Method for producing a silane crosslinked rubber composition

Abstract

This invention provides a method for manufacturing a chlorinated polyethylene, a base polymer component used in coating materials, that utilizes a silane crosslinking method while possessing high durability that satisfies abrasion resistance under harsh test conditions and also exhibits good flexibility. [Solution] A method for producing a silane crosslinked rubber composition, comprising the steps of: obtaining a silane graft rubber composition by grafting a base polymer, in which chlorinated polyethylene and an ethylene copolymer resin are mixed in a mass ratio of 90:10 to 50:50, with a silane coupling agent; and obtaining a silane crosslinked rubber composition by mixing the silane graft rubber composition with a masterbatch having a silanol condensation catalyst in a mass ratio of 160.9:3 and crosslinking the silane by the action of water, wherein the heat of fusion of the silane crosslinked rubber composition, as determined by differential scanning calorimetry (DSC), is in the range of 5 J / g to 20 J / g.

Description

Technical Field

[0001] The present invention relates to a method for producing a silane-crosslinked rubber composition obtained by subjecting a silane-grafted rubber composition to silane crosslinking.

Background Art

[0002] In the case of coating materials for electric wires and cables, in order to improve various properties including heat resistance, crosslinking treatment for chemically bonding between polymer molecules of the coating material is often performed. The crosslinking treatment includes a method in which a crosslinking agent is previously blended in the coating material and energy such as heat or electron beam is applied after cable coating, but both methods require large-scale equipment and a great deal of energy.

[0003] On the other hand, the silane crosslinking method involves previously bonding a silane coupling agent to polymer molecules of the coating material, and after cable coating, the silane groups introduced by the action of moisture and a silanol condensation catalyst are bonded to each other to form crosslinking between polymer molecules. Therefore, it is a manufacturing method excellent in economy and environmental friendliness that does not require large-scale equipment and a great deal of energy.

[0004] In applications where flexibility and durability are required, rubber materials are mainly used as coating materials, and the manufacture of electric wires and cables by the above silane crosslinking method is also carried out. Although rubber materials used for electric wire and cable coating materials are diverse, among them, chlorinated rubber is known as a high-functional material excellent in flame retardancy and oil resistance (for example, see Patent Document 1).

[0005] We have been promoting the development of silane crosslinking technology using highly economical chlorinated polyethylene in chlorinated rubber and have created various inventions so far.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] However, unlike other crosslinking methods that control the degree of crosslinking of polymers by the amount of crosslinking agent or electron beam irradiation dose, the silane crosslinking method typically results in a relatively low degree of crosslinking because the degree of crosslinking is determined by the amount of silane groups grafted onto the polymer molecule.

[0008] In the silane crosslinking method, radicals generated when organic peroxides are thermally decomposed are used to extract hydrogen from polymer molecules, thereby grafting the silane coupling agent. Therefore, to obtain a high degree of crosslinking, it is effective to increase not only the silane coupling agent but also the amount of organic peroxide.

[0009] However, if the amount of organic peroxide is increased excessively, the amount of radicals generated in the polymer molecules increases, which promotes the bonding of polymer molecules (premature crosslinking), a side reaction. This reduces fluidity when coating wires and cables, making molding defects more likely.

[0010] As a result, while the silane crosslinking method can provide sufficient crosslinking to the covering material for many of the properties required for the functionality of electric wires and cables (such as heat resistance and oil resistance), it is unsuitable for types that require particularly high durability (such as abrasion resistance under harsh conditions), and it has been difficult to achieve sufficient performance in such applications.

[0011] The object of the present invention is to provide a method for producing a chlorinated polyethylene, which is a component of the base polymer used in the covering material of electric wires and cables, that has high durability performance that satisfies abrasion resistance under harsh test conditions, and also has good flexibility, while utilizing a silane crosslinking method. Other purposes and novel features will become apparent from the description and accompanying drawings herein. [Means for solving the problem]

[0012] A brief overview of some of the representative embodiments disclosed in this application is as follows:

[0013] The present invention provides a method for producing a silane crosslinked rubber composition, comprising the steps of: obtaining a silane graft rubber composition by grafting a base polymer, in which chlorinated polyethylene and an ethylene copolymer resin are mixed in a mass ratio of 90:10 to 50:50, with a silane coupling agent; and obtaining a silane crosslinked rubber composition by mixing the silane graft rubber composition with a masterbatch having a silanol condensation catalyst in a mass ratio of 160.9:3 and crosslinking with silane by the action of water, wherein the heat of fusion of the silane crosslinked rubber composition, as determined by differential scanning calorimetry (DSC), is in the range of 5 J / g to 20 J / g.

[0014] In the method for producing the silane crosslinked rubber composition of the present invention, it is preferable that the silanol condensation catalyst is an octyl tin compound.

[0015] In the method for producing the silane crosslinked rubber composition of the present invention, it is preferable that the ethylene-based copolymer resin is an ethylene vinyl acetate copolymer resin or an ethylene ethyl acrylate copolymer resin. [Effects of the Invention]

[0016] By using the present invention, it is possible to provide a method for producing a silane-crosslinked rubber composition that satisfies abrasion resistance under harsh conditions and has good flexibility and processability, while using silane crosslinking, which is an energy-saving and economical crosslinking method for electric wires and cables. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic cross-sectional view of a cable, which is one embodiment of the present invention. [Figure 2] This diagram shows the schematic configuration of the extruder used in the example to carry out the cable manufacturing (extrusion) process. [Modes for carrying out the invention]

[0018] Hereinafter, embodiments will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, members having the same function are denoted by the same reference numerals, and repeated descriptions thereof are omitted. Further, in the following embodiments, descriptions of the same or similar parts are not repeated in principle unless particularly necessary.

[0019] <Background of the inventors' study> Examples of general-purpose cables coated with rubber materials include cab tire cables. Cab tire cables are roughly classified into fixed and movable types according to their usage. Among these, in the movable type, since the cable itself moves, requirements such as flex resistance to repeated bending and wear resistance to rubbing in various environments are required.

[0020] Particularly for wear resistance, test conditions are set according to the size of the cable. In the Electrical Appliance Safety Act (Appendix 1) and JIS C3327, for a conductor cross-sectional area of 38 mm 2 In the following multi-core cables, conditions of a weight of 5 kg and a rotation speed of 750 revolutions are defined as the most severe conditions. In order to improve the wear resistance of the silane-crosslinked chlorinated polyethylene material so as to be able to cope with such severe test conditions, the following methods were considered.

[0021] The first method is an increase in the degree of crosslinking. However, as described above, if an excessive amount of organic peroxide is added to increase the silane to be grafted, crosslinking between polymers will proceed, which may cause defects such as rough appearance and tubbing during cable molding. Although it may be possible to suppress crosslinking between polymers to some extent by increasing the amount of silane added together with the organic peroxide, it cannot be said to be a practical countermeasure method due to a decrease in tensile strength, wear resistance, electrical insulation, and an increase in material cost due to softening of the material.

[0022] The second method is the application of chlorinated polyethylene having a high molecular weight. By increasing the molecular chain length, it is considered that the entanglement between molecules increases and the abrasion resistance is improved. When considering its application to silane cross-linked materials, although the abrasion resistance was improved, it was found that shear heat generation occurred due to an increase in the viscosity of the coating material, making early cross-linking, which is a side reaction, likely to occur, and a high load was applied during cable coating with an extruder, making molding difficult. As a countermeasure, reducing the material viscosity by extrusion at a high temperature can be mentioned, but since chlorinated materials such as chlorinated polyethylene may cause significant deterioration due to the desorption of chlorine (as hydrogen chloride) in a high-temperature environment, it is not practical.

[0023] The third method is the application of chlorinated polyethylene having a high crystallinity. Chlorinated polyethylene is mainly manufactured using high-density polyethylene as a raw material, and various grades that retain crystals derived from high-density polyethylene have also been produced. By introducing crystals into the material, at temperatures below the crystal melting point, some molecules take on a strong crystal structure, and an improvement in abrasion resistance is expected. As a result of considering its application to silane cross-linked materials, the abrasion resistance was improved.

[0024] However, it was revealed that when the base polymer is only chlorinated polyethylene, the material viscosity increases, resulting in a large load during material kneading and cable extrusion coating.

[0025] Therefore, in order to improve the processability, it was considered to alloy an ethylene-based copolymer resin that exhibits high compatibility with chlorinated polyethylene and has higher heat fluidity than chlorinated polyethylene, and graft a silane coupling agent onto this alloy material. The ethylene-based copolymer resin also has crystals in its structure, and the amount of crystals is gently correlated with the melting point of the resin. As a result of extensive studies, by appropriately controlling the amount of crystals that strongly affect the abrasion resistance in chlorinated polyethylene and the melting point in the ethylene-based copolymer resin, while also controlling the mixing ratio of the two materials and the amount of crystals in the entire cross-linked rubber composition, conditions were found that can achieve both abrasion resistance under severe test conditions and good processability during material kneading and cable extrusion coating. <Silane crosslinked rubber composition>

[0026] The silane crosslinked rubber composition in this embodiment is characterized by limiting the total amount of crystals in the silane crosslinked rubber composition while controlling the mixing ratio of the composition within an appropriate range, in order to achieve both abrasion resistance and good processability when extruding and coating cables.

[0027] This silane crosslinked rubber composition is obtained by crosslinking a silane graft rubber composition, and the silane graft composition will be described below.

[0028] [Silane graft rubber composition] The silane graft rubber composition used here is a resin composition that has been grafted by grafting a silane coupling agent onto a resin composition containing the base polymer described below.

[0029] (Base polymer) The base polymer of this silane graft rubber composition comprises chlorinated polyethylene and an ethylene copolymer resin, and is characterized by the fact that these components are mixed in a predetermined ratio before use.

[0030] The chlorinated polyethylene used here can be any known chlorinated polyethylene, and is not limited by its physical properties. From the viewpoint of improving abrasion resistance, it is preferable to use crystalline grade chlorinated polyethylene. Specifically, as a chlorinated polyethylene having a crystal content that is generally considered to be of crystalline grade, chlorinated polyethylene with a DSC heat of fusion of 2 J / g to 80 J / g is useful. The DSC heat of fusion of chlorinated polyethylene is preferably 5 J / g to 30 J / g, and more preferably 10 J / g to 20 J / g, considering the balance between abrasion resistance and flexibility.

[0031] In this specification, the DSC heat of fusion is measured by differential scanning calorimetry (DSC) and is defined by the heat of fusion of the crystals contained in the resin. The melting of chlorinated polyethylene crystals occurs at approximately 100-130°C. The measurement is performed using an aluminum pan under the conditions of a heating rate of 10°C / min, a cooling rate of 5°C / min, an upper temperature limit of 150°C, and a lower temperature limit of 25°C. To eliminate the influence of thermal history, the heat of fusion value from the second heating was used. The amount of crystals in the resin can be evaluated from this heat of fusion. Therefore, below, this heat of fusion may also be described as the numerical value of the amount of crystals.

[0032] Furthermore, chlorinated polyethylene is preferably chlorinated to have a chlorine content of 20-45% by mass and a Mooney viscosity of 120 or less. In terms of balancing flame retardancy and flexibility, it is more preferable to have a chlorine content of 25-40% by mass and a Mooney viscosity of 90 or less.

[0033] The ethylene copolymer resin used here may be any known ethylene copolymer resin, such as ethylene vinyl acetate copolymer resin, ethylene methyl acrylate copolymer resin, ethylene ethyl acrylate copolymer resin, ethylene propylene copolymer, ethylene propylene diene copolymer, modified versions thereof, or mixtures thereof.

[0034] Among these, it is preferable to use ethylene vinyl acetate copolymer resin, ethylene ethyl acrylate copolymer resin, etc., in order to maintain a balance between abrasion resistance, flexibility, and good moldability when extruding and covering cables.

[0035] Furthermore, examples of ethylene-based copolymer resins include those with a melting point of 70°C or higher. From the viewpoint of the amount of crystals in the resin, ethylene-based copolymer resins with a melting point of 80°C or higher are preferred, and those with a melting point of 85°C or higher are even more preferred.

[0036] Multiple types of ethylene-based copolymer resins with a melting point of 80°C or higher may be used in combination, and in the region where the properties are expressed, ethylene-based copolymer resins with a melting point of 80°C or higher may be mixed with ethylene-based copolymer resins with a melting point of 80°C or lower. Examples of such ethylene-based copolymer resins include ethylene α-olefin copolymers, specifically ethylene butene copolymers.

[0037] While there are no limitations on the physical properties of the ethylene copolymer resin, for example, a melt mass flow rate (MFR) of 6 g / 10 min or less is preferred, and 1 g / 10 min or less is more preferred from the viewpoint of improving abrasion resistance.

[0038] The chlorinated polyethylene and ethylene copolymer resin used as 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 with a good balance of abrasion resistance, processability, and flexibility. A mass ratio of 80:20 to 60:40 is preferred, and a ratio around 70:30 is particularly preferred as it provides excellent properties in all aspects of abrasion resistance, processability, and flexibility.

[0039] (Silane coupling agent) The silane coupling agent used here is a compound that imparts silane crosslinking properties to the resin constituting the base polymer by grafting.

[0040] Any silane coupling agent can be used that has an organic functional group that exhibits addition reactions to radicals and an alkoxy group. For example, general-purpose silane coupling agents that have both organic functional groups such as vinyl groups, methacrylic groups, acrylic groups, and styryl groups and alkoxy groups such as methoxy groups and ethoxy groups can be used.

[0041] Examples of silane coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-acryloxypropyltrimethoxysilane, p-styryltrimethoxysilane, and mixtures thereof. However, any alkoxy oligomer possessing both the aforementioned organic functional group and alkoxy group is acceptable, and the invention is not limited to the compounds exemplified above.

[0042] In particular, among silane coupling agents having an unsaturated bond in the molecule that reacts with radicals, it is preferable to use a methacrylic group-containing silane coupling agent from the viewpoint of having a relatively high flash point and excellent fire safety when kneaded into a polymer. More specifically, examples include 3-methacryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane.

[0043] The amount of silane coupling agent added is preferably 0.1 to 20 parts by mass, and more preferably 1 to 10 parts by mass, per 100 parts by mass of the base polymer. By keeping the content within this range, it is possible to obtain a silane graft rubber composition in which a sufficient amount of silane coupling agent is bonded to the base polymer, thereby having excellent mechanical properties and abrasion resistance in the silane crosslinked rubber composition, while suppressing side reactions during the silane graft reaction.

[0044] (Additives) This silane graft rubber composition can further be mixed with additives such as organic peroxides for grafting silanes, hydrogen chloride scavengers to efficiently capture hydrogen chloride that may be generated from chlorinated polyethylene, as well as plasticizers, lubricants, reinforcing agents, fillers, and flame retardants.

[0045] Examples of organic peroxides that can be used include 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, and t-butylperoxy-2-ethylhexyl carbonate. These can be used individually or in combination of two or more.

[0046] The amount of peroxide added is preferably 0.01 to 1 part by mass, and more preferably 0.1 to 0.5 parts by mass, per 100 parts by mass of the base polymer. By keeping the content within this range, a sufficient amount of silane coupling agent can be introduced into the base polymer to obtain excellent mechanical properties and wear resistance in the silane crosslinked rubber composition while suppressing side reactions during the silane graft reaction.

[0047] Examples of hydrogen chloride scavenging agents include epoxy group-containing compounds, hydrotalcites, lead-containing compounds such as tribasic lead sulfate, tin-containing compounds, and metal soaps.

[0048] Examples of plasticizers include phthalates such as bis(2-ethylhexyl) phthalate, diisononyl phthalate, diisodecyl phthalate, and diundecyl phthalate; adipic acids such as bis(2-ethylhexyl) adipate, diisononyl adipate, diisodecyl adipate, and bis(2-butoxyethyl) adipate; polyesters; phosphoric acids; epoxys; and trimellitic acids. These can be used individually 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 dioxide, magnesium carbonate, dolomite, and aluminum oxide.

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

[0052] Furthermore, by adding antioxidants or silanol condensation catalysts to the above-mentioned silane graft rubber composition, heat resistance can be improved and the crosslinking reaction can be accelerated. However, since these can inhibit the silane graft reaction or cause molding defects, it is preferable to mix them with the silane graft rubber composition during the final molding stage (extrusion coating onto conductors or cable cores in the case of electric wires and cables).

[0053] Examples of silanol condensation catalysts include Group II elements such as magnesium and calcium, Group VIII elements such as cobalt and iron, or elements and metal compounds such as tin, zinc, and titanium, as well as metal salts of octic acid or adipic acid, amine compounds, and acids.

[0054] More specifically, silanol condensation catalysts include dioctyltin dineodecanoate, dibutyltin dilaurylate, 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, and organic acids such as toluenesulfonic acid, acetic acid, stearic acid and maleic acid.

[0055] In particular, it is preferable to use an octyl tin compound that has high catalytic activity and does not contain dibutyltin, which is considered to have a relatively large environmental impact. Specific examples of octyl tin compounds include dioctyl tin dineodecanoate and dioctyl tin dilaurate.

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

[0057] The amount of silanol condensation catalyst added is preferably 0.01 to 1 part by mass, and more preferably 0.02 to 0.4 parts by mass, per 100 parts by mass of the base polymer. By keeping the content within this range, the crosslinking reaction described later can be efficiently promoted. [Silane crosslinked rubber composition]

[0058] The silane-grafted rubber composition obtained as described above can be further converted into a silane-crosslinked rubber composition by crosslinking the grafted base polymer with a silane coupling agent. Silane crosslinking can be formed by reacting the alkoxy groups of the silane coupling agent introduced into the base polymer with a silanol condensation catalyst and water in the presence of water, thereby crosslinking the polymer molecules.

[0059] Furthermore, it is preferable that the heat of fusion of the obtained silane crosslinked rubber composition, as determined by differential scanning calorimetry (DSC), be in the range of 5 J / g to 20 J / g. By achieving this crystal content, a silane crosslinked rubber composition with excellent abrasion resistance can be obtained. The heat of fusion at this time is the sum of the peaks from approximately 60 to 100°C derived from the ethylene copolymer resin and the peaks from approximately 100 to 130°C derived from the chlorinated polyethylene. The measurement is performed using an aluminum pan under the conditions of a heating rate of 10°C / min, a cooling rate of 5°C / min, an upper temperature limit of 150°C, and a lower temperature limit of 25°C. To eliminate the influence of thermal history, the heat of fusion value from the second heating is used.

[0060] [Method for producing silane crosslinked rubber composition] A silane graft rubber composition can be obtained by grafting a silane coupling agent onto a base polymer in a resin composition containing the raw material components described above for the silane graft rubber composition.

[0061] This grafting process can be carried out, for example, by kneading a resin composition containing a base polymer comprising chlorinated polyethylene and an ethylene copolymer resin, a silane coupling agent for imparting silane crosslinkability to the base polymer, and a peroxide at a temperature above the melting point of the base polymer and below the decomposition temperature of the peroxide, and then heating the mixture to a temperature above the decomposition temperature of the peroxide to introduce the silane coupling agent into the base polymer by a graft reaction.

[0062] When producing a silane crosslinkable resin composition by the grafting process described above, the base polymer is first melted, and the silane coupling agent and peroxide are kneaded in advance at a temperature below the peroxide decomposition temperature. Subsequently, the mixture is heated and kneaded above the peroxide decomposition temperature to graft the silane coupling agent onto the base polymer, thereby avoiding the application of excessive heat to the resin composition during and after the grafting process.

[0063] Here, the decomposition temperature of the peroxide is defined as a temperature 30°C lower than the 1-minute half-life temperature of the peroxide. In other words, by keeping the temperature below the decomposition temperature of the peroxide during mixing, the components are thoroughly mixed at a temperature at which thermal decomposition of the peroxide is unlikely to occur. Subsequently, in order to carry out the graft reaction, the mixture is heated above the decomposition temperature of the peroxide, allowing the peroxide to decompose and the base polymer to be efficiently grafted.

[0064] In this case, the grafting temperature is preferably at or above the 1-minute half-life temperature of the peroxide. Furthermore, the grafting time is preferably at least 3 times the time it takes for the peroxide to be halved at the grafting temperature (the half-life of the peroxide), more preferably at least 4 times, even more preferably at least 5 times, and particularly preferably at least 6 times.

[0065] In parallel with this, a masterbatch pellet is prepared. This masterbatch pellet is not particularly limited as long as it is a polymer material that does not cause any problems in this embodiment when mixed with the silane graft resin composition described above. This polymer material may have the same components as the base polymer described above, or it may have different components.

[0066] 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 may be used, and there are no particular limitations. In addition, a release agent may be used to prevent the pellets from sticking together.

[0067] As described above, the silane graft rubber composition pellets and masterbatch pellets are fed into an extruder and kneaded together. The silanol condensation catalyst contained in the masterbatch pellets causes the silane graft rubber composition to crosslink with each other, resulting in a silane-crosslinked rubber composition.

[0068] As described above, by specifying the formulation of the resin composition, a silane crosslinked rubber composition having suitable properties for flame retardancy and electrical insulation, which are required for use as a coating material for electric wires and cables, can be obtained.

[0069] [Electric wires and cables] The electric wire / cable in this embodiment comprises a conductor and a covering layer that covers and protects the conductor, wherein the covering layer is made of the silane crosslinked rubber composition of this embodiment described above. The covering layer can be used to directly cover the conductor to form an electric wire, or it can be used to indirectly cover the conductor and the insulating layer covering the conductor to form a cable.

[0070] Figure 1 shows a cross-sectional view of a cable according to one embodiment of the present invention. As shown in Figure 1, the cable 1 is composed of a conductor 2, an insulating layer 3, and a covering layer 4.

[0071] The conductor 2 can be any commonly used metal wire, such as copper wire, copper alloy wire, aluminum wire, gold wire, or silver wire. Alternatively, the conductor 2 may be a metal wire with a metal plating such as nickel applied to its circumference. Furthermore, the conductor 2 can also be a stranded conductor made by twisting together metal wires.

[0072] The insulating layer 3 can be formed from an insulating material commonly used in cables, and is not particularly limited. Examples of insulating materials for this insulating layer 3 include ethylene-propylene copolymer mixtures, 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 this embodiment above.

[0073] As a method for manufacturing this cable, the cable 1 can be produced by using an extruder to coat the outer circumference of the insulating layer 3 formed on the conductor 2 with the silane graft rubber composition described above. More specifically, in the extrusion coating process, a so-called two-shot silane crosslinking method can be used, in which a silane graft rubber composition in which a silane compound has been grafted is mixed with a resin composition containing a silane condensation catalyst. After the extrusion coating process, the silane crosslinking reaction is carried out by natural storage or by supplying moisture to the coating material in a steam chamber at 100°C or below, and the final product is obtained.

[0074] Figure 2 is a schematic diagram showing an example of an extruder for manufacturing cables in this embodiment. As shown in Figure 2, the extruder 11 comprises a cylinder 20, a screw 13 rotatably mounted within the cylinder 20, a hopper 12 for supplying material into the cylinder 20, and a crosshead 16. The extruder 11 also comprises a neck 15 between the crosshead 16 and the screw 13, and a breaker plate 14 between the neck 15 and the screw 13. The crosshead 16 has a die 17, and a cable core 18, made by twisting together electric wires (conductors covered with an insulator) that pass through the crosshead 16, is covered with a sheath within the crosshead 16, passes through the die 17 and is drawn out from inside the crosshead 16 as a cable 19 (cable 1).

[0075] The cable obtained in this way is, for example, a cable with the configuration shown in Figure 1, and in particular, a multi-core cable with a conductor cross-sectional area of ​​38 mm² as specified in the Electrical Appliances and Materials Safety Act (Appendix 1) and JIS C3327. 2 This is suitable for those with wires of the following sizes. [Examples]

[0076] Next, this embodiment will be described in detail with reference to examples and comparative examples.

[0077] [Examples 1-8, Comparative Examples 1-5] The following procedures were carried out: mixing of silane coupling agents and various additives with the base polymer, silane grafting, preparation of a crosslinking catalyst masterbatch, and further manufacturing of cables using the prepared compounds, followed by crosslinking. The following conditions are examples only and are not limiting.

[0078] (Preparation of resin composition and grafting) In a 25L pressurized kneader (kneader tank temperature controlled to 100°C), chlorinated polyethylene, ethylene copolymer resin, silane coupling agent, organic peroxide, hydrogen chloride scavenger, plasticizer, lubricant, reinforcing agent, filler, flame retardant, etc., are added according to the formulations shown in Tables 2-3, and the mixture is pressurized and kneaded for 10 minutes at a rotor speed of 10 rpm.

[0079] Here, pre-dissolving the organic peroxide in a silane coupling agent improves its dispersibility in the polymer, and impregnating fillers such as reinforcing agents with the silane coupling agent (which dissolves the organic peroxide) at the time of addition reduces the adsorption of the silane coupling agent into the kneader tank. Furthermore, adding ethylene-based copolymer resins such as ethylene vinyl acetate copolymer at the end of the kneading process increases the material viscosity during additive mixing, thereby improving the dispersibility of the additives. Note that these conditions are examples only and are not limited to these methods.

[0080] Next, after the above mixing, the material is kneaded and heated using the same apparatus (a 25L pressurized kneader with the kneader tank temperature controlled to 100°C) at a rotor speed of 30 rpm until the material temperature reaches 180°C. This operation can be performed continuously without discharging the material after the above mixing. After reaching 180°C, the rotation speed is reduced and isothermal kneading is performed for 3 minutes and 30 seconds to dynamically graft the silane coupling agent onto the polymer.

[0081] After grafting is complete, the material is promptly discharged into a single-screw extruder hopper, extruded into strands, water-cooled, and then pelletized to produce pellets of the silane graft composition. Here, the granulation method is not limited to the above; for example, pellets may be produced using a hot-cutting device without water cooling. In addition, a release agent can be used to prevent the pellets from sticking together. The release agent can be of any form, such as powder, liquid, or mist, but for economic reasons, using talc, for example, is effective.

[0082] (Preparation of masterbatch pellets) In a 25L pressurized kneader (kneader tank temperature controlled to 100°C) with the same capacity as above, polymer (a hydrogen chloride scavenger can also be used in the case of chlorine-based materials), antioxidant, silanol condensation catalyst, etc. are added, and pressurized kneading is performed at a rotation speed of 10 rpm for 10 minutes. The polymer may be the same chlorinated polyethylene and ethylene copolymer resin as the main material, or other resin materials may be used, and there are no particular limitations. Similar to the silane graft treatment described above, the material after kneading is granulated into pellet shape, and a release agent may be used to prevent the pellets from sticking together.

[0083] The masterbatch pellets (the crosslinking catalyst in Tables 2-3) were prepared using the formulation shown in Table 4, as follows.

[0084] A polymer, a crosslinking catalyst (silanol condensation catalyst), a hydrogen chloride scavenger, and an antioxidant were kneaded in a 25L pressurized kneader (kneader tank temperature above the melting point of the base polymer) at a rotor speed of 20 rpm for 5 minutes. After kneading, the material was discharged from the kneader tank, extruded into strands, water-cooled, and then pelletized to produce a masterbatch pellet as a crosslinking catalyst.

[0085] Here, the granulation method is not limited to the above; for example, pellets may be produced using a hot-cutting device without water cooling. Furthermore, a release agent can be used to prevent the pellets from sticking together.

[0086] In this embodiment and comparative example, the extruder 11 shown in Figure 2 was used to manufacture the cables as follows. Table 1 shows the extrusion conditions in the cable extrusion process. At this time, cylinders 1 to 5 are connected from the hopper side to the head side in order from top to bottom, forming cylinder 20.

[0087] (Cable manufacturing and cross-linking process) Multiple strands of tinned soft copper wire are twisted together to form a conductor with a cross-sectional area of ​​38 mm². 2A wire core was obtained by extruding a 1.2 mm thick ethylene-propylene rubber copolymer mixture as an insulator onto a conductor (outer diameter 9.1 mm) and crosslinking it. Three of these wire cores were twisted together to form a cable core, and a dry blend of the silane graft rubber compositions and masterbatch pellets from each of the above examples was extruded to a thickness of 3.0 mm using a single-screw extruder with a screw diameter of 90 mm under the conditions described in Table 1 to produce a cable (finished outer diameter approximately 31 mm). The fabricated cable was subjected to a crosslinking treatment by storing it at 60°C in a saturated water vapor atmosphere for 24 hours.

[0088] To achieve the above-mentioned kneading and grafting processes, any commonly used kneading or reaction equipment such as roll presses, extruders, mixers, or autoclaves can be used, not just kneaders, and the kneading and grafting conditions are not limited to those described above. Similarly, cable manufacturing is just one example, and the extruder, cable core, cable structure, and crosslinking conditions are not limited to those described above.

[0089] [Table 1]

[0090] [Evaluation of characteristics] The compound after mixing and the cable after cross-linking were evaluated as follows. The evaluation results, along with the composition, are shown in Tables 2 and 3.

[0091] (1) Crystal quantity Differential scanning calorimetry (DSC) was performed to measure the heat of fusion in the silane crosslinked rubber composition. Peaks around 100-130°C were attributed to chlorinated polyethylene, and peaks around 60-100°C were attributed to ethylene copolymer resin. The heat of fusion values ​​at each peak were summed and evaluated as the amount of crystals. Measurements were performed using an aluminum pan under the conditions of a heating rate of 10°C / min, a cooling rate of 5°C / min, an upper temperature limit of 150°C, and a lower temperature limit of 25°C. To eliminate the influence of thermal history, the heat of fusion value from the second heating cycle was used.

[0092] (2) Wear characteristics (wear resistance) The test was conducted in accordance with JIS C3005 using cross-linked cables. The weight was 5 kg, and the grinding disc rotated at 750 rpm. Cables that did not expose the insulation after the test were classified as good (marked ○ or ◎), and those that did expose the insulation were classified as poor (marked ×). For cables that did not expose the insulation, the depth of the worn area was calculated using a micrometer with the following formula, and those with a depth of less than 2.5 mm were judged to have particularly excellent wear resistance (marked ◎). • Wear depth = Cable outer diameter before testing - Cable thickness at the worn portion after testing

[0093] (3) Mooney viscosity (heat fluidity and processability) The Mooney viscosity (value after 1 minute preheating and 4 minutes elapsed) was measured at 130°C using the composition after silane grafting. Lower Mooney viscosity indicates lower load during cable extrusion and better processability. In actual production, lower viscosity allows for larger discharge volumes and higher cable extrusion speeds. Furthermore, at high-speed extrusion, residual extrusion strain is less likely to remain, and thermal shrinkage after cable laying can be suppressed, among other advantages. A Mooney viscosity of less than 65 was classified as good (symbolized as ○ or ◎), and a viscosity of 65 or higher was classified as poor (symbolized as ×). Additionally, a Mooney viscosity of less than 60 was judged to have particularly excellent processability (symbolized as ◎).

[0094] (4) Modulus (flexibility) The test was conducted in accordance with JIS C3005 using cross-linked cables. Dumbbell-shaped test pieces punched out with a JIS No. 3 die were pulled at a speed of 200 mm / min, and the tensile strength at 100% elongation was measured. Higher flexibility is advantageous for the practical handling of wires and cables. Normally, as the amount of crystals increases, the rubber composition becomes harder, raising concerns about a decrease in flexibility. Therefore, flexibility was confirmed using the 100% modulus value. A 100% modulus of less than 9 MPa was considered good (symbolized as ○ or ◎), and a value of 9 MPa or higher was considered poor (symbolized as ×). Furthermore, a 100% modulus of less than 8 MPa was judged to have particularly excellent flexibility (symbolized as ◎).

[0095] (5) Overall Judgment In the characteristics shown in (2) to (4) above, those with all characteristics in good condition were marked as pass (symbol ○ or ◎), and those with even one characteristic in poor condition were marked as fail (symbol ×). Those with all characteristics in excellent condition (symbol ◎) were judged to be excellent in the overall assessment (symbol ◎).

[0096] [Table 2]

[0097] [Table 3]

[0098] Of the products shown in Tables 2 and 3, *1: "CM3685" (crystal weight 0.1 J / g) is manufactured by Keli Chemical Co., Ltd. (China), *2: "Elastrene 252B" (crystal weight 20 J / g), *3: "Elastrene 402B" (crystal weight 8 J / g), *4: "Elastrene 303C" (crystal weight 84 J / g) is manufactured by Showa Denko Corporation, *5: "EV170" (melting point: 62°C, MFR: 1 g / 10 min), *6: "EV270" (melting point: 72°C, MFR: 1 g / 10 min) is manufactured by Mitsui Dow Polychemical Company. *7: "VF-120T" (melting point: 85℃, MFR: 1g / 10min) is manufactured by Ube Maruzen Polyethylene Co., Ltd., *8: "A1150" (melting point: 100℃, MFR: 0.8g / 10min) is manufactured by Nippon Polyethylene Co., Ltd., *9: "KBM-503" (3-methacryloxypropyltrimethoxysilane) is manufactured by Shin-Etsu Chemical Co., Ltd., *10: "DCP" (dicumyl peroxide) is manufactured by NOF Corporation, *11: "Carbon black" (arithmetic mean particle size: 68nm) is manufactured by Nippon Steel Carbon Co., Ltd. Furthermore, the "masterbatch" is a mixture with the formulation shown in Table 4 below.

[0099] [Table 4]

[0100] The above results show that increasing the amount of crystals in the material improves wear resistance. Furthermore, it was found that increasing the amount of ethylene copolymer resin reduced Mooney viscosity and improved processability, while increasing the modulus and decreasing flexibility.Therefore, it was found that a good balance of wear resistance, processability, and flexibility can be obtained by mixing chlorinated polyethylene and ethylene copolymer resin in a mass ratio of 90:10 to 50:50, and further adjusting the ratio to 70:30 yields superior properties in all three aspects.

[0101] Furthermore, Comparative Examples 1 and 2 showed that excessively increasing the addition ratio of chlorinated polyethylene resulted in poor processability, and excessively increasing the addition ratio of ethylene copolymer resin resulted in poor flexibility. Comparative Examples 3 and 4 showed that reducing the amount of crystals in the silane crosslinked rubber composition reduced abrasion resistance. Comparative Example 5 also revealed that excessively increasing the amount of crystals in the silane crosslinked rubber composition caused problems with processability and flexibility. In addition, Comparative Examples 3 to 5 confirmed that in order to achieve an ideal amount of crystals in the silane crosslinked rubber composition, the amount of chlorinated polyethylene crystals needs to have a melting heat of 2 J / g to 30 J / g, and the melting point of the ethylene copolymer resin needs to be 70°C or higher.

[0102] From the results above, it was found that in order to achieve a good balance of abrasion resistance, processability, and flexibility, the amount of crystals in the silane crosslinked rubber composition, as well as the amount of crystals in the chlorinated polyethylene, the melting point of the ethylene copolymer resin, and the mixing ratio of the two materials are important, and that the desired properties can be obtained by appropriately controlling these factors.

[0103] Although the present inventors have described the invention in detail based on embodiments above, 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 its essence. [Explanation of symbols]

[0104] 1. 19 Cable 2 conductors 3. Insulating layer 4 Covering layer 11 Extruder 12 Hoppers 13 Screw 14 Breaker Plate 15 neck 16 Crosshead 17 dice 18 Cable Cores 20 cylinders

Claims

1. A step to obtain a silane graft rubber composition by grafting a base polymer, which is a mixture of chlorinated polyethylene and an ethylene copolymer resin in a mass ratio ranging from 90:10 to 50:50, with a silane coupling agent, A method for producing a silane crosslinked rubber composition, comprising the steps of: mixing the silane graft rubber composition and a masterbatch having a silanol condensation catalyst in a mass ratio of 160.9:3 and crosslinking the silane by the action of water to obtain a silane crosslinked rubber composition, A method for producing a silane crosslinked rubber composition, wherein the heat of fusion of the silane crosslinked rubber composition, as determined by differential scanning calorimetry (DSC), is in the range of 5 J / g to 20 J / g.

2. In the method for producing the silane crosslinked rubber composition described in claim 1, The method for producing a silane crosslinked rubber composition, wherein the silanol condensation catalyst is an octyl tin compound.

3. In a method for producing a silane crosslinked rubber composition according to claim 1 or claim 2, A method for producing a silane crosslinked rubber composition, wherein the ethylene-based copolymer resin is an ethylene vinyl acetate copolymer resin or an ethylene ethyl acrylate copolymer resin.

4. In a method for producing a silane crosslinked rubber composition according to any one of claims 1 to 3, A method for producing a silane crosslinked rubber composition, wherein the silane coupling agent contains a methacrylic group as an organic functional group.

5. In a method for producing a silane crosslinked rubber composition according to any one of claims 1 to 4, A method for producing a silane crosslinked rubber composition, wherein the ethylene copolymer resin has a melting point of 70°C or higher.

6. In a method for producing a silane crosslinked rubber composition according to any one of claims 1 to 5, A method for producing a silane crosslinked rubber composition, wherein the heat of fusion of the chlorinated polyethylene, as determined by differential scanning calorimetry (DSC), is 2 J / g or more and 80 J / g or less.

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