General Information on Paper Coating

The main reason of coating is to improve the surface quality of paper or board. The excellence improvement can be aimed at optical properties such as brightness, gloss or opacity, at tactile property such as smoothness, but, most importantly, at print-ability and print image value.
imagesThe application of (usually white) pigments to the base paper surface enhances the brightness of the paper. In addition, the opacity increases due to the high light scattering of the pigments. This improves the optical appearance, because the shine through of the back side printing is reduced. Also, the coat layer evens out the surface landscape of the sheet, resulting in an improved smoothness, which in turn gives a better gloss.

The coat layer reduces the diffusion of ink into the paper sheet. Therefore, the ink does not spread as much and the print image is clear and sharp. The print density and the print gloss are enhanced, and the ink insists is reduced compared to uncoated papers.For specialty papers, the coat layer can have functional properties. Examples are the thermo sensitive layer of thermal papers or the capsule containing coat layer of carbonless papers.

The benefits of applying a coating layer become very apparent when comparing paper surfaces with different coatings.coatpapersurface_480 The SEM (scanning electron microscope) micrograph of an 80 gsm wood free base paper shows multiple layers of intersecting fibers. The paper surface is characterized by hills and dales formed by the fiber mesh. The voids between the fibers impair the smoothness and uniformity of the paper surface. The next micrograph shows a percolated paper at the same magnification for comparison.

Paper_CoatingA pre-coating of just 10 gsm per side suffices to cover up the majority of voids and fiber crossings. This helps to smooth and even out the paper surface. Paper surface quality can be further enhanced by the application of a top coat. Coating the paper with another 12 g m–2 per side distinctly enhances the existing pre-coated surface quality, with a number of dominants fiber structures and valleys still remaining visible. Subsequent calendaring achieves an additional quality gain by enhancing smoothness and gloss. The resulting surface is flat, with a minimum of irregularities. An electron microscope picture of a microtome cut from a coated paper sample. In the center of the sheet, the fibers can be seen. The lighter and more densely packed structure on the outside of the paper sheet is the pigments of the coat layers.

coating-impregnating-machines-2The caliper of the coat layer varies according to the changing thickness of the base sheet. The surface is smooth so, by coating, paper and board can be upgraded to a higher quality level with added value.


What type of paper to choose for printing?

So you have got designed your flyer or pamphlet, found an esteemed printer and currently you’re prepared for printing. However the big question is currently what paper stock (paper material) to choose? Should you use a gloss or matt paper or however regarding an uncoated sheet? These area unit necessary inquiries to ask, the right choice of paper will enhance your design and image; the wrong choice could spoil the print job and leave you disappointed. Which one is right to use? But what are all these different papers?

There are basically two main categories of paper used today for printing, coated and uncoated paper.

Coated Paper or board

This paper incorporates a coating applied to either one or both sides of the sheet. it’s typically mentioned as art paper. The coating may be a mixture of china clay, latex and alternative compounds that once applied improve the smoothness of the paper surface giving top quality printing. Coated paper is the natural selection for full color prime quality print work like flyers, brochures or posters. The coating allows for sharp pictures, spirited color and improved ink drying.

Gloss finish (Gloss Art or Gloss) encompasses a shiny coating. This coating permits for fast ink drying and allows for the foremost spirited of colors. Gloss is extensively used for flyers, booklets and posters among others.

Matt finish (Matt Art) is additionally a smooth sheet however with a dull finish. it’s rarely used nowadays, however would be a decent alternative if there are giant areas of text. Some individuals like the unostentatious finish of Matt art as a part of their image.

Coated paper is available during a range of different finishes the main ones being matt and gloss.

Uncoated Paper (offset)

Uncoated paper has no coating applied to the paper. though there are a range of various qualities of finish, uncoated paper still has pits within the surface of the paper. the lack of coating doesn’t provide for the most effective results in full color printing. Drying times also increase once using uncoated paper. this kind of material is best suited to company stationery like letterheads or for newsletters.

Paper weights

Paper is measured, in the UK, as grams per square meter or GSM. The upper the GSM the thicker and bulkier the paper, although paper thickness and bulk will vary greatly between completely different paper brands of identical GSM. Typically silk art is bulkier (or thicker) than a glossy paper of identical weight. Paper weights vary from 70gsm up to 400gsm for the majority of print jobs. Heavier board is offered however not sometimes used for general print jobs.

Generally letterheads are written on either a 100gsm or a 120gsm Uncoated paper, leaflets on a 130gsm or 150gsm, flyers on a 300gsm or 350gsm.

In the A series size of papers, A0 size is one area unit, therefore associate A4 sheet of paper can weigh one sixteenth of the quoted gsm e.g. one A4 stationery written on 100gsm can weigh 6 grams.

A good plan before inserting any print work is to raise your printer to send samples of the paper stock they use, evoke a spread of accessible weights and if attainable evoke written samples on the fabric to grant you a decent plan on the finish.