US2005811A - Method of preparing and maturing alkali cellulose - Google Patents

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June 25, 1935. F, $TE|MM|G 2,005,811

METHOD OF PREPARING AND MATURING ALKALI CELLULOSE Filed Feb. 23, 1935 Patented Jene 25, 1935 f PATNT OFFICE METHOD F PREPARING AND MATURING ALKALI (JELLULOSEV Franz Steimmig, Hermsdorf, near Kynast,

Germany Application February 23, 1933, Serial No. 658,132

In Germany 2 Claims.

My invention relates to an improved method of preparing and ripening of alkali cellulose for the production of viscose.

With the methods hitherto known sheets or. slates of cellulose are subjected in vats to 'the action of an alkali solution of about 18% for several hours, whereupon they are freed by pressure from the excess of lye and are comminuted during several hours. The succeeding maturing process takes place in large receptacles of sheet iron at a temperature of to 24 C. and lasts two to four days.

'I'hese known methods require a great lot of long lasting operations, much power, and big and expensive apparatus. Then again the single steps of the process which are continued at intervals must be carefully watched and the attendants are exposed to the unhealthy effects of the used materials.

Now I do away with these inconveniences by using a continuous thin strip or web of cellulose which is successively conveyed in a continuous operation through the mercerizing lye, is freed from the excess of lye by pressing rollers, and is led through the ripening room. By these means the whole process is simplified, cheapened and improved.

An important feature of my invention consists in the use of a roll of paper or of paper board instead of sheets or slates. The web of such a roll, which may be previously dried, is conveyed by a suitable transporting support, for instance by a wire net preferably of a stainless material, through the lye bath of the usual concentration of about 18% NaOH. This bath is contained in an iron vat and suitable rollers keep the wire net and the cellulose band underneath the level of the liquid.

The mercerizing effect begins as the cellulose 4o web enters into the lye and is nished in a comparativelylshort time inasmuch as the cellulose is introduced in the form of a thin layer. It is deemed superiluous to give exact numbers for the time needed for the mercerization as this depends upon the thickness and the density of the cellulose web. But it may be pointed out that the velocity of the transport of the web and the length of the Vat are to be chosen with relation to the thickness of the web of the cellulose. Under normal conditions a length of the vat of 10 to 12 meters and a conveying velocity of one meter in a minute will sufllce. But I wish it to be understood that I do not conne my invention by these gures.

Instead of one conveying band for carrying the March '1, 1932 (C1. 26o-1o) between which the cellulose strip is inserted. With a high vat it is possible to lead therein the cellulose strip in a zigzag path, so that the vat may then be shorter. It is also possible'to convey two or more cellulose layers one above the other through the vat.

At the exit end of wthe vat there are arranged two or more squeezing rollers, between which the cellulose web reposing upon the conveyer is introduced for pressing out the excess of lye. The distance of the pressing rollers or the pressure to be exerted upon the material ought to be adjustable in order to be able to denne the amount of alkali remaining in the cellulose and to obtain the usual relation of 1 :2.

After leaving the pressure device the squeezed layer of alkali cellulose is removed from the conveying support and is led by means of a second conveyer into the ripening room, while the rst conveyer returns to the entrancev side to receive a fresh cellulose and to so repeat continuously its operation.

In the case that the alkali cellulose in leaving the pressing device should adhere' to the squeezing rolls a scraper may be provided for wiping off of the cellulose. One roll or more lof the pressure device may be covered with rubber or any other material suitable for carrying out the work to be done. In some c ases two or more pressing devices may be arranged one behind the other.

If it is desired to fully remove the hemi cellulose from the cellulose treated with the lye this may be in an eflicient manner obtained by the present invention. To this end it is only necessary to lead the cellulose band through two or more baths of lye. Between the single baths the excess of lye can be removed from the cellulose and the time of the passage of the single bath which may be of diierent concentrations can'accordingly be abbreviated. It is also possible to add to the bath some substances as for instance hydrochinon or molasses adapted to iniluence the mercerizing effect. Means are also to be provided for supplying fresh lye.

After the alkali cellulose band has left the pressing device the mercerizing process is nished and the product obtained is now to be subjected to the ripening process. To this end the alkali cellulose band leaving the pressing device is led on to a second conveyer which for instance may consist 0f a suitable cotton material. By means of this conveyer the cellulose band is brought through a slot into the heating receptacle, wherein the ripening is obtained. The receptacle has a temperature higher than 30. It is special advantage of this part of the invention that the alkali cellulose owing to the form of a thin layer is ripened in a much shorter time at a certain temperature than with the usual methods. The known methods can be carried out at a low temperature only as the alkali cellulose has the form of quite irregular pieces. The ripening lasts therefore longer because the temperature used depends upon whether the mass treated can be rapidly and with certainty cooled at/the right moment for interrupting the ripening. With the known methods it is very diftlcult to act accordingly owing to the irregular form of the mass treated. On the other hand this is easily carried out with the new method because the layer of alkali cellulose is thin and of an equal thickness. As it is possi le to cool speedily the thin layer of cellulose by ringing it into a cooling zone and to so prevent a progressive ripening, I am able to use a higher ripening temperature. Of course the timeof passing the material through the ripening room and the temperature used must yagree with the desired degree of ripening desired.

To prevent an undesirable drying of the alkali cellulose the air within the ripening room can be conditioned with humidity, for instance by blowing into it steam from a boiler.

During the whole operation the alkali cellulose can be protected against the carbonio acid contained in the air by appropriately enclosing the whole apparatus or by circulating fresh air through the shop.

summarizing I may say that the above process aifords the advantages of 'a continuous economical working on the least space and with the least liability of any harm to the attendants. Moreover the new process allows to vary its different steps and to adapt them to the quality of the used primary materials.

In the accompanying drawing I have' diagrammatically illustrated the mode of carrying out the new process. v

I1 is a shaft or any other support for the supply roll I of the cellulose band 2 which'ls unwound and led between the rolls 3 and 4 into the' alkali lye contained in the vat 5. The cellulose band is carried by the endless conveyer 6 and the cooperating rolls 1, 8, 9 and I0 through the bath between the squeezing rolls, I I, I2. After leaving the squeezing rolls the conveyer 6 returns into the vat giving oiI the cellulose band to the second conveyer I3 which brings it into the ripening cabinet Il. Here the cellulose band is successively taken hold of by a series of horizontal endless conveyers Ilia, lib, Ic etc. arranged one above the other. The cellulose band thus leaves the ripening cabinet Il at the exit I6 for the cool-N ing zone outside of the cabinet. But the cooling zone may be arranged within the cabinet.

For the sake of clearness I have indicated the conveyers by dotted lines and the cellulose band by dash and dot lines.

What I claim is:

1. A'method of preparing and maturing alkali cellulose for the production of viscose, comprising the use of a roll of a thin strip or web of cellulose, unwinding this continuous strip from the roll and introducing it into the mercerizing lye, freeing it at the exit from the lye from the excess of lye by squeezing rolls, leading it into and through an enclosed, uniformly heated atmosphere to ripen the same, and controlling therein the degree of moisture.

2. A method of preparing and maturing alkali cellulose for the production of viscose, comprising I the use of a roll of thin stripor web of cellulose, unwinding this continuous strip from the roll and introducing it into the mercerizing lye, freeing it at the exit from the lye from the excess of lye by squeezing rolls, leading it into and through a ripening room. heated to a temperature higher than 30 C. and controlled with regard to the degree of moisture and then into a cooling zone.

` FRANZ STEIMMIG.'

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