Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2000-11-13
2002-10-15
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S105000
Reexamination Certificate
active
06464348
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the use of thermoplastic ionomer-based clear toners to create a clear overcoating for inkjet printed images.
BACKGROUND OF INVENTION
The use of inkjet printing systems has grown dramatically in recent years. This growth may be attributed to substantial improvements in print resolution and overall print quality coupled with appreciable reduction in cost. Today's inkjet printers offer acceptable print quality for many commercial, business, and household applications at costs fully an order of magnitude lower than comparable products available just a few years ago. Notwithstanding their recent success, intensive research and development efforts continue toward improving inkjet print quality, while further lowering cost to the consumer.
An inkjet image is formed when a precise pattern of dots is ejected from a drop-generating device known as a “printhead” onto a printing medium. The typical inkjet printhead has an array of precisely formed nozzles located on a nozzle plate and attached to an inkjet printhead substrate. The substrate incorporates an array of firing chambers that receive liquid ink (colorants dissolved or dispersed in a solvent) through fluid communication with one or more ink reservoirs. Each chamber has a thin-film resistor, known as a “firing resistor,” located opposite the nozzle so ink can collect between the firing resistor and the nozzle. In particular, each resistor element, which is typically a pad of a resistive material, measures about 35 &mgr;m×35 &mgr;m. The printhead is held and protected by an outer packaging referred to as a print cartridge, i.e., inkjet pen.
Upon energizing of a particular resistor element, a droplet of ink is expelled through the nozzle toward the print medium, whether paper, transparent film or the like. The firing of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements, thereby forming alphanumeric and other characters on the print medium.
The need exists to protect and stabilize inkjet printed images against scratch and image resistance and against unwanted retransfer of ink from the inkjet image to unwanted surfaces.
Tutt & Tunney (U.S. Pat. No. 5,847,738, issued on Jan. 8, 1999 and assigned to Eastman Kodak Co.) disclose a process for applying a protective overcoat on an inkjet printed media. The protective coat is obtained through:
a) Charging the printed imaged element to a given polarity or applying a voltage across the surface of the element which is attracted to a conductive surface behind the element;
b) Applying colorless charged particles to the imaged element which causes them to be electrostatically attracted to the surface of the image layer; and
c) Heat-fusing the particles to obtain a protective overcoat over the entire surface of the image layer.
Colorless toner particles well-known in electrophotography are used in the coating process of Tutt & Tunney. Examples of materials mentioned in the patent are: chlorinated polyolefins, polyacrylic acid esters, cellulose derivatives, modified alkyd resins, polyesters, polyurethanes, poly(vinyl acetate), polyamides, ketone resins, (polyvinylbutyral, copolymers of vinyl polymers with methacrylates or acrylates, low molecular weight polyethylene, copolymers with siloxanes, polyalkenes, and poly(styrene-co-butyl acrylate), etc.
In a preferred embodiment in Tuft & Tunney's disclosure, the colorless particles are made of either a polyester or poly(styrene-co-butyl acrylate). In order to achieve easy fusibility of these particles during the overcoat formation and obtain a highly glossy surface, polymers used in electrophotographic toners should have low melt viscosity. This would mean using polymers of relatively low molecular weight (from~a few thousand to 15,000). As a result, brittle coatings with relatively poor flexibility and hence inferior abrasion resistance are likely. If, in order to increase abrasion resistance, crosslinked, branched or higher molecular weight polymers were used, the melt viscosity would be high. Furthermore, covalent cross-linking during the overcoat fusing process would be irreversible, thus leading to a dramatic increase of melt viscosity. This in turn would lead to an overcoat with poor gloss and non-uniform thickness.
Nagashima (U.S. Pat. No. 4,738,555 assigned to Toshiba) discloses the use of a thermal print ribbon to thermally transfer and laminate a transparent protective layer of wax, vinyl chloride, vinyl acetate, acrylic resin, styrene or epoxy on the printed image portion of a record substrate.
Tang et al. (U.S. Pat. No. 5,555,011 assigned to Eastman Kodak) disclose a method of laminating, using a thermally-transferable polymeric material, a transparent protective layer over an ink-printed image on a substrate.
Abe et al. (U.S. Pat. No. 5,954,906 assigned to Canon) discloses a method for protecting and covering a printed material on a substrate with a pressure-sensitive transferring protective covering material with at least (a) a first flexible substrate, (b) an adhesive layer, (c) a solid resin layer, and (d) a second flexible substrate, stacked in this order.
Malhotra (U.S. Pat. No. 5,612,777 assigned to Xerox) discloses a method of applying a clear, scratch-resistant, lightfast coating for a substrate having photocopied color images by first, depositing color toner images on a charge retentive surface; second, depositing a clear polymer toner material onto the charge retentive surface; and third, fusing the color toner images and clear polymer toner material onto a substrate.
Another Malhotra patent (U.S. Pat. No. 5,906,905 assigned to Xerox) discloses a method of creating photographic quality prints using imaging such as xerography or ink jet by, first, reverse reading toner images on a transparent substrate and then adhering the transparent substrate to a coated backing sheet, coated with a polymeric lightfastness material.
Typically, clear toner materials currently used in the industry are based on a few basic polymer types. In the table below are listed the advantages and disadvantages of these materials when used as an overcoat for inkjet printed images:
Toner based on:
Advantages
Disadvantages
Styrenated Acrylics
Good Elasticity &
Poor Fusability (high
Toughness
softening temperature); Poor
gloss and clarity
Low MW Polyesters
Low melting
Very poor mechanical
temperature; low
properties (no flexibility and
melt viscosity; good
abrasion resistance); poor
clarity; fair gloss
resistance to inkjet ink
solvents
Polyolefins
Good fusibility;
Poor abrasion resistance;
good elasticity
Poor clarity and gloss; waxy
feel
Thermoplastic ionomers have been used for films, coatings and molded articles. They are known for their good impact strength, high melt viscosity, high melt strength, good transparency and relatively low continuous service temperatures. As thin films, they have high tear strengths with a combination of toughness and good abrasion resistance, as well as good adhesion on impact, which makes them a good surface covering for shoe soles, shoe heels, golf ball covers, bowling pin covers and glass bottles. In such applications, the ionomer coatings are extruded or blow molded. There has previously been no attempt to use thermoplastic ionomers as a coating material for printed images, since the extrusion and/or blow molding processes conventionally used with ionomers do not lend themselves to such application.
SUMMARY OF THE INVENTION
The present invention relates to a method of using thermoplastic ionomers to form a clear protective coating on color toner image printed by offset, inkjet or xerographic means.
The present invention also relates to a protective coating comprising thermoplastic ionomers wherein the protective coating is formed on color toner image printed by offset, inkjet or xerographic means.
The present invention also relates to an apparatus for creating color toner images, said apparatus comprising:
a) means including a plurality of developer housings for fo
Kasperchik Vladek P
Kwasny David M
Barlow John
Haymond W. Bradley
Hewlett--Packard Company
Shah Manish S.
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