Electrically heated transparent panel

(54) Name: Laminated, electrically heated glass pane and method of making the pane

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Briefly, this invention relates to an electrically heatable laminated glass pane, preferably a vehicle pane, having a clear, intermediate polymer layer with partially embedded, pleated or wrinkled resistor wires oriented therein in a three dimensional, non-parallel random manner, thereby reducing the mixture from reflections in the wires. The individual resistance wires are partially embedded in the polymer sheet by a technique which utilizes the shrinkage thereof from its original dimensions when heated to a high temperature and the deformation of the individual wires when relieved from tension forces in the wire. An improved form of electrode means in the form of a busbar is attached to the opposite ends of the individual resistance wires by heat adhesion directly to the thermoplastic polymer sheet.

This invention relates generally to a heatable safety glass pane, which is generally suitable as a vehicle window including a windshield, side window and rear window. More specifically, it relates to a layered glass, which has an intermediate layer S in the form of a transparent sheet with resistance wires partially embedded therein and which is substantially free from reflections when light passes therethrough. Special electrode means in the form of busbars are connected to the resistance wires, which enables simplified and more reliable assembly of the finished construction together with improved heating of the window.

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Patent protection has previously been sought for a composite sheet member which consists of a layer of transparent thermoplastic polymer which has been heat shrunk from its original dimensions by heating to a higher temperature, with a plurality of pleated or wrinkled resistor wires partially embedded in one of its surfaces, which lie in a dense , separate relationship and which are oriented in relation to each other on a 'non-parallel, randomly so that parts of the individual resistor wires protrude from the surface of the thermoplastic polymer layer and form a three-dimensional heating wire structure with improved fabrication and work advantages. In one embodiment of the new transparent heating plate which constitutes the otherwise conventional inner layer of a laminated safety pane, certain electrode means are also described in the form of busbars, which consist of a single band of electrically conductive material attached to each end of the individual resistor wires to form a parallel-connected electrical circuit in between. The simple strip electrodes are in direct contact with protruding parts of the individual resistance wires and provide a generally reliable connection which is not subjected to mechanical breakage of the heating wires at the electrical connections. On the other hand, these simple busbar straps are attached by heat adhesion directly to a surface of the thermoplastic polymer sheet and the individual resistance wires are attached to the opposite side of the strap. Such a connection can lead to temporary faults in the direct electrical contact between the belts and the heating wires, which are caused by excessive flow of the polymeric material when the finished box assembly is manufactured. Even without excessive flow of the plastic material, increased contact resistance can occur due to chemical reaction between the copper busbars and the plastic material after the finished unit has been put into use.

They have also applied for patent protection for methods and apparatus for assembling the electrically heatable transparent disc as well as for the finished safety glass pane assembly. In one method of making the electrically heatable transparent sheet, the electrical resistance wire forming the heating wire pattern is biased to provide creases or wrinkles when the resistance wire is not under voltage. The prestressed wire is applied under tension to one side of the transparent thermoplastic polymer sheet in a pattern of closely spaced parallel orientation with respect to the individual wires, after which the tension on the individual resistor wires is relieved while maintaining contact between the resistance wire pattern and the thermoplastic polymer sheet surface. During the following heating step, the polymer sheet can

7307015-3 as the wires expand and contract in the direction of the wire path. The composite element is heated by applying electricity to the individual resistor wires so that the parts of the folds which are in contact with the surface of the polymer sheet become embedded and the remaining parts of the individual wires protrude from the surface of the plastic sheet. The composite element having an electrode shape of the busbar type and the resistance wire pattern as described above can then be used as the intermediate layer of an otherwise conventional safety glass pane construction in a number of already known ways. The final heating adhesion step leading to the laminated glass pane is also generally performed under sufficient heating and compression forces which provide significant flow of the polymeric material.

A special apparatus for producing the composite element is also described, which uses a shrinkable drum on which the element is formed. When this is done, the thermoplastic polymer sheet is first wound on the drum, followed by the application of separate heating electrodes and busbar-type electrodes, after which the prestressed resistance wire is wound in the form of a spiral over the wound polymer sheet. The composite element is then formed by shrinking the drum with a predetermined reduction in its diameter, after which the resistance wire and the adjacent single electrodes of the busbar type are adhesively terminated or heat adhered to the polymer sheet.

The product and method of the present invention are improvements over those described above, which can utilize the same general apparatus for providing the electrically heatable transparent sheet of the present invention. Accordingly, no repeated detailed description of the apparatus need be made in the present description except as required to explain the manner of carrying out the present invention.

The present invention aims to reduce a great difficulty encountered in a parallel arrangement of resistance heating wires in a laminated safety glass pane. Although the glare phenomenon encountered is not currently fully understood, it is believed that they can be attributed to the direction of the thread rather than the distance between the individual threads. By making the wire direction random in accordance with the practical application of the present invention, it becomes possible to sense the light reflection or diffraction from the individual wires in all directions and thereby reduce or eliminate the glare. While a complete random placement of the individual wires would be most difficult to achieve, it has been found that a controlled random distribution with three-dimensional orientation is sufficient to substantially eliminate the glare problem.

This object is achieved by means of a glass pane and a method of manufacturing it according to what is stated in the appended claims, from which also what particularly characterizes the invention appears.

The invention is described in more detail below in connection with the accompanying drawing, in which Fig. 1 is a perspective view of a curved, laminated glass pane according to the present invention, Fig. 2 is a section taken along line 2-2 through a longitudinal outer edge of the 1, and Fig. 3 is a section taken along line 3-3 through the other outer edge of the same window structure.

Controlled random construction of the resistor wire pattern is obtained by placing biased resistor wires on one side of the sheet of transparent thermoplastic material and then utilizing the ability of the polymeric material to shrink from its original dimensions when heated to high temperatures sufficient to cause it to surround portions of the individual threads in the surface of the thermoplastic material with which they are in contact. More specifically, a pattern of biased resistor wires is applied to a surface of the thermoplastic sheet so that individual wires are in a closely spaced, parallel relationship in the composite member thus fabricated, which is then heated under conditions that allow the individual resistor wires to expand and assume a shape. which can be attributed to the biasing forces. Subsequent cooling of the composite element allows the threads to be partially embedded in the softened thermoplastic material and provides the final random distribution in the thread pattern so that the individual threads have a wrinkled or irregular shrinkage at irregular intervals along their length. A non-parallel relationship between adjacent threads is thereby achieved with those parts of the thread projecting from the surface of the thermopolymer layer at different heights where they are not embedded. The final non-parallel wire pattern will be governed by thermal expansion differences between the polymer sheet and the wire, the nature and extent of the biasing forces applied to the resistance wire prior to insertion into the polymer surface, and the heat shrinkage properties of the thermoplastic material. It has also been observed during experiments with

This method of manufacturing that certain sheets of polyvinyl butyral polymers commonly used as the inner layer of laminated safety glass undergo greater shrinkage in a direction along the surface than in a surface direction perpendicular thereto. By fitting the direction with greater shrinkage with the thread direction, it thereby becomes possible to further improve the randomness of the thread pattern so that a non-parallel design is present both in the plane of a surface of the polymer sheet and in planes at an angle thereto.

The relatively high heating capacity of the thread pattern obtained in the above manner is due to the use of thin thread having a diameter from about 0.0075 to about 0.0230 mm with a distance of between 10 and 30 threads per 25 mm. Recognizing that the wattage consumption that can be obtained by connecting the wire pattern to a source of electric current will depend on the contact resistance as well as other factors, it becomes desirable to provide an efficient means for connecting the wire pattern to the electric power source. For this reason and as a basic principle of the present invention, a new busbar-type electrode means has been invented for coupling to the wire pattern at each end of the individual resistor wires as a continuous part of the electrically heated transparent disk. This new electrode means in the form of a busbar together with its construction method will now be described in connection with the drawings which are attached to this description.

Fig. 1 of the drawings is a schematic view of an otherwise conventional car windshield with a curved contour and which includes the substantially glare-free resistor wire pattern according to the present invention. More specifically, a laminated safety glass pane 10 is shown, which consists of a pair of outer glass layers 12 and 14, which are heat-adhered to the intermediate transparent sheet 16 according to the present invention. The electrically heatable transparent sheet 16 which acts as the intermediate layer of the safety glass (as shown more clearly in Fig. 2) constitutes a composite element comprising a sheet of transparent thermoplastic polymer 18 having a plurality of wrinkled resistance wires 20 partially embedded in one of its surfaces, which are oriented relative to each other in a three-dimensional and non-parallel, random pattern. Electrode elements 22 and 24 in the form of busbars form an integral part of the composite element and are located at each end of the individual resistor wires for electrical connection to them for heating

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the wires from the available power source in the vehicle. Both busbars are located longitudinally along most of the window structure and are both located near as well as parallel to opposite outer edges 26 and 28 of the curved safety glass pane structure. In the embodiment according to fig. 1 the resistance wire pattern 20 is arranged in the transverse direction of the pane, wherein sections 30 and 32 of the wire pattern, which lie beyond the outermost ends of the longitudinal busbars, do not form any part of the electric heating system.

Fig. 2 shows a vertical section through the windscreen construction in Fig. 1 to more clearly illustrate the shape of the busbars according to the present invention. While the random three-dimensional arrangement of the resistance wires, which is present when the electrically heatable transparent disk is constructed according to the invention, is somewhat hidden in fig. 2 however, due to the compressive forces applied during the assembly of the finished safety glass pane structure, one can still see portions 34 and 36 of an individual resistance wire projecting from the surface 38 of the thermoplastic polymer sheet. Thus, it can be seen that portions of the individual resistor wires projecting at different heights from the surface of the polymer sheet can move freely when compressed by the adjacent glass layers during the press lamination of the finished glass pane when the present electrically heatable transparent sheet is used. When this is done, the individual resistance threads undergo further random orientation relative to the plane of the polymer sheet surface in the final heat adhesion under pressure. In this process of making the finished window assembly, the thermoplastic polymer can move relatively freely during the final heat adhesion step and can interfere with the proper electrical connection between the individual resistor wires unless means were provided to prevent such action.

As shown in Figs. 1 and 2, the busbar-shaped electrode 22 in the finished glass laminate consists of a thin foil strip 40 with a segmented construction shown by the slots 43, 44 and 46, which are fixed by heat adhesion to the underlying thermoplastic layer, and a continuous foil web d 42 of greater width and thickness, which lies over the underlying segmented strips and which is likewise heat-adhered directly to the thermoplastic layer. The slot openings extending completely through the segmented strip 40 provide an interrupted electrically conductive path when the individual resistor wires are thermally adhered to the thermoplastic polymer sheet in a manner which will be explained in more detail below. One side

7307015-3 of the continuous film strip is in direct contact with the inside of the outer glass layer 12 while its other side is in electrical contact with both an individual heating wire 20 and underlying segmented strips 40. The direct contact between the film strips, both of which may be constructed of an electrically conductive metal, e.g. copper, is achieved by partial deformation of the underlying segmented strip, which occurs both during heat sticking of individual resistor wires at the thermoplastic polymer sheet and the finished window assembly in a manner which will also be further explained. The section in Fig. 2 is also chosen to illuminate a tab 48 of the continuous foil strip 42, which allows electrical connection to the vehicle's power source for the window heating system.

Fig. 3 is a partial longitudinal section through the busbar-shaped electrode member according to the present invention. More specifically, the section 3-3 is taken through the laminated glass pane in a direction perpendicular to the section 2-2 shown, in Fig. 2, to give a clearer picture of the final assembled shape of an individual busbar-shaped electrode. Thus, a laminated safety glass structure is shown with the outer glass layers 12 and 14 adhered to each side of the electrically heatable transparent sheet 16, where the individual resistance wires shown at 50, 52, 54 and constituting the heating pattern 20 are located between the continuous film strip 42 and adjacent segmented bands 40. As can be seen, the underlying segmented band has been partially deformed to enclose the outer surface of the individual resistor wires according to a suitable method of manufacturing the electrically transparent disk with such busbar-shaped electrode means as an integral part. It should also be noted that in the construction with such busbars, parts of the segmented belt which do not enclose the individual resistance wires are in direct electrical contact with the overlying continuous belt 42.

A suitable method of making the electrically heatable transparent disk having a three-dimensional non-parallel random pattern for the resistor wires together with the busbars of the present invention utilizes the general process previously described. Thus, the general process which does not form part of the present invention need not be described in the present application with the exception of the application of the improved busbars to the electrically heated transparent disk. Consequently, a pair of segmented foil strips are first applied to one

7307015-3 side of the sheet of transparent thermoplastic polymer, which shrinks from its original dimensions when heated to a high temperature, adjacent to and parallel to an opposite outer edge of the contour forming a curved safety pane. Thereafter, a transverse pattern of resistance wires is applied with parallel orientation relative to each other between the segmented foil strips and so that the wire pattern extends beyond the segmented strip. This step is followed by attaching the wire pattern to the same side of the polymer sheet using electric heating electrodes placed at the ends of the individual resistor wires according to the known method. Electricity can then be applied to the heating electrodes so that the polymer sheet and the resistance wires can expand and contract during heating to embed parts of the wires in the surface of the polymer sheet even according to the known process. The foil strips are segmented to apply electrical force uniformly with the heating electrodes as the curved contour of the window and the correspondingly shaped wire pattern give individual resistance wires of different lengths which would otherwise be subjected to non-uniform heating. The segmented foil strips undergo some deformation during this heat setting which is sufficient for partial contact with the subsequently applied continuous foil strips and further provides a barrier layer at the electrical connections against each flow of thermoplastic polymer material during the final heat adhesion step. The continuous foil strips 42, which are of sufficient width and thickness to satisfy the electrical current conduction requirements and which allow direct adhesion to the same surface of the polymer sheet, are then secured by additional heat adhesion, which may occur after removal of the heating electrodes. The usual final heat adhesion step used in the manufacture of glass laminates further deforms the segmented foil strips, where the strips enclose the outer portions of the individual resistance wires, leading to direct and electrical contact with the overlying continuous foil strips.

The above-described methods of designing the improved busbars of the present invention can be performed on the same apparatus as previously mentioned. More specifically, this known apparatus uses a shrinkable drum which cooperates with mechanical means for biasing the resistor wires in order to obtain the pleated shape thereof. This is accomplished by applying a transverse pattern of the biased resistor wire under tension between the segmented foil strips prior to heat gluing the resistor wires with thermoplastic.

7307015-3 polymer sheet. In the present method of mounting the busbars, the shrinkable drum blank of the known apparatus can be provided with template means which give the curved window shape. For example. For example, a template pattern for the box of Fig. 1 should be in line with its longitudinal dimension in the direction of the longitudinal axis of the drum. This template means may simply be a plotted line located on the periphery of the drum surface, over which the sheet of transparent thermoplastic polymer is wound. When using this modified apparatus to produce the electrically heatable transparent sheet, the segmented foil strips are applied to the outside of the wound polymer sheet so that each strip is placed adjacent to and parallel to an opposite outer edge of the curved pane at the locations determined by the template means. A coil of resistance wire is then wound around the periphery of the drum, which is then attached to the outside of the polymer sheet and with the heating electrodes then placed on the outside of the window surface. As a more detailed explanation of the embodiment of the present method with the known apparatus, the method of manufacturing the electrically heatable transparent sheet comprises the following steps: a) the segmented foil strips are applied to the outside of the thermoplastic polymer sheet adjacent to and parallel to an opposite outer edge of the curved safety glass pane; c) a transverse pattern of prestressed wire is applied under tension between the segmented foil strips so that the wire pattern extends beyond the bands and the wire pattern is attached to the periphery of the shrinkable drum with heating electrodes placed on the outside surface of the pane; d) resistance wires and the surface of the thermoplastic polymer so that the polymer sheet can contract in the direction of the wire web, e) electric current is supplied to the heating electrodes sufficiently to embed the parts of the wire which are in contact with the surface of the polymer sheet therein, and f) the continuous foil strips are fixed by heat adhesion at the same side of the polymer sheet for direct contact with the individual resistor wires and the underlying segmented foil strips.

From the above method it can be seen that the foil strips are aligned along the longitudinal outer edges of the curved safety glass pane and as further mentioned the continuous foil strips can be applied by a further heat sticking step after the transparent sheet has been removed from the periphery of the drum by heating means other heating means. After attaching the continuous film strips to complete the busbars of the present invention, the disc can then be easily handled to produce a laminated safety glass pane in a conventional manner.

Particular operation of the known apparatus for producing such an electrically heatable transparent disc comprises the following essential steps: a) a sheet of transparent thermoplastic polymer is wound around the circumferential surface of the shrinkable drum and both ends of the sheet are attached to the drum, b) a pair of segmented foil strips are applied to the outside of the polymer sheet at locations adjacent and parallel to its opposite outer edges, c) a spiral of prestressed resistance wires is wound in a closely spaced relationship on the periphery of the drum in contact with the outside of the attached polymer sheet and the tension is maintained in each turn of the resistance wires, d) the wire coil is attached to the outside of the polymer sheet with heating electrodes placed between the segmented foil strips and not in the area of ​​the box, e) the drum is shrunk by predetermined reduction of its diameter, f) electricity is supplied to the heating electrodes sufficiently to embed portions of the wire in the polymer sheet. , and g) continuous foil strips are applied for direct contact with the individual resistor wires and underlying segmented foil strips to provide the finished busbar.

It can be seen from the above that the reduction of the circumference of the drum allows the composite element to arc under the gravitational forces from the surface of the drum, which relieves the tension forces on the resistor wires, thereby enabling them to shrink or wrinkle while still maintaining point contact with the polymer sheet. When electric current is applied by means of the heating electrodes to the wire pattern while it is in a suspended state, the polymeric material is heated to its softening point, whereby parts of the wire are still allowed to be in contact with the polymer surface to be embedded therein. Under these heating conditions, both the polymer sheet and the thread pattern are allowed to expand and contract in

7307015-3 the longitudinal direction of the wire pattern depending on the individual thermal expansion characteristics while still remaining in contact. It has also been observed during this heating operation that the polymer sheet is visibly contracted while still being heated after first undergoing thermal expansion at right angles to the direction of the wire web. When the heating is interrupted by interrupting the electrical power supply to the wire pattern after the shrinkage has taken place and the composite element is then allowed to cool, an adhesion is generated at the embedded parts of the wire pattern. By further fitting between the wire web and the direction of shrinkage of the polymer sheet, it can be seen that a greater randomness is achieved in the final wire pattern than would otherwise occur.

From the above description of suitable embodiments, it will be appreciated that other methods may be used to provide an improved busbar with comparable results. It will also be appreciated that the methods described herein may be used to provide the same type of busbar for different heating wire patterns in a safety glass pane. As an example, the busbars may be oriented in the transverse direction of the window element with the heating wire pattern extending in the longitudinal direction. In addition, the present busbar shape can be used in a non-random parallel set of heating wires to provide some of the same benefits that have emerged from this invention. The intention is not to limit the invention but consequently the scope of the invention is determined only by the appended claims.

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