Method for producing resin molded body and resin molded body

Abstract

To provide a method for manufacturing a resin molded body capable of easily forming a skin layer on the whole of the resin molded body and improving the surface appearance of the resin molded body.SOLUTION: The resin-molded body manufacturing method includes a step R2 of generating a first mixed molten-resin S3, a step R2 of retaining a retained molten-resin R3 composed of the first mixed molten-resin S4 inside the hot-runner portion 20 and the cold-runner portion 30, a step R3 - 1 of generating a deaerated molten-resin R41 and a R42 by discharging a foaming agent from the retained molten-resin, a step - 2 of generating a second mixed molten-resin S5, a step of forming the skin layer 2 by injecting and filling the deaerated molten-resin and the into the mold 40, and a step of forming the core layer 3 inside the skin layer 2 by injecting and filling the second mixed molten-resin into the mold 40 while foaming. S7 R2 R2 S6 S5 S6 R42 R41. The foaming agent in the staying molten plastic R3 is discharged from a gap G1 formed in the hot-runner part 20.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a resin molded article produced by foam injection molding, and the resin molded article. [Background technology]

[0002] Traditionally, in the field of resin molding, foam injection molding has been widely used to reduce the amount of resin used or to improve dimensional accuracy by preventing warpage or sink marks. Resin foam molding can be broadly divided into chemical foaming and physical foaming. In these foaming methods, the blowing agents are typically nitrogen gas, carbon dioxide gas, carbon monoxide, ammonia gas, or water vapor. However, in recent years, with a view to reducing environmental impact, there has been an increase in examples of resin foaming using physical foaming, which uses inert gases such as carbon dioxide or nitrogen as the blowing agent. For example, a molding method using high-pressure supercritical fluids, as disclosed in Japanese Patent No. 2625576 (Patent Document 1), and a molding method using low-pressure gases, as disclosed in Japanese Patent No. 6139038 (Patent Document 2), have been put to practical use.

[0003] The main problems with this type of foam molding are a decrease in strength due to a decrease in the amount of resin and a deterioration in the surface appearance of the resin foam molded product. The deterioration in surface appearance is caused by the fact that during injection molding, the gas blowing agent is discharged from the tip of the flowing resin and becomes trapped between the mold and the flowing resin, which deteriorates the mold transferability of the surface of the resin foam molded product and causes unevenness on the surface of the resin foam molded product. This unevenness is a defect generally known as swirl marks. Therefore, this type of foam molding method has traditionally been used to manufacture mechanical parts and other components that do not require good appearance.

[0004] On the other hand, methods for improving surface appearance are generally known, including the counterpressure method, the heat-and-cool method, and foam molding using an insulated mold. The counterpressure method involves introducing pressurized gas such as air into a mold before injecting and filling the mold with a fluid resin to prevent the gas from escaping from the tip of the fluid resin. However, the counterpressure method requires sealing gaps within the mold with a seal or other device. The heat-and-cool method involves increasing the mold temperature when injecting and filling the mold with a fluid resin to prevent the fluid resin from solidifying before mold transfer, and then cooling the mold after the fluid resin is completely filled to improve mold transferability. However, the molds used in the heat-and-cool method have complex structures, which increase costs. The foam molding method using an insulated mold involves coating the mold surface with a material with low thermal conductivity to delay the solidification of the fluid resin. However, the foam molding method using an insulated mold has problems such as a short lifespan of the insulated mold and difficulty in producing resin foam molded products with complex shapes.

[0005] International Publication No. 2013 / 129659 (Patent Document 3) discloses a foam injection molding method (a method for manufacturing foam molded articles) that can suppress the release of gasified physical blowing agent into the mold, which causes swirl marks on the surface of the molded article, and prevent the molded article from having poor appearance. In the foam injection molding method, a nozzle unit located between the plasticizing cylinder and the mold cools and solidifies the flow front of the molten resin, evacuates the physical blowing agent from the solidified flow front to reduce the physical blowing agent concentration, and then heats and melts the solidified flow front again and injects it into the mold. This suppresses the release of gasified physical blowing agent from the flow front into the mold (see paragraphs "0138," "0139," and "0141" to "0148" of the specification of Patent Document 3, Figure 10, etc.).

[0006] Japanese Patent No. 6422548 (Patent Document 4) discloses a hot runner unit capable of highly efficient discharge of gas generated from molten resin. The hot runner unit is disposed between the gate of an injection mold and an open nozzle that discharges molten resin. The hot runner unit has a nozzle connection portion to which the nozzle is connected, and a sprue portion having an internal molten resin flow path for guiding the molten resin discharged from the nozzle to the gate. A section of the molten resin flow path in the sprue portion is a vent section whose tubular wall is made of a vent member having multiple micropores sized to allow only gas to pass through but not molten resin. In addition, a small-diameter section with an inner diameter smaller than that of the vent section is provided on the gate side of the vent section of the molten resin flow path. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 2625576 [Patent Document 2] Patent No. 6139038 [Patent Document 3] International Publication No. 2013 / 129659 [Patent Document 4] Patent No. 6422548 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the foam injection molding method of Patent Document 3, the surface area of ​​the solidified resin is small, it takes time to expel the physical foaming agent from the solidified resin, and it is not easy to adjust the amount of resin at the flow front where the concentration of the physical foaming agent needs to be reduced. Therefore, there is still room for further research into more efficient expulsion of the physical foaming agent.

[0009] Furthermore, in the hot runner unit of Patent Document 4, a vent section is provided in a continuous space extending from the nozzle to the gate, making it difficult to control the amount of resin that releases gas. Furthermore, the small diameter section increases the pressure in the molten resin flow path upstream of the small diameter section, making it easier to discharge gas in the molten resin flow path to the outside through the fine holes in the vent section, but conversely, there is a risk that gas may be unnecessarily discharged from the foaming molten resin that is subsequently injected and filled into the injection mold, resulting in a problem of reduced foamability.

[0010] Therefore, an object of the present disclosure is to provide a method for manufacturing a resin molded body and a resin molded body that can make it easier to form a skin layer over the entire resin molded body and improve the surface appearance of the resin molded body. [Means for solving the problem]

[0011] In order to solve the above problems, the present disclosure is configured as follows: That is, a method for manufacturing a resin molded body according to the present disclosure is a method for manufacturing a resin molded body by injection molding a resin molded body having a core layer made of a foamed resin and a skin layer covering the core layer, and includes the steps of preparing a molding machine having a nozzle, a mold, a hot runner section disposed between the molding machine and the mold and having a first flow path communicating with the interior of the molding machine via the nozzle, and a cold runner section disposed between the hot runner section and the mold and having a second flow path communicating with the first flow path and the interior of the mold, mixing a first molten resin and a first foaming agent containing a gas inside the molding machine to produce a first mixed molten resin, and flowing the first mixed molten resin from the interior of the molding machine into the first flow path through the nozzle, and then closing the nozzle of the molding machine to close the first flow path and the second flow path. the second mixed molten resin is injected into a mold by flowing the second mixed molten resin through a nozzle into the first and second flow paths, and a foamed resin is produced from the second mixed molten resin and injected into the mold; and the degassed molten resin and the foamed resin are cooled and solidified to form a skin layer and a core layer. The hot runner unit has a first plate disposed between the molding machine and the cold runner unit, and a second plate disposed between the first plate and the cold runner unit. A gap communicating with the first flow path is formed either between the first plate and the second plate or between the second plate and the cold runner portion, and in the step of producing a degassed molten resin, the first foaming agent is discharged through the gap.

[0012] The resin molded article according to the present disclosure has a core layer made of a foamed resin, a skin layer covering the core layer, and a gate portion through which a resin material is injected during foam injection molding. The core layer is formed in the vicinity of the gate portion.

[0013] The resin molded article according to the present disclosure has a gate portion through which a resin material is injected during foam injection molding, and the specific gravity of a portion near the gate portion is smaller than the specific gravity of a portion located farther from the gate portion than the portion near the gate portion. [Effects of the Invention]

[0014] According to the method for producing a resin molded article of the present disclosure, it is possible to easily form a skin layer over the entire resin molded article, thereby improving the surface appearance of the resin molded article.

[0015] According to the resin molded article of the present disclosure, the occurrence of sink marks near the gate portion can be suppressed, thereby improving the appearance of the resin molded article. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a flowchart of the method for producing a resin molded article according to the first embodiment. [Figure 2] FIG. 2 is a schematic diagram of a manufacturing apparatus used in the manufacturing method shown in FIG. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the hot runner section and the cold runner section shown in FIG. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing a hot runner portion and a cold runner portion of a modified example. [Figure 5] FIG. 5 is a schematic diagram showing the state of the retention step in FIG. [Figure 6] FIG. 6 is a schematic diagram showing the degassed molten resin producing step shown in FIG. [Figure 7] FIG. 7 is a schematic diagram showing the injection step of FIG. [Figure 8] FIG. 8 is a schematic diagram showing the injection step of FIG. [Figure 9] FIG. 9 is a schematic diagram showing the cooling step of FIG. [Figure 10] FIG. 10 is a schematic diagram of a manufacturing apparatus used in the manufacturing method of the second embodiment. [Figure 11]FIG. 11 is a schematic diagram of a plastic model according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Configuration 1) A method for manufacturing a resin molded body according to an embodiment of the present disclosure is a method for manufacturing a resin molded body by injection molding a resin molded body having a core layer made of a foamed resin and a skin layer covering the core layer, and includes the steps of preparing a molding machine having a nozzle, a mold, a hot runner section disposed between the molding machine and the mold and having a first flow path communicating with the interior of the molding machine via the nozzle, and a cold runner section disposed between the hot runner section and the mold and having a second flow path communicating with the first flow path and the interior of the mold, mixing a first molten resin and a first foaming agent containing a gas inside the molding machine to generate a first mixed molten resin, and flowing the first mixed molten resin from the interior of the molding machine through the nozzle and then closing the nozzle of the molding machine to close the first flow path and the second flow path. the second mixed molten resin is injected into a mold by flowing the second mixed molten resin through a nozzle into the first and second flow paths, and a foamed resin is produced from the second mixed molten resin and injected into the mold; and the degassed molten resin and the foamed resin are cooled and solidified to form a skin layer and a core layer. The hot runner unit has a first plate disposed between the molding machine and the cold runner unit, and a second plate disposed between the first plate and the cold runner unit. A gap communicating with the first flow path is formed either between the first plate and the second plate or between the second plate and the cold runner portion, and in the step of producing a degassed molten resin, the first foaming agent is discharged through the gap.

[0018] In this way, by discharging the first foaming agent through the gap from the retained molten resin retained in the retention space, it becomes easier to form a skin layer over the entire resin molded body depending on the size or shape of the resin molded body, thereby improving the surface appearance of the resin molded body.

[0019] (Configuration 2) In the method for producing a resin molded product according to Configuration 1, the first flow path may include a groove formed in either a surface of the first plate facing the second plate or a surface of the second plate facing the first plate. A gap may be formed between the first plate and the second plate and communicate with the groove. This allows the first foaming agent to be effectively discharged from the retained molten resin.

[0020] (Configuration 3) In the method for producing a resin molded product according to the first or second aspect, in the step of retaining the retained molten resin, the amount of the retained molten resin may be adjusted by changing the internal volume of the first flow path, thereby enabling appropriate skin layers to be formed for resin molded products of various shapes and sizes.

[0021] (Configuration 4) In the method for producing a resin molded product according to any one of Aspects 1 to 3, the first foaming agent may be either a chemical foaming agent or a physical foaming agent mixed at a pressure of 10 MPa or less. The method for producing a resin molded product according to the present disclosure can be suitably used in a production method using a chemical foaming agent or a low-pressure physical foaming agent.

[0022] (Configuration 5) In the method for producing a resin molded product according to any one of aspects 1 to 4, the first or second foaming agent may be either carbon dioxide or nitrogen. Carbon dioxide and nitrogen are inert gases that have little impact on the environment, which can contribute to reducing the environmental load.

[0023] (Configuration 6) The resin molded article according to this embodiment is a resin molded article obtained by foam injection molding, and includes a core layer made of foamed resin, a skin layer covering the core layer, and a gate portion through which the resin material is injected during foam injection molding. The core layer is formed near the gate portion. By forming the core layer near the gate portion in this manner, it is possible to suppress the occurrence of sink marks near the gate portion and improve the surface appearance of the resin molded article.

[0024] (Configuration 7) The resin molded article according to this embodiment has a gate portion, which is the portion into which the resin material is injected during foam injection molding. The specific gravity of the portion near the gate portion is lower than the specific gravity of the portion located farther from the gate portion than the portion near the gate portion. By making the specific gravity near the gate portion relatively low in this manner, a core layer can be formed near the gate portion, and the occurrence of sink marks near the gate portion can be suppressed, thereby improving the surface appearance of the resin molded article.

[0025] The method for producing a resin molded body and the resin molded body according to the present disclosure will be specifically described below with reference to Figures 1 to 11. Note that the same or corresponding components in the figures are denoted by the same reference numerals, and the same description will not be repeated. To facilitate understanding of the description, the drawings referred to below show simplified or schematic configurations, and some components are omitted.

[0026] [First embodiment] First, a method for producing a resin molded body according to a first embodiment of the present disclosure will be specifically described with reference to Figures 1 to 9. As shown in Figure 1, the method for producing a resin molded body includes a preparation step S1, a first molten resin production step S2, a first mixed molten resin production step S3, a retention step S4, a degassed molten resin production step S5-1, a second mixed molten resin production step S5-2, an injection step S6, a cooling step S7, and a demolding step S8.

[0027] [Preparation process S1] First, as shown in Fig. 2, a manufacturing apparatus 100 used in the method for manufacturing a resin molded body is prepared. The manufacturing apparatus 100 for a resin molded body includes a molding machine 10, a hot runner section 20, a cold runner section 30, and a mold 40. In Fig. 2, arrow F indicates the flow direction of molten resin, etc. That is, in Fig. 2, the right side of the illustration is upstream and the left side of the illustration is downstream.

[0028] [Forming machine] The molding machine 10 has a cylindrical plasticizing cylinder 11 including a starvation zone 111, a screw 12 disposed inside the plasticizing cylinder 11, a hopper 13 for feeding resin material into the plasticizing cylinder 11, a cylinder 14 and a pressure reducing valve 15 for feeding a blowing agent into the plasticizing cylinder 11, a pressure vessel 16, a nozzle 17 located at the tip of the molding machine 10, and a valve 18 for opening and closing the nozzle 17. The valve 18 is, for example, a needle valve as shown in the figure.

[0029] [Hot runner section] The hot runner section 20 is disposed between the molding machine 10 and the cold runner section 30. As shown in FIGS. 2 and 3, the hot runner section 20 has a plate 21 (first plate) and a plate 22 (second plate). The plate 21 is disposed between the molding machine 10 and the plate 22. The plate 22 is disposed between the plate 21 and the cold runner section 30. A flow path 21a is formed inside the plate 21. A flow path 22a is formed inside the plate 22. The flow paths 21a and 22a are connected to each other. The upstream side (right side in the figure) of the flow path 21a is connected to the nozzle 17 of the molding machine 10. The downstream side (left side in the figure) of the flow path 22a is connected to the upstream side of a flow path 31a in the cold runner section 30, which will be described later.

[0030] More specifically, as shown in FIG. 3 , the plate 21 has a surface 21b facing the plate 22. The plate 22 has a surface 22b facing the plate 21. The flow passages 21a of the plate 21 of the hot runner section 20 are composed of flow passages 21aA drilled from an opening on the upstream side along the flow direction F and grooves 21aB formed in the facing surface 21b of the plate 21 and extending from the downstream end of the flow passages 21aA along the facing surface 21b of the plate 21. That is, the flow passages 21a are composed of the flow passages 21a and the grooves 21aB, the openings of which are covered by the facing surface 21b of the plate 22. Note that such grooves may be formed on the facing surface 22b of the plate 22, or may be formed on both the facing surfaces 21b and 22b.

[0031] 3, a small gap G1 is formed between the plates 21 and 22. As will be described later, the gap G1 has a dimension W1 that allows a gas-containing blowing agent to be discharged from the retained molten resin R3 retained in the flow paths 21a, 22a, and 31a of the plates 21, 22, and 31, respectively, and prevents the molten resin of the retained molten resin R3 from flowing into the gap G1. The gap G1 is formed by slight surface roughness of at least one of the opposing surfaces 21b and 22b when the opposing surfaces 21b and 22b of the plates 21 and 22 are overlapped, or by bending of the plates 21 and 22. Alternatively, the gap G1 may be formed by providing irregularities on at least one of the opposing surfaces 21b and 22b.

[0032] The dimension W1 of the gap G1 along the flow direction F is preferably 1 μm to 50 μm, preferably 5 μm to 30 μm, and more preferably 10 μm to 20 μm, from the viewpoint of discharging the foaming agent from the retained molten resin R3 and preventing the molten resin from flowing in. If the dimension W1 of the gap G1 is too small, it becomes difficult to discharge the foaming agent. Therefore, the dimension W1 of the gap G1 is preferably 1 μm or more, preferably 5 μm or more, and more preferably 10 μm or more. If the dimension W1 of the gap G1 is too large, the molten resin of the retained molten resin R3 will easily flow into the gap G1. Therefore, the dimension W1 of the gap G1 is preferably 50 μm or less, preferably 30 μm or less, and more preferably 20 μm or less. The dimension W1 may be controlled by providing a spacer or a step between the plates 21 and 22, or may be controlled by the amount of deflection of the plates 21 or 22 that occurs when the plates 21 and 22 are fixed together using bolts or the like.

[0033] As shown in FIG. 3, gap G1 communicates with the groove 21aB. Therefore, the larger the area of ​​communication between gap G1 and groove 21aB, the easier it is to discharge the foaming agent from the retained molten resin R3. If the width of groove 21aB is large, it becomes difficult to discharge the foaming agent from the end of groove 21aB. Therefore, it is preferable that the width of groove 21aB is small. From this perspective, by forming groove 21aB in a meandering or U-shape, the area of ​​communication between gap G1 and groove 21aB can be increased while reducing the width of groove 21aB, making it easier to discharge the foaming agent.

[0034] As shown in FIG. 4, a small gap G2 is formed between the plate 22 and the cold runner portion 30. Similar to gap G1, gap G2 has a dimension W2 that allows the gas-containing blowing agent to be discharged from the retained molten resin R3 retained in the flow paths 21a, 22a, and 31a of the plates 21, 22, and cold runner portion 30, respectively, and prevents the molten resin of the retained molten resin R3 from flowing into gap G1. Gap G2 is formed by slight surface roughness of at least one of the opposing surfaces 22c and 31b of the plate 22 facing the cold runner portion 30, or by deflection of the plate 22 or the cold runner portion 31, when the opposing surface 22c and the opposing surface 31b of the cold runner portion 30 are overlapped. Alternatively, gap G2 may be formed by intentionally providing irregularities on at least one of the opposing surfaces 22c and 31b. The details of the gap G2 and the dimension W2 are the same as the dimension W1 of the gap G1, and therefore will not be described here. By providing the gap G2, the foaming agent can be more effectively discharged from the retained molten resin R3. The following description will be given using the hot runner section 20 and the cold runner section 30 shown in FIG. 3.

[0035] The gap G1 or G2 is not limited to this. For example, either the gap G1 or the gap G2 may be provided, or the hot runner section 20 or the cold runner section 30 may be further divided into multiple plates, with a gap provided between each plate. Furthermore, heat insulating plates may be provided between each plate to improve heating or cooling efficiency.

[0036] 3, the hot runner section 20 has an inlet hole 201 formed in the plate 21 and communicating with the inside of the nozzle 17, an outlet hole 202 communicating with the flow path 31a of the cold runner section 30, a temperature sensor (not shown), and a heater (not shown). The heater heats the inside of the flow path 21a of the hot runner section 20. The temperature sensor controls the temperature inside the flow path 21a of the hot runner section 20.

[0037] [Cold runner section] 2 and 3, the cold runner section 30 is disposed between the hot runner section 20 and the mold 40. As shown in Fig. 3, the cold runner section 30 has a plate 31 and a flow path 31a formed by penetrating the plate 31 along the flow direction F and including an inlet hole 301 and an injection hole 302. In the present disclosure, the above-mentioned flow paths 21a, 22a, and 31a may be collectively referred to as a "retention space."

[0038] The inlet hole 301 is connected to the outlet hole 202 of the hot runner section 20 and communicates with the flow path 22a of the hot runner section 20. The injection hole 302 communicates with the interior of the mold 40. The flow path 31a of the cold runner section 30 has a smaller internal volume than the flow paths 21a and 22a of the hot runner section 20. The inner circumferential surface of the flow path 31a has an expanded diameter portion 31aA and a reduced diameter portion 31aB. The expanded diameter portion 31aA is located between the inlet hole 301 and the reduced diameter portion 31aB, and gradually expands in diameter from the inlet hole 301 toward the reduced diameter portion 31aB, i.e., along the flow direction F. The reduced diameter portion 31aB is located between the injection hole 302 and the expanded diameter portion 31aA, and gradually contracts in diameter from the expanded diameter portion 31aA toward the injection hole 302, i.e., along the flow direction F. In the flow direction F, the length of the reduced diameter portion 31aB is shorter than the length of the expanded diameter portion 31aA. The angle of inclination of the reduced diameter portion 31aB with respect to the flow direction F is greater than the angle of inclination of the expanded diameter portion 31aA. As will be described later, the mixed molten resin R2 retained in the flow path 31a of the cold runner portion 30 solidifies slightly near the injection hole 302. This closes the injection hole 302 in the retention space. In other words, the cold runner portion 30 can function as a closing portion for closing the injection hole 302 in the retention space. Although not specifically shown, a separate flow path may be formed in the cold runner portion 30, through which a cooling medium such as a coolant can flow.

[0039] [Mold] 2 and 3, the mold 40 has a cavity 41 and a core 42. A resin molded body is manufactured by cooling and solidifying molten resin injected into the mold 40 from the flow path 31a of the cold runner section 30. The internal shape of the mold 40 is not particularly limited and can be changed according to resin molded bodies having various shapes or sizes.

[0040] [First molten resin generation step S2] Next, as shown in FIG. 2, a resin material (resin pellets) (not shown) is fed from a hopper 13 of a molding machine 10 into a plasticizing cylinder 11, and the interior of the plasticizing cylinder 11 is heated to produce a molten resin (first molten resin) R1. The resin material is not particularly limited as long as it is a thermoplastic resin. That is, the thermoplastic resin may be any of general-purpose plastics, engineering plastics, and super-engineering plastics. General-purpose plastics are thermoplastic resins having a deflection temperature under load of less than 100°C, such as polyethylene (PE) or polypropylene (PP). Engineering plastics are thermoplastic resins having a deflection temperature under load of 100°C or higher, such as polycarbonate resin (PC), modified polyphenylene ether (m-PPE), syndiotactic polystyrene (SPS), polyamide (PA), and polybutyl terephthalate (PBT). Super engineering plastics are thermoplastic resins that have a deflection temperature under load of 150°C or higher, such as polyphenylsulfone (PPSU), polysulfone (PSU), polyarylate (PAR), polyetherimide (PEI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyethersulfone (PES), polyamideimide (PAI), polyvinylidene fluoride (PVDF), tetrafluoroethylene perfluoroalkylvinyl copolymer (PFA), etc.

[0041] The resin material may also contain various types of additives to the extent that they do not significantly affect the effects of the present disclosure. The types of additives are not particularly limited, but include, for example, bubble nucleating agents, crystal nucleating agents, lubricants, surfactants, tension modifiers, shrinkage inhibitors, flow modifiers, impact modifiers, fillers, reinforcing agents, antioxidants, heat stabilizers, light stabilizers, UV absorbers, plasticizers, lubricants, mold release agents, antistatic agents, colorants (pigments, dyes, etc.), surface effect additives, infrared absorbers, radiation stabilizers, drip-proofing agents, and antioxidants. The amount of additive added can be selected appropriately as long as it does not impair bubble formation, and the amount used in molding conventional thermoplastic resins can be used. Reinforcing fillers such as glass fiber, carbon fiber, or organic fiber, or inorganic fillers such as talc or calcium carbonate, can also be mixed.

[0042] [First mixed molten resin production step S3] Next, as shown in FIG. 2, the screw 12 is rotated to flow the molten resin R1 in the flow direction F. A blowing agent (first blowing agent) is injected into the starvation zone 111 to produce a mixed molten resin (first mixed molten resin) R2, in which the blowing agent is kneaded and dissolved in the molten resin R1. At this time, the nozzle 17 of the molding machine 10 is closed by the valve 18. The blowing agent may be either a chemical blowing agent or a physical blowing agent, as long as it contains a gas. From the perspective of contributing to reducing environmental impact, a physical blowing agent, such as an inert gas such as carbon dioxide or nitrogen, is preferably used as the blowing agent. The blowing agent is injected into the plasticizing cylinder 11 from the cylinder 14 via the pressure reducing valve 15 and the pressure vessel 16. The pressure reducing valve 15 reduces the nitrogen gas pressure to a constant level. The mixed molten resin R2 can be produced, for example, by a low-pressure gas physical foam molding method described in Japanese Patent Publication No. 6139038. In this case, the gas pressure introduced into the cylinder 14 can be 10 MPa or less.

[0043] The foaming agent can be selected appropriately depending on the internal volume of the retention space, the concentration or pressure of the foaming agent, or the amount of resin in the retained molten resin R3 retained in the retention step S4 described below. In other words, the amount of resin in the retained molten resin R3 may be determined depending on the concentration or pressure of the foaming agent. For example, in the case of chemical foam molding using a chemical foaming agent or physical foam molding using a low-pressure gas, even if the foaming agent is discharged from the retained molten resin R3 in an amount less than the amount of resin that forms the skin layer 2 in the cooling step S7 described below, the amount of foaming agent mixed in the foamed resin R5 that forms the core layer 3 is reduced, thereby making it possible to obtain a foam injection-molded part with excellent appearance and little adverse effect on the skin layer 2.

[0044] [Retention process S4] Next, the nozzle 17 of the molding machine 10 is opened, and the mixed molten resin R2 is caused to flow in the retention space (flow paths 21a, 22a, and 31a). As shown in FIG. 5, a retained molten resin R3 consisting of the mixed molten resin R2 is retained in the retention space. At this time, a portion of the retained molten resin R3 solidifies slightly near the injection hole 302 of the cold runner section 30. This closes the injection hole 302. After the flow of the mixed molten resin R2 into the retention space is completed, the nozzle 17 of the molding machine 10 is closed by the valve 18. The amount of retained molten resin R3 retained in the retention space is calculated in advance according to the shape and size of resin molded products, and can be adjusted by changing the inner diameter or length of the flow path 21a, 22a, or 31a, i.e., by changing the internal volume of 21a, 22a, or 31a. Alternatively, the amount of retained molten resin R3 may be adjusted by closing the nozzle 17 of the molding machine 10 after a predetermined amount of retained molten resin R3 has been retained inside the retention space.

[0045] The resin amount of the retaining molten resin R3 is preferably 10% by volume to 85% by volume, and more preferably 10% by volume to 50% by volume, based on the resin material of the entire resin molded body. Therefore, the resin amount of the retaining molten resin R3 is preferably 10% by volume or more, preferably 85% by volume or less, and more preferably 50% by volume or less, based on the resin material of the entire resin molded body. As described below, the retaining molten resin R3 is degassed and then used to form the skin layer of the resin molded body. If the resin amount of the retaining molten resin R3 is too small, it becomes difficult to form a skin layer throughout the entire resin molded body. On the other hand, if the resin amount of the retaining molten resin R3 is too large, it may take a long time for the foaming agent to be exhausted, making it difficult to suppress the occurrence of swirl marks due to foaming when the core layer (described below) is formed. However, when the mixed molten resin R2 is foamed only inside the mold 40 near the injection hole 302, the resin amount of the retaining molten resin R3 may be 10% by volume to 20% by volume, based on the resin material of the entire resin molded body.

[0046] [Degassed molten resin production process S5-1] Next, as shown in FIG. 6, the foaming agent is discharged from the retained molten resin R3 in the retention space through gap G1 (and gap G2 shown in FIG. 4) formed between plates 21 and 22 of hot runner section 20, producing degassed molten resin R41 and degassed molten resin R42 with reduced foaming agent concentrations. Degassed molten resin R41 is degassed molten resin produced from retained molten resin R3 retained in flow path 31a of cold runner section 30. Degassed molten resin R42 is degassed molten resin produced from retained molten resin R3 retained in flow paths 21a and 22a of hot runner section 20. At this time, to facilitate the discharge of the foaming agent, a vacuum pump (not shown) may be provided outside hot runner section 20 to suck the foaming agent.

[0047] The method for producing a resin molded body according to the present disclosure can be suitably used for producing a resin molded body by chemical foam molding or physical foam molding using low-pressure gas. As described above, in the retention step S4, the injection hole 302 of the cold runner 30 is closed by the solidification of a portion of the retained molten resin R3. In other words, chemical foam molding or physical foam molding using low-pressure gas prevents a portion of the solidified retained molten resin R3 from being extruded toward the mold 40, thereby appropriately forming a retention space. From this perspective, when physical foam molding is used, the introduction pressure of the foaming agent is preferably 10 MPa or less, and preferably 6 MPa or less. The lower limit of the introduction pressure of the foaming agent is not particularly limited, but can be 1 MPa or more.

[0048] [Second mixed molten resin production step S5-2] 6, at the same time as the above-described degassed molten resin producing step S5 is being performed, that is, simultaneously, a new molten resin (second molten resin) R11 and a foaming agent (second foaming agent) are mixed together inside the plasticizing cylinder 11 of the molding machine 10, to produce an upstream mixed molten resin (second mixed molten resin) R21. Note that the second mixed molten resin R21 is produced separately from the above-described first mixed molten resin R2, but is basically the same as the first mixed molten resin R2.

[0049] [Injection process S6] Next, the degassed molten resin R41, the degassed molten resin R42, and the mixed molten resin R21 are injected and filled into the mold 40 in one step. More specifically, as shown in FIG. 7, the nozzle 17 of the molding machine 10 is opened, and the mixed molten resin R21 produced in the second mixed molten resin production step S5-2 flows toward the flow path 21a of the hot runner section 20. Accordingly, the degassed molten resin R41 in the flow path 31a and the degassed molten resin R42 in the flow paths 21a and 22a are injected into the mold 40 from the injection hole 302, as if being pushed out by the upstream mixed molten resin R21. The extruded degassed molten resin R41 and degassed molten resin R42 flow along the inner wall of the mold 40, as shown in FIG. 8.

[0050] Returning to FIG. 7 , the upstream mixed molten resin R21 is passed into the mold 40 without being retained in the retention space. The mixed molten resin R21 then foams around the time it enters the flow path 31a of the cold runner section 30, forming foamed resin R5. As shown in FIG. 8 , when the mixed molten resin R21 is further extruded from the molding machine 10, the foamed resin R5 is injected into the mold 40 and fills the degassed molten resin R41 and the degassed molten resin R42. The degassed molten resin R41 and the degassed molten resin R42 are pushed outward by the foaming of the foamed resin R5, bringing them into close contact with the inner surface of the mold 40. This improves the mold transferability of the molten resin and prevents swirl marks from forming on the outer surface of the resin molded body. At this time, as shown in FIG. 9 , the mixed molten resin R21 further extruded from the molding machine 10 remains in the retention space, similar to the retention step S4, to generate a new retained molten resin R31.

[0051] [Cooling process S7] Next, as shown in Figure 9, by cooling and solidifying the degassed molten resin R41 and the degassed molten resin R42 and the foamed resin R5 filled inside the degassed molten resin R41 and the degassed molten resin R42, a skin layer 2 made of the degassed molten resin R41 and the degassed molten resin R42 with a low foaming agent concentration and a core layer 3 made of the foamed resin R5 covered with the skin layer 2 can be formed.

[0052] Furthermore, at the same timing as the cooling step S7, i.e., during the period in which the degassed molten resin R41, the degassed molten resin R42, and the foamed resin R5 are cooled, the foaming agent is discharged from the retained molten resin R31 (shown in FIG. 9) retained in the retention space, as in the above-described degassed molten resin production step S5-1, to produce new degassed molten resin (not shown). Also, at the same timing as the cooling step S7, as in the above-described second mixed molten resin production step S5-2, a third mixed molten resin R22 is produced further upstream, as shown in FIG.

[0053] [Mold release process S8] Finally, the cooled and solidified resin molded body 1 (not shown in detail) having the skin layer 2 and core layer 3 is removed from the mold 40. In this way, it is possible to manufacture a resin molded body 1 that is easy to form the skin layer 2 over the entire resin molded body 1, suppresses the occurrence of swirl marks, and improves surface appearance.

[0054] After the above-described demolding step S8 is completed, a degassed molten resin (not shown) newly produced from the retaining molten resin R31 and a newly produced mixed molten resin R22 (shown in FIG. 9) are injected and filled into the mold 40 in one step. That is, the newly produced mixed molten resin R22 is discharged from the nozzle 17 of the molding machine 10, and the degassed molten resin produced from the retaining molten resin R32 is injected and filled into the mold 40 as if being extruded by the mixed molten resin R22. The mixed molten resin R22 is further injected and filled into the degassed molten resin, which is then cooled and solidified. Through this series of cycles, the resin molded body 1 can be produced continuously and efficiently.

[0055] [Second embodiment] Next, a second embodiment of the method for manufacturing a resin molded body will be specifically described with reference to Fig. 10. Explanation of the same components as in the method for manufacturing a resin molded body of the first embodiment will be omitted, and basically, components different from the method for manufacturing a resin molded body of the first embodiment will be described.

[0056] As shown in FIG. 10 , in the method for manufacturing a resin molded product according to the second embodiment, the cold runner 30 may have a plurality of injection holes 302. That is, in the plate 21 of the hot runner 20, the groove 21aB may be formed so as to extend in two directions, up and down, from the flow path 21aA. In addition, in the cold runner 30, the flow path 31a may be provided in two locations, up and down, as shown. Both ends of the groove 21aB may be formed so as to communicate with one flow path 31a and the other flow path 31a, respectively. This allows two injection holes 302 to be provided. The number of injection holes 302 is not limited to two, and may be three or more.

[0057] This manufacturing method for producing a resin molded body by providing multiple injection holes 302 is particularly suitable for producing relatively large resin molded bodies. Furthermore, in the manufacturing method for a resin molded body according to the present disclosure, the degassed molten resin R41 and the degassed molten resin 42 are injected and filled into the interior of the mold 40, and then the foamed resin 5 is injected and filled. Therefore, a core layer 3 is formed near the injection holes 302, which tends to reduce the specific gravity of the area near the injection holes 302. By injecting and filling the degassed molten resin R41, the degassed molten resin R42, and the foamed resin R5 through multiple injection holes 302, the specific gravity of each area of ​​the resin molded body can be made relatively uniform. Meanwhile, by selecting the position of the injection hole 302, i.e., the position within the mold 40 where the injection filling is performed, the position where the core layer 3 is formed in the resin molded body 1 can be appropriately selected.

[0058] [Plastic model] The methods for manufacturing a resin molded body according to the above-described embodiments can be suitably used to manufacture a plastic model 200, as shown in FIG. 11 . Although not specifically illustrated, the plastic model 200 includes multiple parts 210 for forming the assembled model and a framework 220 for connecting the multiple parts 210 to one another. The multiple parts 210 include a difficult-to-form part 210a and an easy-to-form part 210b. The difficult-to-form part 210a is a relatively thick part that is prone to sink marks and low shape accuracy. The easy-to-form part 210b is a relatively thin part that is less prone to sink marks and easier to maintain shape accuracy. This is because it is difficult to supply a sufficient amount of mixed molten resin R2 to the interior of a mold 40 used to form the difficult-to-form part 210a, particularly to the edges of the mold 40.

[0059] 11 , during the above-described injection molding, the hard-to-form part 210a is placed near the injection hole 302, and the easy-to-form part 210b is placed farther from the injection hole 302 than the hard-to-form part 210a. That is, in the plastic model 200, the hard-to-form part 210a is placed near the gate 230, where the resin material is injected from the injection hole 302, and the easy-to-form part 210b is placed farther from the gate 230 than the hard-to-form part 210a. According to the manufacturing method of the resin molded product disclosed herein, first, the degassed molten resin R41 and the degassed molten resin R42 are injected and filled into the mold 40. The amount of resin injected and filled with the degassed molten resin R41 and the degassed molten resin R42, i.e., the amount of resin of the retained molten resin R3 retained in the retention space, is adjusted. The amounts of degassed molten resin R41 and degassed molten resin R42 should be sufficient to form the distant easy-to-form part 210b and the skin layer 2 of the nearby difficult-to-form part 210a. The downstream mixed molten resin R2 is then injected to fill the skin layer 2 of the nearby difficult-to-form part 210a, generating foamed resin R5 and forming the core layer 3. By positioning the difficult-to-form part 210a near the injection hole 302 in this way, sink marks that could occur in the difficult-to-form part 210a can be suppressed.

[0060] [Resin molded body] The resin molded body 1 manufactured by the above-described manufacturing method has, like the example of the plastic model 200 described above, a gate portion 230, a core layer 3 made of foamed resin, and a skin layer 2 covering the core layer 3. The core layer 3 may be formed throughout the entire interior of the resin molded body 1, or may be formed in the vicinity of the gate portion 230.

[0061] Furthermore, the specific gravity of the resin molding 1 in the vicinity of the gate 230 can be made smaller than the specific gravity of the region farther from the gate 230 than the vicinity thereof.

[0062] The resin molded body 1 manufactured by the manufacturing method according to this embodiment is foam-molded, which allows for a reduction in the amount of resin used. As a result, the resin molded body 1 can contribute to improving resource utilization efficiency, easing transportation burdens, reducing energy consumption, and reducing CO2 emissions. By providing the resin molded body 1 to society, it is possible to contribute to the achievement of Goal 7 (Affordable and Clean Energy), Goal 9 (Industry, Innovation and Infrastructure), and Goal 11 (Sustainable Cities and Communities) of the 17 Sustainable Development Goals (SDGs) established by the United Nations. Furthermore, since the resin molded body 1 according to this embodiment can be melted and reused, it can contribute to the achievement of Goal 12 (Responsible Consumption and Production).

[0063] Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. [Example]

[0064] The appearances of the resin molded article of Example 1 manufactured by the manufacturing method according to the first embodiment described above (see FIGS. 1 to 10) and the resin molded article of Comparative Example 1 made of a non-foaming resin were observed.

[0065] The manufacturing conditions for the resin molded article of Example 1 are as follows. Resin material: Polycarbonate resin (Sumitomo Chemical Co., Ltd. SF5301V, 30% glass fiber, specific gravity 1.42) Foaming agent: Nitrogen, Nitrogen cylinder gas pressure: 6MPa Mold conditions: Flat cavity with a center direct gate as shown in Figure 1 (Width 20cm, height 40cm, thickness 3mm, volume 240cm 3 ) Hot runner flow path shown in Figure 4: Internal volume 75 cm 3 , heating temperature 260℃ Groove (U-shaped) Length 75mm, width 2mm, depth 5mm Cold runner section flow path shown in Figure 4: Internal volume 5 cm3 , cooling temperature 20℃ Resin material volume: Total 240cm 3 , degassed mixed molten resin 80cm 3 (approximately 30% of the total)

[0066] In the resin molded body of Example 1, a core layer was formed up to 10 mm from the vicinity of the injection-filled area. Furthermore, the weight of the resin molded body of Example 1 was 250 g, a 26% weight reduction compared to the resin molded body of Comparative Example 1. When the tip of the resin molded body of Example 1 was pressed, the amount of warping on the surface opposite the pressed surface was approximately 0.3 mm, which was less than the warping amount of approximately 1.5 mm of the resin molded body of Comparative Example 1. Furthermore, the surface roughness Ra of the resin molded body of Example 1 was approximately 1 μm. However, this surface roughness Ra value was due to the floating of glass fibers contained in the resin material, and in reality, no swirl marks due to foam molding were observed. [Explanation of symbols]

[0067] S1 preparation process, S2 first molten resin generation process, S3 first mixed molten resin generation process, S4 retention process, S5-1 degassed molten resin generation process, S5-2 second mixed molten resin generation process, S6 injection process, S7 cooling process, S8 demolding process, 100 resin molding manufacturing apparatus, 10 molding machine, 20 hot runner section, 21 plate, 21a flow path, 22 plate, 22a flow path, 30 cold runner section, 31 plate, 31a flow path, 40 mold, G1 G2 gap, W1 W2 dimension, R1 molten resin, R2 mixed molten resin, R3 retained molten resin, R41 R42 degassed molten resin, R5 foam resin, 200 plastic model, 210 part, 210a non-easy to form part, 210b easy to form part, framework 220, gate section 230, 1 Resin molding, 2 skin layers, 3 core layers

Claims

1. A method for manufacturing a resin molded article by injection molding a resin molded article having a core layer made of a foamed resin and a skin layer covering the core layer, a step of preparing a molding machine having a nozzle, a mold, a hot runner unit disposed between the molding machine and the mold and having a first flow path communicating with the interior of the molding machine via the nozzle, and a cold runner unit disposed between the hot runner unit and the mold and having a second flow path communicating with the first flow path and the interior of the mold; mixing a first molten resin and a first blowing agent containing a gas inside the molding machine to produce a first mixed molten resin; a step of causing the first mixed molten resin to flow into the first flow path from the inside of the molding machine through the nozzle, and then closing the nozzle of the molding machine to cause a retained molten resin made of the first mixed molten resin to remain in the first flow path and the second flow path; discharging the first foaming agent from the retained molten resin to produce a degassed molten resin having a reduced foaming agent concentration; mixing a second molten resin and a second foaming agent containing a gas inside the molding machine at the same time as the step of producing the degassed molten resin, to produce a second mixed molten resin; a step of injecting the degassed molten resin into the inside of the mold by flowing the second mixed molten resin from the inside of the molding machine through the nozzle into the first and second flow paths, and generating and injecting a foamed resin from the second mixed molten resin into the degassed molten resin injected into the mold; and a step of cooling and solidifying the degassed molten resin and the foamed resin injected into the mold to form the skin layer and the core layer, the hot runner section includes a first plate disposed between the molding machine and the cold runner section, and a second plate disposed between the first plate and the cold runner section; a gap communicating with the first flow path is formed either between the first plate and the second plate or between the second plate and the cold runner portion, In the step of producing the degassed molten resin, the first foaming agent is discharged through the gap.

2. A method for producing the resin molded article according to claim 1, the first flow path includes a groove portion formed in one of an opposing surface of the first plate facing the second plate and an opposing surface of the second plate facing the first plate, The gap is formed between the first plate and the second plate and communicates with the groove portion.

3. A method for producing the resin molded article according to claim 1, A method for manufacturing a resin molded body, wherein in the step of retaining the retained molten resin, the amount of resin in the retained molten resin is adjusted by changing the internal volume of the first flow path.

4. A method for producing the resin molded article according to claim 1, The method for producing a resin molded body, wherein the first foaming agent is either a chemical foaming agent or a physical foaming agent mixed at a pressure of 10 MPa or less.

5. A method for producing the resin molded article according to claim 1, The method for producing a resin molded body, wherein the first foaming agent is either carbon dioxide or nitrogen.

6. A resin molded body obtained by foam injection molding, a core layer made of a foamed resin; a skin layer covering the core layer; a gate portion through which a resin material is injected during foam injection molding; The core layer is formed in the vicinity of the gate portion.

7. A resin molded body obtained by foam injection molding, It has a gate portion through which the resin material is injected during foam injection molding, A resin molded body, wherein a specific gravity of a portion in the vicinity of the gate portion is smaller than a specific gravity of a portion located farther from the gate portion than the portion in the vicinity.

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