Thermography is the technique of spreading thermal powders on the wet ink of a print application and heating it in order to melt the powder in to a single solid mass which is raised above the printed surface. It is also called "imitation engraving", however an engraving die is not needed with thermography. The technique is faster than engraving and it is less expensive.
Applications
Thermography can add value to lots of ordinary print applications. Among the lots of applications that can benefit from thermography are letterheads, greeting cards, invitations, business cards, promotion applications, announcements, and envelopes. Thermography can make the appearance of lots of print applications more unique, providing a custom-made appearance that cannot be achieved with any other technique.
Thermographic Technique
Thermography is thriving when the powdered resins are applied to a printed surface on which the printing ink is still wet. This allows the powder to stick to the printed areas. Any powder on non-image areas and any excess powder on the picture areas is suctioned off the substrate before the heating takes place.
The heat is produced with electric heating elements that are placed inside an oven or tunnel. The powdered substrate passes in to the heat tunnel where the powder melts onto the heated substrate and is fused with the wet ink. The substrate must be raised to the temperature of the melting point of the powder in order for the technique to work correctly. When the heating technique is complete, the sheet is cooled and the melted powder hardens in to the raised thermographic picture.
Important points to think about when designing a project for the thermographic technique include:
Thermography won't improve or mask the flaws of a poor design or a poorly printed application.
Type sizes less than 6 point ought to not be avoided because they can fill in. Type faces that are fine can also fill in.
Sizable solid areas & small type ought to be avoided on the same page because each of the elements requires a different type of resin.
Lots of print applications using thermography may require special techniques for trimming because the raised print makes it difficult to cut stacks of thermographed sheets using a standard guillotine cutter. The cost of trimming thermographic applications may be more pricey than print projects without thermography. Some applications such as business cards (which are printed with lots of per sheet) are sent through special slitting machines in order to be separated.
Sizable wholesale thermography companies handle sizable volumes of standard items & are the most cost effective source for standard products, but they may not offer specialized or custom-made thermography.
Thermographic Powders
Thermographic powders are made from plastic resins which were introduced in the 1970's. They have taken the place of resin materials that were historically manufactured with a base made from ground tree sap. There's a selection of thermographic powders obtainable that produce an countless variety of effects. The powders come in lots of particle sizes to suit any application. A choice of finishes, such as gloss, semi-gloss, semi-dull, & matte are also obtainable.
Types of Powder
In addition to standard powders, the following types of thermographic powders are obtainable:
Metallic Resin: Metallic resin powders produce a metallic sheen after being melted & they are less pricey than foil stamping. Metallic resins are unaffected by the color of the paper stock & they are well suited for dark colored paper stocks. Applications include presentation folders, marketing, & announcements. Metallic resins come in silver, gold, bronze, & copper.
Glitter: Glitter can be added to thermal resins to produce a sparkling effect after processing. Depending on the application, the glitter can be varied for different effects.
Varnish: Varnish can be applied as an all over coat on applications such as color technique jobs to give the color images a thermographic appearance.
Pearlescent Resin: Special ingredients are contained in pearlescent resin along with pigments to produce a pearlescent sheen after the application is processed.
Static Resistant: The build up of static electricity on the application is reduced with the use of static resistant powders.
High Viscosity: A high viscosity powder is used to maintain the detail on images that are made up of fine lines.
Laser Safe Powders: drawback with standard resins is that the raised coatings on applications such as letterheads can remelt in the event that they come in contact with other heat producing equipment such as laser printers & photocopiers. Laser safe resins are treated with ultraviolet light after they are applied & melted on the substrate. This gives the resins the ability to be unaffected by additional heat sources.
All of the above powders can be used alone or they can be combined in various ways to produce multiple effects. For example, adding glitter to metallic resin produces a sparkling effect on the metallic finish. Most resins can be mixed with a variety of substances such as tinsel, sequins, & diamond dust to generate even more effects.
Particle Sizes
Different particle sizes are obtainable ranging from fine to coursework. Fine powder is used on images with fine detail & narrow lines. Heavier images can be processed with coursework powder.
Additional Fine: Used for fine details & type sizes 14 point & smaller.
Fine: A fine particle can be used for most purposes except the finest details & it works well with type sizes from 12 to 30 points.
Medium: Used for solids & types sizes from 24 to 42 point.
Coursework: Large solids & type sizes over 36 point are well suited for coursework powder.
Equipment
Table Top Models
Table top machines were developed in the 1970's which made it simpler for more print manufacturers to offer thermography as an option for their customers. Some table top models involve mostly manual operations to produce the thermographic images. The powdered resins are applied to the printed sheet by hand & the excess is shaken off the sheet. The sheet is placed in the thermographic unit which is fundamentally a heat tunnel. The sheet is removed & another sheet is placed in the machine. This can be a very time consuming method & may not be economical to make use of on runs over a few hundred unless a job is printed with lots of images per sheet such as a business card application.
Floor Models
Larger floor models are fully automated & are attached to & synchronized with press equipment in order to eliminate manual procedures. The printing press may require to be equipped with slow down pulleys in order to be properly synchronized with the thermographic unit. The desired speed of the equipment depends on the design of the application, the materials used, & the type of equipment used for printing the application & for producing the thermographic picture.
Paper Stock
Some points to think about when selecting a paper stock suitable for thermography are weight, moisture content, color, and texture. Don't assume that any paper stock can be used. Some paper stocks are not suitable for thermography chiefly because of the high temperature necessary for the technique. Paper stocks must be able to be heated to at least 250 degrees Fahrenheit in order for the technique to work properly because the heat on the paper is what melts the resin. Paper stocks such as twenty lb. bond cannot handle the high temperature without adverse effects. The amount of thermographic raise that is achieved also changes depending on which paper stock is used.
Paper stocks ought to have a hard surface and a low moisture content. Excessive moisture in the paper may cause the paper to curl when it is subjected to high temperatures. Curling can also occur when uneven heating is applied to the paper. Curling often happens when side of the paper is heated more intensely than the other side. Excessive moisture content in the paper can also leave the thermographic picture with a cloudy appearance due to moisture being released from the paper in the coursework of the heating technique and being trapped in the thermal coating. Paper that has a moisture content which is low may absorb the ink so rapid that the thermographic powder may not stick to the ink.
The heavier and thicker the paper, the more heat is necessary to raise the temperature of the paper to the melting point of the thermal powder. Some heavily textured stocks may need special resins in order to produce a smooth thermographic finish over the printed areas.
Ink
The quality of the ink and the quality of the printed picture are directly related to the degree of quality that can be expected when applying thermography to the application. The ink ought to be tacky (sticky) when entering the thermographic device. The tackiness of the ink is what causes the thermographic powder to adhere to the printed surface before it is melted. If the ink is not tacky , the vacuum used to remove excess powder from the non-image area can also remove a number of the powder from the picture area leading to substandard thermography. The press operator may must run more ink and/or less water than normal to accomplish the proper ink coverage and ink tackiness necessary for thermography and yet the coverage must not be so great as to produce setoff on the back side of the printed sheet. Thermography works best when as much ink as feasible is laid down on the paper with a maximum amount of impression. Inks with tiny or no drier additives are well suited to thermography because the ink stays wet longer and the ink acts as the adhesive for the thermal powder.
(Gold Printing Group)