Natalie Thomas, of MHM Direct GB, explains why every printshop should own, and use,
an exposure calculator.
How many times during a print run, do you experience problems
such as premature stencil breakdown, pin-holing, and
poor mesh adhesion from your emulsion? Unfortunately,
for some printers this can be a regular occurrence, resulting
in screens having to be remade, patched or 'spotted out';
finished garments being scrapped; and the stencil making department
becoming a bottleneck for the factory. Why do these problems occur? In
all likelihood it's because your stencil maker does not periodically use an
exposure calculator as part of their quality control process. In fact, it is
estimated that only a half of all the UK's print shops actually own an exposure
calculator; and for those that do, the exposure calculator is, more
often than not, locked away in a drawer!
The 'problem' is that few stencil makers (or printshop owners) appreciate
the importance of using an exposure calculator as a calibration device
for their exposure unit: without one your exposures could be 'all over
the place'. The resulting premature stencil breakdown or compromised
durability of your screens could be costing you money, not to mention the
downtime and headache of having to remake those screens.
There are many different exposure calculators on the market – every
major emulsion or capillary film manufacturer offers their own – but they
all have the same common goal; of helping you to determine the correct
exposure time for a stencil with the print characteristics that you require
for each print run.
What is an exposure calculator?
On all exposure calculators, you will find either a step wedge or filters
with varying densities that allow/block, a specific amount of light. These
enable you to quickly carry out multiple exposures on one 'test' screen in
order to precisely calculate the optimum exposure. Emulsion thickness,
mesh count, mesh colour and lamp age all have an impact on the correct
exposure time, so being able to calculate your exposures quickly and accurately
will increase both quality and efficiency throughout your entire
production process.
The CPS Exposure Calculator is simple and easy to use. It is a film
positive comprising five columns. Each column has a resolution target, a
set of halftone tints and various lines of text. It is marked with a 'factor'
number, and four of the columns are backed with a grey neutral filter
of different densities. These allow more or less light to pass through
during exposure. This format enables five different exposures to be made
simultaneously on the same 'test' screen.
Calculating correct exposure times using the CPS Exposure Calculator involves
the production of a 'test screen' and the evaluation of that screen.
To produce the test screen perform the following three-step process:
Step 1 Estimate the correct exposure time using the guidelines supplied
by your chosen emulsion manufacturer, and then double it.
Step 2 Use the exposure calculator as your film positive and expose the
>stencil in the normal way; wash out the screen and dry thoroughly.
Step 3 Examine the stencil to determine the correct exposure. For direct
emulsions and direct stencils this is the point at which the entire thickness
of the exposed stencil is fully hardened by the UV light from the
exposure unit. This process of exposing/hardening is accompanied by a
colour change in the stencil.
Once you have produced your 'test screen' you can determine the correct
exposure time for your set-up. This is a relatively straightforward twostep
procedure, as follows:
Step A The stencil will show variations in colour from one factor to
the next. Follow the colour change from the lightest to the darkest until
it stops. The factor where the colour change stops is the column that
represents the optimum exposure. Direct stencils are fully and correctly
exposed where no colour change occurs between the arrows.
Step B Once the correct factor has been chosen, multiply the factor by
the test exposure time. This gives the precise exposure time (or number
of light units) for that particular stencil/mesh count/light source combination.
For example, if the 'correct factor' is 0.7 and the 'test exposure
time' was 10 minutes, then the 'correct exposure time' will be 7 minutes
(0.7 x 10 minutes = 7 minutes).
Bear in mind that a colour change between factor 0.7 and factor 1 on the
test screen indicates an underexposed stencil. In this event, double the
original test exposure time, and repeat the test.
Underexposure can result in a weak stencil with poor mesh adhesion,
along with reduced resistance to printing inks and screen cleaning solvents
and so on. It can also make the stencil more difficult to reclaim.
Conversely, overexposure leads to loss of fine detail, but will not compromise
mesh adhesion or solvent resistance.
An exposure calculator also contains definition targets and halftone
tints, which can be used to assess edge definition, print resolution, dot
loss and dot gain. The booklet that accompanies the Autotype/CPS Exposure
Calculator explains in detail how to perform these additional tests .
Remove the guesswork
Incorrect exposure is the single biggest cause of premature stencil failure.
Periodically using an exposure calculator to provide quick, accurate
confirmation of correct exposure times will remove the guesswork and
greatly assist you in understanding the performance of your photostencil.
The exposure calculator is a key piece of equipment that any quality conscious
printshop should never be without.
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New bags and jackets from Regatta
Regatta’s schoolwear offering for 2010/11 goes from strength to
strength with the launch of a new range of school bags.
The new bags include the TRB035 Kids Gymsac, TRB036 Book Bag,
TRB039 School Backpack 20l, TRB008 Highschool Rucksack 10l,
TRB029 Scholar Backpack 20l, and TRB058 Sports Bag 30l. All feature
ample areas for branding and will be available in a range of colours
that co-ordinate with the Regatta schoolwear range.
The brand’s school jackets include the TRW432 Fresher – a lightweight
water-repellent and windproof fleece-lined jacket, in six school
inspired colours.
The TRA652 Kids Uproar softshell is Regatta’s first kid’s softshell for
the school uniform market, and provides a sporty, stylish alternative
to conventional school outerwear. Made from resilient Regatta Softshell
fabric with water-repellent finish, it features reflective trim and a
printed name label. "This jacket is ready for the rough and tumble of
the playground,” Regatta advises.
The TRW418 Kids Dover Jacket, with its snug fleece lining and Thermoguard
insulation, is the children’s version of the popular adults’
waterproof Dover style. Made from Hydrafort fabric, the jacket’s waterproof
protection is guaranteed, states Regatta.
A staple of the Regatta schoolwear range, the TRA900 Kids Term
Time waterproof reversible jacket is made from peached polyester
with a reversible fleece inner, making it a versatile choice for the winter
term. It can be worn as either a warm lined waterproof jacket, or
reversed and worn as a fleece with waterproof lining.
The Regatta TRF542 Kids Thor III Fleece is made from 250 series
anti-pill Symmetry fleece. It has two lower pockets, an adjustable
shockcord hem on sizes 7 years and upwards, and is available in five
traditional school colours. The Kids Thor III is, "A hardwearing and
smart addition to any school uniform,” according to Regatta.
The brand also offers the KW943 Kids Breathable Packaway II Jacket
and KW944 Overtrousers, and the W908 Kids Stormbreak Jacket and
W808 Overtrousers. "These continue to be great sellers in the schoolwear
market," says Regatta.
www.regattacorporatewear.com.
New bags and jackets from Regatta
Regatta’s schoolwear offering for 2010/11 goes from strength to
strength with the launch of a new range of school bags.
The new bags include the TRB035 Kids Gymsac, TRB036 Book Bag,
TRB039 School Backpack 20l, TRB008 Highschool Rucksack 10l,
TRB029 Scholar Backpack 20l, and TRB058 Sports Bag 30l. All feature
ample areas for branding and will be available in a range of colours
that co-ordinate with the Regatta schoolwear range.
The brand’s school jackets include the TRW432 Fresher – a lightweight
water-repellent and windproof fleece-lined jacket, in six school
inspired colours.
The TRA652 Kids Uproar softshell is Regatta’s first kid’s softshell for
the school uniform market, and provides a sporty, stylish alternative
to conventional school outerwear. Made from resilient Regatta Softshell
fabric with water-repellent finish, it features reflective trim and a
printed name label. "This jacket is ready for the rough and tumble of
the playground,” Regatta advises.
The TRW418 Kids Dover Jacket, with its snug fleece lining and Thermoguard
insulation, is the children’s version of the popular adults’
waterproof Dover style. Made from Hydrafort fabric, the jacket’s waterproof
protection is guaranteed, states Regatta.
A staple of the Regatta schoolwear range, the TRA900 Kids Term
Time waterproof reversible jacket is made from peached polyester
with a reversible fleece inner, making it a versatile choice for the winter
term. It can be worn as either a warm lined waterproof jacket, or
reversed and worn as a fleece with waterproof lining.
The Regatta TRF542 Kids Thor III Fleece is made from 250 series
anti-pill Symmetry fleece. It has two lower pockets, an adjustable
shockcord hem on sizes 7 years and upwards, and is available in five
traditional school colours. The Kids Thor III is, "A hardwearing and
smart addition to any school uniform,” according to Regatta.
The brand also offers the KW943 Kids Breathable Packaway II Jacket
and KW944 Overtrousers, and the W908 Kids Stormbreak Jacket and
W808 Overtrousers. "These continue to be great sellers in the schoolwear
market," says Regatta.
www.regattacorporatewear.com.
