Stock material or miscellaneous articles – Ink jet stock for printing – Particles present in ink receptive layer
Reexamination Certificate
2001-08-28
2003-09-16
Hess, B. Hamilton (Department: 1774)
Stock material or miscellaneous articles
Ink jet stock for printing
Particles present in ink receptive layer
Reexamination Certificate
active
06620470
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink-jet recording sheet which is capable of producing a print of photo-grade quality, and particularly relates to an ink-jet recording sheet which has high ink absorbance and yields a high quality print of high cockling resistance, high bleeding resistance, and high image density.
BACKGROUND OF THE INVENTION
Ink-jet recording methods, which is also called a recording method hereafter, are carried out by impinging micro-droplets employing various working principles and placing them onto a recording sheet to record images, text characters, and exhibits advantages such as relatively high speed, low noise, easy preparation of multicolor images. Regarding this method, conventional problems with nozzle clogging and maintenance have been overcome by improvements in both aspects of ink and instrument, and currently, it is being increasingly employed in various fields such as printers, facsimile machines, and computer terminals.
Ink-jet recording sheets, which are also called a recording sheet hereafter, employed in ink-jet recording methods have generally needed to meet requirements such as the density of printed dots to be high and the hue to be bright and clear; ink needs to be quickly absorbed and when printed dots are superimposed, ink neither is to flow nor spread; diffusion of the printed dots in the horizontal direction is not larger than required and the border is smooth and results in sharpness.
Specifically, at low rates of ink absorption on a recording sheet when recording is carried out by superimposing at least two color ink droplets, previous droplets result in repellence to cause density unevenness, and in the boundary area of different colors, different color inks blend with each other. As a result, image quality tends to be markedly degraded. Therefore, it is required that the recording sheets exhibit high ink absorbability.
In order to overcome these problems, as is common, a great number of techniques have been proposed.
For example, Japanese Patent Publication Open to Public Inspection No. 52-53012 describes a recording sheet in which minimally sized paper is damped with paint employed for surface treatment; Japanese Patent Publication Open to Public Inspection No. 55-5830 describes a recording sheet comprising a support on the surface of which is provided an ink-absorbable coating layer; Japanese Patent Publication Open to Public Inspection No. 56-157 describes a recording sheet comprising a covering layer containing non-colloidal silica powder as a pigment; Japanese Patent Publication Open to Public Inspection No. 57-107873 describes a recording sheet comprising an inorganic pigment and an organic pigment in combination; Japanese Patent Publication Open to Public Inspection No. 58-110287 describes a recording sheet which exhibits a two peak void distribution; Japanese Patent Publication Open to Public Inspection No. 62-111782 describes a recording sheet composed of an upper porous layer and a lower porous layer; Japanese Patent Publication Open to Public Inspection Nos. 59-68292, 59-123696, 60-18383, and others describe a recording sheet featuring amorphous cracking; Japanese Patent Publication Open to Public Inspection No. 61-135786 and others describe a recording sheet having a fine powder layer; Japanese Patent Publication Open to Public Inspection Nos. 63-252779, 1-108083, 2-136279, 3-65376, 3-27976, and others describe a recording sheet comprising pigments and fine silica particles having specified physical parameters; Japanese Patent Publication Open to Public Inspection Nos. 57-14091, 60-219083, 60-210984, 61-20797, 61-188183, 5-278324, 6-92011, 6-183134, 7-137431, 7-276789, and others describe a recording sheet containing fine silica particles such as colloidal silica; Japanese Patent Publication Open to Public Inspection Nos. 2-276671, 3-67684, 3-215082, 3-251488, 4-67986, 4-263983, 5-16517, and others describe a recording sheet containing fine hydrated alumina particles.
As the ink-jet recording sheet, various kinds of ink-jet recording sheets have been employed. For example, there have been employed ordinary paper, various coated papers (art paper, coated paper, cast-coated paper, etc.) prepared by coating a layer comprising a hydrophilic binder and an inorganic pigment on a paper support. Furthermore, there have been employed recording sheets prepared by coating an ink absorptive layer as a recording layer on various supports such as the above-mentioned papers, various kinds of transparent or opaque plastic film supports, or various supports prepared by covering both sides of paper sheets with a plastic resin.
The above-mentioned ink absorptive layer is divided into two main groups, that is, one is a so-called swelling-type ink absorptive layer composed mainly of a hydrophilic binder, and the other is a void-type ink absorptive layer having a layer of voids in the recording layer.
The advantages of the swelling-type ink absorptive layer are that after an ink solvent (water or a high boiling point solvent) is completely vaporized, remarkably high glossiness and high density are obtained. On the other hand, the ink-absorbing rate is smaller than that of the void type recording sheet mentioned above and described below, and there is also a problem in which in a high ink density region, image quality tends to be deteriorated due to the formation of roughness caused by beading. Furthermore, vaporization of an ink solvent, especially a high boiling point organic solvent, is extremely slow and after printing, the high boiling point organic solvent remains in the hydrophilic binder for some time. Thus, there is a problem in which the hydrophilic binder is under a swelled and wet state for a fairly long period of time.
As a matter of fact, for several hours after printing, in some cases, for several days after printing, the situation is that it is impossible to rub the printed surface strongly or to stack the printed sheets of paper.
On the other hand, the void type ink absorptive layer, having voids in the recording layer, results in great ink absorptivity. Accordingly, as compared to the swelling-type, there is negligible image beading in the high ink density area and degradation of the image quality in the high density area is minimal.
Furthermore, when the void type ink absorptive layer has a sufficient void volume, compared to that of the ink, immediately after printing, the surface acts as if dried, even though the organic solvent remains in the void structure. Thus, it is possible to touch the surface and to have printed sheets be in contact with.
For this type of ink absorptive layer, fine particles having a low refractive index (a refractive index of 1.6) and a small diameter (200 nm or less) are preferably employed because they form a relatively highly transparent layer. Of the particles, fine particle silica which satisfies such conditions is particularly preferably employed, since it efficiently forms voids, and further, results in relatively high glossiness and images having high maximum density.
The ink-jet recording sheet comprising a support having thereon the above-mentioned void type ink absorptive layer is excellent, resulting in particularly high glossiness, a high void ratio and high maximum density. In addition, when a support having relatively good flatness is employed, a ink-jet recording sheet having a high glossy surface is obtained.
Of these, ink-jet recording sheets having many voids for absorbing or keeping ink in the ink absorptive layer, show high ink absorbance and low bleeding at the border of the image. As a result, images of high quality can be produced.
However, the amount of ink absorbed in the void-type ink absorptive layer is limited, because the effective volume used for incorporating ink is limited by the presence of void forming material. This situation can be understood by an example: When a void-type ink absorptive layer of a dry thickness 40 &mgr;m is formed by using a 22 &mgr;m material, the maximum void volume per m
2
can be calculated as follows; 0.0001
Nojima Takahiko
Ohbayashi Keiji
Hess B. Hamilton
Konica Corporation
Squire Sanders & Dempsey L.L.P.
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