The thixotropy of the drum screen printing ink should be as small as possible. In order to eliminate this unfavorable factor, the ink must be fully agitated before printing to return it to its normal state and then printed. The more irregular the pigment particles in the ink, the greater the thixotropy, and conversely, the less thixotropy. Such as black ink, thixotropy is large; while the white ink and yellow ink is less thixotropic. In addition, there are more binders in the ink, less pigment, and less thixotropy, and vice versa.
3 ink flow 
The degree of fluidity of the drum screen printing ink is the reciprocal of the viscosity. That is, the viscosity is large, the fluidity is small, the viscosity is small, and the fluidity is large. 
The degree of fluidity of the drum screen printing ink can be regarded as the degree of natural flow of a certain amount of ink in a certain period of time and a certain leveling surface without external force. The fluidity of the ink can measure the thickening of the ink. In the drum screen printing ink, its fluidity is generally controlled at 30 ~ 50mm. The measurement method is to take 1 mL of ink, and after 15 min under a pressure of 50 g, measure its diameter. 
Practice has proved that when the steel drum screen printing, the greater the degree of ink flow, the greater the degree of ink diffusion after printing, so that the small gaps of thin lines can not be resolved clearly combined; the ink flow is small, after printing In the ink of the graphic and text, there are broken lines and lack of ink, and printing is also difficult.
4. Plasticity of ink
Plasticity refers to the property of deforming completely or partially after being deformed by an external force. Screen printing ink has both fluidity and plasticity. High pigment and other solids content, the ink appears thick, plasticity is large; pigments and other solids are low, the ink is thin, and the plasticity is small. Screen printing ink requires a certain degree of plasticity in order to maintain the printing accuracy. 
5. Ink Viscosity
The viscoelastic property of the drum screen printing ink is the property that the ink is sheared and fractured after being pressured by the squeegee, and the screen plate rebounds and the ink quickly rebounds. The sticking of ink and steel drums and the detachment of wire meshes have caused rapid retraction, which is a typical phenomenon of ink viscoelasticity. 
The viscoelasticity of the ink, which has a large influence on screen printing, is the phenomenon of drawing. The drawing phenomenon is that when the squeegee is scraped and the screen is bouncing, many ink filaments appear between the screen and the steel drum. This is the most bogey phenomenon in the drum screen printing. It is not only easy to make the steel drum and screen plate dirty, and even make the drum screen printing impossible.
The length of the drawing is related to the viscosity of the ink. The viscosity is large and the ink is long; otherwise it is short. For this reason, the viscosity of the ink is often reduced by increasing or decreasing the viscosity or decreasing the molecular weight of the resin, thereby improving the ink viscoelasticity and reducing the drawing phenomenon. 
The drawing phenomenon is also related to the time of action. In the same ink, if the separation speed is rapidly split by elasticity, the ink is short; the separation speed is very slow, and the ink flows completely like a pure liquid and does not become filamentous. 
6. Dryness of ink
Drum screen printing requires that the ink on the screen plate can not dry the conjunctiva for a long time, and that after printing, the drying on the steel drum should be as fast as possible. In this way, the printed images can be kept clean and clear. Not only can the printing quality of steel drums be guaranteed, but they can also meet the requirements for timely delivery.
7. The hardness of ink
The hardness of the drum screen printing ink coating refers to the degree of deformation of the ink film, which can be divided into penetration hardness and scratch resistance hardness. From the actual application of the steel drum, the scratch resistance is measured. If the same force is used, the fully dried ink film is marked with a pencil of different hardness, and the H value of the pencil that can break the ink film is the hardness of the measured ink. . The hardness of the ink during drum printing is an important parameter for drum screen printing. (To be continued)