WO2013091031A1

WO2013091031A1 - Antimicrobial communication board

Info

Publication number: WO2013091031A1
Application number: PCT/BE2012/000051
Authority: WO
Inventors: Leo Gypen; Wout VAN DE BROEK
Original assignee: Polyvision, Naamloze Vennootschap
Priority date: 2011-12-21
Filing date: 2012-12-05
Publication date: 2013-06-27
Also published as: CN104105400A; HK1199372A1; JP5982006B2; JP2015500753A; EP2793575A1; BE1020337A3

Abstract

Antimicrobial communication board that is provided with an enamel coat on the writing side of the communication board, on which an antimicrobial coating is applied that consists of a composition of nanoparticles of an antimicrobial metal or a metal oxide, that is applied onto the surface in one or two layers by sol-gel coating, or by means of chemical vapour deposition under atmospheric pressure.

Description

Antimicrobial communication board.

The present invention relates to an interactive (or otherwise) enamelled visual communication board, whether an erasable board that can be written on with dry erasable felt-tip pens for example, or a coloured chalkboard or similar that can be written on with chalk.

Communication boards in offices and classrooms are used by a number of people every day, which makes the board a potential risk for the spread of microorganisms as a result of contamination by contact or coughing for example, such that the board acts as a transfer medium for microorganisms.

Users of such boards are interested in a board with an antimicrobial action to limit the use of antimicrobial products in the classroom or office.

In general antimicrobial materials and coatings are obtained by adding specific agents with a microbicidal activity.

Inorganic antimicrobial agents such as metals Ag, Cu, Au, Zn, etc, or metal oxides such as ZnO, CaO or MgO, or salts such as AgN0₃ are preferable because they are temperature resistant in contrast to organic antimicrobial agents. For metals, it is in fact the metal ions (Ag+, Cu2+, Zn2+, etc) that are the active ingredient. This means that moisture must be present in the environment to enable the metal to form ions.

The antimicrobial activity of metal oxides such as ZnO is attributed to the formation of H₂0₂, 0" and OH^" that can penetrate the cell wall and kill the bacteria.

The most popular metals are Ag and Cu, which can be added in different forms: as nanoparticles, as metal oxide particles, as a metal salt or even more complex forms, but also directly as ions on an ion exchange medium such as zeolite .

Communication boards of enamelled steel offer specific advantages, such as their dry erasability, their acid resistance and colour stability, and their wear-resistant durability.

An antimicrobial enamel in which the antimicrobial agent is integrated in the enamel itself has already been described:

US 6.303.183 (2001) describes antimicrobial porcelain enamel in which metallic silver is preferably used in a concentration of 0.1 to 3%, but zinc or copper is also used.

The antimicrobial effect of silver-containing enamel has been clearly demonstrated by Voss et al. (Evaluation of bacterial growth on various materials, 20 International Enamellers Congress, 15-19 May 2005, Istanbul) .

WO 2006/133075 describes a cost-effective and practical acid-resistant porcelain enamel with antimicrobial properties for steel substrates. The porcelain enamel contains an optimum quantity of zinc and other constituents with good antimicrobial properties, without having to lose other important properties such as acid resistance .

More recently a study by Luca Pignatti et al. described the addition of Ag20, CuO and ZnO to different types of enamel compositions. Antibacterial tests clearly demonstrate the antibacterial effects (Definition of a new range of porcelain enamels with antibacterial characteristics and the method of the antibacterial power control, 21^st International enamellers Congress, 18-22 May 2008, Shanghai) .

However, enamelled communication boards need an antimicrobial coating that is on the enamel coat, where the antimicrobial action is required, but which is nonetheless durable in order to maintain the antimicrobial action .

This certainly applies to enamelled communication boards of the interactive type in which their position-coding pattern must remain optically readable, even after long- term use, and whereby the reading instrument must remain able to form a positioned electronic reproduction of the information written on the communication panel.

Such an interactive communication board and the accompanying reading instruments have been described in detail in WO. 01/16872, whose content is incorporated in the present text by reference to it.

WO 2009/000053 describes an interactive communication board of enamelled steel, on which a position-coding pattern has been affixed by applying a print in a ceramic material that is annealed on the enamel coat at temperatures above 500 °C.

To obtain antimicrobial surfaces on the enamel surface, a biocide in the form of a metal such as silver nanoparticles can be incorporated in layers that are cast on the surface of a substrate via a sol-gel coating, as described in WO 2005/115151.

A disadvantage of such sol-gel coatings is that they are difficult to apply in a position-coding pattern for an interactive communication board.

Another disadvantage is that the application of such layers via a sol-gel coating is time-consuming because it comprises a number of steps, such as the generation of nanoparticles of the metal separate from the coating process itself, and consequently is less suitable for a continuous industrial production process with a high transit speed and low cost. A technique that enables the application of an antimicrobial layer of metallic nanoparticles and a metal oxide on a metal substrate at a high transit speed is chemical vapour deposition.

Chemical vapour deposition under atmospheric pressure is particularly attractive for this because it is suitable for continuous or semi-continuous production processes with high transit speed.

This technique is used to apply a thin layer of metal such as anticorrosion layers or scratch-resistant layers.

With thermal chemical vapour deposition under atmospheric pressure, temperatures above 500 °C can be reached, and this to obtain the desired characteristics of hardness, durability and structure.

However, at such high temperatures the oxidising effect of the evaporated chemicals harms the hot metal surface, and undesired surface properties arise such that this technique is less suitable for coating metal itself.

GB 2.466.805 describes a technique to enable the coating of iron or steel materials by chemical vapour deposition under atmospheric pressure.

To this end use is made of flame-assisted chemical vapour deposition under atmospheric pressure. The flame provides all or part of the energy needed to activate the evaporation process.

There are two variants of this: chemical vapour deposition with combustion, whereby the precursor or its solvent are flammable and thus contribute to the energy of the flame, or flame-assisted chemical vapour deposition whereby little or no energy comes from the precursor itself or its solvent .

GB 2.466.805 uses this technique to apply an antimicrobial layer on a metal substrate at a higher temperature (for example 300°C) .

To this end use is made of chemical precursors and solvents of low cost and low toxicity.

For example, an aqueous solution of a silver salt was atomised in a combustible carrier gas such as propane, which yields evaporated silver on the metal substrate at 300°C and whereby the silver layer consists of small islands of metallic silver a few tens of nm large at a distance apart of a few tens or hundreds of nm, whereby good transparency and durability was obtained.

A second layer was applied on top of this, consisting of silica of around 20 nm to 1 μπι thick, depending on the desired properties.

The quantity of silver that diffuses into this silica layer can be controlled by the temperature. Alternatively the silver can also be applied simultaneously with the silica in one layer in one single vapour deposition process.

The antimicrobial action can be further reinforced by again coating with silver in a flame-assisted chemical vapour deposition stage as a final finishing stage.

Because this technique is suitable for the application of antimicrobial layers in a continuous process at high temperature (500 °C) , we also tested this on a metal communication board, equipped with an enamel coat on the writing side and the reverse side .

Such communication boards are indeed manufactured by enamelling a steel base at temperatures above 500 °C, after which the enamelled steel formed is immediately and continuously provided with an antimicrobial coating by atmospheric chemical vapour deposition.

The purpose of the present invention is to provide a solution to the aforementioned and other disadvantages, by providing an antimicrobial communication board that is provided with an enamel coat on both the writing side and the reverse side of the communication board, and on which an antimicrobial coating is applied to the writing side that consists of a composition of nanoparticles of an antimicrobial metal or metal oxide, that is applied in one or two layers on the surface by sol-gel dip coating, or by means of chemical vapour deposition of a sol-gel coating under atmospheric pressure.

An advantage of such a communication board is that the writing side presents a high antimicrobial action, without detrimentally affecting the properties useful for its use as a communication board.

Indeed, the high scratch-resistance and durability of such antimicrobial communication boards is preserved, as well as good wipeability, good acid-resistance and colour stability, and this even after many cycles of use.

The antimicrobial action is assured by a hard-wearing layer that remains a source of antimicrobial metal ions for the lifetime of the board, because silver ions can continuously diffuse into the sol-gel coat.

The technique of chemical vapour deposition provides the advantage that it can form part of a continuous production process for communication boards, whereby production time is saved and whereby material losses, and more specifically silver losses, can be avoided.

An advantage of silver or silver oxide is that its antimicrobial action already occurs at low doses of silver ions, so that the quantity of silver or silver oxide in the antimicrobial coating needs to be no more than 10% by weight, and as of 0.1% by weight the antimicrobial action is already perceptible. With the intention of better showing the characteristics of the invention, a preferred embodiment of an enamelled visual communication board according to the invention is described hereinafter by way of an example, without any limiting nature, with reference to the accompanying drawings, wherein: figure 1 shows a schematic perspective view of an antimicrobial communication board according to the invention;

figure 2 shows a perspective view of a continuous production process for an antimicrobial communication board according to the invention;

figure 3 shows a non-continuous production process for applying an antimicrobial sol-gel coating onto an enamelled communication board.

The antimicrobial enamelled communication board 1 as shown in figure 1 primarily consists of a steel plate 2 that is

0.35 mm thick in this case, which on the front 3 and the back 4 is provided with an enamel undercoat 5 of 0.035 mm thick in this case, on which on one side 3 a second, primarily white, enamel topcoat 6 is applied. On top of this an antimicrobial sol-gel coating 7 of 10 to 200 nm thick is then applied.

Figure 2 shows the continuous production process according to the invention of an antimicrobial communication board

1, whereby in a first stage steel 2 is enamelled on both sides at a temperature of 820 °C; in a second stage, on the visible side 6 a primarily white enamel topcoat is applied and annealed at a temperature of approx. 800°C; in a third stage it is coated by thermal chemical vapour deposition with an antimicrobial coating 7 with an antimicrobial metal and metal oxide in one layer 7, or in two coats 8, 9 by means of chemical vapour deposition under atmospheric pressure; the cutting of the coated communication board to the desired format, or the rolling of it into a roll for subsequent processing, and all this in one transit through production.

Figure 3 shows the production process for applying an antimicrobial sol-gel 12 coating onto an enamelled communication board 1, whereby the process does not proceed continuously but in batches, and whereby the steel 2 is first provided with an enamel undercoat 5 on both sides at a high temperature, an enamel topcoat 6 at high temperature, and then is cooled and cut. The enamelled communication boards 1 are then processed batch-wise in a bath 13 with the desired sol-gel 12 coating, that is applied by dip coating.

Experimental section

An enamelled communication board 1 was provided with a silver-containing finishing layer by means of, on the one part, dip coating with a silver-containing sol-gel 12 layer or, on the other par , by means of chemical vapour deposition under atmospheric pressure in the following experiments .

The antimicrobial action of the cast sol-gel 12 layer and the layer deposited by evaporation were measured each time by an antimicrobial test according to ISO 22196 (JIS Z 2801) whereby a reduction factor due to the effects of the antimicrobial layer of certain strains of bacteria was measured. The reduction factor is expressed on a logarithmic scale as the difference between the number of bacteria per cm² without, and the number per cm² with the antimicrobial layer.

If for example the number of bacteria falls from 1 million/cm² (Log 6) to 100/cm² (Log 2), the difference is Log 4, or the logarithmic reduction factor is 4.

EXPERIMENT 1 A solution of the following composition was made.

1) 94% 2-propanol

2) 4% TEOS (tetraethyl orthosilicate)

3) 1% AgN0₃ solution of 1 M

4) 0.8% HN0₃

To this end 17.71g TEOS was added to 22.7g 2-propanol. This mixture was mixed with 3. 1g AgN0₃ 1 M solution and acidified with 3.41 HN0₃ 1M. The mixture was then mixed for 20 minutes. After mixing another 360.40g 2-propanol was added. The solution was applied by means of dip coating, whereby a layer thickness of 40 to 60 nm was obtained, after which a thermal curing stage followed at 400°C for 10 minutes.

To do the antimicrobial test, use was made of

1) a suspension medium: nutrient broth 1/500 NB;

2) an inoculum test: a bacterial suspension in 1/500 NB was diluted to obtain a bacterial concentration of between 2.5 x 10⁵ and 10 x 10⁵ cells/ml, with a target concentration of 6 x 10⁵ cells/ml;

3) the following strains of bacteria:

- Staphylococcus aureus

- Escherichia coli.

4) an incubation: the samples inoculated with the bacterial suspension were incubated at a temperature of 35 +/- 1 °C for 24 +/- 1 h, at a relative humidity of no less than 90%.

For the bacteria Escherichia coli, the following antimicrobial effect was measured:

Without antimicrobial layer: 13,666,667 KVE/ml or 854,167 KVE/cm2 (Log 7.13 or Log 5.88).

With antimicrobial layer: 17 KVE/ml or 1 KVE/cm2 (Log 1.23 of Log 0) . The reduction factor due to the antimicrobial layer is consequently Log 5.9 or a reduction by a factor of around one million.

EXPERIMENT 2

A solution of the following composition was made.

1) 94% 2-propanol

2) 4% TEOS (tetraethyl orthosilicate)

3) 1% AgN0₃ solution of 1 M

4) 0.8% HN0₃

To this end 17.71g TEOS was added to 22.7g 2-propanol. This mixture was mixed with 3.41g AgN0₃ 1 M solution and acidified with 3.41 HN0₃ 1M. The mixture was then mixed for 20 minutes. After mixing another 360.40g 2-propanol was added.

The solution was applied by means of chemical vapour deposition with combustion by atomisation in propane, whereby the energy of the flame was used to thermally cure the coating. Coat thicknesses of 40 to 60 nm were obtained.

Antimicrobial tests were done as described above for Escherichia coli, with the following result.

Without antimicrobial layer: 12,100,000 KVE/ml or 756,250 KVE/cm2 (Log 7.08 or Log 5.88). With antimicrobial layer: 99,017 KVE/ml or 6,245 KVE/cm2 (Log 5.0 or Log 3.8).

The reduction factor by the antimicrobial coat is consequently Log 2.1 or a reduction by a factor of more than one hundred in 24 hours.

It goes without saying that the continuous production process that makes use of the chemical vapour deposition of antimicrobial agents is much more efficient and cost- effective than the discontinuous production process that makes use of antimicrobial sol-gel liquid coating solutions .

The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but such a communication board that is provided with antimicrobial metals or metal oxides can be realised in other embodiments, that coat antimicrobial sol-gels or chemically deposit antimicrobial constituents by evaporation, without departing from the scope of the invention.

Claims

1. Antimicrobial communication board (1) that is provided with an enamel coat (5) annealed at temperatures above 500 °C on both the writing side and the reverse side of the communication board, and on which an antimicrobial coating (7) is applied onto the writing side that consists of a composition of nanoparticles of an antimicrobial metal or an antibacterial metal oxide or an antibacterial metal salt, that is applied in one (7) or two (8, 9) layers on the surface by sol-gel (12) dip coating, or by means of chemical vapour deposition of a sol- gel coating under atmospheric pressure.

2. Antimicrobial communication board (1) according to claim 1, characterised in that the antimicrobial metal is silver or copper.

3. Antimicrobial communication board (1) according to claim 1, characterised in that the metal oxide is a silicate .

4. Antimicrobial communication board (1) according to claim 1, characterised in that the chemical vapour deposition is a flame-assisted or combustion- chemical vapour deposition under atmospheric pressure .

Antimicrobial communication board (1) according to claim 1 or 2, characterised in that the metal and metal oxide or metal salt consist of silver, silver oxide or silver nitrate.

6. Antimicrobial communication board (1) according to claim 1, characterised in that the action of the antimicrobial coating (6) reduces the number of E. coli bacteria per unit area by a factor of at least 100 in 24 h.

7. Method for manufacturing an antimicrobial communication board (1) as described in claim 1, characterised in that the method provides a continuous production process, whereby in a first stage steel (2) is enamelled on both sides at a temperature of 820 °C; in a second stage a primarily white enamel topcoat is applied onto the visible side 6 and annealed at a temperature of approx. 800 °C; in a third stage it is coated by means of thermal chemical vapour deposition with an antimicrobial coating 7 with an antimicrobial metal and a metal oxide in one layer (7) or in two layers (8), (9); the cutting of the coated communication board to the desired format or the rolling of it into a roll for subsequent processing, and all this in one transit through production.