Screen Printing Equipments

Group 3: II- Edison

BASIC MATERIALS

Screen Printing Equipment:

Emulsion 

Photo emulsion is what makes the modern day screen printing process possible. The emulsion

is a substance that reacts to ultraviolet light. Once it has been exposed to the correct ultraviolet wavelength, the

emulsion hardens and becomes impermeable. There are many different types of emulsion in the market, as well as many

different methods of application. In a later post, I’ll dive into the two most popular methods for coating the screen mesh with

emulsion.

 Squeegee

A squeegee is a flat, rubber or urethane blade set into a

handle. Some people may argue that this is not

necessary and that brushes or sponges can be used to

push the ink through the screen. They are correct and

it can be done, but the results and time

consumption can lead to very mixed results. Almost

all professional screen printers use squeegees to

produce consistent, high quality results.

Scoop Coater

This is a tool that is used to coat the screen

with a thin, uniform layer of liquid photo

emulsion. Without the scoop coater it is possible to use a

squeegee to spread the photo emulsion but this can sometimes lead to uneven thickness and poor exposure results.

Film Positive (Artwork) 

The film positive refers to the artwork which is typically printed or

drawn onto on a transparent medium. The artwork must be

opaque in order to produce proper results when exposing the screen.

One of the cheapest ways to create the film positive is to print directly

onto transparency film from your laser or ink jet printer. Be sure to

have the printer settings set to produce the darkest black possible for your artwork. As an alternative,

vellum can also be used as a film positive. If you are using vellum add approximately 20% to the exposure

time due to the reduced transparency of the vellum.

Light Source 

In order to properly expose the emulsion

and “burn” the screen, a light source is

required that contains Ultraviolet Radiation in

the 350-420 Nanometer spectrum. Fluorescent unfiltered tubes, metal halide lamps and even the sun can be used to

expose a screen.

Hinge Clamps 

These are essential if you plan on screen

printing paper goods or other flat objects. The

hinge clamps you to keep your screen in the same position, allowing

for easy registration and consistent prints.

 Tape

There are kinds of tape that I use on a regular basis. The first is painter’s tape which use for easy registration of

screens, positioning acetate, etc. The second type of tape that I use is a tape made for

screen printing which is water and solvent resistant.

This one is used for taping my screens. I have also used

plastic packing tape with great results.

Yellow Light Safe Bulb

During the coating and exposure process it is

important to create light safe conditions. Premature

exposure to UV light (sunlight, regular household

lights, etc) can pre-expose the coated screens resulting in poor results. Yellow bulbs

filter out the spectrum of light that can expose the

emulsion, making it “safe” to work under those conditions.

INKS

Screen Printing Equipment:

There are two main types of inks that are used for screen printing, each with their own advantages and disadvantages.

Water-based inks utilize either dyes or pigments in a suspension with water as the solvent. The evaporation of the water is necessary to set or cure the ink.

Plastisol is a thermoplastic ink. It is composed of PVC (polyvinyl chloride) particles suspended in a plasticizer. High temperatures are required to cause the molecules of PVC resin and plasticizer to cross-link and fully cure.

Advantages of Water-based Inks

Water-based inks tend to be a little more environmentally friendly and give printed fabrics a soft “hand”. A soft hand means that your hand cannot easily feel the ink when it passes across the surface of the fabric. Water based inks printed on fabric can also be ironed (Plastisol will melt and smear if heated up to it’s curing temperature). For paper screen printing applications water-based inks are ideal as they will air dry as the water content in the ink evaporates. Clean up is easy and can be done without much impact to the environment.

Disadvantages of Water-based Inks

Water-based ink is much more difficult to cure than plastisol for fabric applications. With water-based ink, the curing temperature must be reached and then held until all of the solvent (water) is removed. If you don’t fully cure the ink (for example on a T-shirt), the ink will fade with repeated washings. If water-based ink is left in open mesh for even a short period of time, it can clog the mesh and ruin the screen. You don’t really have to worry with regards to paper applications however. The other thing is that water-based inks will break down regular emulsion very quickly and even break down water resistant emulsions over time leading to screen breakdown for longer print runs.

Advantages of Plastisol

Plastisol inks are not water-soluble and the ink will not dry if left in the screen for extended periods of time. It can be left in the screen for extended periods of time without worrying about clogging the mesh. Platisol will not break down the screen emulsion like water-based inks. They also happen to be very opaque and great for applications on colored fabric

Disadvantages of Plastisol Plastisol inks will not air dry and need to be cured

(heated) as a result. Curing the inks can be done with a flash dryer, or more inexpensively, any home oven. Be careful not to burn your house down! Most plastisols need to reach a temperature of about 350 Fahrenheit before being fully cured.

Plastisol tends to sit on top of the threads instead of soaking into them, which typically results in a raised, plasticized texture. There are, however, plastisol additives that can give the ink a softer “hand”. If the ink is under-cured, the print will crack and peel over time.

Plastisol inks are generally considered harsher on the environment. Fortunately, there are a number of plastisol inks on the market that contain less toxins, and there are also eco-friendly solvents that are available for clean up.

Inks

Screen Frame

Screen Printing Equipment:

The screen frame is a structure that the woven mesh is stretched upon and adhered to. Screen frames come in a variety of shapes and sizes, depending on the size of the art work and printing surface. The mesh is either stapled or glued to the frame with sufficient tension to provide a flat printing surface that will not buckle.

Typically, frames are made out of wood or aluminum. Personally I recommend aluminum frames over wood because they are easily cleaned and can be reused indefinitely without losing their shape.

Wood screens will be fine for a while but repeated water exposure tends to warp the frame over time. Over time, with extended use, both wood and aluminum screen meshes will lose some tension which may result in poorer quality printing results. If you start to notice this occurring it’s best to have the screens re-meshed.

Always choose a screen frame that is larger than the area you are attempting to print by at least 2 inches on every side. This will make your life easier when applying emulsion, exposing artwork and printing.

The SCREEN FRAME

Screen MESH

Screen Printing Equipment:

Woven mesh is the “silk” in silkscreen. Typically this mesh is made out of mono-filament polyester fabric which is stretched taut over a screen frame. The spaces between the mesh make the fabric porous which allows ink to pass through.

Screen fabric come in a wide variety of mesh counts. Lower mesh counts means that the fibers of the mesh are spaced farther apart, allowing more ink to pass through. Higher mesh counts deposit smaller amounts of ink and are generally better for fine details and line work. A general rule of thumb is 110 – 160 mesh count for fabrics and 230+ if you are printing on paper. If you are on a budget and only want one screen, 150 should do the trick for both fabric and paper.

Screen mesh is available in either white or dyed mesh (typically yellow). Dyed mesh cuts down the amount of light diffusion during the exposure process which leads to a sharper print. For lower mesh counts around 110 it doesn’t really make a difference if the color is white or dyed.

The SCREEN MESH