Manufacturing method of rubber products

Abstract

Provided is a method for producing a rubber product in which insufficient crosslinking is suppressed even when stored for a long period of time. [Solution] A method for manufacturing a rubber product includes kneading a base rubber, surface-untreated fumed silica, and peroxide to prepare an uncrosslinked rubber composition, storing the uncrosslinked rubber composition in a dehumidified atmosphere, and after removing the uncrosslinked rubber composition from the dehumidified atmosphere, molding the uncrosslinked rubber composition into a predetermined shape and crosslinking it.

Description

[Technical field]

[0001] The present invention relates to a method for producing a rubber product. [Background technology]

[0002] It is known that a rubber composition for forming a rubber product contains surface-untreated silica. For example, Patent Document 1 discloses that a silicone rubber composition for a roller contains surface-untreated fumed silica. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-74912 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an uncrosslinked rubber composition that contains untreated fumed silica and uses peroxide as a crosslinking agent, if the storage time from the time of kneading and preparation is long, there is a problem that defects due to insufficient crosslinking occur and adhesion to the mold occurs.

[0005] An object of the present invention is to provide a method for producing a rubber product in which insufficient crosslinking is suppressed even when stored for a long period of time. [Means for solving the problem]

[0006] The present invention provides a method for producing an uncrosslinked rubber composition by kneading a base rubber, surface-untreated fumed silica, and a peroxide, and then subjecting the uncrosslinked rubber composition to Moisture is removed The method for producing a rubber product includes storing the uncrosslinked rubber composition in a dehumidified atmosphere, and after releasing the uncrosslinked rubber composition from the dehumidified atmosphere, molding the uncrosslinked rubber composition into a predetermined shape and crosslinking the uncrosslinked rubber composition. Effect of the Invention

[0007] According to the present invention, by storing an uncrosslinked rubber composition containing surface-untreated fumed silica and peroxide in a dehumidified atmosphere, insufficient crosslinking can be suppressed even during long-term storage. [Brief description of the drawings]

[0008] [Figure 1A] 1 is a graph showing the relationship between the number of days of storage and the maximum torque MH in Example 1 and Comparative Example 1. [Figure 1B] 1 is a graph showing the relationship between the number of storage days and the 90% vulcanization time tc(90) in Example 1 and Comparative Example 1. [Figure 2A] 1 is a graph showing the relationship between the number of days of storage and the maximum torque MH in Example 2 and Comparative Example 2. [Figure 2B] 1 is a graph showing the relationship between the number of storage days and the 90% vulcanization time tc(90) in Example 2 and Comparative Example 2. [Figure 3A] 1 is a graph showing the relationship between the number of days of storage and the maximum torque MH in Reference Examples 1 and 2. [Figure 3B] 1 is a graph showing the relationship between the number of storage days and the 90% vulcanization time tc(90) in Reference Examples 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The embodiments will be described in detail below.

[0010] In the manufacturing method of the rubber product according to the embodiment, a base rubber, surface-untreated fumed silica (hereinafter referred to as "untreated fumed silica"), and a crosslinking agent peroxide are kneaded to prepare an uncrosslinked rubber composition, the uncrosslinked rubber composition is stored in a dehumidified atmosphere, and after the uncrosslinked rubber composition is released from storage in the dehumidified atmosphere, the uncrosslinked rubber composition is molded into a predetermined shape and crosslinked.

[0011] According to the method for producing a rubber product according to the embodiment, by storing an uncrosslinked rubber composition containing untreated fumed silica and peroxide under a dehumidified atmosphere, insufficient crosslinking can be suppressed even when stored for a long period of time. The inventors investigated the cause of insufficient crosslinking occurring when the storage time from the kneading preparation of an uncrosslinked rubber composition containing untreated fumed silica and peroxide is long, and as a result, they found that the untreated fumed silica absorbs water during storage of the uncrosslinked rubber composition, hydroxyl groups are formed on its surface, and the protons of the hydroxyl groups dissociate in the presence of moisture to form an acidic atmosphere, and the peroxide is ionized in the acidic atmosphere. Based on this knowledge, the inventors came up with the idea of ​​storing the uncrosslinked rubber composition under a dehumidified atmosphere in order to suppress the formation of hydroxyl groups on the surface of the untreated fumed silica.

[0012] Examples of rubber products include sealing materials, automobile parts, industrial rubber products, electrical insulating materials, civil engineering and building materials, etc. In particular, since untreated fumed silica is used, it is suitable for rubber products for semiconductor-related applications and food-related applications.

[0013] Examples of the base rubber include fluororubber (F), silicone rubber (Q), ethylene-α-olefin elastomer (EPDM, EPR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), etc. Examples of the fluororubber (F) include tetrafluoroethylene (TFE) polymer (PTFE), vinylidene fluoride (VDF) polymer (PVDF), copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (binary FKM), copolymer of vinylidene fluoride (VDF), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE) (ternary FKM), copolymer of tetrafluoroethylene (TFE) and propylene (Pr) (FEP), copolymer of vinylidene fluoride (VDF), propylene (Pr), and tetrafluoroethylene (TFE) ... Examples of such copolymers include copolymers of ethylene (E) and tetrafluoroethylene (TFE) (ETFE), copolymers of ethylene (E), tetrafluoroethylene (TFE) and perfluoromethylvinylether (PMVE), copolymers of vinylidene fluoride (VDF), tetrafluoroethylene (TFE) and perfluoromethylvinylether (PMVE), copolymers of tetrafluoroethylene (TFE) and perfluoromethylvinylether (PMVE) (FFKM), copolymers of vinylidene fluoride (VDF) and perfluoromethylvinylether (PMVE), etc. The base rubber preferably contains one or more of these, and from the viewpoint of obtaining a high effect of suppressing insufficient crosslinking after long-term storage, it is preferable to contain a fluororubber (F), and more preferably to contain a binary and / or ternary FKM.

[0014] The untreated fumed silica is so-called hydrophilic silica that has not been subjected to a surface treatment for hydrophobization with a silane coupling agent or the like.

[0015] The specific surface area of ​​the untreated fumed silica is preferably 100 m from the viewpoint of obtaining a high effect of suppressing insufficient crosslinking after long-term storage. 2 / g or more 300m 2 / g or less, more preferably 150m 2 / g or more 250m 2 / g or less. The moisture content of the untreated fumed silica during kneading to prepare the uncrosslinked rubber composition is preferably 3% by mass or less, more preferably 2% by mass or less. The moisture content of the untreated fumed silica is the percentage of the mass loss before and after heating when the untreated fumed silica before kneading is heated in a temperature atmosphere of 200°C for 1 hour, relative to the mass before heating. The moisture content of the untreated fumed silica can be controlled by the storage time when it is stored in a thermostatic chamber set to a predetermined temperature (e.g., 40°C) before kneading.

[0016] The content of untreated fumed silica in the uncrosslinked rubber composition is preferably 3 parts by mass or more and 20 parts by mass or less, and more preferably 5 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of the base rubber, from the viewpoint of obtaining a high effect of suppressing insufficient crosslinking after long-term storage.

[0017] Examples of peroxides include dialkyl peroxides such as dicumyl peroxide, 1,3-di(t-butylperoxy)diisopropylbenzene, 1,4-di(t-butylperoxy)diisopropylbenzene, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane-3; peroxyketals such as 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, and n-butyl-4,4-di(t-butylperoxy)valerate; and peroxyesters such as 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-hexylperoxybenzoate, and t-butylperoxybenzoate. The peroxide preferably contains one or more of these, and from the viewpoint of obtaining a high effect of suppressing insufficient crosslinking after long-term storage, it is preferable that the peroxide contains a dialkyl peroxide, and more preferably contains 2,5-dimethyl-2,5-di(t-butylperoxy)hexane.

[0018] The peroxide content in the uncrosslinked rubber composition is preferably 0.3 parts by mass or more and 3 parts by mass or less, and more preferably 1 part by mass or more and 2 parts by mass or less, per 100 parts by mass of the base rubber, from the viewpoint of obtaining a high effect of suppressing insufficient crosslinking after long-term storage.

[0019] The uncrosslinked rubber composition may further contain a crosslinking aid. Examples of the crosslinking aid include allyl-based crosslinking aids such as triallyl isocyanurate (TAIC), diallyl fumarate, diallyl phthalate, tetraallyloxyethane, and trimethallyl isocyanurate; maleimide-based crosslinking aids such as N,N'-m-phenylene bismaleimide, maleimide, and phenylmaleimide; methacrylate-based crosslinking aids such as trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and polyethylene glycol dimethacrylate; and 1,2-polybutadiene. The content of the crosslinking aid in the uncrosslinked rubber composition is, for example, 2 parts by mass or more and 6 parts by mass or less relative to 100 parts by mass of the base rubber.

[0020] The uncrosslinked rubber composition may further contain rubber compounding agents such as carbon black, processing aids, antioxidants, and plasticizers, as required.

[0021] The kneading means for preparing the uncrosslinked rubber composition is not particularly limited, but examples thereof include a roll, a kneader, a Banbury mixer, and the like.

[0022] Examples of the storage means for the uncrosslinked rubber composition in a dehumidified atmosphere include storage in a desiccator containing a desiccant such as silica gel, storage in a vacuum storage cabinet, etc. Storage means using a desiccator is preferred from the viewpoint of simplicity. The storage temperature is preferably 10°C or higher to 40°C, more preferably 20°C or higher to 30°C, from the viewpoint of obtaining a high effect of suppressing insufficient crosslinking after long-term storage. From the same viewpoint, the storage humidity is preferably 15% or lower, more preferably 10% or lower. From the same viewpoint, the storage period in a dehumidified atmosphere after kneading and preparation of the uncrosslinked rubber composition is preferably 60 days or less, more preferably 40 days or less.

[0023] The maximum torque MH at 165°C after the storage release of the uncrosslinked rubber composition is preferably 2.2 N·m or more. The maximum torque MH at 165°C after the storage release of the uncrosslinked rubber composition is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more of the maximum torque MH at 165°C after kneading preparation, i.e., at the start of storage. The 90% vulcanization time tc(90) at 165°C after the storage release of the uncrosslinked rubber composition is preferably less than 6 minutes. These maximum torque ML and 90% vulcanization time tc(90) are measured using a die vulcanization tester (Curelastometer (registered trademark)) based on JIS K6300-2:2001.

[0024] The molding method for the uncrosslinked rubber composition after release from storage is not particularly limited, but examples thereof include press molding, injection molding, extrusion molding, blow molding, and transfer molding. EXAMPLES

[0025] (Uncrosslinked rubber composition) Uncrosslinked rubber compositions of Example 1, Comparative Example 1, Example 2, Comparative Example 2, and Reference Examples 1 and 2 were prepared.

[0026] <Example 1 and Comparative Example 1> Ternary FKM is used as the base rubber, and untreated fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd., specific surface area: 200 m2) with a moisture content of 1% by mass is used for 100 parts by mass of the base rubber. 2 An uncrosslinked rubber composition 1 was prepared by mixing and kneading 10 parts by mass of 1,2-dichloro-2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Perhexa 25B, NOF Corp.) as a crosslinking agent, 4 parts by mass of TAIC (TAIC, Nippon Kasei Chemical Co., Ltd.) as a crosslinking aid, and 1.5 parts by mass of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Perhexa 25B, NOF Corp.) as a peroxide as a crosslinking agent. The moisture content of the untreated fumed silica was adjusted by storing it for two weeks in a desiccator storage cabinet at a temperature of 25°C and a humidity of 10%. The moisture content of this untreated fumed silica is the percentage of the mass loss before and after heating when heated for one hour in a temperature atmosphere of 200°C, relative to the mass before heating.

[0027] In Example 1, the uncrosslinked rubber composition 1 was stored in a desiccator containing silica gel at a temperature of 22°C and a humidity of 9%. On the other hand, in Comparative Example 1, the uncrosslinked rubber composition 1 was stored in an atmosphere at a temperature of 22°C and a humidity of 15%.

[0028] <Example 2 and Comparative Example 2> An uncrosslinked rubber composition 2 was prepared having the same composition as the uncrosslinked rubber composition 1, except that untreated fumed silica that had been allowed to absorb water and had a moisture content of 16 mass % was used.

[0029] In Example 2, this uncrosslinked rubber composition 2 was stored in a desiccator containing silica gel at a temperature of 22°C and a humidity of 9%. On the other hand, in Comparative Example 2, this uncrosslinked rubber composition 2 was stored in an atmosphere at a temperature of 22°C and a humidity of 80%.

[0030] <Reference Examples 1 and 2> In Reference Example 1, an uncrosslinked rubber composition was prepared similarly to Uncrosslinked Rubber Composition 1 except that untreated fumed silica with a moisture content of 3 mass% was used, and stored in an atmosphere with a temperature of 25° C. and a humidity of 20%. The moisture content of the untreated fumed silica was adjusted by storing it in a thermostatic chamber set at 60° C. for 5 days.

[0031] In Reference Example 2, an uncrosslinked rubber composition having the same composition as Uncrosslinked Rubber Composition 1 was prepared, except that untreated fumed silica that had been absorbed with water to adjust the moisture content to 16% by mass was used, and the composition was stored in an atmosphere having a temperature of 25°C and a humidity of 20%.

[0032] (Test Method and Results) For each of Example 1 and Comparative Example 1, the maximum torque ML and the 90% vulcanization time tc(90) were measured at storage days of 1, 8, 15, 22, 29, 36, 43 and 57 days, based on JIS K6300-2:2001, under the measurement conditions of a temperature of 165°C and a time of 20 minutes. Figure 1A shows the relationship between the storage days and the maximum torque ML, and Figure 1B shows the relationship between the storage days and the 90% vulcanization time tc(90).

[0033] For each of Example 2 and Comparative Example 2, the maximum torque ML and the 90% vulcanization time tc(90) were measured after storage for 1 day, 7 days, 14 days, and 21 days in the same manner as in Example 1 and Comparative Example 1. Fig. 2A shows the relationship between the number of storage days and the maximum torque ML, and Fig. 2B shows the relationship between the number of storage days and the 90% vulcanization time tc(90).

[0034] For each of Reference Examples 1 and 2, the maximum torque ML and the 90% vulcanization time tc(90) were measured after storage for 2, 9, and 16 days in the same manner as in Example 1 and Comparative Example 1. Fig. 3A shows the relationship between the number of storage days and the maximum torque ML, and Fig. 3B shows the relationship between the number of storage days and the 90% vulcanization time tc(90). [Industrial Applicability]

[0035] The present invention is useful in the technical field of methods for producing rubber products.

Claims

1. A base rubber, surface-untreated fumed silica, and peroxide are kneaded to prepare an uncrosslinked rubber composition; The uncrosslinked rubber composition is stored in a dehumidified atmosphere in which moisture is removed, After the uncrosslinked rubber composition is released from storage under the dehumidified atmosphere, the uncrosslinked rubber composition is molded into a predetermined shape and crosslinked.

2. The method for producing a rubber product according to claim 1, The method for producing a rubber product, wherein the base rubber contains fluororubber.

3. The method for producing a rubber product according to claim 1, The method for producing a rubber product comprises storing the uncrosslinked rubber composition in a dehumidified atmosphere using a desiccator.

4. The method for producing a rubber product according to claim 1, The method for producing a rubber product, wherein the moisture content of the untreated fumed silica during kneading and preparation of the uncrosslinked rubber composition is 3 mass % or less.

5. The method for producing a rubber product according to claim 1, The method for producing a rubber product, wherein the maximum torque MH at 165°C after release from storage of the uncrosslinked rubber composition is 80% or more of the maximum torque MH at 165°C at the start of storage.

6. The method for producing a rubber product according to claim 1, The method for producing a rubber product, wherein the uncrosslinked rubber composition has a 90% vulcanization time tc(90) at 165° C. after release from storage of less than 6 minutes.

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