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
• • 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
  • D21B1/14—Disintegrating in mills
• • 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
  • D21B1/02—Pretreatment of the raw materials by chemical or physical means

Definitions

• This invention relates to the production of mechanical and chemi-mechanical pulp with a yield of above 85% from ligno ⁇ cellulose-containing material for the making of paper or board products .
• the first step normally is pressurized, i.e. the refining takes place at temperatures exceeding 100°C, usually immediately below or at the so-called softening temperature (Tg) of the lignin.
• Tg softening temperature
• the softening temperature of the lignin which has proved to be an important variable at the refining of chips in mechanical and chemi-mechanical pulp processes, has been determined in the most recent decades in a number of scientific investigations for a plurality of wood types concerned. At the investigations standard equipment and conventional measuring principles for the determination of viscoelastic parameters have been used. For wood, as for other viscoelastic materials, the softening temperature varies with the load frequency at the measurements. At a higher load frequency, the softening temperature increases. At the processing frequencies normally applied in refiners the softening temperature of coniferous wood was determined to be between 125°C and M 5°£ , while it proved to be somewhat lower for our most usual hardwood types. The softening temperature can be shifted by the addition of different chemicals. It can be lowered, for example, after impregnation by usual lignin softening chemicals, of the type sulphite.
• the present invention relates to such a method, where the mechanical processing, for example refining, takes place in at least two steps.
• the material at its feed into the first processing step has a temperature below the softening temperature of the lignin, and at its feed into at least one subsequent processing step has a temperature exceeding the softening temperature of the lignin.
• refining takes place in at least two steps.
• the chips are fed into the refiner at a temperature below the softening temperature of the lignin and then are processed under relatively intensive conditions, for example in a double-disc refiner with a speed of at least 1200 rpm or in a single-disc refiner with high relative speed between the refiner discs (at least 1800 rp ⁇ , preferably at least 2400 rpm).
• the energy input in the first step is chosen to be on such a low level, that the long fiber content of the pulp which a.o. yields the potential for the later strength development at the refining, is not deteriorated appreciably.
• the freenes (CSF) of the pulp after the first step therefore, shall be high, preferably
• a subsequent refining step is carried out under conditions where the lignin of the fiber material is well softened.
• the fiber material then is fed into the refiner at a temperature exceeding the softening temperature of the lignin.
• the temperature should exceed 150°C, suitably 160°C and preferably 170°C.
• the temperature should exceed 135°C, suitably 150°C and preferably 160°C.
• temperatures over 200°C should be avoided, a.o. with regard to dark colouring of the fiber material.
• the processing frequency preferably can be high (relative speed at least 24.00 rpm) at the processing of the well- ⁇ oftened fiber material, which has proved especially favourable from an energy point of view.
• the temperature difference between the temperatures of the material at its feed into the first and, respectively, a subsequent processing step should be at least 15°C, suitably at least 25°C and preferably at least 35°C.
• fractures and fracture indications in the material initially are guided to layers in the fiber wall- not rich in lignin.
• the known fact then can be utilized, that the fiber material can be separated with low energy inputs in areas rich in lignin at temperatures above the softening temperature of the wood lignin.
• the fractures initially having been guided to areas not rich in lignin, it is thereby avoided to obtain a fiber material with only lignin-jovered surfaces which are difficult to fibrillate. This has previously been the great problem when it was tried to utilize refining temperatures above the softening temperature of the lignin at the production of mechanical pulps for printing paper or board products.
• Fine material from areas between the initial fracture zone and the middle lamina of the fiber rich in lignin also is easily released at temperatures above the softening temperature of the lignin in the later refining step, which can explain the low total energy consumption to a certain freeness (C. q F) in this process step and in the entire process according to the invention.
• the production of fine material otherwise is the most energy requiring part of the mechanical pulp process using conventional technique.
• Thermomechanical pulp from sprucechips was produced after refining in two steps in a 20" single-disc refiner of a well-equipped test plant.
• the first refining step (defibering) was carried out after preheating the chips at 115°C for about 3 minutes, i.e. at a temperature below the softening temperature of the lignin.
• the refiner was driven by a 3000 rpm motor, in order to ensure that the initial defibering should not take place under too mild conditions.
• the effect input in the first step was 64.O kWh/t, which yielded a pulp with freeness (CSF) 518 ml.
• the second refining step the conditions were varied according to the following Table:
• Fi g - 1 shows freeness as a function of energy consumption. It appears that by carrying out the second refining step at temperatures above the softening temperature of the lignin the energy input at refining to a certain freeness can be reduced considerably compared to conventional second step refining at temperatures below the softening temperature of the lignin (compare Tests A and B).The energy reduction will be still greater when, in addition, the speed is increased from 1500 to 3000 rpm (compare Test B with Tests C and D) .
• Fig. 2 shows the shives content as a function of ' the energy consumption. It appears that second step refining at temper ⁇ atures above the softening temperature of the lignin yields a clearly lower shives content at a certain energy input than refining at a temperature below the softening temper ⁇ ature of the lignin (compare Test A with Tests B-D) . Also in this case the higher speed yields the most favourable values. This proves to be a further advantage by using the conditions according to the invention.
• Fig- 3 shows the long fiber content as a function of freeness.
• Fig. 4 show,-; the tear index as a function of freeness. It appears that the tear index of the pulp can be maintained all the way down to the freeness range 150-200 ml, in spite of the iarge energy reduction at refining at the conditions of the invention.
• Figs. 5 and 6 show the tensile index and, respectively, light scattering as a function of freeness. It appears that- all tested pulps develop tensile index and, respectively, light scattering coefficient in a similar way when they are valued conventionally against freeness.
• thermomechanical pulp was made from spruce chips after refining in two steps by single-disc refiners.
• the first refining step was carried out at temperatures above the softening temperature of the lignin in the same equipment which was used previously in the test.
• the conditions in the first refining step and the freeness after refining with a certain energy input are described in the following Table:
• Fig. 7 shows that the energy consumption is considerably higher when the TMP-process is initiated with a refining step at a temperature above the softening temperature of lignin than that obtained with conditions according to the invention (compare Fig. 1).
• Fig. 8 shows that the light scattering coefficient is considerably lower when the TMP-process is initiated with a refining step at temperatures above the softening temperature of lignin than that obtained with conditions according to the invention (compare Fig. 6).
• the pulps produced, according to the invention, there ore, are clearly most suitable for use as printing paper pulps, where just the light scattering coefficient must be sufficiently high for achieving the desired optical properties.
• chemicals can be added advantageously after or during the first refining step, in order to avoid dark colouring at the high temperatures above the softening temperature of lignin in subsequent refining steps.
• the chemicals also can have a bleaching effect. Examples of such chemicals are sodium sulphite, sodium bisulphite, sodium ditionite, peroxide etc.
• the initial processing can be carried out, besides in refiners, also in grinders, compressing screws or other mechanical processing equipment.
• this reject with a temperature above the softening temperature of lignin shall be fed into at least one subsequent processing step.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Chemical And Physical Treatments For Wood And The Like (AREA)

Priority Applications (10)

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Publications (1)

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Cited By (5)

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Citations (2)

• 1992
  • 1992-12-30 SE SE9203943A patent/SE470555B/sv not_active IP Right Cessation
• 1993
  • 1993-12-08 EP EP94904362A patent/EP0677122B1/en not_active Expired - Lifetime
  • 1993-12-08 KR KR1019950702542A patent/KR950704567A/ko not_active Application Discontinuation
  • 1993-12-08 WO PCT/SE1993/001058 patent/WO1994016139A1/en active IP Right Grant
  • 1993-12-08 JP JP51147694A patent/JP3258019B2/ja not_active Expired - Fee Related
  • 1993-12-08 DE DE69320989T patent/DE69320989T2/de not_active Expired - Fee Related
  • 1993-12-08 AU AU58445/94A patent/AU678802B2/en not_active Ceased
  • 1993-12-08 BR BR9307748A patent/BR9307748A/pt not_active IP Right Cessation
  • 1993-12-08 CA CA002151364A patent/CA2151364C/en not_active Expired - Lifetime
  • 1993-12-08 NZ NZ259595A patent/NZ259595A/en not_active IP Right Cessation
  • 1993-12-08 RU RU95113478/12A patent/RU95113478A/ru unknown
  • 1993-12-08 PL PL93309195A patent/PL309195A1/xx unknown
  • 1993-12-08 AT AT94904362T patent/ATE170940T1/de active
  • 1993-12-14 ZA ZA939370A patent/ZA939370B/xx unknown
  • 1993-12-30 CN CN93121607A patent/CN1052049C/zh not_active Expired - Fee Related
• 1995
  • 1995-06-29 NO NO19952613A patent/NO312206B1/no not_active IP Right Cessation
  • 1995-06-29 FI FI953229A patent/FI115844B/fi not_active IP Right Cessation

Patent Citations (2)

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