METHOD DEVELOPMENT AND APPLICATION TO STANDARD TEST METHODS A N ANAL YTICAL A P P R O A C H TO STANDARD PERFORMANCE TESTING OF PSA TAPES

Jane Workinger, Analytical R&D Group Leader, Adhesives Research, Inc., Glen Rock, PA

Introduction Standard test methods are widely used by industrial laboratories to establish performance

criteria, to assess conformance to a requirement, and to solve problems. Frequently, the data generated does not predict how well the product will function in a particular application or the data generated is too variable to be meaningful. This situation occurs for various reasons. Sometimes the specifics about the application are unknown so it is difficult to choose the appropriate test parameters. Other times a standard test is performed without considering the application. When this occurs a standard test is chosen based on experience, simply because it measures an attribute which is understood to be important in the industry (e.g. 5 minute dwell, 180 ° angle peel adhesion test is commonly used in the PSA industry).

Improvements in performance testing can be made by employing method development principles to standard test methods, when applied to new products or materials. During the method development process, the optimum test parameters are identified to ensure applicability and reliability of the data. This paper will outline the method development process and demonstrate how this process is useful when applied to standard test methods.

Background For the purposes of this paper, standard test methods are those methods which have been

compiled by organizations like American Society for Testing and Materials (ASTM), Pressure Sensitive Tape Council (PSTC), Technical Association for the Pulp & Paper Industry (TAPPI), U.S. Pharmacopeia (USP), Environmental Protection Agency (EPA) and Association of Official Analytical Chemists (AOAC). These methods are classified as standard because each one has been subjected to studies to demonstrate that the method has met its intended purpose and has met established requirementsto verify that the method is accurate and reliable. These standard methods are made available through various compendia and publications to be used by scientists in their work.

However, without the appropriate studies, issues can arise when standard test methods are used to evaluate materials that are different from what was intended. Some issues that may occur are"

* Accuracy may be compromised by sample matrix effects (i.e. variation in adhesive thickness or composition impacts accuracy in static headspace gas chromatography) o Precision may not be adequate to determine significant differences between production batches

of the same material o An impurity may be present which interferes with quantifying the component of interest

It is important to assess the applicability and reliability for each new material and determine if the method is suitable, under the appropriate conditions, for the intended purpose. Otherwise, the data generated by the method may not be relevant to the application, may not be capable of assessing the quality nor be helpful in solving a specific problem. When applying standard methods to new materials,

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the user should optimize and characterize a standard test method for their specific application and verify its suitability. It is important to characterize the test method of analysis before relying on the resulting data to characterize the product.

The Method Development Process Method Development & a seven-step process that determines test method capabilities through selection and optimization of analytical test parameters (see Table 1). lt provides a high degree of assurance that the test method will meet or surpass the established requirements. The method requirements are the means f or judging whether the method has met the needs of the intended purpose.

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Step 1 Define the Motivation or Rationale Questions or thoughts to consider in defining the motivation for developing a new method or adopting a standard test method include the following:

• Why is there a need for a new test method or why adopt this standard test method? • What is the rationale for performing this test? • Is this attribute critical to the functionality of the material? • How much do you know about the application? • What properties do the materials have? • Are there materials properties that can be used to advantage in the method, (e.g. UV

wavelengths of detection, or the backing material on a PSA tape is sufficient for testing without additional sample preparation)?

• Can optimal ranges or targets be established before method development begins? • What information is needed? • How will the information be used? • Will the test method be used to assess the quality or to solve a problem?

The motivation or rationale defines the intended purpose of the test method. Therefore, the reason for performing the test should be clearly defined. It is essential that the test method meet the intended purpose at the end of the method development process

Example: Adhesion has been identified as a critical attribute for a specific application. Based on customer feedback, on several prototypes, it was determined that there is an optimal level of adhesion. If the adhesion is too high or low, the tape does not work for the application. An adhesion test is required to establish specification limits and to monitor the performance of the tape after commercialization.

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Step 2 Establish Goals for the Test Method The test method requirements and the quality characteristics of the data produced when the method is performed need to be determined. A good understanding of what is required of the method is critical to choosing the proper technique. Questions to consider include the following:

• Is qualitative identification of a single component required? • Is quantitative determination, at trace levels, which are accurate, precise, and

reproducible necessary? • How sensitive does the technique need to be? • How accurate, precise and reproducible does the method need to be? • Is rapid analysis time necessary? • Will the test be performed by more than one laboratory?

By answering these questions, goals can be established. The goals define the requirements for the method..Ultimately all of the goals will be met at the end of the method development process. The goals will be used to ascertain whether the test method is suitable for the intended purpose.

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Example: The adhesion test method must be capable of measuring adhesion to plastic, reliably, at levels between 8 and 20 oz/in and will be used by several Quality Control laboratories.

Once it is understood why a test needs to be performed and what the data should reveal, the next step is to select an analytical approach or a standard test method.

Step 3 Select an Approach or Standard Test Method Based on the information from steps 1 and 2 select a suitable analytical approach. If available, choose a standard test method that is appropriate for the analysis on similar materials. It would be inefficient to develop a new method if a suitable method exists. It is common practice to begin method development with a standard test method and make slight modifications or improvements as needed. As mentioned earlier there are several organizations that has compiled standardized methods. Employment of a standard test method can save a lot of time and effort. Always consider using a standard test method first.

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Example: PSTC-1 "Peel Adhesion for Single Coated Pressure Sensitive Tapes at 180°Angle ''1 is the selected standard test method to measure adhesion on a prototype tape.

If a standard test method is not available, it may then be necessary to develop a new test method. Some reasons to develop a new test method are:

• Standard test methods are too prone to error or are unreliable (poor accuracy or precision). 2 • Standard test methods are too expensive, time consuming, energy intensive, or unable to be automated. 3 • Standard test methods do not provide adequate sensitivity or analyte selectivity in samples of interest. 4 • Advances have been made with newer analytical techniques or instrumentation, which provide opportunities for improvement. 5

6 • Necessity to confirm original result by an alternative method for legal or scientific reasons.

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Example: A new compound has been synthesized. A method is needed which is very specific to this new compound in several matrixes. No standard test method exists. Based on the characteristics of the new compound and the matrixes, it is believed that High Performance Liquid Chromatography (HPLC) is a viable approach.

Step 4 Literature Review Perform a comprehensive literature search for available information regarding the selected analytical approach. Benefits of performing a literature search include the following:

• Determination of whether a standard test method already exists using the proposed analytical approach. • Acquisition of an up-to-date understanding of similar analytical approaches used to solve a similar problem or measure the same attribute. • Identification of critical test parameters, those operating factors that when varied, significantly affect the results, such as a specified operating temperature range. • Insight into analytical performance characteristics. For example, methods, that have been developed and validated for a very specific analysis, typically include information on method accuracy, precision, robustness and ruggedness. • Additional information on instrumentation requirements, sample throughput, etc. found, is also valuable in assessing the proposed analytical approach.

The method selected should satisfy the criteria identified in Steps 1 and 2. The information obtained is useful in determining the suitability of the method for a given application.

Even when a standard test method has been selected, a literature search may be useful to verify its suitability for the intended application. Pay particular attention to any reported information regarding the analytical performance characteristics and the critical test parameters that are identified in the test procedure. If the intent of the standard test method is for application to a wide variety of similar materials, the less likely the method will contain information specific to method validity and error. This is because the data elements are dependent on the material tested. Unless the published procedure pertains specifically to the identical material of interest, the user should optimize and characterize the method for the specific application.

If the approach or test method chosen is performed routinely in-house, a review of available historical data for application of the method to similar types of products may yield valuable insight.

Example: Following is a list of pertinent information found in PSTC-1 "Peel Adhesion for Single Coated Pressure Sensitive Tapes at 180°Angle"7: 1. Test specimen size, conditioning, selection, and test conditions are specified: 2. How and where the sample is taken is importantl 3. Several types of equipment are specified with accompanying requirements. 4. Panel cleaning is important and a cleaning procedure specified. 5. Air entrapment must be prevented during application of the tape to the panel. 6. Special laminating instructions for samples under 1" wide are included. 7. Dwell time after lamination is critical. 8. Pull speed and angle are specified. 9. Describes which values to discard and which ones to report.

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Step 5 Optimize the Method Critical test parameters need to be identified and evaluated through experiments designed to determine a suitable operating range for each one. Earlier, critical test parameters were defined as the operating factors that, when varied, significantly affect the results. Critical test parameters usually have defined limits for optimum results.

Characterization of the selected test method begins by performing preliminary experiments. If available, evaluate standards by the selected analytical approach. For materials where standards are not available, prepare or select control samples to be evaluated by the proposed method. Control samples should be as ideal as possible to minimize specimen variability. The intent of these experiments is to establish an appropriate operating range for each critical test parameter identified which, when established, will adequately demonstrate that the method is suitable for the intended purpose. Include enough replicates to determine measurement error. During the optimization studies, it is important to remember the goals of the method. Verify that the instrument meets the requirements of the method.

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Example: The motivation for using the method of choice (PSTC-1) is to establish specification limits and to monitor the performance of the tape after commercialization. The goal is to measure adhesion to plastic, reliably, at levels between 8 and 20 oz/in and several Quality Control laboratories will use the method. Since the test method will be performed at various laboratories and not all laboratories have precise environmental control; experiments will be performed under a range of environmental conditions to determine the effect on the results. Due to the tight specification range, the instrument sensitivity is critical, so an instrument sensitivity requirement will be specified. Because adhesion to plastic is critical, customer supplied panels will be used for testing. Panel qualification protocols, including cleaning procedures, will need to be established. In some instances the customer will be removing the tape in order to rework parts. Therefore experiments will be designed to evaluate various dwell times, pull speeds and pull angles. Other test parameters to consider for PSTC-1 is sample thickness (backing and adhesive) and backing stiffness.

Method development activities should be documented including the rationale used for designing each set of experiments being evaluated and a conclusion for each. These records will be invaluable for trouble shooting problems after the method is in use and will aid in the development of validation criteria if formal method validation is required.

After the optimization is complete, a complete description of the optimized method should be written to include instrumentation, operating conditions, procedure and equations for calculating final results. The written method will be followed during Step 6, the characterization step.

Step 6 Characterize the Method The characterization step involves the design and execution of additional experiments to study the capability of the optimized method by measuring the appropriate analytical performance characteristics or data elements. Analytical performance characteristics or data elements are the statistics or information that explain the behavior and quality of the analytical method

The analytical performance characteristics or data elements that are necessary to demonstrate the method is capable of meeting the requirements must be identified. The data elements outlined in Table 2 should be considered to demonstrate the validity of a test method. These data elements are appropriate for a wide variety of quantitative and qualitative analytical test methodologies. Precision, ruggedness and robusmess are typically used to demonstrate the suitability of

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performance tests. A more in-depth review and determination of these data elements can be found in "The Official Compendia of Standards" published by the USP. 8

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Table 2. Data Elements

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Once the data elements are identified, experiments can be designed and conducted to assess optimized method performance. Standards or control samples should continue to be used to maximize the sensitivity, quantitation limit, accuracy, precision, ruggedness and robustness and minimize detection limit. The results generated during these experiments will be used to establish requirements or validation criteria, which will be used to judge the validity of the test method.

This is an important step when developing a new or improving a standard test method. The method capability needs to be characterized prior to setting specification limits for a material or component. An understanding of the data elements for a given method is required to determine whether the method can discriminate between a product that is suitable or not for the intended application. When measurement error is too great, the test method will not be reliable.

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Method optimization and characterization are the most time consuming steps in the method development process. "They require an iterative procedure to be followed, constant replication, and a large amount of quantitative data. ''2° However, the time is well spent when the method is shown to meet its intended purpose reliably.

Example: For Standard Test Method PSTC-1 the data elements required are precision, robustness and ruggedness. Experiments will be designed to determine precision at the ideal conditions determined during Step 5. The ideal conditions chosen were 20 + 2.5 minute dwell, 135 ° + 2 ° pull angle and pull speed of 12 + 0.5 in/min. Variation in the environmental conditions explored during Step 5 did not cause a significant difference in the results so environmental conditions will not be included in the robustness studies. The adhesion built rapidly during the first 5 minutes of dwell, after lamination, and then leveled off. If the peel adhesion test is performed within the 20 + 2.5 minute dwell established, the results will not vary significantly so dwell time will not be included in the robustness studies. Slight variation in pull angle did significantly affect results so experiments will be performed, to demonstrate robustness at 135 ° + 2 °. These experiments will be used to measure the error associated with normal variation in peel angle. The pull speed, 12 + 0.5 in/min, must be within the instrument capabilities and will not be part of these studies. Ruggedness studies will include lab to lab, analyst to analyst, instrument to instrument and day to day.

Step 7 Finalize the Method The final step in the method development process is to evaluate actual samples, by the new or improved standard method, confirming the suitability for use. Experiments should be designed to challenge the test method. Evaluate the optimized and characterized method by testing actual sample extremes where possible. For instance, if there is a tolerance for the thickness of the adhesive layer on a backing, evaluate samples at the upper and lower limit. It may be important to determine if the test method can differentiate between products manufactured at varying processing conditions and whether the method is capable of measuring the differences in samples that have been altered slightly.

Make any final adjustments, to the procedure, to address any problems encountered while evaluating actual samples. Additional experiments may be necessary if the adjustments are outside the scope of the studies performed during the optimization and characterization steps. Some of the optimization and characterization studies may need to be repeated using the adjusted procedure.

A comparison of the results generated using control samples, from the characterization experiments (Step 6), versus the results for actual samples can be used to establish test method error inherent to the procedure versus error from sample or product variation. It is important to understand how well the test method can discriminates between different sample populations. Where appropriate, it should be verified that the method error is allowable for the proposed specification limits.

The documented test method should be revised to include any changes made to the procedure during the finalization step or to add any additional information, which may be beneficial to the user. In addition to specific information on the requirements for instrumentation, operating conditions, steps of the procedure and the equations for calculating final results, include any information, which is critical to successfully apply the method. For instance there may be a very specific way to prepare the sample where the outcome is increased accuracy and precision.

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When the combined studies sufficiently demonstrate that the test method has fulfilled all of the original goals and requirements (Step 1,2 and 6), the method can be deemed valid and suitable for the specific intended application.

For some industries regulated by government agencies, it is required to formally validate the newly developed or improved standard test method. "Validation of a test method is the process by which it is established, by laboratory studies, that the analytica,!performance characteristics of the method meet the requirements for the intended application. 21 Formal validation requires additional studies beyond the method development studies. There are many approaches to the method validation process but there is no single validation approach, which satisfies every need. It is up to the individual to choose the correct validation approach to satisfy the appropriate regulatory body. Although method validation is beyond the scope of this paper, it is worth noting that the method development process provides a foundation adequate for establishing validation criteria and designing validation studies.

Summary and Conclusions By applying the seven-step method development process to standard test methods, improvements

in testing can be achieved. During the first and second steps of the method development process the motivation and goals are clearly established. It is important to understand the purpose for the measurement and quality requirements of the resulting data before selecting a standard test method. After a standard test method has been selected, information found through a literature search, which is specific to the proposed standard test method can save time. By reviewing available information, an assessment can be made regarding the suitability of the standard test method without experimentation. The information can be used to design experiments for the optimization step, which explores and defines test parameters. After the critical test parameters are identified and operating ranges established, the new or improved test method is characterized. By completing the characterization step the test method capabilities are realized. The test method capabilities are critical to defining specification limits. In the final stage, actual samples are evaluated using the new or improved standard test method. By evaluating actual samples a determination is made to the suitability of the method and whether the method has met the intended purpose.

After a standard method has been through the process once, applying the method development process becomes easier and more efficient when used again for similar products or materials. The resulting documentation from the first development can be leveraged for developing future method development protocols. However it is important to recognize that the motivation and goals for the method must be reconsidered with each new application. Although the same standard test method may be selected, the intended purpose or method requirements may be different. A questionnaire could be written specific to the industry or types of applications to facilitate completion of Steps 1 and 2. Analysis of historical data may be ongoing as part of Quality Control and be easily accessed as needed. Since the test parameters and data elements will be constant for the same test, the experiments designed for Steps 5 and 6 can be repeated to verify that the material behaves similarly. The number of repetitions may be less depending on the response of the new product. Some products will give consistent results over a wide range of variables while others will not. However, the targets and requirements will vary with each new product. It is therefore necessary to optimize and characterize the method with each new product or material. The data generated is a necessary input when setting performance specifications.

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The uniqueness of materials, products and their aligned applications determine the suitability of a standard test method. By applying the method development process to standard test methods, the data generated is expected to be more meaningful. The consequent improved data quality enables decisions to be made with increased confidence. Not only can problems be identified quickly when reliable data is available but also solutions are easier to develop. The method development process ensures the data applicability and reliability. The outcome is a more in-depth understanding of standard test methods and additional insight gained into the relationship between test methodology and product performance.

Literature Citations

1 Test Methods for Pressure Sensitive Adhesive Tapes; Pressure Sensitive Tape Council: Chicago, Illinois, 1996; pp 23-24. 2 Ira S. Krull, Jeff R. Mazzeo and Carl M Selavka; "A Rationale for Analytical Methodology Development". The American Chemical Society, 1995 3 Ira S. Krull, Jeff R. Mazzeo and Carl M Selavka "A Rationale for Analytical Methodology Development" The American Chemical Society, 1995 4 Ira S. Krull, Jeff R. Mazzeo and Carl M Selavka "A Rationale for Analytical Methodology Development" The American Chemical Society, 1995 5Ira S. Krull, JeffR. Mazzeo and Carl M Selavka "A Rationale for Analytical Methodology Development" The American Chemical Society, 1995 6 Ira S. Krull, Jeff R. Mazzeo and Carl M Selavka "A Rationale for Analytical Methodology Development" The American Chemical Society, 1995 7 Test Methods for Pressure Sensitive Adhesive Tapes; Pressure Sensitive Tape Council: Chicago, Illinois, 1996; pp 23-24. 8 USP 24 NF 19; General Information / <1225> Validation of Compendial Methods, 2000 9 USP 24 NF 19; General Information / <1225> Validation of Compendial Methods, 2000 l0 USP 24 NF 19; General Information/<1225> Validation of Compendial Methods, 2000 11USP 24 NF 19; General Information / <1225> Validation of Compendial Methods, 2000 12 USP 24 NF 19; General Information/<1225> Validation of Compendial Methods, 2000 13 USP 24 NF 19; General Information/<1225> Validation of Compendial Methods, 2000 14 USP 24 NF 19; General Information / <1225> Validation of Compendial Methods, 2000 15USP 24 NF 19; General Information/<1225> Validation of Compendial Methods, 2000 16 USP 24 NF 19; General Information/<1225> Validation of Compendial Methods, 2000 17 USP 24 NF 19; General Information / <1225> Validation of Compendial Methods, 2000 18USP 24 NF 19; General Information / <1225> Validation of Compendial Methods, 2000 19 USP 24 NF 19; General Information/<1225> Validation of Compendial Methods, 2000 20 Ira S. Krull, Jeff R. Mazzeo and Carl M Selavka "A Rationale for Analytical Methodology Development" The American Chemical Society, 1995 21USP 24 NF 19; General Information/<1225> Validation of Compendial Methods, 2000

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