Method and apparatus for making paper by contracting the forming carrier to compact the web

Sept 21, 1965 j. r. wagner etail. 3,207,657

METHOD AND APPARATUS FOR MAKING PAPER BY CONTRACTING THE FORMING CARRIER TO COMPACT THE WEB

Filed Jan. 22, 1963 3 Sheets-Sheet 1

<img file="US3207657A_D0001.tif" />

Sept. 21, 1965 j. r. wagner etal 3,207,657

METHOD AND APPARATUS FOR MAKING PAPER BY CONTRACTING THE FORMING CARRIER

TO COMPACT THE WEB

Filed Jan. 22, 1963 3 Sheets-Sheet 2

<img file="US3207657A_D0002.tif" />

Sept. 21, 1965 j. r. wagner etal

METHOD AND APPARATUS FOR MAKING PAPER BY CONTRACTING THE FORMING CARRIER

3,207,657

TO COMPACT THE WEB

Sheets-Sheet 3

Filed Jan. 22, 1963

<img file="US3207657A_D0003.tif" />

3,207,657

Patented Sept. 21, 1965

United States Patent Office

3,207,657

METHOD AND APPARATUS FOR MAKING PAPER BY CONTRACTING THE FORMING CARRIER TO COMPACT THE ¥/EB

Joseph Robert Wagner and Charles A. Lee, Knoxville, 5 Tenn., and Gordon J. Chalmers, Wolfville, Nova Scotia, Canada, assignors to Huyck Corporation, Stamford, Conn., a corporation of New York

Filed Jan. 22, 1963, Ser. No. 253,112

Claims. (CI. 162—208) _χθ

The present application relates generally to papermaking and more particularly to novel papermaking methods and apparatus which are designed to improve certain physical characteristics in the formed paper, in particular its stretch. 15

The present application includes a method of forming paper which comprises the steps of flowing a stock suspension of fibrous material onto a continuously moving foraminous carrier, draining sufficient liquid from the stock suspension to form a wet web of fibrous material 20 on the foraminous carrier, causing controlled dimensional changes to be made in said web thereby to impart improved characteristics to the sheet being formed. The web is compacted laterally or longitudinally or both laterally and longitudinally while it is in a relatively wet state, 25 leaving the web in such condition that, when dried in a conventional manner, the resulting paper has improved qualities, particularly improved stretch.

In the manufacture of paper by conventional procedures, an aqueous suspension of papermaking fibers, ³⁰with or without additional papermaking materials, is delivered to a foraminous carrier or forming fabric. In the usual Fourdrinier machine the forming material constitutes an endless woven wire belt. In order to accomplish good formation of the paper web, the suspension of ³θ fibers is quite dilute, rarely containing in excess of a few percent of fibers and usually less than one percent. The web which is formed on the forming carrier is generally quite fragile in nature. As it is carried by the forming carrier, water is drained from the web and the solids con- ⁴⁰tent increases. Conventionally, a plurality of suction boxes beneath the carrier suck water from the web through the carrier to reduce the water content. At the end of this section of the machine, the solids content may be as much as 20 percent.

The web is generally transferred from the forming carrier to a felt which carries the web through a press section of the papermaking machine where further water is removed from the formed web down to a solids content of 25 to 35 percent. From the press section of the machine, the web is carried by suitable felts through a drier section which may consist of heated rolls or cylinders wherein the bulk of the water remaining in the web is evaporated and the fibers become chemically bonded to one another by the mucilage-like material in the stock. ^J,&gt;After leaving the drier section, the web is usually carried through a calendering section where suitable calender rolls smooth the web and provide the desired finish or gloss to the web. The web coming off of the calender section is then wound upon a suitable take-up reel. ⁶θ It has now been discovered that important improvements in certain physical characteristics of the formed paper can be accomplished by mechanically working the paper web while it has a relatively low solids content and before the fibers are chemically bonded together. Specifically, in accordance with one form of this invention, the web is laterally compacted while on the forming carrier. More specifically, this procedure, which is a material divergence from accepted papermaking practices, γθ imparts additional stretch to the paper web with generally little if any loss in tensile strength.

The principal object of the invention is the provision of improved papermaking methods and apparatus which result in the formation of paper having improved physical properties. A more specific object of the invention is the provision of an improved method of forming paper which imparts stretch to the formed sheet without substantial loss in tensile strength in the sheet. A further object of the invention is to provide a papermaking procedure wherein stretch is imparted to a web by work performed on the web during the time that the web is on the forming carrier.

These and other objects of the invention will be made apparent in the accompanying drawings and the following description of certain preferred embodiments of the invention. In the drawings:

FIGURE 1 is a diagrammatic illustration of the wet end of a papermaking machine capable of forming a paper web in accordance with the present invention;

FIGURE 2 is a top plan view of the papermaking machine illustrated in FIGURE 1;

FIGURE 3 is a diagrammatic illustration of another part of a papermaking machine for compacting a paper web longitudinally in accordance with the present invention;

FIGURE 4 is a diagrammatic illustration of a papermaking machine incorporating features shown in FIGURES 1 and 2 with those shown in FIGURE 3; and

FIGURE 5 is a diagrammatic illustration of a modified form of the apparatus of FIGURE 4.

As noted above, a paper sheet is initially formed as a fragile web of very low solids content. In the present invention, the web is subjected to mechanical working by causing controlled dimensional changes to be made in the web, preferably while the moisture content of the web is more than about 70 percent of its weight. As a result of the process certain improved physical qualities including additional stretch are given to the paper web.

Stretch is a quality desired in many grades of paper and board, particularly in paper used in packaging. It is also advantageous in paper used for printing, as a backing, etc. Stretchability as used herein refers to the quality of paper to deform under load without rupture, but not necessarily to return to its original state when the stress has been relieved.

All paper and board normally formed on a Fourdrinier papermaking machine or on a cylinder machine using wire faced cylinders has some stretch in both the cross direction and the machine direction. However, such stretch is low, and it is the purpose of the present invention to increase this characteristic in the paper which is formed.

In one method of forming paper in accordance with the present invention the usual Fourdrinier forming carrier (which is formed of a wire screen or wire cloth) is replaced by a generally flexible foraminous carrier formed of synthetic resinous material having high tensile strength and suitable resistance to abrasion, fatigue due to flexing, and the like, whether wet or dry. Nylon, a polyamide fiber, is particularly suitable. Other suitable materials are polyesters such as Dacron, or acrylic fibers such as Orlon, Dynel and Acrinan, or copolymers such as Saran.

The above described flexible forming carriers possess a high degree of elasticity and a relatively low modulus of elasticity as compared to the usual Fourdrinier forming wire. When tension is applied mechanically to the forming carrier, dimensional changes are produced in the carrier and in the web which is formed thereon. If such dimensional changes are produced while the fiber mat which forms the paper web is in intimate contact with the fabric weave, any dimensional change in the fabric

3,207,657 ³ will produce a similar dimensional change in the paper web being formed.

Referring to FIGURES 1 and 2, there is shown one example of the wet end of a papermaking machine suitable for performing the method of the present invention. The papermaking machine is provided with a headbox 10 adapted to discharge stock of suitable consistency containing fibers for making paper onto a continuous flexible forming fabric 12 at a breast roll 14. The fabric 12, as previously indicated, may be formed of synthetic fibers. The forming fabric 12 is supported to receive stock discharge from the headbox in a continuous stream and is normally driven at a selected uniform rate.

After the stock has been discharged onto the forming fabric 12, the latter permits sufficient liquid to drain so that a web 16 begins to form in the well known manner. As shown in the drawings, it is conventional to support the forming fabric by one or more table rolls 18 to facilitate draining and formation of the web. At this point, the web has a solids content of a few percent. The carrier and web are thereupon passed over suction boxes 2®A and 20 which suck water from the web through the carrier, further increasing the solids content of the web to as much as 20 percent. The forming fabric passes over a couch roll 22 which may be driven by suitable means, such as a gear 23 and then around suitable guide, support and stretch rolls 24, and expanding rolls 26 back to the breast roll 14. The web 16 is taken off the fabric 12 at the couch roll 22, whence the web passes through a press section and thence to a dryer section.

In the machine structure shown in FIGURES 1 and 2, the suction boxes 20 cause drag on the fabric 12. The couch roll 22 drives the fabric forward, while the suction box drag holds it back. This places the fabric in tension in the machine direction and stretches the fabric in that direction. In this form of the invention, the fabric must be such that tension in the machine direction produces a contraction in the cross direction. This fabric may be made in the manner disclosed in the copending application of Joseph Robert Wagner, Serial No. 253,129, filed January 22, 1963, for “Papermaking Fabric.” As there disclosed, the fabric is made of synthetic yarn with relatively straight yarns in the cross direction and relatively tortuous yarns in the machine direction. In such a case, the stretching of the fabric in the machine direction straightens the yarns in the machine direction and forces the cross yarns to take a more tortuous path. The cross yarns then do not extend so far in the cross direction and the fabric necks down or contracts in the cross direction. A certain amount of necking down has been found in previously known fabrics; see, for example, “Oy Kaukas Finds Plastic Wires Are Fine,” by Olli Saarnio, Paper Trade Journal, September 12, 1960, page 49. However, the prior art has sought to avoid or compensate for this condition which is used and taken advantage of in the present invention. The drag of the suction boxes and the drive of the couch roll thus stretches the fabric in the machine direction and contracts it in the cross direction. Since this happens while the fiber mat forming the web 16 is in intimate contact with the fabric weave, the dimensional change in the width of the fabric 12 produces a similar dimensional change in the fiber mat on the fabric carrier. This results in a compacting of the web 16 in the cross direction which results in a higher stretch in this direction. In order to improve the stretch of the formed sheet in the cross machine direction significantly, the reduction in width of the web 16 should be at least one percent and should occur while the mosture content of the web is more than 65 percent of its weight and preferably between about 75 and about 85 percent of its weight.

Although it is known in the prior art to utilize forming fabrics made of synthetic fibers on conventional Fourdrinier papermaking machines and although such fabrics have a certain amount of stretch, this stretch has been unintentional and incidental and the fabrics were finished in such a manner as to limit their stretch, for this stretching makes the fabrics difficult to handle and could result 5 in their wrinkling and in spoiling of the paper. The present invention does not relate to the use of these known synthetic fabrics on conventional Fourdrinier papermaking machines, but rather contemplates the use of more stretchable fabric arranged on a conventional Fourdrinier machine in such manner as to provide compaction of the web at a critical point in its travel. There is no great advantage in compacting the web while it is in a substantially fluid state, as when the solids content is less than about 10 percent. In this highly fluid state, the web does 15 not stay compacted, if indeed it follows the contraction of the forming fabric at all; rather the fibers are relatively free to flow back into their uncompacted state. It is important, therefore, that at least a substantial amount of contraction of the fabric occur after a substantial amount 20 of water has been removed from the web. At the same time, it is important that there be no substantial contraction after the web has achieved any substantial amount of chemical bonding. As the paper is dried, the fibers become chemically joined together by the setting of the 25 mucilage-like materials between the fibers. If the compaction occurs after this chemical bonding has been achieved, the bonds are often ruptured, thus materially reducing the tensile strength of the paper.

In the present invention the compaction is achieved 30 while the fibers are water lubricated and before appreciable chemical bonding has been achieved so that there is no substantial breaking of bonds. At the same time, there is some bonding through surface tension of the water; yet the amount of water is not so great that the 35 fibers are merely floating around. The compaction in the critical region repositions and bends the fibers. It compacts the fibers so that they are mechanically bound together better, at the same time placing them closer together so that the later chemical bonding is more effec40 tive. Still further, the individual fibers are bent and otherwise deformed to provide a pre-stressing of the fibers in the finished paper. This improved bonding and prestressing results in a paper in which there is an added amount of stretch in the paper as the pre-stressing is relieved, thus permitting appreciable stretching of the paper before the fibers ever reach the relaxed condition of the fibers in conventionally made paper. At the same time, the improved bonding permits this stretching of the paper without appreciable rupturing of the bonds.

₅θ In methods of the prior art, stretchable paper has been made by a shrinking operation carried on in the drier section of the machine. Such methods have the disadvantage that they are carried out after there has been chemical bonding of the fibers, therefore resulting in rup₅₅ turing of these bonds and weakening of the tensile strength of the paper. By use of the present invention, stretchable paper is made without substantial reduction in the tensile strength of the paper, thus permitting the use of thinner paper, at a saving of material. The particular qq region on the machine where the compaction of the web can be most effectively achieved depends upon the particular paper being made as well as upon the manner of operation of the machine. Ordinarily, however, the compaction should not be made until after at least one suction box 20A. The drag of the first suction box 20A, however, tends to contact the fabric laterally as it passes over the suction box 20A. Such contraction is premature, and it is preferable to maintain the fabric at full width until after this first suction box 2ΘΑ.

γθ As shown in the drawings, wheels 30 and 32 may be provided to stretch the fabric laterally to keep it at its full dimension until the point where it is desired to compact the web. The wheels 30 and 32 may be covered with pneumatic tires, and in fact these may be ordinary 75 airplane tires and wheels. By pressure exerted on

3,2 E mounting brackets 31, wheels 30 are pressed against wheels 32 with the fabric therebetween. The wheels 30 and 32 are located on the edge of the fabric outside the part on which the web is laid. The wheels are canted outwardly so as to drive the fabric outwardly and thus keep it at its full dimension. Inasmuch as the fabric is in tension even before it reaches the first suction box 20A, the fabric is not at its full lateral dimension in this region unless it is stretched laterally in this region as well. A series of rolls 34 and 36 are provided to operate in the same manner as rolls 30 and 32 to stretch the fabric in the region where the web is still in a substantially fluid state. This stretching may be sufficient to stretch the fabric even beyond its normal relaxed width. This adds to the amount the fabric, and hence the web, is contracted when the critical region has been reached. By such means, it is possible to provide a contraction of as much as 5 percent. Because of certain difficulties in handling the fabric when it is very stretchable, it is preferable that the compaction be no more than necessary to achieve the desired results. Hence, it has been found satisfactory to provide a compaction of the order of 3 percent in many instances.

As shown in FIGURES 1 and 2, the web is taken from the couch roll while the fabric is laterally contracted and before it is again permitted to expand. Were the tension on the fabric to be relieved while the web was on the fabric the web would be stretched back to its original uncompacted condition.

The apparatus of FIGURES 1 and 2 can be used to develop stretch in the cross direction. In FIGURE 3, there is illustrated apparatus which may be used to provide stretch in the machine direction. The apparatus of FIGURE 3 may be located between the forming section shown in FIGURES 1 and 2 and the press section of the papermaking machine, or it may constitute the press section itself. Depending upon the particular machine and the particular paper being made, it may on occasion be located between the press section and drier section. The important condition is that the apparatus be located to compact the web in the machine direction before there has been any substantial chemical bonding of the fibers.

The apparatus shown in FIGURE 3 includes a pair of fabrics 38 and 40. Fabric 38 is supported and driven by press rolls 42 and 44, and fabric 40 is supported and driven by press rolls 46 and 48. Fabric 38 is additionally supported by rolls 50 and 52. Fabric 40 is similarly supported by rolls 54 and 56. Stretch rolls 58 and 60 are provided to take up the stretch in the fabrics 38 and 40, respectively, and to provide appropriate tension in the fabrics.

Fabrics 38 and 40 are preferably made of synthetic fibers as in the case of the forming fabric 12; however, they are preferably made so as to contract very little in the cross direction when placed in tension in the machine direction. These fabrics will then not expand laterally when the tension is relieved in the machine direction. These fabrics 38 and 40 may be made in the manner disclosed in the copending application of Joseph Robert Wagner, Serial No. 253,099, filed January 22, 1963, for “Papermaking Fabric.” As there disclosed, the fabric is made with relatively straight yarns in the machine direction and relatively tortuous yarns in the cross direction. In such a case, the placing of the fabric in tension in the machine direction does not cause the cross yarns to take a more tortuous path and the fabric does not neck down or contract in the cross direction. At the same time, it is desirable that the fabrics 38 and 40 be stretchable in the machine direction. This may be achieved by utilizing yarns that themselves will stretch. Nylon is particularly suitable for this purpose. Also suitable are elastic or spandex yarns, such as Lycra, or stretch yarns such as Helanca. High twist yarns exhibit substantial stretch properties. 75

07,657

As shown in FIGURE 3, the fabrics 38 and 40 are placed against opposite sides of the web 16 between press rolls 42 and 46 as the web is received from couch roll 22. Unless the apparatus is used in the press section itself, 5 the pressure exerted by the press rolls need not be sufficient to remove any substantial amount of water but merely sufficient to bind the web between the two fabrics 38 and 40 so that any contraction of the fabrics provides similar contraction of the web. The pressure may be 10 exerted through mounting brackets 43. Similarly, press rolls 44 and 48 are pressed together so that the web 16 is held relatively firmly between the two fabrics 38 and 40; additional rolls or press shoes, such as shoes 49 and 51, may be pressed together with the fabrics therebetween, 15 as by brackets 53, to hold the web 16 relatively firmly between the fabrics 38 and 40 as they travel from press rolls 42 and 46 to press rolls 44 and 48. In this form of the invention, the stretch rolls 58 and 60 are adjusted to provide sufficient tension in the fabrics 38 and 40, that the 20 fabrics are stretched several percent, preferably at least 5 percent, in the region other than where the two fabrics 38 and 40 are pressed together with the web therebetween.

Rolls 42 and 46 are driven, as by gears 45, at circumferential speed equal to that of couch roll 22, and rolls 44 25 and 48 are driven, as by gears 47, at a slightly less circumferential speed thereby relieving part of the tension on the fabrics 38 and 40 in the region between the rolls. This results in contraction (shrinking) of the fabrics in the machine direction in this region and hence compaction ^j0 of the web in the machine direction. The tension should not be completely relieved, or the fabrics will go slack and not be pulled properly through the shoes, and the web may pull away from one or both of the fabrics without being compacted. The web 16 is removed from ⁰ between the fabrics 38 and 40 before they are again stretched. The web thus compacted in the machine direction is then passed on to the next section of the papermaking machine, as to rolls 62 and 64 of a succeeding press section.

If the compacting action in the web 16 described above is accomplished before the fibers in the web are substantially bonded together and the formation set, the characteristic of stretch is imparted to the web without any material reduction in tensile strength of the web.

Although only certain embodiments of papermaking machines capable of performing the method of the present invention have been disclosed, it is to be understood that these are merely by way of example and are not to be considered in any manner as limitations. For example, 50 the methods of the present invention may be applied to Yankee papermaking machines of the Fourdrinier type which are commonly used to provide light basis weight papers. It is contemplated that various modifications may be made within the scope of the claims without 55 departing from the spirit or scope of the invention.

For example, it is not always necessary or desirable to provide stretch in both the machine and cross directions. Further, means other than wheels 30, 32, 34 and 36 can be used such as spreader or expander rolls, par60 ticularly those known as Mt. Hope rolls. It is also within the scope of this invention to compact the web in the cross direction after it has left the couch roll. This may be done in much the same fashion as described in connection with FIGURES 1 and 2, or it may be achieved 65 with the apparatus shown in FIGURE 3. In the latter case, the fabrics 38 and 40 should be as described for fabric 12, and rolls 42 and 46 should be driven at a slightly slower circumferential rate than rolls 44 and 48 so that the fabrics neck down as they leave rolls 42 and 46. 70 Still further, drag on the fabric may be supplied by means other than the suction boxes 20 and 20A; for example, a retarded roll may be used. Also, the stretching of the fabric 12 in the machine direction is not always necessary; the release of the tension applied by the wheels 30, 32, 34 and 36 often provide sufficient compaction of the web in

3,207,657 invention is, therefore, limited only as set forth in the following claims.