GB2206315A - Wall panel suitable for use as a blackboard - Google Patents

Abstract

A wall panel suitable for use as a blackboard includes a sheet of glass 1 having one face roughened by chemical corrosion to provide irregular undulations constituted by convex raised portions (2; figure 1) linked tangentially to concave hollows (3), and an opaque material (e.g. paint 4) adjacent to or on the other face of the sheet. Roughening the glass by chemical corrosion results in a blackboard surface with improved anti-reflectant characteristics and satisfactory, erasure characteristics <IMAGE>

Description

2 '172 0 6 37 15 1 - ir c WALL PANEL SUITABLE FOR USE AS A BLACKBOARD AND

METHOD OF MANUFACTURE This invention relates to a wall panel which is suitable for use as a blackboard, on which writing with a dry-erasing pen is possible and to a method of manufacture thereof.

The panel has a permanent surface whose service life is practically indefinite, and which enables perfectly sharp and defined writing to be made thereon.

Blackboards on which it is possible to write with a felt pen, or a similar writing instrument, which allows for dry-erasing are normally made from a wooden board whose surface is covered with a rolled-on non- porous coating of a plastics material in order to avoid the pen sinking into the superficial roughness of the surface and forming accumulations of ink which would irreparably stain the surface of the blackboard.

For this reason the so-called melamine plastics panels, which are laid directly on to the wood, are not suitable, while those boards which incorporate a sheet of plastics material whose surface has been polished through the action of rollers to make it perfectly flat are suitable.

There is, however, a problem arising from the fact that this treatment results in the flat surface of these blackboards being shiny, and the fact that light thus reflects from their surface in an uncomfortable manner, creating problems in classrooms for those pupils who, in one way or another, are subjected to glare from the windows or from artificial sources of light.

- It is impossible to solve this light reflection problem completely, since shading the surface - the only valid 2 solution - would mean a return to porosity and, as such, to dry ink accumulating in the crevices, thereby marking the blackboard.

Apart from the previously mentioned light reflection problems, this type of blackboard has the additional problems, resulting from the plastics nature of the front sheet which forms the working surface of the blackboard, of progressive wear and scratching causing it to become useless after a certain period of time.

It may be thought that it would be easy to obtain a durable blackboard simply by using a piece of glass that is sufficiently thick and strong to prevent it being shattered, and to apply an opaque coat, for example of white material to its inner surface, so that any felt pen writing on it would be clearly seen. Unfortunately, this is not a feasible solution either, due to the fact that glass treated in this way turns into a light reflecting source which it is impossible to control.

In endeavouring to solve these problems, the applicant, who is also the inventor of an arrangement described in Spanish Utility Model Application No. 291,568 which refers to and claims awallblackboard formed by a sheet of glass, which has been abraded on one surface and secured to the painted surface of another thicker sheet of glass by means of a layer of butyral adhesive. This solution of shading the outer surface of the glass by machine abrasion although it is acceptable in principle, has been found in practice not to be efficient. In the first place, machine abrading results in a comparatively irregular finish and, no matter how much the operation of abrasion is controlled, some grooves do appear, and some material is removed with the result that microscopic holes are formed which, sooner or later, accumulate dry ink which mark the surface. This W 1 - 3 solution has the points in its favour, however, when compared with the plastics laminate covered blackboards, that its surface is not so subject to wear and it may be washed with a solvent. Its cost however is comparatively high, since machine abrasion is a slow and expensive process, which requires very strict operational control, subsequent inspection and rectification of faults and careful final washing. The risk of shattering, moreover, is comparatively high and stress may be caused in the glass which reduces its mechanical strength.

An embodiment of a wall panel to be used as a blackboard and to be described below provides a solution which considerably reduces costs, as a result of a much faster shading procedure which minimises light reflections and provides a surface which is comparatively free from grooves which would otherwise collect dry ink and make the erasure of writing more difficult.

More particularly, the solution to be described achieves a shading effect by means of chemical corrosion based on an acid solution which attacks the glass, while coating it in a homogeneous manner.

In a particular embodiment, the procedure begins using a 3 mm thick plate of the commonly called "double glass", whose tolerance is always 3% positive; that is, its thickness varies between 3 and 3.09 mm.

Chemical corrosion is comparatively homogeneous and may result in a layer of material of approximately 0.05 mm, the equivalent of 1/60 of the glass thickness being removed, depending on the tolerance used by the glass manufacturer.

The roughness thus obtained enables a functional surface for the blackboard to be provided with much improved - 4 anti-reflectant characteristics and with satisfactory erasure characteristics. In a preferred embodiment, nonhomogeneous roughening has been obtained, formed by curved and convex raised portions which define a series of concave hollows with tangential linking radii, so that no ridges or cavities are formed which would not permit access to a soft erasing element, for example, a textile or cellulose cloth.

To provide the glass sheet with mechanical strength, it is bonded to another sheet of the same or greater thickness, by means of a butyral sheet. A coat of opaque paint, generally white paint,is applied between the butyral sheet and the glass, to form a background against which felt pen writing may be clearly seen.

In the previously proposed embodiments paint was applied by silk screening methods when securing the sheets of glass to one another, the resulting strength depending on the resistance of the paint on one hand and on the glassto-glass bonding on the other. Silk screening was also applied in the previously proposed embodiments to the nonabraded surface of the double glass or double thickness structure, while a perimetral border was left uncovered in order to obtain a perimetral keying. Practice has shown that this perimetral border was not sufficient and that silk screened paint does not have sufficient resistance or keying qualities. Another problem that occurred was that of the temperature reached during the bonding process between the two layers of glass. This bonding process was carried out using heat by placing the assembly inside an autoclave, after the assembly of all its elements, and subjecting it to a temperature ranging between 120 and 16CC, with a pressure of between 10 and 14 atmospheres.

While the pressure does not represent a problem for tt.

the paint, the temperature does, sometimes causing denaturalization in some areas, which tends to affect the colour and/or strength of the paint.

Experiments have shown that a layer of two-component paint applied by a gun is resistant to temperature as well as to pressure, and provides a resistance which is sufficient to guarantee an optimum bonding between the two layers of glass.

In a preferred embodiment of the present invention, the sheet of glass, one of whose surfaces is subjected to a corrosion process, has the paint applied to it on the other surface; thus only one single sheet of high quality glass is required. The other sheet remains hidden and, since it does not form a support for the paint, its surface may be irregular and bear pores, ridges, etc, which would otherwise be visible when "reproduced" by the paint. Obviously, this construction provides a. substantial saving in cost.

On the other hand, the covering power and the mechanical strength of this paint make it possible to write longitudinal and/or vertical lines, in a slightly contrasting tone with respect to the paint, which may later cover the totality of the surface, forming lines, grid squares, columns, music keys, etc. which may be seen through the surface on which the felt pen is to write, and which help considerably in the graphic representation of texts, figures, drawings, musical scales, etc., thus making work easier for teachers and pupils alike.

The inner or facing edges of both the glass sheets are preferably bevelled, to facilitate a peripheric silicone sealing and to provide the assembly with a good finish, free from cutting edges.

As in the previously proposed embodiments, the above described structure may be complemented by a sintered panel, provided with means for attachment to a wall, with which the double sheet is incorporated, and a frame may optionally be added to finish the assembly.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:- Figure 1 shows an enlarged detail of a section through an outer glass panel which forms part of a wall panel to be used as a blackboard manufactured and illustrating the effect of corrosion on the plate, Figure 2 shows a plan view of the corrosion-affected surface shown in Figure 1, Figure 3 shows an enlarged detail, similar to that of Figure 1, of a section through another sheet of glass, and Figure 4 shows a cut-away perspective view of a part of a wall panel assembly.

Referring to the drawings, in which similar parts bear the same reference numerals, the construction of a wall panel is illustrated, firstly by reference to Figs. 1 and 2 in which there is shown a sheet of glass (1) on whose outer or operative surface irregular undulations are established, constituted by curved and convex raised portions (2) linked to curved and concave hollows (3), and totally free from sharp edges. That is, the curved and convex raised portions (2) and the curved and concave hollows (3) are joined together by tangential connections.

4 These surface irregularities in plate (1) are obtained through chemical corrosion in such a way that, in accordance with representation in Figure 3, and for a glass sheet (1) having a depth A, and a depth of chemical corrosion B and the average distance between the highest point or the raised curves(20) and the lowest point of the hollows (3) is C, the following conditions exist:- B = A _ 0 C = B _f _O C = A 600 In accordance with a particular practical example of the preferred embodiment, the value of A is 3 mm, from which the two remaining dimensions may easily be calculated.

Furthermore, and with particular reference to Fig. 4, there is shown a sheet of glass (1), which has been specifically treated on its outer or operative surface, in the way described above and to which a coat of paint (4) which, as previously stated, has two components has been applied by means of a spray gun to the inner surface of the sheet (1). Previous to this spray-gun painting operation, a series of lines (5) has been added to the inner surface of the sheet (1) in such a way that the lines(5) are later visible from the outer surface when the sheet is used as a blackboard. These lines(5)are, of course, optional. A reinforcing sheet of glass (6) is then secured to the outer surface of the blackboard by means of a butyral layer (7) and, optionally, a panel (8) is also secured to the assembly, the panel (8) being provided with wall attachment means which may be a sintered panel. A frame (9) may also be added, optionally, to this assembly.

In accordance with another feature the glass sheets (1) and (6) have their facing edges bevelled (10), the bevels being provided in a perimetral manner and defining - 8 a perimetral slot by means of which the assembly formed by the two glass sheets containing a layer of paint (4), and a layer of butyral is hermetically sealed with a silicone bead (11).

The above description has been given by way of example, and it will be understood that variations and modifications may be made within the scope of the appended claims given a purposive construction. For example, the coat of paint (4) may be applied to the face of the reinforcing sheet of glass (6) which is adjacent to the sheet (1). It is alter natively possible to employ a reinforcing sheet of some other material than glass. In preferred embodiments the average distance between the highest point of the raised portions (2) and the lowest point of the hollows (3) is between three and five thousandths of a mm.

Claims (10)

1. A wall panel suitable for use as a blackboard, including a sheet of glass having one face roughened by chemical corrosion to provide irregular undulations constituted by convex raised portions linked tangentially to concave hollows, and an opaque material adjacent to or on the other face of the sheet.

2. A wall panel as claimed in claim 1 including a second sheet of glass bonded by a layer of butyral to the other face of the first mentioned sheet of glass.

3. A wall panel as claimed in either claim 1 or claim 2 including a sintered panel for attaching the assembly to a wall.

4. A wall panel as claimed in claim 3 including a frame surrounding the perimeter of the assembly.

5. A wall panel as claimed in any one of the preceding claims in which the average distance between the height of the raised portions and the lowest point of the hollows of the undulating surface of the roughened face of the first mentioned sheet is between three and five thousandths of a mm.

6. A wall panel as claimed in any one of the preceding claims in which the opaque material is a two-component paint which is applied with a gun on to the other surface of the glass, the paint being resistant to heat and pressure.

7. A wall panel as claimed in claim 6 in which a series of grid lines is applied to the other surface of the glass before the paint is applied, the grid lines being visible - through the glass from the roughened face and forming key lines on the panel when used as a blackboard.

8. A wall panel as claimed in any one of claim 2 or claims 2 - 7 when dependent upon claim 2 in which the adjacent edges of each of the two glass sheets are bevelled, defining a perimetral groove or channel between the sheets in which there is a sealing bead, preferably of silicone.

9. A wall panel as claimed in claim 1 substantially as described herein with reference to the accompanying drawings.

10. A method of manufacturinga wall panel for use as a blackboard which includes the steps of roughening one face of a sheet of glass by means of chemical corrosion to provide irregular undulations constituted by convex raised portions linked tangentially to concave hollows thereon and providing an opaque material adjacent to or on the other face of the sheet.

51 Published 1988 at The Patent Office, State House. 66.71 High Holborn. London WC1R 4TP. Further copies may be obtained from The Patent O:Mce, Sales Branch, St Mary Cray, Orpington, Kent. BR5 3RD. Printed by m. wtlplex techniques ltd, St Mary Cray. Kent. Con. 1187.