How to handle and measure processless plates?

Today in the age of computer-to-plate and high-resolution printing plates, quality control in prepress is critical to quality print. Accurate measurement of correct dot transfer on offset printing plates is a key segment of comprehensive process control in the printing industry. Measurement is accurate only when the appropriate measurement technology is applied.

Years ago, the use of densitometers on printing plates was common practice. However, densitometers are designed for measuring printed paper substrate, leading to limitations when reading plates.

The challenges are exacerbated with the latest generations of chemistry-low, process-low (so called "processless") plates ( an environmentally friendly solution that has been gaining in popularity over the last few years; for more on processless plates, see our blog https://techkonusa.com/what-is-the-process-free-or-processless-plate-and-what-to-consider-when-switching/ ), but which typically have an extremely low contrast. So low in fact, that the image is almost invisible to the eye. The highest reflection lies in the infrared area at 810nm, the same wavelength as the Laser that is used for exposure.

In order to achieve accurate measurements, it is therefore necessary to use illuminant above the visible range. The SpectroVision All-Vision plate measurement device is equipped with additional infrared-LED illumination. When measuring processless plates, the correct wavelength illumination is selected automatically. The light source dims noticeably, and in fact, the remaining visible light is used for proper positioning purposes only.

By using the correct illumination for each type of plate (Conventional and chemistry free, polyster and paper) and all types of screening (including AM, FM, and Hybrid form low to high resolutions), the SpectroPlate All-Vision provides accurate measurements for over 170 plate brands that are stored in device memory for instant reference accuracy. New plates on the market are implemented quickly through firmware updates. Supported processless plates include:

• Agfa Inkjet Solutions Ecplise
• Fujifilm Print Superia Ecom-T, SuperiaPro-T3, ZD, ZP
• IBF Direct T
• 伊士曼柯达 Sonora X, Sonora XP
• Lucky Huaguang Graphics Co., Ltd. PPVG, PS, TPU
• Heidelberger Druckmaschinen AG SaphiraThermal FND 300, SaphiraThermal ND
• SLP Liberty NXP

How to measure low contrast plates?

Before they can be measured, most processless plates need to have the protection coating be removed after exposure. Typically, the developing of the plate happens in the press, but manual uncoating is possible. To uncoat plates manually, certain treatment und procedure is required.

In order to uncoat and measure a processless plate, you will need:

• SpectroPlate All-Vision
• 3 x Cotton Cloth
• Timer
• Cleaning solution (recommendation of manufacturer)
• For safety: Safety Goggles and Gloves

Here is the correct procedure step by step to clean and measure:

Step 1: Soak one cloth with ~ 40-50ml of the cleaning solution

Step 2: Apply cloth softly to wet the plate and give it a dwell time of 20-30 seconds

Step 3: Wipe the plate with high pressure for another 30 seconds, turn the cloth after 15 seconds for better cleaning results

Step 4: Use the second cloth, soaked with water to neutralize the liquid. Dry the plate with the third cloth.

Step 5: Set your SpectroPlate All-Vision to the plate profile matching with your plate and start to measure

It is important to clean the plate properly as particles staying on the surface will affect the measuring result. The plate needs to be measured within the first few minutes as the surface will change quickly over time by a process similar to oxidation. It is not possible to re-measure the plate at a later stage, e.g. the next day.

For more information on the SpectroPlate All-Vision, or if you have questions about processless plates in general, please see our SpectroPlate details page at https://techkonusa.com/products-2/spectroplate-digital-microscope/ where you can request consultation with one of our experts and/or learn more about the technical specifications.