JPS6111963B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for crosslinking polyolefins.

This type of crosslinking method that has been proposed in the past involves measuring and mixing a polymer such as a polyolefin, a silane compound, and a radical generator, extruding it while heating to cause a graft reaction, and granulating the resulting silyl-modified polyolefin impeller. A crosslinked product is finally obtained by supplying a hopper with a premixed siloxane condensation catalyst masterbatch pellet and extrusion molding and exposing it to moisture after extrusion.

According to this method, the work is complicated because it includes the steps of extrusion and granulation while carrying out the graft reaction.
In addition to high production costs, there was a great concern that the silyl-modified polyolefin impellets would absorb moisture and cause a crosslinking reaction, resulting in poor quality, and there were troublesome problems such as the need for adequate storage management.

In addition, in catalyst masterbatches, moisture absorption during the granulation process leads to early crosslinking during the extrusion molding process, resulting in extremely poor appearance. Ta.

The present invention provides a crosslinking method that improves these drawbacks, and involves omitting the grafting reaction of polyolefin → granulation step and using pellets pre-impregnated with a silyl modifier and a siloxane condensation catalyst. The obtained pellets are each supplied to a hopper of an extruder, and are heated and reacted in the extruder to perform grafting and extrusion molding.

That is, the main points of the present invention are as follows: (1) Additives such as a polyolefin impellet, a silane compound, a radical generator, and optionally an antioxidant are placed in a Henschel mixer and heated and stirred to impregnate the mixture, or The materials are mixed using a mixing device such as a ribbon blender, transferred to a closed container, and heated to 70-80°C for impregnation.

(2) Similarly, impregnate polyolefin pellets with a siloxane condensation catalyst.

(3) Thereafter, the materials obtained in (1) and (2) are continuously metered and mixed into the extruder hopper, and heated and reacted through the extruder to form the desired molded product.

According to this method, (1) By using pellets impregnated with a grafting agent and a catalyst separately, it is possible to prevent condensation and deterioration of the grafting agent that occurs when they coexist.

(2) Grafting is possible without the need for an extruder with a special kneading effect or a particularly large screw L/D, and since the barrel temperature can be raised from near the hopper, grafting efficiency can be increased and crosslinking can be achieved. A high quality product can be obtained.

(3) Products with a smooth appearance and stable quality can be obtained.

The polyolefin used in the present invention is a polyolefin polymer or a polymer containing an olefin, such as polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene copolymer, polypropylene, halogenated polyolefin, or These include those obtained by graft-polymerizing vinyl chloride monomers.

Silane compounds are aliphatically unsaturated hydrocarbons that contain hydrolyzable organic groups, such as methoxy, ethoxy, and butoxy groups, and that are reactive with free radical sites generated in organic polymers. Compounds having a group or a hydrocarboxy group are preferred, and typical examples include vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriacetoxysilane.

As a radical generator, dicumyl peroxide, benzoyl peroxide, 2,5-dimethyl-
Mention may be made of organic peroxides such as 2,5-di(tert-butyl-peroxy)hexyne-3 and azo compounds such as azobisisobutyronitrile and dimethylazoisobutyrate.

Examples of siloxane condensation catalysts include dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctaate, lead naphthenate, and stannous acetate, as well as acids such as inorganic acids and fatty acids, and organic acids such as ethylamine, dibutylamine, and hexylamine. Examples include bases.

The temperature at which the silane compound, radical generator or siloxane condensation catalyst is mixed and impregnated into the polyolefin is preferably 60 to 90°C.

Examples of the present invention will be described below along with comparative examples.

Example 1 Low-density polyethylene (UBEF- manufactured by Ube Industries, Ltd.) having a density of 0.922 g/cm ³ and a melting index of 5.0 g/10 min.
522), a liquid prepared by dissolving 0.2 parts of dicymyl peroxide (DCP) and 0.5 parts of poly-2,2,4-trimethyl-1,2-hydroquinoline in 20 parts of vinylsilane was heated in advance with steam. Impregnated pellets (A)
was created. Similarly, 0.5 part of dibutyltin dilaurate was impregnated and absorbed into 100 parts of pellets of low density polyethylene (UBEC-400 manufactured by Ube Industries, Ltd.) having a density of 0.922 g/cm ³ and a melting index of 1.0 g/10 min. Impregnated pellets (B) were prepared.

The ratio of (A)/(B) is 19/1, and the mixture is fed to the hopper using an automatic quantitative mixing device (2 hopper type), and then single-screw extrusion is carried out at 65 m/m (L/D=22/1). An electric wire was produced by extrusion coating on the circumference of the conductor using a machine under the following conditions.

Temperature of barrel zone 1 in extruder 160℃ 〃 Temperature of barrel zone 2 230℃ 〃 Temperature of barrel zone 3 230℃ 〃 Temperature of crosshead part 230℃ Wire size...Conductor (core wire) diameter 16mmφ Single wire extruded insulation thickness 0.9 mm The obtained electric wire was immersed in hot water at 80°C for 15 hours to crosslink it, and the insulator was immersed in xylene at 110°C for 24 hours, thoroughly dried, and the insoluble gel content was measured and found to be 77%. Furthermore, the surface of the obtained electric wire was very smooth, with almost no protrusions that were considered to be caused by gel particles.

Comparative Example Using the same resin and materials as in Example 1, an electric wire was produced according to the previously proposed crosslinking method described above.

(1) Polyethylene, vinylsilane, DCP, and poly-2,2,4-trimethyl-1,2-dihydroquinoline are blended and extruded into pellets (after passing through a cooling water tank, water is removed using an air knife). (2) Catalyst masterbatch prepared in a similar manner and
A blend at a ratio of 19/1 was extruded onto the circumference of the conductor using an extruder, and crosslinked by immersing it in hot water at 80°C for 15 hours.

The insoluble gel content of the insulator of this electric wire was 71.0%.

Example 2 80 parts of ethylene-propylene-dienterpolymer (EPT1045 manufactured by Mitsui Petrochemicals, Ltd.), 20 parts of low-density polyethylene (same as in Example 1) and poly-2.2.4-trimethyl-1. Pellet prepared by blending 0.5 part of 2-dihydroquinoline with a ratio of vinylsilane and DCP of 10:
22 parts of the liquid dissolved in step 1 was poured into a Heisyl mixer (capacity 41) heated to 65°C by steam heating and stirred for 15 minutes to prepare impregnated pellets.

This and a catalyst masterbatch (impregnated pellets (B)) prepared with the same composition and conditions as in Example 1 were continuously supplied to the hopper at a ratio of 19/1.
Using an m/m single-screw extruder under the same extrusion conditions as in Example 1, the conductor was coated by extrusion to produce an electric wire.

This electric wire was crosslinked by immersing it in hot water under the same conditions as in Example 1, and then measured using the same method.The insoluble gel content was 81.8%, and the extruded appearance was very good.

The present invention has significant improvements over conventionally known methods in terms of economy, workability, and performance, particularly in the following points.

(1) 2 impregnated with grafting agent and catalyst separately
Since extrusion is carried out using pellets, there is no room for moisture to be involved, and a stable product with an extremely smooth appearance can be obtained.

(2) Since the grafting agent is dispersed in the polyolefin impellets beforehand and then fed into the extruder, homogeneous grafting is possible without the use of a special extruder with a large L/D, and the barrel temperature is close to the hopper. Grafting efficiency can be improved because the grafting efficiency can be increased from

(3) Manufacturing costs are reduced by omitting the granulation process, and there is no need for strict storage management to prevent pellets from deteriorating in quality.

The present invention is applicable not only to the production of electric wires as explained in the above embodiments, but also to the production of crosslinked products such as tubes, pipes, and sheets, and furthermore to injection molded products using the same extrusion method. Great results can be expected.

Claims (1)

[Claims] 1. A polyolefin impeller impregnated with a silane compound and a radical generator and a polyolefin impeller containing a siloxane condensation catalyst are respectively charged into an extruder, mixed in the extruder, and extruded while being heated and reacted. A method for crosslinking polyolefins, which comprises bringing the obtained extruded product into contact with moisture for crosslinking.