Resin molded product and method for manufacturing the resin molded product

Abstract

To provide resin molded products and a method for manufacturing the resin molded products in which the generation of secondary weld lines can be suppressed without any restrictions on the external shape.SOLUTION: The resin molded product contains thermoplastic resin and needle and / or plate-shaped filler. It has a gradual change in thickness, and a primary weld line on the surface extends in the vicinity of the above gradual change, and a confluence interface of the thermoplastic resin extending from the above primary weld line penetrates from thicker to thinner in the center of the thickness direction, and the filler in the above confluence interface has its longitudinal direction in the fillers at the above confluence interface are oriented in the direction that intersects the thickness direction of the above plastic molded product, thus preventing the occurrence of secondary weld lines.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a resin molded product and a method for manufacturing the resin molded product, and more particularly, to an injection-molded resin molded product and a method for manufacturing the resin molded product.

Background Art

[0002] The injection molding method can produce large-sized molded products and molded products with complex shapes, and in addition, since the number of steps is relatively small, cost reduction is possible, and it is used in a wide range of fields.

[0003] For example, large-sized parts such as automobile bumpers and instrument panels are often manufactured by the injection molding method, and for such large-sized parts, an injection material containing a filler is used to improve their rigidity and strength.

[0004] When injecting a large-sized part, in order to shorten the length of the flow of the injection material in the mold, the injection material is often injected from a plurality of gates. Also, when the molded product has a shape with an opening, the injection material flows from two directions and merges, so a merging interface of the injection material is formed in the resin molded product.

[0005] The injection material injected into the cavity flows so as to spout from the central flow layer of the cavity toward the mold side along the fountain flow at the tip. Therefore, when the filler is needle-shaped or plate-shaped, the filler is oriented standing in the thickness direction of the resin molded product at the above-mentioned merging interface.

[0006] And, as the injection material cools and solidifies, even if the molten thermoplastic resin shrinks in volume, the filler in the injection material is originally solid, so almost no volume shrinkage occurs.

[0007] Therefore, if there is a filler oriented standing in the thickness direction of the part, only that part is prevented from shrinking in the thickness direction, and an appearance defect (secondary weld line) in which the vicinity of the merging interface bulges occurs.

[0008] Patent Document 1 discloses that, at the resin confluence part in the cavity, by rotating a part of the mold surface of the mold element that contacts the injection material on the spot, an external force is applied to the injection material to mechanically change the orientation of the filler and suppress the secondary weld line.

Prior Art Document

Patent Document

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, in the method described in Patent Document 1, since the surface of the mold is rotated to apply an external force to the injection material, the rotating part of the mold must be flat, and it is difficult to suppress the secondary weld line generated in the curved surface part of the resin molded product. In addition, the mold becomes complicated and the cost increases.

[0011] The present invention has been made in view of such problems of the prior art, and an object thereof is to provide a resin molded product capable of suppressing the generation of a secondary weld line without being restricted by the external appearance shape, and a method for manufacturing the resin molded product.

Means for Solving the Problems

[0012] As a result of intensive studies to achieve the above object, the present inventor has found that by thinning a part of the resin molded product to provide a gradual change part where the plate thickness gradually changes, a difference occurs in the cooling rate of the injection material across the gradual change part, and the filler is oriented in the in - plane direction, thus completing the present invention.

[0013] That is, the resin molded product of the present invention contains a thermoplastic resin and needle - shaped and / or plate - shaped fillers. And it has a creep portion with a gradually changing thickness, a primary weld line on the surface extends in the vicinity of the creep portion, a confluence interface of the thermoplastic resin extending from the primary weld line penetrates from the thicker side to the thinner side at the central portion in the thickness direction, and the filler of the confluence interface is oriented in a direction intersecting the thickness direction of the resin molded product in its longitudinal direction.

[0014] Moreover, the method for manufacturing a resin molded product of the present invention is a method for manufacturing a resin molded product for manufacturing the resin molded product, and includes a step of manufacturing a mold and a molding step of injecting an injection material into the mold. And the step of manufacturing the mold is analyzing the flow of the injection material in the mold from the mesh model of the resin molded product, and confirming the generation position of the primary weld line and the generation direction of the secondary weld line with respect to the primary weld line; changing the mesh model of the resin molded product to a mesh model in which a creep portion with a gradually changing thickness and a thin portion connected to the creep portion are formed based on the generation position of the primary weld line; analyzing the flow of the injection material in the mold from the changed mesh model, and confirming whether a primary weld line is generated in the creep portion, and includes repeating the step of changing the mesh model and the step of confirming whether a primary weld line is generated in the creep portion, and manufacturing a mold based on the mesh model in which a primary weld line is generated in the creep portion.

Advantages of the Invention

[0015] According to the present invention, a part of the resin molded product is thinned to provide a creep portion with a gradually changing thickness, a difference in the cooling rate of the injection material is caused across the creep portion, and the filler is oriented in the in-plane direction. Therefore, it is possible to provide a resin molded product that suppresses the generation of secondary weld lines without being restricted by the external shape, and a method for manufacturing a resin molded product.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

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Figure 9

Mode for Carrying Out the Invention

[0017] The resin molded product of the present invention will be described in detail. The resin molded product of the present invention contains a thermoplastic resin and needle-shaped and / or plate-shaped fillers. And, as shown in FIG. 1, it has a creep part whose thickness gradually changes, and has a thick part and a thin part sandwiching the creep part.

[0018] The above-mentioned creep part is provided in the vicinity of the location where the injection material converges during injection molding. Therefore, since the injection material converges in the vicinity of the creep part, a primary weld line extends along the creep part on the surface of the resin molded product near the creep part.

[0019] Further, the resin molded product may, if necessary, be provided with another creep part on the side opposite to the creep part side of the thin part, and a thick part connected thereto may be formed.

[0020] This optionally provided creep portion is provided from the viewpoint of the strength balance of the resin molded product due to the formation of the thin-walled portion, etc., and is not provided for preventing the generation of the secondary weld line. Therefore, it is not necessary for the primary weld line to extend in the vicinity of all the creep portions of the resin molded product.

[0021] In the present invention, "in the vicinity of the creep portion" means the range obtained by combining the entire creep portion, the range from the boundary between the thick-walled portion and the creep portion to the thick-walled portion side by 10 mm, and the range from the boundary between the thin-walled portion and the creep portion to the thin-walled portion side by 10 mm.

[0022] Here, in a general resin molded product with a constant thickness, since the cooling rates of the flow fronts of the merged injection materials are the same, the merged injection materials stop flowing almost simultaneously. And when the pressure applied to the merging interface is unbalanced, as shown by the dotted line in Fig. 2, a bow-shaped merging interface is formed, the fillers in the vicinity of the merging interface are oriented standing in the thickness direction of the resin molded product, and a secondary weld line is formed at a position deviated from the primary weld line.

[0023] Since the resin molded product of the present invention has different thicknesses with the creep portion in between, the injection materials merged in the vicinity of the creep portion from the in-plane direction of the resin molded product have the thinner injection material cooled first and the flow stopped, while the thicker injection material still has fluidity.

[0024] Therefore, a pressure difference occurs at the merging interface in the pressure holding process, as shown by the size of the arrow in Fig. 3, and pressure is applied from the thicker injection material toward the thinner injection material.

[0025] Also, looking at the out-of-plane direction of the resin molded product, since the injection material is cooled by contacting the mold, as shown in Fig. 4, even when the injection material on the mold side solidifies, the injection material at the center still has fluidity.

[0026] And at the confluence interface, since pressure is applied from the thicker side to the thinner side as described above, as shown in Fig. 5, at the center in the plate thickness direction, the injection material penetrates from the thicker side to the thinner side of the plate thickness, and a confluence interface is formed where the penetration tip bends at an acute angle.

[0027] The filler near this confluence interface is oriented along the confluence interface bent at the acute angle, so its longitudinal direction is oriented in a direction intersecting the plate thickness direction of the resin molded product.

[0028] Therefore, the proportion of the filler in the thickness direction of the confluence interface decreases, the difference in shrinkage between the vicinity of the confluence interface and other parts due to the volume shrinkage of the thermoplastic resin becomes smaller, and the entire injection material shrinks uniformly, so the generation of the secondary weld line is prevented.

[0029] It is preferable that there are few fillers near the confluence interface whose longitudinal direction and the plate thickness direction of the resin molded product form an angle of less than 30°, and the thickness of the region where the standing fillers exist is preferably 0.7 mm or less.

[0030] The filler existing near the confluence interface can be confirmed by observing the cross-sectional image of the resin molded product. In the present invention, the filler existing near the confluence interface was observed, and the thickness of the region where the standing fillers exist was measured.

[0031] The penetration length of the confluence interface, that is, the length from the root where the curvature of the confluence interface changes rapidly at the center in the plate thickness direction to the penetration tip, is preferably 2 mm or more.

[0032] And by smoothing the surface side of the resin molded product and inclining only the back side to form the creep portion, there is no change in appearance due to the formation of the creep portion, and appearance defects due to the secondary weld line can be prevented.

[0033] Furthermore, in the resin molded article of the present invention, since the confluence interface is bent, even if stress is applied in the vicinity of the confluence interface, this stress is dispersed at the bent confluence interface. Therefore, compared with the case where the confluence interface is planar, a decrease in strength in the vicinity of the confluence interface is prevented.

[0034] In the present invention, "the longitudinal direction of the filler is oriented in a direction intersecting the thickness direction of the resin molded article" means that it is sufficient if the filler at the confluence interface is inclined with respect to the thickness direction to such an extent that the generation of a secondary weld line can be prevented, and it does not mean that there is no filler facing the thickness direction at the penetration tip. In addition, in the cross-sectional views of this specification, only the fillers near the surface and near the confluence interface of the resin molded article are shown.

[0035] The above-mentioned creep portion depends on the thickness of the resin molded article. For example, when the thickness of the resin molded article is 1.5 to 5 mm, the amount of change in thickness is preferably 0.5 mm to 1.5 mm, and the length in the direction in which the thickness changes is preferably 30 mm or more.

[0036] Since the thickness of the resin molded article changes gradually rather than abruptly, in the process of solidification of the injection material, a portion having fluidity at the center in the thickness direction remains in a wedge shape. Therefore, the confluence interface penetrates deeply toward the thinner side of the thickness, and its tip becomes an acute angle.

[0037] Therefore, the fillers in the vicinity of the confluence interface are oriented in a state where their longitudinal directions lie in a direction substantially orthogonal to the thickness direction, so that appearance defects due to secondary weld lines can be prevented.

[0038] As the above-mentioned thermoplastic resin, conventionally known resins used in injection molding can be used. For example, polypropylene resin, polyamide resin, thermoplastic urethane resin, thermoplastic polyester resin, acrylic resin, polyolefin resin, etc. can be mentioned.

[0039] In addition, as the filler, in addition to acicular or plate-like fillers such as talc, mica, graphite, wollastonite, glass flakes, barium sulfate, calcium carbonate, etc., carbon fibers such as PAN-based and pitch-based, glass fibers, etc. can be used, and the content of the filler in the resin molded product is preferably 10 to 30% by mass.

[0040] Next, a method for manufacturing a resin molded product capable of preventing the generation of secondary weld lines will be described. As described above, since the generation of secondary weld lines can be prevented by forming a confluence interface in the vicinity of the creep portion, in the present invention, a mold in which a creep portion is formed in the vicinity of the position where the confluence interface is formed during injection molding is used. The manufacturing procedure of the mold is shown in FIG. 6.

[0041] Specifically, from the CAD shape data of the resin molded product having a desired shape, a mesh model capable of performing a flow analysis of the injection material is created by the finite element method, the finite volume method, or the like.

[0042] Based on this mesh model, injection molding conditions such as injection pressure and gate position, and physical property data of the injection material, the flow of the injection material in the mold is analyzed, and from the analysis data, the generation position of the primary weld line and the generation direction of the secondary weld line with respect to the primary weld line are confirmed.

[0043] Then, based on the generation position of the primary weld line and the generation direction of the secondary weld line, the mesh model is changed to a mesh model provided with a creep portion in the vicinity of the generation position of the primary weld line.

[0044] At this time, by setting the position of the creep portion so that a thin-walled portion connected to the creep portion is formed on the side where the secondary weld line is generated, the injection material on the thin-walled portion side loses fluidity first, so that a confluence interface is easily formed in the vicinity of the creep portion.

[0045] Depending on the gate position and the shape of the resin product, the pressure from the thin-wall part side may be higher than that from the thick-wall part side, and the position of the creep part can be set so that a thin-wall part leading to the creep part is formed on the side opposite to the side where the secondary weld line is generated.

[0046] Then, similarly, based on the modified mesh model having the above-mentioned creep part, the flow of the injection material in the mold is analyzed, and it is confirmed whether a primary weld line is generated in the above-mentioned creep part.

[0047] When the primary weld line does not occur in the set creep part, the mesh model is again changed to a mesh model with different positions, lengths of the creep part, and thicknesses of the thin-wall part, and the flow of the injection material is analyzed. The mesh model is repeatedly changed until a primary weld line is generated in the above-mentioned creep part.

[0048] Then, when a primary weld line is generated in the above-mentioned creep part, a mold is fabricated based on the mesh model in which this primary weld line is generated in the creep part.

[0049] By performing injection molding under the injection molding conditions in which the above-mentioned flow analysis was performed using the fabricated mold, a primary weld line is formed in the vicinity of the creep part, and a resin molded product of the present invention in which the filler at the confluence interface is oriented in a direction intersecting the thickness direction can be obtained. An example of the tip shape of the confluence interface formed in the vicinity of the confluence interface of the resin molded product is shown in FIG. 7.

[0050] Note that the flow analysis of the injection material simulates the flow of the injection material using a mesh model, and does not completely match the flow state of the injection material when actually fabricating a resin molded product. Therefore, the fact that a primary weld line is generated in the creep part in the mesh model does not mean that a resin molded product with a primary weld line formed in the creep part can be obtained. In the resin molded product, a primary weld line is formed in the vicinity of the creep part.

[0051] According to such a method for manufacturing a resin molded product, since it is not necessary to provide a mover or a valve gate in the mold, the cost of the mold can be reduced, and since it is not necessary to control these movable mechanisms during molding, the molding conditions are simplified and the robustness is improved.

Example

[0052] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0053] [Example] A thin-walled portion with a thickness of 1.5 mm was provided at the center of a cavity with a length of 320 mm and a width of 80 mm, a creep portion with a length of 60 mm was provided on one side of this thin-walled portion, and a creep portion with a length of 30 mm was provided on the other side. The cavity was set such that thick-walled portions with a thickness of 2.5 mm were formed at both ends so that the amount of change in the thickness of these creep portions was 1.0 mm.

[0054] From both ends of this cavity, a polypropylene resin containing 20% by mass of plate-shaped talc was injected and joined at the center of the creep portion with a length of 60 mm to obtain a plate-shaped resin molded product.

[0055] Also, while fixing the amount of change in the thickness of the creep portion at 1.0 mm, the thickness of the thin-walled portion and the thickness of the thick-walled portion were changed to obtain a plate-shaped resin molded product.

[0056] [Comparative Example] A plate-shaped resin molded product was obtained in the same manner as in Example 1, except that a cavity with a constant thickness of 1.5 mm was set without providing a creep portion. Also, similarly, a plate-shaped resin molded product was obtained by changing the thickness without providing a creep portion.

[0057] The cross-sections of the resin molded products of the example and the comparative example were observed. In the resin molded product of the example, the fillers near the confluence interface were oriented in a direction intersecting the plate thickness direction, while in the resin molded product of the comparative example, the fillers near the confluence interface were oriented standing in the plate thickness direction.

[0058] The relationship between the plate thickness of the examples and the comparative examples and the amount of swelling of the secondary weld line is shown in Fig. 8, and a schematic diagram of the orientation state of the filler in the vicinity of the creep portion of the examples and the comparative examples is shown in Fig. 9.

[0059] When the plate thickness was 2.5 mm, the thickness (L) of the region where there was a filler with an angle of less than 30° between the longitudinal direction of the filler existing near the joining interface and the thickness direction of the resin molded product was 0.2 mm for the resin molded product of the example and 1.6 mm for the resin molded product of the comparative example. Also, all the examples with varying plate thicknesses were 0.7 mm or less, while the comparative examples exceeded 0.7 mm.

[0060] From Fig. 8, it can be seen that in the resin molded product of the present invention, the amount of swelling of the secondary weld line is suppressed to about 1 / 3 of that of the resin molded product of the comparative example, and it is possible to prevent the occurrence of appearance defects caused by the secondary weld line.

Explanation of symbols

[0061] 1 Resin molded product 2 Creep portion 3 Thin-walled portion 4 Thick-walled portion 5 Joining interface 51 Penetration portion 6 Primary weld line 7 Secondary weld line 8 Filler 9 Solidified portion 10 Flow layer

Claims

1. A resin molded product containing a thermoplastic resin and needle-shaped and / or plate-shaped fillers, having a creep portion with a gradually changing thickness, wherein a primary weld line on the surface extends in the vicinity of the creep portion, a confluence interface of the thermoplastic resin extending from the primary weld line penetrates from the thicker side to the thinner side at the central portion in the thickness direction, and the fillers at the confluence interface are oriented in a direction in which the longitudinal direction intersects the thickness direction of the resin molded product. A resin molded product characterized by this.

2. The thickness of the region where there are fillers with an angle of less than 30° between the longitudinal direction and the thickness direction of the resin molded product existing in the vicinity of the confluence interface is 0.7 mm or less. The resin molded product according to Claim 1, characterized by this.

3. The amount of change in thickness in the creep portion is 0.5 mm to 1.5 mm. The resin molded product according to Claim 1 or 2, characterized by this.

4. The length in the direction in which the thickness of the creep portion changes is 30 mm or more. The resin molded product according to any one of Claims 1 to 3, characterized by this.

5. The thickness of the thick portion connected to the creep portion is 1.5 to 5 mm. The resin molded product according to any one of Claims 1 to 4, characterized by this.

6. A method for manufacturing a resin molded product according to any one of Claims 1 to 5, having a step of manufacturing a mold and a molding step of injecting an injection material into the mold, wherein the step of manufacturing the mold includes a step of analyzing the flow of the injection material in the mold from a mesh model of the resin molded product and confirming the generation position of the primary weld line and the generation direction of the secondary weld line with respect to the primary weld line, a step of changing the mesh model of the resin molded product to a mesh model in which a creep portion with a gradually changing thickness and a thin portion connected to the creep portion are formed based on the generation position of the primary weld line, and a step of analyzing the flow of the injection material in the mold from the changed mesh model and confirming whether a primary weld line is generated in the creep portion. The method for manufacturing a resin molded product, characterized by including a process of repeatedly performing the step of changing the mesh model and the step of confirming whether a primary weld line is generated in the creep portion, and manufacturing a mold based on the mesh model in which a primary weld line is generated in the creep portion.

7. The method for manufacturing a resin molded product according to claim 6, characterized in that the step of changing the mesh model includes a process of forming a thin portion on the side where the secondary weld line is generated.

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