JP2025065699A - Heat-resistant container - Google Patents

Abstract

To provide a container having heat resistance up to 130°C and excellent transparency.SOLUTION: A container 10 is a heat-resistant container having a container body 11 formed from a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent, and the volume change rate of the container body after heating at 130°C for 60 minutes is within ±1%. The total haze value of the container body is 60.0% or less when measured according to JIS K7136. A sheet is made from a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent, and has a total haze value of 60.0% or less.SELECTED DRAWING: Figure 1

Description

This technology relates to heat-resistant containers.

Traditionally, plastic containers made from petroleum resources and the like have been used in large quantities as containers for storing fresh foods such as meat, fish, and vegetables, or processed foods such as boxed lunches, prepared meals, frozen foods, confectioneries, and noodles, because they are easy to mold, can be mass-produced, and have low manufacturing costs. Materials used for these plastic containers include, for example, polypropylene resin, polyethylene resin, and polystyrene resin. Among these, polypropylene resin has a heat resistance of around 120°C, is excellent in moisture resistance and chemical resistance, and is inexpensive, making it a commonly used material for heat-resistant containers.

In recent years, food manufacturers have come to widely use steam convection ovens, which can heat ingredients using steam in addition to the functions of a regular oven (Patent Documents 1 and 2).

However, when cooking in a steam convection oven, the temperature rises to around 130°C, and conventional polypropylene resins have insufficient heat resistance. In order to improve heat resistance, it has been proposed to add a filler to the polypropylene resin (Non-Patent Document 1).

JP 2002-335927 A JP 2005-110570 A

Plastic Materials Lecture [7] Polypropylene Resin (Takagi Kenyuki, Sasaki Heizo, editors, Nikkan Kogyo Shimbun), published February 1, 1982, first edition, 8th printing, page 86

At the food manufacturer, the food ingredients stored in the container are cooked in a steam convection oven and then sealed in the container with a fitting lid or the like. The containers with the food ingredients stored in them are transported to convenience stores, supermarkets, etc. while still in a refrigerated or frozen state. In convenience stores, supermarkets, etc., the containers with the food ingredients stored in them are usually displayed for sale. For this reason, the containers are required to have excellent transparency so that the purchaser can fully see the food ingredients stored in them. However, containers molded from polypropylene resins that contain fillers to improve heat resistance have the problem of poor transparency.

One of the objectives of the present invention is to provide a heat-resistant container that has heat resistance up to 130°C and excellent transparency.

This technology is
Polypropylene resin,
A container body formed from a polypropylene-based resin composition containing a nucleating agent,
The heat-resistant container has a volume change rate of ±1% or less after heating at 130° C. for 60 minutes.
A heat-resistant container, wherein the total haze value of the container body is 60% or less when measured in accordance with JIS K7136.
The polypropylene resin may have a meso pentad fraction (mmmm) of 96.0 to 99.5 mol %.
The nucleating agent may be a metal salt of a cyclic fatty acid.
The nucleating agent may be a metal hexahydrophthalate.
The heat-resistant container may be a heat-resistant food container for containing food.
In addition, this technology:
Polypropylene resin,
A sheet formed from a polypropylene-based resin composition containing a nucleating agent,
Also provided is a sheet having a total haze value of 60.0% or less.
In addition, this technology:
A first outer layer, a second outer layer, and an intermediate layer provided between the first outer layer and the second outer layer,
the first outer layer is made of a first resin composition containing a first polyolefin-based resin,
the second outer layer is made of a second resin composition containing a second polyolefin-based resin,
A multi-layer sheet, wherein at least the intermediate layer is made of a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent,
Also provided is a multilayer sheet having a total haze value of 60.0% or less.
In addition, this technology:
A polypropylene resin composition preparation step of mixing a polypropylene resin and a nucleating agent to prepare a polypropylene resin composition;
a sheet molding step of extruding the polypropylene-based resin preparation as is or after pelletization into a sheet;
a container body forming step of forming a container body from the sheet;
A method for manufacturing a heat-resistant container comprising the steps of:
Furthermore, this technology:
A polypropylene resin composition preparation step of mixing a polypropylene resin and a nucleating agent to prepare a polypropylene resin composition;
a sheet molding step of extruding the polypropylene-based resin preparation as is or after pelletization into a sheet;
A method for producing a sheet is also provided.

This technology can provide heat-resistant containers that are heat-resistant up to 130°C and have excellent transparency.

FIG. 2 is a perspective view showing an example of a heat-resistant container according to the first embodiment. FIG. 2 is a perspective view showing an example of a heat-resistant container body according to the first embodiment. FIG. 2 is a front view showing an example of a heat-resistant container according to the first embodiment. FIG. 2 is a plan view showing an example of a heat-resistant container body according to the first embodiment. FIG. 4 is a front view showing another example of the heat-resistant container according to the first embodiment. FIG. 6 is a plan view showing the heat-resistant container body of FIG. 5 . 6 is a front view showing a state in which a fitting lid is placed on the heat-resistant container body of FIG. 5. FIG. FIG. 8 is a plan view of the fitting lid of FIG. 7 . 8 is an enlarged view of a fitting portion between the fitting lid and the heat-resistant container body shown in FIG. 7. FIG. 2 is a perspective view showing how to measure a volume change rate of a heat-resistant container according to the embodiment. FIG. 13 is a diagram showing a special tool used when measuring the volumetric change rate of a heat-resistant container. FIG. 1 is a diagram showing a flat plate with a hole in the center used when measuring the volume change rate of a heat-resistant container. FIG. 11 is a cross-sectional view showing an example of a multilayer sheet according to a third embodiment. FIG. 11 is a schematic diagram showing an example of a multilayer co-extrusion molding machine used in the method for producing a multilayer sheet according to a third embodiment.

The following describes preferred embodiments for implementing the present technology. Note that the embodiments described below are representative embodiments of the present technology, and the scope of the present technology is not limited to these embodiments.

This technology will be described in the following order.
1. First embodiment (example of heat-resistant container)
(1) Structure of the heat-resistant container (2) Manufacturing method of the heat-resistant container (3) Physical properties of the heat-resistant container 2. Second embodiment (example of sheet)
(1) Structure of the sheet (2) Manufacturing method of the sheet (3) Physical properties of the sheet 3. Third embodiment (example of multilayer sheet)
(1) Structure of the multilayer sheet (2) Manufacturing method of the multilayer sheet (3) Physical properties of the multilayer sheet 4. Fourth embodiment (example of the multilayer sheet)
(1) Structure of the multilayer sheet (2) Manufacturing method of the multilayer sheet (3) Physical properties of the multilayer sheet 5. Examples

1. First embodiment (an example of a heat-resistant container)

(1) Heat-resistant container structure

Hereinafter, the configuration of the heat-resistant container according to this embodiment will be described with reference to the drawings.
In this specification, the "direction perpendicular to an object (e.g., a container, etc.) placed on a horizontal plane with the surface on which food or the like is placed facing upward" is referred to as the "thickness direction," and the "any direction in the plane perpendicular to the thickness direction" is referred to as the "planar direction." Also, "viewing an object (e.g., a container, etc.) placed on a horizontal plane with the surface on which food or the like is placed facing upward in the thickness direction from above in the vertical direction" is referred to as a "planar view." Furthermore, of the two surfaces facing each other in the thickness direction of a packaging container, the surface on which food or the like is placed is referred to as the "inner surface," and the other surface opposite thereto is referred to as the "outer surface."

The heat-resistant container of this embodiment is composed of a heat-resistant container body (hereinafter, abbreviated as "container body") and a lid. The container body is formed from a polypropylene-based resin composition, and has, for example, a bottom surface, a side surface extending upward from the periphery of the bottom surface, and an opening surrounded by the upper end of the side surface. The container body may further have, for example, a flange portion formed toward the outside at the opening. The lid is, for example, fitted to the inside of the container body to close the opening of the container body. The heat-resistant container of this embodiment may also be used as a heat-resistant container for food to store food, or may be used for steam convection.

In the container body, the shape of the bottom surface and the opening may be, for example, a circle, an ellipse, a polygon, or a substantially polygonal shape, but is not particularly limited. The shapes of the bottom surface and the opening may be the same or different. The side surface may be perpendicular to the bottom surface, or may be tapered. The shape of the container body having the bottom surface, the side surface, and the opening may be, for example, a bottomed cylindrical shape or a bottomed inverted truncated cone shape, but is not particularly limited.

The container body of this embodiment may be, for example, a container body formed by thermoforming using the polypropylene-based resin composition. The thermoforming may be, for example, deep-draw thermoforming. That is, the container body of this embodiment may be a deep-draw container body. In this specification, a deep-draw container body means a container body having an expansion ratio of 2.5 or more. In this specification, the expansion ratio of the container body is the ratio of the total area of the side and bottom parts to the area of the opening, and is a value calculated by the following formula. The larger the expansion ratio, the more deeply the container body is drawn.

Expansion ratio of container body = (area of side surface + area of bottom surface) / area of opening

The expansion ratio of the container body may be, for example, preferably 1.1 to 5.5, more preferably 1.2 to 5.3, and even more preferably 1.3 to 5.0. By having the expansion ratio in this range, it is possible to ensure the capacity and prevent the thickness of the side part of the heat-resistant container from becoming excessively thin to an extent that it cannot withstand practical use.

The heat-resistant container of this embodiment will be described below with reference to the drawings.

Figure 1 is a perspective view of an example of a heat-resistant container of this embodiment (hereinafter, also referred to as "container 10"). As shown in Figure 1, container 10 is composed of a container body 11 and a lid material 12. Figure 2 is a perspective view of container body 11 showing a state in which lid material 12 has been separated from container 10 of this embodiment. As shown in Figure 2, container body 11 has a bottom surface portion 15, container body side surface portion 16 that extends and spreads upward from the outer edge of bottom surface portion 15, and flange portion 14 that extends outward from the upper end of container body side surface portion 16. Also, as shown in Figure 2, container body 11 has an opening portion 13 surrounded by the upper end of container body side surface portion 16.

Figure 3 is a front view of the container 10 of this embodiment. As shown in Figure 3, a stacking protrusion 19 may be formed near the upper end of the container body side portion 16 of the container body 11.

It is preferable that a container body fitting portion 17 into which a lid material fitting portion (not shown) fits is formed on the upper portion of the container body side portion 16. The container body fitting portion 17 may be provided around the entire circumference.

The shape of the container body fitting portion 17 may be various. For example, the container body fitting portion 17 may be an inverted taper shape that gradually narrows toward the top, or may be a vertical shape (straight shape) or a forward taper shape with a fitting recess that is recessed on the outside. In this embodiment, the container body fitting portion 17 may be configured to have a fitting recess that is recessed on the outside. The cross-sectional shape of the fitting recess may be various, but it is preferable that it is a shape that curves toward the outside, and is an arc shape or a trapezoid shape when viewed in cross section.

As shown in FIG. 3, the container body fitting portion 17 is provided at the upper end of the container body side portion 16. The container body fitting portion 17 extends substantially vertically (vertically or with a slight reverse taper or slight forward taper) along the up-down direction. It is preferable that a step portion 18 is provided below the container body fitting portion 17. The step portion 18 is inclined upward toward the outside or extends substantially horizontally. The container body fitting portion 17 extends upward from the outer edge of the step portion 18.

The flange portion 14 may be provided with a knob (not shown) to facilitate opening the lid. The outer edge of the flange portion 14 is formed with a container body border portion 21 that extends outward, for example, horizontally or slightly downward. From the viewpoint of reinforcing the container body, it is preferable to form a large number of extremely fine irregularities in the outer region of the entire width of the container body border portion 21 in the inward and outward directions. These irregularities are wavy when viewed enlarged from the front, and the direction in which the numerous peaks and valleys extend is the width direction (inward and outward direction).

Figure 4 is a plan view of the container body 11 of this embodiment. As shown in Figure 4, multiple stacking protrusions 19 may be formed along the circumferential direction. The container bodies 11 are transported in a stacked state (also called a stacked state) to a line for filling the contents such as foodstuffs. The stacking protrusions 19 ensure gaps between the stacked container bodies 11, making it easier to remove the container bodies 11. As shown in Figure 4, the opening 13 and bottom surface portion 15 of the container body 11 are circular in shape. As shown in Figure 4, the bottom surface portion 15 has a recess 20 formed concentrically.

As shown in Figures 2 and 3, the shape of the container body 11, which has a bottom surface portion 15, a container body side portion 16, and an opening portion 13, is an inverted truncated cone shape.

As shown in FIG. 3, the lid material 12 covers the opening 13 of the container body 11 and may be a top seal made of a single layer or multiple layers with gas barrier properties that is attached to the flange portion 14 of the container body 11. Such a top seal may be attached to the flange portion 14 by thermal welding (fusion) or with a specified adhesive.

5 is a front view of another example of the heat-resistant container of this embodiment. As shown in FIG. 5, the container body has a bottom surface portion 55, a container body side surface portion 56 that extends from the outer edge of the bottom surface portion 55 while expanding upward, and a flange portion 54 that extends outward from the upper end of the container body side surface portion 56. The flange portion 54 may be provided with a knob portion (not shown) for facilitating the opening operation. The outer edge of the flange portion 54 is formed with a container body edging portion 51 that extends outward, for example, horizontally or slightly downward. From the viewpoint of obtaining a reinforcing effect of the container body, it is preferable to form a large number of extremely fine irregularities in the outer region of the entire width of the container body edging portion 51 in the inward and outward directions. The irregularities are wavy when viewed enlarged from the front, and the direction in which the numerous peaks and valleys extend is the width direction (inward and outward direction). As shown in FIG. 5, the container body has an opening portion 53 surrounded by the upper end of the container body side surface portion 56.

As shown in FIG. 5, a stacking protrusion 59 is formed near the upper end of the container body side portion 56 of the container body. FIG. 6 is a plan view of another example of the container of this embodiment. As shown in FIG. 6, the stacking protrusion 59 may be formed along the circumferential direction. The container bodies are transported in a state where many of them are stacked (also called a stacked state) to a line where contents such as food are filled. The stacking protrusion 59 ensures a gap between the stacked container bodies, making it easier to remove the container bodies. As shown in FIG. 6, the shape of the opening 53 and the bottom portion 55 of the container body is a square with four arc-shaped corners. As shown in FIG. 6, the bottom portion 55 has a recess 60 formed along the entire circumferential direction.

As shown in Figures 5 and 6, the shape of the container body, which includes the bottom surface portion 55, the container body side surface portion 56, and the opening portion 53, is approximately an inverted truncated pyramid shape.

As shown in FIG. 5, the lid material 52 covers the opening 53 of the container body, and may be a top seal composed of a single layer or multiple layers having gas barrier properties that are attached to the flange portion 54 of the container body. Such a top seal may be attached to the flange portion 54 by heat welding (fusion) or with a specified adhesive. In the case of a top-sealed container, if the dimensions of the container body change during high-temperature processing such as steam convection processing, the container body cannot be fixed in the sealing bucket when sealing with the lid material, and seal misalignment may occur. Therefore, it is desirable that the volume change rate is as small as possible, preferably 1% or less.

A fitting lid may be used instead of the lid material 52 shown in FIG. 5. FIG. 7 is a front view showing the state in which the fitting lid is placed on the container body. FIG. 8 is a plan view of the fitting lid. FIG. 9 is an enlarged view of the fitting portion between the fitting lid and the container body shown in FIG. 7. Like the container body, the fitting lid may be formed from a polypropylene resin composition containing a polypropylene resin and a nucleating agent, and the total haze value of the fitting lid may be 60% or less when measured according to JIS K7136. The physical properties of the fitting lid and the manufacturing method of the fitting lid are the same as those described for the container body, so the explanation will be omitted.

As shown in FIG. 7, the fitting lid includes a fitting lid protrusion 80, a fitting lid top surface 70, a fitting lid side surface 71 extending downward from the outer edge of the fitting lid top surface 70, a fitting lid extension 81 extending substantially horizontally outward from the lower end of the fitting lid side surface 71, a fitting lid fitting portion 72 extending upward from the outer edge of the fitting lid extension 81, and a fitting lid flange portion 73 extending outward from the upper end of the fitting lid fitting portion 72.

As shown in FIG. 7, the upper end of the container body side portion 77 is provided with a container body fitting portion 75 into which the fitting portion 72 of the fitting lid is fitted. The container body fitting portion 75 may be provided around the entire circumference. The container body fitting portion 75 also extends substantially vertically along the up-down direction. Furthermore, the flange portion 74 extends outward from the container body fitting portion 75.

The cross-sectional shape of the fitting lid fitting portion 72 preferably corresponds to the cross-sectional shape of the container body fitting portion 75. The fitting lid fitting portion 72 and the container body fitting portion 75 preferably have curved surfaces with approximately the same curvature in their cross-sectional shapes. At least one of the cross-sectional shape of the fitting lid fitting portion 72 corresponding to the cross-sectional shape of the container body fitting portion 75 and the fitting lid fitting portion 72 and the container body fitting portion 75 having curved surfaces with approximately the same curvature in their cross-sectional shapes allows for surface contact between the fitting lid fitting portion 72 and the container body fitting portion 75, increasing the fitting strength. In the case of the fitting lid method, if the container body changes in dimensions under high-temperature processing such as steam convection processing, the fitting lid cannot be fitted, so it is desirable that the volume change rate is as small as possible, preferably 1% or less.

As shown in FIG. 8, a lid knob 82 may be provided on the outer edge of the fitting lid flange 73 to facilitate the lid opening operation.
The container body of the present embodiment is formed from a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent. The polypropylene-based resin composition will be described below.

[Polypropylene resin composition]

The polypropylene resin composition forming the container body of this embodiment contains a polypropylene resin and a nucleating agent.

(Polypropylene resin)

In this embodiment, the polypropylene resin contained in the polypropylene-based resin composition is preferably homopolypropylene. Homopolypropylene refers to a polypropylene resin obtained by polymerizing essentially only propylene, but also includes those in which 99.5 wt% to 100 wt% of the total constituent units of the resin are propylene units.

The mesopentad fraction (mmmm) is an index representing the isotactic stereoregularity of a polypropylene resin, and the larger the mesopentad fraction (mmmm), the higher the isotactic stereoregularity. From the viewpoint of improving heat resistance, the polypropylene resin is preferably one having high isotactic stereoregularity, and the mesopentad fraction (mmmm) is preferably 96.0 to 99.5 mol%, more preferably 97.0 to 99.5 mol%, and even more preferably 98.0 to 99.5 mol%. The mesopentad fraction (mmmm) was measured in accordance with ¹³ C-NMR disclosed by A. Zambelli (Macromolecules, Vol. 6 (1973), p. 925) and Macromolecules, Vol. 8 (1975), p. 687.

Commercially available polypropylene resins can also be used as the polypropylene resin. Examples of such polypropylene resins include "Novatec (registered trademark) EA9HD" (meso pentad fraction [mmmm] in the range of 96.0 to 99.5 mol%) manufactured by Japan Polypropylene Corporation, "VS200A" (meso pentad fraction [mmmm] in the range of 96.0 to 99.5 mol%) and "VS200M" (meso pentad fraction [mmmm] in the range of 96.0 to 99.5 mol%) manufactured by SunAllomer Co., Ltd.

The content of polypropylene resin in the resin component is preferably 85% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on the mass of the polypropylene-based resin composition.

(Nucleating agent)

In this embodiment, the nucleating agent contained in the polypropylene resin composition is a component added to improve the crystallization rate and generate uniform and fine crystals in the polypropylene resin contained in the polypropylene resin composition. Examples of such nucleating agents include cyclic fatty acid metal salts and hexahydrophthalic acid metal salts.

As the fatty acid metal salt, a cyclic fatty acid metal salt is preferred. An example of such a cyclic fatty acid metal salt is a hexahydrophthalic acid metal salt represented by the following general formula (1).

(In general formula (1), _M1 and _M2 are each independently selected from the group consisting of calcium, sodium, strontium, lithium, zinc, magnesium, and monobasic aluminum; R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 are each independently selected from the group consisting of hydrogen and C1-C9 alkyl; and any two of the R3-R10 alkyl groups adjacent to each other may be optionally bonded to form a carbon ring.)

Examples of metal salts of hexahydrophthalic acid include calcium salts of hexahydrophthalic acid and sodium salts of hexahydrophthalic acid, and preferably calcium 1,2-cyclohexanedicarboxylate. Commercially available products of metal salts of hexahydrophthalic acid include HYPERFORM HPN-20E (manufactured by Milliken Japan LLC).

The amount of the nucleating agent is preferably 100 ppm or more and 10,000 ppm or less, more preferably 100 ppm or more and 5,000 ppm or less, and even more preferably 100 ppm or more and 3,000 ppm or less, based on the mass of the polypropylene resin composition.

(Additives)

The polypropylene resin composition forming the container body of this embodiment may further contain additives. Such additives include antioxidants, neutralizing agents, light stabilizers, ultraviolet absorbers, lubricants, antistatic agents, flame retardants, dispersants, plasticizers, etc.

Additives can be used alone or in combination of two or more.

For example, the amount of antioxidant or neutralizing stabilizer is preferably 0.01 to 2 parts by weight, more preferably 0.01 to 1 part by weight, and even more preferably 0.01 to 0.5 parts by weight, per 100 parts by weight of the polypropylene resin composition.

(2) Manufacturing method for heat-resistant containers

The method for producing a heat-resistant container according to this embodiment will be described below.
The method for producing a heat-resistant container according to this embodiment includes a polypropylene resin composition preparation step of mixing a polypropylene resin and a nucleating agent to prepare a polypropylene resin composition, a sheet molding step of extruding the polypropylene resin preparation to form a sheet, and a container body molding step of molding the sheet into a container body. Each step will be described below.

[Polypropylene resin composition preparation process]

In the polypropylene resin composition preparation process, the polypropylene resin and the nucleating agent are heated and mixed at 300°C or less. In this process, the raw materials such as the polypropylene resin and the nucleating agent may be mixed first. After mixing of the raw materials is completed, the mixed raw materials may be heated and kneaded. In the above process, the polypropylene resin may be heated to a temperature at which it can melt. The temperature may be appropriately selected by a person skilled in the art depending on the type of nucleating agent used and its content ratio.

In the above process, for example, when the nucleating agent is a cyclic fatty acid metal salt, the kneading is preferably performed at a temperature equal to or higher than the melting point of the polypropylene resin, more preferably equal to or higher than 180°C, and even more preferably equal to or higher than 200°C. Also, the kneading is preferably performed at a temperature equal to or lower than 300°C, more preferably equal to or lower than 280°C, and even more preferably equal to or lower than 260°C.

The mixing of raw materials such as polypropylene resin and nucleating agent may be performed, for example, by a mixer such as a high-temperature agitator, a Henschel mixer, a tumbler mixer, a Banbury mixer, or a kneader mixer. The mixed raw materials may be heated and kneaded, for example, by a single-screw kneading extruder or a twin-screw kneading extruder. As these kneading extruders, devices known in the art may be used. Preferably, the above process includes at least a heating and kneading process by a twin-screw kneading extruder. As the twin-screw kneading extruder, a co-rotating twin-screw kneading extruder or a counter-rotating twin-screw kneading extruder may be used. By performing the kneading process by a twin-screw kneading extruder, a polypropylene-based resin composition can be obtained, which is a kneaded product in which the raw materials are more uniformly dispersed.

The polypropylene resin composition obtained in the above step as a kneaded product may be directly subjected to a sheet molding step without being pelletized, thereby making it possible to omit the pelletizing step.
The polypropylene-based resin composition obtained as a kneaded product in the above step may be pelletized. The pelletized polypropylene-based resin composition as a kneaded product may be subjected to a sheet molding step.

[Sheet forming process]

In the sheet molding step, the polypropylene resin composition obtained in the polypropylene resin composition preparation step is molded to obtain a sheet. For example, the polypropylene resin composition obtained in the polypropylene resin composition preparation step is transferred to a sheet molding machine, and the polypropylene resin composition is molded using the sheet molding machine to form a sheet. The temperature when molding the sheet may be set preferably to a temperature equal to or higher than the melting temperature of the polypropylene resin composition, and may be set, for example, to a temperature between the melting point of the polypropylene resin and 300°C. The molding pressure may also be set appropriately.

When forming the sheet, various forming machines such as a T-die extruder and a calendar forming machine can be used. After the sheet is formed by the forming machine, the temperature of the take-up roll can be set appropriately, and the sheet formed to a predetermined thickness can be cooled immediately, and taken up and wound as a raw roll. The thickness of the sheet can be, for example, 100 μm or more.

In the molding, for example, the polypropylene resin composition may be extruded directly from the molding machine without being pelletized, or the pelletized polypropylene resin composition may be melted and the molten polypropylene resin composition may be extruded from the molding machine. The extrusion temperature may be appropriately selected by a person skilled in the art depending on the type and content of the nucleating agent contained in the polypropylene resin composition.

[Container body forming process]

In the container body forming process, the sheet obtained in the sheet forming process is softened by heating, and the softened sheet is attached to a forming die by suction to vacuum-form a recess in which the packaged item is to be accommodated, thereby forming the container body. Vacuum forming or vacuum-pressure forming is used as the forming method. Plug assist is also performed depending on the expansion ratio. The depth of the recess can be set appropriately according to the application, and for example, the depth of the recess may be preferably 1 to 5 cm. Deep drawing molding with an expansion ratio of 2.5 or more may also be performed. The sheet surface temperature immediately before forming in the forming machine measured with a non-contact radiation thermometer is preferably heated to 140°C to 170°C, the heating time is preferably set to 6 to 15 seconds, and the forming time is preferably set to 6 to 15 seconds. Here, a higher sheet surface temperature immediately before forming reduces residual stress in the formed container and is advantageous in terms of heat resistance, but the optimal sheet surface temperature is selected from the viewpoint of the thickness unevenness balance of a multi-cavity container. According to the present invention, even if the sheet surface temperature is below the melting point of PP, it is possible to produce a container that satisfies a volume change rate of ±1% or less after heating at 130°C for 60 minutes.

The container body molding process is not limited to the thermoforming method, but may be an injection molding method in which a mixture of the specific polypropylene resin and the nucleating agent is melted and plasticized by heating and kneading, and the container is then injected into a mold, pressure-dampened, cooled, opened, removed, and closed.

In the in-line molding method, the container body is molded, the packaged item is filled in it, and then a top film is placed over it as a lid material as shown in FIG. 1, heat sealed, and then cut. Such a top film is not particularly limited, but may be made of a single layer or multiple layers of polyethylene resin, polypropylene resin, polyamide resin, ethylene-vinyl alcohol copolymer resin, polyethylene terephthalate resin, etc. as appropriate. Also, a fitting lid as shown in FIGS. 7, 8, and 9 may be used instead of the top film.

(3) Physical properties of heat-resistant containers

The physical properties of the heat-resistant container according to this embodiment are described below.

[Volume change rate]

The heat-resistant container of this embodiment satisfies the requirement that the volumetric change rate of the heat-resistant container after heating at 130°C for 60 minutes is ±1% or less, preferably ±0.9% or less, and more preferably ±0.8% or less. The volumetric change rate of the heat-resistant container after heating at 120°C for 60 minutes is ±0.9% or less, preferably ±0.8% or less, and more preferably ±0.7% or less.

(Measurement of volume change rate)

To measure the rate of volume change, the volume of the container before heating and that of the heated heat-resistant container are measured. The heat-resistant container is placed in a high-temperature incubator heated to the specified temperature, and the heat-resistant container is heated with the damper open to 75 degrees. After the specified temperature is reached, the heat-resistant container is heated for an additional hour. After one hour has passed, the heat-resistant container is exposed to room temperature and left for at least one day, after which the rate of volume change of the heat-resistant container is measured.

The volume change rate of the heat-resistant container is measured by the following procedure.
(i) First, the container water filling amount Wb (g) before heating is measured. FIG. 10 is a perspective view showing how to measure the volume change rate of a heat-resistant container. FIG. 11 is a diagram showing a dedicated jig. FIG. 12 is a diagram showing a flat plate with a hole in the center. First, as shown in FIG. 10, the heat-resistant container 103 is placed on a dedicated jig 104 on an electronic balance 101 (FX-2000i, manufactured by A&D Co., Ltd.) with the bottom surface of the heat-resistant container 103 as the bottom, and a flat plate 102 with a hole of φ7 mm in the center larger than the top surface of the heat-resistant container 103 is placed on the top surface and fixed with masking tape, and the zero point is adjusted.
(ii) Water is added from the hole in the center of the flat plate 102 using a dropper or the like, and the amount of water filled in the container Wb (g) when it is full is measured (to cancel the surface tension of the water). Measurements are performed for n=5. The obtained values are arithmetically averaged to obtain Wb _ave .
(iii) Set the high temperature incubator "LP-201" (manufactured by Espec Corporation) to a specified temperature and heat it. Place the heat-resistant container 103 in the heated state inside the high temperature incubator, and heat the heat-resistant container 103 with the damper open to 75. After the specified temperature is reached, heat it for one hour. After one hour has passed, expose the heat-resistant container 103 to room temperature and leave it for one day or more, and then measure the container water fill amount Wa (g) after heating in the same manner as the container water fill amount Wb (g) before heating.
(iv) The volume change rate is calculated from the following formula: The measurement is performed for n=5, and the obtained values are arithmetically averaged to be designated as Wa _ave .
Volume change rate (%) = [1 - Wa _ave / Wb _ave ] x 100

[Total haze value]

The heat-resistant container of this embodiment has a total haze value of 60% or less, preferably 55% or less, more preferably 53% or less, and even more preferably 50% or less, when measured according to JIS K7136. The total haze value (total haze) refers to a haze value obtained by adding up the external haze value (surface haze) and the internal haze value (inner haze), and is expressed by the following formula.
Total haze value (%) = External haze value (%) + Internal haze value (%)
The measurement principle of internal haze is the same as for total haze, but by applying silicone to both outer surfaces of the sample and sandwiching it between glass plates, the measurement can be performed while eliminating external haze factors caused by unevenness on the outer surface of the sample.
The external haze can be calculated from the measured total haze and internal haze values using the above formula.

(Measurement of total haze value)

Using a haze meter "HZ-V3" (manufactured by Suga Test Instruments Co., Ltd.), measure the center part of the side of the heat-resistant container before heat treatment in accordance with JIS K7136. The measurement is performed by measuring four or more points on the side part of the heat-resistant container, and the total haze value is plotted against the thickness of the measured part. The total haze value for a specific thickness is calculated from the approximation line of the plot.

2. Second embodiment (example of sheet)

(1) Sheet configuration

The configuration of the sheet according to this embodiment will be described below: The sheet according to this embodiment is a single-layer sheet.
The sheet according to this embodiment is formed from a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent. All of the descriptions regarding the polypropylene-based resin composition described in the above 1. "(1) Configuration of the container" also apply to the second embodiment. Therefore, the description of the polypropylene-based resin composition is omitted.

(2) Sheet manufacturing method

The method for producing a sheet according to this embodiment includes a polypropylene resin composition preparation step in which a polypropylene resin and a nucleating agent are mixed to prepare a polypropylene resin composition, and a sheet molding step in which the polypropylene resin composition is extruded to form a sheet. Note that, for the polypropylene resin composition preparation step and the sheet molding step, all of the explanations regarding the polypropylene resin composition preparation step and the sheet molding step described in 1. above, "(2) Container manufacturing method", also apply to the second embodiment. Therefore, the explanations regarding the polypropylene resin composition preparation step and the sheet molding step according to the second embodiment will be omitted.

(3) Physical properties of the sheet

[Total haze value]

The sheet of this embodiment has a total haze value of 60% or less, preferably 55% or less, more preferably 53% or less, and even more preferably 50% or less, when measured according to JIS K7136.

(Measurement of total haze value)

Using a haze meter "HZ-V3" (manufactured by Suga Test Instruments Co., Ltd.), measurements are made in accordance with JIS K7136 on the sheet before heat treatment. The total haze % and thickness are measured at four or more points on the sheet, and the total haze value is plotted against the thickness of the measured area. The total haze value for a specific thickness is calculated from the approximation line of the plot.

3. Third embodiment (example of multilayer sheet)

(1) Multilayer sheet structure

Here, a three-type three-layer sheet is shown, but there is no particular limitation on the number of layers, and it is sufficient that the multilayer sheet is formed by laminating at least one layer having "homopolypropylene with a mesopentad fraction of 96.0 to 99.5 mol % and a nucleating agent" and a thermoplastic resin.
As shown in FIG. 13, the multilayer sheet of this embodiment has a first outer layer 111, a second outer layer 113, and an intermediate layer 112 disposed between the first outer layer and the second outer layer.

[First outer layer]

The first outer layer 111 is made of a first resin composition containing a first polyolefin-based resin. The first polyolefin-based resin is preferably a polymer obtained by polymerization using olefins (e.g., α-olefins) as the main monomer. The polyolefin-based resin may be, for example, a polyethylene (PE) resin or a polypropylene (PP) resin, or a combination thereof.

The polyethylene resin may be, for example, a low density polyethylene resin (LDPE: Low Density Polyethylene), a high density polyethylene resin (HDPE: High Density Polyethylene), a very low density polyethylene resin (VLDPE: Very Low Density Polyethylene), a linear low density polyethylene resin (LLDPE: Linear Low Density Polyethylene), an ethylene-vinyl acetate copolymer (EVA: Ethylene-Vinyl Acetate Copolymer), or an ethylene copolymer such as an ultra-high molecular weight polyethylene resin (UHMW-PE: Ultra High Molecular Weight-Polyethylene), or a combination thereof.

The polyolefin resin may be, if desired, preferably a biomass-derived polyolefin resin (such as a biomass-derived polyethylene resin), for example, a biomass polyethylene resin. The biomass polyethylene resin may be, for example, LDPE, LLDPE, or HDPE. Biomass polyethylene can be considered carbon neutral and can reduce CO2 emissions compared to petroleum-derived polyethylene.

The polyolefin resin may be a polyolefin resin produced using a metallocene catalyst. That is, the thermoplastic resin may be, for example, a metallocene-catalyzed polyethylene resin or polypropylene resin, or a combination thereof.

The polyester resin as another first resin composition is a polymer in which monomers are polymerized through ester bonds. The polyester resin may be, for example, polyethylene terephthalate resin (PET), polyethylene naphthalate resin (PEN), polybutylene terephthalate resin (PBT), polylactic acid resin (PLA), polycarbonate resin (PC), polybutylene adipate terephthalate resin (PBAT), polybutylene succinate resin (PBS), polyhydroxyalkanoate resin (PHA), or a combination of two or more of these.

The polystyrene-based resin as another first resin composition is a polymer formed by polymerizing a styrene-based monomer, and may be a metallocene catalyst-based polystyrene-based resin. The polystyrene-based resin may be, for example, polystyrene resin, rubber-reinforced polystyrene resin (high impact polystyrene resin, HIPS), syndiotactic polystyrene resin, acrylonitrile-styrene copolymer (AS resin), methacrylate ester-styrene copolymer, acrylonitrile-acrylic rubber-styrene copolymer, acrylonitrile-ethylene propylene-styrene copolymer, or a combination of two or more of these.

The first polyolefin resin may preferably be the polypropylene resin composition of the first embodiment. The first resin composition may be composed only of resins other than polypropylene resin.

The first resin composition may preferably contain the nucleating agent of the first embodiment.

[Second outer layer]

The second outer layer 113 is made of a second resin composition containing a second polyolefin resin. The same description as for the first polyolefin resin applies to the second polyolefin resin. Therefore, the description of the second polyolefin resin is omitted. The second polyolefin resin may be the same type as the first polyolefin resin, or may be a different type. The second resin composition may be composed only of a resin other than polypropylene resin.

[Middle class]

As shown in FIG. 13, the intermediate layer 112 is provided between the first outer layer and the second outer layer. The intermediate layer is made of a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent.

The polypropylene resin composition and nucleating agent that form the intermediate layer are the same as those described in the first embodiment, so their description will be omitted.

(2) Manufacturing method for multilayer sheets

The method for producing the multilayer sheet of this embodiment may include, for example, a resin composition preparation step and a multilayer extrusion molding step.

[Resin composition preparation process]

In the resin composition preparation process, a first resin composition, a second resin composition, and a polypropylene-based resin composition are each prepared. The explanation of the polypropylene-based resin composition preparation process in the first embodiment is applicable to the first resin composition and the second resin composition, except that the first resin composition and the second resin composition are used instead of the polypropylene-based resin composition, and therefore the explanation is omitted.

[Multi-layer extrusion molding process]

In the multi-layer extrusion molding process, the first resin composition, the polypropylene-based resin composition, and the second resin composition are extruded and molded so that the resin layers are laminated to each other to obtain a multi-layer sheet. The multi-layer sheet can be obtained, for example, by using a multi-layer co-extrusion molding machine 300 shown in FIG. 14. The multi-layer co-extrusion molding machine 300 may have a first outer layer extruder 301, an intermediate layer extruder 302, a second outer layer extruder 303, a feed block 304, and a die 305. The multi-layer co-extrusion molding machine 300 co-extrudes a three-layer structure multi-layer sheet 306 in which the first outer layer, the intermediate layer, and the second outer layer are laminated, with the intermediate layer containing the polypropylene-based resin composition as the middle layer and the first outer layer and the second outer layer as the surface layers. The intermediate layer extruder 302 extrudes the polypropylene-based resin composition prepared in the resin composition preparation process, and the first outer layer extruder 301 and the second outer layer extruder 303 may each extrude a different type of resin composition from the polypropylene-based resin composition extruded from the intermediate layer extruder 302, or may extrude the same polypropylene-based resin composition.

(3) Physical properties of multilayer sheets

[Total haze value]

The multilayer sheet of this embodiment has a total haze value of 60% or less, preferably 55% or less, more preferably 53% or less, and even more preferably 50% or less, when measured according to JIS K7136.

(Measurement of total haze value)

The measurement of the total haze value of a multilayer sheet is the same as that described in 2. (3) Physical properties of the sheet, above, so the description is omitted here.

4. Fourth embodiment (example of multilayer sheet)

(1) Multilayer sheet structure

In the multilayer sheet of the present embodiment, the first outer layer 111 and the second outer layer 113 may be made of a polypropylene resin composition containing a polypropylene resin and a nucleating agent, and the intermediate layer 112 provided between the first outer layer and the second outer layer may be made of a first resin composition containing the first polyolefin resin or a second resin composition containing the second polyolefin resin. In addition, the multilayer sheet of the present embodiment may be a two-layer sheet having either the first outer layer 111 or the second outer layer 113 and the intermediate layer 112 in the multilayer sheet of the third embodiment shown in FIG. 13, and the first outer layer 111 or the second outer layer 113 may be made of a polypropylene resin composition containing a polypropylene resin and a nucleating agent, and the intermediate layer 112 provided between the first outer layer and the second outer layer may be made of a first resin composition containing the first polyolefin resin or a second resin composition containing the second polyolefin resin.

The present technology can also adopt the following configuration.
[1]
Polypropylene resin,
A container body formed from a polypropylene-based resin composition containing a nucleating agent,
The heat-resistant container has a volume change rate of ±1% or less after heating at 130° C. for 60 minutes.
A heat-resistant container, wherein the total haze value of the container body is 60% or less when measured in accordance with JIS K7136.
[2]
The heat-resistant container according to [1], wherein the polypropylene resin has a meso pentad fraction (mmmm) of 96.0 to 99.5 mol%.
[3]
The heat-resistant container according to [1] or [2], wherein the nucleating agent is a cyclic fatty acid metal salt.
[4]
The heat-resistant container according to any one of [1] to [3], wherein the nucleating agent is a metal salt of hexahydrophthalic acid.
[5]
The heat-resistant container according to any one of [1] to [4], wherein the heat-resistant container is a heat-resistant container for food for storing food.
[6]
The heat-resistant container is a heat-resistant container for steam convection use, and has a container body formed from a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent.
[7]
A first outer layer, a second outer layer, and an intermediate layer provided between the first outer layer and the second outer layer,
the first outer layer is made of a first resin composition containing a first polyolefin-based resin,
the second outer layer is made of a second resin composition containing a second polyolefin-based resin,
At least the intermediate layer is made of a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent,
A heat-resistant container in which the volumetric change rate of the container body after heating at 130° C. for 60 minutes satisfies ±1% or less, and the total haze value is 60.0% or less.
[8]
Polypropylene resin,
A sheet formed from a polypropylene-based resin composition containing a nucleating agent,
A sheet having a total haze value of 60.0% or less.
[9]
A first outer layer, a second outer layer, and an intermediate layer provided between the first outer layer and the second outer layer,
the first outer layer is made of a first resin composition containing a first polyolefin-based resin,
the second outer layer is made of a second resin composition containing a second polyolefin-based resin,
A multi-layer sheet, wherein at least the intermediate layer is made of a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent,
A multilayer sheet having a total haze value of 60.0% or less.
[10]
A polypropylene resin composition preparation step of mixing a polypropylene resin and a nucleating agent to prepare a polypropylene resin composition;
a sheet molding step of extruding the polypropylene-based resin preparation as is or after pelletization into a sheet;
a container body forming step of forming a container body from the sheet;
A method for manufacturing a heat-resistant container comprising the steps of:
[11]
A polypropylene resin composition preparation step of mixing a polypropylene resin and a nucleating agent to prepare a polypropylene resin composition;
a sheet molding step of extruding the polypropylene-based resin preparation as is or after pelletization into a sheet;
A method for manufacturing a sheet comprising the steps of:

5. Example

The present invention will be described in more detail below based on examples. Note that the examples described below are representative examples of the present invention, and the scope of the present invention is not limited to these examples. The evaluation methods used in the examples are the same as those described above in 1. (3) Properties of the container and 3. (3) Properties of the multilayer sheet.

(Example 1)

A polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) is supplied to the first outer layer single screw extruder 301 of the multi-layer co-extrusion molding machine 300 shown in FIG. 14 via a hopper so that the amount of the polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) is 97.5% by mass relative to the mass of the first resin composition, and a hexahydrophthalic acid metal salt masterbatch (product name: HYPERFORM HPN-20E, manufactured by Milliken Japan LLC, containing 4% nucleating agent component) is 2.5% by mass. A polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation) is supplied to the middle layer twin screw extruder 302 via a loss-in type weight feeder (not shown) so that the amount of the hexahydrophthalic acid metal salt masterbatch (product name: HYPERFORM HPN-20E, manufactured by Milliken Japan LLC, containing 4% nucleating agent component) is 97.5% by mass relative to the mass of the polypropylene resin composition, and a hexahydrophthalic acid metal salt masterbatch (product name: HYPERFORM HPN-20E, manufactured by Milliken Japan LLC, containing 4% nucleating agent component) is 2.5% by mass. 97.5% by mass of polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation) and 2.5% by mass of hexahydrophthalic acid metal salt masterbatch (product name: HYPERFORM HPN-20E, manufactured by Milliken Japan LLC, containing 4% nucleating agent component) were supplied to the second outer layer single screw extruder 303 via a hopper, relative to the mass of the polypropylene resin composition. The resin compositions supplied to the first outer layer single screw extruder, intermediate layer twin screw extruder, and second outer layer single screw extruder were co-extruded, cooled by a three-roll take-up machine (not shown) with each roll temperature of 50°C, and film-formed at a take-up speed of 26.0 m/min. After edge trimming, a roll of a three-layered multilayer sheet with a sheet width of 775 mm was obtained.

The cylinder temperatures and adapter temperatures of the first outer layer single screw extruder 301 (L/D=30, φ75mm), the intermediate layer twin screw extruder 302 (L/D=30, φ113mm), and the second outer layer single screw extruder 303 (L/D=30, φ75mm) were set to 220-250°C. The output of the intermediate layer twin screw extruder 302 was set to 620kg/h, and the output of the first outer layer single screw extruder 301 and the second outer layer single screw extruder 303 was set to 30kg/h. The resin temperatures of the first outer layer single screw extruder 301 were 224°C, the intermediate layer twin screw extruder 302 was 248°C, and the second outer layer single screw extruder 303 was 224°C.

The multilayer extrusion molding resulted in a multilayer sheet (hereinafter also referred to as "multilayer sheet of Example 1") having a thickness of 552 μm, whereas the target thickness was 550±27.5 μm. In the multilayer sheet of Example 1, the first outer layer had a thickness of 22 μm, whereas the target thickness of the first outer layer was 30±10.0 μm; the intermediate layer had a thickness of 508 μm, whereas the target thickness of the intermediate layer was 490±20.0 μm; and the second outer layer had a thickness of 22 μm, whereas the target thickness of the second outer layer was 30±10.0 μm. The obtained multilayer sheet had a total haze value of 51.0% at a thickness of 550 μm. The measurement results are shown in Table 1 below.

The multilayer sheet obtained was then heated to 150°C using a radiation thermometer on the molding machine, and then vacuum-pressure molded into multiple cup-shaped containers. The expansion ratio of the resulting cup-shaped container was 2.6. The volume change rate of the resulting cup-shaped container after heating at 120°C for 60 minutes was -0.2%, and the volume change rate after heating at 130°C for 60 minutes was -0.5%. Furthermore, the total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 44.3%. The measurement results are shown in Table 2 below.

(Example 2)

A polypropylene resin (product name: VS200M, manufactured by Sunallomer Co., Ltd., homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) is supplied to the first outer layer single screw extruder 301 and the second outer layer single screw extruder 303 via a hopper so as to be 100.0 mass% relative to the mass of the resin composition, and a polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) is supplied to the intermediate layer twin screw extruder 302 via a loss-in type weight feeder (not shown) so as to be 97.5 mass% relative to the mass of the polypropylene resin composition, and a hexahydrophthalic acid metal salt masterbatch (product name: HYPERFORM) is supplied to the intermediate layer twin screw extruder 302 via a loss-in type weight feeder (not shown). HPN-20E, Milliken Japan LLC, containing 4% nucleating agent) was supplied to the first outer layer single screw extruder, the intermediate layer twin screw extruder, and the second outer layer single screw extruder, and the resin compositions supplied to each were co-extruded and film-formed at a take-up speed of 25.9 m/min. After edge trimming, a roll with a sheet width of 775 mm was obtained. This resulted in a three-layered multilayer sheet (hereinafter also referred to as "multilayer sheet of Example 2") having a thickness of 548 μm, compared to a target thickness of 550±27.5 μm. In the multilayer sheet of Example 2, the thickness of the first outer layer was 21 μm, the thickness of the intermediate layer was 507 μm, and the thickness of the second outer layer was 21 μm.

The film-making equipment, equipment temperature, and extrusion rate were the same as in Example 1. The resin temperatures of the first outer layer single-screw extruder 301 were 225°C, the intermediate layer twin-screw extruder 302 was 248°C, and the second outer layer single-screw extruder 303 was 225°C.

The multilayer sheet of Example 2 obtained had a total haze value of 51.3% at a thickness of 550 μm. The measurement results are shown in Table 1.

The resulting multilayer sheet was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The resulting cup-shaped container had a volume change rate of -0.3% after heating at 120°C for 60 minutes, and a volume change rate of -0.6% after heating at 130°C for 60 minutes. The total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 45.0%. The measurement results are shown in Table 2.

(Example 3)

The same procedure as in Example 1 was carried out except that 97.5% by mass of polypropylene resin (product name: VS200M, manufactured by SunAllomer Co., Ltd., homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) and 2.5% by mass of hexahydrophthalic acid metal salt master batch (product name: HYPERFORM HPN-20E, manufactured by Milliken Japan LLC, containing 4% nucleating agent component) were supplied to the first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303, relative to the mass of the resin composition, to obtain a three-layered multilayer sheet (hereinafter also referred to as the "multilayer sheet of Example 3"). In the multilayer sheet of Example 3, the thickness of the first outer layer was 22 μm, the thickness of the intermediate layer was 510 μm, and the thickness of the second outer layer was 21 μm.

The film-making equipment, set temperature, and extrusion rate were the same as in Example 1. The resin temperatures were 227°C for the first outer layer single screw extruder 301, 249°C for the intermediate layer twin screw extruder 302, and 227°C for the second outer layer single screw extruder 303. The resin was made into a film at a drawing speed of 25.7 m/min, and after edge trimming, a roll with a sheet width of 775 mm was obtained.

The multilayer sheet of Example 3 obtained had a total haze value of 52.8% at a thickness of 550 μm. The measurement results are shown in Table 1.

The resulting multilayer sheet was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The resulting cup-shaped container had a volumetric change rate of 0.1% after heating at 120°C for 60 minutes, and a volumetric change rate of -0.2% after heating at 130°C for 60 minutes. The total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 47.3%. The measurement results are shown in Table 2.

(Example 4)

The same procedure as in Example 1 was carried out except that 98.5% by mass of polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) and 1.5% by mass of hexahydrophthalic acid metal salt master batch (product name: HYPERFORM HPN-20E, manufactured by Milliken Japan LLC, containing 4% nucleating agent component) were supplied to the first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303, relative to the mass of the resin composition, to obtain a three-layered multilayer sheet (hereinafter also referred to as the "multilayer sheet of Example 4"). In the multilayer sheet of Example 4, the thickness of the first outer layer was 23 μm, the thickness of the intermediate layer was 503 μm, and the thickness of the second outer layer was 22 μm.

The manufacturing equipment and set temperatures were the same as in Example 1, the output of the twin-screw extruder 302 for the intermediate layer was 420 kg/h, and the output of each of the first single-screw extruder 301 for the outer layer and the second single-screw extruder 303 for the outer layer was 20 kg/h. The resin temperatures of each were 222°C for the first single-screw extruder 301 for the outer layer, 250°C for the twin-screw extruder 302 for the intermediate layer, and 222°C for the second single-screw extruder 303 for the outer layer. The resin was formed into a film at a drawing speed of 17.8 m/min, and after edge trimming, a roll with a sheet width of 775 mm was obtained.

The multilayer sheet of Example 4 obtained had a total haze value of 44.9% at a thickness of 550 μm. The measurement results are shown in Table 1.

The resulting multilayer sheet was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The resulting cup-shaped container had a volume change rate of -0.3% after heating at 120°C for 60 minutes, and a volume change rate of -0.6% after heating at 130°C for 60 minutes. The total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 50.6%. The measurement results are shown in Table 2.

(Example 5)

The same procedure as in Example 1 was carried out except that 87.5% by mass of polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%), 10.0% by mass of polyethylene resin (product name: KS260, manufactured by Japan Polyethylene Corporation), and 2.5% by mass of hexahydrophthalic acid metal salt master batch (product name: HYPERFORM HPN-20E, manufactured by Milliken Japan LLC, containing 4% nucleating agent component) were supplied to the first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303, relative to the mass of the resin composition, to obtain a multilayer sheet having a three-layer structure (hereinafter also referred to as the "multilayer sheet of Example 5"). In the multilayer sheet of Example 5, the thickness of the first outer layer was 21 μm, the thickness of the intermediate layer was 505 μm, and the thickness of the second outer layer was 21 μm.

The film-making equipment, set temperature, and extrusion rate were the same as in Example 4. The resin temperatures were 223°C for the first outer layer single screw extruder 301, 250°C for the intermediate layer twin screw extruder 302, and 222°C for the second outer layer single screw extruder 303. The resin was made into a film at a drawing speed of 18.2 m/min, and after edge trimming, a roll with a sheet width of 775 mm was obtained.

The multilayer sheet of Example 5 obtained had a total haze value of 38.6% at a thickness of 550 μm. The measurement results are shown in Table 1.

The resulting multilayer sheet was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The resulting cup-shaped container had a volume change rate of -0.4% after heating at 120°C for 60 minutes, and a volume change rate of -0.5% after heating at 130°C for 60 minutes. The total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 44.4%. The measurement results are shown in Table 2.

(Example 6)

The first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303 were supplied with 97.5 mass% polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) and 2.5 mass% hexahydrophthalic acid metal salt masterbatch (product name: HYPERFORM HPN-20E, manufactured by Milliken Japan LLC, containing 4% nucleating agent component) relative to the mass of the resin composition, and the same procedure as in Example 1 was carried out except that the take-up speed was 17.8 m/min. A roll of a three-layered multilayer sheet (hereinafter also referred to as the "multilayer sheet of Example 6") was obtained, with a thickness of 798 μm compared to the target thickness of 800±40.0 μm, and a sheet width of 795 mm after edge trimming. In the multilayer sheet of Example 6, the target thickness of the first outer layer was 30±10.0 μm, whereas the thickness of the first outer layer was 31 μm; the target thickness of the intermediate layer was 740±20.0 μm, whereas the thickness of the intermediate layer was 737 μm; and the target thickness of the second outer layer was 30±10.0 μm, whereas the thickness of the second outer layer was 30 μm.

The resin temperatures of the first outer layer single screw extruder 301 were 224°C, the intermediate layer twin screw extruder 302 was 248°C, and the second outer layer single screw extruder 303 was 224°C.

The multilayer sheet of Example 6 obtained had a total haze value of 59.1% at a thickness of 800 μm. The measurement results are shown in Table 1.

The resulting multilayer sheet was then vacuum-pressurized into a cup-shaped container of a different shape from that of Example 1 with an expansion ratio of 3.8, using the same method as in Example 1. The resulting cup-shaped container showed a volume change rate of -0.3% after heating at 120°C for 60 minutes, and a volume change rate of -0.7% after heating at 130°C for 60 minutes, even though the expansion ratio was increased to 3.8. Furthermore, the total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 45.2%. The measurement results are shown in Table 2.

(Comparative Example 1)

The same procedure as in Example 4 was carried out except that polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) was supplied to the first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303 so as to be 100.0 mass% relative to the mass of the resin composition, and a multilayer sheet with a three-layer structure (hereinafter also referred to as "multilayer sheet of Comparative Example 1") was obtained. In the multilayer sheet of Comparative Example 1, the thickness of the first outer layer was 25 μm, the thickness of the intermediate layer was 498 μm, and the thickness of the second outer layer was 24 μm.

The film-making equipment, set temperature, and extrusion rate were the same as in Example 4. The resin temperatures were 222°C for the first outer layer single screw extruder 301, 249°C for the intermediate layer twin screw extruder 302, and 222°C for the second outer layer single screw extruder 303. The resin was made into a film at a drawing speed of 18.0 m/min, and after edge trimming, a roll with a sheet width of 775 mm was obtained.

The multilayer sheet obtained in Comparative Example 1 had a total haze value of 50.2% at a thickness of 550 μm. The measurement results are shown in Table 1.

The multilayer sheet obtained was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The volume change rate of the obtained cup-shaped container after heating for 60 minutes at 120°C was 1.1%, and the volume change rate after heating for 60 minutes at 130°C was 1.3%. Furthermore, the container after heating at 120°C and 130°C showed swelling and deformation at the bottom, making it difficult to put into practical use. Furthermore, the total haze value at a thickness of 210 μm on the side of the obtained cup-shaped container before heating was 56.0%. The measurement results are shown in Table 2.

(Comparative Example 2)

The same procedure as in Example 4 was carried out except that 97.5% by mass of polypropylene resin (product name: E-304GP, manufactured by Prime Polymer Co., Ltd., homopolypropylene with a mesopentad fraction in the range of 90.0 to 93.0 mol%) and 2.5% by mass of hexahydrophthalic acid metal salt master batch (product name: HYPERFORM HPN-20E, manufactured by Milliken Japan LLC, containing 4% nucleating agent component) were supplied to the first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303, relative to the mass of the resin composition, to obtain a three-layered multilayer sheet (hereinafter also referred to as "multilayer sheet of Comparative Example 2"). In the multilayer sheet of Comparative Example 2, the thickness of the first outer layer was 22 μm, the thickness of the intermediate layer was 503 μm, and the thickness of the second outer layer was 22 μm.

The film-making equipment, set temperature, and extrusion rate were the same as in Example 4. The resin temperatures were 222°C for the first outer layer single screw extruder 301, 249°C for the intermediate layer twin screw extruder 302, and 222°C for the second outer layer single screw extruder 303. The resin was made into a film at a drawing speed of 17.7 m/min, and after edge trimming, a roll with a sheet width of 775 mm was obtained.

The multilayer sheet obtained in Comparative Example 2 had a total haze value of 37.1% at a thickness of 550 μm. The measurement results are shown in Table 1.

The multilayer sheet obtained was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The volume change rate of the obtained cup-shaped container after heating at 120°C for 60 minutes was 0.9%, and the volume change rate after heating at 130°C for 60 minutes was 1.1%. Furthermore, the container after heating at 120°C and 130°C showed swelling and deformation at the bottom, making it difficult to put into practical use. Furthermore, the total haze value at a thickness of 210 μm on the side of the obtained cup-shaped container before heating was 41.5%. The measurement results are shown in Table 2.

(Comparative Example 3)

The same procedure as in Example 1 was carried out except that 98.0% by mass of polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) and 2.0% by mass of dispersion-type nucleating agent (registered trademark: RiKACRYSTA P1, manufactured by New Japan Chemical Co., Ltd., containing 5% nucleating agent component) were supplied to the first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303, relative to the mass of the resin composition, to obtain a multilayer sheet with a three-layer structure (hereinafter also referred to as the "multilayer sheet of Comparative Example 3"). In the multilayer sheet of Comparative Example 3, the thickness of the first outer layer was 23 μm, the thickness of the intermediate layer was 504 μm, and the thickness of the second outer layer was 22 μm.

The film-making equipment, set temperature, and extrusion rate were the same as in Example 1. The resin temperatures were 224°C for the first outer layer single screw extruder 301, 249°C for the intermediate layer twin screw extruder 302, and 224°C for the second outer layer single screw extruder 303. The resin was formed into a film at a drawing speed of 26.0 m/min, and after edge trimming, a roll with a sheet width of 775 mm was obtained.

The multilayer sheet obtained in Comparative Example 3 had a total haze value of 54.8% at a thickness of 550 μm. The measurement results are shown in Table 1.

The resulting multilayer sheet was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The resulting cup-shaped container had a volume change rate of -0.5% after heating at 120°C for 60 minutes, and a volume change rate of -1.5% after heating at 130°C for 60 minutes. The total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 54.3%. The measurement results are shown in Table 2.

(Comparative Example 4)

The same procedure as in Example 4 was carried out except that 98.0% by mass of polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) and 2.0% by mass of phosphate ester metal salt master batch (registered trademark: ADKSTAB NA11, manufactured by ADEKA Corporation, containing 5% nucleating agent component) were supplied to the first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303, relative to the mass of the resin composition, to obtain a multilayer sheet with a three-layer structure (hereinafter also referred to as the "multilayer sheet of Comparative Example 4"). In the multilayer sheet of Comparative Example 4, the thickness of the first outer layer was 22 μm, the thickness of the intermediate layer was 504 μm, and the thickness of the second outer layer was 21 μm.

The film-making equipment, set temperature, and extrusion rate were the same as in Example 4. The resin temperatures were 223°C for the first outer layer single screw extruder 301, 250°C for the intermediate layer twin screw extruder 302, and 223°C for the second outer layer single screw extruder 303. The resin was made into a film at a drawing speed of 17.7 m/min, and after edge trimming, a roll with a sheet width of 775 mm was obtained.

The multilayer sheet obtained in Comparative Example 4 had a total haze value of 32.4% at a thickness of 550 μm. The measurement results are shown in Table 1.

The resulting multilayer sheet was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The resulting cup-shaped container had a volume change rate of -1.1% after heating at 120°C for 60 minutes, and a volume change rate of -1.2% after heating at 130°C for 60 minutes. The total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 45.2%. The measurement results are shown in Table 2.

(Comparative Example 5)

The same procedure as in Example 4 was carried out except that 97.5% by mass of polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) and 2.5% by mass of fatty acid metal salt master batch (registered trademark: AL-PTBBA, manufactured by Oxalis Chemicals Corporation, containing 4% nucleating agent component) were supplied to the first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303, relative to the mass of the resin composition, to obtain a multilayer sheet with a three-layer structure (hereinafter also referred to as the "multilayer sheet of Comparative Example 5"). In the multilayer sheet of Comparative Example 5, the thickness of the first outer layer was 21 μm, the thickness of the intermediate layer was 505 μm, and the thickness of the second outer layer was 22 μm.

The film-making equipment, set temperature, and extrusion rate were the same as in Example 4. The resin temperatures were 224°C for the first outer layer single screw extruder 301, 250°C for the intermediate layer twin screw extruder 302, and 223°C for the second outer layer single screw extruder 303. The resin was made into a film at a drawing speed of 17.9 m/min, and after edge trimming, a roll with a sheet width of 775 mm was obtained.

The multilayer sheet obtained in Comparative Example 5 had a total haze value of 40.4% at a thickness of 550 μm. The measurement results are shown in Table 1.

The resulting multilayer sheet was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The resulting cup-shaped container had a volume change rate of -1.1% after heating at 120°C for 60 minutes, and a volume change rate of -1.5% after heating at 130°C for 60 minutes. The total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 49.6%. The measurement results are shown in Table 2.

(Comparative Example 6)

The same procedure as in Example 4 was carried out except that 97.5% by mass of polypropylene resin (product name: EA9HD, manufactured by Japan Polypropylene Corporation, homopolypropylene with a mesopentad fraction in the range of 96.0 to 99.5 mol%) and 2.5% by mass of benzylidene sorbitol-based compound master batch (registered trademark: Mirado 3988, manufactured by Milliken Japan LLC, containing 10% nucleating agent component) were supplied to the first outer layer single screw extruder 301, the intermediate layer twin screw extruder 302, and the second outer layer single screw extruder 303, relative to the mass of the resin composition, to obtain a multilayer sheet with a three-layer structure (hereinafter also referred to as the "multilayer sheet of Comparative Example 6"). In the multilayer sheet of Comparative Example 6, the thickness of the first outer layer was 23 μm, the thickness of the intermediate layer was 502 μm, and the thickness of the second outer layer was 24 μm.

The film-making equipment, set temperature, and extrusion rate were the same as in Example 4. The resin temperatures were 223°C for the first outer layer single screw extruder 301, 250°C for the intermediate layer twin screw extruder 302, and 223°C for the second outer layer single screw extruder 303. The resin was made into a film at a drawing speed of 18.2 m/min, and after edge trimming, a roll with a sheet width of 775 mm was obtained.

The multilayer sheet obtained in Comparative Example 6 had a total haze value of 22.5% at a thickness of 550 μm. The measurement results are shown in Table 1.

The resulting multilayer sheet was then vacuum-pressurized into a cup-shaped container of the same shape as in Example 1 (expansion ratio 2.6) using the same method as in Example 1. The resulting cup-shaped container had a volumetric change rate of -1.6% after heating at 120°C for 60 minutes, and a volumetric change rate of -1.6% after heating at 130°C for 60 minutes. The total haze value at a thickness of 210 μm on the side of the resulting cup-shaped container before heating was 38.0%. The measurement results are shown in Table 2.

10 Container 11 Container body 12 Lid 13 Opening 14 Flange 15 Bottom 16 Container body side 17 Container body fitting 18 Step 19 Stacking projection 21 Container body edging S/C: Screen changer G/P: Gear pump F/B: Feed block Die: T-die

Claims (11)

Polypropylene resin,
A container body formed from a polypropylene-based resin composition containing a nucleating agent,
The heat-resistant container has a volume change rate of ±1% or less after heating at 130° C. for 60 minutes.
A heat-resistant container, wherein the total haze value of the container body is 60% or less when measured in accordance with JIS K7136. The heat-resistant container according to claim 1, wherein the polypropylene resin has a mesopentad fraction (mmmm) of 96.0 to 99.5 mol%. The heat-resistant container according to claim 1, wherein the nucleating agent is a cyclic fatty acid metal salt. The heat-resistant container according to claim 1, wherein the nucleating agent is a metal salt of hexahydrophthalic acid. The heat-resistant container according to claim 1, wherein the heat-resistant container is a heat-resistant food container for storing food. This heat-resistant container is intended for steam convection applications and has a container body formed from a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent. A first outer layer, a second outer layer, and an intermediate layer provided between the first outer layer and the second outer layer,
the first outer layer is made of a first resin composition containing a first polyolefin-based resin,
the second outer layer is made of a second resin composition containing a second polyolefin-based resin,
At least the intermediate layer is made of a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent,
A heat-resistant container in which the volumetric change rate of the container body after heating at 130° C. for 60 minutes satisfies ±1% or less, and the total haze value is 60.0% or less. Polypropylene resin,
A sheet formed from a polypropylene-based resin composition containing a nucleating agent,
A sheet having a total haze value of 60.0% or less. A first outer layer, a second outer layer, and an intermediate layer provided between the first outer layer and the second outer layer,
the first outer layer is made of a first resin composition containing a first polyolefin-based resin,
the second outer layer is made of a second resin composition containing a second polyolefin-based resin,
A multi-layer sheet, wherein at least the intermediate layer is made of a polypropylene-based resin composition containing a polypropylene resin and a nucleating agent,
A multilayer sheet having a total haze value of 60.0% or less. A polypropylene resin composition preparation step of mixing a polypropylene resin and a nucleating agent to prepare a polypropylene resin composition;
a sheet molding step of extruding the polypropylene-based resin preparation as is or after pelletization into a sheet;
a container body forming step of forming a container body from the sheet;
A method for manufacturing a heat-resistant container comprising the steps of: A polypropylene resin composition preparation step of mixing a polypropylene resin and a nucleating agent to prepare a polypropylene resin composition;
a sheet molding step of extruding the polypropylene-based resin preparation as is or after pelletization into a sheet;
A method for manufacturing a sheet comprising the steps of: