Discussion on Flexo Printing of Folding Carton

Carton printers know that the market for folding cartons has become more and more difficult in the past few years. Customers demand higher print quality products. At the same time, middlemen are also seeking lower and lower prices. Under such oppression, some carton manufacturers went bankrupt, while others were forced to unite and wait and see the market together.

Fortunately, there are also some good news. Some carton manufacturers have found a novel technique for producing folding cartons from a web flexographic printing press to challenge these pressures. The quality of today's flexographic printing is comparable to lithographic printing and is easily accepted by most carton manufacturers. The design of the printing press adopts a web feeding method, which reduces the one-time scanning requirements of many carton products, thereby bringing good economic benefits to the middlemen who need to get rich, even under such difficult market conditions.

This article is to introduce the basic knowledge of the production of carton machines for flexographic printing, so that those manufacturers who are unfamiliar with the process can obtain the general requirements for entering flexographic printing, and demonstrate that flexographic and lithographic printing are Similarities and differences in production processes.

Prepress section

Graphics and pictures. Compared to lithography, flexo printed pictures are in digital format. The hardware and software used to process image files in lithography can also be used for flexo image files. The difference lies in the way the two handle the appropriate files. For example, the strength of a flexographic plate is good, so its color separation will be different. Since the flexographic printing press uses a multi-unit operation that far exceeds the number of units of the flat press, its color separation process is more flexible. This provides better color matching, density and repeatability for text printing or line printing. In any case, after the file is processed, the artwork (artwork) will be sent to the next process, that is, film output or digital platemaking.

Film / traditional platemaking. Conventional film and platemaking processes are also widely used by many printers and prepress production studios. Digital printing plates have many advantages in production processing and printing quality, and they will gradually replace the traditional plate-making methods. First use a film to describe the correct file for each plate/color, and then expose the sensitized plate. The plates are cleaned, dried, and ready for installation on the plate cylinder. The repeatability of the plate cylinder determines the repeatability of the printing. Plates are advantageous for specific jobs and it is not necessary to group plates together for proofing.

Digital printing plate. Digital platemaking technology has developed late, but it has many advantages over traditional plate making. Not using film is a clear advantage. More importantly, its improved printing characteristics (due to better dot structure) have enabled flexographic print quality to reach a higher level and can compete with the traditional lithography market. The digital version is laser imaged and includes processes such as exposure, cleaning, stencil and mounting to a plate cylinder.

In all flexographic processes, equipment, ink, anilox, base materials, printing plates, and coatings/adhesives must be properly combined to obtain the highest quality folding carton.

Prepress suppliers and platemaking studios. Compared to lithography, flexographic prepress jobs can be completed in the studio or outsourced to professional prepress suppliers. More and more companies can complete at least some of the prepress work, which can help control costs and get faster printing speeds. Businesses usually choose to produce the documents required for flexo platemaking in a professional prepress studio, and then send the documents (films) to the packaging carton processing plant for making plates. There is also a common method: the plate-making staff completes most of the work in the prepress studio but sends more challenging work to professionals with extensive work experience.


Water-based and UV inks and coatings. Among the many options, the first decision is whether to use water-based ink or UV ink (or both) to print the carton. Since each ink has its own advantages and disadvantages, many factors must be considered.

Serving the special market is the biggest deciding factor. Compared to lithography, the two inks share the same advantages: color consistency and repeatability.
The operator's adjustment of the metal ink stick and squeegee had little effect on the color. The correct color is obtained by the choice of a metal ink stick and the ink formulation. This ensures that when the same color is printed, the matching of the colors can still be achieved after the two shifts shift.

Guarantee the same copy quality. If the same kind of ink is used on the same metal ink stick, the color reproduction will be the same. In today's flexo folding carton printing, the added value of glazing and laminating can all be done on a single line, making production more flexible and reducing costs. Ultraviolet, water-based inks and EB coating and film (adhesive) are widely used in various performance characteristics and surface features. When choosing the ink, whether it is UV ink, water-based ink, or EB coating and laminating, a variety of factors must be taken into consideration.

Base material considerations. The choice of type of substrate material will also greatly affect the print quality of the finished cartons. For example, smooth surfaces have smaller dot gains and stronger color reproduction than rough surfaces. No matter how white the surface color is, this factor will affect the overall effect of the printing tray. Matte gray "white" will eventually affect the color of the printed ink. The correctness of illustrations in the pre-plate making process can reduce these effects and even eliminate them in some cases. Every printer wants to use the highest quality substrate material at any time, but in any case for economic reasons, the quality of the available cardboard is usually specified.

Use inks, metal ink rollers, and plates to achieve the desired result. In any flexographic printing process, the proper combination of inks, substrate materials, printing plates, and coating/adhesive materials can often achieve the best quality on folding cartons. The most important factor should be to enable flexographic printing to compete with lithography. It is not that every job in lithography can be imitated in flexo printing, but the main work must be strictly required, and each progress is narrowing the gap. For example, a flexographic printing with a higher reference line can use the latest high-strength ink and digital printing plates, and the printed product outlets can be clearer and smoother.

The combination of flexographic testing and substrate material selection is the best starting point when deciding how to separate components and how to manipulate files in color reproduction. This is particularly important in the folding carton market because it gives more carton bases. The experience and knowledge of each base material must be obtained, and the effects on printing should be known before production.

After the basic work is completed, the choice of materials such as inks, adhesives, and printing plates in flexographic printing is determined by the substrate material, and the prepress process uses appropriate curves. Completing the test and all the components greatly reduces the preparation time and waste, and the copy quality is improved.

Competing with the quality of lithographic finished products does not mean that the process has to compete. For example, for flexographic printing, the number of colors, the order of ink discharge, and the prepress process are almost the same as lithographic printing. Flexo products sometimes have to be delivered to the end customer who normally only accepts lithographic cassettes. For end customers, they only care about the quality of printed products, and do not care about which printing method to use. In some cases, this is a challenge for the middlemen, but it is important that the middlemen should send this information to the customer without having to fully apply the lithography method in the flexographic printing.

The improvement of all the components in the flexographic printing brings to the flexographic printing a high quality level that can compete with offset printing.

Die cutting and (paper products) processing

On-line rotary die cutting: an alternative method. Although this method requires higher costs, rotary die cutting can meet more and more requirements for folding carton processing. More and more processors have realized the high productivity and quality benefits brought by rotary die cutting. At the same time, the increased demand for rotary die-cutting has also enabled die-cutting machine manufacturers to realize that large-volume production can save costs and transfer these savings to their customers.

Today's rotary die-cutting machines are of higher quality, cheaper and farther away. Although rotary die cutting machines are much more expensive than flat-bed steel die-cutting machines that can do the same job, smart processors know the savings that come from the high productivity and low consumption of rotary die-cutting machines. Accumulation far exceeds the additional cost of die-cutting machines.
Cutting method and molding method. The novelty of rotary die-cutting is the type of change in impressions. For how to classify these choices and better grasp, it is a very effective method to distinguish between cutting methods and moulding methods.

There are two basic methods for cutting. The first method, which is the most commonly used method, is stamping and cutting. This method is very simple, use a sharp cutting blade and a hard, smooth knife cut into the cardboard. This method is consistent with the platform press.

The second method involves a relative die forming apparatus that achieves the effect of breaking by rolling the cardboard to cut the fibers of the paper. This method can generally be called pressure cutting.

The cost and operation of these two methods are not the same, but the point can be known: the pressure die cutting cost is about twice that of the stamping die cutting, and the number of the carton obtained before the waste detection is ten times that of the stamping die.

There are at least four fundamental changes in the molding method, but the most prominent ones are fixed molding and variable (or "wrapped") molding. As its name implies, fixed moulding refers to the way in which the image is indented on a solid steel roll and cut and indented. Variable molding is the adsorption of thin paper on a magnetic plate cylinder mandrel. Processors generally use fixed mold presses to produce large-volume products, while variable mold presses produce small-capacity and simpler products.

Waste removal and carton transfer. Some of the often overlooked operations have a great influence on flexographic printing efficiency. In short, if waste cannot be removed as quickly as possible, it will slow down the entire printing process. It is also necessary to fill in the blanks in the finished product transmission. High-speed assembly linkage printing presses must be equipped with transmission equipment. Some printer manufacturers have neglected these two important aspects in order to keep the cost of printing presses inconvenient for customers' actual production.

There are two methods for processing wastes on the print, one is the separation matrix method and the other is the “positioning stripping” technique. The way the material is removed is simple. However, the down time is longer and more paper is wasted. Positioning stripping technology successfully avoids downtime, reduces waste and improves cart design efficiency, saving valuable cardboard. A printer equipped with a positioning stripping device can easily save 2%-4% of paper compared to printers without a device.

Most printers use the output of a blank page or a predetermined height or a predetermined number of output products in the output of the finished product. The operator usually manually removes blank pages, stacks them in boxes or transfers them to paper clips or fixed locations. In any case, the blank pages of the finished product must be handled. Good control is the most important feature of the printing machine. The processing equipment that does not have a transmission system costs much more in printing than it did when the company purchased the machine. The sensible printing company understands these factors and invests according to the situation.

Commercial flexo printing

Productivity. No one can deny that folded cartons are commodities. Although we hope to see more artistic products, the products also have the status of commodities, such as

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