Injection molding die and resin molding method

Abstract

To provide a metal mold for injection molding capable of molding even a thin wall molded article having a convex by suppressing a manufacturing cost of a metal mold, and suppressing degradation of a thin wall molded article.SOLUTION: A metal mold 10 for injection molding forms a resin molded article having a convex and a flat part by injecting molten resin into a cavity 13 formed between a core mold 12 and a cavity mold 14, where the cavity 13 comprises: a convex space part 13A which forms a convex; a flat space part 13B which forms a flat part around the convex; and a guide zone space part 13C which is formed for at least one of the convex space part 13A and the flat space part 13B, and has a wall thickness thicker than the convex space part 13A and the flat space part 13B, where the guide zone space part 13C comprises a convex-surrounding guide zone space part 13X which contacts a boundary part between the convex space part 13A and the flat space part 13B, and circulates the boundary part, and the cavity mold 14 is equipped with a gate 16 for injecting molten resin for the guide zone space part 13C.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an injection mold for injection molding and a resin molding method.

Background Art

[0002] Conventionally, as a technique for molding various resin molded products with a relatively thin wall thickness, such as egg packs (hereinafter, also simply referred to as "molded products"), a vacuum molding technique is known. Since the vacuum molding technique uses a resin material processed in advance into a sheet shape having a predetermined wall thickness, it is relatively easy to mold a molded product with a thin wall thickness.

[0003] However, in the vacuum molding technique, it is necessary to process the resin material into a sheet shape in advance. Therefore, there is a problem that it is limited to resin materials that can be obtained in a processed sheet shape. Further, since the sheet-shaped resin material is stretched over a frame, heated, and attached to a mold by vacuum suction for molding, the bent portions of the molded product are stretched and thinned, making it vulnerable, and it is difficult to maintain the dimensional accuracy of the wall thickness. There are also problems such as it is difficult to make the wall thickness very thin in a molded product with a complicated shape having many irregularities.

[0004] Also, as a technique for molding resin molded products, an injection molding technique is well known. The injection molding technique melts a resin material and injects and fills molten resin into a molding space (hereinafter, also referred to as a "cavity") formed inside an injection mold (hereinafter, also simply referred to as a "mold") that has been processed to provide a molten resin flow path or the like in a metal block. After cooling and solidifying, the separable mold members constituting the mold are separated to open the molding space (hereinafter, also referred to as "mold opening"), and the molded product is taken out to mold the molded product. For example, Patent Document 1 discloses a mold in which a gate (pinpoint gate), which is an inlet from a runner to a molding space, is formed as the mold.

[0005] Compared to vacuum forming, injection molding technology has the advantage of not stretching at bends, forming according to the mold cavity shape, resulting in high dimensional accuracy and no loss of strength at bends. Furthermore, unlike vacuum forming technology, injection molding technology can use a wider variety of resin materials, and used resin materials such as polypropylene (PP) can be recovered, remelted, and reused, thus reducing the environmental impact.

[0006] However, injection molding technology requires the molten resin to be poured and filled into every corner of the cavity, so the difficulty of molding depends largely on the shape and dimensions of the molded product. In particular, for molded products that are relatively thin-walled and large in size, or for molded products with complex shapes where flat and uneven surfaces are intricately mixed, there are many factors that hinder the smooth flow of the molten resin, making it relatively difficult to fill the cavity completely with molten resin without creating defects or internal distortions in the molded product.

[0007] Furthermore, Patent Document 2 also contains a proposal by the present inventor that contributes to solving the above-mentioned problems in injection molding technology. Patent Document 2 discloses a buffer body with a complex shape having a mixture of flat and convex portions, which is molded using a mold.

[0008] According to the buffer technology described in Patent Document 2, it is possible to mold a relatively thin-walled molded product with a thickness of about 0.4 mm. In the mold used for the buffer in Patent Document 2, a guide band extending from the gate (a rib-like portion in the molded product) surrounds the cavity portion corresponding to the protrusion of the buffer, and the guide band further branches out to climb up the portion corresponding to the protrusion. According to the proposal in Patent Document 2, compared to a case without such a guide band, the flow of molten resin in the portion corresponding to the protrusion of the buffer becomes smoother, which in turn reduces the number of gates and has the effect of suppressing molding defects that occur in the protrusion. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Utility Model Publication No. 6-5929 [Patent Document 2] Japanese Patent Publication No. 2020-097433 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, through subsequent prototype experiments and research by the inventors, it was confirmed that the effect of suppressing molding defects occurring in the convex portions described above can be obtained for specific shapes such as the buffer structure in Patent Document 2. However, it became clear that for general molded product shapes that are thinner and have complex convex portions, it is not easy to determine the optimal positional relationship between the portion corresponding to the convex portion in the cavity and the guide band.

[0011] Patent Document 2 does not disclose any method for reducing the flow resistance of the cavity bend at the boundary between the flat portion and the convex portion of a molded product having a convex portion. Therefore, even if the technology proposed in Patent Document 2 is used, repeated trial and error is required to determine an appropriate mold shape, including the arrangement of the guide band, and the problem of high costs remains.

[0012] The present invention has been made in view of the above-mentioned problems, and aims to provide a mold and molded products formed using such a mold that can simplify the number and arrangement of gates, reduce mold manufacturing costs, and suppress deterioration of molded product quality, even for molded products that are relatively thin-walled and large in size, or molded products with complex shapes in which flat and uneven surfaces are intricately mixed. [Means for solving the problem]

[0013] An injection molding die according to Embodiment 1 of the present invention comprises a core mold and a cavity mold, and is used to mold a resin molded product having a convex portion and a flat portion by overlapping the core mold and the cavity mold and injecting molten resin into the cavity formed between the core mold and the cavity mold, wherein the cavity comprises a convex portion space for forming the convex portion, a flat portion space for forming the flat portion around the convex portion, and a guide zone space formed in at least one of the convex portion space and the flat portion, having a greater wall thickness than the convex portion space and the flat portion, the guide zone space comprises a convex portion circumferential guide zone space that is in contact with the boundary between the convex portion space and the flat portion and encircles the boundary, and the cavity mold is provided with a gate for injecting molten resin in the guide zone space.

[0014] According to the above configuration, the molten resin injected from the gate into the guide zone space of the cavity quickly reaches the end of the guide zone space that circulates the planar space and convex space at a point far from the gate, via the guide zone space, which has a thicker flow path wall than the convex space and planar space, and therefore has lower flow resistance than the convex space and planar space. Furthermore, since the end of the flow path with low flow resistance along the guide zone space is connected to a section with high flow resistance, after the molten resin fills the end of the guide zone space, pressure is accumulated in the molten resin inside the guide zone space in accordance with the continuously applied injection pressure.

[0015] As a result, the molten resin flows and spreads along the guide zone space into the adjacent planar and convex spaces in a lateral direction under relatively high pressure. Compared to molds without a guide zone space, this results in better filling performance, making it less prone to defects such as shorts, and enabling the molding of high-quality thin-walled molded products.

[0016] In the above configuration, the guide zone space is formed mainly in a planar space where a relatively straight flow path can be secured, from the viewpoint of flow resistance. However, depending on the dimensions and shape of the molded product, the guide zone space may be formed in a convex space, or in both a planar space and a convex space. Furthermore, the gate for injecting molten resin into the guide zone space is preferably located in the guide zone space formed in the planar space, from the viewpoint of efficiently arranging the guide zone network starting from the gate. However, depending on the dimensions and shape of the molded product, any number of gates can be provided at any location in the guide zone space.

[0017] Furthermore, according to the above configuration, the guide zone space includes a convex-circumferential guide zone space that is adjacent to and surrounds the base of the convex portion. This convex-circumferential guide zone space acts as a molten resin reservoir, and the entire length of the convex-circumferential guide zone space acts as a film gate to the convex portion space. As a result, the flow-inhibiting effect of the flow channel bend at the base of the convex portion, which is a factor that obstructs the flow of molten resin from the planar space to the convex portion space and increases flow resistance, is reduced. Therefore, compared to molds without such a convex-circumferential guide zone space, defects such as shorts in the convex portion are less likely to occur, and high-quality thin-walled molded products can be molded. It is desirable that the corners of the flow channel bend have an R shape (rounded) on both the inner and outer circumferential wall surfaces.

[0018] In the injection molding die according to embodiment 2 of the present invention, in embodiment 1, at least one of the core mold and the cavity mold is provided with a residual gas discharge section that discharges residual gas remaining at the top of the protruding space from the top of the cavity.

[0019] According to the above configuration, by providing a convex-circumferential guided zone space in contact with the base of the convex portion, the filling efficiency of the molten resin into the convex portion space is improved. In addition, at least one of the core mold and the cavity mold is equipped with a residual gas discharge section that discharges residual gas from the top of the convex portion space. As a result, residual gas accumulating near the top of the convex portion space is appropriately released to the outside of the mold by the residual gas discharge section. This prevents the residual gas concentrated near the top of the convex portion space from being excessively compressed and becoming high pressure, which would hinder the flow of the molten resin, and further improves the filling efficiency of the molten resin into the convex portion space.

[0020] In this invention, the residual gas discharge section may have any structure or shape as long as a gas passage is formed that penetrates from a cavity through which molten resin cannot pass but residual gas can pass, to the outside of the mold. For example, it may have a gas vent hole provided in at least one of the core mold and the cavity mold, reaching from the outer surface of the mold to the top of the convex space, and a plug member detachably inserted into the gas vent hole, wherein the plug member is a rod-shaped member in which at least the entire outer surface of the portion in contact with the top of the convex space is in close contact with the entire inner surface of the gas vent hole, and a gas passage is formed between the outer surface of the rod-shaped member in the contact portion and the inner surface of the gas vent hole, through which molten resin cannot pass but residual gas can pass.

[0021] Furthermore, in the present invention, if a gas vent hole is used as the residual gas discharge section, a vacuum device may be connected to the outlet of the gas vent hole, and the residual gas discharged from the gas vent hole may be sucked out by the vacuum device, thereby promoting the discharge of residual gas from the top of the convex space.

[0022] As a third aspect of the present invention, a resin molding method may be configured to mold a resin molded product using the injection molding die described in the first aspect. The resin molding method in this configuration, as described in the first aspect, can provide a high-quality resin molded product in which quality degradation due to distortion, insufficient filling, discoloration, etc., in the molded product is suppressed. [Effects of the Invention]

[0023] According to the present invention, even for a thin-walled molded product having a convex portion, the degree to which the flow of the molten resin in the cavity is inhibited due to the convex portion is alleviated. As a result, even if the injection pressure of the molten resin is reduced, good cavity filling performance can be obtained. Furthermore, by this low-pressure molding, it is also possible to reduce the generation of pressure distortion or burrs remaining inside the molded product.

[0024] In addition, since such a margin in the molding conditions can be obtained, the number of mold trial productions for ensuring sufficient filling performance can also be reduced, the manufacturing cost of the mold can be suppressed, and it is possible to provide a mold and a molded product capable of suppressing quality deterioration even for a thin-walled molded product and performing molding.

Brief Description of the Drawings

[0025] [Figure 1] The injection mold according to this embodiment is a cross-sectional view for explaining the cross-section along the line A-A' in FIG. 2 with the top and bottom reversed. [Figure 2] The cavity mold of the injection mold according to this embodiment is a bottom view for explaining it when viewed from the side where the cavity is formed. [Figure 3] It is a perspective view for explaining another example of the plug member.

Modes for Carrying Out the Invention

[0026] Embodiments of the present invention will be described below. In the following description of the drawings, the same parts and similar parts are denoted by the same reference numerals or similar reference numerals. However, the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thicknesses of each device and each member, etc. are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Also, there are portions where the dimensional relationships and ratios are different between the drawings.

[0027] <Thin-Wall Molding Technology> Before explaining the configuration of the injection mold according to this embodiment, first, the thin-wall molding technology will be explained.

[0028] In the following description of the present invention, "cavity mold" refers to the mold part of an injection molding machine that is connected to the molten resin injection nozzle and has a gate that serves as the discharge port for the molten resin into the cavity. The mold is divided into two main parts so that molten resin can be filled into the cavity, which is the molding space inside the mold, and the molded product can be removed from the cavity after it has cooled and solidified.

[0029] Furthermore, "core mold" refers to the mold component that is positioned opposite the "cavity mold" among the two divided mold components mentioned above.

[0030] Furthermore, "flow resistance" refers to the force that obstructs the flow of molten resin, caused by physical factors such as the viscosity of the molten resin as a fluid injected into the cavity, and morphological factors such as distance, wall thickness, bending, and changes in width along the flow of molten resin within the cavity.

[0031] Furthermore, "wall thickness" refers to the dimension of the shortest axis of the cross-section perpendicular to the flow direction of the molten resin in a cavity or molded product. "Thin wall" refers to the wall thickness of a cavity or molded product where the "flow resistance" along the flow of molten resin within the cavity is large, making it relatively difficult for the molten resin to reach the end of the cavity and fill the entire cavity before it cools and loses its fluidity. It does not mean a wall thickness below a specific thickness.

[0032] Furthermore, "thin-walled molded product" refers to a molded product with a "thin" wall thickness. Additionally, "thin-walled molding technology" refers to a resin molding technology that incorporates special techniques to stably mold "thin-walled molded products," which are relatively difficult to fill with molten resin.

[0033] Furthermore, a "guidance zone" refers to a strip-shaped flow path provided within the cavity so that the flow resistance of the molten resin injected into the cavity is particularly low in a specific direction, where the cavity thickness of this flow path portion is thicker than the cavity thickness of the surrounding area, and the end of this flow path portion either connects to a portion where the cavity thickness is thinner than that portion or extends to the mold wall and ends in a dead end (hereinafter, the portion where the cavity thickness is thinner than the flow path portion of this "guidance zone" will also be called a "thin-walled portion").

[0034] Furthermore, the gate is typically located at a position where molten resin is directly injected into the guided zone channel. The guided zone channel starts at this gate location and ends at the point furthest from the gate location, where it connects to the thin-walled section. Therefore, if a gate is located in the middle of a continuous guided zone channel, two guided zone channels are provided extending from that gate location on both sides. Additionally, the guided zone channels can branch or merge along the way.

[0035] Furthermore, "convex portion" refers to a portion of a molded product that is recessed or protruding perpendicular to the main flat portion of the molded product, and the recessed or protruding portion is formed with a relatively thin wall thickness along its uneven surface. In the case of a cavity, it refers to any part of the uneven shape of the cavity formed by overlapping the corresponding uneven portions of the cavity mold and the core mold. Furthermore, "convex base portion" refers to the boundary portion between the convex portion and the flat portion in a molded product, and the boundary portion between the convex space portion and the flat space portion in a cavity. Furthermore, "convex circumferential guide zone space portion" refers to the cavity space that forms a guide zone that surrounds and is adjacent to the convex base portion.

[0036] Furthermore, in this invention, the term "convex portion" is used as a general term for both recessed and protruding portions relative to a standard flat portion in a molded product, as defined above. In addition, in a cavity for molding a molded product, the uneven shape is formed according to the unevenness of the cavity mold and the core mold, but there is no definition of which is the recessed portion and which is the protruding portion. Therefore, similar to the uneven portion of a molded product, the term "convex portion" is used as a general term without distinguishing between the two.

[0037] Furthermore, "residual gas" refers to the gas present in the cavity during the process of filling it with molten resin. This gas consists of air that was initially present in the cavity, air that was present in the runners and sprues when the injection of molten resin began, and volatile components of the resin.

[0038] Furthermore, "short" refers to a phenomenon in which a portion of a molded product is insufficiently filled due to reasons such as the molten resin cooling and solidifying before it reaches the end of the cavity when it is injected and filled, or the delayed discharge of "residual gas" causing the molten resin to solidify without filling the area where the residual gas is located.

[0039] Generally, in injection molding of molded products, residual gas exists in the cavity. As the molten resin injected from the gate fills the cavity, the residual gas is pushed away from the gate and compressed. This residual gas pressure acts to hinder the flow of the molten resin, contributing to a decrease in the filling speed.

[0040] On the other hand, the injected molten resin cools down from the part that comes into contact with the low-temperature mold wall within the cavity, eventually losing all fluidity and solidifying, preventing further filling. Therefore, in injection molding, it becomes a race between the time it takes for the molten resin injected into the cavity to solidify and the time it takes for the molten resin to release all residual gases and completely fill the cavity (hereinafter also referred to as "cavity filling time"). If the latter time is longer, a short, which is one of the defects of insufficient filling, will occur.

[0041] The cavity filling time increases as the difference between the injection pressure at the gate, which is the starting point of the molten resin flow path within the cavity, and the pressure of the residual gas at the leading edge of the flowing molten resin comes into contact with it (hereinafter, this pressure difference will also be referred to as "flow pressure").

[0042] In addition to the general properties of injection molding described above, when molding thin-walled products, the cross-sectional area per unit width in the flow path is narrower compared to thicker products, which makes it easier for residual gas to become high pressure and increases flow resistance. These factors contribute to longer cavity filling times.

[0043] Therefore, if the residual gas discharge rate is slow, the residual gas is compressed by the injection of molten resin, becoming high pressure and lowering the fluid pressure, which hinders filling. Furthermore, the adiabatic compression of the residual gas causes a temperature rise, potentially exceeding the ignition point of the molten resin and causing it to burn. This combination of flow resistance and fluid pressure behavior tends to result in longer cavity filling times in thin-walled molding compared to thicker molded products. This is a major reason why thin-walled molding is so difficult.

[0044] As mentioned above, in thin-wall molding, high flow resistance and high pressure of residual gas are unavoidable. However, continuous development of thin-wall molding technology has allowed the range of thin-walled molded products that can be formed by injection molding to gradually expand.

[0045] One such technological development is the development of guidance band technology.

[0046] When using a guide band to fill the cavity with molten resin, compared to filling thin-walled sections with high flow resistance sequentially from the gate without using a guide band, the molten resin can reach and fill thin-walled sections further from the gate with a relatively short delay, making it easier to mold thin-walled products.

[0047] <Configuration of injection molding dies> As shown in Figure 1, the injection molding die 10 according to this embodiment is an injection molding die 10 having a core mold 12 and a cavity mold 14. By overlapping the core mold 12 and the cavity mold 14 and injecting molten resin into the cavity 13 (molding space) formed between the core mold 12 and the cavity mold 14, a molded product having a convex portion and a flat portion is formed. The injection molding die 10 also has a gate 16 and a residual gas discharge portion 18.

[0048] (Cavity) The cavity 13 according to this embodiment comprises a convex space 13A, a planar space 13B, and a guide zone space 13C. In this embodiment, the thickness of the cavity 13 is approximately 0.4 mm, but this can be changed as appropriate in the present invention. The convex space 13A forms the convex portion of the molded product. The planar space 13B forms a planar portion around the convex portion of the resin molded product. The guide zone space 13C is strip-shaped and is formed in the convex space 13A and the planar space 13B, and has a thickness greater than the convex space 13A and the planar space 13B. In the present invention, the guide zone space may be provided in either the convex space or the planar space. Furthermore, in this embodiment, the guided zone space 13C is formed up to the middle of the convex space 13A between the base and the top, as shown in Figures 1 and 2. However, in the present invention, when a guided zone space is provided in the convex space, it may be formed up to any position from the base to the top of the convex space, depending on the shape of the convex, etc.

[0049] (Convex orbital guidance zone space) In this embodiment, the convex circumferential guidance zone space 13X branches off from the guidance zone space 13C and is adjacent to the convex base portion, which is the boundary portion between the convex space 13A and the planar space 13B, and encircles the convex base portion. The convex circumferential guidance zone space 13X is arranged to encircle the entire circumference of the convex base portion of each convex space 13A. In this invention, the convex circumferential guidance zone space may be arranged to encircle only a portion of the convex base portion, taking into consideration the thickness and height of the convex portion, or it may be arranged to encircle multiple locations of the convex base portion.

[0050] As shown in Figure 2, the surface of the cavity type 14 facing the core type has a convex space corresponding portion 14A corresponding to the convex space portion 13A, a planar space corresponding portion 14B corresponding to the planar space portion 13B, a guidance zone space corresponding portion 14C corresponding to the guidance zone space portion 13C, and a convex circumferential guidance zone space corresponding portion 14X corresponding to the convex circumferential guidance zone space portion 13X. In Figure 2, an example is shown where there are four convex space corresponding portions 14A, but in the present invention, the number of convex space corresponding portions can be changed as appropriate to one or more.

[0051] Furthermore, in this invention, by providing a convex circumferential guide zone space, this convex circumferential guide zone space acts as a molten resin reservoir, and the entire length of the convex circumferential guide zone space acts as a film gate to the convex space. As a result, the flow-inhibiting effect of the flow channel bend at the base of the convex, which is a factor that obstructs the flow of molten resin from the planar space to the convex space and increases flow resistance, is reduced. In addition, it is desirable that the corners that are formed in the cavity due to the bending at the base of the convex and the convex circumferential guide zone space contacting the base of the convex, be rounded in order to reduce the flow-inhibiting factors at the corners.

[0052] (gate) In this embodiment, the gate 16 injects molten resin into the guide zone space 13C. The gate 16 is a pin gate. In this invention, other types of gates, such as tunnel gates, may be used.

[0053] (Residual gas discharge section) In this embodiment, the residual gas discharge section 18 consists of a gas vent hole 18A and a plug member 18B. However, the residual gas discharge section is not limited to this in the present invention. For example, a parting surface may be used as the residual gas discharge section. Specifically, depending on the shape of the molded product, the mold can be designed so that the parting line passes through the apex of the protrusion, and the parting surface can be used as a residual gas outlet.

[0054] Furthermore, in this embodiment, the residual gas discharge section 18 is formed in both the cavity type 14 and the core type 12. However, in this invention, the residual gas discharge section 18 may be formed only in the core type 12 or only in the cavity type 14. Also, in this invention, the residual gas discharge section is not essential.

[0055] (Gas vent hole) The gas vent hole 18A according to this embodiment is a hole that penetrates from the outside of the mold to the top of the protruding space 13A, with one end opening at the top of the protruding space 13A.

[0056] However, the present invention does not prevent the opening position of the gas vent hole from being placed at any position between the top of the protruding space and the gate. In this embodiment, the gas vent hole 18A discharges residual gas from the top of the protruding space 13A.

[0057] In this embodiment, the opening of the gas vent hole 18A facing the molded product is circular in shape with a diameter of approximately 2.0 mm. In this invention, the dimensions and shape of the opening can be changed as appropriate. The shape of the gas vent hole can be set to any geometric shape, such as a polygon or an ellipse.

[0058] (Stopper component) The plug member 18B according to this embodiment is provided in a state in which it is detachably inserted into the gas vent hole 18A. The plug member 18B is a cylindrical material that is in close contact with the inner circumference of the gas vent hole 18A. The plug member 18B has a shaft portion and a head portion (flange portion) that is larger in diameter than the shaft portion. The head portion is not shown in the figure, but it is designed to be detachably fixed to the mold by screws or the like. The outer diameter of the shaft portion of the cylindrical material of the plug member 18B is approximately equal to the inner diameter of the gas vent hole 18A. In this invention, the shape of the plug member is not limited to a cylindrical shape, and may be other shapes such as a rectangular prism depending on the shape of the gas vent hole.

[0059] Since the stopper member 18B according to this embodiment can be removed from the gas vent hole 18A, it is easy to clean the stopper member 18B and the gas vent hole 18A when not being molded.

[0060] A gas channel 20 is formed on the outer circumferential surface of the cylindrical plug member 18B according to this embodiment, having an opening diameter that prevents molten resin from passing through but allows residual gas to pass through. The opening diameter according to this embodiment is approximately 2 / 100 mm. However, in the present invention, the opening diameter is not limited to this, and the appropriate opening diameter varies depending on the type of resin material used for molding, the temperature of the molten resin, molding conditions such as injection pressure, the length and flexibility of the gas channel, etc., and an appropriate opening diameter can be arbitrarily determined by considering these factors when designing the mold.

[0061] (Gas flow path) The gas flow path 20 illustrated in Figure 1 is formed by bringing the outer surface of the stopper member 18B into close contact with the inner surface of the gas vent hole 18A, and between the inner surface of the gas vent hole 18A and the outer surface of the shaft portion of the stopper member 18B.

[0062] In this embodiment, the gas passage 20 provided on the outer surface of the shaft portion of the plug member 18B facing the inner surface of the gas vent hole 18A is a planar gap parallel to the axial direction of the plug member 18B, as shown in Figure 1. When the gas passage 20 provided on the outer surface of the shaft portion of the plug member 18B is a planar gap parallel to the axial direction, the plug member 18B according to this embodiment can be easily manufactured by cutting a cylindrical material to a predetermined thickness in a plane parallel to the axial direction.

[0063] In this invention, as shown in Figure 3, the gas flow path 20 may be composed of, for example, a plurality of linear longitudinal grooves 18B1 extending along the axial direction of the cylindrical material. Furthermore, in this invention, the gas flow path is not limited to a planar or cylindrical gap or linear longitudinal groove along the axial direction, but for example, a gas flow path may be formed by sandblasting the outer circumferential surface of the cylindrical material to create a combination of a plurality of randomly bent flow paths.

[0064] As shown in Figure 3, the head of the stopper member is not essential in this invention, and the stopper member may have only a shaft portion.

[0065] Furthermore, in the present invention, the groove width of the vertical groove 18B1 as the gas passage 20 illustrated in Figure 3 only needs to be such that the residual gas can pass through but the molten resin cannot pass through the inlet portion of the residual gas. The shape and dimensions of the gas passage thereafter are arbitrary; for example, they may be widened in diameter toward the outside, which is the outlet for the residual gas, or the vertical grooves may be connected by grooves along the outer circumference.

[0066] (Air injection mechanism) Although not shown in the illustration, in the injection molding die 10 according to this embodiment, a flow path is connected to the outlet of the gas vent hole 18A, with the other end connected to an air injection device (not shown). In the injection molding process, after the cooling and solidification of the molten resin is completed and the mold is opened, the air injection device is activated and air is injected from the outlet of the gas vent hole 18A toward the outer surface of the protrusion of the molded product. By using the pressure of the air, the molded product that is stuck to the core mold 12 or cavity mold 14 can be pushed out and released.

[0067] In this invention, in addition to the gas vent holes, an arbitrary number of air injection holes, each having a flow path connected to an air injection device at one end, are provided at arbitrary positions in at least one of the core mold and cavity mold, allowing the molded product adhering to the core mold or cavity mold to be pushed out and released by air pressure. Such air injection holes are provided in the core mold or cavity mold on the side to which the molded product adheres during mold opening, which is determined according to the shape of the molded product, the selection of the mold parting surface, etc.

[0068] (Bypass route mechanism) Furthermore, in the injection molding die 10 according to this embodiment, a gas vent hole 18A is formed in the core mold and the cavity mold 14. Although not shown in the figures, a bypass passage is formed inside the core mold 12 and the cavity mold 14, branching off from the gas vent hole 18A. That is, one end of the bypass passage communicates with the gas passage 20 at a position slightly upstream from the head of the plug member 18B that is in close contact with the gas vent hole 18A, while the other end of the bypass passage communicates with the outside of the mold, discharging residual gas to the outside air.

[0069] Furthermore, the bypass passage is provided in a state where it branches off from the middle of the gas vent hole 18A toward the side of the core type and cavity type 14. In this invention, by appropriately providing the bypass passage, the outlet for residual gas to the outside air is not limited to the position of the top of the protrusion, but can be provided at any position.

[0070] (Resin molded product) By using the injection molding die 10 according to this embodiment, a molded product having a convex portion and a flat portion formed around the lower part of the convex portion can be molded. Traces of gas vent holes provided in the die are formed on the top of the convex portion of the molded product, and traces of the gate 16 are formed on the flat portion. In addition, ribs are formed on the molded product by the resin molding method performed using the injection molding die 10, which are traces of a guide band (convex portion circumferential guide band space 13X) that is in contact with the boundary between the convex portion and the flat portion and runs along the boundary.

[0071] (Effects and Benefits) According to the injection molding die 10 of this embodiment, the molten resin is first injected into the cavity 13 from a gate 16 located at the position of the guide zone space 13C, which has a flow path thickness greater than that of the convex space 13A and the planar space 13B, and therefore has a flow path resistance lower than that of the convex space 13A and the planar space 13B. The injected molten resin then quickly reaches the end of the guide zone space 13C at a point away from the gate 16 (i.e., where the flow path resistance increases from that point onward).

[0072] On the other hand, when the molten resin reaches the end of the guide zone space C, the flat space 13B and the convex space 13A adjacent to the guide zone space 13C, which have high flow resistance, are not very filled with molten resin. However, when the molten resin reaches the end of the guide zone space C, the flow of the molten resin is blocked in the region with high flow resistance, resulting in the accumulation of molten resin pressure inside the guide zone space C. The accumulated molten resin then permeates and spreads almost simultaneously along the guide zone space C to the adjacent flat space 13B and the convex space 13A. As a result, a high-quality thin-walled molded product can be molded compared to a mold without a guide zone space 13C.

[0073] Furthermore, according to this embodiment, the molten resin injected from the gate 16 into the guide zone space 13C adjacent to the planar space 13B flows down through the guide zone space 13C adjacent to the planar space 13B, reaches the base of the convex portion which is the boundary between the planar space 13B and the convex portion space 13A, flows into the convex portion circumferential guide zone space 13X which branches off from the guide zone space 13C, and from there fills the convex portion space 13A toward the top.

[0074] Since the convex circular guide zone space 13X is provided in contact with the bent portion formed by the planar space 13B and the convex space 13A, it has the effect of expanding the flow path in the bent portion formed by the planar space 13B and the convex space 13A, thereby reducing the flow resistance associated with the bending of the flow path.

[0075] Furthermore, since the convex circumferential guide zone space 13X is provided around the base of the convex, and the molten resin within the convex circumferential guide zone space 13X is pressurized to a state close to the liquid pressure at approximately the gate position, the convex circumferential guide zone space 13X acts as if it were a film gate for the convex space 13A, improving the filling of the convex space. As a result, a high-quality thin-walled molded product can be formed compared to when there is no convex circumferential guide zone space 13X in contact with the base of the convex.

[0076] Furthermore, according to this embodiment, the residual gas discharge section 18, which discharges residual gas, is located at the top of the convex space 13A. Therefore, residual gas inside the cavity 13 tends to concentrate at the top of this convex space 13A due to the fluid pressure of the molten resin, but the residual gas in the cavity that has concentrated at this top is released outside the mold by passing through the residual gas discharge section 18. As a result, quality degradation of molded products due to gas burning, short circuits, warping, etc. caused by residual gas can be suppressed.

[0077] Furthermore, according to this embodiment, residual gas is appropriately released to the outside of the mold by the residual gas discharge section 18, thereby preventing excessive pressurization of residual gas concentrated at the top of the convex space 13A. Consequently, the molding pressure required to fill the cavity with molten resin can be reduced, and the pressure load on the molding machine is also reduced, making it possible to use a smaller molding machine and contributing to cost reduction.

[0078] Furthermore, according to this embodiment, the gate 16 is not located at the top of the convex space 13A, but rather in the guided zone space 13C provided adjacent to the planar space 13B. Therefore, for example, within the cavity 13, a flow path formed in the guided zone space 13C extending from one gate 16 can be branched into multiple flow paths also formed in the guided zone space, and multiple convex spaces 13A can be arranged downstream of the branched flow paths.

[0079] In other words, compared to the conventional method in which a gate 16 is provided at the top of each protruding space 13A, even when multiple protrusions are provided on the molded product, it is not necessary to arrange multiple gates 16 in the mold according to the number of protrusions. Consequently, the runner configuration for supplying molten resin to the gates 16 in a balanced manner becomes relatively simple, and the cost of designing and manufacturing the mold can be reduced.

[0080] Furthermore, according to this embodiment, appropriate degassing can be performed by appropriately replacing the stopper member 18B with different residual gas discharge performance depending on the type of resin and the amount of residual gas. In addition, the residual gas discharge passage gradually becomes dirty and clogged with tar-like volatile components of the molten resin, so cleaning is necessary from time to time. However, with the above configuration, it is easy to remove the stopper member 18B and clean the gas passage 20 from time to time.

[0081] Furthermore, according to this embodiment, by connecting a flow path connected to an air injection device to the outlet of the gas vent hole 18A, the molded product can be pushed out of the injection molding die 10 by air pressure after the mold opening process is completed.

[0082] Furthermore, according to this embodiment, when demolding a molded product by using the gas vent hole 18A of the molded product and air injection pressure, there is no mechanical impact on the molded product during demolding, compared to demolding using an ejector pin.

[0083] Furthermore, according to this embodiment, by connecting a flow path (not shown) connected to a vacuum device to the outlet of the vent hole 18A, it becomes possible to suction residual gas from the cavity 13 through the vent hole 18A. As a result, the efficiency of residual gas discharge from the cavity is improved, and quality degradation due to gas burning, short circuits, warping, etc. of molded products caused by residual gas can be suppressed.

[0084] Furthermore, according to the resin molding method using the injection molding die 10 of this embodiment, even thin-walled molded products can be molded efficiently and with high quality.

[0085] <Note> Based on the embodiment described above, the present invention will be further explained below as an addendum.

[0086] (Review of prior art) Generally, residual gas exists within the cavity. The pressure of this residual gas is approximately atmospheric pressure when the molten resin is first injected, but it increases as the injection progresses. Meanwhile, as the molten resin fills the cavity, some of the residual gas is pushed out through tiny gaps in the parting surface of the mold and other areas.

[0087] However, the gaps in the mold are extremely narrow, preventing molten resin from leaking out, and therefore the rate at which residual gas is expelled is usually relatively slow. As a result, the pressure of residual gas in the cavity continues to rise until the residual gas is completely expelled or until the injection of molten resin is stopped. Furthermore, this pressure of residual gas in the cavity acts as a force that inhibits the flow of the injected molten resin within the cavity.

[0088] This increase in internal pressure due to residual gas obstructs the flow of molten resin within the cavity, resulting in insufficient filling, uneven wall thickness, or even shorts where molten resin is not filled at all. Furthermore, as residual gas is adiabatically compressed and its pressure increases, the gas temperature also rises, eventually exceeding the ignition point of the molten resin and causing the resin surface to scorch. In other words, this leads to a decrease in the quality of thin-walled molded products.

[0089] Patent Document 1 does not disclose anything regarding the resistance of the molten resin flow path within the cavity during injection molding of molded products, nor the influence of residual gases. Therefore, the technology described in Patent Document 1 alone cannot solve the problem of reduced molded product quality caused by high flow path resistance and delayed discharge of residual gases during injection molding.

[0090] Furthermore, regarding the technology described in Patent Document 2, the present inventors investigated and confirmed that it is possible to improve the filling efficiency of molten resin during injection molding by providing a guide zone within the cavity. However, it was found that depending on the shape and dimensions of the molded product, such as the thickness of the wall and the number of protrusions, it may not be possible to obtain sufficient quality.

[0091] In injection molding of a molded product having a protrusion as shown in Patent Document 2, one possible method for suppressing the pressure buildup of residual gas in the cavity portion corresponding to the protrusion is to position the gate, which is the starting point of the molten resin flow, at a mold position corresponding to the top of the protrusion.

[0092] However, this method requires that all gates be positioned in the mold corresponding to the tops of the protrusions, meaning that the number of gates increases as the number of protrusions increases. For example, if the molded product is an egg carton, there are usually more than 10 protrusions required in a single molded product, and if the lid is also molded integrally, nearly twice that number of gates will be needed. Consequently, it becomes necessary to arrange runners according to the gate placement, making it difficult to balance injection between gates, and the mold becomes more complex, increasing the processing burden on the mold. As a result, there is a problem of increased mold manufacturing costs.

[0093] (Convex orbital guidance zone space) In this invention, through the inventor's prototyping and research, it was found that in injection molding of thin-walled, complexly shaped molded products with uneven surfaces, when attempting to fill the molten resin to the end of the cavity according to the shape, the flow path is long relative to the flow path cross-sectional area, and the flow path has many bends, resulting in high flow resistance and reduced filling efficiency.

[0094] Therefore, first, a gate is provided in a guide zone space formed in a part of the planar space, and this guide zone space acts as a pseudo-runner to guide the molten resin to the vicinity of the base of the convex, which is the most bent part. Furthermore, a convex circumferential guide zone space is provided in contact with the base of the convex, preferably around the entire circumference of the base of the convex. However, if there is no room to provide a guide zone space depending on the shape of the molded product, the convex circumferential guide zone space may be provided in a part of the base of the convex. This convex circumferential guide zone space guides the molten resin around the base of the convex, and this convex circumferential guide zone space acts as a pseudo-film gate, injecting the molten resin, which has been pressurized in the convex circumferential guide zone space, from the base of the convex into the thin-walled portion that constitutes the wall surface of the convex. The mold cavity structure is designed in such a configuration.

[0095] Furthermore, in the arrangement of this convex circumferential guidance zone space, if the convex portion is large and the filling of the thin-walled portion of the convex portion with molten resin is insufficient, it is also permissible to provide a guidance zone space that branches off from the convex circumferential guidance zone space and climbs up the side wall of the convex portion.

[0096] Furthermore, the convex circumferential guide zone space is formed to be in contact with the base of the convex, preferably extending across to the convex wall surface, and even more preferably the boundary between the convex circumferential guide zone space and the convex wall surface is formed to be smooth and curved without any corners. If, depending on the shape of the molded product, it is not possible to provide the convex circumferential guide zone space in contact with the base of the convex, then the distance from the convex circumferential guide zone space to the base of the convex should be close enough that the flow resistance in that distance does not become a major obstacle to filling the convex with molten resin.

[0097] By adopting such a mold structure, the flow resistance of the flow path from the gate to the tip of the protrusion is significantly lower compared to cases where a guide zone space around the protrusion is not used, providing a solution to the problem of reduced filling performance of the protrusion, particularly in thin-wall molding.

[0098] Furthermore, reducing the flow resistance during molten resin filling allows for a lower injection pressure of the molten resin. Consequently, the liquid pressure of the molten resin also decreases, resulting in a low-pressure molding state. Combined with measures to discharge residual gases to the outside of the mold, this also has the effect of suppressing the buildup of high-pressure residual gases.

[0099] Furthermore, if the residual gas pressure does not become too high, the temperature of the residual gas will not exceed the ignition point of the molten resin due to adiabatic compression, gas burning defects can be suppressed, and distortion due to high pressure will not remain in the molded product. In addition, the reduced pressure load will allow molding to be done with a smaller molding machine, resulting in cost reduction.

[0100] Furthermore, by providing exhaust holes for residual gas at the apex of the protrusions, it becomes possible to further reduce the pressure of the residual gas. As a result, the repulsive force of the residual gas decreases, improving filling performance, similar to when flow resistance is reduced, and enabling low-pressure molding. This also results in effects such as suppression of gas burning and distortion, and miniaturization of the molding machine.

[0101] The key feature of this invention is the proposal to provide a convex circumferential guide zone space adjacent to the base of the convex portion, which is a technique to improve the flow resistance of the convex portion's bend, and the proposal to provide a gas vent hole at the apex of the convex portion is a technique to improve the discharge of residual gas in the convex portion. Both of these have the effect of improving the filling performance of the convex portion and suppressing the buildup of high pressure of residual gas throughout the cavity.

[0102] Furthermore, the effects obtained by suppressing the high pressure of residual gas include, in addition to the effects mentioned above, the suppression of burr formation caused by residual gas pressure, the ability to keep the injection pressure of molten resin low, the reduction of stress on the resin when it solidifies, which suppresses warping and deformation of molded products, the ability to shorten the cooling time required to correct warping and deformation, which shortens the molding cycle, the ability to miniaturize the injection molding machine due to the reduced injection pressure, which reduces costs, and the ability to reduce the clamping force due to the reduced injection pressure, which increases the ability to discharge residual gas from the parting surface, which further reduces the pressure of residual gas.

[0103] The embodiments described in the following embodiments 1 to 3 are conceptualized and included in the present invention.

[0104] An injection molding die according to Embodiment 1 of the present invention comprises a core mold and a cavity mold, and is used to mold a resin molded product having a convex portion and a flat portion by overlapping the core mold and the cavity mold and injecting molten resin into the cavity formed between the core mold and the cavity mold, wherein the cavity comprises a convex portion space for forming the convex portion, a flat portion space for forming the flat portion around the convex portion, and a guide zone space formed in at least one of the convex portion space and the flat portion, having a greater wall thickness than the convex portion space and the flat portion, the guide zone space comprises a convex portion circumferential guide zone space that is in contact with the boundary between the convex portion space and the flat portion and encircles the boundary, and the cavity mold is provided with a gate for injecting molten resin in the guide zone space.

[0105] According to the above configuration, the molten resin injected from the gate into the guide zone space of the cavity quickly reaches the end of the guide zone space that circulates the planar space and convex space at a point far from the gate, via the guide zone space, which has a thicker flow path wall than the convex space and planar space, and therefore has lower flow resistance than the convex space and planar space. Furthermore, since the end of the flow path with low flow resistance along the guide zone space is connected to a section with high flow resistance, after the molten resin fills the end of the guide zone space, pressure is accumulated in the molten resin inside the guide zone space in accordance with the continuously applied injection pressure.

[0106] As a result, the molten resin flows and spreads along the guide zone space into the adjacent planar and convex spaces in a lateral direction under relatively high pressure. Compared to molds without a guide zone space, this results in better filling performance, making it less prone to defects such as shorts, and enabling the molding of high-quality thin-walled molded products.

[0107] In the above configuration, the guide zone space is formed mainly in a planar space where a relatively straight flow path can be secured, from the viewpoint of flow resistance. However, depending on the dimensions and shape of the molded product, the guide zone space may be formed in a convex space, or in both a planar space and a convex space. Furthermore, the gate for injecting molten resin into the guide zone space is preferably located in the guide zone space formed in the planar space, from the viewpoint of efficiently arranging the guide zone network starting from the gate. However, depending on the dimensions and shape of the molded product, any number of gates can be provided at any location in the guide zone space.

[0108] Furthermore, according to the above configuration, the guide zone space includes a convex-circumferential guide zone space that is adjacent to and surrounds the base of the convex portion. This convex-circumferential guide zone space acts as a molten resin reservoir, and the entire length of the convex-circumferential guide zone space acts as a film gate to the convex portion space. As a result, the flow-inhibiting effect of the flow channel bend at the base of the convex portion, which is a factor that obstructs the flow of molten resin from the planar space to the convex portion space and increases flow resistance, is reduced. Therefore, compared to molds without such a convex-circumferential guide zone space, defects such as shorts in the convex portion are less likely to occur, and high-quality thin-walled molded products can be molded. It is desirable that the corners of the flow channel bend have an R shape (rounded) on both the inner and outer circumferential wall surfaces.

[0109] In the injection molding die according to embodiment 2 of the present invention, in embodiment 1, at least one of the core mold and the cavity mold is provided with a residual gas discharge section that discharges residual gas remaining at the top of the protruding space from the top of the cavity.

[0110] According to the above configuration, the guide zone space includes a guide zone space that surrounds the base of the protrusion, thereby improving the filling of the molten resin into the protrusion space. Furthermore, at least one of the core type and the cavity type is equipped with a residual gas discharge section that discharges residual gas from the top of the protrusion space, further improving the filling of the molten resin into the protrusion space.

[0111] In this invention, the residual gas discharge section is provided in at least one of the core mold and the cavity mold and includes a gas vent hole that extends from the outer surface of the mold to the top of the convex space, and a plug member that is detachably inserted into the gas vent hole. The plug member is a rod-shaped member in which at least the entire outer surface of the portion in contact with the top of the convex space is in close contact with the entire inner surface of the gas vent hole. A gas passage may be formed between the outer surface of the rod-shaped member in the contact portion and the inner surface of the gas vent hole, through which molten resin cannot pass but residual gas can.

[0112] Furthermore, in the present invention, if a gas vent hole is used as the residual gas discharge section, a vacuum device may be connected to the outlet of the gas vent hole, and the residual gas discharged from the gas vent hole may be sucked out by the vacuum device, thereby promoting the discharge of residual gas from the top of the convex space.

[0113] As an embodiment 3 of the present invention, a resin molding method may be configured in which a resin molded product is molded using the injection molding die described in embodiment 1 above. As described in Embodiment 1, the resin molded product in the above configuration can provide a high-quality resin molded product in which quality degradation due to distortion, insufficient filling, discoloration, etc. in the molded product is suppressed.

[0114] <Other Embodiments> Although the present invention has been described by the embodiments disclosed above, the descriptions and drawings that constitute part of this disclosure should not be understood as limiting the present invention. The present invention includes embodiments that appropriately combine each of the embodiments described above, as well as various embodiments not described above, and the technical scope of the present invention is defined solely by the inventive features of the claims that are reasonable from the above description. [Explanation of Symbols]

[0115] 10 Injection mold 12-core type 13 Cavity 13A Convex space 13B Plane space section 13C Guidance zone space 13X Convex Circumferential Guidance Zone Space 14 Cavity type 14A Convex portion space corresponding section 14B Planar Space Corresponding Section 14C Guidance Zone Space Corresponding Section 14X Convex Circular Guidance Zone Space Corresponding Section Gate 16 18 Residual gas discharge section 18A Gas vent hole 18B1 Vertical groove 18B Plug member 20 Gas flow path

Claims

1. An injection molding die comprising a core mold and a cavity mold, wherein the core mold and the cavity mold are superimposed, and molten resin is injected into the cavity formed between the core mold and the cavity mold to form a resin molded product having a convex portion and a flat portion, The cavity comprises a convex space for forming the convex portion, a planar space for forming the planar portion around the convex portion, and a guide zone space formed in at least one of the convex space and the planar space, wherein the dimension of the shortest axis of the cross-section perpendicular to the flow direction of the molten resin is longer than that of the convex space and the planar space. The aforementioned guidance zone space includes a convex circumferential guidance zone space that is adjacent to the boundary between the convex space and the planar space and encircles the boundary, The cavity mold is provided with a gate for injecting molten resin in the guide zone space. Mold for injection molding.

2. At least one of the core type and the cavity type is provided with a residual gas discharge section that discharges residual gas remaining at the top of the protruding space. The injection molding die according to claim 1.

3. A resin molding method for molding a resin molded product using an injection molding die as described in claim 1.

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