to approximately 85% of the total area, for example, 10% to 80%, preferably 20% to 70%, and more preferably 30% to 60%. If this area percentage is too small, the rigidity (deformation resistance) of the tooth section may be insufficient, and the belt's running performance and durability will also decrease; conversely, if it is too large, the belt's bending rigidity may become high, its flexibility (flexibility) insufficient, and its durability will also decrease. In applications where belt durability is important, the above-mentioned area percentage is preferably 15% to 65%, and more preferably 20% to 60%.

[0076] The shape of the second rubber layer is not limited to an approximate trapezoid formed between the first rubber layer and the core wire. It can also be a layered shape formed along the first rubber layer, or an approximate trapezoid formed along the first rubber layer and between other rubber layers and the core wire. From the viewpoint of improving the flexibility of the teeth, the shape that connects to the core wire is preferred, that is, the approximate trapezoid formed between the first rubber layer and the core wire, or the approximate trapezoid formed between the aforementioned other rubber layers and the core wire. The approximate trapezoid formed between the first rubber layer and the core wire is particularly preferred.

[0077] The rubber hardness Hs of the first rubber layer (the first cross-linked rubber composition constituting the first rubber layer), measured in D-type hardness, is, for example, 70-85 degrees, preferably 75-83 degrees, more preferably 76-82 degrees, more preferably 77-82 degrees, and most preferably 77-80 degrees. If the hardness is too low, the rigidity of the teeth may decrease, resulting in reduced resistance to deformation; conversely, if the hardness is too high, the flexibility of the belt, especially its winding (meshing) property towards the smaller diameter pulley, may decrease.

[0078] The rubber hardness Hs of the second rubber layer (the second cross-linked rubber composition constituting the second rubber layer), measured in D-type hardness, is, for example, 60 to 80 degrees (e.g., 60 to 66 degrees), preferably 62 to 78 degrees (e.g., 62 to 66 degrees), more preferably 63 to 75 degrees, more preferably 63 to 72 degrees, and most preferably 63 to 70 degrees (especially 63 to 66 degrees). If the hardness is too low, the resistance to deformation may decrease; conversely, if it is too high, the flexibility of the belt, especially its winding (engagement) with smaller diameter pulleys, may decrease.

[0079] It should be noted that in this application, the D-type hardness of the first and second rubber layers is determined using a D-type hardness tester according to the hardness test of a spring-type hardness tester as specified in JIS K 6253 (2012) (Vulcanized rubber and thermoplastic rubber - Method for determining hardness -), sometimes abbreviated as rubber hardness. More specifically, it can be determined by the method described in the examples below, and can be used as the hardness of the rubber sheet obtained by crosslinking the rubber composition used to form the belt.

[0080] Typically, the hardness of rubber compositions is mostly determined using Type A hardness (a value measured using a Type A hardness tester). However, when the value measured using a Type A hardness tester exceeds 90 degrees, a Type D hardness tester is preferred. In the toothed belt of the present invention, the hardness of the rubber layer constituting the teeth is higher than the hardness 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.

[0081] Within the scope of not impairing the effects of the present invention, the tooth portion may include other rubber layers besides the first and second rubber layers. Examples of other rubber layers include, for instance, an adhesive rubber layer sandwiched between the tooth cloth and the first rubber layer, and an intermediate rubber layer sandwiched between the first and second rubber layers. The adhesive rubber layer may be a layer used to improve the adhesion between the tooth cloth and the first rubber layer. Furthermore, the intermediate rubber layer may be a layer having a tensile modulus of elasticity smaller than that of the first rubber layer and larger than that of the second rubber layer. Preferably, the adhesive rubber layer (third rubber layer) is used. The thickness of the adhesive rubber layer should be sufficient to 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, 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.

[0082] As for the tooth structure, it is preferable to have a structure that only includes an adhesive rubber layer as other layers, and it is particularly preferable to have a structure that does not include other layers, that is, a structure consisting of a toothed cloth covering the circumferential surface, a first rubber layer formed along the toothed cloth, and a second rubber layer formed between the first rubber layer and the core wire.

[0083] (Cross-linked rubber composition)

[0084] The first and second rubber layers can be formed from cross-linked rubber compositions commonly used in toothed belt rubber compositions. The cross-linked rubber composition can be a cross-linked rubber composition containing rubber components. By appropriately adjusting the composition, the mechanical properties such as the elastic modulus of each layer constituting the rubber layer, particularly the first and second rubber layers, can be adjusted. There are no particular limitations on the method for adjusting the elastic modulus; it can be adjusted by changing the composition and / or type of the components constituting the composition. From the viewpoint of simplicity, it is preferable to adjust by changing the proportion and / or type of cross-linking agents, short fibers, and fillers.

[0085] (A) Rubber composition

[0086] Rubber components (first rubber component and second rubber component) that form the crosslinked rubber composition of the first and second rubber layers can include, for example, 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 terpolymer (EPDM), etc.), chlorosulfonated polyethylene rubber (CSM), alkylated chlorosulfonated polyethylene rubber (ACSM), epichlorohydrin rubber, acrylic rubbers, silicone rubbers, urethane rubbers, fluororubbers, etc.]. These rubber components can be carboxylated, such as carboxylated SBR and carboxylated NBR. Two or more of these rubber components can be used alone or in combination.

[0087] Particularly preferred rubber components are hydrogenated nitrile butadiene rubber (HNBR), and chloroprene rubber (CR) and ethylene-propylene-diene terpolymer (EPDM) are also preferred. Especially for applications involving high loads, preferred rubber components are those with high heat aging resistance, particularly carboxyl-modifiable hydrogenated nitrile butadiene rubber (HNBR) (hereinafter, this also includes carboxylated hydrogenated nitrile butadiene rubber, sometimes simply referred to as hydrogenated nitrile butadiene rubber). The proportion of the above-mentioned preferred rubber components in the rubber component is preferably 50% by mass or more (for example, about 80% to about 100% by mass), particularly preferably 100% by mass. The carboxyl-modifiable hydrogenated nitrile butadiene rubber can be partially hydrogenated or fully hydrogenated. The hydrogenation rate of the carboxyl-modifiable hydrogenated nitrile butadiene rubber can be selected from the range of about 50% to about 100%, and can be 70% to 100%.

[0088] It should be noted that, in this application, HNBR refers to a rubber whose heat resistance is improved by chemically hydrogenating the unsaturated bonds (carbon-carbon double bonds) of conventional nitrile rubber to prevent the aging of rubber elasticity caused by the recombination reaction of sulfur during heat aging, while maintaining the advantages of conventional nitrile rubber, namely oil resistance.

[0089] The iodine value (unit: mg / 100mg) of HNBR is, for example, 5 to 60 (e.g., 7 to 50), preferably 8 to 40 (e.g., 8 to 35), and more preferably 10 to 30.

[0090] It should be noted that in this application, the iodine value is an indicator of the amount of unsaturated bonds. The higher the iodine value, the more unsaturated bonds are contained in the polymer molecular chain. The iodine value is determined by adding excess iodine to the test sample to allow it to react completely (so that the iodine reacts with the unsaturated bonds) and then quantifying the amount of remaining iodine using redox titration. If the iodine value of HNBR is low, the cross-linking reaction between HNBR molecules may be insufficient, resulting in lower rigidity of the cross-linked rubber and thus reduced resistance to deformation during belt running. On the other hand, if the iodine value of HNBR is high, the amount of unsaturated bonds may be excessively increased, leading to thermal and oxidative degradation of the cross-linked rubber and a shorter belt life.

[0091] The rubber component preferably contains at least hydrogenated nitrile butadiene rubber that can be carboxylated. The proportion of such hydrogenated nitrile butadiene rubber in the rubber component can be 80–100% by mass, preferably 90–100% by mass, and more preferably 100% by mass.

[0092] The rubber component preferably contains a composite polymer or polymer alloy comprising hydrogenated nitrile butadiene rubber and an unsaturated carboxylic acid metal salt (hereinafter referred to as "HNBR containing unsaturated carboxylic acid metal salt"). It should be noted that, 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 improve the elastic modulus and hardness of the teeth, and can inhibit rubber deformation and crack growth.

[0093] Unsaturated carboxylic acid metal salts can be compounds formed by ionic bonding of unsaturated carboxylic acids with one or more carboxyl groups to a metal.

[0094] Unsaturated carboxylic acids, as metal salts of unsaturated carboxylic acids, can include, for example, 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.

[0095] Metals that are unsaturated carboxylic acid metal salts can be exemplified by polyvalent metals, such as Group 2 elements (magnesium, calcium, etc.), Group 4 elements (titanium, zirconium, etc.), and Groups 8 to 14 elements (e.g., iron, cobalt, nickel, copper, zinc, aluminum, tin, lead, etc.). These metals can also be used alone or in combination of two or more. Preferred metals are Group 2 elements (magnesium, etc.) and Group 12 elements (zinc, etc.).

[0096] Preferred unsaturated carboxylic acid metal salts include zinc (meth)acrylate and magnesium (meth)acrylate. Two or more unsaturated carboxylic acid metal salts may also be used alone or in combination.

[0097] The mass ratio of hydrogenated nitrile rubber to unsaturated carboxylic acid metal salt can be selected from a range of about 100 / 80 to about 100 / 180, preferably 100 / 85 to 100 / 175, and more preferably 100 / 90 to 100 / 175. If the proportion of unsaturated carboxylic acid metal salt is too small, the elastic modulus and hardness of the crosslinked rubber composition (or teeth) may decrease; conversely, if it is too large, the processability and flexibility of the belt will decrease.

[0098] It should be noted that the HNBR containing unsaturated carboxylic acid metal salts described above can be commercially available. For example, a substance obtained by highly dispersing zinc methacrylate, which is an unsaturated carboxylic acid metal salt, in the HNBR can be used (e.g., manufactured by Zeoforte Co., Ltd. of Japan, under the trade name "Zeoforte (ZSC)").

[0099] Furthermore, HNBR containing unsaturated carboxylic acid metal salts is preferably used in the form of a mixture with hydrogenated nitrile butadiene rubber (HNBR) that does not contain unsaturated carboxylic acid metal salts. The mass ratio of hydrogenated nitrile butadiene rubber to unsaturated carboxylic acid metal salt can be adjusted by mixing commercially available HNBR containing unsaturated carboxylic acid metal salts with commercially available hydrogenated nitrile butadiene rubber. The modulus of elasticity and hardness can be adjusted by changing the mixing ratio of the two.

[0100] The proportion of HNBR containing unsaturated carboxylic acid metal salts can be 10% by mass or more of 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 containing unsaturated carboxylic acid metal salts in the first rubber layer is preferably 80% by mass or more (especially 100% by mass) of the rubber component (first rubber component), and in the second rubber layer is preferably 30% by mass or more (especially 100% by mass) of the rubber component (second rubber component). These proportions can be those specified in the trade name "Zeoforte (ZSC)".

[0101] As other rubber components combined with HNBR containing unsaturated carboxylic acid metal salts, at least one is preferably selected from the group consisting of HNBR, EPDM, and CR. The proportion of other rubber components in the 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.

[0102] To ensure the tightness between the layers, the first rubber layer and the second rubber layer preferably contain the same series or the same type of rubber components, more preferably the same type of rubber components, and even more preferably the same rubber components.

[0103] (B) Filler Compounds

[0104] The crosslinked rubber composition (first crosslinked rubber composition and second crosslinked rubber composition) may also contain filler compounding agents (fillers). Examples of filler compounding agents (first filler compounding agent and second filler compounding agent) include reinforcing inorganic fillers, non-reinforcing fillers, short fibers, etc.

[0105] 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 alone or in combination of two or more. The reinforcing inorganic fillers can be in powder form.

[0106] The average particle size (average primary particle size) of the carbon black is, for example, 5–200 nm, preferably 10–150 nm, more preferably 20–100 nm, and even more preferably 30–80 nm. The iodine adsorption capacity of the carbon black is, for example, 5–200 mg / g, preferably 10–150 mg / g, more preferably 15–100 mg / g, and even more preferably 20–80 mg / g.

[0107] Silica includes dry silica, wet silica, and surface-treated silica. Furthermore, silica can also be classified according to its manufacturing method, such as dry-process silica, wet-process silica, colloidal silica, and precipitated silica. These silicas can be used alone or in combination of two or more. Among these silicas, silica with surface silanol groups (silicic anhydride, hydrated silicic acid) is preferred, as hydrated silicic acid with more surface silanol groups has a stronger chemical bonding force with rubber components.

[0108] The average particle size (average primary particle size) of silica is, for example, 1 to 500 nm, preferably 3 to 300 nm, more preferably 5 to 100 nm, and even more preferably 10 to 50 nm.

[0109] In addition, the nitrogen adsorption specific surface area of ​​silica obtained by the BET method is, for example, 50–400 m². 2 / g, preferably 100-300m 2 / g, further preferably 150-200m 2 / g.

[0110] It should be noted that, 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) through image analysis of electron microscope images containing scanning electron microscope images.

[0111] The proportion of the reinforcing inorganic filler relative to 100 parts by weight of the rubber component can be 10 parts by weight or less, preferably 5 parts by weight or less, more preferably 1 part by weight or less, and more preferably 0 parts by weight. When the reinforcing inorganic filler is used as needed, the proportion of the reinforcing inorganic filler relative to 100 parts by weight of the rubber component can be, for example, 0.1 to 8 parts by weight, preferably 0.5 to 5 parts by weight, and more preferably 1 to 3 parts by weight. If the proportion of the reinforcing inorganic filler is too high, the heat generation of the rubber composition increases and the heat resistance decreases, which may lead to cracking and tooth loss due to thermal degradation.

[0112] Examples of non-reinforcing fillers 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 a portion of silicon is replaced by polyvalent metal atoms, such as aluminum silicate, magnesium silicate, magnesium aluminum silicate, etc.; minerals with silicates as the main component, such as clay containing aluminum silicate, talc and mica containing magnesium silicate, etc.), zinc barium white, silica sand, etc. These non-reinforcing fillers can be used alone or in combination of two or more.

[0113] The preferred non-reinforcing filler is at least one selected from calcium carbonate, magnesium carbonate, aluminum hydroxide, barium sulfate, and silicates [alumina silicate, magnesium silicate, magnesium aluminum silicate, etc.; silicate minerals (talc, clay, mica, etc.)]. Furthermore, from the viewpoint of greatly improving the processability of the belt, the dispersibility of the compounding agents, and minimizing the occurrence of poor dispersion of the compounding agents, the non-reinforcing filler preferably contains at least one selected from talc containing calcium carbonate, magnesium silicate, or magnesium silicate, and clay containing aluminum silicate or aluminum silicate; calcium carbonate is particularly preferred. Commercially available powdered fillers used as rubber fillers can be used as non-reinforcing fillers.

[0114] The average particle size (average primary particle size) of the non-reinforcing filler can be selected from, for example, a range of about 0.01 μm to about 25 μm (e.g., about 0.2 μm to about 20 μm), preferably about 0.5 μm to about 17 μm (e.g., about 1 μm to about 15 μm). The average particle size (average primary particle size) of the non-reinforcing filler can 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 can be relatively large. Furthermore, the average particle size (average primary particle size) of the non-reinforcing filler can 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). It should be noted that, depending on the type of non-reinforcing filler, such as magnesium silicate or its minerals, the non-reinforcing filler may be pulverized or crushed during the mixing process with rubber components, etc. The average particle size of such non-reinforced fillers with pulverizing or crushing properties can be the average particle size before mixing with rubber components, etc. Non-reinforced fillers in each crosslinked rubber composition generally have an average particle size within the above range (e.g., 0.1 to 10 μm, preferably 0.5 to 5 μm, more preferably 1 to 3 μm).

[0115] It should be noted that, in this application, the average particle size of the non-reinforcing filler can be determined as the volume average particle size using a laser diffraction particle size distribution measuring device. Additionally, the average particle size of nanoscale fillers can be calculated as the arithmetic mean particle size of an appropriate number of samples (e.g., 50 samples) through image analysis of electron microscope images containing scanning electron microscope (SEM) photographs.

[0116] The proportion of the non-reinforcing filler is, for example, 70 parts by weight or less, preferably 40 parts by weight or less, and more preferably 30 parts by weight or less, relative to 100 parts by weight of the rubber component. When using a non-reinforcing filler as required, the proportion of the non-reinforcing filler relative to 100 parts by weight of the rubber component can be, for example, 3 to 70 parts by weight, preferably 5 to 40 parts by weight, and more preferably 10 to 30 parts by weight. If the proportion of the non-reinforcing filler is too high, the dispersibility of the compounding agents may become poor.

[0117] In the process of preparing uncrosslinked rubber sheets by calendering a rubber composition compounded using a Banbury mixer or similar machine using rollers or a calender, short fibers can be oriented (arranged) in a predetermined direction. In the rubber layer constituting the teeth, it is preferable that the orientation direction of the short fibers is oriented circumferentially towards the belt. Furthermore, the short fibers are preferably arranged such that the side closest to the teeth is oriented along the contour of the teeth, and that the short fibers are oriented approximately parallel to the core wire as they approach the core wire.

[0118] Examples of short fibers include: polyolefin fibers (polyethylene fibers, polypropylene fibers, etc.), polyamide fibers [aliphatic polyamide fibers (nylon fibers), aromatic polyamide fibers, etc. such as polyamide 6 fibers, polyamide 66 fibers, polyamide 46 fibers, etc.], polyester fibers [polyalkylene aryl fibers (e.g., polyethylene terephthalate (PET) fibers, polypropylene terephthalate (PTT) fibers, polybutylene terephthalate (PBT) fibers, polyethylene naphthalate (PEN) fibers, etc. C] 2-4 Alkylene C 8-14 Aromatic ester fibers; polyaryl ester fibers, liquid crystal polyester fibers, and other fully aromatic polyester fibers, etc.; vinylon fibers, polyvinyl alcohol fibers, poly(p-phenylene benzo[a]pyrene) Synthetic fibers such as polyoxoyl oxynitride (PBO) fiber; natural fibers such as cotton, linen, and wool; regenerated cellulose fibers such as rayon and cellulose ester fibers; and inorganic fibers such as carbon fiber and glass fiber. These short fibers can be used alone or in combination of two or more. In particular, fibers with high elastic modulus, such as polyamide fiber, PBO fiber, glass fiber, and carbon fiber, are preferred, and aliphatic polyamide fiber (nylon fiber) or aromatic polyamide fiber, such as PBO fiber, are even more preferred.

[0119] The average fiber diameter of the short fibers is, for example, 1–100 μm (e.g., 3–70 μm), preferably 5–50 μm (e.g., 7–30 μm), more preferably 10–25 μm (particularly 12–20 μm). The average fiber length of the short fibers is, for example, 0.3–10 mm (e.g., 0.5–7 mm), preferably 1–5 mm (particularly 2–4 mm). If the average fiber diameter of the short fibers is too small or the average fiber length is too long, it may be impossible to uniformly disperse the short fibers; if the average fiber diameter is too large or the average fiber length is too short, the mechanical properties of each rubber layer may be reduced.

[0120] Adding short fibers can improve the elastic modulus and hardness of the crosslinked rubber composition. However, it can also cause microcracks at the interface between the rubber component and the short fibers. Therefore, it is necessary to adjust the proportions to a suitable level. The proportion of short fibers is 10 parts by weight or less per 100 parts by weight of the rubber component, preferably 7 parts by weight or less, and more preferably 5 parts by weight or less.

[0121] Furthermore, it is preferable to perform a conventional adhesive treatment (or surface treatment) on the short fibers, attaching an adhesive component to at least a portion of the surface of the short fibers. This adhesive treatment improves the adhesion between the short fibers and the rubber component, suppressing the generation of microcracks originating at the interface between the short fibers and the rubber component. Examples of adhesive treatments include those using epoxy compounds (or epoxy resins), polyisocyanates, silane coupling agents, and resorcinol-formaldehyde-latex (RFL).

[0122] The proportion of filler compounding agents is, for example, 3 to 70 parts by mass relative to 100 parts by mass of rubber component, preferably 5 to 50 parts by mass, more preferably 10 to 40 parts by mass, and more preferably 20 to 30 parts by mass.

[0123] (C) Crosslinking agents

[0124] The rubber composition contains a crosslinking agent (vulcanizing agent) for crosslinking the rubber components. Co-crosslinking agents, crosslinking aids (vulcanizing aids), crosslinking accelerators (vulcanizing accelerators), and crosslinking delay agents (vulcanizing delay agents) may be added as needed. Preferably, the crosslinking compounding agents (first crosslinking compounding agent and second crosslinking compounding agent) 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.

[0125] As a crosslinking agent (first crosslinking agent and second crosslinking agent), conventional components can be used depending on the type of rubber component, such as organic peroxides, sulfur crosslinking agents, metal oxides, etc.

[0126] Examples of organic peroxides (first and second organic peroxides) include: di-tert-butyl peroxide, dicumyl peroxide, tert-butylcumyl peroxide, 1,1-tert-butylperoxide-3,3,5-trimethylcyclohexane, 1,3-bis(tert-butylperoxide-isopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexyn-3, 1,3-bis(tert-butylperoxide-diisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxide)hexane, tert-butylperoxidebenzoate, tert-butylperoxide-2-ethyl-hexyl carbonate, etc. These organic peroxides can be used alone or in combination of two or more.

[0127] Examples of sulfur-based crosslinking agents include: powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, and sulfur chlorides (sulfur monochloride, sulfur dichloride, etc.). These sulfur-based crosslinking agents can be used alone or in combination of two or more.

[0128] Examples of metal oxides include magnesium oxide, zinc oxide, and lead oxide. These metal oxides can be used alone or in combination of two or more.

[0129] The crosslinking agent can be appropriately selected according to the type of rubber component, with organic peroxides and metal oxides being preferred, and organic peroxides being particularly preferred.

[0130] The proportion of the crosslinking agent is, for example, 1 to 20 parts by mass relative to 100 parts by mass of the rubber component, preferably 3 to 15 parts by mass, and more preferably 5 to 10 parts by mass. If the proportion of the crosslinking agent is too small, the elastic modulus and hardness of the rubber composition will decrease; conversely, if the proportion is too large, the flexibility of the belt will decrease.

[0131] The proportion of the organic peroxide is selected relative to 100 parts by mass of the rubber component from about 0.5 parts by mass to about 20 parts by mass (e.g., about 1 part by mass to about 10 parts by mass), typically 1 to 5 parts by mass (e.g., 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 relative to 100 parts by mass of the first rubber component, preferably 1.5 to 10 parts by mass, and more preferably 1.5 to 4 parts by mass. In the second rubber layer, the proportion of the second organic peroxide is, for example, 0.5 to 5 parts by mass relative to 100 parts by mass of the second rubber component, preferably 0.8 to 4 parts by mass, and more preferably 1 to 3 parts by mass.

[0132] As co-crosslinking agents (crosslinking aids or co-vulcanizing agents), well-known crosslinking aids can be listed, 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., zinc (meth)acrylate, magnesium (meth)acrylate, etc., polyvalent metal salts of (meth)acrylate], oximes (e.g., quinone dioxime, etc.), guanidines (e.g., diphenylguanidine, etc.), polyfunctional (meth)acrylates [e.g., alkyl diol di(meth)acrylates such as ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, etc., alkyl diol di(meth)acrylates, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, etc., alkyl diol di(meth)acrylates, etc.] Hydrocarbon polyols [poly(meth)acrylates], bismaleimides (aliphatic bismaleimides, such as N,N'-1,2-ethylidene dimaleimide, N,N'-hexamethylene bismaleimide, 1,6'-bismaleimide-(2,2,4-trimethyl)cyclohexane and other alkylene bismaleimides; aromatic bismaleimides or aromatic bismaleimides, such as N,N'-m-phenylene dimaleimide, 4-methyl-1,3-phenylene dimaleimide, 4,4'-diphenylmethane dimaleimide, 2,2-bis[4-(4-maleimide phenoxy)phenyl]propane, 4,4'-diphenyl ether dimaleimide, 4,4'-diphenyl sulfone dimaleimide, 1,3-bis(3-maleimide phenoxy)benzene, etc.), etc. These co-crosslinking 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 (such as N,N'-m-phenylene dimaleimide and other aromatic bismaleimides or aromatic bismaleimides) are preferred, with bismaleimides being particularly preferred. By adding co-crosslinking agents (such as bismaleimides), the degree of crosslinking can be increased, thereby increasing the elastic modulus.

[0133] The proportion of co-crosslinking agents (crosslinking aids) such as bismaleimide relative to 100 parts by weight of rubber component, calculated in terms of solid content, is, for example, 0.2 to 40 parts by weight, preferably 0.5 to 30 parts by weight, more preferably 0.8 to 20 parts by weight, and even more preferably 1 to 15 parts by weight. In the first rubber layer, the proportion of co-crosslinking agent (first co-crosslinking agent) relative to 100 parts by weight of first rubber component is, for example, 1 to 40 parts by weight, preferably 2 to 30 parts by weight (e.g., 5 to 20 parts by weight), more preferably 2.5 to 18 parts by weight (e.g., 8 to 15 parts by weight), more preferably 3 to 14 parts by weight (e.g., 4 to 12 parts by weight), and most preferably 6 to 11 parts by weight (e.g., 5 to 7 parts by weight). In the second rubber layer, the proportion of the co-crosslinking agent (second co-crosslinking agent) is, for example, 0.2 to 25 parts by mass relative to 100 parts by mass of the second rubber component, preferably 0.5 to 10 parts by mass, more preferably 0.7 to 7 parts by mass (for example, 0.8 to 5 parts by mass), more preferably 0.8 to 4 parts by mass (for example, 0.8 to 3 parts by mass), and most preferably 0.8 to 2 parts by mass.

[0134] The proportion of the crosslinking compounding agent, calculated based on solid components, is, for example, 0.2 to 50 parts by weight of the rubber component per 100 parts by weight, preferably 0.5 to 40 parts by weight, more preferably 1 to 30 parts by weight, and even more preferably 2 to 20 parts by weight. In the first rubber layer, the proportion of the crosslinking compounding agent (first crosslinking compounding agent) is, for example, 1 to 40 parts by weight of the first rubber component per 100 parts by weight, preferably 5 to 20 parts by weight, and even more preferably 10 to 15 parts by weight. In the second rubber layer, the proportion of the crosslinking compounding agent (second crosslinking compounding agent) is, for example, 0.3 to 25 parts by weight of the second rubber component per 100 parts by weight, preferably 0.5 to 10 parts by weight, and even more preferably 1 to 5 parts by weight.

[0135] (D) Other compounding agents

[0136] Crosslinked rubber compositions may also contain additives commonly used in toothed rubber compositions. Commonly used additives include, for example: metal oxides (calcium oxide, barium oxide, iron oxide, copper oxide, titanium oxide, aluminum oxide, etc.), softeners (paraffin oil, cycloalkanes, etc.), 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, sebacic acid ester plasticizers, etc.), aromatic carboxylic acid ester plasticizers (phthalate ester plasticizers, trimellitate ester plasticizers, etc.), hydroxy carboxylic acid ester plasticizers, phosphate ester plasticizers, ether plasticizers, ether ester plasticizers, etc.], anti-aging agents (antioxidants, heat aging agents, flexural cracking agents, ozone deterioration agents, etc.), colorants, thickeners, plasticizers, coupling agents (silane coupling agents, etc.), stabilizers (UV absorbers, heat stabilizers, etc.), flame retardants, antistatic agents, etc. In addition, crosslinked rubber compositions may include adhesive modifiers (resorcinol-formaldehyde cocondensates, amino resins, etc.) as needed. These additives may be used alone or in combination of two or more.

[0137] (Preferred fit between the first rubber layer and the second rubber layer)

[0138] The elastic modulus of the first and second rubber layers can be adjusted by changing the proportions of specified components that affect the elastic modulus of the rubber layers. For example, the content of at least one component selected from filler compounding agents (fillers, short fibers) and crosslinking compounding agents [crosslinking agents, co-crosslinking agents (bismaleimides, etc.)] in the first rubber layer can be increased compared to that in the second rubber layer. In particular, in the toothed belt of the present invention, by adjusting the content of the co-crosslinking agent (especially bismaleimides), the elastic modulus (tensile elastic modulus) of the first and second rubber layers can be adjusted in a balanced and appropriate manner, thus taking into account both the rigidity (deformation resistance) and flexibility (flexibility) of the teeth, which are in an opposing relationship.

[0139] Furthermore, in the toothed belt of the present invention, in order to obtain the rigidity of the teeth that can withstand higher loads, it has a high elastic modulus, and in order to balance the rigidity (deformation resistance) and flexibility (flexibility) of the teeth in a reverse relationship, the following combination is preferred.

[0140] A preferred embodiment may be as follows: In the first rubber layer, the first rubber component comprises 80% by mass or more of HNBR containing an unsaturated carboxylic acid metal salt; relative to 100 parts by mass of the first rubber component, the proportion of the first reinforcing inorganic filler is 10 parts by mass or less, the proportion of the first short fiber is 5 parts by mass or less, the proportion of the bismaleimide as the first co-crosslinking agent is 1 to 40 parts by mass, and the proportion of the organic peroxide as the first crosslinking agent is 1 to 20 parts by mass; and in the second rubber layer, the second rubber component comprises 30% by mass or more of HNBR containing an unsaturated carboxylic acid metal salt; relative to 100 parts by mass of the second rubber component, the proportion of the second reinforcing inorganic filler is 10 parts by mass or less, the proportion of the second short fiber is 5 parts by mass or less, the proportion of the bismaleimide as the second co-crosslinking agent is 0.2 to 25 parts by mass, and the proportion of the organic peroxide as the second crosslinking agent is 0.5 to 5 parts by mass.

[0141] (Dental cloth)

[0142] The toothed fabric constituting the inner circumferential surface of the belt (the surfaces of the teeth and the base of the teeth) can be formed from fabrics such as woven fabric, knitted fabric, and non-woven fabric. Woven fabric (canvas) is conventionally the most common, consisting of warp yarns extending in the width direction of the belt and weft yarns extending in the circumferential direction. The weave of the woven fabric is not particularly limited as long as the warp and weft yarns are regularly intersected in the longitudinal and transverse directions; it can be any of the following: plain weave, twill weave (or bias weave), satin weave (satin weave), or a combination of these weaves. Preferred woven fabrics have twill and satin weave structures.

[0143] In addition to the same short fibers mentioned above, the fibers used as weft and warp yarns in forming the toothed fabric can also include polyphenylene ether fibers, polyether ether ketone fibers, polyether sulfone fibers, polyurethane fibers, etc. These fibers can be used alone or in combination of two or more. Among these fibers, general organic fibers are preferred, as are cellulose fibers such as cotton or rayon, polyester fibers (PET fibers, etc.), polyamide fibers (aliphatic polyamide fibers such as polyamide 66 fibers, aromatic polyamide fibers, etc.), PBO fibers, and fluoropolymer fibers [polytetrafluoroethylene (PTFE) fibers, etc.]. Furthermore, composite yarns of these fibers with elastic yarns that have stretchability (e.g., elastic yarns of polyurethane formed from elastic fibers with stretchability, processed yarns that have undergone stretching processing (e.g., wool processing, crimping processing, etc.)) are also preferred.

[0144] The form of warp and weft yarns is not particularly limited, and can be multifilament yarn (made by combining or twisting a single long fiber, i.e., monofilament yarn), multifilament yarn (made by twisting short fibers), or staple fiber yarn (made by twisting short fibers). The aforementioned multifilament yarn or staple fiber yarn can be a blended yarn or a mixed yarn using two or more types of fibers. The weft yarn preferably contains the aforementioned elastic yarn with stretchability. From a weaving point of view, the warp yarn usually does not contain elastic yarn in most cases. To ensure the compressibility of the toothed fabric in the circumferential direction of the belt, the weft yarn containing elastic yarn extends in the circumferential direction of the belt, and the warp yarn extends in the width direction of the belt.

[0145] The average diameter of the fiber (or yarn) is, for example, 1–100 μm (e.g., 3–50 μm), preferably 5–30 μm, and more preferably 7–25 μm. Regarding the average fiber diameter (fineness) of the yarn (twisted yarn), the weft yarn can, for example, be about 100 tex to about 1000 tex (particularly about 300 tex to about 700 tex), and the warp yarn can, for example, be about 50 tex to about 500 tex (particularly about 100 tex to about 300 tex). The density of the weft yarn (threads / cm) can, for example, be about 5 to about 50 (particularly about 10 to about 30), and the density of the warp yarn (threads / cm) can, for example, be about 10 to about 300 (particularly about 20 to about 100).

[0146] Woven fabrics can have multiple weave structures (such as double weave structures). In a weave with warp and weft yarns, at least a portion of the weft yarns can be formed from fibers with a low coefficient of friction (or low-friction fibers), such as fibers containing fluoropolymers (including composite yarns made of fibers formed from fluoropolymers such as PTFE). For example, the warp yarns can be formed from polyamide fibers such as nylon 66, polyester fibers, etc., and the weft yarns can be formed solely from fibers formed from the aforementioned fluoropolymers; the weft yarns can be formed from composite yarns of fibers formed from the aforementioned fluoropolymers and second fibers such as polyamide fibers, polyurethane fibers (elastic yarns); and the weft yarns can be formed from composite yarns of such composite yarns and second composite yarns formed from two or more of the aforementioned second fibers.

[0147] In this method, the weft yarn located on the surface side of the toothed cloth (the side that meshes with the toothed pulley) is preferably made of fluorinated fibers (e.g., PTFE fibers) with a low coefficient of friction to reduce friction between the toothed cloth and the toothed pulley. On the other hand, for the weft yarn located on the back side of the toothed cloth (the adhesive side to the toothed rubber layer), using fibers other than fluorinated fibers can improve the adhesive strength between the toothed cloth and the rubber constituting the teeth. With this type of toothed cloth, friction during meshing with the toothed pulley can be reduced, thus suppressing noise generation.

[0148] Furthermore, when using fluorinated fibers, it is preferable to arrange low-melting-point fibers with a melting point that melts at the crosslinking (vulcanization) temperature at the teeth and back of the fluorinated fibers, using rubber as a base material, around the fluorinated fibers. Specifically, in the form of composite yarn containing fluorinated fibers, there are forms in which fluorinated fibers and low-melting-point fibers are twisted together, and forms in which fluorinated fibers are covered by low-melting-point fibers. It should be noted that the crosslinking (vulcanization) conditions at the teeth and back are not particularly limited, and are generally performed at a crosslinking (vulcanization) temperature of 100 to 200°C for a crosslinking (vulcanization) time of about 1 minute to about 5 hours.

[0149] In a method where low-melting-point fibers are arranged around fluorinated fibers, the low-melting-point fibers melt during cross-linking (vulcanization) at the teeth and back, flow into the spaces between the fibers forming the toothed fabric, and then cool below their melting point, thereby crystallizing. Therefore, when inserted into or removed from the toothed pulley, the cutting or scattering of fluorinated fibers due to impact or abrasion on the surface of the toothed fabric is suppressed. If the weft yarn used in this manner is used as the toothed fabric of the toothed belt, the teeth and back can be protected for a longer period through the aforementioned effects, thus preventing tooth loss and achieving a longer lifespan under high-load operation.

[0150] The average thickness of the toothed cloth (the toothed cloth in the toothed belt) is, for example, 0.1 to 2 mm, preferably 0.2 to 1.5 mm. It should be noted that the average thickness of the toothed cloth as raw material (the toothed cloth before forming) is, for example, 0.5 to 3 mm, preferably 0.75 to 2.5 mm.

[0151] To improve adhesion to the first rubber layer, the fabric forming the toothed fabric can be subjected to an adhesive treatment. Examples of adhesive treatments include: immersing the fabric in an RFL treatment solution followed by heating and drying; treating the fabric with an epoxy compound or isocyanate compound; dissolving a rubber composition in an organic solvent to prepare a rubber paste, immersing the fabric in the rubber paste, and then heating and drying; and combinations of these treatments. These methods can be performed individually or in combination, and the order and number of treatments are not limited. For example, the fabric can be pretreated with an epoxy compound or isocyanate compound, then immersed in an RFL treatment solution, and then heated and dried.

[0152] Furthermore, to improve the adhesion between the toothed fabric and the first rubber layer, an uncrosslinked rubber sheet formed by calendering a rubber composition can be laminated on the back side (the adhesive side with the first rubber layer) of the fabric forming the toothed fabric. This rubber composition (the third crosslinked rubber composition) can be appropriately selected from the crosslinked rubber compositions exemplified as forming the aforementioned first and second rubber layers, and can be a conventional adhesive rubber composition. It should be noted that the uncrosslinked rubber sheet obtained from this rubber composition can form a third rubber layer (adhesive rubber layer) sandwiched between the toothed fabric and the first rubber layer within the toothed belt. The fabric subjected to the above adhesive treatment is referred to as the toothed fabric precursor.

[0153] [Base of teeth]

[0154] The tooth cloth forms the surface of the tooth and also forms the surface of the back of the tooth (the surface at the bottom of the tooth).

[0155] On the back side corresponding to the bottom of the tooth, a first rubber layer and a second rubber layer can be sandwiched between the toothed cloth and the core wire. However, only the first rubber layer can be sandwiched, or the toothed cloth can be in contact with the core wire without sandwiching the first and second rubber layers. Even when the first rubber layer is sandwiched on the back side corresponding to the bottom of the tooth, or when both the first and second rubber layers are sandwiched, the thickness of the first rubber layer and the thickness of the second rubber layer are both thinner than the tooth portion in either case.

[0156] [Back rubber layer]

[0157] The back has the aforementioned teeth and tooth bases formed on its inner circumferential surface, and a back rubber layer forming an outer circumferential surface on its outer circumferential surface. Furthermore, the aforementioned back rubber layer is formed of a cross-linked rubber composition (a fourth cross-linked rubber composition). Figures 1-3 In this configuration, the other surface (with a back side) of the side without the teeth is not covered with fabric (woven fabric, knitted fabric, nonwoven fabric, etc.), but may be covered as needed. Including the preferred configuration, the fabric can be selected from fabrics exemplified as toothed fabrics.

[0158] (Fourth crosslinked rubber composition)

[0159] From the viewpoint of reducing the bending stiffness of the belt, ensuring flexibility (winding with the pulley), and resisting bending fatigue, the hardness of the fourth cross-linked rubber composition is preferably lower than that of the first and second cross-linked rubber compositions constituting the teeth.

[0160] Specifically, the rubber hardness Hs of the fourth crosslinked rubber composition, measured in A-type hardness, is, for example, 80 to 89 degrees. By adjusting the A-type hardness of the back rubber layer to the above range, the flexural stiffness of the back layer is reduced, resulting in excellent resistance to flexural fatigue. If the A-type hardness of the fourth crosslinked rubber composition is too low, cracks may occur on the back layer due to impacts from foreign objects; conversely, if it is too high, the resistance to flexural fatigue may decrease, leading to cracks on the back layer.

[0161] It should be noted that, in this application, Type A hardness refers to the hardness of the surface of the backing rubber layer, which can be measured using a Type A hardness tester according to the hardness test of the spring-type hardness tester specified in JIS K6253 (2012).

[0162] The fourth crosslinked rubber composition is not particularly limited as long as it does not impair the adhesion between the back rubber layer and the teeth. For example, it can be selected from the crosslinked rubber compositions exemplified as the first and second rubber layers, and the rubber hardness can be appropriately adjusted to the range described above.

[0163] In the fourth crosslinked rubber composition, from the viewpoint of improving the adhesion between the back rubber layer and the teeth, the rubber component (fourth rubber component) preferably contains rubber components of the same series or the same type as the second rubber layer (inner rubber layer), and more preferably rubber components of the same type.

[0164] The fourth rubber component preferably contains HNBR comprising an unsaturated carboxylic acid metal salt. The proportion of HNBR comprising an unsaturated carboxylic acid metal salt in the fourth rubber component can be 5% or more by mass, for example, 5 to 50% by mass, preferably 10 to 30% by mass, and more preferably 15 to 25% by mass. The fourth rubber component can also be a combination of HNBR without an unsaturated carboxylic acid metal salt and HNBR comprising an unsaturated carboxylic acid metal salt.

[0165] The filler compound can be a reinforcing inorganic filler (fourth reinforcing inorganic filler), preferably a combination of carbon black and silica. The proportion of carbon black is, for example, 1 to 50 parts by mass relative to 100 parts by mass of silica, preferably 2 to 30 parts by mass, and more preferably 3 to 10 parts by mass. The proportion of the fourth reinforcing inorganic filler is, for example, 10 to 100 parts by mass relative to 100 parts by mass of the fourth rubber component, preferably 20 to 80 parts by mass, and more preferably 30 to 50 parts by mass.

[0166] The crosslinking agent (fourth crosslinking agent) can 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 relative to 100 parts by mass of the fourth rubber component, preferably 0.8 to 4 parts by mass, and more preferably 1 to 3 parts by mass. The proportion of the fourth metal oxide is, for example, 1 to 15 parts by mass relative to 100 parts by mass of the fourth rubber component, preferably 2 to 10 parts by mass, and more preferably 3 to 8 parts by mass.

[0167] The co-crosslinking agent (fourth co-crosslinking agent) can be a bismaleimide. The proportion of the fourth co-crosslinking agent is, for example, 0.2 to 10 parts by weight relative to 100 parts by weight of the fourth rubber component, preferably 0.5 to 5 parts by weight, and more preferably 1 to 3 parts by weight.

[0168] The fourth crosslinked rubber composition may contain a plasticizer. The plasticizer may be selected from those exemplified in the first and second rubber layers. The plasticizer may be used alone or in combination of two or more. Among the plasticizers, ether ester plasticizers are preferred.

[0169] The proportion of plasticizer relative to 100 parts by weight of the fourth rubber component is, for example, 1 to 50 parts by weight, preferably 2 to 30 parts by weight, more preferably 3 to 20 parts by weight, and more preferably 5 to 15 parts by weight.

[0170] The average thickness of the backing rubber layer is, for example, 0.3 to 3 mm, preferably 0.5 to 2 mm. The average thickness of the backing (the average thickness of the backing at the bottom of the tooth) is, for example, 1 to 5 mm, preferably 1.5 to 4 mm.

[0171] [Core wire]

[0172] On the back side, a core thread extending circumferentially along the belt is embedded on the inner circumferential side of the aforementioned back rubber layer. This core thread acts as a tensile element, improving the running stability and strength of the toothed belt. Furthermore, on the back side, the core threads, which are typically twisted ropes extending circumferentially along the belt, are embedded at predetermined intervals in the belt width direction. Two or more core threads parallel to the length direction can be arranged, and from a productivity point of view, they are usually embedded in a spiral pattern. In the case of a spiral arrangement, the angle of the core thread relative to the belt length direction can be, for example, 5° or less; from the viewpoint of belt runnability, the closer to 0°, the better.

[0173] More specifically, such as Figure 1As shown, the core wires can be embedded from one end of the back strip in the width direction at a predetermined interval (or spacing) (or at equal intervals). The distance between the centers of adjacent core wires, i.e., the interval (pitch), only needs to be greater than the diameter of the core wire, for example, 0.5 to 3.5 mm, preferably 0.8 to 3 mm, and more preferably 1 to 2.8 mm, depending on the diameter of the core wire.

[0174] The core thread can be formed by twisting two or more strands or multifilament yarns together. Among them, a twisted rope made of strands is preferred, and a strand can be formed by binding filaments (long fibers). There are no particular restrictions on the thickness of the filaments forming the twisted rope, the number of filaments, the number of strands, and the twisting method.

[0175] The twisted rope forming the core can be made of unidirectional twist, multi-ply twist, or co-twisted rope. By setting the core to co-twisting with the same twisting direction for the initial twist and the final twist, the bending stiffness is reduced compared to multi-ply twist or unidirectional twist, resulting in excellent resistance to bending fatigue.

[0176] There are no particular restrictions on the fibers used to form the core wire; examples include: polyester fibers (polyalkylene arylate fibers, poly(p-phenylene naphthalene dicarboxylate) fibers), poly(phenylene oxide) fibers, etc. Synthetic fibers such as azole fiber, acrylic fiber, and polyamide fiber (aliphatic polyamide fiber, aromatic polyamide fiber, etc.), as well as inorganic fibers such as glass fiber, carbon fiber, and metal fiber (steel fiber), are used. These fibers can be used alone or in combination of two or more. As fibers forming the core, from the viewpoint of low elongation and high strength, such as general-purpose polyester fiber, synthetic fibers such as polyamide fiber, and inorganic fibers such as glass fiber and carbon fiber are used.

[0177] Especially in applications involving high loads, multifilament yarns made of carbon fiber are preferred. For example, carbon fiber can be manufactured under the trade name "Toray Industries" by Toray Industries, Inc.

[0178] Carbon fiber multifilament yarns can be selected from multifilament yarns with different filament counts, such as 6K and 12K. 6K indicates multifilament yarn with 6,000 filaments, and 12K indicates 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.

[0179] When the fineness of carbon fiber multifilament yarn is greater than 1000 tex, its resistance to bending fatigue may decrease. Conversely, when the fineness of carbon fiber multifilament yarn is less than 300 tex, the material cost increases, and the number of initial twisted yarns required to produce a core with sufficient tensile strength increases, thus leading to an increase in processing time.

[0180] In one embodiment of the toothed belt of the present invention, a carbon fiber rope (12K-1 / 0) formed by unidirectionally twisting a single 12K multifilament yarn (with a fineness of approximately 800 tex) is used as the core thread. Alternatively, a single 12K multifilament yarn (with a fineness of approximately 800 tex) can be initially twisted to produce a pre-twisted yarn, and four pre-twisted yarns can be combined and then final twisted, with the resulting forward-twisted carbon fiber rope (12K-1 / 4) used as the core thread 4. It should be noted that "12K-1 / 0" refers to a twisted rope formed by unidirectionally twisting a single 12K multifilament yarn, and "12K-1 / 4" refers to a twisted rope formed by initially twisting a single 12K multifilament yarn to produce a pre-twisted yarn and then combining four pre-twisted yarns and final twisting them. Similarly, for example, "12K-1 / 3" means that a 12K multifilament yarn is initially twisted to make a twisted yarn, and the twisted yarn is combined into three yarns and then twisted to make a twisted rope. "12K-4 / 0" means that a 12K multifilament yarn is combined into four yarns and twisted in one direction to make a twisted rope.

[0181] To improve adhesion to the fourth crosslinked rubber composition, the core wire can be subjected to an adhesive treatment. One method of this adhesive treatment is to immerse the twisted rope 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 twisted rope. The RFL treatment solution is a mixture of resorcinol and formalin in a latex, such as chloroprene rubber, styrene-butadiene-vinylpyridine terpolymer (VP latex), nitrile rubber, hydrogenated nitrile rubber, etc. Alternatively, the adhesive treatment can be performed by pretreatment with an epoxy compound or isocyanate compound followed by treatment with the RFL treatment solution.

[0182] The average diameter (average wire diameter) of the twisted rope (or core wire) is, for example, 0.2–2.5 mm, preferably 0.5–2.3 mm, more preferably 0.7–2.2 mm, and particularly preferably 0.8–2.1 mm in applications involving high loads. If the core wire diameter is too thin, the elongation of the core wire may increase, resulting in missing teeth (damage to the teeth). If the core wire diameter is too thick, the core wire may break due to a decrease in its resistance to bending fatigue. In one embodiment of the invention, the core wire diameter is adjusted to 1.1 mm.

[0183] [Manufacturing method of toothed belt]

[0184] The toothed belt of the present invention can be manufactured, for example, by the following process (pre-forming process). First, a toothed cloth precursor for forming the toothed cloth, an uncrosslinked rubber sheet forming two or more rubber layers, such as an uncrosslinked rubber sheet forming a first rubber layer (outer rubber layer), an uncrosslinked rubber sheet forming a second rubber layer (inner rubber layer), and an unvulcanized rubber sheet forming a back rubber layer are prepared.

[0185] (Preforming process)

[0186] Next, a toothed cloth precursor is formed by winding the toothed cloth around the outer periphery of a cylindrical mold having two or more grooves (recesses) corresponding to the teeth of the toothed strip. Then, an uncrosslinked rubber sheet forming a first rubber layer (surface rubber layer) and a crosslinked rubber sheet forming a second rubber layer (inner rubber layer) are sequentially wound around its outer periphery to form a laminate. The laminate is heated to a temperature (e.g., about 70°C to about 90°C) using a prescribed device, while simultaneously applying pressure from the outer periphery, forcing the rubber composition of the uncrosslinked rubber sheet and the toothed cloth precursor into the grooves (recesses) of the cylindrical mold to form the teeth, resulting in a semi-crosslinked preform. During this pressing process to form the teeth, a layer structure is formed as follows: the toothed cloth extends in a shape following the contour of the teeth and is disposed on the outermost surface; a first rubber layer is disposed along the contour of the teeth on its inner side; and a second rubber layer is disposed on its inner side.

[0187] It should be noted that the method for obtaining the semi-crosslinked preform can also be to use a flat pressing mold (flat die) with two or more grooves (recesses) corresponding to the teeth, instead of a cylindrical mold, and press the uncrosslinked rubber sheet composition and the toothed fabric precursor into the grooves (recesses) of the flat die by heating and pressing according to the above steps to form the teeth. In this method, after the preform is demolded from the flat die, the preform is wound and mounted on a cylindrical mold with two or more grooves (recesses) corresponding to the teeth (so that the teeth and grooves are engaged), and then moved to the next process.

[0188] (Cross-linking molding process)

[0189] The twisted rope constituting the core wire is wound in a spiral shape at a specified interval (in such a way that the interval is specified in the axial direction of the cylindrical mold) around the outer periphery of the obtained preform. Then, an uncrosslinked rubber sheet forming a back rubber layer is wound around its outer periphery to form an uncrosslinked tape-shaped body (uncrosslinked laminate).

[0190] Next, with the uncrosslinked tape molded body positioned on the outer periphery of the cylindrical mold, a rubber jacket serving as a vapor barrier material is applied to its outer side. The jacketed tape molded body and the cylindrical mold are then housed inside a crosslinking molding apparatus such as a vulcanizing tank. The tape molded body is then heated and pressurized inside the crosslinking molding apparatus, forming a desired shape. Through the crosslinking reaction of the uncrosslinked and semi-crosslinked rubber components contained in the tape molded body, the constituent components bond and solidify into a single unit, forming a sleeve-shaped crosslinked molded body (crosslinked tape sleeve).

[0191] (Cutting process)

[0192] Finally, by cutting the cross-linked tape sleeve, which has been demolded from the cylindrical mold, into a specified width, two or more toothed tapes are obtained.

[0193] Example

[0194] The present invention will now be described in more detail based on embodiments, but the present invention is not limited to these embodiments.

[0195] [Rubber Composition]

[0196]

[0197] [Materials used in the rubber composition]

[0198] HNBR: "Zetpol2010" manufactured by Zeon Corporation of Japan, with an iodine value of 11mg / 100mg.

[0199] HNBR containing unsaturated carboxylic acid metal salt: "Zeoforte ZSC2295CX" manufactured by Zeon Corporation, Japan; base HNBR: unsaturated carboxylic acid metal salt (mass ratio) = 100:110; base HNBR iodine value 28 mg / 100 mg

[0200] Aromatic polyamide staple fiber: "Cornex" manufactured by Teijin Corporation, with an average fiber length of 3mm and an average fiber diameter of 14μm.

[0201] Stearic acid: "TSUBAKI Stearic Acid" manufactured by Nippon Oil Co., Ltd.

[0202] Carbon black SRF: "Stone S" manufactured by Tokai Carbon Co., Ltd., with an average particle size of 66 nm and an iodine adsorption capacity of 26 mg / g.

[0203] Silica: "Ultrassil VN-3" manufactured by Evonik Degussa Japan Co., Ltd., with a specific surface area of ​​155-195 m². 2 / g

[0204] Calcium carbonate: "Super#1500" manufactured by Maruo Calcium Co., Ltd., with an average particle size of 1.5μm.

[0205] Zinc oxide: Two types of zinc oxide manufactured by Sakai Chemical Industry Co., Ltd., with an average particle size of 0.55 μm.

[0206] Anti-aging agent: p,p'-dioctyldiphenylamine, "Noncondiphenylamine OD3" manufactured by Seiko Chemical Co., Ltd.

[0207] Organic peroxide: 1,3-bis(tert-butylperoxyisopropyl)benzene, theoretical active oxygen content 9.45%

[0208] Co-crosslinking agent: N,N'-m-phenylene bismaleimide, "Barnock PM" manufactured by Ouchi Shinsei Chemical Co., Ltd.

[0209] Plasticizer: "ADK CIZER RS700" manufactured by ADEKA Co., Ltd.

[0210] [Core wire]

[0211] A carbon fiber rope (12K-1 / 0, tensile modulus 230GPa) was made by unidirectionally twisting a single 12K multifilament yarn [Toray Industries, Inc.'s "Treka T700SC-12000", single yarn fineness 0.67 tex, total fineness 800 tex] and then bonding it with an HNBR-based coating agent to obtain a core wire with a core diameter of 1.1 mm.

[0212] [Tooth paper and its treatment]

[0213] The toothed fabric precursor was prepared by impregnating the woven fabric shown in Table 2 with RFL treatment solution and rubber paste. Specifically, in the RFL treatment, the two RFL treatment solutions (RFL1 and RFL2) shown in Table 3 were used, and the impregnation was performed in the order of RFL1 and RFL2. Furthermore, the rubber paste treatment also used the two rubber pastes shown in Table 4 (rubber paste 1 and rubber paste 2), and the impregnation was performed in the order of rubber paste 1 and rubber paste 2.

[0214] [Table 2]

[0215] Table 2: Composition of Woven Fabrics

[0216]

[0217] ※1: PTFE fiber [Toray Industries, Inc. "Toyofuron 1330 tex"]

[0218] ※2: Polyester fiber [“Cornetta” manufactured by UNITIKA Co., Ltd., a core-sheath type composite fiber with a core melting point of 256°C and a sheath melting point of 160°C]

[0219] [Table 3]

[0220] Table 3: RFL Composition (parts by weight)

[0221] Cooperate RFL1 RFL2 Hydrogenated nitrile butadiene rubber latex (40% by weight) 100 100 RF condensate dispersion (20% by mass) 50 25 NaOH aqueous solution (10% by mass) 0 2 Maleimide compounds in aqueous dispersion (50% by mass) 0 20 water 110 110

[0222] [Table 4]

[0223] Table 4: Rubber Paste Composition (parts by weight)

[0224] Cooperate Rubber paste 1 Rubber paste 2 Hydrogenated nitrile butadiene rubber paste rubber compound 5 15 Polymer MDI 5 0 Methyl ethyl ketone 90 85

[0225] [Production of Uncrosslinked Rubber Sheets]

[0226] As uncrosslinked rubber sheets used to form the teeth and back (back rubber layer), the rubber compositions shown in Table 1 are compounded using a Banbury compounding mill. The resulting compounded rubber is then calendered to a specified thickness using calendering rolls to produce uncrosslinked rubber sheets. The short fibers contained in the uncrosslinked rubber sheets are oriented along the rolling direction. In this application, each rubber composition is designated as R1 to R12.

[0227] [Hardness (Type D)]

[0228] Uncrosslinked rubber sheets were pressed and heated at 165°C for 30 minutes to produce crosslinked rubber sheets (100mm × 100mm × 2mm thickness). A laminate of three overlapping crosslinked rubber sheets was used as a sample. The hardness of the crosslinked rubber sheet was determined using a type D hardness tester according to the spring-type hardness test specified in JIS K 6253 (2012) (Vulcanized Rubber and Thermoplastic Rubber - Methods for Determining Hardness).

[0229] [Tensive Modulus of Elasticity]

[0230] Uncrosslinked rubber sheets were pressed and heated at 165°C for 30 minutes to produce crosslinked rubber sheets (100mm × 100mm × 2mm thickness). Test pieces were then cut into dumbbell shapes (size 5) according to JISK 6251 (2017). In samples containing short fibers, dumbbell-shaped test pieces were cut with the fiber orientation (texture parallel direction) as the stretching direction. The test pieces were then clamped at both ends with a chuck and stretched at 500mm / min. The tensile modulus (tensile stress at 1% elongation) was calculated by dividing the tensile force at a specified elongation (1%) by the initial cross-sectional area of ​​the test piece. The tensile modulus of each rubber composition is shown in Table 5.

[0231] [Compressive modulus]

[0232] Uncrosslinked rubber was pressed and heated at 165°C for 30 minutes to prepare crosslinked rubber test pieces (cylindrical; 25 mm thick, 17.8 mm in diameter) according to JIS K 6254 (2016) C method. In samples containing short fibers, the short fibers were arranged circumferentially with the fiber direction (texture parallel direction) aligned with the cylindrical test piece. The test piece was then clamped with a silicone-coated metal plate and compressed at 10 mm / min until the test piece reached 5% strain. The force was immediately removed at 10 mm / min. This operation was repeated three times consecutively, and the relationship between compression force and strain (compression force-deformation curve) was recorded for a total of four times. Using the fourth curve, with the rising point of the curve as the origin, the compressive modulus (compressive stress at 2% compressive strain) was calculated by dividing the compressive force (compressive stress at 2% compressive strain) by the initial cross-sectional area of ​​the test piece relative to the thickness of the test piece before the first compression.

[0233] [Manufacturing of toothed belts]

[0234] In the embodiments and comparative examples, as shown below, a toothed belt with a total thickness of 5.6 mm, tooth profile G8M, tooth height (including toothed cloth) of 3.5 mm, tooth pitch of 8 mm, number of teeth of 140, circumference of 1120 mm, and width of 12 mm was produced using the preforming process described in this embodiment.

[0235] Table 5 shows the composition (layer structure) of the teeth and the rubber composition used in each rubber layer for the toothed belts produced in each embodiment and comparative example.

[0236] (Example 1)

[0237] A toothed cloth precursor, an uncrosslinked rubber sheet (R6, sheet thickness 0.20 mm) forming the first rubber layer, and an uncrosslinked rubber sheet (R2, sheet thickness 1.50 mm) forming the second rubber layer are sequentially stacked on a pressing mold (flat mold) having two or more grooves (concave strips) corresponding to the teeth of the toothed belt. The preform in a semi-crosslinked state is produced by pressing for 160 seconds at a temperature of 90°C and a pressing pressure (surface pressure) of 20.2 MPa.

[0238] Next, a preform is wound and installed in a cylindrical mold (so that the teeth and grooves fit together), and a twisted rope (tension: 150-250 N / coil, pitch: 1.25 mm, winding speed: 1.5 m / s) forming the core wire is spirally wound around the outer circumference of the preform. Then, an uncrosslinked rubber sheet (R12, sheet thickness 0.90 mm) forming the back rubber layer is wound around its outer circumference to form an uncrosslinked tape (uncrosslinked laminate).

[0239] Next, a vulcanizing tank is used to perform cross-linking molding for 40 minutes at a heating temperature of 179°C and a steam pressure of 0.83 MPa to produce a cross-linked molded body (cross-linked tape sleeve).

[0240] Finally, the cross-linked tape sleeve, which has been demolded from the cylindrical mold, is cut into 12mm wide pieces to obtain the toothed tape.

[0241] (Example 2)

[0242] The thickness of the uncrosslinked rubber sheet forming the first rubber layer is set to 0.35 mm, and the thickness of the uncrosslinked rubber sheet forming the second rubber layer is set to 1.35 mm. Otherwise, the toothed belt is made by the same method as in Example 1.

[0243] (Example 3)

[0244] The thickness of the uncrosslinked rubber sheet forming the first rubber layer is set to 0.70 mm, and the thickness of the uncrosslinked rubber sheet forming the second rubber layer is set to 1.00 mm. Otherwise, the toothed belt is made by the same method as in Example 1.

[0245] (Example 4)

[0246] The thickness of the uncrosslinked rubber sheet forming the first rubber layer is set to 1.00 mm, and the thickness of the uncrosslinked rubber sheet forming the second rubber layer is set to 0.70 mm. Otherwise, the toothed belt is made by the same method as in Example 1.

[0247] (Example 5)

[0248] The thickness of the uncrosslinked rubber sheet forming the first rubber layer is set to 1.35 mm, and the thickness of the uncrosslinked rubber sheet forming the second rubber layer is set to 0.35 mm. Otherwise, the toothed belt is made by the same method as in Example 1.

[0249] (Comparative Example 1)

[0250] The uncrosslinked rubber sheet forming the teeth is set to only R2 (sheet thickness 1.70 mm), otherwise the toothed belt is made by the same method as in Example 1.

[0251] (Comparative Example 2)

[0252] The uncrosslinked rubber sheet forming the teeth was set to only be R6 (sheet thickness 1.70 mm), otherwise the toothed belt was made by the same method as in Example 1.

[0253] (Comparative Example 3)

[0254] The uncrosslinked rubber sheet forming the first rubber layer is designated as R2 (sheet thickness 0.85 mm), and the uncrosslinked rubber sheet forming the second rubber layer is designated as R6 (sheet thickness 0.85 mm). Otherwise, the toothed belt is made by the same method as in Example 1.

[0255] (Example 6)

[0256] The uncrosslinked rubber sheet forming the first rubber layer is set as R3 (sheet thickness 0.70 mm), and the toothed belt is otherwise made by the same method as in Example 3.

[0257] (Example 7)

[0258] The uncrosslinked rubber sheet forming the first rubber layer is set to R4 (sheet thickness 0.70 mm), and the toothed belt is otherwise made by the same method as in Example 3.

[0259] (Example 8)

[0260] The uncrosslinked rubber sheet forming the first rubber layer is set to R7 (sheet thickness 0.70 mm), and the toothed belt is otherwise made by the same method as in Example 3.

[0261] (Example 9)

[0262] The uncrosslinked rubber sheet forming the first rubber layer is set to R8 (sheet thickness 0.70 mm), and the toothed belt is otherwise made by the same method as in Example 3.

[0263] (Example 10)

[0264] The uncrosslinked rubber sheet forming the first rubber layer is set to R9 (sheet thickness 0.70 mm), and the toothed belt is otherwise made by the same method as in Example 3.

[0265] (Example 11)

[0266] The uncrosslinked rubber sheet forming the first rubber layer is set as R3 (sheet thickness 0.20 mm), and the toothed belt is otherwise made by the same method as in Example 1.

[0267] (Example 12)

[0268] The uncrosslinked rubber sheet forming the first rubber layer is set to R7 (sheet thickness 1.00 mm), and the toothed belt is otherwise made by the same method as in Example 4.

[0269] (Example 13)

[0270] The uncrosslinked rubber sheet forming the first rubber layer is set to R7 (sheet thickness 1.35 mm), and the toothed belt is otherwise made by the same method as in Example 5.

[0271] (Example 14)

[0272] The uncrosslinked rubber sheet forming the first rubber layer is designated as R3 (sheet thickness 0.70 mm), and the uncrosslinked rubber sheet forming the second rubber layer is designated as R1 (sheet thickness 1.00 mm). Otherwise, the toothed belt is made by the same method as in Example 3.

[0273] (Example 15)

[0274] The uncrosslinked rubber sheet forming the first rubber layer is designated as R6 (sheet thickness 0.70 mm), and the uncrosslinked rubber sheet forming the second rubber layer is designated as R3 (sheet thickness 1.00 mm). Otherwise, the toothed belt is made by the same method as in Example 3.

[0275] (Example 16)

[0276] The uncrosslinked rubber sheet forming the first rubber layer is set as R8 (sheet thickness 0.70 mm), and the uncrosslinked rubber sheet forming the second rubber layer is set as R3 (sheet thickness 1.00 mm). Otherwise, the toothed belt is made by the same method as in Example 3.

[0277] (Example 17)

[0278] The uncrosslinked rubber sheet forming the first rubber layer is designated as R7 (sheet thickness 0.70 mm), and the uncrosslinked rubber sheet forming the second rubber layer is designated as R4 (sheet thickness 1.00 mm). Otherwise, the toothed belt is made by the same method as in Example 3.

[0279] (Example 18)

[0280] The uncrosslinked rubber sheet forming the first rubber layer is set as R9 (sheet thickness 0.70 mm), and the uncrosslinked rubber sheet forming the second rubber layer is set as R4 (sheet thickness 1.00 mm). Otherwise, the toothed belt is made by the same method as in Example 3.

[0281] (Example 19)

[0282] The uncrosslinked rubber sheet forming the first rubber layer is designated as R7 (sheet thickness 0.70 mm), and the uncrosslinked rubber sheet forming the second rubber layer is designated as R5 (sheet thickness 1.00 mm). Otherwise, the toothed belt is made by the same method as in Example 3.

[0283] (Example 20)

[0284] The uncrosslinked rubber sheet forming the first rubber layer is set as R9 (sheet thickness 0.70 mm), and the uncrosslinked rubber sheet forming the second rubber layer is set as R5 (sheet thickness 1.00 mm). Otherwise, the toothed belt is made by the same method as in Example 3.

[0285] (Example 21)

[0286] The uncrosslinked rubber sheet forming the first rubber layer is designated as R9 (sheet thickness 0.70 mm), and the uncrosslinked rubber sheet forming the second rubber layer is designated as R1 (sheet thickness 1.00 mm). Otherwise, the toothed belt is made by the same method as in Example 3.

[0287] (Example 22)

[0288] The uncrosslinked rubber sheet forming the first rubber layer is designated as R11 (sheet thickness 0.70 mm), and the uncrosslinked rubber sheet forming the second rubber layer is designated as R10 (sheet thickness 1.00 mm). Otherwise, the toothed belt is made by the same method as in Example 3.

[0289] [Bending Stiffness Test]

[0290] For toothed belts, the bending stiffness E is determined by bending tests using an Olsen bending tester, according to JIS K7106 (1995). r The obtained E r Multiply by the second moment I of the toothed belt section calculated by the following formula (1). r The bending stiffness E of the toothed belt can be calculated using the following formula (2). r I r Here, the dimensions of the toothed belt test piece were set as follows: length: 80 mm, width: 12 mm, thickness: 2.1 mm, and the distance S between the supports was set to 25.4 mm. The oscillator moment M at 100% load scale was set to 0.343 N·m. Furthermore, the test was conducted at a temperature of 23 ± 2 °C and a humidity of 65 ± 5%. A smaller bending stiffness value indicates better bending performance (flexibility). The criteria for determining bending stiffness are shown below.

[0291] I r =b×h 3 / 12 (1)

[0292] [In the formula, I] r The cross-sectional second moment of the test piece (mm) 4 ), b represents the width of the test piece (mm), and h represents the thickness of the test piece (mm).

[0293] E r I r =[(S×M) / 300]×[N / (D×0.01745)] (2)

[0294] [In the formula, E] r Indicates the bending stiffness of the test piece (N / mm) 2 ), I r The cross-sectional second moment of the test piece (mm)4 S represents the distance between the support points (mm), M represents the oscillator torque (N·m), D represents the bending angle (degrees) (1 degree = π / 180 = 0.01745 radians), and N represents the reading of the load scale corresponding to the bending angle (degrees) (%).

[0295] (Criteria for determining bending stiffness)

[0296] a: Bending stiffness less than 700MPa (qualified)

[0297] b: Bending stiffness is above 700MPa and less than 800MPa (qualified)

[0298] c: Bending stiffness is above 800MPa (unacceptable).

[0299] [Tooth rigidity test]

[0300] like Figure 4 As shown, the teeth of the toothed belt 1 are attached to the protrusion 11a of the toothed shearing fixture (conceived as a rigid body in the shape of the teeth of a toothed pulley). Under constant pressure (tightening torque of 0.98 cNm / 1mm width) pressing on one tooth, the tooth load relative to displacement during tensile testing at a speed of 1mm / min using a universal testing machine is defined as the tooth rigidity (tooth rigidity) for evaluation. The value of the tooth load relative to displacement is the numerically stable value from the third cycle, such as... Figure 5 The tooth stiffness value is obtained by linear approximation within the range of tooth load from 50 to 400 N / 12 mm width. A higher tooth stiffness value indicates better tooth rigidity (resistance to deformation). The following shows the criteria for determining tooth stiffness.

[0301] (Criteria for determining tooth stiffness)

[0302] a: Tooth rigidity is above 1300 N / mm (qualified)

[0303] b: Tooth stiffness is above 1100 N / mm and below 1300 N / mm (qualified)

[0304] c: Tooth stiffness less than 1100 N / mm (unacceptable)

[0305] [Tooth skipping test]

[0306] Using a biaxial torque measuring machine, a toothed belt was wound between a drive pulley (22 teeth) and a driven pulley (22 teeth), and the distance between the pulley shafts was adjusted to a belt tension of 230 N. Then, the drive pulley was rotated at 1800 rpm to move the belt, while the load on the driven pulley was continuously increased. The load torque applied to the drive pulley at the point of tooth skipping (tooth slippage) was measured as the tooth skipping torque. The value of the tooth skipping torque is used as an indicator of tooth skipping performance; it can be said that a larger tooth skipping torque value indicates a superior toothed belt that is less prone to tooth slippage.

[0307] It should be noted that, regarding the value of the skipped tooth torque, the skipped tooth torque value (101 N·m) of Comparative Example 1, which consists of only a single layer of rubber with a low elastic modulus, is set to 1.00. The skipped tooth torque values ​​of each embodiment and comparative example are shown as relative values. If the value is less than 1.00, it indicates that no reinforcement effect relative to the tooth profile of Comparative Example 1 is exhibited. If it exceeds 1.00, it indicates that the rigidity (deformation resistance) of the tooth is improved due to the reinforcement effect. It can be said that the larger the value, the more highly the reinforcement effect is achieved.

[0308] (Judgment criteria for the skipped tooth test)

[0309] a: Tooth skipping torque exceeds 1.10 (has an enhancing effect)

[0310] b: Skip torque exceeds 1.00 but is below 1.10 (has an enhancing effect)

[0311] c: Skip torque is 1.00 (no enhancement effect)

[0312] d: Tooth skipping torque less than 1.00 (no enhancement effect)

[0313] [Endurance Running Test]

[0314] A toothed belt was installed on a biaxial running test machine equipped with a drive pulley (22 teeth) and a driven pulley (22 teeth). The running time until the toothed belt failed (tooth damage) was measured as the running life. The installation tension of the toothed belt was set to 230 N, the speed of the drive pulley was set to 1800 rpm, the load of the driven pulley was set to 9.0 kW, and the ambient temperature was set to 25 °C (room temperature).

[0315] It should be noted that, regarding the running time until the failure (hereinafter, running time), the running time (52 hours) of Comparative Example 1, which consists of only a single layer of rubber with a low elastic modulus, is set to 1.00. The running times of each embodiment and comparative example are shown as relative values. If the value is less than 1.00, it indicates that no reinforcement effect relative to the toothed belt of Comparative Example 1 is exhibited. If it exceeds 1.00, it indicates that the durability of the running is improved due to the reinforcement effect. It can be said that the larger the value, the more highly the reinforcement effect is achieved.

[0316] (Judgment criteria for durability running test)

[0317] a: The travel time until the failure exceeds 1.50 (enhanced effect).

[0318] b: The travel time up to the point of failure exceeds 1.00 but is less than 1.50 (enhanced effect).

[0319] c: The travel time until the failure is 1.00 (no enhancement effect)

[0320] d: The travel time until the failure is less than 1.00 (no enhancement effect)

[0321] [Comprehensive Judgment]

[0322] The skip torque and durability running performance are comprehensively evaluated according to the following criteria.

[0323] Grade A: Both skipped torque and durability / running speed are rated as Grade A (Pass).

[0324] Grade B: Both skipped torque and endurance running are judged as grade B, or one is judged as grade A and the other as grade B (Pass).

[0325] Grade C: A case where one of the skip torque or endurance running conditions is graded C, and the other is graded A or B (Pass).

[0326] Grade D: Both skipped torque and durability / running performance are graded as C, or one of them is graded as D (unacceptable).

[0327] The test results for the toothed belts of the embodiments and comparative examples are shown in Tables 5-8. Furthermore, cross-sectional views of the teeth of the toothed belts in the embodiments and comparative examples are shown in... Figure 6 middle.

[0328] [Table 5]

[0329] Table 5

[0330]

[0331] [Table 6]

[0332] Table 6

[0333]

[0334] [Table 7]

[0335] Table 7

[0336]

[0337]

[0338] (Examples 1-5)

[0339] Examples 1-5 are examples of toothed strips with a two-layer structure consisting of a first rubber layer (surface rubber layer) disposed on the surface side along the tooth profile and a second rubber layer (inner rubber layer) disposed inside the tooth. The first rubber layer is formed of R6 (crosslinked rubber) with a tensile modulus of 5.7 MPa, and the second rubber layer is formed of R2 (crosslinked rubber) with a tensile modulus of 2.3 MPa. The ratio of the tensile modulus of the first rubber layer to the tensile modulus of the second rubber layer is 2.5. It should be noted that this ratio (tensile modulus of the first rubber layer / tensile modulus of the second rubber layer) will be expressed below as "the ratio of the tensile moduli of the two layers".

[0340] In Examples 1 to 5, in the cross-sectional view of the tooth, the ratio of the area occupied by the first rubber layer to the total area of ​​all rubber layers constituting the tooth is changed to 10% (Example 1), 20% (Example 2), 40% (Example 3), 60% (Example 4), and 80% (Example 5).

[0341] As a result, the tooth rigidity was 1225 N / mm (Example 1: b judgment), 1354 N / mm (Example 2: a judgment), 1454 N / mm (Example 3: a judgment), 1510 N / mm (Example 4: a judgment), and 1546 N / mm (Example 5: a judgment), all of which were at the qualified level, and increased as the proportion of the area of ​​the first rubber layer increased.

[0342] On the other hand, the bending stiffness was 605MPa (Example 1: a judgment), 638MPa (Example 2: a judgment), 676MPa (Example 3: a judgment), 691MPa (Example 4: a judgment), and 735MPa (Example 5: b judgment), all of which were qualified levels, and increased as the proportion of the area of ​​the first rubber layer increased.

[0343] In addition, regarding dynamic performance, the relative values ​​of skipped teeth torque are 1.06 (Example 1: b judgment), 1.15 (Example 2: a judgment), 1.18 (Example 3: a judgment), 1.21 (Example 4: a judgment), and 1.27 (Example 5: a judgment), all of which are at the qualified level. Following the same tendency as tooth rigidity, it increases as the proportion of the area of ​​the first rubber layer increases.

[0344] Furthermore, the durability running time (running time until failure (relative value)) was 1.38 (Example 1: b judgment), 2.02 (Example 2: a judgment), 2.63 (Example 3: a judgment), 1.78 (Example 4: a judgment), and 1.04 (Example 5: b judgment), all of which were at the qualified level, and were particularly increased in the range of 20% to 60% of the area of ​​the first rubber layer.

[0345] Based on the above comprehensive judgment, the toothed belts of Examples 1 to 5 are qualified (Grade A or B).

[0346] (Comparative Examples 1-3)

[0347] Comparative Example 1 is an example of a toothed strip formed entirely of R2 (crosslinked rubber) with a tensile modulus of elasticity of 2.3 MPa (relatively low) forming the second rubber layer of Examples 1-5. The flexural stiffness is 553 MPa (a-judgment), better than the Example, but the tooth stiffness is 1092 N / mm (c-judgment), which is unacceptable. In dynamic performance, the skip torque is as low as 101 N·m, and the endurance running time (running time until failure) is also short at 52 hours. Therefore, Comparative Example 1 is judged as unacceptable (Grade D) overall.

[0348] Comparative Example 2 is an example of a toothed strip formed entirely from R6 (crosslinked rubber) of the first rubber layer forming Examples 1-5, which has a tensile modulus of elasticity of 5.7 MPa (relatively high modulus of elasticity). The tooth rigidity is 1592 N / mm (a-judgment), better than the Example, but the flexural rigidity is 832 MPa (c-judgment), which is unacceptable. In dynamic performance, the skip torque (relative value) is 1.32 (a-judgment), better than the Example, but the durability running time (running time until failure (relative value)) is 0.46 (d-judgment), resulting in an overall unacceptable grade (D).

[0349] Comparative Example 3 is an example that, like the embodiment, has a two-layer structure with 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 uses R2 (crosslinked rubber) with a tensile elastic modulus of 2.3 MPa (relatively low), and the second rubber layer uses R6 (crosslinked rubber) with a tensile elastic modulus of 5.7 MPa (relatively high). It should be noted that, in the cross-sectional view of the tooth, the proportion of the area occupied by the first rubber layer relative to the total area of ​​all rubber layers constituting the tooth is set to 50%. As a result, the tooth stiffness is 1275 N / mm (judgment b), which is acceptable, but the flexural stiffness is 812 MPa (judgment c), which is unacceptable. In dynamic performance, the skip torque (relative value) is 1.07 (judgment b), which is acceptable, but the durability travel (travel time until failure (relative value)) is 0.85 (judgment d), resulting in an overall unacceptable (grade D) result.

[0350] If the tooth section is formed entirely of a low-modulus rubber layer as in Comparative Example 1, the rigidity (deformation resistance) of the tooth section is insufficient. If the tooth section is formed entirely of a high-modulus rubber layer as in Comparative Example 2, the flexibility (low bending rigidity) is insufficient. Furthermore, if, as in Comparative Example 3, the tooth section is made of two layers but the interior is formed of a high-modulus rubber layer compared to the surface, not only is the flexibility (low bending rigidity) insufficient, but the level of rigidity (deformation resistance) of the tooth section is also reduced.

[0351] In contrast, this embodiment can be said to be a way to achieve a balance between the rigidity (high elastic modulus) of the teeth that can withstand higher loads and the rigidity (deformation resistance) and flexibility (low bending rigidity: flexibility) of the teeth that are in opposite relationships.

[0352] (Examples 6-10)

[0353] Compared to Example 3 (in the cross-sectional view of the teeth, the proportion of the first rubber layer to the total area of ​​all rubber layers constituting the teeth) which has the best durability and running performance among Examples 1-5, Examples 6-10 are examples of toothed belts using rubber compositions with different elastic moduli in the first rubber layer. Example 6 uses R3 (tensile elastic modulus 3.1 MPa), Example 7 uses R4 (tensile elastic modulus 4.0 MPa), Example 3 uses R6 (tensile elastic modulus 5.7 MPa), Example 8 uses R7 (tensile elastic modulus 7.0 MPa), Example 9 uses R8 (tensile elastic modulus 9.2 MPa), and Example 10 uses R9 (tensile elastic modulus 12.0 MPa) to form the first rubber layer.

[0354] It should be noted that the variable of elastic modulus is adjusted by changing the proportion of the first co-crosslinking agent contained in the first rubber layer to 3 parts by mass (Example 6), 6 parts by mass (Example 7), 11 parts by mass (Example 3), 14 parts by mass (Example 8), 20 parts by mass (Example 9), and 25 parts by mass (Example 10).

[0355] The results showed that the tooth rigidity was 1185 N / mm (Example 6: b judgment), 1362 N / mm (Example 7: a judgment), 1454 N / mm (Example 3: a judgment), 1527 N / mm (Example 8: a judgment), 1561 N / mm (Example 9: a judgment), and 1582 N / mm (Example 10: a judgment), all of which were at the qualified level, and increased as the elastic modulus of the first rubber layer increased.

[0356] On the other hand, the bending stiffness is 602 MPa (Example 6: a determination), 652 MPa (Example 7: a determination), 676 MPa (Example 3: a determination), 724 MPa (Example 8: b determination), 805 MPa (Example 9: c determination), and 845 MPa (Example 10: c determination), which increases as the elastic modulus of the first rubber layer increases.

[0357] In addition, regarding dynamic performance, the skip torque (relative value) was 1.05 (Example 6: b judgment), 1.11 (Example 7: a judgment), 1.18 (Example 3: a judgment), 1.19 (Example 8: a judgment), 1.21 (Example 9: a judgment), and 1.23 (Example 10: a judgment), all of which were at the acceptable level. Following the same trend as tooth rigidity, it increased with the increase of the elastic modulus of the first rubber layer, which can be said to have an enhancement effect relative to Comparative Example 1.

[0358] On the other hand, the durability running time (running time until failure (relative value)) varied as follows: 1.61 (Example 6: a determination), 3.06 (Example 7: a determination), 2.63 (Example 3: a determination), 2.10 (Example 8: a determination), 1.00 (Example 9: c determination), and 1.00 (Example 10: c determination). In Examples 9 and 10, where the elastic modulus of the first rubber layer was large, no reinforcing effect was observed, similar to Comparative Example 1.

[0359] Based on the above comprehensive assessment, the toothed belts of Examples 3, 6-8 exhibit enhanced performance in both skip torque and durable running performance, thus meeting a high level of qualification (Grade A or B). While the toothed belts of Examples 9 and 10 did not show enhanced durable running performance, they did exhibit enhanced skip torque, therefore meeting a qualification level (Grade C).

[0360] Based on these results, the appropriate range for the elasticity of the first rubber layer can be described as 3.0–7.0 MPa (particularly 4.0–6.0 MPa) in terms of tensile modulus and 1.0–1.5 MPa (particularly 1.3–1.4 MPa) in terms of compressive modulus. Furthermore, the appropriate range for the proportion of the first co-crosslinking agent contained in the first rubber layer can be described as 3–14 parts by mass (particularly 6–11 parts by mass).

[0361] (Examples 11-13)

[0362] Examples 11-13 are examples that verify the correlation between the area ratio (hereinafter, area ratio) of the first rubber layer relative to the total area of ​​all rubber layers constituting the tooth in the cross-sectional view of the tooth and the elastic modulus of the first rubber layer (the proportion of the first co-crosslinking agent contained in the first rubber layer). Example 11 is an example near the lower limit of the reinforcing effect (the case of a small area ratio and a small elastic modulus), set to an area ratio of 10% and a tensile elastic modulus of 3.1 MPa (3 parts by mass of the first co-crosslinking agent). Conversely, Examples 12 and 13 are examples near the upper limit of the reinforcing effect (the case of a large area ratio and a large elastic modulus), set to an area ratio of 60% and a tensile elastic modulus of 7.0 MPa (14 parts by mass of the first co-crosslinking agent) in Example 12, and an area ratio of 80% and a tensile elastic modulus of 7.0 MPa (14 parts by mass of the first co-crosslinking agent) in Example 13.

[0363] As a result, the tooth stiffness was 1133 N / mm (Example 11: b judgment), 1601 N / mm (Example 12: a judgment), and 1615 N / mm (Example 13: a judgment), all of which were at the qualified level.

[0364] On the other hand, the bending stiffness was 573 MPa (Example 11: a judgment), 795 MPa (Example 12: b judgment), and 798 MPa (Example 13: b judgment), all of which were at the qualified level.

[0365] In addition, regarding dynamic performance, the skip torque (relative value) was 1.04 (Example 11: b judgment), 1.24 (Example 12: a judgment), and 1.28 (Example 13: a judgment), all of which were at the qualified level, and it can be said that it has an enhanced effect relative to Comparative Example 1.

[0366] On the other hand, the durability running time (running time until failure (relative value)) was 1.15 (Example 11: b determination), 1.06 (Example 12: b determination), and 1.00 (Example 13: c determination). In Examples 11 and 12, an enhancement effect was shown relative to Comparative Example 1, but in Example 13, which had the largest area ratio of the first rubber layer and the largest elastic modulus, no enhancement effect was shown, the same as in Comparative Example 1.

[0367] Based on the above comprehensive assessment, the toothed belts of Examples 11 and 12 exhibit enhanced performance in both skip torque and durable running performance, thus meeting a high level of compliance (Grade B). While the toothed belt of Example 13 did not show enhanced durable running performance, it did exhibit enhanced skip torque, therefore meeting a level of compliance (Grade C).

[0368] (Examples 14-21)

[0369] In Examples 1-5, compared to the configuration of Example 3 (in the cross-sectional view of the teeth, the proportion of the area occupied by the first rubber layer to the total area of ​​all rubber layers constituting the teeth) which has the best durability and running performance, Examples 14-21 are examples of toothed belts with a change in the combination of the elastic modulus of the cross-linked rubber composition used in the first rubber layer and the second rubber layer.

[0370] Example 14 is an example of a toothed belt with a first rubber layer formed of R3 (crosslinked rubber) with a tensile modulus of 3.1 MPa and a second rubber layer formed of R1 (crosslinked rubber) with a tensile modulus of 1.0 MPa. The ratio of the tensile moduli of the two layers is 3.1. Compared with Example 3, Example 14 is a toothed belt with a smaller elastic modulus in either rubber layer, a flexural stiffness of 584 MPa (a-judgment), and a tooth stiffness of 1141 N / mm (b-judgment). In dynamic performance, the tooth skipping torque (relative value) is 1.03 (b-judgment), and the durability running time (running time until failure (relative value)) is 1.34 (b-judgment), and the overall judgment is acceptable (Grade B).

[0371] Example 15 is an example of a toothed belt with a second rubber layer using R3 (tensile modulus of elasticity 3.1 MPa), a first rubber layer using R6 (tensile modulus of elasticity 5.7 MPa), and a tensile modulus ratio of 1.8 between the two layers. Compared to Example 3, Example 15 is a toothed belt with the same elastic modulus of the first rubber layer and a larger elastic modulus of the second rubber layer, a flexural stiffness of 684 MPa (a-judgment), and a tooth stiffness of 1496 N / mm (a-judgment). In dynamic performance, the skip torque (relative value) is 1.19 (a-judgment), and the durability travel (travel time until failure (relative value)) is 2.47 (a-judgment). The overall judgment is the same as Example 3, which is a qualified level (A-level).

[0372] Example 16 is an example of a toothed belt with a second rubber layer using R3 (tensile modulus of elasticity 3.1 MPa), a first rubber layer using R8 (tensile modulus of elasticity 9.2 MPa), and a tensile modulus ratio of 3.0 between the two layers. Compared to Example 15, Example 16 is a toothed belt with the same elastic modulus of the second rubber layer and a larger elastic modulus of the first rubber layer, with a flexural stiffness of 819 MPa (c-judgment) and a tooth stiffness of 1582 N / mm (a-judgment). In dynamic performance, the skip torque (relative value) is 1.22 (a-judgment), and the durability running time (running time until failure (relative value)) is 1.00 (c-judgment). Although it does not show an enhanced effect on durability running performance, it does show an enhanced effect on skip torque. Therefore, the overall judgment is acceptable (C-level).

[0373] Example 17 is an example of a toothed belt with a second rubber layer using R4 (tensile modulus of elasticity 4.0 MPa), a first rubber layer using R7 (tensile modulus of elasticity 7.0 MPa), and a tensile modulus ratio of 1.8 between the two layers. Compared to Example 3, Example 17 is a toothed belt with a high elastic modulus for either rubber layer, a flexural stiffness of 773 MPa (criteria b), and a tooth stiffness of 1570 N / mm (criteria a). In dynamic performance, the skip torque (relative value) is 1.23 (criteria a), and the durability travel (travel time until failure (relative value)) is 1.77 (criteria a). The overall assessment is equivalent to Example 3, and is at a qualified level (Grade A).

[0374] Example 18 is an example of a toothed belt with a second rubber layer using R4 (tensile modulus of elasticity 4.0 MPa), a first rubber layer using R9 (tensile modulus of elasticity 12.0 MPa), and a tensile modulus ratio of 3.0 between the two layers. Compared to Example 17, Example 18 is a toothed belt with the same elastic modulus of the second rubber layer and a larger elastic modulus of the first rubber layer, with a flexural stiffness of 858 MPa (c-judgment) and a tooth stiffness of 1603 N / mm (a-judgment). In dynamic performance, the skip torque (relative value) is 1.29 (a-judgment), and the durability running time (running time until failure (relative value)) is 1.00 (c-judgment). Although it does not show an enhanced effect on durability running performance, it does show an enhanced effect on skip torque. Therefore, the overall judgment is acceptable (C-level).

[0375] Example 19 is an example of a toothed belt with a second rubber layer using R5 (tensile modulus of elasticity 5.0 MPa), a first rubber layer using R7 (tensile modulus of elasticity 7.0 MPa), and a tensile modulus ratio of 1.4 between the two layers. Compared to Example 17, Example 19 is a toothed belt with the same elastic modulus of the first rubber layer and a larger elastic modulus of the second rubber layer, with a bending stiffness of 791 MPa (judgment b) and a tooth stiffness of 1585 N / mm (judgment a). In dynamic performance, the skip torque (relative value) is 1.28 (judgment a), the durability travel (travel time until failure (relative value)) is 1.45 (judgment b), and the overall judgment is acceptable (grade B).

[0376] Example 20 is an example of a toothed belt with a second rubber layer using R5 (tensile modulus of elasticity 5.0 MPa), a first rubber layer using R9 (tensile modulus of elasticity 12.0 MPa), and a tensile modulus ratio of 2.4 between the two layers. Example 20 is the toothed belt with the highest elastic modulus of the two layers in this example, with a flexural stiffness of 869 MPa (c-judgment) and a tooth stiffness of 1624 N / mm (a-judgment). In dynamic performance, the skip torque (relative value) is 1.30 (a-judgment), and the durability running time (running time until failure (relative value)) is 1.00 (c-judgment). Although it does not show an enhanced durability running performance, it does show an enhanced skip torque; therefore, the overall assessment is acceptable (C-level).

[0377] Example 21 is an example of a toothed belt with a second rubber layer using R1 (tensile modulus of elasticity 1.0 MPa), a first rubber layer using R9 (tensile modulus of elasticity 12.0 MPa), and a tensile modulus ratio of 12.0 between the two layers. Example 21 has the largest tensile modulus ratio between the two layers in this example, but its flexural stiffness is 820 MPa (c-judgment), and its tooth stiffness is 1524 N / mm (a-judgment). In dynamic performance, the skip torque (relative value) is 1.27 (a-judgment), and the durability running time (running time until failure (relative value)) is 1.00 (c-judgment). Although it does not show an improvement in durability running performance, it does show an improvement in skip torque; therefore, the overall assessment is acceptable (C-level).

[0378] (Example 22)

[0379] Example 22 is an example of a toothed belt that does not use a reinforcing inorganic filler (carbon black), compared to the configuration of Example 7 (first rubber layer is R4, second rubber layer is R2) which has the best durability and running performance among Examples 1 to 21. That is, Example 22 is an example of a toothed belt formed by a cross-linked rubber composition in which the first rubber layer is formed of R11 (tensile elastic modulus of 3.9 MPa) after removing carbon black from R4, and the second rubber layer is formed of a cross-linked rubber composition in which R10 (tensile elastic modulus of 2.3 MPa) after removing carbon black from R2.

[0380] The bending stiffness is 648 MPa (judgment A), and the tooth stiffness is 1360 N / mm (judgment A). In dynamic performance, the skip torque (relative value) is 1.11 (judgment A), and the endurance travel (travel time until failure (relative value)) is 2.97 (judgment A). The overall judgment is the same as that of Example 7, which is a qualified level (grade A).

[0381] Based on the above results, it can be confirmed that by forming a first rubber layer with teeth along the toothed fabric and a second rubber layer 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, the rigidity and flexibility of the teeth in a reverse relationship can be taken into account, tooth slippage during running can be suppressed, and tooth defects can be suppressed, making it suitable for long service life under high load running.

[0382] Industrial availability

[0383] The toothed belt (meshing transmission belt or toothed drive belt) of this invention, when combined with a toothed pulley, can be used in various fields requiring synchronization of input and output, such as power transmission mechanisms in vehicles like automobiles or motorcycles, power transmission mechanisms in industrial machinery such as electric motors and pumps, automatic doors, automated machinery, copiers, and printing presses. In particular, it can be used as a power transmission belt (synchronous belt, toothed belt) for high-load (high-horsepower) industrial machinery and rear-wheel drive in motorcycles.

[0384] The present invention has been described in detail with reference to specific embodiments, but it will be apparent to those skilled in the art that various modifications and alterations can be made without departing from the spirit and scope of the invention.

[0385] This application is based on Japanese Patent Application No. 2021-122815 filed on July 27, 2021, Japanese Patent Application No. 2022-041284 filed on March 16, 2022, and Japanese Patent Application No. 2022-107110 filed on July 1, 2022, the contents of which are incorporated herein by reference.

[0386] Symbol Explanation

[0387] 1…toothed belt

[0388] 1a…teeth

[0389] 1b…bottom of the tooth

[0390] 1c…back

[0391] 2…tooth cloth

[0392] 3…First rubber layer

[0393] 4…Second rubber layer

[0394] 5…core wire

[0395] 6…back rubber layer

Claims

1. A toothed belt comprising a back portion having a core wire embedded therein extending circumferentially along the belt, and two or more teeth spaced apart circumferentially on the inner circumferential surface of the back portion, comprising a back rubber layer formed relative to the core wire on the outer circumferential side of the belt, and a first rubber layer and a second rubber layer formed relative to the core wire on the inner circumferential side of the belt, wherein the inner circumferential surface of the belt is composed of toothed fabric, wherein the toothed belt, The back includes the back rubber layer. The elastic modulus of the first rubber layer is greater than that of the second rubber layer. The toothed portion includes the toothed cloth, a first rubber layer formed along the toothed cloth, and a second rubber layer sandwiched 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 in the circumferential cross-sectional view is 10 to 80% of the total area of ​​the first rubber layer and the second rubber layer.

3. The toothed belt according to claim 1 or 2, wherein, The tensile elastic modulus of the first rubber layer is 0.6 to 20 MPa, and the tensile elastic modulus of the second rubber layer is 0.5 to 5 MPa.

4. The toothed belt according to claim 1 or 2, wherein, The tensile elastic modulus of the first rubber layer is 1.2 to 4 times that of the second rubber layer.

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

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

7. A method for manufacturing a toothed belt according to any one of claims 1 to 6, comprising a preforming step of making a preform, said preform being formed by stacking a toothed cloth precursor for forming a toothed cloth, an uncrosslinked rubber sheet for forming a first rubber layer, and an uncrosslinked rubber sheet for forming a second rubber layer.

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