Discussion on the Influence of Printing Plate Development on Plate Quality

A, CTP plate printing technology

In the development process of traditional printing plates and films, there are generally no problems, but in the field of computer-to-plate, the development process will afflict us like a devil, and it will affect the quality of plate production anytime and anywhere. Therefore, we should incorporate the purchase of developing equipment into our investment strategy when we introduce CTP plate-making equipment. We often encounter such a situation in the usual printing production process: the newly installed plate has just been printed for a while, the plate is dirty, and our workers report the quality of the plate. In fact, the reason for this phenomenon may be caused by the printed version of the body, it may be due to improper development.

Let's discuss the effect of plate development on the quality of printing plates.

1) The structure of the developing machine
The length of the exposure time of a traditional printing plate mainly depends on the sensitivity of the printing plate, the output power of the UV light source, and the distance between the light source and the printing plate. The usual exposure time is more than 10 seconds. The CTP exposure system uses visible light, infrared light, or ultraviolet light to complete the tanning work of the printing plate's internet point in milliseconds or microseconds. This requires that the CIP plate has a sufficiently high sensitivity, and accordingly, the CTP printing The requirements for the development process are also more stringent than the traditional printing plates.

Under the premise of constant developer concentration, the requirements for the development time of the CTP plate are much more stringent than the requirements for the development time of the traditional plate. In the CTP plate development, the allowed variation range of time is ±10% to ± 15%, while the allowable variation in time is ±50% in traditional plate development. During the development of the traditional printing plate, the temperature variation of the developing tank is allowed to be within 2-3°C, while the temperature of the developing tank during the development of the CTP printing plate is only allowed to fluctuate within 0.5°C of the soil. Affects the quality of plate imaging. It can be seen that if the development parameters are set unreasonably during the development process, the normal operation of the entire CTP process will be affected. The light source used for the polyester plate imaging is usually visible light, such as a 488 nm argon ion laser, a 532 nm single-frequency YAG laser, and the like. For the heat-sensitive printing plates, light sources in the infrared region of the electromagnetic spectrum are commonly used, for example, 830 nm LCD lasers and 1064 nm dual-frequency YAG lasers.

Like traditional plate printing, CTP plate processor is also composed of several parts such as developing, cleaning, gluing and drying. For CTP development equipment, the priority is not the length of the development channel, the size of the developer tank, the structure of the development brush, but the stability of the development process and the replenishment of the developer. In particular, it is ensured that the developer is oxidized as little as possible during the development process, the stability of the supplementary flow rate of the developer is ensured as much as possible, and the effect of the developing solution showering on the transfer of the printing plate is reduced. If the developer supply flow rate and the developer washing method are improperly controlled, it will cause a virtual halo at the edge of the smooth dot on the printing plate and cause a greater burden on the developer recovery and utilization.

The amount of developer supply should be based on the test. Previously, we usually only detected the length of the printing plate. In fact, this is inaccurate, because the width of the printing plate we use may be inconsistent, so it is more accurate to detect the printing. The actual area of ​​the edition. In addition, we may also determine whether the developer should be replenished by measuring the conductivity of the developer. If the conductivity of the tested developer changes, it means that a new developer should be added. The Techno-Grafica processor is said to measure both the plate area and the conductivity of the developer.

The bottom of the developing tank of the developing machine is now designed as a column, because dirt and other deposits in the developing solution are usually deposited on the bottom of the tank. This design is conducive to protecting the plate from being contaminated by dirt and other deposits. Pollution, secondly, this structure facilitates the introduction of these dirt and other deposits into the output pipe. Of course, in order to reduce the dirt and other deposits in the developer, we have to filter the developer into the developer tank beforehand to measure the pH.

Previous CTP plate printers were usually used in conjunction with printing plates and developers. With the advancement of technology, there have been the development of both photosensitive CTP plates, thermal CTP plates, and even the development of traditional PS plates. The developing device. It is also possible to add a flushing unit to the front of the processor for a specific printing plate in order to remove the protective layer on the printing plate surface.

2) Preheating or not preheating

Early CTP plates usually had a pre-heating process before development because the sensitivity of this CTP plate was relatively low, and the energy of the laser could only cause cross-linking reaction in the exposed portions of the plate, so after exposure was completed and before development, There must be a pre-heating process in order to allow the exposed part of the printing plate to fully cross-link to improve the print durability of the plate. Normally the CTP preheating temperature used in newspaper printing is controlled at about 1000C, and the pre-heating temperature for parts printing CTP plates is at least 1400C.

CTP plates commonly used in the market today include: Agfa's N91, Fujifilm's Brillia LP-NS, LH-NI, LP-NN, KPG's DITP830, DITP Gold, Thermal News, Fujifilm LP-NN, etc. . In order to improve the printing plate printing rate, we can carry out the roasting processing on these printing plates. After the roasting plate processing, their printing rate can reach more than 1 million printing.

In view of the fact that the pre-heating device on the developing machine is relatively expensive, and occupies the production space, and also prolongs the development time, the newly-issued plates have in principle abandoned the pre-heating process, that is, do not use pre-heated positive CTP plates. . Although the living space of pre-heated printing plates is currently being eroded, the thermal printing plate will not withdraw from the historical stage due to its alcohol resistance, solvent resistance, and particularly high printing rate. It is suitable for UV inks. Printing and other advantages.

3) Silver halide plate development

Since Drupa 2000, violet laser light sources suitable for internal drum CTP exposure machines have appeared at a wavelength of 405 nm on the market. The biggest advantage of the inner drum CTP system over the outer drum CTP system is that it significantly reduces the production cost. This satisfies the needs of many small and medium-sized printing companies for the output of B2 format CTP plates.

Since the current violet laser has a minimum output power of 5 milliwatts, which requires a sufficiently high sensitivity, people have opted for silver halide materials. For example, Agfa and Mitsubishi have provided silver halide prints that can be operated under a yellow safety light. The edition is said to have been supplied by Fujifilm since Ipex2002.

However, it is a pity that CTP printing plate marketing in the current market is matched with the sales of developer machines of specific manufacturers. This means that if the user wants to change the type of plate he uses, he also needs to replace the used developing machine. This shows that the cost will be staggering. The violet laser with an output power of 30 mW was recently introduced on the market, so it can be used to image polyester plates. Correspondingly, the standard CTP processor can be used for plate development.

4) Ecological Development

With the birth of the eco-development technology developed by Mitsubishi Corporation (now the patent right has been granted), the promotion of the silver salt CTP plate has been promoted. The specific process is as follows: The applicator is used to apply the developer to the horizontal running plate, and the squeeze roller removes the developer on the plate immediately after (about 12 seconds), and the waste liquid is directly discharged into the waste canister and is not reused. This will avoid the instability of the concentration of the developer solution caused by each time the liquid is added; the next step will be the fixing process of the printing plate, that is, the water washing process often used in the conventional process, and the method of applying the fixer in the ecological development technology. In the fixing process, the Agx emulsion layer of the exposed portion and the unexposed portion and the exposed portion of the positive layer are removed under the action of the fixer, and the positive layer of the unexposed portion is retained after the action of the fixer. This development process does not require a water washing process, and the consumption of the developer is also very low. A 1m2 plate requires only about 80 ml of the developer. To prevent the crystallization phenomenon of the coating head, the developer should be sprayed when it is not working. The pump is turned on and off several times. If the amount of developing solution loss is recorded at this time, the average amount of developer consumed per square meter of plate is about 100 ml.