Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
1998-10-22
2001-02-13
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S136000, C162S265000, C118S257000, C118S313000, C427S348000
Reexamination Certificate
active
06187142
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for acting on a still-wet or moist material web, e.g., a paper or cardboard web, with one of a fluid and pasty coating medium in the manufacturing process, and a device for coating the still-wet or moist material web with one of the fluid and pasty coating medium in the manufacturing process.
2. Discussion of Background Information
Processes and devices similar in general to above-noted process and device are disclosed in U.S. Pat. No. 5,152,872. In this patent, a coating process and a coating device are disclosed for applying a fluid or pasty medium onto a still-wet paper web. The application of the coating medium is carried out directly onto the surface of the wet material web.
Another similar process and device have been disclosed in unexamined, published German Patent application DE-OS 1 942 348. In this document, a process and a device are disclosed for acting on a still-wet paper web with a coating medium. The coating medium is applied onto the web surface through a wire resting on the material web.
The two above-mentioned processes and devices suffer from the disadvantage that the surface of the coating medium may not be smooth and even, due to either wire soiling or insufficient uniformity in the application.
SUMMARY OF THE INVENTION
The present invention relates to a process and a device for acting on a still-wet material web, e.g., a paper or cardboard web, which does not suffer from the above- noted drawbacks of the prior art and that improves the uniformity of the application onto the web.
In accordance with the present invention, it is advantageous to treat a material web onto which a coating medium is to be delivered and/or a wire through which the coating medium is to be introduced onto the material web with water, and preferably steam, to condition these elements in a coating point region. In this manner, the uniformity of the application onto the traveling material web is improved.
Moreover, an increase in the application efficiency can be achieved. The application efficiency is a relationship between a quantity of coating medium that actually remains adhered to the material web after the coating process and a quantity of coating medium processed in the coating device. In the case of screen conditioning, a reduction of screen soiling, i.e., a reduction of the propensity for the screen to become soiled, is achieved. In this manner, an increase in the permeability of the screen is produced. Furthermore, because the screen heats up beforehand, it advantageously turns out that a temperature gradient between the coating medium (or application color) and the screen is reduced.
Another advantage is that, because of the additional cleaning of the screens, binder-rich coating mediums or application colors, e.g., a starch additive, may be used in the dual screen region of a web making machine.
If conditioning of the screen is carried out by heating the screen, then a local widening of the screen mesh may also occur, as well as a reduction in the viscosity of the coating medium. In this manner, an improved penetration of the screen and an evening-out of the coating are produced.
If conditioning of the screen is carried out after the application, i.e., when the screen is still resting on the web surface, then a reduction in the viscosity of the coating medium may be achieved and an increase in the drainage speed of the coating medium into the web occurs. Additionally, there is a flushing effect with respect to the screen. In this event, the paper or cardboard web partially absorbs the water.
If conditioning of the screen is carried out after the screen, through which the coating medium is applied to the material web, has been removed from the material web, then the conditioning increases the penetration speeds and improves cleaning. This is also the result of additional removal procedures. In any case, regardless of the point at which the conditioning of the screen is performed, an increase in the penetration speed of the coating medium through the screen is achieved. As a result of the improved penetration speed, the components retained in the screen, or the remainder of the coating medium, are reduced and a caking of the color coating medium onto the screen is prevented. Another advantage of conditioning the screen is that, due to the improved application efficiency, a reduction of the water loading via the coating medium is achieved through the screen cleaning.
In the exemplary embodiments of the process of the present invention, it may be advantageous if treatment of the material web, e.g., with steam or water, occurs directly before or after the coating point.
Further, it can be advantageous to perform conditioning on both sides of the material web or on screens positioned on both sides of the material web. Another advantageous embodiment includes a suctioning of excess fluid or impurities during or after conditioning. This can occur, for example, because a suction box may be attached opposite the applicator or because the conditioning of the screen or material web occurs on a suction roll.
Another advantageous embodiment of the process includes mixing steam or water with washing-active additives, such as tensides (surfactants), release agents, chemical barriers, or similar agents. For example, a pigment-free or pigment- containing slurry, or application color can be used as a possible coating medium. Further, kaolin, clay, calcium carbonate, zeolite, bentonite, TiO
2
, or the like can be used as fillers of the coating medium. Starch, latex, surface sizing agents are examples of suitable binders. Retention agents, optical brighteners, or other additives for improving printability can be used as chemical additives. Anti-sticking agents can also be used. It is noted that the above list is exemplary and should not be construed as conclusive, and that all coating mediums known from paper coating can be used and combinations of the above-mentioned agents can be used or can be used in succession.
The above-described wet or moist material web may be, e.g., a paper or cardboard web that has a solids content of approximately 3-60% by weight, preferably approximately 3-23% by weight, and most preferably approximately 3-17% by weight.
An advantageous reaction time of the water or the steam for conditioning the material web and/or the screen may be preferably between approximately 0.1 and 10 milliseconds, and maximally up to approximately 15 milliseconds. The coating Weight, preferably after oven-drying, per side lies between approximately I and 15 g/m
2
.
An advantageous water or steam quantity that is supplied to the screen lies in the region of the free screen volume, i.e., which corresponds to the interstices in the screen.
The above-mentioned process of the present invention, which has been described with respect to conditioning screens, may be likewise used to condition felts of the press section of the material web making machine.
According to the process of the present invention, a wet section of a paper or cardboard machine includes a wire section and a press section, each section having at least one endless, water-permeable belt, and at least one coating device for either direct or indirect application of a fluid or pasty coating medium onto at least one side of a still-wet paper or cardboard web is improved in the region in which the material web and/or belt come into contact with the coating medium. An applicator device is provided for acting on the at least one belt and/or the material web with steam and/or water. The advantages obtained by using the applicator device in the wet section have been described above.
In a particular embodiment of the wet section of the present invention, the applicator can be positioned directly above the web surface without an interposed screen or felt so that the applicator acts directly upon the surface of the material web. In this manner, further liquefaction of the coating medium may be achieved, whereby a flowing of a previously exist
Cedra Ingolf
Gallina Peter
Heinzmann Helmut
Schmidt-Rohr Volker
Trefz Michael
Greenblum & Bernstein P.L.C.
Nguyen Dean T.
Voith Sulzer Papiertechnik Patent GmbH
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