Modification technology and application of thermoplastic elastomer SIS
Principle and method of SIS modification
At present, the research on the modification of SIS hot-melt pressure sensitive adhesive mainly focuses on three aspects: the first is to modify SIS elastomer, introducing polar groups or segments on the elastomer to change the polarity of molecules, including epoxidation and grafting modification.
The second is to modify SIS pressure-sensitive adhesive, mainly by adding other types of adhesives or additives to change the surface tension and polarity of the adhesive, so as to improve the bonding force between the adhesive and the adhered material; Secondly, the pressure-sensitive adhesive is modified by changing the components;
Thirdly, under the irradiation of electron beam or ultraviolet light, the double bond of SIS elastomer breaks to produce free radicals, and then the polymerization, grafting, crosslinking and other processes are carried out within molecules, between molecules and with other polymers.
1) epoxidation modification
As polystyrene and polyisoprene are non-polar substances, their miscibility with polar substances and the indirectness of the adhesive formed are limited. The modification of SIS is mainly to introduce polar groups into it. The performance of the pressure sensitive adhesive prepared by epoxy modified ESIS according to the best formula was compared with that prepared by unmodified SIS according to the best formula. The results show that the peel strength, tack resistance and aging resistance of ESIS pressure-sensitive adhesive are better than those of unmodified SIS pressure-sensitive adhesive.
2) Graft modification
There are double bonds in SIS elastomer, which can increase the initial viscosity, heat resistance and cohesiveness of the adhesive through grafting. SIS was grafted with monomers similar to polyolefin in structure and surface properties.
Grafting of acrylic acid and acrylic ester
At present, the research on the grafting modification of SIS with acrylic esters in China generally adopts the solution grafting method, in which methyl methacrylate (MMA), butyl methacrylate (BMA), acrylonitrile (AN) and acrylic acid (MAH) are used as monomers to modify SIS. The experimental results show that MMA, BMA and their mixture can effectively graft SIS under the action of benzoyl peroxide (BPO), enhance its polarity and flexibility, and improve its adhesion with polar materials.
Butyl rubber modification
The polyisoprene chain segment in SIS is easily broken, degraded and crosslinked by oxygen, heat and light, which affects the performance of pressure sensitive adhesive. The low chemical unsaturation of butyl rubber and the inactivity of polyisobutylene chain make the heat resistance and oxidation resistance of butyl rubber far superior to other common rubbers.
3) modification of 3)SIS pressure sensitive adhesive
SIS elastomer itself has no initial viscosity, so when it is prepared into pressure-sensitive adhesive, it is necessary to add adhesive resin, softener, antioxidant and other additives.
There are two main ways to modify SIS pressure-sensitive adhesive. One is to change the composition or content of pressure-sensitive adhesive, and choose different tackifying resins, solvents and their additives or the content of each component according to the requirements of adhesives. The second is blending modification, which increases the polarity of the system by adding other types of adhesives or additives, so as to increase the adhesive force between the mixed adhesive and polar fabrics. This is a common method to produce adhesives with special properties at present.
The modification of SIS pressure-sensitive adhesive can significantly improve the adhesive force with polar materials, and the heat resistance and weather resistance are also improved. This modification is relatively simple, and the required equipment is relatively simple. Compared with elastomer modification, the consumption of raw materials and energy is lower, so it is suitable for the company to produce adhesives that meet different performance requirements.
4) UV or electron beam modification
Or ultraviolet beam modification means that after the hot melt pressure sensitive adhesive is coated, the double bond of SIS elastomer is broken to generate free radicals through short electron beam or ultraviolet irradiation, and then polymerization reaction is carried out. Generally, after coating, the elastomer is cooled to below the Tg of SIS chain segment, then SIS is only physically crosslinked, and then irradiated by electron beam or ultraviolet light, and then partially chemically crosslinked, which can make up for the deficiency of physical crosslinking and greatly improve the temperature resistance and solvent resistance of the adhesive without affecting the viscosity.