Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

1、 Causes of water absorption and expansion of paper

       In the performance of paper, there is an index of expansion rate, which is expressed as the percentage of size increment to original size. It indicates the relative change of paper format after wetting and drying. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

      Newsprint fiber is thicker, the density is small, the surface sizing amount is small, and the water absorption elongation is greater than that of coated paper and offset paper. It has a great impact on the overprint accuracy when printing color newspaper.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       The offset printing process commonly used in color newspaper printing is to apply fountain solution on the plate first, and then add ink for printing. The main component of fountain solution is water, which will be transferred from printing plate to blanket and then to paper through pressure. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       There must be expansion and contraction of paper due to water absorption and drying in the printing process.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       The expansion and contraction of paper is closely related to the performance of paper. The better the paper performance, the smaller the water absorption, the better the dimensional stability after water absorption, Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

      and the smaller the expansion rate, which is very beneficial to color newspaper printing.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

        Among the various performance indexes of paper, sizing degree, surface strength, moisture content, tightness, smoothness, duality and moisture content all have a certain impact on the expansion and contraction of paper. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

      From the perspective of newsprint of different brands such as Jilin, Nanping, Guangzhou, Hansong and offen, which are widely used at present, the expansion rate is very different.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

2、 Influence of paper stretching on registration accuracy

        The water absorption and expansion of paper has a great influence on the registration accuracy of color newspaper. In the case of prepress and plate making, Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

      The water absorption and expansion of paper can not be well solved, which will not guarantee the overprint accuracy. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       Inaccurate overprint will greatly affect the sensory quality of color newspaper. Even if the ink, dot, color, paper and other raw materials are better, the overall sensory effect will be greatly reduced.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

      Influence Of Water Absorption And Expansion Of Paper In Color Newspaper PrintingInfluence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

        The transverse water absorption expansion of paper has the most obvious and direct impact on the registration. The longitudinal shrinkage parallel to the running direction of the paper caused by water absorption and drying of the paper is generally eliminated by adjusting the registration adjustment roller between the units. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

        In the transverse grain direction of newsprint, the diameter of a fiber can be increased by 30% after it is completely wet, while its length direction can only increase by 1% – 2%. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       Therefore, the longitudinal expansion and contraction along the grain in the printing process is small, about 1 / 2-1 / 3 of that in the transverse direction, which has little impact on the overprint accuracy. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

         The telescopic change in the transverse direction has a great impact on the overprint accuracy of newspapers, and its maximum change can reach about 0.15%. Without taking certain elimination measures, the maximum overprint error can reach more than 0.3mm. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

         Generally, when one version is registered, there is no way to register the four versions, and this error gradually expands from one side. It can not be adjusted simply by the roller borrowing method of the printing press, which greatly affects the printing quality of color newspaper.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

           The influence of water absorption shrinkage on registration accuracy is also very different with different equipment structures. The printing process of newspaper is to print four colors on continuous paper in turn.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

         For the unit with Y-shaped printing structure, two units are generally online to jointly complete four-color printing, and each unit prints two colors.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

        If the unit is a tower structure, the paper path between the two units is short and the shrinkage is not large; If it is placed horizontally, especially if the drum arrangement structure is inverted Y, the paper path will be longer and the shrinkage will be greater. The satellite printing unit is very beneficial to the color newspaper printing. 

       The paper path between the satellite color groups is very short, and there is almost no drying time. The change of the expansion amount of the paper after water absorption generally has no effect on the registration.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

        The paper from the satellite printing unit generally needs another BB printing (generally black). Due to a certain time, the paper also has a certain amount of stretching change.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

3、 Elimination and control of water absorption expansion

        Of course, before we talk about the influence of water absorption and expansion on overprint accuracy, we must well solve other process problems such as prepress image processing, film output, plate making and printing registration, Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

        otherwise, the elimination of water absorption and expansion will be drowned in other factors.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

The elimination and control of paper water absorption and expansion are mainly carried out from the following aspects:Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

      When the equipment with long paper path between units and no fan-shaped expansion device prints color newspaper, the water absorption and expansion of paper has a significant impact on the registration accuracy. In this case, according to the size of paper stretch in printing, 

       The influence of paper water absorption and expansion on overprint accuracy can be eliminated by making up and borrowing lines on the film on one side of the fourth plate. Take the four page newspaper as an example.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       For example, the printing structure of the printing press is Y-type.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

           The first unit prints C and m colors, and the second unit prints y and K colors. We found that under the condition of accurate composition and complete registration of the first edition,Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

        the overprint error between C, m, y and K on the leftmost side of the fourth edition is about 0.2mm, C and m are left, y and K are right. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       Then, when making up the plate, we will borrow and spell the CM two-color film to the right by 0.2mm, that is,Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing move 0.2mm to the middle seam to offset the shrinkage caused by drying the paper after absorbing water.

        We note that when making up according to the process requirements, the film is required to face upward, that is, the film is made upside down, and its left and right directions are exactly the opposite, so it is convenient to determine the borrowing direction with the middle seam as the reference line;

      It is best to draw a line on the layout paper to make the amount borrowed each time consistent; The paper brand level is different, and its expansion amount is also different. Different borrowing amounts should be determined for different paper.

2. Control the ink and water balance in the printing process. When printing, the water volume of the first unit is the main factor that determines the influence of paper expansion after water absorption on overprint. When printing, the water amount of fountain plate shall be uniform and consistent, and must not be large or small. 

       Especially when using paper with poor quality, it has large water absorption and large expansion rate, which is more prominent. For the equipment with fan-shaped expansion mechanism such as eight color tower unit,Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       It is not necessary to borrow the spelling when making up, and it is more required to control the water volume.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

3. At present, when ordering new equipment, all factories should pay attention to adding fan-shaped expansion rollers for both double width machines and single width machines, so as to improve the control of water absorption and expansion of paper. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       Due to the different conditions of the paper used by various factories, there is still a certain gap between the quality of domestic paper and imported paper. It is very necessary to control the water absorption and expansion of paper from the equipment.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

4. Try to use high-quality paper, which not only has small water absorption and expansion, but also is good for dot reproduction, color reproduction, ink balance and other printing processes. To produce good quality color newspaper, the performance of paper is a very important condition.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

5. The process structure of the printing machine for printing color newspaper is preferably tower type, so that the paper path between the four-color printing of the paper is short, which is conducive to controlling the water absorption and expansion of the paper and improving the overprint accuracy. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

        The satellite structure is basically continuous printing between the satellite color groups, which is of great benefit to the overprint accuracy. The dot reproduction quality is good, but the cost is high, and the newly ordered machines are rare. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       At present, we can see a Ten Drum Tower printer, which is a new satellite printer with good process structure.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

6. The paper used for printing color newspaper shall not be too dry, otherwise it is not only easy to break the paper during printing, but also has large water absorption and high expansion rate. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       The storage environment of paper shall meet the specification requirements, and the time shall not be too long.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

7. The outer packaging of paper should be removed about 1 hour before printing. If the paper is not packaged for a long time, there will be a certain degree of humidity difference between both sides and inside of the paper.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

         The moisture on the cross section of the paper is different, and its water absorption and expansion will be different, which will not only affect the overprint accuracy, but also wrinkle easily during printing.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

        On the premise of careful analysis of the water absorption and expansion of paper, through appropriate process adjustment, we can effectively control the impact of water absorption and expansion of paper on printing quality.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

          At the same time, the control of water absorption and expansion should also be considered when selecting raw materials and ordering new equipment. Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing

       Through the joint efforts of technology, materials and equipment, the overprint accuracy of color newspaper can be effectively improved, so as to ensure the printing quality of color newspaper.Influence Of Water Absorption And Expansion Of Paper In Color Newspaper Printing