Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-06-01
2003-09-02
Schwartz, Pamela R. (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
Reexamination Certificate
active
06613419
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ink jet recording sheets exhibiting high image quality and in particular to ink jet recording sheets which are improved in glare due to surface gloss to minimize difference in gloss between images and which provides an ink jet print having a high grade feel.
BACKGROUND OF THE INVENTION
Along with rapid technological innovation in ink jet recording, its print quality is comparable with that of silver salt photographic prints. The print quality achieved by ink jet recording depends on three factors: the printer, the ink and the recording sheet. Specifically, recent technological innovation of the former two factors is marked from the view point of image quality and the difference in performance of the ink jet recording sheet (hereinafter, also noted simply as recording sheet) is very important for final print quality.
To obtain ink jet prints close to silver salt photographic prints, various improvements have been made from the view-point of the recording sheets. Specifically, an ink jet recording sheet which comprises a paper base covered with polyolefin such as polyethylene on both sides thereof, having thereon an ink absorbing layer, has recently spread widely in terms of being relatively low in cost, compared to plastic films, and as a print with a high grade feel, close to silver salt photography in massiveness, softness, flatness and glossiness.
Ink jet recording sheets are mainly classified into those which exhibit ink-absorptivity, such as paper and those which comprise a support having thereon an ink absorbing layer. In the former case, ink directly permeates into the support, so that problems occurred in that high maximum density could not be obtained, or the support absorbs an ink solvent, causing wrinkles in the images and high grade prints could not be obtained.
Ink-absorbing layers provided on the support are those generally classified into a swelling type and a void-type. The swelling type ink absorbing layer is mainly comprised of hydrophilic polymer such as gelatin, polyvinyl alcohol, polyvinyl pyrrolidine or polyethylene oxide. Although there are several methods for preparing the void-type ink absorbing layer, the representative void-type ink absorbing layer is a layer containing a small amount of a hydrophilic polymer and a large amount of fine particles, so that voids are formed among the particles.
Texture sometimes depends on personal taste but glossiness or other characteristics necessary for a print having a high grade feel are sometimes required according to its intended use. For example, there are such cases that fingerprint resistance, reduced tackiness or paste stain and to avoid strong light reflection making low quality appearing images.
To respond to such desires, there are known ink jet recording sheets having a matte or semi-matte surface resulting in lowered glossiness. As a technique for making the surface semi-matte are known providing an ink absorbing layer on the matted support or incorporation of a matting agent into the ink absorbing layer surface. In either case, it is common to form protrusions of heights of the 1 &mgr;m order on the ink absorbing layer surface. When ink jet printing is made on a recording sheet obtained by optimally roughing the surface, however, problems are produced such that glossiness varies from image to image, resulting in non-uniform glossiness. Such problems deteriorate print quality of ink jet prints superior in high grade feel, for which an improvement thereof is desired.
Although its cause is not fully understood, it is supposed that when an ink jet recording is made, a low-volatile organic solvent remains in the ink absorbing layer, producing a difference in gloss among fine protruding images on the surface. When such non-uniform difference in gloss of the images is present on the semi-matte surface, surface glare is produced on the images, making the print unnatural and losing its high grade appearance.
Such a problem is more marked when the support does not absorb the ink solvent, but even when the support absorbs the ink solvent, ink jet printing produces a slight difference among protrusions on the print surface, resulting in a difference in gloss among successive images. The problem is likely to become more marked when printing with a pigment ink. Thus, when printing with a pigment ink, the image is fixed with swollen pigment particles, resulting in lowered gloss or producing coagulated pigment particles exhibiting metallic gloss. In cases when printing with a pigment ink which inherently tends to cause variation in gloss and when protrusions are formed on the surface with a matting agent to control glossiness, the gloss difference tends to be further contrasted.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention was achieved. It is an object of the present invention to provide an ink jet recording sheet reduced in surface glare, without forming a marked difference in gloss between printed and non-printed areas, achieving images with a high grade feel and forming uniform images.
The above object of the invention can be accomplished by the following constitution:
1. An ink jet recording sheet, characterized in that the surface of the ink absorbing layer side of the sheet exhibits a center-line mean roughness (Ra) of 0.4 to 2.5 &mgr;m and a ten-point mean roughness (Rz) of 5×Ra to 20×Ra when measured at a reference length of 2.5 mm and a cut-off value of 0.8 mm;
2. The ink jet recording sheet described in 1, characterized in that a support is paper coated with polyolefin resin on both sides thereof;
3. The ink jet recording sheet described in 1 or 2, characterized in that the ink absorbing layer is a porous coat containing voids.
DETAILED DESCRIPTION OF THE INVENTION
The ink jet recording sheet according to this invention has an ink absorbing layer on a support.
As supports for use in the recording sheet of the invention can be used any one of water absorbing supports and non-water-absorbing support, of which the non-water-absorbing support is preferred, since it can form semi-glossy surface without wrinkling. The water absorbing support usable in this invention is typically a support mainly made of natural pulp but may also a mixture of synthetic pulp and natural pulp.
Examples of the non-water-absorbing support include a plastic resin film support and a paper support covered on both sides with plastic resin film. The plastic resin film support include, for example, polyester film, polyvinyl chloride film polypropylene film, cellulose acetate film and polystyrene film. The plastic rein film support may be transparent or semi-transparent, of which the transparent support is preferred. In this invention, a preferred support is a paper support having both sides of paper covered with a plastic resin (or plastic resin double coated paper support), of which polyolefin resin double coated paper support is more preferred.
The polyolefin resin double coated paper support (hereinafter, also denoted as polyolefin resin coated paper) will now be described in detail. Raw paper of the paper support is generally made of a wood pulp raw material and may optionally include a synthetic pulp such as polypropylene or synthetic fibers such as nylon or polyester. Preferred examples of the wood pulp include LBKP, LBSP, NBKP, NBSP, LDP, NDP, LUKP and NUKP. It is preferred to use large proportions of LBKP, NBSP, LBSP, NDP or LDP, each mainly having high proportions of shorter fibers. The proportion of LBSP or LDP is preferably between 10% and 70% by weight. The pulp is preferably chemical pulp (e.g., sulfate pulp, sulfite pulp), since they have negligible impurities. Pulp which is subjected to a bleaching treatment to enhance whiteness, may also be employed.
To the raw paper, there may optionally be added a sizing agent such as a higher fatty acid or alkylketene dimer; a white pigment such as calcium carbonate, talc or titanium white; a paper-strengthening agent such as starch, polyacrylamide or polyvinyl alcohol; a fluorescent brightening
Ohbayashi Keiji
Yoshitsuka Kenichi
Frishauf Holtz Goodman & Chick P.C.
Schwartz Pamela R.
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