Impressions - March 2011 - (Page 54)

HANDS ON >> SCREEN PRINTING >> HANDS ON TECH TIPS HANDS ON >> HANDS ON For Screen Printers Only SCREEN PRINTING HANDS ON TECH TIPS HANDS ON How to Prep a Screen Understand the different types of emulsions available and the necessary screen-making steps to ensure quality designs. Scoop coaters ensure an even coating of liquid emulsion is applied to the screen. It is important to have this and the other tools needed for screen coating within arm’s length of your coating station. Teaching screen making to industry newcomers can be challenging because it initially seems to be a confusing process to comprehend. But in my decades of training screen printers, I have learned that once a person is comfortable with coating a screen, the rest of the process naturally falls into place. So my approach is to have the student use a scoop coater to coat a few screens, even if he doesn’t yet understand the ﬁner points of what he is doing. This gives him a general understanding of the process, which makes it easier for me to explain the detailed types of emulsions and coating techniques available without losing him in the dialog. Once a printer is comfortable with the basic concept of screen coating, determining mesh selection for a speciﬁc job is an important next step in the screen-making process. For athletic jobs requiring a thick ink deposit, coarse meshes in the 60 to 156 monoﬁlament range are common. Using emulsions with higher solids content is necessary to bridge across the open areas of the mesh. For more detailed designs, mesh counts in the 195 to 230 range are desired, and choosing an emulsion with a lower solids count is important to achieving a quality screen. To ensure you are using accurate materials, always read the technical data sheet provided with the screen emulsion. I cannot stress enough the importance of using high-tensioned screens because no matter how good your emulsion-coating technique is, mesh that is tensioned lower than 8 N/cn can be a real problem when attempting to coat screens. One beneﬁt to 54 Impressions >> March 2011 coating a higher-tensioned screen is that it is easier to apply a uniform coat of emulsion to the screen’s surface. This is because the scoop coater meets the middle of the screen much better than it does on a lower-tensioned screen, thus eliminating an uneven buildup of emulsion on the edges of the screen. DEGREASING & CHOOSING EMULSION Correctly degreasing a screen to prep it for the next job is important for quality screen making. But before doing so, check the screen’s tension with a tension meter to determine if the screen is even worth coating in the ﬁrst place. Set aside any ultra low-tensioned screens because you won’t save money by keeping them. Degreasing is achieved by using a standard garden hose and sprayer, scrub brush and commercial degreaser. Wet the screen with water and scrub the degreaser in all directions for several minutes on each side of the screen. Next, rinse the screen with water and dry it in a particle-free environment or screen dryer. Haze removers also are available to remove ink stains from previous print jobs. Remember that safety comes ﬁrst, so always wear gloves and eye protection when using haze removers. Three main types of screen emulsions are available: diazo two-part, dual-cure diazo and pre-sensitized pure photopolymer emulsions. Diazo two-part emulsions are widely used because of their lower cost, good image resolution and easy reclaiming properties. For high resolution and better stencil durability on long print runs, the dual-cure diazo emulsions work well. Dual-cure emulsions usually include 35% to 40% solids content, are easy to reclaim and moderately priced. Pre-sensitized pure photopolymer emulsions also are popular because they offer superb coating properties, excellent image detail and include 40% to 50% solids content. Also, the pre-sensitized emulsion requires no mixing and is ready to use right off the shelf. The downside to pre-sensitized emulsion is that it can be expensive compared to the other types. Capillary ﬁlms also are an option for screen printers instead of direct liquid emulsion. Also known as direct ﬁlm, this stencil system is a sheet or layer of photo An exposure calculator, such as this “grayscale” sensitivity guide from Saati Print Co., has 21 continuous-tone steps to help assess whether the emulsion is properly exposed. This exposure guide is taped to the contact side of the screen next to the ﬁlm positive to be exposed. impressionsmag.com http://www.impressionsmag.com

Table of Contents for the Digital Edition of Impressions - March 2011

Impressions - March 2011
Contents
First Impressions
From the Show Director
FYI
Product Gallery
Mainstream Fashion Drives a Womenswear Evolution
Styled for Her
QR Codes: Mobile Marketing Technology
Production
Design & Digitizing
Production
For Screen Printers Only
Perfecting Sublimation on Pre-Sewn Garments
Online Directory
Business to Business
Classifieds
Ad Index

Impressions - March 2011