JPH05186626A - Foamable thermoplastic resin composition - Google Patents

Abstract

PURPOSE:To provide the composition using clean carbon dioxide as a foaming agent and capable of readily and safely giving highly foamed products at a low pressure by impregnating a resin composition comprising a thermoplastic resin and a specific porous material with the inorganic gas. CONSTITUTION:(A) A resin composition comprising (i) 100 pts.wt. of a thermoplastic resin (e.g. polyethylene, polypropylene, 6 nylon), (ii) 5-100 pts.wt. of a porous material (e.g. zeolite, silica gel) having an average particle diameter of <=500mum (preferably 100mum) and, if necessary, a filler and an antioxidant is charged in a pressure container, and the container is filled with (B) an inorganic gas, followed by heating and pressing the charged materials at a temperature above the softening point of the component (i) to obtain the objective composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamable thermoplastic resin composition impregnated with a clean foaming agent, inorganic gas, and more specifically, by adding a porous material powder to the thermoplastic resin, Easily dissolves and adsorbs inorganic gas,
The present invention relates to a foamable thermoplastic resin composition that gives a foam having a high expansion ratio at low pressure.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a thermoplastic resin foam, there is a chemical foaming agent method in which a pyrolytic chemical foaming agent is kneaded into a resin and heated to a temperature equal to or higher than the decomposition temperature of the foaming agent for foaming. Gas foaming that causes an organic gas or volatile liquid having a boiling point below the melting point of a resin, such as butane, pentane, or dichlorodifluoromethane (CFC R-12), to be injected into the molten resin and then released into the low-pressure region for foaming. The law is known.

By using the chemical foaming agent method, a foam having uniform and fine closed cells can be obtained, but discoloration and odor of the foam due to the decomposition residue of the foaming agent remaining in the foam. Occurs, and food hygiene problems occur.

On the other hand, in the gas foaming method, when the foaming agent used is a low-boiling organic solvent such as butane or pentane, an explosive gas is generated during the production of the foam, which causes a danger of explosion. Also, when the blowing agent used is dichlorodifluoromethane (CFC R-12), there is little danger of explosion, the bubble film can be rapidly cooled and solidified by the latent heat of vaporization associated with the vaporization during foaming, and gas permeation to the cell film Although it is easy to obtain a high foam due to its poor property, due to environmental problems such as ozone layer depletion, CFC-based gas is being abolished.

In order to solve the problems of the conventional method, a method has been proposed in which carbon dioxide, nitrogen, an inorganic gas (gas) such as air, or water is used as a foaming agent. These foaming agents are clean and do not cause the above problems, but have the following problems.

For example, Japanese Patent Application Laid-Open No. 60-31538 discloses that
Although an extrusion foaming method using a polypropylene-based resin with an inorganic gas is disclosed, a high-magnification foam cannot be obtained because the solubility of the inorganic gas in the resin is low. And
In order to increase the expansion ratio, it is necessary to press the inorganic gas into the resin at a high pressure using an extruder to dissolve it. This high-pressure mixed melt must be maintained in its high-pressure state until it is extruded from the extruder die into the atmosphere. If the pressure is lowered in the extruder or the die, the resin and the inorganic gas are easily separated and a high-magnification foam cannot be obtained.
Also, even if the high pressure state is maintained up to the base, the resin will not withstand the expansion pressure and will be torn due to the rapid expansion at the moment when the base is released into the atmosphere, and as a result, a high pressure will result. A beautiful foam cannot be obtained at a magnification.

Further, British Patent No. 899,389 discloses a method of foaming cross-linked polyethylene with nitrogen gas in a pressure resistant container. However, in order to obtain a high-magnification foam, it is extremely high. Pressure is required, it is dangerous, equipment costs are high, and work efficiency is poor.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to overcome the above-mentioned drawbacks of the prior art and use a clean inorganic gas as a foaming agent and easily and safely manufacture a high-magnification foam at a low pressure. An object of the present invention is to provide a foamable thermoplastic resin composition.

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, a foamable composition obtained by impregnating a resin composition composed of a porous material having an average particle diameter of 500 μm or less and a thermoplastic resin with an inorganic gas. It was found that a high-foaming foam can be easily and safely produced at a low pressure by using. The present inventors have completed the present invention based on these findings.

[0010]

According to the present invention, a foamable thermoplastic resin composition characterized in that a resin composition containing a thermoplastic resin and a porous material having an average particle size of 500 μm or less is impregnated with an inorganic gas. A resin composition is provided.

The present invention will be described in detail below. In the case of producing a thermoplastic resin foam by the gas foaming method, in order to obtain a high-magnification foam having an expansion ratio of 10 to 40, at least 10 to 40 should be taken into consideration in consideration of gas escape during foaming.
A gas of about cc [STP; standard condition (0 ° C., 1 atm)] must be dissolved in 1 g of the resin composition.

It is generally known that the solubility of gas in a molten resin is almost proportional to the gas pressure.
At the same pressure, the solubility of the inorganic gas is lower than that of the organic gas. FIG. 1 (a) shows the gas pressure dependence of the amount of dissolved carbon dioxide in low-density polyethylene in the molten state.
Carbon dioxide is 10-40c for 1g of low-density polyethylene
In order to dissolve at a ratio of c (STP), 30 to 12
It can be seen that a high gas pressure of 0 kg / cm ² is required.

Therefore, as a result of various studies on means for obtaining the same gas solubility with a lower pressure gas, the present inventors have found that by incorporating a porous material having an adsorbing ability for gas into a thermoplastic resin, It was found that the solubility of the inorganic gas in the resin composition can be improved. FIG. 1B shows the gas pressure dependency of the carbon dioxide impregnation amount of the resin composition in which 20 parts by weight of zeolite was added to 100 parts by weight of low-density polyethylene. As can be seen from FIG. 1, the carbon dioxide impregnation amount under the same gas pressure is increased by adding the porous body. Moreover, since the amount of the inorganic gas impregnated can be adjusted by adjusting the number of parts of the porous body, it is possible to control the expansion ratio of the foam.

The thermoplastic resin used in the present invention is not particularly limited, and examples thereof include polyethylene, polypropylene, polymethylmethacrylate, polyvinyl chloride,
Polyvinyl fluoride, ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene-diene copolymer, ABS resin, polystyrene,
Polyolefins such as copolymers containing 50% or more of styrene and polystyrene resins; polyamides such as 6-nylon, 66-nylon and 12-nylon; polyesters such as polyethylene terephthalate and polybutylene terephthalate; bisphenol A type polycarbonates; others , Polyphenylene oxide, polyacetal, polyphenylene sulfide and the like. These resins may be used alone or in combination of two or more kinds.

As the porous material, zeolite, activated carbon,
Alumina, silica gel, porous glass, activated clay, diatomaceous earth, clay, or the like, or a mixture of two or more thereof is used.

The porous material used in the present invention has an average particle diameter of 500 μm or less, preferably 100 μm or less. If an average particle size of more than 500 μm is used, a uniform and fine cell foam cannot be obtained, which may cause cell breakage. Further, the porous body having an average particle size of 100 mμ or less acts as a cell nucleating agent by itself, and makes the size of cells fine and uniform, and makes the dispersion uniform.

The amount of the porous material added is 100
5 to 100 parts by weight, preferably 1 part by weight
It is 0 to 70 parts by weight. When the amount of the porous body added is less than 5 parts by weight, the degree of impregnation (dissolution / adsorption) of the inorganic gas into the resin composition does not increase so much, and it is difficult to obtain a high-magnification foam at low pressure. On the other hand, when the amount exceeds 100 parts by weight, the porous body hinders foaming and foam breakage easily occurs,
Also in this case, it is difficult to obtain a high-magnification foam.

Further, in the present invention, if necessary, a filler, an antioxidant, a pigment, a flame retardant, etc. may be added to the composition. As an inorganic gas as a foaming agent,
Examples thereof include carbon dioxide gas, nitrogen, air, oxygen, or an inert gas such as neon or argon. In order to obtain a high-magnification foam, carbon dioxide having a high solubility in a thermoplastic resin or a mixture of carbon dioxide and another inorganic gas is preferable.

To produce the expandable thermoplastic resin composition of the present invention, (1) the thermoplastic resin and an average particle size of 500
a method of injecting an inorganic gas into a resin composition obtained by kneading a porous body having a particle size of mμ or less, (2) a method of kneading a porous resin having an average particle size of 500 mμ or less, in which an inorganic gas is adsorbed in advance, and a thermoplastic resin, 3) A method of further injecting an inorganic gas into a resin composition obtained by kneading a thermoplastic resin with a porous body having an average particle size of 500 mμ or less which has been adsorbed with an inorganic gas in advance,
There is a method such as.

Since the expandable thermoplastic resin composition of the present invention is impregnated with the inorganic gas under high pressure, the inorganic gas is released by reducing the pressure. Therefore, when the expandable thermoplastic resin composition impregnated with the inorganic gas is released from the pressure-applied state to the low-pressure region, the gas desorbed from the porous body and the gas dissolved in the resin expand, and with this The resin composition foams. In this case, it is important to adjust the melt viscosity of the resin composition within an appropriate range in order to prevent foam breakage.

In general, a non-crosslinked thermoplastic resin causes a rapid change in viscosity near its melting point, and therefore has a narrow temperature range exhibiting viscoelasticity suitable for foaming, and it is necessary to control the proper temperature and viscosity during foaming. A high level of technical skill is required. Therefore, it is preferable to crosslink the thermoplastic resin composition in order to facilitate control of the proper temperature and viscosity for foaming.

The cross-linking method of the composition is (1) a method of cross-linking by irradiating an electron beam, (2) a method of adding an organic peroxide and generating a radical by heating to cross-link the composition.
(3) Olefin-based resin, -C = C- group, and -Si (O
R) _n group [R: H or alkyl group, n = 2 or 3]
Examples of the method include producing a silane-grafted polyolefin by heating a silane compound having a silane compound in the presence of a free radical generator, and crosslinking the silane-grafted polyolefin with water and, if necessary, a silanol condensation catalyst.

The degree of crosslinking is 60% or less, preferably 5 to 60%, more preferably 10 to 50 in terms of gel fraction at the time of foaming.
It is desirable to set it as%. When the gel fraction exceeds 60%, the viscosity of the resin at the time of foaming becomes too high, and a foam having a high magnification cannot be obtained. On the other hand, when the gel fraction is less than 5%, the temperature range exhibiting viscoelasticity suitable for foaming is not so different from that in the case of non-crosslinked, and it is still difficult to control the temperature and the viscosity. A crosslinking aid may be added if necessary.

To produce a foam from the expandable thermoplastic resin composition, there may be mentioned a method of foaming with an extruder or a method of foaming in a pressure vessel.

As a method of foaming with an extruder, (1)
A method in which a composition comprising a porous body and a thermoplastic resin is charged into an extruder, and the resin composition is in the molten state in the middle of the extruder, in which an inorganic gas is press-fitted by pressurizing an inorganic gas,
(2) A method in which an inorganic gas is adsorbed in advance on a porous body, the resin composition of the present invention is produced by dry blending, and if necessary, the inorganic gas is pressed in from the middle of the extruder to perform extrusion foaming. 3) A resin composition other than the porous body is supplied from the hopper of the extruder, and the porous body and the inorganic gas in which the inorganic gas is adsorbed in advance are injected simultaneously or separately into the molten state of the composition. Then, there is a method of extrusion foaming.

As a method of foaming in a pressure vessel, first, a composition comprising a porous body and a thermoplastic resin is melt-kneaded,
A sheet-shaped or block-shaped expandable thermoplastic resin which is formed into a sheet-shaped or block-shaped, and then the molded body is put into a pressure vessel, filled with an inorganic gas, and heated and pressed to a temperature not lower than the softening point of the thermoplastic resin. Obtain the composition. In the case of cross-linking, the cross-linking is carried out by heating at this time or before introducing into a pressure vessel. A foam can be produced by sufficiently dissolving an inorganic gas in the resin composition and then reducing the pressure.

[0027]

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

Example 1 <Compound formulation> Zeolite (average particle size 10 mμ) 20 parts by weight Low density polyethylene (density 0.921, MI = 2.0) 100 parts by weight Antioxidant 0.6 parts by weight The mixture was dry-blended and supplied to the hopper of a vent type φ65 mm extruder (L / D = 35) set at 130 ° C. 60 kg of carbon dioxide gas from the vent to the melt where the resin and additives are sufficiently kneaded through the melt.
After press-fitting at a pressure of / cm ² and further thoroughly kneading, 113
When extruded into a rod shape at a discharge rate of 20 kg / cm ² from a φ2 mm die set to ℃, the expansion ratio was 2
A foam having uniform fine cells with a smooth surface of 0.0 times was obtained.

Example 2 <Compound formulation> Zeolite (average particle size 10 mμ) 20 parts by weight Low density polyethylene (density 0.921, MI = 2.0) 100 parts by weight Antioxidant 0.6 parts by weight After kneading with a mixing roll set at 130 ° C., it was formed into a sheet having a thickness of 2 mm by a hot press. The sheet-like molded body was cross-linked by irradiating both sides with an electron beam having a voltage of 540 kev and an irradiation dose of 5.3 Mrad. The gel fraction at this time was 35%. Next, the sheet-shaped molded product is put into a pressure vessel, deaerated by a vacuum pump, carbon dioxide gas is then press-fitted, and heated to 60 kg / cm ² , 14
It was kept at 0 ° C. for 2 hours. Next, the pressure vessel was released, and the pressure was rapidly reduced to atmospheric pressure and cooled, and the firing rate was 25.0.
As a result, a foam having uniform fine cells with a smooth surface was obtained.

Comparative Example 1 When extruded under the same conditions as in Example 1 except that no zeolite was added, a foaming ratio of 14.0 times and a smooth surface but coarse cells was obtained. ..

Comparative Example 2 Extrusion was carried out under the same conditions as in Example 1 except that no zeolite was added and that carbon dioxide gas was pressed in at 80 kg / cm ² in order to obtain the same expansion ratio as in Example 1. A foam with an expansion ratio of 20.0 was obtained partially, but the surface was rough due to gas escape from the die, resin scattering, foaming inside the die, etc. A foam was obtained.

Comparative Example 3 A foam was produced under the same conditions as in Example 2 except that zeolite was not added. As a result, a foam having a foaming ratio of 17.5 times and a smooth surface, but having coarse cells was obtained. Was obtained.

[0033]

EFFECTS OF THE INVENTION By using the expandable thermoplastic resin composition of the present invention, the gas impregnation rate to the resin composition is remarkably improved, and a foam having a high expansion ratio can be safely and efficiently produced with a gas having a relatively low pressure. .. Further, when a porous body having an average particle diameter of 100 mμ or less is used, there is an advantage that it is not necessary to add a cell nucleating agent. The foam according to the present invention comprises a heat insulating material, a cushioning material,
It is extremely useful because it can be applied to various fields such as sealing materials and float materials.

[Brief description of drawings]

FIG. 1 (a) is a carbon dioxide gas solubility in low-density polyethylene in a molten state, and (b) is a carbon dioxide impregnation amount of a resin composition in which 20 parts by weight of zeolite is added to 100 parts by weight of low-density polyethylene. It is a graph which shows.

Claims (1)

[Claims] 1. A foamable thermoplastic resin composition, which is obtained by impregnating a resin composition containing a thermoplastic resin and a porous material having an average particle size of 500 μm or less with an inorganic gas.