Though given little mention when you are looking at purchasing a direct to garment printer, pretreating is one of the most important aspects and processes you can do prior to actually printing your white ink design.
Pretreating is similar in process to primering drywall before it is painted. You apply the primer on your drywall to keep the paint from soaking into the drywall and helping it retain its color and providing a smooth base to which you can apply your final paint coating. You can think of pre-treating as the primer for the dark garment before printing white ink.
Pretreatment is applied to the garment in one of two primary ways. The first is manual application where the pretreatment is usually applied with a power sprayer similar to a Wagner paint gun. This is often the least expensive way to apply the pretreatment, however it is fraught with a variety of variables that can affect the final print quality of your shirt. Uneven application of the pretreatment and inconsistencies in the amount of pretreatment applied will affect your final print visually and directly when the customer washes the garment.
The second method for applying pretreatment is by utilizing any number of automatic pretreatment machines that apply the pretreatment for you. These machines help take out the guesswork on how much pretreatment to apply and usually will provide a much smoother, more accurate application of the pretreatment.
Utilizing an automatic or semi-automatic pretreater will help maintain a smoother, more consistent and accurate application of fluid on the garments. Too little or too much pretreatment can be bad for the shirt. Too little will provide for a weak white and poor adhesion of the white ink to the garment while too much can also cause washability issues with the printed image.
Once the pretreatment is applied, it needs to be dried or cured just like primer on drywall. The curing process of heat and pressure allows the fibers of the shirt to be “trapped” down in the cured layer of pretreatment providing a smoother surface on which to print the white ink. It has been noted that a pneumatic heat press can provide the higher pressures that provide a better cured pretreatment surface than most hand operated manual heat presses. This isn’t to say that a standard heat press won’t work – they obviously do – however a pneumatic makes it much easier and provides a better finished surface for your white ink on which to print.
The key to proper pretreating is to provide the correct amount of pretreatment fluid for the shirt while at the same time making sure that all the moisture is evacuated from the garment. A semi-wet or shirt that has sat around and re-absorbed moisture will provide a sub-par performance for wash performance of the final print.
Generally speaking, you will want to follow the pre-treatment manufacturer’s directions for curing and the application amounts. A good rule of thumb though is the heavier the shirt, the more pretreatment will be required. The darker the shirt, more pretreatment. A light-weight ash colored shirt will require much less fluid than a 6 oz black t-shirt. Many times you will have to do your own experimentations to find the right combination of pretreatment amount and the shirt colors.
You may also want to consider utilizing a multi-step process when pre-treating. Some pretreatments, due to their high salt content, will crystalize if heated immediately. We’ve found that with some pretreatments you need to slightly hover or gently rest the heating element on the shirt to heat it up and start some of the evaporation. Letting this steam off and then pressing the shirt for the recommended time will help keep some of the white crystalization from appearing on the finished pretreated shirt.
It is also suggested to use either a teflon sheet or parchment type paper when heat setting the pretreated garment. The teflon can provide a very smooth finish but depending on the amount of pretreatment and the type of pretreatment used it can apply a smooth, glossy finish to the pretreated shirt. Usually this will “fade out” over time as the shirt re-absorbs moisture from the air, but some people do not like the looks that teflon provides. In that case, a good parchment paper can be used for more of a matte finish.
Once you have properly pretreated your shirt you are ready to print it with white ink. However, some prefer to pretreat one day and then print the next. This is possible, but remember that the shirts are going to absorb moisture from the air. It is highly recommended that if you are going to delay the printing of a pretreated shirt that it is re-pressed in the transfer press for 10-15 seconds to remove any re-acquired moisture. For best results it seems that the sooner you use the pretreated shirt, the better.
Remember that proper pretreatment is the key to successful white ink direct to garment printing. It really is a step in the white direction!