Low temperature resistance of polyurethane adhesive

Polyurethane materials are particularly excellent at low temperature resistance, and low temperature and ultra low temperature polyurethane adhesives made using this feature have been widely used in civil and defense industries.

1. Low temperature resistance of polyurethane adhesive

One of the characteristics of the two-component polyurethane adhesive is particularly excellent low temperature performance, which is not available in other adhesives. It can be seen from the table that the shear strength of polyurethane adhesive at low temperature is much higher than that of other adhesives, and the lower the temperature, the higher the strength. Table 1 Shear Strength (MPa) of RTV adhesives at room temperature.

Features and requirements

The characteristics of cryogenic adhesives applied on spacecraft and requirements for adhesives are as follows.

1. Features

(1) Work at liquid oxygen temperature and liquid hydrogen temperature.
(2) The bonding area is large, often the outer surface (or inner surface) of the entire tank.
(3) It can work under the dual effects of thermal stress generated by cold and heat shocks (filling and release of propellant) and pneumatic flushing during flight.
(4) According to the requirements of the manufacturing process of the vehicle itself, it is better to cure at room temperature or at a lower temperature.

2. Requirements

(1) Sufficient ultra-low temperature toughness and elongation are required to ensure that no debonding occurs due to the difference in the linear expansion coefficient between the metal shell and the non-metallic polymer material during the process of receiving the thermal shock.
(2) It must have sufficient ultra-low temperature strength to prevent the outer insulation layer from falling off.
(3) There must be sufficient antisepsis. When it is waiting for the flight, after the propellant is added, serious suction will occur, and the medium in the air will be adsorbed on the interface of the joint to cause corrosion.
(4) It is required to be able to construct a large area on the surface of a complex carrier.
(5) It is required that no low molecular volatiles be generated during the curing process.
According to these characteristics, when the large area of ​​thermal insulation layer is bonded, the spray coating process is used to apply the adhesive layer. The spraying process first requires that the glue must have a low viscosity and be easy to film.

3.DW series ultra-low temperature adhesive

1. Formulation of glue solution (1) Formulation of DW-1 glue (mass fraction)
Main agent (prepolymer made of trihydroxypolyoxypropylene polyol and isocyanic acid) l00 parts (2) Formulation of DW-3 adhesive (parts by mass)
Main agent (tetrahydrofuran polyether polyol-epoxy resin-isocyanate prepolymer) 100 parts curing agent 590 resin 20 parts KH-550 (silicon coupling agent) 4 parts surfactant 2-5 parts acetone 35-55 parts ( 3) DW-4 plastic formula (mass fraction)
Main agent (epoxy-modified polyurethane prepolymer) 100 parts of curing agent (MOCA) 25 parts

2. Spraying process

The adhered material was surface-treated, and sprayed with the glue according to the above formula, and allowed to stand at room temperature, followed by heating to 60° C. for 2 hours. The open-air phase can fully evaporate the added solvents and other additives, and can also make the film initially gel at room temperature, which can effectively avoid the flow phenomenon that accompanies the heating process.

application

Ultra-low temperature polyurethane adhesives have been widely used in civil and aerospace industries, such as bonding materials for various oxygen production and cooling equipment for civil use, bonding of materials in superconducting research, thermal protection layers on modern astronautics, and adhesion of thermal insulation layers. Wait.

Apollo spacecraft, as well as space shuttles, fuel tanks and thermal insulation structures are all glued structurally. The liquid oxygen fuel tank (boiling point -183°C), liquid hydrogen fuel tank (-253°C), liquid nitrogen tank (-196°C ) Ultra-low temperature polyurethane adhesives are used in manufacturing.

Reprinted from: 21st Century Fine Chemicals Network