JP7669866B2 - Optical filters and sterilizers - Google Patents

Description

The present invention relates to an optical filter that can selectively transmit light in a specific wavelength range and a sterilization device that uses the optical filter.

Optical filters that can selectively transmit light in a specific wavelength range have been widely used in various applications. One such optical filter is a bandpass filter that uses a dielectric film.

In recent years, sterilization devices have been proposed that selectively inactivate DNA in the cells of target organisms such as bacteria by applying ultraviolet light without harming human cells. These sterilization devices use an interference filter as an optical filter to transmit light emitted from a light source with a wavelength range of 190 nm to 230 nm and to cut light with wavelengths outside this range.

For example, the following Patent Document 1 discloses a microorganism inactivation treatment device that inactivates microorganisms by irradiating light emitted from a light source through an optical filter. Patent Document 1 describes that when light emitted from a light source is incident at an incident angle of 0°, the optical filter transmits at least a portion of ultraviolet light in the range of 190 nm to 230 nm and at least a portion of ultraviolet light greater than 230 nm and less than 237 nm, while blocking the transmission of ultraviolet light outside the wavelength range of 190 nm to 237 nm.

JP 2019-115525 A

However, optical filters such as those described in Patent Document 1 become colored when exposed to strong ultraviolet light, which can result in a problem of reduced ultraviolet light transmittance in the wavelength range of 190 nm to 230 nm, which selectively inactivates the cells of the target organisms to be sterilized.

The object of the present invention is to provide an optical filter and a sterilization device using the optical filter, in which the UV transmittance is not easily reduced even when exposed to strong UV rays.

The optical filter according to the present invention is an optical filter comprising a transparent substrate made of glass and a dielectric multilayer film provided on the transparent substrate, and is characterized in that a moisture content in the optical filter is 0.15 mm ^-1 or more in terms of a β-OH value.

In the present invention, the amount of moisture in the optical filter is preferably 0.80 mm ⁻¹ or less in terms of β-OH value.

In the present invention, it is preferable that the dielectric multilayer film has a high refractive index film having a relatively high refractive index and a low refractive index film having a relatively low refractive index, and that the low refractive index film is a film containing silicon oxide.

In the present invention, it is preferable that the high refractive index film is a film containing hafnium oxide.

In the present invention, it is preferable that the high refractive index film is a film containing cubic hafnium oxide crystals.

The sterilization device according to the present invention is a sterilization device for inactivating microorganisms to be treated, and is characterized by having a light source that emits light with a wavelength in the wavelength range of 190 nm to 230 nm, and an optical filter constructed according to the present invention.

The present invention provides an optical filter and a sterilization device using the optical filter that are resistant to a decrease in UV transmittance even when exposed to strong UV rays.

FIG. 1 is a schematic cross-sectional view showing an optical filter according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an optical filter according to a second embodiment of the present invention. FIG. 3 is a schematic diagram showing a sterilization device according to one embodiment of the present invention.

The following describes preferred embodiments. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in each drawing, components having substantially the same functions may be referred to by the same reference numerals.

[Optical filter]
(First embodiment)
Fig. 1 is a schematic cross-sectional view showing an optical filter according to a first embodiment of the present invention. As shown in Fig. 1, the optical filter 1 includes a transparent substrate 2 and a dielectric multilayer film 3. The dielectric multilayer film 3 is provided on the transparent substrate 2.

In this embodiment, the transparent substrate 2 has a rectangular plate shape. However, the transparent substrate 2 may have a shape such as a disk shape, and the shape is not particularly limited.

The transparent substrate 2 is made of glass. In particular, the transparent substrate 2 is preferably glass that is transparent in the wavelength range used by the optical filter 1. More specifically, the transparent substrate 2 preferably has an average light transmittance of 80% or more in the ultraviolet wavelength range of 220 nm to 225 nm.

Examples of the glass constituting the transparent substrate 2 include quartz glass, borosilicate glass, etc. Quartz glass may be synthetic quartz glass or fused quartz glass. The borosilicate glass preferably contains, in mass %, SiO ₂ 55% to 75%, Al ₂ O ₃ 1% to 10%, B ₂ O ₃ 10% to 30%, CaO 0% to 5%, BaO 0% to 5%, Li ₂ O + Na ₂ O + K ₂ O 1.0% to 15%, and more preferably contains TiO ₂ 0% to 0.001%, Fe ₂ O ₃ 0% to 0.001%, and F 0.5% to 2.0%.

The thickness of the transparent substrate 2 is not particularly limited and can be set appropriately depending on factors such as light transmittance. The thickness of the transparent substrate 2 can be, for example, about 0.1 mm to 30 mm.

The transparent substrate 2 has a first main surface 2a and a second main surface 2b that face each other. A dielectric multilayer film 3 is provided on the first main surface 2a of the transparent substrate 2 as a filter section.

The dielectric multilayer film 3 is a multilayer film having a high refractive index film 4 with a relatively high refractive index and a low refractive index film 5 with a relatively low refractive index. In this embodiment, the multilayer film is formed by alternately stacking the high refractive index film 4 and the low refractive index film 5 in this order on the first main surface 2a of the transparent substrate 2.

In this embodiment, the high refractive index film 4 is made of hafnium oxide and is a film containing hafnium oxide as a main component. However, the high refractive index film 4 may also be a film containing aluminum oxide or the like as a main component. These materials for the high refractive index film 4 may be used alone or in combination.

The low refractive index film 5 is made of silicon oxide and is a film containing silicon oxide as a main component. However, the low refractive index film 5 may also be a film containing magnesium fluoride or the like as a main component. These materials for the low refractive index film 5 may be used alone or in combination.

In this specification, a film containing a material as a main component refers to a film containing 50% or more of that material. Of course, it may also be a film containing 100% of that material.

The thickness of each layer of the high refractive index film 4 is not particularly limited, but is preferably 5 nm or more, more preferably 10 nm or more, and preferably 60 nm or less, more preferably 50 nm or less.

The thickness of each layer of the low refractive index film 5 is not particularly limited, but is preferably 5 nm or more, more preferably 10 nm or more, and preferably 80 nm or less, more preferably 60 nm or less.

The total thickness of the dielectric multilayer film 3 is not particularly limited, but is preferably 1000 nm or more, more preferably 1500 nm or more, preferably 3000 nm or less, more preferably 2000 nm or less.

The number of layers constituting the dielectric multilayer film 3 is preferably 20 or more, more preferably 30 or more, and preferably 100 or less, more preferably 80 or less.

The optical filter 1 is a bandpass filter that is designed to selectively transmit light in a specific wavelength range by using optical interference, by having such a dielectric multilayer film 3.

In the optical filter 1, the minimum value of the spectral transmittance at wavelengths of 220 nm to 225 nm is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. In this case, ultraviolet light useful for sterilization treatments such as sterilization treatments of the skin can be transmitted more effectively. The upper limit of the minimum value of the spectral transmittance at wavelengths of 220 nm to 225 nm is not particularly limited, but can be, for example, 95%.

In addition, in the optical filter 1, the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm is preferably 10% or less, more preferably 5% or less, even more preferably 3% or less, and particularly preferably 1% or less. In this case, the transmission of ultraviolet rays that are harmful to the human body can be suppressed even more effectively. The lower limit of the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm is not particularly limited, but can be set to, for example, 0.2%.

In this specification, the spectral transmittance can be determined by measuring the spectral transmittance of the entire optical filter 1 using, for example, a spectral transmittance meter (manufactured by Hitachi High-Tech Science Corporation, product number "U4150"). The measurement conditions can be, for example, measurement from the main surface 1a side of the optical filter 1, with a measurement wavelength of 190 nm to 400 nm.

Furthermore, in the optical filter 1 of this embodiment, the amount of moisture in the optical filter 1 is 0.15 mm ^-1 or more in terms of β-OH value. Therefore, even when exposed to strong ultraviolet light, the ultraviolet light transmittance is unlikely to decrease. Therefore, the optical filter 1 has excellent reliability.

Conventionally, optical filters have been known to become colored when exposed to strong ultraviolet light, resulting in a problem of reduced transmittance of ultraviolet light with wavelengths between 190 nm and 230 nm, which selectively inactivates the cells of organisms to be sterilized.

The present inventors have focused on the moisture content in the optical filter 1, and have found that by making the moisture content in the optical filter 1 equal to or greater than 0.15 mm ^-1 in terms of β-OH value, the optical filter 1 is less likely to become colored even when exposed to strong ultraviolet rays, and a decrease in ultraviolet transmittance can be suppressed.

In the present invention, the moisture content in the optical filter 1, calculated as a β-OH value, is preferably 0.18 mm ^-1 or more, more preferably 0.20 mm ^-1 or more, and preferably 0.80 mm ^-1 or less, more preferably 0.50 mm ^-1 or less. When the moisture content in the optical filter 1 is within the above range, the optical filter 1 is more unlikely to be colored, and the decrease in ultraviolet transmittance can be more effectively suppressed.

The amount of moisture in the optical filter 1 converted into the β-OH value can be determined by a Fourier transform infrared spectrophotometer (FT-IR). Specifically, the FT-IR spectrum of the optical filter 1 is measured, and the amount of moisture can be determined using the following formula (1).

β-OH=(1/t)log ₁₀ (T1/T2)...Equation (1)

In formula (1), t is the thickness (mm) of the optical filter 1, T1 is the transmittance of the reference wavenumber, and T2 is the transmittance of the hydroxyl group absorption wavenumber. For example, the reference wavenumber can be 3846 cm ^-1 (wavelength 2600 nm), and the hydroxyl group absorption wavenumber can be set to the minimum transmittance in the vicinity of 3600 cm ^-1 (wavelength 2800 nm).

The amount of moisture in the optical filter 1 calculated as the β-OH value can be adjusted, for example, by the glass that constitutes the transparent substrate 2. For example, it can be adjusted by the melting temperature, humidity, and melting atmosphere when manufacturing the glass.

In the present invention, it is preferable that the dielectric multilayer film 3 contains hafnium oxide crystals. More specifically, it is preferable that the high refractive index film 4 constituting the dielectric multilayer film 3 contains hafnium oxide crystals, and it is even more preferable that it contains cubic hafnium oxide crystals. In this case, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased.

In this specification, whether or not cubic hafnium oxide crystals are contained can be confirmed by observing whether or not a diffraction peak due to the (1,1,1) crystal plane derived from cubic hafnium oxide crystals is observed in an X-ray diffraction measurement.

In this specification, the X-ray diffraction measurement can be performed by a wide-angle X-ray diffraction method. For example, an X-ray diffraction measurement device manufactured by Rigaku Corporation, model number "SmartLab" can be used. Furthermore, CuKα radiation can be used as the radiation source. Note that in the X-ray diffraction measurement, the entire optical filter 1 is measured from the main surface 1a side.

In the present invention, in X-ray diffraction measurement, it is preferable that the diffraction peak due to the (1,1,1) crystal plane derived from the cubic hafnium oxide crystal is larger than the diffraction peak due to the (-1,1,1) crystal plane derived from the monoclinic hafnium oxide crystal. In this case, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced.

In the present invention, the ratio Ic/Im of the peak area intensity Ic of the diffraction peak due to the (1,1,1) crystal plane derived from cubic hafnium oxide crystal to the peak area intensity Im of the diffraction peak due to the (-1,1,1) crystal plane derived from monoclinic hafnium oxide crystal is preferably 0.1 or more, more preferably 1 or more. When the ratio Ic/Im is equal to or more than the above lower limit, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced. The upper limit of the ratio Ic/Im is not particularly limited, but can be, for example, 10,000.

In the present invention, an anti-reflection film may be provided on the second main surface 2b of the transparent substrate 2. In this case, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased.

The anti-reflection film is not particularly limited, and may be, for example, a multilayer film having a high refractive index film with a relatively high refractive index and a low refractive index film with a relatively low refractive index. The multilayer film may be configured by alternately providing high refractive index films and low refractive index films in this order. As the high refractive index film, for example, a film containing hafnium oxide as a main component may be used. As the low refractive index film, a film containing silicon oxide, aluminum oxide, zirconium oxide, tin oxide, silicon nitride, or the like as a main component may be used. In addition, the number of layers constituting the multilayer film may be, for example, 4 layers or more and 100 layers or less.

A film other than an anti-reflection film may be laminated on the second main surface 2b of the transparent substrate 2, so long as it does not impair the effects of the present invention. Also, a film other than the dielectric multilayer film 3 may be provided on the first main surface 2a of the transparent substrate 2, so long as it does not impair the effects of the present invention. In this case, a film may be provided between the transparent substrate 2 and the dielectric multilayer film 3, or a film may be provided on the dielectric multilayer film 3.

An example of a method for manufacturing the optical filter 1 is described in detail below.

(Method of Manufacturing Optical Filter)
A film-attached transparent substrate forming step;
First, a transparent substrate 2 is prepared. Next, a dielectric multilayer film 3 is formed on a first main surface 2a of the transparent substrate 2. The dielectric multilayer film 3 can be formed by alternately laminating a high refractive index film 4 and a low refractive index film 5 in this order on the first main surface 2a of the transparent substrate 2. The high refractive index film 4 and the low refractive index film 5 can each be formed by a sputtering method.

The temperature of the substrate when forming the high refractive index film 4 is preferably 300°C or less, and more preferably 270°C or less. In this case, in the obtained optical filter 1, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced. The lower limit of the substrate temperature when forming the high refractive index film 4 can be, for example, 20°C.

The high refractive index film 4 can be formed, for example, by using a target of the material that constitutes the high refractive index film 4, setting the flow rate of an inert gas such as argon gas as a carrier gas to 50 sccm to 500 sccm, and applying a power of 0.5 kW to 40 kW.

The low refractive index film 5 can be formed, for example, by using a target of the material that constitutes the low refractive index film 5, setting the flow rate of an inert gas such as argon gas as a carrier gas to 50 sccm to 500 sccm, and applying a power of 0.5 kW to 40 kW.

Heat treatment process;
Next, the obtained film-attached transparent substrate is heat-treated at a temperature of 500° C. or higher. This allows the optical filter 1 to be obtained. In particular, since the film-attached transparent substrate is heated at a temperature of 500° C. or higher, the content of cubic hafnium oxide crystals can be relatively increased. Therefore, in the obtained optical filter 1, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced.

The temperature of the heat treatment of the film-attached transparent substrate is preferably 500°C or higher, more preferably 550°C or higher, and preferably 800°C or lower, more preferably 750°C or lower. When the heat treatment temperature is within the above range, the maximum value of the spectral transmittance at wavelengths of 237nm to 280nm can be further reduced while the spectral transmittance at wavelengths of 220nm to 225nm can be further increased.

The time for the heat treatment of the film-attached transparent substrate is not particularly limited, but can be, for example, 10 minutes or more and 120 minutes or less.

In the present invention, it is preferable that the intensity of the diffraction peak due to the (-1,1,1) crystal plane derived from the monoclinic hafnium oxide crystal is small in the X-ray diffraction measurement of the film-attached transparent substrate before the heat treatment. It is preferable that the intensity of the diffraction peak due to the (-1,1,1) crystal plane derived from the monoclinic hafnium oxide crystal is at the microcrystalline level, and more preferably, the height of the peak intensity is within three times the height of the peak intensity of the amorphous halo. In this case, the heat treatment can further increase the peak area intensity Ic of the diffraction peak due to the (1,1,1) crystal plane derived from the cubic hafnium oxide crystal to the peak area intensity Im of the diffraction peak due to the (-1,1,1) crystal plane derived from the monoclinic hafnium oxide crystal. Therefore, in the obtained optical filter 1, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced.

In the present invention, the transmittance of ultraviolet light at wavelengths of 220 nm to 225 nm and the transmittance of ultraviolet light at wavelengths of 237 nm to 280 nm can be adjusted, for example, by the total number, film thickness, and material of the films constituting the dielectric multilayer film 3, and the heat treatment temperature of the film-coated transparent substrate. In particular, by adjusting the heat treatment temperature of the film-coated transparent substrate, the spectral transmittance of the resulting optical filter 1 at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced.

Second Embodiment
Fig. 2 is a schematic cross-sectional view showing an optical filter according to a second embodiment of the present invention. As shown in Fig. 2, in an optical filter 21, an outermost layer 26 of a dielectric multilayer film 23 is a high refractive index film 4 made of hafnium oxide. Other points are the same as those of the first embodiment.

The optical filter 21 also has a moisture content of 0.15 mm ^-1 or more in terms of β-OH value. Therefore, even when exposed to strong ultraviolet light, the ultraviolet light transmittance is unlikely to decrease. Therefore, the optical filter 21 has excellent reliability.

However, when using an excimer lamp or the like that emits ultraviolet light with a wavelength range of 220 nm to 225 nm, the irradiated light can cause deterioration of the device components and the generation of acidic gases. This gas can erode the film of the optical filter, causing the optical characteristics to change and making it impossible to meet the required characteristics.

In contrast, when the outermost layer 26 is made of hafnium oxide, as in the case of the optical filter 21, erosion by acidic gases can be further suppressed, and changes in optical properties can be further suppressed.

The thickness of the outermost layer 26 is preferably 1 nm or more, more preferably 2 nm or more, preferably 10 nm or less, and more preferably 7 nm or less. When the thickness of the outermost layer 26 is equal to or greater than the lower limit, erosion by acidic gases can be further suppressed, and changes in optical properties can be further suppressed. On the other hand, when the thickness of the outermost layer 26 is equal to or less than the upper limit, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced.

[Sterilization device]
Fig. 3 is a schematic diagram showing a sterilization device according to one embodiment of the present invention. As shown in Fig. 3, the sterilization device 31 includes a housing 32, a light source 33, and an optical filter 1. The light source 33 is disposed inside the housing 32. The light source 33 and the optical filter 1 are disposed to face each other. In the sterilization device 31, the emitted light emitted from the light source 33 is irradiated onto an object 34 to be sterilized via the optical filter 1.

As the light source 33, for example, an excimer lamp can be used. As the excimer lamp, it is preferable to use an excimer lamp that emits ultraviolet light with a wavelength in the range of 220 nm to 225 nm. As such an excimer lamp, for example, a KrCl excimer lamp can be used. The excimer lamp may also be a KrBr excimer lamp.

The sterilization device 31 of this embodiment uses the optical filter 1 described above, so even when strong ultraviolet light is irradiated, the ultraviolet light transmittance is unlikely to decrease, and ultraviolet sterilization can be performed on the sterilization target 34. In ultraviolet sterilization, ultraviolet light can be applied to the DNA in the cells of the organisms to be sterilized, such as bacteria, to selectively inactivate them.

The present invention will be described in more detail below based on specific examples. The present invention is not limited to the following examples, and can be modified as appropriate within the scope of the gist of the invention.

Example 1
First, a fused quartz glass substrate (manufactured by USTRON, product number "FLH311") was prepared as a transparent substrate. This fused quartz glass substrate was formed in a humidified state. Next, a dielectric multilayer film was formed by sputtering on one main surface of the prepared transparent substrate. Specifically, first, argon gas and oxygen gas were used as carrier gases to sputter a hafnium target, and a hafnium oxide film (HfO ₂ film) was formed on one main surface of the transparent substrate. At this time, the flow rates of argon gas and oxygen gas were each set to 100 sccm, and the target applied power (film formation power) was set to 4 kW. Next, argon gas and oxygen gas were used as carrier gases to sputter a silicon target, and a silicon oxide film (SiO ₂ film) was formed on the HfO ₂ film. At this time, the flow rates of argon gas and oxygen gas were set to 100 sccm, and the target applied power (film formation power) was set to 4 kW. By repeating this operation, a dielectric multilayer film having a total of 38 layers of films, in which _HfO2 films and _SiO2 films are alternately laminated one by one, was formed on one main surface of the transparent substrate, and a transparent substrate with a film was obtained. Note that the substrate temperature during film formation was room temperature (20°C). Next, the transparent substrate with the film was heat-treated at a temperature of 600°C for 60 minutes in an air atmosphere to produce an optical filter.

(Comparative Example 1)
An optical filter was produced in the same manner as in Example 1, except that the fused silica glass substrate was changed to one that had been molded in a non-humidified state.

[evaluation]
(β-OH value)
The moisture content in the optical filters obtained in Example 1 and Comparative Example 1 was calculated based on the β-OH value. The FT-IR was performed using a model number "Nicolet iS10" manufactured by Thermo Fisher Scientific K.K., with a measurement wave number of 4000 cm ^-1 to 400 cm ^-1 and 16 scans. The β-OH value was calculated from the obtained FT-IR spectrum according to the following formula (1).

β-OH=(1/t)log ₁₀ (T1/T2)...Equation (1)

(In formula (1), t is the thickness (mm) of the optical filter, T1 is the transmittance at a reference wave number of 3846 cm ⁻¹ (wavelength 2600 nm), and T2 is the minimum transmittance near a hydroxyl group absorption wave number of 3600 cm ⁻¹ (wavelength 2800 nm).)

(Transmittance reduction amount)
The optical filters obtained in Example 1 and Comparative Example 1 were irradiated with a KrCl excimer lamp for 1150 hours, and the difference in spectral transmittance at a wavelength of 222 nm before and after the irradiation was determined.

The spectral transmittance of the optical filters obtained in Example 1 and Comparative Example 1 was measured using a spectral transmittance meter (Hitachi High-Tech Science Corporation, product number "U4150"). Specifically, the incident angle was set to 0°, and the measurement wavelength was set to 190 nm to 400 nm.

The spectral transmittance at a wavelength of 222 nm was obtained before and after irradiation, and the decrease in transmittance was calculated from the difference between the spectral transmittance at a wavelength of 222 nm before and after irradiation.

The results are shown in Table 1 below.

As is clear from Table 1, the optical filter of Example 1, in which the moisture content in the optical filter is 0.15 mm ^-1 or more in terms of the β-OH value, shows a suppressed decrease in ultraviolet transmittance due to irradiation with strong ultraviolet light, compared to the optical filter of Comparative Example 1, in which the moisture content in the optical filter is less than 0.15 mm ^- 1 in terms of the β-OH value.

Reference Signs List 1, 21...optical filter 1a...principal surface 2...transparent substrate 2a...first principal surface 2b...second principal surface 3, 23...dielectric multilayer film 4...high refractive index film 5...low refractive index film 26...outermost layer 31...sterilization device 32...casing 33...light source 34...object to be sterilized

Claims (4)

A transparent substrate made of glass;
A dielectric multilayer film provided on the transparent substrate;
An optical filter comprising:
the dielectric multilayer film has a high refractive index film having a relatively high refractive index and a low refractive index film having a relatively low refractive index,
the high refractive index film is a film containing cubic hafnium oxide crystals,
The optical filter has a moisture content of 0.15 mm ⁻¹ or more in terms of a β-OH value. 2. The optical filter according to claim 1, wherein the amount of moisture in the optical filter is 0.80 mm ⁻¹ or less in terms of a β-OH value. 3. The optical filter according to claim 1, wherein the low refractive index film is a film containing silicon oxide. A sterilization apparatus for inactivating a microorganism to be treated, comprising:
A light source having an emitted light wavelength in a wavelength range of 190 nm to 230 nm;
An optical filter according to any one of claims 1 to 3 ;
A sterilization apparatus comprising:

Images