JP2701014B2 - Rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition having excellent anti-scorch properties and compression set characteristics, and more particularly to a rubber composition useful for power cable accessories.

[0002]

2. Description of the Related Art With the recent increase in power demand, power cables have been increased in pressure, and power cables have been increasing in size. Accompanying this, accessories for power cables, for example, rubber molded parts used for connection parts and terminals of power cables, etc., have also become larger. As the rubber composition used for such a rubber molded part, usually, a composition mainly composed of an ethylene-propylene polymer having excellent heat resistance, electric properties, and the like, and a composition in which a cross-linking agent is added to improve the mechanical properties. Used. However, when a rubber molded part is molded using the composition, as the rubber molded part becomes larger, a scorch problem, that is, a problem that the rubber prematurely cross-links easily occurs.

For example, when a rubber composition in which a cross-linking agent is blended with an ethylene-propylene polymer is used as a rubber molded part for a power cable connecting portion by injection molding, first, an injection device is adjusted to the size and shape of the molded product. The mold is set, the mold is heated in advance to improve the flowability of the rubber composition, and then the rubber composition is injected and filled into the heated mold from the rubber outlet of the injection device. Thereafter, desired molding is performed by heat crosslinking. However, in the case of this molding method, the rubber injection port of the injection device has a fixed shape, so the time required to fill the molding material varies depending on the size of the molded product. Since the rubber composition injected into the mold is in contact with the heated mold for a long time, the rubber composition is heated more than necessary until the entire rubber composition is filled, so that scorch is likely to occur. When scorch occurs, the fluidity of only the rubber composition in that part is reduced, resulting in distortion of the molded product, and the rubber composition with different fluidity does not completely melt and unify, resulting in scouring etc. It becomes a major factor of the cause of failure.

[0004] To solve the above problem, for example, Japanese Patent Laid-Open No.
No. 55708 proposes a composition comprising a polyolefin containing a crosslinking agent containing 1-methyl-4-isopropylidenecyclohexene as a scorch inhibitor,
1-methyl-4-isopropylidenecyclohexene is
Acts to prevent cross-linking of polyethylene during extrusion,
It is said that scorch during extrusion molding can be prevented, and an electric wire or cable with good appearance can be obtained. However, when the scorch inhibitor is blended, the time until scorch is generated becomes longer, but at the same time, the crosslinking speed is suppressed and the crosslinking time becomes longer, which causes a problem in productivity. Therefore, in order to improve productivity, it is desired to develop a rubber composition that not only prevents scorch but also does not reduce the crosslinking speed.

On the other hand, in a rubber molded part used for a connection part or a terminal part of a power cable, an interface fitting property at a connection part between the rubber molded part and the power cable is important from the viewpoint of high reliability of insulation. In addition, it is required that the compression set is small with respect to the pressing performed when the rubber molded component is connected to the power cable.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a rubber composition which prevents scorch without sacrificing the rate of crosslinking and has excellent compression set characteristics, and more particularly, a rubber composition for power cable accessories. It is intended to provide goods.

[0007]

Means for Solving the Problems The inventors of the present invention have found that, based on 100 parts by weight of polyolefin, 0.5 to 3.0 parts by weight of an organic peroxide having a half-life temperature of 165 to 180 ° C. The above object has been achieved by a rubber composition containing 1.0 to 4.0 parts by weight of an organic peroxide having an initial temperature of more than 180 ° C and not more than 210 ° C. That is, the present invention is to prevent scorch by using two kinds of organic peroxides having different half-life temperatures in combination. Furthermore, the present inventors made the polyolefin an ethylene-propylene-based polymer, and further contained a crosslinking aid in the rubber composition.
By being N'-m-phenylenebismaleimide and / or triallyl isocyanurate,
Further, the above object was achieved more effectively by incorporating calcium carbonate and / or graphite into the rubber composition, and by using the rubber composition as a material for power cable accessories.

Next, the rubber composition of the present invention will be described in detail. Examples of the polyolefin used in the present invention include various polyethylenes such as high-density polyethylene, medium-density polyethylene, and low-density polyethylene, ethylene-propylene polymers such as ethylene-propylene polymer and ethylene-propylene-diene polymer, and ethylene-acetic acid. Vinyl polymer, ethylene-ethyl acrylate polymer, ethylene-methyl acrylate polymer and the like can be used,
In particular, ethylene-propylene polymers such as ethylene-propylene polymer and ethylene-propylene-diene polymer are preferably used from the viewpoint of compression set characteristics, and ethylene-propylene is particularly preferable from the viewpoint of compression set characteristics and stress relaxation resistance. -Diene polymers are preferably used. The ethylene-propylene polymer used in the present invention has a ratio of ethylene to propylene of 55:45 in view of compression set characteristics.
~ 75: 25, and ethylene-
As the propylene-diene polymer, those in which the amount of diene is 6 to 26 in iodine value and the diene component is dicyclopentadiene, ethylidene norbonene, etc. are preferably used from the viewpoint of compression set characteristics and stress relaxation resistance. Can be

In the present invention, the half-life temperature is 165 ° C. or higher and 1
An organic peroxide of 80 ° C. or less and an organic peroxide having a half-life temperature of more than 180 ° C. and 210 ° C. or less, that is, two types of organic peroxides having different half-life temperatures are used. The half-life temperature in the present invention refers to a decomposition temperature for obtaining a half-life of one minute.

Examples of the organic peroxide having a half-life temperature of 165 ° C. to 180 ° C. used in the present invention include dicumyl peroxide (171 ° C.) and 2,5-dimethyl-peroxide.
2,5-di (t-butylperoxy) hexane (179
° C), α, α'-bis (t-butylperoxy-m-isopropyl) benzene (179 ° C), t-butylperoxylaurate (165 ° C), cyclohexane peroxide (174 ° C), and the like. In particular, those having a half-life temperature of 170 ° C. or more and 179 ° C. or less are suitably used.
The amount of the organic peroxide having a half-life temperature of 165 ° C. or more and 180 ° C. or less is 0.5 to 3.0 parts by weight based on 100 parts by weight of the polyolefin. If the amount of the organic peroxide is less than 0.5 part by weight, a sufficient crosslinking rate cannot be obtained,
If it exceeds 3.0 parts by weight, the scorch-preventing property is reduced, which is not preferable.

Examples of the organic peroxide having a half-life temperature of more than 180 ° C. and not more than 210 ° C. include di-isopropylbenzene hydroperoxide (205 ° C.) and 2,5-dimethyl-2,5. -Di (t-butylperoxy) hexyne-3 (193 ° C), di-t-
Butyl peroxide (186 ° C.) and the like, particularly those having a half-life temperature of 190 ° C. or more and 205 ° C. or less are suitably used. The amount of the organic peroxide having a half-life temperature of more than 180 ° C and not more than 210 ° C is 1.0 to 4.0 parts by weight based on 100 parts by weight of the polyolefin. If the compounding amount of the organic peroxide is less than 1.0 part by weight, a sufficient scorch prevention effect cannot be obtained, and if it exceeds 4.0 parts by weight, the crosslinking rate is undesirably reduced.

In the present invention, from the viewpoint of scorch prevention, it is preferable to add a total of about 1.5 to 7 parts by weight of two kinds of organic peroxides having different half-life temperatures per 100 parts by weight of polyolefin, More preferably, it is 2 to 5 parts by weight. In the present invention, among the two organic peroxides having different half-life temperatures, dicumyl peroxide (171 ° C.) and 2,5-dimethyl-2,5- Combination with di (t-butylperoxy) hexyne-3 (193 ° C.) is preferred.

The rubber composition of the present invention preferably further uses a crosslinking aid in order to improve mechanical properties. Examples of the crosslinking aid include ethylene glycol dimethacrylate, N, N'-m-phenylenebismaleimide, triallyl isocyanurate, trialmethallyl isocyanurate, triacryloylhexahydro-1,
Known ones such as 3,5-triazine can be used,
N, N'-m-phenylenebismaleimide and / or triallyl isocyanurate are particularly preferred from the viewpoint of mechanical properties and the like. The amount of the crosslinking aid is preferably from 0.3 to 5 parts by weight based on 100 parts by weight of the polyolefin.
If the amount is less than 0.3 part by weight, the effect of improving the mechanical properties tends to be small, and if it exceeds 5 parts by weight, the anti-scorch property tends to decrease.

In the present invention, it is preferable to add a filler in order to improve the mechanical and electrical properties of the rubber composition. Known fillers such as calcium carbonate, clay, talc, silica and various carbon blacks can be used as the filler.In addition to improving the mechanical and electrical properties of the rubber composition, to further improve the fluidity,
It is preferable to use calcium carbonate and / or graphite in combination with other fillers. The total amount of the various fillers is preferably 60 to 200 parts by weight based on 100 parts by weight of the polyolefin, and the calcium carbonate and / or graphite is included in the total amount of the filler in an amount of 10 to 30% by weight. Is preferred. If the amount of calcium carbonate and / or graphite is less than 10% by weight, the fluidity improving effect tends to decrease, and if it exceeds 30% by weight, the compression set characteristic tends to decrease.

The rubber composition of the present invention may further contain, if necessary, an antioxidant such as a phenolic or amine-based compound, a processing aid such as stearic acid or a metal salt of a higher fatty acid, a petroleum-based process oil, and an electric property improving agent. Therefore, an additive such as a lead compound or a silicon compound may be blended.

The rubber composition of the present invention is used as a protective coating material, an electric insulating material, and the like. For example, from 600v
6.6kV class low pressure, 11-33kV class medium-high pressure, 66
It is useful as a material for accessories of high-voltage power cables of up to 275 kV class, and is particularly suitable as a material for accessories of high-voltage power cables of 66 to 275 kV class. As an accessory of the power cable, there is a rubber molded part used for a connection portion, a terminal portion, or the like. Usually, the rubber composition of the present invention is kneaded by a usual kneading means, and then, using a general rubber molding method such as injection molding, compression molding, extrusion molding, injection molding, transfer molding, etc.
It is crosslinked and used by heating at 80 ° C. for 15 to 130 minutes.

[0017]

The rubber composition of the present invention has two different half-life temperatures.
Since scorch is prevented by using a combination of organic peroxides, there is no need to add a scorch inhibitor.
Therefore, the rubber composition of the present invention can be cross-linked without lowering the cross-linking speed and can prevent scorch.

[0018]

【Example】

(Examples 1 to 11, Comparative Examples 1 to 3) Tables 1 and 2 show the respective composition ratios and evaluation results of the examples and comparative examples. In addition,
The evaluation method is as follows. <Scorch Prevention> Each of the components shown in Tables 1 and 2 was subjected to 2
The mixture was kneaded for 0 minutes, and scorch prevention properties were evaluated using the obtained compound. The scorch prevention property was evaluated by measuring the scorch time of the compound by using an L-shaped rotor at a temperature of 125 ° C. in accordance with JIS K6300. The case where the obtained scorch time was 11 minutes or longer was evaluated as ○, and the case where the scorch time was less than 11 minutes was evaluated as ×. <Cross-linking speed> For each of the above compounds, a Curastometer III manufactured by Nippon Synthetic Rubber Co., Ltd. was used at a temperature of 160 ° C.
The cross-linking speed was evaluated by measuring the cross-linking time until reaching a degree of cross-linking of 90%. The obtained cross-linking time was 50 minutes or less, and the case where it exceeded 50 minutes was x. <Compression Permanent Strain Characteristics> After press vulcanization of each of the above compounds (160 ° C., 30 minutes), the compression set was measured at 100 ° C. for 70 hours under heat treatment conditions in accordance with JIS K6301. When the obtained compression set is 20% or less,
The case where it exceeded 0% was evaluated as x.

The organic peroxides used in the examples and comparative examples and their respective half-life temperatures are as follows. Organic peroxide-1: dicumyl peroxide (171)
° C) organic peroxide-2: 2,5-dimethyl-2,5-di (t
-Butylperoxy) hexane (179 ° C.) Organic peroxide-3: 2,5-dimethyl-2,5-di (t
-Butylperoxy) hexyne-3 (193 ° C) Organic peroxide-4: di-isopropylbenzene hydroperoxide (205 ° C) Organic peroxide-5: di-t-butylperoxide (1
86 ° C)

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

The rubber composition of the present invention has the following effects. By blending the polyolefin with two kinds of organic peroxides having different half-life temperatures, scorch can be prevented without lowering the crosslinking rate, so that productivity is improved, and the compression set is excellent. When the rubber composition of (1) is used as a material for an accessory of a power cable, the reliability in insulation becomes high. Further, since the polyolefin is an ethylene-propylene polymer, the compression set is excellent, and the ethylene-propylene-diene polymer is excellent in compression set and stress relaxation. When the composition is used as a material for an accessory of a power cable, the reliability in insulation is increased. In addition, since the mechanical properties are improved by containing the crosslinking aid, the reliability of the strength of the molded article using the rubber composition of the present invention is improved. In particular, the crosslinking aid is N, N'-m- By using phenylene bismaleimide and / or triallyl isocyanurate, the mechanical properties are further improved, so that the reliability of the molded article using the rubber composition of the present invention in the strength is further increased. Further, by containing calcium carbonate and / or graphite, the fluidity of the rubber composition is improved and distortion is less likely to occur in a molded product. Therefore, the rubber composition of the present invention is used as a material for an accessory of a power cable. When used, the reliability in the insulating property is increased. Similarly, when the rubber composition is used as a material for power cable accessories, the reliability of the power cable accessories in terms of insulation and strength is increased.

[Table 1]

[Table 1]

Claims (6)

(57) [Claims] [Claim 1] With respect to 100 parts by weight of polyolefin,
0.5 to 3.0 parts by weight of an organic peroxide having a half-life temperature of 165 ° C. or more and 180 ° C. or less, and 1.0-4.0 parts of an organic peroxide having a half-life temperature of more than 180 ° C. and 210 ° C. or less. A rubber composition characterized by being compounded with parts by weight. 2. The rubber composition according to claim 1, wherein the polyolefin is an ethylene-propylene polymer. 3. The rubber composition according to claim 1, further comprising a crosslinking aid. 4. The rubber composition according to claim 3, wherein the crosslinking assistant is N, N'-m-phenylenebismaleimide and / or triallyl isocyanurate. 5. The rubber composition according to any one of claims 1 to 4, further comprising calcium carbonate and / or graphite. 6. The rubber composition according to claim 1, wherein the rubber composition is for power cable accessories.