■ Liner (Corrugated Paper) Materials In general, the backing materials used in postpress processing are generally classified into the following types:
● Kraft corrugated paper is often used where surface papers are highly resistant, or when the packaging needs to have strong tear resistance. This liner is typically applied to Type A, C, and B type corrugated paper.
● Test liners are an effective, inexpensive liner made from recycled paper. It consists of two layers: a thicker base and a more absorbent outer layer. This liner is also mainly used in A, C and B type corrugated paper.
● Decorative backing paper. There is an alternative between non-coated, semi-coated, and fully coated liners, typically decorative decorative liners. The white backing paper provides the product with a suitable surface for the most attractive print quality, especially for image designs with multiple colors. Decorative liners are increasingly used in B, E, and F type corrugated paper.
■ Photopolymerization printing plates for post-printing In the corrugated printing process, photopolymer printing plates have many basic properties. These properties depend on the nature of the printing process, the substrate materials and the external conditions and factors in the printing process.
Various considerations such as the quality of liner materials, paper and board, ink characteristics, anilox roller parameters, and equipment limitations, as well as other products used in the paper processing industry, occupy the concept and improvement of the printing process technology. Very important position.
Photopolymerized printing plates consist of four major parts: crosslinkers, monomers, photoinitiators and additives. The changes and choices of these ingredients, as well as their performance and interrelationships, play a crucial role in the printing performance. The composition used to produce the photopolymerization printing plate has a great influence on the choice of the water-based ink system. The main issues that should be considered when developing improved photopolymer printing plates are the transferability and hiding of the ink, resolution of the printing plate, stability, oxidation resistance, and printing-related properties (limitation of device speed).
■ Requirements for Printing Plates The development of new photopolymerization printing plates is challenged by issues such as high-mesh printing, high resolution dots, and ink transfer in the field. In the end, printing companies had to use different photosensitive polymer plates in different paper bags, liner backings, and backing material combinations, resulting in a variety of different combinations. This is to make the best use of the special printing plate's characteristic advantages, especially hardness and ink transfer ability, to suit a specific application and specific substrate.
In order to standardize print quality, corrugated paper printing plants are increasingly using thinner photopolymerized plates and two standard calipers: 3.94mm (0.155 inch) and 3.18mm (0.125 inch). The most commonly used standard for printing plates is to produce smooth dense ink transfer and low dot gain.
Another requirement is the precise and clear output of fine reversal films and line elements, reduced filling elements, and smooth printing of harder levels. The minimum tolerance on the specification must be met. The hardness of the plate must not exceed that of Type E or F Corrugated Board 42ShA (ISO) and Type B, C or A Type Corrugated Board 34ShA (ISO) to overcome the surface structure problems of the board. At the same time, the printing plant needs a higher flexibility of the printing plate to reduce the requirements for the performance of the lining paper, reduce the downtime, and facilitate the setting of printing pressure.
Plate makers all want to shorten the cleaning time and reduce the drying time to increase output and production capacity. It is desirable to have a longer back exposure time to broaden the range of the pre-exposure while minimizing the effects of fluctuations during UVA emission. In addition, shorter surface exposure times and longer main exposure ranges are also needed to improve efficiency. Digital printing plates usually have different needs, and these printing systems also have to meet different needs in order to achieve a clearer printing effect.
Due to the limitations of the choice of specific printing plate ingredients, the printing plate and its performance have certain limitations. These limitations are in conflict with many of the requirements mentioned above. The needs of these conflicts can often not be solved simply by means of ink composition, changing plates, padding or adjusting equipment. The combination of primary colors often must be converted to meet most needs. The range of these elements includes aspects from plate composition to application to print production.
■ Compressible liners In order to reduce the overall degree of plate deformation during printing, compressible liner materials are commonly used under the transferred media. Compressible foams absorb most of the extra printing pressure and improve print quality.
The compressibility and memory properties of the foam material affect the ink transfer performance of the above photopolymerizable printing plate. The thickness of the foam should not be greater than the thickness of the plate material used to prevent any possible instability of the system (which may result in non-uniform printed output).
■ The quality of prepress quality in post-print applications can be comparable to the quality of offset lamination, which has become the benchmark for most post-printed paper processing companies to compete for new, more profitable businesses. The increasing paper-carrying capacity of corrugated board, the continuous reduction of equipment downtime, and the improvement of the printability of the liner surface all stimulate printing companies to continuously improve the production of paperboard, seek more reliable paper consistency, better ink transferability, and reduce Outreach features, and the use of higher device speeds.
In order to meet the latest quality requirements in corrugated post-printing applications, the ink should deliver the least amount, ensure minimal dot gain, and achieve the required density, with minimal material cost.
With the introduction of new high-quality corrugated board presses and the application of finer anilox systems, there is an opportunity to use digitally printed plates in the post-printing process, mainly for the semi-coating of printed E and B type corrugated papers. White surface liner. Digital corrugated plates of 0.112 inch and 0.125 inch thickness can provide satisfactory results.
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