Molded body and method for producing the same

Abstract

To provide a method for manufacturing a molded article, which can sufficiently suppress a short shot while contributing to global environmental conservation. and the molded article.SOLUTION: A method for manufacturing a molded article comprises: a step (A) of preparing a molten resin composition containing a resin material containing a biomass-derived polyethylene resin and a fossil fuel-derived polypropylene resin, and a supercritical fluid; a step (B) of injecting the molten resin composition into a mold cavity; a step (C) of holding pressure and cooling the cavity after the step (B); and a step (D) of recovering the molded article from the mold.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a molded body and a method for producing the same. [Background technology]

[0002] In recent years, the impact of microplastics on the global environment has been attracting attention, and there has been a growing trend toward eliminating plastic and reducing the use of plastic products. With regard to disposable plastic containers for food and daily necessities, there has been a growing demand from users to reduce the amount of fossil fuel-derived plastic used, even if only by a small amount.

[0003] In the field of injection molding, which uses plastics as raw materials, there is a desire to move away from fossil fuel-derived materials, just as there is with energy, and the use of biomass-derived materials is attracting attention. Biomass is an organic compound photosynthesized from carbon dioxide and water, and is a so-called carbon-neutral resource, as its combustion does not affect the increase or decrease of carbon dioxide. It is hoped that the use of such biomass-derived plastics will reduce the amount of fossil fuel-derived plastics used.

[0004] Patent Document 1 discloses a resin molded article formed by injection molding a mixture of specific amounts of polyethylene obtained from raw materials obtained by fermentation, polypropylene, and at least one of an olefin-based thermoplastic elastomer and an α-olefin copolymer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-227462 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the research of the present inventors, biomass-derived polyethylene resins tend to have poorer fluidity than fossil-fuel-derived polyethylene resins, even when they have the same density. Therefore, when a resin material contains biomass-derived polyethylene resin, a phenomenon in which the resin material does not reach the end of the flow path of the mold cavity (hereinafter referred to as "short shot") is likely to occur. In particular, when the target molded article has thin-walled portions, short shots are more likely to occur.

[0007] The present disclosure provides a method for producing a molded article that contributes to global environmental conservation and that can sufficiently suppress short shots, and the molded article. [Means for solving the problem]

[0008] One aspect of the present disclosure is a method for producing a molded body, comprising: (A) a step of preparing a molten resin composition containing a resin material containing a biomass-derived polyethylene resin and a fossil fuel-derived polypropylene resin, and a supercritical fluid; (B) a step of injecting the molten resin composition into a cavity of a mold; (C) a step of cooling the cavity while maintaining pressure after the step (B); and (D) a step of recovering the molded body from the mold.

[0009] In one embodiment, the supercritical fluid may contain carbon dioxide. When the supercritical fluid contains carbon dioxide, the amount of the supercritical fluid may be 1 to 3 parts by mass when the mass of the resin material in the molten resin composition is 100 parts by mass.

[0010] In one embodiment, the supercritical fluid may contain nitrogen. When the supercritical fluid contains nitrogen, the amount of the supercritical fluid may be 0.25 to 1.25 parts by mass when the mass of the resin material in the molten resin composition is taken as 100 parts by mass.

[0011] In one embodiment, the content of the biomass-derived polyethylene resin may be 30 to 60 mass % based on the total amount of the resin material.

[0012] Another aspect of the present disclosure is a molded article formed by supercritical fluid molding, the molded article containing a biomass-derived polyethylene resin and a fossil fuel-derived polypropylene resin.

[0013] In one embodiment, the molded body may have a thin-walled portion having a thickness of 0.20 to 0.60 mm.

[0014] In one embodiment, the content of the biomass-derived polyethylene resin may be 30 to 60 mass % based on the total amount of the resin.

[0015] In one embodiment, the molded article may contain microvoids. [Effects of the Invention]

[0016] According to the present disclosure, a method for producing a molded article and a molded article that can contribute to global environmental conservation and sufficiently suppress short shots are provided. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view showing a molded article according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view of the bottom and sidewall of the molded body shown in FIG. [Figure 3] FIG. 3(a) is a photograph showing a container according to Comparative Example 1, FIG. 3(b) is a photograph showing a container according to Example 1, and FIG. 3(c) is a photograph showing a container according to Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present disclosure will be described in detail, but the present invention is not limited to the following embodiments.

[0019] <Method of manufacturing molded body> The method for producing a molded article according to this embodiment includes the following steps. (A) A step of preparing a molten resin composition containing a resin material containing a biomass-derived polyethylene resin and a fossil fuel-derived polypropylene resin, and a supercritical fluid. (B) A step of injecting a molten resin composition into a cavity of a mold. (C) A process of cooling the cavity while maintaining pressure after the process (B). (D) A step of recovering the molded body 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.).

[0020] "(A) Process" A molten resin composition is prepared containing a resin material and a supercritical fluid. The resin material contains a biomass-derived polyethylene resin and a fossil fuel-derived polypropylene resin.

[0021] Examples of biomass-derived polyethylene resins include polyethylene resins derived from plants. Examples of such plants include corn, sugarcane, beet, manioc, and castor beans. Polyethylene resins may be derived from edible or inedible parts of plants. Examples of plant-derived polyethylene resins include those manufactured by Braskem. Braskem produces and sells linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and low-density polyethylene (LDPE) from renewable natural raw materials. For example, plant-derived LLDPE has an α-olefin with 4 or 6 carbon atoms in the side chain, which is represented as C4-LLDPE or C6-LLDPE.

[0022] The melt flow rate (MFR) of the biomass-derived polyethylene resin at 190°C is not particularly limited, but is, for example, 25 g / 10 min or less, preferably 20 g / 10 min or less. Having this value of 20 g / 10 min or less allows the mechanical strength of the molded article to be sufficiently high. This value is, for example, 5 g / 10 min or more, preferably 7 g / 10 min or more. Having this value of 7 g / 10 min or more allows the resin material to maintain sufficient fluidity even when the proportion of biomass-derived polyethylene resin in the resin material is relatively high. Furthermore, the resin can be easily injected during injection molding. The melt flow rate value in the present disclosure refers to a value measured in accordance with the method described in JIS K7210-1:2014 under conditions of a predetermined temperature (190°C or 230°C, as described below) and a load of 2.16 kg.

[0023] The density of the biomass-derived polyethylene resin is, for example, 0.910 to 0.960 g / cm 3 and 0.915 to 0.918 g / cm 3 or 0.953 to 0.959 g / cm 3 The density of the biomass-derived polyethylene resin may be 0.910 g / cm 3 When the density of the biomass-derived polyethylene resin is 0.960 g / cm or more, the rigidity of the molded body can be sufficiently increased. 3 When the content is equal to or less than 100%, the transparency and mechanical strength of the molded article can be sufficiently increased.

[0024] One method for determining whether a polyethylene resin is derived from biomass is, for example, to measure the radioactive carbon (C14) content in the polyethylene resin. This method is described in detail below. Carbon dioxide in the atmosphere contains a certain proportion (105.5 pMC) of C14. Therefore, it is known that the C14 content in plants (e.g., corn) that grow by absorbing carbon dioxide from the atmosphere is also about 105.5 pMC. On the other hand, it is also known that fossil fuels contain very little C14. Therefore, by measuring the C14 content of the total carbon atoms in the polyethylene resin, it is possible to determine whether the polyethylene resin is derived from biomass.

[0025] The biomass ratio (P bio ) may be, for example, 85% or more, 90% or more, 92% or more, 95% or more, or 99% or more, or may be 100%. P bio (%)=P C14 / 105.5×100...Equation (1) [In formula (1), P C14 represents the radioactive carbon (C14) content in biomass-derived polyethylene resin.]

[0026] Examples of polypropylene resins derived from fossil fuels include propylene homopolymers, block copolymers, and random copolymers, and from the viewpoint of moldability, it is preferable to use propylene block copolymers.

[0027] The melt flow rate of the fossil fuel-derived polypropylene resin at 230°C may be, for example, 45 g / 10 min or less, and more preferably 40 g / 10 min or less. When this value is 45 g / 10 min or less, the mechanical strength of the resulting molded article tends to be improved. This value is preferably 3 g / 10 min or more, more preferably 5 g / 10 min or more, and even more preferably 7 g / 10 min or more. When this value is 3 g / 10 min or more, the fluidity of the resin material can be sufficiently maintained even if the proportion of biomass-derived polyethylene resin in the resin material is high.

[0028] The density of fossil fuel-derived polypropylene resin is, for example, 0.900 to 0.910 g / cm 3 When the density of the fossil fuel-derived polypropylene resin is within this range, the occurrence of molding defects can be sufficiently suppressed.

[0029] The content of the biomass-derived polyethylene resin is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on the total amount of the resin material, in order to contribute to global environmental conservation. The content of the biomass-derived polyethylene resin is preferably 90% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less, based on the total amount of the resin material, in order to further reduce the occurrence of short shots.

[0030] The content of the fossil fuel-derived polypropylene resin is preferably 10% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the total amount of the resin material, since this further helps to suppress the occurrence of short shots. The content of the fossil fuel-derived polypropylene resin is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less, based on the total amount of the resin material, since this makes it easier to disperse the biomass-derived polyethylene resin or make it compatible with said resin.

[0031] According to the inventors' investigations, when carbon dioxide is used, 1 to 3 parts by mass of supercritical carbon dioxide is added to 100 parts by mass of resin material to prepare the molten resin composition. By using 1 part by mass or more of carbon dioxide, it is possible to reduce the variation in filling pressure between molding shots, and the addition of carbon dioxide reduces the viscosity of the molten resin composition, thereby suppressing the occurrence of short shots. In addition, foaming caused by supercritical carbon dioxide can be promoted, forming voids inside the molded body. On the other hand, by using 3 parts by mass or less of carbon dioxide, it is possible to set the dwell pressure in step (C) relatively low, which tends to suppress swelling.

[0032] When nitrogen is used, 0.25 to 1.25 parts by mass of supercritical carbon dioxide is added per 100 parts by mass of resin material to prepare the molten resin composition. By using 0.25 parts by mass or more of nitrogen, it is possible to reduce the variation in filling pressure between molding shots, and the addition of nitrogen reduces the viscosity of the molten resin composition, thereby suppressing the occurrence of short shots. In addition, the promotion of foaming due to supercritical nitrogen can form voids inside the molded product. On the other hand, by using 1.25 parts by mass or less of nitrogen, it is possible to set the dwell pressure in step (C) relatively low, which tends to suppress swelling.

[0033] 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 plasticizer, a UV stabilizer, a slip agent, an antistatic agent, and a crystal nucleating agent, as necessary. The total content of the resin material and the supercritical fluid may be 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 99% by mass or more, based on the total amount of the molten resin composition, or may be 100% by mass.

[0034] The temperature of the molten resin composition (screw cylinder temperature) may be set depending on the melting point or MFR of the resin material, but is preferably 200 to 260° C. When this temperature is equal to or higher than the lower limit, the resin flows easily in the cavity, while when the temperature is equal to or lower than the upper limit, burning of the resin tends to be suppressed.

[0035] [(B) Process] The molten resin composition prepared in step (A) is injected into the cavity through a gate of the mold. The injection speed may be constant or may be varied during the injection process. When the injection speed is varied during the injection process, for example, the molten resin composition may be first injected at a first speed and then at a second speed slower than the first speed. By varying the injection speed to a second speed slower than the first speed during the injection process, the occurrence of burrs tends to be suppressed even when producing a molded product having a thin-walled portion. The first speed is preferably 150 mm / sec or more, more preferably 200 mm / sec or more, and even more preferably 250 mm / sec or more. An injection speed of 150 mm / sec or more tends to make it easier for the resin to reach the end of the flow, and the occurrence of short shots tends to be suppressed. The second speed is preferably 100 mm / sec or less, more preferably 80 mm / sec or less, and even more preferably 50 mm / sec or less, since this facilitates the suppression of burrs at the end of the flow. The timing for changing from the first speed to the second speed may be, for example, when the amount of the molten resin composition in the cavity reaches 50 to 90% by volume based on the volume of the cavity.

[0036] 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.

[0037] [(C) Process] After step (B), the cavity is cooled while maintaining the pressure. According to the inventors' investigations, when carbon dioxide is used as the supercritical fluid, the pressure is maintained at a pressure of 15 to 80 MPa. A pressure of 15 MPa or higher tends to suppress the occurrence of short shots, while a pressure of 80 MPa or lower tends to suppress the occurrence of blistering. This value is preferably 15 to 50 MPa, and more preferably 15 to 30 MPa. When nitrogen is used as the supercritical fluid, the pressure is maintained at a pressure of 50 to 150 MPa. A pressure of 50 MPa or higher tends to suppress the occurrence of short shots, while a pressure of 150 MPa or lower tends to suppress the occurrence of blistering. This value is preferably 50 to 135 MPa, and more preferably 50 to 120 MPa. The pressure maintenance time may be, for example, 0.1 to 1.0 seconds, regardless of the type of supercritical fluid.

[0038] From the viewpoint of producing a molded article having a thin-walled portion, it is preferable not to carry out a step called "core-back" for reducing the pressure inside the cavity. Core-back is a step 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.

[0039] [(D) Process] When the temperature of the molded body in the mold drops to about 30 to 60°C, the molded body is removed from the mold. In this embodiment, pressure is maintained in step (C) and "core back" is not performed as described above, so large voids that can be visually confirmed are not formed in the molded body of this embodiment. It can be said that the molded body of this embodiment is primarily intended to be lightweight by thinning rather than by voids.

[0040] [Action and effect] Conventional injection molding has not been able to sufficiently suppress the occurrence of short shots in the production of molded articles containing biomass-derived polyethylene resins. This is presumably because biomass-derived polyethylene resins tend to have poor fluidity (small MFR values). Short shots are particularly likely to occur when the target molded article has thin-walled portions. In contrast, in the method for producing a molded article according to the present embodiment, the resin material contains a fossil fuel-derived polypropylene resin in addition to a biomass-derived polyethylene resin. Furthermore, by using the resin material in combination with a supercritical fluid, the fluidity of the molten resin composition can be enhanced. This sufficiently suppresses short shots. Furthermore, biomass-derived polyethylene resins and fossil fuel-derived polypropylene resins tend to be poorly compatible. However, by using a resin material containing these resins in combination with a supercritical fluid, the biomass-derived polyethylene resin and fossil fuel-derived polypropylene resin become more compatible. Furthermore, the resulting molded articles are comparable in terms of physical properties, such as mechanical properties, to those produced using conventional fossil fuel-derived polyethylene resins or polypropylene resins, and can therefore replace conventional polyethylene resin or polypropylene resin molded articles. Furthermore, if the resulting molded body contains microvoids (air gaps) derived from the supercritical fluid, it is possible to reduce the amount of plastic used compared to a molded body without microvoids, even if the shape is the same.

[0041] <Molded body> The molded body 10 shown in FIG. 1 is a container manufactured through the above process. In a plan view, the molded body 10 has a generally rectangular shape with rounded corners. The molded body 10 has a bottom 1 as a thin-walled portion, a pair of side wall portions 2a and 2b, and flanges 3 provided at the four corners. In a plan view, the side wall portions 2a form the short sides of the molded body 10, while the side wall portions 2b form the long sides of the molded body 10. The flanges 3 serve as guides for a lid (not shown) that fits onto the molded body 10.

[0042] As shown in Fig. 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 molded body 10 increases the drop resistance. That is, even if the molded body 10 is dropped, for example, from a table, the presence of the feet 5 prevents the bottom portion 1 from directly hitting the floor, thereby preventing damage to the bottom portion 1 and its vicinity.

[0043] The thickness of the bottom portion 1 is 0.30 to 0.60 mm, and may be 0.40 to 0.50 mm. A thickness of 0.30 mm or more tends to suppress swelling and ensures drop resistance. On the other hand, a thickness of 0.60 mm or less contributes to weight reduction. Here, an embodiment in which the entire bottom portion 1 has a thickness within the above range has been exemplified, but a part of the bottom portion may be a thin-walled portion (first thin-walled portion) having a thickness within the above range. From the viewpoint of reducing the amount of plastic used, the area ratio of the thin-walled portion in the bottom portion is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more.

[0044] The thickness of the side walls 2a, 2b is 0.20 to 0.40 mm, may be 0.25 to 0.40 mm, or may be 0.30 to 0.35 mm. A thickness of 0.20 mm or more ensures drop resistance. On the other hand, a thickness of 0.40 mm or less contributes to weight reduction. Here, an embodiment has been illustrated in which the entire side walls 2a, 2b have a thickness within the above range, but a thin portion (second thin portion) of each side wall may have a thickness within the above range. From the viewpoint of reducing the amount of plastic used, the area ratio of the thin portion in the side walls is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more.

[0045] The molded body 10 may contain bubbles (microvoids) of a size that cannot be visually confirmed in the bottom 1, the sidewalls 2a and 2b, and the flanges 3 provided at the four corners. This makes it easier to suppress warpage that tends to occur in thin molded bodies. Such microvoids can be confirmed, for example, by cutting the molded body 10 and observing the cut surface under a microscope. The microvoids are derived from the supercritical fluid in the above process. The diameter of the microvoids may be 10 to 200 μm. Within 1 mm of the molded body 10, 2 The number of microvoids per unit area may be 10 to 10,000. The number of microvoids can be measured by counting the number of bubbles in a microscopic image of the cut surface. The lower limit of the diameter of bubbles that can be visually confirmed is generally said to be 200 μm.

[0046] The molded article 10 can be applied to thin-walled containers for storing foods such as butter, yogurt, margarine, cream cheese, etc. The molded article 10 has excellent drop resistance, so it may have a relatively large capacity (for example, an internal volume of 280 cc or more).

[0047] 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 cases in which carbon dioxide or nitrogen is used as the supercritical fluid, argon or helium, for example, may be used instead of these gases.

[0048] In the above embodiment, a thin-walled container for storing food was exemplified as the molded article, but the molded article is not limited to a thin-walled container for storing food. The molded article may be, for example, a container for storing daily necessities such as wet tissues, an ink cartridge, a transport tray, or a building material. The thickness of the thin-walled portion of such a thin-walled container may be 0.20 to 0.60 mm. [Example]

[0049] The present disclosure will be described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0050] <Preparation of container> (Comparative Examples 1 and 5) A single-cavity container having the structure shown in Figure 1 was manufactured by normal injection molding (speed control) using the resin materials shown in Table 1. The molding conditions and the container structure are shown below.

[0051] [Molding conditions] Injection molding machine: MuCell injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd., "MuCell" is a registered trademark of Trexel Co. Ltd.) Screw diameter (Φ): 40mm Screw stroke: 160mm Screw cylinder temperature (5 zones): 210~240℃ Injection speed: When the resin filled into the mold cavity is 0-80% by volume based on the mold cavity, the injection speed is 350 mm / sec, and when the resin filled into the mold cavity is 80-100% by volume based on the mold cavity, the injection speed is 50 mm / sec. Packing pressure: Values ​​shown in Table 1 Pressure retention time: 1.0 seconds Maximum flow length in cavity: 99mm

[0052] [Container configuration] Bottom thickness: 0.348mm (target value: 0.350mm) Side wall (short side) thickness: 0.334 mm (target value: 0.350 mm) Side wall (long side) thickness: 0.343 mm (target value: 0.350 mm) Flange thickness: 0.342mm (target value: 0.350mm)

[0053] Details of the resin materials shown in Table 1 are given below. J667TG (product number, Prime Polymer Co., Ltd., fossil fuel-derived block polypropylene resin, MFR at 230°C: 36g / 10min) SHA7260 (Model number, Braskem, plant-based polyethylene resin, biomass content: 94.5%, MFR at 190°C: 20g / 10min)

[0054] (Comparative Example 2) A molten resin composition was prepared by adding a supercritical fluid to a resin material. Except for using this molten resin composition, a container was produced in the same manner as in Comparative Example 1. The amount of supercritical fluid blended per 100 parts by mass of the resin material and the type of supercritical fluid are shown in Table 1.

[0055] (Comparative Examples 3 and 4 and Examples 1 to 9) A container was produced in the same manner as in Comparative Example 1, except that the resin material, the type and amount of supercritical fluid, and the dwell pressure were as shown in Tables 1 and 2.

[0056] <Measurement of container weight and weight reduction rate> Examples 1 to 9 After removing the container from the mold, the weight of the container was measured. The weight reduction rate of the container was calculated. The results are shown in Tables 1 and 2. The standard for the weight reduction rate was the weight (10.32 g) of the container obtained when the mold cavity was filled with a resin material containing 50 mass % of J667TG and 50 mass % of SHA7260 without excess or deficiency. The standard weight was calculated based on the density (0.928 g / cm) calculated from the weighted average of the resin material. 3 ) by the volume of the container calculated from 3D-CAD. An example of a typical commercially available food container (bottom thickness: 0.483 mm, side wall (short side) thickness: 0.467 mm, side wall (long side) thickness: 0.487 mm, flange thickness: 0.453 mm) weighs approximately 12.80 g.

[0057] <Short shots> (Comparative Examples 1 to 5 and Examples 1 to 9) After removing the container from the mold, the container was visually inspected to check for the presence or absence of short shots. The results are shown in Tables 1 and 2. In the tables, "○" indicates that no short shots were observed, and "×" indicates that short shots were observed.

[0058] <Presence or absence of swelling> Examples 1 to 9 After removing the container from the mold, the container was visually observed. The observation results were evaluated according to the following criteria. The results are shown in Tables 1 and 2. Note that "blister" refers to a bulge that occurred on the surface of the container. [Evaluation criteria] 〇: The total area of ​​the bulging areas is less than 1% of the outer surface area of ​​the entire container. △: The total area of ​​the blistered areas is 1% or more but less than 10% of the outer surface area of ​​the entire container. ×: The total area of ​​the bulging areas is 10% or more but less than 70% of the outer surface area of ​​the entire container.

[0059] <Overall Judgment> The containers were evaluated comprehensively according to the following criteria, and the results are shown in Tables 1 and 2. [Evaluation criteria] ◎: No short shots or swellings were observed. ○: No short shots were observed and swelling was observed ×: Short shot confirmed

[0060] [Table 1]

[0061] [Table 2]

[0062] Containers with a blister rating of "○" had a flat surface overall. The rare bubbles visible to the naked eye were 300 μm or less in diameter. Containers with a blister rating of "△" had only a few blistered areas, and the majority of the container's surface was flat. In the blistered areas, bubbles between 300 μm and 3,000 μm were present. Compared to containers with a blister rating of "△," containers with a blister rating had multiple blistered areas, and more areas of the container's surface appeared bulged. In the blistered areas, bubbles between 300 μm and 20 mm were present.

[0063] Photographs of the containers obtained in Comparative Example 1 and Examples 1 and 5 are shown in Figures 3(a) to (c), respectively. The numbers labeled in the photographs are the study numbers. It can be seen from Figure 3(a) that short shots occurred in the container of Comparative Example 1. It can be seen from Figure 3(b) that no short shots occurred in the container of Example 1, and slight bulging occurred near the boundary between the bottom and side wall of the container. It can be seen from Figure 3(c) that no short shots occurred in the container of Example 5, and no bulging occurred.

[0064] The weight reduction rates of Examples 7 and 8 were smaller than those of the other Examples because the amount of resin material injected into the cavity was increased by increasing the dwell pressure.

[0065] The inventors speculate that the blisters observed in each example and comparative example are caused by foaming generated inside the resin material filled into the mold, which pushes the internal resin toward the surface. The inventors speculate that in Example 5, foaming inside the resin was suppressed, and thus blisters were suppressed, by using the supercritical fluid and dwelling pressure conditions shown in Table 1. Such blisters can be made less noticeable by blending a colorant or the like into the molten resin.

[0066] It was confirmed that when carbon dioxide was used as the supercritical fluid (Examples 1 to 5), swelling was less likely to occur than when nitrogen was used (Examples 6 to 9).

[0067] It was confirmed that the containers obtained using nitrogen as the supercritical fluid (Examples 6 to 9) tended to have a whitish appearance due to microvoids, compared to the containers obtained using carbon dioxide (Examples 1 to 5). [Explanation of symbols]

[0068] 1...bottom part, 2a, 2b...side wall part, 10...molded body.

Claims

1. (A) preparing a molten resin composition containing a resin material containing a biomass-derived polyethylene resin and a fossil fuel-derived polypropylene resin, and a supercritical fluid; (B) injecting the molten resin composition into a mold cavity; (C) after the step (B), a step of cooling the cavity while maintaining pressure therein; (D) recovering the molded body from the mold; Equipped with No core-back process for reducing the pressure in the cavity is provided, the supercritical fluid comprises carbon dioxide; the amount of the supercritical fluid is 2 to 3 parts by mass when the mass of the resin material in the molten resin composition is 100 parts by mass, The method for manufacturing a molded body, wherein the molded body has a thin-walled portion having a thickness of 0.20 to 0.60 mm.

2. The manufacturing method according to claim 1, wherein the content of the biomass-derived polyethylene resin is 30 to 60 mass% based on the total amount of the resin material.

3. A molded body formed by supercritical fluid molding, Contains biomass-derived polyethylene resin and fossil fuel-derived polypropylene resin. The thin-walled portion includes a bottom portion, a pair of first side wall portions, a pair of second side wall portions, and flanges provided at four corners, The thickness of the thin-walled portion is 0.20 to 0.60 mm, A molded body, the cut surface of which contains microvoids having a diameter of 10 to 200 μm.

4. The molded article according to claim 3, wherein the content of the biomass-derived polyethylene resin is 30 to 60 mass% based on the total amount of resin.

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