Contents copyright 2005 Davis Multimedia Intl. Inc. all rights reserved.
The following information is presented here courtesy of The Engravers Journal. More information may be available by visiting the EJ web site (www.engraversjournal.com) and checking out EJ’s archive of articles (1975-present). Key word searches may be performed using the EJ Index of Articles, and most back issues (1975-present) are available.

PLASTIC—OVERVIEW

Today’s manufacturers can choose from hundreds of varieties of plastic materials used to manufacture a variety of items. For direct part marking (DPM) applications, several plastic-marking methods are available, including laser engraving and mechanical engraving, pad printing, hot stamping and others.

Plastics differ greatly in their chemical and physical properties. Most plastics are categorized as "thermoplastics" in that they soften and melt in the presence of heat and re-solidify upon cooling. The other type of plastic is referred to as "thermosetting" plastic. Thermosets are actually cured through the application of heat and, once cured, don’t soften when reheated.
The marking options for DPM of plastic parts varies widely with the type of plastic and the addition of additives, such as plasticizers, designed to change the physical or chemical properties of the material.

Many plastics are commonly referred to as "laser friendly" in that they can be lasered easily with a quality cut and with no adverse effects on the environment or on the equipment. Some plastics, in particular poly vinyl chloride (PVC), are regarded as "laser unfriendly" due to the fact that lasering them creates fumes which are hazardous to breathe and harmful to optical and mechanical components of the engraving equipment. For laser marking applications, CO2 lasers are generally preferred for all plastics.

Most plastics can be mechanically engraved using a rotating cutting tool or end mill, although a liquid, mist or air coolant is sometimes required to prevent melting, i.e. where a glob of molten plastic adheres to the cutter tip almost immediately after starting the cut, particularly when cutting thermoplastics which have a low melting point. This is especially common when rotary engraving injection molded parts.

Plastic engraving stocks are all especially well suited for UID nameplate and labeling applications. Available in various thicknesses from .005" up to _" and in hundreds of color combinations, including simulated metallics, most engraving stocks are somewhat pliable thermoplastics which are formulated for either rotary engraving, laser engraving or, increasingly, for both.

Most engraving stocks are either laminated (conventional) or coated (microsurface) materials available in 2- or 3-ply construction consisting of a thick core layer in a particular color and either one or two contrasting-color surface layers. With traditional laminates (used mostly in mechanical engraving) when you cut through the surface layer, you expose the second-color core layer, which averages approximately .008" in thickness. Microsurface engraving stocks typically have a surface coating approximately .0025" thick, allowing for very shallow engraving depths of .003" or greater and high definition images. One of the chief advantages of plastic engraving stocks is they provide a high contrast mark without the use of contrast enhancers such as paint fillers.

Thermosetting laminated engraving stocks are commonly called "phenolic," or "bakelite." Thermosetting plastics are commonly in the melamine family, the same chemical group as used in high pressure laminates used as countertop laminates. Most thermosets are not well suited for lasering, at least when a deep cut is required.

Generally thermoplastics support combustion and will "burn" when heated to the point of combustion and will continue combustion even after removal of the combustion source. When heat is applied, thermosets will generally become degraded and will "burn" as long as heat is applied from an external source but combustion will cease once the source of combustion is removed.