JPS63172627A - Injection compression molding - Google Patents

Abstract

PURPOSE:To reduce the temp. distribution of a resin molding and to shorten the molding cycle, by transferring a mold temp. returning process before a mold releasing process as an actual molding process, heating the surface layer of the molding at or below the heat distortion temp. of the resin and cooling the central part at or below the heat distortion temp. of the resin. CONSTITUTION:An inserted top 1 of a fixed mold and an inserted top 5 of a movable top are cooled with a cooling medium flown into a medium path 13 by means of a temp. controlling device to cool them down to a cooled mold temp. TM3, which is at or below the mold temp. TM1 at an initial injection time. At the time t3 when the cooling is finished, the surface layer temp. TS of a resin is cooled down at or below the heat distortion temp. T1 but the resin temp. of the central part TC is a little higher than the heat distortion temp. T1. A heater 11 is charged again and the heating medium is flown into the medium path 13 to heat the inserted top 1 of the fixed mold and the inserted top 5 of the movable mold and to return the mold temp. to the mold temp. TM1 at the initial injection time. During this mold temp. returning and compression process, the resin surface layer is heated, while cooling of the central part of the resin is continued. At the time t4 when returning the mold temp. is completed, both the surface layer temp. TS and the central part temp. TC of the resin are approximate to the mold temp. TM1 at injection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an injection compression molding method, and in particular, the present invention relates to an injection compression molding method for molding thick and unevenly-walled resin products, such as plastic lenses.
The present invention relates to an injection compression molding method suitable for molding with high precision and in a short time.

[Conventional technology]

In the conventional injection compression molding method, when molding a resin molded product with thick and uneven thickness, first, the entire molten resin injected and filled into the cavity of the mold is heated to a temperature below the solidification temperature of the resin. The mold gate is sealed.

Then, the resin in the cavity is reheated until the surface layer becomes fluid, and then the mold temperature is lowered while applying compressive force to cool the resin in the cavity. After the molded product is removed from the cavity (mold step), the mold temperature is returned to the temperature at the time of injection and filling (mold temperature return step).

Note that, for example, Japanese Patent Laid-Open No. 12738/1983 is related to this type of method.

[Problem that the invention seeks to solve]

Since the above-mentioned conventional technology heats and cools only the resin surface layer within the cavity, it is necessary to rapidly heat and cool the mold. However, since the heat capacity of the mold is large, it is difficult to actually perform rapid heating and cooling. For this reason, when the resin is reheated, the central part of the resin is also heated and becomes almost flowable, and when it is subsequently cooled, the central part becomes hotter than the surface layer.

Therefore, after cooling, the resin molded product taken out from the cavity has a temperature difference between the surface layer and the center part, and is taken out with a large temperature distribution. As a result, after removal, different parts of the resin molded product shrink in different amounts, deteriorating shape accuracy or generating internal stress. For example, in the case of plastic lenses, this leads to a problem of deterioration of optical performance. There was a point.

In order to prevent temperature distribution from occurring in the resin molded product that has been taken out, it is possible to slowly cool the mold, but this increases the molding cycle and takes time to form. arise.

The present invention improves the problems of the prior art described above, and provides resin molded products with excellent shape accuracy and extremely low internal stress.
The object is to provide an injection compression molding method that allows molding in a short molding cycle.

[Means for solving problems]

The configuration of the injection compression molding method according to the present invention for solving the above-mentioned problems is to inject molten resin into a cavity formed between a fixed mold insert piece and a movable mold insert piece that are arranged to face each other. In the injection compression molding method, in which a resin molded product is molded by injection and filling, and compression force is added to this, the temperature of the fixed mold insert piece and the movable mold insert piece is maintained below the thermal deformation temperature of the resin. Molten resin is injected and filled into the cavity, compressive force is added to it (injection/pressure holding process), and the surface layer of the filled molten resin or the entire resin is cooled to below the solidification temperature of the resin (primary process). After the cooling/compression step), the fixed type insert piece and the movable type insert piece are heated to heat the surface layer or the entire resin thereof to the solidification temperature or higher.Heating/compression step) Next, the fixed type insert piece is heated. Then, the movable input piece is cooled, and both pieces are cooled to below the temperature during the injection/pressure holding process, and the temperature of the surface layer is cooled to below the thermal deformation temperature of the resin.Second cooling/compression process ), then the fixed mold insert piece and the movable mold insert piece are heated again to return the temperature of both insert pieces to the temperature at the time of the injection/pressure holding process (mold temperature return/compression process), and then the cavity is heated again. The resin molded product is removed from the mold (Wi-type process).

More details are as follows.

We focused on the fact that if the temperature of the surface layer of the molded product inside the cavity is lower than the center, even if the surface layer is heated, the center will be cooled to the same temperature as the surface layer. However, the mold temperature return process, which was conventionally included in the molding cycle but performed after the mold release process, is now carried out as an actual molding process before the mold release process and is called the mold temperature return/compression process. ), in this step, the surface layer of the molded product is heated to a temperature below the heat distortion temperature of the resin, and the central part is cooled to below the heat distortion temperature, thereby reducing the temperature distribution of the resin molded product and improving the molding process. This is designed to shorten the cycle.

[Effect]

After returning the mold temperature to the temperature during the injection and pressure holding process,
The resin molded product can be taken out from the cavity. As a result, the cooling time and mold temperature recovery time are shortened, thereby shortening the molding cycle, and at the time of removal, the temperature difference between the surface layer and the center of the resin molded product is reduced, and the temperature distribution is reduced.

〔Example〕

Before going into the description of the embodiments, basic matters related to the present invention will be explained using FIG. 4.

Figure 4 shows a comparison of the main parts of the temporal changes in resin temperature and mold temperature according to the conventional technique and the injection compression molding method of the present invention. Diagram, (b
) is a temperature-hour diagram of the present invention.

The injection compression molding method of the present invention [Fig. 4(b)] differs from the conventional injection compression molding method [Fig. 4(a)] as follows.
In the conventional technology, the mold temperature recovery, which was included in the molding cycle but had nothing to do with the resin molded product, after the M-type process for taking out the resin molded product, was included as an actual molding process. The surface layer of the resin molded product is heated to a temperature below the heat distortion temperature.

By doing this, according to the present invention, the internal temperature difference (=resin center temperature - resin surface layer temperature) of the resin molded product at the time of removal, which was conventionally Δ''', can be changed to 1. Since the difference can be reduced to Δ'r Ho, deterioration in shape accuracy and internal stress after the resin molded product is taken out are significantly reduced.

The molding cycle is also shortened for reasons explained below.

In both the conventional injection compression molding method and the injection compression molding method of the present invention, the temperature of the entire resin molded product at the time of removal must be cooled to a temperature below the heat distortion temperature of the resin. This is because if the material is removed at a temperature higher than the heat distortion temperature, the deformation after removal is large and the shape accuracy deteriorates, so the compressive force is kept applied until the temperature drops below the heat distortion temperature. By the way, conventionally, as shown in FIG. 4(a), the temperature at the center of the resin is higher than the temperature at the surface layer of the resin during cooling, and the resin is taken out in that state. Therefore, it is necessary to wait until the high-temperature central portion of the resin reaches the heat distortion temperature or higher before finishing cooling.

In contrast, in the method of the present invention, as shown in FIG. 4(b), in the subsequent mold temperature return/compression process, the resin surface layer is heated, but the central portion is cooled. Therefore, it is not necessary to cool the central portion of the resin to the heat distortion temperature at the end of cooling, and the method according to the present invention requires a shorter cooling time. In this way, if the cooling time is short, the mold temperature at the end of cooling will be low. The mold temperature at the end of cooling is to cool at least the resin surface layer to below the thermal deformation temperature.

The mold temperature is lower than the initial temperature, that is, during injection filling. Therefore, the higher the mold temperature at the end of cooling, the smaller the temperature return range in the subsequent mold temperature return/compression step. In other words, the method of the present invention in which the mold humidity at the end of cooling is higher results in a shorter mold temperature recovery time.

For the reasons explained above, the cooling time and mold return time can be shortened by taking out the resin molded product after returning the mold temperature as in the present invention. Since the time required for other steps is the same as in the conventional method, the injection compression molding method of the present invention shortens the molding cycle as a whole.

The present invention has been made based on the above-mentioned basic matters, and its outline will be explained using FIG. 1.

FIG. 1 is a process diagram of the injection compression molding method of the present invention.

First, in the injection and pressure holding process, the fixed type input piece and if
While maintaining the temperature of the moving human figure below the thermal deformation temperature of the resin, molten resin is injected and filled into the cavity, and compressive force is applied to it. This compressive force is for shaping and for improving heat transfer, and is applied until the resin molded product is taken out from the cavity.

In the next primary cooling/compression step, the surface layer of the molten resin filled into the cavity or the entire resin is cooled to a temperature equal to or higher than the assimilation temperature of the resin.

At this time, the mold temperature may be kept constant or may be cooled.

In the subsequent heating/compression step, the fixed molded piece and the movable molded piece are heated to heat the surface layer or its entire resin to the assimilation temperature or higher, making it in a flowable state.

Furthermore, in the secondary cooling/compression process, the fixed type insert piece and the movable type insert piece are cooled to a temperature lower than the temperature during the injection/pressure holding process, and the temperature of the surface layer is lowered to the temperature of the resin. Cool to below heat distortion temperature.

Next, in the mold temperature return/compression step, the fixed mold insert piece and the movable mold insert piece are heated again to return the temperature of both insert pieces to a temperature equal to the temperature during the injection/pressure holding step.

In the final mold release step, the resin molded product is removed from the cavity, completing one molding cycle. onwards,
Repeat this molding cycle.

The details of this injection compression molding method will be explained below with reference to Examples.

FIG. 2 is a cross-sectional view of an injection compression molding mold used in the injection compression molding method according to one embodiment of the present invention, and FIG. It is a time diagram.

In FIG. 2, 1 is a fixed mold insert piece that forms a cavity lO with a movable mold insert piece 5, 2 is a fixed sleeve provided between the fixed mold insert piece 1 and the fixed mold 3,
This fixing sleeve 2 does not directly fix the fixed mold insert piece 1 to the fixed mold 3, but is provided so as to be able to accommodate changes in the outer diameter of the fixed mold insert piece 1 to some extent. Note that the fixing sleeve does not necessarily need to be provided.

Reference numeral 4 indicates a fixed mold mounting plate for fixing the fixed mold 3 to an injection molding machine (not shown), and 6 supports the movable mold inserting piece 5 from the rear and absorbs the compressive force generated by the pressure cylinder 14. A pressurizing block 7 for transmitting pressure to the movable mold input piece 5 is an extrusion plate 8 for supporting the pressurizing block 6 and a Z pin 18 to be described later and transmitting the pressurizing force to the movable mold input piece 5. It is a movable sleeve provided between the molding piece 5 and the movable mold 9, and this movable sleeve 8, like the fixed sleeve 2,
It is provided so as to be able to cope with changes in the outer diameter of the movable insert piece 5 to some extent. Furthermore, the movable mold inserting piece 5 slides within this movable sleeve 8. Note that the movable sleeve does not necessarily need to be provided.

9 is a movable mold for fixing the movable sleeve 8; 10 is a movable mold that fixes the movable sleeve 8;
The fixed type input piece 1. Movable human figure 5 and movable sleeve 8
It is a cavity formed by.

11 is a fixed type input piece 1. A heater 12 inserted into the fixed sleeve 2 and the movable sleeve 8 in order to heat the movable input piece 5 is used to detect the temperature of the fixed type input piece 1 and the moving type human piece 5. 13 is a heating and cooling medium passage for temperature regulation; 14 is the extrusion plate 7;
．． A pressurizing cylinder that can apply compressive force to the resin in the cavity 10 via the pressurizing block 6 and the movable mold inserting piece 5, and also extrudes the resin molded product in the cavity 10 from the cavity 10 at the end of the molding cycle. It is.

15 is a heater 11 or heating and cooling medium flowing through the heating and cooling medium passage 13 in response to a temperature signal sent from the temperature sensor 12 that detects the temperature of the fixed type input piece 1 and the nf dynamic type human piece 5. In addition to controlling the refrigerant (not shown), the temperature controller 16 is capable of sending a control signal to the oil pressure control device 16 to control the generated oil pressure; upon receiving the signal from the temperature controller 15, This is a hydraulic control device that controls the hydraulic pressure sent to the pressurizing cylinder 14.

17 is a movable mold mounting plate for supporting the pressure cylinder 14 and attaching the movable mold 9 to the injection molding machine; 18 is a movable mold mounting plate;
Z pin for pulling out the resin in the sprue 19 toward the ri (moving mold 9 side) at the end of the molding cycle.

Reference numerals 19 and 20 denote sprues and runners that constitute the resin passage from the injection molding machine to the cavity 10.

An embodiment of the injection compression molding method of the present invention will be described using an injection compression molding apparatus having an injection compression molding mold configured as described above.

The mold temperature at the start of molding, that is, at the time of injection, is 1゛M1.

Resin heat deformation temperature 'l' is 1 or less. Fixed type 3
Then, the aJ dynamic mold 9 is closed to form the cavity 10.

When the injection compression molding apparatus is turned on, molten resin flows from the injection molding machine onto the sprue 19. It passes through the runner 20 and is filled into the cavity 10.

When the resin is filled into the cavity 10, the injection molding machine directly enters the pressure holding process. At the same time, the hydraulic control device 16 moves the movable mold entry piece 5. A compressive force is applied by a pressurizing cylinder 14 via a pressurizing block 6 and an extrusion plate 7. This results in
The resin in the cavity 10 is shaped, and this resin and the fixed mold insert piece 1. The degree of close contact with the movable mold insert piece 5 is improved, and heat transfer is easily performed.

Thereafter, the resin is cooled while maintaining the mold temperature at T.11. After time t0 when the resin surface layer temperature T5 has been cooled to below the resin solidification temperature T2 and the resin center temperature Tc has also been cooled to at least around the resin solidification temperature, the temperature controller 15 energizes the heater 11 and the heating medium is flowed into the medium path 13 to heat the fixed mold insert piece 1 and the movable mold insert piece 5, and raise the temperature to the mold temperature T, , □ during heating. The mold temperature Tn2 during heating is set to the solidification temperature of the resin 12 or higher. At heating end time t2, the resin surface layer temperature T is heated to a solidification temperature of 12 or higher and is in a flowable state. Resin center temperature T. is also cooled to a temperature equivalent to the resin surface layer temperature T.

Next, the temperature controller 15 supplies the cooling medium to the medium passage 13.
to cool the fixed type input piece 1 and the movable type input piece 5,
Cooling mold temperature TI, lower to 3. This cooling mold temperature T M 3 is lower than the initial injection mold temperature Tr11. Cooling end time t, smell, resin surface M temperature T
, are cooled to below the heat distortion temperature T1, but the resin center temperature Tc is slightly higher than the heat distortion temperature TY.

After that, the temperature controller 15 again controls the heater 11.
is energized, a heating medium flows through the medium passage 13, the fixed mold insert piece 1 and the movable mold insert piece 5 are heated, and the mold temperature is returned to the initial injection mold temperature Tnt. This mold temperature return/
In the compression process, the first surface layer is heated, and the central part of the resin continues to be cooled. At mold temperature return end time t4, the resin surface layer temperature T3. Resin center temperature T. In both cases, the mold temperature during injection is around T, 1. That is, the temperature distribution within the resin is small and is below the thermal deformation temperature T1.

In this state, take out the resin molded product. The removed resin molded product has a small internal temperature distribution, so deformation and internal stress are extremely small. Furthermore, since the mold temperature at the time of take-out is the same as the mold temperature at the initial injection, primary molding can be started from t5 immediately after the resin molded product is taken out.

In the above steps, compressive force is applied until the time of removal for shaping and for improving heat transfer. Further, the magnitude of the compressive force may be changed by the temperature controller 15 and the hydraulic control device 616 in accordance with the temperature change of the fixed type insert piece 1 and the movable type insert piece 5.

A specific example will be shown.

Made of acrylic resin, outer diameter 130mm+, maximum wall thickness 1
A plastic lens having a thickness of 7+ nm and a minimum wall thickness of 3 cm was molded by the method of this example. Mold temperature TM1 during injection
When molding was carried out at 90°C, the heating mold temperature 1°M2 was 140°C, the cooling mold temperature TMa was 70°C, and the compressive force applied to the resin was approximately 290 kg/cd, the molding cycle was 20°C compared to the conventional molding cycle. The time was reduced from 15 minutes to 15 minutes (approximately 3/4), and the shape accuracy was improved from 15 μm to 10 μm.

Furthermore, the generation of internal stress could be significantly reduced, and optical performance could be improved.

According to the embodiments described above, 1) the shape accuracy of the resin molded product is improved (for example, improved by about 2/3), 2) the internal stress of the resin molded product is significantly reduced, and 3 the molding cycle is shortened ( For example, it has the effect of reducing the length to about 3/4).

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide an injection compression molding method that can mold a resin molded product with excellent shape accuracy and extremely low internal stress in a short molding cycle.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of the injection compression molding method of the present invention, FIG. The figure is a temperature one-hour diagram of the injection compression molding method according to this figure 2,
The figure shows a comparison of the main parts of the temporal changes in resin temperature and mold temperature according to the conventional technique and the injection compression molding method of the present invention, and (a) is a conventional temperature one-hour diagram. ,(b)Fig. It is a temperature one-hour diagram of the present invention. 1... Fixed type entering piece, 5... Movable type entering piece, 10...
cavity.

Claims (1)

[Claims] 1. Molten resin is injected and filled into the cavity formed between the fixed molding piece and the movable molding piece arranged facing each other, and compressive force is applied to it to form a resin molded product. In this injection compression molding method, molten resin is injected and filled into the cavity while maintaining the temperature of the fixed mold insert piece and the movable mold insert piece below the thermal deformation temperature of the resin, and compressive force is applied to it. (injection/pressure holding process), after cooling the surface layer of the filled molten resin or the entire resin to below the solidification temperature of the resin (primary cooling/compression process), the fixed type input piece and the movable type input piece are is heated to heat the surface layer or its entire resin to the solidification temperature or higher (heating/compression step), then the fixed type insert piece and the movable type insert piece are cooled, and both the input pieces are subjected to the injection/compression process. The temperature of the surface layer is cooled to below the temperature during the pressure holding step and the temperature of the surface layer is below the thermal deformation temperature of the resin (secondary cooling/compression step), and then the fixed type insert piece and the movable type insert piece are heated again. Then, after returning the temperature of both input pieces to the temperature at the time of the injection/holding process (mold temperature return/compression process), the resin molded product is removed from the cavity (mold release process). Characteristic injection compression molding method.