JPH09183146A - Method for injection molding and mold for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mold a lens with good molding accuracy even with a relatively simple mold structure even when an optical lens with a large difference in thickness between a thick part and a thin part is molded. SOLUTION: A mirror surface core piece 3 on the fixed side and a mirror surface core piece 4 on the movable side are slidably provided on a mold plate 1 on the fixed side and a mold plate 2 on the movable side. Heaters 6 and 7 are respectively provided at the center in each of the mirror surface core pieces 3 and 4. Electric wires 11 are connected to the heaters 6 and 7 and the electric wires 11 are connected to an electric source 9 through a controller 10 and a controller junction point 10a. A thermocouple 13a for detecting the temp. around a thick part and a thermocouple 13b for detecting the temp. around a thin part are provided in the neighborhood of mirror surface parts 3a and 3b of the mirror surface core pieces 3 and 4 and each of the thermocouples 3a and 13b is connected to the controller 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method and an injection molding die capable of easily and highly accurately molding a component such as an optical lens which requires relatively high accuracy.

[0002]

2. Description of the Related Art Conventionally, a method of molding an optical lens is generally used, in which oil or water is used as a heat medium and a mold temperature is adjusted to a constant temperature by a temperature controller, as in general mold parts. Was there. However, since the set temperature at this time is set below the glass transition temperature peculiar to the molding resin, if the cooling rate is high, an extreme temperature difference will occur between the inside of the molded product and the skin layer, and This results in deterioration of quality due to residual distortion.

Therefore, in order to solve the above-mentioned drawbacks, for example, Japanese Patent Laid-Open No. 3-219936 proposes the following invention. In the injection molding method of the above invention, when the molten plastic injected into the cavity is cooled to mold the lens, the solidification speed that varies depending on the wall thickness distribution of the lens molded body is forced by cooling the thick wall portion. In this method, the thin portion is delayed and controlled equally by electromagnetic induction heating or heating with a heating fluid.

One of the mold apparatuses used in the above method is
When the molded product is a convex lens, a fixed and movable base mold provided with a cooling means, a nest mold inside the base mold, and a convex lens molding provided in the parting part of the pair of nest molds. 2), the electromagnetic induction heating means or the heating fluid heating means provided around the cavity side of the double insert mold, and the cooling means by the flow path provided in the central part of the double insert mold.

Another one of the mold apparatuses is a cavity for molding a concave lens provided in a parting portion of a pair of nesting dies, and an electromagnetic induction heating provided in the center of the cavity of both nesting dies. The heating means is constituted by a heating fluid, and the cooling means is constituted by a flow path provided along the peripheral edges of the double insert mold.

Further, the heating and cooling means of the mold device are constituted by cooling passages provided concentrically in the central portion and the peripheral portion on the cavity side of the double insert die, and electromagnetic coils housed in the respective cooling passages. It is composed of both electromagnetic induction heating, and both can be used alternately for heating or cooling according to the shape of the cavity provided in it, and it can be used for molding both concave and convex lenses by exchanging only the cavity Become.

A plurality of sets of nesting dies having the above-mentioned heating and cooling means are internally provided at required intervals in fixed and movable base dies provided with cooling means, and cavities in each nesting die are provided. When connecting to the runner arranged from the center of the fixed side base mold to form a multi-cavity molding mold, the cooling path that cuts off the heat interference between the nested molds is the same as the base mold. It is provided between the insert type.

[0008]

However, the invention described in JP-A-3-219936 has the following drawbacks. That is, in order to alleviate the internal strain of the molded product, the solidification rates of the thick-walled portion and the thin-walled portion are made approximately equal by the cooling means or the heating means, so that temperature control is extremely difficult. Also, the device for that purpose becomes complicated. Another drawback is that the surface of the cavity has a non-uniform temperature distribution as a whole, which causes a difference in thermal expansion and deteriorates the surface accuracy of the cavity surface.

An object of the present invention is to provide a molding method capable of controlling the temperature of the resin in the cavity with a relatively simple mold structure and ensuring a high surface accuracy. . It is an object of claims 2 and 3 to provide an injection molding die capable of further improving the molding accuracy of a molded product and making it stable.

[0010]

According to a first aspect of the invention, there is provided an injection molding method in which a heating element having a temperature controller is loaded on a mirror surface piece forming a mold cavity, and the cavity temperature is freely controlled for molding. While the molten resin injected into the cavity exists in a temperature range higher than the glass transition temperature, the heating element heats the surface of the cavity to a temperature equal to or higher than the glass transition temperature of the molten resin to cool the resin in the cavity. After maintaining the cavity surface at a constant temperature until the absolute value of the temperature difference between the high temperature part and the high temperature part is close to the minimum value, the operation of the heating element is stopped and the molten resin is cooled to a region below the glass transition temperature. It is an injection molding method characterized by the above.

According to the first aspect of the invention, when the mold clamping is completed, the injection molding machine outputs a mold clamping completion signal, and the controller outputs a heating element operation signal. As a result, heating of the heating element is started, and the cavity mirror surface piece holding the heating element is adjusted to an appropriate temperature in the region above the glass transition temperature of the molding resin by heat conduction from the heating element. The injection of the molten resin into the cavity is performed when the surface of the cavity exceeds the glass transition temperature of the resin.

After this, the cooling process is started, but since the cavity surface is adjusted to a temperature not lower than the glass transition temperature of the molding resin, the resin temperature is first in the vicinity of the cavity temperature at this time without being completely solidified. Try to stabilize. This state is maintained until the absolute value of the temperature difference between the low temperature portion, that is, the thin portion and the high temperature portion, that is, the thick portion of the molded product becomes the minimum. As a result, the temperature distribution of the resin in the cavity becomes substantially uniform.

After that, the operation of the heating element is stopped, and the cavity surface is cooled to a region below the glass transition temperature of the resin, but is cooled in a state where there is almost no temperature difference between the thin portion and the thick portion. No internal residual stress or uneven shrinkage distribution is generated. As a result, a lens having extremely good surface accuracy is molded. Then, after being cooled to the take-out temperature, the molded lens is taken out of the mold.

According to a second aspect of the present invention, there is provided an injection molding die in which at least one heating element having a temperature controller is loaded on a mirror surface piece forming a cavity, and the cavity temperature can be freely controlled. The mold for injection molding is characterized in that a heat insulating layer of a low heat conductive member is provided between the mirror surface portion formed on the mirror surface piece.

According to the second aspect of the present invention, the heat insulating layer of the low heat conductive member is formed between the mirror surface portion of the cavity mirror surface piece and the heating element loaded in the mirror surface piece. With this heat insulating layer, in the mirror surface portion, only the vicinity of the heating element does not have a high temperature at the beginning of heating the heating element, and the mirror surface is heated with a relatively uniform temperature distribution. As a result, the molding accuracy of the molded product is always good and stable.

The invention of claim 3 is the injection molding die according to claim 2, wherein the heat insulating layer is an air layer. In the invention of claim 3, since the heat insulation layer is an air layer, direct heat conduction in the mirror surface direction is suppressed, and the temperature of the mirror surface is further raised with a uniform temperature distribution.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIGS. 1 to 3 show this embodiment, FIG. 1 is a schematic configuration diagram of an apparatus used, FIG. 2 is a flow chart of an injection molding method, and FIG. It is the graph which divided and showed in the low temperature part. The fixed-side mold plate 1 and the movable-side mold plate 2 are slidably provided with a fixed-side mirror surface piece 3 and a movable-side mirror surface piece 4 having the same axis and having concave surfaces. The cavity 5 is formed by abutting the mirror surface portions 3a, 4a of these mirror surface pieces 3, 4 together. The mirror surface shape is not limited to the concave shape on both sides,
Any combination of concave and convex shapes may be used.

The mirror surface portion 3 is provided at the center of the inside of each mirror surface piece 3, 4.
Cylindrical heaters 6 and 7 are provided one by one at a fixed distance H from a and 4a. Heaters 6,7
An electric wire 11 is connected to the electric wire 11, and the electric wire 11 is connected to the power source 9 via the controller 10 and the controller contact 10a. The constant distance H between the heaters 6 and 7 and the mirror surface portions 3a and 4a is such that the resin pressure hardly causes bending.

Further, the mirror surface portions 3a, 4 of each mirror surface piece 3, 4
A thermocouple 13a for detecting a temperature near a thick portion and a thermocouple 13b for detecting a temperature near a thin portion are provided near a.
Each thermocouple 13a, 13b is connected to the controller 10. In FIG. 1, 8a is a sprue, 8b is a runner, and 12 is an ejector pin. Other than this, 10
Reference numeral 0 indicates an injection molding machine, and the injection molding machine 100 is connected to the controller 10.

In the injection molding method using the apparatus having the above construction, when the mold clamping is completed, the injection molding machine 100 outputs a mold clamping completion signal, and the controller 10 outputs a heater heating signal. As a result, the controller contact 10a is closed, and the fixed-side and movable-side heaters 6 and 7 start heating. By heat conduction from the heaters 6 and 7, the mirror surface portions 3a and 4a of the mirror surface pieces 3 and 4 for holding the heaters 6 and 7 are held.
Is adjusted to an appropriate temperature in the range above the glass transition temperature of the molding resin.

The molten resin is injected into the cavity 5 when the mirror surface portions 3a, 4a of the mirror surface pieces 3, 4 exceed the glass transition temperature of the resin. The resin temperature at this time corresponds to the value at 0 sec in FIG. 3 regardless of the thin portion and the thick portion.
After this, the cooling step is started, but since the mirror surface portions 3a, 4a are adjusted to a temperature above the glass transition temperature of the molding resin, the resin temperature first tries to stabilize near the temperature of the cavity 5 at this time. However, since the resin at this time is in the range of the glass transition temperature or higher, it is not completely solidified.

The above state is maintained until the absolute value of the temperature difference between the low temperature part and the high temperature part of the molding resin becomes close to the minimum value, and this value is approximated to the thermocouple 13a provided near the thick part and the thin part. Controller 10 via thermocouple 13b provided in the vicinity
Detect by. After the detection, the controller 10 outputs a heater non-heating signal, and the controller contact 10a opens. Up to this point, the resin temperature tendency up to 300 seconds in FIG. 3 is shown.

When the controller contact 10a is opened, the heaters 6 and 7 are rendered non-conductive, and the mirror surface pieces 3 and 4 are cooled to the glass transition temperature or lower. At this time, since the resin is cooled in a state where the temperature difference between the thin portion and the thick portion is substantially minimum, no internal residual stress or uneven shrinkage distribution occurs. This makes it possible to mold a lens with extremely good surface accuracy. Thereafter, the temperature of the lens reaches a temperature at which it can be taken out, and the lens is ejected to the movable side mirror surface piece 4 and the ejector pin 12 together with the sprue 8a and the runner 8b and taken out of the mold.

According to the present embodiment, a heating element whose temperature is controllable is loaded in the mirror surface piece, the temperature distribution of the molding resin is made uniform in the temperature range higher than the glass transition temperature of the molding resin, and then the take-out temperature is set. To cool down. Therefore, even when molding an optical lens having a large difference in wall thickness between the thick portion and the thin portion, it is possible to obtain good molding accuracy even with a relatively simple mold structure. It can contribute to a dramatic improvement.

In the present embodiment, the heater is turned off at 300 seconds, but if more time is spent, the temperature difference between the thin portion and the thick portion can be further reduced, and a better surface can be obtained. It is possible to obtain a lens with accuracy.

(Embodiment 2) FIG. 4 is an enlarged sectional view of an essential part showing this embodiment. The present embodiment is different in that it is configured by providing a heat insulating layer on each mirror surface piece 3 and 4 of the apparatus used in the first embodiment, and other configurations are made up of the same components, and the same components are the same. Are assigned the same numbers and their explanations are omitted. The heat insulating layer in the present embodiment is a conical space 6b, 7b at the mirror surface-side deepest part of the insertion holes 6a, 7a of the heaters 6, 7 provided in the fixed side mirror surface piece 3 and the movable side mirror surface piece 4, respectively. Are provided respectively.

In the apparatus having the above-mentioned structure, when the fixed and movable heaters 6 and 7 start heating, the temperature of each mirror surface piece 3 and 4 also starts to increase due to heat conduction. However, since the conical spaces 6b and 7b of the heater insertion holes 6a and 7a suppress direct heat conduction in the mirror surface direction, the mirror surface portion 3
A non-uniform temperature distribution does not occur in a and 4a. As a result, the mirror surface portions 3a, 4 of the individual mirror surface pieces 3, 4 are
a is maintained in a uniform temperature distribution, and the mirror surface piece 3,
This prevents deterioration of surface accuracy due to uneven thermal expansion of 4 itself.

According to the present embodiment, it is possible to keep the individual mirror surface pieces in a uniform temperature distribution and prevent deterioration of surface accuracy due to uneven thermal expansion of the mirror surface pieces themselves. Therefore, even when an optical lens having a large difference in thickness between the thick portion and the thin portion is formed, it is possible to form a lens having better surface accuracy, and to exert various effects. You can

In this embodiment, the insertion holes 6a and 7a are provided.
The spaces 6b and 7b are the deepest portions on the mirror surface side of the present invention, but in the present invention, the spaces 6b and 7b (even though the space is filled with air).
However, the heat of the heaters 6 and 7 may not be directly transmitted to the mirror surface portions 3a and 4a. For example, even if a heat insulating member having heat resistance such as ceramics is present, the same effect can be obtained.

Further, the shape of each space 6b, 7b is not limited to the conical shape, and the mirror surface pieces 3, 4
As long as it has a size enough to cover the area of the heaters 6 and 7 facing the mirror surface portions 3a and 4a, it may have any shape depending on the material thereof without departing from the gist of the present invention. is there.

[0031]

The effect of claim 1 is that after the temperature-controllable heating element is loaded in the mirror surface piece and the temperature distribution of the molding resin is made uniform in the temperature range higher than the glass transition temperature of the molding resin,
It cools down to the take-out temperature, and even when molding an optical lens with a large difference in wall thickness between the thick part and the thin part, it is possible to obtain good molding accuracy with a relatively simple mold structure.

The effects of the second and third aspects are that the individual mirror surface pieces are each kept in a uniform temperature distribution and the deterioration of the surface accuracy due to the uneven thermal expansion of the mirror surface piece itself is prevented. It is possible to mold a lens having

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment.

FIG. 2 is a flowchart showing the first embodiment.

FIG. 3 is a graph showing the first embodiment.

FIG. 4 is an enlarged sectional view of essential parts showing a second embodiment.

[Explanation of symbols]

 1 Fixed-side mold plate 2 Movable-side mold plate 3 Fixed-side mirror surface piece 4 Movable-side mirror surface piece 5 Cavity 6,7 Heater 8a Sprue 8b Runner 9 Power supply 10 Controller 10a Controller contact 11 Wire 12 Ejector pin 13a, 13b Thermocouple 100 Injection molding Machine

Claims (3)

[Claims] 1. An injection molding method in which a heating element having a temperature controller is loaded on a mirror surface piece forming a mold cavity and molding is performed by freely controlling the cavity temperature, and the molten resin injected into the cavity is glass. While existing in the temperature range higher than the transition temperature, the cavity surface is heated by the heating element to a region above the glass transition temperature of the molten resin, and the absolute temperature difference between the low temperature part and the high temperature part of the resin in the cavity is absolute. An injection molding method, characterized in that the cavity surface is kept at a constant temperature until the value becomes close to the minimum value, and then the operation of the heating element is stopped to cool the molten resin to a region below the glass transition temperature. 2. An injection molding die in which at least one heating element having a temperature controller is loaded on a mirror surface piece forming a cavity, and the cavity temperature is freely controlled, and the heating element and the mirror surface piece are formed. An injection molding die, characterized in that a heat insulating layer is provided between the heat insulating layer and the mirror surface portion. 3. The injection molding die according to claim 2, wherein the heat insulating layer is an air layer.