Several of the variables that affect the amount of pretreatment applied to a shirt to achieve an optimal print are as follows:
- Shirt color
- Shirt weight
- Type of yarn and construction (open-ended, carded, combed, etc.)
- Any chemicals used during the manufacturing of the garment
- Type and concentration of pretreatment
- How the pretreatment is applied
A light-colored shirt will require less pretreatment than a dark-colored shirt. This is due to the optics of the shirt itself and the hiding power of the white ink on that specific colored shirt. A light gray shirt, for exmaple, will not require as much pretreatment or ink to achieve a bright white as does a red or black shirt.
The shirt weight, fabric type, and construction of the garment will also affect the amount of pretreatment required. Remember that we are inkjet printing. The D2 machine will spit out billions of tiny droplets of ink during the printing process. If the weave of the fabric is very loose or thin, there will be a lot of “air gaps” in the weave of the fabric. These gaps do not provide a surface for the jetted ink to sit on and will pass through to the platen. Remember that you cannot print on thin air, nor apply pretreatment to fabric that isn’t there. This will ultimately affect the smoothness of your white ink film.
Yarns used to create a shirt are the foundation of any shirt. An open-end carded fabric will not be as nice to print on as a combed, ring-spun fabric. Typically, a lower thread count, like an 18- to 20-singles, will require more pretreatment and ink to achieve the same quality of print on a 30-singles combed and ring-spun T-shirt. Typically, the higher the thread count and the better the yarns, the less pretreatment is required for an 18- or 20-singles shirt.
During the manufacturing process of the fabric used to make your shirts, different chemicals are applied which can affect how the pretreatment absorbs into the fabric. Some chemicals are used to make the shirt feel softer or give it antibacterial characteristics. Any chemical can have an adverse effect on how the pretreatment interacts with the fabric by either sitting on top or absorbing into the fibers.
Some pretreatments are shipped to the end user in a concentrated form. Depending on mixed the ratio of the pretreatment can have a significant impact on how much pretreatment is required to be applied to achieve a good white ink underbase. You still need a uniform application of the pretreatment across the entire shirt, but two-parts water and one-part pretreatment concentrate will require significantly more grams applied to the shirt than a 1:1 ratio of water and pretreatment to achieve the same results.
Finally, how the pretreatment is applied can also have a significant impact on how much fluid is required. Typically, utilizing an automated pretreatment machine is better than applying it by hand due to the consistent repeatability of the device. However, applying pretreatment by hand is possible, and when done correctly, can allow for less pretreatment used and achieve fantastic results (but that’s a subject for another article).