Transparent glass pane provided with a surface structure

The Invention relates to a pane, a method of manufacturing a transparent pane and a device for manufacturing a transparent pane and in particular a glass pane which is provided with a surface structure for capturing light.

The invention also relates to panes which have such surface structures, a device or a tool which is suitable to the implementation of the method as well as preferred uses of the panes.

From EPO493202B1 are known transparent panes provided with regular surface structures in which a structure impressed in the substrate is formed of pyramid-shaped recesses that are identical to each other and which are separated from each other by distances smaller than the biggest dimension of the recesses. The pyramids or truncated pyramids which are provided in them as a motif can be produced with a hexagonal or square base area but all have approximately plane side surfaces.

Combinations of embossing and of pyramids which protrude from their bottom have also been described. In particular, good light diffusion properties and a reduced visual detection of the presence of individual motifs which form the structure is obtained in this way due to a harmonious overall matt surface appearance.

Moreover, there is known, from WO03/046617A1, the manufacture and use of transparent plates (panes) provided with surface structures in the form of geometric relief which should improve the transmission of light and the light efficiency in particular for panes which are combined with solar cells (that is to say photoelectric cells or photovoltaic cells) and photovoltaic solar modules in solar collectors, flat plasma discharge lamps, image projection screens and projectors. The motifs of the geometric structure can in particular be concave with respect to the overall surface of the structured side of the pane, that is to say hot rolled into the initial substrate or formed in another appropriate way. In general, the motifs have a periodic shape, unlike that which is obtained by sandblasting or by etching methods. For technical production reasons (traversing speed, adhesion of rolled material on the rolls, etc.) it is not however possible to reproduce this periodicity with the desired accuracy. Moreover, undesirable periodic disturbances of the embossing operation can be added to it, for example due to dimensional deviations of the centering of the axes of the rolls when the rolling manufacturing method is used.

Because of this, on these structured surface panes, an optical phenomena is established by which the incident light is reflected differently by panes provided with the same surface motif and disposed or installed close to each other in the same plane or even within one and the same pane. In practice, depending on the assembly position, one part of the surface can reflect brilliantly and brightly whilst an immediately adjacent parallel part of surface has a matt appearance. Even through this effect is purely visual and aesthetic, it does not at all degrade the traversing of the light to the elements, detectors, etc., situated on the other side of the pane.

The cause of the variation of the impression of brightness according to the position on the pane is as follows.

Structures which are entirely regular in the ideal case have a characteristic reflection motif in which, for a given angle of incidence of light, the reflection takes place in specified directions and no reflection takes place in angular ranges which are adjacent to them. If, in a zone of the glass, because of the production tolerances mentioned above, the structures are formed on the surface of the glass in a (slightly) different manner, the characteristic direction of reflection of that zone of the glass is oriented in another direction (another angle). The consequence is that situations appear in which an observer is in the direction of reflection for one part of the glass but not in the direction of reflection of the other part of the glass. Thus, one zone of the glass has a bright appearance (reflecting) and the other as a dark appearance. In principle, this effect also takes place on glass with a smooth surface, but which is for example curved, which also has a bright reflection appearance only at certain places for given positions of the sun and of the observer.

However, it is possible to look for possibilities of giving these glasses a regular appearance of the light reflection in a particular mounting case.

The external appearance of these surfaces should not however be essentially different from the regular structures available at present, and in particular the panes should be able to be used beside one another.

U.S. Pat. No. 4,411,493 discloses a pane for building windows which must contribute to energy saving both in summer (air-conditioning) and in winter (heating). By a linear motif of parallel lines, there is obtained with this configuration a reflection or absorption behavior which strongly depends on the angle of incidence of the light.

Many cases are known of the use of surfaces that are chemically etched or treated by sandblasting in order to give them more or less irregular structures.

Fundamentally, there is known (see DE3805067A1 and DE4102984A1) the technique which consists in impressing random superficial structures on rolled surfaces using rolls on which random surface structures have been created. In all cases on continuously rolled substrates which are longer than one roll revolution, these structures are repeated periodically as a result of the regular rotation of the roll.

The invention as claimed solves the above-mentioned problems.

The invention proposes glazing solving the abovementioned problems as well as a method making it possible to impress, by embossing or rolling a surface of a transparent pane, a structure whose average light reflection intensity depends as little as possible on the angle of observation. A device will also have to be created which is particularly well suited for implementing the method.

Dispensing with the usual present-day method of embossing or rolling in which a very regular overall structure of identical motifs is obtained, according to the invention, the surface of the substrate to be treated is embossed by a plurality of motifs identical or at least similar to a common basic motif but with depths and/or base areas which vary.

Thus, on the variation due to the production of intrinsically identical structures on the embossed or rolled surface and which, in practice, can be avoided only with non-negligible working, there is superimposed a predictable variation of the individual motifs or of structural elements. In this way, a variation is obtained over wide angular ranges in the directions of diffusion of light during reflection. On the one hand, this has the effect of reducing the average absolute intensity of the reflection in each individual angle of reflection and, on the other hand, in this way marked (or pronounced) transitions between the reflecting directions and the non-reflecting directions are avoided.

Globally, according to one embodiment, a more or less straight orientation of the individual embossed or rolled motifs is dispensed with in favor of less regular orientations, for example in the form of arcs of circle or of undulation, but, unlike irregular random structures (obtained for example by sandblasting or etching), a basic motif which varies to a greater or lesser degree is retained.

Thus, the pane (in particular made of glass) according to the invention has on at least one of its main surfaces a surface structure which is constituted by the assembly of individual motifs in relief, in particular pyramids, cones or truncated cones, able to be created by embossing or rolling, the surface of the pane comprising a structure constituted by individual motifs based on one or more basic motifs, said individual motifs varying on the surface of the pane in their depth or their height or the perimeter of their base area or in the position of their peak with respect to their base (the term “or” used between the different types of variations allows combinations of variations and is synonymous with and/or). The motifs are therefore at least partially different from each other. Thus, the motifs on the surface of the pane are similar in their shapes (for example, they are all four-sided pyramids) but the orientation of their surfaces is not the same from one motif to another. It is possible to consider that the variation in the orientation of a surface of a motif amounts to rotating this surface about an axis perpendicular to the overall plane of the pane or about an axis parallel with the overall plane of the pane, or a combination of these two rotations.

If a motif surface is rotated about an axis perpendicular to the pane when moving from one motif to another, the result is that the base lines of these motifs when aligned form zigzag lines. If a motif surface is rotated about an axis parallel with the plate which moving from one motif to another, the result is to vary the height or the depth of the motifs. The shape of the individual motifs varies in surface with respect to the basic motif, but some basic motifs can of course be on the surface.

The retention, as accurately as possible, of a basic motif is particularly advantageous when, by a regular fashioning, an optimal light trapping (or capture) structure is approached as closely as possible. In this case “light trapping” means a surface structure which optimizes the penetration of light into the substrate or into an absorber installed beneath the substrate, for example a solar cell.

Fundamentally, the light trapping effect of a structured surface becomes better as the elements of the structure become more tightly compacted. Basic motifs which can be produced on the surface of a substrate as closely to each other as possible or directly joined to each other, and therefore for example pyramids or truncated pyramids which have a base area which is at least triangular (at least three sides) but preferably of the quadrilateral or hexagonal type and in particular a base area in which all of the sides are equal is preferred. As a variant, and depending on the requirements and the design objectives, it is possible however to use other basic motifs, for example cones or truncated cones, and to modify them in the way proposed by the invention. In this case, it will obviously not be possible to avoid small intermediate spaces.

Preferably, the individual motifs are directly adjacent to each other.