LABELING

Pressure-sensitive adhesive (PSA) labels are often used in rapid diagnostic devices for point-of-care testing. OEMs who make such devices with PSA labels should consider ways to standardize manufacturing to increase processing accuracy, reduce costs, and maintain quality.

Diagnostic devices, such as triage test devices for diagnosing cardiovascular conditions and single-step drug-screening devices, usually consist of a housing, one or more test strips, and a PSA label. The housing is a molded polymer base with cavities for the test strips. The test strips, which contain reagents that cause chemical reactions, are placed into the housing. A label, which often contains clear windows designed to match the cavities of the polymer base, is attached. The label also seals the housing. Although using PSA labels is not the only way to label diagnostic devices, they do have some properties that make them desirable for this purpose:

• PSA labels provide a platform for information. They can hold directions for use, patient names, and other data for accurate identification.
• PSA labels can serve as a lid to keep the reagents clean and prevent the solution from leaking after the test.
• PSA labels are economical. They can be purchased in small or large quantities. The prices per label (a batch size of 10,000, for example) usually range from six cents to eight cents. In a 100,000 batch size, labels are usually less than one cent each.
• PSA labels enable fast, easy, and economical product changeover (e.g., from one triage type to another).

During the application of PSA labels, certain challenges must be overcome to maximize their potential. Such concerns usually include accurate label placement, processing machine flexibility (i.e., the ability of the machine to adapt to label size and type changes), cleanroom requirements, and in-line integration. Using a standardized assembly system can make the label application process easier.

The Challenges

Accurate Labeling. PSA labels are placed on diagnostics either by hand or by machine. Manual application is an inaccurate process. In addition, it is time-consuming and often results in high rework and scrap rates. Inaccurately placed labels are unattractive. Even worse, a poorly placed label can obscure test results. When accuracy is needed to ensure that diagnostic results are clearly visible, manual placement is usually unacceptable.

Process Machine Flexibility. Different label sizes often require different application techniques. In addition, one device may need more than one type of label. The use of multiple label sizes and types is the primary reason that some manufacturers still opt to apply labels manually.

Labeling machines do not lend themselves to quick changeover to accommodate multiple label sizes. Moreover, these machines cannot guarantee tight tolerances. Custom-built equipment is expensive and often is designed for a single type of label.

A standard platform applicator handles a range of labels, shapes, and adhesives while maintaining stringent placement accuracy. Changeover from one product to another requires changing only the material roll and product-specific tooling.

Cleanroom Requirements. Manufacturing diagnostic devices often requires cleanroom assembly to prevent contamination of the sensitive reagents in test strips. Because labeling is the last step and the labels seal the device, manufacturers sometimes apply them in a cleanroom to protect the test strips from environmental particulates.

Typical label applicators have moving components that can create particles, which could contaminate the test strips. Such applicators are best suited for less-sensitive applications. By contrast, equipment designed for cleanroom use incorporates air valve exhaust ports that are connected to an outside vacuum system. Pneumatic cylinders are attached with vacuum collars around the shafts. Bearings are constructed of stainless steel.

In-Line Integration. Depending on the overall manufacturing layout, the labeling process can be either a stand-alone operation or integrated into a fully automated line. When a cleanroom is not required, a stand-alone system is adequate. Integration makes sense when high production numbers justify fully automatic manufacturing or when cleanroom specifications restrict human contact with the product.

To ease integration, several factors should be considered. A standard interface should enable real-time communication between the labeling equipment and the manufacturing line. Various options (e.g., the ability to orient the machine upside down for placement of the label on the bottom of the device, or an option that enables label assembly at an angle) should make mechanical integration easy and enable optimal adaptation of the equipment to the production line.

A standardized label application platform can be used with a variety of diagnostic devices. The following case studies present two possibilities.

Two-Label Diagnostic Cup

A manufacturer that used two PSA labels on a diagnostic cup required equipment integration, cleanroom capabilities, and accurate and convex placement (see Figure 1).

In this case, one label was placed on the lid of the cup. This placement required equipment integrating onto a rotary table. The label had large cutouts, for which accuracy was crucial: the windows had to align precisely with the cavities of the lid.

To meet these requirements, the manufacturer used a dial table for fully automatic operation. (The test strips were first placed into the lid, and then the lid was placed on the cup). Because the strips were sensitive to contamination, the cup had to be assembled in a cleanroom. To complicate matters, short cycle times were required.

The second label was a temperature strip that was applied onto the side of the diagnostic cup. This part of the process could be done outside of the cleanroom after the assembly of the cup and before packaging. Because the temperature strip was dark, even slightly inaccurate placement would be clearly visible. And because of the cylindrical shape of the cup, placement had to be done in three dimensions to ensure that the label would not obscure the test results.

The temperature strip label contained heat-sensitive indicators designed to react to the temperature of liquid (the reaction had to be nonreversible to show temperature history). These indicators could not be integrated into the cup using any other technology. Labels were the only option.

Both labels were placed on the cup using the same standardized platform. An advanced peeling technology ensured accuracy and repeatability, even when labels were difficult to remove from the liner. The platform also included a customized vacuum chuck.

The operation cycle was as follows:

• A stepper motor pulled the liner through its path in the machine. The position sensor identified a label and ensured the positioning of the label below the vacuum chuck.
• The placement actuator extended to firmly grasp the label.
• The drive assembly retracted, pulling the liner around the peel edge and removing the liner from the retained label.
• The placement actuator put the label onto the fixtured target part. When the actuator returned to its original position, the peel edge was extended again, and the cycle started over.

Once the test strips were placed into the cavities, the lid was assembled onto the cup, and the cup was placed under the label applicator. Through an RS-232 reporting module, the applicator was signaled from the host controller, and the label was peeled by the vacuum chuck and placed with an accuracy of ±0.002 in. onto the cup. With the fully automatic process of assembling the cup, yield was improved significantly. The process reduced scrap and rework energy.

For the outer temperature strip, standards were not as critical, and so it could be assembled at a station outside the cleanroom. An operator loaded the cup into a shielded nest under the placement actuator. The shielded nest enabled safe, automatic placement that was triggered upon insertion of the cup, thereby minimizing cycle time. A conforming chuck was designed to be soft enough to conform to a curved shape. It peeled the flat temperature strip off the liner and placed it onto the cup by gentle, controlled pressure while curving it to the shape of the cup.

Rapid Blood Test Device

The manufacturer of a blood test device used a PSA label in a recessed area of the molded part that corresponded with the label design. This application required accurate placement. There also was a risk of contamination, so the manufacturer assembled the device in a cleanroom.

The production numbers for the product did not justify a fully automatic machine, so the manufacturer wanted a flexible machine that could switch to various label types. A standard platform with a maximum peel capacity of 4.0 × 6.5 in. was selected. The changeover from one product to another could be done in a few minutes by simply changing label rolls and label-specific tooling.

An operator loaded the device into a nest under the actuator and cycled the machine using switches. The label was peeled using the previously described technology so that the label would fit within the recessed area. Figure 2 shows a Smart Scope evaluation demonstrating placement accuracy, which was important because even the slightest inaccuracy would impede the visibility of the test strips. The device itself is shown in Figure 3.

Compared with the previous manual process, the manufacturer significantly increased output and reduced the scrap rate from 4% to almost zero.

Conclusion

Die-cut PSA labels are increasingly being used for special applications, such as labeling rapid diagnostic test devices. Standardization of the placement technology offers various benefits to the manufacturers of such devices.

Standardized machines have established operational criteria, predictable quality, and, perhaps of greatest benefit, quantifiable process costs. They also allow for continuous improvement. In addition, standardized platforms may be used with new products. A standardized machine platform also enables prototyping runs and capability studies to be performed before production, which exposes any design problems early in the process. Finally, off-the-shelf platform assembly machines can be quickly reconfigured.

Gunhild Schiller is marketing manager at AccuPlace (Plantation, FL). She can be reached via e-mail at [email protected].

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