Resin molding die

Abstract

To provide a resin molding die capable of preventing both generation of burrs and occurrence of molding defects and molding high-quality resin molded products.SOLUTION: A resin molding die 10 comprises a pair of dies 11, 12, and a resin filling space 13 formed between the pair of dies 11, 12 by clamping of the pair of dies 11, 12. A tapered space 14 having a tapered shape toward mating portions 15, 16 is provided integrally with the filling space 13 in a portion of the filling space 13 adjacent to the mating portions 15, 16 of the pair of dies 11, 12.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a mold for molding a resin, and more particularly to a mold for molding a resin in which a space for filling a resin is formed between a pair of molds by clamping the pair of molds together. [Background technology]

[0002] Conventionally, injection molding has been used to mold automotive resin parts. In injection molding, a pair of molds, one of which is movable and the other is fixed, are clamped together to form a resin filling space between the pair of molds. A specific resin is then injected into this filling space, filling it, and solidifying it to form a resin molded product with a shape corresponding to the filling space (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 4-107021 Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of injection molding, a gap inevitably occurs between the mating surfaces of a pair of molds. Specifically, as shown in FIG. 4 , in this type of resin molding mold 10, a filling space 13 formed between a pair of molds 11 and 12 by the mold clamping operation is usually filled with air. Therefore, during injection molding, when resin is injected into this filling space 13, it is necessary to release the air from the filling space 13. From this perspective, it is difficult to completely seal the mating surfaces 15 and 16 of the pair of molds 11 and 12, and a small gap 18 occurs between the pair of mating surfaces 15 and 16 in the clamped state. If resin seeps into this small gap 18, a very thin film-like or extremely thin thread-like solidified portion (both of which are referred to as flash 2) may remain in the resin molded product 1 at the boundary between the mating surfaces 15 and 16 (also referred to as the parting line), as shown by the two-dot chain line in FIG. 4 .

[0005] This type of burr is considered a molding defect if it remains on the design surface of a resin molded product. Alternatively, if burrs separate from the resin molded product and adhere to the surface of the resin molded product (especially the design surface), they can cause so-called "lump defects" in subsequent processes, such as the painting process. Therefore, when these burrs occur, they must be removed at the appropriate time, which increases the number of steps required.

[0006] One way to prevent this type of flash is to lower the resin pressure (equivalent to the injection pressure in injection molding), but lowering the resin pressure can lead to molding defects such as sink marks and welds, so depending on the conditions, it can be difficult to prevent both flash and molding defects such as sink marks.For example, it could be considered to prevent gaps from occurring by forcing the mating surfaces of the molds to come into stronger contact with each other, but then the air in the filled space cannot escape through the gaps, which could lead to new molding defects such as air bubbles.

[0007] The above-mentioned problems are not limited to injection molding, but can occur in almost any process in which a resin is molded into a predetermined shape using a mold, such as blow molding or compression molding.

[0008] In view of the above circumstances, the technical problem to be solved in this specification is to provide a resin molding die that can prevent both the occurrence of burrs and molding defects and produce high-quality resin molded products. [Means for solving the problem]

[0009] The above-mentioned problems are solved by the resin molding die according to the present invention. That is, this die is a resin molding die in which a filling space for resin is formed between a pair of dies by clamping the dies together, and is characterized in that a tapered space that tapers toward the mating portion is provided integrally with the filling space in a portion of the filling space adjacent to the mating portion of the pair of dies.

[0010] In this way, by forming a tapered space tapered toward the mating portion of the pair of molds integrally with the resin filling space, the resin can be filled and solidified into the tapered space at the initial stage of filling (here, before the filling space is filled with resin). Even if a gap occurs between the pair of mating surfaces that make up the mold mating portion due to the resin solidifying at the entrance of the mold mating portion, the entrance of the mold mating portion is blocked by the solidified portion of the resin that filled the tapered space. This prevents the resin from entering the gap, preventing the formation of burrs that would otherwise solidify if the resin had entered the gap. Furthermore, the mold according to the present invention can suppress the formation of burrs without reducing the resin pressure, allowing the resin to be filled at the same resin pressure as before. This prevents molding defects such as sink marks and welds and enables the production of high-quality resin molded products.

[0011] In the resin molding die according to the present invention, the tapered space may be formed to a size of less than 1 mm.

[0012] The size of the tapered space described above in the resin filling space is important. For example, if the tapered space is too large, even if the resin is filled before the filling space, the filled resin may not cool down quickly enough, and the resin in the tapered space may not solidify when the resin pressure builds up. Therefore, qualitatively, the size should be such that the resin in the tapered space cools sufficiently and solidifies before the resin pressure builds up and the resin flows into the gap between the mating surfaces of the pair of molds. Quantitatively, depending on the type of resin, for example, when molding a general-purpose industrial thermoplastic resin (engineering plastic) such as polypropylene, the tapered space should be less than 1 mm in size, and even better, less than 0.5 mm. Here, a size of less than 1 mm means that the dimension perpendicular to the periphery of the mating surfaces is less than 1 mm (this corresponds to the dimension d1 in Figure 1, described below).

[0013] In addition, in the resin molding die according to the present invention, the tapered space may be formed by a mating surface of one of the pair of dies that constitutes the mating portion and a C-chamfered portion that connects to the mating surface of the other dies.

[0014] When considering the workability of the molding surfaces that make up the tapered space, it would be best to use, for example, an R-shaped chamfer. However, this would result in the molding portion corresponding to the tapered space having an extremely sharp shape, which could cause it to break or fall off after molding, adversely affecting the quality of subsequent processes or the quality of the molded product. In contrast, if the tapered space is configured with one mold mating surface and a C-chamfer that connects to the other mold mating surface, it is possible to prevent breakage or fall off after molding and ensure the quality of subsequent processes or the molded product. Another advantageous feature is that the degree of tapering can be easily adjusted by the chamfer angle. [Effects of the Invention]

[0015] As described above, the resin molding die according to the present invention makes it possible to prevent both the occurrence of burrs and molding defects, and to mold high-quality resin molded products. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view of a main part of a resin molding die according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a main part showing an example of a mode of use of the resin molding die shown in FIG. [Figure 3] FIG. 2 is a cross-sectional view of a main part showing an example of a mode of use of the resin molding die shown in FIG. [Figure 4] FIG. 10 is a cross-sectional view of a main part of a conventional resin molding die. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, the details of a resin molding die according to one embodiment of the present invention will be described with reference to the drawings.

[0018] 1 shows a cross-sectional view of a main portion of a resin molding die 10 according to one embodiment of the present invention. This resin molding die 10 includes a resin filling space 13 formed between a pair of dies 11, 12 by clamping the pair of dies 11, 12, and a tapered space 14 formed integrally with the filling space 13. Each of the dies 11, 12 is provided with a pair of mating surfaces 15, 16 that form a mating portion, and the filling space 13 is formed between the pair of dies 11, 12 by moving (bringing the dies 11, 12 closer together) until these mating surfaces 15, 16 are in close contact with each other. The tapered space 14 is also formed along with the filling space 13.

[0019] The tapered space 14 has a shape that tapers toward the peripheral edges 15a, 16a of the pair of mold mating surfaces 15, 16 that form the mold mating portion. In three dimensions, the tapered space 14 has a three-dimensional shape that corresponds to the peripheral edges 15a, 16a of the pair of mold mating surfaces 15, 16. For example, if the peripheral edges 15a, 16a are annular, the tapered space 14 will also be annular. The cross-sectional shape of the tapered space 14 (here, the shape of the cross section perpendicular to the direction along the peripheral edges 15a, 16a, which is the same direction as the parting line) can be any shape as long as the dimension d1 in the mold clamping direction (the direction in which the mold mating surfaces 15, 16 face each other) decreases toward the peripheral edges 15a, 16a, as shown in FIG. 1, for example. In this embodiment, a tapered space 14 in which the mold clamping direction dimension d1 temporarily decreases is formed by one flat mold mating surface 15 and a C-chamfered portion 17 connected to the other flat mold mating surface 16.

[0020] Next, the size of the tapered space 14 will be described. Due to its function, it is essential that the tapered space 14 be formed to a size that allows the tapered space 14 to be filled with resin and for the filled resin to solidify by cooling before the entire filling space 13 is filled with resin. The larger the size of the tapered space 14 (particularly the mold clamping direction dimension d1), the slower the cooling rate and the longer it takes to solidify, so the above-mentioned requirement corresponds to the upper limit of the mold clamping direction dimension d1 of the tapered space 14. Here, as an example, when injection molding a general-purpose thermoplastic resin such as polypropylene, the size of the tapered space 14 (mold clamping direction dimension d1) should be set to less than 1 mm, and preferably less than 0.5 mm.

[0021] Furthermore, it is essential that the tapered space 14 be formed to a size that allows the resin to flow into the gap 18 between the mold mating surfaces 15, 16 and solidify due to an increase in resin pressure in the clamped state when the tapered space 14 is not present (see FIG. 4). This condition corresponds to the lower limit of the size of the tapered space 14 (here, the dimension d1 in the clamping direction). On the other hand, from the viewpoint of processability, it is essential to set the size of the tapered space 14 so that the dimension d1 in the clamping direction is 0.04 mm or more.

[0022] Next, an example of how the resin molding die 10 having the above-described configuration can be used will be described together with its effects.

[0023] First, a drive unit (not shown) moves a pair of molds 11 and 12 closer to each other to form a resin filling space 13 between the pair of molds 11 and 12, and also forms a tapered space 14 (see FIG. 1). Then, an injection unit (not shown) injects a predetermined resin into the filling space 13 formed between the pair of molds 11 and 12. The injected resin flows into the filling space 13 and also into the tapered space 14 adjacent to the pair of mold mating surfaces 15 and 16 (mold mating portion) of the filling space 13. As described above, the tapered space 14 has a very small mold clamping direction dimension d1, and the mold clamping direction dimension d1 decreases toward the pair of mold mating surfaces 15 and 16 (mold mating portion). Therefore, the resin flowing into the tapered space 14 fills the tapered space 14 at the initial stage of filling (when the filling space 13 is not yet sufficiently filled with resin) and is rapidly cooled and solidified (the state indicated by the two-dot chain line in FIG. 2).

[0024] In this way, the solidified portion 3 is formed in the portion adjacent to the pair of mold mating surfaces 15, 16 (mold mating portion), thereby blocking the entrance to the mold mating portion. Furthermore, the flow of resin near the tapered space 14 is inhibited. Therefore, even if the entire filling space 13 is subsequently filled with resin and the resin pressure increases, the pressurized resin is prevented from penetrating the gap 18 between the pair of mold mating surfaces 15, 16. Meanwhile, once the resin pressure has reached a predetermined level, the entire filling space 13 is filled without leakage. Therefore, a high-quality resin molded product 1 is molded without molding defects such as sink marks (see FIG. 3).

[0025] In this embodiment, the tapered space 14 is formed by one mold mating surface 15 and a C-chamfered portion 17 that connects to the other mold mating surface 16, so the solidified portion 3 as part of the resin molded product 1 has a tapered shape (see FIG. 3). This prevents the solidified portion 3 from becoming extremely sharp, and prevents the solidified portion 3 from being chipped or falling off after molding, which could have an adverse effect on the quality of subsequent processes or molding quality.

[0026] Although one embodiment of the present invention has been described above, the resin molding die according to the present invention can also have other configurations than those described above within the scope of the gist of the invention.

[0027] For example, in the above embodiment, the tapered space 14 is configured by one flat mold mating surface 15 and a C-chamfered portion 17 that connects to the other mold mating surface 16, and the inclination angle θ of this C-chamfered portion 17 with respect to the other mold mating surface 16 is set to 45° (see FIG. 1), but of course this is not limited to this. For example, the inclination angle θ of the C-chamfered portion 17 can be set in the range of 30° to 60°.

[0028] Of course, the shape of the tapered space 14 is arbitrary, and it may be configured by a surface having a shape other than the C-chamfered portion 17. In short, the tapered space 14 can have any shape as long as the mold clamping direction dimension d1 decreases as it approaches the peripheral edges 15a, 16a of the mold mating surfaces 15, 16.

[0029] In the above explanation, the resin molding die 10 according to the present invention is applied to injection molding, but the present invention is not limited to this. It goes without saying that the present invention can be applied to any method of molding resin using a die, such as blow molding or compression molding. [Explanation of symbols]

[0030] 1 Resin molded products 2. Bali 3 Solidification section 10 Resin molding mold 11,12 Mold 13 Filling space 14 Tapering Space 15,16 Mold mating surface 15a, 16a peripheral area 17 C chamfered part 18 Gap d1 Mold clamping direction dimension θ Tilt angle

Claims

[Claim 1] A resin molding die in which a resin filling space is formed inside a pair of dies by clamping the dies together, A resin molding mold, wherein a tapered space tapering toward the mold mating portion is provided integrally with the filling space in a portion of the filling space adjacent to the mold mating portion of the pair of molds.

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