Quality Control of Raw Materials in the Printing Process

C) Quality and consistency

The key to evaluating raw materials is to consider how much the raw material properties can change within the limits of the print quality. It is also necessary to consider that this variation range should not affect the printing speed or cause other problems in the production process.

The properties of the raw materials described above require further testing. If one can specify a specific request value and be able to determine the control range of the data, then the ink or paper properties can be measured and controlled. However, it is difficult to determine the control range.

The final test method for the raw materials in the printing process is used under actual printing production conditions. However, this method is only suitable for large-scale paper mills or ink factories, and most print shops cannot afford such tests. Most laboratory tests more or less lack the ability to predict the actual printing production conditions.

Second, the detection of raw materials

The standard testing methods for raw materials in the printing industry mostly focus on the testing of paper inks. The International Institute of Printing Research literature workers have compiled the printing standards for fifteen countries and two organizations. The publication lists 88 standards or specifications for paper and other printing materials promulgated in Germany and 66 standards for inks and other related materials promulgated in Poland. Some standards are about adhesives and other bookbinding materials, and about photographic materials. But in general, the printing industry pays less attention to materials other than ink and paper.

A large number of detection methods, testing instruments, and inspection images can be evaluated by the printing factory for raw materials, which means that almost all paper or ink properties can be detected to comply with the established standards. The key question now is what testing methods should be used and how much testing should be done on various occasions.

When testing paper or other substrates, it is difficult to obtain a representative sample. It is very difficult for a stack of papers, especially large ones, to randomly sample from them without re-stacking them. For webs, the detection is not possible except for the (less representative) outer layer.

In general, the sampling of ink and photosensitive materials is not a problem. Another problem that should be considered when sampling raw materials is that some detection methods are destructive. Such as paper, cardboard strength testing, photosensitive material sensitivity testing, its samples will be damaged and consumed.

For the selection of a test method for a material, consideration should be given to the use of tests that can obtain data relating to defects in printed images or obstacles to print production.

The frequency of detection of a certain property must be based on the tolerance for the performance change, which in turn is related to the level of quality defects allowed by the final print. The more stringent the quality requirements of printed products, the more frequently the raw materials need to be inspected.

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. (to be continued)