Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/025—Duplicating or marking methods; Sheet materials for use therein by transferring ink from the master sheet
  • B41M5/0256—Duplicating or marking methods; Sheet materials for use therein by transferring ink from the master sheet the transferable ink pattern being obtained by means of a computer driven printer, e.g. an ink jet or laser printer, or by electrographic means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/025—Duplicating or marking methods; Sheet materials for use therein by transferring ink from the master sheet
  • B41M5/035—Duplicating or marking methods; Sheet materials for use therein by transferring ink from the master sheet by sublimation or volatilisation of pre-printed design, e.g. sublistatic
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/40—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used characterised by the base backcoat, intermediate, or covering layers, e.g. for thermal transfer dye-donor or dye-receiver sheets; Heat, radiation filtering or absorbing means or layers; combined with other image registration layers or compositions; Special originals for reproduction by thermography
  • B41M5/42—Intermediate, backcoat, or covering layers
  • B41M5/426—Intermediate, backcoat, or covering layers characterised by inorganic compounds, e.g. metals, metal salts, metal complexes

Definitions

• 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.
• 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.
• thermal retransfer 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.
• heated rolls may be used to provide the heat as the intermediate sheet and article are fed through.
• 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.
• 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.
• 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.
• 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 ⁇ m mean diameter.
• the type of particle is less critical than the proportion used relative to the binder, although other properties may influence the optimum choice.
• 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.
• inorganic particulates such as hydrated alumina and the like.
• organic particles are generally preferred, in view of the more abrasive nature of compositions with high loadings of hydrated alumina.
• poly(alkyls ⁇ lylsesqu ⁇ oxane) 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).
• a metal phosphate salt of stea ⁇ c 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.
• our preferred range for the amount of protective filler is generally from 100% to about 250% by weight of the binder.
• Suitable binders include cellulosic resins, such as cellulose acetate prop ⁇ onate and cellulose acetate butyrate.
• the binder need not be cross-linked in order to benefit in terms of heat resistance from the present high loadings of particulates. However, we generally do prefer to provide some degree of cross-linking by the addition of small amounts of crosslinking agent.
• the cellulose resins can be crosslmked by isocyanates or by melamine cross linking agents in acid conditions.
• the dried backcoat of the invention is preferably within a thickness range of 1-10 ⁇ m, especially 1 -5 ⁇ m, as thicker backcoats provide little extra protection, and lead to lower versatility, especially during the first, image-forming, stage.
• the supporting substrate may typically be paper, especially polyolefin-coated paper. This is a support material which provides a very good quality of retransferred image, but which was particularly prone to heat induced problems during retransfer prior to the protection afforded by the present backcoats.
• Example 1 A backcoat composition A was prepared, and coated onto a substrate of polyethylene coated paper, then dried to give a coating of thickness 3 ⁇ m. An imageable layer had previously been coated onto the other side of the polyethylene coated paper, to complete a retransfer intermediate sheet according to the invention.
• backcoat composition A cellulose acetate proprionate (CAP) 31.45 wt%
• Atmer 190 (antistatic agent) 0.5 wt%
• Tospearl 120 particles - 2.0 ⁇ m mean diameter
• the amount of the particulate Tospearl is approximately 200 % by volume of the binder (CAP). Examples 2-4
• composition B Tospearl 120 at 100 % by weight of the binder Composition
• Apyral at 100 % by weight of the binder (Apyral is a trade mark of QLT in respect of hydrated alumina filler) Test results
• Each intermediate sheet was printed with blocks of colour, in a thermal transfer printer whose heat source was a thermal head having a row of programmable pixel heaters, in normal manner.
• a thermal transfer printer whose heat source was a thermal head having a row of programmable pixel heaters, in normal manner.
• each imaged intermediate sheet was placed in the press together with a mug precoated with a resin to give a dye-receptive surface against which was placed the imaged layer of the intermediate sheet.
• the press was then activated to apply heat and pressure to the back of the intermediate sheet, to thermally retransfer dyes from the intermediate sheet into the dye-receptive surface layer of the mug.
• the press was opened, and the printed mug removed. Both the press and the image retransferred into the mug were examined, and the results were as shown in the table below,
• composition A ++
• a retransfer intermediate sheet according to the invention was prepared essentially as described in Example 1 , except that a anti-blocking agent was also added to the backcoat composition (composition E) to improve handling.
• backcoat composition E cellulose acetate proprionate (CAP) 100 parts by weight
• Tegomer 2311 (silicone levelling agent) 0.1 parts by weight
• the retransfer intermediate sheet thus prepared was used to print mugs in a standard mug-printing press, essentially as described for Examples 1-4. Handling during printing was excellent. When the press was opened and the printed mug removed after the retransfer process, both the press and the image retransferred into the mug were examined and found to be in excellent condition, with no significant degradation of the retransfer sheet being apparent.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)
• Decoration By Transfer Pictures (AREA)

Applications Claiming Priority (3)

Publications (2)

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• 1996
  • 1996-07-16 GB GBGB9614898.6A patent/GB9614898D0/en active Pending
• 1997
  • 1997-07-03 DE DE69702258T patent/DE69702258T2/de not_active Expired - Fee Related
  • 1997-07-03 EP EP97929396A patent/EP0912349B1/de not_active Expired - Lifetime
  • 1997-07-03 JP JP10505704A patent/JP2000514377A/ja active Pending
  • 1997-07-03 WO PCT/GB1997/001760 patent/WO1998002315A1/en not_active Ceased

Non-Patent Citations (1)

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