The Quality Problems of Circular Screens in FM Screening

As the main factor in ensuring the high quality of FM screening, the use of software screening technology is of course a question. "How can we record such small points on the printing plate uniformly and accurately?" This also has a lot to do with the quality of the laser light source as hardware.

1 Problems with circular outlets

1) The shape and size of the light source

The IR laser spot is a circular spot. The diameter of a laser spot is about 25 μm to 30 μm, while many FM screens have a small spot size of only 10 μm to 20 μm. The laser spot is larger than the FM spot and cannot be directly formed into small dots of the correct size. . Complex adjustments are required to output such small dots, and the shape of the dots is not easily maintained, which tends to increase the roughness of the screen.

2) Intensity distribution of IR laser light source

The center of intensity is the strongest, gradually weakening from the center. The dots scanned by such a light source are apt to be affected by the activity of the developer and the change in the sensitivity of the plate. From the standpoint of the stability and continuity of dot reproduction, there are major problems. In addition, due to the large range of imaginary edges, dot gain during print increases and instability is increased. Circular dots are not necessarily suitable for FM mesh points with high uniformity.

3) The problem of the same juxtaposition of multiple laser light sources

The general thermal imaging CTP can be said to use 64 laser sources, it can be imagined as 64 spherical bulbs in a row. Even if there is a new juxtaposition of more light sources, the intensity difference and life span of each parallel light source are different, and the difference of 64 light sources is large. From this point of view, it is difficult to form stable and uniform outlets. Stable and accurate dots cannot be scanned on the plate. The high quality of the FM network is difficult to guarantee.

2 integrated as a light source

Creo's laser source technology "SQUAREspot". Although 24 circular IR laser sources with the same circular dot pattern were used, the light from these 24 laser sources was concentrated on an element called "Light Valve" and 240 elements in front of this element. The 10.6μm × 2.6μm elongated rectangular slits divide the light of the light valve evenly into 240 beams through these slits. The 240 beams with the same light intensity have an optical resolution of 9600dpi and are used in the photosensitive layer of the printing plate. Exactly 10.6μm × 10.6μm square dots are scanned. The usual dot is depicted by a pixel with 2400dpi accuracy, while Creo's "Staccato20" is drawn by four 2400dpi pixels.

The small dots thus depicted have stability and continuity, and the layers reproduce smoothly and flatly.

3 Influence on the image area

The edge of the line scanned by SQUAREspot and Rundspot laser spot was observed by electron microscopy. It can be seen from the electron microscopy image that the edge of the line at the edge of the Rundspot network is unevenly imaged by the laser, forming an indistinct edge with more burrs; the image of the SQUAREspot dot reproduces a sharp, sharp edge. When these printing plates are used, the burrs of the circular dots are difficult to achieve stable printing due to the mutual repulsion of ink and water, while the SQUARE spot dots can be stably printed due to the very clear lines and the small dots.

Source: Ke Yin Network

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