JPH07102103A - Production of foamed article - Google Patents

Abstract

PURPOSE:To obtain a foamed article having an excellent surface state at a high foaming magnification using a blowing agent free from safety and environmental problems by melt-kneading a thermoplastic resin together with inorganic gas and a water-containing alcohol in a kneader and then extrusion-forming the resin. CONSTITUTION:100 pts.wt. of a thermoplastic resin, 0.5-10 pts. wt. of inorganic gas and 0.1-3 pts.wt. of an 1-4C alcohol containing 20-70wt.% of water are fed in a kneader. The mixture is melt-kneaded and then extrusion-foamed from the kneader. Also, the above-mentioned components may by placed in a pressure container, heated and pressurized and then allowed to foam by reducing the pressure. The thermoplastic resin has preferably MF of 0.05-30g/10min. As the inorganic gas, carbon dioxide gas is preferable. As the alcohol, methanol, etc., is used.

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. However, in this example,
The expansion ratio is about 5 times, and no high expansion ratio has been obtained.

[0004] On the other hand, water is clean, and accompanying a phase change in the foaming (decompression) process, the latent heat of vaporization about 10 times that of the organic gas is taken from the molten resin to increase the strength of the bubble film, thereby forming bubbles. The advantage is that it is fixed. However, since the compatibility with the resin is poor, even if water is directly pressed into the molten resin in the extruder as an extrusion method, the water cannot be uniformly dispersed in the molten resin in a microscopic state, and the resulting foam is locally Coarse bubbles are generated. For example, Japanese Patent Publication No. 52-20
Japanese Unexamined Patent Publication No. 500 discloses a method of injecting a small amount of water into an extruder cylinder together with an evaporative foaming agent in extrusion foaming of a polyolefin resin, and fixing bubbles by utilizing latent heat of vaporization of water. However, since there is no means for dispersing water in a microscopic state, there is a problem in that coarse bubbles are generated and a poor appearance occurs.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to use a foaming agent which is environmentally and safety-free and to obtain a surface condition at a high expansion ratio. Another object of the present invention is to provide a method for producing a foam, which is capable of obtaining a foam excellent in quality.

[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, polymethylpentene, chlorinated polyethylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-ethyl acrylate copolymer. Polymers, ethylene-acrylic acid copolymers, ethylene-vinyl acetate copolymers and other polyolefin resins, polystyrene,
Polyvinyl chloride, polyvinyl fluoride, polycarbonate, polyacetal, polyphenylene sulfide, polyphenylene oxide, nylon 6, nylon 6-
6, polyamide resins such as Nylon 12, polyesters such as polyethylene terephthalate and polybutylene terephthalate, acrylic resins, acrylonitrile-butadiene-styrene resins, fiber plastics and the like. These may be used alone or in combination of two or more.

These thermoplastic resins are manufactured according to JIS K 7
The melt flow rate according to 210 is 0.05 to 30 g
/ 10 minutes is preferable. If the melt flow rate of the resin is too small, the melt viscosity becomes high and a foam with a high magnification cannot be obtained, and the load on the extruder increases and extrusion becomes difficult. If the melt flow rate is too high, the viscosity sufficient to withstand the gas expansion pressure during foaming cannot be maintained, and the foam is broken to obtain a high-magnification foam.

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, and if the amount is large, the foam ruptures during foaming and the surface property of the foam deteriorates. It is limited to 0.5 to 10 parts by weight.

The alcohol used in the present invention is
It has 1 to 4 carbon atoms, and includes, for example, methanol (boiling point: 64.1 ° C.), ethanol (boiling point: 78.5 ° C.),
1-propanol (boiling point: 97.4 ° C), 2-propanol (boiling point: 82.4 ° C), 1-butanol (boiling point: 1
17.4 ° C.), isobutyl alcohol (boiling point: 108.
1 ° C.), 2-butanol (boiling point: 100 ° C.), tert-butyl alcohol (boiling point: 82.8 ° C.) and the like. These may be used alone or in combination of two or more. Alcohols with 5 or more carbons
There is no effect in the present invention because of poor compatibility with water.

Water contained in the alcohol used in the present invention is limited to 20 to 70% by weight, preferably 30 to 50% by weight. If the amount of water blended is small, there is a safety problem due to the flammability of alcohol, and if it is large, the compatibility with the thermoplastic resin becomes poor and huge and nonuniform bubbles are formed.

If the amount of the alcohol containing 20 to 70% by weight of water is small, there is almost no effect of fixing the bubbles during foaming, and if the amount is large, water and alcohol are liquefied after foaming. Since the shrinkage of the foam is remarkable and recovery of the shrinkage takes time to cause inconvenience in production, it is limited to 0.1 to 3 parts by weight with respect to 100 parts by weight of the thermoplastic resin, preferably 0.5 to 2 parts by weight.

In the present invention, if necessary, additives such as a nucleating agent, a filler, a synthetic rubber, an antioxidant, a paraffin, a plasticizer, a pigment, a foaming agent, a flame retardant and an antistatic agent may be added to the thermoplastic resin. You may mix in.

The method for producing a foam according to the present invention is characterized in that the alcohol containing the above-mentioned inorganic gas and water is supplied into a kneader, melt-kneaded, and discharged from the kneader to foam.

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 supplying the inorganic gas include a method of using a vent type screw to supply the gas to the vent portion from the middle of the cylinder, and a method of supplying a pressurized gas to the hopper. The inorganic gas may be directly supplied from the gas cylinder, or may be pressurized and supplied using a plunger pump. The method of supplying the alcohol containing water is not particularly limited, and for example, a method of previously absorbing it in a thermoplastic resin,
Examples include a method of using a vent type screw to supply to the vent part from the middle of the cylinder and a method of supplying from a hopper. At the time of supply, it is preferable to perform a fixed amount supply using a gear pump or the like. When a foamed body is obtained by extrusion, the extrusion temperature varies depending on the thermoplastic resin to be molded, but the melting point of the thermoplastic resin to the melting point + 50 ° C is preferable, and the melting point to the melting point + 20 ° C is more preferable.
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 than the melting point. The inorganic gas is preferably supplied at a pressure of 5 to 100 kg / cm ² . Further, the discharge rate from the mold is preferably 1 to 100 kg / hr.

In the production method of the present invention 2, the above-mentioned thermoplastic resin, an alcohol containing an inorganic gas and water is supplied into a pressure vessel, heated and pressurized, and then the pressure in the pressure vessel is reduced to foam. It is characterized by The pressure vessel is not particularly limited as long as it can withstand the pressure when the inorganic gas supplied and the alcohol containing water are vaporized,
An example is an autoclave. The temperature in the pressure vessel and the supply pressure of the inorganic gas are not particularly limited, but in order to obtain a foam having a high expansion ratio, the melting point of the thermoplastic resin-1
5 to 100 kg / cm in the temperature range of 0 ℃ to melting point + 20 ℃
After the pressure is set to ² , it is preferable to open the inside of the pressure vessel to the 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.

[0017]

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

Examples 1 to 8 and Comparative Examples 1 to 6 Predetermined amounts of low density polyethylene (density 0.921, melt flow rate 2.0 g / 10 shown in Table 1 and Table 2)
Min., Melting point 110.7 ° C.), antioxidant (Adeka Argus Chemical Co., Ltd., trade name; Mark 328) and talc (Nihon Talc Co., Ltd., trade name; MS) are mixed, screw diameter 65 mm, L / D = It is supplied to the hopper of the extruder having two inlets at the vent of No. 35, and a predetermined amount of carbon dioxide gas is supplied from the first inlet at the vent of the extruder by the plunger pump, and the second pouring is performed. Ethanol containing a certain amount of water is supplied from the inlet using a plunger pump,
The mixture was melt-kneaded at 0 ° C. and discharged through a mold (113 ° C.) having an inner diameter of 2 mm at 12 kg / hr for foaming to obtain a rod-shaped foam. Since a shrinkage phenomenon was observed in the obtained foam after several hours, the curing period for recovering the shrinkage was 24 hours, 2
After holding in a space of 0 ° C., the following physical properties were measured, and the results are shown in Tables 1 and 2. Further, in Comparative Example 6, the resin was scattered from the die, and the expansion ratio and the closed cell ratio could not be measured.

(Measurement of Physical Properties) Foaming Ratio The obtained foamed product was measured with an electronic hydrometer (manufactured by Mirage, model;
ED-120T) was used to measure the specific gravity, and the average density of the raw material was divided to calculate the expansion ratio.

Closed Cell Rate The obtained foam was measured for its closed cell volume by an air-comparison hydrometer (manufactured by Tokyo Science Co., model: 1000) by the method of 1 to 1/2 to 1 atm to obtain the foam. The closed cell ratio was calculated by dividing by the apparent volume of.

Surface condition The bubble shape and surface condition of the foam were visually observed and evaluated. Regarding the surface condition, the product that is compatible with the product without wrinkles or cracks on the surface is ○, the product with slight wrinkles or cracks on the surface that may be a little problem as the product is △, or the surface is wrinkled or cracked. Those having cracks and incompatible products were marked with x.

[0022]

[Table 1]

[0023]

[Table 2]

Examples 9 to 16 and Comparative Examples 7 to 12 Predetermined amounts of polypropylene shown in Tables 3 and 4 (trade name; Noblen EC9, melt flow rate 0.5 g / 10 minutes, manufactured by Mitsubishi Petrochemical Co., Ltd.) , Antioxidant (Adeka Argus Chemical Co., Ltd., trade name; Mark328) and talc (Nihon Talc Co., Ltd., trade name; MS) are mixed, and two injections are made at the vent part of screw diameter 65 mm, L / D = 35. It is supplied to the hopper of the extruder provided with an inlet, a predetermined amount of carbon dioxide gas is supplied from the first inlet of the vent of the extruder by a plunger pump, and a predetermined amount of water is contained from the second inlet. 210 ethanol is supplied using a plunger pump,
The mixture was melt-kneaded at 0 ° C. and discharged at a rate of 12 kg / hr through a mold (158 ° C.) having an inner diameter of 2 mm 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 Tables 3 and 4. Comparative Example 1
Regarding No. 2, the resin was scattered from the die, and the expansion ratio and the closed cell ratio could not be measured.

[0025]

[Table 3]

[0026]

[Table 4]

Examples 17 to 24, Comparative Examples 13 to 18 Predetermined amounts of low density polyethylene (density 0.921, melt flow rate 2.0 g / 10 shown in Table 5 and Table 6)
Min., Melting point 110.7 ° C.), antioxidant (manufactured by Adeka Argus Chemical Co., Ltd., trade name: Mark328) and talc (manufactured by Nippon Talc Co., Ltd., trade name: MS), and kneaded with a mixing roll at 120 ° C. Then, it was formed into a sheet having a thickness of 2 mm at 120 ° C. by a heating press. The obtained sheet and a predetermined amount of carbon dioxide gas and ethanol containing water were supplied to a pressure vessel (autoclave), and the pressure vessel was heated to 108 ° C.
The pressure was increased to 0 kg / cm ² , left for 1 hour and then released to atmospheric pressure to reduce the pressure, and a sheet-like foam was obtained. Since a shrinkage phenomenon was observed in the obtained foam after several hours, it was held in a space of 20 ° C. for 24 hours as a curing period for recovering the shrinkage, and then its physical properties were measured in the same manner as in Example 1 to obtain the result. Are shown in Tables 5 and 6.

[0028]

[Table 5]

[0029]

[Table 6]

[0030]

As described above, the method for producing a foam of the present invention has a carbon number of 1 including a thermoplastic resin, an inorganic gas and water.
The alcohol of ~ 4 is supplied into the kneading machine, melt-kneaded, and discharged from the kneading machine to foam, so that when foaming, water takes vaporization latent heat from the resin to cool and fix the cell film of bubbles. And a foam having a high expansion ratio can be obtained. At this time, the alcohol mixed with water improves the compatibility between the resin and water, prevents the generation of nonuniform and huge bubbles, and can obtain a foam having uniform and fine bubbles and having an excellent surface condition. In addition, the foaming agent of the present invention has no problem in terms of environment and safety.

As described above, the method for producing a foam of the present invention 2 has a carbon number of 1 including a thermoplastic resin, an inorganic gas and water.
It is characterized in that the alcohols (4) to (4) are supplied into a pressure vessel, heated and pressurized, and then the pressure is reduced to foam, so that the foaming water removes latent heat of vaporization from the resin along with vaporization. By cooling and fixing the cell membrane of bubbles, a foam having a high expansion ratio can be obtained. At this time, the alcohol mixed with water improves the compatibility between the resin and water, prevents the generation of nonuniform and huge bubbles, and can obtain a foam having uniform and fine bubbles and having an excellent surface condition. In addition, the foaming agent of the present invention has no problem in terms of environment and safety.

Claims (2)

[Claims] 1. A kneader is supplied with 100 parts by weight of a thermoplastic resin, 0.5 to 10 parts by weight of an inorganic gas, and 0.1 to 3 parts by weight of an alcohol having 1 to 4 carbon atoms containing 20 to 70% by weight of water. Then, the mixture is melt-kneaded, and discharged from a kneader to foam, thereby producing a foam. 2. A pressure vessel containing 100 parts by weight of a thermoplastic resin, 0.5 to 10 parts by weight of an inorganic gas, and 0.1 to 3 parts by weight of an alcohol having 1 to 4 carbon atoms containing 20 to 70% by weight of water. A method for producing a foam, which comprises supplying, heating and pressurizing, and then reducing the pressure to foam.