JP2000141413A - Manufacture of plastic molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a plastic part having a more accurate transferability at low cost by a method wherein the position and volume of a gap partitioned at the position except transferring surfaces of a plastic molded product are freely expanded. SOLUTION: In the manufacturing method of a plastic molded product with an injection mold having at least one or more transferring surfaces 2 provided on the cavity surfaces partitioning a cavity having a predetermined volume so as to transfer the transferring surfaces to a molded product by the pressure of a resin induced in this cavity, the resin in the cavity is cooled and solidified through a first process of forming a gap 8 between at least one or more surfaces defining the cavity and a resin 7 by retreating a movable piece 3 after the melted resin is injected and filled in the mold heated up to a temperature below the softening temperature of the melted resin, and a second process of expanding the gap 8 to a predetermined volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plastic molded article, and more particularly to a method for producing an optical element such as a plastic lens or a plastic mirror having a highly accurate mirror surface. .

[0002]

2. Description of the Related Art Laser-type digital copying machines, printers, or optical writing units of facsimile machines include:
An optical element such as a rectangular lens or a mirror having a laser beam imaging and various correction functions is used. In recent years, these optical elements have been changed from glass to plastic in order to reduce product cost, and the transfer surface shape is not only spherical but also complex aspherical, in order to supplement multiple functions with minimal elements. In the case of a lens, the lens shape is often a thick lens shape and an uneven thickness shape in which the lens thickness is not constant in the longitudinal direction. On the other hand, the production method of these plastic optical elements has a low production cost, and is suitable for mass production, such as an injection molding method, or a mold for forming a transfer surface arranged in a mold, which can be moved, and the inside of the mold is reduced. In general, a method of securing the shape accuracy by advancing the movable insert to compensate for the volume shrinkage due to cooling of the resin filled in the resin to secure the shape accuracy, that is, a so-called injection compression molding method is generally used. When manufacturing by such an injection molding method or an injection compression molding method, the resin pressure and the resin temperature in the mold become uniform in the step of injecting and filling the resin material heated and melted into the mold and solidifying it by cooling. Is necessary to ensure desired shape accuracy. However, when the lens thickness is uneven thickness, the cooling rate of the filled resin is different in each part in the longitudinal direction due to the deviation of the lens thickness, and the volume shrinkage is different, so that the shape accuracy is deteriorated or the lens thickness is reduced. There is a disadvantage that sinking occurs in this part because cooling is locally delayed in thick places, and in the case of thick molded products, shrinkage occurs due to a large volume shrinkage in the resin cooling process. In addition, there is a method of increasing the injection pressure (to increase the filling amount of the resin) in order to prevent the occurrence of sink marks. However, according to this method, internal distortion increases, which adversely affects optical performance. That is inevitable. In addition, when manufacturing using the injection compression molding method, molding can be performed with a lower injection pressure than the above-mentioned injection molding method.However, if there is a deviation in the lens thickness, there is a difference in volume shrinkage amount in each part in the longitudinal direction. As a result, the movable insert cannot follow the volumetric shrinkage of the resin, and therefore cannot apply an even pressure. As a result, a sink occurs on a part of the transfer surface, and the shape accuracy is reduced. There is.

[0003] As a method for solving the problems of the injection molding method or the injection compression molding method as much as possible, a movable cavity piece (hereinafter referred to as "movable piece") is filled with a molten resin and then cooled to a temperature below a softening temperature. This is called a movable piece)
A molding method has been developed in which a gap is defined between the cavity wall surface and the resin by retreating the resin and separating the resin from the resin (Japanese Patent Application No. 9-164316). Thereby, the shrinkage caused by the cooling can be compensated by moving the resin in the portion facing the gap, and the resin facing the gap can be preferentially shrunk to avoid the sink on the transfer surface. . In this case, when the resin is injected and filled into the cavity, it is necessary to fix the movable piece to be separated against the pressure of the resin in the cavity so as not to move.

On the other hand, as shown in FIG. 1, when the area for separating the movable piece from the resin in the cavity is small, the space (8) defined thereby is small, so that only the portion is preferentially sufficient. It is not possible to sufficiently compensate for uneven shrinkage of the resin by inducing sinks of a size, and as a result, sinks may occur on the transfer surface. In particular, when the transfer area is large, it is necessary to increase the area for inducing sink marks (the area defining the gap) correspondingly. For this purpose, as shown in FIG. There is no other way to increase the area to be separated by, for example, isolating the entire side surface of the resin (7) in 1). However, in this case, it is necessary to press the movable piece with a large force against the pressure of the resin (7) so that the movable piece does not move during injection and filling of the resin. The size of the pressure control device (4) for generating pressure increases, and the mold structure becomes complicated. Further, there are cases where the area to be isolated cannot be increased due to restrictions on the shape of the molded product and the structure of the mold. Further, if the area to be separated is large, the adhesive force between the molded product and the movable piece (3) at the time of separation increases, so that a gap is not defined at a desired place, and as shown in FIG. Is pulled by the retreating movable piece, and the entire shape is deformed.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art as much as possible, by setting the position of a gap defined outside the transfer surface of a plastic molded product. Another object of the present invention is to devise a molding method so that the size of the gap can be freely increased and a plastic part having higher precision transferability can be manufactured at low cost.

[0006]

Means taken to solve the above-mentioned problem are at least one transfer surface on a cavity surface defining a cavity having a predetermined volume, and the transfer surface is generated in the cavity. Assuming a method of manufacturing a plastic molded product using an injection molding die for transferring a transfer surface to a molded product by resin pressure, (a) after injection filling a molten resin into the die heated to a temperature lower than its softening temperature, A first step of retracting the piece to define a gap between at least one or more surfaces defining the cavity and the resin;
(B) The resin in the cavity is cooled and solidified through a second step of expanding the gap to a predetermined size before the resin is cooled below its softening temperature.

[0007]

The gap formed in the first step is enlarged in the second step of injecting high-pressure gas and is expanded to an arbitrary size as appropriate. Therefore, the gap formed in the first step is extremely small. Good. Therefore, the above-mentioned problem in the case where a large gap is formed by retreating the movable piece is solved. In addition, since the operation of expanding the gap is performed freely by appropriate means such as air pressure, the control is appropriately performed according to the shape of the molded product, the position of the transfer surface, the width, the type of resin, the filling temperature, etc. Therefore, it is possible to easily and accurately define a gap of a required size necessary for reliably avoiding sinks on the transfer surface, and the shape of the molded product, the position and the size of the transfer surface. , Regardless of the type of resin, filling temperature,
Plastic molded products can be manufactured with high precision.

[0008]

[Embodiment 1] In the solution, a ventilation hole communicating with the outside of a mold is provided on a cavity surface defining the above-mentioned gap, and high-pressure gas is press-fitted into the cavity from the ventilation hole, thereby defining the cavity surface. Enlarging the voids to a predetermined size.

[Embodiment 2] A vent provided in the above-mentioned cavity surface in Embodiment 1 is arranged at a position where a gap is to be widened.

[Embodiment 3] The size of the void is adjusted by adjusting at least one of the pressure, the injection time, and the injection amount of the high-pressure gas in the embodiment 1 or 2.

[Fourth embodiment] In the first to third embodiments, the gap between the movable piece and the fitting hole of the movable piece is the ventilation hole.

Fifth Embodiment In the first to third embodiments, a communication hole is provided in the movable piece, and the communication hole is used as the above-mentioned vent.

[Embodiment 6] The width of the vent hole in the embodiment 1 to the embodiment 5 is formed to be 0.001 to 0.5 mm.

[Seventh Embodiment] In the above solution, the cavity wall temperature of the portion where the gap is to be widened is made lower than the other cavity wall temperatures.

[Eighth Embodiment] The size of the void is adjusted by adjusting the temperature of the cavity surface defining the void in the above solution or the seventh embodiment.

A ninth aspect of the present invention is that the cavity wall surface is subjected to a surface treatment so as to reduce the adhesive strength between the resin and the cavity wall surface at the portion where the void is to be widened.

[Embodiment 10] The size of the void is adjusted by adjusting the surface treatment range on the cavity surface defining the void in the above-mentioned solution or Embodiment 8.

[Embodiment 11] In the above-mentioned solving means, Embodiment 1
Or any combination of two or more of the tenth embodiment.

[0009]

EXAMPLES Next, examples of the present invention will be sequentially described with reference to the drawings in order to specifically clarify the above-mentioned means and the above-mentioned embodiments. First, the configuration of the plastic molding die of one embodiment shown in FIG. 3 will be described. A cavity (1) having a predetermined volume in this device has a transfer surface (2) for transferring a mirror surface to a molded product, and is open to the molding surface, and a gate (1) for injecting and filling a molten resin material into the cavity. A movable piece (3) having a small end surface area is provided on at least one cavity wall surface other than the transfer surface (2), and a pressure control device (4) is provided on the movable piece (3). Are linked. On the other hand, the movable piece (3)
A clearance (5) between the movable piece (3) and the fitting hole into which the movable piece (3) is loosely fitted is a communication port for communicating the cavity (1) with the outside of the mold. The clearance (5) is connected to a high-pressure gas source (6) outside the mold.

Next, the operation of the embodiment of FIG. 3 will be described. The molten resin is injected and filled into the cavity (1) in FIG. 3 through the gate, and the transfer surface is transferred to the molded product by the resin pressure generated in the cavity, and is cooled and solidified to form the molded product. In the case of performing molding by an injection molding method, the movable piece (3) is connected to the pressure control device 4, and when the molten resin is injected and filled into the cavity (1), the maximum generated in the cavity is obtained. A pressure greater than the resin pressure is applied to the movable piece, and the movable piece (3) is pressed so as not to move by the resin pressure. The opening width of the clearance between the movable piece (3) and its fitting hole into the cavity (1) is set to 0.001 to 0.5 mm, preferably 0.001 to 0.05 mm, and the resin is injected and filled at the time of injection and filling. Intrusion (that can be burred on the molded product by the intruded resin) is avoided. After the filling of the resin, the cooling and solidification of the resin (7) in the cavity (1) proceeds, and when the resin pressure reaches a predetermined pressure, the movable piece (3) is moved so that the distal end surface is separated from the molding surface of the cavity (1). Move to (retreat)
This creates a small gap (8) between the movable piece (3) and the surface of the molded article in the cavity (see FIG. 4, first step). Next, as shown in FIG. 5, a high-pressure gas is supplied from a high-pressure gas source (6) provided outside the mold via a clearance (5) between the movable piece (3) and its fitting hole (5). 1) (see FIG. 5, second step).
The press-in gas enters the cavity (1) while isolating the resin and the cavity surface, and the gap defined between the cavity surface and the molded product is enlarged, thereby causing an uneven resin. The space (8) is expanded to have a sufficient size to absorb the contraction of the air. The gap (8) is adjusted to an appropriate size and depth by adjusting at least one of the time during which pressure is applied by the high-pressure gas, the pressure, and the amount of pressurized gas injected. According to the present invention, even when the end surface area of the movable piece (3) for defining the gap is small, the high-pressure gas is injected from the clearance (5) to cool the resin in the cavity. A void large enough to compensate for the shrinkage of the resin is defined. Therefore, the transfer surface is not deformed or distorted due to the above-described shrinkage, the transfer accuracy of the transfer surface is improved, and the force received by the movable piece (3) when injecting and filling the resin into the cavity is small. The pressure control device (4) for holding the movable piece (3) immovably against the cavity internal pressure may be of a relatively small and simple mechanism. Further, since the movable piece (3) can be small, the degree of freedom in layout of the movable pieces can be increased. Further, since the movable piece (3) can be made smaller and the resin is easily separated from the movable piece when the movable piece (3) retreats due to the effect of pressurizing the high-pressure gas, the movable piece (3)
The resin (7) in the cavity (1) is pulled by the close contact force with the resin, and the molded product is deformed and the entire shape is prevented from being distorted. In the present molding method, since it is not necessary to fill the resin with high pressure in order to suppress sink marks on the molded product, plastic lenses, prisms, and other transmission optical components such as prisms can be molded with this molding method. An extremely accurate transmission optical component can be obtained.

As described above, the high-pressure gas is not limited to be injected from the gap (clearance) between the movable piece (3) and its fitting hole. For example, as shown in FIG. The same effect can be obtained by providing a communication hole (9) for injecting gas into the center. FIG. 7 shows a cavity non-transfer surface (10) that defines a gap, and as shown in FIG. 7, a ventilation groove (10) communicating with a communication hole (9) of the movable piece (3). 11) can also be arranged on the non-transfer surface (10) of the cavity. In this case, if the ventilation groove (11) is provided at a position where the space is desired to be widened, the space can be more efficiently expanded and defined at a desired position.

When there is a temperature distribution in the cavity,
After the movable piece is slid to define the gap, the gap invades and expands to a place where the temperature of the cavity is low. This is because the cooling and solidification of the resin proceeds from the low temperature portion, and the resin shrinks. Therefore, by setting the cavity temperature at a place where the gap is desired to be widened to be lower than that of other parts, the position where the gap is defined can be controlled. In this case, equipment such as a high-pressure gas source is not required as compared with the case where gas is injected. Therefore, for example, a simple and inexpensive equipment can be used by changing the layout of the cooling pipe or using a split heater. In this case, the depth, position, and size of the gap can be controlled as desired by controlling the temperature difference between the low-temperature portion and the high-temperature portion.

Further, by making the adhesive strength (adhesive force per unit area) at a place where the gap is desired to be widened smaller than the adhesive strength of the other cavity surface, a gap is formed at a desired position and the size of the gap is increased. Can be appropriately expanded. As a method of reducing the adhesion strength of the cavity surface, a method of performing surface treatment (coating) on the cavity surface with a material having low adhesion to the resin material can be adopted. As a material having low adhesion to a resin material, TiN
(Titanium nitride), TiCN (titanium cyanide), W2
C (tungsten carbide), Teflon (registered trademark)
And the like. The position, depth, and size of the gap can be adjusted and controlled as desired by adjusting the range of the surface treatment. In the case of the method of reducing the adhesion strength by the surface treatment described above, a heating control means such as a heater is not necessarily required, and the mold can have a simpler structure than in the case of the above-described method of providing a temperature difference. .

The above-mentioned method of injecting a high-pressure gas, the method of providing a temperature difference, and the method of performing a surface treatment can all be carried out independently. It is also possible to use these in combination, so that even if the molded article has a complicated shape, a void having a desired size can be reliably defined at a desired position. These combinations may be selected in consideration of the characteristics of the respective products, the material and shape of the molded product, the resin filling temperature, and the like.

[0015]

The operation and effect of the present invention and the embodiment are already clear from the above description. The main points of the operation and effect for each invention according to the main claims are summarized as follows. It is.

According to the first aspect of the present invention, a small gap is formed on a non-transfer surface by using a small movable piece, and the gap is enlarged to a desired size, so that a gap having a required size is formed at a required position. Can be freely interposed as appropriate. Therefore, the heat shrinkage of the non-uniform resin is sufficiently compensated for by the sink due to the void, and the sink of the optimal size can be reliably guided to the optimal position on the non-transfer surface. Since the movable piece can be made smaller and the movable piece can be made smaller, the force for holding and fixing the movable piece against the resin pressure in the cavity at the time of injection and filling can be small, so the mold Is simplified.

[Regarding the invention according to claim 2] The small gap formed on the resin surface by the retreat of the small movable piece is press-fitted with a high-pressure gas, and is appropriately enlarged as needed. And it can be easily performed. Therefore, a gap with an optimal size is easily and reliably defined at an optimal position, and the position and size of the gap can be freely adjusted to induce sinks on the non-transfer surface, and the size and depth of the sinks. Therefore, the transfer surface with high precision can be reliably obtained. In addition, since the operation is performed by injecting a high-pressure gas, the responsiveness of the operation and control for expanding the gap is extremely good.

According to the third aspect of the present invention, the communication hole may be arranged at a position where the small gap formed by the retreat of the small movable piece is desired to be widened, so that the gap is easily and reliably defined at a required position. be able to.

[Invention of Claim 4] The width and depth of the gap can be easily and freely adjusted by adjusting at least one of the pressure, the injection time, and the injection amount of the high-pressure gas. it can. Therefore, by induction of sink marks,
It is possible to easily and reliably form a highly accurate transfer surface.

According to a fifth or sixth aspect of the present invention, the gap between the movable piece and the fitting hole into which the movable piece is fitted is formed as an air vent through which high-pressure gas is injected into the cavity. Alternatively, a communication hole is provided in the movable piece and the communication hole is used as the ventilation hole. With this, the ventilation hole can be formed simply and easily without performing special processing on the mold. .

[Regarding the invention according to claim 7] The resin in the cavity penetrates into the above-mentioned vent hole into which high-pressure gas is injected,
As a result, formation of burrs on the molded product can be reliably avoided.

The invention according to claim 8 is based on the fact that the temperature of the cavity wall at the portion where the gap is to be widened is lowered. However, since the local temperature control of the cavity wall can be performed by relatively simple means, the high pressure The production equipment is inexpensive as compared with the method of expanding the gap by pressurizing gas.

According to the ninth aspect of the present invention, the temperature of the cavity surface is adjusted, but the local temperature control of the cavity wall surface can be performed by relatively simple means. Compared with the method of expanding the gap, the production equipment is inexpensive, and the local temperature control of the cavity wall surface is performed relatively quickly, so that the operation for controlling the gap and the responsiveness of control are good. Yes, it is relatively easy to induce sink marks and adjust the size of sink marks,
Can be done accurately.

According to the tenth aspect of the present invention, the surface of the cavity at the portion where the void is to be widened is subjected to a surface treatment so as to reduce the adhesive strength with the resin. Alternatively, since there is no need to provide any special means such as a local temperature control means for the cavity wall surface, the cost for implementing the present invention is extremely low.

[Brief description of the drawings]

FIG. 1 is a sectional view of a conventional injection molding apparatus.

FIG. 2A is a cross-sectional view schematically showing a relationship between a movable piece, a gap, and sink of a molded product in another conventional injection molding apparatus, and FIG. It is sectional drawing which shows typically the deformation | transformation state of the molded article at the time of frame retreat.

FIG. 3 is a sectional view of an embodiment of the present invention.

FIG. 4 is a sectional view schematically showing a relationship between a movable piece, a gap, and sink of a molded product in the embodiment of FIG.

FIG. 5 is a cross-sectional view schematically showing a relationship between an enlarged gap and sink marks in the embodiment of FIG.

FIG. 6 is a cross-sectional view of another embodiment of the present invention.

FIG. 7 is a plan view of a cavity non-transfer surface that defines a gap in the embodiment of FIG. 6;

[Explanation of symbols]

 (1) Cavity (2) Transfer surface (3) Movable piece (4) Pressure control device (5) Clearance (6) Gas generation source (7) Resin (molded product) (8) Void (9) Communication hole (10) ) Non-transfer surface (11) Vent groove

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Suji Hatakeyama 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Kiyotaka Sawada 1-3-6 Nakamagome, Ota-ku, Tokyo F term in Ricoh Co., Ltd. (reference) 4F202 AH74 AH76 AM33 AM34 CA11 CB01 CK18 CK52 CM41

Claims (12)

[Claims] 1. An injection molding die having at least one transfer surface on a cavity surface defining a cavity having a predetermined volume, and transferring the transfer surface to a molded product by a resin pressure generated in the cavity. In the method for producing a plastic molded product, after injection and filling of a molten resin into the mold heated to a temperature lower than its softening temperature, a movable piece is retracted, and a gap between at least one or more surfaces defining the cavity and the resin is formed. And a second step of expanding the gap to a predetermined size before the resin is cooled below its softening temperature.
A process for cooling and solidifying the resin in the cavity after the step (c). 2. A cavity defined on the cavity surface is provided with a vent communicating with the outside of the mold on a cavity surface defining the cavity, and high-pressure gas is injected into the cavity through the vent. 2. The method for manufacturing a plastic molded product according to claim 1, wherein the plastic molded product is enlarged to a predetermined size. 3. The method for manufacturing a plastic molded product according to claim 2, wherein the vent provided on the cavity surface is arranged at a position where the gap is desired to be widened. 4. The size of the gap is adjusted by adjusting at least one of the pressure, the injection time, and the injection amount of the high-pressure gas.
Method of manufacturing plastic molded products. 5. The method of manufacturing a plastic molded product according to claim 2, wherein a gap between the movable piece and a fitting hole of the movable piece is used as the vent. 6. The movable piece is provided with a communication hole, and the communication hole is used as the ventilation hole.
Method of manufacturing plastic molded products. 7. The size of the width of the ventilation hole is 0.001 to 0.001.
7. The method for producing a plastic molded product according to claim 2, wherein the plastic molded product is formed to have a thickness of 0.5 mm. 8. The method of manufacturing a plastic molded product according to claim 1, wherein the temperature of the cavity wall surface at the portion where the gap is to be widened is set lower than the other cavity wall surface temperatures. 9. The method according to claim 1, wherein the size of the cavity is adjusted by adjusting the temperature of a cavity surface defining the cavity. 10. The method of manufacturing a plastic molded article according to claim 1, wherein said cavity wall surface is subjected to a surface treatment so as to reduce the adhesion strength between said resin and said cavity wall surface at a portion where said space is to be widened. 11. The plastic molding according to claim 1, wherein the size of the cavity is adjusted by adjusting the surface treatment range on the cavity surface defining the cavity. Product manufacturing method. 12. The method according to claim 1, wherein two or more of the manufacturing methods according to claim 2 to 11 are used in combination.
Method of manufacturing plastic molded products.