JPH06345887A - Production of polypropylene resin foam - Google Patents

Abstract

PURPOSE:To produce a polypropylene resin crosslinked foam improved in surface strength. CONSTITUTION:A foamable resin composition containing polypropylene resin, a thermal decomposition type foaming agent and a crosslinking auxiliary is crosslinked and subsequently heated in a liquid phase or gas phase stepwisely set from a low temperature side to a high temperature side to foam the resin composition. When the foamable resin composition is heated in the liquid phase, the resin composition is subjected to the first heating treatment within a temperature range of -10 to +20 deg.C and subsequently to the second heating treatment within +20 to +50 deg.C on the basis of the decomposition point of the thermal decomposition type foaming agent. When the resin composition is heated in the gas phase, the resin composition is subjected to the first heating treatment within a temperature range of +20 to +50 deg.C and subsequently to the second heating treatment within a temperature range of +50 to +200 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polypropylene-based resin crosslinked foam, and more specifically, a polypropylene-based foam having improved skin surface strength and excellent moldability even for complex and deep shapes. The present invention relates to a method for producing a resin crosslinked foam.

[0002]

2. Description of the Related Art Conventionally, polypropylene-based resin foams have been obtained by irradiating a foamable resin composition containing a polypropylene-based resin, a pyrolytic foaming agent and a crosslinking aid with ionizing radiation to crosslink it, and then at high temperature. It was manufactured by heating at high speed and foaming.

However, the polypropylene resin cross-linked foam thus obtained is subjected to a surface treatment, laminated with a surface material, laminated on a base material layer, and molded into a desired shape to obtain a vehicle interior material. The adhesive may be partially peeled off due to lack of affinity between the adhesive and the skin material or the adhesive and the polypropylene resin crosslinked foam, and gas may be accumulated there. This is blister caused by peeling at the interface (see FIG. 5). In this case, it is dealt with by surface treatment for modifying the surface of the foam or the skin material and improvement of the adhesive.

Moreover, the foam is partially torn in the thickness direction,
Gas may accumulate there. This is blister due to insufficient strength of the subepithelial layer of the foam (see FIG. 6). This is dealt with by resins such as polypropylene and polyethylene, the degree of cross-linking, a cross-linking auxiliary agent associated therewith, and many other approaches (Japanese Patent Laid-Open No. 1-272641, Japanese Patent Application No. 4-326533 by the present applicant).

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of producing a polypropylene resin crosslinked foam having an improved skin strength in view of the above problems of the prior art.

Another object of the present invention is to provide an interior material for a vehicle, which uses the foam obtained by the present invention and has improved skin strength.

As a result of earnest research, the present inventor has found that the above object can be achieved by performing multi-step heating when the polypropylene resin composition is heated and foamed, and the present invention is based on the findings. It came to completion.

[0008]

That is, the present invention provides a polypropylene resin foam in which a foamable resin composition containing a polypropylene resin, a thermal decomposition type foaming agent and a crosslinking aid is crosslinked and subsequently heated to foam. In the manufacturing method of, heating is performed in a liquid phase or a gas phase in which the temperature is set stepwise from the low temperature side to the high temperature side, and foaming is performed,
It is a method for producing a polypropylene resin foam.

The present invention will be described in detail below.

The expandable resin composition in the present invention contains a polypropylene resin, a thermal decomposition type foaming agent and a crosslinking aid.

Examples of the polypropylene resin include polypropylene homopolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer and the like. These may be used alone or 2
More than one species may be used. Moreover, you may use polyethylene resin together. When a polyethylene resin is used in combination, the mixing ratio is preferably 40 to 100 parts by weight of polypropylene and 60 to 0 parts by weight of polyethylene.

The thermal decomposition type foaming agent used in the present invention is one which generates decomposition gas upon heating, and specifically,
Examples include azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, 4,4-oxybis (benzenesulfonyl hydrazide) and the like. These may be used alone or in combination of two or more. The thermal decomposition type foaming agent can be used in an appropriate amount in the range of 1 to 50 parts by weight with respect to 100 parts by weight of the polypropylene resin, depending on the desired expansion ratio. A preferred blending ratio is 4 to 25 parts by weight with respect to 100 parts by weight as the total of the resin components.

The cross-linking aid used in the present invention is preferably a poly-functional cross-linking aid having two or more functional groups such as vinyl group, acryl group and methacryl group in one molecule. As the crosslinking aid, trimethylolpropane tri (meth) acrylate, divinylbenzene, pentaerythritol tri (meth) acrylate, 2,2-
Bis [4- (acryloxydiethoxy) phenyl] propane, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate,
Examples thereof include those active to ionizing radiation such as 1,10-decanediol di (meth) acrylate. Moreover, you may mix | blend a monofunctional monomer as a crosslinking auxiliary depending on the case. These cross-linking aids are generally the sum of the resin components 1
It is blended in a proportion of 0.5 to 10 parts by weight with respect to 00 parts by weight.

In the present invention, the expandable resin composition comprises
Antioxidants, stabilizers, pigments and the like may be added depending on the purpose.

In the present invention, the expandable polypropylene resin composition is melt-kneaded at a temperature lower than the decomposition temperature of the thermal decomposition type foaming agent, and usually extruded into a sheet. The resulting expandable resin composition sheet is irradiated with ionizing radiation to crosslink. As ionizing radiation, α rays, β
Ray, γ ray, electron beam and the like, and the irradiation dose is usually 1 to 20 Mrad.

After the crosslinking, the foamable resin composition sheet is heated in the liquid phase or the gas phase in which the temperature is gradually set from the low temperature side of the crosslinking to the high temperature side to foam to obtain a crosslinked foam. .

When the heating is carried out in the liquid phase, the first heating is carried out in the temperature range of -10 to + 20 ° C based on the decomposition point of the thermal decomposition type foaming agent, and then the temperature range of +20 to + 60 ° C. It is preferable to carry out the second heating. Moreover, you may perform the 3rd heating, the 4th heating, etc. which were further set to high temperature as needed. The decomposition point of the heat-decomposable foaming agent is, by comparison with the foaming agent alone, by being mixed in the resin composition,
Generally, the decomposition point shifts to the low temperature side, but the decomposition point as a reference in the present invention means the decomposition point under the condition of being blended in the resin composition.

When heating in the liquid phase, the first heating and the second heating
The heating and the like may be performed in separate foaming tanks (first foaming tank, second foaming tank, etc.) (see FIG. 1), or if it is possible to set the temperature, use a single foaming tank. Good (Fig. 2
reference). In the foaming tank, a liquid that melts at 100 to 300 ° C. is used as a foaming liquid.

When the heating is carried out in the gas phase, the first heating is carried out within the temperature range of +20 to + 50 ° C., followed by the temperature range of +50 to + 200 ° C., based on the decomposition point of the thermal decomposition type foaming agent. It is preferable to perform the second heating. Further, if necessary, the third heating, the fourth heating, or the like set to a higher temperature may be performed, or the preliminary heating set to a temperature lower than the first heating may be performed prior to the first heating. Good.

When heating in the gas phase, the first heating, the second
The heating and the like may be performed in separate foaming furnaces (first foaming furnace, second foaming furnace, etc.) (see FIG. 3), or if it is possible to set the temperature, use a single foaming furnace. Good (Fig. 4
reference).

[0021]

In the present invention, heating is performed in the liquid phase or the gas phase in which the temperature is set stepwise from the low temperature side to the high temperature side to foam. By performing the first heating at a temperature substantially equal to the decomposition point of the foaming agent, the pyrolytic foaming agent produces a gas corresponding to the temperature. Although the generated gas amount is smaller than that when the decomposition is performed at a high temperature, they do not interfere with each other's growth, so that the bubbles gradually grow and grow sufficiently. That is, according to the method of the present invention performed at a low temperature and a low speed, it is possible to increase the bubble diameter as compared with the conventional foaming performed at a high temperature and a high speed.

However, at this stage, since the sufficient expansion ratio (reciprocal of density) has not been reached, the amount of the thermal decomposition type foaming agent is changed after the second heating, which is higher than the set temperature of the first heating. Expand the foam to the expansion ratio.

The polypropylene-based resin crosslinked foam produced by the method of the present invention has a large number of cells under the epidermis and has a large film thickness of the cells, so that the skin strength is improved and the amount of the thermal decomposition type foaming agent is large. It becomes a foamed product that has been expanded to a foaming ratio corresponding to.

[0024]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Production of Expandable PP Raw Material) 55 parts by weight of polypropylene (MI = 0.5, mp = 143 ° C., ethylene-propylene random copolymer) and polyethylene (MI)
= 8.0, mp = 120 ° C.) 40 parts by weight, 6.5 parts by weight of a crosslinking aid (polyfunctional monomer, trimethylolpropane trimethacrylate) and 10 parts by weight of a thermal decomposition type foaming agent (azodicarbonamide). Was added and sheeting-extruded with an extruder, and this was irradiated with ionizing radiation to be crosslinked to obtain a foamable PP raw fabric. The decomposition point of the heat-decomposable foaming agent in the foamable PP raw fabric is about 200 ° C. This foamable PP raw fabric was used in the following examples and comparative examples.

[Example 1] First, a foamable PP raw material was prepared in 20
Foaming was carried out for 400 seconds in the first foaming tank kept at a constant temperature of 0 ° C., and then for 40 seconds in a second foaming tank kept at a constant temperature of 250 ° C. to produce a foam.

[Example 2] First, 18
After preheating at 0 ° C for 60 seconds, foaming was performed for 160 seconds in the first foaming furnace which was kept at 240 ° C, and then 280 ° C.
Continue foaming for 90 seconds in the second foaming furnace that was kept at constant temperature,
A foam was produced.

Although the horizontal foaming machine is used in the second embodiment, it is of course possible to use the vertical foaming machine.

[Comparative Example 1] A foamable PP raw material was heat-foamed at 270 ° C for 70 seconds in a hot air vertical type foaming furnace to produce a foamed product.

[Comparative Example 2] A foamable PP raw material was placed at 250 ° C.
Foaming was carried out for 60 seconds in a foaming bath kept at a constant temperature to produce a foamed body.

A surface treatment was applied to each of the above-mentioned foams, and a polyethylene-based adhesive shown in Table 1 was used on the treated surface, and a polyvinyl chloride soft sheet containing ABS resin (0.6 mm thick,
PVC polymerization degree 1300 ± 30, plasticizer DOP, ABS
(35 parts), and a composite material composed of a foam and a skin was prepared by laminating a skin.

[0032]

[Table 1]

<Adhesion Test> For each of the above composite materials,
A skin peel strength measurement test was conducted by the following method. That is, the skin is peeled from the foam at the end of the test piece (25 mm × 150 mm) of the composite material, and the foam and the skin are each 200 mm / mm by using a measuring machine Tensilon manufactured by Toyo Seiki.
It was pulled at a speed of min. In the case of high temperature test conditions, the test piece was left in the test box for 5 minutes and then measured.

The test results are shown in Table 2.

[0035]

[Table 2]

The peel strength of Example 1 is improved by about 1.6 times as compared with Comparative Example 1 and by 1.25 times as compared with Comparative Example 2. Further, the peel strength of Example 2 is improved by about 1.8 times as compared with Comparative Example 1 and 1.27 times as compared with Comparative Example 2.

[0037]

Industrial Applicability According to the method of the present invention, a polypropylene resin crosslinked foam having improved skin strength of the foam and excellent moldability even in a complicated and deep shape can be produced. The polypropylene resin crosslinked foam produced by the present invention is particularly suitable as a vehicle member.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a heating method of the present invention (a split type foaming tank).

FIG. 2 is a diagram showing an outline of a heating method of the present invention (continuous foaming tank).

FIG. 3 is a diagram showing an outline of a heating method of the present invention (a split type foaming furnace).

FIG. 4 is a diagram showing an outline of a heating method of the present invention (a continuous foaming furnace).

FIG. 5 is a diagram showing blistering caused by peeling at an interface.

FIG. 6 is a diagram showing blistering due to insufficient strength of the subdermal layer of the foam.

[Explanation of symbols]

 1: Raw fabric feeding side 2: Raw fabric winding side 3: First foaming tank 4: Second foaming tank 5: First foaming furnace 6: Second foaming furnace 7: Foamed body 8: PVC 9: Fukuro

Claims (3)

[Claims] 1. A method for producing a polypropylene resin foam in which a foamable resin composition containing a polypropylene resin, a thermal decomposition type foaming agent and a crosslinking aid is crosslinked, and subsequently heated to foam. To a high-temperature side in a liquid phase or a gas phase in which the temperature is set stepwise, and foaming is performed, the method for producing a polypropylene resin foam. 2. The heating is performed in a liquid phase, and the first heating is performed in a temperature range of −10 to + 20 ° C. based on the decomposition point of the pyrolytic foaming agent, and then a temperature of +20 to + 60 ° C. The method according to claim 1, characterized in that the second heating is performed in the range. 3. The heating is carried out in a gas phase, and the first heating is carried out in a temperature range of +20 to + 50 ° C. based on the decomposition point of the thermal decomposition type foaming agent, and subsequently in a temperature range of +50 to + 200 ° C. The method according to claim 1, characterized in that the second heating is carried out at.