JP2000135727A - Injection molding method and injection molding die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold and its heating method for heating and cooling quickly without complicating the composition of a mold in a precision plastic molding method. SOLUTION: A heating medium such as a heater 4 is disposed in the vicinity of a cavity, and heat insulation layers 3 are disposed mainly in the direction of not disposing the heating medium in the vicinity of the cavity, and the heat conduction from a cavity section being molded to the direction of not disposing the heating medium is restricted, and mold main bodies X and Y are controlled at a given temperature by a separate heating medium 4 (A temperature control medium is supplied in pipelines or a heater is used.), and the temperature in the vicinity of the cavity is controlled directly by a heating medium 1 nearby, and the temperature is set higher than those of the mold main bodies X and Y at all times throughout the whole molding process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the injection molding of precision molded products such as plastic lenses, and is effective for injection molding of plastic optical elements in high-precision optical equipment such as copiers and fax machines. In addition, the heating and cooling cycle of the mold can be shortened without difficulty, and the productivity of precision plastic optical elements by the injection molding machine can be significantly improved.

[0002]

2. Description of the Related Art There are various conventional techniques for improving the molding accuracy of a molded product in injection molding and reducing internal distortion. However, a heating element is loaded in a cavity mirror piece and heated by injection immediately after injection. Japanese Patent Application Laid-Open No. 9-183146 ("Injection Molding Method and Injection Mold") is known to reduce the temperature difference between the resin in the cavity immediately after. By forming a thin-film electric resistor, it is possible to raise the temperature of the cavity while minimizing the extension of the molding time, as described in JP-A-7-329068 (“Plastic injection molding and Plastic injection molding method using the mold ”), the main mold and the cavity component are separate parts, and a heat insulating layer is provided between the two. Patent as to the configuration put the piece and the mold structure in which a temperature control conduit, performs high-cycle molding by supplying hot water and cold water temperature control pipe 9-3146
No. 11 (“a mold structure with easy temperature control”).

In the case of a normal mold in which the mold body is maintained at a constant temperature using a temperature control medium, a heater, or the like, the temperature near the cavity is higher than the set temperature of the entire mold due to heat radiation from the resin immediately after injection. It takes a long time to rise and return to the original temperature. Therefore, the molding cycle cannot be shortened. Further, since the heat radiation from the resin immediately after the injection becomes larger in the thick portion or the large area portion, the temperature distribution near the cavity becomes non-uniform, especially immediately after the injection, and further, in the vicinity of the PL surface due to mold opening, mold clamping, and the like. There is a problem that the temperature of the cavity is easily fluctuated, and that cycle control including rapid heating and cooling is almost impossible. For this reason, precision molding that requires stable temperature control, maintenance of a uniform temperature distribution, or temperature distribution control according to the cavity shape is required for ordinary molds that maintain the mold body at a constant temperature with a heater or the like. It is difficult. Also, a mold in which a heating medium is arranged in the vicinity of the cavity (a heater and a heater for supplying a temperature control medium to a pipeline.
In the case of Japanese Patent Application Laid-Open No. H11-270, heat is released to the entire mold when heated, so that rapid heating and rapid cooling are difficult, and the temperature near the cavity is relatively stable, and the temperature distribution depends to some extent on the arrangement of the heating medium. However, if the partial heating is performed to improve the temperature distribution, there is a problem that the molding cycle becomes longer by that amount.

On the other hand, a mold in which a thin film heater is disposed on the surface of a cavity (for example, Japanese Patent Application Laid-Open No. 7-329068).
In the case of (1), since only the cavity surface is heated, the heat capacity in the heating range is small, rapid heating is possible, and the difference from the mold temperature is large, so rapid cooling after heating is also possible. However, the mold structure is complicated, the life of the thin film heater is short, and the replacement thereof is very expensive. further,
In the case of a mold that uses both a heating medium and a cooling medium in the vicinity of the cavity (supply the cooling medium to the pipeline), rapid heating and cooling can be performed to some extent, but the mold structure is complicated and costly. Furthermore, in the case of a mold in which the vicinity of the cavity is surrounded by a heat insulating layer (for example, Japanese Patent Application Laid-Open No. 9-314611), rapid heating is easy because the heat capacity of the area affected by heating when heating the vicinity of the cavity is small. However, in the case of using only a heating medium, it takes a long time to cool because of a structure in which heat is hardly radiated. On the other hand, rapid cooling is also possible if a cooling medium is used in combination, but this makes the mold structure complicated and expensive, and because the tolerance of the shape of the heat insulating plate is large, the entire cavity is surrounded by a heat insulating layer. The use of a high-precision mold has a problem in that the structure becomes very complicated and costs increase.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to devise a mold and a heating method thereof so that heating and cooling can be performed quickly without complicating the composition of the mold. The task is to do so.

[0006]

Means taken to solve the problem The means taken to solve the above problem are constituted by the following elements (a) to (d). (A) A heating medium such as a heater is arranged near the cavity, and a heat insulating layer is arranged mainly in the direction without the heating medium near the cavity to transfer heat from the cavity being formed to the direction without the heating medium. Restrict. (B) To control the mold body to a constant temperature with another heating medium (supplying a temperature control medium to a pipe or using a heater). (D) The temperature in the vicinity of the cavity is directly controlled by the heating medium in the vicinity, so that the temperature is always higher than the mold body in the entire molding process.

[0007]

In the case of rapid heating, the range of influence of the heat is limited by the heat insulating layer, so that the molding cycle is prevented from being prolonged by that much, and the direction of heat radiation from the cavity is restricted. Since the heat radiation to the mold body is reduced, the amount of heat required to raise the temperature of the cavity is reduced,
In addition, the number or size of the heating medium to be arranged and the power rating (wattage) are also reduced. In addition, since no cooling medium is used, the structure is further simplified, the cavity constituting part itself can be made smaller, and the cost for manufacturing and maintaining the mold is reduced. In addition, since an inexpensive cartridge heater can be used, mold production and maintenance are easy and at low cost, and rapid cooling is possible by setting the mold body to a temperature lower than the vicinity of the cavity. The sylle is shortened, and temperature cycle control including temperature rise can be performed without sacrificing the molding cycle. Further, since the temperature is directly controlled in the vicinity of the cavity, the temperature in the vicinity of the cavity is stabilized even when the mold is opened, and the above-mentioned problem caused by the instability of the temperature in the vicinity of the cavity is effectively avoided.

[0008]

Next, an embodiment will be described with reference to the drawings.

Embodiment 1 [Configuration] In FIG. 1, the mold of the embodiment is made of SUS, and a plastic transmission plate (manufactured by PC, 8 × 20 × 100).
In this case, a total of four cartridge heaters 1 for controlling the temperature of the cavity are installed on a piece constituting the side surface of the cavity at a position 15 mm from the wall surface of the cavity, and a cartridge for controlling the temperature of the cavity is provided. Heater 1
A control thermocouple S is provided between the cavity and the cavity 2, and a heat insulating plate 3 made of a ceramic material is provided in the direction near the cavity without the cartridge heater 1 and outside the mirror surface forming piece.
Is set 25 mm from the cavity wall surface (both the fixed mold X and the movable mold Y). In addition, each of the fixed mold X and the movable mold Y is provided with three cartridge heaters 4 for controlling the temperature of the mold body outside thereof, and thermocouples for temperature comparison are thermocouples A and B. , C are installed. The heater 1 for controlling the temperature of the cavity on the fixed side, the heater 1 for controlling the temperature of the cavity on the movable side, the heater 4 for controlling the temperature of the mold body on the fixed side, and the heater 4 for controlling the temperature of the mold body on the movable side are respectively different program controllers. Connected and controlled individually. The mold body temperature control heaters 4 are both controlled at a constant temperature (110 ° C.), and the cavity temperature control heaters 1 are all controlled at a constant temperature (130 ° C.).

[Operation / Effect] FIG. 2 shows a case where the temperature is controlled by a main mold having a heater and a heat insulating layer in the vicinity of the cavity and a case where the temperature is controlled by a mold in which the heat insulating plate of the same mold is replaced with a SUS plate. The detection temperatures of the thermocouples A, B, and C are shown.
In the case where there was no heat insulating plate, the mold main body was only 15 ° C. different from the cavity 2 due to the heat radiation from the cavity control heater 1, and was actually 115 ° C. However, when there was a heat insulating plate, the temperature was stably controlled at 110 ° C. (furthermore, it was possible to stably provide a temperature difference of up to 40 ° C.). As can be seen from the graph, without a heat insulating plate, the thermocouple near the cavity mirror surface is affected by the heat radiation to the mold body, although the temperature difference between the outer thermocouple C and the thermocouples A and B near the cavity is not so large. The pair B is a thermocouple A near the side
It can be seen that the temperature is lower than the temperature and the temperature distribution near the cavity is not uniform. On the other hand, in the mold according to the present invention in which the heat insulating plate 3 is disposed, there is no large temperature difference between the outer thermocouple C and the thermocouples A and B near the cavity. It can be seen that a uniform temperature distribution can be realized near the cavity as compared with the case of FIG. In this way, by disposing the heat insulating plate to restrict the heat conduction in the direction without the heating medium, a temperature difference can be provided between the mold body and the cavity 2 while maintaining a uniform temperature distribution near the cavity. I understand.

Next, the time change of the temperature measured at 5 mm from the wall near the cavity is compared between the main mold having the heater and the heat insulating layer in the vicinity 2 of the cavity and the normal mold having no heat insulating layer. It is shown in FIG. Normally, the temperature does not drop easily due to heat radiation from the resin, and a sharp drop in temperature is observed when the mold is opened. On the other hand, in the case where a heater and a heat insulating plate are installed near the cavity and the temperature is controlled with a difference of 20 ° C. from the mold body temperature control heater 4, the cooling speed is increased due to the temperature difference between the mold body and the vicinity of the cavity. This indicates that the molding cycle is shortened, and that the temperature is stable even when the mold is opened, because the temperature is directly controlled near the cavity. By lowering the temperature setting of the mold body, cooling can be accelerated and the molding cycle can be further shortened. Therefore, the cooling rate can be increased without using a cooling medium, and the mold structure can be made simpler and more compact. The use of inexpensive cartridge heaters has the advantage of good thermal responsiveness, easy maintenance and low cost.
Since rapid heating and cooling are possible, for example, it is possible to control the temperature of the cavity portion in a cycle including a heating process as shown in FIG. 4 without sacrificing the molding time, and it is possible to correspond to the shape of the molded product. By appropriately arranging the heaters, the optimum temperature and temperature distribution can be freely realized in each molding process.

[0011]

Embodiment 2 [Structure] The embodiment 2 has the structure shown in FIG. 5, and is different from the mold structure of the embodiment 1 in that the heat insulating layer 13 is further extended from the cavity wall along the longitudinal direction near the cavity. The thermocouples D, E, and F are arranged along the longitudinal direction near the cavity for temperature comparison. The mold body temperature control heaters are both controlled at a constant temperature (110 ° C.), and the temperature control heaters 1 and 11 on both sides of the cavity are both controlled at a constant temperature (130 ° C.).

[Operation / Effect] The thermoelectric power generated when the temperature of the mold of this embodiment in which the heat insulating plate is installed along the longitudinal direction near the cavity is controlled, and the temperature of the metal mold in which the SUS plate is disposed at the same position is controlled. FIG. 6 shows a comparison between the detected temperatures of the pairs D, E, and F. It is clear that a uniform temperature distribution can be realized in the longitudinal direction of the cavity when the heat conduction from the end of the cavity to the mold body is limited by disposing the heat insulating plate. That is, by arranging the heat insulating plate so as to limit the heat conduction from the cavity end to the mold body, it is possible to prevent a temperature drop near the cavity end, and to further reduce the heater or power rating ( It is possible to use a heater with a small wattage or reduce the number of heaters to be used, so that a mold having a more compact and simple structure can be obtained.

[0013]

[Others] The heat insulating plates 3 and 3 in the first and second embodiments.
13, a low heat conductive material (a material having a slightly higher thermal conductivity than the heat insulating plate) may be used, or a gap may be provided by a combination of pieces or the like, and the gap may be used for the same heat insulating function as the above-described heat insulating material. A similar effect can also be obtained by providing. Also, the same effect can be obtained by controlling the temperature of the mold body by providing a conduit instead of a heater and supplying a temperature control medium to the conduit to control the temperature to a constant value. Further, the resin material, the mold material, and the heat-insulating layer material are not limited to those used in the above-described embodiments, and may be any material that satisfies the required characteristics. The number of the control means and the number of the control means may be appropriately selected as required to achieve a desired temperature distribution, and the arrangement may be appropriately selected. Furthermore, as for the heat insulating layer and the heating medium to be installed near the cavity, the positions at which the heat insulating layer and the heating medium can be installed are limited by the shape and size of the mold structure and the cavity, and the shape and number of the heating medium. It is more desirable to arrange. In addition, the temperature may be set to an appropriate temperature according to the quality level required for the type of molded article. When using a heating medium for controlling the cavity temperature, the temperature of the heating medium is set to the mold body temperature. It is desirable that the temperature is always higher than the temperature setting of the control heating medium by 2 ° C. or more. If this temperature difference is less than 2 ° C., the effect of cooling the cavity by the mold body is small.
The effect of stabilizing the temperature of the cavity and the effect of shortening the molding cycle are hardly exhibited. Also, the greater the temperature difference, the greater the cooling effect of the cavity by the mold body, which has the advantage that the molding cycle can be greatly reduced.However, if the temperature difference is too large, uneven temperature will occur near the cavity during molding. This is liable to cause deterioration of the quality of the molded article. Therefore, it is advisable to increase the temperature difference as long as the required quality of the molded product can be ensured. However, the value differs depending on the shape of the molded product, the required quality and the mold structure, etc. There is no other choice. In addition, in the case of the said Example, 5 degreeC-30
By setting the temperature difference of ° C., the effect of the present invention was particularly effectively exhibited, and when a temperature difference of 40 ° C. or more was provided, conversely, deterioration and deterioration of molded article quality due to uneven temperature were observed.

[0014]

Advantages of the Invention Advantageous Effects of the Invention According to the first aspect of the present invention, in a method of injection-molding a plastic product in which a cavity formed by a fixed-side mold and a movable-side mold is injected and filled with a resin, and further cooled, a molded product is taken out. The heating medium for controlling the temperature of the cavity disposed in the cavity and the heating medium for controlling the temperature of the mold body disposed in a position away from the cavity are individually controlled in the molding process, compared with the heating medium. Rapid heating of the cavity by restricting heat conduction from the cavity to the direction in which the heating medium for controlling the temperature of the cavity does not exist by disposing a heat insulating material, a low thermal conductivity material, or a void in at least a part of the vicinity. Alternatively, rapid cooling is possible, shortening the molding cycle and increasing the temperature without sacrificing the molding cycle. Temperature cycle control including a temperature process can be performed, and temperature fluctuation due to the influence of disturbance such as mold opening is reduced and stabilized.

2. According to the injection molding method of claim 1, the temperature of the mold body is controlled by controlling the heating medium for controlling the cavity portion temperature and the heating medium for controlling the mold body temperature at different temperature settings. It is set lower than the vicinity of the cavity. As a result, it is possible to rapidly cool without using a cooling medium, and to control the temperature of the cavity freely.

3. In the injection molding method according to claim 1 or 2, the temperature of the heating medium for controlling the temperature of the mold main body is set to be constant in all processes during the molding, so that the molding is repeated. The temperature distribution can be constantly stabilized.

4. In the injection molding method according to any one of claims 1 to 3, the temperature detected by the temperature detector for controlling the cavity temperature is the temperature detected by the temperature detector for controlling the mold body temperature. By controlling the temperature so that it is always kept higher during molding,
Particularly, cooling of the cavity can be accelerated without using a cooling medium.

5. Effect of the Invention According to Claim 5 In the injection molding method according to any one of Claims 1 to 4, the temperature of the cavity is controlled freely and optimally by changing the temperature setting of the heating medium for controlling the temperature of the cavity during the molding process. Can be controlled.

6. Advantageous Effects of the Invention According to Claim 6, at least one heating medium for controlling the temperature of the cavity is provided near the cavity formed by the fixed mold and the movable mold.
And a temperature detector for controlling the heating medium is disposed between the heating medium and the cavity, and further for controlling the temperature of the mold body at a position farther from the cavity than the heating medium. In a mold in which at least one heating medium is disposed, at least a part of the vicinity of the cavity is provided with a heat insulating material or a low thermal conductivity in order to limit heat conduction from the cavity to the direction in which the cavity temperature control heating medium does not exist. By arranging at least one of the material and the void, it is possible to rapidly heat or cool the cavity part, so that the molding cycle can be shortened or the heating process can be performed without sacrificing the molding cycle. Temperature cycle control, and can reduce and stabilize temperature fluctuations due to disturbances such as mold opening. That.

[7] FIG. According to the seventh aspect of the present invention, in the injection mold according to the sixth aspect, the heating medium for controlling the cavity portion temperature and the heating medium for controlling the temperature of the mold body are connected to different control means, so that the mold body is formed. Can be set lower than the vicinity of the cavity, and as a result, the cavity can be rapidly cooled without using a cooling medium.

8. Effect of the Invention According to Claim 8 By using a heater that conducts electric current to the heating medium according to any one of claims 1 to 7, it is possible to realize a mold having a simple structure at low cost with easy maintenance, and high responsiveness. Since it is good, the cavity can be rapidly heated.

9. Advantageous Effects of the Invention According to Claim 9 By using a temperature control medium of water or oil supplied to the pipeline as the heating medium for controlling the temperature of the mold body according to Claims 1 to 7, the temperature of the mold body can be reduced. It can be kept stable and constant.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mold according to a first embodiment.

FIG. 2 is a comparison diagram of a temperature distribution in Example 1.

3A is a temperature change diagram in one cycle near a cavity of a normal mold, and FIG. 3B is a temperature change diagram in one cycle near a cavity in Example 1. FIG.

FIG. 4 is an example of temperature control in a cycle including a temperature increasing process in the first embodiment.

FIG. 5 is a sectional view of a mold according to a second embodiment.

FIG. 6 is a comparison diagram of the temperature distribution in Example 2.

[Explanation of symbols]

 1,11: Cavity temperature control heater 3,13: Insulating plate 4: Mold body temperature control heater A to F: Comparative thermocouple S: Temperature control thermocouple X: Fixed side mold Y: Movable side Mold

Continued on the front page (72) Inventor Suji Hatakeyama 1-3-6 Nakamagome, Ota-ku, Tokyo Co., Ltd. Ricoh (72) Inventor Jun Jun Watanabe 1-3-6 Nakamagome, Ota-ku, Tokyo Co., Ltd. Ricoh (72) Inventor Kiyotaka Sawada 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. 4F202 AH74 AJ13 AK09 AK14 AP05 AR06 CA11 CB01 CN01 CN18 CN21 4F206 AH74 AJ13 AK09 AK14 AP054 AR064 JA07 JL02 JN43 JN44 JP11 JQ81

Claims (9)

[Claims] In a method for injection molding a plastic product, a cavity formed by a fixed mold and a movable mold is injected with a resin, and after cooling, a molded product is taken out, a cavity disposed near a mold cavity. The temperature of the heating medium for controlling the temperature of the part and the heating medium for controlling the temperature of the mold body disposed at a position farther from the cavity than the heating medium are individually controlled in the molding process, and at least a portion near the cavity. An injection molding method characterized in that a heat insulating material, a low thermal conductivity material, or a void is disposed in the cavity to restrict heat conduction from the cavity to a direction in which the cavity temperature controlling heating medium does not exist. 2. The injection molding method according to claim 1, wherein the heating soot body for controlling the temperature of the cavity and the heating medium for controlling the temperature of the mold body are controlled at different temperature settings. 3. The injection molding method according to claim 1, wherein the temperature of the heating medium for controlling the temperature of the mold body is set constant throughout the entire molding process. 4. The injection molding method according to claim 1, wherein the temperature detected by the temperature detector for controlling the cavity temperature is higher than the temperature detected by the temperature detector for controlling the temperature of the mold body.
An injection molding method, wherein the temperature is controlled so that the temperature is always kept high during molding. 5. The injection molding method according to claim 1, wherein the temperature setting of the heating medium for controlling the cavity temperature is changed during the molding process. 6. At least one heating medium for controlling the temperature of the cavity is disposed in the vicinity of the cavity formed by the fixed mold and the movable mold, and a temperature detector for controlling the heating medium is provided. A mold provided with at least one heating medium for controlling the temperature of the mold body at a position farther from the cavity than the heating medium and arranged between the heating medium and the cavity; In order to limit heat conduction in the direction in which the heating medium for cavity temperature control does not exist, at least a part of the vicinity of the cavity has a heat insulating material or a low thermal conductivity material or a void,
A mold for injection molding, wherein at least one of the molds is arranged. 7. The injection mold according to claim 6, wherein the heating medium for controlling the cavity temperature and the heating medium for controlling the temperature of the mold body are connected to different control means. Mold. 8. The injection molding method or the injection mold according to claim 1, wherein the heating medium according to claim 1 is a heater for conducting electric heating. 9. The injection molding method or the injection molding metal according to claim 1, wherein the heating medium for controlling the temperature of the mold body is a medium for controlling the temperature of water or oil supplied to the pipeline. Type.