JP2002264188A - Method for injection compression molding of thin-walled plate-shaped object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of burr in molding a thin-walled plate- shaped object according to an injection compression molding method. SOLUTION: Mold clamping pressure is set and altered small almost simultaneously with the completion of a dweling process to avoid mold re-clamping of a necessary degree or more in molds 12 and 14 opened by injection pressure. By this constitution, the generation of burr in a molded product can be prevented while sufficiently ensuring all of various effects based on injection compression molding such as the preventing effect of molding failure such as a sink or the like, molding precision enhancing effect due to the reduction of internal stress, molding cycle enhancing effect due to the enhancement of mold adhesion or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection compression molding method as a kind of injection molding method for applying a compressive force to a molten resin material injected and filled into a molding cavity, and particularly to a light guide plate used for a liquid crystal display device and the like. The present invention relates to a novel injection compression molding method capable of injection-molding a thin plate-like body with high precision while preventing generation of burrs and the like.

[0002]

2. Description of the Related Art Conventionally, as a method of molding a synthetic resin material, a molten resin material is injected and filled into a molding cavity formed between a fixed mold and a movable mold, which are clamped, and then cooled and solidified. The injection molding method (injection molding method) for producing a molded body having a shape corresponding to the molding cavity is known, and is suitable for mass production. Therefore, it is used for the production of various synthetic resin products. I have.

[0003] As one of such injection molding methods,
Under a condition in which a substantially constant high-pressure mold clamping force is applied, the molding cavity of the mold is injected and filled with the molten resin material, and the mold is opened by a predetermined amount with the injection power, and the subsequent decrease in the injection power. By re-clamping the mold with the release,
Injection compression molding methods for obtaining molded articles of a desired shape have been developed. In such a molding method, since the molten resin material is filled in a molding cavity which is opened by a predetermined amount and enlarged, the molten resin material can be stably applied to the molding cavity of a thin-walled molded product at a low pressure. In particular, in recent years, personal computers, word processors, liquid crystal televisions,
Application to molding of a light guide plate for a liquid crystal panel used in a car navigation system, a mobile phone, and the like is being studied.

[0004] However, in the injection compression molding method, the mold opened by a predetermined amount by the injection power is re-clamped before the molten resin material injected into the molding cavity is cooled and solidified. However, at the time of re-clamping, there is a problem that the molten resin material easily enters the gap formed between the mold mating surfaces on the outer peripheral side of the molding cavity and burrs are easily generated. There was a problem that it became necessary.

[0005]

The present invention has been made in view of the circumstances described above, and an object of the present invention is to prevent occurrence of burrs in a molded product, and to provide a light guide plate and the like. It is an object of the present invention to provide a novel injection compression molding method capable of advantageously producing a thin plate-shaped body of the invention.

[0006]

An embodiment of the present invention which has been made to solve such a problem will be described below. The components employed in each of the embodiments described below can be employed in any combination as possible. In addition, aspects or technical features of the present invention are not limited to those described below, but are described in the entire specification and drawings, or based on the invention ideas that can be understood by those skilled in the art from the descriptions. It should be understood that it is recognized on the basis of.

A feature of the present invention is that a thin resin plate is injected and filled with a molten resin material into a molding cavity formed between a fixed die and a movable die in the direction of the die mating surface. When injection molding a body
(A) In a state where the fixed mold and the movable mold are clamped by a high-pressure mold clamping force, a molten resin material is injected and filled into the molding cavity at a predetermined injection pressure. An injection step of opening the mold by a predetermined amount by applying an injection force to the mold, and (b) injection molding and filling the molding cavity in a state where the fixed mold and the movable mold are clamped by a high-pressure mold clamping force. A pressure-holding step of applying an injection holding pressure to the molten resin material; and (c) at substantially the same time as the completion of the pressure-holding step, a mold clamping force applied to the fixed mold and the movable mold from a high-pressure mold clamping force to a low-pressure mold clamping. A low-pressure mold clamping step of re-clamping the fixed mold and the movable mold by a predetermined amount from the mold opening position in the injection step by changing the force into a force. is there.

In the conventional injection compression molding method, a substantially constant mold clamping pressure is applied to the mold from the injection step to the re-clamping through the pressure-holding step. On the other hand, in the injection compression molding method of the present invention, After the injection process and the pressure-holding process in which the injection power is applied, the mold-clamping force is reduced by a predetermined amount almost simultaneously with the completion of the pressure-holding process. Restriction is performed so as to be a predetermined amount, and re-clamping is performed with a lower clamping force than in the injection step and the pressure-holding step.

That is, as a result of many experiments and studies conducted by the present inventors, the occurrence of burrs in the conventional injection compression molding method is more reproducible than after the injection step in which the highest resin pressure is exerted. It was clarified that this occurred during the tightening process.Based on this knowledge, further studies were conducted.As a result, during injection compression molding, the mold clamping force was reduced almost at the same By limiting the tightening amount to a predetermined amount, it is possible to effectively suppress the occurrence of burrs while securing the technical effects of the injection compression molding method, such as reducing internal stress in molded products and improving molding accuracy. Was newly found, whereby the present invention could be completed.

Therefore, according to the injection compression molding method of the present invention as described above, the occurrence of burrs in a molded product is prevented, so that post-processing such as deburring is not required, and the technical effects inherent in the injection compression molding method are effective. It can be demonstrated in. That is, the molten resin material can be easily and stably injected and filled into the mold opened by a predetermined amount by the injection power, and the internal stress in the molded product is reduced or avoided, and warping or deformation is caused. Is prevented, the molding accuracy is improved by re-clamping, and the molding cycle can be improved by improving the cooling efficiency. In particular, it is possible to stably produce a thin flat plate-shaped molded product with excellent production efficiency while preventing defects such as defective filling and warping. For example, a light guide plate for a liquid crystal display device can be manufactured. By applying the present invention to manufacturing, excellent pattern transferability is realized, and it becomes possible to stably manufacture a target light guide plate with excellent uniform accuracy while suppressing variations in luminance.

In the injection compression molding according to the method of the present invention, the timing at which the clamping force is changed from the high-pressure clamping force to the low-pressure clamping force in the low-pressure clamping process is ± 0. It is desirable to set it within a range of 5 seconds, and more preferably, within a range of ± 0.2 seconds with respect to the completion point of the pressure holding step. If you set the change point from the high pressure mold clamping force to the low pressure mold clamping force earlier than necessary when the pressure holding process is completed,
This is because the mold may be opened and an effective compression force may not be exerted. Conversely, if the mold is set slower than necessary, the re-clamping amount becomes too large and burrs are likely to occur. In general, the completion point of the pressure holding step refers to a point in time after the injection pressure is reduced from the injection pressure (primary injection pressure) to the holding pressure (secondary injection pressure), gradually decreased, and substantially released. .

In the injection compression molding according to the method of the present invention, the amount by which the mold opening is reduced in the re-clamping in the low-pressure mold clamping step is such that the decrease in the mold opening from the mold opening position in the injection step is 100 μm or less. It is desirable that the amount of decrease in the amount of mold opening from the mold opening position in the injection step be 70 μm or less, and it is even more preferable that the amount of decrease in the amount of mold opening be 10 μm or less. ５０50 μm. When the amount of reduction of the mold opening amount is so large as to exceed 100 μm,
This is because burrs are likely to occur during re-clamping.

Furthermore, in the injection compression molding according to the method of the present invention, the re-clamping in the low-pressure mold clamping step is performed by reducing the amount of mold opening from the mold opening position in the injection step by the amount of molten resin injected into the molding cavity. It is desirable to set so as to exceed the cooling shrinkage of the resin material. If the decrease in the amount of mold opening during re-clamping in the low-pressure mold clamping process does not reach the amount of cooling shrinkage of the molten resin material injected and filled into the molding cavity, defects such as sink marks on the molded product may occur. This is because it may occur. The amount of cooling shrinkage of the molten resin material injected into the molding cavity can be generally calculated by multiplying the shrinkage ratio of the molten resin material by the thickness dimension of the molding cavity.

In the injection compression molding according to the method of the present invention, the mold clamping force applied to the fixed mold and the movable mold in the low-pressure mold clamping step is changed to the low-pressure mold clamping force, and after a predetermined time elapses, the mold clamping is performed again. It is also possible to control the mold clamping force in three steps by increasing the force to exert a secondary high pressure mold clamping force. When such a three-stage control is adopted, based on changing the mold clamping force exerted on the fixed mold and the movable mold in the low pressure mold clamping process to the low pressure mold clamping force,
While maintaining the technical effects of the present invention such as the prevention of burr generation and the relaxation of internal stress of the molded product as described above, the adhesion of the mold to the molded product is improved by applying a secondary high-pressure mold clamping force. As a result, the cooling efficiency can be improved, whereby the molding cycle can be further improved. That is, since the skin layer is formed on the surface of the molten resin material in the molding cavity by passing through the low pressure mold clamping process, the problem of burr generation in the molded product is avoided by applying the secondary high pressure mold clamping force. In addition, it is possible to increase the adhesion of the molded product to the mold and improve the cooling efficiency.

When such a three-stage control is adopted, the timing for increasing the clamping force from the low-pressure clamping force to the secondary high-pressure clamping force is preferably set at substantially the same time as the completion of the pressure-holding step. 0.5 after changing to low pressure mold clamping force
This is set at a point after an appropriate time within the range of up to 5.0 seconds, whereby the effect of preventing the generation of burrs and the effect of improving the cooling efficiency can be both achieved more advantageously.

Further, in the injection compression molding according to the present invention, the fixed mold and the movable mold are fitted in the molding direction on the outer peripheral side of the molding cavity, so that the mold mating surface of the mold is outside the molding cavity. It is also possible to adopt a mold having an outer periphery fitting structure that is configured to extend from the peripheral edge in the mold opening and closing direction, but in addition, for example, in a fixed mold and a movable mold, the mold mating surfaces of both molds are A flat-contact type mold that extends directly from the outer peripheral edge of the molding cavity in the mold-matching surface direction and spreads out can also be advantageously employed, and even in such a flat-contact structure mold, a thin plate-like body can be used. In addition, it is possible to stably manufacture while preventing the generation of burrs.

In particular, by employing such a mold having a flat contact structure, the mold structure can be simplified and the required mold dimensional accuracy can be reduced.
Die manufacturability and cost performance can be greatly improved as compared with the die having the outer periphery fitting structure.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, in order to clarify the present invention more specifically, embodiments of the present invention will be described in detail with reference to the drawings.

First, FIG. 1 shows a schematic process chart of an embodiment of the injection compression molding according to the method of the present invention, and specific data of control of a mold clamping pressure and an injection pressure at the time of such molding are as follows. It is shown in FIG.

That is, in this embodiment, first,
As shown in FIG. 1A, the movable mold 14 is matched with the fixed mold 12, and the two molds 12, 1
By applying a predetermined high-pressure mold clamping pressure: PCa between the molds 4, molding cavities 16a and 16b having a shape corresponding to a desired molded product are formed between the mating surfaces of the two molds 12 and 14.

The molds 12 and 14 shown in the figure are respectively provided with two molding cavities 16a and 16b connected through a resin passage 18 composed of a sprue and a runner. Formed as a molding cavity. In addition, the mold 1 of the present embodiment
The two and 14 have a so-called flat contact structure in which a mold matching surface is formed so as to directly spread from the outer peripheral surfaces of the molding cavities 16a and 16b in a direction perpendicular to the mold matching direction.
Furthermore, the high-pressure mold clamping as described above generally involves moving the movable plate on which the movable mold 14 is mounted to the fixed plate on which the fixed mold 12 is mounted so as to be relatively displaceable in the approaching / separating direction. At the same time, using a mold clamping device with actuators for mold opening and closing and mold clamping such as hydraulic and electric,
It can be performed according to a known technique.

Then, under the condition of applying the high-pressure mold clamping force, at the start of injection: Ta, the molten metal was preliminarily heated and melted and measured from the nozzle portion 20 of the heating cylinder of the injection device in which the fixed mold 12 was brought into nozzle contact with the nozzle. The molten resin material 22 is injected at a predetermined injection pressure: PI, and the molten resin material 22 is guided into the molding cavities 16 a and 16 b through the resin passages 18 of the molds 12 and 14 to be filled. Further, when the molten resin material 22 is injected and filled into the molding cavities 16a and 16b, the injection pressure of the molten resin material is set to have a maximum value: PIa, and the injection power based on the injection pressure is set to the fixed mold 12 and the movable mold. It affects the mold opening direction with respect to the mold 14.
Thereby, as shown in FIG. 1B, the movable mold 14 is relatively displaced by a predetermined amount: A in the direction away from the fixed mold 12 to open the mold.

In accordance with the relative displacement of the movable mold 14 with respect to the fixed mold 12 in the mold opening direction, the injection pressure PI is gradually reduced, and the molding cavity 1 is reduced.
After the injection filling of the molten resin material 22 into 6a, 16b,
By controlling the injection pressure to a predetermined injection holding pressure: PIb, the opening amount of the movable die 14 with respect to the fixed die 12 is set to a predetermined amount: A (for example, 100 μm). Subsequently, the injection holding pressure is gradually reduced, and the injection holding pressure: PI is released at the completion time Tb of the pressure holding step after a predetermined time has elapsed.

At the completion of the pressure holding step: Tb, the injection holding pressure: PI is released, and at the same time, the mold 1 is released.
The mold clamping pressure for PCs 2 and 14 is reduced from high pressure mold clamping pressure: PCa to low pressure mold clamping pressure: PCb. Thus, as shown in FIG. 1 (c), the molds 12, 14 are re-clamped based on the action of the low pressure mold clamping pressure: PCb, and the molds are shown in FIG. 1 (b). The relative displacement is made in the mold clamping direction from the mold opening position of the predetermined amount by the radiant output: A to the mold opening position of the predetermined amount by the low pressure mold clamping force: B.

Here, the value of the low-pressure mold clamping pressure: PCb is calculated from the mold opening amount of the molds 12, 14 in the high-pressure mold clamping process: A to the mold opening amount of the molds 12, 14 in the low-pressure mold clamping process. : Re-clamping amount up to B: (AB) is set to a predetermined value. Specifically, the re-clamping amount: (A-
The low-pressure mold clamping pressure is set so that the value of B) is larger than the amount of cooling shrinkage in the thickness direction of the molten resin material 22 injected and filled into the molding cavities 16a and 16b and is 100 μm or less (for example, 20 μm): Set the value of PCb.

According to the injection compression molding method of the present invention as described above, at the same time when the injection pressure is released upon completion of the pressure holding step, the mold clamping pressure is changed to a small setting, and the mold is opened by the injection force. The re-clamping amounts of the dies 12 and 14 thus set are set to a predetermined amount of 100 μm or less, and unnecessary re-clamping is avoided.
As a result, intrusion of the molten resin material 22 into the gap 26 between the mold mating surfaces in the re-clamping step is effectively prevented, so that the occurrence of burrs in the molded product 24 can be advantageously prevented. .

Moreover, in this molding method, the molten resin material 22 is formed in the molding cavities 16a and 16b whose thickness has been increased by opening the mold by a predetermined amount: A by the action of the injection force, similarly to the conventional injection compression molding. Can be injected and filled into the molding cavities 16a and 16b at a relatively low pressure and without significantly increasing the temperature of the mold, thereby causing defects such as sink marks. Therefore, the desired light guide plate can be manufactured stably with high precision and with a good molding cycle.

Further, since substantially uniform pressure can be applied to the molten resin material 22 filled in the molding cavities 16a and 16b, residual stress can be reduced, and occurrence of troubles such as warpage can be prevented. At the same time, the transfer rate of the pattern applied to the molding surface can be improved, and the effect of suppressing variation in luminance in the product, the effect of improving uniform accuracy, and the like can be achieved.

By the way, as shown in FIGS.
Using the same molding die and injection molding apparatus as in the first embodiment as described above, according to the conventional injection compression molding method, through the pressure-holding step from the injection filling step, after the completion of the pressure-holding step, a substantially constant High pressure mold clamping force to mold 12,1
Injection compression molding was carried out under the same molding conditions as in the first embodiment except that the compression compression was continued to reach 4, and the value of (A-B ') of the re-clamping amount after the completion of the holding pressure was changed to the value in the first embodiment. The amount of re-clamping was 4 times or more as compared with (AB), and many burrs were observed on the outer peripheral surface of the molded product.

Subsequently, the molding conditions are set as shown in FIG. 5 by using the dies 12 and 14 and the injection molding machine having the same structure as the above-described embodiment.
Width: 44.65 mm, height: 32.65 mm, thickness: 1.
Two light guide plates for mobile phones having a rectangular flat plate shape of 00 mm
The pieces were injection molded simultaneously. As a result, it was confirmed that a target light guide plate having no burrs on the outer peripheral surface could be continuously and stably formed.

Incidentally, using the same dies 12, 14 and an injection molding machine, the molding conditions are adjusted so as to sufficiently oppose the injection force as shown in FIG. By applying a force of 14.0 MPa to the dies 12 and 14 through the pressure-holding step from the injection filling step and after the pressure-holding step is completed, the dies 12 and 14 are held in a closed state. A conventional general injection molding (injection molding) was performed and compared with the case where the molding according to the method of the present invention was performed.

As a result, in the molding according to the injection compression molding method according to the present invention, the cooling time can be shortened by as much as 4.5 seconds as compared with the general injection molding, and the increase in the dwell time and the increase in the dwell time can be achieved. In addition, the molding cycle time can be reduced by about 5 seconds. Moreover, when the luminance of the obtained molded article was examined, it was confirmed that the molded article according to the injection compression molding method according to the present invention showed a significant improvement in both the standard deviation and the uniformity of luminance.

Further, in FIG. 7, using the dies 12, 14 and the injection molding machine having the same structure as the above embodiment,
Another specific example of molding conditions when performing the molding operation according to the method of the present invention is shown.

That is, in the present embodiment, the primary holding pressure and the secondary holding pressure are set in the holding pressure step, and the holding pressure is reduced in a stepwise manner. After reducing the clamping pressure from 11.0 MPa to 9.5 MPa and switching from high-pressure clamping to low-pressure clamping, after a predetermined time (approximately 1 second) has elapsed, the clamping pressure is again reduced to 11.0 MPa.
a, and the secondary high pressure mold clamping is performed.

In this specific example, it was confirmed that burrs could be effectively prevented by adopting the low pressure mold clamping step. In addition, by employing the secondary high-pressure mold clamping, the adhesion of the molded product to the mold is improved, and further shortening of the cooling time and further improvement of the molding cycle based thereon can be advantageously achieved. Could be confirmed.

The embodiments and specific examples of the present invention have been described in detail above. However, these are merely examples, and the present invention is not limited to any specific description in these embodiments and specific examples. Needless to say, it is not to be interpreted.

For example, in each of the above-described embodiments, the case where the method of the present invention is applied to the formation of a light guide plate for a liquid crystal display device has been described. Any of these can be advantageously applied to the formation of various thin plate-like bodies such as a housing case for a computer.

The molding material that can be employed in carrying out the method of the present invention is not particularly limited, and various known synthetic resin materials such as methacryl, ABS, polyethylene, polypropylene, polyamide, and the like can be used. Various other materials that can be injection molded can be used.

Furthermore, the shape and structure of the molding cavity in the mold are appropriately determined according to the target molded product. For example, only one molding cavity or three or more molding cavities are provided. Molds can also be employed in the present invention.

In addition, although not enumerated one by one, the present invention
Based on the knowledge of those skilled in the art, various changes, modifications, improvements, and the like can be made, and unless such embodiments depart from the spirit of the present invention.
Both are included in the scope of the present invention,
Needless to say.

[0041]

As is apparent from the above description, according to the injection compression molding method of the present invention, the mold clamping pressure is changed to a small value almost simultaneously with the completion of the pressure holding step, and the mold is opened by the injection pressure. Unnecessary re-clamping in the mold can be avoided, thereby preventing molding defects such as sink marks, improving molding accuracy by reducing internal stress, and improving molding cycle by improving mold adhesion. Thus, it is possible to advantageously prevent the occurrence of burrs in a molded product while sufficiently securing various effects based on the injection compression molding, such as.

[Brief description of the drawings]

FIG. 1 is a schematic process diagram of an embodiment of injection compression molding according to the present invention.

FIG. 2 is a graph showing one specific example of molding conditions in the injection compression molding shown in FIG.

FIG. 3 is a schematic process drawing in a general injection compression molding as a comparative example.

FIG. 4 is a graph showing a specific example of molding conditions in the general injection compression molding shown in FIG.

5 is a graph showing another specific example of molding conditions for performing injection compression molding according to the present invention using the mold and the like shown in FIG.

FIG. 6 is a graph showing a specific example of molding conditions for performing general injection molding as a comparative example.

7 is a graph showing still another specific example of molding conditions for performing injection compression molding according to the present invention using the mold and the like shown in FIG.

[Explanation of symbols]

 12 fixed mold 14 movable mold 16a, 16b molding cavity 22 molten resin material 24 molded product

Claims (6)

[Claims] When a thin plate is injection-molded by injecting a molten resin material into a molding cavity formed between a fixed mold and a movable mold and extending in a mold-matching surface between the mold-matching surfaces. In a state where the fixed mold and the movable mold are clamped by a high-pressure mold clamping force, a molten resin material is injected and filled into the molding cavity at a predetermined injection pressure, so that the fixed mold and the movable mold are filled. An injection step of opening the mold by a predetermined amount by applying an injection force to the molten resin material injected and filled in the molding cavity while the fixed mold and the movable mold are clamped with a high clamping force. A pressure-holding step of applying a holding pressure, and substantially simultaneously with the completion of the pressure-holding step, by changing a mold clamping force applied to the fixed mold and the movable mold from a high-pressure mold clamping force to a low-pressure mold clamping force. The fixed mold and the movable mold are A low-pressure mold clamping step of re-clamping by a predetermined amount from a mold opening position in an ejection step. 2. The method according to claim 1, wherein in the low pressure mold clamping step, the mold clamping force is changed from a high pressure mold clamping force to a low pressure mold clamping force within a range of ± 0.5 seconds with respect to a time point of completion of the pressure holding step. The injection compression molding method for a thin plate-like body according to claim 1. 3. The thin plate-shaped member according to claim 1, wherein in the low-pressure mold clamping step, the mold is re-clamped so that the amount of decrease in the mold opening amount from the mold opening position in the injection step is 100 μm or less. Injection compression molding method for body. 4. In the low-pressure mold clamping step, the amount of decrease in the mold opening from the mold opening position in the injection step exceeds the amount of cooling shrinkage of the molten resin material injected and filled in the molding cavity. The injection compression molding method for a thin plate-like body according to any one of claims 1 to 3, wherein the mold is re-clamped. 5. In the low-pressure mold clamping step, the mold clamping force applied to the fixed mold and the movable mold is changed to a low-pressure mold clamping force. The injection compression molding method for a thin plate-like body according to any one of claims 1 to 4, which exerts a high-pressure mold clamping force. 6. The fixed mold and the movable mold have a flat contact structure in which the mold mating surfaces of both molds extend directly from the outer peripheral edge of the molding cavity in the mold mating surface direction and spread. An injection compression molding method for a thin plate-like body according to any one of claims 1 to 5.