CA1089273A - Treating chemically delignified and fiberized cellulosic pulp for pulp property improvement - Google Patents

Treating chemically delignified and fiberized cellulosic pulp for pulp property improvement

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Publication number
CA1089273A
CA1089273A CA313,602A CA313602A CA1089273A CA 1089273 A CA1089273 A CA 1089273A CA 313602 A CA313602 A CA 313602A CA 1089273 A CA1089273 A CA 1089273A
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Prior art keywords
pulp
process
psig
refining
consistency
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CA313,602A
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French (fr)
Inventor
Jordan Kopanidis
David S. Wooley
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Boise Cascade Corp
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Boise Cascade Corp
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Abstract

ABSTRACT OF THE DISCLOSURE
Chemically delignified and fiberized cellulosic pulp having a TAPPI K number of from O to 30 is mechanically refined at a con-sistency of from 10 to 50% by weight, at a steam pressure of from 10 to 60 psig, and at corresponding temperatures for saturated steam under conditions resulting in an energy input into the pulp of from 0.5 to 10 net horsepower days per ton. The resulting tr-eated pulp has significantly improved properties of tear, elonga-tion, bond, and tensile energy absorption, while maintaining its other paper-making properties at high and commercially acceptable levels.

Description

TREATING CHEMICALLY DELIGNIFIED A~D FIBERIZED
CEL~ULOSIC PULP FOR PULP PROPERTY IMPROVE~IENT
Background of the Invention Field of the Invention This invention relates to a process for mechanically treating chemically delignified and ~iberized cellulo~ic pulp and to the pulp product of improved properties resulting therefrom.
De3cription of the Prior Art In the manufacture of paper, strength properties in two areas must be satisfied: Those affecting machine runability and those affecting final product strength. Overall, three areas of fiber characteri~tics are critical: (a) their contribution to the stren-eth requirements, (b) t~elr contributlon to brightness, density, smoothnes~, opacity, and other propertles related to product re-quire~ents; and (c) their co~t~
There are essentially three papermaking ~iber types: (a) ~roundwood (which i9 least expensive and weakest), (b) short chem-ical fiber (which is intermediately expensive and strong), and (c) long chemical fiber (which i8 most expensive and strongest). To achieve the physical property balances required, a substantial pro-portion of long chemical fiber conventionally is blended with gr-oundwood or short chemical ~iber. The lone fiber portion of theseblends adversely a~fects the furnish costs and some product quality aspects.
To minimize the requirements for the relatively expensive long chemical fiber and to improve the product quality of the blends, it is common practice to refine cellulosic ~ibers mechanically pr-ior to final papermaking utilization. This treatment causes a change in the specific surface area and/or shape, size and charac-teristics of the individual pulp fibers, designed to satis~y st-rength properties in the two areas referred to above, viz., the properties affecting machine runability and final product strength.
Specifically, pulp properties sought to be improved are app--1- ~

10~9Z1~3 arent density, burst factorJ tear ~actor, fold, tensils strength, elongation, internal bond and opacity.
The problem has been that the application of treatments which successfully improve the pulp with respect to certain of these properties deteriorates the pulp with respect to others. It i9 di~ficult to devise a mechanical treatment which materially impro-ves the properties of the pulp in any given respect, while still maintaining a satisfactory balance of the other important pulp pr-operties.
The most common mechanical fiber treatment practiced in the papermaking field i9 low consistency beating or re~ining. In these operations the pulp, in the ~orm o~ a slush or slurry in water, having a consistency ~rom about 0.3~ to about 5.0~, is sub~ected to mechanical treat~ent in a beater, a disc re~iner, a con~cal re~
~iner or related equipmenk. This action improves some strength properties of the resultant paper, notably tensile strength and burst strength, However, these strength improvements are achieved at the expenss o~ other desirable properties such as tear strength, tensile energy absorption and pulp ~reeness.
Since low-consistency beating or re~ining procedures induce ~iber damage or fracturing, other techniques o~ processing cellulo-sio pulp have been devised.
In one such process, Hill U.S. 2,516,384 and 3,028,632, as reported in PaPer Trade Journal, Vol. 128, No. 9, pages 17-22 (March 3, 1949~ and Vol. 128, No. 11~ pages 19-27 ~March 17, 1949), fibers are worked at high consistency between two opposed relatively gyrating working elements whils under atmospheric pressure condi-tions.
Although the application o~ this atmospheric pressure procedure improvss some properties9 i.e. tear, opacity and rreeness, it dr-astically reduces the bonding properties o~ the pulp below accept-able limits. Accordingly, this proce~s has not gained widespread commercial acceptance.

~89273 Leask U.S. 3,661,328 defiberizes wood chips and other raw cellulosic material, rather than chemically delignified and fiber-ized cellulo3ic pulp, in a mechanical defiberizer wherein the lig-nocellulose is worked in an atmosphere of steam and accordingly utilizes the high temperature of the ~team to soften the lignin in the raw wood. However, the Leask process does not address itself to the problem toward which the pre~ent invention i5 directed, viz., the problem of the properties of delignified cellulosic pulp, and his product i8 not the same as, nor directed toward the same end purpose, as is the product of our invention. Leask defiberizes raw wood chips to produce lignooellulosic pulp. We refine deligni-fied cellulosic fiber to produce a cellulosia pulp o~ improved properties .
Henderson et al U.8. 3,382,140 describe~ a ~igh conslstoncy refin1ng process for papermaking pulp. This process is termed hereln the "HCR" proces~ to distinguish it from the process of our invention which i~ a high consistency, high temperature refining process, termed herein the "HCTR" process.
While the pulp product of Henderson et al may be converted to a papermaking web having physical properties improved in certain respects, its application is attended by serious disadvantA~es whlch limit its commercial application. For example, even with the refinine power input at its lowest stipulated level, the Henderson process produces pulps of higher density than are desired for the manufacture of fine or publication grade~ of paper. In fact, the ~enderson et al proce~s densifies the pulp so rapidly that as a practical matter it is not possible to control densi~ication to the desired range. As a result, certain papers made from the pulp are commercially unacceptable becauqe of high density and insurficient opacity.
In summary, while the prior art procedures for mechanically refining cellulosic pulps have found wide application in the paper-lOl~9Z73 making industry, nevertheless their effectiveness~ has~not been such as to enable reducti~on of the ~equired proportion of the long chemical fiber content of the papermaking furnish significantly below-its current level. This disappointing result derives from the ever-present pulp property deficits which accompany the property advantages of the refined pulp. Specifi-cally, high tear, stretch, tensile, bonding and opacity at low-power input and low apparent density are not simultaneously achievable by any of the pro-cesses known to the prior art.
Objects of the Inventi~on It accordingly is the general object of the pr~sent invention to provide a process or treatincJ
chcmically delignified and fiberized cel:Luloslc pulp for improvement of its strength and other papermaking properties.
It is another object of the present i,nvention to provide a process for mechanically treating cellulosic pulp to produce a pulp product having an enhanced balance of properties .
It is another object of the present invention to provide a process ~or treating chemically delignified and fiberized cellulosic pulp to enhance its balance of phyi-cal characteristics beyond levels available with conven-tional refining.
In summary of the above, therefore, the above objects are met by the present invention which provides the process for treating cellulosic pulp for property improvement which comprises:providing a quantity of chemicallv delignified and fiberized cellulosic pulp characterized by: a TAPPI K number of from 0 to about 30, a ~onsistency ,,, _ a~ --~()89273 of from about 10% to about 50~ by weigh~, a temperature corresponding to the temperature of saturated steam at a pressure from about 0 to about 60 psig, and mechan-ically refining the pulp at said consistency under a steam pressure of from about 10 to about 60 psig, substantially continuously, at a feed rate and under refining conditions determining an energy input into the pulp of from about 0.5 to about 10 net horsepower days per ton.
Description of the Drawings The four figures of the drawings consist respective-ly, of graphs illustrating the efect on pulp properties of applying a typical high consistency, high temperature reining procedure ~CTR) oE our invention to chemically delianified and fiberized cellulosic pulps, as compared to the effect of applying the conventional high consis-tency refining (HCR) procedure thereto.
Fig. 1 is a graph of apparent density vs. energy in-put for the two procedures. The energy input is express-ed ~s horsepower days per ton (HPD/T). (TAPPI StandardReference No. T-220.) Fig 2 is a plot of elongation vs. energy input.(TAPPI
Standard Reference No. T-457.) Fig. 3 is a plot of tear factor vs. energy input.
(TAPPI Standard Reference No. T-220 . ) Fig. 4 is a plot of Scott internal bond vs. energy input. (TAPPI Standard Reference No. RC-308.) General Statement of the Invention Generally stated, the presently described process comprises mechanically refining chemically delignified, fiberized, preheated 1(~8~273 cellulo~ic pulp in an environment Or high pres~ure ~team but under a condition Or low refining power con~umption.
Stated more specifically, the hereinde~cribed process for treating chemically delignified, fiberized, cellulo~ic pulp compri-ses providing a quantity of the pulp characterized by: (1) a TAPPI
"K" number o~ from 0 to about 30; (2) a con~listency of from about 10~ to about 50~ by weight; and (3) a temperature corre~ponding to the temperature of saturated steam at a pre~sure of from about 10 to about 60 psig. The pulp thus characterized is mechanically re-fined at the stated consistency under a steam pressure ~rom about10 to about 60 psig, sub~tantially oontinuously, at a feed rate and under re~ining conditions predetermined to re~ult in an energy input into the pulp o~ from about 0.5 to about 10 net horsepower dAys pcr ton.
It i~ to be notsd that the procedure Or the invention as out-lined above is directly contrary to the teachings o~ the prior art.
It would be expected that mechanically rerining chemically delig-ni~ied and riberized cellulosic pulp in the presence of high pres-sure steam would oause d~gradation of the cellulose, a le9~ of brightness, and deterioration of other pulp propsrtie~. Ample au-thority is available in support o~ this conclusion, the following being illustrative:
Meohanioal Treatment o~ Chemical Pulps by M. D. FaheyJ Tappi, Vol. 53, No. 11, November, 1970. At Page 2053, first complete paragraph of column 1. See also Page 2062, column 1, fourth com-plete paragraph thereof as well as Page 2063, column 1, third co~plete paragraph and page 2064, column 1, la~t sentence of the fi~th complete paragraph.
West, et al. U.S. 3,445,329, Column 2, at line 65 and ~ollow-ing; column 3, at line 10 and following and lines 27-47 inclusiv0 thereof.
Hill U,S. 2,660,097, column 3, line~ 43-47 inclu3ive.

~089Z73 "The Curlator" Its Application to Hi~h Yield Newsprint Sul-phite, Frank P. Silver - Papsr presented at Annual Meeting of the Technical Section of the Canadian Pulp & Paper Association, Montreal, Quebec, January 26-28, 1949. See the Abstract published in Pulp &
Paper Magazine o~ Canada, Convention Issue, 1949 at page 196; page 199, column 1, first incomplete paragraph thereof, last sentence.
Development o~ 65 Per Cent Yield Sulphiite ~or Newsprint Fur-nish~ Pulp & PaPer Ma~azine of Canada, Convention Issue, 1953; Ab-stract at Page 215; column 1, first complete paragraph at page 218, column 1, fourth complete paragraph at page 219.
Surprislngly, we have discovered that, contrary to t;he teach-ings of the above and other referenc~ sources, where the pro¢edure i~ carried out under the conditions di~closed and claimed herein, mechanically re~ining chemically deligni~ied and riberized cellu-lo~ic pulp at high consi~tency and in a hlgh pres~ure ste~m environ-ment actually improves its papermaking qualities to a significant degree and in important re~pect~, without significantly degrading the cellulose~
Speci~ically, mschanically refining such a pulp under the st-ated conditions improves signirioantly its properties o~ tear, el-ongation, bond, and tensile energy absorption while maintainin~
its apparent density at the desired value and its other papermaking properk~es at satis~actory levels.
The accuracy o~ this conclusion is clearly portrayed in the four figures of the drawings which are, respectively, plots of power con~umption ~horsepower days per ton) vs. apparent density, elongation, tear, and Scott internal bond. An inspection of these plots indicates at once the very greatly improved properties of the pulp produced by the herein described high consistency~ high temp-erature refining procedure (HCTR pulp) as compared with that pro-duced by the high consistency re~ining procedure o~ the prior art (HCR pulp). Fig. 1 indicates, furthermore, that these propertie~
are achieved while mRintaining the apparent density of the pulp 1~139273 at the desired commercially acceptable level chosen from a wide range of values.
The practical aspects of this improvement are Or the greatest importance.
As will be shown hereinafter9 by the practice of the present invention it i9 possible to substitute without sacrifice of paper properties a low cost pulp such a~ a hardwood kraft pulp or a me-chanical pulp ~or a substantial proportion of the high cost, long fiber pulp heretofore required to pruduce papers of certain grades.
In a typical lO00 ton per day paper mill, such a substitution can result in a raw material cost saving o~ over l~ million dollars per year, depending upon the cost and availability of the long riber pulp. Multiply this savin~ by a ~actor corre~ponding to the number Or paper mills making simllQr paper products and the total econo~ic saving made possible by the application of the process o~ our in-vention 19 indeed significant.
In addition, for integrated older mills, which represent the ma~ority of North American paper mills, the present invention makes other substantial prorit opportunities available. For example, if the mill ha~ limited digester capacity which limits pulp pro-duction, use Or the present proce~s can reduce the requirements ~or low yield, long riber pulp, and th0reby increase ~ubstantially the digesters~ effective productivity by using the digester capacity ~or making higher yield pulp.
The same opportunity is present in a mill having limited re-covery facilities. By reducing the need for long cellulosic fibers, the production Or which i9 attended by the production o~ an incr-eased amount Or black liquor to be cycled to recovery, the strain on the recovery unit is relieved, In addition, the present process leads to the procluction of a pulp, and hence Or a paper, which provides a higher profit margin because of its increased use Or lower cost pulp, while maintaining commercial produ¢t properties.
DESCRIPTION OF PREFERRED EMBODIMENTS
OF THE INVENTION
As ~tated above, the pulp treating process o~ our invention essentially comprises mechanically refining chemically deligni~ied and fiberized cellulosic pulp in a preheatedl condition, at high consistency, at high temperature~ in an environment of superheated steam, under a condition of low power consumption.
The chemically delignified cellulosic pulp employed as the starting material may comprise any chemically delignified pulp in fiberized conditlon, e.g. softwood or hardwood pulps or mixtures thereof, wherein the fibers are in the condition of ~ubstantially individual ~ibers.
The pulp8 may be bleached or unb~ea¢hed. Pre~0rably they com-prise the chemio~lly dellgniried ~ulp~ rererred to in the art as "full ohemioal pulp8" . In the manufacture of ~uch pulps, a variety of pulping liquors are employed, for example those employed in the conventional kraft, soda or other alkaline systems; in the sulph-ite, bisulphite or okher acid systemq; in the neutral sulphite Sy9-tems; and the like.
In many chemical pulping operationq the wood is both deligni-rled and ~iberized. In such ca~ss the re~ultant pulp i9 well suit-ed for feeding at the proper ¢onsistency to the refining process of this invention.
On the other hand, it i9 possible to subject wood chips to chemical delignification under conditions whereby, although sub-stantially delignified, the pulp i9 not fully fiberized. In ~uch caqes the delignified pulp may be sub~ected to fiberizing operations under mild conditions which do not adversely affect fiber length.
The re~qultant delignified and fiberized pulp then i5 suitable for employment as a starting material for the proceqq o~ this invention.
In contradiqtinction to lignocellulosic pulps produced by the ~echanical defiberi~ation of wood, the pulps which are ~uitable _9_

2~3 ror our purposes are largely cellulosic in character and contain but a small proportion of lignin. B~ de~inition, a pulp suitable for our purposes mu3t have a lignin content such as to be charac-terized by a permanganate number ("K number"), as measured by TAPPI Standard T-214 t3-50, of from 0 to about 300 Pulps having K numbers hi~her than 30 contain too much lignin to be treated satisfactorily by our process.
The pulp to be treatad must be of high consistency~ i.e. a consistency Or broadly from about 10% to about 50%, preferably rrom about 30 to about 45% by weight. A pulp Or this consistency is obtained by feeding the contents Or the digester in which it is produced into a washer where it is slurr~ed or otherwi3e washed to remove chemical~ and 3~parated lignin. Therea~ter the pulp i~ de-watored in a suitable dewaterin~ system, such as a twin roll presQ, a screw press, a piston press, a vacuum filtsr, or vacuum flashing apparatu~.
The pulp product of any Or the foregoing devices has a con-sistency o~ broadly from about 10 to about 50~. To make it more easily handled, the dewatered pulp prererably is pa~sed through a shredder or similar device which breaks it down into chunks or pieces having cro~s sectional dimen3ions Or the order o~ less than onc in¢h. Pieoes Or this size are be~t suited ~or conveying, hand-ling, steaming and refining under the conditions Or the presently described process.
The ribrous raw material may, if de~ired, contain a proportion Or any of the well known pulping and papermakin~ additives such as alum or caustic ror pH control, polyelectrolytes ror zeta potential control, peroxides ror bleachin~, pigments ror optical control~
resins ror ~izing control, etc.
To achieve the purposes o~ the present invention it is neces-sary that the ribrou3 stock be at a temperature level corresponding to the temperatur0 Or saturated steam at a pre~sure Or ~ro~ about _ln_ ~89273 10 to about 60 p9ig~ pre~erably from about 30 to about 50 p~ig.
Stated otherwiseJ the temperature of the ribrous stock should be at a value of from about 116 to about 153 degrees Centigrade.
Concievably, this condition could be achisved by employing a high consistency pulp the di~ester heat cont;ent o~ which has been preserved. In other words, it is possible t;o feed a high consist-ency, chemically deligniried and fiberizsd pulp into the process flow of the invsntion under conditions whereby it i~ already hot as ~t comes from the digestion process in which it was produced.
Mors practically, however, undsr ths condition~ usually pre-~ailing in the average pulp mill, it i8 nece~sary to heat the high consistency pulp to the pro¢e~sing temperature.
The pulp accordingly is charged through a sealing devlce such a~ a pocket valv~ or tapered ~crew to a pre~teamer wherein it i9 sub~ected in a ~ealed environment to a pressurized atmosphere oom-prising stsam at superatmospheric pressurss of from about 10 to about 60, preferably from about 30 to about 50 psig, and correspond-ing te~perature~ for ~aturated steam.
If desired, the steam may be admixed with air and/or one or more well known pulping and paper~aking agents such as chlorine, chlorine monoxide, chlorine dioxide, oxygen, ozone, etc., provided only that the partial pre~sure Or the steam i8 maintained at at least about 10 psig.
The ribrous feed i9 treated in the presteamer for a time suf-ficient only to heat the fibers to the indicated temperature levelO
In a typical instance, this will require from about 0.2 to about 5 minutes, pre~erably from about 0.5 to about 3 minutes.
Immediately artsr the fibrous charge has reached the indicated temperature, it i~ mechanically refined. It is of critical import-ance to the success of the instant process that the pul;p not besubjected to a presteaming operation for a period of time substan-tially longer than that required to bring it to temperature. As ~(~89;~3 discussed at length above, to do so would subject it to the efrect of high temperature steam ror an unduly long period of time and result in the degradation o~ the pulp and the undesirable reduction of its critical papermaking property values~, Accordingly, the pulp is passed immediately from the presteam-er into the device wherein it is mechanically refined.
The term ~'mechanically refining" as used hereln denotes Q
procedure in which the pulp is introduced under superatmospheric steam pressure into an atmospherically closed reEion between two working surfaces in relative rotation to each other, which are maintained a sufficient distance apart to prevent surface contact under empty running condition~.
The relative motion between these work~n~ ~ur~aces sub~0cts the pulp to both inter~iber and intra~lber ~riction. Without com-mitment to any particular theory, it is believed the mechanical working and resultant ~rictional forces applied to the hot, ~uper-atmospheric pressurized and high consistency pulp cause3 the pre-steamed and delignified fibers to become micro-compressed, kinked, ribrillated and extremely M exible, but without experienclng ex-tensive zone ~racturine. The shapes o~ the ~ibers arter treatmentare such that they lie in more than one plane. These characteris-tics are advantag~ous in developing desirable pulp physical prop-erties. They are achieved in unique balance in the practics o~ our invention by the expedient of presteaming the ~ibers and re~ining them at low horsepower consumption while they are still hot ~rom the presteamîng operation.
The mechanical refining device employed may be any suitable apparatus wherein working sur~aces with relative rotary motion are closely spaced and the working ~pace is maintained under super-atmospherlc steam pres~ure. Pre~erably the refining space withinthe atmospherically closed mechanical re~iner contain~ opposed disc-like working sur~aces relatively rotatable around a common axis.

~3892t73 Steam pressurized double-revolving di~c refiners in which the di~cs rotate in oppo~ed direction~ are most preferred.
An exe~plary refining device i9 the pressuri2ed, double-re-volving-disc refiner illustrated ~nd described in U.S. Patents

3,765,611 and 3,765,613 (e.g., double di~c pressurized re~iners Nos. 418, 420 and 485 o~ the Bauer Brothers Company). However, other type~ such as pressurized single disc re~iner (available from various manufacturers, including for example the l'Ra~inator"
Series RLP 50/54 S of American Defibrator Inc.; Sprout Waldron Models 36 and 42 ICP: and many others), will perform satisfactorily in some applications o~ the process Or this invention.
As in the case Or the pre-~teamer in which the pulp i9 brought to tempera~ure, the pres~urlzed re~iner provides a steam pres~ur-iæed environment for the high conslstency pulp. In most ca3es the steam prossure and temperature ¢onditions in the pre-steamer and refiner are ~imilar. In fact, it is preferred that the two appar-atus unit~ oommunicate with each other. As a result, the steam pressure within both the pre-steamer and the refiner will vary from about 10 to about 60 psig., preferably from about 30 to about 50 20 p9ig., with the temperature being the oorrespondlng temperature ~or saturated steam.
T~us, as the hot, high oon3i~tency, ohemically dellgnified and fiberized pulp i9 ~ed into the inlet of the presxurized refiner and between the spaoed apart, opposed working surface~ thereof, it i3 continuously under superatmospherio steam pressure.
In the usual pressurized double-revolving disc refiner, suoh as the 8auer referred to above, the opposed working surfaces are relatively rotatable about a common axis. The spacing between the working surfaces (orten called "plate clearance") is in the range Or from about 0.002 to about 0.070 inch, typically from about 0.015 to about 0.05 inch, and preferably from about Q.02 to about 0.04 inch. This 3pacing is ad~ustable. The surface~ ordinarily ~ rrad~ rk 1~89~3 are of a somewhat textured or rough character to minimi~e pulp ~lippageO
When using such a refiner in accordance with the proce3s of this invention, the opposed working surfaces are rotated at a rel-ative tangential velocity in the range Or from about 10,000 to about 40,000 ft/min., and preferably from about 20,000 to about 40,000 ft/min. The speciric set of operating conditions for the pressurized reriner will vary somewhat depending upon a number of ractors such as the type, size and design of the refiner used, the nature and consistency of the pulp being processedJ and khe rate of pulp throughput in the system. Such factors can be ascertained and optimiæed readily in any given situation.
Ordinarily the hlgh oon~istency pulp as it pa~ between the worklng ~urrace~ Or the re~iner 1~ prim~rily in chunky, padded form. In other words, in tho practice of this invention it is not necessary to maintain the working space between the working surraces packed with a continuous sheet of high consistency pulp.
In general, the pressurized refiner is operated under condit-ions suitable for causing the high consistency pulp to be mechan-ically worked under superatmospheric steam pressure and temperature~o that the fiber~ retain their length and are refined to yield a pulp product which can be made into Yheet~ of paper having signi~i-cantly hi~her tear factor, elongation and Scott internal bond and acceptable apparent density, as compared to sheet~ of paper made rrom pulp produced ~rom the same kind Or chemically delignified and riberized pulp which has been merely beaten to equal burst strength in lieu of being subJected to the process of this invention.
It is a particular reature of the present invention that in the refiner the power input, i.e. the work done on the pulp, is controlled within stipulated limits in order to develop the desired pulp properties. These limits are well below the power input app-lied to pulps in the conventional procedures rererred to above.
-14;

-` :1089Z73 The power input, as determined by such factors as the ~eed rate o~ the pulp, the pulp consistency, and the clearance of the re~iner plates, is maintained at from about 0.5 to about 10 net horsepower days per ton ~HPD/T), preferably from about 1 to about 5 net horsepower days per ton. By definitic,n horsepower days per ton is the horsepower applied to the pulp divided by the tons per day output of the same.
Increasing theenergy input to the pulp above 10 net horsepower days per ton has the disastrous e~fect, from the standpoint Or the present invention, of increasing the apparent density o~ the pulp product to unacceptable values. See Fig. 1.
In particular, it raises the apparent density of the pulp to level at which the paper made ~rom the pulp i9 too th~n, too ea~y to ~oar, and too light-transmissive ~or satlsfaotory commerc-iAl use ~, A~ter re~ining, the pulp in a hot condition is discharged fromthe refiner and worked up in a suitable manner.
Accordingly, it may be diluted (quenched) in any apparatus having a design calculated to bring the hot, refined pulp into con-tact with water or other appropriate cooling liquids. Therea~terthe pulp is slurried with water to a consistency wh1ch is conven-ient ror use in papermaking, and used in the ~urnish o~ a paper making system~
Although the pulps o~ this invention when used per se as the entire cellulosic pulp content o~ the furnish make paper suitable for some purposes, it is generally advantageous to use them in com-bination with one or more conventional pulps. So doing can result in large pulp cost savings, as is discussed at length supra.
More particularly, the refined pulps o~ this invention may be transferred to a suitable pulp mixer and therein slurried or other-wise mixed in suitable proportions with one or more types of con-ventional pulps to provide a pulp blend which therea~ter may be used 89Z~3 in the rurnish to the paper making systemO
EXAMPLES
The process of the invention and tha pulp products thereof are illustrated in the following examples:
A ~eries of semi-work trials utilizing a Bauer Brothers No~
418 pre3surized double-revolving disc refiner was conducted. The refiner had counter-rotating plates 36 inches in diameter which operated at the normal factory preset speed of 1200 rpm, each plate.
The plates were textured (Manufacturer's plate design numbers 36325 and 36326) with a taper Or 0.001 inch.
All pulp~ u~ed in these trials were prepared from mixed North-ea~tern U. SO softwood~ or mixed Northeastern U. S. hardwood~, all Or the type conventlonally employed in New England paper mills.
The teQt~ performed on the pulp8 involved ln these exampleQ, and the paper made therefrom, were conducted using standard TAPPI
methods (except where otherwise noted). Abbreviations used in the exampleq are as rOllOws:
HCTR = High consistency, high temperature re~ining (Qteam pressurized) HCR = High consistency refining (no applied stsam pre 9 gure ) VIB = Valley Iron Beater (laboratory) HWK = Eardwood kraft SWK = Softwood kraft GWD = Groundwood The units used for the operating conditionq and properties presented in the examples are as follows unless otherwise indicated:
Consistency: dry weight percent of pulp in a slurry Plate Clearance: inches Feed Rate (pulp to Bauer No. 418 refiner): tons/clay VIB Beating Time: minutes Freeness (CSF): cc ~0892~3 Drainage Time: seconds Apparent Density: lb/25" x 38" x 500/mil Burst Factor: (lbs/in2/bs. wt.) x 100 Tear Factor: (grams to tear 16 sheets/bs~ wt.) x 100 Fold: NoO of double folds under 1 kg load Tensile: km o~ web supportable by own skrength Elongation: % at rupture Scott Internal Bond: ft. - lb. x 10-3 Opacity (TAPPI): B & L %
Tensile Energy Absorption: g - cm/cm2 for L~O lb/3300 ~t2 handsheets In the ensuing tables, N/A i8 used to signi~y that the particular oondit~on or property i~ not applioable. Dashe~ ) are used to ~ignl~y the absence o~ the particular determLnatlon or mea3urement.
HPD/T signif'ies net horsepower da~Js per ton of pulp (correcked f'or horsepower wa~ted during idling of the refiner).

-This example illustrates the characteristic changes in the physical properties of bleached (85% Gardner brightness) so~twood kra~t pulp produced by various conditions of' the process o~ this invention (HC~R) a~ compared to those produced by a conventional laboratory beater (VIB).
Conventional Qof'twood kra~t pulp was dewatered ~n an Impco~
twin roll press and wa~ continuously fed to a steam pressurized Bauer Brothers re~ining system, which provided ~or a 2.8 minute re-tention under 50 psig saturated steam pressure prior to ~eeding the pulp under the same pressure through the above described Bauer Brothers No. 418 counter-rotating double disc pressurized ref'iner.
The ref'ined pulp was discharged via a cyclone into a hydrapulper for quenching and dilution. For comparison, ~amples of' the same pulp, but without rerining, were beaten in a Va:Lley Iron laboratory beater (VIB). Table I presents ~urther operating conditions and m~r ~89~:73 the re~ults of the operations.
From the results, it can be seen that handsheetq made from HCTR treated pulp exhibit increases in tear strength, elongation, Scott internal bond, and wet web tensile energy absorption co~pared to hand~heets made from pulp treated in the Valley Iron beater, while suffering losse~ only in opacity and very slight burst and tensile deficits.

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. . . , ~,,, ,, This example illu~trates the characteristic changes in the physical properties Or bleached hardwood kraft pulp produced by various conditions Or the process of this invention.
Convent~onal hardwood kraft pulp bleached to 85~ Gardner br-ightness was treated in the ~ame refining sgstem as that described in Example 1. The operating conditions of the system were the ~ame as in Examp~e 1 except as otherwise indicated in Table II. Com-parison of the HCrrR-treated pulp with the untreated but VIB beaten pulp can be made from the data in Table II.
TABLE Il Processin~ and Perrormance of ~leached Hardwood Kraft PU1P

Untreated Pulp HCTR
; (VIB) Treated Pulp Consisten¢y N/A 24 28 40 Plate Clearance N/A .o25 .015 3 Feed Rate N/A 12.~ 7.7 14.5 VIB Beating Time 20 None None None Freeness (C~F) 251 290 255 284 Drainage Time 5.2 4.3 4.8 4.4 Apparent Den~ity 13.6 13.3 13.8 13.8 Burst ~actor 82 84 92 82 Tear Factor 87 97 100 101 Fold 71 44 107 95 Tensile 6.1 5.5 6.0 5.6 Elongation 3.2 4.2 4.7 4.7 Scott Internal Bond 126 135 151 175 Opacity (TAPPI) 75.0 75,0 72.3 72.0 EIPD/T -- 1.2 2.0 1.1 Theqe results indicate that bleached hardwood kraft pulp sub-~ected to the HCTR proce~s produces handsheets having increases in the same phyqical properties a~ found in the hand~heet~ produced from bleached ~oftwood kraft pulp of Example 1.

This example illustrates that the changes characteristic o~
the process can be produced by treating an unbleached pulp. Fur-thermore, it ~hows that these characteristic 9 can be ~naintained even after bleaching the treated pulp.
Conventional unbleached sortwood kraft pulp having a perman-ganate number of 20 was treatad at 32% consistency and .050 inch plate clearance in the same manner a~ that clescribed in Example 1 using a feed rate Or 8.8 ton~/day. Another portion Or the ~ame initial unbleached pulp was processed in the VIB in lieu of HCTR.
Subsequently, ~ampleQ of the unbleached treated pulp and the un-treated but VIB beaten pulp were blsached in the laboratory by the CEHD sequence to 85% brightness. The results are presented in Table III.
TABLE III
Processing of Unbleached SWK Pulp and Performance With and Without Subsequent Bleachin~
Unbleached Pulp~ Bleachad Pulp~
Untreated Treated Untreated Treated Before (VIB) ~ (VIB) Bleachln~ (HCTR) VIB Beating Tlmo 10None 4 None ~roen~s~ (CS~) 626613 625 633 Drainage Time 4.24.o 4~1 4.o Apparent Density 13.012.9 13.2 13.2 Burst Factor 140115 140 112 Tear ~actor 161235 163 265 Fold 15001000 1000 800 Tensile 8.56.5 7.8 6.1 Elongation 3.24.8 3.8 4.8 Scott Internal Bond 94 124 95 116 Opacity (TAPPI) ~ 71.1 69.8 HPD/T -~ -7 ~~ -7 ~he procedure o~ Example 3 was sub~tAntially ~ollowed in tr-eating conventional unbleaohed fIWK pulp having a permanganate number of 11, at 34~ consistency at a refiner feed rate of 9.4 tons/dAy and at a refiner plate clearance of 0.020 inch (Table IV) and then bleaching by CEHD to 85~ brightne~.

9Z'73 TABL~ IV

Processing of Unbleached HWK Pulp arld Performance With and Without Subsequent Ble~

Unbleached Pulp~ Bleached Pulps Untreated Treated Untre~ated Treated Before (VIB) (HCTR) (VIB) Ble~ohing (HCTR) VIB Beating Time30 None 25 None Freeness (CSF)208 196 3 293 Drainage Time 9.0 5.7 6.0 5.1 Apparent Den~ity14.3 14.4 14.1 14.1 Burst Factor 112 117 102 109 Tear Factor 97 113 102 11~
Fold 270 600 ~20 190 Tensile 7~6 7~3 7~1 6~7 Elongation 3~2 5.0 2a8 5.1 Scott Internal Bond 197 208 152 179 Opacity (TAPPI) -- -- 73~9 71~5 Wet Web TEA -- -- 2~1 2.9 HPD/T -- 1.6 -- 1~6 The forcgoing re~ults (Examples 3 and 4) indicate that the HCrrR proce~s oan be utilized on both unbleaohed and bleach0d kraft pulp~ wlth simllar improvements in lmportant physical properties.
It i~ al~o demonstratod that bleaching after HCTR treat~ent does not materially adversely affect the important physical properties o~ paper made from HCTR treated pulp.

This example illustrates clear~y the advantages of the high consistency re~lning at elevatecl temperatures (HCTR) over the high consiatency rerlnlng wlthout steam pressurization (HCR).
Bleached SWK pulp was treated at 25~ and at 40% consistency in the above Bauer Brothers No. 418 refiner system with and without applied stea~ pressure. In the HCTR run~ the pulp Wa3 held under s~eam at 50 p~ig for 2.8 minutes and then fed into the refiner whioh was likewlse maintalned under 50 p9ig steam pressurization.

In the HCR runs air at a pressure of 50 to 60 psig was u~ed instead of ~team in the operation of the refiner system. Thi~ e~perimenk verified that HCTR of~ers better control than HCR in the densi~i-cation of the pulp. Within a range o~ 2 to 12 HPD/T, the HCR tr-eaked pulps wsre always excessively densified (apparent density in excess of 14.5 lbs/mil), while the HCTR pulp8 had an acceptableapparent density (below 13.8 lbs/mil). Table V shows the property change cau~ed by HCR or HCTR, expressed a~ percent deviation ~rom the corresponding properties of the untreated pulp (VIB) beaten to equal burst ~trength.
TABLE ~

Comparison Between HCTR and HCR With SWK Pulp at Two Di~ferent Consi~tencies HCR _ HCTX HC~ HCTR
o con~i~tency % 2~ 25 40 4 Plate Clearance .o30 .o45 .035 to .062 .095 Feed Rate 8.1 9.4 -- 10.6 Steam Pres~ure Applied p~ig 0 50 0 50 Drainage Time Deviation % 4 0 -5 -2 Apparent Density " ~ 6 0 3 3 Burst ~ %
Tear " ~ 1 35 15 ~B (Fold) ll ~ 2 2 -10 Ten8il0 " ~ 3 9 2 -1 Elongation 1l % 7 33 ~33 25 Soott Int. Bond " % 22 56 60 75 Opa¢ity 11 Points-3.4 -2.2 -2.5 -3.8 Brightness " Point 8-3 -10 0 -9 Wet Web TEA 11 ~ 32 38 __ __ HPD/T 5.6 5.6 __ __ It will be noted that HCR of~ers no tear advantage when com-pared to untreated pulp at equal burst while HCTR offers ~igni~i-cantly higher tear, elongation (and thererore TEA), and higher in-ternal bond. It will also be noted that the hlgher temperatures employed in the HCTR treatment oause a substantially higher bright-nes~ 10~9. Although this disadvantage o~ HCTR can be avoided if desired by treating the pulp before bleaching, it will, in some cases, be of little concern in papermaking when a~sociated with only a small portion o~ the ~urnish, as shown below.
The following two examples illu~trate the unique opportunity to reduce the expensive long fiber portion of a papermaking ~urnish by taking advantage of the charaoteristics of pulps produced by the process of this invention.

About 12 tons o~ bleaohed SWK pulp were treated by HCTR in the above refining syste~ at 40% consistency and at 2-3 HPDjT (Plate Clearance .040 inch; Feed Rate 16 tons/day; 50 psig steam; 2.8 minutes o~ preconditioning under 50 p9ig st3am), and the pulp was used in a paper machine trial to make 38 pounds continuou~ bond.
The HCTR fiber, substituted for conventionally re~ined SWK, allowed the reduction of SWK in the furnish from a regular 27~ SWK - 73~
HWK to as low as 12~ SWK - 88% HWK. Paper machine runability rem-ained excellent even at the loweqt SWK level.
Paper properties indicated that a 30~ reduction in the amount of SWK is possible while achieving all paper specifications. The re~ultq of these experi~ents are ~ummarized in Table VI.

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, . ' ' ~Q89Z73 This example illustrates, again via a production paper machine trial9 the ability to reduce the amount o~ SWK and increase corre~-pondingly the amount of GWD in a publioation coated grade by ~ub-~tituting HCTR treated SWK for conventional:Ly re~ined SWK. About 22 tons of the HCTR treated SWK prepared in a manner similar to that described in Example 6 (Feed Rate 11 tons/day; 38~ average consi~tency; Plate Clearance varied to keep power input constant) allowed the reduction o~ SWK in the rurnish from a normal level o~
o 45-50% to as low a~ 24% without su~ering any uncoated stock run-ability problems. Table VII show~ some o~ the paper propertie~
which were obtained. To maint~in eood perrormance on machine coater runability) the HCTR-SWK levels had to be kept above 30 per-cenb .

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-27- 1()89Z73 ~q,~8~273 From a consideration of the results set ~orth in several of the above Example~ it can be appreciated that the pulp produced pursuant to this invention produces paper which, as compared to paper made from pulp produced from the same kind o~ chemically delignified and fiberized pulp beaten to equivalent burst strength in3tead of being refined in accordance with the process of this in-vention, possesses each of the following advantageous properties:
-- higher tear ~trength -- higher internal bonding strength -- higher elongation or stretch -- higher wet and dry tenslle energy absorption (o~ten termed "TEA") Although the magnitude Or these dl~rerence~ will vary dependin~
upon the type and ~peoie~ Or wood u~ed in maklng the pulps, the ~peciric type and conditions Or the chemical pulping process em-ployed and the specific HCTR conditions utilized, these dif~erences are all significant. They translate into the ability to provide paper having a balance of desirable propertie~ unavailabla from any previously known proce3s.
In order to still ~urther appreciate these improvements ef~-ectcd by the process o~ this invention, there are presented in Table VIII a ~eries Or comparisons between handsheet~ made ~rom variou~ pulps o~ this invention produced a~ described in several o~
the above Examples and handsheets made ~rom a portion of the same original chemical pulp which was beaten to equivalent burst strength instead o~ being sub~ected to the process of this invsntion. Table VIII also set3 forth, for further comparative purposes, the cor-responding physical property characteristics of the corresponding original unrerined chemical pulps themselves. The estimated TEA
values given in Table VIII are not measurements but rather calcula-ted values based on the elongation and tensile determinations.

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~0~9273 The next two examples ~how that it is po~sible to utilize HCTR in combination with conventional refining processes, such as beating.

A typical unbleached sortwood kraft pu:Lp having a permangan-ate number of 21 was treated at 38% consistency and .030 inch plate clearance in the above pressurized re~iner system. In this operation the pulp was subJected to 50 psig steam ~or a period Or 2.8 minutes and thereupon eontinuously introduced at a ~eed rate o~ 10:4 tons/day to the pres~urized refinsr in which 50 p9ig steam pre~sure wa~ likewise maintained. Upon release rrom the pressurized re~lner the pulp wa~ discharged ViEl a oyclone into a hydrapulper ~or quenchlng and dilution. The HCTR-treated pulp was ble~ched u~lng the C~HD sequence to a brightncs~ Or over ~0~0 and a portion o~ the bleached HCTR-pulp was then beaten in the Valley Iron beater.
Table IX ~how~ the properties Or paper samples made from this bleached HCTR/VIB pulp and those made from the same kind of initial sortwood kra~t pulp which was bleached in the same ~a~hion and re-rined solely by beating in the Valle~ Iron beater (no HCTR).
TABLE IX
Porformance Or SWK Pulp Rerined by HCTR Followed by Bleachin~ and Conventional Beatin~
Control Treated (no HCTR) (HCTR) VIB Beating Time 2.0 4.0 Freeness (CSF) 649 421 Drainage Time 4.0 4.6 Apparent Density 12.9 14.2 Burst Factor 122 150 Tear Factor 173 182 Fold 1000 1800 Ten~ile 7.4 8.6 Elongation 3.7 5.1 Scott ïnternal Bond 88 165 ~pacity (TAPPI) 72.8 6l~.7 HPD/T -- 11.6 EXA~IPLE 9 The procedure Or Example 8 was applied to unbl~ached hardwood kra~t having a permanganate number of 12. In this case the pulp was fed to the pressurized refiner at a consistency of 34% and at a ~eed rate of 9.4 tons/day. The plata clearance was .020 inch.
The pulp was then bleached by CEHD to a brightness of over 80%
and a portion thereof beaten in the Valley Iron beater. Table X
~ets forth the properties o~ paper ~amples made from the resultant pulp as well as the properties of paper samples made from pulp produced by bleaching the same kind of initial hardwood kra~t by CEHD also to a brightness o~ over 80% and then beating the bleached pulp in the Valley Iron beater (no HCTR).
TABLE ~
Per~ormance of HWK Pulp Refined by HCTR Followed by Bleaching and Conventional Beating Control Treated (no HCTR) ~IB Beatine Time 20 10 Freeness (CSF) 350 209 Drainage Time 5.2 6.2 Apparent Density 13.7 14.7 Burst Factor 96 120 Tear Factor 104 106 Fold 120 490 Tensile 6.8 7.3 Elongation 2.9 4 .7 Scott Internal Bond 130 211 Opacity (TAPPI) 75.0 69.3 Tensile Energy Absorption 2.0 3.0 HPT/T -- 1.6 Example 10 illustrates the results obtained pursuant to thls invention when exposing high consistencg pulp to presteaming for a relatively short period Or time before re~ining in the steam pres-~urized re~iner.
EXA~PLE 10 In this operation a typical unbleached SWK pulp having a per-manganate number of 21 was subjected to HCTR under the :~ollowing conditions:
Consistency: 32%
Presteaming Time: 1 minute Feed Rate: 8.8 tons/day 1~8~Z73 Plate Clearance: .OL~O inch Steam Pressurization: 50 psig (Steaming Vessel and Refiner) Table XI presents the properties of hand3heets made from this HCTR pulp and the properties of handsheets mada from the same kind of pulp which was treated in the VIB beater (no HCTR).

TABL~ XI

Per~ormance of Unbleached SWK Pulp Refined by HCTR

Untreated Treated (VIB) (HCTR) VIB BeatinE Time 1 Non~
Freeness ~CSF) 679 595 Drainage Ti~e 3.9 )~.0 Apparent Density 12.0 13.3 Burst Factor 90 122 Tear Factor 210 212 Fold 600 1100 T~nsile 6.o 7.0 Elongation 2.7 5.
Soot,t Internal ~ond 68 141 HPT/D -- 1.8 Using the general prooedure of Example 5, bleached SWK was re~ined under HCTR and HCR oonditions, using selected values o~
energy input (not HPD/T) over ~ range Or such values up to 12 HPD/T. This study had for its purpose determination o~ the erfect of varying the enerey input on the apparent den~ity, elongation, tear, and Scott Bond Or the HCTR and HCR pulps. The results, whioh have been discussed supra, are given in Table XII below, as well as in Figs. 1-4 Or the drawing~.
TABLE XII
HCTR _ HCR
HPD/T (nst) 1.9 3.7 5.6 12.0 2.5 3.1 5.6 12.0 Apparent Density 13.7 13.813.9 14.8 14.6 14.6 lL~.6 14.5 E~ongation 5.0 5.5 5.7 5.2 4.6 4.4 l~.5 4.5 Tear 195 219 198 173 158 138 139 130 Scott Bond 163 197 206 227 183 153 177 212 Fro~ the foregoing, it can be seen that the high consistenoy, high temperature, high pressure re~ining process of the present invention, when applied to chemically delignified and fiberized pulp8~ produces treated pulps which have signifi¢antly improved propertie~ making them particularly ~uitable ~or uæe in blending with lower grade, short ~iber, mechanically and/or chemically de-rived pulps for the production of fine papers. Among the physical properties of papers which are improved by utilizing pulps treated according to the prooe~ of the present invention are tear strength, stretch and bonding ~trength. These improvements in physical properties are achieved without signiricant reduction Or the other de~irable paper properties. Long fiber, chemically deligniried and fiberized pulp treated aecording to tha proce~ of the present in-vention i~ particularly u~erul in blending with conventionally re-rined, shorter riber length cellulo3ic pulp~ to produoo the rine paper~ u~ed in book and magazine printingl ledger papers, bu~iness ~orms, and other conventional rine paper products. It has been ~ound that the pulps produced by the present invention permit a reduction Or 20 to 50 percent in the long ~iber portion o~ the blends conventionally used in preparing ~ine grade paper ~tock without introducing any serious product or performance dericiencies.

Claims (9)

The embodiments of the invention in which an exclusive prop-erty or privilege is claimed are defined as follows:
1. The process for treating cellulosic pulp for property impr-ovemant which comprises:
a) providing a quanity of chemically delignified and fiberized cellulosic pulp characterized by:
1) a TAPPI E number of from 0 to about 30, 2) a consistency of from about 10% to about 50% by weight, 3) a temperature corresponding to the temperature of satu-rated steam at a pressure from about 10 to about 60 psig, and b) mechanically refining the pulp at said consistency under a steam pressure of from about 10 to about 60 psig, substan-tially continuously, at a reed rate and under refining condi-tions determining an energy input into the pulp of from about 0.5 to about 10 net horsepower days per ton.
2. The process for treating cellulosic pulp for property improve-ment which comprises:
a) providing a quantity of chemically delignified and fiberized cellulosic pulp characterized by:
1) a TAPPI K number of from 0 to about 30, 2) a consistency of from about 10% to about 50% by weight, b) presteaming the pulp at a steam pressure from about 10 to about 60 psig for a time sufficient to raise the temperature of the pulp to a temperature at least equal to the temperature of saturated steam at about 10 psig, but not above the temp-erature of saturated steam at about 60 psig and c) substantially immediately after the pulp has attained said temperature, mechanically refining it under a steam pressure of from about 10 to about 60 psig and corresponding tempera-tures for saturated steam, at said consistency of from about 10% to about 50% by weight, substantially comtinuously, at a feed rate and under refining conditions determining an en-ergy input into the pulp of from about 0.5 to about 10 net horsepower day per ton.
3. The process of claim 2 wherein the pulp consistency during both presteaming and refining is from about 30% to about 45% by weight.
4. The process of claim 2 wherein the steam pressure during both presteaming and refining is from about 30 to about 50 psig.
5. The process of claim 2 wherein the energy input into the pulp during refining is from about 1 to about 5 horsepower days per ton.
6. The process of claim 2 followed by the step of water quenching the hot refined pulp.
7. The process of claim 2 wherein the consistency of the pulp is from about 30 to about 45% by weight; wherein the steam pressure is from about 30 to about 50 psig; wherein the energy input into the pulp during refining is from about 1 to about 5 net horsepower days per ton and including the step of cooling the hot and refined pulp by diluting it with water.
8. The cellulosic pulp product of the process of claim 1.
9. The cellulosic pulp product of the process of claim 7.
CA313,602A 1978-02-28 1978-10-17 Treating chemically delignified and fiberized cellulosic pulp for pulp property improvement Expired CA1089273A (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989006718A1 (en) * 1988-01-14 1989-07-27 Robert Arthur Olson Method of refining hardwoods to produce paper pulp
US4966651A (en) * 1988-01-14 1990-10-30 P.H. Glatfelter Company Method of paper making using an abrasive refiner for refining bleached thermochemical hardwood pulp
US5348620A (en) * 1992-04-17 1994-09-20 Kimberly-Clark Corporation Method of treating papermaking fibers for making tissue
US5501768A (en) * 1992-04-17 1996-03-26 Kimberly-Clark Corporation Method of treating papermaking fibers for making tissue

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989006718A1 (en) * 1988-01-14 1989-07-27 Robert Arthur Olson Method of refining hardwoods to produce paper pulp
GB2228498A (en) * 1988-01-14 1990-08-29 Robert Arthur Olson Method of refining hardwoods to produce paper pulp
US4966651A (en) * 1988-01-14 1990-10-30 P.H. Glatfelter Company Method of paper making using an abrasive refiner for refining bleached thermochemical hardwood pulp
GB2228498B (en) * 1988-01-14 1992-01-22 Robert Arthur Olson An improved method of paper making
US5348620A (en) * 1992-04-17 1994-09-20 Kimberly-Clark Corporation Method of treating papermaking fibers for making tissue
US5501768A (en) * 1992-04-17 1996-03-26 Kimberly-Clark Corporation Method of treating papermaking fibers for making tissue

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