Printing on Corrugated Board Presented by Sanjay Bhotra Novel Packagig 41/2,b/2, vadgaon sheri, Off nagar road, pune 411014 Tel : (020)27030569,27031466 E- mail : novelpackaging@gmail.com Different types of printing 1
Screen printing The quantity of printing is less than 500 sheets The cost of the screen is relatively low There is a high use of labour in this process One screen can print only one color Screen Printing process is used to print thick/block matter. Very crude and inefficient way of printing. Exposing of Screen PROCESS OF SCREEN PRINTING 2
Exposing of Screen PROCESS OF SCREEN PRINTING Flexo Printing This process is undertaken when the quantity of sheets is medium to high A flexographic print is made by creating a positive mirrored master of the required image as a 3D relief in a rubber or polymer material. Flexographic plates can be created with analog and digital platemaking processes. Flexo printing machines come in configuration from 1 color up to 6 colors with rotary die and slotting attachments. 3
Flexo Printing Flexo printing machines are clubbed with a punching or slotting unit. Very good for high volumes with good board. Flexo printing can print on cardboard sheet. Where the requirement is for reasonably good multicolor printing Where the printed sheets have a big size. Process of printing 4
Anilox Rolls The flexo printing/coating process depends upon the precise controlled transfer of a liquid ink, varnish or coating. An anilox roll is simply a metering roll designed to consistently supply a uniform and measurable volume of ink onto the image carrier. Anilox roll is considered to be the heart of the flexographic press Anilox Rolls Ink receptivity and releasing capabilities of the anilox roll is of higher importance and ink transfer capabilities of the plate are determined by the surface technology of plate, surface tension of plate & ink and plate to ink compatibility. The latest anilox rolls are laser engraved, with cell counts currently up to 500 cells/cm, from a steel roller and coated in a fine ceramic. 5
Anilox Rolls These laser engraved ceramic rolls, could last up to 10 years, depending on the wear they are exposed to from contact with the doctor blade. They provide an even, and consistent ink delivery in a controlled manner and provide narrow web flexo with a competitive edge in the leading packaging markets eg self adhesive labels for wines. Anilox Rolls Once the anilox is charged with ink, the excess is wiped off with a flexible steel doctor blade. Besides the cell geometry, ink release capabilities of the cell is also affected by rheological properties of ink like; viscosity, surface tension, Printing pressure between the plate cylinder and the impression cylinder, substrate properties, etc. 6
Die cutting attachment Types of Ink Distribution. Two roll System Doctor Blade System Chambered Doctor Blade system 7
Two Roll Ink Distribution The two-roll ink distribution system consists of an ink reservoir or pan filled with ink. A rubber fountain or doctor is rotated in the ink pan at a steady, constant rotation. Ink is picked up by the rubber surface and transferred to the anilox roll at every rotation. The anilox roll is rotated at the speed of the printing cylinder, which can be three to 10 times faster than the rotation of the rubber roll. Two Roll Ink Distribution Thus when the fountain roll contacts the anilox roll, it not only fills the cells with ink, but through the slow rotation of the fountain roll, a wiping action occurs at this contact nip. This action wipes the anilox surface clean of excess ink and only the ink-filled cells contact the printing plate. 8
Doctor Blade System The doctor blade system employs an anilox roll rotating in the ink pan followed by a reverse angle doc tor blade that shears or shaves anilox roll, printing plate with contact prior to any surface ink clean. Critical and should be between 28 and 32 degrees to the tangent Doctor blade material is usually plastic or some other polymer such as "mylar. Doctor Blade System This system provides positive ink control over a wide range of operating speeds. The reverse angle doctor is not speed sensitive and offers a uniform film to be printed on all operating press speeds. 9
Chambered Doctor Blades The latest development distribution system is the chambered doctor blade system. This system is a chamber that has been built in an anthology. The chamber uses two doctor blades to create an inking area of approximately 1 to 2 inches along the anilox roll surface. The chamber is usually 3 to 4 inches deep, which allows room for the ink to be pumped under pressure in the chamber. Chambered Doctor Blades The edges of the anilox roll are sealed through the use of pliable plastic pads so that the whole chamber is pressurized. The ink fills the anilox cells and is wiped off the surface of the anilox roll by the doctor blade, while the other blade is called a containment blade and it keeps the chamber inside the chamber. 10
Anilox Roll Maintenance The most critical part of the anilox roll is that it requires a thorough cleaning after each use, and there are myriad of cleaning products and processes. The user of any anilox roll, regardless of whether it is chrome plated or ceramic coated should discuss the cleaning procedures with the anilox roll manufacturer. Manual cleaning. Ultrasonic and soak methods Pressure washing Offset Printing This process is undertaken when the quantity of sheets is medium to high This process is for very fine printing, normally used for multicolor printing. Printing plates are very reasonable facilitating frequent changes in jobs. This process of printing uses printing plates on flat surfaces. Water and ink is applied to the image on a printing plate which is chemically treated so that the colors, types and shape on the plate will accept ink. The most common kind of offset printing is derived from the photo offset process, which involves using light-sensitive chemicals and photographic techniques to transfer images and type from original materials to printing plates 11
Advantages of offset printing compared to other printing methods include: Consistent high image quality. Offset printing produces sharp and clean images and type more easily than, for example, letterpress printing. this is because the rubber blanket conforms to the texture of the printing surface. Quick and easy production of printing plates. Longer printing plate life than on direct litho presses because there is no direct contact between the plate and the printing surface. Properly developed plates used with optimized inks and fountain solution may achieve run lengths of more than a million impressions. Offset printing is the cheapest method for producing high quality prints in commercial printing quantities. Offset printing 12
Digital Printing It generally requires less waste in terms of chemicals used and paper wasted in set up. The colors can also be difficult to adjust or predict since the colors of the image to be printed might be different on the computer monitor. This process is the most favored because of its high quality prints and quick printing process from computer directly to the printer. Plates are not needed on digital printing so it needs lesser man power. Digital Printing Images are sent directly to a printer using graphics software such as InDesign or Illustrator, and digital files such as PDFs, for printing in an office environment. It is ideal for demand printing jobs, variable printing and fine art printing. This technology is expensive but it is picking up and this is the future. 13
Digital printing process 14