JPS5849566B2 - Manufacturing method of polyolefin resin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a thermoplastic resin foam, and more specifically, a method for producing a foam by heating a polyolefin resin molded product containing a decomposable blowing agent. The present invention relates to a method for producing a polyolefin resin foam, characterized in that a substance having the property of decomposing and generating heat during foaming is applied to the surface of a molded product and foamed by heating.

The first object of the present invention is to increase the degree of foaming of the surface layer of a foamed product, and to obtain a foamed product with a low specific gravity and improved feel.

A second purpose is to prevent the destruction of cells in the surface layer of the foam and to obtain a foam having uniform, fine cells in the surface layer.

A third objective is to completely eliminate the coloration of the foam caused by undecomposed products of the blowing agent, and to produce a colorless foam (the foam is actually white because it contains air bubbles).

A phenomenon in the conventional method of heating a polyolefin resin molded product containing a decomposable blowing agent to form a foam is that the internal temperature of the molded product during foaming rises due to the heat of decomposition of the blowing agent, making it higher than the outside surface. It is normal to be kept at .

Therefore, although the foaming agent inside the foam is completely decomposed, that in the surface layer is not sufficiently decomposed, and undecomposed foaming agent remains.

Moreover, as a result, the specific gravity of the surface layer becomes considerably higher than that of the inner layer.

One way to foam the surface layer more fully is to raise the heating temperature, but in this case, the high temperature causes significant thermal deterioration of the base resin, and the bubbles are destroyed, causing the specific gravity to decrease. This results in an increase in

The undecomposed foaming agent remaining in the surface layer is, for example, azodicarbonamide (hereinafter referred to as AC), which is common even though it has a foaming agent, because the undecomposed AC is yellow in color. The current situation is that the products are colored and the product value is significantly reduced.

Although several methods have been proposed in the past to increase the degree of foaming of the surface layer of a foam, none of them can be adopted industrially.

For example, Japanese Patent Publication No. 46-36475 discloses that chlorinated polyphenyl, which acts as an internal heating medium, is mixed into a foamable resin composition to equalize the heating temperature and uniformly foam the inner and outer layers. However, mixing of such media deteriorates the properties of the foam, and there is also a problem of bleeding of the mixed media during processing and use of the foam product.

It has been proposed that a thermoplastic resin film be laminated on the surface of a foam molded product so that the surface during heating and foaming acts as an inner layer of the molded product, thereby increasing the degree of foaming of the surface layer (
(Japanese Unexamined Patent Publication No. 49-36773).

This method not only increases costs due to film lamination, but also
The surface of the resulting foam lacks the feel of bubbles and becomes film-like, which is inconsistent with the purpose of the present invention.

As a method for solving the above-mentioned coloring problem particularly when AC is used as a foaming agent, for example, Japanese Patent Publication No. 7473/1983 proposes irradiating the surface of the foam with ultraviolet rays.

Although this method decomposes undecomposed AC with ultraviolet rays and achieves colorless formation, it has a fundamental drawback in that deterioration of the base resin cannot be avoided.

Furthermore, Japanese Patent Publication No. 46-18636 proposes a method of treating a colored foam with a heated aqueous solution of hydrazine, but this method requires complicated steps such as a treatment step and subsequent washing and drying steps, so it is not suitable for This is not a good method.

As described above, although various methods have been proposed that have the same purpose as the present invention, the fact that no examples have been put into practical use yet makes it difficult to implement these methods industrially. This is because they have disadvantages, such as being economically poor or having unsatisfactory effects.

As a result of extensive research, the present inventors have succeeded in finding a method for producing a good polyolefin resin foam that achieves the above objectives extremely simply and reliably, as described below.

The present invention provides a method for heating a polyolefin resin molded product containing a decomposable blowing agent to form a foam, in which dinitropentamethylenetetramine is added to the molded product as a substance that has the property of decomposing and generating heat during foaming of the molded product. This can be carried out by applying heat to the surface and foaming.

Polyolefin resins used in the present invention include polyethylene, polypropylene, polybutene-1, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, vinyl chloride ethylene copolymer,
It refers to one kind or a mixture of two or more kinds of.

As a blowing agent to be mixed with the above polyolefin resin,
AC1 dinitrosopentamethylenetetramine (DP
T), PP'-oxybisbenzenesulfonyl hydrazide, azobisisobutyronitrile, etc. O. The polyolefin resin molded article containing a blowing agent preferably has a crosslinked structure. After the introduction, or while introducing the crosslinked structure, it is heated and foamed under normal pressure.

One way to introduce a crosslinked structure is to mix a chemical crosslinking agent that generates radicals with the resin when heated.

For example, di-t-butyl peroxide, dicumyl peroxide, t-butyl cumyl peroxide, 2
．． 2'-bis(t-butylperoxy)P-diisopropylbenzene, 2,5-dimethyl-2,5-di(t
-butylperoxy)hexane, 2,5-dimethyl-
One or more types of 2.5-di(t-butylperoxy)hexyne-3, etc. are used.

Another method for introducing a crosslinked structure is to irradiate a resin molded product containing a foaming agent with ionizing radiation such as X-rays, γ-rays, β-rays, and neutron beams.

Furthermore, a method is also used in which crosslinking is achieved by graft polymerizing a vinyl silane compound such as Vinyl IJ methoxysilane to the above resin and then introducing a silanol bond (Japanese Patent Publication No. 481,711).

In the method using a radical-generating crosslinking agent, formation of a crosslinked structure and foaming are performed in the same process.

In the other two methods, the crosslinking step generally precedes the foaming step.

In addition to the above-mentioned foaming agents and crosslinking agents, various additives such as colorants, antioxidants, ultraviolet absorbers, flame retardants, crosslinking aids, etc. can be mixed into the foamable resin moldings as necessary. be.

The substance that acts on the surface of the polyolefin resin or shaped object during foaming, which is unique to the present invention, must be a substance that itself decomposes and generates heat at the foaming temperature of the resin or shaped object, and among these, Stropenta Methylenetetramine (DPT) has an extremely large decomposition heat value and meets sufficient requirements for successfully carrying out the present invention.

Examples of methods for applying the exothermic substance to the surface of the polyolefin resin molded article include applying the exothermic substance directly to the surface of the article in powder form, applying it in a mixed state with thermoplastic resin powder, Alternatively, there is a method in which the coating film is mixed into a synthetic resin solution and applied onto the surface of the molded article.

In particular, when a foam is to be manufactured from a polyolefin resin molded product containing AC as a blowing agent, the foaming degree of the surface layer is improved according to the method of the present invention in which DPT is applied as a heat generating substance to the surface of the resin molded product. Not only that, but also the surface layer A
Undecomposed C (yellow) is completely decomposed, a beautiful white foam can be obtained, and its commercial value can be increased.

DPT may be applied to the surface of the molded article in a thickness of 5 to 309/771''.

Below 5 g/m', the effect is insufficient;
This is because even if the amount is increased by 0 g/1 or more, no improvement in the effect can be expected.

Foaming is carried out by infrared heating, hot air heating, liquid heating, or a combination of these methods.

) ÷ Example 1 and Comparative Example I High pressure polyethylene 10 with MI 1.6 and specific gravity 0.921
8" with 0 parts by weight and 1.7 parts by weight of AC kept at 120℃
Knead with a mixing roll and further 0.5 at 1400G
It was molded into a thick sheet.

Next, this sheet was irradiated with an electron beam of 4 Mrad using a Cockroft type electron beam accelerator to introduce a crosslinked structure, and then foamed in hot air at 230° C. to obtain the results shown in the following table.

Example 2 and Comparative Example 2 A foaming experiment was conducted under the same conditions as in Example 1 and Comparative Example 1, except that the amount of abdicarbonamide was 8.3 parts by weight.

The results are shown in Table-2. Example 3 and Comparative Example 3 High pressure polyethylene 10 with MI 3.5 and specific gravity 0.922
0 parts by weight of abdicarbonamide, 15 parts by weight of abdicarbonamide, and 0.8 parts by weight of dicumyl peroxide were kneaded using an 8" mixing roll kept at 115°C, and further formed into a sheet with a thickness of 2 mm at 120°C.

This sheet was foamed in hot air at 230°C, and the results shown in Table 3 were obtained.

Comparative Example 4 A foaming experiment was conducted under the same conditions except that 13 parts by weight of AC and 2 parts by weight of DPT were added as a blowing agent composition to the polyethylene and crosslinking agent of Example 3 and Comparative Example 3. The product was extremely uneven and had an extremely poor appearance.

Additionally, cracks occurred around the sheet during foaming, making it impossible to obtain a good foam.

In addition, when the foaming behavior of this sample (relationship between heating time and foaming degree/specific gravity) was determined, as shown in the figure, the foaming degree did not converge to a constant value and was very unstable, and the maximum foaming point was It was also found that the specific gravity of

On the other hand, in the case of the sample of the present invention (Example 3) shown in the same figure, the degree of foaming was improved, the specific gravity was low, and stable foaming was possible with the density maintained at a constant value.

As shown in the above Examples and Comparative Examples, according to the present invention, the degree of foaming of the surface layer is improved, and it is possible to stably obtain a good, uncolored foam with an excellent feel.

[Brief explanation of drawings]

The drawing is a graph showing the relationship between heating time and specific gravity in hot air at 230° C. for each comparative example and example, and comparing the foaming behavior.

Claims (1)

[Claims] 1. In a method of heating a polyolefin resin molded product containing a thermally decomposable foaming agent to form a foam, heating and foaming is performed with dinitropentamethylenetetramine coated on the surface of the molded product. Characteristic method for producing polyolefin resin foam.