Pressure-Sensitive Adhesive Testing Methods

FIGURE 31. Pressure-sensitive adhesive test methods. 

As with other pressure-sensitive adhesive tests, the temperature is an important variable and tests are typically carried out at room temperature. A variation on this method is the SAFT test (shear-adhesion-failure temperature) in which the test apparatus is placed in an oven where the temperature is set to rise at 4.5°C/min. The temperature at which the tape fails is recorded as the SAFT value. 

Glossary of Terms. Test Methods for Pressure Sensitive Adhesive Tapes, Pressure Sensitive Tape Council, 1996. 

A method of evaluating the adhesive bond to a plastic coating substrate is a tape test. Pressure-sensitive adhesive tape is applied to an area of the adhesive coating, which is... 

Pressure-sensitive adhesives are used in a great variety of applications, most commonly for adhesive tapes. In that case, they have to be tested by static shear test or dynamic shear test The difference between these two methods is that in static shear test a standard force is being applied to the test specimen and the adhesive failure is reported as the time it takes for failure to occur. The dynamic shear test involves a force being applied to the PSA tape at a specific rate of speed (typically 0.25 mm or 0.1 in. per minute). The value reported is as the peak force per unit area (Ib/in, also abbreviated as psi, and in SI units MPa) required to cause adhesive failure. The standards for adhesion shear tests are ASTM D3654, ISO EN 1943, and PSTC-107.i i ... 

Tack is, of course, of great importance for adhesives and many methods have been used. A summary of work on testing and finite element analysis of adhesive tack has been given136 and it has been questioned whether the methods used for pressure sensitive adhesives really work137. 

In practice the methods of test used most frequently are those that measure adhesion. Wechsberg and Webber17 noted that some pressure-sensitive adhesive tapes adhered more strongly to treated rather than untreated film when tape was pressed in the same manner on samples of film and peeled off under controlled conditions with a tensometer, the force required to separate the tape... 

Test Method for Impact Strength of Adhesive Bonds Test Method for Tensile Properties of Adhesive Bonds Test Methods for Pressure Sensitive Adhesive Coated Tapes Used for Electrical and Electronic Applications... 

D 3121 Test Method for Tack of Pressure Sensitive Adhesives by Rolling Ball... 

This test method is preferably used for the comparative evaluation of adhesives and surface pretreatment methods, since it enables the indication of the differences in the adhesive and cohesive behavior of the adhesive layers with high sensitivity. Pressure-sensitive adhesives (adhesive tapes, adhesive labels) are also tested according to this principle. 

It is assumed in almost all cases, that any pressure-sensitive adhesive to be tested has already been applied to a flexible carrier, which is either in tape form, or which can be cut into tapes for testing, virtually all test methods making this assumption. If this is not the case, then it would be necessary to coat the adhesive onto a suitable flexible carrier, usually 25 pm polyester film, which may need to be suitably pre-primed, the prime coat used depending on the adhesive type. The coat weight chosen should be that used for the practical application of that adhesive, or if this adhesive is still under development, then a series of coat weights can be run, to determine which provides optimum performance. An exponential relationship will be found between coat weight and resulting adhesion. 

The need for the physical testing of a pressure-sensitive adhesive can vary considerably such reasons include the determination that a given pressure-sensitive adhesive will perform satisfactorily for its intended use, that it meets a specific standard, that uniformity exists within a given population, or between populations, or that it could be to compare one system to other similar systems—all of which demand that any test method must be accurate and reproducible. The thermoplastic nature of pressure-sensitive systems can make this objective very difficult to achieve, without a full understanding of their behavior and without observing a number of precautions. 

Finally, it should be recognized that, when a stress is applied to a pressure-sensitive adhesive, it is either a tensile stress, a shear stress, or a combination of both. In the specific end use of a given pressure-sensitive adhesive system, a clear understanding should exist as to what type of stresses can be encountered, to ensure that the test methods applied bear a relationship to use. The various standard test methods can now be considered. 

The test methods presently used to evaluate the adhesion of pressure-sensitive adhesives to release liners are modified adhesion tests, such as the 180° or 90° peel test, with the liner adhered to a test panel, or a T-peel test, where the sample is freely suspended while the tape is peeled at a controlled rate from the release liner. The values obtained by the latter method are alfected considerably by the stiffness of the liner, which alters the angle of peel. 

In conclusion, anyone testing pressure-sensitive adhesive systems should not only be fully acquainted with the fundamental characteristics of pressure-sensitive adhesives and the pitfalls in testing to ensure that the data gathered in whatever test method being used are meaningful, but the tester should also develop the skill to manipulate these test methods to meet specific needs. 

Cariflex Polymers for Adhesives, Coatings and Sealants, Shell Chemicals, technical bulletin TR5.1. Cariflex. Starting Formulations and Test Methods for Pressure Sensitive Adhesives, Shell Chemicals, technical bulletin TR5.2. 

ASTM D3121 -94 (1999) Standard test method for tack of pressure-sensitive adhesives by rolling ball. 

A primary method used to characterize adhesives is the lap shear test. A diagram of the test is shown in Fig. 27.1 and is described in Standard Test Method ASTM D1002 [4]. The specimen is usually 1 in. (2.54 cm) wide. The lap shear test places the adhesive in normal as weU as shear stress [5]. This type of test is used for many types of adhesives, with the exception of pressure-sensitive adhesives (PSAs, defined below). In the tables presented later, lap shear strength is presented in units of mega Pascal (MPa) and pounds per square inch (psi). The latter is shown in parenthesis. The temperature of the test will always be room temperature. 

Viscoelastic characteristics of polymers may be measured by either static or dynamic mechanical tests. The most common static methods are by measurement of creep, the time-dependent deformation of a polymer sample under constant load, or stress relaxation, the time-dependent load required to maintain a polymer sample at a constant extent of deformation. The results of such tests are expressed as the time-dependent parameters, creep compliance J t) (instantaneous strain/stress) and stress relaxation modulus Git) (instantaneous stress/strain) respectively. The more important of these, from the point of view of adhesive joints, is creep compliance (see also Pressure-sensitive adhesives - adhesion properties). Typical curves of creep and creep recovery for an uncross-Unked rubber (approximated by a three-parameter model) and a cross-linked rubber (approximated by a Voigt element) are shown in Fig. 2. 

Figure 13. Standard test methods for peel and shear adhesion of pressure-sensitive adhesive tapes...

Figure 14. Standard test methods fiat the tack of pressure-sensitive adhesive tapes A) Rolling-ball tack B) Rotating-drura tack ...

He presented the first training session on PSA tape technology offered by PSTC at the first world conference on adhesive tapes in 1992. Over the years, John has also presented a number of technical papers for PSTC, including Hot-Melt Pressure-Sensitive Adhesives, Practical Aspects of Formulating and Processing, Tack, The History of the Adhesive Tape Industry and Alternate Methods of Testing Pressure-Sensitive Adhesive Tapes. ... 

During his 61+ years in the pressure-sensitive tape industry, Johnston has worked with every type of pressure-sensitive adhesive system, every industry, consumer and medical group of tapes, every conventional manufacturing process and every related test method, he says. He has designed numerous types of adhesive tapes by taking them from an initial concept through product development, manufacturing scale-up and... 

This is the ability of the adhesive coat to grab the other part and prevent it from moving immediately after assembly. For pressure-sensitive adhesives, it is the ability to stick immediately after application of the tape or label. Tack develops during waiting time and also it may be provided by a thick and sticky adhesive so that there will be a suction effect, for instance, in mastics. Tack may be measured with many different test methods according to the industries. We will just mention a few of these methods. 

We will describe here the main testing methods. Other specific methods will be described in the chapters dealing with the various industries, for instance, in Pressure sensitive adhesives , Electronic adhesives because these industries have their own tests methods. Suppliers of testing equipment are listed in the appendix. 

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