by Jeff Peterson
Screen printers, whether they are involved with screen printing plastic containers, flat sheet displays, or even textiles, all have an important decision to make between creating their own screen making department or utilizing an outside source. There are definite advantages in both directions. Let us explore what is recommended and needed to begin a screen making department and weigh the pros and cons of in-house screen making versus outsourcing your screens.
Screen Making Necessities
The first area you must work with when beginning a screen making department is the prepress. A person who understands how to work with artwork, either camera-ready or electronic, is necessary to properly separate the colors before making the screens. This is especially important on multi-color jobs, where such things as choke, traps, and tints must be mechanically compatible with the ink and mesh. Having an in-house art department is your best solution, however, the cost of the computer equipment and the graphics person can be quite expensive. You may want to consider working with a service bureau to help you create the right film positives for making the screens. This can work well if the service bureau understands the trapping and other issues involved with making film for screens.
The next step in making your own screens is choosing the correct mesh and frames. There are many types of mesh from which to choose. Most commonly, meshes for screen printing on plastic containers are made of nylon or Monofilament Polyester. Frames are available in three main types: aluminum, wood and specialized metal forms. Container decorators may prefer one over the other. Developing a method that best fits for your particular application is the optimal way to decide on the correct frame. Once you have determined the correct mesh and frame to be used, the screen must be stretched before exposure. Frames can be stretched by hand (hand stretchers start at around $500) or a pneumatic system can be used that can range from $3,000 to $8,500. Of course, the number of screens you will be using will determine how sophisticated of a system you will need. There are also some self stretching frames on the market that might be worth looking into.
The next step in creating your own screens is transferring your graphic to the screen. There are several methods of sensitizing (creating a photographic image on the screen). Most screen printers use direct emulsions where a liquid emulsion is coated over the mesh. It is important to remember that some screens require heavier coats of emulsion and others lighter coats, depending on the application.
The screens must then dry using a rack or cabinet. Once the emulsion has dried on the screen, you must expose the image by placing a film positive onto the print side of the screen with the image reversed emulsion side down. The sandwich is placed under a vacuum and under a light source to expose/photo-initiate the emulsion. Recommended light sources are metal halide or mercury vapor. Some people have used tube florescent or black lights as well. This can work, but can sometimes create a lesser quality screen. Prices for a self contained vacuum and light source can range from $1,300 to $4,000 for fundamental units to $5,000 to $6,000 for modern sophisticated metal halide units.
The last step is to wash out the screen in water, utilizing a washout sink and a power water sprayer to dislodge fine emulsion particles in the image area on the screen. You must be very careful with this to not knock out emulsion in the non-image area. Again, the screen must then dry by vacuuming excess water or blotting it with a clean paper. Once the screen has dried, check the non-image area of the screen and touch-up any pin holes with block out.
What do you know, you have a screen for printing your bottles, containers, ad specialties, or other plastic items. Now the question is, do you want to do it yourself?
Pros and Cons
As you can imagine, developing your own screen making department has its pros and cons. Probably the number one advantage is immediate turn-around time. If you are in a situation where turn-around time is critical, it may be a consideration. A well set-up screen making department can create a screen in a few hours versus two to three days by outsourcing it. Another advantage is the ability to make adjustments to your screens on the fly. If you have the ability in-house, it is feasible to control tension levels, registration/pre-registration and squareness. If an outside source has made the screen, you could lose one or two more days sending it back and forth. In addition, if the screen is being shipped to you via a carrier, it can create stress on the screen. Temperature and humidity changes, bumps, knocks, and vibrations can all affect the mesh tension and the overall quality of the screen. Of course, this is not much of an issue if your screen maker is local, or has taken special precautions for shipping purposes.
If you have in-house screen making, you can also pre-coat or sensitize screens that are ready for immediate exposure if a screen is accidently torn or ripped. Lastly, in-house screen making can save you dollars and become a profit center for the company after the initial equipment investment or through amortization. You must analyze the number of screens you use on a monthly basis, the number of employees it will take to run the department, and the equipment investment discussed earlier in this article to conclude if it is worth it. There really is no hard barometer. Every situation is somewhat different.
On the other side of the fence, there are many advanatages of utilizing an outside screen maker as well. First, is the assurance of quality screens from someone who knows how to make them and has the experience to deal with problems that inevitably arise. Yes, creating your screens in-house does provide the advantage of making adjustments yourself. However, this is a moot point if you do not have an experienced person to correct the problem. Space should be a consideration as well. The equipment needed to have a screen making area does take up a fair amount of space with an exposure unit, processor, washout sink, etc. And, of course, an outside source can eliminate at least one additional employee if not more. Another key advantage of outsourcing your screens is eliminating the potential OSHA and EPA requirements which could prevent hazardous materials issues (i.e. adhesives, chemicals for processors).
As cost may be an advantage for keeping screen making in-house, it may also be an advantage for outsourcing. Again, this depends on the number of screens you use, the amount of money you may have to spend on an employee, as well as your equipment investment.
There are no cut and dry answers. If you can develop a relationship with a screen maker that knows your equipment and keeps quick turnaround times, you may not need to consider your own screen making department. If you have decided that you must have control over turnaround times and quality, then making your own screens may be the best decision. Hopefully, this will provide a little food for thought.
Plastics Decorating would like to thank Allen Shust and Bill Zigmond of Chicago Silk Screen Supply Co., Inc. (312-666-1213), and Harold Hallbom of A.W.T. World Trade, Inc. (773-777-7100) for their assistance with this article.