Technology and Printing Suitability of Coated Whiteboard II

3 Classification and Technical Specifications of Coated Whiteboard

The classification of coated whiteboard varies from country to country. At present, there are two types of single-coated white cardboard and double-sided coated white paperboard in China. The rations of single-side coated gray paperboard are 200, 220, 250, 270, 300, 350, 400, 450g/m2; the quantification of double-coated white paperboard is 200, 220, 250, 270, 300, 350, 400g/m2. Coated white paperboard is generally based on flat paper, the size of 787mm × 1092mm, 880mm × 1230mm. There are also reeled white paperboards. The technical specifications of single-side coated gray cardboard can be referred to the QBl011-91 standard, and the technical specifications of double-sided coated white cardboard can refer to the ZBY32024-90 standard.

4 Printability of coated white paperboard

The printability of coated white paperboard refers to the requirements for the paper to meet the requirements of ink, printing plates, and printing conditions to ensure the smooth operation of the print job and obtain the necessary conditions for high-quality prints. The printability of the coated white paperboard is not a certain fixed property, but is compatible with different printing conditions and different print product characteristics, including two aspects of print job suitability and print quality suitability. The former refers to various properties that the paper can successfully meet for the necessary operations on the printing press, such as the smoothness of the paper; the latter refers to the properties of the paper that play a decisive role in the quality of the print, such as whiteness, gloss, thickness, surface strength, Smoothness, ink absorption, etc. The following is a brief analysis of the main properties of coated white paperboard related to print quality suitability.

4.1 Whiteness

The whiteness of paperboard refers to the ability of the paperboard to fully reflect after being illuminated by light, that is, the ratio of reflected light to incident light under certain test conditions. The whiteness of cardboard is one of the important indicators of coated white paperboard. High whiteness paperboard can enhance the contrast between ink and paperboard, and help to distinguish the graphic and text. Printing a color picture on a cardboard with high whiteness can make the picture bright and beautiful.

4.2 Gloss

Cardboard gloss indicates the brightness of the cardboard surface, and the gloss of the cardboard is closely related to printing. The high-gloss paperboard can make the color of the print bright, but the paperboard with too strong gloss will cause the carton print to produce glare, which is not conducive to its display effect. The board is sometimes coated with varnish after printing to increase gloss and protect the ink layer from damage.

4.3 Thickness

Thickness refers to the thickness of the paper. From the printing point of view, the thickness of each batch of cardboard is generally required to be uniform. If the thickness of the cardboard is not uniform, the printing pressure will be unstable during the printing process, and it will suddenly change. So that the printing ink transfer situation changes, imprinting also different shades, affecting the quality of printed matter.

4.4 Surface Strength

The surface strength of coated white paperboard refers to the degree of bonding between fibers, fibers and fillers, and rubber. The stronger the binding force, the higher the paper surface strength, and vice versa. In the printing, the surface strength of the paper surface is often measured by the degree of hair loss, powder removal, and peeling. In the printing process, about half of the ink on the printing plate or the blanket is transferred to the paper each time the printing is performed. That is, the ink layer is separated during printing, and part of the ink is transferred to the paper, and part of the ink remains. On the surface of the plate or blanket. The viscosity of the ink is a force that will prevent the separation of the ink layer, so that the separation sometimes does not occur on the ink film, but occurs at the weakest point where the paperboard fibers, fillers, and glue stick. As the viscosity of the printing ink increases with the increase of the printing speed, the surface of the paper printed on the high-speed printing machine (8000 sheets/hour or more) is subject to a large pulling force. If the bonding force between the surface structure of the cardboard is not sufficient to resist the tension generated when the ink film is separated, fluffing, dusting, or even the peeling of a small piece of paper (called peeling) may occur during printing.

In the reproduction of prints, printing is done in a very short time (instantaneous), and there is a complex mechanical interaction between paper and ink. As the speed of printing presses increases, the effect of peel tension increases. To make the ink transfer to the surface of the paper correctly without destroying the paper surface structure, the surface strength (bonding force) of the paper must satisfy the following formula:

T≥W+Q+N

T-fiber filler and binding force

W-ink adhesion to paper

Q-peel tension

N-print plate attractive for ink

The fibers on the surface of the paper are individually pulled off and called as lint-free fibers. If these fibers are stuck on the surface of the printing plate or blanket, the next few sheets will have defects. When severe hair loss occurs, the paper hair will move against the direction of ink transfer, mix with the ink, and fill in gaps between the printing plate's internet point or lines to cause a paste plate. Mild stencils affect the quality of the printed matter and cause the sharpness of the graphic and text to decline. Severe stencils can cause the plate to be scrapped and the printing job cannot be carried out. During the printing process, due to the poor surface strength of the paperboard, sometimes a small area of ​​surface fiber stripping occurs on the surface of the paperboard. After the peeling, the shredded fragments stick to the printing plate or blanket, and after several times of embossing, they may adhere firmly. On printing plates or blankets, this part of the printing will be higher than the other parts of the printing plate or blanket, and the printed text will show a dot of ink in the corresponding part, and the surrounding area is not printed. White ring of ink - ring white spot. This will have a direct impact on the quality of the product, and even if it is severe, it will make production impossible. (to be continued)