Tackifier function

In this section the rosins and rosin derivative resins, coumarone-indene and hydrocarbon resins, polyterpene resins and phenolic resins will be considered. The manufacture and structural characteristics of natural and synthetic resins will be first considered. In a second part of this section, the characterization and main properties of the resins will be described. Finally, the tackifier function of resins in rubbers will be considered. 

Tackifiers function in several ways to increase tack strength to surfaces. Incorporation of the correct tackifier type and loading will improve the compatibility of the polymer with the adherend. The small tackifier molecules will also reduce the viscosity and elasticity of the polymer molecules allowing better wetting of the adherend surfaee. Frequently this improvement in tack also improves the permanent bond strength on eure. 

The effect of adding tackifiers on the rheological properties of elastomers has been investigated (98-100), and the results are instructive in understanding how a tackifier functions. Figure 9 shows a plot of the shear storage modulus... 

Heteroatom functionalized terpene resins are also utilized in hot melt adhesive and ink appHcations. Diels-Alder reaction of terpenic dienes or trienes with acrylates, methacrylates, or other a, P-unsaturated esters of polyhydric alcohols has been shown to yield resins with superior pressure sensitive adhesive properties relative to petroleum and unmodified polyterpene resins (107). Limonene—phenol resins, produced by the BF etherate-catalyzed condensation of 1.4—2.0 moles of limonene with 1.0 mole of phenol have been shown to impart improved tack, elongation, and tensile strength to ethylene—vinyl acetate and ethylene—methyl acrylate-based hot melt adhesive systems (108). Terpene polyol ethers have been shown to be particularly effective tackifiers in pressure sensitive adhesive appHcations (109). 

Regular PIB may be used as a viscosity modifier, particularly in lube oils, as a thickener, and as a tackifier for plastic films and adhesives. PIB can also be functionalized to produce intermediates for the manufacture of detergents and dispersants for fuels and lube oils (14). 

Resin as the Disperse Phase. Several kinds of resins (10) have been used to reinforce rubbers—e.g., phenolic or coumarone resins for natural rubber, styrene-butadiene resin for styrene-butadiene rubber, etc. One other important system, pressure-sensitive adhesive, also belongs to this class. These adhesives generally contain a low molecular weight resin functioning as a tackifier. In 1957, Wetzel (68) and Hock (19) found that these adhesives were actually two-phase systems (Figure 1). Under... 

Prior to this discovery, in 1954 Silberberg and Kuhn (62) were first to study the polymer-in-polymer emulsion containing ethylcellulose and polystyrene in a nonaqueous solvent, benzene. The mechanisms of polymer emulsification, demixing, and phase reversal were studied. Wetzel and Hocks discovery would then equate the pressure-sensitive adhesive to a polymer-polymer emulsion instead of a polymer-polymer suspension. Since the interface is liquid-liquid, the adhesion then becomes one type of R-R adhesion (35, 36). According to our previous discussion, diffusion is not operative unless both resin and rubber have an identical solubility parameter. The major interfacial interaction is physical adsorption, which, in turn, determines adhesion. Our previous work on the wettability of elastomers (37, 38) can help predict adhesion results. Detailed studies on the function of tackifiers have been made by Wetzel and Alexander (69), and by Hock (20, 21), and therefore the subject requires no further elaboration. 

Figure 21.13 Storage and loss moduli of an SIS triblock copolymer as a function of temperature. Formulation with tackifying resins brings the peak in loss modulus to near ambient temperatures for adhesives...

Resins fall into one of three functional categories (1) extending or processing resins, (2) tackifying resins, and (3) curing resins. Resins have been classified in an almost arbitrary manner into hydrocarbons, petroleum resins, and phenolic resins. 

Part II Function/Application Index tackifier, polymers... 

Specific interactions in binary blends of ethylene-vinyl acetate copolymer with various low molecular weight terpene-phenol tackifying resins (TPR) were systematically investigated, as a function of the composition of the blend and of the electron acceptor ability of the resin, by using attenuated total reflection FTIR spectroscopy. Molecular acid-base were evidenced between TPR hydroxyl groups and EVA carbonyl groups. Quantitative information on the fraction of acid-base bonded entities, the enthalpy and equilibrium constant of pair formation were obtained. A crystalline transition of the EVA copolymer was observed and discussed in terms of enthalpy and entropy considerations based on FTIR and calorimetric DSC investigations. Fundamental results are then summarised to predict the interfacial reactivity of such polymer blends towards acid or basic substrates. 16 refs. 

Shell Oil Co. EB/UV radiation cure of composition comprising a monoalkenyl arene/conjugated diene block copolymer, tackifying resin, and a di-tetra functional acrylate or methacrylate selected from the group consisting of acrylic and methacrylic acid esters of polyols. Improved high-temperature properties and solvent resistance. PSA properties,... 

Modern-day adhesives are often fairly complex formulations of components that perform specialty functions. Very few polymers are used without the addition of some modifying substance such as a plasticizer, tackifier, or inert filler. The selection of the actual ingredients will depend on the end-properties required, the application and processing requirements, and the overall cost target of the adhesive. 

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