Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
2000-04-24
2003-10-07
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S110000, C162S134000, C162S140000, C162S135000, C428S172000, C428S206000, C428S211100, C427S288000, C283S113000, C283S072000
Reexamination Certificate
active
06630055
ABSTRACT:
The present invention relates to coated paper having at least one pseudo-watermark constituted by a mark that gives said paper a visual effect and a texture that resemble those of a watermark.
The present invention also relates to a method of manufacturing coated paper of the invention.
BACKGROUND OF THE INVENTION
In general, watermarked paper is used in the field of anti-falsification paper, e.g. for paper money and checks, and for official documents such as passports, stamped papers, notarized deeds, since the presence of the watermark makes infringement and reproduction by photocopying more difficult, and provides means for recognizing and/or authenticating said paper. Watermarked paper is also used in the field of personalized business paper with the logo, name, or trademark of the business being reproduced in the form of a watermark.
For paper that is intended mainly for printing and/or writing, in particular for personalized business paper, coated paper is preferred since print quality is better. However, in these two fields of watermark applications, the tonnage of paper involved is variable and small compared with the production capacity of a modern coating machine.
Various ways are known for making watermarked paper, depending on whether the watermark is a “real” or a “pseudo” watermark.
At present, various methods have been proposed for making watermarked coated paper and they can be classified in three categories.
1) “Real” watermarks are obtained during fabrication of the sheet of paper in the wet portion of the paper-making machine, by means of round shapes that include imprints or embossing in recessed and/or relief form, or by using watermarking rolls having embossing in relief and/or recessed form associated with a flat plate (Fourdrinier machine). A pattern is then obtained that comprises zones that are pale when the sheet of paper is observed in transmitted light, if the imprints are in relief, or zones that are dark or shaded, if the imprints are formed by recesses. The pale zones are due to the fact that the thickness of the sheet and the quantity of fibers (density per unit area) are smaller in the zones corresponding to the imprints than in the remainder of the sheet of paper. Conversely, the dark zones are due to the fact that the thickness of the sheet and the quantity of fibers are greater in the zones corresponding to the imprints.
To make paper that is both watermarked and coated, those wet methods of watermarking are unsuitable for various reasons. Firstly, when the watermark is made in the supporting paper or medium, the difference in thickness and the difference in opaqueness of the sheet in the watermarked zone made on the medium are degraded or even lost when depositing the coating which makes the surface of the medium uniform and opaque. In addition, wet methods of watermarking require the use of expensive implementation means, such as watermarking rolls, that are specific to each type of watermark. Furthermore, since modern coating machines have very great production capacity, they do not provide the flexibility required for manufacturing watermarked coated paper in the small quantities desired by the market.
2) “Pseudo-watermarks” can be made by means of a compound which is caused to penetrate in or to be printed on determined zones of the paper and which acts by making the mat of fibers constituting the sheet of paper more transparent on a permanent basis, or by glazing the surface. Those methods significantly alter the surface properties of paper treated in that way, and in particular the quality of the coating when said paper supports coating, and suitability for printing when said paper is watermarked coated paper.
3) WO 97/17493 describes coated paper with pseudo-watermarks that result from varying the weight of coating applied in determined zones, thereby giving rise to variation in thickness and opaqueness in said zones where the weight of the coating has been reduced or increased. That method requires coating to be made by means of apparatus including a roll, in particular a backing roll, having imprints formed thereon in relief or as recesses for the purpose of causing the quantity of coating to be greater or smaller in the zone of the imprint.
Independently of any difficulties that may be associated with performance thereof, that method requires the conventional coating method to be modified by using special rolls that are specific to each watermark. That method therefore does not provide the flexibility needed to enable small quantities of paper to be manufactured “to order” under conditions that are economically satisfactory when using modern industrial coating machines that have large production capacity.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to provide coated paper including pseudo-watermarks constituting marks which modify physical characteristics of the paper in localized manner, e.g. its density, and starting from certain properties such as its thickness and possibly its opaqueness.
Another object of the present invention is to provide coated paper having pseudo-watermarks constituting marks which create gloss and/or shade contrast with the remainder of the sheet of coated paper.
Another object of the present invention is to provide a coated paper having pseudo-watermarks made without requiring ink or glazing to be applied to its surface so that the composition of the paper in the zones constituting the pseudo-watermark is not significantly altered.
Another object of the present invention is to provide coated paper with pseudo-watermarks whose properties in use, in particular properties concerning printability in those zones of the surface of the paper which correspond to said marks, are not significantly spoilt relative to unwatermarked coated paper.
Another object of the present invention is to provide coated paper having pseudo-watermarks that can be manufactured in variable and small quantities under conditions that are more economical than is possible using the methods of the prior art, and that can be obtained in machine widths and quantities that are independent of the characteristics of the coating machine, in particular by means of a method enabling modern coating machines to be used that have large production capacity, and without requiring any modification to be made to the operation of the coating machine proper.
Another object of the present invention is to provide a coated paper having a pseudo-watermark in which said watermark is made after the last coating operation, i.e. at the outlet from the coating machine, and possibly on coated paper that has been finished, i.e. remote from the coating production line.
To do this, the present invention provides a method of manufacturing a coated paper having at least one mark resembling a watermark, the method being characterized in that said mark is made after the drying step which follows the last coating operation, and by performing steps in which:
a) a re-wetting solution is applied to at least one face of the coated paper, in one or more determined zones; and
b) pressure and heat are applied in said re-wetted zone(s) of the coated paper so as to evaporate said solution and densify the coated paper in said zone(s) relative to the remainder of the coated paper.
In the present invention, the term “re-wetted coated paper” is used to mean that, in said zone(s), the re-wetting solution has penetrated into the coating and possibly also into the supporting medium, and has not yet evaporated.
In the present invention, said re-wetting solution is evaporated by exerting pressure over the entire sheet of coated paper or only in said zones, and by increasing the temperature of the coated paper, and the coated paper is densified in the zones where said solution was initially applied. This increases the density of the coated paper in said zones relative to the remainder of the sheet of paper, and more precisely this reduces the thickness of the paper while maintaining density per unit area that is identical to the remainder of the paper. Said
Fourmy Nicolas
Goguelin Michel
Arjo Wiggins Papiers Couches
Griffin Steven P.
Halpern M.
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