JP2010060962A - Plastic optical element, optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plastic optical element of high precision, which can be manufactured at the same production cost as before even when being thick-walled and unevenly thick and has an excellent lens surface shape, wherein internal strain is homogeneously reduced to achieve high optical performance; and to provide an optical scanner and an image forming apparatus having the plastic optical element. <P>SOLUTION: The plastic optical element provided at a focusing optical system of the optical scanner has two transferring faces which are formed by producing resin pressure in a resin in a cavity of a metallic mold having a surface to be transferred and then transferring the surface to be transferred and which become an incident surface and an emission surface of light beams and further has non transferring face which is formed by incompletely transferring a cavity shape of the metallic mold at a portion except the transferring face. Deviation of recessing amount of the non transferring face in a light beam transmission region is 0.8 mm or less. Further, the optical scanner and the image forming apparatus having the plastic optical element are also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a plastic optical element applied to an optical scanning system such as a laser-type digital copying machine, a laser printer, a facsimile machine, a plotter, and a complex machine thereof, and is particularly applicable to an optical apparatus such as a video camera. The present invention relates to a plastic optical element such as a thick and uneven plastic scanning lens having a high-precision optical mirror surface, an optical scanning apparatus including the plastic optical element, and an image forming apparatus.

  2. Description of the Related Art Conventionally, rectangular optical elements having laser beam imaging and various correction functions have been used in optical writing units (optical scanning devices) such as laser digital copying machines, printers, and facsimile machines.

  In recent years, these optical elements have been changed from glass to plastic in accordance with the demand for cost reduction of products. Further, in order to cover a plurality of functions with a minimum number of elements, the mirror surface shape is formed not only in a spherical surface but also in a complex aspherical shape. In the case of a lens, the lens thickness is often increased, and in many cases, the lens is designed to have an uneven thickness in which the lens thickness is not constant in the longitudinal direction.

  Even if a plastic molded product has a special shape, it can be mass-produced at low cost by inserting a resin base material into a mold cavity formed in the shape of the molded product or by injection-filling molten resin. it can. In the conventional plastic molding, in the process of cooling and solidifying the molten resin material in the cavity of the mold, the resin pressure and the resin temperature in the cavity are made uniform, and the plastic molded product is accurately molded into a desired shape. Desirable.

  However, for example, when the lens has an uneven shape, the volume shrinkage varies depending on the part having a different lens thickness, so that the shape accuracy is deteriorated, and sinking may occur where the lens thickness is thick.

In the manufacturing method by injection molding in which the molten resin is injected and filled into the mold cavity, when the injection pressure of the molten resin is increased and the injection filling amount is increased, there is a problem that the internal distortion of the plastic molded product increases. If the molded product is thick and uneven, the internal strain may increase and adversely affect optical performance and the like.
In other words, if the injection pressure is lowered to reduce the internal strain and the injection filling amount is reduced, sinking occurs in the thick-walled portion, etc., while if the injection pressure is increased and the injection filling amount is increased, the internal strain increases. There is a problem of becoming.

To solve this problem, by providing a concave shape (non-transfer surface) formed by incomplete transfer on a part other than the transfer surface, the internal pressure or internal distortion of the resin does not remain, resulting in a thick or uneven shape. However, a method capable of realizing the same production cost and shape accuracy as a thin molded product has been proposed (see Patent Document 1).
Furthermore, as a specific method for forming a concave shape (non-transfer surface) on a part other than the transfer surface, a part of the cavity piece that forms the surface including the concave portion (non-transfer surface) is provided slidably. A pair of molds in which at least one cavity is defined by the transfer surface and the cavity piece are heated and held below the softening temperature of the resin, and the molten resin heated above the softening temperature is injected and filled in the cavity Then, after the resin pressure is generated on the transfer surface to cause the resin to adhere to the transfer surface, the slidably provided cavity piece is removed from the resin when the resin is cooled to a softening temperature or lower. A method has been proposed in which a recess (non-transfer surface) is formed by sliding apart and forcibly defining a gap between the resin and the cavity piece (see Patent Documents 2 and 3).

JP 2000-84945 A JP 2000-141413 A Japanese Patent Laid-Open No. 11-028745

  However, there is a problem that the effect of reducing the internal strain by providing a concave shape (non-transfer surface) formed by incomplete transfer on a part of the surface other than the transfer surface varies depending on the concave amount of the concave shape (non-transfer surface). There is. This means that if the concave amount of the concave shape (non-transfer surface) differs from place to place, the degree of release of internal strain in the in-mold cooling process after resin filling varies from place to place. Causes internal strain deviations within the range.

  Further, the deviation of the concave amount also means that the rate of thermal shrinkage in the in-mold cooling process after resin filling varies from place to place, resulting in deterioration of the lens surface shape, particularly its low frequency component. These phenomena ultimately cause deterioration in optical performance, particularly beam spot diameter (field curvature). Further, the concave amount of the concave shape (non-transfer surface) is locally increased, resulting in an appearance defect that blocks light within the effective light range.

The influence on not only the absolute amount of internal distortion but also the optical performance, particularly the beam spot diameter, due to the deviation is a problem that has become conspicuous with the trend toward higher image quality of image forming apparatuses to which optical elements are applied.
As described above, there is a thick, uneven-thick plastic optical element having a high-precision optical mirror surface that can be manufactured without incurring cost increase or productivity reduction due to an increase in manufacturing process or mold design change. It has been demanded.

  Therefore, the present invention has been made in view of the above problems in the prior art, and even with thick and uneven shapes, the production cost is equivalent to the conventional one, the lens surface shape is excellent, and the internal strain is uniform. An object of the present invention is to provide a highly accurate plastic optical element having a highly reduced optical performance, an optical scanning device including the plastic optical element, and an image forming apparatus.

The present invention provided to solve the above problems is as follows.
[1] A plastic optical element provided in the imaging optical system of an optical scanning device having a light source means, an optical polarizer, and an imaging optical system that forms an image of a light beam deflected by the optical polarizer on a surface to be scanned In
It is formed by generating a resin pressure on the resin in the cavity of the mold having the transferred surface and transferring the transferred surface, and has two transfer surfaces which are a light incident surface and a light emitting surface,
A portion other than the transfer surface has a non-transfer surface formed by imperfect transfer of the cavity shape of the mold, and the deviation of the concave amount of the non-transfer surface in the light transmission region is 0.8 mm or less. A plastic optical element characterized by being.
[2] The plastic optical element according to [1], which is made of a transparent resin material.
[3] The plastic optical element according to any one of [1] to [2], which is an fθ lens.
[4] The plastic optical element according to any one of [1] to [3], wherein a rib is provided outside the transfer surface.
[5] An optical scanning device comprising the plastic optical element according to any one of [1] to [4].
[6] An image forming apparatus comprising the plastic optical element according to any one of [1] to [2].

  According to the present invention, even if the shape is thick or uneven, high-precision plastic optics having a high production performance equivalent to the conventional one, excellent lens surface shape, and high optical performance with uniform reduction of internal strain. It is possible to provide an element, an optical scanning device including the plastic optical element, and an image forming apparatus.

As an effect of the present invention, according to the first aspect of the present invention, an optical scanning device having a light source means, an optical polarizer, and an imaging optical system that forms an image of a light beam deflected by the optical polarizer on a surface to be scanned. In the plastic optical element provided in the imaging optical system of
It is formed by generating a resin pressure on the resin in the cavity of the mold having the transferred surface and transferring the transferred surface, and has two transfer surfaces which are a light incident surface and a light emitting surface,
A portion other than the transfer surface has a non-transfer surface formed by imperfect transfer of the cavity shape of the mold, and the deviation of the concave amount of the non-transfer surface in the light transmission region is 0.8 mm or less. Because it is a plastic optical element, while maintaining the effect of reducing internal strain, it reduces the internal strain deviation in the light transmission region (hereinafter also referred to as “light effective range”), and at the same time reduces the thermal shrinkage deviation. As a result, an optical element having improved lens surface shape, particularly the accuracy of its low frequency component, can be obtained. In addition, the concave amount of the non-transfer surface is locally increased, and it is possible to prevent the appearance defect that the light ray is blocked in the light ray effective range.
According to the invention of claim 2, since the plastic optical element according to claim 1 is made of a transparent resin material, a plastic optical element having better optical performance can be obtained.
According to the third aspect of the present invention, since the plastic optical element according to any one of the first to second aspects is an fθ lens, the optical performance, particularly the beam spot diameter (field curvature) is excellent. A plastic optical element is obtained.
According to the invention of claim 4, in the plastic optical element according to claim 1, since the rib is provided on the outer side of the transfer surface, it is possible to prevent the compressed gas from entering the transfer surface. Can do.
According to invention of Claim 5, since it is an optical scanning apparatus provided with the plastic optical element in any one of Claim 1 to 4, more highly accurate optical scanning is attained.
According to the invention of claim 6, since the image forming apparatus includes the plastic optical element according to any one of claims 1 to 4, it is possible to form an image with higher accuracy.

The configuration of an image recording apparatus according to an embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing an example of a plastic optical element of the present invention, which is an example of an fθ lens that is a component of an optical scanning device of a color laser beam printer.
The plastic optical element 10 has an uneven shape that becomes thinner from the center to both ends. By incompletely transferring the cavity shape of the mold to a portion other than the transfer surface 1 where resin internal pressure and internal distortion are likely to occur. The non-transfer surface 2 has a concave shape or a convex shape, and the deviation of the concave amount in the light transmission region of the non-transfer surface 2 is 0.8 mm or less. The transfer surface 1 is formed by generating a resin pressure on the resin in the cavity of the mold having the transfer surface and transferring the transfer surface. As the transfer surface, there are two transfer surfaces which are a light incident surface and an output surface.
Here, the “deviation of the concave amount” refers to the depth of the non-transfer surface formed by incomplete transfer from the virtual surface formed when the cavity shape of the mold is completely transferred. Depth is defined as a concave amount, and the deviation (difference) of the concave amount over the entire non-transfer surface is shown.

  Hereinafter, a method for forming a non-transfer surface (hereinafter sometimes referred to as “concave shape” or “concave portion”) in the production of a plastic optical element will be described with reference to FIGS.

FIG. 2 is a diagram showing a method of forming a non-transfer surface by applying compressed gas to a resin and performing incomplete transfer at the time of molding.
The cavity piece 31 that forms a surface including a non-transfer surface is provided with at least one or more vent holes 32 and at least one or more communication holes that communicate with the vent holes and apply compressed gas to the molded product. A compressed gas supply device provided outside the mold is connected to the mouth, and a pair of molds in which at least one cavity is defined by the transfer surface 33 and the cavity piece 34 are prepared. After being heated and held below the softening temperature, the cavity 35 is injected and filled with the molten resin 35 heated to the softening temperature or higher and then the resin pressure is generated on the transfer surface 33 to bring the resin into close contact with the transfer surface 33. When the molten resin 35 is cooled below the softening temperature, a compressed gas is applied from the vent 32 to the resin 35 in the cavity, and the resin 35 and the cavity piece 31 provided with the vent 32 are strongly pressed. Manner by defining the voids 36 to form a recess.

  By forcibly defining a gap between the resin and the cavity piece, the resin surface of the resin portion facing the gap becomes a free surface, which is easier to move than a surface in contact with another mold. As a result, the heat shrinkage caused by cooling is absorbed by the movement of the resin in this part, and the resin part facing the gap is preferentially attracted to relieve internal strain. Occurrence can be prevented.

FIG. 3 is a diagram showing a method of forming a non-transfer surface by incomplete transfer during molding by sliding a cavity piece that forms a surface including a non-transfer surface.
A cavity piece 37 forming a surface including a recess is slidably provided, and a pair of molds in which at least one cavity is defined by the transfer surface 33 and the cavity piece 34 are prepared. The resin 35 is heated and held below the softening temperature of the resin, and the molten resin 35 heated to the softening temperature or higher is injected and filled in the cavity, and then the resin pressure is generated on the transfer surface 33 to melt the molten resin 35. When the resin 35 is cooled to a softening temperature or lower after being closely attached to the resin, the cavity piece 37 slidably provided is slid away from the resin 35 to forcibly betWeen the resin and the cavity piece. A recess 36 is formed by defining a gap 36 in the surface.

  By forcibly defining a gap between the resin and the cavity piece, the resin surface of the resin portion facing the gap becomes a free surface, which is easier to move than a surface in contact with another mold. As a result, the heat shrinkage caused by cooling is absorbed by the movement of the resin in this part, and the resin part facing the gap is preferentially attracted so that internal strain can be reduced. Can be prevented.

FIG. 4 shows the relationship between the concave amount of the non-transfer surface and the internal strain (phase difference) when the non-transfer surface is formed by the method shown in FIGS. FIG. 4 shows the results when the molding conditions were fixed (not controlled), and a correlation was confirmed between the concave amount on the non-transfer surface and the internal strain (phase difference). In other words, it is possible to reduce internal strain by providing a concave shape (non-transfer surface) formed by incomplete transfer on a part of the surface other than the transfer surface, but the effect of reducing the concave shape (non-transfer surface) It can be seen that the value varies depending on the amount of depressions.
This means that if the concave amount of the concave shape (non-transfer surface) differs from place to place, the degree of release of internal strain in the in-mold cooling process after resin filling varies from place to place. It shows that the deviation of the internal strain within the range is generated. In addition, the deviation of the concave amount also means that the rate of heat shrinkage in the cooling process in the mold after resin filling varies from place to place, resulting in deterioration of the lens surface shape, particularly its low frequency components. Is shown.
The above phenomenon ultimately causes deterioration of optical performance, particularly beam spot diameter (field curvature), and in addition, the concave amount of the concave shape (non-transfer surface) increases locally, and the effective light range. There is also an appearance defect that blocks the light inside.

  From the processing results so far, when the allowable value of the deviation of the internal strain is derived from the optical performance, particularly the beam spot diameter (field curvature), it is about 300 nm. Thereby, an allowable value (about 0.8 mm) of the deviation of the concave amount of the concave shape (non-transfer surface) was obtained.

Therefore, by controlling the deviation of the concave amount of the concave shape (non-transfer surface) to 0.8 mm or less, while maintaining the effect of reducing the internal distortion, the deviation of the internal distortion within the light beam effective range is reduced. By reducing the deviation of thermal shrinkage, it is possible to improve the accuracy of the lens surface shape, particularly its low frequency component.
According to this, it is possible to improve the optical performance, particularly the beam spot diameter (field curvature) without changing the molding method.
Furthermore, the concave amount of the concave shape (non-transfer surface) is locally increased, so that it is possible to prevent an appearance defect such as blocking the light beam in the light beam effective range.

  Hereinafter, a method for controlling the deviation of the concave amount of the concave shape (non-transfer surface) to 0.8 mm or less will be described for each molding method.

<1> In the case of forming a concave surface by applying compressed gas In the method of applying a compressed gas to the resin shown in FIG. 2 and forming a concave portion by incomplete transfer at the time of molding, a method for realizing a concave amount deviation of 0.8 mm or less. Is a method of changing the air pressure, which is usually uniform, according to the pattern of the concave amount (depth). Examples of the concave amount (depth) pattern include a concave shape and a convex shape.

  When the pattern of the concave amount (depth) is concave, the deviation of the concave amount (depth) can be reduced by relatively reducing the air pressure, which is usually uniform, only in the vicinity of the center of the image height. When the concave pattern is convex, the air pressure, which is usually uniform, is increased relatively only near the center of the image height, or the mold (cavity piece) is vented only near the center of the image height. By providing the mouth, the deviation of the concave amount (depth) can be reduced.

  Specific methods for changing the air pressure include (1) optimization of the mold slit position, (2) change of the mold slit width, (3) division control of the air pressure, and (4) optimization of the air injection timing. Etc.

<2> In the case of forming a concave surface by sliding the cavity piece In the method of sliding a part of the cavity piece shown in FIG. 3 and forming the concave part by incomplete transfer at the time of molding, a deviation of the concave amount of 0.8 mm or less is realized. Examples of the method include (1) optimization of the shape of the cavity piece provided in a freely movable manner, and (2) optimization of the separation timing. An example of the sliding cavity piece is shown in FIG.

  In order to achieve the concave amount deviation of 0.8 mm or less by the two methods described above, it is necessary to simultaneously optimize the molding conditions including the resin filling amount.

  Since the plastic optical element of the present invention is molded from a transparent resin material, the optical performance, particularly the beam spot diameter (field curvature) accuracy can be improved without changing the molding method.

  Further, the plastic optical element of the present invention is molded from a transparent resin material and is an fθ lens, so that the optical performance, particularly the beam spot diameter (field curvature) can be improved without changing the molding method. It becomes.

  Further, as shown in FIG. 12, the plastic optical element of the present invention has a rib 14 on the transfer surface, so that it is possible to prevent the compressed gas from entering the transfer surface, and the optical performance, particularly the beam spot. It becomes possible to improve the diameter (field curvature).

  Hereinafter, an optical scanning device and an image forming apparatus equipped with the plastic optical element of the present invention will be described.

14A and 14B are explanatory views for explaining an optical scanning device 20 including the plastic optical element 10 according to an embodiment of the present invention, where FIG. 14A is a top view and FIG. 14B is a side view.
An optical scanning device 20 that scans beams emitted from a plurality of light sources and forms an image according to image information includes a light source 21 that emits a plurality of beams 51c according to image information, and a beam emitted from the light source 21. A deflecting means 22 for deflecting 51c and a plastic optical element 10 of the present invention in which a plurality of the deflecting means 22 are disposed facing each other at a position facing the deflecting means 22 are provided.
As shown in FIGS. 14A and 14B, a plurality of beams 51c emitted from a plurality of laser light sources of the light source 21 are deflected by the same deflecting means 22 (for example, a polygon mirror). Each plastic optical element 10 disposed at a position facing the deflecting means 22 corresponding to the laser light source is imaged on each photoconductor 51a and scanned on the photoconductor 51a, whereby image information is obtained. In response, an image is formed.

FIG. 15 is a schematic diagram illustrating a full-color printer as an embodiment of an image forming apparatus including the plastic optical element 10 and the optical scanning device 20 according to the present invention.
In FIG. 15, an image forming apparatus 50 that scans beams emitted from a plurality of light sources and forms an image according to image information includes an image forming unit 51 that forms an image, and a plurality of beams 51 c in the image forming unit 51. And an optical scanning device 20 for forming an image according to image information.
The image forming apparatus 50 includes an image forming unit 51 that forms a toner multicolor image on a recording medium (P), and a recording medium feeding that feeds the recording medium (P) in the direction of an arrow (B). Section (sheet feeding section) 52 and a sheet discharge tray (not shown) for discharging and storing the recording medium (P).
The recording medium feeding unit 52 includes a sheet feeding cassette 52a (52a-1 and 52a-2) at each stage, and another sheet feeding device can be installed as necessary.

The image forming unit 51 is detachably equipped with a yellow image forming unit 51 (Y), a magenta image forming unit 51 (M), a cyan image forming unit 51 (C), and a black image forming unit 51 (Bk). Thus, a toner recording image can be formed on the recording medium (P) by an electrophotographic image forming process.
Further, an intermediate transfer belt 51g is stretched around each support roller endlessly along a predetermined travel path, and is rotationally driven in the direction of arrow (C) by the intermediate transfer belt rotation driving roller 51g-1.
In each image forming unit of the image forming unit 51, a charging unit 51b for performing a charging process, an optical scanning device 20 for irradiating with a beam 51c, and a static formed by exposure around the drum-shaped photosensitive drum of the photosensitive member 51a. A developing unit 51d that visualizes and develops an electrostatic latent image and a photosensitive member cleaning unit 51f1 of a cleaning unit 51f that removes and collects toner remaining on the drum surface are disposed. As an image forming process, an intermediate transfer belt 51g is provided. However, a single color multicolor image is formed by one rotation.
In the image forming unit in which the image forming units 51 (Y), 51 (M), 51 (C), and 51 (Bk) are arranged, the toner of each color is developed by the developing unit 51 d, and the primary transfer roller of the transfer unit 51 e The image is transferred to the intermediate transfer belt 51g by 51e-1. The downstream side of the conveyance path in which the recording medium (P) that has received the secondary transfer of the superimposed toner recording image is passed by the secondary transfer roller 51e-2 of the transfer means 51e and conveyed in the direction of the arrow (D). In addition, a heating roller 51i-1 and a pressure roller 51i-2 are disposed as a fixing unit 51i for performing a heat fixing process on the recorded image of the toner. The recording medium (P) that has passed through the fixing means 51i is discharged to a discharge tray by a discharge roller 51j.

  The recording medium feeding unit 52 includes a bottom plate (not shown) in which an unused recording medium (P) is accommodated in a paper feeding cassette 52a (52a-1 and 52a-2) and is rotatably supported. Then, the recording sheet of the uppermost recording medium (P) is raised to a position where the pickup rollers 52c (52c-1 and 52c-2) can come into contact. By the rotation of the pickup roller 52c, the uppermost recording medium (P) is sent out from the paper feed cassette 52a and conveyed to the registration roller pair 51h. The registration roller pair 51h temporarily stops the conveyance of the recording medium (P), and the positional relationship between the recording image of the superimposed toner on the intermediate transfer belt 51g and the tip of the recording medium (P) coincides with a predetermined position. Thus, the timing is controlled so that the rotational drive is started.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

Examples of the present invention will be described below.
Example 1
The fθ lens, which is a plastic optical element shown in FIG. 5, was manufactured by the method shown in FIG. A wavy line indicates a light transmission region (light ray effective range) 1. A plastic optical element having a concave pattern (depth) on the non-transfer surface 2 was produced.
FIG. 6 shows the correlation between the lens height and the concave amount (depth). As the target, a value at which the deviation of the concave amount was 0.8 mm or less was set.
FIG. 7 shows a normal air pressure (indicated by STD) and an air pressure improved to satisfy the target (improvement plan).

  As shown in FIG. 6, with normal air pressure, the deviation of the concave amount (depth) due to the lens height is large, but as shown in the improvement plan of FIG. It can be seen that the amount deviation is reduced and a lens having a concave amount deviation of 0.8 mm or less is obtained.

(Example 2)
A plastic optical element having a concave pattern (depth) pattern on the non-transfer surface 2 was manufactured by the method shown in FIG.
FIG. 8 shows the correlation between the lens height and the concave amount (depth). As the target, a value at which the deviation of the concave amount was 0.8 mm or less was set.
FIG. 9 shows a normal air pressure (indicated by STD) and an air pressure improved so as to satisfy the target (improvement plan).

  As shown in FIG. 8, with normal air pressure, the deviation of the concave amount (depth) due to the lens height is large. However, as shown in the improvement plan of FIG. It can be seen that the amount deviation is reduced and a lens having a concave amount deviation of 0.8 mm or less is obtained.

(Example 3)
In the method shown in FIG. 2, a plastic optical element having a concave pattern (depth) pattern on the non-transfer surface 2 is manufactured by providing a vent hole only near the center of the image height.
FIG. 10 shows the correlation between the lens height and the concave amount (depth). As the target, a value at which the deviation of the concave amount was 0.8 mm or less was set.
FIG. 11 shows a normal air pressure (indicated by STD) and an air pressure improved to satisfy the target (improvement plan).

  As shown in FIG. 10, with a normal air pressure, the deviation of the concave amount (depth) due to the lens height is large. However, as shown in the improvement plan of FIG. It can be seen that the amount deviation is reduced and a lens having a concave amount deviation of 0.8 mm or less is obtained.

Example 4
In the method shown in FIG. 3, a lens having a concave deviation of 0.8 mm or less was obtained by performing optimization using the cavity piece having the shape shown in FIG.

It is a perspective view which shows the external appearance of an example of the plastic optical element of this invention. It is sectional drawing which shows an example of the metal mold | die which shape | molds the plastic optical element of this invention. It is sectional drawing which shows the other example of the metal mold | die which shape | molds the plastic optical element of this invention. It is a graph which shows the correlation of the concave amount of a plastic optical element, and an internal distortion. It is a side view of ftheta lens of an example of the plastic optical element of the present invention. 3 is a graph showing an air pressure pattern in Example 1. 6 is a graph showing an example of improving a concave amount (depth) in Example 1. 6 is a graph showing an air pressure pattern in Example 2. 6 is a graph showing an example of improving a concave amount (depth) in Example 2. 10 is a graph showing an air pressure pattern in Example 3. 10 is a graph showing an example of improving a concave amount (depth) in Example 3. It is a figure which shows an example of the f (theta) lens which has a rib on the outer side of a transfer surface. It is a figure which shows an example of the optimized cavity piece. It is a figure which shows the structure in one Embodiment of the optical scanning device based on this invention, (A) is a top view, (B) is a side view. 1 is a schematic diagram illustrating a configuration in an embodiment of an image recording apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transfer surface 2 Non-transfer surface 10 Plastic optical element 14 Rib 15 Sliding cavity piece 20 Optical scanning device 21 Light source 22 Deflection means 23 Housing 31 Ventilation cavity piece 32 Venting port 33 Transfer surface 34 Cavity piece 35 Molten resin 36 Gap 37 Sliding Cavity piece 50 Image forming apparatus 51 Image forming unit 51 (Y) Yellow image forming unit 51 (M) Magenta image forming unit 51 (C) Cyan image forming unit 51 (Bk) Black image forming unit 51 a Photosensitive member 51 a-1 Surface 51 b Charging means 51c Beam 51d Developing means 51e-1 Primary transfer roller (transfer means)
51e-2 secondary transfer roller (transfer means)
51f Cleaning means 51g Intermediate transfer belt 51g-1 Intermediate transfer belt rotation drive roller 51h Registration roller pair 51i-1 Heating roller (fixing means)
51i-2 Pressure roller (fixing means)
51j Paper discharge roller 52 Paper feed unit (recording medium feed unit)
52a Paper cassette 52c Pickup roller

Claims (6)

In a plastic optical element provided in the imaging optical system of an optical scanning device having a light source means, an optical polarizer, and an imaging optical system that forms an image of a light beam deflected by the optical polarizer on a surface to be scanned,
It is formed by generating a resin pressure on the resin in the cavity of the mold having the transferred surface and transferring the transferred surface, and has two transfer surfaces which are a light incident surface and a light emitting surface,
A portion other than the transfer surface has a non-transfer surface formed by imperfect transfer of the cavity shape of the mold, and the deviation of the concave amount of the non-transfer surface in the light transmission region is 0.8 mm or less. A plastic optical element characterized by being.   The plastic optical element according to claim 1, wherein the plastic optical element is made of a transparent resin material.   3. The plastic optical element according to claim 1, wherein the plastic optical element is an fθ lens.   4. The plastic optical element according to claim 1, further comprising a rib on the outer side of the transfer surface.   An optical scanning device comprising the plastic optical element according to claim 1.   An image forming apparatus comprising the plastic optical element according to claim 1.