Cold-resistant transmission belt bottom glue and preparation method thereof

Abstract

The application relates to the technical field of transmission belts, and discloses a cold-resistant transmission belt bottom glue and a preparation method thereof, wherein the cold-resistant transmission belt bottom glue comprises the following raw materials in parts by mass: chloroprene rubber CR121 100 parts, zinc oxide 5 parts, magnesium oxide 4 parts, sulfur 1 part, stearic acid 1 part, N330 carbon black 30-40 parts, white carbon black 10-18 parts, cold-resistant composite softening oil 2-6 parts, antioxidant 4020 1.2-1.8 parts, antioxidant RD 0.8-1.2 parts, rubber dispersing agent EVA 0.8-1.5 parts, and low-temperature anti-brittle cracking cold-resistant additive 2-3 parts. The bottom glue is prepared by synergistically modifying a low-rigidity reinforcing system, a low-temperature crystallization-resistant softening system and a low-temperature anti-brittle cracking additive, and by cooperating with a low-temperature segmented mixing, multi-pass thin-pass stress relief and room-temperature standing curing process. The prepared bottom glue solves the technical problems of low-temperature hardening, brittle cracking and large compression permanent deformation of traditional chloroprene bottom glue, and is suitable for agricultural machinery transmission belts under a super-low-temperature environment of -40 DEG C.

Description

Technical Field

[0001] This invention relates to the field of transmission belt technology, specifically to a cold-resistant transmission belt base rubber and its preparation method. Background Technology

[0002] The base rubber of a transmission belt is the core functional layer responsible for power transmission, shock absorption, and resistance to flexural fatigue. Its performance directly determines the service life and transmission reliability of the transmission belt. Traditional transmission belt base rubbers mostly use conventional neoprene rubber, natural rubber, or EPDM universal formulation systems. Conventional formulation design mainly focuses on room temperature strength, wear resistance, low heat generation, and flexural resistance.

[0003] Neoprene rubber possesses high tensile strength and elongation, and is resistant to aging and heat, making it an important raw material for mid-to-high-end transmission belts. However, its drawbacks include poor cold resistance and storage stability. Due to the highly regular molecular chain of neoprene rubber and the presence of polar side groups, it exhibits a tendency to crystallize. When the ambient temperature drops below freezing, neoprene rubber begins to crystallize, gradually hardening and becoming brittle and prone to cracking. In the winter conditions of northern my country and in outdoor agricultural machinery operations, where ambient temperatures can drop to -20℃ to -40℃, traditional base rubbers have significant technical limitations. (1) At low temperatures, the rubber molecular chains freeze and lose elasticity significantly, making the rubber compound hard and brittle; (2) It is very easy to experience brittle fracture, cracking, and fragmentation under low temperature bending and starting impact load; (3) The low temperature compression rebound is extremely poor, the belt collapses and the pitch changes, resulting in slippage, tooth skipping and transmission failure; (4) Conventional reinforcing fillers have large filling amounts and high rigidity, which further exacerbates low-temperature brittleness defects; (5) Traditional mixing processes do not optimize the dispersion of the softening system for low-temperature formulations, resulting in high internal stress at low temperatures and easy low-temperature cracking.

[0004] Existing cold-resistant rubber formulations are mostly general-purpose cold-resistant compounds, not designed for the dynamic bending and compression fatigue conditions of transmission belt base rubbers. This presents a contradiction between cold resistance and mechanical strength and adhesive performance. For example, some existing technologies improve low-temperature performance by incorporating butadiene rubber into neoprene rubber, but the introduction of butadiene rubber reduces the compound's heat aging resistance and adhesive performance, and its adaptability to ultra-low temperature environments below -20℃ remains insufficient. Other existing technologies use acrylic rubber as a cold-resistant matrix, but its mechanical strength and dynamic fatigue resistance are insufficient to meet the stringent requirements of transmission belt base rubbers. Therefore, we propose a cold-resistant transmission belt base rubber and its preparation method. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing transmission belt base rubbers, such as easy hardening, brittleness, and large compression set in ultra-low temperature environments, and provides a cold-resistant transmission belt base rubber and its preparation method. This invention achieves the technical effect of maintaining high elasticity and being able to be repeatedly bent without cracking even at -40℃ through synergistic modification of a low-rigidity reinforcing system, a low-temperature resistant crystallization softening compound system, a low-temperature anti-brittleness additive, and a flexible cross-linking system, combined with a proprietary low-temperature, low-stress preparation process.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a cold-resistant transmission belt base rubber, comprising, by weight, the following raw materials: 100 parts of chloroprene rubber CR121, 5 parts of zinc oxide, 4 parts of magnesium oxide, 1 part of sulfur, 1 part of stearic acid, 30-40 parts of N330 carbon black, 10-18 parts of silica, 2-6 parts of cold-resistant composite softening oil, wherein the cold-resistant composite softening oil is a compound of naphthenic oil and low-temperature plasticizer, 1.2-1.8 parts of antioxidant 4020, 0.8-1.2 parts of antioxidant RD, 0.8-1.5 parts of rubber dispersant EVA, and 2-3 parts of low-temperature anti-brittleness and cold-resistant additive, wherein the low-temperature anti-brittleness and cold-resistant additive is CPE short-chain chlorinated paraffin.

[0007] Preferably, by weight, it includes the following raw materials: 100 parts of chloroprene rubber CR121, 5 parts of zinc oxide, 4 parts of magnesium oxide, 1 part of sulfur, 1 part of stearic acid, 35 parts of N330 carbon black, 14 parts of silica, 4 parts of cold-resistant composite softening oil, 1.5 parts of antioxidant 4020, 1 part of antioxidant RD, 1 part of rubber dispersant EVA, and 2.5 parts of low-temperature anti-brittleness and cold-resistant additive.

[0008] Preferably, the silica is at least one of fumed silica or precipitated silica.

[0009] Preferably, the mass ratio of naphthenic oil to low-temperature plasticizer in the cold-resistant composite softening oil is 1:0.8 to 1.2.

[0010] Preferably, the chlorine content of the CPE short-chain chlorinated paraffin is 40-70 wt%.

[0011] The method for preparing the cold-resistant transmission belt base rubber of the present invention includes the following steps: Step S1, low-temperature plasticizing: put chloroprene rubber CR121 into a mixer and plasticize at low temperature for 1 to 3 minutes. Then add stearic acid, rubber dispersant EVA, antioxidant 4020 and antioxidant RD in sequence, and continue to mix for 2 to 4 minutes. Step S2, adding reinforcing filler and low-temperature softening system in stages: N330 carbon black, white carbon black and cold-resistant composite softening oil are added to the rubber compound obtained in step S1 in batches, and the mixture is mixed at low speed for 5 to 9 minutes, and the discharge temperature is controlled to be ≤105℃. Step S3, two-stage vulcanization activation: After cooling the rubber compound obtained in step S2, put it into an internal mixer, add zinc oxide, magnesium oxide and sulfur, and mix at low speed for 2 to 4 minutes. Step S4, multiple low-temperature thin-pass stress relief: Place the rubber compound obtained in step S3 on a two-roll mill and repeatedly pass it through the mill 4 to 8 times under a roll gap of 0.8 to 1.5 mm, alternating between triangular wrapping and roll winding operations; Step S5, room temperature curing: allow the rubber compound obtained in step S4 to cure at room temperature for 20-30 hours; Step S6, vulcanization molding: The rubber compound obtained in step S5 is vulcanized at a vulcanization temperature of 145-165℃ and a pressure of 10-20MPa for 15-22 minutes to obtain a cold-resistant transmission belt base rubber.

[0012] Preferably, in step S1, the low-temperature plasticizing time is 2 minutes, and the mixing time after adding stearic acid, rubber dispersant EVA, antioxidant 4020 and antioxidant RD is 3 minutes.

[0013] Preferably, the mixing time in step S2 is 7 minutes and the glue discharge temperature is ≤105℃.

[0014] Preferably, in step S4, the roller gap is 1.2 mm, and the thin pass is repeated 6 times.

[0015] Preferably, in step S6, the vulcanization temperature is 155°C, the pressure is 15 MPa, and the time is 18 min.

[0016] Compared with the prior art, the present invention provides a cold-resistant transmission belt base rubber and its preparation method, which has the following beneficial effects: This invention significantly reduces the amount of hard carbon black and combines it with an appropriate amount of silica to construct a low-rigidity flexible reinforcing system, effectively reducing the low-temperature rigidity of the rubber compound. At the same time, the nano-reinforcing effect of silica ensures the mechanical strength at room temperature.

[0017] This invention employs a special low-temperature softening system composed of naphthenic oil and low-temperature plasticizer, which effectively inhibits the low-temperature crystallization of chloroprene rubber and significantly improves the mobility of rubber molecular chains at low temperatures.

[0018] This invention significantly improves the bending toughness and impact resistance of rubber compounds at low temperatures by adding CPE short-chain chlorinated paraffin as a dedicated low-temperature anti-brittleness additive.

[0019] This invention employs a proprietary preparation process involving low-temperature segmented mixing, multiple low-temperature thin-pass stress releases, and room-temperature static curing. This process effectively eliminates filler agglomeration, micro-defects, and residual processing stress within the rubber compound, thus preventing low-temperature stress cracking from the material structure level.

[0020] The formulation system of this invention is simple, the cost is controllable, and the process is compatible with existing transmission belt production lines, which can be promoted on a large scale for industrialization. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] All raw materials used in the following examples and comparative examples are commercially available industrial products. Specifically, chloroprene rubber CR121 is a product of Shanxi Synthetic Rubber Group Co., Ltd.; N330 carbon black is a product of Cabot Corporation; and silica is fumed or precipitated silica with a specific surface area of ​​150–200 m². 2 / g; naphthenic oil is a product of Karamay Petrochemical Company; low-temperature plasticizer is dioctyl phthalate (DOP) or dioctyl adipate (DOA); CPE short-chain chlorinated paraffin is a product of Shandong Green Hengye Company, with a chlorine content of 52%; the equipment used includes a closed internal mixer, an open rubber mixing mill, a flat vulcanizing mill, a low-temperature brittleness testing machine, a high and low temperature universal tensile testing machine, a Shore hardness tester, a low-temperature rebound tester, a low-temperature flexural testing machine, a constant temperature aging chamber, and an electronic analytical balance.

[0023] This invention provides a cold-resistant transmission belt base rubber, comprising the following raw materials by weight: 100 parts of chloroprene rubber CR121, 5 parts of zinc oxide, 4 parts of magnesium oxide, 1 part of sulfur, 1 part of stearic acid, 30-40 parts of N330 carbon black, 10-18 parts of silica, 2-6 parts of cold-resistant composite softening oil (a compound of naphthenic oil and low-temperature plasticizer), 1.2-1.8 parts of antioxidant 4020, 0.8-1.2 parts of antioxidant RD, 0.8-1.5 parts of rubber dispersant EVA, and 2-3 parts of low-temperature anti-brittleness and cold-resistant additive (CPE short-chain chlorinated paraffin). The silica is at least one of fumed silica or precipitated silica. The mass ratio of naphthenic oil to low-temperature plasticizer in the cold-resistant composite softening oil is 1:0.8-1.2. The chlorine content of CPE short-chain chlorinated paraffin is 40-70 wt%.

[0024] The present invention also provides a method for preparing the above-mentioned cold-resistant transmission belt base rubber, comprising the following steps: Step S1, low-temperature plasticizing: put chloroprene rubber CR121 into a mixer and plasticize at low temperature for 1 to 3 minutes, preferably 2 minutes. Then add stearic acid, rubber dispersant EVA, antioxidant 4020 and antioxidant RD in sequence, and continue to mix for 2 to 4 minutes, preferably 3 minutes. Step S2, adding reinforcing filler and low-temperature softening system in stages: N330 carbon black, white carbon black and cold-resistant composite softening oil are added to the rubber compound obtained in step S1 in batches, and the mixture is mixed at low speed for 5 to 9 minutes, preferably 7 minutes, and the discharge temperature is controlled to be ≤105℃. Step S3, two-stage vulcanization activation: After cooling the rubber compound obtained in step S2, put it into an internal mixer, add zinc oxide, magnesium oxide and sulfur, and mix at low speed for 2 to 4 minutes. Step S4, multiple low-temperature thin-pass stress relief: Place the rubber compound obtained in step S3 on a two-roll mill and repeatedly thin-pass 4 to 8 times under the condition of a roll gap of 0.8 to 1.5 mm. Preferably, the roll gap is 1.2 mm and the thin-pass is repeated 6 times. Triangular wrapping and rolling operations are alternated. Step S5, room temperature curing: allow the rubber compound obtained in step S4 to cure at room temperature for 20-30 hours; Step S6, vulcanization molding: The rubber compound obtained in step S5 is vulcanized at a vulcanization temperature of 145-165℃ and a pressure of 10-20MPa for 15-22 minutes, preferably at a vulcanization temperature of 155℃, a pressure of 15MPa and a time of 18 minutes, to obtain a cold-resistant transmission belt base rubber.

[0025] Example 1 This embodiment provides a cold-resistant transmission belt base adhesive, the raw material formula of which, by weight, is as follows: Chloroprene rubber CR121 100 parts; zinc oxide 5 parts; magnesium oxide 4 parts; sulfur 1 part; stearic acid 1 part; N330 carbon black 35 parts; precipitated silica 14 parts; cold-resistant composite softening oil (naphthenic oil: low-temperature plasticizer DOP=1:1) 4 parts; antioxidant 4020 1.5 parts; antioxidant RD 1 part; rubber dispersant EVA 1 part; CPE short-chain chlorinated paraffin 2.5 parts.

[0026] The preparation method is as follows: Step S1, Low-Temperature Plasticizing: Chloroprene rubber CR121 is added to an internal mixer and plasticized at a low temperature for 2 minutes at a rotor speed of 40-50 r / min. The purpose of this step is to initially plasticize the CR121 raw rubber at a lower temperature, allowing the molecular chains to expand, while avoiding overheating, cross-linking, or degradation of the molecular chains caused by high-temperature plasticizing, thus laying the foundation for the uniform dispersion of subsequent compounding agents. Then, stearic acid, rubber dispersant EVA, antioxidant 4020, and antioxidant RD are added sequentially, and mixing continues for 3 minutes. Stearic acid acts as both an activator and a processing aid in rubber compounds. On the one hand, it participates in the vulcanization reaction in synergy with zinc oxide and magnesium oxide. On the other hand, it can reduce internal friction of the rubber compound and improve processing fluidity. The addition of rubber dispersant EVA can effectively promote the uniform dispersion of carbon black and silica in the rubber matrix and avoid filler agglomeration to form stress concentration points. Antioxidant 4020 (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) and antioxidant RD (2,2,4-trimethyl-1,2-dihydroquinoline polymer) constitute a composite anti-aging system. The former provides excellent protection against ozone and flexural fatigue, while the latter provides efficient protection against thermo-oxidative aging. The synergy of the two can comprehensively ensure the long-term stability of the rubber compound under high and low temperature alternating environments.

[0027] Step S2: Segmented addition of reinforcing filler and low-temperature softening system: N330 carbon black, precipitated silica, and cold-resistant composite softening oil are added to the rubber compound obtained in step S1 in three batches, and mixed at low speed for 7 minutes, strictly controlling the discharge temperature to ≤105℃. The segmented addition method is used because adding a large amount of filler at once can lead to excessively high local concentrations, uneven mixing, and local overheating under high shear, causing the effective components in the low-temperature softening oil to volatilize and become ineffective. It may also cause early cross-linking of the chloroprene rubber molecular chains. N330 carbon black, as a hard reinforcing filler, imparts high tensile strength and abrasion resistance to the rubber compound; precipitated silica, as a flexible reinforcing filler, has a surface rich in silanol groups, which can form hydrogen bonds with the chloroprene rubber molecular chains. While providing a reinforcing effect, its rigidity is lower than that of carbon black, and its contribution to the low-temperature rigidity of the rubber compound is far less than that of an equal amount of carbon black. The addition of cold-resistant composite softening oil can lubricate and isolate the rubber molecular chains, reduce inter-chain friction, and inhibit the orderly arrangement and crystallization of chloroprene rubber at low temperatures. The key to controlling the discharge temperature to ≤105℃ is that chloroprene rubber may undergo premature vulcanization at temperatures above 110-120℃, while the low molecular weight components in the cold-resistant composite softening oil are easily volatilized and lost at high temperatures. Therefore, effective control of the discharge temperature is one of the core process parameters to ensure the realization of the formulation design effect.

[0028] Step S3, Two-stage vulcanization activation: After cooling the rubber compound obtained in step S2 to room temperature, it is put into a mixer, and zinc oxide, magnesium oxide, and sulfur are added. The mixture is then mixed at low speed for 3 minutes. The vulcanization system of chloroprene rubber differs from that of traditional diene rubbers, employing a composite vulcanization system using metal oxides, such as zinc oxide and magnesium oxide, in conjunction with sulfur. Zinc oxide and magnesium oxide not only act as vulcanization activators but also directly participate in the crosslinking reaction of chloroprene rubber: magnesium oxide, as an acid acceptor, absorbs hydrogen chloride generated during vulcanization, preventing dehydrochlorination degradation of the main chain; zinc oxide reacts with the allyl chloride structure on the chloroprene rubber molecular chain to form ionic crosslinks. The addition of sulfur supplements the formation of polysulfide crosslinks, creating a complementary network structure with the metal oxide crosslinks. The core purpose of adding the vulcanization system and reinforcing filler in two stages is to avoid premature reaction of the vulcanization activators and sulfur during the high-temperature mixing stage, which could lead to scorching, while ensuring that all components of the vulcanization system are uniformly dispersed in the rubber compound at a lower temperature.

[0029] Step S4, Multiple Low-Temperature Thin-Pass Stress Relief: The rubber compound obtained in Step S3 is placed on an open mill, maintaining a roll temperature of 40-50°C. It is repeatedly thin-passed 6 times with a roll gap of 1.2mm, alternating between triangular wrapping and roll winding operations. The core functions of the thin-passing operation include three aspects: First, through strong shearing action, it further breaks down and disperses any possible filler agglomerates, achieving submicron-level uniform dispersion of the reinforcing filler; second, through repeated compression and folding, it eliminates defects such as bubbles and micropores within the rubber compound; third, and more importantly, the shear flow during the thin-passing process allows for sufficient relaxation and release of uneven stress frozen within the rubber compound during mixing. Traditional processes often only perform 2-3 thin-passes, resulting in insufficient stress release. These residual stresses are concentrated and released at low temperatures due to the significant increase in the rubber matrix modulus, becoming a major cause of low-temperature cracking. This invention employs 6 thin-passes supplemented by alternating triangular wrapping and roll winding operations to ensure that all parts of the rubber compound undergo sufficient shear flow and stress relaxation.

[0030] Step S5, room temperature curing: The rubber compound obtained in step S4 is cured at room temperature (23±2℃) for 24 hours. While the curing process appears static, it has significant material science implications: First, the residual stress generated during mixing and thin-passing is further released through the slow rearrangement of molecular chains during prolonged room temperature curing. Second, the compounding agents can further reach adsorption equilibrium during curing, especially the silanol groups on the surface of silica and polar additives such as antioxidants and dispersants, resulting in a more uniform and stable filler-rubber interface. Third, the chloroprene rubber molecular chains can undergo a certain degree of stress-induced crystallization relaxation at room temperature, making the internal structure of the rubber compound more uniform.

[0031] Step S6, vulcanization molding: The rubber compound obtained in step S5 is vulcanized on a flat vulcanizing machine at a vulcanization temperature of 155℃ and a pressure of 15MPa for 18 minutes to obtain a cold-resistant transmission belt base rubber test piece.

[0032] Example 2 This embodiment provides a cold-resistant transmission belt base adhesive, the raw material formula of which, by weight, is as follows: Chloroprene rubber CR121 100 parts; zinc oxide 5 parts; magnesium oxide 4 parts; sulfur 1 part; stearic acid 1 part; N330 carbon black 30 parts; fumed silica 18 parts; cold-resistant composite softening oil (naphthenic oil: low-temperature plasticizer DOA=1:0.8) 6 parts; antioxidant 4020 1.2 parts; antioxidant RD 1.2 parts; rubber dispersant EVA 0.8 parts; CPE short-chain chlorinated paraffin 2 parts.

[0033] The preparation method is the same as in Example 1.

[0034] Compared to Example 1, this example uses a higher amount of silica (18 parts) and a lower amount of carbon black (30 parts), further reducing the overall rigidity of the reinforcing system. It also uses fumed silica instead of precipitated silica, as fumed silica has a higher specific surface area and stronger reinforcing efficiency, achieving a similar reinforcing effect at a lower dosage, but its dispersion difficulty is correspondingly increased. The amount of cold-resistant composite softening oil is increased to 6 parts to compensate for potential changes in processing performance due to the change in the filler system. The amount of antioxidant RD is increased to 1.2 parts to address the risk of accelerated thermo-oxidative aging that may result from a higher silica dosage.

[0035] Example 3 This embodiment provides a cold-resistant transmission belt base adhesive, the raw material formula of which, by weight, is as follows: Chloroprene rubber CR121 100 parts; zinc oxide 5 parts; magnesium oxide 4 parts; sulfur 1 part; stearic acid 1 part; N330 carbon black 40 parts; precipitated silica 10 parts; cold-resistant composite softening oil (naphthenic oil: low-temperature plasticizer DOP=1:1.2) 2 parts; antioxidant 4020 1.8 parts; antioxidant RD 0.8 parts; rubber dispersant EVA 1.5 parts; CPE short-chain chlorinated paraffin 3 parts.

[0036] The preparation method is the same as in Example 1.

[0037] This embodiment examines the feasibility of maintaining the low-temperature toughness of the rubber compound by increasing the amount of CPE short-chain chlorinated paraffin by 3 parts and the amount of rubber dispersant EVA by 1.5 parts under the conditions of a relatively high carbon black content of 40 parts and a relatively low softening oil content of 2 parts, in order to verify the boundary adaptability and industrial adjustability of the technical solution of the present invention.

[0038] Comparative Example 1 This comparative example provides a conventional ordinary transmission belt base rubber, and the raw material formula, by weight parts, is as follows: Chloroprene rubber CR121 100 parts; zinc oxide 5 parts; magnesium oxide 4 parts; sulfur 1 part; stearic acid 1 part; N330 carbon black 48 parts; aromatic oil 7 parts; antioxidant 4020 1 part; antioxidant RD 0.5 parts.

[0039] The preparation method adopts the traditional conventional mixing process: after plasticizing chloroprene rubber CR121 in an internal mixer for 2 minutes, all fillers and additives are added at one time, and after mixing at a high temperature of 120-130℃ for 6 minutes, the rubber is discharged, and after passing through a two-roll mill twice, it is vulcanized and molded. The vulcanization conditions are the same as in Example 1.

[0040] Comparative Example 2 This comparative example provides a common modified cold-resistant base rubber, with the following raw material formulation by weight: Chloroprene rubber CR121 100 parts; zinc oxide 5 parts; magnesium oxide 4 parts; sulfur 1 part; stearic acid 1 part; N330 carbon black 43 parts; precipitated silica 8 parts; aromatic oil 5.5 parts; antioxidant 4020 1.2 parts; antioxidant RD 0.8 parts; rubber dispersant EVA 0.5 parts; low temperature cold resistance additive DBS (dibutyl sebacate) 1 part.

[0041] The preparation method adopts a conventional modified mixing process: after plasticizing chloroprene rubber CR121 for 2 minutes, the additives are added, and then the reinforcing filler and softening system are added in batches. After mixing at 110-120℃ for 7 minutes, the rubber is discharged and vulcanized after passing through a two-roll mill 3 times. The vulcanization conditions are the same as in Example 1.

[0042] Comparative Example 3 The formulation of Example 1 was followed, but the preparation process employed a traditional high-temperature mixing process: a first-stage mixing temperature of 130–140°C, a discharge temperature of 120°C, two thin passes, and no room temperature curing; all other conditions were the same as in Example 1. This comparative example was used to verify the uniqueness of the preparation process of this invention.

[0043] Comparative Example 4 The formulation of Example 1 was used, but the CPE short-chain chlorinated paraffin was replaced with an equal amount of DBS (dibutyl sebacate), and all other conditions were the same as in Example 1. This comparative example was used to verify the irreplaceable nature of CPE short-chain chlorinated paraffin as a low-temperature anti-brittleness agent.

[0044] Performance testing The base adhesive test pieces prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests according to the following test methods: 1. Shore A hardness: Tested according to GB / T531.1, with a sample thickness of not less than 6 mm, and tested after conditioning in an environment of 23±2℃ for 24 hours.

[0045] 2. Tensile strength and elongation at break: Tested according to GB / T528, using dumbbell-shaped type I specimens, tensile speed 500 mm / min, and ambient temperature 23±2℃.

[0046] 3. Low-temperature brittleness test: The test is conducted according to GB / T15256. The test temperature is -35℃, the sample size is 25mm×6mm×2mm, the impact speed is 2m / s, and the test is conducted to observe whether brittleness occurs after the impact of 5 samples.

[0047] 4. Low-temperature compression set: The test was conducted according to GB / T7759. The test conditions were -20℃ for 24 hours, with a compression rate of 25%. The sample was type A (diameter 13mm × height 6mm). After decompression, the sample was allowed to recover in an environment of 23±2℃ for 30 minutes before the height change was measured. The compression set rate was calculated according to the formula.

[0048] 5. Low-temperature repeated flexing test: Under a low temperature environment of -20℃, the sample is continuously flexed 50,000 times using a Democia type low-temperature flexing tester, with a flexing frequency of 300 times / min and a flexing angle of 90°. The surface cracking of the sample is observed.

[0049] 6. Low-temperature tensile retention rate: According to GB / T528, after the sample is conditioned in a low-temperature environment chamber at -20℃ for 4 hours, the tensile strength is tested in a low-temperature environment, and the percentage of low-temperature tensile strength to room-temperature tensile strength is calculated.

[0050] 7. Low temperature rebound rate: Tested according to GB / T1681, test temperature -20℃, using a Schopfer rebound tester, the sample is tested after being conditioned in an environment of -20℃ for 4 hours.

[0051] 8. Low-temperature linear shrinkage rate: After placing the vulcanized sample in a -40℃ low-temperature chamber for 72 hours, take it out and measure the dimensional change rate in the length direction.

[0052] 9. Performance retention rate after thermo-oxidative aging: According to GB / T3512, the tensile strength retention rate and elongation at break retention rate are tested after thermo-oxidative aging at 100℃ for 72h.

[0053] Test Results Table 1. Results of Basic Performance Tests at Room Temperature Table 2. Test results of core cold resistance performance Table 3 Performance retention rate after thermo-oxidative aging (100℃×72h) Results Analysis I. Performance Analysis at Room Temperature As can be seen from Table 1: The tensile strengths of Examples 1-3 of this invention are 21.2 MPa, 20.5 MPa, and 19.8 MPa, respectively, all superior to 18.1 MPa of Comparative Example 1 and 9.6 MPa of Comparative Example 2. Notably, the tensile strength of Example 1 is 17.1% higher than that of Comparative Example 1. Although this invention significantly reduces the amount of hard carbon black N330 from 48 parts to 35 parts, the synergistic reinforcing effect of silica not only avoids sacrificing strength but also achieves an increase. This fully demonstrates the effectiveness of the low-rigidity reinforcing system with low carbon black and high silica content in maintaining and even improving room-temperature mechanical strength.

[0054] The elongation at break of the embodiments of the present invention, ranging from 476% to 508%, is significantly better than that of Comparative Example 1 (422%) and Comparative Example 2 (456%), with Example 2 reaching as high as 508%, which is 20.4% higher than that of Comparative Example 1. The increase in elongation at break indicates that the flexibility and toughness of the rubber compound are enhanced, which is directly due to the decrease in rigidity caused by the reduction in carbon black content and the increase in toughness caused by the flexible reinforcement of silica.

[0055] The Shore A hardness of 64-66HA in the embodiments of the present invention is lower than that of 68HA in Comparative Example 1 and 67HA in Comparative Example 2. The decrease in hardness means that the overall rigidity of the rubber compound decreases, which lays the foundation for maintaining the ability of molecular chain movement at low temperatures.

[0056] The tensile strength (19.1 MPa) and elongation at break (441 MPa) of Comparative Example 3 are both lower than those of Example 1, indicating that the proprietary "low-temperature segmented mixing—multiple thin passes—room temperature curing" process of this invention plays an irreplaceable role in fully realizing the potential of the formulation. Although the tensile strength (19.8 MPa) and elongation at break (468%) of Comparative Example 4 are better than those of Comparative Example 2, they are still lower than those of Example 1, indicating that CPE short-chain chlorinated paraffins in the formulation system of this invention are not only low-temperature anti-brittleness additives, but also contribute positively to mechanical properties.

[0057] II. Low Temperature Performance Analysis As can be seen from Table 2: Regarding low-temperature brittleness: In Comparative Example 1, all five samples completely cracked during the -35℃ low-temperature brittleness test. This is a typical low-temperature failure mode for traditional high-carbon black filled chloroprene rubber—the rubber molecular chains freeze at low temperatures, and the hard carbon black filling system further amplifies the rigidity of the material, leading to brittle fracture under impact loads. Comparative Example 2 showed localized cracking, indicating that although the ordinary modified formulation improved the low-temperature brittleness to some extent, it still could not meet the reliability requirements of the transmission belt base rubber in the -35℃ ultra-low temperature environment. Comparative Example 3 also showed localized cracking (1 out of 5 samples cracked), fully demonstrating that even with excellent formulation design, if there is a lack of matching low-stress preparation process, the residual processing stress inside the rubber compound will still become a source of cracking at low temperatures. Comparative Example 4 also showed localized cracking, proving that CPE short-chain chlorinated paraffin, as the unique low-temperature anti-brittleness additive of this invention, is irreplaceable. Although the conventional cold-resistant additive DBS has a certain plasticizing effect, it cannot provide sufficient anti-brittleness protection under ultra-low temperature impact conditions. In the low-temperature brittleness test at -35℃, all five samples of the present invention in Examples 1 to 3 showed no brittleness or cracks. This is due to the synergistic protection of the low-rigidity reinforcement system, the low-temperature crystallization-resistant softening system, the CPE low-temperature anti-brittleness additive, and the low-stress preparation process.

[0058] Regarding low-temperature compression set: Compression set reflects the degree of irreversible slippage and plastic deformation of the molecular chains in the rubber compound under long-term compression. Comparative Example 1 showed a high compression set of 28.6%, meaning the rubber compound almost completely lost its resilience at -20°C. This is a fatal flaw in the base rubber of transmission belts, as the base rubber continuously endures compression-rebound cycles during belt operation. Excessive compression set will cause the belt to collapse, the pitch to change, and ultimately, transmission failure. Comparative Example 2 reduced the compression set to 20.3%, showing limited improvement. Comparative Example 3 was 22.1%, higher than Comparative Example 2, indicating that traditional processes cannot fully utilize the low-temperature advantages of the present invention's formulation. Comparative Example 4 was 18.7%, better than Comparative Example 2 but still significantly higher than Example 1. The present invention's Example 1 was as low as 12.5%, Example 2 was 13.2%, and Example 3 was 14.8%, all significantly lower than the comparative examples. This effect relies on the synergy of three levels: First, the low-rigidity reinforcing system reduces the overall modulus of the rubber compound, making the molecular chains more prone to recoverable elastic deformation rather than irreversible plastic flow under compression. Second, the cold-resistant composite softening oil weakens the intermolecular forces by intercalating between the neoprene rubber molecular chains, inhibiting low-temperature crystallization and allowing the molecular chains to maintain a certain degree of mobility at low temperatures. Third, the short-chain chlorinated paraffin of CPE, as an auxiliary plasticizer, further enhances the low-temperature mobility of the molecular chains and reduces molecular chain breakage during stress relaxation.

[0059] Regarding low-temperature flexural performance: Comparative Example 1 showed severe cracking and spalling after 50,000 flexes at -20℃, a typical low-temperature fatigue failure mode. During repeated bending, microcracks initiated on the hard and brittle surface of the rubber compound. These cracks propagated under cyclic stress, eventually leading to macroscopic cracking and spalling. Comparative Example 2 showed fine cracks, indicating that although the ordinary modified formulation offered some improvement, it still could not meet the requirements for long-term dynamic service. Examples 1-3 of this invention showed intact surfaces without cracks, proving that the rubber compound of this invention has excellent resistance to fatigue cracking under low-temperature dynamic bending conditions. This performance is crucial for the base rubber of transmission belts, as the base rubber of transmission belts continuously endures alternating bending and stretching deformation during operation.

[0060] Regarding low-temperature tensile strength retention: Comparative Example 1 only retained 58% of its room-temperature tensile strength at -20℃, meaning the rubber compound lost nearly half of its mechanical strength at low temperatures. Comparative Example 2 improved to 72%, but the improvement was limited. Example 1 of this invention achieved a high retention rate of 89%, Example 2 86%, and Example 3 82%, meaning the rubber compound retained the vast majority of its mechanical strength at -20℃. This improvement directly stems from the synergistic effect of the various technical features of this invention. The molecular chains are not frozen at low temperatures and can still transfer and disperse applied stress through the movement of molecular chain segments, thereby avoiding premature fracture caused by stress concentration.

[0061] Regarding low-temperature rebound rate: Comparative Example 1 showed a rebound rate of only 32% at -20℃, almost losing the basic characteristics of an elastomer. Comparative Example 2 showed a rebound rate of 41%, indicating limited improvement. Example 1 of this invention achieved a rebound rate as high as 56%, meaning that the rubber compound still maintains excellent elastic recovery ability at low temperatures. This is the core guarantee for the transmission belt base rubber to maintain normal transmission function at low temperatures.

[0062] Regarding the low-temperature linear shrinkage rate: Comparative Example 1 showed a linear shrinkage rate of 2.8% under conditions of -40℃ for 72 hours, indicating that the rubber compound underwent significant volume shrinkage and dimensional changes at extreme low temperatures. Comparative Example 2 showed a rate of 1.9%, indicating limited improvement. Example 1 of this invention showed a rate as low as 0.8%, demonstrating excellent dimensional stability of the rubber compound at extreme low temperatures. This is crucial for the stability of the bonding interface between the bottom rubber of the transmission belt and other components of the belt body, as excessive shrinkage can lead to interfacial stress concentration and adhesive failure.

[0063] III. Analysis of Thermo-Oxidative Aging Performance As shown in Table 3, the tensile strength retention rate (83%–85%) and elongation at break retention rate (70%–72%) of the embodiments of the present invention after thermo-oxidative aging at 100℃ for 72 hours are both superior to those of Comparative Example 1 (82%, 65%) and Comparative Example 2 (78%, 61%). This indicates that the present invention improves low-temperature performance without sacrificing thermo-oxidative aging performance. On the contrary, the appropriate increase in the amount of antioxidants (antioxidant 4020 increased from 1 part to 1.5 parts, and antioxidant RD increased from 0.5 parts to 1 part) improves the aging resistance to a certain extent. This result is of great significance, as transmission belts not only face low-temperature environments during actual service but also high-temperature aging caused by frictional heat generated by the pulleys. The present invention achieves the design goal of "balancing high and low temperature performance".

[0064] Based on the above test results, existing technologies for improving the base rubber of chloroprene rubber transmission belts mostly focus on heat resistance, antistatic properties, and flame retardancy, lacking systematic solutions to problems such as brittleness, hardening, and large compression set in ultra-low temperature environments (-35℃ to -40℃). Although there is a cold-resistant technology route that combines chloroprene rubber and butadiene rubber, the rubber blend system has inherent defects such as poor interfacial compatibility, decreased mechanical properties, and deteriorated adhesive performance. This invention takes a unique approach, solving the above problems through deep modification of a single chloroprene rubber system without using blends.

[0065] This invention is not a simple addition or subtraction of components, but rather a synergistic system in which four indispensable elements are: a low-rigidity reinforcing system, a low-temperature crystallization-resistant softening system, a low-temperature anti-brittleness agent, and a low-stress preparation process. The experimental results of Comparative Examples 3 and 4 fully demonstrate this point; the absence of any one element leads to a significant decrease in low-temperature performance. This synergistic effect of "1+1+1+1>4" is the core embodiment of the invention's inventiveness.

[0066] It is well known to those skilled in the art that while reducing the amount of carbon black improves low-temperature performance, it usually comes at the cost of sacrificing tensile strength. However, this invention, through the introduction of silica and the synergistic effect of CPE, achieves a significant increase in tensile strength from 18.1 MPa to 21.2 MPa (an increase of 17.1%), even with a substantial reduction in carbon black content from 48 parts to 35 parts (a reduction of 27%). This "strength increase instead of decrease" effect is unforeseen by those skilled in the art. Similarly, CPE short-chain chlorinated paraffins are commonly used in the art as flame retardants or auxiliary plasticizers; their use as a low-temperature anti-brittleness agent for chloroprene rubber with such remarkable results also exceeds the conventional expectations of those skilled in the art.

[0067] This invention sets up four comparative examples, which comprehensively compare the four dimensions of "traditional formula" (comparative example 1), "common improved formula" (comparative example 2), "process difference" (comparative example 3), and "additive replacement" (comparative example 4). The test items cover eight major items, including room temperature mechanics, low temperature brittleness, low temperature compression set, low temperature flexural deformation, low temperature tensile retention, low temperature rebound, low temperature shrinkage, and thermo-oxidative aging. The data chain is complete and the evidence is sufficient.

[0068] The formulation system of this invention is simple, the raw materials are widely available, and the cost is controllable. The preparation process is compatible with existing transmission belt production line equipment, and industrialization can be achieved without large-scale equipment modification. At the same time, the comprehensive performance of this invention—not becoming brittle at an extreme low temperature of -40℃ and not cracking during low-temperature flexing—is unattainable by existing technologies and has significant irreplaceability.

[0069] Basis and range for selecting the dosage of each component The dosage ranges of each raw material component in this invention are derived from extensive experimental optimization, and their selection is based on the following criteria: Chloroprene rubber CR121 (100 parts): CR121 is a general-purpose sulfur-modified chloroprene rubber with good physical and mechanical properties and processing performance. Using 100 parts as the standard is a conventional measurement method in this field, which facilitates precise control of the proportions of each compounding agent.

[0070] N330 carbon black (30-40 parts): N330 is a high-abrasion-resistant furnace-processed carbon black, and it is the most commonly used reinforcing filler in the base rubber of transmission belts. When the dosage is less than 30 parts, the reinforcement is insufficient, and the tensile strength decreases significantly; when the dosage is more than 40 parts, the rubber compound becomes too rigid, and its low-temperature performance deteriorates. 35 parts is preferred.

[0071] Silica (10-18 parts): Silica, as a flexible reinforcing filler, has a different reinforcing mechanism than carbon black—primarily through hydrogen bonding between surface silanol groups and rubber molecular chains. When the dosage is less than 10 parts, the flexible reinforcing effect is insufficient; when the dosage is more than 18 parts, due to the large specific surface area and difficulty in dispersion of silica, it may lead to deterioration of the rubber compound's processing properties and a decrease in mechanical properties. 14 parts is preferred.

[0072] Cold-resistant composite softening oil (2-6 parts): Naphthenic oil has good compatibility with chloroprene rubber, and the low-temperature plasticizer (DOP or DOA) can effectively reduce the glass transition temperature of chloroprene rubber. The combination of the two can produce a synergistic effect. A dosage of less than 2 parts results in insufficient softening effect; a dosage of more than 6 parts may lead to a significant decrease in the mechanical strength of the vulcanizate and blooming problems. 4 parts are preferred, and the preferred mass ratio of naphthenic oil to low-temperature plasticizer is 1:0.8-1.2.

[0073] Antioxidant 4020 (1.2–1.8 parts) and antioxidant RD (0.8–1.2 parts): These two constitute a composite anti-aging system. If the dosage is too low, the protection will be insufficient; if the dosage is too high, it may affect the vulcanization rate and cause blooming. The preferred dosages are 1.5 parts and 1 part, respectively.

[0074] EVA (0.8–1.5 parts): Ethylene-vinyl acetate copolymer (EVA) acts as a rubber dispersant, effectively promoting the uniform dispersion of carbon black and silica in the rubber matrix. A dosage below 0.8 parts results in insufficient dispersion; a dosage above 1.5 parts may affect the physical and mechanical properties of the rubber compound. 1 part is preferred.

[0075] CPE short-chain chlorinated paraffin (2-3 parts): In this invention, CPE short-chain chlorinated paraffin serves as a specific low-temperature anti-brittleness additive, possessing both auxiliary plasticizing and anti-brittleness functions. A dosage below 2 parts results in insufficient low-temperature anti-brittleness effect; a dosage above 3 parts may lead to a decrease in the mechanical strength of the vulcanized rubber and surface blooming. Preferably, 2.5 parts are used, with a chlorine content preferably of 40-70 wt%.

[0076] Selection criteria for preparation process parameters A low-temperature plasticizing time (1-3 min, preferably 2 min): If the time is too short, the plasticizing will be insufficient and the compounding agents will be unevenly dispersed; if the time is too long, the chloroprene rubber molecular chains may be degraded or cross-linked prematurely due to mechanical shearing and overheating.

[0077] Segmented mixing time (5-9 min, preferably 7 min) and discharge temperature (≤105℃): If the mixing time is too short, the filler will not be dispersed evenly; if the time is too long, it may overheat. When the discharge temperature exceeds 105℃, the low molecular weight components in the low-temperature softening oil may volatilize and be lost, and the chloroprene rubber may undergo premature vulcanization (scorching).

[0078] The number of thin passes (4-8 times, preferably 6 times) and the roll gap (0.8-1.5 mm, preferably 1.2 mm): Too few thin passes result in insufficient stress release and uneven packing dispersion; too many thin passes may lead to excessive shearing and molecular chain degradation. If the roll gap is too small, the shearing force will be too large and may damage the molecular chain; if the roll gap is too large, the shearing force will be insufficient to effectively disperse the packing and release stress.

[0079] Room temperature standing curing time (20-30h, preferably 24h): If the time is too short, the internal stress will not be fully released and the adsorption balance of the compounding agent will not be established; if the time is too long, the production efficiency will be reduced and the rubber surface may bloom due to prolonged standing.

[0080] Vulcanization temperature (145–165℃, preferably 155℃), pressure (10–20 MPa, preferably 15 MPa), and time (15–22 min, preferably 18 min): Insufficient vulcanization and inadequate crosslinking density result from excessively low vulcanization temperature or time; excessively high vulcanization temperature or time may lead to over-vulcanization, causing excessive development of the crosslinking network and resulting in brittle rubber. Insufficient pressure may lead to air bubble defects inside the sample; excessively high pressure increases the requirements for equipment and may cause rubber to overflow.

[0081] Summary of Comparison between the Invention and the Prior Art The core performance indicators of Embodiment 1 of the present invention are compared with those of Comparative Examples 1 and 2: The above data fully demonstrates that this invention achieves a leapfrog improvement in low-temperature performance without sacrificing, but rather enhancing, the room-temperature mechanical properties. Through the synergistic effect of a low-rigidity reinforcing system, a low-temperature resistant crystallization and softening compound system, a low-temperature anti-brittleness additive, and a proprietary low-temperature and low-stress preparation process, this invention achieves the technical effect of non-brittleness, high resilience, and flexural resistance of the transmission belt base rubber in an ultra-low temperature environment of -40℃, while also taking into account excellent room-temperature mechanical properties. It solves the technical problems of low-temperature hardening, brittleness, and low-temperature flexural failure of traditional neoprene base rubber, and has significant industrial application value and market promotion prospects.

[0082] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cold-resistant transmission belt base rubber, characterized in that, By weight, it includes the following raw materials: The composition includes 100 parts of chloroprene rubber CR121, 5 parts of zinc oxide, 4 parts of magnesium oxide, 1 part of sulfur, 1 part of stearic acid, 30-40 parts of N330 carbon black, 10-18 parts of silica, 2-6 parts of cold-resistant composite softening oil (the cold-resistant composite softening oil being a compound of naphthenic oil and low-temperature plasticizer), 1.2-1.8 parts of antioxidant 4020, 0.8-1.2 parts of antioxidant RD, 0.8-1.5 parts of rubber dispersant EVA, and 2-3 parts of low-temperature anti-brittleness and cold-resistant additive (the low-temperature anti-brittleness and cold-resistant additive being CPE short-chain chlorinated paraffin).

2. The cold-resistant transmission belt base rubber according to claim 1, characterized in that, Preferably, by weight, it includes the following raw materials: Chloroprene rubber CR121 100 parts, zinc oxide 5 parts, magnesium oxide 4 parts, sulfur 1 part, stearic acid 1 part, N330 carbon black 35 parts, silica 14 parts, cold-resistant composite softening oil 4 parts, antioxidant 4020 1.5 parts, antioxidant RD 1 part, rubber dispersant EVA 1 part, low-temperature anti-brittleness and cold-resistant additive 2.5 parts.

3. The cold-resistant transmission belt base rubber according to claim 1, characterized in that, The silica is at least one of fumed silica or precipitated silica.

4. The cold-resistant transmission belt base rubber according to claim 1, characterized in that, The mass ratio of naphthenic oil to low-temperature plasticizer in the cold-resistant composite softening oil is 1:0.8 to 1.

2.

5. The cold-resistant transmission belt base rubber according to claim 1, characterized in that, The chlorine content of the CPE short-chain chlorinated paraffin is 40-70 wt%.

6. A method for preparing a cold-resistant transmission belt base rubber as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step S1, low-temperature plasticizing: put chloroprene rubber CR121 into a mixer and plasticize at low temperature for 1 to 3 minutes. Then add stearic acid, rubber dispersant EVA, antioxidant 4020 and antioxidant RD in sequence, and continue to mix for 2 to 4 minutes. Step S2, adding reinforcing filler and low-temperature softening system in stages: N330 carbon black, white carbon black and cold-resistant composite softening oil are added to the rubber compound obtained in step S1 in batches, and the mixture is mixed at low speed for 5 to 9 minutes, and the discharge temperature is controlled to be ≤105℃. Step S3, two-stage vulcanization activation: After cooling the rubber compound obtained in step S2, put it into an internal mixer, add zinc oxide, magnesium oxide and sulfur, and mix at low speed for 2 to 4 minutes. Step S4, multiple low-temperature thin-pass stress relief: Place the rubber compound obtained in step S3 on a two-roll mill and repeatedly pass it through the mill 4 to 8 times under a roll gap of 0.8 to 1.5 mm, alternating between triangular wrapping and roll winding operations; Step S5, room temperature curing: allow the rubber compound obtained in step S4 to cure at room temperature for 20-30 hours; Step S6, vulcanization molding: The rubber compound obtained in step S5 is vulcanized at a vulcanization temperature of 145-165℃ and a pressure of 10-20MPa for 15-22 minutes to obtain a cold-resistant transmission belt base rubber.

7. The method for preparing a cold-resistant transmission belt base rubber according to claim 6, characterized in that, In step S1, the low-temperature plasticizing time is 2 minutes, and the mixing time after adding stearic acid, rubber dispersant EVA, antioxidant 4020 and antioxidant RD is 3 minutes.

8. The method for preparing a cold-resistant transmission belt base rubber according to claim 6, characterized in that, In step S2, the mixing time is 7 minutes and the discharge temperature is ≤105℃.

9. The method for preparing a cold-resistant transmission belt base rubber according to claim 6, characterized in that, In step S4, the roller gap is 1.2 mm, and the thin pass is repeated 6 times.

10. The method for preparing a cold-resistant transmission belt base rubber according to claim 6, characterized in that, In step S6, the vulcanization temperature is 155℃, the pressure is 15MPa, and the time is 18min.

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