UV Printing

When I worked for US Can in Burns Harbor, Indiana, US, 20 years ago we were already capitalising on the benefits of UV printing. Where the conventional process used to dominate in the US, it has now taken a back seat to UV. This change is now the norm for the curing process as UV’s many advantages have come to the forefront worldwide.

This is now the case for South East Asia. In less than 10 years, companies like Swan, Standard Can, Kian Joo and United Can has invested in high-speed multi-colour UV presses to bring them into the next generation of metal decorating. The rest of South East Asia has taken note of this and have been watching and waiting to start making the conversion to this process. I am here to report that the wait is over. I just returned from one of my many trips from Asia. The number one topic everyone wants to discuss is converting to UV. The smaller printers who do not have a need for high-speed multi-colour lines are looking to capitalise on the benefits of this process.

I have compiled a list of advantages and disadvantages of converting to this process so you can make up your own mind if it is right for your company’s product lines.

Converting from conventional to UV printing

When comparing the two curing methods for conventional and UV inks you will see there are many opportunities to capitalise on. The following is a guide to work from:

Advantages of UV technology in metal decorating

1. Space saving

A typical UV set stack or final drying unit needs only three metres of space in the running direction compared to maybe 30 metres for a conventional gas oven.

2. Running costs

The UV line only needs electrical energy and it is claimed by existing users that the electrical requirements for the UV line are similar to that of a gas oven so the saving is the cost of the gas. Also damaged wicket replacement and associated oven maintenance is also eliminated.

3. Pollution

UV lamps only produce a small amount of ozone, which quickly reverts to oxygen and so the environmental impact is non-existent. Compare this to the increasing difficulties of compliance with gas ovens.

4. Immediate viewing and processing

With UV cured sheets you can immediately see the result and can further process the sheets straight away.

5. Instant availability

UV units can be turned off during make-readies, change overs and so on. It then only takes two minutes to re-start for production.

Compare this to a gas oven which has to be kept up to temperature for long periods and needs a much longer start-up time.

6. Oxidizers

No need to capture UV emissions. UV curing creates ozone. This ozone turns into oxygen within three metres after curing.

7. Manpower

Back end oven personnel no longer needed. Same amount of personnel required to run the press after UV conversion.

8. Maintenance and breakdowns

UV set stack units are much simpler than wicket ovens and require little maintenance, saving both money and time. Also if a lamp fails you can still run it, albeit a little slower, until the lamp can be changed.

Any failure on a wicket oven shuts the whole line down until a repair is affected. Oven maintenance includes: wicket cleaning and repair/replacement, oven cleaning, incinerator up-keep, chain cleaning and replacement, etc.

9. Make-up air

Because UV units remove much less air from inside the building the cost of make-up air is reduced, particularly in periods of low outside temperatures.

With regard to interdeck UV units the benefits are somewhat different:

10. Ink and wash-up solvent usage savings

Because UV inks only cure (or set) under intense UV radiation, it is not necessary to wash-up rollers and clean out ducts overnight thus saving wash-ups, ink, solvent and time. UV inks require better film weight control and this leads to better mileage.

11. Control of dot gain

As each colour is partially set immediately after printing, when doing tone work or 4/6/8 colour process there is no subsequent dot gain from the follow-on printing units. This improves the quality of print.

12. Ability to print colours on top of colours

By setting the ink sufficiently it is then possible to print a following colour on top without fear of problems that normally occur when printing wet on wet.

13. Reduction of work in progress

The use of interdecks allows for up to six (or even eight) colours to be printed and coated at one pass thereby saving many passes through single or two colour machines. This in turn saves money, speeds up production, reduces waste and reduces the cost and space required for work in progress.

Downside of UV curing

1. Initial capital investment cost

2. UV ink and coating material costs are approximately 20 per cent higher

3. Lamps need replacing around every 2,000 operational hours

4. Aluminium reflectors need replacing every 6,000 to 7,000 hours. However, dichroic reflectors have a much longer lifetime

5. Ink/water balance is slightly more sensitive with UV inks. However, this is not to say that it is difficult to achieve or maintain, particularly with modern damping systems. UV inks require fountain adjustors.

6. Converting the supporting materials for UV inks

• Fountain solution

• Press rollers

• Blankets

• Washes

As you can see the advantages far outweigh the disadvantages. When converting your printing process to UV you have two choices:

1. Buy a new line that is UV ready

2. Convert your current press to UV

When converting to UV you will need to make changes in your current press configuration for rollers, blankets, washes and fountain solution. The key is to make sure they are all compatible with UV inks.

Below is a guide to help you become successful working through the conversion process to UV:

Good press practices for UV printing

Wash-up

1. Use only UV press wash solvent.

2. No residual of press wash should be visible on blankets or plate cylinder.

3. Following UV press wash with IPA (isopropyl alcohol) and dry completely. This will remove any residual of UV solvent on ink rollers, blankets and plate.

4. Any solvent film left on blanket, plate or ink rollers can cause ink not to transfer properly and will retard ink cure.

5. Keep pressure cylinder clean, ink could transfer to inside of sheet.

Fountain mix

1. Maintain conductivity readings for UV inks at 1,800 – 2,800 micromho [µ] max.

2. Keep fountain and tank clean of scum build up. Main cause of scum is the dampers picking up ink and solvent from wash up. Leaving no residual solvents with good wash-up practices will reduce this situation.

3. Use only deionised water for fountain mix.

Water balance

1. Set water balance to the minimum to keep plate clean. UV inks are more receptive to take on water.

2. Setting water balance higher than necessary can cause UV inks to have a reduction of cure. The result being soft ink film with the possibility of offsetting in stack.

3. Dampers should be clean and set correctly.

4. Maintaining an even ink film (using densitometer) across the sheet will make water balance easier to maintain at lower level.

Cure and power setting

1. Maintain lowest power setting to accomplish a full cure (thumb pressure twist).

2. Transparent inks require less power, while opaque inks (white) need more. Dark colours (dark blues or blacks) need additional power to cure properly. Refer to power specification sheet for power needed on colours.

3. Ink film weight should be at the lowest to maintain colour standard and have good water balance.

4. Maintaining an even ink film using densitometer will insure a proper cure at power setting.

5. If a heavy ink film is needed to obtain colour standard, maximum power should be used. Notify supervisor to have ink re-formulated.

I also have pocket size trouble shooting guides for those  interested, as well as posters helping pressmen trouble shoot their way through the litho process. Just send me an email and I will send them to you.

Please feel free to contact me anytime via email at jack.knight@inxintl.com.

 

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