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HS-23 SERIES

Ester Resistance of Rubber Materials & Plates
The following hints and advice are primarily for customers using UVACURE for the first time. As mentioned previously, UVACURE Inks demand a suitable quality of roller, blanket and plate. Additionally, unsuitable blankets may be attacked by UVACURE Inks leading to an unacceptable degree of swelling that adversely affects print quality.

We recommend a quick and easy test to proof the quality and suitability of printing blankets and rollers. Apply one drop of UV Reducer to the clean rubber rollers and the printing blanket. If the UV Reducer is absorbed within half an hour or if there is any sign of swelling, the rubber roller or printing blanket will not be suitable for printing with UVACURE Ink.

Certain photopolymer plates may also be unsuitable for UVACURE Inks. Testing prior to use, as mentioned above, should be carried out. In this case, special attention should be paid to the stickiness and/or dissolving of the plate material during to the test.

Drying / Curing Problems
Increased drying speed can only be achieved through increased UV light intensity, whereby the thermal capacity of the printed substrate is the limiting factor, or by adding 1 to 2 % of photo initiator U 0025. Normally, the addition of photo initiators is not necessary because UVACURE Inks are formulated for high printing speeds. The efficiency of the U.V. dryer has to be adapted to each system according to its requirements. The distance from the lamps to the printed surface (focal length) should be perfectly adjusted. As a matter of principle, the U.V. lamps MUST possess the necessary efficiency. Please take careful notice of the lamp life. Reflectors and lamps MUST be clean and therefore have to be regularly serviced. Please observe the manufacturers instructions.

When using UVACURE Inks we recommend a cooling apparatus at the end of the conveyor, so that the cups may be nested at the lowest possible temperature. This will prevent the cups from sticking together and pulling the ink off the cup. UVACURE inks are thermo-plastic (i.e. at higher temperatures, a certain smear may occur which can occasionally be seen at the cup edges). This is caused by nesting cups at excessive temperatures.

Ink related drying problems are normally the result of high film weights. As a consequence, a rub-off of ink in the inside of the cup may be noticed. The reason for high film weights is very often found in the wrong choice of colour or, from an intensity point of view, in the wrong selection of inks. We would gladly supply a higher pigmented ink should colour intensive standards be difficult to reproduce using standard inks. In principle, these higher pigmented inks at normal film weights demand a higher drying time.

Ink Adhesion
Inadequate rub resistance properties as well as lower scotch tape resistance properties on PP/PE, (not withstanding product drying procedures), are very often the result of insufficient or inadequate pre-treatment. It may also be caused by surface oriented additives. In the latter case, an addition of UV Slip Additive U 0035 in quantities of 1 - 2 % is recommended. If this does not clear up the problem, a different substrate should be used. An alternative solution, as far as inks are concerned, is not possible.

Another difficulty is created by the inclusion of anti-static additives in many plastics. These will migrate to the surface and interfere with the plastic's ability to accept the ink. Additionally, these anti-static additives are mainly hydrophilic (absorb water), and can decrease the moisture resistance of the film.

Wet-on-Wet Print / Half Tone Work
For multi-colour printing we recommend the sequence: Yellow-Red-Blue-Black. Normally the tack of the first 2 inks applied should be higher than the tack of the third and fourth inks. If the first 2 are not tacky enough they will be lifted from the cup when the other inks are laid down.

Film Weight
Normally in the dry offset field, the amount of ink distributed onto the rollers is referred to as lay down or film weight. An offset press requires 1 to 1.5 grams per square metre of film weight. High film weights can lead to ink build up on the plates and blankets as well as reduced scratch resistance, adhesion problems and overall curing difficulties. To improve print quality and in order to avoid smudged edges, the film weight must be reduced. Particularly in half-tone work, a film weight in the region of 1 gram per square metre or less is necessary to achieve optimal print quality.

For single colours as well as the most complicated multi-colour wet-on-wet print, it is important to adjust printing pressures and ink ducts to achieve optimal results. Since plastics lack the absorption qualities of paper, (on which high print pressure during the ink transfer can be compensated through the setting effect) increased print pressure on plastics will inevitably result in a push-out of the ink from the original print and distort the image. Even the most skilled printers, reproduction institutions and plate manufacturers must take this unavoidable fact into consideration.

In 4 colour process work, there are two process sets available as follows:

A - When using PANTONE basic colours for process printing, the following UVACURE Inks are recommended:

B - When cleaner process colours are required, the following UVACURE Inks are recommended:

In view of unavoidable technical printing difficulties, we recommend coloured reproductions using the 4 colour process principle in the cup and lid printing field be attempted by experienced printers.

The current technique, which deposits a single colour next to and on top of each other on a single printing blanket and subsequently transfers the combined image to a cup or lid is totally different from the commonly used technology in the offset field. It is therefore highly recommended to select different colours for the multicoloured print, then approach the build-up of the image from a different angle.

In this process the maximum screen value is 54 lines per cm. This degree of difficulty, however, should only be attempted after prolonged technical experience in the printing of half tones. Larger screens (30/40 lines per cm) are ideal to begin with.

It is also advisable to deposit the lightest colour on the blanket first, followed by a darker colour and finishing with the darkest colour.

For example, a combination of yellow, red and black should be deposited as follows:

First Colour            Yellow
Second Colour        Red
Third Colour            Black

Note that by printing wet-on-wet the curing speed of the UV inks decreases. By using the recommended colour order the unavoidable contamination caused by back-trapping will thus be minimized.

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Last modified: March 29, 2004

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