JP2006133709A - Plastic optical element, laser scanning optical device and method of manufacturing plastic optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-birefringence plastic optical element which is excellent in shape precision of an optical effective region of an optical face by inducing the sinks on at least one part of non-optical effective region when defining a face including the region through which light flux passes as the optical face, with respect to the plastic optical element for a laser scanning optical system or the like, and to provide a laser scanning optical device which hardly causes focal position deviation, is excellent in optical characteristics and can attain higher quality than heretofore. <P>SOLUTION: In the plastic optical element having at least one optical face including the region through which light flux passes, the sinks are formed on at least one part of the non-optical effective region outside the optical effective region among the optical faces. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement in a plastic optical element that requires high-precision shape and low birefringence, and more particularly to a plastic optical element such as a plastic lens having a high-precision optical mirror surface, a method for manufacturing the same, and a laser scanning optical apparatus. .

Conventionally, optical elements such as lenses and prisms are mainly made of glass because high accuracy is required for surface shape accuracy and internal birefringence. However, in recent years, plastic products have been increasing for reasons such as excellent shape flexibility and mass productivity. In particular, plastic lenses have been frequently used due to the development of resin materials having low birefringence characteristics and the improvement of molding technology that enables the production of molded articles with good shape accuracy and low birefringence.
Conventionally, polycarbonate and acrylic have been mainly used as resin materials for optical components, but polycarbonate has a large birefringence, while acrylic has a problem in water absorption, so the range of use is limited. It was. However, in recent years, resin materials with low water absorption and low birefringence characteristics have been developed, and the range of use has been expanded. Examples of such resin materials include Zeonex manufactured by Nippon Zeon, APEL manufactured by Mitsui Petrochemical, and Arton manufactured by JSR.
As a molding technique, a method of molding at a low pressure is performed for the purpose of reducing birefringence. However, when molding at low pressure to reduce the birefringence of the plastic lens, the occurrence of sink marks due to resin shrinkage in the mold becomes a problem. In particular, the influence is remarkable in the case of a complicated cavity shape or a thick and uneven cavity shape.
Therefore, filling the resin with low pressure,
(1) Injection compression molding method in which compression is applied via the entire mold or through a frame (2) A molding method has been developed that induces sink marks to a surface other than the transfer surface during pressure molding. Specifically, the method described in Patent Document 1 that selectively induces sink by temperature control, the method described in Patent Document 2 that selectively induces sink by compressed air, or by separating the cavity insert from the resin Examples include a method described in Patent Document 3 that selectively induces sink marks.
As a plastic lens molding method, for example, in Patent Document 1, a thermoplastic resin molding material is supplied to a mold, and the mold is heated to heat a predetermined portion of the thermoplastic resin molding material to a temperature higher than the critical temperature at which sink occurs. Then, a molding method has been proposed in which the thermoplastic resin molding material is compression-molded into a predetermined shape, and the compression-molded thermoplastic resin molding material is gradually cooled.
Also, in the injection molding of plastic products, gas pressure application means is attached to the mold surface that is on the non-visible surface side of the product and is prone to sink, or to the surface of the mold that is in contact with the site with poor transferability and shape accuracy. A method of manufacturing an injection molded plastic product that applies gas pressure has been proposed (see, for example, Patent Document 2).
Also, when cooling the molten resin to below the softening temperature, there is also a plastic molding method for forcibly defining a gap between the resin and the cavity piece by sliding the cavity piece away from the resin. It has been proposed (see, for example, Patent Document 3).
With the development of these molding methods, molded products with good shape accuracy and low birefringence can be obtained. For the reasons described above, plasticization of optical elements tends to be further promoted.
JP-A-11-19956 JP 7-223246 A JP-A-11-28745

However, in low pressure molding, there is a problem that incomplete transfer at the submicron level occurs from the center of the optical surface to the outside even if it is not at a level that can be confirmed from the appearance. Also, regardless of the molding method, in the case of a molded product having a rib structure, in the resin cooling process in the mold, the area around the rib that is in contact with the mold is larger than the resin volume. As a result, incomplete transfer at the sub-micron level occurs from the center of the optical surface to the outside, even if it is not at a level that can be visually confirmed around the optical surface along the rib. was there. In addition, if a stain on the appearance is confirmed on the optical surface, the sink reaches the optical effective region, and there is a problem that adversely affects the optical characteristics.
In particular, in a laser scanning optical device used for an optical instrument such as an optical scanning system of a digital copying machine, a laser printer or a facsimile machine, or a video camera, the birefringence is small, and the shape accuracy of the optical effective area of the optical surface is very high. Therefore, it is problematic to control the sink area generated on the optical surface to an arbitrary position and range.
The present invention has been made in consideration of the above-mentioned actual situation, and when a surface including a region through which a light beam passes is defined as an optical surface, the optical effective region is sinked to at least a part of the adjacent non-optical effective region. It is an object of the present invention to provide a plastic optical element having excellent shape accuracy of an optical effective area of an optical surface and a low birefringence, and a manufacturing method thereof. In particular, it is an object of the present invention to provide 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 apparatus such as a video camera, and a manufacturing method thereof. It is another object of the present invention to provide a laser scanning optical device that uses this plastic optical element, has a small focal position shift, has excellent optical characteristics, and can achieve an unprecedented high image quality.

In order to solve the above problems, the invention of claim 1 is a plastic optical element having an optical surface including a region through which a light beam passes or reflects, and a non-optical effective region outside the optical effective region of the optical surface. It is characterized by having a sink area in at least a part of the above.
According to a second aspect of the present invention, in the first aspect, the plastic optical element has a sink region in a part of the non-optical surface.
A third aspect of the invention is characterized in that, in the first or second aspect, at least a part of the non-optical effective area of the optical surface and a sink area are provided in at least a part of the non-optical surface.
According to a fourth aspect of the present invention, in any one of the first to third aspects, the plastic optical element is made of a thermoplastic amorphous resin.
According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the plastic optical element is a lens having two optical surfaces facing each other.
The invention of claim 6 is characterized in that, in claim 5, the sink region is provided only on at least one of the two optical surfaces of the plastic optical element.
A seventh aspect of the invention is characterized in that, in the fifth aspect, of the two optical surfaces of the plastic optical element, each of the optical surfaces has the sink region.
According to an eighth aspect of the present invention, in any one of the first to fourth aspects, the plastic optical element is a mirror that uses at least one optical surface as a reflecting surface.
According to a ninth aspect of the present invention, there is provided a laser scanning optical apparatus using the plastic optical element according to any one of the first to seventh aspects as a scanning lens.
A laser scanning optical device according to a tenth aspect of the present invention is characterized in that the plastic optical element according to the eighth aspect is used as a scanning mirror.
A method for producing a plastic optical element according to an invention of claim 11 is a method of molding a plastic optical element according to any one of claims 1 to 10 using an injection mold. Thus, the resin residual pressure in the cavity is set to 0 before the molding of the plastic lens optical element is completed and the mold is opened.

  A plastic optical element having at least one optical surface including a region through which a light beam passes has a sink region in at least a part of the optical surface outside the optical effective region (hereinafter, non-optical effective region). As a result, the shape accuracy of the optically effective area of the optical surface can be improved, and the birefringence of the plastic optical element can be extremely reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic perspective view showing a configuration when a plastic optical element 1 according to an embodiment of the present invention is used in an optical system such as a laser printer. The upper and lower surfaces of the plastic optical element 1 in the figure are the optical surfaces 2, and when the plastic optical element 1 is incorporated and used in a laser printer, the laser beam is transmitted from the lower surface toward the upper surface. The material is cycloolefin polymer Zeonex resin, which is a thermoplastic amorphous resin manufactured by Nippon Zeon.
The glass transition temperature of the Zeonex resin according to the DSC test method is 138 ° C. The scanning lens 1 has, for example, a central lens thickness Ha: 14 mm, an end lens thickness Hu: 7 mm, a sub-scanning length D: 14 mm, an effective area d of the optical surface in the sub-scanning direction d: 8 mm, and an optical surface. The main scanning direction effective area 1 is 180 mm, and the main scanning length L is 220 mm.

FIG. 2 shows a schematic sectional view around the cavity of an injection mold 3 for manufacturing the optical element 1 according to this embodiment. The injection mold 3 includes a pair of mirror pieces 4 having a transfer surface for forming (transferring) a part of the optical surface and non-optical surface of the optical element 1 as a molded product, and the non-optical surface of the optical element 1. A pair of side pieces 5 located on both sides of each mirror piece 4, and a transfer surface for transferring a part of the non-optical surface, and sliding in the direction of the arrow. And a pair of sliding pieces 7 provided movably, and a cavity 8 is formed by a space formed between the transfer surfaces. A driving device (not shown) is connected to the pair of sliding pieces 7 that are slidably provided. Further, each side piece 5 is provided with a cartridge heater 9 and a thermocouple 10 for heating the mold, and the cartridge heater and the thermocouple are connected to another temperature control device (not shown) prepared outside the mold. Keep connected.
Here, FIG. 3 shows a detailed view around the cavity 8 including the optical surface of the molded product. A 0.01 mm clearance 11 is provided between the mirror piece 4 and the side piece 5.
Next, the operation of the embodiment will be described. The injection mold 3 is set in an unillustrated injection molding machine (electric injection molding machine ROBOSHOT manufactured by FANUC), and the scanning lens 1 is molded. The injection mold 3 is heated by the cartridge heater 9 so as to be 135 ° C. just below the glass transition temperature of the resin material used, and the cavity 8 is filled with the molten resin. Then, the temperature of the cartridge heater 9 is adjusted so that the mold is maintained at a predetermined temperature that is lower than the glass transition temperature of the resin material used.
Next, pressure is generated on the molten resin in the cavity 8 so that the molten resin is brought into close contact (transfer) with the transfer surface of the pair of mirror surface pieces 4 forming part of the optical surface and the non-optical surface. At this time, when the pressure applied to the resin in the cavity 8 becomes zero, the pair of sliding pieces 7 slidably provided are slid away from the resin to slide with the resin in the cavity 8. A gap is forcibly formed between the pieces 7, and the sink (sink region) 13 is guided to the surface (non-optical surface) 1 a in contact with the sliding piece 7. Next, the solidified plastic molded product is taken out from the injection mold using a molded product take-out device (not shown) and allowed to cool at room temperature.

In this embodiment, as a result of inducing sink marks (concave portions) on the resin surface in contact with the sliding piece 7, the resin internal pressure acting on the optical surface 2 during cooling is brought close to the atmospheric pressure (the resin in the cavity 8 before mold opening). Therefore, a molded product with small internal strain can be obtained. Further, sinks (sink regions) 12 are also induced in the non-optical effective region (both outer regions of the optical effective region 14) of the optical surface 2.
This is because a clearance 11 (see FIG. 3) of 0.01 mm is provided between the mirror piece 4 and the side piece 5, so when the resin pressure in the cavity becomes zero, air flows from the clearance 11. It is considered that sink 12 occurred in the non-optical effective area of the optical surface. Here, FIG. 4 shows a schematic cross-sectional view of the molded product. The scanning lens 1 molded according to the present embodiment has a sink 12 of the non-optical effective area of the optical surface and a sink 13 of the non-optical surface 1a, as compared with the shape of the cavity 8 shown in FIG. Are different, and the optically effective area 14 of the optical surface having no sink has excellent shape accuracy.
According to this embodiment, the plastic optical element 1 having the two optical surfaces 2 and 2 facing each other can be used as a plastic lens. This plastic lens has very good shape accuracy of the optical effective area 14 of the optical surface 2 and extremely low birefringence.
In the plastic optical element molding method, a plastic optical element having extremely little birefringence can be obtained by adding a procedure for setting the residual pressure to 0 when the mold is opened in the molding process. Further, sink marks 12 can be formed in the non-optical effective area of the optical surface, and as a result, the shape accuracy of the optical effective area 14 of the optical surface can be improved.

Next, in the mold for injection molding the plastic optical element 1 according to Comparative Example 1 shown in FIG. 6, the clearance 11 between the mirror piece 4 and the side piece 5 shown in FIG. Other configurations and operations will be described as being the same as those of the mold of FIG. Thus, the plastic optical element (for example, scanning lens) 1 according to the comparative example 1 formed by the mold having no clearance 11 has a non-optical surface 1a as shown in FIG. 6 as compared with the shape shown in FIG. The only difference is that it has only sink marks 13. That is, the sink marks 12 in the non-optical effective area of the optical surface shown in FIG. 4 are not formed.
Here, the measurement results of the sub-scanning shape at the center position in the lens longitudinal direction of Example 1 and Comparative Example 1 are shown in FIG. 7 with the sub-scanning position as the horizontal axis and the shape measurement result Δh in the height direction as the vertical axis. Show. In the optical element of Comparative Example 1, the shape accuracy of the entire optical surface 2 is excellent. However, when the shapes of only the optical effective region 14 are compared, it can be seen that Example 1 is superior in shape accuracy. That is, as in the first embodiment, by guiding the non-optical effective area of the optical surface to have sink marks 12, the shape accuracy of the optical effective area 14 can be improved.
Next, FIG. 8 shows the relationship between the clearance 11 between the mirror piece 4 and the side piece 5, the sink width, and the shape PV value of the optically effective area (deviation amount from the target shape). In this embodiment, the sink 12 of the non-optical effective area of the optical surface can be controlled by setting the clearance 11 between the mirror piece 4 and the side piece 5 to a predetermined size.
In Example 1, the optical surface was molded so as to have sink marks (sink regions) 12 and 13 on the non-optical effective region and the non-optical surface, respectively, but if the resin shrinkage in the mold can be absorbed, FIG. A shape having sinks 12 only in the non-optically effective area of the optical surface as shown in FIG. Further, the sink 12 of the non-optical effective area of the optical surface has a shape that exists only on one surface of the lens surface as shown in FIG. 9B, or the sub-scanning direction of the lens surface as shown in FIG. 9C. A shape that exists only on one side of the frame is also conceivable.

As shown in FIG. 9A, by providing the sink area 12 on both of the two optical surfaces 2 of the plastic lens, it is easy to select the position and range of the sink provided in the non-optical effective area of the optical surface 2. The plastic lens has very good shape accuracy of the optical effective area 14 of the optical surface, and has extremely low birefringence.
As shown in FIG. 9B, by providing a sink region 12 only on one optical surface 2 of the two optical surfaces 2 of the plastic lens 1, the optical effective region 14 of the optical surface is made the incident surface and the output surface. There is a merit that can be changed with. The plastic lens 1 has very good shape accuracy of the optical effective area 14 of the optical surface, and has extremely low birefringence.
Similarly, the non-optical surface sink 13 may be provided only on one side of the non-optical surface as shown in FIGS. 9C and 9D to simplify the mold structure. The difference between FIGS. 9C and 9D is that in FIG. 9C, the sink 13 of the non-optical surface 1a is on both sides, whereas in FIG. 9D, the sink 13 is provided only on one side. is there.
Further, not only the non-optical effective area in the sub-scanning section of the plastic lens 1 as the scanning lens but also the sink 12 is generated in the non-optical effective area in the main scanning direction of the scanning lens as shown in FIG. As shown in FIG. 10B, it is conceivable that sink marks 12 are generated in the non-optical effective areas in both the main scanning direction and the sub-scanning direction of the scanning lens. Further, the sink 12 of the non-optical effective area of the optical surface is generated along the rib 1b (FIG. 1) of the molded product as in the first embodiment, so that a special mold structure is not required. It is possible to control the amount of sink.
The plastic scanning lens 1 manufactured according to Example 1 has very good shape accuracy of the optically effective area 14 of the optical surface, and extremely low birefringence.
In the present embodiment, sink marks 12 are formed in the non-optically effective area of the optical surface by the clearance 11 between the mirror piece 4 and the side piece 5, but the present invention is a method for forming a molding method or sink marks. Regardless of the above, for the purpose of improving the shape accuracy of the optically effective area 14 of the optical surface by forming the sink 12 in the non-optically effective area of the optical surface (the outer area of the optically effective area 14). is there. That is, regardless of how the sink generation method is implemented, all plastic optical elements having sinks in the non-optically effective area of the optical surface are included in the present invention.
Further, the mold structure according to the present embodiment is not limited to the plastic scanning lens having the shape shown in the figure, and the shape accuracy of the optical effective area of the optical surface is improved by generating sink marks 12 in the non-optical effective area of the optical surface. Applies to the manufacture of all molded products that can be made.

In the present embodiment, at the boundary between the optical surface 2 of the plastic optical element 1 and the non-optical surface 1a other than the optical surface, at least a position of the sink in the non-optical region is easily selected, thereby causing a sink. By generating it along the rib 1b of the molded product, the amount of sink can be controlled without requiring a special mold structure. The plastic optical element thus obtained has very good shape accuracy in the optically effective area of the optical surface and has extremely low birefringence.
For example, the molding by the mold of the present invention can be applied to a camera lens 15 as shown in FIG. In addition, optical surface shapes that require high shape accuracy can be applied to optical elements of all shapes such as flat surfaces, spherical surfaces, aspheric surfaces, free-form surfaces.
Moreover, although the cycloolefin polymer was illustrated as used resin of a present Example, this invention is not limited to a used resin material, It applies to all the thermoplastic amorphous plastics from which the said effect is acquired. In other words, the present invention can be applied to any plastic resin that can absorb resin shrinkage in the mold by generating sink marks in the non-optical effective area of the optical surface and improve the shape accuracy of the optical effective area of the optical surface. It is.
In addition, by using a thermoplastic amorphous resin as the resin used, it is possible to obtain a plastic optical element in which the shape accuracy of the optically effective area 14 of the optical surface is extremely excellent and the birefringence is extremely small.
In this embodiment, the resin material is molded into a desired molded product shape in the mold by the injection molding method. However, the present invention generates sink marks in the non-optical effective area of the optical surface. Thus, it is characterized by improving the shape accuracy of the optically effective area of the optical surface, and can be applied regardless of the molding method. For example, in addition to injection molding, it can be applied to various molding methods such as injection compression / press molding, gas assist molding and extrusion molding.

Next, Example 2 will be described. FIG. 12 is a schematic view when the plastic optical element according to the present invention is applied to a scanning lens 16 used in a laser printer. When the upper surface and the lower surface in FIG. 12 are the optical surface 2 and are used by being incorporated in a laser printer, the laser beam is transmitted from the lower surface toward the upper surface. Further, the material is a cycloolefin polymer Zeonex resin manufactured by Nippon Zeon Co., Ltd. as in the case of FIG. The shape dimensions of the scanning lens 16 are the center lens thickness Ha: 35 mm, the end lens thickness Hu: 5 mm, the sub-scanning length D: 8 mm, the effective area d of the optical surface in the sub-scanning direction: 5 mm, and the main surface of the optical surface. Effective area 1 in the scanning direction is 120 mm, and main scanning length L is 160 mm.
Next, FIG. 13 shows a schematic sectional view around the cavity of the injection mold 3 used in Example 2 of the present invention. The mold 3 is formed by a pair of mirror pieces 4 forming the optical surface 2, two pairs of side pieces 5 positioned on the side surfaces of the mirror piece 4, and a pair of cavity inserts 6 forming a part of the non-optical surface. A gas supply device (not shown) which has a cavity 8 and has one end of a vent port 17 penetrating the cavity insert 6 opened in a part of the non-optical surface and communicates with the vent port 17 to apply a compressed gas to the molded product. Keep connected. Further, the mirror piece 4 includes a cartridge heater 9 and a thermocouple 10, and the side piece 5 includes an oil temperature adjusting pipe 18. The cartridge heater 9 and the oil temperature adjusting pipe 18 are respectively provided outside the mold. It is connected to another prepared temperature control device (not shown).

Next, operation | movement of the metal mold | die of Example 2 is demonstrated.
The injection mold 3 is set in an unillustrated injection molding machine (electric injection molding machine ROBOSHOT manufactured by FANUC), and the scanning lens 16 is molded as a molded product. The mold 3 is heated by the cartridge heater 9 so as to be 135 ° C. just below the glass transition temperature of the resin material used, and the cavity 8 is filled with the molten resin. Then, the temperatures of the cartridge heater 9 and the oil temperature adjusting pipe 18 are adjusted so that the mold is maintained at a predetermined temperature that is equal to or lower than the glass transition temperature of the resin material used. At this time, the temperature of the thermocouple 10 provided in each mirror piece 4 is adjusted so that the temperature at the center position in the sub-scanning direction is increased by adjusting the temperatures of the cartridge heater 9 and the oil temperature adjusting pipe 18. A temperature difference of 0.5 ° C. is provided between the center position and the end.
Next, pressure is generated on the molten resin in the cavity 8 so that the molten resin is brought into close contact (transfer) with the transfer surface of the pair of mirror pieces 4 forming the optical surface 2. At this time, when the resin pressure in the cavity 8 becomes zero, a compressed gas of a predetermined pressure is applied from the vent 17 to forcibly form a gap between the resin and one end opening of the vent 17 to vent the sink. Guide to the surface in contact with the mouth 17. Next, the solidified plastic molded product is taken out from the mold 3 using a molded product take-out device (not shown) and allowed to cool to room temperature. In this embodiment, as a result of guiding the sink (concave portion) 13 shown in FIG. 14 to the molded product surface 1a in contact with one end opening of the vent hole 17, the internal pressure of the resin acting on the optical surface 2 at the time of cooling is brought close to the atmospheric pressure (mold) Before opening, the resin pressure in the cavity can be molded to be 0), so that a molded product with small internal strain can be obtained. In addition, since a temperature difference of 0.5 ° C. is provided between the center position and the end in the sub-scanning direction, the temperature of the resin shrinks when the resin pressure in the cavity 8 becomes zero. It is considered that sink 12 occurred in the non-optical effective area of the optical surface as a result of solidification shrinkage progressing from the lower part.
Here, FIG. 14 shows a schematic cross-sectional view of a molded product molded by the mold. The scanning lens 16 molded according to this embodiment is different from the shape of the cavity 8 in FIG. 13 in that it has a sink 12 in the non-optical effective area of the optical surface 2 and a sink 13 in the non-optical surface 1a. ing. The optical effective area 14 of the optical surface 2 has excellent shape accuracy.
Here, as Comparative Example 2, the mold 3 of Example 2 was used, and the temperature difference between the center position and the end in the sub-scanning direction was set to 0 ° C., and other conditions were the same in configuration and operation. explain. The scanning lens 16 molded according to Comparative Example 2 has sink marks 13 only on one non-optical surface 1a as shown in FIG. 15 with respect to the cavity shape of FIG.

Here, the measurement results of the sub-scanning shape at the center position in the lens longitudinal direction of Example 2 and Comparative Example 2 are shown in FIG. 16 with the sub-scanning position as the horizontal axis and the shape measurement result Δh in the height direction as the vertical axis. Show. In Comparative Example 2, the shape accuracy of the entire optical surface is excellent. However, when the shapes of only the optical effective region are compared, it can be seen that Example 2 is superior in shape accuracy.
That is, as in the second embodiment, by having a sink in the non-optical effective area of the optical surface 2, the shape accuracy of the optical effective area 14 is improved. Further, FIG. 17 shows the relationship between the temperature difference between the center position and the end in the sub-scanning direction, the sink width, and the shape PV value of the optically effective area (deviation amount from the target shape). In this embodiment, the sink 12 region of the non-optical effective region of the optical surface can be controlled by setting the temperature difference between the center position and the end in the sub-scanning direction to a predetermined temperature difference. The plastic scanning lens manufactured according to the present embodiment has very good shape accuracy of the optical effective area of the optical surface and extremely low birefringence. In this embodiment, sink marks 12 are formed in the non-optically effective area of the optical surface due to the temperature difference between the center position and the end in the sub-scanning direction. However, the present invention is mainly used in this molding method and the method of forming sink marks. The object is not to have a purpose but to improve the shape accuracy of the optically effective area of the optical surface by generating sink marks in the non-optically effective area of the optical surface.
That is, the present invention is applicable to all plastic optical elements having sink marks in the non-optical effective area of the optical surface regardless of the sink generation method.

FIG. 18 is a schematic diagram of an optical system 19 mounted on a laser printer or a digital copying machine. This optical system 19 is deflected by a semiconductor laser 20 as a light source, a rotating polygon mirror 21 as a changing means having a deflecting surface for deflecting light from the semiconductor laser 20 in a predetermined angular range at a constant angular velocity, and a rotating polygon mirror 21. A laser scanning optical system 22 as an optical system for converting the emitted light into constant velocity light, a folding mirror 23 for changing the direction of the light from the laser scanning optical system 22, and the like.
Here, the scanning lens 16 and the scanning lens 1 are used in the laser scanning optical system 22. The operation of the optical system 19 will be described below. The light emitted from the semiconductor laser 20 is once imaged near the deflection surface of the rotary polygon mirror 21. The rotating polygon mirror 21 rotates at a constant angular velocity in the direction of arrow C in the figure, and the light imaged in the vicinity of the deflection surface is deflected at a constant angular velocity as the rotating polygon mirror 21 rotates.
The deflected light is sequentially transmitted through the scanning lens 16 and the scanning lens 1 to be converted into constant speed light, reflected by the folding mirror 23, and scanned on the surface of the photosensitive member 24 as a scanning target. For example, when the optical system 19 is used in a digital copying machine, the light intensity of the light from the semiconductor laser 20 is modulated by image information corresponding to the copy image, and this light is coupled to the surface of the photoconductor 24. By forming an image, an electrostatic latent image of a copied image is formed on the surface of the photoreceptor.
Accordingly, the accuracy of the laser scanning optical system 22 including the scanning lenses 16 and 1 and the scanning mirror, for example, the shape accuracy of the optical surface, the placement accuracy of the optical elements, and the like have a great influence on the copy image quality. Accordingly, in the laser printer and the digital copying machine according to the present invention, since the scanning lenses 16 and 1 having the configuration manufactured by the mold 3 described above are used, in the actual use state fixed to the optical system. Since the shape error with respect to the design shape is small and the birefringence is small, it has an optical function at the time of design. As a result, accurate scanning is possible, and a high-quality image can be formed. In particular, when applied to a color laser printer or a color digital copying machine, a high-quality color image with little color misregistration can be formed.
Thus, by using a plastic lens as a scanning lens, it is possible to manufacture a laser scanning optical device that has little focal position shift, excellent optical characteristics, and can achieve unprecedented high image quality.

FIG. 19 is a schematic view of a plastic mirror 25 used in a laser printer. When used in a laser printer, the laser beam is reflected by, for example, aluminum deposition on the optical surface (reflection surface) 2. The material is polycarbonate resin (PC optical grade).
PC (glass transition temperature: 145 ° C .: test method DSC)
Plastic mirror shape dimensions: center lens thickness Ha: 6 mm, end lens thickness Hu: 15 mm, short length D: 14 mm, and long length L: 260 mm.
Next, FIG. 20 shows a schematic cross-sectional view of the press molding die 26 used in Example 3 of the present invention. The upper die plate 27 of the press molding apparatus has an upper die member 28 that forms an optical surface, and the lower die plate 29 has a lower die member 30 that forms a non-optical surface. The upper mold member 28 includes an oil temperature adjusting pipe 18 for heating the mold and the thermocouple 10, and further includes a cartridge heater 9 and a thermocouple 10 for locally heating the optical surface. In addition, the lower mold member 30 includes an oil temperature adjusting pipe 18 for heating the mold and a thermocouple 10, and each oil temperature adjusting pipe 18 and the cartridge heater 9 are prepared outside the mold. Do not connect to another temperature control device. On the other hand, in the support recess 30a of the lower mold member 30, a plastic substrate 31 made of a polycarbonate resin previously processed into a substantially final shape by injection molding is provided.

Next, the operation of the third embodiment will be described. The plastic substrate 31 is molded into the plastic mirror 25 shown in FIG. 21 by the press molding die 26. The mold 26 is heated by the oil temperature adjusting pipe 18 so as to be near 150 ° C. above the glass transition temperature of the resin material used. The set temperature of the upper mold member 28 and the lower mold member 30 is shifted by about 1 ° C., and the temperature of the lower mold member 30 is kept low. At this time, the set temperature of the thermocouple 10 provided in the upper mold member 28 is adjusted so that the temperature becomes high at the center position in the sub-scanning direction by adjusting the temperature of the cartridge heater 9 and the oil temperature adjusting pipe 18. A temperature difference is provided between the center position and the end.
Next, by lowering the upper die plate 27 of the press molding apparatus, pressure is generated on the resin of the plastic base material 31 so that the cavity surface (transfer surface) is completely adhered. Thereafter, the mold 28 is gradually cooled at a rate of 1 ° C./min to 120 ° C., which is lower than the glass transition temperature of the resin material used, while maintaining the close contact between the members 28, 30 and the resin 31, and then molded from the mold. Remove the product and let it cool to room temperature. In the slow cooling step, first, the set temperature of the upper mold member 28 and the lower mold member 30 is shifted by about 1 ° C., the temperature of the lower mold member 30 is kept low, and further, the upper mold member 28 is provided in the vicinity of the optical surface. The set temperature of the thermocouple 10 is adjusted by adjusting the temperature of the cartridge heater 9 and the oil temperature adjusting pipe 18 so that the temperature becomes higher at the center position in the sub-scanning direction so that a temperature difference is provided between the center position and the end. Yes.
In the present embodiment, by the temperature control, sink marks 13 are selectively advanced on the bottom surface facing the optical surface (reflection surface) 2 in the mold, and then the end portion of the optical surface 2 in the sub-scanning direction. The sink 12 is selectively generated in FIG. As a result of inducing sinks (recesses) 12 and 13 in the above procedure, the resin internal pressure acting during cooling can be brought close to the atmospheric pressure (molding so that the resin pressure in the cavity is zero before mold opening). A molded product with a small internal strain can be obtained.

Here, FIG. 21 shows a schematic cross-sectional view of the molded product. Compared with the cavity shape of FIG. 20, the plastic mirror 25 molded according to the present embodiment has the non-optical effective area sink 12 on the optical surface 2 and the sink 13 on the non-optical surface 1a. Are different, and the optically effective area 14 of the optical surface 2 has excellent shape accuracy. The plastic scanning mirror manufactured according to the present embodiment has a very good shape accuracy of the optically effective area 14 of the optical surface and extremely small internal distortion. Although the present embodiment is implemented for the above-described scanning mirror, by actively generating sink marks 12 in the non-optical effective area of the optical surface 2 regardless of the shape of the molded product and the type as the optical component, The present invention is applied to all molded product shapes that can improve the shape accuracy of the optical effective area 14 of the optical surface. For example, the present invention can be applied to a large-diameter mirror 32 as shown in FIG.
By using the optical surface of the plastic optical element as the reflecting surface, it is possible to obtain a plastic mirror with very good shape accuracy of the optically effective area of the optical surface.

Next, a fourth embodiment of the present invention will be described. The fourth embodiment relates to a molded product having the same material and shape as the scanning lens 1 of the first embodiment shown in FIGS. 1 and 4 and the structure of a mold for molding the molded product. Further, the configuration and operation of the apparatus are the same except for the shape of the mirror piece 4. That is, additional processing is applied to the shape of the pair of mirror pieces 4 that form part of the optical surface 2 and the non-optical surface 1a shown in the mold of FIGS.
Details are shown below. FIG. 23 shows a detailed view of the mirror piece 4 used in the fourth embodiment. The transfer surface 4a that forms the optical surface of the mirror surface piece 4 was subjected to submicron level additional processing by a focused ion beam device (hereinafter referred to as FIB). In FIB, an ion beam is irradiated from a gallium liquid metal ion source and processed using a sputtering effect. Since there is no chemical influence or thermal damage, it has excellent processing accuracy. Specifically, a V-shaped groove 33 having an opening groove width of 0.2 μm and a depth of 0.15 μm is formed on the transfer surface 4a at the position of the outer periphery of the optical effective area of the optical surface of the transferer Iseyu. I am letting. If the V-shaped groove 33 is formed, for example, the accuracy of the clearance 11 provided between the mirror piece 4 and the side piece 5 shown in FIGS. 2 and 3 is displaced during the assembly of the mold or during the molding cycle. Even in this case, it is possible to control the sink generation area outside the optical effective area 14.

Here, FIG. 24 shows a schematic cross-sectional view of the molded product. The scanning lens 1 molded according to the present embodiment has a sink 12 of the non-optical effective area of the optical surface 2 and a sink 13 of the non-optical surface 1a as compared with the cavity shape. The optical effective area 14 has excellent shape accuracy. The plastic scanning lens manufactured according to the present embodiment has very good shape accuracy of the optically effective area 14 of the optical surface and extremely low birefringence. In this embodiment, the clearance 11 between the mirror piece 4 and the side piece 5 shown in FIG. 3 and the V-shaped groove 33 provided in the mirror piece 4 shown in FIG. Although sink marks 12 are formed and the sink area is controlled to an arbitrary position and range, the present invention is not characterized only by a molding method or a method of forming sink marks, but sink marks 12 are formed in a non-optical effective area of an optical surface. The purpose of this is to improve the shape accuracy of the optically effective area of the optical surface.
In other words, the present invention can be applied to all plastic optical elements having sinks 12 in the non-optical effective area of the optical surface 2 regardless of the sink generation method. In this embodiment, the groove 33 is provided on the outer periphery of the transfer surface 4a for transferring the optically effective area 14, but this groove 33 is intended to control the sink area and is not limited to the shape shown in the figure. For example, as shown in FIG. 25, an uneven portion 34 is provided by sandblasting or the like on the outer peripheral portion of the optically effective region 14 to increase the surface roughness on the level of several tens of nanometers to several hundreds of nanometers, or as shown in FIG. Further, the same effect can be obtained by forming a plurality of minute grooves 35 in the main scanning direction and controlling the sinking direction.

It is a perspective view of the scanning lens used for the laser scanning device of the present invention. It is sectional drawing of the cavity periphery of the injection mold used for this invention. It is detailed sectional drawing of the cavity periphery containing the optical surface of this invention. It is the cross-sectional schematic of the example of the molded article of this invention. It is product sectional drawing in the case of the clearance 0 between the conventional mirror surface and a side piece. It is sectional drawing of the molded product which induced | guided | derived sinking only to the conventional non-optical surface. It is explanatory drawing which shows the output surface subscanning shape measurement result of the lens longitudinal direction of this invention. It is explanatory drawing which shows the relationship between the sink width and shape accuracy PV value of this invention, and the clearance between pieces. It is explanatory drawing of the example of the sink sink which absorbs the resin shrinkage | contraction in the metal mold | die of this invention. It is the schematic which shows the various examples which generate | occur | produce a sink in the non-optical effective area | region of the scanning lens of this invention. It is sectional drawing which shows the example applied to the camera lens etc. of this invention. It is the schematic of the scanning lens for laser printers of this invention. It is sectional drawing of the cavity periphery of the injection mold of this invention. It is sectional drawing of the molded article which induced | guided | derived sink on the non-optical effective surface and non-optical surface of this invention. It is sectional drawing of the example which induced | guided | derived sinking only to the non-optical surface of this invention. It is explanatory drawing of the shape measurement result of the lens sub-scanning direction center position of this invention. It is explanatory drawing which shows the relationship between the sink width of this invention, and the shape PV value inside and outside a non-optical effective area | region. 1 is a schematic view of an optical system mounted on a copying machine of the present invention. It is the schematic of the plastic mirror used for the laser printer of this invention. It is the cross-sectional schematic of the metal mold | die for press molding used for this invention. 1 is a schematic sectional view of a plastic mirror molded article according to the present invention. It is the schematic which shows the example of the large diameter mirror by this invention. It is detail drawing of the mirror surface piece which gave the additional process used by this invention. It is sectional drawing of the molded article which generated the sink in the non-optical effective area | region of the optical surface of this invention. It is the schematic of the example which provided the uneven | corrugated | grooved part in the outer peripheral part of the specular piece of this invention, and enlarged the surface roughness. It is the schematic of the example which formed the minute multiple groove | channel in the outer peripheral part of the mirror surface piece of this invention.

Explanation of symbols

  1 scanning lens, 1a non-optical surface, 1b rib, 2 optical surface, 3 mold for injection molding, 4 mirror piece, 5 side piece, 6 cavity insert, 7 sliding piece, 8 cavity, 9 cartridge heater, 10 thermocouple , 11 Clearance, 12 Sink of non-optical effective area of optical surface (sink area), 13 Sink of non-optical surface (sink area), 14 Optical effective area of optical surface, 15 Camera lens, 16 Scan lens, 17 Vent, 18 Pipe for oil temperature adjustment, 19 Optical system, 20 Semiconductor laser, 21 Rotating polygon mirror, 22 Laser scanning optical system, 23 Folding mirror, 24 Photoconductor, 25 Plastic mirror, 26 Mold for press molding, 27 Upper die plate, 28 Upper die member forming an optical surface, 29 lower die plate, 30 lower die member forming a non-optical surface, 31 plus Click substrate, 32 a large diameter mirror, 33 V-shaped groove, 34 uneven portion, 35 minute plurality of grooves

Claims (11)

  A plastic optical element having an optical surface including an area through which a light beam passes or reflects, wherein the optical surface has a sink area in at least a part of a non-optical effective area outside the optical effective area. element.   The plastic optical element according to claim 1, further comprising a sink region in a part of a non-optical surface of the plastic optical element.   The plastic optical element according to claim 1, further comprising a sink region in at least a part of the non-optical effective area of the optical surface and in at least a part of the non-optical surface.   The plastic optical element according to any one of claims 1 to 3, wherein the plastic optical element is made of a thermoplastic amorphous resin.   The plastic optical element according to any one of claims 1 to 4, wherein the plastic optical element is a lens having two optical surfaces facing each other.   The plastic optical element according to claim 5, wherein the sink region is provided only on at least one of the two optical surfaces of the plastic optical element.   The plastic optical element according to claim 5, wherein the sink region is provided on each of two optical surfaces of the two optical surfaces of the plastic optical element.   The plastic optical element according to any one of claims 1 to 4, wherein the plastic optical element is a mirror using at least one optical surface as a reflecting surface.   A laser scanning optical device using the plastic optical element according to any one of claims 1 to 7 as a scanning lens.   9. A laser scanning optical apparatus using the plastic optical element according to claim 8 as a scanning mirror.   The method of molding a plastic optical element according to any one of claims 1 to 10 using an injection mold, wherein the molding of the plastic lens optical element is completed in the mold cavity and the mold is opened. A method for producing a plastic optical element, wherein the residual resin pressure in the cavity is set to 0 before being performed.

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