ImagesMagUK_Digital-Edition_Nov17

TIPS & TECHNIQUES

Each month, leading manufacturers and DTG print shop owners share their know- how in our new DTG column. This month, Geoff Baxter from M&R’s digital division gives the lowdown on pretreatment and the benefits of automated pretreatment application

Geoff Baxter

T here are several misconceptions about pretreating garments prior to direct-to-garment digital printing. Some print shops view it as an optional step – it isn’t, at least not when you’re printing on black and dark shirts. Others believe there’s no difference between manual and automated pretreatment application – there is! So, what is pretreatment, and why is proper application so important? What is pretreatment? Basically, pretreatment enables white DTG ink to be printed on to dark fabrics to create an effective ‘underbase’ that can then be overprinted with CMYK DTG inks. It comprises a chemical solution that’s applied as a spray: The solution contains a small amount of a binding agent, which helps the white ink to adhere to – and stay adhered to – the fabric; and a chemical component that causes the white-ink formulation to gel (or ‘crash’) on contact, forming a semi-solid ink film onto which the low- viscosity CMYK inks can then be printed. The primary purpose of pretreatment is not only to ensure that the white ink ‘sticks’ to the garment, but also to ensure that it achieves maximum opacity – by preventing the ink from sinking into the fabric, and the fabric colour from showing through the ink. An opaque

Automatically applied pretreatment results in a knock-out image

white allows the CMYK DTG inks to produce bright, vibrant, detailed prints. Without pretreatment, the DTG inks would soak into the garment, resulting in muted or muddy images. So what about pastel and white shirts? Pastels may also require a light pretreatment if a white highlight print is being used. White shirts don’t need to be pretreated, but may benefit from it nonetheless. As a rule, the pretreatment solution used on dark garments should not also be used on white shirts: it may enhance the initial appearance of the print, but it can compromise washfastness and the printed image may even yellow over time. There are, however, a number of pretreatment solutions on the market that are

specifically designed to increase image durability and colour vibrancy on white shirts. You would need to determine for yourself whether any resultant improvements in quality and durability are sufficient to justify the additional time and expense of such pretreatment application on your white shirts jobs. Pretreatment application The pretreatment application process plays a crucial role in obtaining optimal results. The process can be as simple as filling an electric or pneumatic paint sprayer with the solution and hand- spraying it on garments. Unfortunately, while this is both a convenient and inexpensive approach, it has two major drawbacks: control and consistency.

18 images NOVEMBER 2017

www.images-magazine.com