WO2007147842A2

WO2007147842A2 - Substrate with antimicrobial properties and process for the production of an antimicrobial substrate

Info

Publication number: WO2007147842A2
Application number: PCT/EP2007/056126
Authority: WO
Inventors: Florent Scarso
Original assignee: Agc Flat Glass Europe Sa
Priority date: 2006-06-21
Filing date: 2007-06-20
Publication date: 2007-12-27
Also published as: WO2007147842A3

Abstract

A process for the production of a substrate having antimicrobial properties is described and a substrate. It comprises a step consisting of the deposition of a metal non-gelling layer comprising an inorganic antimicrobial agent; and a step consisting of the diffusion of the agent into said at least one exposed surface of the substrate by thermal treatment. Alternatively, the substrate may be first coated with an underlayer and the diffusion occurs in the underlayer. Substrates having antimicrobial properties are also described. In particular, a substrate exhibiting a bactericidal activity measured in accordance with standard JIS Z 2801 of higher than log 2. In particular tempered glass maintaining antibacterial properties after accelerated ageing tests are obtained.

Description

Substrate with Antimicrobial Properties and process for the production of an antimicrobial substrate

The present invention relates to a substrate, in particular glass-type substrate, metallic substrate 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 a process for the production of such a substrate.

In 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.

In 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.

A process for producing a glass substrate having antimicrobial properties is also known from EP 1449816. This process uses AgNO₃ precursors in oil and requires both a drying stage between 20° and 105⁰C and a thermal treatment at 600°-

650⁰C. 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 to the glass antimicrobial properties.

It 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.

Therefore, 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 particular, one aim of the invention is to provide a glass substrate which can be tempered and which keeps antimicrobial properties, preferably bactericide properties, after tempering process.

In 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.

According to one embodiment, the present invention relates to process for the production of a substrate having antimicrobial properties and keeping antimicrobial properties after tempering treatment and at least one accelerated ageing tests, characterised in that it comprises the following steps:

(i) deposition of a metal non-gelling layer comprising an inorganic antimicrobial agent, obtained at the outset from a precursor, in metal, colloid, chelate or ion form, on the at least one part of the exposed surfaces of the substrate;

(ii) diffusion of the agent into or under said at least one exposed surface of the substrate by thermal treatment at a temperature comprised between 120 and 750⁰C. According to another embodiment, the present invention relates to a substrate comprising an antimicrobial agent present at least at one of its exposed surfaces, characterised in that the total quantity of antimicrobial agents it comprises is more than 0.1 mg/m², preferably more than 0.5 mg/m² and particularly preferred more than 0.8 mg/m² of antimicrobial surface and is lower than 100 mg/m2, preferably lower than 50 mg/m2 and particularly preferred lower than 10 mg/m2.

According to one preferred embodiment, the present invention relates to a tempered glass substrate comprising antimicrobial agents present under at least one exposed glass surface at a maximum depth of 500 nm, preferably 200 nm, and particularly preferred less than 100 nm.

Other advantageous characteristics of the process and of the substrate are described in the dependant claims.

The substrate may be a sheet of flat glass, particularly soda-lime glass which may be float glass. The glass may have a thickness within the range of 2.5 to 12 mm. It may be clear glass or coloured glass. 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.

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

When the substrate is a clear soda-lime glass, according to one preferred embodiment, the maximum temperature of the heat treatment is preferably the glass transition temperature which is in the order of 550⁰C.

The 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 metallic form. The process according to the invention advantageously comprises an additional step (iii), which consists of eliminating any excess antimicrobial agent remaining on the surface i.e. that has not diffused during the thermal treatment step

(ii). This elimination can be achieved by washing. In particular, solutions based on HNO₃, FeCl₈ or Fe(NO₃)₃ are suitable for such a washing process. This washing can prevent any antimicrobial agents from remaining on the surface in metallic form in such a quantity that they could cause the treated surface to become too reflective. For some applications, it is preferred that the substrate treated according to the invention does not exhibit any significant increase in light reflection (LR), or any significant reduction in light transmission (LT) in relation to the untreated substrate.

It has been found that with the process according to the invention, a very low quantity of antimicrobial agent can be deposited on said at least one surface of the substrate. However, the use of much higher concentrations does not necessarily impede the result, instead such concentrations have proved to be simply unnecessary and can require excess to be eliminated on a much more significant scale. In some case we have discovered that a higher quantity of antimicrobial agent can not enable a greater quantity of antimicrobial agent to diffuse, in particular when the substrate is a glass substrate coated with an underlayer. In particular a quantity of between 5 and 150 mg of antimicrobial agent peT rn2 of substrate has been considered as particularly preferred.

Various methods known per se can be suitable for depositing the layer comprising the antimicrobial agent. In particular, deposition is possible by pyrolytic spraying, by sputtering, by a method similar to the method used for the production of mirrors, which comprises spraying of a salt of an antimicrobial agent such as AgNO₃ and precipitation by reduction of the antimicrobial agent in metal foτm or by dipping in molten salt bath. In the latter case, the diffusion step takes place in the form of an exchange of ions. Various types of glass substrate can be considered, depending on the applications sought. In addition to the traditional clear soda-lime float glass, glass that is coloured, frosted sand blasted, etched or patterned etc. 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. For example, a coating of paint or enamel or a reflective layer can be applied thereon, e.g. for applications such as wall coverings or mirrors.

The substrate according to the invention 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 standard JIS Z 2801 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 standard JIS Z 2801 if it has an effect higher than log 2. However, the invention also relates to substrates that have a lesser effect (for example a bacteriostatic effect, which means that the bacteria are not necessarily killed but can not developed anymore) .

Other antimicrobial properties are also concerned with the present invention such as antifungal properties.

When the glass 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%,

If the substrate is a coloured glass, it can be considered that 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* ; DeltaE* = [ (L* _x -L*₂)² + (a*j - a*₂)² + (b*j - b*₂)²]^1/2. A DeltaE* lower than 3, preferably lower than 2 may be obtained for an antimicrobial substrate according to the invention.

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

The substrate according to the invention preferably has in particular an antimicrobial effect after any 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® "salle de bain liquide" detergent followed by 5 days of drying.

The present invention shall be described in more detail below, in a non- restrictive manner, with reference to the attached drawings:

Figures Ia to Id are XPS diffusion profiles showing the relative concentration of silver and of the other constituents under the exposed surface of the coated substrate obtained according to Example 4, as a function of the depth; Figures 2a to 2d are XPS diffusion profiles showing the relative concentration of silver under the exposed surface of the coated substrate obtained according to Example 5, as a function of the depth;

Example 1

A sample of clear soda-lime glass 4 mm thick was firstly coated with a double CVD underlayer consisting of 75 nm of SiOxCy and 320 nm fluorine doped tin oxide. The surface is then slightly polished (until the Ra roughness becomes lower than 5 nm) .

The sample was coated with a silver layer by chemical deposition using a method similar to that used to produce mirrors. An aqueous solution of AgNO₃ was sprayed onto the surface of the glass at a quantity of 800 mg/min along with a reducing agent to reduce the silver salt into metallic silver.

To cause the silver to diffuse into the surface, the sample was then subjected to a baking in a furnace at 300⁰C during 15min. The sample was then washed with FeCl₃ to remove the excess of silver having not diffused. The aim is to eliminate any trace of silver on the surface (mainly metallic Ag) and thus to obtain a clear glass without eliminating the silver that has lightly diffused into the surface. Solutions of HNO₃, or Fe(NO₃)₃ are also suitable for such a washing process.

The antibacterial properties were then measured.

Measurement of the antimicrobial effect

The bactericidal properties 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.

The sample was subjected to a common tempering process (670⁰C during 200 seconds) according to standard EN 12150-1.

The antibacterial properties were measured again.

A value of log 4.4 was obtained before tempering and 4.1 after tempering which means that the tempering process has no significant impact on the bactericide properties of the sample.

The optical characteristic of the antibacterial samples are good. They are not significantly modified as compared a non antibacterial glass.

The sample which is in the same time antibacterial and tempered has an appearance that is neutral in reflection. The colorimetric indexes are a* = -4.3; b* = -2.1 and L* 41.5 with a colour purity of 6.9% (measured with illuminant D, angle of 10°, in reflectance).

The Light Transmittance is 81% and the Light Reflectance is 12% (integrated on the visible wavelength).

The haze of the samples is very low (0.36%).

Accelerated ageing tests

The following ageing tests were carried out : - wet spray (test for 20 days in a chamber with a humidity of more than 95% and at 40⁰C);

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

- 24 hours of immersion in an H2SO4 solution (0.1 N),

- 24 hours of immersion in a NaOH solution (0.1 N);

- 48 hours of immersion in Mr Propre® "salle de bain liquide" detergent followed by 5 days of drying.

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

Good bactericide properties were obtained after the UV test (log 3.0) and after the NaOH immersion test (log 3.5)

Example 2

For example 2, no baking has been carried out before the tempering step.

A sample of clear soda- lime glass 4 mm thick was firstly coated with a double CVD underlayer consisting of 75 nm of SiOxCy and 320 nm fluorine doped tin oxide. The surface is then slightly polished (until the Ra roughness becomes lower than 5 nm) .

The sample was coated with a silver layer by chemical deposition using a method similar to that used to produce mirrors. An aqueous solution of AgNO₃ was sprayed onto the surface of the glass at a quantity of 800 mg/min along with a reducing agent to reduce the silver salt into metallic silver. To cause the silver to diffuse into the surface, the sample was subjected to a tempering step (670⁰C during 200 sec.) without any intermediate baking step. The sample was then washed with FeCl₃ to remove the excess of silver having not diffused. T

The bactericidal properties were then measured and a log 4.7 value was obtained.

Bactericidal properties were maintained after the accelerated ageing tests. A log 2.6 was obtained after the H₂SO₄ immersion test; a log 4.6 was obtained after the wet spray test, a log 4.7 was obtained after the UV test, a log greater than 3.5 after the NaOH immersion test, a log 2.5 after detergent immersion test and a log 4.6 after wet spray test.

Example 3

A sample of clear soda-lime glass 4 mm thick was firstly coated with a double CVD underlayer as in the previous examples.

The sample was coated with a silver layer by chemical deposition using a method similar to that used to produce mirrors. An aqueous solution of AgNO₃ was sprayed onto the surface of the glass at a quantity of 200 mg/min along with a reducing agent to reduce the silver salt into metallic silver.

To cause the silver to diffuse into the surface, the sample was then subjected to a baking wherein the temperature of the furnace is maintained higher than 170⁰C during 2 min and let progressively decreased. The sample was then washed with FeCl₃ as for the previous examples.

The antibacterial properties were measured and a value higher than log 3.5 was obtained. The sample was subjected to a common tempering process (670⁰C during 200 sec).

The antibacterial properties were measured again. A value higher than log 3.5 was also obtained.

Example 4

Four samples of clear soda-lime glass of 4 mm thick were firstly coated with a double CVD underlayer consisting of 75 nm of SiOxCy and 320 nm fluorine doped tin oxide. The surface is then slightly polished (until the Ra roughness becomes lower than 5nm) .

The samples were then coated with a silver layer using the vacuum deposition method, also referred to as magnetron sputtering, in a manner known per se using a silver metal target in an atmosphere of argon. The quantity of silver deposited was: for sample 4a, 20 mg/m² of surface treated, for sample 4b: 50 mg/m2, for sample 4c, 100 mg/m2 and for sample 4d, 200 mg/m2.

To cause the silver to diffuse into the surface, the samples were then subjected to a baking treatment at 300⁰C during 15 min. The samples were then washed with FeCl₃ as for the previous examples.

Figures l.a to l.d show the atomic percentage of each constituent of the coated substrate as a function of the pulverisation time, which can be correlated to the depth in the coating (In this case one sec. corresponds to 0.5lA).

We can deduce from fig l.a that the silver has diffused into the SnO2:F underlayer until a maximum depth of 75 nm. In fig l.b, the maximum diffusion depth is 44 nm; in fig l.c and l.d, the maximum diffusion depth is 31 nm. The quantity of silver which has diffused is rather low : around 1 mg/m2 for example 4a and 4b and less than 1 mg/m2 for example 4c and 4d.

Even with such low Ag quantities, a log 3 was obtained for the 4 samples of example 4 before and after tempering.

Example 5

Four samples of clear soda-lime glass of 4 mm thick were firstly coated with a double CVD layer consisting of 75 nm of SiOxCy and 320 nm antimony doped tin oxide.

The samples were then coated with a silver layer using the vacuum deposition method, also referred to as magnetron sputtering, in a manner known per se using a silver metal target in an atmosphere of argon. The quantity of silver deposited was for sample 4a 20 mg/m² of surface treated, for sample 4b, 50 mg/m2, for sample 4c, 100 mg/m2 and for sample 4d, 200 mg/m2.

As for example 4, Figures 2. a to 2. d show the atomic percentage of each constituent of the coated substrate as a function of the pulverisation time, which can be correlated to the depth in the coating (In this case one sec. corresponds to 0.55A).

We can deduce from fig 2. a that the silver has diffused into the SnO2:Sb underlayer until a maximum depth of 23 nm. In fig 2.b, the maximum diffusion depth is 26 nm; in fig 2.c, and in fig. 2.d, the maximum diffusion depth is 36 nm. The quantity of silver which has diffused is rather low : less than 0.5 mg/m2 for the 4 samples of example 5.

Even with such low Ag quantities, a log 3 was also obtained for the 4 samples of example 5.

Claims

1. Process for the production of a substrate having antimicrobial properties and keeping antimicrobial properties after tempering treatment and at least one accelerated ageing tests, characterised in that it comprises the following steps:

(i) deposition of a metal non-gelling layer comprising an inorganic antimicrobial agent, obtained at the outset from a precursor, in metal, chelate or ion form, on the at least one part of the exposed surfaces of the substrate;

(ii) diffusion of the agent into or under said at least one exposed surface of the substrate by thermal treatment at a temperature comprised between 120 and 750⁰C.

2. Process according to claim 1, characterized in that the substrate is coated with an undercoat before the deposition of step (i), and in that the diffusion of step (ii) occurs mainly within the coating.

3. Process according to either claim 1 or claim 2, characterised in that the diffusion of the agent is realized during a tempering step.

4. Process according to either claim 1 or claim 2, characterised in that the temperature of the thermal treatment is comprised between 120⁰C and 190⁰C, preferably between 150°C and 180°C.

5. Process according to either claim 1 or claim 2, characterized in that the temperature of the thermal treatment is higher than 350⁰C, preferably higher than

380°C and particularly preferred higher than 400°C.

6. Process according to either claim 1 or 2, characterised in than the temperature of the thermal treatment is lower than the 550⁰C, preferably lower than 500⁰C, and particularly preferred lower than 480⁰C.

7. Process according to any one of the preceding claims, characterised in that the thermal treatment is conducted for a period greater than 1 minute, preferably greater than 2 minutes and particularly preferred greater than 3 min and lower than 1 hour, preferably lower than 30 min. and particularly preferred lower than 15 minutes.

8. Process according to any one of claim 1 or 2, characterised in that the thermal treatment is conducted at a temperature in the range of between 150° and

190⁰C for a period varying from 1 to 30 minutes.

9. Process according to any one of the preceding claims, characterised in that the layer comprising the antimicrobial agent is deposited either by pyrolytic spraying, vacuum sputtering or by a method involving the precipitation of metal antimicrobial agents by reduction of a corresponding salt.

10. Process according to any one of claims 1 to 8, characterised in that the precursor used in step (i) is in a metallic or ionic form, in particular in ionic form and dissolved in an aqueous solution.

11. Process according to any one of the preceding claims, characterised in that the antimicrobial agent is selected from silver, copper and zinc.

12. Process according to any one of the preceding claims, characterised in that the quantity of antimicrobial agents deposited on said at least one surface of the substrate is greater than 5 mg/m2, preferably greater than 20 mg/m2 and particularly preferred greater than 40 mg/m2 and lower than 1000 mg/m2, preferably lower than 250 mg/m² and particularly preferred lower than 150 mg/m².

13. Process according to any one of claim 2 to 12, characterised in that the undercoat has a function of slowing down the migration of the antimicrobial agent in particular during the tempering process.

14. Process according to any one of claim 2 to 13, characterised in that the underlayer is chosen amongst pyrolitic and sputtered layers, in particular layers comprising metal oxide such as SiOxCy, SiO2, SnO2, TiO2 or metal nitride such as TiN, or metal or metal alloy compound, such as Pd, Ni-Cr, TiOx, NiCrOx, Nb, Ta, Al, Zr or ZnAl, or mixture thereof.

15. Process according to any one of claim 2 to 14, characterised in that the underlayer is deposited by pyrolytic method.

16. Process according to any one of claim 2 to 15, characterised in that the underlayer has a thickness greater than 10 nm, preferably greater than 55 nm and particularly preferred greater than 110 nm.

17. Process according to any one of claim 2 to 16, characterised in that the underlayer comprises a first underlayer, having the function of blocking or slowing down the migration of the antimicrobial agent, and a second underlayer, serving as a reservoir for the antimicrobial agents.

18. Process according to any one of claims 2 to 18, characterised in that the undercoat comprises a first layer based on ZrO2 and a second layer based on TiO2, in particular in the anatase crystallised form.

19. Process according to any one of the preceding claims, characterised in that the substrate is a glass type substrate, in particular a clear soda- lime glass.

20. Substrate comprising an antimicrobial agent present at least at one of its exposed surfaces, characterised in that the total quantity of antimicrobial agents it comprises is more than 0.1 mg/m², preferably more than 0.5 mg/m² and particularly preferred more than 0.8 mg/m² of antimicrobial surface and is lower than 100 mg/m2, preferably lower than 50 mg/m2 and particularly preferred lower than 10 mg/m2.

21. Substrate according to the preceding claim, characterised in that the atomic percentage of antimicrobial agent at the surface is lower than 5%, preferably lower than 2% and particularly preferred lower than 1%.

22. Substrate according to the either of claim 20 or 21, characterised in that on at least one of the following bacteria: E. coli, S. aureus, P. aeruginosa

(measured in accordance with the standard JIS Z 2801), it has a bactericidal effect higher than log 1, preferably higher than log 2 and particularly preferred higher than log 2.5.

23. Substrate according to any one of Claims 20 to 22, characterised in that it has an antimicrobial effect after at least one of the following accelerated ageing tests: wet spray (test for 20 days in a chamber with a humidity of more than 95% and at 40⁰C), 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).

24. Substrate according to any one of Claims 20 to 23, characterised in that the antimicrobial agent is selected from silver, copper and zinc.

25. Substrate according to any of claims 20 to 24 characterised in that it is glass substrate.

26. Glass substrate according to the preceding claim, characterised in that it has a neutral colouration in reflection, i.e. the colorimetric indexes a* and b* are in the range of between -10 and 6, preferably between -8 and 3 and particularly preferred between -6 and 0, and the L* value is lower than 60, preferably lower than 52 and particularly preferred lower than 46.

27. Glass substrate according to any of claim 25 to 26 characterised in that it can be tempered without loosing its antimicrobial properties.

28. Tempered glass substrate comprising antimicrobial agents present under at least one exposed glass surface at a maximum depth of 500 nm, preferably 200 nm, and particularly preferred less than 100 nm.

29. Process for the production of a substrate having antimicrobial properties and keeping antimicrobial properties after tempering treatment and accelerated ageing tests, characterised in that it comprises the following steps:

(i) deposition of an underlayer on at least one of the exposed surface of the substrate;

(ii) deposition of a metal non-gelling layer comprising an inorganic antimicrobial agent, obtained at the outset from a precursor, in metal, colloid, chelate or ion form, on the at least one part of the exposed surfaces of the underlayer;

(iii) diffusion of the agent into or under said at least one exposed surface of the substrate by thermal treatment at a temperature comprised between 120 and 550⁰C;

(iv) cutting the obtained substrate to the dimensions of the finished product;

(v) tempering the cut substrate.