Record receiver having plural interactive leaves or a colorless – Having plural interactive leaves
Reexamination Certificate
1999-08-16
2001-06-26
Hess, Bruce H. (Department: 1774)
Record receiver having plural interactive leaves or a colorless
Having plural interactive leaves
C156S235000, C428S195100, C428S323000, C428S327000, C428S331000, C428S913000, C428S914000
Reexamination Certificate
active
06251825
ABSTRACT:
The invention relates to thermal transfer printing of an article by forming an image in an intermediate sheet by thermal transfer and thereafter thermally retransferring the image to a dye-receptive layer on the article; and in particular to the composition of the retransfer intermediate sheet.
Thermal transfer printing is a process in which one or more thermally transferable dyes are caused to transfer from selected areas of a dye-donor sheet to a receiver by thermal stimuli, thereby to form an image. This is generally carried out in a printer having a thermal head or laser energy source, depending on the kind of dye-donor sheet used. Using a dye-donor sheet comprising a thin substrate supporting a dyecoat containing one or more uniformly spread dyes, printing is effected by heating selected discrete areas of the dye-donor sheet 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 dye-donor sheet.
In order to print articles other than flexible sheets, one method that is commonly used is thermal retransfer. This is a two stage process, employing a retransfer intermediate sheet comprising a supporting substrate having a dye-receptive imageable layer on one side, usually with a backcoat on the other side to promote good transport through the initial printer. In the first stage, an image is formed as above by pressing together a dye-donor sheet and the imageable layer of the intermediate sheet, and applying heat to selected positions of the dye-donor sheet to cause transfer of dye into that imageable layer, thereby to produce the image.
The image-containing intermediate sheet is then separated from the dye-donor sheet, and in the second stage of the process, is pressed against the article, with its image-containing layer contacting a dye-receptive surface of the article. Heat is then applied to effect transfer of the image, usually over the whole area of the image simultaneously and in a press shaped to accommodate the article. Alternatively with some appropriately shaped articles, heated rolls may be used to provide the heat as the intermediate sheet and article are fed through. Thus although thermal retransfer techniques can be used for printing laminar articles such as stiff cards, they are of particular applicability to the printing of three dimensional articles such as mugs.
Not all of the dye which forms the image can retransfer to the article in the thermal retransfer process, but the higher the proportion which can be caused to retransfer, the more intense will be the colours in the printed article. The proportion which does retransfer depends on, amongst other things, the composition of the dye-receptive surface of the article. This may be the natural surface of that article where the latter is formed of an appropriately dye-receptive material, but in most instances it is usual first to provide the article with a coating to form a surface of enhanced dye-receptivity.
A further factor influencing the degree of retransfer is the amount of heat applied in the second, i.e. retransfer, stage. Heated presses shaped according to the mug or other article to be printed, have been sold by a number of manufacturers, and typically these develop temperatures of 140-180° C. Under such conditions, the intermediate sheet can degrade, leaving debris in the press and ultimately sticking to the press when it is opened, causing defects to occur in the retransferred image. We have now developed a heat resistant backcoat composition to provide retransfer intermediate sheets with improved protection against the physical conditions experienced in such retransfer presses.
Accordingly, one aspect of the invention provides a re-transfer intermediate sheet for thermal transfer printing of an article by thermal retransfer, the intermediate sheet comprising a supporting substrate having on one side an imageable layer and on the other a backcoat, wherein the backcoat is a heat-resistant layer comprising a polymeric binder and a protective particulate filler in an amount of at least 50% by weight of the binder.
According to a further aspect of the invention, a method of printing an article having a dye-receptive surface comprises the steps of pressing together a dye-donor sheet and an imageable layer of a retransfer intermediate sheet comprising a supporting substrate having on one side the imageable layer and on the other a backcoat, forming an image in the imageable layer by thermal transfer printing, pressing the thus-formed image-containing layer against the dye-receptive surface of the article, and applying heat to the intermediate sheet to effect retransfer of the image to the dye-receptive layer of the article, characterised in that the backcoat is a heat-resistant layer comprising a polymeric binder and a protective particulate filler in an amount of at least 50% by weight of the binder.
The protective filler most suitably comprises mainly particles of 1-10 &mgr;m mean diameter.
For the purpose of providing thermal resistance, the type of particle is less critical than the proportion used relative to the binder, although other properties may influence the optimum choice. We have used to good effect organic particles in the form of a poly(alkylsilylsesquioxane) compound, such as the methyl substituted compounds marketed in various particle sizes under the trade mark Tospearl, by Toshiba. Equally effective in providing heat resistance are inorganic particulates such as hydrated alumina and the like. However the organic particles are generally preferred, in view of the more abrasive nature of compositions with high loadings of hydrated alumina. Examples of poly(alkylsilylsesquioxane) particulate compounds available commercially include KMP-590 (Shinetsu Chemical); Tospearl 105, Tospearl 108, Tospearl 120, Tospearl 130, Tospearl 145 and Tospearl 240 (Toshiba Silicone); and Torefil R-925 and Torefil 930 (Toray Dow Corning).
Compared with retransfer intermediate sheets with backcoats containing only small quantities of particles, typically about 1-10% by weight of the binder in the past, we find we obtain a noticeable improvement in heat resistance with as little as 50% by weight of the binder. However we prefer to use at least 100%, especially at least 200% by weight of the binder, as the improvement in heat resistance increases with increased loading. At higher loadings, other properties of the backcoat can deteriorate, e.g. to become less readily coatable as a composition during manufacture, or more brittle once dried as a coating, but this depends on the resin used for the binder and on the nature of the particles selected. Some of these difficulties with high filler loadings can be mitigated by incorporating other additives into the composition. For example, in the preferred embodiments using particles at loadings of about 200% by weight of the binder or above, we prefer to include a metal phosphate salt of stearic acid in an amount of from 1 to 20% of the binder, to stabilise the solution and improve manufacturability. It may similarly be added to compositions containing lower particle loadings, but the lower the loading levels, the less is this of benefit. Subject to the above limitations, our preferred range for the amount of protective filler is generally from 100% to about 250% by weight of the binder.
Where other particles are also incorporated, it may be necessary to use less of the protective 1-10 &mgr;m particles than the maximum quantity that could otherwise be used. Examples of such other particles which may usefully be added include slightly larger particles added as an anti-blocking agent to improve handling. Ou
Hess Bruce H.
Imperial Chemical Industries plc
Pillsbury & Winthrop LLP
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