Quality Control of Raw Materials in the Printing Process (Part 2)

Third, detection

For most printing companies, it is impossible to spend as much time, money, material resources, and manpower on detecting raw materials as government departments or extra-large printing companies. The benefits of testing may not be enough to cover the cost of testing. However, this situation refers to a large-scale inspection, but in fact most printing companies can conduct small-scale inspections. All printing companies can properly invest in those tests that are cost-effective.

The following are the tests that control the factors affecting color reproduction:

1, paper detection

Some tests can be implemented with very simple devices.

(1) Thickness: In order to maintain the correct printing pressure on the printer, use a caliper gauge. The thickness of the paper should also be measured with a micrometer. Usually ten sheets of paper are used to measure five points.

(2) Opacity: Opacity The visual scale is an effective measurement tool. A set of characters is printed on a darkened background dot background, the paper under test is covered on it, and the character begins to look unclear somewhere on the scale, which indicates the opacity of the paper.

(3) Absorption: K&N ink is probably the most commonly used and cheapest test method. The ink is composed of a gray dye and an oil base, which is applied to a paper sample and is removed after two minutes. The remaining ash density is the absorbency of the paper.

(4) Gloss: Gloss meter was used to measure the direction of the paper and the average was taken.

(5) Paper Efficiency: This test combines the glossiness and absorbency of the paper to measure the effect of the print material on the ink film color. Absorptive but 100% gloss paper can print the most saturated colors. In contrast, 100% of absorptive 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 densities of red, green, and blue color filters after the calibration using a reflection densitometer. Ideal paper, the density under each filter should be consistent, low density, indicating high lightness. The visual comparison method of paper samples is more meaningful for the detection of paper color and lightness.

(7) Skin Peel: Despite its drawbacks, the Dennisson wax stick peel test is still a suitable method for determining the peeling resistance of a specific substrate. The end of a certain grade of wax stick is melted and pressed against the substrate under test. After fifteen minutes, it is quickly pulled up and the exposed fiber or paint is inspected on the end face.

As with many other raw material tests, the relative significance of the wax stick test is greater than predictive. In other words, if the peeling does not occur, then when the paper whose peel strength is higher than 10 is printed under the same conditions, there will be no problem of peeling.

2, ink detection

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 knife, or a thicker ink layer can be rolled out with a small ink roller. When comparing two inks, it is generally required to scrape two ink samples on the same piece of paper in parallel. There is often an on-site ink bar in the middle of the squeegee.

(1) Opacity: Some inks, such as yellow ink, are not as transparent as other inks. In the case of color printing or overprinting, one must be aware of this property. If the last ink printed is not sufficiently transparent, the overprinted color will shift toward the last printed ink. The opacity can be determined by checking the ink color on the ink bars of the squeegee.

(2) Color: Side-by-side scraping can be used to compare the colors of various color inks, especially for the magenta inks in color printing. The pigments of this ink are mineral red and Rhodamine, and both. mixed. Unless the color of the ink used for the two printings is the same, it is not possible to have a uniform color.

The ink color can be quantitatively expressed using the Preucil ink formula, ie:

In the formula, L, M, and H respectively represent the lowest reading, intermediate reading, and highest reading measured by red, green, and blue color filters using a reflection densitometer. The hue gray value can be marked on the GATF round or triangle chromaticity diagram. The advantage of triangular chromaticity maps is that it is easy to derive the performance range of a group of color inks. By connecting straight lines between the three ink color coordinate points, a triangular region is formed. This region represents two dimensions of the three-dimensional color space, and the edge is the performance limit of the group of color inks.

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

The detection of the pigment content, sometimes referred to as the "whitening" test, involves mixing 1 part of the ink with 50 parts of the opaque white ink, and juxtaposing the ink with the same proportion of the standard ink against the white, and visually checking the difference between the two ink strengths. Densitometer red, green and blue channel readings can be used to quantify this difference. The addition of the white opaque ink continues in the darker ink that is scraped side-by-side until the two inks are the same, thus giving a relative quantitative description of the pigment concentration relationship between the two inks.

(4) Ink adhesion: The ink adhesion affects the adhesion of the ink and the problem of peeling the paper. The adhesion of the two inks can be compared with a simple test. The two inks are each coated with a bit of ink and applied to the plane. Each of the two inks is pressed against each ink sample and the fingers are quickly lifted. The disadvantage of this test method is that a quantitative absolute adhesiveness cannot be obtained and only the relative value of the adhesiveness can be obtained. Of course, the adhesion value can now be quantitatively measured under certain conditions using an electronic ink sticker or other adhesives.

The quality of raw materials has a great influence on the final quality of prints. The quality of raw materials can be guaranteed by looking for manufacturers or sellers who can provide high-quality raw materials, or rejecting unqualified products by testing incoming raw materials. With regard to the detection of raw materials, in spite of the inconvenience of testing, large-scale printers should realize that the investment in testing is still much less than the benefits. Small printing companies can also obtain significant benefits from inspections, as long as they purchase small-scale test equipment with low investment and use existing employees to perform test operations.

As a company's manager, when you intend to implement quality control of raw materials, you should first consider two aspects, weigh whether the amount of investment in testing equipment is less than the benefits that can be brought about. Furthermore, it is necessary to exhaustively analyze and analyze the quality problems and the causes of these problems, so as to better control the quality of the raw materials in the printing process.


Author: Yu Yong