How to get good quality digital printing paper (below)

Inkjet printing paper problem

For paper manufacturers, the biggest problem in digital printing is mainly on color inkjet printers. With the decrease in the cost of color inkjet printers, its use in the home office market is also increasing. For the supply of such printer paper, it is not only required to meet the requirements of office laser printers, but also to be compatible with inkjet printers. This is a very complicated issue for paper manufacturers and paper applicators, so many additional parameters have become goals that must be achieved.

The ink used in the ink jet printer is liquid ink, which needs to be quickly fixed on the surface of the paper and separated from the ink tank. If the ink is absorbed too fast on the surface of the paper, the optical density of the color will be very low, and the phenomenon of overprinting will easily occur. If the ink cannot be absorbed quickly enough, it may flow on the plane of the paper, causing the colors to penetrate each other, creating rough edges and widening lines. The compromise in both cases is to change the paper's porosity and absorption properties. This is not an easy task for uncoated paper. It is especially difficult for coated paper.

This problem has become more complicated due to the variety of printers. In general, we can divide inkjet printers into three categories:

× Piezoelectric (The ink is contained in a cavity made of piezoelectric material. When electric current passes through the piezoelectric cavity, it deforms, discharging ink droplets).

x Inkjet (using a pigment or dye system released after heating)

Phase change or hot melt type of heated inkjet system

All these printers have different paper requirements. For paper manufacturers and coating manufacturers, it is very demanding to be able to use laser printers.

Inkjet printer printing performance issues

When an inkjet printer lands ink on the surface of a sheet of paper, the area occupied by the dots of ink may change, resulting in halftone dots or solid colors, lines or letters. The most basic colors, cyan, magenta, and yellow, can be used in combination to form intermediate tones like traditional printing processes. From the paper manufacturer's point of view, the low viscosity and low surface energy characteristics of such inks can cause problems. For inkjet printers, these two characteristics are the necessary conditions for the ink to reach the surface of the paper through the nozzle. Unfortunately, this means that the ink has a higher surface activity, which makes it easier to penetrate the paper, resulting in a loss of optical density and even causing backside printing.

On non-coated paper, backside offset can be improved by adding internal sizing, making the surface structure of the paper denser, and surface sizing. By relatively adjusting the hydrophobic properties of the surface and interior of the paper, it is possible to guarantee the printing performance of the ink. It is also possible to develop fibers that have the natural tendency to absorb liquid substances in liquid inks, leaving the dyes on the surface of the paper, thereby exhibiting a strong color effect and securing the ink's fixability. However, when the ink is fixed on the surface of the paper, lateral and vertical diffusion occurs. This will cause the colors to infiltrate each other and produce a feeling of roughness, and if the print is a line, the phenomenon of line expansion will also occur. The main reason for this is that while the pigment particles in the ink are fixed, the binder in the ink is also absorbed into the paper fibers, thereby causing the ink to spread in the paper.

The problem of fast fixation and separation of the dye from the ink vehicle is a key issue in understanding the printing performance parameters that affect the inkjet printer. On the surface of the coated paper, the method of fixing the ink on the fiber by absorption cannot be used, and generally the particles of the coating do not have high adsorptive power for the dye and the particles in the ink-jet printing ink. All the ink must be fixed on a silicate desiccant, or the colorant in the dye must be fixed on the coating with sufficient adsorption capacity, and the dye and pigment can be rapidly separated from the liquid.

Printing spots are a frequent problem for inkjet proofs. The appearance of stains also indicates changes in the optical density of the color in the field, and this phenomenon is most easily seen in the solid black or blue area of ​​the coated paper. Stain can be described with two parameters (perimeter ratio (SP), or difference system (CV)). These two parameters can be considered as the cause of the appearance of a stain.

Spots are generally caused by changes in fiber density in the paper base. In general, the size and shape of the flocculent material in the paper base can correspond to SP and CV values. The process of coating and calendering further complicates this problem, but the production of the paper itself and the printing process are decisive factors.

If the smoothness and gloss of the surface are to be increased by the calendering process, the paper making and compression properties will be further complicated in the printing process. Variations in coating thickness and inherent compressibility of the paper due to the printing process and internal floc structure can cause changes in the density and absorbency properties of the coating structure.

Occasionally, some fine granular stains are also seen. This is generally due to the granular nature of the coating and the ink itself. If some large particles appear in the coating layer, the ink layer will be uneven when the ink is dry. These small spots may be present at the same time as large spots appear due to paper manufacturing problems.

The current situation of digital paper

As far as the current situation is concerned, the performance of traditional paper still needs to be improved before it can adapt to the new needs of the market. The emergence of digital printing also has new demands on the properties of coated paper. Although there are some problems with the print quality of dry powder type digital printers and liquid toner type digital printers, the biggest problem for paper makers is the production of paper compatible with inkjet printing. At present, the traditional paper absorbability in the longitudinal direction, expandability to the periphery, and the fixation of the dye have greatly improved, and can ensure good color reproduction, clear edges, and no backside printing phenomenon.

The problem of stains on paper also takes some time to resolve. Although the granularity of the coating layer itself can be processed more finely, the appearance of fine stains can be improved, but the quality of the paper itself is the key to reducing the stain. The costs now appearing are low, and coated papers can run well in inkjet printers and toner-printing systems. Although problems may still arise, they can already be applied.