PROCESS FOR MANUFACTURING A GLAZING, AND GLAZING THEREBY PRODUCED

Abstract

A glazing comprises a glass substrate having an enamel layer adhered to at least a first surface portion, the enamel comprising 20 to 80 wt % frit and 10 to 50 wt % inorganic pigment. The thickness of the enamel layer is 2 ?m to 50 ?m, and the inorganic pigment has an infra-red reflectance such that the infra-red reflectance of the first portion of the glass substrate surface is 37% or higher over a region in the wavelength range 800 nm to 2250 nm. The glazing may be laminated, and may be a vehicle windscreen. A process for producing the glazing involves applying ink to a glass substrate, curing the ink thereby producing an enamel adhered to the glass substrate, and shaping the glass substrate by heating to a temperature above 570? C. The preferred inorganic pigments are of the Fe and/or Cr type in spinel, haematite or corundum crystal form.

Claims

1. A glazing comprising a glass substrate having a layer of enamel adhered to at least a first portion of a surface of the glass substrate, the enamel comprising 20 to 80 wt % frit and 10 to 50 wt % inorganic pigment, wherein the thickness of the layer of enamel is in the range 2 ?m to 50 ?m, the inorganic pigment having an infra-red reflectance such that the infra-red reflectance of the first portion of the surface of the glass substrate is 37% or higher over a region in the wavelength range 800 nm to 2250 nm.

2. A glazing as claimed in claim 1, wherein the infra-red reflectance of the first portion of the glazing is 38% or higher over a region in the wavelength range 800 nm to 2250 nm.

3. A glazing as claimed in claim 1, wherein the region in the wavelength range 800 nm to 2250 nm extends over 400 nm or greater.

4. A glazing as claimed in claim 1, wherein the enamel comprises 10 wt % to 40 wt % inorganic pigment.

5. A glazing as claimed in claim 1, wherein the enamel comprises 30 wt % to 80 wt % frit.

6. A glazing as claimed in claim 1, wherein the inorganic pigment comprises a material exhibiting substantially a spinel crystal structure, an inverse spinel crystal structure, a haematite crystal structure, a corundum crystal structure or a rutile crystal structure.

7. A glazing as claimed in claim 1, wherein the inorganic pigment comprises a pigment selected from a Fe/Cr pigment, a Co/Al pigment, a Co/Al/Cr pigment a Co/Ti pigment, a Co/Cr pigment, a Ni/Fe/Cr pigment, a Ti/Cr/Sb pigment, a Fe pigment, a Cr pigment, a chromium-iron pigment, a ferrite pigment, a chromite pigment, a ferrite/chromite pigment (also known as iron chromite) and/or a mixture of two or more of these pigments.

8. A glazing as claimed in claim 1, wherein the inorganic pigment is selected from one or more of pigment blue 28 (CI 77346), pigment blue 29 (CI 77007), pigment green 50 (CI 77377), pigment black 30 (NiCrMn type; CI 77504), pigment black 33 (CI 77537), pigment blue 36 (CI 77343), pigment green 17 (FeCr type; CI 77288), pigment brown 35 (FeCr type; CI 77501), pigment brown 24 (CI 77310), pigment brown 29 (FeCr type; CI 77500), pigment yellow 164 (CI 77899), pigment brown 33 (ZnFeCr type; CI 77503).

9. A glazing as claimed in claim 1, wherein the enamel comprises iron (determined as Fe.sub.2O.sub.3) in an amount of 5 wt % or greater of the total weight of the enamel.

10. A glazing as claimed in claim 1, wherein the enamel comprises chromium (determined as Cr.sub.2O.sub.3) in an amount of 5 wt % or greater of the total weight of the enamel.

11. A glazing as claimed in claim 1, wherein the enamel comprises chromium (determined as Cr.sub.2O.sub.3) in an amount of 25 wt % or lower of the total weight of the enamel.

12. A glazing as claimed in claim 1, wherein the thickness of the enamel layer adhered to the glass substrate is in the range 4 ?m to 45 ?m.

13. A laminated glazing according to claim 1, comprising a first glass ply serving as the glass substrate having the layer of enamel adhered to at least a first portion of a surface of the glass ply, a second glass ply and a polymer ply of interlayer which extends between the first and second glass plies.

14. A process for producing a glazing, the process comprising, providing a glass substrate, providing an enamel ink comprising 20 to 80 wt % frit, 10 to 50 wt % inorganic pigment and 10 to 40 wt % liquid medium, applying the enamel ink to at least a first portion of a surface of the glass substrate, optionally drying and/or curing the ink, optionally pre-firing the ink to a temperature above 480? C., and shaping the glass substrate by heating to a temperature above 570? C., thereby firing the enamel ink to produce a layer of enamel adhered to at least the first portion of the surface of the glass substrate, wherein the thickness of the layer of enamel is in the range 2 ?m to 50 ?m, the inorganic pigment having an infra-red reflectance such that the infra-red reflectance of the first portion of the surface of the glass substrate is 37% or higher over a region in the wavelength range 800 nm to 2250 nm.

15. A process for producing a shaped laminated glazing, the process comprising, providing a first glass substrate and a second glass substrate, providing an enamel ink comprising 20 to 80 wt % frit, 10 to 50 wt % inorganic pigment and 10 to 40 wt % liquid medium, applying the enamel ink to at least a first portion of a surface of the first glass substrate, optionally drying and/or curing the ink, optionally pre-firing the ink to a temperature above 480? C., and shaping at least the first glass substrate by heating to a temperature above 570? C. thereby firing the enamel ink to produce a layer of enamel adhered to at least the first portion of the surface of the first glass substrate, wherein the thickness of the layer of enamel is in the range 2 ?m to 50 ?m, placing a polymer ply of interlayer between the first and second glass substrates, and laminating the first glass substrate, the polymer ply and the second glass substrate together, the enamel being adapted such that the infra-red reflectance of the first portion of the surface of the first glass substrate is 37% or higher over a region in the wavelength range 800 nm to 2250 nm.

16. A glazing as claimed in claim 1, wherein the infra-red reflectance of the first portion of the glazing is 39% or higher over a region in the wavelength range 800 nm to 2250 nm.

17. A glazing as claimed in claim 1, wherein the infra-red reflectance of the first portion of the glazing is 40% or higher over a region in the wavelength range 800 nm to 2250 nm.

18. A glazing as claimed in claim 1, wherein the infra-red reflectance of the first portion of the glazing is 41% or higher over a region in the wavelength range 800 nm to 2250 nm.

19. A glazing as claimed in claim 1, wherein the region in the wavelength range 800 nm to 2250 nm extends over 450 nm or greater.

20. A glazing as claimed in claim 1, wherein the region in the wavelength range 800 nm to 2250 nm extends over 550 nm or greater.

21. A glazing as claimed in claim 1, wherein the region in the wavelength range 800 nm to 2250 nm extends over 610 nm or greater.

Description

[0080] The present invention will now be described by way of example only, and with reference to, the accompanying drawings, in which:

[0081] FIG. 1(a) is a schematic plan view of a laminated windscreen according to the invention and (b) is a schematic cross-sectional view of the windscreen of (a) on line A-A.

[0082] FIG. 2 is a graph showing IR reflectance as a function of wavelength for a number of enamelled glass substrates using enamels according to Example 1, Example 2, Comparative Example A and Comparative Example B.

[0083] FIG. 3 is a graph showing temperature (T) and ?T as a function of time for enamelled glass substrates using enamels according to Example 1 and Comparative Example C during the firing and annealing temperature zones of the firing/shaping process.

[0084] FIG. 1 illustrates a laminated glazing 10 according to the invention comprising an outer glass ply 18 with an outer surface 26 (surface 1, the outside surface when installed in a vehicle) and an inner glass ply 22 with an inner surface 24 (surface 4, inside when installed in a vehicle) laminated together by means of a polymer interlayer 20 of polyvinyl butyral (PVB).

[0085] The laminated glazing is a windshield for a motor vehicle. Around the periphery of the laminated glazing 10 is printed on the inner glass ply 22, on the inner surface 24, an enamel obscuration band 12. The obscuration band comprises a layer of enamel formed by screen printing an enamel ink on the surface, curing/drying the ink and then firing the it thereby producing an enamel on the inner surface 24. The enamel (having the composition as in Example 1 or Example 2, below) comprises a frit and at least one inorganic pigment containing iron and chromium. At the boundary 16 between the clear glass and the obscuration band 12 there is an area susceptible to buntline optical distortion. In glazings according to the invention, buntline optical distortion is much reduced or prevented owning to the enamel used. At points 1, 2, 3, 4 and 5 as illustrated in FIG. 1 (a) optical distortion in glazings according to the invention (see Examples, below) and comparative examples may be determined.

[0086] A laminated glazing as illustrated in FIG. 1 may be made generally as follows. A flat glass substrate (e.g. 2.1 mm thick soda lime float glass) is subjected to screen printing (using a screen that may have e.g. 50 to 120 threads/cm polyester screen for example 77 or 100 threads/cm polyester screen) by a silk-screen and doctor blade with an enamel ink (having the composition, for example, as in Example 1 or Example 2, see below) to form a screen-printed border which is optionally dried by subjecting this substrate to infrared radiation from an infrared heater at a temperature below 300? C. Two glass substrates (one unprinted) are then stacked and the stacked substrates are subjected to bending. In this stage, a source of heat is provided and bending can be effected, usually by heating over 8 minutes to a temperature of 570? C., held at this temperature for a period of one minute and then bent at this temperature in any standard bending mould or frame by press or sag bending, The substrates are separated and then, after cooling, are laminated together using a PVB interlayer (about 0.76 mm thick).

[0087] The glazing may be laminated by methods involving, for example, first a nip roller or using a vacuum ring applied to the edges of the first and second plies of glass to de-gas the PVB layer. The first and second glass plies and the PVB layer are laminated together in an autoclave in the pressure range 6 bar to 14 bar and in the temperature range 110? C. to 150? C.

[0088] In FIG. 2, a graph of reflectance as determined by a Perkin Elmer Lambda 950 spectrophotometer as a function of wavelength is shown for samples of fired enamel (at 570? C.) on 4 mm float glass showing difference in properties for enamel as used in Example 1 applied using a 77 threads/cm polyester screen (curve 30) or a 100 threads/cm polyester screen (curve 34), enamel as in Example 2 using a 77 threads/cm polyester screen (curve 35) or a 100 threads/cm polyester screen (curve 36) and enamel as used in Comparative Example B (curve 38) or Comparative Example A (curve 40).

[0089] The inventive enamels exhibit reflectance higher than 27% in regions of greater than 400 nm over the range 800 nm to 2250 nm and have proven to be excellent at reducing burnline optical distortion. The enamels used were generally of the composition indicated in Table 1 and Table 2 (Example 1, Example 2 and Comparative Example A, and B), below.

[0090] In FIG. 3, temperature and ?T as a function of time for enamelled glass substrates using enamels as used in Example 1 (enamel ink composition as indicated in Table 1) and Comparative Example C exhibit a significant difference in temperature throughout the process. As shown in Table 5 and 6, Example 1 enamel exhibits much reduced burnline distortion. While not wishing to be bound, it is thought that because the infra-red reflectance and temperature properties of enamels according to Example 1 are closer to the clear, enamel-free glass, the temperature difference between the enamelled and enamel-free areas is reduced, as is the viscosity difference, and hence so is differential glass flow and optical distortion. The behaviour of enamelled and enamel-free areas at glass bending temperatures becomes more uniform, and therefore optical distortion is less likely to occur.

[0091] The invention is further illustrated, but not limited, by the following Examples.

EXAMPLES

[0092] Enamel films were produced by screen printing ceramic ink compositions containing either an infrared reflective inorganic pigment according to the present disclosure or an infrared absorbing conventional inorganic pigment. Table 3 presents details of the frit used for Examples 1 and 2 and Comparative Example A:

TABLE-US-00003 TABLE 3 Component (wt. %) Variance (wt. %) SiO.sub.2 19.92 ?5 Bi.sub.2O.sub.3 59.12 ?1 ZnO 2.73 ?2 K.sub.2O 0.14 ?0.5 Na.sub.2O 3.09 ?3 ZrO.sub.2 0.86 ?0.5 Al.sub.2O.sub.3 2.14 ?2 B.sub.2O.sub.3 10.76 ?5

[0093] Each ink formulation used in the Examples contained 59.7 wt. % (+5 wt. %) frit, 23.3 wt. % (?3 wt. %) pigment, and 17 wt. % (?2 wt. %) vehicle. In Example 1 the pigment used was chromium iron oxide pigment brown 29 (CI 77500; CAS 12737-27-8). In Example 2 the pigment used was chromium green black haematite (CI 77288; CAS 68909-79-5).

[0094] Enamels according to Examples 1 and 2, were screen printed using a 100 or 77 threads/cm screen to print a ceramic ink composition including a frit and an infrared reflective inorganic pigment, both in accordance with the present disclosure. 20-25 micron thick film (we-firing) resulted from 100 threads/cm screen printing; 26-30 micron thick film (pre-firing) resulted from 77 threads/cm screen printing.

[0095] In Comparative Example A the conventional inorganic pigment used was a commercially available standard black pigment.

[0096] As stated above, a compositionally similar frit to that which was used in Examples 1 and 2 and in Comparative Example A. The same vehicle was used, which included glycol and glycol ethers as well as a cellulosic resin. Thus, the only variable changed between Examples 1 and 2 and Comparative Example A was the use of an infrared reflective inorganic pigment in Examples 1 and 2 versus the use of an infrared absorbing pigment in Comparative Example A

[0097] Example 1 had an enamel layer 11.2 ?m thick (by SEM after firing), Example 2 had an enamel layer 12.6 ?m thick (by SEM after firing) and Comparative Example B had an enamel layer 13.6 ?M thick (by SEM after firing).

[0098] X-ray diffraction (XRD) was conducted on the printed fired samples for enamels according to Example 1, Example 2 and Comparative Example B using a Bruker D8 Discover X-ray diffractometer using monochromatic Cu K?1 and Cu K?2 radiation of wavelengths 0.154056 and 0.154439 nm respectively, emitted with a voltage of 40 kV and a current of 40 mA in an intensity ratio of 2:1.

[0099] X ray diffraction shows that (crystalline material only) enamels according to Example 1 and Example 2 contain CrFeO.sub.3 (chromium iron oxide) with corundum type structure (rhombohedral). Enamel according to Comparative Example B contains FeMnNiO.sub.4 (manganese iron nickel oxide) (cubic).

Burnline Example 1 and Comparative Example B

[0100] The composition of the enamel according to Comparative Example B and C is as indicated in Table 4 below. Analysis was semi-quantitative by inductively coupled plasma mass spectrometry (ICP) (for boric oxide and lithium oxide) and X ray fluorescence (XRF) (CERAM, using Methods C201, C15 and BS EN ISO12677). Prior to analysis samples of the ink were dried at 110? C. and fired at a temperature above 400? C. to remove components (including organic components) of the liquid medium.

TABLE-US-00004 TABLE 4 Comparative Comparative Example B Example C Component (dried wt %) (dried wt %) Aluminium Oxide 0.59 1.58 Antimony (III) Oxide 0.01 0.01 Barium Oxide 0.16 0.01 Bismuth (III) Oxide 37.81 39.95 Boric Oxide (by ICP) 4.16 8.22 Calcium Oxide 0.02 0.01 Chromium (III) Oxide 5.99 18.1 Copper Oxide 1.08 9.5 Hafnium (IV) Oxide 0.01 0.01 Iron (III) Oxide 2.27 0.01 Lead Oxide 0.02 0.02 Lithium Oxide (by ICP) 1.5 0.01 Magnesium Oxide 0.05 0.05 Manganese (II, III) Oxide 3.62 0.02 Nickel Oxide 2.92 0.01 Phosphorus Pentoxide 0.15 0.03 Potassium Oxide 0.66 0.11 Silicon Dioxide 25.7 13.68 Sodium Oxide 1.4 1.94 Strontium Oxide 0.02 0.04 Sulphur Trioxide 0.05 0.07 Tin (IV) Oxide 0.33 0.01 Titanium Dioxide 2.98 0.05 Vanadium Pentoxide 0.14 0.01 Zinc Oxide 1.49 1.65 Zirconium Oxide 0.13 0.51

[0101] Enamels according to Example 1 and Comparative Example B were screen printed on surface 4 to produce obscuration bands on laminated windscreens generally as discussed above in relation to FIG. 1.

[0102] Windscreens were laminated and optical distortion at bottom burnline positions 1 to 5 (referring to the points indicated in FIG. 1(a)) was determined using a Zebra test using a printed white under-sheet having parallel black lines 12 mm apart. Distortion was determined by viewing the distorted black lines against a white board and measuring maximum width and minimum width at five positions across the windscreen. The test is deemed passed if the rate of change (maximum width?minimum width)?4 mm and the minimum width>8.5 mm. Inclination angle was 60?.

[0103] Optical distortion results for two repeat comparative samples for Comparative Example B are given in Table 5, below. Results for two repeat samples for Example 1 are given in Table 6 below. Use of the IR reflective enamel according to the invention significantly reduces burnline optical distortion. In Tables 5 and 6, A indicates Maximum Distortion, B Indicates Minimum Distortion, C indicates Rate of Change and D indicates Distance from Band.

[0104] Enamels suitable for use in the invention are available from Prince Minerals Limited, of Duke Street, Fenton, Stoke-on-Trent, Staffordshire, United Kingdom, ST4 3NR; also from Prince Minerals LLC, P.O. Box 251, Quincy, Ill. 62306, USA and 15311 Vantage Parkway West, Suite 350, Houston, Tex. 77032, USA.

TABLE-US-00005 TABLE 5 Point 1 Point 2 Point 3 Point 4 Point 5 Sample A B C D A B C D A B C D A B C D A B C D Comparative Sample n.sup.o1 12.7 8.8 3.9 33.0 12.8 8.2 4.6 39.0 12.7 6.4 6.3 37.0 13.0 7.8 5.2 44.0 12.6 8.3 4.3 45.0 Comparative Sample n.sup.o2 12.2 8.5 3.7 40.0 12.8 7.6 5.2 41.0 12.2 6.1 6.1 43.0 12.8 8.2 4.6 37.0 12.9 8.7 4.2 38.0

TABLE-US-00006 TABLE 6 Point 1 Point 2 Point 3 Point 4 Point 5 Sample A B C D A B C D A B C D A B C D A B C D Example 12.0 10.8 1.2 38.0 12.2 9.8 2.4 39.0 12.3 9.4 2.9 45.0 12.0 10.2 1.8 36.0 12.1 11.3 0.8 34.0 Sample n.sup.o1 Example 12.1 10.6 1.5 34.0 12.0 9.9 2.1 41.0 12.1 9.5 2.6 42.0 12.2 10.1 2.1 39.0 12.2 10.9 1.3 38.0 Sample n.sup.o2