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Temperature Compensation for Computer-to-Plate
Thermal computer-to-plate (CTP) devices from Kodak are extremely accurate and repeatable. In order to automatically ensure that these very tight specifications remain true throughout the entire environment operating range of the machine, Kodak’s CTP devices are equipped with a temperature compensation system.
The effects of temperature variations during plate making
It is well known that film changes size as it reacts to temperature and humidity shifts. As a result, strict controls must be in place both before and during the plating process to ensure adequate on-press registration.
CTP eliminates the registration errors caused by unstable film, but the effects of temperature changes are at least as dramatic on aluminum plates as they are on film.
Aluminum, like many materials, expands and shrinks with changes in temperature. In fact, a 1m wide aluminum plate will stretch by more than 0.127 mm (about one row of dots at 175lpi) if the room temperature increases by a mere 5.6°C (10°F). So plates, especially remakes, made at different times under typical shop conditions can end up being imaged at different sizes, which leads to subsequent on-press registration and color shift problems.
All of the promised CTP benefits of better registration and fit can be lost by the simple act of exposing plates at different temperatures as the platesetter and/or ambient temperature raises and lowers over the course of the day.
The solution: temperature compensation
To eliminate the impact of this problem, Kodak employs a unique temperature compensation system that measures the plate temperature and adjusts the plate image size to maintain fit and register. Repeatability on one Kodak Platesetter is 0.00508 mm for the entire environmental operating temperature range of the machine. The accuracy between plates made on different machines is within 0.02032 mm. For example, a plate imaged at 17°C (63°F) at one location and another at 32°C (90°F) on a different machine will register within 1/7 of a row of dots at 175 lpi - eliminating any noticeable impact to color balance or register on press.
A real world example
Suppose four typical 8-page CMYK plates are exposed during a morning shift at a room temperature of 22°C (72°F).
Suppose four typical 8-page CMYK plates are exposed during a morning shift at a room temperature of 22°C (72°F).
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During the late afternoon one plate is damaged and needs to be re-imaged.
If the ambient temperature has increased over the course of the day to 28°C (82°F), then the first plates and the images on them will have grown by 0.127 mm.
If the new plate is imaged without temperature compensation, the plate will have grown but the image size will remain constant and consequently will be smaller relative to those on the old plates. The new plate image will therefore not fit on press.
However, a plate imaged with a Kodak CTP Device would automatically be adjusted to fit the previous set. This is true even if the re-made plate was imaged on a different Kodak CTP Device from the original set, making the process of re-making a plate simpler, faster, and less prone to error.
