Method
Waterless printing employs silicone rubber-coated printing plates and specially formulated inks. Typically, a temperature-control system is integrated. [4]
Waterless offset presses do not use a dampening solution to keep the plate's non-image areas free of ink. These presses function because the plate's non-image areas consist of a layer of silicone that repels ink. A waterless press resembles a conventional offset press, with the absence of a dampening system. A more common design includes a dampening system to allow the press to function conventionally when required. Direct imaging (digital) offset presses are waterless, with no dampening system.
Waterless offset inks have a higher tack and viscosity (thickness) and are stiffer than conventional offset inks. The temperature of the inks must be strictly controlled to maintain the correct viscosity, as the plate surface is designed to repel inks of a specific viscosity. This temperature distinction is achieved by running chilled water through tubing in hollow cores of two or more vibrating rollers which are found inside ink trains on printing presses.
The image surface of a waterless plate is intaglio (recessed), allowing the plate to carry a greater volume of ink than a conventional plate does and allowing extremely high screen rulings, ranging from 300 to well over 800 lpi (lines per inch). Waterless printing yields higher ink densities and a broader color spectrum than conventional offset printing does. Waterless plates used on sheet-fed presses are commonly rated for runs of 100,000 to 200,000 impressions. The plates designed for use on web-offset presses can yield 300,000 to 500,000 impressions.
When a job needs to be run again, the plate can be rehung on the press, and although the register must be created manually, a portion of the preparation is simplified, since the ink-key profiles can have been saved and reloaded. However, it is more common for the original prepress files, the plate-format that the original prepress files used, or the plate-format bitmaps to be saved or RIPped again. The bitmap data can be reloaded via the direct imaging server, re-imaged on the press, and run normally on press. Direct imaging plates are non-photographic, contain no hazardous waste, and can be recycled through normal aluminum-recycling channels.
History
Waterless printing was originally developed and brought to market by the 3M company under the trade name Driography in the late 1960s. Results with the product, however, were mixed. Several problems were encountered both in the development of suitable inks for this process and more importantly, in the durability of the driography plate. After several years of research and development and many millions of dollars invested, 3M chose not to pursue further development of the product.
In 1972, Toray Industries, a large Japanese company specializing in synthetic materials development and manufacturing, purchased the patents for the driography product from 3M. Related patents were also purchased from the Scott Paper Co., who were working on a similar project.
Toray's experience in working with synthetic materials and advanced polymer compounds allowed them to improve on the original product design. After some five years of research and development, the Toray Waterless Plate was introduced at DRUPA in 1977.
Marketing of the product began in 1978 with the TAP-type positive plate. Because the first plate was based on a positive working format, the product was first marketed in Japan. (The Japanese commercial printing market is about 95% positive working vs. the U. S., which is approximately 5% positive). Cooperative efforts from press, ink and paper manufacturers helped to support the product, and the overall market acceptance was very good.
The first North American demonstration of the waterless process was at Print '80, and with the introduction of the negative (TAN) type plate in 1982 this market could be seriously pursued. Initial acceptance of the waterless printing system in the U.S. was quite slow. There are several reasons for this:
- Memories of the problems encountered with the original 3M system just ten years earlier had left many U. S. printers unreceptive to a new waterless system.
- A suitable source for waterless inks did not exist in the U.S.
- Toray's marketing effort was conservative.
- Verico has 72% of the worldwide market.
Overview
The waterless printing process has three main components: the waterless plate, specially formulated waterless inks, and press equipment outfitted with a temperature control system, like Codimag machines.
The Waterless Plate is based on a laminate design. Aluminum is used as the base material. Light-sensitive photopolymer material is bonded to the aluminum and a two-micron coating of silicone rubber is applied to the photopolymer.
Depending upon the type of Toray or Verico plate used, run lengths for the plates range from 150,000 to more than 600,000 impressions. These run lengths are based on use with a #1 or #2 coated paper. The use of more abrasive stocks will significantly reduce maximum run lengths. Toray waterless plates are recyclable and are not differentiated from conventional aluminum plate material in recycling. Toray plates will fit all popular sheet-fed and web presses.
Exposure of the plate is done using conventional vacuum frames and light sources. Exposure times for the plate material is comparable to most conventional plates. Under exposure, IR light, controlled by the film carrier, passes through the silicone layer of the plate and strikes the photo-polymer layer beneath. IR exposure activates the photopolymer, causing a break in the bond between the photopolymer and the silicone layers. The photo reaction is very precise, and the plate easily achieves resolutions as fine as six micro lines, supporting a dot range from .5% to 99.5% at 175 lines per inch.
After exposure, the plate is ready for processing. Processing equipment for the water-less plate is unique to this system, using specialized chemical and mechanical treatment of the plate. The finished plate now has a non-image area composed of ink-repellent silicone. In the image area, the silicone has been removed to expose the ink-receptive photo-polymer material. This design allows the plate to selectively attract and resist ink without the use of any water, etches, or alcohol.
Simple additions can be made to the water-less plate by scratching or scribing the silicone surface to expose the ink-receptive layers beneath. Deletions are made with the application of a liquid silicone solution which is used to replace silicone in any area where it has been removed (either by photo-imaging or by scribing).
The main difference between waterless and conventional inks is in the resins or vehicles that are used. Vehicles for waterless inks are selected for their rheological properties and tend to have higher viscosities than resins used in conventional ink systems.
The theory behind waterless printing is that the silicone material which makes up the non-image area of the plate has a very low surface energy. This material will resist ink provided the ink's viscosity is such that it has a greater affinity for itself than it does for silicone.
One factor that will affect viscosity is temperature. Removing water from the offset process results in a loss of cooling effect on the surface of the plate. This will tend to cause a primary temperature to increase at the plate cylinder due to friction. Because of the higher initial viscosities of the waterless inks, there is also a secondary heat generation in the roller train caused by the friction of milling the ink through the rollers.
This heat is why press temperature control systems are required to allow for the precise control of temperature within the printing unit. The most popular systems use vibrator cooling, in which coolant is pumped through hollow core vibrator rollers in the inker. This type of system has been in use in high-speed web presses for many years. The technology has been refined and is now being applied to sheet-fed equipment as well. Almost all sheet-fed press manufacturers offer hollow core ink vibrators which can then accept the after-market temperature control systems.
The function of the temperature control system is to circulate enough coolant through the roller train to carry away the heat that is generated by the mechanical actions in the printing unit. The Aniflo technology helps stabilize the temperature and has consistent inking, important parameters for process stability.
This type of system is not designed to chill or refrigerate the inker, but merely to maintain its temperature at a constant throughout the press run. By maintaining a constant temperature, the viscosity of the inks can be maintained at their optimum levels.
Proofing for waterless printing is handled directly from the film. Not all analog proofing systems are capable of rending the low dot gain associated with the process. Experienced waterless printers offer highly accurate proofs. Some waterless printers are using carefully calibrated digital proofing systems successfully. [5]
Lithography is a planographic method of printing originally based on the immiscibility of oil and water. The printing is from a stone or a metal plate with a smooth surface. It was invented in 1796 by the German author and actor Alois Senefelder and was initially used mostly for musical scores and maps. Lithography can be used to print text or images onto paper or other suitable material. A lithograph is something printed by lithography, but this term is only used for fine art prints and some other, mostly older, types of printed matter, not for those made by modern commercial lithography.
Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The earliest known form of printing evolved from ink rubbings made on paper or cloth from texts on stone tablets, used during the sixth century. Printing by pressing an inked image onto paper appeared later that century. Later developments in printing technology include the movable type invented by Bi Sheng around 1040 AD and the printing press invented by Johannes Gutenberg in the 15th century. The technology of printing played a key role in the development of the Renaissance and the Scientific Revolution and laid the material basis for the modern knowledge-based economy and the spread of learning to the masses.
Duplicating machines were the predecessors of modern document-reproduction technology. They have now been replaced by digital duplicators, scanners, laser printers and photocopiers, but for many years they were the primary means of reproducing documents for limited-run distribution. The duplicator was pioneered by Thomas Edison and David Gestetner, with Gestetner dominating the market up until the late 1990s.
Flexography is a form of printing process which utilizes a flexible relief plate. It is essentially a modern version of letterpress, evolved with high speed rotary functionality, which can be used for printing on almost any type of substrate, including plastic, metallic films, cellophane, and paper. It is widely used for printing on the non-porous substrates required for various types of food packaging.
Xerography is a dry photocopying technique. Originally called electrophotography, it was renamed xerography—from the Greek roots ξηρόςxeros, meaning "dry" and -γραφία-graphia, meaning "writing"—to emphasize that unlike reproduction techniques then in use such as cyanotype, the process of xerography used no liquid chemicals.
Digital printing is a method 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.
Prepress is the term used in the printing and publishing industries for the processes and procedures that occur between the creation of a print layout and the final printing. The prepress process includes the preparation of artwork for press, media selection, proofing, quality control checks and the production of printing plates if required. The artwork is quite often provided by the customer as a print-ready PDF file created in desktop publishing.
Offset printing is a common printing technique in which the inked image is transferred from a plate to a rubber blanket and then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier. Ink rollers transfer ink to the image areas of the image carrier, while a water roller applies a water-based film to the non-image areas.
Letterpress printing is a technique of relief printing for producing many copies by repeated direct impression of an inked, raised surface against individual sheets of paper or a continuous roll of paper. A worker composes and locks movable type into the "bed" or "chase" of a press, inks it, and presses paper against it to transfer the ink from the type, which creates an impression on the paper.
Rotogravure is a type of intaglio printing process, which involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a cylinder because, like offset printing and flexography, it uses a rotary printing press.
Photogravure is a process for printing photographs, also sometimes used for reproductive intaglio printmaking. It is a photo-mechanical process whereby a copper plate is grained and then coated with a light-sensitive gelatin tissue which had been exposed to a film positive, and then etched, resulting in a high quality intaglio plate that can reproduce detailed continuous tones of a photograph.
Laser engraving is the practice of using lasers to engrave an object. Laser marking, on the other hand, is a broader category of methods to leave marks on an object, which in some cases, also includes color change due to chemical/molecular alteration, charring, foaming, melting, ablation, and more. The technique does not involve the use of inks, nor does it involve tool bits which contact the engraving surface and wear out, giving it an advantage over alternative engraving or marking technologies where inks or bit heads have to be replaced regularly.
Intaglio is the family of printing and printmaking techniques in which the image is incised into a surface and the incised line or sunken area holds the ink. It is the direct opposite of a relief print where the parts of the matrix that make the image stand above the main surface.
A photopolymer or light-activated resin is a polymer that changes its properties when exposed to light, often in the ultraviolet or visible region of the electromagnetic spectrum. These changes are often manifested structurally, for example hardening of the material occurs as a result of cross-linking when exposed to light. An example is shown below depicting a mixture of monomers, oligomers, and photoinitiators that conform into a hardened polymeric material through a process called curing.
Viscosity printing is a multi-color printmaking technique that incorporates principles of relief printing and intaglio printing. It was pioneered by Stanley William Hayter.
Computer to film (CTF) is a print workflow involving printing of a design file from a computer straight to a film through an imagesetter. Designs are typically created in Adobe Illustrator or CorelDRAW, however they can also be produced in AutoCAD, Inkscape and many other vector based CAD, design and desktop publishing software packages. An imagesetter is an ultra-high resolution large-format computer output device for CTF.
Pad printing is a printing process that can transfer a 2-D image onto a 3-D object. This is accomplished using an indirect offset (gravure) printing process that involves an image being transferred from the cliché via a silicone pad onto a substrate. Pad printing is used for printing on otherwise difficult to print on products in many industries including medical, automotive, promotional, apparel, and electronic objects, as well as appliances, sports equipment and toys. It can also be used to deposit functional materials such as conductive inks, adhesives, dyes and lubricants.
Vitreography is a fine art printmaking technique that uses a 3⁄8-inch-thick (9.5 mm) float glass matrix instead of the traditional matrices of metal, wood or stone. A print created using the technique is called a vitreograph. Unlike a monotype, in which ink is painted onto a smooth glass plate and transferred to paper to produce a unique work, the vitreograph technique involves fixing the imagery in, or on, the glass plate. This allows the production of an edition of prints.
UV curing is the process by which ultraviolet light initiates a photochemical reaction that generates a crosslinked network of polymers through radical polymerization or cationic polymerization. UV curing is adaptable to printing, coating, decorating, stereolithography, and in the assembly of a variety of products and materials. UV curing is a low-temperature, high speed, and solventless process as curing occurs via polymerization. Originally introduced in the 1960s, this technology has streamlined and increased automation in many industries in the manufacturing sector.
A contact copier is a device used to copy an image by illuminating a film negative with the image in direct contact with a photosensitive surface. The more common processes are negative, where clear areas in the original produce an opaque or hardened photosensitive surface, but positive processes are available. The light source is usually an actinic bulb internal or external to the device
