JP3776574B2 - Injection mold and injection molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for injection molding of a resin molded product, particularly a plastic lens, and a mold used therefor.
[0002]
[Prior art]
As a mold used for injection molding of a resin molded product such as a plastic lens, for example, a mold disclosed in Japanese Patent Laid-Open No. 9-29854 is known. An injection molding method using this mold will be described with reference to FIGS.
[0003]
First, as shown in FIG. 1, the molten resin 12 is introduced into the cavity formed between the cavity pin 8, the core 9, and the protruding pins 10 a and 10 b through the sprue 3, runner 4, and gate 5. Fill with injection. At this time, the mold is clamped at a low pressure. Next, as shown in FIGS. 2 and 3, when the cavity pin 8 is advanced to the core 9 side at a high pressure, excess molten resin flows back to the runner 4 side, and a molded product formed in the cavity. 1 and the gate 5 are separated. In FIG. 1, reference numeral 6 denotes a fixed side template, and 7 denotes a movable side template.
[0004]
In the molding method shown in FIGS. 1 to 3, the cavity pin 8 advances to separate the outer peripheral surface of the molded product 1 from the gate 5, but this cutting is performed in a plane including the gate surface. . That is, the exit surface into the cavity of the gate 5 and the cut surface by the cavity pin 8 exist in the same plane.
[0005]
In general, in injection molding using resin, it is known that 'sink' occurs in the part of the molded product corresponding to the gate port, and residual stress and strain occur in the resin part existing near the gate port. ing. Therefore, if cutting is performed in the plane where the gate port exists as in the conventional molding method, residual stress is generated in the injection molded product.
[0006]
Although such residual stress may not be a problem in practice, there is a problem that the refractive index is not uniform when the molded product is a lens. Even if there is no practical problem, there is no residual stress or “sink”.
[0007]
[Problems to be solved by the invention]
Therefore, a technical problem to be solved by the present invention is to provide a mold that does not cause residual stress or “sink” in an injection molded product using a resin or the like.
[0008]
[Means / Actions / Effects to Solve Problems]
The present invention has been devised to effectively solve the above problems, and provides the following injection mold and injection molding method.
[0009]
The injection mold according to the present invention includes: “the first and second end faces facing each other and sliding in one through hole formed linearly in the template, and the inner circumference of the through hole”. A cavity surrounded by a surface ”and“ a gate opening communicating with the inner peripheral surface ”. The cavities are defined as “a main cavity portion located in the through hole” and “in a direction substantially perpendicular to the sliding direction of the first and second pins, that is, with respect to the through hole. And an auxiliary cavity portion extending from the main cavity portion and reaching the gate port in a substantially perpendicular direction. In addition, if the 1st and 2nd pin is arrange | positioned in one through-hole, the same through-hole may be provided with two or more.
[0010]
The injection molding method of the present invention in which injection molding is performed using this mold includes the “first step of filling a fluid material into the cavity of the mold” and “the first or second pin. A second step of separating one of the materials existing in the main cavity portion and a material existing in the auxiliary cavity portion by sliding one of them, and a third step of cooling the material existing in the main cavity portion, It is characterized by including.
[0011]
In an injection molded product, generally, a residual stress is generated in a region extending from the outer surface portion of the product corresponding to the gate port leading to the cavity to the inside of the product. Therefore, by providing the auxiliary cavity part, it is possible to accommodate the part where the residual stress is originally generated in the auxiliary cavity part. In the second step, the material existing in the main cavity portion and the material existing in the auxiliary cavity portion are separated, and the final product is the material existing in the main cavity portion, not in the auxiliary cavity portion. Therefore, it is possible to effectively prevent the residual stress from occurring in the final product.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 4 is a cross-sectional view of the main part showing an embodiment of the mold of the present invention.
[0013]
Through holes 21a and 23a are formed in both the fixed side mold plate 21 and the movable side mold plate 23, respectively, and both through holes are aligned in a straight line to form one through hole. A core pin 51 is slidably disposed in the through hole 21a, and a cavity pin 52 is slidably disposed in the through hole 23a. A cavity 40 is defined in a space surrounded by the opposing end surfaces 51a, 52a of the core pin 51 and the cavity pin 52 and the inner peripheral surface of the through hole. The cavity 40 includes a main cavity portion 40a and an auxiliary cavity portion 40b. The main cavity portion 40a has a circular cross section perpendicular to the paper surface of FIG. 4 and has a substantially cylindrical shape as a whole. That is, the main cavity portion 40a is a portion located in the through hole in the cavity 40. The auxiliary cavity portion 40b is provided around the main cavity portion 40a and has a ring shape. The function of the auxiliary cavity will be described later. Molten resin injected from an injection molding apparatus (not shown) enters the inside of the cavity 40 from the gate 32 through the sprue 30 and the runner 31. The gate 32 is provided at the boundary between the fixed side mold plate 21 and the movable side mold plate 23, and opens in the auxiliary cavity 40b.
[0014]
5 to 8 show a molding process after the molten resin is filled in the cavity. In addition, illustration of resin is abbreviate | omitted in FIGS. In the following, description will be given in order.
[0015]
When the cavity 40 is filled with resin, the ejector pin 53 (see FIG. 4) is driven to advance the cavity pin 52 toward the core pin 51. Excess molten resin moves toward the runner 31 until the cavity pin 52 advances from the position of FIG. 5 to the position of FIG. 6 until the end surface position A of the fixed-side template 21 and the front end surface position B of the cavity pin 52 overlap. And backflow. In the process from FIG. 6 to FIG. 7, the molten resin remaining in the main cavity portion 40a is compressed, and finally, a molded product 60 having a shape defined by the main cavity portion 40a shown in FIG. 8) is created. After cooling, as shown in FIG. 8, the cavity pin 52 is moved backward with respect to the movable mold plate 23 and the entire movable mold plate is moved backward. Thereafter, the core pin 51 is driven to protrude from the fixed side mold plate 21, and the molded product 60 can be taken out. The core pin 51 is moved back and forth by selectively blowing air into air drive holes formed in the fixed side mold plate 21 and the fixed receiving plate 25.
[0016]
A feature of this mold is that a ring-shaped auxiliary cavity portion 40b is provided around the main cavity portion 40a, and a gate 32 is opened in the auxiliary cavity portion 40b. In injection molding, generally, a residual stress is generated in a region extending from the outer surface portion to the inside of a molded product corresponding to the gate port. Therefore, by configuring as described above, a portion where the residual stress of the injection molded product is generated is located in the auxiliary cavity portion 40b. Then, the cavity pin 52 advances further than the state of FIG. 6 and the tip surface position B of the cavity pin 52 exceeds the end surface position A of the fixed-side mold plate 21, whereby the resin in the auxiliary cavity portion 40b is transferred to the main cavity portion. It is separated (separated) from the resin in 40a. Since the resin in the main cavity portion 40a is the final molded product, the portion where the residual stress is generated is cut off by this cutting step. In this sense, the auxiliary cavity portion 40b does not need to be in the form of a ring extending over the entire circumference of the main cavity portion 40a, and may be provided only partially in the vicinity of the gate 35.
[0017]
As described above, in the present invention, the cavity is composed of the main cavity portion and the auxiliary cavity portion, and the portion where the residual stress of the injection molded product is generated is set in the auxiliary cavity portion. The structure which excises is taken. The excision is performed by sliding the cavity pin 52 in the through hole and passing through the auxiliary cavity portion 40b. Therefore, it is preferable that the auxiliary cavity portion 40b extends in a direction substantially orthogonal to the main cavity portion 40a so that such excision can be performed smoothly. In other words, the auxiliary cavity portion 40b extends in a direction substantially perpendicular to the sliding direction of the core pin 51 and the cavity pin 52 in the through hole, that is, in a direction substantially perpendicular to the through hole. It is preferable.
[0018]
The auxiliary cavity portion 40b is not necessarily provided at the boundary between the fixed side mold plate 21 and the movable side mold plate 23, and the inner peripheral surface of the through hole 21a of the fixed side mold plate or the through hole of the movable side mold plate. It may be provided on the inner peripheral surface of 23a. However, it is necessary that the gate port is opened in the auxiliary cavity portion 40b. That is, the gate port communicates with the inner peripheral surface that defines the cavity.
[0019]
In the illustrated molding process, the molten resin is compressed in the process from FIG. 6 to FIG. 7, but such a compression process is not necessarily required in the present invention. That is, the position of the core pin 51 is set to the lower side in the drawing from the position shown in FIGS. 5 to 8, and the shape of the main cavity portion 40a when the cavity pin 52 reaches the position of FIG. You may make it prescribe | regulate goods.
[0020]
However, it is known that the compression process is more advantageous from the viewpoint of suppressing the occurrence of residual stress. That is, residual stress is generated in the region from the outer surface corresponding to the gate opening to the inside of the product in the injection molded product, but by adopting the compression process as described above, the region where the residual stress is generated is about half. It is known that it can be suppressed to. For example, when molding a lens having a diameter of 25 mm, if a compression process is not employed, a residual stress is generated up to a depth of about 5 mm from the product surface. However, this can be reduced to a depth of 2.5 mm by adopting a compression process. Similarly, in the case of a 9 mm diameter lens, if the compression process is not used, residual stress is generated up to a depth of about 2 mm from the product surface. By adopting the compression process, this is reduced to a depth of 1 mm. It can be suppressed. If the area where the residual stress is generated can be reduced, the volume of the auxiliary cavity portion 40b can be reduced by that much, and the yield of the material can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view illustrating a molding process using a conventional injection mold.
FIG. 2 is a schematic cross-sectional view illustrating a molding process using a conventional injection mold.
FIG. 3 is a schematic cross-sectional view illustrating a molding process using a conventional injection mold.
FIG. 4 is a cross-sectional view of a main part showing an injection mold according to the present invention.
FIG. 5 is a schematic cross-sectional view illustrating a molding process using the injection mold according to the present invention.
FIG. 6 is a schematic cross-sectional view illustrating a molding process using the injection mold of the present invention.
FIG. 7 is a schematic cross-sectional view for explaining a molding process using the injection mold of the present invention.
FIG. 8 is a schematic cross-sectional view illustrating a molding process using an injection mold according to the present invention.
[Explanation of symbols]
1 Molded product 3 Sprue 4 Runner 5 Gate 6 Fixed side template 7 Movable side template 8 Cavity pin 9 Core
10a, 10b Protruding pin
12 Molten resin
20 Fixed side mounting plate
21 Fixed side template
21a Through hole
22 Movable side mounting plate
23 Movable side template
23a Through hole
24 Sprue bushing
25 Fixed backing plate
30 sprue
31 Runner
32 gate
40 cavities
40a Main cavity
40b Auxiliary cavity
51 core pins
51a End face
52 Cavity pin
52a end face
53 Ejector pin
60 Molded parts

Claims (2)

Cavity surrounded by opposing end surfaces (51a, 52a) of the first and second pins sliding in one through hole formed linearly in the template and the inner peripheral surface of the through hole (40),
A gate port (32) communicating with the inner peripheral surface,
In an injection mold comprising:
The cavity (40) extends from the main cavity part (40a) in a direction substantially perpendicular to the sliding direction of the first and second pins and the main cavity part (40a) located in the through hole. An injection mold, comprising: an auxiliary cavity part (40b) extending to the gate port (32). A first step of filling a fluid material into a cavity (40) of an injection mold according to claim 1;
A second step of sliding one of the first and second pins to separate the material present in the main cavity portion (40a) from the material present in the auxiliary cavity portion (40b);
And a third step of cooling the material existing in the main cavity portion (40a).

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