Container and manufacturing method thereof

Abstract

To provide a manufacturing method for containers that can achieve a sufficiently high level of both reduced plastic usage and excellent light shielding properties for thin-walled containers.SOLUTION: A manufacturing method of containers according to the present disclosure includes the steps of: (A) preparing a molten resin composition containing at least a resin material and nitrogen in a supercritical state; (B) injecting the molten resin composition into a cavity of a mold; (C) applying dwell pressure and cooling the cavity under the pressure conditions of 5 to 80 MPa after the above (B) step; and (D) recovering a container having a thin-walled section of 0.6 mm or less in thickness from the mold. When the mass of the resin material in the molten resin composition is 100 pts.mass, the quantity of nitrogen in a supercritical state is 0.5 to 2.5 pts.mass.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a container and a method for manufacturing the same, and more particularly to a thin-walled container manufactured by supercritical fluid molding and a method for manufacturing the same. [Background technology]

[0002] In recent years, the impact of microplastics on the global environment has been attracting attention, leading to a growing trend toward eliminating plastic and reducing the use of plastic products. With regard to disposable plastic containers for food and daily necessities, users are increasingly calling for ways to reduce the amount of petroleum-derived plastic used.

[0003] Foam molding is one method for reducing the amount of plastic used. Foam molding can be broadly divided into chemical foam molding and physical foam molding. Chemical foam molding uses a blowing agent. On the other hand, physical foam molding uses a supercritical fluid, and this method is called supercritical fluid molding. Chemical foam molding has issues such as concerns about the negative environmental impact of the blowing agent and mold contamination. Supercritical fluid molding has traditionally been applied to relatively large industrial products such as automotive parts and office equipment. In recent years, with improvements in supercritical fluid generation technology and resin composition mixing technology, the application of supercritical fluid molding to high-cycle injection molding has been considered. Patent Documents 1 to 3 disclose food containers manufactured by supercritical fluid molding. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6085729 [Patent Document 2] Patent No. 6430684 [Patent Document 3] Japanese Patent Application Publication No. 2020-040690 Summary of the Invention [Problem to be solved by the invention]

[0005] Dairy products such as butter, margarine, and cream cheese contain fats and oils that are subject to oxidative degradation due to light (particularly ultraviolet light with a wavelength of 400 nm or less or visible light with a wavelength of 450 to 550 nm). Therefore, in order to prevent the oxidation of fats and oils, containers for storing dairy products have traditionally been made of plastic materials containing multiple colorants and have been given light-blocking properties. The inventors believed that if light-blocking properties could be imparted to containers by utilizing the light-scattering effect of voids created by supercritical fluid molding, the amount of colorant used could be reduced, and they attempted to manufacture thin-walled containers for storing dairy products using supercritical fluid molding. However, the inventors discovered that while thinning the container to reduce the amount of plastic used, which is the original purpose of supercritical fluid molding, tends to increase light transmittance, i.e., there is a trade-off between reducing the amount of plastic material used and ensuring light-blocking properties.

[0006] The present disclosure has been made to solve the above-mentioned problems, and provides a method for manufacturing a container that can achieve a sufficiently high level of both a reduction in the amount of plastic used and excellent light-blocking properties of the thin-walled container. The present disclosure also provides a thin-walled container that uses a reduced amount of plastic and has light-blocking properties. [Means for solving the problem]

[0007] One aspect of the present disclosure relates to a method for producing a thin-walled container using a supercritical fluid. The method for producing a container according to the present disclosure includes the steps of: (A) preparing a molten resin composition containing at least a resin material and nitrogen in a supercritical state; (B) injecting the molten resin composition into a cavity of a mold; (C) after step (B), cooling the cavity while maintaining the pressure in the range of 5 to 80 MPa; and (D) recovering a container having a thin-walled portion with a thickness of 0.6 mm or less from the mold, wherein the amount of nitrogen in a supercritical state is 0.5 to 2.5 parts by mass when the mass of the resin material in the molten resin composition is 100 parts by mass.

[0008] According to the above-mentioned manufacturing method, nitrogen is used as the supercritical fluid, and the amount of nitrogen in the molten resin composition is within the above-mentioned range, and the pressure-holding conditions in step (C) are within the above-mentioned range, so that lightweight, light-blocking, thin-walled containers can be obtained with a high yield.

[0009] The thin-walled portion preferably has a transmittance of 30% or less for light with a wavelength of 500 nm. In this case, deterioration of the contents due to visible light with a wavelength of 450 to 550 nm can be suppressed, and the contents can be made difficult to see from outside the container. The thin-walled portion preferably has a transmittance of 5% or less for light with a wavelength of 300 nm. In this case, deterioration of the contents due to ultraviolet light can be suppressed.

[0010] When the mass of the resin material in the molten resin composition is taken as 100 parts by mass, the amount of colorant in the molten resin composition is preferably 3 parts by mass or less. In a container whose main component is a resin material, a colorant (e.g., a pigment) is a foreign substance that should be removed from the viewpoint of recycling the resin material. From the viewpoint of the recyclability of the container, it is preferable that the amount of colorant in the molten resin composition is as small as possible, and it is more preferable that the molten resin composition does not contain a colorant.

[0011] One aspect of the present disclosure relates to a container that is a molded article formed by supercritical fluid molding. The container has a bottom having a thickness of 0.3 to 0.6 mm and a sidewall having a thickness of 0.25 to 0.40 mm, at least one of the bottom and the sidewall having a transmittance of 30% or less for light with a wavelength of 500 nm, and the amount of colorant in the container is 3 parts by mass or less when the mass of the container is taken as 100 parts by mass.

[0012] The container uses less plastic and has light-blocking properties. This container is applicable to thin-walled containers for storing dairy products such as butter and margarine, as well as thin-walled containers for storing desserts such as parfait ice cream, pudding, shaved ice, and yogurt.

[0013] As described above, the transmittance of light with a wavelength of 500 nm is 30% or less through at least one of the bottom and sidewall. When the container satisfies this condition, deterioration of the contents due to visible light with a wavelength of 450 to 550 nm can be suppressed, and the contents can be made difficult to see from outside the container. It is preferable that the transmittance of light with a wavelength of 300 nm is 5% or less through at least one of the bottom and sidewall. In this case, deterioration of the contents due to ultraviolet light can be suppressed.

[0014] As described above, the amount of colorant in the container (based on 100 parts by mass of the container) is 3 parts by mass or less. In a container whose main component is a resin material, a colorant (e.g., a pigment) is a foreign substance that should be removed from the perspective of recycling the resin material. From the perspective of the recyclability of the container, it is preferable that the amount of colorant in the container be as small as possible, and it is more preferable that the container does not contain any colorant. [Effects of the Invention]

[0015] According to the present disclosure, a method for manufacturing a container is provided that can achieve a sufficiently high level of both a reduction in the amount of plastic used and excellent light-blocking properties of the thin-walled container. Also, according to the present disclosure, a thin-walled container that uses a reduced amount of plastic and has light-blocking properties is provided. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view showing a container according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view of the bottom and sidewall of the container shown in FIG. [Figure 3] FIG. 3(a) is a photograph showing the container according to Comparative Example 1, and FIG. 3(b) is a photograph showing the container according to Comparative Example 2. [Figure 4] FIG. 4 is a photograph showing the container according to Example 1. [Figure 5] FIG. 5 is a graph showing the light transmittance of the containers according to the examples and comparative examples, and a commercially available container. [Figure 6]FIG. 6 is a graph showing the light transmittance of the containers according to the examples and comparative examples, and a commercially available container. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present disclosure will be described in detail, but the present invention is not limited to the following embodiments.

[0018] <Container manufacturing method> The method for manufacturing a container according to this embodiment includes the following steps. (A) A step of preparing a molten resin composition containing a resin material and nitrogen in a supercritical state. (B) A step of injecting a molten resin composition into a cavity of a mold. (C) After the above step (B), a step of holding the cavity under pressure and cooling it. (D) A process of recovering the container having a thin-walled portion having a thickness of 0.6 mm or less from the mold. The series of steps (A) to (D) can be carried out using, for example, a MuCell injection molding machine ("MuCell" is a registered trademark of Trexel Co. Ltd.) (see Patent Documents 1 and 2).

[0019] [(A) Process] First, a molten resin composition containing at least a resin material and nitrogen in a supercritical state is prepared. By using nitrogen as a supercritical fluid, a container containing fine voids (for example, diameters of about 1 to 10 μm) can be finally obtained.

[0020] When the mass of the resin material in the molten resin composition is taken as 100 parts by mass, the amount of supercritical nitrogen is 0.5 to 2.5 parts by mass. By adding 0.5 parts by mass or more of nitrogen, voids due to the supercritical nitrogen can be formed inside the molded body. As a result, the molded body can be made lighter and the entire body can be made opaque. In addition, the variation in filling pressure between molding shots can be reduced, and the addition of nitrogen reduces the viscosity of the molten resin composition, preventing the resin material from reaching the end of the cavity (hereinafter referred to as "short shot"). On the other hand, by adding 2.5 parts by mass or less of nitrogen, the dwell pressure in step (C) can be set relatively low, which tends to prevent post-blistering. Post-blistering refers to the phenomenon in which a molded body swells locally after removal from the mold. It is believed to occur more easily in areas where strain is concentrated due to residual stress during cure shrinkage after molding.

[0021] Examples of resin materials include thermoplastic resins, specific examples of which are polypropylene resin and polyethylene resin. The melt flow rate of the thermoplastic resin is preferably 10 g / 10 min or more, more preferably 12 to 40 g / 10 min, and even more preferably 15 to 36 g / 10 min. A value of 10 g / 10 min or more tends to suppress the occurrence of short shots, while a value of 40 g / 10 min or less tends to enable the production of containers with excellent drop resistance. The melt flow rate (MFR) referred to here means a value measured in accordance with the method described in JIS K7210-1:2014 at a temperature of 230°C and a load of 2.16 kg.

[0022] The temperature of the molten resin composition (screw cylinder temperature) may be set according to the melting point or MFR of the resin material. When polypropylene resin is used, this temperature is preferably about 210 to 250°C. When polyethylene resin is used, this temperature is preferably about 220 to 260°C. When this temperature is equal to or higher than the lower limit, the resin flows easily in the cavity, while when it is equal to or lower than the upper limit, burning of the resin tends to be suppressed.

[0023] The molten resin composition may contain components other than the resin material and the supercritical fluid. That is, the molten resin composition may further contain, for example, a filler, a colorant, a slip agent, an antistatic agent, etc., as needed. However, from the viewpoint of container recycling, it is preferable that the amount of components other than the resin material in the container be as small as possible. For example, when the mass of the resin material in the molten resin composition is 100 parts by mass, the amount of colorant in the molten resin composition is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and it is more preferable that the molten resin composition does not contain a colorant.

[0024] [(B) Process] The molten resin composition prepared in step (A) is injected into the cavity through the gate of the mold. The injection speed is preferably 60 mm / sec or more, more preferably 200 mm / sec or more, and even more preferably 250 mm / sec or more. An injection speed of 60 mm / sec or more tends to make it easier for the resin to reach the end of the flow, and tends to suppress the occurrence of short shots. The upper limit of the injection speed is, for example, 350 mm / sec.

[0025] Even if the distance from the cavity gate to the farthest flow end (hereinafter referred to as the "maximum flow length") is 60 mm or more, it is preferable that the molten resin composition reaches the flow end. The maximum flow length may be, for example, 70 mm or more or 80 mm or more. The upper limit of the maximum flow length is, for example, 120 mm.

[0026] [(C) Process] After step (B) above, the cavity is cooled while being held under pressure. The holding pressure is 5 to 80 MPa. A pressure of 5 MPa or higher tends to prevent the occurrence of short shots, while a pressure of 80 MPa or lower tends to prevent the occurrence of post-blistering. This value is preferably 15 to 50 MPa, and more preferably 30 to 50 MPa. The holding time may be, for example, 0.1 to 1.0 seconds.

[0027] From the viewpoint of producing a thin-walled container, it is preferable not to carry out a process called "core-back" for reducing the pressure inside the cavity. Core-back is a process in which the movable part of the mold is moved to expand the volume of the cavity before the molten resin composition filled in the cavity has completely solidified (see Patent Document 1).

[0028] [(D) Process] When the temperature of the molded body (thin-walled container) in the mold drops to about 30 to 60°C, the molded body is removed from the mold. In this embodiment, pressure dwell is performed in step (C), and the "core-back" process is not performed as described above. Therefore, large voids visible to the naked eye are not formed in the container according to this embodiment. The container according to this embodiment achieves a reduction in the amount of plastic used (amount of resin material used) due to both the fine voids and the thin wall.

[0029] <Container> The container 10 shown in FIG. 1 is manufactured through the above process. In a plan view, the container 10 has a generally rectangular shape with rounded corners. The container 10 includes a bottom 1, a pair of side walls 2a, a pair of side walls 2b, and flanges 3 provided at the four corners. In a plan view, the side walls 2a form the short sides of the container 10, while the side walls 2b form the long sides of the container 10. The flanges 3 serve as a guide for a lid (not shown) that fits onto the container 10.

[0030] As shown in Figure 2, the central portion 1a of the bottom portion 1 corresponds to the gate position of the mold. The bottom portion 1 is formed with feet 5. Providing the feet 5 in the container 10 increases the drop resistance. That is, even if the container 10 is dropped, for example, from a table, the feet 5 prevent the bottom portion 1 from directly hitting the floor, thereby preventing damage to the bottom portion 1 and its vicinity.

[0031] The thickness of the bottom portion 1 is 0.3 to 0.6 mm, and may be 0.3 to 0.4 mm or 0.4 to 0.5 mm. When this thickness is 0.3 mm or more, rear bulging tends to be suppressed and drop resistance can be ensured. On the other hand, when this thickness is 0.6 mm or less, weight reduction can be achieved. The thickness of the side wall portions 2a, 2b is 0.25 to 0.4 mm, and may be 0.3 to 0.35 mm. When this thickness is 0.25 mm or more, drop resistance can be ensured. On the other hand, when this thickness is 0.4 mm or less, weight reduction can be achieved.

[0032] The container 10 can be used as a thin-walled container for storing dairy products such as butter, margarine, and cream cheese. Conventional injection molding of thin-walled containers requires the selection of a resin with high fluidity (high MFR) to prevent short shots. However, highly fluid resin materials tend to have relatively low molecular weights and low strength, making it difficult to manufacture thin-walled containers with excellent drop resistance. In contrast, in this embodiment, even if a resin material has a relatively low MFR, the fluidity of the molten resin composition can be increased by using it in combination with a supercritical fluid. This allows for both excellent short shot prevention and excellent drop resistance. Because the container 10 has excellent drop resistance, it may have a relatively large capacity (e.g., internal volume: 280 cc or more).

[0033] The container 10 can protect the contents (e.g., the dairy products) contained therein from light. Specifically, the fats and oils contained in dairy products undergo oxidative degradation during distribution and storage, making it difficult to maintain a good flavor. If the deterioration in terms of sensory quality progresses and an unusual taste or odor becomes pronounced, this can lead to complaints in the market. Oxidation of fats and oils is particularly accelerated by ultraviolet light, and they are also susceptible to degradation by light with wavelengths of 450 to 550 nm in the visible light range. The light transmittance of the container 10 is significantly reduced due to the bubbling of nitrogen gas. This allows for a significant reduction in the amount of colorant blended into the resin material that constitutes the container 10. This reduces the material cost of the container 10 and improves the recyclability of the container 10.

[0034] At least one of the bottom and sidewall of container 10 has a transmittance of 30% or less, preferably 25% or less, and more preferably 20% or less, for light with a wavelength of 500 nm. Furthermore, at least one of the bottom and sidewall of container 10 has a transmittance of 30% or less, preferably 25% or less, and more preferably 20% or less, for light over the entire wavelength range of 450 to 550 nm. It is more preferable that both the bottom and sidewall satisfy these conditions. When container 10 satisfies these conditions, deterioration of the contents due to visible light with a wavelength of 450 to 550 nm can be suppressed, and the contents can be made less visible from outside the container.

[0035] At least one of the bottom and sidewall of container 10 has a transmittance of 5% or less, more preferably 3% or less, and even more preferably 2% or less, for light with a wavelength of 300 nm. At least one of the bottom and sidewall of container 10 also has a transmittance of 5% or less, more preferably 3% or less, and even more preferably 2% or less, for light with a wavelength over the entire range of 200 to 350 nm. It is more preferable that both the bottom and sidewall satisfy these conditions. When container 10 satisfies these conditions, deterioration of the contents due to ultraviolet light can be suppressed.

[0036] Although the embodiments of the present disclosure have been described above, the present invention is not limited to the above embodiments. For example, although the above embodiments illustrate a container having the shape shown in Fig. 1, the manufacturing method according to the present disclosure may be applied to the manufacture of containers having other shapes with thin-walled portions having a thickness of 0.6 mm or less. [Example]

[0037] The present disclosure will be described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0038] (Comparative Example 1) Using the materials listed below, we attempted to manufacture a single-cavity container with the structure shown in Figure 1 using normal injection molding (speed control). A two-plate mold (hot runner) was used as the mold. The design values ​​for the container were as follows:

[0039] [Container design value] Bottom thickness: 0.350mm Side wall thickness (short side): 0.350mm Side wall thickness (long side): 0.350mm Flange thickness: 0.350mm ·Mass: 10.02g

[0040] [Resin material] Block polypropylene (SunAllomer Co., Ltd., PM870A (model number), MFR: 17g / 10min) [Molding conditions] Screw cylinder temperature: 240℃ ·Injection speed: 250mm / sec - Holding pressure: 80MPa Pressure retention time: 1 second Maximum flow length in cavity: 99mm In the case of thin-wall molding, the injection speed was set to 250 mm / s because, considering filling efficiency, injection filling should be performed as fast as possible. From the viewpoint of foaming promotion, it is ideal to keep the dwell pressure as low as possible and for as short a time as possible, but this increases the possibility of short shots and dimensional deformation. In this example, the dwell pressure was set to 80 MPa from the viewpoint of achieving both foaming promotion and short shot prevention. However, as shown in Figure 3(a), short shots occurred in this example.

[0041] (Comparative Example 2) A molten resin composition was prepared by adding 3.0 parts by mass of supercritical carbon dioxide to 100 parts by mass of resin material. Containers were produced in the same manner as in Comparative Example 1, except that this molten resin composition was used and injection molded under the following conditions. Note that a MuCell injection molding machine ("MuCell" is a registered trademark of Trexel Co. Ltd.) was used in this comparative example and the following examples and comparative examples. [Molding conditions] Screw cylinder temperature: 240℃ ·Injection speed: 250mm / sec - Holding pressure: 80MPa Pressure retention time: 1 second Maximum flow length in cavity: 99mm

[0042] The mass of the container according to Comparative Example 2 was 9.77 g, which was a weight loss rate of 2.50% based on the design mass of the container according to Comparative Example 1. However, as shown in Figure 3(b), the resulting container was slightly transparent overall, with some areas showing cloudy patches.

[0043] Example 1 A molten resin composition was prepared by adding 1.5 parts by mass of supercritical nitrogen to 100 parts by mass of a resin material. A container was produced in the same manner as in Comparative Example 2, except that this molten resin composition was injection molded under the following conditions. [Molding conditions] Screw cylinder temperature: 240℃ ·Injection speed: 250mm / sec - Holding pressure: 50MPa Pressure retention time: 1 second Maximum flow length in cavity: 99mm The holding pressure was set to 50 MPa in order to achieve both foaming promotion and short shot prevention.

[0044] The mass of the container according to Example 1 was 9.67 g, which was a weight loss rate of 3.49% based on the design mass of the container of Comparative Example 1. Furthermore, as shown in Fig. 4, the container obtained was cloudy overall, and was entirely opaque when visually observed.

[0045] <Evaluation of light transmittance> The light transmittance of the containers according to Example 1 and Comparative Examples 1 and 2 was measured. A spectrophotometer UV-2450 (manufactured by Shimadzu Corporation) was used for this measurement, and measurements were taken over a wavelength range of 200 to 800 nm. The measurement object was the side wall portion of the container (thickness 0.35 mm). The results are shown in Figure 5. The graph in Figure 5 also shows the measurement results of a commercially available container as a reference example. The measurement object for the commercially available container was the side wall portion of the container (thickness 0.50 mm). Representative values ​​of the measurement results are shown in Table 1.

[0046] [Table 1]

[0047] Example 2 A container was produced in the same manner as in Example 1, except that the amount of supercritical nitrogen added per 100 parts by mass of resin material was 2.0 parts by mass instead of 1.5 parts by mass. The mass of the container according to Example 2 was 9.62 g, achieving a weight loss rate of 3.99% based on the design mass of the container of Comparative Example 1. Furthermore, the obtained container was cloudy throughout, similar to Example 1, and was entirely opaque when visually observed.

[0048] Example 3 A container was produced in the same manner as in Example 2, except that the following coloring agent was added to the supercritical fluid. Colorant A: Cream color (manufactured by Toyo Color Co., Ltd.) The blending amount of colorant A was 2.50 parts by mass with respect to 100 parts by mass of the resin material. The mass of the container according to Example 3 was 9.62 g, which was a weight loss rate of 3.99% based on the design mass of the container of Comparative Example 1. The resulting container was colored a pale cream color throughout, and was entirely opaque when visually observed.

[0049] Example 4 A container was produced in the same manner as in Example 2, except that the following coloring agent was added to the supercritical fluid. Colorant A: Cream color (manufactured by Toyo Color Co., Ltd.) Colorant B: White (manufactured by Toyo Color Co., Ltd.) The blending amounts of colorants A and B were each 2.50 parts by mass per 100 parts by mass of the resin material. The mass of the container according to Example 4 was 9.64 g, which was a weight loss rate of 3.79% based on the design mass of the container of Comparative Example 1. The resulting container was colored a pale cream color throughout, and was entirely opaque when visually observed.

[0050] (Comparative Example 3) An attempt was made to manufacture a container in the same manner as in Comparative Example 1, except that the following coloring agent was added to the resin material. Colorant A: Cream color (manufactured by Toyo Color Co., Ltd.) The blending amount of colorant A was 2.50 parts by mass with respect to 100 parts by mass of the resin material. However, similar to Comparative Example 1, short shots occurred in this example as well.

[0051] Comparative Example 4 An attempt was made to manufacture a container in the same manner as in Comparative Example 1, except that the following coloring agent was added to the resin material. Colorant A: Cream color (manufactured by Toyo Color Co., Ltd.) Colorant B: White (manufactured by Toyo Color Co., Ltd.) The blending amounts of colorants A and B were each 2.50 parts by mass relative to 100 parts by mass of the resin material. However, similar to Comparative Example 1, short shots occurred in this example as well.

[0052] <Evaluation of light transmittance> The light transmittance of the containers according to Examples 2 to 4 and Comparative Examples 3 and 4 was measured. A spectrophotometer UV-2450 (manufactured by Shimadzu Corporation) was used for the measurements, and measurements were taken over a wavelength range of 200 to 800 nm. The measurement object was the side wall portion of the container (thickness 0.35 mm). The results are shown in Figure 6. The graph in Figure 6 also shows the measurement results of a commercially available container as a reference example. The measurement object for the commercially available container was the side wall portion of the container (thickness 0.50 mm). Representative values ​​of the measurement results are shown in Table 2.

[0053] [Table 2]

[0054] According to Examples 1 to 4, it was possible to manufacture thin-walled containers that were entirely opaque without the occurrence of short shots. Furthermore, according to Examples 1 to 4, it was possible to reduce the amount of plastic used due to the synergistic effect of thinning the container and foaming. According to Example 3, it was possible to significantly reduce the light transmittance due to foaming of nitrogen gas compared to Comparative Example 3. According to Example 4, it was possible to significantly reduce the light transmittance due to foaming of nitrogen gas compared to Comparative Example 4. In Examples 3 and 4, the light transmittance in the ultraviolet region was equivalent to that of commercially available products, but on the other hand, the light transmittance in the visible light region of wavelengths of 450 nm or more was lower than that of commercially available products (see Figure 6). [Explanation of symbols]

[0055] 1...bottom, 1a...center, 2a...side wall (short side), 2b...side wall (long side), 3...flange, 5...foot, 10...container.

Claims

1. (A) preparing a molten resin composition containing at least a resin material selected from a polypropylene resin and a polyethylene resin, and nitrogen in a supercritical state; (B) injecting the molten resin composition into a mold cavity; (C) after the step (B), a step of cooling the cavity while maintaining the pressure at 30 to 50 MPa; (D) recovering the container having a thin-walled portion having a thickness of 0.6 mm or less from the mold; Including, the amount of the nitrogen in a supercritical state is 1.5 to 2.0 parts by mass when the mass of the resin material in the molten resin composition is 100 parts by mass.

2. The method for manufacturing a container according to claim 1, wherein the thin-walled portion has a transmittance of 30% or less for light with a wavelength of 500 nm.

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