JPH04366612A - Manufacture of plastic molded product - Google Patents

Abstract

PURPOSE:To constitute the title method so that a time required for heating and gradual cooling is reduced and a plastic molded product superior in mirror face transfer properties is obtained, by a method wherein a temperature of thermoplastic plastic is made at least its thermal deformation temperature and not exceeding a softening temperature and plastic deformation processing is performed by applying compression force to the title molded product by a mold having a mirror face. CONSTITUTION:A mold 1 for optical parts compression molding having a mirror face fitted to a high pressure press machine is heated at a temperature of at least a thermal deformation temperature of a plastic basic material 3 to be inserted into a cavity 2 and not exceeding its softening temperature. Then the thermoplastic plastic basic material 3 processed into almost the final form by an injection molding method is inserted into the cavity 2 by breaking the mold 1 and mold clamping is performed by a top and bottom punches 4, 5 of the high-pressure press machine. The plastic basic material 3 has a temperature same as the mold temperature by holding within the mold 1 for a fixed time. When the plastic basic material 3 becomes identical, in temperature, with the mold 1 temperature, it is pressurized and then decompressed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing high-precision plastic molded products for use in laser beam printers, optical scanning systems such as facsimiles, video cameras, etc., and more specifically, the production of plastic molded products such as plastic lenses in a short cycle time. The present invention relates to a manufacturing method suitable for manufacturing with high precision.

0002

[Prior Art and Problems to be Solved by the Invention] In all conventional manufacturing methods of this type, high-precision plastic molded products such as lenses are obtained by cooling the resin from above its glass transition temperature or above its softening temperature. . At the very least, molded products with no sink marks, low residual stress, and small birefringence in the case of lenses must be slowly cooled to overcome the temperature difference of several tens of degrees from above the softening temperature to below the heat distortion temperature. This is because it is difficult to obtain. In order to eliminate this sink mark, etc., it is necessary to cool the mold cavity, which is filled with a resin with poor thermal conductivity, while making the temperature as uniform as possible.

FIG. 13 is a graph showing an example of a conventional manufacturing method. Line a in the figure shows the temperature change in an example molded by injection molding, where the mold temperature is maintained above the softening temperature of the resin, high temperature molten resin is injected and filled, the gate is immediately sealed, and the inside of the cavity is filled. After generating a constant internal pressure and maintaining the temperature inside the cavity until it becomes equal and uniform to the mold temperature, the temperature inside the cavity is slowly cooled while keeping it uniform (line a in the figure). ' indicates the pressure change). In the figure, b shows the plastic base material placed in a mold held below its heat deformation temperature, and after clamping, heated to above its softening temperature, creating internal pressure in the cavity due to melting and expansion of the resin, and holding for a certain period of time. This is a line showing the temperature change in an example in which a plastic molded product with excellent mirror transfer properties is obtained by slow cooling (the line b' in the figure shows the pressure change).

[0004] In order to obtain such high-precision injection molded products, it is necessary to use slow cooling using temperature control in either method, but this slow cooling takes several tens of minutes and reduces productivity. The problem is that it's very bad.

Conventionally, there has been a method for efficiently obtaining high-precision plastic molded products such as lenses by injection molding using a cavity unit mold (Japanese Patent Application Laid-open No. 36421/1983);
Injection molding is carried out at a mold temperature higher than the glass transition temperature of the resin.
Method for cooling a lens without distortion (Japanese Patent Application Laid-Open No. 1-200925
(Japanese Unexamined Patent Publication No. 13927/1983), a method in which the workpiece is homogenized in the softening temperature range by compression molding after injection, and then slowly cooled to the heat distortion temperature range (Japanese Patent Application Laid-open No. 13927/1983). Many techniques have been proposed for efficiently molding high-precision plastic molded products, such as heating and melting, press molding, and cooling after holding pressure (Japanese Unexamined Patent Publication No. 64-67309). In these cases, there has been no proposal for a method that eliminates the need for slow cooling, which is an unproductive process that takes several minutes, and reduces the time required for cooling to an extremely short time.

Furthermore, to the knowledge of the present inventors, there has been proposed a method of obtaining a high-precision plastic molded product in a short cycle by separating the injection molding process and the aging process. is 1 cycle 1-2
There is no problem in a short time of minutes, but the problem remains that the aging process takes time. The aging process consists of a reheating process to a temperature above the glass transition temperature of the resin, followed by a slow cooling process, but normally the slow cooling process cannot shorten the time much due to internal distortion of the molded product, and the reheating process As for how to shorten the reheating time, conventional methods such as passing a heat medium through a single mold or heating with an embedded heater do not heat the mold itself and use the heat to form the mold. It takes at least several minutes, usually around 10 minutes, for the molded product itself to reach the desired temperature, and it has not been possible to shorten the cooling process. Furthermore, in applications where only the surface of the molded product is used, such as mirrors, or when a material with low birefringence such as PMMA or Zeonex is used as the resin, the surface layer may be severely distorted due to rapid cooling and sink marks may occur. Although it is only necessary to re-melt only a portion of the mold, conventional methods of heating the mold itself re-melt the entire molded product, which takes time to heat and does not shorten the time required for the entire aging process.

[0007] In order to solve such conventional problems, the present invention deforms the resin above its heat deformation temperature, and since the resin is solid below its softening temperature, the resin does not pass through the softening temperature. Focusing on the fact that there is no need to consider the unbalance between the solid phase and the liquid phase by This is to obtain a high-precision plastic molded product with a mirror surface transferred onto it.

Furthermore, the present invention provides that the technology used to reduce residual stress, distortion, etc. by applying ultrasonic waves during injection molding can also be used to shape plastic lenses, and unlike high-frequency waves, it can be applied to molds and molds. The heat generated at the interface of the molded product melts the molded product rapidly from the surface, significantly shortening the heating time from around 10 minutes to several seconds.In the case of thick molded products, the thermal conductivity of the resin can be reduced. This was done based on the fact that by heating rapidly from the surface layer in a few seconds or less, the center part is solid and the surface layer part where residual stress or sink marks have occurred can be turned into a molten body.

[0009]

[Means for Solving the Problems] In order to achieve the above-mentioned conventional object, the method for producing a plastic molded article according to the present invention sets the temperature of a thermoplastic plastic base material that has been preprocessed into a substantially final shape to its heat deformation temperature. above and below the softening temperature, plastic deformation is performed by applying compression force using a mold for compression molding optical parts having at least one mirror surface,
It is designed to transfer a mirror surface. As mentioned above, the deformation of the resin occurs above its thermal deformation temperature, and the resin remains solid below its softening temperature. You don't have to think about it, but conversely, when the resin temperature exceeds its softening temperature, the resin begins to soften, so although plastic deformation processing becomes easier, it will deform when taken out from the mold.
If the temperature is below the heat deformation temperature, there is no problem with ejecting the material from the mold, but not only is plastic deformation impossible, but the mold itself, including the mirror surface, may be damaged. Therefore, the resin temperature must be higher than its thermal deformation temperature and lower than its softening temperature. However, even in this temperature range, the resin still has some resistance to plastic deformation, so a deformation force above a certain level is required for plastic deformation. Further, if the material is simply deformed, a considerable amount of residual stress remains, and even if a product with excellent mirror transfer properties is obtained at that time, it may become deformed due to changes over time or temperature cycles. For this reason, it is necessary to ensure that residual stress does not become a problem even if deformation occurs.

[0010] Furthermore, the method for producing a plastic molded article according to the present invention is characterized in that the temperature of the thermoplastic base material, which has been preprocessed into a substantially final shape, is set at a temperature higher than its heat deformation temperature and lower than its softening temperature, so that at least one mirror surface is formed. A mold for compression molding optical components is used to perform plastic deformation processing by applying compressive deformation and stretching deformation while attenuating them alternately, thereby transferring a mirror surface.

[0011] The above-mentioned method of applying compressive deformation and stretching deformation while attenuating them alternately uses a structure in which the mold cavity is inserted in the direction perpendicular to the compression direction of the plastic base material, and a spring is placed on the rear side of the inserted piece. It is possible to make only the force vibrate in a damped manner.

[0012] Note that an injection molding method can be used to pre-process the thermoplastic plastic base material into a substantially final shape.

That is, even if the plastic base material is plastically deformed by simply applying pressure in one direction at a temperature above its thermal deformation temperature and below its softening temperature, residual stress is likely to be generated due to molecular orientation, etc., and the mirror transfer property is excellent and stable. However, the method for manufacturing plastic molded products according to the present invention prevents molecular orientation and attenuates deformation force by alternately repeating compressive deformation and stretching deformation. This removes residual stress.

Furthermore, the method for manufacturing a plastic molded article according to the present invention includes an injection molding process in which a molten resin is injection molded into a mold cavity maintained at a temperature below the heat distortion temperature of the resin, and the molded resin is solidified by sealing the gate. The molding process consists of a molding process, and an aging process of applying ultrasonic vibration to heat the resin to a temperature higher than the glass transition temperature of the resin to melt it while maintaining the temperature of the mold below the thermal deformation temperature of the resin, and then cooling it. can do.

[0015] The aging step may be carried out by taking out the molded product obtained in the injection molding step from the mold and placing it in a mold having a cavity having the same shape and volume as the cavity of the mold. can. That is, only the surface layer portion of the molded product where residual stress or sink marks have occurred is melted by ultrasonic waves, and this melted portion is slowly cooled. Melting only this surface layer shows the same behavior as the aging process of a uniform-walled and thin-walled molded product, and since no sink marks occur even if the cooling rate is increased, it is possible to shorten the annealing time.

[0016]

Embodiment FIGS. 1 to 3 show a first embodiment of the method for manufacturing a plastic molded article according to the present invention. First, as shown in FIG. 1, a mold 1 mounted on a high-pressure press is heated to a temperature above the heat deformation temperature of the plastic base material 3 to be inserted into the cavity 2 and below its softening temperature. Then, the thermoplastic plastic base material 3 processed into a substantially final shape by injection molding is inserted into the cavity 2 with the mold 1 opened, and the mold is clamped by upper and lower punches 4 and 5 of a high-pressure press machine. By holding the plastic base material 3 in the mold 1 for a certain period of time, the temperature becomes equal to the mold temperature, but it may be heated in advance to near the heat distortion temperature. When the temperature of the plastic base material 3 is equal to that of the mold 1, the temperature of 0.1 to
Pressure was applied at a rate of n/cm2/sec (I in Figure 2), and 3
After maintaining the high pressure state of ton/cm2 for about 10 seconds (2 in Figure 2) (about 10 seconds), 0.05ton/cm2/s
Depressurize at a rate of ec. (3 in Figure 2). Through this process, a plastic molded product with excellent mirror surface accuracy was obtained.

That is, in this method, the compression pressure is set to 0.5 to 10
ton/cm2, several times to several tens of times the compression pressure during normal injection compression molding or press molding, is applied to plastically deform the plastic base material 3, causing apparent flow to the resin in the plastically deformed area. By imparting this behavior, the slight rebound after the deformation force is released is eliminated, and mirror transfer properties are improved. If the compression pressure is less than the above value, the transfer will be insufficient, and if it exceeds this value, the life of the mold 1 will be significantly shortened, making it impractical. In addition, in this method, the compression speed and decompression speed are set to 0.01 to 1.
Residual stress is reduced by slowly deforming and releasing the deformation at a rate of ton/cm2/sec. If it exceeds this range, the residual stress will be so large that it cannot be used, and if it is less than this range, it will take too much time and is not preferred in practice.

FIG. 3 shows a modification of the method shown in FIG. 2, in which pressurization, pressure holding, and depressurization are performed under the same conditions as in FIG.
The pressure force is made to oscillate at a frequency of z. The vibration width is 1/2 of each pressure during pressurization, holding pressure, and depressurization.
It is set to 0. That is, the pressure amplitude is 10 to 100 Kg/c
The internal stress is reduced by applying vibrations of 0.1 to 10 kHz at m2 by weight, but when applying vibrations by weight, it may be applied all the time from pressurization to depressurization. The vibration may be applied at different times depending on the physical properties of the resin used and the shape of the molded product, such as only when applying pressure or only when reducing pressure. The amplitude and frequency of the applied vibrations also need to be changed depending on the physical properties of the resin and the shape of the molded product, but this vibration causes heat generation of the resin and it is necessary to prevent the temperature inside the cavity from rising above its softening temperature. Note that the resin to be used is not particularly limited as long as it is a thermoplastic resin, but amorphous resins such as acrylic, polycarbonate, polystyrene, and amorphous polyolefin, whose softening temperature is close to the glass transition temperature, are preferable.

[0019] Furthermore, in order to bring the temperature of the plastic base material 3 above its thermal deformation temperature, it is inserted into a mold that has been heated and maintained at that temperature in advance by a heating medium or heater, and then heated by a thermoelectric device. Alternatively, a method may be used in which the periphery of the cavity 2 of the mold 1 is heated by high frequency waves, or the plastic base material itself in the cavity is directly heated by ultrasonic waves. Plastic base material 3 can be formed in a short time from a few seconds to several tens of seconds using ultrasonic heating or high-frequency heating.
can be heated to a temperature above its heat distortion temperature and below its softening temperature. Furthermore, by using injection molding as a pre-processing method into a substantially final shape, it was possible to produce a plastic base material with stable dimensions and weight at a low cost.

4 to 9 show a second embodiment of the method for manufacturing a plastic molded article according to the present invention. It should be noted that overlapping details regarding parts and matters common to the previous embodiments will be omitted. First, as shown in FIG. 4, a mold 10 attached to a high-pressure press is heated to a temperature higher than the thermal deformation temperature of the plastic base material 12 to be inserted into the cavity 11 and lower than its softening temperature. The thermoplastic base material 12, which has been pre-processed into a substantially final shape by injection molding, is held in a mold using a heating medium such as water or oil or a heater at a temperature above its thermal deformation temperature and below its softening temperature. 10 into the cavity 11. Note that the mold 10 is at room temperature,
The vicinity of the cavity 11 may be heated with high frequency to bring the plastic base material 12 to this target temperature, or it is better to bring only the plastic base material 12 inside the cavity 11 to this target temperature using ultrasonic waves. It is possible to save time.

The mold 10 itself is fixed to a clamping die plate 14 of a high-pressure press via a heat insulating plate 13. In the illustrated example, the upper and lower punches 15 and 1 of the high-pressure press are designed to enable pressurization and depressurization from two sides (one direction) of the mold.
6 is attached. Also, this mold 10
has an insert piece structure in which insert pieces 17, 17 are movable in a direction perpendicular to the compression direction of the plastic base material 12 of the cavity 11. Further, springs 18, 18 are arranged on the rear side of the input piece 17.

FIGS. 5 and 6 illustrate the operation of the present invention using the mold structure shown in FIG. High pressure press machine punch 15,
16 pressurizes the mold 10 in the compression direction X,
Compressive deformation occurs in the plastic base material 12 in the pressurizing direction X, and elongation deformation occurs in the vertical direction Y while balancing the force of the spring 18 against the input piece 17. After a certain amount of compressive deformation, when the pressure in the pressing direction It is compressed and deformed by being pushed, and then stretched and deformed in the compressed direction X. Such compressive deformation and stretching deformation are repeated while attenuating the pressing force (see FIG. 6). As a result, the molecular orientation and residual stress of the plastic base material 12 are suppressed to a level that poses no practical problems, resulting in a plastic molded product with excellent mirror transfer properties.

FIGS. 7 and 8 conceptually show an example in which compression and stretching are performed symmetrically. By compressing and deforming by applying pressure from the X direction and at the same time reducing the pressure in the Y direction perpendicular to it to cause stretching deformation, the pressure inside the cavity is positive but not very large, and then the pressure is applied from the side that was stretched and deformed. The side that was compressed and deformed is depressurized, and compressive deformation and stretching deformation occur in the opposite direction. This is then repeated alternately while decreasing the amount of deformation. Naturally, the pressure within the cavity 11 does not vary greatly due to the balance between compression and stretching, and this pressure is small. By repeating compression deformation and stretching deformation alternately while attenuating them in this way, the molecular orientation of the resin and residual stress can be better removed.
Furthermore, since the internal pressure of the cavity 11 can be kept very low, residual stress due to the residual internal pressure can also be reduced to a level that does not pose a problem in practice.

FIG. 9 is a stress-strain diagram of the above two examples. At point A in the figure, a considerable amount of residual stress remains due to mere compressive deformation, and at point B, the residual stress is large, causing deformation that exceeds the final shape. However, when the stress is brought to point C, the strain becomes smaller and in the opposite direction than point B, and below point D
By repeating compression and stretching from point H to point H, it is possible to produce a molded article with no residual stress in its final dimensions due to the reduction in hysteresis.

FIGS. 10 to 12 show a third embodiment of the present invention. FIG. 10 shows the implementation state of the aging process, in which the mold 20 is fixed between clamping plates 21 and 21 of a hot press machine, and an ultrasonic oscillator 23 is installed in the lower mold 22.
is attached so that the inserting piece 26 forming the cavity 25 between the upper die 24 and the upper die 24 can be ultrasonically heated. In the figure, 27 is an ultrasonic oscillator. That is, in order to maintain the temperature of the mold 20 at a constant temperature below the thermal deformation temperature of the plastic base material 28, a heating press with a built-in heater is used to withstand the pressure caused by the expansion of the plastic base material 28 within the cavity 25. A constant pressure can be applied in the vertical direction.

In this example, first, the plastic base material 28 obtained in the injection molding process is molded into the cavity and shape of the injection molding process, where the mold temperature is maintained at a constant temperature below the heat deformation temperature of the plastic base material 28. Cavity 2 with equal volume
Put it within 5. Then, the mold is clamped with a pressure that can withstand the melting and expansion of the plastic base material 28, and the inserted pieces 2 in the lower mold 22 are
Ultrasonic vibrations are applied by an ultrasonic oscillator 27 connected to the plastic base material 28, and the plastic base material 28 is rapidly heated and melted from the surface layer. Due to this heat generation, the plastic base material 28 and the parts of the upper mold 24 and lower mold 22 facing the cavity 25 become hot, but when the ultrasonic vibration is stopped, the heat is transferred to the entire mold and is cooled down. The cooling rate can be changed by providing a heat insulating layer such as air between the insert piece 26 forming the cavity 25 and the upper mold 24 and lower mold 22, or by using a material with low thermal conductivity. It will be done.

[0027] When the temperature becomes lower than the heat deformation temperature of the plastic base material 28, the mold 20 is opened and the plastic base material 28 is taken out. Of course, although a heated press was used to clamp the mold 20 at a constant temperature, other similar methods may be used. FIG. 11 shows the change time of resin temperature in the aging process according to the present method and the same process according to the conventional method. Lines A1 and A2 in the figure are the temperature changes according to the present method, and B is the change according to the conventional method. Compared to conventional methods, both heating and cooling times can be reduced. Note that the line A1 indicates the surface temperature of the plastic base material, and the line A2 indicates the temperature at the center. This differs from the conventional method in that the temperature at the center is still below the glass transition temperature of the resin. In addition, when making high-precision lenses using materials that tend to retain internal distortion, such as polycarbonate resin, the molded product must be completely melted by ultrasonic vibration and then slowly cooled, so the heating time is limited. to shorten.

FIGS. 12A and 12B show changes in the cross section of the molded product when only the surface layer 30 is heated and melted. When the thickness of the molten part 31 becomes uniform and a solidified part 32 is formed on its outer periphery, and the entire part melts and solidifies from the surface as in the molded products shown in FIGS. 12(C) and 12(D), This is different from the case where the thickness of the melted part 33 is non-uniform and the solidified part 34 is formed around the outer periphery.

[0029]

[Effects of the Invention] In the method for manufacturing a plastic molded product according to claims 1 and 2, plastic deformation is caused in a short time at a temperature above the thermal deformation temperature of the plastic base material and below its softening temperature, so that it is better than conventional methods. The effect is that the time required for heating and slow cooling can be shortened, and a plastic molded product with excellent mirror transfer properties can be obtained.

In addition to the above-mentioned common effects, the method for manufacturing a plastic molded product according to claim 3 causes compressive deformation and stretching deformation by changing only the compressive force in one direction,
It is possible to obtain a plastic molded product with excellent mirror transfer properties, and the mold structure can be simplified.

In addition to the above-mentioned common effects, the method for manufacturing a plastic molded product according to claim 4 uses injection molding as a method for processing the plastic base material into a substantially final shape, so that it can be produced at low cost and with stable quality. Since a plastic molded product can be obtained, it is possible to obtain a plastic molded product with excellent mirror transfer properties at a low cost and with stable quality.

[0032] In the method for manufacturing a plastic molded product according to claim 5, it is possible to heat and melt the resin to a temperature higher than the glass transition temperature of the resin in a short time using ultrasonic waves, thereby improving productivity and lowering the cost of the product. It has the effect of being able to change.

[0033] In addition to the above-mentioned common effects, the method for manufacturing a plastic molded product according to claim 6 has the effect of improving productivity and reducing product costs by separating the aging process from the injection molding process. .

[Brief explanation of drawings]

FIG. 1 is a sectional view of a mold used in a first embodiment of the method for manufacturing a plastic molded article according to the present invention.

FIG. 2 is a graph showing a change in the pressure inside the cavity over time.

FIG. 3 is a graph showing another example of the temporal change in the pressure inside the cavity.

FIG. 4 is a sectional view of a mold used in a second embodiment of the method for manufacturing a plastic molded article according to the present invention.

FIG. 5 is a perspective view conceptually showing a method according to a second embodiment of the present invention.

FIG. 6 is a graph showing changes in deformation and cavity pressure in the method of FIG. 5;

FIG. 7 is a perspective view conceptually showing a method according to a second embodiment of the present invention in which the compression and stretching deformation directions are two directions.

FIG. 8 is a graph showing changes in deformation and cavity pressure in the method of FIG. 7;

FIG. 9 is a stress-strain diagram in a second embodiment of the present invention.

FIG. 10 is a sectional view of a mold used in a third embodiment of the method for manufacturing a plastic molded article according to the present invention.

FIG. 11 is a graph showing the change in resin temperature over time in a third embodiment of the present invention in comparison with a conventional method.

FIG. 12 is a cross-sectional view showing the internal structure of a molded product according to a third embodiment of the present invention in comparison with a molded product according to a conventional method.

FIG. 13 is a graph showing temperature changes and cavity internal pressure changes in a conventional method for manufacturing plastic molded products.

[Explanation of symbols]

1, 10, 20 Mold 2, 11, 25 Cavity 3, 12, 28 Plastic base material 13　　　　　　　　　　　　　　　Insulation board 17, 26　　　　　　　　　　　　　　　 18 Spring

Claims (6)

[Claims] Claim 1: The temperature of the thermoplastic base material, which has been preprocessed into a substantially final shape, is set at a temperature higher than its thermal deformation temperature and lower than its softening temperature, and a compressive force is applied using a mold for compression molding optical components having at least one mirror surface. A method for producing a plastic molded product, which is characterized by adding plastic deformation processing to transfer a mirror surface. 2. Compressively deform the thermoplastic base material, which has been preprocessed into a substantially final shape, at a temperature above its thermal deformation temperature and below its softening temperature using a mold for compression molding optical parts having at least one mirror surface. A method for manufacturing a plastic molded product, characterized in that plastic deformation is performed by applying stretching deformation while attenuating it alternately, and a mirror surface is transferred. 3. The compression deformation and elongation are achieved by forming a piece structure in the direction perpendicular to the compression direction of the plastic base material of the mold cavity, and arranging a spring on the rear side of the piece to dampen and oscillate only the compressive force. 3. The method of manufacturing a plastic molded product according to claim 2, wherein the deformation is applied while being alternately attenuated. 4. The method of manufacturing a plastic molded article according to claim 1, wherein an injection molding method is used to pre-process the thermoplastic plastic base material into a substantially final shape. 5. An injection molding step in which the molten resin is injected into a mold cavity maintained at a temperature below the thermal deformation temperature of the resin, the gate is sealed, and the resin is solidified; A method for manufacturing plastic molded products, which comprises an aging process in which the resin is heated to a temperature above the glass transition temperature of the resin to melt it while the resin is maintained below the thermal distortion temperature of , and then cooled. 6. The molded product obtained in the injection molding step is taken out from the mold, and placed in a mold having a cavity having the same shape and volume as the cavity of the mold, and the aging step is performed. The method for manufacturing a plastic molded product according to claim 4.