In an offset printing press, there are three important rollers: PS plate cylinder, blanket cylinder and pressure cylinder, which are installed at a fixed position on the printing press, and the gap between the cylinder and the cylinder is fixed. Therefore, it is necessary to fill the gap between the cylinder and the cylinder through the bottom paper, and then accurately adjust the pressure between the PS plate cylinder and the blanket cylinder, or the blanket cylinder and the pressure cylinder. The bottom paper of the gun will be placed on the bottom of the PS plate or the bottom of the tape. In some machines, it can also be installed on the impression roller.
One of the prerequisites for the continuous stability of printing quality is the need for stable quality bottom paper. This is why for many years, the printing industry has used McGill's bottom paper as a professional backing material: through a special production process-"high pressure calibration "To homogenize the inherently inhomogeneous density, surface and thickness of the paper, and become a standard bottom, thickness and flatness, with the function of calibrating the thickness of the bottom paper.
Since ordinary paper has not been processed by the “high-pressure calibration†process, the heterogeneous characteristics of the paper will undoubtedly affect the printing quality, and adverse results will occur: streaks or fog spots, unstable dots or dot expansion, dot deformation, Ghosting, misplaced outlets, etc.
1. Extremely small manufacturing tolerances
The production process of Maxwell's bottom paper fully complies with the ISO standard, and through its unique technology and professional knowledge, the thickness tolerance value per square meter of its products is controlled within ± 0.01mm. One of the most important factors when using air cushion blankets is that there must be a "hard" gun bottom paper. Because the bottom tape or general paper is too soft, it is not suitable for use as a backing material, otherwise it will have a variety of undesirable consequences: the dots are too large, shifted or ghosted, the blanket will stretch and buckle due to the virtual position, resulting in high temperature, As a result, the ink and ink are unbalanced, the product quality is unstable, and even the printing machine may be damaged in the long term. Only through the compression and "high pressure calibration" process can the bottom paper meet the required hardness requirements.
2. Image transmission
Under normal circumstances, the tolerance range in the printing process is a few millimeters, and the bottom paper must have a variety of thicknesses (McG bottom paper is available in 14 thicknesses, ranging from 0.015 to 0.5 mm) for fine adjustment Printing pressure to get the best printing quality. Especially in multi-color printing does not affect the printing quality.
Even when printing with a lower pressure, the printed area (about 2 mm, the contact point between the PS plate roller and the blanket roller) is subjected to a radial pressure of approximately 100 N / cm2 and a tensile force in the tangential direction of 250 N / cm2.
Due to the rotation of the drum, on the one hand, these forces are transmitted along the tangential direction on the surface of the drum. On the other hand, the tangential force is transmitted to the axial direction through the tape / PS version. sink". Generally, the sinking rate of blankets can be inquired from the manufacturer.
The tape will sink during the entire life cycle, so it is necessary to use different thickness of the bottom paper to compensate for the sinking thickness of the tape, and the bottom tape or the bottom glue cannot achieve the effect of the bottom paper. If the bottom paper is not used as the backing, the non-bottom paper will continue to thin under the aforementioned pressure and the thickness will continue to decrease. Then, the "controllable" rubber cloth sinking, plus the "uncontrollable" non-gun bottom paper sinking, makes the previously pre-calculated sinking amount uncontrollable, resulting in errors due to the drum's effective circumference error problem.
3. Thickness instead of grammage
During the manufacture of the "high pressure calibration", the bottom paper has been pre-pressed to their minimum thickness. Take Mai's bottom paper 0.30mm thick bottom paper as an example: starting from about 0.45mm thick original paperboard, and then calibrated by high pressure to a thickness of only 0.30mm. Because the pressure generated during the "high-pressure calibration" manufacturing process is much greater than the pressure generated during printing, it is impossible for the bottom paper to sink during the printing process.
Contrary to ordinary production paper, Mai's gun bottom paper is manufactured according to thickness as a priority standard, not gram weight (weight per unit area). If non-gun bottom paper is used, printers only know the gram of paper , Instead of thickness, so the thickness of the underlay can only be estimated approximately, then errors caused by printing with non-standard effective circumference of the cylinder are inevitable.
Due to non-standard operation, the gun bottom paper is penetrated by fountain solution or car wash water, and may swell after being used for a period of time. Therefore, some printing masters prefer to use plastic sheets as the substrate sheet. However, the use of plastic sheets as a backing has the following disadvantages: the film will generate static electricity; there is a large error in the thickness of the plastic sheet; the plastic does not absorb moisture, and residual solvents in car wash water or bucket water accelerate the corrosion of the roller; after a long time of use, the film It is often difficult to peel from the roller; it is impossible to increase or decrease the thickness of the plastic sheet to adjust the thickness; when there are foreign objects sandwiched between the rollers, the plastic sheet is not easy to be damaged and absorb the impact force, so the roller is damaged; the plastic sheet is better than the gun Backing paper is more expensive.
Full auto Paper Bag Machine
This machine is designed to manufacture square bottom paper bags without handles from paper roll, and it is an ideal equipment for producing small-size paper bags fast. By implementing steps including paper feeding, tube forming, tube cutting and bottom forming inline, this machine can effectively save labor costs. The equipped photoelectric detector can correct cutting length, so as to ensure cutting precision. The equipped SIEMENS PLC system ensures that the machine can perform quickly and stably. This machine can process very thin paper, as well as produce paper bags very fast, thus this machine is especially suitable for being applied in food industries.
Roll-fed Square Bottom Paper Bag Machine
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