JP5333986B2 - Plastic optical element having fine pattern on optical surface - Google Patents

Description

  The present invention relates to an optical surface of a plastic lens having a fine pattern on the optical surface, has high shape accuracy by molding by injection molding, and can be manufactured at low cost. Optical scanning of a digital copying machine, a laser beam printer, etc. It is used for a plastic diffractive lens used in an optical system.

  As a prior art related to this invention, there is one described in Japanese Patent Laid-Open No. 2005-258392 (Patent Document 1). By using a plastic lens with a diffractive optical surface in the optical scanning optical system, changes in the light source wavelength, refractive index, lens surface shape, and lens thickness due to temperature fluctuations in the optical housing can be canceled by the diffractive optical surface. Therefore, the focus position deviation can be greatly reduced.

  Another conventional technique is described in JP-A-2006-323257 (Patent Document 2). This is because an optical element having a grating on the optical surface is provided with a rib having a predetermined dimension for handling, thereby enabling easy handling without touching the optical surface. This prevents the optical surface from being contaminated and damaged. However, this is technically quite different from the invention of this application.

By the way, in the optical scanning optical system of laser-type image equipment (for example, digital copying machines, printers, etc.), the image density and image quality have been improved, and accordingly, the beam spot on the photoconductor is further reduced in diameter. Is required. In the optical scanning optical system, a lens having a laser beam imaging and various correction functions is used.
One of the factors affecting the reduction of the beam spot diameter is the lens characteristic. The glass lens generally used has a limit in the shape that can be processed. Therefore, the shape of the lens surface is generally a simple spherical surface. Therefore, it is difficult to give this glass lens a special function, and it is extremely difficult to further reduce the diameter of the beam spot.

  In view of this, an effort has been made to reduce the diameter of the beam spot by plasticizing the lens constituting the optical scanning optical system. This is because plastic is formed by transferring a lens surface of a mold, and a plastic lens having a required lens surface shape can be easily manufactured. As a method for molding a plastic lens, an injection molding method is generally used. Since this molding method enables mass production, a high-performance plastic lens can be manufactured at a lower cost than a glass lens. There is a merit.

However, there are the following disadvantages.
That is, since plastic has a large coefficient of linear expansion, the variation in curvature and dimensions due to temperature change is larger than that of a glass lens, and the refractive index variation due to temperature change is also large. Such fluctuations in curvature, size, and refractive index cause fluctuations in the focus position, increasing the beam spot diameter on the photoreceptor, and as a result, degrading the quality of the imaging device. is there.

  Further, when the temperature changes, the wavelength of the semiconductor laser light as the light source also changes. When the wavelength of the semiconductor laser light fluctuates, the focus position fluctuates, and the beam spot diameter increases. As a result, the quality of the image equipment deteriorates.

  FIG. 1 shows a conventional example (same as FIG. 7 of Patent Document 1) in which a plastic lens is used in the optical scanning optical system. FIG. 1A is a plan view of the optical scanning optical system as viewed from above, and FIG. 1B is a schematic diagram illustrating the distance between the lens surfaces by arranging the lenses on a straight line. . This optical scanning optical system 20 includes a semiconductor laser light source 11, a coupling lens 12, an aperture 13, an anamorphic lens 14, a polygon mirror 15, a deflector side scanning lens 16, an image plane side scanning lens 17, a dustproof glass 18, and an image plane. 19.

  The light beam emitted from the light source 11 becomes weak divergent light by the coupling lens 12, passes through the aperture 13, and passes through the anamorphic lens 14 that forms the first optical system. As a result, the main scanning direction becomes parallel light, and the sub-scanning direction becomes a light beam condensed near the polygon mirror 15. Further, the light is deflected by the polygon mirror 15 and imaged on the screen 19 through the dust-proof glass 18 by the deflector side scanning lens 16 and the image plane side scanning lens 17.

In the above Patent Document 1, taking into account fluctuations in the light source wavelength, refractive index, lens surface shape, and lens thickness due to temperature, and calculating fluctuations in the focus position relative to the image plane position, the environmental temperature is reduced from 25 ° C to 45 ° C. It is described that when it changes, it is 11.6 mm in the main scanning direction and 3.3 mm in the sub-scanning direction.
An invention for solving the above problem is described in Patent Document 1. This is a devised optical scanning optical system using a diffractive optical surface as a lens surface, and this optical scanning optical system is shown in FIG. 2 (same as FIG. 1 of Patent Document 1). 2 includes a light source 1, a coupling lens 2, an aperture 3, an anamorphic lens 4, a polygon mirror 5, a deflector side scanning lens 6, an image side scanning lens 7, a dustproof glass 8, and an image plane. The lens is entirely made of plastic, and diffractive optical surfaces are used for the light source side lens surface of the coupling lens 2 and the image surface side lens surface of the anamorphic lens 4.

  The above-mentioned diffractive optical surface is opposite to the normal refractive surface in the direction of change of the refraction angle due to the wavelength change. By utilizing this characteristic, the focus position shift due to the temperature change can be canceled by the diffractive optical surface. As a result, the beam spot can be reduced in diameter without causing a focus position shift.

  Incidentally, according to the description in Patent Document 1, when the variation of the focus position with respect to the image plane position is calculated in consideration of the variation of the light source wavelength, the refractive index, the lens surface shape, and the lens thickness due to the temperature, the environmental temperature is 25 ° C. It can be seen that with respect to the change from 45 to 45 ° C., it becomes −0.2 mm in the main scanning direction and 0.0 mm in the sub-scanning direction, and hardly changes.

[Problems of the prior art]
However, manufacturing plastic lenses having diffractive optical surfaces has the following manufacturing problems (1) and (2).
(1) Problem that shape accuracy of diffractive optical surface decreases due to mold release resistance As a method for manufacturing a plastic lens, an injection molding method that is suitable for mass production and low in manufacturing cost is generally used. The injection molding method is a method in which a heated and melted plastic material is injected and filled into a cavity of a molding die maintained at a constant temperature, and after cooling and solidifying it, it is released from the die and taken out. As a method for controlling the temperature of the molding die, there are a method of controlling the die temperature with a heater, a method of controlling oil and water by circulating in a flow path provided in the die, and the like.

  In addition, the size of the outer dimensions of the plastic lens affects the cycle time of injection molding, which greatly affects the manufacturing cost of the molded product. The larger the outer dimension, the longer the cycle time. If molding is performed with accuracy, the cycle time of injection molding is further increased. Therefore, in order to shorten the cycle time of injection molding, it is effective to design the shape of the plastic lens so as to reduce the peripheral region where the light flux of the plastic lens does not pass. FIG. 3 shows an outer shape of a plastic lens having a diffractive optical surface, and FIG. 4 shows a light beam transmission region viewed from the diffractive optical surface side by a one-dot chain line. On the diffractive optical surface shown in FIG. 4, an elliptical fine pattern is formed in a step shape in the thickness direction of the plastic lens, and both ends of the fine pattern intersect the lens side surface.

  Incidentally, the conventional plastic diffractive lens of FIG. 4 is made of cycloolefin resin, and its outer dimensions are 5 mm in width, 18 mm in length, and 2 mm in thickness at both ends in the length direction. And since this is injection-molded, the left and right side surfaces are inclined surfaces with a draft of 2 to 5 degrees, for example. Due to this draft, the punching resistance is reduced, and distortion of the molded product due to the punching resistance (deformation of the side edge of the fine pattern) is reduced.

  When the plastic diffractive lens as described above is injection-molded, a phenomenon (decrease in shape accuracy) in which the shape error of the molded product with respect to the design shape becomes large at the tip 75 of the fine pattern of the diffractive optical surface is observed. By analyzing this phenomenon in detail, we were able to elucidate the cause of the decrease in shape accuracy. The cause is as follows.

  That is, in the injection molding method, the plastic material heated and melted is filled in a cavity of a relatively low temperature mold, and this portion is rapidly cooled when it comes into contact with the mold. In particular, in the thin part of the molded product, the plastic material is rapidly cooled under high pressure, so that the internal strain increases and the density increases. For this reason, if the entire plastic material in the mold cavity is cooled to a softening temperature or lower and solidified, when the mold is released from the mold, the tip portion 75 of the fine pattern of the plastic diffractive lens 71 is increased in density (thin wall). The part has a large release resistance between the plastic material and the mold, and this part may be slightly deformed (a phenomenon in which the plastic material is turned up) (see FIG. 5). Further, the tip 75 has a small rigidity because the tip e is thin, and there is a reduction in shape accuracy such that the shape error of the molded product with respect to the design shape becomes large at the tip e. If a plastic diffractive lens having a diffractive optical surface 72 with low shape accuracy as described above is used, the beam spot diameter becomes large in the optical scanning optical system. This is problem (1).

(2) The problem of the tip of the fine pattern on the optical surface sticking to the inner surface of the mold due to mold release resistance By the way, if plastic lenses are molded by injection molding, mass production is possible, and complex surface shapes are required. The provided high performance plastic lens can be manufactured at low cost. However, when the plastic lens is a lens having a diffractive optical surface (plastic diffractive lens), the release resistance of the tip (or edge) e of the tip 75 of the fine pattern on the diffractive optical surface is large, and the tip 75 When the angle α is small and the tip e is thin (see FIGS. 3 and 4), the thin portion may have low rigidity. In this case, as shown in FIG. In some cases, the tip e of the tip 75 of the fine pattern 72 does not completely release, but part of the tip e peels off and adheres to the inner surface of the mold. When such a phenomenon occurs, it is impossible to continue the injection molding, and it is necessary to disassemble the mold, remove the plastic material, and clean it. Therefore, the number of times of mold maintenance is increased, the cycle time is greatly impaired, and the maintenance cost is increased. This is problem (2).

The plastic diffractive lens is exemplified as a problem in manufacturing a plastic lens having a fine pattern on the optical surface. However, the plastic lens having another fine pattern as well as the diffractive optical surface has the same problem. Other examples include an anti-reflection function that can significantly reduce reflectivity by forming a serrated Fresnel lens with a fine pattern on the optical surface and grooves with sub-wavelength level pitch and depth. There are attached plastic lenses.
JP 2005-258392 A JP 2006-323257 A

  Therefore, the present invention aims to enable molding with a high shape accuracy without increasing the number of times of mold maintenance and impairing the cycle time of injection molding for plastic lenses having a fine pattern on the optical surface. Furthermore, the shape of the plastic lens is devised so that the plastic material at the tip of the fine pattern on the optical surface is completely released from the mold, and the tip of the fine pattern is not deformed by mold release resistance. This is the issue.

Means for solving the above problems are as follows.
[Means 1]
Means 1, a plastic optical element a step is formed in a predetermined pattern on an optical surface, between the side surface of the predetermined pattern the plastic optical element, the side surface of the predetermined pattern the plastic optical element connecting the door, it is that the vertical plane is provided on a side surface of the plastic optical element (claim 1).

Further, the predetermined pattern formed on the optical surface in the means 1 is a diffraction pattern (Claim 2).

Further, the predetermined pattern formed on the optical surface in the means 1 is a sawtooth-shaped Fresnel pattern whose cross section is a series of triangles.

The predetermined pattern formed on the optical surface of the unit 1, it is a predetermined pattern having a period shorter than the wavelength of the light beam that passes through (claim 4).

( Delete )

Furthermore, in the above means, the side surface shape of the plastic optical element is a plane and the outline is a rectangle ( Claim 5 ).

Further, the tip of the tip of the fine pattern formed by intersecting a predetermined pattern ( fine pattern ) formed on the optical surface in the means 1 and the side surface of the optical element adjacent to the optical surface is perpendicular to the side surface of the optical element. Ru der to have a planar portion.

Further, the tip of the tip of the fine pattern formed by intersecting the predetermined pattern ( fine pattern ) formed on the optical surface and the side of the optical element adjacent to the optical surface in the above means is on the side of the optical element. Ru der be a circular arc surface that is bent in a convex shape in the length direction of the optical surface in vertical.

In the above, the means 1 and various subordinate means have been described. In short, these are tips of a fine pattern formed by intersecting a predetermined pattern ( fine pattern ) on the optical surface and the left and right side surfaces of the optical element. The tip of the optical element is formed into a plane or curved surface that is perpendicular to the side surface of the optical element and perpendicular to the optical surface, so that the tip has a shape that does not have a thin portion. In this case, the problem that the mold release resistance (the mold release resistance between the tip of the tip and the inner surface of the mold) becomes large, the problem that the tip is peeled off and adheres to the inner surface of the mold is prevented. The shape accuracy of the tip portion (accuracy on the shape of the molded product with respect to the design shape) is increased, and the maintenance frequency of the mold is prevented from increasing, thereby solving the above problems.

[Means 2]
The means 2 is a plastic optical element in which a predetermined pattern ( fine pattern ) is formed on one optical surface, and is adjacent to the fine pattern and the optical surface in a region where the light beam on the optical surface side end is not transmitted or reflected. tip of the fine pattern and the optical element side are formed by crossing, Ru der that has a rib integrally projecting upward from the fine pattern.

  The means 2 is provided with a rib projecting upward at the outer peripheral edge of the fine pattern, and the tip of the fine pattern and the rib are integrated to alleviate the rapid cooling rate of the thin tip of the tip and deform it. And the cause of separation of the tip, and the reinforcing function of the rib against the tip prevents deformation and peeling of the tip, thereby improving the shape accuracy of the tip, This reduces the maintenance frequency and thereby solves the above problems.

In addition, since the means of the invention which concerns on Claim 6 is invention of the range of the following embodiment, description here is abbreviate | omitted.

As described above, according to the present invention, when a plastic lens having a fine pattern on an optical surface is injection-molded, it can be efficiently produced with high shape accuracy without impairing the cycle time of the molding cycle. .
In addition, by using a high-precision plastic diffractive lens having a diffraction pattern in the optical scanning optical system, there is no focus position shift due to temperature fluctuations, and therefore an optical scanning optical system with a small beam spot diameter is realized. Can do.
In addition, as described above, a remarkably high quality image can be stably formed by using the image forming apparatus using the optical scanning optical system in which the beam spot has a small diameter.

Next, Embodiment 1, Embodiment 2, and Embodiment 3 will be described with reference to the drawings.
Embodiment 1 is an embodiment of a plastic diffractive lens, Embodiment 2 is an embodiment of a plastic Fresnel lens, and Embodiment 3 is an embodiment of a plastic lens with an antireflection function.

Embodiment 1
[Example 1 of Embodiment 1]
Example 1 of Embodiment 1 is shown in FIG. This Example 1 has a diffractive optical surface 72 in which a number of ellipses having the same center position are formed in a step shape on one optical surface. The step (height) of each ellipse fine pattern in Example 1 is 1.2 μm, and the pitch in the major axis direction of each ellipse fine pattern is 10 to 200 μm.
In the first embodiment, a fine pattern (fine pattern) formed on the diffractive optical surface 72 and an optical element side surface 73 adjacent to the diffractive optical surface 72 are formed to intersect with each other (tip part of the fine pattern). ) 75 has a tip 74 (or edge) e that is a plane 74 substantially perpendicular to the side surface 73 of the optical element. The flat surface 74 has a height h of 1.2 μm and a width w of 3 to 30 μm. The height h corresponds to the step of the fine pattern. The width w is preferably 5 μm or more, and in this example is 7 μm.

  In the lens of Example 1, the tip of the tip 75 of the fine pattern of the plastic diffractive lens is not thin compared to the conventional lens of FIG. Accordingly, when the mold is released from the mold, the mold release resistance between the mold 75 and the mold is not large, and the rigidity of the mold 75 is not low, so the tip 75 is deformed (a phenomenon in which the plastic material is turned up). In addition, the shape error due to deformation at the time of mold release does not occur in the tip portion 75 of the plastic diffractive lens. Therefore, a plastic diffractive lens having a high shape accuracy with respect to the design shape (hereinafter simply referred to as “shape accuracy”) is manufactured.

  Further, the tip 75 of the fine pattern of the diffractive optical surface 72 of the plastic diffractive lens does not have a thin tip. Therefore, the thin tip of the tip 75 of the fine pattern does not peel off and adhere to the inner surface of the mold. Therefore, it is not necessary to disassemble the mold to remove the plastic material and clean it, and the number of mold maintenance is small, and the maintenance cost is low.

The experimental results for Example 1 are as follows.
The relationship between the angle α of the tip 75 of the fine pattern formed by intersecting the fine pattern and the optical element side surface 73 and its shape error was investigated. The result is as shown in FIG.
8A is an angle of the tip of the fine pattern. The angle α depends on the ratio of the major axis to the minor axis of the ellipse, and the major axis / minor axis ratio is larger than that of the ellipse. The circle with 1 is larger. This experimental result was confirmed with respect to 7 points among a large number of tips 75 in one plastic diffractive lens, and the angle α was 35 degrees, 40 degrees, 45 degrees, 90 degrees, 120 degrees, 140 degrees, It is 160 degrees.
The experimental results in FIG. 8B show that the shape error becomes 1 μm or more when the angle α is smaller than 45 degrees, and the shape error increases rapidly when the angle is smaller than this. When the angle α is 30 degrees or less, the tip of the tip 75, that is, the thin portion of the tip e of the tip 75 (see FIG. 4) peels off and adheres to the inner surface of the mold. It is done. The state of the tip 75 after the tip e is peeled is exaggerated in FIG.

From the result of the experiment shown in FIG. 8B, it can be seen that the angle α needs to be 45 degrees or more in order to mold a plastic diffractive lens with high shape accuracy (shape error is 1 μm or less).
Therefore, in the first embodiment, the tip of the fine pattern 75 of the plastic diffractive lens having an angle α of 45 degrees or less is made a flat surface 74 perpendicular to the side surface of the optical element, and the thin portion of the tip (see e in FIG. 4). Is missing.
The thin pattern at the tip of the fine pattern having the angle α of 45 degrees or less may be eliminated. In the first embodiment, since all the tip parts 75 shown in the drawing are 45 degrees or less, all these tip parts are used. The tip of 75 is a flat surface 74 perpendicular to the side surface of the optical element.
The advantage of Example 1 is that the mold can be easily manufactured.

[Example 2 of Embodiment 1]
Example 2 of Embodiment 1 is shown in FIG. In the second embodiment, the tips of all tip portions 75 of the fine pattern formed by intersecting the fine pattern of the diffractive optical surface 72 and the optical element side surface 73 are bent in a convex shape in the length direction of the optical surface. As a result, a thin portion is eliminated from the tip of the tip portion 75.
In the lens of the second embodiment shown in FIG. 9, since there is no thin portion at the tip of the tip 75 of the fine pattern of the optical surface, the release resistance at the tip of the tip 75 when releasing from the mold is not large. The tip 75 is not deformed (a phenomenon in which the plastic material is turned up). Therefore, a plastic diffractive lens with high shape accuracy at the tip of the diffractive optical surface is manufactured. In addition, the number of mold maintenance is small and the maintenance cost is low.
The advantage of the second embodiment is that long-life and highly stable molding can be performed while suppressing deterioration of the corner angle of the fine pattern of the mold over time.

[Example 3 of Embodiment 1]
Example 3 of Embodiment 1 is shown in FIG. In Example 3, the tip of the tip 75 formed by the intersection of the fine pattern formed on the diffractive optical surface and the side surface 73 of the optical element is a circular arc bent in a convex shape from the fine pattern in the thickness direction of the optical element. Surface 104 is formed.
The lens shown in FIG. 10 does not have a thin portion at the tip of the tip portion 75 of the fine pattern. Therefore, the release resistance of the tip portion 75 is not large. There is no turning up phenomenon. Therefore, a plastic diffractive lens having a high shape accuracy of the tip 75 of the fine pattern is manufactured. In addition, the number of mold maintenance is small and the maintenance cost is low.
The advantage of the third embodiment is similar to that of the second embodiment, but can be expected to further reduce the mold release resistance.

[Example 4 of Embodiment 1]
Example 4 of Embodiment 1 is shown in FIG. In the fourth embodiment, the tip 75 formed by intersecting the fine pattern formed on the diffractive optical surface 72 with the side surface 73 of the optical element is integrated with the rib 114 protruding upward (upward in the drawing) from the fine pattern. It has become. In Example 4, the thickness of the rib 114 is 1 mm and the height is 0.2 mm, but the thickness is 0.5 to 1.5 mm, and the height is the total height of the optical surface (referred to as the sag amount in the lens). It may be +0.1 mm. If the thickness is 0.2 or less, the mold itself becomes a release resistance. If the thickness is 2 mm or more, the element becomes unnecessarily large, which is disadvantageous.

  In the lens shown in FIG. 11, the rib 114 protrudes upward on the periphery of the optical surface, and the tip 75 of the fine pattern is integrated with the rib 114, so that the rapid cooling rate when the tip 75 contacts the mold is high. Alleviated. Therefore, the tip 75 has an angle of 45 degrees or less and the tip e is thin, but its release resistance when releasing from the mold is not large, and the tip 114 is reinforced by the rib 114. The rigidity of the tip e of the portion 75 is not low. Therefore, deformation (see FIG. 5) such as the tip e of the tip 75 of the conventional example of FIG. 3 is prevented.

The rib 114 may be attached to the tip portion 75 having the angle α of 45 degrees or less. In the fourth embodiment, the angle α of all the tip portions 75 shown in the drawing is 45 degrees or less. A rib 114 is attached to 75. Even if the tip portion 75 has the angle α of 45 degrees or more, ribs 114 are preferably attached to the entire periphery of the lens in order to balance the shape and the cooling speed.
As described above, a plastic diffractive lens with high shape accuracy of the tip 75 of the fine pattern is manufactured, the number of mold maintenance is small, and the maintenance cost is low.

[Example 5 of Embodiment 1]
Example 5 of Embodiment 1 is shown in FIG. In the fifth embodiment, the shape of the tip (or edge) of the tip 75 formed by intersecting the fine pattern formed on the diffractive optical surface 72 and the side surface 73 of the optical element is an inclined surface 124 inclined in the lens thickness direction. It has become.
The lens shown in FIG. 12 has an inclined surface in which the tip 75 of the fine pattern is inclined in the lens thickness direction, so that the mold can be easily manufactured, and the tip 75 when the mold is released from the injection mold. The mold release resistance at the tip of is not large, and there is no deformation of the tip 75 (a phenomenon in which the plastic material is turned up). Therefore, a plastic diffractive lens with high shape accuracy at the tip of the fine pattern on the diffractive optical surface of the plastic lens is manufactured. Further, since the convex shape does not have an angle of 90 degrees or less, the tip portion 75 does not peel off and adhere to the inner surface of the mold, and therefore the number of times of mold maintenance is small and the maintenance cost is low. Low.
The advantage of the fifth embodiment is that the mold can be easily manufactured.

[Embodiment 2]
FIG. 13 shows a conventional plastic Fresnel lens 81. In the case of this plastic Fresnel lens 81, the tip e of the tip 75 of the fine pattern (Furnel pattern) may be an edge and the angle α may be 45 degrees or less, and this portion is thin. Sometimes. For this reason, when the mold is released from the mold in the same manner as the plastic diffractive lens of the first embodiment, the release resistance of the tip e of the tip 75 of the minute pattern is large and the tip e is deformed (the plastic material is changed). (A phenomenon of turning up) may occur.
When the angle α is 45 degrees or less, the tip e of the tip 75 has low rigidity, and therefore, the shape accuracy of the tip 75 of the fine pattern on the optical surface of the plastic Fresnel lens 81 is reduced.
The second embodiment is an embodiment in which the present invention is applied to the plastic Fresnel lens as described above.

[Example 1 of Embodiment 2]
Example 1 of Embodiment 2 is shown in FIG. In the first embodiment, the tip of the tip 75 of the fine pattern formed by intersecting the fine pattern formed on the Fresnel optical surface 82 and the optical element side surface 83 is a plane 84 perpendicular to the optical element side surface 83. Yes.

In the first embodiment shown in FIG. 14, the means of the present invention may be applied to the tip portion 75 whose angle α of the fine pattern is 45 degrees or less. The means of the present invention is taken to balance the shape, and the tip thereof is a flat surface 84 perpendicular to the optical element side surface 83.
In the first embodiment, since the tip of the tip 75 of the fine pattern is the flat surface 84, there is no thin portion, so that the tip of the tip 75 when the molded product is released from the injection mold is released. The mold resistance is not large and the rigidity of the tip is not low. Therefore, the tip of the tip 75 is not deformed (a phenomenon in which the plastic material is turned up), and a plastic Fresnel lens having a high shape accuracy of the tip 75 is manufactured.

In addition, since the tip of the tip 75 of the fine pattern is not released from the mold and does not adhere to the inner surface of the mold, there is no need to disassemble the mold, remove the plastic material, and clean it. Therefore, the number of mold maintenance is small and the maintenance cost is low.
The advantage of the first embodiment is that the mold can be easily manufactured.

[Example 2 of Embodiment 2]
Example 2 of Embodiment 2 is shown in FIG. In the second embodiment, the tip 75 of the fine pattern formed by intersecting the fine pattern formed on the optical surface and the side surface of the optical element is integrated with the rib 204 protruding upward from the fine pattern.
In the plastic Fresnel lens shown in FIG. 15, since all of the tip portion 75 of the fine pattern is integrated with the rib 204, the mold release resistance at the tip of the tip portion 75 of the fine pattern when releasing from the injection mold. The tip of the fine pattern tip is not deformed (a phenomenon in which the plastic material is turned up). Therefore, the shape error of the tip 75 of the fine pattern is not large, and a plastic Fresnel lens with high shape accuracy is manufactured. In addition, the number of mold maintenance is small and the maintenance cost is low.
The advantage of the second embodiment is that long-life and highly stable molding can be performed while suppressing deterioration of the corner angle of the fine pattern of the mold over time.

[Embodiment 3]
The third embodiment is an embodiment in which the present invention is applied to a plastic lens 91 with an antireflection function.
A conventional plastic lens 91 with an antireflection function is shown in FIG. In this conventional plastic lens with an antireflection function, one optical surface is an antireflection function optical surface 92, and the fine pattern is a fine pattern having a period shorter than the wavelength of the transmitted light beam.
In the case of a plastic lens with an antireflection function, the tip of the tip portion 75 of the fine pattern may be an edge and the angle may be 45 degrees or less, and this portion is thin. For this reason, like the plastic diffractive lens of the first embodiment and the plastic Fresnel lens of the second embodiment, when this is manufactured by an injection molding method, the thin portion at the tip of the tip becomes dense during cooling. And the mold release resistance of this highly densified part is large, and deformation (a phenomenon in which the plastic material is turned up) occurs in the part. Further, the thin portion at the tip has low rigidity. Accordingly, the shape error at the tip of the tip 75 of the fine pattern is large, and the shape accuracy may be low.

[Example 1 of Embodiment 3]
Example 1 of Embodiment 3 is shown in FIG. In the first embodiment, a tip portion 75 formed by crossing the fine pattern formed on the antireflection function optical surface 92 and the optical element side surface 93 is integrated with a rib 304 protruding upward from the fine pattern. .

In the plastic lens with an antireflection function in FIG. 17, since the tip portion 75 of the fine pattern is integrated with the rib 304, the cooling rate of the tip of the fine pattern is reduced by the rib 304. The release resistance at the tip of the tip is not large, and the tip of the tip 75 is reinforced by the ribs, so the rigidity is not low and the tip does not deform. Therefore, the shape error of the tip end portion 75 of the fine pattern portion of the antireflection optical surface of the plastic lens with antireflection function is not large, and the plastic lens with antireflection function having high shape accuracy is manufactured. In addition, the number of mold maintenance is small and the maintenance cost is low.
The advantage of the first embodiment is that the mold can be easily manufactured.

  In addition, the plastic lens with an antireflection function has a draft angle of 2 to 5 degrees on the side surface 93, which makes it easy to take out the molded product with a low die-cutting resistance (in this regard, If the gradient is 1 degree or less, the effect is small, and if it is 10 degrees or more, it is difficult to handle as an adhesive surface at the time of assembly, so the above range is optimal.) Therefore, distortion of the optical surface due to die-cutting resistance is reduced. Therefore, a plastic lens with an antireflection function having a high shape accuracy of the optical surface is manufactured.

(A) is the schematic diagram which looked at the optical scanning optical system from the side, (b) is the schematic diagram which arranged each lens on a straight line, and represented the distance between each lens surface (A) is the schematic diagram which looked at the optical scanning optical system using a diffractive optical surface from the side, (b) is the schematic diagram which arranged each lens on a straight line, and represented the distance between each lens surface Is a perspective view of a general plastic lens having a diffractive optical surface and a partially enlarged view thereof FIG. 3 is a plan view of the plastic lens of FIG. 3 and an enlarged view of one tip portion of its fine pattern structure. FIG. 3 is a perspective view of the plastic lens of FIG. 3 and an enlarged schematic view showing a state where the tip portion of the fine pattern structure of the optical surface is deformed by the mold release resistance. FIG. 3 is a perspective view of the plastic lens of FIG. 3 and an enlarged schematic view showing a state where a part of the tip portion of the fine pattern structure of the optical surface is peeled off. These are the perspective view of Example 1 of Embodiment 1 about a plastic diffraction lens, and the schematic diagram which expands and shows a part of fine pattern structure (A) is a plan view of a general plastic diffractive lens and an enlarged view showing the angle α of the tip of the fine pattern structure, and (b) is the deformation due to the angle α of the tip of the fine pattern structure and the mold release resistance. Of the relationship between size (size error) These are the perspective view of Example 2 of Embodiment 1 about a plastic diffraction lens, and the schematic diagram which expands and shows a part of fine pattern structure These are the perspective view of Example 3 of Embodiment 1 about a plastic diffraction lens, and the schematic diagram which expands and shows a part of fine pattern structure These are the perspective view of Example 4 of Embodiment 1 about a plastic diffractive lens, and the schematic diagram which expands and shows a part of fine pattern structure These are the perspective view of Example 5 of Embodiment 1 about a plastic diffraction lens, and the schematic diagram which expands and shows a part of fine pattern structure Fig. 2 is a perspective view of a general Fresnel lens and a schematic diagram showing an enlarged part of a fine pattern structure. These are the perspective view of Example 1 of Embodiment 2 about a plastic Fresnel lens, and the schematic diagram which expands and shows a part of fine pattern structure FIG. 3 is a perspective view of Example 2 of Embodiment 2 for a plastic Fresnel lens. Is a perspective view of a general plastic lens with antireflection function Is a perspective view of Example 1 of Embodiment 3 of a plastic lens with an antireflection function

Explanation of symbols

71: Plastic diffractive lens 72: Diffractive optical surfaces 73, 83, 93: Optical element side surface 74: Plane plane perpendicular to the optical element side surface 75: Fine pattern tip 81: Plastic Fresnel lens 82: Fresnel optical surface 91: Antireflection function Attached plastic lens 92: Antireflection function Optical surface 94: Arc surface bent convexly in the length direction of the optical surface 104: Arc surface curved convexly in the thickness direction of the optical element 114: Above the fine pattern (drawing Rib 124 protruding upward): inclined surface 124 inclined in the lens thickness direction
204, 304: Rib e: Tip (or edge)

Claims (6)

A plastic optical element having a predetermined pattern of steps formed on an optical surface,
Between the side surface of the predetermined pattern and the plastic optical element, connecting the predetermined pattern and the side surface of the plastic optical element, and characterized in that side surfaces perpendicular plane of the plastic optical element is provided Plastic optical element.   The plastic optical element according to claim 1, wherein the predetermined pattern formed on the optical surface is a diffraction pattern.   The plastic optical element according to claim 1, wherein the predetermined pattern formed on the optical surface is a Fresnel pattern.   2. The plastic optical element according to claim 1, wherein the predetermined pattern formed on the optical surface is a predetermined pattern having a period shorter than a wavelength of a transmitted light beam.   5. The plastic optical element according to claim 1, wherein a side surface shape of the plastic optical element is a plane and has a rectangular outline. 6.   An optical scanning optical system in which a plastic optical element is assembled in an optical housing, wherein the plastic optical element is the plastic optical element according to any one of claims 1 to 4.

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