Transmission belt

Abstract

This invention addresses the problem of providing a new transmission belt that does not use MOCA. The present invention provides a transmission belt characterized by comprising a heat-cured product of a polyurethane composition containing a urethane prepolymer comprising a polyether polyol and diphenylmethane diisocyanate, and either one or both of 1,4-bis-hydroxyethoxybenzene and 1,3-bis-hydroxyethoxybenzene as a curing agent.

Description

Power transmission belt

[0001] The present invention relates to a power transmission belt.

[0002] Power transmission belts made of thermosetting polyurethane are used in various machines such as office automation equipment and transportation equipment. 4,4'-methylenebis(2-chloroaniline) (hereinafter also referred to as MOCA) is widely used as a curing agent for thermosetting polyurethane, but MOCA is listed as a Substance of Very High Concern (SVHC) in the European Union's REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) regulation due to its potential for carcinogenesis, genetic disorders, blood disorders, and toxicity to aquatic organisms, and its use may be banned in the future.

[0003] Instead of MOCA, it is also possible to use amine-based curing agents such as diethyltoluenediamine or 3,5-diamino-4-chlorobenzoate 2-methylpropyl. However, diethyltoluenediamine reacts too quickly, causing it to harden before being poured into a mold, while 3,5-diamino-4-chlorobenzoate 2-methylpropyl reacts too slowly, requiring a long time before it can be demolded from the mold. Both amine-based curing agents have problems with handling. It is also possible to use a slow-reacting curing agent in combination with a reaction accelerator, but it is difficult to achieve a good balance between stability, in which the curing reaction does not proceed until the mold is cast, and reactivity, in which the curing reaction proceeds quickly after casting.

[0004] For example, the following have been proposed as polyurethanes that do not use MOCA. Patent Document 1 proposes a belt-molding material in which a prepolymer having an NCO% of more than 4.7% contains 3,5-dimethylthio-2,4-toluenediamine and 3,5-dimethylthio-2,6-toluenediamine as curing agents. Patent Document 2 proposes a polyurethane composition that uses only two amine-based curing agents, 2-methylpropyl 3,5-diamino-4-chlorobenzoate and dimethylthiotoluenediamine.

[0005] JP 2002-234928 A JP 2017-25191 A

[0006] The main object of the present invention is to provide a novel power transmission belt that does not use MOCA. Another object of the present invention is to provide a power transmission belt that is excellent in durability.

[0007] The present invention provides the following to solve the above problems: 1. A power transmission belt comprising a thermoset product of a polyurethane composition containing a urethane prepolymer made of polyether polyol and diphenylmethane diisocyanate, and either 1,4-bishydroxyethoxybenzene, 1,3-bishydroxyethoxybenzene, or both as a curing agent. 2. The power transmission belt described in 1., which contains a plasticizer, and the temperature at which the plasticizer and the curing agent become compatible is equal to or lower than the melting point of the curing agent. 3. The power transmission belt described in 1. or 2., which is characterized in that the molar ratio of active hydrogen groups of the curing agent to isocyanate groups of the urethane prepolymer (active hydrogen groups / -NCO) is in the range of 0.8 to 0.98.

[0008] The transmission belt of the present invention has a belt running time at least seven times longer than that of a transmission belt made of a conventional thermosetting polyurethane using MOCA as a curing agent, and is therefore excellent in durability. The transmission belt of the present invention has mechanical properties equivalent to or better than those of a transmission belt made of a conventional thermosetting polyurethane using MOCA as a curing agent, and can be used as a replacement for transmission belts made of a conventional thermosetting polyurethane using MOCA as a curing agent. The polyurethane composition used in the present invention does not contain MOCA, and therefore has little adverse effect on workers and the environment. Furthermore, the polyurethane composition used in the present invention has a good balance between stability, in which the curing reaction does not proceed until casting, and reactivity, in which the curing reaction proceeds rapidly after casting, resulting in excellent handleability.

[0009] 1 is a schematic diagram of a V-ribbed belt, which is an embodiment of a power transmission belt.

[0010] The power transmission belt of the present invention is a thermoset product of a polyurethane composition containing a urethane prepolymer made of polyether polyol and diphenylmethane diisocyanate, and either 1,4-bishydroxyethoxybenzene or 1,3-bishydroxyethoxybenzene, or both, as a curing agent. In this specification, "A to B" (A and B are numerical values ​​or ratios) means a numerical range that includes both ends.

[0011] The polyurethane composition used in the present invention (hereinafter also referred to as the polyurethane composition of the present invention) contains either 1,4-bishydroxyethoxybenzene, 1,3-bishydroxyethoxybenzene, or both as a curing agent, and has superior durability compared to conventional polyurethane compositions using MOCA as a curing agent. Furthermore, the polyurethane composition of the present invention has handleability equivalent to that of currently widely used polyurethane compositions using MOCA as a curing agent. That is, the polyurethane composition of the present invention has a good balance between stability, in which the curing reaction does not proceed until casting, and reactivity, in which the curing reaction proceeds rapidly after casting. The transmission belt of the present invention has mechanical properties such as hardness, tensile strength at break, elongation at break, tear strength, and modulus that are substantially equivalent to those of a transmission belt made of a thermosetting polyurethane using MOCA as a curing agent. Therefore, the transmission belt of the present invention can replace a transmission belt made of a thermosetting polyurethane using MOCA as a curing agent.

[0012] "Urethane Prepolymer" The urethane prepolymer used in the present invention is obtained by reacting a polyether polyol with diphenylmethane diisocyanate. Suitable polyether polyols include polytetramethylene ether glycol and polypropylene glycol, with polytetramethylene ether glycol being preferred. The number average molecular weight of the polyol is more preferably 500 to 2500, and even more preferably 800 to 1500. In the present invention, the number average molecular weight refers to the molecular weight calculated from the hydroxyl value of the polyol measured in accordance with JIS-K1557.

[0013] The urethane prepolymer that can be used has an isocyanate group content of 2.0 to 10.0 wt % and a number average molecular weight of 500 to 4000. An example of such a urethane prepolymer is Coronate 4362. The isocyanate group content is preferably 2.0 to 10.0 wt %, and more preferably 3.5 to 6.5 wt %.

[0014] "Curing Agent" The polyurethane composition used in the present invention contains, as a curing agent, either or both of 1,4-bishydroxyethoxybenzene (hereinafter also referred to as BHEB) and 1,3-bishydroxyethoxybenzene (hereinafter also referred to as DER).

[0015] The structural formulae of BHEB and DER are shown in the following chemical formulas (1) and (2).

[0016]

[0017] BHEB and DER can be used alone or in combination. Because BHEB has a linear and highly symmetric molecular structure, the resulting power transmission belt has excellent mechanical properties. Therefore, from the viewpoint of the mechanical properties of the power transmission belt, it is preferable to include BHEB. Meanwhile, DER is a compound with a melting point of approximately 90°C, while BHEB has a melting point of approximately 100°C. Since DER liquefies at a lower temperature, polyurethane compositions containing DER can be cast and thermoset at lower temperatures. Therefore, from the viewpoint of productivity, it is preferable to include DER. When both BHEB and DER are used, the ratio can be adjusted, for example, within a mass ratio of 5:95 to 95:5 (BHEB:DER, total 100) depending on the mechanical properties, productivity, and the like.

[0018] The polyurethane composition of the present invention may contain, in addition to BHEB and DER, other alcohol-based curing agents or amine-based curing agents, but preferably does not contain MOCA. Furthermore, the total proportion of BHEB and DER to all curing agents is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, even more preferably 99.5% by mass or more, even more preferably 99.9% by mass or more, and most preferably 100% by mass.

[0019] The polyurethane composition of the present invention may contain additives such as plasticizers, reaction accelerators, surfactants, lubricants, fillers, pigments, dyes, hydrolysis inhibitors, antioxidants, UV absorbers, and conductive agents, as needed. Among these, it is preferable to contain a plasticizer. A plasticizer is a low-volatility compound that is mixed to lower the softening range and improve processability. It is particularly preferable to contain a plasticizer whose temperature at which it becomes miscible with the curing agent (BHEB, DER) used in the present invention at a 50:50 mass ratio (curing agent:plasticizer) is equal to or lower than the melting point of the curing agent.

[0020] Examples of plasticizers whose compatible temperature is equal to or lower than the melting point of the curing agent include, in the case of BHEB, polyether ester-based plasticizers (e.g., "ADEKACIZER RS735" manufactured by ADECA Corporation, and "SUNFLEX EB-200" manufactured by Sanyo Chemical Industries, Ltd.), castor oil glycidyl ether-based plasticizers (e.g., "RICCIZER GR-5050" manufactured by Ito Oil Mills, Ltd.), castor oil-based plasticizers (e.g., "URIC Y-3601" manufactured by Ito Oil Mills, Ltd.), acetyl tributyl citrate, ethylene carbonate, propylene carbonate, DPGDB (oxydipropyl dibenzoate) / benzoate ester, and benzoic acid-based plasticizers (e.g., "VELSIFLEX342S" manufactured by Velsicol Chemical Co., Ltd.). Among these, polyether ester-based plasticizers and benzoic acid-based plasticizers are preferred. In the case of DER, examples of suitable plasticizers include benzoic acid-based plasticizers (for example, "VELSIFLEX342S" manufactured by Velsicol Chemical Co.), acetyl tributyl citrate, and ethylene carbonate, with benzoic acid-based plasticizers being preferred.

[0021] From the viewpoint of durability, the hardness (duro-A) of the transmission belt of the present invention is preferably 60 to 95 degrees, and more preferably 75 to 95 degrees. The transmission belt of the present invention preferably has a tan δ peak temperature of −15° C. or lower. Here, tan δ (loss tangent) is the ratio (E" / E') of the storage modulus (E') to the loss modulus (E"). The storage modulus E' corresponds to the amount of elastic components in the polyurethane, and the loss modulus E" corresponds to the amount of viscous components in the polyurethane. When tan δ is measured while changing the temperature, it increases up to a certain temperature and decreases above that temperature. That is, when tan δ is measured while changing the temperature, a maximum value appears, and the temperature at which this maximum value appears is the tan δ peak temperature. Polyurethanes form a three-dimensional network structure, and when polyurethanes come into contact with each other at a temperature range above the tan δ peak temperature, highly mobile molecular chains migrate from one polyurethane to the other, causing entanglement of the molecular chains, thereby exhibiting excellent mechanical properties. Furthermore, polyurethane molded articles having a tan δ peak temperature of −15°C or lower can exhibit desired mechanical properties regardless of their application, provided that they are used in a normal atmosphere. In the polyurethane molded article of the present invention, the tan δ peak temperature of the polyurethane is more preferably −18°C or lower, and even more preferably −21°C or lower.

[0022] The method for producing a power transmission belt of the present invention will be described below. The polyurethane composition used in the present invention contains a prepolymer and a curing agent, and the molded article is produced by the prepolymer method. In the prepolymer method, the hardness of the polyurethane suitable for the belt can be adjusted to 60 to 95 degrees (duro A), by adjusting the molecular weight of the prepolymer, the isocyanate fraction (NCO %), which is the ratio of the mass of isocyanate groups remaining in the prepolymer to the mass of the prepolymer, the mixing ratio of the curing agent, whether or not a plasticizer is added, and the amount of plasticizer added. In the polyurethane composition of the present invention, the active hydrogen groups (-OH, -NH ２It is preferable that the molar ratio of the number of moles of -active hydrogen groups to the number of moles of isocyanate groups (-NCO) contained in the prepolymer (-active hydrogen groups / -NCO: hereinafter referred to as the α ratio) is in the range of 0.8 to 0.98. An α ratio of less than 1 means that there is an excess of NCO, but the excess NCO bonds with moisture in the air and urethane groups, and therefore deterioration of physical properties can be prevented.

[0023] FIG. 1 shows a schematic diagram of a V-ribbed belt, one embodiment of a power transmission belt according to the present invention. The V-ribbed belt 1 has multiple V-ribs 2 extending parallel to the belt length on its inner circumferential surface. The number of V-ribs is, for example, between three and six. Cogs 3 are formed on the back surface of the V-ribbed belt 1 to facilitate bending. The cogs may have any configuration, and the back surface of the belt may be smooth and cogless. Furthermore, within the V-ribbed belt 1, a core wire 4 serving as a tension member is arranged in a periodic spiral pattern extending approximately in the belt length direction and in the belt width direction. The core wire may be made of any material, as long as it has sufficient strength to function as a tension member. Examples of the material include glass fiber, carbon fiber, aramid fiber, and polyester fiber. The V-ribbed belt shown in FIG. 1 is merely one embodiment, and the shape of the power transmission belt according to the present invention is not limited thereto. For example, the shape of the belt is not limited to a V-ribbed belt, but may be a V-belt, a toothed belt, a flat belt, a round belt, etc., and the core wire may be exposed in a groove on the surface that comes into contact with the inner mold during belt manufacturing (the outer surface in this embodiment), or a reinforcing cloth may be embedded on the inner surface of the belt.

[0024] Next, a method for manufacturing a V-ribbed belt will be described. <Cord ​​Setting Process> The cord is wound spirally at a predetermined pitch on the outer peripheral surface of a cylindrical inner mold. The inner mold can be engraved with grooves that extend in the axial direction and have an arc-shaped cross section at a predetermined pitch on its outer peripheral surface. These grooves are used to form cogs on the outer peripheral surface of the belt. <Mold Setting Process> The inner mold is fitted into the center of a cylindrical outer mold so that a cavity for injecting the belt molding material is formed between the outer and inner molds.

[0025] <Belt molding material preparation step> A material composition for belt molding is prepared. <Belt molding material injection and curing step> The obtained material composition is injected into the cavity between the outer mold and the inner mold, and heated to thermally cure the belt molding material.

[0026] <Molding process> The inner mold is pulled out in the axial direction, and the cylindrical belt precursor, on which the belt molding material has hardened, is demolded from the inner peripheral surface of the outer mold. <Width cutting process> The demolded belt precursor is sliced ​​into rings of a predetermined width to obtain a strip. <Grinding process> The outer peripheral surface of the strip is ground so that V-ribs extending in the belt length direction are formed at a predetermined pitch in the width direction. The resulting belt is then turned over to obtain a V-ribbed belt. Note that the above manufacturing method is one example, and the power transmission belt of the present invention is not limited to belts manufactured by the above manufacturing method.

[0027] Next, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

[0028] Example 1: 100 parts by weight of 4,4-diphenylmethane diisocyanate (Millionate MT, manufactured by Tosoh Corporation) and 196 parts by weight of polytetramethylene ether glycol (PTMG1000, manufactured by Mitsubishi Chemical Corporation, number average molecular weight 1000) were weighed and mixed under a nitrogen atmosphere at 80°C for 4 hours to obtain a prepolymer. 100 parts by weight of the synthesized MDI-PTMG prepolymer and 13 parts by weight of BHEB were weighed and mixed using a reciprocating rotary mixer Aziter at approximately 115°C for 2 minutes to obtain a material composition. The material composition was poured between metal plates sandwiching a 2 mm spacer, crosslinked and cured at an oven temperature of 110°C for 120 minutes, and then post-crosslinked in an oven adjusted to 100°C for 16 minutes to obtain a 2 mm thick sheet.

[0029] Example 2: A sheet-like material was obtained in the same manner as in Example 1, except that DER was used instead of BHEB. Example 3: 13 parts by weight of BHEB and 10 parts by weight of a polyether ester plasticizer (Sunflex EB-200, manufactured by Sanyo Chemical Industries, Ltd.) were melted at 120°C to obtain a uniform mixture. A sheet-like material was obtained in the same manner as in Example 1, except that the mixture was added to the prepolymer. Example 4: 13 parts by weight of DER, 10 parts by weight of a benzoic acid plasticizer (VELSIFLEX 342S, manufactured by Velsicol Chemical Co., Ltd.), and 0.02 parts by weight of a catalyst (U-CAT 1102, manufactured by San-Apro Co., Ltd.) were melted at 80°C to obtain a uniform mixture. A sheet-like material was obtained in the same manner as in Example 2, except that the mixture was added to the prepolymer. In Examples 3 and 4, the temperature at which the plasticizer and the curing agent become compatible with each other is equal to or lower than the melting point of the curing agent.

[0030] Example 5: 100 parts by weight of 4,4-diphenylmethane diisocyanate (Millionate MT, manufactured by Tosoh Corporation) and 80 parts by weight of polytetramethylene glycol (PTMG1000, manufactured by Mitsubishi Chemical Corporation) were weighed and mixed under a nitrogen atmosphere at 80°C for 4 hours to obtain a prepolymer. 100 parts by weight of the synthesized MDI-PTMG prepolymer, 65 parts by weight of polytetramethylene glycol (PTMG1000, manufactured by Mitsubishi Chemical Corporation), 22 parts by weight of BHEB, and 0.02 parts by weight of a catalyst (TEDA-L33, manufactured by Tosoh Corporation) were weighed and mixed under a reciprocating rotary mixer Ajiter at approximately 115°C for 2 minutes to obtain a material composition. The material composition was poured between metal plates sandwiching a 2 mm spacer, crosslinked and cured at an oven temperature of 140°C for 25 minutes, and then post-crosslinked in an oven adjusted to 100°C for 16 minutes to obtain a sheet-like product with a thickness of 2 mm.

[0031] Example 6: 100 parts by weight of 4,4-diphenylmethane diisocyanate (Millionate MT, manufactured by Tosoh Corporation) and 196 parts by weight of polytetramethylene ether glycol (PTMG1000, manufactured by Mitsubishi Chemical Corporation, number average molecular weight 1000) were weighed and mixed under a nitrogen atmosphere at 80°C for 4 hours to obtain a prepolymer. 100 parts by weight of the synthesized MDI-PTMG prepolymer, 6.5 parts by weight of BHEB, and 6.5 parts by weight of DER were weighed and mixed using a reciprocating rotary mixer agitator at approximately 115°C for 2 minutes to obtain a material composition. The material composition was poured between metal plates sandwiching a 2 mm spacer, crosslinked and cured at an oven temperature of 110°C for 120 minutes, and then post-crosslinked in an oven adjusted to 100°C for 16 minutes to obtain a 2 mm thick sheet.

[0032] Example 7: 100 parts by weight of 4,4-diphenylmethane diisocyanate (Millionate MT, manufactured by Tosoh Corporation) and 196 parts by weight of polytetramethylene ether glycol (PTMG1000, manufactured by Mitsubishi Chemical Corporation, number average molecular weight 1000) were weighed and mixed under a nitrogen atmosphere at 80°C for 4 hours to obtain a prepolymer. 100 parts by weight of the synthesized MDI-PTMG prepolymer, 3 parts by weight of BHEB, and 10 parts by weight of DER were weighed and mixed using a reciprocating rotary mixer agitator at approximately 115°C for 2 minutes to obtain a material composition. The material composition was poured between metal plates sandwiching a 2 mm spacer, crosslinked and cured at an oven temperature of 110°C for 120 minutes, and then post-crosslinked in an oven adjusted to 100°C for 16 minutes to obtain a 2 mm thick sheet.

[0033] Comparative Example 1: 100 parts by weight of a prepolymer of polytetramethylene glycol and tolylene diisocyanate (Hyplen L-100, manufactured by Mitsui Chemicals, Inc., polytetramethylene glycol number average molecular weight 1000) with an isocyanate group content of 4.3 wt%, 12.3 parts by weight of MOCA (Kumiai Chemical Industry Co., Ltd., Curamine MT), and 30 parts by weight of dioctyl adipate (CG Ester Corporation, hereinafter referred to as DOA) were weighed and mixed using a reciprocating rotary mixer Ajiter at approximately 80°C for 2 minutes to obtain a material composition. The material composition was poured between metal plates sandwiching a 2 mm spacer, cured at an oven temperature of 110°C for 90 minutes, and then post-crosslinked in an oven adjusted to 55°C for 12 hours to obtain a 2 mm thick sheet.

[0034] Comparative Example 2: 100 parts by weight of 4,4-diphenylmethane diisocyanate (Millionate MT, manufactured by Tosoh Corporation) and 80 parts by weight of polytetramethylene glycol (PTMG1000, manufactured by Mitsubishi Chemical Corporation) were weighed and mixed under a nitrogen atmosphere at 80°C for 4 hours to obtain a prepolymer. 100 parts by weight of the synthesized MDI-PTMG prepolymer, 20 parts by weight of polytetramethylene glycol (PTMG1000, manufactured by Mitsubishi Chemical Corporation), 13 parts by weight of 1,4-butanediol, 0.27 parts by weight of trimethylolpropane, and 0.04 parts by weight of a catalyst (TEDA-L33, manufactured by Tosoh Corporation) were weighed and mixed under a reciprocating rotary mixer Ajiter at approximately 80°C for 2 minutes to obtain a material composition. The material composition was poured between metal plates sandwiching a 2 mm spacer, crosslinked and cured at an oven temperature of 140°C for 25 minutes, and then post-crosslinked in an oven adjusted to 100°C for 16 minutes to obtain a sheet-like product with a thickness of 2 mm.

[0035] Comparative Example 3: 100 parts by weight of a prepolymer of polytetramethylene glycol and tolylene diisocyanate (KC-23-4, manufactured by Kumiai Chemical Industry Co., Ltd., polytetramethylene glycol number-average molecular weight: approximately 2000) with an isocyanate group content of 4.3 wt % and 15 parts by weight of trimethylene-bis(4-aminobenzoate) (CUA-4, manufactured by Kumiai Chemical Industry Co., Ltd.) were weighed and mixed using a reciprocating rotary mixer Ajiter at approximately 100°C for 2 minutes to obtain a material composition. The material composition was injected between metal plates sandwiching a 2 mm spacer, cured at an oven temperature of 110°C for 120 minutes, and then post-crosslinked in an oven adjusted to 60°C for 12 hours to obtain a 2 mm thick sheet.

[0036] "Manufacturing of Power Transmission Belt" Using the polyurethane compositions described in Example 1 and Comparative Example 1, a friction power transmission belt having a circumferential length of 73.8 mm, a belt width of 10.4 mm, five crests, and a V-ribbed belt shape with a polyester cord as a core was manufactured based on the manufacturing method of the power transmission belt described above, under the same curing conditions as for the sheet.

[0037] "Test Methods" The following tests were performed on the obtained sheet-like materials and power transmission belts. The results are shown in Table 1. - Hardness (Duro A) Six 2 mm thick sheet-like materials obtained in the Examples and Comparative Examples were stacked to a thickness of 12 mm, and hardness (Duro A) was measured using Type A in accordance with JIS-K7312. The measurements were performed at five random locations under an environment of 23°C temperature and 50% RH humidity, and the values ​​were expressed as the arithmetic mean of the measured values. - M5, 100, TB, EB (Tensile Test) Samples (No. 3 dumbbell shape) were prepared from the sheet-like materials obtained in the Examples and Comparative Examples, and the 5% modulus (M5), 100% modulus (M100), tensile stress at break (TB), and elongation at break (EB) were measured under JIS-K7312. The measurements were performed on three samples under an environment of 23°C temperature and 50% RH humidity, and the values ​​were expressed as the arithmetic mean of the measured values. TR-B (Tear Test) Samples (uncut angle shapes) were prepared from the sheet-like materials obtained in the Examples and Comparative Examples, and the tear strength (TR-B) was measured in accordance with JIS-K 7312. The measurement was carried out on three samples in an environment of a temperature of 23°C and a humidity of 50% RH, and the arithmetic mean value of the measured values ​​was shown.

[0038] A sample (width 5 mm, length 35 mm) was cut from the prepared sheet-like material, and the sample was attached to a dynamic viscoelasticity measuring device (manufactured by TA Instruments, device name: RSA3) after "Set Gap" and "Offset Force To Zero". The sample was attached so that the force was -1.0 to -3.0 N, and then measurement was performed in accordance with JIS K7244-4. The temperature dependency curves of storage modulus (E'), loss modulus (E"), and loss tangent (tan δ) were measured under the following set conditions, and the tan δ peak temperature was determined. (Set conditions) Geometry type: Tension / compression mode Distance between chucks: 20 mm Sample width: 5 mm Sample thickness: 150 μm Frequency: 10 Hz Initial temperature: -40°C End temperature: 100°C Heating rate: 2°C / min Strain: 0.03%

[0039] Belt running test: A polyurethane power transmission belt was wound around a φ23 drive pulley and a φ30 driven pulley. The belt was run at room temperature under the following conditions: the drive pulley rotation speed was 10,400 rpm, the driven pulley load was 0.8 N m, and the belt initial tension was 120 N. The belt running time was measured from the start of belt running until it stopped running due to slippage.

[0040]

[0041] "Results" In Comparative Example 2, in which BD / TMP, a commonly used alcohol-based curing agent, was used instead of MOCA, and Comparative Example 3, in which trimethylene-bis(4-aminobenzoate) was used, the resulting polyurethane compositions had high tan δ peak temperatures and were not suitable for use under general temperature conditions. The polyurethane compositions of Examples 1 to 7 of the present invention had mechanical properties equal to or better than those of the polyurethane composition obtained in Comparative Example 1, which used MOCA. Furthermore, the running time of the power transmission belt obtained from the polyurethane composition of Example 1 was 7.7 times (1102 / 144) that of the power transmission belt obtained from the polyurethane composition of Comparative Example 1, demonstrating significantly improved durability.

[0042] 1 V-ribbed belt 2 V-rib 3 Cog 4 Core wire

Claims

1. A power transmission belt comprising a thermoset polyurethane composition containing a urethane prepolymer made from polyether polyol and diphenylmethane diisocyanate, and either 1,4-bishydroxyethoxybenzene, 1,3-bishydroxyethoxybenzene, or both as a curing agent.

2. The power transmission belt according to claim 1, further comprising a plasticizer, wherein the temperature at which the plasticizer and the hardener become compatible with each other is equal to or lower than the melting point of the hardener.

3. The power transmission belt according to claim 1, wherein the molar ratio of the active hydrogen groups of the curing agent to the isocyanate groups of the urethane prepolymer (active hydrogen groups / -NCO) is in the range of 0.8 to 0.98.

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