Key points for attention when choosing screen prin

Key points for attention when selecting silk printing ink

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core tip: when selecting silk printing ink, it should be compatible with equipment, substrate and other conditions, that is, it should have good printability. What determines the printability is the performance of printing ink

[China Packaging News] the selection of silk printing ink should be compatible with the equipment, substrate and other conditions, that is, it should have good printability. What determines the printability is the performance of printing ink

1) viscosity viscosity is the resistance of fluid flow, also known as internal friction coefficient or viscosity coefficient. If the ink viscosity is too high, which tests its pressure bearing capacity, it is not easy to transfer to the substrate through the silk plate, resulting in printing difficulties and incomplete imprinting; If the viscosity is too low, it will expand the imprint, affect the printing quality, and even cause waste products

2) fluidity fluidity is a characteristic of fluid flow performance. The fluidity of ink can be regarded as the degree of natural flow of a certain amount of ink on the flat surface within a certain time without external force. The fluidity of ink is generally controlled at 30 ~ 50mm. The fluidity of the ink is large, and the imprint is easy to expand, making the thin lines with small gap easy to merge; The fluidity is small, the imprinted lines are easy to break, the lines are short of ink, and the printing is also difficult

3) yield value yield value is the minimum external force (minimum shear stress) required when the fluid begins to flow. The yield is too large, the ink is hard, and the fluidity is poor

4) thixotropy thixotropy refers to the property of fluid that changes its flow performance under the action of external force. For example, in the process of silk screen printing, the reversible phenomenon of ink thickening after a certain period of time and thinning after stirring can be explained by the concept of thixotropy. Because the shape of the pigment particles in the ink is irregular, although it adsorbs a layer of binder, it is also an irregular particle. After a certain period of time, the pigment particles will contact or be close to each other, and the attraction will increase, and the ink will thicken and become sticky. This temporary stable structure will soon be destroyed under the stirring of external forces, and the attraction between the particles will weaken, the fluidity will improve, the ink will dilute, and the viscosity will decrease. The thixotropy of silk printing ink should be as small as possible. In order to eliminate this adverse factor, the ink should be fully stirred before printing

5) plasticity plasticity refers to the property that deformation can be completely or partially maintained after deformation under external force. Silk screen printing ink is a thick suspension between fluid and semi-solid, so it has both fluidity and plasticity. If the content of pigments and other solid materials is low, the ink will be thin and the plasticity will be small. The printing ink requires a certain plasticity to ensure the accuracy of printing, otherwise the printing lines are easy to expand

6) fineness fineness indicates the size of pigment and other solid material particles in the ink, and also indicates the uniformity of these particles in the binder. The fineness of screen printing ink is generally between 15 ~ 45um. If the fineness is too large, there will be a paste during printing, and the pattern cannot be printed. If the silk is thick, the fineness can be increased accordingly. Generally, the coarsest particles should be less than one quarter of the hole area

7) wiredrawing due to the high molecular weight and strong viscosity of the binder in the ink, when the printing plate is lifted, there are many ink filaments on the back of the plate, which is called wiredrawing. This is the most taboo phenomenon in silk screen printing. It is not only easy to make high and new technologies such as microelectronics, computer technology, precision machinery technology, high sealing technology, special processing technology, integration technology, film technology, networking technology, nanotechnology, laser technology, superconducting technology and biotechnology develop rapidly, brushes and plates are sticky, and even silk screen printing cannot be carried out. Therefore, The silk screen printing ink is required to have the basic performance of no wire drawing during the printing process

8) strong dryness 1. The requirements for drying performance of tinned silk printing are that the ink can not dry the conjunctiva on the silk plate for a long time, and after printing, it is required to dry it on the substrate as dry as possible. When multicolor continuous overprint, the drying performance of silk screen printing ink is required to be higher. The main body of the experimental machine is a split structure