Screen Printing: A Brief Overview

Uploaded by techEIU on 16.12.2010

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You might take a quick look at this shirt
and think nothing of it.
Graphics on shirts are pretty common place these days.
Texts and images are combined in a variety of
shapes and colors to create that unique or sometimes comical
message that distinguishes all of our clothing.
But how did that image get there?
What did the designer and production personnel have to do
to transfer that image that started out as an idea in
someone's head to the ink on that shirt.
In the following segments, we're going to show you how
that process all comes together.
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Many conceptual designs that end up on t-shirts have to be
created using some sort of drawing program like
Adobe Illustrator or CorelDraw.
Creating graphics in these programs, allows the designer
to size and resize the image without causing
a loss of quality to the image.
We often call these graphics vector images.
These graphics, unlike photographs react more like
objects with filled in areas of color surrounded by
points in space called nodes.
Think of vector graphics as rubber bands.
You can stretch and shape them any way you need them to go
but they always return to the same shape and size
that they started out as.
It's important to note that when you design these kinds
of graphics for screenprinting, we actually need to use
spot colors or channels.
Many conventional printing processes use the combination
of cyan, yellow, magenta and black ink to recreate color.
But to do so for a shirt would be difficult and expensive.
In this case we will open the PANTONE color pallet to
select the two colors that we will use to print our design.
Once they have been implemented we have
a design ready for output.
To create our screens, we actually need to use
a light sensitive process.
in order to transfer our digital images, we need to place them
on a transperancy to create what we call separations.
These separations will be used to create our stencil that will
help transfer the images to the shirt.
To set up the transperancy, make sure that you turn on your
registration marks and your print dialogue, and set up
your print out to come out as separations.
When you print out your document, the design will
actually come out in solid black and in the corresponding
number of colors that you used in your design.
This design is now ready to be transferred to a screen.
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Many screens need to be prepared with
a light sensitive material called emultion.
There are several types of emultion, each with different
colors and intended uses.
The emultion that we will coat our screens
with is a photo polymer.
To coat the screens, we pour the emultion into a scoop coater.
This coater will be used to apply the liquid to the screen.
Our screen will be held in position by a screen clamp
that is especially helpful in holding the screen in place.
Use the coater to evenly spread the liquid emultion
on the screen and repeat for the other side.
The number of passes depends on the emultion
being used and on the intended product to be printed on.
When finished, the screen will need to be placed in a dryer to
allow the emultion to dry.
The emultion we used is water solluable before
being exposed to ultraviolet light.
Thus, if we wash the emultion at this point all
of the emultion will come right out.
However, if we expose the screen to ultraviolet light and then
try to wash the emultion, none of the emultion will wash out.
This is where our transparencies come into play.
Taking a ruler and pencil we will mark the positions
for our transparency and tape it into position.
For multiple colors, this will need to be the exact
same measurement on the other screen.
This side of the screen will be exposed to an ultraviolet
light source at this point.
The black on the transparencies blocks the areas that
do not recieve ultraviolet light.
The rest of the screen will be exposed to ultraviolet light.
Our result when it is washed out, is that our image on the
transparency is open mesh but the rest of
the emultion will be hardened.
We place the screen with the transparency
on our exposure table.
This table allows for us to hold the screen and transparency in
close contact so that we have a good exposure.
We lift the table so that our light source is exposed
to the exposure unit.
We dial in the appropriate time and intensity and allow
the UV light to do all the work.
After the exposure is completed we remove the transparency and
wash out the image area with a little bit of warm water.
The screen is then placed in the dryer to fully dry.
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Once our screens have fully dried we are ready to
load them on the printing press and begin the process of
registering or lining up our screens for print production.
In this case our image that will be printed on our shirt is a
two-color, left-chest design.
We begin the registration process by lining up one of our
separations on a board that will hold our shirt in place.
We do our best to measure out the exact position
by loading our shirt and marking relevant points such as
the top of the collar.
This will assist us later on in production.
Once our separation is properly registered on the board,
we can then begin to line up the screen with
the separation on the board.
The registration marks that were printed on the separation have
also been transferred to our screen.
The name of the game here is to line up the registration marks
on the separtation taped to the board with
the separation marks on the screen.
It may be neccessary to adjust the position of the board to get
the marks in general position.
After it is in general position, you will use the
mircro-registration to ensure the image is lined up properly.
You will need to repeat this process
for each subsequent color.
At this point we are almost ready to do a test print.
Before we do, we need to mask off the screen.
We place the tape around the boundaries on the top side of
the screen in case we get a little messy during our print.
In our image area, we taped off the registration marks
and any pin holes that might have popped up
in the bottom side of the screen.
This will ensure that any unwanted information
does not get printed onto our shirt.
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An important part of ensuring that your print
comes out at the highest quality, deals with
the selection of your squeegee.
Squeegees come in a variety of configurations
and characteristics.
You should consider the kind of ink and fabric that you will be
printing when selecting your squeegee.
In this case we will be printing with plastisal ink,
suited for printing on textiles.
We are now ready to do a test print of our image.
The colors of ink that we will print, will be spread
on their designated screens.
Afteer the inks are spread, we grasp a squeegee and drag
the ink accross the image area with light pressure.
This is called flooding.
Once the image has been flooded, we lock the screen down
in position and grasp the squeegee and apply
a bit more pressure to force the ink through
the open mesh and onto the substrate.
We lift the screen to check our quality.
At this point, we still need to print one more color.
We do not however, want the wet ink to transfer from the shirt
onto our other screen.
In this case, we will move it under our flash curing unit.
The unit uses heat to dry the ink so that we can
print our next color.
Once the ink is dried, we rotate the board and next screen into
position and repeat our printing technique.
We can then remove our test square from the board and run it
through our belt dryer for final curing.
A typical production press will work like this.
All of the boards have been aligned in the proper position.
The shirts have been loaded on the board and one color
at a time is printed.
As each color is printed, the press is rotated and ink is
dried on the newly printed shirt with the flash curing unit.
Meanwhile, the next shirt is printed to allow for
continuous production.
Once all of the shirts are printed, they are removed from
the press and sent to the dryer for final curing.
Your new shirt is now completed and ready to be worn.
Now that wasn't so hard was it?
As you can see, the screenprinting process is
versatile, fun and easy to do.
Hopefully what you've seen here has been informative and helps
get you started to making some great looking t-shirts.
Good luck.
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