KR101667999B1 - Heat resisting material having excellent heat resistance and strength, manufacturing method of the same and packaging container comprising the same - Google Patents

Abstract

The present invention relates to a heat-resistant material having excellent heat resistance and strength, a manufacturing method thereof and a packaging container comprising the same. The heat-resistant material according to the present invention is produced by a simple process extruding and foaming a polyester resin, thereby being able to simultaneously implement excellent heat resistance, light weight, insulating properties, and strength. In addition, warmth or preservation of foods can be easy by being used in a food container.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant material having excellent heat resistance and strength, a method for manufacturing the same, and a packaging container containing the same.

The present invention relates to a heat-resistant material excellent in heat resistance, warmth and durability, a method for producing the same, and a packaging container containing the same.

Products that are normally used as food containers are divided into a foam type and a non-pour type. The foamed product is a product obtained by mixing polystyrene with a foaming gas and extruding it, which has the advantages of maintaining a relatively thick thickness, and maintaining shape, insulation, and cost competitiveness, but has a disadvantage in that harmful substances are detected at high temperatures. In the case of non-foaming containers, products made of thermally stable polypropylene, polyethylene, or polyester film are used, and it is advantageous that the rate of dimensional change at low temperature is low and harmful substances are not detected. However, There is a drawback that does not.

In the past, polystyrene foam containers have been used, but the point that harmful substances are detected at high temperatures has been replaced by paper containers, which are used as disposable heat-resistant containers, .

As modern life becomes more convenient in modern society, the use of disposable products increases, and the demand for food for delivery and convenience food is gradually increasing. Accordingly, the demand for food packaging container is increasing, have. Therefore, there is a need to study packaging containers having both convenience, safety, and environmentally friendly performance.

International Patent Publication No. 2000-018836

The present invention relates to a heat resistant material excellent in heat resistance, warmth and durability, and is intended to provide a heat resistant material excellent in heat resistance at a high temperature, light in weight, excellent in heat insulation property and strength.

The present invention can provide a heat-resistant material having excellent heat resistance and strength, a method for producing the same, and a packaging container containing the same.

As one example of the heat resistant material,

A polyester resin foam,

It is possible to provide a heat resistant material satisfying the following formula (1).

[Equation 1]

| V ₁ -V ₀ | / V ₀ x 100? 5%

In the above equation (1)

V ₀ is the volume (mm ³ ) of the heat-resistant material before exposure for 3 hours at 100 ° C,

V ₁ is the volume (mm ³ ) of the heat-resistant material after exposure at 100 ° C for 3 hours.

As an example of the method for manufacturing the heat resistant material,

The polyester resin foam is extruded through a double annular nozzle,

Among the double annular nozzles,

The difference in density of the foam extruded from the inner nozzle and the density of the foam extruded from the outer nozzle can be 10 kg / m ³ or more.

Further, the present invention can provide a packaging container containing the heat resistant material.

The interior material according to the present invention can be produced by a simple process of extruding and foaming a polyester resin, so that it is excellent in heat resistance, light in weight, heat-insulating property and strength at the same time, .

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

In the present invention, the terms "comprising" or "having ", and the like, specify that the presence of a feature, a number, a step, an operation, an element, a component, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

In the present invention, the term "cell" means a microstructure expanded by foaming in a polymer.

Hereinafter, the present invention will be described in detail.

The present invention relates to a heat-resistant material having excellent heat resistance and strength, a method for producing the same, and a packaging container containing the same,

A polyester resin foam,

It is possible to provide a heat resistant material satisfying the following formula (1).

[Equation 1]

| V ₁ -V ₀ | / V ₀ x 100? 5%

In the above equation (1)

V ₀ is the volume (mm ³ ) of the heat-resistant material before exposure for 3 hours at 100 ° C,

V ₁ is the volume (mm ³ ) of the heat-resistant material after exposure at 100 ° C for 3 hours.

Specifically, the dimensional change rate after the heat resistant material sample was exposed at 100 캜 for 3 hours was measured. This is a measurement value corresponding to the long-term dimensional change rate of the packaging container manufactured using the heat resistant material. For example, the volume may mean a value calculated by multiplying the length of each heat-resistant member, the width, and the length of each thickness. For example, the rate of dimensional change of the formula (1) may range from 0.01 to 5%, from 0.01 to 3%, or from 0.01 to 1%. By satisfying the value of the expression (1) within the above range, it can be seen that the shape of the heat resistant material according to the present invention hardly changes even when used in a high temperature environment. As a result, it can be seen that the heat resistant material according to the present invention is excellent in heat resistance.

When the above formula (1) is more than 5%, it may mean that the heat-resistant material may easily peel off, parts, warpage, discoloration or deformation.

At this time, the polyester resin can be produced by condensation polymerization reaction of 1,4-butanediol with terephthalic acid. The polyester resin according to the present invention includes both aromatic and aliphatic polyesters. In another aspect, the polyester resin includes a flame retardant polyester, a biodegradable polyester, an elastic polyester, and a reusable polyester. For example, the resin foam according to the present invention may be a PET (polyethylene terephthalate) foam. By using the PET, it is eco-friendly and can be easily reused.

The thermal conductivity of the heat resistant material may be 0.04 W / mK or less. For example, the thermal conductivity of the heat resistant material may range from 0.01 to 0.04 W / mK, from 0.01 to 0.035 W / mK, or from 0.02 to 0.035 W / mK. The heat resistant material according to the present invention has thermal conductivity within the above range, so that excellent heat insulating property can be realized.

Such a thermal conductivity can be controlled by varying the degree of foaming in the foaming process of the polyester resin foam. As a result, when a heat-resistant material having excellent heat insulation is used as a packaging container for food or the like, it can be easily preserved or preserved in food.

In the heat resistant material, the density of the polyester resin foam (KS M ISO 845) may be 20 to 230 kg / m ³ . For example, the polyester resin foam may have a density of 20 to 100 kg / m ³ , 20 to 80 kg / m ³ , 50 to 150 kg / m ³ , 110 to 230 kg / m ³ , 110 to 200 kg / ³ or from 130 to 180 kg / m < ³ >. Specifically, the density of the polyester resin foam can be controlled by varying the degree of foaming in the foaming process of the resin foam. For example, when a heat-resistant material having excellent heat insulation properties is used as a packaging container for food or the like through different kinds of foaming agents, it can be easily preserved or preserved in foods.

In the above heat resistant member, the polyester resin foam may satisfy the following expression (2).

&Quot; (2) "

X / Y ≥ 1.5

Wherein X represents the flexural strength (N / cm ² ) of the polyester resin foam layer according to KS M ISO 844 and Y represents the density (kg / m ³⁾ of the resin foam layer according to KS M ISO 845 ).

Specifically, the heat resistant material includes a polyester resin foam, thereby achieving excellent heat resistance and strength as well as excellent light weight.

As an example, the ratio of the density to the bending strength of the resin foam may satisfy the above-mentioned formula (2). For example, the density to flexural strength ratio of the resin foam may be in the range of 1.5 or more, 1.5 to 2, 1.5 to 1.8 or 1.5 to 1.7. The heat resistant material according to the present invention can achieve a heat resistant material having high heat resistance and high strength while having a relatively high foaming magnification by satisfying the density to bending strength ratio of the resin foam within the above range.

In the above formula (2), X may be 30 to 350 N / cm ² , and Y may be 20 to 230 kg / m ³ . For example, X (flexural strength) may be in the 40 to 300 N / cm ^2, 60 to 200 N / cm ^2, 90 to 110 N / cm ^2, 90 to 100 N / cm ² range, Y (density) May range from 25 to 200 kg / m ³ , from 30 to 150 kg / m ³ , from 40 to 75 kg / m ³ , from 50 to 75 kg / m ^3, or from 55 to 65 kg / m ³ .

The structure of the heat resistant material according to the present invention is, for example, a polyester resin foam layer having a density (KS M ISO 845) of 20 to 100 kg / m ³ ; And

And a polyester resin foam layer having a density of 110 to 230 kg / m < ³ >.

Specifically, the heat resistant material may be a composite of a polyester resin foam layer having a relatively low density and a polyester resin foam layer having a relatively high density.

At this time, in the polyester resin foam layer having a relatively low density, 90% or more of the cells may be closed cells (DIN ISO4590). This means that the measured value of the polyester resin foam layer in accordance with DIN ISO 4590 indicates that at least 90% (v / v) of the cells are closed cells. For example, the ratio of the closed cells in the polyester resin foam layer may be 90 to 100% or 95 to 99% on average. By controlling the ratio of the closed cell to the above range, it is possible to increase the heat insulating property and the like. Accordingly, the heat resistant material can be widely used in a construction industry for insulation of a part of a building, for example, a foundation, a wall, a floor and / or a roof. For example, the polyester resin foam layer may comprise 1 to 15 cells, 3 to 15 cells, or 3 to 10 cells per mm ² .

In addition, the average size of the cells may range from 300 to 800 탆. For example, the average size of the cells may range from 300 to 700 mu m, from 300 to 600 mu m, or from 350 to 500 mu m. At this time, the deviation of the cell size may be in a range of, for example, 5% or less, 0.1 to 5%, 0.1 to 4% to 0.1 to 3%. As a result, it can be seen that the polyester resin foam layer according to the present invention uniformly foamed cells of uniform size.

In addition, the polyester resin foam layer having a relatively high density may have a closed cell ratio and a cell size deviation similar to those of the polyester resin foam layer having a relatively low density. However, the polyester resin foam layer having a relatively high density may have a larger number of cells per area, for example, 15 to 30 cells, 15 to 28 cells, or 20 to 30 cells per 1 mm ² .

In addition, the average cell size of the polyester resin foam layer having a relatively high density may be smaller, and may range, for example, from 100 to 300 mu m. For example, the average size of the cells may range from 100 to 300 mu m, from 100 to 280 mu m, or from 100 to 250 mu m.

Such a heat-resistant material can be used as a packaging container for packing food or the like. In this case, when the polyester resin foam layer having a relatively high density of the packaging container is designed to face outward, excellent strength of the packaging container can be expected, At the same time, excellent thermal insulation can be realized due to the relatively low polyester resin foam layer formed inside the packaging container.

Under relative humidity conditions of temperature and 50% of the heat-resistant material is the oxygen transmission rate is 23 ℃, can be not more than 10 cc / m ² / 24h. For example, the oxygen permeability of the heat resistant material may be 0.1 to 10 cc / m ² / 24h, 0.1 to 5 cc / m ² / 24h or 0.1 to 3 cc / m ² / 24h. Since the heat resistant material according to the present invention has oxygen permeability within the above range, it can prevent the food from reacting with oxygen and decaying when used as a food packaging container, and can be easily stored in food.

The mass per unit area of the heat resistant material may range from 500 to 1100 g / m ² . For example, the mass per unit area of the heat resistant member may be 550 to 1000 g / m ² , 600 to 1000 g / m ^2, or 800 to 1100 g / m ² . By satisfying the mass per unit area in the above range, it can be confirmed that the heat resistant material according to the present invention is lightweight.

In the interior material according to the present invention, the polyester resin foam may further include a functional additive. Thus, the desired functionality can be effectively imparted without decreasing the physical properties of the foam, and the process efficiency and degree of freedom can be increased.

The functional additive may include at least one of an insulating agent, a hydrophilizing agent, a waterproofing agent, a flame retardant, an antibacterial agent, a deodorant, and an ultraviolet screening agent.

The heat insulating material may include a carbonaceous component. For example, the adiabatic agent may include graphite, carbon black, graphene, and the like, and may be specifically graphite.

The flame retardant is not particularly limited and may include, for example, a bromine compound, a phosphorus compound, an antimony compound, a metal hydroxide, and the like. The bromine compound includes, for example, tetrabromobisphenol A and / or decabromodiphenyl ether. The phosphorus compound may include an aromatic phosphoric acid ester, an aromatic condensed phosphoric acid ester, a halogenated phosphoric acid ester, and / or the like, and the antimony compound may include antimony trioxide and antimony pentoxide. Examples of the metal element in the metal hydroxide include aluminum (Al), magnesium (Mg), calcium (Ca), nickel (Ni), cobalt (Co), tin (Sn), zinc (Zn) ), Iron (Fe), titanium (Ti), and boron (B). Among them, metal hydroxides of aluminum or magnesium can be used. The metal hydroxide may be composed of one kind of metal element or two or more kinds of metal elements. For example, the metal hydroxide may include at least one of aluminum hydroxide and magnesium hydroxide.

The VOC reducing agent may include Graf and / or Bactoster Alexin and the like. At this time, the toast alecine is a natural sterilizing material extracted from propolis.

The hydrophilic agent is not particularly limited, and examples thereof include anionic surfactants (for example, fatty acid salts, alkylsulfuric acid ester salts, alkylbenzenesulfonic acid salts, alkylnaphthalenesulfonic acid salts, alkylsulfosuccinic acid salts and polyoxyethylene alkylsulfuric acid ester salts) , Nonionic surfactants (for example, polyoxyalkylene alkyl ethers such as polyoxyethylene alkyl ethers, polyoxyethylene derivatives, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, (E.g., alkylamine salts, quaternary ammonium salts, alkylbetaines, amine oxides, etc.), and water-soluble polymers such as polyoxyethylene alkylamines and alkylalkanolamides), cationic and amphoteric surfactants Or a protective colloid (e.g., gelatin, methyl cellulose, hydroxyethyl cellulose, Polyoxyethylene-polyoxypropylene block copolymer, polyacrylamide, polyacrylic acid, polyacrylic acid salt, sodium alginate, and polyvinyl alcohol partial saponification), and the like. can do.

The kind of the waterproofing agent is not particularly limited and may be, for example, silicone, epoxy, cyanoacrylic acid, polyvinyl acrylate, ethylene vinyl acetate, acrylate, polychloroprene Polyester resin mixture series, mixture of polyol and polyurethane resin, mixture of acrylic polymer and polyurethane resin, polyimide series, and mixture of cyanoacrylate and urethane.

The kind of the antibacterial agent is, for example, a composite obtained by adding at least one metal selected from the group consisting of silver, zinc, copper and iron to at least one carrier selected from the group consisting of hydroxyapatite, alumina, silica, titania, zeolite, zirconium phosphate and aluminum polyphosphate . ≪ / RTI >

The deodorant may be a porous material. Since the porous material has a strong tendency to physically adsorb a fluid flowing around the porous material, it is possible to adsorb a volatile organic compound (VOC). The deodorant may be selected from, for example, silica, zeolite and calcium (Ca), sodium (Na), aluminum (Al), silver (Ag), copper (Cu), tin (Zn), iron (Fe), cobalt ) And nickel (Ni), or a mixture of two or more thereof.

The ultraviolet screening agent is not particularly limited and may be, for example, an organic or inorganic ultraviolet screening agent. Examples of the organic ultraviolet screening agent include p-aminobenzoic acid derivatives, benzylidene camphor derivatives, cinnamic acid derivatives, Benzotriazole derivatives, and mixtures thereof. Examples of the inorganic ultraviolet screening agent may include titanium dioxide, zinc oxide, manganese oxide, zirconium dioxide, cerium dioxide, or a mixture thereof.

The present invention can provide a method for producing the heat resistant material.

The method for producing the polyester resin foam contained in the heat resistant agent is not specifically limited, but the resin foam can be produced by extrusion foaming a polyester resin. Specifically, there are types of foaming methods largely bead foaming or extrusion foaming. In general, the bead foaming is a method of heating a resin bead to form a primary foam, aging the resin bead for a suitable time, filling the resin bead in a plate-shaped or cylindrical mold, heating the same again, and fusing and forming the product by secondary foaming. On the other hand, the extrusion foaming can simplify the process steps by heating and melting the resin and continuously extruding and foaming the resin melt, and it is possible to mass-produce, and the cracks, Development and the like can be prevented, and more excellent bending strength and compressive strength can be realized.

As one example of the method for producing the heat resistant material according to the present invention,

The polyester resin foam is extruded through a double annular nozzle,

Among the double annular nozzles,

The difference in density of the foam extruded from the inner nozzle and the density of the foam extruded from the outer nozzle can be 10 kg / m ³ or more.

Specifically, in manufacturing the heat resistant material, the polyester resin can be extruded and foamed using a double annular nozzle. As a result, it is possible to manufacture a heat resistant material having a structure in which two polyester resin foams having a difference in density are combined in a single process, without producing and laminating two polyester resin foams having different density. At this time, the difference in density of the polyester resin foam having the density difference may be in the range of 10 to 100 kg / m ³ , 10 to 80 kg / m ^3, or 20 to 50 kg / m ³ . A heat resistant material having a composite polyester resin foam having a difference in density within the above range can be manufactured in a single process using a double annular nozzle, thereby reducing the processing cost.

The blowing agent supplied in the process of extruding the foam in the double annular nozzle is at least one of a thermally decomposable foaming agent and a volatile foaming agent,

The blowing agent used in extrusion from the inner nozzle and the blowing agent used in extrusion from the outer nozzle may not be the same.

The pyrolytic foaming agent may include, for example, an inorganic foaming agent containing sodium bicarbonate, an azo compound, a nitroso compound, a hydrazine compound, and the like. The volatile foaming agent may include, for example, carbon dioxide gas, an inert gas such as nitrogen, organic foaming agents such as propane, butane, pentane, hexane, methane and the like. At this time, by using at least one of the thermally decomposing foaming agent and the volatile foaming agent, the density of the foam can be controlled by controlling the expansion ratio of the polyester resin foam.

Specifically, the blowing agent used for extrusion from the inner nozzle and the blowing agent used for extrusion from the outer nozzle may be used differently, and the density of the foam foamed in each nozzle may be differently produced.

For example, in the double annular nozzle,

The blowing agent supplied at the time of extrusion from the inner nozzle uses carbon dioxide gas,

As the blowing agent supplied at the extrusion from the outer nozzle, a mixed gas of carbon dioxide gas and cyclopentane can be used.

Specifically, when the carbon dioxide gas having a high diffusion speed is extruded from the inner nozzle, the polyester resin foam extruded and foamed through the inner nozzle may have a low density.

Further, by using a mixed gas obtained by mixing a cyclopentane having a low diffusion speed and a carbon dioxide gas having a high diffusion speed at the time of extruding from an outer nozzle using as a foaming agent, a polyester having a high density as compared with a polyester resin foam produced from an inner nozzle Resin foams can be produced.

At this time, the composite foaming agent of carbon dioxide gas and cyclopentane,

The carbon dioxide gas and the cyclopentane can be mixed at a flow rate ratio of 1: 0.1 to 1:10.

For example, the mixed flow rate ratio of carbon dioxide gas and cyclopentane is 1: 0.1 to 1: 0.5, 1: 0.5 to 1: 1, 1: 0.8 to 1: 3, 1: 3 to 1: 1:10 range. By satisfying the above range, it is possible to control the density of the foam in a range having a uniform cell size.

The present invention can provide a packaging container containing the heat resistant material. Specifically, the packaging container may be used for food packaging. The heat resistant material according to the present invention hardly changes in shape even at a high temperature, and can be excellent in heat resistance. In addition, since the foams located inside and outside the container are manufactured with different densities, excellent strength and heat insulation can be realized at the same time. Further, the packaging container may be light in weight by using a foam produced by extrusion foaming a polyester resin.

Hereinafter, the present invention will be described in detail by way of Examples and the like according to the present invention, but the scope of the present invention is not limited thereto.

Example  One

100 parts by weight of the PET resin was dried at 130 DEG C to remove moisture. In the first extruder, 1 part by weight of the PET resin from which moisture was removed, 1 part by weight of PMDA (pyromellitic dianhydride), 1 part by weight of talc, ) Were mixed and heated at 280 占 폚 to prepare a resin melt. Then, carbonic acid gas was mixed as a blowing agent in the first extruder, and the resin melt was sent to the second extruder and cooled to 220 캜. The cooled resin melt was extruded and foamed through a die to form a resin foam.

The resin foam was then fixed with a calibrator to maintain a constant shape.

Example  2

100 parts by weight of the PET resin was dried at 130 DEG C to remove moisture. In the first extruder, 1 part by weight of the PET resin from which moisture was removed, 1 part by weight of PMDA (pyromellitic dianhydride), 1 part by weight of talc, ) Were mixed and heated at 280 占 폚 to prepare a resin melt. Then, carbon dioxide gas as a blowing agent was mixed in the inside of the nozzle and a mixed gas of carbon dioxide gas and cyclopentane mixed as a blowing agent at a ratio of 1: 1 was mixed on the outside, And cooled to 220 ° C. The cooled resin melt was extruded and foamed through a die to form a resin foam.

Comparative Example

100 parts by weight of polystyrene resin, 0.2 parts by weight of titanium oxide and 1 part by weight of talc were mixed and heated to 220 DEG C to prepare a resin melt. Carbon halide carbon (HCFC-22) and carbon dioxide gas were introduced as a foaming agent, The resin melt thus melted was sent to a second extruder and cooled to 120 ° C. The cooled resin melt was extruded and foamed while passing through a die to form a resin foam.

Experimental Example  1: Measurement of physical properties

Heat conductivity, density and flexural strength were measured using the heat resistant materials prepared in Examples 1 to 2 and Comparative Examples. The measurement method is described below, and the results are shown in Table 1 below.

1) Thermal conductivity measurement (heat insulation measurement)

The thermal conductivity was measured under KS L 9016 conditions.

2) Density measurement

The density was measured under KS M ISO 845 conditions.

3) Measurement of flexural strength

Flexural strength was measured under ASTM D 638 conditions.

Thermal conductivity
(W / mK) Density (kg / m ³ ) Flexural strength
(N / cm ² ) Example 1 0.031 60 60 Example 2 Medial 0.031 45 55 Outside 60 Comparative Example 0.03 40 15

Referring to Table 1, it can be confirmed that the heat resistant material according to the present invention has excellent strength and low thermal conductivity. In comparison with this, in the case of the heat resistant material according to the comparative example, it was confirmed that the bending strength was remarkably low.

In addition, it can be seen that the density is different in the case of Example 2 in which the foam layers having different densities are combined.

Experimental Example  2: Heat resistance measurement

The dimensional change rate measurement experiment was performed on the heat resistant materials in Examples 1 to 2 and Comparative Examples. Specifically, the rate of dimensional change before and after being left at a temperature condition of 100 캜 for 3 hours was calculated by the following equation (1). The results are shown in Table 2 below.

[Equation 1]

| V ₁ -V ₀ | / V ₀ x 100? 5%

In the above equation (1)

V ₀ is the volume (mm ³ ) of the heat-resistant material before exposure for 3 hours at 100 ° C,

V ₁ is the volume (mm ³ ) of the heat-resistant material after exposure at 100 ° C for 3 hours.

Dimensional change ratio (%) Example 1 0.5 Example 2 0.48 Comparative Example 6.8

Referring to Table 2, it can be seen that the heat resistance material according to the present invention has a low rate of dimensional change even under high temperature conditions. On the other hand, in the case of the heat resistant material according to the comparative example, it was confirmed that the dimensional change rate was remarkably high at 6.8% under the above-mentioned high temperature condition.

Claims (11)

A polyester resin foam,
Heat-resistant material satisfying the following formula (1)
[Equation 1]
| V ₁ -V ₀ | / V ₀ x 100? 5%
In the above equation (1)
V ₀ is the volume (mm ³ ) of the heat-resistant material before exposure for 3 hours at 100 ° C,
V ₁ is the volume (mm ³ ) of the heat-resistant material after exposure at 100 ° C for 3 hours.
The method according to claim 1,
Heat resistant material with a thermal conductivity of 0.04 W / mK or less.
The method according to claim 1,
Wherein the polyester resin foam has a density (KS M ISO 845) of 20 to 230 kg / m ³ .
The method according to claim 1,
Wherein the polyester resin foam is a heat resistant material satisfying the following formula:
&Quot; (2) "
X / Y ≥ 1.5
Wherein X represents the flexural strength (N / cm ² ) of the polyester resin foam layer according to KS M ISO 844 and Y represents the density (kg / m ³⁾ of the resin foam layer according to KS M ISO 845 ).
The method according to claim 1,
A polyester resin foam layer having a density (KS M ISO 845) of 20 to 100 kg / m ³ ; And
And a polyester resin foam layer having a density of 110 to 230 kg / m < ³ >.
The polyester resin foam is extruded through a double annular nozzle,
Among the double annular nozzles,
Wherein the density of the foam extruded from the inner nozzle and the density difference of the foam extruded from the outer nozzle are 10 kg / m ³ or more.
The method according to claim 6,
The blowing agent supplied in the process of extruding the foam in the double annular nozzle is at least one of a thermally decomposable foaming agent and a volatile foaming agent,
Wherein the foaming agent used for extrusion from the inner nozzle and the foaming agent used for extrusion from the outer nozzle are not the same.
The method according to claim 6,
In the double annular nozzle,
The blowing agent supplied at the time of extrusion from the inner nozzle is carbon dioxide gas,
Wherein the foaming agent supplied at the time of extrusion from the outer nozzle is a mixed gas of carbon dioxide gas and cyclopentane.
9. The method of claim 8,
The composite foaming agent of carbon dioxide gas and cyclopentane,
Wherein carbon dioxide gas and cyclopentane are mixed at a flow rate ratio of 1: 0.1 to 1:10.
A packaging container comprising a heat-resistant material according to any one of claims 1 to 5.
11. The method of claim 10,
Wherein the packaging container is for food packaging.