FM screen printing has always been the most perfect screen-to-screen image screening method for all printers. It not only solves many problems such as hitting the net, moire and moiré in multicolor printing, but also greatly improves the details and levels of the image. Almost all suppliers of prepress printing equipment have their own FM screening technology, such as Heidelberg's diamond mesh, Agfa's crystal mesh and so on. Of course, they also printed many printed samples of the FM network, everything looks perfect. But ... ten years later, all of this seems to stay in the laboratory, and almost no one actually applies this screening technology to actual work when printing. why? Because the workflow of CTF is too long, it is sometimes too difficult to strictly control the process of each step. The emergence of CTP has solved the process problem to some extent. But even if it is directly imaged on the PS version, the instability of the dot expansion of the small dot is still a serious problem. The solution to this problem is: "square laser dot technology". The company has conducted long-term and in-depth research on FM outlets. From a technical point of view, we believe that square laser dots and secondary FM screening technology are the necessary factors to achieve a truly practical FM network. Both are indispensable. ◠Square laser dot technology The square laser spot that has won many new technology awards internationally is not simply a square shape. The traditional CTP laser is a laser tube that emits a light spot for actual exposure, so the imaging point inevitably inherits the Gaussian energy curve of a single laser tube. The square laser spot is cut by Kodak's patented product-"light valve". The energy curve is almost straight, which can form a light spot with extremely steep edges on the plate. Don't worry about the impact of changes in the back-end printing conditions on the dot size. Compare the data in the left picture: Through the "light valve", it is one of the companies that can accurately control the laser edge to ± 0.2μm (even if the back-end processing conditions change by 10%), we can control the expansion rate of the 10μm FM dot to 4% Within. ◠Secondary frequency modulation screen technology Why is FM screened once or twice? A FM screen only uses a random algorithm to fully break up the original dots in the unit area, so there is a high probability of repetition in the mid-tone places (50% of the flat screen). When the middle tones of multiple color plates are superimposed on each other, streaks like water waves are generated. This is what we call low harmonics. In response to this phenomenon, we will reorganize the FM outlets that have been completely broken up first, and then break them up again to obtain the required secondary FM outlets. The expansion of the usual FM network and the network expansion are relatively large. This is because the expansion of outlets only occurs at the edges of the outlets, and the sum of the perimeters of many small outlets after breaking up a large-amplitude outlet is much larger than the original large outlets. The secondary frequency modulation screen connects the adjacent small dots when reorganizing the dots, greatly reducing the total circumference of the dots, making the dot expansion easy to control. ◠Specific realization of FM screen printing. 1. The printing density and network expansion to obtain customer satisfaction is the first step. The printing consumables used by printing plants in mainland China are more complicated, and the process control of the printing process is relatively poor. Let us first take a look at the network expansion and transfer in an ideal environment (see Figure 1). The actual situation (see Figure 2) is that the control of the film is relatively simple, and the density and linearity can be easily controlled using a transmission densitometer. The link of printing is more confusing, usually 2% of the outlets can still be retained as the standard. Due to the lack of reliable detection equipment, in fact, the loss of the dots is too large (usually around 10%), which eventually leads to runaway during printing. Therefore, the use of amplitude modulation dots to print a controllable constant dot expansion rate of printed matter is an effective means for customers to clearly define their goals. Generally, Chinese customers do not want the expansion curve of printed dots to be like European standards, but prefer brighter and lighter works, so the printing characteristic curve in Japan is sometimes better. Of course, it needs to be adjusted according to different inks and paper. The network expansion curve of Staccato's quadratic frequency modulation network is far from the conventional AM network (see Figure 3). Since the dot expansion can only occur at the edge of the dot, the largest dot expansion of the AM network always occurs at 50% (the longest dot edge at that time). Looking at Staccato again, you will find that the total perimeter of the edge of 75% of the dots is longer than that of 50%, so its dot expansion curve is also very special. This network expansion curve is also very special. Such a dot expansion curve brings great advantages to the actual printing, because the dot expansion usually increases with the increase of ink density, and the largest change of the amplitude modulation network occurs in the middle tone, so the human eye can easily see the difference (People are the most sensitive to middle notes). But for Staccato, with the increase of ink density, the dark tone changes first and the change of the middle tone is not obvious, so FM dot printing can easily ensure the consistency of the printing tone. 3. By adjusting the linear curve of Staccato, the FM network is used to simulate the network expansion rate approved by the customer. We have the actual measured curve and a target curve. All we need to do is to use Staccato to simulate the output of the AM network (see Figure 4). All of this is much easier than you think. BNF HARDWARE CO., LTD , https://www.bnfhandles.com
Imagine that if there is only a 1μm change in the edge of the dot, the unpredictable change of the 200lpi traditional screen dot is less than 3%, but the uncontrollable change of the 10μm FM dot reaches 30%. If 30% of the expansion of a printed matter cannot be adjusted, it means that the finished product we printed is completely non-repeatable, let alone quality control.
2. Measure the printing dot expansion rate of FM dots.