JP2005132913A - Rubber composition for large rubber product and large rubber product, and method for producing large rubber product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition which is used for large rubber products and can prevent the deterioration of physical properties due to over-vulcanization, especially the deterioration of modulus, cross-link density and shear stiffness, to provide a large rubber product using the composition, and to provide a method for producing the large rubber product. <P>SOLUTION: This rubber composition for large rubber products comprises 100 pts. mass of a dienic rubber containing natural rubber in an amount of ≥50 mass % and 0.1 to 5 pts. mass of a vulcanization accelerator represented by the general formula (1) (R<SP>1</SP>and R<SP>2</SP>are each independently a 1 to 6C non-cyclic aliphatic group which may be branched or a 3 to 6C alicyclic group which may be branched). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rubber composition for a large rubber product that does not cause deterioration in physical properties due to overvulcanization (overvulcanization), a large rubber product using the composition, and a method for producing the large rubber product.

Rubber products are generally obtained by crosslinking raw rubber. There are various forms of crosslinking such as sulfur vulcanization, organic peroxide crosslinking, resin crosslinking, metal ion crosslinking, and the like, and a technique using both sulfur vulcanization and organic peroxide crosslinking is also known.
Conventionally, such rubber products, particularly rubber products used in buildings, are rubber bearings (laminates) in which a soft layer made of rubber and a hard layer made of a metal plate or the like are alternately laminated. Is known as a reaction force-dispersing rubber bearing whose main purpose is to disperse a reaction force by elastic modification, and a rubber composition used for a seismic isolation rubber bearing to which a damping property is imparted (for example, Non-Patent Document 1). reference.). Such rubber compositions include those having a laminate having a diameter of more than 1.5 meters, and belong to a very large class as rubber products.

  In such a large rubber product, the heat history is greatly different between the vicinity of the heat source and the part far from the heat source at the time of vulcanization, and when the part far from the heat source is appropriately vulcanized, it is over-vulcanized near the heat source. For this reason, there is a problem that physical properties are likely to be deteriorated near the heat source, the physical properties are uneven in the product, the physical properties are likely to vary depending on the product size, and it is difficult to ensure a certain quality.

Michio Okuyama et al., “Encyclopedia of Rubber”, Asakura Shoten Co., Ltd., November 2000, first edition, first edition, p. 411

  Accordingly, the present invention provides a rubber composition for a large rubber product that can suppress a decrease in physical properties due to over-vulcanization, particularly a decrease in modulus, crosslink density, and shear rigidity (hereinafter sometimes referred to simply as “reversion”), and the rubber composition. An object is to provide a large rubber product using the composition and a method for producing the large rubber product.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a rubber composition containing a diene rubber mainly composed of natural rubber, and a vulcanization accelerator represented by a predetermined structural formula, The present inventors have found that the rubber composition can suppress reversion due to over-vulcanization and have completed the present invention. That is, the present invention provides a rubber composition for large rubber products shown in (I) below, a large rubber product shown in (II) and (III) below, and a large rubber product shown in (IV) and (V) below. A method is provided.

  (I) A large size containing 100 parts by mass of a diene rubber containing 50% by mass or more of natural rubber (NR) and 0.1 to 5 parts by mass of a vulcanization accelerator represented by the following general formula (1) A rubber composition for a rubber product (first aspect).

In the formula, each of R ¹ and R ² independently represents an acyclic aliphatic group having 1 to 6 carbon atoms which may be branched or a cyclic aliphatic group having 3 to 6 carbon atoms which may be branched. .

  (II) A large rubber product (second aspect) comprising the rubber composition for large rubber products described in (I) above.

  (III) The large rubber product according to (II), which is a rubber bearing in which a rubber layer made of the rubber composition for a large rubber product according to (I) and a hard layer are alternately laminated.

(IV) A production method for producing the large rubber product described in (II) above,
A method for producing a large rubber product comprising a vulcanization step of vulcanizing the rubber composition for a large rubber product described in (I) in a time not less than twice the 95% vulcanization time of the rubber composition (No. 1) 3 embodiment).

(V) A production method for producing the large rubber product according to (III) above,
A rolling process for rolling the rubber composition for large rubber products described in (I) into a sheet, and a laminate forming process for forming a laminate by laminating the rubber sheet and the hard layer obtained by the rolling process And a vulcanization adhesion step for adhering the laminate formed by the laminate formation step by vulcanization in a time not less than twice the 95% vulcanization time of the rubber composition. Product manufacturing method.

  According to the present invention, by incorporating a vulcanization accelerator represented by the above general formula (1) into a rubber composition containing a diene rubber containing natural rubber as a main component, reversion by over-vulcanization is performed. Can be suppressed. As a result, when a large rubber product using this rubber composition is produced, it becomes possible to make the rubber physical properties at the same level in a portion close to the heat source and a portion far from the heat source during vulcanization. This is useful because the physical properties of rubber can be made uniform and the variation in physical properties due to product size can be reduced.

Hereinafter, the present invention will be described in detail.
The rubber composition for large rubber products according to the first aspect of the present invention (hereinafter sometimes simply referred to as “the rubber composition for large rubber products of the present invention”) is a diene containing 50% by mass or more of natural rubber. It is a rubber composition for a large rubber product containing 100 parts by mass of a rubber and 0.1 to 5 parts by mass of a vulcanization accelerator represented by the general formula (1).
Next, the diene rubber and vulcanization accelerator forming the rubber composition for large rubber products of the present invention will be described in detail.

<Diene rubber>
The diene rubber used in the rubber composition for large rubber products of the present invention is not particularly limited as long as it contains 50% by mass or more, preferably 70% by mass or more of natural rubber.
In addition to natural rubber, other rubbers that may be contained in the diene rubber are specifically, for example, isoprene rubber (IR), butadiene rubber (BR), 1,2-polybutadiene rubber (1,2 -BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR, NIR, NBIR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR) ), Diene-based synthetic rubbers such as ethylene propylene diene rubber (EPDM); urethane rubber, silicone rubber, acrylic rubber, epoxidized natural rubber, acrylate butadiene rubber, and the like. May be used in combination.
Of these, natural rubber alone or a mixed rubber in which natural rubber and the diene synthetic rubber exemplified above are used in combination is preferable.

<Vulcanization accelerator>
The vulcanization accelerator used in the rubber composition for large rubber products of the present invention is not particularly limited as long as it is a compound represented by the following general formula (1).

In the general formula (1), R ¹ and R ² are each independently a non-cyclic aliphatic group having 1 to 6 carbon atoms which may be branched or a cyclic group having 3 to 6 carbon atoms which may be branched. Represents an aliphatic group.
Here, as the acyclic aliphatic group having 1 to 6 carbon atoms, specifically, for example, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1-methylbutyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, and the like. The group may contain a double bond or a triple bond. Of these, a methyl group and an ethyl group are preferable.
Specific examples of the cyclic aliphatic group having 3 to 6 carbon atoms that may be branched include cyclopropan-1-yl, cyclobutan-1-yl, cyclopentan-1-yl, and cyclohexane- 1-yl and the like can be mentioned.

Specific examples of the compound represented by the general formula (1) having such a substituent in R ¹ and R ² include 2- (N, N-dimethylthiocarbamoylthio) benzothiazole, 2 -(N, N-diethylthiocarbamoylthio) benzothiazole, 2- (N, N-dicyclohexylthiocarbamoylthio) benzothiazole and the like.

  A commercial item can be utilized as such a vulcanization accelerator, and Noxeller 64 (made by Ouchi Shinsei Chemical Industry Co., Ltd.) is illustrated suitably.

Moreover, content of the said vulcanization accelerator is 0.1-5 mass parts with respect to 100 mass parts of said diene rubbers, and it is preferable that it is 0.3-3 mass parts. If the amount is less than 0.1 parts by mass, the effect of suppressing the above-mentioned reversion is not sufficient and the progress of vulcanization is too slow. On the other hand, if it exceeds 5 parts by mass, scorching becomes faster, which may cause a problem in processing.
Therefore, if the content of the vulcanization accelerator is in the above range, the rubber composition for a large rubber product of the present invention obtained is preferable because reversion due to over-vulcanization is suppressed.

  In the rubber composition for large rubber products of the present invention, in addition to the above-described diene rubber and vulcanization accelerator, if necessary, a known vulcanizing agent, vulcanization acceleration represented by the above general formula (1) can be used. Vulcanization accelerators, vulcanization accelerators, vulcanization retarders, colorants (pigments), anti-aging agents, fillers (reinforcing agents), softeners, plasticizers, activators, tackifiers and lubricants Various additives such as can be added as necessary.

Specific examples of the vulcanizing agent include sulfur, organic sulfur-containing compounds such as tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), dipentamethylenethiuram disulfide (DPTT); dicumyl peroxide, and the like. Organic peroxides such as quinonedioxime may be used, and these may be used alone or in combination of two or more.
The content of the vulcanizing agent that can be added as desired is preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the vulcanizing agent is within this range, it is preferable because the vulcanization proceeds sufficiently.

Examples of the vulcanization accelerator other than the vulcanization accelerator represented by the general formula (1) include a sulfenamide vulcanization accelerator, a thiazole vulcanization accelerator, a dithiocarbamate vulcanization accelerator, and a thiuram type. A vulcanization accelerator is preferably exemplified.
Specific examples of the sulfenamide-based vulcanization accelerator include N-cyclohexyl-2-benzothiazolylsulfenamide (Noxeller CZ; manufactured by Ouchi Shinsei Chemical Co., Ltd.), N-tert-butyl-2. -Benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, N, N-dicyclohexyl-2-benzothiazylsulfenamide and the like.
Specific examples of the thiazole vulcanization accelerator include 2- (4′-morpholinodithio) benzothiazole, 2-mercaptobenzothiazole, benzothiazyl disulfide, and the like.
Specific examples of the dithiocarbamate vulcanization accelerator include zinc dimethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate and the like.
Specific examples of the thiuram vulcanization accelerator include tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N), tetramethylthiuram monosulfide (TS), tetraethylthiuram disulfide (TET), and tetramethylthiuram disulfide. (TT), dipentamethylene thiuram hexasulfide (TRA) and the like.
Such vulcanization accelerators may be used alone or in combination of two or more. When used in combination with the vulcanization accelerator represented by the general formula (1), the entire vulcanization accelerator The blending amount is 0.1 to 5 parts by mass with respect to 100 parts by mass of the diene rubber, and the ratio of the vulcanization accelerator represented by the general formula (1) in the entire vulcanization accelerator is: It is 5-80 mass%, and it is preferable that it is 5-50 mass%.

Specific examples of the vulcanization acceleration aid include metal oxides such as zinc white and magnesia; resurge, red lead, calcium hydroxide, fatty acid and the like. More than one species may be used in combination.
The content of the vulcanization acceleration aid that can be added as desired is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the vulcanization accelerating aid is within this range, it is preferable because vulcanization proceeds sufficiently and a material having high physical properties (for example, excellent modulus and hardness) can be obtained.

Specific examples of the vulcanization retarder include organic acids such as phthalic anhydride, benzoic acid, salicylic acid, and acetylsalicylic acid; N-nitrosodiphenylamine, N-nitrosophenyl-β-naphthylamine, N-nitroso- Nitroso compounds such as polymers of trimethyl-dihydroquinoline; Halides such as trichloromelanin; 2-mercaptobenzimidazole, N-cyclohexylthiophthalimide and the like. These may be used alone or in combination of two or more. May be.
The content of the vulcanization retarder that can be added as desired is preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the vulcanization retarder is within this range, it is preferable because the scorch can be stabilized without inhibiting vulcanization.

Specific examples of the colorant include inorganic pigments such as titanium oxide, zinc oxide, ultramarine, bengara, lithopone, lead, cadmium, iron, cobalt, aluminum, hydrochloride, and sulfate; azo pigments, phthalocyanine pigments, Quinacridone pigment, quinacridone quinone pigment, dioxazine pigment, anthrapyrimidine pigment, ansanthrone pigment, indanthrone pigment, flavanthrone pigment perylene pigment, perinone pigment, diketopyrrolopyrrole pigment, quinonaphthalone pigment, anthraquinone pigment, thioindigo pigment, benzimidazolone Examples thereof include organic pigments such as pigments and isoindoline pigments, and these may be used alone or in combination of two or more.
The content of the colorant that can be added as desired is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the colorant is within this range, it is preferable because the color can be colored without impairing physical properties (for example, modulus, hardness, etc.).

Specific examples of the antioxidant include N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine (6PPD), N, N′-dinaphthyl-p-phenylenediamine (DNPD). ), N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD), styrenated phenol (SP), and the like. These may be used alone or in combination of two or more.
The content of the anti-aging agent that can be added as desired is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the anti-aging agent is within this range, it is preferable because the anti-aging effect can be sufficiently obtained.

Specific examples of the filler include fumed silica, calcined silica, precipitated silica, pulverized silica, fused silica, diatomaceous earth and the like; carbon black, white carbon, iron oxide, zinc oxide, titanium oxide , Barium oxide, magnesium oxide, calcium carbonate, magnesium carbonate, zinc carbonate, barium sulfate, aluminum hydroxide, wax stone clay, kaolin clay, calcined clay, talc, mica, etc., and these may be used alone. Two or more kinds may be used in combination.
The filler content that can be added as desired is preferably 20 to 100 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the filler is within this range, it is preferable because sufficient physical properties (for example, elongation at break and hardness) can be obtained.

Specific examples of the softener include plant softeners such as tall oil mainly composed of linoleic acid, oleic acid, and abietic acid, pine tar, rapeseed oil, cottonseed oil, peanut oil, castor oil, palm oil, fuactis; Examples thereof include mineral oil-based softeners such as paraffinic oil, naphthenic oil, and aromatic oil. These may be used alone or in combination of two or more.
The content of the softening agent that can be added as desired is preferably 1 to 150 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the softening agent is within this range, it is preferable because workability such as mixing and rolling is excellent.

Specific examples of the plasticizer include dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, isodecyl succinate, diethylene glycol dibenzoate, pentaerythritol ester, butyl oleate, methyl acetylricinoleate, phosphorus Examples include tricresyl acid, trioctyl phosphate, trimellitic acid ester, propylene glycol adipate polyester, and butylene glycol polyester adipate. These may be used alone or in combination of two or more.
The content of the plasticizer that can be added as desired is preferably 1 to 150 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the plasticizer is within this range, it is preferable because of excellent workability such as mixing and rolling.

Specific examples of the activator include stearic acid, oleic acid, lauric acid, zinc stearate and the like, and these may be used alone or in combination of two or more.
The content of the activator that can be added as desired is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the activator is within this range, it is preferable because vulcanization proceeds sufficiently.

Specific examples of the tackifier include alkylphenol formaldehyde resins, alkylphenol acetylene resins, coumarone indene resins, xylene formaldehyde resins, polybutenes, rosin derivatives, and the like, which are used alone. Or you may use 2 or more types together.
The content of the tackifier that can be added as desired is preferably 1 to 50 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the tackifier is within this range, it is preferable because sufficient tackiness can be obtained without impairing processability.

Specific examples of the lubricant include stearic acid metal soap, high melting point wax, low molecular weight polyethylene, polyethylene glycol, octadecylamine, and the like. These may be used alone or in combination of two or more. May be.
The amount of the lubricant that can be added as desired is preferably 1 to 50 parts by mass with respect to 100 parts by mass of the diene rubber. If the content of the lubricant is within this range, it is preferable because sufficient fluidity can be obtained.

  Moreover, the manufacturing method of the rubber composition for large-sized rubber products of the present invention is not particularly limited, and the vulcanization accelerator represented by the general formula (1) is added to the diene rubber, and the various additives are added as necessary. It can manufacture by mix | blending an agent. Specifically, a roll, a kneader, an extruder, a universal stirrer, the diene rubber, the vulcanization accelerator represented by the general formula (1), and the various additives blended as necessary. A method for producing by kneading using a twin screw extruder, Banbury mixer or the like is preferably exemplified.

The large rubber product according to the second aspect of the present invention (hereinafter sometimes simply referred to as “large rubber product of the present invention”) is the rubber composition for large rubber products according to the first aspect of the present invention described above. A rubber bearing comprising a rubber layer made of the rubber composition for a large rubber product according to the first aspect of the present invention and a hard layer alternately laminated, as a specific example thereof, Preferable examples include large tires (OR tires) to be mounted on industrial vehicles, fenders, lining materials that are vulcanized in a state where multiple long rubber sheets are wound.
Here, the “large rubber” forming the large rubber product of the present invention is a rubber formed from the rubber composition for a large rubber product according to the first aspect of the present invention described above. Thickness that requires a long time that is not suitable for small rubber products during vulcanization, and overcuring occurs near the heat source (rubber surface) when the part far from the heat source (inside the rubber) is properly vulcanized. It is a rubber having a thickness. Specifically, it is a rubber having a distance of 10 cm or more between a portion where the vulcanization is slowest and the surface.
Next, a rubber bearing which is an example of a preferred embodiment of the large rubber product of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a cross-sectional view of a rubber bearing which is an example of a large rubber product of the present invention. The rubber support 10 is a laminated body in which metal flanges 11 and 12 are provided on the upper and lower surfaces, and a plurality of soft layers 13 and hard layers 14 are alternately stacked between the metal flanges 11 and 12. The rubber composition for large rubber products according to the first aspect is vulcanized and molded. The outer periphery of the laminate is covered with a coating layer 15 made of the same rubber composition as that of the soft layer 13.
Further, the hard layer 14 used in the rubber support 10 is not particularly limited as long as it has a higher hardness than the soft layer 13, but as the material thereof, metal, ceramic, plastic, etc. can be used. It is preferable to use it.

The large rubber product of the present invention is obtained by vulcanizing and molding the rubber composition for a large rubber product according to the first aspect of the present invention described above. This is very useful because the deterioration can be suppressed, the rubber physical properties in the resulting large rubber product can be made uniform, and the variation in physical properties due to the product size can be reduced.
In addition, the use of the large rubber product of the present invention is not particularly limited, but when the large rubber product is a seismic isolation rubber bearing, a vibration energy absorbing device (for example, a road) It can be suitably used for bridge support, bridge, building base isolation, detached base isolation, etc.

The method for producing a large rubber product according to the third aspect of the present invention (hereinafter sometimes referred to simply as “the production method of the present invention”) is the above-described rubber for large rubber products according to the first aspect of the present invention. A method for producing a large rubber product comprising a vulcanization step of vulcanizing a composition in a time not less than twice the 95% vulcanization time of the rubber composition.
Here, the vulcanization time in the above vulcanization process “a time more than twice the 95% vulcanization time of the rubber composition” means “8. Vibration by vulcanization tester” defined in JIS K6300-1994. The time (for example, 40% at 148 ° C.) more than twice the 95% vulcanization time (hereinafter, simply referred to as “t95”) of the rubber composition for large rubber products of the present invention, which is obtained according to the “sulfur test” method. More than minutes). This indicates the vulcanization time required for the large rubber forming the large rubber product of the present invention. Specifically, for example, when manufacturing a large tire (diameter 2 m × rubber thickness 20 cm), it is 180. It is 6 hours at a temperature of 3 ° C., and 3 hours at 135 ° C. when a fender (diameter 2 m × length 3 m) is produced.
As such a production method of the present invention, specifically, as described above, a large rubber product obtained as a kneaded product using a roll, a kneader, an extruder, a universal agitator, a twin screw extruder, a Banbury mixer, etc. A method of producing the rubber composition by heating and vulcanizing the rubber composition at a temperature of 120 to 190 ° C., preferably 135 to 150 ° C., for a time not less than twice the t95 of the rubber composition is suitably exemplified. .

In the production method of the present invention, particularly for the production method for producing the rubber bearing described above, a rolling step of rolling the rubber composition for large rubber products according to the first aspect of the present invention into a sheet, and the rolling A laminated body forming step of forming a laminated body by laminating the rubber sheet and the hard layer obtained by the step, and a laminated body formed by the laminated body forming step is at least twice t95 of the rubber composition It is preferable that it is a manufacturing method which comprises the vulcanization | cure adhesion process made to adhere | attach by vulcanizing in time.
Next, (1) rolling step, (2) laminate forming step, and (3) vulcanization bonding step will be described in detail.

(1) Rolling step The rolling step is a step of rolling the rubber composition for a large rubber product according to the first aspect of the present invention into a sheet in an unvulcanized state, whereby a rubber sheet is obtained. It is done.
The sheet obtained by rolling generally has a length of 50 to 70 m × width of 60 to 100 cm × thickness of 0.2 to 0.5 cm when a rolling roll is used. In order to obtain a rubber sheet to be used, it is necessary to stack the obtained sheets so as to have a predetermined thickness (for example, 2.5 cm). In addition, if the sheet | seat obtained by rolling has the thickness of the rubber sheet used for a rubber bearing, it is not necessary to pile up this sheet | seat.
In addition, after the rolling process, if necessary, there may be a process of appropriately chopping the length or width of the rubber sheet in order to obtain a rubber sheet shape suitable for use in the laminate forming process described later. .

(2) Laminate Forming Process The laminated body forming process is a process of laminating the rubber sheet obtained by the rolling process and a hard layer, whereby a laminate is formed. Here, the hard layer is the same as that described above in the second aspect of the present invention.

(3) Vulcanization adhesion process The vulcanization adhesion process is a process in which the laminate formed by the laminate formation process is vulcanized in a time that is at least twice as long as t95 of the rubber composition forming the rubber sheet. It is the process of making it adhere | attach, It is preferable to vulcanize at 120-190 degreeC, and it is more preferable to vulcanize at 135-150 degreeC. As a result, a rubber bearing in which the rubber sheet forming the laminate and the hard layer are vulcanized and bonded is manufactured as a large rubber product.
Specifically, for example, a rubber bearing having a length × width × height of 100 cm × 100 cm × 35 cm can be produced by vulcanization at a temperature of 135 ° C. for 10 hours.

  As described above, the production method of the present invention is obtained by vulcanizing and molding the rubber composition for large rubber products according to the first aspect of the present invention. This is useful because the decrease in rigidity is suppressed and the rubber physical properties of the resulting rubber bearing can be made uniform.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.
(Example 1 and Comparative Example 1)
An unvulcanized rubber composition comprising the composition components (parts by mass) shown in Table 1 below and blending natural rubber (NR), carbon black (CB), anti-aging agent, aroma oil, sulfur and a vulcanization accelerator. Prepared.
In addition, as a composition component in Table 1 below, RSS No. 3 is used as a natural rubber, Showa Black S118 (manufactured by Showa Cabot) as carbon black, and Santoflex 6PPD (manufactured by Flexis) as an anti-aging agent, Extract 4 (made by Showa Shell Sekiyu Co., Ltd.) as oil, oil-treated sulfur (produced by Karuizawa Refinery) as sulfur, and Noxeller CZ (made by Ouchi Shinsei Chemical Co., Ltd.) or Noxeller 64 (large) as vulcanization accelerator Uchisei Chemical Co., Ltd.) was used.

For each rubber composition obtained, as an anti-reversion properties, change rate and the degree of swelling in toluene of 100% modulus (M ₁₀₀₎ (%) was measured by the measuring method described below.
The vulcanization conditions at that time were a vulcanization temperature of 148 ° C., a vulcanization time of 30 minutes, 45 minutes, and 90 minutes, and changes in physical properties due to over-vulcanization were measured. The rate of change of M ₁₀₀ are both 148 ° C., the value of 30 minutes as 100, shown by an index to it.

<Rate of change of the M _100>
The measurement of M ₁₀₀ change rate is based on JIS K6251-1993, and the vulcanized rubber composition obtained under each vulcanization condition is cut into a dumbbell-shaped test piece (dumbbell-shaped No. 3) having a thickness of 2 mm. It was carried out by measuring the M _100. The results are shown in Table 2 below.
From the results shown in Table 2 below, Example 1 using Noxeller 64 as a vulcanization accelerator was over-vulcanized compared to Comparative Example 1 using Noxeller CZ, a sulfenamide vulcanization accelerator alone. It was found that the decrease in modulus was suppressed.

<Toluene swelling degree>
The vulcanized rubber composition obtained under each vulcanization condition was cut into a thickness of 20 mm × 10 mm × 2 mm, and the mass in air (μ ₁ ) and the mass in water (μ ₂ ) of each cut out sample were measured. Further, after the sample was swelled in 500 ml of toluene for 48 hours, the mass in air (μ ₃ ) and the mass in water (μ ₄ ) were measured in the same manner as described above. Each mass was measured using a specific gravity measuring device (manufactured by Shimadzu Corporation) in accordance with JIS K6268: 1998.
The degree of toluene swelling (%) was determined by the following formula (2). The toluene swelling degree (%) is measured as a substitute characteristic of the crosslinking density, and the higher the swelling degree, the lower the crosslinking density due to vulcanization, that is, the progress of reversion. The results are shown in Table 2 below.

  From the results shown in Table 2 above, Example 1 using Noxeller 64 as a vulcanization accelerator was over-vulcanized compared to Comparative Example 1 using Noxeller CZ, a sulfenamide vulcanization accelerator alone. It was revealed that the decrease in the crosslinking density (progress of reversion) was suppressed.

(Example 2 and Comparative Example 2)
Using a rubber layer made of each rubber composition obtained in Example 1 and Comparative Example 1, a laminate (vertical × horizontal × height: 40 cm × 40 cm × 23 cm) in which the rubber layer and an iron plate were alternately laminated. The rubber bearings of Example 2 and Comparative Example 2 were manufactured by forming and press-vulcanizing the laminate under predetermined vulcanization conditions.
The total number of rubber layers used in each laminate is 8; the thickness of one layer is 18 mm; similarly, there are 9 iron plates; the upper and lower end plates are 32 mm thick; The thickness of one sheet was 3.2 mm.
The obtained rubber bearings were subjected to the following shear test, and the relationship between vulcanization time, vulcanization temperature, and shear stiffness change rate was measured.
The predetermined vulcanization conditions include the vulcanization temperature of the rubber composition (145 ° C., 135 ° C., 125 ° C. and 115 ° C.) and t95 at each vulcanization temperature 1.2 times, 2 times, 3 times. It means a combination of times corresponding to 5 times and 10 times.

<Shear test>
The shear test was performed under the conditions shown below using a vibrator (manufactured by Saginomiya), an input signal oscillator, and an output signal processor.
Using each rubber bearing obtained, a rubber bearing produced by proper vulcanization was measured by measuring shear rigidity under a deformation frequency of 0.5 Hz, a shear strain of 175%, and a compressive load of 6 N / mm ² by a biaxial shear tester. The rate of change in shear stiffness produced under each vulcanization condition was calculated on the basis of the shear stiffness. The results are shown in a three-dimensional graph showing the relationship between the vulcanization time (t95 ×), the vulcanization temperature (° C.), and the shear stiffness change rate in FIGS.

  From the results shown in FIGS. 2 and 3, it can be seen that, in the rubber bearing obtained in Example 2, the shear stiffness change rate is hardly affected by the vulcanization time, but mainly affected by the vulcanization temperature. It was found that the rubber bearing obtained in Comparative Example 2 was affected by both the vulcanization time and the vulcanization temperature. This revealed that the rubber bearing obtained in Example 2 was uniform in rubber physical properties throughout the rubber layer without being affected by reversion.

FIG. 1 is a cross-sectional view of a rubber bearing which is an example of a large rubber product of the present invention. FIG. 2 is a graph showing the relationship between the vulcanization time (t95 ×), the vulcanization temperature (° C.), and the shear stiffness change rate in the rubber bearing manufactured in Example 2. FIG. 3 is a graph showing the relationship between the vulcanization time (t95 ×), the vulcanization temperature (° C.), and the shear stiffness change rate in the rubber bearing manufactured in Comparative Example 2.

Explanation of symbols

10 Rubber bearing 11, 12 Flange 13 Soft layer 14 Hard layer 15 Cover layer

Claims (5)

A rubber composition for a large rubber product, comprising 100 parts by mass of a diene rubber containing 50% by mass or more of natural rubber and 0.1 to 5 parts by mass of a vulcanization accelerator represented by the following general formula (1) .

(In the formula, R ¹ and R ² each independently represents an acyclic aliphatic group having 1 to 6 carbon atoms which may be branched or a cyclic aliphatic group having 3 to 6 carbon atoms which may be branched. Represents.)   A large rubber product comprising the rubber composition for a large rubber product according to claim 1.   The large rubber product according to claim 2, which is a rubber bearing in which a rubber layer comprising the rubber composition for a large rubber product according to claim 1 and a hard layer are alternately laminated. A manufacturing method for manufacturing the large rubber product according to claim 2,
A method for producing a large rubber product comprising a vulcanization step of vulcanizing the rubber composition for a large rubber product according to claim 1 in a time that is at least twice the 95% vulcanization time of the rubber composition. A manufacturing method for manufacturing the large rubber product according to claim 3,
A rolling step of rolling the rubber composition for a large rubber product according to claim 1 into a sheet;
A laminate forming step of forming a laminate by laminating a rubber sheet and a hard layer obtained by the rolling step;
A vulcanization adhesion step for adhering the laminate formed by the laminate formation step by vulcanization in a time not less than twice the 95% vulcanization time of the rubber composition;
A method for producing a large rubber product comprising:

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