The main purpose of using hot melt adhesive is to connect the two materials to the required functions. There are many methods for the connection between the material, such as welding, welding, bolt fastening, fastening nails, tenon connection, glue adhesive etc.. Hot melt adhesive is only one of the ways. It is a kind of adhesive (adhesive) that is connected by two or more than two kinds of materials through the action of infiltration and adsorption on the interface and cohesive force of glue. It is also called adhesive.
The adhesion mechanism of hot melt adhesive: must first soaked sticking surface (this is why in addition to HMPSA, other hot melt heating needs to melt bonding), because it is close enough to the interface between the two will produce intermolecular force, the force is the force of Fan Dehua.
Cohesive force (the cohesion value), also called cohesion, is the attraction between adjacent parts of the same substance, and this mutual attraction is the manifestation of molecular force between the same substance molecules. It is shown only when the molecules are very close (less than 10e-6 cm). Cohesion enables a substance to be aggregated into a liquid or a solid. The cohesive force of hot melt adhesive refers to the tensile strength of the glue itself, which is also related to the ratio of the hot melt adhesive formula. The cohesive force of the hot melt adhesive is determined by the content and structure of the main polymer and compatibility with the tackifier and other auxiliaries. The cohesive force of the hot melt adhesive mainly comes from the Fan Dehua force of the glue itself.
Therefore, the ultimate bonding force of hot melt adhesive is the result of the interaction between the fan Edward force of the interface and the cohesive force of the glue itself.
There are many factors that influence the failure of hot melt adhesives. At present, there are no less than twenty kinds of adhesive failure, but there is only one truth: there is no enough Fan Dehua force. The hot-melt adhesive mentioned above does not include hot melt adhesive with chemical reaction.
Van Edward also called intermolecular forces, exists in any interactions, is a kind of weak intermolecular attraction, can the size of only tens of thousands of coke per mole to coke, than bond to 1~2 orders of magnitude less. It consists of three parts of force:
(1) dispersion force: between non-polar molecules, due to the continuous movement of the positive and negative particles of the constituent molecules, the instantaneous center and the negative charge center do not coincide, resulting in the interaction force between the instantaneous dipoles. The larger the molecular weight, the greater the dispersion force. Of course, there is a dispersion force between polar molecules and non polar molecules or polar molecules.
2. Induced force: when polar molecules and non-polar molecules are near each other, nonpolar molecules polarize under the action of polar dipole of the polar molecules, induce induced dipoles, and then induce the attraction between dipoles and natural dipoles to produce molecular force. Of course, there are also inducible forces between polar molecules.
The orientation force: when the polar molecules are close to each other, they will dipole poles repel different poles attract, orientation, produce intermolecular forces. The greater the dipole moment, the greater the orientation force. Fan Dehua gravity is intermolecular a has no direction and saturation, the scope between hundreds of picometers force.
Therefore, the adhesive force of the hot-melt adhesive must first have enough wettability, so that there is enough contact between the adhesive and the sticky material and the distance is within the scope of the van Edward force to produce effective bonding.