Paper Q&A (65-73)

65. How to rationally use the directionality of paper in printing?

Answer: From the printing point of view, the paper should strive to make the longitudinal and lateral directions of the paper close to each other or tend to be the same in the papermaking process, but it cannot be achieved in actual production. Therefore, in the use of paper, the silkiness characteristics of the paper should be used to the maximum extent possible. The directionality of paper plays a decisive role in sheetfed printing, especially offset printing. Due to the effects of fountain solution, the paper fiber absorbs moisture and swells, and the fiber diameter expands more than the longitudinal direction. Therefore, the paper absorbs moisture and laterally stretches. The rate is 2-8 times larger than vertical. Therefore, longitudinal paper tends to be used in sheet-fed offset printing. That is, when the printed paper is cut, the longitudinal direction of the paper is aligned with the longitudinal direction of the paper web, and the width is consistent with the lateral direction of the paper web so that the paper can be maintained during the printing process. The longitudinal direction is parallel to the running direction of the printing press.

In addition, when stapling after printing, pay attention to the vertical direction of the paper in the vertical direction of the page, so that the folding of the page is good, and when the book is opened, it is more flat. In addition, it is also necessary to avoid the use of a combination of vertical and horizontal papers, which results in inaccurate overprinting due to the significant difference in vertical and horizontal expansion ratios of the paper.

66. What is the formation of paper?

A: The uniformity of the paper indicates the homogeneity of the paper structure, that is, the even distribution of the fibers in the paper.

67. How does formation uniformity affect paper performance?

A: Paper formation not only affects the appearance of the paper, but also affects the physical and optical properties of the paper, affecting the homogeneity of these properties. Papers with poor evenness cannot have good smoothness and opacity. Papers with poor conformity also have large differences in folding endurance, tearing strength and tensile strength. Paper formation is poor and thickness is not uniform. The moisture content is also not uniform, and uneven shrinkage occurs when drying, causing some paper diseases (bubbling, wrinkling, etc.); uneven paper, the paper will produce a clear shiny or more transparent spots when passing through the calender Due to the uneven thickness of the paper, in order to balance the moisture, the paper needs to be dried. This will increase the brittleness of the paper and cause static electricity.

68. What is the effect of formation on printed paper?

A: Formation is an important indicator of printed paper and is also the basis for paper quality. Inconsistent uniformity of the paper on the water, ink absorption and absorption are not uniform, the opacity will also appear in different parts of the difference, if the poorly formed paper graphics printing, can not achieve good printing results.

69. What are the methods to detect the formation of paper?

Answer: The easiest way to judge the quality of paper is to point the paper to the light source and observe the uniformity of the light passing through the paper. If the light is transmitted through, the structure of the paper is like a frosted glass, and the structure of the paper is considered to be uniform. If the light is spotted, or if it is like a cloud or a piece of paper, it indicates that the tissue of the paper sheet is uneven, that is, the evenness of the paper is not good. .

The method of accurately detecting the formation of the paper is to use a STFI uniformity meter, a QNSM formation meter, and a MK company's 3D paper sheet structure analyzer for quantitative testing.

70. What is the ration of paper?

Answer: Paper weight is commonly referred to as grammage, which refers to the mass of paper per unit area. It is generally expressed in grams per square meter. The unit is g/m2. There are also many pounds or kilograms per ream. Paper basis weight can also be converted based on paper specifications and the number of sheets per ream.

71. How does the quantification of the paper affect the performance of the paper?

A: Quantitative is the most basic physical index of paper. Its level and uniformity affect all the physical, mechanical, optical and printing properties of paper. The various performance indicators of printing paper, such as thickness, tensile strength, bursting resistance, and opacity, are all closely related to the paper's quantification. If the paper's quantification is significantly lower than the standard's specifications, it is not only prone to print failure, but also Insufficient mechanical strength and paper breakage occurred. When printing the same batch of paper with different quantification, the problem of misprints and shades of printing will occur. When the same piece of paper is unevenly quantized, it is more likely to result in illegible handwriting and inconsistent image color. If the ration is too high, not only the pulp is wasted, but the usable area per ton of paper of the user is not guaranteed.

72. How to estimate the paper quantitative deviation?

Answer: In addition to measuring according to the standard method, the actual weight of a ream paper can also be weighed. The actual mass is divided by the total area of ​​the ream paper as the approximate quantification of the paper. If the mass of the letter 1 787mm×1092mm is actually claimed as 20.8kg, the paper's quantification is:

The calculation results show that the relief paper is very low in quantification (standard quantification should be 52g/m2).

73. What is the cause of uneven paper quality? What is the harm?

A: The uneven quantification of paper, the most prominent manifestation is the inconsistent ration of paper, paper will appear a thin one-half or one-half thick half thin. The reason for this phenomenon is generally due to the uneven flow of pulp from the rafts or due to the difference in flow patterns, resulting in more pulp at one site and less pulp at the other. When this happens, the webs produced will be loose at both ends. This type of paper is susceptible to paper breaks and pleats during printing. When the produced flatbed paper is placed on a table, there will be a situation where one side is high and one side is low. In the case of a periodic quantitative change in the longitudinal direction of the paper web, the sizing device or the paper machine is subject to vibrations and fluctuations in the pulp flow. The relationship between the vibration frequency and the length of the flatbed paper and the speed of the papermaking machine determines whether the flat paper is stacked one by one or low, or high in the middle. Such paper can cause difficulties in feeding the paper and can also affect the print quality.

- "Printing Technology - Equipment and Special Printing"