US2370811A - Conditioning and finishing absorbent webs - Google Patents

Description

March 6, 1945. w OSGQOD, JR 2,370,811

CONDITIONING AND FINISHING ABSORBENT WEBS Filed June 28, 1940 Patented Mar. 6,

CONDITIONING AND FINISHING ABSORBENT WEBS Harry Whitney Osgood, In,

assignor to S. D. M8585,

Westbrook, Maine,

Warren Company, Boston, a corporation of Massachusetts Application June 28, 1940, Serial No. 343,052:

3 Claims.

This invention relates to methods for conditioning and finishing absorbent flexible webs, e. g. webs of fabric, paper, regenerated cellulose, or the like, involving moistening the web by applying steam, substantially free from non-condensable gas, to the free surface thereof while the other surface is in contact with a heat conducting body, such as a metal roll, capable of abstracting heat from the web. This method of moistening webs, and particularly webs of paper, has many applications some of which will be described hereinafter; for example, the moistening may serve to determine the moisture content of the paper, or to control the finish produced on the paper by a calendering or supercalendering treatment, or to control the tendency of the paper to curl, etc., or two or more of these objectsn It is known thatpaper having a relatively high moisture content will fold better andgive less trouble from curlingv and from electrostatic charges than paper of lower moisture content. Paper having a high moisture content has less tendency; under changing atmospheric condimoisture content, when conditionedat normal moisture content, most printing papers have heretofore been finished with a moisture content betions, to develop wavy edges than paper having a lower moisture content. Paper having a high press room humidity, comes to equilibrium by loss low that desired by the printer because papermakers have found it difiicult to produce paper having a high and at the same time uniform moisture content. This is because the paper web on the paper machine customarily is dried'by being passed over a series of heated rolls and in spite of the fact that intelligent efiorts have been made to secure uniform heating the paper generally does not dry evenly across the web. The

edges of the web tend to dry out more than the middle portion and in the case of a wide paper machine two or more relatively moist strips separated by relatively dry strips may be found between the relatively dry edges. When suchpaper is calendered the relatively moist strips or streaks tend to blacken or over-finish producing a defect in the paper. In order to avoid this difficulty it v is customary to over-dry the paper and the resulting paper product does not have the high moisture content desired.

By the present invention the effects of overto a low moisture content as is customary andthen a predetermined quantity of water is distributed uniformly throughout the paper and upon its surface by condensing steam in and upon the web while it is moving in contact with .a heat conducting body at a temperature below that necessary to condense steam, e. g. below 1 90 F. and preferably within the range from F. to F. The heat conducting body may be a metal roll provided with means for circulating a cooling fluid, e. g. water, through passages therein. For most effective moistening substantially pure steam at a temperature 01' about 212 F. should be used; i. e., the steam should be substantially unmixed with uncondensable gas and free from water in liquid form. The steam must, of course, be uniformly distributed as will more fully appear hereinafter. The moistening treatment may be applied to the paper at any time after it has been dried, e. g. just as the paper leaves the drier, or immediately after calendering, or as the paper is being fed to a rewinder or to a sheet cutting machine. In accordance with the invention moistening may be made to assist in improving the density and apparent formation of the paper and the compactness and levelness of the surface in addition to the other effects mentioned above.

When the chief or sole purpose is to increase the moisture content of the paper it suffices to pass the web about a heat-abstracting roll or equivalent device so positioned that the side of the device covered by the web is adjacent to or projects into a steam-box supplied with steam. Such an arrangement is shown in Fig. 3 to be described hereinafter. The quantity of moisture ferred, however, that the steam be blown against a surface of the web at close range while the revers side of the web is in contact with a cooling surface. By impinging a uniform ribbon-like coated and I with a jet of steam from the Jet of steam across the width of the sheet the quantity of steam used can be carefully controlled and instantly varied at will. Besides ease of control, however, steaming by means of an impinging jet affords other advantages as will be explained hereinafter.

Illustrative processes in accordance with the invention will be described in connection with the accompanying drawing which illustrates specific apparatus embodying the invention:

In the drawing:

Fig. 1 illustrates the moistenlng device in connection with a supercalender;

Fig. 2 illustrates the moistening device associated with a machine calender;

Fig. 3 illustrates an alternative form of moistening device.

Fig. 4 is an enlarged perspective view of a portion of the steam nozzle shown in Fig. l, and

Fig. 5 is an enlarged perspective view of a portion of the steam nozzle shown in Figs. 2 and 3.

Referring to Fig. 1, 5 is a supercalender of standard construction consisting of alternate hard or metal and soft or yielding rolls designated by the letters H and S, respectively. I is the paper web which moves, as indicated by the arrows, from the storage roll 2 over the guide roll 3, past the steaming device 4 to the calender stack 5. 6 and 6' are fly rolls which usually are employed in treating coated paper, but are not ordinarily used in treating uncoated paper. From the last nip in the calender stack the paper passes over roll I which is provided with means for cooling it (not shown); for example, it is hollow and connected with means for circulating cold water through it. It is observed that the side of the paper web facing the steaming device 4 contacts the hard rolls of the supercalender and the other side which has contacted the soft rolls faces the steaming device 8. The web then passes over the guide roll II and is wound on the reel l2. 9 is a shield around the steaming device 8 to prevent the escape of steam into the workroom. The steamer 8 and shield 9 are movably mounted on a support l0 so that they may be swung out of the way when threading the machine.

Referring to Fig. 2, A represents the drier section of a paper machine, B the first calender stack, C a second calender stack, and D the windup reel. In the drier section A, the paper web I is dried to a uniform low moisture content, preferably below 3% in the case of book paper, and then passes through one or more nine of the first calender B which is a machine calender of standard construction with all hard rolls, and then passes on to the calender C, the rolls of which are all hard. The web is shown passing through three nips of the calender B. Rolls 13 and Il are hollow or bored and provided with means (not shown) for circulating a cooling fluid through them. The remainder of the rolls of calender C may be of standard construction. The paper web passes down through the stack and over the roll [3 where its free face is contacted steamer 2|; then it passes between rolls I3 and I4 and around roll 14 where its other face is exposed to the steamer 2| and then on through the final nip of the stack to the winding reel D. It is noted that in the above described operation the paper web passes through a nip of the calender stack immediately after steaming and While its surface still carries the film of moisture applied by the steaming device 2|. The steamers 2i and 2! are each provided with hoods 22 and 22' which 'may be connected to ventilators (not shown) to prevent escape of steam into the workroom. Steamers 2| and 2| may be movably supported as described in connection with Fig. 1.

In Fig. 3 a paper web I passes about cooled roll 15. A portion of roll l5 covered by the paper web extends into a steam-box l6 filled with substantially pure, dry steam which enters the box through pipe I! controlled by valve 18 and the rotatable nozzle l9 which may be directed at any angle, either toward or away from the paper. Steam contacting the cooled web inside the box condenses, chiefly on the surface of the paper. Condensate collected inside the box escapes through drain 20. When nozzle is is turned so that its jet does not impinge against the paper the device acts merely as a steam-box and in that event, at least, the box should closely fit the paper to prevent excessive leakage of steam.

A suitable steaming device must assure the de liverance of steam of substantially uniform pressure and quality across the entire width of the sheet. In case a jet is used to give velocity to the steam impinging on the sheet it must deliver a substantially uniform jet or ribbon across the width of the sheet, i. e. the size, shape, velocity and composition of the jet must be uniform; the steam must be free of particles of water of appreciable size which, .if present, will result in imperfections in the paper; the steam must be substantially free of dilution; the jet preferably should be delivered at a substantial pressure and contact the paper at sufiicient velocity to penetrate the paper and displace air therefrom. The jet should be fiat and non-divergent. It has been found that steam at a nozzle pressure approaching 1 pound per square inch delivered from an orifice about /8 inch wide positioned at not more than about 1 inch from the paper gives satisfactory results. The jet in order to afford any appreciable eflect from velocity should strike the paper at a velocity of at least about 5 feet per second and preferably at a velocity of about 25 etrate and condense in the paper when delivered from a. narrow orifice at'high velocity than when delivered from a wide orifice at lower velocity.

Suitable steaming nozzles are shown in Figs. 4 and 5. Referring to Fig. 4 the nozzle consists of a cylindrical pipe 23 provided with a slit orifice 24 and a steam supply pipe 25 extending through the pipe 23 and having outlet orifices directed away from the slit 24. This arrangement serves to trap any drops of water carried by the steam and also to provide a uniform distribution of the steam to the slot. This 'nozzle is of the known,

contacted while being steamed preferably is in the form of. a, metal roll as illustrated, but any other suitable cooling surface, such as a stationary surface over which the paper slides, may be employed.

By controlling the temperature of the cooling surface and the size and impinging velocity of the steam jet, any desired quantity of water up to 10% or over, even up to 20% or more for some yp s of paper, may be added to the paperby a single steaming operation. If more moisture is desired than can be obtained in one passage through the apparatus, two or more of the devices may be used in succession to condense additional steam in the web. For printing paper the desired final moisture content usually does not exceed 10% and in most instances about 6% to 7% is satisfactory. Since the paper generally has a moisture content prior to steaming of about 2 to 3% this means that up to 8% and generally about 3% to of moisture must be added by the steaming operation.

In practically all cases at least 2% of water is added by the operation.

It is known that when one surface of a paper sheet is moistened and the moisture is allowed to evaporate from that surface, the sheet will tend to curl towards the treated surface. In some cases such a tendency to curl is desirable as when it is used to counteract an existing tendency to curl in the reverse direction; in some cases, of course, a tendency to curl is undesirable. steaming a free span of paper, which is not in contact with a cooled roll, as has been done to remove the reverse side finish and curl of one side supercalendered paper, it is known that the greater is the steaming the more pronounced is the effect on curl. But it has been found that even very severe steaming according to the prior practice described adds not over about of moisture to the paper. In contradistinction to this, by steaming in accordance with the present invention while the paper is backed by a conductive surface at below about 190 F. and preferably at from about 100 F. to 140 F. any desired quantity of moisture within reason may be added to the paper, and moreover the moistening operation may also serve to control the finish and curl o'f-the paper. At first thought, since the amount of water in the paper and the degree of curl inthe paper are independent variables,

it might seem difficult or impossible to control both in a single operation. However, it is found that the quantity of steam condensed in the web may be determined as desired by controllingthe temperature of the cooling roll, while the tendency to curlis found to depend largely upon the depth within the sheet at which the condensation takes place, and so may be varied at will by varying the velocity of the steam impinging upon the web. In general the higher the velocity of the steam impinging on the web the deeper is the point of condensation in the sheet and the less tendency is there for sheet to curl towards the steamed side.. For example, paper treated in the apparatus shown in Fig. 3 with the jet pointed away from the paper will develop a strong tendency to curl toward the moistened side, but paper treated by steam of high velocity from the jet shown in Fig. 1 can, if desired, be produced without developing any appreciable tendencyto curl, or with any degree of curl wished for. This simultaneous control of curl and moisture content is entirely novel and is I before or after its second passage through the supercalender because only a small amount of water is expelled from the paper by each passage.

of the paper through the supercalender and enough water may be added at the start to compensate this loss. Or moisture may be added to the paper after its first passage through the supercalender. On the other hand, if such a high moisture content in the finished paper. is desired that the presence of this amount of moisture in the paper duringcalendering would result in blackening. it may be necessary to add part of the water during or after the second supercalendering. When it is necessary to add moisture to the paper after supercalendering and this addition of moisture tends to lower the finish of the paper, this loss of finish can be compensated by giving the paper, before the final mois tenin a higher finish than is desired on the paper product.

The following is illustrative of the moistening effects obtainable. A highly filled book paper weighing 40 pounds per ream (25 x 38-500 sheets) containing 3.1% moisture was lightly steamed, then supercalendered, and then steamed on the reverse side giving a moisture content of 6.1%. The paper was then passed through the '40 supercalender again to finish the reverse side,

without further steaming, and showed a final moisture content of 5.5

The paper may be steamed after partial calendering and then while the applied film of mois ture is still on the surface of. the paper it may be passed between pressure rolls with the wet surface contacting a hard roll. As stated the steam ing may be done against the calender rolls themselves, provided they are designed to be cooled,

or against special cooled fly rolls inserted at any desired point in the path of the paper. A preferred embodiment of-the invention, however, is

that illustrated in Fig. 2 in which at least two of the rolls of a calender stack are designed to tively large amount of water added to it immediately before being calendered and still show no excessive blackening after calendering. Paper, moistened by the present method, may be densified and its look-through properties considerably improved. It may be provided with a very level surface and a gloss finish.

When the invention is practiced in connection with a machine calender, paper having improved" printing qualities is obtained the finish of which may be anything desired from a medium machine finish to a finish higher than that ofso-called English finish paper, these properties being associated with the desired high and uniform moisture content.

The quantity of moisture added to the paper can be positively and accurately controlled by regulating the temperature of the cooling roll and/or the velocity of the jet and the distance of the nozzle from the paper. In general, the moistening is more efiective in giving-the desired finish with a given pressure on the rolls and a given number of nips than other methods of moistening the paper. For example, to produce a machine or English finish it is generally sufficient to employ one or two nips after moistening at normal roll pressures. By employing greater roll pressures after the moistening, densification can be carried to the point at which the paper is more or less translucent and resembles parchment in appearance. In fact, especially when using a supercalender, glassine paper can be made from a suitable glassine stock without the customary seasoning before calendering.

In producing printing paper, blackening must be avoided and this may be done by keeping the temperature low during th calendering of the moist paper. The permissible temperature depends somewhat on the moisture content of the paper, but the rule may be stated that the temperature of the calender rolls should not exceed 150 F. in the treatment of book paper containing more than 6% of moisture. In the preferred temperature range of about 100 F. to about 120 F., it is possible to calender both coated and uncoated paper without excessive blackening at a moisture content of 10 to 12% and even higher in the case of ground wood paper.

The following examples of specific treatments of paper are illustrative:

Example 1.In an apparatus like that illustrated in Fig. 1 paper weighing '70 pounds per ream (25 x 38--500 sheets) and having on one side a 15-pound mineral coating was steamed lightly on the coated side just before entering the supercalender with the coated side contacting the hard rolls. From the last nip of the super calender the paper was taken around the metal rolls I maintained at 110 F. with the high finished side against the roll and the low finished side contacting another steam jet. The paper speed was 650 feet per minute. The moisture content of the paper after the first steaming and before entering the supercalender was 4.7% and after the second steaming 6.6%.

about feet per second. The low finish side of the paper was practically free of finish and the paper was practically free of curl.

Example 2.In an apparatus like that illustrated in Fig. 2 a highly filled book paper of pounds per ream (25 x 38-500 sheets) came from the drier section A with a, moisture content of 3% and was given three light nips in the calender B to smooth out gross irregularities in the web and to take out some of its stretch as is generally done before passing the paper to the finishing calender. The paper then passed through three nips of the calender C. The surface temperature of rolls l3 and I4 was 125 F. and steam was delivered by steamer 8 against the paper at a velocity of 20 feet per second and by steamer 8' at a velocity of 25 feet per second. The speed of the paper was 470 feet per minute and the pressure on the bottom nip 390 pounds per inch of The steam jet was contacted with the paper at a velocity of paper width. The finished paper hada moisture content of 6.7%, a high English finish, was free of blackening and had a bulk or .0119 inch for 4 sheets.

In the foregoing examples the invention has been described in connection with a supercalender (Example 1) and a machine calender (Example 2). The invention is particularly useful in producing one-side coated and uncoated one-side supercalendered paper such as is widely used for lithographic printing in which use a high moisture content is desirable. Such paper can be produced of any desired moisture content and in which curl is controlled to any desired degree.

When paper is printed in more than one color it is necessary for the paper to receive more than one impression. In many cases there is a considerable time interval between the successive printings. If the various .impressions are to be in register and give satisfactory results it is of vital importance that the paper shall not change in shape or dimension during the interval between impressions. Ordinarily it has been the custom. when paper was to be printed with several impressions, for the printer to hang the paper for a period of several hours in the atmosphere of the print shop, in order that the paper may come to equilibrium under the atmospheric conditions of the press-room and so not change in dimensions or go out of shape during the printing operation. The printer says that by so doing he conditions" the paper to the atmosphere of the pressroom.

A successfully achieved object of the present invention was to pre-treat paper during its manufacture so that it could be delivered to the printer containing approximately the desired quantity of water and in such condition that it could be printed immediately and still not go out of shape more than paper actually conditioned by exposure to the press-room atmospher before printing. The simplicity of the process of the invention obviously makes it very advantageous in comparison with the troublesome and timeconsuming method of exposing the paper to a humid atmosphere to take up moisture. Moreover, in the case of one-side coated or one-side supercalendered paper the process has a particular advantage in that all the moisture is added through the unfinished side of the sheet and so avoids all liability of damage to the high finished side as may well be encountered in cases where both sides of the web are exposed to a very humid atmosphere. This feature of the invention itself is of considerable importance.

Unexpectedly, as has been shown by repeated printing tests, papers conditioned according to the process of the invention have actually given better results than papers conditioned by hanging in the press-room atmosphere. Even more surprisingly it has been found that paper conditioned according to the invention so that it contains a relatively high moisture content, say an amount that would be equivalent to that required for equilibrium with an atmosphere of 50 to 65% relative humidity, may be printed directly, without press-room conditioning, in atmospheres the moisture contents of which vary in a wide range, say from 30 to 65% relative humidity, with excellent results. This is a wholly unobvious result given'by the invention. The entire reason for the superior results mentioned is not fully understood at present. Drying the paper to a uniform low water-content as one step in the operation apparently contributes to the result. Possibly adding a substantial quantity of moisture while holding the paper under tension is another contributing factor, or perhaps it is a fact that condensing moisture deep within the web acts to release strains and equalize tensions therein to an extent that on later exposure to varying humidity conditions the sheet reacts less than might be expected. Whatever the true explanation of the phenomenon, the fact remains that the process described yields excellent results and is undoubtedly a valuable advance in the paper making art.

In the use of the machine calender as illustrated in Example 2 it is possible to employ only one cooled roll and one steamer and to produce paper having only one highly finished side. It is also possible to locate the cooled rolls at other positions in the stack and that the paper may pass through nips of the stack before or after, or both before and after, contacting the cooled roll or rolls, or instead of using a roll of the stack as the cooling roll, a fly roll may be employed for this purpose. Thi eliminates the danger of damage to the soft rolls of the supercalender by water which might condense on the ends of the cooled 7 metal roll outside the width of the paper. The

apparatus illustrated in Fig. 2 is designed for calendering uncoated paper in the continuous production of paper on the paper machine. but coated paper also may be calendered with steaming in the same way on an all-metal roll calender.

This application is a continuation-in-part of my application Serial No. 160,681, filed August 24, 1937.

I claim:

1. Process which comprises drying a paper web to a uniform, low water content and then increasing the water content of the web by moving the dried web in contact with the surface of a cooled metal roll maintained at a, temperature below 190 F., impinging a ribbon-like jet of substantially pure dry saturated steam with a portion of the surface of the web opposite that in contact with the cooled metal roll at a velocity of at least 5 feet per second and at an angle approaching the perpendicular to the web from an orifice positioned not more than about linch from the web, thereby avoiding substantial entrainment and mixing of air with the steam at the line 01 contact with the web and condensing the steam in the web to increase its moisture content from about 2 to about 20 percent by weight of the dry web.

2. Process as defined in claim 1 in which the cooled metal roll is maintained at a temperature between F. and F.

3. Process as defined in claim 1 in which the velocity of the steam is at least 25 feet per second.

HARRY WHITNEY OSGOOD, JR.

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