Basic Composition of Adhesives

The components of adhesives include base materials, curing agents, solvents, plasticizers, fillers, coupling agents, cross - linkers, accelerators, toughening agents, tackifiers, thickeners, diluents, anti - aging agents, polymerization inhibitors, flame retardants, initiators, photosensitizers, defoamers, preservatives, stabilizers, complexing agents, and emulsifiers.

Types of Base Materials

The base material is the main component, main agent, or main polymer of the adhesive, playing a bonding role. According to different chemical compositions, the sources of base materials include inorganic compounds and organic compounds. Organic compounds are polymer - based materials in the category of polymer synthesis.

1. Commonly used organic compounds:
   • Thermosetting synthetic resins: Phenolic resin, epoxy resin, amino resin, polyurethane resin, unsaturated polyester, and acrylic resin.
   • Thermoplastic synthetic resins: Rubber - based materials, natural polymer materials, water - based latex - based materials.
   • Rubber - based adhesives
2. Principles for Selecting Adhesive Base Materials: Selection is based on the object, application scenario, and performance requirements of the adhesive. Meanwhile, the molecular structure of the base material is closely related to the bonding performance.
   • It is related to the polarity of the polymer material.
   • It is related to the crystallization performance of the polymer material.
   • It is related to the molecular weight of the polymer material.

Curing Agents (Hardening Agents)

Curing agents are substances that enable the base raw materials to undergo polymerization, polycondensation, or cross - linking reactions through chemical reactions, transforming them into linear polymers or network polymers, endowing the bonded joints with mechanical strength and stability.

1. Selection of Curing Agents:
   • It is preferably a liquid, non - toxic, colorless, and odorless substance.
   • The reaction between the curing agent and the substance to be cured should be stable with low heat release to reduce the internal cohesion of the adhesive layer.
   • For heat resistance, choose a curing agent with more reactive groups in its molecule.
   • For toughness, choose a curing agent with a longer molecular chain.

Adhesive Solvents

Adhesive solvents refer to liquids that can reduce the intermolecular forces of certain solids or liquids, dispersing the dissolved substances into a homogeneous system of molecules or ions. Commonly used solvents are low - viscosity liquid substances, mainly including aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, esters, alcohols, ketones, acids, ethers, terpenoids, amides, and water. However, most organic solvents have certain toxicity, flammability, explosiveness, environmental pollution, safety hazards, and harm to the human body.

1. Functions of Solvents:
   • Medium for polymerization reactions: It makes the reaction milder and easier to control the temperature.
   • Dissolve base materials: To prepare solvent - based adhesives.
   • Diluent: Dilute the adhesive to a certain viscosity, which is beneficial for wetting and easy for coating.
   • Regulate the evaporation rate of the adhesive:
   • Prevent gelation: To increase storage stability.
   • Surface cleaning agent before bonding:
   • Direct bonding for certain plastics:
   • Reduce costs and improve efficiency:
2. Selection of Adhesive Solvents:
   • Polarity: Select a solvent with the same or similar polarity as the base material (based on the principle of similar compatibility).
   • Solubility parameter (related to polarity): The solubility parameter of the solvent should be close to that of the polymer matrix.
   • Volatility of the solvent: Select a solvent with an appropriate volatility or a mixture of fast - and slow - evaporating solvents. If the solvent evaporates too fast, a film is likely to form on the surface of the adhesive liquid, and the solvent under the film is difficult to evaporate; if the solvent evaporates too slowly, the surface - drying time is slow, affecting work efficiency.
   • The selection of the solvent should consider price, toxicity, and source