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In printing, anilox is a method used to provide a measured amount of ink to a flexographic (flexo) printing plate. [1] An anilox roll is a hard cylinder, usually constructed of a steel or aluminum core which is coated by an industrial ceramic, typically chromium(III) oxide powder, whose surface is engraved with millions of very fine dimples, known as anilox cells. In the printing process, the anilox roll is coated in a precise layer of ink that is then transferred to the raised portions of the printing plate. The number, size, and geometry of the anilox cells vary and will determine the amount of ink that the anilox roll delivers to the plate.
Depending on the detail of the images to be printed, the press operator will select an anilox roll with a higher or lower line screen. "Line screen" is the term used for the number of cells engraved on the anilox. Low line screen rolls (100-300 lpi) are used where a heavy layer of ink is desired, such as in heavy block lettering. Higher line screens (500-1500 lpi) produce finer details and are used in four-color process work such as reproducing photographs. Often a job will require a different line screen for each color to be printed. Experienced press operators are skilled at determining the appropriate rolls for a given print job.
Depending on the design of the printing press, the anilox roll is either semi-submerged in the ink fountain, or comes into contact with a so-called metering roller, which is semi-submerged in the ink fountain. In either instance, a thick layer of typically viscous ink is deposited on the roller. A doctor blade is used to shave excess ink from the surface leaving just the measured amount of ink in the cells. The roll then rotates to make contact with the flexographic printing plate which receives the ink from the cells for transfer to the printed material.
Anilox roll selection should be based on cell volume or capacity of the engraved cells. Print results are accomplished with this volume, which transfers to the printing plate and then to the substrate. In general transfer, efficiency is approximately 25% to the substrate. Cell count remains the same for the life of the roll, while volume changes over time due to wear, plugging and damage. Cell count accommodates volume at various cell shapes available from the laser engraving process. The same cell count can be engraved to or wear to different volumes.
Contemporary ink metering systems employ a self contained system known as a chambered doctor blade system which is basically a manifold which delivers ink to the anilox roll. Ink is pumped through a hose to the chamber which fills to capacity. Ink is retained within the system by end seals and doctor blades. One blade works as a retaining blade, simply holding ink within the chamber. The other reverse angle blade works as previously described, removing excess ink from the engraved surface of the anilox roll.
Chambered doctor blade systems are recognized for high quality, consistency and accuracy removing the influence of press speed and some human subjectivity.
Anilox rolls were originally made using a process of mechanical engraving, utilizing hardened steel tools of various cell counts and cell shapes diamond pecking machine, but modern rolls are laser engraved. The characteristics of an anilox roll determine the amount of ink that will be transferred to the plate: angle of the cells, cell volume, and line screen. A 60 degree angle ensures maximum density in a given space. Lower volume makes for less ink. Low line numbers will allow for a heavy layer of ink to be printed, whereas high line numbers will permit finer detail in printing. Both cell volume and line screen are closely correlated.
The rolls are often specified by their line screen, [2] which is the number of cells per linear inch. These often range from around 250 to upwards of 2000, though the precise numbers vary by manufacturer. Most rolls sold are within 800 LPI, although a spike in demand for those with 800–1200 lines has been seen. Anilox rolls are almost always designed to be removed from the press for cleaning and for swapping out with different line screen rolls.
Anilox rolls are properly specified by cell volume for the required print application. Lower volumes = thinner ink films for the highest quality process printing. Higher volumes address combination, screens, line work, solid coverage and coating applications. In virtually all printing applications with various print requirements, one volume will not print all to the highest quality. Limited print stations generally call for a compromise between the highest quality graphics and color.
There are many variables to consider when specifying an anilox roll beyond the print requirements, such as substrate, ink system, plate material, plate mounting tape, press speed, and drying capacity. The best course of action is to consult suppliers of all these components for proper engraving specifications from their experience.
There are two ways to specify anilox roll settings: on transfer volume or on line count. Each specification has both a European standard and an American standard.
Transfer volume is the volume of ink that will be transferred per unit surface area of paper. The European standard for transfer volume is cm3/m2 or cubic centimetre per square meter, which means 1 cm3 of ink will be transferred onto 1 m2 of paper.
Sometimes ink suppliers will give a recommended transfer weight per square meter, expressed in g/m2. This can be converted to cm3/m2 by dividing by the density of the ink in g/cm3.
The American standard for transfer volume is a billion cubic microns per square inch, typically written as BCM / in2, BCM/sq in, or BCM. A cubic micron (μm3) is a unit of volume and one billion cubic microns (1 000 000 000 μm3) is equal to 0.001 cm3. Since one square meter is equal to 1550 square inches, it follows that 1 BCM/in2 = 1.55 cm3/m2.
Line count [3] measures the finesse of the pattern on the anilox roll. It measures how many cells are engraved per centimetre or inch.
In Europe the standard is LPCM or lines per centimeter.
In America, the standard is LPI or lines per inch.
The conversion from transfer volume to line count is not straightforward. This is because depending on the pattern used for the cell and depth of gravure of the anilox roll, the cell might contain higher or lower volumes of ink. The only way to convert cm3/m2 (transfer volume) to LPCM (cell finesse) or BCM to LPI is to look at the conversion chart provided by the anilox roll supplier.
Also, any given anilox roll will age after some time and its actual transfer volume will be less and less.
Though large wide-web flexo rolls are only maneuverable by overhead crane, on smaller presses anilox rolls are often handled directly by operators. Extreme caution must be taken when handling these pieces of hardware as a single bump against a hard surface or sharp corner can destroy the delicate cell structure on the surface and render a roller completely useless, at a cost of around US$5000 for even small narrow-web rollers. Nicks and scratches add up quickly, so fine brushes (never brass brushes) are used for cleaning the anilox roll.
Anilox rollers that are used with water, solvent and oil based inks, which dry when left sitting out and unagitated, must be cleaned immediately after use or a problem known as plugging occurs, where minuscule amounts of ink dry in the cells. This leaves tiny, but unacceptable, pinholes in anything printed from the roll in the future. Anilox rolls can also become damaged if a steel doctor blade breaks and begins to grind the anilox roll. This creates a defect in the print called a "score line" due to the scoring of the anilox.
Ceramic Anilox are routinely manufactured by plasma spraying chromium(III) oxide powders (Cr2O3) on to the roller or sleeve surface.
Chromium oxide is manufactured by calcining sodium dichromate in the presence of carbon or sulfur. [4]
The European Chemical Agency (ECHA) classes sodium dichromate a Substance of Very High Concern (SVHC) [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.
Screen printing is a printing technique where a mesh is used to transfer ink onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen to fill the open mesh apertures with ink, and a reverse stroke then causes the screen to touch the substrate momentarily along a line of contact. This causes the ink to wet the substrate and be pulled out of the mesh apertures as the screen springs back after the blade has passed. One colour is printed at a time, so several screens can be used to produce a multi-coloured image or design.
Printmaking is the process of creating artworks by printing, normally on paper, but also on fabric, wood, metal, and other surfaces. "Traditional printmaking" normally covers only the process of creating prints using a hand processed technique, rather than a photographic reproduction of a visual artwork which would be printed using an electronic machine ; however, there is some cross-over between traditional and digital printmaking, including risograph.
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 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.
Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics by repeatedly passing a laser beam back and forth over a negatively charged cylinder called a "drum" to define a differentially charged image. The drum then selectively collects electrically charged powdered ink (toner), and transfers the image to paper, which is then heated to permanently fuse the text, imagery, or both to the paper. As with digital photocopiers, laser printers employ a xerographic printing process. Laser printing differs from traditional xerography as implemented in analog photocopiers in that in the latter, the image is formed by reflecting light off an existing document onto the exposed drum.
Engraving is the practice of incising a design on a hard, usually flat surface by cutting grooves into it with a burin. The result may be a decorated object in itself, as when silver, gold, steel, or glass are engraved, or may provide an intaglio printing plate, of copper or another metal, for printing images on paper as prints or illustrations; these images are also called "engravings". Engraving is one of the oldest and most important techniques in printmaking. Wood engraving is a form of relief printing and is not covered in this article, same with rock engravings like petroglyphs.
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.
A rotary printing press is a printing press in which the images to be printed are curved around a cylinder. Printing can be done on various substrates, including paper, cardboard, and plastic. Substrates can be sheet feed or unwound on a continuous roll through the press to be printed and further modified if required. Printing presses that use continuous rolls are sometimes referred to as "web presses".
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.
Laser engraving is the practice of using lasers to engrave an object. The engraving process renders a design by physically cutting into the object to remove material. The technique does not involve the use of inks or tool bits that contact the engraving surface and wear out, giving it an advantage over alternative marking technologies, where inks or bit heads have to be replaced regularly.
A calender is a series of hard pressure rollers used to finish or smooth a sheet of material such as paper, textiles, rubber, or plastics. Calender rolls are also used to form some types of plastic films and to apply coatings. Some calender rolls are heated or cooled as needed. Calenders are sometimes misspelled calendars.
Textile printing is the process of applying color to fabric in definite patterns or designs. In properly printed fabrics the colour is bonded with the fibre, so as to resist washing and friction. Textile printing is related to dyeing but in dyeing properly the whole fabric is uniformly covered with one colour, whereas in printing one or more colours are applied to it in certain parts only, and in sharply defined patterns.
Computer-to-plate (CTP) is an imaging technology used in modern printing processes. In this technology, an image created in a desktop publishing (DTP) application is output directly to a printing plate.
Viscosity printing is a multi-color printmaking technique that incorporates principles of relief printing and intaglio printing. It was pioneered by Stanley William Hayter.
Printed electronics is a set of printing methods used to create electrical devices on various substrates. Printing typically uses common printing equipment suitable for defining patterns on material, such as screen printing, flexography, gravure, offset lithography, and inkjet. By electronic-industry standards, these are low-cost processes. Electrically functional electronic or optical inks are deposited on the substrate, creating active or passive devices, such as thin film transistors; capacitors; coils; resistors. Some researchers expect printed electronics to facilitate widespread, very low-cost, low-performance electronics for applications such as flexible displays, smart labels, decorative and animated posters, and active clothing that do not require high performance.
Roller printing, also called cylinder printing or machine printing, on fabrics is a textile printing process patented by Thomas Bell of Scotland in 1783 in an attempt to reduce the cost of the earlier copperplate printing. This method was used in Lancashire fabric mills to produce cotton dress fabrics from the 1790s, most often reproducing small monochrome patterns characterized by striped motifs and tiny dotted patterns called "machine grounds".
In printing, the doctor blade removes the excess ink from the smooth non-engraved portions of the anilox roll and the land areas of the cell walls. Doctor blades are also used in other printing and coating processes, such as flexo and pad printing for the same function. It is believed that the name derives from the blades used in flatbed letterpress equipment for blades used to wipe ductor rolls, and "ductor" became doctor.
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
Anilox Cleaner Source: SRI Specialty Material
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