I have been doing large-format printing for more than 25 years, and when someone tells me about problems they are having printing, I never look to the materials as being the problem; I look to why the printer isn’t set up properly. Yes, there are lots of delicate materials that are difficult to print—and we will deal with them a little later—but first let’s review the basic issues in play that make for a difficult day of printing.

 

Excess heat is one of the most common culprits behind printing problems with thin and/or delicate plastic-based substrates. Fortunately, LED-based curing systems, such as that used in Mimaki’s JFX-1615plus UV-curing printer, require much less heat and make printing onto delicate substrates much easier.

HEAT AND PLASTIC-BASED MEDIA

Heat is the largest problem in wide-format printing, and we are the only industry that needs heat to print. Offset, screen and web-fed technologies do not use heat to print. Remember, a digital printer is a dumb device and it does what the RIP software tells it to do. If you have a profile that runs hot—say 45°C (113°F)—you can expect issues with many plastic-based materials. 

 

Most banner materials do not like heat above 30°C, and when you run banner at 45°C (as many profiles call for), you can get warping or cockling which results in head-strikes or a poor image. You can raise the heads on your printer to avoid head-strikes, but you may still end up getting small waves of dark and light color in the media. 

 

Halogen UV cure-lamps on many flatbed printers tend to weaken over time until they no longer cure the ink properly. Turning up the power on the lights will get the ink to cure again, but will also generate a lot more heat—and as we know, the heat causes issues. I have had black foam board turn brown while printing white-ink jobs because the print heads (and lights) were going over the same spot several times to lay down the white and subsequent colors. The areas of the board without ink coverage turned brown from the heat. Some of the more heat-sensitive materials like thin PVC and polystyrene, some foam boards etc., can buckle in the printer. 

 

Delicate fabrics destined for dye-sublimation must be properly tensioned to prevent them from shifting during the printing process. Slight shifting during printing can result in tiger striping.

Now I am very happy that the new LED-based cure-lamp systems on flatbeds are getting more advanced and becoming accepted as the way to cure UV ink. LED lamps generate much less heat than conventional halogen lamps. Once the heat factor is gone, life becomes easier with many heat-sensitive substrates.

 

MEDIA CURL AND TAKEUP

Another big issue with difficult-to-print materials is media curl. For example, printing to .020 polystyrene is easy on some printers, but due to the curl from the roll (if you get it on the roll) you can have issues getting the media to flow through the printer properly. Plus, since the curl is in the media right off the roll, then you keep the curl going through the printer (unless you reverse roll feed it), and then you add the heat to the media on the back (the printer does this for all solvent printers), then you take up on a 3" core, you are going to have a very curled print when you are done. 

 

If this is an issue, you might want to set up your take-up reel to wind backwards (if it will allow you). Another option is to let the media simply flow onto the floor, but if you do this, remember that polystyrene tends to have a lot of static, so place something like a sheet on the floor to keep the dirt off your prints. You can also print onto sheet-stock rather than rolls, but this is a little more expensive and labor intensive.

 

FABRIC CHALLENGES

Fabric is always a challenge for me. For one thing, fabrics often have a soft or unfinished edge, and the fine fibers of the material can get under the printheads and eventually cause them to clog.

 

For those who dye-sub their fabric (as I do), tiger striping is a killer. Tiger striping occurs when fabric shifts during the sublimation process causing the image to have light and dark stripes through it. Tension and speed is the best control for this, and keeping your room for both the printer and the sublimator at 70°F and 50 percent humidity helps greatly. 

 

When dye-subbing a sheer, thin fabric such as UltraSheer, it’s a good idea to protect the fabric from the sublimator’s belt by using a dye-sublimation paper.

Two fabrics that are notoriously difficult to work with due to their structure are UltraSheer and Lycra. UltraSheer is very translucent and thin. I use double-sided VentureTape for seaming because this stuff cannot be easily stitched. And because it is so thin, we must use dye-sublimation paper to protect it from the belt on the sublimator.

 

Lycra (a similar product to Spandex) has 70 percent stretch one way and 30 percent the other. The difficulty in sublimating this material is because it stretches so easily the image can become distorted as it passes through the system. The good news about Lycra is that most times it is stretched over a frame. The client can stretch the fabric to make it fit, and they can compensate for any perceived image distortion.

 

For those of you who direct print onto coated fabric, heat again comes into play. You need a lot of heat to make the inks look good on the material. The heat does not affect the fabric but can cause your printheads to clog faster. Plus, you need to put down more ink on fabric to get the vibrant results you love. I recommend taking the printhead platen heat to about 40°C and then take the post-heat platen to the max.

 

Finer fabrics like silk, rayon, and nylon are not typically coated, so the best process is direct print to the fabric and then cure after. Ink saturation is an issue with these, but generally they run nicely through the printer.

 

Stretchable fabrics such as Lycra can be challenging to print onto because of the fabric’s inherent stretching qualities. Creative tensioning over a frame can help compensate for image distortions.

SPECIALIZED FILMS 

I have been printing on the special foil films for a number of years, but with limited success. Sometimes the inks just do not hold up on the media, other times I cannot see the image well enough and sometimes it is a home run. In most cases the UV-curable ink tends to look better as it is a more solid ink, but for the films that are holographic, metallic, florescent and reflective, I find the hot solvent works best and looks better as this ink is more translucent.

 

FINAL WORD

The final word for all delicate materials is heat. Basically, the general rule is that the more heat you use, the more problems you encounter. What to do? My rule is test, test, test. 

 

Good luck, and be smart with your money, and I will see you on the show floor.