JPH06340762A - Production of polypropylene-based resin foam - Google Patents

Abstract

PURPOSE:To produce a polypropylene-based resin foam suppressing primary expansion. CONSTITUTION:In production of a polypropylene-based resin foam by molding a polypropylene-based resin, a blowing agent of thermal decomposition type, a cross-linking promoter and a primary expansion inhibitor into a sheet, cross- linking by electron beams and foaming the sheet under heating, a substance having <=200 deg.C boiling point under 1-200mmHg is used as the primary expansion inhibitor and the primary expansion inhibitor is removed under reduced pressure during molding.

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 resin foam used as a heat insulating material or a ceiling material for automobiles.

[0002]

2. Description of the Related Art As a method for producing a foam of a polyolefin resin, conventionally, a polyolefin resin and a pyrolyzable foaming agent are blended, a sheet is formed by melt-kneading and extrusion, and the sheet is crosslinked by radiation and then heated. A method for obtaining a foam is known.

However, at the time of melt-kneading and extrusion, depending on the melting characteristics of the resin composition, the specifications of the extruder, and the operating conditions, the temperature of the resin rises above the decomposition temperature of the thermal decomposition type foaming agent in the molding machine due to shearing heat generation, and the resin inside the sheet Generates fine bubbles (hereinafter referred to as primary foaming). This primary foaming becomes a core of unnecessary foaming in the next heating step for the original foaming, and thus causes problems such as a coarse cell diameter of the product and a failure to obtain a predetermined expansion ratio. When a compounded composition having a low melt viscosity using a resin having a low molecular weight or a viscosity reducing agent is used, the shear heat generation can be reduced, but the mechanical strength and heat resistance of the foamed product are deteriorated, which is limited.

On the other hand, recently, as applications of polypropylene-based resin foams, it has been required to be used for deeper drawing products, and foams having good heat resistance are required in order to withstand high temperatures during secondary processing. . This requires the use of high molecular weight resins, making the problem of primary foaming even more important.

To prevent primary foaming, Japanese Patent Laid-Open No. 1-1606
In JP-A-30, it is proposed that a block-copolymerized polypropylene-based resin is formed into a sheet by using a twin-screw extruder with a small shearing heat generation and extracting air or a decomposition gas of a foaming agent mixed at the time of supplying raw material pellets under reduced pressure. Has been done.

[0006]

However, in the above method, in order to prevent the primary foaming, the raw material resin is specified, and the extruder is specified as the twin-screw extruder, so that the production cost is increased and the shear heat generation is small. Even if a twin-screw extruder is used, there is a problem that operating conditions are limited. The present invention has been made in view of the above problems, by suppressing the primary foaming by improving the manufacturing method, a high-performance foam,
It is an object to provide a manufacturing method for manufacturing at low cost.

[0007]

The present invention has found that the above-mentioned problems can be solved by simultaneously molding a specific substance during extrusion to reduce the shear heat generation that causes primary foaming. That is, polypropylene resin,
A pyrolytic foaming agent, a crosslinking accelerator, and a primary foaming inhibitor having a boiling point of 200 ° C. or less at 1 to 200 mmHg are formed into a sheet, and the sheet is crosslinked with an electron beam or radiation and then heated. This is a method of obtaining a foam by doing so, and the main point is to remove the primary foam suppressing agent by depressurization during sheet molding.

The present invention will be described in detail below. In the present invention, examples of the primary foam suppressing agent include the following.

Air, nitrogen, etc. Alkanes such as methane, ethane, propane, butane, pentane, hexane and heptane. Alkenes such as propene, butene, pentene, liquid polyethylene, liquid polypropylene, liquid polybutene, liquid polyisobutylene. Benzene, dimethylbenzene, trimethylbenzene, ethylbenzene, vinylbenzene,
Aromatic compounds such as divinylbenzene, methylvinylbenzene, ethylvinylbenzene, trivinylbenzene, butylbenzene, naphthalene, anthracene, diallylphthalate, triallylphthalate, allylmellitate, diallylmellitate, triallylmellitate, and their modification Body or substituted compound. Alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, ethylene glycol, and glycerin, and modified or substituted compounds thereof. Trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,6 hexanediol dimethacrylate, methoxyvinylsilane,
Compounds that have been used as cross-linking agents such as ethoxyvinylsilane. However, it is not limited to the above substances.

Of these, divinylbenzene, ethylvinylbenzene, trimethylolpropane trimethacrylate, and trimethylolpropane triacrylate are most excellent.

The polypropylene resin as a main raw material means a homopolymer of propylene or a copolymer containing the same monomer as a main component. Polyethylene or a modified product thereof may be used in combination for reasons of moldability and performance.
As the heat-decomposable foaming agent, those which are usually used can be used, and azodicarbamide, dinitrosopentamethylenetetramine, allophane amide and the like are used, and azodicarbamide is preferably used. A polyfunctional monomer is mainly used as the crosslinking accelerator. Tetraethylene glycol dimethacrylate, divinylbenzene,
Diallyl phthalate, triallyl isocyanurate, trimethylol propane trimethacrylate, trimethylol propane triacrylate and the like are preferably used, but are not particularly limited thereto. In addition to these, various additives used in ordinary blending such as a viscosity reducing agent such as low polymerization degree polybutene, an antiaging agent, a stabilizer, and the like may be used as necessary. The above-mentioned primary foam suppressing agent may be mixed in advance with each composition, or may be separately supplied to the molding machine.

The molding machine for forming the sheet is not particularly limited, but a normal single-screw extruder having a vent port, a twin-screw extruder or the like is preferably used. A plurality of vent ports may be provided. The position of the exhaust vent port is not particularly limited, but it is usually provided at a place where the resin melting part is changed to the metering part. The degree of decompression is
If the depressurization is insufficient, the primary foam inhibitor may stay in the sheet more than the limit to deteriorate the physical properties of the foam or cause the thickness variation of the sheet, resulting in the foam having a uniform thickness. However, it is not necessary to completely remove it by depressurization, as long as it is removed to the extent that it does not adversely affect the physical properties and productivity. Normally, it is performed at an absolute pressure of 1 to 200 mmHg. Be seen.

[0013]

In the present invention, since the primary foaming inhibiting substance is added, the resin can be molded at a low temperature and is removed by decompression, so that foaming at a predetermined ratio can be obtained without temporary foaming. Also, because the resin temperature can be molded low
Since a foam can be obtained using a resin having a high molecular weight, a foam having excellent heat resistance, mechanical strength, and secondary processability can be obtained.

[0014]

The present invention will be described in more detail by the following examples. The present invention is not limited to the examples below. 1. Examples 1, 2, 3 Random copolymerized polypropylene having an ethylene content of 3.2% by weight, MFR = 0.5, 2.0, 8.0 m.p. p. =
MI = 8.70 for each of 70 parts of 3 types at 143 ° C.
0, m. p. = 120 ° C. LLDPE (30 parts), azodicarboxamide (15 parts), and BHT (1 part) were mixed in advance. A co-direction twin-screw extruder having two first and second vent ports in order from the raw material supply port to the die side (φ = 100 mm, L / D =
26) is supplied with the above mixed raw material, divinylbenzene is supplied from the first vent port at a ratio of 8 parts, and divinylbenzene is extracted into a cartridge as shown in FIG. 1 under a reduced pressure of 20 mmHg from the second vent port. The amount of accumulated divinylbenzene was measured. The presence or absence of primary foaming of the obtained sheet was judged visually and by observing the section of the sheet with a microscope. The sheet was irradiated with an electron beam so that the degree of cross-linking was 40% and then foamed in a hot air oven. The expansion ratio was determined by the standard specific gravity liquid method. Next, the obtained foam was adhered to a soft vinyl chloride sheet containing ABS resin with a polyester adhesive, and the material breaking strength was measured at room temperature. The material breaking strength was determined by a method in which the bonded product was cut into a strip of 25 mm width and the peel strength was measured with a Toyo Seiki Tensilon at a speed of 200 mm / min. The results are shown in Table 1.
Shown in. In the table, the material breaking strength vertical and horizontal represent the material breaking strength in the machine direction and the strength in the width direction.

2. Comparative Examples 1, 2 and 3 Comparative Examples 1, 2 and 3 were obtained by not supplying divinylbenzene in Examples 1, 2 and 3. The results are shown in Table 1. Only primary foaming was performed, and only a surface having a non-uniform surface and a non-uniform thickness was obtained, and a sheet-shaped foam was not obtained even when heated.

[0016]

[Table 1]

3. Examples 4, 5, 6 Random copolymerized polypropylene having an ethylene content of 3.2% by weight, MFR = 0.5, 2.0, 8.0, m.p. p. =
MI = 8.0 for 70 parts of each of 3 kinds of 143 ° C.,
m. p. = 120 ° C., 30 parts of LLDPE, 15 parts of azodicarboxamide, 1 part of BHT, and 3 parts of trimethylolpropane trimethacrylate were mixed in advance. Same-direction twin-screw extruder with one vent (φ = 90mm, L /
(D = 21 screw has 2 feed sections, 3 compression sections, and 3 metering sections) and supplies the above mixed raw materials with a quantitative feeder, and trimethylolpropane trimethacrylate is supplied at 20 mmHg from the vent port.
It was pulled out like. The presence or absence of primary foaming of the obtained sheet was judged visually and by observing the section of the sheet with a microscope. The sheet was irradiated with an electron beam so that the degree of crosslinking would be 40% and then foamed in a hot air oven. The expansion ratio was determined by the standard specific gravity liquid method. Next, the obtained foam was adhered to an ABS resin-containing soft vinyl chloride sheet with a polyester adhesive, and the material breaking strength was measured at room temperature. The material breaking strength was determined by a method in which the bonded product was cut into a strip of 25 mm width and the peel strength was measured with a Toyo Seiki Tensilon at a speed of 200 mm / min. The results are shown in Table 2.
Shown in. In the table, the material breaking strength vertical and horizontal represent the material breaking strength in the machine direction and the strength in the width direction.

4. Comparative Examples 4, 5, 6 Comparative Examples 4, 5, 6 were the same as in Examples 4, 5, 6 except that trimethylolpropane trimethacrylate was not added. The results are shown in Table 2. Only primary foaming was performed, and only a surface having a non-uniform surface and a non-uniform thickness was obtained, and a sheet-shaped foam was not obtained even when heated.

[0019]

[Table 2]

5. Examples 7, 8, 9, 10, 11 A random copolymer polypropylene having an ethylene content of 3.2% by weight, MFR = 0.5, m.p. p. = 165 ° C., MFR =
0.5, m. p. = 154 ° C. MFR = 0.5, m.p.
p. = 139 ° C, total of 3 types, MI = 60 parts each
2.0, m. p. = 120 ° C., 40 parts of LLDPE, 15 parts of azodicarboxamide, 1 part of BHT, 4 parts of liquid polybutene and 3 parts of triallyl melitate were added and mixed in advance. Different direction twin screw extruder (φ = 90mm, L / D = 1
5) and a single-screw extruder having first and second vent ports in order from the raw material supply side to the mold side (φ = 100 mm, L / D = 1
The above mixed raw material was supplied to the twin screw extruder side of the two extruders in which 5) was connected so that the kneaded product of the twin screw extruder became the raw material of the single screw extruder. The pressure at the time of depressurizing the first and second vent ports was changed as shown in Table 3 to examine the state of primary foaming and the thickness variation of the extruded sheet. Regarding the presence or absence of primary foaming, the cross section of the sheet was observed under a microscope. The sheet was irradiated with an electron beam so that the degree of crosslinking would be 40% and then foamed in a hot air oven. The expansion ratio was determined by the standard specific gravity liquid method. The thickness variation of the sheet was measured using two thickness sensors in the width direction. The results are shown in Table 3.

6. Comparative Example 7 Comparative Example 7 was the same as Example 7, except that the first and second vent ports were not depressurized. The results are shown in Table 3. The foam was temporarily foamed and had a large variation in thickness, and a foam having a constant thickness could not be obtained by heating after crosslinking, resulting in a foam having uneven thickness and coarse cells.

[0022]

[Table 3]

[0023]

As described above in detail, according to the present invention,
It is possible to produce a polypropylene resin foam using a wide range of materials and molding machines, without specifying the polypropylene resin or molding machine to be used in a narrow range.

[0024]

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a vent suction unit of Examples 1, 2, and 3.

[Explanation of symbols]

 1 Twin-screw extruder barrel 2 Screw 3 Vent port 4 Lid 5 Pressure gauge 6 Cartridge 7 Decompression pump

Claims (2)

[Claims] 1. A polypropylene resin, a pyrolytic foaming agent, a crosslinking accelerator, and a primary foaming inhibitor are molded into a sheet, and the sheet is crosslinked by an electron beam or radiation and then heated to foam. A method for obtaining a body, which is characterized in that: 1) the primary foam suppressing agent is a substance having a boiling point of 200 ° C. or less at 1 to 200 mmHg; and 2) removing the primary foam suppressing agent by depressurization during sheet molding. Method for producing polypropylene-based resin foam. 2. The primary foam suppressant is divinyl benzene,
The method according to claim 1, comprising one kind or a combination of two or more kinds selected from ethylvinylbenzene, trimethylolpropane trimethacrylate, and trimethylolpropane triacrylate.