Although digital printing currently has almost no restrictions on printing materials, if you do not consider the adaptability of printing materials and digital printing management systems, there will often be printing results that you do not want to see, and you will not get a perfect product. Now the printing material in commercial printing is ranked first in paper, so the following is how we should try to make the printing material (paper) and the printing system suitable for some analysis in the application of digital printing equipment.
1. Paper transport characteristics
Paper is a relatively active raw material, and it is sensitive to many external conditions. Whether it is glossy, matte or small in weight, it is sensitive to humidity, temperature, and the mechanical effects it undergoes during processing. . The paper in electrostatic imaging digital printing is affected by all the above factors and more. The good operation of the digital printing process must first consider the characteristics of paper transport and the printability of the paper. Paper transport is affected by the following factors:
Paper hardness and thickness; curling degree; capillary pore characteristics; fiber interweaving structure; conductivity; moisture content, etc.
The frictionless paper conveying system generally depends on the vacuum system to assist, which requires the paper to be as smooth as possible and few pinholes. Of course, a too smooth surface will also cause the paper to slip and cause problems for paper feeding. In order to avoid electrification of the paper, the paper must have good conductivity, because most digital printing is electrostatic printing, which will cause the paper to be charged, and the electric charge must be conducted away, otherwise the printed paper will attract each other and give the post process Paper transport causes problems. Paper with a grammage over 100 will not cause problems for conveyance if it has sufficient stiffness. The paper fiber arrangement direction is also very important for paper transportation. The paper fiber arrangement direction must be compatible with the selected paper grammage. When the grammage is less than 200, the paper fiber arrangement direction is consistent with the printing machine's running direction (Broadband roll paper), when the grammage exceeds 200, the paper fiber direction is perpendicular to the machine running direction (narrow band roll paper). Broadband web refers to the width of the tape when the printed web is cut to a single sheet size; the narrow side is the opposite, and the short side is the width of the tape. The roll paper must be stored at least under the environmental conditions of the printing workshop (the temperature and humidity are the same as the workshop) before being put on the machine! (Hours, the packaging paper on the roll can only be removed before the printing starts, and the roll paper cannot be rolled vertically. It cannot be stored upright.
2. Printability of paper
The surface properties of the paper determine its printing characteristics and have a decisive influence on the toner transport and fixation to the surface of the paper. The factors that affect the printability of paper are:
Relative humidity of paper; thermal sensitivity; conductivity; permeability; chemical properties; tightness and thickness; fiber structure; surface strength; gloss; roughness, etc.
Calendering (smoothed to make it smooth) and the coated paper surface are relatively closed, which is the best prerequisite for the image to be reproduced. In electrostatic dry powder imaging, due to the effect of toner fixation and heating, some key components in the paper are detached from the coating. This will disintegrate the surface of the paper and cause problems for the integrity of printed graphics. In response to this phenomenon, paper production companies have developed a special coating process, the paper produced through this coating process has heat resistance. Uncoated natural paper, the surface is rough with irregular deep holes, printing this paper with electrostatic dry powder imaging mechanism (mostly wood pulp-free paper), the edges of the text and lines will have whiskers, The density on the ground is not up to the standard, the image definition is not high, etc. The quality of the products reproduced by this paper and this process will decline. The solution can use liquid ink, which can penetrate the surface of the paper and will not fall into the capillary pores of the paper like solid toner and disappear. However, the ink film formed by liquid ink has poor adsorption capacity, and the formed image ink layer has poor adhesion. To solve this problem, a layer of glue can be applied to the surface of the paper.
3. The impact of printing on paper
In traditional offset printing, fountain solution is used, and the paper absorbs water from it. In electrostatic dry powder digital printing, the toner fixation needs to be heated to 120 degrees to 150 degrees, and the paper must lose moisture. Normally, the relative humidity of the paper is about 50%, and the relative humidity of the paper after heating by digital printing is only 15% to 20%. Due to the loss of moisture, the paper will become brittle, with ruffled edges, which can easily break or tear when folded. In order to solve this problem, people prepared paper with a relative humidity of 30% for the digital printing system or moved the paper under the condition of air conditioning. Paper with no dense fiber interweaving structure and coated with sensitive elastic coating without wood pulp has a higher folding endurance than wood pulp, so this is the best choice for digital printing that requires heated toner paper.
Zhejiang Shengfa Textiles Printing&Dyeing.,ltd , https://www.chzjsf.com