TEXTURED GLASS FOR GREENHOUSES

Abstract

A transparent sheet includes a texture in relief on a first of its main faces, such that, if n is the refractive index of the material including the texture, P.sub.m is the mean slope in degrees of the textured face and Y(q) is the percentage of the textured surface with a slope greater than q/(n1) in degrees, then the two cumulative conditions exist: Y(q)>3%+f(q)%.P.sub.m.(n1) and Y(q)>10%, with f(q)=24(3.q) and q=2 or 3.

Claims

1. A transparent sheet comprising a texture in relief on a first main face of its main faces to form a textured face, such that, if n is the refractive index of a material comprising the texture, P.sub.m is the mean slope in degrees of the textured face and Y(q) is the percentage of the textured surface with a slope greater than q/(n1) in degrees, then the two cumulative conditions exist:
Y(q)>3%+f(q)%.P.sub.m.(n1)
and Y(q)>10%
with f(q)=24(3.q)
and q=2 or 3.

2. The sheet as claimed in claim 1, wherein Y(q)>5%+f(q)%.P.sub.m.(n1).

3. The sheet as claimed in claim 2, wherein Y(q)>10%+f(q)%.P.sub.m.(n1).

4. The sheet as claimed in claim 1, wherein f(q)=27(3.q), indeed even f(q)=30(3.q).

5. The sheet as claimed in claim 1, wherein q=2.

6. The sheet as claimed in claim 1, characterized in that wherein q=3.

7. The sheet as claimed in claim 1, wherein one of the following combinations exists: Y(q)>5%+f(q)%.P.sub.m.(n1) with f(q)=27(3.q) and q=2; or Y(q)>5%+f(q)%.P.sub.m.(n1) with f(q)=27(3.q) and q=3; or Y(q)>5%+f(q)%.P.sub.m.(n1) with f(q)=30(3.q) and q=2; or Y(q)>5%+f(q)%.P.sub.m.(n1) with f(q)=30(3.q) and q=3; or Y(q)>10%+f(q)%.P.sub.m.(n1) with f(q)=27(3.q) and q=2; or Y(q)>10%+f(q)%.P.sub.m.(n1) with f(q)=27(3.q) and q=3; or Y(q)>10%+f(q)%.P.sub.m.(n1) with f(q)=30(3.q) and q=2; or Y(q)>10%+f(q)%.P.sub.m.(n1) with f(q)=30(3.q) and q=3.

8. The sheet as claimed in claim 1, wherein the refractive index of the material comprising the texture is within the range extending from 1.4 to 1.65 at 587 nm.

9. The sheet as claimed in claim 1, wherein the absorption of the sheet in the spectral range within the range extending from 400 to 700 nm is less than 2%.

10. The sheet as claimed in claim 1, wherein the material comprising the texture is made of mineral glass.

11. The sheet as claimed in claim 1, wherein the roughness of the textured surface is such that the mean R.sub.Sm is greater than 1 mm and less than 8 mm.

12. The sheet as claimed in claim 1, wherein the texture comprises contiguous patterns with a size within the range extending from 2 to 8 mm.

13. The sheet as claimed in claim 1, wherein its second main face also exhibits a texture such that P.sub.m.(n1) is greater than P.sub.m.(n1), P.sub.m representing the mean slope of the second main face and n being the refractive index of the material comprising the texture of the second main face.

14. The sheet as claimed in claim 13, wherein the texture of the second main face has a mean slope such that P.sub.m.2.(n1) is less than 3 and even less than 2.

15. The sheet as claimed in claim 13, wherein, if Y(q) is the percentage of the textured surface with a slope greater than q/(n1) in degrees of the second main face, then there exists the relationship:
Y(q)>3%+f(q)%.P.sub.m.(n1)
with f(q)=24(3.q) and q having the value 2 both for Y(q) and for Y(q), or q having the value 3 both for Y(q) and for Y(q).

16. The sheet as claimed in claim 1, further comprising an antireflective coating on one or on its two main faces.

17. A horticultural greenhouse equipped with a sheet of claim 1.

18. A process for the manufacture of a sheet of claim 1, the process comprising rolling the sheet with a textured engraved roll.

19. The process as claimed in claim 18, wherein the textured engraved roll supports patterns having a mean slope greater than the mean slope of the first main face of the sheet obtained.

20. The process as claimed in claim 19, wherein the textured engraved roll supports patterns having a mean slope greater by at least 0.5 than the mean slope of the first main face of the sheet obtained.

21. The process as claimed in claim 20, wherein the textured engraved roll supports patterns having a mean slope greater by at least 1 than the mean slope of the first main face of the sheet obtained.

22. The sheet as claimed in claim 9, wherein the absorption of the sheet in the spectral range within the range extending from 400 to 700 nm is less than 1%.

23. The sheet as claimed in claim 22, wherein the absorption of the sheet in the spectral range within the range extending from 400 to 700 nm is less than 0.5%.

24. The sheet as claimed in claim 11, wherein the roughness of the textured surface is such that the mean R.sub.Sm is greater than 1.5 mm.

25. The sheet as claimed in claim 24, wherein the roughness of the textured surface is such that the mean R.sub.Sm is greater than 2 mm.

26. The sheet as claimed in claim 14, wherein the texture of the second main face has a mean slope such that P.sub.m.2.(n1) is less than 2.

Description

[0047] FIG. 1 shows the textured face of a glass sheet according to the invention, obtained by rolling and according to Example 1. The texture of a main face comprises hollow and contiguous pyramids having irregular bases. The degree of grayness reflects the depth of the points at the surface, the darkest regions being the deepest. Over each of FIGS. 1 to 3, the lightest points are at the same height and the darkest points are at the same height. The depth of the patterns is the difference in height orthogonally to the general plane of the plate between the lightest points and the darkest points.

[0048] FIG. 2 shows the textured face of a glass sheet according to the invention, obtained by rolling and according to Example 2. The texture of a main face comprises hollow and contiguous pyramids having irregular bases. The pyramids are smaller than in the case of FIG. 1, so that the unintentionally rounded regions are greater. These rounded regions do not necessarily have the desired slope.

[0049] FIG. 3 shows the textured face of a glass sheet according to the invention, obtained by rolling and according to Example 3. The texture of a main face comprises hollow and contiguous pyramids having irregular bases. The pyramids are smaller than in the case of FIGS. 1 and 2, so that the unintentionally rounded regions are greater. These rounded regions do not necessarily have the desired slope.

[0050] FIG. 4 shows the most strongly textured face of an Albarino-S sheet, top view in a) and side view in b). Of course, the patterns in b) are not to scale. It is shown here that the patterns are bosses uniformly distributed at the surface.

[0051] FIG. 5 illustrates the impact of a change in size of pyramidal patterns (and thus of a change in R.sub.Sm). This is because the 2 textures in a) and b) have the same rounded sections with the same radii of curvature at the crests and hollows of the patterns. This is what is obtained in practice by rolling the glass with a textured roll having pyramids at its surface without rounded sections at the crests and hollows of the patterns. The texture of greater size in a) has a texture closer to the ideal texture since it comprises larger regions of suitable slope. The regions marked z are of suitable slope.

[0052] FIG. 6 shows, in the case of q=2, how the invention differs from the prior art by the straight line Y=X, with X=3%+18%.P.sub.m.(n1) because f(q)=18% for q=2. The points in this figure correspond to the examples of Table 1. The range of the invention lies above this straight line and above a horizontal straight line Y=10%.

[0053] FIG. 7 shows, in the case of q=3, how the invention differs from the prior art by the straight line Y=X, with X=3%+15%.P.sub.m.(n1) because f(q)=15% for q=3. The points in this figure correspond to the examples of Table 2. The range of the invention lies above this straight line and above a horizontal straight line Y=10%.

[0054] FIG. 8 shows a sheet 70 according to the invention in cross section. The textures and thicknesses are not to scale. This sheet 70 is made of a soda-lime-silica mineral glass obtained by rolling between two rolls, one of which was textured. The upper face 71 of the sheet exhibits a texture according to the invention with juxtaposed pyramidal patterns. An antireflective layer 72 was deposited on the textured face of the monolithic substrate. The second face 73 of the sheet is flat, without specific texture. The material comprising the texture is the material 70 and not the material of the layer 72.

[0055] FIG. 9 shows a sheet 80 according to the invention in cross section. The textures and thicknesses are not to scale. This sheet 80 is made of a soda-lime-silica mineral glass obtained by rolling between two rolls, both textured. The upper face 81 of the sheet exhibits a texture according to the invention with juxtaposed pyramidal patterns. The second face 82 of the sheet exhibits a texture (according or not according to the invention) with juxtaposed pyramidal patterns, the mean slope over this second face 82 being lower than the mean slope over the first face 81. This sheet is completely monolithic. Its material comprises the textures of each face.

[0056] FIG. 10 shows a sheet 90 according to the invention in cross section. The textures and thicknesses are not to scale. A substrate sheet 91 made of soda-lime-silica glass gives its stiffness to the combination. This substrate sheet 91 is a mineral sheet obtained by hot rolling between two textured rolls. The two faces 92 and 93 of this substrate sheet 91 are consequently textured. It may be considered that the substrate sheet is an Albarino-T sheet. A texture 94 according to the invention was produced above the face 92 of the substrate sheet 91 by embossing a sol-gel layer. The sol-gel material 95 and the material of the substrate sheet 91 exhibit similar refractive indices, the difference in their refractive indices not exceeding 0.1. In this instance, the material comprising the texture according to the invention is the sol-gel material 95.

[0057] In the examples which follow, the sheets had a thickness of 4 mm. The mean slope and the % of slope greater than q/(n1) in degrees, q being equal to 2 for Examples 1 to 9 and to 3 for Examples 10 to 17, was varied. The results are given respectively in Tables 2 and 3. The haze values are measured at 1.5 for Examples 1 to 9 and at 2.5 for Examples 10 to 18. The TLH values are given with respect to flat glass of the same nature and with the same weight per unit area. It is thus the loss of TLH in %, denoted TLH, with respect to flat glass which is concerned. This is because the flat glass necessary has a higher TLH value than the textured glasses in the same material. The aim is for TLH to be as low as possible.

EXAMPLES 1 TO 9

[0058] For Examples 1 to 4, glass sheets exhibiting a main textured face, the texture of which is a repetition of hollow pyramidal patterns having an irregular base of different sizes, as reflected by the R.sub.Sm value, are produced by rolling. The glazings of Examples 5 to 9 are commercially available and comparative. The textures obtained for Examples 1 to 3 are those shown respectively in FIGS. 1 to 3, the depth being the difference in height between the lightest points and the darkest points of these figures. From FIG. 1 to FIG. 3, an increase in the proportion of rounded regions not corresponding exactly to those desired is observed. The texture of Example 4 is similar in top view to that of FIG. 2, the difference being in the depth. Examples 5 to 9 correspond to characteristics measured on textured glasses sold under the brands appearing in the first column of the table. For all the examples, the refractive index of the mineral glass used was 1.52. In the table, X represents 3%+18%.P.sub.m.(n1) because f(q)=18% for q=2.

TABLE-US-00001 TABLE 1 Mean Haze Depth R.sub.Sm P.sub.m Y (% at TLH Example No. (m) (mm) () X (%) (%) 1.5) (%) 1 174 3.6 4 40.44 100 100% 2 2 100 1.8 3.8 38.55 61 75% 1.9 3 100 1.3 4.9 48.9 70 79% 2.5 4 80 1.8 3 31.08 50 60% 1.5 5 0.8 9.5 91.92 80 85% 5 (Albarino-S) 6 0.8 2 21.72 15 20% 1 Albarino-T) 7 2.5 30 283.8 90 95% 15 (Albarino-P) 8 (Arena C) 5 49.8 40 50% 2.5 9 (Vetrasol) 6 59.16 48 56% 3

[0059] It is found that, for Example 5, the haze value is good but that the TLH is greatly reduced. As regards Example 6, the haze value is extremely low. Examples 7 to 9 do not offer very good compromises in properties. Examples 1 to 4 offer excellent compromises in haze and TLH properties. This corresponds to the fact that, for these examples, Y>X.

EXAMPLES 10 TO 17

[0060] For Examples 10 to 12, glass sheets exhibiting a main textured face, the texture of which is a repetition of hollow pyramidal patterns having an irregular base of different sizes, as reflected by the R.sub.Sm value, are produced by rolling. The glazings of Examples 13 to 17 are commercially available and comparative. The textures obtained for Examples 10 to 12 are those shown respectively in FIGS. 1 to 3, the depth being the difference in height between the lightest points and the darkest points of these figures. These textures differ from those of Examples 1 to 3 in the depth, which is in this instance chosen to be deeper.

[0061] Examples 13 to 17 correspond to characteristics measured on textured glasses sold under the brands appearing in the first column of Table 2. For all the examples, the refractive index of the mineral glass used was 1.52. In Table 2, X represents 3%+15%.P.sub.m.(n1) because f(q)=15% for q=3.

TABLE-US-00002 TABLE 2 Mean Haze Depth R.sub.Sm P.sub.m Y (% at TLH Example No. (m) (mm) () X (%) (%) 2.5) (%) 10 260 3.6 6 49.8 100 100% 3 11 150 1.8 5.7 47.5 61 70% 2.9 12 150 1.3 7.4 60.7 70 75% 3.7 13 0.8 9.5 77.1 65 75% 5 (Albarino-S) 14 0.8 2 18.6 8 10% 1 Albarino-T) 15 2.5 30 237.0 88 92% 15 (Albarino-P) 16 (Arena C) 5 42.0 25 30% 2.5 17 6 49.8 30 32% 3 (Vetrasol)

[0062] It is found that, for Example 13, the haze value is good but that the TLH is greatly reduced. As regards Example 14, the haze value is extremely low. Examples 13 to 17 do not offer very good compromises in properties. Examples 10 to 12 offer excellent compromises in haze and TLH properties. This corresponds to the fact that, for these examples, Y>X.