I visit many shops around the country, from small to large print facilities, and one of the biggest and costliest issues that arises is printing white inks. Now everyone prints white ink, you absolutely have too, but are you printing it correctly? And you may ask, what do I mean by correctly?
Proper Mesh Selection
The amount of coverage as well as image detail are going to be the main factors in selecting your mesh. Almost every shop I work with uses 110 mesh for their underbases. When asked why, the response I usually receive is that they want to get better coverage, or the ink is too thick to go through a higher mesh count. While sometimes true, this is certainly not the real issue with printing a premium white ink. Especially one that has gone through hours and hours of testing and development on press in the labs, and at print shops used for beta testing before the ink is released to market.
This of course is the next contributing factor in successfully printing white inks. Lack of stencil or no stencil thickness is the number one main fail point for most printers. If you cannot feel the image area on the substrate side of your screen you will never get a proper lay down of the ink. Emulsion Over Mesh is the commonly used term for having the proper amount of emulsion thickness on the screen. You need to have, for lack of better terms, an ink well on the substrate side of the screen, this will be a major factor in the amount of ink being laid down. Now it has always been up for debate which side of the scoop coater to use: the sharp or rounded side? In my experience, the round side is the only one to use and will give you a proper coat of emulsion starting on the substrate side of the screen and finishing on the print side (then of course drying with the substrate side down). Coating with the sharp edge basically just scrapes off the emulsion. If you ever see or use an automatic coater, you’ll notice the troughs always have a rounded edge for this very reason.
Press Set Up
One factor that can be the most detrimental cause of printing issues is press set up. Even if your mesh is correct and you have a perfect screen and stencil, if the press is not set up correctly the fight starts here. I have noticed that many printers print with entirely too much pressure. But more is good right? Not necessarily.
In fact, you want to print with even pressure between 25 and 40 psi to shear off the ink and clear the screen, leaving the ink on top of the garment and not pushed through it. Another contributing factor is squeegee angle and speed. With proper pressures, 15 to 20 degrees is perfect enough to shear the ink with the edge of the squeegee. And as far as speed, todays inks are formulated to run at very high production speeds, so the traditional theory of using a slower print stroke for a better ink deposit is well…out the door.
Squeegee selection is going to be determined by your mesh count, image detail, and the viscosity of the ink that you are printing. 60/90/60 durometer typically works extremely well for white or gray underbases, and 70/90/70 for any top colors (this is all up to personal choice just a suggestion).
Flash Temperatures and Time
This is the number two issue that I work with most printers on: flash time and temperature. If you have mesh selection and screen/press set up done correctly, it means that you have the proper ink film thickness and therefore you should be able to get a very fast flash time, increasing your production. If you have a thick ink deposit you will have to have a longer flash time which can lead to scorched garments, not getting a true ink film flash cure, or even possibly over-curing the ink which will lead to the top colors coming off during the wash. Most of the white inks available today if printed properly will flash at 265 degrees in about 1.5 to 3 seconds which leads to faster production times and more jobs done in a day.
Cure Time and Temperature
Here is where you need to reference the ink manufacturers recommendations since there are so many different types of white inks available for cotton, 50/50 and polyester garment printing and most will have different settings for their products. Do your research and test your curing temperatures for the best results.
Hopefully this information helps. White ink printing does not have to be the battle that most print shops face on a daily basis!