www.images-magazine.com 28 images APRIL 2022 Industry experts provide insight and guidance in all areas of digital garment and textile printing Digital helpdesk Irida Gogolou, from quality control at Polyprint Chemical Lab, guides you through pretreating garments, including top tips on pretreating in bulk Irida Gogolou may result in stains and cracks or the print lifting off during washing. It also leads to unnecessary waste. Precise pretreatment quantity control is vital, especially when using a spray gun as it can be difficult to always achieve consistency. Pretreatment uniformity When pretreating manually, spray in the same direction and avoid pretreatment overlaps. When uneven pretreated sections are printed, they result in rough prints with patches. A foam roller can help improve uniformity. An automatic pretreating machine makes life easier thanks to its automated process, and offers consistent and reliable results. Pretreatment fixation Most pretreatment liquids are cured for 30 seconds at temperatures around 160170°C. When pretreating light shirts that are prone to yellowing, or when using tricky colours, like reds, that darken under heat, you’ll need to modify your pretreatment curing process. Drop the temperature by about 10-20°C and lower the pressure setting. Heat press for 20 seconds, release and then press for another 20 seconds. An alternative is to send the garment through a conveyor dryer or hover longer with the heat press, then press it for five seconds to lay down the fibres. Pretrteating garments before direct-to-garment (DTG) printing is important; it ensures that prints on white or coloured fabrics remain colourfast and will be durable, allowing you to reduce production time and costs, cut down on material and ink loss, and provide customised, quality products. Pretreating on darks This is a necessary step prior to printing in order for the white ink to ‘hold’ to the garment and not soak into the fabric. DTG printers first print a white underbase on dark textiles and then print the colours on top of the white. This ensures that colours stay vibrant. Pretreating on lights This is an optional step when printing on white and lightcoloured tees. However, if you want those eye-catching results to endure over time, I would advise you to pretreat these tees as well. Pretreating on polyester As a synthetic fibre, polyester repels the water-based inks that are used in DTG. A specifically formulated pretreatment solution enables the inks to be printed and can stop them from bleeding through polyester fibres. Key pretreating factors Fabric type The fabric plays a crucial role in the whole DTG process, including the initial stage of pretreatment. Using a high-quality garment, with a tight-knit weave, ensures better pretreatment and DTG printing results. The smoother and tighter the weave, the better the end result will be and the higher the quality of your product. Media thickness The amount of pretreatment applied will depend on the garment’s density. When printing on ‘heavier’ garments, such as hoodies, for example, you will need to apply twice as much pretreatment as you would on a regular tee. Pretreatment quantity The amount of pretreatment applied on garments affects both the print quality and its washfastness. Not enough pretreatment will result in a faded or uneven underbase and a print that lacks vibrancy. On the other hand, excessive pretreatment By following certain guidelines, garments can be pretreated in bulk and stored, ready to be DTG printed when needed
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