Silane-grafted rubber composition, silane-crosslinked rubber composition, electric wire / cable, and method for producing silane-crosslinked rubber composition

Abstract

To provide a silane grafted rubber composition which suppresses early crosslinking that leads to molding defects while utilizing a silane crosslinking system in chlorinated polyethylene which is a component of a base polymer used for a coating material, a silane crosslinked rubber composition and an electric wire / a cable using the same.SOLUTION: There are provided a silane grafted rubber composition including: a base polymer containing a mixture of chlorinated polyethylene to which a silane coupling agent is graft copolymerized and an ethylene-based copolymer resin to which a silane coupling agent is graft copolymerized; and a hydrogen chloride scavenger containing hydrotalcite which has been subjected to a calcination treatment, and a silane crosslinked rubber composition of the silane grafted rubber composition. There is also provided a cable 1 comprising: conductors 2; an insulating layer 3; and a coating layer 4, wherein the coating layer 4 is composed of the silane crosslinked rubber composition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silane-grafted rubber composition, a silane-crosslinked rubber composition, an electric wire / cable, and a method for producing the silane-crosslinked rubber composition. [Background technology]

[0002] Cabtyre cables are general-purpose cables coated with rubber. Cabtyre cables are classified into fixed and movable types depending on their intended use. For movable types, the cable itself moves, so it is required to have flexibility against repeated bending and abrasion resistance against friction in various environments.

[0003] In order to improve various properties, including heat resistance, the covering materials for electric wires and cables are often subjected to a cross-linking process that chemically bonds the molecules of the polymer that makes up the covering material. Cross-linking is often carried out by blending a cross-linking agent into the covering material beforehand and then applying energy such as heat or electron beams after the cable is covered, but both methods require large-scale equipment and a great deal of energy.

[0004] In contrast, the silane cross-linking method involves first bonding a silane coupling agent to the polymer molecules of the coating material (silane graft reaction), and then, after the cable is coated, bonding the silanes together (forming cross-links between polymer molecules) through the action of moisture and a silanol condensation catalyst. This makes it an economical and environmentally friendly manufacturing method that does not require large-scale equipment or a large amount of energy.

[0005] In applications requiring flexibility and durability, rubber materials are primarily used as covering materials, and the silane crosslinking method is also used to manufacture electric wires and cables. A wide variety of rubber materials are used for covering electric wires and cables, but chlorine-based rubber is known as a highly functional material with excellent flame retardancy and oil resistance (see, for example, Patent Document 1).

[0006] Another characteristic of compounds using chlorine-based rubber is that chlorine (as hydrogen chloride) can be released in high-temperature environments, which can cause significant deterioration, so a hydrogen chloride scavenger must be added to capture the hydrogen chloride.

[0007] We have been developing silane crosslinking technology using chlorinated polyethylene, which is particularly cost-effective for chlorinated rubber, and have created various inventions to date. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-172514 Summary of the Invention [Problem to be solved by the invention]

[0009] The silane crosslinking method involves a multi-step process: first, a silane grafting reaction is carried out to bond silanes to polymer molecules, then molding into the desired shape, and then bonding and crosslinking the silanes together using moisture and a silanol condensation catalyst. Therefore, unlike other crosslinking methods that use heat or electron beams to crosslink, the crosslinking reaction process is complex and it is difficult to control side reactions.

[0010] In particular, if water is present in the material during the silane grafting reaction, the water may cause the silanes to bond together (premature crosslinking) before molding, reducing the fluidity of the material. Premature crosslinking can lead to molding defects when covering electric wires and cables, so it must be suppressed as much as possible.

[0011] Therefore, an object of the present invention is to provide a silane-grafted rubber composition, a silane-crosslinked rubber composition, and an electric wire and cable using the same, which utilize a silane crosslinking method but suppress premature crosslinking that leads to molding defects. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0012] A brief summary of a representative embodiment of the present invention will be given below.

[0013] The silane-graft rubber composition of the present invention comprises a base polymer in which a chlorinated polyethylene graft-copolymerized with a silane coupling agent and an ethylene-based copolymer resin graft-copolymerized with a silane coupling agent are mixed, and a hydrogen chloride scavenger containing calcined hydrotalcite. The silane-crosslinked rubber composition of the present invention is a silane-crosslinked product of the above silane-grafted rubber composition.

[0014] The electric wire or cable of the present invention has a conductor and a covering layer that covers and protects the conductor, and the covering layer is made of the above-mentioned silane-crosslinked rubber composition.

[0015] The method for producing a silane-crosslinked rubber composition of the present invention includes the steps of obtaining a silane-grafted rubber composition having a base polymer in which a chlorinated polyethylene graft-copolymerized with a silane coupling agent and an ethylene-based copolymer resin graft-copolymerized with a silane coupling agent are mixed, and a hydrogen chloride scavenger containing calcined hydrotalcite; and obtaining a silane-crosslinked rubber composition by adding a silanol condensation catalyst to the silane-grafted rubber composition and then silane-crosslinking the resulting mixture by the action of moisture. [Effects of the Invention]

[0016] By using the present invention, it is possible to provide a silane-grafted rubber composition, a silane-crosslinked rubber composition, and electric wires and cables using the same, which utilize a silane crosslinking method but suppress premature crosslinking that leads to molding defects. [Brief explanation of the drawings]

[0017] [Figure 1]1 is a schematic cross-sectional view of a cable according to an embodiment of the present invention; [Figure 2] FIG. 1 is a diagram showing a schematic configuration of an extruder used in the examples to carry out a cable production (extrusion) step. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the embodiments will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, the same reference numerals are used to designate components having the same functions, and repeated explanations thereof will be omitted. In the following embodiments, the explanations of the same or similar parts will not be repeated unless particularly necessary.

[0019] <Background of the study by the inventors> Layered double hydroxide hydrotalcite is widely used as a hydrogen chloride scavenger in the insulation of electric wires and cables that use chlorine-based rubber. Its hydrogen chloride scavenging ability comes from the layered structure of hydrotalcite, which captures hydrogen chloride released from chlorine-based rubber through ion exchange with anions such as carbonate ions present in the structure.

[0020] However, water is also retained within the hydrotalcite structure, and at high temperatures, this interlayer water is desorbed and released from the hydrotalcite. The temperature at which interlayer water is released varies depending on the composition, but is generally between 150 and 210°C, which is close to the silane grafting temperature. Therefore, when hydrotalcite is used as an additive, the released water promotes premature crosslinking in the silane crosslinking method. Therefore, the present inventors have devised the following method to suppress premature crosslinking.

[0021] The first method is to change the hydrogen chloride scavenger. In addition to hydrotalcite, we conducted thermal stability tests on epoxy-group-containing compounds, lead-containing compounds such as tribasic lead sulfate, tin-containing compounds, metal soaps, and magnesium oxide, which are known hydrogen chloride scavengers, and evaluated their hydrogen chloride scavenging ability. The results showed that metal soaps and magnesium oxide have weaker hydrogen chloride scavenging ability than hydrotalcite, and that a significant increase in their usage amount is required to achieve performance equivalent to that of hydrotalcite. Although epoxy-group-containing compounds are inferior to hydrotalcite, they exhibit good hydrogen chloride scavenging ability.

[0022] However, most epoxy-containing compounds are liquid, and adding them in large quantities can adversely affect the cable's properties, such as its abrasion resistance, making them impractical. Furthermore, lead-containing compounds are difficult to use due to their environmental friendliness, and tin-containing compounds are not recommended for use during kneading because they can act as a catalyst for the silane crosslinking reaction.

[0023] The second method is to pre-calcinate hydrotalcite. Interlayer water can be removed from hydrotalcite by calcination. In fact, calcined grades of hydrotalcite are produced by various manufacturers and are easily available. When the hydrogen chloride trapping capacity and water release behavior around the grafting temperature of the calcined hydrotalcite were evaluated, the hydrogen chloride trapping capacity was found to be comparable to that of conventionally used hydrotalcite, while the amount of water released at high temperatures was significantly reduced, a desirable result.

[0024] Therefore, the inventors investigated the application of this to silane cross-linking materials and found that premature cross-linking is suppressed when a base polymer is grafted with a silane coupling agent. Applying this knowledge, they discovered a silane-grafted rubber composition and a silane-cross-linked rubber composition.

[0025] [Silane-grafted rubber composition] The silane graft rubber composition of the present embodiment is a resin composition containing a base polymer described below and a hydrogen chloride scavenger, and the base polymer is obtained by grafting a raw material polymer with a silane coupling agent by graft copolymerization.

[0026] (hydrogen chloride scavenger) The hydrogen chloride scavenger used in this silane-grafted rubber composition is a component that has the effect of scavenging hydrogen chloride derived from the chlorinated polyethylene contained in the base polymer and suppressing deterioration of the resin. This embodiment is characterized in that the hydrogen chloride scavenger contains calcined hydrotalcite.

[0027] The hydrotalcite used here is not particularly limited as long as it is a known hydrotalcite. Hydrotalcite is a compound with a layer structure that has the property of incorporating anions between layers, and is usually M 2+ 1-x M 3+ x (OH)2A n- x / n It has a layered crystal structure and is represented by the formula mH2O. 2+ ) and trivalent (M 3+ ) metal complex hydroxides and anions (A n- ) and an intermediate layer containing water.

[0028] Hydrotalcite is capable of adsorbing anions on the surface and between the layers of the base layer, and due to this ability, when blended with synthetic resins etc., it becomes an excellent stabilizer that has the effect of scavenging hydrogen chloride. In the present embodiment, this hydrotalcite is subjected to a calcination treatment.

[0029] In this case, the calcination treatment of hydrotalcite refers to a heat treatment at a high temperature of 200°C or higher for a certain period of time.

[0030] The calcined hydrotalcite thus obtained can reduce the mass loss rate due to interlayer water (reducing the release of moisture) at temperatures of 150 to 210°C, which are close to the grafting temperature, and can suppress premature crosslinking of the silane-grafted rubber composition. From the viewpoint of suppressing premature crosslinking, this mass loss rate is preferably 5% or less, and more preferably 3% or less. Here, the mass loss rate refers to the difference in mass between 150°C and 210°C when the hydrotalcite is heated in a nitrogen atmosphere from room temperature to 500°C at a heating rate of 3°C per minute using a thermogravimetric analyzer. This mass difference corresponds to the amount of moisture contained between the layers of the hydrotalcite.

[0031] As the hydrogen chloride scavenger, at least the above-mentioned calcined hydrotalcites may be used, but it is also possible to use in combination with other known hydrogen chloride scavengers such as epoxy group-containing compounds, lead-containing compounds such as tribasic lead sulfate, tin-containing compounds, and metal soaps.

[0032] The amount of this hydrogen chloride scavenger (hydrotalcite) added is preferably 0.5 to 10 parts by mass, and more preferably 1 to 3 parts by mass, relative to 100 parts by mass of the base polymer, in view of the balance between hydrogen chloride scavenging ability and economic efficiency.

[0033] (Base polymer) The base polymer used in this silane graft rubber composition comprises a chlorinated polyethylene graft-copolymerized with a silane coupling agent and an ethylene copolymer resin graft-copolymerized with a silane coupling agent.

[0034] The chlorinated polyethylene used as the raw material for the base polymer may be any known chlorinated polyethylene, and there are no limitations on its physical properties.

[0035] The chlorinated polyethylene preferably has a chlorine content of 20 to 45% by mass and a Mooney viscosity of about 120 or less, and from the standpoint of a balance between flame retardancy and flexibility, it is more preferable that the chlorine content be 25 to 40% by mass and the Mooney viscosity be 90 or less.

[0036] The ethylene-based copolymer resin used as a raw material for the base polymer used here may be any known ethylene-based copolymer resin, and examples thereof include ethylene-vinyl acetate copolymer resin, ethylene-methyl acrylate copolymer resin, ethylene-ethyl acrylate copolymer resin, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, modified products thereof, and mixtures thereof.

[0037] The physical properties of the ethylene copolymer resin are not limited, but for example, the melt mass flow rate (MFR) is preferably 6 g / 10 min or less, and from the viewpoint of improving abrasion resistance, the melt mass flow rate (MFR) is more preferably 1 g / 10 min or less.

[0038] The chlorinated polyethylene and ethylene copolymer resin used as raw materials for the base polymer described above can be mixed in a mass ratio of 90:10 to 50:50 to obtain a silane-crosslinked rubber composition having a well-balanced processability, flexibility, etc. This mass ratio is preferably 80:20 to 60:40.

[0039] (Silane coupling agent) The silane coupling agent used here is a compound that is bonded to the resin that is the raw material for the polymer by a graft reaction to impart silane crosslinkability.

[0040] The silane coupling agent may be any silane coupling agent having an organic functional group that exhibits an addition reaction to a radical and an alkoxy group. For example, a general-purpose silane coupling agent having both an organic functional group such as a vinyl group, a methacryl group, an acrylic group, or a styryl group and an alkoxy group such as a methoxy group or an ethoxy group can be used.

[0041] Specific examples of this silane coupling agent include vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-acryloxypropyltrimethoxysilane, p-styryltrimethoxysilane, and mixtures thereof. However, alkoxy oligomers may also be used as long as they have both the aforementioned organic functional group and an alkoxy group, and the agent is not limited to the compounds exemplified above.

[0042] In particular, silane coupling agents having unsaturated bonds in the molecule that react with radicals have a relatively high flash point and are excellent in fire safety when mixed into polymers. From this viewpoint, it is preferable to use a silane coupling agent containing a methacryl group as the silane coupling agent. More specifically, examples of the silane coupling agent include 3-methacryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane.

[0043] The amount of the silane coupling agent added is preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, per 100 parts by mass of the polymer raw material. By setting the content within this range, a silane compound that can be sufficiently crosslinked by silane crosslinking, which will be described later, can be introduced into the base polymer.

[0044] (organic peroxide) The organic peroxide used here is a component for grafting a silane coupling agent onto the resin that is the raw material for the polymer.

[0045] Here, the organic peroxide may be any known organic peroxide used for the above-mentioned purposes, such as dicumyl peroxide, 1,1-di(t-butylperoxy)cyclohexane, t-butylperoxyisopropyl carbonate, t-amylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide, di-t-amyl peroxide, 1,1-di(t-amylperoxy)cyclohexane, t-butylperoxy-2-ethylhexyl carbonate, etc. These may be used alone or in combination of two or more.

[0046] The amount of peroxide added is preferably 0.01 to 1 part by mass, more preferably 0.1 to 0.5 parts by mass, per 100 parts by mass of the polymer raw material. By setting the content within this range, a silane compound that can be sufficiently crosslinked by silane crosslinking, which will be described later, can be introduced into the base polymer.

[0047] (additives) In addition to the above components, the silane-grafted rubber composition may further contain additives such as plasticizers, lubricants, reinforcing agents, fillers, and flame retardants.

[0048] Examples of plasticizers include phthalic acid-based plasticizers such as bis(2-ethylhexyl) phthalate, diisononyl phthalate, diisodecyl phthalate, and diundecyl phthalate, adipic acid-based plasticizers such as bis(2-ethylhexyl) adipate, diisononyl adipate, diisodecyl adipate, and bis(2-butoxyethyl) adipate, polyester-based plasticizers, phosphoric acid-based plasticizers, epoxy-based plasticizers, and trimellitic acid-based plasticizers. These may be used alone or in combination of two or more.

[0049] Examples of lubricants include fatty acid amides, zinc stearate, silicones, hydrocarbons, esters, alcohols, and metal soaps. Examples of reinforcing agents include carbon black and silica.

[0050] Examples of fillers include diatomaceous earth, calcined diatomaceous earth, quartz, cristobalite, kaolinite, kaolin clay, calcined clay, talc, muscovite, wollastonite, serpentine, pyrophyllite, calcium carbonate, barium sulfate, titanium oxide, magnesium carbonate, dolomite, and aluminum oxide.

[0051] Examples of the flame retardant include metal hydroxides, halogen-based, phosphorus-based, and antimony-based flame retardants.

[0052] Furthermore, adding an antioxidant or a silanol condensation catalyst to the silane-grafted rubber composition can improve heat resistance and promote the crosslinking reaction. However, because these can inhibit the silane-grafting reaction or cause molding defects, it is preferable to add and mix them into the silane-grafted rubber composition during final molding (in the case of electric wires and cables, during extrusion coating of the conductor or cable core).

[0053] Examples of the antioxidant include phenol-based antioxidants, sulfur-based antioxidants, phenol / thioester-based antioxidants, amine-based antioxidants, and phosphorous-based antioxidants.

[0054] Examples of silanol condensation catalysts include elements and metal compounds of Group II elements such as magnesium and calcium, Group VIII elements such as cobalt and iron, or elements such as tin, zinc, and titanium, metal salts of octylic acid or adipic acid, amine compounds, and acids.

[0055] More specifically, the silanol condensation catalyst may be dioctyltin dineodecanoate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctaate, stannous acetate, stannous caprylate, lead naphthenate, zinc caprylate, cobalt naphthenate, ethylamine, dibutylamine, hexylamine, pyridine, inorganic acids such as sulfuric acid and hydrochloric acid, or organic acids such as toluenesulfonic acid, acetic acid, stearic acid and maleic acid.

[0056] Furthermore, since the silanol condensation catalyst only needs to be added in a small amount to the silane-grafted rubber composition, it is useful from the standpoint of quality stability and industrial application to add it to the silane-grafted rubber composition as a high-concentration masterbatch.

[0057] The amount of the silanol condensation catalyst added is preferably 0.01 to 1 part by mass, more preferably 0.02 to 0.4 parts by mass, relative to 100 parts by mass of the base polymer. By setting the content within this range, the silane compound introduced into the base polymer can be efficiently crosslinked to obtain a silane crosslinked product.

[0058] (Method for producing silane-grafted rubber composition) The silane graft rubber composition can be obtained by grafting a silane coupling agent onto a base polymer of a resin composition containing the raw material components, additive components, etc. described above for the silane graft rubber composition.

[0059] This grafting treatment can be carried out, for example, by kneading a resin composition containing a raw polymer including chlorinated polyethylene and an ethylene copolymer resin, a silane coupling agent for imparting silane crosslinkability to the raw polymer, and a peroxide at a temperature equal to or higher than the melting point of the raw polymer and lower than the decomposition temperature of the peroxide, and after kneading, heating the mixture to a temperature equal to or higher than the decomposition temperature of the peroxide to introduce the silane coupling agent into the raw polymer by a graft reaction.

[0060] When producing a silane-grafted rubber composition by the above-mentioned grafting treatment, first, the raw polymer is melted and kneaded with the silane coupling agent and peroxide at a temperature lower than the decomposition temperature of the peroxide. Then, the raw polymer is heated to a temperature equal to or higher than the decomposition temperature of the peroxide and kneaded to graft the silane coupling agent onto the raw polymer, thereby avoiding the application of excessive heat to the resin composition during and after the grafting treatment.

[0061] The decomposition temperature of the peroxide is defined as a temperature 30°C lower than the one-minute half-life temperature of the peroxide. That is, by kneading the components at a temperature below the decomposition temperature of the peroxide, the components are thoroughly kneaded at a temperature where thermal decomposition of the peroxide is unlikely to occur, and then the components are heated to the decomposition temperature of the peroxide or higher to initiate the grafting reaction, whereby the peroxide is decomposed and the base polymer is efficiently grafted.

[0062] The grafting temperature is preferably equal to or higher than the one-minute half-life temperature of the peroxide, and the grafting time is preferably at least three times, more preferably at least four times, even more preferably at least five times, and particularly preferably at least six times the time it takes for the peroxide to decrease by half at the grafting temperature (the half-life time of the peroxide).

[0063] In parallel with this, it is also preferable to prepare masterbatch pellets. These masterbatch pellets are not particularly limited as long as they are a polymer material that does not cause problems in this embodiment when mixed with the silane-grafted resin composition. These polymer materials may be the same as or different from the base polymer.

[0064] Such polymer materials (in the case of chlorine-based materials, a hydrogen chloride scavenger can also be used), antioxidants, silanol condensation catalysts, etc., can be kneaded in a kneader or the like and granulated into pellets. The polymer may be the same chlorinated polyethylene and ethylene copolymer resin as the main material, or other resin materials, and is not particularly limited. A release agent may also be used to prevent adhesion between the pellets.

[0065] [Silane-crosslinked rubber composition] The silane-grafted rubber composition obtained as described above can be further converted into a silane-crosslinked rubber composition by silane-crosslinking the base polymer grafted with a silane coupling agent. Silane crosslinking can be formed by condensation reaction of the alkoxysilyl groups of the silane compound introduced into the base polymer in the presence of a silane crosslinking catalyst and moisture, thereby crosslinking polymer molecules together.

[0066] (Method of producing silane-crosslinked rubber composition) As described above, pellets of the silane-grafted rubber composition and masterbatch pellets are fed into an extrusion device and kneaded together, and the silane-grafted rubber composition is silane-crosslinked by the action of the silanol condensation catalyst and moisture contained in the masterbatch pellets, thereby producing a silane-crosslinked rubber composition.

[0067] As described above, by adjusting the compounding recipe of the resin composition to a predetermined formula, it is possible to obtain a silane-crosslinked rubber composition having suitable properties in terms of flame retardancy and electrical insulation required for a covering material for electric wires and cables.

[0068] [Wires and cables] The electric wire / cable of the present embodiment has a conductor and a covering layer that covers and protects the conductor, and the covering layer is made of the silane-crosslinked rubber composition of the present embodiment described above. The covering layer can be formed by directly covering the conductor to form an electric wire, or can be formed by indirectly covering the conductor and an insulating layer that covers the conductor to form a cable.

[0069] A cross-sectional view of a cable according to an embodiment of the present invention is shown in Fig. 1. As shown in Fig. 1, the cable 1 is configured to have a conductor 2, an insulating layer 3, and a covering layer 4.

[0070] The conductor 2 may be any commonly used metal wire, such as a copper wire, a copper alloy wire, an aluminum wire, a gold wire, or a silver wire. Alternatively, a metal wire plated with a metal such as nickel may be used as the conductor 2. Furthermore, a twisted conductor made by twisting metal wires may also be used as the conductor 2.

[0071] The insulating layer 3 is not particularly limited as long as it is made of an insulating material that is normally used for cables, such as an ethylene-propylene copolymer composition, polyvinyl chloride, fluororesin, cross-linked polyethylene, natural rubber, synthetic rubber, etc. The coating layer 4 is formed from the silane-crosslinked rubber composition described in the present embodiment above.

[0072] This cable can be manufactured by using an extruder to coat the outer periphery of the insulating layer 3 formed on the conductor 2 with the silane-grafted rubber composition described above to produce the cable 1. More specifically, the extrusion coating process can use a so-called two-shot silane crosslinking method in which a silane-grafted rubber composition grafted with a silane coupling agent is mixed with a resin composition containing a silane condensation catalyst. After the extrusion coating process, the cable can be stored naturally or placed in a steam chamber at 100°C or below to supply moisture to the coating material, allowing the silane crosslinking reaction to proceed and producing the final product.

[0073] Fig. 2 is a diagram showing a schematic configuration of an example of an extruder for producing a cable according to the present embodiment. As shown in Fig. 2, extruder 11 includes a cylinder 20, a screw 13 rotatably provided within cylinder 20, a hopper 12 for supplying material into cylinder 20, and a crosshead 16. Extruder 11 also includes a neck 15 between crosshead 16 and screw 13, and a breaker plate 14 between neck 15 and screw 13. Crosshead 16 has a die 17, and a cable core 18 formed by twisting together electric wires (conductors covered with an insulator) passing through crosshead 16 is covered with a sheath within crosshead 16, passes through die 17, and is drawn out from within crosshead 16 as cable 19 (cable 1).

[0074] The cable obtained in this way is, for example, a cable with the configuration shown in Figure 1, and in particular, in the case of a multi-core cable, it is possible to obtain a conductor cross-sectional area of ​​38 mm 2 as specified in the Electrical Appliance and Material Safety Law (Appendix 1) and JIS C3327. 2 Suitable for wires of the following sizes: [Example]

[0075] Next, the present embodiment will be described in detail with reference to examples and comparative examples.

[0076] [Example 1, Comparative Example 1] The following procedures were carried out: mixing the raw polymer with a silane coupling agent and various additives, silane grafting, preparation of a crosslinking catalyst masterbatch, and then manufacturing cables using the prepared compounds, followed by crosslinking. The following conditions are examples and are not intended to be limiting.

[0077] (Preparation of Resin Composition and Grafting Treatment) Chlorinated polyethylene, ethylene copolymer resin, silane coupling agent, organic peroxide, hydrogen chloride scavenger, plasticizer, lubricant, reinforcing agent, filler, flame retardant, etc. were added to a 25 L pressure kneader (kneader tank temperature controlled at 100°C) based on the formulation shown in Table 2, and the mixture was kneaded under pressure for 10 minutes at a rotor speed of 10 rpm.

[0078] Here, dissolving the organic peroxide in a silane coupling agent in advance improves the dispersibility of the organic peroxide in the polymer, and impregnating a filler such as a reinforcing agent with the silane coupling agent (dissolving the organic peroxide) before adding it reduces adsorption of the silane coupling agent to the kneader tank. Adding the ethylene copolymer resin at the end of the kneading process increases the viscosity of the material during additive kneading, improving the dispersibility of the additive. These conditions are merely examples and are not limiting.

[0079] Next, after the above kneading, the material is kneaded and heated to 180°C using the same equipment (a 25L pressure kneader with the kneader tank temperature controlled at 100°C) at a rotor rotation speed of 30 rpm. This operation can be carried out continuously without discharging the material after the above kneading. After reaching 180°C, the rotation speed is reduced and the material is kneaded isothermally for 3 minutes and 30 seconds to dynamically graft the silane coupling agent onto the polymer.

[0080] After grafting is complete, the material is quickly discharged into the hopper of a single-screw extruder, extruded into strands, water-cooled, and pelletized to produce pellets of the silane graft composition. The granulation method is not limited to the above, and for example, pellets may be produced using hot-cut equipment without water-cooling. A release agent can also be used to prevent the pellets from sticking together. The release agent can be of any composition and in any form, such as powder, liquid, or mist, but it is effective to use talc, for example, from an economical standpoint.

[0081] (Making masterbatch pellets) The masterbatch pellets (masterbatch serving as the crosslinking catalyst in Table 2) were prepared as follows, with the formulation shown in Table 3.

[0082] The polymer (a hydrogen chloride scavenger can also be used in the case of chlorine-based materials), antioxidant, silanol condensation catalyst, etc. are placed in the same 25 L pressure kneader (kneader tank temperature controlled at 100°C) as above, and pressure kneaded for 10 minutes at a rotation speed of 10 rpm. The kneaded material is discharged from the kneader tank, extruded into strands, cooled with water, and pelletized to produce masterbatch pellets as crosslinking catalysts. The polymer may be the same chlorinated polyethylene and ethylene copolymer resin as the main material, or other resin materials, and is not particularly limited. As with the silane grafting treatment described above, the kneaded material is granulated into pellets, and a release agent may be used to prevent adhesion between the pellets.

[0083] Here, the granulation method is not limited to the above, and for example, pellets may be produced using a hot cut facility without water cooling.

[0084] In this example and comparative example, cables were produced as follows using the extruder 11 shown in Figure 2. Table 1 shows the extrusion conditions for the cable extrusion process. At this time, cylinders 1 to 5 are connected in order from the hopper side to the head side from the top to form cylinder 20.

[0085] (Cable manufacturing and cross-linking) Conductor cross section of 38mm, consisting of multiple strands of tin-plated annealed copper wire 2 A conductor (outer diameter 9.1 mm) was extrusion-coated with an ethylene-propylene rubber copolymer composition as an insulator to a thickness of 1.2 mm, yielding a crosslinked wire core. Three of these wire cores were twisted together to form a cable core, which was then extrusion-coated to a thickness of 3.0 mm using a single-screw extruder with a screw diameter of 90 mm under the conditions listed in Table 1 (finished outer diameter: approximately 31 mm). The fabricated cable was then stored at 60°C in a saturated steam atmosphere for 24 hours for crosslinking.

[0086] To achieve the above-mentioned kneading and grafting treatment, any commonly used kneading or reaction device such as a roll mill, extruder, mixer, or autoclave may be used other than a kneader, and the kneading and grafting conditions are not limited to those described above. Similarly, cable production is also an example, and the extruder, cable core, cable structure, and crosslinking conditions are not limited to those described above.

[0087] [Table 1]

[0088] [Characteristics evaluation] The prepared compound after kneading and the cable after crosslinking treatment were evaluated as follows. The evaluation results are shown in Table 2 together with the composition.

[0089] (1) Difference in Mooney viscosity before and after silane grafting The Mooney viscosities of the rubber composition before silane grafting and the silane-grafted rubber composition were measured using a Mooney viscometer. If water is released from the hydrotalcite during silane grafting, the water causes premature crosslinking, reducing the fluidity of the rubber composition and increasing the Mooney viscosity. Therefore, the Mooney viscosity of the rubber composition before silane grafting was used as the reference, and the difference between this and the Mooney viscosity of the silane-grafted rubber composition was evaluated as an indicator of premature crosslinking in the silane-grafted rubber composition. Measurements were performed using an L-shaped rotor at a rotation speed of 2 rpm, a preheating time of 1 minute, a test time of 4 minutes, and a heating temperature of 130°C. A Mooney viscosity difference of less than 10 was considered good (marked ○ in Table 2), and a Mooney viscosity difference of 10 or more was considered bad (marked × in Table 2).

[0090] (2) Appearance The appearance of the silane graft composition was visually observed, and those with a good appearance were rated as good (marked as ◯ in Table 2), and those with lumps or roughness were rated as poor (marked as x in Table 2).

[0091] (3) Overall Judgment In the characteristics shown in (1) to (2) above, if all the characteristics were good, it was marked as pass (marked as ○ in Table 2), and if any one of the characteristics was bad, it was marked as fail (marked as × in Table 2).

[0092] [Table 2]

[0093] Of the products shown in Table 2, *1: "Elaslen 252B" is manufactured by Showa Denko K.K., *2: "VF-120T" is manufactured by Ube Maruzen Polyethylene Co., Ltd., *3: "KBM-503" (3-methacryloxypropyltrimethoxysilane) is manufactured by Shin-Etsu Chemical Co., Ltd., *4: "DCP" (dicumyl peroxide) is manufactured by NOF Corporation, *5: "Magcera 1" (hydrotalcite; mass loss rate 12.3%) is manufactured by Kyowa Chemical Industry Co., Ltd., *6: "HT-9" (hydrotalcite (calcined treatment); mass loss rate 1.1%) is manufactured by Sakai Chemical Industry Co., Ltd., and *7: "Carbon black" (arithmetic mean particle size: 68 nm) is manufactured by Nippon Steel Carbon Co., Ltd. In addition, the "master batch" in each example is a mixture having the composition shown in Table 3 below.

[0094] Here, the mass loss rate of hydrotalcite is the difference between the mass loss rate at 150°C and the mass loss rate at 210°C when heated from room temperature (25°C) to 500°C at a rate of 3°C per minute in a nitrogen atmosphere using a thermogravimetric analyzer (TG-8121 manufactured by Rigaku Corporation) (corresponding to the mass loss due to dehydration from between the hydrotalcite layers).

[0095] [Table 3]

[0096] From the above results, it was found that the use of calcined hydrotalcite reduces the difference in Mooney viscosity before and after the silane graft reaction, i.e., reduces premature crosslinking, and improves the appearance.

[0097] The invention made by the present inventors has been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited to the above embodiments and can be modified in various ways without departing from the spirit of the invention. [Explanation of symbols]

[0098] 1, 19 Cable 2 conductors 3. Insulation layer 4 Covering layer 11 Extruder 12 Hopper 13 Screw 14 Breaker plate 15 neck 16 Crosshead 17 Dice 18 cable cores 20 cylinders

Claims

1. A silane-graft rubber composition comprising a base polymer in which a chlorinated polyethylene graft-copolymerized with a silane coupling agent and an ethylene copolymer resin graft-copolymerized with a silane coupling agent are mixed, and a hydrogen chloride scavenger containing calcined hydrotalcite, The hydrotalcite has a mass loss rate, which is the mass difference between the mass loss rate at 150°C and the mass loss rate at 210°C, of ​​5% or less when heated from 25°C to 500°C at a rate of 3°C per minute in a nitrogen atmosphere using a thermogravimetric measuring device. Silane-grafted rubber composition.

2. The silane-grafted rubber composition according to claim 1, The silane-grafted rubber composition, wherein the ethylene copolymer resin is an ethylene-vinyl acetate copolymer resin or an ethylene-ethyl acrylate copolymer resin.

3. The silane-grafted rubber composition according to claim 1 or 2, The silane-grafted rubber composition, wherein the silane coupling agent contains a methacrylic group as an organic functional group.

4. The silane-grafted rubber composition according to any one of claims 1 to 3, The silane-grafted rubber composition further comprises a masterbatch containing a silanol condensation catalyst containing an octyltin compound.

5. A silane-crosslinked rubber composition which is a silane-crosslinked product of the silane-grafted rubber composition according to any one of claims 1 to 4.

6. The silane-crosslinked rubber composition according to claim 5, The silane-crosslinked rubber composition, wherein the ethylene copolymer resin is an ethylene-vinyl acetate copolymer resin or an ethylene-ethyl acrylate copolymer resin.

7. The silane-crosslinked rubber composition according to claim 5 or 6, The silane-crosslinked rubber composition, wherein the silane coupling agent contains a methacryl group as an organic functional group.

8. The silane-crosslinked rubber composition according to any one of claims 5 to 7, The silane-grafted rubber composition further comprises a masterbatch containing a silanol condensation catalyst containing an octyltin compound.

9. A conductor and a covering layer that covers and protects the conductor, An electric wire or cable, wherein the coating layer is made of the silane-crosslinked rubber composition according to any one of claims 5 to 8.

10. a step of obtaining a silane-graft rubber composition comprising a base polymer in which a chlorinated polyethylene graft-copolymerized with a silane coupling agent and an ethylene copolymer resin graft-copolymerized with a silane coupling agent are mixed, and a hydrogen chloride scavenger containing calcined hydrotalcite; a step of adding a silanol condensation catalyst to the silane-grafted rubber composition, and then silane-crosslinking the composition by the action of moisture to obtain a silane-crosslinked rubber composition; A method for producing a silane-crosslinked rubber composition comprising: The hydrotalcite has a mass loss rate, which is the mass difference between the mass loss rate at 150°C and the mass loss rate at 210°C, of ​​5% or less when heated from 25°C to 500°C at a rate of 3°C per minute in a nitrogen atmosphere using a thermogravimetric measuring device. A method for producing a silane-crosslinked rubber composition.

11. The method for producing a silane-crosslinked rubber composition according to claim 10, The method for producing a silane-crosslinked rubber composition, wherein the silanol condensation catalyst is an octyl tin compound, and is added to the silane-grafted rubber composition in a state where the silanol condensation catalyst is mixed with a polymer as a masterbatch.

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