Flexographic+Printing

=**Flexographic Printing** (often abbreviated to **flexo**)= Is a form of printing on a rotary press that employs water-based ink, used especially for printing on plastic, paper, or cardboard. It involves pressing raised lettering with ink onto whatever material needs to be printed on. You can say that it is basically an updated version of letterpress that can be used for printing on almost any type of substrate including corrugated cardboard, metallic films, cellophane, newspapers, catalogues, etc. It is widely used for printing on the non-porous substrates required for various types of food packaging (it is also well suited for printing large areas of solid color).

Identifying a Flexographic Printer is not hard, they come in two main forms. The presses are either flat plates that can be pressed onto a surface, or they are cylinders that roll across the surface. These types of presses both use raised lettering or numbering on the surface. The letters or numbers hold a certain amount of ink and they appear as the mirror versions of whatever it is meant to be printed, with everything on this surface place backwards.

**History**
The first Flexographic press was patented by Bibby, Baron and Sons from Liverpool, England in 1890. The device was known as "Bibby's Folly" thanks to the ink, which was water based and smeared easily. Early 1900's the name changed to the aniline printer due to the oil based ink used. During the early 20th Century, Flexography printing was used for in the United States for food packaging. The Food and Drug Administration classified aniline dyes as unsuitable to use for food packing in 1940. The sales plummeted due and individual firms tired to use new names for the process. These names were "Lusto Printing" and "Transglo Printing," but never met with success. When the Drug Administration finally approved of the aniline process in 1949 using new, safe inks, the sales continued to drop due to the fact that some food manufactures still refused to consider using aniline printing. Worried about the image of the printing industry, the packaging representatives decided the process needed to be renamed. Flexography has been labeled antique, until the last decade has seen advances in the presses and pushed them into a position more prominent than even lithography printers.

The presses can be divided into five main categories: stack press, in-line press, common impression cylinder press, newspaper flexographic press, and commercial publication flexographic press.
 * Press Types**

**Stack Press**
The stack press has separate printing units stacked vertically and each printing unit has its own impression cylinder. This was the first type of press developed for flexography. It is difficult to hold registration between multiple colors printed on stretchable substrates using the stack press, even with web tension controls. It is best suited for heavier gauge substances, such as thick paper products, that will not stretch or for applications that do not require good registration.



**In-Line Press**
Like the stack press, the in-line press has separate printing units for each color and each unit \has its own impression cylinder, but they are arranged in a horizontal configuration just like a rotary offset press. Because of the distance between the printing units, problems with print registration can occur. Tension control equipment is used on the press to hold proper registration between multiple colors. The wider in-line presses are used for printing large items such as corrugated cartons and smaller width webs are used for printing pressure sensitive labels at high speeds



**Central (Common) Impression Cylinder Press**
Instead of the printing units being independent from the others, they are all grouped around a common impression cylinder. Substrates do not stretch as they move around the impression cylinder so the common impression cylinder press is a good choice for printing on substrates such as thin plastics that would normally stretch when used on other types of presses. This type of press provides for better registration of multiple colors. Some CIC presses have impression cylinders that are as much as 8 feet in diameter which allows for as many as 8 stations to be placed around the cylinder. The only drawback of the CIC press is that they can only print on one side of the substrate.

**Newspaper Flexographic Press**
A newspaper flexographic press consists of multiple printing units, each unit consisting of two printing stations arranged back-to-back in a common frame. The use of paired stations allows both sides of the web to be printed in one pass. Multiple printing stations are required to print the many pages that make up a typical newspaper. Single and double color decks, stacked units, or 4-, 5-, or 6-color units are sometimes positioned above those units where the publisher wants to provide single or multiple spot color, spot color for both sides of the web, or process color, respectively (Buonicore).



**Commercial Publication Flexographic Press (picture N/A)**
Commercial publication flexographic presses are compact high-speed presses with wide web capability that utilize dedicated 4-, 5-, or 6-color units. Typically, two four-color units are paired in one press to allow printing on both sides of the web. Publication flexographic presses generally incorporate infrared dryers to ensure drying of the waterborne ink after each side of the web is printed (Buonicore).

**Printing Process**
The process of printing in Flexographic operations are: Image preparation, Plate making, Printing, and the finishing. Below is a diagram depicting the break down of the process.



**Image Preparation**
The image preparation begins with camera-ready (mechanical) art/copy or a electronically produced art that is supplied by the customer. Images are captured for printing using a camera, scanner, or computer. Components of the image are manually assembled and positioned in a printing flat when a camera is used. This process is called stripping. When art/copy is scanned or digitally captured the image is assembled by the computer using special software. A simple proof (brown print) is prepared to check the position and accuracy. When colour is involved, a colour proof is submitted to the customer for approval.

**Plate Making**
Photomechanical plate making method begins with an engraving. this is accomplished be exposing a metal plate through a negative and processing the exposed plate in an acid bath. the metal engraved plate is used to make a master which is molded out of bakelite board. the engraving is placed in a mold press. The mold is produced by applying heat and pressure to the mold material (bakelite board), which can be either plastic or glass, against the engraving under controlled temperature and pressure. The bakelite board fills the engraving on the metal plate. When it is cooled the end product is a master mold for the plastic or rubber compound that will be pressed into the mold under pressure and elevated temperature to produce the flexible printing plate with raised areas that will transfer ink.

The second method of flexo plate making is relief plates. This utilizes a solid or liquid photopolymer. The sheet of photopolymer is exposed to light through a negative. The unexposed areas are then washed away with solvent or water wash. This is fast becoming the most common method of plate making.

the process differs depending on whether solid sheets of photopolymer or liquid photopolymer are used, though the two processes are similar in general outline. In both of these processes the plates are made in ultraviolet exposure units. A negative of the job is placed between the photopolymer and the ultraviolet light source. The photopolymer sheet or liquid is then exposed to ultraviolet light, which hardens the image area. Lastly, the plate is processed to remove the unhardened non-image area. Photopolymer plates are replacing rubber plates because they offer superior quality and performance at a lower cost.

Flexographic printing plates may be made by laser engraving, this process is called direct digital platemaking. The image is scanned or computer generated. Then a computer-guided laser etches the image onto the printing plate.

**Printing**
In the typical flexo printing sequence, the substrate (material that is being printed on) is fed into the press from a roll. The image is printed as substrate is pulled through a series of stations, or print units. Each print unit is printing a single color. As with Gravure and Lithographic printing, the various tones and shading are achieved by overlaying the 4 basic shades of ink. These are magenta, cyan, yellow and black. Magenta being the red tones and cyan being the blue.

Printing each colour on a flexo press consists of a series of four rollers: Ink, Meter, Plate, and Impression. The first roller transfers the ink from an ink pan to the meter roller or Anilox Roll, which is the second roller. The Anilox roller meters the ink to a uniform thickness onto the plate cylinder. The substrate then moves between the plate cylinder and the impression cylinder, which is the fourth roller. The Impression cylinder applies pressure to the plate cylinder, which transfers the image onto the substrate. The web, which by now is printed, is fed into the overhead dryer so the ink is dry before it goes to the next print unit. After the substrate has been printed with all the colours the web MAY be fed through an additional overhead tunnel dryer to remove most of the residual solvents or water. the finished product is then rewound onto a roll or is fed through the cutter.

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There are three main types of inks. The inks are water based, solvent, and UV curable. The printing surface (substrate type) dictates what ink type to use. These inks consist of colorants, which may be pigments and soluble dyes along with a binder and various solvents. Both the water and solvent based inks commonly contain various types of alcohol as the primary solvent or drier. The alcohol rapidly dries through evaporation and contributes to VOC emissions (**Volatile Organic Compounds**). The inks may also contain glycol ether and/or ammonia which facilitates drying.
 * Flexographic Ink**

Water based inks dry through evaporation and absorption on paper. This evaporation requires a greater amount of fuel or energy to dry the ink. Coated paper may be used to control the absorption through the paper. Due to the speed of the pressed and the volume of inks consumed daily, a pollution control system may be necessary. This is especially needed if the printer is using solvent based inks. If the product allows, the printer may avoid pollution control equipment if the convert to water based inks or UV curable inks. The cost of pollution control equipment for a small flexo or gravure printer will cost approximately $400,000 (this is a estimate from 1998) and approximately $50,000 for testing and certification. the price will increase as the size and /or volume of the operation increases.

The UV inks are commonly used for top coats, lacquers and are responsible for many improvements in image quality. The use of UV curable coloured inks is rising within flexgraphic printing, but the product and equipment investment are obstacles. Note, water based UV curable inks may not be an option for some printers due to the substrate (printing surface) being printed or design of the product.

**Finishing**
After the printing process, substrates may run through a number of operations to be considered a "finished product" and ready for shipment to the customer. The finishing process may include operations such as coating, cutting, folding, and binding.

**Advantages of Flexographic Printing**
Flexographic Printing is a process that involves inks that adhere to assorted substrates. Typical presses used for flexographic printing feature rollers that deliver ink and help the substrate pass through the press. This structure allows the substrates to be fed into the machine while maintaining enough tension to prevent any wrinkles appearing on the substrate. Several types of presses offer quite a few advantages, depending on what your role in the printing process happens to be.

The stack press, in-line press, and common impression cylinder presses offer advantages to print consumers and the people who run the flexographic printing jobs. Stack presses are very accessible and can print a wide variety of substrates. Central impression presses are known for their ability to maintain print registration. In-line presses can handle printing on material such as corrugated cardboard accurately.

Also the flexo press's ability to print on several substrates that other printers would have trouble printing on such as corrugated cardboard, paperback book paper, kraft paper and gift wrap paper. It also enables printing on papers used for packaging and folding cartons. Using this printing process we can also print on cellophane, polyester film, pressure sensitive substrates or adhesive papers is an option, too.

Wide web flexographic printing presses offer market specific advantages to consumers seeking to print on large pieces of substrate. These presses support the food, dairy, beverage, medical, cosmetic and apparel industries. Produce, bakery and frozen food boxes, beverage containers, plastic bags and industrial sized agricultural bags can all be printed using wide web flexographic presses. Narrow web presses are also very useful to many of the industries mentioned previously, but maybe more by people who are looking for computer, hardware or automotive packaging to be printed and low-quantity print jobs. The narrow web press can handle job sizes that are less than 2 feet wide, which makes them ideal for fast food and candy wrappers as well as other purposes that may include company names and logos.

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