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Lost in the world of linearization and process color screen printing

April 10, 2010 5 comments

Hi friends,

Sorry I could not post any news articles since last week because too many R&D is simultaneously taking place at Grafica and DMI.

1. The EPSON 9900 and POLIRIP

Linearized of Epson 9900 Inkjet Printer is completed with the help of transmission densitometer. Now 50% dot in file is 50% on film (output). Thereafter linearized film were exposed using 4 different screens (with same tension, mesh count) and printed with process color (CMYK) UV inks. While printing the test chart all press condition and parameters were noted to make sure the same conditions are kept in production to get consistent results. High quality PU sharpened squeegee were used to print 100 sheets.

Production screens were used to expose 6 test strips (with dot percentage ranging from 1% dot to 99%), 3 on the top and 3 on the bottom. Full length (30″ x 40″) sheets were used on a the press with 42″ of squeegee length to record press gain. Never take a smaller squeegee to measure the press gain using a smaller test strip and smaller screen to save money or else you will get a huge difference in dot gain.

Finally last 5 sheets were taken to measure the press dot gain to averaged the numbers. Press dot gain was compensated directly into the RIP. There after a high resolution image along with linearization test strips was printed again to check everything is linear.

While sampling all parameters were kept the same and fantastic result was achieved in the first trail itself. There was minor 5% to 6% gain in mid-tones which I re-corrected by editing the same press dot gain compensation setup file.

One major problem solved that now when ever we receive any AI, CDR, PDF, EPS files from customers we need not correct for press linearization using any image editing software the RIP now takes care of all linearization process (positive as well as press). Press dot gain compensation was a big problem in ready embedded files earlier when we use to outsource our positives with various service providers because we had to spent lot of time compensating dot gain in Photoshop earlier by exporting image in TIFF format keeping text in vector so that it overprints all CMY colors.

So in house RIP facility has one big advantage that now we are able compensate press dot gain for a particular ink and substrate thus not to bother about PDF, EPS, TIFF files etc. Directly open in the RIP load any TIFF, EPS, PS, JPEG, PDF files or print the artwork from illustrator, Corel, ID etc. using the print command selecting Epson printers setup file.

IF YOU ARE INTERESTED TO LEARN 100 LPI HALFTONE SCREEN PRINTING IN JUST 2 to 3 DAYS. THAN LET ME KNOW I HAVE STARTED TAKING SPECIAL BATCHES FOR INTERESTED PRINTERS TO LEARN PROCESS COLOR SCREEN PRINTING. BELIEVE ME ITS VERY EASY.

I have also solved the moire issue and you shall not have moire in screen printing even with 100 LPI. No visual angling of positives on screen to eliminate moire pattern.

For complete program details and content kindly contact Ashwini on 9920755561 or email us at marketing@graficaindia.com. She will fix your personalized training program dates.

2. UV Meter development is almost completed and my team is working on standardization of assembly of each parts and we have given it at a very sophisticated lab for calibration to ensure our reading is perfect as per standards.

3. NANO-PRINT my dream project and a dream machine for every screen printers is rocking 3 months 100 machines sold. We have taken another batch of 200 new machines in production. My team is working on accessories related to NANO-PRINT but its a big surprise and I will announce soon. So wait and watch for the BLAST in this HOT SUMMER…

Have a great weekend.

Bhargav

Understand UV curing process in simple way

March 29, 2010 24 comments

UV curable inks and coatings render a durable, high-gloss finish with excellent mar and abrasion resistance. Because UV curable are nearly 100 per cent solids, they will not evaporate solvents into the air. In addition, UV inks and coatings cure only by exposure to UV light, so they will not dry out in the screen.

Finer mesh screens can be used with UV curable inks, which result in greater detail printing. Also UV saves significant floor space compared to wicket dryers or conventional hot air dryers. The nearly instant drying of UV results in more output from existing presses and fast completion of a job order. Also, UV consume less energy than gas or electric conventional dryers.

In general, UV curing or “drying” is achieved through photo-polymerization. Ultraviolet energy is generated by the mercury vapor lamps, which have a strong spectral peak of 3,650 angstroms. This energy is absorbed by the photo-initiator within the liquid formulation of the ink or coating. Free radicals are then produced, which attack the double bonds of the resin (monomeric) molecules. The molecular weight increases as the particles add to them-selves and form cross-linked chains, resulting in a solid polymer film. The whole process of converting a mobile liquid to an immobile solid coating takes place in a fraction of a second. It is accomplished without solvent waste while usually consuming less energy than conventional methods.

There are several factors governing the cure rate of which the most important ones are:

1. The photo-initiator to resin ratio in the liquid or ink.

2. The ability of the pigment and the concentration of the pigment to transmit UV energy, in the case of a screening ink.

3. The intensity of UV energy in watt-seconds/ CM2 produced from the mercury vapor lamps.

4. The thickness of the ink or coating to be cured.

5. The substrate on which the ink and coating are to be cured.

The photo-initiator/resin ratio is determined by the material supplier and is premixed prior to shipment. In almost all cases, the UV inks and coatings are ready to use in their packaged form.

The material supplier also chooses those pigments at an optimum concentration level, which are capable of transmitting UV light. However, some pigments transmit UV energy more readily than others: black and white are perhaps the most difficult inks to cure because black inhibits UV energy penetration and white reflects UV energy. They both can be cured, however, with increased exposure. The spectral hues cure faster than black and white and exhibit little difference in cure rate between themselves.

The intensity of the UV energy is, for the most part, determined by the type of lamp and reflector used. The current standard for the industry is 200 to 300 watts/inch mercury vapor lamp housed in an aluminum reflector of which the inside surface is plated and polished for maximum UV reflectance. At Grafica we have even successfully sold UV Curing Machine up to 600/watts/inch. Higher wattage leads to faster production.

The thickness of the ink and coating is a concern to the screen printer because if too much ink is deposited, the UV will be unable to penetrate, therefore an incomplete cure results. Because the UV curable inks are 100 per cent solids, mesh counts per inch ranging from 140 to 180 threads/cm (355 to 457 threads/inch) can be used to keep thickness in the curable range.

The thickness of the clear coatings is not as critical because they do not contain pigments which reduce cure rates. The substrates on which the ink and coating are to be cured often effect the cure rate. For instance, a surface that reflects UV energy would cure faster than a dark surface that would absorb the UV energy.

When purchasing a UV curing machine for screen printing, two very important features to look for are: how well the manufacturer handles the heat generated by the UV lamps, and how well the conveying system transports the light stock through the reactor.

UV lamps produce three types of energy: ultra-violet energy (which is absorbed by the coating or ink and produces cure), infrared, and visible light. Visible light is contained by the sheet metal enclosure of the curing tunnel, which therefore protects the operating personnel. Infrared or heat produced by the lamps must be controlled to keep the stock dimensionally stable. This is done by either water-cooling the lamps and reflectors or air-cooling the curing tunnel or both.

A separate cooling module can also also be added that allow the screen printer to process the most heat-sensitive substrates, such as vinyls and polyester films after curing.

For conveying light stock, such as pressure sensitizes, a vacuum holdout conveyor should be provided to insure a smooth transport through the curing tunnel. The vacuum holdout should begin one foot before the stock enters the reactor to prevent the sheet from fluttering as it enters the curing chamber. Also, the conveyor belt should consist of a material which rapidly dissipates heat such as a Teflon-coated, open-mesh, fiberglass belt.

Other considerations for purchasing UV curing machine are the number of lamps required to achieve proper cure at desired speed. This should be coordinated with the ink supplier who would recommend the number of lamps needed at a given production speed. Conveyor speed control should be precise and repeatable to prevent over- or under-curing, and drives should be variable from 30 to 150 FPM.

When converting a conventional line to UV, a few problems must be dealt with. Screen fabrics and mesh counts will have to be changed. Again, UV curable are 100 per cent solids and will not discharge solvents; so the amount of ink initially printed is the amount of ink left after cure. Therefore, monofilament screens with 140 to 180 threads/cm (355 to 457 threads/inch) should be used for screen printing UV curable materials.

Opacity in UV inks is somewhat of a problem. If the pigment level in a UV ink is too great, the ink will not cure; so, the screen printer requiring true opacity for a job cannot use UV inks at this time. Anything less than true opacity can be achieved by UV. Adhesion of the UV curable to some substrates has been a problem, but material suppliers are over-coming this obstacle by altering the formulation of the coatings for a specific substrate.

In some UV curable, the monomers in the formulation are cause for concern regarding toxicity. Proper handling should be exercised by the user. The coating supplier will inform the user on the degree of toxicity of his material and will instruct on proper handling.

Incidentally, UV energy is now used in the field of dentistry for curing photo-reactive material in filling cavities. UV curing has a bright future in the screen printing industry. The process is widely accepted and will continue to grow enabling the industry to provide new and better products for its customers. Again, UV curable are 100 per cent solids and will not discharge solvents; so the amount of ink initially printed is the amount of ink left after cure.

Avoid SOLVENT INK SYSTEM where ever you can.

Go for UV CURING SYSTEM and make your business profitable.

Keep growing…

Bhargav

What can screen printers print with UV technology

March 23, 2010 7 comments
Although it is not possible to UV print every job, 90% of those normally printed with solvent inks can now be printed with UV inks.
The following questionnaire provides a few of the answers why:
Q. Is it possible to print opaque inks?
A. Yes. Previously, printing opaque UV inks was very difficult. Because of new developments in the UV formulations, we can print whites, blacks and metallics that compare favorably with solvent inks.
Q. Can UV inks be used for vacuum forming?
A. New developments are beginning to make this possible. This was not so in the past as UV inks are not thermoplastic and are normally of a brittle nature. The ink would crack if there are deep depressions in vacuum forming.
Q. Can plastic bottles be printed UV?
A. Yes, if the bottles are made of normal bottle type plastics (i.e. polyethylene, polystyrene, polypropylene or PVC etc.)
Q. Is UV ink adhesion good on all substrates?
A. Yes, if the surface tension of the substrate is above 38 dynes minimum. However, with surface tensions under 38 dynes, adhesion would be questionable. Therefore, corona or flame treating may be required.
Q. Are UV inks and conventional inks compatible?
A. In theory, they do not like each other; however, there is no reason why you could not combine the two systems to obtain a desired effect. Tests would have to be done to check adhesion between the two inks. When in doubt, consult your ink supplier.
Q. Can UV inks be used on all types of screen printing presses?
A. There are no problems in using UV ink on all types of screen printing presses. However, UV printing requires finer, even deposits of ink lay down. As such, finer meshes and the purchase of a UV dryer are required.
Q. How does UV differ from conventional drying?
A. UV drying is UV curing. As UV inks are 100% solids, there are no solvents present. Therefore, everything will polymerize. When UV inks are exposed to ultraviolet light, a reaction takes place which causes the total ink film to become a solid mass.
Q. Can UV be printed onto most substrates?
A. Yes. With the evolution of inks and dryers, UV printing on the most difficult substrates, such as metal, aluminum, polyethylene, mylar, foil, polystyrene, polypropylene, A.B.S., PVC, ceramic and glass, offers excellent printability.
Q. And finally is UV ink economical compare to solvent?
A. YES, YES & YES as I said earlier that UV ink even if bought at Rs. 1200/- per kg is 60% to 70% cheaper if compare to dirt cheap solvent ink of 350/- per kg plus there are many other advantages which you calculate it can even work more than 100% cheaper compare to solvent ink.
If you get a suitable UV ink for your job then immediately FORGET solvent and go for UV and make huge profits.
Have a great day…
Bhargav

In this workshop I proved that UV Ink is 60% to 70% cheaper than Solvent Ink

18-19-20th March 2010 DMI Workshop Particiapants

“Thank you participants for coming all the way from remote places to attend my workshop which concluded today. Your interest, hunger for knowledge kept me enthusiastic through out the workshop”.

The kind of interest generated by each participant in every workshop on “REFLECTIVE MICRO EMBOSSING” technique is a reflection of new hopes and opportunities in screen printing.

This time I made a special presentation on costing, explaining various parameters about how to arrive at a proper cost per sheet considering a typical screen printing unit. The costing mechanism involved labor cost, overheads, ink consumption calculations, mesh, squeegee, emulsion and chemical wastage etc. to arrive at the final break even cost which has to be charged considering print order ranging from 100 to 2000 sheets and above.

Further, my calculation also removed the misconception of solvent ink to be cheaper and UV ink to be very expensive. But my thorough statistics of ink consumption calculations per kg showed that solvent ink is not cheaper, but is 60% to 70% expensive than UV inks.

Also I am sure that all those who have understood this misconception of UV v/s Solvent will not never attempt to go for solvents ink in future and may immediately shift to UV.

For your information, UV saves lots of space, manpower, time, rejection and is less hazardous for health.

I thank Nirav of Star Labels for giving me valued practical consumption analysis of UV inks which further helped me in arriving at proper of costing worksheet. He was also kind enough to be a part of this workshop for all three days.

I think I shall continue this interesting issue of costing in every workshop at DMI so that printers may not make huge losses because of wrong costing method.

I also thank Mohan Kaikini, COO of SPAI who is always kind enough to come during every workshop to create awareness about SPAI and FESPA activities. This time he gave valued information in detail about the FESPA Awards Competition e.g. how to participate etc. in the forth coming FESPA 2010 exhibition which is scheduled in 22 to 26th June 2010 at Munich, Germany.

I urge every screen printer in India to participate in this prestigious international competition and get a chance to WIN 5000 Euros and make India proud. For more information on the FESPA 2010 awards you may directly email Mohan at info@spai.in or you can also him on 9820287300.

I have already scheduled my next workshop date from 13 to 15 May 2010. For registration log on to http://www.graficaindia.com as there are limited seats.

In the next workshop we are coming out with many new ideas on print finishing like falling calendar with 9 special effects including micro embossing on foils plus process color screen printing on textile transfers and tag-less label as usual.

So let’s stay connected.

Bhargav

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