JPS58974B2 - Hatsupou Plastic Tono Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in the method of manufacturing plastic foam sheets.

Conventional methods for producing plastic foam include irradiating ionizing radiation onto a sheet made of a mixture of plastic, such as polyethylene, with a blowing agent and a crosslinking agent, or a sheet made of a mixture of plastic with a blowing agent added. The sheet-like crosslinked body (hereinafter referred to as a "vessel sheet") is introduced into a heating furnace equipped with an endless belt made of all mesh that moves continuously at a constant speed, placed on the wire mesh, and transferred at the same time as the wire mesh. In addition, hot air is applied from the top and bottom of the wire mesh,
The mother sheet is evenly heated and foamed to obtain a foam.

The mother sheet foams and expands while being partially supported on the wire mesh, and continues to be in a crawling state until the expansion is completed.

However, when the base sheet is heated, it first softens and then expands, but this molten polymer tends to stick to the support, and some of the volatile components of the polymer stick to the wire mesh, inhibiting the expansion of the foam. Therefore, the resulting foam has a non-uniform thickness and is of no commercial value.

In addition, it was necessary to temporarily stop the work on the wire mesh to which the volatile components of the base sheet had adhered and remove the sticky volatile components.

In addition, a method has been proposed in which, before introducing the mother sheet into a heating furnace, only the surface thereof is ignited in advance to first form a crosslinked layer with a high softening temperature, and then the mother sheet is introduced into the heating furnace and foamed. Depending on the method, the adhesion of the base sheet to the wire mesh can be reduced, but it is still not perfect, and there has been a desire for a method to obtain a foam without the base sheet completely adhering to the wire mesh.

As a result of intensive research in response to such requests, the present inventors found that
They found a way to solve this problem by using a special type of wire mesh.

That is, in the present invention, a sheet-like cross-linked body made of a mixture of plastic with a blowing agent and a cross-linking agent added thereto, or a sheet-like cross-linked body made of a mixture of plastic with a blowing agent added thereto, is irradiated with ionizing radiation, and then a sheet-like cross-linked body made of stainless steel is prepared. The method is characterized in that chromium oxide is generated by heating a wire mesh to red heat, and then heated and foamed on the wire mesh.

The present invention is characterized by a wire mesh, and is used as a wire mesh by heating a stainless steel wire mesh to deposit a chromium oxide film on its surface.
Any chromium oxide may be used, but usually Cr
A film of No. 04 was formed, and the resulting stainless steel wire mesh was particularly effective in preventing the molten sheet from sticking when the base sheet was heated and expanded.

Also, any type of stainless steel may be used, but especially when using alastenite or fernite type stainless steel, it will not become brittle even when repeatedly heated to a red-hot state and can withstand continuous use. be able to.

In the present invention, the plastic may be any plastic, but polyolefins such as low-density polyethylene, high-density polyethylene, polypropylene, or copolymers thereof are preferred.

As the crosslinking agent, organic peroxides such as dicumyl peroxide, various azides, etc. are used, and in some cases, a crosslinking aid such as triallyl cyanurate is used together with the crosslinking agent.

Ionizing radiations include X-rays, alpha rays, beta rays, gamma rays, and neutron rays, which are usually used for radiation crosslinking.

As the blowing agent, those whose decomposition temperature is higher than that of the crosslinking agent, such as azosicabonamide and dinitrosopentamethylenetetramine, are used.

In addition, in the present invention, the method of heating a stainless steel wire mesh to deposit chromium oxide on the surface of the wire mesh uses a wire mesh with an endless belt moving in a heating furnace, and at the outlet of the heating furnace, city gas is applied to the surface of the wire mesh. It is obtained by applying a flame of propane, butane, etc. and heating it to a red-hot temperature, and with the inlet of the furnace already sufficiently cooled, the mother sheet is placed on the wire mesh and heated and expanded. be.

Next, examples of the present invention will be described.

Example 1 100 parts by weight of low density polyethylene (M, 1=1), 1 part by weight of dicumyl peroxide, 1 part by weight of azocica-bonamide
5 parts by weight were mixed and extruded into a mother sheet 1.5 mm thick and 400 mm wide without decomposing the crosslinking agent and foaming agent.

Before introducing this mother sheet into a heating furnace, it is ignited from the upper and lower surfaces with an infrared lamp to form a crosslinked layer on the surface.
The material was introduced into a heating furnace equipped with an endless conveyor made of a 25-mesh alastenite stainless steel wire gauze that constantly provided a chromium oxide (CrO4) film on the surface by heating, and was heated and foamed at 220° C. for 5 minutes.

The foam thus obtained had a beautiful surface and a uniform thickness, and no adhesion of the container sheet was observed during the work.

Immediately after the wire mesh leaves the heating furnace, it is heated to red heat, and when it enters the heating furnace, it is cooled and a chromium oxide film is deposited on the surface of the wire mesh, and a foam is produced continuously for three days using the method described above. However, the mother sheet did not stick to the wire mesh surface.

In order to compare with the method of the present invention, the above-mentioned base sheet was heated and foamed without red-heating and oxidizing the alastenite stainless steel wire gauze. occurred, and the foam sheet obtained after 12 hours had partially different thicknesses.

As described in detail above, the method of the present invention has remarkable effects such as obtaining a foam having a beautiful surface and a uniform thickness even when continuous operation is performed for a long time.

Claims (1)

[Claims] 1 In a method for obtaining a sheet-like crosslinked body made of a mixture of plastic with a foaming agent and a crosslinking agent added thereto, or a sheet-like body of a mixture of plastic with a foaming agent added and irradiated with ionizing radiation, the surface 1. A method for producing a plastic foam sheet, which comprises continuously heating and foaming the sheet on a stainless steel wire mesh that is heated red hot to produce chromium oxide and then cooled.