Near-infrared cut filter

Abstract

To provide a near-infrared cut filter which more steeply absorbs light in both a long wavelength region and a short wavelength region, and selectively transmits light in a visible light region.SOLUTION: A near-infrared cut filter (1) has a first glass base material (2) for absorbing at least light in a longer wavelength region than that in a visible light region, a second glass base material (4) for absorbing at least light in a shorter wavelength region than that in the visible light region, and a resin layer (3) which is interposed between the first glass base material and the second glass base material and absorbs light of a specific wavelength.SELECTED DRAWING: Figure 1

Description

Technical Field

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[0001] The present invention relates to a near-infrared cut filter.

Background Art

[0002] Conventionally, a near-infrared cut filter is known in which an inorganic film as a dielectric is deposited on the surface of a transparent substrate, and ultraviolet light and near-infrared light in incident light are selectively reflected by a reflection film, and only visible light is transmitted.

[0003] In such a near-infrared cut filter using reflection, for example, when the near-infrared cut filter is installed in an imaging device, problems such as ghosts and flares due to reflected light occur. Therefore, it has been required to remove unnecessary light by absorption.

[0004] The invention described in Patent Document 1 discloses an invention related to a near-infrared cut filter in which a resin layer that absorbs a specific wavelength is formed on the surface of a transparent substrate made of glass.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0008] The near-infrared cut filter of the present invention is characterized by comprising: a first glass substrate that absorbs light in the wavelength range longer than the visible light range; a second glass substrate that absorbs light in the wavelength range shorter than the visible light range; and a resin layer interposed between the first glass substrate and the second glass substrate that absorbs light of a specific wavelength.

[0009] In the present invention, it is preferable that the resin layer determines the half-power wavelength on the long-wavelength side of the transmittance curve of the near-infrared cut filter, and the second glass substrate determines the half-power wavelength on the short-wavelength side of the transmittance curve of the near-infrared cut filter. [Effects of the Invention]

[0010] According to the present invention, it is possible to abruptly absorb light in both the long-wavelength and short-wavelength regions and selectively transmit light in the visible light region. Furthermore, by sandwiching both sides of the dye-containing resin layer between glass substrates, it is possible to block it from the atmosphere and improve weather resistance. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic cross-sectional view of the near-infrared cut filter in this embodiment. [Figure 2] Figure 2 is a graph showing the spectral transmittance curves of the glass substrate, resin layer, and near-infrared cut filter used in this embodiment. [Figure 3] Figure 3 is a graph showing the spectral transmittance curves of a glass substrate, a resin layer, and a near-infrared cut filter used in another embodiment of a near-infrared cut filter. [Modes for carrying out the invention]

[0012] The following describes in detail one embodiment of the present invention (hereinafter abbreviated as "Embodiment"). It should be noted that the present invention is not limited to the following embodiment, and can be implemented in various modifications within the scope of its gist.

[0013] Figure 1 is a schematic cross-sectional view of the near-infrared cut filter 1 in this embodiment. As shown in Figure 1, the near-infrared cut filter 1 is composed of a first glass substrate 2, a resin layer 3, and a second glass substrate 4.

[0014] As shown in Figure 1, the first glass substrate 2 is formed in close contact with one main surface of the resin layer 3, and the second glass substrate 4 is formed in close contact with the other main surface of the resin layer 3. It is possible to interpose a light-absorbing layer or the like between the first glass substrate 2 and the resin layer 3, and between the second glass substrate 4 and the resin layer 3, but in particular, the first glass substrate 2 and the resin layer 3 can be directly brought into close contact, and the second glass substrate 4 and the resin layer 3 can be directly brought into close contact, without providing a separate light-absorbing layer.

[0015] The near-infrared cut filter 1 shown in Figure 1 may have an appearance such as a rectangular plate or a circular shape, but its shape is not particularly limited.

[0016] [First glass substrate 2] The first glass substrate 2 absorbs light in the longer wavelength range, at least beyond the visible light range. "Absorbing light in the longer wavelength range" means that the spectral transmission curve has the characteristic of falling off at wavelengths beyond the visible light range. Preferably, the half-power wavelength (NIR_λ50) on the longer wavelength side of the transmittance curve of the first glass substrate 2 is in the range of 650 to 800 nm, more preferably in the range of 670 to 770 nm, and even more preferably in the range of 700 nm to 750 nm. "Half-power wavelength (NIR_λ50) on the longer wavelength side" refers to the wavelength at which the transmittance becomes 50% at the falling edge of the transmittance curve.

[0017] Further, although not limited, the first glass substrate 2 preferably has a spectral transmittance of 25% or less at 800 nm or more, 15% or less at 850 nm or more, and 10% or less at 900 nm or more.

[0018] Also, although the short wavelength side of the spectral transmittance curve of the first glass substrate 2 is not particularly defined, it is preferable to transmit ultraviolet rays (particularly, long wavelength ultraviolet rays). For example, the half-value wavelength (UV_λ50) on the short wavelength side is preferably in the range of 300 to 360 nm, more preferably in the range of 310 to 350 nm, and even more preferably in the range of 320 to 340 nm. The "half-value wavelength (UV_λ50) on the short wavelength side" refers to the wavelength at which the transmittance becomes 50% at the rising edge of the spectral transmittance curve. For example, the first glass substrate 2 is an absorption glass substrate made of phosphate glass.

[0019] The thickness of the first glass substrate 2 is not particularly limited, but is preferably in the range of 0.01 to 3.00 mm, more preferably in the range of 0.01 to 2.00 mm, and even more preferably in the range of 0.01 to 1.50 mm.

[0020] Phosphate glass is a glass containing P and O as essential components and other optional components, and those containing Fe2O3 are particularly preferred. By containing Fe2O3, the phosphate glass can more effectively absorb near-infrared light. Examples of other optional components of the phosphate glass include Ca, Mg, Sr, Ba, Li, Na, K, Cs, and the like.

[0021] As specific compositions of the phosphate-based glass, those containing P2O5: 0 to 80%, Al2O3: 0 to 40% by mass, RO: 0 to 40% by mass (where R is at least one selected from Mg, Ca, Sr, Ba, Zn), R'2O: 0 to 20% by mass (where R' is at least one selected from Li, Na, K), and Fe2O3: 0 to 30% by mass are preferred. Alternatively, as specific compositions of the phosphate-based glass, those containing P2O5: 30 to 75% by mass, Al2O3: 1 to 20% by mass, RO: 1 to 10% by mass, and Fe2O3: 0.5 to 25% by mass are more preferred.

[0022] Incidentally, the first glass substrate 2 may be a fluophosphate-based glass.

[0023] FIG. 2 shows the spectral transmittance curve of a phosphate-based glass (model number HA50, manufactured by HOYA Corporation) as the first glass substrate 2. As shown in FIG. 2, it can be seen that it absorbs infrared rays (wavelength of 780 nm or more) and has a high transmittance in the visible light region of about 410 nm to 600 nm.

[0024] As shown in FIG. 2, when the wavelength of the phosphate-based glass (model number HA50) exceeds about 600 nm, the transmittance gradually starts to decrease, and when it reaches about 900 nm, the transmittance falls below 10%. Thus, a tendency for the transmittance to gradually decrease is observed between wavelengths of 600 nm and 900 nm. On the other hand, on the short wavelength side, it can be seen that some ultraviolet wavelengths also have a high transmittance.

[0025] [Second glass substrate 4] The second glass substrate 4 absorbs light in at least a shorter wavelength region than the visible light region. "Absorbing light in a shorter wavelength region" means having a characteristic in which the spectral transmittance curve rises on the shorter wavelength side than the visible light region. The half-value wavelength (UV_λ50) of the transmittance curve in the second glass substrate 4 is preferably in the range of 380 to 430 nm, more preferably in the range of 390 to 420 nm, and even more preferably within the range of 400 nm to 420 nm. "Half-value wavelength (UV_λ50)" refers to the wavelength at which the transmittance becomes 50% at the rise of the transmittance curve.

[0026] Furthermore, the wavelength gradient width, defined by the interval between the wavelength value where the spectral transmittance is 72% and the wavelength value where it is 5%, is 50 nm or less, preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 10 nm or less. In this way, the transmittance curve of the second glass substrate 4 draws a curve that rises steeply on the short wavelength side. The rise of the transmittance curve of the second glass substrate 4 changes more steeply than the fall of the transmittance curve of the first glass substrate 2. The second glass substrate 4 is called a sharp-cut filter.

[0027] The thickness of the second glass substrate 4 is not particularly limited, but is preferably in the range of 0.01 to 3.00 mm, more preferably 0.01 to 2.00 mm, and even more preferably 0.01 to 1.50 mm.

[0028] The second glass substrate 4 includes, for example, SiO2, Al2O3, Li2O, Na2O, K2O, CeO2, TiO2, etc. SiO2 is a basic component of glass and is an important component for the thermal stability and chemical durability of the glass. The SiO2 content is preferably 50-70%, more preferably 55-65%. Al2O3 is an effective component for suppressing phase separation and devitrification of the glass, and the Al2O3 content is preferably 0-5%, more preferably 0-2%. Li2O is a component that improves the meltability of the glass, and the Li2O content is preferably 0-10%, more preferably 0-5%. Na2O is a component that improves the meltability of the glass, and the Na2O content is preferably 0-20%, more preferably 5-15%. K2O is a component that improves the meltability of the glass, and the K2O content is preferably 0-20%, more preferably 5-15%. The total content of Li2O + Na2O + K2O is preferably 10-30%, more preferably 15-25%. RO (MgO, CaO, SrO, BaO, ZnO) is an effective component that assists in the absorption of CeO2 while ensuring transmittance in the visible light range, and further improves the melt-formability, devitrification resistance, and chemical durability of the glass. The total RO content is preferably 5-20%, more preferably 13-18%.

[0029] CeO2 is an essential component for absorbing ultraviolet rays. The CeO2 content is preferably 1-5%, and more preferably 1.0-3%. TiO2 is an effective component for preventing UV degradation when combined with CeO2. The TiO2 content is preferably 0-5%, and more preferably 1.0-3%.

[0030] Figure 2 shows the spectral transmittance curve of the sharp-cut filter glass (model number L42: manufactured by HOYA Corporation) as the second glass substrate 4. As shown in Figure 2, it can be seen that the sharp-cut filter glass (model number L42) absorbs ultraviolet light and transmits light of longer wavelengths.

[0031] As shown in Figure 2, the spectral transmittance of the sharp-cut filter glass (model number L42) rises sharply at wavelengths of approximately 410 nm to 420 nm. Therefore, the wavelength gradient is extremely narrow, less than approximately 10 nm.

[0032] [Resin layer 3] The resin layer 3 is interposed between the first glass substrate 2 and the second glass substrate 4 and absorbs light of a specific wavelength.

[0033] The resin layer 3 is a layer composed of a dye that absorbs light of a specific wavelength and a resin. The resin layer 3 preferably includes, for example, a near-infrared absorbing dye and a transparent resin, in which the dye is uniformly dissolved or dispersed in the transparent resin.

[0034] The thickness of the resin layer 3 is not particularly limited, but is approximately a few micrometers, which is a sufficiently thin film compared to the first glass substrate 2 and the second glass substrate 4.

[0035] As the near-infrared absorbing dye constituting the resin layer 3, for example, one or more selected from cyanine-based dyes, polymethine-based dyes, squarylium-based dyes, porphyrin-based dyes, metal dithiol complex-based dyes, phthalocyanine-based dyes, diimonium-based dyes, and inorganic oxide particles can be used, and of these, one or more selected from squarylium-based dyes, cyanine-based dyes, and phthalocyanine-based dyes are more preferred.

[0036] As the resin constituting the resin layer 3, an adhesive for bonding glass substrates can be used, preferably a UV-curing adhesive. Using radicals and cations generated by ultraviolet irradiation as initiators, a cross-linked structure is formed by reactions between oligomers and monomers with polymerization ability, such as vinyl groups, acryloyl groups, and epoxy groups.

[0037] The resin layer 3 contains a polymerizable oligomer, a polymerizable monomer, a photopolymerization initiator, and various additives. The materials of the polymerizable oligomer, polymerizable monomer, and photopolymerization initiator differ depending on whether photoradical polymerization or photocationic polymerization is performed. In the case of photoradical polymerization, it is preferable to use an acrylic resin, and in the case of photocationic polymerization, it is preferable to use an epoxy resin. In photoradical polymerization, for example, polyester acrylate or urethane acrylate can be used as the polymerizable oligomer, acrylate monomer can be used as the polymerizable monomer, and benzophenone-based or acetophenone-based photopolymerization initiators can be used. Alternatively, in photocationic polymerization, alicyclic epoxy or glycidyl epoxy can be used as the polymerizable oligomer, vinyl ether monomer can be used as the polymerizable monomer, and sulfonium salt-based or iodonium salt-based photopolymerization initiators can be used. In addition to the near-infrared absorbing dye and transparent resin mentioned above, the additive may also contain any other components such as color-correcting dyes, leveling agents, antistatic agents, heat stabilizers, light stabilizers, antioxidants, dispersants, flame retardants, lubricants, and plasticizers, as long as they do not impair the effects of the present invention.

[0038] In this embodiment, an adhesive as a resin layer 3 is applied to the surface of either the first glass substrate 2 or the second glass substrate 4, the other glass substrate is bonded to it, and then ultraviolet light is irradiated. With thermosetting resins that undergo dehydration condensation, even if heat curing is performed with the glass substrates 2 and 4 sandwiched between both sides of the resin layer 3, proper dehydration condensation does not occur, and the resin layer 3 cannot be effectively bonded to the glass substrates 2 and 4. Therefore, in this embodiment, a UV-curing resin is used as the resin layer 3, and ultraviolet curing is performed with the glass substrates 2 and 4 placed on both sides of the resin layer 3. Since the second glass substrate 4 absorbs ultraviolet light, it is preferable to irradiate the resin layer 3 with ultraviolet light from the side of the first glass substrate 2 to UV cure it.

[0039] In this embodiment, the resin layer 3 is configured to absorb light of a specific wavelength, and by setting the absorption wavelength according to the spectral transmittance characteristics of each glass substrate 2, 4, light in the desired visible light region can be extracted.

[0040] The resin layer 3 may contain a near-infrared absorbing dye having a maximum absorption wavelength in the 650-760 nm range. Furthermore, the resin layer 3 may further contain a near-infrared absorbing dye having a maximum absorption wavelength in the 800-1200 nm range.

[0041] The resin layer shown in Figure 2 contains a near-infrared absorbing dye with a maximum absorption wavelength of 650-760 nm, and it can be seen that the transmittance begins to decrease sharply from that of the first glass substrate 2 when the wavelength exceeds approximately 600 nm.

[0042] [Features and effects of the near-infrared cut filter 1 of this embodiment] As is clear from Figure 2, in this embodiment, the decline in spectral transmittance of the first glass substrate 2 is gentler than the rise in spectral transmittance of the second glass substrate 4. Therefore, the rise in the transmittance curve of the near-infrared cut filter 1 can be determined by the half-power wavelength on the short-wavelength side of the spectral transmittance curve of the second glass substrate 4. However, in order to make the decline in spectral transmittance of the near-infrared cut filter 1 as steep as the rise in spectral transmittance, the half-power wavelength on the long-wavelength side of the transmittance curve of the near-infrared cut filter 1 was determined in the resin layer 3. That is, the resin layer 3 includes at least a near-infrared absorbing dye, and is adjusted so that the decline in the transmittance curve of the near-infrared cut filter 1 is steeper than the decline in spectral transmittance of the first glass substrate 2.

[0043] For example, by including a near-infrared absorbing dye with a maximum absorption wavelength of approximately 700 nm in the resin layer 3, the half-maximum wavelength on the longer wavelength side of the transmittance curve of the near-infrared cut filter 1 can be set to around 600 nm to 700 nm, making the fall of the spectral transmittance in the near-infrared cut filter 1 steeper than that of the first glass substrate 2. The amount of near-infrared absorbing dye with a maximum absorption wavelength included in the resin layer 3 can be adjusted in various ways by determining which wavelength range the fall of the spectral transmittance should be set to.

[0044] As a result, in the near-infrared cut filter 1, which consists of a laminated structure of a second glass substrate 4 / resin layer 3 / first glass substrate 2, the spectral transmittance curve has a half-power wavelength (UV_λ50) on the short-wavelength side of the transmittance curve at 380-430 nm and a half-power wavelength (NIR_λ50) on the long-wavelength side at 600-700 nm, making it possible to selectively and accurately transmit light in the visible light range (within the range of 420 nm to 650 nm) and to have characteristics close to human visual sensitivity.

[0045] Figure 2 shows the spectral transmittance curve of a near-infrared cut filter 1 (L42 / resin layer / HA50) consisting of a three-layer structure: second glass substrate 4 (L42) / resin layer 3 / first glass substrate 2 (HA50). As shown in Figure 2, it exhibits excellent transmittance in the visible light range (approximately 420 nm to 600 nm), and a steep change in transmittance is observed in both the short-wavelength and long-wavelength ranges on both sides of the visible light range. As is clear from Figure 2, the second glass substrate 4 (L42) determines the half-power wavelength (UV_λ50) on the short-wavelength side of the transmittance curve of the near-infrared cut filter 1, and the resin layer determines (controls) the half-power wavelength (NIR_λ50) on the long-wavelength side of the transmittance curve of the near-infrared cut filter 1.

[0046] Furthermore, in this embodiment, by covering not only one main surface of the resin layer 3 containing a dye with poor weather resistance, but both main surfaces with a glass substrate, it is possible to block it from the atmosphere and improve the weather resistance of the resin layer 3.

[0047] [Configuration of a near-infrared cut filter in another embodiment] For example, in the laminated structure of L42 / resin layer / HA50 ​​shown in Figure 2, Figure 3 shows a glass substrate made of phthalate-based glass (model number CD700: manufactured by HOYA Corporation) interposed between the resin layer and HA50. As a result, in a near-infrared cut filter consisting of the laminated structure of L42 / resin layer / CD700 / HA50, the transmittance of wavelengths above 700 nm can be sufficiently reduced to approximately 5% or less, allowing for accurate transmission of visible light.

[0048] [Application] The applications of the near-infrared cut filter 1 of this embodiment are not limited, but can be used, for example, in imaging devices, automotive applications (such as windshield glass), and architectural glass. Imaging devices using the near-infrared cut filter 1 of this embodiment can obtain images with excellent color reproduction because ghosting is suppressed. [Industrial applicability]

[0049] The near-infrared cut filter of the present invention can absorb light in both the long-wavelength and short-wavelength ranges more sharply, and selectively transmit light in the visible light range. As a result, the near-infrared cut filter of this embodiment can be suitably applied to imaging devices and the like, and it becomes possible to achieve characteristics close to human visual sensitivity. [Explanation of Symbols]

[0050] 1. Near-infrared cut filter 2. First glass substrate 3. Resin layer 4. Second glass substrate

Claims

1. a first glass substrate that absorbs light in a wavelength range longer than the visible light range; a second glass substrate that absorbs light in a wavelength range shorter than the visible light range; a resin layer interposed between the first glass substrate and the second glass substrate, the resin layer absorbing light of a specific wavelength.

2. 2. The near-infrared cut filter according to claim 1, wherein the resin layer determines a half-value wavelength on the long-wavelength side of a transmittance curve of the near-infrared cut filter, and the second glass substrate determines a half-value wavelength on the short-wavelength side of a transmittance curve of the near-infrared cut filter.

3. A near-infrared cut filter as described in claim 1, characterized in that the wavelength at which the transmittance becomes 50% at the fall of the transmittance curve on the long wavelength side of the first glass substrate is in the range of 650 to 800 nm.

4. The near-infrared cut filter as described in claim 1, characterized in that the first glass substrate has a spectral transmittance of 25% or less at 800 nm or more, a spectral transmittance of 15% or less at 850 nm or more, and a spectral transmittance of 10% or less at 900 nm or more.

5. A near-infrared cut filter as described in claim 1, characterized in that the wavelength at which the transmittance becomes 50% at the rise of the transmittance curve on the short wavelength side of the first glass substrate is in the range of 300 to 360 nm.

6. A near-infrared cut filter as described in claim 1, characterized in that the wavelength at which the transmittance reaches 50% at the rise of the transmittance curve on the short wavelength side of the second glass substrate is in the range of 380 to 430 nm.

7. A near-infrared cut filter as described in claim 1, characterized in that in the second glass substrate, the wavelength gradient width defined by the interval between the wavelength value at which the spectral transmittance on the shorter wavelength side than the visible light region is 72% and the wavelength value at which it is 5% is 50 nm or less.

8. A near-infrared cut filter as described in claim 1, characterized in that the rise rate of the transmittance curve on the short wavelength side of the second glass substrate is larger than the fall rate of the transmittance curve on the long wavelength side of the first glass substrate.

9. A near-infrared cut filter described in any one of claims 1 to 8, characterized in that the resin layer contains a near-infrared absorbing pigment and a transparent resin.

10. The near-infrared cut filter according to claim 9, characterized in that the resin layer contains a near-infrared absorbing pigment having a maximum absorption wavelength in the range of 650 to 760 nm.

11. A near-infrared cut filter as described in claim 9, characterized in that the first glass substrate is made of phosphate-based glass, and the second glass substrate is made of sharp-cut filter glass containing SiO 2 and CeO 2 as essential components and Al 2 O 3, Li 2 O, Na 2 O, K 2 O and TiO 2 as optional components.

12. The near-infrared cut filter as described in claim 11, characterized in that a glass substrate made of fluorophosphate glass is provided between the resin layer and the second glass substrate.

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