US2635509A

US2635509A - Method of processing paper

Info

Publication number: US2635509A
Application number: US705902A
Authority: US
Inventors: Ira C Cowie; Jasper H Purcell
Original assignee: GLASSINE PAPER Co
Current assignee: GLASSINE PAPER Co
Priority date: 1946-10-26
Filing date: 1946-10-26
Publication date: 1953-04-21
Anticipated expiration: 1970-04-21

Description

A ril 21, 1953 l. c. COWIE ET AL 2,635,509

METHOD OF PROCESSING PAPER Filed Oct. 26, 1946 4 Jig: I3: 6 9' INVENTOR. 51 [RH c. cow/5 and .-JH. Z 5E HPURCELL A T TORNEK Patented Apr. 21, 1953 METHOD OF PROCES SING PAPER.

Ira C. Cowie, Norristown, and Jasper H. Purcell, ConshohockemPa assignors to GlassinePaper Company, West Conshohocken, Pa.,..a corporation of Delaware Applicationflctober 26, 1946, Serial No. 705,902-

Q Claims..

Commercial practices, presently followed, for

the production of glassine, or other hard surfaced papers, involve the. treatment of the sheets in such a manner that both surfaces thereof have the same characteristics. This is normally accomplished by passing individual sheets through a super calender. The. density of the sheets is increased, and both surfaces are glazed and polished to the same extent. The finished product is of high quality and finds many uses, but is costly. This high cost bars such paper from many other uses, for which it would other-- wise be selected. For many of such latter uses, one glazed surface, plus proper body characteristics, would meet all requirements. Up to the present, however, the trade has accepted as a fact, that the art of producing glassine, or grease proof papers, has precluded the furnish-- ing of such papers having dissimilar surface preparations. In addition, the trade has also accepted, as a fact, that individual sheets of glassine and grease proof paper, having both of their faces similarly finished, were all that could be obtained for laminating into multiple ply constructions, Hence, considerable effort had to be expended in determining how to secure hard polished faces together.

Our contribution to the art enables the application of dissimilar surface properties to the opposite surfaces of a single sheet of glassine, or

grease proof,,paper. Thisis accomplished, how-- ever; without detracting from the desirable. bod-y characteristics of such papers as heretofore known in the art. In addition, dissimilar surface characteristics can be imparted to two sheets simultaneously with equipment of comparable cost to that heretofore required for imparting identical surfaces to one single sheet. Obviously, then, the cost of super calendering the paper of our invention is materially reduced from that of. the prior art practice. Reduction of the cost factor opens up many more uses for this type. of paper. In addition, the dissimilar surface aspects of our new paper render it highly desirable for a number of other uses.

As examples of new applications where our paper would be particularly desirable the-first is where it is desired to keep, slippage in handling down. lIClI a minimum. This can. be accomplished:

through contact with the unpolished surface of the sheet. Individual fruit wrapping can. be en.- hanced'by the use of this. paper. The wrappers. can. be printed on. the polishedouter surface, thus improvingsales appeal, while retaining the. protection now ofieredby other papers, yet with a reduction in cost. Also, many bags. can be made cheaper, when intended for uses whereglassine surface characteristics are essentialon onlyone side of the wrapper. Finally, a lamination of juxtaposed plies can be produced at a. lower cost and in a more effective. manner.

Considering the manner inwhich our new treatment of paper is carried out, one. might think that the result We were seeking. could be accomplished merely by passing two superimposed sheets through a common. super calender. Such will not work, for where. two sheets are sandwiched together, and run along throughthe common super'calender, as if the sandwich-were one single sheet, various defectsarise. The most common defect. results. from. the generation. of moisture. vapor from the drying of the sheets. This moisture vapor forms into bubbles which ride between the sheets directly. in front of the calender nip. Each of these bubbles acts like a hard marblev between the two sheets. distorting, or distending, them. Then as the distorted, or distended, sheets run into the nip at least one of them is cut. Such cuts run with the travel of the sheet, and continue until the bubbles causing them dissipate in some manner. These cuts, of course, render the cut. sheet worthless. Even though no out results from the presence of the bubbles, a streak occurs which prevents proper super calendering of the sheets, with the result that decidedly inferior paper is produced. This happens so commonly that such a process could not be called satisfactory.

We have discovered, however, that there is a satisfactory way to run two or more sheets through a somewhat modified super calender;

all at the same time. First, it is essential that.

the. sheets must. be separated before they enter. the super ca1ender,. and. that while separated; they must pass over a series. of. spreader boards in order to have. any deficiencies and inequalities in the paper worked out. before the sheets. enter the stack. Next, the sheets must. be kept apart as they go into each nip of the. stackv so that they willnot come together until the exact. in.- stant that they reach the nip. Thus,.the contact of the sheets, andthe. action of the. calender stack on. them, only takesplace for the short distance where theypass betweenv adjacent rollers. The separation of the sheets coming out of the nip is not as critical as the maintaining of them apart until the exact instant that they come together on going into the nip. Nevertheless, the sheets should be separated and maintained apart for a sufficient length of time, to enable air to get at them before they go back into the next nip. I

We have found that the performance of this method, by the employment of a modified calender stack to carry it out, wherein the sheets are separated and brought together again all the way down through the calender stack, imparts the treatment to the paper which is needed to give it the characteristics we were seeking. The outer face of each sheet is ironed to a good glaze, and polished, whereas the inner faces though smooth, will be unpolished.

Two sheets, each with a glaze on its outer face, and even additional intermediate sheets when a glazed face is not needed, can be treated through the method of our invention, at the same speed as has heretofore been employed for the treatment of a single sheet with both faces glazed. Furthermore, the apparatus, though modified is not particularly complicated over that previously used for single sheet production. Obviously, then, considerable economy is introduced into the production of sheet material in accordance with our invention. Its single sheet use is thus widely enhanced over the prior art material as above pointed out. Furthermore, the new material is excellent for laminating, since the fibres on the unpolished surfaces still retain some of their original roundness, and hence furnishincreased securing surface. Transparency, if required, is not impaired, for the laminating cement, more transparent than the paper itself, fillsin the unevennesses in the surfaces, while at the same time securing those surfaces together. Here also the economy of producing the individual sheets is multiplied by the number of sheets secured together, while at the same time a better laminated sandwich results.

If the finished sheets are to be used individually, or if their intended use has not been determined at the time they come off the calender, they can of course be wound up on separate rewind rolls. If, however, it is desired to immediately laminate the sheets they can be led right from the calender into the laminator, with consequent elimination of any intermediate handling. A third alternative would be to wind the sheets direct from the calender on to a single rewind roll, from whence a single rewinding would produce two sheets ready for use, rather than a single one.

If the apparatus of our invention be considered as a sort of a single super calender, then we accomplish more with one super calender at one time, than could previously be done by two or more super calenders, depending upon the number of sheets employed, or than could be done in .twice the time with one super calender. Hence, the labor cost involved in producing the same amount of paper ready to be laminated is cut proportionally. Also, if the paper is led right into a laminator, the labor involved in handling the paper between the super calender and the laminator can be eliminated if desired. Another saving is in the wear and tear on the calender rolls, for obviously there is no more wear on calender rolls when several sheets are passed between them, than there is when only one is em ployed. Hence, the re-flnishing of the calender rolls is likewise cut in proportion to the number of sheets run through the calender stack. Finally, it can be readily appreciated that the production of a calender, with respect to material to be laminated, is multiplied by the process and apparatus of our invention.

It is accordingly an object of our invention to impart dissimilar surface characteristics to sheets of paper.

It is another object of our invention to provide for the imparting of dissimilar surface characteristics to sheets of glassine and grease proof paper.

Another object of our invention is to provide a new process and apparatus for super calendering paper.

Another object of our invention is to produce a more economical paper of the glassine and grease proof type.

Another object of our invention is to provide a method and apparatus for multiplying the speed of finishing paper of the glassine and grease proof type.

Still another object of our invention is to provide a method for improving the adhesive engaging characteristics of a face of fibrous sheet material.

Other objects of our invention are to reduce labor costs in the production of paper of the glassine and greaseproof type; to extend the life of expendable parts of the apparatus employed, to provide a novel super calender-laminator combination and to reduce the cost of handling paper of the glassine and grease proof type.

Further and more detailed objects of the invention will become obvious to those skilled in the art, from a consideration of the following description taken in conjunction with the accompanying drawing, in which:

Figure l is a diagrammatic elevation of the super calendering mechanism of our invention, and for carrying out the process thereof, and

Figure 2 is a diagrammatic end elevation of an illustrative form of laminating mechanism, operable in conjunction with the mechanism of Figure 1.

Figure 3 is a diagrammatic elevation of a rewind roll and a fragment of our super calender, illustrating the rewinding of a plurality of sheets on a single re-wind roll.

Our invention will be described from the point of view of processing papers of the glassine type. It is, of course, understood that our method and apparatus could be employed with and per formed upon other papers which respond in similar fashion to the treatment accorded glassine paper, as described herein. Hence, the reference to glassine is to be considered as in the illustrative and not the limiting sense.

When two sheets of suitable paper are introduced into our super calender each emerges with only one glazed and polished face, as against conventional glassine paper, which has both faces glazed and polished, but it is believed that material so super calendered falls generally within the accepted definitions of glassine. If intermediate sheets are employed they will not have either face glazed or polished, but their density will be increased by the super calendering and they will be effective for a variety of uses including lamination. In the accompanying drawing our invention is illustrated from the point of view of processing merely two sheets of paper. The supply rolls for the same, I and 2, as shown in Figure 1 are of grease-proof paper which has s ampoo already been wetted or hydrated, ready to be passedinto the super ca-lender. The axles 3 andd'of therolls I and 2 are, suitably, and preferably, adjustably .mounted in bearing hangers carried .by and extending from the main frame of the super calender. The sheet '5 coming from the-roll l,, asshown, passes over and in contact with the-sheet .6 from the :roll 2, and the sheets 5 58.1 1115 travel together until they'pass the idler roller From this point on, the sheets are separated "and pass over several sets or pairs of spreader boards :8-19 and ill-1H, which thus :the Sheets in separated relationship across the top of the super calender stack. vAs the sheets are led down in back of the stack, they are passed :over another pair of spreader boards 3:2 sandtlii, .beiore .goingeinto the first :nip Ml.

For "properiperiiormance of ,ourmethod Weha-ve ionnd that the interposit'ion hf several spreader iboards acting on each sheet in advance of the first hip :is .of extreme importance. The .func- .tion of such boards eliminate any inequalities which may v:exist in the sheets passing ithereover. These zboards have their faces which engage the sheets inclined "upwardly from each end towards their dongitudina'l center. The upward projec- :tion .of the common spreader "board at its center is usually about /8". The incline of the boards downwards "from the center tends to force the paper passing thereover outwardlyfro'm the center of the sheet toward the edges, spreading any wrinkles from the center out to the edges. The spreader :boa-rds "also equalize any other deficiencies which may exist in the paper and put it under uniform tension throughout its width. This also eliminates any tendency of the paper to jerk as it moves forward. Obviously where two or more sheets are to pass through a series of nips together, it is desirable that extreme :uni-

formity be imparted to all :of them before they "The location 01 "the spreader boards 12 and I3 with respect to each other, and with respect to the nip M, is also :of particular importance, "for, as already pointed ent, it is a critical characteristic of our invention "that the sheets such as '5 and 6 be kept apart until they meet rig-litin the nip. Normally, the angle at which the sheets com-a together :as they enter the nip should be 30 or more. 4 2 and 1.3, thisclose to the nip, adjustable to vary the angle between the sheets, is also'of prime importance, since it is most desirable to have the sheets extremely uniform, in all respects, when they come into the first nip of thesuper calender.

Rather than describe each roller of our super calender, in detail, we have indicated by arrows the direction in which they travel, and have shown by the letters 'S and '1, respectively, whether the particular roller is a steel one, or a paper .one. The reasons .for providing the rollers or the material shown, and in the relationships indicated, are well known in the art, and it is not "believed necessary to describe the function of each of them in detail. We will thus confine ourselves to identifying those rollers at the respective nips.

' The nip [4 is formed by the rollers l5 and is which tend to come together at the point I4, and would do so save for the sheets of paper interposedtherebetween. As indicatedthe roller I5 is steel and the roller lli is paper. The contact of the

sheets

5 and 6 is only slightly greater than the distance required for them to pass in and but of, the nip HI. Du-ring this time, not

The location of spreader -boards,

only .are'thesheetssubiect to the pressure of "the stack, but the outer face of the .sheetfi is acted upon by the steel :roller l5, while-the outer face of the sheet .5 :is acted upon by the'paper roller I6. The :inner faces of the sheets engage each other. so act against each other to provide a smoothing eflfect. "The sheets :5 and 6 are sepa- :rated as they leave the :nip I4 and pass over the fly rolls 1! and 18,, which are set apart at a convenient distance to "properly separate the sheets and 'to guide them to their next :position. Either or both, of the :fly :rolls H and 1 8 may be adjustable. They are carried :by suitable hangers :on the frame :ofzt'he super calender.

:On leaving the fly rolls 1|] and -18, the sheets *5 and '5 are directed downward *to adjacent the :next nip 1&9 where the sheet :6 passes around the large fly roll 2-0, while sheet 5 passeswaround :an adjustable :fiy roll .21.. These fly irol'ls, "like those previously referred to, are carried on the main frame of the super calender, and the-adjustment of the roller 2! provides ;for whatever adjustment is necessary :in the angle between the sheets 15 and '6, as they come in to the hip 19,. In this nip the outer 'face of the :sheet :5 is again engaged by a paper roll 22, while the outeriface of sheet 6 is engaged by a steel roll 23. On leaving the nip [9 the sheet 5 passes well out "to travel over the fixed fiy roll 24, while the sheet .6 shortly engages the adjustable .fly roll 25, and quickly goes back, at the proper angle with respect to the sheet 5, into the next nip 2.6, where the sheets again meet. On leaving the hip 26, the sheet '6 is the one to be carried out the greater distance, being passed over the fixed fly roll 21, while the sheet 5 passes over the adjustable tfly roll 28,, and turns quickly back into the next nip =29, when it again meets the sheet 6, at the proper angle, but this time between a pair .of paper rolls 3t and 13].

From here :on down, the previous conditions are reversed, since the sheet 6, after :leaving the nip 29, passes over the adjustable .fly roll 32 and into the hip 33, where its outer 'face is engaged by the paper roll 31, rather than :by steel .rolls, as heretofore. The sheet 5 passes out around the fixed fiy ,roll 34 and into the nip 33, where it meets the sheet 6 at the appropriate angle and where its outer surface is engaged by the lower steel roll 35. Again, as the sheets come out of this .nip, they pass over'a pair offiy rolls 36 and 3], at least one of which is adjustable, with the combination of the location and adjustment of theiiy rolls serving to assure the appropriate setting of the angle atwhich the sheets approach each other,10n going :into the next hip.

The upper roll of the next hip 38 is a :steel one 39,-while the lower :one M! is of paper. :From the :nip '38 the sheets make their final pass over the separate fly-rollsi and 42, and go into their last nip 43, between the paper roller 40 and a large steel roll =44. Again the sheets meet at the appropriate angle as they come into the :nip where they are acted upon by the full weight of the stack, with the paper :roll '40 engaging the outer face of the sheet 6 and "the steel -roll 44, the outer faceof the sheet '5. Though-two sheets are thus passed through our modified super calender stack, -it is to be noted that their travel is at substantially the same speed as has'heretofore been employed in the super calendering of single sheets.

As they leave the nip '63, the sheets '5 and 6 are super calendered in the manner contemplated by our invention and are thus ready to be put to any of the uses to which single sheets are adaptable, store, ready for laminating, or may be passed directly into a laminator, as the case may be. In the illustration of Figure l, the sheets and 6 are shown as being wound up on individual rewind rolls 45 and 46. This is the common practice, for then the paper can be put to any use desired. If the paper is to be printed upon, the glazed side should, of course, be used, while if two sheets are to be introduced into a laminator, it will be necessary to make sure that the faces to be brought together with the intermediate film of adhesive, are the inner, unpolished ones. The difference between the faces can be easily determined, since the glaze and polish on the outer surfaces is quite noticeably different from the mere smooth finish given to the inner surfaces. In spite of this smooth finish, however, the fact remains that the fibers on the inner faces are not crushed into the flattened form, the way they would be were a real glaze and polish imparted to them. Nevertheless, the body of the paper has been compressed in the super calendering, so that its density is increased and the smooth surface given to the inner face is of sufiicient hardness, that the desirable moisture, vapor, and grease-proof characteristics are incorporated in the paper.

In Figure 2, we have illustrated a manner in which further savings can be effected by passing the

sheets

5 and 6, on leaving the bottom pair of

rollers

40 and 44 of the calender stack, directly into a laminator. Sheet 5 runs directly from the last nip 43 to the combining roll 41 of the laminator. Sheet 5 runs directly from the last nip 43 to the combining roll 41 of the laminator, while sheet 6 passes up over a waxing roll 48, where its under surface receives a coating of a suitable adhesive. Even spreading of this adhesive is assured by passing the sheet 6 over an additional spreader roller 49 from whence the sheet runs to a combining roll 41, when it is secured to the sheet 5 by means of its coating of adhesive. From the joining position 50, the sheets hug the surface of the combining roller 41, for a substantial arc thereof, and then pass around a substantial portion of the periphery of the roller 5!. From the roller 5| the finished laminated sheet is rolled up on the rewind roll 51. No attempt has been made to show conventional details of a laminator, for it is believed that one skilled in the art could supply the same upon being provided with a diagrammatic showing of Figure 2.

In Figure 3 we have illustrated another manner of winding up the treated sheets as they come from the bottom of the super calender. The bottom rolls 4i) and 44 of the super calender are the same as heretofore described, but we have illustrated three sheets, 5, 6 and 53 passing into the last nip of the same, rather than the two previously shown. Instead of separating these sheets, as they leave the nip, for separate rewindin'r, they are here all Wound up together on a single rewind roll 54. Of course, the footage wound on such a roll would be less than would be the case were a single sheet being wound up, unless the roll were to be much larger than normal. This winding is of particular advantage when the paper is to be laminated since a composite rewind roll, such as 54, can be moved to the laminator, rather than a plurality of individual rolls, as would otherwise be necessary. This composite re-winding could, of course, be done as well with two sheets as with three, or, conversely, with a larger number.

Though we have not gone into detail to show precisely how one or more intermediate sheets of fibrous material could be carried along through our improved super calender, and be treated in accordance with the method of our invention, it is believed that one skilled in the art, following the above teaching, could determined how to do it and what the results would be. It would need to be kept in mind, first, that the initial spreading of each sheet must be fully carried out; next, that the angle by which the sheets approach the nip would have to be the appropriate one, considering the nature and condition of the material being fed thereinto, and also that a separation of the sheets, as they travel from one nip to the next should be effected. Only the two outside sheets would have faces which are glazed and polished, the intermediate sheet, or sheets, having both faces finished merely to a smoothness comparable to that imparted to the inside faces of the outer sheets. Thus, care would need to be taken in selecting the proper sheet, and proper face for the use to which the paper was to be put.

It is believed that various changes in carrying out our process, and in the construction we have disclosed, may be made while still embodying the invention and without departing from the scope thereof. It is thus intended that all matter containedin the above description, or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

Having described our invention what we claim as new and desire to secure by Letters Patent is:

l. The improvement in the art of super calendering sheets of hydrated fibrous material which comprises, directing a plurality of separated sheets of said material toward each other at an angle to meet at substantially a line contact, pressing said sheets together at substantially said line of contact while ironing the outer surfaces thereof, releasing said pressure by separating said sheets and feeding them away from said line of contact, maintaining said sheets in said separated relation while transporting them with both faces of each thereof exposed to the air, directing said sheets toward each other again at an angle to meet at substantially a second line contact, and pressing said sheets together and ironing the outer surfaces thereof at substantially said second line contact.

2. The improvement in the art of super calendering sheets of hydrated fibrous material which comprises, directing two spaced sheets of said material toward each other at an angle to meet at substantially a line contact, pressing said sheets together at substantially said line of contact while ironing the outer surfaces thereof, releasing said pressure by separating said sheets and feeding them away from said line of contact, maintaining said sheets in said separated relation while transporting them with both faces of each thereof exposed to the air, directing said sheets toward each other again at an angle to meet at substantially a second line contact, and pressing said sheets together and ironing the outer surfaces thereof at substantially said second line contact.

3. The improvement in the art of super calendering sheets of hydrated fibrous material which comprises, directing two spaced sheets of said material toward each other at an angle to meet at substantially a line contact, pressing said sheets together at substantially said line of contact while ironing the outer surfaces thereof, releasing said pressure by separating said sheets and feeding them away from said line of contact, maintaining said sheets in said separated relation while transporting them with both faces of each thereof exposed to the air, directing said sheets toward each other again at an angle to meet at substantially a second line contact, pressing said sheets together and ironing the outer surfaces thereof at said second line contact, and releasing said pressure and separating said sheets again to expose both sides of each thereof to the air as they leave said second line contact.

4. The improvement in the art of super calendering sheets of hydrated fibrous material which comprises, spreading separated sheets of said material laterally to render each of them uniform throughout their width, directing said sheets toward each other to meet at an angle at substantially a line contact, pressing said sheets together at substantially said line of contact while ironing the outer surfaces thereof, releasing said pressure by separating said sheets and feeding them away from said line of contact, maintaining said sheets in said separated relation while transporting them with both faces of each thereof exposed to the air, directing said sheets toward each other again at an angle to meet at substantially a second line contact, and pressing said sheets together and ironing the outer surfaces thereof at substantially said second line contact.

5. The improvement in the art of super calendering sheets of hydrated fibrous material which comprises, directing a plurality of separated sheets of said material toward each other to meet at substantially a nip of a super calender stack, pressing and ironing said sheets together in said nip, feeding said sheets past said hip and separating said sheets again to expose both faces of each thereof to the air, transporting said sheets with said faces so exposed, bringing said sheets together again to meet substantially at another nip of said super calender stack, and pressing said sheets together and ironing the outer surfaces thereof in said other nip.

6. The improvement in the art of super calendering sheets of hydrated fibrous material which comprises, directing a plurality of sheets of said material toward each other to meet at substantially a nip of a super calender stack, pressing and ironing said sheets together in said nip, feeding said sheets past said nip and separating said sheets again to expose both faces of each thereof to the air, transporting said sheets with said faces so exposed, bringing said sheets together again to meet substantially at another nip of said calender stack, pressing said sheets together and ironing the outer surfaces thereof in said other nip, and releasing said pressure and separating said sheets again to expose both faces of each thereof to the air as they leave said other nip.

7. The method of super calendering a plurality of sheets of hydrated fibrous material simultaneously which comprises, subjecting a plurality of sheets of such material to a series of similar pressing and ironing operations, each of said series of operations comprising directing said sheets toward each other to meet at substantially a line contact while transporting said sheets with both faces of each thereof exposed to the air, pressing said sheets together at substantially said line of contact while ironing the outer exposed faces thereof, releasing said pressure from said sheets by feeding said sheets past said pressure station, separating said sheets again after release of said pressure and directing said sheets into position for commencement of the next of said series of similar operations.

8. The method as in claim '7 wherein a part of said series of pressing and ironing operations is performed with a rigid member on one side of said sheets and resilient member opposed thereto on the other side of said sheets, and another part of said series is performed with said rigid and resilient members in reversed relation.

9. The method of super calendering a plurality of sheets of hydrated fibrous sheet material simultaneously which comprises, subjecting said sheets to a series of similar pressing and ironing operations in the nips of a super calender stack, one of said similar operations comprising transporting said sheets in separated relation with both faces of each thereof exposed to the air, directing said separated sheets toward each other to meet substantially at a nip of a super calender stack, pressing said sheets together and ironing the outer surfaces thereof while passing said sheets through said nip in superposed relation, releasing said pressure by feeding said sheets past said nip, separating said sheets again as they leave said nip to expose both sides of each of said sheets to the air and transporting said separated sheets into position for introduction into the next nip in said stack.

IRA C. COWIE. JASPER H. PURCELL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,411,656 Colley Apr. 4, 1922 1,462,154 Thoma July 1'7, 1923 1,503,246 Robinson July 29, 1924 1,606,428 Kirschbaum Nov. 9, 1926 1,714,261 Egan et al May 21, 1929 1,862,656 Boyer June 14, 1932 1,896,205 Simpson Feb, 7, 1933 1,986,961 Dodge Jan. 8, 1935 2,251,890 Montgomery Aug. 5, 1941 FOREIGN PATENTS Number Country Date 1,926 Great Britain of 1903 430,309 Great Britain June 17, 1935 515,011 Great Britain Nov. 23, 1939 184,351 Germany Apr. 29, 1907 475,268 Germany Apr. 22, 1929 OTHER REFERENCES Modern Pulp and Paper Making, 2d Ed, Witham, 1942, pages 549 and 550, Rheinhold Publishing Corp., N. Y.