Ink-jet recording material having a polymer matrix coating

Abstract: The present invention is directed to a polymer matrix coating used for ink jet media. The polymer matrix coating has a glass transition temperature that is greater than or equal to about 120°C and less than or equal to about 300°C, an integrity value of greater than or equal to about -20% and a swellability of greater than or equal to about 50%. The coating avoids the problem of pigment ink cracking that can occur in conventional ink jet media.

Description: Field of the Invention This invention relates to a polymer matrix coating, and more particularly to a polymer matrix coating that can be used for ink jet media that receive pigmented inks. Background of the Invention Recently, pigmented inks have been used for ink jet printing to enhance density, color fidelity and reduce color fade. For example, such an ink has been used with a Hewlett-Packard DeskJet 1200C printer and gave excellent ink jet print quality. However, pigmented inks present a challenge for ink jet media development due to pigmented ink cracking. In this regard, such cracking reduces optical density and image resolution. There is an urgent need to have an ink jet medium that can be used with pigmented inks, while avoiding the problem of pigmented ink cracking. Summary of the Invention An object of the present invention is to provide a polymeric matrix coating that can be used for ink jet media. Another object of the present invention is to provide a polymer matrix coating that can reduce or eliminate pigmented ink cracking problems, and at the same time give excellent optical density and image resolution when used for ink jet media. Accordingly, the invention provides a polymer matrix coating that meets the above objects and which can be used in an ink jet media for receiving a pigmented ink. More specifically, the present invention provides an ink jet medium according to claim 1, which comprises an ink receiving polymeric matrix coating that possesses: a glass transition temperature (Tg) greater than or equal to 120°C (preferably greater than or equal to 130°C) and less than or equal to 300°C (preferably less than or equal to 260°C), an integrity value of greater than or equal to -20% (preferably greater than or equal to -10%) as calculated using the integrity value % equation set forth herein, and a swellability of greater than or equal to 50% (preferably greater than or equal to 100%) as calculated using the swellability % equation set forth herein, and contains at least one water-soluble component and at least one water-insoluble component. Detailed Description of the Invention The polymer matrix coatings provided to ink jet films according to the present invention can be either single-layer or multi-layer structures. In either case, the polymer matrix coatings contain at least one water-soluble component. The water-soluble component of the polymer matrix provides ink sorptivity to the polymeric matrix. The water-soluble component can reside in any layer of the provided polymer matrix coatings. Typically, suitable water-soluble components which may be used in the polymeric matrix coatings of the inventive ink jet films should be soluble in water in an amount of at least 1% (preferably in an amount of at least 3%), on a wt/wt basis of the water-soluble component in water at a temperature in the range of 5°C to 100°C. Preferably, the water-soluble component is a component of a polymer. Exemplary of such water-soluble components are the following: poly(vinyl alcohol), cellulose esters, poly(vinyl pyrrolidone), gelatins, poly(vinyl acetate), starch, poly(acrylic acids), poly(ethylene oxide), proteins, hydroxypropyl cyclodextrin, poly(2-ethyl-2-oxazoline), alginates, and water-soluble gums, and the like. The polymer matrix coating also contains water-insoluble components. Preferably, the water-insoluble component is a component of a polymer. The water-insoluble components are employed to adjust the coating solubility, coating swellability, coating strength, coating flexibility, coating tackiness, etc. Exemplary of such water-insoluble components are 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2,3-dihydroxypropyl methacrylate, styrene, 5-hydroxy-3-oxapentyl methacrylate, 8-hydroxy-3,6-dioxaoctyl methacrylate, N-hydroxyethyl acrylamide, urethane, N-hydroxymethyl acrylamide, dimethylaminoethyl methacrylate, alkyl methacrylate, N-methyloacrylamide and hydroxypropyl acrylate, and the like. Typical water-insoluble components can also include crosslinked derivatives of water-soluble components like those described above. The water-soluble or water-insoluble components which can be used in the inventive ink jet media herein disclosed can be in the form of a monomer, an oligomer, a homopolymer, a copolymer or a polymer blend, provided that they otherwise meet the parameters set forth herein. The drying process of a pigmented ink when applied to a polymeric coating of an ink jet media is complicated. First, the polymer coating absorbs the ink vehicle and swells. Then, as the ink vehicle evaporates, the polymer coating shrinks. This deformation of the polymer coating can cause the pigmented ink to crack. The cracking is observed as a non-uniform distribution of the pigmented ink on the coating surface as well as a reduced optical density. Voids are usually also observed on the cracked ink surface. To avoid pigmented ink cracking, the Inventors have discovered that the integrity and rigidness of the polymeric coating must be preserved during printing. In this regard, the Inventors have also discovered that the relatively tough polymer matrix coatings provided herein are capable of maintaining their integrity and rigidness during printing and are capable of reducing or eliminating pigmented ink cracking. Since the glass transition temperature (Tg) of a polymer can be used as an indicator of the polymer's structure, the present Inventors deduced that the structure of a polymeric matrix coating could also be probed by its glass transition temperature, and that a polymeric matrix's Tg could even be used as a criteria for achieving a suitable polymer matrix coating design. For example, a high glass transition temperature implies a compact and rigid polymer structure, while a low glass transition temperature implies an open and flexible polymer structure. To resist ink vehicle attack and sustain volume change upon printing, the Inventors discovered that at least one polymeric matrix coating layer having a Tg that is greater than or equal to 120°C (preferably greater than or equal to 130°C) and less than or equal to 300°C (preferably less than or equal to 260°C), should be present in their inventive ink jet media, if the objects of the invention are to be met. This also implied that for copolymers and polymer blends that have more than one glass transition temperature, at least one of the glass transition temperatures should be greater than or equal to 120°C (preferably greater than or equal to 130°C) and less than or equal to 300°C (preferably less than or equal to 260°C), in the inventive media. The glass transition temperature is measured on a Differential Scanning Calorimeter (TA Instruments, Model DC 2910), calibrated with appropriate standards. Using such an instrument, the reading and baseline errors from replicate DSC experiments lead to a typical accuracy in measuring Tg of 3°C. Measurements of heat flow versus temperature are made upon heating in the range of 40 to 200°C at a heating rate of 10°C/minute. The sample chamber is purged with dry nitrogen. Film-like samples are encapsulated in an aluminum pan. The midpoint method (i.e., identification of the maximum of the derivative of heat flow versus temperature curve) is used to obtain Tg data from the measured DSC curve. The structures of the polymer matrix coating layers present in the Inventor's ink jet media can also be probed according to their integrity values. An integrity value indicates the degree that a polymer coating maintains its integrity in water. The integrity value can be either positive or negative. A negative value indicates that a dissolution of the polymer coating occurs in water. Integrity values are measured according to the following procedure. A sample (approximately 50,8 x 25,4 mm (2"x 1")) of a polymer matrix coating is weighed and then immersed in water (about 25°C) for 15 seconds. The excess water on the surface of the sample is then removed by blotting the surface with a XEROX® 4200 paper. The sample is then weighed again. The same sample is re-immersed in water for an additional 45 seconds. Then the same blotting and weighing procedures are again followed. The integrity value is then calculated as expressed below: Integrity value (%) = [(W 60 - W 15 )/W 15 ] x 100% wherein, W 60 is the weight at 60 seconds immersion, and W 15 is the weight at 15 seconds immersion. To resist ink vehicle attack and sustain volume change upon printing, the Inventors have discovered that at least one of the polymer matrix coating layers in their inventive media should have an integrity value of greater than or equal to -20% (preferably greater than or equal to -10%) as measured using the above test procedure. The polymer matrix coating disclosed in the present invention should be swellable in water at 25°C. The swellability of the coating is measured according to the following procedure. A sample (approximately 50,8 x 25,4 mm (2" x 1")) of a polymer matrix coating is weighed and then immersed in water for 60 seconds. The excess water on the surface of the sample is then removed by blotting the surface with a XEROX® 4200 paper. The sample is then weighed again. The swellability of the coating is calculated as expressed below: Swellability (%) = W 60 - W 0 W 0 x 100 wherein W 60 is the weight at 60 seconds immersion, and wherein W 0 is the weight before immersion. The swellability of the polymer matrix coatings of the present invention should be greater than or equal to 50% (preferably greater than or equal to 100%). It is also thought important that the provided polymer matrix coatings be imageable or have an acceptable image quality. Accordingly, the polymer matrix coatings should be able to receive ink and form images. Preferably, the optical density of a black color image should be greater than or equal to 1.70 (preferably greater than or equal to 1.80) on a transparency substrate having coated on a surface thereof a polymeric matrix coating as provided for herein. The optical density is preferably measured on a Macbeth TD904 Densitomer using a beige filter setting and a 4 mm aperture, with the final density reading being an average of at least three readings. In order to prepare an ink jet media encompassed hereby, the polymer matrix coatings disclosed herein can be applied to any suitable base substrate generally used to prepare an ink jet media. Exemplary of such base substrates are transparent plastics, translucent plastics, matte plastics, opaque plastics or papers. Furthermore, suitable polymeric materials for use in such base substrates include polyester, cellulose esters, polystyrene, polypropylene, poly(vinyl acetate), polycarbonate, and the like. Poly(ethylene terephthalate) films are thought to be particularly preferred as base substrates. Further, while almost any paper can be used as a base substrate, clay coated papers are particularly preferred as base substrate papers. The thickness of the base substrate is not particularly restricted, but should generally be in the range of from 25 to 254 µm (1 to 10 mils) (preferably from 76 to 127 µm (3.0 to 5.0 mils)). The base substrate may be pretreated to enhance the adhesion of coatings thereto. According to a preferred embodiment of the invention, the polymer matrix coatings encompassed by the present invention additionally contain 0. 1 to 15 wt/wt% of particulate(s) based on the weight of the dry coatings. The particulate(s) can be used in the polymeric matrix coatings to modify the properties of the coatings, and include inorganic particulates, such as silica, alumina, kaolin, glass beads, calcium carbonate and titanium oxide, as well as organic particulates such as polyolefins, polystyrene, starch, poly(methyl methacrylate), poly(urethane) and polytetrafluoroethylene. In practice, various additives may also be employed in the disclosed polymeric matrix coatings, if so desired. These additives can include surface active agents which control the wetting or spreading action of coating solutions, antistatic agents, suspending agents, and acidic compounds to control the coatings' pH values. Other art recognized and conventional additives may also be used if so desired. The surface of the base substrate which does not bear the polymer matrix coating may have a backing material placed thereon in order to reduce electrostatic charge and to reduce sheet-to-sheet friction and sticking, if so desired. The backing material may be either be a polymeric coating, a polymer film or paper. Any of a number of coating methods may be employed to coat the polymer matrix onto the substrates. Methods such as roller coating, blade coating, wire-bar coating, dip coating, extrusion coating, air knife coating, curtain coating, slide coating, doctor coating or gravure coating, may be used and are well known in the art. The following examples are given merely as illustrative of the invention and are not to be considered as limiting to the present inventive discovery. In the following Examples, the solid content for the listed ingredients is provided based on a part/part (wt/wt) basis. EXAMPLE 1 A coating composition is prepared according to the following formulation: Polymer matrix coating: PVP K90 18 parts Copolymer A 16 parts Methyl Ethyl Ketone 86 parts Propylene Glycol Monomethyl Ether 25 parts The coating is applied to a polyester film (ICI Films) using a No. 54 Meyer rod. The polymer matrix coating is dried at about 130°C for about 2 minutes. EXAMPLE 2 A coating composition is prepared according to the following formulation: Polymer matrix coating: PVP K120 19 parts Poly(methyl methacrylate) 6 parts Methyl Ethyl Ketone 106 parts Propylene Glycol Monomethyl Ether 70 parts The coating is applied to a polyester film (ICI Films) using a No. 54 Meyer rod. The polymer matrix coating is dried at about 130°C for about 2 minutes. COMPARATIVE EXAMPLE I A coating composition is prepared according to the following formulation: PVP K90 15 parts Methyl Ethyl Ketone 60 parts Propylene Glycol Monomethyl Ether 25 parts The coating is applied to a polyester film (ICI Film) using a No. 54 Meyer rod. The polymer matrix coating is dried at about 130°C for about 2 minutes. COMPARATIVE EXAMPLE II A coating composition is prepared according to the following formulation: Polymer matrix coating: PVP K90 12 parts Copolymer A 4 parts Glyceryl Triacetate 3 parts Methyl Ethyl Ketone 51 parts Propylene Glycol Monomethyl Ether 34 parts The coating is applied to a polyester film (ICI Films) using a No. 54 Meyer rod. The polymer matrix coating is dried at 130 °C for about 2 minutes. COMPARATIVE EXAMPLE III XEROX® ink jet transparency film (3R3351, Lot number XRCCDPB90-808-01). Pigmented ink cracking is evaluated for the above Examples on a Hewlett Packard DeskJet 1200C printer using an HP 51640A ink cartridge. Glass transition temperatures (Tg), integrity values and ink cracking measurements of the polymer matrix coatings in the above Examples are presented in Table I. The pigmented ink cracking is quantitatively rated in Table I with a numerical scale (0=worst and 5=best). When ink cracking is rated below 3, visible ink cracking is observed and the ink jet media are not deemed suitable for many commercial applications. Glass Transition Temperature, Integrity Value and Ink Cracking Example Tg (°C) Integrity Value (%) Ink Cracking I 165 7 4 II 167 8 5 CI 162 -71 0 CII 92 3 2 CIII 142 -76 2 The above results show that the presently disclosed inventive ink jet media exhibit a large advantage in avoiding pigmented ink cracking, when compared with the comparative ink jet media Examples CI-CIII having either Tg or integrity values falling outside those required in the present invention. Specifically, in Examples CI and CIII, the measured integrity values were less than those provided for in the present inventive media, and in Example CII, the measured Tg value was less than that provided for in the present inventive media. It is noted that while ink cracking is evaluated in the above Examples on a Hewlett Packard Deskjet 1200C, pigmented ink cracking can also be, and preferably is, evaluated on the ink jet printer, plotter or copier used in the intended applications.

Claims: An ink jet medium comprising a base substrate that has coated on a surface thereof a polymer matrix coating that can receive a pigmented ink and which contains at least one layer having a glass transition temperature of from 120 º C to 300 º C, an integrity value of at least -20% and a swellability of at least 50% and containing at least one water-soluble component and at least one water-insoluble component. The ink jet medium according to claim 1, wherein said water-soluble component is soluble in water in an amount of at least 1% on a wt/wt basis at a temperature in a range of 5 º C to 100 º C. The ink jet medium according to claim 1, wherein said water-soluble component is selected from the group consisting of poly(vinyl alcohol), cellulose esters, poly(vinyl pyrrolidone), gelatins, poly(vinyl acetate), starch, poly(acrylic acids), poly(ethylene oxide), proteins, hydroxypropyl cyclodextrin, poly(2-ethyl-2-oxazoline), alginates and water-soluble gums. The ink jet medium according to claim 1, wherein said water-insoluble component is selected from the group consisting of 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2,3-dihydroxypropyl methacrylate, styrene, 5-hydroxy-3-oxapentyl methacrylate, 8-hydroxy-3,6-dioxaoctyl methacrylate, N-hydroxyethyl acrylamide, urethane, N-hydroxymethyl acrylamide, dimethylaminoethyl methacrylate, alkyl methacrylate, N-methyloacrylamide and hydroxypropyl acrylate. The ink jet medium according to claim 1, wherein said polymer matrix coating possesses a single layer structure. The ink jet medium according to claim 1, wherein said polymer matrix coating possesses a multi-layer structure. The ink jet medium according to claim 1, wherein said polymer matrix coating upon receiving a pigmented ink gives a black image optical density of at least 1.70 on a transparent substrate. The ink jet medium according to claim 1, wherein said polymer matrix coating possesses multiple glass transition temperatures and wherein at least one of said glass transition temperatures is greater than or equal to 120 º C and less than or equal to 300 º C. The ink jet medium according to claim 1, wherein said polymer matrix coating comprises an inorganic particulate which is selected from the group consisting of silica, alumina, kaolin, glass beads, calcium carbonate and titanium oxide. The ink jet medium according to claim 1, wherein said polymer matrix coating comprises an organic particulate which is selected from the group consisting of polyolefins, polystyrene, starch, poly(methyl methacrylate), poly(urethane), and polytetrafluoroethylene.

Inventors: ATHERTON DAVID, BEHAN NIALL D, HUANG MIAOLING, SARGEANT STEVEN J, SUN KANG, YANG SEN, ATHERTON, DAVID, BEHAN, NIALL D., HUANG, MIAOLING, SARGEANT, STEVEN J., SUN, KANG, YANG, SEN
Applicants: ARKWRIGHT INC, ARKWRIGHT INC.
Application year: 1995
Main classification: B41M5
IPC codes: C08J7, B41M5, B32B27, B05D5