JP4811293B2 - Absorption-type multilayer ND filter and method for manufacturing the same - Google Patents

Description

  The present invention relates to an absorptive multilayer ND filter that attenuates transmitted light in the visible light region, and more particularly to improvement in flatness of spectral transmission characteristics and improvement in environmental resistance in a high-temperature and high-humidity environment.

  As an ND (Neutral Density Filter) filter that attenuates transmitted light in the visible light region, a reflective ND filter that reflects and attenuates incident light and an absorption ND filter that absorbs and attenuates incident light are known. . In particular, when an ND filter is incorporated in a lens optical system in which reflected light is a problem, an absorption ND filter is generally used.

  The absorption type ND filter includes a type in which an absorbing substance is mixed with the substrate itself (color glass ND filter), a type in which an absorbing substance is applied to the substrate, and a thin film formed on the substrate surface without absorption in the substrate itself. There are certain types. In the case of a type in which the thin film has absorption, the thin film can be composed of a multilayer film in order to prevent reflection on the surface of the thin film, and can have an antireflection effect as well as a function of attenuating transmitted light.

In particular, in an absorption type multilayer ND filter used for a small and thin digital camera or the like, a resin film is regarded as an optimal substrate because the mounting space is narrow and the substrate itself needs to be thinned. For example, JP-A-2006-178395, JP-absorption type multi-layer film ND filter and the resin off I Lum oxide dielectric film layer and the metal absorption film layer are laminated alternately to form absorptive multilayer film disclosed Has been.

  Japanese Patent Application Laid-Open No. 2003-322709 discloses a plasma electrode for cleaning a substrate surface on a traveling path of a film, and a vapor deposition source for forming a light absorption film and a transparent dielectric film on the surface. A method is described in which a substrate surface is first cleaned by plasma discharge generated at a plasma electrode, then a light absorbing film is formed by sputtering of a vapor deposition source, and then a transparent dielectric film is formed by sputtering. Here, it is disclosed that plasma treatment is performed on a resin film before film formation in order to improve the adhesion of the absorption multilayer film.

JP 2006-178395 A JP 2003-322709 A

Above-described absorption type multi-layer film ND filter forming the absorption type multi-layer film on the resin off I Lum is generally approximately 25% average transmittance in the wavelength 400 to 700 nm, valley of transmittance near a wavelength of 400~550nm high It has a mold-like spectral transmission characteristic. However, ND filters used for digital cameras and the like are required to have flat spectral transmission characteristics in order to obtain a good color balance.

  In order to flatten the spectral transmission characteristics in the visible light region (wavelength 400 to 700 nm) (to make the transmittance at each wavelength substantially equal), the total number of absorption multilayer films is increased, or another film material is used. By adding, the degree of freedom in film design is expanded, and the variation in flatness of spectral transmission characteristics ((maximum transmittance−minimum transmittance) / average transmittance at wavelengths of 400 to 700 nm) can be further reduced. However, increasing the total number of films or adding another kind of film material is not preferable because the manufacturing cost increases and the film formation process becomes complicated.

  Moreover, since the absorption type multilayer ND filter is incorporated in a digital camera, a security camera, etc., environmental resistance is also required. In particular, an absorptive multilayer film ND filter formed on a substrate made of a resin film may crack in the absorptive multilayer film like a mesh when left in a high-temperature and high-humidity environment. .

  The present invention has been made paying attention to such conventional problems, and relates to an absorptive multilayer ND filter in which a resin film as a substrate is provided with an absorptive multilayer film that attenuates transmitted light in the visible light region. Without changing the film structure of the absorption multilayer film, the absorption multilayer film ND filter has excellent optical characteristics, in particular, excellent flatness of spectral transmission characteristics, and at the same time, does not generate cracks even in a high temperature and high humidity environment. The purpose is to provide.

  As a result of intensive studies to achieve the above object, the present inventor has changed the film structure of the absorption film based on the knowledge that the transparent resin multilayer film is slightly colored by the treatment with plasma or ion beam irradiation. First, it was found that the flatness of the spectral transmission characteristics in the visible light region (wavelength 400 to 700 nm) can be improved by irradiating the resin film with plasma or an ion beam to provide absorption. At the same time, it has been found that when the transparent resin film is slightly colored by plasma treatment or ion beam treatment, the environmental resistance of the absorption multilayer film in a high-temperature and high-humidity environment is improved, leading to the present invention. is there.

That is, the manufacturing method of the absorption type multilayer ND filter provided by the present invention is an average at a wavelength of 400 to 550 nm, in which an absorption type multilayer film that attenuates transmitted light in the visible light region (wavelength 400 to 700 nm) is provided on a resin film. A method of manufacturing an absorptive multilayer ND filter having a transmittance of 3 to 32% , wherein a resin film is subjected to plasma treatment or ion beam treatment, and the transmittance of the resin film at a wavelength of 400 nm is 1 with respect to that before treatment. After attenuation by 0.0% or more, an absorption multilayer film is formed by alternately laminating oxide dielectric film layers and metal absorption film layers on at least one surface of the resin film.

  The present invention provides an absorptive multilayer ND filter, which is an absorptive multilayer ND filter in which a resin film is provided with an absorptive multilayer film that attenuates transmitted light in the visible light region. The average transmittance at a wavelength of 400 to 550 nm is 3 to 32%, and the flatness variation of spectral transmission characteristics in the visible light region ((maximum transmittance−minimum transmittance) / average transmittance at a wavelength of 400 to 700 nm) ) Is smaller by 1% or more than a resin film not subjected to plasma treatment or ion beam treatment.

According to the present invention, by applying plasma treatment or ion beam treatment to a resin film, the transmittance of the resin film serving as a substrate at a wavelength of 400 nm can be attenuated by 1.0% or more. The absorption multilayer film ND filter having an average transmittance of 3 to 32% at a wavelength of 400 to 550 nm on which the absorption multilayer film is formed attenuates the transmittance at a wavelength of 400 to 550 nm, and is in the visible light region (wavelength 400 to 700 nm). Variation in flatness of spectral transmission characteristics ((maximum transmittance−minimum transmittance) / average transmittance at a wavelength of 400 to 700 nm) is 1% or more smaller than that of the resin film not subjected to plasma treatment or ion beam treatment. can do. In addition to improving the adhesion between the absorptive multilayer film and the resin film, it can prevent cracking of the absorptive multilayer film in a high-temperature and high-humidity environment, improving the environmental resistance of the absorptive multilayer film ND filter. Can be made.

  Therefore, the absorption multilayer ND filter of the present invention improves the flatness of the spectral transmission characteristics without changing the film structure of the absorption film and without increasing the manufacturing cost or complicating the film formation process. Thus, it is possible to prevent cracking of the absorption multilayer film in a high-temperature and high-humidity environment, and it can be applied to many applications such as digital cameras and security cameras.

  In the absorption multilayer ND filter of the present invention, before the absorption multilayer film is formed, in order to improve the flatness of the spectral transmission characteristics and prevent cracking of the absorption multilayer film in a high temperature and high humidity environment, Plasma or ion beam is irradiated to the resin film used as a substrate. The conditions for this plasma treatment or ion beam treatment are set so that the originally transparent resin film is slightly colored, and the transmittance of the resin film at a wavelength of 400 nm is attenuated by 1.0% or more compared to before the treatment.

  In general, in order to improve the adhesion of a film formed on a resin film, conventionally, plasma treatment or ion beam treatment has been performed on the resin film. It has also been known that the resin film is colored when the intensity of plasma or ion beam to be irradiated is increased. However, when the resin film is colored, the transmitted light is absorbed and the hue changes, so the treatment is usually limited to the minimum irradiation that can improve the adhesion of the film and has an obvious effect on the optical properties. Was not done.

  The absorptive multilayer film of the absorptive multilayer film ND filter is not a transparent film, and there is no problem even if transmitted light is attenuated by absorption due to coloring of the resin film. Therefore, in the present invention, the phenomenon that the resin film is colored by the plasma treatment or the ion beam treatment is actively used, and the wavelength of the resin film is specifically 400 nm so that the originally transparent resin film is slightly colored. The resin film before film formation is irradiated with plasma or an ion beam so that the transmittance in the film is attenuated by 1.0% or more compared with that before the treatment.

  In the present invention, the transmittance of the resin film at a wavelength of 400 nm is attenuated by 1.0% or more by plasma treatment or ion beam treatment as compared to before treatment. As a result, in the absorption type multilayer ND filter in which the absorption type multilayer film is provided on the resin film, the transmittance at a wavelength of 400 to 550 nm is attenuated, so that the flatness of spectral transmission characteristics can be improved. Specifically, the average transmittance of the absorption multilayer ND filter at a wavelength of 400 to 550 nm is 3 to 32%, and the flatness variation of spectral transmission characteristics in the visible light region ((maximum transmittance−minimum transmittance) / The average transmittance (wavelength 400 to 700 nm) can be reduced by 1% or more compared to the case where the resin film is not subjected to plasma treatment or ion beam treatment.

  At the same time, in the absorptive multilayer film ND filter of the present invention, the adhesion between the absorptive multilayer film and the resin film can be improved, and further, the cracking of the absorptive multilayer film in a high temperature and high humidity environment can be prevented. The reason why cracking of the absorption multilayer film is prevented is not clear, but the above-mentioned plasma treatment or ion beam treatment causes thermal shrinkage of the resin film, and this thermal shrinkage contributes to improving the adhesion of the absorption multilayer film. Thus, it is considered that cracking of the absorption multilayer film is prevented.

  Although the material of the resin film used as a board | substrate is not specifically limited, A transparent thing is preferable and the flexible thing which can be dry-type roll-coated is preferable when mass productivity is considered. A flexible substrate is less expensive than a conventional glass substrate, and is excellent in that it is light and rich in deformability.

  Specific examples of the resin film include a film made of a resin selected from polyethylene terephthalate (PET), polyether sulfone (PES), polyarylate (PAR), polycarbonate (PC), polyolefin (PO) and norbornene, or The composite film which coat | covered the one or both surfaces of the resin film with the acrylic type organic film is mentioned. In particular, norbornene resin is preferable because it has characteristics such as transparency and heat resistance in the visible wavelength range, and representative examples thereof include ZEONOR (trade name) manufactured by Nippon Zeon Co., Ltd., which has a low absorption rate, and film adhesion. A high JSR Arton (trade name) can be mentioned.

The absorption multilayer film provided on one side or both sides of the resin film is composed of a multilayer film in which oxide dielectric film layers and metal absorption film layers are alternately laminated. As the oxide dielectric film layer, SiO ₂ , Al ₂ O ₃ , a mixture of these oxides, or a composite oxide can be used. In addition, as the metal absorption film layer, at least one metal selected from Ni, Ti, Cr, W, Ta, and Nb can be used.

  The oxide dielectric film layer and the metal absorption film layer constituting the absorption multilayer film are subjected to the plasma treatment or the ion beam treatment as described above, and then the vacuum deposition method, the ion beam sputtering method, the magnetron sputtering method, the ion plate method. Each film can be formed by a film forming method such as a coating method. In particular, the characteristics of the metal absorption film layer, such as the refractive index and absorption coefficient, may vary greatly depending on the additive and impurities of the film material, the residual gas during film formation, the gas released from the substrate, and the film formation speed. These conditions may be appropriately selected and set so as to obtain the desired absorption multilayer ND filter characteristics.

Next, the manufacturing method of the absorption-type multilayer ND filter according to the present invention will be described in more detail using specific examples. For example, an absorption multilayer ND filter having an average transmittance of 25% at a wavelength of 400 to 700 nm is composed of a PET film as a substrate, SiO _{2 as} an oxide dielectric film layer of the absorption multilayer film, and Ni as a metal absorption film layer. Then, the film configuration as shown in Table 1 below is obtained. FIG. 1 shows the spectral transmission characteristics of the absorption multilayer ND filter having this film configuration.

  In the method of the present invention, when an absorption multilayer ND filter having the film configuration shown in Table 1 is manufactured, the resin film is first subjected to plasma treatment or ion beam treatment before forming the absorption multilayer film. In the plasma treatment or ion beam treatment, the plasma or ion beam is irradiated so as to attenuate the transmittance of the resin film at a wavelength of 400 nm by 1.0% or more. For plasma processing or ion beam processing, various processing apparatuses can be used.

  For example, FIG. 2 shows changes in spectral transmission characteristics when the voltage of DC plasma treatment is changed for a PET film serving as a substrate in the film configuration of Table 1 above. The plasma irradiation time at this time is 6 seconds. It can be seen that the transmittance of the PET film at a wavelength of 400 to 550 nm is attenuated as the plasma processing voltage is increased. Thus, since the transmittance | permeability in the wavelength of 400-550 nm of a resin film falls, so that the electric power of a plasma processing or ion beam processing is made high, the average transmittance | permeability in the wavelength of 400-550 nm of an absorption type multilayer ND filter is desired. The power for plasma processing or ion beam processing may be adjusted in accordance with the amount of attenuation.

  An oxide dielectric is formed on one or both surfaces of the above-mentioned plasma treatment or ion beam treatment using a film deposition method such as vacuum deposition, ion beam sputtering, magnetron sputtering, or ion plating. By forming the absorption multilayer film by alternately laminating the film layers and the metal absorption film layers, the absorption multilayer film ND filter of the present invention is obtained.

In the double-sided absorption type multilayer ND filter having the film structure shown in Table 1 above, the contribution of film coloring by plasma treatment or ion beam treatment to the transmittance can be considered based on the following calculation formula 1 for each wavelength. it can.
[Calculation Formula 1]
Transmittance of double-sided absorption type multilayer ND filter = transmittance of A-side absorption multilayer film × transmittance due to resin film coloring × B-side absorption multilayer film transmittance

  However, strictly speaking, the refractive index and extinction coefficient at each wavelength of the colored resin film, the refractive index and extinction coefficient at each wavelength of the metal absorption film layer, and the oxide dielectric film layer by spectral ellipsometry, etc. From the refractive index and extinction coefficient at each wavelength, it is desirable to perform theoretical calculation of spectroscopic optical characteristics using optical thin film simulation software or the like.

  The present invention is particularly effective for an absorption type multilayer ND filter having a relatively high transmittance. Specifically, in the double-sided absorption type multilayer ND filter having an average transmittance of 25%, the transmittance of the A-type and B-side absorption multilayer films is 50% (= √0.25). Here, when the absorption of coloring of the resin film by plasma treatment is 3%, the transmittance of the absorption multilayer film is 50% × (100% −0%) × 50% −50% × (100% −3%). ) × 50% = 24.2%, and the transmittance can be corrected by about 0.8%. Specifically, there is an effect of reducing the flatness variation of the spectral transmission characteristics by 3% (= 0.8% / 25%) at the maximum. Here, since the absorption multilayer film also has an antireflection effect on the resin film substrate, the reflection can be ignored.

  On the other hand, in the double-sided absorption type multilayer ND filter having an average transmittance of 6.3%, the transmittance of the A-type and B-side absorption type multilayer films is 25% (= √0.063). Here, when the absorption of coloring of the resin film by plasma treatment or ion beam treatment is 3%, 25% × (100% −0%) × 25% −25% × (100% −3%) × 25% = Although the transmittance can be corrected by only about 0.2%, the flatness variation of the spectral transmission characteristics can be reduced by 3% (= 0.2% / 6.3%) at the maximum.

  Thus, in the absorption type multilayer ND filter having a low transmittance, it can be seen that the attenuation of the transmittance due to the absorption of the coloring of the resin film contributes very little. In addition, it has also been confirmed that there is no change in the reflection characteristics of the absorption multilayer ND filter due to the coloring of the resin film. Therefore, it is difficult and impractical to have the resin film absorb 3% or more by plasma treatment or ion beam treatment due to problems such as heat load.

  The absorption multilayer ND filter having the film structure shown in Table 1 was manufactured as follows. Note that the absorption multilayer ND filter having the film structure shown in Table 1 has a valley-shaped spectral transmission characteristic shown in FIG. 1 in the case of a conventional filter that is not subjected to plasma treatment or ion beam treatment of PET film. The average transmittance at a wavelength of 400 to 700 nm is 25%.

First, the non-deposited portion for measuring the spectral transmission characteristics at the terminal portion of the PET film by subjecting the A side of a 100 μm thick PET film with an easy-adhesion layer (Toyobo) to plasma treatment at a plasma treatment voltage of 1.6 kV Then, an oxide dielectric film layer made of SiO ₂ and a metal absorption film layer made of Ni were alternately stacked to form an absorption multilayer film. After that, the B surface is also subjected to plasma processing at the same position on the A surface with the same plasma processing voltage, and an absorption multilayer film is formed by leaving an undeposited portion at the end of the PET film in the same manner as the A surface. A mold multilayer ND filter was obtained.

  More specifically, a sputtering roll coater equipped with a DC plasma processing mechanism was used to form the absorption multilayer film. The plasma treatment of the PET film was performed by introducing Ar gas into the DC plasma treatment apparatus at 100 sccm and lowering the rotation speed of the turbo pump so that the Ar gas pressure was 3 Pa and the film conveyance speed was 1 m / min. .

For the formation of the absorption multilayer film, a Ni alloy target (manufactured by Sumitomo Metal Mining Co., Ltd.) is used for forming a metal absorbing film layer, and a Si target (Sumitomo Metal Mining) is used for forming an oxide dielectric film layer (Made by Co., Ltd.) was used. That is, the Ni alloy target is formed by a DC magnetron sputtering method in which Ar gas is introduced, the Si target is subjected to dual magnetron sputtering in which Ar gas is introduced, and an oxygen introduction amount is measured by an impedance monitor in order to form SiO ₂ from Si. Controlled.

  Also, an absorption multilayer ND filter was manufactured in the same manner as described above except that the plasma treatment voltage of the PET film was changed. That is, during the plasma treatment of the A side and B side of the PET film, the plasma treatment voltage was set to 1.8 kV, 2.1 kV, 2.3 kV, and 2.5 kV, respectively, and after performing the plasma treatment, An absorptive multilayer film ND filter was manufactured by forming an absorptive multilayer film.

  With respect to the absorption multilayer ND filter obtained under each of the above conditions, the spectral transmittance at a wavelength of 400 to 700 nm of the non-deposited portion of the PET film termination was measured, and the spectral transmittance before plasma treatment was shown in FIG. . Moreover, the spectral transmittance in wavelength 400-700nm of each obtained absorption type multilayer ND filter was measured, and the result was shown in FIG. The spectral transmittance of the PET film and the ND filter was measured using a self-recording spectrophotometer (manufactured by JASCO Corporation, V570).

  Furthermore, the absorption multilayer ND filter obtained under the above conditions was cut into 50 mm squares and left in an environmental tester at a temperature of 80 ° C. and a humidity of 90% for 24 hours. Then, each absorption type ND filter was observed with a 100 × Nomarski differential interference microscope, and the state of cracking of the absorption type multilayer film was examined. The obtained observation results are shown in Table 2 below. Table 2 also shows the transmittance of the PET film before and after the plasma treatment at a wavelength of 400 nm.

  As is clear from FIG. 3, the absorption multilayer ND filter obtained by performing the plasma treatment on the PET film before film formation has a spectral transmission characteristic in a short wavelength region of 400 to 550 nm as compared with the case where the plasma treatment is not performed. The flatness variation ((maximum transmittance−minimum transmittance) / average transmittance at a wavelength of 400 to 700 nm) is small. The improvement in the flatness of the spectral transmission characteristic increases with the plasma processing voltage.

  More specifically, the flatness variation of the absorption-type multilayer ND filter not subjected to the plasma treatment is 19%, whereas the plasma treatment voltage is 1.8 kV, 2.1 kV, 2.3 kV, and 2.5 kV. As a result, the variation in flatness of the spectral transmission characteristics was improved to 18%, 17%, 16%, and 15%, respectively. From these facts, in the case of an absorption multilayer ND filter having an average transmittance of 3 to 32% at a wavelength of 400 to 550 nm, spectral transmission characteristics in the visible light region can be obtained by performing plasma treatment or ion beam treatment on the resin film. It was found that the flatness variation of the film can be improved by 1% or more.

  Further, from the results in Table 2, the effect of preventing cracking of the absorption multilayer film by plasma treatment of the PET film before film formation was 1.8 kV in which the decrease in the transmittance of the PET film at a wavelength of 400 nm was 1.0%. It can be seen that the effect becomes remarkable from the plasma voltage of 2.1 kV or higher, which appears from the vicinity and the decrease in transmittance is 2.0%. However, even in the case of plasma processing at a plasma processing voltage of 1.6 kV, sufficient initial adhesion of the absorption multilayer film was obtained.

  In addition, although the said Example demonstrated only the case where a plasma process was performed to PET film, the result similar to the above was obtained also in the ion beam process.

It is a graph which shows the spectral transmission characteristic of the absorption type multilayer ND filter of the conventional average transmittance | permeability 25%. It is a graph which shows the change of the spectral transmission characteristic of PET film by the plasma processing of this invention. It is a graph which shows the change of the spectral transmission characteristic of the absorption type multilayer ND filter by the plasma processing of the PET film of this invention.

Claims (3)

Production method of absorption multilayer ND filter having an average transmittance of 3 to 32% at a wavelength of 400 to 550 nm, wherein an absorption multilayer film for attenuating transmitted light in the visible light region (wavelength 400 to 700 nm) is provided on a resin film a is, by performing plasma treatment or ion beam treatment in the resin film, after being attenuated to preprocess the transmittance at a wavelength 400nm of the resin film of 1.0% or more, on at least one surface of the resin off I Lum A method of manufacturing an absorptive multilayer ND filter, wherein an oxide dielectric film layer and a metal absorptive film layer are alternately laminated to form an absorptive multilayer film.   The oxide dielectric film layer and the metal absorption film layer are formed by any one of a vacuum vapor deposition method, an ion beam sputtering method, a magnetron sputtering method, and an ion plating method, respectively. Manufacturing method of absorption type multilayer ND filter.   An absorption-type multilayer ND filter in which a resin film is provided with an absorption-type multilayer film that attenuates transmitted light in the visible light region (wavelength 400 to 700 nm), and is manufactured by the method according to claim 1, and has a wavelength of 400 The average transmittance at ˜550 nm is 3 to 32%, and the flatness variation of spectral transmission characteristics in the visible light region ((maximum transmittance−minimum transmittance) / average transmittance at wavelengths of 400 to 700 nm) is plasma on the resin film. An absorptive multilayer ND filter characterized by being 1% or more smaller than those not subjected to treatment or ion beam treatment.

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