Tack and adhesion

Tack refers to the adhesion of two surfaces of the same rubbery polymer. When two such surfaces are pressed together and subsequently pulled apart, the maximum force necessary to break the junction depends on the initial time of contact and the normal force applied, as well as the rate of separation and the temperature and other variables. From the dependence on temperature and polymer molecular weight, it can be inferred that the effectiveness of the bond depends partly on the interdiffusion of molecules across the interface and hence on molecular motions which are reflected in viscoelastic properties in the terminal zone. - However, the effectiveness depends also on the ultimate properties of the polymer itself as discussed in Section E below, and the phenomenon is still not fully understood. 

The more general phenomenon of adhesion between a rubbery polymer and a different surface is frequently studied by tests of the force required to peel a thin layer of polymer from a rigid substrate. 2,53 at different peel rates and different temperatures can be combined by reduced variables with shift factors given by the WLF equation, indicating that here as in friction the process is controlled by rates 

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Cohesive strength is the internal strength of an adhesive or the ability of the adhesive to resist splitting. Unlike tack and adhesion strength, cohesive strength is not influenced by the substrate. 

The solvent plays an important role in the performance of rubber base adhesives. The solvent is the carrier for all components of the adhesive. Furthermore, the solvent controls the viscosity, open time, tack and adhesion of rubber base adhesives. 

Tackifiers. Phenolic resins are added to increase strength, oils resistance and resiliency of NBR adhesives. On the other hand, tack and adhesive properties can be improved by adding chlorinated alkyl carbonates. To impart tack, hydrogenated rosin resins and coumarone-indene resins can be added. 

Plasticizers. Addition of softeners to NBR improve tack and adhesion properties. The most common plasticizers are esters (dibutyl phthalate, tricresyl phosphate), ester gums, alkyd resins, etc. 

Because high-molecular weight polyisobutylene is an inert hydrocarbon polymer, a very small amount of major tackifiers and oils can be dissolved in polyisobutylene. Consequently, a common polyisobutylene adhesive is composed of both high- and low-molecular weight polyisobutylene, which is also the major reason for the relatively low tack and adhesion of polyisobutylene-based adhesives. 

Features Good tack and adhesion high m.w. compat. with resins, film-formers, and oils resist, to oxidation reactive hydroxyl group low volatility... 

The preparation of silicone psas was first disclosed in the mid 1950s when it was observed that blends of silicone resins and polydimethylsiloxane gums (PDMS) produced a material with pressure sensitive adhesive properties (i.e., tack and adhesion under low application pressure). By 1956 a versatile process for the preparation of silicone resins suitable for use in silicone psas was described (6). Rapid progress in the preparation and application of silicone psas was observed from this point to the present. 

Ethylene vinyl acetate (EVA) Good tack and adhesion, relatively low cost. Used in footwear and to bond leather, good flexibility. Low... 

Another undesirable feature of a PSA tape is creep or oozing. This is most often seen with imcross-linked adhesives that undergo viscous flow over long times. This is governed by properties similar to those that govern lift, except that the ability of the adhesive to relax stress through flow (which helps reduce lift) can lead to increased creep. It is usually necessary to strike a balance between lift, creep, and the short-term tack and adhesion properties needed in a PSA tape. 

FDA regulations permit use of up to 25% acrylic acid for copolymers of ethylene in direct food contact. The EAA flexible films have similar chemical resistance and barrier properties as LDPE. However, these have better strength, toughness, hot tack and adhesion than LDPE. As the content of acrylic acid increases, the ciystalhnity decreases and clarity increases. It is used in blister packaging and as an extmded tie layer between aluminum foil and other polymers. EAA films are also used in flexible packaging of meat, cheese, snack foods, skin packaging and in adhesive lamination. 

P. K. Chatterjee ( 2/U>onaZ VAodllcX Co.) What is the definition of tack Is ther any difference between tack and adhesion If so, what ... 

Plasticizers. Softeners are sometimes employed with nitrile rubbers to improve tack and adhesive properties. They are added to high nitrile content rubbers to aid processability. Conunonly employed in cement applications are esters (e.g., dibutyl phthalate, dioctyl phthalate, tricresyl phosphate, tributoxy ethyl phosphate, dibenzyl sebacate), ester gums. 

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