JP2006276721A - Manufacturing method of plastic lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large-sized plastic lens which has high dimensional accuracy and is adequately got rid of inner strain. <P>SOLUTION: The manufacturing method of a plastic lens comprises a process of injection-molding the plastic lens by charging molten synthetic resin material into a cavity of a lens molding die, and by cooling and hardening the synthetic resin material and a process of annealing the injection-molded plastic lens at a temperature lower than the glass transition temperature by 5 to 10°C. Therein, a shape change of the lens produced when performing the annealing with respect to the plastic lens of a desired shape is measured beforehand, the lens molding die is corrected based on the measured value so that the shape change is compensated after the annealing process to obtain the plastic lens of the desired shape, and the plastic lens injection-molded by using the corrected lens molding die is annealed to obtain the plastic lens of the desired shape. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a plastic lens for a scanning optical system used in an image forming apparatus such as a printer, and more particularly to a method of manufacturing a plastic fθ lens improved so as to eliminate internal distortion by annealing.

In an optical scanning unit such as an optical laser scanning type digital copying machine, a laser printer device, or a facsimile machine, laser light emitted from a light source (laser diode) 1 passes through a collimator lens 2 and a cylindrical lens 3 as shown in FIG. Irradiated to the reflecting surface of the rotating polygon mirror 4. Then, the light is condensed by the fθ lens 5 while being deflected and scanned by the rotation of the polygon mirror 4, and a beam spot is projected onto the photosensitive drum 6.
In order to form a high-quality image in the above-described optical scanning unit, the fθ lens is required to have a high degree of dimensional accuracy and to eliminate internal distortion.

Production of plastic lenses with a special shape, such as fθ lenses, at low cost in large quantities by injection-filling a molten synthetic resin material into the cavity of a lens molding die to form a plastic lens Can do.
However, when an uneven-shaped fθ lens is injection-molded, the fθ lens has different cross-sectional areas at the center and end portions of the lens, and therefore has a different cooling rate at the time of injection molding. Therefore, the synthetic resin material constituting the fθ lens Internal distortion occurs, causing birefringence, and optical performance decreases.
Therefore, according to the prior art, the internal strain of the fθ lens can be reduced by selecting a synthetic resin material constituting the fθ lens, making the lens shape difficult to generate internal strain, or annealing after injection molding. Eliminated. (For example, see Patent Documents 1 to 3)
For example, by placing an injection-molded fθ lens in an annealing furnace, heating it at a temperature 15 to 20 ° lower than the glass transition point, and annealing the fθ lens, “strain removal” (takes strain) and adjusts the refractive index. Fθ lenses adjusted to the required refractive index can be obtained.
JP-A-5-188285 JP2002-365576 JP2004-42469

In recent years, a large fθ lens with a maximum wall thickness (lens center) thickness of 20 mm or more is manufactured with high accuracy due to the demand for laser printers that support large format copy paper of A3 size (Japanese standard) or larger. It is hoped to do.
However, in the fθ lens having an uneven thickness obtained by injection molding, the larger the lens size, the larger the internal distortion, and the annealing process was performed under the conventional annealing temperature condition (temperature lower by 15 to 20 ° than the glass transition point). Then, the distortion of the central portion of the fθ lens could not be taken.
On the other hand, if the annealing temperature is raised and the annealing treatment is performed at a temperature 5 to 10 ° C. lower than the glass transition point, the internal distortion of the fθ lens having a large lens size can be sufficiently eliminated, but the fθ lens which is a plastic lens. When the lens is exposed to high temperature conditions, not only the shape change of the lens curvature but also the deformation of the lens surface shape that deforms the swell of the aspheric surface, and the dimensional accuracy of the fθ lens decreases. was there.

According to the prior art, in order to maintain the dimensional accuracy of the fθ lens having a desired shape obtained by injection molding, annealing is performed under temperature conditions (15 to 20 ° C. lower than the glass transition point) that do not cause defects such as shape changes. I was processing.
That is, in order to maintain the dimensional accuracy of the fθ lens, the annealing process cannot be performed at an optimum temperature that can sufficiently eliminate internal distortion, and the internal distortion cannot be sufficiently eliminated particularly in a large fθ lens. .

  Accordingly, the present invention provides a process for injection molding a plastic lens by filling a melted synthetic resin material into a cavity of a lens molding die and manufacturing the plastic lens by cooling and curing the synthetic resin material. And annealing the injection-molded plastic lens at a temperature 5 to 10 ° C. lower than the glass transition point, and the step of annealing the plastic lens having a desired shape was performed. The lens shape change that occurs in the case is measured in advance, and based on the measurement value, after performing the annealing process, the shape change is offset and the plastic lens having the desired shape is obtained. Plastic that has been mold-corrected and injection-molded using the corrected lens-molding mold Sufficiently eliminate internal strain by annealing the lens, and acquires a plastic lens having a desired shape.

In the method for manufacturing a plastic lens for a scanning optical system according to the present invention, the injection molded plastic lens is annealed at an optimum temperature that is 5 to 10 ° C. lower than the glass transition point, thereby allowing the inside of the fθ lens having a large lens size to be processed. Distortion can also be sufficiently removed.
In addition, the lens mold is corrected so as to offset the lens shape change in the annealing process under the optimum temperature condition, and the plastic lens injection-molded using the corrected lens mold is annealed at the optimum temperature. Therefore, an fθ lens having a desired shape can be obtained after the annealing process.

  A method for manufacturing a plastic lens according to an embodiment of the present invention will be described with reference to FIGS.

According to the present invention, when manufacturing a plastic lens for a scanning optical system having a special shape such as an fθ lens, a melted synthetic resin material is filled in a cavity of a lens molding die, and the synthetic resin material The fθ lens is manufactured from the process of injection-molding a plastic lens by cooling and curing, and the process of annealing the injection-molded plastic lens at a temperature 5 to 10 ° C. lower than the glass transition point. By doing so, the internal distortion of the fθ lens is sufficiently eliminated.
By providing a step of annealing at a temperature 5 to 10 ° C. lower than the glass transition point, for example, an fθ lens used in an optical scanning unit corresponding to a large format copy paper of A3 size (Japanese standard) or more, Even in a large fθ lens having a maximum thickness portion (lens center portion) of 20 mm or more, internal distortion can be sufficiently eliminated.

In order to obtain an fθ lens with a desired shape after annealing at an optimum temperature, first, injection molding is performed using a lens molding die to which the lens shape (desired shape) of the final product is transferred, and then the lens shape of the final product is obtained. An fθ lens having a high dimensional accuracy (desired shape) is acquired. The fθ lens with a high degree of dimensional accuracy to which the lens shape (desired shape) of the final product is transferred by injection molding is annealed at a temperature 5 to 10 ° C. lower than the glass transition point, so that internal distortion is sufficiently eliminated and birefringence is eliminated. The optimum temperature at which the rate is the smallest is found, and the change in the shape of the lens when the annealing process is performed at the optimum temperature is measured.
After that, the lens molding die to which the lens shape (desired shape) of the final product is transferred is corrected so as to cancel the lens shape change when annealing is performed at the optimum temperature, and the corrected lens molding die is corrected. A plastic lens injection-molded using a mold is annealed at an optimum temperature (a temperature that is 5 to 10 ° C. lower than the glass transition point) to obtain an fθ lens having a desired shape and high dimensional accuracy.

  According to the embodiment of the present invention, first, using a lens molding die to which a lens shape (desired shape) of a final product is transferred, a molten amorphous polyolefin material APEL 5014DP (manufactured by Mitsui Chemicals, Inc.) is used. By injection-filling the cavity of the lens molding die and cooling and curing it, as shown in FIG. 1 (a), injection molding of a highly dimensional accuracy fθ lens which is the lens shape (desired shape) of the final product. To do.

After that, the fθ lens with high dimensional accuracy obtained by injection molding is annealed at a temperature 5 to 10 ° C. lower than the glass transition point to find the optimum temperature at which the internal refractive index is sufficiently eliminated and the birefringence is minimized. At the same time, a change in the shape of the lens when annealed at the optimum temperature is measured.
Note that when the fθ lens is annealed at a temperature 5 to 10 ° C. lower than the glass transition point, the fθ lens changes its shape, but an optimum temperature at which internal distortion can be sufficiently removed without worrying about the shape change is found.

According to this example, the glass transition point of the amorphous polyolefin material APEL 5014DP (manufactured by Mitsui Chemicals, Inc.) used is 126 ° C., the internal temperature is sufficiently eliminated, and the optimum temperature at which the birefringence is minimized. Was 120 ° C.
When the annealing process is performed at the optimum temperature (120 ° C.), as shown in FIG. 1B, the shape of the fθ lens injection-molded into the final lens shape (desired shape) is lost.

  Subsequently, a lens molding die to which the lens shape change (desired shape) of the final product is transferred based on the measured change in the shape of the lens generated by annealing at the optimum temperature (120 ° C.). Correct. That is, feedback is made to the lens molding die so as to cancel the lens shape change when the annealing process is performed at the optimum temperature.

  Thereafter, the melted amorphous polyolefin material APEL 5014DP (manufactured by Mitsui Chemicals Co., Ltd.) is injected and filled into the corrected cavity of the lens molding die and cooled and cured, as shown in FIG. By obtaining a plastic lens that is different from the fθ lens of the product lens shape (desired shape) and annealing the plastic lens at the optimum temperature (120 ° C.), the internal distortion is sufficiently eliminated and the annealing treatment is performed. By generating a shape change, the lens shape (desired shape) of the final product is restored, and a highly dimensional accuracy fθ lens having a desired shape is obtained after annealing (see FIG. 2B).

It is a figure explaining the state which annealed the ftheta lens of the desired shape at the optimal temperature. It is a figure explaining the state which annealed the plastic lens injection-molded using the correct | amended lens shaping die at optimal temperature. It is a figure explaining the structure of an optical scanning unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator lens 3 Cylindrical lens 4 Polygo mirror lens 5 f (theta) lens 6 Photosensitive drum

Claims (2)

In manufacturing a plastic lens with uneven thickness,
Filling the cavity of the lens mold with a synthetic resin material that has been melted, and cooling and curing the synthetic resin material, and injection molding a plastic lens;
A method for producing a plastic lens from a step of annealing an injection molded plastic lens at a temperature 5 to 10 ° C. lower than the glass transition point,
The shape change of the lens that occurs when the step of annealing the plastic lens having a desired shape is measured in advance, and the shape change is canceled after the step of annealing is performed based on the measured value. The lens mold is corrected so that the plastic lens has the desired shape, and the plastic lens injection-molded using the corrected lens mold is annealed to obtain the desired shape plastic lens. A method for producing a plastic lens. 2. The method of manufacturing a plastic lens according to claim 1, wherein an f [theta] lens used in an optical scanning unit corresponding to a large format paper of A3 size or larger is obtained.

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