Injection molding method and resin component

Abstract

To prevent the appearance defect of a design surface without being accompanied by coating or a design change after molding when a plate-like resin part wherein a groove is provided to the surface on the side opposite to the design surface is injection-molded.SOLUTION: When injection-molding the air bag cover 1 provided with a design surface part 2 having a design surface 4 and a tear line 6 provided on a back surface 5 on the opposite side of the design surface 4, a first layer 11 having the tear line 6 is injection-molded, and then a second layer 12 having the design surface 4 is injection-molded on the opposite side of the tear line 6 of the first layer 11.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an injection molding method and a resin part. [Background technology]

[0002] A groove (tear line) that can be the starting point for cracks is formed on the back surface of an automobile airbag cover. Tear lines are generally formed as a post-processing step after the airbag cover has been molded, but they can also be formed simultaneously with the injection molding of the airbag cover. In this case, productivity is improved compared to when tear lines are formed as a post-processing step, but the sheet thickness rapidly decreases where the tear line is formed, which can cause uneven gloss on the design surface and reduce quality.

[0003] Various proposals have been made to improve the quality degradation caused by tear lines. For example, methods have been proposed to reduce gloss unevenness caused by tear lines by devising the shape of the tear lines (see Patent Document 1 below) or by providing a grid-like rib portion near the tear lines (see Patent Document 2 below). Furthermore, inventions that devise molding methods have been proposed, such as a method of molding an airbag cover using an injection compression method (see Patent Document 3 below) and a method of filling a cavity with a foamed resin (see Patent Document 4 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-6488 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-58953 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-127884 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-269002 Summary of the Invention [Problem to be solved by the invention]

[0005] However, while all of the above methods improve the appearance of the design surface, their effectiveness is limited and they do not fully eliminate gloss unevenness. Therefore, when airbag covers with tear lines are injection molded from resin, the design surface is painted after molding to hide gloss unevenness, or a character line (a curved surface in the design) is designed to be placed above the tear line to make the gloss unevenness less noticeable. However, painting after molding increases the number of steps and leads to higher costs. Furthermore, it may not be possible to place a character line above the tear line due to design constraints.

[0006] The above-described problem is not limited to airbag covers, but also occurs when injection molding a plate-shaped resin part having a groove on the surface opposite to the design surface.

[0007] Therefore, the present invention aims to prevent poor appearance of the design surface when injection molding a plate-shaped resin part with a groove on the surface opposite the design surface, without requiring painting or design changes after molding. [Means for solving the problem]

[0008] In order to solve the above problem, the present invention provides an injection molding method for a resin part having a plate-shaped portion with a design surface and a groove provided on a back surface opposite the design surface, the injection molding method comprising the steps of injection molding a first layer having the groove, and injection molding a second layer having the design surface on the side of the first layer opposite the groove.

[0009] When a first layer with grooves is injection molded in this way, uneven gloss can occur on the side opposite the grooves of the first layer. However, by injection molding the second layer on the side opposite the grooves of this first layer, the surface of the first layer where the uneven gloss occurred (the side opposite the grooves) is covered by the second layer, so the uneven gloss can be hidden. Furthermore, because the second layer does not have grooves, the design surface of the second layer does not have uneven gloss due to the grooves.

[0010] Two-layer resin molding is usually used to create parts with different properties in a single molded product, so each layer is made of a different resin. However, when a second layer is added to hide uneven gloss in the first layer, as described above, the resins of each layer do not need to be different, so they can be made of the same resin.

[0011] The groove may be, for example, a tear line that is the starting point of a crack.

[0012] The present invention can also be characterized as a resin part having a plate-shaped portion with a design surface and a groove provided on the back surface opposite the design surface, wherein the plate-shaped portion has a first layer having the groove and injection-molded from resin, and a second layer having the design surface, provided on the opposite side of the groove in the first layer, and injection-molded from resin. [Effects of the Invention]

[0013] As described above, according to the present invention, when a resin part having a plate-shaped portion with a groove on the surface opposite the design surface is injection molded, it is possible to prevent poor appearance of the design surface without painting or changing the design after molding. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. [Figure 2] FIG. 2 is a cross-sectional view taken along line XX in FIG. [Figure 3] FIG. 3 is an enlarged view of FIG. [Figure 4] 2 is a cross-sectional view of a mold for molding the airbag cover of FIG. 1, showing a state in which a first cavity has been formed. [Figure 5] FIG. 4 is a cross-sectional view showing a state in which the first cavity is filled with resin. [Figure 6] FIG. 4 is a cross-sectional view showing a state in which a second cavity is formed by the mold. [Figure 7] FIG. 4 is a cross-sectional view showing a state in which the second cavity is filled with resin. [Figure 8]FIG. 10 is a cross-sectional view of a mold according to another embodiment, showing a state in which a first cavity is filled with resin. [Figure 9] 9 is a cross-sectional view showing a state in which a second cavity formed by the mold of FIG. 8 is filled with resin. [Figure 10] FIG. 10 is a cross-sectional view of a mold according to yet another embodiment. [Figure 11] 11 is a cross-sectional view showing a state in which the mold of FIG. 10 is clamped and the cavity is filled with resin. [Figure 12] FIG. 12 is a cross-sectional view showing a state in which the mold of FIG. 11 is opened. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] 1 and 2 show an airbag cover 1 as a resin part according to one embodiment of the present invention. The airbag cover 1 has a plate-shaped design surface portion 2 (plate-shaped portion) having a design surface 4, and side portions 3 extending from the design surface portion 2 to the side opposite the design surface 4. In the illustrated example, four plate-shaped side portions 3 are arranged in a cylindrical shape.

[0017] The design surface portion 2 constitutes a part of the vehicle's instrument panel. The design surface portion 2 has a design surface 4 and a tear line 6 provided on a back surface 5 opposite the design surface 4. The tear line 6 is a groove that becomes the starting point for cracks when the airbag deploys. In the cross section (cross section perpendicular to the extension direction) shown in FIG. 2, the tear line 6 has a groove width that narrows in the thickness direction as it approaches the design surface 4, and in the illustrated example, it has a V-shape. In this embodiment, the tear line 6 is provided in an H-shape on the back surface 5 of the design surface portion 2 (see FIG. 1). The shape of the tear line 6 is not limited to this, and various shapes can be used depending on the type of crack that occurs when the airbag deploys.

[0018] The design surface portion 2 has a first layer 11 that forms the back surface 5 and a second layer 12 that forms the design surface 4 (see FIG. 2). A tear line 6 is provided in the first layer 11. As shown enlarged in FIG. 3, the bottom (tip) of the tear line 6 does not reach the second layer 12, and the entire tear line 6 is provided in the first layer 11. In this way, the design surface portion 2 has a two-layer structure consisting of the first layer 11 and the second layer 12 at least in the area where the tear line 6 is formed, and in the illustrated example, the entire design surface portion 2 has a two-layer structure.

[0019] The first layer 11 has a substantially constant thickness except for the area where the tear line 6 is formed. The second layer 12 has a substantially constant thickness throughout. The thickness t1 of the first layer 11 in the area other than the tear line 6 is thicker than the thickness t2 of the second layer 12. The minimum thickness t3 of the first layer 11 in the area where the tear line 6 is formed is, for example, equal to or less than the thickness t2 of the second layer 12, and preferably equal to or less than half of t2. The bottom of the tear line 6 may contact the second layer 12 (i.e., t3 = 0), but the tear line 6 does not extend into the second layer 12, and no thin portion due to the tear line 6 is formed in the second layer 12. The first layer 11 and the second layer 12 are formed of the same resin. In the illustrated example, the first layer 11 and the four side portions 3 are continuously formed of the same material (see FIG. 2).

[0020] The airbag cover 1 is formed by an injection molding method according to one embodiment of the present invention. The injection molding method for the airbag cover 1 will be described below. As shown in Fig. 2, the design surface portion 2 of the airbag cover 1 is slightly inclined and slightly curved with respect to a plane perpendicular to the side portion 3. However, in Figs. 4 to 12, for the sake of simplicity, the design surface portion 2 and the cavity for molding it are shown as flat plates perpendicular to the side portion 3.

[0021] FIG. 4 shows the molding die for the airbag cover 1, and includes a fixed die 21 and a movable die 22. The fixed die 21 is attached to a fixed platen (not shown). The fixed die 21 includes a gate 23, a runner forming surface 24, and a design surface portion molding surface 25. The gate 23 may be a valve gate that can be opened and closed by a valve pin, or an open gate that is always open. The movable die 22 is attached to a movable platen (not shown) and is movable toward and away from the fixed die 21 (left and right in the figure) by a driving means (not shown). The movable die 22 includes a runner forming surface 26, a design surface portion molding surface 27, and a side portion molding portion 28. The design surface portion molding surface 27 of the movable die 22 is provided with a protrusion 29 for molding the tear line 6.

[0022] First, as shown in FIG. 4 , the fixed mold 21 and the movable mold 22 are clamped together to form a first runner 30 between the runner forming surface 24 of the fixed mold 21 and the runner forming surface 26 of the movable mold 22, and to form a first cavity 31 between the design surface portion molding surface 25 of the fixed mold 21 and the design surface portion molding surface 27 and side portion molding portion 28 of the movable mold 22. Then, as shown in FIG. 5 , molten resin is injected into the first cavity 31 through the gate 23 and the first runner 30. As a result, the first layer 11 and side portion 3 made of resin solidified in the first cavity 31 and the first runner resin portion 32 made of resin solidified in the first runner 30 are integrally formed. At this time, a tear line 6 is formed on the back surface 5 of the first layer 11 by the protrusion 29 provided on the design surface portion molding surface 27 of the movable mold 22.

[0023] Next, as shown in FIG. 6 , the movable mold 22 is retracted to the side away from the fixed mold 21 (to the right in the figure). At this time, the first layer 11, side portion 3, and first runner resin portion 32, which were molded earlier, move together while remaining fixed to the movable mold 22, and move away from the design surface portion molding surface 25 and the runner forming surface 24 of the fixed mold 21. At this time, in order to move the integrated unit of the first layer 11, side portion 3, and first runner resin portion 32 together with the movable mold 22, the movable mold 22 may be provided with an undercut portion that engages with the integrated unit in the mold opening direction. As the integrated unit moves away from the fixed mold 21, a second runner 34 is formed between the runner forming surface 24 of the fixed mold 21 and the first runner resin portion 32, and a second cavity 36 is formed between the design surface portion molding surface 25 of the fixed mold 21 and the first layer 11.

[0024] 7, molten resin is injected into the second cavity 36 through the gate 23 and the second runner 34. As a result, a second layer 12 made of the resin solidified in the second cavity 36 and a second runner resin portion 37 made of the resin solidified in the second runner 34 are integrally formed. At this time, the molten resin filled in the second runner 34 and the second cavity 36 comes into contact with the first layer 11 and first runner resin portion 32 made of the same material that have solidified earlier, thereby forming the second layer 12 and the second runner resin portion 37 and simultaneously bonding them to the first layer 11 and the first runner resin portion 32, respectively. As a result, the airbag cover 1 made of the design surface portion 2 and side portion 3 having the first layer 11 and second layer 12 and the scrap portion 38 made of the first runner resin portion 32 and the second runner resin portion 37 are integrally formed. It should be noted that the resin injected into the second runner 34 and the second cavity 36 is the same as the resin injected into the first runner 30 and the first cavity 31, but in Figure 7, these resins are shown with hatching in different directions to make it easier to understand.

[0025] Thereafter, the movable die 22 is further moved away from the fixed die 21 to open the die, and the molded product is removed from the die. Then, the airbag cover 1 and the scrap portion 38 are separated, thereby completing the airbag cover 1 shown in Figures 1 and 2.

[0026] As described above, when tear line 6 is formed simultaneously with the formation of first layer 11 (see FIG. 5), the thickness of first layer 11 changes suddenly where tear line 6 is formed, and therefore, on the surface of first layer 11 opposite tear line 6 (left side in the figure), an appearance defect 33 such as uneven gloss is formed in the area that overlaps with tear line 6 in the thickness direction. In this embodiment, as shown in FIG. 7, by providing second layer 12 on the side of first layer 11 opposite tear line 6 (left side in the figure), the surface of first layer 11 opposite tear line 6 is covered by second layer 12, and therefore the appearance defect 33 formed on this surface can be hidden.

[0027] On the other hand, no grooves or the like are provided in the second layer 12, and the thickness of the second layer 12 is approximately constant throughout. In this embodiment, the movable mold 22 is retracted to form the second cavity 36, and therefore the thickness of the second layer 12 molded in the second cavity 36 in the mold opening / closing direction is constant throughout. As such, since the thickness of the second layer 12 is approximately constant, no defective appearance such as uneven gloss is formed on the design surface 4 of the second layer 12. As a result, no defective appearance such as uneven gloss is formed on the design surface 4 of the design surface portion 2, thereby improving quality.

[0028] 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.

[0029] In the above embodiment, the second cavity 36 is formed by moving the movable mold 22, but this is not limiting. For example, in the embodiment shown in Figures 8 and 9, a movable block 41 is provided in the fixed mold 21, and the second cavity 36 is formed by moving this movable block 41. Specifically, the fixed mold 21 has a fixed mold main body 40 attached to a fixed platen (not shown), and a movable block 41 that is movable relative to the fixed mold main body 40. The movable block 41 is movable in the mold opening / closing direction by a driving means (not shown).

[0030] 8, the fixed mold body 40 and the movable mold 22 are clamped together, and the movable block 41 is brought into contact with the movable mold 22. This forms a first cavity 31 between the molding surface 42 of the movable block 41 and the decorative surface portion molding surface 27 and side portion molding portion 28 of the movable mold 22. Molten resin is injected into this first cavity 31 from a gate (not shown), thereby integrally forming the first layer 11 having the tear line 6 and the side portion 3.

[0031] 9, while maintaining the fixed mold body 40 and the movable mold 22 clamped together, the movable block 41 is moved away from the movable mold 22 (to the left in the figure), and the molding surface 42 of the movable block 41 is moved away from the first layer 11 fixed to the movable mold 22. As a result, a second cavity 36 is formed by the molding surface 42 of the movable block 41 and the first layer 11. Molten resin is injected into this second cavity 36 via a gate 43 and a runner 44, so that the second layer 12 having the design surface 4 is formed and is integrated with the first layer 11.

[0032] However, if the thickness of the second layer 12 of the design surface portion 2 is thin, the thickness of the second cavity 36 will also be thin, making it difficult to completely fill the second cavity 36 with molten resin. Therefore, in the above-mentioned injection molding method, compression injection molding may be applied when molding the second layer 12. Specifically, after the molten resin is injected into the second cavity 36, the movable mold 22 or the movable block 41 is moved in a direction to reduce the volume of the second cavity 36 before the molten resin completely solidifies. In this way, even if the second cavity 36 is not completely filled with molten resin, the volume of the second cavity 36 is reduced by moving the movable mold 22 or the movable block 41, making it possible to fill the second cavity 36 with molten resin up to the edge.

[0033] In the above embodiment, the first layer 11 and the second layer 12 are molded using the same mold. However, this is not limiting and the first layer 11 and the second layer 12 may be molded using different molds. For example, FIG. 10 shows a rotational molding device having two sets of molds. This rotational molding device has a first fixed mold 51 and a first movable mold 52, and a second fixed mold 53 and a second movable mold 54. The first fixed mold 51 and the second fixed mold 53 have the same shape, and each has a design surface molding surface 27 having a protrusion 29 and a side molding portion 28 for molding the side portion 3. The first movable mold 52 has a molding surface 55 for molding the first layer 11, and the second movable mold 54 has a molding surface 56 for molding the second layer 12. The first fixed mold 51 and the second fixed mold 53 are fixed to a rotary plate 57 that can rotate about a rotation axis L. The first movable die 52 and the second movable die 54 can be moved toward and away from the first fixed die 51 and the second fixed die 53 (left and right directions in the drawing) by a driving means not shown.

[0034] In the state shown in FIG. 10 , the first layer 11, which has just been molded, is fixed to the second fixed mold 53. Then, as shown in FIG. 11 , the first movable mold 52 and the second movable mold 54 are brought close to the first fixed mold 51 and the second fixed mold 53, respectively, and clamped. As a result, a first cavity 31 is formed between the design surface portion molding surface 27 of the first fixed mold 51 and the molding surface 55 of the first movable mold 52, and a second cavity 36 is formed between the first layer 11 fixed to the second fixed mold 53 and the molding surface 56 of the second movable mold 54. The first layer 11 is molded by injecting molten resin into the first cavity 31. The second layer 12 is molded by injecting molten resin into the second cavity 36, and is integrated with the first layer 11, thereby forming the airbag cover 1 consisting of the design surface portion 2 and the side portion 3.

[0035] Thereafter, the molds are opened as shown in FIG. 12, and the molded article including the airbag cover 1 is removed from the mold (see arrow A). Then, the rotating plate 57 is rotated 180° as shown by arrow B, thereby switching the first fixed mold 51 and the second fixed mold 53 (see the symbols in parentheses in FIG. 10). In this state, as shown in FIG. 11 (see the symbols in parentheses), the first movable mold 52 and the second movable mold 54 are moved close to the second fixed mold 53 and the first fixed mold 51, respectively, to clamp the molds, and molten resin is injected into the first cavity 31 and the second cavity 36. Thereafter, the molds are opened as shown in FIG. 12 (see the symbols in parentheses), and the molded article is removed, after which the rotating plate 57 is rotated 180°. By repeating the above steps, the airbag covers 1 are successively formed.

[0036] In the above embodiment, the first layer 11 and the second layer 12 are formed from the same resin, but this is not limiting and the first layer 11 and the second layer 12 may be formed from different resins (resins with different types and / or compounding ratios of base resins and / or fillers). For example, because the first layer 11 does not have the design surface 4, it may be formed from a cheaper resin than the second layer 12. In this case, it is necessary to use a mold having a structure that allows different resins to be injected into the first cavity 31 and the second cavity 36. [Explanation of symbols]

[0037] 1 Airbag cover (plastic part) 2 Design surface part (plate-shaped part) 3 Side 4 Design surface 5 Back side 6 Tear line (groove) 11 1st layer 12 2nd layer 21 Fixed type 22 Movable type Gate 23 24 Runner forming surface 25 Design surface molding surface 26 Runner forming surface 27 Design surface molding surface 28 Side molding 29 Convex part 30 First Runner 31 First cavity 32 Runner resin part 33. Defective appearance 34 Second Runner 36 Second cavity 37 Runner resin part 38 Scrap Department

Claims

1. A method for injection molding a resin part having a plate-shaped portion having a design surface and a groove provided on a back surface opposite to the design surface, injection molding the first layer having the grooves; and injection molding a second layer having the design surface on the side of the first layer opposite the groove.

2. A resin part including a plate-shaped portion having a design surface and a groove provided on a back surface opposite to the design surface, The plate-shaped portion is a first layer having the groove and injection-molded from resin; a second layer having the design surface, the second layer being provided on the opposite side of the groove in the first layer, and injection-molded from resin;

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