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Modern papermaking feb 2018 pdf

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Modern papermaking feb 2018 pdf

  1. 1. Pele Oy Modern Papermaking Pekka Komulainen Pekka.Komulainen@clarinet.fi February, 2018
  2. 2. Pele Oy Modern Papermaking Contents Page  Paper and Board Grades 3  Paper Composition 11  Papermaking Processes 23  Paper Structure 80  Surface Sizing and Coating 88  How to Influence on Process and Paper Quality 102  New Papermaking Developments 112  Thank You for Your Attention 129 2
  4. 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. 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. 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. 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. 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 of woodfree grades can be added especially to office papers .
  9. 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. 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
  11. 11. Pele Oy PAPER COMPOSITION 11
  12. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 24. Pele Oy Cardboard recycling process 24 www.millenniumrecycling.com/process/
  25. 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. 26. Pele Oy 26 Papermaking process Slushing Refining Forming Pressing Drying PrecalenderCoatingFinishingConverting Steam Coating colour Pulp bales Fresh water ...or pulp Additives Calender
  27. 27. 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. 27 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
  28. 28. Pele Oy 28 Simplified stock preparation in papermaking Source: Valmet
  29. 29. Pele Oy Conventional approach flow Source: KnowPap Old - holes New - slots 29 Screening
  30. 30. Pele Oy Example of injection flash mixing (www.wetend.com)  Injection flash mixing of chemicals with correct order and late addition after pressure screens can save chemicals as well as improve formation, retention and drainage. 30
  31. 31. Pele Oy Typical inlet header to headbox  Standard headboxes are fed from one end only. It is very difficult to get an equal jet speed to the wire. The correct form of the header is most suitable for only one total flow.  Recirculation must be controlled for each flow to get balance for both ends. Good basis weight CD profile is demanding. Consistency variation affects first to the inlet side. 31
  32. 32. Pele Oy Headbox recirculation control 32  Headbox recirculation valve is often in wrong position. CD profiles are not symmetric but one edge is down and the other edge up.  There should be a pressure difference meter to be able to set the correct position from control room. Sight glass is difficult to see and would require several new settings during a shift. Recirculation valve closed Recirculation valve open
  33. 33. Pele Oy Octopus-type approach flow  The pipes to headbox have same length. There is no need to recirculation (10% smaller flow).  If there is consistency variation it only affects MD variation, and simultaneously in every CD position. CD variation is smaller than with conventional inlet header.  Octopus is suitable for smaller machines. Dilution control is also possible.  It is said that CD-profile and especially edges are even and stable. 33 Picture: GLV
  34. 34. Pele Oy Components of basis weight variation  Systematic variation in MD and CD are mathematically separated and the rest of the variation is called random or residual variation.  MD variation reflects pressure pulsations, CD variation control of slice and residual variation stability of the process and headbox. 34 Random or Residual Variation Cross Machine Direction Variation Machine Direction Variation Picture: Valmet
  35. 35. Pele Oy Scanning mixes MD and CD variations  If scanning speed is 1 m/s and PM speed 20 m/s, it means that single scanning time of a 10 m wide machine is 10 s and the length of measured paper is 200 m.  Main MD variation frequencies are 1-100 Hz. This is 10-1000 MD peaks during one scan.  This means that almost all of the measured CD variation can be MD variation.  Several scans are needed to eliminate MD variation (time dependent) from CD variation (position dependent).  Fixed point measurement is needed to get fast MD variation. Fast CD variation must be measured in lab (Valmet has a system after press section, but it is very expensive). 35 Picture: Valmet
  36. 36. Pele Oy Machine direction BW variation  Pressure variation is fast, consistency variation slow. Pressure variation can be measured with vibration measurement instruments from the pipe after pressure screen. HB feed pump pulsation HB screen pulsation Vibrations of rolls and motors HB pressure variation Fast MD BW variation f >1.0 Hz Thick stock flow variation Poor mixing of thick stock and WW HB consistency variation Slow MD BW variation f<1.0 Hz HB = Headbox, WW = White Water 36
  37. 37. Pele Oy MD variation frequencies 37
  38. 38. Pele Oy Basis weight variability by period  It is important to study the MD variability by period, not by meters.  Pulsations or vibrations are easy to trace to some rotating equipment.  Variation of thick stock mixing is normally 10-100 s. Headbox pressure variation is shorter with wave length from 5 to 10 s. If the basic reason is thick stock mixing, the wave length is not constant.  Final basis weight control can only have effect on quite long variations. Scanning time is 10-30 s and with filtering 3-5 scans are needed to get control changes.  In addition, web travel time from basis weight valve to reel is 1-3 min. 38
  39. 39. Pele Oy Thick stock mixing point  Thick stock should be joined to the white water as close to the mixing pump as possible.  The picture shows a very bad arrangement.  In this case speed difference of flows in the mixing point is so small that there is practically no turbulence. The real mixer is next pump. 39 Current mixing point is on operating floor, far from mixing pump Thick stock White water Mixing with no turbulence Picture: Wet End Technologies
  40. 40. Pele Oy Principle of coaxial mixing  The thick stock pipe connection of the previous slide has two principle faults.  First fault is that the thick stock flow comes sideways in 90 degree angle to the flow direction. It should always come parallel to the flow direction i.e. coaxially.  Second thing is that the incoming pipe should go in to the white water pipe center, not sideways. Recommended solution Thick stock 40
  41. 41. Pele Oy Wet end barring  Wet end barring is a fast pressure pulsation which is magnified on the Fourdrinier wire.  The difference between consistency variation and pressure variation is that pressure peaks travel fast with speed of sound (343 m/s), and consistency peaks travel with flow speed (about 3 m/s).  Consistency peaks will be on the wire very much diagonal while pressure peaks are almost perpendicular to MD. 41 Picture: Valmet
  42. 42. Pele Oy Wet end data collection system  Example of a comprehensive wet end data collection system. This requires very much additional measurements and is seldom done in practice. 42 Picture: Voith Paper
  43. 43. Pele Oy How to analyse MD variation of basis weight  For slow vatiation: Take single point measurements with the scanner.  For fast variation: When machine is stopped unwind about 40 cm wide roll with crawl speed through the scanner and collect data for spectral analysis.  If there is periodic variation the reason is easy to find. Spectral analysis of collected data gives the periodic variations. Temporary Unwind Scanner Pope 43
  44. 44. Pele Oy Effect of entrained air on papermaking  Online measurement of entrained air is a good solution to control foam and chemical usage.  Pipe and channel constructions and design very often enhance air entrainment.  Some of the general air caused problems are the following:  Poor formation  High paper porosity  Pumping problems causing basis weight and tensile variation. 44
  45. 45. Pele Oy 45 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
  46. 46. Pele Oy 46 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
  47. 47. Pele Oy 47 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
  48. 48. Pele Oy 48 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
  49. 49. Pele Oy 49 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.
  50. 50. Pele Oy 50 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.
  51. 51. Pele Oy High dilution forming  There are several paper grades which require high dilution forming to get the required paper formation uniformity. This is due to long special fibers, synthetic or natural.  The picture below is a calculation of headbox opening of 100 gsm paper and 80% retention as a function of consistency.  It is impossible to use slice opening over one meter with a conventional headbox. This is one of the reasons to use inclined wire for long fibers. 51 0 200 400 600 800 1000 1200 1400 0 0.2 0.4 0.6 0.8 1 1.2 Headbox consistency, % Sliceopening,mm
  52. 52. Pele Oy Inclined wire technology (Deltaformer)  Inclined wire former with angle of 15° to 35°, consistencies from 0.01 to 0.2%.  Higher stock dilution is needed to keep long fibers from entangling.  Fiber lengths from 5 up to 38 mm.  Water removal capacity up to 600 l/min/cm, width up to 5 m, speed up to 600 m/min 52 Picture: Glens Falls Interweb
  53. 53. Pele Oy 53 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
  54. 54. 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. 54 Pictures: Voith
  55. 55. 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. 55
  56. 56. Pele Oy 56 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
  57. 57. Pele Oy 57 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.
  58. 58. Pele Oy Laboratory sheet former Fourdrinier Gapformer with high jet/wire speed ratio Counterflow cylinder mold top wire Filtration method and z-directional orientation top wire top wire wire wire 58
  59. 59. Pele Oy Orientation distribution on top and wire sides Top side Random distribution circle MD CD Wire side 59  Fibers from a Fourdrinier machine are more oriented on the wire side.  Axis of sheet curl cylinder is to the machine direction, MD.  Fibers shrink and expand mostly in cross direction, CD.  In moistening wire side expands more and sheet edges will be up from the wire side. This is a good method to check wire side.  Fourdrinier paper is always two-sided, not only concerning fines but also fiber orientation.  Some balancing can be made with topwire but the complete solution is a gapformer.
  60. 60. Pele Oy 60 Paper machine clothing Press felt Wire fabric Dryer fabric Batt fiber needled to form fine surface Laminate fabric
  61. 61. Pele Oy 61 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
  62. 62. 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 62
  63. 63. Pele Oy Dryness and porosity with shoe and roll presses KnowPap 4.0 (2002) 63
  64. 64. 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 64
  65. 65. Pele Oy 65 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 
  66. 66. Pele Oy 66 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
  67. 67. Pele Oy 67 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
  68. 68. Pele Oy 68 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
  69. 69. Pele Oy 69  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
  70. 70. Pele Oy Single nip shoe press  Single nip press gives best bulk but also rough paper. However it is possible to calender paper more to get the required smoothness and printability. 70 Picture: Voith
  71. 71. 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). 71 Pictures: Voith
  72. 72. 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. 72
  73. 73. Pele Oy 73 Principle of drying  In dryer section about one ton water must be evaporated per one ton of final product.  For paper drying and water evaporation, heat must be transferred to the wet web. This is normally done by steam heated cylinder dryers (30 - 60 pieces).  Evaporated water must be transferred from the paper machine hood and fresh dry air blown back. Heat from the exhaust air is returned back to the process.  Paper moisture before coating or surface sizing is 2 - 5%. Final paper moisture is about double (4 - 10%) mainly depending on the mineral content and paper grade. Picture: Knowpap Exhaust air
  74. 74. Pele Oy 74 Hydrogen bond formation Hydroxyl group
  75. 75. Pele Oy 75 Inter-fiber hydrogen bond formation 1  Initial weak bonds via several water molecule layers in the beginning of dryer section. H O H O H O O H fiber wall surface H O H OH OH HO H HO H HO H H O H H O H H O H O H H O H H O H fiber wall surface Smook’s Handbook, 1982, adapted
  76. 76. Pele Oy 76 Inter-fiber hydrogen bond formation 2  Stronger bonds via monolayer of water O H H O H OH OH H O H H O H H O H O H O H O fiber wall surface fiber wall surface Smook’s Handbook, 1982, adapted
  77. 77. Pele Oy 77 Smook’s Handbook, 1982, adapted H O H O O H OH OH H O H O fiber wall surface fiber wall surface Inter-fiber hydrogen bond formation 3  Direct hydrogen bonding between fibers
  78. 78. Pele Oy 78 Remoistening of paper and fiber swelling OH OH OH H O fiber wall surface H O H O H O H O HHO H HO H HO H H O H H O H H O H H O H H O H fiber wall surface HO H Water molecule This is why paper can be recycled!
  79. 79. Pele Oy Shrinkage profile of conventional paper machine  Edges compared to center have: • higher weight • higher caliper • higher roughness • higher porosity • lower dimension stability • long and slack web to the rolls 79
  80. 80. Pele Oy PAPER STRUCTURE Picture: Prof Claire Davies 80
  81. 81. Pele Oy 81 Structure of paper  Paper structure is porous and there is lot of air between fibers and inside the fiber lumens.  Softwood chemical pulp fibers are mainly collapsed in dry paper sheet (picture).  Paper structure is layered. Main part of fiber area is bonded to the other fibers.  Paper thickness (caliper) is from 40 to 120 µm.  Original thickness of softwood fibers is about 30 µm and hardwood fibers about 20 µm.  There are 5 to 20 fiber layers in a printing paper sheet.  Fibers must be collapsed or broken down to thinner particles to be able to make a smooth and even paper sheet. Paper structure is oriented, porous and layered
  82. 82. Pele Oy 82 Breaking lengths of various materials Breaking length km  Single softwood fiber 100-150  Pine Wood 20-25  Printing papers 2-6  Softwood kraft paper 8-10  Steel 4-5  Aluminum 3-4  Graphite 35-40 Breaking length is the theoretical length of a material strip where it breaks due to its own weight.
  83. 83. Pele Oy 83 Moisture sorption isotherms for paper  Paper is hygroscopic and in balance with the air temperature and humidity.  Moisture content (m) also depends on the direction of the change (hysteresis).
  84. 84. Pele Oy 84 Evenness of paper Formation  Flocculation (long fibers) Basis Weight Variation  Machine direction (MD)  Cross machine direction (CD)  Residual variation (all directions)  From lot to lot Two-sidedness  Smoothness, gloss  Absorption, density  Color, brightness  Curl, orientation Orientation  Fibers more in MD  Orientation angle to MD ± 0 - 5º  Tensile strength ratio MD/CD = 2...4 MD CD Bad formation
  85. 85. Pele Oy 85 MD and CD properties of paper  Compared to cross-machine direction paper in machine direction:  has more fiber orientation  has higher gloss  is stiffer  has higher tensile strength  has lower tear strength  has lower elongation  has better dimensional stability i.e. shrinking in drying is bigger in CMD Fibers are more in machine direction. The upper sheet in the picture is stiffer (MD = longer side of copy paper).
  86. 86. Pele Oy 86 Curl directions in sheet moistening  Fibers swell and shrink more in the direction of thickness and paper in the cross machine direction (due to fiber orientation).  MD/CD tensile ratio for roll paper can be 3 - 4 but for sheeted paper it should be 1.5 - 2 to reduce curl and to improve CD stiffness. Wire side - more oriented in MD (not valid if gap former paper)
  87. 87. Pele Oy 87 Basic printing paper properties Importance depends on final usage  information, packaging or hygienic General properties  basis weight, moisture, caliper Strength properties  tensile, tear, burst, folding  surface, bond, dusting Optical properties  brightness, opacity, color Surface properties  roughness, gloss Absorption properties  water, oil, ink Structural properties  formation, orientation, two-sidedness, curl  density/bulk, stiffness  porosity, air permeability Picture: Knowpap Bulk / Density
  89. 89. Pele Oy Main paper coating principles 89 Picture: Katarina Dimic-Misic
  90. 90. Pele Oy 90 Film sizer with air turn www.mhibeloit.com
  91. 91. Pele Oy 91 Main phases in conventional pigment coating Drying of wet coating color with IR, hot air and drying cylinders Application of coating color Leveling of coating color
  92. 92. Pele Oy Main coating methods  Blade coating produces smooth surface but uneven coating. Curtain coating produces even coating layer but rough surface. 92Picture: Voith Paper
  93. 93. Pele Oy Film coating layout Typical coating processes for LWC Blade coating layout Picture: Valmet 93
  94. 94. Pele Oy Coating section of a cartonboard machine  There can be several coating stations in a coated paperboard machine (2-5 pcs).  The picture below shows a coating sequence top-top-back-top. 94 Picture: Voith
  95. 95. Pele Oy 95 Effects of coating on paper  Coating fills the cavities and covers the base paper surface increasing smoothness.  Ink absorption decreases.  Surface strength increases and dusting decreases.  Gloss increases, with the objective often being the increase of print gloss.  Opacity increases, and hopefully also brightness.  Mechanical strength of paper decreases, when coated and uncoated papers are compared at the same basis weight.  Stiffness decreases when papers are compared at the same basis weight. Triple Coated Uncoated
  96. 96. Pele Oy 96 10,000 X Surface of Coated Paper Fine kaolin clay Ground Calcium Carbonate Pictures: SMI Precipitated Calcium Carbonate
  97. 97. Pele Oy 97 Fillers and coatings in paper  Mineral pigments can be added as a filler before headbox or to the surface as a coating with binders. Paper Grades Filler Pigment % Surface size per side g/m2 Coating per side g/m2 Woodcontaining Newsprint, TMP/GW Newsprint, DIP 0 - 5 5 - 15 0 0 - 1.5 0 0 Unctd Mechanical, TD, Bulky SC 5 - 15 15 - 35 0 0 0 - 5 0 Ctd Mechanical, LWC MWC, HWC 5 - 15 8 - 18 0 0 - 2 5 - 15 20 - 40 Woodfree Uncoated Woodfree, Copy Printing 15 - 30 10 - 25 1 - 2 1 - 2 0 0 - 5 Coated Woodfree, standard Premium Art 10 - 15 12 - 18 0 - 2 0 - 2 10 - 15 20 - 35
  98. 98. Pele Oy 98 Structure of coated paper  Coating thickness is relatively smaller than grammage of coating. Density of coating layer is about double (2000 kg/m3) compared to the base paper density (1000 kg/m3). Picture: R. Klein, U. Schulze
  99. 99. Pele Oy 99 Effect of calendering  It is difficult to make matt but smooth paper which would be ideal for reading. Glossy Paper Gloss 50-80 PPS <1 Silk or semimatt Gloss 20-40 PPS 1-2 Matt Gloss 10-20 PPS >2 Pictures: Jouni Marttila
  100. 100. Pele Oy 100 Important properties of coated paper  Good CD profiles (basis weight, caliper, moisture, gloss, roughness, porosity, roll hardness)  Free of faults and holes (for coating), no impurities  Low fiber roughening potential (web offset grades)  High strength (MD tensile, CD tear, internal bond)  Good smoothness and minimum two-sidedness  Good formation (no mottling)  High compressibility (especially for rotogravure)  Optimal porosity and pore distribution  No blistering in heat set offset oven (high temperature)  No cracking (when folding) of higher weights  High brightness and opacity (low grammages)  Good CD stiffness, no curl (web offset grades and sheeted grades)
  101. 101. Pele Oy 101 Offset paper runnability vs. paper properties Pressroom runnability  Low amount of breaks  Low blistering tendency (heat set)  Low fiber roughening  Good folding  Good register control  Small amount of debris on blanket Paper properties  Profiles (moisture, basis weight, caliper, orientation etc.)  Tear- and tensile strength  Mechanical faults  Linting and dusting  Blistering resistance (heat set)  Ply-bond  Porosity  Moisture  Number of shives  Stiffness  Density, stretch dampening unit ink unit plate blanket backing cylinder Paper with dust
  102. 102. Pele Oy How to Influence on Papermaking Process and Paper Quality
  103. 103. Pele Oy 103 Effect of chemical pulp refining on paper Positive effects  Wet web strength   Tensile, surface etc. strengths   Better formation  Coating coverage   Porosity and ink demand   Smoothness and gloss  Negative effects  Water removal and solids content   Bulk and stiffness   Compressibility   Opacity and brightness   Drying shrinkage  dimension stability   Tear strength   Energy consumption  Pictures: E.Gruber Internal fibrillation External fibrillation Fiber bonding + =
  104. 104. Pele Oy 104 Woodfree paper process adjustments Command Variables Process Parameters BHKP %  Refining  Filler %  Grammage  Drainage -- --- + --- Retention - ± -- +++ Formation ++ + +++ -- Wet strength -- ++ --- ± Dry paper runnability -- + -- + Specific energy cons. + -- +++ ± + = positive effect, - = negative effect
  105. 105. Pele Oy 105 Effect of command variables on paper properties Paper Properties BHKP %  Refining  Filler %  Grammage  Optical properties ++ -- +++ + Tear strength - + - - - +++ Other strength properties - ++ --- +++ Better bulk ± -- ± ± Better smoothness + ++ +++ + Dimension stability + -- ++ + Lower porosity + ++ ± +++ Better printability + + +++ + Total costs/ton + -- +++ --- + = positive effect, - = negative effect
  106. 106. Pele Oy 106 Effects of selected parameters on paper properties Increasing the right variables have the effects of arrows in paper properties Longfibers (BSKP) Refining Wetendstarch Filler Moreorientation inMD Wetpressing Finalmoisture Calendering Press dryness      Initial wet web strength, MD       Tear strength, CD         Tensile strength, MD         Dimension stability, CD        Internal bond strength        Smoothness, gloss MD        Porosity        Stiffness, CD         Opacity        Brightness        Costs         Red = negative Green = positive MD = Machine Direction CD = Cross direction = main reason to increase
  107. 107. Pele Oy 107 Advantages of good runnability More - filler - coating Higher - speed - efficiency Good Runnability Decreased - basis weight - long fibre content Less - energy - water Less - chemicals - wires/felts More - short fibres - mech. pulp/DIP Quality - better - more even Lower - labor cost - supplies cost
  108. 108. Pele Oy 108 Improved runnability Lower raw material costs Longer wire life Increased machine speed Less steam & energy/ton Lower furnish cost Cleaner system Steam & el used only once Less starch etc. needed Better CD- profiles Less shade & caliper variation Stronger paper Better bulk & stiffness Better printability Constant filler content Productivity Cost Efficiency Easy wet end chemistry Advantages of low break frequency Product Quality Low Break Frequency Less effluent and fresh water/ton Better and less variable raw materials Less Dry Broke Stable and better paper quality More Net Tons Lower Chemical Consumption Lower losses of fillers & chemicals Higher press solids
  109. 109. Pele Oy 109 Example of paper quality control system Picture: Valmet
  110. 110. Pele Oy CD profile controls  Standard scanning measurements of cross direction profiles are before all surface sizings/coatings and before final reeler. In addition, there can be measurement after press section and before calender.  To make a control loop there must be some adjustable profilers. Scanner measurement – profiler pairs can be:  Basis weight: reel frame to slice screws/dilution.  Moisture: Reel to water spray, size press to steambox/press nip profiler.  Caliper: Reel to calender induction/nip profiler. 110 Picture: ABB
  111. 111. Pele Oy 111 Source: Valmet Consumption values for papermaking News- print LWC Fine paper Opti Concept News Opti Concept LWC Electricity kWh/t of paper 470-570 550-700 500-650 530-630 600-750 Drying steam, t/t of paper 1,7 - 1,8 1,7 - 1,8 1,8 - 1,9 1,1 - 1,3 1,1 - 1,3 Drying gas, kg/t of paper 0 0,08 - 0,1 0 25 - 27 30 - 40 Fresh water m3/t of paper total for the mill 10 - 15 10 - 15 13 - 18 8 - 13 8 -13 Shower water m3/t of paper total for the PM 3 - 5 3 - 5 3 - 5 3 - 5 3 - 5
  112. 112. Pele Oy New Papermaking Developments
  113. 113. Pele Oy 113 Basic process principle is old Combined forming/pressing or pressing/drying ? Do we need water in forming and coating – dry processes?
  114. 114. Pele Oy 114 Flocculation, retention and drainage  The basic problem of papermaking is that it is difficult to get good formation, drainage and retention at the same time. On the other hand, to avoid flocculation too much water is needed, especially for long fibers. Flocculated: • Bad formation • Low strength • Low opacity • High porosity • Good drainage • Good fiber retention Good formation • High strength • Good opacity • Low porosity • Slow drainage • Low fiber retention Better quality Picture: E.Gruber
  115. 115. Pele Oy Headbox dilution in papermaking  The biggest problem of industrial papermaking is fiber flocculation. Flocculation tendency is the basic reason that there must be 100-1000 times water dilution in the headbox.  The other reason to the high dilution is cross-direction profile control. Final paper is less than 0.1 mm thick and it should have thickness accuracy about ±1%. This is ±0.001 mm or ±1 µm. With a 100-fold dilution this accuracy requirement is already ±0.1 mm which is easier to achieve for a 10 m wide web. 115 Fibers occupy a sphere in the headbox Stiff fibers form flocs with friction forces Flocculation results in bad paper formation
  116. 116. Pele Oy Current headbox technology  The principal construction of current hydraulic headbox technology is quite expensive due to the very large area of highly finished surface.  For operator this kind of headbox is also demanding. Principally there is only one optimum very narrow flow window for papermaker and outside this window the turbulence is too high or too low.  The optimum jet-to-wire speed ratio is different for best formation and best fiber orientation in most cases.  The most demanding flow range might be the filler ply in a multilayer board. 116 Picture: Voith
  117. 117. Pele Oy High consistency forming  The main improvement of papermaking should be reduction of water usage of the internal circulations. Conventional solution to this is high consistency forming (1-3%).  In addition to the flocculation tendency the CD accuracy is demanding in high consistency forming.  It is easy to calculate what would be the slice opening for different headbox consistencies. When basis weight is low slice opening is just some millimeters, which is demanding for CD accuracy. The calculation below is for 100% retention. In practice lower retention increases slice opening. 117 SliceOpening,mm Grammage, gsm 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 0 50 100 150 200 250 300 350 HB cons. 1 % HB cons. 3% HB cons. 2 %
  118. 118. Pele Oy High consistency forming and paper quality  The fibers from high consistency forming are randomly oriented in all directions rather than in the plane of the web making this forming process unsuitable for formation of printing papers.  The random grain orientation is believed to be due to collision during drainage of the densely packed fibers. In addition, the formed web has high bulk, high porosity, grainy formation, increased z- direction strength (out of the plane of the web) and reduced in-plane strength. While this web is suitable for some board grades it is not suitable for thin publication papers.  This old picture on the right shows what is the difference between filtering (normal paper) and thickening (high consistency paper). 118
  119. 119. Pele Oy High consistency forming headbox  There is a very interesting patent idea (WO 2013024205 A1) of Matti Luukkanen on High Consistency (HC) forming (2-5%). This could be very suitable for pulp drying machines and several board grades, especially for the filler ply of three-layer board.  The picture below shows how rotating drum inside a curved chamber produces turbulence, pressure and flow to the water removal gap between a solid apron and a moving wire on a dewatering box. 119 Consistency Total mass % tons/dry ton 0,5 200 1 100 2 50 3 33 4 25 5 20
  120. 120. Pele Oy Foam forming to solve flocculation problems New possibilities with increased headbox consistency by foam forming:  New paper properties by using special long fibers with good formation  High bulk products with good strength by combination with nanofibrillated cellulose for insulation materials, filters and tissue products  High bulk with good z-strength for e.g. middle ply of cartonboard 120 Bulk [cm3/g] Picture: VTT
  121. 121. Pele Oy Pilot foam forming machine at VTT Finland 2013  Foam forming gives possibilities to save water, energy and material in papermaking. 121 Picture: VTT
  122. 122. Pele Oy Microfibrillated cellulose  Microfibrillated cellulose is a potential but still today expensive development for papermaking.  MFC can be made by grinding or refining fibers to small pieces called microfibrils. 122
  123. 123. Pele Oy Principle of Valmet water layering technology  With multilayer headbox it is possible to get separation of fiber layers and prevention of flocculation through the layers by using a water layer between the two fiber layers.  It is possible to put different chemicals and filler between the fiber layers with water layering. One example is cationic starch. 123 Picture: Valmet
  124. 124. Pele Oy Multilayer headbox with water layering technology  Valmet had a presentation in PaperCon2015. The following conclusion is from this presentation: 124
  125. 125. Pele Oy Alternatives for containerboard machines  Board making is developed closer to papermaking and relative speed and production development has been faster than in papermaking. Today there are also gapformers in board machines. 125 Picture: Valmet
  126. 126. Pele Oy Wet end rebuild of testliner machine.  This Valmet example is interesting how to get four layers of conventional two-layer testliner machine by using layering headbox. 126
  127. 127. Pele Oy 127 Multigrade cartonboard machine  There are five headboxes and two shoe presses with totally four felts. Five coating stations allow different kind of products.  First calender has hot roll on top side and second calender on bottom side. It is possible to make symmetrical graphical board. Picture: Valmet
  128. 128. Pele Oy Impingement drying possibilities  High-speed machines require good dryness after press section to get runnability. One possibility to save bulk or add filler content is to use impingement drying in the beginning of dryer section. 128 Picture: Valmet
  129. 129. Pele Oy THANK YOU FOR YOUR ATTENTION 129