JP2010115921A - Injection mold of aspheric surface plastic lens, and method of manufacturing aspheric surface plastic lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-precision aspheric plastic lens in which no bubble, sink mark, undulation, or the like occurs. <P>SOLUTION: An injection mold of the aspheric surface plastic lens is provided with an incidence plane to which an radiation enters, and an outgoing radiation plane from which the radiation is emitted. In the injection mold, a first mold provided with a first cavity surface for molding the incidence plane and a second mold provided with a second cavity surface for molding the outgoing radiation plane are constituted to be splittable on a parting line face, a gas vent is provided on the edge of the most distant part from the parting line surface in the first cavity surface and the edge of the most distant part from the parting line surface in the second cavity surface. In the high-precision aspheric surface plastic lens, no bubble, sink mark, undulation, or the like occurs around the optical surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an injection mold for an aspheric plastic lens used in an optical scanning device or the like.

  Conventionally, aspheric plastic lenses are generally used in the optical and electronic fields including optical scanning devices such as laser printers.

  Since this aspherical plastic lens (also simply referred to as “lens”) uses a resin (pellet) such as thermoplastic plastic as a material, it can be processed into various shapes by injection molding. In addition, an aspheric plastic lens using a resin such as thermoplastic as a material can be produced at a low cost and is suitable for mass production. For this reason, in recent years, the fields of use have expanded with the reduction in weight and size of devices. For example, an objective lens for an optical pickup lens, an fθ lens, a collimator lens, and the like can be given.

  In order to manufacture these aspheric plastic lenses with resin, it is necessary to mold them with high quality and high accuracy. Therefore, an injection molding method has been conventionally performed as a method of molding an aspheric plastic lens.

In a general manufacturing method of this aspherical plastic lens, first, a fixed mold and a movable mold that constitute an injection mold are clamped to form a cavity having substantially the same shape as a product. Here, a nest is generally used for the movable side mold and / or the fixed side mold forming the cavity. Then, after filling the cavity with resin that is heated and melted, the cooling water or the like is passed through the flow paths formed in the movable mold and the fixed mold, so that the movable mold and the fixed mold are flown. The molten resin is cooled and solidified to form a product (aspheric plastic lens) (see, for example, Patent Documents 1 to 3).

JP 54-148055 A JP 58-94436 A JP 58-167133 A

  When nesting is used on the surface of the movable mold and / or fixed mold that forms the cavity, the gas generated from the air or molten resin inside the cavity is separated from the movable mold and / or the fixed mold. It escapes to the outside of the injection mold from the gap of the nesting or the gap between the movable mold and the fixed mold.

  However, with the recent increase in accuracy of image formation, aspheric plastic lenses used in image forming apparatuses are required to have high accuracy, and injection molding molds for aspheric plastic lenses are also designed and manufactured with high accuracy. It became so. For this reason, an injection mold designed and manufactured with high accuracy has almost no gap as described above. Therefore, when molten resin is injected and filled into the cavity in the injection mold, the mold in the cavity of the injection mold Most of the gas generated from the air and molten resin remains in the cavity. In particular, an aspheric plastic lens having a complicated shape has a complicated cavity shape, so that gas or the like is difficult to escape and gas or the like tends to remain in the cavity.

  Since the molten resin is cooled and solidified in a state where air and molten resin gas remain in the cavity, there are bubbles and sink marks around the optical surface (incident surface and output surface) of the molded aspheric plastic lens. There is a problem that deformation such as sink mark) and undulation occurs.

  Further, the shrinkage due to the sink is not stable, and there is a problem that it is very difficult to control the molding conditions such as changing depending on the place. If a stable shape cannot be obtained due to this sink, there is a problem that high-precision lens characteristics cannot be obtained.

The present invention has been made in view of the above-described problems, and is for injection-molding a high-precision aspheric plastic lens that does not generate bubbles, sink marks, undulation, etc. around the optical surface of the aspheric plastic lens. An object of the present invention is to provide an injection mold and a method for manufacturing an aspheric plastic lens.

(First invention)
The present invention is an injection mold for injection-molding an aspheric plastic lens having an incident surface on which light is incident and an exit surface from which the light is emitted, and the injection mold includes the incident surface A first mold having a first cavity surface for molding a surface and a second mold having a second cavity surface for molding the emission surface are configured to be separable on a parting line surface. The present invention also relates to an injection mold for molding an aspheric plastic lens.

Then, the injection mold, wherein the farthest from the parting line face the first outer peripheral portion of the cavity surface, and the outer peripheral portion of the second cavity surface farthest from the previous SL parting line surface In addition, a gas vent is provided.

Here, “gas vent” means that the cavity inside the injection mold is communicated with the outside of the injection mold (the two separated spaces are made continuous), and the gas in the cavity is injection molded. It is a degassing passage for discharging to the outside of the mold .

  When the cavity of the injection mold is filled (filled) with the molten resin flowing from the runner of the injection mold through the gate into the cavity, the gas generated from the air and the molten resin in the cavity is the first. It tends to remain in a part of the cavity surface farthest from the parting line surface and a part of the second cavity surface farthest from the parting line surface. However, due to the above-described configuration, such gas or the like escapes from the gas vent to the outside of the injection mold. For this reason, the gas produced from air and molten resin does not remain in the cavity.

  Therefore, it is possible to provide an injection mold capable of molding a highly accurate aspheric plastic lens that does not cause deformation such as bubbles, sink marks, and undulation around the optical surfaces (incident surface and output surface) through which light is transmitted.

(Second invention)
Further, the present invention is formed by preparing the injection mold of the first invention, and clamping the injection mold by aligning the parting line surfaces of the first mold and the second mold. A method for producing an aspheric plastic lens is provided in which a molten resin is injected into a cavity, the cavity is filled with the molten resin, and then the injection mold is cooled to cool and solidify the molten resin. is there.
With this configuration, it is possible to provide a highly accurate aspheric plastic lens that does not cause deformation such as bubbles, sink marks, and undulation around the optical surfaces (incident surface and output surface) through which light passes.

  The present invention can provide a highly accurate aspheric plastic lens in which bubbles, sink marks, undulation, etc. do not occur in the molded aspheric plastic lens.

The schematic sectional drawing of the injection mold for shape | molding the lens which concerns on this invention. (Example 1) The front view (partial enlarged view) which showed the injection mold (fixed side metal mold | die) which concerns on this invention. (Example 1) The front view (partial enlarged view) which showed the injection mold (movable side metal mold | die) which concerns on this invention. (Example 1) The front view (partial enlarged view) which showed the stationary side metal mold | die in FIG. (Example 1) The front view (partial enlarged view) which showed the movable side metal mold | die in FIG. (Example 1) DD sectional drawing which showed the stationary-side metal mold | die in FIG. (Example 1) EE sectional drawing which showed the movable side metal mold | die in FIG. (Example 1) It is the figure which showed the measurement of the sink of an aspherical plastic lens. (Example 1) The front view (partial enlarged view) which showed the injection mold (fixed side metal mold | die). (Example 2) The front view (partial enlarged view) which showed the injection mold (movable side metal mold | die). (Example 2) 1 is a schematic diagram of an image forming apparatus according to the present invention. (Example 3) 1 is a schematic diagram of an optical scanning device according to the present invention. (Example 3)

  Examples for specifically explaining the present invention will be described below. In addition, this invention is not limited at all by these Examples.

1 to 8 show an embodiment according to the present invention.
FIG. 1 is a partial cross-sectional view of an injection mold for producing an aspheric plastic lens according to the present invention as seen from above.

  FIG. 2 is a first mold having a first cavity surface for molding an incident surface of an aspheric plastic lens, as viewed from the N direction (arrow N) when the dotted line portion A of FIG. It is the elements on larger scale of the fixed side metal mold | die. In other words, FIG. 2 shows the vicinity of the first cavity surface 18 when the injection mold shown in FIG. It is a partial enlarged view.

  FIG. 3 is an enlarged view of the dotted line portion A of FIG. 1 as viewed from the M direction (arrow M), and includes a second cavity surface that molds the exit surface of the aspheric plastic lens. It is the elements on larger scale of a movable side metal mold | die. In other words, FIG. 3 is a partially enlarged view of the vicinity of the second cavity surface 19 when the injection mold shown in FIG. 1 is separated by the parting line surface 14 and the movable mold 5 is viewed in the direction of arrow M. FIG.

  FIG. 4 is a partially enlarged view of a peripheral portion of the first cavity surface (fixed side) in which the dotted line portion B in FIG. 2 is enlarged. FIG. 5 is a partially enlarged view of the peripheral portion of the second cavity surface (movable side) in which the dotted line portion C in FIG. 3 is enlarged. 6 is a DD cross-sectional view showing a gas vent path of the fixed mold in FIG. FIG. 7 is a cross-sectional view taken along line EE showing the gas vent path of the movable mold in FIG. FIG. 8A shows the measurement results of the fθ lens when sink marks occur and does not occur, and FIG. 8B is a perspective view of the fθ lens.

  The injection mold shown in FIG. 1 is a two-piece injection mold that simultaneously molds two aspheric plastic lenses in one shot, but the left side of the drawing is omitted because of the same configuration. It is illustrated. Further, for ease of explanation, although enlarged in FIGS. 2 to 5, the dimensions of the gas vent 2 are T = 5 μm to 15 μm, W = 3 mm to 100 mm, and are very small. is there.

[Aspheric plastic lens]
The aspheric plastic lens targeted by the present invention is, for example, the fθ lens 1 used in the image forming apparatus. As shown in FIG. 8B, the fθ lens 1 includes an incident surface 30 on which light is incident and an output surface 31 that emits light incident from the incident surface 30.

[Injection mold]
As shown in FIGS. 1 to 5, an aspheric plastic lens injection molding die 3 according to the present invention includes a first cavity surface 18 that molds an incident surface 30 of an fθ lens 1 as an aspheric plastic lens. Further, the fixed side mold 4 as the first mold and the movable side mold 5 as the second mold having the second cavity surface 19 for molding the emission surface 31 are the parting line surface 14. It is configured to be splittable.

(Nested)
A insert 6 is set in the fixed mold 4 and a insert 7 is set in the movable mold 5, and a part of the cavity surface of the cavity 13 for forming the fθ lens 1 is formed by the insert 6 and the insert 7. Yes. The nest 6 has a first cavity surface 18 for forming the incident surface 30 of the fθ lens 1, and the nest 7 has a second cavity for forming the exit surface 31 of the fθ lens 1. A surface 19 is formed. With other words, the emission surface a first cavity surface 18 is a transfer surface for molding the incident surface 30 of the optical plane of the fθ lens 1, second cavity surface 19 is an optical surface of the f theta lens 1 3 is a transfer surface for forming 31.

(Gas vent)
The peripheral edge 16 of the portion 40 (one-dot chain line) farthest from the parting line surface 14 in the first cavity surface 18, that is, the outer peripheral edge 15 of the first cavity surface 18 farthest from the parting line surface 14 A gas vent 21 is provided. Further, the peripheral edge 20 of the portion 41 (two-dot chain line) farthest from the parting line surface 14 in the second cavity surface 19, that is, the outer peripheral edge of the second cavity surface 19 farthest from the parting line surface 14. 15 is provided with a gas vent 22.

  In other words, in the moving direction of the movable mold 5, the peripheral edge 16 of the cavity 40 (one-dot chain line) of the fixed mold 4 farthest from the parting line surface 14 and the cavity 41 of the movable mold ( Gas vents 21 and 22 are provided at the peripheral edge 20 of the two-dot chain line. The portions 40 (one-dot chain line) and 41 (two-dot chain line) farthest from the parting line surface 14 are portions where the thickness of the fθ lens 1 is thick in the moving direction of the movable mold 5, and the farthest portion. Since the cavity portions 40 and 41 having a large amount of molten resin, gas is easily generated and easily remains.

  Further, in the portions 40 and 41 farthest from the parting line surface 14, the air in the cavity 13 is difficult to escape. For this reason, by providing the gas vents 21 and 22 at the peripheral portions 16 and 20 of the portions 40 (one-dot chain line) and 41 (two-dot chain line) farthest from the parting line surface 14, gas or the like is injected into the injection mold. 3 can be effectively discharged to the outside.

  As shown in FIGS. 6 and 7, gas vents 21 and 22 provided at the peripheral portions 16 and 20 of the portions 40 (one-dot chain line) and 41 (two-dot chain line) farthest from the parting line surface 14. Thus, the cavity 13 communicates with the outside of the injection mold 3. Although not shown in FIGS. 6 and 7, the groove 17 formed in the left-right direction in FIG. 6 and FIG. 7 extends straight in the left-right direction and reaches the outside of the injection mold 3 as it is. ing.

  That is, the air and gas in the portion 40 (one-dot chain line) and 41 (two-dot chain line) farthest from the parting line surface 14 in the cavity 13 of the injection mold 3 are transferred to the fixed mold 4 and the movable mold. 5 is discharged to the outside of the injection mold 3 through the concave groove 17 formed in the path 5, so that bubbles and sink marks are formed around the optical surface (incident surface 30 and output surface 31) through which light is transmitted. It is possible to mold a highly accurate aspheric plastic lens that does not cause deformation such as undulation.

Incidentally, as shown in FIGS. 2-7, the gas vent, if the outer peripheral portion 15 of the first cavity surface 18 and second cavity surface 19, may be multiply provided. Specifically, the first cavity surface 18 of the fixed mold 4 and the second cavity surface 19 of the movable mold 5 that are farthest from the parting line surface 14 (one-dot chain line) and 41 In addition to the gas vents 21 and 22 provided on the peripheral edge portions 16 and 20 (two-dot chain line), a plurality of gas vents 2 may be provided at a plurality of locations.

[Production method of aspheric plastic lens]
Next, a method for manufacturing an aspheric plastic lens using the above-described injection mold 3 according to the present invention will be described. Here, a manufacturing method of the fθ lens 1 as an aspheric plastic lens is illustrated.

(Molding material)
As the resin (pellet) which is a molding material of the fθ lens, amorphous polyolefin resin such as ZEONEX (registered trademark) of Nippon Zeon Co., Ltd. or Apel (registered trademark) of Mitsui Chemicals, Inc. can be used.

(Production method)
First, as shown in FIG. 1, the injection mold 3 is prepared, and the movable mold 5 of the injection mold 3 is moved to the fixed mold 4 and clamped. Then, the molten resin is injected into the injection mold 3 from the resin injection nozzle 8 of the injection molding device 3. The molten resin injected into the injection mold 3 is formed by clamping the injection mold 3 via a sprue bush 9, a sprue 10, a runner 11 and a gate 12 provided in the fixed mold 4. It is injected into the cavity 13 and filled (filled).

  When molten resin is injected into and filled in the cavity 13, the air in the cavity 13 and the gas emitted from the molten resin escape to the outside of the injection mold 3 from the gas vent 2 formed by the concave grooves 17. For this reason, air and gas generated by the molten resin do not remain in the cavity 13.

  Thereafter, by curing (cooling and solidifying) the resin, the first cavity surface 18 for forming the incident surface 30 of the fθ lens and the exit surface 31 of the fθ lens, in which a part of the cavity 13 is formed, are formed. The second cavity surface 19 to be formed is transferred to the resin, and the movable mold 5 is opened, so that the highly accurate fθ lens 1 shown in FIG. 8B can be molded.

(Aspheric plastic lens)
Next, an aspheric plastic lens manufactured by the method for manufacturing an aspheric plastic lens of the present invention will be described. In the fθ lens 1 as the aspheric plastic lens described above, bubbles, sink marks, undulation, etc. do not occur.
[Evaluation]
Next, the fθ lens shown in FIG. 8B is molded by the manufacturing method of the present invention and the conventional manufacturing method, and the effect of the present invention is confirmed.
(Evaluation equipment)
As an evaluation device such as bubbles, sink marks, and sea urchins, a three-dimensional measuring instrument Ultra Accurate 3-D Profilometer (hereinafter abbreviated as “UA3P”) manufactured by Panasonic Corporation was used.

(Evaluation results)
The evaluation results are shown in FIG. FIG. 8A is a table showing measurement results (experimental examples) after molding an fθ lens when sink marks occur and when sink marks do not occur.

  The horizontal axis in FIG. 8A indicates the X-axis direction position (unit: mm, millimeter) from the center O (coordinate origin) of the fθ lens 1 to the X direction 55 mm to 65 mm as shown in FIG. 8B. ing. On the other hand, the vertical axis in FIG. 8A indicates the Z direction position of the lens member as shown in FIG. 8B, and the center “0.0” of the vertical axis is 15 mm from the end in the Z direction. Indicates the position. The unit of the vertical axis is μm (micron).

  In FIG. 8A, black circles are measured values of sink marks of the fθ lens molded by the manufacturing method according to the present invention, and solid lines are measured values of sink marks of the fθ lens molded by the conventional manufacturing method. The alternate long and short dash line is the theoretical value (zero) of sink obtained by simulating the case where sink does not occur due to the molding conditions of the lens.

  As shown in FIG. 8A, the fθ lens molded with the conventional injection mold has a step due to sinking when the position in the X-axis direction is between 60 mm and 61 mm when compared with a theoretical value that does not cause sinking. Yes. That is, it can be confirmed that a sink (shrinkage) of about 1 μm occurs at a position 65 mm from the origin O. On the other hand, it can be seen that the measured value of the fθ lens molded by the manufacturing method of the present invention substantially matches the theoretical value. That is, it can be seen that there is no sink mark around the optical surface of the fθ lens molded by the injection mold according to the present invention.

  As described above, it is possible to provide a highly accurate aspheric plastic lens which does not generate bubbles, sink marks, undulations, etc. around the optical surface of the aspheric plastic lens molded according to the present invention.

Another embodiment of the present invention will be described in detail with reference to FIGS.
Note that portions similar to those of the molding die and the aspheric plastic lens according to the first embodiment of the present invention are denoted by the same reference numerals, description thereof is omitted, and only differences from the first embodiment will be described in detail. .

  FIG. 9 is a first mold having a first cavity surface for molding the entrance surface of the aspherical plastic lens, which is an enlarged view of the dotted line portion A of FIG. FIG. 6 is a partially enlarged view of a fixed mold as a vicinity of a first cavity surface 18; FIG. 10 is a second mold having a second cavity surface that molds the exit surface of the aspheric plastic lens when the dotted line portion A in FIG. 1 is enlarged and viewed from the M direction (arrow M). FIG. 6 is a partially enlarged view of the movable side mold in the vicinity of the second cavity surface 19.

The main difference from the first embodiment of the second embodiment, the gas vent is provided in the outer peripheral portion 15 of the first and second cavity surfaces, farthest cavity portion of the fixed mold 4 from the parting line surface 14 It is a point provided only at the peripheral portion 16 of 40 (one-dot chain line) and the peripheral portion 20 of the cavity portion 41 (two-dot chain line) of the movable mold.
Even with this configuration, the same effect as in the first embodiment can be obtained.

Another embodiment of the present invention will be described in detail with reference to FIGS.
Note that portions similar to those of the molding die and the aspheric plastic lens according to the first embodiment of the present invention are denoted by the same reference numerals, description thereof is omitted, and only differences from the first embodiment will be described in detail. .

[Image forming apparatus]
FIG. 11 is a diagram showing an example of the configuration of the image forming apparatus 501 according to the present invention.
An image forming apparatus 501 shown in FIG. 11 is a so-called tandem type digital color printer using an electrophotographic system. The image forming apparatus 501 includes an image forming process unit 570 that forms an image corresponding to image data of each color, a control unit 580 that controls the operation of the entire image forming apparatus 501, and a personal computer (PC) 503 or a scanner, for example. An image processing unit 581 that performs predetermined image processing on image data received from the image reading device 504 or the like.

  The image forming process unit 570 has four image forming units 510Y, 510M, 510C, and 510K (hereinafter, collectively referred to as “image forming unit 510” collectively) at regular intervals in the vertical direction (substantially vertical direction). Are arranged in parallel. The image forming unit 510 includes a photosensitive drum 511 as an image holding member, a charging roll 512, a developing device 513, and a drum cleaner 514.

  Here, the charging roll 512 uniformly charges the surface of the photosensitive drum 511 with a predetermined potential. The developing unit 513 holds a two-component developer composed of yellow (Y), magenta (M), cyan (C), and black (K) toners and a magnetic carrier in each of the image forming units 10. The electrostatic latent image formed on the photosensitive drum 511 is developed with each color toner. The drum cleaner 514 is for removing, for example, toner or paper dust attached on the photosensitive drum 511 by bringing a plate-like member into contact with the surface of the photosensitive drum 11.

  Further, the image forming apparatus 501 is provided with a laser exposure device 520 as an example of an optical scanning device that exposes the photosensitive drum 511 provided in each of the image forming units 510. The laser exposure unit 520 acquires image data for each color from the image processing unit 581, and on the photosensitive drum 511 of each image forming unit 510 by a light beam (laser light) whose lighting is controlled based on the acquired image data. Are respectively subjected to scanning exposure.

  In addition, a paper transport belt 530 that transports the paper 590 is disposed so as to move in contact with the photosensitive drum 511 of each image forming unit 510. The paper transport belt 530 is a film-like endless belt that electrostatically attracts the paper 590 and is circulated around a drive roll 532 and an idle roll 533.

  In addition, transfer rolls 531 are disposed inside the paper transport belt 530 and facing the respective photoconductive drums 511, and a transfer electric field is formed between the photoconductive drums 511, and on the paper 590, Each color toner image formed by each image forming unit 510 is sequentially transferred.

  Further, on the downstream side of each transfer roll 531, a static elimination lamp 515 that neutralizes the photosensitive drum 511 after the transfer is provided. A fixing device 540 is provided on the downstream side of the paper transport belt 530 in the paper transport direction to perform a fixing process on the unfixed toner image on the paper 590 by heat and pressure.

  Further, as a paper transport system, a paper storage unit 550 that stores the paper 590, a pickup roll 551 that picks up and transports the paper 590 stored in the paper storage unit 550 at a predetermined timing, and a transport roll that transports the fed paper 590. In 552, a registration roll 553 is provided for feeding the paper 590 to the paper transport belt 530 in accordance with the image forming operation.

  In addition, the paper discharge roll 554 that conveys the paper 590 fixed by the fixing device 540, and in the case of single-sided printing, the paper 590 is discharged toward the paper discharge stacking portion 591 provided in the upper part of the apparatus main body, and double-sided printing In this case, a reversing roll 555 or the like for feeding the paper 590 fixed on one side by the fixing device 540 toward the double-sided conveyance path 592 by reversing from the rotation direction toward the paper discharge stacking unit 591 is arranged. It is installed.

  In the image forming apparatus 501, the image forming process unit 570 performs an image forming operation under the control of the control unit 580. That is, image data input from the personal computer 503, the image reading device 504, or the like is subjected to predetermined image processing by the image processing unit 581 and supplied to a laser exposure device 520 as an optical scanning device. In each image forming unit 510, the surface of the photosensitive drum 511 that is uniformly charged with a predetermined potential by the charging roll 512 is controlled to be lit by the laser exposure unit 520 based on the image data from the image processing unit 581. Then, scanning exposure is performed with the light beam (laser light), and an electrostatic latent image is formed on the photosensitive drum 511.

  The formed electrostatic latent image is developed by the developing device 513, and a toner image of each color is formed on the photosensitive drum 511. When the formation of each color toner image in each image forming unit 510 is started, the sheet 590 taken out from the sheet storage unit 550 is conveyed by the sheet conveying belt 530, and each color toner is generated by the transfer electric field formed by the transfer roll 531. Images are sequentially transferred onto paper 590. Thereafter, the sheet is conveyed to the fixing device 540 and the unfixed toner image is fixed on the sheet 590, and then the sheet 590 is stacked on the discharge stacking unit 591.

(Optical scanning device)
Next, an optical scanning device according to the present invention will be described.
FIG. 12 is a side sectional view of a laser exposure device 520 as an optical scanning device. As shown in FIG. 11, the laser exposure unit 520 includes a light source 521 having four semiconductor lasers as light emitting elements that emit light beams (laser light). Then, four collimator lenses 522 serving as first optical elements provided corresponding to the respective light beams from the light source 521 and cylinder lenses (cylindrical lenses) 523 are provided.

  Further, for example, an optical deflector 63 having a polygon mirror (rotating polygonal mirror) 7 formed of a regular hexahedron and a fθ lens 525 of a common lens through which each light beam as a second optical element passes in common. And a plurality of folding mirrors 526. Each component constituting the laser exposure unit 520 is fixed in a resin or metal housing 528. The housing 528 is sealed with a lid 73, and leakage of the light beam to the outside and adhesion of dust and the like to each optical member are prevented.

  The laser exposure unit 520 converts (shapes) the four divergent laser beams LK, LC, LM, and LY as a plurality of light beams emitted from the light source 521 into parallel light by the respective collimator lenses 522. A cylinder lens 523 having a refractive power only in the sub-scanning direction forms (shapes) a long line image in the main scanning direction in the vicinity of the deflection reflection surface (mirror surface) 7a of the polygon mirror 7 inside the optical deflector 63. The The laser beams LK, LC, LM, and LY are reflected by the deflecting / reflecting surface 7a of the polygon mirror 7 that rotates at a high speed at a constant speed, and are scanned at a constant angular velocity.

  As a light beam incident method to the polygon mirror 7, a tangential offset incident method in which a plurality of light beams are incident at an angle in the main scanning direction, or a plurality of light beams at different angles in the sub-scanning direction. There is a sagittal offset incidence method for incidence.

  In the second embodiment, a sagittal offset incidence method in which each of the laser beams LK, LC, LM, and LY incident on the deflecting / reflecting surface 7a of the polygon mirror 7 has an angle in the sub-scanning direction and is offset with respect to each other in the sagittal direction. Adopted. The laser beams LK, LC, LM, and LY incident on the polygon mirror 7 are set so that the reflection positions on the deflection reflection surface 7a coincide with the sub-scanning direction.

  By the way, in the present Example 2, it employ | adopts as a common lens through which each laser beam passes in common, and employ | adopts the f (theta) lens 525 as an aspherical plastic lens of this invention. In the case of a normal scanning optical device, for example, one lens made of a glass member is used for one laser beam, but in this embodiment, four laser beams are used using a resin member. One fθ lens 525 is employed. Depending on the design, it is possible to employ a total of two fθ lenses, one for each of the two laser beams. In this way, a plurality of laser beams are incident on the fθ lens 525, and the scanning object (photosensitive drum 511) is scanned and exposed.

  In the second embodiment, only the collimator lens 522 and the cylinder lens 523 are used as the first optical element. However, depending on the configuration of the image forming apparatus, the folding mirror 526 may be present in the middle. good. Furthermore, in the first embodiment, the fθ lens 525 and the plurality of folding mirrors 526 are shown as the second optical element, but depending on the configuration of the image forming apparatus, only the fθ lens 525 may be used.

  The above-described embodiments have been illustrated for the purpose of explanation, and the present invention is not limited thereto, and can be recognized by those skilled in the art from the description of the claims, the specification, and the drawings. Modifications, deletions, and additions are possible without departing from the technical idea of the present invention.

  In the above-described embodiment, the gas vent and the concave groove are those provided in the fixed side mold and the movable side mold in the injection mold, but only the fixed side mold and the movable side mold. However, it may be provided in the nest, or may be provided in both the injection mold and the nest.

  In the above-described embodiments, the insert mold is provided in the injection mold. However, it is needless to say that the mold may be an injection mold without a insert and is not limited.

  In the above-described embodiment, the first cavity surface for molding the entrance surface of the aspheric plastic lens is provided in the fixed mold, and the second cavity for molding the exit surface of the aspheric plastic lens. Although the surface provided on the movable side mold is shown, the first cavity surface may be provided on the movable side mold, and the second cavity surface may be provided on the fixed side mold, which is not limited. Needless to say.

Further, in the above-described embodiment, the gas vent is provided in the peripheral portion of the first insert and the second insert. However, depending on the shape of the lens to be molded, it may be provided only in one of the inserts.

  Further, in the above-described embodiment, the gas vent is formed with a square hole as shown in the figure. However, the shape and size of the gas vent, the resin material, the temperature at which the resin is melted, and the molding of the lens by the speed at which the resin is injected into the cavity. The shape may be arbitrarily changed depending on conditions. For example, if the hole shape of the gas vent is too large, molten resin will enter the gas vent and gas etc. will not escape, and conversely if it is too small, before the gas etc. completely escapes when the molten resin is filled in the cavity In addition, the resin cools and hardens, and the molding of the lens fails, resulting in a defective product. Further, the location and place where the gas vent 2 is formed may be arbitrarily changed depending on the manufacturing conditions.

  Further, in the above-described embodiment, an aspheric plastic lens having an optical surface composed of a short side and a long side that is thick in the direction in which light enters by using the injection mold of the present invention. The long aspheric plastic lens is characterized in that the thickness is thinner at both ends than the longitudinal direction of the long side of the optical surface and thick at the periphery of the central portion. Can also be molded. For example, it is like the fθ lens shown in FIG.

  Furthermore, the aspherical plastic lens of the present invention can be used for the following optical equipment materials, optical component materials, etc. due to its excellent high-accuracy characteristics in addition to the optical scanning device and image forming apparatus mounted on the present invention. Can also be used.

  Examples of the optical device material include a lens material for a still camera, a lens used for a deck for reading Blu-ray, DVD, and CD, a finder prism, a target prism, a finder cover, a light receiving sensor, and the like; Lenses, viewfinders, etc .; projection television projection lenses, protective film lenses, lens materials for optical sensing devices, and the like.

  Examples of the optical component material include a waveguide, an optical fiber material around an optical connector, a ferrule, an optical passive component, an optical circuit component, and a substrate material around an optoelectronic integrated circuit (OEIC).

  Moreover, this invention can be grasped | ascertained as follows, when the invention which concerns on Claim 1 is made into the 1st invention, and the invention which concerns on Claim 2 is made the 2nd invention.

(Third invention)
The third invention provides an aspheric plastic lens molded by the method for producing an aspheric plastic lens of the second invention.
With this configuration, it is possible to provide a highly accurate aspheric plastic lens that does not cause deformation such as bubbles, sink marks, and undulation around the optical surfaces (incident surface and output surface) through which light passes.

(Fourth invention)
According to a third aspect of the present invention, a light emitting element that emits a light beam, a first optical element that shapes the light beam emitted from the light emitting element, and a polygon that deflects and reflects the light beam shaped by the first optical element. In an optical scanning device including an optical deflector including a mirror and a second optical element that reshapes the light beam deflected and reflected by the polygon mirror, the first optical element and the second optical element The lens is the aspheric plastic lens of the third invention.

  With this configuration, it is possible to provide an optical scanning device with higher accuracy than before. That is, by using the aspheric plastic lens described above, it is possible to provide an optical scanning device capable of forming a highly accurate electrostatic latent image on the photosensitive member.

Here, the optical element means an optical component group including at least a lens. That is, not only a lens but a mirror may be included. Examples of the lens include a cylinder lens (cylindrical lens), a collimator lens, and an fθ lens. Moreover, as a mirror, a reflective mirror (folding mirror) etc. are illustrated.
In addition, shaping the light beam (laser, laser beam) means changing the traveling direction of the light beam to a desired direction using a mirror or the like, or changing the shape of the light beam to a desired shape using a lens or the like.

  An electrostatic latent image is an image formed on the surface (photosensitive layer) of the photoconductor by charging. The specific resistance of the portion of the photoconductive layer irradiated with the laser beam decreases, and the surface of the photoconductor is charged. This is a so-called negative latent image formed by the remaining charge flowing while the portion of the charge not irradiated with the laser beam remains.

  The effective range of light rays that pass (transmit) through the lens surface (incident surface and output surface) as an optical surface is the range of light rays that contribute to the image created by the lens. In other words, it refers to the range of lens surfaces that can produce lens performance as specified.

(Fifth invention)
The fifth invention relates to an image forming apparatus comprising a photoconductor and the optical scanning device of the fourth invention for forming an electrostatic latent image on the photoconductor.
With this configuration, it is possible to provide an image forming apparatus capable of forming an image with higher accuracy than conventional.

  The aspheric plastic lens injection mold according to the present invention and the manufacturing method of the aspheric plastic lens are free from bubbles, sink marks, undulations, etc. around the optical surface of the molded aspheric plastic lens. An accurate aspheric plastic lens can be provided.

1, 525 ... aspherical plastic lens (fθ lens), 2 ... gas vent,
3 ... injection mold, 4 ... fixed mold, 5 ... movable mold,
6 ... 1st nesting (fixed side), 7 ... 2nd nesting (movable side),
8 ... Resin injection nozzle, 9 ... Sprue bush, 10 ... Sprue, 11 ... Runner,
12 ... Gate, 13 ... Cavity, 14 ... Parting line surface,
15 ... outer periphery, 17 ... groove,
18 ... first cavity surface, 19 ... second cavity surface,
40, 41 ... the farthest part,
16, 20 ... the peripheral part of the farthest part,
21, 22 ... the gas vent at the farthest part,
30 ... entrance surface, 31 ... exit surface,
501: Image forming apparatus, 520: Optical scanning apparatus (laser exposure device)

Claims (2)

An injection mold for an aspheric plastic lens having an incident surface on which light is incident and an exit surface from which the light is emitted,
The injection mold includes a first mold having a first cavity surface for molding the incident surface and a second mold having a second cavity surface for molding the emission surface. It can be divided on the surface
A gas vent is provided at a peripheral portion of the first cavity surface farthest from the parting line surface and a peripheral portion of the second cavity surface farthest from the parting line surface. Features an aspheric plastic lens injection mold. Preparing an injection mold according to claim 1;
Injecting molten resin into the cavity formed by clamping the parting line surfaces of the first mold and the second mold together;
After filling the cavity with the molten resin,
A method for producing an aspheric plastic lens, wherein the molten resin in the cavity is cooled and solidified by cooling the injection mold.