Screen Printing - Not Just For T-shirts
Feb 21, 2015
Whether in an industrial art class in high school or when ordering custom t-shirts, screen printing is often a person’s first contact with printing other than desktop computer printing. So screen printing is the term most often used to discuss an item that needs to be printed. Here is more information about the screen printing process as it applies to printing rigid plastic, glass and metal parts.
Product Decorating Services – Screen Printing
Screen printing is a printing method that allows the transfer of large opaque images onto flat (or relatively flat) and cylindrical plastic, glass and metal objects. The origins of screen printing date back thousands of years -- from early Polynesian natives who forced die through cut-out patterns in banana leaves to decorate cloth, to cave walls found in France and Spain that were decorated by way of stencils and colorant applied with blowpipes, to the Japanese creating intricate designs during the Sung Dynasty (A.D 960-1280). Today, screen printing is used to decorate rigid parts for a variety of industries.
The screen printing process is actually very simple – ink is pressed through an image in a screen onto an item. But there is more to understand about screen printing. The procedure starts with a screen that is tightly stretched around a rigid frame; the screen is made of very fine mesh that allows ink to pass through it. Next, a liquid emulsion is applied to the screen. Once the emulsion has had time to air dry, a film positive of the image to be screen printed is placed on the screen. The screen is then exposed to UV light, which hardens the emulsion to the screen except where the film positive is blocking the UV light. The soft emulsion under the film positive, which was not exposed to UV light, is then washed out of the screen. The hardened areas of emulsion prevent ink from passing through, but ink can pass through the open area on the screen which is in the shape of the image to be printed. The screen is then positioned over the item to be printed and ink is poured into the screen; a squeegee is used to press the ink through the image in the screen and onto the part. If using a solvent based ink, the printed items are either left to air dry and cure or passed through a heated oven. If using UV based inks, the printed items must be passed through a UV curing tunnel for the inks to cure.
Why choose Screen Printing?
While screen printing can be used to decorate almost any plastic, glass or metal item, the process is typically used to decorate large flat parts or cylindrical bottles or jars requiring two sided or wrapped images. Unlike other product decorating methods such as pad printing or hot stamping, screen printing is less restricted by image size. So, playing to this strength, the process is best used for parts requiring large images such as plastic or metal control panels or plastic or metal signs. Screen printing is also the preferred method for printing cylindrical items such as plastic bottles, jars, syringes, flow tubes and vials as well as the increasingly popular metal water bottles. When screen printing flexible parts such as polypropylene cosmetic bottles or PET jars, air is forced into the parts to provide the rigidity needed to withstand the printing process. For most semi-automatic equipment, multi-color images are achievable but require a separate pass for each color.
Inks for Nearly Every Material
As with pad printing, screen printing inks are formulated to match the type of material to be printed. Ink lines are developed to provide adhesion and durability for a variety of material such as plastic, glass, metal, wood or ceramic. However, matching ink to the substrate does not stop there. Ink lines are available for practically every plastic material such as (but not limited to) ABS, Acrylic, HIPS, polycarbonate or nylon and for various coatings or paint used on metal products. With certain pre- and post- treatment procedures, more difficult materials such as polypropylene, polyethylene, Delrin or Urea can also be screen printed. For most applications, inks are either solvent-based, which are cured with time or by adding heat to improve adhesion or durability for some substrates, or UV based using ultra-violet light for an instant cure.
Screen Printed Parts in Every Industry
Screen printing is used to decorate plastic, glass, and metal products - practically any rigid item that requires a logo or marking - from many industries including automotive, medical, electronic devices, cosmetic / health & beauty, and plastic molders and manufacturers.
I hope this information has left you with a better understanding of the screen printing process. Feel free to contact me if there is anything more you’d like to learn or understand about screen printing and how it works and relates to your project or business.