Gravure Printing and Printing (I)

Gravure printing, which is one of the main printing methods, has held a relatively stable ratio (10-20%) for many years, which is determined by its specialty, namely, high volume, high quality, and high speed. According to its printed products, it can be divided into two categories: "publishing gravure printing" used for high-grade and large-volume publications and mailing advertisements, and "packaging gravure printing" used for printing of building materials. Faced with the market requirements of “multi-variety, small-batch, short delivery”, in general, despite some improvements, it is difficult for gravure. In recent years, the sudden emergence of flexographic printing has increasingly demonstrated its advantages. However, each has its own advantages and markets. The gravure printing has its own irreplaceable specialties. Now and in the future, it will continue to play a major role in mass publication and packaging printing. This article gives an introduction to the prior art of gravure platemaking and printing.

A gravure printing plate

Relief and lithography express the level of print with the size of the dot area, while gravure expresses the level with the concave part of the gravure (ink mesh). The intaglio concave part can be divided into different shapes according to the shape: 1 the surface area of ​​the concave part is equal in depth; 2 the depth of the concave part is equal to the surface area; 3 the depth and surface area of ​​the concave part are different. Compared to other printing plates, these gravure printing plates that have been fully used today are very complicated to produce. The color separation film (original) used in gravure production also has a complicated and difficult manufacturing process.

Now, the environmental environment surrounding the gravure printing, such as prepress digitalization and non-filming, has also been rapidly promoted. The CTP process of drum production is not limited to the electric carving method. The laser method has also been developed and is entering an era of diverse technologies.

(I) Gravure Printing Method

The conventional method in the gravure platemaking method is a gravure plate making method. The method produces a plate with the same mesh area and expresses the level of printed matter with the depth of the mesh. Its original version has no outlets, and is a continuously adjusted film. The image on the original plate is imaged by UV irradiation on a corrosion-resistant film (film used to corrode the plate cylinder coating) or on carbon paper. The film is then wrapped on a roller, developed in warm water, and chemically passed through ferric chloride. Corrosion, the formation of different shades of mesh. However, in recent years, continuous adjustment of the original version has almost never been used, and the amount of carbon paper has also been greatly reduced.

The current process is basically divided into two types. One is a method using a color separation film, that is, a method of making a screened color separation sheet in exactly the same manner as offset printing; the other is a method of performing full digital processing on an image and printing without a film. Plate roller method.

In the field of packaging printing and special gravure printing, the filmless production method is rapidly being promoted. There has been real progress in the absence of filming in the field of gravure printing.

1. Published Gravure Plate Making

Publication of Gravure Plates Prior to 1975, the use of photogravure plates using carbon paper was the main method, so the original version was a continuous film. During this period, the electronic engraving technology was developed, and an electric carving method using a continuous modulation film emerged. By the early 1980s, the original version began to use offset printing films. Now Europe and the United States use gravure printed publications and postal advertising, and its platemaking can be said to use 100% electric carving. In Japan, three methods are used: 1) Corrosion using offset printing separation film; 2) Electro-engraving using offset color separation sheet; 3) Non-filmed electric engraving using digital data (gravure CTP). Among them, the third mode is growing, with the proportion reaching about 50%.

The laser method (etching method) that is being used on the gravure plate of the package is almost not used in the field of gravure printing. The reasons are: 1 The laser mode is a new thing; 2 The roller is too large to handle; The 3 rollers are also 32 pages minimum. Larger ones are up to 72 pages in size. To fabricate their meshes, high-performance image processing is required; 4 The whole device is too large and expensive.

2. Package gravure plate making

Packaging gravure includes plastic film printing represented by pastry bags, instant noodle bags, and fast food bags, and carton printing represented by cigarette packaging, pastry boxes, and toilet paper packaging boxes. There are a large number of printing companies in this area, and there are many plate-making equipments used. There is also a category of gravure printing called special gravure printing, including the printing of labels, trademarks, cards, securities, building decoration materials, wallpapers, flooring materials, fabrics, etc. Due to the various quality requirements of these printed products, special gravure printing developed a variety of plate cylinder production methods in response to these requirements compared to the publication of gravure printing, including: 1 Screen printing and gravure printing (using gravure printing screens); 2 Electro engraving method using offset color plate or digital file; 3 Laser plate making method using sensitizer (digital data); 4 Laser plate making method using black primer (digital data); 5 Laser plate making method using electroplating alloy (digital Data), and so on.

In addition to Ohio and Haier, the electric engraving equipment manufacturers also joined the Japanese screens. The manufacturer of the sensitizer laser is Japan's THINK LABORATORY. The black primer laser is used to make the German version of the Western Bass Ohio Company. Alloy laser plate making method is Swiss MDC Company.

Packaging-specific platemaking software includes unique software such as connected and seamless images. In addition, gravure printing uses spot colors (including white), and 6 to 7 colors are common. This is obviously different from publishing gravure.

3. The difference between gravure and offset quality

Due to the different printing methods, there are many differences in the printing quality from the perspective of their respective printed products.
• The outline of the text in the field. Offset text on the ground does not require a dot, and its edge is smooth, just like a text manuscript. Gravure prints must have meshes on all occasions. Due to the meshes being spaced apart from one another, the outline edges of the solid characters printed with the indentations appear jagged. In this regard, people have come up with various plate-making methods.

· Intensity of ink in the field. This phenomenon is unique to the use of low viscosity inks in gravure printing. When the ink in the deep part of the mesh is transferred to the substrate such as paper, the density is uneven, and small spots with different shades appear. Countermeasures include: adjusting the ink viscosity, mesh angle (screen angle), change the depth and shape of the mesh.

Hue changes. The same color ink, when the ink film thickness is different, the hue is also different. The offset printing layer is expressed by dot size, and the ink ink layer thickness is theoretically constant (strictly speaking there is a difference); the gravure printing method is in particular the method of expressing the layer depth by the depth of the mesh, and the depth of the ink film is also different for different mesh depths. Therefore, the change of hue that is not considered in offset printing will be generated in gravure according to the different levels, but this phenomenon is not easy to occur for gravure with a certain depth of mesh. This phenomenon will be manifested by color-difference problems that occur in some way with color proofing and on-press printing.

(B) Gravure Printing Plates and Proofing

Compared with the past, the original version no longer requires the production of continuous adjustment of the original version, the production method is almost no different from offset printing. In particular, the production of color screening films, color proofing by offset proofing machine to complete, the process is very simple and time-saving. The previous method was to make a proofing roller the same as the upper plate roller for proofing. However, the environmental conditions for proofing and printing are not the same, and there are differences in the printing quality. Nowadays, for customers with high requirements or quality requirements, on-site proofing is often done on the press. If the quality is approved, the proofing drum is used as the upper drum.

In recent years, due to continuous progress in the digitization and non-filming of plate making, the use of digital color proofing has increased.

1. Publication of Gravure Printing and Color Proofing

The gravure printing method of publishing gravure is carried out from the production of black paper to imposition. It is carried out entirely in accordance with the offset printing method, the same process, and the same quality management. Therefore, when the customer is in a hurry to make a gravure printing product, Even if it is replaced with offset printing, there is no problem.

The gravure platemaking method is divided into two types. One is to make an original (separation film) that is the same as offset printing, and the other is to use a digital file to make a plate. The color proofing of the former method is the same as offset printing. As for the proofing ink, an ink close to the gravure ink is often used, but as described above, it is difficult to completely reproduce the colors due to the different characteristics of the heart ink in the printing method. As for digital color proofing, it is even more difficult to achieve consistency with color reproduction of gravure inks. The reason is that currently on the market printers, all use offset printing as their design and production target. Whether it is the color reproduction range of the used color material or the color matching technology used, the reproduced color is at best the same as that of offset printing, and the reproduction is to be transparent. The color of gravure ink with a sense of sensibility and expressiveness is very difficult. Although there is an ideal dye-based inkjet printer in the printer, no matter what kind of printer is different from printing. When using a printer for proofing, it must be agreed upon with the customer. In addition, due to the lack of spot color, it is easy to achieve proofing effect by using a printer.

2. Gravure plate making and color proofing

Both gravure printing and gravure printing basically use the same plate making method. However, in general, unlike gravure printing, the gravure-printed substrates must be combined with plastic film. The heart often uses spot colors, usually 6-7 colors, and the platemaking method takes these conditions into consideration. This is different from publishing gravure.

Packaging products are often printed using plates that are joined together on the same screen. Platemaking is single-sided plate making, and color proofing is also single-sided proofing. The problem of color proofing can be said to be the same as the publication of gravure, but the topic of spot colors is more. Printing proofing can be consistent with spot color inks, and color printing cannot express spot colors with a combination of three primary colors. Do not expect to achieve high print quality on this occasion.

Summarizing the above points, the special software for packaging gravure plates has: 1 connection function software; 2 splicing function software for creating seamless images; 3 spot color printing software; 4 trapping software (to compensate for printing registration Deviation, a small amount of overlap of the color version of the image outline, mainly for plastic film gravure).

(III) Production of Gravure Rollers

No matter how good the original is made or how accurate the digital plate data is, if a high-precision plate cylinder cannot be produced, the quality of the printed matter cannot be guaranteed. In this respect, gravure can be said to be the most demanding of all kinds of printing plates. The production process is as follows.

1. Production of roller base

The material of the roller base is generally steel pipe because of the low price and firmness of the steel pipe. Weights range from 10 kg (pack gravure) to several hundred kg (published, gravure building materials), and some can weigh up to 1 ton depending on the print product requirements. In recent years, aluminum rollers have been used for packaging gravure printing, and in particular, plastic rollers have recently been used.

The wall thickness of the steel pipe is from 20mm to 30mm, and the large size roller is thicker. Roller is divided into non-axis (mainly package gravure) and shaft.

2. Roller plated copper

Regardless of the type of roller base material (as long as it meets the requirements), the surface of its newly machined roller should be plated with copper. This bottom copper layer is not a copper layer for engraving or etching, but is used to achieve the precision requirements of the drum. For example, the tolerance of the drum diameter is within 10 μm and the parallelism is not more than 10 μm. The thickness of the copper layer is about 600 μm. Next, a layer of copper, which is necessary for etching and engraving, is also plated on the copper layer.