Screen, relief, intaglio and thermographic printing

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Screen, relief, intaglio and thermographic
printing
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The various types of printing.
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Screen printing

• Screen printing uses a stencilwhich is mounted
  to a screento form images.
• Premedia and prepresssame as other processes.
  Prepress processes customized to capabilities of
  screen-printing process.
• Thick opaque inks
• Images cannot be too small due to the fabric of
  the screen

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Printing plate

• http//www.graphics.tech.uh.edu/student_work/scree
  n_101/index.htm
• o What is looks like
• o Frame
• o Polyester screen (not silk)

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Stencil

• Openings in the stencil are the image. Portions
  of the screen that are covered are the non-image.
• Hand cut stencil of paper, plastic, or other
  material.
• Photographically exposed onto light-sensitive
  emulsion from a positive made with film or by
  using a black-and-white laser printer to print a
  black image on a clear polyester sheet.
• Direct to screenink-jet device sprays the
  non-image area onto an uncoated screen.

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Example of Direct to Screen 1
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Example of Direct to Screen 2
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Printing process

• Screen, mounted to a frame, is attached to a
  printing press (see Screen Printing 101 The
  Process page)
• The screen is brought into contact with the
  substrate
• Ink (paint) is applied to the screen.
• A squeegee pushes the ink through the screen and
  onto the substrate.
• The ink (paint) is dried and then the next color
  applied.
• Products are removed, stacked, wrapped, and
  delivered.

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Uses

• Very short runs
• Odd shaped objects (coffee cups, touch-pads for
  electronic devices)
• Fabrics, T-shirts
• Items that need to withstand extreme weather
  abuse (outdoor billboards, point of purchase
  displays)
• Items needing very thick ink (paint) coating
  (street signs, warning signs)
• Extremely large items (billboards, signs in gas
  station parking lots)
• Electronic items (circuits can literally be
  printed using molten metal instead of
  ink/paint)

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Identifying screen-printed products

• Extremely thick ink layer
• Odd-shaped items (cups, Frisbees, ball caps)
• TextilesT-shirts

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Relief printing

• Relief printing processes have raised image areas
  and sunken non-image areas.
• Inked rollers touch the top of the raised image.
  The non-image does not receive ink because it is
  too far below the surface for the ink rollers to
  touch.
• The raised and inked image is then pressed
  directly onto paper or other substrate. The ink
  transfers (splits) from the raised surface to the
  substrate.
• There are two relief printing processesone uses
  a hard raised plate and the other uses a softer
  raised plate.

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• Letterpress uses a hard relief plate (metal or
  hard polyester). The process is the same as
  students used to print on the Columbian and
  Gutenberg presses at the museum of printing
  history. The process is very seldom used nowadays
  except for fine arts and historical applications.
• Flexography uses a softer relief plate. The
  process is used extensively for the production of
  all sorts of packaging materials from labels to
  food boxes to plastic bags.

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• Premedia and prepresssame as other processes.
  Prepress processes customized to capabilities of
  letterpress or flexography.
• Neither letterpress nor flexography can print
  extremely fine text or halftone dots.
• Flexo plates stretch when theyre mounted to a
  press cylinder. The stretch is around the
  cylinder. So, the prepress process must shorten
  the around-the-cylinder length by an amount
  determined by a special formula. The
  across-the-cylinder dimension does not change.
• Since flexo is often used for packaging, the
  specifications for bar codes and RFID tags must
  be followed carefully.

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• Food containers produced by flexo contain
  Nutrition Facts. The design of this portion of
  a package is specified by law and the designer
  must follow those specifications (typeface, size,
  boldness, and so on).
• Documents to be printed by Flexography need to
  adhere to the specifications published in FIRST
  (Flexographic Image Reproduction Specifications
  and Tolerancesavailable through the bookstore on
  www.flexography.org)

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Plates

• Traditionally, both letterpress and flexography
  began with metal type characters (show type in
  type stick and linotype slugs)
• When letterpress was used, the type itself, or a
  curved metal stereotype made from the type, was
  used to directly print onto the substrate. This
  hard plate-against-hard paper resulted in a
  somewhat broken appearance in type (especially
  headlines), solids, and halftone photos.
• The softer flexo plates compress slightly when
  they print on rough stocks and can press the ink
  deeper into the crevices than can letterpress.
  Thus, flexo images are smoother than images
  printed by letterpress.

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• Traditional flexo plates were made by pressing
  the metal type into heated matrix material.
  Then, heated rubber was melted into the matrix.
  The cooled rubber became the plate.
• Contemporary letterpress and flexographic plates
  can be made
• Photomechanicallyby exposing a pre-sensitive
  photopolymer (explain) plate with a negative made
  from an imagesetter.
• Using platesetters designed to expose relief
  plates.

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Plate Maker
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Printing process

• Contemporary relief plate (letterpress or
  flexographic) wrapped around cylinder of printing
  press page 142 of Kenly)
• Cylinder rotates and is inked
• Letterpress hard plate brought into contact with
  soft inking rollers
• Flexographic soft plate is brought into contact
  with hard anilox roller that contains small
  wells that hold liquid ink.
• Ink is applied to the raised portions of the
  plate.
• Paste-like ink for letterpress
• Liquid aniline ink for flexography

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• The cylinder continues to turn until the
  freshly-inked image touches the substrate being
  fed through the press.
• The ink is pressed onto the substrate.
• The ink is dried.
• Products are removed, stacked, wrapped, and
  delivered. Some flexographically-produced
  products are re-rolled for use in automatic
  packaging machines (labels, plastic wrappers for
  candy, and so one)

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Uses

• Letterpress is seldom used
• Flexography is very commonly used for packaging.

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Identifying relief-printed products

• Letterpress images are broken because the hard
  plate cannot press ink into the crevices of
  paper.
• Flexographic images almost always have a halo
  around the edges caused by the compressing and
  expansion of the soft rubber as it prints the
  substrate.

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Intaglio processes

• Intaglio processes are engravedthat is, they
  have sunken (engraved) image areas and raised
  non-image areas.

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• There are three intaglio printing processes
• Gravure the image is created using a stylus to
  peck cells into a metal cylinder. The cells,
  which can vary in circumference and depth, are
  filled with a liquid ink, the excess ink is
  squeegeed off of the raised non-image area (with
  a doctor blade), and the paper is pressed against
  the cylinder. (Refer to the Intaglio Printing
  Process PDF and/or pg 146 of Kenly.

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• Engraving the image, formed of lines rather than
  wells, is cut into a metal plate by hand,
  duplicated, and then the plates are combined on a
  press (Kipphan Fig 2.5-7 on pg 427).
• Ink rollers press ink into the engraved imageand
  cover the non-image, too.
• The ink is wiped off of the non-image area and
  then a large amount of force is applied to press
  the paper into the engraved image. This results
  in a characteristic raised image on the front
  of the sheet and sunken image on the back of the
  sheet.
• This is a time consuming, difficult, and costly
  process used primarily for the production of
  currency, stamps, and other security items.
• Engraving is also a symbol of statusas in the
  old saying, What are you waiting for? An
  engraved invitation? Thus, engraved stationery
  and business cards are associated with wealth or
  rank within an organization.

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• Pad printing What is Pad Printing? See senior
  project website at http//graphics.tech.uh.edu/st
  udent_work/pad_print_php/index.php.)
• An engraved plate (called a cliché) is inked, the
  ink is squeegeed off of the non-image area with a
  doctor blade, and then a transfer pad, known as a
  tampon, removes the ink from the cliché.
• Finally, the tampon moves into position to print
  the objectusually an odd-shaped object (like a
  pen, bottle cap, yo-yo) or a cylindrical object
  like a drink bottle.

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How pad printing works
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Prepress and platemaking

• Prepress and platemaking vary considerably from
  one intaglio process to another and differ from
  lithography and screen-printing.
• Gravure prepress uses digital illustration,
  photographic, and page layout files like
  lithography.
• Completed forms are sent to a RIP that converts
  the entire image, not just photographs, to dots.
  Every imageincluding solids, text, and
  illustrations printed by gravure is composed of
  dots (pass around samples of gravure printing and
  a loupe).
• A HelioKlischograph follows the instructions
  provided by the RIP and engraves wells of varying
  circumference and depth into a copper cylinder.

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A HelioKlischograph
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• Engraving Engraving plates for security purposes
  are generally cut by hand by a master engraver
  and then duplicated for multiple-up printing.
  This is a fundamental part of the security of
  money and other negotiables because engraved
  plates are hard to counterfeit and few people
  have the skill and training to engrave.
• Engraving plates can be cut by laser for more
  mundane purposes such as business cards,
  wedding invitations, and classy stationery.
• Engraving plates can also be prepared
  photographically by exposing an image to a light
  sensitive coating. The image area is washed away
  and then an etch is used to cut into the metal
  plate.

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• Pad printing The cliché is cut by laser or
  through the use of a photographic/etching process
  (There are movies of the process available on the
  What Is Pad Printing website.

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Uses

• Gravurevery long runs like magazines, catalogs,
  gift-wrapping paper, cigarette wrappers.
• Engravingsecurity documents and high-status
  printing
• Pad Printingused in-line to decorate objects
  as they are being manufactured

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Identifying intaglio-printed products

• Gravure every part of the imageincluding text
  and illustrationsis composed of dots.
• Engraving image on the front of the page is
  raised and is sunken on the back.
• Pad printing the image prints on or around an
  object that really couldnt be printed any other
  way.

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Themography

• Imitation engraving
• Since the raised image on an engraved business
  card or letterhead is a mark or status, those who
  cant afford genuine engraving fake it using
  thermography.
• Ink is printed on the sheet using litho and then
  a powder is dusted on the wet ink.
• The powder-dusted sheet passes through a heater
  than causes the powder to swell.
• The result is a raised image on the frontbut a
  flat image on the back. You can tell fake
  engraving by the raised image without a sunken
  back.