Tuesday, May 28, 2013

Digital printing

Digital printing refers to methods of printing from a digital based image directly to a variety of media. It usually refers to professional printing where small run jobs from desktop publishing and other digital sources are printed using large format and/or high volume laser or inkjet printers. Digital printing has a higher cost per page than more traditional offset printing methods but this price is usually offset by the cost saving in avoiding all the technical steps in between needed to make printing plates. It also allows for on demand printing, short turn around, and even a modification of the image (variable data) with each impression. The savings in labor and ever increasing capability of digital presses means digital printing is reaching a point where it could match or supersede offset printing technology's ability to produce larger print runs of several thousand sheets at a low price.Digital printing refers to methods of printing from a digital based image directly to a variety of media. It usually refers to professional printing where small run jobs from desktop publishing and other digital sources are printed using large format and/or high volume laser or inkjet printers. Digital printing has a higher cost per page than more traditional offset printing methods but this price is usually offset by the cost saving in avoiding all the technical steps in between needed to make printing plates. It also allows for on demand printing, short turn around, and even a modification of the image (variable data) with each impression. The savings in labor and ever increasing capability of digital presses means digital printing is reaching a point where it could match or supersede offset printing technology's ability to produce larger print runs of several thousand sheets at a low price.
The main differences between digital printing and traditional methods such as lithography, flexography, gravure, or letterpress are that no need to replace printing plates in digital whereas in analog printing plates are continuously replaced, resulting in a quicker and less expensive turn around time, and typically a loss of some fine-image detail by most commercial digital printing processes. The most popular methods include inkjet or laser printers that deposit pigment or toner onto a wide variety of substrates including paper, photo paper, canvas, glass, metal, marble and other substances.
In many of the processes the ink or toner does not permeate the substrate, as does conventional ink, but forms a thin layer on the surface that may be additionally adhered to the substrate by using a fuser fluid with heat process (toner) or UV curing process (ink).

Digital printing methods of note
Fine art inkjet printing
Fine art digital inkjet printing is printing from a computer image file directly to an inkjet printer as a final output. It evolved from digital proofing technology from Kodak, 3M, and other major manufacturers, with artist and other printers trying to adapt these dedicated prepress proofing machines to fine art printing. There was experimentation with many of these types of printers, the most notable being the IRIS printer, initially adapted to fine art printing by programmer David Coons, and adopted for fine art work by Graham Nash at his Nash Editions printing company in 1991. Initially, these printers were limited to glossy papers, but the IRIS Graphics printer allowed the use of a variety of papers that included traditional and non-traditional media. The IRIS printer was the standard for fine art digital printmaking for many years, and is still in use today, but has been superseded by large-format printers from other manufacturers such as Epson and HP that use fade-resistant, archival inks (pigment-based, as well as newer solvent-based inks), and archival substrates specifically designed for fine art printing.
Substrates in fine art inkjet printmaking include traditional fine art papers such as Rives BFK, Arches watercolor paper, treated and untreated canvas, experimental substrates (such as metal and plastic), and fabric.
For artists making reproductions of their original work, inkjet printing is more expensive on a per-print basis than the traditional four-color offset lithography, but with inkjet printing the artist does not have to pay for the expensive printing plate setup or the marketing and storage needed for large four-color offset print runs. Inkjet reproductions can be printed and sold individually in accordance with demand. Inkjet printing has the added advantage of allowing artists to take total control of the production of their images, including the final color correction and the substrates being used, with some artists owning and operating their own printers.
Digital inkjet printing also allows for the output of digital art of all types as finished pieces or as an element in a further art piece. Experimental artists often add texture or other media to the surface of the final prints, or use them as part of a mixed-media work. Many terms for the process have been used over the years, including "digigraph" and "giclée". Thousands of print shops and digital printmakers now offer services to painters, photographers, and digital artists around the world.
Digital laser exposure onto traditional photographic paper
Digital images are exposed onto true, light sensitive photographic paper with lasers and processed in photographic developers and fixers. These prints are true photographs and have continuous tone in the image detail. The archival quality of the print is as high as the manufacturer's rating for any given photo paper used. In large format prints, the greatest advantage is that, since no lens is used, there is no vignetting or detail distortion in the corners of the image.
Digital printing technology has grown significantly over the past few years with substantial developments in quality and sheet sizes.
Source: Internet







The use of digital printing applications and integration of these applications into traditional print markets is rapidly expanding. Digital, unlike the traditional print processes, is a direct to output device process thus it does not employ a “pre-press” operation as would be associated with traditional commercial printing technologies, i.e., screen or lithographic printing. Instead, the image is created on the computer and transmitted directly to the output device.


The other distinct difference between the use of digital applications and traditional print is the relationship between the equipment and ink delivery system. Output devices such as inkjet printers, are developed with a specific ink and ink delivery system in place which is unique to each digital press. The type of equipment chosen is also driven by the product produced. These factors work to limit product substitution options for most systems.


Equipment options for digital printing are shaped by substrates and the inks that are used. Liquid ink-jet, wet/dry toner systems, solid ink-jet, thermal-transfer and photographic devices are the primary technologies used today. Common digital products include items such as bus wraps, building wraps, in-store displays, reproduction of photographic images, as well as fine art prints to list just a few. Determining when to use digital printing instead of a traditional printing process is highly dependent on the number of prints needed as well as the production speed of the output device.


Ink delivery roll-based digital output devices use a substrate delivered on a roll (as in traditional web printing) and printed after it is fed into the machine. Roll-based devices allow you to print on flexible surfaces including paper, vinyl, fabrics and thin plastics. It is also possible to print on various types of papers that are used in thermal image transfer processes such as dye sublimation.


Flatbed devices allow direct printing on rigid substrates, which can range from the common, such as poster board, foam board or rigid plastics; to the uncommon, including metal, glass, wood and other substrates. Printing directly on these rigid substrates may eliminate the mounting processes required of many images printed on roll-based units.





Liquid Inkjet Technology


There are two primary types of Inkjet technology that are used to produce an image. The first is drop-on-demand. Using this method the heads form ink droplets by applying pressure to the nozzle chamber. This action forces the drop of ink out of the nozzle onto the media or print surface as is needed to create the image. There are two types of drop-on-demand ink jet heads, piezo and thermal.


The second type of Inkjet technology is continuous. Using this method, the ink is continuously under pressure forming a stream of droplets. The droplets required to form the image are channeled to the media, while the unused droplets are recycled.


Highly important to successful inkjet digital imaging is the print head, which literally “jets” the ink onto the substrate. Piezo heads release ink by applying pressure to the head’s nozzle chamber, forcing a drop of ink onto the print surface as needed to create the image. With thermal ink heads, a heating element creates a gas bubble in the nozzle chamber; the bubble yields the pressure needed to force a droplet of ink onto the media.


Inkjet printer inks can be aqueous, solvent-based, or UV curable. The print head dictates the ink type that will be used. Aqueous inks are common but production speeds are limited because of the rate of drying for the inks. For high production speed applications, some printers choose to switch to solvent-based inks, which dry through rapid evaporation.


UV inkjet units use ultraviolet light to cure the ink. While many devices applying UV inks are flatbed devices, designed for rigid substrates, it is important to understand that UV inkjet inks can be used only on devices that are capable of curing UV ink. Without the proper UV light, the ink will not cure and will remain in a wet-state for an indefinite period of time.


Highly important to successful digital imaging is the print head. The two most common types of print heads are piezo and thermal. Piezo heads release ink by applying pressure to the head’s nozzle chamber, forcing a drop of ink onto the print surface as needed to create the image. With thermal ink heads, a heating element creates a gas bubble in the nozzle chamber; the bubble yields the pressure needed to force a droplet of ink onto the media.


As in all types of printing, the ink is distinctly important to the creation of a print that has reliable and accurate color, durability and longevity. In today’s digital inkjet markets, two ink delivery systems have gained prominence and represent nearly 100 percent of inkjet graphics created worldwide.


Due to issues associated with cost and technology, most entry-level wide-format digital printers use either dye or pigment inks. Dye-based and pigment-based ink systems are both aqueous systems, meaning they are water based. Aqueous ink systems are used on indoor signage and other indoor types of prints that require protected (laminated) usage. For outdoor uses, or to increase the durability of the print, the print must be laminated.


As mentioned earlier, UV inks require specific output devices in order to be cured. Once cured, the finished print offers high durability, even outdoors, without the need for


lamination or other steps necessary to protect the print. Currently, UV ink is the ink system that allows for printing on the widest variety of substrates, including products intended for outdoor use.


Solvent-based ink also offers higher durability and is generally less expensive than UV. However, when purchasing a digital printer using a solvent-based ink system, it is important to consider that the use of solvents could lead to significant air emissions, triggering the need to comply with air quality regulations. Without proper ventilation, the fumes from these systems may also be a concern for worker safety and health.


Digital Printing Process


Capturing an Image


Many graphic projects begin with "analog" images such as 35mm slides, transparencies or reflective art. To produce a "digital" image, these elements must be converted to digital files that are then manipulated on a computer system with digital imaging software. This step is usually accomplished by scanning the analog image. The scanner measures reflected or transmitted light from the analog image, assigning numerical values to the colors or tones in the image to create a digital copy. With the image "translated" into a series of numbers, the information can be stored on a computer hard disk or other electronic media such as a removable drive, or CD/DVD.


The graphics produced through the use of these applications can be divided into two primary groups or "graphic types," object oriented and bit-mapped. At the completion of the design and layout phase, all elements have been assembled into one file. This file may include both object-oriented and bit-mapped graphics saved in various file formats. The file is then ready to be managed based on the requirements of the selected output device and can now be reproduced.


Producing the Image


Once the image has been captured, it is then transferred to the printing station. The computer directs the speed of the head technology as well as the machine to produce the image. As with all printing processes, digital prints dots, which in turn trick your eye into seeing a continuous image. Digital technology prints in four color process.


Finishing the Image

Lamination is often used to "finish" digital prints. Using special media, inks and/or laminates, images can be produced which withstand indoor humidity, sunlight and most outdoor weather conditions. Also, adhesives are available which provide the opportunity to apply digital images to various surfaces.

Source: Internet

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