IMPROVED GREENHOUSE GLAZING

Abstract

The present invention discloses a glazing characterized through a high hemispherical light transmission together with an enhanced tuneable light diffusion, what we hereby call a highly transmitting glazing with optimized Hortiscatter. The glazing of the invention is particularly well suitable for a greenhouse. The invention is a global approach which allows to propose different glazing which can be utilized depending on the type of crop and the geographical zone, providing optimized Hortiscatter on demand

Claims

1. A highly transmitting glazing with optimized Hortiscatter having combined features comprising (a) a clear glass quality, (b) a textured glass-surface, and (c) at least one silica-based anti-reflective layer on at least one surface, said textured glass surface being characterized by: (a) a Sa parameter being at least 0.05 μm and at most 3 μm, (b) a Sz parameter being at least 1 μm and at most 12 μm, (c) a Rsm parameter being at least 50 μm and at most 150 μm.

2. The highly transmitting glazing with optimized Hortiscatter of claim 1 such that the at least one textured surface has a roughness characterized by a Sa parameter being at least 0.1 μm, preferably at least 0.2 μm and at most 2.5 μm, preferably at most 2 μm.

3. The highly transmitting glazing with optimized Hortiscatter of claim 1 such that the at least one textured surface has a roughness characterized by a Sz parameter being at least 2 μm, preferably at least 3 μm and at most 10 μm, preferably at most 9 μm.

4. The highly transmitting glazing with optimized Hortiscatter of claim 1 such that the at least one textured surface has a roughness characterized by a Rsm parameter being at least 55 μm, preferably at least 60 μm and at most 140 μm, preferably at most 130 μm.

5. The highly transmitting glazing with optimized Hortiscatter of claim 1 such that only one glass surface is textured.

6. The highly transmitting glazing with optimized Hortiscatter of claim 1 with both surfaces being textured.

7. The highly transmitting glazing with optimized Hortiscatter of claim 5 characterized in that light capture is more efficient with an incident light at 30° to 60°

8. The highly transmitting glazing with optimized Hortiscatter of claim 6 characterized in that light capture is more efficient with an incident light greater than 60°

9. The highly transmitting glazing with optimized Hortiscatter of claim 1 such that the difference of the hemispherical light transmission of the wet textured surface is at most 0.1% less than the hemispherical light transmission of the dry textured surface.

10. The highly transmitting glazing with optimized Hortiscatter of claim 1 such that the hemispherical light transmission of the wet textured surface is higher than the hemispherical light transmission of the dry textured surface.

11. The highly transmitting glazing with optimized Hortiscatter of claim 1 such that the hemispherical light transmission of the wet textured surface is at least 0.5% higher than the hemispherical light transmission of the dry textured surface.

12. The highly transmitting glazing with optimized Hortiscatter of claim 1 such that both surfaces are coated with a silica-based anti-reflective layer.

13. The highly transmitting glazing with optimized Hortiscatter of claim 1 characterized in that the silica-based anti-reflective layer is the only layer deposited on the at least one surface.

14. The highly transmitting glazing with optimized Hortiscatter of claim 1 characterized in that the silica-based anti-reflective layer before heat treatment has a carbon weight content greater than 20%, preferably greater than 25%, more preferably greater than 30% and most preferably greater than 35%

15. The highly transmitting glazing with optimized Hortiscatter of claim 1 such that the at least one silica-based low reflective layer has a refractive index not greater than 1.48, preferably not greater than 1.45, more preferably not greater than 1.40 and most preferably not greater than 1.38.

16. The highly transmitting glazing with optimized Hortiscatter of claim 1 having an hemispherical light transmission greater than 75%, preferably greater than 78% and more preferably greater than 80%.

17. The highly transmitting glazing with optimized Hortiscatter of claim 1 having an Hortiscatter comprised between 0.5 and 80%, preferably between 2 and 78% and more preferably between 4 and 75%.

18. The highly transmitting glazing with optimized Hortiscatter of claim 1 with the at least one silica-based anti-reflective layer on at least one surface, said one surface being characterized by a water contact angle being at most 32°, preferably at most 30° and more preferably at most 28°.

19. The highly transmitting glazing with optimized Hortiscatter of claim 1 having a durability characterized by a loss of the maximal transmittance that remains below 2% after 500 dry brush cycles with sand, preferably below 1.5% after 500 dry brush cycles with sand.

20. Use of the highly transmitting glazing with optimized Hortiscatter of claim 1 as greenhouse glazing.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings and by showing various exemplifying embodiments of the invention.

[0033] FIG. 1 shows the different surface structures providing different Hortiscatter levels.

[0034] FIG. 2 shows the correlation between the roughness and the Hortiscatter

[0035] FIG. 3 is a comparison of hemispherical transmission as a function of Hortiscatter for single AR and double AR coated glass with various textured surfaces.

[0036] FIG. 4 shows the PAR light transmission at different angles of incidence for incoming light for the glass with reference 2 and 5 described in Table 2.

[0037] FIG. 5 shows the evolution of the light transmission before and after the brush cleaning test.

DESCRIPTION

[0038] The features of our invention are the consequence of a combination of glass quality, glass surface treatment and antireflective coating. Each of those characteristics will now be described with more details.

Definitions

[0039] PAR meaning is Photosynthetically active radiation and comprises wavelength between 400 to 700 nm, based on NEN 2675+C1:2018. This is the main part of natural light responsible for photosynthetic activities of plants. [0040] Within the context of horticulture, Hortiscatter is the integral value of geometrical distribution of light intensity by bi-directional transmittance (or reflectance) distribution function BTDF under a given angle of incidence of incoming light beam (3D data), defined by Wageningen University and Research (WUR) in the standard NEN 2675+01:2018. [0041] Hemispherical light transmission (T.sub.hem) and haze are measured following the standard NEN 2675+01:2018. The hemispherical light transmission is a measure of light transmission at different angles from the point of light incidence. [0042] The refractive index n is calculated from the light spectrum wavelength at 550 nm. [0043] The roughness is characterized through the Sa, Sz and Rsm values (expressed in micrometers). The roughness parameters were measured by confocal miscroscopy. The surface parameters (Sa and Sz) according to ISO 25178 standard, and the profile parameter (Rsm) by isolating a 2D profile which then gives access to the parameters defined in the ISO 4287 standard. Alternatively, one can use a 3D profilometer for the surface parameters (according to the ISO 25178 standard) and a 2D profilometer for the profile parameters (according to the ISO 4287 standard). The texture/roughness is a consequence of the existence of surface irregularities/patterns. These irregularities consist of bumps called “peaks” and cavities called “valleys”. On a section perpendicular to the etched surface, the peaks and valleys are distributed on either side of a “center line” (algebraic average) also called “mean line”. In a profile and for a measurement along a fixed length (called “evaluation length”). [0044] Sa (arithmetic mean height) expresses, as an absolute value, the difference in height of each point compared to the arithmetical mean of the surface, the Sa parameter is characterized by a standard deviation of 0.1 μm; [0045] Sz (maximum height) is defined as the sum of the largest peak height value and the largest pit depth value within the defined area, the Sz parameter is characterized by a standard deviation of 0.6 μm; [0046] Rsm (spacing value, sometimes also called Sm) is the average distance between two successive passages of the profile through the “mean line”; and this gives the average distance between the “peaks” and therefore the average value of the widths of the patterns, the Rsm parameter is characterized by a standard deviation of 1.0 μm. [0047] The water contact angle is the angle made between the tangent to a water drop and the surface of the support. The measure is made following the standard method ASTM C 813-75 (1989) [0048] Durability of the coating is assessed by means of the Brush Cleaning Test. The testing procedure is made by analogy to ISO 11998 and ASTM D2486 standards and the brush specifications is according to ASTM D2486 (Nylon 454 g). The effective scrubbing length is 70 mm, the test frequency is 2 Hz and the speed about 24 cm/s (based on DIN EN 1096-2 Appendix E). ISO 12103 defines the uniform distribution of initial 1 g dry Arizona Test Dust fine on the glass surface, with re-deposition of 0.5 g of dust every 100 cycles. Typical set of test cycles are 100, 200, 300, 400 and 500.

[0049] The glass used for the invention is a clear glass or an extra clear glass. The clear glass has a composition characterized by an iron content expressed in weight percent of Fe.sub.2O.sub.3 which is at most 0.1%. This value drops to at most 0.015% for the extra clear glass. The glass substrate of the invention has a thickness that is greater than 1 mm, preferably greater than 1.5 mm and more preferably greater than 2 mm. The thickness of the glass substrate is at most 20 mm, preferably at most 15 mm and more preferably at most 10 mm. Advantageously the thickness of the glass substrate is comprised between 3 and 6 mm. A 4 mm glass substrate with the extra clear composition has a light transmission of about 91.7%.

[0050] At least one surface of the glass has been textured through a mechanical or a chemical process, by methods well known from the man skilled in the art. The textured surface may be manufactured through calendering, sand blasting or chemical etching. Chemical etching may be performed by any known procedure in the art such as dipping, spraying, roller etching, curtain etching.

[0051] For example, texturing may be obtained by means of a controlled chemical attack with an aqueous solution based on hydrofluoric acid, carried out one or more times. Generally, the aqueous acidic solutions used for this purpose have a pH between 0 and 5 and they can comprise, in addition to the hydrofluoric acid itself, salts of this acid, other acids, such as HCl, H.sub.2SO.sub.4, HNO.sub.3, CH.sub.3CO.sub.2H, H.sub.3PO.sub.4 and/or their salts (for example, Na.sub.2SO.sub.4, K.sub.2SO.sub.4, (NH.sub.4).sub.2SO.sub.4, BaSO.sub.4, and the like), and also other adjuvants in minor proportions. Alkali metal and ammonium salts are generally preferred, such as, for example, sodium, potassium and ammonium bifluoride. The acid etching stage according to the invention can advantageously be carried out by controlled acid attack, for a time which can vary as a function of the acid solution used and of the expected result.

[0052] Specific textured surface are achieved (see FIG. 1) and are responsible for various level of Hortiscatter. The table 2 indicates the resulting Hortiscatter and the hemispherical light transmission obtained regarding the texture of one or both surfaces of the glass, the texture being here characterized through its roughness parameters Sa, Sz and Rsm. Absence of value means no texturation has been performed. In all cases, the glazing is either coated with a single nano-porous silica-based antireflective layer on the textured so called air-side glass surface or coated with a double nano-porous silica-based antireflective layer on both air-side and tin-side of the glass. Air-side or tin-side referred to the surface of the glass being in contact with the tin bath or the face in air contact during the float process. Hortiscatter value expressed in percent is given with a range of ±5% and hemispherical transmission value expressed in percent is given with a range of ±0.5%. The AR column is indicating presence or not of an antireflective coating. The references given in the first column will be kept for the rest of the description, meaning for example that “1” refers to the single side textured glass surface having an Hortscatter of 3.0% and a T.sub.hem of 85.4%.

TABLE-US-00002 TABLE 2 Air-side Tin-side Sa Sz Rsm Sa Sz Rsm Hortiscatter T.sub.hem ref (μm) (μm) (μm) AR (μm) (μm) (μm) AR (%) (%) 1 0.205 3.763 110 yes — — — no 3.0 85.4 2 0.653 5.573 78 yes — — — no 14.0 84.0 3 0.857 6.163 80 yes — — — no 28.0 82.9 4 1.557 8.600 76 yes — — — no 65.0 79.8 5 0.218 3.610 89 yes 0.240 3.603 84 no 13.5 84.3 6 0.571 5.337 88 yes 0.464 4.623 98 no 31.6 82.8 7 0.696 5.900 64 yes 0.965 6.663 73 no 59.2 80.8 8 1.490 8.653 72 yes 1.460 8.133 68 no 75.1 78.3 9 0.227 3.483 84 yes 0.565 5.217 66 no 25.5 83.0 10 0.240 3.530 109 yes 0.885 6.377 65 no 41.2 81.8 11 0.227 3.497 130 yes 1.713 9.397 65 no 68.9 78.9 12 0.483 4.707 79 yes 0.921 6.443 69 no 47.0 81.5 13 0.482 5.020 77 yes 1.763 9.060 63 no 70.1 79.0 14 0.753 5.570 73 yes 1.680 9.450 68 no 72.2 78.5 15 0.220 3.610 116 yes — — — yes 6.0 87.7 16 0.603 5.360 84 yes — — — yes 12.2 87.0 17 0.919 6.250 71 yes — — — yes 25.3 85.8 18 1.600 8.350 78 yes — — — yes 53.7 83.5

[0053] The table 2 shows that the different texturations primarily applied on one side of the glass covers a wide range of Hortiscatter. The application of those texturations on the other side of the glass also enables the full coverage of Hortiscatter range with a particular hemispherical transmission value. Combination of both textured glass surfaces offers huge possibilities in terms of resulting hemispherical light transmission and Hortiscatter.

[0054] The nano-porous silica-based antireflective coating may be deposited by any known mean. In a preferred embodiment the nano-porous silica-based antireflective layer is a SiO.sub.x nano-porous layer deposited as described in EP1679291B1 and in DE10159907A1, both incorporated here by reference. The nano-porous SiO.sub.x film will get its final optical and mechanical properties in a two-step production. At first, in the as-deposited state the thin film is coated by a PECVD process and results in high carbon content SiO.sub.xC.sub.y coating, the layer comprises 5 to 30 at. % of Silicon, 20 to 60 at. % of Oxygen, 2 to 30 at. % of carbon and 2 to 30 at. % of hydrogen.

[0055] In order to get the final optical and mechanical properties one needs to bake the glass and the film. The carbon is desorbed during the tempering process leaving increased porosity, pores having a mean diameter greater than 5 nm. Increasing porosity results in a smaller refractive index, responsible for the antireflective performance. Preferably, after tempering the refractive index of the SiO.sub.x layer is at most 1.5, preferably at most 1.4 and more preferably at most 1.38. Temperatures for any heat strengthened glass are between 650° C.-680° C. During this tempering process the organic parts will desorb from the coating and leave a porous SiO.sub.2 film. Advantageously, the final refractive index is 1.37.

[0056] Advantageously, the thickness of the heat treated nano-porous silica-based layer is at least 80 nm, preferably at least 90 nm and more preferably at least 100 nm. The thickness of the silicon oxide based layer is at most 180 nm, preferably at most 140 nm and more preferably at most 120.

[0057] Advantageously, the film thickness after bake is around 110 nm (±5 nm). Based on the special plasma process the surface of the glass together with the coating will be densified. The chemical bond between the Si group in the coating and the Si group on the surface of the glass at the interface of coating-glass surface is the main reason on the better mechanical durability performances. Furthermore regarding the mechanical behaviour, the coating after bake is harder than the uncoated float glass.

[0058] The inventors have discovered that addition of a second nano-porous anti-reflective coating on the second glass surface allows to enhance the hemispherical light transmission by as much as 5% while preserving the Hortiscatter. The 110 nm film thickness results in a maximum hemispherical transmission greater than 89% for a double-sided anti-reflective coated extra clear glass which is more than 5% higher than the uncoated extra clear glass. This is better illustrated on FIG. 3.

[0059] Preservation of the Hortiscatter is due to the presence of special microstructure implemented by texturing the glass surface while the nano-porosity of the anti-reflective coating is only improving the hemispherical light transmission. Moreover the nano-porous anti-reflective coating is also protecting the textured surface from corrosion by acting as diffusion barrier for volatile species inside the core glass, giving enhanced chemical and mechanical durability which enable the longer performance with the minimized deterioration rate, being in line with class A coating based on the norm EN 1096-2.

[0060] The brush cleaning test has been performed on the glazing of the invention and by comparison on a similar textured glazing covered with a known conventional antireflective coating. The FIG. 5 shows that addition of an antireflective coating (ARC) on the textured glass surface increases the light transmission (compare curve solarfloat T (no ARC) with solarfloat HT, FIG. 5.a). FIG. 5, a and b also show that the brush test is responsible for a decrease in light transmission, most probably due to the coating degradation. Nevertheless, the coating of the invention proves to be more durable since the light transmission after 500 brush cycles is comparable with the light transmission of the conventional antireflective coating submitted to only 100 brush cycles.

[0061] The FIG. 4 shows that for equivalent hemispherical light transmission and equivalent Hortiscatter, the light transmission related to the angle of incident light has a different type of distribution related to the presence of a single side or a double sides textured glazing (compare examples 2 and 5). This particular behaviour is an opportunity of better choosing the optimized glazing related to the geographical zone. A single side glass textured is more performant for light transmission at lower angle (closer to the normal incidence) while a double sides textured glazing is a more effective light capture at the higher angle of incidence while both represent the same value for hemispherical light transmission and Hortiscatter. For the particular examples of FIG. 4, the enhanced light transmission at higher angle of incidence could be of importance for the regions with sun always shining at the very low angle versus horizon (correspond to the Ref 2 in table 2) and by opposite the curve #5 (Ref 5 in table 2) present a higher transmission at a smaller incident angle.

[0062] As already pointed previously, when the glass surface is wet, the hemispherical light transmission slightly increases. When the textured glass surface is coated with an anti-reflective coating of the invention, the increase is still greater (see table 3).

TABLE-US-00003 TABLE 3 Difference T.sub.hem of wet material compared to Condensation Ref dry material (ΔT.sub.hem) effect ** 1 0.5% +/− 2 0.2% +/− 3 −0.1%* +/− 4 0.1% +/− 15 0.2% +/− 16 0.2% +/− 17 0.6% + 18 2.25% ++ *a minus sign means that T.sub.hem is decreasing when the surface is wet ** The condensation effect is defined as follow: (− −) very negative < −2%; (−) negative −2% to −0.5%; (+/−) neutral −0.5% to +0.5%; (+) positive +0.5% to +2%; (+ +) very positive > +2%

Description of Embodiments/Examples

[0063] The following examples have been made in accordance with the invention.

[0064] Example 1 (table 2, Ref 2). A 4 mm thick sheet of extra-clear glass has been washed with deionized water and then dried. An acid etching solution, composed by volume of 50% NH.sub.4HF.sub.2, 25% water, 6% concentrated H.sub.2SO.sub.4, 6% of a 50% by weight aqueous HF solution, 10% K.sub.2SO.sub.4 and 3% (NH.sub.4).sub.2SO.sub.4, at 20-25° C., was allowed to contact the glass surface for 1.5 minutes. After removal of the acid solution, the glass surface is rinsed with water and washed. The textured glass sheet is then transferred to a coating line where a single SiO.sub.xC.sub.y layer is deposited by a PECVD method as described in EP1679291B1 and heat treated at a temperature between 650° C. and 680° C. during 15 minutes. Basic coating material is an HMDSO which is heated up in an evaporator outside the line to transfer the chemical fluid from liquid to the gas phase in combination with an plasma in vacuum atmosphere comprising oxygen and forming an amorphous SiO.sub.x film with high organically content on the glass surface. The film thickness after bake is around 110 nm (±5 nm).

[0065] Example 2 (table 2, Ref 3) is made following the same procedure as example 1 except that the contact time of the acid solution with the glass surface is 2 minutes.

[0066] Example 3 (table 2, Ref 5) is made following the same procedure as example 1 except that both glass surfaces have been contacted during 1 minute by the acid solution. The air-side surface is then coated with a 110 nm thick SiO.sub.xC.sub.y layer following the same procedure described in example 1.

[0067] Example 4 (table 2, Ref 15) is the same as example 3 except that only the air-side surface is textured through contact with the acid etching solution during 1.5 minutes and that both surfaces have been coated with the antireflective SiO.sub.xC.sub.y layer.