US1999043A

US1999043A - Method of steeping cellulose and steeping press therefor

Info

Publication number: US1999043A
Application number: US616736A
Authority: US
Inventors: Stuart O Fiedler
Original assignee: DuPont Rayon Co
Current assignee: DuPont Rayon Co
Priority date: 1932-06-11
Filing date: 1932-06-11
Publication date: 1935-04-23
Anticipated expiration: 1952-04-23

Description

April 23, 1935. s. o. FIEDLER 1,999,043

METHOD OF STEEPING CELLULOSE AND STEEPING PRESS THEREFOR Filed June 11, 1952 INVENTOR.

Patented Apr. 23, 1935 UNITED STATES PATENT oFF cs METHOD OF STE PIPING CELLULOSE AND STEEPING PRESS THEREFOR Application June 11, 1932, Serial No. 616,736

Claims.

This invention relates to the alkali treatment of cellulose. The invention also relates to a step in the preparation of viscose. The invention also relates to a steeping press.

In the preparation of viscose the initial steps consist in soaking sheets of wood pulp, cotton linters, or other suitable cellulosic material in a caustic soda solution of approximately 18% concentration and then removing the excess solution by pressing the sheets so that the resultant mass weighs a proximately three times the weight ofthe' original sheets. In these operations it is desirable that every portion-of the finished charge be uniformly treated and have the same chemical composition so that all portions will be uniformly reactive to subsequent chemical treatment; the criterion of good steeping and pressing is how well this condition is fulfilled. In the present systems of steeping and pressing this objective is not fully attained.

In the accompanying drawing Figure 1 is a vertical section through a common type of steeping press taken on the line 1-1 of Figure 3; Figure 2 is a plan view of the same type of steeping press; Figure 3 is a vertical section on the line III-III of Figure 1; Figure 4 is a plan view of my improved steeping press; Figure 5 is a vertical section through my improved steeping press taken on the line VV of Figure 6; Figure 6 is a vertical section of my improved steeping press taken on the line VI-VI of Figure 5.

In Figures 1, 2, and 3 of the accompanying drawing are shown the essentials of a standard type of steeping press. In the manufacture of viscose it is customary to form cellulose into rectangular sheets, place them in the steeping press, flood the press with a caustic soda solution and, at the completion of the reaction, draw off the liquor and press the sheets to a standard caustic content. In the old type of steeping press the sheets are so placed, as shown in Figure 3, that they rest edgewise on the bottom of the tank.

A disadvantage of the old type of steeping press is that unless care is taken the sheets are not placed in the press so that all edges are alined and, even if care is taken, the shrinkage which occurs during steeping throws them out of alinement so that upon pressing of the charge the edges of the sheets which are out of alinement do not receive as much pressing as the other portions of the-sheet, and, consequently, will retain more alkali and water and, upon treatment with the chemicals of the subsequent steps of the process. will react difierently and give a composition which is not uniform, and

which is inferior. Furthermore, the old type of press is unsatisfactory in that during the pressing operation some of the liquor is expressed from the top of the sheets, remains on top during the pressing and soaks back into the tops of the sheets when the pressure is released. Another disadvantage of the old type of press lies in the absorption of liquor from the floor of the press by the edges of the sheets which are in contact with the bottom of the press. Still another disadvantage of the old type of press arises from the tendency of the sheets, made limp by the alkali treatment, to slump, as shown in Figure 1,

when the liquor is run out of the press and before pressing starts even when sandwich plates are used. This slumping causes irregular pressing of the sheets.

It is an object of the invention to prepare uniform alkali cellulose. More particularly it is an object of this invention to uniformly steep sheets of cellulose and to uniformly press alkali cellulose formed therefrom. Another object of the invention is an improved steeping press. Other objects of the invention will be in part apparent and in part set forth in the accompanying description.

In Figures 4, 5, and 6, i0 is a tank of the steeping press in which the steeping takes place; H is a Vshaped bottom in the tank; 2I are sections forming an angularly arranged false bottom in the tank; 22 are perforations in the false bottom to allow the escape of liquor expressed from the sheet; is an inlet pipe by which the alkali solution flows into the tank; 3i is an outlet pipe through which the liquor is drained from the tank; is the plunger by which the caustic liquor is pressed from the sheets; M is the head of the plunger which is placed cornerwise to conform to the arrangement of the sheets and to travel in the trough formed by the V-shaped false bottom; are the sheets of cellulose.

In the preferred form of the invention the cellulose sheets are inserted with the grain of the sheets oblique to the level of the liquor as it rises in the press.

My invention is susceptible of many modifications. For instance, it is not necessarythat the bottom of the tank be made V-shaped. It can be square or of any other shape so long as the false bottom is arranged to support the cellulose sheets cornerwise. Another alteration can be made in the character of the means for supporting the sheets which need not be perforated plates but may be a bar or bars arranged to contact the lower. edges of the sheets.

An advantage of my invention is that, in practice, the sheets automatically aline themselves as they are placed in the trough and, even though the dimensions of the sheet change during steeping, they settle into the trough and maintain their alinement. Since they maintain their alinement they receive a uniform pressing and, consequently, retain in all portions a substantially uniform quantity of steeping liquor. Another advantage of the invention is that the liquor expressed at the top of the sheets runs off readily, just as rain is shed by a gable roof, and, consequently, is not reabsorbed when the pressureof the plunger is relieved. Furthermore, the bottom edges of the sheets are also inclined and rest upon inclined perforated plates so that the liquor expressed from the bottom drains off naturally and rapidly. The lowest corner of the sheets is supported sufiiciently above the bottom of the press to make drainage complete. Another advantage of the invention is in that about one-half of the sheet is completely supported while the unsupported half consists of a triangular section, which, having but little weight at any substantial distance above the support; has substantially eliminated the tendency of the sheet to slump. Still another advantage of my invention is that a better permeation of the sheets by the admitted liquor is achieved. During the admission of the liquor the sheets of cellulose wriggle and curl much more vigorously than in an ordinary press. This wriggling causes the books of pulp to open up more rapidly and completely than they do in the old-type press, results in better steeping, and tends to eliminate the'gelatinous areas commonly called brown spots. Other advantages of my invention will be apparent to those skilled in the art.

As many apparently widely difierent embodimerits of this invention may be made without departing from the spirit and scope thereof, it

is to he understood that I do not limit myself 2. In a means for preparing alkali cellulose, a tank, means to admit liquid to the tank, means to drain the tank, means in the tank for supporting rectangular cellulose sheets comprising a V-shaped, perforated false bottom, and means for pressing the sheets.

3. A method of forming uniform alkali cellulose which comprises supporting cellulose sheets in a steeping press, steeping them in alkali liquor, draining the press, pressing the sheets to expel excess liquid, the top of the sheets as supported in the press afiording drainage by gravity to the liquid expressed from the top thereof.

4. A method of forming uniform alkali cellulose which comprises supporting rectangular cellulose sheets in a steeping press, steeping them in alkali liquor, draining the press, pressing the sheets to expel excess liquid, the sheets being supported corner-wise in the'press so that the tops thereof will aiTord drainage by gravity to the liquid expressed therefrom.

5. In a steeping press a tank capable of receiving sheets of cellulose having angular corners, means in the tank to hold the sheets in the tank with an angular corner upward, means to drain the tank, and means in the tank to press the sheets.

STUART O. FIEDLER.