JP2004117592A - Optical element and its molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce curvature of an optical element constituting a scanning optical system during molding. <P>SOLUTION: Disclosed is a method for molding optical elements 4 and 5 which molds a plurality of optical elements at the same time by injecting resin in a plurality of cavities provided to a metal mold; and the temperature control temperature t1 of a metallic mold part between mutually adjacent cavities 72 and 73 (or 74 and 75) among the plurality of cavities is set lower than the temperature control temperature t2 of a metallic mold part outside the respective cavities. Thus, curvature of an optical element constituting a scanning optical system during can be reduced. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for molding a resin optical element.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a scanning optical device used for a laser beam printer (LBP), a digital copier, or the like, a light beam that is light-modulated from a light source according to an image signal and emitted is periodically emitted by an optical deflector such as a rotary polygon mirror. The beam is converged into a spot on an image forming surface on a photosensitive drum by an image forming optical system having f-seater characteristics. The spot on the image forming surface forms an electrostatic latent image with the main scanning by the optical deflector and the sub-scanning by the rotation of the photosensitive drum, and performs image recording.
[0003]
FIG. 1 shows a scanning optical device. A divergent light beam emitted from a light source 101 is converted into a substantially parallel light beam by a collimator lens 102, the light amount of the light beam is adjusted by a stop 103, and a cylindrical light beam having a refractive power only in the sub-scanning direction. The light enters the lens 104.
[0004]
The parallel light beam incident on the cylindrical lens 104 is emitted as a light beam converging only in the sub-scanning cross section in the state of substantially parallel light in the main scanning cross section, and is formed as a line image on the reflection surface 105a of the rotary polygon mirror 105. Image.
[0005]
The light beam deflected and scanned by the rotation of the rotary polygon mirror 105 forms an image on the image forming surface of the photosensitive drum 120 via an f-theta lens 106 which is an imaging optical element having f-theta characteristics. The point image (spot) formed on the image forming surface scans the photosensitive drum 120 in the direction of arrow B by rotating the rotary polygon mirror 105 in the direction of arrow A. Image recording is performed on the photosensitive drum 120, which is a recording medium, along with such main scanning and sub-scanning due to the rotation of the photosensitive drum 120 around its rotation axis.
[0006]
FIG. 2 illustrates a color image forming apparatus that forms a color image by recording image information for each color on a plurality of photosensitive drums using a plurality of scanning optical devices similar to the above.
[0007]
This apparatus has four scanning optical devices (scanner units) 111 to 114, four photosensitive drums 121 to 124, developing devices 131 to 134, respectively, and a transport belt 141.
[0008]
The four scanning optical devices 111 to 114 correspond to the respective colors of C (cyan), M (magenta), Y (yellow), and B (black), and have image signals on the photosensitive drums 121, 122, 123, and 124, respectively. Is recorded, developed by the developing devices 131 to 134, and transferred to recording paper or the like on the transport belt 141, thereby printing a color image at high speed.
[0009]
In such a color image forming apparatus, since an image is formed by superposing a plurality of scanning lines, it is particularly important to reduce the scanning line deviation (registration deviation) between the colors.
[0010]
The scanning line deviation between the respective colors also occurs due to an error in the shape of the first optical element 106a and the second optical element 106b of the f-theta lens 106. Have a big impact.
[0011]
As a method of adjusting (correcting) this scanning line shift, Japanese Patent Application Laid-Open No. 2000-275559 discloses a deflection scanning means 1, 2, 3 for deflecting the light beam shown in FIG. An imaging optical system including a first f-theta lens 4 and a second f-theta lens 5 for forming an image on an imaging surface, a housing 10 supporting the imaging optical system, and the second f-theta A pivot bearing 20 that pivotally supports the lens in an arbitrary direction on the housing, and a fusing unit for fusing the second f-theta lens to the pivot bearing 20 or the housing 11. By having the center portion or one end of the second f-theta lens pivotally supported in any direction by the pivot bearing 20, the bending or inclination of the scanning line when the scanning light scans the image forming surface is obtained. Second f-theta to detect and eliminate these The rotational position and the inclination angle of the lens, seeking the data or the like that has been examined in advance, the second f-theta lens is pivoted on a pivot bearing, except for the scan line shift of the image plane. In this manner, after removing the scanning line shift that causes color shift in the case of color printing, the second f-theta lens is fused and fixed to the pivot bearing or the housing using a low-temperature molten metal or the like. I do. With this configuration, the second f-theta lens is pivoted in an arbitrary direction on the pivot bearing that supports the second f-theta lens, and is adjusted to a posture that can eliminate the inclination and the bending of the scanning line. Since it is only fixed with a low-temperature molten metal or the like, the number of parts to be assembled is greatly reduced as compared with the case where a complicated pivoting mechanism is provided in each of the two axes to correct the scanning line deviation. Is also simplified, and by greatly simplifying a mechanism for correcting color misregistration in performing color printing or the like, a color image forming apparatus with high image quality and low manufacturing cost can be realized.
[0012]
[Problems to be solved by the invention]
However, according to the above-mentioned prior art, there is a limit to the amount by which the inclination and the bend of the scanning line can be adjusted. In addition, as shown in FIG. When two optical elements are molded at the same time, the mold of FIG. 4 is temperature-controlled as a whole and is maintained at about 70 ° C. to 150 ° C., depending on the physical properties of the resin to be molded. As described above, water pipes 82, 83, 84, and 85 through which temperature-regulated water flows are provided for each cavity. In such a configuration, it was found that the adjacent cavities 72, 73 and 74, 75 of the optical element molded by the mold of FIG. 4 were deformed in the opposite direction, resulting in the deformation as shown in FIG. Even if four optical elements having such a deformation are combined, there is a problem that the dispersion of the scanning lines is large due to the variation in the shape of the optical elements, and the color shift cannot be adjusted completely.
[0013]
For example, in the above conventional example, when the long optical element 5 of FIG. 3 is molded using the four-cavity mold of FIG. 4, the long optical element 5 taken out of the cavities 72, 73, 74, and 75 is used. The deformation of the optical element 5 causes deformation in three directions of the main scanning direction, the sub-scanning direction, and the traveling direction of the laser beam in FIG. In particular, when there is a large amount of warpage in the sub-scanning direction as shown in FIG. 7, the point image formed on the image forming surface of the photosensitive drum 11 in FIG. 6 is scanned while being curved as shown by a broken line D2. Causes a color shift due to the scan line shift.
[0014]
However, in the method of electrically adjusting the scanning line deviation as in the conventional example and the embodiment of JP-A-2000-275559, and in the color image forming apparatus using a plurality of scanning optical devices, the scanning line deviation due to each scanning optical device is reduced. In the method of performing the adjustment by changing the position of the optical element arranged in the imaging optical system of each scanning optical device, there is a problem that the adjustable range is limited, the mechanism is complicated, and the cost is high. Was.
[0015]
In the above-described four-cavity mold, the temperature of the mold member near the water pipe is the same as the temperature of the mold member between the adjacent cavities, and the temperature outside the mold is room temperature. Therefore, the temperature between the cavity and the surface of the mold is a temperature adjustment set temperature in the vicinity of the cavity, but the mold temperature decreases as approaching the mold surface. As a result of searching for the cause of the deformation of the optical element using the mold, it was found that the cooling rate of the resin in the cavity was affected by the decrease in the temperature of the outside part of the mold of the temperature control pipe. Since the temperature of the outside part of the mold of the temperature control water pipe is lower than the temperature between the adjacent cavities, the heat flux on the outer surface of the mold near the cavity is smaller than the heat flux on the side of the adjacent cavity. As a result, the solidification speed of the surface of the molded product outside the mold is faster than the solidification speed of the molded product surface on the side where the cavity is adjacent. As a result, the density of adjacent cavities, where solidification is relatively slow, becomes low, and as shown in FIG. 8, warping occurs in a direction in which the center is deformed outside the mold with respect to the longitudinal end.
[0016]
Therefore, the present invention has been made in view of the above-mentioned problem, and an object of the present invention is to reduce a warp of an optical element constituting a scanning optical system when the optical element is formed.
[0017]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, an optical element according to the present invention is a long optical element formed by injecting a resin into a cavity provided in a mold and molding the resin. The amount of warpage A in a plane parallel to the parting surface is characterized by A ≦ L / 5000 with respect to the length L of the optically effective portion in the longitudinal direction of the optical element.
[0018]
Further, the method for molding an optical element according to the present invention is a method for molding an optical element in which a plurality of optical elements are simultaneously molded by injecting a resin into a plurality of cavities provided in a mold. The temperature control temperature t1 of the mold portion between the adjacent cavities is set lower than the temperature control temperature t2 of the mold portion outside the respective cavities.
[0019]
Further, in the method for molding an optical element according to the present invention, a difference between the controlled temperature t1 and the controlled temperature t2 is set to 1 ° C. or more.
[0020]
Further, an optical element of the present invention is characterized by being formed by the above-described method for forming an optical element.
[0021]
Further, in the optical element according to the present invention, the optical element is an f-theta lens.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0023]
(1st Embodiment)
FIG. 4 is a view showing a schematic configuration of a mold for molding an optical element according to the first embodiment. Cavities 72, 73, 74, and 75, which are cavities of a four-cavity mold, are formed in an integral mold member. Have been. The mold member 76 in FIG. 4 is a member constituting a fixed-side mold. Although not shown, the mold member 76 is integrated with a movable-side mold having a cavity runner opposed thereto to form a cavity runner sprue. .
[0024]
FIG. 9 is a diagram showing the arrangement of water tubes for temperature control with water in the mold member 76 shown in FIG. A water pipe 91a is arranged at a portion of the mold member 76 between the cavity 72 and the outside air, supplies temperature-regulated water from the upper side in the figure of the mold, makes a U-turn near the gate of the cavity 72, and again draws the figure of the mold. It is discharged from the upper middle and returns to the temperature control device to control the temperature of the mold member 76.
[0025]
A water pipe 91b is arranged between the cavities 72 of the mold member 76, and supplies temperature-regulated water from the upper side in the drawing of the mold, makes a U-turn near the gate of the cavity 72, and again draws the drawing of the mold. It is discharged from the upper middle and returns to the temperature control device to control the temperature of the mold member 76.
[0026]
Similar water pipes are also arranged in the cavities 73, 74, and 75 to control the temperature.
[0027]
Here, 91b, 92b, 93b, and 94b are connected to a temperature controller arranged outside the mold, and the temperature is controlled at the setting of t1. At the same time, 91a, 92a, 93a, and 94a are also connected to a temperature controller arranged outside the mold and are temperature-controlled at the setting of t2. The relationship with the temperature-control setting temperature t2 of the mold member near the water pipe is represented by t1. The temperature can be individually adjusted to <t2.
[0028]
Although not shown, the same water pipe arrangement is used in the movable mold.
[0029]
In the molding state, the temperature of the mold is previously adjusted at the setting of t2 = 118 ° C., and at the same time, the temperature is adjusted at the setting of t1 = 115 ° C. The resin plasticized by the plasticizing device of the injection molding machine is injected from the sprue 70 into a mold, filled in the runner 71 and then filled in the cavity. In the cavity, a mirror piece having a shape substantially equal to the shape of the optical element having a desired shape and having such a shape as to become the optical element having the desired shape when cooled to room temperature after removal of the molded product is provided on the movable mold and the fixed side. It is placed in a mold, applies a holding pressure enough to compensate for the shrinkage of the resin in the mold, cools down to a temperature close to the mold temperature over a certain cooling time, and is taken out of the mold.
[0030]
At this time, the heat flux on the outer surface of the mold near the cavity and the heat flux on the surface on the side of the adjacent cavity become substantially equal, and as a result, the solidification rate of the surface of the molded product on the side where the cavity is adjacent Thus, the solidification rate of the surface of the molded product outside the mold becomes equal. This prevents the optical element from warping. Specifically, the amount of warpage A in a plane parallel to the parting surface is A ≦ L / 5000 with respect to the optically effective portion length L of the optical element in the main scanning direction.
[0031]
In an optical system using such an optical element, a plurality of scanning optical devices are used as shown in FIG. 2 to record image information for each color on a plurality of photosensitive drums and form a color image. In the apparatus, the point images formed on the image forming surface of the photosensitive drum 11 substantially coincide with each other, and there is no occurrence of color shift due to the curvature of the scanning line.
[0032]
(Second embodiment)
FIG. 10 is a view showing a schematic configuration of a mold for molding an optical element according to the second embodiment. A four-cavity is formed in a mold member 76, and a cavity is provided between cavities 72 and 74 and the outside air. A water tube 95b is provided between the adjacent cavities 73 and 75, and the temperature of the mold member 76 near the cavities 72 and 74 is controlled by the water tubes 95a and 95b. The cavities 73 and 75 are similarly temperature-controlled by the water pipes 96a and 96b.
[0033]
(Third embodiment)
FIG. 11 is a view showing a schematic configuration of a mold for molding an optical element according to the third embodiment. A six-cavity is formed in a mold member 76, and a cavity is formed between the cavities 172 and 175 and the outside air. A water pipe 97b is provided between the adjacent cavities 173 and 176, and the temperature of the mold members near the cavities 172 and 175 is controlled by the water pipes 97a and 97b. The cavities 174 and 177 are similarly temperature-controlled by the water pipes 99a and 99b. The temperature of the center cavities 173 and 176 is controlled by the water pipes 98a and 98b, but unlike the left and right cavities, there is no need to make a difference in the temperature control temperature setting.
[0034]
As described above, the present invention can be applied to the case where the number of pieces is increased to four or more. For example, the water pipes 95b and 96b in FIG. 10 may be provided as one water pipe without being separately arranged. Depending on the necessity of manufacturing a mold, even if the mold member 76 is divided into individual cavities without being integrated, the same effect can be obtained as the effect of the present invention.
[0035]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the warpage during molding of the optical element constituting the scanning optical system.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a scanning optical device.
FIG. 2 is a diagram illustrating the entire image forming apparatus.
FIG. 3 is a diagram illustrating a direction of an optical element and a traveling direction of a laser beam.
FIG. 4 is a diagram illustrating a schematic configuration of a fixed mold of a four-cavity mold.
FIG. 5 is a diagram illustrating a schematic configuration of a fixed side mold of a conventional four-cavity mold.
FIG. 6 is a diagram illustrating a conventional scanning optical device.
FIG. 7 is a diagram schematically illustrating a modification of a conventional optical element.
FIG. 8 is a view for explaining an outline of deformation of an optical element molded by a conventional four-cavity die. FIG. 9 shows a schematic configuration of a fixed-side mold of the four-cavity die according to the first embodiment. FIG.
FIG. 10 is a diagram illustrating a schematic configuration of a fixed mold of a four-cavity mold according to a second embodiment.
FIG. 11 is a diagram illustrating a schematic configuration of a fixed mold of a six-cavity mold according to a third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser unit 2 Cylindrical lens 3 Rotating polygon mirror 4-5 Optical element (f-theta lens)
10. Main body chassis (housing)
Reference Signs List 11 photosensitive drum 20 pivot bearing 70 sprue 71 runner 72-75 cavity 82-85 water pipe 91-99 water pipe 101 light source 102 collimator lens 103 aperture 104 cylindrical lens 105 rotating polygon mirror 106 f-theta lens 111-114 scanning optical device 120-124 photosensitive Drums 131 to 134 Developing device 141 Conveyor belt

Claims (5)

A long optical element molded by injecting a resin into a cavity provided in a mold,
An optical element, wherein an amount of warpage A in a plane parallel to a parting surface of the mold is A ≦ L / 5000 with respect to a length L of an optical effective portion in a longitudinal direction of the optical element. An optical element molding method for simultaneously molding a plurality of optical elements by injecting a resin into a plurality of cavities provided in a mold,
An optical element, wherein a temperature control temperature t1 of a mold portion between adjacent cavities of the plurality of cavities is set lower than a temperature control temperature t2 of a mold portion outside each of the cavities. Molding method. 3. The method according to claim 2, wherein a difference between the temperature control temperature t1 and the temperature control temperature t2 is set to 1 ° C. or more. An optical element formed by the method for forming an optical element according to claim 2. The optical element according to claim 4, wherein the optical element is an f-theta lens.

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