Analysis of detection points of paper and ink printing raw materials
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The standard test methods for raw materials in the printing industry are mostly focused on the testing of paper oil inks. The documentation of the International Institute of Printing Research has compiled the printing standards of fifteen countries and two organizations. The publication lists 88 standards or specifications for paper and other substrates issued by Germany and 66 standards for inks and other related materials issued by Poland. Some standards are about adhesives and other bookbinding materials, as well as about photographic materials. But in general, the printing industry does not pay enough attention to materials other than ink and paper.
A large number of inspection methods, testing instruments, and inspection images can be evaluated by the printer for raw materials, which means that almost all paper or ink properties can be tested to comply with established standards. The key question now is which test methods should be used and how many tests should be done in various situations.
It is difficult to obtain a representative sample when detecting paper or other substrates. For a stack of paper, especially large ones, it is very difficult to randomly extract samples from them without completely re-stamping them. For webs, except for the (not representative) outer layer, no test can be done.
In general, the sampling of ink and photosensitive materials is not a problem. Another issue that should be considered when sampling raw material testing is that certain testing methods are destructive. For example, the strength of paper and paperboard, the sensitivity of the photosensitive material, the sample will be damaged and consumed.
For the selection of testing methods for a material, consideration should be given to the detection of data relating to print image defects or print production barriers.
The frequency with which a performance is tested must be based on the tolerance for the performance change, which in turn is related to the quality defect level allowed for the final print. The more stringent the quality requirements of the printed products, the more frequently the raw materials need to be tested.
For most printing companies, it is not as much time, money, material and manpower to spend on testing raw materials as government departments or large printing companies. The benefits of testing may not be sufficient to cover the cost of testing. However, this situation refers to large-scale testing, and in fact most printing companies can conduct small-scale testing. All printing companies can make appropriate investments to do those that are cost-effective.
The following are tests that control the factors that affect color reproduction:
1, paper detection
Some tests can be implemented with very simple equipment.
(1) Thickness
To maintain the correct printing pressure on the press, use a bore gauge. The thickness of the paper should also be measured with a micrometer. Generally, ten sheets are used to measure five points.
(2) Opacity
The opacity visual scale is an effective measurement tool. A set of characters is printed on the background of the gradually darkening dot, and the paper to be tested is placed on it, and the character is not visible at some point on the scale, which indicates the opacity of the paper.
(3) Absorptive
K&N inks are probably the most common and cheapest test method. The ink is composed of a gray dye and an oil base, which is applied to a paper sample and rubbed off after two minutes, and the remaining ash density is the absorbency of the paper.
(4) Glossiness
Use a gloss meter to measure in the direction of the paper and take the average.
(5) Paper efficiency
This test combines the gloss and absorbency of the paper to determine the effect of the substrate on the color of the ink film. Non-absorbent paper with 100% gloss can print the most saturated colors. In contrast, 100% absorbent but matte paper (such as newspapers) will print very poor colors.
(6) Color and lightness
The approximate characteristics of paper color and lightness can be obtained by measuring the density of the red, green and blue color filters after the calibration by a reflection densitometer. For ideal paper, the density under each color filter should be the same, and the density value is low, indicating high brightness. The visual comparison of the paper specimens makes more sense for the detection of the color and brightness of the paper.
(7) Uncovering
Denison wax stick peeling test, despite its shortcomings, is still a suitable method for determining the anti-skinning ability of a particular substrate. The end of a certain level of wax rod is melted and pressed against the substrate to be tested, and after 15 minutes, it is quickly pulled up, and the removed fiber or paint is inspected on the end surface.
As with many other raw materials, the relative significance of wax stick testing is greater than predictive. That is to say, if the peeling does not occur, then the paper whose anti-uncrosion strength is higher than 10 will not be peeled off under the same conditions.
2, the detection of ink
The first step in evaluating the ink is to scrape the ink, preferably on the paper to be printed. It is usually operated with a wide ink knife, or a small ink roller can be used to roll out a thicker ink layer. When comparing two inks, it is generally required to scrape two ink samples in parallel on the same sheet of paper. There is often a solid ink stick in the middle of the scraped paper.
(1) opacity
Some inks, such as yellow ink, are not as transparent as other inks. This should be known when printing in color or overprinting. If the final printed ink is not transparent enough, the overprinted color will be biased towards the last printed ink. The opacity can be obtained by checking the ink color on the ink stick of the squeegee sample.
(2) color
Parallel scraping can be used to compare the color of various colored inks, especially for magenta inks in color printing. The pigments of this ink are mineral red and rhoda yellow, and the two are mixed. Unless the color of the ink used for the two printings is the same, it is impossible to have the same color.
(3) Ink strength or pigment concentration
The problem often encountered in color printing is not whether the pigment contained in the ink is consistent, but whether the percentage of pigment content is consistent. The latter problem is that in order to obtain the same color saturation, an ink having a low pigment content requires a thicker ink film than a higher ink.
The detection of the pigment content, sometimes referred to as the "whitening" test, was carried out by mixing one part of the ink with 50 parts of the opaque white ink, and juxtaposing the squeegee sample with the standard white ink of the same ratio, and visually checking the difference in the intensity of the two inks. The red, green, and blue channel readings of the densitometer can be used to quantify this difference. The white opaque ink is continuously added to the darker ink that is being side-striped until the two inks are the same, so that a relatively quantitative description of the pigment concentration relationship between the two inks can be obtained.
(4) Ink adhesion
The degree of ink adhesion affects the adhesion of the ink and the problem of peeling off the paper. The adhesion of the two inks can be compared by means of a simple test. The inks of each of the two inks were applied to the plane, and the fingers were pressed on each of the ink samples to quickly lift the fingers. A disadvantage of this test method is that quantitative absolute adhesion cannot be obtained and only the relative value of the adhesion can be obtained. Of course, it is now possible to quantitatively measure the adhesion value under certain conditions using an electronic ink stick or other adhesive.
The quality of the raw materials has a very large impact on the final quality of the print. The quality of raw materials can be guaranteed by looking for manufacturers or distributors who can provide high-quality raw materials, or rejecting unqualified products by testing raw materials. Regarding the issue of raw material testing, despite the inconvenience of testing, large printers should realize that the investment in testing is much less than the resulting benefit. Small printers can also get significant benefits from testing, as long as they purchase small inspection equipment with low investment and use existing employees to conduct test operations.
As a management person of a company, when you intend to implement quality control of raw materials, you should first consider two aspects, and weigh whether the investment amount of the testing equipment is less than the income that can be brought about by this. Moreover, a detailed review of the quality issues and the causes of these problems should be summarized to better control the quality of the raw materials in the printing process.