JPH06170963A - Polyolefinic resin foam and production thereof - Google Patents

Abstract

PURPOSE:To provide a polyolefinic resin foam not generating the destruction of foams at the time of molding and having the good touch. CONSTITUTION:A foaming agent, a crosslinking agent and other additives are compounded with a polyolefinic resin and the resulting compound is melted and kneaded to be extruded to form a sheet. This sheet is foamed under heating to form a polyolefinic resin foam. In this foam, the relation of A>=1.1B is formed between the crosslinking degree A from one main surface of the foam to the region up to a thickness of 0.25mm and the crosslinking degree B from the other surface of the foam to the region up to a thickness of 0.25mm. In this case, only one main surface of the foam is irradiated with radiation and the other main surface of the foam is not irradiated with radiation.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyolefin resin foam and a method for producing the same. More specifically, it relates to a polyolefin resin foam excellent in skin strength, heat resistance, and moldability, and a method for producing the same.

[0002]

2. Description of the Related Art Polyolefin resin foams such as polyethylene resin foams and polypropylene resin foams are used as heat insulating materials, waterproofing agents, in various fields such as civil engineering, construction and vehicle industry.
It is used as a basic material such as a heat insulating material and a packing material, and is also used as a ceiling material or door material of a vehicle by being formed by various forming methods such as vacuum forming and stamping forming.

In the above-mentioned polyolefin resin foam, the main raw material resin is melt-kneaded with a decomposable foaming agent at a temperature not higher than its decomposition temperature, and this composition is extruded into a sheet to obtain a foamable sheet, Further, the foamable sheet is irradiated with an electron beam or a radiation to be crosslinked, and then the foamable sheet is passed through a heating furnace to be heat-foamed to be manufactured.

As described above, such a polyolefin resin foam has good moldability and is used as an interior material such as a vehicle ceiling material and a door material. However, such a foam is rarely used alone, and a skin material made of PVC (polyvinyl chloride), TPO (thermoplastic polyolefin), or the like is often attached to the surface of the foaming agent ( Japanese Patent Laid-Open No. 1-222936
(See Japanese Patent Laid-Open No. 1-222937).

[0005]

The interior parts such as vehicle doors and instrument panels can be obtained by laminating a foam with PVC and performing vacuum molding or the like. The degree of shearing differs depending on the size of the clearance of the upper mold, and there is a problem in that, where the shearing is large, bubble destruction occurs in the surface layer of the foam and a swelling phenomenon occurs.

Further, in stamping molding and the like, high pressure and high temperature are applied at the time of molding, so that bubble destruction and the like similarly occur. Therefore, it is unavoidable to use a polypropylene-based foam or the like having a high pressure resistance and a foaming ratio of about 15 times, which is relatively low. However, since these are intended to endure severe molding conditions, the resulting foam has problems such as a hard feel and no soft feeling.

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 cell breakage or the like during molding and has a good feel, and a method for producing the same. .

[0008]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors in order to achieve the above-mentioned object, the shearing force received by the foam is dispersed in the thickness direction, and the stress is not locally concentrated. It was found that the bubble destruction can be prevented by doing so. In stamping molding, etc., by changing the hardness of the foam on the core side and the hardness (apparent density) of the foam on the skin side, a foam that can withstand molding and has a good feel (softness) is obtained. It was found that it can be obtained. The inventors have found that the above problems can be solved by adjusting the distribution of the degree of cross-linking in the thickness direction of the foam, and arrived at the present invention.

That is, according to the present invention, a polyolefin resin is prepared by blending a polyolefin resin with a foaming agent, a cross-linking agent and other additives, melt-kneading and irradiating the extruded sheet with radiation to cross-link it, and then heat-foaming the polyolefin resin. In the resin foam, the degree of cross-linking A in a region from one main surface of the foam to a thickness of 0.25 mm and the degree of cross-linking B in a region from the other main surface to a thickness of 0.25 mm are A ≧ 1.1B. There is provided a polyolefin-based resin foam characterized by having the following relationship.

Further, according to the present invention, a polyolefin resin is blended with a foaming agent, a cross-linking agent and other additives, melt-kneaded, and the extruded sheet is irradiated with radiation to be cross-linked. In the method for producing a resin foam, the radiation is applied to only one main surface of the foam, and the degree of crosslinking A in a region from the one main surface to a thickness of 0.25 mm and the radiation are not applied. There is provided a method for producing a polyolefin-based resin foam, which comprises cross-linking so that the cross-linking degree B in the region from the main surface to a thickness of 0.25 mm has a relationship of A ≧ 1.1B.

As described above, by irradiating only one side of the foam when causing the crosslinking reaction, a specific degree of cross-linkage distribution can be formed in the thickness direction of the foam. By forming such a cross-linking degree distribution, the shear stress during molding can be dispersed and the occurrence of the blistering phenomenon can be prevented. Further, in stamping molding, by lowering the degree of cross-linking of the surface layer (the contact surface of the molten resin), gas can be released during foaming and the apparent density can be increased. This can prevent the charge mark from appearing. On the other hand, since the density of the surface to be bonded with PVC can be lowered, the obtained foam has a soft feeling and a high-class feeling.

[0012]

EXAMPLES Examples of the present invention will be described in detail below.

[Example 1] Polypropylene resin (MI
= 2.0, MP = 143, Econt = 40%) 70 parts by weight, linear low density polyethylene (MI = 2/0, MP =
120) 30 parts by weight, ADCA (azodicarbonamide) 10 parts by weight as a foaming agent, antioxidant 0.5 part and DVB (divinylbenzene) 5 parts by weight as a cross-linking agent are added, and a bidirectional extruder (L / L) is used. D = 100) was used and extruded at a temperature not higher than the decomposition temperature of the foaming agent to obtain a foamable sheet having a thickness of 1.4 mm. Then, the condition of voltage 500Kv (6.0M
In rad), only one side of the foamable sheet was irradiated with an electron beam to carry out crosslinking. Then, the foamable sheet
1. Foamed in hot air oven, density 0.04, thickness 2.
A 5 mm foam was obtained.

The distribution of the degree of crosslinking in the thickness direction of this foam is shown in FIG.
It was as shown in. The degree of cross-linking was obtained by impregnating xylene at 120 ° C. with 50 mg of the foam for 24 hours, removing the insoluble matter, and vacuum drying for 8 hours, and dividing the weight by the weight of the original foam and multiplying by 100. It was calculated as a value.

[Examples 2 to 4] Foamable sheets were prepared under exactly the same conditions as in Example 1, and the foaming properties were obtained under various voltage conditions as shown in Table 1 which differ from Example 1 only in electron beam irradiation conditions. Crosslinking was performed by irradiating only one surface of the sheet with an electron beam.
Next, this foamable sheet was foamed in a hot air oven at 250 ° C. to obtain a foamed body having a density of 0.04 and a thickness of 2.5 mm.

[Comparative Examples 1 and 2] Foaming sheets were prepared under exactly the same conditions as in Example 1, and the foaming properties under various voltage conditions as shown in Table 1 differing from those in Example 12 only in the electron beam irradiation conditions. Both sides of the sheet were irradiated with an electron beam to carry out crosslinking. Next, this foamable sheet was foamed in a hot air oven at 250 ° C. to obtain a foamed body having a density of 0.04 and a thickness of 2.5 mm.

Next, a sample having PVC adhered to the surface irradiated with electron beam and a sample having PVC adhered to the surface not irradiated with electron beam were prepared and subjected to a shear test as shown in FIG. went. That is, as shown in FIG. 2A, a sample obtained by laminating PVC 11 on foam 10 is clamped by clamp 12 and heated by heater 13, and then a clearance as shown in FIG.
Each sample was set in a shearing mold 14 that can be changed to 2.5 mm, and a shearing test was performed by changing the clearance (PVC thickness 0.6 mm).

The evaluation results are shown in Table 1. The shear test was evaluated as follows. ○: No swelling △: Small bubble destruction ×: Large bubble destruction In addition, left / right in Table 1 is the irradiated surface / unirradiated (PVC bonded)
The evaluation results of each surface are shown.

[0019]

[Table 1]

[Examples 5 and 6] With the same resin composition as in Example 1, ADCA was adjusted to 10 parts by weight, and extruded thickness was 1.9 mm.
An extruded sheet of Next, this was irradiated with an electron beam on one side under the conditions shown in Table 5, and foamed in a hot air horizontal foaming furnace at 250 ° C. 3 and 4 show the cross-linking degree distribution and the density distribution of the foam of Example 5 in the thickness direction.

[Comparative Examples 3 and 4] With the same resin composition as in Example 1, ADCA was adjusted to 6 parts by weight to obtain an extruded sheet having an extruded thickness of 1.9 mm. Next, this was irradiated with electron beams on both sides under the conditions shown in Table 5, and foamed in a hot air horizontal foaming furnace at 250 ° C. The irradiation of the electron beam in Comparative Example 4 was 2
It is divided into two times and the first time is 800 kv (6.1 Mra
Both sides are irradiated under the condition of d), and the second time is 300 kv (3.0
Both sides were irradiated under the condition of Mrad).

Next, these foams were tested for stamping moldability as shown below. That is, using a 30φ single screw extruder for experiment, MI = 5
Homopolypropylene of 0, mp = 165 ° C. was extruded at each resin temperature, and this molten resin was placed on the surface of the foam that had not been irradiated with an electron beam, and then 100 kg with a pressing machine.
It was compressed at 1 / cm ² for 1 minute, and it was visually observed how much a burnt pattern (charge mark) appeared on the surface of the foam on which the molten resin was not placed.

The evaluation results are shown in Table 2. The stamping moldability was evaluated as follows. ○: Charge mark does not appear △: Charge mark is slightly present ×: Charge mark is present

[0024]

[Table 2]

[0025]

As described above, according to the present invention, it is possible to obtain a polyolefin resin foam which does not cause cell breakage or the like during molding and has a good feel.

[Brief description of drawings]

FIG. 1 is a graph showing the cross-linkage distribution in the thickness direction of the foam of Example 1.

FIG. 2 is a diagram illustrating a method of a disconnection test.

FIG. 3 is a graph showing the distribution of the degree of crosslinking in the thickness direction of the foam of Example 5.

FIG. 4 is a graph showing the density distribution in the thickness direction of the foam of Example 5.

[Explanation of symbols]

 10 Foam 11 PVC 12 Clamp 13 Heater 14 Shearing Mold

Claims (2)

[Claims] 1. A polyolefin resin foam obtained by blending a polyolefin resin with a foaming agent, a cross-linking agent, and other additives, melt-kneading, and irradiating the extruded sheet with radiation to cross-link it, and then heat-foaming it. In the above, the degree of cross-linking A in the region from the one main surface of the foam to a thickness of 0.25 mm and the degree of cross-linking B in the region from the other main surface to the thickness of 0.25 mm are A ≧ 1.1B. A polyolefin-based resin foam characterized by having. 2. A polyolefin resin is blended with a foaming agent, a cross-linking agent and other additives, melt-kneaded, and the extruded sheet is irradiated with radiation to be cross-linked, and this is heat-foamed to form a polyolefin resin foam. In the method for producing, the radiation is applied to only one main surface of the foam, and the degree of crosslinking A in a region from the one main surface to a thickness of 0.25 mm and the other main surface not irradiated with the radiation. A method for producing a polyolefin-based resin foam, which comprises crosslinking so that a degree of crosslinking B in a region up to a thickness of 0.25 mm has a relationship of A ≧ 1.1B.