JP7750249B2 - Optical Filters - Google Patents

Description

The present invention relates to an optical filter.

In order to reproduce color tones well and obtain clear images, imaging devices that use solid-state imaging elements use optical filters that transmit light in the visible range (hereinafter also referred to as "visible light") and block light in the near-infrared wavelength range (hereinafter also referred to as "near-infrared light").

Such optical filters can be made using various methods, such as reflective filters, which alternately stack thin dielectric films with different refractive indices on one or both sides of a transparent substrate (dielectric multilayer film), and use optical interference to reflect the light that needs to be blocked.

Optical filters that block near-infrared light are required to block a wide wavelength range from 750 to 1200 nm, but it is technically difficult to cover this range with a single type of multilayer film. Therefore, it is known to use a combination of multiple dielectric multilayer films with different near-infrared light reflection ranges (Patent Document 1).

Japanese Patent Application Publication No. 2007-183525

In dielectric multilayer films, ripples, or large changes in transmittance, occur due to interference caused by reflected light at the interfaces of each layer depending on the number of layers stacked, and it is known that these ripples are more likely to occur the larger the angle of incidence of light.

When a dielectric multilayer film is combined to block a wide range of near-infrared light, as in the optical filter described in Patent Document 1 above, there is a risk that ripples in the visible light range will not cancel each other out and will be amplified.

In addition, the dielectric multilayer films that make up the thin film stack structure exhibit incident angle dependency, meaning that the light transmission characteristics shift toward shorter wavelengths as the incident angle of light increases. Therefore, in the near-infrared light region near the border with the visible light region, where the transmittance of the multilayer film changes rapidly, there is a risk that the reflection characteristics will deteriorate under high incident angle conditions.

The present invention aims to provide an optical filter that has high transmittance for visible light and high blocking ability for near-infrared light, and that suppresses the occurrence of ripples in the visible light region and a decrease in blocking ability in the near-infrared light region even at high angles of incidence.

In the present invention, a thin film laminate structure is used in which two or more multilayer films are combined by shifting the near-infrared light reflection regions so that ripples in the visible light region are canceled out. However, in such a structure, gaps are generated where the near-infrared light reflection regions of each multilayer film overlap, making light leakage more likely, and this is particularly likely at high incident angles due to the incidence angle dependence of the dielectric multilayer film. Therefore, it has been discovered that the above problem can be solved by further providing a thin film laminate structure that reflects light in the wavelength region where light leakage occurs and by using a dye that absorbs light in that wavelength region.
That is, the present invention provides an optical filter having the following configuration.
[1] a substrate;
a first thin film stack structure and a second thin film stack structure that limit the transmission of light in the near infrared wavelength range;
An optical filter comprising:
the substrate includes a resin film containing a dye that absorbs light in the near-infrared wavelength region;
the first thin film laminated structure includes at least two dielectric multilayer films and is laminated as an outermost layer on one main surface side of the base material,
the second thin film laminated structure includes at least one dielectric multilayer film and is laminated as an outermost layer on the other main surface side of the base material,
The first thin film stack structure satisfies the following optical properties (i-1A) and (i-1B),
The second thin film stack structure satisfies the following optical property (i-2A):
Optical filters.
(i-1A) Maximum transmittance at wavelengths of 850 nm to 950 nm at an incident angle of 40° is 5% or more. (i-1B) Maximum reflectance at wavelengths of 450 nm to 600 nm at an incident angle of 40° is 8% or less. (i-2A) Average reflectance at wavelengths of 850 nm to 950 nm at an incident angle of 40° is 25% to 60%.
[2] The optical filter according to [1], wherein the resin film satisfies all of the following optical properties (ii-1) to (ii-3):
(ii-1) The average internal transmittance at an incident angle of 0° in the wavelength range of 850 nm to 950 nm is 60 to 90%.
(ii-2) Average internal transmittance at an incident angle of 30° in the wavelength range of 850 nm to 950 nm is 60 to 90%
(ii-3) The average internal transmittance at an incident angle of 40° in the wavelength range of 850 nm to 950 nm is 60 to 90%.
[3] The optical filter according to [1] or [2], wherein the resin film further satisfies the following optical characteristic (ii-4):
(ii-4) An optical filter according to any one of [1] to [3], wherein the average internal transmittance at wavelengths of 660 nm to 730 nm at an incident angle of 30° is 10% or less. [4] The second thin film laminate structure is laminated on the surface of the resin film.
[5] The optical filter according to any one of [1] to [4], wherein the resin film further satisfies the following optical characteristic (ii-5):
(ii-5) The optical filter according to any one of [1] to [5], wherein the average internal transmittance at wavelengths of 450 to 600 nm at an incident angle of 0° is 70% or more. [6] The second thin film stack structure has a dielectric multilayer film in which TiO ₂ and SiO ₂ are alternately stacked, and the film ratio represented by the following formula is 0.50 or more.
Film ratio (physical film thickness) = total physical film thickness of _SiO2 / (total physical film thickness of _TiO2 + total physical film thickness of _SiO2 )
[7] The optical filter according to any one of [1] to [6], wherein the resin film contains a polyimide resin.
[8] The optical filter according to any one of [1] to [7], which satisfies all of the following optical properties (iii-1) to (iii-5):
(iii-1) The average transmittance at wavelengths of 400 to 600 nm at an incident angle of 0° is 70% or more. (iii-2) The average reflectance at wavelengths of 450 to 600 nm at an incident angle of 40° is 5% or less. (iii-3) The average reflectance at wavelengths of 450 to 600 nm at an incident angle of 5° is 3% or less. (iii-4) The maximum transmittance at wavelengths of 700 to 900 nm at an incident angle of 40° is 15% or less. (iii-5) The average transmittance at wavelengths of 1000 to 1100 nm at an incident angle of 40° is 5% or less.

The present invention provides an optical filter that has high transmittance for visible light and high blocking ability for near-infrared light, and suppresses the occurrence of ripples in the visible light region and a decrease in blocking ability in the near-infrared light region even at high angles of incidence.

FIG. 1 is a cross-sectional view schematically illustrating an example of an optical filter according to an embodiment. FIG. 2 is a cross-sectional view schematically illustrating an example of an optical filter according to an embodiment. FIG. 3 is a cross-sectional view schematically illustrating an example of an optical filter according to an embodiment. FIG. 4 is a diagram showing the spectral transmittance curve of the first thin film laminated structure 1-4. FIG. 5 is a diagram showing the spectral reflectance curve of the first thin film laminated structure 1-4. FIG. 6 is a diagram showing the spectral transmittance curve of the first thin film laminated structure 1-5. FIG. 7 is a diagram showing the spectral reflectance curve of the first thin film laminated structure 1-5. FIG. 8 is a diagram showing the spectral transmittance curve of the second thin film laminated structure 2-1. FIG. 9 is a diagram showing the spectral reflectance curve of the second thin film laminated structure 2-1. FIG. 10 is a diagram showing the spectral transmittance curve of the second thin film laminated structure 2-2. FIG. 11 is a diagram showing the spectral reflectance curve of the second thin film laminated structure 2-2. FIG. 12 is a diagram showing the spectral transmittance curve of the optical filter of Example 3-1. FIG. 13 is a diagram showing the spectral transmittance curve of the optical filter of Example 3-2. FIG. 14 is a diagram showing the spectral transmittance curve of the optical filter of Example 3-3. FIG. 15 is a diagram showing the spectral transmittance curve of the optical filter of Example 3-4. FIG. 16 is a diagram showing the spectral transmittance curve of the optical filter of Example 3-5. FIG. 17 is a diagram showing the spectral transmittance curve of the optical filter of Example 3-6.

Hereinafter, an embodiment of the present invention will be described.
In this specification, the near-infrared absorbing dye may be abbreviated as "NIR dye."
In this specification, a compound represented by formula (I) is referred to as compound (I). The same applies to compounds represented by other formulas. A dye comprising compound (I) is also referred to as dye (I), and the same applies to other dyes. Furthermore, a group represented by formula (I) is also referred to as group (I), and the same applies to groups represented by other formulas.

In this specification, "limiting light transmission" means that the light transmittance for light of a specified wavelength is less than 5% when incident at an angle of incidence of 0 degrees (perpendicular incidence).

In this specification, the internal transmittance is the transmittance obtained by subtracting the influence of interface reflection from the measured transmittance, which is expressed by the formula {measured transmittance/(100-reflectance)}×100.
In this specification, the transmittance of a substrate and the transmittance of a resin film, including a resin containing a dye, are all "internal transmittance" even when they are referred to as "transmittance." On the other hand, the transmittance of an optical filter having a dielectric multilayer film is an actually measured transmittance.

In this specification, for example, a transmittance of 90% or more in a specific wavelength range means that the transmittance is not below 90% in the entire wavelength range, i.e., the minimum transmittance in that wavelength range is 90% or more. Similarly, for example, a transmittance of 1% or less in a specific wavelength range means that the transmittance is not more than 1% in the entire wavelength range, i.e., the maximum transmittance in that wavelength range is 1% or less. The same applies to internal transmittance. The average transmittance and average internal transmittance in a specific wavelength range are the arithmetic mean of the transmittance and internal transmittance per 1 nm in that wavelength range.
The optical properties can be measured using a UV-visible spectrophotometer.
In this specification, the use of "to" to indicate a range of values includes the upper and lower limits.

<Optical filter>
The optical filter of the present invention comprises a substrate and two thin film stack structures that limit the transmission of light in the near-infrared wavelength region. The substrate includes a resin film containing a dye that absorbs light in the near-infrared wavelength region. The first thin film stack structure includes at least two dielectric multilayer films and is stacked as an outermost layer on one main surface of the substrate, and the second thin film stack structure includes at least one dielectric multilayer film and is stacked as an outermost layer on the other main surface of the substrate. In other words, the optical filter of the present invention includes at least three dielectric multilayer films. The first thin film stack structure and the second thin film stack structure each satisfy the specific optical characteristics described below.

The first thin film stack structure is a composite of two or more dielectric multilayer films, and the near-infrared light reflection region is shifted so that the ripple in the visible light region of each multilayer film cancels out. Meanwhile, the first thin film stack structure experiences light leakage in a specific near-infrared wavelength region, specifically the 850 nm to 950 nm wavelength region. This light leakage is blocked by the reflective properties of the second thin film stack structure and the absorption properties of the dye contained in the resin film, resulting in the overall optical filter achieving high visible light transmittance, high near-infrared light blocking, and reduced ripple in the visible light region. Furthermore, because dyes exhibit absorption properties independent of incident angle dependence, using a dye that absorbs near-infrared light can compensate for the reduced near-infrared light blocking ability caused by the incident angle dependence of the multilayer film.

An example of the configuration of this filter will be explained using the drawings. Figures 1 to 3 are cross-sectional views that schematically show an example of an optical filter according to one embodiment.

The optical filter 1 shown in Figure 1 has a first thin film laminated structure 31 on one main surface side of the substrate 10 and a second thin film laminated structure 32 on the other main surface side. In Figure 1, the first thin film laminated structure 31 has a dielectric multilayer film 31A and a dielectric multilayer film 31B. The substrate 10 also has a support 11 and a resin film 12 laminated on one main surface side of the support.

The optical filter 1 shown in Figure 2 is an example in which the substrate 10 is composed of a resin film 12 without any support.

The optical filter 1 shown in Figure 3 is an example in which the first thin film stack structure 31 has a dielectric multilayer film 31A, a dielectric multilayer film 31B, and a dielectric multilayer film 31C.

<Thin film laminated structure>
The optical filter of the present invention has a first thin film laminate structure and a second thin film laminate structure that limit the transmission of light in the near-infrared wavelength region, and each thin film laminate structure is laminated as an outermost layer on both main surface sides of a substrate.

The first thin film stack is a composite having at least two dielectric multilayer films.
The first thin film stack structure satisfies the following optical properties (i-1A) and (i-1B).
(i-1A) The maximum transmittance T _{850-950 (40 deg) MAX} at a wavelength of 850 nm to 950 nm at an incident angle of 40° is 5% or more. (i-1B) The maximum reflectance R _{450-600 (40 deg) MAX at a wavelength of 450 nm to 600 nm at an incident angle of 40°} is 8% or less.

The first thin film laminate structure is designed by shifting the near-infrared light reflection region so that ripples in the visible light region of two or more dielectric multilayer films cancel each other out, resulting in light leakage in the near-infrared wavelength region. The optical characteristic (i-1A) indicates the wavelength region in which light leakage occurs and the level at which light leakage is acceptable. _{T 850-950 (40 deg) MAX} is more preferably 6% or more, and is also preferably 30% or less, more preferably 20% or less.

Satisfying the optical characteristic (i-1B) means that the reflectance in the visible light region is low. This means that good transmittance is exhibited in the visible light region. _{R 450-600 (40 deg) MAX} is more preferably 7% or less.

The first thin film stack structure preferably further satisfies the following optical property (i-1C).
(i-1C) Average reflectance R _{1000-1100 (40 deg) AVE} at an incident angle of 40° in the wavelength range of 1000 nm to 1100 nm is 95% or more. Satisfying the optical property (i-1C) means that the film has excellent blocking properties for light in the near-infrared light range, particularly light in the range of 1000 nm to 1100 nm.

The second thin film stack includes at least one dielectric multilayer film.
The second thin film stack structure satisfies the following optical property (i-2A).
(i-2A) Average reflectance R _{850-950 (40 deg) AVE} at wavelengths of 850 nm to 950 nm at an incident angle of 40° is 25% to 60%
Satisfying the optical property (i-2A) means that light that could not be blocked due to light leakage from the first thin film stack structure can be blocked by the reflection properties of the second thin film stack structure. Having an R _{850-950 (40 deg) AVE} of 25% or more effectively blocks light leakage that occurs in the first thin film stack structure, and having an R _{850-950 (40 deg) AVE} of 60% or less prevents the physical film thickness of the dielectric multilayer film from becoming excessively thick. _{R 850-950 (40 deg) AVE} is preferably 30% to 55%.

It is preferable that the second thin film laminated structure further satisfies the following optical property (i-2B).
(i-2B) Average transmittance T _{450-600 (0 deg) AVE} at wavelengths of 450 nm to 600 nm at an incident angle of 0° is 80% or more. Satisfying the optical characteristic (i-2B) means that a high visible light transmittance can be obtained as an optical filter. _{T 450-600 (0 deg) AVE} is preferably 90% or more.

The second thin film stacked structure preferably further satisfies the following optical characteristic (i-2C).
(i-2C) Average reflectance R _{1000-1100 (40 deg) AVE} at wavelengths of 1000 nm to 1100 nm at an incident angle of 40° is 25% to 60%
Satisfying the optical characteristic (i-2C) means that the film is excellent in blocking light, particularly light of 1000 nm to 1100 nm in the near-infrared light region.

The first thin film stack structure and the second thin film stack structure are configured to limit transmission of a desired wavelength range using a dielectric multilayer film. The dielectric multilayer film is a film with optical functionality obtained by alternately stacking a selection of low-refractive index dielectric films (low-refractive index films), medium-refractive index dielectric films (medium-refractive index films), and high-refractive index dielectric films (high-refractive index films). Depending on the design, it is possible to utilize optical interference to achieve the function of transmitting light in a specific wavelength range or controlling the transmission restriction of light. Note that low refractive index, high refractive index, and medium refractive index refer to having a high refractive index, low refractive index, or intermediate refractive index relative to the refractive index of adjacent layers.

The high refractive index film is a film having a refractive index at a wavelength of 500 nm of preferably 1.9 or more, more preferably 1.9 to 2.6. Examples of materials for the high refractive index film include Ta ₂ O ₅ , TiO ₂ , and Nb ₂ O _5. Of these, TiO ₂ is preferred from the standpoints of film formability, reproducibility in refractive index, etc., and stability.

The medium refractive index film is a film having a refractive index at a wavelength of 500 nm of preferably 1.5 to 2.1, more preferably 1.8 to 2.0. Examples of materials for the medium refractive index film include Al ₂ O ₃ , Y ₂ O ₃ , and ZrO _2. Of these, Al ₂ O ₃ , ZrO ₂ , or a mixed material containing these two materials are preferred from the standpoint of stability, etc.

The low refractive index film is a film having a refractive index of preferably 1.8 or less, more preferably 1.3 to 1.6 at a wavelength of 500 nm. Examples of materials for the low refractive index film include SiO ₂ , MgF ₂ , and SiO _x N _y . SiO ₂ is preferred from the standpoints of reproducibility, stability, and economy in film formation.

The second thin film laminated structure is a multilayer film in which TiO ₂ and SiO ₂ are alternately laminated, and it is preferable that the film ratio shown in the following formula is 0.50 or more.
Film ratio (physical film thickness) = total physical film thickness of _SiO2 / (total physical film thickness of _TiO2 + total physical film thickness of _SiO2 )
With this configuration, the second thin film laminated structure can achieve reflection characteristics at wavelengths of 850 to 950 nm, specifically, a reflectance of 25 to 60% at an incident angle of 40°. The film ratio is more preferably 0.55 or more, and even more preferably 0.60 to 0.70. The physical film thickness can be measured using a stylus-type surface profiler (Dektak 150, manufactured by ULVAC, Inc.).

When the thin film laminated structure is constructed by alternately laminating thin films of different refractive indexes, the number of layers depends on the optical properties of the dielectric multilayer film, but the total number of thin film layers is preferably 50 to 150. If the total number of layers is 50 or more, the blocking performance for wavelengths of 800 nm to 1000 nm is sufficient. Furthermore, if the total number of layers is 150 or less, the takt time during production of the optical filter is not long, and warping of the optical filter due to the dielectric multilayer film is unlikely to occur, which is not preferable.
Furthermore, from the viewpoint of obtaining high near-infrared shading performance, the total number of layers in the first thin film laminated structure is preferably 20 to 150, and more preferably 20 to 50. From the viewpoint of mass productivity, the total number of layers in the second thin film laminated structure is preferably 50 or less, and more preferably less than 20.

The physical film thickness of the thin film laminated structure is preferably thinner from the viewpoint of making the optical filter thinner, while still satisfying the above-mentioned preferable number of layers.
The physical film thickness of the first thin film laminated structure is preferably 3 μm or more from the viewpoint of obtaining desired optical properties, and is preferably 15 μm or less from the viewpoint of suppressing warping of the optical filter. The film thickness of the second thin film laminated structure is preferably less than 3 μm, more preferably less than 2.5 μm, from the viewpoint of suppressing wrinkling of the resin layer.

The first thin film laminate structure and the second thin film laminate structure may be laminated on either main surface of the substrate, but it is preferable that the second thin film laminate structure be laminated on the surface of the resin film of the substrate. The second thin film laminate structure, which has fewer dielectric multilayer films, has a smaller number of layers than the first thin film laminate structure. The resin film in contact with the thin film laminate structure is subjected to greater stress the more thin films it has. If the stress from the thin film laminate structure is strong, wrinkles will form in the resin film when the resin softens due to heat during assembly processes such as reflow, causing problems with appearance quality. By laminating the film laminate structure with a smaller number of layers on the surface of the resin film, the resin film is subjected to less stress and wrinkles are suppressed, which is preferable.

When forming a thin film laminated structure, for example, dry film formation processes such as IAD (Ion Assisted Deposition) vapor deposition, CVD, sputtering, and vacuum deposition, or wet film formation processes such as spraying and dipping can be used.

<Base material>
In the optical filter of the present invention, the substrate has a resin film containing a dye (IR) that absorbs light in the near-infrared wavelength range and a resin. The absorption characteristics of the dye (IR) can block light leakage in the near-infrared wavelength range that occurs in the first thin film laminate structure. Furthermore, the absorption characteristics of the dye (IR) can compensate for the decrease in the near-infrared light blocking ability that is caused by the incident angle dependency of the multilayer film.

It is preferable that the resin film satisfies all of the following optical properties (ii-1) to (ii-3).
(ii-1) Average internal transmittance T _{850-950 (0 deg) AVE} at wavelengths of 850 nm to 950 nm at an incident angle of 0° is 60 to 90%
(ii-2) Average internal transmittance T _{850-950 (30 deg) AVE} at wavelengths of 850 nm to 950 nm at an incident angle of 30° is 60 to 90%
(ii-3) Average internal transmittance T _{850-950 (40 deg) AVE} at wavelengths of 850 nm to 950 nm at an incident angle of 40° is 60 to 90%

Satisfying the optical properties (ii-1) to (ii-3) means that light can be blocked by the absorption properties of the dye (IR) under incident angle conditions and wavelength ranges where light leakage occurs in the first thin film stack structure.

T _{850-950 (0 deg) AVE} is more preferably 70 to 90%.
T _{850-950 (30 deg) AVE} is more preferably 70 to 90%.
T _{850-950 (40 deg) AVE} is more preferably 70 to 90%.

It is preferable that the resin film further satisfies the following optical property (ii-4).
(ii-4) Average internal transmittance T _{660-730 (30 deg) AVE} at wavelengths of 660 nm to 730 nm at an incident angle of 30° is 10% or less. The wavelength range of 660 nm to 730 nm is close to the border with the visible light range within the near-infrared light range, and is a region where a decrease in reflectivity at high incident angles (grazing incidence shift) is likely to occur due to the incident angle dependency of the dielectric multilayer film. Satisfying the optical property (ii-4) means that near-infrared light that is not fully reflected by the dielectric multilayer film can be blocked by the absorption properties of the dye. _{T 660-730 (30 deg) AVE} is more preferably 20% or less.

It is preferable that the resin film further satisfies the following optical property (ii-5).
(ii-5) The average internal transmittance T _{450-600 (0 deg) AVE} of 70% or more for wavelengths of 450 to 600 nm at an incident angle of 0°. Satisfying the optical property (ii-5) means that the resin film has high visible light transmittance. _{T 450-600 (0 deg) AVE} is more preferably 60% or more.

As a dye (IR) that absorbs light in the near-infrared wavelength range, a dye that has a maximum absorption wavelength between 570 and 950 nm in the resin that makes up the resin film is preferred. Using such a dye can effectively block near-infrared light.

Examples of the dye (IR) include squarylium dyes, cyanine dyes, phthalocyanine dyes, naphthalocyanine dyes, dithiol metal complex dyes, azo dyes, polymethine dyes, phthalide dyes, naphthoquinone dyes, anthraquinone dyes, indophenol dyes, pyrylium dyes, thiopyrylium dyes, croconium dyes, tetradehydrocholine dyes, triphenylmethane dyes, aminium dyes, and diimonium dyes.
Among these, squarylium dyes and cyanine dyes are preferred from the viewpoint of spectral characteristics, and phthalocyanine dyes are preferred from the viewpoint of durability.
The dye (IR) may be composed of one type of compound or may contain two or more types of compounds.

The content of NIR dye (IR) in the resin film is preferably 0.1 to 30 parts by mass, and more preferably 0.1 to 15 parts by mass, per 100 parts by mass of resin. When two or more compounds are combined, the above content is the total of the respective compounds.

The resin film may contain other dyes, such as ultraviolet light absorbing dyes, to the extent that the effects of the present invention are not impaired.
Examples of ultraviolet light absorbing dyes include oxazole dyes, merocyanine dyes, cyanine dyes, naphthalimide dyes, oxadiazole dyes, oxazine dyes, oxazolidine dyes, naphthalic acid dyes, styryl dyes, anthracene dyes, cyclic carbonyl dyes, triazole dyes, etc. Among these, merocyanine dyes are particularly preferred.

The substrate in the present filter may have a single-layer structure or a multi-layer structure, and the material of the substrate is not particularly limited and may be an organic or inorganic material as long as it is a transparent material that transmits visible light.
When the substrate has a single layer structure, a resin substrate made of a resin film containing a resin and an NIR dye (IR) is preferred.
When the substrate has a multi-layer structure, a composite substrate is preferred in which a resin film containing an NIR dye (IR) is laminated on at least one main surface of a support, and the support is preferably made of a transparent resin or a transparent inorganic material.

The resin is not limited as long as it is a transparent resin, and one or more transparent resins selected from polyester resin, acrylic resin, epoxy resin, ene-thiol resin, polycarbonate resin, polyether resin, polyarylate resin, polysulfone resin, polyethersulfone resin, polyparaphenylene resin, polyarylene ether phosphine oxide resin, polyamide resin, polyimide resin, polyamideimide resin, polyolefin resin, cyclic olefin resin, polyurethane resin, polystyrene resin, etc. These resins may be used alone or in combination of two or more.
Among these, polyimide resins are preferred because they have excellent dye solubility, little absorption on the UV side, a high glass transition point (Tg), and excellent adhesion to the support and the dielectric multilayer film.

When multiple compounds are used as NIR dyes (IR) or other dyes, they may be contained in the same resin film, or they may each be contained in a separate resin film.

As the transparent inorganic material, glass or crystalline material is preferred.
Examples of glass that can be used for the support include absorption-type glass (near-infrared absorbing glass) containing copper ions in fluorophosphate glass or phosphate glass, soda-lime glass, borosilicate glass, alkali-free glass, and quartz glass.
As the glass, phosphate glass and fluorophosphate glass are preferred from the viewpoint of absorbing infrared light (especially 900 to 1200 nm). Note that "phosphate glass" also includes silicophosphate glass, in which part of the glass skeleton is composed of _SiO2 .

As glass, chemically strengthened glass may be used, which is obtained by ion exchange at a temperature below the glass transition point to replace alkali metal ions with small ionic radii (e.g., Li ions, Na ions) present on the main surface of the glass plate with alkali ions with larger ionic radii (e.g., Na ions or K ions for Li ions, and K ions for Na ions).

Crystalline materials that can be used for the support include birefringent crystals such as quartz, lithium niobate, and sapphire.

As a support, inorganic materials are preferred, particularly glass and sapphire, from the standpoint of shape stability related to long-term reliability of optical properties, mechanical properties, etc., and ease of handling during filter production.

The resin film can be formed by dissolving or dispersing the dye (IR), resin or resin raw materials, and other optional components in a solvent to prepare a coating solution, which is then applied to a substrate, dried, and optionally cured. The substrate may be the one included in the filter, or a peelable substrate used only when forming the resin film. The solvent may be any suitable dispersion medium or solvent capable of stably dispersing the dye.

The coating liquid may also contain a surfactant to prevent voids caused by tiny bubbles, depressions caused by the adhesion of foreign matter, and repellency during the drying process. Furthermore, methods such as dip coating, cast coating, and spin coating can be used to apply the coating liquid. After applying the coating liquid to a support, a resin film is formed by drying. Furthermore, if the coating liquid contains raw materials for a transparent resin, it may be further subjected to a curing process such as heat curing or photocuring.

The resin film can also be manufactured into a film by extrusion molding. When the substrate has a single-layer structure (resin substrate) consisting of a resin film containing a dye (IR), the resin film can be used as is as the substrate. When the substrate has a multi-layer structure (composite substrate) having a support and a resin film containing a dye (IR) laminated on at least one main surface of the support, the substrate can be manufactured by laminating this film onto the support and integrating them by thermocompression bonding or the like.

The optical filter may have one resin film layer, or two or more layers. If there are two or more layers, each layer may have the same or different configurations.

When the substrate has a single layer structure (resin substrate) made of a resin film containing a dye (IR), the thickness of the resin film is preferably 20 to 150 μm.
When the substrate has a multilayer structure (composite substrate) having a support and a resin film containing a dye (IR) laminated on at least one main surface of the support, the thickness of the resin film is preferably 0.3 to 20 μm. When the optical filter has two or more resin films, the total thickness of the resin films is preferably within the above range.

The shape of the substrate is not particularly limited, and may be a block, plate, or film.
The thickness of the substrate is preferably 300 μm or less from the viewpoints of reducing warpage during the formation of the dielectric multilayer film and reducing the height of the optical element. When the substrate is a resin substrate made of a resin film, the thickness is preferably 50 to 300 μm. When the substrate is a composite substrate comprising a support and a resin film, the thickness is preferably 50 to 300 μm.

<Optical filter (optical characteristics)>
The optical filter of the present invention having the above-mentioned configuration preferably satisfies all of the following optical properties (iii-1) to (iii-5).
(iii-1) Average transmittance T _{400-600 (0 deg) AVE} at wavelengths of 400 to 600 nm at an incident angle of 0° is 70% or more. (iii-2) Average reflectance R _{450-600 (40 deg) AVE} at wavelengths of 450 to 600 nm at an incident angle of 40° is 5% or less. (iii-3) Average reflectance R _{450-600 (5 deg) AVE} at wavelengths of 450 to 600 nm at an incident angle of 5° is 3% or less. (iii-4) Maximum transmittance T _{700-900 (40 deg) MAX} at wavelengths of 700 to 900 nm at an incident angle of 40° is 15% or less. (iii-5) Average transmittance T at wavelengths of 1000 to 1100 nm at an incident angle of 40° is _{1000-1100 (40 deg) AVE} is 5% or less

The optical filter of the present invention, which satisfies all of the optical properties (iii-1) to (iii-5), has high transmittance for visible light and high blocking properties for near-infrared light, and is an optical filter in which ripples in the visible light region are suppressed even at high angles of incidence.

Satisfying the optical property (iii-1) means that the film has excellent transmittance in the visible light region with wavelengths of 400 to 600 nm. _{T 400-600 (0 deg) AVE} is preferably 72% or more.

Satisfying the optical property (iii-2) means that the ripple is small in the visible light region of wavelengths from 450 to 600 nm. _{R 450-600 (40 deg) AVE} is preferably 4% or less.

Satisfying the optical property (iii-3) means that the ripple is small in the visible light region. _{R 450-600 (5 deg) AVE} is preferably 2.5% or less.

Satisfying the optical property (iii-4) means that the film has excellent shielding properties for near-infrared light in the range of 700 to 900 nm even at a high incident angle. _{T 700-900 (40 deg) MAX} is preferably 14% or less.

Satisfying the optical property (iii-5) means that the film has excellent shielding properties for near-infrared light in the 1000 to 1100 nm region even at a high incident angle. _{T 1000-1100 (40 deg) AVE} is preferably 4.5% or less.

The optical filter of the present invention preferably further satisfies the following optical property (iii-6).
(iii-6) The maximum transmittance T _{850-950 (40 deg) MAX} at a wavelength of 850 nm to 950 nm at an incident angle of 40° is 20% or less. Satisfying the optical property (iii-6) means that the light leakage allowed in the first thin film stack structure is blocked by the optical filter. _{T 850-950 (40 deg) MAX} is preferably 15% or less.

When used in an imaging device such as a digital still camera, the optical filter of the present invention can provide an imaging device with excellent color reproducibility. Such an imaging device comprises a solid-state imaging element, an imaging lens, and the optical filter of the present invention. The optical filter of the present invention can be used, for example, by being placed between the imaging lens and the solid-state imaging element, or by being directly attached to the solid-state imaging element, imaging lens, etc. of the imaging device via an adhesive layer.

Next, the present invention will be explained more specifically with reference to examples.
Each optical property was verified using optical thin film simulation software (TFCalc, manufactured by Software Spectra, Inc.) In this application, the refractive index of each film at a wavelength of 500 nm was used as a representative value, but the simulation was performed taking into account the wavelength dependency of the refractive index.
It should be noted that unless the incident angle is specifically stated, the optical characteristics are values simulated at an incident angle of 0 degrees (perpendicular to the main surface of the optical filter).

The dyes used in each example are as follows:
Compound 1 (cyanine compound): Synthesized based on Dyes and Pigments 73 (2007) 344-352.
Compound 2 (squarylium dye): synthesized based on the specifications of U.S. Patent Application Publication No. 2014/0061505 and WO 2014/088063.
Compound 3 (merocyanine compound): Synthesized with reference to Japanese Patent No. 6504176.

<Example 1-1: Resin film>
A polyimide resin (C-3G30G manufactured by Mitsubishi Gas Chemical Company) was dissolved in an organic solvent (cyclohexanone) at a concentration of 10% by mass.
To the polyimide resin solution prepared above, 0.05 parts by mass of compound 1, 2.76 parts by mass of compound 2, and 11.7 parts by mass of compound 3 were added relative to 100 parts by mass of the resin, and the mixture was stirred for 2 hours while heating to 50° C. The dye-containing resin solution was applied to a glass substrate (alkali glass, D263 manufactured by Schott) using spin coating, and thoroughly dried by heating to obtain a resin film (coated film) with a thickness of 5 μm.

<Example 1-2: Resin film>
A resin film was obtained in the same manner as in Example 1-1, except that 0.44 parts by mass of compound 1, 2.76 parts by mass of compound 2, and 11.7 parts by mass of compound 3 were added relative to 100 parts by mass of the resin.

For each resin film, the transmission and reflection spectra were measured using a spectrophotometer in the wavelength range of 350 nm to 1200 nm at an angle of 5° relative to the incident direction. The obtained spectral transmittance curves and spectral reflectance curves were used to calculate the spectral internal transmittance curves, which were normalized so that the transmittance at the maximum absorption wavelength was 10%.
Internal transmittance (%) = transmittance / (100 - reflectance) * 100
The optical properties are shown in Table 1 below.
It should be noted that Examples 1-1 and 1-2 are reference examples.

<Example 2-1: Thin film laminated structure 1-1>
We designed thin film stack structure 1-1 by combining three types of dielectric multilayer films, each consisting of alternating _TiO2 , _SiO2 , and _ZrO2 layers, with different numbers of layers and physical thicknesses. The numbers of layers and physical thicknesses are shown in Table 1 below.

<Example 2-2: Thin film laminated structure 1-2>
Thin film stack structure 1-2 was designed by combining two types of dielectric multilayer films, each consisting of alternating _TiO2 and _SiO2 films, with different numbers of layers and physical film thicknesses. The numbers of layers and physical film thicknesses are shown in Table 1 below.

<Example 2-3: Thin film laminate structure 1-3>
A thin film stacked structure 1-3 was designed in the same manner as in Example 2-2, except that the number of stacked TiO ₂ films and SiO ₂ films and the physical film thicknesses were as shown in Table 1 below.

<Example 2-4: Thin film laminated structure 1-4>
A thin film stacked structure 1-4 was designed in the same manner as in Example 2-2, except that the number of stacked TiO ₂ films and SiO ₂ films and the physical film thickness were as shown in Table 1 below.

<Example 2-5: Thin film laminate structure 1-5>
Referring to the description of Example 4 of Japanese Patent Application Laid-Open No. 2007-183525, a thin film laminate structure 1-5 was designed, which is a dielectric multilayer film in which TiO ₂ films, La ₂ O ₃ films, and Al ₂ O ₃ films are alternately laminated. The number of layers is shown in Table 1 below.

<Example 2-6: Thin film laminated structure 2-1>
We designed a thin film laminated structure 2-1 consisting of a dielectric multilayer film in which TiO ₂ films and SiO ₂ films were alternately laminated. The number of layers and physical film thickness are shown in Table 1 below.

<Example 2-7: Thin film laminated structure 2-2>
With reference to the description of Example 4 of Japanese Patent Application Laid-Open No. 2007-183525, a thin film laminated structure 2-1 was designed, which is a dielectric multilayer film in which TiO ₂ films and SiO ₂ films are alternately laminated. The number of layers is shown in Table 1 below.

The optical properties of the thin film laminate structures 1-1 to 1-5 and the optical properties of the thin film laminate structures 2-1 and 2-2 are shown in Table 1 below.
The spectral transmittance curves and spectral reflectance curves of the thin film laminated structures 1-4 and 1-5 and the thin film laminated structures 2-1 and 2-2 are shown in FIGS. 4 to 11, respectively.
Examples 2-1 to 2-7 are reference examples.

<Example 3-1: Optical filter>
The resin film of Example 1-1 and thin film laminate structure 2-1 were laminated on one main surface of a glass substrate (alkali glass, D263 manufactured by Schott), and thin film laminate structure 1-1 was laminated on the other main surface to obtain an optical filter.

<Example 3-2: Optical filter>
An optical filter was obtained in the same manner as in Example 3-1, except that the thin film laminated structure 1-1 was replaced with the thin film laminated structure 1-2.

<Example 3-3: Optical filter>
An optical filter was obtained in the same manner as in Example 3-1, except that the thin film laminated structure 1-1 was replaced with the thin film laminated structure 1-3.

<Example 3-4: Optical filter>
An optical filter was obtained in the same manner as in Example 3-1, except that the thin film laminated structure 1-1 was replaced with the thin film laminated structure 1-3 and the resin film of Example 1-1 was replaced with the resin film of Example 1-2.

<Example 3-5: Optical filter>
An optical filter was obtained in the same manner as in Example 3-1, except that the thin film laminated structure 1-1 was replaced with the thin film laminated structure 1-4.

<Example 3-6: Optical filter>
Referring to Example 4 of JP-A 2007-183525, a thin film laminated structure 2-2 was laminated on one main surface of a glass substrate, and a thin film laminated structure 1-5 was laminated on the other main surface to obtain an optical filter.

The optical filters thus obtained were measured for transmission spectrum at incident angles of 0° and 40° using a spectrophotometer, and for reflection spectrum at an incident angle of 5°. The optical properties are shown in the table below.
The spectral transmittance curves of the optical filters 3-1 to 3-6 are shown in FIGS. 12 to 17, respectively.
Examples 3-1 to 3-5 are working examples, and Example 3-6 is a comparative example.

Furthermore, the optical filter was evaluated for wrinkles by the following method.
For the wrinkle evaluation, the optical filter was heated in an electric furnace set at 160°C for 10 minutes, then removed from the electric furnace and cooled to room temperature. Next, the central part of the optical filter was observed with an optical microscope to check for the presence or absence of wrinkles. If the optical filter had wrinkles that were visible to the naked eye, it was rated as ×, and if there were no wrinkles that were visible to the naked eye, it was rated as ◯.
The results are shown in Table 1.

The above results show that optical filters 3-1 to 3-5 have high transmittance for visible light and high blocking ability for near-infrared light, suppress the occurrence of ripples in the visible light region at high incident angles, and also suppress the decrease in blocking ability for near-infrared light at high incident angles.Furthermore, the occurrence of wrinkles in the resin film was also suppressed.
On the other hand, optical filter 3-6, which used two types of multilayer film and did not use any dye, exhibited ripples in the visible light region at high incident angles, and the transmission characteristics shifted at high incident angles, resulting in a decrease in blocking ability in the near-infrared light region.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2020-217100) filed on December 25, 2020, the contents of which are incorporated herein by reference.

The optical filter of the present invention has excellent visible light transmittance and good near-infrared light blocking properties, with reduced degradation of near-infrared light blocking properties at high angles of incidence. It is useful for applications in information acquisition devices, such as cameras and sensors for transport aircraft, which have become increasingly sophisticated in recent years.

1...optical filter, 10...substrate, 11...support, 12...resin film, 31...first thin film laminated structure, 31A, 31B, 31C...dielectric multilayer film, 32...second thin film laminated structure

Claims (7)

A substrate;
a first thin film stack structure and a second thin film stack structure that limit the transmission of light in the near infrared wavelength range;
An optical filter comprising:
the substrate includes a resin film containing a dye that absorbs light in the near-infrared wavelength region;
the first thin film laminated structure includes at least two dielectric multilayer films and is laminated as an outermost layer on one main surface side of the base material,
the second thin film laminated structure includes at least one dielectric multilayer film and is laminated as an outermost layer on the other main surface side of the base material,
The first thin film stack structure satisfies the following optical properties (i-1A) and (i-1B),
The second thin film stack structure satisfies the following optical property (i-2A):
the second thin film laminated structure is laminated on the surface of the resin film;
Optical filters.
(i-1A) Maximum transmittance at wavelengths of 850 nm to 950 nm at an incident angle of 40° is 5% or more. (i-1B) Maximum reflectance at wavelengths of 450 nm to 600 nm at an incident angle of 40° is 8% or less. (i-2A) Average reflectance at wavelengths of 850 nm to 950 nm at an incident angle of 40° is 25% to 60%. 2. The optical filter according to claim 1, wherein the resin film satisfies all of the following optical properties (ii-1) to (ii-3):
(ii-1) The average internal transmittance at an incident angle of 0° in the wavelength range of 850 nm to 950 nm is 60 to 90%.
(ii-2) Average internal transmittance at an incident angle of 30° in the wavelength range of 850 nm to 950 nm is 60 to 90%
(ii-3) The average internal transmittance at an incident angle of 40° in the wavelength range of 850 nm to 950 nm is 60 to 90%. 3. The optical filter according to claim 1, wherein the resin film further satisfies the following optical property (ii-4):
(ii-4) The average internal transmittance at an incident angle of 30° in the wavelength range of 660 nm to 730 nm is 10% or less. 4. The optical filter according to claim 1 , wherein the resin film further satisfies the following optical characteristic (ii-5):
(ii-5) The average internal transmittance at an incident angle of 0° for wavelengths of 450 to 600 nm is 70% or more. 5. The optical filter according to claim 1 , wherein the second thin film stack structure has a dielectric multilayer film in which _TiO2 and _SiO2 are alternately stacked, and a film ratio represented by the following formula is 0.50 or more.
Film ratio (physical film thickness) = total physical film thickness of _SiO2 / (total physical film thickness of _TiO2 + total physical film thickness of _SiO2 ) 6. The optical filter according to claim 1 , wherein the resin film contains a polyimide resin. 7. The optical filter according to claim 1 , which satisfies all of the following optical properties (iii-1) to (iii-5):
(iii-1) The average transmittance at wavelengths of 400 to 600 nm at an incident angle of 0° is 70% or more. (iii-2) The average reflectance at wavelengths of 450 to 600 nm at an incident angle of 40° is 5% or less. (iii-3) The average reflectance at wavelengths of 450 to 600 nm at an incident angle of 5° is 3% or less. (iii-4) The maximum transmittance at wavelengths of 700 to 900 nm at an incident angle of 40° is 15% or less. (iii-5) The average transmittance at wavelengths of 1000 to 1100 nm at an incident angle of 40° is 5% or less.