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Screenprinting 101 Part II
By John Benedetto
These articles are written with the beginner in mind, many times there are several answers to the same problem. In this format, the answer comes from my years of experience in the screenpriting industry both as an equipment manufacturer and first and foremost, a screenprinter. The information presented in these articles is general in scope and written with these basics in mind.
Screenprinting is used to enhance a variety of products: T-shirts, jackets, hats, etc. This is only the tip of the iceberg of what you can print. Wood, metal, plastic, leather, paper and glass are a few of the substrates possible to print. The only thing different is not the process, but the type of ink that you may use to print on these items. The rule is ďIf it is flat you can print it!Ē
Screenprinting is a simple science. It has been around for over 5000 years. The Chinese invented the concept. You have to be able to do only three things to be a screenprinter: Make a screen, print a screen and dry the item.
After five years of putting people into the screenprinting business, the biggest hurdle we must overcome is understanding artwork. Most of us are not artists and often we are computer neophytes. To me, artwork is anything I can make a photocopy of.
I am a very good screenprinter but I am a terrible artist. If I had to do the artwork I would not be in this business. I feel that I have two left hands. Here is the key to artwork: It is the customerís responsibility to give you good artwork, and in most cases, camera-ready artwork. It is the customerís responsibility to pay to get good artwork made if it is not usable by you, the screenprinter. Do not give your artwork away. Charge for it! Remember, if you do it for fun it is a hobby if you make a profit it is a business.
We are going to talk about spot color printing for the sake of this article. That is, each color in a design is separate and distinct. Four-color process is more for the advanced than for the beginner.
Artwork needs to be separated into its individual colors. Letís say you have a logo and it is made of red, blue and green. You count the colors and you get three (obvious). You will need three screens to print this design. If you need three screens you will need three separate pieces of artwork to make these screens (One piece of artwork per color in the design). This is called color separations. One piece of artwork, one color, and one screen (simple math).
Most beginners get overwhelmed with the idea of artwork because they see all those shirts and designs that appear to be six to ten colors, and in some case they are six to ten colors. Do not let this cause you concern. Here are some statistics: 80% of all logos in the world are made of one color. Just look at your major companies and corporations. Another ten percent of all logos are two colors. School logos are a good example of this in that they have two colors. The final ten percent is everything else.
Chances are most of your jobs can be and will be simple in design. Start looking at logos and signs to get an idea. The more complicated they are the more they have to pay for printing.
Artwork only comes three ways: A customer gives it to you, you develop your own, or a customer asks you to develop or fix up their artwork. Either way it is a charge to the customer. Profit is not a dirty word.
U. V. Paper
After you have the separations, you need to put them on a medium that allows light (more specifically, ultra violet light) to pass through. In times not too long ago, that medium was called a film positive. It is actually a film process that is expensive and that you need special equipment for.
Now most screenprinters that I know use UV Paper (ultra violet printing paper). It is much easier to use. It can be used in most copiers or laser printers and you can draw right on the paper. It is very cost effective. If you can push the print button on a photocopier you can make artwork.
Note: for the following sections, Screens, Expose and the beginning of Wash Out you will need to be in a Safe light (Yellow Light). Coated screens are like film, if put into white light they will be exposed and rendered useless.
A screen is made up of two parts: the frame and the mesh. The mesh, in most cases, is glued to the frame. In general, the tighter the mesh is pulled (stretched) on the frame the better you can print it.
Screens are labeled by mesh counts. Different mesh counts for different jobs. The higher the mesh count, the finer the detail or line you can hold with your screen and print in your design.
After you have your screen you will need to apply emulsion onto its surface. Emulsion is a photosensitive solution that reacts to UV light. It reacts in the same way that film reacts to light when you take a picture. Emulsions can be in liquid form or in capillary film form.
I prefer the liquid type (personal preference), but they all work. Emulsions come in different colors, single or two-part and they all react different to light so you will need to do a timing chart (discussed later in this article) to determine your exact exposure time for your screens. There are factors that change exposure time: Do you live in a wet or dry environment? Do you live at sea level or in the mountains? How thick do you coat the screens you are going to expose?
I teach my screenprint students to coat the screens with one coat on the squeegee side (inside the screen) and one coat on the print side (bottom of the screen). Most emulsion manufacturers suggest three coats squeegee side and two coats print side. If you are doing print runs under 144 items, my way works very well. It is my belief that emulsion makers are out to sell more emulsion.
After the screens are coated they need to be put horizontal in either a yellow lighted or no light room to dry. It is a good idea to run a small fan at low speed close to the screens to aid in the drying process. After they are dry I put them into a cardboard box and seal it until I need a screen to expose.
Now we are ready to marry the artwork. That is, to join the artwork and emulsion coated screen to create an exposed screen (negative) to print.
Remember you are still operating in the yellow light. Take your artwork that has been printed onto the UV paper (or film positive) and a dry screen with emulsion and go to your exposure unit. In my system, the exposure unit is built into the printer so you will put the artwork on the exposure glass where you are going to print it, in registration. With most all other printers, you must adhere the artwork to the printside of the screen then turn on the exposure lighting system, whichever one you have. I even know of screenprinting companies that take their screens out into the sun to expose them. All these systems work. It just depends on you and your shop philosophy.
I need to back up just a small step here. If you are doing your very first screen or you have changed emulsions types or brands you must determine the correct exposure for screens. For a price, there are timing gauges and kits made to do this.
However, there is an easier and cheaper way to find your correct exposure. It is called a timing ladder. The following is an example:
You now have a screen that has been exposed in four different sections for times of two, four, six and eight minutes. Now we will discuss Wash Out.
After you have exposed the screen it is time to wash out the image. While still in the yellow light take a squirt bottle filled with cool or luke warm water. Spray the screen with a mist spray on both sides then let it sit vertically for about a minute and then repeat the process.
You can know take your screen to the wash out area. It may be a designated area with sinks and tubs in your shop or it can be your bathtub or the garden hose on the side of your house. It all works. Try to keep the screen from direct light as much as possible, but it is not as critical as during exposure.
Take the screen and spray it with a water hose with a spray about the power of your shower. You will see the emulsion in the areas of the artwork begin to melt out of the screen. Continue to wash till the artwork area is clean. This is just like photography. Now you have just made a negative!
If this is your very first screen you will notice the four different areas that you had made for our timing chart. Begin by feeling the screen. If there are areas, usually in the two to four minute ranges, that feel clammy, scummy or slimy on your screen, those areas are under-developed. You want to feel a smooth and solid screen.
If you use a under-developed screen it will breakdown in a very short printing time and your print will not be good for very long.
Now look at the screen. I like to put it up to a strong light. Look for a clean and clear definition of the design in one of the areas. There is a good chance two or three of the timed areas look good. So how do you tell which is correct or the best?
After the screen is dry, set it on top of the artwork. If there is an area where the artwork is a little larger than the design area in the screen the screen is over-exposed in that time slot. If there is an area where the design area of the screen is a little larger than the artwork, the screen is under- exposed. Your exact exposure time is where the artwork and the design area of the screen are the exact same size.
If you want to be more precise in your judgment, do a second screen in smaller time increments to get a more exact time.
Let the screen dry. Tape off the edges and in the next issue we will begin to print.
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