Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1998-08-31
2002-06-18
Copenheaver, Blaine (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S328000
Reexamination Certificate
active
06406796
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a cast-coated paper and, more particularly, to a substrate that enables easy and speed production of a cast-coated paper having excellent ink jet recording characteristics, and to a cast-coating paper produced using such a substrate.
BACKGROUND OF THE INVENTION
In an ink jet recording system, ink droplets jetted out in a variety of ways form images on a recording paper, and such a recording system has features that it makes less noise than a dot-impact recording system and enables high-speed recording as well as easy full color recording. Therefore, amazing progress of ink jet printers has been made in recent years, and even printers of a moderate price have come to provide sufficiently vivid recorded images; as a result, ink jet printers are now widespread.
The following characteristics are basically required for an ink jet recording paper:
i) Having a high ink absorbing capacity enough not to cause repelling, feathering and overflow of ink,
ii) Having good ink-drying properties (high ink-absorbing speed), and
iii) Generating no cockling upon absorption and drying of ink.
Further, with the recent progress of ink jet printers, the images recorded therewith are similar in quality level to images of silver halide photographs, and so it is required for the recording medium to have high gloss on the recording side.
With the intention of conferring high gloss on the recording side of a recording medium, it has been attempted to use as a substrate a plastic film or synthetic paper having no water-absorbing properties. In this case, the coated layer is required to absorb all of the ink printed because the substrate has no ink absorbing power. However, the use of such a substrate has a drawback of decreasing the ink-absorbing speed since the ink absorbing capacity of the coated layer alone is generally insufficient.
On the other hand, cast-coated papers have so far been applied to printing papers and various wrapping materials, and they are characterized by high gloss of the coated layer surface. Hitherto, the so-called base paper, including paper of non-coated type and paper of coated type, has been used as the substrate of cast-coated paper. These substrates have features such that they have high surface smoothness so that their texture has no influence upon the glossy surface and they are highly sized so as to inhibit a coating solution from permeating thereinto. In order to promote these features, the substrate of coated paper type is provided with a special coating.
A cast-coated paper is generally produced by applying a coating solution to a substrate as mentioned above and pressing the coated layer to a hot finishing surface while the coated layer is in a wet or plasticized state to copy the finishing surface on the coated layer surface simultaneously with the drying of the coated layer. The finishing surface is generally a specular metal surface, so that the coated layer surface has high gloss by copying the specular metal surface thereon.
Thus, the cast-coating method is an effective means for conferring high gloss on the coated layer, and already applied to ink jet recording papers (as disclosed, e.g., in Japanese Tokkai Sho 62-95285 and ibid. Sho 63-264391, wherein the term “Tokkai” as used herein means “unexamined published patent application”).
In the cast coating method, however, a coated paper requires to be dried while the wet coating is pressed to the specular surface of metal. Consequently, the water contained in the coated layer should pass through a substrate and evaporate on the back side of the coated paper. In the case where a general coated paper is produced, on the other hand, water is evaporated on the front side or both sides of the coated layer. Therefore, drying efficiency in the cast coating method is far lower than that in the production of a general coated paper; as a result, the operation speed of a coater is low. Consequently, the productivity of cast-coated paper becomes low.
Further, the cast coating method has a problem of being inferior in continuous operability.
More specifically, in the production of a cast-coated paper, the releasability of the coated layer from the finishing surface is impaired when the drying of the coated layer is insufficient, and thereby the coated layer is partially or entirely picked off by the finishing surface, namely the so-called “drum pick” is caused. As a result, the quality of cast-coated paper is extremely damaged. Further, the drum pick sometimes induces the problem that the paper web is broken in a short time. In addition, the paper web break renders the coater dirty in most cases. Consequently, the operation is interrupted for a long period of time for cleaning the coater surface. Such being the case, the productivity is lowered the higher the frequency of paper break becomes.
On the other hand, when the surface temperature of the finishing surface is raised in order to increase the drying speed, the coated layer pressed against the finishing surface is heated rapidly to be liable to boil. If the coated layer boils, it cannot be in close contact with the finishing surface; as a result, it cannot copy the finishing surface to a satisfactory extent, and so the surface quality thereof is considerably lowered. Thus, there is a limit to the increase of a coater speed by making the drying condition hard. Accordingly, the productivity of cast-coated paper is inferior to that of general coated paper.
Further, in order to cover the texture of a substrate and acquire high gloss, it is necessary for a conventionally used substrate of non-coated paper type to be provided with a coated layer having a dry coverage rate of 15 to 30 g/m
2
per side, so that the resulting paper falls under the category of heavily coated paper.
In some cases where substrates of coated paper type are used, on the other hand, sufficiently high gloss can be achieved even when the dry coverage rate per side is of the order of 10 g/m
2
. Therein, however, the coated layer itself is not sufficient in ink absorbing capacity, and the substrate has almost no ink absorbing power. Therefore, the paper obtained in such cases is unsuitable for ink jet recording paper.
As described above, it is required for the ink jet recording paper to secure sufficient ink absorbing capacity. In addition, the cockling phenomenon caused in a recording paper upon absorption and drying of ink can be minimized so far as all the ink stricken in can be accepted by the coated layer. In this aspect also, it is necessary to increase the dry coverage rate of the coated layer.
In a case where the cast-coated layer alone answers for security of the ink absorbing capacity required, it is necessary to increase the dry coverage rate of the coated layer. In this case, however, the drying efficiency is lowered all the more, so that the coater operation speed in the cast coating method is, as described above, considerably decreased in comparison with general coating methods. With respect to the ink absorbing speed, on the other hand, the cast-coated paper for ink jet recording has a low ink absorbing speed due to smoothness on the recording side, compared with general coated paper for ink jet recording. In making up for this defect, it is generally required to deal with this subject along the line of increasing the dry coverage rate.
Furthermore, another reason for the low productivity is in that the coating compositions for ink jet recording paper are low in solids concentration, compared with those for general coated paper. This is because silica and other porous pigments used for securing ink jet recording suitability are poor in dispersibility, and the dispersions thereof have high viscosity and they are inferior in operational easiness; as a result, it is impossible to adequately heighten the solids concentration.
Thus, the productivity of cast-coated paper for ink jet recording is extremely low since it undergoes both influences of the low productivity of a cast coating method and the low productivity of a coating solution for
Ohmura Tomonobu
Ueno Takashi
Copenheaver Blaine
Kruer Kevin R
Millen White Zelano & Branigan P.C.
Nippon Paper Industries Co. Ltd.
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