Coating in printing
Coating of printing production is one of the most popular post press processes. The popularity of coating can be explained by wide functions of decorating, unusual visual effects and good protection.
It is done by creating an overlay of varnish on printed production. An overlay of varnish protects surface from adverse external conditions and improves visual looks of production.
Coating can be full or partial. When doing a full coating all printed area is covered with varnish, but when it is partial – varnish is used for highlighting details. Gloss varnish and matte varnish can be used. Gloss varnish enriches colour effects, brightness and production looks more colourful. Matte varnish helps to avoid from reflections and to make a smarter look. There are a lot of interesting variations how to use different varnishes simultaneously: matte and gloss varnish, gloss and pearly varnish, matte and gloss varnish with glitters or ink pigment etc. Recently varnishes with different aromas become more and more popular.
Varnishes can be divided in three basic types: oil based varnishes for offset print, water dispersion varnish and UV curing varnish. Chemical composition and coating technology is different for each type of varnish. Oil based varnish mainly is strengthened during oxidative polymerization, water dispersion varnish is absorbed and evaporates, but UV curing varnish polymerize in ultraviolet rays.
Coating expanses are counted individually depending from kind of coating, size of printing area, issue, difficulty and other factors.
Coating with oil based offset varnish
Offset varnish is applied in the same way as coloured ink from printing section of offset printing machine. Matte and gloss offset varnish can be used. Like other varnishes also offset varnish improves protection from adverse external conditions and averts quick deterioration of colour layer. Offset varnish is comparatively cheap way of coating for printed production, therefore, it is so widespread.
Offset coating can be done fast and thickness of coating layer is insignificant and usually does not increase paper density.
Coating with water dispersion varnish
For applying water dispersion varnish there should be a special coating section in printing machine. Qualities of water dispersion varnish are the same as for offset varnish. Varnishes not only ensures that printed production is protected from different negative factors but also enriches colour saturation, brightens colours and dues, makes pictures more contrasted. Additional attention to some details of printed design can be attracted by partial coating of water dispersion varnish.
Quality of this kind of varnish is no need to dry printed sheet for long time and it is practically ready for next post press process. Water dispersion varnish not only dries quickly but also colour fixation on printed material is faster and colour does not become yellowish after some time.
UV curing varnish
UV varnish can be applied in very thin layer as well as in thick layer. Special resin curing in ultraviolet rays is used when coating this kind of varnish. It is applied with special printing machines, quite often it is done by using screen printing technique and usually for small runs. Both matte and gloss varnish can be used in UV coating. Recently UV coating with glitters has become widely popular. In coating with glitters there are multicoloured glitters in varnish. Depending from amount, size and colour scale of glitters different visual effects can be achieved giving bright, unique and unforgettable external of oriented production.
Partial UV coating is one of the most popular ways of coating for printed production. Fragmented UV coating gives observable emphasis on design elements by making them more obvious and visible.
Full UV coating means that varnish is applied on all surface of printed production. Full coating is used in production of covers, folders, postcard and other.
UV coating differs from other kinds of coatings with a layer of very high density which can be even compared with lamination.