WO2024003875A1 - Variable light transmission glazing with complex shape and method of manufacture - Google Patents

Abstract

The present invention discloses a thermoformed Variable Light Transmission (VLT) film having complex shape, the method of thermoforming a VLT film with complex shape, and a laminated glazing having the VLT film formed to a complex shape.

Description

VARIABLE LIGHT TRANSMISSION GLAZING WITH COMPLEX SHAPE AND METHOD OF MANUFACTURE

FIELD OF THE INVENTION

The invention relates to the field of automotive glazing and more specifically to glazing having films that can be formed to complex shapes.

BACKGROUND OF THE INVENTION

Many technologies have been developed to dynamically control the level of light transmission through a window. They include electrochromic, photochromic, thermochromic and electric field sensitive films designed to be incorporated into laminated glass.

Glazing that incorporate these variable light transmittance (VLT) technologies are sometimes referred to as variable light transmission, “smart” glass or switchable.

All have the intangible benefit of providing a futuristic function that is infrequently found in any of the glazing produce the market today providing a major product differentiation.

One of the major tangible benefits of VLT glazing is that it can be used to reduce the load on the Heating, Ventilation, and Air Conditioning (HVAC) system. With VLT glazing installed, the tint level can be increased, blocking a substantial portion of the energy from the sun. On cool days, the tint can be minimized allowing the solar energy to heat the interior. The tint can be varied to permit a comfortable level of natural light and can also be used to provide privacy. Each window can be independently controlled allowing the solar load control to vary with the suns’ position as needed and to accommodate personal preferences.

While glazing on which the level of tint can be quickly changed in response to an electrical signal have been available for decades, adaptation has been slow. One would think that this would be a natural technology to incorporate into buildings and automobiles as regulatory requirements mandating minimum levels of energy efficiency have been enacted, as the cost of energy has been increasing and consumers, who are becoming increasingly aware of the environmental impact of their everyday choices and actions, have been demanding green, energy efficient, environmentally friendly products. This is especially true of full electric vehicles, where heating and cooling of the cabin can consume a substantial portion of the energy stored in the traction battery, reducing the range of the vehicle, and contributing to “range anxiety.”

While there are a number of glass fabricators who can supply VLT glazing in commercial quantities, VLT glazing still only occupies a small percent of the world glazing market in both the architectural and automotive markets.

The reasons are varied but include the relative high price of VLT glazing and the fact that the technology is still considered as new and unproven.

The technology has not been in use long enough or on a large enough scale to validate long term durability. Glazing is normally required to last the lifetime of the building or vehicle.

The higher cost of VLT is at least partially offset by the energy savings and the reduction in the need for conventional mechanical blinds and shades. However, as VLT glazing supplements but does not eliminate or likely substantially reduce the capacity required of or the initial installed expense of the HVAC system, the cost benefit ratio is still not favorable. It is more of a comfort convenience technology that also can save energy. However, we can expect to see a decrease in price and an increase in market share as more buildings and vehicles incorporate this technology and as energy prices continue to increase.

In the automotive market, only a very small number of low to moderate volume series production vehicles have been offered with VLT technology. Of these, the take rate has been low. All have been expensive, high end, luxury vehicles and commanded a substantial premium for the VLT option.

There has been more activity in the aftermarket where VLT has been offered as an upgrade to the conventional OEM glazing. These are typically made to order and very expensive.

VLT glazing has been used in some smaller aircraft used in private and commercial aviation. In this market the utility is more of an intangible comfort and convenience nature and as a market differentiator.

In the large commercial passenger aircraft market, there has been interest in VLT as it is necessary to have the cabin window shades drawn during some situations. Rather than having to depend upon the passengers and cabin attendants, VLT allows for control by the flight crew. One of the unique features of the composite body, Boeing 787 Dreamliner, is the VLT cabin windows. The glazing is based upon the technology used to make automatically dimming, VLT, automotive mirrors. The level of tint, and corresponding level of light transmission of each window, can be controlled by the passenger. Passenger control can be overridden by the flight crew as needed. The windows are made using a gel, containing an electrochromic chemical, sandwiched between two flat sheets of glass. The two glass substrates each have a transparent conductive coating, which serves as an electrode, on the face in contact with the gel. A low voltage direct current applied to the conductive coating, induces an oxidation or reduction reaction to take place. In this manner, the tint of the electrochromic chemical containing gel is controlled. The assembled flat electrochromic cell is positioned between the curved interior and exterior glazing.

The electrochromic gel approach is not easily or economically adapted to curved automotive glazing due to issues with maintaining a uniform gap between the electrodes, compliance with regulatory requirements and in meeting the demanding specifications required for automotive applications.

At best, the ability to form a glass sheet into an automotive glazing shape can be controlled to no greater than plus or minus 0.5 mm. A non-uniform gap between the substrates will result in uneven tint of the electrochromic material. In addition, the conductive coating typically used, Indium Tin Oxide (ITO), deposited as an electrode on a glass substrate, cannot be heated and bent to shape without damaging the coating and breaking the electrical continuity of the coating.

Typical automotive specifications require parts to not only meet the functional requirements for the life of the vehicle but also to be able to survive extremes of temperature, 100% humidity, extended exposure to intense UV, as well as exposure to water and salt without degradation.

To meet regulatory requirements, the visibility through the glazing and optical quality also must not deteriorate for the life of the glazing. In certain glazed positions, the glazing must also meet requirements for occupant retention in the event of a wreck and when impacted from the exterior, resistance to penetration and spalling. These requirements can be difficult to meet even with ordinary glazing. This is difficult if not impossible with the electrochromic gel technology.

One approach, which has been found capable of meeting both automotive and architectural requirements, uses a solid electrochromic active variable light transmission material rather than a gel. A number of compounds are known that can change from transparent to dark and back, when undergoing an oxidation or reduction reaction in response to a low voltage direct current. The material, deposited upon a glass substrate, is sandwiched between a set of transparent, conductive coated, electrodes. This eliminates the issue with the gap as only one of the glass layers needs to have the active material and electrodes applied. This type of VLT glazing has been produced for architectural and automotive applications. The primary drawback is that even with the thickness of the active material kept very uniform, the rate of change is dependent upon the electrical current which is difficult to control across the entire surface. States between full dark and full light tend to be non-uniform. As a chemical reaction takes place, the time that it takes to change states is measured in minutes. As the electrodes are only separated by the thickness of the active material measure in microns, the coating deposition must be carefully controlled to prevent the shorting and arcing. Applying a layer of active material with uniform thickness and the conductive coating requires a large capital investment in expensive equipment not normally used to fabricate automotive glazing, as well as a high level of expertise, and licensing of the relevant technology.

One novel approach is based on electrodeposited tungsten oxide, Prussian Blue and a Lithium ion conducting PVB interlayer. A first active material is applied over a transparent conductive coating on one glass surface but rather than having the material sandwiched between a set of transparent conductive coatings on the same substrate, a transparent conductive coating and a second electrochromic material is applied to the adjacent and opposite face of the second glass layer. The glass is then laminated using a Lithium-ion conductive plastic interlayer. When a voltage is applied to the conductive coating of each surface the flow of current through the plastic interlayer results in very uniform change in light transmission through the entire range without the risk of short circuits and arcing.

A number of VLT technologies have been developed that are based upon the kinetic response of a particle or molecule to an electrical field. These include, Suspended Particle Devices (SPD), Polymer Dispersed Liquid Crystal (PDLC), Electrochromic film (EC), Polymer Network Liquid Crystal (PNLC) and Liquid Crystal (LC).

SPD, PDLC and LC have advantages, relative to electrochromic. Electrochromic VLT glazing undergoes a chemical reaction when a current is passed through the active material, in much the same way that a battery functions when it charges and discharges. The active material undergoes an oxidation or reduction reaction as the materials changes from light to dark and back. SPD, LC and PDLC however operate on a different principle. There is no chemical reaction. The molecules that make up the active material undergo a kinetic change in response to the presence of an electrical field. Therefore, the switching time of SPD and PDLC is orders of magnitude faster than electrochromic glazing.

SPD is a type of VLT in which the level of tint can be controlled and varied in response to an applied electrical field. SPD goes from dark in the unpowered state to clear in the powered state. In an SPD film, microscopic droplets of liquid containing needle like opaque particles, known as light vales, are suspended in a polymer matrix. In the off state the particles are in a random state of alignment and block the transmission of light. The degree of alignment and resulting tint can be varied in response to the applied voltage. The level of light transmittance in the on and off states can also be shifted through changes to the thickness and composition of the active material. In the off state, it is still possible to see through SPD. The primary drawback of SPD is its strong blue tint. Haze, sensitivity, long term degradations due to UV exposure, the high operating voltage, and the limited range of light transmission are also issues.

PDLC is a light scattering VLT technology which goes from light scattering with high haze in the off state to clear in the on state. In a PDLC film, microscopic droplets of liquid crystal are suspended in a polymer matrix. In the off state the liquid crystals are in a random state of alignment scattering the light and providing privacy. When an electric field is applied, the crystals align and allow light to pass by matching the refractive index of the LC and polymer matrix when the particles rotate.

The degree of scattering can be controlled by varying the amplitude of the applied voltage. The level of light transmittance in the on and off states can also be shifted by changing the thickness and composition of the active material. PDLC is primarily a privacy product though it can also be used for solar control as it reduces the solar energy transmitted. The primary drawback of PDLC is the whitish color that it takes on in the off state. Like SPD, haze, the operating voltage, degradation from long term UV exposure and the range of light transmission are also issues. PDLC also tends to have a larger voltage drop across the area of the electrodes than other VLT technologies which can result in non-uniform intermediate states.

Upon the loss of power, SPD and PLDC both fail in the dark state. For safety reasons, SPD and PDLC cannot be used in applications where an abrupt loss of visibility would be dangerous as is the case if power is lost. Both also require a relatively high alternating current voltage in the 50-100-volt range. The higher voltage increases the risk of shock and requires additional circuit protection and insulation.

Liquid Crystal (LC) technology is similar to PDLC. The active material in LC is also liquid crystal. However, rather than encapsulating the liquid crystal in a polymer matrix, the two conductive coated substrates are separated by spacers, the perimeter edge is sealed and then the gap between the spacers is filled with liquid crystal forming a liquid crystal film.

Various materials are known that are suitable for use as an edge seal material including but not limited to epoxy, urethane, silicon, acrylic as well as many other curable polymers.

The minimum width for sealing material is typically between 2 mm to 10 mm. The width is dependent upon the shear stress applied during the liquid crystal film forming process as well as the thickness, the strength, and the adhesion to the substrate of the material. The sealing material must remain intact, holding the two substrates together. The sealing material must be applied in sufficient quantity and have sufficient strength to withstand shear stress applied during the forming process to the transversal area of the sealing.

The alignment layer forms a layer over the substrates conductive coating. One or two alignment layers should be present on a liquid crystal film, such as one of the two substrates have one alignment layer deposited over the conductive coating surface or both substrates each have one alignment layer deposited over the conductive coating surface.

LC offers substantial improvements over PDLC. For one, LC can be designed to be either dark or clear in the unpowered off state.

LC that is dark in the OFF state, without power, has haze of less than 10% and light transmission in the 1 - 2% range. In the clear, powered, ON state, it has haze of less than 2% and transmission between 20-40%. LC that is clear in the OFF state, without power, has haze in the range of 1 to 2% and light transmission in the range of 25%-60%, depending on the type of liquid crystal used. In the ON state (dark state) it has haze of less than 2% and transmission between 2% and 30%. LC operates at a range from 5 volts for twisted nematic based mixtures and 20-25 Volts for Guest Host with chiral dopant and dichroic dye mixtures. This places LC in the low-voltage class which lowers the cost of the supporting electronics and wiring. While both haze and transmission are sensitive to the viewing angle LC is less sensitive than PDLC. The biggest advantage of LC is color. LC in the dark state takes on shades of black which is preferred to the deep blue of SPD and the milky white of PDLC.

All three, SPD, PDLC and LC are implemented as a film within a laminated glazing. The film is comprised of a layer of the active material sandwiched between two thin, flexible, plastic substrate layers having a transparent conductive coating on one side of each such that the conductive coating surfaces face each other and sandwich the active material. The conductive coating on the plastic substrates serves as the electrodes.

The Direct Current (DC) resistance of all three is extremely high, in the mega-ohm range so very little real power is consumed. The power drawn is reactive. The two conductive coated plastic substrates, separated by the dielectric of the active material, form a capacitor.

Bus bars are applied to each of the substrates conductive coated surfaces. Conventionally, the VLT film is laminated in between two plastic bonding interlayer layers to form a laminated glazing. The cross section of a laminate with a performance film 12, such as a VLT film, laminated between two interlayers 4 is shown in Figure 1 B.

Figure 2 shows a cross section of a VLT film. The active material 64 is sandwiched between two plastic substrates 60 with each having a transparent conductive coating 62 on the face interior to the film. For LC films, spacers 66 are required to maintain a uniform gap.

The plastic substrate 60 used is typically Polyethylene Terephthalate (PET). In addition to PET, a number of other plastic substrates are available that can be used including but not limited to Polyethylene Naphthalate (PEN), Cellulose Triacetate (TAC), Polycarbonate (PC), Cyclic Olefin Polymer (COP), and Polyimide (PI). However, PET is favored due to its high light transmission and low coefficient of expansion, water absorption ratio and glass transition temperature.

A major limitation of VLT films is encountered when we attempt to implement VLT in a glazing with complex curvature. For the present disclosure, complex curvature or complex shape should be understood as any glazing that has a radius of curvature of less than 4 meter is one direction, or curvature in at least two directions of less than 6 meters in at least one of said at least two directions, or any curvature that requires a substantial amount of plastic deformation, greater than 1 - 3 %, to take place when bending the flat glass to the final design shape or when a liquid core is included in a curved laminate. Additionally, complexity of the glazing could be impacted by the design, elements included, or geometrical shape of the glazing which results in stress concentrators in the edge corresponding to a recess portion or notch. In a preferred embodiment, such recess portion may be of different shapes as semicircular, square or any polygon with corners with a certain radius. By varying the radii of the stress concentrator, the complexity of the shape will vary. Therefore, this type of geometries inducing stress concentration as having a complex curvature.

During conventional glass lamination process, the PET based VLT film is placed between two plastic interlayers and two glass layers, in a clean room, typically chilled to prevent sticking of the interlayers prior to assembly. The assembled laminate is then placed in an airtight bag, or a rubber channel is applied to seal the edge of the assembled laminate. A vacuum is then drawn. Under the pressure created by the vacuum, the PET will stretch and undergo some elastic deformation. However, there is a limit to this deformation such as when surpassing this limit defects such as wrinkles, delamination of the PET layers, shorting of the conductive coating and breaks in the brittle coating can occur.

The glass transition range of PET plastic substrate is quite wide, starting at 70°C and extending up to its’ melting point of 255°C. During the normal lamination process the film will be heated to the glass transition range of the PET and some of the elastic deformation will convert to plastic deformation. At this point, some wrinkles may relax as the stress is relieved.

The limitations of the process are illustrated in Figures 3B and 3C. The size of the flat sheet of VLT film is 800 mm x 1200 mm. In Figure 3A, the film is shown in both the flat state 30 and formed 32 to a cylindrical shape. The radius of curvature is 4 meters along the y axis and the shape is flat in the x direction. As it can be seen, the flat and formed shapes make line contact at centerline. With the flat film 30 set on a positive forming tool, at room temperature, the flat film 30 will tend to sag to the bent shape, closely matching the tools’ contour, under its own weight or with just mild pressure. The concave side of the film will be in compression and the convex side will be in tension. The film cannot be compressed but it can stretch. While the edges need to move by up to ~48 mm to reach the formed shape, the film, with curvature along just one axis, only needs to deform along the y axis and the rate of change is uniform. Clearly this shape, with curvature in just one direction, can be formed with minimal stress and strain. The convex surface area will slightly increase, and the thickness will slightly decrease near the center where the tension is greatest as the film undergoes elastic deformation. Depending upon the type of conductive coating used, the film may be functional after forming. As one would intuitively suspect, the portion of the film that first comes into contact with the mold will undergo the greatest amount of stretching.

Figure 3B shows a complex shape surface 34 with compound curvature with a radius of curvature of 4 meters in the x direction and 2.5 meters in the y. The two surfaces 30 and 34 make point contact at the center. At the corners, the film needs to move by ~70 mm to reach the formed shape. However, the curvature is now in two directions. It is readily apparent that the flat shape cannot be formed to the complex shape without a high level of deformation, otherwise, wrinkles will form. Figure 3C shows the cylindrical shape 32 and the complex shape 34 to further illustrate the difference between the two. The corners of the cylindrical shape still need to move by ~20 mm to reach the formed shape 34 from the partially formed shape 32.

We can predict the feasibility of a forming process for a given shape by looking at the deformation required going from the flat to the formed shape. We know what typical limits are for various materials. For a PET, based upon the material properties, the limit on the change in surface area that can occur before the PET or coating is damaged ranges from 1 % - 3 % depending upon a number of variables including the material, the conductive coating, process temperature, and the rate of change in the shape. PET alone, being a thermoplastic, can be deformed by 30% - 70% without tearing. At an elevated temperature, in the glass transition range of the substrate, failure is likely to first occur in the fragile, brittle, semi-crystalline, ITO coating rather than in the amorphous elastic substrate.

As a result, almost all of the SPD and PLDC glazing that have been produced have been cylindrical, flat, or very close to flat curvature. On some glazing with moderate curvature, most of the curvature is near the edges of the glazing, where the glass meets the metal frame where it is installed. The film is cutback to just outboard of the inner edge of the black obscuration that surrounds the glazing perimeter, i.e. , the VLT film is shorter than the glazing. In this manner, the maxim strain is reduced to a manufacturable level by only having the film disposed in the relatively flat portion of the glazing.

This forming limitation places major constraints upon the designer and the aesthetics of the glazing. Laminated vehicle roofs, typically maintain geometric continuity with the sheet metal body along the edges, transitioning to a larger radius approaching the center of the part, from both the front to back and left to right directions. This compound curvature results in a surface shape that requires high levels of deformation that the VLT film cannot survive.

As a result, laminated VLT film glazing can only be implemented on relatively flat, large radii, parts.

The prior art has attempted to achieve VLT films with radius of curvature below what can be achieved by this invention such as described in US7705959B2, however, the VLT substrate films are either curved separately or they may be curved together however, the VLT material that fills the gap between the substrates are added after the thermoforming step, which adds an additional step into the process and complexity.

It would be highly desirable to have VLT films with complex shapes as well as a method for forming the films while maintaining optical and electrical properties.

BRIEF SUMMARY OF THE INVENTION

The invention is related to a VLT film prior to forming to a complex shape, a method of forming a VLT film to a complex shape and a laminated glazing having a VLT film formed to a complex shape.

The VLT film of the present invention should have the transparent conductive coating modified to prevent cracking of the electrodes during forming. The typical ITO coating used for the electrodes is replaced by a coating including but not limited to: at least one metallic layer and at least one dielectric layer, silver nanowires, carbon nanotubes, ITO combined with a layer of silver nanowires or carbon nanotubes, ITO or a similar brittle coating deposited over a metallic/dielectric ductile coating, graphene, an organic conductive layer such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), a conductive mesh or any combination of the previous coatings and combinations of coatings.

The variable light transmission film of the invention comprises two substrates with each one having two major surfaces wherein one of said two major surfaces of each substrate is coated with an electrically conductive coating, wherein said conductive coating maintains electrical continuity during and after forming, and an electrically variable light transmission active material wherein said active material is disposed in between the two substrates such that the surfaces coated with the conductive coating face each other, and wherein the periphery edge of the active material is offset inboard of the periphery edge of the two substrates along at least a substantial portion thereof. Preferably, the offset of the edge of the active material with respect to the edge of the substrates is no more than 50 mm. More preferably, the offset of the edge of the active material with respect to the edge of the substrates is at least 20 mm all around.

The VLT film, with the modified coating is heated and thermoformed according to the first method described below. The thermoforming method comprises the steps of o providing a sheet of VLT film, wherein said film is comprised of:

■ two substrates with similar dimensions each one having two major surfaces wherein one of said two major surfaces of each substrate is coated with an electrically conductive coating wherein said conductive coating maintains electrical continuity during and after forming;

■ an electrically variable light transmission active material wherein said active material is disposed in between the two substrates such that the surfaces coated with the conductive coating face each other and are in contact with the active material, and said active material does not extend to the periphery of the substrates in at least one region thereof; o providing a mold; o providing a heating means; o providing a film supporting means; o providing a means of applying force to said film o placing said film in the supporting means such that said means are placed in the region of the periphery of the substrates that does not contain the active material; o heating said film and/or mold by the heating means to a temperature below or within the glass transition range of the plastic substrate; o applying force to deform the film to the shape of the mold; o holding the film in the glass transition range to relieve stress; and o cooling the film to below the glass transition range.

A laminated VLT glazing with high complex curvature is then produced by laminating the VLT film formed by the first method of this disclosure.

A second method for thermoforming a VLT film comprises the steps of:

• providing a sheet of VLT film, wherein said film comprises: • two substrates with similar dimensions each one having two major surfaces wherein one of said two major surfaces of each substrate is coated with an electrically conductive coating, o an electrically variable light transmission active material wherein said active material is disposed in between the two substrates such that the surfaces coated with the conductive coating face each other, and o a conductive coating that maintains electrical continuity during and after forming;

• providing a mold;

• providing a heating means;

• providing a film supporting means;

• providing a means of applying force to said film

• placing said film in the supporting means;

• heating said film and/or mold by the heating means to a temperature below or within the glass transition range of the plastic substrate;

• applying force to deform the film to the shape of the mold;

• holding the film in the glass transition range to relieve stress; and

• cooling the film to below the glass transition range.

In a first preferred embodiment of this second method one or more elastic membranes with dimensions larger than the VLT film are disposed either on top, or above and below the VLT film sandwiching it, such that the one or more membranes are secured or affixed in its periphery region to the supporting means.

In a second preferred embodiment of this second method the VLT film active material does not extend to the periphery of the substrates in at least one region.

A laminated VLT glazing with high complex curvature is then produced by laminating the VLT film formed by the second method of this disclosure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Figure 1A Cross section: typical laminated automotive glazing.

Figure 1 B Cross section: typical laminated automotive glazing with performance film

(VLT) and coating. Figure 2 Cross section of a typical VLT film.

Figure 3A 1200 x 800 VLT film, flat and formed to cylindrical shape.

Figure 3B 1200 x 800 VLT film, flat and formed to complex shape.

Figure 3C Complex and cylindrical shape compared.

Figure 4 Top view of laminated variable light transmission roof with complex shape.

Figure 5 Isometric exploded view of laminated variable light transmission roof with complex shape.

Figure 6 Isometric view showing the compound bend of the VLT film.

Figure 7A Isometric view showing the flat VLT film vs. the formed film.

Figure 7B Right view showing the flat VLT film vs. the formed film.

Figure 7C Front view showing the flat VLT film vs. the formed film.

Figure 8A Right view showing the flat VLT film vs. the deformed shape at each of four stages of forming.

Figure 8B Front view showing the flat VLT film vs. the deformed shape at each of four stages of forming.

Figure 9 Perspective exploded view of a glazing according to an embodiment of the present invention, particularly embodiment 1 , having Forming means top positive and negative molds, mounting means and membranes.

Figure 10 Perspective exploded view of a glazing according to an embodiment of the present invention, particularly embodiment 2, having forming means top positive mold, mounting means and membranes.

Figure 11 Perspective exploded view of a glazing according to an embodiment of the present invention, particularly embodiment 3, having forming means top positive mold, mounting.

Figure 12 Perspective exploded view of a glazing according to an embodiment of the present invention, particularly embodiment 5.

Figure 13 Perspective exploded view of a glazing according to an embodiment of the present invention, particularly embodiment 6. Figure 14 Perspective exploded view of a glazing according to an embodiment of the present invention, particularly embodiment 7.

Figure 15 Perspective exploded view of a glazing according to an embodiment of the present invention, particularly embodiment 8.

Reference Numerals of Drawings

2 Glass

4 Bonding/Adhesive layer (plastic Interlayer)

6 Obscuration/Black Paint

12 Infrared reflecting film

20 Infrared reflecting coating

30 Flat film

32 Formed film

34 Partially formed film

36 Variable Light Transmission film

40 Radius 1

42 Radius 2

50 Positive mold

52 Negative mold

54 Membrane

56 Mounting means

60 Plastic substrate

62 Transparent conductive coating

64 Active VLT material

66 Spacer

101 Exterior side of glass layer 1 (201), number one surface.

102 Interior side of glass layer 1 (201), number two surface. 103 Exterior side of glass layer 2 (202), number 3 surface.

104 Interior side of glass layer 2 (202), number 4 surface.

201 Outer glass layer

202 Inner glass layer

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure can be understood more readily by reference to the detailed descriptions, drawings, examples, and claims in this disclosure. However, it is to be understood that this disclosure is not limited to the specific compositions, articles, devices, and methods disclosed unless otherwise specified and, as such can vary. It is also to be understood that the terminology used herein is for the purpose of describing aspects only and is not intended to be limiting.

In addition, while the focus of the embodiments and the discussion is on automotive applications of the inventions, the invention has equal utility in many other types of applications including but not limited to aerospace, architectural, marine, transit vehicle and commercial vehicles.

The following terminology is used to describe the laminated glazing of the invention.

A glazing is an article comprised of at least one layer of a transparent material which serves to provide for the transmission of light and/or to provide for viewing of the side opposite the viewer and which is mounted in an opening in a building, vehicle, wall or roof or other framing member or enclosure.

The term “glass” can be applied to many inorganic materials, including many that are not transparent. For this document we will only be referring to transparent glass. From a scientific standpoint, glass is defined as a state of matter comprising a non-crystalline amorphous solid that lacks the ordered molecular structure of true solids. Glasses have the mechanical rigidity of crystals with the random structure of liquids.

Glass is formed by mixing various substances together and then heating to a temperature where they melt and fully dissolve in each other, forming a miscible homogeneous fluid.

When heated or cooled sufficiently, glass undergoes a glass transition. Most solid materials when heated and cooled are controlled sufficiently, will undergo a phase change. Further, the change in state is abrupt and occurs at a precise temperature as the molecules go from moving about freely to being locked in place and vice versa. This is because all of the bonds between the molecules are identical and break at the same temperature.

In glass, due to the random order of the molecules, the bonds are all different. The bond strength is a function of the stress on the bonds and temperature. In a glass, as the material is heated, it reaches a point where the bonds just begin to break, and the glass starts to soften. As the temperature is increased, more of the bonds continue to break and the glass becomes softer until the glass reaches its melting point where the molecules can move more easily. Some say that the glass is in the liquid state, although this might be controversial. This range of temperatures where the glass transitions from a “liquid” to a “solid” is known as the glass transition range. The center of this range is the glass transition temperature, Tg.

The same principles also apply to thermoplastics as well as glass. Below the transition range, the plastic will only undergo elastic deformation. Once elevated to the glass transition range, permanent plastic deformation can occur.

Laminates, in general, are articles comprised of multiple layers of thin, relative to their length and width, material, with each thin layer having two oppositely disposed major faces, typically of relatively uniform thickness, which are permanently bonded to one and other across at least one major face of each layer. The layers of a laminate may alternately be described as sheets or plies. In addition, the glass layers may also be referred to as panes.

Laminated safety glass is made by bonding two layers of annealed glass together using a plastic bonding layer comprised of a thin sheet of transparent thermoplastic.

The plastic bonding layer (interlayer) has the primary function of bonding the major faces of adjacent layers to each other. The material selected is typically a clear thermoset plastic. For automotive use, the most used bonding layer (interlayer) is polyvinyl butyral (PVB). Automotive grade PVB has an index of refraction that is matched to soda-lime glass to minimize secondary images caused by reflections at the PVB/Glass interface inside of the laminate. In addition to polyvinyl butyral, ethylene vinyl acetate (EVA), thermoplastic polyurethane (TPU), polyolefin elastomers (PoE), optical adhesive resins (OCR) or a combination thereof may be used. Annealed glass is glass that has been slowly cooled from the bending temperature down through the glass transition range. This process relieves any stress left in the glass from the bending process. Annealed glass breaks into large shards with sharp edges. When laminated glass breaks, the shards of broken glass are held together, much like the pieces of a jigsaw puzzle, by the plastic layer helping to maintain the structural integrity of the glass. A vehicle with a broken windshield can still be operated. The plastic layer also helps to prevent penetration by objects striking the laminate from the exterior and in the event of a crash occupant retention is improved.

For very thin conductive materials we typical characterize the resistance in terms of the sheet resistance. The sheet resistance is the resistance that a rectangle, with perfect bus bar on two opposite sides, would have. Sheet resistance is specified in ohms per square. This is a dimensionally unitless quantity as it is not dependent upon the size of the rectangle. The bus bar to bus bar resistance remains the same regardless of the size of the rectangle.

Haze is a measure of how much light is scattered by a transparent material. It is measured by passing a beam of collimated light through the transparent sample being measured into the interior of a hollow sphere with a reflective coating on the inside walls. The intensity of the light is measured by a photodetector perpendicular to the beam mounted to a side of the spere. Opposite the entrance of the sphere a light trap is mounted containing a material that absorbs all of the light. A reflective shutter can be opened and closed to block the light trap. With the shutter reflecting the light we read the total light transmitted through the glass. With the shutter open and the light being absorbed, we only read the light that is scattered by the sample which is the haze.

Automotive laminates will typically have a haze of less than 2% and preferably as low as possible. Some performance films, interlayers and coatings will increase the haze.

In addition to ITO, several coatings besides transparent conductive coatings can be further used. Additional coatings selected from anti-reflective coating, Low-E, antifingerprint and combinations thereof and is deposited in the exterior surface of the second glass layer. A variety of means may be used to deposit them including Magnetron Sputtered Vacuum Deposition (MSVD), spray, controlled vapor deposition (OVD), dip, sol-gel, and others.

As discussed, the three types of VLT films, SPD, PDLC, PNLC and LC, all have similar cross sections. All utilize two layers of transparent plastic as substrates with a transparent conductive coating on one side of each layer. The coating serves an electrode to distribute the electrical field needed to change the alignment of the particles/molecules.

As discussed, while PET is the typical plastic used for as the substrate, there are several other equivalent transparent thermoplastics that may be used. While the discussion and embodiments center around PET, PET is in no way to be considered as a limitation.

As all of the VLT technologies draw very little real power the coating does not require an extremely low sheet resistance. Values of sheet resistance in the range of 100 - 200 ohms per square are typical although substantially higher values of sheet resistance may still function depending upon a number of other factors including but not limited to the active layer thickness, the applied voltage, the type of active material, the size of the active layer and the placement of the bus bars.

The plastic substrate commonly used, PET, is a thermoplastic. It can be formed by heating the plastic into the glass transition range. The primary problem, when used in a VLT film, is the durability of the conductive coating.

Indium Tin Oxide, ITO is the most common transparent conductive coating used to produce VLT films. ITO coatings are relatively easy and inexpensive to apply. ITO is widely used in the display industry to form the transparent conductive traces needed to form the screens used on monitors, televisions, phones, and many other devices.

A number of processes are used commercially to apply ITO. For VLT applications the coating is typically applied to the plastic substrate by means of vacuum sputtering of the ITO.

ITO coatings, however, are brittle, much like glass. When vacuum sputtered, they start as amorphous but start to take on the more brittle crystalline form after a thickness of only 40 pm.

Complex shapes have been defined. Any glazing that requires deformation wherein the surface areas change in excess of 1 - 3% is considered as a complex shape. While the thickness does in fact change during forming the vast majority of the deformation occurs as an increase in the surface area of the part. Complex shapes can include parts with curvature in just one direction but will almost always apply to glazing with curvature in more than one direction. Further, the curvature need not be and frequently is not constant. It is rare to find a true spherical, cylindrical, or toroidal shape. In an automobile, the glazing is usually designed to match the curvature of the sheet metal at the edge of glass, maintaining geometric continuity and then continuing on and changing as the glass surface blends into the other portions of the glass surface. The general requirement is for the final finished product to have what is known as a Class 1 surface finish. This is the requirement for most visible automotive surfaces. To achieve a Class 1 surface requires careful CAD design of the surface as well as smooth high precision tooling to form the part by whatever process is used. Flat areas on Class 1 surfaces are avoided as minor irregularities are easily seen in reflection and it is difficult to heat and bend glass while maintaining flat areas.

For shapes that require deformation of more than a very small value to form, the ITO coating is not likely to survive intact.

When subject to a high enough level of stress, like other brittle materials, the ITO coating will crack, buckle and spall. When this happens, electrical continuity is lost, and the film will no longer function as intended.

There are a number of alternate transparent conductive coating that can be used that are not as brittle and as easily damaged. Coatings that utilize a soft ductile metal are known. Normally, depositing a metallic coating onto a glass substrate will create a mirror. However, by also depositing at least one dielectric layer, the metallic layer can be rendered transparent in the visible light range. This is the principle that solar control coatings are based upon. Such coatings, in addition to their solar properties, retain the ductile properties of the metal and are both transparent and conductive.

Solar control coatings generally have a sheet resistance of less than 10 ohms/sq and so make excellent electrodes. Any ductile solar coating, which does not react with the active material of the VLT film can be used in place of the ITO.

Other conductive coating that are easily applied and which also have excellent conductivity and formability characteristics are known. These include carbon nanotubes and nano-silver wires. Both have the advantage of being monolithic in structure and have been used commercially to produce heated circuits for glazing. Besides coatings, a mesh of fine wires may also be used.

The original unaltered ITO coating can be enhanced and made more durable by the addition of nano-silver wires, carbon nanotubes, graphene, or a conductive metal mesh. While the ITO is still just as brittle and will crack, electrical continuity is maintained by the added conductors. Preferably, the nanowires, graphene, mesh, carbon nanotubes or mesh are added while the ITO is still in an amorphous state of deposition. The ITO will start to crystalize as ~40 pm. This allows the film to be stretched and formed without loss of electrical continuity as the added conductors will tend to move and bridge any gaps formed.

Another option to provide a durable transparent conductive coating is to first deposit a thin, largely amorphous, metallic/dielectric stack and then apply the ITO or other monolithic coating over the first coating layer. This allows for the use of metallic/dielectric coating that otherwise would not be compatible with the active material.

Another modification to the VLT film is the addition of spacers. The micron dimensioned spacers are spaced within the active material and sized to maintain the uniform thickness of the active material and a uniform distance between the two opposite conductive coated surfaces of the plastic substrate. Spacers may or may not be needed with PDLC and SPD films as the polymer matrix is resistant to compression. LC will always require spacers, even when flat, as the active material is a liquid.

The spacers may be applied by a spray, photolithography, or other process. The shape of the spacers includes but is not limited to spheres, columns, and honeycombs structures. The spacers may be fixed and adhered by bonding them to the substrate or they may be free to move. A combination of both fixed and non-fixed spacers may also be used. Deformation of the spacer should be less than 5-10% of its original length (diameter, width, other) to preserve the cell gap between the parallel substrates. The spacer structure must withstand the shear force applied during the forming process. If column spacers are used buckling strength must be considered.

We note that the flat unformed SPD and PDLC sheets will already contain the active material whereas the LC film will not. Liquid crystal will be added to the film after forming. Due to this difference, LC films can be processed at a higher temperature. Due to the limitations of SPD and PDLC, the upper limit is approximately 100 °C. Without the active material it is possible to raise the forming temperature to as high as 180 °C for LC films.

To thermoform the film, the VLT film, with the enhanced conductive coating, is placed upon a supporting means, which holds the film during forming.

The supporting means is any system that looks the film in the desired position, common examples are selected from the group comprising frames, clamps. When indirect clamping is used, the supporting means may also be selected from membranes and carriers, among others. The film may be clamped within the supporting means or supported by just a single or two membranes. If clamped, the clamping means may be configured to place the film in tension so as to facilitate forming. If clamp assisted by membranes, the tension needs to be transmitted to the film by either fixing it with adhesives such as pressure sensitive adhesives (PSAs); optically clear adhesives (OCAs), liquid optically clear adhesive (LOCAs); or eliminating air between the membrane and the film i.e. enhancing friction. For the last case, a seal is included in the perimeter of the two membranes, then the assembly is connected to a compressor for air extraction. To assure air extraction properly, an embossed material could be used in between the film and the membrane.

At least one mold is required. The mold may be positive or negative depending upon the forming process. One or both of the molds may be full surface or partial surface. Plug assisting is also possible, which corresponds to a partial counter mold that promotes film stretching by forcing it to be in that position. The film and the mold are heated. The heating means are heaters of any kind, common examples are selected from the group comprising contact heaters, convection heaters, IR heaters, ceramic, halogen and quartz, among others. The VLT film must be heated to within the glass transition temperature range of the plastic substrates whereas the mold can be heated below the glass transition temperature range. The precise temperature is highly dependent upon the substrate, active material, and the shape. When cooling, the film cooling rate is controlled by the film and mold temperature. The supporting means brings the film/membrane into contact with the mold after being first clamped to the supporting means or placed upon or clamped to a heat resistant elastic membrane affixed to the supporting means or placed or clamped between a set of two elastic membranes affixed to the supporting means. The elastic membrane materials could be selected from silicon elastomer, EPDM, PTFE, PET-G, PET or other thermoformable amorphous material with a glass transition temperature in the same range of the VLT substrates such as PET, PETG among others, when needed an adhesive means is used. The flat VLT film may be fixed to the elastic membranes by any adhesive means such as using any optically clear adhesive (OCA) or pressure sensitive adhesive (PSA) or vacuum. The flat VLT film may be also cut to the size required to produce the final formed shape if the film is not directly clamped. Alternately, the film may be cut to a larger size and the excess film directly clamped to the supporting means as is more typical of thermoformed thin plastic sheets. Excess film is required if clamped to the supporting means. The VLT film may be shaped from a rectangular block size or cut to the approximate shape with just minimal excess. This way the active material of the VLT film does not extend to the periphery of the substrates in at least one region and clamping is done in this at least one region that does not contain the active material i.e., the periphery edge of the active material is offset inboard of the periphery edge of the two substrates along at least a substantial portion. The clamping can also ca be done in the region of the periphery of the substrates that contain the active material. Clamping may be along the entire periphery of the flat sheet or only along at least one region of the periphery. By doing so, any damage caused to the region clamped by the supporting means can be trimmed off in a following step and a curved VLT film with high complex curvature can be achieved without any defects in the border. In general, the excess in the periphery of the VLT film will be in the range of 20 mm to 50 mm depending upon the forming process and shape.

If excess film is used, the portion that will become waste, may be fabricated without the SPD/PDLC active material in that portion of the film. The VLT film may have its conductive coating, in the region where the formed film will be trimmed, LASER ablated, chemically etched, or electrically insulated by any other means between the periphery edge of the active material and the periphery edge of the substrates prior to or after forming to prevent shorting of the two opposite conductive coatings. Cut-off of the excess material is done my means of LASER or mechanical means.

If the forming process results in shorting of the electrodes deposited on the opposite surfaces of the two conductive coated substrates, as may be the case if mechanical means are used to trim the excess, the conductive coating may be removed or rendered non-conductive by a variety of means both before forming or after forming. In the flat state, a LASER can easily be used to oblate the conductive coating through the transparent substrate of the VLT film. LASER oblation can be performed after forming however the complexity of the process is much higher as at least five axis of motion are required to move the LASER around the shape while maintaining the proper incidence angle and focal length. Mechanical means may also be used to remove the coating but tend to be less cost effective.

With the unformed flat film supported and heated, force is then applied so as to cause plastic deformation of the film to occur resulting in the film taking on the shape of the heated mold. The force may be produced by moving the mold or the film or both the mold and the film relative to each other. The force may also be applied by means of a pressurized chamber, atmospheric pressure, a counter mold, plug assistance, applying vacuum, air pressure, , movement of the film relative to the mold, or any combination of these means. The shaped film is held in the glass transition temperature range to allow stress to be relived, and then cooled to below the glass transition range. If the level of strain is too high going directly from the flat film to the final complex shape the final shape may be approached in steps with the film only partially formed at each point and the complexity increasing each time. This method is shown in Figures 8A and 8B where the final shape 32 is approached in four separate forming steps. The flat film 30, transitions to a partially formed 34 shape and then the partially formed is repeated and formed three more times. As each step the maximum stress is not exceeded.

The film may be partially thermoformed 34, with the final complex shape 32 obtained during lamination of the partially formed 34 film.

A counter mold may be employed as well or in place of the other means used to apply force to the film.

In Figures 9, 10 and 11 various forming means are illustrated.

The VLT film of the invention can be laminated into a glazing having high complex curvature. The laminated glazing with high complex curvature comprises at least two glass layers selected from the group of Soda-lime, Borosilicate or Aluminosilicate glass, or a combination thereof. The high complex curvature glazing of the invention further comprises the VLT film of the invention laminated in between said at least two glass layers and at least one plastic bonding layer. In one embodiment, the high complex curvature glazing of the invention comprises additionally a cured liquid optically clear adhesive that serves to bond the VLT of the invention to the glass layers of the glazing. It should be noted that the types of glass that may be used include but are not limited to the common soda-lime variety typical of automotive glazing as well as aluminosilicate, lithium aluminosilicate, borosilicate, glass ceramics, and the various other inorganic solid amorphous compositions which undergo a glass transition and are classified as glass included those that are not transparent.

Methods for manufacturing a laminated glazing having a VLT film as in W02020003252 is included by reference, proposing the . A similar method using a liquid optically clear adhesive for cold lamination can be applied when manufacturing a glazing with high complex curvature having the VLT film of the invention. First of all, at least one plastic bonding layer is placed on the internal surface of a first glass layer of said at least two glass layers having high complex curvature. Subsequently a non-adhesive plastic interlayer is disposed on the surface of the at least one plastic bonding layer not in contact with the first glass layer. The second of said at least two glass layers is disposed onto the non-adhesive plastic interlayer and this product is laminated with heat and pressure. Secondly the second of said at least one glass layer is removed. In one embodiment the non-adhesive plastic interlayer is also removed serving only as a sacrificial layer. In another embodiment the non-adhesive interlayer stays laminated with said at least one plastic bonding layer. Thirdly, the VLT film of the invention which has dimensions smaller than the glass layers is disposed onto either the non-adhesive plastic interlayer or onto said at least one plastic bonding layer in such a way that a gap is formed in between. This is achieved by a spacing means. This gap is filled with a liquid optically clear adhesive that is subsequently cured, bonding the VLT film to the non- adhesive plastic interlayer or said at least one plastic bonding layer. Fourthly, a second spacing means is disposed onto the non-adhesive plastic interlayer or plastic bonding layer surface and the second of said at least two glass layers is disposed on top of the second spacing means such that a second gap is formed between the interlayer and the second of said at least two glass layers. The gap is filled with a liquid optically clear adhesive, and it is subsequently cured, such that it forms the high complex curvature laminated glazing of the invention.

Embodiments

Embodiment one is an 800 mm x 1200 mm sheet of SPD film is formed by means of the apparatus illustrated in Figure 9. The complex compound curvature of the glazing and film is shown in Figure 6. The radius of curvature along the y axis, 42 is 2.5 meters and along the x 40 4 meters. This is a toroidal shape. The laminated glazing in which the film is used is shown in Figures 4 and 5.

The laminated roof has an outer 201 and inner 202 glass layer comprising 2.5 mm solar green glass. A black obscuration is printed on surface two 102 and surface four 104. The formed VLT SPD film 34 is sandwiched between two 0.76 mm thick PVB interlayers. The assembled laminate is vacuum channel preprocessed and then heat and pressure treated in an autoclave.

The film comprises two 120 pm thick PET substrates on which a layer of ITO conductive coating with thickness between 0.2 to 2.0 pm has been enhanced with a layer of carbon nanotubes. The polymer matrix layer, containing the SPD droplets has a thickness of 50 pm. A small quantity of 50 pm diameter beads is added to the polymer and serves as spacers. The flat sheet of film is cut to 50 mm larger than the flat size of the shape. The coating, in the area where the film will be trimmed after forming is rendered effectively non-conductive by etching with a LASER. The LASER oblates the coating through the transparent substrate. Full surface positive 50 and negative 52 molds are used. The positive mold 52 is on the bottom. The supporting means is comprised of a frame 52 with a top and a bottom portion. A thin, heat resistance, elastic membrane 54 is secured to each frame. The flat film 36, is placed between the two silicon elastomer membranes 54. The film is clamped in place around the entire periphery of the film. The two membranes 54 add to the support and protect the surface of the film from possible damage from contact with the forming molds. In operation the film and molds are heated into the middle of the PET glass transition range. The positive mold is stationary. The frame, with the film is brought in contact with the positive mold. The negative mold is then brought into contact with the film. Vacuum is applied to the porous positive mold as the two molds are closed. Vacuum is applied by means of small holes in the positive mold face. The heated molds are held in the closed position for some seconds before the negative mold is retracted. A heat transfer fluid is passed through channels in the molds so as to provide for a controlled decrease in temperature to below the glass transition point of the substrate.

After cooling, the supporting means with the formed film is retracted. The duration is calculated to be long enough to allow any stress in the plastic to be relieved. Prior to retraction of the molds,

The film is formed from the flat to the final formed shape in a single forming step.

After forming the excess is trimmed by means of a CO2 LASER positioned by a five-axis robot.

Embodiment two is similar to embodiment one only differing in the apparatus used to form the film. The forming apparatus of Figure 10 is used. The apparatus in Figure 10 is the same as in Figure 9 with the exception of the negative top mold which has been removed. Rather than full surface contact on both sides, the apparatus of Figure 10 uses only vacuum and the action of the supporting means which first stretches the film over the positive mold, to reach the final formed shape.

Embodiment three further simplifies the apparatus as shown in Figure 11 , dispensing the use of the two membranes. Instead, the VLT film is clamped directly to the supporting means 56. The supporting means stretches the film over the mold and then vacuum completes the forming action as in the previous embodiments.

Embodiment four could be similar to any of embodiments one to three with the exception of the type of VLT film. The film is intended for an LC application. However, the film does not contain the LC. The film is first formed by the methods of the invention and then after forming, filled with liquid crystal, and sealed. The film uses 15 pm diameter spherical spacers. Spacer of other shapes and dimensions may be used as appropriate for the product being produced.

Embodiment five, as shown in Figure 12, may be similar to any of embodiments one to four with the exception of the VLT film. In this case, the film design includes one or more recess portions or notch cut-outs that correspond to II or C shape cuts along the perimeter edges of the VLT film, which acts as stress concentrators during the film forming. Tooling for this embodiment corresponds to a complete surface of the glass without having the notch cut. VLT film 36 will have the final size and connections already in place.

Embodiment six, as shown in Figure 13, may be similar to any of embodiments one to three but after forming the film from the flat to the final shape in a single forming step, the excess will not be trimmed by means of a CO2 LASER positioned by a five-axis robot, but the film is clamped in place by its two mayor surfaces, through the friction forces between the two membranes and the two largest surfaces exposed. No air or other fluid or material will be in between the membranes and the VLT film. In this example, the film 30 includes a recess portion but it may not have it.

Embodiment seven, as shown in Figure 14, may be similar to any of embodiments one to three but after forming the film from the flat to the final shape in a single forming step, the excess will not be trimmed by means of a CO2 LASER positioned by a five-axis robot, but the film is clamped in place by one of its two mayor surfaces, through an adhesive layer between the membrane and the VLT film. In this embodiment, the membrane could be any thermoplastic material such as PET, PETG, among others. In this example, the film 30 includes a recess portion but it may not have it. When a recess portion is included, the adhesive size is smaller or equal to the size of the film.

Embodiment eight, as shown in Figure 15, may be similar to embodiment one with the exception of a partial counter mold, a negative mold being used. This corresponds to a plug assistance approach wherein the plug is intended to provide mechanical forces to the VLT film during the forming process in punctual areas of the mold 50. Plug assistance can also be applied when membranes are used.

Claims

CLAIMS A method for thermoforming Variable Light Transmission (VLT) films, comprising the following steps: providing a sheet of VLT film, wherein said film is comprised of: two substrates having two major surfaces wherein one of said two major surfaces of each substrate is coated with an electrically conductive coating, and wherein said conductive coating maintains electrical continuity during forming, and an electrically variable light transmission active material wherein said active material is disposed in between the two substrates such that the surfaces coated with the conductive coating face each other, and said active material does not extend to the periphery of the substrates in at least one region thereof; providing at least a mold; providing a heating means; providing a film supporting means; providing a means of applying force to said film; placing said film in the supporting means such that said means are placed in the region of the periphery of the substrates; heating said film and/or the mold by the heating means to a temperature below or within the glass transition range of the plastic substrate; applying force to deform the film to the shape of the mold; holding the film; and cooling the film to below the glass transition range before removing the force. The method of claim 1 , wherein the VLT film is clamped within the supporting means. The method of any of the preceding claims, wherein before placing the VLT film on the supporting means, the conductive coating of each of said two substrates is electrically insulated between the regions corresponding to the periphery edge of the active material and the periphery edge of the substrates by means of etching, laser ablating, or providing an electrical insulation using any mechanical, chemical or abrasion means on at least one portion of said coating when defects appear in the film after forming. The method of any of the preceding claims, wherein said at least one region of the periphery of the substrates is trimmed after the deformation step. The method of any of the preceding claims, wherein the formed shape of the film is approached repeating at least once the steps of heating the film and/or the mold, applying a force to deform the film, holding the film in the glass transition range and cooling the film below the glass transition range. The method of any of claims 1 to 5, wherein the film is partially formed and reaches the final desired formed shape when laminated. The method of any of the preceding claims further comprising the steps of disposing the VLT curved film in between at least two glass layers having high complex curvature and laminating it using at least one plastic bonding layer such as to form a laminated glazing with high complex curvature. The method of claim 7, wherein during lamination a liquid optically clear adhesive is used additionally to said at least one plastic bonding layer to achieve glazing lamination. A variable light transmission film comprising: two substrates with each one having two major surfaces wherein one of said two major surfaces of each substrate is coated with an electrically conductive coating, wherein said conductive coating maintains electrical continuity during forming, and an electrically variable light transmission active material wherein said active material is disposed in between the two substrates such that the surfaces coated with the conductive coating face each other, and wherein the periphery edge of the active material is offset inboard of the periphery edge of the two substrates along at least a substantial portion thereof. The variable light transmission film of claim 9, wherein the offset of the edge of the active material with respect to the edge of the substrates is preferably no more than 50 mm, and more preferably at least 20 mm all around. The variable light transmission film of any of claims 9 to 10, wherein the conductive coating of each of said two substrates is electrically insulated between the regions corresponding to the periphery edge of the active material and the periphery edge of the substrates. The variable light transmission film of any of claims 9 to 11 , wherein the conductive coating is selected from the group of: a metallic/dielectric, carbon nanotubes, graphene, silver nanowires, ITO with carbon nanotubes, ITO with silver nanowires, ITO over a metallic/dielectric or graphene or an organic conductive layer comprising PEDOT:PSS or a conductive mesh. The variable light transmission film of any of claims 9 to 12, wherein the conductive coating is an ITO coating having thickness in the range of 0.2 to 2.0 pm. The variable light transmission film of any of claims 9 to 13, wherein the active material is selected from the group consisting of: an SPD film, a PDLC film, an EC film, a PNLC film and a LC film. A laminated glazing with high complex curvature comprising: at least two glass layers each one having high complex curvature; at least one plastic bonding layer; and a VLT film comprising: two substrates with each one having two major surfaces wherein one of said two major surfaces of each substrate is coated with an electrically conductive coating, and an electrically variable light transmission active material wherein said active material is disposed in between the two substrates such that the surfaces coated with the conductive coating face each other, and wherein the periphery edge of the active material is offset inboard of the periphery edge of the two substrates along at least a substantial portion thereof, wherein said VLT film is curved by thermoforming process and is laminated between said at least two glass layers and said at least one plastic bonding layer. The laminated glazing with complex curvature of claim 15, wherein the at least one plastic bonding layer is selected from the group comprising polyvinyl butyral (PVB), ethylene vinyl acetate (EVA), thermoplastic polyurethane (TPU), polyolefin elastomers (PoE), optical adhesive resins (OCR) and a combination thereof. The laminated glazing with complex curvature of claim 15 to 16, wherein the VLT film has its peripheral edges trimmed in the portion that does not contain the active material. The laminated glazing with complex curvature of any of claims 15 to 17, wherein the radius of curvature is less than 4 meters. The laminated glazing with complex curvature of any of claims 15 to 18, wherein the radius of curvature requires plastic deformation of said VLT film that is greater than 1% range to be formed. The laminated glazing with complex curvature of any of claims 15 to 19, wherein any of said at least two glass layers are selected from the group of Soda-lime, Borosilicate or Aluminosilicate glass, or a combination thereof. The laminated glazing with complex curvature of any of claims 15 to 20 further comprising an additional coating selected from anti-reflective coating, Low-E, antifingerprint and combinations thereof and is deposited in the exterior surface of the second glass layer. A vehicle roof or vehicle window comprising a laminated glazing with high complex curvature according to any of claims 15 to 21.