WO2012006690A2 - Enamelled visual communication board - Google Patents

Enamelled visual communication board Download PDF

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Publication number
WO2012006690A2
WO2012006690A2 PCT/BE2011/000041 BE2011000041W WO2012006690A2 WO 2012006690 A2 WO2012006690 A2 WO 2012006690A2 BE 2011000041 W BE2011000041 W BE 2011000041W WO 2012006690 A2 WO2012006690 A2 WO 2012006690A2
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WO
WIPO (PCT)
Prior art keywords
communication board
layer
reflection
board
refractive index
Prior art date
Application number
PCT/BE2011/000041
Other languages
French (fr)
Other versions
WO2012006690A3 (en
Inventor
Joachim Thonissen
Guido Jeanne Louis Vervaeren
Original Assignee
Polyvision, Naamloze Vennootschap
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Polyvision, Naamloze Vennootschap filed Critical Polyvision, Naamloze Vennootschap
Publication of WO2012006690A2 publication Critical patent/WO2012006690A2/en
Publication of WO2012006690A3 publication Critical patent/WO2012006690A3/en

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B43WRITING OR DRAWING IMPLEMENTS; BUREAU ACCESSORIES
    • B43LARTICLES FOR WRITING OR DRAWING UPON; WRITING OR DRAWING AIDS; ACCESSORIES FOR WRITING OR DRAWING
    • B43L1/00Repeatedly-usable boards or tablets for writing or drawing
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B43WRITING OR DRAWING IMPLEMENTS; BUREAU ACCESSORIES
    • B43LARTICLES FOR WRITING OR DRAWING UPON; WRITING OR DRAWING AIDS; ACCESSORIES FOR WRITING OR DRAWING
    • B43L1/00Repeatedly-usable boards or tablets for writing or drawing
    • B43L1/002Repeatedly-usable boards or tablets for writing or drawing chemical details
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/10Optical coatings produced by application to, or surface treatment of, optical elements
    • G02B1/11Anti-reflection coatings
    • G02B1/113Anti-reflection coatings using inorganic layer materials only
    • G02B1/115Multilayers
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/0304Detection arrangements using opto-electronic means
    • G06F3/0317Detection arrangements using opto-electronic means in co-operation with a patterned surface, e.g. absolute position or relative movement detection for an optical mouse or pen positioned with respect to a coded surface
    • G06F3/0321Detection arrangements using opto-electronic means in co-operation with a patterned surface, e.g. absolute position or relative movement detection for an optical mouse or pen positioned with respect to a coded surface by optically sensing the absolute position with respect to a regularly patterned surface forming a passive digitiser, e.g. pen optically detecting position indicative tags printed on a paper sheet
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/033Pointing devices displaced or positioned by the user, e.g. mice, trackballs, pens or joysticks; Accessories therefor
    • G06F3/0354Pointing devices displaced or positioned by the user, e.g. mice, trackballs, pens or joysticks; Accessories therefor with detection of 2D relative movements between the device, or an operating part thereof, and a plane or surface, e.g. 2D mice, trackballs, pens or pucks
    • G06F3/03545Pens or stylus
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B2207/00Coding scheme for general features or characteristics of optical elements and systems of subclass G02B, but not including elements and systems which would be classified in G02B6/00 and subgroups
    • G02B2207/109Sols, gels, sol-gel materials

Definitions

  • the present invention relates to an enamelled visual communication board, with an enamelled surface that can be written on with felt-tip or chalk, for example.
  • Such communication boards can be interactive or otherwise.
  • Interactive boards are able to digitally store the data that are written on the communication board during a presentation for example, and possibly simultaneously project them, and provide various other interactions between the communication board, a computer and various peripheral equipment.
  • Such interactive communication boards of enamelled steel, that make use of an optically readable position-coding pattern, were described in patent BE 1.015.482.
  • BE 1.016.588 describes covering the enamelled surface with a glassy or ceramic anti-reflection coating that is applied as a sol- gel dispersion and then tempered at a suitable higher temperature .
  • the aforementioned sol-gel dispersion thereby consists of a colloidal solution of inorganic metal salts and/or organic metal compounds such as metal alkoxides, whereby this solution, or more specifically this liquid dispersion, is converted during a drying process from the ⁇ sol' to the gel' state, and after tempering at a higher temperature forms the aforementioned anti-reflection coating.
  • the optical thickness of the sol-gel coating is such that it corresponds to one quarter of a wavelength of visible light, or the light from a light source used for reading an interactive communication board by a computer or for projecting an image, which more specifically comes down to a coating thickness for the sol- gel coating that is generally in the range from 50 to 200 nm.
  • the light reflected by the surface that forms the interface between the surrounding air and the sol-gel coating is at least partly neutralised by the light reflected by the surface that forms the interface between the sol-gel coating and the underlying enamel layer, whereby the top layer acts as an anti-reflection coating.
  • the sol-gel coating has an optical thickness of one quarter of a wavelength of the light the reflection of which is intended to be reduced, and the sol-gel coating has a refractive index that is less than that of the underlying layer, in this case an enamel layer, then the two reflected waves present a phase difference of 180° and they entirely or partially cancel each other out through interference, or at least the waves striking the surface at normal incidence.
  • the incoming light waves with a different angle of incidence to the aforementioned normal incidence are also suppressed, albeit to a lesser extent.
  • n.d ⁇ /4
  • n is the refractive index of the sol-gel coating
  • d is the thickness of the coating
  • the wavelength of the incident light.
  • the product of n and d is called the optical thickness of the coating.
  • This anti-reflection coating reduces the gloss of the board and reduces inconvenient light reflections. Because the surface of the anti-reflection coating is smooth, it also ensures the good wipeability of the ink of felt-tip pens, for example, that are used to write on the communication board.
  • the substrate is glass or a polymer material with a refractive index n s of around 1.5.
  • the ideal refractive index of the sol-gel coating is 1.22.
  • the availability of materials with such a low refractive index limits the effectiveness of an anti-reflective coating consisting of one layer.
  • the commonest used materials are MgF 2 with a refractive index of 1.38, and nanoporous Si0 2 is also often used.
  • the white colour is obtained by a deposition of Ti0 2 .
  • the properties of enamel are rather similar to those of borosilicate glass, but due to the presence of Ti0 2 in the enamel, the refractive index is 1.65 to 1.7, which was determined by the inventor by ellipsometric measurements.
  • an anti-reflection coating can be made much more effective by building up the anti-reflection coating from two or more layers with different refractive indices.
  • the structure of an anti-reflection coating with more than two layers is more complex, however, and the design of it requires complicated calculations. In this case, for example, layers are sometimes provided of which the optical thickness corresponds to ⁇ /2 of the light reflection to be reduced.
  • BE 1.017.572 not only describes the use of one top layer with an optical thickness corresponding to a quarter of a wavelength of the visible light spectrum, but also the use of three layers matched to one another, and this for communication boards of the interactive type.
  • These three layers each present a different refractive index and a different layer thickness that are chosen such that they exhibit optimum anti-reflective action for the light source causing the reflection.
  • the first layer presents an optical thickness of ⁇ /4
  • the second layer a thickness of ⁇ /2
  • a third layer again with a thickness of ⁇ /4
  • is the wavelength of the light source the reflection of which is to be suppressed, for example 550 nm for the middle of visible light.
  • the purpose of the invention is to further broaden the spectral bandwidth over which the reflected light is suppressed to a larger proportion of the visible light spectrum or of the spectrum of a light source used.
  • the present invention concerns a communication board on which there is a multilayer anti-reflection coating on the visible side of the enamel layer, consisting of at least three glassy or ceramic layers, where at least one layer has a layer thickness outside the range from 50 to 200 nm.
  • this refractive index is determined by the square root of the refractive index of the enamel, that has been determined by the inventor at 1.65 to 1.70 so that the ideal refractive index for a glassy or ceramic layer is 1.3 to 1.4.
  • An anti-reflection coating can be made even more effective by providing three, four, five or more anti-reflection layers that are matched to one another, whereby the layer thicknesses are calculated and chosen outside the interval of 50 to 200 nm, and whereby different refractive indices can be used for each layer.
  • the increased effectiveness is shown by the reflection spectrum that suppresses the reflection of the incident light over a broader wavelength range, such that the light can be incident over a larger angle without losing the anti-reflection properties of the coating.
  • the communication board can be an interactive board with a position-coding pattern that enables the use of an image detector, whereby the position of the pen or felt-tip on the board can be determined and whereby a picture of what is drawn or written on the board can be saved in a computer.
  • the multilayer anti-reflection coating can be matched to the light source of a pen or felt-tip for an interactive board, to prevent the detection of the coding pattern being affected by inconvenient reflections.
  • the multilayer anti-reflection coatings are obtained from various colloidal solutions of inorganic metal salts and/or organic metal compounds, such as metal alkoxides, whereby these liquid dispersions are applied as a sol to the communication board and converted into a gel state during a drying process and whereby, after tempering at temperatures above 300 °C, dry and hardened anti- reflection coatings are formed.
  • inorganic metal salts and/or organic metal compounds such as metal alkoxides
  • compositions are that they can be applied in the desired layer thicknesses by dip coating at a suitable speed.
  • compositions can be mixed into solutions with the desired refractive index.
  • figure 1 schematically shows a cross-section of a communication board with a five-layered anti- reflection coating according to the invention
  • figure 2 shows the reflection spectrum of figure 1;
  • figure 3 shows a cross-section of a communication board with one anti-reflection coating;
  • figure 4 shows the reflection spectrum of figure 3
  • figure 5 shows a cross-section of a communication board with a three-layered anti-reflection coating
  • figure 6 shows the reflection spectrum of figure 5.
  • the visual communication board 1 shown in figure 1 primarily consists of a steel plate 2, in this case 0.35 mm thick, which on the front has a primarily white enamel coating 3 that is 0.10 mm thick in this case.
  • the front means the side that faces the viewer when the communication board 1 is used.
  • the resulting reflection spectrum 9 of this surface is shown in figure 2.
  • the reflection and transmission of an anti-reflection coating consisting of a number of layers applied to a substrate can be calculated by means of a computer program, for example based on the Abeles matrix calculation method.
  • Table I calculated five-layered anti-reflection coating on an enamelled surface with a refractive index of 1.6.
  • Table III Composition of the Ti0 2 solution The total volume of this composition is 705.38 ml.
  • the first layer 4 on the enamelled layer is obtained by mixing the Si0 2 solution with the Ti0 2 solution in a volumetric ratio of 70/30, whereby a refractive index of 1.7 is obtained.
  • This mixture is applied to the enamelled substrate 3 by dip coating at a speed of 1.40 cm/sec, such that a layer thickness of 85 nm remains after 5 minutes of drying at 400°C.
  • a layer of the Ti0 2 composition is applied to this at a dip coating speed of 0.40 cm/sec, and this second layer 5 is also dried for 5 minutes at 400°C, whereby a layer thickness of 59 nm with refractive index 2.1 remains.
  • a third layer 6 is applied over this, consisting of the Si0 2 /Ti0 2 mixture described above, in the same way at a dip coating speed of 0.47 cm/sec, but with a thinner layer thickness, which after drying at 400°C for 5 minutes yields a layer thickness of 32 nm and refractive index of 1.7.
  • a fourth layer 7 is applied over this, consisting of the Ti0 2 composition, at a dip coating speed of 0.31 cm/sec, which after drying for 5 minutes at 400°C yields a layer thickness of 39 nm and refractive index 2.1.
  • a fifth layer 8 is applied, consisting of the Si0 2 solution described above, at a dip coating speed of 0.91 cm/sec, which this time after drying for 10 minutes at 400°C yields a layer thickness of 98 nm and refractive index of 1.4.
  • the resulting reflection spectrum 9 at normal incidence of the light is shown in figure 2, which shows that the reflection of the visible wavelengths is strongly suppressed as of wavelengths above 450 nm.
  • the light reflected by the surface is expressed as a % of the incident light and is shown as a function of the wavelength Aof the incident light, expressed in nanometres (nm) .
  • the integrated reflection over the proposed wavelength range is less than 1.2% and is defined as follows: ⁇ 2
  • R integrated 1 J R(A) . dA
  • Figure 3 shows a cross-section of a communication board of enamelled steel 10, with a single anti-reflection layer 11 and figure 4 the reflection spectrum 12 of this surface at normal incidence.
  • the anti-reflection coating consists of a Si02 solution, applied as a sol-gel via dip coating.
  • the Si0 2 solution contains the following ingredients:
  • Second layer 15 2.1 0.42 29
  • First layer 14 1.85 1.2 94
  • Table V calculated three-layered anti-reflection coating on an enamelled surface with a refractive index of 1.6.
  • the first layer 14 on the enamelled surface consists of a mixture of the Si0 2 solution with the Ti0 2 solution in a volumetric ratio of 40/60 and yields a refractive index of 1.85.
  • the first layer 14 is applied at a dip coating speed of 1.3 cm/sec, resulting in a layer thickness of 94 nm after drying .
  • the second layer 15 consists of the Ti0 2 solution, that is applied at a dip coating speed of 42 mm/sec, resulting in a layer thickness of 29 nm after drying.
  • the third layer 16 consists of the Si0 2 solution, that is applied at a dip coating speed of 91 mm/sec, resulting in a layer thickness of 101 nm after drying.
  • the resulting reflection spectrum 17 for an angle of incidence of 0° for this anti-reflection finish consisting of three layers is shown in figure 6.
  • a comparison of the reflection spectra of the single- layered, three-layered and five-layered coatings shows that the embodiment with five layers suppresses the reflected light over the widest wavelength range, which yields an integrated reflection between 380 and 780 nm of less than 1.2%, which demonstrates the suppression over a broad wavelength range.
  • the antireflective properties can be further improved by applying additional layers, insofar they are judiciously chosen with regard to layer thickness and refractive index.
  • the present invention is by no means limited to the embodiment described as an example and shown in the drawings, but a number of anti-reflection coatings with three or more layers for a communication board can be realised without departing from the scope of the invention.
  • the enamelled surface can be affixed to a support along one or two sides, or the support can consist of a honeycomb core made of a thermoplastic polymer, which for example is manufactured in-line during the production process of the communication board, on which enamelled sheet steel is laminated in-line.

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Human Computer Interaction (AREA)
  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Optics & Photonics (AREA)
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Abstract

Communication board (1) with an enamelled surface (3), characterised in that a multilayer anti - reflection coating is affixed to the visible side of the enamel layer, consisting of at least three glassy or ceramic layers (4, 5, 6, 7, 8), in which at least one layer has an optical layer thickness outside the range from 50 to 200 ran, and whereby the optical layer thickness of this layer is equal to one quarter of the wavelength of the incident light in nm, divided by the refractive index of the glassy or ceramic layer, and whereby this refractive index is between 1.3 and 1.5.

Description

Enamelled visual communication board.
The present invention relates to an enamelled visual communication board, with an enamelled surface that can be written on with felt-tip or chalk, for example.
Such communication boards can be interactive or otherwise. Interactive boards are able to digitally store the data that are written on the communication board during a presentation for example, and possibly simultaneously project them, and provide various other interactions between the communication board, a computer and various peripheral equipment. Such interactive communication boards of enamelled steel, that make use of an optically readable position-coding pattern, were described in patent BE 1.015.482.
A problem that arises is that certain enamelled communication boards present inconvenient light reflections of light sources, such as lighting or a projector lamp, such that the readability of the communication board is reduced, both for the viewer and for the optical systems that record an image of the surface in the case of interactive communication boards.
In order to remedy this disadvantage it is known to apply one or more anti-reflection coatings to communication boards with an enamelled surface. For example, BE 1.016.588 describes covering the enamelled surface with a glassy or ceramic anti-reflection coating that is applied as a sol- gel dispersion and then tempered at a suitable higher temperature .
The aforementioned sol-gel dispersion thereby consists of a colloidal solution of inorganic metal salts and/or organic metal compounds such as metal alkoxides, whereby this solution, or more specifically this liquid dispersion, is converted during a drying process from the λ sol' to the gel' state, and after tempering at a higher temperature forms the aforementioned anti-reflection coating.
As a rule it is known that the optical thickness of the sol-gel coating is such that it corresponds to one quarter of a wavelength of visible light, or the light from a light source used for reading an interactive communication board by a computer or for projecting an image, which more specifically comes down to a coating thickness for the sol- gel coating that is generally in the range from 50 to 200 nm.
The light reflected by the surface that forms the interface between the surrounding air and the sol-gel coating, is at least partly neutralised by the light reflected by the surface that forms the interface between the sol-gel coating and the underlying enamel layer, whereby the top layer acts as an anti-reflection coating.
If the sol-gel coating has an optical thickness of one quarter of a wavelength of the light the reflection of which is intended to be reduced, and the sol-gel coating has a refractive index that is less than that of the underlying layer, in this case an enamel layer, then the two reflected waves present a phase difference of 180° and they entirely or partially cancel each other out through interference, or at least the waves striking the surface at normal incidence. The incoming light waves with a different angle of incidence to the aforementioned normal incidence are also suppressed, albeit to a lesser extent.
Mathematically this is expressed as n.d = λ/4 where n is the refractive index of the sol-gel coating, d is the thickness of the coating and λ the wavelength of the incident light. The product of n and d is called the optical thickness of the coating.
This anti-reflection coating reduces the gloss of the board and reduces inconvenient light reflections. Because the surface of the anti-reflection coating is smooth, it also ensures the good wipeability of the ink of felt-tip pens, for example, that are used to write on the communication board. A disadvantage of such an anti-reflection coating is that the anti-reflective action of a single top layer is only optimum for one wavelength, which is generally chosen in the middle of the visible light spectrum, i.e. 550 nm. Such a top layer consequently presents minimum reflection in the middle of the visible light spectrum, but not outside it. This minimum reflection depends on the refractive index of the sol-gel coating. The optimum is calculated as n = (n0 . ns)1 2 where n0 is the refractive index of the surrounding medium (usually air where n0 = 1) and where ns is the refractive index of the substrate. In many applications the substrate is glass or a polymer material with a refractive index ns of around 1.5.
In this case the ideal refractive index of the sol-gel coating is 1.22. The availability of materials with such a low refractive index limits the effectiveness of an anti-reflective coating consisting of one layer. The commonest used materials are MgF2 with a refractive index of 1.38, and nanoporous Si02 is also often used.
When the substrate is a white enamelled plate, the white colour is obtained by a deposition of Ti02. The properties of enamel are rather similar to those of borosilicate glass, but due to the presence of Ti02 in the enamel, the refractive index is 1.65 to 1.7, which was determined by the inventor by ellipsometric measurements.
It is also known that an anti-reflection coating can be made much more effective by building up the anti-reflection coating from two or more layers with different refractive indices. An anti-reflection coating with two layers in which the optical thickness of each layer is equal to λ/4 for the light the reflection of which is to be reduced, still has a relatively simple structure. The structure of an anti-reflection coating with more than two layers is more complex, however, and the design of it requires complicated calculations. In this case, for example, layers are sometimes provided of which the optical thickness corresponds to λ/2 of the light reflection to be reduced.
For example, BE 1.017.572 not only describes the use of one top layer with an optical thickness corresponding to a quarter of a wavelength of the visible light spectrum, but also the use of three layers matched to one another, and this for communication boards of the interactive type.
These three layers each present a different refractive index and a different layer thickness that are chosen such that they exhibit optimum anti-reflective action for the light source causing the reflection.
For example the first layer presents an optical thickness of λ/4, the second layer a thickness of λ/2, and a third layer again with a thickness of λ/4, where λ is the wavelength of the light source the reflection of which is to be suppressed, for example 550 nm for the middle of visible light. Although the reflected light with the three-layered top coating is suppressed over a broader wavelength range of the visible light, this wavelength range is small for the users of enamelled communication boards or the requirements of the optical systems used in interactive communication boards made from enamelled steel.
The purpose of the invention is to further broaden the spectral bandwidth over which the reflected light is suppressed to a larger proportion of the visible light spectrum or of the spectrum of a light source used.
To this end the present invention concerns a communication board on which there is a multilayer anti-reflection coating on the visible side of the enamel layer, consisting of at least three glassy or ceramic layers, where at least one layer has a layer thickness outside the range from 50 to 200 nm.
The choice of this refractive index is determined by the square root of the refractive index of the enamel, that has been determined by the inventor at 1.65 to 1.70 so that the ideal refractive index for a glassy or ceramic layer is 1.3 to 1.4.
An anti-reflection coating can be made even more effective by providing three, four, five or more anti-reflection layers that are matched to one another, whereby the layer thicknesses are calculated and chosen outside the interval of 50 to 200 nm, and whereby different refractive indices can be used for each layer.
The increased effectiveness is shown by the reflection spectrum that suppresses the reflection of the incident light over a broader wavelength range, such that the light can be incident over a larger angle without losing the anti-reflection properties of the coating.
Optionally the communication board can be an interactive board with a position-coding pattern that enables the use of an image detector, whereby the position of the pen or felt-tip on the board can be determined and whereby a picture of what is drawn or written on the board can be saved in a computer.
The multilayer anti-reflection coating can be matched to the light source of a pen or felt-tip for an interactive board, to prevent the detection of the coding pattern being affected by inconvenient reflections.
Preferably the multilayer anti-reflection coatings are obtained from various colloidal solutions of inorganic metal salts and/or organic metal compounds, such as metal alkoxides, whereby these liquid dispersions are applied as a sol to the communication board and converted into a gel state during a drying process and whereby, after tempering at temperatures above 300 °C, dry and hardened anti- reflection coatings are formed.
An advantage of these compositions is that they can be applied in the desired layer thicknesses by dip coating at a suitable speed.
Another advantage is that these compositions can be mixed into solutions with the desired refractive index.
With the intention of better showing the characteristics of the invention, a preferred embodiment of a visual communication board, interactive or otherwise, with a five- layered anti-reflection coating on an enamelled surface 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 schematically shows a cross-section of a communication board with a five-layered anti- reflection coating according to the invention;
figure 2 shows the reflection spectrum of figure 1; figure 3 shows a cross-section of a communication board with one anti-reflection coating;
figure 4 shows the reflection spectrum of figure 3; figure 5 shows a cross-section of a communication board with a three-layered anti-reflection coating; figure 6 shows the reflection spectrum of figure 5.
The visual communication board 1 shown in figure 1 primarily consists of a steel plate 2, in this case 0.35 mm thick, which on the front has a primarily white enamel coating 3 that is 0.10 mm thick in this case.
The front means the side that faces the viewer when the communication board 1 is used. On the white enamel coating 3 there are five glassy or ceramic layers 4 to 8 according to the invention. The resulting reflection spectrum 9 of this surface is shown in figure 2.
The reflection and transmission of an anti-reflection coating consisting of a number of layers applied to a substrate can be calculated by means of a computer program, for example based on the Abeles matrix calculation method.
This calculation method is described in detail and demonstrated in the book: "Basics of Optics of Multilayer Systems" by Sh. Furman and A.V. Tikhonravov, Edition Frontieres, Gif-sur Yvette, 1992.
Using this method the inventor calculated, using the experimentally determined refractive indices of the enamelled substrate and the different layers, that an optimum five-layered anti-reflection coating for the wavelength of 550 nm is built up as follows:
Figure imgf000011_0001
Table I: calculated five-layered anti-reflection coating on an enamelled surface with a refractive index of 1.6. Such a structure was realised in practice on the basis of two solutions with the following compositions:
Si02 solution (TEOS = tetraethoxysilane)
Figure imgf000012_0001
Table II: Composition of the Si02 solution
The total volume of this composition is 725.67 ml. 2) TiQ2 solution
Figure imgf000012_0002
Table III: Composition of the Ti02 solution The total volume of this composition is 705.38 ml. The first layer 4 on the enamelled layer is obtained by mixing the Si02 solution with the Ti02 solution in a volumetric ratio of 70/30, whereby a refractive index of 1.7 is obtained.
This mixture is applied to the enamelled substrate 3 by dip coating at a speed of 1.40 cm/sec, such that a layer thickness of 85 nm remains after 5 minutes of drying at 400°C.
Similarly, a layer of the Ti02 composition is applied to this at a dip coating speed of 0.40 cm/sec, and this second layer 5 is also dried for 5 minutes at 400°C, whereby a layer thickness of 59 nm with refractive index 2.1 remains.
In a similar way, a third layer 6 is applied over this, consisting of the Si02/Ti02 mixture described above, in the same way at a dip coating speed of 0.47 cm/sec, but with a thinner layer thickness, which after drying at 400°C for 5 minutes yields a layer thickness of 32 nm and refractive index of 1.7.
In a similar way, a fourth layer 7 is applied over this, consisting of the Ti02 composition, at a dip coating speed of 0.31 cm/sec, which after drying for 5 minutes at 400°C yields a layer thickness of 39 nm and refractive index 2.1.
Finally a fifth layer 8 is applied, consisting of the Si02 solution described above, at a dip coating speed of 0.91 cm/sec, which this time after drying for 10 minutes at 400°C yields a layer thickness of 98 nm and refractive index of 1.4.
The resulting reflection spectrum 9 at normal incidence of the light is shown in figure 2, which shows that the reflection of the visible wavelengths is strongly suppressed as of wavelengths above 450 nm. The light reflected by the surface is expressed as a % of the incident light and is shown as a function of the wavelength Aof the incident light, expressed in nanometres (nm) .
The integrated reflection over the proposed wavelength range is less than 1.2% and is defined as follows: λ2
R integrated = 1 J R(A) . dA
λ2 ~ λι λχ
Figure 3 shows a cross-section of a communication board of enamelled steel 10, with a single anti-reflection layer 11 and figure 4 the reflection spectrum 12 of this surface at normal incidence.
The anti-reflection coating consists of a Si02 solution, applied as a sol-gel via dip coating.
The Si02 solution contains the following ingredients:
Ingr . Product Moles Weight (g) Volume
(No. ) (name) (ml)
1 2-propanol 0.5333 32.05 40.78
2 TEOS 0.1200 25.00 26.60 3 Water 0.2669 4.81 4.81
4 Nitric acid 0.0763 4.81 4.81
5 Triton-X 0.0023 1.44 1.35
6 2-propanol 8.4660 508.81 647.34
Table IV: Composition of the Si02 solution
The total volume of this composition is 725.67 ml. This solution was applied to the enamelled layer 3 by dip coating at a speed of 10 mm/sec and then dried at a temperature of 400 °C for 10 minutes, after which a dry layer thickness of 100 nm was obtained. The resulting reflection spectrum 12 at normal incidence is shown in figure 4, which shows that the reflection of the visible wavelengths is less strongly suppressed than with a five-layered anti-reflection coating. Figure 5 shows a cross-section of a communication board 13 of enamelled steel 2 with a three-layered anti-reflection coating 14, 15, 16.
It was calculated that for the wavelength of 550 nm, an optimum three-layered anti-reflection coating is built up as follows: n opt. thickness d (nm)
(λ/4)
Air 1
Third layer 16 1.4 0.98 101.5
Second layer 15 2.1 0.42 29 First layer 14 1.85 1.2 94
Substrate 3 1.6
Table V: calculated three-layered anti-reflection coating on an enamelled surface with a refractive index of 1.6.
Such a structure was experimentally realised on the basis of the same two solutions, i.e. a Si02 solution and a Ti02 solution with the same compositions, as described for the five-layered anti-reflection coating in figure 1.
The first layer 14 on the enamelled surface consists of a mixture of the Si02 solution with the Ti02 solution in a volumetric ratio of 40/60 and yields a refractive index of 1.85.
The first layer 14 is applied at a dip coating speed of 1.3 cm/sec, resulting in a layer thickness of 94 nm after drying .
The second layer 15 consists of the Ti02 solution, that is applied at a dip coating speed of 42 mm/sec, resulting in a layer thickness of 29 nm after drying.
The third layer 16 consists of the Si02 solution, that is applied at a dip coating speed of 91 mm/sec, resulting in a layer thickness of 101 nm after drying.
The resulting reflection spectrum 17 for an angle of incidence of 0° for this anti-reflection finish consisting of three layers is shown in figure 6. A comparison of the reflection spectra of the single- layered, three-layered and five-layered coatings shows that the embodiment with five layers suppresses the reflected light over the widest wavelength range, which yields an integrated reflection between 380 and 780 nm of less than 1.2%, which demonstrates the suppression over a broad wavelength range.
It goes without saying that the antireflective properties can be further improved by applying additional layers, insofar they are judiciously chosen with regard to layer thickness and refractive index.
The present invention is by no means limited to the embodiment described as an example and shown in the drawings, but a number of anti-reflection coatings with three or more layers for a communication board can be realised without departing from the scope of the invention. For example, the enamelled surface can be affixed to a support along one or two sides, or the support can consist of a honeycomb core made of a thermoplastic polymer, which for example is manufactured in-line during the production process of the communication board, on which enamelled sheet steel is laminated in-line.

Claims

Claims .
1. Communication board (1) with an enamelled surface, characterised in that a multilayer anti-reflection coating is affixed to the visible side of the enamel layer, consisting of at least three glassy or ceramic layers, in which at least one layer has an optical layer thickness outside the range from 50 to 200 nm, and whereby the optical layer thickness of this layer is equal to one quarter of the wavelength of the incident light in nm, divided by the refractive index of the glassy or ceramic layer, and whereby this refractive index is between 1.3 and 1.5.
2. Communication board (1) according to claim 1, characterised in that the communication board is an interactive board with a position-coding pattern that enables the use of an image detector, whereby the position of the pen or felt-tip on the board can be determined, and whereby an image of what is drawn or written on the board can be saved in a computer.
3. Communication board according to claim 1 or 2, characterised in that the multilayer anti-reflection coating (4 to 8) is composed of various colloidal solutions of inorganic metal salts and/or organic metal compounds, such as metal alkoxides, whereby these liquid dispersions are applied to the communication board as a sol and during a drying process converted into a gel state, and after tempering at temperatures above 300 °C form the dry and hardened anti-reflection coating.
4. Communication board (1) according to claim 1, characterised in that the communication board consists of an enamelled surface (3), that is affixed to a support (2) along one or two sides.
5. Communication board (1) according to claim 4, characterised in that the support (2) consists of a layer of steel affixed to a honeycomb core made of a thermoplastic polymer.
6. Communication board (1) according to claim 5, characterised in that the honeycomb core of the support is produced in-line during the production, process of the communication board (1) .
7. Communication board (1) according to claim 1, characterised in that the surface of the multilayer anti- reflection coating (4 to 8) presents an integrated reflection between 380 and 780 nm of less than 1.2 %.
PCT/BE2011/000041 2010-07-12 2011-07-07 Enamelled visual communication board WO2012006690A2 (en)

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BE2010/0424A BE1019415A3 (en) 2010-07-12 2010-07-12 ENAMELED VISUAL COMMUNICATION BOARD.
BE2010/0424 2010-07-12

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Citations (3)

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BE1015482A3 (en) 2003-04-28 2005-04-05 Polyvision Nv Method for manufacturing of visual communication panels and device used thereby.
BE1016588A3 (en) 2005-05-13 2007-02-06 Polyvision Nv METHOD FOR MANUFACTURING A VISUAL COMMUNICATION BOARD.
BE1017572A3 (en) 2007-06-27 2008-12-02 Polyvision Nv INTERACTIVE ENAMELED VISUAL COMMUNICATION PANEL.

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DE356889C (en) * 1921-03-30 1922-08-04 Jacob Kranz Process for the production of an unbreakable writing board
JPH02153080A (en) * 1988-12-05 1990-06-12 Kawatetsu Kinzoku Kogyo Kk Enameled board also acting as marker screen and production thereof
BE1012996A3 (en) * 1998-06-26 2001-07-03 Alliance Europ Nv Enamelled projection screen and method of manufacturing it.

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BE1015482A3 (en) 2003-04-28 2005-04-05 Polyvision Nv Method for manufacturing of visual communication panels and device used thereby.
BE1016588A3 (en) 2005-05-13 2007-02-06 Polyvision Nv METHOD FOR MANUFACTURING A VISUAL COMMUNICATION BOARD.
BE1017572A3 (en) 2007-06-27 2008-12-02 Polyvision Nv INTERACTIVE ENAMELED VISUAL COMMUNICATION PANEL.

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