The invention also relates to a sheet with an image.

Background Laminated glass has many applications as a construction material. It can for example be used to form windows, walls, doors and screens. It can also be used for the construction of articles such as coffee tables, and other small articles of furniture. Laminated glass is specified or desired in a number of applications as a result its inherent safety characteristics compared to normal glass sheets.

Laminated glass is typically formed by joining two sheets of glass using a polyvinyl butyral interlayer. The production process normally involves placing the interlayer between the two sheets of glass, applying heat to soften the interlayer and then passing the sheets through nip rollers that squeeze the glass sheets into contact with the softened interlayer. A further step involves the treatment of the laminate so formed in an autoclave to complete the bonding process.

In many applications it is desirable to provide some form of image on the laminated glass. The image can be for the purposes of decoration or can serve a functional purpose by partially or completely obscuring the view through the laminated glass sheet. Hitherto attempts to produce laminated glass with images have presented serious practical problems. One way that an image has been formed on laminated glass is by screen printing onto the finished laminated sheet.

This is a cumbersome process and limits the images that can be produced both in colour and detail. For example a multi-colour image requires a printing step for

each colour. Additionally the images can only be formed on discrete panels and for practical purposes this means that the images cannot be formed in a regular manner so that the panels can be subsequently arbitrarily cut.

Other attempts have been made to place images within laminated glass. These have taken the form of introducing an additional layer of some type that carries the image into the glass laminate. This approach has the disadvantage of directly interfering with the strength of the bond formed between the glass sheets. This is because the image carrying material results in a reduction in available area for bonding.

It is an object of this invention to provide an image carrying sheet and a method of producing an image carrying sheet that will overcome, or at least ameliorate, the foregoing disadvantages.

Summary of the Invention In accordance with the invention, there is provided an image carrying sheet including : a substrate laminated between rigid layers, the substrate having an image formed by sublimation.

In another aspect, there is provided a substrate for use in the above image carrying sheet, including an image formed on the substrate by sublimation.

In another aspect, there is provided a method of producing a substrate including : providing an image, formed of sublimation dye, on a transfer medium; placing the transfer medium in contact with a substrate;

applying heat and pressure to the substrate and transfer medium whereby the dye from the transfer medium sublimes into a vapour and transfers from the medium to the substrate.

In another aspect, there is provided a method of forming an image carrying sheet, including : placing the substrate over a first one of the rigid layers ; positioning a second one of the rigid layers over the substrate; and laminating the layers and substrate together.

In another aspect, the present invention is an image carrying sheet including a substrate with an image, the image formed by sublimating at least one dye from a transfer medium to the substrate wherein the formed image does not significantly decrease the bonding ability of the image carrying sheet.

Preferably, the image carrying sheet further includes a first sheet bonded to the substrate. More preferably, the image on the substrate can be viewed through the first sheet.

In one embodiment, the first sheet is glass, acrylic, perspex or polycarbonate.

Preferably, the substrate is an interlayer. Even more preferably, the substrate is polyvinyl butyral, polyurethane, ethylene vinyl acetate or ionoplast.

In another embodiment, the substrate is polyester, polypropylene, polyethylenetelephthalate (PET), polybutylene tetephthalate (PBT), acrylic, polymethylacrylate, polymethacrylimide (PMI), polycarbonate, stryeneacrylicnitryl, K-resin (stryenic block copolymer) polyethersulphone, polysulphone, clarified

5polypropylene, vinyl, polystyrene, polyvinyl butyrate, polyacrylate, cellulose acetate or cellulose acetate/butyrate.

In another embodiment, the substrate includes a coating of polyester, polypropylene, polyethylenetelephthalate (PET), polybutylene tetephthalate (PBT), acrylic, polymethylacrylate, polymethacrylimide (PMI), polycarbonate, stryeneacrylicnitryl, K-resin (stryenic block copolymer) polyethersulphone, polysulphone, clarified polypropylene, vinyl, polystyrene, polyvinyl butyrate, polyacrylate, cellulose acetate or cellulose acetate/butyrate.

Preferably, the substrate is a holographic foil.

Detailed Description of the Invention The invention will now be further described, by way of example only, with reference to the accompanying drawings and examples.

Figure 1-A schematic diagram of a substrate, arranged for application of a sublimation process according to one embodiment of the invention.

Figure 2-A schematic diagram of layers of an image carrying sheet, arranged for application of the sublimation process according to another embodiment of the invention.

Figure 3-A schematic diagram of the layers of an image carrying sheet, arranged for application of the sublimation process according to another embodiment of the invention.

Referring to Figure 1, an image is formed on a substrate 2 by sublimating dyes on an image transfer medium 3 such as paper. As the substrate 2 softens during the sublimation process, this sheet is supported on each side by two supporting sheets 1,5. A sheet of heat resistant film 4 is also provided so that the supporting sheet 5 can be easily removed after the sublimation process.

The sublimation process uses heat and pressure to transfer an image from the transfer medium 3 to the substrate 2. The transfer medium 3 is removed from the substrate 2 after the sublimation process. The sublimation process uses a controlled atmosphere with a controllable pressure and temperature. In one embodiment, the sublimation process is undertaken in an autoclave. It is preferable that when using an autoclave that the substrate 2, transfer medium 3, heat resistant film 4 and supporting sheets 1,5 form a layered sandwich and are in a vacuum. This could be formed by packing the layered sandwich in a vacuum bag and creating a vacuum within the bag.

In this figure, the support layer 1 is a layer of the finished product, for example a rigid layer of glass or perspex and is bonded to the substrate 2 during the sublimation process. The support sheet 1 supports the image carrying sheet 2 and allows it to be handled and/or treated with minimal relative movement between the image carrying sheet 2 and the support sheet 1 during the process of forming the image. Some of the processes suitable for forming the image require the sheet to be moved through a processing line which includes, for example, a nip roller, at a consistent rate to prevent"banding and misses"in the printing.

Additionally, many of the processes suitable for forming the image on the substrate 2 involve the use of heat. The substrate can be an interlayer that is very heat sensitive and typically loses much of its mechanical strength at temperatures of 60°C and above. The use of a support sheet 1 allows the interlayer to be handled and/or treated in systems involving the use of heat without unacceptable stretching or damage.

The heat resistant film 4 is provided to assist the removal of the support sheet 5.

The support sheet 5 does not soften, during the sublimation process, so as to provide additional support to the substrate 2, for example PMMA, polycarbonate or glass.

Referring to Figure 2, an image is formed on a substrate 11 by sublimating dyes from an image transfer medium 12 such as paper. As the image carrying sheet 11 softens during the sublimation process, this sheet is supported on each side by two supporting sheets 15,16. A sheet of heat resistant film 13,14 is also provided so that the supporting sheets 15,16 can be easily removed after the sublimation process.

In contrast with the image receiving sheet of Figure 1, the substrate 11 is not bonded to another sheet during the sublimation process. The substrate 11 may therefore represent the final image carrying sheet product, for example a sheet of acrylic, or an intermediate layer of a final product, which will then be bonded to other sheets in further processes. Both supporting sheets 15,16 are removed after the sublimation process.

Referring to Figure 3, an image is formed on a substrate 22 by sublimating dyes on an image transfer medium 23 such as paper. An interlayer sheet 21 of the final image carrying sheet product is also attached. As the image carrying sheet 22 and sheet 21 soften during the sublimation process, these sheets are supported on each side by two supporting sheets 26,27. A sheet of heat resistant film 24,25 is also provided so that the supporting sheets 26,27 can be easily removed after the sublimation process.

As with Figure 1, the substrate 22 such as a polyurethane interlayer and the sheet 21 such as acrylic are bonded together during the sublimation process. Both supporting sheets 26,27 are removed after the sublimation process. The sheet 21 and substrate 22 becomes part of the final product.

Additional sheets may also be applied after the sublimation process to form a laminate of acrylic, polyurethane interlayer, polyurethane interlayer and acrylic. These can be applied by a laminating these layers. or using an autoclave to bond the sheets together.

Additionally, it is preferable that the image is allowed to cure on the substrate before the image carrying sheet is used in further processing such as glass lamination. Depending upon ambient temperatures a curing period of up to 24 hours or more has been found to be beneficial in some cases.

In figures 1 and 3, it is desirable that the image is allowed to cure on the substrate 2,22 with at least some of the supporting sheets remaining attached. The bonding of the sheet 1,21, such as a transparent sheet, is therfore enhanced.

Depending upon ambient temperatures a curing period of up to 24 hours or more has been found to be beneficial in some cases.

In these figures, the substrate can be formed as an interlayer of any appropriate type, for example polyvinyl butyral, polyurethane, ethylene vinyl acetate or ionoplast. For example the image can be printed on interlayers that are substantially transparent once laminated between two sheets that are at least semi transparent. Alternatively, interlayers that are designed to be opaque or partially opaque through for example colouring can be used. Interlayers of any thickness otherwise appropriate for the laminating of glass can be used. Commonly available interlayers are in multiples of 0.38mm in thickness.

Alternatively, the substrate could be any appropriate material, for example a polymer which may include polyester, polypropylene, polyethylenetelephthalate (PET), polybutylene tetephthalate (PBT), acrylic, polymethylacrylate, polymethacrylimide (PMI), polycarbonate, stryeneacrylicnitryl, K-resin (stryenic block copolymer) polyethersulphone, polysulphone, clarified polypropylene, vinyl, polystyrene, polyvinyl butyrate, polyacrylate, cellulose acetate, cellulose acetate/butyrate. The substrate could also be any suitable material such as a holographic foil with a coating of one or more of the above.

Further, the sheet 1,11, 21 could be any appropriate material, for example glass,

acrylic, perspex or polycarbonate. These may be fully transparent or only partially transparent and could include tinting. These sheets may also include a textured finish in the end product. This can include having a textured finish on a non heat softening support sheet so that when heated, for example during the sublimation process, the heat softening material may substantially conform to the textured finish of the non heat softening support sheet. Additionally these sheets may also include coatings for their protection, coatings to assist in the joining process or coatings to assist the reception of an image.

Adhesion promoting coatings are generally polyester based such as Resydrol Van 6113W/42WALG, manufactured by Solutia. Other coatings are aliphatic polyurethane dispersions such as DaotanTM VTW 1233, manufactured by Solutia or Permathane RU41-347, manufactured by Stahl.

The sublimation dye may not be as fade resistant, particularly in outdoor applications, as other dyes. It may be that an UV absorbing additive be incorporated into the adhesion promoting coating. Examples of suitable UV absorbing compounds include hexadecyl 3, 5-di-tert-butyl-4-hydroxy-benzoate, available as Cyasorb UV-2908; 2-hydroxy-4- (octyloxy) benzophenone, available as Cyasorb UV531; 2-(2'-hydroxy-5'-methylphenyl) benzotriazole, available as Tinuvin 900 from Ciba Geigy Corporation; 2- (3', 5'-di-tert-butyl-2'-hydroxyphenyl)-5- chlorobenzotriazole, available as Tinuvin 327 from Ciba Geigy Corporation; 2- (4- benzoyl-3-hydroxyphenoxy) ethylacrylate (available as Cyasorb UV-416) and poly (2- (4-benzoyl-3-hydroxyphenoxy) ethylacrylate) (available as Cyasorb UV- 2126).

The use of a sublimation process to form the image on the substrate has been found to not interfere with the bonding ability of the image carrying sheet and other sheets to an unacceptable extent. In laminated glass produced by this method, the dye sublimes into the molecular structure of the substrate during the sublimation process, as the specific volume of the substrate material increases,

and on cooling back below a plastic softening temperature the image becomes locked into place. As the surface remains substantially the same, the bonding ability of the interlayer is not greatly affected. This is in contrast for example to acrylic based carriers for pigments which tend to pool and reticulate on the surface of the interlayer. The pooling results in a region of the interlayer that cannot bond to the adjacent glass sheets and thus prevents a successful laminated glass being formed. However, it may be desirable in some situations due to the processing or materials to provide a second interlayer to achieve the desired bonding. Such a process would involve further processing to form a laminate of glass, interlayer with image, interlayer and glass.

Accordingly, some of the possible advantages of this invention include : the formation of a high quality image within transparent rigid layers or plies ; the quality of the image formed in this way is superior to that obtained by other printing methods (e. g. screenprinting, flexographic printing); since no liquid inks are applied to the polymer substrate there are no associated problems such as a mismatch in surface tension leading to poor wetting, the need to corona-treat the plastic, the need for solvent evaporation, negative interactions between the plastic film and the ink solvents ; the image can be effectively encapsulated between transparent plies and is thus protected from abrasion, marring and scratching. Additionally the image is protected from damage from cleaning chemicals.

Example 1 The image is printed using a sublimation dye, such as Digistar PES available from

Lechler S. p. A. , to a transfer medium, such as Jetcol HTRO 4000 paper manufactured by Coldenhove Papier. The printed image on the transfer medium is then placed onto the interlayer and a layer of glass. As the glass is non heat softening no further support is required. A heat resistant film, for example DartekX nylon film made by DuPont, is then placed on the other side to the transfer medium and a second layer of glass is used and forming a sandwich with the two layers of glass on the outside. This sandwich is schernatically shown in Figure 1 and is then vacuum packed and transferred to an autoclave which typically operates at a temperature of 135°C at a pressure of 11.5 bar. The heat and pressure of the autoclave transfers the image from the transfer medium to the interlayer by sublimation of the dye.

After the sublimation process has been undertaken the second layer of glass, heat resistant film and transfer medium is removed. The glass and interlayer may be returned to a controlled environment to recondition the interlayer. A second interlayer is applied to the interlayer with the image and another glass layer sandwiches the two interlayers. This sandwich is moved through an oven operating at a temperature of approximately 200°C before passing between nip rollers exerting a pressure of around 10 bar. This results in both the interlayers softening and bonding the two sheets of glass together. The nip rollers ensure that there is no entrapped air in the laminated sheet. The laminated sheets so formed are then transferred to an autoclave which typically operates at a temperature of 135°C at a pressure of 11.5 bar. They are typically autoclaved for around 3.5 hours.

Samples of laminated sheet were prepared in accordance with the above described example using a 0.38mm thick PVB R11 polyvinyl butyral interlayer produced by Solutia Australia Pty Ltd. The glass sheets were 3mm thick.

Example 2

The image is printed to the transfer medium as in Example 1.

The transfer medium is placed onto a heat softening sheet, in this example an acrylic sheet. A heat resistant film, for example DartekX nylon film made by DuPont, is then placed on either side. A non heat softening sheet is then placed on either side of the heat resistant film creating a sandwich. This sandwich is schematically shown in Figure 2 and is then vacuum packed transferred to an autoclave which typically operates at a temperature of 135°C at a pressure of 11.5 bar. The heat and pressure of the autoclave transfers the image from the transfer medium to the interlayer by sublimation of the dye.

After the sublimation process all additional layers are separated leaving the heat softening sheet with the image.

Example 3 A laminated sheet with polyurethane interlayer and acrylic sheets was prepared in a similar manner to Example 1. The only difference being the acrylic sheets were supported during both stages by a non heat softening support sheet such as glass with a heat resistant film between the acrylic sheet and the support sheet. This sandwich is schematically shown in Figure 3.

Example 4 The image is printed to the transfer medium as in Example 1.

The transfer medium is placed onto a holographic foil having a polyester film on the surface which it contacts. A heat resistant film, for example DartekX nylon film made by DuPont, is then placed on either side. A non heat softening sheet is then placed on either side of the heat resistant film creating a sandwich. This sandwich is then vacuum packed transferred to an autoclave which typically operates at a

temperature of 135°C at a pressure of 11.5 bar. The heat and pressure of the autoclave transfers the image from the transfer medium to the interlayer by sublimation of the dye.

After the sublimation process all additional layers are separated leaving the holographic foil with an image. This imaged foil is then adhered to acrylic, glass or similar material using double sided adhesive tape or similar material. This laminate is then nip rolled and a self adhesive vinyl backing is applied so as to protect the holographic foil.

The foregoing describes only certain embodiments of the invention and modifications can be made without departing from the scope of the invention.