Antibacterial sheet and manufacturing method therefor

The present invention relates to an antibacterial sheet and a method for producing the same.

In recent years, the use of electronic devices such as personal computers has been increasing in medical facilities and food processing facilities. In medical facilities and the like, it is required to suppress the growth of harmful microorganisms such as pathogens in the room and keep the room clean. Traditionally, in this type of facility, indoor cleanliness has been maintained by various methods such as cleaning by wiping with water and sterilization using chemicals. In order to maintain the cleanliness of the room by methods such as cleaning and sterilization, it is necessary to perform cleaning and sterilization on a regular basis.

However, since many people frequently touch the interfaces of electronic devices such as keyboards, operation panels, and touch panels, their cleanliness is likely to be impaired. Ideally, in order to keep these parts clean, it is desirable to perform cleaning and sterilization each time they are used, but cleaning each time they are used is extremely complicated. Therefore, it is required to reduce the frequency of cleaning and sterilization.

In response to this problem, a method of covering the interface with a sheet or film having an antibacterial action, that is, an action of suppressing the growth of bacteria, to reduce the frequency of cleaning and sterilization has been attracting attention. For example, Patent Document 1 describes a vacuum in which at least one antibacterial metal thin film is formed on at least one surface of a flexible polymer film base material, and the metal thin film is formed by heating and melting a metal evaporation source. An antibacterial film formed by a vapor deposition method is described.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2010-247450</text></patcit></p>

<p> In the antibacterial film of Patent Document 1, in order for the antibacterial metal thin film to sufficiently exert the antibacterial effect, it is necessary to increase the thickness of the antibacterial metal thin film to some extent. However, as the thickness of the antibacterial metal thin film increases, it becomes difficult for visible light to pass through the antibacterial film. Therefore, when the antibacterial film of Patent Document 1 is used for the interface of an electronic device such as a keyboard, an operation panel, and a touch panel, the visibility of the interface may be deteriorated.</p><p> The present invention has been made in view of such a background, and an object of the present invention is to provide an antibacterial sheet having high transparency of visible light and high antibacterial effect.</p>

<p> One aspect of the present invention includes a resin film and copper particles adhering to at least one surface of the resin film, has a total light transmittance of 20% or more at a wavelength of 380 to 780 nm, and is an average circle of the copper particles. The equivalent diameter is 10 to 30 nm, and the amount of the copper particles attached is 100 to 200 mg / μm.²It is on the antibacterial sheet.</p>

<p> The antibacterial sheet has a resin film and copper particles formed on the resin film and having an average circle-equivalent diameter in the specific range. By setting the amount of copper particles attached to the above-mentioned specific range, an antibacterial sheet exhibiting a high antibacterial effect against various bacteria can be obtained.</p><p> Further, by forming copper particles having an average circle-equivalent diameter in the specific range on the resin film, the transmission of visible light can be remarkably enhanced. As a result, the total light transmittance in the specific range can be realized. The antibacterial sheet having a total light transmittance in a specific range is excellent in visible light transmittance, and can suppress deterioration of visibility of interfaces of electronic devices such as keyboards, operation panels, and touch panels.</p><p> As described above, the antibacterial sheet is excellent in antibacterial effect and transparency of visible light. Therefore, it can be suitably used for protecting the interface of an electronic device.</p>

<figref num="1">It is a partially enlarged sectional view of the antibacterial sheet in an Example.</figref><figref num="2">It is an SEM image of the test material A2 in an Example.</figref><figref num="3">It is an SEM image of the test material A6 in an Example.</figref><figref num="4">It is an SEM image of the test material A11 in an Example.</figref><figref num="5">It is an SEM image of the test material A21 in an Example.</figref><figref num="6">It is a drawing substitute photograph which shows the state which superposed the test material A10 and the printed matter in an Example.</figref><figref num="7">It is a drawing substitute photograph which shows the state which superposed the test material A11 and the printed matter in an Example.</figref><figref num="8">It is a drawing substitute photograph which shows the state which superposed the test material A12 and the printed matter in an Example.</figref><figref num="9">It is a drawing substitute photograph which shows the state which superposed the test material A13 and the printed matter in an Example.</figref>

In the antibacterial sheet, as the resin film, a resin film transparent to visible light can be used. The resin film preferably contains one or more of polyester, polyolefin, polycarbonate, polyurethane, polyvinyl chloride and silicone. Since these resins have a high refractive index, the transparency of visible light of the antibacterial sheet can be further improved. Further, since these resins have high heat resistance, deterioration of the resin film during vacuum deposition in the process of manufacturing the antibacterial sheet can be suppressed.

As the polyester, for example, polyethylene terephthalate, polymethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate and the like can be used. Further, as the polyolefin, for example, a homopolymer of an olefin such as polyethylene or polypropylene, or a copolymer containing an olefin such as an ethylene-propylene copolymer can be used.

The thickness of the resin film can be, for example, 5 to 250 μm. If the thickness of the resin film is less than 5 μm, it tends to be difficult to handle the resin film in the manufacturing process. On the other hand, if the thickness of the resin film exceeds 250 μm, the transparency of visible light may decrease.

A large number of copper particles are attached to the resin film. The copper particles may be composed of pure copper or a copper alloy. When the copper particles are composed of a copper alloy, the content of copper in the copper alloy is preferably 60% by mass or more from the viewpoint of sufficiently exerting the antibacterial effect of copper.

The average circle-equivalent diameter of copper particles is 10 to 30 nm. By setting the average circle-equivalent diameter of the copper particles to the above-mentioned specific range, an antibacterial sheet having excellent visible light transmission can be obtained. When the average equivalent circle diameter of the copper particles is less than 10 nm, visible light is likely to be scattered by the copper particles. Further, in this case, since the layer of copper particles optically behaves as a continuous film, there is a possibility that the transparency of visible light may be lowered.

Further, when the average equivalent circle diameter of the copper particles exceeds 30 nm, the copper particles agglomerate with each other, and the layer of the copper particles becomes a state close to a continuous film. Therefore, even in this case, the transparency of visible light may be lowered.

The average circle-equivalent diameter of the copper particles is a value calculated by the following method. First, the copper particles on the resin film are observed using an SEM (that is, a scanning electron microscope), and an SEM image of the copper particles is obtained. The observation magnification and the visual field area are not particularly limited as long as the number of copper particles in the visual field can be sufficiently increased. For example, the observation magnification can be appropriately selected from the range of 10,000 to 300,000 times. The equivalent circle diameter of the copper particles present in the SEM image obtained by using the image analyzer is calculated. The arithmetic mean of these circle-equivalent diameters may be the average circle-equivalent diameter of the copper particles.

The amount of copper particles attached is 100 to 200 mg / μm.²And. As a result, an antibacterial sheet having both an antibacterial effect and visible light transmission can be obtained. Adhesion amount of copper particles is 100 mg / μm²If it is less than, the amount of copper adhering to the resin film is insufficient, which may lead to a decrease in the antibacterial effect. Adhesion amount of copper particles is 200 mg / μm²If it exceeds, the thickness of the layer of copper particles becomes excessively thick, which may lead to a decrease in the transparency of visible light.

The amount of adhesion of copper particles can be calculated, for example, by measuring the characteristic X-ray intensity of Cu by fluorescent X-ray analysis and then converting the characteristic X-ray intensity into the amount of adhesion using a calibration curve prepared in advance. ..

The number of copper particles exposed on the surface of the antibacterial film is 1500 to 5000 / μm.²Is preferable. In this case, the transparency of visible light of the antibacterial sheet can be further improved. The number of copper particles exposed on the surface of the antibacterial film is the number of copper particles present in the SEM image of the copper particles by an image analyzer after obtaining the SEM image of the copper particles in the same manner as the above-mentioned average circle equivalent diameter. It can be calculated by counting and converting this number into a number per unit area.

The total light transmittance of the antibacterial sheet at a wavelength of 380 to 780 nm is 20% or more. Since the antibacterial sheet having the total light transmittance in the specific range has high visible light transmittance, the antibacterial effect can be exhibited without impairing the visibility of the interface of an electronic device such as a keyboard. Therefore, the antibacterial sheet is suitable for protecting the interface. The total light transmittance of the antibacterial sheet at a wavelength of 380 to 780 nm is a value measured by a method conforming to JIS K7361-1: 1997. For example, a haze meter can be used to measure the total light transmittance.

The total light transmittance at a wavelength of 380 to 780 nm is preferably 30% or more, more preferably 40% or more, further preferably 45% or more, and particularly preferably 50% or more. In this case, since the color of the antibacterial sheet becomes lighter, it is possible to more effectively suppress the change in the color tone of the interface when the antibacterial sheet is coated.

As described above, the antibacterial sheet has a high antibacterial effect and excellent visible light transmission. Therefore, for example, not only an interface having a backlight such as a touch panel but also an interface having no backlight such as a keyboard can be protected without impairing the visibility. Therefore, the antibacterial sheet is particularly suitable as a keyboard cover.

The antibacterial sheet may have a primer layer between the resin film and the copper particles. In this case, the adhesiveness between the resin film and the copper particles can be further improved, and the peeling of the copper particles from the resin film can be suppressed for a longer period of time. As a result, the antibacterial effect of the antibacterial sheet can be maintained for a longer period of time.

As the primer layer, for example, an adhesive having high adhesiveness to both the resin film and the copper particles can be used. Examples of such an adhesive include an adhesive containing a resin such as a polyamide resin, a polyolefin resin, an epoxy resin, a polyester resin, a polyurethane resin, an acrylic resin, and a nitrified cotton resin.

Further, an adhesive layer for sticking to the object to protect the antibacterial sheet may be provided on the back surface of the resin film in the antibacterial sheet, that is, the surface on the side not having copper particles. The material of the adhesive layer is not particularly limited as long as it is transparent. For example, as the adhesive layer, an acrylic adhesive, a rubber adhesive, a urethane adhesive, a silicone adhesive, or the like can be used.

In producing the antibacterial sheet, for example, after preparing the resin film, the pressure is 1 × 10.^-4~1×10^-2A method of forming the copper particles on the resin film can be adopted by performing vacuum deposition under control within the range of Pa.

By setting the pressure during vacuum deposition within the specific range, the average circle-equivalent diameter of the copper particles formed on the resin film can be controlled within the specific range. Pressure during vacuum deposition is 1x10^-4When it is less than Pa, a continuous copper film is likely to be formed on the resin film. Also, the pressure during vacuum deposition is 1 x 10^-2When it exceeds Pa, the average circle-equivalent diameter of the copper particles tends to increase. Therefore, if the pressure during vacuum deposition deviates from the specific range, the transparency of visible light may decrease. From the viewpoint of surely forming copper particles on the resin film, the pressure during vacuum deposition is 1 × 10.^-3~1×10^-2It is preferable to perform vacuum deposition by controlling it within the range of Pa.

The vapor deposition rate during vacuum deposition is preferably 0.5 to 5 nm / sec. By setting the vapor deposition rate within the specific range, it is possible to more reliably form copper particles having an average circle-equivalent diameter in the specific range while avoiding deterioration of productivity. If the vapor deposition rate is less than 0.5 nm / sec, the time required for vacuum deposition becomes long, which may lead to deterioration of productivity. Further, when the vapor deposition rate exceeds 5 nm / sec, a continuous copper film is likely to be formed on the resin film, which may lead to a decrease in the transparency of visible light.

In the above-mentioned production method, after preparing the resin film and before performing vacuum deposition, the resin film may be pretreated if necessary. As the pretreatment, for example, a treatment for normalizing the surface of the resin film can be performed. Specifically, as such a treatment, a surface treatment such as a corona discharge treatment, a plasma treatment, or a glow discharge treatment can be adopted.

<p> Examples of the antibacterial sheet and the method for producing the same will be described with reference to FIG. The specific embodiment of the antibacterial sheet and the method for producing the antibacterial sheet according to the present invention is not limited to the following aspects, and the configuration can be appropriately changed as long as the gist of the present invention is not impaired.</p><p> As shown in FIG. 1, the antibacterial sheet 1 of this example has a resin film 2 and copper particles 3 attached to one side of the resin film 2. The antibacterial sheet 1 can be produced, for example, by the following method.</p><p> First, as the resin film 2, a transparent film having a thickness of 30 μm containing polyethylene terephthalate is prepared. Pure copper is adhered to one side of the resin film 2 by a vacuum vapor deposition method. As the evaporation source in vacuum vaporization, pure copper having a diameter of about 1 mm and having a purity of 99.9% by mass or more is used.</p><p> Vacuum deposition can be performed, for example, as follows. First, the resin film is placed on the cooling stage in the vapor deposition apparatus. After that, the pressure inside the vapor deposition apparatus is reduced. Then, vacuum deposition is performed while cooling the resin film by the cooling stage. By performing vacuum deposition while cooling the resin film in this way, it is possible to suppress the occurrence of heat shrinkage, wrinkles, strain, etc. of the resin film.</p><p> The antibacterial sheets (test materials A1 to A24) shown in Table 1 can be obtained by controlling the pressure in the apparatus within the range shown in Table 1 and appropriately changing the vapor deposition rate and time. The vapor deposition rate in this example is in the range of 0.05 to 5 nm / sec.</p><p> The method for measuring the average circle-equivalent diameter of copper particles, the amount of adhesion, and the number of copper particles exposed on the surface of each test material is as follows.</p><p>-Use an electrolytic emission scanning electron microscope ("SU8230" manufactured by Hitachi High-Technologies Corporation) with an average circle-equivalent diameter to acquire an SEM image of the surface to which copper particles are attached in each test material. The acceleration voltage at the time of SEM image acquisition is 1.0 kV, the working distance is 3.0 mm, and the observation magnification is 100,000 times. From the copper particles shown in the obtained SEM image, 30 copper particles showing the entire particles are randomly selected. Then, the arithmetic mean of the circle-equivalent diameters of these copper particles is defined as the average circle-equivalent diameter of the copper particles. The average circle-equivalent diameter of the copper particles in each test material is as shown in Table 1.</p><p>-Number of copper particles exposed on the surface A square region with a side of 200 nm is randomly set in the above-mentioned SEM image, and the number of copper particles existing in the region is counted. This number is 1 μm²The value converted into the number of hits is taken as the number of copper particles exposed on the surface. The number of copper particles exposed on the surface of each test material is as shown in Table 1.</p><p>-Adhesion amount Using a fluorescent X-ray analyzer ("RIX3100" manufactured by Rigaku Co., Ltd.), perform fluorescent X-ray analysis of the surface to which copper particles are attached in each test material to measure the adhesion amount of copper. The amount of copper particles attached to each test material is as shown in Table 1.</p><p> The method for evaluating the transparency of visible light and the antibacterial effect of each test material is as follows.</p><p>-Using a visible light transmittance haze meter ("NDH-2000" manufactured by Nippon Denshoku Kogyo Co., Ltd.), the total light transmittance of each test material at wavelengths of 380 to 780 nm can be determined by a method that complies with JIS K7361-1: 1997. Measure. The total light transmittance of each test material is as shown in the "Transmittance" column of Table 1.</p><p> Further, in this example, in addition to the above-mentioned transmittance, the visibility of the printed content when the printed matter printed in monochrome by the laser printer and the test material are superposed is evaluated. In the printed matter P used in this example, the characters "ABC" are printed in black on a white paper surface as shown in FIGS. 6 to 9. In the "Visibility of printed matter" column of Table 1, the symbol "A" is entered when the printed matter and the test material are overlapped, and the symbol "B" is entered when the printed matter cannot be visually recognized. did.</p><p>-Antibacterial effect Collect an antibacterial processed test piece showing a square shape with a side of 40 mm from each test material. In addition, an unprocessed test piece having a square shape with a side of 40 mm is collected from the resin film 2 before vacuum deposition. Using these test pieces, antibacterial test is performed by the method specified in JIS Z 2801: 2010. The bacteria used in the test are Staphylococcus aureus and Escherichia coli, and the culture time is 24 hours.</p><p> Based on the viable cell count after culturing for 24 hours in each test piece, the antibacterial activity value indicating the magnitude of the antibacterial effect can be calculated. Specifically, the antibacterial activity value R is a value calculated by the following formula. In the formula below, the symbol Ut is the average logarithm of the common logarithm of the viable cell count after 24-hour culture in the unprocessed test piece, and At is the average logarithm of the common logarithm of the viable cell count after 24-hour culture in the antibacterial processed test piece. The value. R = Ut-At</p><p> Table 1 shows the antibacterial activity values of each test material. In the evaluation of the antibacterial effect, it was judged that the antibacterial activity value R of both Staphylococcus aureus and Escherichia coli was 2.0 or more and passed, and that at least one of them was less than 2.0 was rejected.</p><p><tables num="1"><img file="JP2020066187A_D0001.tif" /></tables></p><p> As shown in Table 1, the test materials A5 to A7, A10 to A12, and A15 to A17 have copper particles 3 having an average circle equivalent diameter of 10 to 30 nm on the resin film 2. The amount of copper particles 3 attached to these test materials is 100 to 200 mg / m.²The total light transmittance at wavelengths of 380 to 780 nm is 20% or more. 3 and 4 show SEM images of test material A6 and test material A11 as representatives of these test materials.</p><p> As shown in FIGS. 3 and 4, in these test materials, fine copper particles 3 are attached to the entire surface of the resin film. Therefore, it can be understood that these test materials have excellent visible light transmission and a high antibacterial effect as shown in Table 1.</p><p> Among these test materials, the test materials A5, A6, A10, A11, and A15 having a total light transmittance of 30% or more at a wavelength of 380 to 780 nm are the test materials A10 and FIG. 7 illustrated in FIG. When the printed matter P and the test material are overlapped with each other as in the test material A11 illustrated in the above, the printed content can be easily visually recognized even when light is not transmitted from the back surface. Therefore, these test materials can exert an antibacterial effect while ensuring visibility in both an interface having a backlight such as a touch panel and an interface having no backlight such as a keyboard.</p><p> On the other hand, the test material having a total light transmittance of 20% or more and less than 30% at a wavelength of 380 to 780 nm is a test material having a total light transmittance of 30% or more like the test material A12 illustrated in FIG. The visibility of the printed matter P is lower than that of the printed matter P. Therefore, when the total light transmittance of the antibacterial sheet is 20% or more and less than 30%, it is desirable to irradiate light from behind the interface using a backlight or the like in order to improve the visibility of the interface. ..</p><p> As shown in the test materials A4, A9, and A14, when the amount of the copper particles 3 adhered is less than the above-mentioned specific range, the antibacterial effect may be insufficient. Further, as shown in the test materials A8, A13, and A18, even if the average circle equivalent diameter of the copper particles 3 is within the above-mentioned specific range, if the amount of adhesion is excessively large, all light rays at a wavelength of 380 to 780 nm. The transmittance is less than 20%. With these test materials, unlike the test material A13 illustrated in FIG. 9, the printed content of the printed matter P can hardly be visually recognized. As described above, an antibacterial sheet having a total light transmittance of less than 20% at a wavelength of 380 to 780 nm is not preferable for protecting the interface because it is difficult to visually recognize the interface through the antibacterial sheet.</p><p> In addition, the pressure inside the device during vacuum deposition is 10^-5When the film is lowered to the Pa level, a continuous film of pure copper is likely to be formed on the resin film 2 as in the test material A2 illustrated in FIG. A continuous film of pure copper has lower visible light transmission than a layer composed of copper particles. Therefore, if an attempt is made to reduce the amount of adhesion in order to increase the transparency of visible light, the antibacterial effect is lowered as in the test material A1. Further, if an attempt is made to increase the amount of adhesion in order to obtain a sufficient antibacterial effect, the total light transmittance at a wavelength of 380 to 780 nm becomes less than 20% as in the test materials A2 and A3.</p><p> In addition, the pressure inside the device during vacuum deposition is 10^-1When it rises to the Pa stand, a continuous film-like structure in which copper particles are agglomerated on the resin film 2 is likely to be formed as in the test material A21 illustrated in FIG. Also in this case, the transmission of visible light is lower than that of the layer made of copper particles having an average circle-equivalent diameter in the specific range. Therefore, as in the case of the continuous film, if an attempt is made to reduce the amount of adhesion in order to increase the transparency of visible light, the antibacterial effect is lowered as in the test material A19. Further, if an attempt is made to increase the amount of adhesion in order to obtain a sufficient antibacterial effect, the total light transmittance at a wavelength of 380 to 780 nm becomes less than 20% as in the test materials A20 to A23.</p>

1 Antibacterial sheet 2 Resin film 3 Copper particles