1. Working principle of screen printing machine

Taking the commonly used hand screen plane 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 to make the ink scraper squeeze the ink and the screen printing plate in motion, so that the screen printing plate and the substrate form an embossing line. Due to the tension N1 and N2 of the screen, the force F2 is generated on the ink scraper, The rebound force makes the screen printing plate not in contact with the substrate except the embossing line. Under the extrusion force F1 of the ink scraper, the ink leaks from the moving embossing line to the substrate through the mesh.

In the printing process, the screen printing plate moves relative to the ink scraper, and the extrusion force F1 and rebound force F2 move synchronously. Under the action of rebound force, the screen returns in time and is out of contact with the substrate to avoid rubbing the imprint. That is, the screen is constantly in deformation and rebound during the printing process.

After one-way printing, the ink scraper is separated from the substrate together with the screen printing plate, and return ink is carried out at the same time, that is, a printing cycle is completed. After ink return, the distance between the upper surface of the substrate and the reverse side of the screen printing plate is called the same plate distance or screen distance, which should generally be 2 ~ 5mm. In manual printing, the skill and proficiency of operators directly affect the formation of embossing line. In practice, silk screen printing workers have accumulated a lot of valuable experience, which can be summarized into six points, that is, to ensure the straightness, uniform speed, equiangularity, pressure equalizing parts, centricity and vertical edge in the movement of the doctor blade. In other words, during printing, the doctor blade should move forward in a straight line without shaking left and right; It is not allowed to be slow before and fast after, fast before and slow after, or slow and fast at a time; The tilt angle of the ink plate should remain unchanged, and special attention should be paid to overcoming the common problem of the gradual increase of the tilt angle; The printing pressure shall be uniform; Keep the distance between the doctor blade and the inner sides of the mesh frame equal; To keep the ink board perpendicular to the frame.

2. Working principle of flat screen curved surface screen printing machine

Flat screen printing refers to screen printing with flat screen on cylindrical or conical surfaces. Under certain conditions, it can also screen print elliptic surface, drum surface, arc surface and other surfaces. Dry screen curved surface screen printing machine is a machine that uses flat screen to print the above curved surface.

Working principle of flat surface silk screen printing machine: a - roller support B - shaft support C - inlaid support. During printing, the plane screen printing plate and the substrate move, while the ink scraper is stationary. The flat screen printing plate is clamped on the screen frame and translated at a uniform speed by the action of the flat screen curved surface screen printing machine. Due to the friction of the screen plate, the substrate placed on the support device rotates accordingly. At the embossing line, the linear speed of the curved substrate is consistent with the moving speed of the plane screen printing plate to realize scraping printing.

In theory, the embossing line should be at the higher bus of the curved substrate, so as to increase the off screen angle and ensure the printing quality. For the convenience of adjustment, the top angle of the doctor blade is generally 60 ° ± 15 °, and the verticality and upper and lower dimensions are required to be adjusted. The vertical adjustment is to ensure that the cutting edge line does not produce lateral displacement when adjusting up and down, and always align with the higher bus a; The scraper with a top angle of 60 ° ± 15 ° is used to ensure that the inclination angle of the scraper is formed after vertical installation α。 In the actual adjustment, in order to ensure that the plane screen printing plate is separated from the curved substrate in time, the embossing line can be slightly ahead, especially when the diameter of the substrate is large, the embossing line should be ahead. The supporting device of curved surface printing is a special device in various forms, which is designed and manufactured by users according to the product requirements.

The curved surface printing of cylindrical container or conical container can adopt two pairs of roller supports, the shaft sleeve support for cover and cup with the ratio of length to diameter less than 1.5, and the soft hollow container can be supported by inflatable device. The elliptical surface is approximately a part of the cylindrical surface, which can be supported by cylinder inlay.

The principle of printing on the surface of the cone is basically the same as that on the surface of the cylinder, except for the graphic shape of the screen printing plate and the motion form of the screen printing plate. When making a screen printing plate for cone surface printing, first draw the expanded drawing of the cone surface, and calculate the center of the fan according to the expanded drawing, and then select an appropriate screen frame to make a screen printing plate.

On the plate efgh that can accommodate the fan-shaped abed, a printing plate consistent with the fan-shaped abed is made. Fix the right angle rod on the plate efgh, and install the plate with o as the axis to make a fan-shaped rotation. Then, like the surface printing of the cylinder, the substrate is supported by four rollers under the plate, the scraper is fixed, the plate frame is moved according to the fan, and the scraper is pressurized to print the surface of the conical plate. When printing, the conical bearing printing is in line contact with the screen printing plate under the pressure of the scraper; When the screen printing plate moves horizontally in a sector around the axis of the sector expansion, the substrate rotates synchronously on the support device; The ink is squeezed by the scraper and misses the surface of the substrate to complete the printing.

3. Printing press process:

(1) Work cycle program of flat screen printing machine. Taking the flat screen platform monochrome semi-automatic hand screen printer as an example, its working cycle is: part feeding → positioning → plate dropping → falling to the ink plate and rising back to the ink plate → ink scraping stroke → rising to the ink plate → falling back to the ink plate → plate lifting → ink return stroke → releasing positioning → receiving.

In the continuous cycle action, as long as the function can be realized, the time occupied by each action should be as short as possible, so as to shorten the synchronization of each work cycle and improve work efficiency.

(2) Imprint line. In the printing process, the ink and screen printing plate are squeezed to the ink plate to form a contact line between the screen printing plate and the substrate, which is called the embossing line. This line is at the edge of the doctor blade, and countless embossing lines form the printing surface. It is difficult to realize the ideal embossing line because the printing stroke is a dynamic process.