JPWO2019181726A1 - Crosslinked rubber composition and method for producing the same - Google Patents

Abstract

The crosslinked rubber composition contains a rubber component and para-aramid short fibers dispersed in the rubber component. An RFL coating is attached to the surface of the para-aramid short fibers, and the RFL coating contains a (meth)acrylic acid ester having a plurality of double bonds in the molecule.

Description

The present invention relates to a crosslinked rubber composition and a method for producing the same.

Crosslinked rubber compositions containing para-aramid short fibers are used in various rubber products. For example, Patent Document 1 discloses a transmission belt using a rubber composition containing para-aramid short fibers. Patent Document 2 discloses a tire using a rubber composition containing para-aramid short fibers. Patent Document 3 discloses a hose using a rubber composition containing para-aramid short fibers.

JP, 2013-108564, A JP, 2013-18893, A JP, 2005-200545, A

The present invention is a crosslinked rubber composition containing a rubber component and para-aramid short fibers dispersed in the rubber component, wherein an RFL coating is attached to the surface of the para-aramid short fibers. The RFL coating contains a (meth)acrylic acid ester having a plurality of double bonds in the molecule.

The present invention is a method for producing a crosslinked rubber composition including a step of kneading a rubber component and a para-aramid short fiber, wherein, before the kneading, the para-aramid short fiber is a yarn of a para-aramid fiber. It is prepared by immersing in an RFL aqueous solution containing a (meth)acrylic acid ester having a plurality of double bonds in the molecule, heating and then cutting it into a predetermined fiber length.
It is a thing.

3 is a graph showing the relationship between the content of polyparaphenylene terephthalamide short fibers (PPTA short fibers) and the elastic modulus after storage. 3 is a graph showing the relationship between the content of polyparaphenylene terephthalamide short fibers (PPTA short fibers) and the Mooney viscosity.

Hereinafter, embodiments will be described in detail.

The crosslinked rubber composition according to the embodiment contains a rubber component and para-aramid short fibers. Then, the RFL coating is attached to the surface of the para-aramid short fibers, and the RFL coating contains (meth)acrylic acid ester having a plurality of double bonds in the molecule. In the present application, “(meth)acrylic acid ester” means acrylic acid ester or methacrylic acid ester. In addition, hereinafter, “(meth)acrylic acid ester having a plurality of double bonds in the molecule” is referred to as “(meth)acrylic acid ester A”.

The crosslinked rubber composition containing the para-aramid short fibers has a problem that even if the content of the para-aramid short fibers is increased, the reinforcing effect is only slightly increased. However, according to the crosslinked rubber composition according to the embodiment, the RFL coating adhered to the surface of the para-aramid short fibers contains the (meth)acrylic acid ester A, so that a high reinforcing effect of the para-aramid short fibers can be obtained. Obtainable. This is because the action of the (meth)acrylic acid ester A contained in the RFL coating adhered to the surface of the para-aramid short fibers suppresses the cutting and fibrillation of the para-aramid short fibers, and thereby the para-aramid short fibers. It is presumed that this is because the reinforcing effect originally possessed by is effectively expressed.

Here, as the rubber component, for example, ethylene-α-olefin elastomer, chloroprene rubber (CR), chlorosulfonated polyethylene rubber (CSM), hydrogenated acrylonitrile rubber (H-NBR), natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile rubber (NBR), butyl rubber (IIR) and the like. The rubber component preferably contains one or more of these, and for a transmission belt, ethylene-α-olefin elastomer, chloroprene rubber (CR), chlorosulfonated polyethylene rubber (CSM), hydrogenated It is preferable to include an acrylonitrile rubber (H-NBR), and it is more preferable to include an ethylene-α-olefin elastomer.

Examples of the ethylene-α-olefin elastomer include ethylene propylene diene monomer (hereinafter referred to as “EPDM”), ethylene propylene copolymer (EPM), ethylene butene copolymer (EBM), ethylene octene copolymer (EOM), and the like. The ethylene-α-olefin elastomer preferably contains one or more of these, and more preferably contains EPDM from the viewpoint of versatility.

Para-aramid short fibers include both polyparaphenylene terephthalamide short fibers (PPTA short fibers) and copolyparaphenylene-3,4′-oxydiphenylene terephthalamide short fibers, both of them. May be included. The para-aramid short fibers preferably include at least polyparaphenylene terephthalamide short fibers (PPTA short fibers) from the viewpoint of obtaining a high reinforcing effect.

The para-aramid short fibers are dispersed in the rubber component. The para-aramid short fibers may be oriented in one direction. The content of the para-aramid short fibers in the crosslinked rubber composition according to the embodiment is preferably 1 part by mass or more and 35 parts by mass or more with respect to 100 parts by mass of the rubber component, from the viewpoint of obtaining a high reinforcing effect of the para-aramid short fibers. Parts by mass or less, more preferably 3 parts by mass or more and 30 parts by mass or less, and further preferably 5 parts by mass or more and 25 parts by mass or less.

The filament fineness of the para-aramid short fibers is, for example, 1.5 dtex or more and 5.0 dtex. The para-aramid short fibers may have a filament diameter of 2.0 dtex or more, preferably 2.3 dtex or more, more preferably 2.5 dtex or more, further preferably 3.0 dtex or more. The fiber length of the para-aramid short fibers is preferably 0.5 mm or more and 10 mm or less, more preferably 1 mm or more and 5 mm or less, and further preferably 2 mm or more and 4 mm or less from the viewpoint of obtaining a high reinforcing effect of the para-aramid short fibers. ..

From the viewpoint of obtaining a high reinforcing effect of the para-aramid short fibers, the RFL coating is preferably attached so as to cover the surface of the para-aramid short fibers. The RFL film contains a condensate of resorcinol and formaldehyde, a latex-derived solid component whose main component is rubber, and a (meth)acrylic acid ester A.

Examples of the (meth)acrylic acid ester A include ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol diacrylate, propylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol diacrylate, 1,9-nonanediol dimethacrylate; diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate; diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, etc. To be The (meth)acrylic acid ester A preferably contains one or more of these, and more preferably contains polyethylene glycol dimethacrylate from the viewpoint of obtaining a high reinforcing effect of the para-aramid short fibers. The degree of polymerization of the ethylene glycol monomer in polyethylene glycol dimethacrylate is preferably 20 or less, more preferably 15 or less, from the viewpoint of obtaining a high reinforcing effect of the para-aramid short fiber. The content of the (meth)acrylic ester A in the RFL coating is preferably 2 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the latex-derived solid content, from the viewpoint of obtaining a high reinforcing effect of the para-aramid short fibers. , More preferably 5 parts by mass or more and 15 parts by mass or less, still more preferably 8 parts by mass or more and 12 parts by mass or less.

In the crosslinked rubber composition according to the embodiment, the rubber component is crosslinked. In this rubber component, even if the organic peroxide is used as a cross-linking agent and cross-linked, or if the sulfur is used as a cross-linking agent and cross-linked, both the organic peroxide and the sulfur are used as the cross-linking agent. It may be either crosslinked and crosslinked, but it is preferable that at least the organic peroxide serves as a crosslinking agent and is crosslinked.

Examples of the organic peroxide of the cross-linking agent include dicumyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and the like. Are listed. The organic peroxide preferably contains one or more of these, and preferably contains dicumyl peroxide from the viewpoint of obtaining a high compression modulus. The blending amount of the organic peroxide in the uncrosslinked rubber composition before crosslinking is preferably 1 part by mass or more and 7 parts by mass or less, and more preferably 100 parts by mass of the rubber component from the viewpoint of obtaining a high compression modulus. It is 2 parts by mass or more and 5 parts by mass or less.

The crosslinked rubber composition according to the embodiment, in addition, if necessary, a reinforcing material such as carbon black or silica, a functional filler, a softening agent, a vulcanization accelerator, a vulcanization acceleration aid, a processing aid, It may contain a rubber compound such as an antioxidant. Further, the crosslinked rubber composition according to the embodiment may contain short fibers other than para-aramid short fibers such as nylon short fibers.

Next, a method for producing the crosslinked rubber composition according to the embodiment will be described.

The method for producing a crosslinked rubber composition according to the embodiment includes a kneading step and a crosslinking step.

In the kneading step, the rubber component and the rubber compound containing the para-aramid short fibers and the crosslinking agent are kneaded using a rubber kneader to obtain an uncrosslinked rubber composition. Examples of the rubber kneader include a closed kneader, a Banbury mixer, and an open type open roll.

Here, the para-aramid short fiber is subjected to RFL treatment in which the yarn of the para-aramid fiber is immersed in an RFL aqueous solution containing a (meth)acrylic acid ester A and heated before kneading, and then a predetermined fiber length is obtained. It can be prepared by cutting into pieces.

The RFL aqueous solution is an aqueous solution in which an initial condensate of resorcin and formaldehyde, a latex, and a (meth)acrylic acid ester A are mixed. Examples of the latex include vinyl pyridine/styrene/butadiene rubber latex (Vp/SBR), styrene/butadiene rubber latex (SBR), natural rubber latex (NR), chloroprene rubber latex (CR), chlorosulfonated polyethylene rubber latex ( CSM), 2,3-dichlorobutadiene rubber latex (2,3-DCB), hydrogenated nitrile rubber latex (H-NBR), carboxylated hydrogenated nitrile rubber latex, butadiene rubber latex (BR), nitrile rubber latex (NBR) ) And the like. The latex preferably contains one or more of these.

The solid content concentration obtained by combining the content of the initial condensate of resorcin and formaldehyde in the RFL aqueous solution and the content of the latex-derived solid content is, for example, 10% by mass or more and 30% by mass or less. The content of the (meth)acrylic acid ester A in the RFL aqueous solution is, as described above, preferably 2 parts by mass or more and 20 parts by mass or less, more preferably 5 parts by mass or more and 15 parts by mass with respect to 100 parts by mass of the latex-derived solid content. Parts by mass or less, more preferably 8 parts by mass or more and 12 parts by mass or less.

Regarding the initial condensate (RF) of resorcin (R) and formaldehyde (F) in the RFL aqueous solution, the molar ratio (R/F) of resorcin (R) to formalin (F) is, for example, 1/0.5 or more 1/ It is 2 or less. The mass ratio (RF/L) of the initial condensate (RF) of resorcin (R) and formaldehyde (F) to the latex-derived solid content (L) in the RFL aqueous solution is, for example, 1/2 or more and 1/10 or less, It is preferably about 1/6.

It should be noted that the para-aramid fiber yarn is subjected to a base treatment in which epoxy or isocyanate (blocked isocyanate) is dissolved in a solvent such as toluene or immersed in a primer solution dispersed in water and heated before RFL treatment. May be given.

By the way, generally, in the uncrosslinked rubber composition before crosslinking, when the content of the para-aramid short fibers is increased, the Mooney viscosity is increased and the kneading processability is lowered, and therefore the content of the para-aramid short fibers is increased. The upper limit will be constrained. However, in the crosslinked rubber composition according to the embodiment, since the para-aramid short fibers having the RFL coating containing the (meth)acrylic acid ester A attached to the surface are used, the content of the para-aramid short fibers is high. Even then, it is possible to suppress an increase in the Mooney viscosity of the uncrosslinked rubber composition before crosslinking. Therefore, even if the content of the para-aramid short fibers is large, the good kneadability of the uncrosslinked rubber composition before crosslinking can be obtained. The amount can be increased to 15 parts by mass or more, or 20 parts by mass or more with respect to parts by mass. It is speculated that this is also because the action of the (meth)acrylic acid ester A contained in the RFL coating suppresses the cutting and fibrillation of the para-aramid short fibers.

In the crosslinking step, the uncrosslinked rubber composition obtained in the kneading step is heated and pressed by a processing method corresponding to the rubber product to crosslink the rubber component.

The crosslinked rubber composition according to the embodiment can be applied to rubber products such as power transmission belts, tires and hoses, and is particularly preferably applied to power transmission belts that undergo severe deformation during use.

(Crosslinked rubber composition)
<Example>
An RFL aqueous solution X was prepared by mixing an initial condensate of resorcin and formaldehyde, latex, and polyethylene glycol dimethacrylate (light ester 14EG, manufactured by Kyoeisha Chemical Co., Ltd., degree of polymerization ≈14). As the latex, a mixed latex of Vp.SBR latex (PYRATEX manufactured by A&L Japan) and SBR latex (J9049 manufactured by A&L Japan) was used. The solid content concentration of the content of the initial condensate of resorcin and formaldehyde in the RFL aqueous solution X and the content of the latex-derived solid content was 16.1% by mass. The content of polyethylene glycol dimethacrylate in the RFL aqueous solution X was 10 parts by mass based on 100 parts by mass of the latex-derived solid content. The molar ratio (R/F) of resorcin (R) to formalin (F) was 1/1.4. The mass ratio (RF/L) of the initial condensate (RF) of resorcin (R) and formaldehyde (F) to the latex-derived solid content (L) was set to 1/6.

Then, a yarn of PPTA fiber (Kevlar Toray-Dupont, filament fineness: 1.7 dtex) is immersed in the RFL aqueous solution X and heated, and then cut into a fiber length of 3 mm to form the RFL aqueous solution X with RFL. PPTA short fibers of the treated para-aramid short fibers were prepared.

Subsequently, EPDM (manufactured by JSR T7241 JSR Co.) was used as a rubber component, and 45 parts by mass of FEF carbon black (manufactured by Seast SO Tokai Carbon Co., Ltd.) as a reinforcing material and 100 parts by mass of the functional filler were added to 100 parts by mass of the rubber component. -Shaped ultra-high molecular weight polyethylene resin (Hi-Zex Million 240S manufactured by Mitsui Chemicals, Inc.) 10 parts by mass, oil as a softening agent (Samper 2280 manufactured by Nippon San Oil Co., Ltd.), and zinc oxide (3 types of zinc oxide) as a vulcanization accelerator. 5 parts by mass of Sakai Chemical Industry Co., Ltd., 1 part by mass of processing aid stearic acid (manufactured by LUNAC Kao Co.), 4 parts by mass of co-crosslinking agent (manufactured by Barnock PM Ouchi Shinko Chemical Co., Ltd.), organic peroxide of crosslinking agent. (Peroximon F40 (purity: 40% by mass), manufactured by NOF CORPORATION) 7 parts by mass (active ingredient: 2.8 parts by mass), and nylon short fibers (Leona 66 manufactured by Asahi Kasei Corporation, filament fineness: 6.7 dtex, fiber length: 3 mm) ), and 5 parts by mass of PPTA short fibers RFL-treated with the RFL aqueous solution X were added and kneaded to prepare an uncrosslinked rubber composition.

Then, this uncrosslinked rubber composition was heated and pressed to obtain a strip-shaped test piece of the crosslinked rubber composition for testing, the length direction of which coincided with the grain direction.

Similarly, the content of the PPTA short fibers RFL-treated with the RFL aqueous solution X was 10 parts by mass, 15 parts by mass, and 20 parts by mass with respect to 100 parts by mass of the rubber component to prepare an uncrosslinked rubber composition. Was heated and pressed to obtain a strip-shaped cross-linked rubber composition test piece for a test whose lengthwise direction coincides with the grain direction.

<Comparative example>
An RFL aqueous solution Y having the same composition as the RFL aqueous solution X except that it does not contain polyethylene glycol dimethacrylate was prepared, and using this, the content of the PPTA short fibers RFL-treated with the RFL aqueous solution Y was the same as in the example. 5 parts by mass, 10 parts by mass, 15 parts by mass, and 20 parts by mass with respect to 100 parts by mass of the rubber component were used. Obtained.

(Test method)
For each of the examples and comparative examples, based on JIS K6394:2007, from a test piece of a strip-shaped crosslinked rubber composition, using a dynamic viscoelasticity tester, a test temperature of 100° C., a test dynamic strain of 0.1%, Also, the storage elastic modulus E′ at 100° C. in the grain direction was measured at a test frequency of 10 Hz.

In addition, for each of the examples and the comparative examples, the Mooney viscosity at 125° C. of the uncrosslinked rubber composition with the content of each PPTA short fiber was measured based on JISK6300.

(Test results)
FIG. 1 shows the relationship between the content of short PPTA fibers and the elastic modulus of storage E′. FIG. 2 shows the relationship between the content of PPTA short fibers and the Mooney viscosity. The test results are shown in Table 1.

According to FIG. 1 and Table 1, the examples in which the RFL coating attached to the surface of the PPTA short fibers contained ethylene glycol dimethacrylate were compared with the comparative examples in which the RFL coating did not contain ethylene glycol dimethacrylate. With respect to the fiber content, the freshly-stored elastic modulus E′ is high, and the increase rate of the freshly-stored elastic modulus E′ due to the increased content of the PPTA short fiber is also high, so that a high reinforcing effect is obtained. I understand.

From FIG. 2 and Table 1, it can be seen that in Examples, in comparison with Comparative Examples, the Mooney viscosity of the uncrosslinked rubber composition is low in the content of each PPTA short fiber.

INDUSTRIAL APPLICABILITY The present invention is useful in the technical field of a crosslinked rubber composition and a method for producing the same.

Claims (11)

A crosslinked rubber composition containing a rubber component and para-aramid short fibers dispersed in the rubber component,
An RFL coating is attached to the surface of the para-aramid short fibers, and the RFL coating contains a (meth)acrylic ester having a plurality of double bonds in the molecule. The crosslinked rubber composition according to claim 1,
A crosslinked rubber composition in which the para-aramid short fibers include polyparaphenylene terephthalamide short fibers. The crosslinked rubber composition according to claim 1 or 2,
A crosslinked rubber composition in which the content of the para-aramid short fibers is 1 part by mass or more and 35 parts by mass or less based on 100 parts by mass of the rubber component. The crosslinked rubber composition according to any one of claims 1 to 3,
A crosslinked rubber composition in which the filament size of the para-aramid short fibers is 1.5 dtex or more and 5.0 dtex or more. The crosslinked rubber composition according to any one of claims 1 to 4,
A crosslinked rubber composition in which the fiber length of the para-aramid short fibers is 0.5 mm or more and 10 mm or less. The crosslinked rubber composition according to any one of claims 1 to 5,
A crosslinked rubber composition in which the (meth)acrylic acid ester having a plurality of double bonds in the molecule contains polyethylene glycol dimethacrylate. The crosslinked rubber composition according to claim 6,
A crosslinked rubber composition in which the degree of polymerization of the ethylene glycol monomer in the polyethylene glycol dimethacrylate is 20 or less. The crosslinked rubber composition according to any one of claims 1 to 7,
The content of the (meth)acrylic acid ester having a plurality of double bonds in the molecule in the RFL coating is 2 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the latex-derived solid content of the RFL film. Crosslinked rubber composition. The crosslinked rubber composition according to any one of claims 1 to 8,
A crosslinked rubber composition in which the rubber component contains an ethylene-α-olefin elastomer. The crosslinked rubber composition according to any one of claims 1 to 9,
The rubber component is a crosslinked rubber composition in which an organic peroxide serves as a crosslinking agent and is crosslinked. A method for producing a crosslinked rubber composition, which comprises a step of kneading a rubber component and a para-aramid short fiber,
Before the kneading, the para-aramid short fibers are heated by immersing the para-aramid fiber yarn in an RFL aqueous solution containing a (meth)acrylic acid ester having a plurality of double bonds in the molecule, and then heating the mixture. A method for producing a crosslinked rubber composition, which is prepared by cutting the fiber length.

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