Injection molding apparatus, method for manufacturing resin molded products, and resin molded products

Abstract

To provide a resin molded product that achieves both an increase in a ratio of a core layer and suppression of penetration of a skin layer by the core layer.SOLUTION: An injection molding device 1 includes a mold 10 and an injection unit 20 that injects a resin P into a cavity 11 of the mold 10. The mold 10 is provided with an inlet 12 for introducing the resin P injected from the injection unit 20 into the cavity 11. The injection molding device 1 includes a temperature control unit 30 that changes a temperature Tc of the mold 10, and a controller 40 that controls the temperature control unit 30 so that the temperature Tc of the mold 10 is lower on the inlet 12 side than on an end 13 side in a flow direction X of the resin P in the cavity 11.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to an injection molding apparatus, a method for manufacturing a resin molded product, and a resin molded product.

Background Art

[0002] A resin molded product (for example, a sandwich resin molded product) including a skin layer and a core layer and a method for manufacturing the same are known. In this type of resin molded product, the appearance quality of the entire resin molded product can be improved by covering a core layer with poor appearance quality with a skin layer having excellent appearance quality.

[0003] In the method for manufacturing a resin molded product (non-uniform wall thickness multi-layer molding method) disclosed in Patent Document 1, in co-injection molding (sandwich molding) in which a skin layer resin and a core layer resin are sequentially injection-filled into a mold cavity to obtain a multi-layer molded product, during molding, the surface temperature of the mold cavity on the front side of the molded product is kept at least 10 °C lower than the surface temperature of the mold core on the back side of the molded product, and the skin layer thickness on the front side of the molded product is formed thicker than the skin layer thickness on the back side of the molded product.

[0004] Further, in the method for manufacturing a sandwich molded product disclosed in Patent Document 2, while maintaining the resin constituting the skin layer at a viscosity of 400 Pa·s or less at a shear rate of 100 / s and maintaining the resin constituting the core layer at a viscosity of 6000 Pa·s or more at a shear rate of 100 / s, the resin constituting the skin layer and the resin constituting the core layer are injected into the mold. Thereby, a sandwich molded product in which the thickness of the skin layer is 10% or less of the thickness of the entire molded product can be manufactured.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] Incidentally, a type of resin molded product that uses virgin resin for the skin layer and recycled resin for the core layer is known to be advantageous from the standpoint of cost and environmental protection. In such resin molded products, from the perspective of cost and environmental protection, it is desirable to make the proportion of the core layer as large as possible.

[0007] However, while Patent Document 1 increases the thickness of the skin layer on the surface side of the molded product, it is difficult to increase the ratio of the core layer to the entire resin molded product.

[0008] Furthermore, while Patent Document 2 allows for the manufacture of sandwich resin molded products with a large core layer ratio, it requires a large viscosity difference between the core layer resin and the skin layer resin. This necessitates selecting materials with significantly different properties for the core layer resin and the skin layer resin, which is not practical.

[0009] On the other hand, if the proportion of the core layer is forcibly increased, the core layer may break through the skin layer and become exposed, potentially degrading the appearance quality.

[0010] Furthermore, the above issues can occur even if virgin resin is not used for the skin layer and recycled resin is not used for the core layer.

[0011] This disclosure has been made in view of the above points, and its purpose is to provide a resin molded product that achieves both an increase in the ratio of the core layer and suppression of the core layer penetrating the skin layer. [Means for solving the problem]

[0012] The injection molding apparatus according to the present disclosure comprises a mold and an injection unit for injecting resin into the cavity of the mold, wherein the mold is provided with an inlet for introducing the resin injected from the injection unit into the cavity, and further comprises a temperature control unit for changing the temperature of the mold and a control unit for controlling the temperature control unit so that the temperature of the mold is lower on the inlet side than on the end side in the flow direction of the resin in the cavity.

[0013] The present disclosure relates to a method for manufacturing a resin molded article comprising a skin layer and a core layer, comprising: a skin injection step of injecting a skin resin corresponding to the skin layer into the cavity of a mold; and a core injection step of injecting a core resin corresponding to the core layer into the cavity after the skin injection step, wherein the mold is provided with an inlet for introducing the injected resin into the cavity, and the temperature of the mold is adjusted such that in at least one of the skin injection step and the core injection step the temperature on the inlet side is lower than the end side in the flow direction of the resin in the cavity.

[0014] The resin molded product relating to this disclosure is a resin molded product comprising a skin layer and a core layer, wherein the skin layer is made of virgin resin, the core layer is made of recycled resin, the ratio of the core layer to the sum of the skin layer and the core layer is 50% or more, and the flow length of the skin layer is 500 mm or more. [Effects of the Invention]

[0015] According to this disclosure, it is possible to provide a resin molded product that achieves both an increased ratio of the core layer and suppression of the core layer penetrating the skin layer. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 shows a method for manufacturing a resin molded product using an injection molding apparatus according to one embodiment of the present disclosure (preparation step). [Figure 2]Figure 2 shows a method for manufacturing a resin molded product using an injection molding apparatus (skin injection step). [Figure 3] Figure 3 shows a method for manufacturing a resin molded product using an injection molding apparatus (core injection step). [Figure 4] Figure 4 shows a method for manufacturing a resin molded product using an injection molding apparatus (completion step). [Figure 5] Figure 5 shows an example of a resin molded product. [Figure 6] Figure 6 is a diagram corresponding to FIG. 4 according to the conventional example.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, an embodiment of the present disclosure will be described in detail based on the drawings. The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present disclosure, its applications, or its uses in any way.

[0018] (Injection Molding Apparatus) FIGS. 1 to 4 show a method for manufacturing a resin molded product P using an injection molding apparatus 1 according to an embodiment of the present disclosure. As shown in FIGS. 3 and 4, the resin molded product P is a sandwich resin molded product and includes a skin layer P1 and a core layer P2. The appearance quality of the skin layer P1 is superior to that of the core layer P2. By covering the core layer P2 with the skin layer P1, the appearance quality of the entire resin molded product P is improved.

[0019] As shown in FIG. 1, the injection molding apparatus 1 includes a mold 10, an injection unit 20 as an injection part, a temperature control unit 30 as a temperature control part, and a controller 40 as a control part. The mold 10 is composed of a movable mold 10a and a fixed mold 10b. The movable mold 10a and the fixed mold 10b face each other in the vertical direction of FIG. 1. A cavity 11 is formed between the movable mold 10a and the fixed mold 10b in the mold 10. The mold 10 is provided with an inlet (gate) 12 that communicates the inside and outside of the cavity 11. The mold 10 is longitudinal in the flow direction X described later.

[0020] The injection unit 20 is composed of an injector. The injection unit 20 is configured such that, for example, the injection path of the skin resin (described later) injected from a first injector (not shown) and the injection path of the core resin (described later) injected from a second injector (not shown) merge midway.

[0021] The injection unit 20 injects the heat-melted resin into the cavity 11 of the mold 10. The resin corresponds to the resin molded product P (hereinafter referred to as "resin P"). The resin P injected from the injection unit 20 is introduced into the cavity 11 through the inlet 12. The resin P introduced into the cavity 11 flows from the inlet 12 side in the flow direction X to the end 13 side. In this embodiment, the flow direction X is linear.

[0022] The temperature control unit 30 is composed of a plurality of pipes 31 arranged in the flow direction X. A medium W flows through each pipe 31. The medium W is, for example, a liquid or a vapor. Each pipe 31 is provided inside the wall of the movable mold 10a and the wall of the fixed mold 10b. Each pipe 31 is arranged in the vicinity of the cavity 11. The pipes 31 are arranged from the inlet 12 side to the end 13 side in the flow direction X. Each pipe 31 is arranged on both sides of the cavity 11 in the vertical direction Y perpendicular to the flow direction X.

[0023] The temperature control unit 30 changes (increases or cools) the temperature Tc [°C] of the mold 10 (movable mold 10a and fixed mold 10b) by causing the medium W to flow through the pipes 31. In other words, heat exchange occurs between the medium W flowing through the pipes 31 and the mold 10.

[0024] In the temperature control unit 30, each pipe 31 is divided into three zones Z1, Z2, and Z3. The first zone Z1 is composed of the pipes 31 arranged on the inlet 12 side in the flow direction X. The third zone Z3 is composed of the pipes 31 arranged on the end 13 side in the flow direction X. The second zone Z2 is composed of the pipes 31 arranged in the middle between the first zone Z1 (inlet 12 side) and the third zone Z3 (end 13 side).

[0025] The controller 40 consists of a known microcomputer and program. The controller 40 controls the temperature control unit 30 so that the temperature Tc of the mold 10 is lower on the inlet 12 side than on the end 13 side in the flow direction X of the resin P in the cavity 11. Specifically, the controller 40 lowers the temperature Tw [°C] of the medium W flowing through the piping 31 located on the inlet 12 side in the flow direction X than the temperature Tw of the medium W flowing through the piping 31 located on the end 13 side in the flow direction X.

[0026] The controller 40 provides a stepped temperature gradient for the temperature Tw of the medium W flowing through the piping 31 in each zone Z1, Z2, and Z3. Specifically, the temperature Tw1 of the medium W flowing through the piping 31 in the first zone Z1 (inlet 12 side) is lower than the temperature Tw2 of the medium W flowing through the piping 31 in the second zone Z2 (intermediate side). The temperature Tw2 of the medium W flowing through the piping 31 in the second zone Z2 (intermediate side) is lower than the temperature Tw3 of the medium W flowing through the piping 31 in the third zone Z3 (end 13 side).

[0027] The controller 40 changes the temperature Tw of the medium W flowing through each pipe 31 by, for example, controlling the operation of heaters and coolers installed in each pipe 31, or by controlling the switching of valves located upstream of each pipe 31.

[0028] (Method of manufacturing resin molded products) The method for manufacturing the resin molded product P will be explained with reference to Figures 1 to 4. The method for manufacturing the resin molded product P comprises a preparation step S1, a skin injection step S2, a core injection step S3, and a completion step S4. Figure 1 shows the preparation step S1, Figure 2 shows the skin injection step S2, Figure 3 shows the core injection step S3, and Figure 4 shows the completion step S4.

[0029] As shown in Figure 1, in preparation step S1, the resin P corresponding to the resin molded product P is prepared. Specifically, in preparation step S1, the skin resin corresponding to the skin layer P1 (hereinafter referred to as "skin resin P1") and the core resin corresponding to the core layer P2 (hereinafter referred to as "core resin P2") are prepared.

[0030] The skin resin P1 is virgin resin. The core resin P2 is recycled resin.

[0031] Here, recycled resin refers to virgin resin that has been crushed after being used in molding at least once, and includes so-called material recycled resin.

[0032] Recycled resins offer advantages over virgin resins in terms of cost and environmental protection. However, recycled resins are at a disadvantage compared to virgin resins in terms of appearance quality. For example, recycled resins are inferior to virgin resins in terms of transparency and color, and are more prone to black spots. Furthermore, recycled resins may experience material strength degradation due to thermal history.

[0033] The skin resin (virgin resin) P1 and the core resin (recycled resin) P2 are composed of the same elements, and the viscosity difference between them is small. For example, the viscosity difference between the skin resin (virgin resin) P1 and the core resin (recycled resin) P2 at a shear rate of 100 / s is 5000 Pa·s or less. Preferably, the viscosity difference is 4000 Pa·s or less, and more preferably 3000 Pa·s or less.

[0034] In preparation step S1, the skin resin P1 and core resin P2 are heated and melted, and then set into the injection unit 20.

[0035] After the preparation step S1, as shown in Figure 2, in the skin injection step S2, the skin resin P1 is injected from the injection unit 20 into the cavity 11 of the mold 10. Specifically, the skin resin P1 injected from the injection unit 20 is introduced into the cavity 11 through the inlet 12. The skin resin P1 introduced into the cavity 11 flows from the inlet 12 side to the end 13 side in the flow direction X.

[0036] In the skin injection process S2, the mold 10 is heated so that the temperature Tc of the mold 10 is lower on the inlet 12 side than on the end 13 side in the flow direction X of the resin P. In other words, in the skin injection process S2, the temperature Tc of the mold 10 is adjusted so that the temperature Tc of the mold 10 is lower on the inlet 12 side than on the end 13 side in the flow direction X of the resin P in the cavity 11 of the mold 10.

[0037] Specifically, in the skin injection process S2, the temperature Tw of the medium W flowing through the pipe 31 located on the inlet 12 side in the flow direction X is made lower than the temperature Tw of the medium W flowing through the pipe 31 located on the end 13 side in the flow direction X (Tw1 <Tw2<Tw3)。

[0038] Preferably, in the skin injection process S2, the temperature Tc [°C] of the mold 10 is equal to or greater than the glass transition point (glass transition temperature) Tg [°C] of the skin resin P1. For example, in the skin injection process S2, the temperature Tw1 of the medium W flowing through the piping 31 in the first zone Z1 (inlet 12 side) is set to the glass transition point Tg + 5°C, the temperature Tw2 of the medium W flowing through the piping 31 in the second zone Z2 (intermediate side) is set to the glass transition point Tg + 10°C, and the temperature Tw3 of the medium W flowing through the piping 31 in the third zone Z3 (end 13 side) is set to the glass transition point Tg + 15°C.

[0039] It is preferable that the temperature of the mold 10 is raised before the injection of the skin resin P1 from the injection unit 20.

[0040] Following the skin injection process S2, as shown in Figure 3, in the core injection process S3, the core resin P2 is injected from the injection unit 20 into the cavity 11 of the mold 10. Specifically, the core resin P2 injected from the injection unit 20 is introduced into the cavity 11 through the inlet 12. The core resin P2 introduced into the cavity 11 flows from the inlet 12 side to the end 13 side in the flow direction X.

[0041] In the core injection process S3, the core resin P2 in the cavity 11 of the mold 10 is covered by the skin resin P1 from both the end 13 side in the flow direction X and the vertical direction Y.

[0042] In the core injection process S3, the mold 10 is cooled so that the temperature Tc of the mold 10 is lower on the inlet 12 side than on the end 13 side in the flow direction X of the resin P. In other words, in the core injection process S3, the temperature Tc of the mold 10 is adjusted so that the temperature Tc of the mold 10 is lower on the inlet 12 side than on the end 13 side in the flow direction X of the resin P in the cavity 11 of the mold 10.

[0043] Specifically, in the core injection process S3, the temperature Tw of the medium W flowing through the pipe 31 located on the inlet 12 side in the flow direction X is made lower than the temperature Tw of the medium W flowing through the pipe 31 located on the end 13 side in the flow direction X (Tw1 <Tw2<Tw3)。

[0044] Preferably, in the core injection process S3, the temperature Tc [°C] of the mold 10 is 10°C or lower than the glass transition point Tg [°C] of the skin resin P1. For example, in the core injection process S3, the temperature Tw1 of the medium W flowing through the piping 31 in the first zone Z1 (inlet 12 side) is set to the glass transition point Tg -20°C, the temperature Tw2 of the medium W flowing through the piping 31 in the second zone Z2 (intermediate side) is set to the glass transition point Tg -15°C, and the temperature Tw3 of the medium W flowing through the piping 31 in the third zone Z3 (end 13 side) is set to the glass transition point Tg -10°C.

[0045] The cooling of the mold 10 is preferably started in conjunction with the injection of the core resin P2 from the injection unit 20. The cooling timing of the mold 10 is preferably adjusted in accordance with the flow of the core resin P2 in the cavity 11. The cooling of the temperature Tw of the medium W flowing through the piping 31 is preferably started in the order of the first zone Z1, the second zone Z2, and the third zone Z3.

[0046] After the core injection process S3, the skin resin P1 may be injected again from the injection unit 20 into the cavity 11 of the mold 10. This ensures that the inlet 12 side of the core resin (core layer) P2 in the flow direction X is covered with the skin resin (skin layer) P1.

[0047] After the core injection process S3, as shown in Figure 4, in the completion process S4, the mold 10 is cooled throughout to lower the overall temperature Tc of the mold 10. Specifically, the temperature Tw of the medium W flowing through the piping 31 is lowered in all zones Z1, Z2, and Z3. A temperature gradient Tw of the medium W flowing through the piping 31 is not required in each zone Z1, Z2, and Z3.

[0048] As shown in Figure 4, the flow length H1 (distance in the flow direction X from the inlet 12) of the skin resin (virgin resin: skin layer) P1 in the cavity 11 is preferably 500 mm or more. More preferably, the flow length H1 is 600 mm or more, and even more preferably 700 mm or more. The flow length H2 of the core resin (recycled resin: core layer) P2 is smaller than the flow length H1 of the skin resin (virgin resin) P1. The flow length H2 is also preferably 500 mm or more, more preferably 600 mm or more, and even more preferably 700 mm or more, similar to the flow length H1.

[0049] Once the resin molded product P has completely cooled and solidified, the mold 10 is opened and the resin molded product P is removed from the mold 10. As shown in Figure 4, the ratio of the core layer (recycled resin) P3 to the total of the skin layer (virgin resin) P1 and the core layer (recycled resin) P2 (the entire resin molded product P) (recycling ratio) R is preferably 50% or more. The recycling ratio R is expressed as core layer P2 / (skin layer P1 + core layer P2). It is more preferable that the recycling ratio R be 60% or more, and even more preferable that it be 70% or more. The recycling ratio R can be expressed as, for example, a volume ratio or a mass ratio.

[0050] Figure 5 shows an example of a molded resin product P. Note that the molded resin product P shown in Figure 5 does not correspond to the molded resin products P shown in Figures 1 to 4. As shown in Figure 5, the molded resin product P has traces of an inlet (gate) 12. In this example, the traces of the inlet 12 are located in the center of the side surface of the molded resin product P. The flow length H1 is the furthest (longest) distance from the traces of the inlet 12 to the end of the skin layer P1, and can be visually confirmed by a person skilled in the art, for example, by cross-sectional observation. The same applies to the flow length H2, although it is not shown in Figure 5. Note that the traces of the inlet 12 may be located at the end of the molded resin product P.

[0051] (Effects and Benefits) As shown in Figure 6, in the conventional injection molding apparatus 1', the temperature Tc' of the mold 10' (movable mold 10a' and fixed mold 10b') is approximately constant from the inlet 12' side to the end 13' side in the flow direction X. That is, the temperature Tc' at the end 13' side of the mold 10' in the conventional injection molding apparatus 1' is lower than the temperature Tc at the end 13 side of the mold 10 in the injection molding apparatus 1 according to this embodiment.

[0052] Therefore, the skin resin P1' injected from the injection unit 20' and introduced into the cavity 11' via the inlet 12' cools and solidifies, increasing its viscosity, before reaching the end 13' side in the flow direction X'. Then, the core resin P2' injected from the injection unit 20' and introduced into the cavity 11' via the inlet 12' is hindered by the increased viscosity of the skin resin P1', making it difficult for it to flow to the end 13' side in the flow direction X'.

[0053] As a result, the core resin P2' does not reach the end 13' side in the flow direction X', so the ratio of the core layer P2' to the entire resin molded product P' (skin layer P1' + core layer P2') becomes small. In addition, the core resin (core layer) P2', whose flow in the flow direction X' is hindered by the increased viscosity of the skin resin P1', attempts to move in the vertical direction Y', especially at the inlet 12' side in the flow direction X', and breaks through the skin resin (skin layer) P1' on both sides of the vertical direction Y', becoming exposed to the outside (burst phenomenon). As a result, the appearance quality of the resin molded product P' deteriorates.

[0054] According to this embodiment, in the skin injection process S2 (see Figure 2), the mold 10 is heated so that the temperature Tc of the mold 10 is lower on the inlet 12 side than on the end 13 side in the flow direction X. In other words, the temperature Tc of the mold 10 on the end 13 side in the flow direction X becomes higher.

[0055] Therefore, in the skin injection process S2, the skin resin P1 introduced into the cavity 11 via the inlet 12 is kept in a low viscosity state by suppressing cooling and solidification at the end 13 in the flow direction X. As a result, the pressure loss at the end 13 in the flow direction X of the cavity 11 is reduced.

[0056] Then, in the core injection process S3 (see Figure 3), the core resin P2 introduced into the cavity 11 via the inlet 12 becomes more fluid to the end 13 in the flow direction X. In addition, the skin resin P1 itself, which is maintained in a low viscosity state, also becomes more fluid to the end 13 in the flow direction X.

[0057] Since the core resin P2 extends sufficiently to the end 13 in the flow direction X, the ratio of the core layer P2 to the entire resin molded product P (skin layer P1 + core layer P2) becomes large. Naturally, the skin resin P1 also extends sufficiently to the end 13 in the flow direction X.

[0058] Furthermore, in the core injection process S3 (see Figure 3), the mold 10 is cooled so that the temperature Tc of the mold 10 is lower on the inlet 12 side than on the end 13 side in the flow direction X. In other words, the temperature Tc of the mold 10 on the inlet 12 side in the flow direction X becomes lower.

[0059] Therefore, in the core injection process S3, the skin resin P1 in the cavity 11 undergoes accelerated cooling and solidification on the inlet 12 side in the flow direction X, resulting in a high viscosity state. As a result, in the core injection process S3, the core resin P2 introduced into the cavity 11 via the inlet 12 is guided by the high viscosity skin resin (skin layer) P1 on both sides of the vertical Y direction, particularly on the inlet 12 side in the flow direction X, and moves toward the end 13 side in the flow direction X.

[0060] Therefore, the core resin (core layer) P2 is prevented from piercing through the skin resin (skin layer) P1 on both sides in the vertical Y direction and being exposed to the outside. As a result, deterioration of the appearance quality of the resin molded product P is suppressed.

[0061] In summary, we can provide a resin molded product P that achieves both an increased ratio of the core layer P2 and suppression of the skin layer P1 being penetrated by the core layer P2.

[0062] In this embodiment, the skin resin P1 is a virgin resin, and the core resin P2 is a recycled resin. Therefore, the recycling ratio R can be improved by increasing the ratio of the core layer P2 to the entire resin molded product P (skin layer P1 + core layer P2).

[0063] According to this embodiment, the skin resin P1 and core resin P2 spread sufficiently to the end 13 side in the flow direction X, so that the flow lengths H1 and H2 can be increased. This is advantageous when molding large resin molded products P. Examples of large resin molded products P include toilets, washbasins, and home appliance casings.

[0064] Furthermore, by increasing the flow lengths H1 and H2, the effect obtained by dividing the mold 10 into zones Z1, Z2, and Z3 and creating a temperature gradient Tc for each zone becomes greater.

[0065] In the manufacture of sandwich resin molded products P, the skin resin P1 and core resin P2 are typically made of materials with similar physical properties in order to maintain high adhesive strength between them. That is, in the manufacture of sandwich resin molded products P, the viscosity of the skin resin P1 and the viscosity of the core resin P2 are usually close to each other.

[0066] According to this embodiment, the ratio of the core layer P2 can be increased even if the viscosity difference between the skin resin P1 and the core resin P2 is not large, as in Patent Document 2. Therefore, there is a greater degree of freedom in selecting the skin resin P1 and the core resin P2 compared to Patent Document 2. Furthermore, since the properties of the skin resin P1 and the core resin P2 are similar to each other, it is advantageous in increasing the adhesive strength between them and suppressing the occurrence of warping.

[0067] (Other embodiments) Although this disclosure has been described above with reference to preferred embodiments, this description is not limiting, and various modifications are, of course, possible.

[0068] In the above embodiment, the appearance quality of the resin molded product P was improved by applying virgin resin as the skin resin P1, but the embodiment is not limited to this. For example, the mechanical strength of the resin molded product P may be improved by applying fiber-reinforced material as the skin resin P1 and / or core resin P2, or desired properties may be imparted to the resin molded product P by applying functional material as the skin resin P1 and / or core resin P2. Alternatively, for example, a colored recycled material may be applied as the skin resin P1 and a recycled resin (of an unattractive color such as black) may be applied as the core resin P2.

[0069] In the above embodiment, the temperature control unit 30 is composed of a plurality of pipes 31 arranged in the flow direction X, but is not limited to this. The temperature control unit 30 may also be a heater that directly raises the temperature of the mold 10, or dry ice, cooling spray, etc. that directly cools the mold 10. The temperature control unit 30 may also be composed of a Peltier element. Furthermore, the temperature control unit 30 may consist of separate pipes through which a heating medium for raising the temperature flows and pipes through which a cooling medium for cooling flows.

[0070] In the above embodiment, the flow direction X was linear, but is not limited to this. The flow direction X may be, for example, arc-shaped or circumferential. Also, the flow direction X may radiate from any point. When the flow direction X is radial, the flow length H1 is the radius of the resin molded product P.

[0071] Regarding the temperature Tc of the mold 10, a temperature gradient may be provided in only two stages, or a continuous temperature gradient may be provided.

[0072] Rather than adjusting the temperature Tc of the mold 10 in both the skin injection process S2 and the core injection process S3, it is sufficient to adjust the temperature Tc of the mold 10 such that the temperature of the resin P in the flow direction X of the mold cavity 11 is lower on the inlet side 12 than on the end side 13. [Industrial applicability]

[0073] This disclosure is extremely useful and has high industrial applicability because it can be applied to injection molding apparatus, methods for manufacturing resin molded products, and resin molded products. [Explanation of Symbols]

[0074] P Resin molded product (resin) P1 Skin layer (skin resin) P2 Core layer (core resin) X Flow direction Y vertical direction W medium Tc temperature Tw temperature Tw1 temperature Tw2 temperature Tw3 temperature Tg (glass transition temperature) Z1 Zone 1 Z2 Zone 2 Z3 Zone 3 H1 Flow length H2 flow length R Recycling Ratio 1 Injection molding equipment 10 molds 11 Cavity 12 Inlet 13 Terminal 20. Injection unit (injection section) 30 Temperature control unit (temperature control section) 31 Piping 40 Controller (Control Unit) S1 Preparation process S2 Skin injection process S3 Core injection process S4 completion process

Claims

1. A method for manufacturing a resin molded product comprising a skin layer and a core layer using an injection molding apparatus, The injection molding apparatus is mold and It comprises an injection unit for injecting resin into the cavity of the mold, The mold is provided with an inlet for introducing the resin injected from the injection section into the cavity. The injection molding apparatus is A temperature control unit that changes the temperature of the mold, The system includes a control unit that controls the temperature control unit so that the temperature of the mold is lower on the inlet side than on the end side in the flow direction of the resin in the cavity, The temperature control unit is composed of a plurality of pipes arranged in the flow direction, The control unit lowers the temperature of the medium flowing through the pipe located on the inlet side in the flow direction to a temperature lower than the temperature of the medium flowing through the pipe located on the terminal side in the flow direction. The aforementioned manufacturing method is A skin injection process in which a skin resin corresponding to the skin layer is injected into the cavity of a mold, The process includes a core injection step in which a core resin corresponding to the core layer is injected into the cavity after the skin injection step, In both the skin injection process and the core injection process, the temperature of the mold is adjusted such that the temperature is lower on the inlet side than on the end side in the flow direction of the resin in the cavity. In the skin injection process, the temperature of the mold is above the glass transition temperature of the skin resin. A method for manufacturing a resin molded product, wherein in the core injection step, the temperature of the mold is 10°C or lower than the glass transition temperature of the skin resin.

2. A method for manufacturing a resin molded article according to claim 1, The skin resin is a virgin resin, The core resin is a recycled resin. The ratio of the core layer to the sum of the skin layer and the core layer is 50% or more. A method for manufacturing a resin molded product, wherein the flow length of the skin resin in the cavity is 500 mm or more.

3. A method for manufacturing a resin molded article according to claim 1 or 2, A method for manufacturing a resin molded product, wherein the difference in viscosity between the skin resin and the core resin at a shear rate of 100 / s is 5000 Pa·s or less.

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