JPS6295210A - Mold for molding plastic - Google Patents

Abstract

PURPOSE:To permit molding of a molded product having a large thickness ratio with a high accuracy by a method wherein cooling structure are arranged properly to equalize the cooling speed of the central portion of a thick portion and a thin portion. CONSTITUTION:A molded lens 6 is molded between a movable insert piece 4a and a fixed insert piece 4b while a movable mold 3a, a fixed mold 3b and cooling blocks 5a, 5b are provided with heat medium flow paths 7a, 7b, 8a, 8b to cool the molded lens 6. The heat medium flow paths 8a, 8b are connecting the centers of the surfaces of the cooling blocks 5a, 5b, which are contacted with the movable insert piece 4a or the fixed insert piece 4b, to the same which are not contacted with the movable insert piece 4a or the fixed insert piece 4b through straight lines while the surfaces which are not contacted with the insert pieces 4a, 4b are the inlet sides of the heat medium. The surfaces, which are contacted with the movable insert piece 4 or the fixed insert piece 4b, recede from the insert pieces 4a, 4b while being expanded outwardly. The heat medium flow path is a scroll type to make a temperature distribution symmetrical with respect to the axis thereof while the heat medium flow paths 7a, 7b are arranged at positions having the same depth substantially as the outer peripheral sections of the heat medium flow paths 8a, 8b. According to this method, the cooling speed of the surface of a thin portion can be slowed down, while the cooling speed of the surface of a thick portion can be quickened.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to injection molding, compression molding, etc. of plastics, and particularly to molded products with a large ratio of thickness between thin and thick parts, such as high precision lenses. This invention relates to a molding die suitable for molding.

[Background of the invention]

In plastic injection molding, compression molding, etc., the temperature distribution of the molding die has a large effect on the accuracy of the molded product. Therefore, in order to obtain a molded product with high precision, a molding die that can provide an appropriate temperature distribution is required.

Furthermore, in the case of optical parts such as lenses, it is required that they be symmetrical about the rotational axis, so the mold temperature must also be kept symmetrical about the rotational axis during molding.

JP-A-57-+8, JP-A-57-+8: A method of periodically heating and cooling a mold to achieve a temperature distribution that is symmetrical about the rotational axis in the shape.
As described in Japanese Patent No. 72M, an apparatus has been proposed in which heat medium flow paths are arranged in a concentric pattern from the center of the rotating shaft to the periphery to uniformize the mold temperature. Making the mold temperature uniform is effective for plate-shaped molded products such as video discs, that is, molded products with substantially uniform wall thickness. However, in the case of molding a molded product having a large ratio of thickness between the thin part and the thick part, such as the lens 1 shown in FIG. 4, it is inappropriate to set the mold temperature to 7 -. If the mold temperature is uniform during the cooling process, as shown in FIG. 5, the cooling rate of the central portion 2a of the thick portion will be slow, and the central portion 24 of the thick portion will be cooled last. As a result, there was a drawback that shrinkage occurred due to shrinkage and accuracy deteriorated.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a molding die that eliminates the above-mentioned drawbacks and is capable of molding a molded product, such as a lens, with a high thickness ratio between a thin part and a thick part with high precision.

[Summary of the invention]

In order to eliminate the above-mentioned drawbacks, the present invention aims to prevent the occurrence of sink marks and achieve high accuracy by properly arranging the cooling structure and equalizing the cooling rate of the thin-walled part and the central part of the thick-walled part of the molded product. This is what you get with lens 7. Therefore, it is better to make the mold temperature uniform (by actively generating temperature distribution).
The cooling rate of the surface of the thin walled part of the molded product is slowed down, and the cooling rate of the surface of the thick walled part is set high.In other words, in the thin walled part, cooling elements such as heat medium channels or heat pipes are placed away from the molded product, and vice versa. The thick portion brings the heat medium or cooling element closer to the molded product.

Furthermore, in order to always match the cooling rate inside the molded product,
Cooling 9y' by changing the arrangement of the cooling element during the cooling process
It has a structure that allows the J rate to be varied.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure only shows particularly important parts of the present invention among the configuration of the molding die. Mold is movable type 3"e fixed type 3b
, a movable inserting piece 4a whose one surface serves as a cavity surface for shaping the lens, a fixed inserting piece 4b, cooling blocks sa, sb, etc. A molded lens 6 is formed between the movable insert piece 44 and the fixed insert piece 4b. Also movable type 5a.

The fixed fi 3b and the cooling blocks 5cL and 5b have heat medium flow paths 7a and 7b for cooling the molded lens 6, respectively.
+3a and ab are provided. The heat medium flow path 8''+8b is a movable entry piece 4a at the center of the cooling block 5ar5b.
A straight line connects the side of the surface that is not in contact with the fixed human piece 4b and the surface that is in contact with it, and the side that is not in contact with it is the inlet side of the heat medium. The surface side that is in contact with the movable insert piece 4'+fixed insert piece 4b then expands in the outer circumferential direction and becomes the movable insert piece 4a.
, moving away from the fixed human piece 4b. In other words, it moves away from the cavity surface. This is because FIG. 3 shows the case of a convex lens; in the case of a concave lens, on the contrary, the arrangement is such that it expands toward the outer periphery and approaches the cavity surface.

Then, the movable entered piece 4α reaches the side that is not in contact with the fixed human piece 4b. This is the outlet for the heat medium. When viewed from the front, the heat medium flow path has a spiral shape as shown in FIG. 2, which prevents deterioration of the axial symmetry of the temperature distribution. Also, the heat medium flow path 7a.

7b are arranged at approximately the same depth as the outer periphery of the heat medium flow paths 8a and 8b, respectively.

The operation of this mold will be explained next. The molded lens 6 is filled with molten resin from an injection molding machine (not shown) into the cavity.
becomes. Both surfaces are shaped by the movable insert piece 4a and the fixed insert piece 4b. At the same time, a heat medium such as oil or water is passed through heat medium channels 7a, 7b, B4, and 8b from a temperature controller (not shown). After the molded lens 6 is cooled down, the movable mold 3Δ
The fixed mold 3b is separated, the movable inserting piece 4a is projected by a projecting plate (not shown), and the molded lens 6 is taken out.

Note that the heat medium flow paths aa and 8 of the cooling blocks stL and sb
Although b has a complicated shape, it can be easily processed by dividing it into a plurality of blocks as shown in FIG.

Another embodiment is shown in FIG. In this case, heat pipes 9a, 9b''& are used in place of the heat medium flow path 84.8b having a complicated shape in the embodiment shown in FIG. 10b
It extends inward. The other ends are located within the cooling blocks sa and sb, and the closer to the outer periphery, the farther away from the cavity surface they are arranged. This also applies to convex lens molding as in FIG. 1, and in the case of a concave lens, the outer periphery is placed close to the cavity surface. Note that a large number of heat pipes 9cL and 9b are arranged concentrically as shown in FIG. Other configurations and operations are the same as in FIG. 1. When changing the cooling arrangement, the embodiment of FIG. 6 is easier to modify than the embodiment of FIG. 1.

FIG. 8 shows an example in which the cooling rate inside the molded product is made more uniform than the above two examples.

The figure shows only the movable side, but the fixed side has the same configuration.

Same as the embodiment shown in Fig. 6 (used with heat pipe 9a. The only difference is the hole 164 for heat pipe qcL.
A gap exists between the heat pipes 9a and the heat pipes 9a can slide back and forth. A spring 1 (5a) is fixed to the tip of the heat pipe 9cL.

On the other hand, at the rear end of the heat pipe 9a, there is a hydraulic shifter 1a,
A hydraulic valve J44 hydraulic bong (not shown) is installed.

In addition, a displacement sensor t that operates in conjunction with the heat pipe 9α
Za, a converter 13tL that converts the detected displacement into a signal
The displacement input from the displacement converter 136 and the set displacement are compared and the hydraulic pump 14cL'? : A control unit is installed.

This operation will be explained. First, the position of each heat pipe 9a during the cooling process is set as a function of time (. Then, when the cooling process starts, the position of each heat pipe 9a is detected by the displacement sensor 124, and the result is sent to the converter 13α. The control unit 15 compares the set displacement and the actually measured displacement, and controls the hydraulic valve 14α so that the position of the heat pipe 9a is the same as the set position.In other words, the heat pipe 9a is further To move the heat pipe 9α forward, increase the oil pressure, and the hydraulic cylinder 17a will push out the heat vibrator 9af.-If you want to move the heat pipe 9α backward, the oil pressure y!-If you lower it, the heat pipe 9α will be pushed out by the force of the spring 16a.
retreats.

Here, in order to improve cooling efficiency and temperature control accuracy, it is preferable that the heat pipe 9α and the cooling block 5a are in contact only near the tip, and that the middle portion is adiabatic. FIG. 9A is a cross-sectional view of a main part showing an embodiment in which a part of the cooling block 5α has a diameter larger than that of the heat pipe 9α (and is provided with an air insulation part 18). The cooling block 5cL may be made thinner as shown in FIG. 9B, a cross section of the main part, and the heat pipe 9α may be installed so as to pass through the heat insulating material 19.

As described above, by changing the position of the heat pipe 9a over time, the temperature distribution of the mold can be varied in various ways. In other words, the cooling rate inside the molded product can be made more uniform.

Using the mold of the embodiment shown in FIG. 8 above, injection molding of a biconvex lens with an outer diameter BOm, a center wall thickness of 20aI, and a thickness ratio of thin and thick parts of 1:6 as shown in FIG. I did it. Polymethacrylic resin was used as the material for the molded lens 1.

The resin was melted in a 2000c17c bath and filled into a mold. The die edge of the mold was uniformly heated to 200°C. As shown in FIG. 11, the distance between the position of the tip of the heat pipe on the cavity side and the cavity surface is kt. FIG. 12 shows the position R of each heat pipe at the start of molding. The horizontal axis indicates the radial distance from the central axis, and the vertical axis indicates the distance t. Distance between the tip of the heat pipe 9cL and the cavity surface at the central axis 7
m25m, the distance M was increased toward the outer periphery, and a heat pipe 9cL was placed near the outermost periphery at the position of l-106. FIG. 13 shows the change in the position of the heat pipe 9a during the cooling process. The horizontal axis shows the cooling time 2, and the vertical axis shows the distance t2 between the heat pipe 9G and the cavity surface. The position of the heat pipe 9α was kept constant within 30 degrees from the central axis. At the outermost periphery, the position of the heat pipe 9a was changed from the initial state j-106m to t==80m in about 4 minutes.
It was advanced to the parrot's position and then held at a constant K. Here, water at 20°C was used as a heat medium. The temperature change on the cavity surface and the temperature change in the central part of the molded product under the above conditions are shown in FIG. 14 and FIG. 15, respectively. The cooling rate of the cavity surface is high on the central axis (r W Ois ), and the cooling rate decreases toward the outer periphery, that is, the thinner part. -The cooling rate of the central temperature of the round-shaped product was uniform from the center axis to the outermost periphery. As a result, it was possible to prevent sink marks caused by the difference in cooling rate in the central part of the molded product, and it was possible to improve the precision of the lens to 1/2 that of the conventional one.

Further, in the embodiment shown in FIG. iA8 above, the position of the heat pipe is expressed as a function of time, but there is no problem in expressing it as a function of the cavity surface temperature. At that time, insert a sensor to detect the cavity surface temperature,
It is preferable to perform calculation processing and control based on the detected temperature.

Further, in this embodiment, the case of injection molding has been explained, but there is no problem in using it for compression molding or a combination of injection molding and compression molding.

[Effect of excuse]

As described above, according to the present invention, the cooling rate inside the molded product can be made uniform when molding a molded product with a large wall thickness ratio between the thin-walled part and the thick-walled part, thereby preventing the occurrence of sink marks. +h L accuracy was improved to 1/2 of the conventional level.

[Brief explanation of drawings]

1 to 3 and 6 to 9 are cross-sectional views showing one embodiment of the present invention. A cross-sectional view showing shape 2 of a molded product with a large ratio, FIG. 5 is an explanatory view of the conventional drawbacks, and FIGS. 11 to 15 are detailed explanatory views of the present invention. 3...S deaf, fixed bottle, 4...movable insert piece, fixed insert piece, 5...cooling block, 6...molded lens, 7, 8.10... heat medium flow path, 9...Heat pipe. 1st evil 3a. (, 41 Figure 6 Opening during cooling ■ Feeling 80 a Eifu first θ evil turn//mouth jku 4a 72th evil member Chiingata ke ■ Kawarai Tee example) Oyl) (I) Enamel / 4 warm feeling / mouth''. Relaxation time (min.

Claims (1)

[Claims] 1. In plastic injection molding, compression molding, or a combination of these, a cooling element such as a heat medium flow path or a heat pipe that cools the thin part of the molded product shape and a cooling element such as a heat pipe that cools the thin part of the molded product shape are provided. The distance between the cavity surface to be molded is made larger than the distance between the heating medium flow path or cooling element that cools the thick part of the molded product shape and the cavity surface that shapes the thick part of the molded product shape. Characteristic plastic molds.