The present and future of flexographic printing

Ding Yi

China Packaging 2001 06

Flexographic printing has become the leading trend in the field of packaging printing The main force. The origins of flexographic printing are still uncertain. Our country only introduced the flexographic printing process in the early 1970s. After many technological innovations, it has now established its position in the field of packaging printing. This article analyzes and introduces the current status and prospects of the popular flexographic printing technology for the benefit of those in the packaging and printing industry.

Evolution

It is said that around 1890, a rotary rubber plate printing press was seen in the UK. At that time, it could only print simple trademarks, paper bags, and packaging paper. Print on it. Because aniline dyes are used to make ink, it is called flexographic printing. Soon, the promotion spread to continental Europe, and it was only spread to the United States after World War I. After improvements in inks, printing machines, and dryers, cellophane began to be printed. It was quickly recognized by society, and then around 1940, the anilox roller was invented in the United States, thus improving the printing quality.

In 1952, at a printing conference held in Stockholm, Sweden, the name flexographic printing was rejected, and the participants unanimously agreed to change it to Flexography. The meaning of the discussion at that time was that because photosensitive resins had sprouted and the emergence of polyethylene and polyester had greatly increased the number of carriers available for printing, the application of Flexography was flexible and could be suitable for various printing purposes. Therefore, it was given this name. Without understanding its background, domestic translators literally translated it as flexographic printing and it spread, and it has become a common practice to this day.

In the first half of the 20th century, after cellophane was used to print transparent non-absorbent packaging materials, its application expanded rapidly, involving polyethylene and various synthetic resin films as a printing method for packaging materials. It has laid the foundation in European and American countries.

Japan only introduced this technology at the beginning of the 20th century and used it to print corrugated paper, paper bags, etc. Unlike Europe and the United States, it was not used in the field of flexible packaging materials and cartons at first. There are two reasons. One is We are not very satisfied with the quality of flexographic printing. Secondly, we have already introduced gravure printing and offset printing technologies to meet the demand. Recently, the pace of expansion has accelerated as the flexographic printing technology environment has caught up with gravure and offset printing.

Technological status

In the past five or six years, the progress of flexographic printing technology is indeed enviable. The reason why it is appreciated is that there have been innovations in various aspects such as ① printing press, ② anilox roller, ③ plate material, ④ plate making, ⑤ ink, etc. The following is an online flexographic printing press suitable for narrow web paper Introduce the center.

(1). Flexographic printing press

According to the unit arrangement of the flexographic printing press, it can be divided into three types (see Figure 1). Among them, in the past, in-line models, especially when printing films such as flexible packaging, in terms of quality and registration accuracy, the Flexopak machine produced by COMCO in the United States adopted a flexible tension adjustment system installed at the delivery part. The machine has been equipped with an S-shaped overlapping mechanism for the unit, and the drying part has been equipped with a chill roller. It has achieved registration accuracy comparable to that of gravure printing. Compare the Flexopak machine produced by COMCO with the previous printing machine units, as shown in Figure 2

In addition, a standard drying device is installed on the COMCO machine, which is integrated with the development of ink , realizing printing that can protect the environment. Furthermore, in order to shorten preparation time and improve operating performance, a standard COMCO programming system was installed to quickly replace plate cylinders, anilox rollers, ink fountain tanks, etc., which is more conducive to multi-variety and small-batch production activities. According to the latest information, a variable repeating system that can continuously change the circumference has been completed, which is closer to gravure printing in structure.

(2). Anilox roller

In the past, the iron core of the anilox roller was chemically corroded, or it was made by mechanical engraving and then hard chromium plating on the surface. The number of lines is no more than 400-500lpi, so the number of printing lines can only be limited to 100-120lpi. Due to factors such as limited printing resolution and unstable quality, it has never been promoted in the fields of flexible packaging and carton printing in Japan.

Later, an anilox roller was developed that used sprayed ceramics for the iron core and then engraved it with laser, with the highest line count reaching 1200lpi. The degree of freedom of the inking hole shape has also been expanded. Therefore, the number of printing lines can reach 300lpi. At present, the line number of gravure printing used in packaging printing in Japan is 1200lpi, and the life of the roller has also been greatly improved, so it is not a problem at all for flexible packaging printing.

(3). Plate materials for flexographic printing

Currently used plate materials, rubber and photosensitive resin (liquid, solid) are the mainstream, especially in packaging printing For high-quality printing, a photosensitive resin solid plate is used. Photosensitive resin plates were born in the early 1970s. Since then, the plate printing process has tended to be rationalized, and thin printing plates can be made, and the printing quality has also been improved.

The plates currently used vary according to their uses. The thickness used for packaging printing is 1.14-1.70mm, and the hardness is generally 50-60 degrees. The surface condition of the plate and its resin composition have a certain impact on the transfer of ink to the substrate, which is very important for quality. Since it is closely related to the ink, it is also important to develop ink that matches the plate. In view of this, further improvement of printing quality requires close collaboration between plate manufacturers and ink manufacturers. Recently, overseas countries are gradually adopting water-based developing plates, which is beneficial to environmental protection.

(4). Plate making and printing plate

In the past, the negative image made in the photographic process was exposed to ultraviolet light to harden the image part and then develop it to remove the unhardened non-image. The image part is made into a printing plate. Recently, this process has been introduced by gravure printing and offset printing. Various specifications of CIP, as shown in the table below, have been developed in European and American countries and have been introduced in Japan using computer mechanisms to use lasers to directly image images onto the plate. The process comparison between the past method and the CIP method is shown in Figure 3 - see below. Compared with the past method, direct plate making using CIP does not require film output, so the delivery time is short and the labor cost is reduced. Because smaller ideas can be reproduced, the reproducibility of highlights is improved, and the performance of thin lines and text is also improved. Great improvements have been made, greatly increasing the performance range of layout design.

(5). Printing ink

The various inks currently used are mainly water-based synthetic resin-based inks, but ultraviolet curable inks (UV) for solvent-free flexographic inks Ink) has been widely used in European and American countries as a measure to control solvents, and Japanese ink manufacturers have also followed up on the development. Compared with water-based ink, UV ink has a high viscosity (1000-3000cps). The hardened ink film is durable and has good adhesion to various plastic materials and surface smoothness. It is expected to have better development in the future. The composition of UV ink is shown in Table 2. Currently, free-based UV inks are the mainstream. In the future, from the perspective of safety, cationic inks will become the mainstream in packaging and printing.

In addition, various flexographic printing machines equipped with UV curing devices have been introduced. Here are photos of the Flexopak machine manufactured by the American COMCO Company (see Figure 4), which is specially used for packaging printing.

Outlook

After entering the 21st century, the market environment surrounding the printing industry is: multiple varieties, small batches, personalization and low prices. In addition, the printing industry is becoming legalized. Environmental regulations represented by the Container and Packaging Recycling Act and the Chemical Substance Emission Control Act will become increasingly stringent and become a major issue that the printing industry must solve in the early 21st century.

To solve these problems, we cannot make small reforms to the production project or simply change the business content of the enterprise as in the past. Instead, we must change the production method and adopt a comprehensive reform of the enterprise organization to activate it. Okay, let's first talk about the problems existing in gravure printing and offset printing in their prosperous period, and finally describe the prospects of flexographic printing.

①. Gravure printing

To meet the needs of the market environment, printing speed is not a problem, but there are certain limitations in adapting to small batches, productivity cannot be improved, and delivery time must be dealt with at the same time There are still problems.

As for regulatory responses, in the case of solvent inks, exhaust (combustion, recycling) equipment is required. Due to problems such as initial investment and working capital, it is also necessary to consider improving the working environment. It is also necessary to consider that the ink is water-based, which will reduce the speed and lead to a decrease in productivity. In addition, there are many problems such as the need for drainage treatment equipment.

②. Offset printing

There are currently no problems with regulations, but when it comes to printing films for flexible packaging, new inks and drying methods need to be developed, and there are still unknown areas. Few, it is not easy to solve it immediately. In addition, carbon dioxide from high boiling point solvent processing is also a problem that must be solved from the perspective of global environmental protection.

③. Flexographic printing

Water-based and solvent-free (UV) printing are easy to achieve, especially UV ink, which fully meets the needs of environmental protection. In addition, when narrow-width web paper is used, the time required for job replacement is very small. On the COMCO 16-inch printing press, each unit only takes 90 seconds to complete the replacement, and there are few errors. For small batches and multiple varieties, , it has an absolute advantage over the above two methods, especially when the batch printing is less than 10,000 meters.

At present, the problem encountered is to comprehensively innovate gravure printing for packaging. What needs to be solved is high investment and too much operating load, which cannot be done for the time being. At the same time, flexographic printing and the above two methods There is still a subtle quality difference, which is also a resistance. However, from the perspective of environmental protection constraints, it should be given priority. Therefore, it is necessary for the packaging and printing industry to introduce more narrow-width flexographic plates that can cope with small batches and short delivery times as soon as possible. printing press to revolutionize the packaging and printing industry.

If the flexographic CIP is further improved and the seamless printing plate that is in the process of development is introduced, it will be able to cope with not only small batches but also large batches of printing jobs if the quality is not significantly different from other formats. Come down, by then, in the early part of the # century, we will usher in flexographic printing that is environmentally friendly, has high quality and high productivity, and it will undoubtedly become the mainstream of packaging printing.