US2389254A - Manufacture of paper - Google Patents

Description

Nov. 20, 1945. M. A. GOLDMAN A MANUFACTURE OF PAPER Filed Sept. 27, 1940 @HHM N NN thickness.

Patented Nov. 20, 194,5

MANUFACTURE F PAPER Maurice A. Goldman, New Brunswick, N. J., as-

signor, by mesne assignments, to Saco-Lowell- Shops, Biddeford, Maine, a corporation of Maine Application September 27, 1940, Serial No. 358,583

v2 claims.

This invention relates to the manufacture of paper and has for its principal object to provide an improvement in manufacturing paper and an improved paper product.

In usual processes of making paper, the constituent fibers are made into a sheet which exhibits paper-like properties by means of a sequence of operations typified by a beater in which the fibers are gelatinized and dispersed in water, a Fourdrinier or its equivalent, in which the fibers are shaped into a sheet and the water of the dispersion is expressed, and a press in which the sheet is compacted into paper.

My improved process aims to simplify the steps of gelatinizing fibers and o-f forming them into a, sheet of paper, and in a preferred embodiment of the invention herein described the principal functions of gelatinizing and compacting are performed at a single stage of the process by a greatly simplified apparatus. l

My invention provides for the manufacture of paper which may have all of the qualities of paper made by usual processes, but avoids certain disadvantages and removes several limita.- tions that exist in the art of paper making.

For example, in the usual process 0f making paper, a very large quantity of water is used both during the beating process and in the subsequent step of laying the sheet of fibers from the water dispersion. A typical water dispersion suitable for the production of a water laid sheet may contain, for example, 99 times by weight as much water as fibers, and the supplying and dispo-sal of thehuge quantities of water necessary in the paper mill constitute a large item of expense.

In addition, in usual paper making processes there are, depending upon the particular cellulosic material employed, rather definite limitations on the lengths of the fibers which will appear finally in the finished paper. It is necessary that the water dispersion used in a machine such as a Fourdrinier exhibit a certain degree of stability, that is, the fibers must not immediately settle to the bottom of the dispersed mixture nor rise to the top, but must remain uniformly dispersed so that as the water is drawn off, as by vacuum, th'e fibers will be deposited in an even As a usual thing, the preceding mechanical operations which are employed to beat and mix the fibers in water will insure that the fibers are in a condition in which they are properly dispersed in th'e water. The action of beating which is customarily employed to prepare the fibers, has a tendency to reduce the fiber length of such cellulosic marials as wood fibers and cotton fibers to a length of only a few millimeters. The limiting eect upon the fiber length,

created by the necessity of an even dispersion,

would be more apparent if one should attempt to increase materially the length of cotton fibers that are employed in making a cotton paper by usual processes. Cotton fibers of more than a few millimeters in length tend to curl and mat or ball and thus form bunches when suspended in water.

The invention aims to avoid these limitations on the length of the fibers that can be used by avoiding the operation of forming a', water dispersion of the usual kind and thus to avoid the necessity of reducing fibers t0 very short lengths for use in paper making. For example, in present processes of making paper from cotton, rag stock is used, and it is necessary to reduce this stock to very short lengths. This necessity'is avoided by th'e present invention, which permits paper to be made directly from new cotton fibers and without the need of reducing the fiber length. A further advantage of the invention is that it provides an expeditious way of cleaning the cellulosic fibrous material that goes to make up the paper. The present paper making processes,

which' in general begin with operations which re duce the fiber length and form a water suspension, render it difficult or impossible to remove certain impurities from the fibers. Thus, when raw cotton fibers are put into water, impurities, such as particles of leaf, stem, seed or hull, that usually accompany the fibers, are very difiicult to bleach out and can not be removed and must be allowed to go on through' the paper making process. The present invention, on the other hand, renders it possible to produce a web of fibers that have been effectively cleaned in th course of the preparation of the web.

Other objects of invention and features of advantage and utility will be apparent from this specifications and its drawing, wherein the inveny tion is explained by way of example.

'I'he drawing shows diagrammatically equipment arranged for practicing the portionfof the process of this invention which comprises converting a web of loosely associated unbonded cellulosic fibers into a paper sheet.

As a supply of material for the apparatus shown in the drawing, there is prepared by suitable preparatory processes a web of loosely associated and unbonded cellulosic fibers, in which web the fibers are not adhered so as to impart paper-like properties to the web,

In a preferred instance, as applied to the manui facture of cotton paper, raw stock cotton nbers, which may economically be cotton linters mainly of a quarter of an inch or more in length, or, if desired, may be much longer cotton fibers than such linters, are ilrst subjected to opening, cleaning and picking operations which may be performed by conventional cotton machinery. After such treatment, if desired, the fibers may be bleached and then again subjected to another picking operation. As a iinal preparatory operation, the fibers are passed through a carding engine, which for cotton fibers of the linter type is preferably a roller card.

These preparatory operations and the operation of the `cardixig engine besides forming a web in which the fibers are uniformly distributed but loosely associated, also serve to clean the iibers and throw out from the mass of iibers all objectionable foreign particles.

Preferably, there is provided an endless conveyor belt I4 for receiving the fibrous web as it is doil'ed from the card and for carrying this web Ato the apparatus for bonding the iibrous web. 'As

shown in the drawing, the right-hand or delivery end of this conveyor I4 passes around a roll I5 and there discharges the iibrous web I Ii close to and directly above a pair of nipping rollers I1, I8. As diagrammatically shown in the drawing, a liquid bath I9 is provided at the entrance to the nipping rollers.

The liquid bath I9 consists of a suitable solution adapted .to react with the cellulose of the iibers to gelatinize the surface portions of krthe fibers. A number of solutions capable yof gelatinizing the surfaces of cellulosic iibers are available, among these being zinc chloride, caustic soda. and various acids. Preferably the solution consists of sulphuric acid in a concentration of approximately 66%, this having been found to be the most effective concentration, and the quick action of sulphuric acid being preferred.

In passing between nipping rollers I1, I8, the excess of acid is squeezed out of the web, and the fibers are effectively squeezed together under pressure. v

In order that the web may leave the squeeze rollers I1, I8 without a tendency to wind up on these rollers, these rollers are surfaced With a suitable material adapted to present a fairly dry surface to the web leaving the nip. Suitable surfacing materials for the rolls are crepe or sponge rubber, which may have a thickness, of, for example, t/s".

Preferably, the gelatinizing action is allowed to proceed only up to a point where the surface portions of the fibers are suiciently gelatinized to form the necessary bond between fibers, it being ordinarily unnecessary for the interior of the liber to be gelatinized, although this may be done in some cases. l

The web is thereupon subjected to suitable operations for checking the action of the gelatinizing solution and for the removal of this solution from the web, and these operationsmay be carried on by apparatus of various forms. Preferably, a` short distance below the nipping rollers I1, I8, the web I6 is passed through a water bath 20 in advance of the nip of rollers 2I, 22, the water bath immediately checking the action on the iibers of the solution I9.

The web, which now has its fibers bonded together in the form of a sheet of paper, is preferably passed through a suitable washing tank 24, a neutralizing tank 25 (containing any appropriate solution to neutralize any remaining traces of the treating liquid I9), and a further washing tank 2G, the web being subjected to the action of squeeze rolls 29 on leaving each of these tanks.

At this stage the web may, if desired, be subjected to any suitable sizing operation wherein any desired sizing or iilling agent may be added to the paper. For this purpose, there is preferably provided a back 30 adapted to hold the sizing solution 3| and a suitable calender 32 adapted to force the sizing solution into the paper.

Any suitable drying apparatus may then be ernployed to dry the sheet, this drying apparatus being diagrammatically shown in the drawing as comprising a heated cylinder 35 against which the web I6 is pressed by a traveling felt 31, the web of paper being discharged in its finished condition at the right-hand end of the apparatus as shown in the drawing.

A Wide range oi' weights of papers can be made by this process, for example, light weight paper comparable to onion skin, weighing approxi- 'mately 10 pounds to the 50B-sheet ream of per square yard), pa-` 24" x36" size (210 grains pers oi bond weight weighing from 30 to 50 pounds to the ream (630 to 1050 grains per square yard). and papers of ledger weight of, for example,

Vpounds to the ream (1890 grains per square yard).

In general the weight of the finished paper is determined by the weight of the web I6 delivered to the treating bath I9 plus any sizing material that may be added subsequently if a sizing operation is employed.

The invention affords the possibility of manu` facturing papers that are entirely or approximately free from sizing or other added material and consist entirely of the bonded cellulosic fibers. A suitable paper of this type has been manufactured by delivering to the treating bath I9 a web of carded cotton iibers weighing approximately 200 grains per square yard, the iinished paper having approximately the same weight.

It will be apparent from this description that the invention permits the incorporation in paper of cotton fibers which are considerably longer than those customarily employed. The invention is similarly applicable to hemp iibers. For exam ple, in place of or in addition to the cotton fibers, fibers of hemp tow of I/2 inch or more in length may be subjected to the process, producing a paper partly or entirely of hemp in which the hemp fibers are considerably longer than in previously made hemp papers.

For the manufacture of mixed papers of which the fibrous content consists partly of cotton of hemp and partly of wood bers, the same general sequence may be employed. For this purpose, it is only necessary to feed dry loose wood iibers into the carding engine along with the cotton or hemp fibers. 'I'he cotton or hemp bers in this case will serve to retain the wood fibers and enable the web to be doled from the carding machine in a continuous sheet. For certain classes of papers, the web delivered by the carding engine, and the iinished paper, may contain cotton or hemp fibers and Wood iibers in the ratio of 25 parts of cotton or hemp fibers and 75 parts of wood fibers by weight. Other smaller proportions of wood fibers may obviously be employed, with corresponding increase in the proportion of cotton or hemp bers.

. 'I'he invention offers the further possibility and advantage of production of a paper having a high degree of strength in the crosswise direction, or similar degrees of strength in the lengthwise and crosswise directions. The bers of a web delivered from a carding machine are not only evenly distributed, but are laid in the web in different directions so that many of the fibers or many portions of the fibers are directed more or less in a crosswise direction. Thus when without disarranging these fibers the web is bonded together, a considerable amount of the strength of the web will be in a crosswise direction. The exact amount of crosswise strength may be regulated by adjusting the action of the dofflng mechanism of the card to secure more or less crosswise direction of the fibers.

The invention further offers the possibility and advantage of providing a paper having a high wet strength. By sufficiently gelatinizing the surfaces of bers at the nipping rollers I1, I8 and sufficiently compressing the web together, very strong bonds can be formed between the fibers and this combined with the relatively long length of fibers which may be employed, permits the production of papers having a high wet strength, for example 50% of the dry strength. It will be observed that the paper formed by this process need not depend upon sizing or the addition of any added ingredients to give the desired strength. Accordingly, the paper, not depending for its strength on any added ingredient which may be weakened or washed out, in general exhibits a high degree of wet strength.

Although in the preferred form of practicing the invention the fibers of the paper are bonded together only by the union of the gelatinized surfaces of the fibers, so that sizing and lling need not be depended upon for strength but only for finish and weight, yet the invention facilitates the incorporation of sizing and filling because the improved process renders possible the manufacture of a less dense and more porous sheet that will take on sizing and filling better than will a water-laid web.

Iclaim:

1. Process of manufacturing paper comprising delivering, unsupported, to pressure rolls a web, having the weight of paper, namely, from about two hundred to about eighteen hundred grains per square yard, of substantially uniformly distributed unattached cellulosic fibers in a substantially dry state, there applying to the web a quickly acting gelatinizing solution adapted to react on cellulose to gelatinize the surface portions of the fiber, and immediately upon application of the solution thereto and before any substantial travel of the web in a wet state compacting the web by pressurel and thereafter suppressing the gelatinizing action of the solution in the web after passage of the web between the pressure rolls.

2. Process of manufacturing paper comprising delivering downwardly into the nip between pressure rolls a web, having the weight of paper, namely, from about two hundred to about eighteen hundred grains per square yard, of substantially uniformly distributed unattached cellulosic fibers in a substantially dry state, there applying to the web a quickly acting geiatinizing solution adapted to react on cellulose to gelatinize the surface portions of the ber, and immediately upon application of the solution thereto and before any substantial travel of the web in a wet state compacting the web by pressure, and thereafter .suppressing the gelatinizing action of the solution in the web after passage of the web between the pressure rolls.

MAURICE A. GOLDMAN.

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