Printing Technology

EDBOK Guide

What is Printing Technology?

To set the context, Printing Technology covers the engineering and execution of getting marks on paper. In the decades since enterprise printing began to evolve the requirements for printing have gone through many changes, including evolutions in how data is developed, generated and integrated into print files. This topic is meant to focus on the physical attributes of printing equipment.

Printing Technology Terminology

There are a variety of technologies in use, each with their own terminology. The following terms and definitions are not comprehensive, but meant to provide the basics to understand the following sections.

Impression/Page/Sheet

In a cut sheet print environment an impression is a single side of a physical piece of paper. Some vendors state their machine speed in impressions per minute. In a continuous web print environment an impression is a printed page image on the web. Remember that print devices capable of multi-up printing can have a higher impression per minute value.

Dots per inch (DPI)

The resolution of the printer. The accurate representation is dots per inch squared because the resolution describes the horizontal and vertical number of dots in a square inch. Resolutions may be the same in horizontal and vertical directions or may be different.

Pixel or pel

A picture element, which is a screen resolution measurement sometimes used to describe print resolution. It is the smallest addressable element of resolution.

Lines per inch

The vertical print speed for impact and other early line-oriented print devices.

Print Media Alignment

The process of ensuring that paper is in alignment with the marking technology. Processes exist for both cut sheet and web fed devices.

Bit depth

The number of bits used to describe a dot.

Anti-aliasing

The process of smoothing perceived jagged edges in type, graphics and images.

Dot size

Measured in Pico liters, this is the amount of ink placed by pulse in inkjet technology.

Dot gain

The percentage that ink spreads away from its original placement.

Points

A point is approximately 1/72 of an inch. It is the common measurement for type sizes.

Simplex/Duplex

Simplex describes printing on a single side of a physical page. Duplex describes printing on both sides of a physical page.

Portrait/Landscape

Portrait describes formatting across the narrow dimension of the page. Landscape describes formatting across the widest dimension of the page.

PPM/IPM

This is a rating of the speed of the device. Pages per minute versus impressions per minute.

Duty Cycle/Monthly Volume

This is the maximum throughput of a print engine over a one month period.

Production Printing Imaging Technology

Electro-Mechanical Technology

Electro-mechanical printers cause a piece of type to impact a ribbon and create marks on paper behind the ribbon. Impact printers are in use today supporting applications that require multi-part form printing and printing in hardened environments where mechanical devices are more appropriate.

The IBM 1403 line printer was introduced as part of the IBM 1401 computer in 1959. The original model could print 600 lines of text per minute and could skip blank lines at up to 75 inches/second. The standard model had 120 print positions, with an additional 12 positions available as an option. A print chain with at least five copies of the character set spun horizontally in front of the ribbon and paper. Hammers struck the paper from behind at exactly the right moment to print a character as it went by. In later models the print chain was replaced by a print train where print slugs were placed in a track instead of being mounted on a chain. The hammer struck the page hard enough that the printer could support applications requiring multi-part carbon form printing.

The standard 1403 chain or train could print 48 different characters: 26 letters, 10 digits, and 12 special characters: &, . - $ * / % # @ ≠ ⌑. The ink ribbon was a long roll the width of the print area that was positioned between the print chain and the paper. The roll came in two parts, the feeder roll and take-up roll that was wound and rewound during printing.

The 1403 used fan-folded box fed paper often pre-printed with green bars or gray bars and pre-processed with perforated edges for tractor feeding (pin fed). A carriage control tape or, later, a buffer under program control, specified form length and the form line where printing was to begin so that various paper sizes could be used.

The line mode data format for the 1403 became a standard and still exists today in legacy applications.

As printing volumes increased, various impact technologies were introduced to allow these printers faster speeds. Rather than a fixed print train, the printhead moved across the paper. These technologies include Daisy Wheel (a print disc containing the typeface characters), Dot Matrix (prints each character within a grid), and Line Matrix (prints a page-wide line of dots; it builds up a line of text by printing lines of dots).

Electro-Photographic (EP) Technology

EP print technology is based on an electrically charged drum that is targeted with focused beams of light. Wherever the light hits, the drum loses its electrical charge. When the drum meets a supply of toner, the toner sticks to the non-charged parts of the drum creating the image.

Most toner is a carbon powder and polymer substance. The formulation is unique to the printer, and critical to its performance: key characteristics are granule size, melting point and polymer type. For most toner-based printing the fuser heats the toner and roller pressure binds the toner to the page. In Electron Beam Imaging the process is slightly different; the image is transferred to the drum using electron particles instead of heat.

EP Pioneers

Early EP devices from Xerox include the Xerox 1200 Computer Printing System. Introduced in 1973 this solution combined both copying technology and a computer. It printed at 4,000 lines per minute or about 60ppm. The follow-on product was the 9700 production laser printing system in 1977. This cut sheet laser-based printing system operated at 120 impressions per minute.

In 1975 IBM introduced the 3800 continuous forms printer allowing it to handle the same paper media as the 1403, but at 180 impressions per minute.

EP Process

Electrophotographic process in laser printers, involves six basic steps:

1. A photosensitive surface (photoconductor) is uniformly charged with static electricity by a corona discharge.
2. The charged photoconductor is exposed to an optical image through light to discharge it selectively forming a latent or invisible image. This is called exposition.
3. Development of the latent image is achieved by spreading toner, a fine powder, over the surface. This adheres only to the charged areas, making the latent image visible.
4. An electrostatic field transfers the developed image from the photosensitive surface to a sheet of paper.
5. The transferred image is fixed permanently to the paper, by fusing the toner with pressure and heat.
6. The excess toner and electrostatic charges are cleaned from the photoconductor to make it ready for the next cycle.

Laser printers and LED (laser-emitting diode) printers typically offer the highest resolution. The difference between them is the method of exposition or formation of the latent image.

EP Imaging Technology

EP Printers are characterized by:

• the imaging technology used: laser, LED, or electron beam imaging,
• the paper transport type: cut sheet or continuous forms, and
• color capability: mono, highlight, full color.

''Laser Printers

Laser printers use electrical charges to write images on a drum where toner will adhere until transferred to the intended substrate, usually paper. You may encounter the terms Corona Wire or Charged Roller. These are the mechanisms for putting a positive charge onto the drum to prepare it for laser imagining. The laser causes the points on the drum where the beam hits to discharge preparing the drum to accept toner.

With the toner now on the drum it is transferred to the substrate and then the drum continues to revolve around to the charging area. Transfer may be direct or to a transfer belt and then to the substrate.

LED Printers

LED printheads use an array of Light Emitting Diodes (LEDs) to flash the image on the drum. Depending on the timing and intensity of the LED the image quality can vary, though modern LED printheads have mastered the management of these mechanisms. Just as in the Laser printer, the drum begin it’s revolution positively charged and the LEDs image the drum to prepare it for the toner. The toner image is transferred to the substrate, usually paper. Transfer may be direct or to a transfer belt and then to the substrate.

Electron Beam Imaging

Delphax Systems was founded in 1980 in Canada. Delphax developed a cold fusing technology using electrons to image the drum. Patented as Electron Beam Imaging (EBI) it formed the core of technology for printing at high speed on a variety of substrates. EBI technology requires 30% fewer components than laser printers.

In 1997, Xerox owned one-third of Delphax shares and purchased the remaining two- thirds to gain control of the company. In 2001, Xerox sold its interests in Delphax to Check Technologies. The combined company is now called Delphax Technologies.

EBI advantages include:

• reliability,
• speed,
• uniform and durable imaging,
• enhanced dot uniformity, and
• better image control.

The following steps take place in the EBI process:

1. Image placement.
2. Toner application.
3. Fusing:
4. pressure fusing,
   • pressure fusing,
   • radiant heat fusing.
5. radiant heat fusing.
6. Toner and charge removal.

Inkjet Technology

Inkjet printing involves the use of jetting modules to release ink that lands on the substrate. Inkjet technologies are used in individual print modules that may be mounted on analog printing presses, inserting equipment or other finishing equipment to add variable data or they may be incorporated into paper transport devices to create inkjet printing systems.

There are many engineering options for getting the ink to the paper. The two main technologies are drop-on-demand (DOD) technology, where each drop of ink is released on command for specific placement to form characters and images, or continuous inkjet technology (CIJ), where ink rains from the print module but only designated droplets land on the page. Remaining droplets are pulled back to recirculation systems for reuse.

Continuous Inkjet

Continuous Inkjet technology evolved from work done in the 1860s by Lord Kelvin. While Siemens introduced the first commercial inkjet printing systems in the 1950s for medical recording, today Kodak is the primary vendor in the CIJ inkjet space.

Beginning with technology acquired from Mead Paper, Kodak marketed inkjet modules and printers under the Diconix brand. That division was sold to Scitex to form Scitex Digital Printing, which was sold back to Kodak in 2005. The core technology remained CIJ-based print modules and web presses.

The first generation of their CIJ used electrical charges to cause ink to drop to the paper or divert to the recycling system. The Prosper press series uses air deflection techniques to manage droplets. In both cases Kodak is the designer and manufacturer of their print modules.

Inks may be water-based or solvent-based and may be dye-based, pigment-based or a blend depending on the target application. For most enterprise printing ink is generally water-based dye or pigment.

Drop-on-Demand Inkjet

Most of the other vendors in the inkjet market sell Drop-on-Demand systems. Canon, HP, Kodak, Ricoh and Xerox have products in this market, along with a variety of companies selling proprietary solutions such as the RR Donnelly ProteusJet.

DOD printheads use Thermal jetting (TIJ), where ink is heated causing it to expand and jet through a nozzle, or Piezoelectric jetting (PIJ), where a charge causes the ink to jet through a nozzle.

While HP designs and manufacturers their own TIJ printheads most other vendors use PIJ printheads sourced from the Japanese technology companies Seiko-Epson, Kyocera and Panasonic. Vendors using printheads purchased from the Japanese Original Equipment Manufacturers (OEM) are using PIJ technology. Most consumer inkjet printers, including those from Canon, Hewlett-Packard, and Lexmark, use the thermal inkjet process.

Print Controller Architecture

The Print Controller is designed to ensure that each component of the printing system performs its function at the right point in the print job.

Figure 1 - Print Controller Architecture

It has several elements:

Print Spooler:

• responsible for receiving jobs from Network via various protocols, and
• attaches to print server.

Print RIP:

• responsible for imaging pages,
• converts print streams into raster images, and
• machine image controller (MIC).

Print Supervisor:

• responsible for controlling print run and responding to operator commands,
• manages servo-motors in paper path,
• monitors paper jam sensor,
• monitors photoconductor charge strength,
• error control, and
• reporting.

User Interface:

Responsible for communicating to the Printing System:

• micro code or programming,
• provides programming for control unit, and
• manages printer and its functions.

RIP (Raster Image Processing) Technology

The job of the RIP is to digest the print stream and build the raster or bitmap representation of a page at a speed that is as fast as or faster than the speed of the print engine. First generation RIPs did not have the processing speed or memory capabilities of current generation products which limited their options for print directions, printing on diagonals and other sophisticated imaging.

Electronic Overlay Memory

Electronic Overlay Memory provided additional options for adding electronic images of content that might have been previously produced on pre-printed forms by creating a single matrix the size of a printed page, with some 11 million dots. The Overlay

Memory provided a migration path away from older techniques that involved using film to flash images onto the paper to replace forms.

RIP Subsystem Specialization

As the capabilities of print streams became more sophisticated the functions of the RIP had to follow along. As Document Objects changed such as bitmap fonts to outline fonts, RIPs added sub-processing functions to handle building the bit map representation of the font on the fly. When vector graphics were added, the RIP added a module to process 2D vector graphics. To handle color processing of four different bitmaps to represent CYMK, RIPs added another subsystem. The end goal was to produce a page at least as fast as the print engine. When a RIP cannot keep up with the print engine undesirable results occur. Either the print engine stops, and waits for more pages to be buffered, or in the worst case the engine starts and stops, sometimes called clutching. It is not good for the printer engine and is usually a sign something is not going as expected inside the RIP.

Cut Sheet Printing Systems

Cut sheet printers enabled a wider variety of mixed media types within a job. These machines are used in mid-to-high volume shops enabling applications that required multiple colored papers, sizes, tabs, and NCR (carbonless multi-part) paper media. Their speed ranged initially up to 120 pages per minute, and today cut sheet solutions exceed 300 ppm. Duplexing was accomplished by using a turnover mechanism, and running each page through a second pass. Current technologies provide simultaneous duplexing using two imaging units to image the page in a single path. Typically, the shorter the paper path, the more reliable and less jamming occurs. Since paper flies through the engine, paper acclimatization and environmental conditioning of a cut sheet print room are critical.

Cut Sheet Technology Components

Component Name	Area	Description
Input Drawer	Cut sheet paper input	Manual and/or automated power drawers Multiple drawers Multiple paper sizes or media types Also called a hopper
Picker/ Paper Transport Unit	Imput	Unit that pulls paper into paper path
Marking Engine	Print Engine	Builds and transfers image to media
Bypass/Sample Tray	Print Engine	Tray used to make samples from the print run for quality checks.
Stacker	Output	Straight or off-set stacking of output pages
Interposer	Post Print Engine	Used to pick pre-printed material possibly color to add into the document
Peripheral Devices Folder Job Finisher Saddle-Stitch/ Booklet Maker Perfect Binder Professional Punch/3HP	Post Print Engine	Various Folds Single/Double Stitch Offset Stack Booklets Perfect Bound Simple or GBC Punching

Continuous Forms Printing Systems

Continuous Forms printers differ from cut sheet print devices in that the paper is pulled through the printer from a box or roll of paper. This limits printing to a single media type without changing out the roll. Due to the method of pulling paper through the printer, these devices can print at much higher speeds and typically experience few paper jams than cut sheet devices.

One limitation of this design is that to print duplex, a second engine is needed. The first engine images the front side, and the second engine images the back. There are tri-plex configurations where a second color can be added.

As these machines became faster, more sophisticated pre/post-processing equipment was created. Unwinders capable of holding 50 inch diameter rolls of paper were used instead of boxed stationery. A variety of post processing equipment was developed to meet various needs. Rewinders allowed the paper to be rewound onto a roll after printing; these rolls could be taken and fed into inserting and other finishing equipment. Roll-to-cut or Cutter/Trimmer/Stacker was another popular variant, as well as roll-to-fold.

While the original continuous forms machine required pin/tractor fed paper, newer models are offered in pinless options. The main advantage is the ability to expand the print width and not having to strip off the ½ inch on each side during the inserting process, producing less waste and eliminating a device on the inserter to dispose of the trim waste.

Component Name	Area	Description
Un-winder	Input – Variances: Core Size, Roll Width	Handles feeding paper roll into the printer; 1 to 3 hours Print Time between roll changes
Auto Loader	Input	Automatic threading of paper through print engines
Marking Engine	Middle	Area where the page image is built and transferred to the media
Pressure Roller	Input	Pulls paper through without holes
Tractor Feed	Throughout	Pulls holes along paper sides
Pinless	Throughout	Eliminate disposal of trim waste
Cutter / Trimmer / Stacker	Output (CTS)	Cuts rolls into sheets of paper (usually A4 or Letter) Sorts into sequence
Folder / Seperator	Output	Creases and folds papers Seperates paper at print job boundaries
Rewinder	Output	Used to create Roll-to-Roll processing solutions

Resolution vs. Quality

One approach to getting higher image quality when using legacy 300 dpi bitmap fonts is to perform anti-aliasing or edge enhancement. This works best with characters with curved or diagonal edges and helps to smooth the appearance of characters on the page.

MICR

Magnetic ink character recognition (MICR) is a character-recognition technology used in direct mail marketing and financial services, as well in check imaging to ease the processing and clearance of checks and other documents. The most common application is the MICR encoding is called the MICR line and is found at the bottom of checks and other vouchers. The technology allows MICR readers to scan and read the information directly into a data-collection device. Unlike barcodes and similar technologies, MICR characters can be read easily by humans.

The two most common MICR fonts are the 14-character E-13B and the 15-character CMC-7. The E-13B font is part of the ISO 1004:199 but CMC-7 is most commonly found in Europe. MICR solutions use MICR ink that contains pieces of metal which become magnetized when printed.

The MICR E-13B font is the standard in Australia, Canada, the United Kingdom, the United States, and other countries. The 13 in the font name comes from the 0.013- inch grid used to design it. In addition to numeric characters it includes the ⑆ (transit: used to delimit a bank branch routing transit number), (amount: used to delimit a transaction amount), (on-us: used to delimit a customer account number), and (dash: used to delimit parts of numbers—e.g., routing numbers or account numbers). Major European countries, including France and Italy, use the CMC-7 font, developed by Groupe Bull in 1957. CMC 7 MICR lines are usually printed as close to 8 characters per inch as possible to accommodate the MICR readers. The font is available in a variety of resolutions.

MICR Quality

The quality of MICR printing must adhere to national and international standards established for MICR documents. In the United States, these standards are developed by the Accredited Standards Committee (ASC) on Financial Services, X9, operating under the procedures of the American National Standards Institute (ANSI). The key elements of performance for MICR toner include the following:

• Character Signal Strength: A measurement of the magnetic property of the toner.
• Adhesion: The ability to adhere or fuse the toner to the paper stock.
• Durability: The performance of the toner through multiple passes in reader/ sorters.
• Contamination: The effect of MICR toner on the base printer hardware.

Color Printing

Color Printing for Transaction Applications is either spot color or full color. Spot Color provides black plus one other color option. Full Color Technology may be based on red, green and blue plus black (RGB), or cyan, magenta and yellow plus black (CYMK).

EP Color

Due to the physical limitations of EP imaging engines it is necessary to make multiple passes over the page depositing the colors that build up to render the author/designer intent.

Inkjet Color

In inkjet technology a full color impression can be achieved in a single pass through the printer. Arrays of printheads deliver the various colored inks effectively in a simultaneous process.

Density

Color density is much like greyscale and impacts the gamut of colors that can be represented on a page. A very low color density like 4 bits may not accurately represent the colors of the original full color image. However, there are eventually diminishing returns with higher and higher density levels.

All printers have a limit to the color spectrum or envelope of colors that they are able to produce. At some point higher color densities may exceed the envelope of the print engine. There is also a cost in the volume of data to represent these higher densities, and a consequential impact on the RIP processing time.

Color Density Impact:''

• 8-bit results in 256 color combinations,
• 24-bit results in 16.7 million combinations, and
• 32-bit results in 16.7 million colors plus indicators for opacity.

Ink

Inks fall into two broad categories: Pigment-based inks that stay on the paper surface and dye inks that are absorbed into the paper. Each manufacturer has their own process for formulating ink that is appropriate to the jetting technology and printing intent.

Water-based dye inks and pigment inks are the most common in the enterprise printing environment, while solvent-based pigment inks are commonly found in industrial inkjet environments. The key characteristics of inks used in the enterprise print space are that they must adhere to the paper to survive finishing and mailing operations and they must provide sufficient image quality to be acceptable to the brand owners. The paper used is a key component of how well the image quality is perceived since how the ink is absorbed by and adhered to the paper surface is a major determining factor in perceived print quality.

Over the last half century, the ability to create inkjet droplets that are smaller and to use ink that is more refined has led to the ability to create inkjet print devices capable of higher resolutions. Controlling the size of the droplets, and therefore the amount of ink dropped onto the paper, impacts drying times and the precision of text edges and grain in images. The paper selected for printing also impacts the quality of print since the interaction of the paper and ink, and the rate at which the ink is absorbed into the paper (porosity) impacts the perceived clarity of the print.

Another facet that impacts print quality in inkjet is the concept of dot gain. This is the amount of spreading from the initial droplet that occurs when the ink hits the paper. This is a common discussion in offset printing, but only entered the digital printing discussion with the rise of inkjet since toner-based printing does not experience dot gain.

Depending on the size of the droplets, measured in pico liters, and the porosity of the paper, dot gain may be limited or the ink may expand considerably beyond the droplet boundary. In all inkjet applications the combination of ink and paper determines the dot gain, and therefore the perceived clarity of the print, so testing for acceptability by the end customer is essential.