1. Viscosity: A property that prevents the flow of liquid, ie the resistance to liquid flow. If the viscosity is too large, the ink is not easy to pass through the screen and the ink is imprinted; the viscosity is too low, which can cause the imprint to expand, affecting the fineness and resolution.
2. Plasticity: refers to the nature of the ink before it is deformed after the ink is deformed by external forces. The plasticity of the ink helps to improve the printing accuracy.
3. Thixotropy: It is an exchange phenomenon between the ink sol and the gel. It shows that the ink becomes thick after a certain period of time, and the viscosity becomes large. After the ink is agitated, it becomes thinner and the viscosity becomes smaller, which is favorable for ensuring the fidelity.
4. Fluidity (leveling): The extent to which the ink spreads around in the external force. The fluidity is the reciprocal of the viscosity. The fluidity is related to the plasticity and thixotropy of the ink. The plasticity and thixotropy are large, and the fluidity is small; On the contrary, it is big. The large flowability of the imprinting is easy to expand, the flowability is small, the printing is easy to appear netting, and the phenomenon of ink formation (nodes intertwined) is also known as reticulation. The fluidity of the screen printing ink is generally between 30-50mm.
5. Viscoelasticity: It refers to the ink's rapid rebound performance after being cut and fractured during the scraping process. It is required that the ink be deformed quickly, and that the ink rebound will be favorable for printing quickly.
6. Dryness: It is required that the slower the ink is dried on the screen, the better the ink is dried as soon as the ink is transferred to the substrate.
7. Fineness, pigment, and solid material particle size (15-45um for printing) should be 1/3-1/4 of the mesh opening.
8. Drawing property: When the ink is picked up by the ink scoop, the filamentous ink is not broken so that it is drawn. The ink is long, the ink appears many filaments on the printing surface, so that the substrate and the printing plate are stained (nets are enlarged and the dots are blocked and fluffed) cannot be printed.
The occurrence of the drawing phenomenon is related to the excessive connection molecular weight in the ink and the large viscosity of the ink. In some cases, drawing occurs due to ink expiration.
A blackboard (also known as a chalkboard) is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate, known, when used for this purpose, as chalk. Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.
A blackboard can simply be a board painted with a dark matte paint (usually black, occasionally dark green).Matte black plastic sign material (known as closed-cell PVC foamboard) is also used to create custom chalkboard art.Blackboards on an A-frame are used by restaurants and bars to advertise daily specials.
A more modern variation consists of a coiled sheet of plastic drawn across two parallel rollers, which can be scrolled to create additional writing space while saving what has been written. The highest grade blackboards are made of a rougher version porcelain enamelled steel (black, green, blue or sometimes other colours). Porcelain is very hard wearing, and blackboards made of porcelain usually last 10–20 years in intensive use.
Lecture theatres may contain a number of blackboards in a grid arrangement.The lecturer then moves boards into reach for writing and then moves them out of reach, allowing a large amount of material to be shown simultaneously.
The chalk marks can be easily wiped off with a damp cloth, a sponge or a special blackboard eraser usually consisting of a block of wood covered by a felt pad. However, chalk marks made on some types of wet blackboard can be difficult to remove. Blackboard manufacturers often advise that a new or newly resurfaced blackboard be completely covered using the side of a stick of chalk and then that chalk brushed off as normal to prepare it for use.
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