Like offset printing and gravure printing, flexographic printing also places great emphasis on pre-press proofing technology.
For the flexographic printing process, pre-press proofing has two meanings. One is the proofing before plate making. This is the requirement of advertising creativity or customer's printing effect. It combines the characteristics of the flexographic printing press used, the characteristics of the printing substrate and the ink, and is processed by the computer to make a sample. Creative advertising department, or directly to customers, request approval. If you meet the customer's requirements, you can make a plate; if there is a gap from the customer's requirements, you need to modify it according to the characteristics of the flexographic printing process until the customer satisfaction. The second is to obtain the printing plate, on the special plate-making machine, the printing double-sided adhesive is affixed to the plate roller, and the quality of the plate to be printed is checked again before printing on the machine, and the accuracy of the plate is checked. If the quality standard is met, the machine can be arranged for payment; if there is a defect in quality, it must be reworked. There is a problem with the printing plate that is corrected by the printing department, and if it is incorrect, it must be re-posted. The meaning of these two proofings differs greatly, and the craftsmanship is also very different.
First, pre-plate proof digital proofing before flexo plate making, the domestic most used is DuPont's Cromartin digital proofing (DOPONT CROMALIN), it is said that previously also used analog technology, but since the 90s, several foreign countries The professional plate-making companies that are at the forefront of flexo plate making have entered the domestic market one after another. Most of them use Cromartin digital proofing.
The prevailing flexographic prepress workflow is: the advertising creative department stores the design draft on the CD-ROM. The plate-making company makes the compensation curve correction according to the data provided on the CD-ROM and combines the data provided by the printing factory. Then, according to DuPont's color, The management system, which obtains color control and color synthesis, helps the operator to liberate from the traditional mechanical work and provides a faster, more flexible, and more convenient way to successfully complete the proofing task. Cromartin digital proofing uses special paper and special ink to complete the proofing by ink jet method. The output image can be completed with FM network points, and can also be done with circular screen points to simulate the dots on the flexographic version.
The author believes that the sample color output by the FM network outlet is very beautiful, but there is a gap with the actual printing effect, and it is often easy to mislead the customer. Because the dot is the most basic element of the composition of the printing screen, the flexographic printing adopts circular dots. This is mainly because the expansion of dot dots is not easy to distinguish like the enlargement of square dots, diamond dots, etc., that is, the dots of dots are at the dot. The ability to hide ugliness when expanding is stronger. However, the FM network is another concept. It is not based on the area of ​​the dot but on the basis of density. The difference between the proofing effect and the flexographic effect is very obvious. As mentioned above, the pre-plate proofing is mainly for the purpose of confirming the effect for the customer. The proofs provided are so good that they often encounter such an embarrassing situation. The client who signed the sample will take the inkjet injection from Cromartine. Samples must be printed to achieve the color effect of the proofs. The printing house cannot really achieve the same effect as flexo printing. They can only then move out of the platemaking company and come forward to explain the difference between the two. Therefore, it is most welcomed by the printing factory to use the membrane to circularly sample the site and provide the customer with the closest approach to flexo printing. According to the author's knowledge, in Dalian, there is a flexographic plate making company that uses Crotone dots to conduct Cromax digital proofing, and its proofing effect is very close to the printing effect.
Of course, there are also some companies in the flexographic platemaking industry that do not use Koromalin digital proofing. Instead, they fully tap potential on the basis of the original proofing equipment to meet the requirements of customers.
The author knew that such a company, originally an offset printing platemaking company, had developed a flexographic platemaking business since last year, but they did not have DuPont's Cromarin digital proofing system. Instead, they fully tapped potential in the area of ​​offset printing that they were good at. , Use the phototypesetting machine to output the Yin and Yang pictures of the circular dot screen, and then use the Yin picture to make the flexible version, and the memorable picture of the Yang picture is used to make the PS version, and use PS to proof on the offset proofing machine. The proofs are also very realistic with flexo printing, and are accepted by the printing and advertising creative departments.
In the proofing of the flexographic plate making, there is sometimes a case where there is a trapping problem between the yellow, magenta, cyan, and black color versions when the trademark is printed. For example, the red version is larger than the yellow version. In mm, the cyan version is 0.1mm larger than the magenta version. The size of this color group is called trapping, and in the south it is also called a buckle. As the flexo dot expansion is more serious, it usually needs to reach 15-20% (the flexiprint expansion rate of the author's unit is about 15%). If the trapping problem is not taken into consideration during the platemaking, it is easy to cause problems during printing. Or overprint too much to form a dark border; or missing print, dew, due to lead, must first check the setting parameters before the plate is reasonable, in this case, using Cromartin digital proofing and Offset PS version The simulation of circular dot proofing is not very helpful, but it requires another proof of proof.
Here is a description of a method I have used. DuPont Co., Ltd. has a new type of proofing material for polyester film bases. Its English name is CHORMACHECK. It is suitable for color image proofing. It has three colors: magenta, yellow and cyan. Its color is slightly different from the three primary colors. The new material was placed on the duplicator together with the negative image and exposed for 45 seconds to obtain a plate-like image. By combining these several Selenium sheets representing each color version by cross lines, the trapping parameters to be tested can be easily obtained. At present, this kind of material is still rarely used in China because its price is relatively expensive and the application is not very wide. (To be continued)