JPH07329093A - Method and apparatus for producing polyolefin resin foam - Google Patents

Abstract

(57) [Summary] [Structure] A crosslinked or uncrosslinked expandable polyolefin resin composition sheet is introduced into a foaming furnace having a preheating region and a foaming region, and the preheating region is conveyed by a conveying device equipped with an endless belt. While producing, in the method for producing a polyolefin-based foam which is continuously heated and foamed in the foaming region,
A method for producing a polyolefin resin foam, characterized in that, as the endless belt, a metal net body impregnated with a room temperature curable or thermosetting fluororesin or silicone resin is used. [Effect] In the preheating region, the foamable resin composition sheet is uniformly and efficiently heated, and the heat-melted foaming sheet is smoothly melted and adhered from the endless belt for support in the preheating region to the foaming region. Since it is possible to transfer, endless belt mesh marks, heating unevenness, color unevenness on the surface,
It is possible to continuously and stably manufacture a foam that is smooth and has good thickness accuracy without scratches and irregularities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing a polyolefin foam, and more specifically,
The present invention relates to a method and an apparatus for continuously and efficiently producing a foamed body having no heating unevenness, color unevenness, scratches and unevenness and having a smooth and good thickness accuracy in a stable state.

[0002]

2. Description of the Related Art A manufacturing apparatus for polyolefin foam is
A foaming furnace for heating and foaming the foamable resin composition sheet is provided. Generally, the foaming furnace can be roughly classified into a vertical foaming furnace and a horizontal foaming furnace.Both of them have a preheating region for raising the temperature of the foamable resin composition sheet to a temperature just before the foaming starts, and an atmosphere temperature and a heat medium temperature foaming. It is composed of a foaming region which is higher than the decomposition temperature of the agent and actually foams.

In the preheating region, it is general that the expandable resin composition sheet is conveyed while being supported on an endless belt and heated from above and below with hot air or a heater. What is important in this preheating step is (1) uniform heating from the upper and lower surfaces, and (2) the preheated foamable resin composition sheet is smoothly separated from the endless belt and transferred to the foaming region. (3) To prevent the occurrence of unevenness in thickness, scratches, and unevenness due to the shape of the endless belt, and so on. No foam can be obtained. Further, it is desirable that the belt does not burn even when the foamable resin composition sheet ignites due to a trouble or the like and that the endless belt can be used for a long period of time. As a conventional method, Japanese Unexamined Patent Publication No.
The one described in JP-A-4288 is exemplified, but this one uses a net body made of glass fiber impregnated and coated with a fluororesin as a belt and baked at a high temperature. Although it is considered that 1) to (3) are satisfied,
When the foamable resin composition sheet is ignited due to a trouble or the like, the belt is heated to a considerably high temperature, so that it is inevitable to burn it. Therefore, this belt cannot be said to be a method or a device which satisfies all the required characteristics.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the problems of the above-mentioned prior art and to continuously produce a foam having no heating unevenness, color unevenness, scratches, and unevenness and having a smooth and good thickness accuracy. It is another object of the present invention to provide a method and an apparatus for efficiently and stably manufacturing, and an apparatus excellent in facility maintainability.

In order to efficiently obtain a foam which is uniform in appearance and has no difference in front and back, the present inventors have developed a foamable resin composition in a preheating region of a heating and foaming apparatus (heating furnace). Efficiently and uniformly heats the material sheet from both the upper and lower sides, and the preheated expandable resin composition sheet in the heating and melting state smoothly separates from the supporting endless belt and moves to the foaming region, causing foaming due to a trouble or the like. Considering that it is necessary that the belt does not burn even when the resin composition sheet ignites,
The present invention has been made as a result of intensive investigations focusing on the material of the endless belt and the release agent applied to the belt.

[0006]

According to the present invention, a crosslinked or uncrosslinked expandable polyolefin resin composition sheet is introduced into a foaming furnace having a preheating region and a foaming region, and is conveyed with an endless belt. In the method for producing a polyolefin-based crosslinked foam which is heated and crosslinked by preheating or preheating while conveying the preheating region by an apparatus, the endless belt is a room temperature or thermosetting fluorine-based or The present invention has completed a method for producing a polyolefin cross-linked foam characterized by using a metal net body impregnated with a silicone resin and an apparatus for producing the same.

The present invention will be described in detail below with reference to the drawings.

The heating apparatus for the crosslinked polyolefin foam according to the present invention includes the horizontal foaming furnace shown in FIG. 1 and the vertical foaming furnace shown in FIG. In any foaming furnace, the foaming resin composition sheet 6 includes a preheating region 1 for raising the temperature to a temperature immediately before the start of foaming, and a foaming region 2 in which the ambient temperature and the heat medium temperature are set to be equal to or higher than the decomposition temperature of the foaming agent. Has been done. In the preheating region 1, the expandable resin composition sheet 6 is supported by the endless belt 4 for conveyance, and is heated by hot air from the upper and lower heating devices 3 while being conveyed. The heating device 3 has a system of heating with hot air or a heater.

The foamable resin composition sheet 6 is made of a resin composition containing a polyolefin resin and a thermal decomposition type foaming agent.
It is formed into a sheet at a temperature lower than the decomposition temperature of the foaming agent. When the foamable resin composition sheet 6 is foamed by heating, when it is crosslinked and foamed, it is irradiated with ionizing radiation such as an electron beam to have a predetermined degree of crosslinking, or when it is chemically crosslinked, an organic peroxide or the like. Is preliminarily compounded in the resin composition, and after being sheet-formed, it is pre-aged and cross-linked at the cleavage temperature of the peroxide, or can be cross-linked by pre-heating in the pre-heating region in the heating furnace of the present invention. In some cases, crosslinking may be carried out simultaneously with foaming at the temperature during foaming.

The expandable resin composition sheet 6 preheated in the preheating region 1 is separated (peeled) from the endless belt 4 for conveyance,
Then, it is heated and foamed in the foamed region 2 to become a foamed body.

The supporting transporting endless belt 4 used in the present invention is a net body made of a base material obtained by sufficiently impregnating a metal net body with a room temperature curable or thermosetting fluororesin or silicone resin. , Fire resistance, heat resistance, durability, peelability, etc. This net is an endless belt obtained by abutting and joining both ends of the net in the flow direction. In the present invention, it is an essential condition to use a metal net body impregnated with a room temperature curable or thermosetting fluororesin or silicone resin. Among them, a fluororesin or silicone resin, or a fluorosilicone is used. The use of room temperature curing type or thermosetting type resin
The applied fluororesin or silicone resin adheres to the foamable resin composition sheet and causes unevenness of the foam surface color, and secondary workability such as adhesiveness, adhesive workability, and printability of the foam surface. This is because the heat of impregnation and curing during the use of the preheater cures more completely and the durability is improved.

Regarding the number of meshes of the metal net constituting the endless belt, it is advantageous to reduce the mutual contact area in order to improve the releasability of the foamable resin composition sheet during heating and melting. From the viewpoint of the heating efficiency of the foamable resin composition sheet, it is advantageous that the air permeability of hot air is high, and therefore it is preferable that the sheet is as small as possible. But,
If the number of meshes is too small, the foamable sheet may sag into the mesh during heating and melting, or traces of the mesh may be transferred to the foam. As a result of looking at the relationship with the number of meshes of the mesh body in order to solve such a problem, it was found that the number of meshes is in an extremely limited range. The proper mesh number was 2 to 15 mesh.

The olefin resin used in the present invention is a low-density, medium-density, high-density, linear low-density polyethylene resin, or a copolymer of ethylene and vinyl acetate or an acrylic acid alkyl ester, propylene or the like. Polymer,
Homo- or copolymerized polypropylene, chlorinated polyethylene and the like may be used alone or as a mixture.

Examples of the thermal decomposition type foaming agent used in the present invention include known azodicarbonamide, oxybenzenesulfonyl hydrazide, dinitrosopentamethylenetetramine and the like. Generally, azodicarbonamide and dinitrosopentamethylene are used. Tetramine is used, and the addition amount thereof is appropriately adjusted depending on the desired expansion ratio, but is generally 2 to 25 parts by weight with respect to 100 parts by weight of the resin.

A flame retardant, a colorant, an antioxidant, a filler, a foaming aid, a lubricant, a crosslinking aid and the like can be added to the foamable resin composition sheet in an appropriate amount if necessary. In the case of forming a crosslinked foam, generally, a method using an electron beam or a method using chemical crosslinking with an organic peroxide such as dicumyl peroxide is used, but a crosslinking reactive vinylmethoxysilane or the like is grafted onto a resin or An electron beam irradiation method or a chemical crosslinking method using a copolymerized resin can also be applied. Also, various crosslinking methods may be used in combination.

[0016]

EXAMPLES Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

EXAMPLE 100 parts by weight of low-density polyethylene (density 0.921, melt index 2.0), 15 parts by weight of azodicarbonamide as a foaming agent, 1.5 parts by weight of zinc stearate as a foaming aid and lubricant, pigment As titanium oxide 1.0
Add parts by weight, pre-mix with a Henschel mixer, put the mixture in a 90 mmφ uniaxial extruder (L / D = 25), adjust the resin temperature to 150 ° C. or less so that the foaming agent does not decompose, and knead and extrude. Extruded from die, thickness 1.7
A foamable resin composition sheet having a width of 5 mm and a width of 410 mm was formed.

Next, the expandable resin composition sheet was irradiated with an electron dose of 4.8 Mrad using an electron beam irradiator (750 kV) to be crosslinked to obtain a foamable resin composition crosslinked sheet. The expandable resin composition crosslinked sheet is covered with a room temperature-curable silicone resin (PRX305 dispersion (Toray Dow Corning Silicone Co.)) of the preheater of the heating and foaming apparatus shown in FIG. The stainless steel net body of No. 2 is supplied onto an endless belt made by joining both ends in the flow direction to each other, and while being conveyed, heated by the hot air on the upper and lower surfaces until the surface temperature reaches about 155 ° C, and then the endless belt. The mixture was separated from the sample, moved to the foaming region, and heated to about 220 to 280 ° C., which is higher than the decomposition temperature of the foaming agent, to continuously produce a crosslinked foam.

The obtained foam was smooth and had good thickness accuracy without the endless belt mesh traces, heating unevenness, color unevenness, scratches and irregularities on the surface.

Incidentally, assuming that the foamable resin composition sheet is ignited due to a trouble of the endless belt of the present invention,
A piece of the expandable resin composition sheet was placed on the endless belt and forcibly ignited, and after complete combustion, it was cooled to room temperature, and the combustion part was observed, but no burnout was found. I wiped that part and bent it, but it did not break or break. Furthermore, the endless belt was coated with a room temperature curable silicone resin again and used for production, but no trouble occurred.

Comparative Example 1 As a supporting belt, a 5-mesh plain weave net body made of a woven fabric made of glass fiber (cloth) sufficiently impregnated with polytetrafluoroethylene and fired at high temperature as a base material is endless. A foam was obtained in the same manner as in the example except that the foam was used.

The resulting foam was smooth and had good thickness accuracy without any traces of the endless belt such as mesh marks and joining marks, heating unevenness, color unevenness, scratches and irregularities on the surface. However, assuming that the foamable resin composition sheet is ignited, the foamable resin composition sheet piece is placed on the endless belt to forcefully ignite it, and after complete combustion, it is cooled to room temperature and the combustion part is seen. The belt was burned and was not ready for use again.

Comparative Example 2 A foamed product was obtained in exactly the same manner as in Example 1 except that a stainless steel net covered with a non-curable silicone resin was used as the endless belt as the support belt.

The obtained foam has uneven heating on the surface,
Although there were no scratches or irregularities, since the silicone resin adhered to the foamable resin composition sheet, color unevenness occurred on the surface of the foam, and secondary processing such as adhesiveness, adhesive workability, printability, etc. It was a bad thing.

[0025]

According to the present invention, the expandable resin composition sheet is uniformly and efficiently heated in the preheating region, and
Since it is possible to smoothly transfer the heat-melted foamable sheet from the supporting endless belt in the preheating area to the foaming area without melting and adhering to the surface area, the endless belt mesh traces, heating unevenness, color unevenness, It is possible to continuously and stably manufacture a foam that is smooth and has good thickness accuracy without scratches and irregularities.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example in which a horizontal foaming furnace is used in a manufacturing apparatus for a polyolefin resin foam according to the present invention.

FIG. 2 is a schematic view showing an example when a vertical foaming furnace is used in the apparatus for producing a polyolefin resin foam of the present invention.

[Explanation of symbols]

 1: Preheating area 2: Foaming area 3: Heating device 4: Endless belt for conveyance 5: Heating heat medium 6: Foaming resin composition sheet

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Claims (2)

[Claims] 1. A crosslinked or uncrosslinked expandable polyolefin-based resin composition sheet is introduced into a foaming furnace having a preheating region and a foaming region, and foamed while being conveyed in the preheating region by a conveying device equipped with an endless belt. In a method for producing a polyolefin-based foam that continuously heat-foams in a region, a metal net body impregnated with a room temperature-curable or thermosetting fluororesin or silicone resin is used as the endless belt. And a method for producing a polyolefin resin foam. 2. A foaming furnace having a preheating region and a foaming region, wherein the preheating region is provided with a conveying device provided with an endless belt for conveying a foamable polyolefin resin composition sheet, An apparatus for producing a polyolefin foam, wherein the endless belt uses a metal net body impregnated with a room temperature curable or thermosetting fluororesin or silicone resin.