Printing Ink Methods
Letterpress printing – Since 13th century the oldest method of printing carried out is Typographic or Letterpress printing.It is a profit making printing technique. It involves several stages in printing process such as: composition, imposition and lock-up, and printing. In this method images are repeated on raised surface or roll of paper with undeviating impression of an ink.
In this process relief type of printing plates is used for printing images. The Letterpress printing inks are loaded in the roller passing to an ink bed and fresh films choose for sheet of paper. And then that sheet of paper pressed into a type, moved back and forth and finally removed. After that a new sheet again inserted.
Letterpress printing machines are of two types:
Flat-bed Cylinder Printing – The ink is passed into the plate cylinder with the help of inking roller and an ink fountain. With horizontal or vertical bed the plate is locked and passes over ink roller and next to the substrate. From feed stack to the delivery stack the substrate moves and passes to the region of impression cylinder. As the cylinder moves in a single revolution over the vertical position bed so that substrate and cylinder works in a reciprocating movement. This flat bed cylinder presses has the functioning related to platen press and can print one or two color impressions. The print stock is huge as 42 inches by 56 inches. This machine can work with an hourly production rate and operate slowly with not more than 5000 impressions. Because of this reason nowadays rotary letterpress or lithography is used by most of the Letterpress printing type of press.
Rotary Letterpress Printing – Rotary Letterpress Printing depends on carrying plates for curved image. Some of the trendy variety of plates used is stereotype, molded plastic or rubber and electrotype. While printing on coated papers this rotary letterpress utilize heat-set inks with high-velocity hot air type which is operational with dryers. These are further classified into two types as sheet-fed and web-fed. Web-fed is popular type compared to sheet-fed for letterpress printing. Largely it is used for newspaper printing. It is designed in a way to simultaneously print on both sides of the web. In general they can print across the web upto 4 pages. Still a few new presses print across a 90 inch web upto 6 pages. Magazine printing, long-run commercial, packaging and books utilize rotary letterpress technology. Letterpress printing machines put forth unpredictable amount of pressure on the substrate based on the printing image elements and size. Require secure monitoring while the machine is working and necessitate certain adjustments. So that impression pressure makes them attractive. Some of the important chemicals used in letterpress printing such as roller washes, film developers, fixers and blanket are similar to lithography method of printing.
Application : Commercial and specialty operations which include stamping, imprinting die cutting and so on will make use of Letter Press printing. Some of the printing applications include embossing, posters, hot leaf stamping, letterhead, business cards, company proofs, forms, billheads and others.
Screen Printing – The Screen Printing technology is grown popularly by printing flags, banners at the commencement of First World War in 19th century. This method practiced printing on stencil and absorbent fabric which generates sharp edged images. Either polyester or silk acts as a woven fabric which is stretched out in an aluminum or wooden frame including a part of porous and screen. Then it is positioned on top of a piece of paper. And a non-permeable substance (a stencil) placed on areas of the screen. After that ink is placed and swelled uniformly across the screen using a rubber blade. So that the ink in the screen spread on to the paper or fabric through the open spaces. Finally the screen lifted up and after cleaning it can be re-used. This process can be used to screen print multiple colors on the same surface. First dry the ink on the screen and repeat the screen printing process using different colors on another screen.
Application : Many diverse industries make use of screen printing such as Printed electronics, including circuit board printing, thick film technology, Clothing, Balloons, Medical devices, Snowboard graphics. Some of the printing applications include Signs and displays, Textile fabric, Product labels, ceramics, metal, wood, paper, glass, and plastic.
Flexography Printing Process – This type of Flexography Printing is extensively used in printing packaging materials. Different types of materials including plastics, sacks, and papers make use of this technology to print on variety of products such as plastic bags, corrugated boxes, multi-wall sacks, paper sacks, folding cartons. The machine has flexible printing plates made up of plastic or rubber. So that the inked plates rotates on the cylinder with raised image to some extent. It transmits the image to the substrate. Printing using these machines provides clear impression image on diverse substrates with high quality.
Types of Flexographic Printing Machine
- Stack Type Machine
- Central Impression Cylinder (CIC) Machine
- In-Line Machine
- Newspaper Unit Machine
These Flexography Printing machines perform simple mechanism and easy adjustment for the use of water-based inks. Flexographic machines use fast drying inks since it has high speed of printing process. Widely these machines are used to print on materials which include foils, paper, and acetate films, plastic. It follows a continuous pattern printing on a variety of absorbent and non-absorbent materials.In this system a substrate is sustained into the machine from a roll. And at last pulled off through an arrangement of printing units. As a result of this activity the picture is printed on the substrate. Each one of the color is given by a solitary printing unit.
Application :It discovers application in high quality packaging, for example newspapers, plastic bags, adhesive tapes, milk and beverage cartons ,self-adhesive labels, disposable cups, containers, envelopes and food and candy wrappers.
Gravure Printing Process – The Gravure Printing technique is utilized for long run printing with more honed, fine and clear images. The common operation includes image readiness, cylinder arrangement, printing and finishing. It is a manifestation of intaglio printing. The image is shaped on a discouraged or depressed surface. The area of the image comprises of honeycomb molded cells that are carved or engraved into a copper cylinder. When the cylinder rolls in an ink pan with the use of a steel doctor blade the extra ink is removed from the cylinder. Then the substrate passes in between the impression cylinder and plate barrel. So that the ink is straight forwardly exchanged to the substrate and image is framed.
Application :Some of the gravure printing applications include printing magazines, flexible packaging, gift-wraps, greeting cards, labels, cartons and others.
Printing Machine – Most of the industries make use of printing machines for advertising print materials, printing magazines and cards. For printing the job the machine functions at a very high speed which have extensive running in nature. It involves fine and sharper images which can print on materials including PVC, PE, PET and paper. Both unwinder and rewinder type of turret is utilized in these machines. Using the printing machines both web discharging and automatic splicing can be done. To improve the drying execution and minimize printing abandons, these machines are outfitted with rapid drying frameworks.
Application :Greeting Cards, magazines, advertising materials including brochures, catalogs, flexible packaging, self-adhesive labels
Offset Printing Process Offset is a printing Process technique in which the inked image is offset from a printing plate to a rubber blanket. Further to the printing substrate 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 on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water-based film (called “fountain solution”), keeping the non-printing areas ink-free.
Offset printing are of two types:
Offset Sheet fed Printing – In this method of offset sheet fed printing through the suction bar separate sheets of rolls or paper moved over the press. This lifts each sheet and drops them onto the place. Sheet fed presses use mechanical enrollment to transmit each one sheet to each other to guarantee that they are replicated with the same image. And the image is reproduced on each and every sheet in same position while the press is running. Sheet fed presses are simply that printed sheet by sheet and appropriate for mid-range applications. This printing system is prevalent for little and medium-sized altered jobs, for example, constrained release books.
Web Offset Printing – Typically long run printing jobs have benefited with the web offset presses considering the speed of printing and finishing time. Web Offset Printing utilize roll of papers in the printing press and run in excess with 5 or 10 thousand impressions. Depending upon the ink drying instance web-fed presses classified as heatset and cold or non-heatset offset web presses. When soaked with paper the ink dries in cold web offset printing. In turn heatset web offset printing use heaters or drying lamps to set the inks. Heatset presses used on coated and uncoated paper while coldset presses cannot print on uncoated paper stock. For example: Newspaper – headset for printing color pages and coldset for printing black and white pages. Since drier can possibly added to coldset presses. Web presses have the benefit of inline capability to cut, puncture, and fold.