JP2001310330A - Mold and molding thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precision working method most suited for highly accurately correcting the shape of precision parts such as a complicatedly shaped mold or the like. SOLUTION: The minute unevenness on the surface of a mold is smoothly covered with a thin film made of glass converting material by coating the surface of the mold with glass converting liquid. After that, the resultant mold is sintered under the predetermined conditions. As a result, the surface of the mold is covered by a thin quartz glass film layer, resulting in improving the surface roughness of the mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical element such as an image forming apparatus, a camera or the like, an optical element of a precision machine product, a precision part, a precision molding die or the like using an electrophotographic technique. .

[0002]

2. Description of the Related Art Conventionally, the most general technique for manufacturing a lens is based on a polishing method. For example, JP
As described in JP-203744, a polishing plate is preliminarily processed into a shape having a reciprocal relationship with a lens shape to be processed, and the polishing plate is pressed against a glass material, and abrasive grains are formed in a gap between the polishing plate and the glass material. It is a method of supplying and rubbing. In this method, since polishing is performed using very fine abrasive grains, the processing stress applied to the glass material during processing is small, and therefore, there is an advantage that distortion remaining in the workpiece is small. However, since the processing cannot be performed unless the final finished shape of the workpiece is a simple shape, the degree of freedom in selecting the processing shape is small.

On the other hand, as the performance of the optical system is required to be higher, it is important to improve the accuracy of the lens shape and to make the lens shape aspherical. It is difficult to process an aspherical surface by the above-described polishing method, and generally, an aspherical surface is formed by machining using NC control. According to the NC processing, a desired shape can be processed, but it is difficult to obtain a mirror surface that can withstand use as a lens.
By the way, if the ductile mode grinding is performed, it is possible to obtain a mirror ground surface even with a brittle material such as glass.

For example, according to an aspherical lens processing method described in Japanese Patent Application No. 2-53557, a workpiece is mounted on a table rotated by a motor, and a grindstone for processing these workpieces. Is attached to an air spindle and rotates at a rotation speed of about 10,000 rpm. Then, a pulse is detected from a rotary encoder directly connected to the rotation axis of the rotary table, and processing data is supplied to the piezo actuator based on the pulse, and the linear table is continuously moved back and forth. The air spindle is step-feeded every rotation of the rotary table, and changes its position to change the contact position between the grindstone and the workpiece. According to this method, any non-axisymmetric aspherical shape can be processed. Furthermore, in this method, the cutting depth of the grindstone with respect to the workpiece can be controlled on the order of submicron, so that brittle materials can be ground in ductile mode, and a mirror surface sufficient for use as a lens by grinding alone can be obtained. It is possible to obtain.

[0005] However, this method requires a long processing time for finishing the aspherical surface portion, and further causes variations in shape accuracy due to the processing.

Therefore, there is a molding method as a method for efficiently processing a lens having a complicated and highly accurate surface shape. For example, in the case of plastic molding, this is a technique of injecting molten plastic into a mold and performing pressure molding to obtain a molded product. Further, glass molding is a technique in which heated and softened glass is put into a mold and molded under pressure to obtain a molded product. As described above, in the molding method, the mold shape is transferred and replicated as it is as a molded product shape, so the mold technology is important.
That is, a technique for processing a mold with high precision is required. In particular, in the case of a mold for molding an optical element such as a lens, it is necessary to achieve both surface roughness of the mold surface and shape accuracy. Therefore, as a conventional technique, a method of performing finishing by polishing on a mold surface is often used. When the mold surface is finished by the polishing method, for example, the operation of rubbing diamond abrasive grains with a soft pad such as felt on the finished surface is repeated to prepare the finished surface. When the main purpose is to adjust the shape accuracy, an arbitrary position on the finished surface may be locally polished using a small pad, but the processing time is slow. Further, when polishing is performed using a large pad, the processing time is shortened, but the shape cannot be corrected as a matter of course. Especially when finishing the mold surface with complicated shape,
It is necessary to repeat the polishing operation and the shape measurement operation to improve the surface roughness while taking care not to impair the shape accuracy. Thus, the finish polishing operation requires a lot of processing time and labor.

[0007]

In particular, when processing a mold for molding an optical element such as a lens that requires a high-precision surface, it is necessary to achieve both shape accuracy and surface roughness. That is, since it is necessary to perform polishing with care so as not to impair the accuracy of the shape formed by the pre-processing, a great deal of labor and time are required.

An object of the present invention is to provide a mold processing technique capable of efficiently and accurately processing a mold by a simple method.

[0009]

The processing method of the present invention for achieving the above object is as follows. That is, the surface roughness is improved by applying a silica coating to the surface of the workpiece by a wet method to fill fine irregularities on the surface of the workpiece with a silica film. For example, a polysilazane, which is a kind of a coating type glass inversion liquid (SOG: Spin On Glass), is applied to the surface of a workpiece, and baked to form a silica film and smooth the surface of the workpiece. Polysilazane is an inorganic polymer having a basic structure of -SiH2NH-, and is applied to the surface of a workpiece using a solution obtained by dissolving it in an organic solvent as a coating solution. Fine irregularities on the surface of the workpiece are filled with the coating liquid layer. Next, by firing in the air, the polysilazane on the surface of the workpiece reacts with moisture and oxygen, and is converted into a dense high-purity silica (amorphous SiO 2) film at about 450 ° C. As a result, the surface of the workpiece is covered with a silica layer comparable to quartz glass, which is bulk silica, and the surface roughness is reduced.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings. Embodiment 1 FIG. 1 shows an example of a disk-shaped mold processing process having a mirror surface.

As shown in FIG. 1A, the diameter is 50 mm and the thickness is
The surface of a 10 mm stainless steel (SUS420) disk 1 is machined by a surface grinder 2 until the surface has an average surface roughness of 0.05 μm. Next, as shown in FIG. 1B, this surface has an average surface roughness.
Lap using lapping machine 3 until it becomes 0.015 μm.

On the other hand, the undulation of the surface was measured within a range of the central portion length of 40 mm, and the undulation was 0.35 μm P-P.

Next, in order to improve the surface roughness, a thin quartz glass layer was coated on the surface of the stainless steel disc. 0.5 coat thickness
μm.

In this embodiment, a polymer made of Si, N, H (or an organic group) is used.
The method of applying the polysilazane to be converted to 2) and baking it was used. As shown in FIG. 1C, polysilazane (manufactured by Tonen Corp.) was dissolved in xylene, and the stainless steel disc 1 was immersed in the solution 4 and pulled up to form a thin film. FIG.
As shown in (d), after air drying, firing was performed in an electric furnace 5 at 500 ° C. for 1 hour to obtain a mold 6 having a mirror surface. FIG.
As shown in (e), when the thin film surface was analyzed, it was found to be almost 100% pure quartz glass.

As a result of measuring the surface roughness and the amount of undulation of the mold surface after coating, the average surface roughness was 0.009 μm, and the amount of undulation of the surface was 0.35 μm P-P in the central part length of 40 mm. That is, the surface roughness could be improved without changing the surface undulation. Table 1 shows the average surface roughness and undulation of the mold surface before and after silica coating.

[0016]

[Table 1]

Next, the mold 6 was assembled into a mold body, and a resin disc having a thickness of 3 mm was molded using an injection molding machine. Acrylic was used as the resin material. Molding was performed continuously at a mold temperature of 130 ° C. and a maximum injection pressure of 650 kg / cm 2 for 10,000 shots. The surface accuracy of the molded product is almost the same as the mold surface, that is, the average surface roughness is 0.009 μm.
37 μm P-P. The undulation of the molded article is slightly increased, which is considered to be due to the influence of the deformation of the molded article when the molded article is removed from the mold after molding. (Example 2) Polysilazane was applied to the surface of the mold 6 produced in Example 1 to form a thin film, and then fired in an electric furnace 5 at 500 ° C for 1 hour.

At this time, the film thickness is 0.5 μm. That is, the surface of the mold manufactured in the present embodiment has a two-layer structure of the SiO2 layer, and the surface roughness is further reduced as compared with the mold in the first embodiment. As a result of measuring the surface roughness and the amount of undulation of the mold surface after the second layer coating, the average surface roughness was 0.005 μm, and the amount of undulation of the surface was 0.34 μm P-P in the central part length of 40 mm.

Further, a third layer of SiO
When two layers were formed, the average surface roughness of the mold surface was 0.003μ
m, the amount of surface undulation was in the range of 0.34 μm P-P with a central length of 40 mm. (Embodiment 3) FIG. 2 shows a processing process of an axisymmetric aspheric master lens.

Using glass (glass material BK7), radius of curvature 50m
Process the m-shaped concave axisymmetric aspherical master lens.
As shown in FIG. 2A, first, a glass block 7 is cut into a predetermined size, and then, as shown in FIG.
A rough master lens having a concave aspherical shape with a radius of curvature of 50 mm is manufactured using a grinding machine 8. Next, FIG.
As shown in (1), the grindstone of the grinding machine was replaced with a grindstone for finishing, the cut amount of the grindstone was made extremely small, and the ductile mode grinding was performed to obtain a master lens 9 having a mirror surface. When the shape of the master lens surface was measured, the average surface roughness was 0.012 μm, and the undulation amount was 0.25 μm P-P in the range of the central portion of the sample having a length of 30 mm. Next, in the same manner as in Example 1, to improve the surface roughness of the master lens surface, a polysilazane solution 4 was coated on the surface to a thickness of 0.2 μm, air-dried, and then sintered at 450 ° C. for 1 hour in an electric furnace. (FIGS. 2 (c) and (d)) As a result, as shown in FIG. 2 (e), an extremely smooth quartz glass thin film layer is formed on the surface of the master lens, and the master lens 10 further improved in surface roughness. I got The surface roughness of the master lens 10 after coating with the quartz glass thin film was 0.007 μm in average surface roughness. The undulation amount of the surface was 0.23 μm P-P in the range of 30 mm in the central part of the sample. Table 2 shows the average surface roughness and undulation of the master lens surface before and after silica coating.

[0021]

[Table 2]

Next, the shape of the master lens 10 was transferred to the surface of the convex spherical lens 11 to process a convex aspheric lens. The manufacturing process is shown in FIG. In other words, a convex glass spherical lens 11 having a radius of curvature very close to the radius of curvature of the master lens 10 is used as a substrate lens, and the aspherical shape of the master lens 10
2 is transferred. As the resin 12, an ultraviolet curable resin is used. That is, an appropriate amount of the ultraviolet curable resin 12 is dropped on the surface of the substrate lens 11 (FIG. 3 (a)), and the master lens 10 having an aspherical shape is pressed from above with an appropriate pressure so that the master lens 10
After transferring the shape (FIG. 3 (b)), the resin is irradiated with ultraviolet rays, cured and released. (FIGS. 3C and 3D) The completed lens becomes an aspheric lens 13 having a so-called hybrid structure in which a spherical glass lens and a resin aspheric lens are integrated. As described above, the method of the present invention is also effective for mold processing of a hybrid lens. (Example 4) A non-axisymmetric aspheric lens mold was processed, and an Fθ plastic lens 14 for a laser beam printer was molded using the mold. FIG. 4 shows the lens shape. The surface A is a non-axisymmetric aspherical shape having a radius of curvature R1 in the main scanning direction, a radius of curvature r in the sub-scanning direction different from R1, and r1, r2, and r3 each having a different radius of curvature.
The surface B has a spherical shape. Acrylic resin was used for the lens material. Also, a SUS420 stainless steel material was used for the mold. The working process of the mold is the same as in the second embodiment.

First, a mold flank is cut out to a predetermined size, and a non-axisymmetric aspherical shape having a shape reverse to that of the lens is formed using an NC grinding machine. Next, the mold surface was polished using diamond abrasive grains. The average surface roughness was 0.011 μm, and the amount of undulation of the surface was 0.15 μm P-P in the center length of 20 mm. Next, in order to improve the surface roughness of the mold surface, a 0.2 μm polysilazane solution was coated on the mold surface, and was naturally dried and sintered at 450 ° C. for 1 hour in an electric furnace. As a result, an extremely smooth quartz glass thin film layer was formed on the mold surface. The surface roughness of the mold surface after coating with the quartz glass thin film was 0.007 μm in average surface roughness. The amount of undulation of the surface was 0.14 μm P-P in the center length of 20 mm. Table 3 shows the average surface roughness and undulation of the mold surface before and after silica coating.

[0024]

[Table 3]

This mold was assembled in a mold body, and an aspherical plastic lens was molded using an injection molding machine. Acrylic was used for the lens material. Molding was performed continuously for 10,000 shots at a mold temperature of 115 ° C. and a maximum injection pressure of 670 kg / cm 2. The surface accuracy of the molded plastic lens was comparable to that of the mold surface, that is, the average surface roughness was 0.007 μm, and the undulation amount of the surface was 0.16 μm P-P in the range of the lens center length of 20 mm.

Although a case in which a metal material and glass are used as a mold base material has been described as an example, the present invention is also effective for finishing a mold surface using carbon, ceramics, plastic, or the like as a base material. Needless to say. Also,
The mold of the present invention is effective not only for precision parts such as optical elements such as lenses and prisms and substrates used for optical discs, but also as molds for general plastic molded products.

Further, in this embodiment, the dipping method is shown as a coating method of the liquid compound containing the precursor for forming the SiO 2 layer. However, the spin coating method, the spraying method, the brush coating method using a brush or a brush, the flow coating method, or the like. It can be coated using a method such as a method.

[0028]

As described above, the use of the method according to the present invention makes it possible to easily and efficiently reduce fine irregularities on the mold surface. As a result, processing of a mold for an optical element having a complicated shape and requiring precision can be easily performed in a short time.

[Brief description of the drawings]

FIG. 1 shows a process of processing a disk-shaped mold.

FIG. 2 is a mold processing process for high fidelity molding.

FIG. 3 shows a high-brightness molding process.

FIG. 4 is an external view of an Fθ plastic stick.

[Explanation of symbols]

1: Stainless steel disk, 2: Surface grinding machine, 3: Lapping machine,
4 polysilazane solution, 5 electric furnace, 6 mirror mold, 7
... Glass block, 8 ... NC grinding machine, 9 ... Rough surface master lens, 10 ... Master lens, 11 ... Glass spherical lens, 12 ... UV curable resin, 13 ... Aspherical lens (hybrid structure), 14 ... Fθ plastic lens , A
Surface: non-axisymmetric aspherical shape, B surface: flat or spherical shape,
R1: radius of curvature in the main scanning direction, r1, r2, r3: radius of curvature in the sub-scanning direction.

Claims (7)

[Claims] 1. A mold having irregularities, wherein the irregularities on the mold surface are filled with a SiO2 film having a thickness of 100 μm or less. 2. The method according to claim 1, wherein a liquid compound containing a precursor for forming an SiO2 layer is applied to the surface of the substrate having the irregularities, and the liquid compound is converted into SiO2. Item 7. The mold according to Item 1. 3. A liquid compound containing a precursor for forming an SiO2 layer is applied to the surface of the substrate, and the liquid compound is converted into a SiO2 layer.
On the surface on which the layer is formed, a liquid compound containing a precursor for forming an SiO2 layer is applied, and the liquid compound is converted to Si.
3. The method according to claim 2, wherein the material is made by forming O2.
The mold described. 4. The mold according to claim 1, wherein an organic solvent containing polysilazane is used as the liquid compound containing a precursor for forming the SiO2 layer. 5. The mold according to claim 1, wherein a metal material, glass, carbon, ceramics, or plastic is used as the mold base material. 6. A molded article characterized by being molded using the mold according to claim 5. 7. The method according to claim 5, wherein polysilazane or a modified product thereof is applied to the surface of the mold and fired in a steam atmosphere to form an SiO2 layer.