ImagesMagUK_August_20

www.images-magazine.com 24 images AUGUST 2020 TIPS & TECHNIQUES Brian Walker, founder and CEO of Image Armor and RTP Apparel, demonstrates how to calculate the correct volume of pretreatment for the best DTG prints I may not be able to tell you exactly how much pretreatment to apply – there are so many variables to consider that the amount varies widely – but I can explain how you can work it out yourself by describing a pretreatment test we ran on three shirts. Our test The real question that needs answering is not ‘How much pretreatment should I apply to a shirt?’ but ‘How big a difference does the shirt itself make in determining how much pretreatment is required?’. We used a consistent set of fixed values in our experiment: we applied the same pretreatment using the same pretreatment machine, then used the same ink, printer and curing method. The only variable was the shirt – all were 100% cotton but from different manufacturers and with different weights, processing, thread counts, etc. One way to test how much pretreatment a particular shirt needs is to spray it with a set amount of pretreatment and then increase the volume incrementally for each additional T-shirt of the same brand and style. Print them, cure them, then compare the shirts side by side to find the volume that produces the best result. Repeat this for each brand of shirt you want to test. This could, however, require printing on six to 10 shirts per style per brand and a lot more time and effort than most DTG owners have available. Speedy results A quicker way is to use a pretreatment machine that allows you to test all the different volumes on one shirt. Our Viper Maxx machine laid down six different columns of pretreatments, allowing us to apply 11g, 15g, 20g, 25g, 30g and 35g to the shirt. Once applied, the pretreatment was set using a heat press. If too little pretreatment is applied, the white ink soaks into the shirt, preventing us from achieving a nice, bright white. As increasing amounts of pretreatment are applied, the white ink progressively gets better until the point where there is no noticeable improvement in its quality, allowing you to identify the optimal amount of pretreatment. Because we do all this on a single shirt, it reduces our testing time substantially. If your pretreatment machine doesn’t have the facility to do the pretreatment step test, you can achieve the same effect by laying down a piece of paper that covers the entire shirt except for the area to be sprayed first. Run the pretreatment machine then remove that paper, replace it with a new piece and move it to one side so it exposes more of the shirt to the next spray. The first spray will be coated again with pretreatment along with the second column, which will get its first application of pretreatment. Repeat. Note, however, that many pretreatment machines do not allow for a minimum amount of pretreatment to be applied easily like this. Method I chose three standard T-shirts. It does not matter which ones I chose, this was just to illustrate how much the shirt can affect the optimal pretreatment application amount for the best-looking prints. In the image on the opposite page, you can see how the volume of pretreatment increases in each successive column from left to right. We then printed a white bar across each of the six pretreated columns: first, a single pass of white and then a second pass of white. This is typical of many printers on the market that allow the option of a white underbase and then an additional white or white highlight. Brian Walker Industry experts provide insight and guidance in all areas of digital garment and textile printing Digital helpdesk A s a manufacturer of pretreatments I often get asked: “How much pretreatment should I apply to the shirt?” My response – “I don’t know” – is often met with disbelief! A close-up of wet pretreatment on a shirt showing the columns of different pretreatment volume applied by the Viper Maxx