Methods for testing the performance of paper and ink

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) Absorption: 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 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 glossiness and absorbency of paper, and can 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 lightness: The approximate characteristics of paper color and lightness can be obtained by measuring the density through 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) Peeling: Dennyson wax stick peeling test, despite its shortcomings, is still a suitable method for determining 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.

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 other inks. 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 ink in color printing. This ink has mineral red and rhodamine yellow, and both mixed. Unless the color of the ink used in the two printings is the same, otherwise the colors cannot be the same.

The ink color can be given a certain quantitative expression with Preucil ink color formula, namely:

In the formula, L, M and H represent the lowest reading, middle reading and highest reading measured by the reflection densitometer through the red, green and blue filters. The gray value of the hue can be marked on the circular or triangular chromaticity diagram of GATF. The advantage of the triangular chromaticity diagram is that it is easy to derive the performance range of a certain set of color inks. A straight line is formed between the three ink color coordinate points, which forms a triangle area, which represents the two dimensions of the three-dimensional color space, and its side is the limit of the performance domain of the group of color inks.

(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. 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.

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