When the rotary screen printing machine is printing, after the color paste enters the rotary screen from the pump and the feeding pipe, the color paste is evenly distributed on the full length of the rotary screen through the equalizing device, and is connected with the scraper on one side. Under the action of gravity and pressure, the color paste seeps out from the mesh in the slurry storage area and is printed on the fabric.
Usually, the printing effect is evaluated from the color uniformity, outline definition, color intensity, etc. These factors are related to the flow of color paste. For example, color uniformity requires that the amount of slurry to be kept consistent at each of the same pattern units; outline definition requires clear patterns and line edges, and after the color paste reaches the fabric, there will be less migration and seepage; color intensity requires each pattern The required amount of colorant must be obtained at each type of pixel. Therefore, in order to achieve the ideal printing quality, there should be an appropriate amount of pulp in each printing part of the fabric. Therefore, it is worth studying the influence of the geometric and physical properties of each component of the printing unit and the paste storage area on the flow of the color paste during the application of the color paste, so as to make appropriate configurations according to the degree of their influence.
For the printing effect, the most important thing is the application of the color paste. This is mainly determined by the squeegee technique used. The printing paste flows from the sizing pipe to the inner side of the rotary screen, and the doctor blade and the rotating rotary screen form an open printing paste retention wedge-shaped area. In the wedge-shaped area of the printing paste, due to the rotation of the rotary screen, a layer of color paste close to the rotary screen is driven to generate a swirling flow, resulting in a velocity gradient and shear stress inside the color paste, resulting in a general structure of the printing paste. decline. At the imprinting point, the swirling flow is blocked by the scraper and suddenly stopped, the color paste is squeezed, and the pressure of the scraper and the potential energy of the liquid level in the wedge-shaped area increase the pressure of the color paste in this local area. Fast, due to the thixotropy of the colorant, its slaughter degree is further reduced. Under the action of the above comprehensive factors, the color paste is printed on the fabric through the mesh. After the embossing point, the pressure is removed, the color paste on the fabric is restored, and the seepage is limited. The resistance of the printing paste to penetrate the rotary screen and the resistance of the printing paste to penetrate the fabric are opposite to the direction of the accumulated pressure of the printing paste in the local area. The maximum amount of printing paste that can penetrate the rotary screen can be calculated from the accumulated pressure and reverse resistance of the printing paste.
For the magnetic rod scraper, since the magnetic rod rotates with the rotary screen, the color paste in contact with it is also driven, which forms two color paste flows in the wedge-shaped area of the paste storage, and they are cut off at the imprinting point at the same time. . Moreover, in the rotation direction of the rotary screen, starting from point M, the radial distance between the outer surface of the magnet bar and the inner surface of the rotary screen shrinks faster than the radial distance between the lower surface of the scraper and the inner surface of the rotary screen, so the color paste It is more strongly squeezed, so the peak pressure of the magnetic bar before the embossing point is higher than that of the scraper, so when the magnetic bar is printed, the color paste is transferred to the back of the fabric obviously, the coverage is good, and the pulp consumption is less. Higher paste pressures also increase the likelihood of lateral transfer of the paste, resulting in a loss of contour definition.