Talking about the quality of printing products

The quality of printed products is an important indicator of the quality and economic benefits of printing companies. With the continuous development of our country’s economy and the continuous improvement of people’s living standards, the community’s quality requirements for printed matter have become higher and higher. In order to adapt to the development of the situation, printing companies have continuously improved their printing methods and added new equipment. In 1995 alone, China's imported printing presses and supporting equipment amounted to as much as 597 million U.S. dollars (approximately 5 billion yuan). In the same period, the total output value of China's printing industry was only 2 billion yuan. In fiscal year 95, a total of 101,381 books were published in the country, and 3,319 titles were recognized by the Bureau of Printing and High-quality Product Recognition Expert Committee of the Bureau of Books and Publications. The Department's excellent product rate was 3.27%. It can be seen that the quality of printed products in our country is disturbing.

The quality of printed products refers not only to the pros and cons of printed matter, but also to a series of factors that affect the quality of printed matter in the printing process. The evaluation of printed matter is often based on visual evaluation, but each factory has specific evaluation methods and data standards. In previous years, the national industry standards have been formulated: <Quality Requirements and Inspection Methods for Toppan Prints) (CY/T4-91), <Quality Requirements and Test Methods for Lithographic Prints) (CY/T5-91), and National Standards: <Flat Edition (Standard for prints) (GB7705-87), (Toppan Printing Crystal Standards) (GB7706-87), etc. The author believes that in order to continuously improve the quality of printed products in China, we should pay attention to the following aspects:

First, correctness

The correctness of text and images is the primary issue of print quality. Correctness refers to the correctness of the content of the printed matter. Problems in this area are not the problems of the quality of the printed matter in general, but errors. Errors are not allowed for any printed matter. For prints mainly consisting of text and line images, some images are not easy to distinguish between directional prints and map printing, special attention must be paid to their correctness. To this end, the printing staff should carefully check, if the manuscript is suspicious, it should immediately put forward to the relevant parties in order to promptly correct. The printing personnel should pay attention to the size of the specifications with a serious attitude. The balance of the horizontal lines, the vertical lines, the front and back sides of the layout, the angle errors of the screens, the accuracy of the gauges, the neatness of the four sides, and the layout color, printing sequence, etc. The basic quality prevents errors and causes rework waste. Make sure that the printed crystal does not have political or technical accidents.

Second, reducing

Image quality mainly refers to the reduction performance of printed products. It includes the three aspects of image clarity, tone reproduction and color reproduction.

1. Sharpness: It refers to the ability of printed crystals to reproduce detailed changes. It reflects the sharpness and outline of the image pixel edge. There are problems with overprinting of two or more color printing products, which directly affects the clarity of the final image. There are also sharpness issues in monochrome printing. Its clarity lies entirely in the quality of the image on the original printing plate and whether slippage and ghosting occur during printing.
Observe whether overprinting is accurate or not by overprinting crosshairs. The tolerances for overprinting are specified in all levels of standards, some being 0.1 mm and some ranging from 0.2 mm. Within the allowable error range can be called "registration." However, in the case of registration, there is still a problem of definition, which is overprint accuracy. I am very delicate prints, and they must first be built on very high overlay accuracy. Overprinted crosshairs are thick and thin. The finer the crosshairs, the more conducive to improving overlay accuracy. Only seeking for registration, without high overlay precision, can only be a general product.

To improve the accuracy of overprinting, we must first have excellent printing manuscripts and high-precision, high-stability printing presses, followed by matching of process technology and printed materials.

2. Tonal Reproducibility: It refers to the ability of prints to reflect the original level. We know that it is unlikely that the printing gradation will be completely consistent with the color originals. The reason for this is that the density contrast between the dye and the ink is different. The highest density of the manuscript can reach 3.0, while the current print density is best to only reach 2.2, under normal circumstances does not exceed 1.80. When printing and copying, it is necessary to maintain a density level of 0.2 or more on the original, and to control the contrast of about 1.8, there is a problem that a platemaking operator selects a certain portion of the original to reproduce.

The tone of the manuscript is roughly divided into low-key, mid-tone, and high-profile. The low profile increases, and the high and middle notes decrease. The entire print is "dark." The high profile increased, the medium and low profile reduced, and the entire print was “floating”. The number of high and low-key increases, the middle decreases, and the entire print is “virtual”. The increase in the tone, high and low-key reduction, the entire print on the "light."

The tone of prints is expressed through outlets. Tonal reproduction relies on high quality original dot tone and dot tone transfer. In the transfer process, the expansion and reduction of the dots play a decisive role in tone reproduction. The expansion or contraction of outlets depends on pressure, gasketing methods and printed materials. The dot area changes caused by printing conditions are most sensitive to midtones. However, observing the degree of change in image tone is more convenient for low-key and high-profile adjustments.

The finest prints can be distinguished by the fact that their outlets have a 90% tone and field. For better printed crystals, the tone of the dots at 90% may become the field, but the tone of the dots with 80% or 85% of the dots is still legible. The prints that make the 80% tone of the outlets become on-the-spot can only be called the general level. If the tone of the dots at 70% is indistinguishable from the field, it is a poor print.

Both monochromatic printing and color printing have the problem of tone reproduction. The main factor affecting the reproduction of the tone is the thickness of the network cable. When printing offset paper now, 32-40 lines/em (equivalent to 80-100 lines/inch) are usually used. Compare this with the high-line product number and you can see a clear difference in the level of detail in the image. This is the difference in tone expression.

The tone reproduction of a color image is the combined result of the reproduction of four color gradations. Therefore, the tone reproduction of a color image is much more complex and the requirements are more stringent. It requires that each monotone tone conforms to a certain curve requirement, and that the synthesized tone meets the reproduction requirement. The appearance of the color desktop system has provided us with good reproducible reproduction products and provided good platemaking conditions.

3, color reproduction: color reproduction power refers to the ability of prints to reproduce the original color. There are two ways to express colors in color images: one is spot color, and the other is standard four-color combination. No matter what kind of form, it must correctly and truly reflect the original color.

Continuous color reproduction of the original copy, using four-color printing; its color reproduction is achieved through four-color combination. It is transferred through a dot. Therefore, it is closely related to the tone reproduction. But they reflect the different aspects of image quality. The color reproduction of four-color printing is much more complicated than spot color printing, and any single dot change has a significant impact on correct color reproduction. Among them, not only the monochromatic hue based on the three primary colors should be guaranteed, but also the yellow, magenta, and cyan components should be brought into a neutral gray balance. At the same time, it is necessary to master the amount of black plates used as auxiliary colors. This requires the operator to have a keen sense of color and correct any possible color cast at any time. For operators who use a monochrome machine to print four-color products, they must also have the ability to recognize the color cast of each monochrome sheet when the image is still incomplete.

Third, identity

Batch identity means that all prints in the same batch are printed in the same way regardless of the number of prints. Batch identity is not only the quality of the print itself, but also the stability of the production process. The process before and after printing often changes, there is no superior quality. Therefore, batch identity is an operator, a machine, and even a symbol of the quality and level of a printing house.

There are some printed materials, such as large newspapers, publications, popular and popular literary classics popular universal reference books, primary and secondary school textbooks, famous and long-lasting commodity packaging, stamps, banknotes, etc. Billion. Society requires that their batches must be the same. The printing of a valuable ticket not only requires that the batch be the same, but also that different batches must also be identical. This is indeed a test for the printing factory.

Fourth, appearance

A complete printed product not only includes a single-page imprinting process, but usually also performs processing and binding processing that enhances the appearance effect and makes it suitable for use. These processes also have their own quality requirements, and this type of quality is also essential for most prints. Post-press processing is a very important part. At present, China's post-press processing is lagging and it has become one of the major factors affecting the quality of printed products. The aesthetic appearance of printed crystals not only manifests in the beautification of the exterior packaging, but also in the superior printing and ease of use. The quality of the imprinting process, the quality of post-press processing, and the quality of use constitute the overall quality of the printed matter.

The post-press processing of packaging printing usually includes glazing, laminating, indentation, die-cutting, embossing, punching, hot-stamping, paste forming and the like. The post-press processing of books and periodicals is mainly bookbinding, including folding, cutting, etc. Sometimes, various methods of packaging and printing and post-press processing are adopted.

The quality of books first requires size specifications. The specifications of books and magazines must conform to the national standard <size of books and magazines and their format size (GB788-87). At the same time, the position of the book block should be standardized, not skewed, the page number should be aligned (including the front and back pages), the cutting error should be within 1 mm, and there should be no knife or flash. The quality of the publications also required that there be no multi-page, page-less, white-page, page-page, page-turn, page-serial, page-page, dirty page, page break, wrinkle page, fold, page, side page, bleeding caused by post-press processing. Other ills.

Various binding methods have their own requirements. Saddle-stitching and flat-stitching require that the nails be sawed flat and their positions are reasonable; glue-binding requires firm adhesion; Hardcover books require tight corners, firm waists, and consistent floats. There are also requirements for wrapping, spine, etc.

In short, there are many requirements for the quality of printed products, and the content is very extensive. We only strictly manage the processes of plate making, printing, and binding, and pay attention to the correctness, reducibility, identity, and aesthetics of the printing process. We must not only increase investment in equipment, but also fundamentally change the technology and truly realize the digitization and standardization of the printing process so that the quality of our country's printing products can reach the top of the world.





Liu Ningjun

Source: Print World