JPH1060145A - Production of cross-linked polyolefin resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cross-linked polyolefin resin foam having no external unevenness and an excellent thremoformability in a simple manner by cross- linking a foamable polyolefin resin having a specified compsn. and thermally foaming it at a specified temp. SOLUTION: 40-100wt.% polypropylene resin is mixed with 60-0wt.% polyethylene resin and then with a thermally decomposable blowing agent and a cross- linking aid. The resultant foamable polyolefin resin is cross-linked, e.g. by the exposure to an ionizing radiation or by using an org. peroxide (e.g. dicumyl peroxide) and is thermally foamed at a temp. 20-50 deg.C higher than the decomposition point of the blowing agent, thus giving the objective foam. Pref. examples of the blowing agent are azodicarbonamide and N,N'- dinitrosopentamethylenetramine. Examples of the cross-linking aid are divinylbenzene and trimethylolpropane trimethacrylate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a crosslinked polyolefin resin foam.

[0002]

2. Description of the Related Art Crosslinked polyolefin resin foams are used in a wide range of fields as various heat insulating materials and cushioning materials. For example, in vehicle interior materials, they are used as heat-insulating cushioning materials for ceilings, doors, instrument panels, and the like.
The foam is generally formed into a sheet shape, and a plastic sheet such as a soft vinyl chloride resin sheet or a cloth is laminated with a hot melt adhesive or the like as a skin material, and is used for thermoforming such as vacuum forming and compression molding. To a desired shape. When laminating a skin material to the foam, when the cells of the foam are closed cells, the cells are broken by heat or shear stress, and when the cells are open cells, the cell wall buckles, May have irregularities. Also,
A similar phenomenon occurs when performing thermoforming.

[0003] The above-mentioned problem of the unevenness of the appearance can be solved by increasing the degree of crosslinking of the foam or reducing the expansion ratio, thereby increasing the heat resistance and the compression resistance of the foam surface layer. It is possible. However, when the degree of cross-linking is increased, the elongation of the foam is reduced, so that the moldability is reduced, and when the expansion ratio is reduced, the heat insulating property and the buffering property are reduced, which is disadvantageous in terms of weight reduction and cost reduction. Become.

As a method for solving the above problem, for example, Japanese Patent Application Laid-Open Nos. 5-214143 and 4-50
No. 34 discloses a method for producing a crosslinked polyolefin-based resin foam.

Japanese Patent Application Laid-Open No. 5-214143 discloses a polyolefin resin containing a pyrolytic foaming agent and a crosslinking assistant (polymerized using a stereoregular catalyst and having an ethylene content of 3 to 7% by weight. 40 to 75 parts by weight of an ethylene-propylene random copolymer having a melting point of 130 to 145 ° C, polymerized using a stereoregular catalyst, and having an ethylene content of 1
~ 7 wt%, butene content is 1-7 wt%,
In addition, the total content of ethylene and butene is 4 to 14% by weight, the melting point is 120 to 140 ° C, and the ethylene-propylene-butene random copolymer is 5 to 40 parts by weight and the melting point is 1
A cross-linked polyolefin-based resin foam having improved moldability and improved elongation and tensile strength in a high-temperature region by using 5 to 40 parts by weight of polyethylene resin (total of 100 parts by weight) at a temperature of from 05 to 135 ° C. It has gained. However, in this method, the cell diameter of the foam was small, the cell wall was thin, and irregularities appeared in the appearance during thermoforming.

Japanese Patent Application Laid-Open No. 4-5034 discloses that after a film made of an olefin resin is laminated on one surface of a sheet made of a polyolefin resin composition containing a foaming agent and a crosslinking agent, the other surface of the sheet is made. By cross-linking, excellent heat-sealing property to the skin material and deep drawing formability are excellent,
In addition, a crosslinked polyolefin resin foam having a good appearance is obtained. However, in this method, since a sheet made of a polyolefin-based resin composition and a film made of an olefin-based resin are laminated by a simultaneous two-layer extrusion method, there has been a problem that a manufacturing process is complicated and a manufacturing cost is increased.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a crosslinked polyolefin-based resin foam having no irregularities in appearance and excellent in thermoformability, in which the production process is simple.

[0008]

The foamable polyolefin resin used in the present invention is a polypropylene resin 40.
-100% by weight and polyethylene resin 60-0% by weight
Is obtained by adding a pyrolytic foaming agent and a crosslinking aid to a polyolefin resin composed of

The polypropylene resin may be a propylene homopolymer, a propylene-α-olefin copolymer containing a propylene portion of 85% by weight or more, or a mixture thereof. Examples of the α-olefin include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and 1-octene. The polypropylene resin preferably has a melt index (hereinafter referred to as MI) in the range of 0.4 to 8. If it is less than 0.4, the appearance will deteriorate when formed into a sheet, and if it exceeds 8, the heat resistance will decrease.

The polyethylene resin may be any of a homopolymer of ethylene, a copolymer containing ethylene as a main component, or a mixture thereof. Among them, a linear low-density polyethylene is preferable. Examples of the copolymer containing ethylene as a main component include, for example, an ethylene-α-olefin copolymer containing 80% by weight or more of an ethylene moiety and an ethylene-α-olefin copolymer.
Examples include vinyl acetate copolymers, and examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. MI of the polyethylene resin is 1 to 20
Is preferably within the range. If it is less than 1, the appearance will be reduced when formed into a sheet, and if it exceeds 20, the heat resistance will be reduced.

The MI of the polypropylene-based resin and the polyethylene-based resin is a value measured according to JIS K7210. The test temperature was 230 ° C. for the polypropylene resin and 190 ° C. for the polyethylene resin, and the test load was 2.16 kgf in each case.

When the content of the polypropylene resin is less than 40% by weight or the content of the polyethylene resin exceeds 60% by weight, the heat resistance and rigidity at high temperatures become insufficient, and the thermoformability decreases. Therefore, the blending amount of the polypropylene resin is 4
0 to 100% by weight, and the blending amount of the polyethylene resin is 60 to 0% by weight.

As the thermal decomposition type foaming agent, those having a decomposition temperature of 180 to 270 ° C. are generally used. For example, azodicarbonamide, N, N'-dinitrosopentamethylenetetramine, p-toluenesulfonyl semicarbazide and the like can be mentioned. These may be used alone or in combination of two or more. The amount of the pyrolytic foaming agent to be added is generally 5 to 30 parts by weight based on 100 parts by weight of the polyolefin resin, and is adjusted according to a desired expansion ratio.

The expansion ratio is 10 to 35 in apparent specific volume.
It is preferably adjusted to cc / g. If it is less than 10 cc / g, the heat insulating property and the buffering property decrease. If it exceeds 35 cc / g, elongation at a high temperature is insufficient, so that thermoformability is reduced.

Examples of the crosslinking aid include divinylbenzene, trimethylolpropane trimethacrylate, triallyl trimellitate, and 1,9-nonanediol dimethacrylate. These may be used alone or in combination of two or more. The amount of the crosslinking aid to be added is generally 0.3 to 10 parts by weight with respect to 100 parts by weight of the polyolefin resin, and is adjusted according to a desired degree of crosslinking.

The foamable polyolefin resin is generally formed into a sheet and crosslinked. The sheet is formed by melting and kneading a pyrolytic foaming agent and a crosslinking assistant with a general-purpose kneading device such as an extruder or a roll at a temperature at which the pyrolytic foaming agent does not decompose.

The foamable polyolefin-based resin is added to a foaming agent decomposition accelerator, a cell nucleus modifier, an antioxidant,
A heat stabilizer, a colorant, a flame retardant, an antistatic agent, an inorganic filler, and the like may be added as necessary.

As a method of crosslinking the obtained foamable polyolefin resin sheet, a method of irradiating ionizing radiation or adding an organic peroxide at the time of molding the foamable polyolefin resin is used. A method of decomposing an organic peroxide by heating a polyolefin-based resin sheet may, for example, be mentioned.

Examples of the ionizing radiation include an electron beam, α-ray, β-ray and γ-ray. The dose of ionizing radiation is generally 1 to 20 Mrad, and is adjusted according to a desired degree of crosslinking.

Examples of the organic peroxide include dicumyl peroxide, di-t-butyl peroxide and methyl ethyl ketone peroxide.
The amount of the organic peroxide to be added is 100
It is generally 0.3 to 5 parts by weight with respect to parts by weight, and is adjusted according to a desired degree of crosslinking.

Next, the crosslinked foamable polyolefin resin sheet is foamed by heating to a temperature 20 to 50 ° C., preferably 30 to 40 ° C. higher than the decomposition starting temperature of the thermal decomposition type foaming agent. Thereby, a crosslinked polyolefin resin foam is obtained. When the foaming temperature is lower than the decomposition start temperature of the thermal decomposition type foaming agent + 20 ° C., the foaming does not occur. Therefore, the bubble diameter is small, the bubble wall thickness is small, and the amount of gas generated is large, so that the bubbles are easily broken and the closed cell ratio is reduced. 20 to 50 ° C higher than the decomposition start temperature of the thermal decomposition type foaming agent
When the foaming is performed by heating to a high temperature, the pyrolytic foaming agent is gradually decomposed, and the foamed foam is absorbed by the foamed foam later, so that the bubble diameter increases and the foam wall thickness increases.

The decomposition onset temperature of the above-mentioned pyrolytic foaming agent is the peak onset temperature obtained when the decomposition temperature is measured using a differential thermal analyzer. Examples of the heating method include a method using hot air, infrared rays, a metal bath, an oil bath, and the like.

The bubble diameter is preferably 500 to 700 μm and the bubble wall thickness is preferably 12 to 20 μm. Bubble diameter 50
When the thickness is less than 0 μm or the thickness of the bubble wall is less than 12 μm, irregularities are generated in appearance, and heat resistance is reduced. If the bubble diameter exceeds 700 μm or the bubble wall thickness exceeds 20 μm, the buffering property decreases. When the closed cell ratio is less than 80%, irregularities appear in the appearance when the skin material is laminated or when the thermoforming is performed. The closed cell ratio is a value calculated from the density measured according to JIS K7112. When the crosslinked polyolefin-based resin foam is in the form of a sheet, the thickness thereof is generally preferably 1 to 10 mm.

[0024]

The crosslinked polyolefin resin foam obtained by the production method of the present invention has a larger cell diameter than conventional ones,
Since the cell wall thickness is large, and the closed cell ratio, which was less than 80% in the conventional manufacturing method, has been increased to 90% or more, it is possible to reliably prevent irregularities in appearance that occur during bonding of the skin material and thermoforming. .

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0026]

【Example】

(Example 1, Comparative Examples 1-3) A predetermined amount of propylene-ethylene random copolymer (MI
= 0.5, propylene content 96.8% by weight), linear low-density polyethylene (MI = 8.0, density 0.92 g /
cm ³ ), azodicarbonamide (decomposition start temperature 190
° C), trimethylolpropane trimethacrylate and 1,9-nonanediol dimethacrylate, and the mixture was melt-kneaded at a temperature lower than the decomposition start temperature of azodicarbonamide, extruded into a sheet, and foamed to a thickness of 1.5 mm. A polyolefin resin sheet was obtained.

The obtained foamable polyolefin resin sheet was irradiated with 2.0 Mrad of electron beam to crosslink, and then heated to a predetermined foaming temperature shown in Table 1 in a hot-air vertical foaming furnace to foam. Thus, a foamed crosslinked polyolefin-based resin sheet having a predetermined apparent specific volume (expansion ratio) shown in Table 1 and a thickness of 3 mm was obtained.

Further, a soft vinyl chloride sheet having a thickness of 0.4 mm is heat-bonded to one surface of the obtained crosslinked polyolefin resin foam sheet with a urethane hot melt adhesive.
A foam sheet with a skin material was obtained.

(Average Cell Diameter) The obtained crosslinked polyolefin resin foam sheet was cut, and the cut surface was observed at about five places with an electron microscope, and the average value of the cell diameter was calculated.

(Average Cell Wall Thickness) The average value of the cell wall thickness was calculated in the same manner as in the above average cell diameter.

(Thermoformability) As shown in FIG. 1, a 10 × 20 cm foam sheet with a skin material was
And the surface of the skin 21 of the foamed sheet 20 with the skin is heated to 150 ° C. by the upper mold 11 of the test mold 10.
Then, the surface of the 20 foam sheets 22 is
After heating to 0 ° C., 20 was compression molded at a speed of 15 cm / s. The compression molding was performed until the clearance 40 between the upper mold 11 and the lower mold 12 became 1.0 mm, 1.5 mm, and 2.0 mm. The thermoformability at that time was evaluated as follows, and the results are shown in Table 1. ：: No unevenness was observed in the appearance △: Unevenness was observed in the appearance, and a portion where the unevenness was observed was less than 5% of the whole ×: A portion where the unevenness was observed in the external appearance was 5% or more of the whole Met

(Drawing ratio) The above foam sheet with a skin material is
Heating was performed with a far-infrared heater so that the temperature on both sides was 160 to 170 ° C., and vacuum forming was performed using a cylindrical concave mold having a diameter D of 100 mm. At this time, the maximum depth of the concave mold from which a good molded product was obtained was defined as H, and the drawing ratio (H
/ D) is shown in Table 1.

[0033]

[Table 1]

[0034]

According to the method for producing a crosslinked polyolefin resin foam of the present invention, the production process is simple because it is constituted as described above, and the obtained foam has a large cell diameter and a large cell wall thickness. Is thick, so that there is no unevenness in the appearance and the thermoformability is excellent.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for testing the thermoformability of a foam sheet with a skin material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Test mold 11 Upper mold 12 Lower mold 20 Foam sheet with skin material 21 Skin material 22 Foam sheet 30 Clamp 40 Clearance

Claims (1)

[Claims] 1. After cross-linking a foamable polyolefin-based resin comprising 40 to 100% by weight of a polypropylene-based resin and 60 to 0% by weight of a polyethylene-based resin and containing a pyrolytic foaming agent and a crosslinking aid, A method for producing a crosslinked polyolefin-based resin foam, comprising heating and foaming at a temperature 20 to 50 ° C. higher than the decomposition start temperature of the pyrolytic foaming agent.