Bar Code Printing
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A LabAutopedia invited article
Bar Code Printing
Authored by: Niels Wartenberg and Susan Snyder; Microscan Systems Inc.
Media
Before selecting a printing method, it is important to note that a label is not just a label. Labels consist of specific layers. Any variation in one of the layers changes the media’s application. This is particularly important in the life sciences where labels must withstand many different changes in the environment, depending on the application. For example, bar code labels on microplates are often subjected to extreme environmental conditions. Freeze/thaw cycles and exposure to chemical solvents can affect the integrity of the adhesives.10 Tables 2 and 3 provide reference information on the environmental performance properties of 1 mL polyester.
| Environment | Test method | Typical results |
|---|---|---|
| High service temperature* | 30 days at elevated temperatures | Slight discoloration at 230°F (110°C), no visible effect to print. Material discolored but functional up to 266°F (130°C) |
| Autoclave | 3 cycles of 1 hour in 250°F (121°C)/15 psi pressure cooker and 23 hours at room temperature | No visible effect after 3 cycles |
| Liquid nitrogen | 3 cycles at 4 hours at -320°F (-196°C) and 20 hours at room temperature | No visible effect after 3 cycles |
| Freezer | 3 cycles of 16 hours at -94°F (-70°C) and 8 hours at room temperature | No visible effect after 3 cycles |
| Liquid nitrogen to boiling water | 1 hour at -320°F (-196°C) then placed in boiling water 212°F (100°C) for 10 minutes | No visible effect |
| Freezer to boiling water | 1 hour at -94°F (-70°C) then placed in boiling water 212°F (100°C) for 10 minutes | No visible effect |
| Objective observation of visual change | ||||
|---|---|---|---|---|
| Effect to label stock | Effects to printed image | |||
| Chemical reagent | Flat | Wrapped | Without rub | With rub wrapped |
| Ethanol | No visible effect | No visible effect | 1 | 1 |
| Toluene | Slight adhesive ooze | Slight adhesive ooze | 1 | 1 |
| Isopropanol | No visible effect | No visible effect | 1 | 1 |
| Chloroform | Adhesive ooze | No visible effect | 1 | 1 |
| Xylene | No visible effect | No visible effect | 1 | 1 |
| Dimethylsulfoxide (DMSO) | No visible effect | Slight adhesive ooze | 1 | 1 |
| Methylene chloride | Adhesive ooze | Slight adhesive ooze and label unwrap | 1 | 1 |
| 50% acetic acid | No visible effect | No visible effect | 1 | 1 |
| 10% hydrochloric acid | No visible effect | No visible effect | 1 | 1 |
| 10% sodium hydroxide | No visible effect | No visible effect | 1 | 1 |
| 10% chlorox solution | No visible effect | No visible effect | 1 | 1 |
Printing
The printing options available to laboratories can be placed into two categories. The lab must first decide whether to print the labels themselves or have them pre-printed. There are two common methods of off-site printing. Preprinted labels can be purchased from a label manufacturer and then applied on site either by hand or by an automated machine. Or the lab can choose to purchase pre-labeled plates from a plate vendor. Some vendors also offer microplates with pre-marked individual wells.[1]
Off-site printing is best for large volumes of labels containing fixed data that does not change. Print-ondemand, on-site printing is better suited for small to medium volumes of labels or for applications with variable data. There is less waste involved, and the time required for inventory management of label stock is minimal. There are several different print-on-demand methods of printing available to laboratories:
Dot matrix drives a small round pin into an ink ribbon that makes contact with the media. Advantage: It is inexpensive and readily available. Disadvantage: It generates poor print permanence and poor print quality. It also has high maintenance costs and typically is not compatible with chemically resistant labels.
Laser printing can be described as the surface of media exposed to an optical image, which generates an electrostatic image that is brought into contact with toner particles.
Advantage: It’s the most common method for printing bar codes. The equipment is readily available and it produces an excellent quality bar code. Disadvantage: Laser printing has low print permanence and higher costs due to more expensive media and a higher percentage of media waste. A full sheet of label stock must be used, regardless if one label or a sheet of labels is needed.
In the Thermal Transfer printing process, the print head comes in contact with the ribbon that releases ink above certain threshold temperatures. The image is created by heat generated by the printhead that is then transferred to the ribbon. Advantage: Thermal transfer printing produces the most stable image for a variety of environments. A wide variety of substrate and ribbon formulations meet the needs of many applications. It is also an economical print method and provides increased control of waste while delivering excellent print quality. Disadvantage: Since thermal transfer offers so many options, operator training is generally recommended. Routine maintenance is critical to maintain optimal print quality.
References
- ↑ Bar Coding Introduction for Drug Discovery/High Throughput Screening. http://www.hudsoncontrol.com/products/barcode_intro.htm. (accessed June 2003)
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