Method For Treating Paper

Abstract

A method of and apparatus for pressure treating a paper web between a pair of rolls, at least one of the rolls having a plastic work engaging surface. The width of the paper web under treatment is regulated so that it is no less than the width of the plastic surfaced roll and thereby prevents direct contact of the plastic roll with the roll adjacent thereto. Cutting means are further provided, either prior to or subsequent to the rolls, to effect trimming the edges of the paper web under treatment.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to a method of treating a paper web in which the web passes through a pair of nip forming rolls, and more particularly to a calendering machine wherein at least one of the pair of rolls forming the nip has a plastic work engaging surface.

Customarily, rolls for the treatment of a paper web are somewhat longer than the width of the web so that the roll nip can act upon the entire width of the web in a uniform manner. In using rolls made of plastic material, particulary at high working speeds such as are used in paper making, the uneven heating of the plastic rolls creates problems. Heating of the plastic roll may occur for several reasons. It may be caused for instance in a situation where the plastic roll is working opposite to a heated steel roll. Even when operating with unheated rolls, however, a heating effect occurs because of the deformation of the surface of the plastic roll upon each rotation, which generates heat of considerable magnitude. In the portion of the nip through which the web passes, the heating has no effect because the heat is constantly carried off by the travelling paper web and a constant cooling effect by virtue of the moving web takes place.

Excessive heating at the ends of the rolls causes numerous problems. The same deformation and consequent heat generation as in the remainder of the nip, takes place at the edges of the rolls. Moreover, in the case of a heated counter roll, the ends of the plastic roll extending beyond the width of the paper web, are in direct contact with the heated surface of the counter roll. No carrying off of this heat takes place.

In the prior art which included rolls formed of paper, this heating effect did not result in any particular complication because the coefficient of expansion of paper rolls is substantially less than that of plastic rolls. Heating the ends of the plastic rolls however, results in an elongation of their plastic materials producing an increase in the diameter of the plastic roll, at the end portions beyond the paper web width because of the excessive heat present. At low nip pressures, this could result in contact between the plastic roll and its counter roll only at the ends so that the desired nip pressure is applied only partially or in some instances, not at all. At higher linear pressures, the increased diameter at the ends of the plastic roll increases the deformation occuring with each rotation so as to further increase the heating of the plastic roll with the result that the ends of the plastic roll may be destroyed.

In the textile industry, cooling arrangements for plastic rolls in the form of blowers are utilized. Such cooling apparatus is either inefficient or not sufficiently effective in a paper machine however, because the working speed and thus the rate of rotation of the rolls is substantially higher than that used in the textile industry. Corresponding to the higher rate of rotation of the roll, the amount of heat generated per unit of time also increases to levels which can no longer be effectively cooled by a cooling apparatus such as utilized in the textile industry.

SUMMARY OF THE INVENTION

Briefly stated, the method of this invention includes treating a web of paper being passed through a pair of rolls one of which has a plastic work engaging surface. More specifically, the ends of the plastic roll are provided such that they do not extend beyond the paper web. In this manner, the entire breadth of the plastic rolls runs in contact with the paper web and thus is subject to its cooling action along its entire length. Uneven heating over the length of the plastic roll and the resulting uneven deforming of the plastic roll are thus avoided.

Accordingly, it is an object of this invention to provide a method wherein undesirable heating effects of plastic rolls utilized in treating paper webs is eliminated.

The invention, as disclosed, is also provided with a cutting apparatus which cuts off the edges of the paper web being treated. In one form of the invention, the cutting apparatus is positioned ahead of the roll pair, one of which is the plastic roll, and severs the edge portions of the paper web in the form of strips so that the paper web entering into the nip is exactly the width of the plastic roll acting upon it.

In another embodiment the cutting arrangement is positioned subsequent to the roll pair containing the plastic roll and cuts off the edges of the web not treated by the plastic roll.

By positioning the cutting apparatus ahead of the roll pair containing the plastic roll, the width of the paper web passing through the nip of the plastic roll can be trimmed to correspond exactly to the width of the plastic roll. The cutting apparatus is positioned in exact alignment with the edges of the plastic roll so that the web edges are in alignment with the edges of the plastic roll as the web passes through the nip.

In the case of positioning the cutting arrangement subsequent to the plastic roll nip, portions of the web extending beyond the width of the plastic roll are not treated. These edge portions are subsequently cut off. The narrow edge portions cut off in both cases constitute waste, but the amounts involved are not significant.

It is preferred to position the cutting apparatus directly ahead of or directly subsequent to the roll pair containing the plastic roll. Positioning the cutting apparatus directly ahead of the plastic roll nip permits an exact adjustment of the edge with respect to the roll because the paper web will not deviate laterally in the short distance between the cutting apparatus and the plastic roll nip. Cutting the edges immediately after the web leaves the plastic roll nip, in the other case, is advantageous because generally, a web non-uniformly treated over its width will not remain planar but will tend to form waves. Moreover, such a web is hard to wind because the edge portions, besides being wavy, also have a greater thickness than the remainder of the width, this additional thickness becoming significant as the paper web is coiled into many layers.

In the case of the cutting arrangement being positioned subsequent to the plastic roll nip, it is advantageous to position the plastic roll in such a manner that the edge portions of the paper web on both sides of the web remain untreated by the plastic roll.

At the edge of the plastic roll, the working pressure is decreased from its normal value of nip pressure to zero over a small range. Consequently, there is some non-uniformity of levelness and strength of the paper web in this limited range. To eliminate this, it is of advantage to arrange the cutting apparatus disposed subsequent to the plastic roll, in such a manner that a small portion of the edges of the web within the limits of the plastic roll is cut off. The cutting apparatus as disclosed herein, includes rotating knives positioned on both sides of the paper web.

The invention may also be used when the roll nip comprises two plastic rolls operating opposite each other, one of which is no wider than the paper web being treated.

The invention is particularly advantageous in connection with high and uniform nip pressures. It is consequently advantageous if at least one of the rolls of the roll stack is a controlled deflection roll such as is described and claimed in U.S. Pat. No. 2,908,694.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, is a side elevation view of a calendering machine incorporating the features of this invention;

FIG. 2, is a plan view of the calendering machine of this invention illustrating the cutting apparatus positioned directly upstream of the pair of rolls;

FIG. 3, is a plan view of the calendering machine of this invention illustrating the cutting apparatus positioned directly downstream from the pair of rolls;

FIG. 4, is a schematic perspective view of the pair of rolls of this invention with the cutting apparatus positioned upstream or directly ahead of the pair of rolls; and

FIG. 5, is a schematic perspective view of the pair of rolls of this invention with the cutting apparatus positioned downstream or directly subsequent to the pair of rolls.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the drawings, particularly FIG. 1, the web of paper 1 being treated passes through the calendering machine in the direction of the arrow 2. A pair of rolls, indicated generally as 3, are provided on the calendering machine, with the paper web 1 under treatment passing therethrough. The upper roll 4 is preferably fabricated from polyamide or polyurethane material, while the lower roll 5 is preferably a steel roll which may also be heated. Both rolls of the preferred embodiment are shown as controlled deflection rolls of the type described and claimed in U.S. Pat. No. 2,908,694.

With reference particularly to FIGS. 2 and 4, rotating cutting knives 8 and 9 are disposed ahead or upstream of the pair of rolls 4 and 5. The cutting knives 8 and 9 are adjusted, as best seen in FIG. 2, so that the cutting edges are in line with the edges of the polyamide roll 4. In this manner, the cutting knives 8 and 9 sever the edges of the paper web 1 which extend beyond the ends of the polyamide roll 4, the severed edges being in the form of waste strips 10 and 11. The remaining portion of paper web 1, is then of the same width as the polyamide roll. In this manner as the paper web passes between the rolls 4 and 5, there is no direct contact between the pair of rolls 4 and 5. Therefore, the generated heat is carried off by the travelling paper web 1 without any excessive heat being generated between the pair of rolls.

As illustrated in FIGS. 3 and 5, the rotating cutting knives 8' and 9' are disposed subsequent or downstream of the pair of rolls 4 and 5. In this embodiment, the polyamide roll 4 is narrower than the width of the web of paper passing through the pair of rolls. Consequently, at the edges of the web there remain edge portions 6 and 7 which were not treated by the polyamide roll 4. These edge portions are severed by the cutting knives 8' and 9' to separate them from the paper web 1 in the form of waste strips 10' and 11'.

In positioning, the cutting knives 8 and 9 or 8' and 9', either directly ahead of or directly subsequent to the pair of rolls 3, it is advantageous to provide a common frame for both the pair of rolls 3 and the cutting apparatus.

In certain instances it may also be more desirable to space the cutting apparatus somewhat away from the pair of rolls 3. For example, in the embodiment wherein the cutting arrangement is positioned subsequent to the pair of rolls 3, an intermediate apparatus or stations may be provided in the machine. It is also possible to position the shortened polyamide roll asymetrically with respect to the paper roll so that one of the incompletely treated edge portions of the web is wider than the other.

Claims

What is claimed is:

1. A method of pressure treating a paper web between a pair of rolls positioned adjacent one another, at least one of which has a work-engaging surface of plastic material, comprising the step of passing a paper web of a width no less than the width of the plastic-surfaced roll between the pair of rolls, whereby the paper web prevents any direct contact between the plasticsurfaced roll and the other roll of the pair of rolls.

2. The method of claim 1 which further comprises the step of cutting the edge portions of the paper web which extend beyond the ends of the plastic-surfaced roll.

3. A method of pressure treating a paper web between a pair of rolls positioned adjacent one another, at least one of which has a work-engaging surface of plastic material, comprising the steps of passing a paper web of a width no less than the width of the plastic-surfaced roll between the pair of rolls, whereby the paper web prevents any direct contact between the plastic-surfaced roll and the other roll of the pair of rolls, and cutting the edge portions of the paper web which extend beyond the ends of the plastic-surfaced roll to a width equal to that of the plastic-surfaced roll at a point prior to the paper web passing through the pair of rolls.

4. A method of pressure treating a paper web between a pair of rolls positioned adjacent one another, at least one of which has a work-engaging surface of plastic material, comprising the steps of passing a paper web of a width no less than the width of the plastic-surfaced roll between the pair of rolls, whereby the paper web prevents any direct contact between the plastic-surfaced roll and the other roll of the pair of rolls, and cutting the edge portions of the paper web which extend beyond the ends of the plastic-surfaced roll to a width equal to that of the plastic-surfaced roll at a point immediately prior to the paper web passing between the pair of rolls.

5. The method of claim 2 in which the edge portions are cut off at a point subsequent to the paper web passing between the pair of rolls.

6. The method of claim 2 in which the edge portions are cut off at a position immediately subsequent to the paper web passing between the pair of rolls.