NBR and ethylene blend

Abstract

A rubber composition comprising a terpolymer of nitrile and ethylene, particularly a polymer blend of acrylonitrile-butadiene copolymer (NBR) and an ethylene polymer. The NBR in the composition is 30 to 50% by weight of the total composition. In some embodiments, the ethylene polymer is EPDM rubber, ethylene acrylic elastomer, or chlorinated polyethylene. The composition can include an organic peroxide or other accelerators. The rubber composition is useful for synchronous belts with medium to high temperature resistance, good fuel resistance, flexibility down to -40°C, and high structural integrity. Furthermore, the rubber composition can reduce the amount of reinforcing materials such as carbon black.

Description

Technical Field

[0001] The present disclosure relates to a composition, particularly a rubber composition, for use in flexible belts such as synchronous belts having medium to high temperature resistance, good oil resistance, flexibility down to -40°C, and high structural integrity.

Background Art

[0002] HNBR, a hydrogenated version of NBR rubber, is a synthetic rubber with very good heat resistance and excellent oil resistance, and is widely used in synchronous belt compounds to meet the service conditions.

[0003] Alternative materials that meet the service conditions of synchronous belts such as heat resistance and oil resistance are in demand.

Summary of the Invention

[0004] This summary of the invention is provided to introduce in a simplified form a selection of concepts that are further described in detail in the detailed description. This summary of the invention and the background art above are not intended to identify key or essential aspects of the subject matter of the claims. Further, this summary of the invention is not intended to be considered in determining the scope of the subject matter of the claims.

[0005] The present disclosure relates to a rubber composition having a polymer blend of a terpolymer of nitrile and ethylene, particularly a composition of acrylonitrile-butadiene copolymer (NBR) and an ethylene polymer. This composition contains NBR as 30 to 50% by weight of the total composition. In some embodiments, the ethylene polymer is EPDM rubber (a known rubber made from ethylene, propylene, and a diene comonomer that enables crosslinking by sulfur vulcanization). In other embodiments, the ethylene polymer is an ethylene acrylic elastomer. In still other embodiments, the ethylene polymer is chlorinated polyethylene. This composition may contain an organic peroxide or other accelerators.

[0006] This rubber composition is useful for synchronous belts having medium to high temperature resistance, good oil resistance, flexibility down to -40°C, and high structural integrity. Further, this rubber composition can reduce the amount of reinforcing materials such as carbon black while maintaining the properties required for synchronous belts.

[0007] These and other aspects of the technology described herein will become apparent upon consideration of the detailed description and drawings herein. However, it should be understood that the scope of the subject matter of the claims is defined by the issued claims and is not defined by whether the given subject matter addresses some or all of the problems recited in the background art or includes some or all of the features or aspects recited in the summary of the invention.

Brief Description of the Drawings

[0008] Non-limiting and non-exhaustive embodiments including preferred embodiments of the disclosed technology are described with reference to the following figures, in which, unless otherwise specifically noted, like reference numerals refer to like parts throughout the figures.

[0009] Figure 1A is the chemical structure of acrylonitrile butadiene rubber (NBR). Figure 1B is a qualitative mapping of the mechanical properties of NBR.

[0010] Figure 2A is the chemical structure of EP DM containing ethylidene norbornene (ENB) as a non-conjugated diene. Figure 2B is a qualitative mapping of the mechanical properties of EPDM.

[0011] Figure 3 is a qualitative mapping of the mechanical properties of an NBR / EPDM blend.

[0012] Figure 4 is a qualitative mapping of the mechanical properties of HNBR.

[0013] Figure 5 is a perspective view of an example of a belt manufactured with the composition of the present application.

Best Mode for Carrying Out the Invention

[0014] As described above, the present disclosure relates to a rubber composition having a polymer blend of a nitrile polymer and an ethylene polymer. Specifically, this composition has an acrylonitrile-butadiene copolymer (NBR) and an ethylene polymer, where NBR is 30 to 50% by weight of the total blend, and the ethylene polymer is 20 to 40% by weight of the total blend. The remainder consists of components such as activators, fillers, curing agents, reinforcing materials, anti-degradants (e.g., antioxidants, UV stabilizers), plasticizers, antistatic agents, colorants, processing aids, homogenizers, co-agents, catalysts, etc.

[0015] The base polymers of the composition are readily available. The composition can be cured by organic peroxide curing or accelerator curing. The cured composition can have a minimum Mooney viscosity of less than 60 MU when tested at 133°C. This composition has a tensile strength exceeding 18 MPa, temperature resistance up to 135°C while maintaining physical properties, and excellent adhesion strength. The cured composition has good oil resistance at high temperatures because it has a volume expansion of less than 20% in IRM901 oil at 135°C for 168 hours. Furthermore, the cured composition maintains flexibility even at -35°C.

[0016] In the following description, reference is made to the accompanying drawings that form a part hereof and in which are shown, by way of illustration, at least one specific embodiment. In the following description, additional specific embodiments are provided. These embodiments are disclosed in sufficient detail so that those skilled in the art can practice the invention. It is to be understood that other embodiments are contemplated and can be practiced without departing from the scope or spirit of the present disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense, and the scope of the present disclosure is not limited to the following description, but rather is defined by the appended claims. Through the description of the embodiments including the figures shown below, various aspects of the present disclosure can be understood. In some cases, sub-labels consisting of lowercase letters may be associated with a reference number to indicate one of a plurality of similar components. When referring to a reference number without specifying a sub-label, the reference is assumed to refer to all such plurality of similar components.

[0017] The present disclosure relates to rubber compositions having a polymer blend of nitrile and ethylene polymers, particularly acrylonitrile-butadiene copolymer (NBR) and ethylene polymers. Examples of suitable ethylene polymers include EPDM rubber (a well-known rubber produced from ethylene, propylene, and a diene comonomer that enables crosslinking by sulfur vulcanization), ethylene acrylic polymers or elastomers, and chlorinated polyethylene polymers. The composition includes NBR as 30 to 50% by weight of the total composition. In some embodiments, the composition includes an organic peroxide or other accelerator added during curing. Also, in some embodiments, the composition includes a non-conjugated diene of less than 15% by weight of the ethylene polymer weight.

[0018] The rubber composition is very suitable for use in synchronous belts for automotive and industrial applications because the cured composition has medium to high temperature resistance, good oil resistance, flexibility down to -40°C, and high structural integrity.

[0019] As described above, the composition comprises a blend of acrylonitrile-butadiene copolymer (NBR) and an ethylene polymer, and optionally contains a third monomer, a non-conjugated diene, of less than 15% by weight of the ethylene polymer.

[0020] Figure 1A shows the chemical structure of acrylonitrile-butadiene rubber (NBR), and Figure 1B is a qualitative mapping of the mechanical properties of NBR. NBR is excellent in mechanical properties, water resistance, oil resistance, and solvent resistance. NBR has excellent cold resistance but not excellent high-temperature resistance. However, due to the presence of unsaturation in the polymer backbone, its ozone resistance and heat aging resistance are poor. Therefore, blending NBR with other polymers can improve its heat resistance and ozone resistance.

[0021] The blend of NBR and an ethylene polymer provides a composition of better quality than either material. For example, the composition of NBR and EPDM provides better properties than either polymer alone.

[0022] Figure 2A shows the chemical structure of EPDM containing ethylidene norbornene (ENB) as a non-conjugated diene, and Figure 2B is a qualitative mapping of the mechanical properties of EPDM. EPDM has excellent heat resistance and good water resistance at both low and high temperatures, but its oil resistance and solvent resistance are low even in the cured state. EPDM also has excellent heat aging resistance and ozone resistance.

[0023] The blend of NBR and EPDM is unexpected. This is because it is well known that NBR and EPDM have poor compatibility. NBR is a polar polymer due to the presence of acrylonitrile groups, while EPDM is a non-polar rubber. However, when a non-conjugated diene is present in EPDM, some polarity is induced in the ethylene-propylene chain, improving the compatibility of the two polymers. Both the acrylonitrile content of NBR and the diene content of EPDM promote good compatibility between the polymers. This composition blend has high tensile, elongation, and tear properties, indicating improved compatibility between the polymers.

[0024] The obtained blend composition of NBR and EPDM has a desirable balance of heat resistance, aging resistance, ozone resistance, and solvent resistance. This composition has sufficient flexibility even at a low temperature of -40°C, which is a common requirement for synchronous belts in automotive and industrial applications. Also, when compounded with a selected adhesive, this composition exhibits excellent adhesiveness.

[0025] Figure 3 is a qualitative mapping of the mechanical properties of the NBR / EPDM blend. It can be seen that all the properties of the blend are generally improved compared to those of the two polymers alone. The blend composition has excellent mechanical properties, water resistance, and oil resistance. This composition has excellent heat resistance at both low and high temperatures.

[0026] Figure 4 is a qualitative mapping of the mechanical properties of HNBR, which is an alternative to the blend of NBR and ethylene polymer. It can be seen that the properties of the blended composition are equivalent to or close to those of HNBR.

[0027] Other ethylene polymers suitable for blending with NBR include ethylene acrylic elastomer, chlorinated polyethylene, ethylene propylene elastomer (EPM), ethylene butene (EBM), ethylene pentene, ethylene octene (EOM), etc.

[0028] The selection of the polymer grade affects the flow characteristics of the blended compound. A polymer grade with a high Mooney viscosity has poor fluidity and poor formation of belt teeth, so it is not desirable for synchronous belts in automotive applications. However, the final cured material (e.g., vulcanizate) has excellent physical properties such as tensile strength, modulus of elasticity, and elongation. On the other hand, a low molecular weight grade increases fluidity, but the blended vulcanizate may not have sufficient physical strength. There are many commercially available NBR grades with different molecular weights (such as Mw and Mn). These are characterized by the Mooney viscosity (ML1+4 at 100°C) of the polymer in the range of 30 - 90 MU.

[0029] NBR polymers typically contain from about 20 to about 50 wt% acrylonitrile. Due to the presence of acrylonitrile groups, NBR has excellent solvent resistance, and this property can be further improved by selecting NBR with a high acrylonitrile content. However, acrylonitrile groups reduce the low-temperature flexibility of NBR and blend compositions. For example, the glass transition temperature of NBR with a 34% acrylonitrile content is close to -35°C. As the acrylonitrile content increases, the glass transition temperature also rises, and the low-temperature flexibility of both NBR and blend compositions decreases.

[0030] The amounts of NBR and ethylene polymer are from 25 wt% to 75 wt% of the total weight of the raw materials forming the uncured blend composition, with NBR being from 30 to 60 wt% of the total weight and the ethylene polymer being from 10 to 30 wt% of the total weight. In some embodiments, NBR and ethylene are from about 40 wt% to 70 wt% of the total weight of the raw materials, and in other embodiments from about 45 to 60 wt%.

[0031] The weight ratio of NBR to ethylene is from 3:1 to 1:1, and in some embodiments, the weight ratio of NBR to ethylene is about 2:1.

[0032] Examples of ethylene polymers suitable for blending with NBR include EPDM, ethylene propylene elastomer (EPM), ethylene acrylic elastomer, chlorinated polyethylene, ethylene butene (EBM), ethylene pentene, and ethylene octene (EOM).

[0033] EPDM is a terpolymer of ethylene and propylene and includes a saturated polymer backbone, a saturated non-conjugated diene monomer, and an ethylene propylene copolymer. Examples of diene monomers present in EPDM include dicyclopentadiene (DCPD), ethylidene norbornene (ENB), 1,4-hexadiene, and methylidene norbornene.

[0034] EPDM is usually composed of about 30% to about 80% by weight of ethylene and about 0% to about 15% of non-conjugated diene. Usually, the diene content can be identified by an iodine value of about 5 to about 30. The Mooney viscosity (ML1+4 at 125 °C) is usually about 40 to about 100 MU. When ethylene exceeds 70% by weight, the EPDM polymer exhibits crystalline characteristics.

[0035] In addition to NBR and ethylene polymers, the blend composition may include additional rubber stocks including, but not limited to, natural rubber, styrene-butadiene rubber (SBR), chloroprene rubber (CR), hydrogenated nitrile-butadiene rubber (HNBR), and fluoroelastomer (FKM).

[0036] The rubber stocks (NBR, EPDM, and others) are often in the form of solid powder, pellets, bales, or blocks, but may be liquid or semi-liquid depending on the embodiment.

[0037] As described above, the blend composition may include an organic peroxide or other accelerator to promote curing of the blend composition. Various types of organic peroxides can be used in the blend composition. The organic peroxide decomposes at a specific temperature to generate radicals that initiate a cross-linking reaction within the compound. Specific examples of organic peroxides used for NBR and EPDM include α,α-bis(t-butylperoxy) diisopropylbenzene. In some embodiments, the total amount of the organic peroxide is less than about 2.5% by weight of the raw materials.

[0038] Polymer compositions cured with organic peroxides exhibit higher heat resistance because C-C crosslinks are formed between polymer chains. In contrast, sulfur-cured polymers form C-S-C or C-(S)x-C bonds. The formation of monosulfide (i.e., C-S) bonds or polysulfide (i.e., S-S) bonds leads to a decrease in the heat resistance of the polymer. The C-C bond energy (346 kJ / mol) is higher than both the C-S (272 kJ / mol) and S-S (226 kJ / mol) bond energies, which is reflected in the high heat resistance of peroxide-cured vulcanizates.

[0039] The blend composition can include various additives such as activators, fillers, curing agents, reinforcing agents, anti-degradants (e.g., antioxidants, UV stabilizers), plasticizers, antistatic agents, colorants, processing aids, homogenizers, co-agents, catalysts, etc. Generally, the total weight percentage of additives is less than 65% by weight of the raw materials of the total composition, and in some embodiments, less than 50% by weight.

[0040] Examples of activators include stearic acid and zinc oxide. Stearic acid is generally solid, available as flakes or pellets, and has a specific gravity of about 0.85. Stearic acid typically contains up to 10% by weight of iodine. The acid value ranges from 193 to 213. Zinc oxide is also solid, for example, a fine powder with a surface area of 4 to 6 m 2 / g and a specific gravity of 5.6. Zinc oxide may contain impurities such as CuO < 0.0005% by weight, MnO < 0.0005% by weight, SiO2 < 0.02% by weight, and / or water-soluble salts < 0.05% by weight. In some embodiments, the total amount of the activator is less than about 5% by weight of the raw materials, and in some embodiments, less than about 3% by weight. Long-chain fatty acids (LCFs) can be used as homogenizers and, when combined with zinc oxide, can act as activators.

[0041] Any suitable curing agent or material can be used, and the agent promotes or aids during curing. Examples of suitable curing agents include sulfur and peroxides. In some embodiments, the amount of curing agent used is less than about 8% by weight, such as less than 5% by weight, of the total weight of the raw materials.

[0042] Silica can be added to increase the tensile strength, modulus of elasticity, compression set, and abrasion resistance of the blend composition. Silica is typically a solid, such as a powder, and can be treated or untreated. The surface area of the silica is typically 120 - 200 m 2 / g. An example of treated silica with 5 - 8% by weight of an organic silane treatment has a specific gravity of 1.9 - 2.0. The silica in this example has a volatile content of 3 - 5% and a pH value of 6 - 8. The organic silane is of the trialkoxysilane type. Thus, the treated silica material has low hygroscopicity and significantly less generation of volatile matter during mixing and processing. In some embodiments, the total amount of silica is about 10 - 35% by weight of the raw materials.

[0043] Carbon black and / or graphite can be used as fillers for rubber compounds. Examples of other fillers include metal oxides such as aluminum oxide, magnesium oxide, copper oxide, zinc oxide, clay, montmorillonite clay, pulp, mica, and the like.

[0044] The raw materials of the mixed composition may include a reinforcing material such as chopped fiber segments, but other reinforcing materials such as elongated segments, fibers, or nanotubes can also be used. Whether chopped or elongated, the reinforcing material is, for example, aramid, polyester (PET), cotton, nylon, glass, carbon fiber cord, hybrid cord, metal, ceramic, other plastics, and the like. The reinforcing material may be made from an organic material, a synthetic material, or a mixture of an organic material and a synthetic material.

[0045] The dimensions of the reinforcing material are generally not limited. In some embodiments, the shredded fibers have a high aspect ratio with lengths ranging from 0.2 mm to 3 mm. In some embodiments, the aspect ratio of the reinforcing material (e.g., shredded fibers or elongated material) is from 10 to 250. In some embodiments, the amount of the reinforcing material is from 5 wt% to 30 wt% of the total weight of the raw materials. The reinforcing material is mixed with the raw materials, and in the resulting belt, the reinforcing material is uniformly dispersed throughout the blended composition.

[0046] In some embodiments, the amount of the filler (including silica, carbon black, or carbon reinforcing fibers) is from 5 wt% to 45 wt% of the total weight of the raw materials, while in other embodiments, the filler is from about 10 wt% to about 20 wt% of the total weight of the raw materials. The polymer blend of NBR and ethylene polymer makes it possible to reduce the amount of carbon reinforcing fibers or other carbon while still obtaining the properties acceptable for a synchronous belt and increase the amount of other fillers. In some embodiments, the ratio of silica to reinforcing carbon is from 5:1 to 3:1, for example, about 4:1.

[0047] Polymers deteriorate when exposed to various environmental factors such as oxygen, heat / temperature, ultraviolet light, weathering, catalytic degradation by heavy metal ions, and dynamic fatigue. Failures observed in rubber compounds due to environmental degradation include a decrease in elasticity and tensile strength, the formation of a cracked surface, and the appearance of cracks. The presence of unsaturation in the polymer can increase the tendency for failure due to thermal aging due to the allylic C-H bonds in the unsaturated chemical structure. The bond energy of allylic C-H is the weakest among different types (primary, secondary, tertiary) of C-H bonds. This factor promotes the formation of free radicals and peroxy radicals in the presence of oxygen and heat, causing chain scission. When the main chain of the polymer is cleaved, the compound begins to lose its physical and mechanical strength and starts to deteriorate. Antioxidants act as radical traps. They remove radicals to prevent the scission of polymer chains and extend the service life of the resulting product.

[0048] Antioxidants that can be used in rubber compounds, especially NBR, NR, BR, and SBR compounds, are polymerized quinoline derivatives, 1,2-dihydro-2,2,4-trimethylquinoline. Another antioxidant is a condensate of an alkylated imidazole and a diarylamine or a ketone, and another is a condensate of mercaptobenzimidazole and diphenylamine / acetone. These are powerful non-staining antioxidants for natural and synthetic rubbers, providing excellent temperature and flex protection at high temperatures.

[0049] Plasticizers can be added to elastomer compounds for various reasons, such as improving softness or flexibility, lowering the glass transition temperature, reducing crystallization, improving dispersibility, or reducing the cost of the compound. Common plasticizers used in elastomer compounds are mineral oils and esters such as phthalic esters, sebacic esters, and adipic esters. NBR is compatible with various types of ester plasticizers such as adipates, phthalic esters, and trimellitates.

[0050] Dialkyl esters and dioctyl adipate (DOA) are highly efficient plasticizers that can be used to impart excellent low-temperature flexibility and impact resistance to the compound. In addition to their high efficiency and contribution to low-temperature properties, they are chemically stable and do not discolor even when exposed to temperature and ultraviolet light for a long time. The combination of low viscosity and efficiency results in excellent dry blend and processing properties.

[0051] Microcrystalline wax can be added as a physical antiozonant for unsaturated rubbers. Polymer chains containing double bonds are vulnerable to ozonolysis reactions and chain scission in the presence of ozone. Microcrystalline wax provides a shielding layer or barrier on the compound, protecting the compound from degradation due to chain scission.

[0052] Modified resorcinol is a resorcinol formaldehyde homopolymer resin modified with a selected group and can be used as a precondensed drying binder. Chemically, it is a resorcinol formaldehyde homopolymer resin modified with a selected group. Modified resorcinol promotes the homogeneity of the mixed composition.

[0053] Metal acrylates such as zinc dimethacrylate can be used to enhance the physical and mechanical properties of the compound and act as an auxiliary agent. In the presence of an organic peroxide, the metal auxiliary forms an ionic bond and improves the tear strength, modulus of elasticity, and flex resistance of the compound.

[0054] Modified polybutadiene (containing maleic anhydride) can be used as a bonding accelerator for peroxide-cured vulcanizates. Chemically, this is a low molecular weight, low vinyl butadiene functionalized with maleic anhydride. The anhydride functional group can react with epoxy, amine, and hydroxyl groups, enabling the creation of unique adhesives, sealants, encapsulants, and coating agents. It also improves the compatibility of non-polar elastomers such as EPDM and enhances the adhesion of peroxide-cured elastomers to polyester, aramid, or metal substrates.

[0055] Substituted phenol derivatives such as 2,6-di-tert-butyl-N,N-dimethylamino-p-cresol can be used as scorch inhibitors for peroxide-curing systems. This first forms an adduct to capture radicals from the peroxide and affects the processing and flow time of the compound.

[0056] The above elastomers (NBR and ethylene polymers) and other components can be blended by conventional rubber blending methods. In some embodiments, mixing generally involves using an industrial mixer such as a Banbury mixer to mix all the raw materials, although other mixing techniques and methods can also be used. For example, roll mills and internal mixers can be used. In some embodiments, the individual raw materials are added to the mixer in a specific order to ensure sufficient incorporation and dispersion of the raw materials. In some embodiments, specific raw materials can be mixed together before being added to the mixture in sequence.

[0057] Tables 1 and 2 show exemplary component ranges of the blend compositions in the present disclosure. [Table 1] [Table 2]

[0058] The compositions obtained from Table 1, Table 2, or any of the above can be used, for example, to form belts such as synchronous belts for automobiles. FIG. 5 shows a general belt 500 having a body 502 formed of a flexible material with a back surface 504 and a front surface 506. Inside the body 502 are a plurality of load-bearing cords 508. In a particular embodiment, the cords 508 are bundled into three bundles, but in other embodiments, the cords 508 may be a single cord or bundled in other ways. The cords 508 may be, for example, carbon cords, polymer cords (e.g., polyester, aramid), glass fiber cords, etc. A plurality of teeth 510 are formed on the front surface 506. In FIG. 5 of this embodiment, trapezoidal teeth are depicted, but the shape of the teeth is not limited to this and can take any shape compatible with a sprocket, gear, or other gear. Each tooth 510 extends perpendicular to the longitudinal length of the belt 500, and the plurality of teeth 510 run along or around the length of the belt 500. In use, the teeth 510 on the front surface 106 contact a drive mechanism such as a gear or sprocket. Although not shown in FIG. 5, the belt 500 is an endless belt having a loop shape with no beginning or end.

[0059] <Example>

[0060] The objects and advantages of the present disclosure are further illustrated by the following non-limiting examples. The specific materials and their amounts recited in these examples, as well as other conditions and details, should not be construed as unduly limiting the present disclosure. Unless otherwise specified, all percentages, ratios, etc. in the examples and the remainder of this specification are by weight.

[0061] · Example 1

[0062] The materials listed in Table 3 were used in the recited amounts (in grams) to prepare a first blend composition according to the present disclosure.

Table 3

[0063] Semi-reinforcing black had a specific gravity of 1.8, a DBP absorption of 30 - 48 CC / 100g, an iodine absorption of 6 - 12 mg / g, a maximum heat loss of 1%, a residue on a 325-mesh sieve of 0.1%, an ash content of less than 0.5%, and a pellet hardness of 30g.

[0064] The specific gravity of the precipitated silica was 2.0, and its appearance was a white, odorless fine powder. The BET surface area of the silica was 130 - 200 m 2 / g. The loss on drying (105°C, 2 hours) was 3 - 7%. The loss on ignition (1000°C, 2 hours) on an anhydrous basis was at most 6%. The pH of a 5% aqueous slurry was in the range of 6 - 8, the % of SiO2 hydrate was at least 87%, and the DBP absorption value was 200 - 280 mL per 100g.

[0065] The specific gravity of the treated silica used was 1.9 - 2.0. The content of the trialkoxysilane treatment was 5 - 8%. The volatile content of this treated silica was 3 - 5%, the pH value was 6 - 8, and its appearance was a white powder. The specific surface area of this silica grade was 120 - 150 m 2 / g.

[0066] Zinc oxide was an odorless white fine powder with a specific gravity of 5.6 and a surface area of 4 - 6 m 2 / g. The heat loss value of this grade was at most 0.5% at 110°C. The ash content of this grade was 99%, the wet sieve residue (% remaining on #325 mesh) was 0.05 or less, and (% remaining on #200 mesh) was less than 0.02. The presence of CuO was <0.0005%, MnO <0.0005%, SiO2 <0.02%, and water-soluble salts <0.05%.

[0067] The mixing of the components was carried out in three stages. In the first stage, all materials except the curing agent were charged into the mixer at 10 - 20 RPM. The total mixing time was 8 - 12 minutes at a discharge temperature of 150°C. In the second stage, the compound was mixed again at 150°C to enhance dispersion and homogeneity. The peroxide curing agent was added in the third stage of mixing, the RPM was maintained at 8 - 10, and the batch was discharged at 95°C.

[0068] The blended stock was cured at 180 °C for 20 minutes using a hydraulic press.

[0069] The physical properties of the cured slab were determined by stress-strain tests, and the tensile strength, modulus of elasticity, elongation (ASTM D412), tear test (ASTM D624), Shore A hardness (ASTM D2240), volume expansion rate when immersed in IRM901 at 135 °C for 168 hours (ASTM D471), and compression set over 168 hours at 135 °C (ASTM D395) were measured.

[0070] The ozone test was carried out by placing dumbbell-shaped samples in an ozone chamber containing 50 ppm of ozone at 40 °C with elongation (20% and 30%). These samples were inspected for the presence or absence of cracks at regular time intervals using a magnification of 7 times.

[0071] The cold flexibility was tested by placing strips of the cured compound (dimensions: 6 inches × 1 inch × 0.75 inches) in a cooling chamber at -35 °C for 24 hours and then bending the samples at an angle of 180° after the specified conditioning time had elapsed.

[0072] The results of the above tests are shown in Table 4.

Table 4

[0073] A test (Example) synchronous belt was fabricated using a cured slab of the NBR / EPDM blended compound, and a series of static tests were carried out. Table 5 shows a comparison between a control (Comparative Example) belt made of an existing compound and the test (Example) belt made of the NBR / EPDM blended compound in Table 3.

Table 5

[0074] · Example 2

[0075] The materials listed in Table 6 were used in the amounts (in grams) listed to prepare another blend composition according to the present disclosure. [Table 6]

[0076] For Example 2, the same tests as in Example 1 were conducted, and the results are shown in Tables 7 and 8 below. [Table 7] [Table 8]

[0077] From the above, it will be understood that certain embodiments of the present invention have been described herein for purposes of illustration, but that various changes can be made without departing from the scope of the present invention. Accordingly, the present invention is limited only by the appended claims.

[0078] This technology is described in terms specific to particular structures and materials, but it should be understood that the invention as defined by the appended claims is not necessarily limited to the particular structures and materials described. Rather, the particular embodiments are described as forms of carrying out the claimed invention. Since many embodiments of the present invention can be implemented without departing from the spirit and scope of the present invention, the present invention belongs to the appended claims below.

[0079] Unless otherwise noted, all numerical values or expressions representing dimensions, physical properties, etc. used in the specification (other than the claims) are understood to be modified in all cases by the term "about". At least, not as an attempt to limit the application of the doctrine of equivalents to the claims, each numerical parameter described in the specification or claims and modified by the term "about" should be construed at least in accordance with the rounding technique in light of the significant digits given. Further, all ranges disclosed herein are to be understood to encompass and provide support for any and all sub-ranges contained therein or any and all individual values described in the claims contained therein. For example, a range defined as from 1 to 10 encompasses and provides support for claims that describe any sub-range or individual value between the minimum value 1 and the maximum value 10, and / or including both. That is, all sub-ranges where the minimum value starts at 1 or more and the maximum value is 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, etc.), or any sub-ranges including any value from 1 to 10 (e.g., 3, 5.8, 9.9994, etc.).

Claims

1. A synchronous belt formed from an uncured composition containing acrylonitrile-butadiene rubber (NBR) and an ethylene polymer, characterized in that the NBR and the ethylene polymer are present in the uncured composition in an amount of 25 to 75% by weight.

2. A belt formed from the uncured composition according to claim 1, characterized in that the NBR is present in the uncured composition in an amount of 30 to 60% by weight, and the ethylene polymer is present in the uncured composition in an amount of 10 to 30% by weight.

3. A belt formed from the uncured composition according to claim 1, characterized in that the NBR is 30 to 50% by weight of the uncured composition.

4. A belt formed from the uncured composition according to claim 1, characterized in that the uncured composition further contains an organic peroxide.

5. A belt formed from the uncured composition according to claim 1, characterized in that the ethylene polymer is an ethylene-propylene-diene terpolymer (EPDM).

6. A belt formed from the uncured composition according to claim 1, characterized in that the ethylene polymer is an ethylene acrylic elastomer.

7. A belt formed from the uncured composition according to claim 1, characterized in that the ethylene polymer is chlorinated polyethylene.

8. A belt formed from the uncured composition according to claim 1, characterized in that the uncured composition further contains a carbon-reinforced filler and silica.

9. A belt formed from the uncured composition according to claim 8, characterized in that the silica is present at a higher level than the carbon-reinforced filler.

10. A belt formed from the uncured composition according to claim 9, characterized in that the silica is present at a level of about 10 to 35% by weight of the uncured composition, and the carbon-reinforced filler is present at a level of about 3 to 8% by weight.

11. A belt formed from the uncured composition according to claim 9, characterized in that the silica is present in a ratio of about 4:1 to the carbon-reinforced filler.

12. A belt formed from the uncured composition according to claim 1, characterized in that the tensile strength of the belt is 18 MPa or more.

13. A belt formed from the uncured composition according to claim 1, characterized in that the belt is easily flexible at -35°C.

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