Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2002-09-20
2004-03-02
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S101000, C347S100000, C428S032100
Reexamination Certificate
active
06698880
ABSTRACT:
FIELD OF THE INVENTION
An inkjet recording system comprising an inkjet recording element for use with a pigment-based ink is disclosed. In particular, the recording element has a porous substrate with relatively large pores and a relatively thin porous overlaying surface layer which traps pigments, from an applied pigmented ink, at or near the surface while not unduly restricting ink flow into the underlying porous substrate.
BACKGROUND OF THE INVENTION
In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
Inks used in various inkjet printers can be classified as either dye-based or pigment-based. In dye-based inks, the colorant is molecularly dispersed or solvated by a carrier medium. In pigment-based inks, the colorant exists as discrete particles. It is known that pigment-based inks perform better than dye-based inks with respect to stability properties such as light fade or ozone fade.
An inkjet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-forming layer. The ink-receiving layer can be either porous or swellable.
In general, porous inkjet receivers absorb ink much faster than swellable inkjet receivers. This allows handling of the print sooner. Also, the propensity of image artifacts such as coalescence are reduced. There are many porous inkjet receivers available today. They include porous glossy receivers comprised of small (<200 nm) inorganic particles and binder. The void space created between the particles allow ink to penetrate into the structure. In addition, small pore sizes caused by the packing of the inorganic particles prevents the pigments in the ink from penetrating into the porous structure. This results in high image density. However, the small pores in the structure together with the slower absorbing pigmented inks slow down the rate at which the ink can be absorbed. This slow-down in ink flux is often below the acceptable levels for high speed printing and can result in coalescence as well as poor dry times. Although it is known that larger pores allow ink to be absorbed faster, as predicted by the well-known Lucas-Washburn equation for describing fluid flow in a cylinder, the tradeoff is lower image density.
Other porous receivers include matte-type inkjet receivers. These are often comprised of larger inorganic particles (>1 micron) and binder. In this case, the void space between particles is typically larger than described above. Although the rate of ink penetration can be faster than with the smaller inorganic particles, the larger pore sizes still allow the pigments from the ink to penetrate deeper into the porous structure. Thus, this still results in lower image densities.
WO Patent Number 99/03685 discloses an inkjet printable microporous film comprised of a so-called fluid management system and a so-called pigment management system for use with pigmented inkjet inks. The patent teaches impregnating a microporous structure with pigment-mordanting materials such as silica or metal salts. Since the mordanting materials are contained throughout the microporous structure, the pigments can still penetrate into the microporous structure. Thus, this still results in a lower image density than if the pigment particles stayed on the surface.
WO Patent Number 99/33669 discloses a fibrous inkjet printing media that has been treated with a positively charged species in order to make the pigments in jetted inks bind to the fibers of the media. While this improves the waterfastness of the inks in the media, the pigment particles can still penetrate into the fibrous structure yielding a lower image density than if the pigment particles stayed at the surface.
WO Patent Application Number 01/38102 A1 discloses a silica-filled microporous substrate having an organometallic multivalent metal salt on the silica surface of the silica-filled microporous substrate for improved image waterfastness when printed with pigmented inks. In this case, the pore size is relatively small (<100 nm) and is the same at the surface as well as throughout the entire microporous substrate structure. Pigments from the jetted ink will stay at the surface, due to the relatively small pore size, resulting in good image density. However, the small pore sizes throughout the microporous substrate will restrict the rate of ink flow into the substrate when compared to substrates with larger pore sizes.
U.S. Pat. No. 6,409,334 discloses an inkjet recording element that provides a fast ink dry time and good image density, which element comprises an ink-permeable polyester substrate comprising a base polyester layer and an ink-permeable upper polyester layer. The upper polyester layer comprises a continuous polyester phase having an ink absorbency rate resulting in a dry time of less than about 10 seconds and a total absorbent capacity of at least about 14 cc/m
2
, the substrate having thereon a porous image-receiving layer characterized by interconnecting voids. However, the porous imaging-receiving layer on the surface was not designed to trap ink pigment particles at the surface for optimal image density and also allow for quick ink absorption rates.
In view of the above, there is a need for an inkjet printing system having a porous inkjet receiver designed specifically for pigmented inks, which receiver produces high-density and long-lasting images with fast ink absorption rates.
SUMMARY OF THE INVENTION
It is a purpose of this invention to provide an inkjet recording system comprising a pigment-based ink and a inkjet recording element. In particular, the recording element is comprised of a porous substrate with relatively large pores and a relatively thin overlying porous surface layer that traps pigment particles from an applied pigmented ink, at or near the surface, while not unduly restricting ink flow into a porous underlying substrate.
Another aspect of the present invention relates to an inkjet printing method, comprising the steps of a) providing an inkjet printer that is responsive to digital data signals; b) loading the printer with an inkjet recording element according to the present invention; c) loading the printer with a pigment-based ink; and d) printing on the ink-receiving layer of the inkjet recording element using the inkjet ink in response to the digital data signals.
DETAILED DESCRIPTION OF THE INVENTION
As indicated above, the present invention relates to an inkjet recording system in which the recording element comprises at least two layers: a porous ink-pigment-trapping surface layer and an underlying porous base unit layer. The ink-pigment-trapping surface layer has a thickness that is smaller than the porous base unit layer. The ink-pigment-trapping surface layer has a median pore size, r
1
, that is less than the median pore size, r
2
, of the porous base layer. The median pore size of the ink-pigment-trapping surface layer is approximately the size of the pigment particles used in the ink. This size of the pores is necessary to trap pigment particles near the surface, thus yielding a high print density of colorant.
The ink-pigment-trapping surface layer has a thickness less than three microns, preferably 0.25 to 2.5 microns, most preferably 1 to 2 microns, wherein the median pore diameter in the ink-pigment-trapping surface layer is less than 500 nm, preferably 10 nm to 200 nm, most preferably 25 nm to 125 nm. In order to trap the pigment particles, in the applied inks, on the surface of the recording element, the ratio of the median pore diameter of the ink-pigment-trapping surface layer and the median pigment particle size needs to be less than 1.5, preferably less than 1.1.
The porous
Campbell Bruce C.
Reczek James A.
Todd Lisa B.
Eastman Kodak Company
Konkol Chris P.
Meier Stephen D.
Shah Manish
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