JP3580560B2 - Elastic compression molding method and elastic compression mold - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for precisely injection-molding molded articles having different thicknesses without defects such as sink marks, and a mold for performing the method.
[0002]
[Prior art]
It is desirable that the injection-molded product is designed in advance so that all the thicknesses are substantially equal in order to prevent solidification evenly and defects such as sink marks on the product surface. However, there are cases where the wall thickness cannot be made equal in all parts due to the essential properties of the product such as a lens.
[0003]
Hereinafter, as a problem of the conventional example, a case of lens molding will be described. FIG. 3 shows a method generally called molding. According to this method, a molding material (21) is injected into a convex-shaped mold cavity (20) from a portion to be a periphery of a lens (B), and solidified as it is. It is a method of taking out. In this case, the filling density of the gate entrance portion (22) becomes dense, and the filling density becomes coarser as the distance from the gate (23) increases. As a result, when solidified, the amount of shrinkage is greater on the opposite side (24) than near the gate (22), causing the problem that the lens surface is distorted. At the same time, since the central part of the molded article (B) is thicker than the peripheral part, there is a problem that solidification is slower than the peripheral part, shrinkage occurs, and the central part is further distorted. Therefore, the lens (B) made by such ordinary molding is limited to a very low-grade lens. The shape of the lens (B) deformed by solidification is indicated by a two-dot chain line (25).
[0004]
Therefore, a micromolding method as shown in FIG. 4 has been proposed as a method of manufacturing a precision lens. That is, according to this method, the partial molds (30a) (30b) constituting the cavity are prepared separately from the mold bodies (31a) (31b), and the molding material (33) for the cavity (32) is prepared. ) Is completed, the partial mold (30a) constituting the cavity is operated to hydraulically compress and solidify.
[0005]
According to this method, since the entire molded article (33) is solidified while applying pressure, the strain is smaller than that of the ordinary molding, but there is still a problem. That is, the thickness of the molded article (33) is different between the peripheral portion (34) and the central portion (35). Therefore, the peripheral portion (34) solidifies faster than the central portion (35). Then, the molds (30a) and (30b) constituting the cavity portion (32) compress the solidified peripheral portion (34), and the pressing force is not applied to the central portion (35) in the molten state. Become.
[0006]
As a result, sink marks occur in the central portion (35), and slight distortion occurs on the lens surface of the central portion (35), and sufficient accuracy cannot be obtained. Moreover, since no pressing force is applied to the central portion (35), the packing density is lower than that of the peripheral portion (34), and the refractive index of light is slightly different between the peripheral portion (34) and the central portion (35). Problem remains.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and is directed to an elastic compression molding method and an elastic compression molding method capable of continuously applying a pressing force until the molding material in the cavity solidifies in all portions. Its purpose is to provide a mold for performing.
[0008]
[Means for Solving the Problems]
A method for solving the above-mentioned problem is to provide a cavity (10) on the back side of a cavity (7) of a fixed mold (4) and a movable mold (2 ) by providing a cavity ( 10). The molding material is injected into a mold cavity (7) in which all parts constituting the mold (7) are configured to be elastically deformable, and the fixed mold (4) and the movable mold are moved in a direction in which the volume in the cavity is expanded by the injection pressure. The mold (2) is elastically deformed and solidified while applying an elastic compressive force to the entire surface of the molding material in the mold cavity (7) . "
As a result, uniform pressure is applied to the entire molded product until solidification of the entire molded product is completed, and extremely precise molding can be performed.
[0009]
Claim 2 is an elastic mold for carrying out the method, wherein a portion forming the cavity (7) of the fixed mold (4) and the movable mold (2) is formed to a thickness capable of being elastically deformed. It is characterized by. Thus, the fixed mold by the molding material injected into the mold cavity (4) and cavity volume cavity portion by elastic deformation of the movable mold (2) is expanded, the elastic force by the elastic deformation entire Until the solidification of the molding material is completed, the molding material is almost evenly applied to the entire surface of the molding material in the mold cavity, so that a molded product having a uniform and low distortion can be formed throughout.
[0010]
Claim 3 relates to an embodiment of the elastic mold, wherein the elastic mold is elastically deformable by providing a gap (10) on the back side of the cavity (7) of the fixed mold (4) and the movable mold (2). It is formed to have a great thickness ”. By providing a gap behind the mold cavity, the mold portion of the cavity portion is elastically deformed.
[0011]
【Example】
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. Reference numeral (1) denotes a movable die plate, and a movable mold (2) is detachably attached to a predetermined position on the plane in the traveling direction. A fixed die plate (3) has a fixed mold (4) detachably mounted on the inner surface thereof at a position where the fixed mold (4) is pressed against the movable mold (2). The movable die plate (1) and the fixed die plate (3) are supported by four tie bars (5), and the movable die plate (1) is appropriately provided (toggle mechanism (6) in this embodiment). Thus, it is slidably supported so as to be pressed against and separated from the fixed die plate (3).
[0012]
For example, a cavity (7) for forming a convex lens is formed in the parting surface of both the movable and fixed molds (2) and (4). (11) is a gate communicating with the cavity (7), and (12) is a sprue.
[0013]
The back surface of the mold portion (9) constituting the mold cavity (7) of both the movable and fixed molds (2) and (4) is concave, and in the case of forming a convex lens, the center of the cavity (7) is formed. It is set so that it gradually becomes thinner as it approaches. When the movable and fixed dies (2) and (4) are attached to the movable die plate (1) and the fixed die plate (3), a gap (10) is formed on the back surface of the cavity (7). . Then, the mold portion (9) constituting the mold cavity (7) by the gap (10) {or the recess} can be elastically deformed by injection-pressing the material (8) into the molding.
[0014]
The shape of the recess (10) is a circular depression when a lens is formed, but the corner (13) may be rounded as shown by the broken line in FIG. Also, the size of the recess (10) may be larger or smaller than the cavity (7). In short, the diameter of the recess (10), the thickness of the mold portion (9) constituting the mold cavity (7), the diameter of the recess (10), the size of the corner portion (13), and the like are formed. Radius, diameter, material, and physical properties (linear expansion coefficient, tensile strength, thermal conductivity, Young's modulus, Poisson's ratio, etc.) of the lens (8) on the mold (2) (4) side The optimal dimensions are selected by
[0015]
Then, the movable mold (2) is pressed against the fixed mold (4) by operating the toggle mechanism (6), and subsequently, the molten resin as the molding material (8) is injected into the cavity (7). I do. The molding material (8) injected into the cavity (7) expands the mold portion (9) constituting the mold cavity (7) by elastic deformation by injection pressure (= resin pressure) as shown in FIG. . In other words, the molding material (8) in the cavity (7) is uniformly tightened over the entire surface by the mold portion (9).
[0016]
When the injection is completed, a pressure-holding step is started. At this stage, the molding material (8) in the cavity (7) cools while releasing gas, and gradually solidifies and contracts. In this case, solidification starts from a thin portion such as the gate (11) and the peripheral portion (14), and gradually solidifies into a thick central portion (15).
[0017]
At this time, since the entire mold portion (9) is elastically deformed, even if the peripheral portion (14) solidifies, the elastic pressure is applied to the non-solidified portion independently of the peripheral portion (14). The molding can be continuously performed, and the shape of the molded article (A) can be corrected to the final shape. That is, the gas escapes and shrinks in the process of cooling the molding material (8), and the cavity (7) returns to its original shape as the resin pressure decreases. As a result, the molded product (A) receives an even tightening force over the entire surface from injection to solidification, and the entire surface of the molded product (A) is homogeneous, as well as the accuracy of the lens surface. It can be produced in large quantities.
[0018]
When the molded product (A) solidifies, the toggle mechanism (6) is operated in the folding direction to open the mold, the molded product (A) is taken out, and is ready for the next injection molding operation.
[0019]
In the present invention, the lens molding has been described as an example. However, it is needless to say that the present invention is not limited to this, but can be widely applied to injection molding having uneven thickness. In other words, the thickness of the mold part in the part where solidification is slow is made thinner so that it can be elastically deformed. In addition to preventing defects from appearing on the surface, it is also possible to obtain a molded article that exactly conforms to the cavity shape.
[0020]
【effect】
According to the method of the present invention, the molding material is injected into the mold cavity to elastically deform the mold cavity in the enlargement direction and solidify while applying an elastic force to the entire surface of the molding material in the mold cavity. Even though the solidified part can be applied to the non-solidified part independently and elastic pressure can be applied continuously, the advantage that the shape of the molded product can be corrected to the final shape that was in the cavity shape is there.
[0021]
According to the second aspect of the present invention, since the mold portion constituting the mold cavity is formed to have a thickness capable of being elastically deformed, gas is released and contracted during the cooling process after injection of the molding material. Then, as the resin pressure decreases, the cavity returns to its original shape, and the molded product receives an even tightening force over its entire surface from injection to solidification. Of course, the precision of the product is of course uniform throughout, so that extremely high quality molded products can be manufactured easily and in large quantities.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of one embodiment of a mold and a toggle mechanism of an injection molding apparatus according to the present invention. FIG. 2 is a cross-sectional view of one embodiment of an elastic compression molding die according to the present invention. FIG. 4 is a cross-sectional view of a mold part for lens molding by a conventional micromolding method. FIG. 5 is an enlarged cross-sectional view of a cavity part of FIG.
(1) Movable die plate (2) Movable die (3) Fixed die plate (4) Fixed die (5) Tie bar (6) Toggle mechanism (7) Mold cavity (8) Molding material (A) Molded product (9) Mold part forming cavity (10) Void (11) Gate (12) Runner (13) Corner (14) Peripheral edge (15) Center

Claims (3)

A cavity is provided on the back side of the cavity of the fixed mold and the movable mold, and the molding material is injected into a mold cavity in which both of the cavities are configured to be elastically deformable. An elastic compression molding method characterized in that a fixed mold and a movable mold are elastically deformed in a direction in which the mold is expanded, and solidified while applying an elastic compressive force to the entire surface of the molding material in the mold cavity. An elastic compression mold, characterized in that portions constituting the cavities of the fixed mold and the movable mold are formed to have a thickness capable of being elastically deformed. The elastic compression mold according to claim 2, wherein the fixed mold and the movable mold are formed to have elastically deformable thickness by providing gaps on the back side of the cavities, respectively.

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