CA1228256A - Process for preparing groundwood pulp as short fiber and long fiber fractions - Google Patents
Process for preparing groundwood pulp as short fiber and long fiber fractionsInfo
- Publication number
- CA1228256A CA1228256A CA000449449A CA449449A CA1228256A CA 1228256 A CA1228256 A CA 1228256A CA 000449449 A CA000449449 A CA 000449449A CA 449449 A CA449449 A CA 449449A CA 1228256 A CA1228256 A CA 1228256A
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- CA
- Canada
- Prior art keywords
- fraction
- fiber
- pulp
- accepts
- groundwood pulp
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
- D21B1/00—Fibrous raw materials or their mechanical treatment
- D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
- D21B1/12—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by wet methods, by the use of steam
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- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Wood Science & Technology (AREA)
- Mechanical Engineering (AREA)
- Paper (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
- Disintegrating Or Milling (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process comprising: (1) grinding lignocellulosic material to form an aqueous groundwood pulp fiber suspension;
(2) screening the groundwood pulp fiber suspension through a coarse screen having screen openings not less than about 5 mm; (3) defibrating lignocellulosic material separated out on the coarse screen; (4) recycling the defibrated lignocellulosic material to the groundwood pulp fiber suspension from the grinding step (1); (5) separating the groundwood pulp fiber suspension from step (2) into (a) an accepts fraction and (b) a rejects fraction, the latter comprising from about 30% up to about 85% by weight of the fiber suspension; (6) screening the rejects fraction 5(b) of the groundwood pulp fiber suspension through a screen having screen openings of less than about 5 mm; (7) separat-ing the fiber suspension from step (6) into (a) an accepts fractions and (b) a rejects fraction; (8) recycling the rejects fraction 7(b) to the defibrating step (3) and then to the groundwood pulp fiber suspension from the grinding step (1); (9) screening the accepts fraction 7(a) to form (a) a short-fiber: accepts fraction of which from about 15 to about 60% comprises fibers passing through a sieve No. 150 in a Bauer-McNett classifier; and (b) a long-fiber rejects fraction of which at least 80% comprises long fibers retained on a sieve No. 150 in a Bauer-McNett classifier; (10) with-drawing the long-fiber rejects fraction 9(b) as groundwood pulp product (ii); (11) blending the short-fiber accepts fraction 9(a) with accepts fraction 5(a); and (12) withdraw-ing the resulting blend as short-fiber accepts fraction groundwood pulp product (i).
A process comprising: (1) grinding lignocellulosic material to form an aqueous groundwood pulp fiber suspension;
(2) screening the groundwood pulp fiber suspension through a coarse screen having screen openings not less than about 5 mm; (3) defibrating lignocellulosic material separated out on the coarse screen; (4) recycling the defibrated lignocellulosic material to the groundwood pulp fiber suspension from the grinding step (1); (5) separating the groundwood pulp fiber suspension from step (2) into (a) an accepts fraction and (b) a rejects fraction, the latter comprising from about 30% up to about 85% by weight of the fiber suspension; (6) screening the rejects fraction 5(b) of the groundwood pulp fiber suspension through a screen having screen openings of less than about 5 mm; (7) separat-ing the fiber suspension from step (6) into (a) an accepts fractions and (b) a rejects fraction; (8) recycling the rejects fraction 7(b) to the defibrating step (3) and then to the groundwood pulp fiber suspension from the grinding step (1); (9) screening the accepts fraction 7(a) to form (a) a short-fiber: accepts fraction of which from about 15 to about 60% comprises fibers passing through a sieve No. 150 in a Bauer-McNett classifier; and (b) a long-fiber rejects fraction of which at least 80% comprises long fibers retained on a sieve No. 150 in a Bauer-McNett classifier; (10) with-drawing the long-fiber rejects fraction 9(b) as groundwood pulp product (ii); (11) blending the short-fiber accepts fraction 9(a) with accepts fraction 5(a); and (12) withdraw-ing the resulting blend as short-fiber accepts fraction groundwood pulp product (i).
Description
~L22~%5~
S PE CIFICATION
Groundwood pulp is prepared by grinding lignocellulosic rnaterial such as logs or wood chlps in contact with a rotating grindstone. Water is spraye(l into the grinding area for cooling, and 5 the resulting aqueous groundwood pulp eibex ~uspension is screened through a coarse screen to remove the coarse particles" which are the~ defibrated, using for example a disc refiner, and recycled to the fiber suspension from the grindstone, while the accepts raction rom the coarse screen is passed to a fine screen, where the remaining coarse 10 particles are separated out ~s a rejects fractio. The rejects fraction is normally recycled to the defibration stage, while the accepts fraction containing the fiber suspension which passçs through the fine screen is passed to a wet ~achine or paper machine, optionally after further purification in a vorte}~ cleaner, and optionally also, aftex bleaching.
Groundwood pulp prepared in this way is norrnally used for the manufacture of newsprint and other types of printing paper, and also for the manufacture of soft crepe paper. Such papers requixe that the pulp have a low shives content,that is, the cvntent of partially defibrated wood particles. In the manufacture of paper, a high shives 20 content results in web breakages, and imparts to the paper a high degree of surface roughness, which gives rise to printing irregularities.
It is therefore important to reduce the shives content in the manufacture of groundwood pulp to a low level, but this poses a serious problem, that has not yet been fully overcome.
The groundwood pulp used in the manufacture of such papers is ground to a relati~Tely low freeness, of the order of 70 to 200 ml C. S. F.
12~8256 Groundwood pulp also can be u~ed for the manufacture of cardboard and paperboard~ in Q~vhich it is also desirable to have a low shives content in the pulp. Groundwood pulp used to produce cardboard shoulcl have a relatively high freeness, of the order from 250 to 400 ml C.S. F. One disadvantage with grinding to a high freeness, however, is that the pulp may have a relatively high shi~es content, and be relatively weak.
In recent years, a chemirnechanical pulp designated ~chemitherrnomechanical pulp"g abbreviated CTMP, has been produced that has a relatively high fr~eness of the order oE 400 to 700 ml C. S. F.
and also a low shives content, and is therefore very suitable for the manufacture of absorbent paper products. It is I~Ot possible to produce groundwood pulp having a freeness above 500 ml C. S. F. in a groundwood mill, using grindstones and present day techniques. Groundwood pulp 15 having such a high freeness has only a small percentage of fibers~ and consists mainly of shives and splinters, so that it cannot be used to manufacture absorbent paper products.
These difficulties are overcome by the process of the pres~nt invention, which makes it possible to produce a gxoundwood pulp having 20 afreeness of above 500 ml C.S.F., by the simple expedient of preparing the groundwood pulp in two fractions, a s hort-fiber fraction and a long-fiber fraction, of which the long-fiber fraction has the higher freeness.
The short-fiber fraction has a negligible proportion of shives, while the long-fiber fraction has a low proportion of shives. The short~fiber 25 fraction is further characterized by high opacity, and a freeness comparable to that of ordinary groundwood pulp.
In the process according to the invention, groundwood pulp is prepared at a low energy consurnption as (i) a short-fiber fraction thal; is essentially shive-free and has a low freeness, low surface roughne~s alld high opacity; and ~ii) a long-fiber fraction that ba~ a low resin content, as well as a high free~es~:9 which corxlprise$ the ~teps o:
(1) grmding lignocelluloslc ~l~aterial t:o forrn an a~ueous groundwood pulp fiber suspension)
S PE CIFICATION
Groundwood pulp is prepared by grinding lignocellulosic rnaterial such as logs or wood chlps in contact with a rotating grindstone. Water is spraye(l into the grinding area for cooling, and 5 the resulting aqueous groundwood pulp eibex ~uspension is screened through a coarse screen to remove the coarse particles" which are the~ defibrated, using for example a disc refiner, and recycled to the fiber suspension from the grindstone, while the accepts raction rom the coarse screen is passed to a fine screen, where the remaining coarse 10 particles are separated out ~s a rejects fractio. The rejects fraction is normally recycled to the defibration stage, while the accepts fraction containing the fiber suspension which passçs through the fine screen is passed to a wet ~achine or paper machine, optionally after further purification in a vorte}~ cleaner, and optionally also, aftex bleaching.
Groundwood pulp prepared in this way is norrnally used for the manufacture of newsprint and other types of printing paper, and also for the manufacture of soft crepe paper. Such papers requixe that the pulp have a low shives content,that is, the cvntent of partially defibrated wood particles. In the manufacture of paper, a high shives 20 content results in web breakages, and imparts to the paper a high degree of surface roughness, which gives rise to printing irregularities.
It is therefore important to reduce the shives content in the manufacture of groundwood pulp to a low level, but this poses a serious problem, that has not yet been fully overcome.
The groundwood pulp used in the manufacture of such papers is ground to a relati~Tely low freeness, of the order of 70 to 200 ml C. S. F.
12~8256 Groundwood pulp also can be u~ed for the manufacture of cardboard and paperboard~ in Q~vhich it is also desirable to have a low shives content in the pulp. Groundwood pulp used to produce cardboard shoulcl have a relatively high freeness, of the order from 250 to 400 ml C.S. F. One disadvantage with grinding to a high freeness, however, is that the pulp may have a relatively high shi~es content, and be relatively weak.
In recent years, a chemirnechanical pulp designated ~chemitherrnomechanical pulp"g abbreviated CTMP, has been produced that has a relatively high fr~eness of the order oE 400 to 700 ml C. S. F.
and also a low shives content, and is therefore very suitable for the manufacture of absorbent paper products. It is I~Ot possible to produce groundwood pulp having a freeness above 500 ml C. S. F. in a groundwood mill, using grindstones and present day techniques. Groundwood pulp 15 having such a high freeness has only a small percentage of fibers~ and consists mainly of shives and splinters, so that it cannot be used to manufacture absorbent paper products.
These difficulties are overcome by the process of the pres~nt invention, which makes it possible to produce a gxoundwood pulp having 20 afreeness of above 500 ml C.S.F., by the simple expedient of preparing the groundwood pulp in two fractions, a s hort-fiber fraction and a long-fiber fraction, of which the long-fiber fraction has the higher freeness.
The short-fiber fraction has a negligible proportion of shives, while the long-fiber fraction has a low proportion of shives. The short~fiber 25 fraction is further characterized by high opacity, and a freeness comparable to that of ordinary groundwood pulp.
In the process according to the invention, groundwood pulp is prepared at a low energy consurnption as (i) a short-fiber fraction thal; is essentially shive-free and has a low freeness, low surface roughne~s alld high opacity; and ~ii) a long-fiber fraction that ba~ a low resin content, as well as a high free~es~:9 which corxlprise$ the ~teps o:
(1) grmding lignocelluloslc ~l~aterial t:o forrn an a~ueous groundwood pulp fiber suspension)
(2) screening the groundwood pulp fiber suspension through a coarse screen having screen openings not less than about 5 m~n;
(3) defibrating reject lignocellulosic nlaterial separated out on the coarse screen;
(4) recycling the defibrated lignocellulosic material to the 15 groundwood pulp fiber suspension from the grinding step (l)j
(5) separating the groundwood pulp fiber suspension From step (2) into:
a) an accepts fraction; and (b) a rejects fraction, the latter comprising from 20 about 30~ up to about 85~k by weight of the fiber suspension;
a) an accepts fraction; and (b) a rejects fraction, the latter comprising from 20 about 30~ up to about 85~k by weight of the fiber suspension;
(6) screening the rejects fraction 5~b) through a ~
screen having screen ope~ings of less than about 5 mm;
screen having screen ope~ings of less than about 5 mm;
(7) sepàrating the fiber suspension fro~ step (6) into ta) an accepts fraction; and (b) a rejects fraction;
(8) recycling the rejects fraction 7(b) to the defibrating step (3) and then to the groundwood pulp fiber suspension from the grinding step (1);
(9) screerling the accepts fraction 7(a`
5 to forrn:
(a) a short~fiber accepts fraction of which from about 15 to about 60~, comprises ~ort f~elig pa~ g tllrou:gh a.~i~v~
No. 150 in a Bauer-McNett ~::la~sifier; and (b) a long-fiber reJects fraction of which at least
5 to forrn:
(a) a short~fiber accepts fraction of which from about 15 to about 60~, comprises ~ort f~elig pa~ g tllrou:gh a.~i~v~
No. 150 in a Bauer-McNett ~::la~sifier; and (b) a long-fiber reJects fraction of which at least
10 80~ comprises long fiber~ retained on a sieve No. 150 in a Bauer-McNett classifier;
(lp) withdrawing the long-iber rejects fraction 9(b) as groundwood pulp product (ii);
(lp) withdrawing the long-iber rejects fraction 9(b) as groundwood pulp product (ii);
(11) blendir.g the short-fiber accepts fraction 9(a) with 15 accepts fraction 5(a); and
(12) withdrawing the resulting blend as short-fiber accepts fraction groundwood pulp product (i).
The invention further.provides two novel aqueous groundwood pulp suspension s:
(a) a short-fiber groundwood pulp suspension of which from about 15 to about 60~. cornprises F~hort fiher~q pa~si~g through a si~e No. 150 in a Bauer-McNett classifier; and having a freeness within the range from about 50 to about 200 ~1 C~ S~ F. and ~ ~hiv~ content below abou~ 0. 05 (b) a long-fiber groundwood pulp suspension of which at least 80ck cornprises long fibers retai~ed on a sieve No. 150 in a Bauer-;
l~cNett classif~er and having a f~eeness wi~hin th~ ~ange ~m about 9;~56 200 to about 750 rnl C. S. F. and a resin content of less than about 0. 3~ DK~, The short-fiber pulp fraction because it ha~; a low surface roughness and high opacity is suitable for producing light-weight coating paperF~, and also 5 for mixing with other pulps suitable for the production of high quality prir3tingpapers.
The long-fiber pulp fraction is produced at a very low energ~y consumption and because it has a low resin content and a freeness within the range fromai30ut 200 to about 700 ml C.S. F. can be admi~ed with pulps intended for use in the preparation of absorbent paper products of 10 high bulk, good absorption rates, and high absorptivityO The long-.fiber pulp fra~tion also is suil;able for use in pulps intended for the manufacture of cardboard or paperboard.
By the process of the invention it is possible to bring the properties of groundwood pulp in the form of short--fiber and long-15 fiber fractions to the high standard of chemithermornechanical pulps,while keeping mamlIacturing costs low9 due to the low energy consumption.
In the drawings:
Figure 1 is a flow sheet illustrating the ~nanufacture of groundwood pulp in accordance with the conventional groundwood pulp 20 process, and Figure 2 is a flow sheet showing ~reparation of short-fiber and long-~iber groundwood pulps in accordance with the process of the inventionO
The procedure illustral;ed in Figure 1 begins with the grLnding oE logs or wood chips in a grincl~r lL3 ~he aqueous groundwood ~ulp iber 25 suspension from the grinder contains wood knotsg splinters and other coarse wood residues~ and is passed by way o~ the conduit 2 to the coarse screen 3, in the form of a bull screen, which rnay comprise a vibratory sc reen with vibrating screen plates provided with holes or slots. The bull screen has apertures exceeding 5 mm 5 in diameter. The coarse particulate material separated as rejects rom the bull screen normally is more than 50 mm lon~, and is passed by way of a conduit 4 to the defibrator 5~ for example, a disc refiner.
The defibrated material is recycled via conduit 6 to conduit Z where it is blended with groundwc3od pulp suspension from the grinder 1.
The accepts fraction, the fiber suspens ion passing through the bull screen 3, now freed from coarse wood residues, is led by the conduit 7 to the screen room 8~ which n~ay be equipped with pressurized screens having perEorated screen plates with openings about t . 75 mm in diameter.
The arnount of the iber suspension coming into the screen room 8 that is separated as rejects and is recycled is controlled by the valve 17. The valve is so set that up to about 20~ by weight of the Eiber suspension is separated, and sent via conduit 9 through the defibrator 5 and then via conduit 6 for blending witll suspension in 20 conduit 2. The accepts fraction from the screen room 8 is withdrawn by way of conduit 10 as the groundwood pulp product, and normally has a freeness of from 70 to 200 ml C.S. F.~ and a shives content of from about 0. 08 to about 0. 20~/, . The accepts fraction can be passed from conduit 10 to the wet machine, after being cleansed in a 25 vortex cleaner (not shown).
In the process of the invention as shown in ~igurQ 2, logs or wood chips are grollnd in the grinder 1, and then passed by way of conduit 2 to the coarse screen 3, as in the conventional process illustrated in Figure 1 The coarse wood xesidues ~eparated out by 5 the screen 3 pass via conduit 4 to a de~ibrator 5~ for example, a disc refiner, after which the defibrated material is recycled to the suspension in conduit ~ by way of the conduit 6, as in the cbnventional process. The accepts fraction from the screen 3 passes by way of conduit 7 to the screen xoom 8, which may contain pressurized -10 screens, as in the system o Figure 1. However, the amount of rejectsfrom the screen room 8 is increased, either by increasing the flow through conduit 9, by increasing the opening of the valve 17, or by reducing the diameters of the openings of the screen plates, or both, so that from about 30 to about 85% by weight of the fiber suspension arriving 15 via conduit 7 is separated out as reJects, and passes through the conduit 9 to the separator 11. Here, resldual shives and splinters having a length above 4 mr~, preferably above 8 mm, are removed. This separator ma~ comp rise, for example, a vibratory scréen ha~T ing smaller opening diameters than the vibratory screerl 3.
The suspension is separated at separator 11 into an accepts fraction and a rejects Eraction. The rejects fraction passes through the conduit 12 back to the conduit 4, for recycling to the defibrator 5,, at2r which the fraction is returned vla conduit 6 to the groundwood pulp ~uspension fro~ the grinder in conduit 2. The accep~s fraction frorn the separ~tor 11 25 passes via conduit 13 to a second separator 14, which may comprise for example a centrifugal screen or a curved screen, -for fractionating 5~
the accepts fraction into a long-fiber raction of which at least 80%
of the fibers are retained on a sieve No. ~ 50 in a Bauer-~cNett classifierO
The long-fiber fraction from the separator 14 is wlthdrawn via conduit 16 at C as long-iber groundwood pulp product~ and can 5 be dewatered and then used for special ~purposes.
The short fiber accepts fractioll from the separator 1~ is withdrawn via conduit 15 and blended with the accept~ flow from the screen room 8 in the conduit 10. The blencl is withdrawn at B as short-iber fraction groundwood pulp product~
In a particularly preferred embodiment of the invention, the white water obtained in dewatering the ~ong-fiber fraction is recycled as dilution water to the separator 11. The white water has a fiber content below 200 mg/l, and can be obtained by incorporating a separate filter in the circuit.
Because more than the ~ormal proportion o rejects i~
withdrawn at the screen room 8; the short-fiber fraction obtained in the conduit 10 as accepts fraction from the screen room 8 has an extremely low shives content, within the range from about 0 to about 0. 05%, and a freeness of frorn about 50 to about 200 ml C. S. F. ~orresponding 20 conventional groundwood pulps of comparable freeness have a shives content of from 0. 08 to 0. 20~ shives content of such a magnitude considerably impairs the usefulness of the pulp in the manufacture of printing paper, and contributes to a surface roughness of the paper which causes the paper to display a nonuniform ink absorbency.
In addition, the short ~iber pulp fraction according to the invention has a different fiber distribution than conventional groundwood pulp, and affords the aclvantage of a higher tensile index and a hîgher opacity in printing paper produced from the fraction than paper produced from conventional groundwood pulp. Consequently, it is suited for the manufactur~ of printing paper of the highest quality.
Tixe long-fiberpulp fraction according to the invention has an unusually high Ireeness, within the range from about 200 to about 750 ml C. S. F., and a low resin content, below 0. 3% DK~ (after bleaching the resin content is less than 0.15(~j DKM). Frorn about 80 to about lOO'yo of the long-fiber pulp fraction comprises fibers which are xetained 10 on a sieve No. 150 in a Bauer-McNett classifier. The long fiber pulp fraction has e~traordihary properties, rendering it suitable for the manufacture of absorben~ products, and provides high bulk, good absorption rates and an extremely good absorption capacity. In the process according to the invention, from about 15 to about 75~ of the lignocellulosic 15 material that is ground up is recovered as long-fiber fraction.
Thus, instead of producing a single product which is inferior to chemithel momechanical pulp, the process o~ the invention makes it possible to obtain two groundwood pulp products, each of which has egtremely good properties, which make them suitable for special purposes.
20 These pl:'O~J.lCtS are produced in a higher yield than conventional groundwoed pulp, while using less energy. The total energy consumed when producing the long-iber pulp fraction according to the invention is from 300 to 50~ ~Wh/ton of dry pulp~ while energy consumption in the prepar~tlon ~f comparable chemithermomechanical pulp is about 1, 000 25 kWh!ton ~ dry pulp.
. . .
. 9 5~
The energy consumption in manufacturing the short-fiber pulp fraction is from 1300 to 1500 kWh/ton of pulp, while about 2000 kWh/ton of dry pulp is needed to prepare chemithermomechanical pulp of corresponding qualil;y.
When practicing the process of the invention, a$ least 96~ of the wood is converted to groundwood pulp~ as compared from 92 to 94~, in the manufacture of chemithermomechanical pulp.
The long-fiber pulp fract~on obtained in accordance with the invention is suited for admixture with other pulps, such as sulfite pulp, sulfate 10 pulp and chemimechanical pulp. It is also well suited for the manufacture of cardboard and paperboard, as well as the manufacture of absorbent products. Other fiber materials such as recycled fibers, peat fibers and synthetic ~ibers can also be rnixed with the long-fiber pulp fraction.
The process according to the invention can also be applied 15 with good results in the manufacture of pressure-ground groundwood pulp, in which case the energy consumption is about 10% lower.
The following Example in the opinion of the inventor represents a pre~erred embodirnent of the invention EXAMPIE
As a control, groundwood pulp was manufactured from spruce wood in accordance with the flow sheet shown in Figure 1. The spruce was ground in the grinder 1, and the resultant abùeous fiber suspension (which had a pulp consistency of 2.1~) was passed through the conduit 2 to a Jonsson-type vibratory screen 3 having screen plates with 6 mm 25 diameter openings, where the coarse wood residues were screened out.
The rejects obtained in the vibratory screen 3, comprising coarse .~
1~2~3%~i~
splinters and sh~ves and constituting about 3~ by weight of the groundwood iber suspension feed, was passed through the conduit 4 at a pulp ~onsistency of 5~ to the disc refiner 5, where the coarse material was defibrated to separate fibers. The defibrated rejects fraction 5 was passed via the conduit 6 and the conduit 2 back to the vibratory screen 3.
The accepts from the vibratory screen 3 had a pulp conæistency of 1. 3%, and was passed through the conduit 7 to a pressurized screen 8 having a fixed cylindrical screen basket, to the inner cylindrical 10 surface of which the pulp suspension was passed under superatmospheric pressureO The screen was also provided with an internal rotating scraper. The openings in the perforated screen plates had a diameter of 1.75 mm.
The flow of fiber suspension to the pressurized screen 8 was 15 so regulated that 20~i by weight of the fiber content of the fiber suspension fed to the screen remained on the screen plates, and passed as rejects via the valve 17 through the conduit 9 to the conduit 4, for further defibration in the disc refiner 5, after which the material was recycled to the conduit 2. The pulp consistency in the conduit 9 was 1. 9%.
Acceptæ from the pressurized screen 8 had a pulp consistency of 1.1~ and was removed via the conduit 10, where the pulp product was further cleaned in a vortex cleaner (not shown). Samples designated A were removed, for determination o the shives content and fiber CQmpOSitiOn.
The groundwood pulp prepared in accordance with the invention, following the flow sheet shown in Figure 2, was al~o prepared from ~ 2~ ;6 spruce wood. The fiber suspension in the conduit 2 had a pulp consistency ~ 2.1~,,. and was closely screened in the vlbratory screen 3 at an opening diameter of 6 mm. The rejects comprised 3% by weight of the fiber suspension feed, and was passed via the 5 conduit 4, wbere the pulp consistency was 5~i~ to the disc refiner 5. The defibrated rejects pulp suspension had a pulp consistency of 5~O, and was recycled through the conduit 6 to the conduit 2 for rescreening in the yibratory.screen. 3.
The accepts from the vibratory screen 3 had a pulp co~sistency 10 o~ 1. 3'3h, and was passed via conduit 7 to the pressurized screen 8. The screen plates were changed to an opening diameter of 1. 60 mm instead of 1. 75 mm. At the san~e time, the valve 17 was opened furtber, so that the amount of rejects passing through the valve rose to 70% by weight of the fiber content of the fiber suspension feed. The rejects 15 pulp fxaction obtained in the pressurized screen 8 had a freeness of 245 ml C. S~. F.; a 8 hives content of 2. 95~ accordin.g ~o ,Sommerville~ 33.1~.
of the fiber~ was retained on a ~ieve No. 20 and 41 5~/O on a siéve No. 150 in a Bauer-~cNett classifier, and 25. 4~, passed through the sieve NoO 150~ :
~oThe r ejects was brought to a pulp consistency of 1. 5~oj7 and . ~assed via conduit 9 to $he separator 11, which was in the form of a vibratory scre0n provided with screen plates having an opening diameter VI 3. 0 mm. The vibratory screen was so adjusted that the amount oP
rejects was 0.8~o by weight of the fiber suspension feed. The rejects 25 from the vibratory screen separator 11 had a shives content o 73~i according to Sommerville, and passed via conduit 12 to the conduit 4, for further : .
~L22~
defibration in the disc refiner 5, after which it was returned via conduit 6 to the condult 2~
The pulp consistency in the conduits 6 and 2 was the same as that in the control.
l'he accepts pulp fraction from the vibratory screen separator 11 was brought to a pulp consistency 1. 2(3~o~ and passed through the conduit
The invention further.provides two novel aqueous groundwood pulp suspension s:
(a) a short-fiber groundwood pulp suspension of which from about 15 to about 60~. cornprises F~hort fiher~q pa~si~g through a si~e No. 150 in a Bauer-McNett classifier; and having a freeness within the range from about 50 to about 200 ~1 C~ S~ F. and ~ ~hiv~ content below abou~ 0. 05 (b) a long-fiber groundwood pulp suspension of which at least 80ck cornprises long fibers retai~ed on a sieve No. 150 in a Bauer-;
l~cNett classif~er and having a f~eeness wi~hin th~ ~ange ~m about 9;~56 200 to about 750 rnl C. S. F. and a resin content of less than about 0. 3~ DK~, The short-fiber pulp fraction because it ha~; a low surface roughness and high opacity is suitable for producing light-weight coating paperF~, and also 5 for mixing with other pulps suitable for the production of high quality prir3tingpapers.
The long-fiber pulp fraction is produced at a very low energ~y consumption and because it has a low resin content and a freeness within the range fromai30ut 200 to about 700 ml C.S. F. can be admi~ed with pulps intended for use in the preparation of absorbent paper products of 10 high bulk, good absorption rates, and high absorptivityO The long-.fiber pulp fra~tion also is suil;able for use in pulps intended for the manufacture of cardboard or paperboard.
By the process of the invention it is possible to bring the properties of groundwood pulp in the form of short--fiber and long-15 fiber fractions to the high standard of chemithermornechanical pulps,while keeping mamlIacturing costs low9 due to the low energy consumption.
In the drawings:
Figure 1 is a flow sheet illustrating the ~nanufacture of groundwood pulp in accordance with the conventional groundwood pulp 20 process, and Figure 2 is a flow sheet showing ~reparation of short-fiber and long-~iber groundwood pulps in accordance with the process of the inventionO
The procedure illustral;ed in Figure 1 begins with the grLnding oE logs or wood chips in a grincl~r lL3 ~he aqueous groundwood ~ulp iber 25 suspension from the grinder contains wood knotsg splinters and other coarse wood residues~ and is passed by way o~ the conduit 2 to the coarse screen 3, in the form of a bull screen, which rnay comprise a vibratory sc reen with vibrating screen plates provided with holes or slots. The bull screen has apertures exceeding 5 mm 5 in diameter. The coarse particulate material separated as rejects rom the bull screen normally is more than 50 mm lon~, and is passed by way of a conduit 4 to the defibrator 5~ for example, a disc refiner.
The defibrated material is recycled via conduit 6 to conduit Z where it is blended with groundwc3od pulp suspension from the grinder 1.
The accepts fraction, the fiber suspens ion passing through the bull screen 3, now freed from coarse wood residues, is led by the conduit 7 to the screen room 8~ which n~ay be equipped with pressurized screens having perEorated screen plates with openings about t . 75 mm in diameter.
The arnount of the iber suspension coming into the screen room 8 that is separated as rejects and is recycled is controlled by the valve 17. The valve is so set that up to about 20~ by weight of the Eiber suspension is separated, and sent via conduit 9 through the defibrator 5 and then via conduit 6 for blending witll suspension in 20 conduit 2. The accepts fraction from the screen room 8 is withdrawn by way of conduit 10 as the groundwood pulp product, and normally has a freeness of from 70 to 200 ml C.S. F.~ and a shives content of from about 0. 08 to about 0. 20~/, . The accepts fraction can be passed from conduit 10 to the wet machine, after being cleansed in a 25 vortex cleaner (not shown).
In the process of the invention as shown in ~igurQ 2, logs or wood chips are grollnd in the grinder 1, and then passed by way of conduit 2 to the coarse screen 3, as in the conventional process illustrated in Figure 1 The coarse wood xesidues ~eparated out by 5 the screen 3 pass via conduit 4 to a de~ibrator 5~ for example, a disc refiner, after which the defibrated material is recycled to the suspension in conduit ~ by way of the conduit 6, as in the cbnventional process. The accepts fraction from the screen 3 passes by way of conduit 7 to the screen xoom 8, which may contain pressurized -10 screens, as in the system o Figure 1. However, the amount of rejectsfrom the screen room 8 is increased, either by increasing the flow through conduit 9, by increasing the opening of the valve 17, or by reducing the diameters of the openings of the screen plates, or both, so that from about 30 to about 85% by weight of the fiber suspension arriving 15 via conduit 7 is separated out as reJects, and passes through the conduit 9 to the separator 11. Here, resldual shives and splinters having a length above 4 mr~, preferably above 8 mm, are removed. This separator ma~ comp rise, for example, a vibratory scréen ha~T ing smaller opening diameters than the vibratory screerl 3.
The suspension is separated at separator 11 into an accepts fraction and a rejects Eraction. The rejects fraction passes through the conduit 12 back to the conduit 4, for recycling to the defibrator 5,, at2r which the fraction is returned vla conduit 6 to the groundwood pulp ~uspension fro~ the grinder in conduit 2. The accep~s fraction frorn the separ~tor 11 25 passes via conduit 13 to a second separator 14, which may comprise for example a centrifugal screen or a curved screen, -for fractionating 5~
the accepts fraction into a long-fiber raction of which at least 80%
of the fibers are retained on a sieve No. ~ 50 in a Bauer-~cNett classifierO
The long-fiber fraction from the separator 14 is wlthdrawn via conduit 16 at C as long-iber groundwood pulp product~ and can 5 be dewatered and then used for special ~purposes.
The short fiber accepts fractioll from the separator 1~ is withdrawn via conduit 15 and blended with the accept~ flow from the screen room 8 in the conduit 10. The blencl is withdrawn at B as short-iber fraction groundwood pulp product~
In a particularly preferred embodiment of the invention, the white water obtained in dewatering the ~ong-fiber fraction is recycled as dilution water to the separator 11. The white water has a fiber content below 200 mg/l, and can be obtained by incorporating a separate filter in the circuit.
Because more than the ~ormal proportion o rejects i~
withdrawn at the screen room 8; the short-fiber fraction obtained in the conduit 10 as accepts fraction from the screen room 8 has an extremely low shives content, within the range from about 0 to about 0. 05%, and a freeness of frorn about 50 to about 200 ml C. S. F. ~orresponding 20 conventional groundwood pulps of comparable freeness have a shives content of from 0. 08 to 0. 20~ shives content of such a magnitude considerably impairs the usefulness of the pulp in the manufacture of printing paper, and contributes to a surface roughness of the paper which causes the paper to display a nonuniform ink absorbency.
In addition, the short ~iber pulp fraction according to the invention has a different fiber distribution than conventional groundwood pulp, and affords the aclvantage of a higher tensile index and a hîgher opacity in printing paper produced from the fraction than paper produced from conventional groundwood pulp. Consequently, it is suited for the manufactur~ of printing paper of the highest quality.
Tixe long-fiberpulp fraction according to the invention has an unusually high Ireeness, within the range from about 200 to about 750 ml C. S. F., and a low resin content, below 0. 3% DK~ (after bleaching the resin content is less than 0.15(~j DKM). Frorn about 80 to about lOO'yo of the long-fiber pulp fraction comprises fibers which are xetained 10 on a sieve No. 150 in a Bauer-McNett classifier. The long fiber pulp fraction has e~traordihary properties, rendering it suitable for the manufacture of absorben~ products, and provides high bulk, good absorption rates and an extremely good absorption capacity. In the process according to the invention, from about 15 to about 75~ of the lignocellulosic 15 material that is ground up is recovered as long-fiber fraction.
Thus, instead of producing a single product which is inferior to chemithel momechanical pulp, the process o~ the invention makes it possible to obtain two groundwood pulp products, each of which has egtremely good properties, which make them suitable for special purposes.
20 These pl:'O~J.lCtS are produced in a higher yield than conventional groundwoed pulp, while using less energy. The total energy consumed when producing the long-iber pulp fraction according to the invention is from 300 to 50~ ~Wh/ton of dry pulp~ while energy consumption in the prepar~tlon ~f comparable chemithermomechanical pulp is about 1, 000 25 kWh!ton ~ dry pulp.
. . .
. 9 5~
The energy consumption in manufacturing the short-fiber pulp fraction is from 1300 to 1500 kWh/ton of pulp, while about 2000 kWh/ton of dry pulp is needed to prepare chemithermomechanical pulp of corresponding qualil;y.
When practicing the process of the invention, a$ least 96~ of the wood is converted to groundwood pulp~ as compared from 92 to 94~, in the manufacture of chemithermomechanical pulp.
The long-fiber pulp fract~on obtained in accordance with the invention is suited for admixture with other pulps, such as sulfite pulp, sulfate 10 pulp and chemimechanical pulp. It is also well suited for the manufacture of cardboard and paperboard, as well as the manufacture of absorbent products. Other fiber materials such as recycled fibers, peat fibers and synthetic ~ibers can also be rnixed with the long-fiber pulp fraction.
The process according to the invention can also be applied 15 with good results in the manufacture of pressure-ground groundwood pulp, in which case the energy consumption is about 10% lower.
The following Example in the opinion of the inventor represents a pre~erred embodirnent of the invention EXAMPIE
As a control, groundwood pulp was manufactured from spruce wood in accordance with the flow sheet shown in Figure 1. The spruce was ground in the grinder 1, and the resultant abùeous fiber suspension (which had a pulp consistency of 2.1~) was passed through the conduit 2 to a Jonsson-type vibratory screen 3 having screen plates with 6 mm 25 diameter openings, where the coarse wood residues were screened out.
The rejects obtained in the vibratory screen 3, comprising coarse .~
1~2~3%~i~
splinters and sh~ves and constituting about 3~ by weight of the groundwood iber suspension feed, was passed through the conduit 4 at a pulp ~onsistency of 5~ to the disc refiner 5, where the coarse material was defibrated to separate fibers. The defibrated rejects fraction 5 was passed via the conduit 6 and the conduit 2 back to the vibratory screen 3.
The accepts from the vibratory screen 3 had a pulp conæistency of 1. 3%, and was passed through the conduit 7 to a pressurized screen 8 having a fixed cylindrical screen basket, to the inner cylindrical 10 surface of which the pulp suspension was passed under superatmospheric pressureO The screen was also provided with an internal rotating scraper. The openings in the perforated screen plates had a diameter of 1.75 mm.
The flow of fiber suspension to the pressurized screen 8 was 15 so regulated that 20~i by weight of the fiber content of the fiber suspension fed to the screen remained on the screen plates, and passed as rejects via the valve 17 through the conduit 9 to the conduit 4, for further defibration in the disc refiner 5, after which the material was recycled to the conduit 2. The pulp consistency in the conduit 9 was 1. 9%.
Acceptæ from the pressurized screen 8 had a pulp consistency of 1.1~ and was removed via the conduit 10, where the pulp product was further cleaned in a vortex cleaner (not shown). Samples designated A were removed, for determination o the shives content and fiber CQmpOSitiOn.
The groundwood pulp prepared in accordance with the invention, following the flow sheet shown in Figure 2, was al~o prepared from ~ 2~ ;6 spruce wood. The fiber suspension in the conduit 2 had a pulp consistency ~ 2.1~,,. and was closely screened in the vlbratory screen 3 at an opening diameter of 6 mm. The rejects comprised 3% by weight of the fiber suspension feed, and was passed via the 5 conduit 4, wbere the pulp consistency was 5~i~ to the disc refiner 5. The defibrated rejects pulp suspension had a pulp consistency of 5~O, and was recycled through the conduit 6 to the conduit 2 for rescreening in the yibratory.screen. 3.
The accepts from the vibratory screen 3 had a pulp co~sistency 10 o~ 1. 3'3h, and was passed via conduit 7 to the pressurized screen 8. The screen plates were changed to an opening diameter of 1. 60 mm instead of 1. 75 mm. At the san~e time, the valve 17 was opened furtber, so that the amount of rejects passing through the valve rose to 70% by weight of the fiber content of the fiber suspension feed. The rejects 15 pulp fxaction obtained in the pressurized screen 8 had a freeness of 245 ml C. S~. F.; a 8 hives content of 2. 95~ accordin.g ~o ,Sommerville~ 33.1~.
of the fiber~ was retained on a ~ieve No. 20 and 41 5~/O on a siéve No. 150 in a Bauer-~cNett classifier, and 25. 4~, passed through the sieve NoO 150~ :
~oThe r ejects was brought to a pulp consistency of 1. 5~oj7 and . ~assed via conduit 9 to $he separator 11, which was in the form of a vibratory scre0n provided with screen plates having an opening diameter VI 3. 0 mm. The vibratory screen was so adjusted that the amount oP
rejects was 0.8~o by weight of the fiber suspension feed. The rejects 25 from the vibratory screen separator 11 had a shives content o 73~i according to Sommerville, and passed via conduit 12 to the conduit 4, for further : .
~L22~
defibration in the disc refiner 5, after which it was returned via conduit 6 to the condult 2~
The pulp consistency in the conduits 6 and 2 was the same as that in the control.
l'he accepts pulp fraction from the vibratory screen separator 11 was brought to a pulp consistency 1. 2(3~o~ and passed through the conduit
13 to a se~ond separator 14, where the pulp was fractionated ir3to two fractions, one having long fibers and one having short fibers. The fractiDnator was a Cowan type centri~l screen having a stationary 10 cylindrical screen basket, against the inner cylindrical surface of which the fibe~ suspension was slung by a rotating device. As distinct from vib~atory screens, centrifugal screens are so constructed as to utilize ~he mutual autogenous effect of the fibers at the screen surfaces3 and have larger opening diamete1rs. The centrifugal screen 15 ~e1para~or 1~ had an opening diameter OI 1. 50 mm.
20% of the fiber suspension leaving the vibratory screenæeparatorll through the conduit 13 was removed as accepts in the centrifugal screen separator 14.
This accepts fraction had a freeness- of 140 ml C. S. Fl j and a ~0 shives content of 0.04~0 according to Sommerville. 3.1% of the accepts fraction was retained nn a sieve No. 20 and 82'3~, on a sieve No. 150 in a Bauer-~cNett classifier, ~nd 14~ passed through the sieve ~oO 15û.
This accepts fraction was given a pul~ conslstency of 0. 9~O) 25 and was passed b~r the conduit 15 to conduit 109 and ~lended with the accepts flow from the pressurized screen 8~ This accepts flow had a ... ... . .. . . . ...................... .
. - :
.'' ~22f~ 6 freeness of 90 ml ~. ~. F., a shives content of 0. Ol~o~ according to Sommerville, and a fiber distrrbution such that 2. 3~i was retained on a sieve No. 20 and 63. 7~k on a sieve No. 150 in a Bauer-Mc:~ett classifier, and 34~, passed through the sieve No. 150.
The mixed aceepts from the pressurized screen 8 and the centrifugal screen separ~tor 14, the short-fiber fractio~, was withdrawn throughthe conduit 10 as short fiber groundwood pulp product B, and further cleaned in a vorte~{ cleaner (not shown in the Figure).
The amount of short fiber product withdrawn as B, calculated on the basis aE the wood material feed, was 44~O, of which 31. 2~o was fed via conduit 15.
The rejects fraction from the centrifugal screen separator 14 comprised 80~ of the fiber suspension leaving the vibratory screen separator 11 through the conduit 13, and was brought to a pulp consistency o-f 1. 9~O~ and then re~noved as long-fiber groundwood pulp C through the conduit 16.
The ratio of short fiber pulp product B to long fiber pulp product was 1 to 2.2.
Samples of pulp A, short-iber pulp B and long-fiber pulp C
were taken, for determining freeness, shives content and fiber distribution.
Table I sets forth the freeness, shives content and fiber distribution of the (: ontrol, sarnple A9 the short fiber pulp B, the long fiber pulp C, and a typical chemithermomechanical pulp as D.
20% of the fiber suspension leaving the vibratory screenæeparatorll through the conduit 13 was removed as accepts in the centrifugal screen separator 14.
This accepts fraction had a freeness- of 140 ml C. S. Fl j and a ~0 shives content of 0.04~0 according to Sommerville. 3.1% of the accepts fraction was retained nn a sieve No. 20 and 82'3~, on a sieve No. 150 in a Bauer-~cNett classifier, ~nd 14~ passed through the sieve ~oO 15û.
This accepts fraction was given a pul~ conslstency of 0. 9~O) 25 and was passed b~r the conduit 15 to conduit 109 and ~lended with the accepts flow from the pressurized screen 8~ This accepts flow had a ... ... . .. . . . ...................... .
. - :
.'' ~22f~ 6 freeness of 90 ml ~. ~. F., a shives content of 0. Ol~o~ according to Sommerville, and a fiber distrrbution such that 2. 3~i was retained on a sieve No. 20 and 63. 7~k on a sieve No. 150 in a Bauer-Mc:~ett classifier, and 34~, passed through the sieve No. 150.
The mixed aceepts from the pressurized screen 8 and the centrifugal screen separ~tor 14, the short-fiber fractio~, was withdrawn throughthe conduit 10 as short fiber groundwood pulp product B, and further cleaned in a vorte~{ cleaner (not shown in the Figure).
The amount of short fiber product withdrawn as B, calculated on the basis aE the wood material feed, was 44~O, of which 31. 2~o was fed via conduit 15.
The rejects fraction from the centrifugal screen separator 14 comprised 80~ of the fiber suspension leaving the vibratory screen separator 11 through the conduit 13, and was brought to a pulp consistency o-f 1. 9~O~ and then re~noved as long-fiber groundwood pulp C through the conduit 16.
The ratio of short fiber pulp product B to long fiber pulp product was 1 to 2.2.
Samples of pulp A, short-iber pulp B and long-fiber pulp C
were taken, for determining freeness, shives content and fiber distribution.
Table I sets forth the freeness, shives content and fiber distribution of the (: ontrol, sarnple A9 the short fiber pulp B, the long fiber pulp C, and a typical chemithermomechanical pulp as D.
14 Table I
Fiber Distribution Shlve Content (Ba~ler McNett) %
according to retained ~ _ pas~ng Freene~sSommerville ~n - o~ - through Sample C S~F.,ml ~, sieveNo.20sieveNo150sieveNo. 150 . . _ 120 0006 8.558.4 33.1 B 115 0.03 2.762.3 35.0 C 622 0. 40 48 145. 2 6~ 7 D 600 0.35 35024601 18.9 The Table show~ that the short fiber pulp B in accordance ~ h the invention has a very low shives content. The long fiber pulp C~ in accordance with the invention has a very high freeness, a low shïves
Fiber Distribution Shlve Content (Ba~ler McNett) %
according to retained ~ _ pas~ng Freene~sSommerville ~n - o~ - through Sample C S~F.,ml ~, sieveNo.20sieveNo150sieveNo. 150 . . _ 120 0006 8.558.4 33.1 B 115 0.03 2.762.3 35.0 C 622 0. 40 48 145. 2 6~ 7 D 600 0.35 35024601 18.9 The Table show~ that the short fiber pulp B in accordance ~ h the invention has a very low shives content. The long fiber pulp C~ in accordance with the invention has a very high freeness, a low shïves
15 content, and a very high content of l~ng fibers.
Some of the samples taken were bleached; us ing 3% hydrogen peroxide calculated per ton of dry pulp, and ~ere then washed, dewatered and dried to form laboratory sheets, which were analyzed with respeçt to resin content and brightness. Part ~f the laboratory 20 sheets were dîsintegrated in a disc refiner to form flu~f pulp, of which the bulk7 absorption rate, and absorption capaci~r wer~ determined.
The data are set forth in Table 11 below, with su~ite pulp added for comparison as sample E.
Table Il E~esin Extractives ~bsorption Absorption ContentBrightness Bulk Time Capacity Sample DKM ~ 0~ cm3/g seconds g H20/g pulp 0.95 80.0 12.5 4.6 9.9 ~ ~.08 78.2 17.7 6.0 lO.tl D 0.19 74. 6 17.9 7.3 10.9 ~ 0.32 92.5 16.2 5.0 9.2 The da~a in Table II shows that the long fiber pulp sample ~ in accordance with the invention had a very high bulk and absorption capacit~r, equal to the high yield chernitherrrlomechanical pulp, considered best up to now for the manufacture of absorbent products.
5 The properties of the long fiber pulp ~ also are marl~edly better than those of the sulfite pulp. The long fiber fraction ~ had a lower resin content7 and at the same time a higher brightness than the chemithermo-mechanical pulp. This high brightness is suprising, since the pulp has a low light-scattering coeficient (see Table m, below).
lû Papers w~re produced from samples A and B, and the properties of the papers determined. The results are set forth in Table III.
Table ~II
Tensile TearLight-scattering~
~dex ~Ide~coefficient Opacity Sample Nm/g mN~ m2/gm2/kg A 31.8 3.7 59.5 92.5 B 34.2 3.3 63.5 95.6 The short iber pulp B in accordance with the invention had a 20 higher tensile index and a considerably higher opacity than the conventional groundwood pulp of sample A.
~ ccordingly, the method according to the invention makes it possible to produce improved groundwood pulp products as short~fiber and long-fiber fractions for widely varied uses, such as finer pulps for 25 the manufacture of printing papers of high quality, and.coarser pulps for the manufacture of fluff and cardboard, while consuming less energy than required in the manufacture of conventional gr~ndwoocl pulps.
.
Some of the samples taken were bleached; us ing 3% hydrogen peroxide calculated per ton of dry pulp, and ~ere then washed, dewatered and dried to form laboratory sheets, which were analyzed with respeçt to resin content and brightness. Part ~f the laboratory 20 sheets were dîsintegrated in a disc refiner to form flu~f pulp, of which the bulk7 absorption rate, and absorption capaci~r wer~ determined.
The data are set forth in Table 11 below, with su~ite pulp added for comparison as sample E.
Table Il E~esin Extractives ~bsorption Absorption ContentBrightness Bulk Time Capacity Sample DKM ~ 0~ cm3/g seconds g H20/g pulp 0.95 80.0 12.5 4.6 9.9 ~ ~.08 78.2 17.7 6.0 lO.tl D 0.19 74. 6 17.9 7.3 10.9 ~ 0.32 92.5 16.2 5.0 9.2 The da~a in Table II shows that the long fiber pulp sample ~ in accordance with the invention had a very high bulk and absorption capacit~r, equal to the high yield chernitherrrlomechanical pulp, considered best up to now for the manufacture of absorbent products.
5 The properties of the long fiber pulp ~ also are marl~edly better than those of the sulfite pulp. The long fiber fraction ~ had a lower resin content7 and at the same time a higher brightness than the chemithermo-mechanical pulp. This high brightness is suprising, since the pulp has a low light-scattering coeficient (see Table m, below).
lû Papers w~re produced from samples A and B, and the properties of the papers determined. The results are set forth in Table III.
Table ~II
Tensile TearLight-scattering~
~dex ~Ide~coefficient Opacity Sample Nm/g mN~ m2/gm2/kg A 31.8 3.7 59.5 92.5 B 34.2 3.3 63.5 95.6 The short iber pulp B in accordance with the invention had a 20 higher tensile index and a considerably higher opacity than the conventional groundwood pulp of sample A.
~ ccordingly, the method according to the invention makes it possible to produce improved groundwood pulp products as short~fiber and long-fiber fractions for widely varied uses, such as finer pulps for 25 the manufacture of printing papers of high quality, and.coarser pulps for the manufacture of fluff and cardboard, while consuming less energy than required in the manufacture of conventional gr~ndwoocl pulps.
.
16
Claims (4)
1. A process for preparing groundwood pulp at a low energy consumption as (i) a short-fiber fraction that is essentially shive-free and has a low freeness, low surface roughness and high opacity; and (ii) a long-fiber fraction that has a low resin content, as well as a high freeness;
which comprises the steps of:
(1) grinding lignocellulosic material to form an aqueous groundwood pulp fiber suspension;
(2) screening the groundwood pulp fiber suspension through a coarse screen having screen openings not less than about 5 mm;
(3) defibrating reject lignocellulosic material separated out on the coarse screen;
(4) recycling the defibrated lignocellulosic material to the groundwood pulp fiber suspension from the grinding step (1);
(5) separating the groundwood pulp fiber suspension from.
step (2) into (a) an accepts fraction and (b) a rejects fraction, the latter comprising from about 30% up to about 85% by weight of the fiber suspension;
(6) screening the rejects fraction 5(b) through a screen, having screen openings of less than about 5 mm;
(7) separating the fiber suspension from step (6) into (a) an accepts fraction and (b) a rejects fraction;
(8) recycling the rejects fraction 7(b) to the defibrating step (3) and then to the groundwood pulp fiber suspension from the grinding step (1);
(9) screening the accepts fraction 7(a) to form (a) a short-fiber accepts fraction of which from about 15 to about 60% comprises fibers passing through a sieve No. 150 in a Bauer-McNett classifier; and (b) a long-fiber rejects fraction of which at least 80% comprises long fibers retained on a sieve No. 150 in a Bauer-McNett classifier;
(10) withdrawing the long-fiber rejects fraction 9(b) as groundwood pulp product (ii);
(11) blending the short-fiber accepts fraction 9(a) with accepts fraction 5(a); and (12) withdrawing the resulting blend as short-fiber accepts fraction groundwood pulp product (i).
which comprises the steps of:
(1) grinding lignocellulosic material to form an aqueous groundwood pulp fiber suspension;
(2) screening the groundwood pulp fiber suspension through a coarse screen having screen openings not less than about 5 mm;
(3) defibrating reject lignocellulosic material separated out on the coarse screen;
(4) recycling the defibrated lignocellulosic material to the groundwood pulp fiber suspension from the grinding step (1);
(5) separating the groundwood pulp fiber suspension from.
step (2) into (a) an accepts fraction and (b) a rejects fraction, the latter comprising from about 30% up to about 85% by weight of the fiber suspension;
(6) screening the rejects fraction 5(b) through a screen, having screen openings of less than about 5 mm;
(7) separating the fiber suspension from step (6) into (a) an accepts fraction and (b) a rejects fraction;
(8) recycling the rejects fraction 7(b) to the defibrating step (3) and then to the groundwood pulp fiber suspension from the grinding step (1);
(9) screening the accepts fraction 7(a) to form (a) a short-fiber accepts fraction of which from about 15 to about 60% comprises fibers passing through a sieve No. 150 in a Bauer-McNett classifier; and (b) a long-fiber rejects fraction of which at least 80% comprises long fibers retained on a sieve No. 150 in a Bauer-McNett classifier;
(10) withdrawing the long-fiber rejects fraction 9(b) as groundwood pulp product (ii);
(11) blending the short-fiber accepts fraction 9(a) with accepts fraction 5(a); and (12) withdrawing the resulting blend as short-fiber accepts fraction groundwood pulp product (i).
2. A process according to claim 1, which comprises controlling the proportions separated as accepts fraction and rejects fraction in steps (5), (7) and (9) and the proportions blended in step (11) so that the weight ratio of the long-fiber fraction to the short-fiber fraction is within the range from 1:3 to 3:1.
3. A process according to claim 2 in which an amount within the range from about 15 to about 75% of the lignocellulosic material ground in step (1) is taken out as a long-fiber pulp product (ii).
4. A process according to claim 3 in which the screening steps (2), (6) and (9) and the defibrating step (3) are carried out in a manner such that the shives content of the short-fiber pulp product (i) is less than 0. 05% by weight.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE8301359A SE435941B (en) | 1983-03-14 | 1983-03-14 | PROCEDURE FOR THE PREPARATION OF IMPROVED GRINDING MASS |
SE8301359-9 | 1983-03-14 |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1228256A true CA1228256A (en) | 1987-10-20 |
Family
ID=20350348
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA000449449A Expired CA1228256A (en) | 1983-03-14 | 1984-03-13 | Process for preparing groundwood pulp as short fiber and long fiber fractions |
Country Status (10)
Country | Link |
---|---|
JP (1) | JPS59173395A (en) |
AT (1) | AT385789B (en) |
AU (1) | AU567714B2 (en) |
CA (1) | CA1228256A (en) |
DE (1) | DE3409121A1 (en) |
FI (1) | FI72354C (en) |
FR (1) | FR2542774B1 (en) |
NO (1) | NO156378C (en) |
NZ (1) | NZ206982A (en) |
SE (1) | SE435941B (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
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SE444825B (en) * | 1984-09-10 | 1986-05-12 | Mo Och Domsjoe Ab | PROCEDURE FOR THE PREPARATION OF IMPROVED HOG REPLACEMENT MASS |
SE8701423L (en) * | 1987-04-06 | 1988-10-07 | Kamyr Ab | PROCEDURE FOR MANUFACTURING FIBER CONTENT WITH DIFFERENT FRAME MATERIALS |
FI113552B (en) * | 1999-12-09 | 2004-05-14 | Upm Kymmene Corp | Process for producing printing paper |
DE102012215577A1 (en) * | 2012-09-03 | 2014-03-06 | Voith Patent Gmbh | pressure screens |
JP6263931B2 (en) * | 2013-10-01 | 2018-01-24 | セイコーエプソン株式会社 | Sheet manufacturing apparatus and sheet manufacturing method |
JP6481749B2 (en) * | 2017-12-20 | 2019-03-13 | セイコーエプソン株式会社 | Sheet manufacturing apparatus and sheet manufacturing method |
Family Cites Families (7)
Publication number | Priority date | Publication date | Assignee | Title |
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US3411720A (en) * | 1966-08-18 | 1968-11-19 | Cons Paper Bahamas Ltd | Production of mechanical pulp from wood chips |
US3791917A (en) * | 1973-03-07 | 1974-02-12 | Bird Machine Co | Process for producing kraft paper laminate of top stock and base stock layers |
US3925150A (en) * | 1973-04-06 | 1975-12-09 | Black Clawson Co | Selective reclamation of waste paper products |
CS205557B1 (en) * | 1978-10-26 | 1981-05-29 | Svetozar Vagac | Low-grade waste paper processing plant |
SE433954B (en) * | 1980-03-25 | 1984-06-25 | Mo Och Domsjoe Ab | PROCEDURES AND DEVICES FOR REDUCING THE PREPARATION OF GRINDING MACHINES FROM WOODWOODS IN STONE GRINDING GROUPS REMOVE AND SPETOR YEAR REGULATION OF THE FREENESS OF THE MASS |
ZA816810B (en) * | 1980-10-10 | 1982-09-29 | Beloit Corp | Method for producing a fiber pulp having improved opacity at a high yield from bagasse |
SE431571C (en) * | 1982-07-02 | 1985-09-09 | Nils Anders Lennart Wikdahl | SET FOR CLEANING A FIBER SUSPENSION |
-
1983
- 1983-03-14 SE SE8301359A patent/SE435941B/en not_active IP Right Cessation
-
1984
- 1984-01-30 NZ NZ20698284A patent/NZ206982A/en unknown
- 1984-02-06 AU AU24099/84A patent/AU567714B2/en not_active Ceased
- 1984-03-09 JP JP4637784A patent/JPS59173395A/en active Granted
- 1984-03-13 CA CA000449449A patent/CA1228256A/en not_active Expired
- 1984-03-13 AT AT83284A patent/AT385789B/en not_active IP Right Cessation
- 1984-03-13 NO NO840971A patent/NO156378C/en unknown
- 1984-03-13 DE DE19843409121 patent/DE3409121A1/en active Granted
- 1984-03-13 FI FI841013A patent/FI72354C/en not_active IP Right Cessation
- 1984-03-14 FR FR8403898A patent/FR2542774B1/en not_active Expired
Also Published As
Publication number | Publication date |
---|---|
FI841013A0 (en) | 1984-03-13 |
FI72354B (en) | 1987-01-30 |
NZ206982A (en) | 1987-05-29 |
FR2542774A1 (en) | 1984-09-21 |
JPS6352154B2 (en) | 1988-10-18 |
NO156378C (en) | 1987-09-09 |
FI72354C (en) | 1987-05-11 |
JPS59173395A (en) | 1984-10-01 |
SE8301359D0 (en) | 1983-03-14 |
NO840971L (en) | 1984-09-17 |
DE3409121A1 (en) | 1984-09-20 |
DE3409121C2 (en) | 1990-06-21 |
AU567714B2 (en) | 1987-12-03 |
SE8301359L (en) | 1984-09-15 |
AT385789B (en) | 1988-05-10 |
FR2542774B1 (en) | 1989-06-30 |
ATA83284A (en) | 1987-10-15 |
SE435941B (en) | 1984-10-29 |
FI841013A (en) | 1984-09-15 |
AU2409984A (en) | 1984-09-20 |
NO156378B (en) | 1987-06-01 |
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