The printing industry's standard testing methods for raw materials mostly focus on the testing of paper ink. The writers of the International Association of Printing Institutes have compiled the printing standards of fifteen countries and two organizations. This publication lists 88 standards or specifications issued by Germany on paper and other printing materials, and 66 standards issued by Poland on inks and other related materials. Some standards are about adhesives and other book binding materials, and some are about photosensitive materials. But in general, the printing industry does not pay enough attention to materials other than ink and paper.
A large number of testing methods, testing instruments, and testing images can be evaluated by printing houses for raw materials, which means that almost all properties of paper or ink can be tested to comply with the set standards. The key question now is what testing methods should be used and how many tests should be done in various situations.
When testing paper or other substrates, it is difficult to obtain a representative sample. For a stack of paper, especially large-sized papers, it is very difficult to take samples from them randomly without re-stacking them at all. For the roll paper, except for the (less representative) outer layer, nothing can be detected.
In general, the sampling of ink and photosensitive materials is not a big problem. In the sampling of raw material testing, there is another issue that should be considered is that some testing methods are destructive. Such as the strength test of paper and cardboard, and the sensitivity test of photosensitive materials, their samples will be damaged and consumed.
To select a test method for a certain material, consideration should be given to tests that can obtain data related to print image defects or print production barriers.
The frequency of testing a certain performance must be based on the tolerance of the performance change, and this tolerance is related to the quality defect level allowed by the final printed product. The more demanding the quality of the print, the more frequent the inspection of raw materials.
For most printing companies, they cannot spend as much time, money, material resources, and manpower on testing raw materials as government departments or very large printing companies. The benefits of testing may not be sufficient to cover the costs 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 invest appropriately and do those tests with high economic benefits.
The following are tests to control the factors that affect color reproduction:
1. Paper detection
Some tests can be implemented with extremely simple equipment.
(1) Thickness
To maintain the correct printing pressure on the printer, use a tube diameter gauge. The thickness of the paper should also be measured with a micrometer. Generally, ten sheets of paper are used to measure five points.
(2) Opacity
Opacity visual scale is an effective measurement tool. Print a group of characters on the background of darkening dots, cover the paper to be tested, and the characters can no longer be seen somewhere on the scale.
(3) Absorbability
K & N ink is probably the most commonly used and cheapest test method. The ink is composed of gray dye and oil base. Apply it to the paper pattern and wipe it off after two minutes. The remaining gray density is the absorbency of the paper.
(4) Glossiness
Measure along the paper grain direction with a gloss meter and take the average value.
(5) Paper efficiency
This test combines the gloss and absorbency of the paper to measure the effect of the printing material 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 extremely poor colors.
(6) Color and brightness
The approximate characteristics of the color and brightness of the paper can be obtained by measuring the density through the red, green, and blue color filters after calibration with a reflection densitometer. In an ideal paper, the density under each color filter should be the same, and the density value is low, indicating high brightness. Paper sample specimen visual comparison method is more meaningful for the detection of paper color and brightness.
(7) Skinning
Despite the shortcomings of the Denison wax stick peeling test, it is still a suitable method to determine the peeling resistance of a specific printing material. Melt the end of a certain wax stick and press it against the substrate to be tested. After fifteen minutes, quickly pull it up and check the removed fiber or paint on the end surface.
As with the testing of many other raw materials, the wax rod test has a greater comparative significance than predicted significance. In other words, if peeling does not occur, there is no peeling problem when printing on paper with a peeling resistance higher than 10 under the same conditions. [next]
2. Detection of ink
The first step in evaluating 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 piece of paper. There is often a solid ink bar in the middle of the scraped paper.
(1) Opacity
Some inks, such as yellow ink, are not as transparent as others. In color printing or overprinting, you must know this property. If the ink printed last is not transparent enough, the color after overprinting will be biased towards the ink color printed last. The opacity can be obtained by checking the ink color on the ink bar of the scraped sample.
(2) Color
Parallel scratching can be used to compare the colors of various color inks, especially for magenta inks in color printing. This ink has mineral red and rhodamine yellow, and a mixture of the two. Unless the color of the ink used in the two printings is the same, otherwise the colors cannot be the same.
(3) Ink color intensity 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 achieve the same color saturation, inks with low pigment content require thicker ink films than inks with high content.
The detection of the pigment content is sometimes referred to as the "whitening" test. One part of the ink is mixed with 50 parts of opaque white ink, and a standard ink with the same ratio of whitening is used as a parallel ink scraping sample. The readings of the red, green, and blue channels of the densitometer can be used to quantify this difference. Continue to add white opaque ink to the darker inks of the parallel scraping samples until the two ink scraping samples are consistent, so that a relative quantitative description of the pigment concentration relationship between the two inks can be obtained.
(4) Ink adhesion
Ink adhesion affects ink adhesion and paper peeling issues. A simple test can be used to compare the adhesion of the two inks. Take two ink samples of the two inks and apply them on a flat surface. Press the index fingers of both hands on the ink samples and quickly lift the fingers. The disadvantage of this test method is that it cannot obtain a quantitative absolute adhesion, only the relative value of adhesion. Of course, it is now possible to quantitatively measure the adhesion value under certain conditions with an electronic ink adhesion meter or other adhesion meters.
The quality of raw materials has a great influence on the final quality of printed matter.
The quality of raw materials can be guaranteed by looking for manufacturers or distributors who can provide high-quality raw materials, or by rejecting unqualified products by inspecting the raw material goods that have arrived. Regarding the testing of raw materials, despite the many inconveniences of testing, large printing plants should realize that the investment in testing is still much less than the resulting benefits. Small-scale printing plants can also obtain obvious benefits from testing, as long as they purchase small-scale testing equipment with low investment and use existing staff to conduct testing operations.
As a manager of an enterprise, when you plan to implement quality control of raw materials, you should first make two considerations, and weigh whether the investment in testing equipment is less than the benefits that can be brought about by it. Moreover, the quality problems and the causes of these problems should be summarized and analyzed in detail, so as to better control the quality of the raw materials in the printing process.
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