Reviewer

• Lithography


  A chemical process that is almost opposite to letterpress which is more of a mechanical process
• Lithography is the most dominant of the printing processes
• Lithography


  Works on the principle that oil and water do not mix
• Lithographic plate


  • Image areas are sensitized to be oleophilic (oil-living)
  • Non-image areas are treated to be ink repelling or oleophobic
• Lithographic printing process


  1. Plate is charged by dampening rollers with dampening solution

  2. Plate is charged by inking rollers

  3. Non-image areas repel ink as they are coated with water
• Lithographic printing process


  • Operates with 3 basic cylinders: plate, blanket, and impression
• Plate cylinder


  Carries the printing plate that has the image to be printed
• Blanket cylinder


  Has a rubber blanket to compensate for unevenness of the substrate
• Impression cylinder


  Provides the necessary pressure to impress the image from blanket to the substrate
• Image transfer in lithography

  1. Image areas accept ink and transfer them to the blanket

  2. Orientation of image becomes unreadable on the blanket

  3. Image is then transferred to the paper between the blanket and impression cylinder
• Offset printing


  Another name for lithography, as the image is transferred from the plate to the substrate through an intermediate rubber blanket
• Types of offset presses

  • Sheet-fed presses
  • Web-fed presses
  • Perfecting presses
• Configurations of multicolor presses

  • Two-color
  • Four-color
  • Five-color
  • Six-color
  • Eight-color
  • Ten-color
• Lithographic plate


  Has a flat surface and is called planographic, with no physical or mechanical separation between image and non-image areas
• Plate cylinder


  • Holds the plate in register
  • Comes into contact with dampening system
  • Comes into contact with inking system
  • Transfers inked image to the blanket
• Dampening system


  Applies a very thin layer of fountain solution (water mixed with chemicals) to the plate
• Fountain solution


  Keeps the non-image areas of the plate desensitized and printing clean
• Separation between printing image area and non-printing area

  • Image areas repel water and accept ink (hydrophobic)
  • Non-image areas accept water and repel ink (hydrophilic)
• Types of dampening systems

  • Non-contact (e.g. spray)
  • Contact (e.g. conventional, continuous)
• Perfecting


  Printing on both sides of a sheet of paper in a single pass through the press
• Inking system


  Applies an accurately measured or metered amount of ink to the plate
• Factors involved in ink distribution

  • Fountain roller
  • Fountain blade
  • Ink keys
  • Ductor roller
  • Ink train
  • Oscillating or vibrator rollers
  • Form rollers
• Offset lithography uses paste ink and rollers for ink distribution
• Offset printing


  Indirect image transfer method where the image is transferred from the plate to the substrate through an intermediate rubber blanket
• Offset lithography produces text and line art that is sharp and crisp with excellent edge definition, and halftones with high resolution screen rulings of 133–300lpi
• Waterless offset


  Eliminates the use of water from the lithographic printing process
• Waterless offset plates


  • Image areas are in recess from the non-image areas
  • Plate has an aluminum base with a thin silicon coating
• Exposure and development of waterless offset plates

  1. Plate is exposed to UV light, breaking the bond between silicon and photopolymer

  2. Plate is developed using a chemical process with tap water and glycol-based solutions
• Waterless offset plates


  • Can hold a dot range from 0.5% to 99.5%
  • Image areas are protected by silicon walls, minimizing dot gain
• Waterless offset plates


  Can produce very high screen frequencies, up to 200-300 lpi for negative working and 400-600 lpi for positive working plates
• Waterless offset printing


  • Requires strict temperature and humidity control in the press room
  • Non-image areas made of silicon can get scratched by poor quality stock or abrasive particles