Antibacterial member and antibacterial product

Abstract

To provide an antibacterial member and an antibacterial product having a surface suitable for expressing of antibacterial activity.SOLUTION: An antibacterial member satisfies at least one of the following conditions A and B. Condition A: A surface has a recess with an opening having a diameter of 100 nm or less. Condition B: A surface has a recess with an opening having an average diameter of 50 nm or less.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present invention relates to an antibacterial member and an antibacterial product.

Background Art

[0002] It is known that when a fine three-dimensional structure is formed on the surface of an article, an antibacterial action is exhibited on the surface. For example, Patent Document 1 describes a method of providing an antibacterial action by forming innumerable dimpled minute recesses on the surface of an article.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 describes that a pitch of dimpled recesses of 0.4 μm to 8.0 μm is effective in the expression of antibacterial action, but the relationship between the state of individual recesses (such as the diameter of the recesses) and the antibacterial action has not been studied. There is still room for study as to what kind of state is suitable for the surface of an article to exhibit an antibacterial action. In view of the above circumstances, an object of one embodiment of the present disclosure is to provide an antibacterial member and an antibacterial product having a surface suitable for the expression of antibacterial action.

Means for Solving the Problems

[0005] Means for solving the above problems include the following embodiments. <1> An antibacterial member having recesses with an opening diameter of 100 nm or less on the surface. <2> An antibacterial member having recesses with an average opening diameter of 50 nm or less on the surface. <3>The antibacterial member according to <1> or <2>, wherein an average center-to-center distance between the recesses is 100 nm or less. <4>The antibacterial member according to any one of <1> to <3>, having a region where the number of the recesses is 100 or more per μm. 2 <5>The antibacterial member according to any one of <1> to <4>, having recesses with an average diameter of the openings of 10 nm or less on the surface. <6>The antibacterial member according to any one of <1> to <5>, wherein a peripheral portion of the recess contains aluminum oxide. <7>The antibacterial member according to any one of <1> to <6>, wherein the recesses are present in an anodic oxide film disposed on a substrate containing aluminum. <8>The antibacterial member according to <7>, wherein a thickness of the anodic oxide film is 500 nm or more. <9>An antibacterial product including the antibacterial member according to any one of <1> to <8>.

Advantages of the Invention

[0006] According to one embodiment of the present disclosure, there are provided an antibacterial member and an antibacterial product having a surface suitable for expressing antibacterial action.

Brief Description of the Drawings

[0007]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 3A

Figure 3B

[0008] ​In the present disclosure, a numerical range indicated using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range of other step-by-step descriptions, or may be replaced with the value shown in the examples. In the present disclosure, the amount of each component in the material means the total amount of a plurality of substances present in the material when there are a plurality of substances corresponding to each component in the material, unless otherwise specified.

[0009] <First Embodiment> The first embodiment of the present disclosure is an antibacterial member that satisfies at least one of the following conditions A or condition B. Condition A: having on the surface recesses with an opening diameter of 100 nm or less Condition B: having on the surface recesses with an average opening diameter of 50 nm or less

[0010] As shown in the examples described later, an object that satisfies at least one of condition A or condition B exhibits excellent antibacterial action on the surface. That is, an object that satisfies at least one of condition A or condition B is useful as an antibacterial member.

[0011] In the present disclosure, the "antibacterial member" means a member that exhibits an antibacterial action. In the present disclosure, the "antibacterial action" includes an action of killing bacteria or suppressing the growth of bacteria (antibacterial action) and an action of inactivating viruses (antiviral action). That is, the target of the antibacterial action of the antibacterial member may be bacteria only, viruses only, or a combination of bacteria and viruses.

[0012] In the present disclosure, the "recess" means a relatively sunken area (recess) surrounded entirely by a relatively raised area (protrusion) on the surface of the antibacterial member. In the present disclosure, the "diameter of the opening" is defined as the maximum value of the distance between two parallel lines circumscribing the region corresponding to the opening of the recess on the surface where the recess of the antibacterial member is present, in an image obtained by photographing the surface with an electron microscope. The "average diameter of the opening" is the arithmetic mean value of the diameters of the openings of a plurality of recesses.

[0013] When the antibacterial member satisfies Condition A, the diameter of the opening of the recess present on the surface of the antibacterial member is not particularly limited as long as it is 100 nm or less. The diameter of the opening of the recess may be, for example, 80 nm or less, 60 nm, or 50 nm or less. From the viewpoint of exhibiting an antibacterial action (antiviral action) against viruses, the antibacterial member may have recesses with an opening diameter of 10 nm or less on its surface. The diameter of the opening of the recess may be, for example, 2 nm or more, 5 nm or more, 10 nm or more, or 15 nm or more.

[0014] When the antibacterial member satisfies Condition B, the average diameter of the opening of the recess is not particularly limited as long as it is 50 nm or less. The average diameter at the opening of the recess may be, for example, 45 nm or less, 35 nm, 30 nm, or 10 nm or less. From the viewpoint of exhibiting an antibacterial action (antiviral action) against viruses, the antibacterial member may have recesses with an average opening diameter of 10 nm or less on its surface. The average diameter of the opening of the recess may be, for example, 2 nm or more, 5 nm or more, or 10 nm or more.

[0015] The shape of the recess is not particularly limited. For example, the shape of the recess may be a shape where the maximum inner diameter inside the recess is equal to or the difference between these and the diameter of the opening is small (cylindrical shape), a state where the diameter of the opening is larger than the maximum inner diameter inside the recess (cup shape), a shape where the diameter of the opening is smaller than the maximum inner diameter inside the recess (ink bottle shape), etc. From the viewpoint of arranging recesses with an opening diameter of 100 nm or less or an average opening diameter of 50 nm or less on the surface of the antibacterial member at a high density, the shape of the recess is preferably cylindrical. The recessed part may be in a branched state (for example, a state in which one opening is shared by a plurality of recessed parts), or may not be branched.

[0016] The aspect ratio of the recessed part may be, for example, 5.0 or more, 10.0 or more, or 15.0 or more. The aspect ratio of the recessed part may be, for example, 50.0 or less, 30.0 or less, or 20.0 or less. In the present disclosure, the "aspect ratio of the recessed part" is a value obtained by dividing the depth of the recessed part by the diameter of the opening (depth / diameter). The depth of the recessed part is the maximum value of the height difference between the bottom of the recessed part and the surrounding convex part. The depth of the recessed part may be, for example, 500 nm or more, 1000 nm or more, or 1500 nm or more.

[0017] From the viewpoint of exhibiting sufficient antibacterial action, it is preferable that the antibacterial member has a plurality of recessed parts on its surface. When the antibacterial member has a plurality of recessed parts on its surface, it is preferable that the arithmetic mean value of the diameters of the openings of the plurality of recessed parts present on the surface of the antibacterial member satisfies the conditions of the diameter of the opening of the recessed part described above. When the antibacterial member has a plurality of recessed parts on its surface, it is preferable that the arithmetic mean value of the depths or aspect ratios of the plurality of recessed parts present on the surface of the antibacterial member satisfies the conditions of the depth or aspect ratio of the recessed part described above.

[0018] When the number of recessed parts present on the surface of the antibacterial member is extremely large, the arithmetic mean value of the diameter, depth, or aspect ratio of the openings of the recessed parts may be the arithmetic mean value of the diameter, depth, or aspect ratio of the recessed parts randomly selected from the recessed parts present on the surface of the antibacterial member. In this case, from the viewpoint of measurement accuracy, it is preferable that the number of randomly selected recessed parts is 20 or more. The calculation of the arithmetic mean value is performed, for example, by acquiring an electron microscope image of the surface of the antibacterial member on which the recessed part exists, and based on the values measured from the recessed parts selected from the region including 20 or more recessed parts in the image.

[0019] When the antibacterial member has a plurality of recesses on its surface, it is preferable that the variation in the diameters of the openings of the plurality of recesses present on the surface of the antibacterial member is small. Specifically, among the plurality of recesses present on the surface of the antibacterial member, it is preferable that the proportion of the recesses whose measured value D of the opening diameter satisfies the following formula (1) is 50% or more based on the number, more preferably 80% or more, even more preferably 90% or more, and even more preferably 100%. D in formula (1) av means the arithmetic mean value of the diameters of the openings of the plurality of recesses present on the surface of the antibacterial member. Formula (1): 0.8×D av ≦D≦1.2×D av

[0020] When the antibacterial member has a plurality of recesses on its surface, the antibacterial member preferably has a region where the center-to-center distance of the recesses is 300 nm or less. When the antibacterial member has a region where the center-to-center distance of the recesses is 300 nm or less, the antibacterial action tends to be fully exhibited. The center-to-center distance of the recesses may be, for example, 250 nm or less, 200 nm or less, or 150 nm or less. The center-to-center distance of the recesses may be, for example, 10 nm or more, 15 nm or more, or 20 nm or more.

[0021] The antibacterial member preferably has a region where the average center-to-center distance of the recesses is 100 nm or less. When the antibacterial member has a region where the average center-to-center distance of the recesses is 100 nm or less, the antibacterial action tends to be fully exhibited. The average center-to-center distance of the recesses may be, for example, 100 nm or less, 50 nm or less, or 40 nm or less. The average center-to-center distance of the recesses may be, for example, 10 nm or more, 15 nm or more, or 20 nm or more.

[0022] In the present disclosure, the "distance between the centers of the recesses" is defined as the distance between the centers of the regions corresponding to the respective openings when observing the openings of a pair of adjacent recesses. The "average distance between the centers of the recesses" is the arithmetic mean value of the distances between the centers of a plurality of recesses present on the surface of the antibacterial member.

[0023] When the number of recesses present on the surface of the antibacterial member is extremely large, the arithmetic mean value of the distances between the centers of the recesses may be the arithmetic mean value of the distances between the centers of the recesses randomly selected from the recesses present on the surface of the antibacterial member. In this case, from the viewpoint of measurement accuracy, it is preferable that the number of randomly selected recesses is 20 or more. The calculation of the arithmetic mean value is performed, for example, by acquiring an electron microscope image of the surface of the antibacterial member where the recesses are present, and based on the values measured from the recesses selected from the region including 20 or more recesses in the image.

[0024] The antibacterial member preferably has a region where the number of recesses is 100 or more per μm 2 or more. When the antibacterial member has a region where the number of recesses is 100 or more per μm 2 or more, the antibacterial action tends to be sufficiently exhibited. The number of recesses in the above region is, for example, 120 or more per μm 2 or more, 150 or more per μm 2 or more, or 200 or more per μm 2 or more. The number of recesses in the above region is, for example, 1000 or less per μm 2 or less, 800 or less per μm 2 or less, or 600 or less per μm 2 or less.

[0025] The material of the antibacterial member is not particularly limited. Examples of the material of the antibacterial member include inorganic materials such as metals and ceramics, organic materials such as resins, and combinations of inorganic materials and organic materials.

[0026] From the perspective of durability in the state where the concave portion is formed on the surface, it is preferable that the material of at least the surface where the concave portion exists in the antibacterial member is an inorganic material such as metal or ceramic.

[0027] From the perspective of forming concave portions with little variation in the diameter of the openings at a high density, the antibacterial member may be obtained by anodizing the surface of a substrate containing aluminum. Anodization is a process of forming a film made of aluminum oxide on the surface of a substrate by immersing a substrate containing aluminum as a positive electrode and a negative electrode in an acidic aqueous solution, connecting a DC power source between the electrodes, and applying an electric current. It is known that the film formed by anodization is in a state (porous alumina) containing cylindrical concave portions with the depth direction being the thickness direction of the film. That is, in the antibacterial member of the present embodiment, the peripheral portion of the concave portion may contain aluminum oxide. The concave portions on the surface of the antibacterial member of the present embodiment may exist in the anodic oxide film disposed on the substrate containing aluminum.

[0028] When forming the concave portions existing on the surface of the antibacterial member by anodization, the state (diameter, depth, center-to-center distance, etc.) of the concave portions contained in the anodic oxide film can be controlled by changing the conditions of the anodization. The method for controlling the state of the concave portions formed by anodization is not particularly limited, and known methods can be applied. As the acidic aqueous solution used for anodization, for example, an aqueous solution containing at least one acid selected from the group consisting of formic acid, acetic acid, oxalic acid, tartaric acid, phosphoric acid, sulfuric acid, chromic acid, citric acid, and malic acid can be used. The content rate of the acid contained in the etching solution can be selected, for example, from the range of 0.1% by mass to 1.0% by mass.

[0029] After performing anodization on the surface of the substrate containing aluminum, pore widening may be performed to expand the diameter of the openings of the concave portions formed by the anodization. Examples of the pore widening method include a method of bringing the surface of a substrate subjected to anodization into contact with an etching solution. As the etching solution used for pore widening, for example, an aqueous solution containing at least one acid selected from the group consisting of formic acid, acetic acid, oxalic acid, tartaric acid, phosphoric acid, sulfuric acid, chromic acid, citric acid, and malic acid can be used. The content rate of the acid contained in the etching solution can be selected, for example, from the range of 5% by mass to 20% by mass. By changing the components, temperature, and contact time contained in the etching solution, the diameter of the opening of the recess formed by anodization can be controlled.

[0030] <Antibacterial product> A second embodiment of the present disclosure is an antibacterial product including the antibacterial member of the first embodiment. The antibacterial product of this embodiment may consist only of the antibacterial member of the first embodiment or may be a combination of the antibacterial member of the first embodiment and other members. The type of the antibacterial product is not particularly limited, and examples thereof include various articles such as medical and pharmaceutical supplies (medical pads, surgical instruments, caps for medicine bottles, dental materials, etc.); housing-related supplies (doorknobs, handrails, etc.); food and cooking-related supplies (tableware, cooking utensils, sinks, faucets, serving trays, etc.); infrastructure-related supplies (pipes used for water treatment or factory facilities, etc.); automobile-related supplies (doorknobs, etc.); miscellaneous goods (pen holders, rulers, mechanical pencils, calculators, etc.); electronic devices (personal computers, smartphones, etc.); and entertainment-related supplies (medals used in gaming machines, etc.).

Examples

[0031] Hereinafter, the present disclosure will be described more specifically with reference to examples. However, the present disclosure is not limited to these examples.

[0032] <Production of antibacterial member> Pretreatment was performed on a substrate made of aluminum in the following order: degreasing, water washing, etching (using caustic soda), water washing, neutralization (using nitric acid), and water washing. An anodizing treatment was carried out on the substrate after pretreatment, and then washing with pure water was performed. After washing, a pore widening treatment was carried out on the substrate, and then washing with pure water was performed. For the anodizing treatment, an aqueous sulfuric acid solution was used as the electrolyte, and the treatment was carried out under the conditions of 15°C to 30°C and a voltage of 20 V or less. For the pore widening treatment, an aqueous sulfuric acid solution was used as the etching solution, and the temperature and immersion time were adjusted so that an anodic oxide film containing recesses satisfying the conditions shown in Table 1 was formed on the surface of the substrate.

[0033] <Electron Microscopic Observation of Antibacterial Member> Pt evaporation treatment for imparting conductivity was performed on the surface of the antibacterial member obtained in Example 1, and an electron microscope image was taken. An image of the surface of the antibacterial member obtained in Example 1 is shown in Fig. 1A (magnification: 200,000), and an image of the cross-section of the antibacterial member is shown in Fig. 1B (magnification: 10,000). An image of the surface of the antibacterial member obtained in Example 2 is shown in Fig. 2A (magnification: 200,000), and an image of the cross-section of the antibacterial member is shown in Fig. 2B (magnification: 10,000). An image of the surface of the antibacterial member obtained in Example 3 is shown in Fig. 3A (magnification: 200,000), and an image of the cross-section of the antibacterial member is shown in Fig. 3B (magnification: 10,000). As shown in Fig. 1A, Fig. 1B or Fig. 1C, recesses with an opening diameter of 100 nm were formed on the surface of the antibacterial members obtained in Examples 1 to 3. As shown in Fig. 1B, Fig. 2B or Fig. 3B, a layer (anodic oxide film) containing cylindrical recesses extending along the thickness direction was observed between the substrate and the Pt evaporation layer of the antibacterial members obtained in Examples 1 to 3. Table 1 shows the measurement results of the maximum diameter, minimum diameter, average diameter, average center-to-center distance, number and depth of the recesses observed in the images of the antibacterial members.

[0034]

Table 1

[0035] The "maximum diameter" and "minimum diameter" of the recesses shown in Table 1 are the maximum diameter and minimum diameter of the opening diameters of the recesses observed in the region (200 nm × 200 nm) in the images shown in FIGS. 1A, 1B, or 1C. The "average diameter" and "average center - to - center distance" of the recesses shown in Table 1 are the arithmetic mean values of the opening diameters and center - to - center distances of 20 recesses randomly selected from the region (200 nm × 200 nm) in the images shown in FIGS. 1A, 2A, or 3A. The "number" of the recesses shown in Table 1 is the number of recesses observed in the region (1 μm 2 ) shown in FIGS. 1A, 2A, or 3A. The "depth" of the recesses shown in Table 1 is the arithmetic mean value of the depths of 20 recesses randomly selected from the cross - sectional images of the antibacterial members shown in FIGS. 1B, 2B, or 3B.

[0036] <Antibacterial test of antibacterial member> Against the antibacterial members obtained in Examples 1 to 3, an antibacterial test in accordance with JIS Z 2801 was carried out. The same antibacterial test was also carried out on the substrate without anodizing treatment (Comparative Example 1). In the test, the viable - cell number ratios were measured 0.5 hour, 1 hour, 5 hours, and 24 hours after inoculating the test pieces with bacteria. Staphylococcus aureus was used as the bacteria, and the concentration of the bacteria was 2.5×10 5 CFU / mL to 10 6 CFU / mL, and the culture medium was 1 / 25NB. The results are shown in Table 2.

[0037] <Antiviral test of antibacterial member> Against the antibacterial members obtained in Examples 1 to 3, an antiviral test in accordance with ISO 21702:2019 was carried out. The same antibacterial test was also carried out on the substrate without anodizing treatment (Comparative Example 1). In the test, the infectious titers were measured 0.5 hour, 1 hour, 5 hours, and 24 hours after inoculating the test pieces with the virus. The infectious titer is an index representing the degree of virus inactivation and is a value measured by TCID50 (50% tissue culture infectious dose). As the virus, feline calicivirus (size: 27 nm to 32 nm, non-enveloped) was used. The results are shown in Table 3.

[0038]

Table 2

[0039]

Table 3

[0040] As shown in Table 2, all of the antibacterial members of Examples 1 to 3 having recesses on the surface with an opening diameter of 100 nm or less or an average opening diameter of 50 nm or less exhibited excellent antibacterial effects. Furthermore, as shown in Table 3, the antibacterial member of Example 1 having recesses on the surface with an average opening diameter of 10 nm or less exhibited antiviral effects as well as antibacterial effects.

Claims

**Claim 1** An antibacterial member having recesses with an opening diameter of 100 nm or less on its surface. **Claim 2** An antibacterial member having recesses with an average opening diameter of 50 nm or less on its surface. **Claim 3** The antibacterial member according to claim 1 or claim 2, wherein an average center-to-center distance between the recesses is 100 nm or less. **Claim 4** The number of the recesses is 100 pieces / μm ２ The antibacterial member according to claim 1 or 2, having a region where the above is satisfied **Claim 5** The antibacterial member according to claim 1 or claim 2, having recesses with an average opening diameter of 10 nm or less on its surface. **Claim 6** The antibacterial member according to claim 1 or claim 2, wherein a peripheral portion of the recess contains aluminum oxide. **Claim 7** The antibacterial member according to claim 1 or claim 2, wherein the recesses are present in an anodic oxide film disposed on a substrate containing aluminum. **Claim 8** The antibacterial member according to claim 7, wherein a thickness of the anodic oxide film is 500 nm or more. **Claim 9** An antibacterial product comprising the antibacterial member according to claim 1 or claim 2.

Images