JPH06182886A - Manufacture of foamed material - Google Patents

Abstract

PURPOSE:To obtain a foamed material having excellent surface state with a high foaming magnification without danger of explosion with a small quantity of organic solvent by specifying thermoplastic resin, inorganic gas, organic solvent to specific quantities, mixing them in a kneader when the resin is melted in the kneader, discharging it from the kneader, and foaming it. CONSTITUTION:0.5-20 pts.wt. of inorganic gas such as carbon dioxide gas, nitrogen, oxygen, etc., and 0.1-10 pts.wt. of organic solvent such as n-butane, n- hexane, benzene, xylene, etc., are mixed to 100 pts.wt. of thermoplastic resin such as polyethylene, polypropylene, chlorinated polyethylene, polystyrene, etc., in a kneader. As the kneader, an extrusion molding machine, an injection molding machine, etc., is used. The inorganic gas is mixed directly from a gas cylinder, or pressurized by a plunger pump, and then mixed. The organic solvent is previously absorbed to the resin, or mixed by using a bent type screw. Thus, after the mixture, it is extruded from the kneader to obtain a foamed material.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a foam.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a thermoplastic resin foam, a chemical foaming 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 to foam, 1,2- A gas foaming method is known in which an organic solvent having a low boiling point, such as dichloro-1,2-difluoroethane, butane, or pentane, is mixed into a thermoplastic resin for foaming. However, in the chemical foaming method, the decomposition residue of the foaming agent remains in the foam, resulting in discoloration of the foam, generation of odor, and food hygiene problems. Further, in the gas foaming method, since a large amount of organic solvent having a low boiling point is used for foaming, there is a risk of explosion during molding, which is not preferable.

In order to solve such a problem, JP-A-60-31538 proposes a method in which an inorganic gas such as carbon dioxide, nitrogen or air is mixed with a thermoplastic resin and extruded to foam. There is.

[0004]

However, according to the above method, in order to obtain a foam having a narrow proper foaming temperature and a high expansion ratio, it is necessary to mix an inorganic gas at a high pressure, resulting in foaming. At times, there were defects such as the foam bursting, and the resulting foam had a poor surface condition.

An object of the present invention is to solve the above problems and to obtain a foam having a high expansion ratio and an excellent surface condition without danger of explosion without using a regulated halogen-based solvent. It is an object of the present invention to provide a method for producing a foam that can be manufactured.

[0006]

The thermoplastic resin used in the present invention softens and exhibits plasticity when heated,
It is not particularly limited as long as it is a plastic that solidifies when cooled, and examples thereof include polyethylene, polypropylene, polybutene, chlorinated polyethylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-ethyl acrylate copolymer, propylene copolymer. Polymers, polyolefin resins such as ethylene-vinyl acetate copolymer, polystyrene, polyvinyl chloride, polyvinyl fluoride, polycarbonate, polyacetal, polyphenylene sulfide, polyphenylene oxide and polyamide resins such as nylon 6, nylon 6-6, nylon 12, polyethylene. Examples thereof include polyesters such as terephthalate and polybutylene terephthalate, acrylic resins, acrylonitrile-butadiene-styrene resins, and fiber plastics. These may be used alone or in combination of two or more.

The inorganic gas used in the present invention is an inorganic substance which is a gas at room temperature and is not particularly limited as long as it does not deteriorate the thermoplastic resin. For example, carbon dioxide gas, nitrogen, argon, neon, Examples include helium and oxygen. These may be used alone or 2
You may use together more than one kind. Particularly when it is desired to obtain one having a high expansion ratio, a gas having a high solubility in a thermoplastic resin such as carbon dioxide gas is preferable.

If the amount of the inorganic gas is small, a high-magnification foam cannot be obtained. If the amount is large, the foam ruptures at the time of foaming and the surface property of the foam deteriorates. It is limited to 0.5 to 20 parts by weight.

The organic solvent used in the present invention is an organic substance that can be liquefied at the molding temperature of the thermoplastic resin and is not particularly limited as long as it does not deteriorate the thermoplastic resin, and for example, n-butane, n- Aliphatic hydrocarbons such as pentane, n-hexane, n-heptane, aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, styrene, methylstyrene, alicyclic hydrocarbons such as cyclohexane, methanol, ethanol, 1- Propanol,
2-Propanol, 1-butanol, 2-methyl 1-propanol, alcohols such as trimethylcarbinol, ethers such as ethyl ether, and the like, and chloromethane, dichloromethane, monochlorodifluoromethane, 1,
2-difluoroethane, 1-chloro-1,1-difluoroethane, 1,1-dichloro-1-fluoroethane, 1,1-dichloro-
Halogen-based organic solvents whose use is not restricted, such as 2,2,2-trifluoroethane, 1,1,1,2-tetrafluoroethane and chlorobenzene, can also be used. These may be used alone or in combination of two or more.

When the organic solvent has a low boiling point, it cannot be mixed in the kneader as a liquid at room temperature, and even if mixed at a low temperature, it does not disperse in the thermoplastic resin and boils to obtain a uniform foam. If it is not high and remains high in the foam, the boiling point of the solvent is preferably between −50 ° C. and the molding temperature of the thermoplastic resin.

If the amount of the organic solvent is small, it is impossible to obtain a molded product having a high expansion ratio, and if the amount is large, there is a risk of explosion or the like at the time of molding, so 0.1 to 100 parts by weight of the thermoplastic resin is used. Limited to 10 parts by weight.

Alcohol is preferably used as the organic solvent in consideration of the danger of explosion. However, since alcohol has poor compatibility with the thermoplastic resin, it is preferable to use the alcohol-absorbing polymer or the porous body together with the thermoplastic resin.

The above-mentioned alcohol-absorbing polymer means a polymer capable of absorbing 500 parts by weight or more of alcohol based on 100 parts by weight of the polymer, for example, starch-acrylic acid graft copolymer, vinyl alcohol-acrylic acid salt copolymer, Examples thereof include polyvinyl alcohol-based copolymers and crosslinked polyethylene oxide. These may be used alone or in combination of two or more. In particular, the cross-linked polyethylene oxide has a large amount of absorbed alcohol and has good compatibility with the thermoplastic resin, and thus can be preferably used.
Examples of such cross-linked polyethylene oxide include Sumitomo Seika Chemical Co., Ltd., trade name: Aqua Coke.

If the average particle size of the alcohol-absorbent polymer is large, the bubbles in the resulting foam will become coarse and cause breakage of the bubbles, so it is preferably 200 μm or less, more preferably 80 μm or less. If the amount of the alcohol-absorbing polymer is too large, a uniform foamed product cannot be obtained and foam breakage easily occurs. Therefore, it is preferably 30 parts by weight or less relative to 100 parts by weight of the thermoplastic resin.

The above-mentioned porous material has a large number of small voids capable of absorbing alcohol inside and on the surface of a solid,
Examples thereof include zeolite, activated carbon, alumina, silica gel, porous glass, activated clay, diatomaceous earth, clay and the like. These may be used alone or in combination of two or more.

If the average particle size of the above-mentioned porous body is large, the bubbles in the resulting foam will become coarse and cause breakage of the bubbles, so it is preferably 200 μm or less, more preferably 80 μm.
m or less. If the amount of the porous body is too large, a uniform foamed product cannot be obtained and foam breakage easily occurs. Therefore, it is preferably 30 parts by weight or less relative to 100 parts by weight of the thermoplastic resin.

When the porous body is used, the alcohol adsorbed on the porous body is not completely desorbed during foaming,
The amount of alcohol is preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the thermoplastic resin.

In the present invention, when the thermoplastic resin is an olefin resin, the organic solvent is preferably styrene. In particular, a thermoplastic resin whose molding temperature is higher than the boiling point of styrene (145 ° C) is
7210 has a melt flow rate of 0.1 to 20 g /
It is particularly preferable to use a resin in the range of 10 minutes.

In the present invention, if necessary, additives such as synthetic rubber, paraffin, plasticizer, pigment, foaming agent, flame retardant and antistatic agent may be mixed.

In the method for producing a foam of the present invention, in the step of supplying the thermoplastic resin into the kneading machine and melting it, the inorganic gas and the organic solvent are mixed in the kneading machine and discharged from the kneading machine to foam. Is characterized by.

The kneading machine used in the present invention is not particularly limited, and examples thereof include an extrusion molding machine and an injection molding machine. Examples of the method of mixing the inorganic gas include a method of mixing a vent type screw into the vent portion from the middle of the cylinder, and a method of mixing a pressurized gas into the hopper. The inorganic gas may be mixed directly from the gas cylinder, or may be mixed under pressure using a plunger pump. The method of mixing the organic solvent is not particularly limited, and examples thereof include a method of preliminarily absorbing it in a thermoplastic resin, a method of mixing a bent type screw into the vent portion from the middle of the cylinder, and a method of mixing from a hopper. In addition, when mixing, it is preferable to perform a fixed amount supply using a gear pump or the like. When a foam is obtained by extrusion, the extrusion temperature varies depending on the thermoplastic resin to be molded, but is preferably the melting point of the thermoplastic resin to the melting point + 50 ° C, and the mold temperature is 5 ° C lower than the melting point of the thermoplastic resin, It is preferably in the range of 10 ° C. higher. The inorganic gas is preferably mixed at a pressure of 5 to 100 kg / cm ² . Further, the discharge rate from the mold is preferably 1 to 100 kg / hr.

The manufacturing method of the present invention 2 is the same as that of the present invention except that an external lubricant is further fed into the kneader. The external lubricant is a substance that provides lubricity and releasability between the resin and the kneader, and any one can be selected depending on the thermoplastic resin used. For example, a polyolefin resin as the thermoplastic resin. When used, calcium stearate, stearic acid amide, fatty acid derivatives such as oleic acid amide, polyethylene wax, etc. are preferably used, and when polystyrene resin is used, stearic acid, ethylene bis stearic acid amide, etc. are preferably used. To be done.

In the production method of the present invention 3, the above-mentioned thermoplastic resin, inorganic gas and organic solvent are mixed in a pressure vessel,
It is characterized in that the pressure in the pressure vessel is reduced to cause foaming. The pressure vessel is not particularly limited as long as it can withstand the pressure of the mixed inorganic gas, and examples thereof include an autoclave. The temperature in the pressure vessel and the mixing pressure of the inorganic gas are not particularly limited, but in order to obtain a foam having a high expansion ratio, in the temperature range from the melting point of the thermoplastic resin to 20 ° C. higher than the melting point, 5 to 100 kg / cm. After mixing at a pressure of ² ,
It is preferable to open the inside of the pressure vessel to atmospheric pressure. Further, the thermoplastic resin may be previously molded into a molded product such as a sheet by a method such as a mixing roll or a heating press.

[0024]

EXAMPLES The details of the present invention will be described below with reference to examples.

Examples 1 to 5, Comparative Examples 1 and 2 Predetermined amounts of low density polyethylene (density 0.9
21, melt flow rate 2.0 g / 10 minutes, melting point 11
0.7 ° C.), antioxidant (manufactured by Adeka Argus Chemical Co., Ltd., trade name: Mark328), talc (manufactured by Nippon Talc Co., trade name: MS), cross-linked polyethylene oxide (manufactured by Sumitomo Seika Chemical Co., Ltd., trade name: Aqua) Coke: average particle size 50 μm, alcohol absorption amount 3000 parts by weight), zeolite (manufactured by Tosoh Corporation, trade name; A5: average particle size 10 μm, pore size 5Å, alcohol absorption amount 20 parts by weight) and stearic acid amide are mixed, Feed into the hopper of an extruder with a screw diameter of 65 mm and L / D = 35 vents with two inlets, and extrude 2-propanol (boiling point 82.4 ° C) and ethanol (boiling point 78.5 ° C). Mix with a gear pump from the first injection hole of the vent part of the machine, mix a predetermined amount of carbon dioxide gas from the second injection port with a plunger pump at a predetermined pressure, and knead at 130 ° C. 2mm of the mold (113 ℃)
And discharged at a rate of 12 kg / hr for foaming to obtain a rod-shaped foam. The following physical properties were measured using the obtained foam, and the results are shown in Table 1.

(Measurement of Physical Properties) Expansion Ratio Thirty minutes after obtaining the foam, the specific gravity of the obtained foam was measured using an electronic hydrometer (Model Mirage; ED-120T), and the average of the raw materials was measured. The expansion ratio was calculated by dividing the density.

Closed cell ratio 30 minutes after obtaining the foam, the obtained foam is used for 1 to 1/2 to 1 atm method using an air-comparison hydrometer (manufactured by Tokyo Science Co., model: 1000). The closed cell volume was measured by and was divided by the apparent volume of the foam to calculate the closed cell rate.

Surface condition The surface condition of the obtained foam is visually observed, and ○ indicates that uniform and fine closed cells are obtained, ○ indicates that coarse bubbles are locally generated, and closed cells A mark was given to those having poor properties, and a mark was given to those in which foam breakage occurred or in which foaming was extremely unevenly generated.

Examples 6 to 9 and Comparative Examples 3 and 4 Predetermined amounts of low density polyethylene (density 0.9
21, melt flow rate 2.0 g / 10 minutes, melting point 11
0.7 ° C.), antioxidant (manufactured by Adeka Argus Chemical Co., Ltd., trade name: Mark328), talc (manufactured by Nippon Talc Co., trade name: MS), cross-linked polyethylene oxide (manufactured by Sumitomo Seika Chemical Co., Ltd., trade name: Aqua) Coke: average particle size 50 μm, alcohol absorption amount 3000 parts by weight) and zeolite (manufactured by Tosoh Corp., trade name; A5: average particle size 10 μm, pore size 5Å, alcohol absorption amount 20 parts by weight) are mixed, and 120 by mixing roll After kneading at ℃, press the hot press at 120 ℃ thickness 2m
m sheet. The obtained sheet and a certain amount of 2-propanol (boiling point 82.4 ° C), ethanol (boiling point 7
(8.5 ° C) is put in a pressure vessel (autoclave), a predetermined amount of carbon dioxide gas is mixed at a predetermined pressure using a plunger pump, the pressure vessel is heated to 120 ° C, left for 1 hour and then opened to atmospheric pressure. The pressure was reduced to obtain a sheet-shaped foam. The physical properties of the obtained foam were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0030]

[Table 1]

Examples 10 to 13 and Comparative Examples 5 to 11 Predetermined amounts of polypropylene shown in Table 2 (manufactured by Mitsubishi Petrochemical Co., Ltd.,
Product name: Noblen EC9, Melt flow rate 0.5
g / 10 minutes), low density polyethylene (density 0.921,
Melt flow rate 2.0 g / 10 minutes, melting point 110.7
℃) Antioxidant (Adeka Argus Chemical Co., Ltd., trade name; M
ark328) and talc (manufactured by Nippon Talc Co., Ltd., trade name;
MS), screw diameter 65 mm, L / D = 35
Was fed to the hopper of an extruder having two inlets in the vent part, and a predetermined amount of styrene, n-pentane or 1-chloro-1,1-difluoroethane shown in Table 2 was added to the vent part of the extruder. The first injection hole mixes with a gear pump, the second injection hole mixes a predetermined amount of carbon dioxide gas with a plunger pump at a predetermined pressure, and the mixture is kneaded at a predetermined temperature to set an inner diameter set to a predetermined temperature. It was discharged through a 2 mm mold at 12 kg / hr for foaming to obtain a rod-shaped foam. The physical properties of the obtained foam were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0032]

[Table 2]

[0033]

As described above, in the method for producing a foam of the present invention, in the step of supplying the thermoplastic resin into the kneading machine and melting it, the inorganic gas and the organic solvent are mixed into the kneading machine and discharged from the kneading machine. Since it can be foamed with a small amount of organic solvent, it is possible to obtain a foam having a high expansion ratio and an excellent surface condition without risk of explosion or the like.

As described above, in the method for producing a foam according to the second aspect of the present invention, since the external lubricant is further fed into the kneader in the step of the present invention, the shear heat generation during molding is suppressed, By keeping the temperature suitable for foaming constant, it is possible to continuously obtain a foam having a high expansion ratio and a high closed cell ratio and excellent surface condition.

As described above, in the method for producing a foam according to the third aspect of the present invention, in the step of supplying and melting the thermoplastic resin in the pressure vessel, the inorganic gas and the organic solvent are mixed in the pressure vessel and the mixture is fed from the kneader. Since it is characterized by being discharged and foamed, it is possible to foam with a small amount of an organic solvent, and it is possible to obtain a foam having a high expansion ratio and an excellent surface condition without danger of explosion or the like.

When alcohol is used as the organic solvent in the present invention, a foam having a high expansion ratio and an excellent surface condition can be obtained without danger of explosion.

In the present invention, when styrene is used as the organic solvent when the thermoplastic resin is an olefin resin, the proper foaming temperature is widened and a foam having a high expansion ratio and excellent surface condition can be obtained.

Claims (3)

[Claims] 1. In a step of supplying and melting a thermoplastic resin in a kneader, 0.5 to 20 parts by weight of an inorganic gas and 0.1 to 10 parts by weight of an organic solvent are kneaded with respect to 100 parts by weight of the thermoplastic resin. A method for producing a foam, which comprises mixing in a machine and discharging from a kneader to foam. 2. The method for producing a foam according to claim 1, further comprising supplying an external lubricant into the kneader. 3. In the step of supplying and melting the thermoplastic resin in a pressure vessel, 0.5 to 20 parts by weight of an inorganic gas and 0.1 to 10 parts of an organic solvent are added to 100 parts by weight of the thermoplastic resin.
A method for producing a foam, comprising mixing parts by weight into a pressure container and then reducing the pressure to foam.