Packaging material knowledge to improve the quality of printed matter and several key points of printing paper
Guide: The quality of printed matter depends on many factors, and the paper characteristics are undoubtedly one of the important factors. The paper with excellent performance can complete the ink transfer completely, so that the image and text can be clearly and fully reproduced on the paper, thus obtaining a satisfactory reproduction effect. Here are some key points of printing paper, which are for reference by friends of the superior packaging system:
It refers to all kinds of printed products and the general term of all kinds of finished products produced by printing technology. In daily life, people come into contact with newspapers, books and magazines, trademarks, labels, business cards, packaging boxes, gift boxes, etc., all of which belong to the category of printed matter. Printed matter is almost full of people's clothing, food, housing and transportation, and it is very close to people's life.
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01 The influence of paper characteristics on the gloss of printed matter
In the printing process, the ink film is transferred to the paper surface and filled with the unevenness of the paper surface, so that the printed surface is quite smooth. The specular reflection of light from the ink film surface of printed matter determines the gloss of printed matter, and the ink film surface is closely related to the characteristics of paper.
● Ink film thickness
The ink film thickness is the main factor affecting the gloss of printed matter. After the paper absorbs the ink binder to the maximum extent, the remaining binder remains in the ink film, which can effectively improve the luster of the printed matter. The thicker the ink film is, the more binders remain, which is more conducive to improving the luster of the printed matter.
The gloss increases with the ink film thickness, which is different for different papers. When the ink film of high gloss coated paper is thin, the gloss of its printed matter decreases with the increase of the ink film thickness. This is because the ink film covers up the original high gloss of the paper itself, while the gloss formed by the ink film itself decreases due to the absorption of the paper. With the increase of ink film thickness, the higher gloss of the paper itself is more difficult to be reflected through the ink film. When the ink film thickness reaches 1.5 μ M, the absorption of paper to binder is basically saturated. After that, as the ink film thickness continues to increase, the more binders are retained, the gloss will continue to improve. The gloss of coated paperboard prints increases rapidly with the increase of ink film thickness when the ink film is thin, and the ink film thickness increases to 3.8 μ After m, the gloss no longer increases with the increase of ink film thickness. However, no matter what kind of paper, the amount of gloss increases with the increase of ink film thickness should have a certain limit.
● The influence of paper characteristics on the gloss of printed matter
The paper forms capillary network structure due to fiber interweaving, which has a large number of pores, and becomes the basis for absorbing ink. The balance between the absorption time and fixation time of the ink binder in the paper capillary network determines the degree of binder penetration when the luster of printed matter is formed. Generally, the gloss of printed matter decreases with the increase of paper absorption capacity.
Paper smoothness and its own gloss affect the gloss of printed matter. The high smoothness is conducive to the formation of a uniform and smooth ink film, thereby improving the luster of the printed matter. The good gloss of the paper itself can improve the reflectivity of the ink film, especially for transparent ink. The correlation between the gloss of printed matter and the gloss of paper itself is stronger than that between the gloss of printed matter and the absorption capacity of paper.
From the above discussion, it can be found that there is also a correlation between the smoothness, gloss and absorption capacity of the paper. It is easy to explain this from the papermaking process. For example, calendering can improve the smoothness and luster of the paper, and reduce the amount of porosity of the paper, thereby reducing the absorption capacity of the paper. In addition, the pH value of the paper surface is also a factor that can not be ignored in the formation of the printed matter luster. The high pH value is conducive to the drying of the ink, so it is conducive to improving the luster of the printed matter.
02 The influence of paper characteristics on the reproduction of order of printed images
The reproduction of the ideal tone is the most important process to obtain high quality printed images. Most bad prints are caused by the reproduction of the tone.
The primary requirement for image reproduction is that the copied image visually match the original. But in most cases, the density range of the original manuscript is larger than that of the printed image, and as the quality of the paper decreases, the range of reproducible density is smaller, also for saturation and color.
The solution is to compress the scale range of the manuscript, so that it and paper can reproduce the density of the range to match.
03 Paper characteristics on the influence of dot increase
● Dot increase
Dot increase has more effect on hue change than any other variable. The amount of ink printed on the paper will affect the dot increase, and dot increase will affect the printing contrast. In the printing of black and white or color mesh images, dot enlargement will change the picture contrast and cause the loss of image detail and clarity. In multicolor printing, dot increase can lead to loss of contrast, dark image, dot paste death and cause dramatic color changes.
● Paper characteristics on the dot increase a lot of influence
The smooth surface of the ink produces the best field density on the higher quality paper. When the paper quality decreases, the field ink density decreases, resulting in a certain dot expansion, which affects the quality of the printed matter.
The higher the number of network cables, the smaller the dot diameter, the tiny pits on the paper can also distort or miss small printing plate dot. Therefore, the higher the number of network cables, the higher the smoothness of the paper is required. This is a principle of paper selection. But in the actual work, it can also be appropriate to adjust some performance of the ink or change the process parameters to adapt to the characteristics of the paper.
04The influence of paper characteristics on the overprint accuracy
For fine prints, the alignment requirements are higher, and the error is generally allowed within 0.05mm. In multi-color printing, there are many reasons for inaccurate overprinting, but the paper deformation caused by the change of water content in the printing process is an important factor.
As we all know, the change in water content of paper not only leads to the expansion or contraction of paper, but also changes the local size of paper due to the change in water content, resulting in other forms of deformation, such as curling, creasing, etc. This deformation seriously affects the printing workers of printed matter is concerned about the effect of relative humidity on the water content of paper.
At constant room temperature, the change rate of water content caused by relative humidity change at high humidity is much larger than that caused by relative humidity change at medium humidity. The same is true with low humidity. From this point of view, printing is most advantageous under moderate humidity conditions.
Paper humidity lag phenomenon: a relative humidity condition to reach the balance of water volume of the paper, if after hygroscopic (dehumidification), back to the original relatively wet ambient air, the water content than the original to increase (reduce).
In order to make the water content of the paper in the whole paper to maintain uniform, and with the temperature and humidity of the printing workshop; At the same time, in order to reduce the sensitivity of paper to environmental humidity and improve the stability of paper size, it is generally necessary to carry out humidification (hanging) treatment before printing.
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