FR3118461A1 - METHOD FOR MANUFACTURING GREENHOUSE GLAZING AND SUCH GREENHOUSE GLAZING - Google Patents

Abstract

The invention relates to a method for manufacturing greenhouse glazing by enamel screen printing and greenhouse glazing comprising patterns of dry or fluid enamel. Figure 1

Description

METHOD FOR MANUFACTURING GREENHOUSE GLAZING AND SUCH GREENHOUSE GLAZING

The invention relates to the field of highly transparent and diffusing glazing, in particular for greenhouses, particularly the roofing of agricultural, horticultural or urban greenhouses.

High light transmission is necessary for plant growth. At the same time, it turns out in particular that the yields of crops installed in greenhouses are improved by the use of diffusing glazing. Transmission is said to be diffuse when radiation incident on the glass at a given angle of incidence is transmitted in several directions. Diffuse and homogeneous lighting optimizes plant growth. In particular, it has been observed that diffusion avoids hot spots on the plants and allows better light penetration over the entire height of the plant. To do this, glasses having at least one textured face have been developed. Such textured glasses are obtained by rolling the glass, i.e. by passing the hot glass between rollers which are themselves textured, which imprint the surface of the glass and create a relief.

This process has several disadvantages:

• lack of flexibility in the design: impossibility to reach very small or specific textures
• constraints on the choice of glass: impossibility of texturing glass that is too thin, etc.

The invention relates to an alternative process to the manufacture of glazing for a greenhouse without the aforementioned drawbacks.

Thus the subject of the invention is a process for manufacturing a glazing for a greenhouse (by depositing liquid material in a discontinuous manner) which comprises the formation of a glazing with a set of dry enamel patterns (/hardened/solid ) involving the following steps:

- a supply of a fluid enamel composition (screen-printable) often called enamel paste, in particular shear thinning, comprising (and even consisting of) a glass frit, an organic medium which comprises an organic resin, an optional organic solvent, composition capable of forming a transparent enamel after firing, in particular colorless and little (retro)diffusing (devoid or reduced content of diffusing or reflecting particles and/or pigments, and/or crystals and even with a reduced content of diffusing bubbles after firing, in particular at least at the heart of the enamel)

- positioning of a flat sheet of glass with a given thickness E in particular of at most 56mm or 4mm and even at least 0.3mm), with a first main face (bare or coated) spaced apart (parallel) and below a screen printing screen, at a given distance Hg from the first main face, Hg having a value between 2mm and 20mm, preferably between 4mm and 8mm, the canvas being blocked by an emulsion (emulsion not transferable on the glass sheet) in zones called filled zones determining a set of disjoint fillable zones (often called screen designs) defined by a width W0, a length L0, a height H0 and an interzone distance D0 between fillable zones (edge on board)

- coating with the fluid composition on the canvas (parallel to the plane of the canvas), in particular above a table receiving the sheet of glass, leading to filling with the fluid enamel composition of said fillable zones, preferably filling at room temperature and/or at most 60°C, preferably without activation or heating, without hardening or crosslinking of the fluid composition

- (by contact with the first sheet) a transfer of the fluid enamel composition onto the first main face (directly onto the first face or onto an undercoat covering the first face)

- scraping of the fluid enamel composition on said canvas (parallel to the plane of the canvas), leading to a transfer of the fluid composition onto the first main face and thus to the formation of a set of patterns of disjointed fluid enamel, in particular in the form of studs (rounded, with a convex surface) for example defined by a height Hf.

Fillable areas are defined by

- an L0/W0 ratio ranging from 0.1 to 10, in particular from 0.5 to 2, (0.8 to 1.2 and if necessary from 0.95 to 1.05)

- W0 is in a range from 200 to 2000µm, better still from 300 to 500µm,

- L0 is in a range from 200 to 2000µm, better from 300 to 500µm

- D0 is in a range from 150 to 1000µm, better from 200µm to 900µm,

- H0 (in other words the thickness of the fabric) is in a range from 40µm (150.27 fabric) to 170µm (32.100 fabric).

The method comprises, after formation of said set of fluid enamel patterns, a step of hardening (solidification) of the fluid composition by a (first) treatment- in particular suitable for removing any organic solvent and/or hardening (in particular cross-linking) the organic resin -, in particular heat treatment at a temperature of at most 250° C., better still at most 200° C. or by UV treatment or electronic beam ('Ebeam' in English), leading to said set of dry enamel patterns (hardened ) in particular with a convex surface, in particular defined by:

- a first lateral dimension of dry enamel pattern W1, called first width W1 in a range going from 200 μm to 2000 μm, better still from 300 μm to 500 μm,

- a second lateral dimension of dry enamel pattern L1 called second width, preferably perpendicular to W1: in a range going from 200 µm to 2000 µm, better still from 300 µm to 500 µm,

- a height of dry enamel pattern H1 in a range from 8µm to 60µm, better still from 8µm to 50µm

- a distance from the interpattern vertex D1 in a range from 150µm to 1000µm, better still from 200µm to 900µm

- in particular an H1/W1 aspect ratio in a range from 1/20 to 1/130, even from 1/10 to 1/38

The height strongly depends on the width:

- H1=8µm is easily obtained for the minimum width W1=200µm

- H1=60µm is easily obtained for the maximum width W1=2000µm.

Preferably if W1 is at most 500µm then H1 ranges from 8 to 40µm.

Preferably if W1 >500µm then H1 ranges from 8 to 60µm or 50µm.

The greenhouse glazing with enamel patterns according to the invention is manufactured by localized deposition of a fluid enamel composition adapted by screen printing. This glass has transparent enamel patterns on its surface, giving the glass an overall texture. The arrangement of the patterns allows the light to be diffused, which leads to a more uniform light and avoids too direct exposure which would burn the plants.

The method may include the deposition of the fluid composition directly on the first face (floated, smooth) or on a functional sub-layer, for example mineral (suitable for cooking) and/or of submicron thickness.

The method may include a step of cutting, shaping, and/or storing, and/or transporting the glazing with the dry enamel patterns.

The method preferably comprises, after the hardening step, a baking - a (second/last) heat treatment called melting - of at least 500° C., better still at 600° C. for at least 80 s, better still 120 s, leading the formation of a set of transparent baked enamel patterns (and even colorless, and even little diffusing) defined in particular by:

- a first lateral dimension of baked enamel pattern W2, called first width, W2 in a range going from 200 μm to 2000 μm, better still from 300 μm to 500 μm,

- a second lateral dimension of baked enamel pattern L2 called second width, perpendicular to W2, L in a range going from 200 μm to 2000 μm, better still from 300 μm to 500 μm,

- a height of baked enamel pattern H2 in a range from 4µm to 30µm, better still from 4µm to 25µm

- a distance from the interpattern vertex D2 in a range from 150µm to 1000µm, better still from 200µm to 900µm

- preferably an H2/W2 aspect ratio in a range from 1/40 to 1/65, better still from 1/20 to 1/33

Baking is preferably a heat treatment of at least 500°C, better still at 600°C for at least 80s, better still 120s followed by a quenching operation.

Baking can be done following hardening (in the line of deposition, drying) or in another line (after transport). The glazing with dry enamel patterns supports transport.

The height strongly depends on the width:

- H2=4µm is easily obtained for the minimum width W2=200µm

- and H2=30µm is easily obtained for the maximum width W2=2000µm.

Preferably if W2 is at most 500µm then H2 ranges from 4 to 15µm.

Preferably if W2 >500µm then H2 ranges from 4 to 30µm or 25µm.

The fluid composition is sufficiently viscous not to creep significantly after deposition when the shear is stopped.

The chemical composition of the glass frit may be different from that of the glass sheet, glass frit in particular of Zn and/or Bi borosilicate type.

The composition is chosen so that the baked enamel patterns are as transparent and as mass-diffusing as possible. We limit the absorption, the backscattering of incident light by the patterns so that the light transmission is as high as possible.

The presence of dry or baked glaze patterns with slopes helps to create blurring, which is beneficial for plant growth

The dry or baked enamel patterns do not necessarily all have the same average slope.

The fluid composition is optimized in terms of grain size distribution (sinter), as well as the organic (resin and any solvent) / inorganic (sinter) ratio, to be as transparent as possible after firing (heat treatment, etc.).

The percentage of textured surface with a slope beyond 2.5° or even 1.5° contributes to the value of the blur.

Since the fluid composition is not instantaneously frozen (dried) on the surface during transfer, it has creep (very limited, controlled by viscosity), the width and length of the fillable zones are slightly less than the width and length of the final patterns (dry or cooked).

The patterns deposited, dried, fired are rounded studs, with a convex surface.

Especially :

- the baked enamel pattern (with a convex surface) has a crater, (substantially) at the top, with a height of at most 5 µm and/or at most H2/10, in particular visible on the magnification optical microscope images x3 or x10

- or in particular the enamel pattern has a form of streaking on the surface which is the mark of the frame, particularly visible on the images under an optical microscope at x3 or x10 magnification.

If you look at the edge, it is sometimes possible to detect slight zigzag hatching. This observed defect is called sawtooth and is caused by the orientation of the meshes of the fabric with respect to the frame of the screen.

The hardening step leads to a loss of material (elimination of any solvent) in particular a reduction in height. The hardening step can last up to 30 min, in particular a treatment between 80°C and 180°C for 5 min to 30 min.

The possible cooking step also leads to a loss of material (elimination of the organic medium). The height of the baked enamel patterns H2 is lower than that of the dry enamel patterns H1, in particular H2, is at most 0.9, even 0.8, or 0.75 and in particular ranges from 0.4 or 0.5H1 to 0.7H1. The width and length of the baked enamel patterns may be the same or similar to the width and length of the dry enamel patterns. The firing can last from 1 min to 10 min depending on the thickness of the glass, in particular about 45s /mm of glass, and/or be at a temperature in particular of 650°C to 730°C

H1 or H2, L1 or L2, W1 or W2, D1 or D2 can be average values.

It may be desired to produce substantially identical dry or fired enamel patterns. In particular, for example, 80% or 90% of the dry enamel patterns have substantially identical dimensions H1, L1, W1, D1 at ±20% or even ±10%. For example at least 80% or 90% of the transparent baked enamel patterns having substantially identical dimensions H2, L2, W2, D2 at ±20% or even ±10%.

The shape, the distribution of the fillable areas depends on the desired final patterns and the desired arrangement. Fillable areas can be symmetrical, isotropic (same width and length), geometric in shape.

The fillable areas have a limited length, are disjoint just as the patterns (deposited, dried or baked) are disjoint.

The length of the fillable areas can be greater than or equal to the width of the fillable areas.

The fillable areas (and resulting patterns) can be distributed according to a regular, periodic (cubic, hexagonal, etc.) pseudo-periodic or random mesh.

The patterns (deposited, dry or fired) retain the hexagonal mesh arrangement but have a circular type base or shape.

The hexagonal mesh allows all fillable areas (and resulting patterns) to be the same distance apart in all directions. This mesh is the most compact mesh, so with it we can have the maximum of patterns per unit area, and consequently a maximum of % of area with slopes

For a square mesh, the diagonal fillable areas are further than the horizontal or vertical ones.

The fillable areas (or resulting patterns) can be all identical, some identical or all different (pseudo-random distribution) in terms of shape / spacing / aspect ratio / width… Only the height remains fixed for a given screen printing screen .

Concerning the dimensions and the distribution of the fillable zones, it is possible to have at least one of the following characteristics:

- D0 is at least 200µm, better from 200µm to 900µm

- and/or: L0 is in a range from 300 to 500µm, W0 is in a range from 300 to 500µm,

- and/or the fillable zones are defined by a L0/W0 ratio of between 0.8 and 1.2 and even between 0.95 and 1.05

and/or the rate of coverage of the fillable zones is in a range going from 10% to 50%, in particular from 20% to 40%.

Preferably, at least one of the following characteristics can be provided:

- the topping speed and/or the screen printing scraping speed is at least 100mm/s and preferably at most 1000mm/min or even 700mm/min

- the fluid composition has a viscosity in a range from 100 to 200Poises and even from 120 to 160Poises

- the tension of the bonded fabric is isotropic and between 15 N/cm and 25 N/cm, preferably between 18 N/cm and 22 N/cm.

- the weave of the fabric being defined by a number of threads per centimeter (value A) and by a diameter of thread in µm (value B), the nature of the fabric is denoted A.B; the emulsion is of the HHU, HB Y type or equivalent (resistant to water and solvents) clogs the fabric (due to the pair of A.B values combined with the localized application of emulsion, the structured surface is obtained with the disjoint fillable areas)

In addition, the screen printing screen can include a (metallic) frame on which the fabric is glued (weaving based on woven monofilaments of Polyester (PET) or Polyamide (PA 6.6, Nylon)). A polyurethane squeegee with a thickness ranging from 15mm to 35mm, preferably from 20 to 30mm, with a hardness expressed in ShoreA between 65 and 85 can be used.

The pressure exerted by the squeegee during its travel makes it possible to deform the fabric by a height Hg and to bring the fluid composition into contact with the first face (bare or coated).

The composition is adapted (formulated) so that the enamel is transparent (not opaque and even slightly diffusing in volume) after firing and even colorless.

The absorption and even the diffusion of the patterns are limited so that the light transmission is as high as possible.

The composition of fluid enamel can include (essentially) in particular and even consist of:

- from 45% to 80% glass frit, preferably 55% to 80%, capable of being transparent after firing, in particular based on zinc borosilicate and/or bismuth,

- from 20 to 55%, preferably 20% to 45% of the organic medium, preferably comprising from 2%, preferably 5% to 15% of organic resin and from 85% to 95% or 98% of organic solvent, in particular solvent with boiling temperature high enough for transfer

the cumulative % in glass frit and organic medium being 98% or even 99% or 100%.

In particular, the fluid enamel composition comprises at most 2% or 1% of mineral pigment and/or diffusing or reflecting particles and preferably is free of mineral pigment and/or diffusing or reflecting particles, in particular mineral, in particular crystals or oxide particles. metallic. Preferably, it is free of mineral pigment and/or of diffusing or reflecting particle.

The glass frit capable of being transparent after firing is notably devoid of or reduced in Fe, Co or Cr oxide content.

The glass frit can be silicated, in particular with alkaline elements such as Na, K or Li, and metal oxides such as Zn, Zr, Ti, Bi. It is in particular based on zinc and/or bismuth borosilicate.

In particular, it has a softening point that is sufficiently low compared to the cooking temperature, in particular a softening temperature of less than 590°C which can be measured by differential scanning calorimetry (also called DSC – for Differential Scanning Calorimetry) , and has a D90 (obtained by laser granulometry) of 5 to 20 μm and preferably of 5 to 18 μm.

To reduce blurring and increase transparency, the enamel composition (deposited, dry or baked) is devoid of or comprises a very low content of particles - solid and possibly even hollow particles - in particular diffusing or more widely any type of particles (unmelted , crystals, white or colored pigments etc). In particular, it contains few or no (solid) particles chosen from particles of alumina, zirconia, silica, titanium dioxide, calcium carbonate, barium sulphate. In particular, the baked enamel is preferably devoid of any devitrified zone. In particular, adding (in addition to the frit) crystals or metal particles or metal oxide is avoided.

The glass frit and even the baked enamel can be a vitreous matrix based on zinc borosilicate and/or bismuth, preferably based on zinc borosilicate.

Preferably, the glass frit of the dry or fired enamel has a chemical composition according to at least one of the following characteristics (preferably cumulative): the weight content of ZnO +B₂O₃+ Bi₂O₃+SiO₂+Na₂O is at least 80%, 90% or 95% of the total weight of the vitreous material (enamel).

It is also preferred to avoid transition metal oxides from column 5 to 11 and even 12 -except zinc- of the periodic table of the elements (or with a weight content of less than 1% of the total weight of the enamel) . It is preferable to avoid lead, cadmium and mercury oxide as well as chromium if the latter is in the +VI oxidation state (or with a weight content of less than 0.1% of the total weight of the enamel for lead, mercury as well as Chromium VI and with a weight content of less than 0.01% of the total weight of the enamel for cadmium).

The total content of alkali oxides other than Na ₂ O (such as Li ₂ O, K ₂ O) is preferably at most 3% by weight of the glass frit of the dry or fired enamel (and even of the dry or baked enamel), especially 2% and even 1% or 0.5%.

It is possible to limit to 5% 2%, 1% or 0.5% by weight of the glass frit of the dry or baked enamel (and even of the dry or baked enamel), the weight content of cumulative metal oxides alkaline earth Mg, Ca, or even Mg, Ca and Ba.

Preferably, concerning the constitution of the enamel layer, one or more of the following alternative or cumulative characteristics is provided:

- the content by weight of diffusing (solid) particles is preferably at most 1% of the total weight of the enamel deposited, dry or baked, in particular 0.5% and even 0.1%, or even zero

- and/or the weight content of pigments is preferably at most 1% of the total weight of the enamel deposited, dry or baked, in particular 0.5% and even 0.1%, or even zero

- more broadly, the content by weight of particles (in particular unmelted, crystals, pigments, and which may be diffusing particles, etc.) is preferably at most 1% of the total weight of the enamel deposited, dry or baked, in particular 0.5% and even 0.1%, or even zero

- to be colorless, the total content by weight of coloring elements (Fe ₂ O ₃ , CuO, CoO, Cr ₂ O ₃ , MnO ₂ , Se, Ag, Cu, Au, Nd ₂ O ₃ , Er ₂ O ₃ ) is d at most 0.5% and even 0.1% of the total weight of the vitreous matrix and even of the baked enamel and preferably zero (except for unavoidable impurities)

- the weight content of the vitreous matrix is at least 80%, 90%, 95% and even 100% of the total weight of the baked enamel

- the dry or baked enamel contains a weight content of impurities of at most 0.5% of the total weight of the enamel

For each of the aforementioned oxides or groups of oxides, each of the lower limits can be combined with each of the upper limits, all of the possible ranges not being recalled here for the sake of conciseness. Likewise, each range for a given oxide can be combined with any other range for the other oxides. Here again, not all combinations can be indicated so as not to make this text unnecessarily heavy.

Preferably, the glass frit of the dry or baked enamel (and even the dry or baked enamel) has a coefficient of thermal expansion and a glass transition temperature adapted to those of the glass sheet, and a low aptitude for devitrification.

The glass transition temperature Tg1 of the glass frit is low enough to be able to fire at temperatures at which the glass sheet cannot deform. At the same time, the frit must not crystallize (devitrify) during firing, which would have the effect of generating excessive roughness and high optical absorption.

Advantageously, the glass frit has a glass transition temperature Tg lower than that of the first sheet of glass, in particular lower than 590°C.

We consider here the beginning of the curve (“onset temperature”) for the determination of the Tg.

The coefficient of linear thermal expansion of the glass frit can also be adapted to that of the glass sheet, generally being close to the latter, or slightly lower, in order to avoid during cooling the appearance in the vitreous material of stresses mechanics that could damage it.

The coefficient of linear thermal expansion CT1 between 20 and 300°C of the glass constituting the glass frit is preferably within a range ranging from 70 to 100.10 ^-7 /°C, in particular 70 to 90.10 ^-7 /°C. In particular, the first sheet of glass has a coefficient of linear thermal expansion CT0 between 20 and 300°C tq CT0-CT1 is positive and is at most 10.10 ^-7 /°C.

The solvent serves to dilute if necessary to adjust the viscosity for the transfer generating at least partially disjoint patterns. It is also used to reduce the dry extract and therefore to reduce the thickness deposited.

For the choice of solvent, it is chosen such that the boiling temperature is high enough for it not to evaporate during the transfer (for the stability of the deposit). Preferably it is at least 190°C, 200°C or even 210°C.

The medium, the fluid composition, can be water-soluble or oil-compatible.

The organic resin can be of the acrylate or polyacrylate resin, alkyd resin, epoxy resin, polyurethane resin, amino resin, acrylic resin, polyester resin, polyamide resin, phenolic resin, and/or cellulosic resin type.

An alternative organic medium comprises (essentially) or even consists of a resin that can be crosslinked (by UV) without the addition of solvent. Curing then involves the cross-linking of the resin.

The invention also relates to greenhouse glazing, in particular obtained by the manufacturing process defined above, comprising a sheet of glass (soda-lime, float, clear or extra-clear, smooth) comprising on a first main face a set of dry enamel patterns capable of being transparent after firing, comprising a glass frit and an organic resin or transparent baked enamel comprising a molten glass frit forming a vitreous matrix, in particular rounded studs (with a convex surface, curved outwards), defined by :

a first lateral dimension of pattern, called first width, along a first given direction X, in particular width of the glazing, in a range going from 200 μm to 2000 μm, better still from 300 μm to 500 μm,

- a second lateral pattern dimension called second width, along a second given direction Y perpendicular to X: in a range going from 200 μm to 2000 μm, better still from 300 μm to 500 μm,

- a height H1 of dry enamel pattern in a range from 8µm to 60µm or a height H2 of fired enamel pattern in a range from 4µm to 30µm

- and a distance to the interpattern vertex in a range from 150µm to 1000µm, better still from 200µm to 900µm

- and for dry enamel patterns a height to first width aspect ratio in a range from 1/20 to 1/130 or for baked enamel patterns a height to first width aspect ratio of pattern d enamel in a range from 1/40 to 1/65.

Screen-printed enameled glazing is widely used in the following applications:

• as a decorative opaque layer or forming a masking frame, with a black enamel, and possibly a gradient of patterns in the direction of the glass clear
• as a diffusing opaque layer for optical functions such as video projection of images or for the extraction of light from a light guide, forming a layer forming for example a set of discrete white patterns.

Their opacity, optical properties and dimensions are not suitable for greenhouse glazing.

The desired blur value is dependent on the climate: the fewer the clouds, the more direct sunlight, the greater the blur should be.

To obtain a diffusing glass, while having a high transmission, a glass with patterns having specific slopes is advantageous.

The invention relates in particular to greenhouse glazing, in particular obtained by the manufacturing method defined above, comprising a sheet of glass (soda-lime, float, clear or extra-clear, smooth) comprising on a first main face a set of enamel patterns dry capable of being transparent after firing, comprising a glass frit and an organic resin, in particular rounded lumps (with a convex surface, curved outwards), defined by:

- a first lateral dimension of dry enamel pattern W1, called first width, along a first given direction X, in particular width of the glazing, W1 being in a range going from 200 μm to 2000 μm, better still from 300 μm to 500 μm,

- a second lateral dimension of dry enamel pattern L1 called second width, along a second given direction Y perpendicular to X: L1 being in a range going from 200 μm to 2000 μm, better still from 300 μm to 500 μm,

- a dry enamel pattern height H1 in a range from 8µm to 60µm,

- and a distance to the interpattern vertex D1 in a range going from 150µm to 1000µm, better still from 200µm to 900µm

- an H1/W1 aspect ratio in a range from 1/20 to 1/130.

The invention relates in particular to greenhouse glazing, in particular obtained by the manufacturing method defined above, comprising a sheet of glass (soda-lime, float, clear or extra-clear, smooth) comprising on a first main face a set of enamel patterns transparent baked comprising a molten glass frit forming a vitreous matrix, in particular rounded lumps (with a convex surface, curved outwards), defined by:

- a first lateral dimension of baked enamel pattern W2, called first width, along a first given direction X, in particular width of the glazing, W2 in a range going from 200 μm to 2000 μm, better still from 300 μm to 500 μm,

- a second lateral dimension of baked enamel pattern L2 called second width, preferably perpendicular to the first width, in a range going from 200 μm to 2000 μm, better still from 300 μm to 500 μm,

- a baked enamel pattern height H2 in a range from 4µm to 30µm

- and a distance to the interpattern vertex of baked enamel D2 in a range from 150µm to 1000µm, better still from 200µm to 900µm

- an H2/W2 aspect ratio in a range from 1/40 to 1/65.

The preferred ranges of dry or fired enamel patterns are:

the first width (W1 or W2) is in a range from 300µm to 500µm

- the second width (L1 or L2) is in a range from 300µm to 500µm

- the height H1 of dry enamel pattern is in a range from 8µm to 50µm, the height H2 of baked enamel pattern is in a range from 4µm to 25µm

- the distance to the interpattern vertex in a range from 200µm to 900µm

- and preferably for dry enamel patterns a height to first width (and even second width) aspect ratio in a range from 1/10 to 1/38 or for baked enamel patterns a ratio of height aspect over first enamel pattern width (and even over second width) in a range from 1/20 to 1/33.

Transparent enamel may be colorless. The glazing with the baked transparent enamel patterns according to the invention preferably has in the international colorimetry system L, a*, b* calculated in transmission (with D65 illumination):

- an absolute value of a* which is less than 10 or even 5 and preferably is less than 3

- and an absolute value of b* which is less than 10 or even 5 and preferably is less than 3

Preferably, the dry enamel composition comprises in % relative to the total weight of the dry enamel:

- 87.5% or 89% to 91% of glass frit capable of being transparent after firing

- 7.5% or 9% to 11% organic resin

and the cumulative % of glass frit and organic resin preferably being at least 98% or even 99% or 100%.

In particular, the dry enamel composition comprises at most 2% or 1% or 0% of mineral pigment and/or diffusing or reflecting particles.

Preferably, the baked enamel composition comprises, in % relative to the total weight of the enamel, at least 98% or even 99% of molten glass frit forming a transparent vitreous matrix (and even consists of the transparent vitreous matrix). In particular, the baked enamel composition comprises at most 2% or 1% of mineral pigment and/or diffusing or reflecting particles and preferably is free of mineral pigment and/or diffusing or reflecting particles.

The transparent baked enamel preferably has at most 5% by volume of porosities (open and/or closed) and preferably at most 3% by volume. In particular, the porosities are in lower concentration at the heart of the patterns.

Clear baked enamel may exhibit an intrinsic haze of at most 20% or even at most 10%. Intrinsic haze is the haze value when the baked enamel is a continuous layer at thickness H2.

The haze or Haze parameter is a standardized parameter, measured with a BYK Hazeguard device and described in ASTM D1003-C: Test Method for Haze and Luminous Transmittance of Transparent Plastics (haze at 2.5°).

The glass sheet, in particular float, smooth, is clear or extra-clear and the glazing with the patterns of transparent baked enamel has a light transmission within the meaning of standard EN410 of at least 70%, and even of at least 80% or 85%.

It is useful to characterize the enamel patterns optically in particular the diffusion given by the overall texture.

In one embodiment, the glazing (with the dry enamel or the baked enamel) has an average slope which is less than or equal to 12°, better still 10°, calculated in a zone of the glazing surface, called surface of analysis, square including at least 10 of said dry enamel or transparent baked enamel patterns and better still at least 50 patterns of said dry enamel or transparent baked enamel patterns or 100 patterns of said dry enamel or clear baked enamel

The percentage of textured surface with a slope beyond 2.5° or 1.5° contributes to the value of the blur.

To define the texture generated by the enamel patterns, it is measured using an optical profilometer such as the Micromesure 2 commercial device from STIL.

This measurement gives an elevation map of a surface.

The slope at a point on the surface designates the angle formed between the tangent plane at this point and the general plane of the glass sheet. The slope at a point is calculated from the measurement of the variation in height in the vicinity of this point obtained by the measurement with the profilometer and with respect to the general plane of the glass sheet.

From the surface topography data x,y,z (altitude z measured for pairs of surface coordinates x,y) we calculate the directional gradients along the principal axes x and y according to the method of Horn (Horn, BK ( 1981). Hill shading and the reflectance map. Proceedings of the IEEE , 69 (1), 14-47) which consists in estimating the gradient along one of the axes by the convolution of the altitude values and a kernel 3x3.

[Math 1]

dz/dx = [ (z(i-1, j + 1) + 2 z(i, j + 1) + z(i+1, j + 1)) - (z(i-1, j - 1) + 2z(i, j - 1) + z(i+1, j - 1)] / (8* step_x)

[Math 2]

dz/dy = [ (z(i - 1, j-1) + 2 z(i - 1, j) + z(i - 1, j+1)) - (z(i + 1, j-1) + 2 z(i + 1, j) +z(i + 1, j+1)) ] / (8* step_y)

To obtain the local slope, we then calculate the arctangent of the norm of the bidirectional gradient .

The measurement is carried out according to a selected square mesh of adapted micrometric period (for example 5 μm) and of adapted size (10×10 mm²) which makes it possible to calculate a distribution of the values of slopes of this zone. The average slope (Pm) of the surface is determined from the calculation of slopes on this zone.

From the distribution of slopes called DP, we calculate the diffusion function generated by the slope by refraction.

More precisely, in a zone of the glazing surface, called analysis surface, square including at least 10 of said patterns of dry enamel or of transparent baked enamel of enamel and better still at least 50 patterns or 100 patterns, one defines the following functions which depend on the angle θ of deviation of the light with respect to the normal incidence of the glazing, functions measured with a micrometric mesh of the analysis surface and

scattering function of a perfect Lambertian scatterer

diffusion function of said glazing

DP being the distribution of slopes, slopes between each pair of adjacent points of said mesh

[Math 5]

d(θ) = Y _s (θ) –Y _L (θ)

the difference of diffusion functions

we introduce the parameter d(θ)) which is the standard deviation of d(θ) with ranging from 0° to 75

which is in a range from 0.01 to 0.10.

And preferably

when parameters W1 and L1 are at most 800µm or parameters W2 and L2 are at most 800µm, the analysis surface is 10x10mm², with a square mesh with a pitch of 10µm or better than 5µm,

when the W1 and/or L1 parameter is greater than 800µm or the W2 and/or L2 parameter is greater than 800µm, the analysis surface is 50x50mm², with a square mesh with a pitch of 20µm.

Especially :

- d(θ)) ranges from 0.02 to 0.055 or even from 0.065 to 0.1.

- d(θ)) is within a range of 0.02 to 0.031 or 0.035 to 0.055 or 0.065 to 0.1.

The enamelled glazing according to the invention (dry or baked) can have a distribution of slopes as a function of the angle which is a decreasing function from 0° without rebound or peak from 1°

The enamelled glazing according to the invention (dry or baked) can have a distribution of slope as a function of the angle which is a decreasing function from 0° presenting a rebound or peak from 1° in particular starting at most at 6 ° or even 5° and preferably ending at less than 40° or 30° or 20° or 15°. Preferably, the angular distribution of slope has a point of inflection after the maximum of the rebound at an angle of at most 30° or even 25° or even 20°.

The enamelled glazing according to the invention (dry or baked) can have a distribution of slopes as a function of the angle which is an increasing function starting from 0° then decreasing after having reached a local maximum at most at 4° or even 3° and preferably ending at less than 40° or 30° or 20° or 15°. Preferably, the angular distribution of slope has a point of inflection after the local maximum at an angle of at most 30° or even 25° or even 20°.

The enamelled glazing according to the invention (dry or baked) can have a slope distribution as a function of the angle which is an increasing function starting from 0° then decreasing after having reached a local maximum at most at 4° or even 3° and exhibiting a rebound or peak starting at 3° and preferably ending at less than 40° or 30°. Preferably, the angular distribution of slope has a point of inflection after the maximum of the rebound at an angle of at most 30° or even 25° or even 20°.

Preferably the distribution of slopes as a function of the angle is determined in a zone of the glazing surface, called analysis surface, square including at least 10 of said dry enamel or transparent fired enamel patterns and better still at least 50 patterns of said dry enamel or clear baked enamel patterns or 100 patterns of said dry enamel or clear baked enamel patterns.

The analysis surface is advantageously meshed according to a chosen square mesh of adapted micrometric period (for example 5 μm) and of adapted size (for example 10x10mm²).

More precisely :

when parameters W1 and L1 are at most 800µm or parameters W2 and L2 are at most 800µm, the analysis surface is 10x10mm², with a square mesh with a pitch of 10µm or better than 5µm,

when parameter W1 and/or L1 is greater than 800µm or parameter W2 and/or L2 is greater than 800µm, the analysis surface is 50x50mm², with a square mesh with a pitch of 20µm.

The invention finally relates to a double glazing for a greenhouse comprising an external glazing and an internal glazing spaced apart and connected by a gasket at the periphery, one of the external or internal glazing being said glazing with the transparent baked enamel patterns already defined above, preferably the enamelled main face being the external face F1 or the face F2 of the external glazing.

The double glazing comprising sealing means, in particular against water and/or gas and water vapour, which are formed by means for fixing and/or sealing the spacer to the main faces of the two glazing. In particular, the sealing means comprise on the one hand means for fixing the spacer by bonding (the means for fixing by bonding being arranged at the interface between the spacer and the internal faces of the glazing), said means fixing forming a barrier to gas and water vapor such as butyl, and on the other hand a waterproof sealant, such as polyurethane, or polysulphide or silicone, arranged between the glazing (their inner face) and on the outer face of the spacer opposite the gas gap.

An example of a spacer has a rigid base body consisting of a thermoplastic material, of the styrene acrylonitrile (SAN) or polypropylene type, and reinforcing fibers, of the glass type, which are mixed with the thermoplastic material, as well as a sheet providing gas and water vapor tightness bonded to the face intended to be the outer face of the spacer in the position mounted in the glazing (arranged opposite the gas layer). The base body is hollow and additionally accommodates a desiccant. Such a spacer, based on SAN and glass fibers, is known for example under the trade name SWISSPACER ^® of the Applicant when the sealing sheet of the base body is made of aluminum, and under the name SWISSPACER V ^® when the Base body sealing sheet is made of stainless steel. Another example of a spacer is a flexible spacer made of solid material and incorporating desiccant.

There shows the general steps in the manufacture of a greenhouse glazing with enamel patterns by screen printing according to the invention.

The manufacturing process includes:

- a supply of a fluid composition of shear-thinning enamel, comprising a glass frit, an organic medium which comprises an organic resin and an organic solvent, composition capable of forming a transparent enamel after firing

- a positioning of a flat glass sheet 1 and with a first main face 11 spaced parallel and below a screen printing screen comprising a canvas 3 and a metal frame 40, at a non-zero distance Hg from the first main face between 2mm and 20mm, preferably between 4mm and 8mm, the canvas being blocked by an emulsion in areas called filled areas determining a set of separate fillable areas (in gray) defined by a width W0, a length L0, a height H0 and an interzone distance D0 between fillable zones, flat glass sheet on a table 5

- coating with the fluid composition on the canvas parallel to the plane of the canvas, leading to filling of said fillable areas with the fluid enamel composition,

- scraping of the fluid enamel composition on said canvas parallel to the plane of the canvas, using a polyurethane doctor blade 41 with a thickness of between 15mm and 35mm, preferably between 20 and 30mm, of hardness expressed in ShoreA of between 65 and 85, leading to a transfer of the fluid composition onto the first main face and thus to the formation of a set of disjoint fluid enamel patterns 20.

The pressure exerted by the squeegee during its stroke deforms the fabric by a height Hg and brings the enamel fluid into contact with the glass sheet.

The screen printing topping and/or scraping speed is at least 100mm/s and preferably at most 1000mm/min or 700mm/min.

The fluid composition has a viscosity in a range from 100 to 200 poise.

The fluid enamel composition comprises, in % relative to the total weight of the fluid enamel:

- from 45% to 80% of glass frit capable of being transparent after firing

- from 20 to 55% of the organic medium preferably comprising from 2% to 15% by weight of organic medium of organic resin and from 85% to 98% by weight of organic medium of organic solvent having a boiling point of at minus 190°C

the cumulative % in glass frit and organic medium being at least 95% or 98% or even 100%

Deposition of the fluid composition directly on the first face or on a functional underlayer on the first face.

Fillable areas are defined by

- W0 is in a range going from 200 to 2000µm better from 300 to 500µm,

- L0 is in a range going from 200 to 2000µm better from 300 to 500µm,

- an L0/W0 ratio ranging from 0.1 to 10, in particular from 0.5 to 2, (0.8 to 1.2 and if necessary from 0.95 to 1.05)

- D0 is in a range from 150 to 1000µm, better from 200µm to 900µm,

- H0 is in a range from 40µm to 170µm.

After the formation of said set of fluid enamel patterns, there is a step of hardening the fluid composition by treatment, in particular heat treatment at a temperature of at most 250° C. or by ultraviolet treatment or by electron beam, leading to said set disjoint patterns of dry enamel 21.

The composition of dry enamel comprises, in % relative to the total weight of dry enamel:

- from 89% to 91% of glass frit capable of being transparent after firing

- from 9% to 11% organic resin

the cumulative % in glass frit and organic resin being 98% or even 99% or 100%.

After the hardening step, a firing of at least 500° C., better at 600° C., takes place, leading to the formation of a set of transparent baked enamel patterns 22, preferably the firing being a heat treatment followed by a quenching operation.

The baked enamel composition comprises in % relative to the total weight of the enamel from 98% to 100% of transparent glass frit.

Clear baked enamel exhibits intrinsic haze of at most 20% or even at most 10%.

Glazing with baked transparent enamel patterns has in the international colorimetry system L, a*, b* calculated in transmission:

- an absolute value of a* which is less than 10 or even 5 and preferably is less than 3

- and an absolute value of b* which is less than 10 or else 5 and preferably is less than 3.

The glass sheet is clear or extra-clear and the glazing with the transparent baked enamel patterns has a light transmission within the meaning of the EN410 standard of at least 70%, and even at least 80% or 85%.

EXAMPLES

Six enamelled glazing units for greenhouses according to the invention, numbered from 1 to 6, were produced.

All the glasses are Diamond glass from the applicant company, 4mm thick, washed in a washing machine before screen printing.

Table 1 lists the main process parameters

Example glass frit Viscosity (poise) design mesh screen Cooking 1 Zn Borosilicate 120 1 32.70 690°C/190°s 2 Zn Borosilicate 120 1 32.70 710°C/185s 3 Zn Borosilicate 120 2 120.34 690°C/190°s 4 Bi Borosilicate 120 1 32.70 690°C/190°s 5 Bi Borosilicate 200 1 32.70 690°C/190°s 6 Bi Borosilicate 120 2 120.34 690°C/190°s

Design 1 is defined by round fillable areas of 0.4mm diameter forming a hexagonal mesh, with a D0 spacing of 0.4mm. 32.70 means a fabric weave with 32 threads per cm and a thread diameter of 70 µm.

Design 2 is defined by round-shaped fillable areas of 0.4mm diameter forming a hexagonal mesh, with a D0 spacing of 0.2mm. 34 µm wire.

The emulsion is of the HHU, HB Y or equivalent type (resistant to water and solvents)

Fluid composition A for examples 1 to 3 comprises a glass frit, an organic resin and an organic solvent which is tripropylene glycol methyl ether; (T boiling = 243°C)

The fluid composition B for examples 1 to 3 comprises a glass frit, an organic resin and an organic solvent which is dipropilenglicol monomethylether; (T boiling = 190°C).

Table 2 indicates the dimensions of the dry and then fired patterns.

W1 (µm) D1 (µm) H1 (µm) W2 (µm) H2 (µm) D2(µm) 1 400 400 29.1 300 20.4 500 2 400 400 30.8 300 21.6 500 3 400 200 12.8 350 9 450 4 400 400 19.4 300 12.6 500 5 400 400 19 250 14 550 6 400 200 10.8 350 7 450

Examples 1 and 2 differ only in the firing conditions

Figures 2 and 3 are optical microscopy images of Example 1.

Figures 4 and 5 are optical microscopy images of Example 3.

Examples 4 and 5 only differ in viscosity

Figures 6 and 7 are optical microscopy images of Example 4

Figures 8 and 9 are optical microscopy images of Example 5.

Figures 10 and 11 show profiles obtained with a contact profilometer of example 4 and example 5.

Figures 13 and 14 are optical microscopy images of Example 6.

There is a set of graphs showing the angular distribution of the slopes (on the ordinate number of strokes in arbitrary units and on the abscissa angle in degrees) for examples 4 (curve 2) and 5 (curve 1).

We observe for each a local maximum at less than 10°.

The viscosity of the enamel paste is adjusted to obtain patterns with interesting slopes. Indeed, an enamel with too low a viscosity will lead to a very flat pattern, with few slopes. For example, under the same deposit conditions, the same enamel with two different dilution rates gives different slopes

The patterns of Example 4 have a larger diameter than that of the enamel of Example 5. This logically leads to lower slopes in the case of the enamel of Example 5.

For example 4, the enamel creeped more (edge of the stud with a smooth appearance and width of the stud of 0.6 mm at the enamel/glass interface).

For example 5, the enamel has little or no creep (edge of the stud less smooth in appearance and width of the stud of 0.5mm at the enamel/glass interface). We also see at the top of the plot a significant roughness (or crater) which also contributes to the distribution of slopes.

DIFFUSION

To define the texture generated by the enamel patterns, it is measured using an optical profilometer such as the Micromesure 2 commercial device from STIL.

This measurement gives an elevation map of a surface.

The slope at a point on the surface designates the angle formed between the tangent plane at this point and the general plane of the glass sheet. The slope at a point is calculated from the measurement of the variation in height in the vicinity of this point obtained by the measurement with the profilometer and with respect to the general plane of the glass sheet.

From the surface topography data x,y,z (altitude z measured for pairs of surface coordinates x,y) we calculate the directional gradients along the main axes x and y according to the method of Horn (Horn, BK ( 1981). Hill shading and the reflectance map. Proceedings of the IEEE , 69 (1), 14-47) which consists in estimating the gradient along one of the axes by the convolution of the altitude values and a kernel 3x3.

[Math 7]

dz/dx = [ (z(i-1, j + 1) + 2 z(i, j + 1) + z(i+1, j + 1)) - (z(i-1, j - 1) + 2z(i, j - 1) + z(i+1, j - 1)] / (8* step_x)

[Math 8]

dz/dy = [ (z(i - 1, j-1) + 2 z(i - 1, j) + z(i - 1, j+1)) - (z(i + 1, j-1) + 2 z(i + 1, j) +z(i + 1, j+1)) ] / (8* step_y)

To obtain the local slope, we then calculate the arctangent of the norm of the bidirectional gradient .

The measurement is carried out according to a selected square mesh of adapted micrometric period (for example 5 μm) and of adapted size (10×10 mm²) which makes it possible to calculate a distribution of the values of slopes of this zone. The average slope (Pm) of the surface is determined from the calculation of slopes on this zone.

From the distribution of slopes called DP, we calculate the diffusion function generated by the slope by refraction.

More precisely, we define the following functions which depend on the angle θ of deviation of the light with respect to the normal incidence of the glazing,

scattering function of a perfect Lambertian scatterer

diffusion function of said glazing

DP being the distribution of slopes, slopes between each pair of adjacent points of said mesh

[Math 11]

d(θ) = Y _s (θ) –Y _L (θ)

the difference of diffusion functions

we introduce the parameter d(θ)) which is the standard deviation of d(θ) with ranging from 0° to 75

Table 3 collates the measurements of std and other optical parameters of various examples already described.

example Std(d) PM (°) TL (%) H (%) 1 0.028 3.6 91.1 23.5 2 0.034 5.2 91.2 22.6 4 0.035 3.8 89.6 22.2 6 0.039 2.2 91.5 18

There shows an altitude map of example 1 according to the invention.

There shows a map of the slope distribution of the example of the .

There is a set of graphs showing the angular distribution of the slopes (on the ordinate number of strokes normalized in arbitrary units and on the abscissa angle in degrees) for examples 1 (curve 1) 2 (curve 2) 4 (curve 3), 6 (curve 4).

We observe for each a local maximum at less than 10°.

Claims (19)

Process for manufacturing a glazing for a greenhouse characterized in that it comprises the formation of a glazing with a set of dry enamel patterns comprising the following steps:
- a supply of a fluid enamel composition, comprising a glass frit, an organic medium which comprises an organic resin and an optional organic solvent, composition capable of forming a transparent enamel after firing,
- a positioning of a flat glass sheet with a spaced first main face and below a screen printing screen comprising a canvas, at a non-zero distance Hg from the first main face, the canvas being blocked by an emulsion in zones called filled zones determining a set of disjoint fillable zones defined by a width W0, a length L0, a height H0 and an interzone distance D0 between fillable zones,
- coating with the fluid composition on the canvas leading to filling of said fillable areas with the fluid enamel composition,
- scraping of the fluid enamel composition on said canvas leading to a transfer of the fluid composition onto the first main face and thus to the formation of a set of disjointed fluid enamel patterns
characterized in that:
- fillable areas are defined by
- W0 is in a range from 200 to 2000µm
- L0 is in a range from 200 to 2000µm
- an L0/W0 ratio ranging from 0.1 to 10,
- D0 is in a range from 150 to 1000µm,
- H0 is in a range from 40µm to 170µm.
and in that it comprises, after the formation of said set of fluid enamel patterns, a step of hardening the fluid composition by a treatment, in particular heat treatment at a temperature of at most 250° C. or by ultraviolet treatment or by electron beam, leading to said set of dry enamel patterns . Method of manufacturing a glazing for a greenhouse according to Claim 1, characterized in that the sheeting speed and/or the screen printing scraping speed is at least 100mm/s and preferably at most 1000mm/min or even 700mm/min. Process for the manufacture of glass for a greenhouse according to one of the preceding claims, characterized in that the fluid composition has a viscosity in a range extending from 100 to 200Poises and even from 120 to 160Poises. Process for manufacturing greenhouse glazing according to one of the preceding claims, characterized in that the fluid enamel composition comprises, in % relative to the total weight of the fluid enamel:
- from 45% to 80% of glass frit capable of being transparent after firing
- from 20 to 55% of the organic medium preferably comprising from 2% to 15% by weight of organic medium of organic resin and from 85% to 98% by weight of organic medium of organic solvent
the cumulative % of glass frit and organic medium being at least 95% or 98% or even 100%. Process for manufacturing greenhouse glazing according to one of the preceding claims, characterized in that the organic medium comprises an organic solvent having a boiling point of at least 190°C. Process for manufacturing greenhouse glazing according to one of the preceding claims, characterized in that it comprises depositing the fluid composition directly on the first face or on a functional underlayer on the first face. Process for manufacturing a glazing for a greenhouse according to one of the preceding claims, characterized in that it comprises, after the hardening step, a firing of at least 500°C, better still at 600°C leading to the formation of a set of transparent baked enamel patterns, preferably the baking being a heat treatment followed by a quenching operation. Glazing for a greenhouse, in particular obtained by the manufacturing method according to one of the preceding claims, characterized in that it comprises a sheet of glass comprising on a first main face carrying a set of dry enamel patterns capable of being transparent after firing, comprising a glass frit and an organic resin, or of transparent baked enamel comprising a molten glass frit forming a vitreous matrix, patterns, in particular with a convex surface, patterns defined by:
a first lateral dimension of enamel pattern, called first width, along a first given direction X, in particular width of the glazing, in a range going from 200 μm to 2000 μm,
- a second lateral dimension of enamel pattern called second width, along a second given direction Y perpendicular to X, in a range going from 200 μm to 2000 μm,
- a height H1 of dry enamel pattern in a range from 8 μm to 60 μm or a height H2 of fired enamel pattern in a range from 4 μm to 30 μm
- a distance to the interpattern vertex in a range from 150µm to 1000µm,
- and for dry enamel patterns a height to first width aspect ratio in a range from 1/20 to 1/130 or for baked enamel patterns a height to first width aspect ratio of pattern d enamel in a range from 1/40 to 1/65. Greenhouse glazing according to the preceding claim, characterized in that:
the first width is in a range from 300µm to 500µm
- the second width is in a range from 300µm to 500µm
- the height H1 of dry enamel pattern is in a range from 8 µm to 50 µm, the height H2 of baked enamel pattern is in a range from 4 µm to 25 µm
- the distance to the interpattern vertex in a range going from 200 μm to 900 μm. Greenhouse glazing according to one of the preceding glazing claims, characterized in that the dry enamel composition comprises, in % relative to the total weight of the dry enamel:
- from 87.5% to 91% of glass frit capable of being transparent after firing
- from 7.5% to 11% organic resin,
preferably the cumulative % of glass frit and organic resin being 98% or even 99% or 100%. Greenhouse glazing according to one of the preceding glazing claims, characterized in that the baked enamel composition comprises, in % relative to the total weight of the enamel, from 98% to 100% of transparent glass frit. Greenhouse glazing according to one of the preceding glazing claims, characterized in that the transparent baked enamel has at most 5% by volume of porosities and preferably at most 3% by volume. Greenhouse glazing according to one of the preceding glazing claims, characterized in that the transparent baked enamel has an intrinsic haze of at most 20% or even at most 10%. Greenhouse glazing according to one of the preceding glazing claims, characterized in that the glazing with the fired transparent enamel patterns has in the international colorimetry system L, a*, b* calculated in transmission:
- an absolute value of a* which is less than 10 or even 5 and preferably is less than 3
and an absolute value of b* which is less than 10 or else 5 and preferably is less than 3. Greenhouse glazing according to one of the preceding glazing claims, characterized in that the glass sheet is clear or extra-clear and the glazing with the transparent baked enamel patterns has a light transmission within the meaning of standard EN410 of at least 70 %, and even at least 80% or 85%. Greenhouse glazing according to one of the preceding glazing claims, characterized in that it has an average slope which is less than or equal to 12°, better still 10°, calculated in a zone of the glazing surface, called the surface of analysis, square including at least 10 of said dry enamel or clear fired enamel patterns. Greenhouse glazing according to one of the preceding glazing claims, characterized in that in a zone of the glazing surface, called the analysis surface, square including at least 10 of the said dry enamel or transparent fired enamel patterns of enamel and better still at least 50 patterns or 100 patterns, the following functions are defined which depend on the angle θ of deviation of the light with respect to the normal incidence of the glazing, functions measured with a micrometric mesh of the analysis surface And

scattering function of a perfect Lambertian scatterer

diffusion function of said glazing
DP(2θ) being the distribution of slopes, slopes between each pair of adjacent points of said mesh
[Math 15]
d(θ) = Y _s (θ) –Y _L (θ)
d(θ) being the difference of the diffusion functions
we introduce the parameter d(θ)) which is the standard deviation of d(θ) with ranging from 0° to 75

which is in a range from 0.01 to 0.10 Greenhouse glazing according to the preceding claims, characterized in that d(θ)) ranges from 0.02 to 0.055. Double glazing for a greenhouse comprising an external glazing and an internal glazing spaced apart and connected by a seal at the periphery, one of the external or internal glazing being the said glazing with the patterns of transparent baked enamel according to one of the preceding claims of glazing, preferably the enamelled main face being the external face F1 or the face F2 of the external glazing.