Bacterial static method

Abstract

To provide a bacteriostatic method that suppresses the growth of bacteria while suppressing the effects on the human body.SOLUTION: Provided is a bacteriostatic method, which is a bacteriostatic method that suppresses the growth of bacteria within the target region, and includes step (a) in which the target area is irradiated with ultraviolet ray with a main peak wavelength of 200 nm or more and 230 nm or less at an average illuminance of DMax (μW / cm2) or less as defined by the following formula (1). DMax=9391.1×exp(-0.043λ) --- (1). Here, in formula (1), λ is the main peak wavelength (nm).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bacteriostatic method, and more particularly to a bacteriostatic method utilizing ultraviolet light. [Background technology]

[0002] Conventionally, a sterilization method using ultraviolet light is known, as described in Patent Document 1 below. According to Patent Document 1 below, the ultraviolet light has an intensity of 0.008 to 0.17 mW / cm 2 (8~170μW / cm 2 It is described that by irradiating ultraviolet light of 1000 kJ / cm², E. coli and mold can be killed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-136113 Summary of the Invention [Problem to be solved by the invention]

[0004] It is known that DNA exhibits the highest absorption characteristics around a wavelength of 260 nm. Low-pressure mercury lamps, on the other hand, exhibit a high emission spectrum around a wavelength of 254 nm. Therefore, low-pressure mercury lamps are commonly used as light sources for sterilization using ultraviolet light.

[0005] Although Patent Document 1 does not specify wavelength in the strict sense, it is considered that a low-pressure mercury lamp is used as the light source, considering that it relates to sterilization technology, that it is simply specified as an "ultraviolet lamp" without any particular explanation, and that the experimental results are based on this.

[0006] However, light with a wavelength of around 254 nm may have adverse effects when irradiated onto the human body. In other words, the sterilization method described in Patent Document 1 can only be used when there are absolutely no people in the area to be sterilized. Therefore, to prevent any accidents, its use is limited to specific environments where people with specialized knowledge are present.

[0007] In view of the above problems, an object of the present invention is to provide a bacteriostatic method that suppresses bacterial growth while minimizing the effects on the human body. [Means for solving the problem]

[0008] There is a demand for inhibiting the growth of bacteria in places where mold and other bacteria are likely to grow, such as bathrooms, toilets, washrooms, kitchens, and air conditioner filters. There is also a demand in hospitals and other facilities to inhibit the growth of bacteria in order to improve the ability to prevent hospital-acquired infections.

[0009] When suppressing bacterial growth, it would certainly be desirable to completely eliminate any existing bacteria, i.e., to sterilize them. However, even if a "sterilizing" state cannot be achieved, if a so-called "bacteriostatic" state in which bacterial growth is suppressed can be achieved, there are significant benefits, such as easier cleaning and reduced frequency of cleaning.

[0010] The present invention provides a bacteriostatic method for inhibiting bacterial growth in a target area, comprising: Ultraviolet rays with a main peak wavelength of 200 nm or more and 230 nm or less are defined as D defined by the following formula (1): Max (μW / cm 2 The method is characterized by including a step (a) of irradiating the target area with an average illuminance of not more than 100 nm. D Max = 9391.1 × exp(-0.043λ)···(1) In the formula (1), λ is the main peak wavelength (nm).

[0011] Even if ultraviolet rays with a main peak wavelength between 200 nm and 230 nm are irradiated onto human skin, they are absorbed by the stratum corneum and do not penetrate further inward (toward the basal layer). Because the keratinocytes contained in the stratum corneum are dead cells, there is almost no risk of them being absorbed by living cells in the spinous layer, granular layer, dermis, etc., causing DNA damage, as occurs when ultraviolet rays with a wavelength of 254 nm are irradiated.

[0012] According to the above method, a bacteriostatic effect is achieved by irradiating ultraviolet light with a wavelength that has a lower impact on the human body than the wavelength band of ultraviolet light emitted from a low-pressure mercury lamp at an irradiance that is significantly lower than the irradiance used in conventional sterilization methods. This suppresses the growth of bacteria in the target area while minimizing the impact on the human body. This point will be described later in the "Mode for Carrying Out the Invention" section.

[0013] In this specification, the term "fungi" is a concept that encompasses bacteria and mold (fungi).

[0014] An excimer lamp filled with a light-emitting gas containing Kr and Cl can be used as a light source for this ultraviolet light. In this case, the main peak wavelength of the ultraviolet light emitted from the excimer lamp is around 222 nm.

[0015] In the step (a), the ultraviolet light is irradiated at a density of 1 μW / cm 2 The step of irradiating the target area with the following illuminance may be adopted.

[0016] the bacterium is Staphylococcus aureus, The step (a) is 0.4 μW / cm 2 The step may be a step of irradiating the target area with the ultraviolet light at the above illuminance.

[0017] the fungus is a mold, The step (a) is 0.29 μW / cm 2 The step may be a step of irradiating the object with the ultraviolet light at the above illuminance.

[0018] The step (a) may be performed intermittently at time intervals of 2 hours or less.

[0019] As will be described later in the "Mode for Carrying Out the Invention" section, it has been confirmed that the bacteriostatic effect decreases if two hours or more have passed since the step (a) of irradiating with ultraviolet light was performed immediately beforehand. According to the above method, a high bacteriostatic effect can be achieved on the target area without constantly irradiating with ultraviolet light.

[0020] The bacteriostatic method comprises: (b) detecting whether a human is present in the target area using a human presence sensor; The ultraviolet rays are applied to the target area at a wavelength D defined by the formula (1). Max (μW / cm 2 and step (c) irradiating the surface with an average irradiance higher than that of the surface of the substrate. If the presence of a human being in the target area is detected in the step (b), the process may proceed from the step (c) to the step (a).

[0021] According to this method, if a human is not present in the target area, D Max (μW / cm 2 ) and if a person is present in the target area, the ultraviolet irradiance is D Max (μW / cm 2 ) or less. This further enhances the effect of suppressing bacterial growth in the target area while suppressing the impact on the human body. [Effects of the Invention]

[0022] According to the present invention, it is possible to suppress the growth of bacteria while suppressing the effects on the human body. [Brief explanation of the drawings]

[0023] [Figure 1]1 is a diagram schematically illustrating the implementation of a bacteriostatic method according to the present invention. [Figure 2] FIG. 1 is a perspective view schematically illustrating an example of the appearance of an ultraviolet irradiation device. [Figure 3] 3 is an exploded perspective view of the main body casing and the lid of the lamp house of the ultraviolet irradiation device, taken from FIG. 2. FIG. [Figure 4] FIG. 2 is a plan view schematically showing the positional relationship between an excimer lamp and an electrode block. [Figure 5] 1 is a diagram showing the spectrum of ultraviolet light emitted from an excimer lamp containing KrCl as a light-emitting gas. [Figure 6] 1 is a graph for explaining the threshold illuminance DMax (μW / cm 2 ) defined by the following formula (1). [Figure 7] 1 is another diagram schematically illustrating the implementation of the bacteriostatic method according to the present invention. [Figure 8A] 1 is a photograph showing the results of Comparative Example 1 in Verification 1. [Figure 8B] 10 is a photograph showing the results of Comparative Example 2 in Verification 1. [Figure 8C] 1 is a photograph showing the results of Example 1 in Verification 1. [Figure 9A] 10 is a photograph showing the results of Comparative Example 3 (spore liquid of Cladosporium) in Verification 2. [Figure 9B] 10 is a photograph showing the results of Comparative Example 3 (Cladosporium strain) in Verification 2. [Figure 9C] 10 is a photograph showing the results of Example 2 (spore liquid of Cladosporium) in Verification 2. [Figure 9D] 10 is a photograph showing the results of Example 2 (Cladosporium strain) in Verification 2. [Figure 9E] 10 is a photograph showing the results of Comparative Example 4 (spore liquid of Cladosporium) in Verification 2. [Figure 9F] 10 is a photograph showing the results of Comparative Example 4 (Cladosporium strain) in Verification 2. [Figure 9G] 10 is a photograph showing the results of Example 3 (spore liquid of Cladosporium) in Verification 2. [Figure 9H] 10 is a photograph showing the results of Example 3 (Cladosporium strain) in Verification 2. [Figure 9I] 1 is a photograph showing the results of Examples 4, 6, and 7 for Cladosporium spore fluid in a contaminated state (#2). [Figure 9J] 1 is a photograph showing the results of Examples 4, 6, and 7 for Cladosporium strains in a contaminated state (#2). DETAILED DESCRIPTION OF THE INVENTION

[0024] An embodiment of the bacteriostatic method according to the present invention will be described with reference to the drawings as appropriate.

[0025] Fig. 1 is a diagram schematically illustrating an implementation of a bacteriostatic method according to the present invention. The bacteriostatic method according to the present invention is a method for suppressing bacterial growth in a target area 40 by irradiating the target area 40 with ultraviolet light L1 from an ultraviolet irradiation device 1. Fig. 1 illustrates a state in which the ultraviolet irradiation device 1 is mounted in a housing 50 and ultraviolet light L1 is irradiated onto the target area 40 from a light extraction surface 10 of the ultraviolet irradiation device 1.

[0026] Fig. 2 is a perspective view schematically showing the appearance of the ultraviolet irradiation device 1. Fig. 3 is a perspective view in which the main body casing 2a and the lid 2b of the lamp house 2 of the ultraviolet irradiation device 1 are disassembled from Fig. 2. However, the structure of the ultraviolet irradiation device 1 described below is merely an example, and the structure of the light source used in the bacteriostatic method according to the present invention is not limited thereto.

[0027] In the following drawings, the explanation will be made with reference to an XYZ coordinate system in which the extraction direction of the ultraviolet light L1 is the X direction and the plane perpendicular to the X direction is the YZ plane. More specifically, as will be described later with reference to the drawings from FIG. 3 onwards, the tube axis direction of the excimer lamp 3 is the Y direction, and the direction perpendicular to the X and Y directions is the Z direction.

[0028] As shown in FIGS. 2 and 3, the ultraviolet irradiation device 1 includes a lamp house 2 having a light extraction surface 10 formed on one side. The lamp house 2 includes a main casing portion 2a and a lid portion 2b, and the main casing portion 2a accommodates an excimer lamp 3 and electrode blocks (11, 12). FIG. 3 shows, as an example, a case in which four excimer lamps 3 are accommodated in the lamp house 2. The electrode blocks (11, 12) are electrically connected to a power supply line 8 and form electrodes for supplying power to each excimer lamp 3. FIG. 4 is a plan view schematically showing the positional relationship between the excimer lamp 3 and the electrode blocks (11, 12).

[0029] As shown in FIGS. 2 to 4, the ultraviolet irradiation device 1 of this embodiment has two electrode blocks (11, 12) arranged so as to contact the outer surfaces of the arc tubes of the respective excimer lamps 3. The electrode blocks (11, 12) are arranged at positions spaced apart in the Y direction. The electrode blocks (11, 12) are made of a conductive material, and preferably a material that is reflective to the ultraviolet rays emitted from the excimer lamps 3. As an example, the electrode blocks (11, 12) are both made of Al, Al alloy, stainless steel, or the like. The electrode blocks (11, 12) are both arranged so as to straddle each excimer lamp 3 in the Z direction while contacting the outer surfaces of the arc tubes of the respective excimer lamps 3.

[0030] The excimer lamp 3 has an arc tube with its tube axis oriented in the Y direction, and the outer surface of the arc tube of the excimer lamp 3 is in contact with each of the electrode blocks (11, 12) at positions spaced apart in the Y direction. A light-emitting gas 3G is sealed in the arc tube of the excimer lamp 3. When a high-frequency AC voltage of, for example, about 10 kHz to 5 MHz is applied between the electrode blocks (11, 12) through the power supply line 8 (see FIG. 2), the voltage is applied to the light-emitting gas 3G via the arc tube of the excimer lamp 3. At this time, a discharge plasma is generated in the discharge space in which the light-emitting gas 3G is sealed, and atoms of the light-emitting gas 3G are excited to an excimer state, and excimer light emission occurs when these atoms transition to the ground state.

[0031] The luminescent gas 3G is made of a material that emits ultraviolet light L1 with a main emission wavelength of 200 nm or more and 230 nm or less during excimer emission. Examples of the luminescent gas 3G include KrCl and KrBr. In addition to the above gas species, inert gases such as argon (Ar) and neon (Ne) may also be mixed.

[0032] For example, when the luminescent gas 3G contains KrCl, ultraviolet light L1 having a main peak wavelength of about 222 nm is emitted from the excimer lamp 3. When the luminescent gas 3G contains KrBr, ultraviolet light L1 having a main peak wavelength of about 207 nm is emitted from the excimer lamp 3. Figure 5 is a diagram showing the spectrum of ultraviolet light L1 emitted from an excimer lamp 3 whose luminescent gas 3G contains KrCl.

[0033] When carrying out the bacteriostatic method according to the present invention, the ultraviolet irradiation device 1 emits a threshold irradiance D defined by the following formula (1): Max (μW / cm 2 ) or less (step (a)). In equation (1), λ is the main peak wavelength (nm) of the ultraviolet light L1. That is, when the light source mounted in the ultraviolet irradiation device 1 is an excimer lamp 3 containing KrCl in the light emitting gas 3G, λ=222 nm. D Max = 9391.1 × exp(-0.043λ)···(1) Note that exp(x) is e x is synonymous with.

[0034] The ultraviolet irradiation device 1 may include a control unit (not shown), which controls the supply of electricity to each electrode block (11, 12) through the power supply line 8. The control unit determines whether the average irradiance of the ultraviolet light L1 on the target area 40 is D Max (μW / cm 2 The power supplied to each electrode block (11, 12) is controlled so that:

[0035] When the ultraviolet light L1 is continuously irradiated onto the target area 40 from the ultraviolet light irradiation device 1, the illuminance is D Max (μW / cm 2 On the other hand, as will be described later, when the ultraviolet irradiation device 1 is turned on intermittently, the average illuminance in the target area 40 may be set to be equal to or less than D Max (μW / cm 2 ) is set as follows:

[0036] As mentioned above in the "Problem to be Solved by the Invention" section, ultraviolet light in the vicinity of 260 nm, which exhibits high absorption characteristics in DNA, is known to have a significant effect on the human body. For this reason, restrictions are imposed on the handling of ultraviolet light, and it is currently recommended that exposure be kept within the regulatory limits set by the American Conference of Governmental Industrial Hygienists (ACGIH). Table 1 below shows the TLVs (Threshold Limit Values) set by ACGIH. Considering that industrial workers typically work eight hours a day, TLVs indicate the upper limit of exposure permitted within that period.

[0037] [Table 1]

[0038] The values ​​shown in Table 1 specify the radiation exposure dose for an eight-hour period. This is converted into a value per unit time (second) and plotted on a graph, which corresponds to the plot line shown in Figure 6(a). As shown in Table 1, ACGIH specifies radiation exposure dose discretely for each wavelength. For this reason, the graph in Figure 6(a) is drawn by converting the value for each wavelength into a value per unit time (second) and then linearly interpolating.

[0039] In Figure 6, graph (b) was created based on the ACGIH-TLV values ​​shown in (a) multiplied by a safety factor of 0.9. On the other hand, graph (c) is a curve defined by the above formula (1). As shown in Figure 6, graph (c) does not exceed the values ​​of graph (b), which are based on the ACGIH-TLV values ​​multiplied by a safety factor of 0.9, within the range of 200 nm to 270 nm.

[0040] That is, the ultraviolet irradiation device 1 emits the D defined by the above formula (1). Max (μW / cm 2 ) or less, it is possible to suppress the effects on the human body even if a person is present in the target area 40. In particular, if the target area 40 is a location where it is unlikely that the same person will remain for more than eight hours, even if a person is present in the target area 40, the effects on the human body of the person will be extremely low.

[0041] For example, if the target area 40 is a place where water is present, such as a bathroom, toilet, washroom, or kitchen, or an air conditioner filter, it is unlikely that the same person will stay in such a place for more than 8 hours. Also, even if the method of the present invention is used for bacteriostatic treatment from the viewpoint of preventing hospital-acquired infections in a hospital, in an area where it is unlikely that the same person will stay for more than 8 hours, D Max (μW / cm 2 By irradiating ultraviolet light L1 at an illuminance of 1000 kJ / h or less, the effects on the human body can be suppressed while ensuring a bacteriostatic effect.

[0042] If the ultraviolet light L1 has a main peak wavelength of 200 nm or more and 230 nm or less, D defined by the above formula (1) Max (μW / cm 2 ) or less, the effect of suppressing the growth of bacteria in the target area 40 is obtained, which is a new finding discovered through the inventor's intensive research. For example, in the case of ultraviolet light L1 with a main peak wavelength of 222 nm, this value is 1 μW / cm according to FIG. 2It has not been known until now that such extremely weak ultraviolet light L1 can have the effect of inhibiting bacterial growth, and this is a truly surprising effect. This point will be described later with reference to the examples.

[0043] Furthermore, ultraviolet light L1 with a main peak wavelength of 200 nm or more and 230 nm or less is hardly absorbed by oxygen, so no ozone is generated, and from this point of view, it can be said that its impact on the human body is extremely low.

[0044] 7, the housing 50 may include, in addition to the ultraviolet irradiation device 1, a human presence sensor 30 that can detect whether or not a human is present within the target area 40. When the human presence sensor 30 detects the presence of a human within the target area 40 (step (b)), it outputs a signal to that effect to a control unit included in the ultraviolet irradiation device 1, and the control unit performs control to reduce the illuminance of the ultraviolet light L1 emitted from the ultraviolet irradiation device 1 (step (c)).

[0045] That is, in the embodiment of FIG. 7, when no human being is present in the target area 40, the ultraviolet irradiation device 1 emits the ultraviolet ray D defined by the above formula (1). Max (μW / cm 2 ) to the target area 40. This achieves a strong bacteriostatic effect and a strong bactericidal effect in the target area 40. On the other hand, when the human presence sensor 30 detects that a human is present (or may be present) in the target area 40, the illuminance of the ultraviolet light L1 from the ultraviolet irradiation device 1 in the target area 40 is adjusted to D Max (μW / cm 2 ) or less. This ensures a bacteriostatic effect within the target area 40 even when a person is present within the target area 40.

[0046] Bacteria have the tendency to grow over time unless they are completely killed. Furthermore, even if a sterilization treatment is performed once, if the area is left as is, there is a good chance that bacteria will attach to the area from the outside over time. Once the bacteria grow and form colonies, a great deal of effort is required to remove them. However, as in the above method, by irradiating the target area 40 with ultraviolet light L1 at an illuminance level that has almost no effect on the human body, even if the bacteria cannot be completely killed, the growth of the bacteria is suppressed, and the effort required to remove the bacteria can be significantly reduced. In particular, after the sterilization treatment, the D defined by the above formula (1) Max (μW / cm 2 By continuing to irradiate the ultraviolet light L1 at an illuminance of 1000 W or less, it is possible to prevent the proliferation of bacteria in the target area 40 while suppressing the effects on the human body.

[0047] From the viewpoint of ensuring higher safety, the ultraviolet ray L1 may be irradiated only when the human sensor 30 confirms that no human is present in the target area 40. In other words, the ultraviolet ray irradiation device 1 controls the ultraviolet ray L1 to be irradiated only when no human is present in the target area 40. Max (μW / cm 2 ) or less, and when the human presence sensor 30 detects the presence of a human in the target area 40, the irradiation of the ultraviolet light L1 may be stopped.

[0048] [verification] Hereinafter, the illuminance of ultraviolet light L1 on the target area 40 is defined as D Max (μW / cm 2 ) or less, the proliferation of bacteria in the target area 40 can be suppressed. This will be explained with reference to examples.

[0049] (Test 1: Staphylococcus aureus) Experiments were conducted on Staphylococcus aureus. In order to simulate the bacteria's habitat, the experiments were conducted under three conditions: no load (ideal condition), clean condition, and contaminated condition. The EN test method, which is the basic test method for evaluating bactericidal activity, specifies clean and contaminated conditions as conditions that indicate different levels of contamination expected in the target area. Both of these correspond to conditions in which a load substance is added to simulate a contaminated condition. In addition to these two conditions, this verification also examined a no load condition (ideal condition) in which no load substance was added at all.

[0050] For each of the unloaded, clean, and contaminated samples, a model soiling protein (BSA: bovine serum albumin) was added to Staphylococcus aureus solution and smeared onto a standard agar medium in a petri dish. Table 2 below shows the amounts of Staphylococcus aureus and BSA used to prepare these samples.

[0051] [Table 2]

[0052] In Table 2, CFU means colony forming unit.

[0053] The condition of each sample in each state in Table 2 above was checked when it was not irradiated with ultraviolet light (Comparative Example 1), irradiated with ultraviolet light at a wavelength of 254 nm (Comparative Example 2), and irradiated with ultraviolet light at a wavelength of 222 nm (Example 1).

[0054] In Comparative Example 1, the sample was left as it was without any treatment. In Comparative Example 2, the D defined by the above formula (1) Max (μW / cm 2 ) which is less than 0.22 μW / cm 2 The sample was irradiated with ultraviolet light having a wavelength of 254 nm from a low-pressure mercury lamp for 72 hours at an illuminance of 1000 nm. Max(μW / cm 2 ) or less, 0.43 μW / cm 2 The samples were irradiated with ultraviolet light having a wavelength of 222 nm from a KrCl excimer lamp at an illuminance of 1000 kJ / cm for 72 hours. In Comparative Example 2 and Example 1, the samples were left overnight after the irradiation treatment and then checked. The respective results are shown in Figures 8A to 8C and Table 3.

[0055] In Table 3, the evaluation is as follows: "A" indicates that no colonies were visually confirmed to have formed (highly bacteriostatic effect), "B" indicates that only a small number of colonies were confirmed to have formed (bacteriostatic effect was observed), and "C" indicates that many colonies were confirmed to have formed (bacterial growth was not suppressed).

[0056] [Table 3]

[0057] According to Example 1, regardless of the contamination state, the light intensity was 0.43 μW / cm 2 It was confirmed that even with ultraviolet light of extremely low illuminance, such as 254 nm, the growth of Staphylococcus aureus can be suppressed by continuous irradiation. On the other hand, it was confirmed that colonies were formed in both Comparative Examples 1 and 2. In Comparative Example 2, in the "clean state" where the degree of contamination was low, the growth of colonies was suppressed to some extent, but in the "contaminated state" where the degree of contamination was high, the growth of colonies could not be suppressed. In the case of ultraviolet light of 254 nm, which corresponds to the main peak wavelength of ultraviolet light from a low-pressure mercury lamp commonly used as a germicidal lamp, as in Comparative Example 2, the D defined by the above formula (1) Max Since the value is smaller than 222 nm, it is thought that even if ultraviolet light is irradiated continuously, a sufficient bacteriostatic effect is not obtained.

[0058] (Test 2: Mold) Experiments were conducted on the black mold species Cladosporium cladosporioides (NBRC.6368), Penicillium citrinum (NBRC 6352), and Aspergillus niger (NBRC 105649). As with Verification 1, in order to simulate the habitat of the fungi, experiments were conducted under three conditions: no load (ideal condition), clean condition, and contaminated condition.

[0059] Furthermore, in this verification 2, in order to simulate both the presence of ungrown mold and the state in which mold has already grown, two types of samples were prepared: one in which a mold spore liquid was introduced into the medium, and one in which the strain itself was injected into physiological saline and then introduced into the medium. The former simulated a situation in which mold is actually present, even though it is invisible to the naked eye, while the latter simulated a situation in which mold has grown to the point where it can be seen.

[0060] The spore liquid was tested for mold resistance in accordance with JIS Z 2911. 4 / mL~10 6 The concentration was adjusted to 1 / mL. Commercially available potato dextrose agar medium (PDA medium) was used as the medium and introduced into the petri dish. For the clean and contaminated samples, agar medium smeared with BSA was used as a model stain. Table 4 below summarizes the preparation conditions for the samples prepared in this verification 2.

[0061] [Table 4]

[0062] For Samples #1 to #6 in each state in Table 4 above, the state of each sample was checked when not irradiated with ultraviolet light (Comparative Example 3 to Comparative Example 4) and when irradiated with ultraviolet light at a wavelength of 222 nm (Examples 2 to 8). The seasons when the tests for Comparative Example 3 and Example 2 were conducted were different from the seasons when the tests for Comparative Example 4 and Examples 3 to 8 were conducted, and therefore the ambient temperature and humidity conditions during the tests were different. Specifically, the ambient temperature during the tests for Comparative Example 3 and Example 2 was 15 to 18°C, and the humidity was approximately 30% RH. The ambient temperature during the tests for Comparative Example 4 and Examples 3 to 8 was 22 to 26°C, and the humidity was approximately 40% RH.

[0063] The following describes the irradiation conditions for Examples 2 to 8. Examples 2 and 3 correspond to continuous irradiation, and Examples 4 to 8 correspond to intermittent irradiation.

[0064] [Continuous irradiation] (Example 2) D defined by the above formula (1) Max (μW / cm 2 ) or less, 0.76 μW / cm 2 The sample was irradiated with ultraviolet light having a wavelength of 222 nm from a KrCl excimer lamp at an intensity of 1000 kJ / cm for 72 hours. (Example 3) Illuminance: 0.29 μW / cm 2 The sample was irradiated with ultraviolet light under the same conditions as in Example 2, except for the above.

[0065] [Intermittent irradiation] (Example 4) 0.76 μW / cm 2 The conditions were the same as in Example 2, except that the samples were irradiated with an irradiance of 0.57 μW / cm for 45 minutes followed by 15 minutes without irradiation, and this cycle was repeated for 72 hours. In this case, the average irradiance over 72 hours was 0.57 μW / cm. 2 Corresponds to. (Example 5) The irradiation time cycle was different from that of Example 4. Specifically, the same conditions as Example 4 were used except that a process of irradiating for 30 minutes and then stopping irradiation for 30 minutes was repeated. In this case, the average irradiance over 72 hours was 0.38 μW / cm 2 Corresponds to. (Example 6) The irradiation time cycle was different from that of Example 4. Specifically, the same conditions as Example 4 were used except that a process of irradiating for 2 hours and then stopping irradiation for 2 hours was repeated. In this case, the average irradiance over 72 hours was 0.38 μW / cm 2 Corresponds to. (Example 7) The irradiation time cycle was different from that of Example 4. Specifically, the same conditions as Example 4 were used except that a process of irradiating for 3 hours and then stopping irradiation for 3 hours was repeated. In this case, the average irradiance over 72 hours was 0.38 μW / cm 2 Corresponds to. (Example 8) The irradiation time cycle was different from that of Example 4. Specifically, the same conditions as Example 4 were used except that a process of irradiating for 4 hours and then stopping irradiation for 4 hours was repeated. In this case, the average irradiance over 72 hours was 0.38 μW / cm 2 Corresponds to.

[0066] The results are shown in Tables 5 and 6 and Figures 9A to 9H. Note that Table 5 omits verification of the no-load state (#6) in Examples 3 to 8, but in light of the results of Comparative Example 3 and Example 2, it is expected that results at least equal to or better than those in the clean state (#1) will be obtained, so verification has been omitted.

[0067] The photographs in each figure correspond to the following conditions: Since it would be extremely overwhelming to list all the photographs of the areas where results are presented in Tables 5 and 6, only representative photographs of Cladosporium are shown in the drawings.

[0068] FIG. 9A is a photograph showing the results of Comparative Example 3 (spore fluid of Cladosporium). FIG. 9B is a photograph showing the results of Comparative Example 3 (Cladosporium strain). FIG. 9C is a photograph showing the results of Example 2 (spore fluid of Cladosporium). FIG. 9D is a photograph showing the results of Example 2 (Cladosporium strains). FIG. 9E is a photograph showing the results of Comparative Example 4 (spore fluid of Cladosporium). FIG. 9F is a photograph showing the results of Comparative Example 4 (Cladosporium strain). FIG. 9G is a photograph showing the results of Example 3 (spore fluid of Cladosporium). FIG. 9H is a photograph showing the results of Example 3 (Cladosporium strains). FIG. 9I is a photograph showing the results of Examples 4, 6, and 7 for the spore fluid of Cladosporium in a contaminated state (#2). FIG. 9J is a photograph showing the results of Examples 4, 6, and 7 for Cladosporium strains in a contaminated state (#2).

[0069] 9I and 9J, the notation "45 min / 15 min" means that a cycle of 45 minutes of UV irradiation followed by 15 minutes of no irradiation is repeated. The same applies to the notations "2 hr / 2 hr" and "3 hr / 3 hr."

[0070] [Table 5]

[0071] [Table 6]

[0072] In this verification 2, in order to confirm the difference in effect due to intermittent irradiation, the evaluation B used in verification 1 was further divided into three stages, evaluations B1 to B3. That is, among those in which a bacteriostatic effect was observed (evaluation B), evaluation B1 was given when the number of colonies was less than 30, evaluation B2 when the number of colonies was 30 or more but less than 300, and evaluation B3 when the number of colonies was 300 or more but mycelia were not observed. Evaluation C was given when a large number of colonies were formed and mycelia were observed.

[0073] A colony count of less than 30 corresponds to a count below the microbiological detection limit, and a colony count of 300 or more corresponds to a count limit.

[0074] According to Example 2, both the spore solution and the strain were 0.76 μW / cm 2 It was confirmed that even with ultraviolet light of extremely low illuminance, the growth of black mold could be suppressed. On the other hand, in Comparative Example 3, it was confirmed that colonies were formed in both the case of the spore liquid and the case of the bacterial strain. In particular, according to Example 2, as simulated by Samples #3 to #5, it was confirmed that the growth of mold could be suppressed by irradiation with ultraviolet light of a wavelength of 222 nm even when mold had already grown.

[0075] According to Example 3, the value is 0.29 μW / cm, which is even lower than that of Example 2. 2 It was confirmed that the growth of black mold was inhibited even with ultraviolet light of this illuminance. However, compared to Example 2, the effect of inhibiting the growth of black mold was slightly reduced.

[0076] Examples 4 to 8 correspond to cases where ultraviolet light was irradiated intermittently. In the cases of Examples 7 and 8, where the non-irradiation time from the last irradiation was 3 hours or more, it was confirmed that the effect of inhibiting the growth of black mold was reduced compared to Examples 4 to 6, where the non-irradiation time was 2 hours or less. In other words, when the average irradiance of ultraviolet light irradiated to the sample was the same D MaxIt is estimated that even if ultraviolet light is irradiated for the same period (72 hours), the longer the period without irradiation, the more likely black mold will grow during this time. In other words, when irradiating ultraviolet light intermittently to suppress bacterial growth, it is preferable to set the irradiation interval to within 2 hours.

[0077] In addition, when comparing the photograph of the contamination state (#4) of Comparative Example 4 shown in FIG. 9F with the photograph of Example 7 shown in FIG. 9J, which were both under the same atmospheric temperature and humidity conditions, it is difficult to see in the photograph, but mycelia can be seen in the photograph of Comparative Example 4, whereas mycelia cannot be seen in the photograph of Example 7. From this, it can be seen that even in the case of Example 7, in which ultraviolet light was irradiated in a 3-hour cycle, bacterial growth was suppressed more than in Comparative Example 3, in which ultraviolet light was not irradiated. However, since the number of colonies in Example 7 was greater than in Examples 4 and 6 shown in FIG. 9J, when ultraviolet light is irradiated intermittently, it is preferable to limit the non-irradiation period to 2 hours or less in order to further enhance the bacteriostatic effect.

[0078] In Example 1, the illuminance was 0.43 μW / cm 2 In Example 2, the illuminance was 0.76 μW / cm 2 In Example 3, the illuminance was 0.29 μW / cm 2 Furthermore, among Examples 4 to 8, which were irradiated intermittently, Example 4 had an average irradiance of 0.57 μW / cm 2 In Examples 5 to 8, the average illuminance was 0.38 μW / cm 2 However, it goes without saying that the higher the illuminance, the greater the bacteriostatic effect. In other words, D, as defined by the above formula (1), Max (μW / cm 2 By increasing the average illuminance within the range below, it is possible to achieve a high bacteriostatic effect while suppressing the impact on the human body.

[0079] [Another embodiment] Another embodiment will be described below.

[0080] <1> In the above embodiment, the ultraviolet irradiation device 1 equipped with the excimer lamp 3 is used as the light source. However, the structure of the light source is not limited as long as it emits ultraviolet light L1 having a main emission wavelength of 200 nm or more and 230 nm or less. For example, a solid-state light source such as an LED or a semiconductor laser element may be used.

[0081] Furthermore, if the ultraviolet irradiation device 1 is provided with a filter on the light extraction surface 10 that blocks light of 230 nm or longer, it is also possible to use a light source that outputs light in a wavelength range exceeding 230 nm, as long as it outputs light in part of the wavelength range from 200 nm to 230 nm. In this case, the main peak wavelength of the ultraviolet light L1 extracted from the light extraction surface 10 via the filter is 200 nm or longer and 230 nm or shorter.

[0082] <2> An illuminance meter may be installed in the area where the ultraviolet light L1 is irradiated (corresponding to the target area 40 in FIG. 1) in order to detect the illuminance of the ultraviolet light L1 irradiated from the ultraviolet irradiation device 1. An example of such an illuminance meter is a spectroradiometer, specifically, the USR-45D manufactured by Ushio Inc.

[0083] The detection result by this illuminance meter may be transmitted to the ultraviolet irradiation device 1. The ultraviolet irradiation device 1 may be provided with a control unit, and the control unit may calculate the average illuminance by integrating the illuminance in the target wavelength band (200 nm to 230 nm). Alternatively, the illuminance meter may be equipped with a calculation processing function, and information relating to the average illuminance may be transmitted to the ultraviolet irradiation device 1.

[0084] The control unit of the ultraviolet irradiation device 1 determines whether the calculated average illuminance Ai is D defined by the above formula (1). Max (μW / cm 2 ) It is acceptable to check whether the value is within the range below. In this case, Ai <D MaxIf Ai is D, the control unit continues to control the light source mounted in the ultraviolet irradiation device 1 to continue irradiating the ultraviolet light L1. Max It is approaching the value of Ai>D soon. Max If there is a possibility that Ai <D Max Alternatively, the control may be performed so as to continuously satisfy the above condition.

[0085] <3> In the above embodiment, the time period used as the calculation reference for the "average illuminance" can be any time period, but a typical example would be the previous 8 hours in accordance with the ACGIH standard. In other words, the average illuminance can be calculated by dividing the integrated value of the illuminance over the past 8 hours, with the current time as the reference, by 8 hours. [Explanation of symbols]

[0086] 1: Ultraviolet irradiation device 2: Lamp House 2a: Main casing 2b: Lid part 3: Excimer lamp 3G: Luminous gas 8:Power line 10: Light extraction surface 30: Human sensor 40:Target area 50: Housing D Max : Threshold illuminance L1: Ultraviolet light

Claims

1. A bacteriostatic method for inhibiting bacterial growth in a target area where humans may be present, comprising: Ultraviolet light having a main peak wavelength of 200 nm or more and 230 nm or less is defined as D defined by the following formula (1): Max (μW / cm 2 (a) irradiating the target area with an average irradiance of not more than 100 nm; A bacteriostatic method, characterized in that the average illuminance is a temporal average value of illuminance in the target area. D Max = 9391.1 × exp(-0.043λ)・・・(1) In the formula (1), λ is the main peak wavelength (nm).

2. In the step (a), the ultraviolet light containing a light component with a wavelength of 222 nm is irradiated at a wavelength of 0.29 μW / cm 2 2. The bacteriostatic method according to claim 1, wherein the step of irradiating the sample with an illuminance of at least 1000 uV.

3. In the step (a), the ultraviolet light is irradiated at a concentration of 1 μW / cm 2 The bacteriostatic method according to claim 2, characterized in that the step of irradiating the target area with an illuminance of:

4. the bacterium is Staphylococcus aureus, The step (a) is 0.4 μW / cm 2 The bacteriostatic method according to any one of claims 1 to 3, characterized in that it is a step of irradiating the target area with the ultraviolet light at an illuminance of at least 1000 nm.

5. the fungus is a mold, The step (a) is 0.29 μW / cm 2 The bacteriostatic method according to any one of claims 1 to 3, characterized in that it is a step of irradiating the target area with the ultraviolet light at an illuminance of at least 1000 nm.

6. (b) detecting whether a human is present in the target area by a human presence sensor; The ultraviolet rays are applied to the target area in a range of D defined by the formula (1). Max (μW / cm 2 and step (c) irradiating the surface with an average irradiance higher than that of the surface of the substrate. When the presence of a human being in the target area is detected by the step (b), the step (c) transitions to the step (a). A bacteriostatic method according to any one of claims 1 to 5.

7. The bacteriostatic method according to any one of claims 1 to 6, wherein the step (a) is a step of irradiating the ultraviolet light from an excimer lamp in which a light-emitting gas containing Kr and Cl is sealed.

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