GLASS SHEET WITH HIGH NEAR-IR TRANSMISSION AND VERY LOW VISIBLE TRANSMISSION

Abstract

A glass sheet having a high near-IR transmission and very low visible transmission. The glass sheet is a silicate-type and has a composition that includes, in a content expressed as weight percentages, by total weight of glass: total iron (expressed as Fe.sub.2O.sub.3) 0.02-1%, Chromium (expressed as Cr.sub.2O.sub.3) 0.05-0.8%, Cobalt (expressed as Co) 0.03-0.175%. The glass sheet shows, intrinsically, a very low visible transmission together with a high IR transmission at wavelengths of interest (i.e. 850, 900 and 950 nm) and low amounts of Cr.sup.6+ species. The glass sheet is therefore valuable within the context of autonomous cars and in particular, those with fully integrating LiDAR systems.

Claims

1: A glass sheet of silicate-type comprising: in a content expressed as weight percentages, by total weight of glass: TABLE-US-00008 total iron (expressed as Fe.sub.2O.sub.3)    0.02-1%, Chromium (expressed as Cr.sub.2O.sub.3)  0.05-0.8%, Cobalt (expressed as Co) 0.03-0.175%, and having wherein: Cr.sub.2O.sub.3<1-5.5*Co, and 1.2<Cr.sub.2O.sub.3/Fe.sub.2O.sub.3≤2.7.

2: The glass sheet according to claim 1, wherein the composition comprises: chromium (expressed as Cr.sub.2O.sub.3)≤0.5%.

3: The glass sheet according to claim 1, wherein the composition comprises: chromium (expressed as Cr.sub.2O.sub.3)≤0.3%.

4: The glass sheet according to claim 1, wherein the composition comprises: chromium (expressed as Cr.sub.2O.sub.3)≥0.1%.

5: The glass sheet according to claim 1, wherein the composition comprises: total iron (expressed as Fe.sub.2O.sub.3)≤0.8%.

6: The glass sheet according to claim 1, wherein the composition comprises: total iron (expressed as Fe.sub.2O.sub.3)≥0.04%.

7: The glass sheet according to claim 1, wherein the composition comprises: total iron (expressed as Fe.sub.2O.sub.3)≥0.06%.

8: The glass sheet according to claim 1, wherein the composition comprises: cobalt (expressed as Co)≤0.12%.

9: The glass sheet according to claim 1, wherein the composition comprises an Fe.sup.2+ content (expressed in the form of FeO) of less than 40 ppm.

10: The glass sheet according to claim 1, wherein the glass sheet comprises a TLD4 lower than 10%.

11: The glass sheet according to claim 1, wherein the glass sheet comprises a T.sub.850 higher than 80%.

Description

4. DETAILED DESCRIPTION OF THE INVENTION

[0024] The invention relates to a glass sheet of silicate-type having a composition comprising, in a content expressed as weight percentages, by total weight of glass:

TABLE-US-00001 total iron (expressed as Fe.sub.2O.sub.3)    0.02-1%, Chromium (expressed as Cr.sub.2O.sub.3)  0.05-0.8%, Cobalt (expressed as Co) 0.03-0.175%,
and having:

[0025] Cr.sub.2O.sub.3<1-5.5*Co,

[0026] 1.2<Cr.sub.2O.sub.3/Fe.sub.2O.sub.3≤2.7.

[0027] Hence, the invention lies on a novel and inventive approach since it enables to find a solution for the disadvantages of prior art. The inventors have indeed found that, it is possible to get a glass sheet showing at the same time (i) a very low intrinsic visible transmission, (ii) a high IR transmission in the region 850-950 nm and (iii) a low amount of Cr.sup.6+ species, by using in an iron-based glass matrix, chromium and cobalt in specific amounts while carefully adjusting, in a narrow range, the ratio between chromium and total iron.

[0028] In order to obtain high transmission in the infrared region in soda-lime silicate glasses including intrinsically some amounts of iron coming as an impurity in the majority of the starting materials used, it is known to reduce at maximum the amount of ferrous Fe.sup.2+ ions in the glass. Indeed, ferrous ions (sometimes expressed as oxide FeO) in soda-lime-silicate glasses absorb in the near infrared region due to their broad absorption band centered on 1050 nm. In known chromium-containing low-iron glasses, chromium is added in an amount adapted to oxidize all Fe.sup.2+ into Fe.sup.3+ in order to get high near-IR transmission. As chromium is known since years as a classical powerful colorants for glass, increasing further the chromium content of the glass above the threshold required to fully oxidized iron will bring a strong decreasing of visible transmission while keeping the high level of IR transmission as Fe.sup.2+ is at zero-amount, as described in WO2015/091106. However, in those glasses, the amount of Cr.sup.6+ in the composition is high (above 300 ppm). It was surprisingly found by the inventors that it is possible to drastically reduce the amount of Cr.sup.6+ (while keeping high IR transmission) by carefully adjusting the ratio Cr.sub.2O.sub.3/Fe.sub.2O.sub.3 in a matrix richer in iron so that the final glass has both low Fe.sup.2+ and Cr.sup.6+ concentrations.

[0029] In present description and claims, to quantify the visible transmission (also called luminous transmission/transmittance or TL) of a glass sheet, one considers the visible transmission with illuminant D65 for a sheet thickness of 4 mm (TLD4) at a solid angle of observation of 2° (according to standard ISO9050). The visible transmission (TL) represents the percentage of radiation flux emitted between wavelengths 380 nm and 780 nm which is transmitted through the glass sheet.

[0030] In present description and claims also, to quantify the IR transmission, one considers the transmission for a sheet thickness of 4 mm at a solid angle of observation of 2° (according to standard ISO9050), representing the percentage of radiation flux emitted at a specific wavelength in the near IR range namely 850 nm (T.sub.850), 900 nm (T.sub.900) and 950 nm (T.sub.950) which is transmitted through the glass sheet.

[0031] Other features and advantages of the invention will be made clearer from reading the following description of preferred embodiments, given by way of simple illustrative and non-restrictive examples.

[0032] Throughout the present text, when a range is indicated, the extremities are included, except if explicitly described in another way. In addition, all the integral and subdomain values in the numerical range are expressly included as if explicitly written. Also, throughout the present text, the values of content are in percentage by weight expressed with respect to the total weight of the glass (also mentioned as wt %), except if explicitly described in another way (i.e. in ppm). Moreover, when a glass composition is given, this relates to the bulk composition of the glass.

[0033] The term “glass”, within the meaning of the invention, is understood to mean a completely amorphous material, thus excluding any crystalline material, even partially crystalline material (such as, for example, glass-crystalline or glass-ceramic materials).

[0034] The glass sheet of the invention may be manufactured starting from melting a glass raw materials batch in a glass melting furnace/tank and then forming the resulting molten glass into the desired shape, using a floating process, a drawing process, a rolling process or any other process known to manufacture a glass sheet starting from a molten glass composition. In an embodiment of the invention, the glass sheet is a float glass sheet. The term “float glass sheet” is understood to mean a glass sheet formed by the known float glass process. Other forming/processing treatment may follow the manufacturing process.

[0035] By “glass sheet” in present invention, it is meant a glass article in a sheet-like form including flat glass, curved glass, bent glass, lens, etc.

[0036] The glass sheet according to the invention may have varied sizes, from small sizes (for example, for cover lenses), through medium sizes (for example, for automotive glazings) to very large sizes (up to “DLF” or “PLF” sizes). The glass sheet according to the invention may also have a thickness of from 0.1 to 25 mm, depending on the targeted applications. Preferably, the glass sheet according to the invention has a thickness of from 1 to 8 mm and, more preferably, from 1.5 to 5 mm.

[0037] According to the invention, the composition comprises total iron (expressed in terms of Fe.sub.2O.sub.3) as follows: 0.02-1%. In present description, when talking about total iron content in glass composition, “total iron” and “Fe.sub.2O.sub.3” are used as well and total iron is expressed in terms of Fe.sub.2O.sub.3. According to an advantageous embodiment, the composition comprises total iron≤0.8%. Preferably, the composition comprises total iron≤0.6%, or even better ≤0.4%. More preferably, the composition comprises total iron≤0.3%, or even better ≤0.2%. According to another advantageous embodiment, the composition comprises total iron ≤0.03%. Preferably, the composition comprises total iron≥0.04%, or even better ≥0.05%. More preferably, the composition comprises total iron≥0.06%.

[0038] According to an embodiment of the invention, the composition of the glass sheet is free of manganese. By “free of manganese” according to the invention, it is meant that the composition comprises manganese (expressed as MnO)≤0.02%. More preferably, the composition comprises manganese (expressed as MnO)≤0.01%, even ≤0.005%.

[0039] According to another embodiment of the invention, the composition of the glass sheet is free of lithium. By “free of lithium” according to the invention, it is meant that the composition comprises lithium (expressed as Li.sub.2O)≤0.1%. More preferably, the composition comprises lithium (expressed as Li.sub.2O)≤0.05%. even ≤0.01%.

[0040] According to another embodiment of the invention, the composition of the glass sheet is free of barium. By “free of barium” according to the invention, it is meant that the composition comprises lithium (expressed as BaO)≤0.1%. More preferably, the composition comprises barium (expressed as Ba0)≤0.05%. even ≤0.01%.

[0041] According to the invention, the composition comprises chromium (expressed as Cr.sub.2O.sub.3) as follows: 0.05-0.8%. Preferably, the composition comprises chromium (expressed as Cr.sub.2O.sub.3)≤0.5%, even better ≤0.4%. More preferably, the composition comprises chromium (expressed as Cr.sub.2O.sub.3)≤0.3%, even more better ≤0.25%. Preferably, the composition comprises chromium (expressed as Cr.sub.2O.sub.3)≥0.08%, even better ≥0.1%. More preferably, the composition comprises chromium (expressed as Cr.sub.2O.sub.3)≥0.15%.

[0042] According to the invention, the composition comprises cobalt (expressed as Co) as follows: 0.03-0.175%. Preferably, the composition comprises cobalt (expressed as Co)≤0.15%, even ≤0.12%. More preferably, the composition comprises cobalt (expressed as Co)≤0.1%.

[0043] According to an embodiment of the invention, the composition comprises an Fe.sup.2+ content (expressed in the form of FeO) of less than 40 ppm. This range of contents makes it possible to obtain highly satisfactory properties in terms of transmission of the IR radiation. Preferably, the composition comprises an Fe.sup.2+ content (expressed in the form of FeO) of less than 30 ppm, even less than 20 ppm. Very preferably, the composition comprises an Fe.sup.2+ content (expressed in the form of FeO) of less than 10 ppm and even better, less than 5 ppm.

[0044] According to an embodiment of the invention, the composition comprises a SO.sub.3 content as follows: 0.1-<0.2%.

[0045] According to another embodiment of the invention, the glass sheet has a visible transmission TLD4 lower than 15% and preferably lower than 12%, or even lower than 10%. More preferably, the glass sheet has a visible transmission TLD4 lower than 8%, or even lower than 7%, or better lower than 6%, or even more better lower than 5%. Opacity is improved when TLD4 decreases more and more. Ideally, the glass sheet has a visible transmission TLD4 lower than 3%, even lower than 1%. Complete opacity is reached when TLD4 approaches closely or is equal to 0.

[0046] According to another embodiment of the invention, the glass sheet has a transmission T.sub.950 higher than 80% and preferably higher than 82%. More preferably, the glass sheet has a transmission T.sub.950 higher than 85% and very preferably higher than 87%. In a very preferred embodiment, the glass sheet has a transmission T.sub.950 higher than 90%.

[0047] According to another embodiment of the invention, the glass sheet has a transmission T.sub.900 higher than 80% and preferably higher than 82%. More preferably, the glass sheet has a transmission T.sub.900 higher than 85% and very preferably higher than 87%. In a very preferred embodiment, the glass sheet has a transmission T.sub.900 higher than 90%.

[0048] According to still another embodiment of the invention, the glass sheet has a transmission T.sub.850 higher than 80% and preferably higher than 85%. More preferably, the glass sheet has a transmission T.sub.850 higher than 87% and very preferably higher than 90%.

[0049] According to still another embodiment of the invention, the composition comprises a Cr.sup.6+ content ≤60 ppm. Preferably, the composition comprises a Cr.sup.6+ content≤40 ppm, even ≤30 ppm. More preferably, the composition comprises a Cr.sup.6+ content≤20 ppm, even ≤10 ppm. In a most preferred embodiment, the composition is free of Cr.sup.6+. The Cr.sup.6+ content in glass can be computed, in a known manner, based on the transmission spectra and the linear absorption coefficients of the cation. These absorption coefficients are based on Bamford data (Bamford, C. R. (1977). Colour generation and control in Glass. Glass Science and Technology, 2, pp 224, Elservier Scientific Publishing Company.)

[0050] The glass sheet according to the invention may be a glass sheet obtained by a float process, a drawing process, or a rolling process or any other known process for manufacturing a glass sheet from a molten glass composition. According to a preferred embodiment according to the invention, the glass sheet is a float glass sheet. The term “float glass sheet” is understood to mean a glass sheet formed by the float process, which consists in pouring the molten glass onto a bath of molten tin, under reducing conditions. A float glass sheet comprises, in a known way, a “tin face”, that is to say a face enriched in tin in the body of the glass close to the surface of the sheet. The term “enrichment in tin” is understood to mean an increase in the concentration of tin with respect to the composition of the glass at the core, which may or may not be substantially zero (devoid of tin).

[0051] The silicate glass sheet according to the invention is made of glass which may belong to various categories. The glass can thus be a glass of soda-lime-silicate, aluminosilicate or borosilicate type, and the like. Preferably, the composition of the glass sheet comprises the following in weight percentage, expressed with respect to the total weight of glass:

TABLE-US-00002 SiO.sub.2 40-78%  Al.sub.2O.sub.3 0-18% B.sub.2O.sub.3 0-18% Na.sub.2O 0-20% CaO 0-15% MgO 0-10% K.sub.2O 0-10% BaO .sup. 0-5%.

[0052] In an embodiment, the composition of the glass sheet comprises MgO≥0.1% and preferably, MgO≥0.5%.

[0053] More preferably, notably for low production costs reasons, the glass composition is a soda-lime-silicate-type glass. According to this embodiment, by “soda-lime-silicate-type glass”, it is meant that the composition comprises the following in weight percentage, expressed with respect to the total weight of glass:

TABLE-US-00003 SiO.sub.2 60-78 wt % Al.sub.2O.sub.3 0-8 wt % B.sub.2O.sub.3 0-4 wt % CaO 0-15 wt % MgO 0-10 wt % Na.sub.2O 5-20 wt % K.sub.2O 0-10 wt % BaO 0-5 wt %.

[0054] According to this embodiment, preferably, the glass composition comprises the following in weight percentage, expressed with respect to the total weight of glass:

TABLE-US-00004 SiO.sub.2 60-78 wt % Al.sub.2O.sub.3 0-6 wt % B.sub.2O.sub.3 0-1 wt % CaO 5-15 wt % MgO 0-8 wt % Na.sub.2O 10-20 wt % K.sub.2O 0-10 wt % BaO 0-1 wt %.

[0055] In another embodiment of the invention, the composition comprises the following in weight percentage, expressed with respect to the total weight of glass:

[0056] 65≤SiO.sub.2≤78 wt %

[0057] 5≤Na.sub.2O≤20 wt %

[0058] 0≤K.sub.2O<5 wt %

[0059] 1≤Al.sub.2O.sub.3<6 wt %

[0060] 0≤CaO<4.5 wt %

[0061] 4≤MgO≤12 wt %

[0062] (MgO/(MgO+CaO))≤0.5.

[0063] In particular, examples of base glass matrixes for the composition according to the invention are described in published PCT patent applications WO2015/150207A1, WO2015/150403A1, WO2016/091672, WO2016/169823 and WO2018/001965.

[0064] The composition of the glass sheet can comprise, in addition to the impurities present in particular in the starting materials, a low proportion of additives (such as agents which help the melting or the refining of the glass) or of components originating from the dissolution of the refractories constituting the melting furnaces.

[0065] The glass composition of the invention may also comprise some other colorants than those described in relation with present invention (namely iron, cobalt and chromium), as impurities due mainly to particular contaminated raw materials. Examples of such impurities are molybdenum, nickel, copper.

[0066] Advantageously, the glass sheet of the invention may be tempered, mechanically or chemically. It may also be bended/curved, or in a general manner, deformed to reach any desired configuration (by cold-bending, thermoforming, . . . ). It may also be laminated.

[0067] According to one embodiment of the invention, the glass sheet of the invention may be covered by at least one coating. Examples of such coating are: [0068] a transparent and electrically conducting thin layer (i.e. a layer based on SnO.sub.2:F, SnO.sub.2:Sb or ITO (indium tin oxide), ZnO:Al or also ZnO:Ga; [0069] an antireflection layer; [0070] an anti-fingerprint layer or has been treated so as to reduce or prevent fingerprints from registering; [0071] a lay-out of black enamel for aesthetics and improvement of bonding; [0072] a network of silverprint for heating function; and/or [0073] an anti-soiling and/or hydrophobic layer.

[0074] According to the targeted applications and/or properties desired, other layer(s)/treatment(s) can be deposited/done on one and/or the other face of the glass sheet according to the invention.

[0075] The glass sheet of the invention can advantageously be used as an automotive glazing, especially as a trim. In such a case, in the context of autonomous cars, a LIDAR system may be fully integrated in the car (thereby guaranteeing aesthetic and preventing damages to the system), mounted behind internal face of said glazing.

[0076] Therefore, the invention also relates to the use of the glass sheet according to the invention in: [0077] as an automotive glazing, preferably as a trim element; or [0078] as a cover lens for a LIDAR sensor.

[0079] Even if the context of present invention has been described with the specific application of car-integrated LIDAR systems, the glass sheet of the invention can also advantageously be used in any other technology requiring very low transmission or a very intense colour for the glass, together with very good performances in the near IR range, especially for 850-950 nm. For example, it can be enhanceable in value in the “Planar Scatter Detection” (PSD) or “Frustrated Total Internal Reflection” (FTIR) optical technology for detecting the position of one or more objects (for example, a finger or a stylus) on a surface of said sheet which, in view of its more or less intense to opaque color, is capable of partially or completely hiding objects/components found behind/under it.

[0080] Still as examples of uses, the glass sheet of the invention can also be enhanced in value:

[0081] (1) as decorative panel positioned in front of/around radiant heating, hiding (partially or completely) the unattractive side of the heating but allowing the IR radiation to pass and thus making possible a good output from said heating;

[0082] (2) as architectural or decorative spandrel glass;

[0083] (3) as cooking plate, in replacement of the expensive special glasses commonly used (vitroceram or borofloat or even pyrex);

[0084] (4) as pointing device on portable computers (commonly known as “touchpad”), sometimes using a technology requiring infrared radiation. In this case, the glass sheet is preferably very dark, indeed even opaque, in color and thus hides the electronic components located under it;

[0085] (5) as front face element of furniture and in particular of furniture intended to include remote controllable electrical/electronic appliances, hiding from view the unattractive side of such appliances but allowing the signal emitted by the remote controls to pass. This is because the majority of domestic electrical/electronic appliances (televisions, hi-fis, DVD players, games consoles, and the like) are remote controllable using a housing which emits signals in the near infrared region. However, this remote control system exhibits in particular two disadvantages: (i) the signal is often disrupted by the presence of secondary radiation in the visible region (sun, lights), which render it less sensitive, and (ii) it requires that the appliances be reachable by the IR signal of the remote control and thus these cannot be concealed inside an item of furniture, even if demand is nevertheless proceeding in this direction for aesthetic reasons.

[0086] Embodiments of the invention will now be further described, by way of examples only, together with some comparative examples, not in accordance with the invention. The following examples are provided for illustrative purposes, and are not intended to limit the scope of this invention.

EXAMPLES

[0087] Different glass sheets/samples, according to the invention or comparative, were either (i) prepared in the lab (“lab”), or (ii) calculated/simulated (“simu”), with variable amounts of total iron, chromium, cobalt.

[0088] * For the lab preparation of glass sheets: the starting materials were mixed in the powder form to produce about 240 g of a reduced batch according to the following table, to which were added starting materials comprising total iron, chromium and cobalt in variable amounts as a function of the contents targeted in the final composition (it should be noted that the iron being already, at least in part, present in the starting materials of the base composition as impurity):

TABLE-US-00005 Raw material Amount (g.) sand 141-146 limestone   0-10.3 dolomite 39-52 soda 47-48 Alumina (Al.sub.2O.sub.3) 0-2 Coke  0.1-0.12 Sulfate (Na.sub.2SO.sub.4) 1.4

[0089] The mixture was placed in a crucible and then heated up in an electrical furnace to a temperature allowing complete melting of the mixture.

[0090] The base glass composition finally obtained was:

TABLE-US-00006 SiO.sub.2 (wt %) 70.8-72.2 Al.sub.2O.sub.3   0-0.62 CaO 8.7-9.2 MgO 4.1-5.5 Na.sub.2O 13.7-14.3 SO.sub.3 0.15-0.19

[0091] The optical properties of each sample, moulded and processed in the form of a sheet, were determined on a Perkin Elmer Lambda 950 spectrophotometer equipped with an integrating sphere with a diameter of 150 mm, and in particular: [0092] the near-infrared transmission was determined according to the ISO9050 standard for a thickness of 4 mm at a solid angle of observation of 2° and for specific wavelengths, namely 850 nm (T.sub.850), 900 nm (T.sub.900) and 950 nm (T.sub.950); [0093] the light transmission TL was also determined according to the ISO9050 standard for a thickness of 4 mm at a solid observation angle of 2° (with illuminant D65) and for a wavelength range between 380 and 780 nm.

[0094] * For the simulation/computation of glass sheets: the optical properties were computed on the basis of optical properties of different glass colorants (using linear absorption coefficient, determined for the concerned base glass matrix, to build the complete optical spectra and compute the parameters of interest). The base glass matrix considered in computation is the same as for lab samples.

[0095] Table 1 presents the composition features and optical properties for Examples 1 to 12.

[0096] Examples 1 to 4 and 11-12 correspond to comparative examples while Examples 5-10 correspond to glass sheets according to the invention.

[0097] Each Examples 5-10 according to the invention was optimized to reach: [0098] 1) to maximize its transmission of near infrared radiation, especially at 850, 900 and/or 950 nm, to reach in particular values above 80% and better above 85%;

[0099] while [0100] 2) minimizing its visible transmission TL, in particular to reach values <15% and more preferably values below 10%, 5% (reaching then almost opacity), and [0101] 3) low amounts of hexavalent chromium, Cr.sup.6+ (especially, below 30 ppm and better below 20 ppm, and more better close to 10 ppm).

TABLE-US-00007 TABLE 1 Ex1 Ex2 Ex3 Ex4 Ex5 Ex6 Ex7 Ex8 Ex9 Ex10 Ex11 Ex12 lab lab lab lab lab lab lab lab simu lab lab lab Fe.sub.2O.sub.3 (wt %) 0.038 0.10 0.053 0.066 0.076 0.086 0.11 0.18 0.26 0.146 0.26 0.195 Cr.sub.2O.sub.3 (wt %) 0.19 0.37 0.19 0.19 0.19 0.19 0.19 0.28 0.40 0.19 0.28 0.19 Co (wt %) 0.10 0.07 0.10 0.10 0.12 0.10 0.10 0.10 0.07 0.10 0.10 0.10 TLD4 (%) 2.16 3.7 2.22 2.25 1.4 2.27 2.47 1.97 3.8 2.24 1.9 2.27 T.sub.850 (%) 88.04 86.2 87.88 87.96 87.70 87.76 87.51 84.2 87.8 87.6 72.8 70.8 T.sub.900 @ (%) 87.73 87.5 87.69 87.69 87.20 87.64 87.34 84.4 88.7 87.5 71.8 69.2 T.sub.950 @ (%) 86.26 86.4 86.23 86.24 84.70 86.16 85.87 83.06 86.3 86.1 70.1 67.3 1-5.5*[Co] 0.45 0.62 0.45 0.45 0.34 0.45 0.45 0.45 0.62 0.45 0.45 0.45 Cr.sub.2O.sub.3/Fe.sub.2O.sub.3 5.02 3.70 3.59 2.90 2.50 2.23 1.75 1.56 1.55 1.30 1.08 0.98 Cr.sup.6+ (ppm) 52 51 47 39 26 24 12 4 11 18 0 0 FeO (ppm) 1 2 1 1 2 2 3 13 9 10 233 315

[0102] The objective of the invention, namely getting 1), 2) and 3) in a glass sheet can be reached, as shown by the results from table 1 with the features of claim 1.