JPH0637585B2 - Ethylene copolymer composition for wire coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an ethylene copolymer composition for coating electric wires. More specifically, the present invention relates to a high-density polyethylene-based copolymer composition for electric wire coating, which has a low back pressure during high-speed electric wire coating molding, has an improved electric wire surface roughness, and is excellent in stress crack resistance.

[Problems to be Solved by Conventional Techniques and Inventions] Conventionally, various thermoplastic resins have been used as electric wire coating materials. Among them, low-density polyethylene resin and high-density polyethylene resin, which have excellent electrical characteristics, have been widely used as insulating coating materials for communication cables and power cables. However, although the high-pressure low-density polyethylene resin has a smooth surface, it has a problem that cracks are likely to occur when twisting due to its low surface hardness and electrical insulation is impaired, resulting in electrical leakage. On the other hand, the high-density polyethylene resin has a problem that the back pressure at the time of molding becomes high and the surface texture becomes rough in the high-speed coating of 1000 to 2000 m / min.

However, with the recent need for thinner wire cores due to higher communication densities, there is a reduction in back pressure during high-speed molding with high-density polyethylene resin, which has high surface hardness and excellent wear resistance. Improvement of surface skin has been desired. As an improvement of this high density polyethylene resin, the density is 0.935 g / c
A composition comprising a high-density polyethylene resin of m ³ or more and an ethylene-propylene random copolymer (JP-A-51-3974).
No. 4), a composition consisting of two kinds of high-density polyethylene resin and low-density polyethylene resin having a different melting index of 0.94 g / cm ³ or more and a low-density polyethylene resin (JP-A-52-11235), and having different densities and melt indexes. Composition containing calcium hydroxystearate and coprecipitated mixture of calcium stearate in two polyethylene resins (JP-A-55-155038)
Or melt flow rate is 5.0 to 2000g / 10min
And ethylene polymer having a density of 0.965 to 0.975 g / cm ³ and ethylene having a melt flow rate of 0.01 to 0.20 g / 10 min and a density of 0.890 to 0.950 g / cm ³ and an α-olefin copolymer having 4 to 20 carbon atoms Composition with (Japanese Patent Publication Sho 61-
No. 26169) has been proposed. However, the present inventors have studied the development of an ethylene copolymer composition having a lower back pressure during molding, improved front surface roughness, and excellent wear resistance and stress crack resistance. It has arrived.

MEANS FOR SOLVING THE PROBLEM The present invention provides (A) ethylene having a density of 0.961 to 0.969 g / cm ³ and a melt flow rate of 300 to 1000 g / 10 min.
34 to 50% by weight of butene-1 copolymer component, (B)
10 to 25% by weight of an ethylene-propylene copolymer component having a density of 0.955 to 0.962 g / cm ³ and a melt flow rate of 10 to 30 g / 10 min, and (C) a density of 0.925 to
Melt flow rate of 0.040 to 0.20 g at 0.940 g / cm ³
/ 10 min ethylene-butene-1 copolymer component in an amount of 32 to 47% by weight, and the composition has a density of 0.947 to 0.953 g / cm ³ and a melt flow rate of 0.9.
The back pressure at the time of molding is low, the surface roughness is improved, and the wear resistance is characterized by being in the range of 0 to 2.0 g / 10 min.
It is intended to provide an ethylene copolymer composition for electric wire coating, which is also excellent in stress crack resistance.

The high melt flow rate ethylene-butene-1 copolymer component (hereinafter referred to as the component A) used in the present invention includes
The density must be in the range of 0.961 to 0.969 g / cm ³ and the melt flow rate (JIS K 6760: load 2.16 kg; hereinafter referred to as MFR) must be in the range of 300 to 1000 g / 10 min.
When a copolymer having a density of less than 0.961 is used, it is necessary to use a high density ethylene-propylene copolymer component or a low melt flow rate ethylene-butene-1 copolymer component, which results in stress crack resistance. Inferior results are not preferable. Also, the density is 0.969 g / c
m ³ or more and a low melt flow rate ethylene - must be used as low density as butene-1 copolymer component, a part becomes slurry properties during slurry polymerization is poor is soluble in a solvent, producing A process problem occurs. Further, if the density of the low melt flow rate ethylene-butene-1 copolymer component is too low, the strength of the obtained composition may decrease.

On the other hand, if the MFR exceeds 1000 g / 10 min, the slurry properties in the slurry polymerization will be deteriorated, and not only the production stability will be deteriorated, but also the strength of the final composition may be lowered. Meanwhile, MF
If R is less than 300 g / 10 min, the back pressure during molding will be high, and not only moldability will be poor, but also the surface texture of the wire will be rough.
The object of the present invention cannot be achieved.

The ethylene-propylene copolymer component (hereinafter referred to as component B) used in the present invention has a density of 0.955 to 0.962.
g / cm ³ and MFR is 10 to 30 g /
It is in the range of 10 min. If the density exceeds 0.962, the strength of the final composition may decrease. On the other hand, the density is 0.
Below 955, low melt flow rate ethylene-butene-
Since the density of the 1-copolymer component must be increased, stress crack resistance is inferior, which is not preferable. On the other hand, when the MFR is less than 10 g / 10 min, the back pressure at the time of molding becomes high, the moldability becomes poor, and the surface texture of the electric wire becomes rough, so that the object of the present invention cannot be achieved. On the other hand, MFR is 3
When it is 0 g / 10 min or more, the MFR of the composition becomes high and the stress cracking resistance is deteriorated, which is not preferable.

In the case of using only the ethylene-butene-1 copolymers having different melt flow rates, Comparative Examples 7 and 1 described later were used.
No. 1, obviously, even when the physical properties of the final composition are those of the present invention, the back pressure at the time of molding becomes high and the surface of the wire becomes rough. In the present invention, by blending an ethylene-propylene copolymer as the component B, the back pressure during molding can be reduced, and a wire coating composition having a smooth surface roughness of the molded wire and good electric wire coating can be obtained.

The low melt flow rate ethylene-butene-1 copolymer component (hereinafter referred to as component C) used in the present invention has a density in the range of 0.940 to 0.925 g / cm ³ , and an MFR of 0.04 to 0.20 g. It is in the range of / 10 min.
If the density exceeds 0.940, the strength and stress crack resistance of the final composition may decrease. On the other hand, if the density is
If it is less than 0.925, it is necessary to increase the density of component A or component B in order to obtain the composition of the present invention.
It is not preferable because the strength of the final composition also decreases due to the significant decrease in the strength of each of the copolymer components. If the MFR is less than 0.04 g / 10 min, the back pressure during molding will be relatively high and the moldability will be poor, and also the surface texture of the wire will be rough due to the formation of lumps, and the object of the present invention will not be achieved. If the MFR exceeds 0.20 g / 10 min, the strength and stress crack resistance of the final composition may decrease.

The ethylene copolymer composition for electric wire coating of the present invention has the above A
It has a density of 0.947 to 0.953 g / cm ³ and an MFR of 0.90 to 2.0 g / 10 min. If the density of this final composition is less than 0.947, the rigidity and wear resistance as an electric wire are poor, and the density is 0.
If it exceeds 952, the stress crack resistance deteriorates. Also M
If the FR is less than 0.90, not only the back pressure at the time of molding becomes high, the moldability becomes poor, but also the surface texture of the electric wire becomes rough, which is not preferable. On the other hand, when the MFR exceeds 2.0, the moldability and the surface roughness of the electric wire are improved, but the strength and stress crack resistance are deteriorated, which is not preferable. Further, although these electric wires are often foam-molded, it is not preferable because the melt viscosity becomes low and the foam-holding property at the time of foaming becomes poor.

In order to obtain the ethylene copolymer composition for electric wire coating of the present invention, the amount of the above component A is 34 to 50% by weight, the amount of the component B is 10 to 25% by weight, and the amount of the component C is 32 to 47% by weight. It is obtained by mixing the respective copolymer components. When the content of the component A is less than 34% by weight, the melt flowability is poor and the back pressure at the time of molding is high, not only the moldability is poor, but also the surface texture of the electric wire is rough, which is not preferable. Further, if the component A exceeds 50% by weight, the moldability and the surface roughness of the electric wire are improved, but the strength and stress crack resistance are deteriorated, which is not preferable. On the other hand, if the content of B component is less than 10% by weight, the improvement of surface roughness is not sufficient. In addition, the B component is 25% by weight
If it exceeds, the strength of the final composition becomes poor, which is not preferable. When the content of the C component is less than 32% by weight, the strength and stress crack resistance of the final composition are inferior, which is not preferable. On the other hand, when the C component exceeds 47% by weight, the melt flowability is poor and the back pressure at the time of molding is high.
It is not preferable because the surface of the wire becomes rough.

As the method of mixing the above-mentioned A component, B component and C component, a method of mechanically mixing the separately polymerized components using, for example, a Banbury mixer, a kneader, a twin-screw kneader, a single-screw extruder, or the like, There is a method of uniformly mixing the powder after each polymerization in three polymerization vessels, but the method is not particularly limited.

The method for producing the components A and C used in the present invention is, for example, a low pressure slurry polymerization method using a Ziegler type catalyst composed of a transition metal catalyst and an organic aluminum compound as described in JP-A-57-212210. It is obtained by polymerizing ethylene and butene-1 to have a predetermined density. At that time, a chain transfer agent such as hydrogen may be used to control the MFR. As the method for producing the component B, ethylene and propylene may be polymerized to a predetermined density and MFR using the same catalyst as described above.

In obtaining the composition of the present invention, an antioxidant, an ultraviolet absorber, a lubricant, an antistatic agent, a colorant, a foaming agent, and other various additives usually used for polyolefins are used within a range not impairing the object of the present invention. It can be mixed and used.

Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[Examples and Comparative Examples]

(1) Polymerization method Component A A n-hexane was used as a polymerization solvent in a polymerization vessel, a titanium-based supported catalyst was used as a catalyst, and triethylaluminum was used as a co-catalyst, and a predetermined amount of hydrogen was supplied as an MFR regulator at a temperature of 85. Butene-1 as a comonomer while maintaining at ℃
Was continuously introduced, and ethylene, which is the main component of the polymerization, was continuously fed so as to keep the total pressure at 8 kg / cm ² , slurry polymerization was carried out, and the following MFR (g / 10 min) and density (g / g
A is an ethylene-butene-1 copolymer having a cm ³ ).
Component A-1 to A-3 and component B of Comparative Example B
-1 'and B-2' were obtained.

A-1: MFR 320, density 0.966 A-2: MFR 550, density 0.965 A-3: MFR 660, density 0.961 A-4: MFR 250, density 0.966 A-5: MFR 960, density 0.969 B-1 ': MFR 20.8, density 0.961 B-2 ': MFR 17.0, density 0.956 B component Introducing propylene instead of butene-1 and polymerizing in the same manner as A component, the following MFR (g / 10min) and density (g
/ Cm ³ ), an ethylene-propylene copolymer having a component B of B-1 to B-4 was obtained.

B-1: MFR 23.4, density 0.966 B-2: MFR 16.4, density 0.965 B-3: MFR 8.5, density 0.961 C component Polymerized in the same manner as A component except that the temperature was 75 ° C and the total pressure was 4 kg / cm ^2. The following MFR (g / 10min) and density (g / cm
C-1 to C-7 of Component C, which is an ethylene-butene-1 copolymer having ³ ), were obtained.

C-1: MFR 0.075, density 0.932 C-2: MFR 0.092, density 0.932 C-3: MFR 0.050, density 0.932 C-4: MFR 0.11, density 0.926 C-5: MFR 0.20, density 0.926 C-6: MFR 0.034, Density 0.932 C-7: MFR 0.25, Density 0.933 (2) Blend The A component, B component and C component obtained as described above are mixed at the predetermined ratios shown in Tables 1 to 4. , High molecular weight phenolic and thioether antioxidants, chlorine scavengers of hydrotalocite compounds and lubricants of higher fatty acid metal salts were added and kneaded and granulated using a twin-screw extruder to obtain each composition. It was

The ESCR of the obtained composition was measured according to JIS K 6760 with a press sheet thickness of 2 mm, a notch depth of 0.3 mm, a temperature of 50 ° C., and a surfactant: nonion NS210 10% aqueous solution.

(3) Electric Wire Coating Molding Each composition obtained in (2) above was subjected to electric wire coating molding under the following conditions, and the results are shown in Tables 1 to 4.

Electric wire molding conditions Molding machine: 65mmφ single screw extruder Conductor: 0.4mmφ copper conductor Conductor preheating temperature: 135 ℃ Finishing outer diameter: 0.68mmφ Molding speed: 1200m / min Screen: 80/100/120/80 mesh Setting temperature: C ₁ C ₂ C ₃ CH D 190 210 230 230 230 The surface roughness of the molding line was measured according to the center line average roughness specified in JIS BO601.

The composition of the present invention has an ESCR of 20 or more and a back pressure of about 500 at an electric wire coating forming tension speed of 1200 m / min.
Hereinafter, those having a surface roughness of about 1 μmRa or less were regarded as good.

As is clear from the examples and comparative examples, the A component is 3
In Comparative Example 3 (A component: 30%) of 4% or less, the back pressure at the time of molding the electric wire coating becomes high, and it is not suitable as the electric wire coating composition. Further, in Comparative Example 19 in which the component A is 50% or more, the MFR of the composition is 2 or more, the density is increased, and the ESCR is lowered, which is not preferable.

In Comparative Examples 6 and 8 in which the B component exceeded 25%,
The MFR of the composition exceeds 2, and the ESCR becomes poor.

〔The invention's effect〕

The present invention relates to an electric wire coating composition comprising at least two ethylene-butene-1 copolymers having different melt flow rates and an ethylene-propylene copolymer, which is a conventional ethylene-butene copolymer containing polyethylene as a main component. When the composition of the present invention is used for coating an electric wire, as compared with a composition obtained by combining with a polymer or the like, the back pressure at the time of high-speed extrusion molding can be made lower than that of a conventional coating, resulting in higher work efficiency and industrial efficiency. Above useful.

Further, the obtained coated surface is smooth without any spots,
It has excellent moldability and is highly resistant to stress cracks.

Therefore, by performing the wire coating molding by high-speed molding using the wire coating ethylene copolymer composition of the present invention, the back pressure at the time of molding is low, the molding processability is good, and the coated wire with less surface roughness is obtained. Can be molded. Further, the obtained electric wire has high rigidity and excellent wear resistance, and since it has good stress crack resistance, it is suitable for a communication cable in the city.

Continuation of the front page (72) Inventor Susumu Otomo 8-1 Goi Minami Kaigan, Ichihara, Chiba Ube Industries Ltd. Chiba Petrochemical Factory (72) Inventor Mikio Tokita 1-8 Goi Minami Kaigan, Ichihara, Chiba Ube Industries, Ltd., Chiba Petrochemical Factory (56) References JP-A-61-148703 (JP, A) JP-B-61-26169 (JP, B2)

Claims (1)

[Claims] 1. An ethylene-butene-1 copolymer component having a density (A) of 0.961 to 0.969 g / cm ³ and a melt flow rate of 300 to 1000 g / 10 min.
(B) 10 to 25% by weight of an ethylene-propylene copolymer component having a density of 0.955 to 0.962 g / cm ³ and a melt flow rate of 10 to 30 g / 10 min, and (C) a density of 0.925.
To 0.940 g / cm ³ with a melt flow rate of 0.04 to
0.20 g / 10 min of ethylene-butene-1 copolymer component 3
Ethylene for electric wire coating, characterized in that the composition has a density of 0.947 to 0.953 g / cm ³ and a melt flow rate of 0.90 to 2.0 g / 10 min. Copolymer composition.