Stock material or miscellaneous articles – Ink jet stock for printing
Reexamination Certificate
1999-03-08
2003-10-14
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Ink jet stock for printing
C428S032240, C428S032380
Reexamination Certificate
active
06632485
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high gloss ink jet medium. More particularly, the present invention relates to an ink jet medium comprised of a gelatin containing ink receiving layer. The ink jet medium of the present invention exhibits excellent curl stability and flexibility.
2. Description of the Related Art
Ink jet printing technology is a non-impact printing technique in which color dots are formed on a substrate from the ink droplets ejected from nozzles in the print head. The inks are generally composed of water, water-soluble or water-dispersible dyes, water-miscible cosolvents, and surfactants. The ink receiving layer is usually made from water-soluble or water-swellable polymers coated on a film or paper substrate. The coating absorbs ink through rapid swelling of the coated polymers and forms an image. High resolution photo-realistic color images can be formed on a well designed ink jet media based on water-soluble or water-swellable polymers. The major disadvantages of this type of coating, however, are long ink dry time and low water resistivity of both the coating and the printed image.
In order to obtain a high quality image without ink bleeding and/or coalescence, the polymeric coating needs to absorb a high amount of water rapidly. On the other hand, the coating needs to be water-resistant to provide good durability. These two requirements frequently conflict with each other. There have been many attempts to improve the water resistivity while maintaining the high water adsorption rate of ink jet recording media. One approach suggested is to use a blend of hydrophilic and hydrophobic polymers in the coating, such as described in U.S. Pat. Nos. 4,935,307 and 5,101,218. Another approach suggests forming a semi-interpenetrating polymer network where at least one of the polymeric components is crosslinked to form a continuous network through which uncrosslinked hydrophilic polymers are intertwined. For example, see EP patents 0482836, 0482837 and 0482838. A third approach for attempting to achieve a combination of a high ink adsorption rate and good coating durability is to utilize polymers which form a hydrogel at ambient conditions. The most popular polymer for this approach is gelatin, which absorbs water and swells quickly at ambient conditions while maintaining the physical integrity of the coating. The physical strength of the gelatin coating saturated with ink can be further improved through crosslinking.
Gelatin based coating has the advantages of high gloss, fast water absorbing properties, easy to achieve high water resistance, and good dye fading resistance. U.S. Pat. No. 4,649,064 describes an ink jet media comprised of gelatin crosslinked by a vinylsulfonyl compound to render the coating water resistant. This coating also contains multivalent metal ions to mordant the dye molecules. U.S. Pat. Nos. 5,474,843 and 5,656,378 describes an ink jet media composed of hardened gelatin and a dye mordant selected from one of the following groups: quaternary ammonium, amino compounds, phospholipids, divalent group II metal ions, and polyvinyl pyridine. U.S. Pat. No. 5,141,599 describes an ink jet media composed of a blend of gelatin and starch. U.S. Pat. No. 5,650,216 describes an ink jet media which is composed of two layers of coatings where the base layer is a blend of gelatin and an acrylic polymer to promote adhesion to the substrate, and the top layer is a blend of gelatin with a hydrophilic polymer. U.S. Pat. No. 5,532,064 covers a crosslinked gelatin network for ink jet application, which contains a small percentage of dicyandiamide (less than 1%). This small amount of dicyandiamide is alleged to help retain water in the coating. European Patents 704314 and 701902 describe an ink jet coating which is a blend of gelatin and polymethyl methacrylate (PMMA) beads. A large amount of PMMA beads (20-1500 wt % based on gelatin) is claimed to help reduce the ink dry time.
There are two major disadvantages to a gelatin-based coating which are not addressed in the existing art, i.e., curl and brittleness of the coating. Generally, a gelatin coating curls tremendously toward the end of drying process, which increases processing difficulties. Gelatin coated sheets also curl severely in a dry environment, which is highly undesirable for its printing and handling. Another disadvantage of a gelatin coating is that the coating is very brittle in a low humidity environment. The brittleness may become so severe when the humidity drops below 30% relative humidity (RH) that the coated sheet cracks during handling.
It would be of great advantage to the industry if an ink jet medium were available which not only takes advantage of the gelatin based coating to provide high gloss, good water resistance, fast ink dry time, and good dye fading resistance, but also overcomes the curl and brittleness of this type coating. It is therefore an object of the present invention to provide such an ink jet medium.
These and other objects of the present invention will become apparent to the skilled artisan.
SUMMARY OF THE INVENTION
The present invention provides a gelatin-containing ink jet medium which provides high gloss, superb imaging characteristics, fast ink dry time, good image fade resistance, good durability in terms of water resistance and crack resistance, and good dimensional stability in terms of curl resistance. The high gloss ink jet receiving medium of the present invention comprises an ink receiving layer on a substrate, which layer is comprised of a polypeptide such as gelatin or modified gelatin. The layer further comprises at least one of the following two types of plasticizers: a) 2-Pyrrolidone and its derivatives such as hydroxyethyl pyrrolidone and N-cyclohexyl-2-pyrrolidone, and/or b) urea and its derivatives such as imidazolidinyl urea, diazolidinyl urea, 2-hydroxyethylethylene urea, and ethylene urea. The presence of these specific plasticizers in the gelatin containing ink receiving layer have been found to reduce the curl of the medium at low humidity. A polyurethane dispersion is incorporated into the ink-receiving layer to increase the flexibility of the layer at low humidity and to reduce the tack of the layer at high humidity. The polymers can be crosslinked with one or a combination of crosslinkers, preferably selected from the group of trivalent metal ions, polyfunctional aziridine, or polyamide-epichlorohydrin resin. The medium of the present invention allows one to reduce curl without sacrificing the following properties of the coating: fast ink dry time, good coating durability, and good image fade resistance. The medium of the present invention also allows increased flexibility and reduced tack of the coating in a high humidity environment.
In another embodiment, the blending of other polymers containing carboxyl groups into the ink receiving layer has been found to help absorb the high boiling point solvents (humectants) in the ink.
In another embodiment of the present invention, applying a thin overcoat on top of the ink-receiving layer which, overcoat is more hydrophobic than the basecoat, has been found to reduce coating tack and to reduce ink dry time.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A pure gelatin coating or a crosslinked gelatin coating will have substantial residual tensile stress in the dried coating and this residual stress causes curl toward the coating surface. The magnitude of the stress and the resultant curl is a function of humidity and temperature of the environment. The curl is most profound at low humidity environment when the equilibrium amount of moisture in the gelatin coating is low. As the humidity increases, the coating absorbs moisture from the atmosphere and the moisture plasticizes the coating and reduces the tensile stress in the coating. An anhydrous gelatin coating exhibits glass transition temperature (T
g
) around 175° C.[A. G. Ward etc]. The Tg decreases as the humidity increases and it reaches room temperature at 80% relative humidity&l
Tang Yu Ying
Taylor A. Richard
Vo Son T.
Burns Doane Swecker & Mathis L.L.P.
Grendzynski Michael E.
Hess Bruce H.
InteliCoat Technologies, LLC
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