Process for improving the surface of offset paper

Details Process for improving the surface of offset paper Process for improving the surface of offset paper

2000-04-24

2002-12-17

Nguyen, Dean T. (Department: 3629)

Paper making and fiber liberation

Processes and products

With coating after drying

C162S137000, C162S175000, C427S424000, C427S479000, C427S482000, C427S485000

Reexamination Certificate

active

06494988

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 21 592.8, filed on May 7, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an application device, e.g., a nozzle dampener, for a paper machine, having a plurality of nozzles distributed across the machine width for spraying a passing paper web. The present invention further relates to a paper machine for producing rotogravure and offset paper having at least one drying section and one calender. In addition, the present invention relates to the use of a nozzle dampener for improving the paper properties of offset paper. Finally, the present invention also relates to a process for improving the surface of paper for use as offset printing paper.
2. Discussion of Background Information
In order to be able to achieve optimal printing quality, different printing processes place different requirements on the quality and properties of the paper being produced. Thus, high-quality printing is produced using, e.g., the rotogravure process or the offset printing process.
In the case of the rotogravure process, the printing ink is applied to the paper by the ink first accumulating in the recesses of a printing plate so that it can then be applied to the paper that passes by when the printing plate unrolls.
In contrast to this, in the offset printing process, the print image is projected onto a surface (hydrophilic/hydrophobic), whereby the surface properties change according to the print image. Hydrophobic locations absorb the positive printing inks, while hydrophilic locations absorb water.
Due to the great difference in printing techniques, different requirements are also placed on the quality and the properties of the paper to be printed. Thus, for example, paper that is especially suited for rotogravure is enriched with a very high proportion of filler in order to be able to optimally adjust the surface properties in the calendering process. Furthermore, in the case of offset printing, it is also very essential for the paper being used to have a high surface strength, give off as little dust as possible, and have only a low tendency to tear in order to be able to achieve the desired high printing quality and good pressroom runnability.
Most paper machines that are suited especially for producing one or the other type of paper are manufactured and operated according to these requirements. However, problems arise when the attempt is made to equip the same paper machine in such a way that it is suited for producing both variations of paper, i.e., rotogravure paper and offset paper, without having to make great adjustments when changing the paper type.
It is known from the unexamined German Patent Application DE 196 32 673 A1 that, in order to produce high-quality printing paper for the offset printing process, an attempt is made to add an auxiliary agent to the mass to increase the strength in the z-direction of the paper (perpendicular to the surface of the paper) or the surface strength. The disadvantage of this measure is the rather low efficiency of adding auxiliary agents to the mass in paper production. This means that a disproportionately high quantity of auxiliary agent (binding agent) is needed in the mass to achieve a sufficient effect on the surface.
In addition, it is generally known that the surface of a finished paper web is coated off-line with the aid of suitable application units subsequent to its production process and that this produces the high surface quality that is suitable for offset printing.
The disadvantage of this known process is that high production and investment costs are required for the additional application units, possibly for a separate facility for off-line application, and these units drive up the production costs for this type of paper.
Furthermore, nozzle dampeners that are used to spray water on a finished paper web in order to give the paper web a desired moisture profile that is as uniform as possible are known in prior art. After this treatment, the paper web is usually fed through calenders, thereby achieving an especially smooth surface that is as uniform as possible. Reference is made to documents EP 0 345 670 B1 and DE 38 19 761 C2 with respect to the nozzle dampeners, the disclosures of which are explicitly incorporated by reference herein in their entireties. A calender or glazing roller is known from unexamined German Patent Application DE 195 42 191 A1, for example.
SUMMARY OF THE INVENTION
The present invention discloses one single paper machine which is equally suited for selectively producing either rotogravure paper (self-contained paper) or offset paper as desired without protracted adjustments being necessary.
According to the invention, the paper machine to selectively produce rotogravure and offset paper includes at least one drying section and a calender, and at least one nozzle dampener located in the area of the drying section. The at least one nozzle dampener can be substantially exclusively utilized to homogenize the moisture cross profile of the paper web when producing rotogravure paper, and can be substantially exclusively utilized to apply a binding agent, e.g., starch, when producing offset paper.
By using the nozzle dampener in the drying section of the paper machine to apply binding agent, the instant invention enables both rotogravure paper as well as high-quality offset printing paper to be produced on one and the same paper machine without special adjustments having to be made.
If the paper is supposed to be suitable for offset printing on both sides, at least one nozzle dampener can be provided on both sides of the paper web.
In positioning the nozzle dampener or even another applicator operating with nozzles, it can be advantageous to maintain a distance of approximately 10 to 200 mm, preferably approximately 20 to 150 mm, and most preferably approximately 20 to 100 mm between the nozzle exit points of the nozzle dampeners and the paper web in order to avoid an excess formation of mist.
According to the invention, an application device, e.g., a nozzle dampener, is provided for a paper machine with a plurality of nozzles distributed across the machine width to spray a passing paper web, in which at least one row of nozzles is provided for the throughput of water and/or binding agent solution.
As a result of this embodiment, it is possible to adjust to the special properties of the binding agent solution so that the nozzles can be adapted according to the different consistency, viscosity, and throughput volume.
In this connection, it can also be advantageous for at least one row of nozzles, through which the binding agent flows, to be provided with nozzle openings that create a closed binding agent film on the passing paper web.
It can also be favorable, as a function of the binding agent used, to provide at least one row of nozzles with openings that form a spray jet with a droplet size of approximately 20 to 250 &mgr;m, preferably approximately 50 to 70 &mgr;m.
Another advantageous embodiment of the application device according to the invention provides that, for at least one row of nozzles, through which the binding agent flows, a device can be provided which regulates or controls the longitudinal profile and/or the cross profile of the applied mass of binding agent across the width of the machine. Thus, it is possible either to make sure that there is an uniform application layer in the production process or even to regulate or control the cross profile of the layer thickness across the web.
However, there is also the alternative possibility of compensating for irregularities in the previous paper thickness over a specific length and/or a specific section of the paper web by adapting the layer thickness of the application of the binding agent and, in this way, achieving an overall uniform mass cross profile and/or mass longitudinal profile of th

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