JPS6328455B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for foaming thermoplastic resins, and more particularly to a method for producing thermoplastic resin foams using an aqueous medium as a foaming agent.

Conventionally, methods for producing thermoplastic resin foams include melting a thermoplastic foam under pressure together with a thermoplastic resin and a thermally decomposed blowing agent that decomposes to generate nitrogen gas or carbon dioxide, or a low-boiling point liquid or liquefied gas. The method used is to lower the pressure after kneading and foaming. However, in the case of thermally decomposable foaming agents, decomposition residues are generated, causing coloration and bad odor of the resin foam, and it is also difficult to control foaming. On the other hand, when a low boiling point liquid or liquefied gas is used as a blowing agent, there are risks such as flammability, explosiveness, and hygiene of the blowing agent during storage of expandable beads and foams or during the foaming process. There is a problem in handling.

The inventors of the present invention have conducted extensive research into a method for producing thermoplastic resin foams free from the above-mentioned drawbacks, and have found that if an aqueous medium is used in combination with a hydrophilic solid fine powder, thermoplastic resins can be easily produced in an aqueous medium. They discovered that it can be foamed and completed the present invention.

Therefore, according to the present invention, (a) the thermoplastic resin powder is coated with a hydrophilic solid fine powder, and the hydrophilic solid fine powder is substantially at the melting temperature of the resin powder. A porous mass formed by aggregation and mutual fusion of a large number of thermoplastic resin powder particles that do not melt and are partially embedded in an exposed state on the surface of the resin powder particles. (b) treating the resin compound with an aqueous medium so that the aqueous medium adheres to and retains the porous aggregate; (b) pressurizing the resin compound treated with the aqueous medium under pressurizing conditions such that evaporation of the aqueous medium is substantially suppressed; (c) Then, the melt-kneaded resin composition is released from pressurized conditions and foamed.

Since water is a liquid with a relatively low boiling point, it can theoretically be used as a blowing agent for thermoplastic resins.
In general, it is not compatible with hydrophobic resins, and the filler added to the resin is used after drying to remove moisture. Therefore, conventionally, it was completely unthinkable to use water as a foaming agent for resins. However, the fact that this has been made possible by the method of the present invention is completely unexpected from the prior art and is groundbreaking.

According to the method of the present invention, since an aqueous medium having a large latent heat of vaporization is used as a foaming agent, the cell walls are rapidly cooled during foaming due to vaporization of the aqueous medium, and the foam film strength is significantly improved. Therefore, the method of the present invention enables melt extrusion at relatively high temperatures and high speeds, unlike foaming that generates heat, such as with the above-mentioned thermally decomposed foaming agent, and produces high-quality resin foams. can be manufactured with high productivity. Furthermore, the method of the present invention does not produce decomposition residues that color the resin or generate bad odors, unlike thermally decomposable blowing agents, and the aqueous medium used in the present invention is Unlike low-boiling liquids and liquefied gases, it is not flammable, explosive, or sanitary, and is a clean and easy-to-handle blowing agent. Therefore, the method of the present invention is an industrially extremely advantageous method for producing thermoplastic resin foams.

The method of the present invention will be explained in more detail below.

The thermoplastic resin used in the method of the present invention is not particularly limited, and any of those conventionally used in various plastic moldings can be used, such as high-density polyethylene, low-density polyethylene, polypropylene, and polybutene. , olefin resins such as ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, petroleum resin; diene resins such as polybutadiene and polyisoprene; polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, polyvinyl alcohol, etc. Vinyl resins; Acrylic resins such as polymethyl methacrylate; Styrenic resins such as polystyrene, acrylonitrile-styrene copolymers, acrylonitrile-butadiene-styrene copolymers; Polyamides such as nylon-6, -66, -12 Resin: Includes polyester resins such as polyethylene terephthalate. Each of these can be used alone, or two or more kinds can be used in a blend.

On the other hand, the hydrophilic solid fine powder used in combination with the above resin is either hydrophilic itself or consists of an organic or inorganic substance imparted with hydrophilicity by a hydrophilic treatment.

Furthermore, the hydrophilic solid fine powder used in the present invention does not substantially dissolve at the melting temperature of the resin powder used in combination with the hydrophilic solid fine powder, and desirably may swell with an aqueous medium. be selected from those that do not dissolve easily. That is,
Solubility in water is generally less than 10g/at 25℃,
Preferably less than 5 g/g is advantageously used.

Hydrophilic solid fine powders that can be preferably used in the present invention include, for example, shell powder such as starch and wheat flour; plant powder such as wood flour; hydrophilic solid powder such as urea resin, melamine resin, and phenol resin. metal powders such as iron and aluminum; inorganic powders such as talc, clay, calcium carbonate, silica, alumina, and glass powder. These solid fine powders have sufficient hydrophilicity by themselves, but they may also contain substances (hereinafter referred to as surfactants) that make the surface of these fine powders more susceptible to water, such as fatty acids. Nonionic surfactants such as alkanolamides, fatty acid monoglyceroids, polyethylene glycol fatty acid esters; fatty acid amides, fatty acid metal salts,
Anionic surfactants such as alkyl sulfate and alkyl phosphate types; cationic surfactants such as ammonium salts; fatty acids; polyhydric alcohols such as polyethylene glycol, polypropylene glycol, and glycerin; ethers such as polyethylene glycol diethyl ether; Surface treatment with polyvinyl alcohol or a mixture thereof can further increase hydrophilicity and improve affinity between the resin and the fine powder.

Furthermore, even if a substance is hydrophobic, it can be made hydrophilic by surface treatment with a surfactant such as those mentioned above, or a hydrophilic substance such as polyvinyl alcohol, fatty acids, polyhydric alcohols, or ethers. It can be used in the same manner as the hydrophilic substances described above.

The hydrophilic solid fine powders described above can be used alone or in combination of two or more. In the present invention, talc, calcium carbonate, clay, silica, and alumina having an average particle size of 1 to 15 microns are particularly preferably used.

A portion of the above-mentioned hydrophilic solid fine powder, generally up to 20% by weight, preferably 10% by weight or less of the total amount of the solid fine powder used, may be added to, for example, pulp, cotton, silk, etc.
It can also be replaced by organic short fibers such as hemp, wool, synthetic fibers, and recycled fibers, or inorganic short fibers such as glass fibers, carbon fibers, and asbestos.
By using these short fibers in combination, the mechanical strength of the foam can be significantly improved.

The particle size of the hydrophilic solid fine powder used in the present invention is not strictly limited, and can be varied widely depending on the desired degree of foaming, type of resin, physical properties required of the foam, etc. However, it is generally appropriate that the average particle size is 100 microns or less, preferably in the range of 0.1 to 50 microns, and more preferably in the range of 0.5 to 30 microns. In addition, when using short fibers as described above, the fiber length is generally 10 mm or less, preferably 5 mm or less, and
The fiber diameter is generally less than 100 microns, preferably 1
A range of ˜50 microns is preferred.

From the thermoplastic resin and the hydrophilic solid fine powder described above, a thermoplastic resin powder coated with the hydrophilic solid fine powder (hereinafter sometimes referred to as "composite resin powder") is prepared. When doing so, it is important that the solid fine powder is attached and buried in an exposed state on the surface of the resin powder (however, of course, the resin powder also has the solid fine powder inside it). (may contain powder dispersed). The amount of solid fine powder adhered to and embedded in the resin powder particles is determined by the fact that most of the surface of each resin powder particle is covered with the exposed solid fine powder, and when observed with an electron microscope at a magnification of 300 times, the resin powder is It is desirable that the amount be such that the base of the grains is hardly visible.

Furthermore, it was found that a large number of the resin particles coated with the exposed hydrophilic solid fine powder aggregated, and the individual particles partially fused to each other to form a porous mass. is important. When such a porous aggregate is treated with an aqueous medium, it must be capable of stably adhering and retaining the aqueous medium, and therefore, the porous aggregate must have a water vapor adsorption rate of at least 0.05%, preferably 0.3%. It is highly desirable that this is the case.
Here, "water vapor adsorption rate" means that a porous aggregate of ₁ g of W after being kept in a constant temperature and humidity chamber at a temperature of 25 °C, a relative humidity of 30%, and a pressure of 1 atm for 24 hours has a temperature of 105 °C,
After keeping it in a closed atmosphere with a water vapor pressure of 1.2 atm for 1 hour, take it out and leave it on paper for 3 minutes, then
When placed in a drying oven at 105°C for 3 minutes and immediately weighed, the amount is defined as W ₂ g. This is the value calculated using the following formula.

Water vapor adsorption rate (%) = W ₂ − W ₁ /W ₁ ×100 The size of the above porous aggregate is not important and can be any size, but it is easy to handle and melt-knead as described below. From the perspective of
A particle size range of 0.1 to 20 mm, preferably 0.3 to 5 mm is suitable. Therefore, if the particle size is larger than this, it is preferable to use a pulverizer, mixer, etc. to reduce the particle size to the above range.

One effective method for preparing such porous aggregates is to mix the thermoplastic resin and hydrophilic solid fine powder described above using a high-speed (vortex) mixer, such as a Henschel mixer (manufactured by Mitsui Miike Manufacturing Co., Ltd.), a super This is a method of high-speed mixing at a temperature higher than the melting temperature of the thermoplastic resin in a mixer (manufactured by Kawada Seisakusho) or the like. This high-speed mixing generally begins at a point where the motor's rotational resistance fluctuates and increases from about 50 to about
It lasts for 250 seconds, preferably from about 70 to about 200 seconds, after which time the melt-mixed resin composition is discharged from the mixer. This results in a porous mass.

The ratio of the hydrophilic solid fine powder to the thermoplastic resin when charged into the above-mentioned mixing mixer depends on the type of resin and solid fine powder, the water absorption rate and water vapor adsorption rate required for the resulting porous aggregate, etc. Although it can vary widely depending on the situation, in general, the solid fine powder is used in an amount of 30 to 250 parts by weight, preferably 60 to 150 parts by weight, and more preferably 80 to 120 parts by weight per 100 parts by weight of the thermoplastic resin. They can be used alone or in a mixture of two or more. As mentioned above, when a part of the solid fine powder is replaced by a fibrous substance, it is appropriate that the fibrous substance accounts for 20% by weight or less, preferably 10% by weight or less of the total solid fine powder. .

In addition, when preparing the above-mentioned porous aggregate, in addition to the resin and solid fine powder, resin additives such as antioxidants, surfactants, colorants, ultraviolet absorbers, flame retardants, etc. may be added as necessary. . Examples of antioxidants that can be used include thiopropionic acid ester antioxidants such as dilauryl thiodipropionate; phenolic antioxidants such as alkylphenols and alkylbisphenols; or mixtures thereof. Examples of the surfactant include those mentioned above. The antioxidant is usually used as a solid fine powder in an amount of 0.01 to 5 parts by weight per 100 parts by weight, and the surfactant is used as a solid fine powder in an amount of 0.01 to 5 parts by weight per 100 parts by weight.
It can generally be blended in a proportion of 0.1 to 10 parts by weight per part by weight. In addition, examples of colorants include dyes and pigments such as cadmium red, chrome orange, chrome yellow, chrome green, cobalt aluminate blue, titania, phthalocyanine blue, and azo dyes, and examples of ultraviolet absorbers include salicylic acid, Examples include benzophenone-based and benzotriazole-based ultraviolet absorbers, and examples of flame retardants include phosphoric acid esters, halogenated hydrocarbons, antimony oxide, etc., which have been conventionally used as resin additives in normal amounts. Can be blended.

The porous mass thus prepared is used as is as a resin compound and treated with an aqueous medium as blowing agent according to the method of the invention.

Water is generally used as the aqueous medium, which can be used to adjust the boiling point and vapor pressure of the medium, increase affinity for the porous aggregates, improve the dispersion stability of the aqueous medium during melt-kneading of resin compounds, and create bubbles. For the purpose of improving the uniformity of the water, surfactants, water-soluble polymers, polyhydric alcohols, water-miscible organic solvents, etc. can be appropriately added to the water. As the surfactant, those mentioned above can be used, and these can be added in a concentration of generally 0.1 to 50 g/, preferably 1 to 10 g/to water. Examples of water-soluble polymers and polyhydric alcohols include polyvinyl alcohol with a degree of polymerization of about 500 to about 2000 and a degree of saponification of 85% or more, mono- or polyethylene glycol with a number average molecular weight of up to 400, glycerin, etc. are included, and these generally range from 1 to
It can be added at a concentration of 100g/, preferably 10-50g/. Further, water-miscible organic solvents that can be used include, for example, alcohols such as methanol, ethanol, propanol, and cyclohexanol; esters such as ethyl acetate and butyl acetate; ethers such as diethyl ether, dioxane, and trioxane; acetone, Examples include ketones such as methyl ethyl ketone, which can be blended in a concentration of generally 1 to 100 g/, preferably 10 to 50 g/to water.

The amount of the aqueous medium mentioned above can be varied over a wide range depending on the desired expansion ratio of the foam, but is generally 1 to 15 parts by weight, preferably 1 to 15 parts by weight, per 100 parts by weight of the porous aggregate. may be 2 to 5 parts by weight. Treatment of the resin compound with an aqueous medium can be carried out by combining the two and mixing in a mixer.

The resin compound treated with the aqueous medium as described above is then melt-kneaded under pressurized conditions in which evaporation of the aqueous medium is substantially suppressed. This melt-kneading can be carried out in the same manner as melt-kneading during the production of ordinary resin foams, and can be carried out using an extruder such as a non-vented single-screw extruder or a non-vented multi-screw extruder. . Here, "pressurized conditions under which evaporation of the aqueous medium is substantially suppressed" refers to pressure conditions higher than the vapor pressure of the aqueous medium impregnated in the resin compound at the melt-kneading temperature. The operation of the extruder is not special and can be carried out by a method known per se.

The resin composition sufficiently melted and kneaded in this way is
Extrude it through die lips of various shapes in the molten state, or
The mixture is injected into a suitable mold or placed in a press molding machine, released from the pressurized state, and foamed and solidified. As a result, resin foams processed into shapes such as corrugated sheets, flat sheets, stretched sheets, and irregular extrudates are obtained.

According to the method of the present invention described above, there are various advantages as described below compared to conventional methods for manufacturing resin foams.

(a) Conventionally, it was considered technically difficult to industrially foam polyolefin resins such as polyethylene and polypropylene to a high degree, but according to the present invention, even non-crosslinked polyolefin resins can be easily and uniformly foamed at high expansion ratios. It can be made into a foam with a fine closed cell structure.

(b) Conventionally, it was virtually impossible to produce resin foam containing a large amount of filler;
According to the method of the present invention, a resin foam containing a large amount of filler can be easily produced industrially.

(c) According to the method of the present invention, resin can be melt-extruded at a higher temperature and higher speed than conventional methods, so high-quality resin foam can be manufactured with high productivity.

(d) According to the method of the present invention, since an aqueous medium with a large latent heat of vaporization is used as a foaming agent, as mentioned above, the foaming film force is significantly increased and it is difficult to form fine and uniform closed cells. can.

(e) Unlike conventional thermally decomposable blowing agents, no decomposition residue is produced, and the resin does not become colored or generate bad odors. Additionally, unlike conventional low-boiling liquids and liquefied gases, it is not flammable, explosive, or sanitary.

(f) The foaming operation is not complicated, the equipment used is simple, and resin foams can be produced at low cost.

(g) Easy to control foaming, ranging from small foaming ratios to large foaming ratios (approximately 2 volume ratios)
(from 30 times to about 30 times) can be made freely.

(h) Furthermore, according to the method of the present invention, a resin foam having a skin layer can be easily produced.

The method of the present invention will now be further illustrated by examples.

Example 1 Blending amount Kg g Resin: Polypropylene (Noblen manufactured by Mitsubishi Yuka Co., Ltd.
MA-8A; M1=0.7, density=0.9) 10000 Fine powder: Talc (MS made by Nippon Talc Co., Ltd.; average particle size 9μ) 10000 Surfactant: Fatty acid alkanolamide (Amizole LDE made by Kawaken Fine Chemical Co., Ltd.) 100 Fatty acid Monoglyceroid (Rikemar S-100 manufactured by Riken Vitamin Co., Ltd.) 50 Fatty acid amide (Alflo P- manufactured by Nippon Oil & Fats Co., Ltd.)
10) 50 Colorant: Titanium oxide (anatase type, A100 manufactured by Ishihara Sangyo Co., Ltd.) 500 Antioxidant: Dilaurylthiodipropionate 30 1,1,3-Tris(2-methyl-4-hydroxy-5-t- Butyl phenyl) butane 10 Using a high-speed mixing mixer (Kawada Seisakusho Super Mixer SMG100 mixing motor 22KW 4P/8P), the mixing tank (tank capacity 100) was heated by circulating heated oil at 140° to 150°C through the jacket. In addition, all the above formulations were put into the mixing tank of the mixer and mixed at high speed.

After about 20 minutes, the current of the mixing motor began to fluctuate and increase (mixture temperature: 195℃). After 80 seconds, it suddenly increased and reached 80A (mixture temperature: 210℃) in 40 seconds (120 seconds in total), so the discharge port was opened to release the mixture.

The discharged mixture is rapidly cooled and coarsely crushed by a low-speed rotating mixer with strong air cooling to produce a resin compound consisting of partially fused porous aggregates of resin powder coated with fine powder. Obtained.

Next, a crusher (TC-3 type 3 manufactured by Morita Seisakusho)
Grind to a maximum particle size of 5 mm or less at 50 to 300 r.pm.
Transfer to a mixing rotary mixer and add an aqueous medium of 500 c.c. (2.5 parts by weight based on 100 parts by weight of resin compound) of tap water containing 1% alkylbenzene sulfonate (Nitsun Yurex H manufactured by NOF Corporation). The mixture was added and mixed for 5 minutes or more to obtain a resin compound impregnated with an aqueous medium.

A circular die is attached to the 70 mm extruder, and air rings are installed inside and outside the die lip to cool the tip of the die lip and the produced sheet.The blow ratio of the circular die/mandrel is set to 1.8 times, and the mandrel circulates cooling hot water to cool the outer periphery. This is a device that cools with a ring, pulls it up while stretching it, cuts it, and obtains a sheet using a puller/winder.The maximum temperature of the extruder cylinder is 225℃, the die temperature is 195℃ (resin temperature 198℃),
The resin compound impregnated with the above aqueous medium at a die lip of 190°C and a mandrel warm water of 90°C was foamed and extruded to form a film.

Resin foam made from this aqueous medium has a thin skin layer on the surface, has a closed cell structure with no bubble breakage, and is a homogeneous foam with a foam diameter of 0.5 mm or less, often 0.1 to 0.3 mm, and the foaming ratio (volume, magnification) is It was 9.8 times higher.

This foamed sheet is preferably vacuum-formed or pressure-formed for use in food packaging containers such as trays, and is also used in the fields of cushioning materials and white paperboard.

Example 2 Blend amount Kg g Resin: Low density polyethylene (Novatek LF101A manufactured by Mitsubishi Kasei Corporation; MI = 0.45, density = 0.922) 10000 Fine powder: Ground calcium carbonate (Whiten SSB manufactured by Shiraishi Calcium Co., Ltd.; average particle size 1.5μ ) 3000 Heavy calcium carbonate (Whiten B manufactured by Shiraishi Calcium Co., Ltd.; average particle size 3.6μ) 7000 Surfactant: Fatty acid alkanolamide (Amizole CDE manufactured by Kawaken Fine Chemicals Co., Ltd.) 120 Polyethylene glycol (manufactured by Sanyo Chemical Co., Ltd.)
PEG6000) 60 Coloring agent: Titanium oxide (anatase type, A100 manufactured by Ishihara Sangyo Co., Ltd.) 300 Cobalt aluminate blue (manufactured by Dainichiseika Chemical Co., Ltd.)
0.1 Antioxidants: dilauryl thiodipropionate 10 22'-methylenebis(4-methyl-6-tert-butylphenol) 20 nonylphenyl phosphite 10 All formulations were prepared using the same high speed mixer as in Example 1. was added and mixed at high speed. After about 16 minutes, the current of the mixing motor started to fluctuate and increase slightly (mixture temperature: 190℃), and after 120 seconds, it suddenly increased and reached 50A (mixture temperature: 200℃) in 5 to 10 seconds (total of 125 to 130 seconds). So I opened the outlet and released the mixture.

The discharged mixture is rapidly cooled and coarsely crushed by a low-speed rotating mixer with strong air cooling to produce a resin compound consisting of partially fused porous aggregates of resin powder coated with fine powder. Obtained.

Next, a crusher (Morita Seisakusho Tc-3 type 3)
Grind to a maximum particle size of 5 mm or less, transfer to a mixer with a mixing rotation of 50 to 300 rpm, add an aqueous medium of 700 c.c. of tap water (3.5 parts by weight based on 100 parts by weight of resin compound), and mix for 10 minutes. A resin compound impregnated with an aqueous medium was obtained.

A T-die is attached to a 50mm extruder, and air knives are installed on both sides of the die lip to cool the tip of the die lip and the produced sheet, and then roll it up while stretching it.
Extruder cylinder maximum temperature 205℃, die temperature 170℃
(resin temperature 175°C), was rapidly cooled with an air knife at a die lip of 160°C, stretched and taken off, and the resin compound impregnated with the aqueous medium was foamed and extruded to form a corrugated foamed film.

The resin foam made from this aqueous medium is stretched into a corrugated foam sheet and has a directional closed-cell structure, with a foam diameter of 0.8 mm or less, and in most cases homogeneous foam with a diameter of around 0.5 mm. The magnification) was 16x.

This foam sheet was suitable as a flexible cushioning material.

Example 3 Blending amount Kg g Resin: Acrylic-butadiene-styrene copolymer (JSR ABS85 manufactured by Japan Synthetic Rubber Co., Ltd.; Specific gravity =
1.05, MI=1.7) 10000 Fine powder: Heavy calcium carbonate (Whiten SB manufactured by Shiraishi Calcium Co., Ltd.; average particle size 1.8μ) 8000 Wood flour (dry fine powder, particle size 100M/S pass) 500 Surfactant: Fatty acid alkanolamide (Amizole LDE manufactured by Kawaken Fine Chemical Co., Ltd.) 150 Fatty acid amide (Alflo P- manufactured by Nippon Oil & Fats Co., Ltd.)
10) 50 Glycerin 100 Colorant: Ceramic Yellow 100 Antioxidant: Distearylthiopropionate 10 2,6-di-t-butyl p-cresol 10 Using the same high-speed mixer as in Example 1, add the entire formulation. and mixed at high speed.

After about 18 minutes, the current of the mixing motor started to fluctuate and increase slightly (mixture temperature 220℃) After 160 seconds, it suddenly increased and reached 50A (mixture temperature 240℃) in 20-25 seconds (total 180-185 seconds). So I opened the outlet and released the mixture.

The discharged mixture is rapidly cooled and coarsely crushed by a low-speed rotating mixer with strong air cooling to produce a resin compound consisting of partially fused porous aggregates of resin powder coated with fine powder. Obtained.

Next, it was crushed to a maximum particle size of 5 mm or less using a crusher (Tc-3 type 3P manufactured by Morita Manufacturing Co., Ltd.), transferred to a mixer with a mixing rotation of 50 to 300 rpm, and polyoxyethylene fatty acid amine (Amit 308 manufactured by Kao Soap Co., Ltd.) 1 % of ion-exchange resin treated water (approximately 2.5 parts by weight based on 100 parts by weight of the resin compound) was added and mixed for more than 10 minutes to obtain a resin compound impregnated with an aqueous medium.

A 50mm extruder is equipped with an odd-shaped (thick plate-like) mold and a cooling sizing die, and is equipped with a take-off machine.The maximum temperature of the extrusion cylinder is 260℃, the die temperature is 210℃, and the cooling water is circulated through the sizing die and taken out. The resin compound impregnated with an aqueous medium was foamed and extruded.

This resin plate-like foam made from an aqueous medium constituted a skin layer, had a smooth surface, had a closed cell structure, had a foam diameter of 0.6 mm or less, and had a foaming ratio of 7.5 times.

This foamed plank material is suitable for use as synthetic wood and has excellent workability.

Example 4 Blend amount Kg g Resin: High impact polystyrene (Dialex HI-516 manufactured by Mitsubishi Monsanto; MI=2.2,
Density = 1.05) 10000 Fine powder: Talc (MS manufactured by Nippon Talc Co., Ltd.; average particle size 9 μ) 3000 Starch (constarch manufactured by Aito Co., Ltd.) 500 Surfactant: Monoethylene glycol 50 Alkylbenzene sulfonate (Nitsun Niurex manufactured by Nippon Oil & Fats Co., Ltd.) H) 10 Coloring agent: Titanium oxide [anatase type, A100 manufactured by Ishihara Sangyo Co., Ltd.] 500 Antioxidant: dilauryl thiodipropionate 10 2,6-di-t-butyl p-cresol 10 High-speed mixing mixer as in Example 1 Using a machine, ingredients other than the resin were added, the mixture was rotated at high speed, and after 6 minutes, the resin was added. After 21 minutes from the beginning, the current of the mixing motor fluctuated wildly and started to increase slightly (mixture temperature 205
°C), after 120 seconds, the temperature rises rapidly for 5 to 10 seconds (total 125 to 130
When the temperature reached 50A (mixture temperature 210°C), the outlet was opened and the mixture was discharged.

The discharged mixture is rapidly cooled and coarsely crushed by a low-speed rotating mixer with strong air cooling to produce a resin compound consisting of partially fused porous aggregates of resin powder coated with fine powder. Obtained.

Next, a crusher (Morita Seisakusho Tc-3 type 3)
Grind to a maximum particle size of 5 mm or less with They were mixed to form a resin compound impregnated with an aqueous medium.

Using the same 70 mm extruder as in Example 1 to obtain a sheet, the resin compound impregnated with the above aqueous medium was foamed and extruded to form a film at an extrusion cylinder maximum temperature of 210°C, die temperature of 190°C (resin temperature of 192°C), and die lip of 180°C. did.

The resin foam made from this aqueous medium has a smooth closed cell structure with relatively thick cell walls, although bubble breakage is observed on the surface, and the cell size is homogeneous with a cell diameter of 0.4 mm or less, and the foaming ratio (volume ratio) was 10.5 times higher.

This foamed sheet is preferably vacuum-formed or pressure-formed and used for food containers such as trays.

Example 5 Blend amount Kg g Resin: Ethylene-vinyl acetate copolymer (Mitsubishi Yuka Co., Ltd. Yucalon Eva EVA20F; MI = 2; Density = 0.93) 10000 Fine powder: Heavy calcium carbonate (Shiraishi Calcium Co., Ltd. Whiten SB; average Particle size: 1.8μ) 12000 Pulp powder (Sanyo Kokusaku Pulp Co., Ltd. KC Flot; W200; particle size 200M/S pass) 500 Surfactant: Fatty acid alkanolamide (Kawaken Fine Chemical Co., Ltd. Amizole CDE) 150 Fatty acid monoglyceroid ( Manufactured by Riken Vitamin Co., Ltd.
Rikemar S-100) 50 Calcium stearate (manufactured by Toa Rika Co., Ltd.) 100 Colorant: Titanium oxide (anatase type, manufactured by Ishihara Sangyo Co., Ltd. A100) 500 Antioxidant: Pentaerythol tetrakis (β
- lauryl thiopropionate) 20 Hindered phenolic antioxidant 10 Using the same high-speed mixer as in Example 1, ingredients other than the resin were added, the mixer was rotated at high speed, and after 8 minutes, the resin was added. After 2 minutes from the beginning, the current of the mixing motor fluctuated wildly and started to increase slightly (mixture temperature 185
°C), after 160 seconds, the temperature rises rapidly for 20-25 seconds (total 180-185
When the temperature reached 50A (mixture temperature 195°C), the outlet was opened and the mixture was discharged.

The discharged mixture is rapidly cooled and coarsely crushed by a low-speed rotating mixer with strong air cooling to produce a resin compound consisting of partially fused porous aggregates of resin powder coated with fine powder. Obtained.

Next, a crusher (Morita Seisakusho Tc-3 type 3)
Grind to a maximum particle size of 5 mm or less, transfer to a mixer with a mixing rotation of 50 to 300 rpm, and heat-melt 2% polyvinyl alcohol (manufactured by Kuraray Co., Ltd.) in tap water 675 c.c. (approx. (parts by weight) of an aqueous medium was added and mixed for 5 minutes to obtain a resin compound impregnated with an aqueous medium.

A T-die is attached to a 50mm extruder, and air knives are installed on both sides of the die lip to cool and stretch the die lip tip and the produced sheet while winding it up.The extruder cylinder maximum temperature is 200℃ and the die temperature is 170℃.
(resin temperature 170°C), was rapidly cooled with an air knife at a die lip of 165°C, stretched and taken off, and the resin compound impregnated with the aqueous medium was foamed and extruded to form a corrugated foamed film.

Resin foam made from this aqueous medium is stretched into a corrugated foam sheet and has a directional closed cell structure.The foam diameter is homogeneous with a large diameter of 0.7 mm or less, often around 0.5 mm, and a foaming ratio (volume). The magnification) was 12.5 times.

This foam sheet is flexible and elastic and is suitable as a cushioning material.

Claims (1)

[Claims] 1 (a) It consists of a thermoplastic resin powder coated with a hydrophilic solid fine powder, in which case the hydrophilic solid fine powder is substantially melted at the melting temperature of the resin powder. A resin compound consisting of a porous mass formed by aggregation and mutual fusion of a large number of thermoplastic resin powder particles that are partially embedded in an exposed state on the surface of the resin powder particles. (b) treating the resin compound with the aqueous medium under pressurized conditions in which evaporation of the aqueous medium is substantially suppressed; 1. A method for producing a resin foam using an aqueous medium, comprising: (c) melt-kneading the resin composition, and then releasing the melt-kneaded resin composition from pressurized conditions to foam it.