JPS6177018A - Filter - Google Patents

Abstract

PURPOSE:To increase transmittivity in a desired wavelength region and to decrease the same in an unnecessary wavelength region by providing an odd number of dielectric layers in order of low refractive indices and high refractive indices on one main surface of a metallic film and an odd number of dielectric layers in order of the high refractive indices and low refractive indices on the other surface. CONSTITUTION:The two multi-layered dielectric films are provided on both main surfaces of the metallic film 13. One of the multi-layered dielectric films is constituted of an odd number of the layers laminated alternately with the low refractive index dielectric layers 4, 16, then high refractive index dielectric layer 15 in this order from the film 13 side. The other of the multi-layered dielectric films is constituted of an odd number of the layers laminated alternate ly with the high refractive index dielectric layers 10, 12, then low refractive index dielectric layer 11 in this order from the film 13 side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a filter, and particularly to a filter suitable for an optical system of a copying machine.

[Prior art]

Generally, the light source, optical system, and photoreceptor in a copying machine each have different spectral characteristics (energy, transmittance, sensitivity), so the spectral characteristics of the entire copying machine appear as a superposition of these characteristics. However, this spectral characteristic is different from the relative luminous efficiency, and in order to obtain a custom spectral characteristic close to the relative luminous efficiency, it is usually necessary to arrange and adjust various types of filters in the optical system.

For example, a CdS-based photoreceptor has relatively high sensitivity in the long wavelength region of red, as shown in FIG.

However, if the spectral energy distribution of the light source is biased towards the long wavelength side as shown in Figure 2, the photoreceptor's sensitivity characteristics may overlap (sometimes reinforcing each other), and the copied image corresponding to the red part of the original will be distorted. However, due to overexposure, the image appears white. In order to eliminate these inconveniences, filters have traditionally been used to adjust the spectral characteristics of the entire copying machine to those close to the relative luminous efficiency.

Filters include dye filters, colored glass, dielectric multilayer filters, etc.; from the viewpoint of performance and cost, dielectric multilayer filters are generally used. This filter is made of a multilayer film in which dielectric materials with a high refractive index and dielectric materials with a low refractive index are alternately laminated on a positive substrate, and is manufactured by a vacuum evaporation method or the like. Figure 3 is an example of the spectral characteristics of a multilayer filter consisting of five layers.The transmittance should be 90% or more at wavelengths of 400 to 580 nm, and the transmittance should be low at longer wavelengths of 680 nm or more. This gives spectral characteristics close to relative luminous efficiency.

However, the spectral characteristics of the light source and photoreceptor are 800 to 900
It has sensitivity even in the nanometer range, and as can be seen from FIG. 3, the filter's ability to cut near-infrared light in this region is insufficient. If the ability to cut near-infrared light is to be further improved, it is necessary to laminate one or more dielectric layers, which increases manufacturing costs. Furthermore, in devices such as copying machines where the angle of incidence on the filter is large, the spectral characteristics vary depending on the angle of incidence due to the formation of a multilayer film, making it impossible to obtain uniform spectral characteristics.

[Purpose and outline of the invention]

The first object of the present invention is to eliminate the drawbacks of the conventional examples, to increase the transmittance in the visible range, and to sufficiently reduce the transmittance in the near-infrared range, even in wavelength ranges that have been difficult to achieve in the past. The goal is to provide filters that can.

A second object of the present invention is to provide a filter that has excellent spectral characteristics as described above and is particularly suitable for use in copying machine optical systems.

The above object is a filter composed of a metal film and two dielectric multilayer films bonded to both surfaces of the metal film, wherein one of the dielectric multilayer films has a lower refractive index than the metal film side. It is composed of an odd number of layers alternately stacked in the order of a dielectric layer and then a high refractive index dielectric layer, and another dielectric multilayer film.
This is achieved by the filter of the present invention, which is comprised of an odd number of layers alternately stacked in the order of high refractive index dielectric layers and then low refractive index dielectric layers from the metal film side.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows the optical system of a typical copying machine. In the figure, 1 is a document, 2 is a Rodan Lang, 3 is a condensing mirror, 4, 5.6 are mirrors for bending the optical path, 7 is a transmission projection lens, and 8 is a photosensitive drum equipped with a CdS photosensitive member. be. Here, the light emitted from the run f2 illuminates the original 1 either directly or by being condensed by the condensing mirror 3. The original light scattered and reflected on the original surface is reflected by mirrors 4 and 5.
It is reflected every day, is refracted and converged by the projection lens 7, and is reflected by the mirror 6.
After being reflected, an image is formed on the photosensitive drum 8.

Here, the projection lens 7 has the configuration shown in FIG. 5, for example, and a filter 9 is bonded to the convex surface 7' of the projection lens on the document side.

The filter 9 basically has the structure of a multilayer interference thin film as shown in Fig. 6, and 7 in the figure is a base body such as the projection lens shown in Fig. 5, and usually has an optical power such as BK-7. ° Consists of laths.

10.12.15 is a high refractive index dielectric layer with a refractive index n
= 2.0 to 2.4 Tie□, ZrO2, CeO□
,, HfO□.

S10. Made of material such as Ta205. 11,14゜1
6 is a dielectric layer with a low refractive index, and the refractive index n ~1.38~
It is made of materials such as 1.5 Na ALF and MgF2.5IO2.

Reference numeral 13 is a thin metal film, preferably made of silver or aluminum. These metal thin films and dielectric layers are formed by a vacuum deposition method (including ion blating, sulfur 4 tattering), or the like. Silver has low absorption in the visible region and high reflectance in the near-infrared region. 7th
The figure shows the reflectance calculated using an electronic computer when silver is formed on a glass substrate with a film thickness d ranging from 50 to 400λ. The thickness of the silver layer is suitably about 130X to 200X in consideration of the above-mentioned spectral characteristics and film formation state. Based on the spectral characteristics of this silver thin film, in order to increase the transmittance in the visible range and the reflectance in the near-infrared range, by sandwiching the metal film between dielectric layers, Tie2r ZnO2, which has a particularly high refractive index as a dielectric, is used. *By using CeO2, etc., it is possible to increase the transmittance in the visible range and widen the width of the transmission range. The idea of sandwiching this gold film between dielectric layers is known in the art, for example, in 0PTICA ACTA 1978.
, VoL, 25. However, the structure is different from that of the present invention.

In order to adjust the overall spectral characteristics of a copying machine, it is necessary to have spectral characteristics close to the relative luminous efficiency characteristics.
As shown in the figure, the wavelength separation section is too close to the long wavelength side, making it impossible to achieve the original purpose.

Therefore, in the present invention, an odd number of dielectric layers sandwiching an intermediate metal film are formed, and a seven-layer filter as shown in FIG. 6, for example, has been found. The thickness of each dielectric layer is basically the mismeasured reference wavelength λ, which is approximately the center of the high reflection band. However, the exact design wavelength must be adjusted according to the radiant energy characteristics of the light source and the spectral sensitivity characteristics of the photoreceptor, and the film thickness is optimized using a computer.

As the number of dielectric layers increases, the wavelength separation section of the spectral characteristics becomes more vertical, and the high transmittance band also becomes narrower. Multi-layering improves the wavelength cutting ability of the chassis, but the contrast for blue, green, and cyan colors decreases, so it is necessary to have a moderate slope. Considering this point, it is necessary to have about 7 layers as mentioned above. is appropriate. Compared to conventional filters, they have the same transmittance in the visible region and the same wavelength cutting ability, but whereas conventional filters have transmittance that increases toward longer wavelengths, the intermediate metal layer Since the reflectance of a certain silver is high on the long wavelength side, the transmittance in the long wavelength region can be kept low.

As Example 1, in the seven-layer structure shown in FIG. 6, the spectral characteristics and film configuration are shown in FIG. Shown in the table. According to this example, in terms of spectral characteristics, the transmittance is high in the wavelength range of 400 to 560 nm, and the transmittance is low on the long wavelength side, and even at a wavelength of 1000 nm, the transmittance is high.
It is below 0%. It also has excellent mechanical and chemical durability, and no deterioration was observed in the adhesion test using Syscotch Teig and the abrasion resistance test. Further, in a moisture resistance test, no change in spectral characteristics or appearance was observed even after being left in a constant temperature M humidity chamber at 45° C. and relative humidity of 95° C. for 1000 hours.

f&, as Example 2, T t O2 as the high refractive material
Minutes when using S s 02 as a low refractive index material
The F property and membrane structure are shown in FIG. 10 and Table 2. This example also has the same optical characteristics and mechanical properties as Example 1.
Chemical durability was obtained.

Notes to Table 1: *The refractive index of Ag is λ = 620 nm The film thickness of lAg is the physical thickness and the unit is also Table 2 Note: The refractive index of 1Ag is λ = 620 nm The film thickness of lAg is the physical thickness [Effects of the Invention] As explained above, the present invention provides an optical system for a copying machine that includes a projection lens, a reflecting mirror, etc. for projecting light from an original onto a photoreceptor. By using it as one surface of the projection lens or as a filter, it is possible to increase the transmittance in a desired wavelength range and decrease the transmittance in an unnecessary wavelength range, and it is possible to obtain desired spectral transmittance characteristics. Furthermore, it requires fewer layers than conventional methods and has improved chemical durability.

By installing the filter according to the present invention between the light source of the copying machine optical system and the document, it not only functions as a filter that makes the light from the light source have the desired spectral characteristics, but also has a high reflectance in the near-infrared region. , reflects near-infrared light. As a result, the conventional problem of temperature rise on the document table is improved.

In addition, as a sensitivity correction filter for silicon detectors, whereas conventionally used hot mirrors have a multilayer film of 20 or more layers, the filter of the present invention has fewer layers and requires less optical performance. Characteristics can also be obtained. As a result, manufacturing becomes easier and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 shows the spectral sensitivity characteristics of CdS, which is a photoreceptor for a copying machine. FIG. 2 shows the wavelength distribution of spectral energy of a light source of a copying machine. Figure 3 shows the spectral characteristics of a five-layer near-red cut filter formed on a glass substrate, with the vertical axis showing the transmittance (cA) and the gutter axis showing the wavelength (nm). Fig. 5 shows the optical system of the copying machine. Fig. 5 specifically shows the projection lens in Fig. 4, which is a positive meniscus lens. Fig. 6 shows a cross-sectional view of the filter according to the present invention. Figure 7 shows Ag film thickness 50λ to 4oo' on a glass substrate.
It shows the spectral characteristics when formed in the IL range. Figure 8 shows TiO2/Ag/ :[
It shows the spectral characteristics when formed with a film configuration of 'i0°. FIG. 9 shows the spectral characteristics of the filter according to Example 1. FIG. 10 shows the spectral characteristics of the filter according to Example 2. 10.12.15...High refractive index dielectric layer, 11°14
．． 16...Low refractive index dielectric layer, 13...Metal film. Figure 4 Figure 5

Claims (3)

[Claims] (1) A filter composed of a metal film and two dielectric multilayer films bonded to both main surfaces of the metal film, wherein one of the dielectric multilayer films has a lower refractive index than the metal film side. It is composed of an odd number of layers alternately stacked in the order of dielectric layer and then high refractive index dielectric layer, and another one of the dielectric multilayer films is
1. A filter comprising an odd number of layers alternately stacked in the order of high refractive index dielectric layers and then low refractive index dielectric layers from the metal film side. (2) The filter according to claim (1), wherein the metal film is made of silver or aluminum. (3) The filter according to claim (1), wherein the metal film has a thickness of 130 to 200 angstroms.