JPH11106542A - Manufacture of polyolefin resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a polyolefin resin foam requiring less investment for device, excellent in uniformity of obtd. crosslinked foam, and the used foam being able to be recovered, and melted and molded, again. SOLUTION: A hundred pts.wt. polyolefin resin and 0.1-20 pts.wt. bis maleimide are melt and mixed at a temperature not lower than 200 deg.C to modify the resin, and a thermal decomposition type chemical foaming agent is mixed to the obtd. modified resin composition, and the obtd. foaming resin composition is heated to foam. This polyolefin resin is, for example, a polypropyrene resin. This bis maleimide is such as N,N'-p-phenylene bis maleimide, N,N'-m-phenylene bis maleimide, diphenylmethane bis maleimide, or polymaleimide.

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 foam of a polyolefin resin, particularly a polypropylene resin, having excellent recyclability.

[0002]

2. Description of the Related Art Polyolefin foams are widely used as industrial materials because they have excellent balance between mechanical and thermal properties and can be heated and shaped later. BACKGROUND ART For interior materials such as doors and ceilings of automobiles, for example, foams mainly composed of polypropylene resin have become mainstream because of their good heat resistance.

[0003] Conventionally, in order to produce a sheet-like foam of a polypropylene-based resin, as in the case of other polyolefin-based resins, the polymer is cross-linked so as to have a foamable melt strength. There is a need to. For example, a foaming agent is added to a polypropylene-based resin composition, the composition is shaped into a sheet, and the composition is crosslinked until a gel fraction of about 30 to 50% is exhibited. A production method of thermally decomposing and foaming is employed.

The sheet-like polypropylene resin composition can be crosslinked by irradiation with radiation or electron beam, irradiation with ultraviolet rays, a method using a thermal decomposition type chemical crosslinking agent such as an organic peroxide, or polypropylene. There is a method of introducing an alkoxysilyl group and subjecting it to a condensation reaction.

[0005]

SUMMARY OF THE INVENTION Among these methods,
The crosslinking method using an electron beam has excellent productivity and is widely practiced industrially. For example, Japanese Patent Publication No. 6-45717 discloses that
A specific ethylene copolymer, a specific ethylene-α-olefin copolymer, and a specific vinyl monomer are added to a polypropylene resin, and a blowing agent is further added to a sheet-shaped extrudate of the melt mixture to continuously form an electron beam. To a gel fraction of 20
A method for producing a crosslinked foam in which the obtained continuous crosslinked sheet is foamed after setting the content to ６０60% is disclosed. However, this method requires a large capital investment for an electron beam irradiation apparatus, and furthermore, since crosslinking occurs only in the non-crystalline portion of the polymer, the subsequent foaming becomes uneven and has pinholes and the like. I hate to have defective products.

In recent years, as a measure against environmental resource problems,
In particular, automobile parts are required to be recyclable, and technical efforts have already been made on polypropylene parts such as bumpers and interior skin materials. However, since foams of polyolefin-based resins such as polypropylene-based resins are usually crosslinked as described above, they cannot be re-melted even if collected after use, and are not suitable for recycling.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to reduce the capital investment, to obtain an excellent uniformity of the obtained cross-linked foam, and to recover and melt and mold the used foam again. To provide a method for producing a polyolefin-based resin foam that can be used.

[0008]

The method for producing a polyolefin resin foam according to the present invention has been devised to achieve the above object, and comprises 100 parts by weight of polyolefin resin and 0.1 to 20 parts by weight of bismaleimide. Part temperature 200
The resin is modified by melting and mixing at a temperature of not less than ° C., a pyrolysis type chemical blowing agent is kneaded with the obtained modified resin composition, and the obtained foamable resin composition is heated and foamed. How to

The polyolefin in the present invention is a homopolymer or a copolymer of an olefin monomer, and is not particularly limited, but includes polyethylene, polypropylene, polybutene and the like.

Examples of polyethylene include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene. As the ethylene-based copolymer, ethylene-propylene copolymer, ethylene-propylene-diene terpolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, Examples thereof include an ethylene-acrylate copolymer.

Examples of the polypropylene include a homo-type polypropylene and a random or block copolymer containing propylene as a main component. Examples of the propylene-based copolymer include a random copolymer of propylene and an α-olefin, and a block copolymer of propylene and an α-olefin (provided that the α-olefin is ethylene, 1-hexene, Methyl-1-pentene, 1-octene, 1-butene, 1-pentene and the like are exemplified).

The above-mentioned polyolefins may be used alone or in combination of two or more. In the method of the present invention, polyethylene and / or polypropylene are particularly preferably used, and polypropylene is most preferred.

In the present invention, a polyolefin resin means that the polyolefin may be a blend with another resin. In the case of a polypropylene-based resin, examples of other resins include polyethylene, ethylene-vinyl acetate copolymer, olefin-based thermoplastic elastomer, polystyrene, and styrene-based thermoplastic elastomer. The proportion of polyolefin is preferably 50 to 100% by weight of the whole blend. If this proportion is less than 50% by weight, the characteristics of polyolefin such as light weight, chemical resistance, flexibility, elasticity, etc. cannot be exhibited, or in the case of blending with other polyolefin-based resins, the melt viscosity required for foaming is reduced. It can be difficult to secure.

The bismaleimide used in the present invention has the formula

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A compound having at least two maleimide structures in a molecule represented by the following formula, for example, the following compounds.

N, N'-p-phenylenebismaleimide

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N, N'-m-phenylenebismaleimide

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Diphenylmethane bismaleimide

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.Polymaleimide

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(In the formula, n is 0 or an integer of 1 to 5) The above exemplified compounds of bismaleimide may be used alone or in combination of two or more.

The amount of bismaleimide is 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the polyolefin resin. If the amount is less than 0.1 part by weight, the melt viscosity required for foaming cannot be imparted. If the amount exceeds 20 parts by weight, the degree of crosslinking becomes too high, extrudability deteriorates (for example, a high load is applied, melt fracture occurs, etc.), and a foaming agent to be added later is added to the resin composition. It cannot be uniformly kneaded in the material, and the gel fraction is unnecessarily increased excessively, thereby impairing recyclability. In addition, the proportion of bismaleimide remaining in the product as an unreacted material increases, causing irritation to the human body and lowering product efficiency with respect to raw materials.

In order to obtain a modified resin composition, a polyolefin resin and bismaleimide are melt-mixed. Specifically, the above-mentioned two substances are charged in required amounts into a kneading device such as a screw extruder or a kneader, and are melt-mixed. The melt mixing temperature is 200 ° C. or higher and the decomposition temperature of the polyolefin resin or lower, preferably 220 ° C. to 300 ° C. If the melt mixing temperature is lower than 200 ° C., the expansion ratio of the foam finally obtained will not be sufficiently high, and if it exceeds 300 ° C., the polyolefin resin will be easily decomposed.

The kneading apparatus used for the melt kneading may be a screw kneader or any other melt kneading apparatus that can be generally used in plastic molding.
Examples thereof include a rotor and a continuous kneader. Among them, a screw extruder capable of continuous operation is preferable, and a single-screw extruder, a twin-screw extruder, a multi-screw extruder having three or more screws, and the like are all suitably used. As a single screw extruder, in addition to a general full flight screw, an extruder having a discontinuous flight screw, a pin barrel, a mixing head, and the like are also used. Further, as the twin screw extruder, a meshing co-rotating extruder, a meshing different direction rotating extruder, a non-meshing different direction rotating extruder and the like can be suitably used. Providing a vacuum vent at the latter stage of the extruder is effective for preventing volatiles from remaining in the resin composition.

When a screw extruder is used, the polyolefin-based resin is fed into the extruder from a usual hopper.
It is also preferable to use a weight control type quantitative feeder or the like.

The bismaleimide may be supplied from the hopper to the extruder simultaneously with the polyolefin resin, but the bismaleimide and the polyolefin resin are dry-blended in advance, and the obtained blend is supplied from the hopper to the extruder. May be. Further, the polyolefin-based resin and the bismaleimide may be supplied to the extruder from separate supply sites. For example, bismaleimide can be supplied to the middle of the extruder from a supply hole by a side feeder provided downstream of the supply hopper for the polyolefin resin. Also in the supply of bismaleimide, it is preferable to use a screw type quantitative feeder, a weight control type quantitative feeder, or the like in order to increase the quantitativeness.

The thermal decomposition type chemical blowing agent used in the present invention is not particularly limited as long as it generates a decomposition gas by heating. A typical example of a pyrolytic chemical blowing agent is
Azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, and 4,4-oxybis (benzenesulfonylhydrazide). These may be used alone or in combination of two or more. Among them, azodicarbonamide is particularly preferably used.

The thermal decomposition type chemical blowing agent is the modified resin composition 1
1 to 50 parts by weight, preferably 2 to 50 parts by weight,
It is used in an appropriate amount in the range of 35 parts by weight depending on the desired expansion ratio.

In order to obtain a foamable resin composition by mixing a thermally decomposable chemical foaming agent with the modified resin composition, a melt kneading apparatus for reforming and a separate foaming agent for mixing foaming agent are used. Using a kneading apparatus (the structure may be the same as that of the melt kneading apparatus for reforming), the two are mixed at a temperature not higher than the maximum temperature at which the blowing agent does not substantially decompose. The mode of the melt kneading is as follows.

(A) A polyolefin-based resin and bismaleimide were melt-mixed in a reforming melt-kneading apparatus, and the resulting modified resin composition was taken out of the melt-kneading apparatus, solidified, and granulated. Thereafter, the resin composition is transferred to a kneading device for mixing a foaming agent, a foaming agent is charged therein, and the two are melt-kneaded to obtain a foamable resin composition.

(B) The polyolefin resin and the bismaleimide are melt-mixed at a temperature of 200 ° C. or more in a melting and kneading apparatus for reforming, and the resulting modified resin composition is heated to a temperature of 190 ° C. After cooling in the kneading device until
The resin composition is transferred to a kneading device for mixing a foaming agent, and the foaming agent is charged into the kneading device in a batch system, and the two are melt-kneaded to obtain a foamable resin composition.

(C) In order to carry out continuous operation, a polyolefin resin and bismaleimide are melt-mixed with one screw extruder, and the resulting modified resin composition is heated to a temperature of 190 ° C. or lower using a water-cooled jacket or the like. After the temperature is lowered to about 180 ° C., a foaming agent is added to the mixture through a vent or the like, and the two are melt-kneaded to obtain a foamable resin composition.

(D) In another mode of the continuous operation, two screw extruders and the like are connected, and the polyolefin resin and the bismaleimide are melt-mixed in the first unit, and the resulting modified resin composition is obtained. Is cooled in the same manner as described above, the same resin composition is transferred to a second unit, a foaming agent is added thereto, and the two are melt-kneaded to obtain a foamable resin composition.

The resin composition kneaded with the thermal decomposition type chemical foaming agent may be further shaped. As a shaping method, in addition to extrusion molding, a method generally performed in plastic molding such as press molding, blow molding, calendaring molding, injection molding, or the like can be applied.

In particular, according to the above methods (a) and (b), the polyolefin resin and the bismaleimide are melt-mixed with a screw extruder, and the resulting modified resin composition is extruded from the extruder and granulated. Then, while melt kneading the modified resin composition and the foaming agent in another screw extruder, a method of continuously shaping the obtained foamable resin composition into a sheet shape, or, (a) (c) According to the method of (d), 2
A method of directly connecting two extruders and performing continuous shaping is preferable from the viewpoint of productivity.

The foamable resin composition comprising the modified resin composition and a foaming agent is usually shaped into a sheet. The foamable resin composition thus shaped can be foamed to a desired expansion ratio by heating it under an appropriate temperature condition using an appropriate foaming apparatus. The heating is usually performed from the decomposition temperature of the thermal decomposition type chemical blowing agent (decomposition temperature + 100 ° C).
It is performed in the temperature range up to. As the foaming device, operating in an air atmosphere, a vertical or horizontal foaming furnace, a hot air thermostat, or an oil bath, a metal bath, a wet foaming bath using a hot bath such as a salt bath, and further a rod or pipe or In order to obtain an irregularly shaped article, an in-mold foaming apparatus for foaming a molded article while sliding it through a lubricant in a mold is used.

The gel fraction of the polyolefin resin foam obtained by the production method of the present invention is preferably less than 18%, more preferably less than 15%. When the gel fraction is 18% or more, the viscosity of the resin composition is too high in a general screw extruder and the composition does not melt and flow, so that there is a possibility that the recycling of used products may not be possible. . The lower the gel fraction, the better the melt moldability during recycling.

The gel fraction was determined by heating the polyolefin resin foam in xylene at 130 ° C. for 24 hours to elute the dissolved components into xylene, and then filtering the remaining solid through a 200 mesh metal net. Dried in a vacuum dryer at 80 ° C,
The obtained xylene-insoluble matter is weighed, and is a weight% calculated by the formula: (weight of insoluble matter / weight of foam) × 100.

The expansion ratio (specific volume of the foam) of the polyolefin resin foam obtained by the production method of the present invention is preferably 10 times (cc / g) or more, and more preferably 12 times (cc / g).
Times (cc / g) or more. If the expansion ratio is less than 10 times, a foam excellent in heat insulation, cushioning, sound insulation, flexibility, buoyancy and the like may not be obtained.

[0039]

According to the production method of the present invention, a polyolefin-based resin undergoes a hydrogen abstraction reaction in a molten state at 200 ° C. or higher, thereby generating polymer radicals. The bismaleimide mixed therewith undergoes a graft reaction with the polymer radical, resulting in resin modification due to a small amount of polymer crosslinking, and the polymer is once functionalized. The modified resin composition thus obtained has a melt strength that allows foaming at the same time while maintaining a melt fluidity that allows kneading and shaping with a foaming agent later.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described more specifically with reference to embodiments.

Example 1 Melt Kneading Apparatus for Reforming A screw extruder shown in FIG. 1 was used. In FIG. 1, 1 is a screw extruder, 2 is a molding die, 3 is a fixed amount feeder for resin, 4 is a fixed amount feeder for bismaleimide, 5 is a hopper, 6 is a suction pump, 7 and 8 are thermocouples, and 9 is a suction vent. , C1 to C12 are first to twelfth cylinder barrels.
The screw extruder has the following configuration.

Extruder: TEX-44 type (manufactured by Nippon Steel Works Co., Ltd.) Co-rotating twin screw extruder Screw: Self-wiping 2 strips, L / D: 45.
5, D: 47 mm cylinder barrel: 1st to 1st from upstream to downstream of extruder
2-cylinder barrel die: sheet-shaped T-die i) Preparation of modified resin composition Using a melting and kneading apparatus for reforming having the above-mentioned configuration, a hopper 5 is supplied by a resin constant feeder 3 with a polypropylene resin.
To the first cylinder barrel C1, and bismaleimide was also supplied from the hopper 5 to the first cylinder barrel C1 by the bismaleimide quantitative feeder 4, and both were melt-mixed to obtain a modified resin composition.

Operating conditions Suction vent: Installed in ninth barrel to collect volatiles Thermocouple: Thermocouple for measuring resin temperature. Resin temperature measured by thermocouple 7 installed between barrels 8 and 9:
T1, resin temperature measured by thermocouple 8 installed in adapter part: T2.

[0044] Screw rotation speed: 100 rpm Polypropylene resin: Homopolymer of propylene (Novatech “EA8”, manufactured by Nippon Polychem Co., Ltd., MI;
8, density: 0.9 g / cm ³ ) Supply amount of polypropylene resin: 14 kg / h Bismaleimide: diphenylmethane bismaleimide (D
PMBMI) per 100 parts by weight of polypropylene
The weight is determined by the bismaleimide quantitative feeder 4 so that the amount becomes 1 part by weight.
Supplied to

Resin temperature: T1; 225 ° C., T2: 275
° C.

Ii) Preparation of foam The obtained modified resin composition is taken out of the melting and kneading apparatus for reforming, solidified, granulated, etc., and then the resin composition is mixed with a foaming agent. To the kneading device (not shown)
A thermal decomposition type chemical blowing agent was added thereto, and both were melt-kneaded. The foamable resin composition thus obtained was shaped into a sheet by press molding, and the sheet was heated and foamed to obtain a polypropylene resin foam.

Blowing agent: azodicarbonamide (ADC)
A) Kneading of foaming agent: Roll kneading; 180 ° C., 20 rpm, 5
Min Mixing amount of foaming agent: 15 parts by weight of ADCA per 100 parts by weight of modified resin composition Press molding: 100 kg of foamable resin composition at 180 ° C.
/ Cm ² for 2 minutes and then cooled for 3 minutes to form a 2 mm square sheet into a rectangular sheet. Foaming: A sheet-like molded product of the foamable resin composition was placed in a 230 ° C. hot air dryer for 5 minutes. Neglect.

Iii) Physical properties of foam Expansion ratio (measured value of specific volume of foam sample): 22 cc /
g Gel fraction (the measuring method is as described above): 10% Reflowability evaluation: 20% by weight of the pulverized product of the obtained foam and 80% by weight of the original polypropylene resin were kneaded and extruded.

Extruder and die; as above Cylinder barrel set temperature; 220 for first to fourth zones
C. The appearance of the extrudate was checked. Reflowability evaluation result: Sheet formability was good, and there was no foreign matter.

Example 2 The same operation as in Example 1 was performed except for the following points.

Polypropylene resin: random copolymer of propylene (“EG8” manufactured by Nippon Polychem Co., Ltd., MI;
0.8, density: 0.9 g / cm ³ ) Supply amount of polypropylene resin: 14 kg / h Bismaleimide: N, N'-m-phenylenebismaleimide (MPBMI) is added to 5 parts by weight based on 100 parts by weight of polypropylene. It was quantified by a bismaleimide quantitative feeder 4 and supplied from a hopper 5 to a first cylinder barrel C1.

Resin temperature: T1, 225 ° C., T2, 274
° C.

The physical properties of the obtained foam were measured. The results are as follows: Expansion ratio (specific volume of foam): 20 cc / g Gel fraction: 8% When reflowability was evaluated by the same method as in Example 1, sheet formability was good. There was no foreign matter.

Comparative Example 1 The same operation as in Example 1 was carried out except that the blending amount of DPMBMI was 0.05 parts by weight with respect to 100 parts by weight of the polypropylene resin. However, resin temperature: T1; 220 ° C, T2; 260 ° C.

The physical properties of the obtained foam were measured. The results are as follows: Foaming ratio: 4 cc / g Gel fraction: 2% Reflowability was evaluated by the same method as in Example 1, but was not possible.

Comparative Example 2 The same operation as in Example 1 was performed except that the blending amount of DPMBMI was 25 parts by weight with respect to 100 parts by weight of the polypropylene resin. However,
Resin temperature: T1; 230 ° C, T2: 285 ° C.

The state of extrusion in the screw extruder was very poor, melt fracture occurred, and a high load was applied. Further, the foaming agent could not be uniformly kneaded with the resin composition.

The reflowability was evaluated in the same manner as in Example 1, but was not successful.

Comparative Example 3 The same operation as in Example 1 was performed except for the following points.

[0060] Screw rotation speed: 40 rpm Resin temperature: T1: 185 ° C., T2: 186 ° C. The physical properties of the obtained foam were measured. The results are as follows: Expansion ratio: 3 cc / g Gel fraction: 0%.

The reflowability was evaluated in the same manner as in Example 1, but was not successful.

The operating conditions of Examples 1 and 2 and Comparative Examples 1 to 3 and the physical properties of the obtained foams are shown in Table 1.

[0063]

[Table 1]

In Table 1, in "Appearance of sheet-like molded article", "O" means good and "x" means bad. The “reflowability” indicates the result of heating and melting the foam again and checking the presence or absence of the fluidity.
-Means that the foam did not expand and the reflowability could not be evaluated.

[0065]

According to the production method of the present invention, a small amount of polymer is crosslinked to maintain a melt fluidity that allows kneading and shaping with a foaming agent later, and at the same time, a foaming degree that allows foaming. A modified resin composition having body strength can be obtained, and by using this modified resin composition, a foam having excellent homogeneity can be obtained.

As described above, according to the production method of the present invention, it is possible to produce a polyolefin-based resin foam having excellent recyclability, which can recover the used foam and melt and mold it again with a small capital investment. While you can
By heating the foam to a temperature equal to or higher than the melting point of the resin, the foam can be thermally shaped into an arbitrary shape.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a screw extruder.

[Explanation of symbols]

 1: Screw extruder 2: Molding die 3: Resin quantitative feeder 4: Bismaleimide quantitative feeder 5: Hopper 6: Suction pump 7, 8: Thermocouple 9: Suction vent

Claims (2)

[Claims] 1. 100 parts by weight of a polyolefin resin and 0.1 to 20 parts by weight of bismaleimide are melt-mixed at a temperature of 200 ° C. or higher to modify the resin, and the resulting modified resin composition is subjected to thermal decomposition type chemistry. A method for producing a polyolefin resin foam, comprising: kneading a foaming agent; and heating and foaming the foamable resin composition obtained. 2. The method for producing a polyolefin resin foam according to claim 1, wherein the polyolefin resin is a polypropylene resin.