Thin plate technology in corrugated board printing

Corrugated board preprinting and postprinting (direct printing) are undergoing drastic changes. Monochrome printing has been replaced by a variety of colorful prints, and the common washboard phenomenon in corrugated printing has also been effectively improved. The cardboard weight of corrugated cartons is getting higher and higher, the enamel type becomes finer, and the surface flatness is getting better and better. The carton is further playing the role of packaging and enhancing the attractiveness of the interior products. Manufacturers of printing machinery, corrugated board, anilox rollers, inks and plates have made positive contributions to the development of corrugated printing.

As early as the early 1990s, thin-plate technology was already being promoted in the carton processing industry to improve the quality of printing after corrugating. This technological trend has caused a rapid increase in the quality of printing and a substantial reduction in costs. Halftone effects have become commonplace in corrugated paper printing. Processors often print UPC bar codes on paperboard. Advances in board production, improved ink quality and anilox roller technology have also made thin plate technology truly successful.

Demand drives supply

In corrugating printing, many different types of printing plates are involved, resulting in a diverse combination of plate types, plate thicknesses, adhesive tapes, and gasketing materials. But the standard has not yet been established, which makes corrugated printers face many uncertainties in the surface structure of the plate, pressure absorption, ink transfer characteristics and field effects; many processors have tried different types of plates, viscose Ribbons, liner materials, and inks are associated with different print results.

While processors are doing everything possible to find ways to meet the printing requirements of various paperboard materials, the need for a standard printing plate system is becoming more and more urgent.

For a long time, corrugated printers have been looking for a specific plate material that can be easily processed without being limited by material properties; images can be processed on any plate making equipment in tropical, subtropical or continental climates. In response, a new type of polyester structural material came into being; providing stable development time under different climatic conditions, even after millions of prints, the amount of ink delivery tends to be consistent. The customer's demand for versatile printing capabilities has strongly promoted the development of thin corrugated plates.

Recently, digital plate materials have also become an important issue for corrugated printing. Newer, thinner plates continue to emerge; Sensitive black masks on plates can be ablated in CTP laser devices for more comprehensive printing.

The trend is toward digital imaging, while at the same time providing customers with optimized print quality. In order to open the market, plate suppliers increased the number of plate sizes and specifications. The new thin/soft sheet-fed polyester version became a mature representative of this type of product. Now thanks to the superior ink transfer and halftone effects of the soft version, even cardboard prepressors have turned their production from harder plates to soft plates. Plate processing time is reduced, which also shortens the printer's pre-press preparation time and saves material and process costs.

Overcome the effects of "seesaw" and outlet overflow

In the case of flexo printing on corrugated sheets, the printing pressure is often increased in order to overcome the effect of "seesaw". As a result, the overflow of outlets is increased. Excessive plate deformation can cause dot gains, lower print quality, and can only reproduce coarse screen effects and large areas of whitening. In order to reduce the amount of deformation, the thin plate technology has taken an important first step in the direct quality of corrugated printing.

The second step is the development of new polyester materials to achieve a standardized printing plate system. In the past few years, this kind of printing plate has already appeared in the market, and the continuous improvement in exposure latitude also makes the thin version become the first choice for obtaining high-grade corrugated printing.

Preprint and postprint

Whether it is pre-printed or post-printed, thin plates with a hardness of 32 to 34 shore A (Shore) can meet the requirements of corrugated board printing. This type of plate is designed for multi-color half-tone printing and can reproduce lines and solid manuscripts on any paper or cardboard. After the main exposure, there is a strong color change in the exposed and unexposed areas of the printing plate, thereby making the exposure quality control of the entire etching area easy.

The advantages of the new polyester version also include: higher ink hiding power (even for various rough-surfaced boxboard, paper bag and carton board materials), fine single dot element reproduction, fine whitening effect and UPC bar code lines, etc. . If the printing plate is processed under standard conditions, its range of adjustment is very wide and can be optimized. The long exposure width is also a great advantage of the new polyester material.

As corrugated board becomes more and more delicate, from F楞 and E楞 to N楞 and G楞, the demands for printing are brighter, and the coverage of ink coverage and contrast are excellent, and printers are also increasing. Turn to thin plate technology. The technical demarcation line between corrugated board printing and folding board printing is less obvious.

Choose the right plate

Plate makers have to adapt to changes to meet the diversified needs of half-tone printing, such as reducing dot gains, optimizing ink transfer, further weakening “seesaw” effects and enhancing contrast contrasts. Fine halftones and linework require a stable plate base. This type of job recommends the use of a new thin/soft plate or other thin/slightly hard standard plates. Plates must have high resilience and deformation resistance.

The use of a compressible cushioning material is also required when using thin plates. The foam cushioning material absorbs excess printing pressure and reproduces sharp, sharp dots. This makes it necessary to adapt the type of printed corrugated board to the pressure of printing, and the requirements for the thin and hard 楞 (E楞) and thick and soft 楞 (B) types vary.

The correct "plate-pad" combination needs to be tested, depending on the undercut of the cylinder and the type of corrugated cardboard and stencil, the thin plate processing time is shorter, between the film and the plate The amount is also smaller, the thin version of the corrosion is less than 0.039 inches, because a slightly larger point of printing pressure may cause the fine anti-white areas to be stuck. This is the reason why thin plate technology applied to corrugated printing is recommended, and the recommended base is 0.039 to 0.043 inches.

Select anilox roller

The anilox roller is used to ink the printing plate. When selecting, it is required to be able to handle fine halftone dots, increase the transfer rate of the ink from the printing plate, and adapt the ink with stronger coloring power. The following anilox rollers can be used for different grades of corrugated board printing.

B, coated paperboard: It is recommended to use 356 lines per inch of the anilox roller, the theoretical amount of ink transferred 4.20-4.52BCM (6.5 ~ 7.3cm3/m2) to obtain the best half-tone, line effect;

B. Uncoated paperboard: The ink transfer is largely affected by the plate hardness and the combination of the plate liners. Recommended 305 lines per inch, the theoretical transfer amount of ink 5.81-6.13 BCM (9.0 ~ 9.5 cm3/m2) anilox roller;

E楞, coated paperboard: The impact of different types of printing plates, plate hardness and plate-pad combinations is the key to the printing of these materials, so it is only recommended to use between 356 and 405 lines per inch. Theoretical transmission Anilox roller with an ink volume of 3.23-4.52 BCM (5.0-7.0 cm3/m2).

In addition, the ink composition and viscosity have a great influence on its transmissibility. When choosing a plate for any printing method, you must be aware of the interactive effects of the various components in the system - the plate, the liner material, the inking roller, and the ink itself are also very important. So carefully selected materials will result in consistent and successful jobs.