White paper glue, paper body separation

Paper quality problems

Whiteboard paper is a kind of hard packaging paper, which is used for printing various kinds of goods, such as packaging cartons and goods, and is often used to print various kinds of lottery tickets and children's educational pictures.

There are two types of whiteboard paper, paper whiteboard and ordinary whiteboard. According to the bottom is divided into: gray and white two. The specifications of whiteboard paper include several types such as 220g/m2, 240g/m2, 250g/m2, 280g/m2, and 35Og/m2.

The base paper has a great influence on the production and quality of coated paper. Therefore, there are special requirements for the composition, strength, surface properties and absorbency of the base paper.

1 raw paper composition
The coated paper base paper generally contains about 70% hardwood pulp, and the remainder is softwood pulp. It is generally required that the original paper has high tensile strength and surface strength. In order to increase the strength of the base paper, in addition to improving the composition of the pulp, it is also sometimes possible to appropriately increase the degree of beating and surface sizing.

2 surface properties
The surface properties of coated paper base paper are relatively strict. The base paper must not be too rough or too smooth. Too rough raw paper can not meet the printing requirements even if the surface smoothness after coating is too smooth, and the effective binding area of ​​the coating and the base paper is small, and the bond strength between the coated layer and the paper surface is insufficient.

3 Absorption and uniformity
The attractiveness of the base paper must be moderate, the absorption is too large, and the powder dropping phenomenon is easy to occur after coating: the absorption is too poor. After coating, the base paper and the coating layer do not bond firmly. The homogeneity of the base paper is better to facilitate the uniform coating.

2. Coating performance control

1 Coating
Coated paper must first have two major characteristics: coating suitability and printability. Coating adaptability means that a uniform coating amount can be achieved at the time of coating. The printability of printing is the effect of smooth printing quality.

The coating has a wide range of concentration distribution and can be between 30% and 70%. In general, the higher the concentration, the greater the viscosity and the worse the fluidity, which will affect the uniformity of the coating.

2 coating amount
The amount of coating is increased within a certain range, which will make the paper have improved smoothness, good dot appearance effect, uniform ink absorption, good ink receiving performance, and easy to uniformly transfer ink to the coating surface, thereby achieving improved coating The purpose of printing paper adaptability.

3. Development of a new printing paper special printability improver
Combining the production process of coated paper, research and development of printability improver for coated paper is one of the important approaches in the field of printability improvement of coated paper in the future. For example, the “Printability Improvement Aid for Coated Papers” developed by the Hangzhou Chemical Research Institute has shown good results in use, resulting in a significant improvement in the printability of coated papers and a significant increase in the quality of coated paper products. Moreover, the product has a reasonable production process and low cost, meets the requirements of environmental protection, and has good economic benefits.

1. Pulp fiber ratio whiteboard paper is made from batter and each layer of bottom pulp. Therefore, the slurry is generally divided into batter (surface layer), second layer, three layers, and four layers. The ratio of fibers in each layer of slurry is different, and the ratio of fibers in each layer of slurry is different according to the quality of papermaking. Under normal circumstances, the basic principle of the ratio of white paper fiber is a layer: 100% domestic (or imported) bleached chemical pulp; Second: 100% mechanical pulp: three: 30% mechanical pulp, 50% of the book Tablets, 20% reported. Four layers: 1oo%~E paper. Under normal circumstances, the fiber ratio of the surface pulp is basically the same, while the second, third, and fourth layers of slurry are determined according to specific conditions, such as the source of raw materials, the quality requirements of papermaking, and so on. However, adjustments must be made only if quality requirements are met.

In addition to fibers, the surface layer of the whiteboard paper also includes a certain amount of fillers, compounds, and whiteners in the surface layer slurry, and an appropriate amount of fillers and compounds are also added to the fourth layer of slurry.

2. Whiteboard Features
Due to the relatively uniform fibrous tissue, the surface layer has filler and rubber composition, and the surface is evenly coated with a certain amount of coating, and it is calendered by multiple rollers, so the texture of the cardboard is more compact and the thickness is relatively uniform. The surface of whiteboard paper is generally uniform. All white and smooth, with a more uniform ink absorption, the surface of the powder off and hair loss is relatively small, the paper surface toughness and flexion resistance are better, but the white paper has a higher water content, a slight degree of flexibility . This will have a certain impact on printing.

Now compared with Japan and South Korea, home-made whiteboard papers have certain gaps in certain quality indicators, but there are still gaps, such as ink absorption and elasticity. White paper If the surface strength of the paper is not enough, the fibers do not bond tightly to each other. Soon after printing on the machine, many small paper scraps will appear on the blanket, affecting the quality of the printed product.

Solution: 1 white paper off powder, hair loss phenomenon, requiring off-work offset rub blanket; 2 printed before the first light agent, white ink to increase the paper's surface strength, until the print is dry and then color printing.

If the paper is not evenly packed, the amount of sizing is insufficient, and the phenomenon of two sheets of paper and a sticky blanket may also occur during printing. There are also serious problems with the quality of papermaking. The uniform coating of white paper on the surface and the looseness of the underlying paper often cause paper separation during the printing process. This type of poor quality whiteboard paper must be purchased and used blindly.

Printing pressure

After printing pressure, ambassador paper produces post-rolling force, which destroys the binding force of the internal fibers of the paper. When the paper is pressed after the printing is completed, the rapid reduction force of the blanket and the reducibility of the paper cause peeling of the paper (commonly known as two skins). ).

Solution: According to the quality and thickness of the white paper, according to the technical requirements of the equipment used, proper pressure adjustment should be carried out.

During the entire printing process, it is the process of resolving the contradiction between ink and paper. In order to transfer the graphic on the printing plate with ink to the printed paper, it must be applied during the graphic transfer process. The printing pressure.

People often say this: "Without pressure, there is no printing." This sentence fully demonstrates the role of printing pressure. In general, the printing pressure is based on the fact that the printed dot is strong, the graphic is clear, the color is bright, and the shade is appropriate. On the basis that the print is sufficiently strong, the uniform pressure is as small as possible.

When printing white board paper, the center distance between the plate cylinder and the blanket cylinder does not change, and only the center distance between the impression cylinder and the blanket cylinder needs to be adjusted. When printing 250-450g/m2 whiteboard paper, the center distance of the roller can be increased by 0.20-0.40mm. Specific approach: If printing 400 g/m2 whiteboard paper, the gap between the plate cylinder and the blanket cylinder is 3.95mm, the gap between the blanket cylinder and the impression cylinder is 3.40mm, the total liner of the printing plate ten liner is 1mm, the eraser The total lining of the drum is 3.15mm. If the paper is thick or thin, the reduced thickness is added to the blanket cylinder from the thickness removed from the plate liner. Otherwise, it is added to the plate cylinder. Ordinary whiteboard paper has poor surface smoothness and is relatively rough, and the tightness of paper is far less than that of coated paper. When printing ordinary whiteboard paper, it is also necessary to pay attention to the pressure of printing.

Ink viscosity is too large
After the paper receives the ink with high viscosity from the blanket, the ink on the paper surface is relatively resistant to the residual ink on the blanket when the pressure is applied, so that the peeling resistance between the surface and the bottom of the paper is unbalanced and the surface of the paper is torn. , face and bottom separate two skin phenomenon.

Solution:

1. To reduce the viscosity of the ink, add 2% of the detackifier to the ink used, or add No. 6 varnish to the ink. There are two roles. First, it plays a dilute effect in the ink; Second, it reduces the viscosity of the ink, increases the ink flowability, and improves the printability of the ink.

2. When printing on-site version of the product, try to use the original barrel ink, without adding the ink, add some detackification agent, anti-adhesive agent: do not add dry oil when the weather is hot. When printed products are often easy to appear back sticky, visco-rubber, paper separation problems, often using the method of dusting to solve. Although the printed anti-adhesive dirty dusting agent is a pure plant material, the dispersion and fluidity are good, but the use of dusting agent will affect the gloss of the printed product, make the ink color not bright, and pollute the environment, but also have an impact on the accuracy of the offset press .

3. Ordinary whiteboard paper surface roughness, loose texture, greater ink absorption, flatness is poor, therefore, full-print version should be printed on the ground background, dark color after printing, background color to be deeper, printed thin, ink color Should not be too large. If the smoothness of the white paper is good, then when printing on the ground, it is necessary to print the dark color first, and the amount of ink is printed on the foot so that the back surface will not be dirty, and then the background color will be overprinted, and the print finish will be compared. Good, at the same time, pay attention to the balance of ink and ink when offset printing, and control the size of the printing plate surface moisture.

4. When the weather is hot in summer, when the white paper is printed in monochrome, the paper suffers from uneven moisture content, uneven wrinkling, poor paper surface strength, etc., which causes hair loss and powder removal. At this time, the air can be printed first. , which can solve this kind of phenomenon.

Reprinted from: Fuzhou Government Printing Online