Viscoelasticity of pressure sensitive adhesives
When the polymer is subjected to external force for a long time, the elastic deformation of the ordinary solid occurs, there is a strange high elastic deformation, and the similar viscous activity of the liquid occurs. This kind of property is called viscoelasticity. Adhesive characteristics of pressure-sensitive adhesives (such as peeling force, fast adhesive force, etc.) are strongly dependent on the viscoelasticity of the polymer that makes up the pressure-sensitive adhesives. In other words, the importance of pressure-sensitive characteristics of pressure-sensitive adhesives depends on the viscoelasticity of the polymer. Because pressure-sensitive adhesives respond to external forces with sectional elasticity and sectional viscosity, it is required that the application temperature scale of polymers used as pressure-sensitive adhesives be limited to above the glass transition temperature Tg and the melting point Tm as follows, namely in the high elastic state. That is, the glass temperature of pressure sensitive adhesive should be -600C~-200C.
Because pressure sensitive adhesive is viscoelastic, when pressure sensitive adhesive tape (piece) is attached to the outside of the adhesive and applied appropriate pressure, pressure sensitive adhesive under the slow and average pressure effect is important to show similar to the viscous activity of liquid, which makes the pressure sensitive adhesive and the outside of the adhesive carefully contact to complete the bonding. On the other hand, when the pressure sensitive tape is removed from the adhesive material. It is mostly stopped at high speed, at this time, this kind of viscoelastomer of pressure sensitive adhesive will make the pressure sensitive adhesive finished product only need to add appropriate pressure force without further curing can get a certain bonding strength.
2 pressure sensitive adhesives to be stuck outside the wet
Pressure-sensitive adhesive and glued the rigorous fight outside also means less than glued together, also must to be stick good wet outside, make it with the glued part to take place close to the level of ability between member outside force, namely stick together, pressure sensitive adhesive for solid outside moisture can from two aspects of thermodynamics and kinetics discretion. Wet first must be satisfied with the premise of thermodynamics and dynamics, when the external tension of pressure sensitive adhesive and the external tension of the adhesive is smaller, the more close it is to the Angle of war, at this time the wetness is better, in natural rubber to participate in the viscosity resin is low external tension, improve interface joint. From the perspective of dynamics, there is a rate of moisture, which depends on the viscosity of the pressure sensitive adhesive and the size of the fighting Angle. The smaller the viscosity, the smaller the fighting Angle or the smaller the external tension, the faster the moisture rate of the pressure sensitive adhesive on the outside of the sticky material, and the better the humidity. In the pressure sensitive adhesive to participate in the softener private letter is to reduce the viscosity, to achieve the goal of improving moisture. To sum up, the ideal pressure sensitive adhesive should be small outside tension, low viscosity, easy to wet and sticky outside.
3 pressure sensitive adhesive four adhesive function balance
The viscoelasticity of the pressure sensitive adhesive and its good moisture on the outside of the adhesive make it have the characteristics of pressure sensitive adhesive. However, as a good pressure sensitive adhesive must be satisfied with the four bonding functions of the balanced relationship. Four adhesive function for fast adhesive T, adhesive force A, cohesion C, adhesive base force K. The pressure-sensitive tape is attached to the outer surface of the adhesive. When peeled off, the pressure-sensitive tape must leave the adhesive completely without residue. It must be satisfied with the following relationship:
T
Otherwise, all kinds of quality results will be presented. For example, if T is not less than A, there will be no sensitive function to pressure; If A is not less than C, then peel off the adhesive product will show damage to the adhesive layer, pressure sensitive adhesive dirt is stuck outside, wire drawing or sticky back, etc., if C is not less than K, degumming signs will occur. In order to develop and produce pressure-sensitive adhesives and finished products must first be satisfied with these functional requirements.