US3124504A

US3124504A - Gloss finishing of uncoated paper

Info

Publication number: US3124504A
Authority: US
Priority date: 1960-04-04
Filing date: 1960-04-04
Publication date: 1964-03-10
Anticipated expiration: 1981-03-10
Also published as: GB976194A; SE302720B; FR1278575A; DE1546304B2; DE1546304A1

Description

March 10, 1964 R. P. MAHoNr-:Y ETAL 3,124,504

f GLOSS FINISHING OF' UNCOATED PAPER Filed April 4, 1960 2 Sheets-Sheet 1 V1 y I March 10, 1964 R. P. 4MAHoNEY ETAL 3,124,504

@Loss FINISHING oF UNcoATED PAPER 2 Sheets-Sheet 2 Filed April 4, 1960 fnl/Enfr Ralf/ Ma on@ Y ya? ZJmstui W 0f M United States Patent liice r 3,124,504 Patented Mar. l0, 1964 3,124,594 GLSS FENEHENG F UNQATED PAPER Ralph l. Mahoney and Edgar l. Justus, Beloit, Wis, assignors, by niesne assignments, to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed Apr. 4, i960, Ser. No. 19,862 '7 Claims. (Cl. 162-206) The present invention relates broadly to the production of paper and related web materials and is more particularly concerned with improved methods and means for glossing uncoated paper and related uncoated web materials.

It has been customary in the prior art to employ at various locations in paper making machine equipment means to smooth and gloss the uncoated paper web. For instance smoothing presses, breaker stacks of calendering and supercalendering presses, and the calendering and supercalendering presses themselves may be employed together or separately in such paper making equipment to smooth, gloss or finish the uncoated paper web.

However, a disadvantage common to all of these smoothing devices exists as a result of the high pressures necessary to obtain the smoothing, glossing or finishing effect desired. The high nip pressures required for the above devices crush and flatten the web thereby reducing the bulk or thickness of the raw uncoated web, cause a marked variation in spot or local densities thereby producing the Well known glassy surface spots which refuse to take ink, printing, or coatings thus reducing the ink receptivity of the paper web, further affect printability in that the resilience of the paper necessary in the printing nip is decreased, and reduce opacity.

In addition to the above disadvantage, the inherent resilience of the fiber constituents of the paper stock employed cause fibers to rise out of the surface of the web after having been subjected to a smoothing, calendering or related and similar treatment. Under microscopic inspection, at least the surface of the usual paper or board has a rough appearance of a fibrous network, protruding fibers, and void spaces. As aforesaid, calendering or Smoothing press treatment does not alter this physical characteristic of paper or board to a significant extent or, on the other hand, if pressures are high enough, such treatments crush the higher surfaces into the web causing a marked. variation in local density and produce the glassy spots which refuse to take ink or'coatings.

Thus if a particular paper making machine employs a plurality of smoothing presses positioned at different locations, breaker stacks and calendering apparatus, the effect of all these pressure treatments contribute to produce an end product the thickness or bulk of which is altered considerably as a result thereof.

It will be appreciated that if means were provided to obtain a smooth, uniform leveling of at least the surface fibers of the raw or stock web and to coalesce the fibers thus leveled thereby obtaining a substantially closed or sealed surface without substantially affecting the bulk or thickness of the web, and, in addition, without crushing or damaging the thus leveled surface of the paper stock, a paper product, when dried, would be obtained which could. be employed for numerous applications heretofore considered unobtainable in the trade.

By employment of the present invention, we provide means for overcoming the difficulties and problems of the prior art and, in addition, provide means for eliminating the requirement for conventional smoothing or calendering treatments, obtaining improved web surface characteristics without the necessity for the brute force treatment of calendering devices.

It is therefore among the objects of the present invention to provide means for gloss finishing uncoated paper and related uncoated web materials.

It is another object of the present invention to finish uncoated paper and related uncoated web materials without substantially reducing the bulk or thickness of the paper stock.

It is still another object of the present invention to permanently level and to smooth the fibers in raw paper stock without substantially crushing the paper stock.

lt is yet another object of the present invention to coalesce and permanently seal or close the surface of uncoated paper web stock to a degree heretofore unobtainable without crushing of the web.

lt is a further object of the present invention to provide means for permanently sealing or coalescing at least the surface fibers of uncoated paper stock while producing a paper product of substantially uniform density.

It is still another object of the present invention to finish the surface of uncoated paper stock by improving the characteristics thereof without reducing brightness or opacity.

It is a further object of the present invention to produce paper stock having improved printability and ink receptivity characteristics.

It is a still further object of the present invention to provide uncoated paper stock surfaces which are smooth and coalesced thereby increasing the receptivity of the surfaces for ink, coatings and surface waxing.

It is a further object of the present invention to provide a method of gloss finishing uncoated paper and related uncoated web materials by contacting the uncoated surface with a finishing surface under conditions of temperature and pressure sufficient to permanently level, blend and coalesce said surface without substantially reducing the hulk of the paper material.

Yet another object of the present invention is to provide an improved method of glossing uncoated paper stock and related web materials by introducing the web into a nmrow width and hard nip defined by a non-resilient finishing roll and a resilient backing roll of high hardness under conditions of temperature and pressure suicient to level, blend and coalesce the fibers of at least the surface of the web in contact with said finishing roll without crushing said web by mechanical working of said web while in said nip.

Another object of the present invention is to provide means for gloss finishing uncoated paper web stock and related web materials which is simple and compact in construction and efficient and high speed in operation.

These and other objects, features and advantages of the present invention will become more apparent upon a careful consideration of the following detailed description, when considered in conjunction with the accompanying drawing, illustrating preferred embodiments of the concepts of our invention, wherein like reference characacters and numerals refer to like or corresponding parts throughout the several views.

On the drawings:

FIGURE 1 is a partially diagrammatic view in side elevation illustrating apparatus constructed in acocrdance with our invention for finishing and/ or for glossing one side of uncoated paper web stock;

FIGURE 2 is a partially diagramamtic view in side elevation illustrating apparatus constructed in accordance with our invention for finishing and for glossing both sides of uncoated paper web stock;

FIGURES 3A and B are broken schematic views in side elevation illustrating a plurality of finishing devices constructed in accordance with our invention for on-thepaper making machine applications;

FIGURE 4 is a schematic View in side elevation illustrating an alternate arrangement of apparatus adapted for finishing paper products; and

FIGURE 5 is an enlarged fragmentary graph illustrating the cooperative effects on web deformation of pressure and the resilient hard backing roll at the nip.

As shown on the drawings:

Briefiy stated, the present invention contemplates apparatus for imparting improved surface characteristics to and for finishing and/or glossing of uncoated paper web and related uncoated web materials comprising a first rotatable roll having a finished smooth surface, a second roll having a hard surface resiliently yieldable under pressure cooperating with said first roll to define a hard, narrow width nip, means for maintaining said nip at a temperature sufficient to heat the paper stock and coalesce at least the surface of the web in contact with said finishing surface and means for transversely and uniformly applying pressures at the nip suflicient to level, smooth and blend the surface of the web.

As appears in FIG. l, apparatus constructed in accordance with the principles of the present invention may be employed for finishing one side of uncoated paper web stock and related uncoated web materials.

In the arrangement shown in FIG. 1, the glossing apparatus may take the form of a roll 12 having a highly polished finishing surface and a pair of hard surfaced but

resilient backing rolls

13 and 14 cooperating to define a pair of hard and narrow width nips.

Backing rolls

13 and 14 may be driven by contact with the web 11 and finishing roll 12 or drive means (not shown) may be provided.

The finishing roll 12 may be constructed to provide the surface temperature required to plasticize at least the fibers in the surface of the web in the nip. For this purpose, a suitable source of heat medium may be introduced into the chamber defined by the finishing roll 12 through a conduit 15. The

backing rolls

13 and 14 may preferably comprise a metal core and a rubber cover of the required hardness for applying the pressure necessary to level, blend and smooth the plastic fibers in at least the surface of the web material while in the nip to thereby obtain the desired surface finish or gloss. The metal nishing roll 12 having a highly polished surface defines the aforesaid narrow-width hard nip with the resiliently surfaced backing roll 13 which preferably has a high hardness, less than 30 P. and I. OAS" ball). The finishing surface of the roll 12 may be plated, as with chrome or nickel, and, as aforementioned the resilient roll 13 may comprise a metal core having a rubber cover of the requisite hardness.

For particular applications and in order to obtain a smooth level surface having excellent ink receptivity and printability properties, While avoiding the high specular gloss comparable to that obtained by the cast coating methods achieved with the chrome plated or highly polished finishing surfaces, a smooth finished roll may be substituted for the highly polished

rolls

13 and 14. We have also found that the web may be immediately removed from the finishing nip without the necessity of maintaining the web in extended -contact with the finishing roll and without damage to the finish of the uncoatedy web or to the other desirable characteristics of the web.

In order to minimize the operating pressure loading of the respective rolls, it is desirable that the

resilient rolls

13 and 14 be quite hard, e.g. less than 30 P. and J. ball). Employment of a hard surface roll permits concentration of total pressure loading on a relatively narrow nip, in the direction of travel of the web, and, excellent results have been obtained when the nip is of a cross-sectional width, less than 1 inch and preferably about '1/2 inch. The development of high unit pressures in the narrow nip is desirable only below the crushing point of the Web fibers. The hard( and narrow nip assures uniform pressure loading across the entire width of the sheet. It will be appreciated of course that continued use of the nip will tend to cause the resilient or hard rubber surfaced

rolls

13 and 14 to soften slightly due to the temperature conditions existing at the nip and due to the effects of working engagement with the Web during operation. Thus to maintain the backing rolls at the desired high hardness level and thereby the nip width within the desired limits, means may be employed, if desired, to cool the resilient rolls. As will be fully appreciated by those versed in the art, this may be done in various Ways and is shown schematically in FIG. l by coolant supply lines 29a and 30a leading to the

rolls

13 and 14. For this purpose, a cooling agent may be maintained in the interior of each of the backing rolls introduced by conduit 13a.

The temperature maintained at the nip must be sufficient to induce momentarily or temporarily a condition of plasticity in the particular uncoated paper stock undergoing treatment to permit the pressure applied by the backing roll to level, blend and smooth mechanically at least the surface of the web in the nip while in the plastic state. Generally the temperature at the nip is maintained above the boiling point of water and no known upper temperature limits exist other than the decomposition of the particular stock undergoing treatment and the other materials involved. Thus any paper stock or related web stock material may be employed in the practice of the present invention. Satisfactory finishing results have been obtained for various web stock with the finishing surface of the finishing roll heated to a temperature within the range of from about 220 F. to about 400 F., although we prefer to employ temperatures within the range of from about 280 F. to about 360 F. Experience has indicated that the transversely and uniformly distributed high intensity unit pressure at the nip is preferably within the range from about 250 lbs. per sq. in. to about 2400 lbs. per sq. in., depending primarily upon the particular paper web stock involved.

Thus, in the nip, the high pressure and the high surface temperature of the finishing roll induce a condition of temporary plasticity in at least the surface fibers of the web stock and permanently level the majority of surface bers While in the plastic state thereby permitting the high pressure to coalesce the plastic fibers and thus providing a surface which is closed or sealed to an extent heretofore unobtainable, while at the same time the resilience of the hard surfaced pressure backing roll permits sufficient yielding thereof in the nip to minor web thickness inequalities whereby the bulk and opacity of the web is not materially reduced.

The above degree of resiliency in the backing roll avoids the disadvantages inherent in conventional smoothing and calendering apparatuses and methods in which spot density of the web is increased as a result of the high pressures resulting from unequal weight distribution thereby producing hard glassy spots which will not accept printing impressions. It will be noted that the unit pressures employed are significantly less than those employed in paper calendering machines and the speeds obtainable in the practice of our invention are higher than those normally found in cast coating applications.

Satisfactory finishing results are obtained at any practical operating speeds and, therefore, finishing operating speeds are limited only by the operational speeds of the paper machine itself or the web supply means and of the nip rolls. =`It will be appreciated that finishing temperatures are generally directly related to operating speeds.

If the uncoated web undergoing finishing treatment had been previously dried as for example to an atmospheric moisture content, the finished web may be immediately removed from the nip Without the necessity for permitting extended contact with the finishing roll and then wound on a reel (not shown) or, alternatively, may be permitted to remain in contact with the finishing roll for purposes of positioning the coated web in the proper manner preparatory to a second finishing treatment. It will be appreciated thatthe web fibers are only momentarily or temporarily plastic while in the nip and that,

upon leaving the nip, almost instantaneously return to their previously set or plasticized condition without any deleterious effects on the web but with a finished coalesced surface permanently leveled.

To vary the pressure `applied at the nip for finishing various web stock of different thicknesses, such as board, means therefor may take the form of a hydraulically or pneumatically operated piston assembly i6 having its piston rod 17 connected to a cross arm 1.2i` of a pair of support members 19 which carry the bearing brackets 20 for the shaft 21 of the backing roll 13. The support members 19 may be pivotally mounted to the frame support stanchion 22. Pneumatic or hydraulic operating pressures of the piston arrangement need only be increased or decreased in order to produce corresponding pressure effects on the finishing roll and uncoated web undergoing treatment.

A similar piston arrangement may be employed for controlling application of finishing pressure by the resilient roll 14 which includes a piston housing (not shown) and a piston rod 23 mounted on the cross arm of a pair of support members 24 which carry the bearing brackets 25 for backing roll 13. Support arms 24 may be fulcrumed to a clevis 26 which is mounted on the frame stanchion 27. By employment of a pair of support members 24 uniformly transverse pressure is applied at the nip.

Thus, in operation, the uncoated web is introduced into the hard, narrow-width nip defined by the finishing roll l2 and backing roll 13 with the surface of the web to be finished in Contact with the finishing roll.

Depending upon web moisture content, the finishing roll surface is heated to a temperature substantially above the boiling point of water for high moisture content webs, and, in any event, to a temperature sufficient to induce a condition of plasticity in at least the contacting surface fibers of the web to thereby cause the fibers to become coalesced, and the cooperating pressure applied assists in leveling and smoothing the surface of the web. The surface fibers of the web are displaced and blend the irregularities of the original surface into a smooth, closed or sealed, and finished level surface. The yielding characteristics of the backing roll 13 prevents crushing of the web and cooperates with the temperature and pressure conditions at the nip to permit leveling and finishing of the web surface while avoiding or preventing reduction in bulk or thickness by crushing of the web. Thus improved surface characteristics may be imparted to an uncoated or raw web by employment of the finishing roll and backing roll under the conditions aforementioned.

After leaving the finishing nip defined by finishing roll 12 and backing roll 13, the web may be immediately removed from the nip or alternatively may be permitted to remain in contact with the finishing roll for introduction thereof into a second finishing nip defined by finishing roll 12 and backing roll 14 for a second finishing treatment. Finishing roll 14 is similar in construction and operation to backing roll 13. The temperature and pressure conditions at the second nip are similar to those employed at the first nip and the finished surface of the web may then undergo a second finishing treatment therein.

In the arrangement shown in FIG. 4, the web may be immediately removed from the first nip and led around a pair of fiy rolls 30 and 31 for subsequent introduction of the web to the second nip defined by rolls l2 and 14. Employment of fly rolls 30 and 3l is made possible since the finished web surface is only temporarily plastic in the nip and upon removal therefrom immediately sets without interruption or damage to either the web or finished surface.

Afterleaving the second nip, the web may be then fed over a guide roll 32 to be wound on a reeler (not shown) if the uncoated web had been previously dried, or may be carried over a plurality of guide rolls if the apparatus above described is substituted for smoothing presses, breaker stacks or calendering sections for the paper making machine applications.

As appears in FIG. 2, an alternate arrangement may be provided for on or off .the machine finishing of both sides of uncoated paper stock. lIn this arrangement, the web is fed over a guide roll for introduction thereof into the narrow-width and hard finishing nip defined by the heated finishing roll 33 and backing roll 34. ARolls 33 and 34 are identical in construction and operation to rolls `12 and 13, respectively, of FIG. 1. The web is introduced into the nip with an uncoated surface in contact with the nishing surface of roll 33.

The surface fibers of the web in contact with the finishing surface of roll 33 are temporarily or momentarily rende-red plastic and finished while in the nip. Upon leaving the nip, the fibers of the finished surface of the web immediately set or become hardened and immobile and, if desired, may be permitted to remain in contact with the finishing roll to -be introduced into a second glossing nip defined by finishing roll 3-3 and a second resilient backing roll 35 which is identical in construction .and operation -to backing roll 34.

Alternately, the apparatus appearing in FIGURE 4 may be employed wherein the web is introduced into a first nip dened by roll A14 and nishing roll 12, traverses a pair of fly rolls 30 and 3l yfor introduction into the second nip `defined by rol-

ls

13 and 12 whereby one side of the web is finished. The web may then be introduced into a second nip dened by Ia backing roll 14a and `finishing roll 12a, guided around fiy rolls 30a Iand 31a for introduction of the same side of the web 4into a second finishing nip defined by backing roll 13a and finishing roll 12a, whereby ythe other side of fthe web may be finished.

Means are provided for varying the pressure applied by rolls 34 and 35 and may take the form of a hydraulically or pneumatically operated bellows arrangement 36. The end cover 37 of the bellows arrangement may be connected to a movable link 38 which is pivotally connected at one end to an 39 fulcru-med to` the bearing of the shaft 40er roll 34. Arm 39 is `connected at the other end `to a lbracket 41 mounted on the frame stanchion 42. Similarly, the end plate 43 of the bellows arrangement may be connected to a movable link 44 which is pivotally connected to a member `45 fulcrumed to the bearing of shaft 46 of backing roll 35. Arm 45 yis pivotally connected to a bracket 47 mounted on the machine frame member 42. Similar arm, link and bracket assemblies (not shown), connect the bellows arrangement to the opposite sides of rolls 34 and 35 to obtain equal distribution of pressure transversely across the hard, narrowwidth nip. Thus, as pressure in the bellows is increased, the |bellows expand and rolls 34 and 35 will exert greater pressure against the nishing roll 33. Conversely, when pressure is decreased in the bellows, the bellows contract and less pressure is exerted by backing rolls 34 and 35 on finishing roll 33. It Wil-l be appreciated, however, that any conventional means may be employed to vary pressure application by either one or a pair of backing rolls depending upon the glossing arrangement adopted. The temperature of the finishing surface of roll 33 is of course substantially above the boiling point of water in all cases land is sufiicient to induce a condition of plasticity in the uncoated web stock undergoing treatment and the pressure `applied is sufficient to finish the surface contacting the finishing roll.

Therefore, depending upon the particular rheology of the particular raw web stock undergoing treatment, simple and effective means are provided to vary the pressure necessary to level, smooth land finish the desired surface in the nip. Roll 35 is similar in construction and operation to roll 34.

After leaving the hard, narrow-width nip defined by

rolls

33 and 34, the fibers in at least the finished surface of the web are permanently leveled and coalesced and the web may now be fed around guide rolls 49 and 50 for introduction of the uncoated web into a similar hard, narrow-'width nip defined by ra finishing roll 51 and a hard backing roll 52 resiliently yieldable under pressure for finishing the unfinished side of the paper Web. An additional finishing treatment may be given this second side, if desired, in a similar nip defined by finishing roll 51 and a backing roll 53. Finishing roll 51 may be similar in construction and operation to finishing roll 33, and, likewise, backing rolls 52 and 53 may be similar in construction and operation to backing roll 34. Means 54 similar in construction and operation to means 36 may be employed to vary the pressure applied by backing rolls 34 and 35, respectively, Ias shown.

In treating and finishing both sides of an uncoated web stock, We have found that it is unnecessary to treat first the preferred side (usually that which was not in contact with the forming wire), since the first side to be glossed and/or finished does not lose any of the gloss and/ or finish during the subsequent glossing and/.or finishing of the second side. Nor are any of the other desirable characteristics of the web materially or substantially affected. Thus finishing and/or glossing of the second side of the web occurs without disruption of or material damage to the initially finished and/or glossed surface when leaving the finishing nips.

'The web with both sides now finished may then traverse one or more guide rolls (not shown) and may be taken off the paper making machine for storage if the web had been pre-dried to a marketable moisture content prior to the finishing treatment or, may be carried to the next stage in the paper treatment process -for ion the paper making machine applications.

It will be appreciated that embodiments of our invention may be used advantageously for a variety of on or off the paper making machine purposes. For example, the finishing treatment may be performed on either one or both sides of an uncoated raw or lbase stock web which had been dried to a marketable moisture content and the Web then coated on one or both sides in any conventional manner with standard coating apparatus. After having been thus coated, the coated web may next be dried to the final moisture content and stored for subsequent disposition. In addition, the dried coated web may thereafter be glossed on or off the paper making machine in Iany conventional manner. The concepts of our invention further contemplate finishing uncoated raw or base stock web while of a moisture content less than 50%, drying of the web to a marketable moisture content followed by printing of the uncoated dried web and glossing thereof lafter printing, and, alternately, coating of the dried Web, drying of the coating, printing of the dried coated web and thereafter glossing of the printed web.

For on the paper making machine applications, apparatus as shown in FIGURES 1, 2 or 4 may be employed, either separately or in combination, to perform the functions of smoothing presses, breaker stacks and calendering sections resulting, however, in finished uncoated webs with substantially uniform densities and without substantial reduction in the bulk or thickness thereof.

Such apparatus may be positioned at any suitable location in the dryer section, and, when so employed, is preferably located in a position where the raw or base stock paper is introduced into the finishing nip With a moisture content generally less than 50%. For most grades of paper the stock at this moisture level is sufficiently integralto undergo a finishing treatment since the relative volume of water and fiber in the compressed condition is adaptable to such treatment. Thus, the choice of the most suitable location in the dryer section of the apparatus depends primarily upon the moisture content of the raw or base stock paper and the grade and weight of the stock to undergo the finishing treatment.

Experience has indicated that the finishing apparatus may be advantageously employed not only as a substitute for smoothing presses in the dryer section but'at any location in the paper making machine where the particular paper stock is of a moisture content from 0 to about 50%, preferably less than about 35%.

For on the paper making machine application where our apparatus may be employed in both the dryer section and in the calendering section, the degree of finish of the web may be increased progressively by finishing the web surface or surfaces while of progressively lower moisure content at different stages in the paper f0rrna= tion process.

As exemplified by the apparatus in FIG. 3 (a and b), the devices of FIGS. 1, 2 and 4 may be employed for on the paper making machine applications.

Paper stock slurry may be supplied from a conventional stock formation housing 515 to any suitable Fourdrinier Wire traversing breast roll 56 and couch roll S7. The paper stock is then conveyed by transfer felts 53 and 59 through a pair of press roll couples 60 and 61, and, if desired, then through a smoothing press 62 for introduction thereof into the dryer section, generally indicated by the numeral 63.

For purposes of illustration, finishing apparatus 64 similar in construction and operation to the apparatus appearing in FG. 2 has been shown. The most suitable location of the finishing apparatus 64 in the dryer section of a paper making machine depends, as aforesaid, to a large extent upon the grade and type of paper stock undergoing the finishing treatment as well as the moisture content level, and may be substituted for a smoothing press in which case the web will generally be at a moisture content of about 35%. Additional finishing devices may be employed elsewhere in the dryer section for progressively finishing one or both sides of the raw or base stock web in subsequent locations where the moisture content of the web stock is less than that present when the stock undergoes the first finishing treatment. The raw or base stock web, upon leaving the last nip 65 then traverses the remainder of the dryer rolls in the dryer section.

With' conventional paper making machine equipment, the web upon leaving the dryer section, is usually introduced to a calendering section for final finishing treatment of the uncoated stock and, the stock, having been calendered, is either then wound on a reel for subsequent disposition or, if employed, is coated on the machine with any standard coating apparatus.

By employment of our invention, apparatus of FIGS. 1, 2 or 4 may be substituted for the conventional calendering stacks and, for purposes of illustration, apparatus similar in construction and operation to that of FIG. 1 is shown. Thus as the dried web stock leaves the dryer section with a moisture content normally required for calendering, depending upon the particular roll or base stock involved, the web may be fed into our apparatus 66 for a finishing treatment at this moisture content level. With both sides of the uncoated stock now having been subjected to a finishing treatmentq the web may be fed to a winding reel 66a for subsequent disposition.

If on the other hand, coating apparatus is employed with the paper making equipment, the web, upon leaving the finishing section which was substituted for a calendering device, may be introduced into the coating apparatus 67 and dried thereafter by any conventional dryer means 63 and the coated surface thereafter subjected to a finishing treatment by employing apparatus 69 constructed in accordance with our invention. The web, with either one or both of its sides now glossed may thereafter be fed to a reel (not shown) for subsequent disposition. In addition, we have found that if a conventional calendering treatment is desired, the apparatus of our invention may be substituted for the conventional calendering breaker stacks.

An important feature of the present invention resides in the improved contact with the heated surface of the 9 finishing roll thereby enhancing and promoting drying of the raw or base stock web made possible by the temperature and pressure conditions existing at the nip and the cooperative action of the hard surfaced backing roll.

Thus it will be appreciated that an uncoated raw or base stock web may be subjected to finishing treatments at various locations on paper making equipment while at various moisture content levels to thereby obtain gloss finishes on uncoated web materials without materially reducing the bulk or thickness of the web and producing finished products which are adaptable for many applications heretofore unobtainable with conventional smoothing and calendering treatments.

It is to be understood that if the uncoated web material to be finished in accordance with the practice of our invention had been predried to a marketable moisture content (usually from 92% to 95% bone dry) or to an atmospheric moisture content, the finishing surface may be heated to a temperature sufficient to render the uncoated surface of the web plastic in the nip, whereas, if the moisture content of the web is materially higher, the finishing surface is heated to a temperature above the boiling point of water to assist in drying of the web since, at higher moisture levels, the finishing apparatus will be normally located in the dryer section.

In general, the heat and pressure in the hard, narrow nip should be controlled to conform the surface being finished to the surface of the finishing roll without crushing the web and under conditions which accommodate removal of the web without disturbing the conformed web surface. Usually, tolerable moisture contents are lessened with increases in either nip temperature or nip pressure and enlarged with increases in basis web weight. Additionally, the lower the moisture content, the higher the degree of finish, and the gloss finish is progressively pronounced within the range of web moisture content from about to zero.

FIGURE 5` presentsfa graphical illustration of the combined influence on paper web material deformation of the pressure applied at the nip and the resilient yielding characteristics of the hard backing roll. Under microscopic examination, the web W is of varying cross-sectional thickness, as shown exaggerated in FIGURE 5, consisting of surface peaks of higher density and valleys of lower density. The valleys, of course, contain fibers and fibrils; however, the density of the web at the valleys is less than the density of the web at the peaks.

Conventional calendering operations, wherein high pressures are applied to the web, have an effect on web density and thickness which differs from the effect of the nip conditions of the present invention which permits lower pressures to be applied to the web in the hard narrow nip.

The curve A in FIGURE 5 illustrates the characteristic deformation of the web caused by the high pressures applied when conventional calendering apparatus is employed. The calendering pressures cause the greatest deformation of the web W at the peaks P and the least deformation of the web at the valleys V. The web W is shown in FIGURE 5 as having peaks and valleys of equal and sequential height and depth for purposes of clarity only; however, it will be appreciated that the peaks and valleys are, in fact, of irregular heights and depths. The deformation of the web caused by the high pressures applied in calendering operations at the peaks result in the hard glassy spots aforementioned which refuse to accept ink or print.

However, by employment of our invention, the other conditions at the narrow nip, defined by the finishing roll 12 and the hard resiliently yieldable backing roll 13, cooperate to permit employment of lower pressures than those used in conventional calendering treatments and result in lesser web deformation. In addition, the lesser web deformation results in a more uniformly finished web surface.

As shown in curve 3, the resilient backing roll 13 yields at the peaks P1 to an extent causing less web peak deformation and also less web Valley deformation than that caused by the conventional calendering treatments in the valleys Vb thus resulting in an overall smoother leveling of the web surface being finished. It will be appreciated, therefore, that the provision of a resiliently yieldable backing roll cooperating with the other nip conditions of the present invention permit uniform deformation and leveling of the web surface to a degree unattainable by employment of conventional calendering treatments,

It is also apparent that the magnitude of the deformation of the backing roll is large only with regard to the thickness of the web being finished. Likewise the magnitude of deformation of the backing roll is small in the transverse direction to insure maintenance of the hard, narrow nip l"), at high unit pressures.

As used herein, the term dried is to be understood to mean the web is dried sufiiciently within the ranges herein specified so as not to adhere to the non-resilient finishing surface while in the nip.

As used herein, the term polished refers to the treatment of the non-resilient finishing surface to render the surface smooth, and the surface may be mirror-finished or polished to a matte or like surface.

Although various minor modifications might be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent warranted hereon all such embodiments as reasonably and properly come within the scope of our contribution to the art.

We claim as our invention:

l. A method of making a finished glossed paper web comprising removing moisture from a moist web to reduce the moisture to a dryness of less moisture than 35% moisture, and immediately passing the web through first and second high pressure nips each formed between a heated smooth non-resilient roll and a roll having a surface of resilient plastic material having a high hardness heating the web in the nips and applying pressure to the heated web to plasticize the surface fibers of the web and coalesce the surface fibers and to further effect drying with the surface of the non-resilient roll, engaging one surface of the web in the first nip with the surface of the non-resilient roll, engaging the other surface of the web in the second nip with the surface of the non-resilient roll to finish both sides of the web, and guiding means separating the web from the surface of the heated roll of each nip substantially immediately following the nip.

2. The method of making a finished glossed paper web comprising continuously forming a travelling paper web on a Fourdrinier section of a paper machine, removing moisture from the web in a press section and a dryer section of the machine to a dryness of less than 35 moisture and immediately passing the web through a high pressure nip formed between a heated smooth non-resilient roll heated to a temperature between a lower limit of 220 F. and an upper limit up to the decomposition point of the web and a roll having a surface of a resilient material with a high hardness for heating the web in the nip, and applying pressure to the heated web in the nip in the range of 250 pounds per square inch to 2400 pounds per' square inch to plasticize the surface fibers of the web and coalesce the surface fibers and to further effect drying.

3. A method of making a finished glossed paper web comprising removing moisture from a moist web to reduce the moisture to a dryness of less than 35% moisture, and immediately passing the web through a high pressure nip formed between a heated smooth non-resilient roll heated to a temperature between a lower limit of 220Q F. and an upper limit up to the decomposition point of the web and a roll having a surface of resilient material with a high hardness for heating the web in the nip, and applying pressure to the heated web in the nip in the range of 250 poundsrper square inch to 2400 pounds per square inch to plasticize the surface fibers of the web and coalesce the fibers.

4. In a mechanism for making a finished glossed paper web having a supply means for providing a moist paper web and having drying means for receiving the travelling web from the supply means, and for at least partially removing the moisture from the web to a dryness of less than 35% moisture, a surface finishing apparatus positioned after said drying means comprising a first roll having a smooth precisely finished non-resilient surface, a second roll formed of a metal core and an outer cover of resilient material of high hardness being in nip-defining relationship With the first roll, heating means for heating the surface of the first roll to plasticize the surface fibers of the web and coalesce the fibers and effect further drying, means forcing the rolls together forming a transversely uniformly distributed high intensity unit of pressure in the nip, a third roll formed of a metal core and an outer cover of resilient material of high hardness being in nip-defining relationship with said first roll at a location to form a second nip substantially diametrically opposed from the first nip, and means forcing the third roll against the first roll forming a transversely uniformly distributed high intensity unit of pressure in said second mp.

5. In a mechanism for making a finished glossed paper web having a supply means for providing a moist paper web and Yhaving drying means for receiving the travelling web from the supply means, and for at least partially removing the moisture from the web to a dryness of less than 35% moisture, a surface finishing apparatus positioned after said drying means comprising, first and second high pressure nips positioned for receiving the web from said drying means and each including a first large diameter roll having a smooth precisely finished non-resilient surface, and a second roll of smaller diameter formed of a metal core and a relatively thin outer cover of resilient material of high hardness being in nip-defining relationship with the first roll, heating means for heating the surface of the first roll to plasticize the surface fibers of the web and coalesce the fibers and further effect drying, and means forcing the rolls together forming a transversely uniformly distributed high intensity unit of pressure in the nip, said nips arranged so that one surface of the web will be engaged by the first roll in the first nip and the opposite surface of the web will be engaged by the first roll in the second nip to smooth both sides of the web.

6. In a mechanism for making a finished glossed paper web having a supply means for providing a moist paper web and having drying means for receiving the travelling web from the supply means, and for at least partially removing the moisture from the web to a dryness of less than 35% moisture, a surface finishing apparatus positioned after said drying means comprising a first roll having a smooth precisely finished non-resilient surface, a second roll formed of a metal core and an outer cover of resilient material of high hardness being in nip-defining relationship with the first roll, heating means for heating the surface of the first roll to a temperature in the range of from a lower limit of 220 F. to an upper limit of the decomposition point of the web to plasticize the surface fibers of the web and coalesce the fibers and effect further drying, and means forcing the rolls together forming a transversely uniformly distributed high intensity unit of pressure in the nip in the range of 250 to 2400 pounds per square inch.

7. In a mechanism for making a finished glossed paper web having a supply means for providing a moist paper web and having drying means for receiving the travelling web from the supply means, and for at least partially removing the moisture from the web to a dryness of less than 35% moisture, a surface finishing apparatus positioned after said drying means comprising a first roll having a smooth precisely finished non-resilient surface, a second roll formed of a metal core and an outer cover of resilient material of high hardness of less than 30 P. and J. (l/s" ball) being in nip-defining relationship with the first roll, said second roll being smaller than said first roll and forming a narrow nip therebetween, heating means for heating the surface of the first roll to a temperature in the range of a lower limit of 220 F. to an upper limit of the decomposition point of the web to plasticize the surface fibers of the web and coalesce the fibers and further effect drying, and means forcing the rolls Vtogether forming a transversely uniformly distributed high intensity unit pressure in said nip in the range of 250 to 2400 pounds per square inch.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Pulp and Paper Manufacture, vol. 23 (1953), McGraw-Hill, N.Y., pp. 275 and 511-517 relied on.

Manufacture of Pulp and Paper (3rd ed.), vol. V, McGraw-Hill (1939), N.Y., pp. 2 and 3 of section 1; pp. 16 to 26 of section 3 relied on.

Claims

2. THE METHOD OF MAKING A FINISHED GLOSSED PAPER WEB COMPRISING CONTINUOUSLY FORMING A TRAVELING PAPER WEB ON A FOURDRINIER SECTION OF A PAPER MACHINE, REMOVING MOISTURE FROM THE WEB IN A PRESS SECTION AND A DRYER SECTION OF THE MACHINE TO A DRYNESS OF LESS THAN 35% MOISTURE AND IMMEDIATELY PASSING THE WEB THROUGH A HIGH PRESSURE NIP FORMED BETWEEN A HEATED SMOOTH NON-RESILIENT ROLL HEATED TO A TEMPERATURE BETWEEN A LOWER LIMIT OF 220*F. AND AN UPPER LIMIT UP TO THE DECOMPOSITION POINT OF THE WEB AND A ROLL HAVING A SURFACE OF A RESILIENT MATERIAL WITH A HIGH HARDNESS FOR HEATING THE WEB IN THE NIP, AND APPLYING PRESSURE TO THE HEATED WEB IN THE NIP IN THE RANGE OF 250 POUNDS PER SQUARE INCH TO 2400 POUNDS PER SQUARE INCH TO PLASTICIZE THE SURFACE FIBERS OF THE WEB AND COALESCE THE SURFACE FIBERS AND TO FURTHER EFFECT DRYING.