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Modern Papermaking September 2016

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1. Pele Oy Modern Papermaking Pekka Komulainen 12 May, 2016 2. Pele Oy Modern Papermaking Contents Page  Paper and Board Grades 3 …
  • 1. Pele Oy Modern Papermaking Pekka Komulainen 12 May, 2016
  • 2. Pele Oy Modern Papermaking Contents Page  Paper and Board Grades 3  Paper Composition 11  Papermaking Processes 23  Surface Sizing and Coating 69  How to Influence on Process and Paper Quality 83  New Papermaking Developments 92  Thank You for Your Attention 109 2
  • 4. Pele Oy 4 European unofficial paper grade classification  Printing and writing papers  Mechanical printing papers  Woodfree printing and writing papers  Paperboards  Cartonboards  Containerboards  Special boards  Tissue  Hygiene products  Other tissue products  Air-laid paper  Specialty papers
  • 5. Pele Oy 5 Printing paper grades News print MF Spesial. SC-A+ SC-A SC-B SC-C MFC LWC FCO HWC MWC WF Unctd WF Coated Relative Value Relative Quality
  • 6. Pele Oy 6 Uncoated woodfree Coated surface Coated & ca- lendered European classification of P&W paper grades Uncoated Woodfrees Coated Woodfrees Woodfree Printing and Writing Papers Uncoated Mechanicals Coated Mechanicals Mechanical Printing Papers Next level classification according to pigment coating (surface quality) Pulping Method (Brightness)
  • 7. Pele Oy 7 European mechanical paper grades Newsprint TD, Bulky etc. SC-papers RG and offset Uncoated Mechanicals LWC FCO MFC Single Coated MWC HWC 2-3 coatings Coated Mechanicals Mechanical Paper Grades Mechanical paper grades include mainly mechanical pulp (SGW, TMP, CTMP etc.) or deinked pulp from mechanical recovered papers. Amount of bleached softwood kraft pulp (BSKP) is 0-50 % depending on paper grade.
  • 8. Pele Oy 8 European woodfree paper grades Office Papers Cut Size like A4, A3 Printing Papers Folio Sheets and Rolls Uncoated Woodfree Single Coated Gloss/Matt Folio or Rolls Multi Coated Gloss/Matt Folio or Rolls Coated Woodfree Woodfree Papers in Sheets and Rolls Woodfree paper grades are made mainly from chemical hardwood pulp. Some BSKP must be added to coated grades. Coated grades can include 5-20% hardwood BCTMP. Deinked pulp made from woodfree grades can be added especially to office papers .
  • 9. Pele Oy 9 Classification of coated grades Coated one side C1S Single Coated Rolls Sheets Gloss Finish Matt Finish Double Coated Triple Coated Coated two sides C2S Coated Woodfree Coated Mechanical Coated Board Coated Grades
  • 10. Pele Oy 10 Paper grades and printing methods Printing Method Paper Grade CSWO HSWO Sheet Fed Offset Roto- gravure Flexo Elektrogr. & Inkjet Newsprint xxx x MF Specialties xxx xx x x x SC xx xxx MFC xxx x x FCO xxx LWC xxx xx x MWC, HWC xxx x x WFC xx xxx xx WFU xx x xx xxx xxx = most common usage, xx = common usage, x = some usage
  • 12. Pele Oy Fibers and paper properties  Chemical pulp can be bleached up to brightness 90 %. Bright mechanical pulps have brightness 75-85 %.  Mechanical pulps give opacity, bulk and stiffness to the paper. Hardwood chemical pulp and softwood mechanical pulp can be used up to 100 % of paper furnish.  Softwood chemical pulp and hardwood mechanical pulp are normally additional pulps to give special properties to printing papers and are not normally utilized without other pulps.  More BCTMP from hardwoods is used for woodfree papers and boards. Some lignin from BCTMP will be dissolved in alkaline papermaking conditions. Dissolved lignin and extractives increase anionic trash and make the control of wet end chemistry more complex.  DIP, mechanical pulps and BCTMP have lower brightness than chemical pulp. Carbonates are best pigments to improve brightness as filler and in coating. 12 Hardwood, Short fibers Softwood, Long fibers Chemical Pulp, Flexible Mechanical Pulp, Stiff Fiber/Pulp Type Wet and dry strength Stiffness, opacity Formation, brightness Printability, runnability
  • 13. Pele Oy Hardwood vs. softwood chemical pulp  Short hardwood fibers will be more available than long softwood fibers.  Hardwood kraft gives smoothness, bulk and optical properties. This means that printability of final product is good.  Average length of hardwood pulp fibers is slightly less than one millimeter.  Refined softwood fiber is about 2 mm long. Longer fibers give better strength for coating, finishing and printing purposes.  Filler pigments decrease paper strength at the wet end of paper machine but also in surface sizing and coating where water moistens base paper.  The trend is to increase hardwood and filler and to decrease softwood. However, where softwood is integrated it can be used more together with less expensive filler. Hardwood Chemical Pulp (Birch) Softwood Chemical Pulp (Pine) 13
  • 14. Pele Oy Fiber combinations in European white papers Hardwood 100 % News SC White Kraft Uncoated Woodfree LWC Opacity Bulk Brightness Coated Woodfree Softwood 100 % StrengthFormation 14
  • 15. Pele Oy Thin Eucalyptus fiber with thick fiber wall Vessel cell of Eucalyptus Plantation hardwood pulps  Thin and quite long fibers of Eucalyptus having thick fiber wall can be developed by refining without loss in bulk and tear strength. However, short and thick vessels cells must be handled to prevent picking problems. There are several usable species of eucalyptus, which have different properties for papermaking.  Eucalyptus is well suited for all kind of paper and board grades. Acacia is the other competitive fiber but has thinner fiber walls and is not as good for grades requiring high bulk and stiffness. 15
  • 16. Pele Oy Pulps and paper grades  Actual fiber furnishes may vary largely and can be quite different especially in small unintegrated paper mills.  Very often the price of fiber seems to be more important than the performance of fiber in the product; within each end-product the quality and the price of end-products may vary largely.  It is important to understand how each furnish component contributes the quality of the product and the performance in the paper machine, finishing, and converting. 16 Paper Grades Short fibers for printability Long fibers for runnability Mechanical grades GW, PGW, TMP, BCTMP, DIP Long fiber: softwood (BSKP)Woodfree grades BHKP, DIP Non-wood grades Several non-woods (bagasse, wheat straw etc.) Bamboo, kenaf etc.
  • 17. Pele Oy 17 Recovered paper usage Container Board Special Office Papers Mixed to Office PapersDeinked fibers Hygienic Products Mixed to Tissue Papers News, SC, LWC Printing Papers Deinked fibers Corrugating Medium OCC, Kraft Paper Testliner Board Office Waste ONP OMG Mixed Waste Recycled fibers Recycled fibers Deinked fibers Cartonboards White Lined Chipboard ONP = Old Newspapers OMG = Old Magazines
  • 18. Pele Oy 18 Uncoated paper raw materials Material Mech. % WF % Comment Fibers 60 - 100 70 - 100 Wood or non-wood fibers Fillers 40 - 0 30 - 0 Mineral or synthetic pigments Surface sizes - 0 - 5 Starch, CMC, PVA, synthetic size, optical brighteners etc. Functional chemicals 0 - 1 0 - 2 Internal sizes, dyes etc. (effect on paper properties) Performance chemicals for process <1 <1 Retention aids, defoamers, biocides etc. (effect on process performance) Water 5 - 10 4 - 7 To be in balance with ambient air
  • 19. Pele Oy 19 Long and short fibers in paper  Most papers contain long fibers (BSKP) to give runnability and short fibers (BHKP or mechanical pulp) to give printability or other end use properties. Uncoated WF Newsprint Kraft Papers (Bleached or Unbleached) LWC Magazine SC Magazine Coated WF Long fibers, BSKP Short fibers, BHKP or Mechanical pulp 0 % 100 % 0 %100 %
  • 20. Pele Oy 20 Conventional LWC base paper raw materials Chemical pulp 30 - 50%  Bleached softwood kraft, hardwood is not used Mechanical pulp 70 - 50%  Stone groundwood (SGW), pressure groundwood (PGW), thermomechanical pulp (TMP) or chemithermomechanical pulp (CTMP, BCTMP) Broke  10 - 30% of the primary fiber furnish  Uncoated and coated broke (separately dosed) Filler pigments  Normally 4 -10 % of base paper (25 -100 % of this amount returned back as coated broke)  Kaolin clay, talc, calcium carbonate, titanium dioxide. Functional Chemicals  Cationic starch, slight hydrophobic sizing, dyes
  • 21. Pele Oy 21 Effect of long fiber addition on paper properties Positive  Wet and dry runnability Improve  Strength properties Increase (also tear)  Folding endurance Increases Negative  Printability Decreases  Formation Less uniform  Smoothness Decreases  Porosity Increases  Ink holdout Lower  Bulk and stiffness Decrease  Dimensional stability Decreases  Energy consumption Increases  Costs Increase
  • 22. Pele Oy 22 Sizing alternatives  Internal size is pumped to the pipe before headbox.  Surface size is added with size press (film sizer today) Type of Size Internal Sizing Surface Sizing Dry strength improvement (starch, CMC etc.) WF papers, mechanical printing papers, paperboards WF papers, WFC not always, paperboards Wet strength improvement (resins) Tissue, packaging papers, specialties Can be added to surface size Hydrophobic sizes (water repellent) WF papers, paperboards (coated WF not always) Can be added to surface size
  • 24. Pele Oy Cardboard recycling process 24
  • 25. Pele Oy 25 Pulper Screw press Disperging Post flotation Thickening 2 Pulp storage Thickening 1 Slot screens Pulp storage Cleaners Flotation CleanersHole screens Consistencies = Small = Average = Very high= High Conventional deinking process  The filtrate from thickening 1 and 2 is flotated and reused in the process again.
  • 26. Pele Oy 26 Papermaking process Slushing Refining Forming Pressing Drying PrecalenderCoatingFinishingConverting Steam Coating colour Pulp bales Fresh water ...or pulp Additives Calender
  • 27. Pele Oy 27 Papermaking principle (= water removal) Headbox & wire  Formation  Orientation  Strength  Smoothness  Two-sidedness >99% 50% 3% 20% 8% 7%80% Drying  Strength  Smoothness  Two-sidedness  CD profiles Indicative water content Wet Pressing  Porosity, bulk  Strength  Smoothness  Two-sidedness Surface Sizing/Coating  Porosity, ink abs.  Surface strength  Smoothness  Brightness, gloss  Two-sidedness Calendering  Porosity, ink abs.  Smoothness, gloss  Brightness, opacity  Bulk, stiffness  Two-sidedness
  • 28. Pele Oy 28 Simplified stock preparation in papermaking Source: Valmet
  • 29. Pele Oy Paper machine white water system  The objective of the white water system is to reduce water consumption and to minimize fiber losses by recirculating water. 29 The amount of suspension per ton of dry material in different positions: Pulp MixThick stock fiber recovery Fresh water Forming Excess water for reuse or to effluent Long circulation Short circulation Additives White water tank Wire pit White water tower Dilutions at web breaks HB Stock prep Position Consistency % m3 / ton of dry mat. Stock 4.0 25 To Headbox 0.5 200 After wire 20.0 5
  • 30. Pele Oy Conventional approach flow Source: Knowpap Old - holes New - slots 30 Screening
  • 31. Pele Oy 31 Attention! – 182 m long machine will appear! Wet end of copy paper machine Picture: Voith Paper Wire SectionPress section Headbox & Former  Formation  Orientation  Strength  Smoothness  Two-sidedness Wet Pressing  Porosity  Bulk  Strength  Smoothness  Two-sidedness
  • 32. Pele Oy 32 Predrying and surface sizing Surface sizing or coating Predrying cylinders Drying  Moisture (MD, CD)  Two-sidedness  Curl Sizing/Coating  Porosity  Ink absorption  Strength  Smoothness, Gloss  Brightness, opacity  Two-sidedness Picture: Voith Paper
  • 33. Pele Oy 33 Afterdrying, calendering and reeling Reeling Calendering Afterdrying Calendering  Caliper and porosity  Ink absorption  Smoothness & gloss  Brightness & opacity  Two-sidedness  Bulk and stiffness Picture: Voith Paper
  • 34. Pele Oy 34 Forming Drying DryingPressing Coating Reeling WindingCalendering Surface sizing Coated woodfree papermaking line  About 10 m wide and 10 mm thick stock flows from the headbox to the wire. The final paper caliper is less than 0.1 mm.  About 50% of the paper volume is air.
  • 35. Pele Oy 35 Formers and speed Picture: Valmet Paper  Hybrid formers are suitable for non-wood and specialty papers where speed must be slow due to the very difficult dewatering.
  • 36. Pele Oy 36 Crescent Former for tissue paper  Wire speed is about 20% higher than reeler speed due to the shortening in creping.  Release chemicals can be sprayed on the dryer surface to help creping. Picture: Voith Headbox Yankee dryer + hot air hood Pope reel PressGap former
  • 37. Pele Oy ATMOS tissue technology  According to Voith the big advantage of this technology is that for premium tissue production it consumes 35% less energy than TAD and the investment costs are much lower. While through-air drying uses only air pressure, ATMOS uses also vacuum.  Depending on application, it also enables fiber savings and the use of 100% recovered paper furnish. 37 Pictures: Voith
  • 38. Pele Oy Retention of fibers, fillers and fines  Fibers are long compared to wire fabric openings. Retention of long fibers is good against the wire, but fillers and fiber fines are smaller than wire openings.  Mechanical retention of fillers and fiber fines is possible when the fiber mat is thick enough with smaller voids between fibers than in wire openings.  Common practice is to flocculate fine material to larger aggregates. However, this can flocculate also fibers and impair paper formation. 38
  • 39. Pele Oy 39 Principle of paper formation  Originally there is over100 times as much water as fibers. Low concentration is needed to be able to avoid flocculation and to control basis weight (thickness).  Suction or pressure against the fabric is needed for dewatering.  Fourdrinier wire is pressing a pattern called wire mark to the paper. This causes two- sidedness.  Twin wire sections are used to avoid two- sidedness and to get easier dewatering with high speed.  Solids content after wire is 18-22 %.  Wire section removes about 98% of the total water. However, very expensive equipment and most of the energy are needed for press- and dryer sections.  To get the final dryness dewatering by pressing and by evaporation is needed after wire section. Wire fabric Filtered web Free fibers in water Removed water Picture: Knowpap
  • 40. Pele Oy 40 Filtration in gap former Picture: Knowpap Wire Wire  Two separate fiber mats are formed on the wires.  Middle part of the paper web has lower fines content and lower bonding strength.  Water removal capacity is more than double compared to Fourdrinier.  Both surfaces have very little dusting and linting material (fiber fines and fillers). This kind of paper is very suitable for offset printing. In addition, it is possible to use more filler without linting.  Fiber orientation is similar on both surfaces. Curling tendency is very low.
  • 41. Pele Oy 41 Paper machine clothing Press felt Wire fabric Dryer fabric Batt fiber needled to form fine surface Laminate fabric
  • 42. Pele Oy 42 Pressing of wet web  There are 1...4 nips in the press section. Earlier nips had only one felt (picture). Today double felted nips are increasingly used. Solids content after press section is 45 - 55%.  Web will be rough but compacted against the felt side and smooth but open on the roll side.  Paper is bulkier if less wet pressing and more drying is used. This, however, increases steam consumption. Felt Web Picture: Knowpap
  • 43. Pele Oy Wet pressing theory  Wet pressing has a strong effect on the properties of paper. The press geometry, rolls and their covers, felts and linear pressure combinations must be selected to conform to the running speed and the paper grade to be produced. Picture: Valmet 43
  • 44. Pele Oy Dryness and porosity with shoe and roll presses KnowPap 4.0 (2002)
  • 45. Pele Oy Press draw and porosity  A high press draw is not only question of runnability but also paper quality is lower when low porosity is needed.  Porosity measurement is also a good tool for evaluating what is a too high press draw 200 400 600 800 0 1 2 3 4 5 Porosity,Bendtsen,ml/min Press Draw, % Picture modified from: Valmet 45
  • 46. Pele Oy 46 Effect of press nip on paper  Felt and roll patterns are copied to the paper surface (felt is rough and roll is smooth).  Paper web close to the felt is compressed due to the lower water pressure but higher mechanical pressure. Paper becomes dense but rough on the felt side. Picture: M.A.MacGregor Roll side Felt side Smooth and open Rough but dense 
  • 47. Pele Oy 47 One-sided felt and water removal – rough and compacted felt side surface. Two-sided felt and water removal – symmetric web, both surfaces rough and compacted. Effect of felt on paper surface nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn nnnnnnnnnnnnnnnnnnnnnnnnnnmnnnnnnn nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn Rigid plate like press roll
  • 48. Pele Oy 48 Impulse in pressing and calendering  Paper is viscoelastic. This means that not only the pressure, but also the time under the pressure has effect in pressing and calendering.  Total effect of pressure forces is related to the sum of pressure impulse in all nips.  If speed is doubled it would require double linear load or double number of nips. Shoe press and belt calender are very effective. Impulse = pressure x time Pressure = linear load / nip length Time = nip length / speed Impulse = linear load / speed time Impulse = area Impulse = pressure x time = speed Σ linear load Nip pressure
  • 49. Pele Oy 49 Water content of the web  After wire section there is about 80% water in the web, even if more than 97% of the original water is removed. Removal of the final 2% is very expensive in the press and drying sections.  After press section solids content (and water content) is about 50%. Picture: Knowpap Pick-up felt H2O 50% H2O 80% Press section of a slow machine: open draw after 2nd nip
  • 50. Pele Oy 50  Basic concept for woodfree coated and uncoated: two shoe presses with transferbelt. This gives good runnability and CD profiles, but more two- sidedness than double-felted last press. Modern press section Better web run through press No rewetting after 2nd nip Quick start-up with new fabrics Picture: Voith Paper
  • 51. Pele Oy Paperboard machine press sections  On the right press section of a cartonboard machine has a separate smoothing press after double felted shoe press.  Kraftliner machine can have last press double felted because smoothness requirements are not critical (picture below). 51 Pictures: Voith
  • 52. Pele Oy Typical cartonboard machine  Cartonboard machines can have higher speeds when there are more wires. Drainage of each wire is similar to papermaking drainage of grammage less than 100 gsm.  Development of double shoe presses with totally supported web run increases web dryness to dryers 4-5 %-unit. Increased dryness allows 20 % higher speed, when drying capacity is limited or 20 % lower energy consumption with same speed.  Higher dryness means that web is stronger when transferred to dryers and there are less web breaks and sticking to dryer surfaces.  The paper machine in the picture below is Bohui PM1 cartonboard machine in China supplied by Voith. Smoothing press after double felted shoe presses is without felt. 52
  • 53. Pele Oy 53 Principle of drying  In dryer section about one ton water must be evaporated per one ton of final product.  For paper
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