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High-Volume Screenmaking: Eliminating the Crisis

(December 1999) posted on Wed Dec 15, 1999

Willey explains how to maximize efficiency in your screen department.

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By Jane Willey

Editor's note: Several years ago, Jane Willey developed this comprehensive guide to screenmaking efficiency, which was published in our March 1994 issue. Since the article appeared, Willey has shared its principles and procedures with one consulting client after another. "These techniques have withstood the test of time, and they work," she concludes. Here, we present an updated version of the article to help prevent bottlenecks in your screenroom and ensure smooth production. The definition I use for screen department efficiency is meeting press demands for screens in both quantity and quality at the lowest cost. The ability to keep print production running is essential, no matter what problems crop up to influence daily screen output. To meet screen demand, you must have the correct number of screens in the loop, an adequate physical space with good workflow, quick response time to emergencies, and the ability to produce screens that will perform predictably every time. In the real world, however, such perfect screenrooms rarely exist. In fact, I often find that print-production problems begin in the screen department, which is frequently ignored and underbudgeted. Consequently, it is often under fire for being unable to produce quality screens at a rate that will meet press demand. In many cases, screen quality is so inconsistent that it becomes impossible for the screen department to meet demand because the remake rate is out of control. I typically see conditions in the screen department that vary anywhere from deplorable to okay, at best. Usually, the area is physically scattered and inadequately lighted, with little or no temperature or humidity controls, water on the floor, clutter and dirt everywhere, and no clear pattern of workflow. How can you expect to have efficient and quality production under these circumstances? Remember, the screen is the printing plate. A stable, accurate, and durable frame, mesh, and stencil are required to print quality work repeatably. In addition, these quality screens must be available in the right quantities, mesh counts, and sizes when production needs them. Until the screen department has adequate space, equipment, and, most importantly, a controlled process, high-volume screen-printing plants will never be able to meet the demands of increasingly complicated art and escalating production rates in an efficient manner, let alone a cost-effective one. This is particularly true in high-volume garment-printing plants, where screen volume is often higher and mistakes lengthen setups and press downtime. So how can you achieve this optimum level of screenmaking and, in turn, print-production efficiency? First, you need to determine your shop's capabilities. While many variables determine the size and production capacity of individual screen departments, several constants must be considered as minimum parameters to meet quality and efficiency for all screen departments. To understand what these constants are, it's important to first understand the components of the screen loop. The screen loop The screen loop is a standardized set of steps and procedures that are repeated daily to produce press-ready screens (Figure 1). The more streamlined and uninterrupted the screen loop, the more efficient your screen department will be. The goal of the perfect loop is to adequately supply production with the needed volume and mix of high-quality screens and be able to react to the occasional ripped screen without interrupting the daily screen output. But note that no loop can be successful unless you have proper scheduling and planning in place. As you can see from Figure 1, the amount of handling and steps needed in screenmaking are numerous. Each step has a direct bearing on the finished product. The steps shown here can be applied to both a static-frame (stretch-and-glue) or a retensionable-frame screen loop. All are based on a non-library reclaiming system, where most screens are reclaimed after use, not stored with the stencil intact for repeat jobs. Although a library would typically reduce the number of screens produced per day, it would require many more screens and would not reduce the number of steps in the loop. Each step in the loop is important, and the penalty for neglecting one is severe. I will assume that you know basic procedures and techniques for each step. The areas I'll discuss are ones that are most often overlooked or cause devastating results if not given close attention, including: * fabric retensioning * degreasing * proper screen inventory in stretched and coated storage * sufficient drying for coated screens * quality inspections and controls When parts of the loop are eliminated or frequently ignored, it's usually because the screen department is operating in a crisis environment. The rule of "we don't have time to..." takes the place of following proper procedures. This results in screens that are not durable for press runs or do not image correctly and have to be remade a second or even a third time. If the problem isn't discovered until the screen goes to press, print production is likely to experience unscheduled downtime. Soon, a state of crisis becomes the norm instead of the exception, and no screen leaving the department has been through all of the required steps. At this point, not only is efficiency gone, but you are now playing "screen roulette," where there is no guarantee that any given screen will have the quality or durability standards you desire. Here's a short synopsis of the repercussions you face for neglecting each of the most commonly skipped steps. Retensioning This is the first crucial step in screenmaking. Unfortunately, it's often circumvented, especially when using static frames. As Figure 1 shows, at least one relaxation/retensioning step is required. This is particularly important for static frames because this is the only time that you can enhance mesh stability before the frame is cut loose from the stretcher. Stable tension means a stable image, more accurate registration on press, and longer mesh life. All of this yields better screenroom efficiency. While recent testing indicates that you can skip the relaxation and retensioning steps in screen stretching, practical application in a production environment proves these steps necessary, particularly with higher mesh counts (305 threads/in. or higher). You just can't achieve maximum tension levels in a single tensioning, and attempts to do so actually weaken the mesh and increase breakage rates. Degreasing When you skip this step, you invite the possibility of "fisheyes" (uncoated areas on the screen), pinholes, and even stencil breakdown during a press run. You must degrease your screens to ensure that you have a clean surface to which the emulsion can bond. If you're using capillary film, abrading the mesh before degreasing is also a must. Minimum numbers of stretched and coated screens This is absolutely critical to the maintenance of your loop. Approximately 40% of your total screen loop should be maintained in these two stages of your screen cycle to serve as a shock absorber. If a substrate doesn't arrive in time for production or if a rush job is moved up in the schedule, these extra screens cushion the blow. If breakage or makeover rates constantly drain your screen reserves below these minimum numbers, then you need to determine the root of the problem and take steps to correct it. Without adequate reserves, you cannot react in a timely manner to a screen that is damaged during a press run or to a rush job that must go out. Nor can you meet daily screen output minimums. Drying After retensioning and degreasing, the next most neglected step is thoroughly drying coated screens. Complete drying of the stencil is a function of time, temperature, humidity, and airflow. If you compromise one of these, you compromise screen integrity. Dry your coated screens horizontally, print side down, in a temperature- and humidity-controlled, safelighted environment. The amount of time will be dictated by the emulsion, capillary film or other stencil system you are using and your plant's specific environmental conditions. However, if water is on the floor and/or in the air of the drying area, the drying time becomes days or never instead of minutes or hours. Incorrectly or partially dried screens may result in a myriad of problems including pinholes, poor image resolution, and stencil breakdown on the press. Inspection and quality control Pushing screens through the loop faster than intended usually means that something is going to be bypassed. Setting up a press and then discovering that a screen is ripped, incorrectly imaged, out of register, or unprintable for some other reason is both costly and frustrating. Setting up inspection and quality-control points throughout the screen loop can prevent this from happening. Not only will the QC points keep less-than-perfect screens from reaching the press, but they will also provide a constant check on the screenmaking process. Keeping good records will illuminate recurring problems and the conditions that lead to them. By noting a condition that historically has created problems, you can correct it during the screenmaking process and keep it from interrupting the loop now. Some key conditions that you need to monitor are listed in Figure 2.


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