Recording sheet and process for producing it

Details Recording sheet and process for producing it Recording sheet and process for producing it

1999-11-19

2002-08-13

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S211100

Reexamination Certificate

active

06432517

ABSTRACT:

The present invention relates to a recording sheet, particularly a recording sheet for an ink jet printer which presents a clear color, and a process for producing it.
An ink jet recording system has been widely used in recent years in the field of a color copying machine or hard copy from e.g. computers and videotapes, since full coloring is easy, and printing speed can be made high. In such a field, the following are required: (1) a high resolution, (2) an excellent color reproducibility (adequately secured color tone), (3) capability of high speed printing, and (4) excellent preservation properties, etc.
To achieve these, improvements have been made in both printers and recording materials. As the conditions of the recording materials to be satisfied may, for example, be such that (1) it exhibits a high color density of each ink dot, (2) it quickly absorbs inks, (3) ink dots are moderately spread thereon, (4) it exhibits a practically adequate freshness, and (5) it adequately absorbs inks and is free from wrinkles to be generated at the printed portion, particularly at the printed portion with a large amount of inks (hereinafter referred to as cockling).
Conventionally, as such a recording material, one comprising a paper sheet, and porous particles of silica, alumina or an alumina hydrate and a binder such as a polyvinyl alcohol, coated on the surface of the paper sheet, has been known.
However, the above recording material has such defects that when silica is coated thereon, although the ink will be quickly absorbed thereon, the ink will infiltrate from the surface into the deeper part, whereby the color density will be low, and further, the ink dots tend to be small, whereby the color density of the entire printed product tends to be low. Further, the cocklings can hardly be avoidable. To overcome such defects, attempts have been made such as increasing the coating amount, or making the ink-absorbent layer have a multi-layer structure. However, although the degree of cocklings will decrease, the ink will infiltrate into the deeper part, whereby the color density will not be adequate. Further, the cost will increase.
On the other hand, when the ink-absorbent layer is formed by coating a porous material containing alumina or an alumina hydrate, although the ink is quickly absorbed and a high color density can be obtained as compared with silica, the cocklings can hardly be avoidable. To overcome such defects, an attempt to increase the coating amount has been made. However, although the degree of cocklings can be suppressed, the defects can not essentially be solved. Further, the cost will increase. Further, as disclosed in Japanese Patent No. 2,605,585, an attempt has been proposed to provide a silica porous layer as an underlayer of the porous layer containing alumina or an alumina hydrate, with a defect such as increase in steps.
Under these circumstances, the present inventors have conducted extensive studies to overcome the above problems, and they have found that by providing alumina or an alumina hydrate on a certain specific substrate as an ink-receiving layer, inks are quickly absorbed, and the inks are present at the surface, whereby a high color density can be obtained, and by increasing the content of a filler in the substrate, an excessive amount of moisture can be absorbed, whereby cocklings can be prevented, and the present invention has been accomplished.
Namely, it is an object of the present invention to provide a recording sheet which has a high ink absorption rate with a small amount of ink-receiving layer, which has an adequate color density, which is free from cockling, and which presents a clear image, and a process for producing it.
The present invention provides a recording sheet which comprises a substrate and a porous layer containing alumina or an alumina hydrate formed on the substrate, wherein the substrate is made of fibers for paper and a filler, and the content of the filler in the substrate is from 10 to 60 wt % to the total weight of the substrate.
The present invention further provides the recording sheet, wherein the substrate contains a microfibrillated cellulose in an amount of from 1 to 50 wt % to the total weight of the fibers for paper and the microfibrillated cellulose. The present invention further provides the recording sheet, wherein the substrate further contains a crystalline cellulose in an amount of from 1 to 50 wt % to the total weight of the fibers for paper, the microfibrillated cellulose and the crystalline cellulose. The present invention further provides the recording sheet, wherein the orientation ratio of the fibers of the substrate is from 1.0 to 2.0, and the coating amount of the porous layer on the substrate is at least the minimum coating amount as obtained from the following formula (1):
minimum coating amount (g/m
2
)=33.3×{(orientation ratio of the fibers)−1}+2  (1).
Further, the present invention provides a process for producing a recording sheet comprising a substrate and a porous layer containing alumina or an alumina hydrate formed on the substrate, which comprises sheeting an aqueous slurry containing fibers for paper and a filler to form a substrate made of the fibers for paper and the filler, wherein the content of the filler in the substrate is brought to a level of from 10 to 60 wt % to the total weight of the substrate. The present invention further provides the process for producing a recording sheet, wherein the orientation ratio of the fibers of the substrate is from 1.0 to 2.0, and the coating amount of the porous layer on the substrate is at least the minimum coating amount as obtained from the above formula (1).
The content of the filler in the substrate of the present invention is preferably from 10 to 60 wt % to the total weight of the substrate. If the content of the filler is less than 10 wt %, the ink absorptivity tends to be poor, whereby cocklings will form. If the content of the filler exceeds 60 wt %, the paper strength tends to be low. As the filler to be used in the present invention, at least one of a metal oxide, a metal phosphate, a metal carbonate and a metal silicate may be optionally used.
The above-mentioned metal oxides include hydrated oxides. Particularly preferred is silica or alumina. As the alumina, an alumina hydrate is preferred, and aluminum oxide as anhydride may be used. As the silica, hydrate silicic acid which is so called white carbon, silica gel, silica-alumina composite gel or diatomaceous earth may, for example, be mentioned. As the aluminum oxide, specifically activated alumina, alumina gel or activated bauxite may, for example, be mentioned. As another metal oxide, titanium oxide, zirconium oxide or magnesium oxide may, for example, be mentioned.
The metal phosphate may, for example, be calcium phosphate (e.g. apatite such as apatite fluoride or hydroxyapatite, or calcium primary phosphate). The metal carbonate may, for example, be heavy calcium carbonate, light precipitated calcium carbonate or magnesium carbonate. The metal silicate may, for example, be magnesium silicate such as talc, sepiolite or Florisil, calcium silicate, aluminum silicate such as kaolin, activated clay or acid clay.
Among the above-mentioned fillers, silica is preferably used as it is excellent in ink absorptivity. A substrate having a filler content of from 10 to 60 wt % to the total weight of the substrate, can be obtained by sheeting an aqueous slurry containing a filler and fibers for paper.
The substrate to be used in the present invention is preferably made by a conventional method in such a manner that fibers for paper are adjusted to have a freeness of from 250 to 700 ml C.S.F. (Canadian Standard Freeness), a filler is added thereto, followed by sheeting by a known paper machine such as cylinder paper machine or Fourdrinier paper machine. Further, the orientation ratio of the fibers of the substrate is preferably from 1.0 to 2.0, and the coating amount of the porous material on the substrate is preferably at least the minimum coati

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