SBS, SIS hot melt adhesive mainly includes SBS, SIS thermoplastic rubber, tackifying resin, plasticizer, stabilizer and other components. Face to analyze and discuss.
1 Structure and performance of SBS and SIS
SBS and SIS are a type of block copolymer. Its rubbery midblock molecules are unsaturated rubber. It has the solubility and thermoplasticity of polystyrene, but at room temperature it means vulcanized natural rubber or vulcanization: diene toughness and elasticity. Its characteristics are derived from its unique molecular structure.
In addition to the linear structure, SBS and SIS block copolymers also have on-type structures. All of these block copolymers have a two-phase composition. Dynamic mechanical tests of SBS and SIS block copolymers have found that there are 2 Tg peaks in SBS and SIS block copolymers. Pentadiene) phase. Depending on the preparation process, the morphology or shape of the two dispersed phases can be spherical, cylindrical, or plate-like.
2 Tackifying resin
The effect of tackifier resin on the performance of the adhesive depends on its distribution tendency between the two phases of the block copolymer. Polyarene, terpene resin, coomalon-indene or petroleum resin with softening point higher than 85 ° C has good compatibility with polystyrene plastic terminal blocks. It is mainly used to adjust the melt viscosity of the adhesive and control the viscosity of the adhesive. The modulus allows the adhesive to have high cohesive strength at high temperatures. The low-softening point resin viscosity is opposite to the above, which makes the adhesive sticky at low temperatures and reduces the operating temperature of hot melt adhesives. Aliphatic olefin resins, rosin ester resins, polyterpene resins, terpene phenolic resins, C3 petroleum resins, etc. have good compatibility with the middle rubber block, which is mainly just to give the initial adhesion of the adhesive and the peeling force, Improve the adhesive strength of the adhesive to the polar substrate, control the modulus of the adhesive, and soften the adhesive. Such resins reduce the low-temperature flexibility of the adhesive, and can be improved by adding corresponding plasticizers. According to the performance requirements of the adhesive, one or more tackifying resins can be selected for use in order to obtain satisfactory results.
Plasticizers are used to improve the adhesive strength, cold resistance, impact resistance and flexibility of adhesives, reduce the melt viscosity of adhesives, and improve the operability of adhesives. SBS, SIS type hot melt adhesives should generally choose welding oils that are compatible with the block copolymer intermediate rubber block phase and poorly compatible with the terminal polystyrene plastic phase, such as naphthenic oil, hydraulic oil, 40 # Motor oil, etc. If a plasticizer with good compatibility with the terminal polystyrene plastic phase, such as DOP, is used, the terminal plastic phase region will be softened, and the adhesive strength of the adhesive will decrease rapidly. In actual use, according to the characteristics of each plasticizer, one or more plasticizers are selected for use in order to meet various performance requirements.
As mentioned above, the rubber-like middle block molecules of SBS and SIS block copolymers are unsaturated rubbers, which are susceptible to chemical attack at the carbon-carbon double bond, and undergo oxidative degradation or molecular cross-linking to form a refractory network. Structures that cause performance degradation of the adhesive. Therefore, stabilizers such as antioxidants, anti-ozone penalties, and UV stabilizers need to be added for protection. The choice of stabilizer depends on the choice of different formula ingredients, the choice of product stability index and other properties. Commonly used stabilizers are 1010, 168, 264, Butyl Zimate and so on. Studies have shown that when mixed with various stabilizers, Chuanshi can obtain a good protective effect.