US2593149A - Apparatus for embossing paper - Google Patents

Description

April 15, 1952 p 2,593,149

APPARATUS FOR EMBOSSING PAPER Filed 001;. 1'7, 1946 Bnventor Gttomeg Patented Apr. 15, 1952 j .ARPARArus FOR EMBOSSING PAPER Paul R. Illner, Hamilton, Ohio, .assignor to The Ghampion'iiaper and Fibre Company, Hamilton, Ohio, ascorporation of Ohio Application October 17, 1946, ,Serial No. 703,768

2 Claims. 1

This invention relates to embossing calenders,particularl;y such as are used for embossin paper, and has for its primary object the provision of a calender on which paper can be embossed in greater widths and at higher speeds than have heretofore been practicable. Other objects and advantages of the invention will be apparent "from the following detailed description. In the past the machines most generally used for embossing paper were two-roll calendars wherein the paper was embossed between an engraved steel "roll and aroll having a yielding surface composed, usual y, 10f compressed paper. The diameter of the compressed paper roll is commonly twice, though occasionall-yjtis some other multiple, of that of the engraved roll. When the paper is to be embossed clear through,

the rolls are geared together so that the pattern becomes impressed in the paper roll. When it is desired to emboss only the surface, the gearing is omitted and a third roll, with a smooth'metallic surface is sometimes run against the opposite side of the compressed paper roll to *iron out.

any impressions formed on the surface of the paper roll by the embossing operation,

The heavy pressures necessary in the embossing operation inevitably cause the rolls to spring to a certain degree, thus necessitating a corresponding degree of crown, normally all provided on the compressed paper roll, in order to give a enceat the middle of the compressed paper roll has tended to pull the paper web through the machine faster in the center than at the edges. By holding the web under proper tension, using crowned draw bars, and other knownexpedients, it has in the past been possible to compensate for this tendency atuthe speeds heretofore used. Prior to my invention, there appears to have been no realization of the fact that compensationswhich were satisfactoryat the usual speeds might not function equally well at higher speeds. I have discovered, however, that thecompensating action appears to require an appreciable time interval. Therefore, as speeds are increased above those heretofore used, the available time becomes inadequate to permit full compensation and difliculties such as poorembossing, wrinkling of the web, etc., becomes increasingly troublesome with further increases in speed. My investigations have accordingly led me to believe that the crown on the embossing roll has been the heretofore unrecognized barrier which, in the past, has limited embossing speeds to a mere fraction of the speeds commonly used in supercalendering paper. 7

I have further discovered that the crown also constitutes the primary limiting factor on the width of machine which will give satisfactory performance. The amount of crown required increases as the third power of the width and soon reaches a magnitude which cannot be compensated in the customary manner even at slow speeds. It is, I now believe, for this reason that it has always been necessary to emboss paper in widths considerably narrower than those in which similar grades of paper were commonly passed through supercalenders.

I have now found that paper can be successfully embossed in widths and at speeds far beyond the previously accepted limits, and approximating those used in supercalendering paper of similargrade and weight, if the cooperating embossing rolls are both made cylindrical in form, '1. e. free from crown. In order to prevent deleterious springing of cylindrical embossing rolls and consequent uneven embossing, I provide a backing roll against each of the embossing rolls. The compressed paper roll maybe backed up by a smooth surfaced metal roll which will serve to iron out the depressions in the compressed paper roll, as is desirable in surface erabossing. The engraved steel roll must be backed up by a roll which will not harm the engraved pattern. A compressed paper ;roll similar to the other embossing roll is suitable. It is then generally :advisable to back up this paper roll with anothermetal roll because of the superior stifinessof metal. The metal backing rolls are preferably materially larger in diameter than the embossing rolls themselves. Further, if necessary to maintain satisfactory uniformity of em bcssing-pressure across the width of the web when using cylindrical embossing rolls, these metal backing rolls may be crowned without bringing about the deleterious results caused by crowning the embossing rolls themselves. Another advantage of my improvements lies in the fact that with these backing rolls, the embossing rolls themselves may be made of smaller diameter than is :otherwise necessary.

My improvements will be better understood by reference to the accompanying drawing in which:

Figure l is a diagrammatic cross sectional view of an embossing calender made in accordance with my invention.

Figure 2 is a diagrammatic elevational view showing, in extreme exaggeration, the use of crowned backing rolls to give uniform pressure throughout on cylindrical embossing rolls.

Referring first to Figure 1, an engraved steel embossing roll II runs against a compressed paper or similar yielding-surfaced roll I2 which in turn is supported on a larger diameter steel, or chilled cast iron roll I 3. Embossing roll II is pressed down by another compressed paper or similar yielding-surfaced r011 I4 which is in turn pressed down by another larger steel or chilled cast iron roll I5. The journals of these rolls are mounted in vertical guides, the journals of the bottom'roll I3 are supported in suitable bearings mounted on the machine frame and the journals of the top roll are pressed downward by screws, weights and levers, hydraulic mechanism or other known type of pressure device. These roll supports and pressure devices may be of any suitable known type. They form no part of the present invention and will not be further described.

A paper web I6 is illustrated as passing over the compressed paper supporting roll I2 while being embossed by the engraved steel roll II. The embossing pressure, except for the weight of the rolls themselves, is transferred by roll I from its journals, through roll I4 to engraved roll If the top and bottom rOlls I5 and I3 are of large enough diameter relative to their length and the embossing pressures required, they need not be crowned. Otherwise, they should be crowned to a degree such that, when under pressure as indicated in Figure 2, the lower side of top roll I5 and the upper side of bottom roll I3 will be substantially straight. Under these conditions the entire crown (diametrical) will appear on the top side of top roll I5 and on the bottom side of bottom roll I3, as indicated in the figure where the crown is shown exaggerated to an extent to render it readily perceptible. The term substantially straight in this connection means sufiiciently near. a straight line that the yielding-surfaced rolls l4 and I2 will take up the difference without causing a significant difference in embossing pressure across the width of the machine.

It has been found in practice that, so long as the patterns used are not widely different in depth, different rolls II containing different patterns can be interchanged and the pressures P1 and P2 regulated to the degree required to give the desired embossing effect without disturbing the substantial straightness of the bottom and top surfaces respectively of top and bottom rolls I5 and I3, as defined, and without changing the degree of crown.

It is obvious that, instead ofembossing the 4 paper between rolls I I and I2, it can be embossed between rolls II and I4, or if desired, it could be passed between rolls II and I 4, around roll I I, and then between rolls I I and I2, to give a double embossing action, in case of papers which are hard to emboss or on which an enhanced embossing effect is desired.

By use of my invention, I have found it possible to emboss paper in widths and at speeds far in excess of those heretofore used, and approximately the same as those used in supercalendering paper of similar grade and weight,

with no more difficulty than formerly experienced with narrower webs at slower speeds.

By the term cylindrical as applied to the embossing rolls I mean to distinguish them from rolls which are provided with a crown, or slightly larger diameter at the middle than at the ends.

The term "engraved as used herein to define the steel embossing roll is to be understood as defining a roll carrying a pattern in relief on its surface, and not to impose any limitation as to the manner in which the pattern may have been formed on the roll surface.

Where the surface speed of the embossing roll is defined as substantially 'uniform across the width of the paper web, the degree of uniformity is to be understood as greater than that obtained in the rotation of a crowned roll and to be equal to that obtained with a roll which is cylindrical within practical obtainable limits.

It will be readily understood that the number of rolls is not limited to that shown in the drawing, since the present invention is independent of the actual number of rolls in the stack so long as the embossing rolls themselves are cylindrical, the pressure exerted on them by the adjacent rolls is substantially uniformly distributed along their length, and only yieldingsurfaced rolls contact the engraved metallic rolls.

I claim:

1. Anembossing calender comprising an engraved metallic embossing roll cooperating with a yielding-surfaced embossing roll which is parallel thereto, each of said rolls being of uniform diameter throughout its length, and means for pressing said embossing rolls together with substantially uniform pressure throughout the width of the web being embossed, said means comprising: a pair of metallic pressure-exerting rolls disposed with their axes on opposite sides of and substantially in the same plane with the axe of said embossing rolls; a yielding-surfaced pressure-transmitting roll, with its axis substantially in the same plane, interposed between the engraved metallic roll and the associated metallic pressure-exerting roll; and means for apply ing opposed pressures to the journals of said metallic pressure-exerting rolls; said pressureexerting rolls being slightly crowned to adapt them to transmit the pressure applied to their journals and apply it to the surfaces of the embossing rolls substantially uniformly distributed along the length thereof.

2. In a high speed rotary paper-web embossing machine comprising an engraved steel embossing roll which is long relative to its diameter, and a yielding-surfaced embossing roll parallel thereto and cooperating therewith, means for causing the paper to be fed through and embossed uniformly at high speeds, which comprises uniformity of diameter of each of said embossing rol'ls throughout its length, combined with means for maintaining substantial uniformity of embossing pressure throughout the width of the web being embossed, said means comprising: two metallic pressure-exerting rolls disposed with their axes on opposite sides of, and substantially in the same plane with, the axes of, said embossing rolls yielding-surfaced pressure-transmitting roll interposed between said engraved metallic embossing roll and theassociated metallic pressure-exerting roll; means for applying pressures to the journals of said pressure-exerting rolls, in directions to press said rolls towards said embossing'j 'rolls; said pressure-exerting rolls being formed vvith a slight crown to assist in render-' ,ing the loaded side thereof straight. under uniformly {distributed embossing pressure, and to J adapt said rolls to transmit embossing pressure applied to the journals thereof and distribute it file of this patent:

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