Preprinted bar code labels can be produced using any printing process. In fact, some preprinted labels are produced using the same printing systems found in on-site printing systems. However, most preprinted label vendors use one or more of the following preferred printing systems because of their speed and accuracy: Film Master/Printing Plate, Ion-Deposition, or Photocomposition.
The film master/printing plate approach to preprinted labels use a very accurate photographically produced film master of the bar code. This film master is used to produce a printing plate, and the plate is used in a variety of commercial printing presses to produce the preprinted label. Since the data coded in the film master bar code is fixed, This system cannot produce sequences of bar coded serial numbers, or bar coded variable, customer supplied data.
Ion deposition is an electrographic, non-impact imaging process capable of printing bar codes and other information on substrates such as paper, vinyl, polyester, and tag stock at very high speeds. The ion deposition printing station operates similar to a xerographic photocopier, except the image of the bar code is electrostatically placed on a dielectric drum rather than optically imaged on a photosensitive drum. Sequential labels and variable data labels can be printed by ion deposition.
The "best" preprinted bar code symbols are produced by photocomposition. The use of the photographic process to produce consecutively numbered bar code labels has some advantages over other commercial production methods. If the primary considerations are: (1) overall quality of the bar code image; (2) high density messages; or (3) flexibility in label size and construction to meet special application requirements, then the photographic process may be particularly suitable.
Because of the cost and complexity of the technology, photographically produced bar code labels can only be produced by preprinted label companies specializing in this printing process.
Photographically printed bar code symbols are produced by special computer controlled photographic printing machines that produce original images of each bar code symbol, not copies. The hardware and software that make up the photographic process are complex. The actual process of creating the image, however, is relatively straightforward.
A moving beam of intense light "strokes" the bar code image through a lens system onto photosensitive material. This is done in a raster fashion, similar to the way a television image is produced. Instructions for creating the size, shape and placement of each individual bar and character are stored electronically in the computer's memory.
After the image is created, the photosensitive material is processed to develop and "fix" the image, much as photographic film is developed into slides or prints. Next, one of a variety of pressure-sensitive adhesives is applied to the back of the image-bearing material.
After the adhesive with its accompanying release liner is applied, die-cutting is done to create individual labels or label sets of the size and shape required. Die making, previously an inexact art, is now a science, and is being aided by lasers and other computer-controlled processes to produce labels to very exacting tolerances.
In most cases, the photosensitive material that bears the bar code image is photographic paper. But unlike a conventional label where ink rests on the surface of the paper, the photographic process allows the image to be formed within the paper. In this way the bar code image is naturally protected from excessive abrasion, smudging, or smearing. Another important advantage in the photographic process is the nature of the paper and the way the image is developed. This means that it will not fade when exposed to sunlight or ultraviolet radiation, important for bar code labels that depend so heavily on contrast between the background and the bars.
Photographically produced bar code image quality remains constant regardless of the material chosen for the photographic process. Typical resolution is 3,000 lines per inch with a bar dimension tolerance of less than 1 mil X-dimension This extremely high resolution makes very high density bar codes possible using the photographic process.
Read more...
