Coating processes – Application to opposite sides of sheet – web – or strip
Reexamination Certificate
2001-12-28
2004-06-08
Beck, Shrive P. (Department: 1762)
Coating processes
Application to opposite sides of sheet, web, or strip
C427S243000, C427S391000, C427S395000
Reexamination Certificate
active
06746713
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to high quality ink jet recording media, and to a high quality ink jet recording medium of exceptionally low cost that is ideally suited for high-speed printing, especially high-speed multi-color printing in web form.
BACKGROUND OF THE INVENTION
High quality ink jet recording media are typically made by applying a single layer of coating to a substrate, such as paper or plastic film. The coating is necessarily designed for multi-functionality, e.g., absorption for rapid penetration of ink vehicle, reactivity to hold out ink colorant at the coating surface for maximum print quality, strength for rub-resistance, and wet resistance, water fastness, fade-resistance, etc. The coating layer must be applied in an amount sufficient to provide this multi-functionality, and particularly to provide for absorbency of the ink carrier vehicle (usually water) needed for rapid drying time.
To maintain dimensional stability of the coated sheet, paper substrates for ink jet recording media typically have a basis weight of at least 35 pounds and up to 150 pounds per 3,000 square feet ream (55-236 grams per square meter). Typical coat weights are five to eight pounds per functional side per 3000 square feet ream (8-13 grams per square meter per side).
It has also been suggested, see for example U.S. Pat. Nos. 4,460,637 and 5,985,424, that the requisite functionalities might be better or more easily attained by the use of two layers of coating materials having different constituents and different characteristics for serving different purposes. U.S. Pat. No. 5,985,424 in particular proposes use of a first or base coating designed to have high absorptivity for the ink vehicle and to be compatible in performance with various ink receptive top coat formulations comprised, in this case, of various ratios of fumed silica and styrene-vinylpyrrolidone. The base coat formulation comprises precipitated calcium carbonate, calcined clay and titanium dioxide dispersed in a binder comprising polyvinyl acetate and soy protein.
Whether the substrate is coated with a single layer of coating material or multiple layers of diverse coating materials, the coating is conventionally comprised of an absorptive pigment having a high void volume for absorbing the ink carrier vehicle, a binder for the pigment, frequently a hydrophylic binder such as polyvinyl alcohol (PVOH), a sizing agent, an ink holdout agent, and a cationic or conductive agent reactive with the ink to aid in rapid setting or fixing of the ink. Boric acid is frequently incorporated as a coagulating, gelating or hardening agent for PVOH.
U.S. Pat. No. 4,877,686, for example, discloses a coating comprised of one or more absorbent fillers dispersed in a binder comprised of fully or completely hydrolyzed polyvinyl alcohol, and utilizing boric acid and/or its derivatives as a jelling or coagulating agent for the polyvinyl alcohol. (Air Products and Chemicals. Inc., a manufacturer of polyvinyl alcohol (PVOH), in its U.S. Pat. No. 4,343,133, column 1, line 56 to column 2, line 18, defines “fully hydrolyzed” PVOH as being 95-99% hydrolyzed and defines “partially hydrolyzed” PVOH as being 80-95% hydrolyzed. Partially hydrolyzed PVOH actually comprises a co-polymer of polyvinyl alcohol and polyvinyl acetate.) According to the disclosure of U.S. Pat. No. 4,877.686, the boric acid may be incorporated in the base sheet, or applied as a coating to the base sheet, or incorporated in the absorbent filler/PVOH coating composition. In the latter instance, it is said that the boric acid must be deactivated before application to the substrate and reactivated upon application, inasmuch as the gelling of the binder has to take place during the coating operation and not before.
U.S. Pat. No. 4,877,686, for example, discloses a coating comprised of one or more absorbent fillers dispersed in a binder comprised of fully or completely hydrolyzed polyvinyl alcohol, and utilizing boric acid and/or its derivatives as a jelling or coagulating agent for the polyvinyl alcohol. (Air Products and Chemicals. Inc., a manufacturer of polyvinyl alcohol (PVOH), in its U.S. Pat. No. 4,343,133, column 1, line 56 to column 2, line 18, defines “fully hydrolyzed” PVOH as being 95-99% hydrolyzed and defines “partially hydrolyzed” PVOH as being 80-95% hydrolyzed. Partially hydrolyzed PVOH actually comprises a co-polymer of polyvinyl alcohol and polyvinyl acetate.) According to the disclosure of U.S. Pat. No. 4,877.686, the boric acid may be incorporated in the base sheet, or applied as a coating to the base sheet, or incorporated in the absorbent filler/PVOH coating composition. In the latter instance, it is said that the boric acid must be deactivated before application to the substrate and reactivated upon application, inasmuch as the gelling of the binder has to take place during the coating operation and not before.
U.S. Pat. No. 6,037,050 proposes that the boric acid be added to the filler/PVOH composition just before coating, specifically that the boric acid be added to the composition and allowed to stand at least ten minutes, preferably thirty minutes or more, before application to the substrate.
The coating compositions are said to produce very uniform and well-shaped ink jet spots or dots.
The art has provided several ink jet recording media. However, for the most part, currently available high-quality ink jet recording media are relatively expensive, relatively slow in response time, and limited to relatively slow speed printing in sheet-fed presses and printers.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide high quality ink jet recording media having an exceptionally rapid response time from ink application to ink set.
A second object of the invention is to provide high quality ink jet recording media ideally suited for high-speed printing in continuous web form and especially suited for high-speed multi-color ink jet printing.
A third object of the invention is to provide high-quality ink jet recording media at exceptionally low cost.
In accordance with the invention, a dimensionally stable and highly absorbent paper substrate or base-sheet (in web form) is coated with a composition that forms on the surface of the base-sheet a three-dimensional screen or sieve which allows rapid penetration of the ink vehicle carrier through the coating to the absorbent base-sheet while at the same time holding the ink dye or pigment out on the surface of the coated paper and facilitating rapid setting of the ink.
The three-dimensional screen or sieve that is formed on the surface of the base sheet or substrate is comprised principally of partially-hydrolyzed PVOH and boric acid that have been cooked together in an aqueous solution to achieve complete dissolution of both the PVOH and the boric acid in the aqueous solution. During the cooking process, the PVOH and boric acid begin forming a three-dimensional structure which allows only limited direct bonding of PVOH to PVOH and instead forms bonds of PVOH-boric acid-PVOH. This is in marked contrast to the prior art where boric acid acts simply as an essentially instant coagulant for the PVOH. After the PVOH/boric acid cook is complete, i.e., after both have been substantially completely dissolved in the makedown water, a glyoxal-based insolubilizer and/or other immobilizing agent is added to the solution to complete the formation of the three-dimensional structure and render the structure permanent. An ink-setting reagent, such as a cationic resin, is also added at this time. The formulation of the coating, i.e., the cook, is carried out at a controlled rate such that the polyvinyl alcohol molecules remain reasonably close to one another to impart strength and wet-resistance to the coating, but are nevertheless sufficiently spaced to facilitate penetration of the ink vehicle carrier through the porous coating and into the paper base sheet.
Even at very low coat weights, pigments, dyes and colorants do not penetrate through the coating and cause objectionable print show-through
Schade Robert L.
Schliesman Leonard J.
Beck Shrive P.
Greer Burns & Crain Ltd.
Jolley Kirsten Crockford
Stora Enso North America Corporation
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