JPH08174545A - Production of foamable polypropylene resin composition - Google Patents

Abstract

PURPOSE: To prevent the cutting of the molecular chain of a polypropylene resin by adding a foaming agent having decomposition temp. exceeding a control temp. within a specific temp. range and a crosslinking aid to the polypropylene resin on the way of movement through an extruder. CONSTITUTION: 100 pts. wt of a propylene homopolymer is charged in the hopper of a same direction rotary twin-screw extruder as a polypropylene resin to be mixed and kneaded at about 190 deg.C (within a temp. range from the m.p. of the resin to temp. higher than the m.p. by 35 deg.C). The extrusion temp. of the molten resin is controlled to about 190 deg.C and about 10 pts.wt. of a foaming agent (decomposition temp.; about 200 deg.C) is supplied to the kneading part from the side part of the extruder to be kneaded with the resin and about 2 pts.wt. of a crosslinking aid is further supplied to the melting part from the side part of the extruder to be kneaded with the molten resin and the molten kneaded mixture is extruded to produce a foamable polypropylene resin compsn. The primary foaming due to the thermal decomposition of the foaming agent and a polymer of the crosslinking agent are not generated in the obtained foamable polypropylene resin compsn.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing an expandable polypropylene resin composition. A foamable resin composition such as a foamable sheet obtained by the method of the present invention is heat-foamed in a subsequent step, and the obtained foam is vacuum-molded or stamped-molded to be used for interiors of automobile doors, ceilings, measuring instruments, etc. Used as a material.

[0002]

2. Description of the Related Art Conventionally, a crystalline thermoplastic resin such as polypropylene resin or polyethylene resin has been used in various fields as a foamable resin composition such as a foamable sheet because of its ease of molding due to thermoplasticity. When an expandable resin composition is produced from a crystalline thermoplastic resin, when azodicarbonamide having a decomposition temperature of 190 to 230 ° C. is used as a foaming agent, primary foaming occurs due to decomposition of the foaming agent in the extrusion process. Therefore, when the resin composition is foamed by electron beam irradiation in a later step, the bubbles generated by the primary foaming may further expand into large bubbles having a diameter of about 3 mm, or the foam may be broken in some cases. is there.

As a measure against the above problems, it has been proposed to manufacture a foamable sheet by lowering the melting point of polypropylene resin, which is a high melting point resin. For example, Japanese Patent Publication No. 46-31754.
In the manufacturing method of No. 1, a resin having a low melting point such as a random polypropylene resin is used, and in the manufacturing method of JP-A-59-230038, the melting point is lowered by radically decomposing a high molecular weight polypropylene resin.

[0004]

However, with such a method, a foamed product excellent in heat resistance could not be obtained because of the low melting point of the polypropylene resin.

In view of the above points, the object of the present invention is to eliminate the risk of primary foaming due to decomposition of the foaming agent in the extrusion process,
Moreover, it is to provide a method for producing a foamable polypropylene resin composition suitable for obtaining a foamed product having excellent heat resistance.

[0006]

The method for producing a foamable polypropylene resin composition according to the present invention has been devised to achieve the above-mentioned object. The polypropylene resin is melted by an extruder and crosslinked with a foaming agent. Addition of an auxiliary agent, further melt-kneading in an extruder, and in producing an expandable polypropylene-based resin composition by extrusion, while controlling the polypropylene-based resin in the range of its melting point and 35 ° C. higher than this,
The polypropylene resin is characterized in that a foaming agent and a cross-linking auxiliary agent having a decomposition temperature exceeding the above-mentioned control temperature are added to the polypropylene resin while moving in the machine.

In the method of the present invention, the melting point of the resin is JI.
The value measured by the method according to SK-7121.

Further, the decomposition temperature of the foaming agent has a half-life of 6
It is the temperature at which a minute comes.

The extruder is not particularly limited as long as it is capable of melting and plasticizing a polypropylene resin and kneading the molten resin with a foaming agent and a crosslinking aid. Usually, the co-rotating twin-screw extruder is used because the dispersibility of the foaming agent and the crosslinking aid, the kneading property, and the uniformity of the resin temperature are good. A single-screw extruder can also be used as appropriate.

In the extruder, the temperature for melting the resin is
It may be higher than the melting point of the polypropylene resin, but it is preferably in the vicinity thereof, and more preferably in the range of the melting point of the polypropylene resin and a temperature 35 ° C. higher than this. Within this range, low temperature is preferable.

The polypropylene resin used in the present invention is
A resin composed of propylene alone as a monomer unit, or a resin composed of a polymer containing propylene as a monomer unit. For example, a homopolymer, a block copolymer, a random copolymer of propylene is used. Further, the polypropylene resin used in the present invention may be a blend system of polypropylene resin and other polyolefin resin. For example, 10 parts by weight of polyolefin resin to 100 parts by weight of polypropylene resin
Blends of up to 100 parts by weight are used. This blend ratio is a value set so as to obtain a high expansion ratio. As a polypropylene-based resin, a melt flow rate (M
FR) is in the range of 0.3 to 20 g / 10 minutes,
Those having a melting point in the range of 155 to 200 ° C. are preferable.
Particularly when a foamable sheet having high heat resistance is manufactured, a polypropylene resin having a high melting point (for example, about 190 ° C.) is suitable. On the other hand, as the polyolefin resin, for example, a high density polyethylene resin, a branched low density polyethylene resin, a linear low density polyethylene resin, a high molecular weight polyethylene resin, a polyamide resin or the like can be used. As a polyolefin resin, in sheet extrusion processing,
Those having an MFR in the range of 0.2 to 30 g / 10 minutes are preferable. In addition, an antioxidant may be added for the purpose of preventing deterioration of mechanical or chemical properties due to deterioration of polypropylene resin due to oxidation. The addition amount of the antioxidant is 1 with respect to 100 parts by weight of the polypropylene resin.
It is preferably ˜3 parts by weight. As an antioxidant,
For example, alkylphenol, alkylenebisphenol, alkylphenol thioether, β, β'-thiopropionic acid ester, organic phosphite ester, aromatic amine, phenol-nickel complex and the like can be appropriately used.

After the polypropylene resin is melt-kneaded, the temperature of the molten resin is set to the melting point of the polypropylene resin and
The temperature is controlled to be 5 ° C. higher. When the temperature exceeds the above range, after the foaming agent and the crosslinking aid are added, in the process of melt-kneading the resin, the molecular chain breakage of the polypropylene-based resin occurs, and the resulting foam has deteriorated the original heat resistance. As a result, the desired high quality expandable polypropylene resin composition cannot be obtained. Further, when the temperature is lower than the above range, the polypropylene-based resin does not melt, the resin pressure when the resin is compressed in the extruder becomes extremely high, and extrusion of the expandable polypropylene-based resin composition having a desired high quality is possible. Can not. The extrusion temperature of the molten resin is preferably controlled in the range of the melting point of the polypropylene resin and a temperature higher by 25 ° C., more preferably in the range of the melting point of the polypropylene resin and a temperature higher by 5 ° C. than the melting point.

Under this temperature condition, a foaming agent is added to the molten resin and kneaded with the resin. The supply position of the foaming agent is on the way of movement of the molten resin in the extruder, that is, between the base end portion and the tip end portion of the screw, and preferably the foaming agent is supplied from the side portion of the extruder to the kneading section.

The amount of the foaming agent added depends on the expansion ratio of the foam, but is 2 with respect to 100 parts by weight of the polypropylene resin.
Is preferably 20 to 20 parts by weight, more preferably 5 to
15 parts by weight. Considering that the polypropylene resin is melted within the range of a melting point of the resin and a temperature 35 ° C. higher than the melting point, the foaming agent has a decomposition temperature of 190 ° C. to 2 ° C.
Azodicarbonamide at 30 ° C and decomposition temperature of 160
N, N′-dinitrosopentamethylenetetramine having a temperature of up to 200 ° C. is appropriately selected.

With or independently of the blowing agent supply,
A cross-linking aid is added to the molten resin and kneaded with the resin. For example, while the blowing agent is uniformly added and kneaded in the molten resin in the kneading section of the extruder in the above temperature range, the crosslinking aid is uniformly added and kneaded in the molten resin in the melting section of the extruder. To do.

The supply position of the crosslinking aid is on the way of movement of the molten resin in the extruder, that is, between the base end portion and the tip end portion of the screw, and preferably, the crosslinking aid is fed from the side portion of the extruder to the melting portion. Supply. The supply of the crosslinking aid is preferably performed by a monomer press-in machine into the melting section of the extruder.

The cross-linking aid is for electron beam cross-linking in a later step, and is generally a polyfunctional monomer having two or more functional groups such as unsaturated groups in one molecule, and trimethylolpropane trimethacrylate. , Divinylbenzene, diallyl phthalate and the like. A silane cross-linking agent may be used as in chemical cross-linking. The addition amount of the crosslinking aid is preferably 1 to 5 parts by weight, and more preferably 1.5 to 3 parts by weight, based on 100 parts by weight of the polypropylene resin.

Finally, it is preferable to suppress the retention of the obtained kneaded material in the extruder as much as possible and extrude the kneaded material in the extruder. The retention of the kneaded material in the extruder is suppressed in order to prevent the crosslinking aids from polymerizing thermally or temporally during the retention of the kneaded material in the extruder. This polymer appears in the form of minute foreign substances.

[0019]

According to the method of the present invention, while controlling the temperature of the melting point of the polypropylene-based resin and the temperature higher by 35 ° C., the decomposition temperature exceeding the above-mentioned control temperature is applied to the polypropylene-based resin while it is moving in the machine. Since the foaming agent and the crosslinking aid that it has are added, the residence time of the foaming agent and the crosslinking aid in the extruder can be shortened, and the primary foaming by the decomposition of the foaming agent and the polymerization of the crosslinking aids in the extrusion process. It is possible to obtain a foamable polypropylene-based resin composition free from decomposition products of the foaming agent and polymers of the crosslinking aids.

Since the extrusion temperature of the molten resin is controlled as described above, in addition to avoiding the primary foaming and the polymerization of the crosslinking aid, the molecular chain scission of the polypropylene resin can be prevented. Therefore, a foamed product having excellent heat resistance can be obtained in the subsequent step.

[0021]

EXAMPLES The method for producing the expandable polypropylene resin composition according to the present invention will be specifically described below with reference to examples.

Example A homopolymer of propylene as a polypropylene resin (melting point 190 ° C., MFR of JIS-K7210 0.5 g
/ 10 minutes) 100 parts by weight were put into a popper of a co-rotating twin-screw extruder and melt-kneaded at 190 ° C. The extrusion temperature of the molten resin was controlled at 190 ° C., and azodicarbonamide (decomposition temperature 200
10 parts by weight) and kneaded with the molten resin. Further, 2 parts by weight of trimethylolpropane trimethacrylate as a crosslinking aid is supplied from the side of the extruder to the melting portion from the side of the extruder to the melting portion by a monomer injection machine and kneaded with the molten resin. The melt-kneaded product was extruded to produce a foamable polypropylene resin composition.

The expandable polypropylene-based resin composition obtained does not have primary foaming due to thermal decomposition of the foaming agent or a polymer of the cross-linking aid, and has a desired high quality and high heat resistance in the subsequent steps. A foamed product could be obtained.

Comparative Example Using the same extruder as in Example, 100 parts by weight of the same polypropylene resin as in Example, 2 parts by weight of alkylphenol as an antioxidant and 10 parts by weight of azodicarbonamide as a foaming agent (decomposition temperature of 200 ° C.) were used. Supplied, melt-kneaded at 200 ° C., and further supplied with 2 parts by weight of trimethylolpropane trimethacrylate as a crosslinking aid,
It was kneaded with a molten resin at 190 ° C., and the melt-kneaded product was extruded to produce a foamable polypropylene resin composition.

The resulting expandable polypropylene-based resin composition is dotted with primary foaming due to thermal decomposition of the foaming agent and a polymer of a cross-linking aid, and has a high heat-resistant foamed product having desired high quality in a subsequent step. Couldn't get

[0026]

EFFECTS OF THE INVENTION Since the production method according to the present invention is constituted as described above, primary foaming due to decomposition of the foaming agent in the extrusion step and polymerization of the crosslinking aids are prevented to prevent decomposition products of the foaming agents and crosslinking aids. It is possible to obtain a foamable polypropylene resin composition having no polymer of the agents. Further, it is possible to prevent the molecular chain breakage of the polypropylene resin, and it is possible to obtain a foamed product having excellent heat resistance in the subsequent step.

Thus, according to the method of the present invention, it is possible to provide a desired high-quality foamed product in the subsequent step.

Claims (1)

[Claims] 1. A polypropylene-based resin for producing a foamable polypropylene-based resin composition by melting a polypropylene-based resin with an extruder, adding a foaming agent and a cross-linking aid, melt-kneading with the extruder, and extruding. It is characterized in that, while controlling the resin in the range of its melting point and a temperature higher by 35 ° C. than that, a blowing agent and a cross-linking auxiliary agent having a decomposition temperature exceeding the above-mentioned control temperature are added to the polypropylene resin while it is moving in the machine. And a method for producing an expandable polypropylene resin composition.