Substrate with antimicrobial properties

SUBSTRATE WITH ANTIMICROBIAL PROPERTIES

0002The present invention relates to a substrate of any type: metal, glass, glass ceramic, or plastic type substrate, wherein at least one of its surfaces has antimicrobial, in particular antibacterial or antifungal, properties. The present invention also relates to processes for the production of such a substrate.

0003In the field of ceramic substrates, EP 653 161, for example, describes the possibility of covering these with a glaze composed of silver to provide them with antibacterial properties.

0004In the field of glass-type substrates, sol-gel type processes are known to provide an antimicrobial surface. These processes require a hardening stage of the sol-gel layer, which involves elevated temperatures in the order of 500°-600°C (sintering temperature). Processes are also known that require the substrate to be dipped in a composition comprising a silver salt. In this case, a silver layer is not deposited, but an ion exchange takes place in the solution at an elevated temperature.

0005A process for producing a glass substrate having antimicrobial properties is also known from EP 1449816. This process uses AgNO₃ in oil and requires both a drying stage between 20° and 105⁰C and a thermal treatment at 600°-650°C. This thermal treatment has some disadvantages particularly with respect to cost and uniformity of the product. Moreover, it renders the process very poorly reproducible, since it has been found that at these temperatures the diffusion of the silver is very rapid and a slight variation in the duration of the thermal treatment results in a significant variation in the depth of diffusion of the silver, and therefore this causes variation in the antibacterial properties of the substrate. In particular, we have observed that with such a process, the majority of the silver has diffused between around 1 and 2 μm and that at the surface the quantity of silver is too low to give antimicrobial properties to the glass.

0006It may also be noted that such a thermal treatment causes an undesirable yellow colouration of a soda-lime glass substrate. Furthermore, if the thermal treatment is carried out during a tempering process, after having been treated, the product may no more be cut into particular size.

0007WO 95/13704 describes anti-microbial materials, in particular for medical devices. In example 9, separated layers of Ag and ZnO were deposited sequentially by RF magnetron sputtering in a ratio of 75-25 wt%. The total thickness of the layers is 330 nm. RF magnetron sputtering is a deposition method which is hardly industrialisable today.

0008Therefore, there is a need to provide a substrate, either glass or metallic, with antimicrobial properties, which is easy to use and inexpensive to produce in an industrial manner.

0009In particular, there is a need to provide a glass substrate which can be tempered and which keeps antimicrobial properties, preferably bactericide properties, after tempering process.

0010In particular, one aim of the invention is to provide a glass substrate which can be tempered and which keeps antimicrobial properties after accelerating ageing tests carried out after tempering process.

0011According to one embodiment, the present invention relates to a substrate coated with at least one mineral layer, particularly selected from metal oxides, oxynitrides, oxycarbides, carbides, DLC (diamond like carbon) or nitrides, said layer comprising at least one antimicrobial agent, the coated substrate maintaining antimicrobial properties after accelerated ageing tests. In particular, the mineral layer can be selected from oxides of silicon, tin, nickel, chrome, zinc, titanium, niobium, aluminium, zirconium or mixtures thereof, for example ZnxSnyOz and NiCrOx. Particularly preferred nitrides are silicon, titanium and aluminium nitrides and mixtures thereof.

0012The antimicrobial agent can be selected from various inorganic agents known for their antimicrobial properties, in particular silver, copper, gold and zinc. Advantageously, the antimicrobial agent is in ionic form.

0013The substrate can be metallic, e.g. made of steel, or stainless steel or ceramic type or plastic or thermoplastic type substrate or a glass-type substrate, in particular a sheet of flat glass, particularly soda-lime glass which may be float glass. It may be clear glass or coloured glass. Frosted or patterned glass can also be used. The glass sheets can be treated on one or on both of their faces. The face opposite the treated face can be subjected to any desired type of surface treatment. It may comprise a reflective layer (to form a mirror) or a layer of enamel or painting (for wall covering), generally at the surface opposite to the antimicrobial surface.

0014The substrate may have a thickness within the range of 0.2 to 12 mm.

0015The substrate may have a surface area of greater than 0.8 m to 0.8m; it may be adapted to be cut to a finished size by a subsequent cutting operation.

0016It is conceivable that the antimicrobial glass substrate thus obtained is subjected to a thermal treatment stage such as, in the case of glass substrate, a thermal tempering, bending or hardening, while still retaining its antimicrobial properties.

0017In some embodiments of the invention, a substrate having antimicrobial agents present at least at one exposed surface may be a sheet of annealed glass. The term annealed sheet of glass is used herein to mean that the glass may be cut to size without breaking in the way that a tempered or hardened sheet of glass would break upon cutting. Such a sheet of annealed glass preferably has a surface compression of less than 5 MPa. After the eventual cutting operation, the substrate is able to be tempered and antimicrobial properties are maintained.

0018In an advantageous embodiment of the invention, the substrate can be first coated with an underlayer that blocks or slows down the diffusion of the antimicrobial agents during the tempering treatment. The function of the underlayer can be ascertained on a product made according to the invention by comparing the antimicrobial effect of similar products with and without undercoating and/or by analysing diffusion profiles.

0019In the case of metallic substrates, particularly preferred undercoat and/or mixed layers are chosen amongst titanium oxide, titanium nitride, zirconium oxide, silicon oxide or silicon oxinitride.

0020The substrate according to the invention preferably has an antibacterial effect on a large number of bacteria, whether gram positive or gram negative bacteria, in particular on at least one of the following bacteria: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus hirae. The antibacterial effect, measured in accordance with the JIS Z 2801 standard, is in particular, at least on any one of these bacteria, higher than log 1, preferably higher than log 2 and particularly preferred higher than log 2.5. The substrate will be considered bactericidal according to the JIS Z 2810 standard if it has an effect higher than log 2. However, the invention also relates to substrates that have a lower effect (for example bacteriostatic effect, which means that the bacteria are not necessarily killed but can not develop any more).

0021It has been found that it is possible to deposit the mineral layer and the antimicrobial agent in one single step over the entire substrate, whether it is made of metal, e.g. steel, or is a glass-type substrate.

0022In particular, with the well known method of magnetron sputtering, it is possible to form a layer, e.g. of a metal oxide doped with an antimicrobial agent, e.g. silver, using two metal targets in the same deposition chamber (co-sputtering) or using a single target with mixed materials. Targets with mixed materials may be metallic but it can be particularly advantageous to mix ceramic materials for one of the cathode in the co-sputtering process or to mix ceramic materials with metals for the single cathode in the single cathode process. For example, Ag, Cu, Au and Zn can be mixed with oxides of Ti, NiCr, Zr and other pure or mixed oxides in order to produce mixed ceramic-based targets which lead to highly efficient processes in terms of deposition rate and process stability.

0023It has also been found that a wide range of magnetron sputtering processes can be used to obtain the desired antimicrobial glass. Mid DC power as well as mid-frequency pulsed DC or AC power has been used successfully both in the co-sputtering mode and in sputtering mixed targets. Gas mixtures including Ar, 02 and N2 have been used over the whole range of 0 to 100% for each gas, depending on the type of material desired for the layer comprising the antimicrobial agent.

0024With these processes, no additional or subsequent diffusion of the antimicrobial agent may be needed. We obtain an antimicrobial substrate in one step, without any thermal treatment, which is cost saving.

0025It has also been discovered that, if a tempered and antimicrobial glass is required, the same process may be used, and optionally an underlayer may be added. Antimicrobial (in particular bacteriostatic but also bactericidal) properties may be maintained even after a tempering process (implying high temperature treatment during approximatively 2 to 10 min).

0026Layers of Ag doped metal oxide deposited in a single step by co- sputtering or sputtering of mixed targets, have been made which have antimicrobial properties with a simple process that does not require any thermal treatment.

0027When the substrate used is a clear glass, it can advantageously have antimicrobial properties as well as a neutral colouration in reflection. In particular, the colorimetric indexes (CIELAB system) in reflection a* and b* (Illuminant C, 10° observer) may be in the range of between -10 and 6, preferably between -8 and 3 and particularly preferred between -6 and 0, and the purity may be less than 15%, preferably less than 10% and particularly preferred less than 5%. If an underlayer is deposited a slight absorption in the visible (around 5 to 25 %) may be imparted to the underlayer. It may have a visible light reflection around 8 and 15%,

0028If the substrate is a coloured glass, antimicrobial properties may be obtained without changing very much the initial colour of the substrate. The change of coloration is generally expressed with the colorimetric index by Delta E* ; Delta E* = [ (L*j - L*₂)² + (a*j - a*₂)² + OΛ - b*₂)²]^1/2. A Delta E* lower than 3, preferably lower than 2 may be obtained for an antimicrobial substrate according to the invention.

0029When the substrate is transparent (glass, plastic, ...), it may be advantageous to obtain antimicrobial properties while keeping the substrate essentially transparent. In particular, with a clear soda-lime glass of 4mm, the average light transmission in the visible range of the coated substrate according to the invention may be higher than 50%, preferably higher than 60% and most preferably higher than 65%.

0030When the glass substrate used is a clear glass, it may advantageously have both antimicrobial properties and a low visible light absorption.

0031The substrate according to the invention has an antimicrobial effect after at least one of the following accelerated ageing tests: wet spray test (test over 20 days in a chamber with a humidity of more than 95% at 40⁰C), after 500 hours of UV irradiation (4 340A ATLAS lamps, chamber at 60⁰C), after 24 hours immersed in a solution of H₂SO₄ (0.1 N), after 24 hours immersed in a solution of NaOH (0.1 N), 48 hours of immersion in Mr Propre® detergent followed by 5 days of drying.

0032It may be advantageous to use an undercoat comprising an oxide of zirconium. This may particularly be so when the mixed layer comprises an antibacterial agent and an oxide of titanium, particularly a titanium oxide in its anatase crystallised form. Additional or alternative embodiments of the present invention are also described in dependant claims.

0033The present invention shall be described in more details below, in a non-restrictive manner:

0034Example 1 (comparative)

0035One sample of clear soda-lime glass having a thickness of 4 mm was coated with a layer of SiO₂(Al) :Ag by co-sputtering. Two metal targets were used in a mixed atmosphere of argon and oxygen: one was composed of silicon doped with 8% Al and the second target was a metallic silver target. The Si(Al) target was sputtered with a pulsed DC power supply at 100 kHz while the Ag target was sputtered with DC power supply. The electric power supplies were regulated in order to obtain 10 mg of Ag in the layer per square meter of substrate with the totaljayer thickness of 24 nm.

0036Measurement of the antimicrobial effect

0037The bactericidal properties (in particular on E. CoIi) of all the samples were analysed in accordance with standard JIS Z 2801. A log 1 level indicates that 90% of the bacteria inoculated onto the surface of the glass were killed in 24 hours in the conditions of the standard; log 2 indicates that 99% of the bacteria were killed; log 3 indicates that 99.9% of the bacteria deposited were killed etc. If the value indicated is greater than a particular amount, this mean that the maximum of countable bacteria was killed.

0038A value greater than log 4 was obtained before tempering the sample.

0039Tempering treatment

0040The coated sample was subjected to a common tempering treatment

0041(670⁰C during 200 sec). And the bactericidal properties were analysed in same way as for the sample before tempering step. A log 0.76 was obtained which means that no bactericidal nor bacteriostatic properties were maintained after tempering the coated glass.

0042Examples 2 and 3

0043Samples of the same clear soda-lime glass (4 mm thick) were first coated with an underlayer and then coated with a layer of 24 nm of SiO₂-Ag by co- sputtering using the same conditions as in example 1. The electric power supplies were regulated in order to obtain 20 mg/m² of Ag in the layer.

0044In example 2, the underlayer is a double underlayer deposited by CVD (Chemical Vapor Deposition) consisting of 75 nm of SiOxCy and 320 nm of fluorine doped tin oxide, the surface being slightly polished after deposition.

0045In example 3, the underlayer is also a double SiOxCy/ SnO2:F layer but not polished.

0046The antibacterial effect was measured in the same manner as in example 1. Values greater than log 4 were obtained.

0047After a tempering treatment carried out in the same manner as in example 1, antibacterial values greater than log 4 were maintained.

0048Accelerated ageing tests

0049The following ageing tests were carried out :

0050- wet spray (test for 20 days in a chamber with a humidity of more than

005195% and at 40⁰C);

0052- 500 hours of UV irradiation (4 340A ATLAS lamps, chamber at 60⁰C),

0053- 24 hours of immersion in an H₂SO₄ solution (0.1 N), - 48 hours of immersion in Mr Propre® "salle de bain liquide" detergent followed by 5 days of drying.

0054The antibacterial properties were again measured on the samples having been tempered and then subjected to the accelerated ageing tests.

0055The sample of example 2 maintained a log 4.9 value after H₂SO₄ immersion, a log 4.7 value after the wet spray test, a log 4.1 after the detergent immersion test and after the UV test.

0056The sample of example 3 maintained a log 4.5 value after H₂SO₄ immersion, a log 4.7 value after the wet spray test, a log 3.6 after the detergent immersion test and a log 4.1 after the UV test.

0057Example 4

0058Samples of the same clear soda-lime glass (4 mm thick) was first coated with a CVD underlayer of 75 nm of SiOxCy and 320 nm of fluorine doped tin oxide, and the surface has been slightly polished after deposition.

0059The samples have then been coated with a layer of 15 nm of SiO₂-Ag by co-sputtering. As in example 1, two metal targets were used in a mixed atmosphere of argon and oxygen: one was composed of silicon doped with 8% Al and the second target was a metallic silver target. Both targets were sputtered with one single AC electric power supply operating at 27 kHz and being regulated in order to obtain 15 mg of Ag in the layer per square meter of substrate.

0060The antibacterial effect was measured in the same manner as in the other examples. Values greater than log 4 were obtained.

0061After the tempering treatment carried out in the same manner as in example 1, antibacterial value of log 4.6 was maintained. The tempered samples were then subjected to accelerated ageing tests. After a wet spray test, the antibacterial properties were maintained to a value greater than log 4. After the detergent immersion test, a value of log 3.7 was obtained and after the UV test, a log 2.5 was obtained.

0062Example 5

0063Samples of the same clear soda-lime glass were first coated with the same double CVD underlayer as in examples 2 and 4. A layer of SiZrOx doped with

0064Ag was then deposited by co-sputtering using two metallic targets (Si-Zr (10wt%Zr) and Ag). Both targets were sputtered with one single electric power supply being regulated in order to obtain a total thickness of 19 nm and 21 mg/m² of Ag.

0065The antibacterial effect was measured in the same manner as in the previous examples. On the samples before tempering (a value greater than log 4 was obtained), after tempering (a value greater than log 4.6 was obtained). The tempered samples were subjected to accelerating ageing tests. After the H₂SO₄ immersion test, a bactericidal value greater than log 4.9 was maintained. After the wet spray test, a value greater than log 4.7 was obtained and after the detergent immersion test, a log 4.1 was obtained.

0066Examples 6 and 7

0067Samples of the same clear soda-lime glass were first coated with the same double CVD underlayer as in examples 2 and 4. A layer of TiAlOx doped with Ag was then deposited by co-sputtering using one Ag metal target and one ceramic target TiAlOx (12wt% AlOx) in a mixed atmosphere of argon and oxygen.

0068In example 6, the Ti(Al)Ox target was sputtered with a pulsed DC power supply at 100 kHz while the Ag target was sputtered with a DC power supply. The electric power supplies were regulated in order to obtain a thickness of 60 nm and 26 mg/m² of Ag in the layer.

0069In example 7, both targets were sputtered with one single AC power supply regulated in order to obtain a thickness of 7 nm and 30 mg/m² of Ag in the layer. The antibacterial effect was measured in the same manner as in the previous examples. On the sample before tempering a value greater than log 4 was obtained, after tempering a value greater than log 4.6 was obtained.

0070Good antibacterial properties were obtained for all examples of the invention before and after tempering treatment. Whereas in the comparative example 1 where no underlayer was deposited the antibacterial properties were no more observable when then sample has been tempered.

0071Each time an accelerating ageing test has been carried out, the sample according to the invention maintained good antibacterial properties.

0072Furthermore a sand abrasion test was carried out in order to measure the mechanical resistance of the coated samples. In this test, a piece of felt is rubbed on the sample for 600 passes. A weight of 1050 g is applied on the felt while an abrasive solution is poured on the sample (160 g of sand, mesh 500 per litre of water). After the test is completed, the change of reflected colour in the abraded zone is measured and expressed as delta E*. For example 6, a delta E* of 2.2 was obtained, which means that the mechanical resistance of the layer is acceptable.

0073For example 7, a delta E* of 0.5 was obtained, which means that the change of colour is undetectable with the eyes and that the mechanical resistance of the layer is very good.

0074The antibacterial properties were measured also after the abrasion test. For example 6, same very good level of antibacterial activity was obtained. For example 7, a log 2.4 was obtained which means that the sample was still bactericidal.

0075Example 8

0076One sample of clear soda-lime glass having a thickness of 4 mm was coated with a layer of ZrO₂: Ag by co-sputtering. Two metal targets were used in a mixed atmosphere of argon and oxygen: one was composed of zirconium and the second target was a metallic silver target. An unipolar pulsed electric power supply was used and was regulated in order to obtain 7 wt% of Ag in the layer. The layer thickness was 225 nm.

0077The bactericidal properties of the sample was analysed in accordance with Standard JIS Z 2801 before and after tempering process

0078The coated sample was subjected to a tempering treatment (670⁰C during 200 sec). And the bactericidal properties were analysed. A log 3.8 was obtained which means that the sample has good bactericidal properties after tempering.

0079Examples 9 and 10

0080Samples of the same clear soda-lime glass (4 mm thick) was first coated with a CVD underlayer of 75 nm of SiOxCy and 320 nm of fluorine doped tin oxide, and the surface has been slightly polished after deposition as in the previous examples 2 and 4-7. A layer of TiOx doped with Ag has been deposited by magnetron co- sputtering using one metal target of Ag and one ceramic target TiOx respectively in a mixed atmosphere of argon and oxygen for example 9 and in a atmosphere comprising mainly argon for example 10.

0081For both samples, the Ag target was sputtered with a pulsed DC power supply at 50 kHz with 50 μs one time, while the TiOx target was sputtered with DC power supply. The electric power supplies were regulated in order to obtain a layer of respectively 38 nm thick for example 9 and 11 nm for example 10. The layer comprises respectively 5 mg/m2 of Ag in example 9 and 4 mg/m2 of Ag in example 10.

0082The samples were tempered as in the previous examples and the H2SO4 and NaOH accelerated ageing tests described above were carried out. Antibacterial effect was measured in the same manner as described above.

0083For ex 9, values of log 2.4 and 1.9 were obtained respectively after H2SO4 test and NaOH test.

0084For ex 10, values of log 2.8 and 2.0 were obtained respectively after H2SO4 test and NaOH test.

0085After the sand abrasion test described in examples 6-7, the delta E* was respectively 0.9 (Ex 9), and lower than 0.5 (Ex. 10). This means that the mechanical resistance of the layer is very good.

0086Example 11

0087A sample of the same clear soda-lime glass was first coated with the same double CVD underlayer as in examples 2 and 4-7, 9-10. A layer of SiOxNy doped with Ag was then deposited by co-sputtering using one target of silicon and one target of silver in a mixed atmosphere of argon, nitrogen and oxygen. The Si target was sputtered with a pulsed DC power supply at 50 kHz with 5 μs while the Ag target was sputtered with a DC power supply. The electric power supplies were regulated in order to obtain a layer of 12 nm with 1 mg/m2 of Ag.

0088A sand abrasion test was carried out as described hereinabove. The delta E* measured was 1.6 which means that the mechanical resistance of the layer is good.

0089Example 12

0090A sample of the same clear soda-lime glass (4 mm thick) was first coated with a CVD underlayer of 75 nm of SiOxCy and 320 nm of fluorine doped tin oxide, and the surface has been slightly polished after deposition as in the previous examples 2 and 4-7.

0091A layer of TiOx doped with Ag has been deposited by magnetron sputtering using a single target of mixed ceramic titanium and Ag (1.3 wt%). The single target was sputtered with a normal DC power supply in a mixed atmosphere of argon and oxygen. The electric power supply was regulated in order to obtain a layer of 36 nm with 2.2 mg/m2 of Ag.

0092Very good antibacterial properties were obtained after tempering and after sand abrasion test (Iog4.7).

0093The colour in reflection was measured on the coated side for most of the samples. The results are summarized in the following table. All the values are obtained according to the Cielab system (D65, 10°). The light transmission integrated on the visible wavelengths has also been measured from some samples in D65, 2°.

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0095For the ease of the manipulations, all the examples have been done with Ag as antimicrobial agent, but the same results are expected with Cu or Au which are also known for their antimicrobial properties.