Research on Platemaking of Flexible Plates (II)

5. Post-exposure analysis

Figure 9 shows the effect of post-exposure time on the relief depth of the printing plate (back exposure: 160 units; front exposure: 7 minutes; plate wash speed: 200 mm/min; plate press pressure: 0.04 mm; drying temperature: 60°C: Drying time: 2 hours; Stable treatment: left in air for 24 hours at room temperature), Figure 10 shows the effect of post-exposure time on the dot size of the printing plate (back exposure: 160 units; front exposure: ? Minutes; Plate washing speed: 200 mm/min; Washing plate pressure: 0.04 mm; Drying temperature: 60°C; Drying time: 2 hours; Stable treatment: Let stand in air at room temperature for 24 hours, passing through Fig. 9 With the analysis of Fig. 10, it can be concluded that the post-exposure time has almost no effect on the emboss depth of the printing plate and the size of the dot, or influences the micro-leveling.

6. Viscosity analysis

The effect of de-sticking time on the relief depth of printing plates is shown in Fig. (back exposure: 160 units; front exposure: 7 minutes; plate speed: 200 mm/minute; plate press pressure: 0.04 mm; drying temperature: 60 °C; dry for 2 hours; stable treatment: left in air for 24 hours at room temperature), Figure 12 (back exposure: 160 units; front exposure: 7 minutes; plate speed: 200 mm/minute; Wash plate pressure: 0.04 mm: Drying temperature: 60°C; Drying time: 2 hours; Stable treatment: 24°J in air at room temperature) . Analysis of Figure 11 and Figure 12 shows that the detackification processing time has almost no influence on the emboss depth of the printing plate and the size of the printing plate Internet point.

The cause of cracks in the plate surface can be analyzed from the perspective of photochemical reactions. When the printing plate is exposed to the front surface, there will still be a certain amount of unsaturated components remaining on the surface of the printing plate, and the surface of the printing plate will have a certain viscosity. The purpose of the post-exposure and de-tacking process is to remove the remaining unsaturation, remove the printing plate viscosity, and ensure the plate finish. Therefore, in the two processes, the plates were exposed to UV-a (36 5 nm) and UV-c (245 nm) light sources, respectively, for corresponding exposure treatment.

The photon energy generated by UV-a (365nm) abundance [!UV-c (245nm) light source is 309 dry coke/beam and 461 dry coke/beam, respectively, and these two kinds of energy can stimulate a series of effective reactions. Since the penetrating ability of short-wavelength light (uV-c) is very weak, the energized reaction occurs only on the upper surface of the printing plate, resulting in a drastic increase in the crosslinked polymerization density of the printing plate surface. In this case, if the detackification treatment time is too long, the stress between the surface layer of the printing plate and the layer immediately below it will be increased. When the stress is increased to a certain degree, the surface of the printing plate may be cracked.

to sum up

Platemaking process is one of the key factors affecting the quality and performance of the printing plate. The traditional flexo platemaking process includes back exposure, front exposure, mid-wash, drying/stable exposure, and de-bonding processes and steps, in order to ensure A high-quality printing plate is required, and high-quality female pictures must be used when making a plate.

During the production process of the flexographic plate, the back exposure process serves to enhance the plate base and ensure the relief depth. In the exposure device, the integrated UV light source illumination system helps the printing plate to obtain an accurate relief depth. Simultaneously. It is also possible to measure the photosensitivity of different types of flexographic media with the aid of backside exposure. For example, Asahi's AFP HD media used in this study had a photopolymerization rate that was relatively slower than that of MacDerm's old EPIC media.

The frontal exposure ensures that the graphic detail (print) portion is formed on the plate. In most cases, the dot size on the plate cannot be exactly the same as the dot size on the Yin picture. A reasonable frontal exposure time ensures that the printing plate gets the correct dot size (usually larger than the size of the dot on the female picture), the right shoulder point of the dot, and at the same time it guarantees that the negative or negative lines will not stick. If the frontal exposure is not sufficient (for example, only 2 minutes exposure), it will result in the loss of fine dots or fine line information, or even cause the relief depth to change. If the frontal exposure is excessive (such as exposure for 25 minutes), the dots on the plate will be seriously increased. In this experimental condition, Asahi HD media showed a very good exposure latitude.

The plate-washing step causes significant swelling on both the solid and halftone dots on the plate. The purpose of the plate was to remove the unsensitized (or non-photopolymerized) portion of the plate and to obtain a suitable emboss depth for the plate. In order to obtain a satisfactory platewashing effect, it is necessary to select an appropriate platewashing solvent and to control the platewashing conditions (such as platewashing pressure, platewashing speed, etc.). Under the condition of washing plate used, whether the fine dot or fine line information on the printing plate can be preserved intact can be used as one of the basis for judging whether the front exposure is reasonable or not. Obviously, during the entire process of washing, the speed of the wash plate has a much larger effect on the size of the dot than that of the wash plate.

The main purpose of the drying/stabilization process is to remove the residual solvent absorbed by the printing plate. In order to ensure that the plate can be restored to its original thickness and the dot size on the plate remains stable, it is necessary to stabilize the plate for a certain period of time (for example, 24 hours).

The purpose of post-exposure is to remove the various unsaturated polymers left on the printing plate. Through ultraviolet (365 nm) irradiation, all the parts that have insufficient photosensitivity and are not completely hardened are hardened. This process is almost the same as the depth of printing plates and the size of the dots. No effect.

The purpose of irradiating a printing plate with a UV light source is to remove the tackiness of the printing plate surface without using any chemical substances, that is, to remove the tackiness. This step has no influence on the emboss depth of the printing plate and the dot size on the printing plate. However, if the processing is excessive, cracks may occur on the surface of the printing plate, which is worth noting.