JPS6210116A - Ethylene copolymer and its production - Google Patents

Abstract

PURPOSE:To obtain a copolymer excellent in dielectric breakdown characteristic, long-term performance retention and flexibility and containing no metallic catalyst residues, by polymerizing ethylene containing phenyl or benzyl (meth) acrylate in specified conditions. CONSTITUTION:Ethylene containing 0.01-2mol%, based on the total, monomer represented by the formula (wherein R is H or -CH3 and n is 0 or 1) at a reaction temperature >=120 and a reaction pressure >=500kg/cm<2> in the presence of a free radical-generating initiator. Examples of the monomers of the formula include phenyl acrylate, phenyl methacrylate, benzyl acrylate and benzyl methacrylate. With respect to the polymer structure of the ethylene copolymer, a random copolymer or a graft copolymer obtained by grafting a monomer of the formula onto an ethylene polymer skeleton is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a novel ethylene copolymer and a method for producing the same.

The novel ethylene copolymer of the present invention serves as a material for power cables that has excellent dielectric breakdown properties such as withstand voltage properties, particularly electrical tree properties and water tree properties.

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, such cross-linked polyethylene insulation chamber capules for high voltage use have the disadvantage that the insulation thickness becomes extremely thick, and a material with even better withstand voltage characteristics is desired.

If the material itself has the function of avoiding charge concentration, it can be manufactured with a thin material.Therefore, attempts have been made to use calcium stearate, various aromatic compounds, etc. as voltage stabilizers, but methods using these additives have not been successful. , additives may bleed out, causing problems in long-term performance retention (for example, Japanese Patent Publication No. 48-24809, West German Patent No. 12)
48773, French Painting Patent No. 1464601, etc.).

Summary of the Invention In view of these current circumstances, the present inventors have focused on developing an ethylene copolymer with excellent dielectric breakdown properties, long-term performance retention, flexibility, and no metal catalyst residue. Successfully developed a copolymer.

That is, the present invention first relates to a copolymer of ethylene and a monomer represented by the general formula (1) (wherein R represents H or -CH, and n represents 0 or 1, respectively). Second, an ethylene copolymer containing 0.005 to 10 mol of phenyl or benzyl ester group units is prepared by the general formula (I), (where RijH or -CH3 is represented, and n represents O or 1, respectively). 0.01 to 2 mol% (
The present invention provides a method for producing an ethylene copolymer, which comprises polymerizing ethylene containing (based on the total amount) at a reaction temperature of 120° C. or higher and a reaction pressure of 500 #/i or higher using a free radical generation initiator. be.

Effects of the Invention The novel ethylene copolymer of the present invention satisfies all required performances as an insulating material for electrical cables, including voltage resistance, long-term performance retention, flexibility, no metal residue, and cable coating properties. In particular, it shows extremely excellent performance as an insulating material for high-voltage power cables.

DETAILED DESCRIPTION OF THE INVENTION The ethylene copolymer of the present invention is a novel copolymer that has not been described in any literature. 0.005 to 10 mol%, preferably 0.005 to 10 mol%, preferably 0.005 to 10 mol% of phenyl or benzyl ester group units. It contains about 5 to 5 mol of Oo.

Specifically, the monomer represented by general formula (1) is phenyl acrylate, phenyl methacrylate, benzyl acrylate, and benzyl methacrylate.

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 (I) is grafted onto the ethylene polymer main chain is desirable.

The ethylene copolymer of the present invention comprises ethylene and general formula (I)
In addition to the monomer represented by, other monomers can be added for modifying the resin, and the modifying monomer can be contained up to 10 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, ethyl methacrylate, and butyl methacrylate, and ethylene such as acrylic acid and methacrylic acid. They are α, β unsaturated acids.

The novel ethylene copolymer of the present invention has a number average molecular weight of 10
00 or more. When the molecular weight is less than 1000, long-term performance deteriorates. Preferably, the molecular weight is 3000 or more.

The ethylene copolymer of the present invention can be applied to various uses in addition to the above-mentioned use as an insulating material for power cables. For example, it can be used as an insulating material for wires and cables by extrusion molding, or it can be formed into a film by a T-die method or an inflation method and used as an insulating film or a general-purpose film.

The ethylene copolymer of the present invention can also be used to produce various molded products by blow molding, injection molding, extrusion molding, etc. As a specific example of extrusion molding, a laminated film can be obtained by extrusion coating a film made of another plastic or a material other than plastic (metal foil, paper, cloth, etc.).

Since the ethylene copolymer of the present invention falls under the category of thermoplastic resins, it can be used with other thermoplastic resins such as polyethylene, polypropylene ethylene-vinyl acetate copolymers, etc., which are commonly used in this type of resin materials. It can also be used by blending with coalescents, 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.

Further, it can also be used as a crosslinked product by a chemical crosslinking agent, electron beam, or graft copolymerization of vinyltrimethoxysilane or the like. In this case, commonly used chemical crosslinking agents such as dicumyl peroxide and percadox can be used, and furthermore, it is not impossible to use anti-aging agents and other additives in combination.

The ethylene copolymer of 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.

The catalyst used in this radical polymerization is a compound that generates free radicals, such as oxygen, tertiary butyl peroxide, tertiary butyl cumyl peroxide,
Dialkyl peroxide such as dicumyl peroxide, diacyl peroxide such as acetyl peroxide, isobutyl peroxide, octanoyl peroxide, diisopropyl peroxydicarbonate, di-2
- Peroxy dicarbonates such as ethylhexyl oxydicarbonate, peroxy esters such as tert-oxyisobutyrate, tert-butyl peroxypivalate, tert-butyl peroxylaurate, methyl ethyl ketone peroxide, cyclohexanone Ketone peroxide such as peroxide, oxyketal (such as 1,1 bistaryabutyl peroxycyclohexane, 2,2 bistaryabutyl peroxyoctane, etc.), tert-oxyketal, tertiarybutylhydronoxide, cumenepyroper Hydroperoxides such as oxide, azo compounds such as 2.2 azobisisobutyronitrile.

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.

The polymerization can be carried out as a single zone process using these single reactors, but many reactors can be used in series, possibly with connected condensers, or several internal sections can be used for each zone process. A single reactor can also be used, effectively divided into zones. In each zone method, the reaction conditions in each zone are varied to control the properties of the polymer obtained in each reactor or reaction zone. It is common to adjust body composition, catalyst concentration, molecular weight regulator concentration, etc. When multiple reactors are connected in series, in addition to the combination of two or more seed reactors or two or more tube reactors, one or more seed reactors and one or more tube reactors are used. Combinations with type reactors can also be used.

In the present invention, ethylene and a monomer represented by general formula (T) are supplied to the above-mentioned polymerization apparatus, and radically polymerized in the presence of the above-mentioned catalyst. In this case, ethylene and the general formula (
The proportion of the monomer represented by 1) is appropriately selected so that the ethylene copolymer of the present invention has a desired composition, but the polymerization ability of the monomer represented by general formula (I) is compared to that of ethylene. Since the monomer represented by the general formula (1) is large in size, the monomer represented by the general formula (1) is usually polymerized in the state of ethylene containing 0.01 to 2 molti, preferably 0.01 to 1 molti based on the total amount in the polymerization system.

The polymerization pressure employed is above soow/d, preferably in the range of 1000 to 4000 #/-. 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 the present invention, the reactor is preferably a seed reactor in order to obtain a 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
0 weight S weight S type.

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 present invention, all chain transfer agents used in ordinary high-pressure radical polymerization can be used.

For example, alkanes such as ethane, propane, butane, hexane, heptane, alkenes such as propylene, butene, hexene, alcohols such as ethanol, methanol, propatool, ketones such as acetone, methyl ethyl ketone, acetaldehyde, propionaldehyde, etc. Aldehydes such as, and many other compounds used in high-pressure methods 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 of the present invention produced in the reactor is separated from monomers in a separator according to the conventional method of high-pressure radical polymerization, and becomes a product as it is. This product may be used as it is, or may be subjected to various post-treatment steps such as those already used for products obtained by high-pressure radical polymerization.

The novel ethylene copolymer of 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, ethylene-methacrylic acid copolymer, Ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-This grafting method uses known grafts in proportions that will result in the ethylene copolymer of the present invention, and further adds the above-mentioned After mixing the organic peroxide-added material using a super mixer, etc., use a single-screw, twin-screw extruder, or Pan Bali S mixer.
For this method, conditions commonly used for graft modification of polyethylene and the like can be employed.

Experimental Examples Example 1 Using a stirred autoclave type continuous reactor with an internal volume of 1.56 cm, ethylene was fed at a 2 #/hour, benzyl methacrylate (abbreviated as BMA) was fed at 64 P/hour, propylene was fed at 5 s o t/hour, As a catalyst, a solution dissolved in n-hexane at a ratio of 2 P/l of tertiary butylperoxyisobutylene was continuously supplied at a rate of 600 mj/hour, and polymerization was carried out at a polymerization pressure of 2400 kg/-1 and a polymerization degree of 220°C. An ethylene copolymer was produced.

The obtained ethylene copolymer has MFR=3.0P/l0
The number average molecular weight was 20,000, and the content of BMA in the polymer was 0.16 mol.

Example 2 Using the same reactor as Example 1, HMA was fed at 320 P/hour,
An ethylene copolymer was produced by polymerizing in the same manner as in Example 1, except that propylene was used at 500 t/hour, the same catalyst used in Example 1 was used at 320 ml/hour, and the polymerization temperature was 218°C.

The obtained ethylene copolymer had MFR=3F/10 minutes,
The number average molecular weight was 19,900, and the content of HMA in the polymer was 0.83 mol.

Example 3 Example 10 Phenyl methacrylate (P) instead of BMA
(abbreviated as MA) was used at 671/hour, and the polymerization temperature was 22.
An ethylene copolymer was produced by polymerizing in the same manner as in Example 1 except that the temperature was 3°C.

The obtained ethylene copolymer had MFR=4y/10min,
The number average molecular weight was 18,900, and the content of PMA in the polymer was 0.18 mol.

Reference Examples 1 to 4 (Evaluation of properties of uncrosslinked products) Ethylene copolymers of the present invention produced in Examples 1 to 3 and commercially available high-pressure polyethylene [Yukalon ZF30RJ (Mitsubishi Yuka)
(MFR=1.0P/l0min) was used as a sample polymer to evaluate the characteristics of these polymers.

The measurement method used for this characteristic evaluation is as follows.

(1) Molecular weight: Based on the Köl permeation chromatography method.

(2) Comonomer content: Based on infrared spectroscopy.

(3) MFR: JIS K6760 (4) Density: JIS K6760 (5) Gel fraction: JIS C3005 (6) Electric tree properties: The sample polymer was made into a 5-layer sheet at 160°C and 150 #/i. 20 tIIIX 2 of each molded product
It was cut out at 0 m. This cut piece has a diameter of III + 1.
Fifteen segments of a needle 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 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/sec, and the voltage at which electrical tree generation started was measured.

(7) Water tree properties: The sample polymer was heated at 160°C and 1 sow/d.
25m x 25m each formed into m-thick sheets
I cut it out. Insert a syringe needle with a diameter of 20 mm into this cut piece.
After insertion, it was pulled out for 15 cm while injecting distilled water, and a 10 cm wide aluminum foil was pasted on the side opposite to where the injection needle was inserted to prepare a test piece (see Figure 2).

After applying an alternating current voltage of 60 H2, 10 KV to this test piece for 50 hours, the average growth length of water trees was observed using an optical microscope.

The characteristics evaluation results of the ethylene copolymers of the present invention produced in Examples 1 to 3 and Yucalon ZF30RJ are shown in Table 1. To prepare samples for 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 3 parts by weight of Santonox R40 as an antiaging agent were added. In addition, each sample was kneaded for 5 minutes, and the mixed wire sample was preformed to a thickness of 511II using a hot plate press kept at 130°C.
These were also heated at 180℃ using a hot plate press at a rate of 100 per centimeter/c.
The mixture was heated and pressed at tI gauge pressure for 20 minutes to form a crosslinked product.

Cut pieces similar to those in Reference Examples 1 to 4 were made using this crosslinked body, and test pieces were made using the cut pieces.

The results of this characteristic evaluation are shown in Table 2.

(Leaving space below) From the results shown in the reference examples above, the novel ethylene copolymer of the present invention has extremely excellent electrical tree properties and water tree properties, which are particularly important as materials for high-voltage power cables, and is also suitable for use as power cables. Usually, a crosslinked product is used, but it is clear that this crosslinked product has particularly excellent water tree properties compared to an uncrosslinked product, and this excellent effect was obtained for the first time with the ethylene copolymer of the present invention. It is something.

[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. Agent Patent Attorney Hidetoshi Furukawa Agent Patent Attorney Masahisa Hase Figure 1 Figure 2

Claims (2)

[Claims] (1) Ethylene and the general formula (I), ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) (However, R represents H or -CH_3, and n represents 0 or 1, respectively) A copolymer with a monomer containing 0.005 to 0.005 phenyl or benzyl ester group units.
Ethylene copolymer containing 10 mol%. (2) General formula (I), ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) (However, R represents H or -CH_3, and n represents 0 or 1, respectively). 0.01 to 2 mol% (
A method for producing an ethylene copolymer, which comprises polymerizing ethylene (based on the total amount) at a reaction temperature of 120° C. or higher and a reaction pressure of 500 kg/cm^2 or higher using a free radical generating initiator.