Process for manufacturing glazed paper

Details Process for manufacturing glazed paper Process for manufacturing glazed paper

1999-06-24

2001-07-24

Fortuna, Jose (Department: 1731)

Paper making and fiber liberation

Processes and products

Running or indefinite length work forming and/or treating...

C162S181100, C162S181200, C162S181400, C162S181500, C162S207000

Reexamination Certificate

active

06264794

ABSTRACT:

CROSS-REFERENCE OF RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 198 28 952.9, filed on Jun. 29, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a process of making glazed paper from treated stock.
2. Description of Background and Relevant Information
Processes of this type are conventionally used to produce high-quality, smooth papers. It is known, for example to consider a large number of parameters during paper production in order to the obtain a paper with the required quality in all specifications. In such a process, the production of a smooth surface and, at the same time, good optical properties is of utmost importance. A smooth surface is usually produced when the web of paper is guided at a defined residual moisture level and at specific temperatures between at least two, and usually several, smoothing rolls which are pressed against each other. This process utilizes calenders and has been known and has proven itself for a long time. However, the process encounters limits when, as a result of the pressing force required in the calenders, an optical drawback appears in the form of areas having little opacity. This phenomenon is known as black glazing and, in many cases, it limits optimum glaze production. To be sure, the glaze can be increased by a higher calender pressure; however, at the same time, the optical quality of the paper may be so greatly reduced that, especially with thin papers, significant disadvantages may arise.
SUMMARY OF THE INVENTION
Therefore, the invention provide a process with which a paper can be produced that has both a high glaze and good optical characteristics.
By utilizing of the sequence of process sections described herein, it is possible to make the fibers more resistant to the pressure applied in the calender. It is further possible to increase the fiber volume through these measures, since certain substances can penetrate into the interstitial spaces of the paper fibers and expand them. Furthermore, layers which better distribute the pressure forces of the glazing process can also be formed on the outer surfaces of fibers.
The introduction of substances into the fibers is called fiber loading. To load the fibers, it is possible, for example, to introduce substances such as dissolved salts into the fibrous material suspension. Since paper fibers are known to be hydrophilic and capable of swelling, the dissolved salts can pass through the fiber walls into the interior of the fibers. By using the appropriate chemical treatment, crystal growth, which can expand the fibers, is stimulated within the fibers. Existing fiber cavities (lumens) become coated from the inside by a relatively hard layer or at least filled in some locations. Even if the layer breaks apart during the glazing process, it nevertheless prevents the fiber walls from touching each other. An inexpensive, suitable substance is calcium carbonate, which can be stimulated to crystal growth, for example, by addition of CO
2
to an aqueous Ca(OH)
2
solution.
EP 0 690 938 B1 discloses a special process in which, with the use of calcium carbonate, it is possible to fill the fiber lumen. This is done to incorporate the maximum amount of fillers into the paper. Fillers are white and opaque. By this process, losses of strength caused by overloading the sheet of paper are claimed to be avoided and, in addition, sheet weight is increased using a relatively inexpensive substance. In this regard, it is reported that the price of carbonate is approximately 20 to 30% of the price of the fibrous material. This process is known as fiber loading.
The process according to the present invention makes use of the special characteristic which paper fibers can acquire by means of the loading of their internal cavities or lumens. It is based on the knowledge that problems which occur at the end of the paper production process, i.e., during glazing, can initially be solved during stock preparation by a special treatment of the fibers.
According to one aspect of the invention there is disclosed a process for the production of glazed paper wherein a stock is prepared by providing a fibrous material suspension for processing in a paper making machine; a paper web is formed, such that the paper web is dried and produced from the fibrous material suspension; and the paper web is glazed using glazing surfaces which are pressed against each other at a pressure. The stock is also subjected to fiber loading in the preparing step using substances which are transported into the paper fibers such that the substances increase the volume of the fibers in their transverse dimension by forming expanding solid layers.
According to another aspect of the invention, the process provides for the paper fibers to have interior cavities defined by fiber walls and the substances are deposited in the interior cavities during fiber loading so as to form a solid layer, thereby providing, one of, a coating on the interior cavities or filling them in some locations. The solid layers are also made to break apart during the glazing step so as to form a separation layer between the fiber walls.
According to another aspect of the invention, the process provides for the substances to penetrate into the paper fibers during the preparation step. The substances being calcium carbonate, such that the calcium carbonate is made to crystallize inside the paper fibers.
According to another aspect of the invention, the process provides for the substances to comprise at least two components which are added to the fibrous material suspension at different times.
According to another aspect of the invention, the process provides for the fibrous material suspension to be produced from recycled paper which is freed of ink by a de-inking process.
The process provides for the glazing to be performed at a pressure of at least 30 N/mm
2
, and preferably at a pressure of at least 60 N/mm
2
. The process also provides for the glazing to be performed by a supercalender.
According to one aspect of the invention there is disclosed a process for the production of glazed paper wherein a stock is prepared by providing a fibrous material suspension for processing in a paper making machine; a paper web is formed, such that the paper web is dried and produced from the fibrous material suspension; and the paper web is glazed using glazing surfaces which are pressed against each other at a pressure. The stock is also subjected to fiber loading in the preparing step using substances which are transported into the interior of the paper fibers so as to increase their resistance against compression.
According to another aspect of the invention, the process provides for the paper fibers to have interior cavities defined by fiber walls and the substances are deposited in the interior cavities during fiber loading so as to form a solid layer, thereby providing, one of, a coating on the interior cavities or filling them in some locations. The solid layers arc also made to break apart during the glazing step so as to form a separation layer between the fiber walls.
The process provides for the substances to penetrate into the paper fibers during the preparation step. The substances being calcium carbonate, such that the calcium carbonate is made to crystallize inside the paper fibers.
The process provides for the substances to comprise at least two components which are added to the fibrous material suspension at different times.
According to another aspect of the invention, the process provides for the fibrous material suspension to be produced from recycled paper which is freed of ink by a de-inking process.
The process provides for the glazing to be performed at a pressure of at least 30 N/mm
2
, preferably at a pressure of at least 60 N/mm
2
. The process also provides for the glazing to be performed by a supercalender.
According to another aspect of the invention, the process is for the production of glazed paper wherein a stock is prepared by providing a fibrous ma

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