The type of treatment of substrate with which the invention is concerned is the application of decorative coating material to the surface of a substrate, so as to provide any required visible (decorative) appearance to the substrate.

The substrate therefore provides the necessary strength to the composite article (the substrate plus the decorative coating), and the only requirement of the. decorative coating is that it can remain secured to the surface of the substrate throughout the required"life"of the article, and can withstand any environmental factors to which it may be exposed in use, and which may tend to separate the coating from the substrate. In other words, a durable decorative coating for a substrate is required, and which can be applied to the substrate in an easy and reliable manner, and without adversely affecting the structural integrity of the substrate.

The present invention has been developed primarily, but not exclusively, in connection with the coating of a glass substrate for architectural use, e. g.-as windows in buildings or in glass, in which case the coating will usually be on the inside face of the substrate. Alternatively, for other uses, e. g. in shower screens, the coating will usually be on the outside face of the substrate. Other possible uses will include use in the automotive industry. The invention is also applicable to flat substrates of other materials; e. g. ceramics, earthen ware, clay ware and any other materials to which ceramic inks can be applied by the treatment process and apparatus described here after.

It is of course well known to apply paper or vinyl based decorative sheets to glass or ceramic substrate, using suitable adhesives, and which can be acceptable for indoor use, but such sheets are not durable and can only remain attached to a substrate on a temporary basis.

For external use on buildings, a decorative effect on structural glass sheets can be obtained on a commercial basis by expensive"tinting"procedures in which suitable colouring material is incorporated into the constituent materials from which glass is made. This requires careful control over the mixing process, so as to achieve substantially uniform tinting of the glass, and in addition to being expensive, this does not give any flexibility in enabling decorative effects to be achieved which are other than uniform colour tinting throughout the glass. Alternatively, a required decorative effect can be achieved by surface printing with ceramic or enamel inks.

However, due to registration problems printing in more than one colour is very difficult.

It is already known to apply durable coatings to glass sheets which are incorporated into a"a wall or walls"of a squash court (or similar), in which spaced dots of ceramic ink are applied to the surface of the sheets in such a way that, (1) to players in the court the inside face of the wall appears opaque and (2) to spectators externally of the court and looking in, the wall appears transparent.

The use of transparent/opaque glass walls in sports courts has proved to be very successful commercially, and has enabled large numbers of spectators to view sports activities which would not previously have been possible. The coating must be applied to the glass substrate in a way such that it is durable, since the coating will be exposed to repeated impact by the ball, and also to occasional heavy impact of a player against the wall.

The required series of dots are applied by a printing technique, in which ceramic ink dots are applied to a water based transfer or slide paper, and then are transferred to the surface of the glass. Immersion of the paper in water allows the ink dots to be transferred to the surface like a "transfer", and which remain temporarily adhering to the glass in required positions which are determined by entirely manual techniques.

To achieve the required transparent/opaque properties, a pattern of typically lmm alternate clear and white dots is printed, and also behind the white dots a black dot is printed.

This has the effect, inside the court, with the bright lights shining on the white dots, of making the inside facing surface appear opaque to the player, whilst on the other side of the glass, the spectator in darkness looking into the bright court through the printed clear dots and black side of the white dots, sees the wall as being transparent.

After the transfer and temporary positioning of the dots on the glass surface, the glass substrate is then subjected to a normal"tempering"process of the type used to make toughened glass. The technique of tempering glass will be well known to those of ordinary skill in the art of glass technology, and need not be described in detail herein.

A key factor in the success of this technique (durable coating of a glass substrate), is that the ceramic ink"dots"which are transferred to the glass surface become fused to the glass during the subsequent tempering process to which the substrate is required to be subjected, bearing in mind the load factors which it will be required to withstand in service.

However, while this technique has proved to be a commercial success, and of benefit to customers, it is a somewhat specific application of a technique for applying durable coatings to a glass substrate, and which require significant manual skills, and particularly in the transfer of the ceramic ink dots to the glass substrate, prior to tempering. This means that the production time is dependent on manual skills, and the quality of the coating is dependent on the attention devoted to the task by the person exercising these skills. This is acceptable commercially for this specific application, but is not a viable technique for larger scale application of decorative coatings to substrate, of the type with which the invention is concerned.

Thus, the use of water slide transfers necessarily requires manual operations, and which is acceptable for transfer of small areas of image on a repeated basis, but is not acceptable for large volume commercial processes. Also, production size at the moment is limited to single sheets approximately 60 x 80cm.

The technique of using screen printed water slide transfers has also been used for many years in the pottery and chinaware industry (to apply transfers which are subsequently baked on to the article), and the necessary manual skills required is acceptable in that industry for quality work. Indeed the technique for applying the ceramic ink dots to glass walls in squash courts was derived from that industry, being unique at that time in applying water slide transfers to tempered glass products.

However, as an initial attempt to broaden the concept of transfer of ceramic ink dots, and subsequent fusing to the surface of the glass during the tempering process, there is an existing technique which effectively enables printing"in colour"to be applied to windows as substantially permanent decorative coatings, and in this technique a water slide transfer or"decal"and subsequent tempering process has been used, and in which first of all a solid image is printed i. e. a full coating of the glass substrate, and then subsequently the image is perforated with similar lmm holes (to allow viewing outwardly through the windows). Thereafter, the perforated image is transferred to the substrate by a manually controlled water-slide technique. Apart from being the negative of the all over printed concept, this had the advantage of doing away with the registration problem of printing a number of colours on top of each other, as the printing of solid colours could be done first, and perforated afterwards, so as to see through it.

However, while this extension of the squash court technique has become accepted by major glass manufacturers, and is commercially viable, it still relies upon the use of water slide transfers or decals, and therefore manual skills, with the disadvantages as to time of production and labour costs which this involves.

There does therefore exist a clear need to provide an improved glass treatment process, whereby durable decorative coatings can be applied, and in a way which allows automated continuous production techniques to be utilised, while maintaining reliability and accuracy of placement of the printed images on the substrate. Also, it will be desirable to allow use of image sheets up to as large as, but not limited to 2.15 metres wide, and as a continuous loop, such as by the web printing method, or by the sheet printing method joined to form a supply reel.

The present invention addresses this requirement, and utilises a unique combination of process and apparatus feature to achieve the required objectives.

The invention therefore utilises a different type of transfer bearing any required image (s), and which can be applied to a substrate prior to fixing of the image to the substrate by heat treatment and/or tempering of the substrate in a way which allows the process to be automated and continuous, so as to increase the rate of production while still maintaining a satisfactory quality of image after transfer and subsequent adhesion to the substrate as a consequence of the heat treatment and/or tempering process.

According to one aspect of the invention there is provided an automated method of decorating a substrate comprising a plurality of articles, including the steps of: continuously feeding the substrate and heat release decals on a decal carrier to a laminating station; applying heat to the decal carrier so as to simultaneously release the decal from the carrier and deposit the decal on an exposed face of the substrate continuously passing through the laminating station; transferring decal-deposited substrates to a decal- securing oven ; slowly heating the substrate to a predetermined temperature so as to remove all binding agents from the decal and to fix the decal to the substrate thereby decorating the substrate.

The temperature may be sufficient to fuse the decals to the substrate and cure the decal so as to gloss up the colours of the decal. If an article which does not require tempering is to be decorated then the decal securing furnace applies a heating action to the coated article so as to fuse the image to the substrate. The decal securing furnace may be an intermediate furnace in the process or may be a final tempering furnace in the process. If the article does require tempering, then the temperature may be sufficient to also temper the substrate.

The method may include the steps of: slowly cooling the decorated substrate in the decal securing oven; and feeding decorated substrates to a tempering furnace and rapidly heating and cooling the decorated substrates so as to temper the substrates, fuse the decal to the substrate and cure the decal so as to gloss up the colours of the decal.

Preferably, the method includes the step of pre-heating the substrate so that the substrate has a predetermined temperature when the decal is deposited on it so as to enhance adherence of the decal to the substrate.

The substrate may be in the from of a single item, comprising a plurality of articles, or the substrate may be in the form of a continuous item comprising a plurality of individual articles. The position of the plurality of individual items is preferably constrained so that they present a common substantially flat surface to the carrier strip; i. e. the plurality of items mimic a flat sheet substrate comprised of a single item. A locating device may be used to constrain the position of the plurality of items.

The invention therefore utilises a heat transfer type of image (of ceramic ink) on a carrier strip, and which is transferred to the substrate as they pass together through the laminating station and which enables the coated article to be made on an automated, or at least semi-automated, continuous basis, which increases the speed of production to render the process commercial, while utilising the surprising discovery that an accurate placement and reliably adherent image can be secured to the substrate during the tempering process to which the substrate can be subjected. Hence the fusion and tempering processes may be considered to be simultaneous in that instance.

The tempering process is used in order to toughen the substrate and make it suitable for use in a building or other environment, and the type of image and the means of supply and feeding of the carrier strip and the substrate allows the time and energy involved in the tempering process to be utilised also in the securement of the image to the substrate.

Any required image can be printed on the carrier sheet using colour printing techniques e. g. web offset printing or screen printing, in which a required master (art work) is first formed and is then scanned, prior to usually four colour, individual spot colour or augmented four colour printing of the required image on the carrier sheet.

The carrier sheet is preferably formed into a supply roll, and from which the sheet can be withdrawn when needed to the laminating station.

One of the major surprising aspects of this invention has been that an acceptable image can be reliably applied to the substrate on a semi-continuous, or continuous basis, thereby automating the process, and an acceptable quality of image is fused onto the substrate during the tempering process.

If enhanced quality of image is required, it may be advantageous to first pass the coated sheet, as it issues from the laminating station, through an intermediate decal securing furnace, which preferably comprises a Lehr type of furnace.

A slow firing can take place in this decal securing furnace for, say, half an hour, which brings the coated substrate up to a temperature of about 450°C. However, the heating could be up to, say, 3 hours and up to 450°C. After this stage the image is securely fused to the substrate which then can be tempered if required. It then issues from this furnace and goes to the tempering furnace proper, where radiant energy inside the tempering furnace can typically be of the order of 650°C to 705°C, or even up to 735°C in the case of specific designs of tempering furnace. The decal securing furnace can be used to fuse the decal to the substrate and cure the decal so as to gloss up the colours of the decal is no subsequent tempering stage is to be used.

Depending upon the thickness of the coated substrate which issues from the tempering furnace, following typical values may be obtained, giving acceptable results: Thickness of Exit surface coated sheet temperature 3mm 630°C 4mm 622°C 6mm 615/618°C 12mm 608°C 15/19mm 600°C 19/25mm 595°C The method and apparatus of the invention therefore enable a durable decorative coating to be reliably and accurately secured in position to any desired face of the substrate. The image will take any required form, including one or more colour (multi-colour) if required.

The invention therefore may be used to form, for example, a full colour image on a glass sheet, and which would be particularly suitable for so called"spandrel"type of glass uses in building.

However, in some circumstances, it may be desirable to apply an image which has spaced holes in it or as an array of dots, to render the coating transparent, so that, when such a coating is applied to the inside face of e. g. a building window, people within the building can see outside, whereas from the outside the visible effect will be that of a decorative sheet, with the holes, or inter spaces, not being apparent.

An image of this type may be formed conveniently, in a preferred development of the invention, by provision of an additional process step. This involves a pre-coating of the substrate, prior to feeding of the substrate to the laminating station. The pre-coating involves application of spaced dots made of a release agent e. g. wax or grease, and which might typically be applied in a pattern at lmm spacing. This pre- coated substrate then passes to the laminating station, at which the image proper is then transferred from the carrier strip as described above, and which overlies the precoated dot pattern of heat release material.

In the laminating station, preferably the heating means takes the form of a heated roller, and which applies heat to one side of the carrier strip, sufficient to allow the image to be transferred to the substrate, but the heating is not of such a capacity as to have any significant influence on the pre- coated dot pattern on the substrate.

The laminate thus formed i. e. substrate, pre-coated dot pattern and image, then pass to the tempering station, and optionally via the Lehr furnace, and the heating which is then applied to the pre-coated dot pattern causes the heatable material e. g. wax to vaporise, and to exit from their containment in the only way possible, which is to burst through the overlying ceramic ink image. By this means, simple pin holes are formed in the ceramic ink coated image, thereby forming a perforated image on the substrate after the tempering process is completed.

The process may include an initial heating step in which the substrate is heated to a high enough temperature to help activate an adhesive provided with the ceramic ink to help secure the ceramic ink image to the substrate. The substrate may be heated to an initial temperature of approximately 90°C.

Preferably the substrate is initially heated to a temperature of approximately 120°C.

According to a further aspect of the invention there is provided an automated decorated substrate production line for decorating a face of a substrate comprising a plurality of articles, comprising: feeding means for feeding a substrate to a laminating station; decal feeding means for feeding heat release decals on a decal carrier to a laminating station; a heating device arranged at said laminating station for receiving said decal carrier and the substrate and the heating device being operable simultaneously to effect heat release of a decal from the decal carrier and to deposit the decal on an exposed face of the substrate; intermediate feeding means for feeding a decal deposited substrate to a decal securing oven; and heating means in said decal securing oven operative slowly to heat the decal deposited substrate to a predetermined temperature so as to remove all binding agents from the decal and fix the decal to the substrate and thereby decorate the substrate.

Preferably, the predetermined temperature is sufficient to fuse the decal to the substrate and cure the decal so as to gloss up the colours of the decal.

Preferably, the production line includes a tempering furnace arranged downstream of said decal securing oven and having heating means for heating a decorated substrate to a tempering temperature so as to temper the decorated substrate, fuse the decal to the substrate and cure the decal so as to gloss up the colours of the decal.

Preferably the feeding means includes a locating device to ensure registration of the substrate. In this way registration of the substrate and the decal to be deposited on the substrate is ensured.

Preferably, the production line includes: an upstream pre-heating furnace for continuously receiving a substrate and heating it to a pre-heating temperature and discharging pre-heated substrate to the feeding means, in which the pre-heating temperature is chosen so as to enhance adherence of the decals to the substrate.

A preferred embodiment of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic diagram of an automated production line according to the invention and suitable for carrying out the method of the invention; Figure la illustrates an upstream pre-heating furnace part of the production line; Figure 2 shows a plan view of a substrate consisting of a number of items in a locating tray; and Figures 3a and 3b respectively show plan views of a substrate consisting of a number of square items or round items guided on a locating conveyor.

The same items in different Figures share common reference numerals.

Referring now to Figure 1, the upper part of the drawing is a block diagram of the process steps involved in transferring a master (art work) through a scanning process for colour printing, and to end up with a roll of a carrier strip e. g. a paper roll with a heat release image of ceramic ink carried thereon.

The lower part of the schematic drawing shows how one example of a method and apparatus according to the invention can be operated.

Thus, the method and apparatus of the invention enable semi- automated, or automated production of a decoratively coated substrate to be carried out, in which the substrate comprises a continuous fed number of glass sheets 10 each having a face 11 which requires to be coated. The coating is derived from a heat release type of printed image formed from ceramic ink and which image is carried initially by carrier strip 12 derived from roll 13.

Each glass sheet 10 and the carrier strip 12 are fed simultaneously to a laminating station 14, by respective feeding means (not shown in detail), and heat is applied to the carrier strip 12 as it passes through the laminating station 14. This effects release of the image and allows the image to be transferred to the face 11 of the glass sheet 10, and thereby to form a decoratively coated glass sheet which issues from the laminating station 14, and as shown by reference 10a.

The laminating station includes a heated roller 15 which effects release of an image, which is shown by reference 16, overlying the face 11 of the substrate 10.

The coated glass sheet 10a is then fed to a tempering station 17 in which the coated sheet is subjected to a heating action of a type sufficient to temper the substrate and toughen the glass, and surprisingly it has been found that this also achieves satisfactory fusion of the image 16 to the substrate as well as glossing up the decal colours.

In order to improve the quality of the fused-on image or to fully fuse and colour up the image if tempering is not required, it may be desirable to provide an intermediate heating stage, which is shown by a dashed outline and reference 18, which is a decal securing furnace in which slow firing may take place for e. g. half an hour and up to, say, 450°C.

Thereafter, the partly fired glass sheet and fused image coated thereon is fed to the tempering station 17, where the tempering action takes place. Alternatively, the substrate may be heat treated in the intermediate furnace alone to fuse the image to the substrate and gloss up the colours.

The duration of the tempering process, and the heat capacity will be dependent upon the thickness of the glass, and typical figures which may apply are set out below: Glass Exit surface thicknesstemperature 3mm630°C 4mm 622°C 6mm 615/618°C 15/19mm 600°C 19/25 595°C A preferred pre-heating step of the method and apparatus suitable for it is illustrated in Figure la. The production line includes upstream glass feeding means in the form of a loading table 30 approximately 2-4m long, for receiving glass sheets to be decorated. The loading table has positioning means to allow the glass sheets to be correctly positioned.

Preferably the positioning means are in the form of rubber ball castors to facilitate the position of the glass sheet, although rollers are shown in Figure lb. The glass feeding means may include a locating device 31, in the form of rails, to locate the multiple articles of the substrate so that a correctly positioned continuous surface is presented to the laminating station. The glass feeding means may have powered transport means (not shown) so as to automatically feed glass sheets into the production line.

The production line then has a pre-heating furnace 32 approximately 4m long. The pre-heating furnace has infrared heating means and temperature control apparatus to allow the glass leaving the furnace to be controlled to have a pre- determined pre-heating temperature. The pre-heating temperature is selected so as to enhance adherence of a decal to an exposed surface of the substrate passing through the pre- heating furnace. Heating of the substrate enhances adhesion of the decal to the carrier as the decal has a heat activated adhesive top layer and so a heated substrate improves the adhesion of the decal. Heating the substrate also improves the release of the decal from the decal carrier as the substrate heat acts on the heat release layer agent to enhance release of the decal on the heat release agent. A substrate temperature of approximately 120°C has been found to be particularly effective for the wax based heat release agents, commonly used in the art.

The pre-heated substrate is then fed to the laminating station 14 and on to a transfer table 34 either to the decal securing furnace 18 or to the tempering furnace 17.

The method and apparatus thus are described enables a full colour image to be fused-on as a decorative coating on a multi- article substrate. If it is required to form a regular pattern of holes in the fused-on image, an additional pre-coating stage may be involved. The glass substrate 10 may receive a printed pattern of dots of heat release material e. g wax or grease, arrange at spacing a part of, say, 14 mm, and this pre-coated substrate 10 then passes to the laminating station 14, where it then joins with the carrier strip 12, and thereafter the process and apparatus is much the same as described above.

However, the pre-coated pattern of dots of heat release material become effectively trapped between the image 16 and the face 11 of the substrate, and the action of heating the coated substrate in the subsequent stages causes this material to evaporate and force itself through the ceramic image 16, to form pin prick holes in it. The resulting coated image of the substrate, as it issues from the tempering station 17, is then a suitably coloured image, with pin holes in it, to render the coating transparent to someone viewing through the glass from the coated side and looking outwardly.

In the preceding example the substrate is comprised of a continuous substrate of single items viz glass sheets. The invention is envisaged to encompass any substrate comprising a number of items which present a common surface onto which a decorative coating can be applied by the method of the invention and utilising the apparatus of the invention. As the multiple items comprising the substrate have the whole of an image deposited over them, registration problems associated with depositing parts of images on separate items are obviated.

The term substrate is considered to encompass a plurality of articles presented as a single item, as illustrated in Figure 2, and also a plurality of articles presented in a continuous manner so as to provide a seamless item, as illustrated in Figure 3a. With reference to Figure 2, there is shown a substrate 10 comprising a number of items in the form of square tiles 20. The tiles are generally rectangular in shape with a flat upper surface 21. The tiles may be made of glass or ceramic or any material to which a decorative coating of ceramic ink may be fused by the method of the invention. The tiles are arranged in an array and their upper surfaces 21 lie in a common substantially flat plane so as to present a common surface so as to act like the upper surface of a substrate comprised of a single item.

The multiple items are held in the desired position by a locating device in the form of a locating tray 22. The locating tray may be made of metal or any other material capable of withstanding the temperatures used in the process without substantially deforming or degrading. The locating tray holds the multiple tiles in position so that they present a common flat surface to the processing apparatus of the invention.

As the multiple items are constrained to behave like a substrate comprised of a single item, e. g. a single sheet of glass, multiple items may be decorated in a continuous automated process, rather than having to be decorated individually and images fused or substrates tempered in batches as per previous systems. Multiple items can be decorated simultaneously in a continuous manner as they pass through the laminating station and then proceed, optionally via the decal securing intermediate furnace, to the tempering station in a continuous process, so that trays of multiple decorated articles are continuously processed rather than fired in batches.

Each item may have the same design decorated upon it or a single design may be used to cover all the items so that the items each bear a different component part of the overall design; akin to a jigsaw. As a single design can be applied to cover all the items there is no difficulty in ensuring that the different parts of the design align correctly when the tiles are assembled to reproduce the design. Further, as the decoration applied to the tiles is from the same heat release transfer, each respective colour on the different tiles will be the same and so there will be no variations in the supposedly same colour between tiles as can happen with tiles decorated using different batches of ceramic inks.

With reference to Figures 3a and 3b there are shown plan views of apparatus for processing a substrate comprising a number of separate items. The substrate 10, comprises a number of separate items 20 having upper surfaces 21 which lie in a substantially flat plane so as to present a common surface.

As shown in Figure 3a, each item comprises a rectangular tile.

The tiles are located on a conveying device 22 which transports the articles through the processing apparatus. They conveying device 23 cooperates with guide rails 24 to provide a form of locating device to locate the multiple articles so that they occupy a desired position. The guide rails 24 may be connected to supports 25 by resilient members in the form of springs 26 so that the guide rails engage the items to correctly position the items. The surface of the conveying device is positioned so as to ensure that the upper surface 21 of the multiple items present a common surface at the laminating station so that decoration can be applied to the substrate comprised of multiple items in the same continuous automated manner as for a substrate comprised of a single item. Further, the multiple items may be arranged to provide a continuous surface to which the decoration can be applied.

Figure 3b shows a substrate comprised of a number of items 20 which present an upper surface 21 all located in a common substantially flat plane. The items are positioned by retaining members 27 which co-operate with a conveying device 28 to provide a form of locating device which correctly positions the upper face of the items so that they present a common surface to which decoration can be automatically and continuously applied by the laminator. The items may be space apart longitudinally or may provide a continuous surface when the periphery of adjacent items are in contact.

It will be appreciated that multiple items of various forms can be treated by the decorative process by providing suitable locating devices so that the multiple items present a substantially flat surface onto which the decoration can be automatically and continuously applied by the laminating station.

It will be appreciated that, when the substrate is a transparent material, the method and apparatus are suitable for manufacturing one way'transparent substrates. The general technology and methodology of producing transparent decorated items which are substantially transparent when viewed from one side and substantially opaque when viewed form the opposite side by providing a perforated or dot pattern of appropriate reflectivity has been discussed already.

The heat release decal utilised in the present invention is particularly suitable for the formation of perforated or dot images by a number of methods according to further aspects of the invention. Rather than pre-perforating the decals, the decals may be perforated as they are released from the decal carrier and deposited on the substrate. In this deposition perforation method, the decal carrier is specially prepared.

An intermittent layer of heat release agent is provided on the decal carrier below the ceramic inks of the decal that provide the image. A pattern of heat release agent corresponding to the pattern of ceramic ink it is intended to deposit on the glass is provided on the decal carrier. The decal is then printed on top of the intermittent layer of heat release agent. Then, when the decal is presented to the surface of the substrate at the laminator station, only those parts of the decal deposited on the heat release agent will be transferred to the substrate with the remainder of the decal remaining on the decal carrier as those parts are not heat releasable from the decal carrier.

It will be appreciated that any pattern of heat release agent may be provided on the decal carrier. In order to provide a perforated ceramic image, a perforated layer of heat release agent should be provided. Those parts of the decal printed onto the perforations in the heat release agent layer will remain on the decal carrier and so the decal will be simultaneously perforated and deposited on the glass sheet at the laminator. In order to provide a ceramic image in the form of an array of dots, an intermittent layer of heat release agent in the form of an array of dots would be provided on the decal carrier, so that the only part of the decal deposited would be the part on the array of dots.

A further feature of the process method is that it allows curved decorated glass articles to be manufactured. The decal is deposited and fixed to a flat glass sheet substrate. The flat glass sheet may then be formed in the tempering furnace without distortion of the image fixed thereto. In this way, tempered and decorated glass sheets of a particular shape may be manufactured, e. g. curved corner windows for offices or curved windscreens for cars. As the image is deposited on and secured to a flat sheet substrate there is no distortion of the image when the sheet is formed into the desired shape and so the quality of the image is maintained.