JP4267517B2 - Plastic optical element, molding method thereof, and optical scanning unit - Google Patents

Description

  The present invention relates to a plastic optical element molding method and an optical element that are applied to laser-type optical scanning systems such as digital copying machines, facsimiles, and printers, and optical equipment such as video cameras.

  In recent years, in an optical scanning system such as a laser type digital copying machine, a facsimile machine, and a laser type printer, each beam emitted from a plurality of laser beams is exposed to light via an image forming unit such as a deflecting unit and a plastic optical element. There is an optical scanning unit of a multicolor image forming apparatus that guides on a body and forms an image on the photosensitive body according to image information. In recent years, in order to cope with higher speed and higher image quality of multi-color image forming apparatuses, four photoconductive drums are arranged in the transport direction of output paper, and simultaneously exposed with beams corresponding to the photoconductive drums. A system in which images developed by developing devices of different colors (yellow, magenta, cyan, black) are sequentially transferred and superimposed to form a color image has been put into practical use.

  In order to reduce the birefringence of the plastic optical element and reduce the beam spot diameter to a desired size for the purpose of improving the image quality, the present applicant has previously proposed Japanese Patent Application Laid-Open No. 2000-176944. In Japanese Patent Laid-Open No. 2000-176944, at least one nest forming a non-transfer surface of a plastic optical element slides during molding, forming a gap between the plastic optical element and the nest, and the gap Disclosed a molding method for inducing sink marks. In this molding method, since the occurrence of internal strain accompanying cooling is suppressed, a great effect is produced in reducing birefringence. However, the gap exists between the sinking surface and the sliding insert, and the surface opposite the sinking surface is in contact with the metal insert. It takes a longer time to cool to the heat deformation temperature or less than the opposite side. For this reason, there is a problem that the plastic optical element is warped to the sink surface as a whole.

  Furthermore, the surface having the optical function of the plastic optical element used in the optical scanning unit is designed to be asymmetric with respect to the optical axis in order to improve the field curvature of the beam diameter for the purpose of improving the image quality. A lot is happening. Further, when attaching the plastic optical element to the holding member, there is a method of providing a reference on one side of the plastic optical element and abutting the reference to the attachment member in order to improve the attachment accuracy. For this reason, the outer shape of the plastic optical element is increasingly asymmetric with respect to the optical axis due to its accuracy and ease of assembly. However, when the plastic optical element has an asymmetric shape and the plastic optical element is installed in the optical scanning unit with the direction (direction) indicated by the asymmetric shape being the same direction for all colors, the tendency of the warping direction is different. There is a problem that the color shift becomes larger.

As a means for correcting the warp of the plastic optical element, for example, Japanese Patent Application Laid-Open No. 2002-182145 applies an external force in the sub-scanning direction of the plastic optical element to forcibly cause the bending caused by molding. A method of adjusting to the above has been proposed.
JP 2000-176944 A JP 2002-182145 A

  However, in the method of Patent Document 2, if the plastic optical element has the asymmetric shape, the adjustment direction (orientation) is not constant if the asymmetric shape is installed in a certain direction (orientation). And costly. Furthermore, when plastic optical elements are used by being stacked in multiple layers by bonding or the like, if the warp directions of the plastic optical elements forming the multilayer are different from each other, it is difficult to ensure the bonding accuracy.

  SUMMARY OF THE INVENTION The present invention solves the above-described problems, and an object thereof is to provide a plastic optical element that can suppress color misregistration at low cost and can secure adhesive strength, a molding method thereof, and an optical scanning unit. It is said.

  The invention according to claim 1 includes at least one transfer surface having an asymmetric shape with respect to the optical axis, and at least one sink portion selectively guided to a non-transfer surface other than the transfer surface having the asymmetric shape. In a plastic optical element molding method, in which a plurality of optical elements having a plurality of cavities are simultaneously molded by a single mold having a plurality of cavities, the direction of the asymmetric shape of the transfer surface and the position of the selectively induced sink portion The plastic optical element molding method is characterized in that the relationship is uniformly molded among the plurality of cavities.

  The invention according to claim 2 is the plastic optical element molding method according to claim 1, wherein the transfer surface having the asymmetric shape has an optical function.

  The invention according to claim 3 is a mold heating and holding step for heating and holding a pair of molds provided with a plurality of cavities defined by the transfer surface and the non-transfer surface, below the softening temperature of the resin, A molten resin filling step of injecting and filling a molten resin heated to a softening temperature or higher in the cavity; a resin pressing step of generating a resin pressure on the transfer surface to bring the resin into close contact with the transfer surface; and the resin When cooling below the softening temperature, a compressed air is applied to the resin in the cavity from the vent on the non-transfer surface, and a void defining step is performed to define a void between the resin and the non-transfer surface. The method for molding a plastic optical element according to claim 1, wherein the plastic optical element is molded.

  The invention according to claim 4 is a mold heating and holding step for heating and holding a pair of molds provided with a plurality of cavities defined by the transfer surface and the non-transfer surface, below the softening temperature of the resin; A molten resin filling step of injecting and filling a molten resin heated above the softening temperature into the cavity, and a nest that forms the non-transfer surface is separated from the resin when the molten resin is cooled below the softening temperature. 3. The method for molding a plastic optical element according to claim 1, further comprising a gap defining step of sliding a gap between the molten resin and the insert to define a gap. 4.

  According to a fifth aspect of the present invention, in the nest that forms the transfer surface having the asymmetric shape, the direction indicated by the asymmetric shape can be determined outside the range of the portion that forms the optical function portion of the transfer surface. The method for molding a plastic optical element according to claim 1 or 2, wherein a standard is provided.

  The invention described in claim 6 is characterized in that the transfer surface having the asymmetric shape is provided with a reference capable of determining the direction indicated by the asymmetric shape outside the range of the portion having the optical function of the transfer surface. The method for molding a plastic optical element according to claim 1 or 2.

  The invention according to claim 7 is characterized in that the positional relationship between the direction indicated by the asymmetric shape, the selectively induced sink portion, and the gate is uniform among all the cavities. Item 7. A method for molding a plastic optical element according to any one of Items 1 to 6.

  The invention according to claim 8 is a plastic optical element molded by any one of the molding methods 1 to 7 described above.

  In the ninth aspect of the present invention, a plurality of the plastic optical elements according to the eighth aspect are prepared, and a surface having a sink portion in which the plurality of plastic optical elements are selectively guided and a surface opposed thereto are bonded to each other. It is a plastic optical element characterized in that it is fixed by and laminated in multiple layers.

  According to a tenth aspect of the present invention, there is provided at least one transfer surface having an asymmetric shape with respect to the optical axis, and at least one sink portion selectively guided to a non-transfer surface other than the transfer surface having the asymmetric shape. A plastic optical element having a laminated structure in which a positional relationship between a direction of the asymmetric shape of the transfer surface having the asymmetric shape and a selectively induced sink portion is laminated. It is.

  According to an eleventh aspect of the present invention, in the plastic optical element according to the eighth aspect, the positional relationship between the direction of the asymmetric shape of the transfer surface having the asymmetric shape and the selectively induced sink portion is aligned. The optical scanning unit is arranged.

  According to the first aspect of the present invention, the plastic optical element is formed by molding so that the positional relationship between the direction (direction) indicated by the asymmetric shape with respect to the optical axis and the sink portion of the non-transfer surface is always constant. The direction (orientation) of the warp generated in can be made constant. As a result, when the plastic optical element is incorporated in a writing unit, taking into account the direction (orientation) indicated by the asymmetric shape, the warping direction is unified, preventing color misregistration due to the difference in the warping direction, and improving the mounting accuracy by ensuring adhesive strength. Etc. are obtained.

  Further, according to the second aspect of the invention, the molding is performed so that the positional relationship between the direction (direction) of the asymmetric shape having an optical function and the sink portion of the non-transfer surface having the sink portion is always constant. In addition, the positional relationship between the warp direction generated in the plastic optical element and the direction (orientation) indicated by the asymmetric shape can be made constant. Accordingly, when the plastic optical element is incorporated in a writing unit or the like in consideration of the direction (direction) indicated by the asymmetric shape, the warping direction is unified, and it is effective in preventing color misregistration due to the difference in the warping direction.

  According to the third aspect of the present invention, it is possible to manufacture a plastic optical element having low distortion and ensuring the shape accuracy of the transfer surface.

  According to the fourth aspect of the present invention, it is possible to manufacture a plastic optical element having low distortion and ensuring the shape accuracy of the transfer surface.

  According to the fifth aspect of the present invention, it is possible to confirm the reference when installing the nest having an asymmetric shape in the mold in order to form the plastic optical element. The risk of misdirection (direction) can be reduced.

  According to the sixth aspect of the present invention, the reference is confirmed when a nest having an asymmetric shape is incorporated in the mold to form the plastic optical element or when the plastic optical element is installed in the optical scanning unit. Therefore, it is possible to reduce the risk of incorrect mounting direction (orientation).

  According to the seventh aspect of the present invention, since the change in molding characteristics such as temperature deviation and pressure deviation occurring near the gate side and the final filling position is always constant with the asymmetric shape, the plastic optical element has The characteristics can be made uniform between cavities, and a more accurate plastic optical element can be provided.

  Further, according to the eighth aspect of the present invention, since the plastic optical element is molded by any one of the first to seventh methods, the warping direction of the lens and the direction (orientation) indicated by the asymmetric shape are determined. It is possible to unify.

  According to the ninth aspect of the present invention, since the plastic optical element according to the eighth aspect is formed into a multilayer by adhering the selectively induced sink surface and the surface opposite thereto, the asymmetric shape is shown. The positional relationship between the direction (orientation) and the warp of the plastic optical element is unified, and high-precision writing with suppressed color misregistration becomes possible.

  According to the invention described in claim 10, the positional relationship between the direction (orientation) indicated by the asymmetric shape of the transfer surface having an asymmetric shape and the selectively induced sink portion is unified and laminated. Therefore, highly accurate writing with suppressed color misregistration is possible.

  According to the eleventh aspect of the present invention, the plastic optical element according to the eighth aspect further includes a sink portion selectively guided with a direction (orientation) indicated by the asymmetric shape of the transfer surface having the asymmetric shape. Therefore, the warp direction that occurs in the vertical direction of the non-transfer surface that forms the sink part and the direction indicated by the asymmetric shape with respect to the optical axis of the plastic optical element are always placed in the same direction. A scanning unit can be obtained, and color misregistration can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining the direction (orientation) indicated by the asymmetric shape with respect to the optical axis. In FIG. 1, the vertical axis represents the distance from the apex of the plastic optical element to the element surface in the optical axis direction, and the horizontal axis represents the distance from the apex of the plastic optical element. In FIG. 1, symbol OA indicates the optical axis, and symbol A indicates the direction (orientation) indicated by the asymmetric shape.

  As shown in FIG. 1, the direction (orientation) A indicated by the asymmetric shape is a portion at an equal distance from the optical axis with respect to the transfer surface, and the transfer surface in the optical axis direction from the apex of the transfer surface through which the optical axis passes. Is a transfer surface (distance L1> distance L2 in FIG. 1) where the distance to the surface is different on both sides of the optical axis.

  That is, the direction A indicated by the asymmetric shape of the transfer surface is, for example, as shown in FIG. 1, from the apex of the plastic optical element that is a long lens with respect to a portion that is equidistant from the center (optical axis). The distances L1 and L2 to the element surface in the optical axis direction are different (L1> L2), and in the case of FIG. 1, as indicated by the arrow A, the direction from the distance L1 side to the distance L2 side. is there. In addition, the direction A indicated by the asymmetric shape of the transfer surface may be the direction from the distance L2 side to the distance L1 side in the direction opposite to the arrow A in FIG.

  FIG. 2 is a diagram showing the relationship between the cavity and the amount of warping of the plastic optical element. In FIG. 2, the vertical axis represents the amount of displacement from the center reference of the plastic optical element, and the horizontal axis represents the distance from the center reference of the plastic optical element. In FIG. 2, the cavity 1-1 is the first cavity of the first sample, the cavity 1-2 is the first cavity of the second sample, and the cavity 2-1 is the second cavity of the first sample. Cavity 2-2 indicates a second cavity of the second sample, respectively. In FIG. 2, an arrow B indicates a warping direction.

  As shown in FIG. 2, the plastic optical elements formed by the cavities 1-1 to 2-2 are all in the direction (direction) of the non-transfer surface 2 (hereinafter referred to as the sink surface 2) from which the sink portion 21 is guided. There is a tendency to warp (hereinafter, the direction (direction) of warping occurring in a molded product is referred to as “warping direction B”).

  FIG. 3 is a view showing an optical element molded body (or cavity) immediately after molding, which is molded by the plastic optical element molding method according to one embodiment of the present invention. As shown in FIG. 3, in this embodiment, a pair of plastic optical elements 1 which are optical element molded bodies immediately after molding by two cavities are connected by a gate 3. In the plastic optical element 1 on the left side of FIG. 3, the direction A indicated by the asymmetric shape is upward, sink marks are induced on the right side, and the warp direction B is from left to right. Also, the plastic optical element 1 on the right side of FIG. 3 has an asymmetric shape direction A downward, sink marks are induced on the left side, and a warp direction B is from right to left.

  If the positional relationship between the direction A indicated by the asymmetric shape of the transfer surface and the selectively induced sink portion 21 is the same, the direction A indicated by the asymmetric shape of the transfer surface and the direction of the warp caused by the sink portion 21 (FIG. 3). The direction of arrow B in the middle) is the same.

  FIG. 4 is a view showing a plastic optical element according to an embodiment of the present invention. As shown in FIG. 4, a transfer surface having an optical functional surface 11, a transfer surface having an optical functional surface 12 facing the optical functional surface 11, and a non-transfer surface having a sink surface 21 are provided. . As described above, the transfer surface having the optical functional surface 11 is formed in an asymmetric shape with respect to the optical axis, and has a direction A indicated by the asymmetric shape. Further, it has a warping direction B toward the sink part 21.

  The cavity surface forming a cavity of a predetermined capacity has at least one transfer surface having an asymmetric shape with respect to the optical axis (FIG. 1), and the transfer surface serving as an optical surface is transferred by the resin pressure generated in the cavity. An injection mold is filled with molten resin from the gate 3 (see FIG. 3), and sink marks are selectively induced on a transfer surface other than the transfer surface serving as the optical surface during resin cooling (for example, FIG. 6 described later). Alternatively, when sinking is selectively induced as shown in FIG. 7 and the plastic optical element 1 (see FIG. 4) is manufactured by taking out the molded product from the mold after cooling the resin and naturally cooling the molded product, As shown in FIG. 2, there is a tendency to warp in a warping direction B which is the direction (direction) of the transfer surface 2 (hereinafter referred to as the sinking surface 2) on which sink marks are entirely induced.

  When a plurality of molds are simultaneously formed by using this manufacturing method, variation occurs between cavities in the direction A and the warp direction B indicated by the asymmetric shape. Therefore, when the positional relationship between the direction A and the warp direction B indicated by the asymmetric shape is not constant between the cavities, the direction A indicated by the asymmetric shape is unified and the plastic optical element 1 is installed on a holding member (not shown). However, the warping direction of the plastic optical element 1 is different.

  Therefore, in the present invention, as shown in FIG. 3, the direction A indicated by the asymmetric shape is arranged so that the warping direction B is always constant between the cavities. That is, the direction A and the warp direction B indicated by the asymmetric shape are arranged so that the relationship between the direction A and the warp direction B indicated by the asymmetric shape is constant.

  FIG. 4 shows an example of the plastic optical element 1 molded by the molding method, and the positional relationship between the direction A indicated by the asymmetric shape and the sink surface 2 is constant between the cavities. Further, FIG. 5 shows an example in which the plastic optical element 1 is aligned in the direction A indicating the asymmetric shape and is made into a multilayer with, for example, an adhesive. As shown in FIG. 5, in the laminated plastic optical element 1, the direction A and the warp direction B indicated by the asymmetric shape are aligned in the same direction (direction).

  Further, by integrating the plastic optical element 1 in the optical scanning unit by unifying the direction A indicated by the asymmetric shape, the warp direction B of the plastic optical element 1 is unified. Reduction is possible.

  Further, in one embodiment of the present invention, a method for selectively inducing sink marks is shown in FIG. 6 or FIG. 6 and 7 are both cross-sectional views of an injection mold for manufacturing the plastic optical element 1 according to the embodiment of the present invention.

  As shown in FIG. 6, the injection mold 4 as an example for manufacturing the plastic optical element 1 of the present embodiment forms a surface having the sink portion 21 as means for selectively forming the sink portion 21. The insert 5 is provided with at least one or more vents (compressed air inflow holes) 5a and at least one or more vents (not shown) that communicate with the vents 5a and apply compressed air to the molded product. It has been.

  In the method for selectively guiding the sink portion used in the plastic optical element molding method of this embodiment, at least one cavity is defined by the transfer surface of the injection mold 4 and the insert 5. A mold heating and holding step for heating and holding the pair of injection molds 4 below the softening temperature of the resin, a molten resin filling step for injecting and filling the molten resin heated to the softening temperature or higher into the cavity, and the transfer A resin pressurizing step for generating a resin pressure on the surface to bring the resin into close contact with the transfer surface, and when the resin is cooled to a softening temperature or lower, a compressed gas is applied to the resin in the cavity from the vent 5a, A void defining step of defining a void 6 between the resin and the insert 5 provided with the vent 5a. By these steps, compressed air is applied, a difference in heat conduction occurs between the surface on which the gap 6 is defined and the other transfer surface, and sink marks occur on the resin surface in contact with the gap 6.

  As shown in FIG. 7, another example of the injection molding die 4 for manufacturing the plastic optical element 1 according to this embodiment includes a nesting portion 21 as a means for selectively forming the sink portion 21. A part of 5 is slidably provided.

  Another method for selectively inducing the sink portion used in the plastic optical element molding method of this embodiment is that at least one cavity is defined by the transfer surface of the injection mold 4 and the insert 5. A mold heating and holding step of heating and holding the pair of injection molding molds 4 below the softening temperature of the resin, a molten resin filling step of injecting and filling the resin heated above the softening temperature into the cavity, When the resin is cooled to the softening temperature or lower, a gap defining step is defined in which the insert 5 is slid away from the resin to define a gap 6 between the resin and the insert 5. By these steps, a difference in heat conduction occurs between the surface in contact with the gap 6 and another transfer surface, and sink marks are generated in the resin surface in contact with the gap 6.

  In the above, the positional relationship between the direction (orientation) indicated by the asymmetric shape of the transfer surface and the selectively induced sink marks is uniform among the plurality of cavities, for example, from the distance L1 side to the distance L2 side. It is assumed that the positional relationship between the direction toward the side and the sink part is unified among a plurality of cavities. In addition, the positional relationship between the direction (orientation) indicated by the asymmetric shape of the transfer surface and the selectively induced sink part is uniform among the plurality of cavities, for example, from the distance L2 side to the distance L1 side. It may be said that the positional relationship between the direction toward the surface and the sink portion is unified among a plurality of cavities.

  FIG. 8 is a view showing an optical element molded body (or cavity) immediately after molding, which is molded by the plastic optical element molding method according to the second embodiment of the present invention. The second embodiment is different from the first embodiment only in that the reference mark 7 is provided on the mold, and the other configuration is the same as that of the first embodiment, and thus the description of the same parts is omitted.

  When the nesting is incorporated so that the direction A indicated by the asymmetric shape is always constant between the cavities B of the plastic optical element 1, it is difficult to visually determine the direction A indicated by the asymmetric shape, and the shape is measured. The direction must be determined. Therefore, by providing the reference mark 7 so that the direction of the asymmetric shape can be discriminated in the nest that forms the transfer surface having the asymmetric shape, the nest can be incorporated in the mold without error.

  Further, as shown in FIG. 8, a reference mark 7 capable of discriminating the direction A indicated by the asymmetric shape is provided on the transfer surface outside the range 8 having the optical function of the nesting having the transfer surface for transferring the asymmetric shape. As a result, when an insert having an asymmetric shape is incorporated into an injection mold for molding the plastic optical element 1, the direction A indicated by the asymmetric shape can be incorporated without mistake. Further, since the reference mark 7 is also transferred to the molded product, it is easy to determine the direction A indicated by the asymmetric shape when the plastic optical element 1 is incorporated into the optical scanning unit.

  FIG. 9 is a view showing an optical element molded body (or cavity) immediately after molding, which is molded by the plastic optical element molding method according to the third embodiment of the present invention. As shown in FIG. 9, in the third embodiment, as in the first embodiment, the direction A indicated by the asymmetric shape and the warp direction B of the plastic optical element generated by molding are unified between the cavities. In addition, the positional relationship of the gate 3 is unified and molded. In the injection molding method in which the molten resin is poured into the cavity from the gate 3 with a constant pressure, and the resin flows from the gate 3 to the final resin filling position, the heat of the molten resin is formed in the nest that forms the cavity. Is taken away, the resin temperature decreases, and the fluidity of the resin deteriorates. Further, in the pressure-holding step after the resin filling, a pressure difference occurs between the vicinity of the gate 3 and the resin final filling position. Variations in molding characteristics depending on the location of these molded products affect the shape and outer shape of the transfer surface having the optical function of the plastic optical element 1, the internal refractive index distribution, and the like. Therefore, in the third embodiment, as shown in FIG. 9, the direction A indicated by the asymmetric shape and the positional relationship between the sink portion 21 and the gate 3 are unified between the cavities, thereby the direction A indicated by the asymmetric shape and Warpage direction B, and also the tendency of the molding characteristics were unified. In addition, this invention is not limited to the said Example. For example, in the above embodiment, the case where the long plastic optical element has an asymmetric shape in the cross section along the longitudinal direction has been described, but the present invention is also applied to the case where the cross section along the short direction has an asymmetric shape. be able to. Moreover, although the said embodiment demonstrated two cases as a some cavity, this invention is easily applicable even if there are three or more cavities. That is, various modifications can be made without departing from the scope of the present invention.

It is a figure for demonstrating the direction (direction) which the asymmetrical shape shows with respect to an optical axis. It is a figure which shows the relationship between a cavity and the curvature amount of a plastic optical element. It is a figure which shows the optical element molded object immediately after shaping | molding shape | molded by the shaping | molding method of the plastic optical element of one Embodiment which concerns on this invention. It is a figure which shows the plastic optical element of one Embodiment which concerns on this invention. It is a figure which shows the plastic optical element laminated | stacked on the multilayer of other embodiment which concerns on this invention. It is a metal mold | die sectional view for demonstrating the method of guide | inducing a sink selectively. It is a metal mold sectional view for explaining other methods for selectively inducing sink marks. It is a figure which shows the optical element molded object immediately after shaping | molding shape | molded by the shaping | molding method of the plastic optical element of 2nd Embodiment which concerns on this invention. It is a figure which shows the optical element molded object immediately after shaping | molding shape | molded by the shaping | molding method of the plastic optical element of 3rd Embodiment which concerns on this invention.

Explanation of symbols

1 Plastic optical element 2 Non-transfer surface (sink surface)
DESCRIPTION OF SYMBOLS 3 Gate 4 Injection mold 5 Nest 5a Vent 6 Air gap 7 Reference mark 8 Effective range of optical characteristics 11 Optical functional surface 12 Optical functional surface 21 Sink part A Direction of asymmetric shape B Warp direction

Claims (10)

An optical element having at least one transfer surface having an asymmetric shape with respect to the optical axis and at least one sink part selectively guided to a non-transfer surface other than the transfer surface having the asymmetric shape is provided with a plurality of cavities. In a plastic optical element molding method in which a plurality of molds are molded simultaneously with a single mold having
A plastic optical element molding method, wherein the positional relationship between the transfer surface and the selectively induced sink part is unified between the plurality of cavities.   The method for molding a plastic optical element according to claim 1, wherein the transfer surface having the asymmetric shape has an optical function. A mold heating and holding step of heating and holding a pair of molds provided with a plurality of cavities defined by the transfer surface and the non-transfer surface, below the softening temperature of the resin;
A molten resin filling step of injecting and filling the molten resin heated above the softening temperature into the cavity;
A resin pressurizing step for generating a resin pressure on the transfer surface to bring the resin into close contact with the transfer surface;
When the resin is cooled below the softening temperature, a compressed gas is applied to the resin in the cavity from the vent of the non-transfer surface to define a void between the resin and the non-transfer surface. The method for molding a plastic optical element according to claim 1, further comprising a step. A mold heating and holding step of heating and holding a pair of molds provided with a plurality of cavities defined by the transfer surface and the non-transfer surface, below the softening temperature of the resin;
A molten resin filling step of injecting and filling the molten resin heated above the softening temperature into the cavity;
When the molten resin is cooled to a softening temperature or lower, a gap is formed between the molten resin and the insert by sliding the insert forming the non-transfer surface away from the resin. A plastic optical element molding method according to claim 1, further comprising a forming step. Claims, characterized in that providing the direction distinguishable criterion asymmetrically shaped portion having an optical function of the transfer surface of the charged element to form the transfer surface to the outside of the portion for molding having the asymmetric shape Item 3. A method for molding a plastic optical element according to Item 1 or 2. 3. The plastic optical according to claim 1, wherein a reference capable of discriminating the direction of the asymmetric shape is provided outside the range of the transfer surface having the optical function of the transfer surface having the asymmetric shape. Element molding method. Before Symbol transfer surface, plastics according to claim 1 and a sink unit which is selectively induced, further, characterized in that the positional relationship between the gate is unified among all the cavities Optical element molding method. Plastic optical element molded by any molding method of claims 1 to 7 is more ready, face-to-face and are contact adhesive facing thereto with a shrinkage portion plastic optical element is selectively induced in said plurality of A laminated plastic optical element characterized in that it is fixed with an agent and laminated in multiple layers. In a plastic optical element having at least one transfer surface having an asymmetric shape with respect to the optical axis and at least one sink part selectively guided to a non-transfer surface other than the transfer surface having the asymmetric shape,
Plastic optical element of the stack, wherein a positional relationship between the front Kiten imaging surface and selectively induced shrinkage portion are laminated are unified. The plastic optical element molded by the molding method according to any one of claims 1 to 7 is arranged so that a positional relationship between the direction of the asymmetric shape of the transfer surface having the asymmetric shape and a selectively induced sink portion is aligned. Optical scanning unit.

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