Injection molding method

Abstract

To suppress generation of large bubbles in the vicinity of a bulkhead due to shrinkage of wall thickness of the bulkhead even when a core-back is performed, to prevent decrease in rigidity in the vicinity of the bulkhead and prevent generation of sink marks.SOLUTION: The present invention relates to an injection molding method of a sandwich molded body having an inner layer and an outer layer covering the inner layer. The injection molding method according to the present invention comprises: a first step of injecting a first molten resin for forming an outer layer in a molding cavity provided in a pair of molds; a second step of injecting a second molten resin for forming an inner layer in the inside of the first molten resin; and a third step of retracting one of the pair of molds in a first direction from the other, to perform a core-back. In the third step, a core advanceable / retractable in the first direction provided in at least one of the pair of molds is relatively protruded with respect to the mold.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an injection molding method suitable for obtaining a molded body having a plurality of layers called a sandwich molded body including an inner layer and a surface layer covering the inner layer.

Background Art

[0002] Conventionally, a sandwich molded body including an inner layer and a surface layer covering the inner layer has been known. As an injection molding method for molding a sandwich molded body, a multi-stage molding method is known. The inner layer is sometimes called a core layer, and the surface layer is sometimes called a skin layer. The multi-stage molding method is a method in which after injecting a molten resin for the surface layer into a molding cavity, injecting a molten resin for the inner layer into the molten resin for the surface layer to fill the molding cavity with these two molten resins.

[0003] For example, as disclosed in Patent Document 1, when performing a multi-stage molding method, after injecting and filling a molten resin for the surface layer into a mold cavity, the volume of the mold cavity may be expanded before injecting and filling a molten resin for the inner layer. Expanding the volume of the mold cavity is called core back because the movable mold of a pair of molds is retracted from the fixed mold.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In an injection molding method with core back, when the retraction amount of the movable mold, that is, the core back amount, is large, the partition wall may be thinned as the partition wall is greatly stretched in the core back direction, that is, the thickness direction of the molded product, due to the core back. As the wall thickness of the partition wall decreases, voids are formed in the vicinity of the partition wall and decompressed, so there is a risk that bubbles due to foaming in the vicinity of the partition wall will grow, expand, or burst, generating large bubbles and reducing the rigidity in the vicinity of the partition wall. In addition, due to the tension of the internal partition wall, sink marks may occur on the outer surface near the partition wall, resulting in poor appearance of the molded product.

[0006] From the above, an object of the present invention is to suppress the generation of large bubbles in the vicinity of the partition wall accompanying the shrinkage of the wall thickness of the partition wall even during core back, prevent the reduction of the rigidity in the vicinity of the partition wall, and prevent the occurrence of sink marks.

Means for Solving the Problems

[0007] The injection molding method of the present invention is an injection molding method of a sandwich molded body including an inner layer and a surface layer covering the inner layer, a first step of injecting a first molten resin for forming a surface layer into a molding cavity provided in a pair of molds, a second step of injecting a second molten resin for forming an inner layer into the inside of the first molten resin, and a third step of performing core back by retracting one of the pair of molds from the other in a first direction, In the third step, a core pin provided on at least one side of the pair of molds and capable of advancing and retracting in the first direction is protruded relative to the mold.

[0008] In the third step of the injection molding method of the present invention, preferably, the relative protrusion amount of the core pin with respect to one of the molds is the same as the retraction amount of the mold due to core back, or smaller than the retraction amount of one of the molds due to core back.

[0009] In the third step of the injection molding method of the present invention, preferably, The relative protrusion speed of the core pin with respect to one of the molds is the same as the retraction speed of one of the molds by core back, or less than the retraction speed of one of the molds by core back.

[0010] In the injection molding method of the present invention, preferably, in the third step, after protruding the core pin, the core pin is retracted at a predetermined timing until the completion of the cooling step of the first molten resin and the second molten resin.

[0011] In the second step of the injection molding method of the present invention, preferably, the second molten resin is injected and filled while being biased toward a partial region inside the first molten resin, or the second molten resin is injected and filled by being divided into a plurality of regions inside the first molten resin.

Advantages of the Invention

[0012] According to the present invention, the core pin is relatively protruded with respect to the mold that performs core back when performing core back. Therefore, according to the injection molding method of the present invention, even when core back is performed when obtaining a sandwich molded body by injection molding, generation of large bubbles in the vicinity of the partition wall due to shrinkage of the wall thickness of the partition wall can be suppressed, so that a decrease in rigidity in the vicinity of the partition wall can be prevented and generation of sink marks can be prevented.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0014] Hereinafter, two embodiments of the present invention will be described with reference to the accompanying drawings. In both of the two embodiments, after sequentially performing injection and filling (first step) of the first molten resin A for forming the outer layer, and injection and filling (second step) of the second molten resin B for forming the inner layer, a core back (third step) is performed. Also, both of the two embodiments are provided with a movable core facing the molding cavity, and when performing the core back, the core is advanced relative to the mold that performs the core back, that is, protruded, so as to maintain the volume of the molding cavity before and after the core back. Thus, in this embodiment, by maintaining the volume of the molding cavity through the core back, even when a foaming resin is used as the inner layer molten resin (second molten resin B), it is possible to suppress the generation of large bubbles in the inner layer. Hereinafter, the common matters of the first embodiment and the second embodiment, and the contents of the first embodiment and the second embodiment will be described in order. In the first embodiment, it corresponds to an example in which the second molten resin B is injected and filled while being biased in a partial region in the width direction W inside the first molten resin A, and in the second embodiment, the second molten resin B is divided into a plurality (two) of regions in the width direction W inside the first molten resin A and injected and filled.

[0015] 〔Common matters: Refer to FIGS. 1 and 8〕 FIG. 1 shows a main part of the injection molding apparatus 1 applied to the embodiment. The injection molding apparatus 1 includes a mold part 10 for molding an injection molded product, and an injection part 20 for injecting and filling a first molten resin A and a second molten resin B toward the mold part 10. Further, in the present embodiment, an example will be described in which a non-foaming resin is applied as the first molten resin A and a foaming resin is applied as the second molten resin B. The mold part 10 and the injection part 20 of the injection molding apparatus 1 are controlled to operate according to an instruction from a controller composed of a computer apparatus (not shown). In the injection molding apparatus 1, a thickness direction (first direction) T, a width direction (second direction) W orthogonal to the thickness direction T, front (F) and rear (R) are defined as shown in FIG. 1 and the like.

[0016] [Mold part 10] The mold part 10 includes a fixed mold 11 whose position is fixed, and a movable mold 15 that can move forward and backward with respect to the fixed mold 11. In a mold clamping state where the fixed mold 11 and the movable mold 15 are abutted against each other, a molding cavity 17 is formed between the fixed mold 11 and the movable mold 15. A first resin gate 12 and a second resin gate 13 are formed in the fixed mold 11, and the molten resin plasticized by the injection part 20 is injected and filled into the molding cavity 17 through the first resin gate 12 and the second resin gate 13. The first molten resin A for the surface layer is supplied to the first resin gate 12, and the second molten resin B for the inner layer is supplied to the second resin gate 13. A first gate valve 18 for controlling the flow of the first molten resin A is provided at the first resin gate 12, and a second gate valve 19 for controlling the flow of the second molten resin B is provided at the second resin gate 13. Controlling the flow means allowing the flow of the molten resin toward the molding cavity 17 and stopping the flow of the molten resin toward the molding cavity 17. The control of the first gate valve 18 and the second gate valve 19 is performed by the controller. In addition, in the second embodiment, a second resin gate 14 is provided in addition to the second resin gate 13.

[0017] In the mold part 10, the operation in which the movable mold 15 moves forward (F) away from the fixed mold 11 is called mold opening or retraction, and conversely, the operation in which the movable mold 15 moves backward (R) closer to the fixed mold 11 is called mold closing or advancement.

[0018] Although not shown in the figure, the fixed mold 11 is attached to the fixed platen, and the movable mold 15 is attached to the movable platen. A plurality of tie bars for connecting the two are provided between the fixed platen and the movable platen, and by applying the pressure of, for example, a hydraulic cylinder between the fixed platen and the movable platen via the tie bars, mold clamping or mold opening is performed.

[0019] In the injection molding apparatus 1, in addition to the first molten resin A, the second molten resin B is filled in the molding cavity 17, and for the region where the first molten resin A and the second molten resin B are laminated in the thickness direction (thickness direction T), core back is performed to expand the volume of the molding cavity 17, while for the region where only the first molten resin A is filled, preferably the volume is maintained so as not to expand. In the present embodiment, the operation of performing core back for the region where both the first molten resin A and the second molten resin B are filled and laminated in the thickness direction is called the first operation, and the operation of preventing the volume of the molding cavity 17 from expanding for the region where only the first molten resin A is filled is called the second operation, and the first operation and the second operation are performed in parallel.

[0020] The injection molding apparatus 1 is provided with a movable mechanism 16 on the movable mold 15 in order to perform the second operation. The movable mechanism 16 includes a movable core 16A capable of moving forward and backward with respect to the movable mold 15, and an actuator 16B for moving the movable core 16A forward and backward. The movable core 16A according to the present embodiment is, as an example, an element that forms a part of the movable mold 15 and forms the molding cavity 17 together with the movable mold 15. Further, the movable core 16A is provided in a part of the width direction W of the movable mold 15, and this part corresponds to a region where only the first molten resin A is injected and filled. The volume of the molding cavity 17 of this part is maintained because the distance between the movable core 16A and the fixed mold 11 is constant before and after the core back. As shown in the upper part of FIG. 1, the movable core 16A in a state where the molding surface 15A of the movable mold 15 and the molding surface 16C of the movable core 16A are flush is said to be in the initial position.

[0021] [Injection part 20] The injection part 20 includes a first injection unit 21 capable of injecting and filling the first molten resin A for the surface layer into the molding cavity 17, and a second injection unit 22 capable of injecting and filling the second molten resin B for the inner layer into the molding cavity 17. The first molten resin A from the first injection unit 21 is injected into the molding cavity 17 through the first resin gate 12, and the second molten resin B from the second injection unit 22 is injected into the molding cavity 17 through the second resin gate 13.

[0022] Each of the first injection unit 21 and the second injection unit 22 includes, for example, a heating cylinder, an injection nozzle provided at the front end of the heating cylinder, a screw rotatably provided inside the heating cylinder, and a heater wound around the heating cylinder. The pellet-shaped raw material resin is supplied into the heating cylinder through a raw material inlet provided in the heating cylinder. The heater heats the resin inside the heating cylinder. The screw can move forward or backward and rotate forward or backward inside the heating cylinder. The injection nozzle is provided with a resin gate penetrating in the front-rear direction inside, and the plasticized molten resin is supplied to the first resin gate 12 and the second resin gate 13 through the resin gate. Each of the first injection unit 21 and the second injection unit 22 includes a driving device (not shown) for advancing or retracting a screw and a driving device for rotating the screw forward or backward. These driving devices include, for example, an electric motor, and this electric motor performs necessary operations according to instructions from a controller.

[0023] [Formed bodies 100A, 100B (sandwich formed bodies): See FIGS. 6(a) and (b)] The formed bodies 100A and 100B according to the present embodiment belong to sandwich formed bodies. However, as shown in FIG. 6(a), in the formed body 100A, except for both end portions in the width direction W, the inner layer IL only partially exists with respect to the surface layer OL, and the resin material constituting the surface layer OL where the inner layer IL does not exist occupies the thickness direction T. Further, as shown in FIG. 6(b), in the formed body 100B, in the width direction W, the inner layer is divided into two, an inner layer IL1 and an inner layer IL2, and the resin material constituting the surface layer OL occupies the thickness direction T between the respective inner layers IL. In FIGS. 6(a) and (b), the portion where the resin material constituting the surface layer OL occupies the thickness direction T is referred to as a partition wall BH.

[0024] By including the partition wall BH, in the formed bodies 100A and 100B, there is a possibility that bubbles generated by foaming in the vicinity of the partition wall BH grow, expand, or burst during injection molding, resulting in the generation of large bubbles. The first embodiment and the second embodiment can suppress the enlargement of bubbles in the vicinity of the partition wall BH even in the formed bodies 100A and 100B having the partition wall BH.

[0025] The molded bodies 100A and 100B are one of the multi-layer molded products composed of various combinations of different materials, the same materials, different colors, and the same colors in resin molded products. The molded bodies 100A and 100B are multi-layer molded products in which the entire circumference of the inner layer IL is covered by the surface layer OL, and the inner layer IL is not exposed to the outside from the surface layer OL. Therefore, while ensuring the appearance and design of the resin molded product with the non-foaming resin surface layer OL, a low-cost recycled resin or the like is adopted for the inner layer IL as an example. In this case, it is preferable to increase the volume of the low-cost inner layer IL as much as possible while reducing the volume of the high-cost surface layer OL. Further, the inner layer IL uses a foaming resin for the purpose of weight reduction, vibration damping, heat insulation and sound insulation, flexibility, or a functional resin such as a high-strength resin, a resin for blocking and absorbing electromagnetic waves and ionizing rays, a water-absorbing resin, and a non-permeable resin, and bears the functionality according to the application.

[0026] [First Embodiment: See FIGS. 2 and 3] With reference to FIGS. 2 and 3, an injection molding method (hereinafter, the first process) of the molded body 100A according to the first embodiment will be described. In the first process, the first molten resin A injected to form the surface layer OL is injected and filled, and then the second molten resin B injected to form the inner layer IL is injected and filled. At this time, in the molding cavity 17, the fixed mold 11 and the movable mold 15 are in close contact with each other by mold clamping. Also, the movable core 16A at this time remains in the initial position.

[0027] [First A Step (Injection of the First Molten Resin A): See FIG. 2] The first process starts from the first A step of injecting the first molten resin A into the molding cavity 17. At this time, the first gate valve 18 provided at the first resin gate 12 is open, while the second gate valve 19 provided at the second resin gate 13 is closed. When the first gate valve 18 and the second gate valve 19 are open, the illustration of the first gate valve 18 and the second gate valve 19 is omitted in FIG. 2 and the like. Before the injection of the first molten resin A, the molding cavity 17 is empty. When the first molten resin A is injected by a specified amount, the injection of the first molten resin A is stopped. The first molten resin A injected in the first A step is an amount less than the volume of the molding cavity 17, and voids remain on both sides in the width direction W of the molding cavity 17.

[0028] [Second A step (injection of the second molten resin B): See Fig. 2] After the first A step is completed, the process then proceeds to the second A step of injecting the second molten resin B. In the second A step, the first gate valve 18 of the first resin gate 12 is closed, and the second gate valve 19 of the second resin gate 13 is opened. That is, in the second A step, the injection into the molding cavity 17 is switched from the first molten resin A to the second molten resin B. The second molten resin B that has passed through the second resin gate 13 passes through the previously injected first molten resin A and is injected into the interior of the first molten resin A. When the molding cavity 17 is filled (packed) without gaps by injecting the second molten resin B and combining it with the previously injected first molten resin A, the injection of the second molten resin B1 is stopped. At this time, the second molten resin B is injected to fill approximately half of the width direction W of the molding cavity 17 as an example. Note that the start of the second A step is not limited to after the end of the first A step and may also be during the operation of the first A step. In this case, when the first A step and the second A step are being performed simultaneously, both the first gate valve 18 and the second gate valve 19 are open.

[0029] [Third A step (core back + movable core protrusion): See Fig. 3] After the second A step is completed, the core back for retracting the movable mold 15 is then performed as the third A step. At this time, both the first gate valve 18 and the second gate valve 19 are closed. The foaming of the second molten resin B made of the foaming resin is promoted by the core back, and the second molten resin B expands, increasing the volume it occupies in the molding cavity 17.

[0030] In the 3A step, regardless of the core back, the movable core 16A remains at the previous initial position. Therefore, the movable core 16A protrudes relatively from the movable mold 15 toward the fixed mold 11, but the distance between its tip surface and the fixed mold 11 is the same before and after the core back. The protrusion of the movable core 16A is for the purpose of preventing large air bubbles from occurring in the partition wall BH, which is a layer made of the first molten resin A that is a non-foaming resin, and in the vicinity thereof where the second molten resin B is not provided in the thickness direction T. The protrusion operation of the movable core 16A is preferably continued until the core back is completed, but the protrusion operation of the movable core 16A may be terminated before the core back is completed, or the protrusion operation of the movable core 16A may be continued even after the core back is completed. Note that the protrusion of the movable core 16A is an expression used for the movable mold 15, regardless of whether the movable core 16A moves or not. That is, as one pattern, even if the movable mold 15 retreats without the movable core 16A advancing from the initial position, the movable core 16A protrudes from the movable mold 15. The first embodiment follows this pattern.

[0031] The protrusion amount L16 of the movable core 16A is preferably set based on the retreat amount L15 of the movable mold 15 due to the core back, that is, the core back amount. For example, it is preferable that the protrusion amount L16 of the movable core 16A and the core back amount L15 are the same. In the case of the first embodiment, since the distance between the tip of the movable core 16A and the fixed mold 11 does not change, the protrusion amount of the movable core 16A and the core back amount are the same (L16 = L15). If the protrusion amount of the movable core 16A is made the same as the core back amount, the partition wall BH does not extend, so the pressure reduction around the partition wall BH can be minimized, and the generation of excessive air bubbles can be suppressed. Also, if the protrusion amount of the movable core 16A is made smaller than the core back amount (L16 < L15), the extension of the partition wall BH can be reduced, and the generation of excessive air bubbles can be suppressed. In this case, the movable core 16A retreats from the initial position, and the distance from the fixed mold 11 becomes larger than before the core back.

[0032] Also, it is preferable to set the protruding speed V16 of the movable core 16A based on the core-back speed V15. In the case of the first embodiment, since the movable core 16A remains at the initial position and does not advance, the protruding speed V16 of the movable core 16A and the core-back speed V15 become the same (V16 = V15). As an example, if the protruding speed is made the same as the core-back speed, the partition wall BH does not extend, so the decompression around the partition wall BH can be minimized, and the generation of excessive bubbles can be prevented. Further, if the protruding speed of the core is made smaller than the core-back speed (V16 < V15), the extension speed of the partition wall BH at the part in contact with the movable core 16A can be reduced, so the expansion of the partition wall BH will be carried out gently. As a result, the elongation of the resin constituting the partition wall BH can follow the expansion of the cavity wall thickness of the partition wall BH part, so the generation of bubbles inside the partition wall BH can be suppressed. Note that the core-back speed corresponds to the retraction speed of the movable mold 15.

[0033] In the 3A step, the portion where the movable core 16A protrudes and enters the first molten resin A becomes a void, as is clear from the 4A step of FIG. 2. Therefore, the expression "movable core" 16A is used.

[0034] [Step 4A: Retraction of the movable core to the initial position: Refer to FIG. 2] At a predetermined timing after the foaming of the second molten resin B is completed and until the completion of the cooling process for solidifying the first molten resin A and the second molten resin B, it is preferable to perform a fourth A step of retracting the movable core 16A so that the molding surface 15A of the movable mold 15 and the molding surface 16C are flush. By retracting the movable core 16A after protruding it, a gap is generated between the outer surface of the first molten resin A in contact with the movable core 16A and the movable core 16A. As a result, the heat of the outer surface of the first molten resin A in contact with the movable core 16A is not taken away by the movable core 16A, so the temperature drop of the outer surface of the first molten resin A is slowed down and it can be made into a surface with free displacement. As a result, the shrinkage of the first molten resin A at the site in contact with the movable core 16A is biased or concentrated on the outer surface side in contact with the movable core 16A, so the amount of shrinkage generated at the site in contact with the movable core 16A can be absorbed by the displacement on the outer surface side of the first molten resin A in contact with the movable core 16A. For this reason, the outer surface of the first molten resin A on the fixed mold 11 side, which is on the side opposite to the outer surface in contact with the movable core 16A, can be solidified without separating from the fixed mold 11. Thereby, it is possible to eliminate or suppress the degree of the dent generated on the outer surface of the first molten resin A on the fixed mold 11 side, which promotes the transfer of the cavity wall surface and serves as the design surface.

[0035] [Mechanism for suppressing the extension of the partition wall: Refer to FIGS. 3(a) and (b)] Next, with reference to FIG. 3, the mechanism for suppressing the extension of the partition wall by the protrusion of the movable core 16A will be described. Assume that the movable core 16A is provided according to this embodiment and the movable core 16A is protruded from the movable mold 15 during core back (after in FIG. 3(a)). Since the wall thickness L of the first molten resin A in the thickness direction T can be maintained the same as before the protrusion of the movable core 16A (before in FIG. 3(a)), the partition wall BH does not shrink even during core back. Also, if the protrusion speed of the movable core 16A is made slower than the core back speed, the expansion speed of the partition wall BH portion can be made slower than the core back.

[0036] When the movable core 16A is not provided (FIG. 3(b)), it is as follows. Since the partition wall of the first molten resin A is rapidly pulled in the thickness direction T, the first molten resin A, which is a non-foaming resin, cannot follow the deformation and minute bubbles p are generated inside. The generation of these minute bubbles p leads to a decrease in the rigidity of the partition wall BH. Also, in the partition wall BH, since the first molten resin A is pulled in the thickness direction T, the partition wall BH rapidly contracts in the width direction W. Due to this contraction of the partition wall BH, the pressure in the vicinity of the partition wall BH in the second molten resin B becomes low, and large bubbles P are locally generated. The generation of these large bubbles P can also cause a decrease in rigidity. Furthermore, since the resin pressure inside the partition wall BH decreases, there is a possibility that sink marks S, which cause poor appearance, are generated on the outer surfaces on both sides in the thickness direction T.

[0037] [Operations associated with the first A step to the fourth A step] Prior to the first A step in the first process, a mold clamping process of bringing the fixed mold 11 and the movable mold 15 into close contact with each other, and a plasticizing and metering process of heating, melting, and plasticizing the raw resin pellets of the first molten resin A and the second molten resin B inside the heating cylinder are performed. Also, after the fourth A step, a holding and cooling process of cooling until the filled first molten resin A and second molten resin B solidify, a mold opening process of opening the fixed mold 11 and the movable mold 15, and a take-out process of taking out the molded body 100A cooled and solidified in the molding cavity 17 are sequentially performed.

[0038] [Effects achieved by the first embodiment] The first process according to the first embodiment exhibits the following first to fourth effects. [First effect] The movable insert 16A protrudes relatively with respect to the movable mold 15 to maintain the dimension in the thickness direction T of the partition wall BH made of the first molten resin A that constitutes the non-foaming layer. Thus, according to the first embodiment, even when core-back occurs, the generation of large bubbles in the vicinity of the partition wall BH due to the shrinkage of the wall thickness in the width direction W of the partition wall BH can be suppressed. Therefore, a decrease in rigidity in the vicinity of the partition wall can be prevented, and the generation of sink marks can be prevented.

[0039] [Second effect] If the protruding amount of the movable core 16A is made the same as the core-back amount, the partition wall BH does not extend, so the pressure reduction around the partition wall can be minimized, and the generation of excessive bubbles can be prevented. Also, if the protruding amount of the movable core 16A is made smaller than the core-back amount, the extension of the partition wall BH can be reduced, and the generation of excessive bubbles can be suppressed.

[0040] [Third effect] If the protruding speed of the movable core 16A is made the same as the core-back speed, the partition wall BH does not extend, so the pressure reduction speed around the partition wall BH can be minimized, and the generation of excessive bubbles can be prevented. Also, if the protruding speed of the movable core 16A is made smaller than the core-back speed, the extension speed of the partition wall BH can be reduced, so the deformation speed of the partition wall BH is reduced. As a result, the resin constituting the partition wall BH can follow the extension of the partition wall, so the generation of bubbles inside the partition wall BH can be suppressed.

[0041] [Fourth effect] By retracting the movable core 16A after protruding it, the recesses generated on the outer surfaces of the molded bodies 100A and 100B facing the molding surface 16C of the movable core 16A can be eliminated or the recesses can be suppressed.

[0042] [Second Embodiment: See FIGS. 4 and 5] Next, an injection molding method (hereinafter, the second process) according to the second embodiment will be described with reference to FIGS. 4 and 5. The second process is different from the first process in that the foamable second molten resin B is injected from two gates, and is applied when obtaining the molded body 100B. However, since the second process has parts in common with the first process, the description of the same parts as the first process will be omitted as much as possible below. Also, below, an example will be described in which after filling the second molten resin B from one of the two gates, the second molten resin B is injected from the other gate, but the injection of the second molten resin B may be started simultaneously from the two gates.

[0043] [First B Step (Injection of First Molten Resin A): See FIG. 4] The first molten resin A is injected from the second resin gate 13 into the molding cavity 17. When the first molten resin A is injected by a specified amount, the injection of the first molten resin A is stopped. In the second embodiment, the second molten resin B is injected and filled by dividing the interior of the first molten resin A into a plurality of regions, particularly two regions, in the width direction W. The movable core 16A is arranged while being divided into two. The movable core 16A is waiting at the initial position.

[0044] [Second B step (injection of the second molten resin B): Refer to FIG. 4] After finishing the first B step, the process proceeds to the second B step of injecting the second molten resin B. In the second B step, in addition to the second molten resin B being injected and filled from the second resin gate 13, the second molten resin B is also injected and filled from the second resin gate 14. To distinguish between the two, the second molten resin B injected from the second resin gate 13 is referred to as the second molten resin B1, and the second molten resin B injected from the second resin gate 14 is referred to as the second molten resin B2. Hereinafter, an example in which the second molten resin B1 and the second molten resin B2 are injected and filled in this order will be described.

[0045] The second molten resin B1 that has passed through the second resin gate 13 passes through the previously injected first molten resin A and is injected into the interior of the first molten resin A. However, as shown in FIG. 4, as an example, it is injected to fill approximately half of the width direction W of the molding cavity 17. When the filling of the second molten resin B1 is completed, a part of the molding cavity 17 remains as a void.

[0046] When the injection and filling of the second molten resin B1 are completed, the injection of the second molten resin B2 is started. When the molding cavity 17 is filled with the first molten resin A, the second molten resin B1, and the second molten resin B2 that are injected in advance, the filling of the second molten resin B2 is completed. Note that the start of the second B step is not limited to after the end of the first B step, and it may be during the operation of the first B step. In this case, when the first B step and the second B step are being performed simultaneously, both the first gate valve 18 and the second gate valve 19 are open. When the filling of the second molten resin B is completed, the region filled with the second molten resin B1 and the region filled with the second molten resin B2 are independent, and a partition wall BH in which only the first molten resin A exists in the thickness direction T between the two is formed. A movable core 16A is provided at a position corresponding to this partition wall BH.

[0047] [Third B step (core back + movable core protrusion): See Figure 4] After completing the second B step, next, a core back that retracts the movable mold 15 is performed as the third B step. The core back promotes the foaming of the second molten resins B1 and B2 made of the foaming resin, and the second molten resins B1 and B2 expand, increasing the volume they occupy in the molding cavity 17.

[0048] In the third B step, simultaneously with performing the core back, the movable core 16A is protruded from the movable mold 15 toward the fixed mold 11. The protruding amount and protruding speed of the movable core 16A may be set in the same manner as in the first step.

[0049] [Fourth B step: Retraction of the movable core: See Figure 4] When the foaming of the second molten resin B is completed, at a predetermined timing until the completion of the cooling process for the solidification of the first molten resin A, the second molten resin B1, and the second molten resin B2, it is preferable to perform a fourth B step of retracting the movable core 16A in the same manner as in the fourth A step. Thereby, it is possible to eliminate the recesses generated on the outer surface of the first molten resin A on the fixed mold 11 side that is the design surface, or to suppress the degree of the recesses.

[0050] [Mechanism for suppressing extension of partition wall: Refer to FIGS. 5(a) and 5(b)] Next, with reference to FIG. 5, the mechanism for suppressing the extension of the partition wall BH by the protrusion of the movable core 16A will be described. Assume that the movable core 16A is provided between the second molten resin B1 and the second molten resin B2 according to the present embodiment, and the movable core 16A is protruded from the movable mold 15 during the core-back (after FIG. 5(a)). Since the wall thickness L of the partition wall BH of the first molten resin A in the thickness direction T can be maintained the same as before the protrusion of the movable core 16A (before FIG. 5(a)), the width direction W of the partition wall BH does not shrink even during the core-back. Further, if the protrusion speed of the movable core 16A is made slower than the core-back speed, the expansion speed of the partition wall BH portion can be made relatively slower than the core-back.

[0051] When the movable core 16A is not provided, the situation is as follows. Since the partition wall BH of the first molten resin A between the second molten resin B1 and the second molten resin B2 is rapidly pulled in the thickness direction T, the first molten resin A, which is a non-foaming resin, cannot follow the deformation and minute bubbles p are generated inside. The generation of these minute bubbles p leads to a decrease in the rigidity of the partition wall BH. Also, in the partition wall BH, since the first molten resin A is pulled in the thickness direction T, the width direction W rapidly contracts. Due to the contraction of this partition wall BH, the pressure in the vicinity of the partition wall BH in the second molten resin B becomes low, and large bubbles P are locally generated in each of the second molten resin B1 and the second molten resin B2. The generation of these large bubbles P can also cause a decrease in rigidity. Furthermore, since the resin pressure inside the partition wall BH decreases, there is a possibility that sink marks S, which cause poor appearance, are generated on the outer surfaces on both sides in the thickness direction T.

[0052] [Effects achieved by the second embodiment] The second process also achieves the same effects as the first process. In particular, even if the second molten resin B is divided into two, namely the second molten resin B1 and the second molten resin B2, and injected and filled, by providing the movable core 16A during the division, the first to fourth effects described above can also be obtained by the second process.

[0053] In addition to the above, as long as the gist of the present invention is not deviated from, it is possible to make selections from the configurations listed in the above embodiments or to appropriately modify them to other configurations. Some patterns included in the present invention regarding the protrusion of the movable core 16A will be described with reference to FIGS. 7 and 8. In FIGS. 7 and 8, the upper row shows the state before the core back, and the lower row shows the state after the core back. Also, in FIGS. 7 and 8, only the movable core 16A of the movable mechanism 16 is shown. FIG. 7(a) shows the pattern adopted in the first embodiment and the second embodiment. In FIG. 7(b), the movable core 16A protrudes from the movable mold 15 before the core back, and the first molten resin A is injected in this state. Then, when the movable mold 15 performs a core back, the protrusion amount of the movable core 16A becomes larger than before, but the distance between the movable core 16A and the fixed mold 11 is maintained.

[0054] In FIG. 8(a), the movable core 16A does not protrude from the movable mold 15 before the core back, and the first molten resin A is injected in this state. Then, while the movable mold 15 performs a core back, the movable core 16A moves forward toward the fixed mold 11, so that the movable core 16A is relatively protruded from the movable mold 15. In FIG. 8(b), the movable core 16A is retracted more than the movable mold 15 before the core back, and the first molten resin A is injected in this state. Then, while the movable mold 15 performs a core back, the movable core 16A moves forward toward the fixed mold 11, so that the movable core 16A is relatively protruded from the movable mold 15.

[0055] Regarding the movable core 16A, an example of constituting a part of the movable mold 15 has been described, but the core capable of advancing and retreating in the first direction (T) in the present invention is not limited to this. For example, an ejector pin used for taking out the molded body after solidification from the mold can also be used as the core of the present invention. The core composed of this ejector pin functions as a part of the movable mold during injection molding and functions as an ejector pin when taking out the molded body after injection molding. Also, regarding the movable core 16A, an example of providing it on the side of the movable mold 15 has been described, but the core in the present invention can also be provided on the side of the fixed mold 11. This core moves forward toward the side of the movable mold 15 as the movable mold 15 retreats during core back.

Explanation of Reference Numerals

[0056] 1 Injection molding apparatus 10 Mold part 11 Fixed mold 12 First resin gate 13, 14 Second resin gate 15 Movable mold 15A Molding surface 16 Movable mechanism 16A Movable core 16B Actuator 16C Molding surface 17 Molding cavity 18 First gate valve 19 Second gate valve 20 Injection part 21 First injection unit 22 Second injection unit 100A, 100B Molded body A First molten resin B, B1, B2 Second molten resin BH Partition wall IL, IL1, IL2 Inner layer OL Surface layer P, p Bubble S Sink mark

Claims

1. An injection molding method for a sandwich molded body including an inner layer and a surface layer covering the inner layer, A first step of injecting a first molten resin for forming the surface layer into a molding cavity provided between a pair of molds, A second step of injecting a second molten resin for forming the inner layer into the first molten resin, And a third step of performing a core back by retracting one of the pair of molds from the other in a first direction, In the third step, A core that can move forward and backward in the first direction and is provided on at least one side of the pair of molds is caused to protrude relative to one of the molds, Injection molding method.

2. In the third step, The relative protrusion amount of the core with respect to one of the molds is The same as the retraction amount of one of the molds due to the core back, or Smaller than the retraction amount of one of the molds due to the core back, The injection molding method according to claim 1.

3. In the third step, The relative protrusion speed of the core with respect to one of the molds is The same as the retraction speed of one of the molds due to the core back, or Smaller than the retraction speed of one of the molds due to the core back, The injection molding method according to claim 1.

4. In the third step, after the core is relatively protruded, The core is retracted at a predetermined timing until the completion of the cooling process of the first molten resin and the second molten resin, The injection molding method according to any one of claims 1 to 3.

5. In the second step, The second molten resin is injected and filled while being biased toward a partial region inside the first molten resin, or the second molten resin is divided into a plurality of regions inside the first molten resin and injected and filled. The injection molding method according to any one of claims 1 to 3.

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