The following article is previewed from the March 2011 issue of Impressions Magazine. Blue Heron's Kevin Kelly is known as the King Of Digital Darks when it comes to custom tee shirts. The company has become well known through out the world for its consistent productom quality on black custom t-shirts.

Achieving High Quality Digital Prints on Dark Shirts

Pretreatment, Photoshop, heat, humidity, and curing are all factors that have to be controlled to achieve top results when digitally printing on dark t-shirts..

By Kevin Kelly

When I first ventured into digital printing, I was a screen printer whose biggest niche was entertainment, a market that prefers black shirts. I purchased my first digital printer, a Kornit, in 2007 as a way to capture business I was forced to turn away because of the poor-quality artwork I was consistently getting. In one week, I once turned down 25 screen printing jobs, because the artwork was not ready to be separated.

With a digital printer, I was able to convert poor-quality art into a usable format for printing. With an estimated 90% of my jobs on dark shirts, I had to learn how to get the best digitally printed results on darks. Consequently, I have built a reputation as being the King of Digital Darks.

Color Accuracy
What I have learned over the past four years is one of the biggest challenges when printing on darks is color accuracy.

The quality of the white underbase is a big part of achieving color accuracy on darks, but the most important factor is the translation between the art file and the machine. In our shop, all of our equipment has been linearized in order to maximize our reproduction possibilities. The art computers running PhotoShop files have been calibrated to our printing machines and visa versa. When we print solid Pantone colors, we use a few of our own tricks for translating these colors to CMYK.

One of the fallacies of digital printing verses screen printing is that you can’t match color, and this is untrue. The first thing that a lot of people don’t understand is that when you print digitally you are printing a CMYK file that is being viewed through an RGB color spectrum.

Experience and detailed records are the key to accurate reproduction. All of our files are prepped using external ripping software such as Kornit’s Quick P. We prep each file according to the nature of the art. Files that contain fades and feathers will receive different attention than a file that is essentially a square block.

If you use a Window-based driver system, you don’t have the same control as you do when you use external ripping software. Our printing methods require that we have 100% control over the finished product.

You are always going to have some issues to work out with color in direct-to-garment printing. No two monitors present exactly the same visual reference. So having good PhotoShop files with layers and transparent backgrounds will let you capture the color profile that the artist placed in the file.

CMYK color adjustments as small as 1-2% combined with our linearizations can make a world of difference. Our Kornit machines and our proprietary techniques enable us to control color quite accurately. Not all digital printing equipment gives you the ability to control the parameters that affect the color. Files such as .jpeg and .gif don’t have all of the data that an original PhotoShop file has due to the way data is reduced and color is averaged during conversion.

Environmental conditions also dramatically affect color and print quality. We fight a pretty big battle with heat and humidity. We often see temperatures of 100 degrees in the production area during the summer months. During the winter, humidity can fall as low as 25%. This requires constant monitoring. Ideally, the temperature should be 70 to 85 degrees F. with humidity in the 50% range. We print with water-based inks so we are particularly concerned about the atmospheric conditions in the shop. We have systems in place to help alleviate some of these challenges.

The consistency of the pretreatment application is another factor that can affect color. An advantage of the Kornit technology is that it pretreats onboard, which allows for 100% consistency and repeatability. When you have to pretreat off the machine, it’s tougher to have a consistent laydown of pretreatment. Too much or too little pretreat will kill your color regardless of brand.

There is no one in this industry who states on their terms and conditions that all Pantone colors will be exact in digital printing. The standard is to come as close as possible. That is how we operate, and we hit it pretty darn close.

Unless the garment is being printed on a white shirt, we rip all of our files to print for black. If we are in the darker shades of light, we can choose to sometimes put down a very low percentage of underbase to bump color up or take color down. Sometimes we alter color by using the underbase to mute or highlight a color. It is like any process printing so your color range is limited to the CMYK gamut. By adjusting underbase characteristics on the fly, we can affect the overall outcome right on the machine

Creating the right underbase plays a big role in the quality of a digital print. We actually separate our digital print files like screen print files. Although there are a lot of the digital print programs that are designed for plug and play, my advice to anybody who wants to become proficient at printing on darks is you have to master PhotoShop.

Curing Challenges
The other big challenge is proper curing, and I’m seeing digital printers in the industry struggling with that. Some of them can’t get an image to stay on the shirt. Customers are taking their shirt home and once they run it through the washing machine, there is a T-shirt with no art on it.

I also see a problem with overcuring. Depending on your machine model, this can burn out the color. We cure with gas-fired ovens in the exact same manner we cure screen printed shirts. The philosophy of time and temperature applies to digital printing as well.

Overcuring in digital printing is similar to overcuring in screen printing. Once the ink hits a preset temperature and the molecular reactions that create a solid cure have occurred, additional heat can be detrimental. In screen printing, wash fastness is compromised, in digital printing water-based ink color will appear washed out and faded. Digital printers using heat presses can experience the same problems.

Because dark shirts require a pretreatment layer, a white underbase layer, and then the colors, they take longer to cure than white tees that are digitally printed or screen printed. The amount of ink used depends on the way the design is set up and how the underbase is created.

Another factor is if the artist has taken advantage of using the substrate color in the same way a shirt is designed for simulated process screen printing. If an order contains multiple shirt colors for the same design, there may be more than one production file that will be used to create a uniform look across the whole color palette.

In a lot of applications you are doing double whites depending on a dual underbase, and you can control that ink usage to a degree by manipulating the opacity of the underbase and highlight whites.

With Kornit, we are able to print highlight whites so we can sometimes reduce the opacity of our white underbase and ramp up the density of the highlight whites. However, in general, a dark design is going to use 40% to 50% more ink. Consequently, it costs about 65% more to print dark vs. light colors. Dark shirts typically take between 5 and 7 minutes to cure at 325 degrees F. in our case. White tees can be cured in half that time.

Return-Feed Dryer Increases Output
One factor that has allowed us to increase our curing productivity is the use of a return- feed dryer. It has a two-level belt. Operators place uncured shirts on the top belt and cured shirts return at knee level on the bottom belt back to the same operator. The dryer has 10 feet of heat and 28 total feet of belt.

The whole purpose of the return feed dryer is that your digital operator is unpacking, printing, retrieving, and boxing his own goods. With digital printing, your operators have time to do other things while they are waiting. It is not like a screen printing pallet is indexing every 2 seconds. So you shouldn’t see shirts sitting on a table, they should be in a box.

With Kornit equipment, I feel the hand of a digital print on darks is similar to a process screen print. One factor that contributes to that is because we use a gas dryer. We do not own heat presses. When you heat press a digital print, it gives it the glossy look of a transfer. Our digital prints have a matte finish and a soft, but perceptible hand.

An advantage of specializing in digital on darks is we don’t have to compete with screen printing. Because digital printing is still relatively new, there are competency and consistency issues. An advantage Blue Heron has is we are printing on darks day after day. We have learned how to manage the variables. Our repeat order rate is extremely high with retailers.

I have found for small orders, digital is extremely profitable and on the medium-size orders, it is still a lot more profitable than screen printing. When you get up into the bigger orders is when you start looking at the production/time equation. At that point, profitability declines significantly and is more in line with standard screen printing when viewed from a percentage perspective. There is no magic formula to get rich doing digital printing.

If you want to be successful at digital printing, plan on investing a lot of time on R&D. This was our biggest expense in setting up our digital operation. We printed cases and cases of shirts to learn what worked.

BIO
Kevin Kelly started screen printing in 1976 as a high school student and has been involved in decorated apparel for more than 34 years. He opened his current business, Blue Heron Industries, Inc. in Little Falls, N.J. in 2002. Blue Heron offers volume screen printing, embroidery and direct-to-garment services. In 2007, Kelly purchased two Kornit Thunder 932 direct-to-garment printers. Since that time, he has established a reputation as one of the best direct-to-garment printers of dark custom T-shirts in the country. You can reach Kevin at kkelly@goblueheron.com or visit http://www.goblueheron.com.

03/02/2011
Little Falls, New Jersey 07424