JP2001206968A - Thermoplastic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic resin foam excellent in thickness and density accuracies. SOLUTION: This foam is produced while keeping the amount of the added foaming agent based on that of the thermoplastic resin constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a thermoplastic resin foam. More specifically, a thermoplastic resin foam obtained by adding and mixing a foaming agent to a thermoplastic resin, and extruding and foaming, wherein the variation rate of the thickness of the foam in the extrusion direction is ± 10% or less, The present invention also relates to a thermoplastic resin foam having a rate of change in density in the extrusion direction of ± 10% or less. Since the foam obtained by the present invention has excellent thickness accuracy and density accuracy, it has good moldability when the foam is subjected to secondary molding, and is suitably used, for example, in a molded container.

[0002]

2. Description of the Related Art A foam made of a thermoplastic resin represented by a polyolefin resin, a polyester resin, etc.
Due to its excellent heat insulation, cushioning, and sealing properties,
Widely used in various fields. Particularly in recent years, in addition to the conventional foam trays for selling fish and meat, a large number of bento boxes and cooked foods have been sold at convenience stores and supermarkets due to changes in lifestyles. The molded product obtained by the subsequent molding is used as the container.

[0003] In addition to the above food containers, when the foam is subjected to secondary molding such as vacuum pressure molding, it is required that the foam have a uniform thickness and density. In recent years, molded articles made of a thermoplastic resin have been widely used as electric circuit boards, insulating materials, and the like in the electronic and communication industries. These are required to have high strength and high heat resistance, such as adhesiveness or plating property, and solder heat resistance. Therefore, resins having excellent heat resistance called engineering plastics and super engineering plastics are used.

In these fields, since the frequency band used is in the high frequency range, it is important to reduce the loss of transmission energy, and a material having a small relative dielectric constant and a small dielectric loss tangent is desired. Introducing bubbles into it,
That is, an attempt has been made to reduce the relative dielectric constant and the dielectric loss tangent by using a foam. In such applications, dimensional accuracy is required when assembling or using at high temperatures.
It is required that the density and thickness of the foam be uniform.

In addition, impact resistance, abrasion resistance, chemical resistance,
Special polyolefin resins such as high molecular weight polyolefin resins and cyclic polyolefin resins are used in various fields because of their excellent properties such as lubricity. From the viewpoint, use as a foam has been widely studied, and it is also required that the density and the thickness be uniform.

[0006] In the width direction of the foam (the direction orthogonal to the extrusion direction), it is relatively easy and uniform to adjust the opening degree of the die lip.
Regarding the extrusion direction, it is necessary to keep the amount of the foaming agent added to the thermoplastic resin constant, so that it is difficult.

The chemical foaming method, which is one of the typical methods for producing these thermoplastic resin foams, generally involves mixing a raw material with a low-molecular-weight chemical foaming agent that decomposes at a molding temperature to generate a gas. And foaming by heating the foaming agent to a temperature higher than the decomposition temperature of the foaming agent. In this method, the generation of gas is sharp with respect to the decomposition temperature, the decomposition temperature can be easily adjusted by adding a foaming aid or the like, and a foam having closed cells can be obtained.

[0008] However, these foams are expensive due to the use of a special foaming agent, and in addition to discoloration of the foam due to the decomposition residue of the foaming agent remaining in the foam,
It causes odor and food hygiene problems. In addition, contamination of the molding machine due to the chemical foaming agent and molding defects associated therewith are also problematic. For example, a decomposition residue called so-called grease adheres to the die lip, so that a line is formed on the foam sheet surface. However, there is a problem in that the appearance of defective appearance occurs, and there is a problem that production is interrupted every several hours and a cleaning operation is required, which is very disadvantageous economically.

In general, since a chemical foaming agent itself has a particle size distribution, it is always mixed with a raw material such as resin pellets and classified when it is put into an extruder. It was very difficult to keep adding the amount. Therefore, the thickness and density of the resin sheet discharged from the die are not constant, and the molded product obtained by performing secondary molding of the sheet has an uneven thickness, or the molded product is continuously formed under a constant condition. In some cases, problems such as difficulty in obtaining them may occur, and there is a need for a method for solving these problems.

On the other hand, the gas foaming method, which is a physical foaming method,
Where the resin is melted by the molding machine, butane, pentane,
In this method, a low-boiling organic compound such as dichlorodifluoromethane is supplied, kneaded, and then discharged into a low-pressure region to foam and mold. The low-boiling organic compound used in this method is excellent in solubility because it has an affinity for the resin,
In addition, since it has excellent foam retention, it can be added to a resin in a desired amount, so that various types of foams can be obtained from low magnification to high magnification. .

[0011] However, these foaming agents have a risk of flammability and toxicity in addition to an increase in cost, and flammability is a problem. There is also a secondary problem that the gas must be cured for a certain period of time until the gas concentration decreases.
In addition, CFC-based gases such as dichlorodifluoromethane have been abolished due to environmental problems caused by ozone layer depletion, and will not be used in the production of foams in the near future, including alternative CFCs. In order to solve such problems of the conventional physical foaming method, many methods using a clean and inexpensive inert gas such as carbon dioxide and nitrogen as a foaming agent have been proposed.

These inert gases are free from the danger and environmental load of the low-boiling organic compounds described above.
No excessive safety measures are required on the equipment,
It is possible to open to the atmosphere even if there is no equipment or process such as removal. In addition, economic effects are remarkable, for example, the product curing period after production and curing equipment are not required.

However, a method of stably adding an inert gas into a molding machine has not been established, and as in the case of production by chemical foaming, uneven foaming is likely to occur in the product, and the foam is continuously and uniformly produced. It was difficult to produce.
If stable addition is not possible, the thickness and density of the manufactured foam will fluctuate without showing constant values, and the incidence of non-standard defective products will increase, making it unsuitable for industrial production. Means no. Therefore, it has been considered that a foam production method using an inert gas is not suitable for industrial production in applications requiring density accuracy and thickness accuracy. That is, in the conventional chemical foaming method, the width of the expansion ratio of a thermoplastic resin foam that can be produced is narrow, and even if a known method for producing a foam using an inert gas is applied, the thermoplastic resin foam can be produced. It must be said that it is difficult to produce a film having a constant thickness and density.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to provide a thermoplastic resin foam excellent in thickness accuracy and density accuracy.

[0015]

Means for Solving the Problems The present inventors have conducted intensive studies on a thermoplastic resin foam having excellent thickness accuracy and density accuracy in the extrusion direction, and have reached the present invention. That is, the present invention includes the following inventions and embodiments.

(A) A foam obtained by adding a foaming agent to a thermoplastic resin and extruding and foaming the foam has a thickness variation in the extrusion direction of ± 10% or less and a density variation in the extrusion direction. Is less than ± 10%.

(B) The thermoplastic resin foam according to (A), wherein the thermoplastic resin is a composition comprising one or more of a polyolefin resin and a polyester resin.

(C) The thermoplastic resin foam according to (A), wherein the thermoplastic resin is a composition comprising one or more of engineering plastics and super engineering plastics.

(D) The thermoplastic resin foam according to (A), wherein the thermoplastic resin is a composition comprising one or more special polyolefin resins.

(E) The thermoplastic resin foam according to any one of (A) to (D), wherein the blowing agent is carbon dioxide.

(F) The thermoplastic resin foam according to any one of (A) to (E), wherein the blowing agent is carbon dioxide in a supercritical state.

(G) A molded container comprising the thermoplastic resin foam according to any one of (A) to (F).

(H) The thermoplastic resin foam according to (E) or (F), wherein the variation in the amount of addition of carbon dioxide as a blowing agent is ± 2% or less. Production method.

(I) As a method of adding carbon dioxide as a foaming agent, carbon dioxide is injected into a metering pump while maintaining the liquid state, and the discharge pressure of the metering pump is changed from the critical pressure of carbon dioxide (7.4 MPa) to 40 MPa. The pressure is controlled by the pressure-holding valve (3) so as to maintain a constant pressure within the range described above, and then the temperature is raised to the critical temperature of carbon dioxide (31 ° C.) or more to form supercritical carbon dioxide, which is then added to the molten thermoplastic resin. (H) The method for producing a thermoplastic resin foam according to (H).

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION In the present specification, the thermoplastic resin includes a thermoplastic resin to which a pyrolytic foaming agent, an aliphatic carboxylic acid and its derivative, an inorganic fine powder and the like which are added as necessary are added. Further, in the present specification, the molten thermoplastic resin composition means a state in which a foaming agent and a molten thermoplastic resin are uniformly mixed.

The thermoplastic resin used as a raw material of the thermoplastic resin foam of the present invention is not particularly limited, and any resin can be used as long as it can be melted by heating in an extruder. Yes, for example, various elastomers,
Styrene resin (for example, polystyrene, butadiene / styrene copolymer, acrylonitrile / styrene copolymer, acrylonitrile / butadiene / styrene copolymer, etc.), ABS resin, high density polyethylene, low density polyethylene, linear low density Polyethylene, polypropylene,
Ethylene-propylene resin, ethylene-ethyl acrylate resin, ethylene-methacrylate resin, ionomer, polyolefin resin such as polybutene, ultrahigh molecular weight polyethylene resin, ultrahigh molecular weight polypropylene resin,
-Methyl-pentene-1 resin, special polyolefin resin such as cyclic polyolefin resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polymethyl methacrylate, saturated polyester resin (for example, polyethylene terephthalate, polybutylene terephthalate, etc.), raw Degradable polyester resins (for example, condensates of hydroxycarboxylic acids such as polylactic acid, condensates of diols and dicarboxylic acids such as polybutylene succinate), further, polycarbonates, polyacetals, polyphenylene oxides, polyamide resins, polyamideimide resins , Polyetherimide resin, polyimide resin,
Fluororesins, polysulfones, polyethersulfones, polyarylates, polyetheretherketones, engineering plastics such as liquid crystal polymers, super engineering plastics, etc., one or a mixture of two or more thereof, and modified products thereof, and the like. All commercially available resins are included.

When the thermoplastic resin foam is formed into a food container or the like by secondary molding, a polyolefin resin or a polyester resin is preferable from the viewpoint of heat resistance, heat insulation and cost. In the case where high heat resistance is required, such as an electric board, engineering plastics and super engineering plastics are preferable. The thermoplastic resin melt flow rate (ASTMD-
1238) is not particularly limited, but is 0.01 to 50.
g / 10 minutes, particularly preferably in the range of 0.1 to 30 g / 10 minutes.

When the melt flow rate is 0.01 g / 10 min or more, the heat generated by shearing during foam extrusion is not excessive, and a predetermined expansion ratio can be obtained. In addition, there is no problem that the surface appearance is deteriorated because the surface is broken. When the melt flow rate is 50 g / 10 minutes or less, the resin has sufficient viscosity at the time of melting, so that the foaming agent can be retained and a predetermined magnification can be obtained. Also, there is no problem such as low toughness of the obtained foam. The foaming agent that can be used in the present invention is not particularly limited, and any of a chemical foaming agent and a physical foaming agent can be suitably used, but from the viewpoint of easily producing a wide range of foams from low foaming to high foaming. Is more preferably a physical foaming agent.

Examples of the chemical foaming agent include ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium nitrite, azodicarbonamide, azobissulfonium amide, azobisisobutyronitrile, diazoaminobenzene, N, N'- Dinitrosopentanemethylenetetramine, N, N'-dimethyl-N, N'-dinitrosoterephthalamide, benzenesulfonium hydrazide, p-toluenesulfonium hydrazide, p, p'-
Oxybisbenzenesulfonium semicarbazide, p-
Examples include toluenesulfonium semicarbazide, trihydrazinotriazine, barium azodicarboxylate and the like. These foaming agents can be used alone or in combination.

In addition to these foaming agents, the use of known foaming aids for controlling the decomposition temperature, the amount of generated gas and the decomposition rate is not limited.

As physical blowing agents, carbon dioxide, nitrogen,
Argon, propane, normal butane, isobutane, pentane, normal hexane, isohexane, heptane,
Isoheptane, diethyl ether, dimethyl ether,
Examples include petroleum ether, acetone, benzene, and toluene. These foaming agents can be used alone or in combination. As these physical foaming agents, use of carbon dioxide alone or a mixture of two or more kinds mainly containing carbon dioxide is preferable, and use of carbon dioxide alone is particularly preferable.

The amount of the foaming agent to be added is not particularly limited and can be appropriately selected according to the expansion ratio of the foam to be produced. -30 parts by weight, preferably 0.05
To 20 parts by weight, more preferably 0.1 to 10 parts by weight.

When the amount of the foaming agent is 0.01 to 30 parts by weight, a sufficient foaming ratio can be obtained while having an excellent surface appearance. Further, when a physical foaming agent, particularly carbon dioxide, is used, it is preferable that a supercritical state is formed inside the molding machine from the viewpoints of solubility, permeability, diffusibility and the like in the molten thermoplastic resin.

The method of adding the physical blowing agent to the molten thermoplastic resin is not particularly limited. For example, a method of injecting a gaseous blowing agent directly or under pressure, a method of adding a foaming agent in a liquid state to a plunger There is a method of adding with a pump or the like. In particular, when carbon dioxide is used as a foaming agent, as shown in FIG. 1, for example, carbon dioxide is injected from a liquefied carbon dioxide cylinder (1) into a metering pump (2) while maintaining the liquid state, and the metering pump is used. The discharge pressure of (2) is controlled by the pressure-holding valve (3) so as to be constant within the range of the critical pressure of carbon dioxide (7.4 MPa) to 40 MPa, and then discharged. In this case, a method in which the temperature is raised to supercritical carbon dioxide and then added to the molten thermoplastic resin is suitably used.

In the present invention, when a physical foaming agent is used as a foaming agent, one or more of the aforementioned chemical foaming agents can be used in combination with a physical foaming agent as a foam nucleating agent for uniform foaming. It is. When a chemical foaming agent is used as the foam nucleating agent, the amount used is 0.01 to 0.5 part by weight, preferably 0.01 to 0.5 part by weight, per 100 parts by weight of the thermoplastic resin.
It is preferably 0.4 parts by weight, more preferably 0.2 to 0.6 parts by weight. When the physical foaming agent and the chemical foaming agent are used in combination, it becomes easier to make the thickness and density of the obtained foam uniform.

One or more of various additives can be added to the thermoplastic resin used in the present invention in order to improve the surface appearance of the obtained foam without breaking the foam. As these additives, known ones used in ordinary foam molding can be used. For example, aliphatic carboxylic acids and derivatives thereof are preferably used.

The aliphatic carboxylic acids and derivatives thereof include aliphatic carboxylic acids, acid anhydrides, alkali metal salts,
Alkaline earth metal salts and the like. As the aliphatic carboxylic acid, an aliphatic carboxylic acid having 3 to 30 carbon atoms is preferable. For example, lauric acid, stearic acid, crotonic acid,
Oleic acid, maleic acid, glutaric acid, montanic acid and the like are preferable, and from the viewpoints of dispersibility in a resin, solubility, the effect of improving the surface appearance, etc., stearic acid, stearic acid derivatives, montanic acid and montanic acid. Derivatives are preferred,
Further, alkali metal salts and alkaline earth metal salts of stearic acid, particularly zinc stearate and calcium stearate, are particularly preferred.

[0038] The amount of these additives to be added is as follows.
It is preferably in the range of 0.01 to 10 parts by weight, preferably 0.05 to 8 parts by weight, more preferably 0.1 to 5 parts by weight with respect to 00 parts by weight.

When the amount of the additive is 0.01 part by weight or more, it is easy to prevent the foam from breaking.
When the amount is less than the weight part, the resin can maintain a viscosity enough to withstand the gas pressure at the time of foaming, and the surface appearance can be improved without foaming. Further, in the present invention, it is possible to use, as an additive of the thermoplastic resin, a foam nucleating agent or an inorganic fine powder which acts as a strength or durability improving agent.

Examples of the inorganic fine powder include talc, calcium carbonate, clay, magnesium oxide, zinc oxide, glass beads, glass powder, titanium oxide, carbon black, and anhydrous silica. Titanium and anhydrous silica, particularly preferably talc, having a particle size of 50 μm or less, preferably 10 μm or less, more preferably 5 μm or less. When the inorganic fine powder having a particle size of 50 μm or less is used, the surface appearance of the foam is improved.

The amount of the inorganic fine powder to be added is 0.01 to 60 parts by weight per 100 parts by weight of the thermoplastic resin composition.
Parts by weight, preferably 0.05 to 40 parts by weight, more preferably 0.05 to 20 parts by weight, more preferably 0.1 to 40 parts by weight.
It is preferably in the range of 10 parts by weight. When the amount of the inorganic fine powder is 0.01 part or more and 60 parts by weight or less, the surface appearance of the foam is good.

The thermoplastic resin composition obtained by adding an aliphatic carboxylic acid and its derivative, inorganic fine powder, and the like to the thermoplastic resin, if necessary, is exemplified as long as the characteristics of the present invention are not impaired. In addition to inorganic fine powder, aliphatic carboxylic acid and its derivatives, resin, peroxide, sulfur, process oil, anti-adhesion agent, plasticizer, pigment, stabilizer, filler, metal powder, etc. It is possible to use.

The method for producing the thermoplastic resin composition used as the raw material of the thermoplastic resin foam of the present invention is not particularly limited, and a generally known method can be employed. For example,
After uniformly mixing the thermoplastic resin and the additives to be added as necessary with a high-speed stirrer or the like, the mixture is melt-kneaded with a single-screw or multi-screw extruder having sufficient kneading ability, a mixing roll, a kneader, a Brabender, or the like. It can be manufactured by a method or the like. The thermoplastic resin and the additives to be added as necessary may be used in a state of being uniformly mixed.

In the present invention, the method for producing a thermoplastic resin foam is not particularly limited as far as it is not specified in the present invention, and can be applied to a molding machine used in a known extrusion foaming method. The continuous plasticizer described herein is included in these molding machines.

An example of an embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, (1) is a gas cylinder, (2)
Is a metering pump, (3) is a pressure holding valve, (4) is a refrigerant circulator,
(5) is a heater, (6) is a flow meter, (7) is a first extruder, (8) is a second extruder, (9) is a connecting portion, (10) is a die, and (11) is a foam. , (12) is the hopper, (1)
3) is a screw, and (14) is a cooling device.

The thermoplastic resin is charged into a first extruder (7) having a line for adding the blowing agent to the molten thermoplastic resin, which constitutes the entrance side of the continuous plasticizer, and the blowing agent is heated and melted. To form a molten thermoplastic resin composition in which the thermoplastic resin and the foaming agent are compatible with each other.

As a method of adding a blowing agent to a molten thermoplastic resin in a continuous plasticizing apparatus, for example, a method of injecting a gaseous blowing agent directly or under a pressurized state, a method of adding carbon dioxide in a liquid state to a plan A method of adding with a jar pump or the like can be used.

Thereafter, the molten thermoplastic resin composition is transferred to the second extruder (8) constituting the outlet side of the continuous plasticizing device, and the temperature is gradually lowered to the optimum temperature condition for foaming. At this time, the pressure and temperature conditions up to the tip of the second extruder (8) are preferably in a supercritical state at a critical pressure or higher and a critical temperature or higher of the foaming agent.

Preferably, an adapter having a mixing section is provided at a connection section (9) between the first extruder (7) and the second extruder (8). This further promotes the mixing of the molten thermoplastic resin and the foaming agent, facilitates the formation of a compatible state between the thermoplastic resin and the foaming agent, and controls the temperature with the adapter to form a molten thermoplastic resin composition. To
It becomes easy to cool to a viscosity suitable for the subsequent foaming.

The type of the adapter having the mixing section is not particularly limited, but an adapter having a built-in static mixer capable of kneading and cooling the molten thermoplastic resin composition is preferably used. However, in the first extruder (7), if a compatible state of the molten thermoplastic resin composition can be sufficiently formed and cooling to the optimum foaming temperature is possible, the continuous plasticizing device is connected to the second extruder (8). ) Does not need to be a tandem type foam extruder, and may be configured with only one extruder.

Next, the molten thermoplastic resin composition is transferred to a die (10) connected to the end of a continuous plasticizing apparatus set to an optimum foaming temperature, and the pressure is reduced to start foaming.

In the method for producing a thermoplastic resin foam by extrusion molding according to the present invention, the gas dissolving step of forming a compatible state between the thermoplastic resin and the foaming agent includes the first step constituting the inlet side of the continuous plasticizing apparatus. After the thermoplastic resin is heated and melted in the extruder (7), a foaming agent is added to the melted thermoplastic resin and uniformly mixed.

The cooling step is a step of cooling the molten thermoplastic resin composition at the outlet side of the continuous plasticizing apparatus and adjusting the composition to have a viscosity suitable for foaming.

The nucleation step is to reduce the pressure of the molten thermoplastic resin composition in a die (10),
This is a step in which the blowing agent is supersaturated to generate a large number of cell nuclei in the supersaturated molten thermoplastic resin.

The foam control step is a step of rapidly cooling the foam (11), controlling the growth of the generated cells, and controlling a desired expansion ratio.

The thermoplastic resin is added from the hopper (12) into the first extruder (7) constituting the entrance side of the continuous plasticizer, and is melted at a temperature higher than the plasticizing temperature of the thermoplastic resin. The foaming agent is injected from the gas cylinder (1) into the metering pump (2), where the pressure is increased and the pressure-controlled foaming agent is added to the molten thermoplastic resin in the first extruder (7).

At this time, the foaming agent present in the first extruder (7) greatly increases the dissolution and diffusion of the molten thermoplastic resin, and allows the foaming agent to penetrate into the thermoplastic resin in a short time. The inside of the system is preferably maintained at a temperature higher than the critical pressure and a temperature higher than the critical temperature of the foaming agent. The foaming agent added to the first extruder (7) may be heated and pressurized before being added to the first extruder (7), and may be added after being in a supercritical state.

The thermoplastic resin and the foaming agent melted in the first extruder (7) are kneaded by the screw (13) to form a compatible state between the thermoplastic resin and the foaming agent.

In the post-compatibility cooling step, the molten thermoplastic resin is heated by controlling the temperature at the tip of the second extruder (8) constituting the outlet side of the continuous plasticizing apparatus, so that the plasticizing temperature of the molten thermoplastic resin composition is reduced. Above, at a temperature not higher than 50 ° C. higher than the plasticization temperature of the molten thermoplastic resin composition, and cooled to a temperature not higher than the melting temperature in the gas melting step, so that the viscosity becomes suitable for subsequent foaming. adjust.

An example of a method for continuously producing a foamed sheet by the method for producing a thermoplastic resin foam of the present invention will be described below with reference to the drawings. Here, an example in which carbon dioxide is used as a foaming agent and a T-die is used as a die is described, but the use of another foaming agent or a circular die is also included in the present invention.

In FIG. 2, (1) is a liquefied carbon dioxide cylinder, (2) is a metering pump, (4) is a refrigerant circulator,
(3) is a holding pressure valve, (5) is a heater, (6) is a flow meter,
(12) is a hopper, (13) is a screw, (15)
Is a plunger pump, (16) is a T-die, (17)
Is a foam sheet, (18) is a cooling roll, and (19) is an extruder.

In FIG. 2, in the gas dissolving step, 100 parts by weight of a thermoplastic resin is added from a hopper (12) into an extruder (19) constituting the entrance side of a continuous plasticizing apparatus, and is heated and melted. In addition, carbon dioxide is temperature-controlled by a liquefied carbon dioxide cylinder (1) and a metering pump (2)
And pressurized and pressure-controlled carbon dioxide is added to the molten thermoplastic resin in the extruder (19) to perform a gas dissolving step. At this time, the extruder (19)
The carbon dioxide present in the resin significantly increases the dissolution and diffusion of the molten thermoplastic resin, and allows the carbon dioxide to penetrate into the thermoplastic resin in a short time. It is preferred that the temperature be maintained at or above the temperature.

In the case of carbon dioxide, the critical pressure is 7.4MP
a, the critical temperature is 31 ° C., the pressure in the extruder (19) is in the range of 7.4 to 40 MPa, preferably 10 to 30 MPa, and the temperature is 150 to 300 ° C., preferably 160 to 28 MPa.
A range of 0 ° C. is preferred.

The carbon dioxide to be added to the thermoplastic resin melted in the extruder (19) may be heated and pressurized before being added, and may be added after being brought into a supercritical state.

The thermoplastic resin and carbon dioxide melted in the extruder (19) are kneaded by the screw (13),
A compatible state between the thermoplastic resin and carbon dioxide is formed.

In the post-compatibility cooling step, the temperature is lowered to a temperature suitable for foaming in order to increase the solubility of carbon dioxide in the thermoplastic resin. The temperature at this time varies depending on the resin.
Cooling is performed while maintaining the temperature at 0 ° C., preferably 80 to 230 ° C. and higher than the plasticizing temperature of the polypropylene resin, and adjusting the temperature so as to have a viscosity suitable for subsequent foaming.

This cooling step is a step for reasonably approaching a temperature condition suitable for foaming. By sufficiently cooling in this step, continuous and stable production of a thermoplastic resin foam becomes easy.

Next, the molten thermoplastic resin composition is transferred to a T-die (16) connected to the outlet side of a continuous plasticizing apparatus set to an optimum foaming temperature, and foaming is started. The pressure is reduced under controlled conditions at the outlet of the T-die (16) to supersaturate the carbon dioxide. The supersaturated molten thermoplastic resin composition becomes thermally unstable and generates many cells.

The molten thermoplastic resin composition which has begun foaming is extruded from the T-die (16) outlet and starts foaming at the same time, but the cooling roll (18) installed at the tip of the T-die (16) The resin is cooled while adjusting the thickness in the above manner, and is shaped into a sheet to obtain a foamed thermoplastic resin sheet (17).

In the present invention, it is necessary to prevent the molten thermoplastic composition from separating into a thermoplastic resin and carbon dioxide until the gas dissolving step and the cooling step are completed. Is preferably maintained at a pressure equal to or higher than the critical pressure of carbon dioxide.

In the method for producing a thermoplastic resin foam by extrusion molding of the present invention, carbon dioxide is added to the molten thermoplastic resin in the extruder (19), and the mixture is sufficiently kneaded. At the outlet side of the continuous plasticizing apparatus, the temperature of the molten thermoplastic resin composition is lowered, foaming is started by the pressure drop, and the cooling apparatus (1) is formed.
By controlling the expansion ratio in 4), it is possible to continuously manufacture a thermoplastic resin foam having excellent thickness accuracy and density accuracy with a constant quality.

The method for producing a thermoplastic resin foam of the present invention is not particularly limited in the form of a product that can be produced, but is excellent in thickness accuracy and density accuracy.
It is suitably used for containers, stationery, boxes, cores, etc., which require secondary molding, such as food trays, transport dividers, and file covers.

Hereinafter, the present invention will be described with reference to examples, but the contents of the present invention are not limited thereto.

FIG. 1 is a schematic diagram showing an example of the method for producing a thermoplastic resin foam of the present invention.

FIG. 2 is a schematic structural view showing an example of a method for continuously producing a foamed sheet by the method for producing a thermoplastic resin foam of the present invention.

[0076]

EXAMPLES Evaluation of physical properties described in Examples and Comparative Examples was carried out according to the following methods. 1) Uniformity of density A foam sheet is continuously manufactured, and a sample is prepared every 5 minutes.
Got points. The obtained sample is processed into a size of 300 mm (extrusion direction) x 300 mm (width direction), and cut out from the front end, center, and rear end of each sheet to a size of 30 mm (extrusion direction) x 30 mm (width direction). The density was measured using an electronic densitometer. ◎ 10% when all three measured values have an error from the predetermined density within 5%
The case of less than or equal to was evaluated as そ れ, the other was evaluated as x, and the case where ○ was 3 or more out of all 5 samples was regarded as passed. 2) Uniformity of thickness A foam sheet is manufactured continuously, and a sample is prepared every 5 minutes.
Got points. The obtained sample was processed into a size of 300 mm (extrusion direction) × 300 mm (width direction), and the thickness of three points at the front end, center, and rear end of each sheet was measured. In all three measured values, when the error from the predetermined thickness is within 5%, the result is ◎. When the error is within 10%, the result is そ れ.
Of the samples, the case where ○ was 3 or more was regarded as a pass. 3) Secondary formability A foam sheet is manufactured continuously, and one sample is taken every 10 minutes.
Scored 0 points. The obtained foamed sheet is processed into a size of 300 mm (extrusion direction) x 300 mm (width direction), and a corner having an opening of 100 mm in both length and width, a bottom of 75 mm in both length and width, and a depth of 30 mm is formed by a vacuum forming machine. The container was shaped. When all 10 points were molded under the same conditions, wrinkles, uneven thickness, surface roughness, surface breakage, etc. were obtained without any problems. The heating temperature was 320 ° C. and the heating time was 50 seconds.

Example 1 In this example, for the purpose of manufacturing a molded container, a thickness of 1.0 mm was used.
A foam sheet having a thickness of 0.3 mm and a density of 0.3 g / cm ³ was produced.

As a continuous plasticizing device, a screw diameter of 50 was used.
A T-die (16) having an exit gap of 0.2 mm and an exit width of 300 mm was connected to the tip of the extruder (19) using a extruder (19) having a diameter of 0.2 mm. 50
A cooling roll (18) set to ° C was used.

The foaming agent addition section was provided near the center of the extruder (19).

As the thermoplastic resin, a propylene homopolymer 100 having a melt flow rate (ASTM D-1238, 230 ° C., 2.16 kg load) of 1.5 g / 10 min.
Using parts by weight, the propylene homopolymer was added to the extruder (19) from the hopper (12), and was heated and melted at 220 ° C.

Using butane gas as a foaming agent, press-fitting was carried out from a foaming agent addition part. At this time, the flow rate of butane gas was measured with a flow meter (6), and the pressure was adjusted successively so that the supply fluctuation rate was within a range of ± 2%. The mixture was added to the extruder (19) at a ratio of 0 parts by weight and uniformly mixed with the screw (13). Next, adjust the resin temperature to 188 ° C, and
Extruded from the T-die (16) at an extrusion rate of / hour. The die pressure at this time was 8 MPa. The extruded propylene homopolymer foams out of the T-die (16) at the same time as it comes out of the T-die (16), and is cooled by a cooling roll (18) installed at the tip of the T-die (16) to produce a foamed sheet (17). did. The obtained foam sheet (17) has a width of 300 mm and a thickness of 300 mm.
The appearance was 1.0 mm and the appearance was beautiful.

Table 1 shows the evaluation results of the foamed sheet. Excellent secondary moldability due to excellent thickness accuracy and density accuracy,
It was the intended foam of the present invention.

Example 2 In this example, for the purpose of manufacturing a molded container, a thickness of 1.0 mm was used.
A foam sheet having a thickness of 0.3 mm and a density of 0.3 g / cm ³ was produced.

As a continuous plasticizing device, a screw diameter of 50 was used.
A T-die (16) having an exit gap of 0.2 mm and an exit width of 300 mm was connected to the tip of the extruder (19) using a extruder (19) having a diameter of 0.2 mm. 50
A cooling roll (18) set to ° C was used. The foaming agent addition section was provided near the center of the extruder (19).

As the thermoplastic resin, propylene homopolymer 100 having a melt flow rate (ASTM D-1238, 230 ° C., 2.16 kg load) of 1.5 g / 10 min.
Using parts by weight, the propylene homopolymer was added to the extruder (19) from the hopper (12), and was heated and melted at 220 ° C.

Carbon dioxide was used as a blowing agent, and carbon dioxide was added as follows. The carbon dioxide cylinder was connected to a pressure booster, and the pressure of carbon dioxide was increased and added to the molten propylene homopolymer in the extruder (19). At this time, the pressure of the molten resin in the addition section was 20 MPa.

In this way, the carbon dioxide was measured with the flow meter (6), and the pressure of the pressure-increasing compressor was successively adjusted so that the supply fluctuation rate was within the range of ± 2%. 1.5 parts by weight with respect to parts by weight was added into the extruder (19) and uniformly mixed with the screw (13). Next, the resin temperature was adjusted to 188 ° C., and 1
It was extruded from a T-die (16) at an extrusion rate of 0 kg / hour. The die pressure at this time was 8 MPa. The extruded propylene homopolymer foams out of the T-die (16) at the same time as it comes out of the T-die (16), and is cooled by a cooling roll (18) installed at the tip of the T-die (16) to produce a foamed sheet (17). did. The obtained foam sheet (17) has a width of 300 m.
m, the thickness was 1.0 mm, and the appearance was beautiful. Table 1 shows the evaluation results of the foam sheet. It was a foam intended for the present invention, having excellent thickness accuracy and density accuracy and also excellent secondary moldability.

Example 3 In this example, for the purpose of manufacturing a molded container, a thickness of 1.0
A foam sheet having a thickness of 0.3 mm and a density of 0.3 g / cm ³ was produced.

As a continuous plasticizing device, a screw diameter of 50 was used.
A T-die (16) having an exit gap of 0.2 mm and an exit width of 300 mm was connected to the tip of the extruder (19) using a extruder (19) having a diameter of 0.2 mm. 50
A cooling roll (18) set to ° C was used. The foaming agent addition section was provided near the center of the extruder (19).

As the thermoplastic resin, propylene homopolymer 100 having a melt flow rate (ASTM D-1238, 230 ° C., 2.16 kg load) of 1.5 g / 10 min.
Using parts by weight, the propylene homopolymer was added to the extruder (19) from the hopper (12), and was heated and melted at 220 ° C.

Carbon dioxide was used as a blowing agent. Carbon dioxide was added as follows.

As the carbon dioxide cylinder, a siphon type liquefied carbon dioxide cylinder (1) was used so that carbon dioxide could be directly taken out from the liquid phase portion. The flow path from the liquefied carbon dioxide cylinder (1) to the plunger pump (15) is cooled with an aqueous ethylene glycol solution adjusted to -12 ° C using a refrigerant circulator (4), and the carbon dioxide is converted into a liquid state in a plunger. It was made possible to inject up to the pump (15). Next, the plunger pump (15) was controlled so that the injected liquid carbon dioxide became 1 kg / hour, and the discharge pressure of the plunger pump (15) was adjusted by the pressure holding valve (3) so as to be 30 MPa. At this time, the volumetric efficiency of the plunger pump (15) became constant at 65%. Next, the line from the pressure holding valve (3) to the carbon dioxide addition section of the extruder (19) is heated by the heater (5) to 50 ° C.
Carbon dioxide was added to the molten polypropylene resin composition in the extruder (19). At this time, the pressure of the molten resin in the addition section was 20 MPa. That is, carbon dioxide immediately before dissolving in the molten polypropylene-based resin composition,
The temperature is 50 ° C. or higher, the pressure is 20 MPa, and carbon dioxide is in a supercritical state.

In this way, carbon dioxide in a supercritical state was measured by a flow meter (6), and 100 parts by weight of a molten propylene homopolymer was controlled while controlling the supply variation within a range of ± 1%. To the extruder (19) at a ratio of 1.5 parts by weight to the extruder (19) and uniformly mixed with the screw (13). Next, the resin temperature was adjusted to 188 ° C., and the resin was extruded from the T-die (16) at an extrusion rate of 10 kg / hour. The die pressure at this time was 8 MPa. The extruded propylene homopolymer foams out of the T-die (16) at the same time as it comes out of the T-die (16), and is cooled by a cooling roll (18) installed at the tip of the T-die (16) to produce a foamed sheet (17). did.
The obtained foamed sheet (17) has a width of 300 mm and a thickness of 1.
At 0 mm, the appearance was beautiful.

Table 1 shows the evaluation results of the foam sheet. Excellent secondary moldability due to excellent thickness accuracy and density accuracy,
It was the intended foam of the present invention.

Comparative Example 1 In Example 1, when the pressure of the booster was operated at the initial set value, the supply amount of butane gas fluctuated sequentially due to fluctuations in the pressure of the blowing agent supply section and the like. A foam sheet (17) was obtained according to Example 1 except that the supply amount of the foaming agent was not controlled during the operation.

Table 1 shows the evaluation results of the foamed sheet. Due to large variations in thickness and density, the intended foam of the present invention could not be produced.

Comparative Example 2 In Example 2, when the pressure of the booster was operated at the initial set value, the supply amount of carbon dioxide fluctuated sequentially due to the fluctuation of the pressure of the carbon dioxide supply part.

A foamed sheet (17) was obtained according to Example 2, except that the amount of carbon dioxide supplied was not controlled during the operation. Table 1 shows the evaluation results of the foam sheet. Due to large variations in thickness and density, the intended foam of the present invention could not be produced.

Example 4 In Example 3, the thickness was 1.5 mm and the density was 0.18 g /
A foamed sheet was obtained in accordance with Example 3, except that the amount of carbon dioxide added was changed to 2.0 parts by weight in order to produce a sheet of cm ³ .

Table 1 shows the evaluation results of the foam sheet. Excellent secondary moldability due to excellent thickness accuracy and density accuracy,
It was the intended foam of the present invention.

Example 5 In Example 3, a thickness of 2.0 mm and a density of 0.09 g /
A foamed sheet was obtained according to Example 3, except that the amount of carbon dioxide added was changed to 2.5 parts by weight in order to produce a sheet of cm ³ .

Table 1 shows the evaluation results of the foam sheet. Excellent secondary moldability due to excellent thickness accuracy and density accuracy,
It was the intended foam of the present invention.

[0103]

[Table 1]

Comparative Example 3 In Example 4, when the booster was operated with the pressure of the booster kept at the initial set value, the supply amount of carbon dioxide fluctuated sequentially due to fluctuations in the pressure of the carbon dioxide supply part.

A foam sheet (17) was obtained according to Example 2, except that the supply of carbon dioxide was not controlled during the operation.

Table 1 shows the evaluation results of the foamed sheet. Due to large variations in thickness and density, the intended foam of the present invention could not be produced.

Comparative Example 4 In Example 5, when the booster was operated with the pressure of the booster kept at the initial set value, the supply amount of carbon dioxide fluctuated sequentially due to fluctuations in the pressure of the carbon dioxide supply part.

A foamed sheet (17) was obtained according to Example 2, except that the supply of carbon dioxide was not controlled during the operation.

Table 1 shows the evaluation results of the foam sheet. Due to large variations in thickness and density, the intended foam of the present invention could not be produced.

Example 6 Polyether sulfone was used as a thermoplastic resin.
A foamed sheet having a thickness of 1.0 mm and a density of 0.7 g / cm ³ was produced in accordance with Example 3 except that the temperature was changed so that the polyether sulfone was melted in the extruder.

Table 2 shows the evaluation results of the foamed sheet.

In order to further evaluate the heat resistance, the sheet was
Processed to 0mm (extrusion direction) x 30mm (width direction)
It was left in a gear oven maintained at 00 ° C. for 24 hours. After the standing, visual observation was carried out, and it was found that the foam had no deformation such as warpage and was excellent in heat resistance.

Example 7 As a cyclic olefin resin which is a thermoplastic resin, ethylene and 1,4,5,8-dimetano-1,2,3,4,4
a) According to Example 3, except that a random copolymer with a, 5,8,8a-octahydronaphthalene was used, and the temperature was changed so that the cyclic olefin-based resin was melted in the extruder. 1.0mm, density 0.5g / cm
Production of foam sheet No. ³ was performed.

Table 2 shows the evaluation results of the foamed sheet.

To further evaluate the heat resistance, the sheet was
Processed to 0mm (extrusion direction) x 30mm (width direction)
It was left in a gear oven maintained at 00 ° C. for 24 hours. After the standing, visual observation was carried out, and it was found that the foam had no deformation such as warpage and was excellent in heat resistance.

[0116]

[Table 2]

[0117]

According to the present invention, there is no change in the thickness and density in the extrusion direction of the foamed sheet, so that a foamed sheet having excellent secondary formability can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a method for producing a thermoplastic resin foam of the present invention.

FIG. 2 is a schematic configuration diagram showing an example of a method for continuously producing a foamed sheet by the method for producing a thermoplastic resin foam of the present invention.

[Explanation of symbols]

 (1) Liquefied carbon dioxide cylinder (2) Metering pump (4) Refrigerant circulator (3) Holding pressure valve (5) Heater (6) Flow meter (7) First extruder (8) Second extruder (9) Connection Part (10) Dies (11) Foam (12) Hopper (13) Screw (14) Cooling device (15) Plunger pump (16) T-die (17) Foam sheet (18) Cooling roll (19) Extruder

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B29L 7:00 B29L 7:00 (72) Inventor Masahiro Takedate 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Chemicals Inside (72) Inventor Haruo Inoue 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Inside Mitsui Chemicals Co., Ltd. (72) Inventor Yoko Shimada 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Chemicals Corporation (72) Inventor Masao Eriguchi 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 4F074 AA16 AA57 AA65 AA70 AA71 AA74 AA77 AA97 BA32 BA86 CA22 CC03X DA02 DA23 DA34 4F207 AA03 AA13 AA21 AA24 AB02 AB07 AB12 AH56 AH58 AR12 AR15 KA01 KA11 KF03 KF04 KW41

Claims (9)

[Claims] 1. A foam obtained by adding a foaming agent to a thermoplastic resin, extruding and foaming, has a thickness variation rate of ± 10% or less in the extrusion direction and a density variation rate in the extrusion direction of not more than ± 10%. Thermoplastic foam not more than ± 10%. 2. The thermoplastic resin foam according to claim 1, wherein the thermoplastic resin is a composition comprising one or more of a polyolefin-based resin and a polyester-based resin. 3. The thermoplastic resin foam according to claim 1, wherein the thermoplastic resin is a composition comprising one or more of engineering plastics and super engineering plastics. 4. The thermoplastic resin foam according to claim 1, wherein the thermoplastic resin is a composition comprising one or more special polyolefin-based resins. 5. The thermoplastic resin foam according to claim 1, wherein the blowing agent is carbon dioxide. 6. The thermoplastic resin foam according to claim 1, wherein the blowing agent is carbon dioxide in a supercritical state. 7. A molded container comprising the thermoplastic resin foam according to any one of claims 1 to 6. 8. The method for producing a thermoplastic resin foam according to claim 1, wherein the variation in the amount of carbon dioxide as the blowing agent is ± 2% or less. 9. A method for adding carbon dioxide as a foaming agent,
The carbon dioxide is maintained in a liquid state and injected into the metering pump, and the discharge pressure of the metering pump is controlled by the pressure-holding valve (3) so as to be constant within the range of the critical pressure of carbon dioxide (7.4 MPa) to 40 MPa. The thermoplastic resin foam according to claim 8, wherein after discharging, the temperature is raised to a temperature higher than the critical temperature of carbon dioxide (31 ° C) to form supercritical carbon dioxide, and then added to the molten thermoplastic resin. Manufacturing method.