Ultraviolet irradiation device

Abstract

To provide an ultraviolet light irradiation device of which pathogen inactivation capacity is improved, while securing high safety to human beings and animals.SOLUTION: A ultraviolet light irradiation device includes a light source that emits ultraviolet light belonging to a wavelength band of 200 nm or more and less than 240 nm, and an optical filter on which the ultraviolet light is incident, wherein a transmission spectrum of the optical filter that is incident at an incident angle of 0 degrees has a first transmission band and a second transmission band that transmit 0 degree light, and a first restriction band that limits transmission of the 0 degree light, and the first transmission band is present within a wavelength band of 200 nm or more and less than 240 nm, the second transmission band exists within a wavelength band of more than 300 nm and less than 400 nm, and the first restriction band exists over the entire wavelength range of at least 240 nm or more and less than 300 nm, and the upper limit of the first restriction band is formed within a range of more than 300 nm and 380 nm or less.SELECTED DRAWING: Figure 9A

Description

[Technical Field]

[0001] This invention relates to an ultraviolet light irradiation device. [Background technology]

[0002] Ultraviolet light in the wavelength range of 200 nm to 280 nm (UVC band) is known to inactivate pathogens such as bacteria and viruses present in the environment and is used in germicidal lamps, etc. However, this ultraviolet light is also known to penetrate deep into the skin and damage cells within the skin. Furthermore, in recent years, research on the effects of ultraviolet light on humans has progressed, and it has been confirmed that ultraviolet light in the UVC band with wavelengths shorter than 240 nm is more easily absorbed by the skin surface or corneal epithelium as the wavelength becomes shorter, and the cells inside the skin are less affected, thus increasing safety. Therefore, ultraviolet light irradiation devices that actively irradiate the human body or the environment in which people are present with ultraviolet light in the wavelength band shorter than 240 nm have been put into practical use (see Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6908172 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In recent years, partly due to the COVID-19 pandemic, there has been a growing need to inactivate pathogens such as bacteria and viruses in the environment using ultraviolet (UV) light. Therefore, further utilization of devices that emit UV light in the 200nm to 240nm wavelength range is desired. On the other hand, UV light in the 240nm to 280nm wavelength range is relatively more harmful to the human body, so it is necessary to more appropriately suppress the emission of UV light in this range to prevent excessive exposure.

[0005] The present invention aims to provide an ultraviolet light irradiation device that improves the ability to inactivate pathogens while ensuring high safety for humans and animals. [Means for solving the problem]

[0006] One embodiment of the ultraviolet light irradiation device according to the present invention is: A light source that emits ultraviolet light belonging to the wavelength band between 200 nm and less than 240 nm, The optical filter, which includes a dielectric multilayer film, is positioned so that the ultraviolet light is incident upon it. The transmission spectrum of the optical filter, in which ultraviolet light is incident on the optical filter at an incident angle of 0 degrees, has a first transmission band and a second transmission band that transmit the 0-degree light, and a first limiting band that limits the transmission of the 0-degree light. The aforementioned first transmission band is located within a wavelength range of 200 nm to less than 240 nm. The aforementioned second transmission band is located within a wavelength range exceeding 300 nm and less than 400 nm. The first limiting band exists across the entire wavelength range of at least 240 nm to 300 nm, and the upper limit of the first limiting band is formed within the range of over 300 nm and up to 380 nm.

[0007] Ultraviolet light in the wavelength range of 200 nm to less than 240 nm has little effect on the human body, but when irradiating an environment where people are present with this ultraviolet light, it may be necessary to suppress the amount of ultraviolet light exposure. For example, ACGIH (American Conference of Governmental Industrial Hygienists) or JIS Z 8812 (Methods for Measuring Harmful Ultraviolet Radiation) stipulate that the amount of ultraviolet light exposure to a person per day (8 hours) should be below the Threshold Limit Value (TLV).

[0008] However, the TLV (Total Light Volume) defined for each wavelength may be revised as research into the effects of ultraviolet light on the human body progresses. For example, under the current ACGIH standards, the TLV for light with a wavelength of 222 nm is 22 mJ / cm² per day (8 hours). 2 It is believed that the TLV (Total Light Level) will be relaxed in the future as the safety of 222nm wavelength light for the human body becomes clearer.

[0009] When TLV is relaxed, the amount of ultraviolet light irradiated in the wavelength range of 200 nm to less than 240 nm can be increased to improve inactivation capabilities. On the other hand, ultraviolet light in the 240 nm to 280 nm range, which is relatively more harmful to the human body, will also increase. As will be explained in detail later, the above-mentioned ultraviolet light irradiation device can more effectively suppress ultraviolet light in the 240 nm to 280 nm range even when the amount of ultraviolet light irradiated in the wavelength range of 200 nm to less than 240 nm is increased.

[0010] The following section provides definitions of terms used in this specification, and then details the ultraviolet light irradiation device and its operation and effects.

[0011] In this specification, ultraviolet light belonging to the wavelength band of 200 nm to less than 240 nm emitted from a light source means that at least a portion of the emission spectrum emitted by the light source shows intensity in the wavelength band of 200 nm to less than 240 nm. It is not necessarily required that intensity be shown across the entire wavelength range of 200 nm to less than 240 nm.

[0012] Examples of light sources that emit ultraviolet light belonging to the wavelength band between 200 nm and less than 240 nm include KrCl excimer lamps, KrBr excimer lamps, and LEDs that emit light in which at least a portion of the emitted light exhibits intensity in the wavelength band between 220 nm and less than 240 nm.

[0013] Light exhibiting intensity in the wavelength range of 200 nm to less than 240 nm has the effect of inactivating pathogens and is light with low harmfulness to humans and animals. Therefore, ultraviolet light irradiation devices using light sources that emit such light can be installed in spaces where people frequently pass through or where people work for long periods of time. The wavelength range that is safe for humans and animals is preferably 200 nm to 237 nm, more preferably 200 nm to 235 nm, and even more preferably 200 nm to 230 nm. In this specification, light belonging to the wavelength range of 200 nm to less than 240 nm may be referred to as "target light".

[0014] In this specification, "pathogen" includes bacteria, fungi (molds), and viruses. "Inactivation" is a concept that encompasses killing pathogens or rendering them infective or toxic.

[0015] As described above, an optical filter containing a dielectric multilayer film is placed at the position where ultraviolet light emitted from a light source is incident. The characteristics of the optical filter can be evaluated by a transmission spectrum in which the transmitted wavelength is plotted on the horizontal axis and the relative intensity of the transmitted light is plotted on the vertical axis. As will be described in detail later, the transmission spectrum of an optical filter differs depending on the angle of incidence to the optical filter. Therefore, in this specification, the characteristics of the optical filter are evaluated by distinguishing between angles of incidence. In this specification, light incident on an optical filter at an angle of incidence θ degrees is expressed as "θ-degree light". θ is 0 degrees (0deg) or greater and less than 90 degrees (90deg).

[0016] The optical filter has a transmission spectrum of 0-degree light, in which ultraviolet light is incident on the optical filter at an incident angle of 0 degrees, which includes a first transmission band and a second transmission band that transmit 0-degree light, and a first limiting band that restricts the transmission of 0-degree light.

[0017] In this specification, the transmittance is obtained by measuring the spectral spectrum of the light beam incident on the optical filter at a predetermined incident angle and the spectral spectrum of the light beam exiting from the optical filter with a spectrophotometer, respectively, and calculating (light intensity exiting from the optical filter / light intensity incident on the optical filter) × 100 (%).

[0018] In this specification, when there is no special mention of the specific numerical value of the transmittance and it is simply indicated as the "first transmission band" and the "second transmission band", the transmittance of the optical filter in the "first transmission band" and the "second transmission band" is 15% or more. However, the transmittance in the first transmission band is preferably 30% or more, more preferably 50% or more, still more preferably 60% or more, still more preferably 70% or more, and still more preferably 80% or more. However, the transmittance in the second transmission band is preferably 20% or more, more preferably 25% or more, still more preferably 30% or more, still more preferably 35% or more, still more preferably 40% or more, still more preferably 45% or more, and still more preferably 50% or more. Also, the transmittance in the second transmission band is preferably 10% or more higher than the maximum transmittance in the first limiting band described later, more preferably 15% or more higher, and still more preferably 20% or more higher.

[0019] In this specification, when there is no mention of the specific numerical value of the transmittance of the ultraviolet light transmitted through the optical filter, the transmittance of the first limiting band that limits the transmission of the optical filter is less than 5%. However, the transmittance in the first limiting band is preferably limited to 4% or less, more preferably 3% or less, still more preferably 2% or less, and still more preferably 1% or less. In particular, when the proportion of harmful light emitted from the light source is large, it is desirable to adopt a smaller numerical value for the transmittance of the first limiting band.

[0020] The first transmission band will now be explained. The statement that the first transmission band exists within the wavelength range of 200 nm to less than 240 nm means that, in the transmission spectrum of the optical filter, the first transmission band exhibiting a transmittance of a predetermined value or higher (unless otherwise specified, a transmittance of 15% or higher) is included in at least a portion of the wavelength range of 200 nm to less than 240 nm. The first transmission band does not necessarily have to exist across the entire wavelength range of 200 nm to less than 240 nm.

[0021] Let's explain the first limiting band. The first limiting band exists at least across the entire wavelength range from 240 nm to 300 nm, which means that in the transmission spectrum of the optical filter, a transmittance below a predetermined value (less than 5% unless otherwise specified) exists throughout the entire wavelength range from 240 nm to 300 nm.

[0022] Of the light in the wavelength range between 240 nm and 300 nm, the light in the wavelength range between 240 nm and 280 nm is particularly prone to adverse effects on humans and animals (hereinafter sometimes referred to as "harmful light"). Harmful light is not light that is emitted intentionally, but rather light that is inevitably emitted due to the nature of the light source. Therefore, optical filters are used to limit the transmission of harmful light.

[0023] One of the distinguishing features of the aforementioned optical filter is that its first limiting band (for example, the wavelength band in which the transmittance is less than 5%) extends beyond the wavelength band of harmful light (240 nm to less than 280 nm) to 280 nm to 300 nm. As will be explained in detail later, by expanding the first limiting band in the transmission spectrum for 0-degree light to the entire wavelength range from 240 nm to 300 nm, harmful light incident on the optical filter at a wide angle can also be appropriately limited. As a result, even when the TLV is relaxed and the amount of ultraviolet light irradiation is increased, harmful light incident at a wide angle can be effectively limited.

[0024] One of the distinguishing features of the aforementioned optical filter is that its transmission spectrum of 0-degree light has a second transmission band. The second transmission band will now be explained. The presence of the second transmission band within a wavelength range between 300 nm and 400 nm means that, in the transmission spectrum of the optical filter, there is a portion within the wavelength range between 300 nm and 400 nm with a transmittance of a predetermined level or higher (15% or more unless otherwise specified). The second transmission band does not necessarily have to exist across the entire wavelength range between 300 nm and 400 nm.

[0025] This section explains the effects of having a second transmission band. To raise the upper limit of the wavelength band that restricts light transmission, it is effective to increase the thickness of the dielectric multilayer film that constitutes the optical filter. However, arbitrarily increasing the thickness of the dielectric multilayer film will lower the transmittance of the desired first transmission band, and thus attenuate the desired light as well. In addition, increasing the thickness increases the cost of forming the dielectric multilayer film.

[0026] If the second transmission band is located within the wavelength range of the transmission spectrum of 0-degree light, between 300 nm and 400 nm, the thickness of the dielectric multilayer film is relatively thin, which prevents a decrease in the transmittance of the first transmission band.

[0027] Light in the wavelength range between 300 nm and 400 nm is neither the target light defined herein nor harmful light; therefore, the transmission characteristics of optical filters for light in this wavelength range have not been considered conventionally. An optical filter having a second transmission band within the wavelength range of 300 nm to 400 nm in the transmission spectrum of 0-degree light is based on a design concept that is not an extension of conventional design concepts.

[0028] In the transmission spectrum of the optical filter at 0 degrees, an optical filter may be used in which the cut-off upper wavelength is located within a wavelength band of 310 nm or more and less than 380 nm. In this specification, the "cut-off upper wavelength" is determined from the transmittance curve of a transmission spectrum where the first axis is transmittance [%] and the second axis perpendicular to the first axis is wavelength [nm]. Specifically, in the wavelength band sandwiched between the first limiting band and the second transmission band, the cut-off upper wavelength is the wavelength at the intersection of the tangent line to the transmittance curve at the point where the transmission spectrum reaches the second transmission band (for example, transmittance of 15%) and a reference line parallel to the second axis that passes through transmittance of 0%. Exceptionally, if the wavelength at the intersection is within the first limiting band, the upper wavelength of the first limiting band shall be defined as the "cut-off upper wavelength". The cutoff upper wavelength may be set within the wavelength band of 310 nm to 370 nm, or within the wavelength band of 310 nm to 360 nm.

[0029] In the transmission spectrum of the optical filter at 0 degrees, the upper limit wavelength of the first limiting band is set within the range of 300 nm to 380 nm. Here, the upper limit wavelength of the first limiting band may be 301 nm or more, 303 nm or more, 305 nm or more, or 307 nm or more. The longer the wavelength of the upper limit wavelength of the first limiting band is set, the more effectively harmful light emission can be limited to light components of a wider angle.

[0030] In the transmission spectrum of the optical filter at 0 degrees, the first limiting band may further extend over the entire wavelength range from 300 nm to less than 310 nm, and the upper limit of the first limiting band may be formed within the range of 310 nm to 360 nm. When this configuration is provided, the first limiting band extends over the entire wavelength range between the lower limit wavelength of 240 nm or less and the upper limit wavelength formed within the range of 310 nm to 360 nm. Here, the upper limit wavelength of the first limiting band may be 313 nm or more, 315 nm or more, or 317 nm or more. The longer the upper limit wavelength of the first limiting band is set, the more appropriately the emission of harmful light can be limited to light components at a wider angle. In addition, the cut-off upper limit wavelength may be formed within the range of 320 nm to less than 370 nm.

[0031] In the transmission spectrum of the optical filter at 0 degrees, the first limiting band may further extend over the entire wavelength range from 310 nm to less than 320 nm. Furthermore, the cut-off upper wavelength may be formed within the range of 310 nm to less than 360 nm, or within the range of 320 nm to less than 350 nm.

[0032] The second transmission band may exist across the entire wavelength range from 380 nm to less than 400 nm. The second transmission band may further exist across the entire wavelength range from 370 nm to less than 400 nm. The second transmission band may further exist across the entire wavelength range from 360 nm to less than 400 nm. The second transmission band may further exist across the entire wavelength range from 350 nm to less than 400 nm.

[0033] The transmission spectrum of the optical filter at 0 degrees may further include a second limiting band that does not transmit 0-degree light, within a wavelength range of 200 nm to 210 nm. This allows for more appropriate restriction of ultraviolet light emission near 200 nm, which generates ozone in the atmosphere, and enables more precise suppression of ozone generation in the environment.

[0034] The transmission spectrum of the optical filter, when ultraviolet light is incident on the optical filter at an incident angle of 50 degrees, may have a third limiting band that limits the transmission of the 50-degree light across the entire wavelength range from 240 nm to less than 280 nm. This directly demonstrates that even when the TLV is relaxed and the amount of ultraviolet light irradiation is increased, harmful light incident at a wide angle of 50 degrees can be effectively limited.

[0035] The dielectric multilayer film includes a laminate in which high refractive index layers and low refractive index layers are alternately stacked, and the thickness of the laminate may be between 1.0 μm and 3.0 μm. In order to limit harmful light over a wide wavelength range in the transmission spectrum of the optical filter, it is desirable that the laminate has a total thickness of at least 1.0 μm. However, as the thickness increases, it becomes more difficult to transmit light belonging to the target wavelength band of 200 nm to less than 240 nm, so it is desirable that the total thickness of the laminate be 3.0 μm or less. Furthermore, the thickness of the laminate may be between 1.0 μm and 2.0 μm.

[0036] The aforementioned laminate is constructed by alternately stacking HfO2 layers and SiO2 layers. The total thickness of all HfO2 layers in the laminate may be 0.5 μm or more and less than 2.0 μm. In this dielectric multilayer film, HfO2 functions as a high refractive index layer, and SiO2 functions as a low refractive index layer. [Effects of the Invention]

[0037] We can provide an ultraviolet light irradiation device that improves the ability to inactivate pathogens while ensuring a high level of safety for humans and animals.

[0038] Providing ultraviolet light irradiation equipment aligns with United Nations Sustainable Development Goal (SDG) 3, "Ensure healthy lives and promote well-being for all at all ages," and makes a significant contribution to Target 3.3, "By 2030, eradicate AIDS, tuberculosis, malaria and neglected tropical diseases, and combat hepatitis, waterborne diseases and other infectious diseases." [Brief explanation of the drawing]

[0039] [Figure 1] This figure shows one embodiment of an ultraviolet light irradiation device. [Figure 2] Figure 1 shows the ultraviolet light irradiation device as viewed from the +Z side. [Figure 3] This is a cross-sectional view of the ultraviolet light irradiation device shown in Figure 1, viewed in the X direction. [Figure 4] This is a graph showing the emission spectrum of the light source in this embodiment. [Figure 5] This diagram shows the relationship between irradiation time and irradiation dose for both target light and harmful light. [Figure 6] This figure shows the intensity distribution of light incident on an optical filter at different incident angles. [Figure 7] This is a diagram illustrating the angle of incidence. [Figure 8] This diagram illustrates the propagation of light emitted from a point light source as a uniform beam in all directions. [Figure 9A] This is the transmission spectrum of the optical filter used in this embodiment. [Figure 9B] This is a transmission spectrum of an optical filter, used as an example. [Figure 10] This diagram illustrates a method for obtaining a transmission spectrum from an optical filter. [Modes for carrying out the invention]

[0040] The drawings are shown using the XYZ coordinate system as appropriate. The specification is described with reference to the XYZ coordinate system as appropriate. In this specification, when expressing a direction, positive and negative directions are distinguished, and are indicated with a sign such as "+X direction" and "-X direction". When expressing a direction without distinguishing between positive and negative directions, it is simply described as "X direction". That is, in this specification, when simply described as "X direction", both "+X direction" and "-X direction" are included. The same applies to the Y direction and Z direction.

[0041] [Overview of UV light irradiation device] An overview of one embodiment of the ultraviolet light irradiation device will be described with reference to Figures 1 to 3. Figure 1 is a schematic diagram showing the external appearance of one embodiment of the ultraviolet light irradiation device 1. Figure 2 is a view of the ultraviolet light irradiation device 1 of Figure 1 from the +Z side. Figure 3 is a cross-sectional view of the ultraviolet light irradiation device 1 of Figure 1 when viewed in the X direction.

[0042] The ultraviolet light irradiation device 1 of this embodiment comprises a housing 60, a light source 30 (see Figures 2 and 3) housed inside the housing 60, and a light extraction unit 20 that extracts the light emitted by the light source 30 to the outside of the housing 60.

[0043] As shown in Figure 2, the light source 30 of this embodiment is an excimer lamp comprising a plurality of discharge tubes 30a arranged in the X direction and a pair of electrodes 30b. Each discharge tube 30a extends in the Y direction. Each discharge tube 30a emits light when a voltage is applied between the electrodes (30b, 30b). The Z direction is perpendicular to the X and Y directions. The emitted light is extracted from the light extraction unit 20.

[0044] In the ultraviolet light irradiation device 1, the length of the discharge tube 30a of the light source 30 in the tube axis direction (Y direction) is 70 mm, the distance between the light source 30 and the optical filter 40 is 8 mm, and the size of the optical filter 40 is (X,Y) = (60 mm, 45 mm). Note that the size configurations described here are merely examples, and the individual sizes are arbitrary.

[0045] As shown in Figure 3, the optical axis Lc of the ultraviolet light L1 emitted from the ultraviolet light irradiation device 1 is indicated along with an arrow indicating the direction of emission. In this embodiment, the optical axis Lc is aligned with the Z-axis. An optical filter 40 is located in the light extraction unit 20. All light emitted from the ultraviolet light irradiation device 1 passes through the optical filter 40. Details of the optical filter 40 will be described later.

[0046] The excimer lamp used in this embodiment is a KrCl excimer lamp. The KrCl excimer lamp contains krypton (Kr) gas and chlorine (Cl) gas as the light-emitting gas G1 in the discharge tube 30a. Figure 4 is a graph showing the emission spectrum of the KrCl excimer lamp. The KrCl excimer lamp emits ultraviolet light L1, which shows the maximum peak in light intensity I(λ) at a wavelength of 222 nm, as shown in Figure 4. In the emission spectrum of Figure 4, the vertical axis shows the light intensity at each wavelength, with the light intensity at a wavelength of 222 nm set to 100 (%).

[0047] As shown in Figure 4, the light emitted by the KrCl excimer lamp also shows a small intensity in the wavelength range of harmful light (240 nm to less than 280 nm) that may adversely affect humans and animals. The emission spectrum in Figure 4 has a small maximum value m1 around 258 nm, and the light around this m1 is excited Cl * allies ( * This light is caused by a phenomenon called chlorine emission, where atoms (indicating an excited state) collide and emit light. In particular, when the concentration of Cl sealed in the discharge tube 30a is high, a large amount of this light is emitted.

[0048] However, as shown in Figure 4, the light intensity of harmful light is significantly lower than the light intensity of the target light (e.g., 222 nm). Therefore, when the overall amount of ultraviolet light irradiation is low, harmful light is not a problem as long as an optical filter that blocks the transmission of harmful light is used. However, optical filters do transmit a small amount of harmful light. The inventors have found that when the TLV is relaxed and the overall irradiation amount increases, depending on the operating conditions of the ultraviolet light irradiation device 1, the small amount of harmful light transmitted through the optical filter may become a problem.

[0049] [Reasons why harmful light is a problem] The reason why the trace amounts of harmful light transmitted through the optical filter 40 are a concern is explained below. The inventors considered increasing the emission intensity or actual irradiation time of the ultraviolet light irradiation device 1 in response to the relaxation of the TLV. However, research revealed that the following problems occur when the emission intensity or actual irradiation time is increased.

[0050] This problem will be explained with reference to Figure 5. Figure 5 is a graph showing the relationship between irradiation time ti (horizontal axis) and daily irradiation dose D (vertical axis) for target light L10 and harmful light L20. Irradiation time ti represents the total time (cumulative time) of irradiation throughout the day. The ultraviolet light irradiation device 1 may operate not only by continuously irradiating ultraviolet light throughout the day, but also by intermittently alternating between irradiation and non-irradiation. The longer the irradiation time ti (unit: sec), the higher the irradiation dose D (unit: mJ / cm²). 2 ) will become larger.

[0051] Conventionally, the TLV of the target light L10 was V11 (mJ / cm²). 2 ) and the TLV of harmful light L20 is V2 (mJ / cm 2 Let's assume that it was previously defined as follows: Conventionally, the irradiation dose of the target light L10 was V11 (mJ / cm²). 2 The irradiation limit time was set to t1 (sec) so as not to exceed ). In other words, only region A11 was being focused on. The irradiation dose of harmful light L20 was V2 (mJ / cm²). 2 Since it falls far short of that, if we only focused on region A11, there was no need to focus on region A21.

[0052] Here, when the TLV of the target light is relaxed, a scenario is considered where the reference value of the irradiation dose D is newly set higher by ΔV1 from the conventional V11 (mJ / cm 2 ) to V12 (mJ / cm 2 ). When considering extending the irradiation time to t2 (sec) in response to the relaxation of the TLV, it was found that the irradiation dose of the harmful light L20, which did not need to be considered conventionally, approaches V2 (mJ / cm 2 ), which is the TLV of the harmful light L20 (see region A22).

[0053] Then, in order to set the irradiation time according to the relaxation of the TLV, not only does the irradiation dose of the target light L10 not exceed V12 (mJ / cm 2 ) (see region A21), but it is also necessary to ensure that the irradiation dose of the harmful light L20 does not exceed V2 (mJ / cm 2 ), which is the TLV of the harmful light (see region A22). Therefore, when the TLV is relaxed and the irradiation dose increases, there is a risk that the harmful light transmitted through the optical filter will become a problem.

[0054] [Optical Filter Considering Light Incident at a Wide Angle] Due to the above circumstances, the inventor of the present invention studied an ultraviolet light irradiation device that can further suppress the harmful light transmitted through the optical filter. As a result of intensive research, the inventor found that an optical filter through which light incident at a wide angle on the optical filter is difficult to transmit should be designed or selected. The reason is explained below.

[0055] FIG. 6 shows the relative value (relative intensity) of the light intensity for each angular component of the ultraviolet light irradiated on the optical filter 40 in the ultraviolet light irradiation device 1. This figure was derived by calculation from the light distribution of the ultraviolet light emitted from the ultraviolet light irradiation device 1. The horizontal axis represents the incident angle on the optical filter 40, and the vertical axis represents the relative intensity of the ultraviolet light. The incident angle is the angle θ formed between the normal line N1 of the incident surface 40s of the optical filter 40 and the light ray L3 incident on the optical filter 40, as shown in FIG. 7.

[0056] Figure 6 shows that most light rays are present in the range of incident angles from 10 to 60 degrees, particularly in the range of 20 to 50 degrees. In particular, the light ray components incident on the optical filter 40 at incident angles of 30 to 40 degrees are much more numerous than the light ray components incident on the optical filter 40 at an incident angle of 0 degrees.

[0057] Using Figure 8, we will explain why the light ray component incident on the optical filter 40 at an incident angle of 30 to 40 degrees is greater than the light ray component incident on the optical filter 40 at an incident angle of 0 degrees. Figure 8 is a diagram illustrating the propagation of light emitted from a point light source Q1 as a uniform luminous beam in all directions. As shown in Figure 8, we assume that light is emitted from the point light source Q1 as a uniform luminous beam in all directions, and that a portion of it illuminates a plane Px.

[0058] Then, as shown in Figure 8, the region on the plane Px where the light beam emitted from the point light source Q1 is incident at an incident angle θ of 0 degrees is defined as P0, and the region where it is incident at an incident angle θ of 30 degrees is defined as P30. As can be seen from Figure 8, on the plane Px, region P0 is just one point, while region P30 is a circular region centered on region P0.

[0059] Furthermore, as mentioned above, if light is emitted from a point light source Q1 in a uniform beam in all directions, it can be seen that the total beam of light incident on the entire annular region at position P30 is greater than the beam of light incident on only one point at position P0. In other words, assuming the light source is a point light source, the total amount of beam of light incident on a given surface increases as the angle of incidence θ increases from 0 degrees. This means that the relative intensity of each angular component of the beam is greater at position P30 than at position P0.

[0060] The light source 30 mounted in the ultraviolet light irradiation device 1 of this embodiment can be considered equivalent to a system in which point light sources are arranged along the axial direction of the discharge tube 30a. In this case, considering the case of each of the arranged point light sources, the light beam incident on the optical filter 40 is minimum when the incident angle θ is 0 degrees, and the total amount of light beam gradually increases as the angle increases from 0 degrees.

[0061] The intensity of ultraviolet light incident on the optical filter 40 is proportional to the amount of light flux. The amount of light flux incident on the optical filter 40 increases as the incident angle θ increases from 0 degrees. When the incident angle θ is in a certain large range, the amount of light flux that cannot be incident on the optical filter 40 increases, and therefore the amount of ultraviolet light flux decreases. The incident angle θ at which the amount of incident light flux begins to decrease is adjusted by the distance between the light source 30 and the optical filter 40, the size of the discharge tube 30a of the light source 30, the area on which the optical filter 40 is formed, etc.

[0062] As shown in Figure 6, the relative intensity for each angular component is not affected by wavelength. For example, the same trend is observed whether it is target light or harmful light. Based on this finding, the inventors have investigated optical filters that can block the transmission of light rays incident at a wide range of incident angles.

[0063] The features of the optical filter 40 will be described with reference to Figures 9A and 9B. Figure 9A shows the transmission spectrum of the optical filter 40 in this embodiment. Figure 9B shows the transmission spectrum of the optical filter 90, which is a reference example. Both Figures 9A and 9B are optical filters that include a dielectric multilayer film. Details of the dielectric multilayer film will be described later.

[0064] The transmission spectra shown in Figures 9A and 9B are as follows: "0deg" is the transmission spectrum of 0-degree light incident at an incident angle of 0 degrees to the optical filter (40,90). Similarly, "20deg" is the transmission spectrum of 20-degree light, "30deg" is the transmission spectrum of 30-degree light, "40deg" is the transmission spectrum of 40-degree light, "50deg" is the transmission spectrum of 50-degree light, and "60deg" is the transmission spectrum of 60-degree light.

[0065] As shown in Figures 9A and 9B, the transmission spectrum tends to shift to shorter wavelengths as the angle of incidence increases. This is sometimes called "blue shift." The blue shift is thought to be due to a difference in optical path length caused by the shift between the position of light reflected by the multilayer film and the position of light traveling back and forth within the multilayer film, as the angle of incidence increases when light enters a dielectric multilayer film.

[0066] First, the transmission spectrum of the optical filter 90 shown in Figure 9B, which is a reference example, will be explained. Based on the transmission spectrum of 0-degree light, it has a first transmission band TB1 that transmits the target light (here, transmittance of 15% or more), a first limiting band RB1 that limits the transmission of harmful light (here, transmittance of less than 5%), and a second transmission band TB2 (here, transmittance of 15% or more). Since the first transmission band is located in the wavelength range of 200 nm to less than 240 nm, it can be seen that it transmits the target light. Since the first limiting band RB1 is located across the entire wavelength range of harmful light, from 240 nm to less than 280 nm, it can sufficiently block the transmission of 0-degree light.

[0067] However, the transmission spectra of 30-degree, 40-degree, 50-degree, and 60-degree light show a transmittance of 5% or more in the wavelength band of harmful light, which is between 240 nm and 280 nm. This indicates that the optical filter 90 easily transmits harmful light incident on it at a wide angle (30 to 60 degrees). As shown in Figure 6, a large amount of light is incident on the optical filter 90 at a wide angle, especially between 30 and 40 degrees. Therefore, even if the TLV is relaxed and the irradiation dose is increased, when using the optical filter 90, a large amount of harmful light incident at a wide angle is transmitted through the optical filter 90, and the increase in irradiation dose is limited by the TLV of the harmful light.

[0068] Furthermore, looking at Figure 9B, we can see that the first limiting band RB1 does not satisfy the requirement of "existing across the entire wavelength range from 240 nm to less than 300 nm" because the transmittance of 0-degree light in the first limiting band (280 nm to less than 300 nm) is not suppressed to less than 5%. Considering the fact that the transmission spectrum tends to shift to shorter wavelengths as the incident angle increases, in the transmission spectrum of 0-degree light, the first limiting band must be extended not only to the wavelength range of harmful light (240 nm to less than 280 nm) but also to longer wavelengths in order to block harmful light incident on the optical filter 90 at a high angle.

[0069] Next, the transmission spectrum of the optical filter 40 of this embodiment, shown in Figure 9A, will be described. The transmission spectrum has a first transmission band TB1 that transmits the target light (here, transmittance of 15% or more), a first limiting band RB1 that limits the transmission of harmful light (here, transmittance of less than 5%), and a second transmission band TB2 (here, transmittance of 15% or more). Since the first transmission band is located in the wavelength band of 200 nm to less than 240 nm, it can be seen that it transmits the target light. Since the first limiting band RB1 is located across the entire wavelength range of harmful light, from 240 nm to less than 280 nm, it can sufficiently block the transmission of 0-degree light.

[0070] Furthermore, unlike Figure 9B, the optical filter 40 in Figure 9A can limit the transmission of light in the harmful light wavelength range of 240 nm to less than 280 nm in the transmission spectra of 30-degree, 40-degree, 50-degree, and 60-degree light. The optical filter 40 in Figure 9B is less permeable to harmful light incident at wide angles (30 to 60 degrees), so even if the TLV is relaxed and the amount of ultraviolet light irradiation is increased, harmful light incident at wide angles can be effectively limited. Therefore, it is not necessary to set the irradiation amount based on the TLV of harmful light, and the irradiation amount can be set considering only the TLV of the target light.

[0071] As can be seen in Figure 9A, in the transmission spectrum of 0-degree light from optical filter 40, which does not transmit harmful light incident at a wide angle, the first limiting band RB1 exists across the entire wavelength range from 240 nm to less than 320 nm. Considering the fact that the transmission spectrum tends to shift to shorter wavelengths as the incident angle increases, it can be said that the transmission of wide-angle light is prevented precisely because the first limiting band in the transmission spectrum of 0-degree light is extended to longer wavelengths than the wavelength range of harmful light.

[0072] In the transmission spectrum of 0-degree light, if the only goal is to extend the first limiting band to wavelengths longer than the wavelength band of harmful light, then, for example, simply increasing the thickness of the dielectric multilayer film is sufficient. However, as mentioned above, in order to maintain the transmittance of the first transmission band necessary for transmitting the target light and to suppress the formation cost of the dielectric multilayer film, there is an upper limit to the thickness of the dielectric multilayer film.

[0073] In such optical filters, where the dielectric layer film thickness is not excessive, a second transmission wavelength band appears on the longer wavelength side of the first limiting band in the transmission spectrum of 0-degree light. That is, an optical filter 40 having a second transmission band TB2 located in the wavelength band of 320 nm or more on the longer wavelength side of the first limiting band in the transmission spectrum of 0-degree light can maintain the transmittance of the first transmission band necessary for transmitting the target light and suppress the formation cost of the dielectric multilayer film.

[0074] According to the inventor's diligent research, when the light intensity of the target light (light with a wavelength of 222 nm; the same applies hereinafter) is set to 1 when no optical filter is placed, the light intensity of the target light in an optical filter in which the first limiting band is limited to the wavelength band of harmful light (240 nm to less than 280 nm) (not extended) is generally in the range of 0.80 to 0.90, although this also depends on the quality of the dielectric multilayer film deposition.

[0075] Furthermore, an optical filter with an extended first limiting band from 240 nm to less than 320 nm requires only a slight increase in the total thickness of the film compared to an optical filter without an extended first limiting band. Therefore, the light intensity of the target light in the extended optical filter is about the same as, or only slightly lower than, the light intensity of the target light in the unextended optical filter. In other words, even if the upper limit wavelength of the first limiting band of the optical filter is extended to less than 320 nm, or even less than 330 nm, the light intensity of the target light can easily be maintained at a high level. Thus, an optical filter with an extended first limiting band from 240 nm to less than 320 nm is effective because it can suppress the transmission of light incident at a wide angle while suppressing the decrease in the light intensity of the target light.

[0076] In contrast, with an optical filter in which the first limiting band is extended from 240 nm to 400 nm, the light intensity of the target light tends to decrease, for example, to 0.6 to 0.75 (with the light intensity of the target light being 1). In other words, when the first limiting band is extended from 240 nm to less than 400 nm, the amount of decrease in the light intensity of the target light decreases by 0.10 to 0.15 (i.e., 10 to 15%). Because the amount of decrease in the light intensity of the target light is too large, it is difficult to achieve the objective of improving the irradiation dose. Therefore, it is effective for the second transmission band to exist in a wavelength range between 300 nm and less than 400 nm. In particular, if the second transmission band exists from a shorter wavelength side in the range between 300 nm and less than 400 nm, so as not to extend the first limiting band too much, the amount of decrease in the light intensity of the target light can be further suppressed.

[0077] Shifting our focus to the cut-off upper wavelength C1 appearing in the transmission spectrum of 0-degree light, in Figure 9B, the cut-off upper wavelength C1 is below 310 nm, whereas in Figure 9A, the cut-off upper wavelength C1 is within the wavelength band of 320 nm to less than 350 nm. The optical filter 40 in Figure 9A can be distinguished from the optical filter 90 in Figure 9B even when using the cut-off upper wavelength C1.

[0078] According to the inventors' diligent research, it has been found that the amount by which the transmission spectrum shifts to the shorter wavelength side as the incident angle increases is approximately 0.6 to 0.8 nm (nm / deg). In other words, for every 1 degree increase in the incident angle, the transmission spectrum at a particular incident angle shifts to the shorter wavelength side by 0.6 to 0.8 nm.

[0079] Considering the finding from Figure 6 that the largest number of light components enter the optical filter 40 at an incident angle of 30 to 40 degrees, it is desirable that the optical filter 40 be an optical filter that takes into account light with an incident angle of 40 degrees or less. In an optical filter that takes into account light with an incident angle of 40 degrees or less, the first limiting band in the transmission spectrum of 0-degree light exists across the entire wavelength range from 240 nm to 300 nm, and the wavelength that serves as the upper limit of the first limiting band in the transmission spectrum of 0-degree light is formed in the range from 300 nm to 380 nm. Furthermore, the second transmission band exists within the wavelength range from 300 nm to less than 400 nm, which is the longer wavelength side of the first limiting band.

[0080] The first limiting band may further extend across the entire wavelength range from 300 nm to less than 310 nm, and the upper limit of the first limiting band may be formed within the range of 310 nm to 360 nm. Alternatively, the first limiting band may further extend across the entire wavelength range from 310 nm to less than 320 nm.

[0081] In addition to considering light with an incident angle of 40 degrees or less, in order to prevent the transmission of even wider-angle light, it may be considered to use optical filters that consider light with an incident angle of 50 degrees or less, and also to use optical filters that consider light with an incident angle of 60 degrees or less. For optical filters that consider light with an incident angle of 60 degrees or less, the first limiting band in the transmission spectrum of 0-degree light is present across the entire wavelength range from 240 nm to less than 330 nm. For example, an optical filter can be used in which the upper limit wavelength of the first limiting band is formed within the range of 330 nm to 360 nm. The second transmission band is then present within the wavelength range from the upper limit wavelength of the first limiting band to less than 400 nm.

[0082] Furthermore, the optical filter 40 having the transmission spectrum shown in Figure 9A used in this embodiment restricts the transmission of ultraviolet light belonging to the wavelength band between 200 nm and 210 nm compared to the optical filter 90 shown in Figure 9B, which is a reference example. For example, in 0-degree light, there is a wavelength band between 200 nm and 210 nm in which the transmittance of ultraviolet light transmitted through the optical filter 40 is less than 5%. This wavelength band is called the second limiting band RB2. The second limiting band RB2 makes it possible to more appropriately restrict the emission of ultraviolet light near 200 nm, which generates ozone in the atmosphere, and to suppress ozone generation in the environment with higher precision. This also contributes to preventing ozone degradation of surrounding components.

[0083] The above-mentioned effect of the second limiting band RB2 is obtained by limiting ultraviolet light near 200 nm. The second limiting band RB2 may, for example, limit the entire wavelength band from 200 nm to 202 nm, limit the entire wavelength band from 200 nm to 205 nm, limit the entire wavelength band from 200 nm to 207 nm, or limit the entire wavelength band from 200 nm to 210 nm.

[0084] The transmittance in the second limiting band RB2 is exemplified as being limited to 5% or less. However, it is preferable that the transmittance in the second limiting band RB2 be limited to 4% or less, more preferably to 3% or less, more preferably to 2% or less, and even more preferably to 1% or less.

[0085] Furthermore, in the optical filter applied to the present invention, it is preferable that the wavelength band between the first limiting band RB1 and the second transmission band TB2 in the transmission spectrum of 0-degree light is narrow. In other words, it is preferable to achieve a cut wavelength obtained from the intersection with a tangent with a steeper slope to the transmittance curve. This makes the boundary between the first limiting band RB1 and the second transmission band TB2 clearer, and allows for a clearer definition of the bandwidth of the first limiting band RB1 and the bandwidth of the transmission band. Specifically, the wavelength width between the first limiting band, where the transmittance is less than 5%, and the second transmission band, where the transmittance is 15% or more, is preferably 10 nm or less, and more preferably 5 nm or less. Narrowing the wavelength band between the limiting band and the transmission band, not limited to the area between the first limiting band RB1 and the second transmission band TB2, results in a more suitable characteristic for providing a limiting band and a transmission band with high performance in a desired wavelength range.

[0086] [How to determine the transmission spectrum] Figure 10 illustrates an example of a method for obtaining a transmission spectrum from an optical filter 40. The optical filter 40 is removed from the ultraviolet light irradiation device 1 and attached to an experimental system equipped with a light source 30 and a spectrophotometer 50. As shown in Figure 10, the optical filter 40 is tilted and positioned so that a light ray from the center Q2 of the light source 30 toward the incident surface of the optical filter 40 obtains a predetermined incident angle θ with respect to the normal N1 of the optical filter 40. Directional light L2 is incident on the optical filter 40 from the light source 30. The light intensity of the light transmitted through the optical filter 40 is measured with the spectrophotometer 50. By dividing the measured light intensity by the light intensity of the emitted light without the optical filter, the transmission spectrum of the optical filter 40 at a predetermined incident angle θ is obtained. Furthermore, by measuring while changing the incident angle θ, transmission spectra for each incident angle can be obtained.

[0087] [Structure of optical filters] The optical filter 40 is composed of a dielectric multilayer film formed on a base material. The dielectric multilayer film is composed of a laminate in which high refractive index layers and low refractive index layers are alternately stacked. In this embodiment, a laminate in which HfO2 layers and SiO2 layers are alternately stacked is used for the dielectric multilayer film of the optical filter 40. The laminate may also be, for example, one in which SiO2 layers and Al2O3 layers are alternately stacked. A dielectric multilayer film layer in which HfO2 layers and SiO2 layers are alternately stacked can reduce the number of layers required to obtain the same wavelength selective characteristics as a dielectric multilayer film layer in which SiO2 layers and Al2O3 layers are alternately stacked, and thus can increase the transmittance of selected ultraviolet light. Other materials such as TiO2 and ZrO2 can also be used as the dielectric multilayer film.

[0088] The matrix material used to form the dielectric multilayer film is composed of a material capable of transmitting the target light. Specific materials for the matrix material include, for example, ceramic materials such as quartz glass, borosilicate glass, sapphire, magnesium fluoride, calcium fluoride, lithium fluoride, and barium fluoride, as well as resin materials such as silicon resin and fluororesin.

[0089] As mentioned above, if the dielectric multilayer film is too thick, the transmittance in the first transmission region decreases, making it difficult for the target light to pass through the dielectric multilayer film. If the film is too thin, harmful light (especially light rays incident on the optical filter at a wide angle) will be transmitted. Considering these circumstances, the dielectric multilayer film laminate generally has a film thickness of 1.0 μm to 3.0 μm, and more preferably between 1.0 μm and 2.0 μm. When the film thickness of the laminate is within this range, it is possible to maintain the transmittance in the first transmission region for transmitting the target light while easily blocking harmful light (especially light rays incident on the optical filter at a wide angle).

[0090] The transmission spectral characteristics of an optical filter vary not only by the total thickness of the dielectric multilayer laminate, but also by the combination of materials of the dielectric multilayer, the total thickness of each material, the number of layers, and the surface roughness of each film constituting the dielectric multilayer. Therefore, for example, in a laminate in which HfO2 layers and SiO2 layers are alternately stacked, it may be specified that the total thickness of all HfO2 layers is 0.5 μm or more and less than 2 μm. If the total thickness of the HfO2 layers is 0.5 μm or more, a sufficient effect of blocking harmful light can be obtained. On the other hand, if the total thickness of the HfO2 layers is 2 μm or more, the transmittance of the target light may be limited. Therefore, it is desirable that the total thickness of the HfO2 layers be less than 2 μm. In this way, the specified optical filter can block harmful light (especially light rays incident on the optical filter at a wide angle) while maintaining the transmittance of the first transmission band for transmitting the target light.

[0091] This concludes the description of one embodiment of an ultraviolet light irradiation device. The present invention is not limited in any way to the above-described embodiment, and various modifications or improvements can be made to the above embodiment without departing from the spirit of the present invention.

[0092] In this embodiment, a KrCl excimer lamp is used as the light source 30, but it is not limited to this. An excimer lamp containing other gases (for example, an excimer lamp containing Kr gas and Br gas that exhibits maximum intensity around 207 nm) may be used as the light source 30. Alternatively, a solid-state light source such as an LED may be used as the light source 30. The present invention is valid even when an excimer lamp containing other gases or a solid-state light source such as an LED is used.

[0093] For example, the light source 30 can be any light source that emits ultraviolet light whose main emission wavelength is in the range of 200 nm to less than 240 nm. The light source 30 is not limited to an excimer lamp, and a solid light source such as an LED may be used as the light source 30. For example, AlGaN-based LEDs or MgZnO-based LEDs having a main emission wavelength of less than 240 nm can be used as the light source 30. Furthermore, when a coherent light source is used as the light source 30, a light source that emits coherent ultraviolet light from a gas laser or solid laser element may be used, or a light source that uses a wavelength conversion element to generate new coherent light of a different wavelength using light emitted from a gas laser or solid laser element may be used. As a wavelength conversion element, for example, a nonlinear optical crystal that multiplies the frequency of light emitted from a laser element to generate high-order high frequencies such as second harmonics (SHG) and third-order high frequencies (THG) can be used. Furthermore, the light source 30 may be a light source that utilizes a phosphor that emits ultraviolet light whose main emission wavelength is in the range of 200 nm or more and less than 240 nm. Here, "main emission wavelength" refers to the wavelength λi in the wavelength range Z(λi) that shows an integrated intensity of 40% or more of the total integrated intensity in the emission spectrum, when a wavelength range Z(λ) of ±10 nm for a certain wavelength λ is defined on the emission spectrum of the light source 30. [Explanation of Symbols]

[0094] 1: Ultraviolet light irradiation device 20: Light extraction section 30:Light source 30a: Discharge tube 30b: Electrode 40: Optical filter 40s:Incidence surface 50: Spectrophotometer 60: Enclosure 90: Optical filter

Claims

1. A light source that emits ultraviolet light belonging to the wavelength band of 200 nm to less than 240 nm, The optical filter, which includes a dielectric multilayer film, is positioned so that the ultraviolet light is incident upon it. The transmission spectrum of the optical filter, in which ultraviolet light is incident on the optical filter at an incident angle of 0 degrees, has a first transmission band and a second transmission band that transmit the 0-degree light, and a first limiting band that limits the transmission of the 0-degree light. The aforementioned first transmission band has a transmittance of 15% or more and is located within a wavelength band of 200 nm or more and less than 240 nm. The aforementioned second transmission band has a transmittance of 15% or more and is located within a wavelength band exceeding 300 nm and less than 400 nm. An ultraviolet light irradiation device characterized in that the first limiting band has a transmittance of less than 5% and exists over the entire wavelength range of at least 240 nm to 300 nm, and the upper limit of the first limiting band is formed within the range of more than 300 nm and 380 nm or less.

2. The ultraviolet light irradiation apparatus according to claim 1, characterized in that the first limiting band further extends over the entire wavelength range from 300 nm to less than 310 nm, and the upper limit of the first limiting band is formed within the range of 310 nm to 360 nm.

3. The ultraviolet light irradiation apparatus according to claim 2, characterized in that the first limiting band further extends over the entire wavelength range of 310 nm to less than 320 nm.

4. The ultraviolet light irradiation apparatus according to claim 1, characterized in that the second transmission band exists over the entire wavelength range of 380 nm to less than 400 nm.

5. The ultraviolet light irradiation apparatus according to claim 4, characterized in that the second transmission band further extends over the entire wavelength range of 360 nm to less than 380 nm.

6. The ultraviolet light irradiation apparatus according to claim 5, characterized in that the second transmission band further extends over the entire wavelength range of 340 nm to less than 360 nm.

7. The ultraviolet light irradiation apparatus according to any one of claims 1 to 6, characterized in that the transmission spectrum of the 0-degree light further has a second limiting band that limits the transmission of the 0-degree light in a wavelength band of 200 nm to 210 nm.

8. The ultraviolet light irradiation device according to any one of claims 1 to 6, characterized in that the transmission spectrum of the optical filter, when the ultraviolet light is incident on the optical filter at an incident angle of 50 degrees, has a third limiting band that limits the transmission of the 50-degree light, which is present across the entire wavelength range of 240 nm to less than 280 nm.

9. The dielectric multilayer film includes a laminate in which high refractive index layers and low refractive index layers are alternately stacked, The ultraviolet light irradiation apparatus according to any one of claims 1 to 6, characterized in that the laminate has a film thickness of 1.0 μm or more and 3.0 μm or less.

10. The ultraviolet light irradiation apparatus according to claim 9, characterized in that the laminate has a film thickness of 1.0 μm or more and 2.0 μm or less.

11. The aforementioned laminate is HfO ２ Layer and SiO ２ The layers are stacked alternately, All HfO contained in the aforementioned laminate ２ The ultraviolet light irradiation apparatus according to claim 9, characterized in that the total thickness of the layers is 0.5 μm or more and less than 2.0 μm.

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