JPS5848335B2 - Method for manufacturing polyolefin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyolefin foam having a smooth surface layer with no broken cells. , carry out crosslinking reaction and foaming reaction,
A method for producing a polyolef in-foam, characterized in that the surface of the foamable resin or shaped composition is maintained in a state where it does not come into contact with air from the initial stage of heating until at least the foaming reaction becomes obvious. This is the manufacturing method.

Conventionally, as a method for manufacturing polyolefin foam, a method has been known in which a polyolefin resin composition containing a crosslinking agent and a blowing agent is heated to proceed with a crosslinking/foaming reaction to form a foam. form is manufactured.

However, the polyolefin in-foam obtained by this method has a serious defect in that the surface layer has many pores caused by the destruction of air bubbles, resulting in a rough and unpleasant feel, resulting in a foam with extremely low commercial value. Ta.

The inventors of the present invention have conducted extensive research with the aim of producing a foam that is smooth and has a good feel.As a result, the disadvantage of the above-mentioned polyolefin foam is that the crosslinking degree of the extremely thin layer on the surface is extremely low. The present invention was developed based on the discovery that the foam cannot withstand the foaming pressure of 100%, causing the bubbles to collapse on the surface, which impairs the smoothness of the foam and impairs its feel and appearance.

That is, the present invention refers to a method for producing a polyolefin in-foam, which focuses on improving the degree of crosslinking of the surface layer of a foamable resin molded composition to the same degree as that of the inner surface.

For example, Japanese Patent Publication No. 46-27318 discloses a method of heating and crosslinking and foaming a kneaded mixture of a polyolefin resin, a crosslinking agent, and a blowing agent on a support to form a foam before heating and crosslinking and foaming. A method of crosslinking the surface by igniting the surface layer of an object is described, but since this method performs the above surface crosslinking in air, the degree of crosslinking of the outermost layer in contact with air is extremely low, and it does not have the above-mentioned drawbacks. It cannot be removed.

As in the present invention, it is an essential requirement for the present invention to maintain the foamable resin molding composition in a state where it does not come into contact with air from the initial stage of heating until at least the foaming reaction becomes obvious, and to allow the crosslinking reaction to proceed. By satisfying this condition, it becomes possible to produce a chemically crosslinked polyolefin foam that is smooth and has excellent feel and appearance.

In the present invention, when manufacturing a polyolefin foam by heating a foamable resin molding composition consisting of a polyolefin resin, a blowing agent, and a crosslinking agent to advance a crosslinking/foaming reaction,
This can be carried out by keeping the foamable resin composition in a state where it does not come into contact with air from the preheating step until at least the foaming reaction becomes obvious.

The reason why the foamable resin molding composition is kept in a state where it does not come into contact with air at least until the foaming reaction becomes clear in the present invention is explained as follows.

That is, in the method of the present invention in which a foamable resin molding composition is heated to simultaneously advance a crosslinking reaction and a foaming reaction to obtain a polyolefin foam, the crosslinking reaction of the polyolefin resin and the decomposition reaction of the blowing agent are performed independently of each other. However, in order to obtain a good foam, it is necessary that the crosslinking reaction precedes the reaction, and at the point when the decomposition reaction of the blowing agent begins, the polyolefin resin is sufficiently strong to withstand the pressure of the decomposed gas of the blowing agent. It must be crosslinked to a degree that it has good viscoelastic properties.

On the other hand, it is said that the crosslinking effect of organic peroxides on polyolefin resins is significantly reduced in an oxygen atmosphere. This is thought to be because oxygen is added, and as a result, polymer radicals that should originally participate in the crosslinking reaction are consumed.

? OOR radical) PH+RO・ -radical) P-02 →POO・ POO・+P・ →POOP POOP →2PO・ 2POO・ →2PO・+0 PO・ →cleavage, stable compound → P・+ROH (P・volima→2RO・(RO・Peroxide In other words, in the conventional manufacturing method of polyolefin foam, the crosslinking reaction is carried out in the air, so the degree of crosslinking on the surface of the foamable resin molding composition that comes into contact with air does not improve, and therefore the foamable resin molding The surface layer of the composition could not withstand the pressure of decomposed gas from the blowing agent, and the bubbles could not avoid being destroyed in the surface layer.

The present inventors focused on this point, and by proceeding the crosslinking and foaming reaction under conditions that do not reduce the degree of crosslinking of the surface layer of the foamable resin molding composition, a polyolefin in-foam with a significantly improved surface condition can be obtained. I discovered that.

The polyolefin resin in the present invention includes polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, etc. manufactured by high pressure method, medium pressure method, or low pressure method, and these can be used alone. Or use a mixture.

Further, ABS resin, chlorinated polyethylene, chlorosulfonated polyethylene, EPDM, polybutadiene, SBR, polybutene, etc. may be mixed with these resins.

The crosslinking agents that can be used in the present invention include di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α,α'-bis(t-butylperoxy)P-di-isopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane,
It is an organic peroxide such as 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne, and has the ability to decompose by heating and introduce crosslinks into the polyolefin resin.

The blowing agent of the present invention is a substance that generates gas by thermal decomposition, such as azodicarbonamide, benzenesulfonylhydrazide, dinitrosohentamethylenetetramine, toluenesulfonylhydrazide, 4,4-oxybis(benzenesulfonylhydrazide). etc. are used.

Among the crosslinking agents and blowing agents mentioned above, the crosslinking agent most suitable for the production of polyolefin foams is dicumyl peroxide, and the blowing agent commonly used is azodicarbonamide.

In the present invention, a method of heating the foamable resin molding composition while keeping it in a state where it does not come into contact with air includes, for example, completely protecting both sides of the foamable resin molding composition with a gas-impermeable film or sheet. These films or sheets are removed from the surface of the foamable resin molded composition before foaming, or the atmosphere around the foamed resin molded composition is completely filled with an inert gas such as nitrogen during heating. There are methods to replace the original, or a combination of these methods.

An example of a manufacturing apparatus for implementing the present invention will be described with reference to the drawings.

In the drawing, a foamable sheet 1 containing a polyolefin resin, a crosslinking agent, and a foaming agent is introduced into a pair of non-adhesive belt conveyors 2, and pressure rolls 3 are applied to both sides of the foamable sheet 1.
The non-adhesive belt conveyor 2 is placed in complete contact with the sheet so that the sheet surface does not come into contact with air, and in this state it is heated by the infrared heater 4.

Here, the non-adhesive belt conveyor 2 means that the belt conveyor itself is made of a low-energy material such as polytetrafluoroethylene, or that the belt conveyor 2 is made of a non-adhesive material on a high-strength conveyor such as a wire mesh conveyor. It may also have a structure on which a sex film or sheet is placed.

Furthermore, a stainless steel plate itself with a smoothed surface can be used as the non-adhesive belt conveyor.

In any case, such a non-adhesive belt conveyor,
It is important that the foam sheet be brought into close contact with both sides of the foam sheet, that air be completely expelled from both sides of the foam sheet, and that it not come into contact with the surrounding air.

When the foam sheet is heated and its surface begins to soften, the surface of the foam sheet and the non-adhesive belt conveyor come into complete contact with each other due to the action of the pressure roll.

In the foamable sheet that is covered with the non-adhesive belt conveyor and subjected to the thermal heat treatment in this manner, the crosslinking reaction proceeds to the same extent in both the inner layer and the surface layer.

At the same time, the blowing agent begins to decompose.

At time point 5, when the decomposition reaction of the blowing agent becomes evident, the foamable sheet 1 is released from the non-adhesive belt conveyor 2 and the sheet is discharged into a free space.

That is, the foaming reaction is completed while the foaming sheet is suspended with hot air 6 at a high temperature in which the decomposition reaction of the foaming agent sufficiently proceeds.
Take out as polyolefin insert 7.

8 is a take-off cooling port.

In addition to an infrared heater, the means for heating the foam sheet encased on a non-adhesive belt conveyor can also be used to uniformly heat the sheet by circulating hot air in the same way as an infrared heater.

Example M11.8, high pressure polyethylene 100 with specific gravity 0.92
15 parts of azodicarbonamide as a foaming agent and 1.0 part of dicumyl peroxide as a crosslinking agent were kneaded and extruded into a sheet shape. Foaming was carried out using the manufacturing equipment shown in .

However, the non-adhesive belt conveyor is made of glass cloth impregnated with polytetrafluoroethylene.

The heating temperature of the infrared chamber was about 240°C, and the temperature of the hot air outlet was 220 to 230'C.

The properties of the obtained polyethylene foam are compared with a conventional method that does not use a non-adhesive belt conveyor (heating and crosslinking is performed with only the top surface of the foam sheet open) and is shown in the table below.

Here, the upper surface layer and the lower surface layer include the respective layers.
．． These are the results for samples with a thickness of 3 mm.

The central part is the Q. of the upper and lower layers. Refers to the part excluding 3 mm (thickness 5.5 mm).

As is clear from the above description, the present invention can improve the surface defects of conventional foams and increase their commercial value.

[Brief explanation of drawings]

The drawing is a front view showing an example of a manufacturing apparatus used in the present invention. Explanation of symbols, 1... Foaming sheet, 2... Non-adhesive belt conveyor, 3... Press roll, 4... Infrared heater, 5... Foaming start point, 6... Hot air ,7...
Form, 8...Take-back cooling roll.

Claims (1)

[Claims] 1. A method for producing a polyolefin foam by heating a foamable resin molding composition consisting of a polyolefin resin, a foaming agent, and a crosslinking agent to cause a crosslinking reaction and a foaming reaction, from the initial stage of heating until at least the foaming reaction becomes obvious. A method for producing a polyolefin in-foam, which comprises maintaining the surface of the foamable resin molding composition in a state where it does not come into contact with air during the process.