Polyurethane structural adhesive
The definition of structural adhesives refers to adhesives that are used in the bonding of force structural parts and can withstand large dynamic loads, static loads, and long-term use. In layman's terms, structural adhesives are structural components that replace metal, plastic, glass, wood, etc. in the form of bolts, rivets, or welds, and are adhesives that can withstand heavy loads over a long period of time and can still be trusted.
People have already been familiar with epoxy adhesives for structural applications, but the use of structural polyurethane adhesives has been gradually recognized. Polyurethanes are block copolymers composed of hard and soft segments. The hard segment molecules provide shear, peel strength, and heat resistance, while the soft segment molecules have resistance to impact, fatigue, and fatigue. By adjusting the composition or structure of the hard and soft sections, a variety of structural polyurethane adhesives having a strength that meets the requirements can be obtained.
1. Development of structural adhesives
Structural Polyurethane Adhesives Since the beginning of FRP (Fiber Reinforced Plastics) for automobiles, great progress has been made over the past 20 years. In addition to its application in the automotive industry, it is also widely used in waterborne vehicles [for the bonding of FRP decks and hulls and the bonding of SMC (plate model composite) towers, SMC floodgates, etc. These adhesives have Excellent vibration resistance and impact resistance], elevators (bonding of elevator doors, wall panels), septic tanks (bonding of FRP flanges, partitions), baths (SMC-tiles, ceilings-tiles Bonding), as well as residential (adhesion between the exterior decorative material cement preforms) and other fields.
(1) Adhesion of automotive components Originally successfully used as a polyurethane structural adhesive for automobiles was piogrip, Coodysr, USA, which is a solvent-free two-component reactive adhesive and used in 1967 for the bonding of 5MC engine covers for trucks. . Subsequently, companies such as GM, Ford, Mack, etc. successively bonded to SMC parts of large-sized trucks. Then it was widened to the FRP part.
Japan introduced technology from the United States and modified it. In 1984, Nissan Polyurethane Adhesive was used to bond Toyota's plastic structural parts with satisfactory results. It can produce adhesives with different morphologies, different viscosities, and different sag resistance properties depending on the structure and composition of the isocyanate-based guanlulu main agent and the polyol curing agent, and its adhesive strength is unchanged; The shear strength is comparable to that of the epoxy resin and at the same time shows a higher peel strength.
(2) Application of elevator paneling Panels used for walls, doors, and the like of elevators have been developed toward lightweight and high-grade in recent years. Among them, weight reduction is achieved through the use of highly rigid lightweight auxiliary materials and the thinning of surface materials. The material of the elevator panel is a steel plate with surface-attached PVC film (abbreviated as PVC steel plate), steel plate, galvanized steel plate, stainless steel plate and non-ferrous stainless steel plate, brass plate, and red copper plate. Panels are usually made of a reinforcing material such as galvanized steel sheet or steel plate bonded to the inner surface of the panel.
The requirements of the paneling on the adhesive are as follows: 1 It can be applied to various materials such as steel plate, PVC steel plate, stainless steel plate, galvanized steel plate, etc.; 2 Peeling strength> 150N/25mm; 3 Impact strength> 1.98j/cm2; 4 Shear strength > 15MPa; 5 destruction of the internal destruction of the adhesive; 6 moisture resistance, 60 °C, 90% RH environment after 60 days, its strength retention rate of 70% or more, and moisture absorption aging before drying, adhesive recovery Good; 7 Creep resistance, excellent fatigue resistance; 8 Even if the thin plate will not be caused by adhesive curing shrinkage and other deformation; 9 With baking paint baking temperature (up to 175 °C) heat resistance; 10 PVC The heat resistance of the steel plate is poor, so the curing temperature requirement is below 80°C; 10 the curing time is within 20min; 10 is suitable for automation.
Japan has successfully developed structural polyurethane adhesives and primers for elevator panels. First, a phosphate ester modifier was used as the main component, and a trace amount of PVC polymer was added (to improve moisture resistance) to make a solvent-type primer. A thin layer was sprayed on the material surface with a sprayer. After the solvent was dried, the coating was applied. Cloth adhesive for bonding. The structural polyurethane adhesive is a two-component adhesive composed of a polyether polyol and an MDI prepolymer.
Currently, structural polyurethane adhesives can not only be used to bond plastics and metals, but also widely used in the bonding of other materials; not only can be used for automotive assembly, and has been extended to the construction, machinery and other industrial fields. In order to make the structural polyurethane rubber more competitive, various countries are continuing to devote a great deal of improvement work, such as reducing the cost, changing the components into single components, further improving the heat resistance and strength, eliminating the direct use of the primer, and simplifying Mixing, extrusion and other construction operations, rich variety, crystal grade, to adapt to more types of sticky materials and more fields of application.
2. resolve resolution
Structural polyurethane adhesives are generally prepared by reacting a polyol with an excess of polyisocyanate to make an isocyanate-terminated prepolymer, and then adding a diamine for chain extension and cross-linking during chain extension and cross-linking. Actually forms urea chains and biuret junctions
Therefore, such polyurethane adhesives should be strictly referred to as "polyurea" adhesives.
1. Polyurethane-polyurea adhesive
The main agent of this structural adhesive is a reaction product of TDI and polyoxypropylene glycol (molecular weight 2000 and 1000) to prepare an NCO-containing prepolymer. The curing agent is the reaction of an anhydride with an arylamine (arylamine acylation) to produce aromatic amides (curing agents).
The structural polyurethane adhesive is a solvent-free type, has the characteristics of simple use process, convenient storage and transportation, can be cured at room temperature or heat, and its adhesive layer has elasticity and high shear strength. Therefore, this structural adhesive has been used to achieve satisfactory results for the dolphin helicopter rotor wing tip seal, metal-carbon fiber composite material bonding and component repair.
2. Polyurethane - Epoxy Resin - Polyurea Adhesive
Epoxy adhesives have the characteristics of low flexibility, high hardness, high chemical resistance and high shear strength. If combined with polyurethane adhesives, they can take advantage of both: complementary disadvantages, can be turned out to have certain Softness, but also a good structural adhesive adhesive strength. Therefore, a great deal of research work has been done on epoxy-modified polyurethane adhesives abroad. The synthesis principle is that the polyurethane prepolymer containing NCO end groups is reacted with an alcohol containing an epoxy group to produce an epoxy-terminated polyurethane, the latter skeleton has polyurethane properties; the cross-linking cures through epoxy groups and amines The reaction is completed, generally using a polyurea containing an amino functional group. The resulting adhesive layer was a polyurethane-epoxy-polyurea structure.
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