JPH1062612A - Plastic mirror - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the change of optical characteristic such as distortion by humidity change as much as possible by forming a film on the whole surface other than the surface of a plastic base in substantially the same thickness as a reflecting film by use of the same material as the reflecting film. SOLUTION: A reflecting film 2 is formed on the surface 3 of a plastic base 1, and the same film as the reflecting film is formed on the reverse side and the side surfaces. The surface 3 and the reverse side have the same moisture absorptivity. Namely, the same film as the surface 3 is formed on the reverse side so that the moisture absorbing quantity is uniformed between both the surfaces, the deformation in moisture absorption can be extremely minimized to a degree having no practical problem. Even in a case where the same film 6 as the reflecting film is formed on the surface 3 and the reverse side 4, but no film is formed on the side surfaces, momsture permeability near the central part of the surface 3 forming the reflecting surface to be used is substantially uniformed when the sectional form of the plastic base 1 has a thin and uniform thickness, or thin and substantially symmetrical to the thickness directional center line, and no shape change is caused in the practical range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plastic mirror having a reflective film formed on the surface of a plastic substrate.

[0002]

2. Description of the Related Art Conventionally, an optical element such as a lens formed of a plastic material such as PC (polycarbonate resin) or PMMA (polymethyl methacrylic resin) is lower in cost than an optical element using a glass material. Since it can be processed relatively easily and has mass productivity, it is used in various optical devices. For example, even in a print output device using an electrophotographic method, such as a laser printer or a digital copier, which performs printing by irradiating a photoconductor with laser light modulated according to image data to form an electrostatic latent image. An optical system made of a plastic material, for example, a plastic mirror is used for various optical systems arranged in an optical path from a laser light source to a photoconductor.

However, since a plastic material has a hygroscopic property, an optical system using a plastic material as a substrate has a higher temperature and temperature than an optical system using a glass substrate.
It is easily affected by changes in the atmosphere such as humidity, and the plastic material expands and contracts due to the change in the atmosphere, deforming the shape, causing aberrations, changing the refractive index, and causing unstable optical characteristics. There is a disadvantage that. For this reason, many measures have been conventionally proposed to improve the above-mentioned disadvantage of the hygroscopic property of the plastic material. For example, Japanese Patent Application Laid-Open No. 58-162901 discloses a plastic optical element having a hydrophobic thin film formed on the surface by plasma polymerization. Also, JP-A-60-490
No. 1 discloses an optical system in which a transparent carbon is coated on a plastic surface by a plasma decomposition deposition method. Japanese Patent Application Laid-Open No. 100510/1991 discloses an optical element having a moisture-proof film formed on the entire surface of a plastic substrate. Furthermore, Japanese Patent Application Laid-Open No. Sho 57-144501 discloses a plastic lens in which a light opaque part is subjected to a moisture-proof treatment. Also, Japanese Patent Application Laid-Open No. 62-40638
Japanese Patent Application Laid-Open Publication No. H11-139,086 discloses an optical head in which the surface of a portion that is exposed to the atmosphere is subjected to a moisture-proof treatment. As described above, conventionally, moisture is prevented by forming a hydrophobic thin film on the surface of a plastic material, and deterioration of optical characteristics caused by expansion and contraction of a plastic substrate is prevented.

[0004]

However, if the above-described hydrophobic thin film is formed on the plastic surface to compensate for the plastic's hygroscopicity defect, the reason for using a plastic material for the optical system is low. A problem arises in that the advantages of cost, ease of processing, and mass productivity are reduced. In particular, in the case of a plastic mirror, when the above-described conventional method is applied to prevent distortion due to moisture absorption, an additional time is required in addition to a reflective film forming step such as vacuum evaporation which originally requires a long time. Since a process for forming a moisture-proof film is also required, there is a problem that manufacturing cost is increased and mass productivity is reduced. An object of the present invention is to provide a plastic mirror in which changes in optical characteristics such as distortion are extremely small even when a humidity changes.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plastic substrate having a hygroscopic property, a reflective film formed on the surface of the plastic substrate, and a film substantially the same as the reflective film formed of the same material as the reflective film. And a film formed on the entire surface other than the surface of the plastic substrate. Further, the object is to provide a plastic substrate having hygroscopicity, a reflective film formed on the surface of the plastic substrate, and a film having substantially the same thickness as the reflective film on the rear surface of the plastic substrate using the same material as the reflective film. And a formed film. Further, in the above-mentioned plastic mirror, the object is also achieved by a plastic mirror, wherein the plastic base has a cross-sectional shape substantially symmetrical with respect to the center line in the thickness direction between the front surface and the back surface. Achieved. Further, the above object is also achieved by a plastic mirror in which the plastic base is chamfered substantially symmetrically with respect to a center line in a thickness direction.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plastic mirror according to an embodiment of the present invention will be described with reference to FIGS. First,
The shape of the plurality of plastic substrates 1 used in the present embodiment will be described with reference to FIG. FIG. 4A shows a disc-shaped plastic substrate 1, and when formed as a plastic mirror, a circular surface 3 of the plastic substrate 1.
Is used as a reflecting surface. FIG. 4 (b) shows a plastic substrate 1 which is concave and has a predetermined radius of curvature on the front and rear surfaces, and is generally a rectangular flat plate. When formed as a plastic mirror, one concave surface 3 is used as a reflecting surface. FIG. 4C shows a rectangular flat plastic substrate 1 having a surface 3 used as a reflecting surface. FIG. 4D shows a plastic substrate 1 having a cylindrical surface shape, and the inner surface 3 of the cylindrical surface is used as a reflection surface. The plastic substrate 1 shown in FIG. 4 is manufactured by machining, mold / injection molding, or the like, has a thickness of about 1 to 3 mm, and a long side or diameter of about 20 to 30 cm.

In this embodiment, a plastic substrate 1 having a relatively small thickness with respect to the width of the reflection surface is used. Distortion or deformation due to moisture absorption in a relatively thin plastic substrate is not a small amount of the total amount of moisture absorption of the plastic substrate, but regions where the moisture absorption is different are unevenly distributed,
That is, this is caused by the uneven distribution of the region where the expansion amount is large and the region where the expansion amount is small. Referring to FIGS. 5 and 6, it will be described that distortion or deformation due to moisture absorption in such a thin plastic substrate is caused not by the total amount of moisture absorption of the plastic substrate but by uneven distribution of moisture absorption regions. FIG. 5 is a diagram showing the hygroscopicity of a plastic substrate. FIGS. 6A to 6D are cross-sectional views of a conventional plastic mirror in which the reflection film 2 is formed only on the surface 3 of the plastic substrate 1 shown in FIGS. 4A to 4D. .

In FIG. 5, .largecircle. Indicates a plastic substrate 1 having a radius of curvature shown in FIG. 4 (b), on which no reflective film is formed, and .circle-solid. As shown in FIG. 6 (b). FIG. 4B shows a plastic mirror in which the reflection film 2 is formed only on the surface 3 of the plastic substrate 1 having the radius of curvature shown in FIG. The horizontal axis in FIG. 5 represents the elapsed time, and the vertical axis represents the radius of curvature. FIG. 5 shows that these plastic substrates and a conventional plastic mirror are exposed to an atmosphere of a temperature of 28 ° C. and a relative humidity (RH) of 85% for 24 hours, and then left in a normal temperature and normal humidity environment (23 ° C., 55% RH). The change of the radius of curvature on the surface 3 in the above process is shown in a time series. In the conventional plastic mirror having the reflection film 2 formed only on the surface 3, the radius of curvature greatly changes in a moisture absorption process in a high humidity environment and a subsequent moisture removal process. On the other hand, a plastic substrate having no reflective film and no hydrophobic protective film formed has almost no change in the radius of curvature even under an atmosphere in which temperature and humidity greatly change. In other words, it can be seen that even if the total amount of moisture absorption of the plastic substrate is large, the uneven distribution of the amount of moisture absorption is small, so that the expansion as a whole does not affect the change in the radius of curvature which affects the optical characteristics of the mirror. On the other hand, in the case of a conventional plastic mirror in which the reflective film 2 is formed only on the surface, regions having different moisture absorption due to the difference in moisture permeability between the surface 3 on which the reflective film 2 is formed and the other plastic surface are unevenly distributed. That is, it can be seen that the difference in the amount of expansion between the surface 3 and the other surface increases, causing deformation of the plastic substrate, which affects the variation in the radius of curvature.

Accordingly, in the case of a flat or thin plastic mirror having a uniform thickness, the reflecting surface and the back surface thereof have the same moisture absorption characteristics, that is, the amount of moisture absorption between the surfaces is made uniform. By forming the same film on the back surface as that of the reflection surface, the amount of expansion due to moisture absorption can be made uniform, and the deformation due to moisture absorption can be made extremely small so that there is no practical problem. The step of forming a film on the entire surface of the exposed portion of the plastic substrate or on the back surface of the reflective surface significantly increases the processing time simultaneously with the step of forming the reflective film or by improving the jig for film formation. It can be realized without.

FIG. 1 shows a cross section of the plastic mirror according to the present embodiment. FIG. 1 (a) to (d)
Are plastic mirrors each having a reflective film 2 formed on the entire surface, that is, the front surface, the back surface, and the side surface of the plastic substrate 1 shown in FIGS. Since the reflective film 2 is formed on the surface 3 of the plastic substrate 1 and the same film as the reflective film is formed on other surfaces, it is possible to make the moisture permeability over the entire surface of the plastic substrate 1 uniform. it can. Therefore, even if there is a change in the atmosphere such as humidity, it is possible to prevent the shape change of the plastic base 1 from occurring. The plastic mirror is formed by depositing a reflective film of a metal such as aluminum or copper by vacuum deposition or the like. If necessary, a protective film such as SiO2 may be further laminated to form a reflective film. In order to form a reflective film on the entire surface, a jig for rotating a plastic substrate is used in a process of forming the reflective film, for example, in a vacuum deposition process. It is possible not to let it.

FIG. 2 shows a cross section of a plastic mirror according to another embodiment of the present invention. FIG. 4 (a),
With respect to the plastic substrate 1 shown in (c) and (d),
A reflection film 2 is formed on the front surface 3 of the plastic substrate 1 and the same film 6 as the reflection film 2 is formed on the back surface 4 of the front surface 3.
Is formed. The same film 6 as the reflection film 2 is not formed on the side surface of the plastic base 1 and the plastic base 1 is exposed. If the cross-sectional shape of the plastic substrate 1 is thin and substantially uniform in thickness, or thin and substantially symmetrical with respect to the center line in the thickness direction, the central portion of the surface 3 which is a reflecting surface actually used optically is ,
The moisture permeability in the vicinity is almost uniform, which is similar to the case of a plastic substrate on which no reflective film is formed, so that the shape does not change in a practical range.
In the step of forming the reflection films on the two surfaces of the plastic substrate 1 in this manner, since it is only necessary to invert the plastic substrate 1, it is necessary to form the reflection films on the entire surface as shown in FIG. A jig having a simpler mechanism than the jig can be used.

FIG. 3 shows a cross section of a plastic mirror according to still another embodiment of the present invention. A chamfered area 5 is formed on the side surface of the plastic
This is a plastic mirror in which the same film 6 as the reflection film 2 is also formed on the back surface 4. In a process such as vacuum deposition, a chamfered area 5 around the surface on which the reflective film 2 is to be formed is provided with:
At the same time, the same film as the reflection film 2 is formed. By providing the chamfered area 5 on which the same film as the reflective film 2 is formed, the exposed portion of the plastic base 1 can be minimized even if a simple jig that only reverses the plastic base 1 is used. It is possible to manufacture a plastic mirror that does not cause a change in shape.

[0013]

As described above, according to the present invention, the same film as the reflection film is formed on the entire surface of the plastic substrate of the plastic mirror or on the back surface of the reflection surface of the plastic mirror. It is possible to realize a plastic mirror in which the deformation of the plastic base is suppressed as much as possible. In addition, the plastic mirror of the present invention eliminates the need for a long-time process of forming a moisture-proof film, and can be formed without significantly increasing the time required for a reflective film forming process such as vacuum deposition, so that cost and mass productivity are reduced. Is also excellent.

[Brief description of the drawings]

FIG. 1 is a diagram showing a plastic mirror according to an embodiment of the present invention.

FIG. 2 is a view showing a plastic mirror according to another embodiment of the present invention.

FIG. 3 is a view showing a plastic mirror according to still another embodiment of the present invention.

FIG. 4 is a diagram showing a plastic substrate used in the embodiment of the present invention.

FIG. 5 is a diagram showing a change in a radius of curvature of the surface of a plastic substrate in an atmosphere in which temperature and humidity change.

FIG. 6 is a view showing a plastic mirror in which a reflection film is formed only on one surface of a plastic substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plastic base 2 Reflective film 3 Front surface 4 Back surface 5 Chamfer area

Claims (4)

[Claims] 1. A plastic substrate having hygroscopicity, a reflective film formed on the surface of the plastic substrate, and a plastic film having substantially the same thickness as the reflective film made of the same material as the reflective film. And a film formed on the entire surface other than the surface of the substrate. 2. A plastic substrate having hygroscopicity, a reflective film formed on the surface of the plastic substrate, and a plastic film having substantially the same thickness as the reflective film made of the same material as the reflective film. A plastic mirror, comprising: a film formed on a back surface of a base. 3. The plastic mirror according to claim 2, wherein the plastic base has a cross-sectional shape substantially symmetrical with respect to a center line in a thickness direction between the front surface and the back surface. And plastic mirror. 4. The plastic mirror according to claim 3, wherein the plastic substrate is chamfered substantially symmetrically with respect to the center line in the thickness direction.