JPS6210120A - Electrical-insulatinb crosslinked ethylene copolymer - Google Patents

Abstract

PURPOSE:The titled crosslinked copolymer excellent in impulse breakdown resistance, AC breakdown resistance, inhibition of deterioration due to water tree, flexibility, etc., comprising a crosslinked copolymer of ethylene with an ethylenically alpha,beta-unsaturated benzophenone derivative. CONSTITUTION:An ethylene copolymer of a number-average MW >=1,000 is obtained by radical-polymerizing ethylene with 0.00065-1.3mol% ethylenically alpha,beta-unsaturated benzophenone derivative of the formula (wherein R is H or -CH3 and n is 0 or 1) at a temperature >=120 deg.C and a pressure >=500kg/cm<2> in the presence of a catalyst, e.g., 1-butyl peroxyisopivalate. 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 benzophenone derivative group unit 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 Cv
Although it is widely used as a cable insulation material, dielectric breakdown occurs under ultra-high voltages, and there is a need for materials with 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 characteristics. Therefore, impurity removal technology is being considered mainly for materials for ultra-high voltage cables, and Clean polyethylene, which does not contain any contaminants, and dry crosslinking technology, which does not create pores, have been developed. By making full use of these technologies, 275
Even KV 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 ■, 9
No. 5 (June 1980)) 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 However, there was a problem with long-term performance retention due to additive bleed-out (for example, Japanese Patent Publication No. 48-24809, West German Patent No. 124).
8773, French Painting Patent No. 14646-01, etc.).゛Summary of the Invention In view of these current circumstances, the inventors of the present invention have focused on developing crosslinked ethylene copolymers with excellent dielectric breakdown properties, long-term performance retention, flexibility, and no metal catalyst residue. We have succeeded in developing a crosslinked ethylene copolymer with excellent properties that satisfy the following requirements.

That is, the present invention relates to ethylene and the general formula (I), (wherein R
represents H or -〇H3, and n represents 0 or 1, respectively), and the crosslinked material contains a copolymer of an ethylenically type α,β unsaturated acid with a benzophenone derivative. Benzophenone derivative group unit is o, oos ~ 10
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 a measuring method specified in JIS C3005.

"Jjito Mugi i 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. Shows extremely excellent performance as an insulating material for high-voltage 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.
1), (wherein R represents H or -CHa, and n represents 0 or 1, respectively) A copolymer of an ethylenically type α,β unsaturated acid with a benzophenone derivative, the benzophenone derivative group It contains about 0,000 s to 10 mol% of units, preferably about 0.005 to 5 mol%.

Specifically, the monomer represented by general formula (1) is 2-
(4-benzoyl-3-hydroxyphenoxy)ethyl methacrylate, 2-(4-pensoyl-3-hydroxyphenoxy)ethyl acrylate, 2-hydroxy-
There are 4-(2-hydroxy-3-methacryloxy)propoxybenzophenone and 2-hydroxy-4-(2-hydroxy-3-acryloxy)propoxybenzophenone.

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 be contained up to mol%. As the modifying comonomer, monomers known to be copolymerizable with ethylene can be used.

For example, vinyl esters such as vinyl acetate and vinyl propionate, acrylic esters such as ethyl acrylate, methyl acrylate, and butyl acrylate, methacrylic esters such as methyl methacrylate, ether 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 falls within the category of thermoplastic resins, 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, and can be produced using a known high-pressure polyethylene production apparatus using radical polymerization.

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

The ethylene copolymer used in the present invention is produced by supplying ethylene and a monomer represented by the general formula (1) to the above-mentioned polymerization apparatus, and radically polymerizing the same in the presence of the above-mentioned catalyst.

In this case, the ratio of ethylene to the monomer represented by the general formula (I) is appropriately selected so as to obtain an ethylene copolymer of the desired composition, but the polymerizability of the monomer represented by the general formula (CI) is is large compared to ethylene, so the monomer represented by general formula CI) is usually 0.0% based on the total amount in the polymerization system.
0065-1.3 mol%, preferably 0.00065-1.3 mol%
Polymerization is carried out in the form of ethylene containing 0.8 mol 5.

The polymerization pressure employed is above 500 #/d, preferably in the range 1000 to +oooAy/-. 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 a polymer.

In addition, in the above-mentioned method, a seed reactor is preferable in order to obtain an ethylene copolymer having 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 (1), 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 aliphatic 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 ordinary high-pressure radical polymerization can be used.

These gaseous substances are injected into the suction side of the compressor, and the liquid substances are injected into the reaction system by a pump.

The ethylene copolymer produced in the reactor and used in the present invention may be separated from the monomer in a separator according to the conventional method of high-pressure radical polymerization and used as is, but Various post-treatment steps such as those used in manufactured products 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 the general formula CI) 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 method of manufacturing.

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 (1) are used in such a proportion that an ethylene copolymer used in the present invention having a desired composition is obtained, and the above-mentioned organic peroxide is further added thereto. The mixture is mixed in a super mixer, etc., and then heated and kneaded in a single-screw or twin-screw extruder, or a Banbury mixer. Can be adopted.

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 crosslinked with an electron beam by irradiation of about 5 to 20 megarads with cobalt 60 or a linear linear accelerator. It is also possible to crosslink a polymer obtained by copolymerizing a vinyl hexamer 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-7'thylperoxy)hexene-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 the general formula (-I), and the crosslinked product contains benzophenone derivative group units of o, o
It is contained in an amount of os to 10 mol%, preferably o, os to 5 mol%. And the crosslinked body is JIS
The gel fraction determined by the measurement method specified in C3005 is 4
It is 0% or more. If the gel fraction is smaller than this value, the thermal deformation rate determined by the above-mentioned measuring method becomes large, which poses a practical problem.

Experimental Example Reference Example 1 Using a stirred autoclave type continuous reactor with an internal volume of 1.5 t, ethylene was mixed at 32 #/hr with 2-(4-benzoyl-3-hydroxytaphenoxyether methacrylate (B).
(abbreviated as HPEMA) dissolved in toluene at a ratio of 7°1/1 was used at 590 d/hour, and propylene was dissolved at 4 Oa.
At time t1, tert-butyl peroxy isopivalate 3 as a catalyst? A solution dissolved in n-hexane at a ratio of 550-7 hr was continuously supplied at a polymerization pressure of 220 hr/L.
Polymerization was carried out at 0°C to produce an ethylene copolymer.

The obtained ethylene copolymer has MFR=3.0r/10
min, number average molecular weight 19,900, BHPE in polymer
The content of MA was 0.09 mol%.

Reference Example 2 Using the same reactor as Reference Example 1, B) IPEMA was 709
/L dissolved in toluene at a ratio of 3.42L/L
An ethylene copolymer was produced by polymerizing in the same manner as in Reference Example 1, except that propylene was used at 330 t/hr, the same catalyst used in Reference Example 1 was used at 59 ota/hr, and the polymerization temperature was 200°C.

The obtained ethylene copolymer had MFR=4.0f/10
minute, number average molecular weight 18,800. BHPE in polymer
The content of MA was 0.45 mol%.

Reference Example 3 BHPEMA was added to 2-hydroxy-4-(2-hydroxy-3-methacryloki7)propoxybenzophenone (H
(abbreviated as HMPB), and change HHMPB to rot/l.
An ethylene copolymer was produced by polymerizing in the same manner as in Reference Example 1, except that the solution dissolved in toluene was supplied at a rate of 59 oy/hour and the polymerization temperature was changed to 201°C.

The obtained ethylene copolymer had an MFR of 3. of/10
min, number average molecular weight 20,000, HHMP in polymer
The content of B was 0.08 mol%.

Examples 1 to 3, Comparative Example 1 Sample polymerization of the ethylene copolymers produced in Reference Examples 1 to 3 and commercially available high-pressure polyethylene "Yukalon ZF30RJ (manufactured by Mitsubishi Yuka, MFR = 1.0 f/10 minutes)" The characteristics of these cross-linked polymers were evaluated using these materials.

To prepare samples for production and characteristic evaluation of crosslinked polymers, the temperature of the Prabender 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 [ as an antiaging agent] Santonox RJ
After adding 3 parts by weight of O, and kneading for 5 minutes each, the mixed wire sample was preformed to a thickness of 5 m using a hot plate press kept at 130°C, and then kneaded using the same hot plate press at 180°C for 1 minute.
It was heated and pressed for 20 minutes at 00I4/- gauge pressure to form a crosslinked sheet of 5-thickness.

The measurement method used to evaluate the properties of this crosslinked product was as follows:
It is as follows.

(1) Molecule Jl: According to Köl permeation chromatography.

(2) Comonomer content: Based on infrared spectroscopy.

(3) MFR: JIS K6760 (4) Density: JIS K6760 (5) Gel fraction: JIS C3005 (6) Electric tree properties: 20
It was cut out to w x 20m. A needle with a diameter of 11 m and a tip radius of curvature of 5 μm was inserted into the cut piece for 15 μm. On the other hand, a test piece was prepared by applying silver paste to the opposite side to where the needle was inserted (see Figure 1).

An alternating current voltage was applied to this test piece at a voltage increase rate of 500 V/see, and the voltage at which electric tree generation started was measured.

(7) Water tree properties: Each sheet was molded into a 5m thick sheet and cut into 20cm x 20+w* pieces.

After inserting a syringe needle with a diameter of 1 mm into this cut piece for 20 m, it was pulled out for 15 m while injecting distilled water, and a 10 m wide aluminum foil was pasted on the side opposite to where the syringe needle was inserted. (See Figure 2).

After applying an AC voltage of 60H1, 10KV to this test piece for 50 hours, the average length of water tree growth was observed using an optical microscope.

Table 1 shows the characteristics evaluation results of the crosslinked product.

(Left below) Examples 4 to 7, Comparative Examples 2 to 3 Ethylene copolymers obtained in Reference Examples 1 to 3 and "Yukalon Z"
Using F30RJ as a sample polymer, 6 KV class, 1 x 250-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 manufacture. The breakdown voltage is 1 after applying 200ff/3 times.
It was determined by stepping up 0ff/3 times. Further, the obtained cable was subjected to submergence charging under the charging conditions of 6ff and IKHz.

After applying the water immersion voltage, the insulator was sliced into 0.5-inch thick slices, and after boiling, the number of bowtery in the insulator was measured using an optical microscope at 400 times magnification. In addition, for the sample after water immersion voltage application, the AC breakdown value (AC breakdown value) was determined under the conditions of applying 40KV/30 minutes and then stepping up to 5KV/30 minutes.

(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 drawings]

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. Patent applicant Mitsubishi Yuka Co., Ltd. Patent applicant Furukawa Electric Co., Ltd. Agent Patent attorney Hidetoshi Furukawa Agent Patent attorney Masahisa Hase Figure 1

Claims (1)

[Claims] (1) Ethylene and the general formula (I), ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) (In the formula, R represents H or -CH_3, and n represents 0 or 1, respectively) A crosslinked product containing a copolymer of an ethylenically type α,β unsaturated acid with a benzophenone derivative, the crosslinked product having a benzophenone derivative group unit of 0.
005 to 10 mol%, and the gel fraction of the crosslinked product determined by the measuring method specified in JISC3005 is 40
% or more of ethylene copolymer crosslinked material for electrical insulation.