Patent Description:
Glazings for electric heating having a conductive coating on a glass substrate are well known. Busbars are known to supply current to the conductive coating. It is known to remove areas of the conductive coating to make non-conductive barriers which constrain current flow paths to achieve a desired heat distribution.

<CIT>) discloses a glass plate having a conductive film. Current is not supplied to the entire surface of the film, but is limited by slits in the film, so the current is supplied along a limited current path.

<CIT>) discloses an electrically heatable glazing panel with a conductive coating layer, divided into zones.

<CIT>) discloses an electrically heatable glass panel with a conductive coated layer divided into at least two separated zones.

<CIT>) discloses a laminated glazing with an electrically conductive layer, first and second busbars arranged along two opposing edges and ablation lines of the conductive layer closing on themselves forming non-conducting strips, each strip occupying a major portion of the distance between the busbars.

<CIT>) discloses an electrically heated window with a conductive film. A first region is provided with openings so that current flowing in the region is bypassed by the openings. <CIT>) discloses a region between two busbars having a plurality of openings.

<CIT> discloses a glazing according to the preamble of claim <NUM>.

There remains a need for an alternative glazing for electric heating.

An objective of the invention is to provide a glazing for electric heating having, in use, a desired heat distribution and/or improved defrosting. Another objective is to provide a simple method of manufacturing a glazing for electric heating.

In a first aspect, the present invention provides a glazing for electric heating comprising the features set out in claim <NUM>.

The invention provides a glazing for electric heating, comprising a glass sheet; a conductive coating arranged on a surface of the glass sheet; first and second busbars spaced from each other and in electrical contact with at least part of the conductive coating to form a heated coating; a plurality of coating-free lines arranged in at least two rows in the heated coating; wherein each coating-free line is surrounded by the heated coating and each line is separated from the next line in a row by a gap, and wherein an opening ratio of gap length divided by a sum of gap length and line length is in a range from <NUM> to <NUM> %. If line length and next line length differ, then opening ratio is calculated from the longer of the two.

The invention is greatly advantageous because a glazing having coating-free lines arranged in at least two rows in a heated coating so that each coating-free line is surrounded by the heated coating has a more desirable heat distribution and thus improved defrosting. Perceived defrosting occurs faster because at least one series of lines and gaps has an opening ratio in a predetermined range.

Surprisingly, the inventors have found that coating-free lines surrounded by the heated coating allow current to flow around both ends of each line forming warm spots at each end, rather than an undesirable hotspot at one end and a cold spot at the other end. Warm spots arranged in a row cause faster perceived defrosting along the row than in a conventional glazing, because a user perceives sooner that defrosting has started.

Furthermore, warm spots arranged in at least two rows cause faster defrosting in a region between the rows than in a conventional glazing because lengths of gaps in each row can be chosen to arrange current paths in the region, in particular to avoid cold edges of the heated coating and/or to provide more heat in a central vision area.

A result of the invention is that the glazing meets industrial test requirements for defrosting, for example for a vehicle window.

The invention also eliminates the unheated areas of conventional glazings, which have lines closing on themselves forming non-heated portions of conductive coating.

In an advantageous embodiment, adjacent rows are arranged so that their warm spots are aligned with each other in columns to provide a plurality of straight current paths between busbars. The plurality of straight current paths between busbars provides a low resistance heating element in the form of an "abacus".

In an alternative advantageous embodiment, adjacent rows are arranged so that their warm spots are offset from each other to provide a plurality of meandering current paths. Meandering current paths form a labyrinth eliminating a straight current path between busbars. The labyrinth allows warm spots to be arranged in various patterns, such as "ducks", where adjacent offset warm spots resemble beaks and tails and adjacent regions between warm spots resemble heads and bodies of ducks.

Preferably, each line at the end of a row is more than a minimum distance from an edge of the heated coating, more preferably the minimum distance from the edge of the heated coating is in a range from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, most preferably from <NUM> to <NUM>.

Preferably, each line comprises first and second ends.

Preferably, the gaps in adjacent rows are aligned with each other to provide a plurality of straight paths for current.

Preferably, the gaps in adjacent rows are offset from each other to provide a plurality of meandering current paths.

Preferably, the lines have a shape selected from straight, arcuate, or sinusoidal.

Preferably, the lines have a length in a range from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, most preferably from <NUM> to <NUM>.

Preferably, the gaps have a length in a range from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, most preferably from <NUM> to <NUM>.

An opening ratio of gap length divided by a sum of gap length and line length is in a range from <NUM> to <NUM> %, preferably from <NUM> to <NUM> %, most preferably from <NUM> to <NUM> %.

Preferably, all lines in a row have one of two lengths, more preferably all lines in a row have equal length, most preferably lines in a row have similar lengths to lines in an adjacent row.

Preferably, all gaps in a row have one of two lengths, more preferably all gaps in a row have equal length, most preferably gaps in a row have similar lengths to gaps in an adjacent row.

Preferably, gaps having a first gap length are between a first series of lines having a first line length to form a first heating zone. Preferably, gaps having a second gap length are between a second series of lines having a second line length to form a second heating zone. Preferably, first and second lines in a row are separated by a first gap having a first gap length. Preferably, second and third lines in the row are separated by a second gap having a second gap length. Preferably, the second gap length is greater than or equal to the first gap length. Preferably, first and second series of lines alternate to form interleaved heating zones. Preferably, gaps in the row are aligned with gaps in an adjacent row to form a channel.

Preferably, the conductive coating comprises a layer of a metal or a transparent conductive oxide, preferably a doped transparent conductive oxide. Preferably, the layer comprises silver, or tin oxide, or fluorine doped tin oxide. Preferably, the conductive coating comprises two, three or four layers of silver. Preferably, an undercoat layer is positioned between the conductive coating and the glass plate, the undercoat layer comprising silicon, more preferably silicon and oxygen, most preferably silicon and oxygen and carbon. Preferably, the conductive coating is pyrolytically deposited or sputtered.

Preferably, the conductive coating has sheet resistance less than <NUM> ohms/square, more preferably less than <NUM> ohms/square, most preferably less than <NUM> ohms/square.

Preferably, a power density in the heated coating is in a range from <NUM> to <NUM>,<NUM> W/m<NUM>, more preferably from <NUM> to <NUM>,<NUM> W/m<NUM>, most preferably from <NUM> to <NUM> W/m<NUM>.

Preferably, first and second busbars are arranged along opposite edges of the glass sheet.

Preferably, first and second busbars comprise silver. First and second busbars may be printed using a conductive ink comprising silver powder, silver spheres, graphite powder, graphite rods, carbon nanotubes or glass flakes having a conductive coating or are printed using sprayed particles or are shaped as strip or braid comprising copper.

Preferably, the coating-free lines have width in a range from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, most preferably from <NUM> to <NUM>.

In a second aspect, the present invention provides a method for manufacturing a glazing comprising the steps set out in claim <NUM>.

The invention provides a method for manufacturing a glazing according to the invention, comprising steps: providing a glass sheet; arranging a conductive coating on a surface of the glass sheet; arranging first and second busbars spaced from each other and in contact with at least a part of the conductive coating to form a heated coating; arranging a plurality of coating-free lines in at least two rows in the heated coating; wherein each coating-free line is surrounded by the heated coating; wherein each line is separated from the next line in a row by a gap; and wherein an opening ratio of gap length divided by a sum of gap length and line length is in a range from <NUM> to <NUM> %.

Preferably, the method for manufacturing a glazing further comprises a step of pyrolytically depositing the conductive coating. Preferably, the coating is deposited by Chemical Vapour Deposition (CVD).

Preferably, the method for manufacturing a glazing further comprises a step of forming the lines by laser deletion of the heated coating.

In a third aspect, the present invention provides use of a glazing according to the invention as a heated window of a vehicle for land, sea and air, for example as a windshield, a rear window, a side window or a roof window of a motor vehicle. The invention may also be used as an electric heater for a building, for example mounted on a wall or a window in a refrigerator door or in street furniture.

The invention will now be further disclosed by non-limiting drawings, non-limiting examples and a comparative example.

<FIG> discloses a glazing (<NUM>) for electric heating according to the invention comprising a glass sheet (<NUM>) and a conductive coating (<NUM>) arranged on a surface of the glass sheet.

The glass sheet is preferably soda lime silica glass, manufactured using the float process. Glass thickness is preferably in a range from <NUM> to <NUM>. The glass sheet may be toughened glass with surface stress greater than <NUM> MPa, or heat strengthened glass with surface stress in a range from <NUM> to <NUM> MPa, or semi-toughened with surface stress in a range from <NUM> to <NUM> MPa, or annealed glass. The glass sheet may be monolithic or laminated to another glass sheet having between them a ply of interlayer material, preferably polyvinyl butyral (PVB).

The conductive coating (<NUM>) may comprise a transparent conductive oxide such as tin oxide or fluorine-doped tin oxide deposited on the glass sheet (<NUM>) during the glass manufacturing.

First and second busbars (<NUM>, <NUM>) are arranged spaced from each other and in electrical contact with at least part of the conductive coating (<NUM>) to form a heated coating (<NUM>').

The heated coating (<NUM>') is partly bounded, for example at top and bottom as shown in <FIG>, by inner edges of first and second busbars (<NUM>, <NUM>). First and second busbars (<NUM>, <NUM>) may have any shape, for example straight or arcuate. First and second busbars (<NUM>, <NUM>) may comprise any conductive material, for example silver.

A portion of the conductive coating (<NUM>) between first and second busbars (<NUM>, <NUM>) forms the heated coating (<NUM>').

The heated coating (<NUM>') may be partly bounded, for example at left and right sides as shown in <FIG>, by left and right sides of the conductive coating (<NUM>).

An optional deletion line (not shown) in the conductive coating (<NUM>) may prevent current flow to a portion of the conductive coating (<NUM>) where heating is not required. For example, in a trapezoidal windscreen having horizontal busbars, a vertical deletion line may electrically isolate a side portion where heating may not be required.

A plurality of coating-free lines is arranged in at least two rows (<NUM>, <NUM>) in the heated coating (<NUM>'). The lines may be any shape, for example straight, arcuate or sinusoidal. The rows may be parallel with each other. The rows may be substantially parallel with first or second busbars (<NUM>, <NUM>) or substantially parallel with both. Substantially parallel means parallel within <NUM> degrees.

Removal of conductive coating material may be by laser deletion, mechanical abrasion or other methods known in the art. Width of the coating-free lines is typically in a range from <NUM> to <NUM>.

Each coating-free line is surrounded by the heated coating (<NUM>'). By contrast, conventional glazings disclose a deletion line serving as a barrier to current flow arranged at an edge of the heatable area, resulting in an undesired cold spot at the edge and an undesired hot spot at a distal end of the deletion line.

First and second rows (<NUM>, <NUM>) comprise lines and gaps between the lines. In the first row (<NUM>), lines may be of any non-zero lengths and gaps may be of any non-zero lengths. Second row (<NUM>) may also have lines of any non-zero lengths and gaps of any non-zero lengths and may be aligned with, or at any offsets from, the first row (<NUM>). For example, in <FIG> lines in a row are of similar line length, gaps in a row are of similar gap length, and adjacent rows are similar to each other. In use, current paths are straight, aligned vertically through the gaps. Warm spots are at each gap, like beads on an abacus. An "abacus" pattern provides a low resistance heating element.

<FIG> discloses an advantageous glazing (<NUM>) according to the invention, similar to <FIG>. Each line at the end of a row is more than a minimum distance (<NUM>) from an edge of the heated coating (<NUM>'). For example, the minimum distance (<NUM>) from the edge of the heated coating (<NUM>') is in a range from <NUM> to <NUM>. The minimum distance is non-zero and may be selected, in combination with a gap length at a distal end of the line, to provide a desired warm spot at each end of the line.

In <FIG>, second row (<NUM>) is offset from first row (<NUM>). In use, meandering current paths form a labyrinth. The labyrinth allows warm spots to be arranged in a "ducks" pattern, where warm spots offset from each other horizontally in adjacent rows resemble beaks and tails of ducks marching in single file, and adjacent regions between the warm spots resemble heads and bodies of the ducks.

<FIG> discloses a glazing (<NUM>) according to the invention like <FIG> but further comprising a gap length (<NUM>) between lines in first and second rows (<NUM>, <NUM>) and a line length (<NUM>) of the lines in first and second rows (<NUM>, <NUM>). As disclosed in relation to <FIG>, line lengths and gap lengths may be any non-zero lengths.

<FIG> discloses a glazing (<NUM>) according to the invention like <FIG>, but further comprising an offset (<NUM>) between adjacent rows. As disclosed in relation to <FIG>, gaps may be aligned or offset horizontally in adjacent rows.

<FIG> discloses a glazing (<NUM>) according to the invention like <FIG> and <FIG> but also comprising further rows (<NUM>', <NUM>'). As disclosed in relation to <FIG>, an "abacus" pattern provides a low resistance heating element, but to keep resistance low and have more rows it is necessary to increase gap length (<NUM>).

<FIG> discloses a glazing (<NUM>) according to the invention like <FIG> but also comprising a further gap length (<NUM>') and/or a further line length (<NUM>'). Any number of heating zones may be provided. For example, as shown in <FIG>, original dimensions (<NUM>, <NUM>) are for left and right edge zones and the further dimensions (<NUM>', <NUM>') are for a centre zone, making a total of three heating zones having smaller gaps in centre zone than edge zones. <FIG> shows a short gap (<NUM>) alternating with a long gap (<NUM>') forming interleaved heating zones and an offset (<NUM>) between rows (<NUM>, <NUM>).

<FIG> discloses a glazing (<NUM>) according to the invention like <FIG>, in use as seen with infrared imaging equipment. The "abacus" pattern comprises three heating zones. Left and right edge heating zones have warm spots of higher temperature than warm spots in the centre heating zone. Warm spots in the edge heating zones form warm channels which are advantageous for defrosting.

<FIG> discloses the embodiment of <FIG> in use, as simulated with thermal modelling software. The "ducks" pattern is visible, as disclosed in relation to <FIG>.

A comparative example and an example of a glazing according to the invention were manufactured for a rear window of a motor vehicle. In a defrosting test, similar to ISO <NUM>:<NUM> "Passenger cars - Windscreen defrosting and demisting systems - Test method" or <NUM> CFR section <NUM> "Windshield defrosting and defogging systems" glazings were cooled to -<NUM> (or <NUM> °F) then heated by applying a voltage to busbars on the glazing. First visible defrosting time and defrosting completed time were recorded.

The comparative example was a glazing comprising a conductive coating and two horizontal busbars at top and bottom, defining a heated coating. The applied voltage of <NUM> V provided a power density of <NUM> W/m<NUM>. First visible defrosting was at <NUM> minutes. Defrosting completed at <NUM> minutes.

The example according to the invention was a glazing comprising a conductive coating and two horizontal busbars at top and bottom, defining a heated coating. The heated coating had four rows of deletion lines. Each deletion line was surrounded by the heated coating. Line length was <NUM>. Gaps between the lines alternated between a first gap length <NUM> and a second gap length <NUM>, as <FIG>. Opening ratio was <NUM>% for the first gap length divided by the sum of that and line length. The applied voltage of <NUM> V provided a power density of <NUM> W/m<NUM>. First visible defrosting was at <NUM> minutes. Defrosting completed at <NUM> minutes. The example had a faster time to first visible defrosting. Defrosting completed later than the comparative example, but the difference was not significant because perceived defrosting performance was improved.

Examples according to the invention, as shown in present <FIG>, disclose coating-free lines in rows (<NUM>, <NUM>, <NUM>', <NUM>'), each line surrounded by heated coating (<NUM>'). Table <NUM> below discloses results of simulations using thermal modelling software (Examples <NUM>-<NUM> and <NUM>) and glazing samples (Examples <NUM>-<NUM>).

Claim 1:
A glazing (<NUM>) for electric heating, comprising:
- a glass sheet (<NUM>);
- a conductive coating (<NUM>) arranged on a surface of the glass sheet (<NUM>);
- first and second busbars (<NUM>, <NUM>) spaced from each other and in electrical contact with at least part of the conductive coating (<NUM>) to form a heated coating (<NUM>');
- a plurality of coating-free lines arranged in at least two rows (<NUM>, <NUM>) in the heated coating (<NUM>');
- wherein each coating-free line is surrounded by the heated coating (<NUM>'); and
- wherein each line is separated from the next line in a row by a gap;
characterised in that an opening ratio of gap length divided by a sum of gap length and line length is in a range from <NUM> to <NUM> %.