JPH10152575A - Method for foaming thermoplastic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fine, uniform and dense foamed state in a foaming molding by extrusion or injection of a thermoplastic resin, a clean surface, and a foamable foam having a desired specific gravity. To provide a foam molding method. SOLUTION: A heat-expandable microcapsule is mixed with a thermoplastic resin, and the heat-expandable microcapsule is expanded by kneading heat of fusion and foam-molded by extrusion molding or injection molding. As a result, each bubble can be stably foamed in a state of being wrapped in the microcapsule, and can be made into a fine, uniform and dense foaming state, and the surface can be made clean and foamed to a desired specific gravity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for foaming a thermoplastic resin by extrusion molding or injection molding, and more particularly to a molding method capable of foaming uniformly and densely.

[0002]

2. Description of the Related Art Foam molding using a thermoplastic resin is used for molding various synthetic resin products. By foaming, it is possible to reduce the weight of the synthetic resin product, improve heat insulation, and impart cushioning properties. ing.

[0003] As a general method of such foaming molding using a thermoplastic resin, for example, a chemical foaming agent is mixed with a thermoplastic resin raw material, and the chemical foaming agent is thermally decomposed by heat at the time of melting the thermoplastic resin raw material. There are a method of generating a gas by causing the gas to flow, and a method of injecting a gaseous gas such as water vapor, nitrogen or carbon dioxide gas into a molten thermoplastic resin.

[0004]

In the foam molding method using such a thermoplastic resin, foam molding is carried out by using a pyrolysis gas or a gas to be injected separately in a state where the thermoplastic resin raw material is melted and the viscosity is extremely reduced. I am trying to
The bubble state changes greatly due to the slight pressure fluctuation of the pyrolysis gas or the injected gas, making it difficult to obtain a uniform and dense molded product. There is a problem that it is difficult to obtain a molded product having a specific gravity.

[0005] In the case of extrusion molding using a thermoplastic resin, when the foamed resin passes through the die, the gas further expands due to a sudden pressure drop, thereby causing fine irregularities on the surface of the molded product. There is a problem that a phenomenon in which the surface is roughened like a shark skin easily occurs and a clean surface cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. In foam molding by extrusion or injection of a thermoplastic resin, a fine, uniform and dense foam state can be obtained, and the surface is clean. It is an object of the present invention to provide a method for foaming a thermoplastic resin which can be foamed to a specific gravity.

[0007]

In order to solve the above-mentioned problems of the prior art, according to the present invention, in the method of directly dispersing a gas in a molten resin according to the prior art, the dispersion is controlled and the diameter of bubbles is reduced. It is based on the difficulty of stabilization, and the specific configuration is to mix the thermoplastic resin raw materials with the heat-expandable microcapsules in the foaming method by extrusion or injection molding of the thermoplastic resin. Then, the heat-expandable microcapsules are expanded and molded by heat of kneading and melting by extrusion molding or injection molding.

According to the method for foaming and molding a thermoplastic resin, the heat-expandable microcapsules are mixed with the thermoplastic resin, and the heat-expandable microcapsules are expanded by kneading and melting heat to carry out extrusion molding or injection molding. In order to make each bubble stably foamed by microcapsules, it can be made into a fine, uniform and dense foaming state, the surface is clean, and it can be foamed to the desired specific gravity I have.

Here, the thermoplastic resin is, for example, an engineering plastic such as PVC (vinyl chloride), PS (polystyrene), PP (polypropylene), PPO, or PE (polyethylene) which is known as a general thermoplastic resin. (Polybutylene terephthalate), nylon, PC (polycarbonate),
EEA (ethylene-ethyl acrylate copolymer), AAS (acrylonitrile acrylate styrene copolymer), EVA (ethylene vinyl acetate copolymer), TPU (thermoplastic urethane elastomer), TP as elastomers such as PET (polyethylene terephthalate)
EE (thermoplastic ester elastomer) and the like can be used, and a lubricant, a plasticizer, an antioxidant and the like are added to these as an auxiliary agent.

A heat-expandable microcapsule is a synthetic resin capsule in which a liquid or a gas that expands when heated is included, and the heat of kneading and melting by a screw or the like during extrusion molding or injection molding. The liquid or gas contained therein expands to expand the microcapsules that become the outer shell by expansion, but depending on the temperature conditions at the time of molding, a material that completes molding without melting or bursting is used.

As a material for the microcapsules, a copolymer containing acrylonitrile as one of the monomer components is used. As other monomer components which may be copolymerized with acrylonitrile, for example, acrylic acid, methacrylic acid, acrylic acid Examples include, but are not limited to, esters, methacrylates, styrene, vinyl acetate, vinylidene chloride, and the like.

The liquid or gas contained in the microcapsules is a gas or a gas that expands at a temperature lower than the softening point of the microcapsules. For example, propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane , Hexane, peptane, petroleum ether, halides of methane such as methyl chloride, methylene chloride, CCl ₃ F, CCl ₂ F
_In addition to low-boiling liquids such as chlorofluorocarbons such as ₂ and tetraalkylsilanes such as tetramethylsilane and trimethylethylsilane, compounds such as AIBN that is thermally decomposed by heating and becomes gaseous are used.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below. In the thermoplastic resin foam molding method of the present invention, when extrusion molding or injection molding is performed using a thermoplastic resin, the thermoplastic resin as a raw material and the thermally expandable microcapsules are simultaneously charged into a hopper and mixed. In this method, the thermoplastic resin and the heat-expandable mamicrocapsules are pressed into a die or a mold by an extruder or an injection machine in a mixed state and foamed.

In this extrusion molding or injection molding, the outer shell made of synthetic resin of the heat-expandable microcapsules is softened when the thermoplastic raw resin is heated and melted, and the liquid or gas contained therein is heated to form a gas. Then, the outer shell made of synthetic resin is expanded by pushing and expanding to obtain a foamed state.

Therefore, the outer shell of the heat-expandable microcapsule must have a temperature characteristic of softening but not melting under the molding temperature conditions of the thermoplastic resin raw material. The material and temperature characteristics are appropriately selected from among the heat-expandable microcapsules, and the low-boiling liquid, etc., which is contained inside is also selected from those that have become gaseous and expand at the melting temperature of the thermoplastic resin raw material. Used to choose.

In extrusion molding and injection molding, the raw material supplied from the hopper is kneaded by an extruder or an injection machine by a screw or the like, so that shearing force due to kneading is applied to the heat-expandable microcapsules. Since a pushing force and a radiating force are applied when the microcapsule is extruded into a die or a mold, the microcapsule must be one that does not break even when these forces are applied, and the size is selected.

As described above, by the extrusion molding or the injection molding, a foam can be molded in a state where the thermally expandable microcapsules are expanded and contained in the thermoplastic resin.
Each bubble is stable in a state of being wrapped in microcapsules, and in the case of extrusion molding, even when the pressure is released by extruding from the die, gas does not escape directly to the outside of the molded product, and the surface appearance A good foam can be obtained.

Therefore, in the foam molded article formed by such extrusion molding or injection molding, the amount and size of the bubbles are determined by the number (mixing amount) and the particle size of the thermally expandable microcapsules after expansion. From these, the specific gravity of the molded body is determined, so that the number (mixing amount) of the unexpanded thermally expandable microcapsules to be mixed with the thermoplastic resin raw material and the particle size of the thermally expandable microcapsules after expansion due to the heating amount during molding According to the prediction, it is possible to control the foaming state, and it is possible to easily obtain the target specific gravity without escaping only the gas to the outside as compared with the conventional case where the gas is directly expanded.

Accordingly, when lightweight and heat insulating properties are required as in building materials, the size of the thermally expandable microcapsules is made relatively large, and the mixing amount is increased. can do.

When a uniform and dense foaming state is required as in the case of a foaming roller for office equipment, the heat-expandable microcapsules to be mixed with the thermoplastic resin are made to be very small and spherical. By using one having a particle size of 5 to 30 μm and a particle size after expansion of 10 to 100 μm, a uniform and dense foamed product can be obtained.

Further, even in the case where foam such as a sponge for a shoe sole or the like needs to be formed so as to prevent water from penetrating, the closed cells are formed by the heat-expandable microcapsules. Thus, there is no water permeation, and it can be dealt with by controlling the size and amount of bubbles according to the required cushioning property.

[0022]

EXAMPLES Examples of the present invention and comparative examples will be described below.

(Example 1) Four types of extrusion molding were performed using a thermoplastic urethane elastomer as a thermoplastic resin and changing the blending amount of the heat-expandable microcapsules (Examples A to D).

As a comparative example, foam extrusion extrusion was carried out by adding a chemical foaming agent to the same thermoplastic resin raw material.

The resin used is a thermoplastic urethane elastomer (TPU) (manufactured by Nippon Milactran).

Trade name as heat-expandable microcapsule:
Expancel (manufactured by Nippon Philite) was used. The shell of this heat-expandable microcapsule is a vinylidene chloride / acrylonitrile copolymer and the contained gas is isobutane. The properties of the heat-expandable microcapsule before and after expansion are as shown in Table 1.

The amount of the heat-expandable microcapsules is 1.5 parts per 100 parts (weight, the same applies hereinafter) of the thermoplastic resin.
Three, five, and ten parts were provided.

Azodicarbonamide was used as the chemical blowing agent of the comparative example. Various other auxiliaries were added.

The density of the foam molded article thus obtained was measured, and the surface appearance and the cell structure of the cross section were observed. The results are shown in Table 2.

[0030]

[Table 1]

[0031]

[Table 2]

As is clear from the table, the foamed molded product obtained by extrusion molding using the heat-expandable microcapsules of the present invention has good surface appearance without any roughening, and has a uniform cell structure in cross section. there were.

Further, it has been confirmed that the density of the foamed molded article changes according to the blending amount of the heat-expandable microcapsules.

Example 2 Three types of extrusion molding were performed using vinyl chloride as the thermoplastic resin and changing the blending amount of the heat-expandable microcapsules (Examples A to C).

As a comparative example, foam extrusion extrusion was performed by adding a chemical foaming agent to the same thermoplastic resin raw material.

The resin used was vinyl chloride having a degree of polymerization of 800, and 0.5 part of lead-based lead stearate was added as a stabilizer.

Example 1 as a heat-expandable microcapsule
Same product name as: Expancel (Nippon Philite)
Was used.

The amounts of the heat-expandable microcapsules were 1.5, 3, and 10 parts per 100 parts of the thermoplastic resin.

Azodicarbonamide was used as the chemical blowing agent of the comparative example.

In addition, 0.5 part of calcium stearate was added as a lubricant, and fillers, pigments and the like were added as various auxiliaries.

The density of the foam molded article thus obtained was measured, and the surface appearance and the cell structure of the cross section were observed. The results are shown in Table 3.

[0042]

[Table 3]

As is clear from the table, the foamed molded article obtained by extrusion molding using the heat-expandable microcapsules of the present invention has good surface appearance without any roughening, and has a uniform cell structure in cross section. there were.

Further, it was confirmed that the density of the foamed molded article changed according to the blending amount of the heat-expandable microcapsules.

In Examples 1 and 2, the amount of the heat-expandable microcapsules was from 1.5 parts to 10 minutes based on 100 parts of the thermoplastic resin raw material. It can be appropriately changed according to the required specific gravity and the like, and is not limited to Examples 1 and 2.

[0046]

According to the method for foaming and molding a thermoplastic resin of the present invention, as described above in detail together with one embodiment, the thermally expandable microcapsules are mixed with the thermoplastic resin. Since the heat-expandable microcapsules are expanded by extruding or injection molding by expanding by kneading and melting heat, each bubble can be stably foamed by the microcapsules, and a fine, uniform and dense foaming state can be obtained. But it can be foamed to the desired specific gravity.

Thus, the uniform and dense air bubbles required for paper feeding of the foaming roller for office equipment can be provided, the lightweight and heat insulating properties of building materials can be improved, and the cushioning properties of sponges for shoe soles can be improved. It can easily be made to have characteristics that make it impermeable to water.

Claims (1)

[Claims] In a foam molding method by extrusion molding or injection molding of a thermoplastic resin, a heat-expandable microcapsule is mixed with a thermoplastic resin raw material, and the heat-expandable microcapsule is heated by kneading and melting heat by extrusion molding or injection molding. And foaming the thermoplastic resin.