JP2010224350A - Absorption-type multilayer film nd filter and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absorption-type multilayer film ND filter which has a resin film as a substrate and is superior in low reflectivity and environmental resistance, and to provide a manufacturing method therefor. <P>SOLUTION: In the absorption-type multilayer film ND filter, an absorption type multilayer film formed, by laminating dielectric film layers and absorbing film layers alternately is provided on at least one surface of a resin film substrate; the absorbing film layers include a metal film, and the dielectric film layers comprise an SiOx (x is 2 or smaller); and an MgF<SB>2</SB>film layer is laminated on the dielectric film layer on the outermost surface side. The dielectric film layers are constituted of an SiOx (1.5<x<2), which is formed by physical vapor deposition using a film-forming material having SiC and Si as the main components and has an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm, and the absorbing film layers are constituted of a metal film which is formed by physical vapor deposition and has a refractive index of 1.5 to 3.0 and an extinction coefficient of 1.5 to 4.0 at a wavelength of 550 nm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an absorptive multilayer ND filter that attenuates transmitted light in the visible light region, and in particular, an absorptive multilayer ND filter having a low reflectivity and environmental resistance using a resin film as a substrate, and a method for manufacturing the same. It is about.

  As ND (Neutral Density Filter) filters, there are known a reflective ND filter that reflects and attenuates incident light, and an absorption ND filter that absorbs and attenuates incident light. When incorporating into the system, an absorption ND filter is generally used. In addition, in the absorption type ND filter, there are a type in which an absorbing substance is mixed (colored glass ND filter) or applied to the substrate itself, and a type in which the thin film formed on the surface of the substrate itself does not absorb and has absorption, In the latter case, in order to prevent reflection on the surface of the thin film, the thin film is formed of a multilayer film (absorption type multilayer film), and has an antireflection effect as well as a function of attenuating transmitted light. Incidentally, the absorption multilayer ND filter used for a small and thin digital camera requires a thin substrate itself because the filter mounting space is small, and a resin film is the optimum substrate.

Patent Document 1 discloses an absorptive multilayer ND filter in which the thin film is constituted by a multilayer film in which dielectric film layers and absorption film layers are alternately laminated, and as a material constituting the absorption film layer. A metal film such as Ti is exemplified, and SiO ₂ and MgF ₂ are exemplified as a material constituting the dielectric film layer. An ND filter using a metal oxide film such as TiOx or Ta ₂ Ox that intentionally introduces oxygen during the formation of the absorption film layer and absorbs oxygen deficiency is also known as the absorption film layer. ing.

Here, when the metal film constituting the absorption film layer and the metal oxide film are compared, the metal film such as Ti has the same extinction coefficient as compared with the metal oxide film such as TiOx and Ta ₂ Ox. In order to obtain an extinction coefficient, the thickness of the absorption film layer can be reduced by using a metal film. When forming an absorption multilayer film on the resin film substrate having flexibility, the film thickness is reduced compared to the metal oxide film in consideration of the warp of the resin film substrate, film cracking, film formation time, etc. It is advantageous to adopt a metal film that can be set. Therefore, a metal film is mainly used as an absorption film layer of an absorption type multilayer ND filter used for a digital camera or the like.

On the other hand, as a material constituting the dielectric film layer, SiO ₂ , MgF _2, or the like is applied as described above. In order to reduce the surface reflection of the absorption multilayer ND filter, the lower the refractive index of the dielectric film layer located on the outermost surface side, the better. When comparing the above-described SiO ₂ and MgF ₂ , SiO ₂ It is desirable to apply MgF ₂ having a lower refractive index. However, MgF ₂ has a slight hygroscopicity, and when the absorption type multilayer ND filter to which MgF ₂ is applied is exposed to a high-temperature and high-humidity environment, it has a disadvantage of poor durability and is widely used. However, it is difficult to form MgF ₂ by the sputtering method for technical reasons described later. For this reason, SiO ₂ is mainly used for the dielectric film layer of the absorption multilayer ND filter.

By the way, when the surface reflection of the absorptive multilayer ND filter is high, ghosts and flares occur in the captured image. The conventional absorption multilayer ND filter in which SiO ₂ having a higher refractive index than MgF ₂ is applied to the dielectric film layer has a problem that the surface reflection is high and the low reflectivity of the ND filter is inferior.

On the other hand, metal films and metal oxide films such as TiOx and Ta ₂ Ox easily oxidize and the extinction coefficient decreases. Therefore, an ND filter in which the metal film or metal oxide film is applied to the absorption film layer is transparent. It is known that the rate increases with time, and this is remarkable when the absorption film layer is a metal film. When an ND filter in which a metal film or a metal oxide film is applied to the absorption film layer is exposed to a high temperature and high humidity environment, the absorption of the absorption film layer may progress and the transmittance may increase over time. It was a problem. Here, it is considered that oxygen that oxidizes a metal film or a metal oxide film is supplied in the air, or from a resin film substrate or a dielectric film layer. In particular, when the metal film has a thickness of 10 nm or less, it is easily affected by oxidation. In order to prevent oxidation of the metal film or the like, a method has been proposed in which heat treatment is performed in the air or in an oxygen atmosphere so that the vicinity of the interface of the metal film or the like is oxidized in advance and the oxidation does not proceed to the inside.

For example, Patent Document 2 discloses a thin-film ND filter in which a light absorption film and a dielectric film are stacked on a transparent substrate, and the light absorption film is formed by vapor deposition using a metal material as a raw material. A structure containing an oxide of a metal material generated in a state where a mixed gas containing oxygen is introduced at the time of film formation and the degree of vacuum is kept constant between 1 × 10 ⁻³ Pa and 1 × 10 ⁻² Pa ND filters are disclosed. A method has been proposed in which a light absorption film and a dielectric film are stacked on a transparent substrate, and then heated in an oxygen atmosphere containing 10% or more of oxygen to saturate changes in optical characteristics. Further, in Patent Document 3, in a thin-film ND filter in which one or more transparent dielectric films and a light absorption film are laminated on a light transmissive substrate, the light absorption film is unlikely to have high transmittance due to oxidation. A method employing a lower metal nitride film layer has been proposed.

  However, in the method described in Patent Document 2 in which the vicinity of the interface of the metal film or the like is previously oxidized by heat treatment in the air or in an oxygen atmosphere, the oxidation proceeds completely to the inside in a thin metal film having a thickness of 10 nm or less. Therefore, it has been difficult to form an oxide film only near the interface. Further, when heat treatment is performed in the air or in an oxygen atmosphere, warpage and cracks may occur due to the difference in thermal expansion coefficient between the formed absorption multilayer film and the resin film substrate. On the other hand, the method described in Patent Document 3, which employs a lower metal nitride film layer that does not easily increase the transmittance, has solved the drawback of increasing the transmittance, but the lower metal nitride film layer is more effective than the metal film layer. There is a problem that the film thickness becomes large because the attenuation coefficient is small, and when the metal oxide film is used as the absorption film layer, the resin film substrate is warped or cracked when formed on the resin film substrate. Etc. have a problem that is likely to occur.

Thus, a conventional absorption multilayer ND filter comprising an absorption multilayer having a structure in which a dielectric film layer made of SiO ₂ and an absorption film layer made of a metal film are alternately laminated on at least one surface of a resin film substrate. However, it has problems of low reflectivity and environmental resistance.

Japanese Patent Laid-Open No. 5-93811 JP 2003-43211 A JP 2003-322709 A International Publication No. WO2001 / 027345 International Publication WO2004 / 011690

  The present invention has been made paying attention to such problems, and the problem is that an absorption-type multilayer ND filter excellent in low reflectivity and environmental resistance using a resin film as a substrate and a method for producing the same Is to provide.

  Therefore, the present inventor has conducted extensive research to provide an absorption type multilayer ND filter that is excellent in low reflectivity and environmental resistance using a resin film as a substrate. As a result, the inventors have found the following method. .

First, when the metal film constituting the absorption film layer is oxidized in a high temperature and high humidity environment, oxygen is supplied from the oxide dielectric film layer made of SiO ₂ . Therefore, if the amount of oxygen contained in the oxide dielectric film layer made of SiO ₂ is reduced so that oxygen is hardly supplied, the progress of oxidation in the metal film can be suppressed.

  However, the oxide dielectric film is slightly colored when it is not sufficiently oxidized, and therefore cannot be used for an antireflection film or a reflection film that requires a transparent film. However, in the absorption type multilayer ND filter, since an absorbing metal film is used in the first place, even if the oxide dielectric film layer is slightly colored and absorbed, there is no particular problem.

  If the oxide dielectric film layer absorbs little, it is not necessary to consider the extinction coefficient of the oxide dielectric film layer when designing the absorption multilayer film. If the absorption of the body film layer is large and greatly affects the transmittance of the ND filter, it is considered that the extinction coefficient of the oxide dielectric film layer should be taken into consideration when designing the film of the absorption multilayer film. . From this idea, it has been found that the environment resistance of the absorption multilayer ND filter can be improved by forming the oxide dielectric film with SiOx (where x is less than 2) in which the amount of oxygen is reduced.

On the other hand, when all of the dielectric film layers are composed of SiOx with reduced oxygen content (where x is less than 2), the reflectivity becomes higher as the MgF ₂ film layer having a lower refractive index than the SiOx film layer is applied. It cannot be reduced, and the low reflectivity of the absorption multilayer ND filter cannot be improved. Therefore, after forming the outermost SiOx film layer, an additional MgF ₂ film layer is laminated on the outermost SiOx film layer to improve the low reflectivity, and the MgF ₂ film Since there is a non-hygroscopic SiOx film layer below the layer, there is no problem of hygroscopicity using the MgF ₂ film layer. From such an idea, it has been found that the low reflectivity of the absorption multilayer ND filter can be improved by adopting a structure in which an MgF ₂ film layer is further added on the outermost SiOx film layer. The present invention has been completed through such technical studies.

That is, the invention according to claim 1
In an absorptive multilayer ND filter comprising an absorptive multilayer film in which dielectric film layers and absorptive film layers are alternately laminated on at least one surface of a substrate made of a resin film,
The absorption film layer is composed of a metal absorption film layer composed of a metal film, the dielectric film layer is composed of an oxide dielectric film layer composed of SiOx (where x is less than 2), and an oxide on the outermost surface side. An MgF ₂ film layer is laminated on the dielectric film layer,
The invention according to claim 2
In the absorption multilayer ND filter according to the invention of claim 1,
SiOx (1.5 <x <2) film having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm formed by physical vapor deposition using a film forming material containing SiC and Si as main components The oxide dielectric film layer is formed by the above, the refractive index at a wavelength of 550 nm formed by physical vapor deposition is 1.5 to 3.0, and the extinction coefficient is 1.5 to 4.0. The metal absorption film layer is constituted by a metal film.

The invention according to claim 3
In the absorption multilayer ND filter according to the invention of claim 1,
The flatness of the spectral transmission characteristic defined by the value obtained by dividing the difference between the maximum transmittance and the minimum transmittance in the visible wavelength range (wavelength 400 nm to 700 nm) by the average transmittance is 10% or less,
The invention according to claim 4
In the absorption multilayer ND filter according to the invention of claim 1,
The maximum reflectance in the visible wavelength region (wavelength 400 nm to 700 nm) is 1.5% or less,
The invention according to claim 5
In the absorptive multilayer ND filter according to claim 1 or 2,
The film in contact with the substrate of the absorption multilayer film is the oxide dielectric film layer,
The invention according to claim 6
In the absorptive multilayer ND filter according to claim 1 or 2,
Each thickness of the oxide dielectric film layer is 3 nm to 150 nm,
The invention according to claim 7 provides:
In the absorptive multilayer ND filter according to claim 1 or 2,
The MgF ₂ film layer has a thickness of 20 nm to 150 nm, and the total thickness of the outermost oxide dielectric film layer and the MgF ₂ film layer is 200 nm or less.

Next, the invention according to claim 8 is:
In the absorptive multilayer ND filter according to claim 1 or 2,
The metal film constituting the metal absorption film layer is composed of Ni alone or a Ni-based alloy,
The invention according to claim 9 is:
In the absorption type multilayer ND filter according to the invention of claim 8,
The Ni-based alloy is a Ni-based alloy to which one or more elements selected from Ti, Al, V, W, Ta, and Si are added,
The invention according to claim 10 is:
In the absorption multilayer ND filter according to the invention of claim 9,
The addition ratio of Ti element is 5 to 15% by weight,
The invention according to claim 11 is:
In the absorption multilayer ND filter according to the invention of claim 9,
The addition ratio of Al element is 3 to 8% by weight,
The invention according to claim 12
In the absorption multilayer ND filter according to the invention of claim 9,
The addition ratio of V element is 3 to 9% by weight,
The invention according to claim 13 is:
In the absorption multilayer ND filter according to the invention of claim 9,
The addition ratio of W element is 18 to 32% by weight,
The invention according to claim 14 is:
In the absorption multilayer ND filter according to the invention of claim 9,
The addition ratio of Ta element is 5 to 12% by weight,
The invention according to claim 15 is:
In the absorption multilayer ND filter according to the invention of claim 9,
The addition ratio of Si element is 2 to 6% by weight.

Furthermore, the invention according to claim 16 provides
An absorption multilayer film comprising alternately laminated dielectric film layers and absorption film layers is provided on at least one surface of a substrate made of a resin film, and the absorption film layer is composed of a metal absorption film layer made of a metal film. The dielectric film layer is composed of an oxide dielectric film layer made of SiOx (where x is less than 2), and an MgF ₂ film layer is laminated on the outermost oxide dielectric film layer. In the manufacturing method of the type multilayer ND filter,
SiOx (1.5 <x) having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm by a physical vapor deposition method using a film forming material containing SiC and Si as main components and controlling the amount of oxygen gas introduced. <2) a step of forming an oxide dielectric film layer made of a film;
Formed a metal absorption film layer composed of a metal film having a refractive index of 1.5 to 3.0 and an extinction coefficient of 1.5 to 4.0 at a wavelength of 550 nm by a physical vapor deposition method in which the introduction of oxygen gas is stopped. And a process of
Forming a MgF ₂ film layer on the outermost oxide dielectric film layer by vapor deposition or wet coating;
It has each process of,
The invention according to claim 17 provides:
In the manufacturing method of the absorption-type multilayer film ND filter concerning the invention of Claim 16,
After the outermost oxide dielectric film layer is formed by physical vapor deposition, the substrate made of the resin film in which the metal absorption film layer and the oxide dielectric film layer are laminated is taken out from the film forming apparatus, Next, an MgF ₂ film layer is formed on the outermost oxide dielectric film layer using a deposition apparatus by vapor deposition, or an outermost oxidation is performed using a coating apparatus by wet coating. A MgF ₂ film layer is formed on the dielectric film layer,
The invention according to claim 18
In the manufacturing method of the absorption type multilayer ND filter concerning the invention of Claim 16 or 17,
It is characterized in that an oxide dielectric film layer, a metal absorption film layer, and a MgF ₂ film layer are formed on a long resin film substrate by a roll-to-roll method,
The invention according to claim 19 is
In the manufacturing method of the absorption type multilayer ND filter which concerns on invention in any one of Claims 16-18,
The film in contact with the substrate made of a resin film is an oxide dielectric film layer,
The invention according to claim 20 provides
In the manufacturing method of the absorption type multilayer ND filter which concerns on invention in any one of Claims 16-19,
Each film thickness of the oxide dielectric film layer is 3 nm to 150 nm,
The invention according to claim 21 is
In the manufacturing method of the absorption type multilayer ND filter which concerns on invention in any one of Claims 16-20,
The MgF ₂ film layer has a thickness of 20 nm to 150 nm, and the total thickness of the outermost oxide dielectric film layer and the MgF ₂ film layer is 200 nm or less.

An absorptive multilayer ND filter according to the present invention comprising an absorptive multilayer film having a structure in which dielectric film layers and absorptive film layers are alternately laminated on at least one surface of a substrate made of a resin film,
The absorption film layer is composed of a metal absorption film layer composed of a metal film, the dielectric film layer is composed of an oxide dielectric film layer composed of SiOx (where x is less than 2), and the outermost oxide dielectric layer. An MgF ₂ film layer is laminated on the body film layer.

  Since the oxide dielectric film is composed of SiOx (where x is less than 2) in which the amount of oxygen is reduced, it is difficult to supply oxygen from the oxide dielectric film to the metal absorption film layer. The progress of oxidation in the film layer can be suppressed.

  Therefore, even when exposed to a high-temperature and high-humidity environment, the metal absorption film layer hardly oxidizes, so that the environment resistance of the absorption multilayer ND filter can be improved.

Furthermore, it has a structure in which an MgF ₂ film layer having a refractive index lower than that of SiOx is additionally laminated on the outermost oxide dielectric film layer composed of SiOx (where x is less than 2). Therefore, the low reflectivity of the absorptive multilayer ND filter is improved, and the hygroscopicity of the ND filter is not lowered because the SiOx film layer exists below the added MgF ₂ film layer.

Moreover, according to the manufacturing method of the absorption multilayer ND filter according to the present invention,
SiOx (1.5 <x) having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm by a physical vapor deposition method using a film forming material containing SiC and Si as main components and controlling the amount of oxygen gas introduced. <2) a step of forming an oxide dielectric film layer made of a film;
Formed a metal absorption film layer composed of a metal film having a refractive index of 1.5 to 3.0 and an extinction coefficient of 1.5 to 4.0 at a wavelength of 550 nm by a physical vapor deposition method in which the introduction of oxygen gas is stopped. And a process of
Forming a MgF ₂ film layer on the outermost oxide dielectric film layer by vapor deposition or wet coating;
Because it has each process of
An absorption multilayer film comprising alternately laminated dielectric film layers and absorption film layers is provided on at least one surface of a substrate made of a resin film, and the absorption film layer is composed of a metal absorption film layer made of a metal film. The dielectric film layer is composed of an oxide dielectric film layer made of SiOx (where x is less than 2), and an MgF ₂ film layer is laminated on the outermost oxide dielectric film layer. The absorption multilayer ND filter of the invention can be reliably manufactured.

The SiOx film obtained corresponding to the impedance control setting value when the SiOx (1.5 <x <2) film constituting the oxide dielectric film layer of the absorption multilayer ND filter according to the present invention is formed. The graph which shows a spectral transmission characteristic. The absorption multilayer ND filter according to the present invention (indicated as “C: Structure of the present invention” in FIG. 2) and the absorption multilayer ND filter according to Reference Examples 1 and 2 (“A: Reference in FIG. 2) FIG. 4 is a graph showing spectral transmission characteristics of “Structure of Example 1” and “B: Structure of Reference Example 2”. The absorptive multilayer ND filter according to the present invention (shown as “C: structure of the present invention” in FIG. 3) and the absorptive multilayer ND filter according to Reference Examples 1 and 2 (“A: Reference in FIG. 3) FIG. 6 is a graph showing spectral reflection characteristics of “Structure of Example 1” and “B: Structure of Reference Example 2”.

  Hereinafter, embodiments of the present invention will be described in detail.

First, an absorptive multilayer ND filter according to the present invention includes an absorptive multilayer film in which a dielectric film layer and an absorptive film layer are alternately laminated on at least one side of a substrate made of a resin film, The film layer is composed of a metal absorption film layer composed of a metal film, the dielectric film layer is composed of an oxide dielectric film layer composed of SiOx (where x is less than 2), and the oxide dielectric on the outermost surface side An MgF ₂ film layer is laminated on the film layer.

  Furthermore, in the present invention, the oxide dielectric film layer is formed by physical vapor deposition using a film forming material containing SiC and Si as main components, and has an extinction coefficient of 0.005 to 550 nm. The SiO 2 (1.5 <x <2) film of 0.05, and the metal absorption film layer formed by physical vapor deposition has a refractive index of 1.5-3. It is characterized by comprising a metal film having 0 and an extinction coefficient of 1.5 to 4.0.

  Here, examples of the physical vapor deposition method include a vacuum deposition method, an ion beam sputtering method, a magnetron sputtering method, and an ion plating method.

Hereinafter, each configuration of the absorption multilayer ND filter according to the present invention will be described.
(1) Absorption film layer In the absorption-type multilayer ND filter according to the present invention, the absorption film layer is composed of a metal absorption film layer made of a metal film. It is formed of a metal film having a refractive index of 1.5 to 3.0 and an extinction coefficient of 1.5 to 4.0, which is formed by vapor deposition.

The metal film formed without intentionally introducing oxygen at the time of film formation is, for example, TiOx or Ta ₂ Ox having absorption due to oxygen deficiency formed by intentionally introducing oxygen at the time of film formation as described above. The extinction coefficient is higher than that of a metal oxide film. When forming an absorption multilayer film by alternately laminating dielectric film layers and absorption film layers on a flexible resin film substrate, warp of the resin film substrate, film cracking, film formation time, etc. In consideration, as described above, it is desirable to employ a metal film having a high extinction coefficient because the film thickness can be made thinner than that of the metal oxide film. However, it is known that the metal film easily oxidizes and the extinction coefficient decreases, and the transmittance of the ND filter using the metal absorption film layer increases with time.

Therefore, in the absorption multilayer ND filter according to the present invention, the dielectric film layer adjacent to the metal absorption film layer is composed of an oxide dielectric film layer made of SiOx (where x is less than 2), thereby absorbing the metal. Oxidation of the film layer is suppressed. The metal absorbing film layer is formed by the physical vapor deposition method in which the introduction of oxygen gas is stopped as described above, but the oxide dielectric film layer made of SiOx (x is less than 2) is formed. Due to the film, it may be slightly oxidized by oxygen gas slightly remaining in the physical vapor deposition apparatus. However, the degree of oxidation is extremely low as compared with metal oxide films such as TiOx and Ta ₂ Ox that have absorption due to oxygen vacancies, the refractive index at a wavelength of 550 nm is 1.5 to 3.0, and the extinction coefficient is 1.5. If the requirement of -4.0 is satisfied, it can be applied as the metal absorption film layer.

  And the metal absorption film layer formed of a metal film having a refractive index of 1.5 to 3.0 and an extinction coefficient of 1.5 to 4.0 formed by physical vapor deposition at a wavelength of 550 nm. The film thickness is desirably 3 nm to 20 nm. If the film thickness is less than 3 nm, the metal film may be completely oxidized to the inside, which is not preferable. On the other hand, when the film thickness exceeds 20 nm, it is expected that the film stress will be reduced if the soft metal film layer is thickened compared to the dielectric layer, but the spectral transmittance is extremely reduced. There is.

  The metal film constituting the metal absorption film layer is preferably made of Ni alone or a Ni-based alloy. This is because any metal material used as the absorption film layer of the optical thin film tends to be oxidized and its extinction coefficient decreases, but Ni alone or a Ni-based alloy is a metal that is relatively difficult to oxidize. In particular, the Ni-based alloy is preferably a Ni-based alloy to which one or more elements selected from Ti, Al, V, W, Ta, and Si are added.

  The reason for this is as follows.

  In other words, since pure Ni material is a ferromagnetic material, when the metal film is formed by DC magnetron sputtering using Ni material (target), it is placed on the back side of the target for acting on plasma between the target and the substrate. The magnetic force from the magnet is shielded by the Ni target material and the magnetic field leaking to the surface becomes weak, and it becomes difficult to concentrate the plasma and form the film efficiently. In order to avoid this, it is preferable to perform sputtering film formation by using a cathode (strong magnetic field cathode) in which the magnetic force of a magnet disposed on the back side of the target is increased (400 Gauss or more) and by increasing the magnetic field passing through the Ni target. However, even when such a method is adopted, another problem as described below may occur during production. That is, when the thickness of the target decreases with continuous use of the Ni target, the leakage magnetic field in the plasma space becomes stronger in the portion where the thickness of the target is reduced. When the leakage magnetic field in the plasma space becomes stronger, the discharge characteristics (discharge voltage, discharge current, etc.) change and the film formation rate changes. In other words, if the same Ni target is used continuously for a long time during production, there is a problem that the deposition rate of the Ni film changes as the Ni target is consumed, and the absorption multilayer ND filter with uniform characteristics is stabilized. Making it difficult to produce. In order to avoid this problem, the metal film may be formed using a Ni-based alloy material to which one or more elements selected from Ti, Al, V, W, Ta, and Si are added as described above. .

For example, it is preferable to use a Ni-based alloy material containing Ti element in a range of 5 to 15% by weight. The reason why the lower limit of the amount of Ti is 5% by weight is that the ferromagnetic characteristics can be extremely weakened by including 5% by weight or more, and direct current magnetron sputtering film formation is performed even on a cathode on which a normal magnet having a low magnetic force is arranged. Because it can. Further, since the magnetic field shielding ability of the target is low, the change in the leakage magnetic field in the plasma space depending on the target consumption is small, and a constant film formation rate can be maintained, so that film formation can be performed stably. Moreover, the reason why the upper limit of the amount of Ti is set to 15.0% by weight is that if the Ti content exceeds 15.0% by weight, a large amount of intermetallic compounds may be formed. Further, the addition amount of Al element, V element, W element, Ta element and Si element is also determined for the same reason, and when adding such Al element, V element, W element, Ta element and Si element, Al is added. The addition ratio of the element is 3 to 8 wt%, the addition ratio of the V element is 3 to 9 wt%, the addition ratio of the W element is 18 to 32 wt%, the addition ratio of the Ta element is 5 to 12 wt%, It is preferable to use a Ni-based alloy material added in an addition ratio of 2 to 6% by weight.
(2) Dielectric film layer Next, in the present invention, the oxide dielectric film layer made of the above-mentioned SiOx (where x is less than 2) is formed by physical vapor deposition using a film-forming material mainly composed of SiC and Si. The SiOx (1.5 <x <2) film having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm is formed by the method. When the extinction coefficient of the SiOx film exceeds 0.05, the difference between the maximum transmittance and the minimum transmittance in the visible wavelength region (wavelength 400 nm to 700 nm) of the completed absorption type multilayer ND filter is averaged. It becomes difficult to set the “flatness of spectral transmission characteristics” defined by the value divided by the ratio to 10% or less. In particular, in order to obtain flat spectral transmission characteristics, the extinction coefficient of the SiOx film is preferably 0.03 or less. In order to obtain a SiOx film having such flat spectral transmission characteristics, the amount of oxygen introduced during film formation may be controlled so that the extinction coefficient at a wavelength of 550 nm is 0.005 to 0.03.

  The thickness of each oxide dielectric film layer is preferably 3 nm to 150 nm. This is because if each film thickness is less than 3 nm, the contribution as an optical thin film is small, and the film thickness control may be difficult. Furthermore, it may be difficult to suppress a phenomenon in which the transmittance increases due to oxidation of the metal absorption film layer in a high temperature and high humidity environment. On the other hand, when each thickness of the oxide dielectric film layer exceeds 150 nm, such a thick film is not necessary in the design of an optical thin film that needs to control the extinction coefficient at a wavelength of 550 nm and the production efficiency. This is because it is not preferable.

Furthermore, in order to suppress the supply of oxygen from the resin film substrate, it is desirable that the film in contact with the resin film substrate of the absorption type multilayer film is composed of the oxide dielectric film layer.
(3) MgF ₂ film layer In the absorption multilayer ND filter according to the present invention, an MgF ₂ film layer is additionally laminated on the outermost oxide dielectric film layer made of the SiOx film. It is a feature.

In order to reduce the surface reflection of the absorptive multilayer ND filter, the lower the refractive index of the dielectric film layer located on the outermost surface side, the better. Among the general dielectric film materials, the lowest refractive index is MgF ₂ having a refractive index of 1.38 at a wavelength of 550 nm, and the _second lowest refractive index is a refractive index of 1 at a wavelength of 550 nm. .45 SiO ₂ . Accordingly, it can be seen that MgF ₂ having the lowest refractive index may be applied as a material constituting the dielectric film layer in order to obtain an absorption multilayer ND filter having excellent low reflectivity.

However, if an attempt is made to form a film of MgF ₂ that is a fluoride dielectric by a widely used sputtering method, fluorine is dissociated and exhausted at the time of film formation, so that the film material is not suitable for sputtering film formation. Further, the MgF ₂ film is so hard that it is used on the outermost surface of a camera lens or the like for which surface hardness is required, but the internal structure of the film often takes a columnar structure and has some hygroscopicity. Therefore, the film material is inferior to the SiOx film in the function of preventing the progress of oxidation of the metal absorption film layer in a high temperature and high humidity environment.

However, MgF ₂ is a film material suitable for the vacuum evaporation method, and can be formed by either the electron beam evaporation method or the resistance heating evaporation method.

Therefore, in the absorption-type multilayer ND filter according to the present invention, an oxide dielectric film layer composed of a SiOx film is applied to suppress the progress of oxidation of the metal absorption film layer, and the absorption-type multilayer ND filter In order to reduce the reflectivity, an MgF ₂ film layer is additionally formed on the outermost oxide dielectric film layer made of the SiOx film.

In order to form an additional MgF ₂ film layer on the outermost oxide dielectric film layer made of the SiOx film, for example, the outermost oxide dielectric film layer is formed by a sputtering roll coater. After the film formation, the resin film substrate on which the metal absorption film layer and the oxide dielectric film layer are laminated is taken out of the sputtering roll coater, and then set on the electron beam vacuum deposition roll coater to form the MgF ₂ film layer. Alternatively, a MgF ₂ film layer may be formed by applying a coating liquid in which MgF ₂ particles are dispersed using a coating apparatus such as a wet coater or a dip coater and drying the film with hot air. Is optional. Also, the resin film substrate on which the metal absorption film layer and the oxide dielectric film layer are laminated is taken out from the sputtering roll coater, and the taken out resin film substrate is cut into a sheet shape and then processed into an electron beam vacuum deposition apparatus. The MgF ₂ film may be formed by setting. Further, a MgF ₂ film layer may be continuously formed on the outermost oxide dielectric film layer made of the SiOx film using a roll coater equipped with both a sputtering method and a vacuum evaporation method.

The thickness of the MgF ₂ film layer formed on the outermost oxide dielectric film layer by vapor deposition or wet coating is 20 nm to 150 nm, and the outermost oxide dielectric film layer. The total film thickness of the MgF ₂ film layer is preferably 200 nm or less. When the thickness of the MgF ₂ film layer is less than 20 nm, the effect of preventing reflection by MgF ₂ layer of low refractive index is not be expected so much, the thickness of the MgF ₂ film layer exceeds 150nm opposite the MgF ₂ film layer This is because the film stress due to the film becomes too large. Furthermore, when the total film thickness of the outermost oxide dielectric film layer and the MgF ₂ film layer exceeds 200 nm, such a thick film is not necessary to obtain an antireflection effect in the visible wavelength region. In addition, it is not preferable because the production efficiency is lowered.
(4) Absorption-type multilayer ND filter The absorption-type multilayer ND filter according to the present invention is an absorption-type multilayer film in which dielectric film layers and absorption film layers are alternately laminated on at least one surface of a substrate made of a resin film. And the absorption film layer is composed of a metal absorption film layer composed of a metal film, the dielectric film layer is composed of an oxide dielectric film layer composed of SiOx (where x is less than 2), and the outermost surface side. An MgF ₂ film layer is laminated on the oxide dielectric film layer, and the oxide dielectric film layer is formed by physical vapor deposition using a film-forming material mainly composed of SiC and Si. The film is composed of a SiOx (1.5 <x <2) film having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm, and the metal absorption film layer is formed by physical vapor deposition. The refractive index at a wavelength of 550 nm is 1.5 to .0 and extinction coefficient are characterized by being composed of a metal film of 1.5 to 4.0.

  The absorption multilayer ND filter having such a configuration is a flat spectral transmission characteristic defined by a value obtained by dividing the difference between the maximum transmittance and the minimum transmittance in the visible wavelength region (wavelength 400 nm to 700 nm) by the average transmittance. Has excellent optical properties of 10% or less. Furthermore, it has a characteristic that the maximum reflectance in the visible wavelength region (wavelength 400 nm to 700 nm) is 1.5% or less.

By the way, in order to design the film configuration of the ND filter, it is necessary to know the optical constants (refractive index, extinction coefficient) of the oxide dielectric film layer and the absorption film layer. In order to measure these optical constants, there are a spectroscopic ellipsometry method and a spectroscopic interferometry method. As described above, the metal absorption film layer made of metal as a raw material undergoes oxidation after being exposed to the atmosphere after film formation, so that the optical constant measured only by the absorption film layer (single layer) and the ND filter The measured values of the optical constants may be greatly different when configured. Therefore, with the ND filter configured, measure the optical constants of the oxide dielectric film layer and the absorption film layer, and redesign the ND filter film structure again based on the optical constants obtained here. It is ideal to obtain the optimum film configuration by repeating the above.
(5) Manufacturing method of absorption type multilayer ND filter An absorption type multilayer film formed by alternately laminating dielectric film layers and absorption film layers is provided on at least one surface of a substrate made of a resin film. Is composed of a metal absorbing film layer made of a metal film, the dielectric film layer is composed of an oxide dielectric film layer made of SiOx (where x is less than 2), and the outermost oxide dielectric film layer The manufacturing method of the absorption type multilayer ND filter according to the present invention, in which the MgF ₂ film layer is laminated,
SiOx (1.5 <x) having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm by a physical vapor deposition method using a film forming material containing SiC and Si as main components and controlling the amount of oxygen gas introduced. <2) a step of forming an oxide dielectric film layer made of a film;
Formed a metal absorption film layer composed of a metal film having a refractive index of 1.5 to 3.0 and an extinction coefficient of 1.5 to 4.0 at a wavelength of 550 nm by a physical vapor deposition method in which the introduction of oxygen gas is stopped. And a process of
Forming a MgF ₂ film layer on the outermost oxide dielectric film layer by vapor deposition or wet coating;
It is characterized by having each process of these.

Here, for the above-described step of forming the MgF ₂ film layer on the outermost oxide dielectric film layer, after forming the outermost oxide dielectric film layer by physical vapor deposition, The substrate made of the resin film in which the metal absorption film layer and the oxide dielectric film layer are laminated is taken out from the film formation apparatus, and then the outermost oxide dielectric film layer is formed using a film formation apparatus by vapor deposition. or forming the MgF ₂ film layer thereon, or a method of film formation are mentioned a MgF ₂ layer on the oxide dielectric film layer on the outermost surface side by using a coating apparatus according to a wet coating method.

Also, a method of adopting a long resin film substrate and forming an oxide dielectric film layer, a metal absorbing film layer, and an MgF ₂ film layer on the resin film substrate by a roll-to-roll method May be taken.

  Here, as a film forming material (target) mainly composed of SiC and Si, any material can be applied as long as it is a film forming material mainly composed of SiC and Si.

  For example, it is composed of a material containing SiC and Si, and the volume ratio of SiC (%) = [total volume of SiC / (total volume of SiC + total volume of Si)] × 100. A sputtering target (see Patent Document 5) having a content of 50% to 70% or SiC powder is molded by a casting molding method, a press molding method or an extrusion molding method. In the atmosphere, Si melted at a temperature of 1450 ° C. or more and 2200 ° C. or less is impregnated to fill the pores of the molded body with metal Si, and the atomic ratio of C to Si including SiC and metal Si is 0.5 or more and 0. And a sputtering target (see Patent Document 4) of .95 or less.

Next, PET (polyethylene terephthalate) is applied as a resin film substrate, and an oxide dielectric film layer (three layers on one side) made of SiOx and a metal made of Ni-Ti are formed on both surfaces of the resin film substrate, respectively. A book having an average transmittance of 12.5% composed of an absorption film layer (two layers on one side) and an MgF ₂ film layer (one layer on one side) formed on the outermost oxide dielectric film layer made of SiOx The film structure of the absorption type multilayer ND filter according to the invention is shown in Table 1 (indicated as “C: Structure of the present invention” in Table 1).

For comparison, PET (polyethylene terephthalate) is applied as a resin film substrate, and an oxide dielectric film layer (three layers on one side) made of SiOx and Ni—Ti respectively formed on both surfaces of the resin film substrate. Table 1 (“A: Reference Example 1 in Table 1” shows the film structure of the absorption-type multilayer ND filter according to Reference Example 1 having an average transmittance of 12.5% composed of the metal absorption film layer (two layers on one side). Similarly, an oxide dielectric film layer (one side 2) made of SiOx, which is formed by applying PET (polyethylene terephthalate) as the resin film substrate and forming the film on both surfaces of the resin film substrate, respectively. Layer), a metal absorption film layer made of Ni—Ti (two layers on one side), and an MgF ₂ film layer (one layer on one side) formed on the outermost metal absorption film layer made of Ni—Ti. The film structure of the absorption multilayer ND filter according to Reference Example 2 having an average transmittance of 12.5% is shown in Table 1 (indicated as “B: Structure of Reference Example 2” in Table 1).

これ等の吸収型多層膜ＮＤフィルターにおいて、酸化物誘電体膜層にはＳｉＣおよびＳｉを主成分とする成膜材料（ターゲット）を用いかつ酸素ガスの導入量を制御したマグネトロンスパッタリング法により成膜したＳｉＯｘ（１．５＜ｘ＜２）膜が適用され、また、吸収膜層にはＮｉ−Ｔｉ膜層が採用されている。

In these absorptive multilayer ND filters, the oxide dielectric film layer is formed by a magnetron sputtering method using a film forming material (target) mainly composed of SiC and Si and controlling the amount of oxygen gas introduced. An SiOx (1.5 <x <2) film is applied, and a Ni—Ti film layer is adopted as the absorption film layer.

  Regarding the film formation conditions for the oxygen-deficient oxide dielectric film layer composed of the SiOx (1.5 <x <2) film layer, it is technically difficult to analyze the composition of the SiOx film. The film forming conditions are controlled by controlling the optical characteristics of the SiOx film so that the extinction coefficient at a wavelength of 550 nm is finally 0.005 to 0.05.

  In addition, the film forming conditions of the metal absorption film layer composed of the Ni—Ti film layer can be obtained depending on the additives and impurities of the film forming material, the residual gas during film formation, the gas released from the substrate, and the film forming speed. The refractive index and extinction coefficient of the metal absorption film layer to be obtained may differ greatly. Therefore, Ni—Ti alloy is used as a film forming material, and introduction of oxygen gas is stopped, and any one of physical vapor deposition methods such as vacuum deposition, ion beam sputtering, magnetron sputtering, and ion plating is used. The metal absorption film layer obtained by film formation according to the above conditions is such that the metal film having a refractive index at a wavelength of 550 nm of 1.5 to 3.0 and an extinction coefficient of 1.5 to 4.0 is satisfied. It is necessary to control the film conditions.

  In order to suppress oxidation of the metal absorption film layer, an oxide dielectric film made of a SiOx (1.5 <x <2) film is preferably used for the film of the absorption multilayer film in contact with the resin film substrate (PET). It is good to comprise with a layer (refer Table 1).

In the absorptive multilayer ND filter according to the present invention, the MgF ₂ film layer is formed on both sides of the resin film substrate (PET) with a sputtering roll coater from the air side to the second SiOx film. Then, after taking it out into the atmosphere, it is set again on an electron beam evaporation roll coater to form MgF film layers on both sides.

In this way, when forming the MgF ₂ film layer by a separate process, the sputtering roll coater with the metal absorption film layer made of Ni—Ti on the outermost surface like the absorption type multilayer ND filter according to Reference Example 2 is used. If it is taken out from the metal, oxidation proceeds from the surface of the metal absorption film layer during the formation of the MgF ₂ film layer.

  Therefore, when manufacturing the absorption type multilayer ND filter according to the present invention, the sputtering roll is continuously formed from the air side to the second SiOx film layer (that is, the outermost oxide dielectric film layer made of SiOx). It is desirable to form a film with a coater and take out the metal absorption film layer in the air after applying a means for preventing the metal absorption film layer from proceeding with oxidation.

  Here, although the material which comprises a resin film board | substrate is not specifically limited, What is transparent is preferable, When considering mass productivity, it is preferable that it is a flexible substrate in which the dry type sputtering roll coating mentioned later is possible. The flexible substrate is excellent in that it is cheaper, lighter and more deformable than a conventional glass substrate. And as a specific example of the resin film constituting the substrate, it is selected from resin materials of polyethylene terephthalate (PET), polyether sulfone (PES), polyarylate (PAR), polycarbonate (PC), polyolefin (PO) and norbornene. Or a composite of a single resin film selected from the above resin materials and an acrylic organic film covering one or both sides of the single resin film. In particular, as for norbornene resin materials, representative examples include ZEONOR (trade name) manufactured by ZEON Corporation, Arton (trade name) manufactured by JSR Corporation, and the like.

  Next, specific examples of the present invention will be described.

  First, using a target mainly composed of SiC and Si as a film forming material, and using a 100 μm thick PET film slit to a width of 300 mm for the resin film substrate, the amount of oxygen gas introduced during film formation is controlled. Then, the change of the spectroscopic optical characteristics due to the change of the oxygen introduction amount of the obtained SiOx (1.5 <x <2) film was examined.

  A sputtering roll coater is used for film formation, and the target for forming the oxide dielectric film layer is a target mainly composed of SiC and Si as described above (however, SiC: Si is a weight) 70-90% by ratio: 30-10%), or a target made of high purity SiC was used.

  A turbo molecular pump was used as the exhaust pump. Sputtering was performed by dual magnetron sputtering using a target containing SiC and Si as main components, and oxygen gas introduction was controlled by an impedance monitor. The smaller the impedance control set value is, the more oxygen gas is introduced.

  Here, in dual magnetron sputtering, in order to form an insulating film at a high speed, a medium frequency (40 kHz) pulse is alternately applied to two targets to suppress the occurrence of arcing, and an insulating layer is formed on the target surface. It is a sputtering method to prevent.

  In addition, the impedance monitor applies the phenomenon that the impedance between the target electrodes changes depending on the amount of oxygen introduced, so that the film to be formed becomes a film of a desired mode in the transition region between the metal mode and the oxide mode. It is used to control and monitor the amount of oxygen introduced to form an oxide dielectric film layer at high speed.

The SiOx film obtained by forming a film using the above-mentioned target containing SiC and Si as main components increases the oxygen partial pressure during film formation (the amount of oxygen introduced during film formation increases). Value approaches 2 (ie, changes to a SiO ₂ film).

  FIG. 1 shows the spectral transmittance of SiOx (1.5 <x <2) films formed with impedance control set values of 36, 38, 40, 42, 44, 46, 48, and 49. In FIG. 1, the impedance control set values correspond to the order of 36, 38, 40, 42, 44, 46, 48, and 49, and the transmittance of the formed SiOx film at the wavelength of 550 nm increases in order. That is, the transmittance at a wavelength of 550 nm of the SiOx film formed with the impedance control set value set to 36 is the highest, and the transmittance at the wavelength of 550 nm of the SiOx film formed with the impedance control set value set to 49 The rate is the lowest.

  The physical film thickness of the SiOx film is about 80 nm. Table 2 shows the impedance control set value during the deposition of SiOx, the cathode voltage when the input is 4 kW, and the extinction coefficient of the SiOx film.

  When the impedance control setting value during film formation is 38 or less, the SiOx film appears to be transparent visually. Furthermore, when the impedance setting value is 35 to 45, the film formation speed at the same 4 kW input is improved by about 30%, so that a reduction in film formation time (production cost) can be expected.

上記のようにインピーダンスモニターを用いて成膜中の酸素導入量を制御し、成膜時に導入する酸素ガスを減じることにより、波長５５０ｎｍにおける消衰係数が０．００５〜０．０５の酸化物誘電体膜層を得ることができる。

As described above, an oxide dielectric having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm is obtained by controlling the amount of oxygen introduced during film formation using an impedance monitor and reducing the amount of oxygen gas introduced during film formation. A body membrane layer can be obtained.

  When the extinction coefficient of the SiOx film exceeds 0.05, the difference between the maximum transmittance and the minimum transmittance in the visible wavelength region (wavelength 400 nm to 700 nm) of the completed absorption type multilayer ND filter is averaged. It becomes difficult to set the “flatness of spectral transmission characteristics” defined by the value divided by the ratio to 10% or less. In particular, in order to obtain flat spectral transmission characteristics, the extinction coefficient of the SiOx film is preferably 0.03 or less. In order to obtain a SiOx film having such flat spectral transmission characteristics, the impedance control set value is set to 37 to 45 from the data shown in Table 2 in correspondence with the extinction coefficient of 0.005 to 0.03 at a wavelength of 550 nm. You only have to set it.

Next, the impedance control set value at the time of forming the oxide dielectric film layer is set to 40, and the present invention having the film structure shown in Table 1 (shown as “C: structure of the present invention” in Table 1) is applied to the present invention. Such an absorption type multilayer ND filter was obtained. The absorption multilayer ND filter according to the present invention is formed with a sputtering roll coater from the air side to the second SiOx film layer, and is positioned on the outermost oxide dielectric film layer made of SiOx. The MgF ₂ film layer to be formed is formed by an electron beam evaporation roll coater.

For comparison, the absorption multilayer ND filter according to Reference Example 1 (indicated as “A: Structure of Reference Example 1” in Table 1) and the absorption multilayer ND filter according to Reference Example 2 (“B: The structure of “Reference Example 2” is also produced. In addition, the oxide dielectric film layer (three layers on one side) of SiOx and the metal absorption film layer (two layers on one side) made of Ni-Ti of the absorption type multilayer ND filter according to Reference Example 1 are formed by a full-layer sputtering roll coater. A film is being formed. In addition, for the absorption type multilayer ND filter according to Reference Example 2, up to the oxide dielectric film layer (single-sided two layers) made of SiOx and the metal absorbing film layer (one-sided two layers) made of Ni-Ti are used. The MgF ₂ film layer located on the outermost metal absorption film layer made of Ni—Ti is formed by an electron beam evaporation roll coater.
[Spectral transmission and reflection characteristics]
Spectral transmission characteristics and spectral reflection characteristics of the manufactured absorption multilayer ND filter according to the present invention and absorption multilayer ND filters according to Reference Example 1 and Reference Example 2 were measured. The measurement results are shown in the graphs of FIGS.

  The absorption multilayer ND filter according to the present invention shown in the graph of FIG. 2 (indicated as “C: structure of the present invention” in FIG. 2), and the absorption multilayer ND according to Reference Example 1 and Reference Example 2 Comparing the spectral transmission characteristics of the filters ("A: Structure of Reference Example 1" and "B: Structure of Reference Example 2" in FIG. 2), it is confirmed that there is almost no difference.

However, the absorption multilayer ND filter according to the present invention shown in the graph of FIG. 3 (indicated as “C: structure of the present invention” in FIG. 3), and the absorption multilayers according to Reference Example 1 and Reference Example 2 Comparing the spectral reflection characteristics of the film ND filter (shown as “A: Structure of Reference Example 1” and “B: Structure of Reference Example 2” in FIG. 3), the MgF ₂ film layer provided on the outermost surface side The reflectances of the absorption multilayer ND filter according to the invention and the absorption multilayer ND filter according to Reference Example 2 are significantly higher than those of the absorption multilayer ND filter according to Reference Example 1 in which the SiOx film layer is provided on the outermost surface side. Has been reduced. This is because the MgF ₂ film layer having a low refractive index is provided on the outermost surface side.
[Environment resistance]
Next, the absorption type multilayer ND filter according to the present invention and the absorption type multilayer ND filter according to Reference Example 1 and Reference Example 2 are respectively placed in an environmental test machine (manufactured by Espec Corp.) set at 85 ° C. and 90%. The environment resistance was investigated.

  Then, after 24 hours, each absorption type multilayer ND filter was taken out from the environmental testing machine, and the spectral transmission characteristic was measured with a self-recording spectrophotometer (manufactured by JASCO Corporation), and the environmental resistance was examined from the change over time.

  The environmental test results are shown in Table 3.

表３に示された本発明に係る吸収型多層膜ＮＤフィルター（表３中「Ｃ：本発明の構造」と表示）と、参考例１および参考例２に係る吸収型多層膜ＮＤフィルター（表３中「Ａ：参考例１の構造」「Ｂ：参考例２の構造」とそれぞれ表示）の波長５５０ｎｍにおける透過率の変化量ΔＴ（％）を比較すると、環境試験後の本発明に係る吸収型多層膜ＮＤフィルターと参考例１に係る吸収型多層膜ＮＤフィルターは透過率の増加が小さい。これは、金属吸収膜層であるＮｉ−Ｔｉ膜層をＳｉＯｘで被覆しているため、Ｎｉ−Ｔｉ膜層の酸化が進行し難かったためであると考えられる。

The absorption multilayer ND filter according to the present invention shown in Table 3 (indicated as “C: Structure of the present invention” in Table 3) and the absorption multilayer ND filter according to Reference Example 1 and Reference Example 2 (Table 3, “A: Structure of Reference Example 1” and “B: Structure of Reference Example 2”, respectively, are compared, and the amount of change ΔT (%) in transmittance at a wavelength of 550 nm is compared. The increase in the transmittance of the type multilayer ND filter and the absorption type multilayer ND filter according to Reference Example 1 is small. This is presumably because the Ni—Ti film layer, which is a metal absorption film layer, was covered with SiOx, so that the oxidation of the Ni—Ti film layer did not easily proceed.

On the other hand, the absorption multilayer ND filter according to Reference Example 2 after the environmental test (shown as “B: Structure of Reference Example 2” in Table 3) has a large increase in transmittance. This is because the MgF ₂ film provided on the outermost surface side in contact with the Ni—Ti film layer has hygroscopicity, and it is considered that the extinction coefficient decreased due to oxidation of the Ni—Ti film layer.

  Note that the reflectance change ΔR (%) after the environmental test is almost different between the absorption multilayer ND filter according to the present invention and the absorption multilayer ND filter according to Reference Example 1 and Reference Example 2. It was confirmed that there was no.

  As described above, it is confirmed that only the absorption multilayer ND filter according to the present invention has a low spectral reflectance in the visible wavelength region of 400 to 700 nm and a small increase in transmittance due to an environmental test.

  The absorptive multilayer ND filter according to the present invention is excellent in low reflectivity, so that ghosts and flares are not generated in a photographed image, and furthermore, it is excellent in environmental resistance so that it is reliable for a long time in a severe environment. Therefore, the present invention has industrial applicability for use in small and thin digital cameras and the like that are required.

Claims (21)

In an absorptive multilayer ND filter comprising an absorptive multilayer film in which dielectric film layers and absorptive film layers are alternately laminated on at least one surface of a substrate made of a resin film,
The absorption film layer is composed of a metal absorption film layer composed of a metal film, the dielectric film layer is composed of an oxide dielectric film layer composed of SiOx (where x is less than 2), and an oxide on the outermost surface side. An absorptive multilayer ND filter, wherein an MgF ₂ film layer is laminated on a dielectric film layer.   SiOx (1.5 <x <2) film having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm formed by physical vapor deposition using a film forming material containing SiC and Si as main components The oxide dielectric film layer is formed by the above, the refractive index at a wavelength of 550 nm formed by physical vapor deposition is 1.5 to 3.0, and the extinction coefficient is 1.5 to 4.0. 2. The absorption multilayer ND filter according to claim 1, wherein the metal absorption film layer is formed of a metal film.   The flatness of spectral transmission characteristics defined by a value obtained by dividing the difference between the maximum transmittance and the minimum transmittance in the visible wavelength range (wavelengths of 400 nm to 700 nm) by the average transmittance is 10% or less. 2. The absorption-type multilayer ND filter according to 1.   2. The absorption multilayer ND filter according to claim 1, wherein a maximum reflectance in a visible wavelength region (wavelength 400 nm to 700 nm) is 1.5% or less.   The absorption multilayer ND filter according to claim 1 or 2, wherein the film in contact with the substrate of the absorption multilayer film is the oxide dielectric film layer.   3. The absorption multilayer ND filter according to claim 1, wherein each thickness of the oxide dielectric film layer is 3 nm to 150 nm. The thickness of the MgF ₂ film layer is 20 nm to 150 nm, and the total thickness of the outermost oxide dielectric film layer and the MgF ₂ film layer is 200 nm or less, or 3. The absorption multilayer ND filter according to 2.   The absorption multilayer ND filter according to claim 1 or 2, wherein the metal film constituting the metal absorption film layer is made of Ni alone or a Ni-based alloy.   9. The absorptive multilayer film ND according to claim 8, wherein the Ni-based alloy is a Ni-based alloy to which one or more elements selected from Ti, Al, V, W, Ta, and Si are added. filter.   The absorption multilayer ND filter according to claim 9, wherein the addition ratio of Ti element is 5 to 15 wt%.   The absorption multilayer ND filter according to claim 9, wherein the additive ratio of Al element is 3 to 8 wt%.   10. The absorption multilayer ND filter according to claim 9, wherein the addition ratio of V element is 3 to 9% by weight.   The absorption multilayer ND filter according to claim 9, wherein an addition ratio of W element is 18 to 32% by weight.   The absorption multilayer ND filter according to claim 9, wherein an addition ratio of Ta element is 5 to 12 wt%.   The absorption multilayer ND filter according to claim 9, wherein an addition ratio of Si element is 2 to 6 wt%. An absorption multilayer film comprising alternately laminated dielectric film layers and absorption film layers is provided on at least one surface of a substrate made of a resin film, and the absorption film layer is composed of a metal absorption film layer made of a metal film. The dielectric film layer is composed of an oxide dielectric film layer made of SiOx (where x is less than 2), and an MgF ₂ film layer is laminated on the outermost oxide dielectric film layer. In the manufacturing method of the type multilayer ND filter,
SiOx (1.5 <x) having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm by a physical vapor deposition method using a film forming material containing SiC and Si as main components and controlling the amount of oxygen gas introduced. <2) a step of forming an oxide dielectric film layer made of a film;
Formed a metal absorption film layer composed of a metal film having a refractive index of 1.5 to 3.0 and an extinction coefficient of 1.5 to 4.0 at a wavelength of 550 nm by a physical vapor deposition method in which the introduction of oxygen gas is stopped. And a process of
Forming a MgF ₂ film layer on the outermost oxide dielectric film layer by vapor deposition or wet coating;
The manufacturing method of the absorption-type multilayer ND filter characterized by having each process of these. After the outermost oxide dielectric film layer is formed by physical vapor deposition, the substrate made of the resin film in which the metal absorption film layer and the oxide dielectric film layer are laminated is taken out from the film forming apparatus, Next, an MgF ₂ film layer is formed on the outermost oxide dielectric film layer using a deposition apparatus by vapor deposition, or an outermost oxidation is performed using a coating apparatus by wet coating. 17. The method for manufacturing an absorption multilayer ND filter according to claim 16, wherein an MgF ₂ film layer is formed on the dielectric film layer. 18. The oxide dielectric film layer, the metal absorption film layer, and the MgF ₂ film layer are formed on a long resin film substrate by a roll-to-roll method, according to claim 16 or 17. Manufacturing method of absorption type multilayer ND filter.   19. The method for producing an absorptive multilayer ND filter according to claim 16, wherein a film in contact with the substrate made of a resin film is an oxide dielectric film layer.   20. The method for manufacturing an absorptive multilayer ND filter according to claim 16, wherein each thickness of the oxide dielectric film layer is 3 nm to 150 nm. The film thickness of the MgF ₂ film layer is 20 nm to 150 nm, and the total film thickness of the outermost oxide dielectric film layer and the MgF ₂ film layer is 200 nm or less. 21. A method for producing an absorption multilayer ND filter according to any one of 20 above.

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