JPH0524126A - Manufacture of polyolefin resin crosslinked foam - Google Patents

Abstract

PURPOSE:To provide a manufacture of polyolefin resin crosslinked foam excellent in molding processability by controlling drawdown at the time of hot molding. CONSTITUTION:A resin composition containing polyolefin resin and heat decomposable foaming agent is molded into a foamable resin composition sheet at a temperature of less than the decomposition temperature of the foaming agent. Then this is a manufacture of a polyolefin resin crosslinked foam where after crosslinking in a manufacture of the crosslinked foam to be heated and foamed, the first time widening of a foamed sheet is performed while a surface temperature of the foamed sheet is within 120-290 deg.C in the vicinity of a terminal point of foaming and then the second time widening of the foamed sheet is performed to a width wider by 1-50% than that of the foamed sheet widened at the first time.

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 polyolefin resin crosslinked foam, and more specifically, a polyolefin resin crosslinked foam excellent in molding processability by suppressing drawdown during thermoforming. Regarding the method.

[0002]

2. Description of the Related Art Conventionally, polyolefin resin cross-linked foams have been used for a wide range of applications such as heat insulating materials, cushioning materials, and sundries, and recently, as interior materials for vehicles such as automobiles, ceilings, doors, It is widely used as a heat insulating material for instrument panels. These heat insulating materials and the like are generally commercialized by processing a sheet-shaped polyolefin resin crosslinked foam (foamed sheet) into a predetermined shape by a thermoforming method such as vacuum forming or pressure forming.

The thermoforming method generally includes a step of heating a foamed sheet, a step of molding the foamed sheet with a force of vacuum or compressed air or a mold, a step of cooling the foamed sheet, and cutting an extra portion from a molded product. It consists of the process of doing. In the step of heating the foamed sheet, the foamed sheet held between the clamps is heated and softened, but during this heating, a drooping phenomenon (drawdown) occurs due to the weight of the foamed sheet. Depending on the crosslinked foamed polyolefin resin, the drawdown may be so severe that molding may not be possible, the molded product may be wrinkled, or the thickness may become non-uniform and the commercial value may be impaired.

On the other hand, recently, a foam molded product having a complicated and deep shape has been required, and a high degree of deep drawing has been required. However, for deep drawing, it is necessary to heat the foamed sheet to a considerably high temperature,
As a result, drawdown becomes more severe and thermoforming becomes more difficult.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to minimize the drawdown of a foamed sheet in a heating step in thermoforming such as vacuum forming and to improve the molding processability of a polyolefin resin crosslinked foam. It is to provide a manufacturing method of.

As a result of earnest studies to overcome the problems of the prior art, the inventors of the present invention have found that in the process of manufacturing a polyolefin resin crosslinked foam, when the foamed sheet is widened near the foaming end point, It has been found that a foamed sheet in which drawdown is significantly suppressed can be obtained by widening the width in stages, and the present invention has been completed based on the findings.

[0007]

According to the present invention, a resin composition containing a polyolefin resin and a pyrolytic foaming agent is molded into a foamable resin composition sheet at a temperature lower than the decomposition temperature of the foaming agent. Then, in the method for producing a crosslinked foam which is then foamed by heating after crosslinking, in the vicinity of the foaming end point in the foamed sheet, (1) the surface temperature of the foamed sheet is 120 to 290.
The first widening was carried out while the temperature was at 0 ° C, and then (2) while the surface temperature of the foam sheet was at 80 to 120 ° C, the first
Provided is a method for producing a polyolefin resin crosslinked foam, which comprises performing a second widening to a width that is 1 to 50% wider than a width of a foamed sheet widened for a second time.

The present invention will be described in detail below. In the manufacturing process of the polyolefin resin crosslinked foam, first,
A polyolefin resin is mixed with a thermal decomposition type foaming agent, and if necessary, an antioxidant, a crosslinking aid, a pigment, etc., and the mixture is melted and kneaded at a temperature lower than the temperature at which the foaming agent decomposes. It is formed into a sheet by an extruder, a twin-screw extruder, a pressure kneader, etc.).

The foamable sheet thus obtained is irradiated with ionizing radiation (α-ray, β-ray, γ-ray, electron beam, etc.) to crosslink it.
For the cross-linking, a chemical cross-linking method using an organic peroxide, a water cross-linking method by grafting or copolymerizing vinyltrimethoxysilane or the like with a resin, and the like may be adopted.

The crosslinkable foamable sheet is foamed by heating above the decomposition temperature of the foaming agent. As the foaming method, there are various methods such as a method of passing through a preheating area and a foaming area in a foaming furnace by using a vertical blowing furnace or a horizontal foaming furnace of a hot air circulation type, or a salt bath method. The heat-foamed foamed sheet is expanded in width so that the foamed sheet has a predetermined width in the vicinity of the foaming end point (widening step).

To widen the foamed sheet, for example, a method of sucking both ends of the foamed sheet with a suction type guider, a method of pulling both ends of the foamed sheet with a tenter, or a width direction outside of the foamed sheet with a circular guider or a roll type guider is used. Examples include a method of applying a contact frictional force to one side.

The manufacturing method of the present invention is characterized in that this widening step is performed in two stages. That is, in the vicinity of the end point of foaming, (1) the surface temperature of the foamed sheet is 120 to 2
The first widening is performed while the temperature is 90 ° C., and then (2) while the surface temperature of the foam sheet is 80 to 120 ° C., the width is 1 to 50% wider than the width of the first expanded sheet. The second widening is performed.

The vicinity of the end point of foaming means the state immediately after the foamed sheet leaves the foaming furnace or the salt bath, and is in the state where the decomposition of the foaming agent is completed or just before completion. In this state, the surface temperature of the foam sheet is usually about 120 to 290 ° C.

Therefore, in the first widening, the surface temperature of the foamed sheet is 120 to 290 ° C., preferably 120 to 20.
Perform at 0 ° C. Conventionally, when widening a foam sheet,
Only the first widening process has been performed.

When the first widening step is completed, the foamed sheet is cooled so that the surface temperature of the foamed sheet becomes 120 ° C. or lower, and the width is temporarily fixed. There are various methods of cooling such as natural cooling, air cooling, passing on a roll containing water, and passing through a heat medium.

Then, in the second widening, the surface temperature of the foamed sheet is 80 to 120 ° C., preferably 105 to 12
While it is at 0 ° C., it is widened to a width that is 1 to 50%, preferably 3 to 15% wider than the width of the first expanded foam sheet.

The surface temperature of the foamed sheet is measured with a heat label or a heat gun. The relationship between the surface temperature of the foam sheet and the temperature condition in the foam furnace in advance, or
If the state of the temperature change between the second widening process and the second widening process is checked, it is possible to save the trouble of measuring the temperature one by one.

In the foamed sheet thus widened in two steps, drawdown is suppressed and the formability (vacuum formability, deep drawing formability, etc.) is improved.

The polyolefin resin used in the present invention includes low density polyethylene (LDPE), high density polyethylene (HDPE) and linear low density polyethylene (L).
LDPE), polypropylene (PP), ethylene-vinyl acetate copolymer (EVA) and the like can be used, but not limited thereto.

Examples of the heat-decomposable foaming agent include azodicarbonamide, oxybenzenesulfonyl hydrazide, dinitrosopentamethylenetetramine and the like. The addition amount thereof is appropriately adjusted depending on the desired foaming ratio, but usually 100 parts by weight of resin. 2 to 25 parts by weight.

If desired, flame retardants, coloring agents, antioxidants (phenolic antioxidants, etc.), fillers, foaming aids, lubricants and the like may be added.

[0022]

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

Example 1 70 parts by weight of ethylene-propylene random copolymer (melting point = 148 ° C., MI = 2.0), LLDPE (melting point = 122 ° C., MI = 6.0) 30
10 parts by weight of azodicarbonamide was added to parts by weight to obtain a sheet having a width of 400 mm and a thickness of 1.0 mm with a twin-screw extruder.

After irradiating the sheet with an electron beam having a dose of 8.0 Mrad to crosslink the sheet, the sheet was introduced into a vertical air blowing furnace of hot air circulation type and preheated to about 155 ° C. by hot air from the side and bottom surfaces. To a foaming region, and heated and foamed with hot air at 230 ° C. The foamed sheet was sucked at both ends of the foamed sheet with a suction type guider arranged adjacent to the foaming furnace, and widened to a width of 800 mm. At this time, the surface temperature of the foamed sheet was 160 ° C.

Then, the foamed sheet having the surface temperature lowered to 110 ° C. by passing through the cooling roll was subjected to the second widening by the tenter device, and the width was 880 mm and the thickness was 2.0.
A foam having a size of mm and a density of 0.04 cc / g was obtained.

Example 2 LDPE (melting point = 108 ° C.,
50 parts by weight of MI = 4.0 and LLDPE (melting point = 12
13 parts by weight of azodicarbonamide was added to 50 parts by weight of 2 ° C. and MI = 6.0) and a sheet having a width of 500 mm and a thickness of 1.05 mm was obtained with a single-screw extruder.

After irradiating the sheet with an electron beam having a dose of 4.0 Mrad, the sheet was introduced into a hot air circulation type horizontal foaming furnace, preheated to about 155 ° C. by hot air from the upper and lower surfaces, and then transferred to the foaming region. It was heated and foamed with hot air at 250 ° C. The expansion of the foamed sheet is 1000 mm wide with the air guider at the first time (surface temperature of the foamed sheet is 135 ° C.) and 1050 mm wide at the second time (surface temperature of the foamed sheet is 105 ° C.) with a tenter device, and the thickness is 1050 mm. 2.
A foam having a size of 5 mm and a density of 0.04 cc / g was obtained.

[Comparative Example 1] A width of 80 was obtained in the same manner as in Example 1 except that the expansion in the foaming step was performed only the first time.
A foam having a thickness of 0 mm, a thickness of 2.0 mm and a density of 0.04 cc / g was obtained.

[Comparative Example 2] A width of 10 was obtained in the same manner as in Example 2 except that the expansion was performed only the first time in the foaming step.
A foam having a thickness of 00 mm, a thickness of 2.5 mm and a density of 0.04 cc / g was obtained.

Table 1 shows the measurement results of the physical properties of the foams obtained in the above Examples and Comparative Examples. The methods for measuring physical properties are as follows.

<Vacuum Formability> The foam is heated with a far infrared heater so that the surface temperature of the foam is 150 to 160 ° C., and vacuum molding is performed using a cylindrical female die.
The value of the ratio (H / D) between the depth H and the diameter D at the time of molding is displayed. The larger this value, the better the moldability.

<Heating Sagging Property> The foam was cut into 70 × 70 cm, held by a clamp, and heated from the upper and lower surfaces by a heater until the surface temperature reached 160 ° C. At that time, the foam droops due to its own weight, but the drooping length (mm) of the largest part of the droop at the center of the foam sheet was measured.

[0033]

[Table 1]

As is evident from Table 1, according to the method of the present invention, two foams are used rather than foams which have been widened only once.
The foamed product has a better balance between the flow direction (MD) and the width direction (TD), and the heating dimensional change is smaller.
The foam produced by the production method of the present invention has a small drawdown (heating sag property) and is excellent in moldability.

[0035]

EFFECTS OF THE INVENTION According to the production method of the present invention, a polyolefin resin crosslinked foam having a drastically suppressed drawdown and excellent moldability is provided.

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Claims (1)

Claims: 1. A resin composition containing a polyolefin resin and a thermal decomposition type foaming agent is molded into a foamable resin composition sheet at a temperature below the decomposition temperature of the foaming agent, and then crosslinked. After that, in the method for producing a crosslinked foam to be foamed by heating,
In the vicinity of the foaming end point of the foamed sheet, (1) the first widening is performed while the surface temperature of the foamed sheet is 120 to 290 ° C., and then (2) the surface temperature of the foamed sheet is 80 to 12
A method for producing a polyolefin resin crosslinked foam, comprising performing a second widening 1 to 50% wider than the width of the first expanded foamed sheet while being at 0 ° C.