We were given a presentation and small task today set by our tutor about the different types of screen printing that can be used within industry and the advantages and disadvantages of each of them.
there are many different processes used within industry and they are all used for different reasons mainly because of different costs and user ability. as designers we work to a process called the digital work flow, this is operated in three different sections, prepress, printing and finishing.
the printing processes:
- Offset Lithography
- Screen Printing
- Digital Printing
the finishing processes:
- cutting and trimming
- machine folding
- special finishing
different special finishes:
- foil blocking
- die cutting
- paper engineering
Flexographic Printing is used as a mass-production print system capable of printing mono- and multi-colour images onto almost any kind of product. Originally developed in the early part of the 20th century for the cheaper web-fed packaging market using hand-cut rubber plates and methylated spirit based aniline inks, it has naturally adapted to printing on cellulose, plastics, metal foil, etc. becoming a major method of production in the packaging field, amongst others.
Gravure Printing is a high-volume printing system used to produce quality printed work where initial print runs commence at 300,000-plus copies. It is a unique form of printing requiring large investments to create and maintain plant, consequently there are fewer companies operating in this field than that of offset lithography. The equipment used tends to be very large in size and extremely heavy; there are also major considerations of health and safety associated with the materials used, particularly the inks which are quite volatile. Print runs are huge, and as you will see, printed products can include such items as confectionery wrappings; if you consider just how many of these are purchased each and every day, you might get an idea of the print runs likely to be needed.
Offset Lithography is the world’s most-used professional printing process. It is concerned with the mass production of printed material and can range from low to very-high quality depending upon the demands of the client. As with all of the printing processes it requires that some form of design, layout and production of a master image activity takes place before it can commence its work.
Reproduction of images by dabbing ink or paint through shapes cut out of thin sheets of material is an extremely old form of printing, and our modern screen process system goes back to the early 20th century. Whether for commercial production printing, or as an art form, this process is now used for printing single or multi-coloured images onto a wide range of fibre-based substrates. Equipment required can be quite simple consisting of a frame over which an image-carrying mesh is placed through which ink can be passed to a substrate; equally it can appear more complex when seen within a multi-unit production system.
The latest addition to the main printing processes; still relatively in its infancy, this process is an evolving one which will possibly have considerable impact on the printing production scene in the future. Investment costs for electrophotographic devices are reasonably high but the range of short print runs at economic costs available from these devices indicate a bright future. Thermal and ink-jet devices, as part of this area, can provide a wide range of proofing and one-off print options.
Digital Printing devices come in a wide variety; this Element considers the following:
- Thermal printers – Direct and Transfer
- Thermal Dye Diffusion
- Ink Jet
Thermal printers – Direct and Transfer
operates in a very similar manner, controlling a thermal print head to melt spots of dry ink on a donor ribbon which are transferred to the substrate.
Thermal Dye Diffusion
This system is often known as dye sublimation. Kodak, Tektronix, 3M manufacture such systems. Dye-sublimation is a colour printing technique at the ‘high end’, requiring special transfer and receiver materials.
There is a wide range of ink jet devices available – they are used for home and commercial purposes. Liquid ink jet printing gives bright, highly saturated colours but requires special printer papers – if plain paper is used colours may lose brightness as ink soaks into the paper.
There are two main types:
- Continuous flow
- Drop-on-Demand (Bubble jet and Piezo)
Continuous flow: the print head directs ink droplets in a continuous stream towards the paper. Ink is deflected into a waste tray unless a particular ink spot is needed on the paper. Ink is continuously pumped from the print head for the full duration of the print, whether it is needed or not – so this incurs high running costs.
Drop-on-Demand: here, ink-jet droplets are directed at the paper only as needed through a pulse mechanism. In bubble-jet systems, the ink is heated and vapourised, forming a bubble which expands forcing ink from a nozzle towards the paper. Heat is then switched off, the bubble shrinks, and more ink flows into the print head from a reservoir.
These devices operate on the basis of selective electrical charging of a surface to produce a latent image which will attract (or repel) charged toner particles.
the basics of these systems is that of the photocopier; they use drums or metal plates coated with photoconductors which are given an overall electronic corona charge, which are then exposed to an image by light which removes the charge in the non-image areas. Then liquid or powder toners are attached to the image areas (the remaining charged areas on the plate or drum), transferred to the substrate and then fused by heat or other fixing methods.