GLASS OR GLASS-CERAMIC PLATE AND METHOD OF MAKING AND USE

Abstract

A glass or glass-ceramic plate is provided that has two side faces, a thickness of between 2 mm and 6 mm, a circumferential edge face, a flatness less than or equal to 0.1%, and a region of a first face having a mean surface roughness of less than 0.5 m and a standard deviation of the surface roughness of less than 0.1 m. The mean surface roughness and the standard deviation are determined by measuring a roughness at nine points on the first face by measuring a line profile with a stylus device and with evaluation according to ISO 4827. The nine points are at least 5 cm apart from one another. The plate further includes a coating on two subregions of the region that are at least 3 cm apart from one another, where the coating has a raggedness in the subregions that differ by not more than 10%.

Claims

1. A glass or glass-ceramic plate, comprising: two mutually opposite side faces; a thickness between the side faces of between 2 mm and 6 mm; a circumferential edge face; a flatness less than or equal to 0.1% of a lateral dimension between the side faces, a region of a first face of the side faces having a mean surface roughness of less than 0.5 m and a standard deviation of the surface roughness of less than 0.1 m, wherein the mean surface roughness and the standard deviation of the surface roughness are determined by measuring a roughness at nine points on the first face by measuring a line profile with a stylus device and with evaluation according to ISO 4827, and wherein the nine points are at least 5 cm apart from one another; and a coating on two subregions of the region, wherein the two subregions are at least 3 cm apart from one another, and wherein the coating has a raggedness in the two subregions that differ by not more than 10%.

2. The plate of claim 1, wherein the raggedness is determined according to ISO 24790.

3. The plate of claim 1, wherein the side faces are parallel to one another.

4. The plate of claim 1, wherein the glass or glass-ceramic plate is a lithium aluminium silicate glass or a lithium aluminium silicate glass-ceramic.

5. The plate of claim 1, wherein the nine points are at least 15 cm apart from one another.

6. The plate of claim 1, wherein the two subregions are at least 15 cm apart from one another.

7. The plate of claim 1, wherein the coating is an inkjet print coating.

8. The plate of claim 1, wherein the coating comprises a glass flux and/or is an enamel.

9. The plate of claim 8, wherein the coating further comprises a pigment.

10. The plate of claim 9, wherein the pigment comprises no pigment particles having a primary grain size, determined as d.sub.50 of equivalent diameter, of more than 1.0 m and/or comprises no pigment particles having a primary grain size, determined as d.sub.90 of equivalent diameter, of more than 2.5 m.

11. The plate of claim 1, wherein the side faces each lack a nubbed structure or wherein the first face lacks a nubbed structure and a second face of the side faces has a nubbed structure.

12. The plate of claim 1, wherein the glass or glass-ceramic plate comprises a volume-coloured glass-ceramic and/or comprises no vitreously embodied surface zone on the first face.

13. The plate of claim 1, wherein the glass or glass-ceramic plate is configured for use as a cooking surface.

14. A process for producing a coated plate, comprising: providing a plate comprising a glass or a glass-ceramic having two mutually opposite side faces, a thickness between the side faces of between 2 mm and 6 mm, and a circumferential edge face; grinding a first face of the side faces; polishing the first face; applying a coating on two subregions of the first face, wherein the two subregions are at least 3 cm apart from one another; and baking the coating so that the coated plate has a flatness less than or equal to 0.1% of a lateral dimension between the side faces, a region of a first face of the two side faces having a mean surface roughness of less than 0.5 m and a standard deviation of the surface roughness of less than 0.1 m, wherein the mean surface roughness and the standard deviation of the surface roughness are determined by measuring a roughness at nine points on the first face by measuring a line profile with a stylus device and with evaluation according to ISO 4827, and wherein the nine points are at least 5 cm apart from one another, and the coating having a raggedness in the two subregions that differ by not more than 10%.

15. The process of claim 14, wherein the step of applying the coating comprises a contactless printing of the coating.

16. The process of claim 14, wherein the coating comprises a glass flux and/or an enamel.

17. The process of claim 16, wherein the coating comprises a pigment.

18. The process of claim 16, wherein the pigment comprises no pigment particles having a primary grain size, determined as d50 of equivalent diameter, of more than 1.0 m and/or comprises no pigment particles having a primary grain size, determined as d.sub.90 of equivalent diameter, of more than 2.5 m.

19. The process of claim 14, wherein the plate is a green glass and the step of baking the coating further comprises ceramicizing the green glass into a glass-ceramic.

20. The process of claim 14, wherein the plate is a green glass, the process further comprising ceramicizing the green glass into a glass-ceramic, and wherein the step of baking the coating comprises in a secondary firing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0108] The invention is elucidated further below with figures, in which

[0109] FIGS. 1a-1c show schematic representations for explaining raggedness,

[0110] FIG. 2 shows a plan view of a schematic plate, not to scale, according to one embodiment, and

[0111] FIGS. 3 and 4 show respective side views of schematic plates, not to scale, according to embodiments.

DETAILED DESCRIPTION

[0112] FIGS. 1a-1c are schematic representations explaining the principle of raggedness and its determination.

[0113] Represented in FIG. 1a and FIG. 1b are two printed images, of which that represented in FIG. 1a has only low raggedness and that in FIG. 1b high raggedness. Raggedness, or brokenness, may be conceived as a measure of the quality of a printed image, more particularly of its edge definition. In this relationship, high raggedness denotes low edge definition, and vice versa.

[0114] FIG. 1a and FIG. 1b show enlargements of two line prints. In FIG. 1b, the representation with high raggedness, the individual drops are in some cases still readily apparent, since they were able to run out only insufficiently to give a homogeneous printed image. The edge definition developed is low, with holes visible in the printed image in some cases.

[0115] This is contrasted by the representation in FIG. 1a, in which the edge definition is obviously bettercorresponding in turn to low raggedness.

[0116] FIG. 1c shows, schematically, the enlarged printed image of a line. Selected first is the region which is significant in terms of the line width 1, and a straight line is fitted to each of the edges of the line. These two straight lines, which show the borders of the ideal line, are represented schematically in the representation in FIG. 1c as white lines on the black printed image.

[0117] On the basis of these two lines, the standard deviation of the real borders of the printed image on both sides from the ideal line is then determined, as is represented schematically at the site 2 in FIG. 1c .

[0118] The raggedness is the arithmetic mean of the standard deviations on one side, here the left-hand side, and the other side, here the right-hand side.

[0119] The plate according to one embodiment is preferably configured such that the raggednesses in the two subregions differ from one another only by at most 10%. The ratio of the raggedness in one subregion, R1, to the raggedness in the second subregion, R2, i.e., the value R1/R2, is preferably between 0.5 to 2, more preferably between 0.75 to 1.5, very preferably between 0.9 to 1.1.

[0120] FIG. 2 is a schematic representation, not to scale, of a plate 3 according to one embodiment. The plate 3 comprises a glass or a glass-ceramic. The glass may in particular be a lithium aluminium silicate glass, the glass-ceramic a lithium aluminium silicate glass-ceramic. The plate 3 preferably has a thickness of between 2 mm and 6 mm. The plate has two mutually opposing, preferably parallel, side faces, with presently only the side face 31 being visible, and also the circumferential edge face 33. The flatness of the plate 3 is less than or equal to 0.1% of a lateral dimension 5, which in this case, illustratively, is the diagonal of the rectangularly configured plate 3. The lateral dimension 5 under consideration may preferably be the maximum lateral dimension of the plate 3for example, the diameter of a circular plate 3.

[0121] On at least one side of the plate 3, in this case the side 31, the plate has a mean surface roughness R.sub.z,mean in at least one region, presently the region 311, of less than 0.5 m, with a standard deviation of the surface roughness, .sub.Rz of less than 0.1 m. R.sub.z,mean and the standard deviation of the surface roughness, .sub.Rz, are preferably determined by measuring the roughness R.sub.z at nine points on the plate 3, which are each at least 5 cm, preferably at least 10 cm and more preferably at least 15 cm apart from one another, and, from these nine measurement values, determining the arithmetic mean and the standard deviation; with particular preference, R.sub.z is determined by measurement of a line profile using a stylus device and with evaluation according to ISO 4287.

[0122] The roughness Rz is also referred to as roughness depth, and indicates the maximum height difference along a centre line over a specified measurement distance.

[0123] The plate 3 further comprises a coating 5, which is disposed on at least two different subregions 3101, 3102 of the region 311 of the at least one side 31 of the plate 3. Here, illustratively, the coating 41 is embodied as a cooking zone marking, specifically in the form of four rings applied to the side 31. The region 311 here comprisesillustrativelyone of these cooking zone markings.

[0124] In principle it is possible for the region 311 to encompass the entire area of the side 31. In particular it is also possible, furthermore, for the subregions 3101 and 3102 of the region 311 to relate to different cooking zone markings.

[0125] The raggednesses of the coating 5 in the two subregions 3101 and 3102 differ from one another by not more than 10%, the raggedness being determined preferably according to ISO 24790.

[0126] According to one embodiment, the coating 5 may preferably be an inkjet printed coating.

[0127] FIG. 3 shows a schematic side view of, not to scale, and a section through, a plate 3 according to one embodiment. The plate 3, comprising a glass or a glass-ceramic, more particularly a lithium aluminium silicate glass or a lithium aluminium silicate glass-ceramic, has a thickness d which is preferably between 2 mm and 6 mm. The thickness of the plate 3 is understood generally to be the distance between the two side faces 31 and 32 of the plate 3. The two side faces 31 and 32 of the plate 3 are opposite one another and are preferably disposed parallel to one another within the bounds of measurement accuracy, as in the representation in FIG. 3.

[0128] An arrangement is understood to be parallel when the normal angles to the side faces 31 and 32 form an angle with one another of not more than 5, preferably of not more than 2 and very preferablywithin the bounds of customary manufacturing and measurement tolerancesof 0.

[0129] If one side 31, 32 of the plate 3 has a nubbed embodiment, the normal angle is determined on the basis of the surface produced by the nub tips. This is shown schematically later on below with FIG. 4.

[0130] Further represented in FIG. 3 is the circumferential edge face 33 of the plate 3.

[0131] At least the side 31 on which, in particular, the coating 5 is also disposed has in at least one region 311, as set out, only a low mean roughness R.sub.z,mean of less than 0.5 m with a standard deviation of the surface roughness, .sub.Rz, of less than 0.1 m.

[0132] Furthermore, the plate 3 comprises a coating 5 which is disposed on at least two different subregions 3101, 3102 of at the at least one region 311. The at least two subregions 3101, 3102 are at least 3 cm, preferably at least 9 cm and more preferably at least 15 cm apart from one another, with the raggednesses of the coating 5 in the two subregions 3101, 3102 differing from one another by not more than 10%, the raggedness being determined preferably according to ISO 24790.

[0133] Provision may be made for the side 32 as well to be embodied as a very smooth and/or very planar face. However, it is likewise possible, and may indeed be preferable, for only one side to have the particularly good roughness and flatness, in this case the side 31, which faces the user or operative in the operation of an appliance, such as a hob, for example. Provision may be made in particular for the region 311 of the side 31 of the plate 3 to encompass the entire area of the side 31that is in other words, for the entire side 31 to be embodied as a very smooth, flat face. In this way, indeed, it is possible to achieve uniformly good printed images on the entire side 31, including in particular in a contactless printing process such as inkjet printing, for example.

[0134] In the case where the side 32 of the plate 3, which is opposite the side 31 configured as the top side, is not likewise so smooth and flat in its embodiment as the side 31, provision may be made for the side 32 to have, for example, a nubbed embodiment. This may be combined advantageously, for example, with the plate 3 comprising a glass-ceramic which is coloured, since in this case the nubs are not disruptively visible through the intrinsic colouration of the glass-ceramic comprised by the plate 3. Such a configuration may be advantageous in particular in the case where particularly good strength of the plate 3 is desired.

[0135] FIG. 4, in a schematic representation not to scale, shows a side view of a plate 3 according to one embodiment. The plate 3 has a side 31 which exhibits very good flatness and has a very low mean roughness depth, thus being very smooth in its embodiment. The side 31 is embodied as the top side, thus being intended to face the user in the operational use of an appliance for which the plate 3 is used as covering plate (for example, for a hob). On the side 31 of the plate 3, the coating 4, which may have been applied in particular by a contactless printing process, such as inkjet printing, for example, is disposed in the two subregions 3101, 3102 of the region 311, which has at least the good flatness and smoothness. Generally, for example, without restriction to the plate 3 example represented specifically here, the coating 4 may be embodied as a cooking zone marking, or else as a logo. In particular, the coating 4 may be embodied as a glass flux-based coating or may comprise a glass flux or may be embodied as an enamel, and it is additionally possible, and may even be preferable, for the coating 4 to be embodied as a glass flux-based coating (or to comprise a glass flux) or to be embodied as an enamel and additionally to comprise at least one pigment, more particularly a ceramic pigment. The at least one pigment preferably comprises no pigment particles having a primary grain size, determined as d.sub.50 of the equivalent diameter, of more than 1.0 m, very preferably no pigment particles having a primary grain size, determined as d.sub.90 of the equivalent diameter, of more than 2.5 m.

[0136] The plate 3 here, in the schematic depiction of FIG. 4, not to scale, is embodied such that the side 32 of the plate 3, which is opposite the side 31, has a nubbed embodiment. The two opposite sides 31, 32 are embodied here in such a way that they are parallel to one another. In order to determine this, as represented schematically in FIG. 4, the normal angle to the two sides 31, 32 is determined, i.e., the angles n.sub.31 and n.sub.32. For the case of a nubbed side 32, a surface 32a, represented in the schematic sectional representation of FIG. 4 as a dashed line, is ascertained for this purpose, this surface being produced by the tips of the nubs. The normal angle to this surface is then taken as the normal angle n.sub.32 of the side 32.

[0137] As is apparent from the schematic representation in FIG. 4, the normals to the two sides 31, 32 are parallel to one another within the bounds of measurement accuracy, and so the sides 31, 32 are embodied parallel to one another within the bounds of measurement accuracy as well.

LIST OF REFERENCE SIGNS

[0138] 1 line width [0139] 2 variance from edge of printed image [0140] 3 plate [0141] 31, 32 side faces of plate [0142] 32a ascertained area of a nubbed plate or side 32 [0143] 33 circumferential edge face [0144] 311 region of side 31 [0145] 3101, 3102 subregion of 311 [0146] 4 coating [0147] 5 lateral dimension of 3 [0148] n.sub.31, n.sub.32 normal angles to 31, 32