JP7498649B2 - Molding components and their uses - Google Patents

Description

The present invention relates to molding members used to manufacture cross-linked molded articles such as tires and belts, and their uses.

In recent years, against the backdrop of societal demands for energy conservation and compactness, the ambient temperature around the engine compartment of an automobile has risen compared to the past, and with this rise in ambient temperature, the environmental temperature in which power transmission belts are used has also risen. Traditionally, the mainstream polymers used for transmission belts (particularly V-ribbed belts) have been natural rubber, styrene-butadiene rubber, and chloroprene rubber, but with the increasing demand for improved heat resistance and materials that do not contain environmentally hazardous substances, ethylene-α-olefin elastomers have been adopted, and organic peroxides have come to be used as crosslinking agents for these polymers.

As one method of manufacturing the V-ribbed belt, Japanese Patent Application Laid-Open No. 2009-119846 (Patent Document 1) discloses a method in which the components that make up the belt (core wire, rubber sheet, etc.) are wound in order around the outer peripheral surface of a bladder (flexible jacket) attached to a cylindrical molding drum (inner mold) to form an unvulcanized belt sleeve, and the inner mold with this belt sleeve attached is placed inside an outer mold, and the bladder is expanded while the outer mold is heated, and the ribs are formed while the unvulcanized sleeve is pressed against the outer mold, which has groove-shaped markings corresponding to the ribs on its inner peripheral surface.

In this manufacturing process, when the bladder is shrunk and returned to its original state after vulcanization, the outer diameter of the bladder becomes smaller than the inner diameter of the vulcanized belt sleeve, making it possible to separate the bladder from the vulcanized belt sleeve. If the releasability of the bladder decreases, workability, particularly in an automated manufacturing line, decreases significantly. In addition, because the bladder is used repeatedly to vulcanize the belt sleeve, damage due to deterioration over time during repeated use and reduced releasability also become an issue.

Conventionally, butyl rubber, which has excellent heat resistance and low gas permeability, has been used as the rubber material for the bladder. For example, JP-A-10-130441 (Patent Document 2) discloses a tire manufacturing bladder made by vulcanizing a rubber composition containing a rubber component including methylolated phenolic resin and butyl rubber.

However, if a rubber composition containing an organic peroxide as a cross-linking agent is used in the rubber layer of the belt sleeve, the butyl rubber is attacked by radicals generated by the decomposition of the organic peroxide, which mainly causes a decomposition reaction. In particular, if a rubber layer made of a rubber composition containing an organic peroxide is in direct contact with a bladder made of butyl rubber, the butyl rubber of the bladder will be damaged. Therefore, compared to belt sleeves made of conventional sulfur-crosslinked rubber compositions, the surface of the bladder that comes into contact with the rubber layer of the belt sleeve will harden and deteriorate significantly, and the number of repeated uses that can be used will be shorter.

As an example of a bladder that does not use butyl rubber, Japanese Patent Application Laid-Open No. 2010-221506 (Patent Document 3) and Japanese Patent Application Laid-Open No. 2011-161767 (Patent Document 4) disclose tire manufacturing bladders that use silicone rubber or fluororubber.

However, silicone rubber has excellent releasability, but has poor hydrolysis resistance and tear resistance (tear and crack resistance), resulting in a short lifespan. Fluorine rubber also has a longer lifespan, but is an expensive material and therefore difficult to adopt from a cost perspective.

As an example of an improvement of conventional butyl rubber using an inexpensive material, ethylene-α-olefin elastomer, JP-T-2018-513248 (Patent Document 5) discloses a tire manufacturing bladder formed of a rubber composition containing 20 to 50 parts by mass of a copolymer of ethylene, C _3-23 α-olefin, and polyene monomer, such as ethylene-propylene-diene terpolymer (EPDM), and 50 to 80 parts by mass of a butyl type rubber, such as butyl rubber. Furthermore, JP-A-2012-232517 (Patent Document 6) discloses a molding member formed of a rubber composition containing butyl rubber and ethylene-α-olefin elastomer in a ratio of the former/the latter of 10/90 to 60/40 (mass ratio) as a vulcanization molding member (jacket) for a transmission belt.

JP 2009-119846 A Japanese Patent Application Laid-Open No. 10-130441 JP 2010-221506 A JP 2011-161767 A JP 2018-513248 A JP 2012-232517 A

However, in recent years, as ethylene-α-olefin elastomers have been adopted as the rubber component of transmission belts and crosslinking temperatures have risen, the rubber component that constitutes the bladder also needs to have a high degree of heat resistance in order to extend the durable life of molding components such as bladders. For this reason, as with the molding components in Patent Documents 5 and 6, rubber components that take heat resistance into consideration are now required, because sufficient heat resistance cannot be obtained if butyl rubber is included.

As mentioned above, when butyl rubber or silicone rubber is repeatedly used as a bladder for manufacturing a transmission belt from an unvulcanized sleeve formed from a rubber composition containing an organic peroxide, the mechanical properties (tear resistance, etc.) of the bladder deteriorate, shortening the durability life and reducing the releasability of the resulting belt.

In addition, even if the tear resistance is improved, the durability of the bladder may reach its end due to permanent deformation (permanent strain). In detail, in the molding of the transmission belt, the core wire with tension applied to the outer periphery of the bladder is spun to produce the molded body, so the bladder to which the molded body is attached is in a state of being tightened by the core wire. If the bladder is expanded in this state in the crosslinking process, the core wire will bite into the bladder, and if the bladder is used repeatedly in the crosslinking process, the traces of the core wire will gradually be transferred (unevenness along the shape of the core wire will be formed) to the outer periphery of the bladder and will not return. If crosslinking molding is performed using a bladder with traces of the core wire formed on its outer periphery, the traces of the core wire will also be transferred to the inner periphery of the molded body (the surface in contact with the bladder). Since the inner periphery of the molded body is the part that becomes the back surface of the transmission belt, the appearance of the back surface of the transmission belt will be poor. In this application, such deformation in which traces of the core wire are formed and cannot be returned is called permanent deformation (permanent strain). In other words, the bladder's durable life is also reached when it is used repeatedly and the outer periphery of the bladder is permanently deformed to the extent that traces of the core wire are transferred to the inner periphery of the molded body (the back surface of the transmission belt) that is cross-linked.

Furthermore, even if the tear resistance and permanent deformation resistance are improved, the arrangement of the core wires of the transmission belt may be disturbed during crosslinking molding. In detail, V-ribbed belts are usually manufactured by a molded method. In the molded method, it is necessary to press a molded body in which tension rubber, adhesive rubber, core wire, compressed rubber, fabric, etc. are laminated against an outer mold. At this time, the pressure of pressing the molded body acts to make the tension rubber and adhesive rubber flow out through the gaps in the core wires to the compressed rubber side. For example, in a molded body in which tension rubber, core wire, compressed rubber, and fabric are laminated, a force acts to make the tension rubber flow out to the compressed rubber side, and in a molded body in which tension rubber, adhesive rubber, core wire, and compressed rubber are laminated, a force acts to make the adhesive rubber, or the adhesive rubber and tension rubber, flow out to the compressed rubber side. Therefore, the core wire is easily pushed out toward the compressed rubber side, or conversely, the core wire is easily cut into the tension rubber side. As a result, the position of the core wire in the belt thickness direction becomes uneven. If the core wires are not aligned properly, the durability of the belt will decrease, so it is necessary to improve the alignment of the core wires.

The object of the present invention is therefore to provide a molding member that has excellent heat resistance, can improve durability such as resistance to permanent deformation, and can stabilize the position of the core wire in the belt thickness direction in the resulting cross-linked molded body, and its use.

As a result of intensive research into achieving the above-mentioned objectives, the inventors have discovered that by forming a molding member for producing a crosslinked molded body from a crosslinked rubber composition that combines an ethylene-α-olefin elastomer with a specific ratio of soft carbon with a primary particle size of 40 nm or more and hard carbon with a primary particle size of less than 40 nm, and an organic peroxide, it is possible to obtain a product with excellent heat resistance, improved durability such as resistance to permanent deformation, and the position of the core wire in the obtained crosslinked molded body in the belt thickness direction, thereby completing the present invention.

That is, the molding member of the present invention is a molding member for producing a crosslinked molded body by crosslinking an uncrosslinked body in a state of contacting the uncrosslinked body, and is formed of a crosslinked body of a rubber composition containing a rubber component, carbon black, and an organic peroxide, the rubber component contains an ethylene-α-olefin elastomer, the carbon black contains hard carbon having a primary particle diameter of less than 40 nm and soft carbon having a primary particle diameter of 40 nm or more, the ratio of the hard carbon is 28 to 70 parts by mass relative to 100 parts by mass of the rubber component, and the ratio of the soft carbon is 35 to 90 parts by mass relative to 100 parts by mass of the rubber component. The ratio of the soft carbon may be 80 to 300 parts by mass relative to 100 parts by mass of the hard carbon. The ratio of the carbon black may be 70 to 120 parts by mass relative to 100 parts by mass of the rubber component. The BET specific surface area of the hard carbon may be 70 to 140 m ² /g. The BET specific surface area of the soft carbon may be 25 to 60 m ² /g. The ethylene content of the ethylene-α-olefin elastomer may be 50 to 70 mass %, and the diene content may be 0.4 to 5 mass %. The ratio of the organic peroxide may be 2 to 8 parts by mass with respect to 100 parts by mass of the rubber component. The molding member may have a compression set of 5 to 20% in accordance with JIS K 6262. The molding member may have a breaking elongation of 100 to 500% in accordance with JIS K 6251. The molding member may be a bladder for producing a transmission belt. The transmission belt may include a core wire having an elastic modulus of 50 GPa or more. The uncrosslinked body may include an organic peroxide.

The present invention also includes a method for producing a crosslinked molded body by crosslinking the uncrosslinked body while the molding member is in contact with the uncrosslinked body. In this method, the molding member may be deformed to crosslink the uncrosslinked body.

In the present invention, the molding member for producing the crosslinked molded body is formed of a crosslinked body of a rubber composition that combines an ethylene-α-olefin elastomer, soft carbon with a primary particle diameter of 40 nm or more and hard carbon with a primary particle diameter of less than 40 nm, which are combined in a specific ratio, and an organic peroxide, and therefore has excellent heat resistance and can improve durability such as resistance to permanent deformation. For example, even when used as a bladder for producing a transmission belt, durability can be improved and the position of the core wire in the obtained crosslinked molded body can be stabilized in the belt thickness direction. For example, the position of the core wire of a V-ribbed belt, which has a high elastic modulus and low elongation, can be stabilized in the belt thickness direction. In particular, regarding durability, the durability life due to tear cracks can be improved and the durability life due to permanent deformation can be improved. In addition, even when repeatedly used as a molding member for producing a crosslinked molded body from an uncrosslinked body formed of a rubber composition containing an organic peroxide, the mechanical properties (tear properties, etc.) of the molding member can be suppressed from decreasing, and the releasability from the obtained crosslinked molded body can be suppressed.

FIG. 1(a) is a schematic perspective view showing an example of an inner mold of a belt forming apparatus for producing a V-ribbed belt, and FIG. 1(b) is a partially enlarged schematic sectional view thereof. FIG. 2(a) is a schematic perspective view of the state in which a belt sleeve is attached to the inner mold of FIG. 1, and FIG. 2(b) is a partially enlarged schematic sectional view thereof. 3A is a schematic perspective view showing the process of inserting the inner mold with the belt sleeve of FIG. 2 attached into the outer mold, and FIG. 3B is a partially enlarged schematic cross-sectional view showing the state in which the inner mold has been inserted into the outer mold. 4A is a schematic perspective view of the belt forming apparatus in which an inner mold is inserted into an outer mold of FIG. 3 and a bladder is inflated, and FIG. 4B is a partially enlarged schematic cross-sectional view thereof. 5A is a schematic perspective view showing a step of removing an inner mold from the belt forming apparatus of FIG. 4, and FIG. 5B is a partially enlarged schematic cross-sectional view showing the state after the inner mold has been removed from the belt forming apparatus. FIG. 6 is a schematic cross-sectional view showing an example of a V-ribbed belt. FIG. 7 is a schematic diagram for explaining a method for measuring the amount of deviation of the core wire in the belt thickness direction in the examples.

[Method of manufacturing crosslinked molded article]
The molding member of the present invention is used to crosslink an uncrosslinked body in contact with the uncrosslinked body to produce a crosslinked molded body. The crosslinked molded body may be any crosslinked molded body formed of rubber or the like, and may be, for example, a tire or a belt. Among these, the crosslinked molded body produced using the molding member of the present invention is preferably a belt, and particularly preferably a power transmission belt (power transmission belt). Examples of the power transmission belt include flat belts; friction power transmission belts such as wrapped V belts, low-edge V belts, low-edge cogged V belts, and V-ribbed belts; meshing power transmission belts such as toothed belts and double-sided toothed belts, and V-belts such as V-ribbed belts are commonly used. Below, a method for producing a V-ribbed belt using the molding member of the present invention as a bladder, which is a flexible jacket for producing a V-ribbed belt, will be described.

(Belt forming device)
A V-ribbed belt can be manufactured by a belt molding device including an outer mold and an inner mold that can be inserted into and detached from the hollow portion of the outer mold. Fig. 1 is a schematic perspective view (a) showing an example of an inner mold of a belt molding device for manufacturing a V-ribbed belt, and an enlarged schematic cross-sectional view (b) of the upper part of the inner mold. Fig. 3 is a drawing relating to a belt molding device in which an outer mold is combined with the inner mold, and more specifically, Fig. 3 is a schematic perspective view (a) showing a process of inserting the inner mold with the belt sleeve of Fig. 2 described later attached thereto into the outer mold, and a partially enlarged schematic cross-sectional view (b) showing the state in which the inner mold is inserted into the outer mold.

As shown in FIG. 1, the shape of the inner mold 1, which is a metal mold, is columnar or cylindrical. At both ends (top and bottom ends) of the longitudinal direction of the inner mold 1, a disk-shaped upper end flange 22a and a lower end flange 22b are formed, which protrude in the outer circumferential direction. In this example, the upper end flange 22a is formed with a larger diameter than the lower end flange 22b, and is formed with a larger diameter than the outer diameter of the bladder 5, which is attached to the inner mold 1 and will be described later.

A cylindrical bladder 5, which is a molding member of the present invention, is attached to the outer peripheral surface of the inner mold 1. More specifically, the outer peripheral surface of the inner mold 1 is in contact with the inner peripheral surface of the cylindrical bladder 5 by fitting the inner mold 1 into the cylindrical interior of the flexible bladder 5. As described below, the material of this bladder 5 is formed of a crosslinked body of a rubber composition that is stretchable and airtight. The entire circumference of both end faces (upper end face and lower end face) in the longitudinal direction of this bladder 5 is attached by adhering them to the upper end flange 22a and the lower end flange 22b, respectively. Therefore, the space between the outer peripheral surface of the inner mold 1 and the inner peripheral surface of the bladder 5 is sealed by the flanges at both the upper and lower ends.

The inner mold 1 also has a fluid supply passage 23 that penetrates the upper end flange 22a and the inner mold 1. The upper end opening of this fluid supply passage 23 is located above the upper end flange 22a, penetrates the upper end flange 22a, and further curves and penetrates the inner mold 1 to extend to the inner peripheral surface of the bladder 5, forming an opening at the boundary between the outer peripheral surface of the inner mold 1 and the inner peripheral surface of the bladder 5. In the inner mold 1, a fluid such as air can be supplied between the outer peripheral surface of the inner mold 1 and the inner peripheral surface of the bladder 5 through this fluid supply passage 23. When fluid is supplied through the fluid supply passage 23 in this way, the space between the outer peripheral surface of the inner mold 1 and the inner peripheral surface of the bladder 5 is sealed at both the top and bottom ends, so that the bladder 5 expands outward as the fluid flows in. Also, when no fluid is supplied from the fluid supply passage 23, the bladder 5 is in close contact with the outer peripheral surface of the inner mold 1.

As shown in FIG. 3, the outer mold 6 has a cylindrical shape into which the inner mold 1 can be inserted, and as shown in FIG. 3(b), molding convex portions 45 are formed on the inner peripheral surface that becomes the molding surface of the outer mold 6. The molding convex portions 45 are formed as a mold shape (inverted shape) corresponding to the desired rib portion, and protrude over the entire inner peripheral surface of the outer mold 6, with many of them formed in parallel at predetermined regular intervals in a direction perpendicular to the circumferential direction of the inner peripheral surface of the outer mold 6.

The V-ribbed belt is manufactured using this belt molding device, and the specific steps are a molding process for molding an uncrosslinked belt precursor, a crosslinking process for crosslinking the uncrosslinked belt precursor, and a finishing process for manufacturing a V-ribbed belt from the crosslinked belt precursor (belt sleeve).

(Molding process)
The molding step is a step of forming an uncrosslinked belt precursor 4 using an inner mold 1 having a bladder 5 attached to the outer circumferential surface thereof.

2 shows the state of the belt forming device in the forming process, and in detail, it is a schematic perspective view (a) of the state in which the belt sleeve is attached to the inner mold 1 of FIG. 1, and an enlarged schematic cross-sectional view (b) of the upper part thereof. As shown in FIG. 2, the uncrosslinked belt precursor 4 is formed as a laminate of the core wire 2 wound in a spiral shape around the outer peripheral surface of the bladder 5 and the precursor sheet 3 wound around the outer peripheral surface of the bladder 5. In the embodiment of FIG. 2, the precursor sheet 3 uses at least two types of sheets including an uncrosslinked rubber sheet, and the laminate materials of the sheet 3a for forming the extension layer, the core wire 2 forming the core body, and the uncrosslinked rubber sheet 3b for forming the compression layer are wound and laminated in order from the inner peripheral side around the outer peripheral surface of the bladder 5 to form the uncrosslinked belt precursor 4. The sheet 3a for forming the extension layer is made of a cloth or an uncrosslinked rubber sheet. In addition, when the core body (core wire) is embedded in the adhesive rubber layer to form a core layer, an uncrosslinked rubber sheet for forming an adhesive rubber layer in which to embed the core body (core wire) may be provided between sheets 3a and 3b, and the layer structure is not limited to the above.

(Crosslinking process)
The crosslinking process is a process in which the uncrosslinked belt precursor 4 is compression molded (molded) into a desired shape corresponding to the shape of a mold, thereby causing a crosslinking reaction of the rubber components constituting each rubber layer, and bonding and integrating the laminated materials constituting the uncrosslinked belt precursor 4 to form a belt sleeve (crosslinked belt precursor) 4A (FIG. 5(b) to be described later). In this crosslinking process, the uncrosslinked belt precursor 4 is crosslinked, and the rib portion 7 is formed to obtain the belt sleeve 4A, so that in the crosslinking process, the compressed rubber layer is molded at the same time as the crosslinking.

Figure 3 shows the preparation stage for providing the uncrosslinked belt precursor to the crosslinking step, as described above in detail. Figure 4 shows the state of the belt forming device in the crosslinking step, and in detail, is a schematic perspective view (a) of the state in which the bladder of the belt forming device in which the inner mold is inserted into the outer mold of Figure 3 is inflated, and a partially enlarged schematic cross-sectional view (b) of the same.

In detail, in order to subject the uncrosslinked belt precursor to the crosslinking process, as shown in FIG. 3, the inner mold 1 with the uncrosslinked belt precursor 4 attached thereto is inserted into the cylindrical interior (hollow interior) of the outer mold 6. The inside of the outer mold 6 is formed as a sealed hollow section around the entire circumference, with a heating/cooling jacket 35 formed above the outer peripheral wall 6a of the outer mold 6 for supplying a heating medium such as steam, and a refrigerant supply port 37 formed below the outer peripheral wall 6a for supplying a cooling medium such as cooling water.

In the crosslinking process, as shown in FIG. 4, a heating medium is supplied from the heat medium supply port 36 to heat the outer mold 6 with the heating/cooling jacket 35, and a fluid such as air is supplied from the fluid supply path 23 between the outer periphery of the inner mold 1 and the inner periphery of the bladder 5. As shown in FIG. 4(b), the pressure of the fluid causes the bladder 5 to expand toward the inner periphery (rib mold) of the outer mold 6, and the uncrosslinked belt precursor 4 wrapped around the outer periphery of the bladder 5 is pressed against the inner periphery of the outer mold 6, and the uncrosslinked belt precursor 4 is heated and pressurized between the bladder 5 and the outer mold 6. At this time, the uncrosslinked belt precursor 4 is pressed against the inner periphery of the outer mold 6 and pressurized, so that the outer periphery of the uncrosslinked belt precursor 4 is pressed into the recess between the molding protrusions 45 of the outer mold 6, and the rib portion 7 can be formed on the outer periphery. The heating temperature is, for example, 120 to 180°C, the molding pressure is, for example, 0.5 to 1.5 MPa, and the heating time is, for example, 15 to 30 minutes. Through this process, the uncrosslinked belt precursor 4 is crosslinked and molded to obtain the belt sleeve 4A.

(Finishing process)
In the finishing step, a V-ribbed belt is manufactured from the belt sleeve 4A obtained in the cross-linking step. Fig. 5 shows the belt forming apparatus in the finishing step, and is a schematic perspective view (a) showing the step of removing the inner mold from the belt forming apparatus in the state shown in Fig. 4, and a partially enlarged schematic cross-sectional view (b) showing the state after the inner mold has been removed from the belt forming apparatus.

In the crosslinking process, after the belt sleeve 4A is crosslinked and heating is stopped, the supply of fluid from the fluid supply path 23 is stopped to contract the bladder 5 and return it to its pre-expansion state, and a cooling medium is then supplied from the refrigerant supply port 37 to cool the outer mold 6. When the bladder 5 contracts to its original state, the outer diameter of the bladder 5 becomes smaller and is smaller than the inner diameter of the crosslinked belt sleeve 4A, so that the inner mold 1 can be removed from the outer mold 6 while leaving the crosslinked belt sleeve 4A on the inner circumference of the outer mold 6, as shown in FIG. 5.

The inner mold 1 is removed from the outer mold 6, and the belt sleeve 4A with multiple ribs on the outer periphery is removed from the outer mold 6. Then, using a cutter, the belt sleeve 4A is cut into rings of a specified width in the belt longitudinal direction, separating the belt into individual pieces, and the inner and outer periphery are turned inside out (inverted) to create a V-ribbed belt.

Thus, in the manufacture of V-ribbed belts, the bladder as a molding member is heated and used while being deformed by expanding and contracting to form the ribs. The molding member of the present invention can improve durability even in applications where heating and deformation are repeated. Therefore, the molding member of the present invention can be preferably used in applications (particularly bladders) where it is heated for crosslinking and deformed during crosslinking molding.

[Molding member]
The molding member typified by the above-mentioned bladder is formed from a crosslinked product of a rubber composition containing a rubber component, carbon black and an organic peroxide.

(Rubber component)
The rubber component includes an ethylene-α-olefin elastomer. Since the ethylene-α-olefin elastomer does not contain a double bond in the main chain, it has excellent heat resistance and is preferable as a material for a molding member that is repeatedly heated. In particular, in the crosslinking step using a molding member such as the bladder, the uncrosslinked body comes into contact with the molding member. When the rubber composition of the uncrosslinked body includes an organic peroxide, if the rubber component constituting the molding member is attacked by radicals generated by the decomposition of the organic peroxide and decomposed, the mechanical strength (particularly, tear property) of the molding member decreases, or the releasability of the uncrosslinked body from a crosslinked molding (such as a belt sleeve) decreases. In the present invention, the softening and deterioration of the molding member can be suppressed by using an ethylene-α-olefin elastomer that is not decomposed by attack of radicals generated by the decomposition of the organic peroxide as the rubber component.

Ethylene-α-olefin elastomers may contain ethylene units and α-olefin units as constituent units, and may further contain diene units. Ethylene-α-olefin elastomers include ethylene-α-olefin copolymer rubber, ethylene-α-olefin-diene terpolymer rubber, etc.

Examples of the α-olefin for forming the α-olefin unit include linear α-C _3-12 olefins such as propylene, butene, pentene, methylpentene, hexene, octene, etc. Among these α-olefins, α-C _3-4 olefins such as propylene (particularly propylene) are preferred.

As the diene monomer for forming the diene units, a non-conjugated diene monomer is usually used. Examples of non-conjugated diene monomers include dicyclopentadiene, methylenenorbornene, ethylidenenorbornene, 1,4-hexadiene, and cyclooctadiene. Of these diene monomers, ethylidenenorbornene and 1,4-hexadiene (particularly ethylidenenorbornene) are preferred.

Typical ethylene-α-olefin elastomers include, for example, ethylene-propylene copolymer (EPM) and ethylene-propylene-diene terpolymer (EPDM).

These ethylene-α-olefin elastomers can be used alone or in combination of two or more. Among these, ethylene-α-olefin-diene terpolymer rubber is preferred because of its excellent crosslinking efficiency due to the diene units, and ethylene-propylene-diene terpolymer (EPDM) is particularly preferred.

In the ethylene-propylene-diene terpolymer, the ratio (mass ratio) of ethylene to propylene may be from 35/65 to 90/10, preferably from 40/60 to 80/20, more preferably from 45/55 to 70/30, and most preferably from 50/50 to 60/40.

The ethylene content of the ethylene-α-olefin elastomer (particularly ethylene-α-olefin-diene terpolymer rubber such as EPDM) may be 30% by mass or more (e.g., 30 to 80% by mass), preferably 50 to 70% by mass, further preferably 52 to 65% by mass, even more preferably 53 to 60% by mass, and most preferably 54 to 58% by mass. If the ethylene content is too low, there is a risk of reduced heat resistance.

In this application, the ethylene content means the mass ratio of ethylene units among all units constituting the ethylene-α-olefin elastomer, and can be measured by a conventional method, but may also be the monomer ratio.

The diene content of the ethylene-α-olefin elastomer (particularly ethylene-α-olefin-diene terpolymer rubber such as EPDM) may be 10% by mass or less (e.g., 0.1 to 10% by mass), preferably 0.3 to 8% by mass, more preferably 0.4 to 7% by mass (e.g., 0.4 to 5% by mass), more preferably 0.5 to 6% by mass, and most preferably 1 to 5% by mass. In the present invention, heat resistance is improved by using a rubber component that does not have a double bond in the main chain, but a high level of heat resistance can be ensured by suppressing the double bonds due to the diene units introduced as side chains to a small amount. If the diene content is too high, there is a risk that a high level of heat resistance cannot be ensured.

In this application, the diene content means the mass ratio of diene monomer units among all units constituting the ethylene-α-olefin elastomer, and can be measured by a conventional method, but may also be the monomer ratio.

The Mooney viscosity [ML(1+4)125°C] of the unvulcanized ethylene-α-olefin elastomer may be 80 or less, and is, for example, 10 to 80, preferably 20 to 70, more preferably 30 to 60, and most preferably 35 to 50, from the viewpoint of adjusting the Vm of the rubber composition and improving the dispersibility of carbon black. If the Mooney viscosity is too high, the flowability of the rubber composition may decrease, and the processability during kneading may decrease.

In this application, Mooney viscosity can be measured according to JIS K 6300-1 (2013), and the test conditions are as follows: an L-shaped rotor is used, the test temperature is 125°C, preheating is 1 minute, and the rotor operation time is 4 minutes.

The proportion of ethylene-α-olefin elastomer in the rubber component may be 50% by mass or more, but is preferably more than 90% by mass, more preferably 95% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass. If the proportion of ethylene-α-olefin elastomer in the rubber component is too low, there is a risk of reduced heat resistance.

The rubber component may further contain other rubber components. Examples of other rubber components include diene rubbers [natural rubber, isoprene rubber, butadiene rubber, chloroprene rubber, styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (nitrile rubber), hydrogenated nitrile rubber, etc.], chlorosulfonated polyethylene rubber, alkylated chlorosulfonated polyethylene rubber, epichlorohydrin rubber, acrylic rubber, silicone rubber, urethane rubber, fluororubber, etc.

The rubber component may contain these other rubber components in a proportion that results in the proportion of ethylene-α-olefin elastomer falling within the above range, so long as the effect of the present invention is not impaired. However, in order to improve the heat resistance and tear resistance of the molding component, the rubber component does not substantially contain butyl rubber.

The proportion of butyl rubber in the rubber component should be less than 10% by mass, preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, and most preferably 0% by mass.

(Carbon black)
The rubber composition forming the molding member may further contain carbon black in addition to the rubber component, thereby improving the durability of the molding member.

Carbon black is generally classified into several grades based on differences in primary particle size, iodine adsorption amount, BET specific surface area, etc. Carbon black with a small primary particle size has a high reinforcing effect on rubber, while carbon black with a large primary particle size has a low reinforcing effect on rubber.

ASTM classifies carbon black into N0** to N9** based on the amount of iodine adsorption, but traditional classifications based on the performance of the rubber product to which it is compounded (SAF, HAF, GPF, etc.) are also used. Carbon black with small primary particle diameters such as N110 (SAF), N220 (ISAF), and N330 (HAF) are called hard carbon, while carbon black with large primary particle diameters such as N550 (FEF), N660 (GPF), and N762 (SRF) are sometimes called soft carbon. There is a close relationship between the amount of iodine adsorption and the primary particle diameter, and the smaller the primary particle diameter, the greater the amount of iodine adsorption. Using the Seast (registered trademark) series manufactured by Tokai Carbon Co., Ltd. as an example, the relationship between the amount of iodine adsorption and the average primary particle diameter is as shown in Table 1.

In this application, carbon black contained in a rubber composition is not classified by raw material, but is referred to as "soft carbon" when the primary particle diameter is 40 nm or more, and as "hard carbon" when the primary particle diameter is less than 40 nm.

In this application, the primary particle size of carbon black can be measured by number using, for example, a transmission electron microscope.

In the present invention, resistance to permanent deformation can be improved by combining hard carbon with a primary particle diameter of less than 40 nm and soft carbon with a primary particle diameter of 40 nm or more in a specific ratio.

The primary particle diameter of the hard carbon may be less than 40 nm (e.g., 15 to 35 nm), but the maximum primary particle diameter may be, for example, 38 nm or less, preferably 35 nm or less, and more preferably 30 nm or less. If the maximum primary particle diameter of the hard carbon is too large, there is a risk that the tear resistance will decrease. The minimum primary particle diameter may be, for example, 5 nm or more, preferably 8 nm or more, and more preferably 10 nm or more. If the minimum primary particle diameter of the hard carbon is too small, there is a risk that it will be difficult to prepare the hard carbon itself.

The average primary particle size of the hard carbon is, for example, about 10 to 35 nm, preferably about 15 to 33 nm, and more preferably about 20 to 32 nm (particularly about 25 to 30 nm). If the average primary particle size of the hard carbon is too small, it may be difficult to prepare the hard carbon itself, and conversely, if it is too large, there is a risk that the tear resistance will decrease.

The BET specific surface area of the hard carbon is, for example, 60 to 160 m ² /g, preferably 65 to 150 m ² /g, further preferably 70 to 140 m ² /g, further preferably 75 to 130 m ² /g, and most preferably 75 to 100 m ² /g. If the BET specific surface area is too small, the rubber composition may be difficult to stretch, and conversely, if it is too large, the hardness of the rubber composition may be too high.

In this application, the BET specific surface area refers to the specific surface area measured using nitrogen gas by the BET method.

The iodine adsorption amount of the hard carbon may be 60 g/kg or more, for example, 60 to 150 g/kg, preferably 65 to 130 g/kg, more preferably 70 to 100 g/kg, and most preferably 75 to 90 g/kg. If the iodine adsorption amount is too low, there is a risk that the tear resistance will decrease, and conversely, if it is too high, there is a risk that it will be difficult to prepare the hard carbon itself.

In this application, the iodine adsorption amount of carbon black can be measured in accordance with the standard test method of ASTM D1510-17.

The proportion of hard carbon is 28 to 70 parts by mass, preferably 29 to 60 parts by mass, more preferably 30 to 50 parts by mass, even more preferably 30 to 48 parts by mass (particularly 30 to 40 parts by mass), and most preferably 35 to 45 parts by mass, per 100 parts by mass of the rubber component. If the proportion of hard carbon is too low, the stabilization of the core wire decreases and the tear resistance also decreases, and conversely, if the proportion is too high, the resistance to permanent deformation decreases.

The primary particle diameter of the soft carbon may be 40 nm or more (e.g., 40 to 100 nm), but the maximum primary particle diameter may be, for example, 300 nm or less, preferably 200 nm or less, and more preferably 100 nm or less. If the maximum primary particle diameter of the soft carbon is too large, the reinforcing properties of the carbon black may decrease, and tear resistance may decrease.

The average primary particle size of the soft carbon is, for example, 45 to 100 nm, preferably 50 to 90 nm, more preferably 53 to 80 nm, even more preferably 55 to 70 nm, and most preferably 60 to 65 nm. If the average primary particle size of the soft carbon is too small, there is a risk of reduced resistance to permanent deformation, and conversely, if it is too large, there is a risk of reduced reinforcing properties of the carbon black and reduced tear resistance.

The BET specific surface area of the soft carbon measured by the BET method is, for example, 10 to 60 m ² /g (e.g., 25 to 60 m ² /g), preferably 15 to 55 m ² /g, further preferably 20 to 50 m ² /g, more preferably 22 to 40 m ² /g, and most preferably 23 to 30 m ² /g. If the BET specific surface area is too small, the reinforcing properties of the carbon black may decrease, and tear resistance may decrease, whereas if it is too large, permanent deformation resistance may decrease.

The iodine adsorption amount of the soft carbon may be less than 60 g/kg, for example, 10 g/kg or more and less than 60 g/kg, preferably 15 to 50 g/kg, more preferably 18 to 40 g/kg, and most preferably 20 to 30 g/kg. If the iodine adsorption amount is too low, the reinforcing properties of the carbon black may decrease, and tear resistance may decrease, whereas if the iodine adsorption amount is too high, permanent deformation resistance may decrease.

The proportion of soft carbon is 35 to 90 parts by mass, preferably 40 to 80 parts by mass, more preferably 50 to 70 parts by mass, and most preferably 55 to 65 parts by mass, per 100 parts by mass of the rubber component. If the proportion of soft carbon is too low, the permanent deformation resistance decreases, and conversely, if it is too high, the tear resistance decreases.

The mass ratio of the soft carbon may be 80 to 300 parts by mass (e.g., 80 to 230 parts by mass) per 100 parts by mass of the hard carbon, for example, 100 to 300 parts by mass, preferably 120 to 250 parts by mass, further preferably 130 to 230 parts by mass, more preferably 150 to 220 parts by mass, and most preferably 180 to 210 parts by mass. If the ratio of the soft carbon is too low, there is a risk of reduced resistance to permanent deformation, and conversely, if it is too high, there is a risk of reduced stabilization of the core wire and reduced tear resistance.

The total proportion of carbon black is, for example, 50 to 150 parts by mass, preferably 70 to 120 parts by mass, more preferably 75 to 110 parts by mass, even more preferably 80 to 100 parts by mass, and most preferably 85 to 95 parts by mass, per 100 parts by mass of the rubber component. If the total proportion of carbon black is too low, the rubber composition may be too soft and durability may decrease, and conversely, if it is too high, the rubber composition may be too hard and durability may decrease.

(Organic peroxides)
The rubber composition forming the molding member can improve the durability of the molding member by further containing an organic peroxide in addition to the rubber component and carbon black.

Organic peroxides include conventional components such as diacyl peroxides (dilauroyl peroxide, dibenzoyl peroxide, etc.), peroxyketals [1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, etc.], alkyl peroxyesters (t-butylperoxybenzoate, etc.), dialkyl peroxides [di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 1 , 1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,3-bis(2-t-butylperoxyisopropyl)benzene, 2,5-di-methyl-2,5-di(benzoylperoxy)hexane, etc.], diaralkyl peroxides (dicumyl peroxide, t-butylcumyl peroxide, etc.), peroxycarbonates (t-butylperoxyisopropyl carbonate, t-butylperoxy-2-ethyl-hexyl carbonate, t-amylperoxy-2-ethyl-hexyl carbonate, etc.), etc.

These organic peroxides can be used alone or in combination. Among these, peroxides having a dialkyl group are preferred, and diaralkyl peroxides such as dicumyl peroxide are more preferred.

The proportion of organic peroxide is, for example, 0.1 to 20 parts by mass, preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, even more preferably 2.5 to 7 parts by mass, and most preferably 3 to 5 parts by mass, per 100 parts by mass of the rubber component. If the proportion of organic peroxide is too low, the rubber composition may be too soft and durability may decrease, and conversely, if the proportion is too high, the rubber composition may be too hard and durability may decrease.

(Other ingredients)
The rubber composition forming the molding member may further contain, in addition to the rubber component, carbon black and organic peroxide, additives that are conventionally compounded with rubber as other components.

Examples of additives include other crosslinking agents or vulcanizing agents (inorganic peroxides, sulfur-based vulcanizing agents, etc.), co-crosslinking agents (bismaleimides, etc.), vulcanization aids or vulcanization accelerators (thiuram-based accelerators, etc.), vulcanization retarders, reinforcing agents (silica, clay, calcium carbonate, talc, mica, short fibers, etc.), metal oxides (zinc oxide, magnesium oxide, calcium oxide, barium oxide, iron oxide, copper oxide, titanium oxide, aluminum oxide, etc.), softeners (paraffin oil, naphthenic oil, and other oils), processing agents or processing aids (stearic acid, metal stearates, wax, paraffin, fatty acid amides, etc.), silane coupling agents, antiaging agents (antioxidants, heat antiaging agents, flex crack inhibitors, ozone degradation inhibitors, etc.), colorants, tackifiers, stabilizers (ultraviolet absorbers, heat stabilizers, etc.), flame retardants, antistatic agents, etc. These additives can be used alone or in combination of two or more. The metal oxides may act as crosslinking agents.

The total proportion of conventional additives is, for example, 5 to 50 parts by mass, preferably 10 to 30 parts by mass, and more preferably 15 to 25 parts by mass, per 100 parts by mass of the rubber component.

(Characteristics of molding members)
The molding member of the present invention has high resistance to permanent deformation. Therefore, the compression set of the molding member of the present invention may be 20% or less, for example, 5 to 20%, preferably 8 to 18%, more preferably 9 to 17%, more preferably 10 to 16%, and most preferably 12 to 15%. If the compression set is too small, the rubber composition may be too hard and the durability may decrease, and conversely, if it is too large, the resistance to permanent deformation may decrease.

In this application, the compression set can be measured in accordance with JIS K 6262 by compressing the material at 120°C for 24 hours, and more specifically, by the method described in the Examples below.

The hardness (JIS A) of the molding member of the present invention is, for example, 75 to 90°, preferably 77 to 88°, further preferably 78 to 85°, more preferably 79 to 83°, and most preferably 80 to 82°. If the hardness is too high, it may be too hard and the durability may decrease, and conversely, if the hardness is too low, it may be too soft and the durability may decrease.

In this application, hardness (JIS A) refers to the value Hs (JIS A) measured in accordance with the durometer hardness test (A type) specified in JIS K 6253 (2012) (vulcanized rubber and thermoplastic rubber - Determination of hardness).

The tensile strength of the molding member of the present invention is, for example, 10 to 30 MPa, more preferably 15 to 25 MPa, even more preferably 16 to 20 MPa, and most preferably 17 to 19 MPa. If the tensile strength is too small, it may be too soft and have reduced durability, and conversely, if it is too large, it may be too hard and have reduced durability.

The breaking elongation of the molding member of the present invention is, for example, 100 to 500%, preferably 120 to 300%, further preferably 130 to 250%, more preferably 150 to 200%, and most preferably 160 to 180%. If the breaking elongation is too small, it may be too hard and have reduced durability, and conversely, if it is too large, it may be too soft and have reduced durability.

In this application, the tensile strength and elongation at break can be measured in accordance with JIS K 6251 (2010), and more specifically, can be measured by the method described in the examples below.

[Crosslinked Molded Article]
As described above, examples of the cross-linked molded article obtained by using the molding member of the present invention include tires, belts, etc. As described above, the cross-linked molded article is preferably a cross-linked molded article produced by heating and deforming the molding member of the present invention, and a schematic cross-sectional view (cross-sectional view in a direction perpendicular to the belt longitudinal direction) of a V-ribbed belt, which is an example of such a cross-linked molded article, is shown in Figure 6.

As shown in FIG. 6, the V-ribbed belt 50 is composed of a core layer 53 including a core wire 52, a compression rubber layer 51 that is disposed on the inner side of the core layer 53 and constitutes a V-rib portion 51a that is a pulley contact portion, and an extension layer 54 that is disposed on the outer side of the core layer. The compression rubber layer 51 is formed with a plurality of grooves that are V-shaped in cross section and extend in the belt longitudinal direction, and between these grooves are formed a plurality of ribs (V-rib portion 51a) that are V-shaped in cross section (inverted trapezoid). Two inclined surfaces (surfaces) of the ribs form friction transmission surfaces that contact the pulley to transmit power (friction transmission). The extension layer may be formed of a rubber composition or a fabric (reinforced fabric) such as a woven fabric. A surface layer may also be provided on the surface of the V-rib portion.

As the crosslinked molded article, a crosslinked molded article (such as a belt sleeve of a V-ribbed belt) in which the surface in contact with the molding member is formed of a rubber composition containing an organic peroxide is preferred. In the case of a V-ribbed belt, the surface in contact with the molding member may be the rubber composition or fabric (or fabric containing a rubber composition) that forms the tension layer.

The rubber composition containing an organic peroxide may be a rubber composition containing an ethylene-α-olefin elastomer and an organic peroxide. As the ethylene-α-olefin elastomer and the organic peroxide, the ethylene-α-olefin elastomer and the organic peroxide described as materials for forming the moldable member can be used. The ratio of the organic peroxide to the rubber component is also the same as that of the organic peroxide for forming the moldable member. The moldable member of the present invention can improve durability even when used in the manufacture of a cross-linked molded product formed from a cross-linked product of a rubber composition containing an organic peroxide.

A core wire (or core body) with a high elastic modulus and low elongation is preferred. It is difficult to stabilize the alignment in the belt thickness direction in such a transmission belt, but the use of the molding member of the present invention can improve the stabilization of the core wire.

Examples of fibers that form such core wires include fibers with high elasticity, such as high-strength polyethylene fibers, PBO fibers, polyester fibers (polyalkylene arylate fibers such as PET fibers and PEN fibers, polyarylate fibers, etc.), polyamide fibers (aramid fibers, etc.), and inorganic fibers such as carbon fibers. These fibers can be used alone or in combination of two or more.

The core wire can usually be a twisted cord (e.g., double twist, single twist, Lang twist, etc.) using multifilament yarn. The average diameter of the core wire (fiber diameter of the twisted cord) can be, for example, about 0.5 to 3 mm, preferably 0.6 to 2 mm, and more preferably 0.7 to 1.5 mm.

The tensile modulus of the fibers forming the core wire can be selected from a range of about 1 to 500 GPa, but in order to effectively exert the effects of the present invention, a high modulus of elasticity of 50 GPa or more is preferable, for example, 50 to 500 GPa, preferably 55 to 300 GPa, and more preferably 60 to 200 GPa (particularly 65 to 150 GPa). Such high modulus fibers include, for example, aramid fibers and carbon fibers. In the present invention, the stability of the core wire can be improved even when the core wire is formed from high modulus fibers with a tensile modulus of elasticity of 50 GPa or more.

The average fineness of the fiber (monofilament yarn) may be, for example, about 0.1 to 5 dtex, preferably about 0.3 to 3 dtex, and more preferably about 0.5 to 1 dtex. The fiber can be used in the form of a multifilament yarn as a raw yarn (for example, a multifilament yarn containing about 1,000 to 50,000 monofilament yarns, preferably about 5,000 to 20,000 monofilament yarns).

To increase the tensile strength, the core wire can usually be used in the form of a twisted cord (e.g., multiple twist, single twist, Lang twist, etc.) using multifilament yarns. The core wire is often used as a cord, for example, a twisted cord (twisted yarn) in which the multifilament yarns are used as a core yarn (untwisted yarn, preferably first twisted yarn) and then top twisted in a specified direction (e.g., the same direction as the first twisted yarn or the opposite direction). The average diameter (average wire diameter) of the core yarn may be, for example, about 0.2 to 1 mm, preferably 0.3 to 0.8 mm, and more preferably 0.4 to 0.7 mm, and the average diameter (average wire diameter) of the cord (or core wire) may be, for example, about 0.3 to 1.5 mm, preferably 0.5 to 1.3 mm, and more preferably 0.7 to 1.2 mm.

The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. Details of the raw materials used in the examples are shown below.

[material]
EPDM1: "EPT3070" manufactured by Mitsui Chemicals, Inc., Mooney viscosity (125°C) ≒ 47, ethylene content 58% by mass, diene content 4.7% by mass
EPDM2: "EPT2060M" manufactured by Mitsui Chemicals, Inc., Mooney viscosity (125°C) ≒ 40, ethylene content 55% by mass, diene content 2.3% by mass
Butyl rubber: "Butyl 268" manufactured by JSR Corporation, Mooney viscosity (125°C) ≒ 51
Hard carbon 1: "Seat 3" manufactured by Tokai Carbon Co., Ltd., average particle size 28 nm, BET specific surface area 79 m ² /g
Hard carbon 2: "Seat 6" manufactured by Tokai Carbon Co., Ltd., average particle size 22 nm, BET specific surface area 119 m ² /g
Soft carbon 1: "Seest V" manufactured by Tokai Carbon Co., Ltd., average particle size 62 nm, BET specific surface area 27 m ² /g
Soft carbon 2: "Seat S" manufactured by Tokai Carbon Co., Ltd., average particle size 66 nm, BET specific surface area 27 m ² /g
Zinc oxide: "Zinc oxide type 2" manufactured by Hakusui Tech Co., Ltd.
Stearic acid: NOF Corp. "Stearic Acid Camellia Beads"
Softener: "NS-90" (paraffin-based process oil) manufactured by Idemitsu Kosan Co., Ltd.
Antioxidant: Diphenylamine-based antioxidant, "Nocrac AD-F" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Organic peroxide: NOF Corp.'s "Perkmyl D"
Resin crosslinking agent: "SP-1055" (alkylphenol-formaldehyde resin) manufactured by Schenectady Chem.
Crosslinking assistant: "PM-40" manufactured by Denka Co., Ltd.
Nylon staple fiber: "66 nylon" manufactured by Asahi Kasei Corporation
Hydrated silica: "Ultrasil VN3" manufactured by Evonik Industries AG, BET specific surface area 180 m ² /g
Resorcin-formaldehyde condensate: solution containing 2.6 parts by mass of resorcin, 1.4 parts by mass of 37% formalin, 17.2 parts by mass of vinylpyridine-styrene-butadiene copolymer latex, and 78.8 parts by mass of water. Vulcanization accelerator: "Noccela (registered trademark) DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Hexamethoxymethylolmelamine: Power Plast "PP-1890S"
Sulfur: manufactured by Bigen Chemical Co., Ltd. Core: A twisted yarn cord made by plying 1,000 denier polyethylene terephthalate fibers in a 2 x 3 configuration with a top twist coefficient of 3.0 and a bottom twist coefficient of 3.0 to create a total denier of 6,000 cord that has been adhesively treated, core diameter 1.0 mm.

[Preparation of bladder]
The rubber compositions for bladder having the formulations shown in Tables 2 and 3 were kneaded in a Banbury mixer and rolled to a predetermined thickness with a calendar roll. A rolled sheet having a thickness of 3 mm and a face length of 630 mm was wrapped around a cylindrical mold, covered with a jacket, and heated at 170°C for 20 minutes to perform crosslinking molding. The mixture was cooled and demolded to obtain a cylindrical bladder. The cylindrical bladder was set on the outer periphery of the inner mold of the belt molding device, and flanges were attached to the entire circumference of both ends of the opening of the bladder to fix it, thereby sealing the space between the outer periphery of the inner mold and the inner periphery of the bladder at both upper and lower ends.

[Physical Properties of Rubber Composition for Bladder]
1) Measurement of hardness A crosslinked rubber sheet (100 mm x 100 mm x 2 mm thick) was prepared by pressing and heating (temperature 170°C, surface pressure 2.0 MPa) the uncrosslinked rubber sheets of the rubber compositions shown in Tables 2 and 3 for 30 minutes using a press. A laminate of three crosslinked rubber sheets was used as a sample in accordance with JIS K 6253 (2012), and the hardness was measured using a durometer A-type hardness tester.

2) Measurement of tensile properties (tensile strength, elongation at break) According to JIS K 6251 (2010), a dumbbell-shaped No. 3 test piece taken from the crosslinked rubber sheet in the anti-grain direction was subjected to a tensile test at room temperature at a tensile speed of 500 mm/min, and the tensile strength (MPa) and elongation (%) at the time of break of the test piece were calculated. The tensile tester used was "Autograph AG-5000A" manufactured by Shimadzu Corporation. When used as a bladder, in order to prevent breakage and cracks from occurring even when expanded by crosslinking molding, it is considered that the elongation at break of the rubber composition is 100% or more.

3) Measurement of Compression Set According to JIS K 6262 (2013), the rubber composition was rolled into a sheet, and then placed in a mold to crosslink at 165°C for 30 minutes to prepare a cylindrical sample with a diameter of about 29 mm and a thickness of about 12.5 mm. The obtained sample was compressed under the test conditions of a compression rate of about 10% (spacer thickness 11.25 mm), a test temperature of 120°C, and a test time of 24 hours, and the thickness of the sample before and after compression was measured to calculate the compression set. In detail, the thickness of the sample before compression was h0 (mm), the thickness of the sample after compression was h1 (mm), and the thickness of the spacer was hS (mm), and the compression set: CS (%) was calculated by the following formula.

CS = [(h0-h1)/(h0-hS)] x 100

4) Measurement of tear properties (tear strength) The crosslinked rubber sheet was punched out in a crescent shape according to JIS K 6252 (2015), and a 1.00±0.05 mm notch was made in the center of the indentation. A tear test was performed at a tensile speed of 500 mm/min to measure the tear strength when the test piece broke. The tensile tester used was Shimadzu Corporation's "Autograph AG-5000A". In addition, in the accelerated aging test, a Method A AA-2 forced circulation type heat aging tester (crosswind type) was used.

The measurement results are shown in Tables 5 and 6.

[Bladder performance evaluation]
In the manufacturing apparatus shown in Figures 1 to 5, the bladders made from the rubber compositions of Examples 1 to 14 and Comparative Examples 1 to 10 were used to repeatedly manufacture (crosslink molding) belt sleeves that serve as precursors of V-ribbed belts, and the durability life of the bladders in permanent deformation was verified.

(Belt sleeve used for verification)

The tension layer, including the contact surface with the bladder, is a tension rubber layer, and the core layer is a belt sleeve in which the core wire is embedded in the adhesive rubber layer.

Rubber composition 1 was used for the tension rubber layer, rubber composition 2 for the compression rubber layer, and rubber composition 3 for the adhesive rubber layer. Each rubber composition was mixed in a Banbury mixer and rolled to a specified thickness with a calendar roll to produce an uncrosslinked rubber sheet for forming the tension rubber layer, an uncrosslinked rubber sheet for forming the compression rubber layer, and an uncrosslinked rubber sheet for the adhesive rubber layer.

Next, an uncrosslinked rubber sheet for forming the tension rubber layer was wound around the outermost circumference of the cylindrical inner mold fitted with the bladder, and a core wire for forming the core body was spun in a spiral shape around the outer circumference. An uncrosslinked rubber sheet for the adhesive rubber layer and an uncrosslinked rubber sheet for the compression rubber layer were then wound in that order to form an uncrosslinked molded body.

Furthermore, a cylindrical outer mold with multiple rib patterns engraved on its inner peripheral surface is used, and the inner mold with the uncrosslinked molded body formed therein is placed concentrically within this outer mold. The bladder is then expanded toward the inner peripheral surface (rib pattern) of the outer mold, and the outer peripheral side (compressed rubber layer) of the uncrosslinked molded body is pressed into the rib pattern, and heated at 180°C for 20 minutes to crosslink the molded body. The inner mold is then removed from the outer mold, and the belt sleeve with multiple ribs on the outer periphery is then demolded from the outer mold.

(Bladder durability)
This belt sleeve was repeatedly produced (crosslinked molding), and the time until traces of the core wire were transferred to the inner circumferential surface of the crosslinked molded body (the back surface of the transmission belt) and the back surface of the transmission belt was judged to have a poor appearance was defined as the durability life due to permanent deformation, and the number of uses until the durability life was reached was compared and verified. The number of uses was judged as good or bad according to the following criteria. Note that ○ and △ are practical pass levels.

○: 180 times or more △: 120 times or more but less than 180 times ×: Less than 120 times.

(Misalignment of the cord in the belt thickness direction)
The obtained belt sleeve was cut into a predetermined width and turned over to finish it into a V-ribbed belt (number of ribs: 3, circumference: 1100 mm, belt shape: K-shape, belt thickness: 4.3 mm, rib height: about 2 mm, rib pitch: 3.56 mm). The deviation of the core wire in the belt thickness direction was measured to evaluate the degree of variation in the distance from the back surface of the belt to the center of the core wire. The specific measurement procedure is shown below. First, the V-ribbed belt is cut parallel to the width direction, and the cross section is observed at 20 times magnification with a microscope. As shown in FIG. 7, the distance (L _nt ) from the back surface of the belt to directly above the core wire and the distance (L _nb ) from the back surface of the belt to directly below the core wire are measured for each core wire. At this time, the core wires to be measured are limited to those whose entire cross section can be observed, and those whose entire cross section cannot be observed (part of which hangs over the end surface of the belt) are excluded from the measurement. The measurement is performed on all of the core wires (n core wires: n is an integer of 2 or more) to be measured. The amount of deviation of the core wires in the belt thickness direction: X is calculated by the following formula.

X _2-1 = |(L _2t + L _2b ) - (L _1t + L _1b ) |/2
X _3-2 = |(L _3t + L _3b ) - (L _2t + L _2b ) |/2
...
_Xn-(n-1) = |( _Lnt + _Lnb ) - (L _(n-1)t + L _(n-1)b )|/2
X = (X _2-1 + X _3-2 + ... + X _n-(n-1) ) / (n-1)

The calculation results are shown in Tables 5 and 6. Furthermore, the calculated core wire misalignment amount X in the belt thickness direction was evaluated according to the following criteria. 〇 and △ are practical pass levels.

◯: Less than 0.06 mm △: 0.06 mm or more but less than 0.08 mm ×: 0.08 mm or more.

(Comprehensive assessment)
If the durability of the bladder and the arrangement of the core wires were both at an acceptable level (evaluated as ◯ or △), the sample was judged to have passed.

The results of the comparison are shown in Tables 5 and 6.

As is clear from the results in Table 5, in Examples 1 to 14, in which two types of carbon black (hard carbon and soft carbon) were blended and the blending amounts per 100 parts by mass of the rubber component were in the range of 30 to 60 parts by mass of hard carbon and 40 to 80 parts by mass of soft carbon, the durability life of the bladder (the number of uses until it reaches the end of its life due to permanent deformation) was achieved to be 120 times or more (rated as ○ or △). Furthermore, the alignment of the core wires (the amount of misalignment of the core wires in the belt thickness direction) also achieved an acceptable level (rated as ○ or △).

Among them, Examples 1 to 5 and 9 to 11 had high levels of both bladder durability and cord arrangement. Among Examples 1 to 5 and 9 to 11, Example 1 had the best balance. In other words, among Examples 1 to 3 in which the ratio of organic peroxide was changed, Example 1, which mixed 4 parts by mass of organic peroxide per 100 parts by mass of rubber component, had the best balance. Compared to Example 1, Example 4, which used EPDM with a low diene content, had results that were almost the same as Example 1. Also, Example 5, in which the types of hard carbon and soft carbon were changed compared to Example 1, had results that were almost the same as Example 1, but Example 1 had a slightly longer bladder life. Furthermore, Examples 9 to 11, in which the amounts of hard carbon and soft carbon mixed were changed compared to Example 1, had results that were almost the same as Example 1, but Example 1 had a slightly longer bladder life.

On the other hand, in Examples 6, 8, and 12 to 14, the blending ratio of hard carbon to soft carbon was relatively high, resulting in a shorter bladder durability life (rated as △). Also, in Example 14, which had the highest total carbon content, the tensile strength and tear strength also decreased slightly. However, in all cases, the core wire alignment was at a high level (misalignment amount of 0.01 to 0.03 mm) and was good. Note that in Example 9, although the blending ratio of hard carbon to soft carbon was high, the total carbon content was an appropriate amount, so both the bladder durability life and core wire alignment were at a high level.

In Example 7, the ratio of soft carbon was high, and the total amount of carbon black was too high, resulting in a shorter durability life (rated △). The alignment of the core wires also became more misaligned (rated △).

Comparative Example 1 is an example in which only one type of carbon black (hard carbon) was used, and although the reinforcing effect increased the tensile strength, the permanent deformation (compression set) was large. As a result of this balance, the core wire alignment was good (evaluated as ○), but the durability life of the bladder was short at 60 cycles (evaluated as ×).

Comparative Example 2 contains two types of carbon black, but the amount of soft carbon is small and the amount of hard carbon is large. The ratio of soft carbon is also high at 400 parts by mass compared to 100 parts by mass of hard carbon, and the total amount of carbon is also large. Although the tensile strength is high due to the reinforcing effect of the carbon, the permanent deformation (compression set) is large. Furthermore, the durability life of the bladder was 63 times (judgment x), and the amount of misalignment in the core wire arrangement was large (judgment x; 0.08 mm).

Comparative Example 3 contains two types of carbon black, but the amount of soft carbon is small, and the ratio of soft carbon is also low at 75 parts by mass compared to 100 parts by mass of hard carbon. The durability of the bladder was 110 times (evaluated as x), and the misalignment of the core wires was large (evaluated as △; 0.06 mm).

Comparative Example 4 is an example in which two types of carbon black are blended, but the amount of soft carbon blended and the total amount of carbon are small. The durability of the bladder was 118 times (evaluated as x), and the misalignment of the core wires was large (evaluated as 0.07 mm).

Comparative Example 5 contains two types of carbon black, but the amount of hard carbon is high, the ratio of soft carbon is low at 75 parts by mass compared to 100 parts by mass of hard carbon, and the total amount of carbon is high. When the amount of hard carbon is high and the total amount of carbon black is excessive, the rubber as a whole becomes hard, so the core wire alignment is good (evaluated as ○), but the compression set is large and the bladder durability life is only 80 times (evaluated as ×).

Comparative Example 6 is an example in which only one type of carbon black (soft carbon) was used, and although the permanent deformation (compression set) was small, the reinforcing effect was lacking, resulting in low tensile strength and tear strength. As a result of this balance, the durability life of the bladder (the number of uses until it reaches the end of its life due to permanent deformation) was short at 115 times (rating: x), and the core wire arrangement was not rated as pass.

Comparative Example 7 is an example in which butyl rubber was used as the rubber component, but the compression set was very large, the durability of the bladder was short at 60 cycles (evaluated as x), and the misalignment of the core wires was very large (evaluated as x; 0.10 mm).

Comparative Example 8 is an example in which two types of carbon black are blended, but the amount of hard carbon blended is small. The durability life of the bladder (the number of uses until it reaches the end of its life due to permanent deformation) was 180 times (rated △), which is an acceptable level, but the amount of misalignment in the core wire arrangement was large (rated ×; 0.08 mm).

Comparative Examples 9 and 10 are examples in which two types of carbon black are blended, but the amount of soft carbon blended is significantly higher. When the total amount of carbon black is in excess of 140 parts by mass or more, the entire rubber becomes hard, and although the core wire alignment is good (evaluated as ○), the compression set is large, and the durability life of the bladder is shortened (evaluated as ×).

The molding member of the present invention can be used as a molding member for producing crosslinked bodies such as tires and belts, and is particularly useful as a molding member (particularly a bladder) such as a jacket or bladder (flexible jacket) for producing transmission belts such as V-ribbed belts.

1... Inner mold 4... Uncrosslinked belt precursor 5... Bladder 6... Outer mold

Claims (13)

A molding member for producing a crosslinked molded article by crosslinking an uncrosslinked article while being in contact with the uncrosslinked article, comprising:
The rubber composition is formed from a crosslinked product of a rubber component, carbon black, and an organic peroxide.
The rubber component contains an ethylene-α-olefin elastomer,
The proportion of the ethylene-α-olefin elastomer in the rubber component is 90% by mass or more,
The carbon black contains hard carbon having a primary particle diameter of 5 nm or more and less than 40 nm and soft carbon having a primary particle diameter of 40 nm or more and 300 nm or less ,
The molding member has a ratio of the hard carbon of 28 to 70 parts by mass per 100 parts by mass of the rubber component, and a ratio of the soft carbon of 35 to 90 parts by mass per 100 parts by mass of the rubber component. The molding member according to claim 1, wherein the ratio of the soft carbon is 80 to 300 parts by mass per 100 parts by mass of the hard carbon. The molding member according to claim 1 or 2, wherein the ratio of the carbon black is 70 to 120 parts by mass per 100 parts by mass of the rubber component. 4. The molding member according to claim 1, wherein the hard carbon has a BET specific surface area of 70 to 140 m ² /g, and the soft carbon has a BET specific surface area of 25 to 60 m ² /g. The molding member according to any one of claims 1 to 4, wherein the ethylene-α-olefin elastomer has an ethylene content of 50 to 70% by mass and a diene content of 0.4 to 5% by mass. The molding member according to any one of claims 1 to 5, wherein the ratio of the organic peroxide is 2 to 8 parts by mass per 100 parts by mass of the rubber component. The molding member according to any one of claims 1 to 6, which has a compression set of 5 to 20% according to JIS K 6262. The molding member according to any one of claims 1 to 7, which has a breaking elongation of 100 to 500% according to JIS K 6251. The molding member according to any one of claims 1 to 8, which is a bladder for manufacturing a transmission belt. The molding member according to claim 9, wherein the transmission belt includes a core wire having an elastic modulus of 50 GPa or more. The molding member according to any one of claims 1 to 10, wherein the uncrosslinked body contains an organic peroxide. A method for producing a crosslinked molded body by crosslinking an uncrosslinked body while contacting the molding member according to any one of claims 1 to 11 with the uncrosslinked body. The method according to claim 12, in which the molding member is deformed to crosslink the uncrosslinked body.

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