How is a digital plate layered?
Aluminium/primer layer (bonding agent) Polymer printing layer (printing) Silicone rubber layer (non-printing).
What is the resolution capacity of a CTP plate and what are its characteristics?
Sensitivity: 170 mj/qcm Wavelength: 830 Nm (thermal IR) Smallest printable dot: 10 µm Resolution: 4000 dpi Print run stability: 120,000 copies with uncoated paper 200,000 copies with coated paper.
Which setting values are recommended by TORAY, for the parameters used during development and exposure?
180-190 mj energy should be applied to the plate. No fixed setting values are available for this, since the variety of exposure heads is so large and even identical laser diodes provide different values. Furthermore, laser diodes are subject to wear and tear, which varies to manufacturer and also to the production conditions. The following applies for exposure processing: In the case of 3-brush machines; Pre-Treatment temperature of 35 °C; processing speed 90-100 cm/min. For 2-brush machines; Pre-Treatment temperature 38 °C; processing speed 50-70 cm/min.
Does a new plate require a more intensive exposure/development than an old plate?
Yes. As on the new plate processing unit, the conditions for post-polymerisation of the plate is improved. It is less sensitive to scratching, harder and therefore more stable for long-term use, while the minimum requirement of energy has risen from 130 mj to 170 mj. In addition, the new plate works with a broader bandwidth, namely it works at 810 to 845 Nm, instead of precisely at 830 Nm. However, it uses a flatter peak, since the wavelengths of some exposure systems vary to a greater degree.
What is the maximum time that a plate should be exposed to light?
30 minutes of daylight can do no harm. However, we recommend the use of UV-minimised ceiling lights or yellow light. UV light contains rather high IR components and we recommend protective measures, since no one can say precisely how high this share is at a certain workplace.
Why are platess sometimes baked?
Plates are sometimes baked to make them resistant to solvents, for instance when printing is done with UV inks.
Is baking possible for higher print runs?
Yes, baking is possible. However, this lowers the stability of the print run, since the rubber share in silicone is vaporized. The plate layer loses elasticity and becomes brittle, which makes the surface especially sensitive. Even the smallest paper particles will roughen the surface, which becomes mat and starts toning.
How long can plates be stored – in the open (dark), packed, exposed and unexposed?
The shelf life usually is about two years. Our plates are guaranteed for a shelf life of one year, after the date of delivery. The age of plates can be recognized by means of a laser code on the back of the plate. Imaged plates, however, can be archived without problems for an unlimited time.
What influence does the age of a plate have and how can changes be detected?
Analog plates can continue to polymerise and become so hard after approx. 2 years that they can no longer be developed. CTP, by contrast, reacts differently. While the RG plate is resistant to ageing, due to its protective foil, the RL plate ages, becomes soft and sensitive to scratches due to the influence of oxygen also assuming that the plates are not exposed to extreme temperatures.
Will the silicone layer be permanently weakened by pre-treatment?
The plate is completely soaked and is therefore weakened by the influence of the pre-treatment. Post-hardening takes place after development. The stronger the effect of the pre-treatment, the longer this process takes. In the case of a normal pre-treatment, the plate once again gets completely re-hardened after approx. 15 minutes. This also becomes apparent if one tries to post-process the plate a second time. This is only possible within a relatively short time window.
Can an unexposed silicone layer also be partially removed during rinsing?
An unexposed silicone layer for instance, can be removed by a too long soaking time in the pre-treatment. This may at times occur completely and first at the edges of the plate. The layer is however not "milled off" and does not become thinner.
Is the digital plate positive, negative or neither?
We are talking about a negative plate, since images are exposed for printing there. With positive CTP plates, those parts that are not used for printing are processed. Positive plates are usually less problematic, since banding will never occur in the non-printing area.
Does aluminium print just as well after too deep exposure or without dyeing?
Yes, printing is possible from aluminium. This occurs especially in the case of very high print runs. It can however lead to a bad laydown in a solid surface, due to the different surface tension of the aluminium. However, one will not notice any disadvantages.
Can one draw conclusions about the later printing quality from the quality of the dye in the processed plate?
Yes, regardless of whether one prints light or dark sections, everything that has to be printed should be covered by the dye. Halftone dots that have not been dyed do not print.
How can one explain the different dyeing intensity?
In the event of very high energy, it is definitely possible that the printing layer is punctured and that the primer layer, or the aluminium, is dyed lightly or spottily. An inexperienced observer can easily mistake this for bad development. The plate is nevertheless perfectly usable for printing in this condition, although it is very difficult to make an evaluation on this and it cannot be substantiated through measurements.
Which layer accepts the dye?
The dyeable polymer layer accepts the dye. A difference in dye occurs primarily through a fluctuation in the energy flow. This means: Low energy = dark colorization, high energy = light colorization.