JPH045164B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to a mirror for an imaging system that also serves as a filter for an electrophotographic copying machine.

(b) Background of the invention In electrophotographic copying machines, Se-
When using an As photoconductor, an amorphous silicon photoconductor, etc., these photoconductors are sensitive to long wavelengths and short wavelengths centered around a wavelength of 550 nm, so a white light source such as a halogen lamp cannot be used. If this method is used, there is a problem in that the red and blue parts of the original document are poorly captured. As a countermeasure to this problem, colored glass filters or interference film filters are usually combined to cut out light on the short wavelength side and light on the long wavelength side, respectively, but since two or more filters are combined, there is a loss in the amount of light. However, there was a problem in that the cost would also increase. This problem can be solved to some extent by using a multilayer mirror that has the characteristics of a bandpass filter, but conventional multilayer mirror bandpass filters have unsatisfactory characteristics. Let me explain this point in a little more detail.

FIG. 1 shows the film structure of a conventional multilayer mirror.
G is the glass substrate and A is the external air area.
H is a high refractive index layer, L is a low refractive index layer, and each layer has an optical thickness of λ _p /4 (the value obtained by multiplying the actual thickness by the refractive index) as shown in the figure. Here, λ _p is the center wavelength of the reflection region. The layer structure is such that the layer in contact with the glass substrate and the layer in contact with air have a high refractive index, and H and L layers are alternately stacked in between. FIG. 2 shows the spectral reflectance characteristics of a mirror with such a film configuration. As shown in the figure, the reflection characteristics exhibit those of a bandpass filter, but ripples appear on both sides of the band region. Since this ripple portion is exposed to light by the photoreceptor, the reproducibility of the red and blue portions of the document is not improved much.

Attempts have also been made to improve the spectral reflection characteristics as shown in FIG. Figure 3 is an example.
In the film structure shown in the figure, the H layer in contact with the glass substrate and the H layer in contact with air each have an optical thickness of λ _p /8. In this case, the spectral reflectance characteristic becomes as shown in FIG. 4, and the ripples on the longer wavelength side disappear, but the ripples on the shorter wavelength side become stronger than in the configuration shown in FIG. 1. If the film structure shown in FIG. 3 is replaced with H and L, the ripples on the short wavelength side will be removed, but the ripples on the long wavelength side will be enhanced compared to the characteristics shown in FIG. 2.

(c) Purpose The purpose of the present invention is to improve the spectral reflectance characteristics when using a multilayer mirror in an electrophotographic copying machine.

(D) Structure The present invention has a layer in contact with a glass substrate with a high refractive index, a layer in contact with air with a low refractive index, and an even number of layers with high and low refractive indexes arranged in the middle alternately. The optical thickness of the layer in contact with the air layer is λ _p /8, the optical thickness of the next low refractive index layer in contact with the H layer in contact with the glass substrate is λ _{p /4 or less, and the optical thickness of each other layer is λ p} /4 or less. A multilayer mirror having a thickness of λ _p /4 is provided.

(E) Embodiment An embodiment of the present invention is shown in FIGS. 5 and 6.
As in FIG. 1, G is a glass substrate, A is external air, H is a high refractive index layer, and L is a low refractive index layer. For convenience of explanation, each layer is numbered below, and the glass substrate G
The layer in contact with the layer is called the first layer, the second layer, etc.
The last layer in contact with air will be called the outermost layer. Further, the high refractive index layer is called the H layer, and the low refractive index layer is called the L layer, and the thickness of each layer is not specified, but indicates the optical thickness. λ _p is the design wavelength, and is selected to be, for example, 550 nm.

ZrO2, TiO2, ZnS, CeO2, etc. are used as the H layer. MgF2, SiO2, cryolite, etc. are used as the L layer. A glass substrate G having a refractive index of about 1.52 is used.

In the embodiment shown in FIG. 5, the first H layer and the outermost L layer have a thickness of λ _p /8, and all other layers have a thickness of λ _p /4. FIG. 7 shows the spectral reflectance characteristics of the mirror of this example, and as can be seen from the comparison with FIG. 2, the ripples on both sides of the band region are reduced.

In the embodiment shown in FIG. 6, the thickness of the second L layer is λ _p /
It was made slightly thinner than 4 and set to 0.23λ _p . In practice, the thickness of the same layer is preferably in the range of 0.23 to 1.2λ _p . The spectral reflectance characteristics of this example are shown in FIG. It can be seen that the ripple on the long wavelength side is further reduced compared to the embodiment shown in FIG. The purpose of this embodiment is to further suppress ripples on the long wavelength side.
If the second layer is made too thin to be less than 0.2λ _p , the ripples on the short wavelength side will become stronger, the reflectance will become more than 25%, and the reproducibility of blue will deteriorate. 0.23λ _p ~
In the range of 0.25λ _p , there is not much difference from the embodiment shown in FIG. This example attempts to improve the reproducibility of the red side more than the one shown in Figure 5, but
In the case of the Se-As photoconductor, it is sensitive not only to red light but also to near-infrared light, which not only reduces the reproduction of the red part but also has effects that adversely affect the image forming process such as memory effects. Therefore, in such a case, we recommend using a 6th wave filter that particularly suppresses ripples on the long wavelength side.
The configuration in the diagram is valid.

FIG. 9 shows an example of the configuration of an electrophotographic copying machine using the mirror of the present invention. 1 is the glass plate of the manuscript table,
2 and 3 are scanning mirrors, and scanning mirror 3 moves half the distance that scanning mirror 2 moves. 4 is a coupling lens, 5
are both mirrors according to the present invention and their positions are fixed, and 6
is the photoreceptor drum. Functionally, the mirror of the present invention may be adopted as any of the mirrors 2, 3, and 5, but since the mirror 5, which is always near the imaging lens, has the smallest area, the mirror 5 of the present invention may be adopted as the mirror of the present invention. It is advantageous in terms of manufacturing to adopt this method.

(f) Effects As mentioned above, the multilayer mirror of the present invention differs from the conventional example in that the refractive index of the first layer is H and the other is L, and the thickness of each is λ _p /8. We succeeded in lowering the ripple on both sides of the band range than before, and improved reproducibility in both blue and red in electrophotography can be achieved without the trouble of combining two or more types of filters. By setting the thickness of the second layer to λ _p /4 or less, it was possible to further suppress ripples on the long wavelength side and prevent the memory effect in a photoreceptor having sensitivity up to near infrared rays.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the film structure of an example of a conventional multilayer mirror, FIG. 2 is a graph of the spectral reflectance characteristics of the mirror, and FIG. 3 is a diagram showing the film structure of another conventional mirror. Fig. 4 is a graph of the spectral reflectance characteristics of the same mirror, Fig. 5 is a film structure diagram of a mirror according to one embodiment of the present invention, Fig. 6 is a film structure diagram of a mirror according to another embodiment of the present invention, and Fig. 7 is a film composition diagram of a mirror according to another embodiment of the present invention. FIG. 5 is a graph of the spectral reflectance characteristics of the mirror, FIG. 8 is a graph of the spectral reflectance characteristics of the mirror shown in FIG. 6, and FIG. 9 is a side view of essential parts of an example of an electrophotographic copying machine using the mirror of the present invention. It is. G...Glass substrate, A...External air area, H...
...High refractive index layer, L...Low refractive index layer.

Claims (1)

[Claims] 1 The first layer in contact with the glass substrate has a high refractive index, the outermost layer in contact with external air has a low refractive index, and the optical thickness of both layers is set to λ _p /8 with respect to the design wavelength λ _p
An even number of low refractive index layers and high refractive index layers are alternately interposed between the two layers in order from the first layer side, and in these intervening layers, the optical properties of the low refractive index layers in contact with the first layer are A multilayer mirror characterized in that the optical thickness is 0.23λ _p to 0.2λ _p and the optical thickness of each other layer is λ _p /4.