Digital Printing Paper Features and Development (1)

At present, digital printing technology has gradually been integrated into the printing industry. Due to the fundamentals of digital printing technology and the need for traditional printing and editing, there are new requirements for paper as a printing substrate.

This article will focus on the requirements of digital printing technology for paper based on digital printing imaging principles.

Digital printing paper special:

1. The status of digital printing paper

In recent years, digital information technology has received unprecedented attention, and new paper types serving digital information technology are emerging. The paper size of Digital Seal C paper is usually 21.59cmX 27.94cm to 35.56cmX 50:8em, suitable for various new high-speed digital printers.

The digital printing format specification originated from the office A4 sheet-fed color copying market, and is limited by the digital image formation mechanism, such as the laser imaging range and the arrangement of light-emitting diodes. In addition, many digital printing machines are installed in express printing shops or offices. There is no complicated automatic feeder unit, and there is a limit to the width and weight of the paper roll. With the advent of A3+ format sheets and 500mm web digital presses, B2 size papers have been used. At present, the new type of digital printing coated paper that has been developed worldwide has the following major categories:

(1) Coated paper for electronic imaging printing - gloss full chemical pulp coated paper.
(2) Commercial Digital Printing Machines. (Liquid coloring agent) Coated paper for printing + - gloss coated paper with chemical pulp.
(3) Coated papers used for inkjet printers - various ink jet printing papers.

Although digital printing paper currently accounts for only a small share of the paper market (about 30,000 tons, 2%), several major paper manufacturers place great importance on this market. In addition, some large-scale digital press manufacturers, such as Xeikon and HP IndIigo, have established a set of inspection procedures. Through corresponding experiments, a set of operating parameters for digital printing of paper or other special printing media is drawn, and lists suitable for them. The digital press paper product directory.

Another market survey showed that 40% of the respondents think that they should consider the impact of digital printing paper when choosing a digital printing system. Although many digital printer manufacturers are working to produce equipment that does not require the use of special paper, The current choice of digital printing paper is still a major problem, and paper manufacturers must accept the challenge of producing digital printing paper.

2. New requirements for digital printing paper

People may think that digital printing is non-contact printing without the substrate, and the pigment particles or ink droplets will be accurately distributed to form images; in fact, the technical requirements for digital printing on paper are still very complicated.

(1) High smoothness,

Smoothness is a key factor in achieving high-resolution printing results, and a smooth and smooth printing surface can exhibit fine dot changes. For a frictionless paper conveying system, the vacuum system is generally used to assist the feeding of paper, and the paper is also required to be as smooth as possible and less porous. Of course, a surface that is too smooth can also cause the paper to slip, causing problems for feeding the paper.

(2) Proper conductivity

Balanced, controlled conductivity in a certain range can avoid the occurrence of artifacts such as stencils, brush spots, and maintain good color stability and good adhesion of pigments. In order to avoid paper electrification, it is required that the paper has a good conductivity, because most of the digital printing is electrostatic printing, which will cause the paper to be charged, and have a certain conductivity to guide away the charge, to avoid mutual adsorption of printed sheets, and to convey the paper afterwards. Bring problems.

(3) Orientation of fibers

For paper transport, the orientation of the fibers in the paper is quite important + the orientation of the fibers in the paper must be compatible with the chosen paper basis, and the direction of alignment of the paper fibers must be the same as that of the printing press.

(4) Coated paper

The surface properties of paper have a decisive influence on the transfer and fixation of toner to the paper surface. The relative sealing of the surface of the calendered and coated paper is a prerequisite for optimal image reproduction; in the electrostatic dry toner image, some key components of the paper will be removed from the coating due to the effect of toner fixing. Break away from the surface of the paper and affect the integrity of printed graphics; for this phenomenon, paper manufacturers have developed a special rhyme to improve the heat resistance of the paper.

At present, internationally, there are relatively many types of coated paper used for digital printing, and new requirements are also put forward for digital printing coated paper: 1 The surface of the paper is white or white; 2 The paper is crisp, clean and opaque; 3 paper bright wife, high strength and gloss; 4 paper high anti-bubbling: 5 using the pressure metering method for micro-coating; 6 paper can be printed on both sides.

(5) Non-coated paper

The surface is rough and has irregular pores. If the paper is printed with electrostatic dry powder imaging mechanism (mostly without wood pulp paper), the text and lines are also falsified. The density in the field does not meet the requirements, and the image clarity is not high. The solution is to use liquid ink as much as possible. The liquid ink can adhere to the surface of the paper and does not fall into the capillary pores of the paper as the solid toner does. However, the ink film formed by the liquid ink has poor adsorption capacity and the formed image ink layer has low fixation fastness. In order to solve this problem, a layer of rubber can be coated on the surface of the paper.

(6) Paper moisture content

Digital printing paper is very sensitive to the environment. In the electrostatic dry powder imaging Wei, toner fixing needs to be heated to 1 20 - 1 50 °C while the paper to lose moisture, under normal circumstances the relative humidity of the paper from about 50%, reduced to 15% to 20%. Due to the loss of moisture, the paper becomes brittle, flounces, and breaks or tears easily during folding. In order to solve this problem, a paper with a relative humidity of 30:6 must be prepared for the printing system or the paper should be fed under air conditioning.

(?) Production process requirements

The production of digital printing paper is generally done by mixing bleached broad-leaf wood-kraft pulp with bleached broad-leaf wood Kraft wood pulp. The resulting paper has good strength, opacity, bulk, stiffness and whiteness. Degree, and uniform organization, the surface of the paper is smooth and clean, there is no fiber spot and dust, no lint, powder, good optical properties and printing performance. In the manufacturing process, it is generally necessary to add certain fillers, such as precipitated calcium carbonate.

Digital printing paper adopts neutral papermaking and neutral sizing technology, and correspondingly uses a variety of chemical additives. For non-coated inkjet printing paper, a reasonable choice of sizing agent can achieve different results. Retention aids are another common auxiliant in the production of digital printing paper, but the amount is not suitable, often affect the formation of the paper. For papermaking with recycled fiber pulp, starch or synthetic resin enhancers may be used to increase the strength of the paper to compensate for insufficient fiber strength.

Digital printing papers are mostly small-size papers, and require high fiber bonding strength, cleanliness, and both sides of the paper surface. The paper machine should use advanced top web formers to minimize the two sides of the paper. Soft calendering should also be used to obtain good smoothness. In order to prevent the paper surface from falling hair and entraining burrs, debris, paper scraps, requires a sharp edge of the paper blade.