JPH0651332B2 - Injection compression molding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an injection compression molding method, and in particular, to a resin molded product having a large thickness and an uneven thickness, such as a plastic lens,
The present invention relates to an injection compression molding method suitable for molding with high accuracy and in a short time.

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

Then, the surface layer of the resin in the cavity is reheated until it becomes fluid, and then the mold temperature is lowered while applying a compressive force to cool the resin in the cavity, and the cooled resin After taking out the molded product from the cavity (mold releasing step), the mold temperature is returned to the temperature at the time of injection / filling (mold temperature returning step).
A method related to this type of method is disclosed in, for example, Japanese Patent Laid-Open No. 58-12738.

[Problems to be solved by the invention]

In the above-mentioned conventional technique, only the resin surface layer in the cavity is heated and cooled, so that it is necessary to rapidly heat and cool the mold. However, since the heat capacity of the mold is large, it is actually difficult to carry out rapid heating / cooling. Therefore, when the resin is reheated, the central portion of the resin is also heated to be in a state in which it can flow, and during the subsequent cooling, the central portion becomes higher in temperature than the surface layer.

Therefore, after cooling, the resin molded product taken out of the cavity has a temperature difference between the surface layer and the central part thereof, and is taken out in a state where the temperature distribution is large. For this reason, after taking out, different amounts of shrinkage are generated in each part of the resin molded product to deteriorate the shape accuracy or generate internal stress. For example, in the case of a plastic lens, the optical performance is deteriorated. There was a point.

In order to prevent temperature distribution from occurring in the resin molded product taken out, it is conceivable to cool the mold, but if this is done, the molding cycle will become longer and the molding will take longer. Occurs.

The present invention improves the above-mentioned problems of the prior art, and has excellent shape accuracy and a resin molded product with an extremely small internal stress,
It is an object of the present invention to provide an injection compression molding method capable of molding in a short molding cycle.

[Means for solving problems]

The structure of the injection compression molding method according to the present invention for solving the above-mentioned problems is to provide a 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 an injection compression molding method in which a resin molded product is molded by injecting and filling and applying a compressive force to this, in a state where the temperature of the fixed mold insert and the movable mold insert is kept below the thermal deformation temperature of the resin. The molten resin is injected / filled into the cavity, a compressive force is applied to this (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 (1 After the subsequent cooling / compression step), the fixed mold insert and the movable mold insert are heated to heat the surface layer of the molten resin or the entire resin to a temperature exceeding the solidification temperature (heating / compression process), Next, the fixed mold insert and By cooling the mold inlet piece, to cool the temperature of the surface layer of the molten resin to below the heat distortion temperature of the resin by cooling both incoming frame to less than the temperature at the time of the injection-pressure holding process (2
(Next cooling / compression process), and then heating the fixed mold insert and the movable mold insert again to restore the temperature of both insert molds to the temperature of the injection / pressure holding process (mold temperature return / compression process). After that, the resin molded product is taken out from the cavity (mold release step).

More details are as follows.

If the temperature of the surface layer of the molded product in the cavity is lower than that of the central portion, it will be noted that even if the surface layer is heated, the central portion is cooled to the same temperature as the surface layer. However, the mold temperature returning process, which was conventionally performed after the mold releasing process even though it is included in the molding cycle, is carried before the mold releasing process as an actual forming process (this is called a mold temperature returning / compressing process). ), In this step, the surface layer of the molded product is heated in a range not higher than the heat distortion temperature of the resin, and the central portion is cooled to a temperature not higher than the heat distortion temperature to reduce the temperature distribution of the resin molded product, and It is designed to shorten the cycle.

[Action]

After returning the mold temperature to the temperature during the injection / pressure holding process,
I took out the resin molded product from the cavity. Thereby, the cooling time and the mold temperature recovery time are shortened to shorten the molding cycle, and at the time of taking out, the temperature difference between the surface layer and the central portion of the resin molded product is reduced, and the temperature distribution is reduced.

〔Example〕

Before starting the description of the embodiments, the basic matters according to the present invention will be described with reference to FIG.

FIG. 4 shows a comparison of essential portions of changes in resin temperature and mold temperature with time according to the conventional technique and the injection compression molding method of the present invention, and FIG. 4 (a) shows the conventional temperature-time. Diagram,
(B) The figure is a temperature-time 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)] in that
In the prior art, the mold temperature restoration, which was included in the molding cycle but unrelated to the resin molded product and was performed after the resin molded product was taken out (mold release process), was introduced as the actual molding process. The surface layer of the resin molded product is heated within a range not higher than the heat distortion temperature.

In this way, according to the present invention, the internal temperature difference (= resin central portion temperature-resin surface layer temperature) of the resin molded article at the time of taking out according to the present invention is ΔT. Since ≈0 can be achieved, deterioration of the shape accuracy after taking out the resin molded product and internal stress are significantly reduced.

The molding cycle is also shortened for the 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 taking out must be cooled to the heat deformation temperature of the resin or lower. This is because if the product is taken out at a temperature exceeding the heat deformation temperature, the deformation after taking out is large and the shape accuracy is deteriorated, so that the compressive force is kept applied until the temperature becomes equal to or lower than the heat deformation temperature. By the way, conventionally, as shown in FIG. 4 (a), the temperature of the resin central portion is higher than the temperature of the resin surface layer during cooling, and the resin is taken out in that state. Therefore, it is necessary to wait until the temperature of the central portion of the resin, which has a high temperature, becomes equal to or lower than the heat distortion temperature and complete the cooling.

On the other hand, in the method of the present invention, as shown in FIG. 4 (b), the resin surface layer is heated in the subsequent mold temperature restoration / compression step, 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 cooling time is shorter in the method according to the present invention. Thus, when the cooling time is short, the mold temperature at the end of cooling becomes high. The mold temperature at the end of cooling is lower than the mold temperature at the initial stage, that is, at the time of injection filling, because at least the resin surface layer is cooled to the heat deformation temperature or lower. Therefore, the higher the mold temperature at the end of cooling, the smaller the temperature recovery width in the subsequent mold temperature recovery / compression process. That is, in the method of the present invention in which the mold temperature at the end of cooling is high, the mold temperature recovery time is shorter.

For the reason described above, by cooling the mold temperature and then removing the resin molded product as in the present invention, the cooling time and the mold return time can be shortened. Since the time of the other steps is the same as the conventional one, the injection compression molding method of the present invention shortens the molding cycle as a whole.

The present invention has been made on the basis of the basic matters described above, and its outline will be described with reference to FIG.

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

First, in the injection / pressure-holding process, while maintaining the temperature of the fixed mold insert and the movable mold insert below the heat deformation temperature of the resin, inject and fill molten resin into the cavity, and apply compressive force to it. To do. 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 in the cavity or the entire resin is cooled to a temperature below the solidification temperature of the resin. At this time, the mold temperature may be constant or may be cooled.

In the subsequent heating / compressing step, the fixed mold insert and the movable mold insert are heated to heat the surface layer of the molten resin or the entire resin to a temperature above the solidification temperature to make it in a fluid state. .

Further, in the secondary cooling / compression process, the fixed mold insert and the movable mold insert are cooled to a temperature lower than the temperature in the injection / pressure holding process, and the temperature of the surface layer of the molten resin is adjusted. Cool to below the heat distortion temperature of the resin.

Next, in the mold temperature restoration / compression process, the fixed mold insert piece and the movable die insert piece are heated again, and the temperature of both insert pieces is returned to a temperature equal to the temperature in the injection / pressure holding step.

Then, in the final mold release step, the resin molded product is taken out from the cavity and one molding cycle is completed. Or later,
This molding cycle is repeated.

Hereinafter, the details of the injection compression molding method will be described with reference to Examples.

FIG. 2 is a sectional view of an injection compression molding die used for carrying out the injection compression molding method according to one embodiment of the present invention, and FIG. 3 is a temperature chart of the injection compression molding method according to FIG. It is a time diagram.

In FIG. 2, reference numeral 1 is a fixed mold insert piece which forms a cavity 10 with the movable mold insert piece 5, and 2 is a fixed sleeve provided between the fixed mold insert piece 1 and the fixed die 3. Yes,
The fixed sleeve 2 is provided so as not to directly fix the fixed mold insert piece 1 to the fixed mold 3 but to some extent be able to cope with a change in the outer diameter of the fixed mold insert piece 1. The fixed sleeve does not necessarily have to be provided.

Reference numeral 4 denotes a fixed die mounting plate that fixes the fixed die 3 to an injection molding machine (not shown), and 6 supports the movable die insert piece 5 from the rear portion and compresses the compression force generated by the pressure cylinder 14. A pressure block for transmitting to the movable die insert piece 7,
Is a push-out plate that supports the pressure block 6 and a Z pin 18 to be described later to transmit a pressure-pushing force, and 8 is a movable plate provided between the movable mold insert 5 and the movable mold 9. Like the fixed sleeve 2, the movable sleeve 8 is provided so as to be able to cope with a change in the outer diameter of the movable mold insert 5 to some extent. Further, the movable die insert 5 slides in the movable sleeve 8. The movable sleeve does not necessarily have to be provided.

9 is a movable type for fixing the movable sleeve 8 and 10 is a movable type.
Fixed mold insert 1, movable mold insert 5, and movable sleeve 8
This is the cavity formed by

Reference numeral 11 denotes a heater fitted into the fixed sleeve 2 and the movable sleeve 8 to heat the fixed mold insert 1 and the movable mold insert 5, and 12 denotes the fixed mold insert 1 and the movable mold insert 5. A temperature sensor for detecting the temperature, 13 is a heating and cooling medium passage for adjusting the temperature, and 14 is a resin in the cavity 10 through the extrusion plate 7, the pressure block 6 and the movable mold insert 5. It is a pressurizing cylinder that can apply a compressive force to the resin and that pushes out the resin molded product in the cavity 10 from the cavity 10 at the end of the molding cycle.

Reference numeral 15 denotes a heating and cooling medium flowing in the heater 11 or the heating and cooling medium passage 13 in response to a temperature signal sent from the temperature sensor 12 that detects the temperatures of the fixed mold insert 1 and the movable mold insert 5. A temperature controller capable of controlling the hydraulic pressure (not shown) and sending a control signal to the hydraulic pressure control device 16 to control the generated hydraulic pressure.
It is a hydraulic control device that receives a signal from the temperature controller 15 and controls the hydraulic pressure sent to the pressurizing cylinder 14.

Reference numeral 17 denotes a movable die mounting plate that supports the pressure cylinder 14 and attaches the movable die 9 to the injection molding machine.
A Z pin for drawing the resin in the sprue 19 toward the movable mold 9 at the end of the molding cycle, and 19, 20 are sprues forming a resin passage from the injection molding machine to the cavity 10.
It's Lanna.

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

The mold temperature T _M1 at the start of molding, that is, at the time of injection is equal to or lower than the resin heat deformation temperature T ₁ . The fixed mold 3 and the movable mold 9 are closed to form the cavity 10.

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

When the resin is filled in the cavity 10, the injection molding machine directly enters the pressure holding step. At the same time, the hydraulic control device 16 applies a compressive force to the resin in the cavity 10 during the pressure holding by the pressurizing cylinder 14 via the movable mold insert 5, the pressurizing block 6 and the extruding plate 7. This allows
The resin in the cavity 10 is shaped, and the degree of adhesion between the resin and the fixed mold insert piece 1 and the movable mold insert piece 5 is improved so that heat can be easily transferred.

Then, the resin is cooled while the mold temperature is maintained at T _M1 . After the time t ₁ at which the resin surface layer temperature T _s is cooled to the resin solidification temperature T ₂ or lower and the resin central portion temperature T _c is also cooled to at least near the resin solidification temperature, the temperature controller 15 energizes the heater 11 The heating medium to the medium passage 1
Then, the fixed mold insert 1 and the movable mold insert 5 are heated to 3 and heated to the heating mold temperature T _M2 . The heating mold temperature T _M2 is set to a temperature higher than the resin solidification temperature T ₂ . At the heating end time t ₂ , the resin surface layer temperature T
_s is heated to a temperature higher than the solidification temperature T ₂ and is in a flowable state. The resin central portion temperature T _{c is} also cooled to a temperature equivalent to the resin surface layer temperature T _s .

Next, the temperature controller 15 causes the cooling medium to pass through the medium passage 13
To cool the fixed mold insert 1 and the movable mold insert 5,
During cooling, the mold temperature is lowered to T _M3 . The cooling mold temperature T _M3 is lower than the initial injection mold temperature T _M1 .
At the cooling end time t ₃ , the resin surface layer temperature T _s is cooled to the heat deformation temperature T ₁ or lower, but the resin central portion temperature T
_c is slightly higher than the heat distortion temperature T ₁ .

After that, the temperature controller 15 again causes the heater 11 to
The heating medium is supplied to the medium passage 13 to heat the fixed mold insert 1 and the movable mold insert 5, and the mold temperature is returned to the initial injection mold temperature T _M1 . This mold temperature recovery
In the compression step, the resin surface layer is heated and the central portion of the resin is continuously cooled. At the time t _{4 at} which the mold temperature is restored, both the resin surface layer temperature T _s and the resin central portion temperature T _c are close to the injection mold temperature T _M1 . That is, the temperature distribution in the resin is small and the temperature is not more than the thermal deformation temperature T ₁ .

In this state, the resin molded product is taken out. The resin molded product taken out has a small internal temperature distribution, so that the deformation and internal stress are extremely small. Further, since the mold temperature at the time of taking out is the same as the mold temperature at the time of initial injection, the next molding can be started from t ₅ immediately after taking out the resin molded product.

In the above steps, the compressive force is added until the time of taking out for the purpose of shaping and improving the heat transfer. The magnitude of the compressive force may be changed by the temperature controller 15 and the hydraulic control device 16 in accordance with the temperature change of the fixed mold insert 1 and the movable mold insert 5.

A specific example is shown.

Using acrylic resin, outer diameter 130 mm, maximum wall thickness 17 m
A plastic lens with m and a minimum wall thickness of 3 mm was molded by the method of this embodiment. Mold temperature T _M1 at injection is 90
C., the mold temperature T _{M2 during} heating is 140 ° C., the mold temperature T _{M3 during} cooling is 70 ° C., and the compression force applied to the resin is about 290.
When molding was performed at kg / cm ² , the molding cycle was shortened from the conventional 20 minutes to 15 minutes (about 3/4), and the shape accuracy was improved from 15 μm to 10 μm. In addition, the generation of internal stress could be significantly reduced, and the optical performance could be improved.

According to the embodiment described above, the shape accuracy of the resin molded product is improved (for example, it is improved to about 2/3), the internal stress of the resin molded product is significantly reduced, and the molding cycle is shortened (for example, about It shortens to 3/4)).

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to provide an injection compression molding method capable of molding a resin molded product having excellent molding accuracy and extremely small internal stress in a short molding cycle.

[Brief description of drawings]

FIG. 1 is a process diagram of the injection compression molding method of the present invention, and FIG. 2 is a sectional view of an injection compression molding die used for carrying out the injection compression molding method according to an embodiment of the present invention. The figure shows the temperature-time diagram of the injection compression molding method according to FIG.
The figure compares and shows the principal part of the time variation of the resin temperature and the mold temperature according to the conventional technique and the injection compression molding method of the present invention. (A) is a conventional temperature-time diagram , (B) is a temperature-time diagram of the present invention. 1 ... Fixed type insert, 5 ... Movable type insert, 10 ... Cavity.

Claims (1)

[Claims] 1. A resin molded product obtained by injecting and filling a molten resin into a cavity formed between a fixed mold insert and a movable mold insert, which are arranged to face each other, and applying a compressive force thereto. In the injection compression molding method, the molten resin is injected into the cavity while the temperature of the fixed mold insert and the movable mold insert is kept below the thermal deformation temperature of the resin.
Filling, applying compressive force to this (injection / pressure-holding process), and 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)
After that, the fixed die insert piece and the movable die insert piece are heated to heat the surface layer of the molten resin or the entire resin thereof to a temperature exceeding the solidification temperature (heating / compression step), and then the fixed die insert piece. The bridge and the movable mold insert are cooled, both insert molds are cooled to a temperature lower than the temperature in the injection / pressure-holding step, and the temperature of the surface layer of the molten resin is cooled to the heat deformation temperature of the resin or less (2 (Next cooling / compression step), then the fixed mold insert and the movable mold insert are heated again to restore the temperature of both insert molds to the temperature of the injection / pressure holding process (mold temperature restoration / compression process). After that, take out the resin molded product from the cavity (mold release process)
An injection compression molding method characterized by the above.