Tack Adhesives

Compounding is quite different for the two systems. The solvent base system is dependent on magnesium oxide and a /-butylphenoHc resin in the formulation to provide specific adhesion, tack, and added strength. Neither of these materials have proven useful in latex adhesive formulations due to colloidal incompatibihty. In addition, 2inc oxide slowly reacts with carboxylated latexes and reduces their tack. Zinc oxide is an acceptable additive to anionic latex, however. Other tackifying resins, such as rosin acids and esters, must be used with anionic latexes to provide sufficient tack and open time. 

Interesting products may also be produced by introducing boron atoms into the chain. The amount of boron used is usualy small (B Si 1 500 to 1 200) but its presence increases the self-adhesive tack of the rubber, which is desirable where hand-building operations are involved. The products may be obtained by condensing dialkylpolysiloxanes end-blocked with silanol groups with boric acid, or by reacting ethoxyl end-blocked polymers with boron triacetate. 

After some early uncertainty in the literature about the nature of the pressure sensitive bond, Dahlquist [5,6] related modulus data to tack-temperature studies and observed that the compression modulus of the adhesive had to be less than about 3 X 10 dyne/cm (3 x lO Pa) before any adhesive tack was observed. This was explained as the highest modulus that still allowed the adhesive to be sufficiently compliant to wet out or come into molecular contact with the substrate and form dispersive bonds. As other investigators [7-9] accepted this requirement it was termed the Dahlquist Criterion . 

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. 

Methacrylates, peroxide crosslinking Pressure-sensitive adhesives Tack variable... 

Rosin exploitation, a part of the so-called Naval Stores Industry, is at least as old as the construction of wooden naval vessels. In recent years, rosin components have attracted a renewed attention, notably as sources of monomers for polymers synthesis. The purpose of the present chapter is to provide a general overview of the major sources and composition of rosin. It deals therefore with essential features such as the structure and chemical reactivity of its most important components, viz. the resin acids, and the synthesis of a variety of their derivatives. This chemical approach is then followed hy a detailed discussion of the relevant applications, the resin acids and their derivatives, namely in polymer synthesis and processing, paper sizing, emulsion polymerization, adhesive tack and printing inks, among others. 

Rosin, Resin acids. Chemical modification. Paper sizing. Emulsion polymerization. Adhesive tack. Polymer chemistry and processing. Printing inks... 

Adhesive tack involves a separation apparently at the original interface between the materials. This kind of tack applies particularly to Pressure-sensitive adhesives, although such adhesives may display cohesive tack under extreme conditions of rate or temperature. 

Autohesive tack differs from the other types in that it involves mutual diffusion of polymer molecules across the interface it is discussed elsewhere (see the articles on Diffusion theory of adhesion and Polymer diffusion replation and interdigitation). Adhesive tack between elastomeric materials and other, usually rigid, surfaces is considered in this article. 

Some rubbery materials adhere firmly to themselves (autohesive tack or auto-hesion) or to a different surface (adhesive tack) after brief contact imder light pressure. They have a liquid character which results in rapid bond formation, yet, without setting, they resist detachment like a solid, ie, they are sfrong and soft. (Tacky substances are stroft, like toilet paper.) Typically, adhesive tack involves bonding to a hard substrate and interdiffusion is absent or minimal. Adsorption is the principal mechanism of adhesion. On the other hand, autohesion involves both molecular contact and interdiffusion. Autohesion is important in the manufacture of articles, such as tires, which are built by laminating rubbery components. 

Adh6SiV6 Tack. Adhesives that exhibit adhesive tack are often called pressure-sensitive adhesives (PSAs), since joint strengths depend on the pressure applied during bonding. In practice, PSAs are usually carried on a backing tapes and labels are examples. In order to secure rapid wetting on common surfaces, a PSA must have a creep compliance after 1 s greater than about 10" m /N... 

Finally, it should be noted that the barriers to molecular contact may be different for adhesive tack and autohesion. Surface impurities, eg, from bloom, may readily redissolve into the bulk elastomer during autohesive bonding. On the other hand, impurities on common substrates, such as surface moisture, may not be readily displaced by an adhesive that is too stiff. Molecular mobility and microscopic flow are expected to aid displacement of impurities. 

Rate and Temperature Effects. Like adhesive tack, autohesion of elastomers is strongly dependent on test rate and temperature. Furthermore, as shown in Figure 13 for the T-peel autohesion of a cold emulsion SBR, relative autohesion Pr (for a given time and pressure of contact) is not unique, but it too depends markedly on test conditions (104). 

The influence of critical surface tension on peel adhesion, tack, and residues was investigated experimentally for rubber-resin [213], [214] and polyacrylate [215] pressure-sensitive adhesives (PSAs). 

Adhesion on Contact. Some adhesives have the special property (adhesive tack) of sticking firmly after brief contact under a light pressure. Thus, they wet the surface quickly. 

Tack is the measurement of the quick grab or stickiness of an adhesive. Tack is a surface phenomenon that is not always indicative of an adhesive s performance. There are several methods of measuring tack. One test is called the quick stickIt is a measure of the force required to remove a tape at a 90 angle from a surface to which it has been applied under no other pressure than the weight of the tape itself. Another version of this test is called loop tack, in which the pressure sensitive tape is applied in a loop form using only the pressure of the... 

Dew condensation on the surface of substrates before bonding is another problem. The dews can corrode the surface before bonding and inhibit adhesive tack. Just after the start of room heating in winter, cold members may cause dews on their surfaces. Therefore, humidity control is also necessary in this situation. 

---