Pressure sensitive adhesive characteristics

A typical product has the following characteristics number average molecular weight, — 1800 carboxyl assay, — 1.1 meq./gram color, amber bulk viscosity (Brookfield synchrolectric viscometer) 70°F., 8000 poises, 100°F., 2000 poises, 150°F., 250 poises, and 250°F., 15 poises. The product can be cured with polyfunctional epoxides, aziridines, and isocyanates for applications such as thermoset and pressure sensitive adhesives, electronic component encapsulation, rocket propellant binders, epoxy flexibilizers, etc. Detailed vulcanization data can be obtained for the 1800 molecular weight material, EMD-590, from the Enjay Chemical Co., Cranford, N. J. 

Benedek, I. Heymans, L.J. Adhesive performance characteristics. In Pressure-Sensitive Adhesives Technology Marcel Dekker, Inc. New York, 1997 163-252. 

Holding Power— The characteristic of a pressure sensitive adhesive to resist removed. 

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. 

Good processing characteristics Adhesives are often used as a contact bond type— either in water- or solvent-based systems—as a hot melt, or as a pressure sensitive, in curing systems, or as heat or solvent reactivatible systems. Block copolymers provide superior pressure sensitive adhesives, but can also be compounded for contact bond adhesive or sealant applications. 

Water-based systems have good aging characteristics, resisting the effects of heat, ultraviolet (UV) light, and oxidation. Thus use of antioxidants is not normally necessary. Table 2 lists the major advantages and disadvantages of the various types of pressure-sensitive adhesives. 

Because of the unique properties of pressure-sensitive adhesives, special tests not applicable to other types have been developed. While standard physical tests such as nonvolatile content, viscosity, and specific gravity are performed to ensure consistency of application, these tests do not predict adhesive performance. For pressure-sensitive adhesives, three critical performance characteristics are usually measured tack, peel, and shear strength. 

Pressure-sensitive adhesives (PSAs) are a class of elastomer-based materials that have the foUowing characteristics they are aggressively and permanently tacky, they adhere without the need of more than finger pressure, they require no heat or activation, they adhere well, and they can be... 

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. 

In this section we describe the peeling of two common pressure-sensitive adhesives in terms of the characteristics of the photon emission (phE) and long-wavelength electromagnetic radiation (RE) accompanying this form of fracture. In particular, we show that the emission is in the form of bursts, and determine the time distributions of the phE bursts, the time and intensity correlations of the phE and RE bursts,( i) the optical spectra of the phE(45) and the spatial distributions (i.e., images) of the phE for particular substrates.( 3,46,83)... 

Table 61.20 compares the materials. Pressure-sensitive adhesives (PSAs) provide a low-cost solution due to their simple application process. A problem of PSA is creep characteristics under mechanical stress, as PSA cannot maintain the exact positions of the stiffener boards under the stress. Thermosetting adhesives provide a reliable bonding between the layers, but they require a long processing time in a heat press with suitable press pad materials and impose a higher processing cost. 

Adhesives can be classified on the basis of chemical composition [29], setting mechanism [30], and adhesion mechanism as pressure-sensitive, adhesion, and diffusion adhesives [31]. Lucre [32] proposed a flexible classification in which each adhesive is characterized and classified according to various characteristic features, such as chemical basis, form of application, application temperature, thermal behavior, and uses. A classification such as this provides for very detailed coverage of the individual features of an adhesive and is a helpful guide for industrial users. However, it is extremely comprehensive and goes beyond the scope of this treatise. For this reason, a classification based on the setting mechanism is given here [30]. 

Pressure-sensitive adhesives are compounded and coated in the fluid state and used in the solid state. Key characteristics of the process are the fluidization and solidification procedures. Four alternative types of process can be applied (Table 4). 

A pressure-sensitive adhesive must have the following characteristics ... 

Experimental work has shown that a chemically depolymerized latex exhibits the characteristics of a pressure-sensitive adhesive." Good peel strength was found without the addition of resin, and as the low glass transition temperature of natural rubber was not affected by the reaction, these materials may be of interest in low temperature applications. Blends... 

The most important properties of any pressure sensitive adhesive are a balanced relationship of tack, cohesion, and adhesion. To these properties, acrylic pressure sensitives add the valuable qualities of heat resistance and resistance to aging and UV radiation. Another desirable characteristic of acrylics is that, in general, tackifiers are not required because tack can be designed into the polymer through the proper choice of acrylic monomers. These and other properties of acrylic pressure sensitive... 

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