JP2006301489A - Near-infrared ray cut filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a near-infrared ray cut filter which can be made thin, has high transparency in a visible light region and has excellent interception ability in a near-infrared ray region. <P>SOLUTION: The near-infrared ray cut filter is composed of a transparent substrate 1, optical multilayer films 2, 3 formed on a half surface or both surfaces of the substrate 1 and at least one layer of resin absorption film 4 formed on at least a half surface of the substrate 1. The optical multilayer films 2, 3 are made by alternately laminating at least two kinds of thin films H, L having different refractive indexes, exhibits high transmission characteristic on visible light region and exhibits low transmission characteristic on near-infrared ray region. The resin absorption film 4 is made by applying resin material to which dye or pigment is added into a film shape, wherein the dye or pigment has absorption in near-infrared ray region. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a near-infrared cut filter used for a digital imaging optical system such as a camera or a video.

  In video cameras and electronic still cameras, color CCD elements are used to convert optical image data into electrical signals. Unlike the sensitivity of the human eye (generally, the visible region of the human being is 400 nm to 700 nm), the CCD element has a high sensitivity up to about 1100 nm in the near infrared region. Therefore, in order to reproduce the color balance as seen by the human eye, it is necessary to trim the light using a filter that cuts off near-infrared light that becomes unnecessary light and extracts visible light. A near-infrared cut filter is used for this purpose.

Infrared cut filters have been developed in various structures, but can be roughly divided into three types. First, a near-infrared cut filter using a metal complex held on a substrate made of glass or resin and utilizing its absorption is known, for example, described in Patent Documents 1 and 2 below. Second, an optical multilayer film formed by alternately laminating two or more kinds of dielectric thin films having different refractive indexes on the surface of a transparent substrate is formed, and the optical interference effect by the optical multilayer film is utilized. Infrared cut filters are known, and are described, for example, in Patent Documents 3 and 4 below. Thirdly, near-infrared cut filters using absorption of dyes or pigments are known, and are described, for example, in Patent Documents 5 and 6 below.
Japanese Patent Application Laid-Open No. 07-281021 JP-A-11-160529 JP 2000-314808 A JP 2003-029027 A JP 2001-133623 A JP 2003-227922 A

  In recent years, there has been an increasing demand in the market for reducing the size, thickness and weight of imaging optical systems, mainly in portable applications, and the same is required for all optical components used. Even near-infrared cut filters are desired to be thinner and lighter, but the three conventional methods described above are becoming difficult to meet market demands.

  The first method using the absorption of the metal complex has a limit to the concentration of the metal complex that can be held on the substrate, and in order to obtain the necessary optical characteristics, a thickness of about 0.4 mm or more is required. It is an obstacle to thinning. Since Patent Documents 1 and 2 both use a phosphoric acid compound as a metal complex, there is a problem in the environment.

  In the second method using the optical multilayer film in which the transparent dielectric thin films are laminated, the difference in refractive index of the dielectric material to be used is about 1 at most. About 40 thin films are required. For this reason, it is difficult to adjust the film stress, and the substrate is likely to warp or peel off. In order to prevent the warpage of the base material, the thickness of the base material is inevitably increased, which is an obstacle to thinning. In addition, when a resin base material is used instead of the glass base material, deformation, film peeling, cracks, and the like frequently occur, which is an obstacle to weight reduction. Also, the production cost will be large.

  The third method using absorption of dyes and pigments can be formed at a relatively low temperature and can be applied to a resin base material. However, when the transmittance in the blocking region (near infrared region) is lowered, the transmittance in the transmission region (visible region) is also lowered.

  As described above, each of the first to third methods has advantages and disadvantages and cannot meet the current market demand. Therefore, the present invention provides a near-infrared cut filter that can be thinned by combining different methods, has high transparency in the visible light region, and has excellent blocking power in the near-infrared region. Let it be an issue.

  In order to solve the above-mentioned problems of the prior art, the following measures were taken. That is, the near-infrared cut filter according to the present invention includes a transparent base material, an optical multilayer film formed on one or both sides of the base material, and at least one resin absorption film formed on at least one side of the base material. The optical multilayer film is formed by alternately laminating two or more types of thin films having different refractive indexes, exhibits high transmission characteristics in the visible light region and low transmission characteristics in the near infrared region, Is characterized in that a resin material to which a dye or pigment is added is applied in the form of a film, and the dye or pigment has absorption in the near infrared region.

  Preferably, the near-infrared wavelength range blocked by the resin absorbing film partially overlaps with the near-infrared wavelength range blocked by the optical multilayer film or included in the near-infrared range blocked by the optical multilayer film. It is. The substrate is made of a resin film.

  According to the present invention, the near infrared cut filter has a configuration in which an optical multilayer film and a resin absorption film are combined. The optical multilayer film exhibits high transmission characteristics in the visible light region and has excellent blocking performance in the near infrared region. By overlapping this with a resin absorption film to which a dye or pigment having absorption in the near infrared region is added, the infrared ray blocking ability in the near infrared region can be improved. Compared with the case where a near-infrared cut filter is constituted by an optical multilayer film alone, the number of layers of the optical multilayer film can be reduced by using a resin absorption film in combination. By reducing the number of layers of the optical multilayer film, it becomes easy to adjust the film stress, and it is possible to suppress warping of the substrate and peeling of the film. For this reason, a base material can be made thin compared with the past. On the other hand, in the visible light region, the resin absorbing film may absorb some visible light. However, it is possible to reduce absorption in the visible light region by combining with an optical multilayer film exhibiting high transmission characteristics in the visible light region. Compared with the case where an infrared cut filter is constituted only by the resin absorption film, the concentration of the dye or pigment contained in the resin absorption film can be reduced by combining the optical multilayer film. Thereby, unnecessary absorption in the visible light region can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a configuration of a near-infrared cut filter according to the present invention. As shown in the figure, the near-infrared cut filter includes a basically transparent substrate 1, optical multilayer films 2 and 3 formed on one or both surfaces of the substrate 1, and at least one surface of the substrate 1. It is composed of at least one formed resin absorption film 4. The optical multilayer films 2 and 3 are formed by alternately laminating two or more kinds of thin films having different refractive indexes, and exhibit high transmission characteristics in the visible light region and low transmission characteristics in the near infrared region. In the illustrated example, thin films of high refractive index material H and thin films of low refractive index material L are alternately laminated to form optical multilayer films 2 and 3. On the other hand, the resin absorption film 4 is obtained by coating a resin material that has absorbed a dye or pigment in the form of a film, and the dye or pigment has absorption in the near infrared region. Preferably, the near-infrared wavelength range blocked by the resin absorption film 4 partially overlaps the near-infrared wavelength range blocked by the optical multilayer films 2 and 3, or the near-infrared wavelength range blocked by the optical multilayer film 2 or 3 All included in the range. The substrate 1 is made of a resin film such as PET.

  Hereinafter, each component such as the substrate 1, the optical multilayer films 2 and 3, the resin absorption film 4 and the like will be described in detail. First, the base material 1 is a PET film having a thickness of 0.1 mm in this embodiment. However, the present invention is not limited to this, and other transparent resin films such as PC, PEN, and polyolefin may be used instead of the PET film. In some cases, a glass substrate can be used.

Next, the optical multilayer film 2 is formed on the surface of the transparent substrate 1 as shown in the figure, and a plurality of transparent thin films made of the high refractive index material H and transparent thin films made of the low refractive index material L are alternately arranged. Laminated. In the present embodiment, the odd-numbered layers counted from the surface of the substrate 1 are made of the low-refractive index material L and the even-numbered layers are made of the high-refractive index material H, and a total of 11 layers are stacked. In the present embodiment, a high refractive index material H in titanium dioxide (TiO _2), are made of a low refractive index material L to silicon dioxide (SiO _2). These transparent thin films form an optical multilayer film 2 by alternately stacking up to 11 layers of silicon dioxide thin films and titanium dioxide thin films from the surface of the transparent substrate 1 so as to have the physical film thickness shown in FIG. .

  As described above, the optical multilayer film 2 is formed by alternately laminating a plurality of transparent thin films made of a high refractive index material H such as titanium dioxide and transparent thin films made of a low refractive index material L such as silicon dioxide. It uses light interference to selectively block light in the near-infrared wavelength region. The light transmittance at each wavelength is determined by the optical film thickness (the product of the refractive index of the thin film and the physical film thickness of the thin film) of each transparent thin film that is alternately laminated, and is laminated so as to block light in the near infrared wavelength region. The refractive index, film thickness, and number of layers of the transparent thin film are designed.

In this embodiment, TiO ₂ is used as the high refractive index material and SiO ₂ is used as the low refractive index material. However, the present invention is not limited to this. As other dielectric thin film materials, MgF ₂ , Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O _{3 and the} like are also applicable.

  The optical multilayer film 3 formed on the back side of the substrate 1 is basically the same as the optical multilayer film 2. The optical multilayer film 3 is composed of a total of 11 layers. Basically, 11 layers of high refractive index material H and low refractive index material L are alternately laminated to obtain desired transmission characteristics. However, the optical film thickness is designed to be different from that of the optical multilayer film 2 by appropriately adjusting the physical film thickness of each thin film. By combining the optical multilayer film 2 and the optical multilayer film 3, desired blocking characteristics in the near infrared region are obtained.

  The resin absorption film 4 is basically a film obtained by coating a resin material with a dye or pigment added thereto. The added dye or pigment has absorption particularly in the near infrared region, and by combining with the optical multilayer films 2 and 3 described above, an almost ideal near infrared ray blocking ability can be obtained. In the present embodiment, a coating liquid in which an acrylic transparent resin and a dye are dissolved in an organic solvent is prepared, and this is coated on the optical multilayer film 3 with a thickness of 10 μm. The dye used at this time was a product number no. 8630. The resin material of the resin absorbing film 4 may be any base material other than an acrylic material as long as it is transparent in the visible range, and for example, a polyester resin is also preferable. The dye added to the resin is basically preferably a material that is highly transparent in the visible region and absorbs in the near infrared region. For example, phthalocyanine-based, thiol metal complex-based, azo compound-based, polymethine-based, diphenylmethane-based, triphenylmethane-based, quinone-based, diimonium-based, or the like can be used. Also in the case of a pigment, a material having high transparency in the visible light region and absorption in the near infrared region is selected. For example, fine particles of ITO, which is a composite oxide of indium and tin, can be used for the pigment. ITO is widely used for transparent electrodes such as liquid crystal displays, and is almost transparent in the visible range, but has absorption in the near infrared range. In the case of a near-infrared cut filter applied to an imaging system, it is necessary to refine the pigment to a particle size that does not cause blurring of the image. The particle size is, for example, several tens of nm or less.

  With reference to FIG. 1, an example of the manufacturing method of the near infrared cut filter will be described. In this example, titanium dioxide and silicon dioxide are alternately deposited on the PET film substrate 1 by vacuum deposition. The temperature of the substrate 1 is maintained at 100 ° C., for example. However, the film forming method is not limited to the vacuum deposition method, and a method such as an ion plating method, an ion assist method, or a sputtering method can be used. First, the film substrate 1 is loaded into a vacuum container of a vacuum deposition apparatus, and pellet-like or granular titanium dioxide and silicon dioxide are separately put into two electron beam deposition sources provided in the vacuum container. Exhaust.

When the pressure in the vacuum container becomes 1 × 10 ⁻³ Pa or less, the electron beam evaporation source is irradiated with an electron beam to heat and evaporate titanium dioxide and silicon dioxide, respectively. Opening and closing shutters are provided directly above the two electron beam evaporation sources. When depositing titanium dioxide, the shutter on the titanium dioxide side is opened and the shutter on the silicon dioxide side is closed. When depositing silicon dioxide, The titanium dioxide side shutter is closed and the silicon dioxide side shutter is opened, and transparent thin films of titanium dioxide and silicon dioxide are alternately laminated on the film substrate 1. When the optical multilayer film 2 is formed on the surface side of the film substrate 1 in this manner, the optical multilayer film 3 is formed by performing the vacuum deposition process again with the film substrate 1 turned over. That is, vapor deposition of titanium dioxide and silicon dioxide is repeated for a desired number of layers to complete the optical multilayer film 3.

  The film thickness of each transparent thin film is measured during deposition by a film thickness monitor, and the film thickness is controlled by closing the shutter at a predetermined film thickness. When the predetermined number of layers is deposited, the operation of the electron beam deposition source is stopped, the vacuum vessel is evacuated, and the pressure is returned to atmospheric pressure. The film base material after vapor deposition is taken out of the vacuum container and subjected to the next coating treatment.

  In the coating process for forming the resin absorbing film, first, a base polyester serving as a dispersion medium is manufactured. The prepared base polyester is used as a binder resin, a desired infrared absorbing dye and a solvent are added thereto, and the mixture is placed in a flask and stirred while heating to dissolve the dye and the binder resin. As a solvent, a simple substance or a mixture of methyl ethyl ketone, tetrahydrofuran, toluene or the like is used. The thus-dissolved resin is coated on one surface of the PET film substrate on which the optical multilayer films 2 and 3 are formed in the previous step using an applicator having a gap of 50 μm, for example, and dried at a drying temperature of 90 ° C. for 1 hour. . The coating thickness obtained at this time is 10 μm. The coating method is not limited to the examples, and any of a dipping method, a gravure method, a lip method, a CAP coating method, a spray method, a spin coating method, and the like can be used.

  FIG. 2 is a graph showing optical characteristics of the near-infrared cut filter according to the present invention. The vertical axis represents transmittance, and the horizontal axis represents wavelength. The plot of □ shows the optical characteristics when only the optical multilayer film 2 is formed on the surface of the substrate 1, the plot of Δ shows the optical characteristics when only the optical multilayer film 3 is coated on the back surface of the substrate, These plots represent the optical characteristics when only one side of the substrate is coated with the resin absorbing film 4. As is apparent from the graph, the optical multilayer film 2 has a large stopping power in the wavelength range of 650 nm to 950 nm. Most of the stopping power of the optical multilayer film 2 depends on reflection. On the other hand, the optical multilayer film 3 has a near-infrared blocking ability in the wavelength range of 800 nm or more. In addition, the optical multilayer film 2 and the optical multilayer film 3 have different transmission characteristics in the near-infrared region, and are basically designed to block a predetermined near-infrared region 700 to 1100 nm by combining both. Yes.

  On the other hand, the resin absorption film 4 has a visible region with a wavelength of 400 nm to 700 nm, a slightly lower transmittance than the optical multilayer films 2 and 3, and a slight absorption. When the wavelength exceeds 700 nm, the transmittance gradually decreases and becomes maximum absorption around 900 nm. Further, when the wavelength is longer than this, the transmittance is increased again. As is apparent from the graph, the absorption characteristics of the resin absorption film 4 in the near infrared region partially overlap with the near infrared wavelength range blocked by the optical multilayer film 3. The near-infrared wavelength range blocked by the resin absorption film 4 is all included in the near-infrared range blocked by the other optical multilayer film 2.

  The plot of * represents the optical characteristics when the optical multilayer film 2 and the optical multilayer film 3 are combined. As is apparent from the graph of FIG. 2, when both are combined, the transmittance is 10% or less in the near infrared region exceeding the wavelength of 700 nm, which is almost a practical level. Subsequently, the ♦ plot shows optical characteristics when the resin absorption film 4 is stacked in addition to the optical multilayer films 2 and 3. As apparent from the graph of FIG. 2, the addition of the resin absorbing film 4 according to the present invention can further improve the near-infrared ray blocking ability particularly in the wavelength range from 800 nm to 900 nm, and the transmittance is 5%. It is as follows. By powerfully blocking near infrared rays in this range, excellent color reproducibility can be obtained when used in an imaging system. If it is attempted to reduce the transmittance at 800 to 900 nm to about 5% using only the optical multilayer films 2 and 3 without using the resin absorbing film 4, the total number of layers of the optical multilayer film reaches about 40 layers. Warpage and film peeling become a problem. On the other hand, in the present invention, it is possible to reduce the number of layers on the optical multilayer film side by adding the resin absorbing film 4, and it is possible to suppress warpage of the substrate and peeling of the film. For this reason, it is possible to make a base material thin compared with the past.

  On the other hand, even in the visible light region, when the resin absorbing film 4 is added, the transmittance can be maintained at a level of 90%, and there is no practical problem. If a near-infrared cut filter is constituted only by the resin absorption film 4, the transmittance in the visible light region is reduced to about 80%, which causes a problem depending on the application. In contrast, by combining the optical multilayer films 2 and 3 having higher transparency in the visible light region than the resin absorbing film 4, the transparency in the visible light region of the near-infrared cut filter can be increased to about 90%.

  FIG. 3 is a schematic cross-sectional view showing various modifications of the near-infrared cut filter according to the present invention. In the example shown in (A), the optical multilayer film 2 is formed on the front surface side of the base material 1, while the resin absorption film 4 is formed on the back surface side of the base material 1. It has the simplest configuration and can produce a near infrared cut filter at a low cost.

  In the example shown in (B), the resin absorption film 4 and the optical multilayer film 2 are formed only on the surface side of the substrate 1. Since the optical multilayer film 2 and the resin absorption film 4 are disposed only on one side of the base material 1, there is an advantage that manufacture and handling become easy.

  In the example shown in (C), the resin absorption film 4 is formed on the back surface side of the substrate 1, while another resin absorption film 5 and the optical multilayer film 2 are formed on the surface side of the substrate 1. By combining the resin absorption films 4 and 5 having different absorption characteristics in the near infrared region, a desired near infrared ray blocking ability can be obtained.

  In the example shown in (D), the resin absorption film 5 and the optical multilayer film 2 are sequentially formed on the front surface side of the substrate 1, while the resin absorption film 4 and the optical multilayer film 3 are sequentially formed on the back surface side of the substrate 1. is doing. By forming the resin absorption film and the optical multilayer film on the front surface and the back surface of the base material 1, respectively, the film stress can be balanced. Thereby, even when a thin glass substrate or a resin film substrate is used, it is possible to prevent warping, film peeling and cracks.

  In the example shown in (E), the optical multilayer film 2 is formed on the front surface side of the substrate 1, while the optical multilayer film 3 and the resin absorption film 4 are formed on the back surface side of the substrate 1. This is exactly the same as the configuration described with reference to FIG. 1, and further detailed description thereof is omitted.

  In the example shown in (F), the optical multilayer film 2 is formed on the front side of the substrate 1, while the optical multilayer film 3 is formed on the back side of the substrate 1. A resin absorbing film 5 is formed so as to protect the surface of the optical multilayer film 2. Similarly, a resin absorbing film 4 is formed so as to protect the optical multilayer film 3 formed on the back surface side of the substrate 1. By doing in this way, the near-infrared cut filter excellent in reliability can be provided.

It is typical sectional drawing which shows the structure of the near-infrared cut off filter concerning this invention. It is a graph which shows the optical characteristic of the near-infrared cut off filter concerning this invention. It is typical sectional drawing which shows the various modifications of the near-infrared cut off filter concerning this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Optical multilayer film, 3 ... Optical multilayer film, 4 ... Resin absorption film, 5 ... Resin absorption film

Claims (3)

A transparent base material, an optical multilayer film formed on one side or both sides of the base material, and at least one resin absorption film formed on at least one side of the base material,
The optical multilayer film is formed by alternately laminating two or more types of thin films having different refractive indexes, exhibits high transmission characteristics in the visible light region and low transmission characteristics in the near infrared region, and the resin absorption film comprises a dye Alternatively, a near-infrared cut filter, which is formed by coating a resin material to which a pigment is added into a film, and the dye or pigment has absorption in the near-infrared region.   The near-infrared wavelength range blocked by the resin absorption film partially overlaps the near-infrared wavelength range blocked by the optical multilayer film, or is included in the near-infrared wavelength range blocked by the optical multilayer film. The near-infrared cut filter according to claim 1.   The near-infrared cut filter according to claim 1, wherein the substrate is made of a resin film.

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