Flexography
Flexographic printing uses flexible printing plates and the application of liquid ink, as opposed to paste ink. The printing plate is commonly backward reading to impart a correct reading impression on the plastic part. However, a correct reading printing plate is used to print on the backside of clear film, which reads correctly from viewing. Flexographic printing most often utilizes rotary methods and is limited to a single color per pass. Multi color systems are created by mounting color stations around a common drum or in tandem.
Dry Offset
This method is based on a rigid, correct reading printing plate with a raised image. The ink is paste. The image is transferred to a smooth piece of elastomer material known as a blanket, which accepts the ink from the printing plate and transfers the copy to the part. Dry offset printing, where flat bed or rotary is capable of printing either single or multi colors. The offset blanket can engage a tandem series of printing heads, each of which applies a separate color to the blanket. The complete design, now superimposed on the blanket, is transferred to the plastic part in a single pass.
Gravure
Liquid ink is flowed into the backward reading depressed etching that forms the image in gravure printing. A knife-like doctor blade next removes any excess, and the ink left in the depression is then transferred to the substrate.
Rotogravure
In most printing applications involving webs (continuous plastic sheets or films) gravure printing is limited to a rotary process (rotogravure). Here too, printing is limited to a single color per pass. Multi colors are accomplished by printing in tandem or around a common impression cylinder.
Rotogravure Offset
This process, like dry offset, utilizes a blanket. The ink from the correct reading, doctored, depressed area is transferred to an elastomeric material, normally silicone, which prints the impression on the plastic substrate. The process is rotary with multi colors normally achieved through the use of tandem stations.
Flexapex Process
This process, like dry offset, utilizes a blanket. The ink from the rigid, correct reading printing plate with a raised image, is transferred to a smooth piece of elastomer material known as a blanket, which accepts the ink from the printing plate and transfers the copy to the part. The main difference, when compared to dry offset, is that the process uses a combination of technologies and liquid inks, metered through anilox rolls to suit the inking density requirements of specific artworks. This process allows printing of heavier, more dense, solids than can be achieved with conventional offset inking systems, providing an ink lay down that is more comparable with silk screening or rotary gravure printing. The process is solvent (VOC) free, which is an important factor in many plants today.
Pad Printing
In this method, the image to be printed is depressed in a flat format. A doctor blade meters the flooded ink from the surface of the correct reading flat plate allowing the pad, a soft silicone material, to accept the ink from the valley. Using a reciprocating motion, the ink is transferred to the part by the pad. Because of the flexible, low durometer nature of the pad, products of unusual shapes and wide tolerance can easily be printed. Multicolors are printed by tandem operations. As with rotogravure and rotogravure offset, pad printing uses high solvent based inks, which allows for multi colors and over printing to be accomplished with relatively short drying distance between the tandem colors.
Screen Printing
All but the image to be printed is opaque on the printing plate, a screen made of tightly drawn fabric with fine openings, originally silk, but now usually other materials including stainless steel mesh. The ink is placed onto the opaque area of the screen, the printing mechanism is a squeegee, generally a semi-flexible elastomer material, which wipes the ink across the screen forcing it through the open area onto the product to be printed. The screen process is limited to a single color per pass and is available both in flat and rotary techniques. Multi colors require repeated passes or tandem processing with re-registering in most cases between colors.
Digital Offset
This is a print technique in which digital images formed by means of desk top processing allows direct on-press printing. As in all offset printing, the ink is first applied to a blanket. In multi color work, each color is applied sequentially with rotation of the blanket drum. All colors are then, in a final rotation of the blanket drum, transferred simultaneously to the substrate. Because each print transfers 100 percent of the blanket's image to the substrate, the blanket may then receive a totally different image from the one just printed.
Hot Stamping
This is a dry process using a relieved, backward reading, rigid, metal plate to print color carried by foil. The dry color is laminated to a carrier, such as mylar, in a roll format with layered coatings that first enhance release and then adhesion. For each impression, a fresh section of foil is delivered by the system to a heated die, which presses it against the product, transferring the image from the die to the product. The systems are available in flat bed as well as rotary versions.
