Method for producing two layer structure molded article

Abstract

To provide a method for manufacturing a two layered structure molded product capable of easily realizing the suppression or elimination of the color irregularity of the appearance of a resin surface layer part or the stable ensuring of aesthetic appearance.SOLUTION: A primary molding step of molding a molded article base portion 25 by injection molding using a metallic resin material in a cavity 13 by using a molding die 10 having a first mold 11 and a second mold 12 that opens and closes with respect to the first mold 11, and a movable portion retracting step of retracting a partially movable portion 11b, which is a part of the first mold 11, from the cavity 13 while the first mold 11 and the second mold 12 are closed after the primary molding step; And a secondary molding step of molding the resin surface layer part 26 on the surface of the molded article base part 25 by injection molding of the same material as that of the primary molding step to form the two layer structure molded article.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a two-layer structure molded product having a resin surface layer formed on the surface of a resin base portion from a metallic resin material, which is a resin material having dispersed therein fine particles of a lustrous material such as metal powder, or a resin surface layer formed from a resin material having scattered coloring agents mixed therein. [Background technology]

[0002] Currently, painting and plating are the mainstream methods for metallic decoration of plastic molded products such as automobile parts. However, painting requires processes that are considered to have a high environmental impact, such as the disposal of paint dust. Plating (electroless plating on plastic molded products) requires special equipment and is considered to have a high environmental impact due to the waste liquid treatment. For these reasons, there is a movement to adopt other methods in consideration of the environmental impact. A method other than painting and plating that can achieve metallic decoration of plastic molded products is metallic dyeing.

[0003] Metallic decoration using metallic dyes is achieved by adding a pellet-shaped master batch containing fine particles of metallic powder or other lustrous material dispersed into a base color resin material, heating it to melt it, and mixing it with the base color resin material (hereinafter also referred to as the dyed resin material), which is then injection molded onto the surface of an already molded resin product to adhere and integrate it. Metallic decoration using metallic dyes can be achieved by selecting or modifying an injection molding machine that can inject dyed resin materials into pre-formed resin molded products. Furthermore, metallic decoration using metallic dyes does not require environmentally hazardous processes such as the disposal of paint dust and plating solutions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-131390 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-225354 Summary of the Invention [Problem to be solved by the invention]

[0005] The lustrous pigments in the base dye resin material of metallic base dyes are often non-spherical or non-cubic in shape, such as thin flakes or elongated flakes, and their orientation can change the appearance of the metallic decoration. However, metallic base dyes can have uneven color when adjacent regions have different orientations of the lustrous pigment in the base dye resin material, making it extremely difficult to form metallic base dyes without uneven color. For example, the technology described in Patent Document 1 involves injection molding two types of resin materials containing different luster pigments from different injection barrels, and injecting one resin material from a different injection barrel onto the surface of a molded product made from one resin material to obtain a two-layer structure molded product. However, it is extremely difficult to design a mold taking into account the orientation of the luster pigments in the resin materials that are injected into the mold from each injection barrel and flow within the mold.

[0006] Another proposed molding method (the second conventional molding method) involves a first-layer molding process in which a base molded product is formed by injecting a resin material into a closed mold. This process involves slightly moving the first mold member, which is one side of a split mold, relative to the second mold member, which is the other side, in the mold opening direction, and then forming a second layer on the surface of the base molded product by injecting the resin material into the gap between the base molded product and the first mold member. In the second conventional molding method, the first and second layer molding processes are performed by injection molding the same resin material, including a luster material, from the same injection barrel (see, for example, Patent Document 2). However, in the second conventional molding method, if a gap large enough to cause resin leakage is formed between the first mold member and the second mold member, which are moved slightly relative to the second mold member in the mold opening direction to perform the second layer molding process, resin molding becomes impossible. Furthermore, when the mold is opened by moving the first mold member slightly relative to the second mold member in the mold opening direction to perform the second layer molding process, the first mold member is not fixed to the second mold member. This makes it easy for a gap to form between the first and second mold members that allows gas to pass freely without causing resin leakage. If a gap that allows gas to pass freely between the first and second mold members forms, it becomes difficult to maintain pressure inside the mold during molding, making it difficult for the resin to adhere to the inner surface of the mold, and resin molding using the inner surface of the mold becomes difficult. Furthermore, the slight relative movement of the first mold member relative to the second mold member in the mold opening direction to perform the second layer molding process is performed by a function of the injection molding machine, and cannot be achieved depending on the performance of the injection molding machine.

[0007] If the entire resin molded product were to be formed in a single molding operation using the same dyed resin material as that used for metallic dyeing, the presence of protrusions such as ribs on the back side of the plate-shaped part of the molded product, and local differences in the thickness of the plate-shaped part itself, would likely cause disruptions in the density and orientation of the lustrous material, resulting in uneven color. The presence of protrusions such as ribs on the backside of the plate-like portion of a molded product, or local variations in the thickness of the plate-like portion itself, can cause variations in the density of microparticles mixed into the resin material used to mold the resin molded product, and this occurs not only when a dyed resin material is used, but also in all resin molded products made using resin materials with dispersed microparticles mixed in. For example, in the molding of resin molded products made using resin materials with scattered colorants mixed in to achieve a marbled finish, the presence of protrusions such as ribs on the backside of the plate-like portion of the molded product can cause variations in the density of the colorant in the resin material, affecting the design of the surface.

[0008] The problem that some embodiments of the present invention aim to solve is to provide a method for producing a two-layer structure molded article that can easily suppress or eliminate color unevenness in the appearance of the resin surface layer and ensure a stable aesthetic appearance. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides the following aspects. [1] A method for manufacturing a two-layer structure molded product, comprising: a primary molding process in which a molding die having a first die and a second die that opens and closes relative to the first die is used, and a metallic resin material, which is a resin material having a powdered lustrous material dispersed and mixed therein, is injection molded into a cavity secured inside the first die and the second die of the molding die; a movable part retraction process in which, after the primary molding process, a partial movable part that is part of the first die is retracted from the cavity while the first die and the second die of the molding die are kept closed; and a secondary molding process in which, after the movable part retraction process, a resin surface layer is formed on the surface of the molding die base by injection molding the same material as in the primary molding process, to form a two-layer structure molded product, and the primary molding process, the movable part retraction process, and the secondary molding process are performed using the same injection molding machine having only one barrel for injecting the resin material. [2] A method for manufacturing a two-layer structure molded product, comprising: a primary molding process in which a molding die having a first die and a second die that opens and closes relative to the first die is used, and a molded product base portion is formed by injection molding using a resin material interspersed with coloring agents in a cavity secured inside when the first die and the second die of the molding die are closed together; a movable part retraction process in which, after the primary molding process, a partial movable part that is part of the first die is retracted from the cavity while the first die and the second die of the molding die are kept closed; and a secondary molding process in which, after the movable part retraction process, a resin surface layer is formed on the surface of the molded product base portion by injection molding the same material as in the primary molding process, to form a two-layer structure molded product, wherein the primary molding process, the movable part retraction process, and the secondary molding process are performed using the same injection molding machine having only one barrel for injecting the resin material. [3] A method for manufacturing a two-layer structure molded product according to [1] or [2], wherein the injection molding machine is configured to be able to adjust the amount of retraction of the partially movable part of the mold. [Effects of the Invention]

[0010] The method for manufacturing a two-layer structure molded product according to the present invention can easily suppress or eliminate color unevenness in the appearance of the resin surface layer and ensure a stable aesthetic appearance, even when molding a two-layer structure resin using the same injection molding machine. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating a molding die of an injection molding machine, illustrating an outline of a method for producing a two-layer structure molded article according to one embodiment of the present invention. [Figure 2] 2 is a diagram showing the configuration of the vicinity of a partially movable part of a first die of the molding die of FIG. 1, as viewed from the side of the parting surface where the first die is closed with a second die of the molding die. FIG. [Figure 3] 2 is a diagram showing the configuration of the vicinity of the molding recess of the second die of the molding die of FIG. 1, as viewed from the side of the parting surface where the second die is closed with the first die of the molding die. FIG. [Figure 4]FIG. 4 is a diagram showing a resin molded product molded by applying a method for manufacturing a two-layer structure molded product according to one embodiment of the present invention using a mold having the first and second dies shown in FIGS. 1 to 3, and is a top view showing the configuration of the resin molded product as viewed from the design surface side of the plate-shaped main body. [Figure 5] 5 is a diagram showing the configuration of the resin molded product of FIG. 4 as viewed from the bottom side opposite to the design surface side of the plate-shaped main body. FIG. [Figure 6] 6 is a diagram showing a cross-sectional structure of the resin molded product of FIG. 5, and is a cross-sectional view taken along line BB of FIG. 5. [Figure 7] 6 is a diagram showing a cross-sectional structure of the resin molded product of FIG. 5, and is a cross-sectional view taken along the line AA of FIG. 5. [Figure 8] FIG. 1 is a diagram illustrating an outline of a method for manufacturing a two-layer structure molded product according to one embodiment of the present invention, and is a model diagram illustrating the primary molding process for molding a molded product base portion of a resin molded product in a molding die in which a first die is closed to a second die with a partially movable part positioned in its initial position before retraction. [Figure 9] FIG. 9 is a model diagram showing the state in which the molding die is opened after the primary molding step of FIG. 8 is completed. [Figure 10] 10 is a model diagram illustrating a gate cutting step (first gate cutting step) for removing a molded piece in the gate that projects from a molded product base portion in a state where the molded product base portion is attached to the partially movable portion of the first mold in FIG. 9. FIG. [Figure 11] This is a model diagram that explains how, after Figure 10, the first mold is closed to the second mold, and a movable part retraction process is performed in which the partial movable part of the first mold is retracted from the cavity of the molding mold and fixed at a retracted position shifted from its initial position to the opposite side of the cavity, and then a secondary molding process is performed in which a resin surface layer is molded on the surface of the molded product base part in the molding mold, thereby forming a resin molded product. [Figure 12] FIG. 12 is a model diagram showing the state in which the mold is opened after the secondary molding step of FIG. [Figure 13] 13 is a model diagram illustrating a gate cutting step (second gate cutting step) for removing a molded piece in the gate that projects from a molded product base portion in a state where the molded product base portion is attached to the partially movable portion of the first mold in FIG. 12. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will be omitted. The dimensional ratios in the drawings may be exaggerated for the purpose of explanation, and do not necessarily correspond to the actual dimensional ratios. Furthermore, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

[0013] FIG. 1 is a diagram for explaining an outline of a method for producing a two-layer structure molded article according to an embodiment of the present invention, and is a cross-sectional view showing a molding die 10 (a metal mold in this embodiment) of an injection molding machine. 8 to 13 are model diagrams illustrating an outline of a method for producing a two-layer structure molded article according to an embodiment of the present invention. As shown in Figures 1 and 8 to 13, the molding die 10 has a first die 11 and a second die 12 that open and close relative to each other. In the embodiment described here, the second die 12 is a fixed die that is fixed by a support member and supported in a stationary state. The first die 11 is a movable die that is moved forward and backward relative to the second die 12 by an advancing and retreating mechanism, opening and closing the space between the first die 11 and the second die 12.

[0014] As shown in FIG. 1, a cavity 13 is defined inside the first mold 11 and second mold 12 of the molding die 10 when they are closed together, and this cavity 13 is a space into which heated and melted resin material (molten resin material) is injected from an injection device of an injection molding machine, filled, and molded. The second mold 12 is formed with a spool (not shown), a runner (not shown), and a relay gate 12d (see FIG. 3) for guiding the resin material supplied from the injection cylinder of the injection molding machine to the cavity 13. The resin material supplied from the injection cylinder of the injection molding machine passes through the spool, runner, and relay gate 12d in this order before being guided to the cavity 13.

[0015] The first mold 11 has a block-shaped first mold body 11a with a parting surface 11f formed therein to be closed with the second mold 12, and a partial movable part 11b housed in a movable part accommodating hole 11g formed through the first mold body 11a so as to be movable toward and away from the cavity 13 of the first mold body 11a. The partial movable part 11b can be moved relative to the first mold body 11a in the axial direction of the movable part accommodating hole 11g by a movable part moving mechanism 14 provided on the back side of the first mold body 11a opposite to the cavity 13 side. One axial end of the movable part accommodating hole 11g opens into the parting surface 11f of the first mold 11.

[0016] 1, the partially movable part 11b can be supported by the movable part movement mechanism 14 in a state in which its tip part protrudes toward the cavity 13 of the first mold body 11a relative to the first mold body 11a. In addition, the partially movable part 11b can be switched by the movable part movement mechanism 14 between two support positions P1 and P2, which have different protrusion dimensions from the first mold body 11a toward the cavity 13, relative to the first mold body 11a. The two support positions of the partially movable part 11b relative to the first mold body 11a, which have different protrusion dimensions from the first mold body 11a toward the cavity 13, are the initial position P1 and the retracted position P2, where the protrusion dimension from the first mold body 11a toward the cavity 13 is smaller than that of the initial position. The movable part moving mechanism 14 can move the partial movable part 11b from the initial position P1 to the rear side opposite the cavity 13 with respect to the first mold body 11a to place it at the retracted position P2, and can move the partial movable part 11b at the retracted position P2 toward the cavity 13 with respect to the first mold body 11a to place it at the initial position P1. The movable part moving mechanism 14 can also switch between fixing and releasing the partial movable part 11b to the first mold body 11a for each of the initial position P1 and the retracted position P2.

[0017] The partially movable portion 11b is slidable in the axial direction of the movable portion accommodating hole 11g relative to the inner circumferential surface of the first mold body 11a that faces the movable portion accommodating hole 11g. The movable part accommodating hole 11g of the first mold body 11a is formed to extend (penetrate) through the first mold body 11a with a constant cross-sectional dimension. The partial movable part 11b has a movable part main body 11h which is a member extending with a cross section that matches with the cross section of the movable part accommodating hole 11g of the first mold body 11a with high precision, and is provided on the first mold body 11a by inserting the movable part main body 11h into the movable part accommodating hole 11g. The movable part main body 11h of the partial movable part 11b is provided on the first mold body 11a with the extending direction of the movable part main body 11h coinciding with the axial direction of the movable part accommodating hole 11g.

[0018] 1, the dimension of the movable part main body 11h in the extension direction is longer than the dimension of the movable part accommodating hole 11g in the axial direction. The partial movable part 11b is provided in the first mold main body 11a by inserting the portion of the movable part main body 11h between both ends in the extension direction into the movable part accommodating hole 11g. The tip of the partial movable part 11b refers to a part located further toward the tip of the partial movable part 11b (toward the cavity 13) than the tip of the movable part main body 11h that protrudes from the first mold main body 11a toward the cavity 13. A molding protrusion 11i and a fan gate molding surface 11e for molding a resin molded product 20 (see FIGS. 4 to 7) are formed at the tip of the partial movable part 11b.

[0019] The resin molded product 20 shown in Figures 4 to 7 is formed in a shape having a recess. This resin molded product 20 has a plate-shaped main body 21, a side wall portion 22 that protrudes from almost the entire periphery of the plate-shaped main body 21 toward the back side opposite the design surface of the plate-shaped main body 21, and ribs 23 that protrude from multiple locations on the back side of the plate-shaped main body 21. The recess of the resin molded product 20 is an inner area surrounded by the plate-shaped main body 21 and the side wall portion 22. The recess of the resin molded product 20 is formed in a shape that is recessed toward the plate-shaped main body 21 from an opening on the inside of the tip of the side wall portion 22 that protrudes from the plate-shaped main body 21 on the side opposite the plate-shaped main body 21.

[0020] 4 to 7, the plate-like main body 21 of the resin molded product 20 is composed of an arc-shaped main plate portion 21a and a rear plate portion 21b formed to close a rear end opening on one side of the main plate portion 21a in the curved axis direction. The main plate portion 21a is formed in a tapered shape such that the dimension in the curved circumferential direction increases from the front end, which is one end of the main plate portion 21a in the curved axis direction, to the rear end, which is the other end in the curved axis direction. Furthermore, the main plate portion 21a has an elongated shape in which the dimension in the curved axis direction is significantly larger than the distance between both ends in the curved circumferential direction at its rear end. The ribs 23 are formed so as to protrude from the rear surface side of the plate-like body 21 into the recess.

[0021] The resin molded product 20 illustrated in FIGS. 4 to 7 includes a molded product main body composed of a plate-shaped main body 21, side wall portions 22, and ribs 23, as well as a fan gate molding projection 24 (see FIGS. 4 and 5) projecting outward from the molded product main body. The fan gate molding projection 24 is formed in a plate shape projecting from the outer periphery of the plate-shaped main body 21, corresponding to a portion of the circular side wall portion 22 where a circumferential portion is omitted, toward the outer surface of the resin molded product 20, opposite the inner surface. As shown in FIGS. 4 and 5, the fan gate molding projection 24 is formed in a triangular plate shape that tapers from the outer periphery of the plate-shaped main body 21 toward the protruding tip toward the outer surface of the resin molded product 20, with the protruding tip being the apex. The fan gate molding projection 24 is formed to extend from the outer periphery of the plate-shaped main body 21 toward the outside of the molded product main body in a direction perpendicular to the depth direction of the recess in the molded product main body.

[0022] 4 to 7 show examples of the resin molded product 20. The resin molded product 20 is not limited to the configurations exemplified in FIGS. 4 to 7, and various shapes can be adopted. For example, the plate-shaped main body 21 is not limited to a configuration formed by an arc-shaped main plate portion 21a and a rear plate portion 21b, but may be a configuration in which the entire body is a curved dome-shaped plate portion, a configuration having a plurality of flat plate portions with recesses formed on the inside, etc. Also, the plate-shaped main body 21 may be configured to have a plurality of recesses recessed from the back surface side of the plate-shaped main body 21 (rear surface-opening recesses), or a configuration in which a recess recessed from the back surface side of the plate-shaped main body 21 and a recess recessed from the design surface side of the plate-shaped main body 21 are secured. The resin molded product 20 itself is not limited to a configuration in which only one recess (molded product rear surface opening recess) opening on the rear surface side opposite the design surface of the plate-shaped main body 21 is secured as shown in Figures 6 and 7, and various configurations can be adopted.

[0023] 1, 6, and 7, the resin molded product 20 is formed by a resin molded product base portion 25 and a resin surface layer portion 26 laminated and integrated with the plate-shaped molded portion of the molded base portion 25. The molded base portion 25 is configured to have a plate-shaped molded portion and a side wall portion 22 and a rib 23 that protrude from one side of the plate-shaped molded portion. The side wall portion 22 and the rib 23 are each formed to protrude from the same side (rear side) of the plate-shaped molded portion. The plate-like main body 21 of the resin molded product 20 is formed by a plate-like molded portion of a molded product base portion 25 and a resin surface layer portion 26 laminated and integrated onto the surface opposite to the back surface of the plate-like molded portion. The molded article base portion 25 and the resin surface layer portion 26 are made of the same resin material. The side wall portion 22 and the ribs 23 of the resin molded product 20 are part of the molded product base portion 25 and are formed solely by the molded product base portion 25 .

[0024] 1, the second mold 12 has a molding recess 12e formed therein into which the entire tip-side protrusion, which is the portion of the partially movable part 11b of the first mold 11 that protrudes from the first mold body 11a toward the cavity 13, is inserted when the first mold 11 is closed. The molding recess 12e is a recess formed in the second mold 12, recessed from the parting surface 12c of the second mold 12 that is closed with the first mold 11 (specifically, the first mold body 11a).

[0025] By inserting the tip of the partially movable part 11b into the molding recess 12e of the second die 12, a cavity 13, which is a space for molding the resin molded product 20, can be secured between the tip and the inner surface of the molding recess 12e. A portion (base end) of the tip-side protrusion of the partial movable part 11b closer to the first mold body 11a than the tip of the partial movable part 11b abuts against the inner circumferential surface of the opening of a molding recess 12e that opens into the parting surface 12c of the second mold 12 when the first mold body 11a is closed to the second mold 12. As a result, the entire tip-side protrusion of the partial movable part 11b is positioned relative to the second mold 12, and a cavity 13 of a desired size is secured between the tip-side protrusion and the inner surface of the molding recess 12e. The base end of the tip-side protrusion of the partial movable part 11b abuts against the inner circumferential surface of the opening of the molding recess 12e without any gap, preventing leakage of resin material from the cavity 13.

[0026] As shown in Figures 1 and 3, the inner bottom of the molding recess 12e of the second mold 12 is formed with a molding recess 12a for molding the design surface of the plate-shaped main body 21 of the resin molded product 20, and a fan gate molding surface 12b for molding the fan gate molding protrusion 24. As shown in Figure 1, the tip of the partially movable part 11b of the first mold 11 is formed with a molding protrusion 11i for molding the inner surface of the opening recess on the back side of the molded resin product 20, and a fan gate molding surface 11e for molding the fan gate molding protrusion 24. When the first mold 11 is closed to the second mold 12 and the entire tip-side protrusion of the partial movable part 11b of the first mold 11 is inserted into the molding recess 12e of the second mold 12, the molding protrusion 11i at the tip of the partial movable part 11b of the first mold 11 is positioned facing the molding recess 12a of the second mold 12, and the fan gate molding surface 11e at the tip of the partial movable part 11b of the first mold 11 is positioned facing the fan gate molding surface 12b of the second mold 12.

[0027] A relay gate 12d that opens onto the fan gate molding surface 12b is formed in the second mold 12. The resin material for molding the molded product body of the resin molded product 20 flows from the end of the relay gate 12d that opens onto the fan gate molding surface 12b into the molding region of the molded product body in the cavity 13, via the region between the fan gate molding surface 11e at the tip of the partially movable part 11b of the first mold 11 and the fan gate molding surface 12b of the second mold 12.

[0028] As shown in FIGS. 1 and 5, the molding protrusion 11i at the tip of the partially movable part 11b of the first die 11 has a rib forming groove 11d recessed from the surface of the molding protrusion 11i for forming the rib 23. As shown in Figures 1 and 2, a side wall forming groove 11c is formed on the side periphery of the tip of the partially movable portion 11b of the first mold 11 to allow resin material to flow between the tip and the inner surface of the molding recess 12e of the second mold 12 and to ensure molding space for the side wall portion 22 of the resin molded product 20. The rib forming groove 11d and the side wall forming groove 11c are part of the cavity 13. The rib forming groove 11d and the side wall forming groove 11c can be used to mold the ribs 23 and the side wall portions 22 by allowing the resin material flowing into the cavity 13 from the terminal opening of the relay gate 12d to enter them.

[0029] 6 and 7, the resin molded product 20 is a two-layer structure molded product having a molded product base portion 25 molded from a metallic resin material, which is a resin material having powdered lustrous material dispersed and mixed therein, and a resin surface layer portion 26 formed on the design surface (front surface) opposite to the back surface on which the ribs 23 and the like are formed of the molded product base portion 25. The resin surface layer portion 26 is formed from the same material as the molded product base portion 25.

[0030] Next, a specific example of a method for producing the two-layer structure molded article of this embodiment will be described. First, as shown in Figure 8, a primary molding process is performed to mold the molded product base portion 25 of the resin molded product 20 in a molding mold 10 in which the first mold 11 is closed to the second mold 12 while the partially movable portion 11b of the first mold 11 is supported in an initial position relative to the first mold main body 11a by a movable portion moving mechanism.

[0031] Next, the molding die 10 is opened as shown in Figure 9. Here, the molded product base portion 25 is moved together with the first die 11 relative to the second die 12 while remaining attached to the tip of the partially movable portion 11b of the first die 11. A gate molding protrusion 27 is integrally formed on the molded product base portion 25, protruding from the molded product base portion 25 on the side opposite the tip of the partially movable portion 11b. The gate molding protrusion 27 may be formed, for example, within the relay gate 12d.

[0032] Next, as shown in FIG. 10, a gate cutting step (first gate cutting step) is carried out to remove the gate molding protrusion 27 protruding from the molded product base portion 25 attached to the tip of the partially movable portion 11b of the first mold 11.

[0033] Next, as shown in Figure 11, the first mold 11 is closed to the second mold 12, and a movable part retraction step is performed in which the partially movable part 11b of the first mold 11 is retracted from the cavity 13 of the molding die 10 and fixed at a retracted position shifted from the initial position to the opposite side of the cavity 13. The first mold 11 is closed to the second mold 12 while the molded product base part 25 remains attached to the tip of the partially movable part 11b of the first mold 11. Note that the position of the partially movable part 11b of the first mold 11 relative to the first mold main body 11a is maintained in its initial position from Figure 8 to the completion of the steps in Figure 10. Next, a secondary molding step is carried out in the molding die 10 to form a resin surface layer 26 on the surface of the molded article base portion 25, thereby forming the resin molded article 20.

[0034] As shown in FIG. 12, after the secondary molding step is completed, the molding die 10 is opened and the completely molded resin molded product 20 is removed from the molding die 10. The resin molded product 20 is moved together with the first mold 11 relative to the second mold 12 while being attached to the tip of the partially movable part 11b of the first mold 11. A gate molding protrusion 27 that protrudes from the resin molded product 20 on the side opposite to the tip of the partially movable part 11b is integrally formed with the resin molded product 20. The gate molding protrusion 27 may be formed, for example, within the relay gate 12d.

[0035] Next, as shown in FIG. 13, a gate cutting step (second gate cutting step) is carried out to remove the gate molding protrusion 27 protruding from the molded product base portion 25 attached to the tip of the partially movable portion 11b of the first mold 11.

[0036] From the start of molding of the molded product base portion 25 (first layer) explained in FIG. 8 to the completion of the first gate cut step in FIG. 10, the control program for the injection molding machine uses the program for the first layer. After the first gate cutting process is completed, the control program of the injection molding machine is switched to the second layer program to carry out the processes shown in Figures 11 to 13. When the second gate cutting process shown in Figure 13 is completed, the control program of the injection molding machine is switched from the second layer program to the first layer program, and the process returns to molding the molded product base portion 25 (first layer) shown in Figure 8.

[0037] The injection molding machine used in the method for producing a two-layer structure molded article of this embodiment has only one barrel for injecting the resin material. In the manufacturing method of the two-layer structure molded product of this embodiment, the primary molding process, the movable part retraction process, and the secondary molding process are performed using the same injection molding machine having only one barrel for injecting the resin material. As a result, it is possible to easily suppress or eliminate color unevenness in the appearance of the resin surface layer 26 and ensure a stable aesthetic appearance. The primary molding process and the secondary molding process can be performed using the same molding die 10 without changing the molding die 10. Moreover, by performing the primary molding process and the secondary molding process using the same injection molding machine having only one barrel for injecting the resin material, it is also possible to perform secondary molding using the same molding die 10.

[0038] In the method for manufacturing a two-layer structure molded product according to the embodiment described here, the primary molding step and the secondary molding step are carried out using a metallic resin material, which is a resin material in which a powdery lustrous material is dispersed and mixed.

[0039] The movable part retraction step and the subsequent secondary molding step in FIG. 11 are performed while the first mold body 11a and the second mold 12 are kept closed together. As a result, pressure retention within the molding die 10 can be reliably achieved, and as a result, the internal pressure of the molding die 10 can increase the degree of adhesion of the resin material within the molding die 10 to the inner surface of the molding die 10, thereby improving molding accuracy.

[0040] The resin material used in the primary molding step and the secondary molding step may be a resin material interspersed with coloring agents to achieve a marbled finish. By selecting and using colorants with different melting points, it is possible to create various designs depending on the temperature at which the resin material is used during molding (molding temperature), etc.

[0041] The embodiments of the present invention are not limited to those described above, and various modifications are possible. For example, in the above embodiment, an example was described in which the first mold 11 is movable and the second mold 12 is fixed, but the present invention is not limited to this, and a configuration in which the first mold is fixed and the second mold is movable, or both the first mold and the second mold are movable, can also be adopted.

[0042] In the above embodiment, a method for manufacturing a two-layer structure molded product including a first gate cut step and a second gate cut step has been described, but the first gate cut step and the second gate cut step may be omitted by using a molding die (second die) with a valve gate. In a manufacturing method using a molding die (second die) with a valve gate, closing the valve gate after the cavity in the molding die has been filled with resin prevents the formation of a protruding piece molded within the gate that is continuous with the molded product. This makes the first gate cut step and the second gate cut step unnecessary. [Explanation of symbols]

[0043] Molding mold 10, first mold 11, first mold body 11a, partially movable part 11b, side wall forming groove 11c, rib forming groove 11d, fan gate molding surface 11e, parting surface 11f, movable part accommodating hole 11g, movable part body 11h, molding protrusion 11i, side wall forming groove 11j, second mold 12, molding concave surface 12a, fan gate molding surface 12b, parting surface 12c, relay gate 12d, molding concave portion 12e, cavity 13, movable part moving mechanism 14, fan gate 15, resin molded product 20, plate-like body 21, main wall portion 21a, rear wall portion 21b, side wall portion 22, rib 23, fan gate molding protrusion 24, molded product base portion 25, plate-like molded portion 25a, resin surface layer portion 26, gate molding protrusion 27.

Claims

1. The method comprises a primary molding step in which a molded product base portion is formed by injection molding using a metallic resin material, which is a resin material having a powdered lustrous material dispersed and mixed therein, in a cavity secured inside by closing the first and second dies of the mold; a movable part retraction step in which, after the primary molding step, a partial movable part, which is a part of the first mold, is retracted from the cavity while keeping the first and second dies of the mold closed; and a secondary molding step in which, after the movable part retraction step, a resin surface layer portion is formed on the surface of the molded product base portion by injection molding using the same material as in the primary molding step, to form a two-layer structure molded product. A method for manufacturing a two-layer structure molded product in which the primary molding process, the movable part retraction process, and the secondary molding process are carried out using the same injection molding machine having only one barrel for injecting the resin material.

2. The method comprises a primary molding step in which a molded article base portion is formed by injection molding using a resin material interspersed with a colorant in a cavity secured inside the first and second molds of the mold, the cavity being secured by closing the first and second molds of the mold; a movable part retraction step in which, after the primary molding step, a partial movable part that is a part of the first mold is retracted from the cavity while the first and second molds of the mold are kept closed; and a secondary molding step in which, after the movable part retraction step, a resin surface layer portion is formed on the surface of the molded article base portion by injection molding using the same material as in the primary molding step, to form a two-layer structure molded article. A method for manufacturing a two-layer structure molded product in which the primary molding process, the movable part retraction process, and the secondary molding process are carried out using the same injection molding machine having only one barrel for injecting the resin material.

3. 3. The method for manufacturing a two-layer structure molded product according to claim 1, wherein the injection molding machine is configured so that the amount of retraction of the partially movable portion of the mold is adjustable.

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