Optical filter

Abstract

To provide an optical filter with an improved resistance to weather.SOLUTION: An optical filter 10 includes: an infrared absorptive glass 11; an adhesive layer 13 on a main surface of the infrared absorptive glass; and a resin layer 15 on the adhesive layer, for absorbing light of a specific wavelength. The optical filter has a protective member 17 on the opposite surface to the adhesive layer of the resin layer. The protective glass is formed of white glass and the adhesive layer is formed of an ultraviolet curable or acrylic adhesive agent. A reflection prevention film 21 is formed on the opposite surface to the resin layer of the protective glass.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an optical filter installed and used on the incident side of an imaging device such as an image sensor.

Background Art

[0002] In an imaging device such as a digital camera, an optical filter that realizes an image in a wavelength range suitable for human visual sensitivity is used because it is desirable to obtain an image in such a wavelength range. As an example of this type of optical filter, for example, Patent Document 1 discloses a near-infrared cut filter. This filter includes a transparent substrate having a transmittance of 3% or less in a wavelength range of 800 to 950 nm, and a resin layer formed on at least one main surface of the transparent substrate that absorbs light of a specific wavelength (for example, claim 1 of Patent Document 1). By using the resin layer, light in a desired visible light region can be extracted in combination with the transparent substrate (for example, paragraph 54 of Patent Document 1).

[0003] Patent Document 1 also discloses a configuration including an adhesive layer that enhances the adhesion between the transparent substrate and the resin layer (for example, claim 10, FIG. 16, etc. of Patent Document 1). By providing the adhesive layer, the reliability of the filter can be improved (for example, paragraph 105 of Patent Document 1). As the material of the adhesive layer, those containing one or more atoms selected from Si atoms, Ti atoms, Zr atoms, and Al atoms are preferably used (for example, paragraph 106 and paragraph 111 of Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The optical filter disclosed in Patent Document 1 helps an image device obtain an image in a wavelength range that matches the human visual sensitivity. However, since the resin layer is exposed, there are concerns in terms of weather resistance and the like. This application has been made in view of the above points. Therefore, the object of this application is to provide an optical filter that can improve weather resistance compared to the prior art and a manufacturing method that can easily manufacture this optical filter.

Means for Solving the Problem

[0006] To achieve this object, according to the invention of the optical filter of this application, in an optical filter comprising an infrared-absorbing glass, an adhesion layer formed on the main surface of the infrared-absorbing glass, and a resin layer formed on the adhesion layer that absorbs light of a specific wavelength, a protective member is provided on the surface of the resin layer opposite to the adhesion layer. In implementing the invention of this optical filter, the protective member can be composed of any material that can satisfy the specifications of the optical characteristics and weather resistance of the optical filter. Preferably, it is preferably selected from white plate glass, ultraviolet-absorbing glass, and quartz glass. Also, in implementing the invention of this optical filter, the adhesion layer is preferably an acrylic-based adhesive. In particular, it is preferably an acrylic-based adhesive that does not contain Si atoms, Ti atoms, Zr atoms, and Al atoms. However, "not containing" excludes cases where Si atoms, Ti atoms, Zr atoms, and Al atoms are unavoidably contained. Since an ultraviolet-curable adhesive is provided for the acrylic-based adhesive, it is convenient for manufacturing. Also, when it is an acrylic-based adhesive that does not contain Si atoms, Ti atoms, Zr atoms, and Al atoms, it seems that the softness of the adhesion layer is easier to obtain compared to the case where it does not. In implementing the invention of this optical filter, the protective member is preferably selected from white plate glass, ultraviolet-absorbing glass, and quartz glass. In implementing the invention of this optical filter, the resin layer is preferably a resin layer having infrared absorption properties.

[0007] Also, according to the invention of the method for manufacturing an optical filter of this application, when manufacturing an optical filter including an infrared-absorbing glass, an adhesion layer formed on the main surface of the infrared-absorbing glass, a resin layer formed on the adhesion layer and absorbing light of a specific wavelength, and a protective member provided on the surface of the resin layer opposite to the adhesion layer, preparing one type of glass selected from soda-lime glass, ultraviolet-absorbing glass, and quartz glass as the protective member, and forming the resin layer on the main surface of the glass; preparing the infrared-absorbing glass, and forming an adhesive for the adhesion layer on the main surface thereof; superposing and bonding the infrared-absorbing glass on which the adhesive has been formed and the protective glass on which the resin layer has been formed with the adhesive and the resin layer facing each other; characterized by including the above. In addition, when implementing the invention of the method for manufacturing this optical filter, it is preferable that the adhesive is an acrylic adhesive.

Effects of the Invention

[0008] According to the invention of the optical filter of this application, since the protective member is provided, the resin layer is not directly exposed to the environment in which the optical filter is used, so the weather resistance of the optical filter is improved. According to the invention of the method for manufacturing an optical filter of this application, a resin layer is formed on the protective member. Here, the protective member can be composed of, for example, white glass or quartz glass. White glass and quartz glass are generally harder than infrared-absorbing glass, have a high surface flatness, and a fine surface roughness. Therefore, the adhesion and surface accuracy of the resin layer formed on the protective glass can be improved. That is, compared with the case where the resin layer is formed on the infrared-absorbing glass side, the present invention can improve the adhesion and surface accuracy of the resin layer, so that the characteristics of the optical filter can be improved. Therefore, according to the invention of the method for manufacturing an optical filter of this application, an optical filter excellent in weather resistance and further excellent in characteristics can be easily manufactured.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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Figure 6

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of each invention of this application will be described with reference to the drawings. Note that each drawing used in the description only schematically shows the inventions to the extent that they can be understood. In addition, in each drawing used in the description, the same components are denoted by the same numbers, and the description thereof may be omitted. Further, the shapes, materials, etc. described in the following embodiments are merely preferred examples within the scope of this invention. Therefore, the present invention is not limited only to the following embodiments.

[0011] 1. Optical Filter of the First Embodiment FIG. 1 is a cross-sectional view for explaining the optical filter 10 of the first embodiment. This optical filter 10 includes an infrared absorbing glass 11, an adhesion layer 13 formed on the main surface of the infrared absorbing glass 11, a resin layer 15 formed on the adhesion layer 13 and absorbing light of a specific wavelength, and a protective glass 17 as a protective member provided on the surface of the resin layer 15 opposite to the adhesion layer 13. Therefore, this optical filter 10 can be used as an infrared cut filter. The infrared-absorbing glass 11 is configured to have a transmittance characteristic of absorbing light in a predetermined wavelength range, for example, the infrared region or the near-infrared region, according to the design of the optical filter 10. The planar shape of the infrared-absorbing glass 11 can be any shape according to the design of the imaging device using the optical filter 10, and typically, it is a rectangular shape, for example, a rectangular shape. The planar size of the infrared-absorbing glass 11 is any size according to the design of the imaging device. The thickness of the infrared-absorbing glass 11 can be any thickness according to the design of the imaging device using the optical filter 10. This infrared-absorbing glass 11 can be selected and used from commercially available products or individually specified products, and any product according to the design of the optical filter 10 can be used. As commercially available products, for example, BG38 and BG39 (trade names) manufactured by SCHOTT can be used.

[0012] The adhesion layer 13 is provided to enhance the adhesion between the infrared-absorbing glass 11 and the resin layer 15. The adhesion layer 13 is a material capable of ensuring adhesion, and it is preferably composed of a material that can minimize optical losses at the interface between the infrared-absorbing glass 11 and the adhesion layer 13 and at the interface between the resin layer 15 and the adhesion layer 13. Therefore, for the infrared-absorbing glass 11 and the resin layer 15, those with similar refractive indices are preferred for the adhesion layer 13. The thickness of the adhesion layer 13 can be any thickness according to the design of the optical filter 10. Although not limited to this, for example, 3 to 20 μm, preferably 3 to 10 μm is good. The forming material of the adhesion layer 13 can be selected and used from commercially available products or individually specified products, and any product according to the design of the optical filter 10 can be used. As commercially available products, for example, an acrylic-based adhesive can be mentioned. Specifically, Photo Bond #300K (product name) manufactured by Sunrise MSI can be used. Since Photo Bond #300K is an ultraviolet-curable adhesive, it is convenient in the manufacture of optical filters.

[0013] The resin layer 15 is a layer that absorbs light of a specific wavelength. Here, the specific wavelength is, for example, a wavelength selected from the infrared region, the near-infrared region, or the ultraviolet region on the short-wavelength side in order to supplement the optical characteristics of the infrared-absorbing glass 11. This can be achieved, for example, by incorporating a dye that absorbs in the specific wavelength range into the resin layer 15. By doing so, in combination with the infrared-absorbing glass 11, the transmittance characteristics, angle-of-incidence dependence, etc. of the optical filter 10 can be controlled. The thickness of the resin layer 15 can be set to any thickness according to the design of the optical filter 10. Although not limited to this, for example, 1 to 20 μm, preferably 1 to 5 μm is good. As the material for forming the resin layer 15, any commercially available or custom-made material can be selected and used according to the design of the optical filter 10. As a commercially available product, for example, IX-2-KT-B (trade name) manufactured by Nippon Shokubai Co., Ltd. can be used.

[0014] The protective glass 17 is provided to protect the resin layer 15 against the usage environment of the optical filter 10. Therefore, the protective glass 17 is provided on the surface opposite to the adhesion layer 13 of the resin layer 15. The planar shape and dimensions of the protective glass are typically the same as those of the infrared-absorbing glass 11, but may be different as long as the purpose of protecting the resin layer 15 is not impaired. The thickness of the protective glass 17 can be set to any thickness according to the design of the optical filter 10. Although not limited to this, for example, 0.3 to 1 mm is good. As the material of the protective glass 17, it is preferable to use a material that has as little adverse effect as possible on human visual sensitivity. Furthermore, considering the manufacturing method described later, it is preferable to use a material with a high softening point and high hardness. Therefore, as the material of the protective glass 17, it is preferable to select, for example, from white glass, quartz glass, and ultraviolet-absorbing glass. As the material for forming the protective glass 17, any commercially available or custom-made material can be selected and used according to the design of the optical filter 10. As a commercially available product, for example, the white plate glass B270i (trade name) manufactured by SCHOTT can be used. Since the optical filter 10 of the first embodiment includes the protective glass 17 as a protective member, the resin layer 15 is not exposed to the use environment of the optical filter 10, so that the resin layer 15, which can increase the degree of freedom of optical characteristics, can be protected against the use environment of the optical filter 10. Specifically, since the resin layer 15 has a hardness of only about 10B in terms of pencil hardness, it is easily scratched, and since it is a resin, its moisture resistance is not very high. The protective glass 17 can compensate for the above-mentioned drawbacks of the resin layer 15.

[0015] 2. Embodiment of the manufacturing method Next, an embodiment of the invention of the manufacturing method of the optical filter will be described. FIGS. 2(A) to (E) are partial process diagrams therefor, and are process diagrams showing a sample during the manufacture of the optical filter 10 in a cross-sectional view. In the manufacturing method of this embodiment, the following processing is performed. As the protective glass 17, one type of glass selected from white plate glass, ultraviolet-absorbing glass, and quartz glass is prepared, and a resin layer is formed on the main surface of this glass (FIGS. 2(A) and (B)). Specifically, for example, white glass (for example, white plate glass B270i (trade name) manufactured by SCHOTT) is prepared as the glass for the protective glass, and a resin layer forming material 15a (for example, IX-2-KT-B (trade name) manufactured by Nippon Shokubai Co., Ltd.) is applied to its main surface with a spin coater or the like (FIG. 2(A)), and then it is heat-cured in a temperature bath at a predetermined temperature to obtain the protective glass 17 provided with the resin layer 15 (FIG. 2(B)).

[0016] On one hand, an infrared-absorbing glass 11 (e.g., BG38 (trade name) manufactured by SCHOTT) is prepared, and an adhesive 13a (e.g., Photo Bond #300 (product name) manufactured by Sunrise MSI) for forming the adhesion layer 13 is applied to its main surface ((Figs. 2(C) and (D)). Then, the infrared-absorbing glass on which the adhesive has been formed and the protective glass on which the resin layer has been formed are bonded with the adhesive and the resin layer facing each other (Fig. 2(E)). The opposed samples may be left for a predetermined time in a self-weight state or a pressurized state, and are processed so that the adhesive is evenly interposed between the resin layer 15 and the infrared-absorbing glass 11. Next, since the Photo Bond #300K is an ultraviolet-curable adhesive, the sample is irradiated with ultraviolet rays under predetermined conditions to complete the adhesion, and the optical filter 10 shown in Fig. 1 is obtained.

[0017] According to the invention of this manufacturing method, a resin layer 15 is formed on a protective glass 17 made of a hard, excellent flatness, and easily fine surface roughness white glass or the like compared with the infrared-absorbing glass 11, and then an adhesion treatment is performed. Therefore, the resin layer can be easily formed on the protective glass with good adhesion and flatness, and a desired optical filter 10 can be manufactured simply and with good characteristics. Note that the order of the step of forming the resin layer on the protective glass and the step of forming the adhesive on the infrared-absorbing glass may of course be reversed from the above procedure. However, when the adhesive is likely to cure or gel in a short time, it is preferable to first perform the step of forming the resin layer on the protective glass.

[0018] 3. Other Embodiments of the Optical Filter 3-1. The Second Embodiment of the Optical Filter Fig. 3 is a cross-sectional view for explaining an optical filter 20 according to the second embodiment. The difference between the optical filter 20 according to the second embodiment and the optical filter 10 according to the first embodiment is that an antireflection film 21 is provided on the surface of the protective glass 17 opposite to the resin layer 15. The antireflection film 21 can be composed of a material according to the design of the optical filter 20 and can be a single layer or a multilayer. The antireflection film 21 is typically designed to allow light in a wavelength range corresponding to human visual sensitivity to enter the optical filter 20 side as much as possible and reflect light in other wavelength ranges as much as possible, and can typically be composed of a dielectric multilayer film. In the case of the optical filter 20 of the second embodiment, in addition to the effect of protecting the resin layer 15 in the optical filter of the first embodiment, an effect that light in a wavelength band corresponding to human visual sensitivity is likely to enter the optical filter 20 can be obtained.

[0019] 3-2. Third Embodiment of Optical Filter FIG. 4(A) is a cross-sectional view for explaining the optical filter 30 of the third embodiment. The difference between the optical filter 30 of the third embodiment and the optical filter 10 of the first embodiment is that on the back surface side of the infrared absorbing glass 11, in order from the infrared absorbing glass 11 side, an adhesion layer 31, that is, a second adhesion layer 31, and a second protective glass 33 as a second protective member are provided. In the case of the optical filter 30 of the third embodiment, the back surface side of the infrared absorbing glass 11 is protected by the second protective glass 33. Compared with white glass or quartz glass that constitutes the protective glass, the infrared absorbing glass is often inferior in scratch resistance and weather resistance. In the case of this third embodiment of the optical filter, in addition to the effect of the optical filter 10 of the first embodiment, by protecting the back surface side of the infrared absorbing glass 11 with the second protective glass 33, the scratch resistance and weather resistance of the optical filter 30 can be further enhanced. Specifically, since the infrared absorbing glass 11 has a hardness of only about 3H in terms of pencil hardness, it is easily scratched. The protective glass 33 on the back surface side can compensate for the above-mentioned drawbacks of the infrared absorbing glass 11.

[0020] 3-3. Fourth Embodiment of Optical Filter FIG. 4(B) is a cross-sectional view for explaining the optical filter 40 of the fourth embodiment. The optical filter 40 of the fourth embodiment is an improved version of the optical filter 30 of the third embodiment, in which a first antireflection film 41a is provided on one main surface of the optical filter 30 of the third embodiment, and a second antireflection film 41b is provided on the other main surface. The optical characteristics of the first antireflection film 41a and the second antireflection film 41b can be changed according to the specifications of the optical filter 40. For example, the first antireflection film 41a and the second antireflection film 41b may have substantially the same optical characteristics, or the first antireflection film 41a on the light incident side and the second antireflection film 41b on the imaging element side may have different optical characteristics. According to the optical filter 40 of the fourth embodiment, an optical filter with a highly flexible design for antireflection can be provided. For convenience of explanation, the first antireflection film 41a has been described as the one on the incident side and the second antireflection film 41b has been described as the one on the imaging element side, but the incident direction may be reversed.

[0021] 4. Examples and Comparative Examples The optical filter according to the present invention is an infrared absorption filter provided with a resin layer, and the weather resistance of the resin layer is improved. To deepen the understanding, examples of the optical characteristics of the optical filter of the example and examples of the experimental results of the weather resistance are shown below. 4-1. Optical Characteristics of the Example Using the above BG39 as the infrared absorbing glass, the above Photo Bond #300K as the adhesion layer, the above IX-2-KT-B as the resin layer, the above B270i as the protective glass, and a predetermined dielectric film as the antireflection film, the optical filter 40 of the fourth embodiment was prototyped. Then, its transmittance characteristics were measured. FIG. 5 shows the transmittance characteristics with the wavelength (nm) on the horizontal axis and the transmittance (%) on the vertical axis. From FIG. 5, it can be seen that even the optical filter of the present invention provided with the protective glass and the adhesion layer can realize a desired infrared absorption filter that transmits light in the wavelength band corresponding to the human visual sensitivity and attenuates light of other wavelengths.

[0022] 4-2. Weather resistance test As a comparative example optical filter, one with a resin layer directly formed on the main surface of the infrared absorbing glass 11 was prepared. Also, as the optical filter of the example, the optical filter 10 of the first embodiment shown in FIG. 1 was also prepared. In both samples, BG39 described above was used for the infrared absorbing glass, and IX-2-KT-B described above was used for the resin layer. Also, in the sample of the example, Photo Bond #300K described above was used for the adhesion layer, and B270i described above was used for the protective glass. Both samples were placed in a high temperature and high humidity layer with a temperature of 60 °C and a humidity of 95% to evaluate the weather resistance. As a result, as shown in FIG. 6, in the case of the comparative example optical filter 50, it was found that cracks 51 had occurred at many locations in the resin layer 15 in the observation after 120 hours. Note that these cracks 51 were observed and photographed under the condition of 50 times magnification with an optical microscope. It is presumed that the resin layer 15 partially expanded due to containing moisture, inducing the cracks 51. On the other hand, in the optical filter of the example, even after conducting the high temperature and high humidity test for 120 hours and then for a considerable time, it was found that no cracks were observed, and it maintained a good state without fogging.

Explanation of reference numerals

[0023] 10: Optical filter of the first embodiment 11: Infrared absorbing glass 13: Adhesion layer 15: Resin layer 17: Protective member (protective glass) 20: Optical filter of the second embodiment 21: Anti-reflection film 30: Optical filter of the third embodiment 31: Second adhesion layer 33: Second protective member (second protective glass) 40: Optical filter of the fourth embodiment 41a: First anti-reflection film 41b: Second anti-reflection film 50: Comparative example optical filter 51: Crack

Claims

1. In an optical filter comprising an infrared absorbing glass, an adhesion layer formed on a main surface of the infrared absorbing glass, and a resin layer formed on the adhesion layer and absorbing light of a specific wavelength, the optical filter is characterized in that a protective member is provided on a surface of the resin layer opposite to the adhesion layer.

2. The optical filter according to claim 1, wherein the protective member is selected from a white plate glass, an ultraviolet absorbing glass, and a quartz glass.

3. The optical filter according to claim 1, wherein the protective member is a white plate glass.

4. The optical filter according to claim 1, wherein the adhesion layer is an acrylic adhesive.

5. The optical filter according to claim 1, wherein the adhesion layer is an acrylic adhesive containing no Si atom, Ti atom, Zr atom, and Al atom.

6. The optical filter according to claim 1, wherein an antireflection film is provided on a surface of the protective member opposite to the resin layer.

7. The optical filter according to claim 1, wherein a second adhesion layer and a second protective member are provided in this order on a surface of the infrared absorbing glass opposite to the adhesion layer side.

8. The optical filter according to claim 7, wherein a first antireflection film is provided on the protective member, and a second antireflection film is provided on the second protective member.

9. The optical filter according to claim 7, wherein the second protective member is selected from a white plate glass, an ultraviolet absorbing glass, and a quartz glass.

10. The optical filter according to claim 7, wherein the second protective member is a white plate glass.

11. In manufacturing an optical filter comprising an infrared absorbing glass, an adhesion layer formed on a main surface of the infrared absorbing glass, a resin layer formed on the adhesion layer and absorbing light of a specific wavelength, and a protective member provided on a surface of the resin layer opposite to the adhesion layer, preparing one kind of glass selected from a white plate glass, an ultraviolet absorbing glass, and a quartz glass as the protective member, and forming the resin layer on a main surface of the glass; preparing the infrared absorbing glass, and forming an adhesive for the adhesion layer on a main surface thereof; a step of bonding the infrared absorbing glass on which the adhesive has been formed and the protective glass on which the resin layer has been formed by opposing the adhesive and the resin layer to each other. A method for manufacturing an optical filter, characterized by including [

12. ] The method for manufacturing an optical filter according to claim 11, characterized in that an ultraviolet curable and acrylic adhesive is used as the adhesive.

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