Date Published: 2008-12-01
Direct-to-garment Troubleshooting
Geoff Baxter, of M&R, looks at the most common causes of poor quality direct-to-garment digital prints and provides expert solutions to ensure top quality results every time…
Bear in mind that these are generic recommendations: ultimately, you should consult the manufacturer(s) of your printer and consumable products for advice specific to your unit.
Poor washfastness
When properly processed and cured, the direct-to-garment inks that are currently on the market will hold up to laundering quite well. If you are experiencing problems, consider the following potential causes – all of which can impact the washfastness of digital prints. UndercureMost direct to garment digital inks need to be heated at between 163 - 176.5 °C (325 - 350 ° F) for around a minute to affect a proper cure. Dark shirts printed with white ink may take up to twice as long. Undercure is the single biggest cause of washout. Since the vast majority of these inks are water-based, then it is best to 'float' the transfer press, (presuming you are using a press to cure the ink), over the shirt for 30 - 45 seconds to boil off as much water as possible before applying pressure to affect the curing process. Garment fabric
Many direct-to-garment digital inks are designed for cotton fabrics only. When used on 50&percent; cotton/50&percent; polyester or synthetic fabrics, image degradation may occur when the garment is laundered. Check with your supplier for their recommendations regarding print parameters for synthetics. Pre-treatment
The level of pre-treatment on dark shirts will drastically affect print quality and washability. Too little treatment will cause the image to be pitted, and light: too much can negatively affect adhesion. While relatively easy to master, the pre-treatment process does require some practice. Fibrillation
I have found that what often appears to be ink washing out is, in reality, caused by fibrillation – that is, the process whereby the fibres of the cotton garment protrude through the ink after washing. The degree of fibrillation is largely influenced by the technique used to spin the yarn that is used to knit the fabric. Print results will vary dramatically depending on the garment you use. You should test and evaluate shirts from several manufacturers to find the ones that work best for your application. Often times a second pass through the printer will increase the washability on white shirts, as the additional inks help to matt down the shirt fibres. Pre-treatment on lights.
That may sound like an oxymoron, but I've seen printers apply pre-treatments to light garments. The treatments used for dark shirts are, in the main, formulated to react with the chemistry of the white ink: they do not react in the same fashion with the CMYK colours. Furthermore, pre-treatment applied to shirts that do not use a white under-print will quite possibly cause substantial image degradation when the garment is washed.
Dark shirt disasters
Printing white ink on dark garments using a digital printer is an absolutely achievable goal; however, there are far more variables and pitfalls than when printing on white shirts. I like to equate the differences to when my dad taught me to drive in a car with an automatic transmission, and then sent me off for a drive in his thee-speed manual truck: there was lots of grinding noises until I figured it out! The following are the most common causes of less than desirable dark shirt prints… Improperly applied pre-treatment
If your printer sits idle for any period of time, the white pigment in the ink has a tendency to settle, and separate from the ink's carrier. White ink cartridges and bulk feed containers should be agitated at least twice a day to keep the pigment evenly suspended in the carrier. Failure to agitate the white can also be the cause of printhead failure, as the thicker white pigment can be drawn through the system into the heads, resulting in clogged nozzles. Clogged printhead nozzles
If you allow the nozzles in your printheads to become clogged you are also likely to end up with prints that show an insufficient level of white ink. If the whites on your prints are less than you expected, run a nozzle check, and consult your supplier or owner's manual for directions to perform a head cleaning. Contaminated capping stations
Many of the digital garment printers on the market are based upon Epson printers. These units allow the head to rest over what is called the capping station. If this station is not kept clean, cross contamination of the white nozzles can take place causing the first few prints after start-up to take on a blue, or grey cast. Running a scrap shirt, or running a cleaning cycle, will help to minimise this problem.
Colours don't match original
Colour balance and saturation can vary on both white, and dark shirts. The synergy between the inks that are used, the RIP employed, the garment printed, and the printer itself is what determines colour quality. Any combination of the following can negatively impact colour quality… Ink agitationWhile not as pronounced as with the white ink, the pigment in the colours can settle, causing variances in colour balance. Coloured inks should also be lightly agitated twice a day to ensure even distribution of the pigments. WYSINWYG (what you see is not what you get)
Keep in mind that you are working with CMYK colours. While this combination of pigments can produce a wide colour gamut, it is far from being capable of reproducing all of the hues in the spectrum. The RGB (additive colour) scheme of your monitor can reproduce a colour gamut that's approximately 30 percent wider than the colour gamut the CMYK (subtractive colour) inks are capable of reproducing. The bottom line is this: there really is no such thing as WYSIWYG (what you see is what you get)! RIP profiles
The RIP software employed by your system must be properly profiled for the specific hue and density of the colorants used. Your supplier should have done this before delivering your system. Changes in ink formulation can dramatically impact colour balance. If your supplier has changed their product, or you have made a decision to change ink manufacturers, the RIP will need to be re-profiled to accommodate these changes. Bear in mind the three 'Ps' of accurate colour balance: Proper Profiling is Paramount. Selectively clogged nozzles
If just some of the printhead's nozzles are clogged this will usually result in colours that are 'off'. This happens because the RIP determines the correct amount of the primary colour needed to reproduce a speci.c shade, but the printhead cannot deliver the correct amount to the 'nonfiring' nozzles, thus altering critical colour-to-colour balance. That is, the lack or complete absence of one or more ink colours will dramatically alter the colour of the final print. You should run a nozzle check, and perform the manufacturer's recommended cleaning procedure if any area appears clogged. (See Clogged printheads, below, for more detailed information on how to avoid clogging issues.)
Colour intensity diminishes when dried
There is nothing more frustrating than taking a great looking print off the printer just to have the colours 'die' when the print is cured. This problem can be caused by one of the following…
Excessive heat or exposure can cause the colours to fade during pressing. Use only the recommended time and temperature specifications provided by your supplier. Pressure control
Applying too much pressure with the heat press can drive the ink into the shirt. Use only the minimum amount of pressure needed to make contact with the printed ink. As stated previously, it often helps to 'float' the transfer press over the shirt for 30 - 45 seconds to boil off as much water as possible and gel the surface before applying pressure.
Clogged printheads
Head clogging is an unfortunate, but inherent, characteristic of inkjet technology. It cannot be eliminated, but it can be greatly reduced by following a few simple procedures… A clean environmentThe working environment is incredibly important. The area should be as clean and dust/lint-free as possible. Inkjet printheads work best with a relative humidity level of between 50 – 75 &percent;. Humidity levels below those recommended by the manufacturer can dramatically affect head clogging, and the useful life of the printheads. An accurate thermo-hygrometer is an essential purchase – don't be without one. If humidity falls below an acceptable level, place a cool water humidifier in the room. Capping station cleanliness
On Epson-based units, and other applicable printers, follow the recommendations for cleaning the capping station and edges of the printhead. Dried ink in these areas can be scrubbed into the nozzles, causing anything from minor problems to catastrophic head failure. Pre-treatment contamination
Avoid using the pre-treatment solution anywhere near the printer. This chemistry is specifically designed to cause the white ink to gel. The ink has no way of knowing whether it is on the shirt, or in the print head. Even a minute amount of airborne pre-treatment solution can negatively affect the head. To this end, it is also a good idea to leave the printer cover closed at all times to avoid exposure to pre-treatment chemicals and other potential contaminates. If the head comes into contact with any area of shirt that is treated you will most certainly experience nozzle blockages. Avoid wrinkles, collars, and sleeve seams in the path of the printhead if at all possible. Cleaning cycles
Regardless of the manufacturer of the printer, it is good practice to run a cleaning cycle at the beginning of each work session.
Frequent use inkjet heads work better when they are used often. The more they are run the fewer problems you will usually have. Eight hours a day of operation is much better that one hour every eight days. If your printer is going to sit idle for any period of time the inks should be purged with cleaning solution. Some manufacturers now incorporate a timed self-cleaning mode into their system. If this is available it is a good idea to have the machine clean itself at regular intervals when not in use. If there is one secret to successful direct-togarment printing, it is this:
you must religiously follow the manufacturer's preventative maintenance and cleaning schedules. Nothing else is more important!
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Geoff Baxter is the director of M&:R’s Digital Products Division. Previously, he served as vice president of sales for Martin/Atlantic Sign & Screen Supply, and president and co-founder of Atlantic Screen Supply. His 30-year industry career includes management positions with L0g0-7, Harlequin Nature Graphics, Advance Pro and Precision Screen Machines. Geoff has written numerous articles for trade publications and spoken at many industry events. |
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