JPH058279A - Preparation of polyethylene foam - Google Patents

Abstract

PURPOSE:To continuously prepare long polyethylene foam of good quality without adding a crosslinking agent such as org. peroxide. CONSTITUTION:A silane coupling agent is added to a polyethylene resin to be grafted thereto and this resin is continuously subjected to extrusion flaming using a chemical foaming agent and the obtained foam is brought into contact with a stannous catalyst to be crosslinked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously producing a polyethylene foam suitable as a heat insulating material for building materials, home appliances, automobiles, energy plants and the like.

[0002]

2. Description of the Related Art Conventionally, in order to obtain a polyolefin-based high foam (foaming ratio about 30 times) such as polyethylene foam, a chemical foaming agent and a cross-linking agent such as an organic peroxide are added to a polyolefin resin. It was necessary to carry out crosslinking prior to foaming or to carry out crosslinking and foaming simultaneously.

This is because a polyolefin resin is cross-linked to prevent a decrease in viscosity at the time of foaming and melting so that the gas generated during foaming does not easily escape from the resin melt, and a highly foamed body having closed cells is formed. To get it.

However, when the polyolefin resin composition containing the crosslinking agent is kneaded, the kneading temperature must be kept below the decomposition temperature of the crosslinking agent, and there is a problem that sufficient kneading cannot be performed.

When the above composition is kneaded in an extruder to crosslink and foam, the crosslinking may proceed too much and the resin may not be discharged, and the kneading temperature cannot be raised to the foaming temperature. For this reason, it was not possible to continuously produce a long plate-shaped or tubular foam in one step.

[0006]

Therefore, the object of the present invention is to solve the above-mentioned inconvenience caused by the addition of a cross-linking agent, to perform sufficient kneading, to sufficiently perform foaming by a chemical foaming agent, and to obtain a high-magnification ratio. It is to obtain a foam continuously in one step.

[0007]

This problem is solved by adding a silane coupling agent to a polyethylene resin to form a silane graft, and continuously extruding and foaming this with a chemical foaming agent. It is solved by contacting with a catalyst and crosslinking.

The present invention will be described in detail below. In this invention, first, a silane coupling agent is added to a polyethylene resin to obtain a silane-grafted polyethylene resin. As the polyethylene resin here, high density polyethylene (HDPE), low density polyethylene (LD
PE), polyethylene such as linear low density polyethylene (LLDPE), ethylene-ethyl acrylate copolymer (EEA), ethylene-vinyl acetate copolymer (EV)
A), copolymers of ethylene with other monomers such as ethylene-acrylic acid copolymer (EAA), ethylene-propylene copolymer, ethylene-butene-1 copolymer, ethylene-propylene-diene copolymer Etc. or a blend of a plurality of polymers and the like are used.

As the silane coupling agent, a silane compound having a double bond such as a radically polymerizable vinyl group represented by the following general formula [I] is used alone or in combination. The amount of the silane coupling agent added is 0.5 with respect to 100 parts by weight of the polyethylene resin.
The range is from 10 to 10 parts by weight. If it is less than 0.5 part by weight, the viscosity retention effect at the time of foaming will not be obtained, and also the mechanical properties after crosslinking will be poor, and if it exceeds 10 parts by weight, the viscosity of the molten resin at the time of foaming will be too high, resulting in bubbles. Growth is hindered.

[0010]

[Chemical 1]

Silane grafting is carried out by adding a predetermined amount of the above silane coupling agent to the above-mentioned polyethylene resin, further adding a small amount of organic peroxide, and kneading with heating. This organic peroxide is for binding a silane coupling agent to a polyethylene resin for grafting, and includes dicumyl peroxide, tert-butyl cumyl peroxide, 2,5-dimethyl-2,5-dicarboxylic acid. (Tertiary butyl peroxy) hexane, 1,3-bis (tertiary butyl peroxy isopropyl) benzene, etc. are used, and the compounding amount thereof may be smaller than that for crosslinking, and 100 parts by weight of the polyethylene resin. Therefore, the amount is 0.2 to 2 parts by weight. The heating and kneading is carried out by using an ordinary extruder or the like, and the temperature is not lower than the melting temperature of the polyethylene resin and is 5-1.
Heat and mix for about 0 minutes. By this heating and kneading, the silane molecule of the silane coupling agent is radically bonded as a side chain to the carbon chain of the polyethylene resin molecule to perform silane grafting. This silane-grafted polyethylene resin has a high viscosity when melted.

Then, a chemical foaming agent is added to the silane-grafted polyethylene resin, and the mixture is heated and kneaded in an extruder to foam and extrude into a continuous long foam. As the chemical foaming agent used here, azodicarbonamide, azobisisobutyronitrile, N, N′-dinitrosopentamethylenetetramine,
There are p-toluenesulfonyl hydrazide, P, P'-oxybisbenzenesulfonyl hydrazide, baking soda, etc.,
These may be used alone or in a mixture of two or more. The amount of the chemical foaming agent added is in the range of 5 to 30 parts by weight with respect to 100 parts by weight of the polyethylene resin, and is appropriately determined according to the desired expansion ratio. If the amount of the chemical foaming agent added is less than 5 parts by weight, the foaming will be insufficient, and if it exceeds 30 parts by weight, the foaming will be nonuniform and "su" will be contained inside.

The extrusion foaming is carried out by supplying a mixture of a silane-grafted polyethylene resin and a chemical foaming agent to an extruder and kneading the mixture at a temperature not lower than the decomposition temperature of the chemical foaming agent. During this heating and mixing, the melt viscosity of the silane-grafted polyethylene-based resin is higher than that of the polyethylene-based resin, so the gas generated from the chemical foaming agent does not escape during foaming, and A high magnification foam is obtained. Further, the shape of the foam is determined by the shape of the die of the extruder, and it is possible to continuously manufacture a long foam such as a plate, a cylinder, or a column.

Next, the foam thus obtained is brought into contact with a tin-based catalyst to crosslink it. As the tin-based catalyst here, an organic tin compound such as dibutyltin dilaurate or dibutyltin dimaleate is used, which is used as an aqueous solution having an arbitrary concentration. The contact method includes a method of immersing the foam in the catalyst aqueous solution, a method of spraying the catalyst aqueous solution on the foam, a method of introducing the foam extruded from the extruder directly into the catalyst aqueous solution tank, and continuously treating the foam. and so on. As a result, the side chain silane residues of the polyethylene-based resin are condensed with each other to crosslink the polyethylene-based resin molecules.

According to such a method for producing a foam, since the molten polyethylene resin at the time of foaming is in a state where the silane coupling agent is grafted, the viscosity of the molten resin becomes relatively high and the chemical foaming agent is used. It is possible to obtain a foam having a high expansion ratio by effectively acting without causing the foaming gas generated from the gas to escape. Further, since it is not necessary to add a crosslinking agent at the time of foaming, the resin is not clogged in the extruder.

In the present invention, the chemical foaming agent may be added at the same time as the silane coupling agent, and the mixture may be heated and kneaded so that the silane grafting and the chemical foaming are simultaneously performed.
In addition, an ultraviolet absorber, an antioxidant, a colorant, and a flame retardant can be appropriately added to the polyethylene resin, if necessary.

(Example) Low density polyethylene (density: 0.
92, melt index 5.0) 100 parts by weight, triethoxyvinylsilane 2 parts by weight and dicumyl peroxide 0.5 parts by weight were added, and the mixture was kneaded by an extruder at a temperature of 150 ° C. to obtain silane-grafted low density polyethylene. Was manufactured. 100 parts by weight of this silane-grafted low-density polyethylene was mixed with 30 parts by weight of azodicarbonamide, and the mixture was kneaded in an extruder at 150 to 200 ° C. and foamed at the same time, and an outside diameter of 10 mm was obtained from a die (temperature 220 ° C.) of the extruder. A cylindrical polyethylene foam having an inner diameter of 20 m was continuously manufactured. This polyethylene foam was continuously introduced into a tank filled with a 2 wt% aqueous solution of dibutyltin dilaurate and crosslinked to obtain a desired crosslinked polyethylene foam.

The foamed product thus obtained had a foaming ratio of 29 to 31 times and was uniformly foamed, and the degree of crosslinking was 85 to 87 in terms of gel fraction.
%Met. Further, the extrusion foaming work could be stably carried out for a long time, and neither resin clogging nor scorch phenomenon in the extruder was observed.

[0019]

As described above, according to the method for producing a polyethylene foam of the present invention, a silane coupling agent is added to a polyethylene resin for silane grafting, and this is continuously extruded and foamed by a chemical foaming agent. After that, this foam is cross-linked by contacting it with a tin-based catalyst, so various inconveniences caused by the addition of a conventional cross-linking agent are eliminated, and a long foam of good quality in a uniform foaming state is continuously formed. Can be manufactured in a simple manner.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Matsuura 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Wire Co., Ltd. (72) Toshio Niwa 1-5-1, Kiba, Koto-ku, Tokyo Fujikura (72) Inventor Shuji Nishino 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Electric Line Co., Ltd.

Claims (1)

Claim: What is claimed is: 1. A silane coupling agent is added to a polyethylene resin to form a silane graft, which is continuously extruded and foamed by a chemical foaming agent. A method for producing a polyethylene-based foam, which comprises contacting and crosslinking.