Quality Control of Raw Materials in Printing Process (Chinese)

2, chemical properties and quality requirements

(1) pH (pH): The pH of the paper should be 7.0, which is neutral, otherwise it will affect the drying time and make the back sticky.

(2) Temperature and Relative Humidity: The relative humidity (RH) and temperature of the paper should be consistent with the temperature and humidity of the workshop. The temperature and humidity differences between the workshop and the paper can cause problems such as overprinting and wrinkling.

(3) Drying time: The performance of the ink must be taken into account when it is dry. It must not be dried on the printing roller, but must be quickly fixed on the paper.

3, physical properties and quality requirements

(1) Dust off and hair loss: Flocking can lead to defects in the traces or graphic parts of the non-graphic part. Sheets must be free from falling powder on paper.

(2) Paper Strength: Paper with low surface strength When high-viscosity inks are used, the paper surface will be napped and even cracked, which requires the surface strength of the paper to be high.

(3) Length of ink: If the ink is too short, a pile of paper will be produced. If the ink is too long, ink mist will splash and the image quality will be affected.

(III) Stable and consistent quality

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.