WO2004082934A1

WO2004082934A1 - Laminated vehicular glazing

Info

Publication number: WO2004082934A1
Application number: PCT/IT2004/000135
Authority: WO
Inventors: Giovanni Gagliardi; Luigi Di Mario
Original assignee: Pilkington Italia S.P.A.
Priority date: 2003-03-21
Filing date: 2004-03-19
Publication date: 2004-09-30
Also published as: JP2006523601A; EP1608504A1

Abstract

A laminated vehicular glazing (10, 30) comprising electrical heating means and at least one busbar (11) of electrically conductive material far connecting the electrical heating means to a power source is disclosed. Glazing (10, 30) is constructed from at least two plies of glazing material (21, 22) and a ply of interlayer material (23) extending therebetween. The electrical heating means may include an array of wires (12) or a conductive coating (31). The electrically conductive material is a polymeric material (preferably a thermoplastic) having electrically conductive particles (preferably silver flakes) dispersed within it. Further disclosed is: a) a method of manufacturing a laminated vehicular glazing (10, 30) including the step of imparting heat to the electrically conductive material as it is applied to a surface of glazing (10, 30) thereby creating an adhesion between the two, and b) an apparatus (70) far manufacturing a laminated vehicular glazing (10, 30) comprising means far dispensing (72) the electrically conductive material onto a surface of glazing (10, 30) and means to pre-heat (73) the surface of glazing (10, 30) prior to the electrically conductive material being dispensed.

Description

LAMINATED VEHICULAR GLAZING

DESCRIPTION

The present invention relates to a glazing, and a method and apparatus for the manufacture of such a glazing. More particularly the present invention relates to a laminated vehicular glazing constructed from at least two plies of glazing material and a ply of interlayer material which extends between the plies of glazing material, the glazing comprising electrical heating means and at least one busbar of electrically conductive material which provides an electrical connection between a power source and the electrical heating means, and a method and apparatus for the manufacture of such a glazing. The invention is especially concerned with the provision of electrical power to the heating means via said one or more busbars.

Electrically heated glazing panels are currently used by the automotive industry for their defrosting and de-misting capabilities. They can be installed as front glazings (windshields) and rear glazings (backlights) , the former usually being laminated, and both usually exhibiting some degree of curvature in one or more dimensions. At present, an electrically heated vehicular glazing panel may be manufactured in one of two different ways, depending upon which other properties are sought of the glazing. In the first technique, thin wires

(approximately 18-28 μm in diameter) are embedded into the surface of a plastic interlayer ply, e.g. a layer of polyvinylbutyral ("PVB"), which is used to laminate two glass plies. Each of the wires is soldered at each end thereof between a pair of metallic busbars, e.g. tinned copper strips, which span the extent of the wires. Furthermore, an electrical connector is soldered to each busbar pair. The wired glazing assembly is laminated in an autoclave, where application of specific temperatures and pressures over a pre-determined period of time ensure achievement of the necessary adhesion between the interlayer ply and the surrounding glass plies, as is known in the art. Resistive heating of the resultant glazing panel by the wires is effected by connection of the electrical connectors to the power supply of the vehicle.

The second technique is also well-known in the art and involves application of a silver-based infrared- radiation reflecting film as a coating onto either a surface of one of the glass plies that forms a laminate, or a flexible transparent support, e.g. a sheet of polyethylene terephthalate ("PET"), which is then interleaved between two PVB sheets forming a composite interlayer. Busbars, e.g. tinned copper strips or strips of printed conductive ink, are either laid onto the coated surface of the relevant glass ply or are incorporated into the composite interlayer (whichever is applicable) such that at least two opposing edges of the coating are in contact with a busbar. Electrical connectors are again soldered to the busbars prior to lamination of two glass plies and an interlayer ply.

The two types of conductive busbar discussed in relation to the two techniques above are normally from 75 μm to 150 μm thick, 6 mm to 10 mm wide and are capable of conveying currents of at least 20 Amps, and often substantially more. Electrically heated glazings may produce significant power densities, e.g. in the range 600-900 W/m², and it is important for the busbars to have substantial current-carrying capacity, given the low voltage available in vehicles. Metallic strip busbar application is a labour- intensive process, especially for the creation of a wired glazing, as each wire requires soldering between the busbar pairs both at the top and at the bottom of their lengths. A further disadvantage is that compared to the cost of the wires, the metallic busbar strips and interlayer material are expensive components. Breakage of wires may occur during assembly of a glazing panel; if this happens subsequent to soldering the wires to the busbars, the interlayer ply, busbars and wires must all be discarded (as none are re-usable) , thus incurring unwanted expense. When metallic strip busbars are used in conjunction with a bent coated glazing ply they may only be applied to that ply subsequent to it being bent. Specifically, because bending glass plies usually involves a relatively high temperature process (be it using press bending or sag bending technologies), metallic busbars cannot be applied prior to this bending process. As a result they have to be applied to a pre-bent glass ply. Busbar application needs then to be a manual process so that each busbar can be bent as required to follow the curvature and contour of the glazing, and to ensure correct positioning with respect to both the top and bottom edges of the glazing.

Printing ceramic ink busbars is also a time- consuming process; busbars are usually screen-printed onto a relevant flat surface, and often more than one pass of the printing screen is required so that a thorough coating can be achieved. However, each successive layer of coating has to be dried before any further processing, e.g. bending, can occur. Generally, a peripheral band of black ceramic ink (known as an obscuration band) is additionally printed onto one or more surfaces of the glazing to prevent the conductive busbars from being seen either from outside or inside the vehicle. When a bent screen-printed glazing is required, the desired curvature may be obtained by specifically and precisely heating particular areas of one or more of the glass plies. The black ink used to print an obscuration band normally exhibits high emissivity, i.e. when heat is directed towards it, a greater proportion is absorbed than is reflected, which is advantageous for bending processes and achieving correct curvature in a glass ply. However, the silver ceramic ink normally used to print busbars exhibits low emissivity, i.e. when heat is directed towards it, a greater proportion is reflected than is absorbed. A low emissivity coating therefore is not a desirable addition to a glass ply that is to be bent. As a remedy, a further layer of black ceramic ink is usually printed over the silver ink. The overall printing process is long and time-consuming, particularly given that each of the printed layers needs to be dried before the next layer can be overprinted. Finally the conductive coating can be applied, however application is over the top of multiple coatings below, each of which has a degree of porosity. Moreover, the greater the number of process steps leading up to the final lamination process, the greater the number of rejected pieces that are likely to occur and, thus the greater overall cost of producing a laminated glazing.

A further disadvantage arises from use of silver ceramic ink, in particular from the porosity of the ink. A dried, ceramic ink busbar exhibits a porous and rugose topography, i.e. a plurality of microscopic peaks and troughs extend over its surfaces. When a coating is applied to the surface of a glass ply, overlapping the relatively rough busbar, the quality of the contact with the resultant coating may be poor. A consequence of the poor quality contact is that the area over which electrical current can be transferred from the busbar to the coating is reduced, and the electrical resistance is increased. Use of the full current conveying capacity of the busbar is precluded.

It is therefore an object of the present invention to provide a laminated vehicular glazing comprising a busbar that does not suffer from the application and usage problems currently encountered when conventional metallic strip or printed busbars are employed.

It is a further object of the present invention to provide a method of manufacturing a laminated glazing that is both quicker and simpler than existing methods and which simplifies the overall production process.

It is yet a further object of the present invention to provide an apparatus for use in the manufacture of a laminated glazing according to the invention, which may be used in combination with the method disclosed herein.

According to the present invention there is provided a laminated vehicular glazing, constructed from at least two plies of glazing material and a ply of interlayer material which extends between the plies of glazing material, comprising: electrical heating means, and at least one busbar of electrically conductive material which provides an electrical connection between a power source and the electrical heating means, wherein the electrically conductive material is a polymeric material which has electrically conductive particles dispersed within it.

The plies of glazing material are typically panes of glass, for example soda-lime-silica glass, whilst the ply of interlayer material is typically a plastics material, for example PVB.

Usually the electric heating means extends over, so as to provide heat to, substantially the entire glazing, but does not protrude beyond the edges of the three glazing plies. A laminated glazing is typically provided with a pair of mutually spaced busbars which contact the electrical heating means at opposing ends thereof (for example, the busbars may lie along the top and bottom edges of the glazing, as viewed when the glazing is installed in a vehicle) , and which are themselves comprised in the laminate structure.

The polymeric material from which the at least one busbar is made can, ordinarily, be made to adhere to at least one ply of the glazing (for example, it may be made to adhere to a ply of glazing material, and optionally to the interlayer ply as well) ; the adhesion being achieved by means of the induced adhesive properties of the polymeric material itself. For the avoidance of doubt, and for purposes of clarity, this means that no additional adhesive substance is required or used to adhere the at least one busbar to any ply of the glazing. A laminated vehicular glazing incorporating busbars of polymeric material which has electrically conductive particles dispersed within possesses many advantages associated with its manufacture, compared to glazings which include conventional busbars. Many aspects of busbar provision are simplified, saving time and expense during the manufacture of the glazings. Electrical contact between the busbar and the electrical heating means is improved, resulting in a better quality product, and unwanted emissivity effects of silver ink are avoided. A further advantage is that external connectors no longer need to be soldered to the busbars. An external connector merely needs to be positioned in contact with a polymeric busbar prior to lamination (whereupon complete bonding is achieved and a reliable electrical connection created) , with the sole proviso that there is sufficient overlap to achieve a maximised electrical connection between the two. Moreover, it is anticipated that removal of the busbar from the glazing will also be facilitated, which will be of increasing importance as the requirement to recycle vehicles and their constituent parts increases .

Preferably the polymeric material has a resistivity less than 5.0 x 10^"4 ohm cm such that its electrical conductivity is maximised. Further preferably the resistivity is less than 1.0 x 10^~4 ohm cm, most preferably is less than 4.5 x 10^"5 ohm cm, and may be around 4.3 x 10^"5 ohm cm. Resistivity values given here are "original" values, i.e. they represent the resistivity of the polymeric material in the state in which it is obtained from a supplier. By reducing the resistivity of the busbar material, and hence increasing the electrical conductivity, the busbar itself becomes a more efficient carrier of electric current. The polymeric material may be provided in the form of a tape, which may be unwound and deposited in strips, or it may be in the form of a paste (which may be stabilised by, for example dimethylformamide "DMF", or other suitable solvent which gives the paste a comparable viscosity) which may be suitably dispensed to form the at least one busbar.

The electrical heating means may be constructed from an array of wires. If so, it is preferable that the wires are embedded into the ply of interlayer material. Alternatively a conductive coating may provide the electrical heating means. Use of wires or a conductive coating as the electrical heating means are conventional techniques currently applied to laminated glazings. The busbars of the present invention can be employed with either wiring or conductive coating technologies, thus busbars of conductive polymeric material are compatible for use with many of the laminated glazings that are currently available. Use of thermoplastic busbars with a glazing having a conductive coating is particularly advantageous as the emissivity problems associated with silver ink-printed busbars are removed. Furthermore, a conductive coating may now be applied to a glazing prior to thermoplastic busbar application, rather than the coating being deposited over the black and silver ink stack as was the case previously, resulting in achievement of a much improved electrical connection between the coating and the busbars. Where the polymeric material is provided in the form of a tape, it may be preferable that the at least one busbar comprises two or more contacting layers of electrically conductive material. A greater width of busbar may thus be achieved, particularly in the regions of the glazing where its shape requires that the busbar follows a path having a small radius of curvature, e.g. a corner of a glazing. If a paste form of the polymeric material were used, the means by which the paste is dispensed could be modified so as to achieve a greater width of busbar.

Preferably the polymeric material is a thermoplastic material. Thermoplastics have a linear chain structure, which affords them their characteristic re-workability when heated.

Further preferably the thermoplastic material is polyurethane. The temperature at which polyurethane becomes tacky, and thus is able to adhere to a surface of the glazing, falls within the temperature window used in the autoclave during the lamination process.

The electrically conductive particles are normally particles of metallic silver, which may be in the form of flakes. Pure silver has the highest electrical conductivity of all known metals. As such it is the first preference for inclusion in the polymeric material. Advantageously, the particles of metallic silver may be present in two approximate sizes: a larger, more frequently occurring size and a smaller, less frequently occurring size. The smaller particles are believed to "bridge" between the larger particles, creating a greater number of electrical pathways in the polymeric material (giving it a greater conductivity) compared to the polymeric material having a single (approximate) size of silver flakes.

According to a second aspect of the present invention there is provided a method of manufacturing a laminated glazing of the present invention comprising: causing heat to be imparted to the polymeric material during its application onto a surface of the glazing such that an adhesion between the polymeric material and the surface of the glazing is achieved.

A laminated glazing is generally made from a pair of glazing plies, which may be plies of glass. The processing steps which may be performed in addition to the step described in the preceding paragraph to create such a laminated glazing are typically as follows. Two sheets of flat glazing material may be cut to the requisite shape (for example the shape of a vehicle windscreen), before being subjected to a washing and drying process to remove any glazing material-powder residue from the cutting step and any other debris that may be present on one or both plies of glazing material. A surface of one or both glazing plies may then have a black enamel ink screen-printed onto it to form, for example an obscuration band. The ink normally has to be dried before any further processing of the glazing plies may occur.

If the laminated glazing is to be curved (as many are) , the pair of glazing plies may be bent singly or as a pair (as is known in the art, especially when glass plies are used) to a predetermined curvature so that a laminated glazing of substantially uniform thickness may eventually result.

One of the glazing plies of the pair may then be temporarily put to one side (when the plies are bent, it is usually the ply with the slightly smaller radius of curvature that is put to one side) . If the laminate is to have heat provided to it by a coating, the remaining ply of glazing material may have a coating deposited onto it prior to application of the polymeric material to form busbars. If the laminate is to be wire-heated, the remaining ply of glazing material may simply have the polymeric material applied directly to it.

Electrical connectors may then be positioned in contact with the polymeric material before firstly the interlayer of PVB, and secondly the other glazing ply of the pair, are joined with the remaining glazing ply to form a laminate construction whose plies are ready to be laminated together in an autoclave (as is known in the art) .

Electrically conductive polymeric materials, such as those used in this method do not directly adhere to any of the surfaces of a laminated glazing at room temperature conditions. For the avoidance of doubt, surfaces of the laminated glazing include the surfaces of the plies of glazing material and the surfaces of any of the interlayer plies. However, the surface of the glazing to which the polymeric material adheres is typically a surface of a ply of glazing material, for example a pane of glass. Use of electrically conductive polymeric materials as busbars was therefore precluded until the inventors surprisingly discovered that many of these materials gained sufficient adhesive properties when heated (i.e. enough temporary adhesion may be achieved between the polymeric material and the surface of the glazing so that the newly applied polymeric material (in the form of busbars) may retain their integrity, which consequently facilitates succession completion of the remaining processing steps described above) .

Heat may be imparted to the material either by directly heating the material itself or by pre-heating the surface of the ply onto which the material is to be deposited, such that heat is then transferred from the surface to the material as it is deposited. When using a tape form of the polymeric material, the preferred method of the present invention includes a step wherein the surface onto which the material is to be deposited is pre-heated, rather than the material itself being heated because the latter results in the material being more difficult to handle. When using a paste form of the polymeric material, the preferred method of heating the paste is the one which most efficiently and safely evaporates the solvent from the bulk of the paste. Prior to application onto a surface of the glazing, the material ought to be kept in its room temperature state, for as long a period as possible to ensure accurate shaping and bonding to the pre-heated surface of the glazing ply.

Preferably the electrical conductivity of the polymeric material is increased as heat is imparted to it; it is believed that the electrically conductive particles within tend to agglomerate into a distribution that provides an enhanced electrical conductivity (when compared to the state of the material and its conductivity prior to heating) . Agglomeration of electrically conductive particles, resulting in increased electrical conductivity, is more likely to occur if the pressure under which the material is deposited is also controlled.

The temperature to which the polymeric material is heated is preferably maintained between 50°C and 150°C. More preferably the temperature is maintained between 60°C and 120°C, and most preferably around 85°C. These temperatures reflect the potential fluidity of the polymeric material and hence the tackiness and workability of the material over a range of temperatures. When using a tape form of the polymeric material, the temperature to which it is heated is especially important because if the tape becomes too hot, it may be more likely to tear or snap. When using a paste form of the polymeric material, the temperature to which the paste is heated is interdependent on the period of time for which it is heated to achieve maximum evaporation of solvent from the bulk of the paste.

Typically, a pathway on the surface of the glazing to which the polymeric material is to be applied is heated according to a pre-programmed route. Although the surface may be heated according to an arbitrarily chosen route that is defined as the heating process progresses, such a method is more likely to encounter problems in accuracy and reproducibility of deposition of the material .

Preferably the polymeric material is applied onto the surface of the glazing under a pressure which is maintained between 0 kPa and 100 kPa . More preferably the pressure is maintained between 20 kPa and 80 kPa, and most preferably around 50 kPa . As with the temperatures given previously, these pressures are instrumental in controlling both the physical and chemical states of the polymeric material. In particular pressure may be used to define the shape, width and thickness of the material as it is deposited onto a surface of the glazing. Further, because applied pressure will alter the density of the material, the dispersion of the electrically conductive particles therein, and hence the electrical conductivity of the material, may be controlled.

Advantageously the adhesion achieved between the polymeric material and the surface of the glazing endures for at least 30 minutes. Complete adhesion may not be achieved at the temperatures and pressures given above. However, for the purposes of constructing a laminated glazing, a minimum adhesion time of 30 minutes is desirable. During the lamination process complete adhesion is usually achieved as a result of the temperature and pressure conditions in the autoclave. According to a further aspect of the present invention there is provided apparatus for manufacturing a laminated glazing according to the invention comprising: a frame, a support shaft, about which a reel of tape of polymeric material may revolve, attached to the frame, and tape dispensing means, which includes a tape application wheel, also attached to the frame.

The relative locations on the frame of the support shaft and the tape dispensing means to one another may be such that when a reel of tape is fitted to the support shaft, the tape may easily be fed to the tape application wheel. Typically the reel of tape is fitted to the support shaft in an orientation such that the circumference of the reel is perpendicular (or thereabouts) to the horizontal (as viewed when the apparatus is in a resting position, in which the support shaft is usually substantially horizontal) . By "resting position" is meant a position of the apparatus when it is not in use or a position taken on the occasions when the apparatus is stationary when it is in between applying tape to consecutive glazings; in a resting position the tape application wheel normally rests in a plane that is perpendicular to the horizontal.

The tape application wheel is an important feature of the apparatus because it is the final element of the apparatus which has contact with the tape of polymeric material as tape is deposited onto a glazing as busbar. The tape has to be accurately positioned on the surface of the glazing to ensure that a) it makes, or will make, electrical contact with the electrical heating means (for example wires or a coating, as discussed earlier) so that heat may be provided to the glazing, and b) it does not stray into the transparent area of the glazing from its preferred location where it is obscured by an obscuration band. Ordinarily the tape is centred with respect to the tape application wheel, thus ensuring the tape application wheel follows an accurate deposition pathway may effectively achieve accurate deposition of the tape.

Preferably the frame comprises a primary frame and a secondary frame movably connected to the primary frame. The support shaft and tape dispensing means are usually attached to the secondary frame. Such a frame construction allows for part of the frame (typically the primary frame) to be stationary or to have simple motion

(for example forwards or backwards in one plane) , and the other part of the frame (typically the secondary frame) to perform all or most of the intricate motion (for example following a complex three-dimensional contour of a glazing) that may be required of the apparatus.

When the apparatus is in use, the secondary frame may be slidable about a substantially vertical axis of the primary frame, thereby facilitating height adjustment of the tape dispensing means in relation to the glazing. This means that, for example, when applying polymeric material to a curved glazing, the motion of the primary frame may be limited to a predetermined height range above the glazing, where it is able to move around in a corresponding horizontal plane, whilst the secondary frame may move with additional vertical motion thereby allowing the tape dispensing means to follow the contours of the glazing.

Often the apparatus may include pressure-exerting means, for applying pressure to the tape of polymeric material as it is dispensed. Typically the pressure- exerting means movably connects the primary and secondary frames. Variation in both the width and thickness of the tape of polymeric material may be achieved by application of pressure to it. Pressure may be applied by the secondary frame, which itself has pressure applied to it by the pressure-exerting means. The density of the material may also be varied by the applied pressure, which often leads to an increase or decrease in the electrical conductivity of the material compared to its original state, as discussed previously. Generally, the greater the pressure exerted on the tape as it is applied to a glazing, the better the adhesion achieved between the tape and the glazing. Preferably the reel of tape of polymeric material is fixed relative to the support shaft; this shaft is preferably rotatable, for example by the action of a motor. Although the reel of tape may be free to rotate and unwind about the horizontal axis of the support shaft (as viewed when the apparatus is in a resting position) , it is preferred that the reel of tape is fixed to the support shaft so that when the support shaft is immobile, the reel of tape cannot unwind. Furthermore, by fixing the reel of tape to the support shaft, when the support shaft is rotated, the reel may unwind in a controlled manner to limit the amount of excess tape unwinding from the reel and interfering with the deposition process. Advantageously, the tape dispensing means comprises a pivoting member to which the tape application wheel is mounted. The pivoting member typically includes a returning element which, when acted upon by an external force, may return the member to a rest position (i.e. to a position in which the tape application wheel rests in a plane that is perpendicular to the horizontal) . A cam device may be the returning element which is acted on to return the pivoting member to a rest position. An element of the tape dispensing means may be rigidly fixed to the secondary frame, but because the tape application wheel is mounted to a pivoting member, it is able to follow the curvature of a bent glazing. Typically the pivoting member pivots about a horizontal axis of the tape dispensing means; said axis extends parallel with the plane in which the tape unwinds from the reel, thus the pivoting member may exhibit angular motion of, for example ± 10° from its rest position, in a plane that is perpendicular to the plane in which the tape unwinds from the reel which compensates for the curvature of a bent glazing.

A tape position detector, for monitoring the position of the tape relative to the tape application wheel, may be located on the frame. A reel of tape may not be perfectly plane, thus as it unwinds there may be variation in the location of the tape relative to both the reel and the tape application wheel. However, as discussed earlier, the tape that is fed to the tape application wheel should be centred with respect to that wheel to ensure accuracy of the tape deposition of the glazing. To minimise the effect of this potential problem with a reel of tape, a tape position detector may be used. Any variation in the location of the tape relative to the tape application wheel may be compensated by lateral adjustment of the position of the support shaft (on which the reel is located) with respect to the tape dispensing means. The frame of the apparatus is preferably provided with a tape tensioning system, for varying the tension in the tape as it is applied to the glazing. Further preferably, a reel monitoring system, for monitoring the diameter of the reel of tape as tape is deposited on a glazing, may be provided on the frame in conjunction with the tape tensioning system. The tape tensioning system may include a cylindrical element which is in contact with the tape on the reel and which is driven, for example by the action of a motor. The cylindrical element may also be in communication with the reel monitoring system; as tape is applied to a glazing, the diameter of the reel of tape decreases, yet the cylindrical element may remain in contact with the tape on the reel as a result of the monitoring system.

The pressure exerted on the reel of tape by the cylindrical element may be controlled so as to vary the tension in the tape that is applied to the glazing. The greater the pressure on the tape, the more likely the tape will deform (for example, stretch). Deformed tape may be less likely to crease when a corner having a small radius of curvature has to be followed, however it may be more likely to tear as a result of the stress introduced into it - thus a tape of higher tension may be desired in some circumstances, but not in others - the ability to vary the tension applied to the tape is clearly advantageous, especially given the fragility of the tape and its propensity for tearing or snapping if the tension introduced into it is not carefully monitored and adjusted.

Typically, a robot guides the frame around a surface of the glazing according to a pre-programmed route. Preprogramming means a defined and accurate route may be followed; the route may be complex in nature. Moreover, it allows reproducibility, which is an important factor if laminated glazings are to be produced on a large scale. This robot and its associated computer programming may also control one or more of the motors, the pressure- exerting means, the tape tensioning system and the reel monitoring system referred to earlier.

Advantageously, the apparatus further comprises heating means for pre-heating a surface of the glazing prior to application of the polymeric material. Ordinarily the heating means comprises a source of hot air. Typically it is the glazing that is heated, therefore a non-destructive means is required to ensure minimal damage, if any, is done to the final glazing. The source of hot air preferably supplies filtered air. Non- filtered air may contain particulates that remain present on the surface of the glazing as the polymeric material is dispensed. Such particulates and contaminants would ultimately feature in the final glazing. Alternatively the heating means may comprise an infrared radiative beam, which is another non-destructive heating means.

In one embodiment of the further aspect of the present invention there is provided apparatus for manufacturing a laminated glazing according to the method of the present invention comprising: a dispensing head, which includes means for dispensing the polymeric material onto a surface of the glazing, and means to pre-heat a surface of the glazing prior to the polymeric material being dispensed.

The benefit of this particular apparatus is that the polymeric material is automatically dispensed by the dispensing means subsequent to the surface of the glazing being heated, in a time period during which the temperature of the surface is still within the range as claimed in the method above. As both the dispensing means and the heating means form a part of the same dispensing head, a co-operative relationship exists between the two means such that the polymeric material will be accurately dispensed onto the pre-heated pathway in a controlled manner. Further, the manner in which the material is dispensed ensures that potential damage to both the glazing and polymeric material as a result of handling is minimised.

For a better understanding, the present invention will now be more particularly described by way of non- limiting example with reference to, and as shown in, the accompanying drawings (not to scale) wherein:

Figure 1 is a plan view of a laminated glazing in which the electrical heating means includes an array of wires embedded in a PVB interlayer ply, Figure 2 is a cross sectional view taken in the direction of the arrows along the line A-A of Figure 1,

Figure 3 is a plan view of a laminated glazing in which the electrical heating means includes a conductive coating on a surface of a ply of glazing material, Figure 4 is a cross sectional view taken in the direction of the arrows along the line B-B of Figure 3,

Figure 5 is a cross sectional view which corresponds to Figure 4, but shows a laminated glazing in which the electrical heating means includes a conductive coating on a surface of a ply of interlayer material,

Figure 6 is a further cross sectional view corresponding to Figures 4 and 5, showing a laminated glazing in which the busbar is constructed from at least two overlapping busbars, Figure 7 is a side view of apparatus of the present invention which is partially cut away to show underlying structure,

Figure 8 is a sectional view taken in the direction of arrows along the line C-C of the apparatus shown in Figure 7,

Figure 9 is a plan view of the apparatus shown in Figures 7 and 8, and

Figure 10 is a diagrammatic side view of an alternative embodiment of apparatus which may be used to manufacture a laminated glazing of the present invention; this apparatus includes heating means in the form of a hot filtered-air gun. Laminated glazing 10 of Figure 1 comprises electrical heating means in the form of electrically conductive wires 12, which extend over glazing 10 from its top edge to its bottom edge. Each wire 12 is in electrical contact at both ends thereof with electrically conductive busbars 11 of polymeric material in the form of a thermoplastic. For reasons of clarity, Figure 1 only shows a small number of wires, at a greatly enlarged spacing. Busbars 11 located along the top and bottom edges of glazing 10 are obscured from internal view (with respect to a vehicle which may house glazing 10) by obscuration band 13a, which is deposited on the innermost face of glazing 10 (known as surface 4; the outermost face of glazing 10 being known as surface 1) . Figure 2 provides more detail about the construction of laminated glazing 10 of Figure 1. Glazing 10 further comprises inner glazing ply in the form of glass ply 21 and outer glazing ply in the form of glass ply 22, in between which interlayer ply in the form of a sheet of PVB 23 is interleaved. Wires 12 (of which again only a nominal number are shown, greatly enlarged) are embedded into PVB interlayer ply 23. In addition to obscuration band 13a that can be seen in Figure 1, which exists on surface 4, there is also obscuration band 13b which exists on surface 2, i.e. the inner face of outer glass ply 22. The purpose of obscuration band 13b is to obscure busbars 11 from external view.

Similarly to Figure 1, laminated glazing 30 of Figure 3 comprises obscuration band 13a which obscures busbars 11 from internal view. In this Figure the electrical heating means is in the form of conductive coating 31.

Figure 4 provides further detail about the construction of laminated glazing 30 of Figure 3. Glazing 30 further comprises inner glass ply 21 and outer glass ply 22, in between which PVB interlayer ply 23 is interposed. Conductive coating 31 is deposited on surface 2 (of outer glass ply 22) . Alternatively, conductive coating 31 could be deposited on surface 3 (of inner glass ply 21) . Busbars 11 each overlap with an opposing edge of conductive coating 31 (only one edge and corresponding busbar 11 is shown in Figure 3) , thereby creating an electrical connection to conductive coating 31 when electrical connectors are connected to busbars 11. Glazing 30 again includes obscuration bands 13a, 13b on surfaces 2 and 4 respectively. In Figure 5 conductive coating 31 is applied to interlayer ply in the form of a PET foil 51. Busbars 11 each overlap with an opposing edge of conductive coating 31 (again, only one edge and corresponding busbar 11 is shown in Figure 5). PET interlayer ply 51, upon which conductive coating 31 lies along with busbars 11, itself forms an interlayer in between two PVB plies 23. The resultant composite interlayer ply exists between inner glass ply 21 and outer glass ply 22 of glazing 30.

In any of the embodiments of the invention (as shown in Figures 1 to 5) , busbars 11 may be applied in multiple overlapping passes so that their overall width is increased. This technique is especially useful where the busbar has to pass around a corner, because multiple passes of relatively narrow tape are less likely to wrinkle at the corner than a single pass of relatively wide tape. Figure 6 illustrates overlapping busbars 11 in the case where the electrical heating means is provided by conductive coating 31, which is applied directly to outer glass ply 22. From Figure 6 it is clear how this technique could be replicated with the existing alternative embodiments of the invention. A greater width of busbar 11 may be required to carry a higher electrical current to wires 12 or conductive coating 31. The width of busbar 11 is altered rather than its thickness because, given that glazing 10,30 is a laminate, too great a thickness of the thermoplastic material may cause bubbles to develop within the laminate. Additionally an electrical connector has to overlap with busbar 11 to create an electrical connection with a power source, which is normally an external power source.

The thickness of the thermoplastic material is preferably from 25 μm to 600 μm, more preferably from 75 μm to 500 μm and most preferably from 100 μm to 400 μm; 250 μm being the optimum thickness. The width of the thermoplastic material when laid in a single application is preferably from 5 mm to 25 mm, more preferably from 7 mm to 15 mm and most preferably from 9 mm to 12 mm. If a wider busbar is required, when using a tape form of the polymeric material a further application of tape which contacts the first may be necessary; when using a paste form of the polymeric material suitable alteration of the means used to dispense the paste may be necessary.

A laminated glazing as shown in any of Figures 1 to 6 may be constructed using tape dispensing apparatus 70 of Figure 7. This apparatus comprises primary frame 71 in the form of a base frame, and secondary frame 72 in the form of a mobile frame. Primary frame 71 includes guides 73, which are vertically slidable about an axis of primary frame 71, and pressure-exerting means 74 in the form of a piston, which extends downwardly from its top end away from primary frame 71. Secondary frame 72 is connected to primary frame 71 via guides 73 and is also attached to the bottom end of pressure-exerting means 74.

Secondary frame 72 is provided with tape dispensing means 75 in the form of a dispensing head, support shaft

76 i the form of a rotatable rod onto which a reel of tape of polymeric material 707 is fixed, guide roll 77 in the form of a freely rotatable rod, tape position detector 78 in the form of a system of two arrays of light emitting diodes and corresponding optical feedback sensors - an array and its sensor being positioned on opposite sides of the width of tape of polymeric material, with one array on each side of the width of tape for detecting opposing direction of movement of the position of the tape, and tape tensioning system 79 which includes cylindrical element 701.

Tape dispensing means 75 comprises head 702 and pivoting member 703 which is pivotably connected to head 702 such that it can pivot in a plane that is equivalent to movement into and out of the page on which Figure 7 is illustrated (i.e. pivoting member 703 pivots about a horizontal axis of head 702 which extends parallel to the plane in which tape unwinds from reel of tape 707, thereby exhibiting angular motion with respect to the plane in which tape unwinds from reel of tape 707). Tape application wheel 704 is connected to pivoting member 703 and is itself freely rotatable about a horizontal axis of pivoting member 703 (referenced when apparatus 70 is in a resting position) . The direction in which tape application wheel 704 freely rotates is indicated by the curved arrow labelled "D". Tape dispensing means 75 further comprises at least one guide roll 705 which guides the feed of polymeric tape from reel of tape 707 to tape application wheel 703, and returning element 706 in the form of a cam device which may be acted upon by positioning cylinder 709 which is able to move tape dispensing means 75 back into a rest position once deposition of tape onto a glazing is complete. Also shown in Figure 7 are pincers 708 which hold the loose tape when apparatus 70 is in a rest position and tape is not being dispensed.

The section of apparatus 70 shown in Figure 8 provides more detail about the locations and relative positions of the various elements of apparatus 70 hereinbefore described. Curved arrow labelled E-E further illustrates the directions and extent of pivoting movement exhibited by pivoting member 703. Arrow E-E is bisected by a plane in which reel of tape 707 lies - the pivoting movement of pivoting member 703 is at right angles to this plane at the point of bisection. Figure 8 also shows that support shaft 76 is rotatably connected to drive means 80 in the form of a motor (for example a direct current motor) , which rotates support shaft 76 and thereby unwinds reel of tape 707 which is fixed to support shaft 76. Furthermore double-headed arrow labelled F-F indicates the direction of horizontal movement (referenced when apparatus 70 is in a resting position) that support shaft 76 may follow if lateral adjustment of the position of support shaft 76 is required to compensate for variation in the location of tape (as detected by tape position detector 78) as it unwinds from reel 707 relative to tape application wheel 704.

Figure 9 additionally shows that primary frame 71 is provided with reel monitoring system 90 which operates in conjunction with tape tensioning system 79. Reel monitoring system 90 comprises arm 91 which is connected at one end to positioning cylinder 92 and at the other end to tape tensioning system 79 whose position relative to reel of tape 707 can be adjusted accordingly as reel monitoring system 90 monitors the diameter of reel of tape 707. From Figure 9 it is clear that tape tensioning system 79 includes drive means 93 in the form of a motor (for example a direct current motor) which rotates cylindrical element 701 and applies pressure to the tape, thereby introducing tension into the tape as it unwinds from reel of tape 707. The curved arrows labelled "G" and "H" respectively indicate the direction of rotation of each of support shaft 76 and cylindrical element 701. G represents clockwise rotation whilst H represents anticlockwise rotation (as viewed in Figure 9) - these directions are opposite to one another so that any excess tape that it unwound from reel of tape 707 is immediately prevented from progressing towards tape dispensing means 75 by cylindrical element 701. An alternative embodiment of the apparatus shown in Figures 7, 8 and 9 is illustrated in Figure 10. Dispensing apparatus 100 of Figure 10 comprises dispensing head 101, which includes dispensing means in the form of a tape dispenser 102 and heating means in the form of a hot filtered-air gun 103. Hot air gun 103 is movably, tiltably mounted within dispensing head 101 such that a spatially variable relationship exists between it and tape dispenser 102. This relationship ensures that the contours of the surface onto which busbars 11, in the form of tape, are to be laid may be accurately followed - initially by hot air gun 103, followed co-operatively by tape dispenser 102. Dispensing apparatus 100 may include driving means in the form of a robotically driven arm 104 (not shown in detail) . Robotic arm 104 guides dispensing head 101 over the surface of the glazing that is to have the tape deposited onto it, in addition to providing the necessary pressure under which the tape is to be applied, via dispensing head 101. Similarly, hot air gun 103 is provided with positioning means 105 to vary the spatial relationship between it and tape dispenser 102. Positioning means 105 enables dispensing apparatus 100 to work over contoured surfaces; although a co-operative relationship exists between hot air gun 103 and tape dispenser 102, each possesses sufficient independence of movement to ensure that a range of contoured surfaces may have thermoplastic tape deposited onto them. From Figure 10 it is clear how tape dispenser 710 could be substituted with dispensing equipment to suit the form that the busbar material is commercially available in, e.g. a nozzle for paste dispensation.

The thermoplastic conductive material used for busbars 11 in each of Figures 1 to 6 is a polyurethane based material which includes flakes of silver as the conducting element. It is commercially available as STAYSTIK™ 571 Tape or 171 Thermoplastic Adhesive Paste from Cookson Semiconductor Packaging Materials, a division of Cookson Electronics. These materials exhibit poor room-temperature adhesion to the surfaces of the plies which form laminated glazing 10,30. In practice it is therefore not possible simply to shape and apply the material onto the desired surface. In order to apply the material accurately onto the requisite surface of glazing 10,30, heat, and desirably pressure, ought to be applied to it. Furthermore, it has been found that through application of both heat and pressure to the thermoplastic material, the electrical conductivity of it can be increased and made more uniform along the length of the busbar. Experimentation with the thermoplastic material under varying temperature and pressure conditions led to the discovery of optimum values for each of these parameters and to achievement of maximum possible conductivity, which will now be described.

Glazing ply 21,22,23,51 is fixed into position on conventional glazing-retention apparatus (not shown) comprising fixing means, such as vacuum cups, as is known in the art. Correct positioning of the glazing ply with respect to dispensing apparatus 100 is ensured, thus application of the thermoplastic tape may proceed. Typically both primary frame 71 and secondary frame 72 of apparatus 70 (or dispensing head 101 of figure 10) accurately follows a pre-programmed route over the surface of glazing ply 21,22,23,51. The pre-programmed route may be effected by a computer program that drives primary frame 71 of apparatus 70 (or dispensing head 101 of Figure 10) via a robot (not shown in Figures 7, 8 and 9) , for example a robotic arm 104 illustrated in Figure 10. As the pre-programmed route is followed, polymeric tape is applied to glazing ply 21,22,23,51. During application of polymeric material onto a surface of glazing 21,22,23,51, heat must be imparted to the material such that an adhesion between the polymeric material and the surface of the glazing is achieved (i.e. a level of adhesion which may not be complete adhesion but which is sufficient to at least temporarily adhere the material to the glazing is required) . When apparatus 70 of Figures 7, 8 and 9 is used, heat may be imparted to the polymeric material in a number of ways. Heat may be applied directly to the polymeric material, by heating with a hot filtered-air gun for example, or indirectly to the polymeric material. The latter may be achieved by locally heating glazing 21,22,23,51 with an infrared beam for example, or by providing heating resistors in the glazing retention apparatus (not shown) at positions corresponding to the pathway on glazing 21,22,23,51 over which polymeric material is to be applied, such that heat is transferred from glazing 21,22,23,51 to the polymeric material as it is deposited, or by transfer of heat that may be residual in glazing 21,22,23,51 from an earlier processing step, for example bending.

If the apparatus depicted in figure 10 is used, two consecutive stages of the busbar application process cooperatively occur. Firstly, hot air gun 103 directly heats a pathway on the surface of glazing ply 21,22,23,51 over which the thermoplastic material is to be laid. The temperature of the surface is preferably maintained around 150°C. As dispensing head 101 moves over the surface of glazing ply 21,22,23,51 such that the pathway is heated by leading hot air gun 103, thermoplastic tape is dispensed onto the pre-heated surface of the ply in a co-operative second phase of the process. Tape dispenser 102 applies the thermoplastic material to the pre-heated surface of glazing ply 21,22,23,51 under an applied pressure. Preferably this pressure is maintained around 50 kPa. The spatially variable relationship that exists between hot air gun 103 and tape dispenser 102 results in the surface of glazing ply 21,22,23,51 being pre-heated immediately prior to the thermoplastic tape being applied. Heat is thus imparted to the thermoplastic as it is applied under pressure, which leads to an adhesion between it and the surface of glazing ply 21,22,23,51 onto which it has been applied.

At standard room temperature and humidity conditions, the thermoplastic material maintains its imparted shape and adhesion to glazing 21,22,23,51 for at least 30 minutes, during which time intermediate process steps, e.g. those using nip-roll, bag-furnace or vacuum- ring technologies, may be completed before the final lamination process in an autoclave. During this process the at least two plies of glazing material and the at least one ply of interlayer material which have been assembled as described previously are fused together, with complete bonding of the thermoplastic material to the relevant surface within glazing 10,30 being achieved.

Claims

1. A laminated vehicular glazing, constructed from at least two plies of glazing material and a ply of interlayer material which extends between the plies of glazing material, comprising: electrical heating means, and at least one busbar of electrically conductive material which provides an electrical connection between a power source and the electrical heating means, wherein the electrically conductive material is a polymeric material which has electrically conductive particles dispersed within it.

2. A laminated vehicular glazing as claimed in claim 1 wherein the polymeric material has a resistivity of less than 5.0 x 10^~4 ohm cm.

3. A laminated vehicular glazing as claimed in claim 1 or claim 2 wherein the electrical heating means includes an array of wires.

4. A laminated vehicular glazing as claimed in claim 3 wherein the wires are embedded into the ply of interlayer material.

5. A laminated vehicular glazing as claimed in claim 1 or claim 2 wherein the electrical heating means includes a conductive coating.

6. A laminated vehicular glazing as claimed in any preceding claim wherein the at least one busbar comprises two or more contacting layers of electrically conductive material .

7. A laminated vehicular glazing as claimed in any preceding claim wherein the polymeric material is a thermoplastic material.

8. A laminated vehicular glazing as claimed in claim 7 wherein the thermoplastic material is polyurethane.

9. A laminated vehicular glazing as claimed in any preceding claim wherein the electrically conductive particles are particles of metallic silver, which may be in the form of flakes.

10. A method of manufacturing a laminated vehicular glazing as claimed in claim 1 comprising: causing heat to be imparted to the polymeric material during its application onto a surface of the glazing such that an adhesion between the polymeric material and the surface of the glazing is achieved.

11. A method according to claim 10 wherein the electrical conductivity of the polymeric material is thereby increased.

12. A method according to claim 10 or claim 11 wherein the temperature to which the polymeric material is heated is maintained between 50°C and 150°C.

13. A method according to any of claims 10, 11 and 12 wherein a pathway on the surface of the glazing to which the polymeric material is to be applied is heated according to a pre-programmed route.

14. A method according to any of claims 10 to 13 wherein the polymeric material is applied onto the surface of the glazing under a pressure which is maintained between 0 kPa and 100 kPa .

15. A method according to any of claims 10 to 14, wherein the adhesion achieved between the polymeric material and the surface of the glazing endures for at least 30 minutes.

16. Apparatus for manufacturing a laminated vehicular glazing as claimed in claim 1 comprising: a frame, a support shaft, about which a reel of tape of polymeric material may revolve, attached to the frame, and tape dispensing means, which includes a tape application wheel, also attached to the frame.

17. Apparatus as claimed in claim 16 wherein the frame comprises a primary frame, and a secondary frame movably connected to the primary frame.

18. Apparatus as claimed in claim 17 wherein, in use, the secondary frame is slidable about a substantially vertical axis of the primary frame, thereby facilitating height adjustment of the tape dispensing means in relation to the glazing.

19. Apparatus as claimed in claim 17 or 18 including pressure-exerting means, for applying pressure to the tape of polymeric material as it is dispensed.

20. Apparatus as claimed in any of claims 16 to 19 wherein the reel of tape of polymeric material is fixed relative to the support shaft.

21. Apparatus as claimed in any of claims 16 to 20 wherein the tape dispensing means comprises a pivoting member to which the tape application wheel is mounted.

22. Apparatus as claimed in claim 21 wherein the pivoting member includes a returning element by which the member may be returned to a rest position.

23. Apparatus as claimed in any of claims 16 to 22 wherein a tape position detector, for monitoring the position of the tape relative to the tape application wheel, is located on the frame.

24. Apparatus as claimed in any of claims 16 to 23 wherein a tape tensioning system, for varying the tension in the tape as it is applied to the glazing, provided on the frame.

25. Apparatus as claimed in claim 24 wherein a reel monitoring system, for monitoring the diameter of the reel of tape, is provided in conjunction with the tape tensioning system.

26. Apparatus as claimed in any of claims 16 to 25 wherein a robot guides the frame around a surface of the glazing according to a pre-programmed route.

27. Apparatus as claimed in any of claims 16 to 26 further comprising heating means for pre-heating a surface of the glazing prior to application of the polymeric material.

28. An apparatus for manufacturing a laminated vehicular glazing according to the method of claim 10 comprising: a dispensing head, which includes means for dispensing the polymeric material onto a surface of the glazing, and means to pre-heat the surface of the glazing prior to the polymeric material being dispensed.