Coating  is a process of application onto paper or cardboard of a layer that confers the material gloss and a range of special properties. The layer content includes adhesives and plasticizing agents, as well as chalk or kaolin used as a pigment. There are some methods of coating: machine, off-machine and molded coating. Only the first of them is carried out directly by a papermaking machine, special equipment is necessary for other two methods.
Besides molded coating, there is also blade coating.In case of this method, an excessive amount of coverage is applied onto the surface of paper or cardboard and then a long thin plane called blade smoothes and levels this layer.
Depending on its destination, cardboard may be coated with one or several layers. Multiple layers of coverage assure attractive appearance, whiteness and gloss of the surface.

Structure of coated board

Coated board consists of several layers, whose quantity and quality depend on sort, kind and destination of the material. There is distinguished cardboard with one-side coating – duplex– and cardboard with two-side coating – triplex.
Duplex has a lower layer, inner, upper layer and coating coverage. The lower layer is made of a rather qualitative raw material – bleached or unbleached pulp or wastepaper. It is followed by a rather thick inner made of wood pulp, wastepaper or pulpstock of low quality. Bleached or unbleached pulp, pulpstock or whitened wastepaper is used for the upper layer.
In case of triplex manufacturing, the structure differs a bit. The inner remains the same but raw materials for the layers surrounding it shall be rather qualitative. Coating coverage is applied onto both sides of cardboard, that’s why a ready sheet has two “front-face” areas.

Classification of coated board

According to the European classification, coated board is divided into three types: SBB (SBS), FBB and WLC.
SBB (SBS) - Solid Bleached Board (Sulphate) represents integral cardboard with the density of 185 - 390 g/m2 manufactured from bleached pulp and having one-side or two-side coating coverage.
FBB - Folding Boxboard is a chrome-substitute product. This is cardboard with the weight of 170-850 g/m2 composed of three layers: the inner contains wood pulp; upper and lower layers are made of bleached chemical pulp. Coating is usually made on the both sides of cardboard.
WLC - White lined Chipboard (GD-1или GD-2) is coated chipboard entirely made of wastepaper stock or with addition of wood pulp. Cheap cardboard is used as inner; upper and lower layers are made of high-quality wastepaper. Coating is carried out both on one side or on the both sides.
According to the Russian standards, coated board is marked with the letter “M” and a series of other letters indicating its additional characteristics. For example, M is cardboard of bleached pulp having coating on the upper layer; MHO is cardboard having coating on the unbleached base, and MO is coated cover board.

Advantages of coated board and its use

Coated board compares favorably with simple one, first of all, due to its appearance. Molded coating confers it almost specular gloss and reduces porosity of the front-face, that assuring the best result upon overprinting: qualitative bright image remains on the cardboard surface.
Due to its properties, coated board is widely used for manufacturing of the most various products: sets for child development and creation, table games, and polygraphic products. And, of course, one of trends of use of coated board is manufacturing of packages.
Chrome-substitute cardboard is widely used for manufacturing of packages for foodstuffs, medical preparations, CD-disks, computer components and accessories, as well as for household equipment of small sizes. As a rule, polygraphic or other image is applied on the outer sides of a box of chrome-substitute products. As for bigger goods, package of boxboard is used that has a bigger thickness than chrome-substitute products and weight from 170 to 2500 g/m2.
High-quality coated board is an irreplaceable material for manufacturing of gift wrapping. In such a case, special requirements are put in such qualities as whiteness and smoothness of the surface, possibility to apply print and glossy coverage.
When manufacturing food packaging, cardboard resistance to external physical and chemical influence, for example, humidity resistance and grease proofness. These qualities are achieved due to application of a special coverage onto a side.
Thus, coated board is one of the most popular materials for manufacturing of different kinds of package. Its smooth white surface assures qualitative print and confers attractive appearance to ready products.

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