JPH02162007A - Method for molding molded item - Google Patents

Abstract

PURPOSE:To make the temperature control of a cavity surface, onto which precise and minute projected and recessed surface is provided, possible by a method wherein a mold is heated with a high frequency induction heating means and at the same time cooling medium, the temperature of which is held at the predetermined value, is circulated. CONSTITUTION:A temperature controller 14 controls the temperature of cooling medium to the predetermined value and, at the same time, circulates the cooling medium through a circulating path 14A in a fixed mold 2A and a movable mold 2B. The cooling medium circulates in the molds on one hand and the cavity of the mold is rapidly heated through the high frequency induction oscillation up to the peak temperature tB. When the peak temperature tB is detected with sensors 20A and 20B, a temperature detecting means 22 sends the oscillation stop signal to a high frequency oscillation controlling section 16A. At the same time, a moving means 18D retreats a heating coil 16B. Though the temperature of the molds lowers the temperature lowering curve (b) is formed in the form of a certain curve ranging from the peak temperature tC to the injection temperature tB through the instantaneous heating by high frequency induction heating and the cooling operation by the cooling medium during heating, resulting in keeping the injection temperature tC constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a method of molding a molded article. In particular, the present invention relates to a method of heating and molding a mold using high-frequency heating means.

[Prior art to the invention]

Conventionally, injection molding by heating a mold by high-frequency heating involves having an oscillation electrode and a cooling channel inside the mold, and an oscillation area and an external oscillation area, as described in Japanese Patent Laid-Open No. 50-45039. It is configured to have a cooling water pump, and when filling with resin, the mold is instantaneously heated by an oscillating electrode installed in the mold, and after filling is completed, the oscillation is stopped, and the cooling water pump pumps cooling water into the mold. A method has been proposed in which the resin is poured into a container, cooled, and solidified.

Furthermore, Japanese Patent Publication No. 58-40504 discloses that when injection molding a thermoplastic resin, the surface of the mold on which the surface of the injection molded product is to be formed is preheated by high-frequency induction to a temperature higher than the heating deformation temperature of the thermoplastic resin. An injection molding method for injection molding has been proposed.

[Problems solved by the invention]

One of the problems in injection molding a molded product by heating a mold using the conventional high-frequency heating described above is the difficulty in controlling the temperature of the mold. A high-frequency induction heating inductor is installed between the stationary mold and the movable mold, and the inductor is inserted between the stationary mold and the movable mold to oscillate a high frequency, while the mold cooling water flows through the metal. By preventing fluid from flowing inside the mold, the mold can be efficiently heated to a predetermined temperature in a short time.

However, after heating to a predetermined temperature, the mold is opened for the inductor to exit, the mold is closed, the injection material is injected, pressure molding, cooling, and the molded product is released. It is difficult to control the temperature of the mold to the required temperature. This is because after the mold is heated by high-frequency induction heating, it is rapidly cooled down from a high temperature state due to the escape of heat by opening the mold and cooling by cooling water after the molding process, making it very difficult to control the temperature of the mold.

The above-mentioned problem becomes very important when the shape of the molded product is complex or when the molded product surface requires high accuracy in surface roughness.

For example, when optical parts such as lenses are manufactured by injection molding, surface roughness precision of the molding cavity surface of the mold is required, and temperature control of the mold is particularly important.

The temperature of the mold immediately before injection has a large effect on the fluidity of the injection material, and the injection material flows and fills every corner of the cavity of the mold. After that, when the injection material solidifies along the shape of the molded product, the mold is cooled down by a cooling means, but if the solidification of the molded product and the cooling temperature of the mold are not well matched, the molded product may swell. or distortion of the molded product.

These problems do not pose a particular problem when the molded product has a relatively large wall thickness or depending on the required functions of the molded product, but if the molded product is the optical component mentioned above, the molded product This will lead to pass/fail results.

The present invention uses high-frequency induction heating of the mold when injection molding optical parts such as camera lenses and Fresnel lenses, and accurately controls the mold temperature until the end of the molding cycle, thereby reducing the shrinkage of the optical parts. We propose an injection molding method that does not cause distortion.

For example, when injection molding a Fresnel lens 100 as shown in FIG. 6 as an optical component, the tip 100B of the apex corner 100A with curvature must form a certain acute angle on the incident side of the imaging light beam. However, in injection molding using the conventional technology mentioned above, as the temperature of the mold progresses and the shape of the injected material solidifies, sink marks and distortions occur in the resin of the molded product, causing the acute angle of the tip to collapse and accuracy to deteriorate. Molded products such as Fresnel lenses with high temperatures could not be produced. The present invention proposes a molding method that makes it possible to control the temperature of a cavity surface of a mold, such as the aforementioned Fresnel lens, in which a fine and fine uneven surface is provided.

[Means and actions for achieving the task]

In the present invention, a high-frequency induction heating means is arranged movably between a stationary side mold and a movable side mold, and a flow passage through which a cooling medium circulates is arranged in the mold, and the high-frequency induction heating means By circulating the cooling medium in the flow path during the heating operation of the means, the mold is heated by the high frequency induction heating means and the cooling medium is kept at a predetermined temperature and circulated. be.

[Explanation of Examples]

FIG. 1 is a configuration diagram of an injection molding apparatus for explaining the present invention in detail, FIG. 2 is a temperature curve diagram of a mold, and FIG. 3 is a timing chart diagram of each unit constituting the apparatus.

In the figure, reference numeral 1 indicates the main body of the injection molding machine, which includes a stationary mold 2A having a cavity (not shown) for forming a molded product, a movable mold 2B, and a mold plate 4 that supports the mold.
A・4B・Movement guide, ID member 6, and hopper 8,
It consists of an injection cylinder 10, a driving means 12 for opening and closing the mold, and the like.

14 is a temperature regulator for adjusting the temperature of the mold;
4 is connected to a cooling medium flow path (not shown) in the molds 2A and 2B via a vibrator 14A, so that the cooling medium can be circulated by a pump (not shown).

Reference numeral 18 denotes a high-frequency induction heating means, which includes a high-frequency induction control section 18A, a coil section 18B, a support member 18c that supports the coil section 18B, and drives the support member forward and backward in the direction of arrow A in the figure. means of transportation, 18 D
The devices 20A and 20B are temperature detection sensors, which detect the temperature of the cavity surface of the mold and output a detection signal (embedded at an appropriate position in the mold, and detect the temperature of the cavity surface of the mold). The detection signal is input to the temperature detection means 22 via the lead wire 22A.

Reference numeral 24 indicates a molded product take-out means, and the means 24 takes out the molded product molded by the automatic hand 24A.

26 is a controller that controls the entire molding apparatus.

Next, the operation of the apparatus shown in FIG. 1 will be explained with reference to FIGS. 2 and 3. By the molding starting operation (not shown) of the controller 26,
The movable mold 2B, which is in the initial mold opening position, starts moving in the direction of closing the mold, and the movable mold 2B moves to the fixed mold 2A.
When the mold 2 on the moving side reaches the first position where it is kept at a predetermined distance from
B stops moving.

When the movable mold 2B reaches the first position and stops, a signal P1 for controlling the high frequency induction heating means 16 is output from the controller 26. Upon receiving the control signal P1, the moving means 16D starts moving the heating coil 18B, which had been evacuated outside the opening/closing movement area of the molds 2A and 2B, between the moving mold 2B and the stationary mold 2A. . Heating coil 18B
is a position facing a cavity surface (not shown) of the mold, and stops when it reaches a position suitable for heating the cavity surface.

When the heating coil 18B is stopped, the high-frequency induction control section 16A performs high-frequency oscillation, thereby transmitting the high-frequency oscillation to the heating coil 18B, which heats the molds 2A and 2B by a known high-frequency induction heating operation. temperature is second
As shown in the figure, the temperature rises from the temperature tA at the oscillation start time 1 to the peak temperature t8 along a curve a. Control part 2
6, the temperature regulator 14 is activated and the signal P2 is activated, and the temperature regulator 14 is activated at the initial operation of the molding starting operation of the controller. The temperature regulator 14 adjusts the temperature of a cooling medium in a storage tank (not shown) to a predetermined temperature, and at the same time operates a pump (not shown) to circulate the cooling medium into the stationary mold and the movable mold through the flow path 14A. . While the cooling medium circulates within the mold, the cavity of the mold is rapidly heated to the second
The temperature rises to the peak temperature tB shown in the figure. The temperature of the mold is detected by sensors 20A and 20B installed in each mold, and the detection signal is input to the temperature detection means 22.

When the temperature detecting means 22 detects the peak temperature t8, the temperature detecting means 22 sends an oscillation stop signal to the high frequency oscillation control section 16A, and at the same time, the heating coil 16 is activated by the moving means 16D.
Evacuate B. Simultaneously with the completion of retraction of the heating coil 16B, the movable mold 2B is closed by the mold driving means 12, and a mold clamping operation is performed.

When the mold clamping operation is completed, the mold is ready for injection of the resin material, but it takes time from time t2 shown in FIG. There is a time lapse Δt leading to t3.

During this elapsed time Δt1, the temperature of the mold is (tB tc)
However, due to instantaneous heating by high-frequency induction heating, which is one of the features of this device, and cooling operation using a cooling medium during the heating, the injection temperature t is lowered from the peak temperature tB.
The temperature drop curve up to c always forms a constant curve, and the injection temperature t. The temperature remains constant throughout the injection molding cycle.

The control unit 26 operates the injection cylinder 10, and the molten resin material in the hopper 8 is injected into the mold cavity through a gate (not shown). After a predetermined amount of the resin material is injected, the mold is cooled along a temperature curve C, and the molten resin inside the cavity solidifies along the cavity shape to form a molded product.

Thereafter, the mold temperature reaches a temperature t suitable for mold release. When the movable mold 2B descends, a mold opening signal is sent from the control section 26 to the mold driving means 12, and the movable mold 2B moves. When the mold opening is completed, the molded product ejecting means 24 is activated and the molded product is taken out by the automatic hand 24A, thereby completing the molding and completing one cycle of molding.

When the above-mentioned molded product is a Fresnel lens as shown in Figure 6, the molten resin material injected into the cavity survives in every corner of the cavity that forms the acute angle part of the lens, so that no voids are created. To achieve this, it is necessary to set the mold temperature to a high temperature to promote the fluidity of the resin, and at the same time, no matter how many times the molding cycle is repeated, the temperature shown in Figure 2 must be maintained at every cycle. Although it is necessary to maintain a temperature curve, the results of the present invention were sufficiently satisfactory using the above-mentioned molding method.

Table 1 shows comparative data of each molding condition of Examples 1 and 2 using the same mold and the same apparatus according to the molding method of the present invention, and a comparative example using the conventional technology. In Table 1,
In the comparative example, the output of 6.5 Kwatt was oscillated at a frequency of 132 KHz, and the temperature measurement of several cycles of molding using a temperature sensor resulted in a peak temperature t8 = 182 to 215°C.
Injection temperature tc=llO~142°C, mold opening temperature t. =6
The temperature ranged from 5 to 94°C, and variations occurred in the measurement distribution of each temperature for each molding cycle.

In this comparative example, the operation of the temperature regulator 14 was turned off during the operation time of the high-frequency induction heating means 16.
The temperature of the cooling medium inside the cooling flow path and inside the mold becomes uneven, and the temperature of the mold becomes uneven due to the cooling effect of the cooling medium, which is not stable in response to the instantaneous high-temperature heating of the mold due to high-frequency induction heating. Ta.

Example 1 and Example 2 show examples using polycarbonate and polymethyl methacrylate, respectively, and have a diameter of 8°2 Kwa.
tt, the oscillation operation is performed at a frequency of 132 KHz with an output of 6.5 Kwatts, and the temperature regulator 14 is activated from the beginning according to the operation signal of the molding control section to heat the coolant by the heater and to cool the coolant inside the mold by the pump. The cooling medium temperature is 80℃ and 50℃, respectively.
Keep it. The heating operation is performed under the above conditions and the peak temperature t8=
The mold was heated to 244°C/218°C and the temperature was measured from the sensor, and the mold temperature was repeated several cycles at 1o-1. As a result, the peak temperature t B = 244°C/2
18°C, mold temperature t during injection. It was possible to control the mold opening temperature t to =160°C/135°C and the mold opening temperature t to =110°C/80°C. According to the data described above and shown in Table 1, in the examples using the molding method of the present invention, the peak temperature of the mold due to high frequency induction heating was always high even in the case of the same material as the comparative example. In addition, the injection temperature tc was always the same temperature (110°C, 80°C) in Examples 1 and 2.
) can be obtained, and furthermore, the peak temperature t8 shown in Fig. 2 can be obtained.
It was confirmed that the temperature drop curve from tc to injection temperature tc always falls along the same curve.

FIGS. 4A and 4B are schematic diagrams showing the molding results of molded products according to the molding method according to the present invention and the comparative example described above based on the data in Table 1 above.

The molded product shown in FIG. 4A-B above shows an enlarged view of the cross section of a Fresnel lens, and FIG. 4B shows the molding method of the prior art. Curled up. On the other hand, FIG. 4A shows the molding method of the present invention, in which the apex angle is accurately acute and the tip is not rounded.

In the case of a Fresnel lens, the incident lights X1, x2, etc. need to be refracted at the lens surface and focused at one point on the optical axis. In the embodiment of the present invention, as shown in FIG. 4A, the light incident on the vertex is refracted accurately, so each incident light can be focused on one point, and the image called a ghost of the image is eliminated. No blurring occurs. On the other hand, in the case of the prior art, as shown in FIG. 4B, the refraction angle of the light incident on the apex portion becomes small due to the blurring of the apex angle, and the incident light is focused at one point on the optical axis. This results in ghosting and blurring of the image.

There is a method shown in Fig. 5 as a guideline for measuring the molding accuracy of Fresnel lenses. It can be said that the larger the ratio h/H of the height h actually obtained by molding to the designed height H from the bottom to the apex of the Fresnel lens, the higher the molding accuracy.

According to this method, in the case of the prior art, it was about 60 to 80%, but in the case of Examples 1 and 2 of the present invention, it was 98 to 99%.
We were able to obtain a very high percentage.

〔Effect of the invention〕

According to the present invention, temperature management of a mold can be controlled with high precision. There is no variation in mold temperature due to repeated molding cycles, and the mold temperature at the time of injection and the mold temperature at the time of mold opening can always be controlled to a predetermined temperature for each cycle. As a result, as explained in FIGS. 4A-B and 5 above, it is possible to obtain extremely high molding accuracy, and it is possible to obtain molded products that are excellent as a method for molding optical elements and optical parts. did it.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a molding apparatus that implements the molding method of the present invention. FIG. 2 is a temperature curve diagram of the mold of the molding method according to the present invention. FIG. 3 is a timing chart diagram of each component unit of the apparatus shown in FIG. 1. FIGS. 4A and 4B are explanatory diagrams of the molding accuracy of the molded product. FIG. 5 is an explanatory diagram of measuring molding accuracy of a molded product. FIG. 6 is a diagram in which the molding method of the present invention is applied to a Fresnel lens.

Claims (1)

[Claims] (1) In the open state of a mold for molding a molded article during clamping, a high-frequency heating means is inserted into the mold to rapidly heat the mold, and during the high-frequency heating operation of the mold, A cooling medium having a substantially constant temperature is circulated in a cooling medium path provided in the mold, and the high-frequency heating means is withdrawn and mold clamping is resumed based on temperature detection by a sensor that measures the temperature of the mold, and the molding material is removed. A method for molding a molded article, characterized in that a molding cycle of the molded article is performed by an injection operation, and the temperature of the cooling medium is kept substantially constant during the molding cycle.