Offset: web printing versus sheet-fed printing
Most marketers have experience of printing catalogues and other promotional materials, which were made in the technology of offset printing. Many of them, however, would not be certain of which printing technique was used. It is a pity because each technique yields specific benefits for the market and their company. It is worth boasting of new savings, the shortening of lead time or using innovative refinements – the selection of a suitable technique will allow to execute these goals with future printing projects.
This article will help you to understand the world of offset and allow a more conscious direction of your print work to suitable print supplier with web offset presses or sheet-fed specialization.
Offset is currently one of the most frequently used printing techniques. Although manufacture seems costly, with suitable outlays this technique proves the most effective in economic and qualitative terms.
Offset printing is an industrial variation of flat printing allowing the manufacture of high-quantities of copies, ensuring the best quality and relatively low prices. The greater quantity of copies produced results in a lower final price of a single copy, because the cost of manufacture preparation is spread over more copies.
The advantages of offset printing
Offset printing allows the best colour reproduction. Using this technology, works of the highest quality are printed – exclusive magazines, catalogues, albums and other promotional materials, whose quality is to reflect the company’s image. However, it is necessary to remember about minimum input. Offset printing proves perfectly useful with a quantity of at least 1,000 sheets of one layout. Offset also gives the capability to print on other bases than paper. It allows handling colours in the printing process and using additional Pantone colours, such as gold or silver. In this technique there is also no problem to make one- or two-colour prints, preserving the highest quality of a printed product.
Web offset printing versus sheet-fed offset printing
The final cost of a product printed with this technique is also dependent on the type of offset printing. Most of several thousand printing houses in Poland have sheet-fed machines as their plant, so they offer more sheet-fed printing. Only few printing houses can boast about offset web presses. These machines are very expensive to purchase and on account of their dimensions need an immense amount of space in the production hall.
In sheet-fed offset printing the paper has the form of a sheet, which is printed with offset inks of high viscosity fixed by absorption and polymerization, and in the case of UV and hybrid inks by polymerization initiated by ultraviolet. After printing, sheets of paper must dry before the following processes, which makes production’s lead times longer. After a suitable time needed for ink to dry, printed sheets are subsequently refined with foil, UV or without additional special finishes they are folded to the final format. The folded sheets are then transferred to the post-press department for saddle stitching or perfect binding.
Web offset presses use paper from a roll, which is printed with inks intended for a specific type of printing. We distinguish two ways of web offset printing:
- Coldset web offset: ink is fixed by absorption into paper
- Heatset web offset: ink is fixed by absorption into paper and evaporation at high temperatures
Coldset web offset is used in printing less demanding products like newspapers or supermarket flyers. Whereas, heatset web offset printing is used for the high-quantity printing works, such as periodicals, magazines or catalogues. The other technique is used particularly for publications of the highest quality printed on better paper.
The distinctive feature of heatset web offset machines is a very high speed of printing, four or five times higher than in sheet-fed printing, which allows to complete the order faster in comparison with sheet-fed printing. Additionally, directly in the machine, after the printing process, there is the automatic folding system, turning sheets into the final format product. It eliminates additional processes, which are essential in the case of sheet-fed printing, where we obtain a printed non-folded sheet. Thanks to the faster process of printing and folding directly in one process, web offset printing is more economical and allows proposing to the customer much lower unit prices than in the case of sheet-fed printing. Additionally, paper in a roll is cheaper when purchased than sheet paper.
An important aspect related to web offset printing with the heatset web printing method is the drying of printed paper in a special heating unit. Drying causes paper to shrink slightly, and then, after finishing production, it starts to gain moisture again from the air and the paper starts to “come out” from under the cover. This effect is common. When we decide on this method, it is worth remembering that, as a result of the production process, the inlet of a magazine or a catalogue can protrude from the cover by about 1 mm. It is not the fault of the unsuitable trimming of the cover, because after binding, the whole, that is the cover with the centres, is trimmed to the same format in one binding process. The distinctiveness of the material, that is paper in this case, decides that paper shrinks first passing through a heating unit, and then external factors start to affect the paper, for example moisture and it starts to gain volume. Of course this effect arises only when the work is made with two techniques – the inlet printed with web heatset press and the cover, for example due to high paper weight and the planned special finishes, is printed on a sheet-fed press.
The wrong fibre
Another aspect is fibre direction in the paper. In the web offset printing, paper fibre runs along the band of paper. In sheet-fed printing, it is possible to order paper with suitable fibre direction, so the fibre direction can run parallel to the ridge in the finished product, which causes ease in browsing through a catalogue or a periodical. In the web printing, there is no such possibility and with some non-standard formats, fibre direction in the finished product may be transverse. In the case of saddle stitching, the fibre direction does not greatly affect its use. In the case of perfect binding, however, it is the case. Then when browsing through this publication the paper strains, which slightly impacts the quality of using a given publication. So if we decide on web offset printing of some magazine with a non-standard format, and we plan perfect binding, it is worth making sure that fibre direction is suitable. In the case of transverse fibre it is worth requesting a printing house to send a sample copy with transverse fibre to assess if it suits us.
Which option to choose?
When choosing a sheet-fed or a web offset printing it is worth starting from the quantity of copies that we want to print and the paper selection which matches our expectations.
Web offset printing presses require a quantity above 20 thousand copies, then it is really profitable. If we have an input suitable for the web, then it is necessary to ponder the choice of paper. Normally, printing occurs on a roll with paper from 42 to 130 g/m2 and it depends on the technical facilities of a printing house. It is possible to choose coated and uncoated paper of worse or better quality, including art paper. This technique is used to print magazines, periodicals, catalogues. The format is limited by cutting off and the width of a role. The standard format in web offset printing is usually A4 format, but – depending on the technical capabilities of a given machine – it is possible to obtain various final formats.
Uncoated and coated paper is used for sheet-fed printing. The variety of sheet paper is very great. Paper weight mostly ranges from 60 to 350 g/m2. The lowest quantity profitable for the customer for sheet-fed printing run is approximately 1000 sheets, and the upper limit – depending on the budget and lead time – unlimited. Conventionally, however, above a quantity of 20,000 copies the customer is recommended to use web offset printing – of course with the assumption that a given printing house has these capabilities. Sheet-fed printing is used in the printing of books with lower inputs, albums, folders, special catalogues, periodicals or leaflets with high paper weight. A sheet of paper has a specific size, and after folding, it is possible to obtain a specific number of pages of a specific format.
The choice between web offset printing and sheet-fed printing is primarily an economic question – wanting to optimise the costs, it is worth asking about all possible options. Sometimes a slight change in technical details, can be translated into finances and generate big savings in the budget.
A web offset printing or a sheet-fed offset printing?
Web heatset offset printing:
- a very beneficial price per copy with medium and large quantities
- higher speed of printing (35-55 thousand sections per hour)
- elimination of additional processes (after printing we obtain folded section ready for binding)
- capability of obtaining a finished product (for example finished glued promotional leaflets)
- high quality of printing
- no capability of printing on paper above 130g/m2
- necessity to wait for paper about five – six weeks
- a limited number of possible formats
- no capability of using special finishes in the inlet
Sheet-fed offset printing:
- high quality of printing
- fast availability of paper
- selection of suitable fibre direction
- a capability of printing any format
- a capability of using any special finishes
- an equal length of a cover and inlet
- a capability of using additional colours (Pantone)
- a lower speed of printing (7-10 thousand sheets per hour)
- the necessity of additional processes after printing like folding
- the necessity of the drying of sheets before the finishing processes
- not profitable with medium and large quantities
- a long lead time of the production for medium and large quantities
- a limited capability of printing on paper with low paper weight
Elanders Poland has web presses (heatset and coldset) as well as sheet-fed machines so we can objectively recommend to our customers the printing technology tailored to a given work.
Article: Printing & More. Elanders Poland Magazine No. 1.