Tackifiers exert a wetting effect on the substrates to be bonded; under specific conditions of temperature, pressure, and time, they facilitate surface or internal diffusion to generate substances with high adhesive strength. Most tackifiers are low-molecular-weight thermoplastic resins; at room temperature, they exist either as viscous liquids or solids on their own, or they become fluid when combined with appropriate solvents.
To function effectively as a tackifier, a substance must meet the following criteria: ① It must exhibit good compatibility with the main adhesive resin. ② The tackifier itself must possess strong inherent tackiness. ③ Its tackifying effect must be durable and exhibit minimal variation over time. ④ It must not interfere with the vulcanization process of the rubber.
In typical formulations for rubber-based pressure-sensitive adhesives (PSAs), the optimal proportion of tackifying resin is approximately one part per one part by weight of the rubber elastomer. If the resin has a high softening point, a smaller quantity may suffice; conversely, if the softening point is low, a larger quantity should be used. Furthermore, when manufacturing PSA products that require excellent aging resistance, it is essential to prioritize the selection of tackifying resins with superior aging stability-such as alicyclic petroleum resins, hydrogenated rosin esters, or terpene resins-which contain few to no double bonds within their molecular structures. When manufacturing electrical insulation tapes, tackifying resins with superior electrical insulation properties should be selected whenever possible.
When manufacturing medical-grade PSA products, acidic tackifying resins-such as rosin and its derivatives, or certain phenol-formaldehyde modified resins-can often trigger dermatitis; therefore, great care must be exercised during their selection. Conversely, when manufacturing lower-end products, the cost of the tackifying resin becomes a primary consideration.
Generally speaking, tackifiers that possess an appropriate relative molecular weight, a branched molecular structure, polar or semi-polar functional groups, and groups that provide steric hindrance tend to exhibit superior tackifying effects; this principle serves as a useful reference for the design and selection of tackifiers. The various types of tackifying resins available include terpene resins, petroleum resins, copolymer resins, rosin, hydrogenated rosin, polymerized rosin, rosin glycerol esters, coumarone-indene resins, modified rosins, and others.
