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 Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone. Hanging Chalkboard,Custom Chalkboard,Portable Chalkboard,Wood Framed Chalkboard Jinan Tri-Tiger Technology Development Co., Ltd , https://www.jinanfurniture.com
2. Attention should be paid to the problem of overprinting, and the overprinting is not allowed to have mechanical reasons and human factors.
3, pay attention to the "branch" problem, "branch" is generally caused by friction.
4, pay attention to the paste problem, resulting in paste version is mainly due to the rubber roller pressure is too large, there are too thin ink adjustment, too much oil or too much auxiliary materials, too much ink and so on.
5, pay attention to the problem of heaping ink, causing the cause of heaping ink is not suitable for pressure, rubber blanket is too strong, poor ink mixing, viscosity is not appropriate, too dry oil and paper off powder and other reasons.
6, pay attention to the color sequence problem, proofing paper and printing paper as uniform as possible, proofing the color sequence and printing color sequence.
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.
Problems to be aware of when simulating a proof
1. Firstly, it is required to print according to the standard when printing the pattern, and at the same time, the factor of the dot enlargement during the proofing should be taken into consideration. Note the dot gain due to ink emulsification. Also note that the blanket is not tightened, and the dots caused by excessive pressure between the plate and the blanket cylinder increase.