Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
1996-08-30
2001-05-29
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S101000, C347S100000
Reexamination Certificate
active
06238047
ABSTRACT:
The present invention relates to a recording medium and a recording method suitable for an ink jet recording system employing a pigment ink.
In recent years, reflecting wide spread use of electronic still cameras and computers, the hard copy technology to record images thereof on paper sheets or the like has been rapidly developed. The ultimate objective of such a hard copy technology is quality of a silver halide photography, and it is a theme for research and development how to bring the color reproduction, the color density, the resolution, the gloss, the weather resistance, etc. to the levels of the silver halide photography. As hard copy recording systems, various systems have been known including not only the system wherein a display indicating an image is directly photographed by silver halide photography, but also a sublimation type dye diffusion thermal transfer system, an ink jet system, and an electrostatic transfer system. An ink jet system printer has been widely used in recent years, since full coloring is easy, and the printing noise is low. The ink jet system is a system wherein ink droplets are ejected at a high speed from nozzles to a recording material, and the ink contains a large amount of a solvent. Therefore, the recording material for an ink jet printer is required to swiftly absorb the ink and have excellent color density. In such an ink jet recording system, it has been common to employ an ink of the type wherein a dye is dissolved in a solvent. However, it is also known to use an ink (a pigment ink) of the type wherein a pigment is dispersed in a solvent such as water. The ink jet image obtained by using such a pigment ink has a feature that discoloration or color change is little, and it is particularly excellent in the durability.
It is an object of the present invention to provide a recording medium and a recording method, whereby absorption of a pigment ink is excellent, the pigment in the ink is uniformly fixed to show excellent color development, and an ink jet image having a high color density can be obtained.
The present invention provides an ink jet recording medium for a pigment ink, which comprises a substrate, a porous layer of alumina hydrate having a thickness of from 1 to 200 &mgr;m, formed on the substrate, and a water-soluble resin layer having a thickness of from 0.01 to 50 &mgr;m, formed as an upper layer thereon.
Now, the present invention will be described in detail with reference to the preferred embodiments.
The substrate is not particularly limited, various types of substrates can be used. Specifically, plastics including a polyester resin such as polyethylene terephthalate, a polycarbonate resin, and a fluorine resin such as polytetrafluoroethylene (PTFE), and various papers, can suitably be used. Further, cloth, glass or metal may also be used. To such substrates, corona discharge treatment or various undercoatings may be applied for the purpose of improving the bond strength of the alumina hydrate layer. The shape of the substrate is not particularly limited, but it is common to employ a sheet or film having a thickness of from 0.01 to 10 mm.
When a transparent plastic film is used as the substrate, a transparent image may be obtained which can be used, for example, as transparencies for an OHP (overhead projector) sheet. When a paper or an opaque plastic film containing a white pigment is used as the substrate, an image comparable to a silver halide photography can be obtained.
In the present invention, the porous layer of alumina hydrate is considered to function as a layer for absorbing water which is the dispersion medium in the pigment ink. The alumina hydrate is preferably pseudo-boehmite, since it has excellent absorptivity. Here, pseudo-boehmite is an agglomate of alumina hydrate represented by a compositional formula of Al
2
O
3
.nH
2
O (n=1 to 1.5).
The porous layer of alumina hydrate preferably contains a binder. As the binder, an organic material such as starch or its modified product, polyvinyl alcohol or its modified product, a SBR latex, a NBR latex, carboxymethylcellulose, hydroxymethylcellulose or polyvinyl pyrrolidone, can be used. The binder is used preferably in an amount of from 5 to 50 wt % of the alumina hydrate. If the amount of the binder is less than 5 wt %, the strength of the alumina hydrate layer tends to be inadequate. On the other hand, if it exceeds 50 wt %, the ink absorptivity tends to be inadequate.
The porous layer of alumina hydrate preferably has pores having a pore radius of from 1 to 30 nm in a volume per unit weight of from 0.3 to 2.0 cc/g, whereby it shows adequate absorptivity, and the alumina hydrate layer is transparent. Here, if the substrate is transparent, it is possible to obtain a recording medium having high transparency. Even when the substrate is opaque, it is possible to obtain a recording medium which is capable of forming an image of high quality and high color density without impairing the texture of the substrate. More preferably, the alumina hydrate layer has pores having a pore radius of from 3 to 10 nm in a volume per unit weight of from 0.3 to 1.0 cc/g. The pore radius distribution is measured by a nitrogen absorption/desorption method.
The water-soluble resin layer formed on the alumina hydrate layer is required to be made of a material which swells upon absorption of the dispersion medium or solvent in the ink. It is believed that the ink fixing property is achieved by the swelling at the time of recording, followed by drying. It is also believed that the ink drying speed at the outermost surface of the sheet is controlled within a proper range by virtue of the water-soluble resin layer, and the ink surface after drying will be flat and smooth, whereby the image quality is improved.
In the present invention, as the water-soluble resin layer, a water-soluble polymer material is preferably employed. The water-soluble polymer material preferably has a physical property whereby it can form a film uniformly without undergoing agglomeration or gelation. It may, for example, be starch, oxidized starch, a modified starch such as a grafted, etherified or esterified starch, a cellulose derivative such as methylcellulose, carboxymethyl cellulose or hydroxyethyl cellulose, a modified cellulose such as a grafted cellulose, a protein such as agarose, gelatin, casein or soybean protein, partially or completely saponified polyvinyl alcohol, a modified polyvinyl alcohol such as a carboxylated or olefin-modified polyvinyl alcohol, a polymer such as polyvinyl pyrrolidone, polyvinyl acetal, sodium polyarginate, a hydrophilic urethane resin, polyacrylic acid, polyacryloamide, polyvinylmethylether or polyethylene imide, acrylic acid, a vinyl alcohol copolymer, or a mixture thereof.
The water-soluble polymer material is preferably one having a viscosity of from 0.01 to 10,000 centipoise (cp) at 25° C. in its aqueous solution having a concentration of 1 wt %. If the viscosity exceeds 10,000 cp, it tends to be difficult to form a uniform film, since the alumina hydrate layer is porous. More preferably, the viscosity is within a range of from 0.1 to 1,000 cp.
The water-soluble polymer preferably has a solubility parameter (SP value) close to water. The SP value of the water-soluble resin to be used in the present invention is preferably from 8 to 23 cal/cm
3
at 25° C. The above water-soluble resin layer may be a non-porous film or a porous film. In the case of the non-porous film, the water-soluble resin is coated in the form of an aqueous solution. In the case of the porous film, it can be coated in the form of an emulsion of the water-soluble resin, whereby the drying property of ink absorbed in the medium will be excellent. When the water-soluble resin layer is a porous layer, the layer preferably has pores having a pore radius of from 1 to 30 nm in a volume per unit weight of from 0.3 to 2.0 cc/g.
The water-soluble resin layer is formed as a porous layer, and it may contain silica or alumina particles to improve the quick drying property of ink. Silica or alumina may be mix
Kijimuta Hitoshi
Saito Masaaki
Suzuki Shin'ichi
Terayama Sumito
Asahi Glass Company
Barlow John
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Shah Manish
LandOfFree
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