The adhesive of the self-adhesive label realizes the pasting function based on a variety of chemical principles. The following are some common ones:
1. Principle of intermolecular force
Van der Waals force: This is a kind of force that is commonly present in molecules. The molecules in the adhesive and the molecules on the surface of the object to be pasted will produce van der Waals force. For most self-adhesive label adhesives, such as acrylic adhesives, the molecules contain a large number of polar and non-polar groups. When the label is in contact with the object to be pasted, these groups are close to the corresponding groups of the molecules on the surface of the object to be pasted. There are dispersion forces between non-polar groups, and dipole-dipole forces or hydrogen bonds between polar groups. Although these van der Waals forces are very weak individually, due to the large number of adhesive molecules, many tiny forces are superimposed, allowing the label to be firmly pasted on the surface of the object.
Hydrogen bonding: Hydrogen bonds play a key role in pasting between some adhesives and specific surfaces of objects. For example, when the adhesive molecule contains functional groups such as hydroxyl (OH) or amino (NH₂), and the surface of the object to be attached has complementary functional groups, hydrogen bonds will form. When the adhesive with water as the solvent is attached to the glass surface containing a large number of hydroxyl groups, hydrogen bonds will form between the hydroxyl groups of the adhesive molecules and the hydroxyl groups on the glass surface. The bond energy of hydrogen bonds is stronger than the general van der Waals force, so it can enhance the firmness of the attachment.
2. Chemical bonding principle
Chemical reaction adhesive: Some special self-adhesive label adhesives form chemical bonds with the surface of the attached object through chemical reactions. For example, when silicone adhesives come into contact with surfaces containing hydroxyl groups (such as ceramics and glass), the active groups in the adhesive will undergo condensation reactions with the hydroxyl groups on the surface to form covalent bonds. The adhesion formed by this chemical bonding method is very strong, and has good water resistance, chemical resistance and high temperature resistance, and is suitable for use in harsh environments.
3. Adsorption principle
Physical adsorption: The adsorption of adhesive molecules on the surface of the object is also an important mechanism for achieving adhesion. From a thermodynamic point of view, when the adhesive contacts the object, the surface energy of the system decreases, making the entire system more stable. The adhesive molecules will spread on the surface of the object to form a tight adsorption layer. This process is similar to the adsorption of gas on the solid surface and is a spontaneous process. Microscopically, the polar part of the adhesive molecule will preferentially adsorb on the polar surface, and the non-polar part will interact with the non-polar surface, in this way, the adhesion of surfaces with different properties is achieved.
The adhesion function under different chemical principles has its own advantages and disadvantages in practical applications. When choosing a self-adhesive label adhesive, it is necessary to comprehensively consider multiple factors such as the nature of the object, the use environment, the adhesion strength and durability.
