Antimicrobial substrate

ANTIMICROBIAL SUBSTRATE

The present invention relates to an antimicrobial substrate, a method for producing an antimicrobial substrate and to the use of an antimicrobial substrate.

More specifically, the present invention relates to an antimicrobial substrate comprising a sheet of glazing material and a photocatalytic layer, a method of producing same, and the use of same to reduce the presence of microbes on a surface. The invention also relates to antimicrobial articles comprising antimicrobial substrates prepared in accordance with the present invention such as, for example, but not limited to: architectural and automotive glazings, splash-backs, furniture, bottles, wall coverings, mirrors and touchscreens.

There is a need to prevent the transmission of potentially harmful microbes between humans and animals. In relation to the present invention, microbes include bacteria, viruses and fungi as well as yeasts and germs. One way in which microbes are transmitted is by “surface transmission”. This is where an individual interacts with a surface that has previously been seeded with microbes, for example by previous interaction with the surface by infectious individuals.

Transparent and semi-transparent surfaces, such as glazings, mirrors and displays are commonly found in environments which are shared by multiple individuals. As such, transparent and semi-transparent surfaces may act as a vector for the transmission of microbes, especially bacteria and viruses. This is particularly a problem in spaces which may be occupied by large numbers of people in succession, such as toilets, corridors, hospital rooms, shops and workplaces.

In addition, as the extent to which electronic devices are used in the world increases, so the presence of micro-organisms which may reside on a screen surface also increases, and therefore, the potential transfer of micro-organisms from one individual to another. Indeed, touch screens and mirrors located for example in shops and supermarkets may have hundreds of individuals per hour using the touch screen terminal or touching the mirror surface and potentially spreading microbes from one user to another. In addition, as the threat of resistance to antibiotics by certain bacterial strains increases, and as epidemics arise from the transmission of some viruses, there is an ever-increasing need for surfaces, no matter the device or application, to be able to halt the spread of micro-organisms.

Surface transmission can be significantly curtailed if, following seeding of the surface, the number of infectious microbes is reduced, preferably to a level where there is no risk of transmission to subsequent individuals.

Some surfaces are inhospitable to microbes, such that over time, microbes upon them are denatured and are no longer infectious. For example, it has been known for some time that microorganisms including bacteria, viruses and yeasts may be killed or rendered inactive if brought into contact with certain metallic or organic surfaces.

However, smooth surfaces, such as those typically used for glazing materials, are known to be environments upon which many microbes may survive for long periods of time. For example, whilst the SARS-Cov-2 virus is denatured to half the initial level on wood in around three hours, the same reduction on glass requires 24 hours, and on stainless steel requires 96 hours to attain the same level of reduction (“Stability of SARS-CoV-2 in different environmental conditions”, Chine et al, The Lancet Microbe, CORRESPONDENCE, Volume 1 , Issue 1 , E10, May 01 2020).

It is known to modify surfaces to produce an antimicrobial effect. However, the ability to incorporate antimicrobial properties into surfaces which are required to remain transparent to a required standard such as the glazing in windows and doors and which are also resistant to for example wear and scratching, has proved difficult. This is because, not only it is difficult to impart lasting antimicrobial activity to glass substrates, but also, any modification or coating applied to a glass substrate which provides antimicrobial activity must still provide the required parameters of a glazing whilst retaining a pleasing aesthetic appearance at an acceptable cost.

Attempts have been made to impart antimicrobial activity to a substrate surface. For example, in WO 2009/098655 there is described a method for conferring antibacterial properties to a substrate which comprises coating said substrate with a silver film by radio-frequency sputtering. However, the document is silent with respect to the properties of the glass substrate after treatment.

In WO 2005115151 there is disclosed a functional sol-gel coating agent which comprises a nano-particulate additive and which is said to have both an antimicrobial function and a decorative function as a result of the surface of the particle being modified by attachment of a dispersing aid and/or an adhesion promotor in the formed of functional silanes, that is, oligomers with a high OH group content.

Likewise, in JP 2005119026 there is described a substrate which provides antibacterial and anti-staining properties at the same time by way of a film comprising substituted siloxane molecules with surface hydroxyl groups on the entire surface of the substrate, the film further containing particles of silver.

WO 2007108514 A1 aims to provide a glass plate having an antibacterial film by forming an antibacterial film having a film thickness of 2 nm or more but not more than 100 nm on a glass plate either directly or via an undercoat film. Similarly, WO 2014112345 A1 aims to provide a base with an antiviral film. The antiviral film has a layer that is mainly composed of titanium oxide and an island part arranged on the surface of the layer and mainly composed of a Cu-based material.

However, there exists a need for a surface which even though located in areas of persistent human contact, may be readily cleaned to provide a safer environment.

In order to rapidly reduce the number of microbes adhered to a surface, it is usual to clean a surface with a detergent. However, such cleaning is often performed manually and is time consuming. In addition, common cleaning agents may erode surfaces, especially coated glass surfaces and mirrored surfaces leading to impaired appearance and performance.

Surfaces which are modified to provide a self-cleaning effect are known. For example, WO 2000075087 A1 discloses a self-cleaning coated substrate, especially a glass substrate, having high photocatalytic activity and low visible light reflection and a durable self-cleaning coated glass and a process for making same. The process comprises depositing a titanium oxide coating on the surface of the substrate by contacting it with a fluid mixture containing a source of titanium and a source of oxygen, the substrate being at a temperature of at least 600 °C. The coated surface has good durability, a high photocatalytic activity and a low visible light reflection. Most preferably the deposition temperature is in the range 645 °C to 720 °C which provides especially good durability. The fluid mixture preferably contains titanium chloride and an ester, especially ethyl acetate.

Unfortunately, for some applications, a surface may not be sufficiently inhospitable to microbes, and traditional cleaning practices and products may not successfully remove sufficient levels of microbes. In such cases, it is common to use a “disinfection” process whereby the number of infectious microbes on a smooth surface is further reduced to a safe level by denaturing, rendering many of the microbes inactive.

One method of disinfection is by cleaning surfaces using a germicidal cleaner, such as a bleach. However, the use of bleach as a disinfectant may give rise to similar problems as stated above in respect of cleaning with a detergent, namely impaired appearance and performance of the substrate surface. However, cleaning performed manually with a germicidal product can often be more damaging and corrosive to the surface. Furthermore, germicidal cleaners may not sufficiently denature all microbes on the surface.

An alternative method of disinfecting surfaces is by UV disinfection. In this situation, UV light irradiation is used to denature microbes on a surface. UV is the term given to light in the wavelength range 100 to 400nm. UV light is commonly divided into UVA (320 to 400 nm), UVB (280 to 320 nm), and UVC (100 to 280 nm). UV light is particularly effective for disinfecting surfaces, as the light penetrates microbes and alters their DNA structure, impairing and preventing replication.

In some cases, UV disinfection may be used in addition to disinfection with a germicidal cleaner. The additional UV disinfection step further reduces the prevalence of microbes on the surface, therefore reducing the likelihood of infection due to contact with the surface. An advantage of using UV disinfection in addition to disinfection with a germicidal cleaner is that this may allow the use of less corrosive cleaners, or may allow increased confidence that the surface is fully disinfected. However, UV light may also be harmful to humans and animals, causing burns and DNA damage. Therefore, UV disinfection is often only performed in a way that prevents humans and animals being exposed to UV light, thereby reducing the risk to individuals. UV light with a higher energy and therefore a shorter wavelength has the potential to be particularly harmful to individuals. As such, the exposure of individuals to UVB and UVC light is required to be much less than the exposure of individuals to UVA light.

It is therefore an object of the present invention to provide an antimicrobial substrate which may be effectively disinfected in an efficient manner and which minimises exposure and potential risk to individuals in the environment of the substrate. In addition, it is also an object of the present invention to provide an antimicrobial substrate which further provides the required optical and durability requirements of a glazing material, in particular a glass sheet, and that thereby meets the standards and requirements of the glazing industry.

According to a first aspect of the invention there is provided an antimicrobial substrate comprising: a sheet of glazing material, wherein the sheet of glazing material comprises a first surface and a second surface; and a photocatalytic layer, wherein the photocatalytic layer is located directly or indirectly on the first surface of the sheet of glazing material; and wherein the antimicrobial substrate further comprises a UV light reflective layer, wherein the UV light reflective layer is located between the photocatalytic layer and the first surface of the sheet of glazing material, or directly or indirectly upon the second surface of the sheet of glazing material.

According to the present invention, and for the avoidance of doubt, microbes comprise herein bacteria, viruses, yeasts, fungi and germs. Particular microbes which may be denatured by the antimicrobial substrate of the present invention include for example but are not limited to: gram positive and gram negative bacteria, including Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus (MRSA), and corona viruses including SARS-CoV-2. Therefore, according to the present invention, an antimicrobial substrate may be a substrate that reduces the survival of one or more microbes, such as for example bacteria or viruses present on the substrate, compared for instance to a non-coated sheet of the same substrate, such as a non-coated sheet of same glazing material.

According to the present invention, a sheet of glazing material may be a planar body that transmits at least 10% of incident visible light, or may be reversibly modified to transmit at least 10% of incident visible light.

In addition, reference to a layer being located directly on a surface means that no intervening layers are present between the layer and the surface, whereas, reference to a layer being indirectly located on a surface means that one or more intervening layers may be located between the layer and the surface.

Also in relation to the present invention, UV light is electromagnetic radiation with a wavelength of from 30 nm to 400 nm.

In relation to the present invention, the inventors have surprisingly found that photocatalytic layers which provide for example self-cleaning properties, may also provide an antimicrobial effect. In particular, the photocatalytic layers may provide an antibacterial and/or antiviral effect. Further, the inventors have found that by applying a UV reflective layer to the antimicrobial substrate, the photocatalytic effect of the antimicrobial substrate may be enhanced compared to a comparative antimicrobial substrate without the UV reflective layer.

Without wishing to be bound by any particular theory, it is proposed that a portion of the UV light that is not absorbed by the photocatalytic layer may be transmitted through the photocatalytic layer. The transmitted UV light is therefore not used by the photocatalytic layer for denaturing microbes such as viruses. However, the application of a UV light reflective layer to the antimicrobial substrate in accordance with the present invention, allows incident UV light not adsorbed by the photocatalytic layer to be reflected back to the photocatalytic layer and the effective intensity of UV light incident upon the photocatalytic layer to be increased. That is, the inventors have found that increasing the intensity of UV light incident upon the photocatalytic layer of the antimicrobial substrate, the antimicrobial performance of the antimicrobial substrate may be improved both during irradiation with UV light, and also in the period after irradiation has ceased.

Indeed, the photocatalytic activity of certain photocatalytic layers may continue long after irradiation has ceased, producing a so called “battery effect”. A particularly effective battery effect may continue to provide photocatalytic antimicrobial action for in excess of two hours after the cessation of irradiation with UV light.

Increasing the intensity of UV light incident upon the photocatalytic layer in this way may also be used to reduce the irradiation time of an antimicrobial article to which the antimicrobial substrate of the present invention is applied, without compromising antimicrobial activity. For example, in a clinical setting, this may allow antimicrobial substrates to be irradiated for comparatively short periods of time, promoting the antimicrobial effect, but which minimises disruption to individuals in the environment of the antimicrobial substrate. In exceptional circumstances, UV irradiation may be sufficiently short in duration that it may be carried out without any risk to individuals in the environment of the antimicrobial substrate.

Preferably the photocatalytic layer comprises titanium oxide, preferably titanium oxide with a predominantly anatase crystal structure. More preferably, the photocatalytic layer comprises titanium oxide with a greater than or equal to 50% anatase crystal structure. It has been found that a photocatalytic layer comprising titanium oxide has excellent antimicrobial properties, especially when illuminated with UV light. Furthermore, it has been found that, following irradiation of the photocatalytic layer with UV light, an increased antimicrobial effect persists even in the absence of any light at all. This effect has been demonstrated over 90 minutes, following irradiation.

Preferably the photocatalytic layer has a photocatalytic activity of greater than 5 x 10³ cm ¹ min^-1. More preferably the photocatalytic layer has a photocatalytic activity of greater than 1 x 10^-2 cm^-1 min^-1. Even more preferably the photocatalytic layer has a photocatalytic activity of greater than 3 x 10^-2 cm^-1 min^-1. Photocatalytic activity for the purposes of this application is determined by measuring the rate of decrease of the integrated absorbance of the infra-red absorption peaks corresponding to the C-H stretches of a thin film of stearic acid, formed on the coated substrate, under illumination by UV light from a UVA lamp having an intensity of about 32 W/m²at the surface of the coated substrate and a peak wavelength of 351 nm.

The stearic acid film may be formed on samples of the glasses, 7 to 8 cm square, by spin casting 20 pi of a solution of stearic acid in methanol (8.8 x 10³mol dm^-3) on the coated surface of the glass at 2000 rpm for 1 minute. Infra-red spectra may be measured in transmission, and the peak height of the peak corresponding to the C-H stretches (at about 2700 to 3000 cm ¹) of the stearic acid film measured and the corresponding peak area determined from a calibration curve of peak area against peak height. A suitable UVA lamp is a UVA-351 lamp (obtained from the Q-Panel Co., Cleveland, Ohio, USA) having a peak wavelength of 351 nm and an intensity at the surface of the coated glass of approximately 32 W/m² The photocatalytic activity is expressed in this specification as the rate of decrease of the area of the IR peaks (in units of cm ¹ min ¹).

Preferably, the photocatalytic layer meets the EN 1096-5-2016 standard test method and classification for the self-cleaning performances of coated glass surfaces.

Preferably, the photocatalytic layer has a thickness of 50 nm or lower. More preferably, the photocatalytic layer has a thickness of 40 nm or lower.

Preferably, the photocatalytic layer has a thickness from 10 nm to 40 nm. More preferably, the photocatalytic layer has a thickness from 15 to 30 nm. Even more preferably, the photocatalytic layer has a thickness from 15 to 20 nm.

Preferably the first surface further comprises an alkali metal ion blocking layer, wherein the alkali metal ion blocking layer is located between the first surface of the sheet of glazing material and the photocatalytic layer.

Preferably, the alkali metal ion blocking layer comprises silicon oxide. Preferably, the alkali metal ion blocking layer comprises silicon oxide having a thickness of from 15 to 40 nm, more preferably between 25 and 35 nm. Also in relation to the present invention, the sheet of glazing material preferably comprises glass. Preferably, the sheet of glazing material comprises flat glass. Preferably the sheet of glazing material comprises float glass. Preferably the sheet of glazing material comprises soda-lime silica float glass. Soda-lime silica float glass is particularly beneficial as it is widely available and therefore cost effective to use. In addition, soda-lime silica float glass may be coated using highly efficient online coating processes.

It is particularly preferred that the glass is low-iron glass. According to the present invention, low-iron glass comprises less than 200 ppm by weight iron.

When the UV reflecting layer is located on the second surface of the sheet of glazing material, it is particularly beneficial that the sheet of glazing material comprises low-iron glass. The low-iron glass increases the transmission of UV light through the glazing material, which in turn increases the amount of UV light reflected back to the photocatalytic layer by the UV reflecting layer.

Alternatively, the sheet of glazing material comprises down-drawn or rolled glass. Alternatively, the sheet of glazing material may comprise resin, such as polycarbonate.

Preferably, the antimicrobial substrate demonstrates a log reduction of at least 3 against one or more of Staphylococcus aureus, SARS-CoV-2, E.coli, P. gingivitis, or S. mutans. More preferably, the antimicrobial substrate demonstrates a log reduction of at least 4 against one or more of Staphylococcus aureus, SARS-CoV-2, E.coli, P. gingivitis, or S. mutans. Even more preferably, the antimicrobial substrate demonstrates a log reduction of at least 5 against one or more of Staphylococcus aureus, SARS-CoV-2, E.coli, P. gingivitis, or S. mutans.

Preferably the UV light reflective layer reflects greater than or equal to 20% of incident UV light at the peak wavelength in the UV reflection spectrum, or preferably, the UV light reflective layer reflects greater than or equal to 30% of incident UV light at the peak wavelength in the UV reflection spectrum. More preferably the UV light reflective layer reflects greater than or equal to 40% of incident UV light at the peak wavelength in the UV reflection spectrum. Even more preferably the UV light reflective layer reflects greater than or equal to 50% of incident UV light at the peak wavelength in the UV reflection spectrum, yet more preferably the UV light reflective layer reflects greater than or equal to 60% of incident UV light at the peak wavelength in the UV reflection spectrum.

Preferably, the UV light reflective layer reflects greater than 20% of incident UV light when irradiated with a broad spectrum 300 to 400 nm ilium inant, more preferably the UV light reflective layer reflects greater than 45% of incident UV light when irradiated with a broad spectrum 300 to 400 nm ilium inant. Even more preferably the UV light reflective layer reflects greater than 50% of incident UV light when irradiated with a broad spectrum 300 to 400 nm ilium inant, or the UV light reflective layer reflects greater than 60% of incident UV light when irradiated with a broad spectrum 300 to 400 nm ilium inant. Yet more preferably, the UV light reflective layer reflects greater than 80% of incident UV light when irradiated with a broad spectrum 300 to 400 nm ilium inant.

Preferably, the UV light reflective layer comprises a metal sublayer and/or a metalloid sublayer. Preferably, the metalloid sublayer comprises silicon. Preferably the metal sublayer and/or the metalloid sublayer has a thickness from 20 to 30 nm. Preferably, the UV light reflective layer comprises a metal oxide sublayer. Preferably the metal oxide sublayer comprises tin oxide. Preferably the metal oxide sublayer has a thickness from 15 nm to 25 nm. Preferably the UV light reflective layer comprises 2 or more sublayers.

Alternatively, in relation to the present invention the UV light reflective layer comprises a metal mirror layer. Preferably the metal mirror layer is located on the second surface of the sheet of glazing material.

Also in relation to the present invention, an encapsulating layer is preferably located indirectly on the second surface of the sheet of glazing material, such that the metal mirror layer is located between the encapsulating layer and the sheet of glazing material. The encapsulating layer preferably protects the metal mirror layer from damage, tarnishing and corrosion.

Preferably, the UV light reflective layer comprises a metal mirror layer. Preferably, the metal mirror layer comprises one or more of silver, chromium, nickel, tin, or aluminium.

Preferably, the antimicrobial substrate comprises a visible light reflective layer located between the photocatalytic layer and the first surface of the sheet of glazing material, or alternatively, directly or indirectly upon the second surface of the sheet of glazing material. In some embodiments, the antimicrobial substrate comprises a first visible light reflective layer between the photocatalytic layer and the first surface of the sheet of glazing material and a second visible light reflective layer directly or indirectly upon the second surface of the sheet of glazing material. The first and second visible light reflective layers may be the same material or different materials.

In some embodiments, the visible light reflective layer, and/or the first visible light reflective layer where present and/or the second visible light reflective layer where present, may be continuous. Alternatively, the visible light reflective layer, and/or the first visible light reflective layer where present and/or the second visible light reflective layer where present, may be discontinuous. According to the present invention a discontinuous layer may be formed for example as pattern. Herein, patterns include, but are not limited to, stripes and/or dots.

Preferably, the visible light reflective layer comprises an insulating layer. Preferably, the insulating layer is a silicon oxide sublayer. Preferably, the insulating layer has a thickness from 75 to 100 nm.

Preferably the UV light reflective layer is a visible light reflective layer. Alternatively, the visible light reflective layer is a different layer to the UV light reflective layer.

Preferably, the visible light reflective layer comprises a metal layer and/or a metalloid layer.

In some applications it may be preferable to provide a metal mirror layer with minimal visible light transmission, wherein, the metal mirror layer preferably has a thickness of from 100 nm to 1 cm. Thicker coatings are less cost effective, while thinner coatings may not be sufficiently opaque (non-transmissive). The thickness of the metal mirror layer should preferably be sufficient that the majority of visible light is reflected rather than transmitted.

Alternatively, it may be desirable to provide a so called “half mirror”. In such cases, a balance may be found between the reflection and transmission of visible light. In such a case, the metal mirror layer preferably has a thickness of from 20 nm to 100 nm. In accordance with the present invention, the photocatalytic layer preferably comprises copper and/or silver. Preferably, the photocatalytic layer comprises copper and/or silver containing particles. Preferably the particles are nanoparticles and/or microparticles.

According to the present invention, a nanoparticle may be particle with a diameter less than 100 nm. According to the present invention, a microparticle may be a particle with a diameter less than 1000 nm.

In addition, the antimicrobial substrate according to the present invention may further comprise an antimicrobial layer. The antimicrobial layer is preferably applied to the sheet of glazing material such that the photocatalytic layer is located between the sheet of glazing material and the antimicrobial layer.

Preferably, the additional antimicrobial layer comprises copper and/or silver. Preferably, the antimicrobial layer is in direct contact with the photocatalytic layer. Preferably, the additional antimicrobial layer is in the form of islands, such that at least as portion of the photocatalytic layer is exposed to the environment between islands of the additional antimicrobial layer. Preferably, the ratio of the sum of the areas of the island portions to the sum of the area of exposed photocatalytic layer is from 0.01 to 0.20.

Preferably, the diameter calculated by converting the average area of the island portion into a circle when observed along the cross-section of the antimicrobial layer is 1 to 20 nm. Such additional antimicrobial layers may be formed through processes described in WO201 4112345A1 .

Alternatively, the antimicrobial layer may comprise a matrix comprising particles of copper and/or silver. The particles of copper and/or silver may be nanoparticles and/or microparticles. Copper and silver metals act upon microbes, especially bacteria, by oligodynamic action which may cause complete inhibition of the microbe.

In some embodiments, the UV light reflective layer comprises a first UV light reflective layer located between the photocatalytic layer and the first surface of the sheet of glazing material, and the antimicrobial substrate further comprises a second UV light reflective layer directly or indirectly upon the second surface of the sheet of glazing material. The first and second UV light reflective layers may be the same material or different materials.

In some embodiments, the UV light reflective layer, and/or the first UV light reflective layer where present and/or the second UV light reflective layer where present, may be continuous. Alternatively, the UV light reflective layer, and/or the first UV light reflective layer where present and/or the second UV light reflective layer where present, may be discontinuous. According to the present invention a discontinuous layer may be formed for example as pattern. Herein, patterns include, but are not limited to, stripes and/or dots.

According to a second aspect of the invention there is provided a method for producing an antimicrobial substrate according to the first aspect of the invention, comprising the steps of: i) providing a sheet of glazing material with a first surface and a second surface; ii) applying a photocatalytic layer directly or indirectly to the first surface; and iii) applying a UV light reflective layer directly or indirectly to the first and/or second surface.

Preferably the photocatalytic layer is applied by chemical vapour deposition. Preferably the photocatalytic layer is applied by chemical vapour deposition during the float glass production process, and is therefore referred to as an ‘online coating’. As used herein, ‘online coating’ relates to the use of chemical vapour deposition coating beam during the float glass production process.

Where the photocatalytic layer is applied by chemical vapour deposition it may be possible to produce the antimicrobial substrate in large volumes. In addition, where the photocatalytic layer is applied by chemical vapour deposition and the photocatalytic layer comprises titanium oxide, a higher proportion of UV action anatase crystal structure titanium oxide may result.

Preferably, the photocatalytic layer is applied by chemical vapour deposition using a precursor gaseous mixture comprising for example titanium tetrachloride, TiCU. Photocatalytic layers applied by chemical vapour deposition using precursor gaseous mixtures comprising TiCU provide a higher proportion of anatase crystal structure titanium oxide than alternative precursor mixtures.

Alternatively, the photocatalytic layer may be a coating applied by physical vapour deposition. Physical vapour deposition is also known as sputtering. Where the photocatalytic layer is applied by physical vapour deposition, it may be possible to impart the layer structure with different advantageous properties.

Alternatively, the photocatalytic layer may be formed by curing a liquid coating precursor. Examples of liquid coating precursors include tetraorthoxysilicate (TEOS) and perhydropolysilazane (PHPS). Where a liquid coating precursor is used photocatalytic particles may be included in the precursor mixture. Forming the photocatalytic layer from a liquid coating precursor may allow different properties to be imparted to the layer.

Preferably the UV light reflective layer is applied by chemical vapour deposition. It may be beneficial that both the UV light reflective layer and the photocatalytic layer are coatings applied by chemical vapour deposition. When both the UV light reflective layer and the photocatalytic layer are coatings applied by chemical vapour deposition, it is preferable that they are both located on the first surface of the sheet of glazing material. Such a formation allows for an antimicrobial substrate to be formed efficiently. Where the sheet of glazing material comprises glass, “online coating” processes may be preferably employed to provide an antimicrobial substrate in an exceptionally efficient and cost effective method. As such when both the UV light reflective layer and the photocatalytic layer are coating layers preferably applied by chemical vapour deposition to the first surface, the step of applying a photocatalytic layer directly or indirectly to the first surface of the sheet of glazing material is preferably carried out prior to the step of applying a UV light reflective layer directly or indirectly to the first surface of the sheet of glazing material.

As used herein, “online coating” preferably relates to the use of chemical vapour deposition coating beams during the float glass production process.

Alternatively, the UV light reflective layer may be formed by physical vapour deposition or by curing a liquid coating precursor. Alternatively, the UV reflecting layer may comprise a metal mirror layer. Preferably, the metal mirror layer is formed by curtain coating. Alternatively, the metal mirror layer may be formed by alternative coating methods, including for example draw coating, spray coating, roll coating, sputtering, or electrodeposition.

Preferably, the metal mirror layer comprises one or more of silver, chromium, nickel, tin or aluminium.

Preferably, the method for producing an antimicrobial substrate according to the present invention further comprises the step of: iv) applying an encapsulating layer to the second surface of the sheet of glazing material, and wherein the UV light reflecting layer is located between the sheet of glazing material and the encapsulating layer

According to a third aspect of the invention, there is provided an antimicrobial article comprising an antimicrobial substrate according to the first aspect or produced according to the second aspect of the invention, preferably wherein the antimicrobial article is a glazing or a mirror.

According to a fourth aspect of the invention there is provided a use of an antimicrobial substrate according to a first aspect of the invention or produced according to a second aspect of the invention in a glazing frame, wall, ceiling, bulkhead, blind, and/or door, wherein the antimicrobial substrate is installed to allow the photocatalytic layer to face towards an environment.

As defined herein, the environment of an antimicrobial substrate is an area that one or more humans or animals may occupy or pass through, such that the humans or animals may come into contact with the antimicrobial substrate. As a result, the environment may be an indoor or external environment.

Preferably, the use of an antimicrobial substrate may further comprise the step of irradiating the antimicrobial substrate with UV light from a UV light source for a period of 1 minute to 24 hours. Preferably, the step of irradiating the antimicrobial substrate with UV light from a UV light source is for a period of 1 minute to 60 minutes. More preferably, the step of irradiating the antimicrobial substrate with UV light from a UV light source is for a period of 1 minute to 30 minutes. Yet more preferably the step of irradiating the antimicrobial substrate with UV light from a UV light source is for a period of 1 minute to 15 minutes. A shorter time period may be more convenient to users of the space in which the antimicrobial substrate is installed, but may not provide a sufficient antimicrobial effect. A longer time period may be inconvenient and more costly for users of the space. Such a period of irradiation is suitable for denaturing microbes already on the surface of the antimicrobial substrate.

Alternatively, the step of irradiating the antimicrobial substrate with UV light from a UV light source is for a period of 30 minutes to 24 hours. Preferably, the step of irradiating the antimicrobial substrate with UV light from a UV light source is for a period of 30 minutes to 10 hours. More preferably, the step of irradiating the antimicrobial substrate with UV light from a UV light source is for a period of 1 to 2 hours. Such a period of irradiation is suitable for activating the battery effect, such that the antimicrobial substrate will denature microbes that arrive upon the surface of the antimicrobial substrate after irradiation is ceased. A shorter period of time may not activate the battery effect, while a longer period of time may be inconvenient and costly. In some embodiments, it may be beneficial to combine such a period of irradiation with UVA irradiation.

Preferably the UV light has a peak wavelength above 200 nm, more preferably above 220 nm, even more preferably above 250 nm.

According to the present invention, the peak wavelength of light is the wavelength with the highest intensity in the light spectrum. For example, the peak wavelength of UV light is the wavelength with the highest intensity in the UV spectrum of 10 to 400 nm.

Preferably in relation to the present invention, the UV light is activated using an automated sensor process or a timer. The automated sensor process may include a sensor device for sensing parameter information, and may also include a communication system for relaying the parameter information to a computational device which determines a response. Preferably the UV light source is a mobile UV light source. Preferably the mobile UV light source may be actuated between a position where light from the UV light source may impinge upon the antimicrobial substrate, and a position in which light from the UV light source does not impinge upon the antimicrobial substrate.

Preferably, the mobile UV light source is attached to a robotic device. Preferably the robotic device is: an actuating arm; a wheeled, legged or tracked mobile carrier; or a retracting arm.

Preferably the use of an antimicrobial substrate according to the present invention further comprises a cleaning step, preferably wherein the antimicrobial substrate is cleaned with a cleaning product, preferably a detergent and/or a germicidal cleaning product.

Preferably the cleaning step is an automated cleaning step, wherein the antimicrobial substrate is cleaned using sprayers, air knives and/or wipers. Alternatively, the cleaning step is a manual cleaning step.

It will be appreciated that preferable features disclosed herein according to the first, aspect of the present invention may also be applied to the second, third and fourth aspects of the present invention respectively.

Embodiments of the present invention will now be described by way of example only with reference to the following examples and drawings in which:

Figure 1 illustrates a cross sectional view through an antimicrobial substrate according to a first embodiment of the present invention.

Figure 2 illustrates a cross sectional view through an antimicrobial substrate according to a second embodiment of the present invention.

Figure 3 illustrates a cross sectional view through an antimicrobial substrate according to a third embodiment of the present invention.

Figure 4 illustrates a cross sectional view through an antimicrobial substrate according to a fourth embodiment of the present invention. Figure 5 illustrates the calculated UV absorption spectrum of photocatalytic films P1 and P2.

Figure 6 illustrates the Colony Reduction % of a coated comparative example compared to an uncoated comparative example.

Figure 7 illustrates the transmission spectrum of 200 to 400 nm light of glass sheets.

Figure 8 illustrates the measured reflection spectrum of 200 to 400 nm light of reflecting layers.

Figure 9 illustrates the calculated integrated reflection of 300 nm to 400 nm of examples without photocatalytic layers illuminated with a 300 - 400 nm equal intensity UV illuminant.

Embodiments of the invention will now be described in which like features are indicated by like numerals.

In a first embodiment of the present invention there is provided an antimicrobial substrate 10 as depicted in Figure 1 , comprising a sheet of glazing material 1 and a photocatalytic layer 2, wherein the sheet of glazing material 1 comprises a first surface 1 a and a second surface 1 b, and wherein the photocatalytic layer 2 is applied to the first surface 1a. The photocatalytic layer 2 may be directly applied to the first surface 1a. Alternatively, the photocatalytic layer 2 may be indirectly applied to the first surface 1a. For example, an ion migration blocking layer may be located between the photocatalytic layer 2 and the sheet of glazing material 1. The antimicrobial substrate 10 may further comprises a UV light reflective layer 3 applied to the second surface 1 b. The UV light reflective layer 3 may be directly or indirectly applied to the second surface 1 b, provided that any intervening layers are at least partially UV transmissive.

In this first embodiment, a low-iron glass may be used as the sheet of glazing material, to increase the transmission of UV light through the sheet of glazing material and thereby increase the amount of UV light reflected back to the photocatalytic layer by the UV reflecting layer. The arrangement of layers specified in this first embodiment may be particularly preferred where different layer forming processes are used to produce the antimicrobial substrate, or where it is advantageous to protect the UV reflecting layer 3 from the environment.

It is particularly preferred that the UV reflecting layer 3 comprises metal and the photocatalytic layer 2 comprises titanium oxide. Preferably the metal comprises silver metal, chromium metal, aluminium metal, tin metal, nickel metal or a combination thereof. It is also preferred that the metal UV reflecting layer 3 is provided with an encapsulating layer (not shown) that protects the metal from damage, corrosion and tarnishing. The encapsulating layer may comprise a colourant layer such as for example but not limited to a paint layer.

In a second embodiment of the present invention, there is provided an antimicrobial substrate 10 as depicted in Figure 2, comprising a sheet of glazing material 1 and a photocatalytic layer 2, wherein the sheet of glazing material 1 comprises a first surface 1a and a second surface 1b. The photocatalytic layer 2 is indirectly applied to the first surface 1a. The antimicrobial substrate 10 further comprises a UV light reflective layer 3 located between the photocatalytic layer and the first surface 1 a.

The arrangement of layers specified in this second embodiment may be particularly preferred where similar layer forming processes are used to produce the antimicrobial substrate, as in this embodiment, all of the layers are applied to the first surface. In addition, manual handling requirements may be reduced when producing this embodiment.

In a third embodiment of the present invention there is provided an antimicrobial substrate 10 as depicted in Figure 3. This third embodiment preferably comprises a sheet of glazing material 1 and a photocatalytic layer 2. The sheet of glazing material 1 comprises a first surface 1 a and a second surface 1 b, and the photocatalytic layer 2 is preferably indirectly applied to the first surface 1a. The antimicrobial substrate 10 preferably further comprises a UV light reflective layer 3 located between the photocatalytic layer and the first surface 1a. In this third embodiment, the UV light reflective layer 3 preferably comprises a first sublayer 3a, a second sublayer 3b and a third sublayer 3c.

The arrangement of layers described in relation to the third embodiment of the present invention may be preferred when the UV light reflection layer comprises a multilayer reflection layer system. Such multilayer reflection layer systems have the advantage of providing increased transparency and optical properties compared with alternative reflection layers, such as metal layers.

In a particularly beneficial embodiment of the third embodiment of the invention, the first sublayer 3a may comprise metalloid silicon, the second sublayer 3b may comprises tin oxide, and the third sublayer may comprise silicon oxide. It is further advantageous in this third embodiment that the photocatalytic layer 2 comprises titanium oxide.

In a fourth embodiment of the present invention there is provided an antimicrobial substrate 10 as depicted in Figure 4. In this fourth embodiment, the antimicrobial substrate comprises a sheet of glazing material 1 and a photocatalytic layer 2, wherein the sheet of glazing material 1 comprises a first surface 1a and a second surface 1b, and wherein the photocatalytic layer 2 is applied to the first surface 1a. The antimicrobial substrate 10 may further comprises a UV light reflective layer 3 located between the photocatalytic layer and the first surface 1a. Alternatively, the UV light reflective layer 3 may be applied to the second surface 1b (not shown). The antimicrobial substrate 10 may further comprises an additional antimicrobial layer 4. The additional antimicrobial layer preferably comprises islands 4a, and apertures 4b through which the photocatalytic layer 2 may be exposed to the environment.

The arrangement of layers described in relation to the fourth embodiment of the present invention may be preferred where an increased antimicrobial effect is desired.

In a particularly beneficial embodiment of the invention, the islands 4a comprise copper and/or silver.

Examples of embodiments of the invention will now be described. A first comparative example was prepared, comprising a sheet of glazing material of soda-lime silica glass (Pilkington Optifloat). A photocatalytic layer of titanium oxide with predominantly anatase crystal structure (thickness 17 nm) was applied to a first surface of the glass, and an alkali metal ion blocking under-layer of silicon oxide (thickness 30 nm) was applied between the surface of the glass and the photocatalytic layer.

A second comparative example was prepared, comprising a sheet of glazing material of low-iron glass (Pilkington Optiwhite). A photocatalytic layer of titanium oxide with predominantly anatase crystal structure (thickness 17 nm) was applied to a first surface of the glass, and an alkali metal ion blocking under-layer of silicon oxide (thickness 30 nm) was applied between the surface of the glass and the photocatalytic layer.

A first example of the invention, prepared according to the first embodiment of an antimicrobial substrate described in relation to Figure 1 , comprises: a sheet of glazing material of soda-lime silica glass, a photocatalytic layer of titanium oxide with predominantly anatase crystal structure (thickness 17 nm) applied to a first surface of the glass; an alkali metal ion blocking under-layer of silicon oxide (thickness 30 nm) applied between the surface of the glass and the photocatalytic layer and applied directly to the first surface of the glass.

In this example the UV reflecting coating is a silver metal mirror layer produced by curtain coating and is directly applied to the second surface of the glass. An encapsulating layer is also applied to the silver metal mirror layer.

The calculated UV absorption spectrum of a film comprising a titanium oxide layer in combination with a silicon oxide layer according to this first example and the first and second comparative examples, is shown in Figure 5 and indicated as line P1. In this example the spectrum is calculated without a glass sheet, that is the spectrum is calculated with a vacuum on each side of the film structure. Considering the spectrum, it can be seen that the % adsorption for P1 below 320 nm is in the region of 50% and then decreases as the wavelength shifts towards the UVA range.

Figure 5 also depicts as line P2, the UV absorption spectrum of an alternative photocatalytic layer comprising a layer of titanium oxide with predominantly anatase crystal structure, thickness 40 nm, in combination with, in order from the glazing sheet surface: an underlayer of tin oxide, thickness 30 nm; a layer of silicon oxide, thickness 22 nm; and a layer of fluorine doped tin oxide, thickness 230 nm.

Considering the spectrum in Figure 5 it can be seen that the absorption for P2 below 320nm is in the region of 70%, and then decreases as the wavelength shifts towards the UVA range.

UV light above 320 nm is termed UV-A, and the inventors have found that the titanium oxide photocatalytic coating is effective both for denaturing organic matter such as microbes, but also for producing a “battery effect” when irradiated with light of this wavelength range. The term “battery effect” is used herein to describe an arrangement where a photocatalytic layer has been irradiated with UV light and continues to have a potent photocatalytic activity after the UV light irradiation has ceased.

For example, samples consisting of comparative example 1 were prepared (without the silver metal mirror layer or the encapsulation layer). These samples were exposed to UVA 340 nm radiation produced by a Q Panel 340 Lamp in a dark room at a distance of 45 nm for 20 hours. The samples were then inoculated with Staphylococcus aureus strain F and the “colony reduction % ” of the samples investigated. Half of the samples were irradiated with light from the same lamp for 0, 5, 10, 20, 40, 60 and 90 minutes, and the other half of the sampler were kept in darkness for the same length of time. At the end of the time periods the samples were washed into a nutrient solution, the dilutions cultured overnight at 37 °C using 0.1 mml of 10^-2 bacterial dilutions on agar plates, and the colony counts measured.

Figure 6 depicts the percentage “colony reduction rate” for the comparative example samples, - Coated -, compared to the percentage “colony reduction rate ” for the comparative uncoated samples, - Uncoated - . The “colony reduction rate” % is calculated by Formula (1 ):

Colony Reduction % = 100 - (colony numben=_x/ initial colony numben=o ^c 100) (1) Surprisingly, the results indicate that a coated sample is more effective after irradiation has ceased - sample Coated (Dark) - , compared to an uncoated sample with continuing irradiation - Uncoated (Light).

The colony reduction rate % demonstrated by the comparative example sample irradiated with UVA for 24 hours were then kept in the dark for 90 minutes after inoculation demonstrates a log reduction of 6 upon Staphylococcus aureus strain F.

As such, it is demonstrated that irradiation of a photocatalytic coating, in particular a titanium oxide photocatalytic coating, is particularly beneficial for the disinfection of substrates. Such an effect may occur even when the sample is no longer irradiated with UV light, that is a so called “battery effect” is observed.

However, this effect may be improved by increasing the intensity of UV irradiation of the glass samples, thereby reducing the amount of time required to produce prolonged photocatalytic disinfection effects.

Figure 7 depicts the UV transmission spectra of soda-lime silica glass and low-iron glass. Soda-lime silica glass transmits UV light above a wavelength of approximately 315 nm, and low-iron glass transmits UV light above a wavelength of approximately 275 nm. As such, soda-lime silica glass transmits a large proportion of UVA light, and low-iron glass transmits a large proportion of UVB and UVA light.

As such, a proportion of ‘useful’ UV light not absorbed by the photocatalytic coating may be transmitted by glazing material sheets, such as soda-lime silica glass and low-iron glass. Therefore, when examples are prepared according to the first embodiment of the present invention, with a UV light reflecting coating applied to the second surface of the glazing sheet, this UV-light reflecting coating will reflect light transmitted by the photocatalytic layer and the sheet of glazing material back to the photocatalytic layer and thereby increase the UV light incident upon the photocatalytic layer, thereby improving the antimicrobial effect.

It will be appreciated that the selection of the UV reflecting coating and its position on the glazing material may be modified according to the requirements of balancing cost, the antimicrobial effect, and the optical properties required of the antimicrobial substrate. Figure 8 depicts the UV reflection spectra of a number of UV reflecting layers.

UV1 relates to a UV reflecting layer comprising a silver mirror coating, and the reflection spectra is measured through a 4 mm soda-lime silica glass sheet. Such a mirror coating provides extremely high reflection in the visual spectrum, does not influence the colour of the reflection and is completely opaque, which may find particular benefit in some applications.

UV2 relates to a UV reflecting layer comprising a silver mirror coating, and the reflection spectra is measured through a 4mm low-iron soda-lime silica glass sheet. The use of a low-iron soda-lime silica glass sheet improves the transmission of UV light through the glass sheet, allowing lower wavelength light to be reflected. This allows more energy to be returned to the photocatalytic layer.

Alternative examples embodiments may be prepared according to the example of Figure 2, using alternative UV reflecting layers.

UV3 relates to a UV reflecting layer comprising a first coating of metalloid silicon, thickness 24 nm with an overcoating of silicon dioxide of thickness 30 nm.

UV4 relates to a UV reflecting layer comprising a first coating of metalloid silicon of thickness 18 nm with an overcoating of silicon dioxide of thickness 30 nm.

UV5 relates to a UV reflecting layer comprising a first coating of metalloid silicon of thickness 18 nm with an overcoating of silicon dioxide of thickness 85 nm and a further overcoating of tin oxide of thickness 65 nm.

UV6 relates to a UV reflecting layer comprising a first coating of silicon oxynitride of thickness 36 nm with an overcoating of nichrome with a thickness of 1 nm, a further overcoating of chrome metal with a thickness of 32 nm, and a further overcoating of silicon oxynitride with a thickness of 23 nm. The use of a reflective layer comprising chrome improves the resistance of the layer to tarnishing, especially in humid environments.

As depicted by Figure 8, it can be seen that UV3 and UV4 both provide excellent broad UV reflectivity. As such, these may be particularly beneficial for enhancing the photocatalytic effect, when the photocatalytic layer is irradiated with broad UV illumination and/or with UVC light. In addition, UV3 and UV4 are partially light transmissive, and therefore may be used in for example but not limited to display articles.

As UV3 and UV4 are reflective through the UV spectrum, even at wavelengths not transmitted by soda-lime silica glass and low-iron glass, alternative examples may be prepared according to the second embodiment of the present invention as described in relation to Figure 2, or the third embodiment of the present invention as described in relation to Figure 3, wherein the UV light reflecting layer is between the photocatalytic layer and the glazing sheet. These alternative embodiments may provide more reflected UV light below 300 nm to the photocatalytic layer, as there is no absorption by the glazing sheet prior to reflection.

A particular benefit of the present invention, especially when incorporating a photocatalytic layer comprising titanium oxide, is that UVA light may be used to activate the photocatalytic layer and produce an antimicrobial effect. This allows, for example, UVA disinfection lamps to be utilised, which are less harmful to humans and animals than UVB and UVC disinfection lamps. This arrangement may also allow the antimicrobial substrate to undergo a UV disinfection cycle without requiring humans and animals to vacate the immediate environment of the antimicrobial substrate. Where UVA light is used alone, the embodiment of the present invention as described in relation to Figure 1 , incorporating UV reflecting layers UV1 and UV2 may be particularly beneficial.

Table 1 shows the layer structures of examples and comparative examples with layer thicknesses provided in nm. In each case the glass thickness was 6 mm. Where the term “S-L S Glass” is used, this represents soda-lime silica glass, available from Pilkington Group Limited under the trademark Optifloat™, and where the term “Low-iron glass” is used this is low-iron glass available from Pilkington Group Limited under the trademark Optiwhite™.

In addition, Table 1 provides details of the associated optical data for the examples and comparative examples.

For example 1 and example 2, a silver layer of 100 nm was provided. However, the silver layer may be of increased thickness when applied by curtain coating. Tvis is the calculated visible transmission of the sample, and R_Vis is the calculated visible reflection of the sample, both when measured with light incident upon the photocatalytic layer using a CIE C illuminant. The comparative examples have high visible light transmission and comparatively low reflection, while examples 1 and 2 have zero light transmission and extremely high visible light reflection, due to the thick silver layer. Examples 3, 4 and 5 provide a balance between transmission and reflection, and are particularly suitable for half-mirror /one-way mirror applications.

The a* b* parameter is the calculated a* and b* values of the reflected light from the sample using the lab colour space and a CIE C illuminant. Comparative examples 1 and 2 have a relatively neutral reflection colour, with a* and b* values each within the range of from -20 to +20. Example 1 exhibits excellent colour neutrality, with a* and b* each within the range from -3 to +3, and example 2 exhibits exceptional colour neutrality, with a* and b* each within the range from -1 to +1. This indicates that embodiments including a silver layer on the opposite side of a glazing sheet to the photocatalytic layer and incorporating low-iron glass are exceptionally useful for high quality antimicrobial and/or antiviral visible light reflective mirrors due to a high UV light reflection, thereby leading to an increase in photocatalytic effect when irradiated with UV light, extremely high visible light reflection and exceptional colour neutrality.

Examples 3 and 4 are less colour neutral than other examples, with both a* and b* within the range from -10 to +36. These examples are more ‘coloured’, and are therefore beneficial in applications where aesthetic appearance may be enhanced by a coloured reflective surface, such as but not limited to for example displays and signage.

The partial transmission of example 5 and good colour neutrality with a* and b* both in the range -10 to +10 makes it particularly useful for example in displays and one-way mirror applications.

Therefore, in some embodiments it is preferred that R_Vis is greater than 90%, more preferably greater than 95%.

Alternatively, in some embodiments it is preferred that R_Vis is from 30% to 80%. Preferably a^* and/or b^* are in the range -10 to +36, more preferably -10 to +10. In some applications it is desirable for a^* and b^* to both be in the range -3 to +3.

R3oo-4oo^Sub is the calculated measurement of the percentage of UV light in the 300 to 400 nm range incident upon surface 1 reflected by the sample when illuminated with a broad UV illuminant with equal intensity of all wavelengths from 300 to 400 nm, measured without the photocatalytic layer and S1O2 underlayer. The measurement is depicted in Figure 9. Comparative example 1 and comparative example 2 both lack UV light reflecting layers, and the only reflection is from the glass surface. Therefore, the reflection of UV light back to the photocatalytic layer is comparatively low. Example 1 and example 2 comprise silver metal UV reflecting layers, and example 3, 4 and 5 comprise silicon metalloid UV reflecting layers.

Example 1 indicates a considerable improvement in UV reflection compared to the comparative examples. Surprisingly, example 2 has a very high UV reflection, despite the reflection being attenuated by passing through the glass layer twice. This may lead to a particularly good photocatalytic effect when irradiation is by UVA light. Examples 3, 4 and 5 provide a good UV reflection in this range, while providing visible light transparency which is useful for certain applications, such as glazings and displays. As depicted in Figure 8, UV reflecting layers comprising metalloid silicon may provide a broader UV reflection, making them particularly beneficial when broad UV irradiation is used, or when UVC irradiation is used.

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TABLE 1

The antimicrobial substrates prepared in accordance with the present invention may be used for example in but not limited to, automotive glazings and architectural glazings including commercial and residential applications as well as in food and healthcare applications. The present invention may also find application in for example electronic devices, such as touch screens, mobile phones, laptop computers, book readers, video gaming devices, and automated teller machines. Indeed, the present invention is applicable to any application or situation where a glass substrate is used and may be touched, or where information displayed on a glass screen is retrieved by touch.

In some cases, it may be beneficial to provide an antimicrobial substrate with extremely high visible light transmission, as well as high UV light reflection. Such an antimicrobial substrate may be used in a glazing, in particular an automotive glazing. In this embodiment, the glazing may have a T_Vis of 80% or greater, and a UV reflection R300- ₄oo^Sub greater than 50%.

In addition, the antimicrobial substrate may be used for instance with coated and uncoated substrates, for example, glass substrates such as but not limited to float glass coated using chemical vapour deposition (CVD) and/or physical vapour deposition (PVD) to produce an antimicrobial substrate with coating layers; the coating layers being located either above or below the antimicrobial coatings.

Further, when the antimicrobial substrate comprises a glass substrate, the glass substrate may comprise flat glass such as for example float glass or alternatively, the glass substrates may comprises alternative forms of glass such as for example but not limited to: borosilicate glass, rolled plate glass, ceramic glass, toughened glass, chemically strengthened glass, hallow glass or glass shaped for articles such as bottles, jars and medical containers.