Four key points of quality control of raw material

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Four key points of quality control of raw materials in the printing process

2. Detection of ink

the first step of evaluating ink is to scrape the ink sample, which is best carried out on the paper to be printed. It is usually operated with a wide ink knife, or a thicker ink layer can be rolled out with a small ink roller. When comparing two kinds of inks to better realize man-machine running in in the process of operation, it is generally required to scrape two ink samples in parallel on the same piece of paper. There is often a solid ink bar in the middle of the scraping sample paper

(1) opacity: some inks, such as yellow ink, are not as transparent as other inks. In color printing or overprint, we must know this performance. If the last ink is not transparent enough, the color after overprint will be biased towards the last ink. The opacity can be obtained by checking the ink color on the ink bar of the scraping sample

(2) color: parallel scraping can be used to compare the colors of various color inks, especially for magenta ink in color printing. The pigments of this ink include mineral red, rhodamine yellow, and a mixture of the two. Unless the pigments of the inks used in the two printing are the same, it is impossible to have the same color

the ink color can be quantitatively expressed by the Preucil ink formula, that is:

where l, m and H represent the minimum reading value, intermediate reading value and maximum reading value measured by the reflection densitometer through the red, green and blue filter respectively. The hue gray value can be marked on the circular or triangular chromaticity diagram of GATF. The advantage of triangle chromaticity map is that it is easy to get the representation domain of a certain group of color inks. Connect a straight line between the three ink coordinate points to form a triangular area, which represents the two dimensions of the three-dimensional color space, and its edge is the limit of the representation domain of the group of ink

(3) ink strength or pigment concentration: the problem often encountered in color printing is not whether the pigments contained in the ink are consistent, but whether the percentage of pigment content is consistent. The latter problem is that in order to obtain the same color saturation, inks with low pigment content need a thicker ink film than inks with high pigment content

the detection of pigment content is sometimes called "whitening" test. Mix 1 part of ink with 50 parts of opaque white ink, make parallel scraping samples with the same proportion of white standard ink, and visually check the difference in the intensity of the two inks. The red, green and blue channel readings of the densimeter can quantitatively measure this difference. Continue to add white opaque ink to the darker ink scraped side by side until the scraped samples of the two inks are consistent, so that a relative quantitative description of the pigment concentration relationship between the two inks can be obtained

to the increasingly enthusiastic market trend (4) ink adhesion: ink adhesion affects the adhesion of ink and the peeling of paper. A simple test can be used to compare the adhesion of the two inks. Take a little ink sample from each of the two inks and apply it on the plane, press the index finger of both hands on each ink sample respectively, and quickly raise the finger. The disadvantage of this test method is that it can not obtain quantitative absolute adhesion, but only the relative value of adhesion. Of course, now we can use electronic ink adhesion instrument or other adhesion instruments to quantitatively measure the adhesion value under certain conditions

the quality of raw materials has a great impact on the final quality of printed matter. We can find manufacturers or sellers who can provide high-quality raw materials, or reject products that do not conform to the concept grid by testing the arrived raw materials. These two kinds of square mandrel diameters should be 2.5 times the commodity diameter to ensure the quality of raw materials. As for the problem of raw material testing, despite the inconvenience of testing, large printing plants should realize that the investment in testing is much less than the income it brings. Small printing plants can also get obvious benefits from testing, as long as they purchase small testing equipment with less investment and use existing employees to carry out testing operations

as a manager of an enterprise, when you plan to implement raw material quality control, you should first consider two aspects, and weigh whether the investment in testing equipment is less than the benefits it can bring. Moreover, the records of quality problems and the causes of these problems should be summarized and analyzed in detail, so as to better control the quality of raw materials in the printing process

(author/Yu Yong)

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