JPH08127037A - Molding die - Google Patents

Abstract

PURPOSE: To control the unevenness of surface accuracy of a molded product even when the cavity volume of respective cavities flutuates a little and improve the yield by forming a clearance for developing flashes in compliance with the resin internal pressure and the resin temperature at the glass transition temperature or over on a part of a cavity. CONSTITUTION: A clearance 5 which is formed on a part of a cavity 4 for developing flashes in compliance with the resin internal pressure and the resin temperature at the glass transition temperature or over on a part of a cavity is formed on the mold opening faces 2 and 3. Pressure lowering in the cavity 4 is generated by the effect of the clearance 5. When the internal pressure in the cavity 4 is large, the development of flashes gets faster in the clearance 5 of given width, while the internal pressure is small, the development of flashes is slow. Therefore, when a given temperature higher than the resin glass transition temperature is kept for a given time, the pressure lowering is larger for large initial internal pressure, while the pressure lowering is smaller for small initial internal pressure because of the above reason. Therefore, when initial pressure difference is retained for a given time, the pressure difference gets smaller to reduce the pressure difference generated by the difference of cavity volumes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding die, and more particularly to molding a laser beam printer, a copying machine, an optical scanning system such as a facsimile, a plastic lens such as a camera, a plastic mirror and a prism. It can be applied to the plastic precision molding dies used. Especially, when many molded products are taken, even if the cavity volume varies a little for each cavity, there is no need to perform the troublesome work of correcting in advance. The present invention relates to a molding die capable of suppressing variations in internal pressure of a resin due to variations in volume between cavities and variations in weight between plastic base materials, suppressing variations in surface accuracy of molded products, and improving yield.

[0002]

2. Description of the Related Art Heretofore, as a method for producing a plastic molded article, there is one reported in Japanese Patent Application Laid-Open No. 4-163119. In this conventional method for producing a plastic molded product, an injection molding process in which a predetermined resin is heated to a temperature at which the resin can flow or higher and is injection-molded into a mold held at a temperature not higher than the heat deformation temperature of the resin to perform gate sealing. Then, the mold filled with the resin is heated so that the temperature of the injection-molded resin becomes the glass transition temperature of the resin or higher, and the temperature is kept at the glass transition temperature or higher for a predetermined time. It is configured so as to include an aging step of gradually cooling until the following.

For this reason, the mold temperature can be set below the heat deformation temperature of the resin, so that it is necessary to cool the resin temperature in the mold after injection and filling of the resin so as not to fall below the glass transition temperature thereof. There is an advantage that it can be eliminated and the time required for injection filling can be shortened. In the conventional method for producing a plastic molded article reported in Japanese Patent Application Laid-Open No. 4-163119, the glass transition of the resin is considered in consideration of obtaining a highly accurate molded article having no transfer and excellent transferability. A constant resin internal pressure is generated at a temperature above the temperature, and the pressure is set to a pressure which is equal to or lower than the atmospheric pressure below the heat deformation temperature of the resin. For this reason, it is desirable to use a constant weight of plastic matrix for a constant cavity volume.

At this time, if the cavity volume is constant,
The variation in the weight of the plastic base material is preferably ± 0.2% or less, more preferably ± 0.15% or less, considering that there is no shrinkage or the like and a highly accurate molded product having excellent transferability is obtained. Is. With this level, a plastic base material having a substantially final shape can be easily and accurately formed in advance by a precision injection molding machine.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the conventional method for producing a plastic molded article reported in Japanese Patent No. 63119, the pressure generated at the time of molding is set to be a fraction of that of the conventional injection molding method or the like, because it is heated above the glass transition temperature of the resin. Because it can be made smaller,
The mold material can be made thin to easily form a plurality of cavities in the mold. For this reason, a plurality of cavities formed in this mold can be used to obtain a large number of molded products, and the cavity interval can be easily shortened while making the mold material thin, resulting in extremely good thermal efficiency. Has the advantage that

However, when a large number of molded products are to be taken in this way, a plurality of cavities must be formed in the mold, so that in machining the cavities, variations in volume and the like will inevitably occur between the cavities. easy. Further, when a large number of molded products are to be taken, it is necessary to mold a plurality of plastic base materials having the same volume as the cavity. However, in processing the plastic base materials, variations in volume and the like tend to occur among the plastic base materials.

Therefore, when a large number of molded products are taken,
If there is volume variation between cavities and weight variation between plastic base materials, the resin internal pressure generated between cavities during molding tends to vary, making it difficult to achieve uniform surface accuracy of the molded product, resulting in a high yield. There was a problem of lowering. Therefore, in order to suppress the variation in resin internal pressure that occurs between the cavities, the variation of each plastic base material should be
The mold may be configured so as to be 0.15% or less. However, in this method, in order to suppress the variation between each plastic base material and each cavity, it is checked beforehand whether or not the plastic base material and the mold are constant at the time of manufacturing the plastic base material and the mold, and the correction is performed so as not to cause the dispersion. The additional work has to be performed again, which is troublesome and troublesome. In particular, the more complicated the cavity shape and the larger the number of cavities, the more difficult the work becomes.

Therefore, according to the present invention, when a large number of molded products are taken, even if the cavity volume varies a little for each cavity, the volume variation between the cavities does not occur without performing a troublesome work of correcting the cavity in advance. An object of the present invention is to provide a molding die that can suppress variations in the internal pressure of the resin due to variations in the weight of each plastic base material, suppress variations in the surface accuracy of molded products, and improve the yield.

[0009]

According to the first aspect of the present invention,
A mold is obtained by inserting a plastic base material having a substantially final shape into a cavity having at least one or more cavities and having the same or substantially the same volume as the plastic base material of the mold having at least one or more mirror surfaces. After tightening, it is heated to the glass transition temperature of the plastic base material or higher, the mirror surface is transferred by the resin internal pressure generated from the plastic base material, and then slowly cooled to a temperature not higher than the thermal deformation temperature of the plastic base material, and When the pressure in the cavity becomes the same or almost the same as the atmospheric pressure, the mold is opened and the molded product is taken out. In a molding die for a plastic molded product, burrs progress above the glass transition temperature according to the resin internal pressure and the resin temperature. A gap is provided in a part of the cavity.

According to a second aspect of the present invention, in the above-mentioned first aspect, the width of the gap is 10 μm or more and 500 or more.
It is characterized in that it is in the range of μm or less. According to a third aspect of the invention, in the first aspect of the invention, the volume of the gap is in the range of 0.05% to 0.3% of the cavity volume.

According to a fourth aspect of the present invention, in the above-described first to third aspects, the gap is provided on the mold opening surface. According to a fifth aspect of the present invention, in the above-described first to third aspects, the gap is provided in a direction perpendicular to the mold opening surface and in a direction adjacent to the mirror surface. .

According to a sixth aspect of the present invention, in the above-mentioned first to fifth aspects, when the weight of the plastic base material having the substantially final shape is smaller than the target weight, the heating temperature is lowered to set the substantially final temperature. When the weight of the shaped plastic base material is larger than the target weight, the heating temperature control means for raising the heating temperature is provided.

[0013]

The operation of the invention according to claim 1 is a comparative example (conventional example).
The explanation will be given in comparison with. First, a comparative example will be described with reference to the drawings. 1 is a sectional view showing the structure of a plastic base material, FIG. 2 is a sectional view showing the structure of a molding die of a comparative example, FIG.
FIG. 4 is a diagram showing a change in mold temperature and a change in resin generated pressure in a cavity from insertion of a plastic base material of a comparative example to removal of a molded product.

In FIGS. 1 and 2, 1 is a plastic base material, and 2 and 3 are an upper die and a lower die having a cavity 4 and a mirror surface 4a. In the comparative example, a constant weight of plastic base material is put into a cavity of a certain volume and heated to a temperature above the glass transition temperature of the plastic base material to generate a constant resin internal pressure in the cavity 4 due to the plastic base material.

At this time, if the volume of the cavity 4 is larger than the target volume (the volume at which the resin internal pressure becomes atmospheric pressure at a temperature equal to or lower than the heat deformation temperature at the time of taking out), the plastic matrix generated in the cavity 4 is generated. The pressure generated by the material becomes small, a negative pressure part is generated at the time of taking out, and shrinkage occurs. Conversely, when the volume of the cavity 4 is smaller than the target volume, residual pressure occurs at the time of taking out and this becomes a stress and mirror surface transfer There was a problem of causing defects.

Therefore, in the invention described in claim 1, by utilizing the phenomenon that the progress of the burr changes depending on the magnitude of the resin internal pressure and the level of the resin temperature (the magnitude of the resin melt viscosity), the resin is kept at a temperature not lower than the glass transition temperature. A gap is formed in a part of the cavity in which burr progresses according to the internal pressure and the resin temperature. Therefore, when a large number of molded products are taken, the burrs that progress according to the resin internal pressure and the resin temperature can be appropriately adjusted by the gap provided in a part of the cavity.

Therefore, when a large number of molded products are taken, even if the cavity volume varies a little for each cavity, there is no need to perform a complicated work such as a correction in advance, and there is a variation in capacity between each cavity and each plastic mother. Since it is possible to suppress the variation in the internal pressure of the resin due to the variation in the weight between the materials, it is possible to suppress the variation in the surface accuracy of the molded product and improve the yield.

In particular, when the resin internal pressure is large or the resin temperature is high and the resin has a low viscosity, burrs are advanced in the gap provided in the cavity to automatically operate so as to reduce the internal pressure. be able to. Further, in particular, when forming a molded product in an uneven thickness state in which a thin wall and a thick wall are mixed, variations in the resin internal pressure distribution are likely to occur between the thin wall portion and the thick wall portion. It is preferable to apply the invention of.

Next, the operation of the invention described in claim 2 will be described. If the width of the gap is smaller than 10 μm, it is not preferable because it is difficult for burr to enter the gap and it is difficult to obtain the effect of the invention of claim 1. The width of the gap is 500 μm
If it is larger than this, a large amount of burr is likely to occur and shrinkage is likely to occur, which is not preferable.

Taking these into consideration, the width of the gap is 10 μm.
The range from m to 500 μm is preferable. In this case, by limiting the width of the gap, the variation in the volume between the cavities can be easily corrected, and the occurrence of burrs can be appropriately controlled within a certain range. In particular, it is possible to prevent the pressure decrease from becoming too large due to the progress of burr.

Next, the operation of the invention described in claim 3 will be described. If the volume of the gap is smaller than 0.05% of the cavity volume, burrs are less likely to enter the gap and the effect of the invention of claim 1 is difficult to be obtained, which is not preferable. Further, if the volume of the gap is larger than 0.3% of the cavity volume, a large amount of burrs is apt to occur and shrinkage is apt to occur, which is not preferable.

Considering these, the volume of the gap is 0.
The range of 05% or more and 0.3% or less is preferable. in this case,
By limiting the volume of the gap, it is possible to easily correct the volume variation between the cavities, and it is possible to appropriately control the occurrence of burrs within a certain amount. In particular, it is possible to prevent the pressure decrease from becoming too large due to the progress of burr.

Next, the operation of the invention described in claim 4 will be described. In the invention according to claim 4, since the gap is provided on the mold opening surface, it can be used together with the gas vent. Also, when the final shape plastic base material is put into the cavity and clamped, it is possible to prevent some shavings of the plastic base material from being caught, making it easy to mold the product without damaging the mold. You can take it out.

Next, the operation of the invention described in claim 5 will be described. In the invention according to claim 5, since the gap is provided in the direction perpendicular to the mold opening surface (the mold opening direction) and in the direction adjacent to the mirror surface, the pressure on the mirror surface can be easily equalized. it can. Next, the operation of the invention described in claim 6 will be described.

According to the sixth aspect of the present invention, the heating temperature is lowered by the heating temperature control means when the weight of the plastic base material having the substantially final shape is smaller than the target weight, and the weight of the plastic base material having the substantially final shape is reduced. When the weight is higher than the target weight, the heating temperature is increased. Therefore, when the weight of the plastic base material in the substantially final shape is smaller than the target weight, the heating temperature can be lowered to prevent burrs from occurring, and the weight of the plastic base material in the almost final shape can be targeted. When it is larger than the weight, the heating temperature can be raised to facilitate the production of burrs.

As a result, the heating temperature can be changed according to the weight of the plastic base material to appropriately control the amount of burrs. Therefore, even if the weight of the plastic base material changes, not only the internal pressure of the resin, By optimizing the temperature as well, it is possible to correct the weight variation of the plastic base material. Therefore, since the resin internal pressure can be efficiently made constant, a highly accurate plastic molded product can be obtained.

Next, in the present invention, the heating temperature may be kept constant, and the holding time may be lengthened or shortened, and may be appropriately adjusted. In this case, the invention according to claim 6 may be adopted. Similar effects can be obtained.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a cross-sectional view showing the structure of a molding die according to an embodiment of the present invention. In FIG. 4, reference numeral 5 is a gap provided in a part of the cavity 4 in which burrs progress above the glass transition temperature in accordance with the resin internal pressure and the resin temperature. It is provided and configured.

The influence of the gap 5 causes a pressure drop in the cavity 4 as shown in FIG. As shown in FIG. 5, when the internal pressure of the cavity 4 (internal pressure of the resin) is large, the progress of the burr is fast in the gap 5 having a constant width, and conversely, when the internal pressure of the cavity 4 is small, the progress of the burr is slow. For this reason, if the temperature is kept at a temperature higher than the glass transition temperature of the resin for a certain period of time, the one with a large initial internal pressure has a large pressure drop, and the one with a small initial internal pressure has a small pressure drop. There was a considerable pressure difference between the two, but after holding for a certain period of time, the difference between the two becomes smaller.

In this way, the pressure difference caused by the difference in the volume of the cavity 4 can be reduced by the gap 5. On the other hand, when the heating temperature is raised and the temperature of the resin is raised, the internal pressure of the resin increases due to expansion by the resin,
Further, its viscosity decreases and acts in a direction in which burr progresses, that is, a direction in which pressure decreases. Therefore, if the pressure generated in each cavity 4 is detected and the heating temperature is changed for each of the cavities 4, the pressure drop due to the burr generation can be efficiently controlled.

In the present embodiment, by utilizing the phenomenon that the progress of burrs changes depending on the magnitude of the resin internal pressure and the resin temperature (the resin melt viscosity), the resin internal pressure and the resin temperature above the glass transition temperature can be obtained. Accordingly, the gap 5 in which the burr progresses is provided in a part of the cavity 4. Therefore, when a large number of molded products are taken, the burrs that progress according to the resin internal pressure and the resin temperature can be appropriately adjusted by the gap 5 provided in a part of the cavity 4.

Therefore, when a large number of molded products are taken, even if the volume of the cavities 4 varies a little for each cavity 4, there is no need to perform a complicated work for correcting the cavities 4 in advance, and there is a variation in capacity between the cavities 4. Since it is possible to suppress the variation in the resin internal pressure due to the variation in the weight between the plastic base materials, it is possible to suppress the variation in the surface accuracy of the molded product and improve the yield. In particular, when the resin internal pressure is large or the resin temperature becomes high and the resin becomes low in viscosity, burrs progress in the gap 5 provided in the cavity 4 to automatically operate so as to reduce the internal pressure. You can

Further, in particular, when forming a molded product in an uneven thickness state in which thin and thick are mixed, variations in the resin internal pressure distribution are likely to occur between the thin portion and the thick portion. It is preferable to apply the examples. In the present embodiment, the gap 5 is provided on the mold opening surfaces of the molds 2 and 3, so that it can be used together with the gas vent. Further, when the plastic base material having a substantially final shape is put into the cavity 4 and the mold is clamped, it is possible to prevent a part of the shavings of the plastic base material from being caught, so that the molded product can be taken out easily. .

In this embodiment, the heating temperature is lowered when the weight of the plastic base material having the substantially final shape is smaller than the target weight, and when the weight of the plastic base material having the substantially final shape is larger than the target weight. The heating temperature is increased. Therefore, when the weight of the plastic base material in the substantially final shape is smaller than the target weight, the heating temperature can be lowered to prevent burrs from occurring, and the weight of the plastic base material in the almost final shape can be targeted. When it is larger than the weight, the heating temperature can be raised to facilitate the production of burrs.

Therefore, since the heating temperature can be changed according to the weight of the plastic base material to appropriately control the amount of burrs, even if the weight of the plastic base material changes, not only the internal pressure of the resin but also the temperature. By also optimizing, it is possible to correct the weight variation of the plastic base material. As a result, the internal pressure of the resin can be made constant, so that a highly accurate plastic molded product can be obtained.

Next, if the width of the gap 5 is smaller than 10 μm, it is not preferable because it is difficult for burr to enter the gap 5 and it is difficult to obtain the effect of the above-described embodiment. Further, if the width of the gap 5 is larger than 500 μm, a large amount of burrs is apt to occur and shrinkage is apt to occur, which is not preferable. Considering these, the width of the gap 5 is preferably in the range of 10 μm or more and 500 μm or less. In this case, the variation in volume between the cavities 4 can be easily corrected, and the occurrence of burrs can be appropriately controlled within a certain amount. In particular, it is possible to prevent the pressure decrease due to the progress of burrs from becoming too large.

Next, as shown in FIG. 6, when the volume of the gap 5a is smaller than 0.05% of the cavity volume,
Burrs are less likely to enter the gap 5a, and it is difficult to obtain the effects of the above embodiment, which is not preferable. The volume of the gap 5a is
If it is larger than 0.3% of the cavity volume, a large amount of burr tends to be generated and shrinkage is likely to occur, which is not preferable.

Taking these into consideration, the volume of the gap 5a is
The range of 0.05% or more and 0.3% or less is preferable. In this case, the variation in volume between the cavities 4 can be easily corrected, and the occurrence of burrs can be appropriately controlled within a certain amount. In particular, it is possible to prevent the pressure decrease due to the progress of burrs from becoming too large. Next, in the present invention, as shown in FIG. 7, the gap 5b is provided in the direction perpendicular to the mold opening surface (the mold opening direction) and in the direction adjacent to the mirror surface 4a. The pressure can be made uniform easily. In this case, the gap 5b is replaced by the mirror surface 4a.
The pressure adjustment on the mirror surface 4a can be performed with better responsiveness by being provided adjacent to. Moreover, since it is possible to prevent burrs from being generated in the direction perpendicular to the mold opening direction that is normally used as the fixing portion, it is possible to prevent the burrs from becoming an obstacle during fixing.

According to the present invention, as shown in FIGS. 4 and 5, when a burr is formed on the mold opening surface perpendicular to the mold opening direction, the plastic base material is inserted into the cavity 4 at this portion. There is a risk that the plastic base material will have burrs when it is clamped by a die, or if the part where the plastic base material is present is larger than this cavity 4, shavings and the like will be generated and the die will be damaged by sandwiching it. .

In this case, since it can be escaped through the gap 5 from the beginning, it is possible to prevent such a mold from being damaged. In this method, the pressure is adjusted by burrs, so it is desirable to use a plastic base material having a weight slightly higher than the target weight.

[0041]

According to the present invention, when a large number of molded articles are taken, even if the volume of the cavities varies slightly between the cavities, the cavities between the cavities do not have to be corrected without performing a complicated work in advance. It is possible to suppress variations in the internal pressure of the resin due to variations in volume and variations in weight between the plastic base materials, and it is possible to suppress variations in surface accuracy of molded products and improve yield.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of a plastic base material.

FIG. 2 is a cross-sectional view showing a structure of a molding die of a comparative example.

FIG. 3 is a diagram showing changes in mold temperature and changes in resin generated pressure in a cavity from insertion of a plastic base material of a comparative example to removal of a molded product.

FIG. 4 is a cross-sectional view showing the structure of a molding die according to an embodiment of the present invention.

5 is a diagram showing a state in which a pressure drop in the cavity is caused by the gap shown in FIG.

FIG. 6 is a sectional view showing a structure of a molding die applicable to the present invention.

FIG. 7 is a sectional view showing a structure of a molding die applicable to the present invention.

[Explanation of symbols] 1 plastic base material 2, 3 mold 4 cavity 4a mirror surface 5, 5a, 5b gap

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Jun Watanabe 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (6)

[Claims] 1. A cavity in which a plastic base material having a substantially final shape has at least one or more cavities and which has the same or substantially the same volume as the plastic base material of a mold having at least one or more mirror surfaces. , The mold is clamped, heated to a temperature above the glass transition temperature of the plastic base material, the mirror surface is transferred by the resin internal pressure generated from the plastic base material, and then gradually cooled to thermally deform the plastic base material. In a molding die for a plastic molded product, which is opened below the temperature and when the pressure in the cavity becomes the same or approximately the same as the atmospheric pressure to take out the molded product, depending on the resin internal pressure and the resin temperature above the glass transition temperature. A molding die, characterized in that a gap for advancing burrs is provided in a part of the cavity. 2. The width of the gap is 10 μm or more and 500 μm
The molding die according to claim 1, which is in the following range. 3. The volume of the gap is 0.
The molding die according to claim 1, which is in a range of from 05% to 0.3%. 4. The molding die according to claim 1, wherein the gap is provided on a mold opening surface. 5. The molding die according to claim 1, wherein the gap is provided in a direction perpendicular to the mold opening surface and in a direction adjacent to the mirror surface. 6. The heating temperature is lowered when the weight of the plastic base material having the substantially final shape is smaller than the target weight, and the heating temperature is lowered when the weight of the plastic base material having the substantially final shape is larger than the target weight. The molding die according to any one of claims 1 to 5, further comprising heating temperature control means for raising the temperature.