Synthesis of the hottest polyurethane structural a

2022-08-05
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Synthesis method of polyurethane structural adhesive

the definition of structural adhesive refers to the adhesive that can bear large dynamic load and static load and can be used for a long time when applied to the bonding of stressed structural parts. Generally speaking, structural adhesives are used to join metal, plastic, glass, wood and other structural components in the form of bolts, rivets or welding. They are adhesives that can withstand heavy loads for a long time and still have reliable performance

people have been familiar with epoxy resin adhesives for structures for a long time, but the application of polyurethane adhesives for structures is gradually recognized. Polyurethane is a block copolymer composed of hard and soft segments. Hard segment molecules provide shear, peel strength and heat resistance, while soft segment molecules have impact, impact and fatigue resistance. By adjusting the composition or structure of hard and soft segments, a variety of structural polyurethane adhesives with required strength can be prepared

1. development of structural adhesives

structural polyurethane adhesives have made great progress in the past 20 years since they were used in FRP (fiber reinforced plastics) of automobiles. At present, in addition to being applied in the automotive industry, it is also widely used in water vehicles [for bonding FRP deck and hull, SMC (plate model composite material) tower, SMC sluice, etc., which have excellent vibration resistance and impact resistance], elevators (bonding of doors and wall panels in electric elevators), purification tanks (bonding of FRP flanges and diaphragms), baths (bonding of SMC tiles and ceiling tiles), And residential (bonding between cement prefabricated parts of exterior decoration materials) and other fields

(1) the adhesion of automobile parts was first successfully used as a polyurethane structural adhesive for automobiles by pliogrip of American coolyesr company, which is a solvent-free two-component reactive adhesive. It was used for the adhesion of 5mC engine hood of trucks in 1967. Subsequently, WangChuanFu basically maintained the frequency of meeting one core supplier every week. GM, Ford, Mack and other companies successively bonded SMC parts of large trucks. Then it is extended to FRP components

Japan imported technology from the United States and modified it. In 1984, Nissan polyurethane adhesive was used to bond Toyota plastic structural parts, and the effect was satisfactory. According to the different structure and composition of isocyanate terminated yanqulu main agent and polyol curing agent, it can produce adhesives with different formability, different viscosity and different sag resistance, while its adhesive strength remains unchanged; Its shear strength is equivalent to that of epoxy resin, and it also shows high peel strength

(2) the application of elevator panels the panels used for the walls and doors of elevator rooms have developed in the direction of lightweight and advanced in recent years. Among them, lightweight is realized by the adoption of high rigidity and light auxiliary materials and the thinness of surface materials. The materials of elevator panels include steel plate with PVC film on the surface (PVC steel plate for short), steel plate, galvanized zinc steel plate, stainless steel plate, non-ferrous stainless steel plate, brass plate, red copper plate, etc. with appropriate heat treatment process. The panel is usually composed of galvanized steel plate or steel plate and other reinforcing materials bonded to the inner part of the surface plate

the panel has the following requirements for adhesives: ① it can be applied to various materials, such as steel plate, PVC steel plate, stainless steel plate, galvanized steel plate, etc; ② Peel strength 150n/25mm; ③ Impact strength > 1.98j/cm2; ④ Shear strength 15MPa; ⑤ The failure state is the internal failure of the adhesive; ⑥ Humidity resistance: after 60 days in the environment of 60 ℃ and 90%rh, the strength retention rate is more than 70%, and the adhesive can be dried after moisture absorption and aging, with good recoverability; ⑦ Excellent creep resistance and fatigue resistance; ⑧ Even the thin plate will not be distorted due to the curing shrinkage of the adhesive; ⑨ It has heat resistance to paint baking temperature (up to 175 ℃); ⑩ Due to the poor heat resistance of PVC steel plate, the curing temperature is required to be below 80 ℃; ⑩ Curing time is within 20min; ⑩ Suitable for automation

Japan has successfully developed structural polyurethane adhesive and primer for elevator panels. First, a solvent based primer is prepared by adding a small amount of PVC polymer (to improve the moisture resistance) with phosphate ester modifier as the main component. A layer can be sprayed with a spray on the surface of the material with a thin stroke of 600 (800) mm. After the solvent is dried, the adhesive is coated for bonding. The structural polyurethane adhesive is a two-component adhesive composed of polyether polyol and MDI prepolymer

at present, structural polyurethane adhesive can be used not only for bonding plastics and metals, but also for bonding other materials; It can not only be used for automobile assembly, but also has been extended to the construction, machinery and other industrial fields. In order to make the structural polyurethane adhesive more competitive, countries are continuing to make a lot of improvement work, such as reducing the cost, changing the two-component into one component, further improving the heat resistance and strength, eliminating the direct use of primer, simplifying the construction operations such as mixing and extrusion, and enriching the product types and crystal grades to adapt to more types of bonded materials and applications in more fields

2. synthesis method

the common preparation method of structural polyurethane adhesives is to first react polyols with excess polyisocyanates to prepare isocyanate terminated prepolymers, and then add binary amines for chain extension and cross-linking. In the process of chain extension and cross-linking, urea chains and biuret structures are actually formed. Therefore, this kind of polyurethane adhesives should be strictly called "polyurea" adhesives

1. Polyurethane polyurea adhesive

the main agent of this structural adhesive is a prepolymer containing NCO group prepared by the reaction of TDI and polyoxypropylene glycol (molecular weight 2000 and 1000). The curing agent is the reaction of anhydride and aromatic amine (acylation of aromatic amine) to produce aromatic amide (curing agent)

the structural polyurethane adhesive is solvent-free, with the characteristics of simple use process and convenient storage and transportation. It can be cured at room temperature or heat. Its adhesive layer has elasticity and high shear strength. Therefore, the structural adhesive has been applied to seal the wingtip cover of the "dolphin" helicopter rotor, to bond metal carbon fiber composites and to repair components with satisfactory results

2 Polyurethane epoxy polyurea adhesive

epoxy resin adhesive has the characteristics of low flexibility, high hardness, high chemical resistance and high shear strength. If it is combined with polyurethane adhesive, the advantages of the two can be used: complementary disadvantages, and it can be used to create an ideal structural adhesive with a certain softness and considerable adhesive strength. Therefore, a lot of research work has been done on epoxy modified polyurethane adhesive abroad. The synthesis principle is that the polyurethane prepolymer containing NCO end group reacts with the alcohol containing epoxy group to form epoxy end group polyurethane, and the latter skeleton has the characteristics of polyurethane; The cross-linking and curing is completed by the reaction of epoxy group and amine. Generally, polyurea containing amino functional group is used. The adhesive layer is polyurethane epoxy polyurea structure

reprinted from: fine chemicals in the 21st century

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