JPH1177791A - Production of crosslinked polyolefinic plastic molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a crosslinked polyolefinic plastic molded product of a high crosslink degree and high capacity. SOLUTION: A crosslinked polyolefinic plastic molded product is produced by mechanically mixing polyolefinic plastic, a grafting aid and a silane coupling agent at temp. lower than the b.p. of a coupling agent at least by 30 deg. and also lower than the decomposition temp. of the grafting aid at least by 30 deg. and subjecting the resulting mixture to extrusion molding at temp. higher than the decomposition temp. of the grafting aid at least by 30 deg.C. This method is extremely useful in the production of various water crosslinked polyolefinic plastic molded products, especially, a crosslinked polyolefinic plastic insulated wire.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a crosslinked polyolefin plastic molded article by a water crosslinking technique, and more particularly to a method for producing a crosslinked polyolefin plastic insulated wire.

[0002]

2. Description of the Related Art In the case of producing a crosslinked polyethylene molded article by a water crosslinking technique for a polyolefin-based plastic such as polyethylene, as is generally well known, a polyethylene which has been modified to be water crosslinkable by grafting a silane coupling agent. Is water-crosslinked. Specifically, a mixture of three components of polyethylene, a grafting aid, and a silane coupling agent is charged into an extruder,
The high temperature in the extruder is used to cause a graft reaction in the extruder to modify the polyethylene to be water-crosslinkable, extrude, and then water-crosslink. By the way, conventionally, in order to cause a graft reaction in an extruder to be sufficiently and uniformly generated, it is necessary to sufficiently mix the above three components in advance before putting them into the extruder. Was melt-kneaded and mixed at a temperature higher than the melting point of polyethylene. However, the cross-linked polyethylene molded article produced by this conventional method may have a considerably good degree of cross-linking, but often has a problem that the degree of cross-linking is lower than a designed value, or in some cases, the degree of cross-linking is abnormally low. is there. Further, there is a problem that even if the degree of cross-linking is as designed, performance, particularly mechanical properties, are not sufficient. Due to these problems, in industrial production of crosslinked polyethylene insulated wires that require a high level of balanced performance, water crosslinking technology is still as widespread as organic peroxide crosslinking and electron beam irradiation crosslinking. I haven't.

[0003] From the research of the present inventors, it has been found that the above-mentioned problems of the conventional water crosslinking technology are caused by the following causes and reasons. That is, polyethylene has a melting point of 110 ° C.
Because of the above, the melt kneading temperature of the above three components reaches a high temperature of 110 ° C. or higher, and a part of the silane coupling agent evaporates due to the high temperature. As a result, the amount of the silane coupling agent involved in the graft reaction becomes less than a predetermined amount, and the degree of crosslinking falls below the design value.

In the water-crosslinking technique, it is preferable to form the polyethylene into a desired shape while water-crosslinkable but not yet crosslinked, and then to crosslink with water. . However, when melt-kneading and mixing at a temperature as high as 110 ° C. or higher as in the conventional method, in the process of kneading and mixing, in other words, some polyethylene is transformed into a water-crosslinking property at a stage before molding, and further during kneading and mixing. Water cross-links occur due to the moisture in the air and the like. Water-crosslinked polyethylene is generally poor in fluidity and therefore difficult or impossible to mold. Water-crosslinkable polyethylene that partially contains water-crosslinkable polyethylene has poor molding processing even if it is not as good as water-crosslinkable polyethylene, so that the molded product has fine burns inside and bumps on the surface. Or Such burns and spots,
The physical properties of the molded article after the water crosslinking are reduced, and bumps impair the appearance of the molded article.

[0005] From the research conducted by the present inventors to solve the above-mentioned conventional problems, unexpectedly, three components of a polyolefin-based plastic such as polyethylene, a grafting aid, and a silane coupling agent were unexpectedly obtained. Rather than melt-kneading and mixing at such high temperatures, simply mechanically mix at a specific low temperature, extrude at a specific high temperature, and then crosslink with water to obtain a high degree of crosslinking and high performance water. It has been found that a cross-linked molded article can be stably manufactured.

[0006]

SUMMARY OF THE INVENTION The present invention has been developed and completed based on the above-mentioned new knowledge and provides a method for producing a high-performance crosslinked polyolefin-based plastic molded article with a high degree of crosslinking. The purpose is to:

[0007]

The present invention has the following features. (1) Polyolefin plastic, grafting aid,
And mechanically mixing the silane coupling agent at a temperature at least 30 ° C. lower than the boiling point of the silane coupling agent and at least 30 ° C. lower than the decomposition temperature of the grafting aid, decomposing the mixture to decompose the grafting aid. A method for producing a crosslinked polyolefin-based plastic molded product, comprising: a molding step of extruding at a temperature higher than the temperature by at least 30 ° C .; and a water crosslinking step of water-crosslinking the extruded product. (2) The method for producing a crosslinked polyolefin-based plastic molded article according to the above (1), wherein the molding step is performed in a state where the temperature at the entrance side in the extruder is lower than the temperature at the exit side. (3) The method for producing a crosslinked polyolefin-based plastic molded article according to the above (1) or (2), wherein the grafting aid is an organic peroxide. (4) The crosslinked polyolefin plastic molded article is a crosslinked polyolefin plastic insulated wire (1)
The method for producing a crosslinked polyolefin-based plastic molded article according to any one of (1) to (3).

[0008]

The three components of a polyolefin-based plastic (hereinafter abbreviated as polyolefin), a grafting aid, and a silane coupling agent (hereinafter, these three components may be abbreviated as main three components) are used as silane cups. Mechanical mixing at a temperature at least 30 ° C. lower than the boiling point of the ring agent and at least 30 ° C. lower than the decomposition temperature of the grafting aid results in evaporation of the silane coupling agent during mixing and early water crosslinking of the polyolefin. Is substantially prevented. On the other hand, the three main components thus mechanically mixed are at least 30 ° C. below the decomposition temperature of the grafting aid.
By extruding at a high temperature, the grafting of the silane coupling agent to the polyolefin effectively proceeds,
Thus, the object of the present invention is achieved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As a polyolefin, DSC
Various types of plastics exhibiting a crystalline melting point on a differential calorimetric curve in (differential scanning calorimeter) can be used. For example,
Low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, polyethylene such as high-density polyethylene, polypropylene, homopolymers of α-olefins such as polybutene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer And copolymers of an α-olefin such as an ethylene-methyl acrylate copolymer and other comonomers, and various thermoplastic elastomers exhibiting a crystalline melting point. The polyolefin is used alone or as a mixture of two or more.

Examples of the grafting aid include those which can function as an aid for grafting a silane coupling agent described below to the polyolefin, such as organic peroxides. Usually, the grafting aid is often used alone, but if necessary, two or more kinds may be used in combination.

As the organic peroxides, those known as crosslinking agents for polyolefins, for example, di-tert-butyl peroxide, dicumyl peroxide, di-peroxide
Tert-butylcumyl peroxide, 1,1-bis (tert-butylperoxy) cyclododecane, 2,2-bis (tert-butylperoxy) octane, 1,1-di-tert-butylperoxy-cyclohexane, 2,5-dimethyl-
2,5-di (tert-butylperoxy) hexane, 2,5
-Dimethyl-2,5-di (tert-butylperoxy) hexyne-3,1,3-bis (tert-butylperoxyisopropyl) benzene, 2,5-dimethyl-2,5-di (benzoylperoxy) Hexane, 1,1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane, n-butyl-4,4-bis (tert-butylperoxy) valerate, benzoyl peroxide, m-toluylper Oxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butylperoxyisobutyrate, tert-butylperoxy 2-ethylhexanoate, tert-butylperoxybenzoate, tert-butylperoxide Oxyisopropyl benzoate, tert-butyl peroxyisopropyl carbonate, tert-butyl Over oxy-allyl carbonate, tert-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, p- menthane hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide,
Examples thereof include 2,5-dimethylhexane-2,5-dihydroperoxide.

Among the above-mentioned organic peroxides, the above-mentioned examples such as dicumyl peroxide and other dialkyl peroxides are particularly preferable from the viewpoint of handling properties and graft efficiency.

As the silane coupling agent, those conventionally known or used in the field of water crosslinking technology can be used in the present invention. For example, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane,
N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-chloropropylmethoxysilane, γ-chloropropyl Methyldimethoxysilane, γ-chloropropylmethyldiethoxysilane,
Examples thereof include γ-mercaptopropyltrimethoxysilane, γ-glycoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropylmethyldimethoxysilane. The silane coupling agent is used alone or as a mixture of two or more. Among the silane coupling agents, the above examples such as vinyltrimethoxysilane and other alcohol-type silane coupling agents are preferable from the viewpoint of water crosslinking efficiency.

The mixing ratio of the polyolefin, the grafting aid, and the silane coupling agent, ie, the three main components, is as follows:
It may be the same as in the case of the conventional water crosslinking technique. For example, per 100 parts by weight of polyolefin,
２2 parts by weight, especially 0.05-1 part by weight, and the silane coupling agent is 0.1-5 parts by weight, especially 0.5-3 parts by weight.

The method of the present invention proceeds in the order of a mixing step, a molding step, and a water crosslinking step. In the present invention, water crosslinking (early crosslinking) of the polyolefin at the stage after the completion of the molding step is somewhat acceptable. However, in order to produce a high-performance water-crosslinked molded article, it is preferable to perform the mixing step and the molding step in a dry environment so as to minimize the degree of early crosslinking. Hereinafter, each step will be described.

In the mixing step, the three main components are mechanically mixed at a temperature at least 30 ° C. lower than the boiling point of the silane coupling agent used and at least 30 ° C. lower than the decomposition temperature of the grafting aid used. Now, assuming that the boiling point of the used silane coupling agent is T ₁ and the decomposition temperature T ₂ of the grafting aid used is (T ₁ −30) ° C. or lower and (T ₂ −30) ° C. or lower. Mix. In this case, it is natural that mixing is performed at a temperature equal to or lower than the lower temperature by comparing (T ₁ -30) ° C. and (T ₂ -30) ° C. The decomposition temperature T ₂ of the grafting aid is a temperature at which the half-life is 1 minute under the condition of an initial concentration of the test grafting aid of 0.1 mol / liter in toluene.

In order to further reduce the amount of evaporation and evaporation during the mixing of the silane coupling agent, the mixing temperature of the three main components is set to (T ₁ -50) ° C. or less, and the early decomposition of the grafting aid is reduced. Alternatively, to prevent this, the mixing temperature of the three main components should be (T ₂ -50) ° C. or less,
It is particularly preferred to mix at ₁ -50) ° C. and (T ₂ -50) temperature below the temperature of the lower of ° C..

At the above-mentioned mixing temperature, one or both of the grafting aid and the silane coupling agent may be liquid or solid. The three main components can be mechanically mixed by various mixers, such as a simple stirring device, a low-speed mixer such as a ribbon blender, or a high-speed mixer such as Henschel mixer (registered trademark).

In order to increase the mixing uniformity as much as possible, the polyolefin is preferably 5 mm or less on one side, particularly 2 mm or less.
It is preferable to use the following small-sized square pellets, or spherical or other irregular shaped pellets of the same size as the square pellets. When both the grafting aid and the silane coupling agent are solid, each agent is a small particle that passes 100% through a 10 mesh Tyler standard sieve or a particle smaller than that, particularly a small particle that passes 100% through a 50 mesh. Alternatively, it is preferable to use smaller particles.

The mixing step in the present invention comprises a high-speed mixer,
Especially, it is particularly preferable to mix using a closed high-speed mixer such as a Henschel mixer. The reason for this is that since it is a closed type, evaporation and escape of the silane coupling agent can be more reliably prevented, and the dispersibility of the grafting aid to the polyolefin pellets and the silane coupling agent is improved. It is. I will explain a little more about the latter reason. The three main components are all stirred at high speed in the mixing chamber by the high-speed rotation of the stirring blade, and at this time, the particles repeatedly collide with each other. At the moment of such collision, the surface of the polyolefin pellets temporarily rises in temperature and softens, and the grafting aid and the silane coupling agent that have collided with the softened surface slightly enter into the pellet from the surface. Thus, a mixture in which the grafting aid and the silane coupling agent are immersed in the surface layer of each polyolefin pellet is obtained. When microscopically observed for each pellet, the immersion component has a concentration difference between the surface layer and the inside of the pellet, but is substantially very uniform as a whole assemblage of the pellets. For the reasons described above, when a closed high-speed mixer is used, it is preferable to mix the stirring blades at a rotation speed of at least 300 rpm, particularly at least 500 rpm. The mixing time is
Although it depends on the volume of the mixing chamber, the amount of the components to be mixed, and the rotation speed of the stirring blade, it is generally about 1 to 30 minutes,
In particular, it is about 5 to 15 minutes.

The mixture of the three main components obtained from the mixing step is extruded in a molding step. In the molding process, the main three-component mixture is first kneaded and mixed in a molten state by the kneading and mixing function generally provided by the extruder to further homogenize the composition. After the polymerization, the high temperature in the extruder causes the reaction of the three main components to transform the polyolefin into a water-crosslinkable form, which is then shaped via the extruder head. As the extruder, various types can be used as long as the extruder has the above-described functions. For example, an extruder having a single-channel screw, a multiple-channel screw, a mixing screw, or another screw can be used. There is no particular limitation on the L / D of the extruder barrel.
About 30 and especially about 8 to 15 are suitable.

If the temperature in the extruder is too low,
Further homogenization of the main three components by mixing and polyolefin
The degree of denaturation of the resin to water crosslinkability becomes poor. Therefore push
The temperature inside the output machine depends on the decomposition of the grafting aid used.
Temperature T_TwoAt least 30 ° C higher, ie at least
M (T_Two+30) ° C, preferably at least (T_Two+5
0) Set to ° C. The temperature inside the extruder is too high
So-called burns may occur in the polyolefin in the extruder
Because (T_Two+120) ° C or less, especially (T _Two+10
0) It is preferable that the temperature is not higher than 0 ° C.

The inside of the barrel of the extruder is maintained in the above-mentioned temperature range from the entrance (below the hopper or about 1-2 cm from immediately below the hopper) to the tip of the barrel (immediately before the head). At that time, the temperature between the entrance and the end of the barrel may be maintained at a substantially uniform temperature, or an arbitrary temperature gradient may be provided. If there is little concern about burning of the polyolefin, but it is desired to further homogenize the three main components and increase the degree of modification of the polyolefin to water crosslinkability, a uniform high temperature between the inlet and the tip of the barrel is required. Or it is desirable to keep the temperature from the entrance to the barrel tip. In the case opposite to the above, if the high temperature is maintained for a long time, the burn is more likely to progress, so that the temperature is maintained at a relatively low temperature from the entrance to the middle of the barrel, and then the temperature is increased toward the barrel tip. It is desirable to do. In general, the latter is often more convenient, and the entrance (T
It is particularly preferable that the temperature be about ₂ +30) to (T ₂ +50) ° C., and that the tip of the barrel be about (T ₂ +70) to (T ₂ +100) ° C. The temperature of the extruder head is not particularly limited as long as it is a temperature at which the polyolefin can be extruded. You may.

The extrudate from the molding step can be water-crosslinked with, for example, high-temperature water or steam in the water-crosslinking step of the present invention in the same manner as in the conventional water-crosslinking technique.
The advantage of water-crosslinking technology not found in other crosslinking technologies is that extruded products made of water-crosslinkable modified polyolefin are left in the air (for example, storage in a warehouse, installation and installation at desired locations, etc.). The point is that it is water-crosslinked with time due to atmospheric moisture during standing. Therefore, the water crosslinking step of the present invention may be such a leaving action or a leaving state.

In the present invention, in addition to the three main components, other chemicals known or used in the conventional water crosslinking technology, such as a silanol condensation catalyst such as dibutyltin dilaurate, an antioxidant, a flame retardant, a filler, A coloring agent or the like can be blended in a usual amount. Chemicals other than the silanol condensation catalyst may be mixed together with the main three components in the mixing step, but the silanol condensation catalyst is used in the extruder in the molding step in the same manner as in the conventional water crosslinking technique in order to prevent early crosslinking. It is preferable to inject directly into the solution.

The present invention can be applied to the production of various crosslinked polyolefin molded articles, but is particularly preferably applied to the production of crosslinked polyolefin insulated wires. In this case, as in the case of ordinary insulated wire manufacturing, a water-crosslinkable polyolefin is extruded from an extruder equipped with a crosshead to form an electric insulating layer made of the polyolefin on a conductor, and then the electric insulating layer is made of water. Crosslink.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 100 parts by weight of low-density polyethylene pellets averaging 2 mm square, dicumyl peroxide (decomposition temperature: 171 ° C.)
The three components of 0.1 part by weight and 2.0 parts by weight of vinyltrimethoxysilane (boiling point: 123 ° C.) were charged into a Henschel mixer, and stirred and mixed for 10 minutes. The mixing room temperature in this stirring and mixing was 70 ° C. at the maximum.
The mixture obtained is then subjected to L / D equipped with a single screw.
Extrusion molding on a stranded copper conductor having a nominal cross-sectional area of 38 mm ^{2 by} an extruder No. 28, followed by heating in a steam oven for 15 hours to form a water-crosslinked polyethylene having a 1.2 mm thick water-crosslinked electrically insulating layer. Insulated wires were manufactured. The extruder was inclined such that the inlet temperature was 175 ° C. and the barrel tip temperature was 220 ° C., during which the temperature was increased almost monotonically. The inside of the crosshead was kept at 220 ° C. Further, dibutyltin dilaurate was injected into the barrel from just below the hopper of the extruder barrel at a flow rate equivalent to 5 parts by weight per 100 parts by weight of the low-density polyethylene.

Example 2 The mixing and stirring time was 10 minutes with a Henschel mixer (the mixing room temperature in this stirring and mixing was 90 ° C. at the maximum).
The inlet temperature of the extruder was 200 ° C., the barrel tip temperature was 240 ° C., and the same size and the same size of water were used in the same manner and conditions as in Example 1 except that the temperature was inclined so that the temperature became almost monotonically high. A crosslinked polyethylene insulated wire was manufactured.

Comparative Example 1 Low-density polyethylene, dicumyl peroxide, and vinyltrimethoxysilane were melt-mixed in the air using an open roll set at a roll temperature of 110 ° C., and then extruded into pellets having an average of 2 mm square. A water-crosslinked polyethylene insulated wire of the same size was manufactured in the same manner and under the same conditions as in Example 1 except that the wire was put into the machine.

The gel fraction (hereinafter, secondary gel fraction) of each of the water-crosslinked polyethylene insulating layers of the water-crosslinked polyethylene insulated wires manufactured from Example 1, Example 2, and Comparative Example 1 was measured. Further, the gel fraction (hereinafter, primary gel fraction) of each water-crosslinked polyethylene insulating layer immediately after extrusion (before the water-crosslinking step) was also measured. In addition, the measuring method of the above-mentioned primary and secondary gel fractions is both JIS-C-3005.
by.

As a result of the above measurements, the primary gel fraction and the secondary gel fraction in Example 1 were 0% and 78%, respectively.
The primary gel fraction and the secondary gel fraction in Example 2 were 25% and 68%, respectively. In contrast, in Comparative Example 1, both the primary gel fraction and the secondary gel fraction were 0%.
%Met. From the results of these measurements, it is clear that in Comparative Example 1, in which both the primary and secondary gel fractions were 0%, vinyltrimethoxysilane was evaporated and evaporated during melt mixing with an open roll. On the other hand, in Examples 1 and 2, the primary gel fraction was as low as 0% or 25%, and premature crosslinking did not substantially proceed. It can be seen that is progressing highly.

[0033]

According to the present invention, three components of a polyolefin, a grafting aid, and a silane coupling agent are
High-performance water-crosslinked molded products with a very high degree of crosslinking by simply mechanically mixing at low temperatures, for example, room temperature to 50 ° C, without melt-kneading and mixing at high temperatures higher than the melting point of polyolefin as in the past. Can be manufactured. Therefore, the present invention is extremely useful for production of various water-crosslinked polyolefin molded articles, particularly, crosslinked polyolefin insulated wires.

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Claims (4)

[Claims] 1. The method of claim 1 wherein the polyolefin-based plastic, the grafting aid and the silane coupling agent are mechanically cooled at a temperature at least 30 ° C. below the boiling point of the silane coupling agent and at least 30 ° C. below the decomposition temperature of the grafting aid. A cross-linking polyolefin system, comprising: a mixing step of extruding the mixture at a temperature at least 30 ° C. higher than the decomposition temperature of the grafting aid; and a water-crosslinking step of water-crosslinking the extruded product. Manufacturing method of plastic molded products. 2. The method for producing a crosslinked polyolefin-based plastic molded article according to claim 1, wherein the molding step is performed in a state where the temperature at the entrance side in the extruder is lower than the temperature at the exit side. 3. The method for producing a crosslinked polyolefin-based plastic molded article according to claim 1, wherein the grafting aid is an organic peroxide. 4. The method for producing a crosslinked polyolefin-based plastic molded article according to claim 1, wherein the crosslinked polyolefin-based plastic molded article is a crosslinked polyolefin-based plastic insulated wire.