Notes > Paper & Printing

Paper & Printing
By Linda M. Perry

Papermaking Machine Fourdrinier section Treated "stock" or pulp: 1% pulp, 99% water. Forced through tiny straining slots onto woven wire mesh. Wire mesh is moving, endless screen, constantly vibrating. Interweaves, mats fibers. Fibers tend to flow lengthwise. Directional tendency is grain.

• Dandy roll applies first surface pressure to top of paper. Used for watermarking.
  •  Watermark: A distinctive design; usually imprint of manufacturer’s name.
    • Becomes an integral part of paper.
    • Design formed with wire and attached to dandy roll, which impresses it into the wet paper.

• From the presses, the paper moves unsupported to the drying section.
• Last step is calendering
• Calendering--Stack of 5 to 9 rollers incorporated into the dry end.
  • For ironing and smoothing.
  • Adds to gloss of finish.
  • All paper known as machine-finished (wood paper)

 Out of machine

• Supercalendering
  • Extra step outside papermaking machine
  • Used for magazines and booklets.
  • Finished by stack of calender rolls.
    
    
• Coated stock
  • (art paper)
  • Smooth, shiny finish.
  • Web passes through vat with coating mixture.
    • Coating emulsion adheres to paper.
    • White china clay mixed with other agents.
  • Gloss produced by supercalendering.
  • Retains more ink on surface.
    • More brilliant, denser color, so best for color pictures.

 Definitions

• Ream—500 sheets
• Basis size—Standard size of given paper grade.
  • The size in which paper is normally and most conveniently produced.
  • Book stock is 25” x 80” (63.5 cm x 96.52 cm).
• Basis weight—Weight of ream of basis size.
  • 500 sheets of 25" x 38" at 70 lbs. = basis 70
    • (63.5 cm x 96.52 cm at 31.75k, or 105.35 grams per square meter [gsm])
      • Individual sheet is 70-lb. stock, or substance 70
• Caliper thickness—Heavy stock, measured with micrometer.
  

 
Major Classifications:

• Book stock—25" x 38"  (63.5 cm x 96.52 cm)
  • From 45 to 120 lb. (67.7 to 54.43 k)
• Writing stock—17" x 22"
  • Bond papers from 9 to 24 lb. (60 to 90 gsm; 80 gsm close to 20 lb bond)
  • Ledger papers from 24 to 40 lb. (90 to 150 gsm)
  • Manifold (onion skin) 9 lb.
• Cover stock—20" x 26"
  • 50 and 80 lb.
  • Heavier is measured in caliper thickness.
    

International conversions for equivalent weights at http://www.paper-paper.com/weight.html.


Singapore conventions:

• Thin paper, 70-110 gm (writing stock)
• Thick paper, 120-160 gm (writing to cover stock)
• Super thick, 170-260 gm (cover to caliper thickness)
• A5 128 gsm art paper (book stock, coated, glossy)
• A5 157 gsm art paper (cover stock, coated, glossy)
• A4 and A3, 128 gsm art paper (book stock, coated, glossy)
• A4 and A3, 157 gsm art paper (cover stock, coated, glossy)

Your Magazine

• Choose a weight that works well for self-cover magazine
  • Super-calendered is good
  • Coated more expensive
  • Weight between 120-160 gms
  • Basis size for signature

Offset Printing

• Offset printing, or offset lithography
  • Photographic lithography
  • Difference between image & nonimage areas are maintained chemically
  • Based on principle: grease (oil) & water don’t mix
    • Printing area is grease-, ink-receptive
    • Nonprinting areas are water-receptive, ink-repellant
    • Plates are kept moistened with rollers
      • Nonprinting areas moistened, repelling ink
      • Ink adheres to image areas
• Composite negatives (called flats) printed on photosensitive metal plates. (positives)
  • Being replaced by computer-to-plate techniques
  • One plate for each color
  • Wraps around platen on press
• Plate "offsets" image to a rubber blanket (negative) which puts the ink on paper.
  • Image goes from positive (on plate)
  • to negative (on blanket)
  • to positive (on paper) again.
• Inexpensive.
• High quality, clearer impression.
• Uses less ink than other methods
  • Decreases drying time and
  • Minimizes smudging.