Benefits using UV technology in Screen Printing

Indian screen printing industry is now waking up to the reality of UV-age. More and more screen printers are now adopting UV and dumping the foul smelling solvent which many feel a curse to the screen printing. That’s because it is not only it requires lot of space for drying but also environmentally hazard and wastage is rampant. In some areas such as decals and industrial printing UV has not made successful inroads and still they have to use only solvent inks. However, screen printers, wherever applicable, should consider UV because of its immense benefits. Screen printers should also note that other processes such as offset and digital are also roaring with UV. And I feel UV will soon become the norm for all printing.

Based on my continued experiments and R&D at DMI institute and feedback from customers, I can vouch for UV technology. The future of UV is bright that’s because it offers screen printers with great production advantages over solvent.

Screen printing, though a most versatile printing process, requires different types of drying system, viz, UV curing, IR drying, Hot air drying and most commonly screen printers use whole floor of their printing unit to dry the printed stuffs on racks. Now-a-days, most advanced wicket dryers are available as an online racking-cum-drying system.

With UV technology (UV inks and UV curing system), screen printers can now expect to achieve great deal of efficiency in their work and higher productivity and why not profitability!

The biggest nightmare for screen printers is ink choking in screen during small intervals and even during printing which restricts screen printers to deliver finer details. But now with UV Inks the problem of ink choking up in screens is never a issue.

Interestingly, one of our customers, dealing in industrial printing revealed that he has recovered his investment on table top UV system within one month. In another case, amazingly one of my dealers has stopped his 3-4 decade old business of dealing in solvent inks and screen printing consumables and focussed on promoting and marketing UV inks in a big way along with our Nano-Print and Nano-UV curing machine. That’s because even as a supplier he felt UV is the future.

With UV, benefits unbound:

- Sharp and finer print details

- Environment-friendly than hazardous solvent

- Clean work environment

- Economic print solution

- No ink drying on screen, no choke up hence saves lot of time

- Faster job turn around

- Waste reduction

Faster job turn around: Curing of UV ink happens almost instantly as compared to solvent inks which requires lot of time to dry.

Space saving: Since drying (curing) takes place instantly lot of space otherwise required for putting up drying racks can be saved and use it for other productive use. And UV curing system as such requires less space to position it along with printing machine.

Fine print quality: Vibrant print quality in process color screen printing.

UV – an economical and profitable printing solution: I always highlight in my workshops that screen printer should never compare the face value of UV ink with solvent ink which is cheaper than UV price wise. But look at the output per kg? In solvent, printers end up wasting lot of ink, substrate because very nature of solvent ink, whereas with UV every drop of ink is usable or can be put it back on the tin after printing is over. It is my research that UV ink gives times mileage than solvent ink. When we take into consideration the greater benefits and mileage of UV ink, it is definitely cheaper than solvent overall.

Word of caution: UV, UV, UV do not simply jump on it. Take cautious step instead of burning your hands later. First study the market. Analyze the return on investment. Study the supply sources, talk to them and understand UV better. You should thoroughly understand the whole UV technology, how it works, its technicalities, UV lamp, UV inks, UV curing system, and more importantly its application in relation to different substrates and safety aspects. And our DMI workshop orients screen printers on some of these aspects. But it is better to have regular interaction with printing machine/UV curing machine, UV inks manufacturer/suppliers, substrate suppliers, etc to keep yourself updated on regular basis. And knowledge seeking will definitely ensure you are on right track and deriving maximum benefits from UV.

Food for thoughts!

- Where do I get training?
- How much my machine supplier (both printing machine and UV curing system manufacturer or dealer) know about UV?
- How much UV ink supplier knows about UV?
- How much substrate supplier knows about UV?
- Can all these people are capable of guiding me or giving me training properly
- Yes ink wise you will find UV is priced on higher side. But how do I workout my costing to ensure that I do not charge more than what I used to charge earlier for a job using solvent inks.

If at all the cost works out more how do I convince my customers.

Other than normal UV inks, is there any potential for various UV special effects and how much I know about print finishing and value addition, what is the market for this special segment.

Do I need to employ skilled manpower or the existing manpower could be trained in UV?

Remember half knowledge is dangerous and if you practice based on half knowledge given by half-knowledgeable suppliers you will burn your hands in UV business.

And do not just see the current market but plan yourself and prepare a project report with a long term vision for an economically viable business proposition.

Technically speaking: Since application of UV in screen printing is growing day by day, I strongly recommend that screen printers should make every effort to acquire as much as knowledge in UV inks, printing, UV curing and all related areas.

In UV inks, the liquid coating (printing) gets cured to a solid state after being exposed to UV light. This chemical change is known as ultraviolet (UV) polymerization.

Usually, UV ink consists of:
- Oligomers
- Monomers
- Photoinitators

Besides there are other components such as pigments, stabilizers, flow controls, flatting agents.

I shall touch upon this aspect in my future blogs.

UV lamps: UV curing takes place based on UV radiation activating and UV sensitive chemicals. UV ink contains liquid prepolymers, photo initiators and pigments. As the ink is exposed to UV radiation it gets polymerized instantly into hardness.

UV radiation is facilitated through a UV lamp which releases radiation of about 240-400 nm. UV lamp (bulb and reflector) is fitted in separate modules to facilitate easy handling and replacement whenever needed.

UV lamps in a curing unit must be replaced after a certain number of hours use. Some lamps do last up to 3,000 hours, but replacement and running costs are a consideration.

Mesh and machine: Is there any difficulty hitch in using UV ink on all types of screen printing machines?

There is no problem, but printing with UV ink requires finer and even ink deposition. Therefore it is advisable to use finer mesh say 165 or 180 mesh and you have to buy a UV curing machine as per print area/curing area required.

Substrate: With the availability of UV inks and UV curing machine, screen printing even on most difficult substrates, viz, PVC, metal, polyethylene, foil, polystyrene, PP, ABS, PVC, besides paper is now possible.

Surface tension: or energy level, can best be explained by the understanding that a material with high surface tension levels has a greater degree of cohesive force and intermolecular attraction, and is less adhesive to another material.

For example, water has a surface energy level of around 80-90 dynes/cm2. As water molecules have a great internal attraction to each other, they readily form a bead or droplet.

Non-polar solvents, on the other hand, typically have energy levels between 10-20 dynes and have much greater wetting ability and less tendency to “bead”.

UV ink monomers and oligomers lie between these two extremes at around 30-36 dynes (milliNewtons/M2).

It is an established fact that plastic substrates require a surface tension level of at least 38 to achieve good adhesion. Too low a level will reduce the attraction between the substrate and ink/coating, and will cause reticulation and poor adhesion.

Suppliers of corona discharge treating equipment go so far as to say that a ten (10) dyne difference between substrate and applied coating or ink is required to achieve good results.

Therefore, with UV inks having energy levels of 30-36 dynes, theoretically film treatment levels of 40-46 dynes would be required.

UV screen printing: Devices required. There are many devices to monitor UV output which are passed under the UV source to measure temperature and UV output.

A light sensitive tape is used to gauge the level of absorbed UV when passed under a UV source. This tape changes color as per the intensity of lamp and speed of the conveyor, which is then checked as per calibration chart.

Best of luck…

Bhargav