Injection molded product and its manufacturing method

Abstract

To provide an injection-molded product in which generation of a weld line on a design surface is suppressed.SOLUTION: An injection molded product comprises: a body part that has a design surface and an opposite surface; and a projecting part that is provided to a peripheral edge portion of the body part and that protrudes toward a side opposite to the design surface in the thickness direction of the body part, in which a thickness A of the body part and a thickness B of the projecting part satisfy the following relation A≥B.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to injection molded articles. [Background technology]

[0002] Since resin structures are lighter than metals, they are widely used as vehicle structural parts, vehicle mounted items, housings for electronic devices, etc. Among resin structures, resin molded products in particular are lighter, and their use in vehicle parts such as automobiles is expected to improve fuel efficiency.

[0003] Known injection foam molding methods for resin molded products used as interior base materials for automobiles and the like include the method described in Patent Document 1. In Patent Document 1, molten resin is injected into a cavity of a molding die formed by a movable die (movable die) and a fixed die (fixed die), and then foaming treatment is carried out with the movable die moved slightly apart (core back) to obtain a resin molded product. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-238726 A Summary of the Invention [Problem to be solved by the invention]

[0005] When molten resin is injected into a cavity, the part in contact with the molding die cools and solidifies to form a film-like skin layer. When the movable die is then cored back against the fixed die to expand the volume of the cavity, the molten resin covered by the skin layer foams to form a foam layer, producing a plastic injection-molded product.

[0006] The flow speed of the molten resin flowing inside the cavity is affected by the width between the movable and fixed dies that form the cavity. The flow speed of the molten resin tends to increase as the width between the movable and fixed dies increases.

[0007] In order to ensure strength such as bending rigidity of the injection molded product, a protruding portion (hereinafter, sometimes referred to as a flange) may be provided on the periphery of the main body of the injection molded product. When the width between the movable side mold and the fixed side mold in the part corresponding to the main body of the cavity is narrower than the width between the movable side mold and the fixed side mold in the part corresponding to the flange of the cavity, the flow speed of the molten resin in the part corresponding to the flange of the cavity becomes higher than the flow speed of the molten resin in the part corresponding to the main body of the cavity. Then, the molten resin flowing in the part corresponding to the flange of the cavity precedes the molten resin flowing in the part corresponding to the main body of the cavity. As a result, the molten resin flowing in the part corresponding to the flange of the cavity merges in the part corresponding to the main body of the cavity, and a streak-like defect (hereinafter, sometimes referred to as a weld line) may occur at the merged part of the molten resin. If the weld line appears on the design surface of the injection molded product, it may cause a defect in the appearance of the injection molded product.

[0008] The present disclosure has been made in consideration of the above-described conventional circumstances, and aims to provide an injection-molded product in which the occurrence of weld lines in the design surface is suppressed. [Means for solving the problem]

[0009] Specific means for achieving the above object are as follows. <1> A main body portion having a design surface and an opposite surface; a protruding portion provided on a peripheral edge of the main body portion and protruding toward an opposite side to the design surface in a thickness direction of the main body portion, An injection-molded product in which a thickness A of the main body portion and a thickness B of the protruding portion satisfy the relationship of the following formula (1). A≧B formula (1) <2> a fixed-side mold having a gate for injecting a resin material, and a movable-side mold movable in an opening / closing direction relative to the fixed-side mold and forming a cavity between the fixed-side mold and the movable-side mold, the mold being manufactured through a manufacturing process including a step of injecting a resin material from the gate into the cavity of the mold, The flow distance of the resin material in the cavity is 600 mm or less. <1> 1. An injection molded article according to claim 1. <3> the manufacturing process further includes a step of expanding a volume of the cavity by moving the movable mold in an opening direction from the fixed mold after filling the cavity with the resin material in the injecting step, The main body has a foam layer therein. <2> 1. An injection molded article according to claim 1. Effect of the Invention

[0010] According to the present disclosure, an injection molded product is provided in which the occurrence of weld lines on the design surface is suppressed. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a rear view of the injection molded product of the present embodiment. [Diagram 2] FIG. 2 is a longitudinal sectional view of the injection-molded product of FIG. 1 (a sectional view taken along line 2-2 in FIG. 1). [Diagram 3] 2 is a plan view for explaining the shape of a cavity 22 formed by a movable mold and a fixed mold. FIG. [Figure 4] This is a cross-sectional view (cross-sectional view along line AA in Figure 3) for explaining the shape of cavity 22 formed by the movable mold and the fixed mold, and shows the case where width A of cavity 22A and width B of cavity 22B have a relationship of A=B. [Diagram 5] 2 is a schematic diagram for explaining the state of a resin material flowing inside a cavity 22. FIG. [Figure 6]It is a cross-sectional view (cross-sectional view taken along line A-A in FIG. 3) for explaining the shape of the cavity 22 formed by the movable mold and the fixed mold, and shows a case where the width A of the cavity 22A and the width B of the cavity 22B are in the relationship of A < B. [Figure 7] It is a schematic diagram for explaining the state of the resin material flowing in the cavity 22. [Figure 8] It is a schematic diagram for explaining the state of the resin material flowing in the cavity 22, and is a diagram showing a location where the resin from the cavity 22B flowing toward the cavity 22A merges. [Figure 9] It is a schematic cross-sectional view of the mold.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments for carrying out the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, its components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present disclosure.

[0013] In the present disclosure, the term "step" includes not only a step independent of other steps, but also the step even if it cannot be clearly distinguished from other steps as long as the purpose of the step is achieved. In the numerical range indicated by "~" in the present disclosure, the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. In the present disclosure, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area.

[0014] First, the injection molded product of the present embodiment will be described, followed by a manufacturing apparatus (mold) and a manufacturing method for manufacturing the injection molded product of the present embodiment.

[0015] <Injection molded products> The injection-molded product of the present disclosure has a main body having a design surface and an opposite surface, and a protrusion provided on the peripheral edge of the main body and protruding to the opposite side of the design surface in the thickness direction of the main body, wherein a thickness A of the main body and a thickness B of the protrusion satisfy the relationship of the following formula (1). A≧B formula (1) The protruding portion provided on the peripheral edge of the main body may be a flange for improving the strength of the injection molded product. When the thickness of the main body is not constant, the thickness A of the main body is the arithmetic mean value of the thicknesses at any five points on the main body. When the thickness of the protruding portion is not constant, the thickness B of the protruding portion is the arithmetic mean value of the thicknesses at any five points on the protruding portion.

[0016] Specific examples of injection molded products will be described with reference to the drawings, but the present disclosure is not limited thereto. In addition, the size of each part in each drawing is conceptual, and the relative relationship between the sizes of each part is not limited thereto. The injection molded article of the present embodiment can be used, for example, as an automobile part. However, the use of the injection molded article is not limited to automobile parts.

[0017] The injection molded product 10 shown in Fig. 1 is an automobile part, and is attached to a vehicle body 30 (see Fig. 2). Examples of automobile parts include bumpers, side mudguards, fenders, back door garnishes, spoilers, and radiator grilles.

[0018] As shown in Fig. 2, the injection molded product 10 is made of a resin material and has a main body 11 having a design surface 11A and an opposite surface 11B, and a protruding portion 12 provided on a peripheral portion 11C of the main body 11 and protruding in the thickness direction of the main body 11 (the direction indicated by the arrow T in Fig. 2) to the opposite side to the design surface 11A. The main body 11 is formed in a plate shape that is bent at a bending portion 11E, and a plurality of vehicle body mounting portions 11D (see Fig. 1) are formed on the opposite surface 11B. The vehicle body mounting portions 11D are used to mount the main body 11 (injection molded product 10) to a vehicle body 30 using a mounting member not shown. 1, when observing the back surface of the main body 11, the overhanging portion 12 is provided around the peripheral portion 11C (the outer periphery of the main body 11). Note that the present disclosure is not limited to the above configuration, and the overhanging portion 12 may be configured to be provided intermittently along the peripheral portion 11C of the main body 11, or may be configured to be provided on a part of the peripheral portion 11C of the main body 11.

[0019] 2, in the present disclosure, the protruding portion 12 is present at the end of the main body portion 11 when observing a cross section of the main body portion 11. In addition, the surface of the protruding portion 12 that continues from the design surface 11A of the main body portion 11 may or may not be a design surface. In addition, the surface of the protruding portion 12 that continues from the opposite surface 11B of the main body portion 11 may not be a design surface.

[0020] The injection molded product 10 is formed by injecting molten resin into a cavity of a molding die formed by a movable die and a fixed die, and by slightly core-backing the movable die as necessary.

[0021] Figures 3 and 4 are schematic diagrams for explaining the shape of cavity 22 formed by a movable-side mold and a fixed-side mold, with Figure 3 being a plan view of cavity 22 and Figure 4 being a view showing a cross section of cavity 22 taken along line AA shown in Figure 3. In Figures 3 and 4, in order to make it easier to understand the shape of cavity 22, the movable-side mold and fixed-side mold that form cavity 22 are not shown.

[0022] As shown in FIG. 4, the cavity 22 has a cavity 22A corresponding to the main body portion of the injection molded product and a cavity 22B corresponding to the flange of the injection molded product. In FIG. 4, the width A of the cavity 22A and the width B of the cavity 22B satisfy the relationship A = B.

[0023] The resin material injected into the cavity 22 from the gate 38 in FIG. 3 reaches the ends of the cavity 22 along the directions of arrow Q and arrow R in FIG. 3 within the cavity 22.

[0024] FIG. 5 is a schematic diagram for explaining the state of the resin material flowing within the cavity 22. The width A of the cavity 22A and the width B of the cavity 22B satisfy the relationship A = B, and the flow rate of the resin material flowing through the cavity 22A and the flow rate of the resin material flowing through the cavity 22B are approximately equal. Then, the resin material flowing through the cavity 22B does not precede the resin material flowing through the cavity 22A (see FIG. 7), and the resin material that has flowed through the cavity 22B does not merge in the cavity 22A. As a result, the generation of weld lines in the cavity 22A is suppressed. Therefore, the generation of weld lines on the design surface of the injection molded product is suppressed.

[0025] On the other hand, as shown in FIG. 6, when the width A of the cavity 22A and the width B of the cavity 22B are in the relationship A < B, the flow rate of the resin material flowing through the cavity 22A becomes lower than the flow rate of the resin material flowing through the cavity 22B. Then, since the resin material flowing through the cavity 22B precedes the resin material flowing through the cavity 22A (see FIG. 7), a part of the resin material that has flowed through the cavity 22B flows toward the cavity 22A (see FIG. 8). The resin from the cavity 22B that has flowed toward the cavity 22A merges in the region indicated by the dotted line in FIG. 8. Weld lines may occur at the resin merging location.

[0026] When the injection-molded product of the present disclosure is molded by an injection molding method without core-backing the mold, the width A of cavity 22A corresponds to the thickness of the main body of the injection-molded product, and the width B of cavity 22B corresponds to the thickness of the flange of the injection-molded product. On the other hand, when the injection-molded product of the present disclosure is molded by core-backing the movable mold, the width B of cavity 22B and the thickness of the flange of the injection-molded product roughly match, but the width A of cavity 22A and the thickness of the main body of the injection-molded product do not match, and the thickness of the main body is thicker than the width A of cavity 22A. When the injection-molded product of the present disclosure is molded by core-backing the movable mold, in order to ensure the fluidity of the resin material in cavity 22A, it is desirable for the thickness A of the main body and the thickness B of the protruding portion to satisfy the relationship of the following formula (1'). A>B formula (1')

[0027] When the thickness A of the main body and the thickness B of the protrusion in an injection-molded product molded by core-backing the movable mold satisfy the relationship of formula (1'), the width A of cavity 22A and the width B of cavity 22B tend to satisfy the relationship A≧B, and the occurrence of weld lines in the design surface of the injection-molded product is easily suppressed. In addition, when the injection-molded product of the present disclosure is molded by core-backing the movable mold, it is desirable that the width A of cavity 22A and the width B of cavity 22B before core-back satisfy the relationship of formula (1).

[0028] The resin material that forms the injection-molded product 10 of this embodiment will be described later.

[0029] <Mold> The mold for molding the injection-molded product of this embodiment comprises a fixed-side mold and a movable-side mold that is movable in the opening and closing direction relative to the fixed-side mold and forms a cavity, which is a gap, between the fixed-side mold and a movable-side mold. The mold can be used for injection molding, and is preferably used for foam molding, and more preferably for injection foam molding, although it is not limited to these uses.

[0030] Hereinafter, specific examples of the mold will be described with reference to the drawings, but the present disclosure is not limited thereto. In addition, the sizes of the members in each drawing are conceptual, and the relative relationships between the sizes of the members are not limited thereto.

[0031] 9, the molding device 18 includes a fixed mold 20 and a movable mold 24 that is movable in the opening and closing direction relative to the fixed mold 20 and forms a cavity 22, which is a gap, between the fixed mold 20 and the movable mold 24. Hereinafter, the fixed mold 20 and the movable mold 24 may be collectively referred to as a "mold 26."

[0032] The cavity 22 corresponds to the shape of the injection molded product 10. Furthermore, at a location corresponding to the tip of the protruding portion 12 in the cavity 22, a seam (parting line, PL) between the fixed mold 20 and the movable mold 24 is located.

[0033] In this embodiment, the cavity surface 20A formed in the fixed-side mold 20 forms the front surface (design surface 11A) of the main body 11 of the injection molded product 10 and a surface continuing from the design surface 11A of the main body 11 at the protruding portion 12. The cavity surface 24A in the movable-side mold 24 forms the back surface (opposite surface 11B) of the main body 11 of the injection molded product 10 and a surface continuing from the opposite surface 11B of the main body 11 at the protruding portion 12. The cavity 22 is a gap between the cavity surface 20A and the cavity surface 24A when the fixed-side mold 20 and the movable-side mold 24 are closed.

[0034] The molding device 18 also includes a gate 38 that penetrates the fixed mold 20 to the cavity 22, and an injection machine 40 that injects and fills the cavity 22 with a molten resin material R through the gate 38. The injection machine 40 includes a hopper (supply unit) (not shown) and a cylinder (not shown). In the injection machine 40, a mixture containing a resin, a foaming agent, an additive, and the like is supplied from the hopper (supply unit) to the cylinder, and is stirred in the cylinder with a screw or the like to prepare the resin material R, and the resin material R is injected and filled into the cavity 22 through the gate 38 at a predetermined pressure. Note that the injection machine 40 is not limited to the above configuration as long as it can inject and fill the cavity 22 with the molten resin material R through the gate 38.

[0035] <Manufacturing method of injection molded products> The injection molded product of this embodiment may be manufactured through a manufacturing process including a step of injecting resin material from a gate into a cavity of a mold including a fixed side mold having a gate for injecting resin material, and a movable side mold that is movable in an opening / closing direction relative to the fixed side mold and forms a cavity that is a gap between the fixed side mold and the movable side mold. When the injection molded product is a foam molded product, the foam molded product can be manufactured through a process of injecting a resin material from a gate into a cavity of a mold including a fixed mold having a gate for injecting a resin material, and a movable mold that is movable in an opening / closing direction relative to the fixed mold and forms a cavity between the fixed mold and the movable mold, and a process of moving the movable mold in an opening direction from the fixed mold to expand the volume of the cavity after filling the cavity with the resin material in the injection process, but the manufacturing process of the foam molded product is not limited to the above method. The foam molded product has a main body having a foam layer inside.

[0036] 9, a resin material R containing a foaming agent is injected from an injector 40 through a gate 38 to fill the cavity 22. When the resin material R is made of a thermoplastic resin, the resin material R is heated and fluidized before being supplied into the cavity 22.

[0037] Here, it is preferable to set the cylinder temperature in the region from the hopper outlet of the resin material R in the injector 40 to 1 / 3 to 1 / 2 of the total cylinder length to 250°C or less. However, this region is the temperature excluding the hopper outlet. By setting the cylinder temperature in this region to 250°C or less, it is possible to suppress the escape of foaming gas from the hopper outlet side, and it is easy to obtain effects such as improvement and stabilization of foaming properties during molding.

[0038] The resin material used in this embodiment is not particularly limited. For example, the resin material used in injection foam molding generally contains a resin and a foaming agent. The resin used in the resin material R includes at least one selected from the group consisting of polyethylene resin, polypropylene resin (PP), composite polypropylene resin (PPC), polystyrene resin, polyethylene terephthalate resin, polyvinyl alcohol resin, vinyl chloride resin, ionomer resin, polyamide resin, acrylonitrile-butadiene-styrene copolymer resin (ABS) and polycarbonate resin. Among these, at least one selected from the group consisting of polypropylene resin (PP), composite polypropylene resin (PPC) and acrylonitrile-butadiene-styrene copolymer resin (ABS) is preferred.

[0039] Examples of the foaming agent include organic foaming agents such as azodicarbonamide, and inorganic foaming agents such as sodium hydrogen carbonate (also known as sodium bicarbonate or baking soda). Currently, inorganic sodium hydrogen carbonate is mainly used as a foaming agent in foam molding of automotive interior parts, but from the viewpoint of improving the coating film performance (warm water resistance, etc.), organic foaming agents are preferred.

[0040] Examples of the organic foaming agent include azodicarbonamide (ADCA), N,N-dinitrosopentamethylenetetramine (DPT), 4,4-oxybisbenzenesulfonylhydrazide (OBSH), hydrazodicarbonamide (HDCA), and the like, with azodicarbonamide (ADCA) being preferred.

[0041] Moreover, the mold 26 is usually at a lower temperature than the supplied resin material R. Therefore, when the resin material R is filled into the cavity 22, the resin material R starts to solidify from the portion in contact with the mold.

[0042] It is preferable to fill the cavity 22 with nitrogen gas beforehand, and more preferably to fill the cavity with heated nitrogen gas, beforehand, before injecting the resin material R into the cavity 22. By heating the nitrogen gas to be filled, a sudden drop in temperature inside the cavity 22 (mold) can be suppressed, and the foaming property of the resin material R can be stabilized. In addition, by heating the nitrogen gas to be filled, the foaming power of the resin material R can be made less dependent on the outside air temperature, and the foaming property of the resin material R can be stabilized.

[0043] The flow distance of the resin material R in the cavity 22 is not particularly limited, and is preferably 600 mm or less, and more preferably 400 mm or less. When the flow distance of the resin material R is 600 mm or less, the distance from the gate 38 to the end of the cavity 22 is shortened, thereby preventing a drop in the temperature of the resin material R and making it easier to suppress pressure loss in the cavity 22. As a result, the occurrence of pockmarks and swirls on the design surface tends to be suppressed.

[0044] Next, the movable mold 24 is opened (cored back) a predetermined amount in the opening direction (mold opening direction) relative to the fixed mold 20, and the unsolidified resin material R is foamed to form a foam layer in the foam-molded product. Thereafter, the fixed mold 20 and the movable mold 24 are opened, and the foam-molded product is removed from the fixed mold 20, thereby obtaining the foam-molded product.

[0045] The present disclosure is not limited to the specific configurations of the embodiments described above, and various modifications are possible without departing from the spirit and scope of the present disclosure.

[0046] The disclosure of Japanese Patent Application No. 2019-187076, filed on October 10, 2019, is incorporated herein by reference in its entirety. In addition, all publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0047] 10 Injection molded products 11 Main body 12 Overhang 18 Molding equipment 20 Fixed side mold 22 Cavity 24 Movable mold 26 Molds 30 Body 38 Gate 40 injection machine

Claims

1. A main body portion having a design surface and an opposite surface; a protruding portion having a constant thickness that is provided on the peripheral portion of the main body portion, exists at the end of the main body portion when a cross section of the main body portion is observed, and protrudes in a thickness direction of the main body portion toward the opposite side to the design surface; An injection-molded product in which a thickness A of the main body portion and a thickness B of the protruding portion satisfy the relationship of the following formula (1). A≧B Formula (1)

2. A main body having a design surface and an opposite surface; a protruding portion having a constant thickness that is provided on the peripheral portion of the main body portion, exists at the end of the main body portion when a cross section of the main body portion is observed, and protrudes in a thickness direction of the main body portion toward the opposite side to the design surface; A method for producing an injection-molded product, wherein a thickness A of the main body portion and a thickness B of the protruding portion satisfy the relationship of the following formula (1), a fixed-side mold having a gate for injecting a resin material; and a movable-side mold that is movable in an opening / closing direction relative to the fixed-side mold and forms a cavity between the fixed-side mold and the movable-side mold, the manufacturing process including a step of injecting a resin material from the gate into the cavity of the mold, A method for manufacturing an injection molded product, wherein a flow distance of the resin material within the cavity is 600 mm or less. A≧B Formula (1)

3. the manufacturing process further includes a step of expanding a volume of the cavity by moving the movable mold in an opening direction from the fixed mold after filling the cavity with the resin material in the injecting step, The method for producing an injection molded product according to claim 2 , wherein the main body portion has a foam layer therein.

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