TEXTURED TRANSPARENT SUBSTRATE, IN PARTICULAR FOR GREENHOUSE USE

Abstract

A transparent substrate includes a texture in relief on at least one of its two main faces, such that when the substrate is textured on a single face, the average slope P.sub.m in degrees of this textured face is lower than 2, and when the substrate is textured on both its faces, the sum of the two average slopes (Pm1, Pm2) of the respective faces is lower than 3.

Claims

1. A transparent substrate comprising a texture in relief on at least one of its two main faces, such that when the substrate is textured on a single face, the average slope P.sub.m in degrees of the textured face is lower than 2, and when the substrate is textured on both its faces, each of the faces having a respective average slope (Pm1, Pm2), the sum of the two average slopes of the respective faces is lower than 3, and preferably lower than 2.5.

2. The substrate as claimed in claim 1, wherein: when the substrate is textured on a single face, the average slope Pm in degrees of the textured face is lower than 1.8, when the substrate is textured on both its faces, each of the faces having a respective average slope (Pm1, Pm2), the sum of the two average slopes of the respective faces is lower than 2.5.

3. The substrate as claimed in claim 1, wherein the refractive index of the material comprising the texture is comprised between 1.4 and 1.65 at a wavelength of 587 nm.

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

5. The substrate as claimed in claim 1, wherein the texture of said at least one substrate comprises patterns the period of which is such that the average Rsm is lower than 5 mm.

6. The substrate as claimed in claim 1, wherein: when the substrate is textured on a single face, the average slope Pm in degrees of the textured face is higher than 0.3, when the substrate is textured on both its faces, each of the faces having a respective average slope (Pm1, Pm2), the sum of the two average slopes of the respective faces is higher than 0.6.

7. The substrate as claimed in claim 1, further comprising an antireflection coating on one or both of its main faces.

8. The substrate as claimed in claim 1, wherein the texture is obtained by rolling the material from which the substrate is made between two rollers, a first roller being of smooth surface and a second roller being of textured surface, or both rollers being of textured surface.

9. The substrate as claimed in claim 1, wherein the texture may be produced in a first material placed on a substrate of a second material.

10. A horticultural greenhouse equipped with at least one substrate as claimed in claim 1.

11. A process for manufacturing a substrate as claimed in claim 1, the process comprising rolling a material from which the substrate is made between two rollers, either between a roller of smooth surface and a textured roller with patterns, or between two textured rollers with patterns.

12. The process for manufacturing a substrate as claimed in claim 11, wherein at least one of the textured roller and the two textured rollers with patterns is obtained by electrical discharge machining.

13. The substrate as claimed in claim 1, wherein the sum of the two average slopes of the respective faces is lower than 2.5.

14. The substrate as claimed in claim 2, wherein: when the substrate is textured on a single face, the average slope Pm in degrees of the textured face is lower than 1.3, when the substrate is textured on both its faces, each of the faces having a respective average slope (Pm1, Pm2), the sum of the two average slopes of the respective faces is lower than 1.3.

15. The substrate as claimed in claim 4, wherein the mineral glass comprises iron oxide in a total weight content (expressed in Fe.sub.2O.sub.3) of at most 0.030%.

16. The substrate as claimed in claim 4, wherein the mineral glass is a soda-lime-silica glass with the following weight composition: SiO.sub.2 50-75% CaO 5-15% MgO 0-10% Na.sub.2O 10-20% Al.sub.2O.sub.3 0-5% K.sub.2O 0-5%.

17. The substrate as claimed in claim 5, wherein the texture of said at least one substrate comprises patterns the period of which is such that the average Rsm is lower than 550 m.

18. The substrate as claimed in claim 6, wherein: when the substrate is textured on a single face, the average slope Pm in degrees of the textured face is higher than 1.1, when the substrate is textured on both its faces, each of the faces having a respective average slope (Pm1, Pm2), the sum of the two average slopes of the respective faces is higher than 1.1.

19. The substrate as claimed in claim 7, wherein the antireflection coating is placed against said at least one textured face.

20. The process for manufacturing a substrate as claimed in claim 11, wherein at least one of the textured roller and the two textured rollers possessing imprinting patterns has an average slope higher than an average slope of the associated patterns obtained on the substrate.

Description

[0062] The present invention is now described using merely illustrative and completely nonlimiting examples of the scope of the invention, on the basis of the appended illustrations, in which

[0063] FIG. 1 shows a schematic cross-sectional view of a first example textured substrate according to the invention comprising a single textured face obtained by rolling;

[0064] FIG. 2 is a photograph from above of the example of FIG. 1;

[0065] FIG. 3 is a schematic cross-sectional view of a second example textured substrate according to the invention, comprising its two textured opposite faces.

[0066] The textures and thicknesses of FIGS. 1 and 3 are not to scale.

[0067] The textured substrates 1 and 3 illustrated in the respective FIGS. 1 and 3, in cross section along their edge face, are two respective example embodiments according to the invention, the first example substrate possessing only a single textured main face, whereas the second example has its two opposite main faces textured

[0068] The textured substrates of the invention are such that:

[0069] when the substrate is textured on a single face, the average slope P.sub.m in degrees of this textured face is lower than 2, and

[0070] when the substrate is textured on both its faces, each of the faces having a respective average slope Pm1, Pm2, the sum of the two average slopes of the respective faces is lower than 3, and preferably lower than 2.5.

[0071] In the embodiments illustrated in these figures, the patterns of a textured face are distributed over all the surface of the substrate.

[0072] The textured substrate 1 (example 1) is made of soda-lime-silica mineral glass of thickness comprised between 3 and 5 mm, obtained by hot rolling between two rollers the upper roller of which was of smooth surface, whereas the lower roller had a textured imprinting surface. The substrate 1 possesses its first planar face 10, and its opposite second textured face 11. The patterns in relief of the textured face 11 correspond to the patterns in negative of the textured surface (of the imprinting patterns) of the roller.

[0073] The patterns of the textured face of example 1 schematically shown in FIG. 1 and illustrated in FIG. 2 are formed of an alternating multiplicity of bumps and holes obtained using a roller comprising protruding patterns/features, here of circular base.

[0074] The roughness of the textured surface of the imprinting roller for example 1 has the following characteristics over a profile of given length, the measurements having being carried out according to standard ISO 4287:1997:

[0075] Arithmetical mean roughness of the profile: Ra=2.55 m;

[0076] Maximum height of the profile: Rz=19.85 m;

[0077] Average period or width of the patterns in relief of the profile (already defined above): average Rsm=191 m;

[0078] Density of peaks per centimeter of length of the profile: RPc=52.35/cm.

[0079] The obtained substrate 1 of this example 1 has a texture in relief such that the average slope Pm is 1. The texture is such that the period according to the average Rsm is 0.53 mm and the height Rz is 5.6 m.

[0080] The substrate 2 of the invention (example 2) is made of a soda-lime-silica mineral glass obtained by hot rolling between two rollers of textured printing surface, the substrate possessing its two opposite textured faces 20 and 21.

[0081] The rollers used for example 2 each possess the same textured imprinting surface, the roughness of which is that defined for the roller of example 1.

[0082] The obtained substrate 2 has a texture in relief such that the average slope Pm1 of the first surface (surface obtained by the lower roller) is 1 and the average slope Pmt of the second surface (surface obtained by the upper roller) is 1, the sum of the average slopes being 2 (Pm1+Pm2).

[0083] In table 1 below have been given for the two examples 1 and 2 of the invention and comparative examples 3 to 5 (which do not correspond to the invention), the values of the height Rz, period according to the average Rsm of the textured pattern of the substrate, average slope Pm (substrate textured on one face) or sum of the average slopes (substrate textured on both faces), the TLH of the substrate, the loss of TLH (TLH), and the haze at 1.5.

[0084] The loss of TLH is equal to the difference in TLH between that of the measured substrate and of a reference TLH of flat float glass. The flat float glass taken as reference is the glass called DIAMANT sold by Saint Gobain, which possesses a high TL H of 84% and a haze of 0.

[0085] Example 3, which is a comparative example, is a commercially available glass, Albarino-T. This glass of example 3 has its two opposite faces textured via a roller of given roughness with rolling-process parameters leading to a substrate having respectively a first average slope Pm1 of 2, and a second average slope Pmt of 1.5, this leading the sum of its average slopes to equal 3.5.

[0086] Example 4, which is a comparative example, is a substrate possessing a single textured face, the texture of which is that corresponding to that obtained for one of the faces of the Albarino-T glass of comparative example 3. The substrate has an average slope equal to 2.

[0087] Example 5, which is a comparative example, is a substrate one of the textured faces of which was obtained using the printing roller of textured surface of examples 1 and 2, and the opposite textured face of which was obtained using a roller identical to that procuring one of the textured surfaces of the Albarino-T glass of example 3. The substrate of example 5 has a first average slope Pm1 of 1, and a second average slope Pmt of 2, leading the sum of the average slopes to equal 3.

TABLE-US-00001 TABLE 1 Height Rz Average Pm () or sum of TLH TLH Haze (% at Example n (m) Rsm(mm) the Pm values () (%) (%) 1.5) Diamant 0 84 float glass Example 1 5.6 0.53 Pm = 1 83.7 0.3 5 Example 2 5.6 0.53 Sum of the Pm 83.5 0.5 8 values = 2 Example 3- 25 on one 0.8 on one Sum of the Pm 83 1 19 Albarino- face/13 on face/1.1 on values = 3.5 T the other the other face face Example 4 25 0.8 Pm = 2 83.5 0.5 11 Example 5 5.6 on one 0.53 on one Sum of the Pm 83.2 0.8 14 face/25 on face/0.8 on values = 3 the other the other face face

[0088] It is observed that example 1 of the invention with an average slope lower than 2, in particular equal to 1, is entirely suitable for obtaining the sought-after result, a high TLH with a loss of TLH of less than 1% (in particular of 0.3%), and a haze of 5%, i.e. lower than 10%.

[0089] Likewise, example 2 of the invention with a sum of the average slopes lower than 3, in the present case equal to 2, corresponds to the desired results with a loss of TLH of 0.5% (therefore lower than 1%) and a haze of 8% (therefore lower than 10%).

[0090] In contrast, comparative example 3 shows that with average slopes on each textured face of 2 and 1.5 respectively giving a sum of the average slopes that is not lower than 3, the result is not achieved, the haze of the substrate being too significant because it is 19%.

[0091] Likewise, comparative example 4 with a single textured face that has an average slope of 2 admittedly possesses a loss of TLH of less than 1% but already possesses a significant haze higher than 10%. This substrate is not suitable.

[0092] Likewise, comparative example 5 shows that with two textured faces of average slopes that are however low, respectively 1 and 2, but the sum of which is not lower than 3, the result is not achieved. The loss of TLH is admittedly 0.8% but the haze is too significant with 14% (therefore higher than 10%).

[0093] Table 2 provides an estimation of the haze value in transmission at 1.5 of an extra-clear Albarino matrix comprising a single textured surface, as a function of its average slope Pm.

[0094] This estimation is firstly based on an approximation made of the definition of the slope as a function of roughness parameters, according to the following equation:

[00002]$={\tan }^{-1}.Math.\frac{2.Math.\mathrm{Rz}}{\mathrm{Rsm}}$

[0095] As specified at the start of this text, the parameter Rz corresponds to the maximum height of the profile over an evaluation length l, whereas the parameter Rsm corresponds to an average period of the profile over an evaluation length l. Considering the structure to be relatively uniform, an approximation may be made of Rz as being equal to the average height over the evaluation length. It is then possible to relate the average slope Pm to the values of Rsm and of Rz using the following equation, this leading us to the preceding expression of the slope as a function of roughness parameters.

[00003]$\tan .Math..Math.=\frac{\mathrm{Rz}.Math.\text{/}.Math.2}{\mathrm{Rsm}.Math.\text{/}.Math.4}$

[0096] The estimation of the haze value is based in addition on a second assumption made as to the distribution of slopes having, when considered in their entirety, the desired average-slope value (target value) Pm. To do this, firstly, among the existing sample measurements, the measured sample having the average slope closest to this target value is selected. Subsequently an expansion coefficient is applied to the distribution function of the slopes of this sample in order to simulate a new slope distribution having the target average-slope value. Lastly, the haze associated with this modeled slope distribution is calculated.

TABLE-US-00002 TABLE 2 Example no Rsm/Rz Pm () Haze (% at 1.5) 1 572 0.2 0 2 381 0.3 0 3 229 0.5 0.5 4 163 0.7 0.5 5 127 0.9 0.5 6 114 1 1 7 104 1.1 1 8 95 1.2 1 9 88 1.3 1.5 10 81 1.4 1.5 11 76 1.5 2 12 71 1.6 2.7 13 67 1.7 3.2 14 63 1.8 4.5

[0097] The results of table 2 show that, for each of examples n 1 to 14, for which the slope value is lower than 1.8, a haze lower than 5% is obtained, the haze value increasing at the same time as the average slope Pm.

[0098] Table 3 provides an estimation of the haze value in transmission at 1.5 of an Albarino extra-clear matrix comprising two opposite textured surfaces, as a function of the sum of the average slopes (Pm1, Pm2) of each of these faces. This estimation is made on the basis of the assumptions having permitted the results presented in table 2 to be obtained.

TABLE-US-00003 TABLE 3 Sum of Pm1 and Haze (% Example no Pm1 () Pm2 () Pm2 values () Rsm/Rz at 1.5) 1 0.27 0.27 0.54 212 0 2 0.63 0.63 1.26 90 1 3 1 0.88 1.88 60 2.7 4 0.76 0.76 1.52 75 2.8 5 1 1 2 57 3.2 6 1.2 0.88 2.08 55 3.5 7 1.2 0.7 1.9 60 3.8 8 1.5 0.88 2.38 48 5 9 1.2 1.2 2.4 47 6.5 10 1.4 1 2.4 47 6 11 1.5 1 2.5 45 6 12 1.8 1.5 3.3 34 15.7 13 1.8 1.8 3.6 31 19.4

[0099] The results of table 3 show that a haze lower than 5% at 1.5 is obtained for each of examples n 1 to 7, for which the sum of the slopes is lower than 2.3. Examples n 8 to 11, for which the sum of the slopes is lower than 3, allow for their part a haze lower than 10% to be obtained. Lastly, examples n 12 and 13 have a haze higher than 10% and therefore do not solve the general technical problem of the invention.

[0100] In conclusion, using the rolling process with suitable roughnesses of the imprinting surfaces of the rollers, combined with the implementation parameters of the process, the invention provides transparent substrates that have patterns in relief such that the average slope procures a high TLH and a very low haze, approaching the properties of a float glass, while being aesthetic, the patterns being discrete in size and distributed over all the surface so as to generate a uniform surface appearance.

[0101] According to one particular embodiment, the invention also relates to a horticultural greenhouse equipped with at least one substrate such as those described above.