FOR IMMEDIATE RELEASE
April 2004

SPTF Research Examines Exposure Light Distribution Use of Radiometers Highly Encouraged

FAIRFAX, VA -- Using radiometers, Screen Printing Technical Foundation (SPTF) researchers have demonstrated how exposure light distribution can be measured, as well as showing the effects certain variables have on that distribution.

Exposure is one of the most critical control points in the screen printing process.

“Improper stencil exposure is one of the leading problems occurring in screen printing companies today,” explains SPTF Training and Resource Manager Dawn Hohl. “Incorrect or inconsistent exposure can create costly problems in production—including stencil breakdown on press, excessive pinholes, poor print quality, inaccurate image reproduction, and reclaiming difficulty.”

Stencil exposure has three primary objectives: to faithfully reproduce the original film; to fully harden the stencil so it can endure during the print run; and to allow a stencil to be easily reclaimed.

A number of variables must be controlled to achieve these characteristics.

One important variable affecting exposure, the SPTF research found, is uniformity of light hitting the exposure area: Do the corners of a stencil receive the same intensity and quantity of light as the middle of the screen? If not — and the difference is great enough —a stencil will have inconsistent properties in terms of durability and image reproduction. Light distribution becomes even more critical when emulsion speed increases and/or the emulsion thickness decreases.

High detail and halftone printing is especially impacted by even exposure. The light profile is a result of the lamp type and configuration, lamp distance and placement, reflector design, and lamp age.

Using a grid, SPTF researchers measured UV light output across the exposure surface of several exposure systems.

These variables are complex. SPTF recommends that a radiometer should be used to measure the exposure area and get a true picture of the light distribution for a given set of conditions.

Several step-by-step procedures presented in SPTF’s report detail how to use radiometers to determine acceptable exposure area, fine tune lamp position, monitor lamp life, check an integrator’s performance, and function as an independent integrator.

“It is important that we establish some basic starting points for standardizing exposure practices by determining the capability of equipment and other variables present,” concludes Hohl.

“Time spent improving or tuning an exposure system to make it consistent can easily return dividends of high quality and higher press efficiency. The cost of a radiometer and the time spent to do some simple testing will be quickly returned when fewer problems and screen remakes are experienced.”

Results, presented in this special SPTF report entitled Testing Exposure Light Distribution, have been published and distributed to all SPTF Endowment Investors. An electronic version of the report has been sent to SPTF Operational Fund investors and will be available online to all SGIA members in July.

For more information, please contact Dawn Hohl at Foundation headquarters.

SGIA- Specialty Graphic Imaging Association
Fairfax, VA
Phone: 888.385.3588
E-Mail: dawn@sgia.org
Website URL: www.sgia.org