JPH04180940A - Preparation of cross-linked polyolefin molding - Google Patents

Abstract

PURPOSE:To prepare the title molding cross-linked uniformly with a high cross- link density deep into a thick section by irradiating a molding of a crystalline polyolefin contg. photosensitizers having different ultraviolet absorption bands with ultraviolet rays above the m.p. of the polyolefin. CONSTITUTION:A molding of a crystalline polyolefin (e.g. a low-density polyethylene, or a high-density polyethylene) contg. photosensitizers having different ultraviolet-absorption bands [e.g. benzophenone or 2-benzyl-2- dimethylamino-1-(morpholinophenol)-butanone] is irradiated with ultraviolet rays above the m.p. of the polyolefin, giving a cross-linked polyolefin molding. As all the crystalline part of the polyolefin is in a molten state above the m.p., the polyolefin has a good transparency in the irradiation, improving the transmission efficiency of UV rays significantly, increasing the cross-linking efficiency, and enabling a uniform cross-linking with a high cross-link density deep into a thick section.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for producing a crosslinked polyolefin molded article by an ultraviolet irradiation crosslinking method.

[Conventional technology]

Known methods for crosslinking polyolefins such as polyethylene include radiation crosslinking using electron beams and chemical crosslinking using H peroxide. Is radiation crosslinking good? Is the crosslinking efficiency good? Radiation transmission efficiency ○
For this reason, it is limited to thin-walled molded products with a thickness of about mm or less, and has disadvantages such as high equipment costs and dangerous operation. Chemical crosslinking is not applicable to thick-walled molded products; it takes time for crosslinking, and requires crosslinking equipment for one-time heating and pressurization. Additionally, when extrusion molding or injection molding polyolefin compositions containing organic peroxides, some of the organic peroxides decompose and produce so-called scorch, which hinders long-term operation of molding equipment. Sometimes. Furthermore, in the field of insulated wires, a silane crosslinking method is known. In this case, if the thickness of the coating, such as the insulating layer, which undergoes a crosslinking reaction by reaction with water, is 3 to 4 mm or more, water penetration is slow and crosslinking takes a long time. Maf
Second, there is the disadvantage that a small amount of moisture remains and the electrical characteristics are not sufficient. On the other hand, crosslinking by ultraviolet irradiation has been put to practical use in the fields of ultraviolet curing paints and photorenost. However, cross-linking of crystalline polyolefins such as polyethylene by ultraviolet irradiation is still far from practical use. On the other hand, the present inventors have previously developed methods for crosslinking crystalline polyolefins by subjecting them to crystalline polyolefins at temperatures above their crystal melting point. By irradiating ultraviolet light,
We have discovered that crystalline polyolefins can be efficiently crosslinked with ultraviolet rays, and we are working on its practical application.

[Problem to be solved by the invention] However, if a thick material is crosslinked in a short time using the above method, crosslinking of the surface layer exposed to ultraviolet rays tends to progress, and there is a possibility that the degree of crosslinking tends to vary in the thickness direction. [Means to solve the problem]

The present invention was made in order to solve the above problems, and it is an object of the present invention to produce a molded article consisting of a crystalline polyolefin and various types of photosensitizers having different absorption bands of ultraviolet rays at a temperature higher than the crystal melting point of the crystalline polyolefin. , ultraviolet rays are irradiated at f2.

[Effect]

At temperatures above the crystal melting point, all of the crystalline portions of the crystalline polyolefin are in a molten state, resulting in good transparency. Therefore, the transmission efficiency of ultraviolet rays is greatly improved, and the crosslinking efficiency is increased. Here, the crosslinking efficiency by ultraviolet irradiation is first determined by the degree of light absorption of the irradiated object. Generally, light absorption is expressed by the following formula. A-ε・d-C A: Absorption amount (dimensionless) ε: Molecular extinction coefficient of photosensitizer (1/mol・am) d:
Sample thickness (cm) C・Initiator concentration (mol/]) As is clear from the above equation, when the sample thickness and initiator concentration are constant, the larger the molecular extinction coefficient, the larger the absorption amount. This molecular extinction coefficient is a value inherent in the substance, for example, for hensifhenone, ε = 18900 (λ - 252 nm)
, ε-156 (λ-331 nm). Note that λ is the ultraviolet wavelength of the absorption peak. By the way, it is well known that the longer the wavelength of light such as ultraviolet rays, the greater the transmittance. Therefore, when crosslinking (polymerizing) a thick material, it is essential to absorb ultraviolet rays on the longer wavelength side. Second, in the case of ultraviolet irradiation crosslinking (polymerization), there is an oxygen inhibiting effect in the air, which inhibits crosslinking, so it is necessary to increase the crosslinking (polymerization) efficiency near the surface. In the present invention, the above problem is solved by using a photosensitizer having an absorption band on the long wavelength side and a photosensitizer having an absorption band on the short wavelength side. The present invention will be explained in detail below. The crystalline polyolefin used in this invention includes:
There are ethylene copolymers such as polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-11 ethylene/propylene copolymer, among others, low-density polyethylene, high-density polyethylene, linear polyethylene, ultra-low Polyethylenes such as density polyethylene and ultra-high molecular weight polyethylene are preferred because they have high crosslinking efficiency. Of course, a mixture of these may be used. This crystalline polyolefin is made into a molded product by various molding methods as a mixture with a photosensitizer. This mixture may be further mixed with an ultraviolet absorber or this ultraviolet absorber and a crosslinking aid to form a molded product. The photosensitizers used here include benzophenone,
Benzophenones such as 4-chlorobenzophenone, 2-chlorobenzophenone, 4.4°-dichlorobenzophenone, hexachlorobenzophenone, and 2-benzyl-
2-dimethylamino-1-(4-morpholinephenol)-butanone and chlorendic anhydride,
"Suntory 1000j (trade name: manufactured by Monsanto) etc. are used. In the present invention, from among these photosensitizers, various photosensitizers with different ultraviolet absorption bands are combined to form crystalline polyolefins. The compounding amount of this photosensitizer is 100% of the crystalline polyolefin.
It is preferably about 0.2 to 3 parts by weight. If it is less than 0.2 parts by weight, the effect of improving the crosslinking system cannot be obtained, and if it exceeds 23 parts by weight, it is excessive and the electrical properties of the molded product after crosslinking are reduced. It is undesirable because it deteriorates physical properties, mechanical properties, etc. By adding a photosensitizer, the crosslinking efficiency is greatly improved, making it possible to achieve high crosslinking levels in a short period of time. However, as ultraviolet absorbers, salicylic acid derivatives such as phenyl salicylate, 2-(2°-hydroquino-5-
methylphenyl)hencytriazole, 2-hydroquinohensephenone, 2-hydroquine-4-methoxybenzophenone, 2-hydroquino-4-octoxybenzophenone, 2,2'-dihydroxy-4-meth Hydroquinhensiphenones such as quinfenone are preferably used. For example, phenyl salicylate is optimal because it absorbs ultraviolet rays of 320 nm or less. The blending amount of this ultraviolet absorber is 100% of crystalline polyolefin! It is determined in the range of 0.05 to 1 part by weight. If the amount is less than 0.005 parts by weight, the ability to prevent the deterioration of crystalline polio fins during UV irradiation will be low, while if it exceeds 1 part by weight, it will be possible to control UV deterioration, but the ability to prevent UV rays from being irradiated or UV absorption will be low. The degree of absorption into the agent increases, which reduces the crosslinking effect, which is undesirable. Compounds having a hydrogen accepting group such as triallyl noanurate, triallyl isocyanurate, and N,N'-m-phenylene dimaleimide are used as the crosslinking auxiliary agent. , for promoting the crosslinking reaction. The amount of this crosslinking aid to be blended is preferably in the range of usually 0.3 to 4 parts by weight per 100 parts by weight of the crystalline polyolefin. If it is less than 0.3 parts by weight, the effect of these additions cannot be obtained sufficiently, and if it exceeds 4 parts by weight, it is excessive and has an adverse effect on the physical properties of the molded product after crosslinking, which is disadvantageous. In addition to the above-mentioned photosensitizers, ultraviolet absorbers and crosslinking aids, tetrakis-[methylene-3-(3°.5'-di-tert-butylene-4'-hydroquinophenyl)propionate comethane Additives and fillers that do not impair transparency under the temperature conditions during irradiation, such as anti-aging agents, can be added as appropriate. Furthermore, a foaming agent such as 4,4-oxenobis-sulfonylhydranoate, azonocarbonamide, etc., which foams under the temperature conditions during irradiation, is added, and according to this, a foamed cross-linked molded product can be produced. I can do it. In addition, as a means for molding a mixture of a crystalline polyolefin and a photosensitizer, or a mixture to which an ultraviolet absorber or a crosslinking aid is added, various methods conventionally used for molding crystalline polyolefins can be used. things can be applied. If the molded product is in the form of a belt, film, tube, or pipe, extrusion molding using a normal extrusion molding machine is used. If the molded product is a covering for electric wires or cables, such as insulators or north, an extrusion covering method using an extruder equipped with a rad die or a method of winding a tape may be used. Furthermore, it may be made into a molded product using a normal injection molding method. However, molded products with complex shapes are heated above the crystal melting point when irradiated with ultraviolet rays, which may cause the shape to collapse, so it may not be appropriate, or when irradiated with ultraviolet rays, the molded product must be UV transparent and heat resistant. If a measure is taken to house the molded article inside a mold made of a material having a certain property, such as quartz glass, the molded article may have a complicated shape. Further, the thickness of the molded product is at the upper limit of 10 to 15 rAm if it is shaped like a notebook and can be irradiated with ultraviolet light from both sides, and at the upper limit is 5 to 8 IIIn if it is irradiated only from one side. Of course, if the intensity (energy density) and irradiation time of the ultraviolet rays are increased and the irradiation time is increased, a thicker molded product may be obtained, but care must be taken since the deterioration of the crystalline polyolefin due to the ultraviolet rays also progresses at the same time. Next, the molded article thus obtained is irradiated with ultraviolet rays at a temperature equal to or higher than the crystalline melting point of the crystalline polyolefin. This temperature condition is, in principle, above the crystal melting point, or
Preferably, the temperature is about 10 to 20°C higher than the crystal melting point. However, too high a temperature is undesirable as it may advance thermal deterioration of the crystalline polyolefin. For those made of crystalline polyolefin with a strength higher than that used for moldings,
The temperature condition is set to be higher than the highest crystal melting point. Further, as the ultraviolet irradiation conditions, a radiation source with a wavelength not less than 200 nm is used. For this purpose, a high-pressure mercury lamp (wavelength range 250-600nm) is required.
) or metal halide (wavelength range 200 to 600 nm) are suitable. In particular, metal halide lamps have a large spectrum on the long wavelength side of 350 nm or more, have good transparency, and are suitable for thick objects. In addition, its strength (energy density) is lo-4 to 1O
-6 Einstein/Cm!・A range of minutes is preferable. The irradiation time varies depending on the crosslinking density, the thickness of the molded product, etc., and is usually about 10 to 60 seconds, but is not limited to this range. For example, if only the surface of the molded product is to be crosslinked, , it may be even shorter. Furthermore, if the shape of the molded product is a flat plate such as a sort or a film, if ultraviolet light beams are placed on both sides of the molded product, the thick molded product can be crosslinked in a short time. In addition, electric wire,
In the case of a covering such as a cable, it is also possible to uniformly distribute the light sources outside the periphery of the cable so that the entire outer periphery is uniformly irradiated. If a coating is provided directly above the metal conductor such as copper, the surface of the metal conductor acts as a reflective surface and reflects the ultraviolet rays, making it possible to efficiently utilize the ultraviolet rays. In addition, if the molded product is a hollow cylindrical object such as a tube or a vibrator, it can be uniformly irradiated from the outer periphery in the same way, and if the inner diameter of the hollow part is large, an ultraviolet light source can be placed inside the hollow part. It may be arranged and irradiated from the inside and outside at the same time. Furthermore, an ultraviolet light source may be placed close to the exit portion of the die of the extrusion molding machine, and the ultraviolet light source may be directly irradiated with ultraviolet light at a high temperature equal to or higher than the crystal melting point immediately after extrusion. By irradiating ultraviolet rays under such conditions, for example, polyethylene can be crosslinked to a degree of crosslinking density of up to about 90%, and a polyethylene notebook with a thickness of about 3 mm can be crosslinked in 10 to 30 seconds. The molded product after crosslinking is cooled by cooling means such as natural air cooling or water cooling to become a crosslinked molded product. In this method of manufacturing cross-linked polyolefin molded products, the crystalline polyolefin is completely amorphous and transparent, and is exposed to ultraviolet rays in a good state. When the crosslinking is completed, crosslinking is uniformly performed. In addition, since it is above the crystal melting point,
The movement of polymer molecules becomes active, and the crosslinking reaction progresses more quickly. In particular, by adding a photosensitizer, the sensitizing effect improves the efficiency of light energy utilization and accelerates the crosslinking reaction, and when a crosslinking aid is added, the concentration of active groups increases and the polymer molecule This will promote interchain reactions. In addition, due to the action of the ultraviolet absorber, the photodecomposition of the crystalline polyolefin itself due to ultraviolet rays is minimized, and although there is a slight decrease in the crosslinking rate, the coloring and mechanical strength of molded products due to photodecomposition are prevented. It can be prevented. Hereinafter, specific examples will be shown to clarify the effects.

【Example】

To 100 parts by weight of low-density polyethylene with a melt index (MI) of 1, 1 part by weight of 4-chlorobenzophenone as a photosensitizer, 2-henozyl-2-dimethylamino-1-(4-morpho) 0 to 1 part by weight of (phosphophenol)-butanone and 114 parts of triallylisocyanurate as a crosslinking agent were added, and an insulator was formed to a thickness of 3 cm on a conductor with a cross-sectional area of 100 mm2 at a temperature of 160 °C using an extruder.
mm was coated. After extrusion coating, the insulator temperature is maintained at 150°C or higher, and the UV rays are introduced into the ultraviolet irradiation section, where the wavelength range is 200 to 400.
(nm), intensity 1.5xlO' (Einnouutaine/c
After 20 seconds of irradiation with ultraviolet rays (rn'・min), the material is introduced into a cooling tank.
Obtained insulated wire. Inner layer, middle layer, and outer layer of each insulated wire manufactured with photosensitizers 4-chlorobenzophenone and 2-bentrue-2-dimethylamino-1-(4-morpholinephenol)-butanone in the parts by weight shown in Table 1. Table 1 shows the results for each degree of crosslinking. Table 1 A, B Shelf @ Review (%): Weight! 'Heavyweight section inner layer middle layer? (layer・, 010・00.0 '0 10.j80', 7010 '0 11) 85175', 40 i j jj' 10.5:, 0 1,10', 40', 800・J'
0, 518 ol, go's 5□0, 5-1
185180185□A, 4-chlorobenzophenone B: 2-benzyl-2-dimethylamino-1-(4-morpholinephenol)-butanone From the results in Table 1,
As a photosensitizer, 4-
By using chlorobenzophenone and 2-2-dimethylamino-1-(4-morpholinephenol)-butanone, which absorbs long wavelength ultraviolet rays, in combination, insulation with a uniform degree of crosslinking can be achieved in the inner, middle, and outer layers. Get a body or be recognized for what you can do.

【Effect of the invention】

As explained above, the method for producing a crosslinked polyolefin molded product of the present invention involves adding a molded product consisting of a crystalline polyolefin and various photosensitizers with different ultraviolet absorption bands to a molded product having a temperature higher than the crystal melting point of the crystalline polyolefin. Since ultraviolet rays are irradiated under temperature conditions, even thick polyolefin molded products can be efficiently crosslinked deep within the molded product with a uniform high crosslinking density and in a short time.

Claims (7)

[Claims] (1) Crosslinking characterized by irradiating a molded product made of a crystalline polyolefin and various photosensitizers with different ultraviolet absorption bands with ultraviolet rays at a temperature higher than the crystalline melting point of the crystalline polyolefin. Manufacturing method for polyolefin molded products. (2) Irradiating a molded product made of a crystalline polyolefin, various photosensitizers with different ultraviolet absorption bands, and an ultraviolet absorber with ultraviolet rays at a temperature equal to or higher than the crystalline melting point of the crystalline polyolefin. A method for producing a crosslinked polyolefin molded product characterized by: (3) A molded product consisting of a crystalline polyolefin, various types of photosensitizers with different ultraviolet absorption bands, an ultraviolet absorber, and a crosslinking aid, at a temperature higher than the crystal melting point of the crystalline polyolefin, A method for producing a crosslinked polyolefin molded product, which is characterized by irradiation with ultraviolet rays. (4) In the method for producing a crosslinked polyolefin molded product according to any one of claims (1) to (3), the photosensitizer is chlorobenzophenone and 2-benzyl-2-dimethylamino-1-(4-morpholine). A method for producing a crosslinked polyolefin molded product, characterized in that it is made of phenol)-butanone. (5) Claim in which the molded product is a covering for electric wires or cables (
1) The method for producing a crosslinked polyolefin molded product according to any one of (4). (6) The method for producing a crosslinked polyolefin molded product according to any one of claims (1) to (4), wherein the molded product is a cylindrical object such as a tube or a pipe. (7) The method for producing a crosslinked polyolefin molded product according to any one of claims (1) to (4), wherein the molded product is in the form of a flat plate such as a film or a sheet.