Injection molding method

Abstract

To provide a two-color molding method that can form a gradation.SOLUTION: A primary resin R1 is injected into a cavity 3 from a primary gate 4, and after the primary resin R1 passes through a secondary gate 5, a secondary resin R2 is injected into the cavity 3 from the secondary gate 5. After stopping a supply of the primary resin R1 from the primary gate 4 to the cavity 3, the supply of the secondary resin R2 from the secondary gate 5 to the cavity 3 is stopped to make a flow velocity of the primary resin R1 in the cavity 3 smaller than the flow velocity of the secondary resin R2 in the cavity 3.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an injection molding method. [Background technology]

[0002] A known injection molding method is the so-called two-color molding method, in which molded articles having different colors depending on the location are molded using the same mold. One known two-color molding method is the core-back method (see, for example, FIG. 6 of Patent Document 1 listed below). Specifically, as shown in FIG. 15, a primary cavity is formed by a fixed mold 210, a movable mold 220, and a core 230, and a primary resin is injected into this primary cavity through a primary gate 211 to form a primary molded part A. Next, as shown in FIG. 16, the core 230 is moved backward, and a secondary cavity is formed by the fixed mold 210, the core 230, and the primary molded part A, and a secondary resin is injected into this secondary cavity through a secondary gate 212 to form a secondary molded part B integrated with the primary molded part A (see FIG. 17). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-300406 Summary of the Invention [Problem to be solved by the invention]

[0004] Since resin molded products tend to give an inorganic impression, one method of improving design is to create a gradation, which is a continuous change in color at the boundary between different colored parts. The gradation can create a more three-dimensional, organic visual effect. However, in two-color molded products molded using the method shown in Figures 15 to 17, the color changes at the boundary between the primary molded part A and the secondary molded part B, making it impossible to achieve a continuous color change.

[0005] Therefore, an object of the present invention is to provide a two-color molding method that can form a gradation. [Means for solving the problem]

[0006] When resin is injected into the cavity, the high-temperature resin begins to solidify where it comes into contact with the mold surface, causing the flow speed to increase toward the center in the thickness direction. As a result, at the downstream end of the resin flow direction, the resin flows from the center in the thickness direction to both sides, a phenomenon known as fountain flow (see arrows in Figure 9). The present invention is characterized by using this fountain flow phenomenon to form a gradation.

[0007] That is, the present invention provides an injection molding method using a mold having a cavity and a primary gate and a secondary gate opening into the cavity, the method comprising: supplying a primary resin from the primary gate to the cavity; supplying a secondary resin having a color different from that of the primary resin from the secondary gate into the cavity after the primary resin has passed through the secondary gate; and making the flow rate of the primary resin in the cavity slower than the flow rate of the secondary resin in the cavity.

[0008] In this way, after the primary resin passes through the secondary gate, the secondary resin is supplied to the cavity through the secondary gate. The secondary resin flows between the surface layer (skin layer) of the primary resin that has solidified in contact with the mold surface, pushing out the unsolidified primary resin in the center of the cavity. Then, for example, by stopping the supply of the primary resin before the secondary resin, the flow rate of the primary resin within the cavity is made slower than the flow rate of the secondary resin. This reduces the amount of primary resin supplied to the downstream end of the flow direction, gradually thinning the thickness of the surface layer of the primary resin, and the secondary resin protrudes downstream through the thin surface layer. When viewed from the outside near the downstream end of the primary resin, the color of the secondary resin beneath can be seen through the thin surface layer of the primary resin. The gradually thinning of the surface layer of the primary resin toward the downstream side creates a gradation that continuously changes from the color of the primary resin to the color of the secondary resin.

[0009] An injection-molded product produced by the above-described injection molding method has a primary molded part made of a primary resin, a secondary molded part made of a secondary resin having a color different from that of the primary resin, and a gradation part provided between the primary molded part and the secondary molded part, the gradation portion has surface layers made of the primary resin provided on both surfaces in a thickness direction, and an inner layer made of the secondary resin provided between the surface layers in the thickness direction, An injection molded article can be obtained in which the thickness of the surface layer of the gradation portion gradually decreases from the primary molded portion side toward the secondary molded portion side. [Effects of the Invention]

[0010] As described above, according to the injection molding method of the present invention, it is possible to form a gradation in which the color of the primary resin changes continuously to the color of the secondary resin. [Brief explanation of the drawings]

[0011] [Figure 1] 2. FIG. 3 is a cross-sectional view of a mold used in an injection molding method according to one embodiment of the present invention, taken along line XX in FIG. [Figure 2] FIG. 2 is a side view of the cavity of the mold of FIG. 1 as viewed from the Z direction. [Figure 3] FIG. 2 is a side view of the cavity of the mold when a primary resin is injected from a primary gate. [Figure 4] 4 is a cross-sectional view taken along line XX of the mold in the state shown in FIG. 3. [Figure 5] 4 is a cross-sectional view taken along line YY of the mold in the state shown in FIG. 3. [Figure 6] FIG. 2 is a cross-sectional view of the mold when a secondary resin is injected from a secondary gate. [Figure 7] FIG. 2 is a side view of the cavity of the mold when the secondary resin is exposed on the surface. [Figure 8] 8 is a cross-sectional view taken along line YY of the mold in the state shown in FIG. 7. [Figure 9] FIG. 9 is an enlarged cross-sectional view of a portion P in FIG. 8. [Figure 10] FIG. 2 is a side view of the cavity of the mold when molding is completed. [Figure 11] 11 is a cross-sectional view taken along line YY of the mold in the state shown in FIG. 10. [Figure 12] FIG. 10 is a side view of a cavity of a mold according to another embodiment. [Figure 13] FIG. 10 is a side view of a cavity of a mold according to yet another embodiment. [Figure 14] FIG. 10 is a cross-sectional view of a mold according to yet another embodiment. [Figure 15] FIG. 1 is a cross-sectional view of a conventional mold for two-color molding, showing the state after the primary molding portion has been molded. [Figure 16] FIG. 16 is a cross-sectional view showing a state in which a secondary cavity has been formed in the mold of FIG. [Figure 17] FIG. 16 is a cross-sectional view showing a state in which a secondary molded portion is molded using the mold of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] FIG. 1 shows a mold used in the injection molding method of this embodiment. This mold is used to mold plate-shaped parts, such as automobile exterior panel parts (bumpers, etc.) and interior panel parts (instrument panels, etc.). This mold has a fixed mold 1 and a movable mold 2, and a cavity 3 is formed by clamping the fixed mold 1 and the movable mold 2 together. As shown in FIG. 2, the cavity 3 is provided with a primary gate 4 for injecting a primary resin R1 and a secondary gate 5 for injecting a secondary resin R2, which has a different color from the primary resin R1. Note that in FIG. 2, the fixed mold 1 and the movable mold 2 are not shown, and the cavity 3 is simply represented by a rectangle.

[0014] In this embodiment, the primary gate 4 and secondary gate 5 are side gates that open to the side of the cavity 3. Specifically, as shown in FIG. 1 , the primary gate 4 and primary cold runner 6, and the secondary gate 5 and secondary cold runner 7 are formed by clamping the fixed mold 1 and the movable mold 2 together. The fixed mold 1 is provided with a primary hot runner 8 and a secondary hot runner 9. A valve pin 10 is provided inside each of the hot runners 8, 9, and openings (valve gates 11) at the downstream ends of the hot runners 8, 9 can be opened and closed by moving the valve pin 10 back and forth in the axial direction.

[0015] A method for molding a resin molded product having gradation using the above mold will be described below.

[0016] First, as shown in Figures 3 and 4, the valve pin 10 of the primary hot runner 8 is retracted to open the valve gate 11, and the primary resin R1 is injected into the cavity 3 via the primary cold runner 6 and the primary gate 4. Then, when the primary resin R1 injected into the cavity 3 reaches the secondary gate 5, as shown in Figure 5, the primary resin R1 flows back from the secondary gate 5 into the secondary cold runner 7. At this time, the valve gate 11 of the secondary hot runner 9 is closed. The primary resin R1 that has entered the secondary cold runner 7 reaches the vicinity of the valve gate 11 of the secondary hot runner 9, and in the illustrated example, the secondary cold runner 7 is filled with the primary resin R1.

[0017] Then, after the primary resin R1 injected into the cavity 3 from the primary gate 4 passes through the secondary gate 5, the valve gate 11 of the secondary hot runner 9 is opened at a predetermined timing (see FIG. 6). As a result, the secondary resin R2 is injected into the cavity 3 via the secondary cold runner 7 and the secondary gate 5.

[0018] At this time, the primary resin R1 supplied to the cavity 3 and the secondary cold runner 7 is cooled and solidified by contact with the mold near the surface, but remains molten in the central portion of the mold thickness away from the surface. Therefore, the secondary resin R2 injected from the valve gate 11 of the secondary hot runner 9 pushes the primary resin R1, which remains molten in the cold runner 7 and the central portion of the mold thickness, downstream, and flows between the surface layer (skin layer) of the solidified primary resin R1 near the mold surface. As the primary resin R1 flows downstream, the secondary resin R2 flows downstream within it. At this time, only the primary resin R1 is exposed on both sides of the surface of the resin injected into the cavity 3 in the thickness direction, and the secondary resin R2 is not exposed.

[0019] Thereafter, the valve gate 11 of the primary hot runner 8 is closed to stop the supply of the primary resin R1 from the primary gate 4 to the cavity 3. This causes the flow rate of the primary resin R1 within the cavity 3 to become slower than the flow rate of the secondary resin R2, and as shown in Figures 7 and 8, the secondary resin R2 escapes from inside the primary resin R1 and splashes out downstream. In other words, if the secondary resin R2, which began to be supplied later, splashes out downstream of the primary resin R1, which began to be supplied earlier, it can be confirmed that the process of making the flow rate of the primary resin R1 within the cavity 3 slower than the flow rate of the secondary resin R2 has been carried out.

[0020] The secondary resin R2 that spills out downstream from the inside of the primary resin R1 flows downstream, moving from the center of the thickness direction toward both ends, as shown by the arrows in Figure 9 (the so-called fountain flow phenomenon). Therefore, the secondary resin R2 flows downstream, pushing the molten primary resin R1 at the center of the thickness direction to both sides in the thickness direction. Because the supply of the primary resin R1 is stopped at this time, the amount of primary resin R1 supplied decreases toward the downstream end. This results in the formation of a sloped portion R1a at the downstream end of the surface layer made of the primary resin R1 solidified near the mold surface, with the thickness gradually decreasing toward the downstream end. The area where this sloped portion R1a of the primary resin R1 is provided becomes the gradation portion 103, described below.

[0021] Thereafter, as shown in FIGS. 10 and 11, when the secondary resin R2 reaches the end of the cavity 3, the valve gate 11 of the secondary hot runner 9 is closed to stop the supply of the secondary resin R2 from the secondary gate 5.

[0022] As shown in FIG. 10, the resin molded product 100 molded through the above-described processes has a primary molded portion 101 in which the primary resin R1 is exposed on the surface, a secondary molded portion 102 in which the secondary resin R2 is exposed on the surface, and a gradation portion 103 provided between the primary molded portion 101 and the secondary molded portion 102. As shown in FIG. 9, the primary molded portion 101 has surface layers (skin layers) made of the primary resin R1 provided on both surfaces in the thickness direction, and an inner layer made of the secondary resin R2 provided between the surface layers in the thickness direction. In the primary molded portion 101, the secondary resin R2 is not exposed on the surface of the resin molded product 100, and only the color of the primary resin R1 appears on the surface. The secondary molded portion 102 is formed only from the secondary resin R2, and only the color of the secondary resin R2 appears on the surface.

[0023] The gradation portion 103 has surface layers (inclined portions R1a) made of the primary resin R1 provided on both surfaces in the thickness direction, and an inner layer made of the secondary resin R2 provided between the surface layers in the thickness direction. The surface layer (inclined portions R1a) of the gradation portion 103 is thinner than the surface layer of the primary molded portion 101. Therefore, when viewed from the surface at the thinner portion of the inclined portion R1a, the color of the secondary resin R2 at the back of the inclined portion R1a (the center in the thickness direction) is visible. Furthermore, the thickness of the inclined portion R1a gradually decreases toward the downstream side. Therefore, when viewed from the surface of the gradation portion 103, the color of the secondary resin R2 becomes darker as the thickness of the inclined portion R1a decreases, i.e., closer to the secondary molded portion 102. As a result, when viewed from the surface of the gradation portion 103, the color of the primary resin R1 changes continuously to the color of the secondary resin R2. Thus, the above-described injection molding method can form a resin molded product 100 having the gradation portion 103.

[0024] The present invention is not limited to the above-described embodiment. Other embodiments of the present invention will be described below, but redundant description of points similar to those of the above-described embodiment will be omitted.

[0025] For example, in the above embodiment, the supply of the primary resin R1 from the primary gate 4 to the cavity 3 is stopped before the supply of the secondary resin R2 from the secondary gate 5 to the cavity 3, but this is not limited to this. For example, the flow rate of the primary resin R1 in the cavity 3 may be made slower than the flow rate of the secondary resin R2 by adjusting the degree to which the valve gate 11 is opened by the valve pin 10 of the primary hot runner 8 to reduce the amount of primary resin R1 supplied from the primary gate 4 to the cavity 3.

[0026] Furthermore, the positions and numbers of the primary gates 4 and secondary gates 5 are not limited to those in the above embodiment. For example, in Fig. 12, a pair of primary gates 4 and a pair of secondary gates 5 are arranged facing each other in the same direction (the vertical direction in Fig. 12). In Fig. 13, the primary gate 4 is arranged in one location, and a pair of secondary gates 5 are arranged facing each other in a direction (the vertical direction in Fig. 13) perpendicular to the injection direction of the primary gate 4 (the horizontal direction in Fig. 13). By arranging the primary gates 4 and secondary gates 5 in symmetrical positions in this way, the gradation portion 103 can be made approximately linear.

[0027] Furthermore, the position of the gradation portion 103 can be adjusted by changing the timing at which the supply of the primary resin R1 from the primary gate 4 to the cavity 3 is stopped. For example, if the timing at which the supply of the primary resin R1 is stopped is advanced, the gradation portion 103 moves closer to the secondary gate 5. However, because the primary resin R1 needs to stop after passing the secondary gate 5, the gradation portion 103 is always located downstream of the secondary gate 5 (opposite the primary gate 4). On the other hand, if the timing at which the supply of the primary resin R1 is stopped is delayed, the gradation portion 103 moves away from the secondary gate 5. However, because the secondary resin R2 needs to protrude downstream from the primary resin R1 and expose the secondary resin R2 on the surface, the supply of the primary resin R1 is stopped before the primary resin R1 reaches the end of the cavity 3.

[0028] In the above embodiment, the primary gate 4 and secondary gate 5 are side gates that open to the side of the cavity 3, but the type of gate is not limited to this. For example, as shown in FIG. 14 , the secondary hot runner 9 may be a so-called direct gate that is connected directly to the cavity 3 without an intermediate cold runner. In this case, the valve gate 11 of the secondary hot runner 9 becomes the secondary gate 5. In this case, the primary gate 4 may be either a side gate or a direct gate. Alternatively, the primary gate 4 may be a direct gate and the secondary gate 5 may be a side gate. [Explanation of symbols]

[0029] 1 Fixed type 2 Movable type 3 Cavity 4 Primary Gate 5 Secondary Gate 6 Primary cold runner 7 Secondary cold runner 8 Primary Hot Runner 9 Secondary Hot Runner 10 valve pin 11 Valve Gate 100 Resin molded products 101 Primary molding part 102 Secondary molding part 103 Gradient part R1 Primary resin R1a Slope (surface layer) R2 Secondary resin

Claims

1. An injection molding method using a mold having a cavity and a primary gate and a secondary gate opening into the cavity, supplying a primary resin from the primary gate to the cavity; After the primary resin passes through the secondary gate, while supplying the primary resin from the primary gate to the cavity, supplying a secondary resin having a color different from that of the primary resin from the secondary gate to the cavity; and making the flow rate of the primary resin in the cavity slower than the flow rate of the secondary resin in the cavity.

2. An automobile panel part made of an injection-molded product having a primary molded portion, a secondary molded portion, and a gradation portion provided between the primary molded portion and the secondary molded portion, the primary molded portion and the gradation portion have surface layers made of a primary resin provided on both surfaces in a thickness direction, and an inner layer made of a secondary resin having a color different from that of the primary resin provided between the surface layers in the thickness direction, the secondary molded portion is made of the secondary resin, A panel part of an automobile, wherein the thickness of the surface layer of the gradation portion gradually decreases from the side of the primary molded portion toward the side of the secondary molded portion.

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