Record receiver having plural interactive leaves or a colorless – Having plural interactive leaves
Patent
1999-02-16
2000-07-04
Hess, Bruce H.
Record receiver having plural interactive leaves or a colorless
Having plural interactive leaves
428195, 428206, 428207, 428328, 428403, 428913, 428914, B41M 5035, B41M 538
Patent
active
060838728
DESCRIPTION:
BRIEF SUMMARY
This invention relates to protective overlays for printed matter and in particular to such overlays for use with printed matter produced by thermal transfer printing.
Thermal transfer printing is a process in which one or more thermally transferable dyes are caused to transfer from selected areas of a dyesheet to a receiver by thermal stimuli, thereby to form an image. Using a dyesheet comprising a thin substrate supporting a dyecoat containing one or more uniformly spread dyes, printing is effected by heating selected discrete areas of the dyesheet while the dyecoat is pressed against a dye-receptive surface of a receiver sheet, thereby causing dye to transfer to corresponding areas of the receiver. The shape of the image transferred is determined by the number and locations of the discrete areas which are subjected to heating. Full colour prints can be produced by printing with different coloured dyecoats sequentially in like manner, and the different coloured dyecoats are usually provided as discrete uniform panels arranged in a repeated sequence along a ribbon-shaped dyesheet. High resolution photograph-like prints can be produced by thermal transfer printing using appropriate printing equipment, such as a programmable thermal print head or laser printer, controlled by electronic signals derived from a video, computer, electronic still camera, or similar signal generating apparatus. A typical thermal print head has a row of tiny selectively energizable heaters, spaced to print six or more pixels per miilimetre, often with two heaters per pixel. Laser printers require absorbers to convert the laser radiation to heat, usually in or under the dyecoat, and similarly produce the print by transferring dyes to the receiver pixel by pixel. The transfer mechanism is believed to depend very much on the conditions under which printing is carried out. Thus for example, when using a thermal head, the dyesheet and receiver are pressed together between the head and a platen roller, giving conditions favouring diffusion of the dyes from the dyesheet directly into the receiver, virtually precluding any sublimation. Where a small gap is provided between the dyesheet and receiver, as favoured in some laser driven printers for example, the transfer mechanism appears to be exclusively sublimation. However, in both cases the dyes are mobile molecules which can diffuse into and out of the receiver when warmed, or in the presence of various lyophilic liquids. In particular, grease from a finger holding a print can lead to migration of the dye to the surface, making the print seem dirty or causing smearing of the dyes, and plasticisers in plastic pouches can cause havoc with unprotected D2T2 images. Particularly bad in this respect is dioctylphthalate, used as a plasticiser in polyvinyl chloride from which such pouches are commonly made. For many years various protective covers have been proposed to protect thermal transfer prints against such effects as well as against abrasion.
In addition to the plasticiser type effects, thermal transfer prints are liable to be affected by exposure to uv radiation as present for example in sunlight.
US Pat. No. 4522881 discloses a protective overlay of 10 .mu.m thickness consisting of a polyester resin containing organic uv absorbers such as benzophenones and benzotriazoles in an amount of 0.2% by weight. However, a 10 .mu.m thick overlay can, when applied, have edge problems, ie the edges can be jagged due to incomplete cut-through and/or incomplete adhesion and ideally, the overlay should have a thickness of 2 to 5 .mu.m. To achieve the same degree of uv absorbency, such thin overlays must contain a much greater quantity of the absorber and it has been found that at such quantity there is a deleterious effect on the property of the overlay as a barrier to plasticisers. Moreover, such UV absorbers are known to be prone to loss due to photochemical consumption and can crystallise out resulting in migration to the surface causing an undesirable blooming effect.
According to one aspect of the
REFERENCES:
patent: 5932309 (1999-08-01), Smith et al.
Hess Bruce H.
Imperial Chemical Industries plc
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