US3149025A

US3149025A - Manufacture of cellulosic product

Info

Publication number: US3149025A
Authority: US
Publication date: 1964-09-15
Anticipated expiration: 1981-09-15

Description

Sept. 15, 1964 w. A. DICKENS 3,149,025

MANUFACTURE OF CELLULOSIC PRODUCT Filed Jan. 29, 1962 3 Sheets-Sheet 1 Sept. 15, 1964 w. A. DICKENS MANUFACTURE OF CELLULOSIC PRODUCT 3 Sheets-Sheet 2 Filed Jan. 29, 1962 Sept. 15, 1964 w. A. DICKENS 3,149,025

MANUFACTURE OF CELLULOSIC PRODUCT Filed Jan. 29, 1962 3 Sheets-Sheet 3 m. 59 so I 21 2 2 IL 26 55 soe5 70 75 -80 8:5

CONSISTENCY AFTER FIRST DRYER 7 7'0 28 BASE SHEET g 4.0 k 0: 3.0 A \CAITENDERED, COATED, 2.0 SUPER CALENDERED I- LI. g m M PW I C|OATED,

0 SUPER CALENDERED o 2 3 4 5 6 7 a 9 COAT WEIGHTUbsJREAMXCIS) United States Patent 3,149,025 MANUFACTURE 9F CELLULOSEC PRODUCT William A. Dickens, Neenah, Wis, assignor to Kimberly- Ciark Corporation, Neenah, Wis, a corporation of Delaware Filed lian. 29, 1962, Ser. No. 169,497 2 Claims. (Cl. 162-406) This invention relates to the manufacture of paper Webs and is particularly directed to the attainment of bulk and the control of the surface characteristics of such webs for use in uncoated applications such as newspaper, or in coated form for book and magazine purposes.

In the making of paper employing the usual Fourdrinier machine, the side of the web in contact With the wire during web formation usually acquires a wire mark; in the web-forming operation water draining from the fibers through the wire tends to carry fines from the wire side of the web leaving the lower web surface deficient in this respect, occasioning the wire mark, and causing the character of opposite sides of the web to differ in smoothness, gloss characteristics, printability, and the like. This wire side is normally the rougher side and usually requires a different coating application in bookpaper production than does the felt side if tWo-sidedness is to be avoided in the product. Thus, different coating compositions or the application of different coat weights to the opposite sides of the web is frequently required to achieve suitable wire side printability corresponding to the printability of the felt side.

In one conventional form of paper making machine a freshly formed web of paper is passed in wet condition sequentially from the Fourdrinier or forming wire of the papermaking machine through presses, smoothing rolls, and an extensive battery of dryers with or without a breaker stack until the web is substantially dry; such webs commonly exhibit the wire mark noted above and various special expedients have been employed in papermaking procedures to minimize the effect of such mark.

In an alternate method of paper production a Fourdrinier wire machine may have associated with it a dryer in the form of a large drum commonly termed a Yankee dryer. Papers, designated glazed papers, are made on such machines, and the glaze is imparted by contact of the paper with the smooth surface of the Yankee dryer; auxiliary presses and predryers frequently precede the Yankee dryer in order that some of the Water may be removed from the web prior to application to the Yankee, where drying is normally completed, one side of the paper web being glazed. Generally, the paper web is itself relatively thin, as in tissue paper formation, or glazing of opposite sides is not accomplished or necessary, as in the production of label, plastic coated and specialty papers being formed in this manner. In such instances the wire mark while present is of lesser importance and is tolerated.

However, where paper is to be printed on its opposite sides, either with or without a coating thereon, a smooth surface which reproduces tone value well, which responds smoothly to the printing operation and which is not affected by show through, is required. Further, these characteristics are particularly desired in relatively light basis weight sheets which may be produced without exceptional attention by paper machine operators on equipment of relatively low capital cost, and without intricate specialized procedures.

Thus, this present invention contemplates the provision of a novel method of controlling the surface characteristics on opposite sides of a paper web of a Weight which is satisfactory for newsprint or bookpaper.

A particular object of the invention is the provision of a method for the production of paper webs having a 3,149,025 Patented Sept. 15,1964

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controlled surface smoothness on each of its opposite sides and wherein the surface smoothness of opposite sides may be substantially the same.

An important object of the present invention is to provide amethod of producing a paper web of improved bulk as compared to other papers having an equivalent surface finish or smoothness; to provide a paper web having opposed smoothed sides but in which the web has a high opacity and good printing characteristics even for newsprint use.

Yet another object of the invention is to provide a method of producing a paper web having on each of its opposed sides a surface finish which is readily receptive to the usual paper coating compositions commonly employed in the bookpaper field, and which surface finish characteristics are such that one coating composition may be employed to provide a finished coated sheet having the same characteristics on opposite sides.

Still another object of the invention is to provide a novel method of producing a paper web which may be coated and supercalendered without undue loss of bulk, opacity, and brightness.

A further object of the invention is to provide a novel method of producing a paper web having surface characteristics of such smoothness and coating composition receptivity that calender or breaker stack action is not required prior to application of the coating composition.

I have discovered that the foregoing and other allied objects of the invention may be achieved by presenting the wire side of a formed web first to a Yankee dryer in a moist but mechanically dewatered state and controlling the conditions and extent of drying on the Yankee dryer to such degree that the web leaving this Yankee dryer will be surface smoothed and yet will conform to and be smoothed on the felt side by suceeding drying equip ment, preferably in the form of a second Yankee dryer. For this purpose I have found that with light basis weight webs of about 24 to 30 pounds (25 x 38 x 500 sheets) the web presented to the first Yankee dryer should have a consistency of at least 40% and up to about 46%. The nature of the base sheet, machine speed, pressure of the web on the first Yankee dryer, and dryer temperatures influence the strength, smoothness, bulk, opacity, and printing receptivity of the dried web removed from the noted drying equipment.

The surface smoothness of such webs, on each side, is such that breaker stack action prior to coating is not necessary. Accordingly, the bulk of the paper is not diminished by an ironing action of the breaker or calender, and the bulk of the sheet or web passing to the coaters is greater, providing it with a desirable receptivity for the coating composition. This improved bulk with respect to conventional paper, coated or uncoated, is an important factor in providing an improved surface condition for the reception of ink. While the paper may be ca l endered after coating, such calendering action is at the expense of some loss in the bulk improvement. Thus, while printing may be affected slightly due to bulk loss on calendering, the printing is nevertheless superior to that achieved with more conventional drying and coating processes because of improvement in the web surface itself and web bulk; for example, wire marks are substantially eliminated, materially improving the wire side printability and permitting it to be at least substantially of the same quality as felt side printability.

There is accordingly achieved by the practice of the invention control of surface smoothness on both sides of the uncoated base sheet to levels Which yield equivalent uncoated and coated sheet printing properties. Thus, the smoothness of the Wire side may even be higher than that of the felt side, a factor which offsets the normally or occurring printing disadvantages due to lack of fines on the wire side.

The finish of the side first presented to a Yankee dryer drum, the wire side, it has been found, increases almost linearly with the amount of drying effected through the first dryer; or, stated somewhat differently, the consistency of the sheet leaving the first Yankee dryer governs the surface finish of both sides of the sheet but is of particular importance in connection with the wire side. The felt side finish is more constant than that of the wire side. As will be evident more particularly in connection with graph data presented hereinafter, it is now possible, as noted above, to control the finish or surface smoothness of each side, through moisture control, to achieve desired finish conditions including equivalent surface finishes on opposite sides of the web.

The term finish where employed in this specification and appended claims will be understood to mean the gloss of the paper surface as measured with the Ingersoll glarimeter. (See TAPPI standards T424lvf-52.)

The completion of drying, effected on the felt side, following the first necessary Yankee dryer, may be on conventional drying equipment or on a second Yankee. The latter conserves machine space and is more economical equipmentwise. Smoothing of the felt side is less critical, and the felt side itself is less sensitive to change than the wire side. This is occasioned, at least in part, by the fact that the web after leaving the first Yankee dryer has a moisture content in the range of 25-40%, which is sufficient to insure both conformity of the web with the felt side dryers and some smoothing under pressure on these dryers, but is insufficient to affect fiber lay over a wide range.

The moisture content of the partially dewatered web at the inlet to the first Yankee dryer is an important consideration for the sheet must have sufficient strength at this stage for application to the Yankee while yet having sufiicient moisture content that it is pliable. In general, a sheet or web having a moisture content entering the first Yankee of 54-60%, that is, a web consistency of 46-40%, has been found suitable for webs having a basis weight in the 24-30 pound range (500 sheets 25" X 38"). In general, for the preferably somewhat more dry and somewhat less heated than a similar web applied to a Yankee dryer in a process wherein the Web is completely dried and glazed on the single Yankee.

The coating of the web produced in accordance with this invention may immediately follow the complete drying of the web and on the papermaking machine. ternatively, coating may be applied in an off-the-machine process following windup of the web. In either event, the coating customarily is an aqueous mineral coating compo sition of a kind well known in the art. Important to the coating procedure is that, since the uncoated web may have equivalent coating-receptive sides, the coating material and the mode of its application may be the same for each side.

The sheet or web formed in accordance with this invention has particular application and advantages in connection with printed matter, and in fact, in any area where mailing or shipping costs are involved. This is for the reason that a sheet, some to lighter in weight, may now be produced While yet such sheet has the necessary opacity and printing characteristics of heavier Webs.

The invention will be more fully understood by reference to the following detailed description and accompanying drawings wherein:

RIG. 1 illustrates essential components of a papermaking machine for effecting machine smoothing of opposite sides of a traveling web in accordance with a preferred embodiment of the invention;

FIG. 2 illustrates coating equipment for use in combination with and following the equipment of MG. 1, the provision of a supercalender being optional:

practice of this invention the web is FIG. 3 is a graph illustrating the relationship of surface finish of the paper to the consistency of the sheet leaving the first dryer; and

FIG. 4 is a graph illustrating the relationship of cost weight to wire side printability for a base Weight sheet of 28 pounds.

In the drawings corresponding numerals designate similar parts where convenient.

Referrin. initially to FIG. 1, the numeral 1 designates a paper web of about 28-pound basis weight (25" x 38" x 500 sheets, uncoated) which, as illustrated, is being formed on the usual Fourdrinier wire 3 in conventional manner. One supporting guide roll of the wire is designated at 4. The couch roll of the Fourdrinier is indicated at 5 and is provided with a steam shroud 7; and a vacuum box is designated at 9. Steam shroud '7 at the couch tends to assist moisture removal from the traveling web.

The wet web leaving the Wire is self-supporting and is transferred as shown to the first press section 11 from the wire 3. This press section includes guide rolls 13 and wringer rolls 15 for the carriage of the felt 16; the press rolls are designated 17, 19. The press roll 17 is suitably a suction roll while the upper roll 19 is solid. The web is directed beneath a press felt steam shroud 2t) and between the press rolls 1'7, 19.

The partially dried web leaving the press rolls 17, 19 is readily passed to the second press section 21, which includes the felt 22, the guide rolls 23, suction boxes 24, and the upper and lower press rolls 25, 27; the lower press roll 27 is suitably solid.

From the second press section the web 1 is directed on guide rolls 29, 31 toward the nip 33 adjacent the web entrance to the first Yankee dryer drum 35.

A felt 37 carried on guide rolls 3? passes over pressure roll 41 which, with the first dryer drum, forms the nip 33. It is essential that, at this nip 33, the sheet has a consistency of at least about 40%. Too much water at the nip will cause reslurrying of the fibers and crushing of the sheet. Too dry a sheet will result in lack of adherence to the dryer, doubling over in the nip, and sheet rupture. This Yankee dryer is eight feet in diameter and is driven at a surface speed which is that of the web. Yankee dryers conventionally have a size between about 8 and 15 feet in diameter. The rubber-covered solid steel pressure roll 41 is driven by means (not shown) and operates at a pressure on the first drum of at least about 300 pounds per lineal inch in order to firmly urge the traveling sheet to the dryer drum surface. This drum surface is suitably polished to provide optimum high smoothing. This Yankee drum dryer 35 is steam heated internally, and the temperature of operation is maintained to provide desired drying of the traveling Web. The drum rotates in the same direction as the sheet travels; in fact, the sheet is adhered to the surface of the first dryer. The amount of drying obtainable on this dryer is limited by tendency of the web to flare away from the dryer surface before its normal release point if the temperature of operation becomes too high.

Cleaning doctors 42 engage the drum 35 well down on the drum, and the normal release point precedes these doctors.

From this first dryer drum 35 the sheet or Web 1 is stripped by guide rolls 43, spread by Mt. Hope roll 43A, and passed to the nip 44 of the second dryer 45 formed with the inlet pressure roll 47. Inlet pressure roll 47 exerts a pressure on the web and is of benefit in controlling and effecting felt side smoothness.

Web 1 is retained in contact with the surface of the second Yankee drum by felt 49 which is itself supported on guide rolls 51 as indicated. The felt and roll 47 are driven at substantially web speed by means (not shown) in the direction indicated by the arrows. This felt is not essential to operation but is an aid in retaining relatively dly webs on the second dryer drum and is of assistance in securing optimum drying of the felt side of '5 the web. The felt greatly increases the drying rate on the second dryer by holding the web in intimate contact with the hot surface.

The second drum has a polished surface and is suitably also at least eight feet in diameter; this drum is steam heated internally and, like the first dryer drum, rotates at a speed such that the surface speed is about that of the web. This speed is slightly greater, about 1% greater than that of the first drum to compensate for elongation or stretching of the web as it passes to the second drum. The heating conditions are such that the moisture content of the paper web leaving this second dryer drum is approximately depending upon ambient conditions, the web being suitably dry for passage directly to a coating device (FIG. 2) when coating is desired. Alternatively, the web may be passed over guide rolls 52 and reeled at 53.

In one specific embodiment of the invention, the web 1 had a basis weight, uncoated, of about 28 pounds (25" x 38" x 500 sheets) and was formed of 55% groundwood, 25% sulfite, and 20% long fiber kraft pulp. This web was produced at a speed of about 700 feet per minute on the wire 3 and the moisture content of the web leaving the wire was approximately 80%, that is, a Web consistency of about 20%. The wire and web had a deckle width of about 30 inches. The couch shroud 7, which provided dry steam at a flow rate of about 300 pounds per hour per deckle foot to the Web at the couch roll, facilitated water removal from the web by reducing the viscosity and surface tension of the water in the Web, permitting the water to be drawn out relatively readily.

The steam shroud at 20 served a purpose similar to the couch shroud 7 and provided dry steam to the web on the felt 16 at a flow rate of about 200 pounds per hour per deckle foot. Thus, at the first press the cooperating rolls 17, 19 were effective to materially further reduce the web moisture content, the rolls 17, 19 exerting a -relatively high pressure on the heated web of about 200 pounds per lineal inch.

Press rolls 25, 27 also exerted a relatively high pressure of about 200 pounds per lineal inch on the web, further reducing the water content. Roll 27 was a solid roll, thus constituting a plain press, in order that the moisture content of the web be made more uniform and that suction hole marking be avoided before the web was applied to the dryer.

The press sections were effective to reduce the web moisture content to about 54 to 60%, that is, about 1.17 to 1.50 pounds of water per pound of fiber. It is desirable to control the moisture content of the web as it leaves the press sections and enters on the first Yankee dryer drum. For this purpose water removal between the wire and the end of the press sections is relatively severe. However, other modes of decreasing the water content of the web, such as predryers, may be employed and utilization of the steam shroudsis not required for satisfactory operation and results.

It is important that, as the sheet enters the nip between the first Yankee drum 35 and the pressure roll 41, the sheet consistency be such as to resist crushing and reslurrying in the nip 33, as already noted. The web is brought into the nip 33 essentially out of contact with felt 37 by guide rolls 29, 31 to prevent the web from bubbling in this nip as air is expelled from the felt. Pressure roll 41 and felt 37 cooperate to exert a rolling pressure to securely press the web to the drum 35. Pressure roll 41 should be a solid roll in order to further uniformity in the moisture content of the web and prevent the formation of suction hole marks. With the 28-pound web 1 passing onto the drum, the pressure roll 41 exerted a pressure of about 450 pounds per lineal inch.

The drying rate on this first dryer drum was controlled to limit moisture removal to the extent that, as the web leaves the first Yankee drum 35, the moisture content was sufi'icient for adherence of the web to the second drum while yet providingthe desired smoothness on the wire side traveling against the surface of the first drum. The web 1 of 28-pound basis weight could be taken oif the first Yankee drum at consistencies ranging from 52 to 82% solids and applied to the second Yankee drum. The web traveled over about 270280 of are on the dryer periphery. The drying rate was approximately 16 pounds per hour per square foot of surface wrapped by the traveling web.

The web (FIG. 1) is drawn relatively sharply from the first dryer drum 35 over the guide rolls 43, and spread by Mt. Hope roll 43A. No longitudinal shrinkage of the web occurs on this drum as the web is well adhered to it.

The pressure exerted by pressure roll 47 covered by felt 49 to urge the web onto the dryer drum 45 surface was approximately pounds per lineal inch. In general, the pressure exerted by roll 47 is less than that exerted by the pressure roll 41 on the first dryer. This pressure is limited by a tendency of the web at this relatively lower moisture level to be deformed in the nip 44. The roll 47 is emplbyed when the second drying mechanism is a Yankee dryer as shown; it is also used on the first of a series of can dryers when such follow the first Yankee. The apparent function of the roll 47 in conjunction with the dryer surface is somewhat similar to that of a smoothing press, and it aids smoothness of both sides of the Web.

Drum 45 is also wrapped by the Web to a large angle in excess of 270. The drying rate on this drum for the 28-p0und web is substantially 10 pounds per hour per square foot of Wrapped surface. In the specific example, drum 35 had a temperature of between about l80 F. and drum 45 had a temperature of about 200 F.

Such web 1 (28 pounds), when withdrawn over guide rolls 52 and reeled, is substantially dry (5% moisture) and exhibits a greater bulk and thickness than does paper made under conventional conditions and calendered, as with a breaker stack.

For example, the Web manufactured as described was more than 20% greater in thickness than a sheet of the same stock, produced at the same speed but dried on con ventional can dryers after the presses, and then calendered .to the same finish level as the smoothed sheet 011 the wire side; the bulk, based on a four-ply of the sheet, was in excess of 10% greater for the smoothed web.

The following comparative data further illustrates the nature of paper obtainable with the method of invention described for a number of papers of varying basis weights, the comparison being at the same finish level between sample uncoated webs produced in accordance with the invention and uncoated control webs which were dried conventionally and calendered in a breaker stack 1 Corrected to a constant basis weight.

As illustrated in the graph of FIG. 3, the surface finish of the wire side, the side in contact with the first dryer, increases materially in value as the consistency of the sheet after the first dryer increases. Within the finish range of interest the wire side finish increases continuously and at an increasing rate as the consistency after the first drum dryer increases.

The surface finish values plotted in FIG. 3 are obtained in accordance with standard testing procedures as follows: the webs in each instance are completely dried on the machine but samples were taken after the first drum to measure the moisture content of the webs at this point. Samples from the completely dried web were then conditioned at relative humidity at 72 F. and then were examined for Ingersoll values by means of the standard Ingersoll glarimeter. Such glarimeter is available from Central Scientific Company, Chicago, Illinois.

The felt side finish (FIG. 3) does not change appreciably as the consistency after the first dryer increases. In FIG. 3 the point X designates a crossover point at Which the wire and felt side have substantially the same finish. This is an extremely desirable condition as it eliminates two-sidedness in the uncoated web and provides for the utilization of one coating formulation for both sides of the smoothed web.

It is to be noted that the cross-over point occurs at approximately a 67% consistency of the sheet (ZS-pound web) based on moisture content after the first dryer. Also, at this point the surface finish is above 25 and eminently suitable for high quality use.

The wire side finish of a web to be coated in most instances is not desired to be above about 28 or 29 and usually 26 or 27 is desired. Thus, a consistency of about 75% after the first dryer drum is quite suitable and ordinarily it is not desirable to permit this value to fall below about 65%.

The following table illustrates properties of uncoated base sheets produced as described hereinbefore; comparison in this table is made between three similar paper webs. It is apparent from the table B that the procedure described is effective to provide equivalent surface finishes on opposite sides of a web.

TABLE B Uncoated Base Sheet Properties 1 Corrected to 27.0 lb. basis Weight.

As illustrated in FIG. 2, the paper delivered from the second dryer may be directly passed to a coating device indicated at 54. The coating unit comprises an applicator roll in a pond S7 of aqueous coating composition contained in trough 59. The paper 1 passes over guide roll 56 between the applicator roll and a rubber covered backing roll 61 rotating in the same direction as paper travel. The nip between the driven backing roll and the independently driven applicator roll is open and a volume of fiuid coating composition is carried by the rotation of the applicator roll to the nip, thereby providing an excess of coating on the traveling web. From the nip 63 the web passes on the backing roll upwardly to the knife blade 65 where the excess of coating is troweled from the web and returned to the trough 59. The web then passes over heating and drying roll 67 which effects drying of the web and which carries the web forwardly over guide rolls 68 to the second ooater 71 for the coating of the second side of the paper. The second side is coated in a similar manner as the first side, similar parts being designated with similar numerals but primed, and the web is thereafter dried on a dryer roll designated at 67. This web is of relatively high bulk; if so desired, the coated web may be calendered as at '73 and reeled at 75.

The coating formulation used in conjunction with the novel smoothed paper of this invention may be any suitable formulation, particularly mineral coating compositions well known in the field of coated papers. One such formulation in parts by weight is:

Clay Calcium carbonate 15 Starch 15 Soap 1 Sodium hexametaphosphate 0.3 Sodium hydroxide 0.3

Water sufficient to make solids of 58.7%. The viscosity of this composition is about 40 Brookfield measured at 50 C. at r.p.m. with a No. 6 spindle.

1n the data presented in the following Table C a comparison is made between (a) three separate coated samples of the coated paper of this invention, supercalendered to a given gloss level, (12) a sheet produced in accordance with the invention, subjected to a breaker stack, coated, and supercalendered, and (c) a control sheet produced by conventional drying followed by breaker stack action, coated and then supercalendered, in the same manner and with the same composition. The coating composition in this instance is substantially that set forth above except that no calcium carbonate was employed and 15% additional clay was substituted for the calcium carbonate. Also, both sides of each sheet were coated in a manner similar to that illustrated in FIG. 2.

1 Uncoated sheet property.

9 Corrected to 40 lb. basis weight. It will be noted particularly that in the samples produced in accordance with the invention the wire side and felt side finish are substantially the same. A material improvement in thickness and bulk by the practice of this invention was achieved with respect to that shown by the control sheet. Additionally, the sheets smoothed in accordance with the invention were somewhat easier to supercalender.

FIG. 4 illustrates the elfect of coat weight on a 28- pound basis sheet with respect to printability for smoothed paper made in accordance with this invention, and calendered paper as normally prepared. As will be seen from the illustration, as coat weight increases the halftone value becomes decidedly improved, that is, lower, for the smoothed paper, and the smoothed paper has improved half-tone values relative to the calendered paper at equivalent base sheet finish level at any coat weight. The foregoing applies to the ire side.

Similarly, with 30-pound and 35-pound basis weight sheets, the wire side of the smoothed paper again demonstrated excellent printability as indicated by half-tone Values.

The half-tone values are obtained by a printing test made on a Chandler and Price platen press, and the halftone value is a measure of the papers ability to reproduce line screen with a 50% etch. The specimens are printed under controlled conditions so that any difference observed in the prints are due to the paper employed.

ter the paper samples are printed, they are graded against a set of 11 standard prints. A grading of zero is a very good print whereas a grading'of 10 is a poor printa The more level or smooth the sheet of paper, the better it will reproduce the image on the printing plate.

There has thus been described a novel process and apparatus arrangement for the production of paper of improved characteristics, and which apparatus is of rela tively low capital cost and may be operated at customary papermaking speeds. Further, the paper itself exhibits controlled and desirable features as noted hereinbefore.

It will be understood that this invention is susceptible to modification in order to adapt to dilferent usages and conditions and, accordingly, it is desired to comprehend such modifications within the invention as may fall within the scope of the appended claims.

What is claimed is:

1. The papermaking process for the production of printing paper which process comprises the steps of:

(a) continuously passing a newly formed Web of paper of an uncoated basis weight X 38 X 500 sheets) of 24 to pounds from a forming wire to successive Yankee dryers;

(b) partially dewatering the web as it proceeds to the dryers to provide a web consistency in excess of about 40% and less than about 46% as the web in a pressure nip tangentially enters the first Yankee dryer;

(c) pressing the wire side of the web of the surface of the first Yankee dryer with a pressure of at least about 300 pounds per lineal inch with a solid first pressure roll rotating in the direction of web movement;

(:1) drying the web on the first of the Yankee dryers to a consistency of between about -75% to smooth the wire side of the web;

(e) stripping the web from the first Yankee dryer and continuously passing the web to a pressure nip formed between a second pressure roll and the second Yankee dryer to press the sheet to the surface of the said second dryer;

(f) pressing the sheet with said second pressure roll at a pressure of at least 100 pounds per lineal inch but less than the pressure exerted by the first pressure roll;

(g) substantially completing the drying of the web on the second Yankee dryer by drying the web to a consistency of at least (h) pressing the web to the second Yankee dryer surface throughout the final drying; and

(i) subsequently without further smoothing of the Web coating, drying and supercalendering the web.

2. The papermaking process for the production of printing paper which process comprises the steps of:

(a) continuously passing a newly formed web of paper of an uncoated basis weight (25" x 38 x 500 sheets) of about 24 to 30 pounds from a forming wire to successive Yankee dryers;

(b) partially dewatering the Web as it proceeds to the dryers to provide a web consistency of between about 40-46% as the web in a pressure nip tangentially enters the first Yankee dryer;

(c) pressing the Wire side of the web to the surface of the first Yankee dryer with a pressure of between about 300 and 450 pounds per lineal inch with a solid first pressure roll rotating in the direction of web movement;

(d) drying the web on the first of the Yankee dryers to a consistency of about 67% to smooth the wire side of the Web;

(f) pressing the sheet with said second pressure roll at a pressure of at least pounds per lineal inch but less than the pressure exerted by said first pressure roll;

(g) substantially completing the drying of the web on the second Yankee dryer by drying the web to a consistency of at least 95%;

(h) pressing the web to the second Yankee dryer surface throughout the final drying; and

References (Iited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Wandel: The Function of a Yankee Drier on a Paper Machine, T.A.P.P.I., series XXV, 1942, pages 229-234 (TS 1080-T3, copy in Group

Claims

1. THE PAPERMAKING PROCESS FOR THE PRODUCTION OF PRINTING PAPER WHICH PROCESS COMPRISES THE STEPS OF: (A) CONTINUOUSLY PASSING A NEWLY FORMED WEB OF PAPER OF AN UNCOATED BASIS WEIGHT (25" X 38" X 500 SHEETS) OF 24 TO 30 POUNDS FROM A FORMING WIRE TO SUCCESSIVE YANKEE DRYERS; (B) PARTIALLY DEWATERING THE WEB AS IT PROCEEDS TO THE DRYERS TO PROVIDE A WEB CONSISTENCY IN EXCESS OF ABOUT 40% AND LESS THAN ABOUT 46% AS THE WEB IN A PRESSURE NIP TANGENTIALLY ENTERS THE FIRST YANKEE DRYER; (C) PRESSING THE WIRE SIDE OF THE WEB OF THE SURFACE OF THE FIRST YANKEE DRYER WITH A PRESSURE OF AT LEAST ABOUT 300 POUNDS PER LINEAL INCH WITH A SOLID FIRST PRESSURE ROLL ROTATING IN THE DIRECTION OF WEB MOVEMENT; (D) DRYING THE WEB ON THE FIRST OF THE YANKEE DRYERS TO A CONSISTENCY OF BETWEEN ABOUT 65-75% TO SMOOTHE THE WIRE SIDE OF THE WEB;