JPH0123493B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an ethylene propylene rubber composition that is optimal for producing molded products such as heat-shrinkable tubes with excellent tracking resistance. BACKGROUND OF THE INVENTION Rubber and plastic organic insulating materials are widely used to insulate various electrical devices, but they are susceptible to moisture or mist containing salts, dust, and ionic contaminants. They are generally not suitable for high voltage applications in contaminated atmospheres where leakage currents can flow through the surface of the insulator. This leakage current causes a rise in temperature, which causes moisture to evaporate and a dry zone to form. The voltage applied to these dry zones often exceeds the withstand voltage between the air and the insulation surface,
Causes electrical discharge or spark scintillation.
Spark temperatures are extremely high, often over 2000°C, and the heat generated degrades the insulation surface and creates carbonaceous tracks. These tracks usually become conductive paths in the form of a resin, and as they gradually spread, the organic insulator is broken due to tracking. Many solutions to these problems have been proposed in the past, the most effective of which is the incorporation of hydrated alumina into butyl or ethylene propylene rubber. [Problems to be Solved by the Invention] Regarding hydrated alumina, a mechanism for preventing tracking failure has been shown, but regardless of the correct mechanism, in reality, organic materials containing a large amount of hydrated alumina are It has been found that it prevents tracking and is usually damaged by gradual surface erosion. However, the amount of hydrated alumina required to produce the anti-tracking effect is very high, usually in the range of 50-90% by weight of the total insulation. Particularly when manufacturing heat-shrinkable products by injection molding or extrusion, high filler content can lead to loss of hydration water due to high temperatures during molding and crosslinking, resulting in insulation loss. Creates numerous pores throughout the body,
This is undesirable because it reduces the performance of the insulator. In particular, if the filling amount of hydrated alumina is high, the mechanical strength and elongation will decrease, and it will be easier to break during expansion operations at high temperatures when manufacturing heat-shrinkable products. Cannot be manufactured. An object of the present invention is to improve the drawbacks of the prior art described above and to provide an ethylene propylene rubber composition with excellent tracking resistance. [Means for Solving the Problems] The composition of the present invention comprises () a polyolefin consisting of 50 to 85 parts by weight of ethylene propylene rubber and 15 to 50 parts by weight of polyethylene or ethylene copolymer;
Per 100 parts by weight, () average particle size 5 μm or less,
25 to 100 parts by weight of magnesium hydroxide with a BET specific surface area of 40 m ² or less and surface-treated with either fatty acid, fatty acid metal salt, titanate coupling agent or silane coupling agent, () hydrated alumina and/or It is characterized by containing 0 to 75 parts by weight of talc and () a crosslinking agent. Ethylene propylene diene terpolymer is suitable as the ethylene propylene rubber in the present invention, and ethylene vinyl acetate copolymer, ethylene acrylate copolymer, ethylene butene copolymer, etc. can be used as the polyethylene or ethylene copolymer. Such a polyolefin is crosslinked by blending an organic peroxide-based or sulfur-based crosslinking agent, molding it into a predetermined shape, and then heating it. Since polyolefin and magnesium hydroxide have poor compatibility, agglomeration occurs during roll or banburi kneading, resulting in deterioration of moldability and tensile properties. This is because magnesium hydroxide is an ionic crystal,
This is because polyolefins are non-polar or only slightly polar, and have a low affinity with magnesium hydroxide. In order to improve this, in the present invention, the average particle size
Magnesium hydroxide with a BET specific surface area of 5 μm or less and a BET specific surface area of 40 m ² /g or less is used. If the magnesium hydroxide is outside this range, agglomeration occurs during roll or banburi kneading, resulting in poor formability and tensile properties. In addition, in order to prevent magnesium hydroxide from reacting with water and carbon dioxide in the air and changing into magnesium carbonate, magnesium hydroxide should be treated with fatty acids, fatty acid metal salts, titanate coupling agents, or silane coupling agents. The surface is treated with Fatty acid is RCOOH, fatty acid metal salt is M
(OOCR), which is represented by n. In addition, R
is an alkyl group or an alkene group, M is A,
B, A group metal, n is a natural number. Titanate coupling agents include isopropyl tri(dioctyl phosphate) titanate, titanium di(octyl phosphate) oxyacetate, and isopropyl triisostearoyl titanate, and silane coupling agents include vinyltriethoxysilane and vinyltris(β). -methoxyethoxy)silane, etc. The above-mentioned special magnesium hydroxide must be contained in an amount of 25 to 100 parts by weight per 100 parts by weight of the polyolefin. If it is less than 25 parts by weight, the desired tracking resistance cannot be sufficiently imparted.
If more than 100 parts by weight is added, moldability and tensile properties will decrease. The composition of the present invention contains hydrated alumina and/or talc in addition to the above-mentioned special magnesium hydroxide as an inorganic filler to improve tracking resistance, based on 100 parts by weight of polyolefin.
Blend in a range of 75 parts by weight. If the amount of the above special magnesium hydroxide is close to the lower limit of the above range, it is necessary to use hydrated alumina and/or talc within the above range. When selecting an amount close to the upper limit, hydrated alumina and/or talc do not necessarily have to be used together. In the present invention, in addition to the above components, antioxidants, lubricants, colorants, etc. may be added. [Examples of the Invention] Various components were roll-kneaded using a 12-inch roll in the mixing ratios shown in Table 1. The components except the vulcanizing agent and the vulcanization aid were initially roll-kneaded at 120°C, and then the temperature was lowered to 80°C and all the components were kneaded. Then, 75m/
A tube with an outer diameter of 20 mmφ and an inner diameter of 15 mmφ was extruded at 120℃ using an extruder. After preheating this tube to 170℃, one end was sealed and nitrogen gas was introduced from one end to increase the inner diameter.
A heat-shrinkable tube was fabricated by applying rough internal pressure to a 45mmφ steel tube, expanding it, and then cooling it. The evaluation results for each example are shown in the lower column of Table 1. Dispersibility was determined by rolling out a sheet with a thickness of 0.5 mm after roll kneading, and calculating the magnification.
Observation was made using a 20x microscope. Tensile properties were determined by roll kneading, sheeting to a thickness of 2 mm, vulcanization using a high-pressure steam press at 150°C for 30 minutes, punching out with JIS No. 3 dumbbells, leaving in a constant temperature room at 20°C for 1 day, and conducting a shortcut type tensile test. Depending on the machine, the tensile speed is 200mm/min.
Measurements were made at temperatures of 20℃ and 170℃. The pipe expansion workability was investigated by expanding the pipe using the method described above.
The raw tubes of Comparative Examples 1 to 3 did not expand uniformly and burst during tube expansion, making it impossible to make a heat-shrinkable tube. Tracking resistance was evaluated in accordance with the tracking resistance test method specified in JIS C 3005 Plastic Insulated Wire Test Method (Sho 55-3). The tracking resistance test sample is a heat-shrinkable tube expanded to an outer diameter of 45 mmφ, wrapped around a cross-linked polyethylene insulated wire with an outer diameter of 22 mmφ, and heat-shrinked at 150℃ for 30 minutes.
This is a 150mm sample. In the JIS method, the sample is mounted vertically, a voltage of 4KV is constantly applied between the electrodes 100mm, and 0.2%
A staining solution containing sodium chloride and 0.1% surfactant is sprayed onto the sample in a cycle of 10 seconds of spraying and 20 rests. When a current of 0.5A flows across the surface of the sample between the electrodes, the current circuit is interrupted and a short circuit is determined. Tracking resistance is determined based on the number of fogging cycles of the fouling liquid until the short circuit and the corrosion damage of the sample after the test. Judging from the condition.

【table】

【table】

[Table] All of the samples of Examples 1 to 6 did not cause short circuits and had only slight erosion after being tested up to 20,000 times. on the other hand,
Comparative Examples 1 to 3 were inferior in tensile strength and elongation, and Comparative Example 4 was inferior in tensile strength and elongation.
A short circuit occurred after 18,450 cycles, and the surface was severely eroded and dendritic tracks were formed over almost the entire length between the electrodes. [Effects of the Invention] As explained above, according to the present invention, it is possible to manufacture a heat-shrinkable ethylene propylene rubber molded product with excellent tracking resistance.

Claims (1)

[Claims] 1 () To parts by weight of polyolefin consisting of 50 to 85 parts by weight of ethylene propylene rubber and 15 to 50 parts by weight of polyethylene or ethylene copolymer, ()
With an average particle size of 5μm or less and a BET specific surface area of ^40m2 or less,
Furthermore, 25 to 100 parts by weight of magnesium hydroxide surface-treated with either a fatty acid, a fatty acid metal salt, a titanate coupling agent or a silane coupling agent, () 0 to 75 parts by weight of hydrated alumina and/or talc, and ( ) A tracking-resistant ethylene propylene rubber rubber composition for heat-shrinkable products, characterized by containing a crosslinking agent.