JPH11115008A - Injection mold and injection molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold not generating residual stress or 'sink' in an injection molded product using a resin or the like. SOLUTION: The cavity of a mold is constituted of a main cavity part 40a positioned within a through-hole and the auxiliary cavity part 40b extending in the direction substantially crossing the main cavity part 40a at a right angle (that is, the direction substantially crossing the through-hole at a right angle) to reach a gate port. The cavity of this mold is filled with a flowable material and the material present in the main cavity part 40a and the material present in the auxiliary cavity part 40b are separated to cool the material present in the main cavity part 40a to obtain an injection molded product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin molded product, and more particularly to an injection molding method for a plastic lens and a mold used therefor.

[0002]

2. Description of the Related Art As a mold used for injection molding of a resin molded product such as a plastic lens, for example, JP-A-9-2
No. 9854 is known. An injection molding method using this mold will be described with reference to FIGS.

First, as shown in FIG. 1, a sprue 3, a runner 4, and a gate 5 are used to melt molten metal into a cavity formed between a cavity pin 8 and a core 9 and between protruding pins 10 a and 10 b. The resin 12 is injection-filled. 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 toward the core 9 at a high pressure, excess molten resin flows back to the runner 4 side, and a molded product formed in the cavity. 1
Is separated from the outer peripheral surface of the gate 5. In FIG. 1,
Reference numeral 6 denotes a fixed-side template, and 7 denotes a movable-side template.

In the molding method shown in FIGS. 1 to 3, the outer peripheral surface of the molded product 1 is separated from the gate 5 by the advancement of the cavity pin 8, but this cutting is performed in a plane including the gate surface. Have been done. That is, the exit surface of the gate 5 into the cavity and the cut surface by the cavity pin 8 exist in the same plane.

[0005] In general, in injection molding using resin, in addition to the occurrence of sink marks in the molded product corresponding to the gate opening, residual stress and strain are generated in the resin portion existing near the gate opening. It has been known. Therefore, when cutting is performed in the plane where the gate port exists as in the above-described conventional molding method, residual stress is generated in the injection molded product.

[0006] Such residual stress may not be a problem in practical use, but when the molded product is a lens, there arises a problem that the refractive index is not uniform. Further, even in cases where there is no practical problem, there is no residual stress or no sink mark.

[0007]

SUMMARY OF THE INVENTION Therefore, a technical problem to be solved by the present invention is to provide a mold which does not cause residual stress or sink marks in an injection-molded article using a resin or the like. .

[0008]

SUMMARY OF THE INVENTION The present invention has been made in order to effectively solve the above problems, and provides the following injection mold and injection molding method. is there.

[0009] The injection molding die of the present invention is characterized in that the opposing end faces of the first and second pins sliding in one through-hole linearly formed in the mold plate, And a “gate opening communicating with the inner peripheral surface”. And the cavity is
"The main cavity located in the through hole" and "the direction substantially perpendicular to the sliding direction of the first and second pins, that is, substantially perpendicular to the through hole." An auxiliary cavity portion extending from the main cavity portion to the gate port in the direction. If the first and second pins are arranged in one through hole, a plurality of similar through holes may be provided.

[0010] The injection molding method of the present invention for performing injection molding using the mold includes a "first step of filling the cavity of the mold with a fluid material" and a "first or second step". A second step of sliding one of the pins to separate the material present in the main cavity from the material present in the auxiliary cavity, and a "third step of cooling the material present in the main cavity."".

In an injection-molded product, residual stress generally occurs in a region extending from the outer surface portion of the product corresponding to the gate opening to the cavity to the inside of the product. Therefore, by providing the auxiliary cavity portion, a portion where a residual stress originally occurs can be accommodated in the auxiliary cavity portion. In the second step, the material existing in the main cavity and the material existing in the auxiliary cavity are separated from each other, and the final product is not the material existing in the auxiliary cavity but the material existing in the main cavity. Therefore, it is possible to effectively prevent generation of residual stress in the final product.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 4 is a sectional view of a 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 the two through holes are aligned in a straight line to form one through hole. ing. 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. The cavity 40 is defined in a space surrounded by the opposing end surfaces 51a and 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 40a and an auxiliary cavity 40b. The main cavity portion 40a has a circular cross section orthogonal 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 of the cavity 40 located in the through hole. Auxiliary cavity 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 device (not shown) passes through the sprue 30 and the runner 31 and enters the inside of the cavity 40 from the gate 32. Gate 32
Is provided at the boundary between the fixed mold plate 21 and the movable mold plate 23, and opens into the auxiliary cavity 40b.

FIGS. 5 to 8 show a molding step after the cavity is filled with the molten resin. FIG.
7, the illustration of the resin is omitted. Hereinafter, description will be made in order.

When the cavity 40 is filled with resin, the ejector pins 53 (see FIG. 4) are driven to move the cavity pins 52 toward the core pins 51. Until the cavity pin 52 moves forward from the position shown in FIG. 5 to the position shown in FIG. 6, the excess molten resin is directed toward the runner 31 until the end face position A of the fixed mold plate 21 and the end face 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 (FIG. 7) having a shape defined by the main cavity portion 40a shown in FIG. 8). After the cooling, as shown in FIG. 8, the cavity pins 52 are retracted with respect to the movable mold plate 23 and the entire movable mold plate is retracted. After that, the molded product 60 can be taken out by driving the core pin 51 so as to protrude from the fixed side template 21. The advance and retreat movement of the core pin 51 is performed by selectively blowing air into an air drive hole formed in the fixed mold plate 21 and the fixed receiving plate 25.

The feature of this mold is that a ring-shaped auxiliary cavity 40b is provided around the main cavity 40a, and the gate 32 is opened in the auxiliary cavity 40b. In injection molding, a residual stress generally occurs in a region extending from an outer surface portion to an inner portion of a molded product corresponding to a gate opening. Therefore, with the above configuration, the portion where the residual stress of the injection molded product occurs is located in the auxiliary cavity portion 40b. Then, the cavity pin 52 advances further than the state shown in FIG. 6, and the position B of the front end surface of the cavity pin 52 exceeds the position A of the end surface of the fixed mold plate 21, whereby the auxiliary cavity portion 40
The resin in b is separated (separated) from the resin in the main cavity portion 40a. Since the resin in the main cavity portion 40a is a final molded product, a portion where residual stress occurs is cut off by this cutting step. In this sense, the auxiliary cavity portion 40b does not need to have a ring shape extending over the entire periphery of the main cavity portion 40a, and may be provided only partially near the gate 35.

As described above, in the present invention, the cavity is constituted by the main cavity portion and the auxiliary cavity portion,
The injection molding is set so that the portion where the residual stress is generated is located in the auxiliary cavity portion, and the portion is cut off. The cutting 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 resection can be performed smoothly. In other words, the auxiliary cavity portion 40b extends in a direction substantially orthogonal to the sliding direction of the core pin 51 and the cavity pin 52 in the through hole.
That is, it preferably extends in a direction substantially orthogonal to the through hole.

The auxiliary cavity portion 40b does not necessarily need to be provided at the boundary between the fixed mold plate 21 and the movable mold plate 23. May be provided on the inner peripheral surface of the through hole 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.

In the illustrated molding step, the molten resin is compressed in the process from FIG. 6 to FIG. 7, but such a compression step is not necessarily required in the present invention.
That is, the position of the core pin 51 is set lower than the position shown in FIGS. 5 to 8 in the drawings, and the shape of the main cavity portion 40a when the cavity pin 52 reaches the position in FIG. The product may be specified.

However, from the viewpoint of suppressing the generation of residual stress, it is known that it is advantageous to employ a compression step. That is, the residual stress is generated in a region from the outer surface portion corresponding to the gate port to the inside of the product in the injection molded product. It is known that it can be suppressed. Specific values vary depending on the dimensions of the product.
In the case of molding a 25mm lens, if the compression process is not used, a residual stress will be generated up to an area about 5mm deep from the product surface. Can be reduced to Similarly, in the case of a lens having a diameter of 9 mm, when the compression step is not used, a residual stress is generated up to a region about 2 mm deep from the product surface. It can be suppressed to the point. If the region where the residual stress is generated can be reduced, the volume of the auxiliary cavity portion 40b can be reduced accordingly, 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 molding die.

FIG. 2 is a schematic cross-sectional view illustrating a molding process using a conventional injection molding die.

FIG. 3 is a schematic sectional view illustrating a molding process using a conventional injection molding die.

FIG. 4 is a 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 step using the injection mold of the present invention.

FIG. 6 is a schematic sectional view illustrating a molding step using the injection mold of the present invention.

FIG. 7 is a schematic cross-sectional view illustrating a molding process using the injection mold of the present invention.

FIG. 8 is a schematic sectional view illustrating a molding step using the injection mold of the present invention.

[Description of Signs] 1 Molded product 3 Sprue 4 Runner 5 Gate 6 Fixed side mold plate 7 Movable side mold plate 8 Cavity pin 9 Core 10a, 10b Projecting pin 12 Melt resin 20 Fixed side mounting plate 21 Fixed side template 21a Through hole 22 Movable mounting plate 23 Movable mold plate 23a Through hole 24 Sprue bush 25 Fixed receiving plate 30 Sprue 31 Runner 32 Gate 40 Cavity 40a Main cavity 40b Auxiliary cavity 51 Core pin 51a End face 52 Cavity pin 52a End face 53 Ejector pin 60 Molded product

Claims (2)

[Claims] 1. Opposite end faces of first and second pins sliding in one through hole formed linearly in a template.
(51a, 52a), a cavity (40) surrounded by the inner peripheral surface of the through hole, and a gate port (32) communicating with the inner peripheral surface. The cavity (40) extends from the main cavity portion (40a) in a direction substantially orthogonal to the sliding direction of the first and second pins with the main cavity portion (40a) located in the through hole. Auxiliary cavity part (40b) that reaches the gate port (32)
And a mold for injection molding. 2. A first step of filling a flow material into the cavity (40) of the injection molding die according to claim 1, wherein one of the first and second pins is slid to form a main cavity. Material present in the part (40a) and the auxiliary cavity part
A second step of separating the material present in the main cavity portion (40b); and a third step of cooling the material present in the main cavity portion (40a).
And an injection molding method.