Answer:A damping unit is a roller system in an offset printing press which controls the distribution and flow of damping solution
Question: What is a Densitometer?
Answer: A densitometer is a gauge used to check eg dot gain, blackening or full-tone density. Can be used to measure both film and look-down surfaces.
Question: What is Density?
Answer: Density is a measure of tone range in, for example, colour printing of a particular paper or in a slide original.
Question: What is Digital Printing?
Answer: Digital Printing is a process whereby information is transferred direct from the computer to the printing press and direct to paper.The technique is very similar to a standard desk-top printer and the image can be altered using variable data before every new run. Collective term for various machines and processes, mainly used for low volumes due to cost effective make-readies, but more expensive running costs. Does not involve any printing plates or film therefore is suitable for variable data. Some digital printing machines use a very fine, dry toner, similar to photocopying using CMYK powders. The toner is electrically charged and paper is given the opposite charge. Powder is attracted to the paper in image areas then heat fused onto the paper resting on the surface. Because heat plays an important part in the printing process, papers have to be specially formulated with moisture content, limiting the choice of papers available. Also textured, uncoated stocks are not suitable. Normally A3 sheet sizes or can be 12 inch web printed. Examples of machines are Xeikon, Docutech and Chromapress. Also substituting ink for powder as in Indigo printing press, the principle of process is the same. Inkjet digital printing involves spraying liquid ink onto the paper in fine droplets, similar to dots in Litho, using electrical charges to guide them, again limited stocks of paper available. Usually used in Digital Proofing.
Question: What is Dot Gain?
Answer: Dot Gain is the change in the size of a screen dot at the various stages from film to finished product. Given as a percentage.Images have to be adjusted to compensate for dot gain in connection with4-colour separation. Reduction in the size of printing dot is required to compensate for growth from ink bleeding and transferring from printing plate to blanket. The greatest dot gain happens in mid-tones i.e. 50%, and can vary between 15% and 40% depending upon blankets used, ink, back pressure, screen ruling, coverage and paper used i.e. uncoated papers require more compensation due to dot gain experienced with these papers. Dot gain can reduce contrast in an image which is the difference between the white and black areas. Therefore it has to be compensated for in the reproduction process.
Question: What is Drying Powder?
Answer: Drying Powder is a powder sprayed out between the printed sheets in the page sorter so that ink does not smear onto subsequent sheets. A column of air is created between the sheets. Also called spray powder.
Question: What is Dusting?
Answer: Dusting may occur in the printing process as particles are released from the surface of the paper.
Question: What is a First?
Answer: A First is the first side of the paper to be printed on.
Question: What is Flexography?
Answer: Flexography is a typographic method in which the printing parts are higher than the non-printing. The printing for me is made of rubber or plastic material and is called a flexo stereotype. Similar to letterpress, the plate transfers ink directly to the paper. Flexible plates are attached directly to a plate cylinder. Used in the production of packaging using less viscous inks to facilitate high speed printing. Not as high quality as litho.
Question: What is FM Screening?
Answer: Frequency Modulated Screening is an alternative, more accurate term for stochastic Screening.
Question: What is a Fountain Roller?
Answer: A Fountain Roller is a roll in the printing system that transfers water from a font tray.
Question: What is a Fount Solution?
Answer: A Fount Solution is a composition of water and chemicals used in offset printing to distinguish printing surfaces from non-printing.
Question: What is Gravure?
Answer: Gravure is a printing method in which the printing surfaces consist of cells etched or engraved into a copper plated cylinder used in a cell pattern similar to the printing dots on a litho plate. The cells are filled with ink and the ink is transferred to the paper as the cylinder is pressed against the paper with a back pressure cylinder. Most suitable for large runs and primarily used for printing magazines and packaging. High quality printing using low grammage coated papers. Not suitable for uncoated papers.
Question: What is Hardening?
Answer: Hardening is the second drying phase in the printing process in which the ink is dried e.g. by exposing the printed sheet to ultra violet light (UV hardening) or by adding a catalyst to the ink immediately after printing which causes the binding agents molecules to solidify
Question: What is Isopropyl Alcohol?
Answer: Isopropyl Alcohol is added to the damping solution in offset printing in order to reduce the solutions surface tension and achieve a better balance between moisture and water.
Question: What is Letterpress?
Answer: Letterpress is a typographic printing method in which a flat printing forme is used, usually made of a hard material such as lead, zinc or wood, although a flexible polymer material may also be used.
Question: What does Make Ready mean?
Answer: To Make Ready is a general term for different preparation tasks that have to be done in the printing process before producing an acceptable sheet.
Question: What is a Measuring Strip?
Answer: A Measuring strip is a special measuring panel consisting of small full-coverage colour plates which are printed and then cutaway. The measuring strip is used to check the print quality parameters in the different panels.
Question: What is Offset Printing?
Answer: Offset Printing is a lithographic printing method in which the ink is transferred from the printing plate indirectly via a rubber blanket to the paper. Both the printing and non-printing parts are at the same level on the plate. It is based on the interplay of the surface tension between water and ink. The exposed parts of the printing plate act as water absorbing(non-image)and the unexposed areas (image areas) absorb ink and repel water.Damping or fount solution is vital to the lithographic print process ensuring ink is only applied to the printing areas of the plate using surface tension asa vehicle.
Question: What is Picking?
Answer: Picking is an unwanted phenomenon whereby the printing ink tack causes paper fibres to separate from the paper surface. Can produce unwanted dots on the printed surface.
Question: What are PMS Colours?
Answer: PMS or Pantone Matching System is a reference system for specifying shades or colour in ink. Primarily used for Indexed colours in printing.These are pre-mixed ink colours and metallics used for special colours not reproducible from the four-colour printing process i.e. logos for exact matching.
Question: What is Press Roll Nip/Roll Nip?
Answer: This relates to unwanted deformation of a paper which occurs as it passes between the rolls of a press.
Question: What is Printing?
Answer: Printing is the production of printed products in identical copies by the transfer of ink from a printing forme.
Question: What is Printing Opacity?
Answer: A papers opacity changes during the printing process. Oil and grease in the ink reduce the papers ability to refract light which in turn normally reduces the opacity. The result can be that print shows through to the other side of the paper, this is known as show/shine through.
Question: What is a Rubber Blanket?
Answer:A Rubber Blanket receives the image from the printing plate in an offset press and transfers it to the paper
Question: What is Screen Printing/Silk Screen Printing?
Answer: Screen/Silk Screen Printing is a printing method primarily used for large formats. The method involves cutting out a stencil which is supported by a cloth. The cloth is then tensioned inside a wooden or metal frame and ink is then added and spread out using a doctor blade, and thereby pressed through the cloth into the surfaces not covered by the stencil.
Question: What is Second?
Answer: Second is the reverse side of a sheet of printed paper.
Question: What is Sheet Offset?
Answer: Sheet Offset is an offset printing method. This is the most common printing method, described as placing a pallet of paper sheet into one end of a printing press and collecting them at the other. Four colour presses have four units, five colour presses have five units etc. Ink ducts are filled with ink and adjusted to determine how much ink is applied to the printing plate. Image is transferred from the printing plate to a rubber blanket which then transfers the image onto the paper stock. Back pressure is adjusted to achieve correct density of ink on the paper.
Question: What is Smearing?
Answer: Smearing occurs when ink from one sheet smears on to the next. The phenomenon can occur if too much ink has been used, or if it has not yet dried, this is also called set off.
Question: What is Surface Tension?
Answer: Surface Tension is a physical phenomenon, a typical result being that the damping solution in the offset process does not wet the plate properly without alcohol additives.
Question: What is a Tint Plate?
Answer: Tint Plate is an even tone of shade over a surface, often in screen dots.
Question: What is Typographic Printing?
Answer: Letterpress and flexography are examples of typographic printing, i.e. ink transfer takes place from raised parts of the printing forme.
Question: What is Varnishing?
Answer: Varnishing is a post-production technique primarily used to create a shiny surface on a printed product, thereby enhancing the aesthetic effect. However, the technique does not provide much protection against dirt and wear. Varnish is added either in a standard inking device orin a special varnishing device in an offset press.
Question: What is Waterless Offset?
Answer: Also called Dry Offset. This relates to offset printing without the use of damping solution. Instead a special silicone-coated printing plate is used.
Question: What is Web Offset?
Answer: Web Offset is a printing method whereby the press is fed with paper on a reel, as opposed to sheet offset which uses sheets. Used for high volume printing. Two types of presses are used, heat set and cold set.Because of the high speed of printing, short drying times are a pre-requisite of web printing. Heat set uses a heat dryer or UV (Ultra Violet) light to dry the ink. Cold set uses fast drying absorption inks. Back pressure comes from the opposing colours blanket, as perfecting is the norm (see perfecting). Therefore back pressure on a web press is not a effective as sheet fed.
Question: What is Wet on Wet Printing?
Answer: Wet on Wet printing involves printing several inks consecutively before they have had time to dry.
Question: What is Xerography?
Answer: Xerography is a printing technique found in laser printers, photocopiers and digital machines. An electrostatic printing technique based on the difference between positive and negative electrical charges.
Question: What is Back Pressure?
Answer: Back Pressure plays an important factor in the ink transfer and fill of the paper. It refers to the pressure between the blanket cylinder and impression cylinder. Reducing the distance between the two, where the paper passes through, increases the pressure.
Question: What is Perfecting?
Answer: Perfecting is printing both sides of the paper in a printing press before it is fed into delivery.
Question: What is Set Off?
Answer: Set Off is terminology given to the process when ink transfers from one printed sheet to another when pressure is applied before the ink is dried. Set Off Powder is sprayed onto the sheet to avoid this problem, allowing air to penetrate the stack facilitating drying. Coarseness of powder varies for coated or uncoated papers i.e. finer for coated papers.
Question: What is Thermography?
Answer: Thermography requires a Printing Press fitted with aRelief Aggregate and Heater. After normal printing a chemical powder is sprayed onto the wet ink. The sheet is then heated which causes the printed areas to swell into a relief gloss image. It then dries and hardens. PMS or Indexed colours can be used. No further embossing or foiling can be applied to these areas.
Question: What is a Back Pressure Cylinder?
Answer: A Back Pressure Cylinder is the pressure absorbing cylinder that pushes the paper against the blanket. On uncoated stocks, back pressure should be increased by 20 -40 micrometres.
