1. Working principle of screen printing machine
Taking the commonly used hand-shaped flat screen printing machine as an example, the working principle of the screen printing machine can be described as follows: the power is transmitted through the transmission mechanism, so that the squeegee squeezes the ink and the screen printing plate in motion, so that the screen The printing plate and the substrate form an impression line. Because the screen has tension N1 and N2, it generates a force F2 on the squeegee. The resilience makes the screen printing plate not contact the substrate except the impression line. The ink is in contact with the substrate. Under the action of the squeezing force F1 of the squeegee, the printing is leaked from the moving embossing line to the substrate through the mesh.
During the printing process, the screen printing plate and the squeegee move relative to each other, and the squeezing force F1 and the resilience F2 also move synchronously. Under the action of the resilience, the screen returns in time to disengage from the substrate in order to avoid The blot is dirty. That is, the screen is constantly deformed and rebounded during the printing process.
The squeegee is separated from the substrate together with the screen printing plate after the one-way printing is completed, and at the same time, it returns to the ink to complete a printing cycle. The distance between the upper surface of the substrate and the reverse side of the screen printing plate after the ink is returned is called the same-page distance or screen distance, which should generally be 2 to 5 mm. In manual printing, the technique and proficiency of the operator directly affects the formation of the impression line. In practice, screen printing workers have accumulated a lot of valuable experience, which can be summarized into six points, namely, to ensure the straightness, uniformity, isometric, equalizing, centering and vertical edge in the movement of the squeegee. In other words, the squeegee board should move straight forward during printing, and cannot move left and right; it cannot be slow in front and fast in the back, slow in the front and slow in the back or suddenly slow and fast; the inclination angle to the ink board should remain the same, and special attention should be paid to overcome the inclination angle The common problem of increasing gradually; the printing pressure should be kept even and consistent; the distance between the squeegee and the inner sides of the screen frame should be equal; the ink plate should be perpendicular to the frame.
2. Working principle of flat screen curved screen printing machine
Flat screen curved surface screen printing refers to screen printing with flat screens on cylindrical or conical curved surfaces. Under certain conditions, it can also screen print ellipse, drum, arc and other curved surfaces. The dry-net curved screen printing machine is a machine that uses a flat screen to print the above-mentioned curved surface.
The working principle of the flat surface screen printing machine: a-roller support b-shaft meeting support c-inlaid support. During printing, the flat screen printing plate and the substrate move, while the squeegee is stationary. The flat screen printing plate is clamped on the screen frame and the flat screen curved screen printing machine moves at a constant speed, and the substrate placed on the supporting device rotates due to the friction of the screen. The linear speed of the curved substrate at the impression line is the same as the moving speed of the flat screen printing plate to achieve scraping printing.
Theoretically, the embossing line should be at the highest busbar of the curved substrate to help increase the off-screen angle and ensure the printing quality. In order to facilitate adjustment, the squeegee generally adopts a top angle of 60°±15°, and it is required to be able to adjust the verticality and the upper and lower dimensions. The adjustment to vertical is to ensure that the cutting edge line does not shift horizontally when adjusting up and down, and is always aligned with the highest bus bar A; the squeegee with a top angle of 60°±15° is used to ensure that the squeegee inclination is formed after vertical installation α. In the actual adjustment, in order to ensure that the flat screen printing plate is separated from the curved substrate in time, the impression line can be slightly advanced, especially when the diameter of the substrate is large, the impression line must be offset forward. The support device for curved printing is Various types of special devices are designed and manufactured by users according to product requirements.
Cylindrical container or conical container can be printed with two pairs of roller bearings, sleeve bearings for lids and cups with the ratio of length to diameter less than 1.5, and flexible hollow containers can be supported by inflatable devices. The ellipse is approximately a part of a cylindrical surface, which can be supported by a cylindrical inlay method.
The principle of printing on the surface of a cone is basically the same as that of printing on the surface of a cylinder. The difference is the graphic shape of the screen printing plate and the movement form of the screen printing plate. When making a screen printing plate for printing on the surface of a cone, first draw an expanded view of the cone surface, and find the center of the sector based on the expanded view, and then select an appropriate screen frame to make the screen printing plate.
On the plate efgh that can completely contain the fan-shaped abed, a printing plate that matches the fan shape is produced. Fix the right-angle rod on the plate efgh, and install it with o as the axis to form a plate that can be rotated in a fan shape. Then, just like printing on the surface of a cylinder, 4 rollers are used to support the substrate under the plate, the squeegee is fixed, and the plate frame is moved in a fan shape, and the squeegee is pressurized to print on the surface of the conical plate. During printing, the conical bearing is in line contact with the screen printing plate under a certain squeegee pressure; when the screen printing plate moves in a horizontal fan shape around the axis of the fan-shaped unfolding drawing, the substrate rotates synchronously on the supporting device Movement; the ink is squeezed by the squeegee and leaks to the surface of the substrate to complete the printing.
