JPH05128914A - Polypropylene for electric insulation and its manufacture - Google Patents

Abstract

PURPOSE:To provide polypropylene excellent in the impulse break down electric field strength by adding a polymer having the specific weight average molecular weight while having the specific polarity dielectric value to polypropylene followed by crystallization. CONSTITUTION:A polymer having the weight average molecular weight not less than a hundred thousand, a dielectric constant at 60Hz of 2.0 to 2.4 and a specific crystalline degree 30 to 45% is selected. As such a polymer, there are a polymer of alpha-olefin having C-number 4 to 12 and ethylene as well as low density polyethylene. 10 to 70weight%, in detail in case of the copolymer of prescribed alpha olefin and ethylene 10 to 15weight% while in case of low density polyethylene 60 to 70weight% are mixed with polyethylene 100weight%. Polypropylene and the polymer are mixed together and kneaded at 175 to 185 deg.C for being melted at 175 to 185 deg.C. After isothermal crystallization at 120 to 130 deg.C for 0.5 to 0.75h, rapid cooling up to 0 deg.C is performed so as to be finished.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electrically insulating polypropylene and a method for producing the same.

[0002]

2. Description of the Related Art Polypropylene is used alone or as a blend polymer with low density cross-linked polyethylene or the like, for example, as an electrical insulating material for high voltage cables and equipment. However, the polypropylene obtained by usual means does not have sufficient impulse breakdown electric field strength, and when it is used as an electrical insulating material at a high voltage, there arises a disadvantage that dielectric breakdown easily occurs. Therefore, the advent of polypropylene with high performance and high reliability, which is excellent in impulse breakdown electric field strength, is desired.

[0003]

The present invention is characterized in that polypropylene is blended with a polymer having a weight average molecular weight of 100,000 or more and a dielectric constant at 60 Hz of 2.0 to 2.4 and crystallized. It relates to insulating polypropylene. The present invention also uses polypropylene and a weight average molecular weight of 1
The present invention relates to a method for producing polypropylene for electrical insulation, which comprises isothermally crystallizing a melt composed of a polymer having a dielectric constant of 2.0 to 2.4 at 60 Hz at 60,000 or more and then cooling the melt.

The present invention has been completed on the basis of the following new findings obtained by the present inventors. Polypropylene is a highly crystalline polymer, and when it is cooled from the molten state, particularly when gradually cooled, lamellas grow radially around the nucleus and spherulites of about 100 to 200 μm are generated.
When the spherulites grow sufficiently from a large number of nuclei, collision occurs between the spherulites to form a spherulite interface. The present inventors
When the polypropylene crystal obtained by the above-mentioned conventional method was subjected to impulse breakdown, it was found that the impulse breakdown passed through the spherulite interface, and the spherulite interface was an electrical weak point.

Next, when propylene is crystallized by adding a low molecular weight compound such as paraffin, the spherulite interface becomes clear, and impurities (additives) formed on the spherulite interface become more remarkable as the amount of addition increases. It was found that the fracture path, and in this case the fracture path, passes exclusively through the spherulite interface. On the other hand, when a polymer having the above-mentioned specific properties is added and crystallized, the spherulite interface becomes unclear as the amount of addition increases, and finally the spherulite interface disappears, and its fracture path penetrates the spherulite nucleus. I found that. The polymer having the above-mentioned properties used in the present invention is hard to move in polypropylene and remains in the spherulites even after crystallization of polypropylene, so that the spherulite interface is retained in order to maintain the uniformly dispersed morphology in polypropylene. As a result, the weak points disappear and the impulse breakdown electric field strength increases. On the other hand, low molecular weight compounds such as paraffin have high mobility due to diffusion in polypropylene, and as spherulites grow during the crystallization stage of polypropylene, they are easily excluded from the inside and accumulate at the spherulite interface. , Seems to weaken the spherulite interface.

The weight average molecular weight of the polymer used in the present invention is 100,000 or more. The preferred weight average molecular weight varies depending on the kind of the polymer, but it is preferably 120,000 or more, more preferably 150,000 or more, particularly preferably 250,000 or more, and the upper limit is usually about 400,000. The dielectric constant of the polymer at 60 Hz is 2.
It is 0 to 2.4, preferably 2.0 to 2.3, and more preferably 2.0 to 2.2. Dielectric constant is JIS K676
It is measured by 0. Furthermore, the crystallinity of the polymer is 10 to 50%, preferably 20 to 45%,
More preferably, it is 30 to 45%. Crystallinity is AST
It is calculated from the density according to MD 1505.

As such a polymer, a copolymer of α-olefin having 4 to 12 carbon atoms and ethylene (for example, Tuffmer: manufactured by Mitsui Petroleum Science Co., Ltd.), low density polyethylene (for example, ZF-30R: Manufactured by Mitsubishi Petrochemical Co., Ltd.) and the like.

The α-olefin in the copolymer of α-olefin having 4 to 12 carbon atoms and ethylene preferably has 6 to 10 carbon atoms, more preferably 8 to 9 carbon atoms. The weight average molecular weight of the copolymer is preferably 120,000 or more, more preferably 150,000 or more, and the upper limit thereof is usually about 300,000. The density is usually 0.885 to 0.910, preferably 0.888 to 0.900, and more preferably 0.
889 to 0.895, and the melt index (g /
10 minutes) is usually 2.5 to 5, preferably 3 to 4.5,
More preferably, it is 3.2-4. The melt index is measured by the method of JIS K 6760K (hereinafter the same).

The low-density polyethylene preferably has a weight average molecular weight of 150,000 or more, more preferably 250,000 or more, and its upper limit is usually about 400,000. The density is usually 0.915 to 0.925, preferably 0.918 to 0.
923, more preferably 0.920 to 0.922, and the melt index is usually 0.7 to 2.5, preferably 0.8 to 2.3, and more preferably 1-2.

The blending ratio of the polymer with respect to polypropylene may vary depending on the kind of the polymer, but is usually 5 to 90, preferably 10 to 80, and more preferably 10 to 70 with respect to 100 parts by weight of polypropylene. Specifically, for example, in the case of a copolymer of α-olefin having 4 to 12 carbon atoms and ethylene, it is 5 to 30 parts by weight, preferably 10 to 25, and more preferably 10 to 1 part.
5 parts by weight, 40 to 40 in the case of low density polyethylene
90 parts by weight, preferably 50 to 80 parts by weight, more preferably 60 to 70 parts by weight.

In the present invention, the melt index of the raw material polypropylene is 3 to 11, especially 5 to 7,
The density is 0.905 to 0.915, especially 0.908 to 0.
912, and the elongation at break is 350 to 550.
%, Especially 450 to 500 is preferable. Elongation at break is measured according to ASTM D638.

The method for crystallizing polypropylene in the present invention is carried out, for example, as follows. First, the above polymer is added to polypropylene and kneaded. Next, the kneaded product is melted to obtain molten polypropylene. At that time, the kneading of the polypropylene and the polymer is usually 170 to 19
It is carried out by a roll mill or the like at 0 ° C, preferably 175 to 185 ° C. The melting is usually 170-
It is carried out at 190 ° C, preferably 175 to 185 ° C.
The melting time is usually about 10 to 20 minutes.

The molten polypropylene thus obtained is, for example, 90 to 150 ° C., preferably 100 to 140 ° C., more preferably 120 to 130 ° C., usually 0.25 to 1
After isothermal crystallization for 0.5 hours to 0.75 hours, preferably 30 to -10 ° C, 25 ° C to -5 ° C, most preferably 0.
It is manufactured by quenching to about ℃.

[0014]

[Effect] The impulse breakdown electric field strength of the electrically insulating polypropylene of the present invention is about 1.6 times better than that of the conventional crystalline polypropylene.

[0015]

【Example】

Example 1 An isotactic polypropylene having a density of 0.91 g / cm ³ , a melt index of 7.0 and an elongation at break of 500% was used. The polypropylene was blended with Tuffmer at a blending rate of 0 to 100% by weight, kneaded at 180 ° C. using a roll mill, and once melted in a compression molding machine (1
80 ℃), after isothermal crystallization for 60 minutes at 130 ℃ 0
The polypropylene was crystallized by quenching with water. This was compression molded into a 0.3 mm thick sheet. Tuffmer has a weight average molecular weight of 170,000 and a dielectric constant at 60 Hz of 2.
1, density 0.89, melt index (g / 10
Min) is 3.6 and the crystallinity is 30%.

Example 2 Example 1 except that low density polyethylene (LDPE) was added at a blending rate of 0 to 100% by weight instead of Tuffmer.
The polypropylene was crystallized in the same manner as in. The compression molded shape is a 0.3 mm thick sheet. The low-density polyethylene had a weight average molecular weight of about 260,000, a dielectric constant at 60 Hz of 2.3, and a melt index (g / 10 minutes) of 1.
1, the crystallinity is 44.4%, and the density is about 0.920.

Experimental Example 1 An impulse breakdown test was conducted on the sample obtained above.
That is, in the improved McKeown electrode system shown in FIG.
A negative-polarity impulse standard wave of × 40 μsec was applied by a step-up method of applying 5 kV / 3 times, with an initial value of 70% of the expected breakdown voltage. The sample thickness is 0.3 mm.
As the impulse withstand voltage value, data of 10 samples was collected for each condition, and after the wiper analysis, the breakage value at the failure probability of 63.3% was taken as the impulse withstand voltage value of the sample. The impulse breakdown electric field strength [ImpBDS (kV / mm)] measured in this way is shown in FIG.
This is as shown in FIG. 2 and Table 1.

[0018]

[Table 1]

Comparative Example 1 The polypropylene used in Example 1 was melted (180 ° C.) in a molding machine alone, once isothermally crystallized at 140 ° C. for 3 hours and then left at 25 ° C. for 2 hours to obtain polypropylene. Was crystallized. The impulse breakdown electric field strength of the crystalline polypropylene crystal was 120 kV / mm.

Comparative Example 2 Weight average molecular weight of 3 instead of Tuffmer in Example 1
Thousands of polyethylene (AC polyethylene 617A: manufactured by Allied Chemical Co.) having an induction coefficient of 2.3 was added in an amount of 0 to 30 phr, but the strength only decreased by 20 to 30 kV / mm.

[Brief description of drawings]

FIG. 1 is a diagram showing a measurement result of impulse electric field breakdown strength.

FIG. 2 is a diagram showing measurement results of impulse electric field breakdown strength.

FIG. 3 An improved McK for performing impulse destructive testing
It is a figure which shows an eown electrode system.

[Explanation of symbols]

 1 25mmφ steel ball 2 Polyethylene body 3 Silicon oil 4 Epoxy resin 5 Sample

Claims (3)

[Claims] 1. A polypropylene for electrical insulation, which is obtained by adding a polymer having a weight average molecular weight of 100,000 or more and a dielectric constant at 60 Hz of 2.0 to 2.4 to polypropylene to crystallize. 2. The polypropylene for electric insulation according to claim 1, wherein the polymer is at least one selected from low-density polyethylene and a copolymer of ethylene with an α-olefin having 4 to 12 carbon atoms. 3. An electrical insulation characterized by isothermally crystallizing a melt composed of polypropylene and a polymer having a weight average molecular weight of 100,000 or more and a dielectric constant at 60 Hz of 2.0 to 2.4 and then cooling. Method for producing polypropylene.