Process analysis used in flexible platemaking

There is a saying in the flexographic printing industry that no good printing plate can not produce good products. It can be seen that the quality of flexible printing plates is a prerequisite for the success of flexographic products. So, how can we produce a good flexographic printing plate? The author believes that mainly depends on the following four aspects: 1. Design manuscript suitable for flexo printing; 2. Perfect analysis of plate making process; 3. Professional separation, School coloring experience; 4. Advanced technology equipment.

In fact, most packaging designers lack sufficient understanding of the back-end printing, and it is impossible to design the packaging product according to the characteristics of a certain printing method. There is also a situation where many products are offset or gravure have been printed, and now want to be converted into flexo printing, so the design manuscript suitable for flexo printing is rare, and in a specific period of time, the plate making company Platemaking equipment and technology are also relatively fixed. In this case, to produce a good flexographic printing plate, we must make more efforts in process analysis, color separation, and color correction. If color separation and color correction are the keys to the success of flexible platemaking, then we can say that perfect analysis of the platemaking process and putting forward a reasonable and feasible platemaking plan are prerequisites for the success of the flexible platemaking.

The analysis of the flexographic platemaking process involves almost all aspects of flexo printing. The knowledge it covers spans the entire prepress processing process, the plate making and printing process, and is inseparable from the specific products. It is difficult to systematically discuss the details in a systematic way. . The author used the “Coca-Cola” and “Sprite” labels that he had participated in as an example to obtain a plastic film class award in the 2004 National Flexographic Print Quality Exhibition. This article briefly discusses the importance of process analysis in flexo plate making. , with all of you.

1. Customer provided plate information:

Adobe Illustrator format typography files, including PSD format images, gravure printing reference samples for special green and special blue spot channels.
Customer plate making requirements: Flexographic proofs are as close to gravure printing as possible.

2. Printing customer related information:

Printing presses: AJA hair dryers, 6 color groups.
Anilox roller configuration: There are multiple anilox rollers with 400 to 800 lines available.
Ink: AkzoNobel water-based ink.
Printing materials: popp pearl film.

3. Analysis gravure printing reference sample:

Difficulties in the printing of this label are based on the special green and blue of the background, and they are melding with each other. Gravure printing is soft and natural, especially the gradual blending of the transitions is natural, neither because the dots are overly superimposed, but also because there are no dots. Overlapping is not enough to make the color of the substrate leak out. At the same time, the solid printing ink layer is thick without any traces of broken network.

4. Flexographic printing feasibility study:

The main difficulties in using manuscripts for original manuscripts:
Special blue editions and special green editions include field, gradient and broken net designs;
The printing material is popp pearl film, and it is printed with a water-based ink, and the inking performance is not good;
If you use high-line 175 line printing, you need to configure a higher anilox roller, the number of lines more than 800, this will result in a small amount of ink, making it difficult to achieve field printing gravure printing proofs effect;

If you do not use 175 lines of high-line printing, it is required that the flexographic printing effect is fine and it is difficult to approach the gravure printing proofs;

Because the flexographic dot structure and the gravure dot structure are different, the gradual fusion of the middle portion of the flexographic printing is very easy because the overly superimposed dots cause the fusion portion to be black or because the dot overlap does not cause the color of the substrate to leak out, causing the fusion portion to have a whitish phenomenon.

5. Develop a reasonable plan for making plates:

After full process analysis and understanding of flexographic features, more people believe that the label is not suitable for flexo printing. However, can we overcome these difficulties through reasonable technological arrangements?
To this end, we organized the relevant technical staff to conduct a full process analysis with the customer. Finally, with the permission of the color group, we proposed to add a special blue version to print the gradient background based on the original five spot colors. In other words, with the exception of fine text and bar code, other special blue parts are formed by two special blue prints. At the same time, clarify other plate-making related issues and form the final plate-making plan:

The use of laser digital platemaking effectively avoids the increase in the printing register error due to the size error of each color version of the film used in the traditional plate making. Digital platemaking is distinguished from the traditional version of the photopolymerization process and reaction mechanism, making the height of the high-light network point slightly lower than the dark tone network point and the field part. Compared with the traditional version of the dot network structure, such dot network structure expands the dots under the same pressure. The rate is smaller.

It is possible to use a higher number of anilox rollers and 175 lines of high netting for exclusive blue printing. Because the special blue part is divided into two printings, although each printing has a small amount of ink, two overprinting can ensure that the special blue solid part of the ink is thick. The final printing-related data was printed exclusively on blue and 600 lines of anilox rollers, respectively, with BCMs of 2.0 and 1.8, respectively.

High-line anilox rolls and 175-line high-net lines can be used for special green printing. Taking into account the special blue part because the two printing ink is very thick, the original special green version of the broken part can be tiled with 10% flat screen, so that the specific blue field color change will not be too large, and the lower net can be used. Roller line printing 175 lines of special green net, to ensure that the green version of the amount of ink, so that the green part of the ink coverage is also guaranteed. The final print-related data is printed exclusively on the 500-line anilox roll with a BCM of 5.0.

The original special blue and special green gradient cut-off nets were tiled with 1% and 10% flat screens, respectively, to avoid the formation of printed hard orifices due to gradual cuts.

The use of 175 lines of high-line printing special blue and green, to ensure the fine print, so that the printing effect is almost the same as the gravure printing proofs.

Due to the three dot overlaps in the middle of the gradient fusion part, it is ensured that the gradient fusion part will not whiten because the dots do not overlap enough to cause the color of the sheet to leak out.

When dealing with intermediate gradients, you can use two special blue gradients that are not synchronized to avoid transitions that are not smooth in the intermediate transitions and blackening of the blended parts.

6. The program is determined:

After confirming the above plate-making process plan, we further communicated with customers about follow-up printing related issues. When customers agreed with our plate-making plan, the customer pointed out that due to the large amount of labels, the printing plate must be resistant to wear and high-light spots are not easily lost. After fully considering the customer's surprise, we adjusted the above plate making plan:

The 1% flat screen where one special blue version of the disconnected network is tiled is raised to 5%, and the other 1% flat screen with the blue version of the disconnected network is increased to 3%, ensuring that the high-light network point is not easy to print in large quantities. Lost point.
7. Further improve the program:

After the first trial printing of the printing and printing factory, the printing effect of this label was good and exceeded our original expectations. Looking at the printed samples, the customer also put forward the following opinions, hoping to make further improvements:
The ink on the spot is not as good as 99% of the dots.
Gaoguang outlets began to be damaged after printing 500,000 copies;
The lines on the field and the edges of the text appear to be inkless and have white spaces.
After analysis, we believe that the above problems are mainly related to the characteristics of the media used:

The surface of the plate used is smooth, and 99% of the dots are due to the tiny pits on the surface of the plate. When the ink is transferred from the anilox roller to the printing, a large amount of ink fills in these tiny pits, making the amount of ink on the spot higher than on the spot. Some of them are still large. Therefore, some parts of the ink on the ground are not as good as 99% of the dots.

In order to ensure the amount of ink on the ground, printing will often increase the pressure, and the increase in pressure can easily lead to high-light outlets vulnerable to damage, and the plate is also a poor ability to resist ozone is one of the reasons for the loss of high-light sites.

At the instant when the printing plate comes into contact with the printing material, the edge of the line parallel to the axial direction of the printing plate first touches the substrate. The edge of the line is subject to the highest impact force. The ink at that position is easily affected by the impact force. In the material, after the printing plate leaves the substrate, the ink cannot flow back to the edge of the plate with the greatest force, thus forming a white space that is typical of the flexographic printing.

In view of the above problems, we believe that increasing the volume of ink received by the plate is the key to solving the above problems. Therefore, testing and comparing several commonly used laser digital plates found that because most of the flexible plates are smooth surfaces, they cannot effectively solve the above problems. Only the BASF flexible plates processed on the surface of the plate by a special grinding process ( Model: nyloflex FAH170D) Print better. After BASF's flexible plate surface is specially frosted, a large number of tiny holes are formed on the surface of the plate, so that the amount of ink is greatly increased, and printing can be performed with less pressure, effectively reducing the ink overflow when the plate is pressed. The printing ink is more uniform, and the phenomenon of white spaces on the field lines and characters is greatly reduced, and the high-light network dots are not easily lost due to printing pressure. After trial printing by customers, the print volume has increased from the original 500,000 prints to 1 million prints.

From the impossible to the possible, and then to the award for a quality award for flexographic product quality, it can be said that the successful printing of the label depends first of all on the rationality of its platemaking program, although it does not have much complexity at all. The only difference is that we have made some appropriate adaptations to the product quality requirements when we are making the plate making process, but it is the key to effectively solving the problem. As lithographers of flexographic platemaking companies or flexographic printing companies who are responsible for plate-making process analysis, they are faced with a variety of plate-making manuscripts every day. For them, before starting to make a flexographic plate, they are specific to the manuscripts of the customer. Features, combined with printing conditions and its own plate making equipment, technology and experience, on the basis of meeting customer requirements, the manuscripts are subjected to full process analysis, tailored to the product reasonable plate making program, is the basis for the success of the flexible plate making. ※