Imperial Chemical Industries Limited

Akzo Nobel Coatings International B.v.

Nicholas C Beck

Richard A Hann

Paul A Edwards

Gary W Morrison

John A Pope

Peter A Gemmell

Ian Stephenson

Anthony Joseph Martino

A retransfer intermediate sheet for receiving an image to be printed onto an article by thermal retrasfer comprises a substrate which is preferably heat-deformable; and an image-receiving coating on one side of the substrate, comprising an image-receiving layer for receiving an image by printing, preferably inkjet printing, of dye-containing ink, the image-receiving layer comprising amorphous porous silica, a first, non-dye absorbing polymeric binder and a second, flexible polymeric binder. The sheet is particularly useful for printing on three dimensional articles, e.g. being heated and vacuum formed to conform to an article. The invention also coven a method of printing and an article bearing a printed image.

Thermal transfer printing

An inkable sheet comprises a substrate having on at least one surface thereof an ink absorbent layer comprising a cellulose material and an acid functional resin which is insoluble in water of neutral or acidic pH at room temperature. The acid functional resin may comprise an acid functional polyurethane resin or an acid functional acrylic resin such as a polyacrylate/acrylic acid copolymer. The ink absorbent layer preferably further comprises a weak organic acid or salt thereof and/or at least one crosslinking agent.

Inkable sheets

A thermal transfer printing receiver sheet for use in security laminates, comprises a substrate supporting a receiver coat of a dye-receptive composition on one side and a backcoat on the other, wherein the backcoat comprises a thermoplastic polymer having a Tg less than 130.degree. C., and dispersed therein a particulate solid material in amount 1-24% by weight of the thermoplastic polymer and an average particle size of 0.3-10 .mu.m. The security laminates are prpared after printing the receiver with an image, by bonding a first cover sheet of plastics material to the printed receiver coat so as to overlie the image, and a second cover sheet of plastics material can be bonded to the present backcoat more readily than to a highly crosslinked backcoat, using common adhesives. For greater security, thicker than normal backcoats are used.

Thermal transfer printing receiver

A receiver sheet for thermal transfer printing comprises a substrate having a dye-receiving side and a backcoat on the other side, characterised in that the major component of the backcoat is a partially esterified styrene/maleic anhydride copolymer. This provides a surface which can readily be written on using aqueous inks or ball pens, and can be adhered to by water-activated adhesives. It is also resistant to retransfer of dye from an underlying print, e.g. during storage. The backcoat may also contain antistatic agents and fine inert particles to improve handling properties, appearance and tooth.

A security laminate comprises a thermal transfer print having a receiver layer comprising a thermoplastic dye-receptive polymer doped with a cross-linked silicone-containing release system in which the total silicone content is reduced to 0.01-1% by weight of the thermoplastic dye-receptive polymer, and a cover sheet of plastics material bonded to the receiver layer by heat and pressure, preferably without further adhesives between the print and cover sheet.

Security laminates

In a thermal transfer print, the ready diffusion of dyes through the receiver layer, which is necessary for effecting their thermal transfer from a dyesheet during printing, can also lead to subsequent diffusion within the print, with consequent degradation of print quality. This form of print instability is now countered by using a receiver layer comprising a dye-receptive polymer composition doped with a print stabilizer consisting of a toluene sulphonamideformaldehyde condensation product.

Thermal transfer receiver

A receiver sheet for dye-diffusion thermal transfer printing, comprising a sheet-like dielectric substrate supporting a layer of dye-receptive material on one side, has an antistatic treatment on both sides to improve handling. The antistatic treatment on the side supporting the receiver coat comprises a conductive undercoat located between the substrate and the layer of dye-receptive material. Effective conductive undercoat materials include a cross-linked organic polymer containing a plurality of ether linkages doped with an alkali metal salt to provide conductivity. The antistatic treatment on the other side is preferably incorporated into a heat resistant and/or low friction backcoat, but like that of the receiver side, could also be in the form of a conducting undercoat between the substrate and backcoat.

A receiver sheet for dye-diffusion thermal transfer printing comprises a sheet-like substrate supporting a receiver coat layer in which a dye-receptive polymer composition is doped with a release system comprising the reaction product of at least one silicone having a plurality of hydroxy groups per molecule and at least one polyfunctional N-(alkoxymethyl) amine resin reactive with such hydroxyl groups under acid catalyzed conditions.

A method for improving the stability of a color print formed by dye-diffusion thermal transfer printing, comprises placing against the print a panel of transfer coat comprising a dye-absorbant binder which is substantially free from any thermally transferable materials, and heating at least those areas of the print to which one or more dyes have been transferred, thereby to cause absorption by said panel of dye molecules at the surface of the print. This may conveniently be carried out as part of the printing operation by using a dyesheet having a transfer coat comprising a plurality of uniform panels containing different colored thermally transferable dyes held in a dye-absorbant binder, and further panels comprising a dye-absorbant binder which is substantially free from any thermally transferable materials.

Thermal transfer dyesheet

A dyesheet for thermal transfer printing comprises a substrate supporting a transfer coat comprising a plurality of uniform panels containing different colored thermally transferable dyes, and a further panel in which instead of a colored dye there is a thermally transferable colorless absorber of ultraviolet radiation. Using such a dyesheet, a layer of UV absorber can be applied very simply as an extension of the printing process, by causing the receiver to pass through the printer once more, in contact with the further panel, essentially as though the UV absorber were merely a further color to be added to the print.

A receiver for dye diffusion thermal transfer printing comprises a substrate supporting a receiver coat comprising a dye-receptive material and a dye permeable release agent, characterized in that the receiver coat also contains dissolved or dispersed therein a Bisphenol A-based unsaturated polyester adhesive, to reduce printing adhesion.

A receiver sheet for dye-diffusion thermal transfer printing, comprises a substrate which supports a receiver coat, the receiver coat comprising a dye-receptive material, such as an organic polymer, and a dye-permeable release agent which is a thermoset amino-modified-silicone organic-oligoepoxide resin. The thermoset combination of silicon and organic moieties in the release agent, gives good protection against adhesion between the dyesheet and receiver sheet when they are subjected to short high temperature pulses during printing, while also enabling sharp images of high optical density to be obtained. This balance of properties is best obtained by dispersing the release agent throughout the dye-receptive material, although they can also be applied to the substrate as separate layers.

Growing community of inventors

Manningtree, United Kingdom

Nicholas C Beck