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HS-23 SERIES

Back Trapping
Back-trapping is actually the event of one ink being transferred onto the plate of another colour then back-trapped to the rollers. This contaminates the ink in the ducts and affects the overall colour that is trying to be achieved.

If the second or third colour does not trap on the ink already deposited on the printing blanket, a small correction is required. By using UV Reducer, the tack of the subsequent darker colour is reduced and it will trap satisfactorily on the ink film already deposited. Such additions should be made very carefully at a rate of 1 - 4%, which in most cases will prove more than adequate.

UVACURE Inks have been formulated to a narrow, limited tack range which aids in 2 colour printing. Based on experience, the correction of tack is mostly required when adding a third colour.

Large wet-on-wet prints should be avoided. In this instance, the danger of colour contamination's are particularly acute and under some circumstances the tack may have to be adjusted on the two colours already printed.

When printing wet-on-wet half-tone colour, the dirtying of subsequent colours is negligible. The biggest single cause of contamination in the wet-on-wet printing field is excessive print pressure. Adjustments to ink should only be viewed as adding the finishing touches to achieve optimum results. In addition to the effects of excessive printing pressures, increased printing pressures will also adversely affect ink and colour intermixes.

For optimal adjustments in printing wet-on-wet, each layer should be adjusted individually and be printed with the least possible pressure. In this way, errors and incorrectly adjusted pressures may be easily detected. At the point of pressure, it is advisable to first print two colours and then the subsequent colours later. In this way it is easy to recognize which ink requires an adjustment of tack.

Printing of Transparent and Coloured Substrates
For multi-coloured reproductions and wet-on-wet prints, white substrates are best suited. However, there has recently been a trend to use transparent substrates. This trend, however, which is of growing importance has created additional printing difficulties. On transparent substrates it is increasingly common to print UVACURE white as a contrast colour to dark filling contents (for example, chocolate dessert). It is therefore desirable to provide increasingly opaque and more highly pigmented whites. As mentioned previously, higher pigmentation inevitably leads to difficulties associated with transfers and adhesion. Highly pigmented inks have a reduced content of varnish, which is usually the carrier of the key adhesion capabilities.

Specific problems will arise when printing coloured inks on transparent cups which are intended to carrying goods of different colours. White fillings, such as yogurt and cheese, have little effect on the printed result.

UVACURE Inks, with the exception of white, are manufactured from organic pigments which have a high transparency. They are of prime importance in multi-colour and half-tone printing. Existing Food, Health and Safety regulations prevalent in the world, do not permit the use of certain inorganic pigments in inks intended for cups and lids intended for the food packaging industry. Certain inorganic pigments do, however, offer a greater degree of opacity. In view of this fact, transparent coloured ink can and must be adjusted with an adequate addition of white to insure a certain degree of opacity. However, by increasing the white content and therefore the opacity, the original colour shade is altered. Normally, if a large percentage of opaque white is added to a colour, the final printed colour will be a different shade than the originally approved colour. It is therefore necessary to accept certain tolerances and minimum opacity to ensure a given quality of print. Any additions should be started by adding 10 % (1 in 10), and should be increased gradually in stages of no more than 10 %.

The aforementioned also applies to coloured substrates, especially if the colour is very bright. Additionally, we would like to point out that if a certain colour has been achieved by silk screen, the results achievable by the offset printing technique will vary widely.

Finally, we would like to mention that metallic colours offer excellent opacity, and give good results when printing on a coloured substrate.

Bar Coding
It is known that photo-electric readability of line symbols depends largely on the contrasting effect of line symbols and the surrounding base colours in the measuring range of scanners (normally 633 +/- 20 um). This is easily done if the substrate or colour is white, yellow, orange or red and the line symbols are black, blue, very dirty green or brown (low emission colours).

In the cup printing field, however, we can experience difficulties. White coloured substances show a remission value of approximately 70 %. With thin wall containers this value can even be lower when the contents are dark. Such circumstances demand a very high print contrast of line symbols to surrounding area, so that the readability of the code is insured.

With coloured and transparent substrates a readable code is often no longer possible. Transparent cups, when filled with coloured goods which form a background colour, can exceed the necessary emission to apply a readable line symbol. In many cases the laser beam will be absorbed by the colour of the filling. In such cases using the code as a negative print will also be unsuccessful in view of the low emission capability of the most suitable ink in question (opaque white).

Wash-Ups
During wash-ups of the printing press, protective gloves are recommended as frequent contact with solvents can result in dry and de-greased skin. In extreme cases, dermatological problems may result.

Protective goggles and aprons are also recommended.

Always keep spare aprons and gloves at hand and replace worn or damaged items immediately. In case of eye contact, rinse eyes thoroughly for 15 minutes.

After prolonged skin contact with wash-up solutions, wash hands with a pH negative soap and warm water, do NOT use solvent. We also recommend applying a lanolin based moisturizing cream.

For press wash-up we recommend our imagemaster solution. Residual wash-up left on the rollers and blankets can lead to printing problems, and can detrimentally affect the efficiency of the UV cure.

Alternatively, a mixture of ethyl acetate and isopropyl alcohol (isopropanol) in a 1:1 proportion may be used, but prolonged use of these solvents should be avoided. Please observe the manufacturers instructions. It has been popular to use alternative wash-up solutions, which in many cases have been blended with aromatics, aliphatics and chlorinated hydrocarbons, which have proven both active and economical. However, prolonged use of these solvents adversely affects both blankets and rollers and are therefore costly in terms of blanket and roller replacement and repair. If swelling occurs on the blankets, a "brittling" tendency may result. The following solvents are damaging to butyl rubber and photopolymer plates:

hexane trichloroethylene benzyl alcohol petrol perchlorethylene dimethyl formamid cyclohexane carbon tetrachloride methyl ethyl ketone benzene isopropyl chloride methyl alcohol toluene dichlorfluormethane methylene chloride xylene turpentine dipentene

Note: Chlorinated solvents are suspected cancer causing agents and have been banned from the workplace.

Instructions for Handling UV Inks & Varnishes
We quote extracts from the list of recommendations of the Professional Association - "Print and Paper Converting and the Association of the Printing Ink Industry":

Observe the instructions on the pack or drum.

Skin contact with U.V. curing inks, varnishes, additives and wash-ups has to be avoided. Above all, avoid rubbing any materials on the face.

Wear safety gloves to protect against accidental splashing of inks, or solvents. Avoid the soiling of clothes with U.V. products, as skin can be contacted in this way. Skin contact can also be caused by handling uncured printed product, or from used cleaning rags.

In case of accidental contact, clean affected skin only with mild hand washing gel, or soap and water. Do not wash with solvent.

Immediately change working clothes soiled with ink or solvent.

When properly used and cured effectively, the dried film is chemically inert, so that it is stable, and cannot be affected by external influences. It is possible to detect a residual odour from the UV curing point, which amongst other things can come from ozone or substrate. This odour will dissipate after aeration.

Please Note
The information and recommendations contained herein are offered as a service to our customers, but are not intended to relieve the user from his responsibility to investigate and understand other pertinent sources of information and to comply with all laws and procedures applicable to the safe handling and use of these materials. The information and recommendations provided herein were believed by the Image Group to be accurate at the time of preparation or obtained from sources believed to be generally reliable. However, the Image Group makes no warranty concerning their accuracy and the image group will not be liable for claims relating to any party's use of or reliance on information or recommendations contained herein, regardless of whether it is claimed that the information or recommendations are inaccurate, incomplete or otherwise misleading.

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Last modified: March 29, 2004

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