Presses – Methods
Reexamination Certificate
2001-07-19
2003-05-27
Ostrager, Allen (Department: 3725)
Presses
Methods
C100S07000A, C100S15500G
Reexamination Certificate
active
06568318
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 100 37 835.8, filed on Aug. 3, 2000, 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 a process for operating a calender with at least one nip that is formed by a hard roll and a soft roll with an elastic surface. The invention further relates to a calender with at least one nip that is formed by a hard roll and a soft roll with an elastic surface.
2. Discussion of Background Information
Such calenders are used for subjecting a material web passing through the nip to increased pressure and optionally to an increased temperature as well. In this regard, a compression of the material web occurs and it is possible to influence certain surface properties such as gloss and smoothness by treatment in a nip.
In order to explain the invention, a paper web will be used in the following as an example of a material web. The calendering of a paper web is also the primary application of the invention. However, the invention may also be used with other material webs that are treated in a similar manner.
A nip that is formed by a hard roll and a soft roll with an elastic surface is also referred to as a “soft” nip. Because of the different properties of the two rolls forming the nip, different surfaces generally result on both sides of the paper web after it has passed through the soft nip. The side that was in contact with the hard roll has a very smooth surface. This has the condition that it is possible to provide the hard roll with a smooth surface. This is different in the case of the elastic roll, whose surface is currently primarily formed by a plastic coating. It is relatively difficult to provide the plastic with the desired smoothness. As a rule, the surface roughness of the plastic is much greater than the surface roughness of the hard roll.
It is known from DE 195 06 301 A1 to form the plastic coating of the soft roll in two layers, with the outer layer having a lower elasticity and a greater hardness than the inner layer. For example, the outer layer can be composed of a silicon rubber. While the surface roughness of such a soft roll is relatively low when compared to other soft rolls, it is possible to discern distinct differences in the surface properties of the material web treated in the calender.
SUMMARY OF THE INVENTION
The present invention improves the quality of the material web.
Accordingly, the instant invention is directed to a process of the type mentioned at the outset which also includes the surface of the soft roll built into the calender is provided with a finish.
It is assumed that the surface roughness of the soft roll is caused by pores that form in the plastic. With the aid of the finish, these pores are filled and the roll surface is thus correspondingly made smooth. However, as in other finished surfaces, it can be observed that a roll treated in such a manner only remains smooth for a certain period of time. Obviously, therefore, the pores form again in operation, for example, in that the finish is removed again by a material web passing through. If the roll is then provided with the finish in its built-in state, it becomes possible to repeatedly or constantly apply a wear layer that allows the soft or elastic roll to be very smooth for a certain period of time. This smoothness of the soft roll has a very positive effect on gloss and smoothness of the material web passing through.
It is particularly preferred for a liquid finishing medium to be applied to the surface and dried. With the aid of a liquid finishing medium, an even coating of the surface of the roll with the finishing medium can be achieved relatively quickly. The term “liquid” used here may be interpreted broadly. It can also be a pasty medium that is only fluid in a limited sense. The finishing medium can also be sprayed on in the form of a sprayed mist. Finally, it is also possible for the finishing medium to be initially present in the form of steam and to condense on the surface of the soft roll. The step of drying is advisable in order to prevent the passing material web from being contaminated with the finishing medium. Moreover, a dried finishing medium adheres better to the surface.
It is preferred for the finishing medium to be applied to the surface while the surface is warm. The warmth accelerates the drying process. The roll is normally warm in operation anyway because the elastic roll is flexed during operation, thus producing warmth.
Preferably, the finish is polished. In the most simple case, this can be accomplished in that the roll is moved past a polishing device, for example, a textile cushion. This further improves the smoothness of the surface of the soft roll.
Preferably, the calender is stopped for maintenance purposes in maintenance pauses and the finish is applied outside of the maintenance pauses. In other words, the finishing medium can be applied during operation of the calender such that the surface finish can already be renewed before it has been worn off to the point that an increased roughness results.
It is preferred for the finish to be applied during interruptions in operation. While such interruptions in operation, for example, as a result of a tear in the paper web, are not desirable, they cannot always be prevented. In the case of such an interruption in operation, the calender must be stopped for a certain time anyway in order to remove the torn paper web, for example. This time can be used for applying finishing medium to the surface of the soft roll. However, removal of the roll is still not necessary.
Alternately or in addition to this, the finish can be continually applied. This achieves virtually constant conditions on the surface of the soft roll.
It is particularly preferred for the finish to be applied with the aid of a material web to be calendered in the nip. For example, the paper web can be provided with the finishing medium in such a way that the paper web deposits the finishing medium onto the surface of the soft roll. Of course, there must be compatibility between the paper and the finishing medium so that the quality of the paper web is not diminished.
Alternately or in addition to this, provision can also be made for the finish to be applied during the maintenance pauses. In the maintenance pauses, the calender is stopped, so that the finish can also be applied with the aid of humans without any danger.
More preferably, more than one soft roll is used and a predetermined number of the last soft rolls are provided with finish. This is particularly advantageous when the material web first runs through a calender such that one side only comes into contact with hard rolls, while this smoothed side then, as it passes through the rest of the calender, is pressed by the soft rolls. If these soft rolls are now provided with finish, the quality of this surface will no longer be made worse, but rather the quality will at least be able to be maintained.
The present invention is also directed to a calender of the type mentioned at the outset that also includes a finishing medium application device arranged at the soft roll. Using the finishing medium application device, it becomes possible to apply finishing medium even to a soft roll that is built into a calender for the purpose of making the surface of the soft roll extremely smooth. The application of the finishing medium can even occur during operation under certain conditions such that the surface can be maintained at a constant quality.
Preferably, the finishing medium application device has a dispenser for fluid or pasty finishing medium. The finishing medium can, for example, be sprayed on or applied in another manner. A finishing medium that is fluid in a wider sense can be used to attain an even coverage of the surface of the soft roll.
More preferably, the finishing medium application device has a smoothing device that follows the d
Greenblum & Bernstein P.L.C.
Nguyen Jimmy T
Ostrager Allen
Voith Paper Patent GmbH
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