Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-04-16
2002-10-15
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S323000, C428S327000, C428S423100, C428S480000, C428S500000
Reexamination Certificate
active
06465081
ABSTRACT:
TECHNICAL FIELD
The invention relates to coatings applied to film materials to provide receptor elements for images generated by inkjet printers. More particularly, the invention relates to films having an inkjet image receptor coating on one side and an ink repellent coating on the other to allow contact between a plurality of imaged sheets, during printing, without smearing of ink droplets before an image dries.
BACKGROUND
Printing methods, including inkjet printing and electrophotographic or laser printing have achieved widespread acceptance, for home and office use, to print text and graphic images on a variety of receptor substrates such as paper and films. The films may be used as transparency film for overhead projectors. Inkjet printers are well suited for use with paper substrates that rapidly absorb the image forming ink droplets, drawing them away from the paper receptor surface into the fibrous bulk of the sheet. Migration of the ink droplets into the paper sheet prevents lowering of image quality that could occur if a still-wet image was smeared in some way.
Film materials, unlike paper, have no inherent capacity to absorb inks that are commonly used in inkjet printers. The capture of the image-forming ink droplets on transparency film presents a technical challenge because plastic film is substantially impervious to liquids. A conventional way for forming an ink-receptive surface involves coating the surface of the film with an ink receptive layer. Typically a hydrophilic coating (the ink receptive layer) absorbs ink droplets to minimize loss of image definition that maybe caused by ink migration or bleeding across the film surface.
Hydrophilic coatings, applied to film materials, are known to provide receptor layers for inkjet images. Receptor layers of this type may be porous for absorbing ink droplets via capillary action. Such coatings are described, for example, in U.S. Pat. No. 5,264,275. An alternative type of absorbent inkjet receptive coating comprises polymers that swell while absorbing image forming ink droplets. Such coatings include those described in U.S. Pat. Nos. 3,889,270, 4,503,111, 4,564,560, 4,555,437, 4,379,804, 5,134,198 and 5,342,688. Hydrophilic inkjet-receptive coatings may also include multilayer coatings as described in U.S. Pat. No. 4,379,804.
In addition to an inkjet image receptor coating, a film sheet of inkjet printable media may require further treatment to control the physical properties of the sheet such as surface roughness, static charge accumulation, and curl-set. Backside coatings, opposite the ink receptive coating, may provide surface roughness to assist sheet feeding through the transport rollers of an inkjet printer. Application of antistatic coatings and related treatments curtail the accumulation of static charge that may cause feeding and stacking problems between sheets. A very common function of backside coating on inkjet receptive sheets is control of curl. Under low humidity conditions the ink-receptive coating may lose water to the atmosphere, resulting in overall shrinkage of the layer. This places consequent stress on one side of a flexible substrate causing the film to adopt a curl-set usually towards the image-bearing surface. Therefore it has become common practice to coat a hydrophilic, moisture absorbing coating on the backside of the flexible substrate to counteract the image-side curl. The backside coating may, itself, be an inkjet receptive layer, such that the construction is symmetrical having no preferred orientation during deposition of an inkjet image.
US Patents, including U.S. Pat. Nos. 6,022,677, 5,916,673 and 5,723,211, describe inkjet media backside coatings for controlling physical properties as discussed above. Many of these backside coating formulations were developed for paper and other opaque substrates and may be unsuitable for transparency film applications, especially if the coating itself is not completely transparent.
Improvements in inkjet image receptive coatings and physical property control of text and graphic image recording plastic sheets has allowed an increase in the sheets-per-minute output of inkjet printers. A continuing constraint on the print speed for relatively impervious substrates, such as plastic film, is the rate of image forming droplet absorption by the ink receptive layer. Inkjet printers generally stack the printed output copies, automatically, into an output tray. If the image on one sheet is not dry to the touch before release of a following sheet into the output tray, ink from the wet image, will often transfer to the backside of the next overlying sheet in the stack.
The problem of image transfer between relatively impervious sheets becomes more severe when the sheet is a transparent film bearing text and graphic images for presentation using an enlarging projector, such as an overhead projector. Images deposited on transparency film usually will be high contrast images to avoid the appearance of a washed-out projected image focused on a projection screen. High contrast images may require a higher ink loading to achieve optimum optical density compared to images deposited against a white background such as paper that is viewed by reflected light. As might be expected, the higher ink loading requires a longer drying time. Delayed drying potentially leads to an increasing amount of image transfer or offset between adjacent sheets. For this reason, manufacturers of inkjet printers have generally found it necessary to slow the print rate when printing film transparencies for projection.
In view of the above described deficiencies associated with the use of known inkjet image receptor films, particularly offset of the image formed by ink droplets, the present invention has been developed to alleviate these drawbacks and provide further improvement. These enhancements and benefits are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.
SUMMARY
In its several disclosed embodiments, the present invention alleviates the drawbacks described above with respect to impervious films containing coatings that provide receptor elements for inkjet images. Of particular interest is the use of dissimilar coatings on opposing sides of image receptor sheets. Differences in these coatings minimize, if not deter ink transfer, also referred to herein as image offset, between adjacent surfaces of sheets of a stack produced in the output tray of a printer during inkjet printing.
In a majority of printing and copying methods, the printing equipment used to produce multiple impressions establishes precise positioning of a receptor sheet for image transfer before ejecting the sheet into an output tray. The orientation of the ejected sheet usually places the recently applied image pattern on the exposed, upward facing surface of the sheet. The next sheet to be ejected from the printing equipment may slide across the exposed imaged surface before settling over the previous sheet. With continued operation of a printer, a stack of sheets will form having upward-facing, imaged surfaces in contact with the downward facing surface or backside of the next higher sheet in the stack. The upward-facing image may not be in a fully fixed or in a permanent condition before contact with the backside of the next sheet in the printing sequence. This condition is especially true for inkjet images produced by image forming droplets. Sliding contact between sheets exiting the inkjet printer may cause smearing of still-wet images. Also, contact of adjacent sheets in a stacked configuration may lead to ink transfer or smearing, due to ink migration across the interface between an imaged surface and the backside of its nearest neighbor. Use of coated films according to the present invention substantially eliminates image smearing and image offset problems that occur by ink migration between sheets. Reduction or elimination of ink migration involves applying a non-wetting or ink-repellent coating to the backside of the film. Such coatings were disc
DiZio James P.
Kinning David J.
Sarkar Manisha
Vanderzanden John W.
Florczak Yen Tong
Hess Bruce H.
Shewareged B.
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