Embossing

Embossing is the process of creating a three-dimensional image or design in paper and other ductile materials.

It is typically accomplished with a combination of heat and pressure on the paper. This is achieved by using a metal die (female) usually made of brass and a counter die (male) that fit together and squeeze the fibers of the substrate. This pressure and a combination of heat "irons" while raising the level of the image higher than the substrate to make it smooth. In printing this is accomplished on a letterpress. The most common machines are the Kluge Letterpress and the Heidelberg Letterpress. The term "impressing" enables one to distinguish an image lowered into the surface of a material, in distinction to an image raised out of the surface of a material. Both are "embossing" per se.

The embossing process can be applied to textiles as non-wovens to get better finished products as sanitary napkins, diapers, tissue paper and others. In printing it is used as an accent process and can be used in conjunction with ink called colour register embossing or with no ink called blind embossing. It also can be used with foil stamping which when embossed with foil is known as combination stamping or combo stamping. All of these processes use a die and counter die. Most types of paper and boards can be embossed and there are no restrictions on size.

Gravure Inks - Solvent Based, Water Based

Gravure inks are fluid inks with a very low viscosity that allows them to be drawn into the engraved cells in the cylinder then transferred onto the substrate. In order to dry the ink and drive off the solvents or water, which essentially replaces most of the solvent, the paper is run through Gas fired or electric fired driers. The ink will dry before the paper reaches the next printing station on the press. This is necessary because wet inks cannot be overprinted without smearing and smudging. Therefore, high volume air dryers are placed after each printing station.

The solvent-laden air from the dryers is passed through either a solvent recovery system or solvent vapor incinerator. A typical recovery system uses beds of activated carbon to absorb the solvent. Saturated beds are regenerated by steam. The solvent laden steam is then condensed and the water and solvent separate by gravity. Greater than 95 percent of the ink solvents can be recovered using this process (Buonicore). The solvents can either be reused or destroyed by incineration.

Water based inks, especially used for packaging and product gravure, require a higher temperature and longer drier exposure time in order to drive off the water and lower vapor pressure constituents. As mentioned subsequent sections, Flexo and Gravure inks are very similar and the constituents are essentially the same. Again, a pollution control device may be needed.


Applications:

Typical gravure printed products include:
Food packaging
Wall paper
Wrapping paper
Furniture laminates
Paneling
Greeting cards
Magazines

Gravure Process Flow Diagram

The major unit operations in a gravure printing operation are:
Image preparation
Cylinder preparation
Printing
Finishing

Gravure printing

Gravure printing is an example of intaglio printing. It uses a depressed or sunken surface for the image. The image areas consist of honey comb shaped cells or wells that are etched or engraved into a copper cylinder. The unetched areas of the cylinder represent the non-image or unprinted areas. The cylinder rotates in a bath of ink called the ink pan.

As the cylinder turns, the excess ink is wiped off the cylinder by a flexible steel doctor blade. The ink remaining in the recessed cells forms the image by direct transfer to the substrate (paper or other material) as it passes between the plate cylinder and the impression cylinder.

The major unit operations in a gravure printing operation are:
Image preparation
Cylinder preparation
Printing
Finishing