JPH04201221A - Molding die and molding method using the die - Google Patents

Abstract

PURPOSE:To obtain a molded product having high accuracy with excellent stability by making the release characteristics of a cavity surface shaping the molded product and a resin differ in a stationary mold and a movable mold. CONSTITUTION:A resin injected is cooled in a molding die 1. The resin is fast stuck to cavity surfaces 6a, 9a both in a stationary type insert piece 6 and a movable type insert piece 9 until a cooling process is completed and the mold begins to be opened. Since the surface treating layer of the quality of material having excellent release characteristics with the injected resin is formed in the cavity surface 9a of the movable type insert piece 9 when the resin injected is separated from the cavity surfaces, the cavity surface 9a of the movable type insert piece 9 and the resin are separated at all times, and the cavity surface 6a of the stationary type insert piece 6 and the resin are left as they are fast stuck. When the cooling process is completed, the molding die 1 is separated into a stationary mold 2 and a movable mold 3. A pushing-out plate 12 is slid in a space 15, and a pushing-out pin 13 is slid and pushes out a molded product.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an injection mold for producing a molded product by injecting resin into a cavity composed of a fixed mold and a movable mold. In particular, this invention relates to an injection mold that has been improved so as to be able to stably produce high-precision optical components such as lenses. - [Prior art] Conventionally, injection molding molds used for counting large numbers of high-precision parts such as lenses have been disclosed in Japanese Patent Application Laid-open Nos. 55-25973 and 1983-
As described in Publication No. 123031, it is composed of a fixed mold and a movable mold, and the space or cavity for filling the molding material plastic resin to obtain a molded product is a part of the fixed mold and a part of the movable mold. It is formed of. This structure is basically used for both simple injection molding molds and so-called injection compression molding molds that perform compression after injection molding.

The above-mentioned cavities are often formed by the surfaces of the pieces that are incorporated into the piece structure, rather than from the fixed type or the movable type themselves. .

The fixed type insert piece and the movable type insert piece that form this cavity are made of the same material, and their cavity surfaces are finished in the same surface condition.

When molding plastic lenses, for example, both fixed and movable inserts are made of stainless steel, and the cavity surface that shapes the lens surface is electroless nickel plated and polished to a mirror surface. It becomes like this.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, sufficient consideration was not given to molded shape stability, and there was a problem in that the shapes of molded products molded under the same molding conditions were different, resulting in a significantly low F yield.

To explain in detail, in a certain range of molding conditions, molded product 1" with the shape of FIG. 3(a) and molded product 1" with the shape of FIG. The shape difference δ between molded product 1 and molded product 1'' may range from several tens of microns to several hundred microns.

Figure 4 shows the accuracy and frequency of occurrence of this molded product. Both the group of shape (a) and the group of shape (b) each have a variation width. However, the accuracies of the shape (a) group and the shape (b) group are completely separated, and the difference between them is not due to variation.

For this reason, even if one group achieved the accuracy target, the other group had poor accuracy, reducing the number of molded products that could be effectively used and lowering the yield.

An object of the present invention is to provide a molding method for stably producing a molded product with high precision, a mold used for the molding, and a manufacturing method used for manufacturing the mold.

[Means to solve the problem]

In order to achieve the above object, the present inventors first investigated the cause of the occurrence of the polarization phenomenon of the above-mentioned shape. As a result, these two
It has been found that the polarization phenomenon occurs when the amount of shrinkage that occurs when the resin filled in the mold cavity is cooled within the mold is large.

In other words, if the injection pressure is low or the mold temperature is low,
This occurs when the cooling time is long. Therefore, it is possible to reduce this polarization phenomenon by changing molding conditions such as increasing the injection pressure, increasing the mold temperature, and shortening the cooling time.

However, when the injection pressure is increased, the mold is deformed by the pressure of the resin, which deteriorates the precision of the molded product. For example, in the case of lens molding, the surface formed by the fixed cavity surface and the surface formed by the movable cavity surface may be tilted, or the shape that should be axially symmetrical may become non-axially symmetrical. In addition, internal residual stress increases, and accuracy deteriorates due to stress relaxation and deformation at high temperatures.

In addition, when the mold temperature is increased, the cooling time becomes longer, resulting in a decrease in productivity and a wider range of shape variations. It won't get bigger.

When the polarization phenomenon is reduced by changing the molding conditions as described above, other problems occur. Therefore, in the present invention, this polarization phenomenon is prevented by using a molding die.

When the shrinkage of the resin in the mold is large, a bipolar phenomenon occurs, and this phenomenon is always bipolar and does not become tripolar or more. Furthermore, even if a molded product has a bipolar surface shape, its wall thickness distribution is the same, that is, it is not due to the occurrence of so-called shrinkage, but is similar to a warping phenomenon. It was thought that this polarization phenomenon was caused by the behavior of the resin when it contracted due to cooling and separated from the cavity surface.

The resin filled in the cavity is in close contact with both sides of the cavity. As cooling progresses, the resin contracts and separates from the cavity surface. At this time, it is thought that the fixed side cavity surface and the movable side cavity surface do not separate at the same time, and either the fixed side or the movable side surface separates first. Here, since the surface that can be obtained first is not constant, 2
A type of shape, that is, a polarization phenomenon occurs. For example, if the fixed side surface is separated first, the molded product 1 will have the shape of (a) in Figure 3, and if it is separated from the movable side surface first, the molded product 1 will have the shape of (b). It becomes ゛.

Therefore, in the present invention, the polarization phenomenon is prevented by setting the surface that leaves the cavity first when the resin contracts to either the fixed side or the movable side.

In order to first determine the surface that separates from the cavity, the mold releasability (in other words, the affinity) of the fixed-side cavity surface and the movable-side cavity surface were made different. That is, the surface conditions on the fixed side and the movable side are different.

In the case of molding high-precision optical parts such as lenses, the cavity surface must be a mirror surface, so the surface cannot be roughened. Therefore, the surface was treated by coating.

Furthermore, since the releasability of the molded product and the cavity surface differs depending on the materials of both materials, the fixed side and movable side of the mold (entering piece) having the cavity surface were made of different materials without surface treatment.

[Effect]

If the cavity surface on the fixed side and the cavity surface on the movable side are coated with different materials, the mold releasability (in other words, the affinity) between each surface and the resin will be different. Therefore, when the resin begins to separate from the cavity surface due to contraction during cooling, the surface coated with a coating material with excellent mold release properties always separates first.

If the surface to be separated first is determined to be one surface, only one type of shape of the molded product will be generated.

A similar effect is observed even when the surface layer material is the same, but the affinity due to the difference in surface layer density is made different between the movable and fixed type pieces due to differences in the surface treatment conditions.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention. The molding die 2 is composed of a fixed die 3 and a movable die 4. The fixed mold 3 is composed of a fixed mold frame 5, a fixed mold insert piece 6, and a fixed mold mounting plate 7. The fixed type insert piece 6 is assembled into the fixed type frame body 5.

On the other hand, the movable mold 4 consists of a movable frame 8, a movable insert piece 9, a spacer block 10, a movable mounting plate 11, an extrusion plate 12, extrusion pins 13, 2 pins 14, and two movable human pieces 9. is incorporated into the movable frame 8. The movable mold 8, the spacer block 10, and the movable mold mounting plate 11 form a space 15 in which the extrusion plate 12 slides.

The fixed mold 2 is also provided with a sprue 16 through which molten resin injected from a molding machine (not shown) passes.

Similarly, the movable mold 3 is provided with a runner 17 and a gate 18 through which the resin passes. The fixed mold insert piece 6 and the movable mold insert piece 9 form a cavity 19 in which the resin is finally shaped into a molded product shape.

Here, the cavity surface 9 where the molded product of the movable mold entry piece 9 is shaped.
A surface treatment layer 20 is formed on the surface a as shown in FIG. This surface treatment layer 20 is made of a material that has excellent mold releasability from the resin material of the molded product, in other words, a material that has weak adhesion.

On the other hand, the cavity surface 6 on which the molded product of the fixed mold insert piece 6 is shaped
A is not provided with a surface treatment layer and is made of the original metal material.

The operation of the molding die configured as above will be explained. The resin melted by the molding machine passes through the sprue 16, runner 17, and gate 18, and is injected and filled into the cavity 19.

The filled resin fills the cavity 19, and the cavity surface 6a of the fixed type inserting piece 6 and the cavity surface 9a of the movable type inserting piece 9 are in close contact with the filled resin.

Thereafter, the filled resin is cooled within the molding die 1.

During this cooling process, the filled resin begins to shrink.

If the molding conditions are such that the amount of shrinkage is small, the resin remains in close contact with the cavity surfaces 6a and 9a of both the fixed mold insert piece 6 and the movable mold insert piece 9 until the cooling process is completed and the mold begins to open.

However, under molding conditions where the amount of shrinkage is small, the mold deforms and the precision of the molded product deteriorates. Therefore, the molding conditions are such that the amount of shrinkage is large and the filled resin separates from the cavity surface before the mold begins to open.

When the filled resin leaves the cavity surface, the cavity surface 9a of the movable mold insert piece 9 is provided with a surface treatment layer made of a material with excellent mold releasability from the filled resin. The surface 9a and the resin are separated, and the cavity surface 6a of the fixed type insert piece 6 and the resin remain in close contact.

As the cooling progresses further, the amount of separation between the cavity surface 9a of the movable mold inserting piece 9 and the resin increases. Fixed.

The cavity surface 6a of the molding piece 6 remains in close contact until the cooling process is completed and the mold begins to open.

When the cooling process is completed, the molding die 1 is separated into a fixed die 2 and a movable die 3. Then, the extrusion plate 12 slides in the space 15, and the extrusion pin 13 slides accordingly to extrude the molded product.

The molded product is then taken out and the operation is repeated for the next molding.

The molded product taken out is cooled to room temperature outside the mold.

Through the above operations, a molded product of a certain shape was obtained.

Further, contrary to the above embodiment, a surface treatment layer made of a material with excellent mold releasability is provided in the cavity 6a of the fixed mold insert piece 6 for shaping the molded product, and a surface treatment layer of a material with excellent mold releasability is provided on the cavity surface 9a of the movable mold insert piece 9. If no treatment layer is provided and the metal material of the piece is used as is, when the filled resin leaves the cavity surface during the cooling process,
The cavity surface 6a of the fixed type insert piece 6 and the resin are always separated, and the cavity surface 9a of the movable type insert piece 9 and the resin remain in close contact.

The subsequent steps were the same as in the above example, and a molded product of a constant shape was obtained.

Here, the case where the surface treatment layer 20 is provided on the cavity surface 9a of the movable type inserting piece 9, and the case where the surface treatment layer 20 is provided on the cavity surface 6a of the fixed type inserting piece 6 are shown.
If the shapes of the cavity surfaces 9a and 6a are the same, the shapes of the molded products will be different. Therefore, when the surface treatment layer 20 is provided on the cavity surface 9a of the movable mold insert piece 9, the shape of the cavity surface 9a of the movable mold insert piece 9 and the shape of the cavity surface 6a of the fixed mold insert piece 6 are different from each other when the surface treatment layer 20 is provided on the cavity surface 9a of the movable mold insert piece 9. Movable insert piece 9 when provided on the cavity surface 6a of fixed insert piece 6
The shape of the cavity surface 9d and the shape of the cavity surface 6a of the fixed mold insert piece 6 are different, so that the shape of the molded product becomes the target shape in the case of each cavity surface shape.

In the above embodiment, one cavity surface is the mold material base material itself, and the other cavity surface is provided with a surface treatment layer,
Although the mold releasability of both cavity surfaces is different, the same effect can be obtained even if a surface treatment layer is provided on both cavity surfaces to create a difference in the mold releasability of each.

In this embodiment, since the molded product is an optical component such as a lens, the cavity surfaces 6 of the fixed insert piece 6 and the movable insert piece 9
a and 9a have mirror surfaces.

Next, the material of the surface treatment layer will be explained. The surface treatment layer is formed by plating or coating.

In the case of plating, materials such as Cr (chromium) and Ni (nickel) are used. In the case of coating, the materials are TiC (titanium carbide), TiN (titanium nitride, TiC
○ (Titanium oxycarbonate), T↓CN (Titanium carbonitride), T1
Examples include CN○ (titanium oxycarbonitride), HfC (hafniT cum carbide), and AΩ20° (aluminum oxide).

In this example, PMMA (polymethyl methacrylate) was used as the resin, and the material was selected in consideration of mold releasability from the resin.

When a stainless steel mold material was used and one surface was made of this material, nickel or titanium nitride was used as the material for the surface layer of the other surface.

When surface layers are provided on both sides, one side is made of nickel and the other side is made of titanium carbide, or one side is made of hafnium carbide, and the other side is made of titanium nitride.

As a result of the above, the resin was always released from one side during shrinkage, and a molded product with a constant shape was obtained.

In this embodiment, the molded product is a plastic lens, but the present invention can be similarly applied to other plastic parts such as disks.

Moreover, it can be applied not only to plastic molding but also to die casting molding and glass molding.

Although metal is used as the base material of the mold in this embodiment, the mold may be made of ceramic or glass as the base material.

In addition, in this example, when providing surface treatment layers on both the cavity surface of the fixed type insert piece and the cavity surface of the movable type insert piece, the surface treatment layers were made of different materials, but even if they are made of the same material, the characteristics may differ. A similar effect can be obtained. In producing the surface treatment layer, even the same material can be made to have different properties by changing one or more factors such as pressure (degree of vacuum), temperature, and film forming speed.

〔Effect of the invention〕

As described above, the present invention can make the shrinkage behavior of the resin constant within the molding die, so that the shape of the molded product can be made constant. Therefore, it was possible to obtain a highly accurate molded product with twice the yield when polarization occurs.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a molding die according to an embodiment of the present invention;
The figure is a vertical cross-sectional view of the main part of the molding die shown in Fig. 1, Fig. 3 is an explanatory diagram of the bipolarization of the molded product shape, and Fig. 4 is a two-dimensional diagram of the shape of the molded product shown in Fig. 3.
FIG. 3 is an explanatory diagram of accuracy and frequency when polarization occurs. 1... Molded product, 2... Molding mold, 3... Fixed mold,
4...Movable type, 6...Fixed type entering piece, 9...Movable type entering piece, 6a. 9a...Cavity surface, 20...Surface treatment layer. 2nd country 3rd ward 1.1' Measure 4 Close

Claims (1)

[Claims] 1. In a molding die for obtaining a molded product by injecting and injecting resin into a cavity constituted by a fixed mold and a movable mold, the molded product of the fixed mold is shaped. A molding die characterized in that a mold releasability between a cavity surface and the resin and a mold releasability between a cavity surface for shaping a molded product of the movable mold and the resin are different. 2. In the molding mold according to claim 1, a surface treatment layer is provided on either the cavity surface of the fixed mold or the cavity surface of the movable mold, and the other surface is provided with a surface treatment layer on the cavity surface of the fixed mold or the cavity surface of the movable mold. A molding die characterized by being a surface of a base material of a movable mold. 3. The molding die according to claim 2, wherein the base material of the mold is metal. 4. The molding die according to claim 2, wherein the base material of the mold is made of ceramic. 5. The mold according to claim 2, wherein the base material of the mold is glass. 6. The molding die according to claim 1, wherein the cavity surface of the fixed mold and the cavity surface of the movable mold are provided with surface treatment layers of different materials or characteristics, respectively. 7. The molding die according to any one of claims 1 to 6, characterized in that it is used for molding plastics. 8. The molding die according to claim 7 for molding a plastic lens, wherein the molded product is a plastic lens. 9. The molding die for disc molding according to claim 7, wherein the molded product is a disc. 10. The molding die according to any one of claims 1 to 6, characterized in that it is used for die-casting. 11. Claim 1 characterized in that it is used for glass molding.
Forming molds in Items 6 to 6. 12. The surface treatment is CVD or PVD, and pressure (
7. The method for surface treatment of a molding die according to claim 6, wherein the material or characteristics of the surface treatment layer are controlled by changing the degree of vacuum) and/or temperature and/or film forming speed. 13. In a molding method for obtaining a molded product by injecting and injecting a resin into a cavity constituted by a fixed mold and a movable mold, the resin shrinks during the step of cooling the resin in the cavity. When performing molding, the resin is always released from the cavity surface of the fixed mold that shapes the molded product, or always released from the cavity surface of the movable mold that shapes the molded product. Method.