Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
2000-08-07
2002-07-02
Fortuna, Jose (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S158000, C162S181200, C162S181400, C162S181800, C162S175000, C162S179000, C428S341000, C428S352000, C427S361000, C427S391000, C427S177000
Reexamination Certificate
active
06413370
ABSTRACT:
INTRODUCTION AND BACKGROUND
The invention concerns a coated roll printing paper which is suitable for printing with cold-set offset printing inks using a base paper as the carrier paper, which is formed from paper fiber material and mineral filler, with a coating containing calcium carbonate in the coating pigment, and with a synthetic binder as a binding agent. The invention further concerns the use of such a paper, and a process for its production.
At present, newspapers are nearly all printed by the offset process, using cold-set inks. In contrast to heat-set inks, cold-set inks need not be exposed to heat for drying. Instead, they dry as the water of the printing ink emulsion, as well as the oil in the ink, are absorbed into the carrier, i.e., the paper, as soon as possible, with the pigments of the ink remaining on the paper surface. Oxidative drying is also said to occur here.
Cold-set suitability according to the claimed invention demands a finished paper with hydrophilic properties and, consequently, a base paper with such properties. Thus, two factors are necessary in obtaining an acceptable printing quality using cold-set inks: a) a high and rapid printing ink penetration, and b) a rapid segregation of water and printing ink pigments in order to obtain a required rate of setting, or drying, of the printing ink.
Although print quality generally improves with increasing smoothness of the carrier, while the consumption of ink decreases, smoother papers are generally less absorbent, so that the absorption of the ink emulsifiers is slower. This causes smearing on the printing press guides and deposits in the folder and in the stack of copies. On the other hand, excess absorption causes the ink to penetrate more into the paper, giving an inadequate impression, i.e., poor dot separation and print-through of the print onto the back.
While standard newsprint meets the conditions for adequately rapid drying of cold-set inks, the quality of the image on newsprint is limited. Standard newsprint is an uncoated natural paper. Its pore volume is typically not covered by a coating, since such a coating would prevent absorption of the ink emulsion into the paper. It would be desirable, nonetheless, to modify such paper so as to improve its print quality for other uses, while maintaining the qualities necessary to process the paper in standard newspaper rotary presses. This is because rotary presses for newspapers are usually operated only during a limited portion of the day. It would be advantageous, then, to use such expensive equipment for other printing work, especially job printing, during the idle periods.
Such job printing, however, which may include brochure enclosures or the like, generally requires a higher quality printed image than is possible with standard newsprint. Because of that, there has been much discussion and experimentation with the goal of making improved papers which would be suitable for such applications. Such improved papers would ideally compare favorably with the quality of super-calendered (SC) papers, i.e., highly glazed papers such as are used for heat-set offset printing. As coated papers, they would also compare favorably with LWC (low weight coated) papers. Previous such experiments have not, however, been accepted in the marketplace.
European Patent Application 0 377 983 describes a coated newsprint paper in which suitability for cold-set use is said to be achieved by a certain minimum content of acicular or needle-shaped pigments in the coating pigment, and which is said to exhibit at least a certain oil absorption value. Acicular pigments, such as Satin White, precipitated calcium carbonate, and delaminated or structured kaolins, such as those recommended in the publication, are generally very expensive. Furthermore, because of their structure they require high usage of bonding material, which also increases the production costs. The claimed invention, however, obtains satisfactory results without the need for such acicular pigments.
Accordingly, it is an object of the invention to produce a coated paper which is suitable for printing with cold-set inks, which can be produced economically, which is visually distinguished from standard newsprint, and which can be processed at printing speeds such as those common in offset printing of newspapers, and on the machines intended for such printing.
SUMMARY OF THE INVENTION
In attaining the above and other objects, one feature of the invention is a coated roll print paper suitable for printing with the cold-set offset process, using base paper comprising paper fiber material and mineral filler as a carrier paper, and with a coating which contains a calcium carbonate in the coating pigment and a synthetic binding agent in the binder, wherein the calcium carbonate is typically a ground natural calcium carbonate, which makes up at least 50% by weight of the coating pigment. It will be understood that precipitated calcium carbonate can also be used instead of ground natural calcium carbonate.
Another feature of the invention is a method of making a coated roll print paper which is suitable for printing by the cold-set offset process. The method involves the use of base paper comprising paper fiber material and mineral filler as a carrier paper, which paper is suitable for printing by the cold-set offset process. While such paper has typically not met the needs of such high quality printing demands as printing brochure enclosures or the like, which generally require a higher quality printed image than is possible with standard newsprint, the claimed invention results in a paper suitable for printing by the cold-set offset process, but which is also suitable for such higher quality printing demands.
The method involves applying a coating which contains a calcium carbonate such as ground calcium carbonate in the coating pigment and a synthetic binding agent in the binder, wherein the calcium carbonate is advantageously a ground natural calcium carbonate, for purposes of economy, which makes up at least 50% by weight of the coating pigment. It will be understood, however, that precipitated calcium carbonate can also be used instead of ground natural calcium carbonate. The method according to the invention results in a coated paper which is perfectly suited to the cold-set offset printing process, and which can be processed at printing speeds such as those common in offset printing of newspapers, and on the machines intended for such printing.
A further feature of the claimed invention is providing an essentially unglazed or only very slightly glazed matte grade paper having Bekk smoothness values between about 10 and 50 seconds. Avoiding a high glaze on these papers allows a satisfactory picking resistance of the surface, which is necessary for printability, and also prevents a loss of the microcapillarity required for drying cold-set inks. A feature of the claimed invention is providing a paper having a suitable ink absorption, which is typically less than 1.1, and preferably less than 0.8.
A further feature of the invention is providing a paper having a contact angle measured with a FIBRO tester after 2 seconds which is <70°, and is preferably <55°. For purposes of comparison, standard newsprint has a value of only about 42° after 2 seconds. Such a natural paper has a high wettability.
According to the invention, the two paper properties mentioned above can partially balance each other. For instance, the invention contemplates excellent printing produced with a 2-second contact angle of 45° and an absorption, for both sides of the paper, of 0.5. Papers with contact angles of less than 50° and absorption values of less than 0.7 are considered outstandingly well suited for cold-set printing.
Another feature of the invention is that the total coating pigment has a fineness of at least 65% less than 2 &mgr;m, and the proportion of binder, as dry weight based on the coating pigment, is less than 15%, and preferably less than 13%.
A still further feature of the present invention resides in a process for produ
Hofmann Hans-Peter
Wurster Hartmut
Fortuna Jose
Haindl Papier GmbH
Smith , Gambrell & Russell, LLP
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