This paper focuses on double components solvent-free laminating adhesives, discussing levelling property of solvent-free products.
1. Basic Meaning of Leveling Property
Levelling property is capability of coatings to level evenly and smoothly on the surface of substrates.
2. Relations and Effects of Levelling on Different Stages
In the following discussion, elements of manufacture default to the same, including coating weight, temperature, pressure, etc. Because all the elements will cause changes to final laminates, we will see these variables as fixed.
Because solvent-free adhesive has no solvent to be the base, the levelling property is the performance of adhesive its own. Relatively speaking, it will be purer, but solvent-free adhesive still has its own characteristics.
Firstly, leveling property of SF adhesive has close relation with viscosity of adhesive itself. While viscosity has direct relation with temperature and varies inversely, which means viscosity of SF adhesive will decrease when temperature increase. Then under room temperature, viscosities of raw SF adhesives have huge difference according to different SF adhesive models and physical properties. However, under proper working temperature of one SF adhesive model, the range difference of its viscosity is not very obvious. Thus, a low viscosity product maybe not the better one when comparing one high viscosity SF adhesive model with a low viscosity one. For example, WD8262A/B of KANGDA NEW MATERIALS, under its operating temperature ( around 45℃), its viscosity is 1100 mpa.s. But when laminating PET.INK/ALU, it can achieve fine appearance with no dots during first lamination. As a conclusion, it doesn’t mean low viscosity can bring good appearance. Dynamic change of SF adhesives is a fast period, which needs several elements to reach a good effect. Meanwhile, viscosity has lowest floor. For example, under 80-90℃(Double component SF adhesive), viscosity has little changes with rising temperature.
Frist levelling is physical continuation of mixed adhesive status. After coating process, its leveling property decrease further along with fast reaction between A&B components and dropping of temperature. Generally, first levelling of SF adhesive is regarded as the levelling after laminating winding. At this time the viscosity of adhesive will larger than mixed adhesive on metering rollers.
Levelling of raw adhesive means the levelling property of adhesive in drums before mixed. This levelling property don’t take part in the process of laminating of films or foils.
Second levelling property is that, after laminating process and into curing stage, the SF adhesive goes into stage of fast cross-link reaction under the influence of temperature, and the levelling performance decreases to complete disappearance.
Levelling property of raw SF adhesive before mixed > second levelling property > levelling property of mixed SF adhesive on metering rollers > first levelling property. Therefore, viscosity change trend of SF adhesives actually is a rising process, which is obviously different from SB adhesives.
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Post time: Sep-14-2021