JP2014016565A - Absorption type multilayer film nd filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an absorption type multilayer film ND filter which can be efficiently manufactured by means of a film formation method by plasma and has a low reflection property which is equivalent to those of ND filters that use MgF.SOLUTION: An absorption type multilayer film ND filter comprises an absorption type multilayer film, which has a six layer structure comprising three oxide dielectric film layers D, Dand Dand two absorption film layers Aand Aalternately laminated on top of each other with a SiOfilm layer containing a nanoporous material formed on top as an outermost layer E, provided on each surface of a resin substrate S. The outermost layer E on each side has a refractive index that is 0.95-0.98 times a refractive index of the oxide dielectric film layer Dwhich is the fifth layer on each side counting from the resin substrate S.

Description

  The present invention relates to an absorptive multilayer ND filter that attenuates transmitted light in the visible light region, and is particularly excellent in low reflectivity, in which oxide dielectric film layers and metal layers are alternately laminated on both surfaces of a resin film substrate. The present invention relates to an absorption type multilayer ND filter.

  In a camera system such as a digital still camera or a video camera, an ND (Neutral Density) filter that attenuates light is used to prevent saturation of a CCD or CMOS element, which is an imaging element, due to excessive light incidence. . In particular, in the camera system, since the reflected light inside the camera is regarded as a problem, an absorption ND filter is generally used as the ND filter incorporated in the lens optical system.

  This absorption type ND filter has a thin film formed on the surface, although there is no function to absorb the substrate itself other than the type in which the substrate itself is mixed with an absorbing material (colored glass ND filter) and the type in which the absorbing material is applied to the substrate. There is a type that absorbs. In the case of the type that absorbs with the latter thin film, in order to prevent reflection on the surface of the thin film, the thin film is composed of a multilayer film (absorption type multilayer film) and has a function of attenuating transmitted light and an antireflection function. is there.

As an absorptive multilayer ND filter composed of such multilayers (absorptive multilayers), physical properties such as vacuum deposition and sputtering are applied on transparent resin film substrates such as PET (polyethylene terephthalate) and PC (polycarbonate). There is known an ND filter in which an absorption film layer and an oxide dielectric film layer such as SiO ₂ are alternately stacked by film formation by a chemical vapor deposition method.

As the absorption film layer, an absorption film layer made of a metal oxide such as TiO _x or Ta ₂ O _x having absorption due to oxygen deficiency is known. This metal oxide can be formed by intentionally introducing oxygen, but its extinction coefficient is lower than that of an absorption film layer made of metal formed without intentionally introducing oxygen, Quality problems such as substrate warpage, which will be described later, may occur.

  Therefore, in Patent Document 1, a metal such as Ti or Cr is used as a material for the absorption film layer instead of the metal oxide, and the absorption film layer made of the metal film and the oxide dielectric film layer are alternately formed. Laminated ND filters have been proposed. Patent Documents 2 and 3 describe an absorption multilayer ND filter using a film forming material in which Ti or W is added to Ni as a metal film. These ND filters shown in Patent Documents 1 to 3 can be made thinner to obtain the same extinction coefficient than the absorption film layer made of the metal oxide described above. Therefore, it is possible to efficiently produce an absorption multilayer ND filter having desired transmission characteristics and reflection characteristics.

  That is, the absorption-type multilayer ND filter is cut into a predetermined shape and size to form an ND filter chip, and then incorporated into the above-described digital camera or the like. However, the digital camera or the like is small and thin and has a small installation space. Since the substrate is narrow, a resin film that is thin and flexible per se is the optimum substrate for the substrate of the ND filter. When forming an absorption multilayer film on such a resin film substrate, the metal film can reduce the film thickness of the absorption film layer compared to the metal oxide film, so that the film formation time can be shortened, and thus the film formation time. It is possible to suppress problems such as warpage of the resin film substrate and cracking of the film that can be caused by lengthening the thickness.

Japanese Patent Laid-Open No. 05-093811 JP 2006-058854 A JP 2006-009694 A

Incidentally, when an optical element having a flat surface such as an ND filter is incorporated in a camera or the like, lower reflection characteristics are required. This is because the flat ND filter causes multiple reflection inside the camera, which causes ghost in the video information. In order to reduce the reflection, it is generally effective to lower the refractive index of the outermost surface layer at the boundary with air. Therefore, MgF ₂ which is a material having a lower refractive index is usually used for the outermost surface layer. Often done.

Although the fluorine compound such as MgF ₂ can be formed by a vapor deposition method, fluorine disappeared by a film formation method using plasma such as a sputtering method, and the film could not be formed satisfactorily. Therefore, in the case of stacking the absorption multilayer film with a highly productive film forming apparatus combining the sputtering method and the roll-to-roll method, conventionally, SiO ₂ is used as the material of the outermost surface layer. However, regarding the refractive index, MgF ₂ is 1.38, whereas SiO ₂ is as high as 1.45, and sufficient low reflection characteristics could not be obtained.

Accordingly, there has been a strong demand for an absorption multilayer ND filter that can be efficiently produced by a film formation method using plasma such as sputtering, and has low reflection characteristics comparable to those of an ND filter using MgF ₂ . .

In order to solve the above-mentioned problems, the present inventor has intensively studied to obtain an ND filter exhibiting low reflection characteristics by a simple method while using SiO ₂ having a higher refractive index than that of MgF ₂ as a dielectric material. . As a result, in the ND filter in which the absorption multilayer film in which the three oxide dielectric film layers and the two absorption film layers are alternately laminated is provided on both surfaces of the resin substrate, by providing a fifth layer of SiO _x layer SiO _x layer containing and nanoporous having a refractive index lower than the refractive index of the counting to the sixth layer as the outermost layer, the outermost layer MgF ₂ The present inventors have found that the same reflection characteristics as in the case of a layer are shown, and have completed the present invention.

That is, in the absorption multilayer ND filter according to the present invention, the three oxide dielectric film layers and the two absorption film layers are alternately laminated one by one, and the outermost surface layer is made of SiO containing nanoporous. The absorption multilayer film having a six-layer structure in which the _x film layer is formed is an absorption multilayer film ND filter provided on both surfaces of the resin substrate, and the fifth layer oxidation counted from the resin substrate. The outermost surface layer has a refractive index of 0.95 to 0.98 times the refractive index of the dielectric film layer.

  According to the present invention, the refractive index can be set to a low refractive index in the range of 1.38 to 1.42, and an ND filter having low reflection characteristics can be provided at a low cost by a simple process.

It is typical sectional drawing of one specific example of the absorption type multilayer ND filter which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic front view of a sputtering roll coater device that can suitably produce an absorption multilayer ND filter according to the present invention. 4 is a graph showing spectral transmittance and reflectance at a wavelength of 400 nm to 700 nm of the absorption multilayer ND filter of Sample 1 manufactured in Example 1. FIG. It is a graph which shows the spectral transmittance and spectral reflectance in wavelength 400nm -700nm of the absorption type multilayer film ND filter of the sample 2 produced in Example 1. FIG. 6 is a schematic cross-sectional view of an absorption multilayer ND filter of Sample 3 produced in Example 2. FIG. It is a graph which shows the spectral transmittance and spectral reflectance in wavelength 400nm -700nm of the absorption type multilayer film ND filter of the sample 3 produced in Example 2. FIG. It is a graph which shows the spectral transmittance and spectral reflectance in wavelength 400nm -700nm of the absorption type multilayer film ND filter of the sample 4 produced in Example 2. FIG.

A specific example of the absorption multilayer ND filter according to the present invention will be described below with reference to FIG. This absorption type multilayer ND filter has three oxide dielectric film layers D ₁ , D ₂ , D ₃ and two layers of absorption layer films A ₁ , A _{2 made of} metal alternately stacked one by one. Further, an absorption multilayer film having a six-layer structure in which a SiO _x layer E containing a sixth nanoporous layer is formed as the outermost surface layer is provided on both surfaces of the resin substrate S.

Then, this the counting from the resin substrate S side fifth layer from 0.95 to 0.98 times the refractive index of the refractive index of the oxide dielectric film layer D ₃ of said sixth layer SiO _x layer E Have. Oxides of a three-layer dielectric layer _{D 1,} D 2, _{D 3} is composed of a dielectric film made of SiO _x, thus is from the air side to the third layer, SiO _x layer comprising nanoporous, SiO _x It is comprised in the order of the layer and the metal absorption film layer.

  The absorption multilayer ND filter having such a configuration has a refractive index of the outermost surface layer having a low refractive index in the range of 1.38 to 1.42, and maximum reflection in the visible light wavelength region (400 nm to 700 nm). It has excellent characteristics of a rate of 3% or less. Hereafter, each component which comprises this absorption type multilayer ND filter of this invention is demonstrated in detail.

(1) Outermost surface layer In order to reduce the surface reflection of the absorption multilayer ND filter, the lower the refractive index of the oxide dielectric film layer located on the outermost surface side, the better. In general, the lowest refractive index of the dielectric film material is 1.38 of MgF ₂ , and the next lowest refractive index is 1.45 of SiO ₂ . Therefore, in the present invention, the SiO _x layer containing nanoporous is formed as the sixth layer as the outermost surface layer.

Note that the SiO _x layer is a layer in which various silicon oxide such as SiO or SiO ₂ is mixed in the amorphous, as the refractive index, a higher value than the SiO ₂ in accordance with oxygen deficiency of SiO ₂ It has the feature of showing. This SiO _x layer is formed by performing sputtering in an atmosphere with a small amount of oxygen. Moreover, the layer containing nanoporous means the layer of the porous body containing innumerable micropores of nanometer order.

The outermost surface layer of the SiO _x layer containing nanoporous is formed by a physical vapor deposition method selected from an ion beam sputtering method, a magnetron sputtering method, or an ion plating method using a target mainly composed of SiC and Si. A film can be formed.

In particular, when the film is formed by magnetron sputtering, the gas pressure of argon gas at the time of film formation of the other three oxide dielectric film layers D ₁ , D ₂ , and D ₃ is 1.5 to 5 as described later. A dense film having a low refractive index can be obtained by raising the gas pressure of the argon gas to about twice as high. If the gas pressure of the argon gas is less than 1.5 times, the generation of nanoporous becomes difficult and the effect of the present invention cannot be obtained. If the gas pressure exceeds 5 times, the generation of sputter plasma becomes unstable and film formation cannot be performed. The gas pressure condition of argon gas during film formation is important.

Thus, Ar or oxygen gas is contained in the SiO _x film by making the pressure of the argon gas during film formation higher than that during the film formation of the _three oxide dielectric film layers D ₁ , D ₂ , and D _3. Is taken in more. As a result, a large number of fine bubbles having a refractive index of 1 are formed, and the refractive index is lower than that of the other three oxide dielectric film layers D ₁ , D ₂ , D _3. The refractive index is 0.95 to 0.98 times the refractive index of the _x film layer. The sixth SiO _x layer as the outermost surface layer preferably has an extinction coefficient of 0 to 0.01 at a wavelength of 550 nm.

  That is, if there is a void in the dielectric layer, the refractive index of the void is 1, so the refractive index of the entire layer is smaller than its bulk value. Furthermore, by setting the size of the voids to nanoporous having a size of several nanometers that does not cause visible light scattering, it is possible to achieve a desired low reflectance while preventing haze reduction due to visible light scattering.

The film thickness of the SiO _x layer as the outermost layer is 3 to 150 nm. If the film thickness is less than 3 nm, the contribution as an optical thin film is small, and it becomes difficult to control the film thickness. On the other hand, a film having a thickness of each oxide dielectric film layer thicker than 150 nm may not exhibit desired performance effectively as an optical thin film for visible light in the wavelength region of 400 nm to 700 nm.

A fluororesin layer having a thickness of 2 to 10 nm may be laminated on the upper surface of the SiO _x film layer including the sixth nanoporous layer. The fluororesin layer can be formed by a coating method such as spray coating, dip coating, or spin coating. However, since the film thickness is 10 nm or less, dip coating can be preferably used. Specifically, a fluororesin layer can be formed by dipping a commercially available fluororesin solution (DS-5110Z130 manufactured by Harves Co., Ltd.) as a fluororesin solution for 10 seconds and then air drying for 24 hours. This fluororesin coating can also be expected to have the effect of preventing deterioration of the refractive index of the SiO _x film layer containing nanoporous material over time.

(2) Oxide dielectric film layer (SiO _x layer)
The oxide dielectric film layers D ₁ , D ₂ , D ₃ made of SiO _x located in the first layer, the third layer, and the fifth layer (outermost surface layer) counted from the resin substrate S side are: Film formation can be performed by using an ion beam sputtering method, a magnetron sputtering method, or an ion plating method while using a target mainly composed of SiC and Si and controlling the amount of oxygen gas introduced. As a result, the extinction coefficient of each oxide dielectric film layer at a wavelength of 550 nm can be set to 0.005 to 0.05.

When the extinction coefficient of the SiO _x film exceeds 0.05, the average transmission of the difference between the maximum transmittance and the final transmittance in the visible light wavelength region (wavelength 400 to 700 nm) of the completed absorption multilayer ND filter is completed. It becomes difficult to keep the “spectral transmission flatness” defined by the value divided by the rate as small as 10% or less. In particular, in order to obtain flat spectral transmission characteristics, the extinction coefficient of the SiO _x film is desirably 0.03 or less. In order to obtain a SiO _x film having such flat spectral transmission characteristics, the amount of oxygen introduced during film formation should be controlled so that the extinction coefficient at a wavelength of 550 nm is in the range of 0.005 to 0.03. Good.

The film thicknesses of the first, third, and fifth oxide dielectric film layers D ₁ , D ₂ , and D ₃ are each preferably ₃ to 150 nm. If each film thickness is less than 3 nm, the contribution as an optical thin film is small, and it becomes difficult to control the film thickness. Furthermore, it cannot be expected to suppress a phenomenon in which the transmittance increases due to oxidation of the absorption film layer in a high temperature and high humidity environment. On the other hand, a film having a thickness of more than 150 nm of the oxide dielectric film layer may not exhibit the desired performance effectively as an optical thin film for visible light in the wavelength region of 400 nm to 700 nm, and may be produced. This is not preferable because it only reduces the efficiency.

(3) Absorption film layer (metal layer)
The absorption film layers A ₁ and A ₂ located in the second layer and the fourth layer as counted from the resin substrate S side are composed of metal films. This metal film can be formed by physical vapor deposition using metal as a raw material and stopping the introduction of oxygen gas. The physical vapor deposition method can be selected from an ion beam sputtering method, a magnetron sputtering method, or an ion plating method. The absorption film obtained by the physical vapor deposition method has a refractive index of 1.5 to 3.0 at a wavelength of 550 nm and an extinction coefficient of 1.5 to 4.0.

The metal film formed without intentionally introducing oxygen at the time of film formation is TiO _x or Ta ₂ O _x having absorption due to oxygen deficiency formed by intentionally introducing oxygen at the time of film formation as described above. It is known that it has a high extinction coefficient as compared with metal oxide films such as. And when forming an absorption type multilayer film by alternately laminating an oxide dielectric film layer and an absorption film layer on a flexible resin film substrate, the resin film substrate that can be caused by a long film formation time Taking into account the warpage and cracking of the film, 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, the metal film easily oxidizes and the extinction coefficient decreases, and the ND filter using the metal absorption film has a problem that the transmittance increases with time. Therefore, in the absorption multilayer ND filter according to the present invention, the oxide dielectric film layer adjacent to the metal absorption film is composed of a SiO _x film to suppress oxidation of the metal absorber film layer.

The thicknesses of the second and fourth absorption film layers A ₁ and A ₂ are preferably 3 nm to 20 nm. If each 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 each film thickness exceeds 20 nm, the spectral transmittance may be remarkably lowered.

The material of the metal film constituting the absorption film layers A ₁ and A ₂ is preferably Ni simple substance or Ni-based alloy which is a metal that is relatively difficult to oxidize. In the case of a Ni-based alloy, in particular, a Ni-based alloy containing one or more elements selected from the group consisting of Ti, Al, V, W, Ta, and Si is more preferable. Furthermore, when Ti is contained, the content is within a range of 5 to 15% by mass, when Al is contained, the content is within a range of 3 to 8% by mass, and when V is contained, the content is 3 to 9%. In the range of mass%, when W is included, the content is within the range of 18 to 32 mass%, when Ta is included, the content is within the range of 5 to 12 mass%, and when Si is included, the content is Is preferably in the range of 2 to 6 mass%.

  This is because if the Ti content is 5% by mass or more, the ferromagnetic characteristics can be remarkably weakened, and DC magnetron sputtering film formation can be performed even with a cathode on which a normal magnet having a low magnetic force is disposed. On the other hand, if the Ti content exceeds 15% by mass, a large amount of intermetallic compounds may be formed, which is not preferable. The reason why the contents of Al, V, W, Ta, and Si, which are elements other than Ti, are within the above ranges is the same as in the case of Ti.

(4) Resin substrate The resin substrate used in the present invention is preferably transparent, and is a long resin film substrate capable of dry roll coating by a roll-to-roll method, which will be described later in consideration of mass productivity. It is preferable that This is because the resin film substrate has excellent characteristics such as being cheaper, lighter and more flexible than a conventional glass substrate.

  Specific examples of such a resin film substrate were selected from the group consisting of polyethylene terephthalate (PET), polyethersulfone (PES), polyarylate (PAR), polycarbonate (PC), polyolefin (PO), and norbornene. Examples thereof include a single resin film made of a resin, or a composite in which an acrylic organic film is coated on one or both sides of a single resin film made of the above resin. Typical examples of resin films using norbornene as a material include ZEONOR (trade name) of Nippon Zeon Co., Ltd. and Arton (trade name) of JSR Corporation.

(5) Manufacturing method of absorption type multilayer ND filter Next, a method for manufacturing the absorption type multilayer ND filter of the present invention by a roll-to-roll method will be described. FIG. 2 is a front view showing a schematic configuration of a roll-to-roll physical vapor deposition apparatus (sputtering roll coater apparatus). The physical vapor deposition apparatus shown in FIG. 2 is provided in a sputtering chamber 10 equipped with a vacuum pump (not shown), and includes a first roll 11 for winding and unwinding a long resin film F, and The second roll 12, the water-cooled can roll 13 around which the resin film F conveyed from one of the first roll 11 and the second roll 12 to the other is wound, and the first through the water-cooled can roll 13. Four guide rolls 14, 15, 16, and 17 that define a transport path of the resin film F transported between the roll 11 and the second roll 12 are provided.

  The 1st roll 11 and the 2nd roll 12 are provided with the powder clutch, and, thereby, the tension balance of the resin film F is maintained. Further, the transport direction of the resin film F is determined by the rotation direction of the water-cooled can roll 13, and in this specification, the water-cooled can roll 13 rotates counterclockwise on the paper surface of FIG. The transport direction in which the scale-shaped resin film F is drawn out from the first roll 11 and wound up on the second roll 12 side is defined as the forward rotation direction, and conversely, the water-cooled can roll 13 rotates clockwise on the paper surface of FIG. A reverse direction is defined as a conveyance direction in which the long resin film F rotates and is drawn out from the second roll 12 and wound up on the first roll 11 side.

In the sputtering chamber 10, a sputtering cathode (dual magnetron sputtering cathode) 18 and a sputtering cathode 19 are disposed so as to face the outer peripheral surface of the water-cooled can roll 13. A target for forming an oxide dielectric film layer (for example, a SiO _x film layer) is attached to the sputtering cathode 18. On the other hand, a target for forming a metal absorption film layer (for example, Ni alloy layer) is attached to the sputtering cathode 19.

With this configuration, when the oxide dielectric film layer is formed, the water-cooled can roll 13 is rotated counterclockwise to convey the long resin film F in the forward rotation direction. As a result, the resin film F is drawn out from the first roll 11, guided to the water-cooled can roll 13 through the guide rolls 14 and 15, and is adhered to the outer peripheral surface of the water-cooled can roll 13 and cooled by the sputtering cathode 18. An oxide dielectric film layer (eg, a SiO _x film layer) is formed. The oil film F on which the oxide dielectric film layer is formed is wound around the second roll 12 through the guide rolls 16 and 17.

  When the formation of the oxide dielectric film layer is completed and almost all of the resin film F is wound on the second roll 12, the rotation direction of the water-cooled can roll 13 is reversed and the resin film F is conveyed in the reverse direction. To do. As a result, the resin film F is drawn out from the second roll 12 and guided to the water-cooled can roll 13 through the guide rolls 17 and 16, where it is adhered to the outer peripheral surface of the water-cooled can roll 13 and cooled by the sputtering cathode 19. An absorption film layer (for example, a Ni alloy layer) is formed on the oxide dielectric film layer. The resin film F on which the absorption film layer is formed is wound around the first roll 11 through the guide rolls 15 and 14. Hereinafter, the oxide dielectric film layer and the absorption film layer are formed on one surface of the long resin film F by repeating the oxide dielectric film layer formation process and the absorption film layer formation process described above. An absorption multilayer film laminated alternately is obtained.

  When laminating an absorption multilayer film similar to the above on the other side of the long resin film F, the roll of the resin film F having the absorption multilayer film laminated on one side is once removed from the roll coater device. Then, after rewinding so that the front and back are reversed, the apparatus is again applied to the first roll 11 and laminated in the same manner as described above. The film thickness of the absorption multilayer film can be controlled by controlling the conveyance speed of the long resin film F.

[Example 1]
Using the roll-to-roll physical vapor deposition apparatus (sputtering roll coater apparatus) shown in FIG. 2, three oxide dielectric film layers and two absorption film layers are alternately formed one by one. Absorbing multilayer ND filter of Sample 1 having a laminated five-layered absorbing multilayer film and a sixth layer of nanoporous SiO _x layer formed on the upper surface of the absorbing multilayer film on both sides of the film Was made. Ni-19 mass% W alloy target [W-Ni alloy target with a W addition ratio of 19 mass% manufactured by Sumitomo Metal Mining Co., Ltd.] was used as a target for forming the absorption film layer, and Ar gas was used. Was formed by DC magnetron sputtering.

On the other hand, a Si target [manufactured by Sumitomo Metal Mining Co., Ltd.] was used as a target for depositing SiO _x which is an oxide dielectric film, and was deposited by dual magnetron sputtering in which Ar gas was introduced. In order to form a SiO _x film from Si, the oxygen introduction amount was controlled by an impedance monitor.

  Here, in dual magnetron sputtering, in order to form an insulating film at high speed, medium frequency (40 kHz) pulses are alternately applied to two targets to suppress arcing and prevent formation of an insulating layer on the target surface. It is a sputtering method. The impedance monitor applies a phenomenon in which 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 a transition region between the metal mode and the oxide mode. The amount introduced is controlled and monitored, and is used to form an oxide dielectric film layer at high speed.

  Since the thickness of the film obtained by the film formation method is determined by the transport speed of the resin film substrate and the sputtering power, the sputtering power is set to 7.5 kW when forming the oxide dielectric film layer, and the absorption film Sputtering power was set to 1 kW when forming the layer. And the conveyance speed of the resin film board | substrate was adjusted so that it might become a desired physical film thickness. A PET film was used as the resin film substrate, and six layers on one side of the film structure shown in Table 1 below were first formed on one surface thereof. Thereafter, the roll of the film is removed and rewound so that the front and back are reversed. The film is again mounted on the roll coater and formed on the other surface in the same manner as described above. Six layers were deposited.

Specifically, an absorptive multilayer film was formed along the following film formation steps (1) to (6).
(1) After exhausting the inside of the sputtering chamber 10 of the sputtering roll coater apparatus shown in FIG. 2 to about 1 × 10 ⁻⁴ Pa, the water-cooled can roll 13 is rotated counterclockwise, and the first roll 11 to the second roll. The resin film F was conveyed in the forward rotation direction toward 12. The conveyance speed of the resin film F was adjusted to 1.58 m / min. Furthermore, Ar gas was introduced at 150 sccm to the side of the sputtering cathode 18 to which the Si target was attached, the Ar gas pressure was set to 0.3 Pa, the sputtering output was set to 7.5 kW, and the oxide dielectric of the first layer made of SiO _x was set. the body layer D ₁ was formed. During film formation, the amount of oxygen introduced was controlled by an impedance monitor.

(2) When the formation of the first oxide dielectric film layer D ₁ is completed, the water-cooled can roll 13 is reversed, and the resin film F is reversed in the reverse direction from the second roll 12 toward the first roll 11. Conveyed. The conveyance speed of the resin film F was adjusted to 1.38 m / min. Further, Ar gas was introduced at 150 sccm to the side of the sputtering cathode 19 to which the Ni alloy target (W—Ni alloy target) was attached, the sputtering output was set to 1 kW, and the second absorption film layer A ₁ made of Ni alloy. Was deposited.

(3) by inverting the water-cooled can roll 13 where the deposition of the absorbing layer A ₁ of the second layer is complete, and conveys the resin film F from the first roll 11 in the forward direction toward the second roll 12 . The conveyance speed of the resin film F was adjusted to 0.44 m / min. Further, Ar gas was introduced at 150 sccm to the side of the sputtering cathode 18 to which the Si target was attached, the Ar gas pressure was set to 0.3 Pa, the sputtering output was set to 7.5 kW, and the oxide dielectric of the third layer made of SiO _x was formed. the body layer D ₂ was formed. During film formation, the amount of oxygen introduced was controlled by an impedance monitor.

(4) by inverting the water-cooled can roll 13 where the third layer of the oxide dielectric film layer formation of D ₂ is completed, the resin film F from the second roll 12 in the reverse direction towards the first roll 11 Conveyed. The conveyance speed of the resin film F was adjusted to 1.38 m / min. Further, Ar gas is introduced at 150 sccm to the side of the sputtering cathode 19 to which the Ni alloy target ((W—Ni alloy target) is attached, the sputtering output is set to 1 kW, and the fourth absorption film layer A made of Ni alloy is formed. ₂ was deposited.

(5) When the film formation of the fourth absorption film layer A ₂ is completed, the water-cooled can roll 13 is reversed, and the resin film F is conveyed in the normal rotation direction from the first roll 11 to the second roll 12. . The conveyance speed of the resin film F was adjusted to 1.58 m / min. Furthermore, Ar gas was introduced at 150 sccm to the side of the sputtering cathode 18 to which the Si target was attached, the Ar gas pressure was set to 0.3 Pa, the sputtering output was set to 7.5 kW, and the oxide dielectric of the fifth layer made of SiO _x It was deposited film layer _{D 3.} During film formation, the amount of oxygen introduced was controlled by an impedance monitor.

(6) by reversing the water-cooled can roll 13 where the fifth layer of the oxide dielectric film layer D ₃ of the deposition is completed, and transported at a high speed of the resin film F in the reverse direction without deposition. And the water cooling can roll 13 was reversed and the resin film F was conveyed in the normal rotation direction which goes to the 2nd roll 12 from the 1st roll 11. The conveyance speed of the resin film F was adjusted to 0.44 m / min. Furthermore, 300 sccm of Ar gas was introduced to the sputtering cathode 18 side on which the Si target was attached, Ar gas pressure was set to 0.6 Pa, the sputtering output was set to 7.5 kW, and the SiO _x layer as the sixth layer as the outermost layer. E was deposited. During film formation, the amount of oxygen introduced was controlled by an impedance monitor.

  (7) Take out the long resin film F on which the film formation on one side (front surface) has been completed, invert the front and back and set it on the first roll 11, and repeat the steps (1) to (6) above. An absorptive multilayer film was also formed on the back surface of the long resin film F. The long resin film F having the absorption multilayer film formed on both the front and back surfaces was taken out of the sputtering chamber.

  Spectral transmission including the transmission characteristics of the resin film (PET film having a film thickness of 100 μm) substrate with respect to the absorption type multilayer ND filter of Sample 1 thus prepared (see Table 1 for the multilayer film structure). When the characteristics were measured using a self-recording spectrophotometer (V570 manufactured by JASCO Corporation), the average transmittance in the visible light range of 400 to 700 nm was 12.5%.

  Moreover, when the spectral reflectance of the absorption multilayer ND filter was measured using a spectrophotometer (V570 manufactured by JASCO Corporation), the average spectral reflectance of the absorption multilayer ND filter in the visible light region of 400 nm to 700 nm was 0. It was .75%. FIGS. 3A and 3B show graphs of spectral transmittance and spectral reflectance of the absorption multilayer ND filter of Sample 1 in the visible light region of 400 nm to 700 nm.

For comparison, as shown in Table 2, a method for manufacturing the sample 1 except that formed thicker the thickness of the fifth layer of the SiO _x layer instead of forming the sixth layer which is the uppermost surface layer In the same manner as described above, an absorption multilayer ND filter of Sample 2 was produced. In Sample 2, the fifth SiO _x layer was formed under the conditions of a gas flow rate of 150 sccm and a gas pressure of 0.3 Pa.

When the spectral transmittance and the spectral reflectance of the absorption multilayer ND filter of Sample 2 were measured in the same manner as Sample 1, they were 12.48% and 1.21%, respectively. FIGS. 3A and 3B show graphs of spectral transmittance and spectral reflectance of the absorption multilayer ND filter of Sample 2 in the visible light region of 400 nm to 700 nm. From the results of Sample 1 and Sample 2, it can be seen that excellent low reflection characteristics can be obtained by providing a SiO _x layer containing nanoporous material on the outermost surface layer.

[Example 2]
In the film forming steps (1) to (6), the transport speed of the resin film F is 1.5 m / min, 1.94 m / min, 0.45 m / min, 1.94 m / min, 1. An absorptive multilayer ND filter of Sample 3 was prepared in the same manner as in Example 1 except that the outermost surface was coated with a fluororesin by the following method at 4 m / min and 0.62 m / min.

[Fluorine resin coating]
First, a long resin film substrate F having an absorption multilayer film formed on both sides was cut into a size of 303 mm × 200 mm to obtain a sheet-shaped resin film substrate. This sheet-shaped resin film substrate was dipped in a fluororesin solution (DS-5110Z130: manufactured by Harves Co., Ltd.) for 10 seconds, dried in the air for 24 hours, and then rinsed in a rinse solvent (DS-ZV: manufactured by Harves Co., Ltd.) for 5 minutes. Ultrasonic cleaning was performed to remove excess fluororesin components, followed by air drying. As a result, the absorption multilayer ND filter of Sample 3 provided with the seventh layer fluororesin coating film C as shown in FIG. 5 was obtained.

  With respect to the absorption multilayer ND filter of Sample 3, the spectral transmittance and the spectral reflectance were measured in the same manner as in Example 1. As a result, they were 24.8% and 1.32%, respectively. FIGS. 6A and 6B are graphs of spectral transmittance and spectral reflectance of the absorption multilayer ND filter of Sample 2 in the visible light region of 400 nm to 700 nm.

For comparison, the formation of the outermost oxide dielectric film layer E in the film formation step (6) is omitted, and the fifth oxide dielectric film layer D in the film formation step (5) is omitted. ₃ except that the transport speed of the resin film F at the time of film formation ₃ is 0.45 m / min, the outermost surface layer is not nanoporous like the other SiO _x layer, and fluorine coating is not performed. The absorption multilayer ND filter of Sample 4 was prepared in the same manner as in Preparation Method 3.

  When the spectral transmittance and the spectral reflectance of the absorption multilayer ND filter of Sample 4 were measured in the same manner as in Example 1, they were 24.1% and 1.94%, respectively. FIGS. 7A and 7B are graphs of spectral transmittance and spectral reflectance of the absorption multilayer ND filter of Sample 2 in the visible light region of 400 nm to 700 nm.

The absorption multilayer ND filters of Sample 3 and Sample 4 were subjected to a moisture resistance test that was allowed to stand for 24 hours in an environment at a temperature of 80 ° C. and a humidity of 90%, and changes in spectroscopic optical characteristics were examined. As a result, in Sample 3, the initial average reflectance was 1.32%, and after the moisture resistance test, 1.36% was hardly changed, but the SiO _x layer containing nanoporous was not provided on the outermost surface layer. In sample 4 which was not subjected to fluorine coating, the initial average reflectance was 1.94%, which was high, and further increased to 2.01% after the moisture resistance test.

D ₁ , D ₂ , D ₃
Oxide dielectric film layer A ₁ , A ₂ Absorbing film layer E SiO _x layer C Fluorine resin coat film S Resin substrate 10 Sputtering chamber 11 First roll 12 Second roll 13 Water-cooled can roll 14, 15, 16, 17 Guide roll 18, 19 Sputtering cathode

Claims (5)

Absorption with a six-layer structure in which three oxide dielectric film layers and two absorption film layers are alternately stacked, and a SiO _x film layer containing nanoporous film is formed on the outermost layer. The multi-layer multilayer film is an absorption multi-layer ND filter provided on both surfaces of the resin substrate, and the refractive index of the fifth oxide dielectric film layer from the resin substrate is 0.95-0. An absorptive multilayer ND filter, wherein the outermost surface layer has a refractive index of .98 times. The SiO _x film layer is an oxide dielectric having an extinction coefficient of 0 to 0.01 at a wavelength of 550 nm, formed by using an ion beam sputtering method or a magnetron sputtering method using a target mainly composed of SiC and Si. The fifth dielectric film is a SiO _x film layer having an extinction coefficient of 0.005 to 0.05 at a wavelength of 550 nm, and the absorption film layer is formed by a vacuum deposition method or an ion beam sputtering method. The film is formed by magnetron sputtering or ion plating, and has a refractive index of 1.5 to 3.0 at a wavelength of 550 nm and an extinction coefficient of 1.5 to 4.0. The absorption-type multilayer ND filter described in 1.   3. The absorption multilayer ND filter according to claim 1, wherein each of the three oxide dielectric film layers has a thickness of 3 to 150 nm.   The absorption multilayer ND filter according to any one of claims 1 to 3, wherein the two absorption film layers are made of Ni alone or a Ni-based alloy.   The Ni-based alloy includes one or more elements selected from the group consisting of Ti, Al, V, W, Ta, and Si. When Ti is included, the content is 5 to 15% by mass. Within the range, when Al is included, the content is within a range of 3 to 8% by mass, when V is included, the content is within a range of 3 to 9% by mass, and when W is included, the content is 18 to In the range of 32% by mass, when containing Ta, the content is within the range of 5-12% by mass, and when containing Si, the content is within the range of 2-6% by mass, The absorption multilayer ND filter according to claim 4.

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