JPH038253B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is generally applicable to resin injection molding equipment, particularly for injection molding of molded products that require high surface precision and low warp and birefringence, such as concave lenses, video disks and hard disks as recording media. This invention relates to a molding device.

In the conventional molding method for concave lenses, the volume of the cavity (especially in the thickness direction) is increased at or before the time when molten plastic is filled into the cavity of the main mold, and the inside of the increased cavity is After the molten plastic is injected, the entire cavity block or core block is pressed using hydraulic pressure or the clamping force of a molding machine to compress the plastic in the cavity and obtain a desired lens.

Similarly, the manufacturing method for disks used as recording media is as follows: After injecting molten plastic with the gap between the cavity and core slightly thicker than the required thickness of the molded product,
A method very similar to the lens molding method in which the entire cavity or core is compressed to compress the plastic inside the cavity, or a molding machine with a very high filling speed that cannot be obtained with a general injection molding machine is used to further reduce the melt viscosity of the plastic. The current situation is that they are produced with improved and lowered levels. However, in the conventional injection compression molding method, the entire cavity or core is pressed using hydraulic pressure or mold clamping ^pressure . Also, if compression force is applied during filling, a hesitation mark is created at the point where compression (pressing) starts, that is, at the boundary between the place filled by the molding machine and the place where compression starts. Oil wrinkle-like defects that are exposed are likely to occur,
In addition to these defects, the stability of the wall thickness of the product is also lacking because the cavity or core is moved.

On the other hand, a method using a molding machine capable of high-speed filling,
For example, in manufacturing compact discs using polycarbonate resin, the molecular weight is lowered to lower the melt viscosity of the polycarbonate resin (usually in the molecular weight range of 20,000 to 30,000, but here it is 5,000 to 20,000). The properties of polycarbonate resin, such as strength, environmental stress resistance, and cracking resistance, have been significantly reduced.

The present invention overcomes these drawbacks.
In other words, the characteristics required for lenses and disks as recording media are high surface precision and low warpage and birefringence, but the main cause of problems in these points is that the molten resin is not in contact with the mold. The stress applied to the resin during filling, the degree of orientation of the polymer, and volume changes during the cooling process, such as filling strain, orientation strain, cooling strain, etc. It is said that Conventionally, in a lens molded product or a disk molded product used as a recording medium, the location where these various stresses and strains occur most often is the portion where the cavity and core are joined, which is the end portion of the molded product.
In addition, sink marks tend to occur a little further inside the product, so when used as a recording medium, the recording reading head descends along the sink marks and reaches the outermost periphery. Since the thickness of the disk returns to the basic thickness again, the reading head may collide and break.

The inventor of the present invention has conducted intensive research to solve the problems in conventional injection compression molding, and has found that by using a mold with a special structure that can preferentially apply compressive force only to these parts, the pressure can be reduced. The present invention has been completed based on the discovery that a molded product having a smaller surface area, better compression efficiency, better wall thickness stability, and the required accuracy can be obtained without lowering the viscosity of the material.

That is, the present invention provides an injection compression molding mold having a mold pair of a fixed mold and a movable mold that form a cavity that conforms to the shape of a desired molded product, in which the volume of the cavity 27 increases throughout the molding process. means 17 for reducing the cross-sectional area of the resin flow path between the cavity 27 and the gate 24 proximate to the cavity 27; and said cavity 27 and said means 1.
A mold is provided, characterized in that it has means 18 for pressurizing the molten resin in the resin flow path between the mold and the resin flow path.

The present invention will be described below based on drawings showing examples of molds of the present invention.

FIG. 1 shows an outline of the constituent elements of the present invention, taking as an example a disk mold having an opening. FIGS. 2 and 3 are enlarged views of the gate portion, with FIG. 2 being a view before compression and FIG. 3 being a view after compression.

Based on FIG. 1, the operating state when a molding operation is performed using this mold in an injection molding machine having an injection compression function will be explained. First, mold closing is started, and the mold closing operation is stopped when the mold is opened by an arbitrary thickness ranging from several millimeters to several millimeters/100 millimeters before mold closing is completed. The width opened by this arbitrary thickness is the width between the cavity plate 8 and the back plate 9 in FIG. 1, and therefore there is no gap between the core plate and the capsule plate. This gap is obtained by the force of springs 13 and 14. The strengths of springs 13 and 14 are usually the same, and a total of 10 springs were installed, with 4 springs 14 at 90° angles and 6 springs 13 at 60° angles, centered around the core pin 20 at the center of the molded product (2 tons in total). Next, the material plasticized by the molding machine passes through the sprue 21 and the primary runner 22 and reaches the primary gate 23. If this part is all hot runner, there will be no weld lines on the molded product, but in the case of cold runner,
In order to prevent this from occurring, it is necessary to provide a large number of runners 22 and gates 23. In the case of this figure, a four-point gate is used, and the secondary gate 24 is ring-shaped, and the wall thickness is increased along the flow direction.The upper half of the secondary runner 25, which is also ring-shaped, is circular, and the lower side is square. The weld problem can be solved by increasing the volume of this part by increasing the depth only in the horizontal direction, and by delaying the timing of resin filling up to this part. This part is called an overflow pocket.
From here, the resin further flows into the cavity 27 via a tertiary gate 26 which is ring-shaped and whose thickness decreases along the resin flow direction. (It is better not to design the thickest part of the tertiary gate to be thicker than the thickest part of the secondary gate.) As the filling progresses further, at the point where it is completely filled or on the verge of being completely filled, an arbitrary thickness can be reached. The extra thickness left open is tightened using mold clamping force to reduce it to zero.
At this time, the ring-shaped compression ring 18 set under the secondary runner 25 installed in parallel in a ring shape is pressed with several protruding pins 16, and at the same time the compression ring 18 is pressed under the secondary gate 24. The compression ring 17 set between the primary gate 23 and the secondary runner 25 is connected to several protruding pins 1.
Press with 5. In order to make the compression ring more effectively pressed by the ejector pin, it is preferable to warm the secondary runner near the secondary runner. For this purpose, the secondary runner should be placed as close to the secondary runner as possible on the cavity plate side at the fitting part between the cavity block and the cavity plate, and as close to the secondary runner as possible on the core plate side at the fitting part between the core block and the core plate. A heater can be buried near the runner.
Two heaters 28 are shown in FIG.

When the mold is compressed, pressure is applied to the resin in the secondary runner 25 due to the movement of the compression ring 18, and this pressure is applied to the resin in the tertiary gate 26.
It is transmitted to the resin on the outer periphery of the cavity 27 via the. At this time, the compression ring 17 is moved between the primary gate 23 and the secondary runner 25 so that the pressure generated by the movement of the compression ring 18 does not cause the resin to flow back toward the primary gate 23.
The gap is narrowed by protruding it in the middle.

This mold clamping force (pressing force) is subtracted by the amount that compresses the spring. Figure 4 shows that spring 14 is replaced by spring 1 in order to reduce the loss of mold clamping force.
Cavity block 7 has the same dimensions and strength as 3.
This is a partially enlarged view of a mold made several millimeters thinner than the cavity plate 8. The effects obtained from the above operation outline and design will be summarized below in comparison with the conventional case where a gate is installed at the opening (center) of the disk.

(1) If there is a gate in the center of the disk as in the past, the flow direction of the molten material will be from the apex angle of the isosceles triangle to spread out in an isosceles fan, so the closer it gets to the end of the flow, the lower the flow cross section will be. The increase is significant and the orientation of the material is impaired. Conversely, in this method, the flow flows from the isometric direction to the apex direction (center), so the closer you get to the end of the flow, the smaller the flow cross section and the longer the flow distance, so pressure can be sufficiently transmitted to the end of the flow. , and the pressure difference between near the gate and the end of the flow is small.

(2) The gate cross-sectional area becomes overwhelmingly large, and the filling speed (time) becomes faster.

(3) The orientation of the molten resin becomes uniform.

(4) Since no gate is created in the center of the molded product, the dimensional accuracy of the opening is good. (For a disk as a recording medium, the precision of the opening in the center is more important than the dimension of the outermost circumference.)

(5) Since the outermost portion of the disk can be effectively used as a recording medium, a large amount of information can be recorded.

(6) Since compressive force is applied only to the necessary areas, molded products with a large projected area can be obtained with a small hydraulic pressure or molding machine.

(7) The cavity block does not move and the cavity thickness remains constant throughout, resulting in excellent wall thickness stability.

(8) There is no limit to the viscosity of the resin used, so
There is no need to sacrifice strength or other properties for lower viscosity.

As described above, the mold of the present invention solves the conventional problems and achieves new effects.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a disk manufacturing mold as an example of the present invention, and FIGS. 2 and 3 are enlarged views of the gate portion thereof. FIG. 2 shows the state before compression, and FIG. 3 shows the state after compression. FIG. 4 shows an embodiment in which the cavity block 7 is thinner than the cavity plate 8. FIG. 5 is a cross-sectional view of a mold for manufacturing a concave lens as an example of the present invention, and FIG. 6 is a horizontal cross-sectional view thereof. The numbers in Figures 1 to 6 refer to the following. 1... Locate ring, 2... Sprue bush, 3... Fixed side template, 4... Fixed side receiving plate, 5
...Core plate, 6...Core block, 7...
Cavity block, 8... Cavity plate, 9... Movable side receiving plate, 10... Spacer block, 11... Ejector plate, 12...
...Movable side template, 13, 14...Spring, 1
5, 16... Ejector pin, 17, 18...
Compression ring, 19... Sleeve pin, 20... Core pin, 21... Sprue, 22
...First runner, 23...First gate, 2
4...Second gate, 25...Second runner,
26...Third gate, 27...Molded product, 28...
…heater.

Claims (1)

[Scope of Claims] 1. In an injection compression molding mold having a mold pair of a fixed mold and a movable mold that form a cavity that conforms to the shape of a desired molded product, the volume of the cavity 27 is determined by the molding process. means 17 for reducing the cross-sectional area of the resin flow path between the cavity 27 and the gate 24 proximate to the cavity 27;
7. A mold comprising means 18 for pressurizing the molten resin in the resin flow path between the mold and the mold. 2 Elastic bodies 13 and 14 compressed by mold clamping force are disposed between the mold plate 3 of the stationary mold and the mold plate 12 of the movable mold opposing thereto. Compression of the elastic bodies 13 and 14 in the direction in which the two templates 3 and 12 approach each other and the two means 1
The mold according to claim 1, wherein operations 7 and 18 are performed simultaneously in conjunction with each other. 3. The cavity 27 is a cavity for a disc-shaped product, and a ring-shaped gate 24 is provided surrounding the outer periphery of the cavity 27, and the cross-sectional area of the gate 24 gradually decreases along the flow direction of the molten resin. A mold according to claim 1 or 2. 4. The mold according to any one of claims 1 to 3, wherein a heater 28 is embedded in the vicinity of the resin flow path where the pressurizing means 18 is present.