Gravure paper and manufacturing process for this paper

Details Gravure paper and manufacturing process for this paper Gravure paper and manufacturing process for this paper

2000-05-15

2002-07-23

Chin, Peter (Department: 1731)

Paper making and fiber liberation

Processes and products

Multi-layer waterlaid webs or sheets

C162S185000, C162S186000

Reexamination Certificate

active

06423181

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 22 390.4, filed on May 14, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a manufacturing process for a gravure paper with a maximal roughness depth of approximately 1.40 &mgr;m (measured with the “Parker Print Surf” method according to DIN-ISO 8791-4). The invention also relates to a gravure paper which is manufactured in a single work cycle.
2. Discussion of Background Information
Different printing processes are known from the prior art which place different demands on the quality and properties of the paper to be printed in order to achieve an optimal printing quality. In the gravure process, it is particularly crucial that the surface of the paper used is very smooth or has a very low roughness depth so that a sufficient printing quality is achieved, Furthermore, the porosity must be low in order to assure an optimal color absorption. In order to achieve the best printing quality, the sheet must also have a certain compressibility after being subjected to calendering.
In addition to the low roughness depth, however, a high tensile strength is also required in order to prevent tearing of the paper web during the printing process.
In order to produce a very high surface quality, i.e., a low roughness depth of the paper, the filler content or the pigment content of the fibrous material suspension must be kept as high as possible. This is because these very fine materials produce a very smooth and homogeneous surface of the paper. In addition. a fibrous material is used which has as high a beating degree as possible in order to produce a homogeneous sheet texture by utilizing the high content of fines. The uniformity and closed nature of the paper surface are of particular significance.
However, a high filler content runs counter to the requirement for a high strength of the paper. In order to achieve a high tear strength, an excessive filler content is not desirable since the filler acts as an obstacle to the hydrogen bridge formation between the fibers of the paper. In addition, a high beating degree impairs the strength due to a fiber-shortening effect.
Currently, in order to circumvent these opposing interests, gravure paper is in part manufactured so that coating-base paper is produced as a highly tear-resistant paper whose surface is coated with pigment and filler material in order to obtain a sufficient surface quality. However, this requires a high investment outlay because, in addition to the paper machine required for producing the paper, an investment must also be made in a coating machine, which may function either on-line or off-line in relation to the paper manufacturing process.
If one pursues the other possibility of keeping the beating degree of the paper as high as possible, i.e., in the vicinity less than approximately 40 ml CSF (Canadian Standard Freeness, see TAPI 227), and working with a relatively high total filler content, then this involves a powerful beating of the fibrous material. However, this is very energy intensive since the energy used rises exponentially as the beating degree increases.
The beating degree of fibrous material is frequently expressed in milliliters as Canadian Standard Freeness (CSF). In this connection, a high beating degree, i.e., a high fineness of the fibrous material or a high drainage resistance, corresponds to a low CSF value, whereas a lower beating degree corresponds to a high CSF value or a low drainage resistance.
The Applicant's German Patent Application 196 24 127 A1, the disclosure of which is expressly incorporated by reference in its entirety, discloses a process for manufacturing a paper web with the aid of a multi-layer headbox. With this process for manufacturing a multi-layer fibrous material web, a headbox supplies a number of fibrous suspension streams to a web forming device in which, in order to produce a three-layer fibrous material web, the two outer layers are produced by utilizing two fibrous suspension streams whose composition is selected so that each outer layer is subsequently easier to drain than the inner layer, which is produced by providing a fibrous suspension stream with a correspondingly different composition. However, the specific information relating to the composition of the individual fibrous suspension flows is not given in this document.
Furthermore, the international application PCT/US97/01975 has disclosed applying uncooked starch to the surface of a fibrous material web which is still wet. This is performed in the vicinity of the wet section of a paper machine in order to improve the surface of the paper. However, no indication is given in this document as to the manufacture of a gravure paper.
SUMMARY OF THE INVENTION
The invention is therefore provides for a manufacturing process for gravure papers which is distinguished by a significantly more favorable energy expense and fibrous material utilization as well as a lower investment requirement than is customary in the prior art, The invention also provides for a gravure paper which, as a result of its manufacturing process, is less expensive to produce than in the prior art.
The invention recognizes that it is possible to produce a gravure paper by using a fibrous material that has a low beating degree with values of greater than approximately 50 ml CSF, preferably between approximately 50 ml and approximately 120 ml CSF, without having to use a coating machine in either an “on-line” or “off-line” operation. Moreover, it is possible to situate the majority of the filler or pigment content of the finished paper web in the immediate vicinity of the surface of the finished paper web, such that, on the one hand, the tear strength of the gravure paper produced is increased and, on the other hand, the maximal surface roughness depth of the paper is not impaired. At the same time, however, the manufacturing process also takes place in one work cycle. In this connection, it is important for the dry matter content of the fibrous material web on which the filler and/or the pigment is deposited to be approximately ≦90%, preferably between approximately 3% to approximately 55%, and most preferably between approximately 5% to approximately 20%, since only in this way can a favorable bonding of the filler or the pigment to the fibrous material web be achieved.
With a constant basis weight, a high total filler content requires a lower relative content of strength-inducing fibrous material components. As a result, it is necessary to use higher quality and therefore more expensive fibrous material components. This disadvantage is prevented through the invention by the deliberate application of pigments to the surface of the paper. Consequently, more reasonably priced fibrous materials can be used without loss of quality.
According to one aspect of the invention, there is provided a process for manufacturing gravure paper with a maximal roughness depth of approximately 1.40 &mgr;m which includes producing a stock suspension that has a stock with a freeness (i.e., measure for the beating degree) of greater than or equal to approximately 50 ml CSF (i.e., Canadian Standard Freeness), preferably between approximately 50 ml to approximately 120 ml CSF, and most preferably between approximately 50 ml to approximately 80 ml CSF, producing a fibrous material web using this stock suspension with the aid of a forming system, a first press section, and a drying section, applying at least one pigment and/or filler slurry to the unfinished fibrous material web in the vicinity between the beginning of the forming and a position at which a dry matter content of the fibrous material web is approximately ≦90%, and preferably between approximately 3% and approximately 50%, with the fibrous material content in the pigment and/or filler slurry preferably lying in the range from approximately 2% to

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