Silane-crosslinked rubber molded article and its manufacturing method, silane-crosslinkable rubber composition, and silane-crosslinked rubber molded article

Abstract

To provide a manufacturing method in which a silane-crosslinked rubber molding having excellent appearance characteristics and reduced permanent compression set can be obtained by injection molding, a silane-crosslinked rubber molding obtained by the manufacturing method and a silane-crosslinked rubber molded article, and a silane-crosslinkable rubber composition that is suitable for forming the silane-crosslinked rubber molding.SOLUTION: Provided are a method for manufacturing silane-crosslinked rubber molding by silane crosslinking method that comprises a step of melt-mixing an organic peroxide by 0.01 to 0.6 pts.mass, an inorganic filler by 1 to 100 pts.mass, a silane coupling agent by 1 to 15 pts.mass, and a silanol condensation catalyst for 100 pts.mass of a base rubber containing an ethylene-α-olefin copolymer rubber having a diene component amount of 4.5 to 10 mass% by 5 to 35 mass%, at least one of a styrene elastomer and an olefin elastomer having a MFR of 1 to 15 g / 10 min by 3 to 30 mass% in total, a styrene elastomer having a MFR of less than 0.1 g / 10 min by 5 to 40 mass%, and a mineral oil, and a silane-crosslinked rubber molding and molded article manufactured using the same, and a silane-crosslinkable rubber composition that is used therefor.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a silane-crosslinked rubber molded article and a method for producing the same, a silane-crosslinkable rubber composition, and a silane-crosslinked rubber molded article. [Background technology]

[0002] A low compression set is a required characteristic for rubber products such as coating materials for various industrial cables (including electric wires) and rubber molding materials (for example, glass run channels for automobiles, weather strips, rubber hoses, wiper blade rubber, gaskets, and vibration-proof rubber). Conventionally, crosslinked EP rubber obtained by vulcanizing (crosslinking) ethylene-propylene rubber (EP rubber) has been used for products used in applications requiring small compression set. For example, Patent Documents 1 to 3 disclose a method for producing a silane-crosslinked molded product by a silane crosslinking method using a crosslinked EP rubber. In this case, the silane crosslinking method is a method in which a hydrolyzable silane coupling agent having an unsaturated group is graft-reacted to rubber in the presence of an organic peroxide to obtain a silane graft polymer, and then the silane graft polymer is brought into contact with moisture in the presence of a silanol condensation catalyst to crosslink the rubber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6706870 [Patent Document 2] International Publication No. 2015 / 046476 [Patent Document 3] JP 2015-86385 A Summary of the Invention [Problem to be solved by the invention]

[0004] Known molding methods for producing crosslinked EP rubber include extrusion molding, injection molding, etc. In comparison with extrusion molding, injection molding has the advantage that it can be molded into complex shapes. In general, both the extrusion molding method and the injection molding method undergo a process of melt-mixing and molding the molding material, for example, a process of melt-mixing and molding the molding material in the cylinder of a molding machine. In the case of using the silane crosslinking method, as the residence time in the cylinder in the manufacturing process increases, the heat of the cylinder may cause a condensation reaction between the existing silane coupling agents, a silanol condensation reaction of the silane graft polymer, etc., in some parts, resulting in gel particles or roughness on the surface of the obtained molded product. In particular, when producing crosslinked EP rubber, the injection molding method is more likely to cause poor appearance characteristics such as gel particles, roughness, and flow marks (traces of flow of rubber composition) than the extrusion molding method. In the case of the injection molding method, intermittent retention of the molding material in the cylinder occurs more frequently. In addition, there are many opportunities to stop the molding machine, such as changing the mold, and the retention time of the molding material in the cylinder tends to be longer. In addition, when mass-producing, it is expected that the work will be temporarily stopped or the worker will be changed in the middle of the work. In that case, the retention time may be as long as 3 hours. Due to such intermittent retention and long retention, the above-mentioned gel particles and roughness are likely to occur in the case of the injection molding method. This retention in the cylinder is more noticeable when a large injection molding machine is used. Furthermore, in the case of the injection molding method, the molding material may adhere to the inside of the mold or the wall surface of the cylinder, causing gel particles and flow marks on the surface of the molded product. The manufacturing methods described in Patent Documents 1 to 3 are excellent in extrusion moldability, but are not suitable for injection molding of rubber molded articles.

[0005] An object of the present invention is to provide a production method by which a silane-crosslinked rubber molded article having excellent appearance characteristics and reduced compression set can be obtained by injection molding, a silane-crosslinked rubber molded article obtained by this production method, and a silane-crosslinked rubber molded article. Another object of the present invention is to provide a silane-crosslinkable rubber composition suitable for producing the silane-crosslinked rubber molded article. [Means for solving the problem]

[0006] The present inventors have found that in a method for producing a silane-crosslinked rubber molded article by injection molding using a silane crosslinking method, when a silane-crosslinked rubber molded article is produced by using an ethylene-α-olefin copolymer rubber having a specific diene content as a base rubber, two types of elastomers having different melt flow rates, and a specific amount of mineral oil in combination, the obtained silane-crosslinked rubber molded article can have excellent appearance properties and reduced compression set. Based on this finding, the present inventors have conducted further research and have come up with the present invention.

[0007] That is, the object of the present invention has been achieved by the following means. [1] A method for producing a silane-crosslinked rubber molded product, comprising the following steps (1), (2) and (3): Step (1): A step of melt-mixing 0.01 to 0.6 parts by mass of an organic peroxide, 1 to 100 parts by mass of an inorganic filler, 1 to 15 parts by mass of a silane coupling agent having a graft reaction site capable of undergoing a graft reaction with the base rubber in the presence of radicals generated from the organic peroxide, and a silanol condensation catalyst relative to 100 parts by mass of a base rubber, and grafting the graft reaction site with the graft reaction site of the base rubber by the radicals generated from the organic peroxide to obtain a silane crosslinkable rubber composition containing a silane crosslinkable rubber. Step (2): A step of injection molding the silane-crosslinkable rubber composition to obtain a molded article. Step (3): A step of contacting the molded product with water to obtain a silane-crosslinked rubber molded product. The base rubber is 5 to 35 mass% of an ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10 mass%, 3 to 30 mass% in total of at least one of a styrene elastomer and an olefin elastomer having a melt flow rate of 1 to 15 g / 10 min at 190°C and 2.16 kg, 5 to 40 mass% of a styrene elastomer having a melt flow rate of less than 0.1 g / 10 min at 190°C and 2.16 kg, and Including, In carrying out the step (1), A method for producing a silane-crosslinked rubber molding, wherein, when the entire base rubber is melt-mixed in the following step (a-2), step (1) has the following steps (a-1), (a-2), and (c), and when only a part of the base rubber is melt-mixed in the following step (a-2), step (1) has the following steps (a-1), (a-2), (b), and (c). Step (a-1): A step of mixing the inorganic filler and the silane coupling agent to prepare a mixture. Step (a-2): A step of melt-mixing the mixture and all or a part of the base rubber in the presence of the organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide, and grafting the graft reaction sites with the graft reaction sites of the base rubber by radicals generated from the organic peroxide, thereby preparing a silane master batch containing a silane crosslinkable rubber and having a melt flow rate of 0.8 g / 10 min or more at 190° C. and 10 kg. step (b): melt mixing the remainder of the base rubber and the silanol condensation catalyst to prepare a catalyst master batch; and Step (c): A step of melt-mixing the silane master batch and the silanol condensation catalyst or the catalyst master batch to obtain the silane-crosslinkable rubber composition. [2] The method for producing a silane-crosslinked rubber molded article according to [1], wherein the base rubber contains 5 to 30 mass % of an ethylene-α-olefin rubber having a diene content of 1.0 mass % or less. [3] The method for producing a silane-crosslinked rubber molded product according to [1] or [2], wherein the base rubber contains 20 to 60 mass % of the mineral oil. [4] The method for producing a silane-crosslinked rubber molded article according to any one of [1] to [3], wherein the base rubber contains 1 to 15 mass % of a propylene resin. [5] The method for producing a silane-crosslinked rubber molded product according to any one of [1] to [4], wherein the base rubber contains 5 to 30 mass% of an ethylene-α-olefin rubber having a diene content of 1.0 mass% or less, 20 to 60 mass% of the mineral oil, and 1 to 15 mass% of a propylene resin. [6] The method for producing a silane-crosslinked rubber molded product according to any one of [1] to [5], wherein the inorganic filler is mixed in an amount of 10 to 60 parts by mass per 100 parts by mass of the base rubber. [7] The method for producing a silane-crosslinked rubber molded article according to any one of [1] to [6], wherein the silanol condensation catalyst is blended in an amount of 0.03 to 0.5 parts by mass per 100 parts by mass of the base rubber. [8] The method for producing a silane-crosslinkable rubber molded article according to any one of [1] to [7], wherein the inorganic filler is a metal hydrate, talc, clay, silica, carbon black, or a mixture thereof. [9] The method for producing a silane-crosslinked rubber molded product according to any one of [1] to [8], wherein in the step (1), 10 to 60 parts by mass of the inorganic filler, 1 to 15 parts by mass of the silane coupling agent, 0.01 to 0.6 parts by mass of the organic peroxide, and 0.03 to 0.5 parts by mass of the silanol condensation catalyst are melt-mixed relative to 100 parts by mass of the base rubber.

[10] A silane-crosslinkable rubber composition produced by the step (1) of the production method according to any one of [1] to [9].

[11] A silane-crosslinked rubber molded product produced by the method for producing a silane-crosslinked rubber molded product according to any one of [1] to [9].

[12] A silane-crosslinked rubber molded article comprising the silane-crosslinked rubber molded article according to

[11] .

[0008] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Effect of the Invention

[0009] The present invention provides a manufacturing method for obtaining a silane-crosslinked rubber molded article having excellent appearance characteristics and reduced compression set by injection molding, a silane-crosslinked rubber molded article obtained by the manufacturing method, and a silane-crosslinkable rubber composition suitable for producing a silane-crosslinked rubber molded article having such excellent characteristics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The method for producing the silane-crosslinked rubber molded article of the present invention will be described below.

[0011] First, each component used in the present invention will be described.

[0012] <Base rubber> The base rubber used in the present invention includes an ethylene-α-olefin copolymer rubber having a diene content (meaning the content of the diene component constituting the copolymer rubber) of 4.5 to 10% by mass, at least one of a styrene elastomer and an olefin elastomer having a melt flow rate of 1 to 15 g / 10 min at 190°C and 2.16 kg, a styrene elastomer having a melt flow rate of less than 0.1 g / 10 min at 190°C and 2.16 kg, and a mineral oil. The base rubber may further include a propylene resin, an ethylene resin, etc. All of these components have a site capable of undergoing a graft reaction with a graft reaction site of a silane coupling agent in the presence of a radical generated from an organic peroxide, such as an unsaturated bond site of a carbon chain or a carbon atom having a hydrogen atom in the main chain or at the end thereof. The base rubber may contain rubber or resin other than the above as long as the characteristics are not impaired. Such rubber or resin components are not particularly limited as long as they are polymeric resins or rubbers having a grafting reaction site of a silane coupling agent and a site capable of undergoing a grafting reaction in the presence of an organic peroxide, such as an unsaturated bond site on a carbon chain or a carbon atom having a hydrogen bond in the main chain or at its terminal.

[0013] The diene content of the ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10% by mass is preferably 4.6 to 9% by mass, more preferably 4.8 to 8% by mass. The diene content can be measured, for example, by infrared absorption spectroscopy (FT-IR), proton NMR ( 1 It can be measured by H-NMR, etc. The base rubber may contain an ethylene-α-olefin copolymer rubber having a diene content of 1.0 mass% or less in the copolymer. The base rubber includes an embodiment containing an ethylene-α-olefin copolymer rubber having a diene content of 1.0 mass% or less and an embodiment not containing an ethylene-α-olefin copolymer rubber having a diene content of 1.0 mass% or less. The diene content of the ethylene-α-olefin copolymer rubber having a diene content of 1.0 mass% or less is preferably 0.9 mass% or less, more preferably 0.7 mass% or less. The ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10 mass% and the ethylene-α-olefin copolymer rubber having a diene content of 1.0 mass% or less can be the ethylene-α-olefin copolymer rubber described below, and the diene content is within the above range.

[0014] The ethylene content (meaning the content of the ethylene component constituting the copolymer rubber) of the ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10 mass % is not particularly limited, but is preferably 50 to 80 mass %, more preferably 55 to 75 mass %. The ethylene content of the ethylene-α-olefin copolymer rubber having a diene content of 1.0% by mass or less is not particularly limited, but is preferably 50 to 80% by mass, and more preferably 55 to 75% by mass. The amount of ethylene component is a value measured in accordance with the method described in ASTM D3900.

[0015] The Mooney viscosity of the ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10 mass % is not particularly limited, but is preferably 10 to 100 (ML1+4(125°C)), more preferably 15 to 90 (ML1+4(125°C)), and even more preferably 20 to 80 (ML1+4(125°C)). The Mooney viscosity of the ethylene-α-olefin copolymer rubber having a diene content of 1.0 mass% or less is not particularly limited, but is preferably 10 to 100 (ML1+4(125°C)), more preferably 15 to 90 (ML1+4(125°C)), and even more preferably 20 to 80 (ML1+4(125°C)). Mooney viscosity is measured based on the measurement method specified in JIS K 6300-1:2013. The test is performed as follows. A pair of test samples with a diameter of approximately 50 mm and a thickness of approximately 6 mm is prepared using the roll-pass method described in JIS K 6300-1 5.3.1 as the test pieces to be used. A disk-shaped metal L-shaped rotor is attached to a cylindrical hollow (cavity) formed by two dies, and the rubber test pieces obtained are filled into it. The rotor is then rotated under constant conditions of 1 minute preheat time, 4 minutes rotor rotation time, and test temperature of 125°C, and the torque received by the rotor due to the resistance of the rubber at this time is measured in Mooney units as the Mooney viscosity of the rubber.

[0016] The base rubber contains at least one of a styrene elastomer and an olefin elastomer having a melt flow rate of 1 to 15 g / 10 min at 190° C. and 2.16 kg. Here, the melt flow rate (hereinafter sometimes referred to as MFR) in the present invention means a value measured at a temperature of 190° C. and a load of 2.16 kg in accordance with JIS K 7210, unless otherwise specified. The MFR of the styrene elastomer having an MFR of 1 to 15 g / 10 min and the MFR of the olefin elastomer having an MFR of 1 to 15 g / 10 min are preferably 1 to 12 g / 10 min, more preferably 1 to 8 g / 10 min. If the MFR is too high, the compression set may not be sufficiently reduced. If the MFR is too low, excellent appearance properties may not be obtained when the mixture is allowed to remain in the resin for a long time. As the styrene elastomer having an MFR of 1 to 15 g / 10 min, the styrene elastomer described below and having an MFR within the above range can be used.As the olefin elastomer having an MFR of 1 to 15 g / 10 min, the olefin elastomer described below and having an MFR within the above range can be used.

[0017] As the styrene elastomer having an MFR of less than 0.1 g / 10 min, the styrene elastomer described below and having an MFR within the above range can be used. The MFR of the styrene elastomer having an MFR of less than 0.1 g / 10 min is preferably 0.001 to 0.08 g / 10 min, and more preferably 0.005 to 0.05 g / 10 min.

[0018] Specific examples of the mineral oil contained in the base rubber will be described later.

[0019] - Ethylene-α-olefin copolymer rubber - The ethylene-α-olefin copolymer rubber is a rubber of a copolymer of ethylene, an α-olefin, and a diene. When the amount of the diene component is 0 mass%, the ethylene-α-olefin copolymer rubber is a rubber of a copolymer of ethylene and an α-olefin. The ethylene-α-olefin copolymer rubber is a rubber made of an ethylene-α-olefin copolymer, and examples thereof include a rubber made of a binary copolymer of ethylene and an α-olefin, and a rubber made of a ternary copolymer of ethylene, an α-olefin, and a diene. The diene of the ternary copolymer may be a conjugated diene or a non-conjugated diene, and a non-conjugated diene is preferred. That is, examples of the ternary copolymer include a ternary copolymer of ethylene, an α-olefin, and a conjugated diene, and a ternary copolymer of ethylene, an α-olefin, and a non-conjugated diene. A binary copolymer of ethylene and an α-olefin and a ternary copolymer of ethylene, an α-olefin, and a non-conjugated diene are preferred. Examples of conjugated dienes include butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc., with butadiene being preferred. Examples of non-conjugated dienes include dicyclopentadiene (DCPD), ethylidene norbornene (ENB), 1,4-hexadiene, etc., with ethylidene norbornene being preferred. Each of the conjugated diene compound and non-conjugated diene components may be used alone or in combination of two or more. Suitable examples of the α-olefin include α-olefins having a carbon number of 3 to 12. The α-olefin is not particularly limited, and examples thereof include propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, and 1-dodecene.

[0020] Examples of rubbers made of a binary copolymer of ethylene and an α-olefin include ethylene-propylene rubber, ethylene-butene rubber, and ethylene-octene rubber. Examples of rubbers made of a ternary copolymer of ethylene, an α-olefin, and a diene include ethylene-propylene-diene rubber, and ethylene-butene-diene rubber. Among these, ethylene-propylene rubber, ethylene-butene rubber, ethylene-propylene-diene rubber, and ethylene-butene-diene rubber are preferred, ethylene-propylene rubber and ethylene-propylene-diene rubber are more preferred, and ethylene-propylene rubber or ethylene-propylene-ethylidenenorbornene rubber is particularly preferred.

[0021] - Styrene elastomer - The styrene elastomer is a copolymer block of components derived from an aromatic vinyl compound and a conjugated diene compound, and / or a hydrogenated product of a block copolymer or random copolymer mainly composed of components derived from the above compounds. The aromatic vinyl compound may be one or more selected from, for example, styrene, α-methylstyrene, vinyltoluene, p-tertiary butylstyrene, etc., with styrene being preferred among them. The conjugated diene compound may be one or more selected from, for example, butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc., with butadiene, isoprene, or a combination thereof being preferred among them. As the styrene elastomer, a binary or ternary copolymer composed of a polystyrene block and an elastomer block having a polyolefin structure can be used. The hydrogenated copolymer (hereinafter sometimes referred to as hydrogenated copolymer) preferably contains 5 to 70 mass %, more preferably 10 to 60 mass %, of a component derived from an aromatic vinyl compound. This content can be determined, for example, by measuring the UV absorption spectrum with an ultraviolet spectrophotometer using a chloroform solution. Examples of styrene elastomers include SBS (styrene-butadiene-styrene block copolymer), SIS (styrene-isoprene-styrene block copolymer), SEBS (styrene-ethylene-butylene-styrene block copolymer: hydrogenated SBS), SEEPS (styrene-ethylene-ethylene-propylene-styrene block copolymer), SEPS (styrene-ethylene-propylene-styrene block copolymer: hydrogenated SIS), HSBR (hydrogenated styrene-butadiene random copolymer), etc. The styrene elastomer may be one type or two or more types. Examples of styrene elastomers include "Septon" (product name, manufactured by Kuraray Co., Ltd.), "Tuftec" (product name, manufactured by Asahi Kasei Chemicals Corporation), and "Dynaron" (product name, manufactured by JSR Corporation).

[0022] - Olefin elastomer - The olefin elastomer may be one having a hard segment made of polyolefin such as polypropylene or polyethylene and a soft segment made of rubber such as ethylene-propylene rubber (EPM, EPDM), and may have a structure in which the hard segment and the soft segment are microphase separated. It may be a mixture of a polyolefin component and a rubber component, or may be one obtained by dynamically crosslinking these components, or may be one obtained by polymerizing these components. Examples of olefin elastomers include block copolymers of a polyethylene block and an ethylene-α-olefin copolymer block, block copolymers of a polypropylene block and an ethylene-α-olefin copolymer block, block copolymers of a polybutene block and an ethylene-α-olefin copolymer block, and mixtures of polypropylene (PP) and ethylene-propylene (EP) rubber (TPO, TPV). Examples of olefin elastomers include "INFUSE" (trade name, manufactured by Dow), "ENGAGE" (trade name, manufactured by Dow), and "TAFMER" (trade name, manufactured by Mitsui Chemicals).

[0023] - Mineral oil - The mineral oil used in the present invention is a mixed oil containing an oil having an aromatic ring, an oil having a naphthene ring, and an oil having a paraffin chain. Paraffin oil refers to an oil in which the carbon number (CP) of the paraffin chain is, for example, 50% or more and less than 75% of the total carbon number of the aromatic ring, naphthene ring, and paraffin chain, the carbon number (CN) of the naphthene chain is 20 or more and less than 40%, and the carbon number of the aromatic ring (CA) is 3 or more and less than 10%. Naphthene oil refers to an oil in which CN is 40 or more and less than 60%, CP is 30% or more and less than 50%, and CA is 8% or more and less than 16% of the total carbon number, and aromatic oil refers to an oil in which CA is 16% or more. As the mineral oil (rubber softener), paraffin oil or naphthene oil can be used, with paraffin oil being preferred in terms of mechanical strength. The paraffin oil preferably has a dynamic viscosity at 40°C of 20 to 500 cSt, a pour point of -10 to -15°C, and a flash point (COC) of 180 to 300°C. Examples of mineral oils include "Diana Process Oil" (trade name, manufactured by Idemitsu Kosan Co., Ltd.) and "Cosmo Neutral" (trade name, manufactured by Cosmo Oil Lubricants Co., Ltd.).

[0024] - Propylene resin - The propylene resin (PP resin) may be any resin whose main component is a polymer containing a propylene constituent component, and resins such as a propylene homopolymer, an ethylene-propylene random copolymer, or an ethylene-propylene block copolymer can be used. The ethylene-propylene random copolymer refers to a copolymer having an ethylene content of about 1 to 10% by mass, in which the ethylene component is randomly incorporated into the propylene chain. The ethylene-propylene block copolymer refers to a copolymer having an ethylene or ethylene-propylene rubber (EPR) content of about 5 to 20% by mass, in which the ethylene or EPR component is present independently in the propylene component in an island-sea structure. In terms of appearance, the propylene resin is particularly preferably an ethylene-propylene random copolymer resin. The ethylene content is a value measured in accordance with the method described in ASTM D3900. The propylene resin may be used alone or in combination of two or more kinds.

[0025] - Ethylene resin - The ethylene resin is not particularly limited as long as it is a resin (excluding PP resin) made of a polymer obtained by polymerizing or copolymerizing a compound having an ethylenically unsaturated bond, and those conventionally used for the application of electric wire covering materials can be used. For example, resins made of various polymers such as polyethylene, ethylene-α-olefin copolymer, polyolefin copolymer having an acid copolymerization component or an acid ester copolymerization component can be mentioned. Among them, polyethylene resin, and polyolefin copolymer resin having an acid copolymerization component or an acid ester copolymerization component are preferred. The polyethylene resin may be any resin of a polymer containing an ethylene component, and includes a homopolymer consisting of ethylene alone, a copolymer of ethylene and an α-olefin (preferably 5 mol% or less) (excluding those corresponding to polypropylene), and a copolymer of ethylene and a non-olefin (preferably 1 mol% or less) having only carbon, oxygen and hydrogen atoms in the functional group. The above-mentioned α-olefin and non-olefin may be any known one that has been conventionally used as a copolymerization component of polyethylene, without any particular limitation. Examples of polyethylene resins include LDPE (low density polyethylene), LLDPE (linear low density polyethylene), and MDPE (medium density polyethylene). LLDPE may be LLDPE (linear low density polyethylene) synthesized in the presence of a metallocene catalyst. These polyethylenes may be used alone or in combination of two or more. Among these polyethylenes, it is preferable to use LLDPE synthesized in the presence of a metallocene catalyst. Examples of the ethylene-α-olefin copolymer resin include copolymer resins of ethylene and an α-olefin having 4 to 12 carbon atoms, and examples of the α-olefin include 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, etc. These ethylene-α-olefin copolymer resins may be used alone or in combination of two or more. The acid copolymerization component or acid ester copolymerization component in the polyolefin copolymer resin having an acid copolymerization component or an acid ester copolymerization component is not particularly limited, and examples thereof include carboxylic acid compounds such as (meth)acrylic acid, and acid ester compounds such as vinyl acetate or alkyl (meth)acrylate (preferably having an alkyl group having 1 to 12 carbon atoms). Examples of the polyolefin copolymer resin having an acid copolymerization component or an acid ester copolymerization component include resins such as ethylene-vinyl acetate copolymer (EVA), ethylene-(meth)acrylic acid copolymer, and ethylene-alkyl (meth)acrylate copolymer (preferably ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, and ethylene-butyl acrylate copolymer). The ethylene resin is preferably an ethylene-α-olefin copolymer resin, an ethylene-vinyl acetate copolymer resin, or a mixture thereof. Incidentally, examples of commercially available polyethylene resins and ethylene-α-olefin copolymer resins that can be used for the base rubber according to the present invention include "Evolue" (product name: manufactured by Prime Polymer Co., Ltd.).

[0026] The ethylene resin may be modified with an acid. The acid used for the modification is not particularly limited, and examples thereof include commonly used unsaturated carboxylic acids.

[0027] - Content in base rubber - The content of each component in the base rubber is preferably determined within the following ranges so that the total of each component is 100 mass %. The content of the ethylene-α-olefin copolymer rubber having a diene content of 4.5-10% by mass is 5-35% by mass in 100% by mass of the base rubber. If this content is too high, the injection moldability may decrease and abnormalities such as gel particles may occur in the appearance of the molded product. On the other hand, if the content is too low, the compression set property may decrease. The content of the ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10 mass% in the base rubber is preferably 7 to 32 mass%, more preferably 10 to 30 mass%, based on 100 mass% of the base rubber. Within this range, excellent appearance properties and reduced compression set can be achieved in a well-balanced manner.

[0028] The total content of the styrene elastomer and olefin elastomer having an MFR of 1 to 15 g / 10 min is 3 to 30 mass% in 100 mass% of the base rubber. If the content is too high, the compression set may not be sufficiently reduced. On the other hand, if the content is too low, it may not be possible to impart excellent appearance properties. The content of the styrene elastomer and olefin elastomer having an MFR of 1 to 15 g / 10 min in the base rubber is preferably 4 to 25 mass %, more preferably 5 to 20 mass %, based on 100 mass % of the base rubber. Within this range, excellent appearance properties and reduced compression set can be achieved in a well-balanced manner.

[0029] The content of the styrene elastomer having an MFR of less than 0.1 g / 10 min is 5 to 40 mass % in 100 mass % of the base rubber. If this content is too high, it may not be possible to impart excellent appearance characteristics. On the other hand, if the content is too low, it may not be possible to sufficiently reduce the compression set. The content of the styrene elastomer having an MFR of less than 0.1 g / 10 min in the base rubber is preferably 8 to 35 mass %, more preferably 10 to 32 mass %, based on 100 mass % of the base rubber. Within this range, excellent appearance properties and reduced compression set can be achieved in a well-balanced manner.

[0030] The content of the mineral oil is not particularly limited as long as the mineral oil is contained in the base rubber, but is preferably 20 to 60 mass%, more preferably 25 to 55 mass%, and even more preferably 28 to 50 mass%, based on 100 mass% of the base rubber. Within this range, excellent appearance properties and reduced compression set can be achieved in a well-balanced manner.

[0031] The content of the ethylene-α-olefin copolymer rubber having a diene content of 1.0% by mass or less is not particularly limited, but is preferably 5 to 30% by mass, more preferably 8 to 27% by mass, and even more preferably 10 to 25% by mass, based on 100% by mass of the base rubber. Within this range, excellent appearance properties and reduced compression set can be achieved in a well-balanced manner.

[0032] The content of the propylene resin in 100% by mass of the base rubber is preferably 1 to 15% by mass, more preferably 3 to 13% by mass, and even more preferably 5 to 12% by mass. Within this range, a good balance between excellent appearance properties and reduced compression set can be achieved.

[0033] The content of the ethylene resin in 100% by mass of the base rubber is preferably 1 to 15% by mass, more preferably 2 to 12% by mass, and even more preferably 3 to 8% by mass. Within this range, a good balance between excellent appearance properties and reduced compression set can be achieved.

[0034] The base rubber preferably contains 5 to 30 mass % of ethylene-α-olefin rubber having a diene content of 1.0 mass % or less, 20 to 60 mass % of mineral oil, and 1 to 15 mass % of propylene resin.

[0035] <Organic peroxide> The organic peroxide generates radicals at least by thermal decomposition, and acts as a catalyst to initiate a grafting reaction of the silane coupling agent to the rubber component by radical reaction (a covalent bond forming reaction between the grafting reaction site of the silane coupling agent and the grafting reaction site of the rubber component, also called a (radical) addition reaction). In particular, when the silane coupling agent contains an ethylenically unsaturated group as the grafting reaction site, the organic peroxide acts to initiate a grafting reaction by radical reaction between the ethylenically unsaturated group and the rubber component (including a reaction of abstracting hydrogen radicals from the rubber component). The organic peroxide is not particularly limited as long as it generates radicals. For example, an organic peroxide represented by the general formula: 1 -O-O-R 2 , R 3 -OO-C(=O)R 4 , R 5 C(=O)-OO(C=O)R 6 Preferred are compounds represented by the formula: 1 ~R 6 Each independently represents an alkyl group, an aryl group, or an acyl group. R 1 ~R 6 Among these, it is preferable that all of them are alkyl groups, or that one of them is an alkyl group and the remaining is an acyl group.

[0036] As such organic peroxides, there are mentioned in paragraph 1 of International Publication WO 2015 / 046478.

[0037] The organic peroxides described in are included in the specification, and the contents of the description are incorporated herein by reference. In terms of odor, coloring, and scorch stability, dicumyl peroxide, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, and 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexyne-3 are preferred.

[0037] The decomposition temperature of the organic peroxide is preferably 120 to 195° C., particularly preferably 125 to 180° C. The decomposition temperature of the organic peroxide is equal to or lower than the melt mixing temperature in the step (a-2) described below. In the present invention, the decomposition temperature of an organic peroxide means the temperature at which a single-component organic peroxide undergoes a decomposition reaction into two or more compounds when heated at a certain temperature or temperature range. Specifically, it means the temperature at which heat absorption or heat generation begins when heated from room temperature at a temperature increase rate of 5°C / min in a nitrogen gas atmosphere by thermal analysis such as DSC method.

[0038] <Inorganic filler> In the present invention, the inorganic filler can be used without any particular limitation as long as it has a site on its surface that can form a hydrogen bond or the like with a reactive site such as a silanol group of a silane coupling agent, or a site that can be chemically bonded by a covalent bond. Examples of the site in the inorganic filler that can be chemically bonded with a reactive site of a silane coupling agent include OH groups (hydroxyl groups, water molecules of water of water or crystallization, OH groups such as carboxyl groups), amino groups, and SH groups.

[0039] Examples of inorganic fillers that can be used include metal hydrates such as aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, aluminum oxide, aluminum nitride, aluminum borate whiskers, hydrated aluminum silicate, hydrated magnesium silicate, basic magnesium carbonate, and compounds having hydroxyl groups or crystal water, such as hydrotalcite, boron nitride, silica (crystalline silica, amorphous silica, etc.), carbon black, clay, zinc oxide, tin oxide, titanium oxide, molybdenum oxide, antimony trioxide, silicone compounds, quartz, talc, zinc borate, white carbon, zinc borate, zinc hydroxystannate, and zinc stannate. One type of inorganic filler may be used alone, or two or more types may be used in combination. Of these, the inorganic filler is preferably a metal hydrate (more preferably magnesium hydroxide), talc, clay, silica, carbon black, or a mixture thereof.

[0040] The average particle size of the inorganic filler is preferably 0.2 to 10 μm, more preferably 0.3 to 8 μm, further preferably 0.4 to 5 μm, and particularly preferably 0.4 to 3 μm. The average particle size is determined by dispersing the inorganic filler in alcohol or water and using an optical particle size measuring device such as a laser diffraction / scattering type particle size distribution measuring device.

[0041] The inorganic filler may be surface-treated with a silane coupling agent or the like. For example, silane coupling agent surface-treated metal hydrates include Kisuma 5L and Kisuma 5P (both trade names, magnesium hydroxide, manufactured by Kyowa Chemical Industry Co., Ltd., etc.). The amount of the silane coupling agent used to surface-treat the inorganic filler is not particularly limited, but is, for example, 3 mass% or less.

[0042] <Silane coupling agent> The silane coupling agent has a grafting reaction site (group or atom) that can undergo grafting reaction with a grafting reaction site of the base rubber in the presence of radicals generated by decomposition of an organic peroxide. Also, it has a hydrolyzable silyl group as a site capable of silanol condensation by reacting with a site capable of chemical bonding of an inorganic filler. Examples of such silane coupling agents include silane coupling agents used in conventional silane crosslinking methods. Examples of the silane coupling agent include silane coupling agents having an unsaturated group, and specifically include vinyl alkoxy silanes such as vinyl trimethoxy silane, vinyl triethoxy silane, vinyl tributoxy silane, vinyl dimethoxy ethoxy silane, vinyl dimethoxy butoxy silane, vinyl diethoxy butoxy silane, allyl trimethoxy silane, allyl triethoxy silane, and vinyl triacetoxy silane, and (meth) acryloxy alkoxy silanes such as methacryloxy propyl trimethoxy silane, methacryloxy propyl triethoxy silane, and methacryloxy propyl methyl dimethoxy silane. Among them, vinyl trimethoxy silane or vinyl triethoxy silane is particularly preferred. The silane coupling agent may be used alone or in combination of two or more. The silane coupling agent may be used as it is, or may be used after being diluted with a solvent.

[0043] <Silanol condensation catalyst> The silanol condensation catalyst works to promote the condensation reaction of the hydrolyzable silyl group of the silane coupling agent grafted to the base rubber in the presence of moisture. Based on the action of this silanol condensation catalyst, the base rubbers are crosslinked together via the silane coupling agent. Such silanol condensation catalysts are not particularly limited, and examples thereof include organotin compounds, metal soaps, platinum compounds, etc. Examples of organotin compounds include dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dioctiate, dibutyltin diacetate, and other organotin compounds. The silanol condensation catalyst may be used alone or in combination of two or more kinds.

[0044] <Additives> In the present invention, various additives that are generally used in electric wires, electric cables, electric cords, automotive parts, office automation equipment, building parts, miscellaneous goods, sheets, foams, tubes, pipes, etc. may be appropriately blended within a range that does not impair the intended effects. Examples of such additives include crosslinking assistants, antioxidants, lubricants, metal deactivators, flame retardants (assistants), other resins, etc.

[0045] The crosslinking aid is a compound that forms a partially crosslinked structure with the rubber component in the presence of an organic peroxide, and examples of such compounds include polyfunctional compounds. The antioxidant is not particularly limited, but examples thereof include amine antioxidants, phenol antioxidants, and sulfur antioxidants. Examples of the lubricant include hydrocarbons, siloxanes, fatty acids, fatty acid amides, esters, alcohols, and metal soaps. Flame retardants include, but are not limited to, red phosphorus.

[0046] <Method of Manufacturing Silane-Crosslinked Rubber Molded Article> The method for producing a silane-crosslinked rubber molded article of the present invention will now be described in detail. The method for producing a silane-crosslinked rubber molded article of the present invention includes the following steps (1), (2), and (3). The silane-crosslinkable rubber composition of the present invention is produced by the following step (1).

[0047] Step (1): A step of melt-mixing 0.01 to 0.6 parts by mass of an organic peroxide, 1 to 100 parts by mass of an inorganic filler, 1 to 15 parts by mass of a silane coupling agent having a graft reaction site capable of undergoing a graft reaction with the base rubber in the presence of radicals generated from the organic peroxide, and a silanol condensation catalyst relative to 100 parts by mass of a base rubber, and grafting the graft reaction site with the graft reaction site of the base rubber by the radicals generated from the organic peroxide to obtain a silane crosslinkable rubber composition containing a silane crosslinkable rubber. Step (2): A step of obtaining a molded article by injection molding the silane-crosslinkable rubber composition. Step (3): A step of contacting the molded product with water to obtain a silane-crosslinked rubber molded product.

[0048] The above step (1) includes the following steps depending on the use mode of the base rubber. When the entire base rubber is melt-mixed in the below-described step (a-2), the step (1) includes the below-described steps (a-1), (a-2), and (c), and when a portion of the base rubber is melt-mixed in the below-described step (a-2), the step (1) includes the below-described steps (a-1), (a-2), (b), and (c). Step (a-1): A step of mixing an inorganic filler and a silane coupling agent to prepare a mixture. Step (a-2): A step of melt-mixing the mixture and all or a part of the base rubber in the presence of an organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide to cause a graft reaction between the graft reaction site and the graft reaction site of the base rubber by radicals generated from the organic peroxide, thereby preparing a silane master batch containing a silane crosslinkable rubber and having a melt flow rate of 0.8 g / 10 min or more at 190° C. and 10 kg. Step (b): melt mixing the remainder of the base rubber and a silanol condensation catalyst to prepare a catalyst master batch; Step (c): A step of melt-mixing the silane master batch with a silanol condensation catalyst or a catalyst master batch to obtain a silane crosslinkable rubber composition. Hereinafter, both steps (a-1) and (a-2) may be collectively referred to as step (a).

[0049] In the manufacturing method of the present invention, the "base rubber" is a rubber for forming a silane-crosslinked rubber molded product or a silane-crosslinkable rubber composition. Therefore, in the manufacturing method of the present invention, it is sufficient that the reaction composition obtained in step (1) contains 100 parts by mass of the base rubber. For example, in step (a-2), the method includes "an embodiment in which the entire amount (100 parts by mass) of the base rubber is blended" and "an embodiment in which only a portion of the base rubber is blended."

[0050] When a portion of the base rubber is compounded in step (a-2), 100 parts by mass of the base rubber compounded in step (1) is the total amount of the base rubber mixed in step (a-2) and step (b). Here, when the remainder of the base rubber (sometimes referred to as the carrier) is compounded in step (b), preferably 80 to 95 mass %, more preferably 85 to 92 mass %, of the base rubber is compounded in step (a-2), and preferably 5 to 20 mass %, more preferably 8 to 15 mass %, of the base rubber is compounded in step (b).

[0051] In step (1), the contents of the ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10 mass%, the styrene elastomer and olefin elastomer having an MFR of 1 to 15 g / 10 min, the styrene elastomer having an MFR of less than 0.1 g / 10 min, and the mineral oil in the base rubber, and in addition thereto, the contents of the propylene resin and / or ethylene resin in the case where the base rubber contains these resins, are as described above. The ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10 mass % may be mixed in either step (a-2) or step (b), but is preferably mixed in step (a-2). At least one of a styrene elastomer and an olefin elastomer having an MFR of 1 to 15 g / 10 min may be mixed in either step (a-2) or step (b), but is preferably mixed in step (a-2). The styrene elastomer having an MFR of less than 0.1 g / 10 min may be mixed in either step (a-2) or step (b), but is preferably mixed in both step (a-2) and step (b). The mineral oil may be mixed in either step (a-2) or step (b), but is preferably mixed in both steps (a-2) and (b). The propylene resin may be mixed in either step (a-2) or step (b). The ethylene resin may be mixed in either step (a-2) or step (b), but is preferably mixed in step (b). As the carrier, styrene elastomers and / or olefin elastomers, mineral oils, propylene resins, and ethylene resins having an MFR of 1 to 15 g / 10 min are preferred, and combinations of these are more preferred.

[0052] In step (1), the amount of the organic peroxide is 0.01 to 0.6 parts by mass, preferably 0.01 to 0.5 parts by mass, and more preferably 0.05 to 0.2 parts by mass, based on 100 parts by mass of the base rubber. By setting the amount of the organic peroxide to 0.01 to 0.6 parts by mass, the grafting reaction can be carried out in an appropriate range, and condensation between the silane coupling agents can be suppressed, thereby suppressing the occurrence of gel particles or roughness in the molded product, thereby preventing deterioration of the appearance.

[0053] In step (1), the amount of inorganic filler is 1 to 100 parts by mass, preferably 10 to 60 parts by mass, more preferably 15 to 50 parts by mass, and even more preferably 18 to 45 parts by mass, based on 100 parts by mass of the base rubber. By setting the amount of inorganic filler to 1 to 100 parts by mass, excellent appearance properties and reduced compression set can be achieved.

[0054] In the step (1), the amount of the silane coupling agent is 1 to 15 parts by mass, preferably 1.5 to 7 parts by mass, and more preferably 2 to 5 parts by mass, based on 100 parts by mass of the base rubber. When the amount of the silane coupling agent is 1 to 15 parts by mass, the silane coupling agent is adsorbed on the surface of the inorganic filler, and the silane coupling agent is prevented from volatilizing during kneading, which is economical. In addition, the silane coupling agent that is not adsorbed can be prevented from condensing, causing gel particles or roughness in the molded product, which deteriorates the appearance. Furthermore, the crosslinking reaction can be sufficiently advanced to reduce compression set, if necessary.

[0055] In step (1), the amount of the silanol condensation catalyst is not particularly limited, and is preferably 0.03 to 0.5 parts by mass, more preferably 0.05 to 0.3 parts by mass, further preferably 0.07 to 0.25 parts by mass, and particularly preferably 0.1 to 0.2 parts by mass, relative to 100 parts by mass of the base rubber. When the amount of the silanol condensation catalyst is within the above range, the generation of gel particles during molding can be suppressed, and crosslinking proceeds sufficiently to provide excellent compression set properties.

[0056] From the viewpoint of achieving a good balance between excellent appearance characteristics and reduced compression set, it is preferred in step (1) to melt-mix 10 to 60 parts by mass of an inorganic filler, 1 to 15 parts by mass of a silane coupling agent, 0.01 to 0.6 part by mass of an organic peroxide, and 0.03 to 0.5 part by mass of a silanol condensation catalyst with respect to 100 parts by mass of the base rubber.

[0057] In carrying out step (1), steps (a-1) and (a-2) are carried out in sequence. That is, first, the inorganic filler and the silane coupling agent are mixed, and then the obtained mixture is melt-kneaded with all or a part of the base rubber in the above-mentioned blending amounts at a temperature equal to or higher than the decomposition temperature of the organic peroxide to cause the above-mentioned grafting reaction and prepare a silane master batch. In the present invention, "melt-mixing the mixture with all or a part of the base rubber" does not specify the order of mixing (or compounding) when melt-mixing, and means that the mixing may be performed in any order. In other words, the order of mixing in step (a-2) is not particularly limited. The method of mixing the base rubber is not particularly limited. For example, a base rubber that has been mixed and prepared in advance may be used, or each component, for example, each rubber component, may be mixed separately.

[0058] In the present invention, the silane coupling agent is not introduced alone into the silane master batch, but is premixed with the inorganic filler. That is, the inorganic filler and the silane coupling agent are mixed to prepare a mixture (step (a-1)). The premixed silane coupling agent is present so as to surround the surface of the inorganic filler, and it is considered that a part or all of it is adsorbed or bonded to the inorganic filler. This can reduce the volatilization of the silane coupling agent during the subsequent melt mixing. In addition, it can also prevent the silane coupling agent that is not adsorbed or bonded to the inorganic filler from condensing, making melt kneading difficult.

[0059] The method of premixing the inorganic filler and the silane coupling agent is not particularly limited, but includes mixing methods such as wet processing and dry processing. Specifically, the inorganic filler and the silane coupling agent are mixed by dry or wet processing for several minutes to several hours at a temperature below the decomposition temperature of the organic peroxide, preferably 10 to 60°C, more preferably around room temperature (20 to 25°C), and more preferably, dry processing in which the silane coupling agent is added to the inorganic filler, preferably the dried inorganic filler, with or without heating and mixed is more preferable. In step (a-1), the base rubber may be mixed as long as the temperature is maintained below the decomposition temperature.

[0060] In the manufacturing method of the present invention, the mixture of inorganic filler and silane coupling agent obtained in step (a-1) is then melt-mixed with all or a part of the base rubber in the presence of an organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide (step (a-2)). In this way, excessive crosslinking reaction between the base rubber components can be prevented, and a crosslinked molded product with excellent appearance can be obtained. The melt mixing in step (a-2) causes a graft reaction between the graft reaction site of the silane coupling agent and the graft reaction site of the base rubber by radicals generated from the organic peroxide. As a result, a silane crosslinkable rubber (silane graft polymer) in which the silane coupling agent is covalently bonded to the rubber component is synthesized, and a silane master batch containing this silane crosslinkable rubber is prepared. In step (a-2), the silane coupling agent is grafted to the base rubber in at least the following manner. That is, the silane coupling agent bonded to or adsorbed on the inorganic filler by a weak bond is detached from the inorganic filler and grafted to the base rubber. In addition, the silane coupling agent bonded to or adsorbed on the inorganic filler by a strong bond is grafted to the base rubber while maintaining the bond with the inorganic filler. Regarding the silane coupling agent, examples of the weak bond with the inorganic filler include an interaction due to hydrogen bond, an interaction between ions, partial charges or dipoles, and an action due to adsorption. In addition, examples of strong bonds with inorganic fillers include chemical bonds with sites on the surface of inorganic fillers that can be chemically bonded. In addition, in the silane crosslinkable rubber, the ethylene-α-olefin copolymer rubber containing a diene component is partially crosslinked at the diene component. The same applies to the case where the styrene elastomer contains a diene component.

[0061] In step (a-2), the temperature at which the above components are melt-mixed (also referred to as melt-kneading or kneading) is equal to or higher than the decomposition temperature of the organic peroxide, preferably a temperature of the decomposition temperature of the organic peroxide + (25 to 110) ° C, more preferably 150 to 230 ° C. The decomposition temperature of the organic peroxide is preferably set after the base rubber component is melted. At the above mixing temperature, the above components melt, the organic peroxide decomposes and acts, and the necessary silane grafting reaction proceeds sufficiently in step (a-2). The mixing time may be a time at which the reaction mixture is sufficiently mixed and the silane grafting reaction can be completed, and is appropriately set between 3 and 20 minutes, but is not limited thereto. Other conditions can be appropriately set. The mixing method is not particularly limited as long as it is a method commonly used for rubber, plastics, etc. As a kneading device, a single screw extruder, a twin screw extruder, a roll, a Banbury mixer, various kneaders, etc. are used. From the viewpoint of dispersibility of the base rubber component and stability of the crosslinking reaction, a closed type mixer such as a Banbury mixer or various kneaders is preferred.

[0062] The organic peroxide may be present during the melt mixing in the above step (a-2), i.e., when the mixture obtained in step (a-1) is melt mixed with the base rubber. The organic peroxide may be mixed, for example, in step (a-1) or in step (a-2). The organic peroxide is preferably mixed in step (a-1).

[0063] In steps (a-1) and (a-2), especially in step (a-2), it is preferable to knead the above-mentioned components substantially without mixing a silanol condensation catalyst. This can suppress the condensation reaction of the silane coupling agent, facilitate melt mixing, and allow the desired shape to be obtained during injection molding. Here, "substantially without mixing" does not mean to exclude the silanol condensation catalyst that is inevitably present, but means that it may be present to the extent that the above-mentioned problems due to silanol condensation of the silane coupling agent do not occur. For example, in step (a-2), the silanol condensation catalyst may be present in an amount of 0.01 parts by mass or less per 100 parts by mass of the base rubber.

[0064] In this way, the step (a) consisting of the steps (a-1) and (a-2) is carried out to graft the silane coupling agent with the base rubber to prepare a silane master batch (also called silane MB). The silane MB thus obtained is preferably used together with a silanol condensation catalyst or a catalyst master batch described later in the manufacture of a reaction composition (silane crosslinkable rubber composition) prepared in the step (1) as described later. The silane MB is a mixture containing a silane crosslinkable rubber in which the silane coupling agent has been grafted to the rubber component to such an extent that it can be molded in the step (2) described later.

[0065] From the viewpoint of excellent compression set, the MFR of Silane MB at 190°C and 10 kg is 0.8 g / 10 min or more. From the viewpoint of improving injection moldability and appearance characteristics, the MFR of Silane MB at 190°C and 10 kg is preferably 1 g / 10 min or more, more preferably 2 g / 10 min or more, and even more preferably 5 g / 10 min or more. There is no upper limit, but 20 g / 10 min or less is practical. The MFR of Silane MB refers to a value measured according to JIS K 7210 at a temperature of 190°C and a load of 10 kg. The MFR of Silane MB can be adjusted to satisfy the above value by adjusting the type and amount of each base rubber component, etc. For example, the MFR of Silane MB tends to increase when a styrene elastomer and / or an olefin elastomer with a high MFR is added, the amount of mineral oil added is increased, or an ethylene-α-olefin copolymer rubber with a low Mooney viscosity is added.

[0066] In the manufacturing method of the present invention, when a part of the base rubber is melt-mixed in step (a-2), the rest of the base rubber is melt-mixed with a silanol condensation catalyst to prepare a catalyst master batch (also called catalyst MB) in step (b). Therefore, when the whole of the base rubber is melt-mixed in step (a-2), step (b) does not need to be performed, and the silanol condensation catalyst may be mixed with other base rubber components.

[0067] The mixing ratio of the base rubber as the carrier and the silanol condensation catalyst is not particularly limited, but is preferably set so as to satisfy the above-mentioned blending amounts in step (1). The mixing may be performed by any method that can achieve uniform mixing, including mixing performed under molten base rubber (melt mixing). Melt mixing can be performed in the same manner as in the melt mixing in step (a-2) above. For example, the mixing temperature can be appropriately set to a temperature equal to or higher than the melting temperature of the base rubber component, and is preferably 120 to 200°C, more preferably 140 to 180°C. Other conditions, such as the mixing time, can be appropriately set.

[0068] In step (b), other resins can be used as carriers instead of or in addition to the remainder of the base rubber. That is, in step (b), the remainder of the base rubber when a part of the base rubber is melt-mixed in step (a-2), or a resin other than the rubber component used in step (a-2), can be melt-mixed with a silanol condensation catalyst to prepare a catalyst master batch. When the carrier is another resin, the amount of the other resin is preferably 1 to 60 parts by mass, more preferably 2 to 50 parts by mass, and even more preferably 3 to 40 parts by mass, per 100 parts by mass of the base rubber, in order to promote the grafting reaction in step (a-2) and to prevent the formation of bumps during molding.

[0069] In addition, an inorganic filler may be used in step (b). In this case, the amount of the inorganic filler in step (b) is not particularly limited, but is preferably 350 parts by mass or less per 100 parts by mass of the carrier. By setting the amount of the inorganic filler to 350 parts by mass or less, the silanol condensation catalyst is appropriately dispersed, and crosslinking is likely to proceed.

[0070] The catalyst MB thus prepared is a (molten) mixture of the silanol condensation catalyst and the carrier, with or without a filler. This catalyst MB is used together with the silane MB in the production of the silane crosslinkable rubber composition prepared in step (1).

[0071] In the manufacturing method of the present invention, the next step is to melt-mix the silane MB with the silanol condensation catalyst or catalyst MB to obtain a silane crosslinkable rubber composition (reaction composition). This reaction composition is a composition containing the silane crosslinkable rubber synthesized in the above step (a-2). The mixing method may be any method capable of obtaining a homogeneous reaction composition as described above.

[0072] The mixing is basically the same as the melt mixing in step (a-2). Although there are rubber components, such as elastomers, whose melting points cannot be measured by DSC or the like, the kneading is carried out at a temperature at which at least the rubber components melt. The melt mixing temperature is appropriately selected according to the melting temperature of the base rubber or carrier, and is, for example, preferably 80 to 250°C, more preferably 100 to 240°C, and further preferably 120 to 200°C. Other conditions, such as the mixing (kneading) time, can be appropriately set.

[0073] In step (c), in order to avoid silanol condensation reactions, it is preferable that the mixture of silane MB and silanol condensation catalyst is not kept at high temperature for a long period of time.

[0074] This step (c) may be any step in which the silane master batch is mixed with a silanol condensation catalyst or a catalyst master batch to obtain the above-mentioned reaction composition as a molten mixture thereof, and is preferably a step in which a catalyst master batch containing a silanol condensation catalyst and a carrier is melt-mixed with the silane master batch.

[0075] In this manner, steps (a) to (c) (step (1)) are carried out to produce a silane crosslinkable rubber composition as a reaction composition. This silane crosslinkable rubber composition contains a silane crosslinkable rubber in which a silane coupling agent is grafted onto a base rubber, 1 to 100 parts by mass of an inorganic filler and a silanol condensation catalyst per 100 parts by mass of the base rubber. This silane crosslinkable rubber composition contains a silane crosslinkable rubber with a different crosslinking method. In this silane crosslinkable rubber, the reactive site of the silane coupling agent capable of silanol condensation may be bonded or adsorbed to an inorganic filler, but is not silanol condensed as described below. Therefore, the silane crosslinkable rubber includes at least a crosslinkable rubber in which a silane coupling agent bonded or adsorbed to an inorganic filler is grafted to a base rubber, and a crosslinkable rubber in which a silane coupling agent not bonded or adsorbed to an inorganic filler is grafted to a base rubber. These crosslinkable rubbers may be further crosslinked at the diene component portion. In addition, the silane crosslinkable rubber composition may have a silane coupling agent bonded or adsorbed to an inorganic filler, and a silane coupling agent not bonded or adsorbed to an inorganic filler. Furthermore, it may contain a rubber component that has not reacted with the silane coupling agent. As described above, the silane crosslinkable rubber is an uncrosslinked body in which the silane coupling agent is not condensed with silanol. In practice, when the silane coupling agent is melt-mixed in step (c), partial crosslinking is unavoidable, but the obtained silane crosslinkable rubber composition is one that maintains at least moldability in the molding step in step (2).

[0076] In step (1), steps (a) to (c) can be carried out simultaneously or consecutively.

[0077] In step (1), the amounts of other base rubber components that can be used in addition to the above components and the above additives are appropriately set within ranges that do not impair the object of the present invention. In step (1), the additives, particularly the antioxidant and the flame retardant, may be mixed in any step or component, but are preferably mixed in the carrier. In step (1), particularly in steps (a-1) and (a-2), it is preferable that the crosslinking aid is not substantially mixed. If the crosslinking aid is not substantially mixed, crosslinking between the rubber components during melt mixing is unlikely to occur, and the appearance of the silane-crosslinked rubber molded product is excellent. Here, "not substantially mixed" means that the crosslinking aid is not actively mixed, and does not exclude unavoidable mixing.

[0078] In the method for producing a silane-crosslinked rubber molded article of the present invention, step (2) is then carried out in which the obtained reaction composition is injection molded to obtain a molded article. In this step (2), it is sufficient if the reaction composition can be injection molded, and the injection molding conditions are appropriately selected depending on the form of the silane-crosslinked rubber molded article of the present invention or the silane-crosslinked rubber molded article including the silane-crosslinked rubber molded article. The injection molding temperature cannot be determined univocally depending on the type and amount of base rubber component used, the type and amount of inorganic filler used, etc., but it is preferable to set the temperature at the nozzle to about 180 to 210°C, at the rear of the cylinder (feeder side) to about 130 to 170°C, at the middle of the cylinder to about 140 to 180°C, and at the front of the cylinder (nozzle side) to about 160 to 210°C, and the mold temperature to about room temperature to 40°C. The injection molding can be carried out using a general-purpose injection molding machine for plastics. The mold is appropriately selected depending on the shape, size, etc. of the molded article.

[0079] Moreover, step (2) can be carried out simultaneously with or consecutively to step (c). That is, one embodiment of the melt mixing in step (c) is to melt mix the molding raw materials during or immediately before injection molding. For example, pellets such as dry blends may be mixed together at room temperature or high temperature and introduced into an injection molding machine (melt mixing), or may be melt mixed after mixing, pelletized again, and introduced into an injection molding machine. More specifically, a series of steps can be adopted in which a molding material consisting of silane MB and silanol condensation catalyst or catalyst MB is melt-kneaded in an injection molding machine, and then injection molded into a desired shape. In this manner, a molded article of the silane crosslinkable rubber composition is obtained. As with the silane crosslinkable rubber composition, this molded article is in a partially crosslinked state that retains moldability for molding in step (2), although partial crosslinking is unavoidable. Thus, the silane crosslinked rubber molded article of the present invention is made into a crosslinked or final crosslinked molded article by carrying out step (3).

[0080] In the method for producing a silane-crosslinked rubber molded article of the present invention, a step (3) is carried out in which the molded article obtained in the step (2) is brought into contact with water. As a result, the reactive sites of the silane coupling agent capable of silanol condensation are hydrolyzed to silanol groups, and the hydroxyl groups of the silanol groups are condensed with each other by the silanol condensation catalyst present in the molded article, causing a crosslinking reaction. In this way, a silane-crosslinked rubber molded article in which the silane coupling agent is crosslinked by silanol condensation can be obtained. The treatment in step (3) itself can be carried out by a normal method. Condensation between silane coupling agents proceeds simply by storing at room temperature. Therefore, in step (3), it is not necessary to actively bring the molded body into contact with water. In order to promote this crosslinking reaction, the molded body can also be actively brought into contact with moisture. For example, a method of actively bringing the molded body into contact with water, such as immersion in warm water, placing in a moist heat bath, or exposure to high-temperature steam, can be used. In addition, pressure may be applied at this time to allow moisture to penetrate into the interior.

[0081] In this way, a silane crosslinked rubber molded body is produced from the silane crosslinkable rubber composition of the present invention. As described below, this silane crosslinked rubber molded body contains a crosslinked rubber in which the silane crosslinkable rubber is condensed through a siloxane bond. One embodiment of this silane crosslinked rubber molded body contains a silane crosslinked rubber and an inorganic filler. Here, the inorganic filler may be bonded to the silane coupling agent of the silane crosslinked rubber. Therefore, this silane crosslinked rubber includes at least a crosslinked rubber in which a plurality of crosslinked rubbers are bonded or adsorbed to the inorganic filler by the silane coupling agent, and bonded (crosslinked) through the inorganic filler and the silane coupling agent, and a crosslinked rubber in which the reactive sites of the silane coupling agent of the crosslinkable rubber are hydrolyzed and undergo a silanol condensation reaction with each other, and thus crosslinked through the silane coupling agent. In addition, the silane crosslinked rubber may contain a mixture of bonds (crosslinks) through the inorganic filler and the silane coupling agent and crosslinks through the silane coupling agent. Furthermore, it may contain a rubber component that has not reacted with the silane coupling agent and / or a silane crosslinkable rubber that has not been crosslinked, and a silane crosslinkable rubber that has been crosslinked at a diene component portion.

[0082] According to the manufacturing method of the present invention, a molded article having excellent appearance characteristics and reduced compression set can be obtained by injection molding. According to the present invention, even if the injection molding machine is temporarily stopped and then molding is resumed, the occurrence of defective appearance can be suppressed, and a silane-crosslinked rubber molded article having good appearance can be produced. Here, "resuming after temporary stop" cannot be stated unequivocally because it depends on the composition of the base rubber, processing conditions, and other necessary measures during the manufacturing process, but it means that, for example, even if the molding material is retained in a molten state in the injection molding machine at 200°C for an interval of up to 3 hours, preferably up to 4 hours, and more preferably up to 5 hours, and then injection molding is resumed, defective appearance can be suppressed and molding can be performed. The details of how a silane-crosslinked rubber molded article having such excellent characteristics can be produced are not yet clear, but it is considered as follows. According to the manufacturing method of the present invention, in step (a-1), the inorganic filler and the silane coupling agent are mixed in advance in a specific ratio, so that the silane coupling agent is adsorbed or bonded to the inorganic filler prior to the grafting reaction in step (a-2). In this state, in step (a-2), the silane coupling agent is melt-kneaded with the base rubber in the presence of an organic peroxide, causing a grafting reaction. At that time, the silane coupling agent that is weakly bonded or adsorbed to the inorganic filler is detached from the inorganic filler, while the silane coupling agent that is strongly bonded to the inorganic filler maintains its bond with the inorganic filler. In this way, a silane crosslinkable rubber having a different adsorption state of the inorganic filler is formed. Furthermore, in step (3), these silane crosslinkable rubbers are brought into contact with moisture to form a crosslinked rubber having a crosslinked structure via a silanol bond. In the manufacturing method of the present invention, the formation of a crosslinked structure by the above-mentioned silane crosslinking is assumed, and then, as the base rubber, 5 to 35 mass% of an ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10 mass%, 3 to 30 mass% in total of at least one of a styrene elastomer and an olefin elastomer having an MFR of 1 to 15 g / 10 min, 5 to 40 mass% of a styrene elastomer having an MFR of less than 0.1 g / 10 min, and a mineral oil are used. In the step (a-2), the ethylene-α-olefin copolymer rubber in the base rubber component not only undergoes a silane graft reaction, but also forms crosslinks in the diene portion. (However, since the inorganic filler and the silane coupling agent are premixed, it is considered that the silane graft reaction occurs preferentially over crosslinking between the diene components.) The same is true when the styrene elastomer or the like contains a diene component. On the other hand, a styrene or olefin elastomer with an MFR of 1 to 15 g / 10 min not only imparts excellent fluidity to the base rubber and functions as a fluidized layer, but also has high compatibility with the ethylene-α-olefin copolymer rubber, so that the molded body obtained can have excellent physical properties. In addition to the cooperation of these components, by setting the MFR of the silane master batch to 0.8 g / 10 min or more, gel particles generated in the cylinder can be maintained in a highly fluid state and efficiently discharged outside the cylinder of the molding machine, thereby reducing the impact on the appearance characteristics of the molded body. Furthermore, flow marks can be suppressed. Furthermore, in the finally obtained silane-crosslinked molded article, a crosslinked structure due to crosslinking of the diene component is formed in addition to the crosslinked structure due to silanol condensation, thereby making it possible to reduce compression set. According to the manufacturing method of the present invention, it is possible to realize excellent appearance properties and reduced compression set even under injection molding conditions that result in a long residence time in the cylinder of, for example, 3 hours.

[0083] The manufacturing method of the present invention can be applied to the manufacture of products (including semi-finished products, parts, and members) that require small compression set and excellent appearance properties, and components or members of products such as rubber materials, etc. Therefore, a silane-crosslinked rubber molded body or a silane-crosslinked rubber molded article including a silane-crosslinked rubber molded body is considered to be such a product. Examples of the silane-crosslinked rubber molded product of the present invention or a silane-crosslinked rubber molded product containing the silane-crosslinked rubber molded product include covering materials for electric wires or flame-retardant cables such as flame-retardant insulated electric wires, rubber substitute materials for electric wires and cables, as well as flame-retardant electric wire parts, flame-retardant heat-resistant sheets, flame-retardant films, etc. Further examples include power plugs, connectors, sleeves, boxes, tape substrates, tubes, sheets, packings, cushioning materials, vibration-proofing materials, wiring materials used for internal wiring and external wiring of electric and electronic devices, particularly electric wires and optical cables.

[0084] The silane-crosslinked rubber molded product of the present invention is suitable as a material to be used in areas requiring small compression set and high moldability (particularly injection moldability), and can be used, for example, as a replacement for rubber materials that have traditionally been subjected to a chemical vulcanization process, such as rubber packings and molding materials. EXAMPLES

[0085] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. In Tables 1-1 to 1-3 (collectively referred to as Table 1), the numerical values ​​relating to the blending amounts of each example are in parts by mass unless otherwise specified. Furthermore, blank spaces for each component mean that the blending amount of the corresponding component is 0 parts by mass.

[0086] Example 1 ~6、8~19、21~ twenty three 、Reference Examples 7、20、 In Comparative Examples 1 to 12, a part of the components constituting the base rubber was used as a carrier for the catalyst MB.

[0087] Example 1 ~6、8~19、21~ twenty three 、Reference Examples 7、20、 Comparative Examples 1 to 12) First, the inorganic filler, the silane coupling agent, and the organic peroxide were charged in a rotary blade mixer (product name, Mazera PM, manufactured by Mazera Co., Ltd.) in the mass ratio shown in Table 1, and stirred (premixed) at room temperature (25 ° C) at 10 rpm for 1 minute to obtain a powder mixture (step (a-1)). Next, the obtained powder mixture and the base rubber were charged in the mass ratio shown in Table 1 into a kneader (volume 75 L) previously heated to 100 ° C, mixed at 40 rpm for 5 minutes, and then finished kneaded at 30 rpm for 3 minutes. After confirming that the temperature of the mixture reached 180 to 200 ° C, which is higher than the decomposition temperature of the organic peroxide, the mixture was pelletized using a feeder-ruder and a pelletizer to obtain a silane master batch (step (a-2)). The Silane MB thus obtained contains a silane crosslinkable rubber in which the silane coupling agent has been grafted to the base rubber component. The MFR of the obtained silane master batch was measured in accordance with JIS K 7210 under conditions of a temperature of 190° C. and a load of 10 kg.

[0088] On the other hand, the base rubber, antioxidant, and silanol condensation catalyst were sequentially charged in the mass ratios shown in Table 1 into a kneader (volume 75 L) that had been preheated to 80°C, mixed at 30 rpm for 5 minutes, and then finish-kneaded at 25 rpm for 3 minutes. After it was confirmed that the temperature of the mixture had reached about 160°C and the base rubber had been sufficiently melted, the mixture was pelletized using a feeder-ruder and pelletizer to obtain a catalyst master batch (step (b)). This catalyst MB is a molten mixture of the carrier and the silanol condensation catalyst.

[0089] Next, the silane MB and the catalyst MB were placed in a plastic bag and dry-blended at room temperature (25° C.) for 5 minutes to obtain a dry blend. At this time, the mixing ratio of the silane MB and the catalyst MB was the mass ratio shown in Table 1. Specifically, in Example 1, ~6、8~19、21~ twenty three 、Reference Examples 7、20、 In Comparative Examples 1 to 12, the ratio of the base rubber of Silane MB was 90 parts by mass, and the carrier of Catalyst MB was 10 parts by mass.

[0090] Next, using a 50t injection molding machine (FANUC ROBOSHOTα-50iA) with a screw diameter of 26 mm, the injection temperature conditions were set as follows: nozzle temperature 200°C, and on the feeder side, front 200°C, middle 160°C, rear 150°C, and mold temperature 30°C. The prepared dry blend was fed into this injection molding machine and melt-mixed (step (c)). Thus, a silane-crosslinkable rubber composition was prepared as a reaction composition, which was a molten mixture of Silane MB and Catalyst MB and contained the above-mentioned silane-crosslinkable rubber. The molten mixture was injected into a mold under any one of the following injection molding conditions (1) to (3) to obtain an A4 size sheet with a thickness of 2 mm (step (2)). The mold used was a mold having a cavity with a thickness of 2 mm and an "A4" size (210 mm x 297 mm) as defined by the JIS standard. Conditions common to the above injection molding conditions (1) to (3) Number of nozzles: 1 Gate shape: 4 x 3 mm Filling pressure: 5MPa Mold temperature: 30℃ Screw rotation speed: 100 rpm Injection speed: 60mm / sec Injection time: 10 seconds Holding pressure: 20MPa Pressure retention time: 10 seconds Cooling time: 30 seconds Injection molding conditions (1) The molding was repeated 10 times in succession. Injection molding conditions (2) After the above-mentioned injection molding condition (1), the injection molding machine was stopped (screw rotation speed: 0 rpm), and the injection temperature conditions were maintained to allow the silane-crosslinkable rubber composition to remain in the cylinder in a molten state for 1 hour. After that, injection molding was resumed, and molding was repeated 10 times. Injection molding conditions (3) After the above-mentioned injection molding condition (1), the injection molding machine was stopped (screw rotation speed: 0 rpm), and the injection temperature conditions were maintained while the silane-crosslinkable rubber composition was allowed to remain in the cylinder for 3 hours. Then, injection molding was resumed, and molding was repeated 10 times.

[0091] The uncrosslinked sheet obtained by the 10th molding under the above injection molding conditions (1) to (3) was left for 48 hours under the conditions of room temperature (23°C) and 50% RH to allow silane crosslinking to proceed (step (3)). In this manner, each sheet sample of "A4" size with a thickness of 2 mm was produced under the above injection molding conditions. The silane-crosslinked rubber molded body as the sheet sample has the above-mentioned silane-crosslinked rubber.

[0092] Comparative Example 11 A sheet sample was produced in the same manner as in Example 1, except that when preparing Silane MB, the inorganic filler, silane coupling agent, and organic peroxide were not premixed (step (a-1)), and the components shown in the Silane MB column in Table 1 were added to a kneader in the mass ratio shown in Table 1 to obtain Silane MB.

[0093] In the production of the above examples and comparative examples, when premixing of the inorganic filler, the silane coupling agent, and the organic peroxide (step (a-1)) was performed, it is recorded as "Yes" in the "Premixing" column of Table 1, and when premixing was not performed, it is recorded as "No".

[0094] The components shown in Table 1 were as follows. (1) Ethylene-α-olefin copolymer rubber 1: Nordel 4770P (trade name, manufactured by Dow, ethylene-propylene-diene rubber) (2) Ethylene-α-olefin copolymer rubber 2: Nordel 6565XCF (trade name, manufactured by Dow, ethylene-propylene-diene rubber) (3) Ethylene-α-olefin copolymer rubber 3: Mitsui EPT0045 (product name, manufactured by Mitsui Chemicals, Inc., ethylene-propylene rubber) (4) Styrene elastomer 1: Tuftec N504 (product name, manufactured by Asahi Kasei Corporation, SEBS) (5) Styrene elastomer 2: Septon 2063 (product name, manufactured by Kuraray Co., Ltd., SEPS) (6) Styrene elastomer 3: Septon 2002 (product name, manufactured by Kuraray Co., Ltd., SEPS) (7) Olefin elastomer 1: INFUSE 9000 (trade name, manufactured by Dow, olefin block copolymer (ethylene-1-octene block copolymer)) (8) Olefin elastomer 2: INFUSE 9500 (trade name, manufactured by Dow, olefin block copolymer (ethylene-1-octene block copolymer)) (9) Olefin elastomer 3: Engage 8130 (trade name, manufactured by Dow, ethylene-octene copolymer) (10) Olefin elastomer 4: Engage 8402 (trade name, manufactured by Dow, ethylene-octene copolymer) (11) Propylene resin 1: PB222A (product name, SanAllomer Corporation, random polypropylene) (12) Ethylene resin 1: Evolue SP1071C (product name, manufactured by Prime Polymer, LLDPE) (13) Ethylene resin 2: Sumikathene CU5003 (product name, manufactured by Sumitomo Chemical, LLDPE) (14) Mineral oil 1: Diana Process Oil PW90 (product name, Idemitsu Kosan, paraffin oil) (15) Inorganic filler 1: Kisuma 5L (product name, manufactured by Kyowa Chemical Industry Co., Ltd., magnesium hydroxide) (16) Inorganic filler 2: Aerosil 200 (product name, manufactured by Nippon Aerosil Co., Ltd., fumed silica) (17) Inorganic filler 3: Crystallite 5X (product name, manufactured by Takimori Co., Ltd., crystalline silica) (18) Inorganic filler 4: Talc K-1 (trade name, manufactured by Nippon Talc Co., Ltd., talc) (19) Inorganic filler 5: SATINTONE SP33 (product name, manufactured by Toshin Kasei Co., Ltd., calcined kaolin) (20) Inorganic filler 6: Softon 1200 (product name, manufactured by Bihoku Powder Industry Co., Ltd., calcium carbonate) (21) Silane coupling agent 1: KBM-1003 (product name, manufactured by Shin-Etsu Chemical Co., Ltd., vinyltrimethoxysilane) (22) Organic peroxide 1: Perhexa 25B (trade name, NOF Corporation, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane) (23) Antioxidant 1: Irganox 1076 (trade name, manufactured by BASF, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (24) Silanol condensation catalyst 1: Adeka STAB OT-1 (trade name, manufactured by ADEKA Corporation, dioctyltin dilaurate)

[0095] For each of the obtained sheet samples, various properties were evaluated by the test methods shown below.

[0096] 1. Appearance test (1) The surface of the sheet sample obtained in the 10th molding under the above injection molding condition (1) was visually observed. When flow marks (traces of flow of the rubber composition) were observed on the sheet surface, the area of ​​the flow mark portion was obtained and the flow mark ratio was calculated. Specifically, the boundary of the flow mark portion was surrounded by a line, and the area of ​​the surrounded flow mark portion was measured using a digital microscope VHX-1000 (product name, manufactured by Keyence Corporation), and the flow mark ratio was calculated by the following calculation formula. Flow mark rate (%) = flow mark area / sheet sample area x 100 The evaluation was based on the following criteria: Sheets with no observed flow marks (traces of flow of the rubber composition), gel particles, or roughness on the surface were rated as "A (high surface quality)", sheets with observed flow marks but a flow mark rate of less than 10% and no observed gel particles or roughness were rated as "B (good surface quality)", and sheets with a flow mark rate of 10% or more or with observed gel particles or roughness were rated as "C (fail)". A rating of "B" or higher is the passing level for this test.

[0097] 2. Appearance test (2) The surface of the sheet sample obtained in the 10th molding after resuming injection molding under the above injection molding condition (2) was visually observed. When flow marks were observed on the sheet surface, the flow mark rate was calculated in the same manner as in the appearance test (1). The evaluation was based on the following criteria: Sheets with no observed flow marks (traces of flow of the rubber composition), gel particles, or roughness on the surface were rated as "A (high surface quality)", sheets with observed flow marks but a flow mark rate of less than 10% and no observed gel particles or roughness were rated as "B (good surface quality)", and sheets with a flow mark rate of 10% or more or with observed gel particles or roughness were rated as "C (fail)". A rating of "B" or higher is the passing level for this test.

[0098] 3. Appearance test (3) The surface of the sheet sample obtained in the 10th molding after resuming injection molding under the above injection molding condition (3) was visually observed. When flow marks were observed on the sheet surface, the flow mark rate was calculated in the same manner as in the appearance test (1). The evaluation was based on the following criteria: Sheets with no observed flow marks (traces of flow of the rubber composition), gel particles, or roughness on the surface were rated as "A (high surface quality)", sheets with observed flow marks but a flow mark rate of less than 10% and no observed gel particles or roughness were rated as "B (good surface quality)", and sheets with a flow mark rate of 10% or more or with observed gel particles or roughness were rated as "C (fail)". A rating of "B" or higher is the passing level for this test.

[0099] 4. Compression set test Based on JIS K 6262 A method, the compression set of the sheet sample obtained by the 10th molding under the above injection molding condition (1) was measured. Using a compression device equipped with two compression plates and a spacer (thickness 75% of the thickness of the sheet sample), the sheet sample was compressed by 25% in the thickness direction (compression rate 25%), heated to 70°C in that state, and held for 22 hours. Thereafter, the compression was released at room temperature (23°C), and after cooling for 30 minutes (final temperature was 23°C), the thickness of the sheet sample was measured. The compression set was calculated from the thickness of the sheet sample before and after compression using the following formula: The results were evaluated according to the following criteria. Formula: CS=[(t0-t2) / (t0-t1)]×100 During the ceremony, CS: Compression set (%) t0: thickness of sheet sample before compression (original thickness) (mm) t1: Spacer thickness (mm) t2: Thickness of the sheet sample after compression (thickness after 30 minutes after removal from the compression device) (mm) In this test, a compression set of less than 45% is the pass level. A compression set of less than 45% means that the compression set is at least the same as that of general vulcanized rubber. If the compression set is less than 45%, the material can be suitably used as a component for applications where the number of openings and closings is relatively small, such as optical cable connection boxes (closures). Here, if the compression set differs by about 2%, the life of the component will be shortened accordingly.

[0100] [Table 1-1]

[0101] [Table 1-2]

[0102] [Table 1-3]

[0103] When a base rubber not satisfying the composition specified in the present invention was mixed into the manufacturing method having each step specified in the present invention, a sheet of a silane-crosslinked rubber molded body that passed both the appearance test (1) to (3) and the compression set test could not be obtained (Comparative Examples 1 to 10, 12). Among them, in Comparative Example 1, in which a base rubber containing an ethylene resin 1 (LLDPE) having an MFR of 10 g / 10 min was used instead of a styrene or olefin elastomer having an MFR of 1 to 15 g / 10 min, a sheet of a silane-crosslinked rubber molded body with a sufficiently small compression set could not be produced. It is considered that when LLDPE is used, that part generates plastic deformation. In addition, in Comparative Examples 5 and 6, in which a base rubber containing a styrene elastomer or an olefin elastomer having an MFR of more than 15 g / 10 min was used instead of a styrene elastomer having an MFR of 1 to 15 g / 10 min, a sheet of a silane-crosslinked rubber molded body with a sufficiently small compression set could not be produced. It is considered that this is because the molecular weight of an elastomer showing such an MFR is generally small, and the molecular weight is too small for the effect of the present invention. Unless the inorganic filler and the silane coupling agent were premixed, it was not possible to obtain a sheet of a silane-crosslinked rubber molded article having both excellent appearance properties and compression set properties (Comparative Example 11). In contrast, in a manufacturing method having each step specified in the present invention, when a base rubber satisfying the composition specified in the present invention is blended with inorganic filler, organic peroxide, etc. in specific amounts and premixed, a sheet of a silane-crosslinked rubber molded product that passes both the appearance tests (1) to (3) and the compression set test and has both excellent appearance properties and compression set properties can be manufactured (Example 1 ~6、8~19、21~ 23). In particular, the fact that the product passed the appearance test (3) shows that the product can withstand a residence time of as long as 3 hours during injection molding without any defects in appearance. Furthermore, according to the manufacturing method of the present invention, a molded product with excellent appearance characteristics can be obtained by injection molding alone, without the need for post-treatment such as grinding or polishing.

Claims

1. A method for producing a silane-crosslinked rubber molded product, comprising the following steps (1), (2) and (3): Step (1): A step of melt-mixing 0.01 to 0.6 parts by mass of an organic peroxide, 1 to 100 parts by mass of an inorganic filler, 1 to 15 parts by mass of a silane coupling agent having a graft reaction site capable of undergoing a graft reaction with the base rubber in the presence of radicals generated from the organic peroxide, and a silanol condensation catalyst relative to 100 parts by mass of a base rubber, and grafting the graft reaction site with the graft reaction site of the base rubber by the radicals generated from the organic peroxide to obtain a silane crosslinkable rubber composition containing a silane crosslinkable rubber. Step (2): A step of injection molding the silane-crosslinkable rubber composition to obtain a molded article. Step (3): A step of contacting the molded product with water to obtain a silane-crosslinked rubber molded product. The base rubber is 5 to 35% by mass of an ethylene-α-olefin copolymer rubber having a diene content of 4.5 to 10% by mass, 3 to 30% by mass in total of at least one of a styrene elastomer and an olefin elastomer having a melt flow rate of 1 to 15 g / 10 min at 190° C. and 2.16 kg, 5 to 40% by mass of a styrene elastomer having a melt flow rate of less than 0.1 g / 10 min at 190° C. and 2.16 kg, and 43 to 60% by mass of a mineral oil. Including, In carrying out the step (1), A method for producing a silane-crosslinked rubber molded product, wherein, in the case where the entire base rubber is melt-mixed in the following step (a-2), the step (1) comprises the following steps (a-1), (a-2), and (c), and, in the case where only a part of the base rubber is melt-mixed in the following step (a-2), the step (1) comprises the following steps (a-1), (a-2), (b), and (c). Step (a-1): A step of mixing the inorganic filler and the silane coupling agent to prepare a mixture. Step (a-2): A step of melt-mixing the mixture and all or a part of the base rubber in the presence of the organic peroxide at a temperature equal to or higher than the decomposition temperature of the organic peroxide, and causing a graft reaction between the graft reaction site and a graft reaction site of the base rubber by radicals generated from the organic peroxide, thereby preparing a silane master batch containing a silane crosslinkable rubber and having a melt flow rate of 0.8 g / 10 min or more at 190° C. and 10 kg. step (b): melt-mixing the remainder of the base rubber and the silanol condensation catalyst to prepare a catalyst master batch; and Step (c): A step of melt-mixing the silane master batch and the silanol condensation catalyst or the catalyst master batch to obtain the silane crosslinkable rubber composition.

2. 2. The method for producing a silane-crosslinked rubber molded article according to claim 1, wherein the base rubber contains 5 to 30 mass % of an ethylene-α-olefin rubber having a diene content of 1.0 mass % or less.

3. The method for producing a silane-crosslinked rubber molded article according to claim 1 or 2, wherein the base rubber contains 20 to 60 mass % of the mineral oil.

4. The method for producing a silane-crosslinked rubber molded article according to any one of claims 1 to 3, wherein the base rubber contains 1 to 15 mass % of a propylene resin.

5. The method for producing a silane-crosslinked rubber molded article according to any one of claims 1 to 4, wherein the base rubber contains 5 to 30 mass% of an ethylene-α-olefin rubber having a diene content of 1.0 mass% or less, 20 to 60 mass% of the mineral oil, and 1 to 15 mass% of a propylene resin.

6. The method for producing a silane-crosslinked rubber molded article according to any one of claims 1 to 5, wherein the inorganic filler is blended in an amount of 10 to 60 parts by mass per 100 parts by mass of the base rubber.

7. The method for producing a silane-crosslinked rubber molded article according to any one of claims 1 to 6, wherein the silanol condensation catalyst is blended in an amount of 0.03 to 0.5 parts by mass per 100 parts by mass of the base rubber.

8. The method for producing a silane-crosslinkable rubber molded article according to any one of claims 1 to 7, wherein the inorganic filler is a metal hydrate, talc, clay, silica, carbon black, or a mixture thereof.

9. The method for producing a silane-crosslinked rubber molded product according to any one of claims 1 to 8, wherein in the step (1), 10 to 60 parts by mass of the inorganic filler, 1 to 15 parts by mass of the silane coupling agent, 0.01 to 0.6 parts by mass of the organic peroxide, and 0.03 to 0.5 parts by mass of the silanol condensation catalyst are melt-mixed relative to 100 parts by mass of the base rubber.

10. A silane-crosslinkable rubber composition produced by the step (1) of the production method according to any one of claims 1 to 9.

11. A silane-crosslinked rubber molded article produced by the method for producing a silane-crosslinked rubber molded article according to any one of claims 1 to 9.

12. A silane-crosslinked rubber molded article comprising the silane-crosslinked rubber molded article according to claim 11.

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