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Print Finishing

Graphic Design, X³

Print Finishing

Print Finishing
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Print Finishes

on uncoated, fine and artist papers

 

Projects | Various print finishes on natural, fine and artist papers.
Clients | Various clients.
Years | 1996-2020.
Print finishing | Print finishing of uncoated, fine and artist papers with high and low embossing, hot foil stamping, steel engraving, hot wax sealing and special hand binding techniques.
Services | Graphic Design, Production.

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Background information
for printing on uncoated, fine and artist papers

 

Working with natural, fine and artists’ papers, which are often difficult to process, requires a certain amount of experience with high-quality printed products in pre-press, offset printing and bookbinding. The following tips are the result of many years of production experience.
 
Print grid
Many manufacturers of uncoated papers recommend a fine screen of up to 60 l/cm. Experience shows that this is very risky. At least with uncoated papers, for example with a lot of hemp, cotton or rag. A medium screen up to a maximum of 54 l/cm is recommended here. 60 l/cm is only recommended if the image motif is intentionally run in for design reasons. Especially with uncoated papers the following applies: the finer the screen, the stronger the dot gain. And: the more printing inks are needed for the image motif, the more the motif will run.

Frequency-modulated screens (e.g. Agfa Cristal screen) do not produce better results with heavy uncoated papers. This screening method is better suited for coated and cast-coated papers.
 
Point increase
Natural papers have a noticeably stronger dot gain than coated papers. Therefore, the dot gain of uncoated, fine and artist papers is crucial for the print result. It is not uncommon for some heavy uncoated papers to have up to 30% dot gain ( ! ) in 4c process printing with a 60 screen. Proofs deviate greatly from the print run and therefore make no sense. There are therefore only two ways to compensate for dot gain: First. The 08-15 method. The exposure of the data is done with automatic correction of the gradation curve (especially mid tones) by the software of the imagesetter. Always select the correct paper quality in the software menu. However, the print result is not predictable with this method and only very expensive devices have this menu option.

Secondly. The optimal method. The dot gain is already corrected during image processing. A print of the motif on production paper serves as a sample. The dot gain can thus be optimally corrected. However, one should bear in mind that an offset press (e.g. a Heidelberg Speedmaster) has a different contact pressure and a different ink application than a press proof. This should be taken into account when measuring the print control strip with the densitometer.

Printing presses with a pointed dot (such as Planeta P24 SW or Heidelberger Speedmaster 52) are better suited for printing on uncoated papers.

Colour areas
Large colour areas (e.g. coloured endpapers) in 4c scale printing are not recommended. Here, too, the printed colours differ considerably from the monitor colours and the 4c colour tables. In addition, due to the consistency of uncoated paper, areas of the same colour that are repeated in the printed matter may have different colour tints. Large colour areas from the 4c scale must therefore be printed – like picture motifs. This problem is largely avoided in true colour printing.

Analogue film exposure
Films are – despite digital pre-press – still in use in some print shops today. The data should only be exposed in the highest and finest resolution. At this point it should be pointed out that many exposure studios and printers still confuse the dimensional systems lpi or lpc. Therefore, always make sure that the correct screen ruling is set during exposure. Likewise, care should be taken to ensure that only flawless and fresh chemistry is used for development. In any case, the opacity or opacity of the film and especially the dots must be checked. Are they hard? Are they damaged? Are the registers accurate? In the case of duplex, triplex or quadruplex motifs, has the screen angle been rotated? Uncoated paper is less forgiving than coated paper.

Plates
Only use high quality plates. The films must be copied onto the plates in such a way that there are no halos and the dot remains as hard as possible. Again, only use flawless and fresh chemistry when developing. Make sure to check the plates for dust, dirt, halos and sharpness!

Digital plate exposure
We have had good experience with the use of CtP plates when printing on highly absorbent materials. We expose our printing plates with the Heidelberg Trendsetter, among others. Hollow copies, dot widening due to incorrect exposure, cut edges etc. are of course not an issue with this process.

Running direction
Unfortunately, most natural, fine and artist papers are only available in the unfavourable print format 70 cm x 100 cm narrow web. In order to minimise costs here, it is no problem to print in the wrong running direction, especially on heavy uncoated papers. Differences compared to printing in the correct running direction are not noticeable.

However, this does not apply to bookbinding. Here the principle applies: the bookbinder must determine which running direction he needs for processing. Because the wrong running direction can have disastrous effects on uncoated papers during bookbinding processing. This is particularly true for creasing, folding, laminating and especially gluing. For larger printed matter, such as annual reports, the production of a 1:1 dummy is essential

Climate and storage
Natural, fine and artists’ papers should be stored a few days beforehand in the same environment in which they will be processed. And be careful: incorrect storage will cause edge waves or warping. Especially during transport during the cold and wet season, there is a particularly high risk that the stack humidity will deviate greatly from the ambient temperature. Therefore, the paper must not be unpacked until the temperature has been adjusted to the processing climate.

Proofs
The printing results of a press proof can deviate greatly from the print run with uncoated papers. The contact pressure of an offset press (e.g. a Heidelberg Speedmaster) is different from that of a press proof. The same applies to ink application and colour consistency. The correlation between the press proof and the production run must be discussed with the press proofing company in advance. Not only must the same paper be used for the press proof, but also the same ink. Of course, the best solution is to print the problematic motifs on the offset press that will later be used for the production run.

Accuracy of fit
If the accuracy of fit of the motifs or the design is very important, never print the same sheet in two different passes! 4c printing on a one or two-colour press is therefore very problematic. Natural papers work very hard. Especially papers that contain a high percentage of cotton or hemp. If heavy uncoated papers are printed in the wrong running direction, register differences (inking unit 1 to inking unit 4 and up) can occur

Printing inks
For uncoated papers, use only fast-absorbing, oxidative drying inks, which are, however, only available in scale printing. Add drying agent if ink consumption is high. Never use fresh inks (inks that can remain in the press overnight). Fresh inks cause a blotting effect. Nova and Turbo Board inks are recommended for scale printing. The optimal black ink for uncoated papers is an intensive black with strong pigmentation. Here you have the best possibility to optimally regulate the colour during printing.

If light HKS or Pantone special colours, especially light Pantone colours, are printed, wash the inking units thoroughly! Old inking units usually have dried ink residues in the brittle rollers that cannot be removed even after repeated cleaning. The inking units distort the true colours considerably. Experience has shown that pastes or special chemicals are no longer helpful in obtaining optimally light pantone shades.

Unfortunately, true colours (e.g. HKS and Pantone) have only been available as fresh colours for years. This means that 5 % dry matter must be added. The optimal solution, however, is to have your supplier mix a fast-absorbing, oxidatively drying special colour. From approx. 15 kg, this is done at no extra charge. Below that, you have to reckon with an additional charge of approx. 150-200 euros per colour

Contact pressure
If possible, use a compressible blanket with a hard lift. With heavy uncoated papers (e.g. Arches Expression by Arjo Wiggins) increase the contact pressure to a maximum, even if this contradicts popular opinion. This gives the images more drawing. Increase the pressure so that the typography does not float.

Fount solution additive
Do not use alcohol substitutes or other dampening additives, but only alcohol dampening with a maximum concentration of 10%! The pH value for uncoated papers with oxidative drying inks should be slightly above normal. A pH value of 5.5 is ideal here.

Dust
Heavy uncoated papers often generate a lot of dust during the printing process. To achieve an optimal print result, the inking units must be cleaned regularly. This is especially true for long print runs.

Drying
It is best not to use print dusting during the print run! Properly printed uncoated paper takes longer to dry. The printed paper must not be stacked too high, otherwise motifs or colour areas will be deposited on the next page.

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Wolfgang Beinert