WO2002037409A1

WO2002037409A1 - Method for manufacturing a porcelain enameled writing board

Info

Publication number: WO2002037409A1
Application number: PCT/BE2001/000188
Authority: WO
Inventors: Leo Gypen
Original assignee: Polyvision, Naamloze Vennootschap
Priority date: 2000-11-03
Filing date: 2001-10-30
Publication date: 2002-05-10
Also published as: BE1013822A3; AU2002223308A1

Abstract

The invention concerns a method for manufacturing a writing board, according to which at least one electrically insulating enamel layer (4), at least one layer (5, 7, 8) containing an emission or reception part of an electronic position detection device (13, 14, 15) and at least one porcelain enamel finishing layer (10) are provided on a substrate (2-2a-3) comprising a plate (3) of enamellable metal. The electrically insulating enamel layer (4), the finishing enamel layer (7, 10) and said at least one layer (5, 7, 8) containing the emission or reception part are made from firable compositions which are subjected to a firing.

Description

Method for manufacturing a porcelain enameled writing board.

The present invention concerns a method for manufacturing a porcelain enameled writing board, whereby at least one porcelain enamel layer is provided on a substrate.

Such writing boards are frequently used because of their special qualities. They are particularly wear-resistant, durable and easy to write on and to wipe off again. In many cases, they can be written on with special felt-tip pens as well as with chalk, and they can also be used as a projection screen.

The problem is, however, that what is written on the board cannot be saved, as opposed to what are called 'touch screens', whereby the position of a writing pen or such on the board can be detected and transmitted to a computer.

Such ^λ touch screens' are based on resistive and capacitive methods .

They have for example a layer of glass or transparent plastic which is covered with a resistive layer on the back upon which are provided discrete point electrodes, as described in American patent No. 4.806.709. On the electrodes is provided an alternating current. The currents flowing through the electrodes when a pressure is exerted on the resistive layer are measured.

American patent No. 5.365.461 describes a 'touch screen' with a sensor, consisting of a glass plate, covered with a continuously or discontinuously conducting layer, whereby the whole is covered with a thin protective layer. A varying tension is provided on the conducting layer, and also on the writing pen is provided a tension, and the current on the angles of the sensor is measured.

According to American patent No. 4.616.106, electric signals, emitted by a writing pen, are received by the conductors of a grid and are transmitted to sensors .

A capacitive contact-sensitive screen is also described in American patent No. 5.457.289. A contact-sensitive sensor is provided on a liquid-crystal display or such and is covered on the front side with a non-conducting layer, and on top of that a conducting layer. A tension is provided on the sensor, and a second tension on the conducting layer, and the capacity variations resulting from the contact are measured.

Japanese patent No. 10-222303 describes a screen with rows and columns of conductors onto which are applied pulses in a sequential manner. The position of a pen on the board is determined by medns of electrostatic capacity coupling.

However, the above-mentioned documents do not describe a real writing board which can be written on with a felt-tip pen or with chalk and which can be wiped off. Moreover, the described screens are very sensitive to damage and little wear-resistant.

US-A-4.711.977 discloses an electronic blackboard apparatus comprising an electronic blackboard unit, a writing instrument, a position-detecting control unit and an output section. The electronic blackboard unit comprises a substrate .or rear plate, a first layer with an assembly of first magneto-restrictive transmission medium elements, a second layer with an assembly of second magneto-restrictive transmission medium elements superposed on the first layer using a spacer, and a non-magnetic top plate or writing surface from enamel-finished aluminium or austenitic stainless steel. Both assemblies contain a plurality of rows of position-detecting members surrounded by exciting coils and co-operating with magnets.

The manufacturing of this known blackboard unit is rather complex and expensive. The surface needs to be nonmagnetic .

The invention aims a method for manufacturing a writing board which is relatively simple and whereby the advantages of the porcelain enameled writing boards and of the writing boards with determination of the position of the writing pen or such are combined.

This aim is reached according to the invention in a method for manufacturing a porcelain enameled writing board, according to which at least one layer containing an emission or reception part of an electronic position detection device and at least one porcelain enamel finishing layer are provided on a substrate, wherein a substrate is used comprising a plate of enamellable metal and at least one electrically insulating enamel layer is provided on this substrate before the at least one layer containing the emission or reception part of an electronic position detection device and the finishing layer are provided, whereby the electrically insulating enamel layer, the finishing enamel layer and said at least one layer containing the emission or reception part are made from firable compositions which are subjected to a firing. Via all sorts of among other known techniques of electronic position detection, such as capacitive coupling with high- frequency currents as described in American patents No. 4.686.332, No. 4.806.709, No. 5.365.461, No. 5.457.289 and Japanese patent No. 10.222.303, coupling with a pen which emits an electromagnetic field, or acoustic detection, the position of the pen with which one writes on the board can be detected in an electronic manner and can for example be stored in a memory and/or represented on a screen.

The layer with the emission or reception part is equipped with contacts which are connected to the electronic position detection device.

As an emission or reception part, at least two series of surfaces are preferably provided with at least one electrically insulating porcelain enamel layer in between.

Said surfaces are preferably provided in the shape of paths, whereby the paths of the surfaces of the first series cross the paths of the surfaces of the second series, preferably in a perpendicular manner.

The layers are preferably fired at a temperature between 450°C and 900°C.

In order to better explain the characteristics of the invention, the following preferred embodiments of a method for manufacturing a porcelain enameled writing board according to the invention are described as an example only without being limitative in any way, with reference to the accompanying drawing, which schematically represents the construction of a writing board manufactured according to the invention. In order to manufacture the porcelain enameled writing board represented in the' sole figure, a strip 1 of thin porcelain enamellable steel having a thickness of for example 200 to 1000 micrometre is provided in a continuous porcelain enameling device, which is for example wound off a roll, as well as a porcelain or glassy enamel first layer 2 having a thickness of^" for example 80 micrometre, and as an option, an electrically insulating porcelain enamel coating 2a of for example also 80 micrometre, after which said strip 1 is cut into the shape of plates 3 having the dimensions of the writing board.

According to variants, a plate of stainless steel, a plate of enamellable galvanised steel or a plate of enamellable aluminised steel can be taken as a basis, instead of a plate 3 of porcelain enameled steel.

On the substrate formed by this plate 3 and possibly the porcelain enamel layers 2 and 2a is provided an electrically insulating porcelain enamel layer 4 by coating the plate 3 by an enamel composition, for example by means of silkscreen printing, which is fired at 450°C to 900°C.

By means of silkscreen printing is then built up a contact- sensitive sensor on this insulating porcelain enamel layer 4.

To this end, a series of parallel electrically conductive surfaces are first provided in the shape of paths 5 having a width of for example 0,2 to 2 mm and at a mutual distance of for example 0,5 to 2 mm.

According to a variant, the conductive surfaces are provided in the shape of paths 5 having a width of 0.1 to 10 mm, and at a mutual distance of 0,1 to 5000 mm. These conductive paths 5 are made for example made by coating the layer 4 with an firable printable composition in the form of a paste of silver, silver/platinum or another silver alloy according to a path forming pattern, which paste is dried and fired at a temperature between 450°C and 900°C, for example at 850°C.

At one far end of each of the paths 5 is formed a rectangular contact surface 6.

Apart from a strip above the contact surfaces 6, the paths 5 are entirely covered, and the layer 4 which is visible in between is partly or entirely covered with a second electrically insulating porcelain enamel layer 7 which is also obtained by coating with an enamel composition and firing between 450°C and 900°C.

Further, the sensor is formed by providing a second series of parallel, electrically conducting surfaces in the shape or pattern of paths 8 by means of silk screen printing of a printable firable composition on said porcelain enamel layer 7, and possibly on parts of the layer 4 which are not covered by this porcelain enamel layer 7 and firing at 450°C to 900°C.

These paths 8 are similar to the above-mentioned paths 5, with for example the same width and mutual distances, but they are directed perpendicular to the latter. At their far end, they form contact surfaces 9.

After said silver paths 8 have been fired at 450 °C to 900°C, they are covered, save the contact surfaces 9, with a white, electrically insulating finishing layer 10, together with the parts of the porcelain enamel layer 7 and possibly of the layer 4 lying in between.

This finishing layer 10 is provided as a printable enamel composition by means of silk screen printing, after which it is also fired at temperatures between 450 and 900°C.

This finishing layer 10 may for example consist of a layer of dielectric and one or several white porcelain enamel layers on top of it, of which at least the latter is suitable to be written on with felt-tip pens and to be subsequently wiped off, and/or it is suitable for projection purposes.

Instead of a white layer, a pastel-colored porcelain enamel layer can be provided as finishing layer which is suitable to be written on with felt-tip pens and to be subsequently wiped off, and/or which is suitable for projection purposes .

According to a variant, a mat green or dark porcelain enamel layer can be provided as finishing layer which is suitable for chalk board applications.

Finally, copper contacts 11 are soldered onto the contact surfaces 6 and 9. These contacts 11 can also be glued with electrically conducting glue or they can be connected in a mechanical manner.

The contacts 11 form the far ends of conductors 12 which are connected to an electronic unit 13.

This electronic unit 13 contains an emitter which successively sends high-frequency pulses in a sequential manner through the paths 5 and 8. To this electronic unit 13 is coupled a detection pen 14 which, when it is brought into contact with the writing board, detects the place where it is situated on the electrodes formed by the paths 5 and 8 via an electrostatic capacitive coupling.

The electronic unit determines the position on the basis of the signal of the pen 14 and represents this position on a screen 15 coupled to it.

Finally, the whole consisting of the plate 3 up to the finishing layer 10 is completed to form an electronic writing board by gluing the plate 3, for example by means of neoprene contact adhesive 17, on a rigid base 16, for example a chipboard of 10 mm thick, whereby the wiring is put under the profiled edges of the writing board.

The conductive surfaces must not^' necessarily have the shape of paths 5 and 8. Also other patterns of paths can be applied, such as concentric ones for one series and radial ones for another series .

Also other position detection devices can be used.

For instance, it is possible to provide a current to the horizontal paths 5 alone, whereas the vertical paths 8 are connected to the ground.

The horizontal position of the pen, which in this case does not detect anything and is not connected to the electronic unit 13, can be determined by measuring the change in capacity between two neighboring paths and thus between an even and uneven path. The vertical position of the pen is determined by providing a current to the even vertical paths 8, whereas the horizontal paths are connected to the ground, and by measuring the change in capacity between neighboring vertical paths 8.

Said two determinations are alternately carried out 50 times per second, so that the path of the pen can be followed very precisely.

Another possibility consists in that the pen, which in this case is not connected to the electronic unit 13 either, is located by means of 'electrostatic capacity coupling' as described in the above-mentioned Japanese patent application No. 10-222.303. The horizontal and vertical paths 5 and 8 hereby alternately function as signal emitters and signal detectors.

Yet another possibility consists in making the paths 5 and 8 of resistive material instead of conductive material, or even in replacing these paths 5 and 8 together with the insulating layer in between by a single uniform layer of resistive material with discrete electrodes on it, as described in American patents No. 4.806.709, No. 5.365.461 or No. 5.457.289.

Instead of using a pen which forms a receiver while the paths 5 and 8 emit signals, it is possible to use a pen which emits an electromagnetic field. The paths 5 and 8 then so to say form antennas and thus receiver parts of the position detection device.

As the pen which moves over the writing board makes a high- frequency sound, yet another suitable position detection device is based on an acoustic detection. in this case, one or several electrically insulating layers 7 are provided between the paths 5 and 8 which are microphonic, i.e. which can transform acoustic energy in electric energy and which may for example be piezo-electric . The paths 5 and 8 then function as microphones.

The invention will be further illustrated by means of the following practical examples.

Example 1 :

A strip 1 of porcelain enamellable steel according to EN 10209 having a thickness of 0,35 mm and a width of 1200 mm is continuously porcelain enameled in a continuous coilcoating process at a firing temperature of 830°C for three minutes .

The first layer 2 is hereby provided by means of roller coating. The composition of the dispersion of the first layer to be applied is as follows (in percentages by weight) :

Pemco ground enamel GS1809 50,00

Pemco ground enamel GR 1224 20,00 Ferro ground enamel 2720 30,00

Sibelco quartz 40,00

Pemco clay H231 4,00

Pemco clay H230 6,00

Boric acid ^' 0, 15 Bentonite 0,20

Sodium nitrite 0,05

Water 69,00

The fineness of grind of this first layer dispersion is 3 on a Bayer screen of 3600 mesh. The thickness of the layer after porcelain enameling amounts to 100 μm on the top side and 25 μm on the bottom side.

Then, the porcelain enameled steel strip is cut into plates 3 of 900 x 1200 mm.

These plates 3 are provided with a first porcelain enamel insulating or dielectric layer 4 of Ferro Electronics FX- 11-045 boro-silicate dielectric melting at low temperature, provided by means of a 34T screen.

After infrared desiccation of the solvents present, the preceding step is repeated and thus a new layer of dielectric is provided, followed by infrared drying and the firing of the whole at 630°C in a horizontal oven for 8 minutes .

Subsequently, Heraeus C 8041-2 silver paste is screen- printed (300 mesh screen) on the thus provided dielectric in paths 5 of 1 mm wide and at a mutual distance of 1 mm, followed by drying and firing at 630°C for 8 minutes.

These plates 3 are subsequently provided again with an electrically insulating layer 7 of Ferro Electronics FX-11- 045 boro-silicate dielectric melting at low temperature, provided by means of a 34T screen.

After infrared desiccation of the solvents present, the preceding step is repeated and thus a new layer of dielectric is provided, followed by infrared drying and the firing of the whole at 630°C in a horizontal oven for 8 minutes . Subsequently, Heraeus C 8041-2 silver paste is screen- printed (300 mesh screen) on the thus provided dielectric in paths 8 of 1 mm wide and at a mutual distance of 1 mm, provided that the conducting silver paths 8 are printed perpendicular to the above-mentioned conducting paths 5, followed by drying and firing at 630°C for 8 minutes.

Then, an insulating layer 10 of FX-11-045 dielectric is printed by means of a 34T screen, dried and fired at 630°C for 8 minutes.

Finally, the whole is provided with a white top layer of porcelain enamel (type Colorobbia W1014/02) , printed with a 34T screen, provided in three successive layers, followed by three infrared drying stages.

The top layer is fired at 630°C for eight minutes, so that a whiteboard surface is obtained which can be easily written on and wiped off again, which is also suitable for projection.

During the printing of the silver paths, contact surfaces 6,9 of 2 x 2 are printed on the far ends of the silver paths, and thus on the edges of the whiteboard. No dielectric, nor any white top layer is printed on them.

On these contact surfaces are soldered tin-plated copper contacts by means of 62Sn/36Pb/2Ag soldering paste.

Finally, the whole is completed to form an electronic writing board by gluing the obtained porcelain enameled plate, for example by means of neoprene contact adhesive, on a chipboard of 10 mm thick, whereby the wiring is put under the profiled edges of the board. The signal detection is carried out by means of capacitive reception as described in the above-mentioned Japanese patent No. 10-222303. The required electronics can be provided in the back side and in the sides of the board.

Example 2 :

The method of example 1 is repeated but the application, the drying and the firing steps for producing the dielectric layer 7 are repeated one or more times in order to reduce the risk for electrical shortcutting between the two series of two silver paths 5 and 8.

Example 3

Proceedings in the same manner as example 1, with this difference that the steel plates are first cut and then porcelain enameled in a conventional manner and fired in a horizontal porcelain enamel oven (lay-down oven in which the plates are transported in a horizontal manner) instead of in a continuous porcelain enameling line.

Example 4 :

The method of example 1 is repeated, but the thickness of the blades is now 0,6 mm, and all the firing stages are carried out in a conventional porcelain enameling hanging oven in which the plates are vertically transported.

Of each plate, the strip with the holes required for the vertical suspension is cut off afterwards, for example with scissors or by means of laser cutting or water jetting. Example 5 :

AISI 430 stainless steel with a thickness of 0,6 mm is cut into plates of 1200 x 3000 mm and is alkaline cleaned.

Then, the stainless steel is printed with ESL dielectric 4914 by means of a 200 mesh screen.

Subsequently, the dielectric is dried by means of infrared heating until the solvents have evaporated.

The two preceding steps are repeated and the dielectric is then fired in a lay-down oven at 850 °C for fifteen minutes.

The steel is again printed with ESL dielectric 4914 by means of a 200 mesh screen, and the dielectric is infrared- dried, after which the dielectric is again fired at 850 °C.

Then, in the longitudinal direction of the plate, are printed conducting layers with Hereaus silver/platinum paste C1602 by means of a 325 mesh screen. The line thickness amounts to 0,5 mm and the mutual distance is 1 mm.

The silver/platinum paste is infrared-dried and fired at 850 °C for 15 minutes.

Then, ESL dielectric 4914 is screen-printed by means of a 200 mesh screen, infrared-dried and fired at 850°C for 15 minutes.

In the above-described manner are again provided conducting layers, dried and fired, but now in the cross direction of the plate. Finally, the whole is provided with a white top layer of porcelain enamel (type Colorobbia W1014/02) which is printed with a 34T screen and which is provided in three successive layers, followed by three infrared drying stages.

The top layer is fired at 630°C for eight minutes, so that a whiteboard surface is obtained which can be easily written on and which can be wiped off again, and which is also suitable for projection.

During the printing of the silver paths, contact surfaces of 2 x 2 mm are printed on the far ends of the silver paths, and thus on the edges of the whiteboard. No dielectric is printed on them, nor any white top layer.

Finally, the whole is completed to form an electronic writing board by gluing the obtained porcelain enameled plate with neoprene contact adhesive on a chipboard of 10 mm thick, whereby the wiring is put under the profiled edges of the board.

The signal detection is carried out by means of capacitive reception as described in the above-mentioned Japanese patent No. 10-222303. The required electronics can be provided in the back side and in the sides of the board.

Example 6 :

The method of example 1 is repeated, with this difference that the dimensions of the plate are 900 x 3000 mm, the conducting paths are situated at a distance of 2 mm in relation to one another, and contact surfaces of 2 x 2 mm are printed at one far end of the conducting paths with Ferro Electronics NC-616A gold paste by means of a 325 mesh screen, which is fired after infrared drying at 630°C for 8 minutes .

The contact surfaces and their edges are taped up with a self-adhesive tape, and the chalkboard suspension with the following composition is provided by means of conventional wet spraying:

(in % by weight)

Pemco enamel 8297 ^" 47,0 Ferro enamel 1084 43,0

Pemco enamel P941P 3,0

Pemco enamel GS 1919 7,0

Ferro clay 2 4,0

Ferro clay 10 4,0 Sodium aluminate 0,2

Color pigment Ferro FK 3797 1,9

Color pigment Ferro FK 8512 0,4

Color pigment Ferro FK 1192 0,7

Color pigment Ferro FA 8515 2,5 Water 60,0

The fineness of grind is 2 on a Bayer screen of 3600 mesh. The layer thickness amounts to 90 μm.

As soon as the dispersion has partially dried, the tapes over the contact surfaces are removed.

After it has dried completely, the whole is fired at 630°C for 8 minutes, so that a mat green chalkboard surface is obtained. This surface is glued on a somewhat smaller chipboard with a PVAC glue.

On the contact surfaces which are covered with gold are provided mechanical connectors .

The entire framing is provided by placing the board in a jig with an opening for the output wiring and by casting two-component polyurethane around it.

The chalk holder is provided with an electronic emitter running on batteries which emits high-frequency electromagnetic waves.

When written on with chalk, the x/y co-ordinates of the emitter position are picked up in the underlying longitudinal and cross paths of conductive material .

The invention is by no means limited to the above-described embodiments represented in the accompanying drawings; on the contrary, such a method for manufacturing a porcelain enameled writing board can be made in all sorts of variants while still remaining within the scope . of the annexed claims.

For instance it is not absolutely necessary that the firable compositions for the insulating layers and the layers of the emission or reception part of the electronic position detection' device are pastes or dispersions. One of more of these compositions may be a dry powder, in which case drying before firing is obviously not required.

Also with respect to the application techniques used, there are many variants possible outside wet spraying and silkscreen printing. For instance, one or more of the layers may be applied by means of electrophoresis, electrostatic dry and wet deposition, rollcoating, flow coating, wet Inkjet printing, dry powder jet printing, transfer printing, tampon printing, plasma spraying, sol- gel application and other application techniques.

Claims

Claims .

1. Method for manufacturing a porcelain enameled writing board, according to which at least one layer (5,7,8) containing an emission or reception part of an electronic position detection device (13,14,15) and at least one porcelain enamel finishing layer (10) are provided on a substrate (2-2a-3) , characterized in that a substrate (2- 2a-3) is used comprising a plate (3) of enamellable metal and at least one electrically insulating enamel layer (4) is provided on this substrate (2-2a-3) before the at least one layer (5,7,8) containing the emission or reception part of an electronic position detection device (13,14,15) and the finishing layer (10) are provided, whereby the electrically insulating enamel layer (4) , the finishing enamel layer (7,10) and said at least one layer (5,7,8) containing the emission or reception part are made from firable compositions which are subjected to a firing.

2. Method according to claim 1, characterized in that the layer with the emission or reception part is equipped with contacts (6,9) which are connected to the electronic position detection device (13,14,15).

3. Method according to claim 1 or 2 , characterized in that as an emission or reception part, at least two series of surfaces (5,8) are provided with at least one electrically insulating porcelain enamel layer (7) in between.

4. Method according to claim 3, characterized in that the surfaces are provided in the shape of paths (5,8), whereby the paths (5) of the surfaces of the first series cross the paths (8) of the surfaces of the second series, preferably in a perpendicular manner.

5. Method according to claims 2 and 4, characterized in that at least one extremity of each path (5,8) is provided with a contact surface (6,9).

6. Method according to claim 4 or 5 , characterized in that the paths (5,8) are situated at a mutual distance of 0,5 to 2 mm and have a width of 0,2 to 2 mm.

7. Method according to claim 4 or 5 , characterized in that the paths (5,8) are situated at a mutual distance of 0,1 to 5000- mm and have a width of 0,1 to 10 mm.

8. Method according to any of claims 3 to 7, characterized in that at least a part of the surfaces (5,8) is made of electrically conducting material.

9. Method according to claim 8, characterized in that the composition of the electrically conductive surfaces (5,8) is dominantly silver.

10. Method according to any of claims 3 to 7, characterized in that at least a part of the surfaces (5,8) is made of electrically resistive material .

11. Method according to any of claims 3 to 7, characterized in that the electrically insulating layer (7) in between the series of surfaces (5,8) is made of a material which transforms acoustic energy in electric energy.

12. Method according to claim 1 or 2 , characterized in that the layer comprising an emission or reception part of the detection device (13,14,15) is a uniform layer made of resistive material with discrete point electrodes.

13. Method according to any of the preceding claims, characterized in that the layers (4,5,7,8,10) are fired at a temperature between 450 and 900°C.

14. Method according to claim 13, characterized in that the layers (4,5,7,8,10) are provided by wet compositions, such as dispersions and pastes, which are dried before firing.

15. Method according to any of the preceding claims, characterized in that the metal plate (3) used as a substrate (2-2a-3) is from one of the following materials: steel porcelain enameled with at least one first layer (2a) made of porcelain-like or glass-like porcelain enamel, stainless steel, enamellable galvanised steel and enamellable aluminised steel .

16. Method according to any of the preceding claims, characterized in that as a finishing layer (10) a white, pastel-colored, green or dark porcelain enamel layer is provided which is suitable to be written on with felt-tip pens or chalk and to be subsequently wiped off, or a white or pastel-colored porcelain enamel layer which is suitable for projection purposes, or a porcelain enamel layer suitable for a combination of whiteboard, chalkboard and projection surface applications.

17. Method according to any of the preceding claims, characterized in that the substrate (2-2a-3) and the layers provided on it is provided, for example glued, on a rigid basis (16) so as to form a sandwich panel.