05.06.2020
What is surface application and coating ?
Do you know the difference between coated and uncoated paper? Do you know how to define surface application and do you know what this process consists of?
If you do not work in the paper industry, in principle you won’t. Guyenne Papier will explain it all to you!
In this article, we will explain everything you need to know about surface application or coating and why it is an almost essential step for paper manufacturers.
What is coated paper?
First of all, what is "coated" paper?
It is actually a paper that has undergone a transformation called "surface treatment", during which it has been covered with a "coating mixture".
What is surface application and "coating"?
Surface application is a process which consists of coating the surface of a flexible or rigid support with a specific product (for example, a liquid coating mixture, plastics, aqueous or solvent principles...) having the effect of modifying its appearance and properties, providing it with additional qualities: solidity, impermeability, printability, a shiny aspect, etc.
Coating is a generic term which of course applies to paper, but also to other types of media and describes various surface treatments.
In the paper industry, the more specific term used is that of "coating": paper is coated with a mixture usually water based. But other flexible supports can be coated besides paper: film, cardboard, textiles, non-woven materials ...
Coating provides many benefits:
- It provides aesthetic properties: the color, an iridescent effect, a shiny appearance…
- It improves the technical properties of the support: it is smoother, or more water resistant, or it becomes fireproof and fire resistant.
It makes it possible to make a medium suitable for different printing technologies: inkjet printing, thermal transfer or suitable for sublimation printing ...
The coating mixture
The coating mixture is obtained by mixing water, pigments (mineral products), binders and various additives. The pigments give the mixture good coverage of the support, as well as whiteness, opacity and gloss. The bonding agents allow the components to remain mixed together and avoid phenomena such as dusting or poor adhesion of the layer to the support.
What is the difference between uncoated and coated paper?
"Uncoated" paper comes directly from machine-made paper production. It is mainly made up of cellulose fibers. A4 paper reams are a perfect example. Before surface application, uncoated paper is sometimes calendered, which gives it a smoother, surfaced appearance.
Certain paper machines allow in line coating. The coating is carried out just after the manufacturing and drying of the sheet. This in line coating on a paper machine provides new properties to paper. The application of coating mixture is however limited (barely a few grams) and the speed of the paper machine must allow an easy application of the coating mixture.
A good example of in line coated paper are the glossy pages of magazines.
The coating significantly influences the surface finish of the paper.
An example: look at the before / after photos of the surface of the paper here below. When observed under a microscope, it perfectly illustrates the differences.
Left image: uncoated paper. Right image: coated paper
Source: CERIG pagora Grenoble
And there, you tell yourself that the coating of paper is actually really important, no?
Well you are right!
How to sublimate a support by its coating?
Coating allows a multitude of combinations. In addition to treat the surface on one side, two sides or overlapping the layers, it can treat supports from 2g to 30g per coating station. It is also possible to deposit different layers: for example an absorbent undercoat and a glossy top layer.
Coating is the process which makes it possible to create complex supports, and superimposes, like a layered cake, different characteristics.
Thanks to the coating, you obtain papers with superior printing qualities and you can give them very useful properties.
There you are, now you know (almost) everything about coating!
For all your printing needs, think of Guyenne Papier and choose the “Made in France” quality.
Call us at 05 53 62 20 00 or write to export@guyennepapier.fr, our sales team will be happy to advise you.