JPS6210119A - Electrical-insulating crosslinked ethylene copolymer - Google Patents

Abstract

PURPOSE:The titled crosslinked copolymer excellent in impulse breakdown resistance, AC breakdown resistance and inhibition of deterioration due to water tree, comprising a crosslinked copolymer of ethylene with a specified ethylenically alpha,beta-unsaturated acid halogenated alkyl ester. CONSTITUTION:Ethylene copolymer of a number-average MW >=1,000 is obtained by radical-polymerizing ethylene with 0.001-4mol% ethylenically alpha,beta-unsaturated acid halogenated alkyl ester of the formula (wherein R<1> is H or -CH3 and R<2> is a 1-15 C halogenated alkyl) at a temperature >=120 deg.C and a reaction pressure >=500kg/cm<2> in the presence of a catalyst (e.g., t-butyl peroxyisobutyrate). 100pts. wt. this copolymer is mixed with 0.5-4pts.wt. chemical crosslinking agent (e.g., dicumyl peroxide) and crosslinked to obtain an electrical-insulating crosslinked ethylene copolymer having a halogenated alkyl ester group content of 0.005-10mol% and a gel content (according to the method of measurement as stipulated by JIS C3005) >=40%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crosslinked ethylene copolymer for electrical insulation.

The crosslinked product of the present invention has excellent impulse fracture resistance and A resistance.
In addition to the C-destructive properties, it has particularly excellent water tree properties, so it is industrially useful as a material for electrical cables that can prevent electrical deterioration (water tree deterioration) during actual use.

Cross-linked polyethylene based on prior art low-density polyethylene has excellent electrical properties and heat resistance, so C■
Although it is widely used as a cable insulation material, dielectric breakdown occurs under ultra-high voltages, so there is a need for a material with even higher performance.

For this reason, many studies have been made to improve the dielectric breakdown characteristics under ultra-high voltages.

For example, the presence of impurities such as pores, water, and metals causes charge concentration and deteriorates dielectric breakdown properties, so impurity removal technology is being considered mainly for materials for ultra-high voltage cables. Clean polyethylene that does not contain contaminants of 100μ or more and dry crosslinking technology that does not create pores have been developed. By making full use of these technologies, 27
Even 5KV cables have been put into practical use.

However, insulation deterioration when used for a long period of time under high voltage, such as water tree deterioration (for example, IEEJ Technical Report, Part 1,
No. 11 (August 1972) etc., it is impossible to completely prevent such problems, and therefore attempts have been made to use calcium stearate, various aromatic compounds, etc. as voltage stabilizers, but methods using these additives had problems with long-term performance retention due to additive bleed-out (for example, Japanese Patent Publication No. 48-24809, West German Patent No. 124).
(See Specification No. 8773, French Painting Patent No. 1464601, etc.) 0 Summary of the Invention In view of these current circumstances, the present inventors have developed a new technology that has dielectric breakdown characteristics, long-term performance retention, flexibility, and no metal catalyst residue. As a result of focusing on the development of excellent crosslinked ethylene copolymers, we have successfully developed a crosslinked ethylene copolymer with excellent properties that satisfy these requirements. (I), C = C-
C-0-R"...(I) (in the formula,
R1 is H or -OH, and R2 is C1-1. (indicates each alkyl halide)
, a crosslinked product containing a copolymer of a β-unsaturated acid with a halogenated alkyl ester, the crosslinked product contains o, o s to 10 moles of halogenated alkyl ester group units, and is compliant with JIS C3OOS. The object of the present invention is to provide a crosslinked ethylene copolymer for electrical insulation, which has a gel fraction of 40 or more as determined by the measuring method specified in the above.

Effects of the Invention The crosslinked ethylene copolymer for electrical insulation of the present invention has excellent voltage resistance properties, long-term insulation deterioration prevention properties (water tree deterioration prevention properties), flexibility, molding processability, etc., so it is particularly suitable for high voltage applications. Shows extremely excellent performance as an insulating material for power cables.

DETAILED DESCRIPTION OF THE INVENTION The ethylene copolymer used in the present invention is a novel ethylene copolymer that has not been described in any literature.
I), CH2=C-C-0-R" ......(1
) (wherein, R1 is H or -OH, and R2 is C~1.
A copolymer with a halogenated alkyl ester (monomer) of an ethylenically type α,β unsaturated acid represented by the halogenated alkyl ester (respectively), wherein the monomer represented by the general formula (I) is The degree of engagement is from o, o o s to 10 molar, preferably from o, o o s to 5 molar.

As the monomer represented by the above general formula (I), for example, R2 is dibromomethyl, dichloromethyl, trifluoroethyl, difluoromethyl, trichloroethyl, tribromoethyl, triethyl triiodide, monofluoroethyl,
Monochloroethyl, monochloromethyl, monofluoromethyl, monochloroethyl, trifluoromethyl, trichloromethyl, tribromomethyl, methyl triiodide, tetrafluoroethyl, tetrachloroethyl, tetrabromoethyl, pentafluoroethyl, pentachloroethyl, pentabromoethyl , pentafluoropentaf frog, pentachlorotridecanyl, heptafluorodecanyl, heptadecylfluorodecale, heptadecylchlorodecanyl, hexafluorononyl, and heptadecylchlorodecanyl.

As the halogen atom of R2 in the monomer represented by the general formula (I), F, C, Br, and I are used, and among them, F or (J is preferable, and those having F are particularly preferable.

There are no particular restrictions on the polymer structure of the ethylene copolymer, but a random copolymer or a graft copolymer in which a monomer represented by the general formula (1) is grafted onto the ethylene polymer main chain is desirable.

In the ethylene copolymer used in the present invention, in addition to ethylene and the monomer represented by the general formula (I), another 7-mer can be added for modifying the resin, and the modifying monomer is 10 It can contain up to molar proportions. As the modifying comonomer, a hexamer known to be copolymerizable with ethylene can be used.

For example, vinyl esters such as vinyl acetate and vinyl propylate, acrylic esters such as ethyl acrylate, methyl acrylate, and butyl acrylate, methacrylic esters such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate, and ethylene such as acrylic acid and methacrylic acid. They are α, β unsaturated acids.

The above novel ethylene copolymer used in the present invention has a number average molecular weight of 1000 or more. When the molecular weight is less than 1000, long-term performance deteriorates. Preferably, the molecular weight is 3000 or more.

Since the ethylene copolymer used in the present invention is classified as a thermoplastic resin, other thermoplastic resins, such as polyethylene, polypropylene ethylene-vinyl acetate, etc. It can be used by blending with copolymers, petroleum resins, waxes, stabilizers, antistatic agents, anti-aging agents, voltage stabilizers, carbon black, ultraviolet absorbers, synthetic or natural rubber, lubricants, An inorganic filler or the like may also be mixed therein.

The ethylene copolymer used in the present invention is produced by subjecting predetermined monomers to copolymerization conditions,
It can be manufactured using a known high-pressure polyethylene manufacturing apparatus using radical polymerization.

This polymerization is preferably carried out in a continuous manner. As the polymerization apparatus, a continuous stirring seed reactor or a continuous hole tube reactor, which are commonly used in high-pressure radical polymerization of ethylene, can be used.

To prepare the ethylene copolymer used in the present invention, ethylene and the monomer represented by the general formula (I) are supplied to the above-mentioned polymerization apparatus and radically polymerized in the presence of the above-mentioned catalyst.

In this case, the ratio of ethylene and the monomer represented by the general formula (I) is appropriately selected so as to obtain an ethylene copolymer with a desired composition, but the polymerization of the monomer represented by the general formula (I) Since the monomer represented by the general formula (I) has a large capacity compared to ethylene, the monomer represented by the general formula (I) usually has o, o
Polymerization is carried out in the state of ethylene containing o i to 4 moles, preferably 0.001 to 2 moles.

The polymerization pressure employed must be above 5 ookp/d, preferably in the range 1000 to 4000 yonkp/d. Further, the polymerization temperature is at least 120°C, but preferably in the range of 150 to 300°C.

The polymer produced in the reactor or reactors can be separated from unreacted monomer and processed as in the production of conventional high pressure polyethylene. The mixture of unreacted monomers is mixed with an additional amount of the same monomers,
Repressurize and circulate to the reactor. The additional amount of monomer added as described above is of a composition that returns the composition of the mixture to that of the original polymerization system, and generally this additional amount of monomer is separated from the polymerization vessel. It has a composition roughly equivalent to that of the polymer.

In the above method, the reactor is preferably a seed reactor in order to obtain an ethylene copolymer with a uniform composition.

The catalyst is usually dissolved in a solvent with a small chain transfer effect and directly injected into the reactor using a high pressure pump. Concentration is 0.5-3
Approximately 0% by weight is desirable.

Suitable solvents include, for example, hexane, heptane, white spirit, hydrocarbon oils, cyclohexane, toluene, higher branched chain saturated fatty acid hydrocarbons, and mixtures of these liquids.

In addition, when injecting the monomer represented by general formula (I), it is possible to dissolve it alone or in a solvent with a small chain transfer effect,
Inject directly into the reactor with a high pressure pump. Examples of this solvent include aromatic compounds such as ethyl benzoate, toluene, and methyl benzoate, and fatty acid esters such as ethyl acetate.

In high-pressure radical polymerization, a chain transfer agent is generally used to adjust the molecular weight, except in special cases.

In the above method, any chain transfer agent used in normal high-pressure radical polymerization can be used. These gaseous ones are injected into the suction side of the compressor, and the liquid ones are injected into the reaction system using a pump. .

The ethylene copolymer used in the present invention produced in the reactor may be separated from the monomer in a separator according to the conventional method of high-pressure radical polymerization and used as is.
Various post-treatment steps such as those already used for products obtained by high-pressure radical polymerization may be performed.

The novel ethylene copolymer used in the present invention can be produced by the following method in addition to the high-pressure radical polymerization method described above. That is, commercially available high-pressure polyethylene, low-pressure polyethylene, etc., such as low-density polyethylene,
Medium density polyethylene, high density polyethylene, ethylene-
Vinyl acetate copolymer, ethylene-acrylic acid copolymer,
A monomer represented by general formula (I) is grafted onto an ethylene-methacrylic acid copolymer, an ethylene-methyl acrylate copolymer, an ethylene-methyl methacrylate copolymer, an ethylene-ethyl acrylate copolymer, etc. This is a manufacturing method.

For this graft production method, a known graft polymerization method can be adopted. For example, the above-mentioned commercially available polyethylene and the monomer represented by general formula (I) are used in such proportions that the ethylene copolymer used in the present invention has a desired composition, and the above-mentioned organic peroxide is added to this. After mixing the added ingredients in a super mixer, etc., the mixture is heated and mixed in a single-screw, twin-screw, etc. extruder, or a Banbury mixer, etc.
In this method, conditions commonly used for graft modification of polyethylene and the like can be employed.

The ethylene copolymer thus obtained can be used alone or by crosslinking a composition with a thermoplastic resin such as polyethylene or ethylene-vinyl acetate copolymer, especially an ethylene thermoplastic resin to form a crosslinked product. , this crosslinking is carried out using a common chemical crosslinking agent of 0.5 to 4 parts by weight per 100 parts by weight of the ethylene copolymer.
It can be carried out by adding 1 to 3 parts by weight, preferably 1 to 3 parts by weight, or it can be irradiated with about 5 to 20 megarads using cobalt 60 or phosphorus accelerator to crosslink with electron beams, or it can be crosslinked with ethylene. It is also possible to crosslink a polymer obtained by copolymerizing a vinyl monomer having an alkoxysilane such as vinyltrimethoxysilane in advance or afterward. When used for electric cables, among the above methods, chemical crosslinking is preferred.

As the chemical crosslinking agent, for example, the following free radical generating agents can be used. Specifically, dicumyl peroxide, t-butylcumyl peroxide, 2,5-
Dicumyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2゜5-di(t-butylperoxy)hexane-3, benzoyl peroxide, etc., which are commonly used as chemical crosslinking agents. It is.

The crosslinked product of the present invention obtained as described above contains a copolymer of ethylene and a monomer represented by general formula (1),
The crosslinked product has o-logogenated alkyl ester group units.
, o s to 10 molt, preferably 0.005 to 5
It will include morchi. And the crosslinked body is JIS
The gel fraction determined by the measuring method specified in C3005 is 40 or more. If the gel fraction is smaller than this value, the thermal deformation rate determined by the above measurement method will be large, which will cause a practical problem.

Experimental Example Reference Example 1 Using a stirred autoclave type continuous reactor with an internal volume of 1.51 t, ethylene was mixed at 40 y/hr and trifluoroethyl acrylate (abbreviated as TFEA) was mixed with acetic acid at a rate of 5002/l. 0.17 J/hour dissolved in ethyl,
Polymerization was carried out at a polymerization pressure of 2400 kf/d by continuously supplying propylene at a rate of 570 sl/hour with a solution prepared by dissolving propylene in n-hexane at a ratio of 21 F/7 (tertiarybutylperoxyisoptylene) as a catalyst and at a polymerization pressure of 2400 kf/d. temperature 220
The mixture was polymerized at ℃ to produce an ethylene copolymer.

The obtained ethylene copolymer has an MFR of 2.65'71
0 minutes, number average molecular weight 20,300, TFE in polymer
The content of A was 0.29 molti0 Reference Example 2 Using the same reactor as Reference Example 1, TFEA was added at 500 f/l.
Same as Reference Example 1, except that the mixture was dissolved in ethyl acetate at a ratio of 2.52 n/h, propylene was 23017 h, the same catalyst used in Reference Example IK was +eo*/h, and the polymerization temperature was 210°C. was polymerized to produce an ethylene copolymer.

The obtained ethylene copolymer has an MFR of 3.0t/10
The number average molecular weight was 19,800, and the content of NVI in the polymer was 3.1 mol.

Reference Example 3 The same reactor as Reference Example 1 was used, except that 17 fluorolauryl acrylate dissolved in ethyl acetate at a ratio of 2001711 was fed at 100-7 hours instead of TFEA, and the polymerization temperature was changed to 223°C. Polymerization was carried out in the same manner as in Reference Example 1.

The obtained ethylene copolymer has an MFR of 2.01710
minute, number average molecular weight 20,600. The content of 17 fluorolauryl acrylate in the polymer was 0.05 mole.

Examples 1 to 3, Comparative Example 1 The ethylene copolymers produced in Reference Examples 1 to 3 and commercially available high-pressure polyethylene "Yukalon ZFaoRJ [Mitsubishi Yuka ■, MFR = 1.Of / 10 minutes] were used as samples. The properties of these crosslinked polymers were evaluated using them as polymers.

To produce crosslinked polymers and prepare samples for property evaluation, the temperature of the Brabender mixer was set at 110°C, and 100 parts by weight of each sample polymer, 2 parts by weight of dicumyl peroxide as a crosslinking agent, and " Santonox RJ
3 parts by weight of O was added and kneaded for 5 minutes, and the mixed wire samples were heated to 50 μm each using a hot plate press kept at 130°C.
After preforming to a thickness of m and 5 mm, these were heated and pressed using a hot plate press at 180° C. and a gauge pressure of 1001 tcy/aJ for 20 minutes to form a crosslinked body.

The measurement method used for this characteristic evaluation is as follows0 (1) Molecular weight: Gel Permeation Chromadog2
According to the law.

(2) Comonomer content: Based on infrared spectroscopy.

(a) MFR: JIS K6760 (4) Density: JIS K6760 (5) Gel fraction: JIS c3005 (6)
Electric tree properties: As described above, each of the 5I and 111 thick sheets was molded and cut into 20×20 pieces. This cut piece has a diameter of 1
, 15 needles with a tip radius of curvature of 5 μm were inserted. On the other hand, a test piece was prepared by applying silver paste to the side opposite to where the needle was inserted (
(See Figure 1) 0 An alternating current voltage was applied to this test piece at a boost rate of 500 cm/SeC, and the voltage at which electric trees started to appear was measured.

(7) Water tree properties: As mentioned above, each sheet was molded into 5 sheets thick and 25 [×25 m!] It was cut out at 11. Insert a 1-diameter syringe needle into this cut piece for 20 cm, then pull it out for 15 cm while injecting distilled water, and paste a 10-diameter aluminum foil on the side opposite to where the syringe needle was inserted. This was used as a test piece (see Figure 2).

This test piece was applied with an AC voltage of 60 Hz and 10 KV for 5 minutes.
After the application for 0 hours, the average growth length of the water trees was observed using an optical microscope.

(8) Impulse high-pressure fracture characteristics: Impulse high-pressure fracture characteristics were measured using sheets each molded into a 50 μm thick sheet as described above.

The measurement was carried out using a negative standard impulse voltage, starting from a voltage of approximately 50% of the expected breakdown level, increasing the voltage by stepping up 2KV/3 times, and measuring the voltage at which breakdown occurred.

(9) Nonflammability: Oxygen index was measured according to JIS K7201.

Table 1K shows the characteristics evaluation results of the crosslinked ethylene copolymer.

Examples 4 to 7, Comparative Examples 2 to 3 Ethylene copolymers obtained in Reference Examples 1 to 3 and “Yukalon Z
Using F'3QRJ as a sample polymer, 6y class, 1X250-crosslinked polyethylene insulated cables (insulation thickness 3.5 cm) were prepared at the compounding ratios shown in Table 2. Note that an extruded semiconductive layer compound was used for the inner and outer semiconductive layers.

Impulse destruction tests were conducted on the resulting cables immediately after expansion. The breakdown voltage is l after applying 200KV/3 times.
It was determined by stepping up 0KV/3 times. Further, the obtained cable was subjected to submergence charging under 6 KV, I KHz O charging conditions. After electrification by immersion in water, the insulator was sliced into 0.5mm thick slices, boiled, and the number of bowtery generated inside the insulator was measured under 400x magnification using an optical microscope. After applying 40KV/30 minutes, 5 U 7
The AC breakdown value (AC breakdown value) was determined under the condition of 30 minute step-up.

(The following is a blank space) From the results shown in Tables 1 and 2, the crosslinked product of the present invention has excellent impulse breakdown resistance and AC breakdown resistance, as well as water tree properties, which are important as an insulating material for high-voltage power cables. It is clear that it has particularly excellent bow-tied tree properties and is useful for electrical insulation.

[Brief explanation of the drawing]

Figure 1 shows the second part of the test piece used to measure the electrical tree characteristics.
The figure is a schematic diagram of a test piece used for measuring water tree characteristics.

Claims (1)

[Claims] (1) Ethylene and general formula (I), ▲Mathematical formulas, chemical formulas, tables, etc.▼・・・・・・(I) (In the formula, R^1 is H or -CH_3, R^2 is C_1
A crosslinked product containing a copolymer of an ethylenically type α, β unsaturated acid with a halogenated alkyl ester represented by _ to _1_5 (indicating each halogenated alkyl ester),
The crosslinked product has 0.0 halogenated alkyl ester group units.
A crosslinked ethylene copolymer for electrical insulation, which contains 005 to 10 mol% and has a gel fraction of 40% or more as determined by a measuring method specified in JISC3005.