Basic properties of pressure sensitive adhesives

First, the viscoelasticity of pressure sensitive adhesives

When the polymer is used by an external force, it produces elastic deformation of the general solid, has a unique high elastic deformation, and produces a viscous flow resembling a liquid. This property is called viscoelasticity. The adhesive properties of pressure-sensitive adhesives (such as peel force, fast-adhesion, etc.) strongly depend on the viscoelasticity of the polymer constituting the pressure-sensitive adhesive, or the pressure-sensitive properties of the pressure-sensitive adhesive are mainly caused by the stickiness of the polymer. Elastically determined. Since the response of the pressure-sensitive adhesive to external forces is partially elastic and partially tacky, this requires that the temperature range of use of the polymer for pressure-sensitive adhesives is limited to the glass transition temperature Tg or higher and the melting point Tm or less, that is, in the highly elastic state. That is, the glass transition temperature of the pressure sensitive adhesive should be -600C~-200C.

Since the pressure-sensitive adhesive has viscoelastic properties, when the pressure-sensitive adhesive tape (sheet) is adhered to the surface of the adherend and an appropriate pressure is applied, the pressure-sensitive adhesive mainly exhibits liquid-like viscous flow properties under a slow and uniform pressure. The pressure-sensitive adhesive is brought into close contact with the surface of the adherend to achieve adhesion. On the other hand, when the pressure-sensitive adhesive tape (sheet) is peeled off from the adherend. Most of them are carried out at high speed. At this time, the viscoelastic properties of the pressure-sensitive adhesives will enable the pressure-sensitive adhesives to obtain a certain adhesive strength as long as appropriate pressure is applied without further curing.

Second, pressure sensitive adhesive to the surface of the wet

Only the close contact of the pressure-sensitive adhesive with the adhered surface can not produce the adhesive force, and must also have a good wetting on the adhered surface so that it can reach the molecular closeness to the adhered surface to generate the intermolecular force, ie, the adhesive force. The wetting of solid surfaces by pressure sensitive adhesives can be considered from both thermodynamic and kinetic considerations. Wetting must first meet the thermodynamic and kinetic conditions. When the surface tension of the pressure-sensitive adhesive differs from the surface tension of the adherend, the contact angle of the pressure-sensitive adhesive becomes closer to 00. At this time, the wettability is better, in natural rubber. The addition of a tackifier resin reduces the surface tension and increases the interfacial adhesion. In terms of kinetics, wetting also has a speed problem that depends primarily on the viscosity of the pressure sensitive adhesive and the size of the contact angle. The smaller the viscosity, the smaller the contact angle or the surface tension, the faster the pressure-sensitive adhesive wets the surface of the adherend and the wettability is better. The softening agent memo is added to the pressure sensitive adhesive to reduce the viscosity and improve the wettability. In summary, the ideal pressure-sensitive adhesive should have low surface tension, low viscosity, and easy to wet the adherend surface.

Third, pressure-sensitive adhesive four equal balance of adhesive properties

The viscoelasticity of the pressure sensitive adhesive and good wettability to the adhered surface result in pressure sensitive adhesive properties. However, as a good pressure-sensitive adhesive must also meet the balance of the four major adhesive properties. The four major adhesive properties are fast adhesive force T, adhesive force A, cohesive force C, and adhesive base force K. The pressure-sensitive adhesive tape is adhered to the surface of the adherend. When the pressure-sensitive adhesive peels off, the pressure-sensitive adhesive must completely separate from the adherend without residue, and the following relationship must be satisfied:

T

Otherwise, there will be various quality problems. For example, if T is not less than A, there will be no pressure sensitive performance; if A cannot be less than C, then peeling off the adhesive product will result in the destruction of the adhesive layer, and the pressure sensitive adhesive stain is removed. Sticky surface, drawing or sticking, etc. If C is not less than K, degumming will occur. Therefore, these performance requirements must first be satisfied in the development and production of pressure sensitive adhesives and articles.