The difference between the knowledge star type and the line type of SBS adhesive
The SBS thermoplastic elastomer is a styrene-butadiene-styrene triblock copolymer which has both solubility and thermoplasticity of polystyrene (PS) and flexibility and resilience of butadiene rubber (PB). It has the dual characteristics of thermoplastic and vulcanized rubber. These characteristics are due to the thermodynamic incompatibility of the PS end and the middle section of PB. The PS end aggregation zone is in a glassy state at room temperature, and acts as a rigid network cross-linking point. When it is higher than the PS viscous flow temperature, PS is in a viscous flow state, and the cross-linking is broken, so that plastic processing can be performed. It is precisely because of these characteristics of SBS that it is an important raw material for the preparation of pressure sensitive adhesives.
The solvent-based SBS pressure-sensitive adhesive has a lower viscosity, which makes it possible to produce an adhesive having a higher solid content and suitable for coating. This not only saves solvent but also saves the energy needed to volatilize the solvent.
SBS elastomer is the main material of SBS, and its structure is divided into two categories: linear and star. The linear SBS has a relatively low molecular weight, good solubility, low viscosity, and low cohesive strength.
SBS has a relatively high molecular weight, a large cohesive strength, a high physical crosslink density, and a high heat resistance and elastic modulus than a linear SBS. However, if the amount of star SBS is too large, the shrinkage internal stress of the adhesive will increase. The internal stress existing in the adhesive bonding head will cause the joint strength to decrease, so that the adhesive layer after curing has poor flexibility and brittleness. In addition, the adhesive and the adherend molecules need to be mutually diffused into a strong joint. The star-shaped SBS elastomer has weaker wettability than the linear SBS elastomer, and does not uniformly and sufficiently wet the material to be bonded during bonding. Therefore, the linear structure of SBS1401 (YH-792) was selected as the main material.
Commonly used solvents such as toluene, dichloroethane, carbon tetrachloride, vinyl acetate, cyclohexane, etc. are good solvents for SBS; n-hexane, heptane, petroleum ether, solvent gasoline, acetone, etc. are poor solvents, single solvent It is difficult to meet the comprehensive requirements, and a binary or multi-component mixed solvent composed of a good solvent and a poor solvent is generally used. The poor solvent in the mixed solvent must be volatilized faster than the good solvent. Otherwise, the surface of the film is rough and the bond strength is lowered.