US2719464A - Method and apparatus for improving sheet formation of dissolving wood pulp - Google Patents

Description

Ucit. 4, 1955 F. R. CHARLES J A METHOD AND APPARATUS FOR IMPROVING SHEET FORMATION OF DISSOLVING WOOD PULP Filed Feb, 18, 1952 2 Sheets-Sheet l 2 51 15? Dryew Secfzn; F5747 ryer Sec Z6072:

F. R. CHARLES 2,719,4'64

METHOD AND APPARATUS FOR IMPROVING SHEET FORMATION OF DISSOLVING WOOD PULP 2 Sheets-Sheet 2 Filed Feb. 18, 1952 32 IN V EN TOR. 33' 3/? flan? /?Q?'Z 'S.

United States Patent Ofiice 2,719,464 Patented Oct. 4, 1955 METHOD AND APPARATUS FOR IMPROVING SHEET FORMATION OF DISSOLVING WOOD PULP Frank R. Charles, Hawkesbury, Ontario, Canada, assigncr to Canadian International Paper Company, Montreal, Ontario, Canada, a corporation of Quebec Application February 18, 1952, Serial No. 272,182

18 Claims. (CI. 92-39) This invention relates to new and useful improvements in forming sheets of dissolving pulp and particularly seeks to provide a novel method of and apparatus for so modifying the pulp sheet structure that improved steeping can be attained when the pulp is to undergo conversion into a cellulose derivative.

One of the first steps in converting sheet pulp into cellulose derivatives such as viscose or cellulose others is to subject the pre-cut sheet of pulp to the action of strong caustic soda in a steeping press to form alkali cellulose. The uniformity of penetration of the caustic is dependent upon several factors, including filling speed, density of the pulp sheets and degree of loading of the steeping press. The steeping efiiciency may be and generally is empirically measured by the extent of brown spotting which has occurred in the treated sheets. Thus, if as generally practiced, the pulp sheets are placed vertically in compartments of a steeping press and suthcient caustic soda of about 18% strength is run in until the sheets are covered, then steeping is allowed to continue for the required time (generally between fifteen minutes and two hours) and then the liquor is drained off and the alkali cellulose sheets hydraulically pressed until their weight is about three times their original dry weight, each sheet may be graded as having, for instance, zero, 12 /2%, 25%, 50% or 75% brown spots based on the area affected and averaged for the contents of the whole press.

Since the caustic must be able to contact the entirety of each pulp sheet and since the sheets swell to from three to seven times their original thickness it has been heretofore considered proper practice to load the steeping presses with not more than 5.5 sheets per inch of compartment space based on a sheet weight of 52 grams per square foot. Heretofore, if the loading were increased above this amount free swelling of the cellulose became more and more restricted and penetration of the caustic between the sheets became less and less perfect, resulting in areas of imperfect mercerization, as evidenced first by surface wrinkling of the sheets, then by brown spots. These are bIOW11COl0I6d due to imperfect removal of hemicellulose; they contain only about NaOH instead of the usual 15-16% and react imperfectly with carbon disulphide and etherifying reagents.

Through the practice of the present invention it has been found possible to so improve the physical formation of the pulp sheets that greatly improved steeping will occur with so-called normal loading of the steeping presses and the improvement in steeping is plainly evidenced even when the steeping presses are over-crowded in comparison with the practices which have been heretofore considered proper. In addition to gaining improved steeping when the pulp sheets are subjected to conversion operations this invention also provides means by which it is possible to secure the improved sheet formation without the necessity of employing extremely expensive anti-deflection press rolls.

It is therefore an object of this invention to provide a method and apparatus for so modifying the formation of pulp sheets that greatly improved steeping characteristics will accrue when the sheets are subjected to steeping operations.

Another object of this invention is to provide apparatus by which improved formation of pulp sheets and subsequent steeping operations may be achieved through the use on the nearly dried pulp on a conventional drying machine of press sections in which the nip pressure between the press rolls does not exceed normal practice.

Another object of this invention is to provide consecutively employed press rolls having cooperatively aligned landed surfaces for improving the formation of a nearly dry web of pulp passing therebetween.

Another object of this invention is to provide apparatus of the character stated in which the rolls at one press section are employed to densify parallel areas of a pulp web passing therebetween, and the rolls of another press section are employed to density at least a portion of the remaining areas of the web whereby to render the sheeted pulp more susceptible to uniform caustic penetration when placed in a steeping press.

With these and other objects in view, the nature of which will be more apparent, the invention will be more fully understood by reference to the drawings, the accompanying detailed description and the appended claims.

In the drawings,

Fig. l is a schematic side elevation of the last drying sections of a typical pulp drying machine into which have been incorporated in accordance with the present invention two pairs of special press rolls;

Fig. 2 is an enlarged fragmentary transverse section taken generally along line 2-2 of Fig. l and shows in detail the landed structure of the ends of one pair of press rolls;

Fig. 3 is a view generally similar to Fig. 2 but shows the arrangement of press rolls in which only the upper roll is landed;

Fig. 4 is a view generally similar to Fig. 2 but shows an arrangement of press rolls at the first press for densifyingonly a portion of the web;

Fig. 5 is a view similar to Fig. 4 but shows the disposition of the rolls at the second press in order to complete the densification of the Web while leaving longitudinal ridges of unpressed pulp;

Fig. 6 is a transverse section of a portion of the pulp Web as it appears after having been subjected to pressing actions in which only the upper press rolls have been landed in the same manner as shown in Figs. 4 and 5; and

Figs. 7 and 8 are generally similar to Figs. 4 and 5, respectively, but illustrative a slight modification in the disposition of the lands in order that the web may be uniformly compacted across its full width.

By reference to the drawings in detail it will be seen that Fig. 1 schematically illustrates the dry end sections of a typical continuously operating pulp drying machine comprised of a plurality of steam-heated drying cylinders and including two pairs of special press rolls located where the moisture of the sheet has been reduced to between 19 and 37%. We have found this to be the range of moisture content, reached toward the final section of the pulp drying machine, wherein the compression of the sheet is most readily effected. From the dryer section the web is passed to either sheeting apparatus or reeling apparatus in preparation for subsequent handling.

The principles of this invention may be effected by suitable variations in the configurations of certain of the press rolls, and in Fig. 2 of the drawings, for instance, an enlarged fragmentary end portion of the first press section C is shown in which a top press roll 4 and a lower press roll 5 are disposed in cooperatively opposed relationship. The upper press roll 4 is provided with a series of spaced lands 6 separated by relatively Wide grooves 7, and the lower press roll is similarly provided with a plurality of spaced lands 8 separated by grooved areas 9. In this particular embodiment of the invention the opposed lands of the press rolls serve to compress a partly-dry pulp sheet having a moisture content between 19 and 37% in such a manner that on its upper and lower surfaces spaced parallel grooves are formed within the areas of which the web is densely compacted, and between such grooves the web undergoes substantially no mechanical compacting.

If in the case of the above mentioned embodiment of the invention it were to be assumed that the loading between the upper press roll 4 and the lower press roll was that which would produce with plain roll surfaces a web sufiiciently compact for normal steeping in the steeping press during the rayon conversion operations, it will be appreciated that due to the landed formation of both press rolls the grooving of the web will effect a greatly increased densification thereof by comparison with that which could be produced with smooth surface press rolls. For example, if the press rolls are so constructed as to have /2" wide lands on 2" centers and the loading of the first press section C is on the order of 400 lbs. per lineal inch of roll length, 1600 lbs. pressure will be effected in the areas of the lands, and grooves in the web compressed to an extremely high degree will result. The pulp web then passes to the second press section D in which the rolls thereof are ungrooved where the rolls are subjected to the same pressure of 400 lbs. per lineal inch to give an effect on the remaining portion of the web of 400 %=530 lbs. per lineal incha worthwhile gainsince the grooves, having already been compressed at 1600 lbs. per lineal inch, are not contacted by any portion of the roll faces at the second press section and consequently do not absorb any of the line pressure in the nip therebetween.

Fig. 3 of the drawings illustrates a modification of the present invention slightly different from that shown in Fig. 2 in that the first press section C is provided with an upper roll 4a landed similarly to the press roll 4 with lands 6a and intermediate relatively'wide grooves 7a. In this case, however, the lower press roll 5a is perfectly smooth across its full width in order to provide for groov- 'ting 'only on the upper surface of the continuously moving web which passes between the rolls. The pulp sheet then passes to the second pair of press rolls D, both of rayon conversion activities without having to employ more than normal line pressure in pounds per lineal inchacross the face of the press. The grooves are on only one side of the sheet but are twice as deep and thus afford the same cross-sectional area for caustic penetration.

In Figs. 4 and 5 of the drawings there is illustrated a further modification which maybe made to the rolls of the first and second press sections of the machine in order to effect the improved sheet formations contemplated by this invention. In this modification the first press section C is provided with an upper press roll 10 having a plurality of relatively wide lands 11 andintermediate grooves 12 and a lower press roll 13 having lands 14 and grooves 15 disposed in opposition to the landsand grooves 11 and 12 of the upper press roll. If, for instance, the-upper and lower press rolls 10 and 13 of the first press section C were to be provided with 1 /3 lands on 4" centers with the first lands located at the left-hand end of each press roll, as viewed in .Fig. 4, the resultant formation of .the web G as it passesthrough the nip between thepress =rolls 10 and 13 is clearly indicated in section in Fig. 4 and provides alternate relatively wide bars of highly compressed pulp and uncompressed pulp. 'In this modification the grooving operation has only been partially completed at this stage, and the'web is passed "to the second press "section D "which is provided with an upper press roll 16 having alternate lands 17 and grooves 18 and a lower press roll 19 having lands 20 and grooves 21 disposed in opposition to the lands 17 and grooves 18 of the upper press roll. Channeling also is provided in the finally formed sheets of pulp through the use of the present modification of this invention because the lands of the rolls of the second press section D are slightly less in width than the grooves of the rolls of the first press section C and the lands and grooves of the rolls of D are reversed with respect to their position in C in order that the finally compacted web G may assume the cross-sectional shape as seen particularly in Fig. 5 of the drawings in which each face of the web is provided with a plurality of relatively narrow ridges of unpressed pulp. In the present instance the ridges would be /s wide and spaced on 2" centers. These ridges when the pulp sheets are subjected to steeping operations in the rayon converting processes will keep the sheets from suction contact with each other and permit free access of the steeping caustic to the central area of the sheets. Furthermore, these low density ridges initially swell more rapidly than the densified remainder as the caustic level rises, tending to facilitate further the penetration of caustic to all parts.

Fig. 6 of the drawings illustrates a slight modification of the formation of the Web G that can be produced through the use of press section roll configurations such as previously discussed in connection with Figs. 4 and 5 but having, however, the upper rolls only of the first and second press sections landed, the lower rolls being smooth.

A further modification consists in having the landed roll of the second press section correspond in position with the smooth roll of the first press section whereby a sheet is formed with grooves alternating with respect to sheet face yet still separated by strips of unpressed pulp.

The principles of this invention for compacting the pulp web into various grooved or ridged formations can also be applied to the production of smooth finished pulp webs in which the pulp has been much more greatly compacted than could be obtained through the use of normal press sections without the use of expensive anti-deflection rolls of such a type as to be capable of imparting substantially higher nip pressures on a pounds-per-lineal-inch basis.

Figs. 7 and 8 of the drawings illustrate the manner in which the first and second press sections C and D can have their upper and lower press rolls landed for this purpose. Typically, the first press section C would be provided with an upper press roll 22, being provided with lands 23 and grooves 24 in which the lands might be, say, 4" in width and spaced on 8" centers. The bottom press roll 25 would be provided with lands 26 and grooves 27 disposed in opposition to the respective lands 23 and grooves '24 of the upper press roll 22. In a manner similar to that discussed above in connection with the modification illustrated in Figs. 4 and 5 of the drawings the lands of the upper and lower press rolls are shown as located at the left end thereof as viewed in Fig. 7 of the drawings. In this case also the partially grooved web after leaving the first press section C will pass through the second press section D provided with an upper press roll 28 having lands 29 and grooves 30. The lower press roll 31 of the second press D will be provided with lands 32 and grooves 33 disposed in opposition .to the lands and grooves 29 and 30 of the upper press roll 28. Thus in the second press section D the first lands from the .left hand end as viewed in Fig. 8 of the drawings will be spaced 4" in from the end, and in this manner the firstand second press sections together are enabled to compact the sheet of pulp to -a smooth, uniformly dense body having a cross section of the type indicated in Fig. 8 of the drawings. In this modificationit will be apparent that if in each of the first and second press sections Cand D a line pressure of 300 pounds per lineal inch 'is used its effective'value in compacting the pulp will be equivalent to 600 pounds employed by a single press .section. In this way the present "invention provides means for employing two relatively inexpensive presses instead of a costly anti-deflection press of the type previously found necessary to apply high nip pressures to a Web evenly across the width of the Webforming machine.

In addition to providing for more ready penetration of the caustic during steeping operations, densification of the sheets serves the added function of mechanically expressing a considerable quantity of free air from the sheets and thus to enhance subsequent steeping operations. Densitication also reduces the swelling speed and contorting of the sheets during filling of the steeping press with caustic soda solution. The contorting has the effect of artificially increasing the packing of the sheets between the compartment plates, causing pressure areas where imperfect penetration of caustic occurs.

The following example illustrates some of the benefits which may be obtained through practice of this invention and it should be noted that the conditions of steeping to which the pulp sheets were subjected in the steeping press represent abnormal crowding together of the sheets by comparison with the normal space previously mentioned. It will be remembered that normal steeping is generally effected with not more than 55 sheets per inch of compartment space whereas in the below given example the press was loaded with 7.5 sheets per inch of compartment space. The particular grooving employed in this example was with /8" intensely pressed grooves on 3 centers, the sheets being placed in the steeping press with the grooves vertical.

The value of the grooved sheets is markedly shown by comparing Sample A to Sample D in which the percentage of brown spots was reduced from 4.3 to 1.3. The improvement is also shown strikingly by the Steeping Quality, a figure derived empirically from observations on the degree of disorder of the steeped sheets and the time required for escape of entrapped air from them; 100 represents perfect steeping.

When grooved pulp sheets produced in accordance with this invention are subjected to steeping operations the grooves, of course, swell to the same sheet thickness as the rest of the sheet, but as hereinbefore mentioned, there is a time delay due to the slower swelling of the grooves which enables full penetration of the caustic liquor to the center of the sheets. For instance, in connection with Sample D above the natural filling speed for the grooved areas of the sheets was 1.8" per minute and for the rest of the sheet 3.0" per minute. A filling speed of 7" a minute was actually used.

Thus it will be seen that the present invention provides apparatus and method for so physically improving the formation of continuously formed webs of highly purified cellulose pulp that marked improvements in its steeping qualities are readily apparent when out sheets of the pulp are subjected to steeping operations, and such advantages are even apparent in the event of overcrowding of the steeping presses. This invention further provides means by which abnormally dense compacting of parallel areas of a continuously moving web of pulp can be effected through the use of ordinary drying machine presses without the necessity of employing costly anti-deflection rolls.

It is, of course, to be understood that various details of arrangements and proportions of parts may be modified within the scope of the appended claims.

I claim:

1. Apparatus for physically modifying the crosssectional configuration of a continuously moving sheet of cellulose pulp to enhance its receptiveness to caustic soda solution during subsequent steeping operations comprising, a press section for a pulp drying machine including upper and lower press rolls, one of said rolls being provided with alternate lands and grooves across its full width, said lands being effective to form a series of spaced parallel grooves of greatly compacted pulp in a web of pulp passing through said press section.

2. Apparatus for physically modifying the cross-sectional configuration of a continuously moving sheet of cellulose pulp to enhance its receptiveness to caustic soda solution during subsequent steeping operations comprising, a press section for a pulp drying machine includ ing upper and lower press rolls, one of said rolls being provided with alternate lands and grooves across its full width, the other of said rolls being similarly provided with alternate lands and grooves disposed in alignment with the lands and grooves of said first-mentioned roll whereby to form on each face of a web of pulp passing through said press section a series of spaced parallel grooves of greatly compacted pulp.

3. Apparatus for physically modifying the cross-sec tional configuration of a continuously moving sheet of cellulose pulp to enhance its receptiveness to caustic soda solution during subsequent steeping operations comprising, a first press section for a pulp drying machine including upper and lower press rolls, one of said rolls being provided with alternate lands and grooves across its full width whereby to form on one face of a web of pulp passing through said press section a series of spaced parallel grooves of greatly compacted pulp, and a second press section including upper and lower press rolls, the one of said rolls corresponding in position with the landed roll of said first press section being provided with alternate lands and grooves disposed in staggered offset relationship with respect to those of the corresponding roll of said first press section whereby to form on the same face of said web of pulp a series of spaced parallel grooves of greatly compacted pulp offset with respect to those formed by said first press section.

4. Apparatus in accordance with claim 3 in which the landed roll of the second press section is disposed in a position corresponding to that of the unlanded roll of the first press section whereby to form on the reverse side of the pulp sheet a series of spaced parallel grooves of greatly compacted pulp alternating with those formed by the first press section and separated therefrom by strips of unpressed pulp.

5. Apparatus for physically modifying the cross-sectional configuration of a continuously moving sheet of cellulose pulp to enhance its receptiveness to caustic soda solution during subsequent steeping operations comprising, a first press section for a pulp drying machine including upper and lower press rolls, one of said rolls being provided with alternate lands and grooves across its full width, the other of said rolls being similarly provided with alternate lands and grooves disposed in alignment with the lands and grooves of said first-mentioned roll whereby to form on each face of a Web of pulp passing through said press section a series of spaced parallel grooves of greatly compacted pulp, and a second press section including upper and lower press rolls provided with aligned lands and grooves, the lands of both rolls being offset to coincide with the grooves of the first press section and being narrower than said grooves whereby to form on each face of said sheet a series of spaced parallel grooves of greatly compacted pulp alternating with those formed by the rolls of said first press section and separated therefrom by ridges of unpressed pulp.

6. Apparatus in accordance with claim 3 in which the widths of the lands and grooves of the several press rolls are substantially equal and the amount of staggering of the lands of the second press section is substantially equal to the Width of a single land whereby to greatly compact said web of pulp across its full Width.

7. Apparatus in accordance with claim 5 in which the widths of the lands and grooves of the several press rolls are substantially equal and the amount of staggering of the lands of the second press section is substantially equal to the width of a single land whereby to greatly compact said web of pulp across its full width.

8. In a method of preparing sheets of highly purified wood pulp for conversion into cellulose derivatives, the step of forming on a surface of a web of pulp a series of spaced parallel grooved areas of greatly compacted pulp whereby to permit ready penetration of treating chemicals to the central areas of pulp sheets cut therefrom when such sheets are steeped in a steeping press.

9. The method of claim 8 in which the grooving is initiated while the pulp web is of from 19 to 37% moisture content.

10, The method of claim 8 in which the grooves of greatly compacted pulp are formed on both faces of the web and in which the grooving is initiated while the pulp web is of from 19 to 37% moisture content.

11. The method of claim 8 in which the grooves of greatly compacted pulp are formed on both faces of the pulp web.

12. In a method of preparing sheets of highly purified wood pulp for conversion into cellulose derivatives, the steps of forming on a surface of a web of pulp a series of spaced parallel grooved areas of greatly compacted pulp, and then forming a second series of spaced parallel grooved areas of greatly compacted pulp alternating with the first formed grooves and separated therefrom by ridges of unpressed pulp whereby to permit ready penetration of treating chemicals to the central areas of pulp sheets out therefrom when such sheets are steeped in a steeping press.

13. The method of claim 9 in which the grooves of greatly compacted pulp are formed on both faces of the pulp web.

14. The method of claim 9 in which the second set of formed grooves occupy the spaces between the first formed set of grooves whereby to produce a pulp web that has been greatly compacted across its entire width.

15. The method of claim 9 in which the grooves of greatly compacted pulp are formed on both faces of the pulp web and in which the second set of formed grooves occupy the spaces between the first formed set of grooves whereby to produce a pulp web that has been greatly compacted across its entire width.

Cir

16. In a method of preparing sheets of highly purified wood pulp for conversion into cellulose derivatives, the steps of forming on a surface of a web of pulp a series of spaced parallel grooved areas of greatly compacted pulp, and then forming a second series of spaced parallel grooved areas of greatly compacted pulp alternating with the first formed grooves and separated therefrom by ridges of unpressed pulp whereby to permit ready penetration of treating chemicals to the central areas of pulp sheets cut therefrom when such sheets are steeped in a steeping press, the formation of said parallel grooved areas being initiated while the pulp web is of from 1-9 to 37% moisture.

17. The method of claim 16 in which the second set of formed grooves occupy the spaces between the first formed set of grooves whereby to produce a pulp web that has been greatly compacted across its entire width.

18. The method of claim 16 in which the grooves of greatly compacted pulp are formed on both faces of the pulp web and in which the second set of formed grooves occupy the spaces between the first formed set of grooves whereby to produce a pulp web that has been greatly compacted across its entire width.

References Cited in the file of this patent UNITED STATES PATENTS 159,515 La Monte Feb. 9, 1875 320,614 Beale June 23, 1885 502,337 Wheeler Aug. 1, 1893 951,954 Loebbecke Mar. 15, 1910 1,033,992 Crane July 30, 1912 1,196,912 Week Sept. 5, 1916 1,344,826 Sexton June 29, 1920 1,776,536 Blanco et al. Sept. 23, 1930 1,884,366 Sutherland Oct. 2 5 1 932 1,929,008 Wells Oct. 3, 1933 1,941,783 Bahr Jan. 2, 1934 1,944,093 Maggart Jan. 16, 1934 2,015,416 Toohey Sept. 24, 1935 2,216,803 Benda Oct. 8, 1940 2,245,014 Sherman June 10, 1941 FOREIGN PATENTS 19,250 Great Britain of 1889

Claims (1)

1. 3. APPARATUS FOR PHYSICALLY MODIFYING THE CROSS-SECTIONAL CONFIGURATION OF A CONTINUOUSLY MOVING SHEET OF CELLULOSE PULP TO ENHANCE ITS RECEPTIVENESS TO CAUSTIC SODA SOLUTION DURING SUBSEQUENT STEEPING OPERATIONS COMPRISING, A FIRST PRESS SECTION FOR A PULP DRYING MACHINE INCLUDING UPPER AND LOWER PRESS ROLLS, ONE OF SAID ROLLS BEING PROVIDED WITH ALTERNATE LANDS AND GROOVES ACROSS ITS FULL WIDTH WHEREBY TO FORM ON ONE FACE OF A WEB OF PULP PASSING THROUGH SAID PRESS SECTION A SERIES OF SPACED PARALLEL GROOVES OF GREATLY COMPACTED PUOP, AND A SECOND PRESS SECTION INCLUDING UPPER AND LOWER PRESS ROLLS, THE ONE OF SAID ROLLS CORRESPONDING IN POSITION WITH THE LANDED ROLL OF SAID FIRST PRESS SECTION BEING PROVIDED WITH ALTERNATE LANDS AND GROOVES DISPOSED INSTAGGERED OFFSET RELATIONSHIP WITH RESPECT TO THOSE OF THE CORRESPONDING ROLL OF SAID FIRST PRESS SECTION WHEREBY TO FORM ON THE SAME FACE OF SAID WEB OF PULP A SERIES OF SPACED PARALLEL GROOVES OF GREATLY COMPACTED PULP OFFSET WITH RESPECT TO THOSE FORMED BY SAID FIRST PRESS SECTION.

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