Offset lithographic printing is based on the principle of oil and water working in repulsion. The printer first has to create the printing plates from your supplied artwork file. Modern technique is to use a computer-to-plate (CTP) machine.
The first stage is to create a print ready PDF if artwork has not been supplied in this format. The file is then imposed for print (the pages placed in the correct position on a virtual plate). The imposed file is then ripped. This process splits the artwork file into plate artwork (1 plate for each colour).
The image is then burnt to the plate by lasers and the non image area is then removed when the plate is developed.
There are 2 types of plate with different methods to develop them.
The first is an environmentally friendly method called processless plates (Elle Media Group use processless plates). This method develops the plate using no chemicals. Instead the plates are cleaned and gummed using water based solution.
The second method uses a different plate which requires a chemical developer. Printing plates are made up of two areas. Areas of the plate which are not to be printed (the "white" areas of the paper) absorb a water based fountain solution. When the plate is introduced to the printing ink, the oil based ink is naturally rejected by the areas filled with water. This ensures that non-printing areas remain ink free. The inked image is then transferred (or offset) from the plate to a rubber blanket, and then from the sheet to the printing surface.
While transferring the inked image to a rubber blanket first might seem an unnecessary additional step, it actually serves two important functions. Firstly, the printing plate is quite delicate, so the soft rubber protects it from possible damage during repeated use. And secondly, the flexible rubber conforms exactly to the surface to be printed. This results in a consistently sharp and clear print every time.
In fact, properly developed plates used with quality optimized inks and fountain solution can perform runs of more than a million or more impressions with little to no degradation in print quality.
- Consistently high image quality.
- Quick and easy production of the printing plates.
- Offset printing plates last longer than plates on direct litho presses, due to no contact with the print surface.
- Especially suited to print runs of high quantities.
- Most of the cost lies in press preparation, so the process is expensive for printing small quantities.
Digital printing is an electronic process which uses colour toners instead of inks and imaging drums instead of plates. The printer has four toners and four drums for Cyan, Magenta, Yellow and Black.
Digital print offers a cost effective solution for small print runs. It also offers the opportunity to personalise your print. Every copy can be personalizsed with variable imagery and variable text. Recent technical advances produce quality that is equal to lithographic prints.
- Cost effective for print runs of lower quantities.
- Capable to personalise every copy.
- Automatic collation.
- Limited to flat sizes of SRA3.
Finishing and Binding
Finishing is a broad area which covers anything which is done to a job after it has been printed. Finishing might involve laminating, trimming edges or coating the print surface. Finishing is the process which gives the printed work functionality in the real world - such as mounting a poster into a backlit display, heat transferring an image to a T-shirt, or binding a set of A3 spreads together into an A4 booklet.
Lamination and Encapsulation
A laminate is a thin sheet of transparent plastic which is bonded to one or both sides of the printed paper. It protects the paper from handling and moisture. Lamination is frequently used on the outer covers of company brochures and reports etc.
Encapsulation is similar to lamination but the transparent sheet is thicker and allows much greater protection. A range of different thicknesses can be chosen from, and the encapsulate extends beyond the border of the artwork by 5-10mm. The transparent border seals the artwork inside keeping it completely waterproof. Encapsulation is used for artwork which might be subjected to rainy weather conditions, such as driver's licences or outdoor poster boards.
Trimming simply is the job of cutting a document down to its intended dimensions. Printing presses cannot print to the very edge of a sheet of paper, so artwork is usually printed on larger sheets of paper. After printing a guillotine is used to trim off the excess white borders. Graphic designers set 'bleed' in their artwork to allow for any minimal movement in the printing and cutting process.
Bleed is a commonly used technique in print design. If a background image or colour extends right to the page edge, a designer will extend the element beyond the page boundary. The extension (usually 3mm) beyond the border is called 'bleed.' During printing, paper sheets do not feed into the press in exactly the same position every time. The variation is usually only fractions of a millimetre, but it becomes significant during the finishing stage. It is similarly impossible for a guillotine to cut right down the edge of a design perfectly every time, due to the same margin of feed error. If a page did not have bleed and the guillotine blade cut a fraction outside the page border, a hairline white line would be visible instead of the image carrying all the way to the page edge. Bleeding background elements like colours and pictures beyond the trim border corrects this problem. Crop marks printed outside the artwork area help the cutter by displaying where the page ends and the bleed begins.
Much like trimming is cutting the printed piece to its finished size. You can die cut your job to nearly any shape from a simple circle to a more intricate design such as a butterfly.
Another use is die cutting with lugs in, this allows you to have your shape within a bigger sheet and push out at a later date – often used with offer cards in leaflets.
Is a series of dots designed to allow you to tear part of your finished item with ease. There are a variety of perforations depending on the application.
Folding and Creasing
The most common folds can be found in our Paper Folds Guide
Is a finish applied over the printed piece or a lamination. UV varnish can either be of gloss or matt finish and unlike a laminate can be applied to a specific area of the print, eg. over a logo in the same shape.
Binding is the method used to gather and finish jobs of multiple pages. These range from stitching to wiro-binding.