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Module 2: Printing Processes. Instructor : Doughlas Remy. Topics Covered in This Module. The U.S. printing industry Definition of printing Major printing processes (overview) Where’s the ink? Where’s the paper? Early relief printing

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Module 2: Printing Processes

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Module 2 printing processes

Module 2:

Printing Processes

Instructor: Doughlas Remy


Module 2 printing processes

Topics Covered in This Module

  • The U.S. printing industry

  • Definition of printing

  • Major printing processes (overview)

  • Where’s the ink? Where’s the paper?

  • Early relief printing

  • Text and artwork before and after the invention of photography

  • Relief (Flexography, Letterpress)

  • Planographic printing (offset litho)

  • Gravure (Intaglio)

  • Screen printing (silkscreen, stencil)

  • Digital (electronic) printing

  • Spot colors and process colors

  • Continuous tone vs. halftone

  • Quiz

  • Answer Forms for Printing

(major printing processes)


Module 2 printing processes

What you should know about the U.S. printing industry

  • It has a very low profile.

  • It is composed mainly of small businesses.

  • It has revenues of about $1 billion annually.

  • It is the nation’s largest employer.(It employs nearly 1 million people, or 220,000 more than the auto industry.)

  • There are nearly 100,000 printing establishments in the U.S.

  • Pre-press is considered to be a part of the printing industry.

Source: http://www.wmrc.uiuc.edu/info/library_docs/manuals/printing/domestic.htm


Module 2 printing processes

Definition

Printingis basically the transfer of images from a source (usually printing plates) to a target surface (usually paper) through the application of a medium (usually ink).

Sources

Targets

Media

most common

Plates (e.g., aluminum, polymer, rubber)

Type forms (used in letterpress)

Templates (used in screen printing)

Blocks (made of wood, metal, lino, plastic, stone)

Jets (used in inkjet printing)

Inks

Toners

Dyes

Paints

Paper

Fabric

Metal

Plastic


Module 2 printing processes

Major Printing Processes


Module 2 printing processes

Major Printing Processes

  • Relief(primarily flexography, which evolved from letterpress)

  • Planographic (offset lithography)

  • Gravure (aka Intaglio, Photogravure, Rotogravure)

  • Screen (aka silkscreen, stencil, serigraphy)

  • Digital (aka electronic)


Module 2 printing processes

Major Printing Processes

  • Relief(primarily flexography, which evolved from letterpress)

  • Planographic (offset lithography)

  • Gravure (aka Intaglio, Photogravure, Rotogravure)

  • Screen (aka silkscreen, stencil, serigraphy)

  • Digital

In a category by itself because

it is for low-volume printing; and

its technology is so different from the others.


Module 2 printing processes

Major Printing Processes

  • Relief(primarily flexography, which evolved from letterpress)

  • Planographic (offset lithography)

  • Gravure (aka Intaglio, Photogravure, Rotogravure)

  • Screen (aka silkscreen, stencil, serigraphy)

  • Digital

Now a major printing process and growing exponentially. Its technology is very different from that of the first three on this list.


Module 2 printing processes

Major Printing Processes

  • Relief(primarily flexography, which evolved from letterpress)

  • Planographic (offset lithography)

  • Gravure (aka Intaglio, Photogravure, Rotogravure)

  • Screen (aka silkscreen, stencil, serigraphy)

  • Digital

We will focus on the first three for now.


Module 2 printing processes

Major Printing Processes

  • Relief(primarily flexography, which evolved from letterpress)

  • Planographic (offset lithography)

  • Gravure (aka Intaglio, Photogravure, Rotogravure)


Module 2 printing processes

Major Printing Processes:

Where’s the ink?

Where’s the paper?


Module 2 printing processes

Where’s the ink?

The first three—relief, planographic, and gravure—are easier to understand if we compare the location of the ink in these cross-sections of the printing plates used for each:

Relief

Ink is on a raised surface.

Planographic

Ink is on a flat surface.

Ink is in wells or reservoirs.

Gravure

  • Relief(primarily flexography, which evolved from letterpress)

  • Planographic (offset lithography)

  • Gravure (aka Intaglio, Photogravure, Rotogravure)


Module 2 printing processes

Where’s the paper? (1)

1. The paper may be attached to a flat surface, against which a type form or a printing plate is pressed.

lever attached to screw

NoteThis way of placing the paper was a feature of the earliest printing methods and is rarely used today. (It’s very slow.)

type form

Wooden hand press (aka screw press), a reproduction of Gutenberg’s press.


Module 2 printing processes

Where’s the paper? (1)

A layer of oil-based ink is applied here, and then a roller arm (not shown here) pivots up to collect the ink and then rolls it onto the “chase,” which contains the relief image.

Lever Press

This was a later development, using the same principle of attaching the paper to a flat surface.

The “chase” (relief image)

Paper attached here.

Note that there is no screw.

Message from Ed Evetts at CCS Printing in Bellevue:

..the disc is where the operator places the ink for the press. The ink-carrier roller-arm (not apparent in the illustration) rotates up and rolls across the flat part of the disc, picking up a layer of ink on the roller. Then, on the down-stroke, the ink-carrier roller-arm rotates down and applies a layer of ink to the raised-surface of the copy in the chase.which Doughlas refers to as the "Type form" in the illustration.

FYI: As the ink-carrier roller-arm rotates up to get more ink, the sheet attached to the paper-bed rotates to contact the chase and get "printed". When the ink-carrier roller-arm rotates down to apply more ink to the chase, the paper-bed rotates away from the chase so that the operator can pull off the printed sheet and insert a fresh sheet for printing .


Module 2 printing processes

Where’s the paper? (2)

Cylinder Letterpress

2. The paper may be attached to a cylinder, which then rotates as an inked type form passes beneath it.

Paper

Type

form

NoteThis way of placing the paper, like the previous one, was time-consuming and was abandoned in favor of the last two methods (next slides).

Ink

Rollers

Impression

Cylinder

Press bed


Module 2 printing processes

Where’s the paper? (3)

3. Sheets of paper pass between two flexible printing plates (attached to cylinders) that are carrying the image.

NoteThis technology did not become possible until a means could be found for making the printing plate thin and flexible enough to attach to a cylinder.

Note The process of printing on both sides of the paper (recto and verso) is called “duplexing.”


Module 2 printing processes

Where’s the paper? (4)

4. A continuous “web” of paper passes between two flexible printing plates (attached to cylinders) that are carrying the image.


Module 2 printing processes

Where’s the paper? (4)

Why “Web”?

The American Heritage Dictionary has 11 definitions of “web.”

# 1: “A textile fabric, especially one being woven on a loom or in the process of being removed from it.”

# 11: “A continuous roll of paper, as newsprint, in the process of manufacture in a paper machine or as it comes from the mill.


Module 2 printing processes

Major Printing Processes

  • Relief(primarily flexography, which evolved from letterpress)

  • Planographic (offset lithography)

  • Gravure (aka Intaglio, Photogravure, Rotogravure)

  • Screen (aka silkscreen, stencil, serigraphy)

  • Digital


Module 2 printing processes

Major Printing Processes:

Early Relief Printing


Module 2 printing processes

Modern signet rings

Relief: Letterpress – Historical overview

Signet rings were first used in ancient Babylonia.

a wax seal

No further progress was made in the Western world until the Gutenberg era (15th century).


Module 2 printing processes

Relief: Letterpress – Early Chinese printing

  • Meanwhile, the Chinese were printing from wood blocks as early as the 2nd century A.D. This was made possible by their invention of paper in A.D. 105.

    • Papyrus had been too fragile.

    • Vellum* was too expensive.

*Vellum is a thin tissue taken from inside the hides of newly skinned animals.


Module 2 printing processes

Relief: Letterpress – Early Chinese printing

The Chinese developed movable type around the tenth century A.D., and were even doing two-color printing with it. By the 13th and 14th centuries, they had three-color and four-color printing.

At first, they used clay type, but later developed metal (copper) type.

Movable type was not as practical for the Chinese language as it was for European languages, because it required between 2000 and 40,000 separate characters.


Module 2 printing processes

Relief: Letterpress – Early Western printing

Earliest Western print technology grew up in the Rhine River Valley in the mid-fifteenth century and was probably not influenced by earlier developments in the Far East.


Module 2 printing processes

Relief: Letterpress – Early Western printing

The first printing presses in the West were screw-type presses designed primarily to bring pressure on the printing form, which was placed face up in a flat bed.

Click here for photos of screw-type presses from the Museum of Printing Presses.


Module 2 printing processes

Relief: Letterpress – Early Western printing

Consider this:

Letterpress printing from raised metal type was the primary means of mass communication for over 400 years.


Module 2 printing processes

Relief: Letterpress—Later Developments

  • Later developments in the West:

  • In the 17th century, springs were added to the press to aid in lifting the platen rapidly.

  • Around 1800, iron began to be used in the construction of presses, and levers were substituted for the screws that brought the platen down onto the form.

  • The process was still slow (300 impressions per hour), but much larger forms could be used, so multiple pages could be printed simultaneously.

“Old Reliable,” platen letterpress, 19th century.


Module 2 printing processes

Relief: Letterpress—Later Developments

Cylinderswere not used in letterpress until the 19th century.

Cylinder Letterpress

Paper

The ink rollers apply ink only to the raised areas. Then the ink is transferred to the paper, which is on the impression cylinder.

Type

form

Ink

Rollers

Impression

Cylinder

Letterpress images can be sharp and crisp.

However, the pressure of the plate or cylinder surface on the paper may also spread the ink slightly.

Press bed


Module 2 printing processes

Relief: Letterpress—Later Developments


Module 2 printing processes

Relief: Letterpress

A cylinder letterpress


Module 2 printing processes

Major Printing Processes:

Relief Printing: Text and Artwork Before and After the Invention of Photography


Module 2 printing processes

Relief: Letterpress—Text and Artwork

  • Before the invention of photography and the development of modern printing techniques, the raised image in relief printing could only be produced in two ways:

  • For text: Metal type

  • For artwork: Engravingor etching. These techniques leave a flat, raised surface to which the ink is applied.

Engraving is simply cutting away the areas that will not receive the ink.

Etchinginvolves making incisions on a plate that has been coated with an acid-resistant material, and then applying acid to the entire surface.


Module 2 printing processes

Relief: Letterpress—Text and Artwork

Note that artwork had to be in the form of either engravings or etchings if it was to be printed.

In both techniques, the area that will not receive the ink is removed—either by direct cutting or by application of acid.

Wood engraving, 1830: View of Rochester with a Section of the Aqueduct

Etching: The Soldier and his Wife, by Daniel Hopfer (ca 1470-1536)


Module 2 printing processes

Relief: Letterpress—Text and Artwork

Electrotyping(first used in 1838) was a technique for making duplicate plates from original relief plates.

To create an electrotype duplicate:

Make a mold of the original plate, using any one of various materials (copper, lead, zinc, etc.)

Place the mold in an electrolytic solution (e.g., copper sulfate and sulphuric acid).

Place a sheet of the same or a different metal in the solution, parallel to the mold.

Pass an electrical current through the solution. The mold acts as the cathode and the other metal sheet as an anode. Metal passes from the anode to adhere to the cathode (the mold).

Separate the newly-deposited layer of metal from the mold.

mold

metal sheet

tank containing electrolytic solution


Module 2 printing processes

Relief Printing—Text and Artwork After the Invention of Photography

After the invention of photography, it became possible to dispense with lead fonts and type forms altogether. Photographic transparencies could be used to make plates, and this led to the demise of letterpress.

To understand platemaking from photographic transparencies, we must first understand what a halftone screen is.


Module 2 printing processes

Relief Printing—Text and Artwork After the Invention of Photography

  • Halftone screens:

  • Physical screens (either glass plates or contact sheets), consisting of grids through which light may pass.

  • Placed between a photographic transparency and a photosensitive plate.

  • Light passes differentially through the transparency and then through the halftone screen to the photosensitive plate.

  • The light reacts with the chemicals on the plate to produce areas that are receptive to ink.

  • These ink-receptive areas, if examined under a magnifying glass, will appear as grids of dots.

Glass plates

Contact Sheets


Module 2 printing processes

Relief Printing—Text and Artwork After the Invention of Photography


Module 2 printing processes

Relief Printing—Text and Artwork After the Invention of Photography

Two kinds of halftone screens:

Older screens consist oftwo thin glass plateswith scribed parallel lines running across them; these are cemented together so the lines form right angles. The thickness of thescribingvaries depending on the screen frequency, but the lines and the open spaces are always of equal width. These are now uncommon. Instead, most printersuse contact sheets made of film. Unlike glass screens, the dots on these screens are not completely open. Each dot is clear in the middle with increasing opacity toward the edges.

Glass plates

Contact Sheets


Module 2 printing processes

Relief Printing—Platemaking

Light source

After the invention of photography, relief images could be produced using film positives (or negatives), halftone screens, and photopolymer plates. These plates are made of pre-coated photosensitive plastics, from which unexposed, non-image areas are chemically dissolved.

Film positive

Halftone screen

Printed halftone image on coated light-sensitive plate. More intense light burns larger dots.


Module 2 printing processes

Relief Printing—Platemaking

Darker areas are recessed.

Ink will be applied to the lighter areas, which are raised.

the transparency

the halftone screen

the plate

Keep in mind that the image on this plate is composed of hundreds of thousands of dots.

Also note that the plate would not actually look like this. This image only illustrates the difference between the variable sizes of the dots (0-100%), which translate into amount of ink applied.


Module 2 printing processes

Relief Printing—The Demise of Letterpress

Letterpress has been almost entirely replaced by other printing technologies, especially flexography and lithography (more about these shortly), but it still has a limited “niche” appeal for printing wedding invitations, menus, business cards, etc. It has a very elegant “embossed” look and is very “tactile.”

Lead typesetting (hot type) is mostly an anachronism. This invitation was printed using another kind of relief printing—flexography—which uses photopolymer plates.


Module 2 printing processes

Major Printing Processes:

Relief Printing: Flexography

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Gravure (aka, intaglio, rotogravure, photogravure)

  • Screen (aka, stencil, silk screening, screen printing, serigraphy)

  • Digital (aka, electronic)


Module 2 printing processes

Flexography

  • Like letterpress, flexography is a form of relief printing.

  • Flexography uses:

  • plates of photopolymer or flexible rubber.

  • thin, fast-drying, water-based inks.

  • high-speed web presses.

  • Flexography is widely used for printing gift wrap and packaging materials because of its brilliant colors.

Wine bottle labels printed by Richmark Label, Seattle, WA


Module 2 printing processes

44

Flexography

  • Flexography is also used for the following:

  • Corrugated containers

  • Folding cartons

  • Paper sacks

  • Plastic bags

  • Milk cartons

  • Disposable cups

  • Labels

  • Adhesive tapes

  • Envelopes

  • Newspapers

  • Food and candy wrappers

Other commercial printing by Richmark Label, Seattle, WA


Module 2 printing processes

Flexography

For more information about flexography, visit the following sites:

http://desktoppub.about.com/od/flexography/

http://www.pneac.org/printprocesses/flexography/index.cfm


Module 2 printing processes

Major Printing Processes:

Planographic (Offset Litho)

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Gravure (aka, intaglio, rotogravure, photogravure)

  • Screen (aka, stencil, silk screening, screen printing, serigraphy)

  • Digital (aka, electronic)


Module 2 printing processes

Haven’t I seen “litho-” in other words?

Planographic (offset lithography)

  • By far the most important and versatile printing process today.

  • Developed at the end of the 18th century by Aloys Senefelder.

  • The first chemical printing process.

  • Most newspapers are printed on offset presses.

The prefix “litho-,” from the Greek lithos, means “stone.”

The lithosphere is the solid part of the earth, as distinguished from the hydrosphere and the atmosphere.

The “Paleolithic” era is the era of ancient rocks.

  • Five major printing processes:

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Intaglio (gravure)

  • Screen (stencil, silkscreen)

  • Digital


Module 2 printing processes

Planographic (offset lithography)

But…

Wet limestone repels oil-based ink.

An image drawn with a grease pencil repels water and attracts ink.

  • Five major printing processes:

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Intaglio (gravure)

  • Screen (stencil, silkscreen)

  • Digital


Module 2 printing processes

Planographic (offset lithography)

To print the image on the paper, simply press the paper onto the stone.

Printed image

Sheet of paper

Limestone with inked image + paper

  • Five major printing processes:

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Intaglio (gravure)

  • Screen (stencil, silkscreen)

  • Digital


Module 2 printing processes

Planographic (offset lithography)

Modern litho presses don’t use limestone.

They use thin aluminum plates that carry both the image areas and the non-image areas. (Polyester plates are used for some jobs that involve line copy or that require short runs only.)

The image areas are not raised. They are chemically receptive to oil-based inks, whereas the non-image areas are not receptive to the inks.

The plates, attached to cylinders, are first exposed to water, and then to ink. The image is then transferred to a rubber blanket that is on a second cylinder.

Printed image

  • Five major printing processes:

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Intaglio (gravure)

  • Screen (stencil, silkscreen)

  • Digital


Module 2 printing processes

Planographic (offset lithography)

This transfer of the image from the printing plate to the “blanket” explains the term “offset.”

*

* Inks are now soy-based, not oil-based.


Module 2 printing processes

Planographic (offset lithography)

Most offset presses are web-fed. These web-fed presses print at speeds up to four times faster than sheet-fed presses—up to 3000 feet per minute, or 100,000 impressions per hour.

They are widely used for printing magazines, newspapers, catalogs, and books.


Module 2 printing processes

Planographic (offset lithography)

A modern offset press, made by Heidelberg


Module 2 printing processes

Dry Offset—A Hybrid Process

  • Dry offset is a hybrid printing technology:

  • Like other offset printing, it uses a rubber blanket to carry the image from the printing plate to the printing surface.

  • Like relief printing, however, it has an image area raised above the surface of the plate.

  • Dry offset is a type of relief rather than planographic printing.

Dry offset is mostly used for printing on containers.

http://www.imageinks.ca/support/uvcupinktec1.htm


Module 2 printing processes

Major Printing Processes:

Gravure

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Gravure (aka, intaglio, rotogravure, photogravure)

  • Screen (aka, stencil, silk screening, screen printing, serigraphy)

  • Digital (aka, electronic)


Module 2 printing processes

Gravure (aka, intaglio, rotogravure)

Recessed image areas are etched into a metal plate to form reservoirs or wells—up to 22,500 per square inch—to receive ink.

The size and the depth of the wells control the amount of ink and the density of tone to be transferred to the paper.

  • Five major printing processes:

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Gravure (intaglio)

  • Screen (stencil, silkscreen)

  • Digital

Link: http://www.era.eu.org


Module 2 printing processes

Gravure (aka, intaglio, rotogravure)

  • Two methods

  • Acid etching (traditional)(aka, “chemical gravure”)

    • The gravure process starts with a positive photographic transparency of the “copy” (the page or image to be printed). The halftone screen is placed under the transparency.

    • Carbon tissue coated with light-sensitive gelatin is placed between the halftone screen and the printing surface, which may be a copper-coated plate or cylinder.

    • The gelatin hardens onto the printing surface according to the amount of light that passes through the transparency. (More light = more hardened gelatin)

    • The unhardened areas are washed away and etched with acid.

Positive photographic transparency

Halftone screen

Carbon tissue coated with light-sensitive gelatin

copper-coated plate or cylinder

The inked areas correspond to the areas where the gelatin was not hardened by the greater amount of light passing through the transparency.


Module 2 printing processes

Gravure (aka, intaglio, rotogravure)

  • Two methods

  • Electronic etching (aka, “digital gravure”)

    • No film or chemicals are involved.

    • Digital signals drive engraving heads.

Method 1—acid etching—was developed around 1880 and peaked a century later, when it began to be replaced by method 2, electronic etching.

Electronic etching has now replaced most acid etching in Europe and the USA.


Module 2 printing processes

Gravure (aka, intaglio, rotogravure)

most expensive of all the processes

  • Disadvantages:

  • Cost of presses and components.

    • $1 million for a gravure press vs. $100,000 for a lithographic press.

    • $5000 for a single gravure cylinder vs. $15 for a lithographic plate.

  • Advantages:

  • The gravure cylinder has a long service life and will yield a very large number of impressions without degradation.

  • Speed: An 8-unit press can print almost 10 million four-color A-4 pages per hour. Today’s rotogravure presses can run at 15 meters per second, with paper reel widths up to 4.32 meters wide.


Module 2 printing processes

Gravure (aka, intaglio, rotogravure)

A modern high-speed rotogravure printing machine made by Worldly Industrial Co., Ltd.


Module 2 printing processes

Gravure (aka, intaglio, rotogravure)

  • Gravure offers the best image quality of any printing process. It can also maintain this quality over a very long print run.

  • Therefore, gravure is considered idealfor the following types of printing:

  • Paper currency (banknotes)

  • Postage stamps

  • High-end magazines (Vogue)

  • Mail-order catalogs*

  • Art books (“coffee-table” books)

  • Wallpaper and laminates*

*high-volume printing


Module 2 printing processes

Major Printing Processes:

Screen Printing

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Gravure (aka, intaglio, rotogravure, photogravure)

  • Screen (aka, stencil, silk screening, screen printing, serigraphy)

  • Digital (aka, electronic)


Module 2 printing processes

Screen Printing

The stencil is composed of a screen of silk or other fine mesh. (e.g., nylon, dacron, stainless steel).

  • Process:

  • Areas that are not to receive ink are blocked on the screen by application of some impermeable substance:

    • e.g., adhesive film that has been cut by hand or prepared photographically.

    • e.g., a brush-on coating

  • A squeegee is used to press ink through the screen onto the printing surface.

  • The image is usually built up by using a number of screens with different stencils, each one used to print a separate color.


Module 2 printing processes

Screen Printing

  • Advantages:

  • Suitable for printing on virtually any surface or any shape or size.

  • High opacity and brilliance of color.

  • Inexpensive apparatus

  • Disadvantages:

  • Slow production speeds

  • Reproduction quality not high (but doesn’t need to be…)

  • Uses:

  • Fine Art

  • T-shirts

  • Logos and lettering on vans

“Marilyn Monroe,” by Andy Warhol


Module 2 printing processes

Major Printing Processes:

Digital (Electronic)

  • Relief (letterpress and flexography)

  • Planographic (offset-lithography)

  • Gravure (aka, intaglio, rotogravure, photogravure)

  • Screen (aka, stencil, silk screening, screen printing, serigraphy)

  • Digital (aka, electronic)


Module 2 printing processes

Digital

  • Digital printing is both fast and cost-efficient because the following processes, associated with older printing technologies, are eliminated:

  • Film processing

  • Stripping*

  • Platemaking**

  • *Stripping: Manual assembly and positioning of the image components.

  • **Some of the digital printing processes use plates, but there is no “platemaking” component of the process per se.

  • Digital printing, as the name suggests, produces images from digital data. No film is involved in the process.

  • The term “digital printing” covers almost any type of electronic printing, including the following:

  • Laser (aka, electrostatic, Xerography)

  • Inkjet

  • Dye-sublimation

  • Thermal wax transfer

  • Dot matrix


Module 2 printing processes

Digital Printing

  • Used mainly in offices and for transactional printing of bills, bank documents, etc., because it can handle variable data and images very easily. Can work off database data.

  • The large digital printers used in printing companies are simply larger versions of the inkjet printers used in offices. E.g., the Hewlett-Packard indigo. Prints up to 1000 copies at 2000 sheets/hr. After that it is more cost-effective to go to offset, which prints up to 11,000 sheets/hr.

  • Ideal for “print on demand” because it does not involve film processing, stripping, or platemaking.

  • The digital press or printer combines and allocates CMYK (still as halftones) by following the digital encoding in the graphic file.

  • Uses CMYK inks or toners for color; most digital printers and presses do not print spot colors. (Offers no cost advantage for color monochrome or duotone printing.)

*Where the color of a logo is critical (e.g., Coca-Cola), the logo owner may insist on a spot color, in which case digital printing would not be the best option.


Module 2 printing processes

Types of Digital Printing (Reference)


Module 2 printing processes

Digital Printing—Electrostatic (xerography)

For Reference

  • Electrostatic printers use positively-charged toner particles that are attracted to paper which in turn is negatively charged.

  • The electrostatic process uses a conductive metal (usually aluminum) plate coated with a photoconductive layer of any one of several substances (selenium, silicon, or germanium) that are poor conductors of electricity except when struck by light. When light energy is absorbed (differentially) by their electrons, an electrical current can flow when voltage is applied, and the layer becomes electrostatically charged.

  • The variation in the amount of charge on the coated metal plate establishes an electrostatic pattern of the image.

  • The image is rendered visible by application of toner, a powder that carries an opposite charge to that of the plate.

  • The oppositely charged toner is then transferred to the paper surface and fused there by exposure to solvent vapors or heat.

  • This process takes about five seconds, and the photoconductive insulating layer can be used many thousands of times before being replaced.


Module 2 printing processes

Exercises:

A. Match each of the following printing jobs to a suitable process.

Process

____

____

____

____

____

____

____

____

____

____

____

____

____

1.A mail-order catalog that will be distributed to about 20 million customers nationwide

2.A newspaper

3.3000 milk cartons

4.Bank statements sent to individual customers

5.100 copies of a company report

6.A company logo for printing on the doors of a utility vehicle

7.A “coffee-table” art book containing high-quality photos of artwork by French Impressionist painters

8.Labels for jam jars

9.The glossy cover for a retail catalog that will be sent to thousands of customers. The customers’ mailing addresses will be printed on the cover.

10.An image on a t-shirt.

11.A postage stamp

A college catalog

An embossed invitation

Letterpress

Offset litho

Gravure

Silkscreen

Digital


Module 2 printing processes

Exercises:

B. Complete each sentence with a term from the list on the right.

Process

“Intaglio” is another name for ____.

Offset lithography is an example of ____.

The oldest printing process is ____.

Dot matrix is a kind of ____.

Your worst choice for printing company logos where precise color is critical is ____.

The signet ring was used as a early means of ____.

____ has a very elegant “embossed” look and is used for printing wedding invitations and menus.

____ uses tiny wells to hold the ink.

____ is the slowest printing process.

____ uses a rubber blanket to transfer the image to the paper.

____ uses etching to make the printing plates.

____ is the most expensive printing process.

____ is another name for laser printing

____ uses the simplest apparatus.

letterpress

planographic printing

gravure

xerography

stencil

relief printing

web offset

digital printing


Module 2 printing processes

Spot Colors and Process Colors


Module 2 printing processes

Spot Colors and Process Colors

There are thousands of spot colors. They are simply colored inks that are used to produce a printed image without any gradations of hue.

There are only four process colors*: cyan, magenta, yellow, and black (CMYK). They are used to print halftone images with many gradations of hue.

Simulation of a “greyscale” image printed with black ink.

Simulation of the same “greyscale” image printed with green ink (a spot color).

Simulation of 4-color (process) print output


Module 2 printing processes

Spot Colors and Process Colors

  • In the U.S., the major supplier of spot colors is Pantone, which produces the PMS (Pantone Matching System) colors.

  • Other color systems:

  • Focoltone

  • Toyo Inks

  • TruMatch

  • Munsell

Color swatch books


Module 2 printing processes

Spot Colors and Process Colors

Three spot colors are used in this graphic:

You can create the illusion of more colors by using shades* of spot colors.

  • Black

  • Green

  • Purple

* Also known as “screens,” or “tints.”


Module 2 printing processes

Spot Colors and Process Colors

Atintis created by using percentages of full color. 10% is very light, whereas 80% appears more fully saturated*.

*In reality, the ink has only one “strength,” but the halftone dots at 10% are smaller than at 90%, allowing more of the background color to appear around them, creating the illusion of a lighter tint.

10%

80%

Variable


Module 2 printing processes

Spot Colors and Process Colors

If your job is to be printed by a non-digital process (e.g., offset, flexography, you can select your spot color(s) from a Pantone swatch book.

The colors are printed on both coated and uncoated paper, because your job will be printed on one or the other of these. So make sure you’ve chosen the right one. Here, the “U” after the PMS number indicates “uncoated.”


Module 2 printing processes

Spot Colors and Process Colors

Although you can initially choose your color from the monitor (using software that features it), this is not advisable because of gamut* issues.

After you have chosen your color from the swatch book, then select the same color from your software PMS color list. You will use this color while you are working on your project.

*Gamut: The range of colors that a device or a medium can display. The printer’s gamut will always be more restricted than a monitor’s.


Module 2 printing processes

Spot Colors and Process Colors

When you print a “proof” to your own printer:

You will at some point want to print a “proof”* of your job to your own printer. Once again, remember that the printer is not using spot colors but CMYK, so don’t expect your “proof” to look like the final printed version, which will have been done with spot colors.

Inkjet proof

Final print

* I.e., from your personal or office printer. This is not the same as the proof (“matchprint” or “pressmatch”) that the press will send you for approval.


Module 2 printing processes

Spot Colors and Process Colors

If you want to show a customer a proof from your own printer, a laser printer rather than an inkjet one is recommended. Also, you may use a different kind of Pantone swatch book, called a color specifier, which lets you tear out chips of the PMS colors and place them on your color proof for the customer to see.

Inkjet proof

Final print


Module 2 printing processes

Spot Colors and Process Colors

Process colors

In the 4/c process, four colors are mixed together in various percentages to create thousands of colors. When you send your service bureau a Photoshop file using CMYK mode, the service bureau can separate out the color channels to create the “positives”, which might look like the four lower ones shown here.

Note The film positives shown here are colored for explanatory purposes only. As their only purpose is to let light through differentially, they would all look more or less like the one in the lower right corner.


Module 2 printing processes

Spot Colors and Process Colors

If a part of your graphic is monochrome, you may want to use the Pantone swatches to identify the desired color even if that color is going to be produced as a process color.

The swatches will give you the CMYK values, which you can then key in to the fields next to the color sliders in Photoshop.

Note: The top portion of this ad would have to be printed in 4/c.

All printed in CMYK, but the color for the lower section is selected from a color library. (The CMYK values are keyed in.)

The other option for the lower section is to print it using a spot color—a good choice if there is a company logo (exact color critical).

(This section in a single color)


Module 2 printing processes

Spot Colors and Process Colors

If your graphic uses three or more spot colors, it’s probably more cost-effective to have the printing done in 4/c process.


Module 2 printing processes

Metallic Colors

  • Metallics add expense to the job because they cannot be reproduced using process colors. They are run as an additional spot color.

  • Four-color jobs are usually run on four-color presses, where there’s a station for each color.

  • If you want metallics, you’ll need to find a press that has the extra stations, or the job will need to be run through a second time. You can work with your printer about this.


Module 2 printing processes

Varnishes

Varnishes can be applied to the finished piece, but, again, they require an additionalstation on the press. The main purpose of a varnish is to intensify the colors and to protect the print.


Module 2 printing processes

Continuous Tone vs. Halftone


Module 2 printing processes

Continuous Tone (aka “contone”)and Halftone

Contone image

Halftone image

  • You’ll see continuous tone images in...

  • Photographic prints (no dots)

  • Computer monitor images (composed of pixels)

You’ll see halftone images in...

Printed material (dots)


Module 2 printing processes

Continuous Tone (aka “contone”)and Halftone

  • Halftone dots…

  • are all one color (here, black).

  • have uniform spacing.

  • vary in size.

Contone image

Halftone image

Halftone dots create an optical illusion of continuous tone.

  • Contone dots…

  • are varying saturations of the same color (here, black)

  • have uniform spacing.

  • have uniform size.


Module 2 printing processes

Continuous Tone (aka “contone”)and Halftone

Contone image

Halftone image

Mass printing technologies cannot produce genuine continuous tone. You see continuous tone on yourcomputer monitor.

Photographic prints are also continuous tone, but without the dots (and they are not a mass printing technology).


Module 2 printing processes

Continuous Tone (aka “contone”)and Halftone

Yes, a computer monitor produces continuous tones. Remember, it is ananalog device. While it is true that the monitor projects thousands of tiny spots of light onto a phosphor screen, the spots are all the same size, and each one is capable of displaying colors in their full ranges of hue, saturation, and brightness.

Print technology cannot do this. It can only place dots of ink in varying sizes on a surface (usually paper). Color hue, saturation, and brightness are achieved by layering four colors of ink (CMYK) in various proportions and at various angles. This is true ofboth digital and non-digitalprinting technologies.


Module 2 printing processes

Continuous Tone (aka “contone”)and Halftone

The difference between digital and non-digital printing technologies is in the way the ink gets to the paper.

Whereas digital processes can send an image directly from the computer to an plate or drum, the major non-digital printing processses uses film to produce plates. They accomplishes this through the use of halftonescreens—one for each color of ink that is used.


Module 2 printing processes

Halftone Screens, Halftone Images

  • Clarifications:

  • When we refer to “halftone screens,” we may be referring to one of two things:

    • The actual screens through which light passes to the light-sensitive surface of the printing plate.

    • The image that is produced by this process.

  • Although both digital and non-digital printing work by placing dots of ink on a surface, only non-digital (mainly offset) printing uses halftone screens.

Terminology:

It is preferable to use “halftone image” for the second one of these, but you will sometimes hear it referred to as a “halftone screen.”


Module 2 printing processes

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Printing Halftone Images

In this example, the dots representing gray shades up to 50% will appear as black spots on white.

Those representing shades of gray over 50% will appear as white dots on black.


Module 2 printing processes

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Printing Halftone Images (offset process)

Note:

What you’ve just seen can apply to any of the four CMYK inks. A full-color (4/c) printed image requires one plate for each of the inks.


Module 2 printing processes

Printing Halftone Images (offset process)

  • Halftone resolution:

  • Measured in lines per inch (lpi)

  • Varies according to the number of lines in the (physical) halftone screen

Screen rulings (lpi) range from 30 to 300 lpi.


Module 2 printing processes

33 lpi

53 lpi

75 lpi

Printing Halftone Images (offset process)

low screen frequency

high screen frequency

Line screen frequency, measured in lines per inch (lpi), describes the granularity of the halftone screen.

Some paper, such as newsprint (used for newspapers), is too absorbent for the higher line screen frequencies. Higher line screens require better quality papers.


Module 2 printing processes

Printing Halftone Images (offset process)

Screen Angle

In addition to screen frequency, the printer must take into account the angle of the screen. The illusion of continuous tone in a printed image is best when the screen is angled at 45°.


Module 2 printing processes

Printing Halftone Images (offset process)

All the images below are at 75 lpi, but the pattern of the screen is highly visible when angled at 0° and 20°. A screen set at a 45-degree angle produces an image closer to continuous tone.45° is the preferred screen angle for all grayscale halftones and is always used for black in 4/c process printing.

0 degrees

20 degrees

45 degrees


Module 2 printing processes

Printing Halftone Images (offset process)

Dot gain

  • Dot gainmay result from the following:

  • Overexposure during platemaking

  • Transferring too much ink from the plate to the blanket

  • Using lower-quality paper, which is more porous

The greatest dot gain results from using lower-quality paper.

An example of dot gain


Module 2 printing processes

Printing Halftone Images (offset process)

  • To compensate for dot gain, do the following:

  • Find out from your printer what the percentage of dot gain is expected to be, given the paper quality, the inks, etc.

  • In your imaging software (e.g., Photoshop), find the setting for dot gain and enter that percentage there.

Compensating for dot gain: a pre-press operation


Module 2 printing processes

Module 2 Quiz (1)

Instructions: Mark your answer on the distributed answer sheet. More than one answer may be correct.

  • Vellum is made from...

    • leaves.

    • cotton fiber.

    • animal tissue.

    • wood fiber.

  • Platen letterpress does not use...

    • a cylinder.

    • metal type.

    • a type form.

    • web-fed paper.

  • When it was first invented, lithography used...

    • magnetic toner.

    • metal type.

    • wet limestone.

    • a duplexing unit.

    • rubber rollers.

  • The term “offset” is used because...

    • the printing plate does not contact the paper.

    • the guide rollers are set off from the cylinders.

    • water wets the plate before ink is applied.

  • Nowadays, gravure plates are etched with...

    • acid.

    • engraving heads.

    • knives.

    • laser beams.

  • A press that allows printing on both sides of the paper is said to have ___ capability.

    • offset

    • electrostatic

    • re-imaging

    • duplexing

  • Before the invention of photography, artwork could only be printed by using...

    • contact sheets.

    • glass plates.

    • halftone screens.

    • engravings or etchings.

Continued...


Module 2 printing processes

Module 2 Quiz (2)

  • The transparent dots on a halftone contact sheet are...

    • different sizes.

    • all the same size.

  • The inked dots on a printed photograph (e.g., in a newspaper) are...

    • different sizes.

    • all the same size.

  • To create a halftone image, you must start with...

    • a platen.

    • a rubber cylinder.

    • a film negative or positive.

    • a silk screen.

  • Pantone is a supplier of...

    • spot colors.

    • process colors.

    • Munsell colors.

    • Acrylic paints.

  • Why must you exercise caution when selecting spot colors from a computer program?

    • Not all colors are shown.

    • They are proprietary.

    • They are not as luminous.

    • Monitor and printer gamuts are different.

  • A “matchprint” is a kind of proof that is produced by the...

    • pre-press person.

    • press.

    • customer.

    • page layout software.

  • If you want to show a customer the exact spot color that will be used in a job, you should show the customer...

    • an inkjet proof.

    • a color laser proof.

    • a color swatch.

    • a screen shot from Photoshop.

Continued...


Module 2 printing processes

Module 2 Quiz (3)

(End of quiz)


Module 2 printing processes

End of Module 2

  • Online resources:

  • A Technical Dictionary of Printmaking, by André Béguin: http://www.polymetaal.nl/beguin/alfabet.htm


Module 2 printing processes

Answer forms

Module 3:

Color Theory and Mgmt

Module 2: Printing Processes

Module 1:

Introduction

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Module 2 printing processes

Answer forms

Module 4: Tools and Techniques

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Section 4

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