Composition and application of two-component polyurethane adhesives
PREFACE
Two-component polyurethane adhesives are usually composed of an isocyanate component containing NCO (curing agent) and a hydroxyl component containing hydroxyl (main agent). When used, the two liquid components are mixed according to a certain ratio, and NCO and OH are utilized to react to form a solid polyurethane, which is then bonded to the surface of the substrate using the polar groups of the polyurethane to form a hydrogen bond and other bonding interactions, thus playing a role in bonding.
Two-component polyurethane adhesive came out earlier, the development began in the 1950s, Bayer first developed Desmoders series diisocyanate and Desmophens series of low molecular weight end hydroxyl polyester polyol, the two in accordance with a certain proportion of the configuration, you can get Polystal series of two-component solvent-based polyurethane adhesives, for the future two-component polyurethane adhesives Laid the foundation for the future industrial development of two-component polyurethane adhesives.
Two-component polyurethane adhesive belongs to the reactive adhesive, two components in the mixing of cross-linking reaction and curing adhesive. Usually can be cured at room temperature, can also be heated for curing, its final bonding strength is generally larger than one-component polyurethane adhesive, can meet the requirements of structural adhesives. In addition, the dosage of the two components of two-component polyurethane can be adjusted within a certain range, the formula is flexible, and by adjusting the raw materials and molecular weight of the two components, it can obtain products with different performance, which can be used for bonding of plastics, films, metals, wood, glass and other materials, with a wide range of bonding.
According to the availability of solvents can be divided into two-component polyurethane adhesive solvent and solvent-free type.
Solvent-based two-component adhesives, although good infiltration of the substrate, bonding strength, strong permeability, but not conducive to environmental protection and health.
Solvent-free two-component adhesive does not contain solvents, will not cause pollution due to solvent volatilization, safe operation. Has a better development prospects. Solvent-free two-component polyurethane main agent and curing agent at room temperature viscosity is high, but still has mobility, the use of the two will be mixed proportionally, warmed to 50-60 ℃, so that its viscosity is reduced, because it does not contain solvents, so do not need to be heated and dried by the process can be directly coated on the substrate.
-Composition
Two-component polyurethane adhesive mainly consists of two components, the polyisocyanate component is customarily referred to as component A or A, and the hydroxyl component is referred to as component B or B. In fact, component A (component A) is the main component of the polyurethane adhesive. In fact, the A component (A component) can also be the hydroxyl component, the B component (B component) can be the polyisocyanate component.A component (polyisocyanate component) mainly consists of polyisocyanate, small molecule chain expanding and cross-linking agent, additives, fillers, B component (hydroxyl component) mainly consists of polyols or polyols and isocyanate reaction of the end of the hydroxyl polymers, small molecules of the chain expanding and cross-linking agent, catalysts, additives, filler.
Raw material
Role
Commonly used
Polyisocyanate
Involved in curing reactions
PAPI, MDI, TDI, HDI diurea, TDI-TMP adducts, HDI trimers, and prepolymerized polyisocyanates
Polyols
Involved in the curing reaction
Polyether polyols, polyester polyols, castor oil and its derivatives, etc.
Small molecule chain extenders
Reacting with the terminal NCO group to form a carbamate or urea group to expand the chain.
Ethylene glycol, diethylene glycol, 1,4-butanediol, hexanediol, etc.
Cross-linking agent
Generate crosslinks to form a three-dimensional mesh structure
Trimethylolpropane, glycerol, triethanolamine, etc.
Catalysts
Accelerate the reaction rate
Triethylene diamine, dibutyltin dilaurate, stannous octanoate, bismuth isooctanoate, zinc isooctanoate, etc.
Additives
Increase additional properties
Plasticizers, light stabilizers, antioxidants, colorants, flame retardants, water removers, etc.
Fillers
Reduce cost, improve hardness or other properties
Talc, titanium dioxide, silicon dioxide, molecular sieve powder, etc.
-Application-
Two-component polyurethane adhesive has good mechanical properties, adhesion, chemical resistance, adjustable performance, bonding strength, bonding a wide range of advantages, widely used in metals, plastics, packaging materials, insulating materials and other substrates bonding. From the application classification, it can be divided into general-purpose two-component polyurethane adhesive, two-component adhesive for composite film, two-component adhesive for shoes, two-component polyurethane sealant, two-component polyurethane structural adhesive and so on.
General-purpose two-component polyurethane adhesive.
Usually the early development and application of a class of solvent-based two-component polyurethane adhesive called “two-component polyurethane adhesive”. The main feature of this type of adhesive is: polyethylene glycol adipate diol and toluene diisocyanate as the main raw material of the end-hydroxyl polyurethane organic solution as the main agent, trimethylolpropane – toluene diisocyanate adducts of organic solutions as a curing agent. This kind of adhesive film is strong, impact resistance, water resistance, oil resistance.
