An overview of plastisol performance that can help you choose the right white plastisol for the application at hand.
By Rick Davis
White ink selection for most garment screen printers is a matter of habit. Most of us have a preconceived notion of what we like in a particular ink. Larger garment-printing facilities can typically use any plastisol inks on their automatic presses. Where the selection of a white garment plastisol matters the most is on manual production presses in smaller shops and on manual sampling presses in larger shops. On such presses, the true performance of the inks can be most easily assessed. Although you can make almost any ink work on an automatic, the human element of the manual screen-printing process tends to amplify the characteristics of the inks.
White plastisols play perhaps one of the greatest roles in a manual-press operator's day. More than half of all printed garment graphics require white somewhere in the design. One of the greatest challenges printers face is determining which white will work best for a given application. Almost every major plastisol manufacturer has hundreds of white formulations available, and each actively markets a dozen or so of them at any given time. Even though most white plastisols are formulated for specific purposes, the offerings can still be confusing.
You need to have a good general knowledge of the products available without getting blinded by what can be an overwhelming number of choices. From an application standpoint, you want to minimize your needs to just a few whites. I keep four kinds of white ink on hand for the different applications that I address on the manual press in my shop. They include a basic cotton white, a bleed-resistant white for 50/50 cotton/poly T-shirts, a nylon white, and a polyester white for 100%-poly fabrics and potentially bad bleeders.
Cotton white White plastisol for cotton is the easiest to use. Cotton fabric places fewer restraints on the ink's performance than other materials do. The primary characteristics you want in this product include easy printability, good opacity, and good flashing characteristics. There are numerous versions of this plastisol on the market, and while it's a good idea to try as many as you can in search of the best one for your shop, all of these products really should perform similarly.
Bleed-resistant white Bleed-resistant white plastisols present a huge challenge to both the manufacturer and the end user. It's the most widely used white ink on the market, and the competition for market share is fierce. Plastisol manufacturers typically introduce a new bleed-resistant white to the market every 12-18 months. The manufacturers continually work to improve their white products with new chemistries in order to capture as much of the garment screen-printing market as possible.
Challenges with using bleed-resistant plastisols come from the numerous performance requirements of the product. These include excellent printability, fast flashing, gloss, opacity, soft hand, durability, good matte-down ability, and after-flash characteristics. Each of these considerations requires different formulations from the manufacturer, and thus you wind up with a wide range of bleed-resistant whites on the market. This is a product that you will want to try from a number of different sources to determine which works best in your facility. Most bleed-resistant whites will excel in one area or another; there is no magic in a can that delivers all the previously mentioned performance characteristics.
From the standpoint of a manual press operator, I would prioritize the performance parameters as follows:
3. bleed resistance
4. good after-flash
7. good aging characteristics
The top three in this list are all actually tied for first place in my book. Also, in case you were wondering, "aging characteristics" refers to an ink's ability to maintain its printability over time and not increase in viscosity too rapidly. Although this may sound trivial, you don't want to wind up with a half a gallon (or a half a drum for larger printers) of a product that has become too thick to print. Some whites perform better than others in this aspect, so you again need to test the various products for yourself.
Nylon white Nylon whites are an animal of a different color (no pun intended), as they are manufactured for a much tighter set of specialty performance parameters. Nylon inks are primarily used by shops that service the sports-uniform market. Fabrics here include nylon micro-mesh and high-elongation fabrics, such as Lycra. The composition and construction of these materials may vary from manufacturer to manufacturer, so it is important that you test your inks on these products and research the materials thoroughly. The performance of these whites can vary widely based on the manufacturer and the actual intended application. The primary performance parameters you are looking for in a good nylon plastisol include opacity, printability, and durability.
Polyester whites Polyester whites can pose the greatest challenge of all. This holds especially true for the folks who use manual presses. Polyester whites are specially formulated to deliver the maximum amount of bleed resistance when printed onto the most troublesome polyester fabrics. Not all of the inks available are printer friendly, as their performance parameters are targeted toward compatibility with the fabric and not toward easy printing. The printability of polyester whites can vary greatly from manufacturer to manufacturer, so you'll need to test various brands to determine which you prefer.
When it comes to working with polyester whites, it's essential for the novice to get the opinions of other printers to find what has worked best for them. It's also very important to keep on top of the new inks being introduced to the market and sample them as they are released.
The primary concern for the manual-press operator is to have a product that is easy to use, meaning it doesn't require special handling or greatly modified printing procedures. But that's where the challenge comes in. You need to experiment with the inks, fabrics, and the variables on press. You also must conduct your own bleed testing to confirm that the product is truly bleed resistant on the fabrics you're printing.
The sad truth is that not all fabrics are intended to be screen printed. Consult the manufacturer of the fabric for printing recommendations. I've contacted manufacturers about their tough fabrics and have been told not to print the fabrics at all! That's about the last thing your customer wants to hear, but it's best to share that information before committing to the job. Should you encounter such a fabric, it really is best to pass on the job
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