Compatibility of Tackifier Resin with Acrylate Pressure Sensitive Adhesive
The most important properties of pressure-sensitive adhesive is the initial viscosity, adhesion and holding force, they are not only related to the deformation of pressure-sensitive adhesive materials, but also with the degree of damage to the material is closely related. An acrylic pressure-sensitive adhesive containing a Tackifier Resin is a blend of long chain molecules with small molecule or oligomer molecules. Since compatibility determines the phase structure, it is important to examine the compatibility of the components. If the two are completely compatible, the system is a uniform single phase structure. When the tackifier resin content is low, the physical properties of the material mainly show the characteristics of acrylic copolymer, Tackifier Resin from the role of plasticizers, reducing the viscosity of the whole system, with the increase in Tackifier Resin content, viscosity When the Tackifier Resin content reaches a certain value, the adhesive force reaches the maximum value. At this time, the viscosity of the system is the smallest, and beyond this value, the physical properties of the material are greatly affected by the Tackifier Resin, The cohesive energy decreases, the adhesive force also drops rapidly. If the compatibility of the two is very small or completely incompatible, the phase separation occurs from a low concentration, the Tackifier Resin acts only as a filler, reducing its original pressure-sensitivity.
Generally speaking, the solubility parameter (SP value) similar to the material compatibility is good, this also applies to Tackifier Resin and polymer compatibility relationship between. C5 series of petroleum resin, terpene resin, C5 / C9 series of petroleum resin, C9 series of petroleum resin, rosin series of resin. Studies have shown that [4 ~ 6], petroleum resin, terpene resin and acrylic polymer compatibility is poor, the more the amount of pressure-sensitive properties of the worse; rosin resin, hydrogenated rosin ester and acrylic polymerization Material has a certain compatibility, fast sticking strength and peel strength has increased.
The measurement of the compatibility of the blend can be based on Tg as a criterion. The incompatible blends have two Tg peaks, corresponding to different components. At the onset of two Tg peaks, the Tg of the copolymer increases with the increase of the content of the resin. Position, indicating the separation of the phases.
The degree of compatibility of the blend can be determined by measuring the glass transition temperature Tg of the blend by DSC. The compatibilized blend has a wider glass transition temperature than the tackifier-free acrylate pressure-sensitive adhesive, which is the weight average of the transition temperatures of the components. The Fex equation approximates the Tg of the compatibilized blend: 1 / Tg = w1 / Tg1 + w2 / Tg2 where Tg is the glass transition temperature of the compatibilized blend and w1, Tg1, w2, Tg2 are the polyacrylic acid The glass transition temperature and the weight fraction of the ester and Tackifier Resins. The degree of compatibility of the blends can be evaluated by means of the deviation between the measured values ??and the calculated values.
With the transparency of the film can also be a rough judgment of the compatibility of blends [5 ~ 6]. When the Tackifier Resin is fully compatible with the polyacrylate, the film is transparent; as the compatibility changes from good to bad, the film becomes transparent from opacity to opacity. This is because when the two phases are separated, the Tackifier Resin will be dispersed in the form of discontinuous micro-regions, which differ from the refractive index of the polymer and result in the opacity of the film. But this method can not determine the degree of incompatibility.