Recording medium for pigment ink

Details Recording medium for pigment ink Recording medium for pigment ink

1998-07-13

2001-02-13

Schwartz, Pamela R. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S195100, C428S207000, C428S304400, C428S328000, C428S329000, C428S331000, C428S341000, C428S342000, C428S421000

Reexamination Certificate

active

06187419

ABSTRACT:

The present invention relates to a recording medium for pigment ink, particularly to a recording medium suitable for an ink jet recording system employing an oil-base pigment ink.
In recent years, along with the spread of electronic still cameras or computers, the hard copy technology for recording such images on e.g. paper, has rapidly been developed. The ultimate objective of such hard copy technology is silver salt photography, and the objective for development has been how to bring the color reproducibility, color density, resolution, gloss, weather resistance, etc, close to the levels of silver salt photography. Hard copy recording systems include various types such as a sublimation type thermal transfer system, an ink jet system and an electrostatic transfer system, in addition to a system wherein a display showing an image by silver salt photography, is directly photographed.
The ink jet system printer has been rapidly spread in a recent years, for such merits that full coloring is easy, and printing noise is low. This system is one wherein ink droplets are ejected at a high speed to a recording medium from nozzles. Further, the ink for an ink jet system, contains a large quantity of a solvent. Accordingly, the recording medium for such an ink jet printer is required to swiftly absorb the ink and to have an excellent color-forming property.
In the ink jet 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 employ an ink (pigment ink) of the type wherein a pigment is dispersed in a solvent such as water. The recorded product obtained by ink jet recording employing such a pigment ink, is characterized in that the color fading or discoloration is little, and it is excellent in durability. However, in some cases, the pigment in the ink tends to be hardly fixed on the recording medium.
It is an object of the present invention to provide a recording medium for pigment ink whereby absorption of pigment ink, particularly pigment ink employing an oil-base solvent, is good, the pigment in the ink can uniformly be fixed to present an excellent color developing property, and an ink jet recording product having a high color density can be obtained.
The present invention provides a recording medium for pigment ink, which comprises a substrate, a porous layer comprising alumina hydrate, formed on the substrate, and a pigment-fixing layer comprising agglomerates having an average agglomerate particle size of from 0.1 to 0.5 &mgr;m or monodisperse particles having an average primary particle size of from 0.1 to 0.5 &mgr;m, formed on the porous layer.
Now, the present invention will be described in detail with reference to preferred embodiments.
In the recording medium of the present invention, the pigment-fixing layer is a layer having a function to fix the pigment in the pigment ink. The pigment-fixing layer comprises agglomerates or monodisperse particles having a specific size, whereby proper irregularities of the surface of the recording medium would be formed, and such irregularities will contribute to the improvement in the property for fixing the pigment in the pigment ink.
In the present invention, the agglomerates are particles having a structure wherein primary particles are agglomerated to secondary or higher particles. Whereas, the monodisperse particles are particles having no such an agglomerated structure. These structures can be confirmed, for example, by observing the surface of the recording medium by a scanning electron microscope. In the present invention, in the case of agglomerates, the average agglomerate particle size is required to be from 0.1 to 0.5 &mgr;m, and in the case of the monodisperse particles, the average primary particle size is required to be from 0.1 to 0.5 &mgr;m.
In the case of agglomerates, if the average agglomerate particle size is less than 0.1 &mgr;m, the property for fixing the pigment tends to be inadequate, such being undesirable. If the average agglomerate particle size exceeds 0.5 &mgr;m, the property for fixing the pigment improves, but the transparency or the gloss of the recording medium tends to decrease, such being undesirable. In the case of agglomerates, the average agglomerate particle size is more preferably from 0.15 to 0.4 &mgr;m.
Likewise, in the case of monodisperse particles, if the average primary particle size is less than 0.1 &mgr;m, the property for fixing the pigment tends to be inadequate, such being undesirable. If the average primary particle size exceeds 0.5 &mgr;m, the property for fixing the pigment improves, but the transparency or the gloss of the recording medium tends to decrease, such being undesirable. In the case of monodisperse particles, the average primary particle size is more preferably from 0.15 to 0.4 &mgr;m.
As the substrate to be used in the present invention, plastics, such as, a polyester resin such as polyethylene terephthalate (hereinafter referred to as PET), a polycarbonate resin, a polyvinyl chloride resin or a fluorine resin such as polytetrafluoroethylene, various papers, or synthetic papers, may, for example, be used. Further, glass or metal may also be used. To such substrates, Colonna discharge treatment or various undercoats may be applied for the purpose of e.g. improving the adhesive strength of the porous layer comprising alumina hydrate.
When a transparent plastic film is used as the substrate, a transparent or semi-transparent recording medium can be obtained, which can be used also as a tracing sheet.
In the present invention, the porous layer comprising alumina hydrate, functions as a layer for absorbing the solvent in ink. As the alumina hydrate, boehmite is preferred, since it efficiently absorbs the solvent. Here, the boehmite is an alumina hydrate represented by the compositional formula of Al
2
O
3
.nH
2
O (n=1 to 1.5).
The porous layer comprising alumina hydrate preferably contains a binder. As the binder, starch or its modification product, polyvinyl alcohol or its modification product, a styrene-butadiene copolymer rubber (SBR) latex, an aclyronitrile-butadiene copolymer rubber (NBR) latex, carboxymethylcellulose, hydroxymethylcellulose, or polyvinyl pyrrolidone, may, for example, be used.
The binder is preferably used in an amount of from 5 to 50 wt %, based on the alumina hydrate. If the amount of the binder is less than 5 wt %, the strength of the porous layer tends to be inadequate, such being undesirable. If the amount of the binder exceeds 50 wt %, the absorption of the solvent tends to be inadequate, such being undesirable.
The porous layer comprising alumina hydrate preferably has an average pore radius of from 1 to 20 nm. Further, it is preferred that the pore volume is from 0.3 to 1.0 cm
3
/g, whereby the layer provides adequate absorption, and the porous layer is also transparent. Here, if the substrate is transparent, a recording medium having high transparency can be obtained. In a case where the substrate is opaque, a recording medium having a high quality can be obtained without impairing the texture of the substrate. These pore characteristics were measured by a nitrogen adsorption-desorption method.
The thickness of the porous layer comprising alumina hydrate is optionally selected depending upon the specification of the particular printer. However, it is usually preferred to employ a thickness of from 5 to 100 &mgr;m. If the thickness of the porous layer is less than 5 &mgr;m, the solvent in the ink may not adequately be absorbed. If the thickness of the porous layer exceeds 100 &mgr;m, the transparency may be impaired, or the strength of the porous layer may decrease. More preferably, the thickness of the porous layer comprising alumina hydrate is from 10 to 50 &mgr;m.
As a method for forming the porous layer comprising alumina hydrate, on the substrate, it is preferred to employ a method wherein a binder and a solvent are added to alumina hydrate to form a sol-like coating fluid, which is coated on the substrate, followed by drying. As the alumina hydrate, it is prefer

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