The most well-known and most used printing paper for promotional material and office stationary is gloss finish paper. It comes in a slight gloss or matt effect. This is achieved through what is known as dispersion coating – a form of print coating we will examine in this article.
After the actual print process, in which the four colours Cyan, Magenta, Yellow and Key (CMYK) are placed successively on the paper to create the actual image, the printed sheet is often coated with print coating. Therefore the printing and coating often take place in the same machine. One of the aforementioned colours can be found in each of the first four printing units, in the fifth – the coating unit – the dispersion coating is applied. Sometimes the coating is also applied via a dampening unit or an inking system in the printing press.
In the photo below you can see a typical coating unit in the foreground, which is slightly smaller than the inking system. It is an 8 colour printing machine for the double-sided printing of the sheet in a single process.
Definition of dispersion coating
Dispersion coating refers to a print coating which is applied to the paper after printing. The purely physical drying takes place very quickly, as the hydrous constituent parts evaporate or absorption occurs. This process can be accelerated through the input of heat. The coat provides the print product with either a more glossy or matt look and generally contributes towards an improvement of the characteristics of the paper.
Composition
As already mentioned dispersion coating has a more watery consistency compared with other print coating. It contains polymer dispersions, finely distributed synthetic resins, hydrosols, wax dispersions and film formation aids along with wetting agents and defoamers. Dispersions refer to mixtures of at least two substances of varying amounts. The water-soluble resins stick together during drying through the evaporation of the water and in this way the smooth surface is formed. We generally find a chemical mixture of substances which are not soluble into each other.
Advantages of dispersion coating
Alongside the aforementioned enhancement of the surface finish (glossy or matt), the product is also protected against abrasion by the dispersion coating and is provided with a slightly water-repellent surface. Furthermore the paper does not yellow with age as it is sealed together with the ink through the coating. Consequently the ink does not set off, which means it does not leave ink on the printed sheet above it. Processing such as creasing and grooving and film embossing are also possible, as the coating on the paper remains elastic.
The only disadvantage is that it is harder to write on flyers, business cards or post cards with a ballpoint pen or fineliner after coating. Stamping or printing via an ink-jet or laser printer is difficult because it takes longer for the ink to dry and it quickly smudges.
Use and range of application
Depending on the combination of the individual raw materials the characteristics and viscosity of the coating can be influenced. The print coating is either applied fully or applied as spot coating where only certain areas are coated.
great post. pls comment below to ask any questions
ReplyDelete