How to cure water-based screen printing inks

Screen printing with water-based inks offers a colourful world of vibrant possibilities, but achieving print durability requires proper curing. This is a critical step, particularly when printing on fabric, to ensure the finished product’s longevity, washability and dry cleanability. In this guide, we’ll delve into some of the ins and outs of curing water-based inks versus plastisol inks when printing on fabric such as T-shirts or other textiles and offer some valuable tips to help you master the process.

How does curing work?

Curing is the chemical process required for the wet ink film to form a dry film and to bond to the fabric fibres. Unlike plastisol inks that just dry chemically, water-based inks require both water removal (drying) and cross linking (curing). Drying removes the water from the wet film, while curing ensures the discrete polymer particles cross link and bond chemically to the fabric, resulting in a lasting and durable print.

Curing water-based vs plastisol inks

Curing water-based inks involves some key differences compared to plastisol inks and so, to get a better understanding, we’ll look very briefly at some of the underlying chemistry:

• Looks cured? Is cured. Plastisol inks are typically made from PVC resin particles dispersed in a phthalate, trimellitate or other plasticiser. They cure by simple fusion of the PVC resin particles at elevated temperatures (typically 115–160 °C; 265–320 °F) to form a continuous film. With plastisol inks, if it looks cured and feels cured, then it probably is cured. That’s very quick and very convenient, but that’s where the good news ends. When you cure plastisol inks, a small but significant portion of the PVC resin breaks down to give off fumes of vinyl chloride monomer or VCM. In the short term, VCM is a mucous membrane irritant (think eyes, nose, throat, lungs) and over the long term, is carcinogenic like cigarette smoke.
  
• Evaporation first, then cross-linking: Water-based inks are typically based on polymer particles dispersed in an aqueous medium. Rather than fusing like the PVC particles in plastisol inks, these polymer particles cross-link, but prior to that happening, you need to get rid of the water. So, with water-based inks, there are two very distinct phases; first, removing all the water from the film. It is only once that water has been removed from the wet ink film that the product will start to cure. In some studies, the proportion of energy used to remove water is 90% vs only 10% that goes into curing. Typically, water-based inks require 1-2 minutes at 160 °C (320 °F) with good air movement to achieve full cure.
  
• Curing time and temperature: Water-based inks generally require higher curing temperatures and longer curing times compared to plastisol inks.
  
• Air circulation: Whilst plastisol inks need only adequate heat for an adequate time to ensure complete cure, good air circulation and exhaustion is critical to ensure proper curing of water-based inks. This is because the water vapour needs to leave the film in the first phase before the polymer particles can cross-link in the second.
  
• Available methods: The methods for curing water-based inks are diverse, and some more common methods relevant to and used in small start-ups to larger print shops are discussed below. Plastisol inks primarily rely on high heat to cure whilst water-based inks can be cured with heat, sunlight and in some cases, with microwave dryers.

Methods for curing water-based inks

There are four main methods for curing water-based screen printing ink for print shops and small/mid-size start-ups:

With a heat gun

Ideal for small-scale operations or when printing at home, a heat gun is a handheld option for curing water-based inks. It requires manual attention, as the heat gun is moved over the print to evenly distribute heat. However, it’s also crucial to maintain a safe distance and constant motion to avoid scorching the fabric. On the upside, a heat gun is portable and very compact. On the downside, it’s very time consuming, requires constant attention and is probably the most inefficient option with regard to energy usage and wastage.

With heat presses

For heat-sensitive fabrics or intricate designs, curing water-based ink with a laundry or tailor’s heat press can be effective (with practice, and a great deal of caution, you can also use the type of heat press used for transfer printing). This method uses direct heat, pressure and sometimes steam to cure the ink. It’s worth following the fabric/garment manufacturer’s recommendations for time and temperature settings to ensure proper curing, at least to start, but as you develop more experience, you’re more than likely to develop your own method.

The use of heat transfer heat presses is unlikely to be viable with pure synthetics or fabric with a high synthetic content as the risk of melting would be too high.

This is less wasteful of energy, but like with the heat gun, it’s very time consuming and requires constant attention.

With flash dryer

The flash dryer is a versatile piece of equipment that can combine drying and curing in one step. It employs infrared heat to quickly heat the ink’s surface while simultaneously evaporating moisture. Flash dryers are a popular choice with small shops or start ups as they are relatively compact and don’t take up a lot of room. However, as with heat guns, it is important to take care not to overheat the fabric and cause scorching.

With conveyor dryer

The conveyor dryer stands out as the equipment of choice for curing water-based inks. Printed garments are put through a heated tunnel on a heat resistant conveyor belt. The consistent heat and airflow in the drying tunnel ensure thorough and even curing without hotspots that might singe one part of the fabric whilst leaving other parts uncured. In all cases, it is advisable to ensure that the heat setting being used will not damage the fabric. This is a particular risk with synthetic fabrics.

Tips for curing water-based inks

Here are some of our top tips for curing water-based screen-printing ink:

• Ink application: Apply a lighter weight coat of ink if possible, using the appropriate mesh size. Finer mesh will result in light grammage of ink being laid down. Whilst 43 T (110 tpi) is ideal for beginners, as you develop more experience, you can go as high as 90 T (229 tpi) for Opaque HSA inks or 120 T (305 tpi) for transparent colours. At these higher mesh counts, the transparent inks can be printed wet-on-wet, leading to much faster production times for multi-colour jobs. The use of more concentrated colours like PERMATONE(R) inks can allow reduction in ink usage and improve ink mileage by between 1/3rd + 2/3rds.
  
• Ambient evaporation and air movement: If you can increase the path length on the conveyor prior to the garment entering the drying tunnel and generate some air movement over the garment, you can significantly reduce the burden on the dryer and in doing so, reduce energy usage, costs and carbon footprint.
  
• Ventilation: Do not cure in an enclosed environment without adequate ventilation. All fumes from the curing process should be safely extracted, ideally to the outside atmosphere. If operating commercially, you may need to ensure that there are adequate filters to ensure that exhaust fumes meet local regulatory requirements.
  
• Conveyor dryer advantage: For longer cure times, a conveyor dryer is the best option. It offers more uniform heat distribution throughout the tunnel, minimising the likelihood of hotspots and the resultant damage to the fabric that these might cause.
  
• Temperature monitoring: Use temperature strips and/or IR guns to monitor curing
  temperature accurately during the course of a print run, as these can vary over time. Make sure that you’re testing the ink deposit temperature with the IR gun or very close to it with the temperature strips.
  
• Wash test: After curing, conduct one or more wash/wet-rub tests to confirm that the inks have cured properly and thus exhibit appropriate durability. Particularly for long runs, this is essential.

Get the right ink for the job

Select the right water-based ink for your project. Factors such as fabric type, colour, design complexity, intended use and budget all play a role in your choice. Be sure to explore the range of PERMASET® water-based screen-printing inks and the water-based mixing inks system, PERMATONE®, designed for matching special colours for corporate branding, to meet a wide range of garment and other textile printing needs.

For further questions and assistance, don’t hesitate to reach out to our team.

Moving from Plastisol to water-based inks and mastering the art of curing water-based inks will increasingly become a vital skill for all screen printers. With the right methods, attention to detail, the right equipment and high quality water-based inks, you can achieve stunning, long-lasting prints that stand the test of time. So, unleash your creativity, follow these guidelines and elevate your water-based printing game!