SIS adhesives have a wide range of applications, and the specific applications have different requirements for the softness and hardness, initial viscosity and adhesive properties of the adhesive, so the selection of SIS for the substrate SIS is also different, which is reflected in the block ratio, diblock content and molecular weight of SIS. So how does the latter affect the three properties of glue? Let's take a look at the specific combing below: 3. Adjustment of molecular weight
1. Adjustment of block ratio (S/I).
The block ratio of SIS refers to the ratio of styrene(S) and isoprene(I) segments in the copolymer.
When the block ratio of SIS increases, that is, the content of styrene chain segments increases, the initial viscosity of the prepared glue decreases, and the tackness increases. At the same time, the melt viscosity decreases and the softening point increases. This often results in the glue becoming stiffer because the styrene segments are more rigid.
When the block ratio decreases, that is, the content of isoprene chain segments increases, the initial viscosity of the glue will increase, and the tackability may decrease. This makes the glue softer because the isoprene segment has better elasticity.
2. Regulation of SI content
SI content refers to the proportion of the SIS that contains only polystyrene and polyisoprene segments (without intermediate blocks). The SI cohesion of the two-block segment is small, the heat resistance is poor, but it has high fluidity, high adhesion and good slitting performance.
As the SI content increases, the tensile strength of SIS decreases and the melt flow rate (MFR) increases. The initial adhesion of the prepared glue will increase, and the tack may decrease (but it may tend to stabilize or increase slightly after a certain extent). At the same time, the melt viscosity and softening point are reduced, which usually makes the glue softer.
Conversely, when the SI content decreases, the initial viscosity decreases, the tack increases, and the melt viscosity and softening point increase, resulting in the adhesive becoming stiffer.
The molecular weight of SIS also affects the hardness, initial tack and tackiness of the adhesive.
When the molecular weight of SIS increases, the initial viscosity of the glue decreases, while the tack increases the tack. At the same time, the melt viscosity will increase and the softening point will also increase. This often makes the glue stiffer and stickier.
Conversely, when the molecular weight decreases, the initial tackiness of the adhesive increases, while the tack holding ability may decrease. At the same time, the melt viscosity and softening point are reduced, making the glue softer and easier to flow.
4. Glue making characteristics of some SIS grades
SIS 1124: Preparation of pressure sensitive adhesives for tapes and labels with good wetting and initial adhesion properties.
SIS 1128: Ultra-high melt index, improve the flow of hot melt adhesive products, reduce processing difficulty. High diblock content, good slitting and initial adhesion properties, suitable for paper labels.
SIS 1126: Excellent initial adhesion and die-cutting properties for permanent labels. It has good compatibility with tackifier resins and high transparency of the hot melt adhesive.
SIS 1716: It has the characteristics of good initial adhesion and high peel strength. It has extremely low hardness, good wettability and pressure sensitivity, and has a good bonding effect on difficult-to-stick substrates.
SIS 1125: Good initial tack and peel strength with balanced properties. High cohesive strength improves the transfer resistance of the product and reduces the risk of residual glue.
SIS 1209: High cohesive strength and dimensional stability, good creep resistance, fast crystallization and fast curing effect.
SIS 4016: With an ultra-high melt index, it is effective in improving the flow of the finished hot melt adhesive. The prepared hot melt adhesive is easy to process, low energy consumption, and reduces the risk of oil seepage.
SIS 4019: Better high temperature resistance compared to conventional SIS (except 1209). With a higher melt index, hot melt adhesive products have better fluidity.