JP2003266504A - Plastic optical element and method for manufacturing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a high quality plastic optical element which exhibits a little distribution of refractive index after molding, a short molding cycle and good productivity, and satisfies required characteristics on high accuracy, and to provide the plastic optical element manufactured by the method for manufacturing it. <P>SOLUTION: A molten resin material is filled and cooled in a mold cavity adjusted by providing a temperature difference between a thermally controllable mold member forming an optical face and another thermally controllable mold member forming a non-optical face within a specified temperature range between at least (glass transition temperature -30°C) and at most (glass transition temperature) to solidify and mold the plastic optical element. In addition, after it is adjusted at a temperature within the specified temperature range in the mold or outside of the mold, it is cooled to a temperature lower than the lowest limit of the specified temperature range. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a plastic optical element applied to an optical scanning system of a laser type digital copying machine, a laser printer or a facsimile machine, an optical device such as a video camera, and the like. The present invention relates to a plastic optical element manufactured by the manufacturing method.

[0002]

2. Description of the Related Art Optical elements such as lenses and prisms are required to have high shape accuracy and a small amount of birefringence inside. However, in recent years, plastic products have been increasing due to their flexibility in shape and high productivity. The reason for this is that a resin material having low birefringence characteristics has been developed and a molding technique that enables manufacturing of a molded product having good shape accuracy and low birefringence is improved.

Conventionally, polycarbonate resins and acrylic resins have been the mainstream as resin materials used for optical elements. However, polycarbonate resin has a large birefringence, and acrylic resin has a high water absorption, so the environment (humidity)
The applications have been limited because the shape and the refractive index change with changes. However, in recent years, resin materials having low water absorption and low birefringence characteristics have been developed, and the applications to which these resin materials are applied are expanding. As such a resin material,
For example, there are Zeonex manufactured by Zeon Corporation, Arton manufactured by JSR, and Apel manufactured by Mitsui Chemicals.

Further, not only the improvement of the resin material but also the progress of the molding technique has been advanced. With the development of the injection compression molding method in which the resin material is filled at a low pressure and compression is performed through the entire die or the insert piece, the shape is improved. Since it has become possible to obtain molded articles with high accuracy and low birefringence, there is a tendency for plasticization of optical elements to proceed further.

As described above, it has become possible to obtain an optical element having a high shape accuracy and a low birefringence characteristic, but a refractive index distribution remains inside the optical element after the molding process, and particularly high accuracy is required. However, there is a problem in that the optical element according to the present invention is still insufficient to obtain a satisfactory optical performance.

Generally, the refractive index is higher as it is closer to the surface of the optical element and lower as it is closer to the center, and the refractive index is distributed. However, when the optical element is an imaging lens, this refractive index distribution forms an image. It was a cause of misalignment. For example,
In the case of an optical scanning lens for a laser printer or the like, Japanese Patent Application Laid-Open No. HEI 10-96
As described in JP-A-2888749, the refractive index distribution acts so that the beam spot to be focused on the surface to be scanned is farther from the optical deflector than the designed position, and as a result, on the surface to be scanned. The beam spot diameter at was larger than the designed value, which was a cause of deterioration in the quality of the recorded image.

The cause of the refractive index distribution inside the optical element is that the temperature drop (cooling) in the vicinity of the mold wall surface during molding, that is, the outer peripheral portion of the resin forming the optical element is rapid, whereas This is because the temperature drop in the central part is gentle. Since the vicinity of the mold wall is rapidly cooled and becomes a solid state during injection filling or when a high pressure is applied in the initial holding pressure, the surface has a high density. On the other hand, when the central portion is cooled and becomes a solid state, the pressure is lowered and the density becomes low. As a result, the surface of the molded optical element has a high density, and the density decreases as it approaches the center. Since there is a correlation between the density and the refractive index, the refractive index of the surface of the optical element is large, and the refractive index becomes smaller toward the central portion, which causes a refractive index distribution.

As described above, the main cause of the refractive index distribution is that the resin is rapidly cooled near the wall surface of the mold. Therefore, there is a method in which a resin having a small refractive index distribution is obtained by injection-filling a high temperature mold with resin and then performing slow cooling to reduce the temperature distribution inside the molded product. However, according to this molding method, the molding cycle time becomes extremely long, and there is a drawback that the manufacturing cost becomes high.

Further, a method has been proposed in which the lens shape is thickened (increased) and only the region where the refractive index distribution is small is used. For example, according to the optical scanning device disclosed in JP-A-8-201717 (conventional example 1),
Regarding a lens having a beam thickness (t) in the traveling direction and a height (h) perpendicular to the beam thickness, the lens shape is defined so that h / t> 2. By increasing h,
The temperature distribution during resin cooling is reduced in the region where the beam is transmitted, and the fact that the refractive index distribution in this limited portion is small is used to reduce the deviation of the imaging position.

However, the above method increases the area where the beam is not transmitted, that is, the area outside the effective area.
Molding cycle time (cooling time) to increase the amount of resin used and mold thick-walled optical elements with high accuracy
However, there is a drawback that the manufacturing cost becomes high. Moreover, since the lens shape is limited, the degree of freedom in optical design is impaired.

Further, as a method of performing an optical design in consideration of the refractive index distribution, there is a method disclosed in Japanese Patent Application Laid-Open No. 9-49976 (conventional example 2). This is because the image forming position shift due to the refractive index distribution of the image forming lens is corrected by changing the shape of the image forming lens and the image forming position is shifted to the rotary polygon mirror side, thereby forming a beam on the surface to be scanned. It is a method of making a picture.

[0012] However, the above-mentioned method determines the shape correction value by evaluating the image forming position of the image forming lens obtained by making a mold, determining the molding conditions according to the mold. Therefore, when it is necessary to change the molding conditions due to another defect in molding, the correction value must be changed again, and the mirror surface piece must be remanufactured. Also,
When manufacturing a multi-cavity mold, since it is necessary to change the correction value for each cavity, it is necessary to prepare as many machining programs as there are cavities. Therefore, there has been a drawback that the number of molding trials is extremely large and the number of times of manufacturing the mirror surface piece is increased, resulting in an increase in cost.

A method of reducing the refractive index distribution by an annealing process is disclosed in Japanese Patent Application Laid-Open No. 11-77842 (conventional example 3). This method is a method of reducing the refractive index distribution inside the optical element by performing an annealing process of heating outside the mold, maintaining the temperature within a predetermined range for a predetermined time, and then cooling. According to this, since the refractive index distribution can be reduced to a certain level by a short-time annealing process, it is a more effective method than the conventional examples 1 and 2, but the refractive index distribution can be completely removed. However, when a higher precision optical element is required, it is necessary to further reduce the refractive index distribution.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a small refractive index distribution after molding, a short molding cycle, and good productivity. Another object of the present invention is to provide a method of manufacturing a high-quality plastic optical element that satisfies a high precision required characteristic with a design shape having a small amount of wasted area, and a plastic optical element manufactured by the manufacturing method.

[0015]

In order to solve the above-mentioned problems, the method for manufacturing a plastic optical element according to the present invention comprises:
(Glass transition temperature −30 ° C.) or higher of the resin material used,
(Glass transition temperature) A molten resin material is filled in a mold cavity composed of mold members whose temperature is controlled and controlled within a predetermined temperature range specified below, and the plastic optical element is formed by cooling and solidifying. First step of molding and cooling the molded plastic optical element in a mold or outside the mold from a temperature within the predetermined temperature range to a temperature lower than a lower limit value of the predetermined temperature range. By including at least two steps including the second step, the refractive index distribution is reduced, thereby satisfying the high precision required characteristics of the plastic optical element. Hereinafter, the present invention will be specifically described.

According to the invention of claim 1, the molten resin material is
A heat-controllable mold member for forming an optical surface and optics, which is adjusted to a temperature within a predetermined temperature range defined by (glass transition temperature −30 ° C.) or more and (glass transition temperature) or less of the resin material. First step of solidifying and molding a plastic optical element by filling a mold cavity surrounded by a heat-controllable mold member that forms a non-optical surface other than the surface and cooling the plastic optical element with priority from the non-optical surface And a second step of adjusting the temperature of the plastic optical element to a temperature within the predetermined temperature range inside or outside the mold, cooling to a temperature lower than the lower limit of the predetermined temperature range, and performing heat treatment. A method for manufacturing a plastic optical element, which comprises at least:

According to the structure of claim 1, by controlling the temperature of the mold member in the predetermined temperature range in the first step, it is possible to reduce the residual of the refractive index distribution generated at a temperature higher than the set temperature and to perform the cooling process. By preferentially cooling from the non-optical surface of the plastic optical element, the low density region in the optical element is expanded and the refractive index distribution can be reduced. Furthermore, the heat treatment in the second step can further reduce the refractive index distribution below the glass transition temperature. Since at least two steps of the first step and the second step are included, the refractive index distribution becomes very small. Therefore, when applied to, for example, an imaging lens, the beam spot position (imaging position)
Provided is a method for producing a plastic optical element with good productivity, which is capable of obtaining a high-quality plastic optical element with less deviation.

According to a second aspect of the present invention, in the first step, the temperature of the thermally controllable mold member forming the optical surface and the thermally controllable mold forming a non-optical surface other than the optical surface. The method for producing a plastic optical element according to claim 1, wherein the plastic optical element is solidified and molded by providing a temperature difference from the temperature of the member.

According to a third aspect of the present invention, when the plastic optical element is solidified and molded by providing the temperature difference, a heat-controllable mold member forming the optical surface is heated to form a non-optical surface other than the optical surface. 3. The method for producing a plastic optical element according to claim 2, wherein the temperature is set higher than the temperature of the heat-controllable mold member for forming the mold.

According to a fourth aspect of the present invention, when the plastic optical element is solidified and molded by providing the temperature difference, a heat-controllable mold member forming the optical surface is provided with a heat insulating member so that a non-optical member other than the optical surface is provided. 3. The method for manufacturing a plastic optical element according to claim 2, wherein the temperature is set higher than the temperature of the heat-controllable mold member forming the optical surface.

According to a fifth aspect of the present invention, when the plastic optical element is solidified by providing the temperature difference, the thermally controllable mold member forming the non-optical surface other than the optical surface is cooled to cool the optical surface. 3. The method for producing a plastic optical element according to claim 2, wherein the temperature is set lower than the temperature of the heat-controllable mold member that forms the resin.

According to the second to fifth aspects, the temperature of the mold member forming the optical surface is made higher than the temperature of the mold member forming the non-optical surface, thereby providing a temperature difference. In the process in which the solidified layer is first formed on the surface of the non-optical surface having a low temperature, and then the whole is cooled and solidified, the density inside the lens becomes lower and the low density region expands. This provides a method of manufacturing a plastic optical element in which the effective transmission range of light rays is widened.

According to a sixth aspect of the present invention, in the second step, the plastic optical element is cooled to a temperature lower than a lower limit value of the predetermined temperature range from being adjusted to a temperature within the predetermined temperature range. 6. The method for producing a plastic optical element according to claim 1, wherein the cooling rate is 3 ° C. or less per minute.

In the second step of the sixth aspect, the cooling rate from the state of being heated to the predetermined temperature range to the temperature lower than the lower limit value of the predetermined temperature range is 3 ° C. or less per minute. Provided is a method for manufacturing a plastic optical element in which the refractive index distribution is effectively reduced.

According to a seventh aspect of the present invention, the temperature outside the predetermined temperature range of the plastic optical element solidified and molded in the first step is adjusted to a temperature within the predetermined temperature range, and then the first temperature is adjusted. 7. The method for manufacturing a plastic optical element according to claim 1, wherein the heat treatment in the second step is performed.

When the plastic optical element formed in the first step in a temperature state outside the predetermined temperature range according to claim 7 is cooled or heated to adjust the temperature within the predetermined temperature range and then heat-treated for cooling. The residual refractive index distribution generated before the second step can be effectively reduced, which provides a method for manufacturing a high-quality plastic optical element.

The invention of claim 8 is characterized in that a temperature holding step is provided within a predetermined temperature range from when the temperature of the plastic optical element reaches a temperature within the predetermined temperature range until when cooling is started. The method for producing a plastic optical element according to claim 7.

By providing the temperature maintaining step of claim 8, there is provided a method of manufacturing a plastic optical element in which the refractive index distribution inherent in the molded plastic optical element is sufficiently reduced.

A ninth aspect of the present invention is a plastic optical element manufactured by the method for manufacturing a plastic optical element according to any one of the first to eighth aspects.

When the method for producing a plastic optical element according to any one of the above 1 to 9 of the present invention according to claim 9 is applied, the refractive index distribution of the plastic optical element to be molded is small, whereby a high precision requirement is achieved. A high-quality plastic optical element that satisfies the requirements is provided.

A tenth aspect of the present invention is the plastic optical element according to the ninth aspect, characterized in that the plastic optical element is formed of a thermoplastic amorphous plastic material.

By using the thermoplastic amorphous plastic material according to claim 10 to form a plastic optical element by applying the manufacturing method of the present invention, a high-quality plastic optical element with a small refractive index distribution can be obtained. Provided.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below based on Examples. However, the present invention is not limited to the examples. FIG. 1 is a schematic perspective view showing an example of a plastic optical element of the present invention, showing the shape of a scanning lens used in a laser printer used in Example 1 described later. The lower left side surface and the upper right side surface of the scanning lens 1 in FIG. 1 are the optical surfaces 2 (the portions that cannot be seen as a shadow), and when used by being incorporated in a laser printer, they are directed from the lower left side surface to the upper right side surface. The laser beam is transmitted (in the Z direction). In the first embodiment, the lens width in the Y direction is 8 mm, of which the central 4 mm width is the effective range of the light beam and allows the laser beam to pass through during use. In Example 1, as a resin material for the scanning lens 1, a cycloolefin polymer having a glass transition temperature of 138 ° C. (manufactured by Nippon Zeon Co., Ltd., trade name:
Zeonex) is used.

A scanning lens 1 having the shape shown in FIG. 1 is molded by using the injection molding die used in Example 1 described later by a manufacturing method including the first step and the second step of the present invention.
FIG. 2 is a schematic cross-sectional view of the injection molding die used in Example 1. In FIG. 2, the injection molding die 20 includes a pair of mirror surface pieces 3 forming the optical surface 2 and lens side surfaces (upper surface).
21a and the lens side surface (the lower surface that cannot be seen in the shadow) 2
1b has a cavity 5 surrounded by a pair of cavity pieces 4, and the cavity piece 4 is provided with a cartridge heater 6 as a temperature control means and a thermocouple 7.
The mirror surface piece 3 has a cartridge heater 8 and
Equipped with thermocouple 9, cartridge heater 8 and thermocouple 9
Are connected to a temperature control device (not shown) prepared outside the mold. Further, the mold base 10 has a cartridge heater 11 for heating the whole mold,
The thermocouple 12 is provided, and the cartridge heater 11 and the thermocouple 12 are connected to another temperature control device (not shown) prepared outside the mold.

Next, the molding operation relating to the first step of molding the scanning lens 1 using the injection molding die 20 will be described. The injection molding die 20 is set in an injection molding machine (not shown), and the scanning lens 1 is molded. The mold base 10 is heated by the cartridge heater 11 to a predetermined temperature below the glass transition temperature of the resin material used, for example, 130 ° C. in the case of the first embodiment, and the molten resin material ( Cycloolefin polymer) and then cooled. At this time, the temperatures of the cartridge heater 6 and the cartridge heater 8 are controlled so that the surfaces other than the optical surface 2 of the scanning lens 1 are preferentially cooled in the cooling process, and the temperatures of the cavity piece 4 and the mirror surface piece 3 are The temperature is set to 133 ° C. and 137 ° C. respectively, and the mirror surface piece 3 is adjusted to be higher. Next, the scanning lens 1 solidified in the cavity 5 is taken out of the mold and left in a room temperature environment to be naturally cooled.

In the solidification molding, the refractive index distribution generated in a temperature region higher than the mold temperature (a predetermined temperature below the glass transition temperature) is obtained by performing the second step described below. Even if it is not removed, it will remain. Therefore, in the first step, it is necessary to perform molding in consideration of reducing the refractive index distribution generated in a temperature region higher than the mold temperature (a predetermined temperature below the glass transition temperature) as much as possible.

In the first step, the solidification layer is quickly formed on the surface of the cooled surface by preferentially cooling from the surface other than the optical surface of the scanning lens, and then the cooling and solidification of the lens progresses. Then, when the inside of the lens is cooled and contracted, the surface of the lens is solidified and immovable, so that the density inside the lens becomes lower. Compared with the case of cooling with a uniform mold temperature, by molding with the temperature difference, the low-density region expands, so that the effective range of the beam through which the laser beam is transmitted results in a refractive index distribution. Can be reduced.

Further, in the process of cooling to room temperature after taking out from the mold, that is, in the temperature region below the mold temperature (a predetermined temperature below the glass transition temperature, which will be described later), the refractive index distribution is further generated. However, the refractive index distribution generated in this process can be removed by the heat treatment in the second step thereafter.

Next, the second step will be described based on the first embodiment as in the above. After the scanning lens 1 molded in the first step is once cooled to room temperature, the scanning lens 1 is placed in a constant temperature bath having a temperature control means (not shown), and any temperature within a predetermined temperature range, for example, the embodiment In the case of 1, the temperature is raised to 125 ° C., and the temperature is kept at 125 ° C. for 1 hour to uniformly heat the inside of the scanning lens 1. This makes it possible to remove the refractive index distribution that occurs when cooled to room temperature after molding. Next, at a temperature below the lower limit of the predetermined temperature range, for example, 100 in the case of the first embodiment.
By gradually cooling to 1 ° C per minute at a rate of 1 ° C, the regeneration of the refractive index distribution is reduced, and the scanning lens 1 with a small refractive index distribution
Can be obtained.

Here, the predetermined temperature range refers to a range of (glass transition temperature −30 ° C.) or higher and a glass transition temperature or lower of the resin material used, and the temperature range may be defined under these conditions. is important. This predetermined temperature range is
It is set based on the experimental results. That is, according to the experiment, it was found that the temperature range in which the refractive index distribution was formed was in the range of the glass transition temperature of the resin material used to the glass transition temperature of -30 ° C, and the lower limit of the predetermined temperature range was used. It was also confirmed that there is no need to cool by slow cooling to an unnecessarily low temperature region, and an optical element with a small refractive index distribution can be obtained by accelerating the cooling at a temperature lower than the lower limit and even in a short time. It is defined by. For example, Zeon of the resin material used in Example 1 described later is used.
The glass transition temperature of ex (manufactured by Zeon Corporation) is approximately 138 ° C.
Therefore, the predetermined temperature range in this case is about 108
Corresponds to ~ 138 ° C.

The “predetermined temperature range” defined above (glass transition temperature −30 ° C.) and below glass transition temperature is
Any amorphous thermoplastic material can be applied. However, since the glass transition temperature varies depending on the resin material, the predetermined temperature range varies depending on the resin material.

When the scanning lens 1 is solidified and molded under the conditions of the first step and then heat-treated by applying the conditions of the second step, the refractive index distribution is small, so that the light is condensed as compared with the conventional method. It is possible to obtain the high-quality scanning lens 1 in which the displacement of the beam spot hardly occurs and the displacement of the imaging position is small. Particularly, in the case of a scanning lens for a laser printer, the beam spot to be focused on the surface of the photoconductor is close to the designed position, and the quality of the recorded image to be written can be improved.

In addition, Example 1 described later in the first step
As the temperature control means arranged in the mold member shown in FIG. 2 used for the above, various electric heaters such as a plate-shaped heating element and a film-shaped heating element can be used in addition to the rod-shaped cartridge heater.

Alternatively, instead of performing the heat treatment in the second step by the batch treatment with the thermostatic bath of Example 1 described later, a far infrared heating device is arranged on the movable conveyor so that the scanning lens 1 can be moved. The same effect can be obtained by performing slow cooling in a continuous process.

Further, the plastic optical element applied to the present invention is not limited to the shape and configuration of the scanning lens 1 shown in FIG. 1, but a plastic optical element having various shapes and configurations such as a circular lens and a long lens. It is applicable to devices.

Although the embodiment of the present invention has been described based on Example 1 described later, the present invention is not limited to this. For example, in the temperature setting of the mold member in the first step,
It is possible to set a temperature higher than that of the temperature-controllable metal member 4 for forming the non-optical surface by providing a heat insulating material on the temperature-controllable metal member 3 for forming the optical surface, or for controlling the temperature for forming the non-optical surface. A temperature-controllable metal member 3 which is provided with piping on the metal member 4 and is cooled by a cooling medium to form an optical surface.
It can be adjusted by setting the temperature lower.

[0047]

EXAMPLES The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the examples.

Example 1 As described in the embodiment, the first step and the second step of the present invention
Applying the process of plastic optical element (scanning lens)
Was molded. That is, first, as a first step, the injection molding die 20 having the configuration shown in FIG. 2 is set in an injection molding machine, and a cycloolefin polymer having a glass transition temperature of 138 ° C. (manufactured by Nippon Zeon Co., Ltd. Name: Z
Eonex) was used to mold the scanning lens 1 (1-1) having the shape shown in FIG. Molding in the first step is performed by the mold base 10 at a temperature of 130 ° C. and the cavity piece 4
The temperature was set to 133 ° C. and the temperature of the mirror surface piece 3 to 137 ° C., and the temperature was controlled. Next, the scanning lens 1 (1-1) solidified by cooling in the cavity 5
Was taken out from the mold and left to stand at room temperature to be naturally cooled.

Next, as a second step, the scanning lens 1 (1-1) molded in the first step and cooled to the room temperature state.
Was placed in a constant temperature bath having a temperature control means, heated to 125 ° C., kept at a temperature of 125 ° C. for 1 hour, and uniformly heated to the inside of the lens. From this state to 100 ℃ 1 ℃ per minute
Scan lens 1 (1-2) by slowly cooling at the speed of
Got The obtained scanning lens 1 (1-2) was used as the following evaluation sample. The approximate size of the scanning lens 1 (1-2) is 150 m in the X direction as shown in FIG.
The lens width in the m and Y directions is 8 mm, and the width in the Z direction (center portion) is 30 mm.

Example 2 A schematic sectional view of the injection molding die used in Example 2 is shown in FIG. 3 below. The injection molding die 30 having the configuration shown in FIG. 3 was set in the injection molding machine used in Example 1, and as a resin material, a cycloolefin polymer having a glass transition temperature of 138 ° C. (manufactured by Zeon Corporation, Product Name: Zeo
Next, the scanning lens 1 (2-2) having the same shape and size as shown in FIG. 1 was formed by applying the first step of the present invention.

In FIG. 3, an injection molding die 30 includes a pair of mirror surface pieces 3 forming an optical surface and a lens side surface (upper surface) 2.
1a and lens side surface (lower surface that cannot be seen in shadow) 21
There is a cavity 5 surrounded by a pair of cavity pieces 4 forming b, the mirror surface piece 3 is provided with a cartridge heater 8 and a thermocouple 9, and a temperature control device (not shown) prepared outside the mold is provided. Connect to. Further, the cavity piece 4 is provided with a pipe 13 for flowing a cooling medium,
It is connected to a mold temperature control device (not shown) prepared outside the mold. Further, the mold base 10 has a cartridge heater 11 and a thermocouple 1 for heating the entire mold.
2 equipped with a cartridge heater 11 and a thermocouple 12
Is connected to another temperature control device (not shown) prepared outside the mold.

Molding conditions for the first step of molding the scanning lens 1 (2-1) using the injection molding die 30 shown in FIG. 3 were as follows. That is, the mold set in the injection molding machine has a predetermined temperature below the glass transition temperature of the resin material used, and in this case, the mold base 10 has a temperature of 135 ° C.
It is heated by the cartridge heater 11 so that it becomes so that the cavity 5 is filled with the molten resin material and cooled. At this time, the temperatures of the cartridge heater 8 and the cavity piece 4 of the mirror surface piece 3 are controlled so that the surface other than the optical surface 2 of the scanning lens 1 (2-1) is preferentially cooled in the cooling process, and the mirror surface piece 3 is controlled. And the temperature of the cavity piece 4 are set to 137
C. and 135.degree. C., and adjust so that the mirror surface piece 3 becomes higher. Then, the scanning lens 1 (2-1) solidified by cooling in the cavity 5 is taken out from the mold and left to stand at room temperature to be naturally cooled.

Next, in the second step, the room temperature scanning lens 1 (2-1) molded in the first step was placed in a constant temperature bath having temperature control means in the same manner as in Example 1. 1
The temperature was raised to 25 ° C., and the temperature was kept at 125 ° C. for 1 hour to uniformly heat the inside of the lens. By gradually cooling from this state to 100 ° C. at a rate of 1 ° C./min, the scanning lens 1
(2-2) was obtained. The obtained scanning lens 1 (2-2) was used as the following evaluation sample.

Comparative Example 1 A schematic sectional view of the injection molding die used in Comparative Example 1 is shown in FIG. An injection molding die 40 having the structure shown in FIG. 4 was set in the injection molding machine used in Example 1, and a cycloolefin polymer having a glass transition temperature of 138 ° C. (Nippon Zeon Co., Ltd.) was used as a resin material as in Examples 1 and 2. Product name: Z
Eonex) was used to mold the scanning lens 1 (3-2) by applying the first step of the present invention in the same shape and size as shown in FIG.

In FIG. 4, the injection molding die has an optical surface 2
And a cavity 5 surrounded by a pair of cavity pieces 4 forming lens side surfaces. The mold base 10 has a cartridge heater 11 for heating the entire die. , The thermocouple 12 is provided, and the cartridge heater 11 and the thermocouple 12 are connected to another temperature control device (not shown) provided outside the mold.

Molding conditions for the first step of molding the scanning lens 1 (3-1) using the injection molding die 40 shown in FIG. 4 were as follows. That is, the mold set in the injection molding machine has a cartridge heater 1 so that the temperature is 135 ° C., which is lower than the glass transition temperature of the resin material used.
It is heated at 1, and the cavity 5 is filled with a molten resin material and cooled. Then, the scanning lens 1 (3-1) solidified by cooling in the cavity 5 is taken out from the mold and left to stand at room temperature to be naturally cooled. Next, as a second step, the room temperature scanning lens 1 (3-) formed in the first step is formed.
1) was placed in a constant temperature bath in the same manner as in Examples 1 and 2,
The scan lens 1 (3-2) was obtained by heat treatment under the same temperature conditions, temperature holding time, and cooling rate. Obtained scanning lens 1
(3-2) was used as the following evaluation sample.

Results of measuring the refractive index distributions of the evaluation samples of the scanning lenses 1 (1-2), (2-2) and (3-2) obtained in Examples 1 and 2 and Comparative Example 1 Is shown in Table 1. Incidentally, the refractive index distribution measurement is carried out by the method described in JP-A-8-12221.
Using the method disclosed in Japanese Patent Publication No. 0, the test wave is incident in the direction (Z direction) in which the laser beam of the scanning lens 1 shown in FIG. 1 is transmitted to refract the central portion of the lens (center in the X direction). The rate distribution was measured. Here, the lens width direction (Y direction)
The PV value (maximum value-minimum value) of the refractive index within the effective range (4 mm) of the light beam through which the laser beam is transmitted is defined as the refractive index distribution.

[0058]

[Table 1]

As a result of the above evaluation, in the case of molding by the manufacturing method including at least the first step and the second step of the present invention, a non-optical surface other than the optical surface of the scanning lens in the cooling process of the first step. By preferentially cooling and solidifying below the glass transition temperature, the refractive index distribution at a temperature higher than the molding temperature is reduced as much as possible, and then the scanning lens solidified in the second step (glass transition temperature- (30 ° C) to a glass transition temperature below a predetermined temperature range,
By performing heat treatment by cooling to a temperature slightly lower than (glass transition temperature −30 ° C.), it is possible to obtain a high-quality scanning lens with a reduced refractive index distribution and less distortion as compared with the conventional method of the comparative example. confirmed.

[0060]

According to the invention of claim 1, the resin material has a glass transition temperature of -30 ° C. or higher and a glass transition temperature of
The first step of filling a molten resin material into a mold cavity whose temperature is adjusted to the following predetermined temperature range, preferentially cooling from a non-optical surface and molding, and a molded plastic optical element, By including at least a second step of adjusting the temperature within a mold to a temperature within a predetermined temperature range, cooling to a temperature lower than the lower limit value of the predetermined temperature range, and performing heat treatment, Since it is extremely small, it is possible to provide a manufacturing method with improved productivity that can obtain a high-quality plastic optical element.

In the inventions according to claims 2 to 5, a temperature difference is set between the temperature of the mold member forming the optical surface and the temperature of the mold member forming the non-optical surface (claim 2). The mold member forming the optical surface is heated (Claim 3), the heat insulating material is provided on the mold member forming the optical surface (Claim 4), or the mold member forming the non-optical surface is cooled. (Claim 5) A low-density region inside the molded article is expanded by making a temperature difference by any one of the methods, so that a plastic optical element in which a light transmission effective range is expanded is obtained. It becomes possible to provide.

According to the sixth aspect of the invention, the cooling rate from the state where the temperature is adjusted within the predetermined temperature range in the second step to a temperature lower than the lower limit value of the predetermined temperature is 3 per minute.
Since the refractive index distribution is effectively reduced by setting the temperature to not higher than 0 ° C., it is possible to provide a manufacturing method by which a high-quality plastic optical element can be obtained.

In the inventions according to claims 7 and 8, the temperature of the plastic optical element molded in the first step, which is outside the predetermined temperature range, is adjusted by heating or cooling to within the predetermined temperature range. By cooling and performing heat treatment (Claim 7), by providing a temperature holding step within a predetermined temperature range before starting cooling (Claim 8), the residual refractive index distribution generated before the second step can be determined. Since it can be effectively reduced, it is possible to provide a manufacturing method capable of obtaining a high-quality plastic optical element with good productivity which can be molded without unnecessary cooling time.

In the invention according to claim 9, the refractive index distribution can be reduced by applying the method for manufacturing a plastic optical element according to any one of claims 1 to 9 of the present invention. It is possible to provide a high-quality plastic optical element that meets high precision requirements.

According to the tenth aspect of the present invention, by using the thermoplastic amorphous plastic material as the molding resin material for the plastic optical element, the first step and the second step in the manufacturing method of the present invention can be performed. Since molding conditions and heat treatment conditions can be applied and the refractive index distribution can be reduced, it is possible to provide a high-quality plastic optical element with a wide range of application.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing the shape of a scanning lens for explaining an example and an embodiment of the present invention.

FIG. 2 is a schematic configuration cross-sectional view showing an injection molding die for explaining the first embodiment and the embodiment of the present invention.

FIG. 3 is a schematic configuration sectional view showing an injection molding die in Example 2.

FIG. 4 is a schematic configuration cross-sectional view showing an injection molding die in Comparative Example 1.

[Explanation of symbols]

1 scanning lens 2 Optical surface 3 Mirror piece 4 cavity pieces 5 cavities 6 cartridge heater 7 thermocouple 8 cartridge heater 9 thermocouple 10 Mold base 11 Cartridge heater 12 thermocouple 13 Piping 20 Mold for injection molding 21a lens side 21b lens side 30 Injection Mold 40 Injection Mold

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomohiro Harada             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F-term (reference) 4F202 AA04 AH73 AR06 CA11 CB01                       CN21 CN27                 4F206 AA04 AH73 AR064 JA07                       JN43 JP17 JQ81 JW06

Claims (10)

[Claims] 1. A molten resin material is adjusted to a temperature within a predetermined temperature range defined by (glass transition temperature −30 ° C.) or more and (glass transition temperature) or less of the resin material,
Fill a mold cavity surrounded by a heat-controllable mold member that forms an optical surface and a heat-controllable mold member that forms a non-optical surface other than the optical surface, and give priority to the non-optical surface. The first step of cooling and solidifying the plastic optical element, and adjusting the temperature of the plastic optical element within the predetermined temperature range inside the mold or outside the mold, and the lower limit value of the predetermined temperature range. Second, heat treatment by cooling to a lower temperature
And at least the step of manufacturing a plastic optical element. 2. In the first step, the temperature of a heat-controllable mold member forming the optical surface and the temperature of a heat-controllable mold member forming a non-optical surface other than the optical surface. The method for producing a plastic optical element according to claim 1, wherein the plastic optical element is solidified and molded by providing a temperature difference therebetween. 3. A heat control for forming a non-optical surface other than the optical surface by heating a heat-controllable mold member forming the optical surface when the plastic optical element is solidified and molded by providing the temperature difference. The method for producing a plastic optical element according to claim 2, wherein the temperature is set higher than the temperature of the mold member that can be used. 4. When solidifying a plastic optical element by providing the temperature difference, a heat-controllable mold member that forms the optical surface is provided with a heat insulating member to form a non-optical surface other than the optical surface. The method for producing a plastic optical element according to claim 2, wherein the temperature is set higher than the temperature of the mold member that can be thermally controlled. 5. A heat control for forming the optical surface by cooling a heat-controllable mold member forming a non-optical surface other than the optical surface when solidifying a plastic optical element by providing the temperature difference. The method for producing a plastic optical element according to claim 2, wherein the temperature is set lower than the temperature of the mold member that can be molded. 6. In the second step, a cooling rate for cooling the plastic optical element from a state of being adjusted to a temperature within the predetermined temperature range to a temperature lower than a lower limit value of the predetermined temperature range is set. 6. The method for producing a plastic optical element according to claim 1, wherein the temperature is 3 ° C. or less per minute. 7. The temperature outside the predetermined temperature range of the plastic optical element solidified and molded in the first step,
7. The method for manufacturing a plastic optical element according to claim 1, wherein the heat treatment in the second step is performed after adjusting the temperature within the predetermined temperature range. 8. A temperature holding step within a predetermined temperature range is provided after the temperature of the plastic optical element reaches a temperature within the predetermined temperature range and before cooling is started. A method for producing the plastic optical element according to claim 1. 9. A plastic optical element manufactured by the method for manufacturing a plastic optical element according to claim 1. 10. The plastic optical element according to claim 9, wherein the plastic optical element is molded from a thermoplastic amorphous plastic material.