JPH06172575A - Polyolefin resin foam - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a polyolefin resin foam which does not cause a drawdown phenomenon when vacuum-formed. [Structure] A decomposable foaming agent is melt-kneaded with a polyolefin-based resin at a temperature not higher than its decomposition temperature, and further irradiated with an electron beam or radiation to be crosslinked to form a foamable sheet, which is then passed through a heating furnace. 1 when heating and foaming
The heating dimensional change rate in each of the width direction, the flow direction and the thickness direction of the foamable sheet at each temperature at the time of heating in the temperature range of 20 ° C. to 200 ° C. is −0.1% or less, − Heat to 0.5% or less and + 0.5% or more.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyolefin resin foam. More specifically, the present invention is a basic material such as a heat insulating material, a waterproof material, a heat insulating material, and a packing material in various fields such as civil engineering, construction, the vehicle industry, and packaging, and particularly vacuum such as a vehicle ceiling material and a door material. The present invention relates to a polyolefin resin foam that is molded and used.

[0002]

2. Description of the Related Art In the case of producing a foamed product, a resin is melt-kneaded with a decomposable foaming agent at a temperature not higher than its decomposition temperature, and further irradiated with an electron beam or radiation to be crosslinked to form a foamable sheet. The flexible sheet is passed through a heating furnace to be heated and foamed to produce a foam.

The foam obtained as described above is vacuum-formed into a desired shape by, for example, a vacuum forming machine and used as a ceiling material or door material of a vehicle. When performing vacuum molding, first, the foam is preheated by using a heater, and the heated foam is placed on a molding die and evacuated to bring it into close contact with the die for molding.

The conventional technique as described above is disclosed in, for example, Japanese Unexamined Patent Publication No. Hei 2
No. 175734.

[0005]

The conventional foam has a metal mold (concave drawing, convex drawing) when performing vacuum forming.
Before molding with, a heater is used for preheating. That is, as shown in FIG. 1, the foam 10 is preheated by the heater 12 while being held by the clamp 11 (see FIG.
(A)). However, when vacuum forming is actually performed, linear expansion of the foam 10 occurs during preheating, and a so-called drawdown phenomenon occurs in which the foam has a wavy shape (FIG. 1B). This drawdown phenomenon (waviness phenomenon)
When the size becomes large, when vacuum molding is performed using the mold 14, wrinkles 13 are often generated and a molding defect may occur.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a polyolefin resin foam which does not cause a drawdown phenomenon during vacuum molding.

[0007]

Means for Solving the Problems In the present invention, a polyolefin resin is melt-kneaded with a decomposable foaming agent at a temperature not higher than its decomposition temperature, and further irradiated with an electron beam or radiation to be crosslinked to form a foamable sheet. A foam obtained by heating and foaming a foamable sheet through a heating furnace, wherein
Width direction (TD direction) and flow direction (MD direction) of each temperature every 1 minute during heating in the temperature range of 20 ° C to 200 ° C
And a heating dimensional change rate in the thickness direction (ZD direction) of -0.1% or less, -0.5% or less, and + 0.5% or more, respectively. .

It can be presumed that the foam body thus prepared can prevent the drawdown phenomenon from occurring because the foam body itself has a strain, especially in the width direction. Usually, in the method for producing a foam, a resin is extruded from a mold into a sheet using an extruder, irradiated with an electron beam or radiation to be crosslinked, and then heated and foamed using hot air, a heater or both. Let

At this time, the extruded sheet is often formed in a state of being stretched in the sheet flow direction. Also in the foaming step, the speed of the foamed sheet is always higher than the speed of feeding the extruded sheet and the speed of winding the foamed sheet, depending on the foaming ratio, so that the film is stretched in the flow direction. Therefore, the heating dimensional change rate (at 120 ° C to 200 ° C) always shows a negative value (contraction tendency) in the flow direction. However, since it is hardly stretched in the width direction, the heating dimensional change rate is often a positive value (expansion). In this way, the heating dimensional change rate becomes negative in the flow direction and positive in the width direction,
The foam tends to expand in the width direction, which is considered to be the main cause of drawdown.

A particularly important factor of the foam whose heat dimensional change rate is adjusted is that it exhibits a negative value (shrinkage tendency) in the width direction. In order to prevent the drawdown phenomenon from occurring, the heating dimensional change rate is preferably in the range of -1.0 to -2.0. It is desirable that the heating dimensional change rate be as described above even at a temperature of 120 ° C. or lower, but a particularly heavy temperature range is 120 ° C. to 160 ° C.

[0011]

EXAMPLES Examples of the present invention will be described below. [Examples 1 to 3] The resin composition of Example 1 is shown in Table 1.
Various compositions corresponding to Nos. 3 to 3, 10 parts of each of these compositions were mixed with a foaming agent, and the composition was extruded using a 120φ single screw extruder to obtain a sheet having a thickness of 1.25 mm. Then
This sheet was irradiated with an electron beam under the respective conditions of Examples 1 to 3 shown in Table 1 to obtain a foamable sheet, and then,
It was heated and foamed in a vertical foaming furnace. After the foaming by heating, the final cooling step is performed. In this final cooling step, a specified width of each of Examples 1 to 3 was formed using a suction type air guider. Next, this foamed sheet was stretched in the width direction using a horizontal uniaxial tenter machine so as to have the specified widths of Examples 1 to 3, thereby obtaining foams of Examples 1 to 3.
The temperatures at the time of stretching are as shown in Table 1.

Comparative Examples 1 to 3 Foams of Comparative Examples 1 to 3 were obtained by producing foams in the same manner as in Examples 1 to 3 except that the stretching in the final step was not performed.

As the resins shown in the resin composition of Table 1, the following resins were used. 1) LLDPE: Linear low density polyethylene (MI = 2.
0, mp = 120) 2) LDPE: low density polyethylene (MI = 4.0, m)
p = 108) 3) PP: polypropylene (MI = 4.0, mp = 14)
8, random) 4) PP: polypropylene (MI = 0.5, mp = 14)
3, Random) 5) LLDPE: Linear low density polyethylene (MI = 8.
0, mp = 120) DVB: divinylbenzene

Then, these foams were vacuum-molded with a vacuum molding machine and the state of drawdown phenomenon was observed.
The results are shown in Table 2. Here, the situation of drawdown at the time of vacuum forming was evaluated as follows. A: No wrinkles were observed. ◯: Wrinkles were slightly observed. Δ: Wrinkles were observed. X: Wrinkles were observed at two places. XX: Three or more wrinkles were observed.

[0015]

[Table 1]

[0016]

[Table 2]

Example 4 Extrusion and irradiation were carried out under the same conditions with the same resin and other additives as in Example 2, and then foam molding was carried out using a vertical tenter as shown in FIG. That is, the foam 10 after foaming supplied from the upper heating furnace (not shown) is molded in the width direction by the guider 20, and then expanded in the width direction by the clip type tenter 21, and finally is cooled by the cooling roll 22. It is wound while being cooled. This foam was molded by a vacuum molding machine and the drawdown situation was observed.

[Comparative Example 4] Foam molding was carried out by the same process as in Example 4 except that foam molding was carried out without using a vertical tenter.
I observed the drawdown situation.

The above results are shown in Table 3.

[Table 3]

[0020]

As described above, according to the present invention, a drawdown phenomenon does not occur during vacuum forming, and it is possible to prevent defective molding.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a drawdown phenomenon of a foam during vacuum forming.

FIG. 2 is a diagram showing a stretching method in a width direction of a foam by a vertical tenter.

[Explanation of symbols]

 10 Foam 11 Clamp 12 Heater 13 Excessive Wrinkle 14 Mold 20 Guider 21 Clip Type Tenter 22 Cooling Roll

Claims (1)

[Claims] 1. A polyolefin resin is melt-kneaded with a decomposable foaming agent at a temperature not higher than its decomposition temperature, and further irradiated with an electron beam or radiation to be crosslinked to form a foamable sheet. The foamable sheet is then placed in a heating furnace. In the foam that has been heat-foamed through, the heating dimensional change rate in the width direction, the flow direction, and the thickness direction of each temperature at 1 minute intervals during heating of the foam in the temperature range of 120 ° C. to 200 ° C. Each −0.
A polyolefin resin foam, which is 1% or less, -0.5% or less, and + 0.5% or more.