My Screens Won’t Reclaim Easily, Why? First what do you clean your screens with?
What does your screen cleaner have to do with screen reclaiming you may wonder? Well emulsions when underexposed are still sensitive to both light and solvent based chemistry which can lock in the emulsion and make reclaiming difficult. In recent years there has been a trend away from mineral spirits, recirculating parts cleaners and paint thinner as a wash up chemical for plastisol inks. Driven by local air quality control agencies trying to limit Volatile Organic Compounds many solvent chemistries have been banned in favor of low VOC screen cleaning chemistry. Yet there are still many areas of the world and shops that use solvent chemistries as well as ‘hotter’ chemistries like MEK, Xylene, Acetone and Screen Openers for faster cleanup of plastisol ink. These chemistries can have an adverse affect on the emulsion and the reclaiming process which we will discuss in a moment.
- The advantage of the newer cleaning products is they have less harmful affects on the worker and the environment. In addition to worker safety the new chemistries do not affect emulsion like the solvent chemistries mentioned above. To understand how emulsion can be affected by screen cleaning chemistry and become difficult to reclaim we need to look at the many different types of emulsions.
- There is a reason for the variety of emulsions in our catalog due to the wide variety of inks that can be printed. The different emulsions can be viewed as a spectrum. You can have emulsions designed to withstand water base and discharge on one end, and emulsions that can withstand hot solvent inks on the other end of the spectrum. There can also be emulsions that fall in between and can withstand both solvents and water but rarely have the durability to withstand them as well as one specifically formulated to withstand either water or solvents.
- Underexposed screens can still be sensitive and have un-cross linked sensitizer. While these chemistries can quickly clean or open up the image the emulsion can get ‘locked’ in and be difficult to reclaim down line in the production process. To fix this issue we need to go back to how the screen was exposed, and did it receive any post exposure to complete the cross linking of all sensitizer?
- I read a lot of the print forums to help our customers solve some of these issues and have found that a lot of us have developed bad habits on screen exposure. There is a major difference between ‘imaging’ and ‘exposing’ a screen. One of the worst habits is underexposing emulsion to get details. I have seen large shops go out of business over this issue. While their underexposed image showed great tonal range, over half the emulsion was being washed down the sink during screen development. Sure it had incredible 5-10% tonal values along with a lot of pinholes that required painstaking block out technique and a screen that will be lucky to make it past 100 pieces without breaking down more.
- Water base or discharge inks? Forget about it! Your emulsions for water based inks will breakdown quickly if you like to underexpose to capture tonal values. Proper, complete exposure is the key to both durable screens and pure photopolymer emulsion reclaiming. Making wild claims that you can expose your screens in 40 seconds on a bargain basement exposure unit may get you an image, but not a screen that will be durable and one that may get chemically ashed causing the emulsion to lock in. Obtaining an image is easy, getting a fully exposed screen with an image is what makes Murakami emulsion different. Our emulsions are designed to be completely exposed and image well, with details and tonal values printable on a durable production screen. Click here to continue reading the article: My Screens Won’t Reclaim