US2786398A - Apparatus and process for producing an extremely thin paper web - Google Patents

Description

March 26, 1957 P. c. sPRoULL ETAL 2,786,398

APPARATUS AND RRocEss RoR PRoDucTNG AN EXTREMELY THIN PAPER NEB Filed Nay 1, 1952 8 lo g 0. 9 8 8 a. 9 u 9 s L la 8 l l-' la l rx 4 a 0 P IO O O C s P 4l 3' I2 P I2 ls 7 e 4 n 2 3 la l Q ,a INVENToRs.

United States Patent APPARATUS AND PROCESS FOR PRODUCING AN EXTREMELY THIN PAPER WEB Reavis C. Sproull, Savannah, Ga., and Herbert G. Hard, Jr., Opelika, Ala., assignors to Sprague Electric Com pany, North Adams, Mass., a corporation of Massachusetts Application May 1, 1952, Serial No. 285,358 Claims. (Cl. 92-44) This invention relates to an apparatus and method for forming an extremely thin web of paper. More particularly this invention relates to an apparatus and method `suitable for producing paper having a thickness of less than .2 mil, and is a continuation in part of prior application, Serial No. 199,328, tiled December 5, 1950, now abandoned.

In accordance with the disclosure of said prior application it has been discovered that a paper of a substantially decreased thickness of the order of .2 mil and less may be produced by conventional and standard equipment. However, the extremely small thickness of this new type paper gives rise to diculties when the prior art type paper-forming apparatus is used.

To facilitate a full comprehension of the instant invention and to illustrate how it may be carried out in practice, reference will now be had to the drawings in which:

Fig. l illustrates a preferred form of the invention; Y

Fig. 2 is an enlarged fragmentary sectional view of a portion of the apparatus of Fig. l more clearly illustrating the pick-up band in cooperation with the forming wire and paper web; and

Fig. 3 illustrates a second form of the invention.

As described in said prior application, paper of a thickness of less than .2 mil may be formed on a standard Fourdrinier papenmaking machine using a pulp slurry which has been prepared by a standard Valley beater apparatus or a standard Bertrum beater apparatus. In the normal construction of a/Eourdrinier machine, a form,L ing web composed of a continuous, looped, line-mesh wire screen is positioned to filter out pulp bers from a slurry deposited from a head box, and carry the wet felted fibrous web thus formed to a position adjacent a drying unit. To transfer the web from the forming wire tothe drier it has been the practice to use a felt or wire screen band, bringing this band into engagement with the Mice conventional forming wire which is adapted to cooperate with the conventional pulp slurry head box (not shown) to filter and felt the pulp ibers P therefrom. This wire is formed, a-s in conventional structures, to be in the shape of a continuous loop guided around an endless horizontally elongated path by means of guide rollers, some of which are illustrated at 2 and 6 in the figure. Adjacent one terminal end of the loop, remote from the head box, is positioned a couch roll 3 which drives `the wire and ydefines the end of paper web travel on the Wire, from which point the wire is guided downwardly and backwardly towards the head box over return guide vroll 2 and a guide and washing roll 6. Water is supplied to the roll 6 in a conventional manner to wash off stray pulp fibers that may adhere to the wire 1.

intermediate the slurry tank (not illustrated) and the couch roll 3 are positioned two spaced support and guide 4rolls 4 and 5. Between these rolls 4 and 5 and the terminal couch roll 3 is positioned a conventional suction box 7 which is adapted to apply suction to the underside of the forming wire and remove a substantial portion of the wet web on the forming Wire, to cause the web to adhere to the band. The band is then withdrawn from the forming wire, carrying the web away with it. While this is a satisfactory method of operating, it is foundv that with extremely thin webs there is a serious tendency for the web to remain at least partially adhered on the forming wire even after engagement with the pick-up band. As a result, the web which has very little tensile Vstrength frequently tears at the pick-up transfer.

Applicant has found that the above tearing difficulties may be considerably reduced or completely circumvented by utilizing a smooth foil-type pick-up band of metal for example in lieu of the prior art type felt belt or mesh screen. ln-the practice of this invention the pick-up `wire of a conventional Fourdrinier apparatus can be replaced by` aloop of vmetallicor plastic foilwhichcooperates with the lforming wirerand transfers the web of pulp fibers from Vthe wire.. p s AIn Fig. l there is. diagrammatically illnstrateda `modied ystructure of a conventional Fourdrinier paper-forming apparatus.v along theuliinesviofvtheconventionalljlarper- Fourdrinier machine in which numeral 1 indicates the moisture remaining in the paper matrix carried thereby. Positioned above the rolls 3, 4 and 5 are a group of secondary rolls 3', 4 and 5', respectively, which cooperate to form `separate pairs of press rolls. These squeeze the paper matrix and press part of the moisture therefrom.

A plurality of guide rolls 8 are positioned above the rolls 3', 4 and 5 to form one section of an endless path for supporting a looped, metallic foil member 10 which cooperates with the forming wire and the paper matrix as hereinafter set forth. The metallic foil 10 is positioned to travel under and over various of the rolls 8 and is looped between the rolls 4 and 4 where it comes into intimate contact with the exposed face of the paper matrix as the latter is carried by the forming wire from the head box. This foil forms a continuous looped band which is held in continual engagement with the outer face -of the paper web P during the rest of its travel on the forming wire 1 and throughout the drier portion of the apparatus. Preferably, the metallic foil 10 is smoothed, burnished and polished to have a very high surface inish which does not disturb the surface ibers of the paper when in contact therewith. p

A second group of guide rolls 9 are positioned adjacent the rolls 8 to form a portion of a second endless path, but which path is of less extent than the former path. Carried by the guide rolls 9 is a conventional felt drying web 11 which is threaded to pass over and under the rolls 9 and between the rolls 5, 5 into intimate contact with the inner or exposed surface of the foil loop 10. The felt band 11 is likewise formed in the shape of a continuous loop.

As will be clear from Fig. l the forming wirev 1 picks up a mixture of pulp fibers and water from the head box and conveys this over the usual table rolls, suction boxes, dandy rolls, etc., between the rolls 4, 4 and 5, 5 at which points the metallic foil 10 and the felt web 11 are sequentially moved into contact therewith. This action produces a composite paper matrix, metal foil and felt web, as indicated in Fig. 2, which then passes over the suction box 7 where a substantial portion of the remaining moisture left in the paper matrix is removed. The composite web then proceeds as a unit through the nip of couch roll 3 and its mating pressure roll 3 where more moisture is removed. At this point the paper matrix P contains'less than 50% moisture and is a fairly compact homogeneousV sheet. After passage through the couch roll 3 and pressure roll 3', the forming wire 1 parts from the paper matrix (see Fig. 2) and is returned in its returnfpath to the headY box over the guide rolls 2, the papermatrix ad- Hering to the underside of the foil web with a relatively strong surface attraction therebetween. This surface attraction materially assists the take-up action of the foil and readily overcomes any tendency of iioers in the paper matrix to adhere to the forming wire. As a result, a very effective transfer is accomplished.

Adjacent the couch roll 3 at the terminal end of the yforming Wire loop there are positioned a plurality of guide rolls 13 which form one portion of the supporting structure for a second drier felt 14. This drier felt is led by one guide roll 13 into contact with the exposed underside of the paper matrix as it leaves the forming wire and remains in continuous engagement with such matrixthroughout the length of its travel over a plurality of drying cylinders 12. These cylinders 12 further function as additional guides which complete the paths for the continuous loops of the foil 19 and the drier felts 11, 14. .After the drier felt 14 contacts the exposed underside of the paper matrix P, the composite layered web, consisting of the felt 14, the paper matrix P, the metal foil y10la'nd theupper felt 1i, is then threaded over and under and 'through the plurality of drying cylinders 12 in order to Asubstantially completely dry the paper. Adjacent the last drying cylinder 12 a plurality of guide rolls 13, 9 and 8 cooperate to return the respective drier felts 11, 14 and metal foil 10 along their looped paths to their starting points. rThe dried paper web is then self-supporting and can be threaded over a guide roll 16 for example, and passed to a winding roll or calender press or any other after-treating apparatus, as may be desired. In some types of operation it may be desirable to design several of the return guide rollers 16 as pony driers to completely dry the felt 14 before it again contacts the paper matrix.

In view of the extremely thin tissue-like character of the paper web, all of the press sections of conventional Fourdrinier apparatus may be dispensed with. As is indicatedjin Fig. 1, the wet paper matrix is carried by the forming wire 1 through the rolls 4, 4 wherel the metal take-up web 10 is threaded into intimate contact ywith the exposedl face thereof. At this point in the travel of the paper therrolls 4, 4 can be pressed together suf-fb ciently to express a portion of the `moisture from the paper matrix. A second pressing or squeezing action is applied when the composite web of forming wire, paper and metal foil is passed between the pressure rolls 5, ,5' where the upper felt is threaded into intimate contact with the exposed surface of the metal foil and where more moisture is removed from the paper. A third moisture removing operation is performed by the suction unit 7 prior to the passage of the paper over the couch roll 3 and under the pressure roll 3'. At this point the paper is about as dry as it can be sucked and squeezed. Due to its extreme thinnessit will dry evenly and com pletely on the drier drums 12 without need for the conventional first, second and third press units that usually precede the drier.

The use of a looped metal foil 10 in lieu of the conventional pick-up wire or felt has several distinct advantages in addition to the decrease of web tearing. When a conventional pick-up felt is used, the upper surface of the paper' web loses some pulp fibers that adhere to the felt. in conventional papers heretofore made, such minor loss was only a very small fraction of the total pulp fibers in the web and is of no appreciable significance. With paper of the thickness of the instant process, however, such loss represents a substantial portion of the fibers of the paper matrix and cannot be tolerated. In fact, this loss of the surface fibers would render the paper too non-uniform to be acceptable. By using a metal foil this trouble is completely eliminated. After passagethrough the pressing rolls 4, 4 and 5, S the metal foil 10 remains in intimate contact with the surface of the paper matrix and provides a much irnproved support and carrier therefor.

The use of a metal foil has a further distinct advantage during the drying of the paper over the drying drurns 12. As is well known in the art, the conventional drier felts become wet and moist when first contacting the paper matrix. This moisture is gradually and progressively removed from the felt as it travels through and over the various drying drums. The rate of moisture removal from the drier felt differs from the rate of moisture removal from the paper and since the drier felt is normally composed of a shrinkable material, such as cotton or wool, it progressively changes in length during its travel over the drying drums` This act produces a burnishing or sliding action on the surface of the paper matrix disturbing its fiber formation and stretching the sheet, thus lowering its Strength. The metal foil on the other hand is not affected by moisture. Furthermore, the foil is lnot attacked or deteriorated by the high temperatures necessary to dry the paper and maintenance problems are accordingly reduced. The surface fibers of the paper Vsheet which are in contact with the foil remain undisturbed during drying, resulting in a finished paper product of high tear-resistance and high gloss.

Another distinct advantage is obtained by using the metal foil as a pick-up web by incorporating the upper drier felt 11 in the apparatus. This felt is positioned to cover the exposed surface of the metal foil and while distinctly advantageous in preventing scarring or pitting of the pressure rolls 3 and 5 and the surfaces of the drier drums 12, it has a second function in forming a backing member for the metal foil to reduce conduction and convection of -heat away from the paper matrix during its travel through thedrying unit of drums 12. The provision of this felt web 'in intimate contact with the exposedfsurfa'ce of the foil thermally insulates the foil to keep down heat'los'ses. The porous nature lof the felt 11 vis Vsuch as Vto permit `alternate drying drums 12 to radiate heat through the felt to the surface of the'foil 10 without unduly reducing the transfer thereof by conduction. This substantially reduces the drying time and the number of drying units required.

If desired, an additional pressure roll indicated by dotted line 1S in vFig. 1 maybe provided to cooperate with the adjacent'guide roll 13 to l'forma single first press prior to the travel of the composite Vweb through the drying units 12. This additional pressing is not normally required, but helps with the expressing of water from the web into the felts. Alternatively, the press rolls 4, 4 and 5, Smay be used as simple pressure-free guide rolls, relying on the subsequent pressing action of rolls 3, 3 or roll 15 with the roll 13 to remove sufiicient moisture before passage to rthe drier roll'12. This alternative construction will ygive maximum assurance against having the underside of the paper bl'emished by Wire marks. Another advantageous 'feature in the use of the metallic pickup-foil in conjunction'with ythe extremely thin paper matrix resides -in the fact-that the heat supplied by the initial drum may be increased to 'the extent that'the thin paper matrix becomes over three-fourths dry, or at least sufficiently so to withstand the longitudinal stresses imposed thereon by the driving action ofthe apparatus, so that the foil 10 and felt 11 may be separated from the self-supporting paper matrix between the first two drying drums l12. Under'such conditions the metalI foil functions to vsupport the "papermatrix during drying Without becoming entangled lwith the `surface' bres thereof, thus permitting such surfacebres to dry in an undisturbed felted and interlocked mesh. `The 'matrix thus ydried is much stronger than a matrix of 'equal dryness but which has the surface fibres thereofentwined witha conventional felt so that upon separation therefrom, the lstrcngthof the matrix would be reduced by'artearing and unlocking of the surface fibres.

'A modiiedform` of'thednven'tion is illustrated'in Fig.

3 in which like elements are indicated by like numerals. This form of the invention is substantially identical to that of Fig. 1 with the exception of the position of the suction box and the use of backing and dryer felts. The paper matrix P is formed on the pick-up wire 1 in the manner specified in the Fig. 1 embodiment and passes over a suction unit 7 prior to being contacted by the looped take-up foil 10. In this construction, the pressure rolls 4, 4 and suction box 7 are positioned closely adjacent the dry end of wire 1 in order that the maximum benefit may be derived from the gravity induced water separation during travel of the paper matrix along the forming wire. The pressure between the rolls 4, 4' can accordingly be substantially increased with an increase in the percentage of moisture removed by the combined operation. The looped, metal-foil, pick-up web 10 is positioned to travel in an endless path in the manner similar to that shown in the Fig. l construction, and intimately contacts the upper exposed surface of the paper matrix P between the pressure rolls 4, 4 and remains in Contact therewith until the paper is discharged as a cornpletely dried product.

After passage through the pressure rolls 4, 4', the composite, layered web of forming wire, paper matrix and metal pick-up web then passes over the couch roll 3 and under the pressure roll 3 where further moisture is removed. The forming wire 1 then returns to its starting point via guide rolls 2 on the discharge side of the couch roll 3. The composite web of foil and paper matrix passes over a guide roll 13 where a felt 18 is positioned to contact the exposed underside of the paper to form a composite web of metal foil, paper matrix, and felt. This composite web is then threaded over the various drying drums 12 to the discharge end of the machine where the metal foil 10 is returned via guide rolls 8 to its beginning point adjacent the pressure roll 4 and the felt 18 is returned to the beginning point of its travel via guide rolls 13, the finished paper web being discharged to a wind-up drum or calendering apparatus or any suitable after-treating apparatus via the guide roll 16.

In the instant construction no backing or protecing web is provided for the exposed surfaces of the metal foil. If desired these exposed foil surfaces may be coated with a suitable resin or other protective material to reduce abrasion.

If desired, the metallic foils 10 may be replaced by webs of plastic materials such as regenerated cellulose, polyvinyl chloride, cellulose acetate or polytetrahaloethylene resins. One particularly advantageous resin for this purpose is polytetratluoroethylene. Other useful resins are polytriuoromonochloroethylene and polydiuorodichloroethylene and the like. These plastic webs provide results that are substantially the same as the metal foil, being practically unstretchable at high temperatures.

In accordance with the present invention other types of drying units such as a Yankee type drying cylinder may be substituted for the drying drums 12, or a Minton vacuum-type dryer may be used in lieu of the drying arrangement shown in the ligures. Furthermore, other forming devices such as a cylinder machine or a hand operated forming wire can be substituted in place of the Fourdrinier wire. In any case, the use of a smooth, flat, non-absorbent continuous pick-up belt to lift the formed fibrous web from the surface on which it is made, provides the advantages pointed out above.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it yis to be understood that this invention is not limited to the specific embodiments hereof, except as defined in the appended claims.

What is claimed is:

l. An apparatus for forming a web of paper having a thickness of the order of .2 mil and less including a forming wire positioned to form a wet web from a slurry, a pick-up carrier having a smooth, impermeable, substantially unstretchable and uninterrupted surface positioned for contacting the exposed surface of said wet web on said wire, a heated drying drum, and operating means cooperating with said carrier to carry the carrier into contact with the web to cause the web to adhere to said carrier and to carry the `carrier with the adherently held web away from the forming wire and around the drying drum.

2. The combination set forth in claim l in which the carrier is in the form of an endless loop and a continuous, looped felt band is positioned to cooperate with said pick-up carrier, and supporting means pressing said felt band into intimate engagement with the surface of the web while it is held by the pick-up carrier and assist in drying said web.

3. The combination of claim 1 in which the pick-up carrier is a metal foil.

4. A method of making paper having a thickness no greater than about 0.2 mil, said method including the steps of forming a wet web of ibers of the required thickness on a porous forming surface, contacting the wet web on the forming surface with an impermeable pick-up carrier having a smooth continuous and uninterrupted flat substantially unstretchable surface to cause the wet web to ,adhere to the carrier, and moving the carrier away from the forming surface to cause the carrier to remove the wet web from the forming surface.

5. The process of claim 3 in which the carrier is a metal foil.

References Cited in the tile of this patent UNITED STATES PATENTS 82,854 Lovell Oct. 6, 1868 158,400 Butler Jan. 5, 1875 742,259 Tompkins Oct. 27, 1903 v 796,601 Perrigot Aug. 8, 1905 1,170,309 Meyers Feb. 1, 1916 1,599,503 Tompkins Sept. 14, 1926 1,651,476 Sheehan Dec. 6, 1927 2,174,744 Hill Oct. 3, 1939 FOREIGN PATENTS 575,453 Germany Apr. 28, 1933

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