Polyurethane sealant is a room temperature curing material for in-situ filling and bonding of joints. Before curing, it is in the form of paste, which can be extruded to fill the gap. After curing, it is an elastomer, which plays the role of interface bonding, anti-leakage, waterproof, dustproof, and withstands vibration or displacement caused by thermal expansion and contraction. .
Polyurethane sealants are available in one-component and two-component packaging styles. Two-component polyurethane sealant is packaged with two components, one is a component containing NCO, and the other is a curing agent containing active hydrogen. When using, the two components are mixed in a certain proportion, and the two components are mixed with active hydrogen through NCO. The reaction is cured into an elastomer. Its advantages are that the room temperature curing speed is faster than that of one-component, and the cost is low, but it is inconvenient to operate. One-component polyurethane sealant is composed of NCO-terminated prepolymers, fillers and additives. It is sealed and stored. When used, it reacts with moisture in the air to cure into an elastomer with a network structure.
Because polyurethane sealant has good adhesion to various materials (such as concrete, metal, glass), and has the characteristics of UV resistance, low temperature resistance, chemical resistance, and high cost performance, it has been widely used in construction engineering, Transportation, aerospace and automotive fields.
Polyurethane sealants are mainly composed of macromolecular polyols, isocyanates, solvents, additives and fillers.
Plasticizer
In order to reduce the viscosity of the material (easy to mix) and increase the flexibility and elongation of the product, a certain amount of plasticizer is often added to the polyurethane sealant. The commonly used plasticizers are mainly diisooctyl phthalate (DOP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), and diisooctyl adipate. (DOA), triethyl phosphate, etc.
A silane coupling agent
In order to improve the compatibility between inorganic fillers and polymer resins and improve the bonding force between organic resins and inorganic fillers, a small amount of silane coupling agent, such as KH-560, is often added to polyurethane sealants.
water remover
In order to maintain the storage performance of the product, a small amount of water scavenger is often added to the polyurethane sealant, such as molecular sieve, p-toluenesulfonyl isocyanate (PTSI), calcium oxide, etc.
filler
Inorganic fillers are closely related to the rheological properties and mechanical strength of polyurethane sealants. Many experiments have proved that different types of fillers, such as pigments (carbon black, etc.), nano-calcium carbonate, can improve the adhesive strength of polyurethane sealants. After organic surface modification, fumed silica can also improve the rheological and mechanical properties of polyurethane sealants, but because it is difficult and expensive to handle, inorganic fillers to replace fumed silica are still being closely watched.
Calcium carbonate is a commonly used filler in the polyurethane sealant industry. Because calcium carbonate particles are large and have not undergone surface treatment, it has little effect on the rheological properties and mechanical properties of polyurethane sealants. Studies have found that calcium carbonate treated with stearate or cationic surfactant can improve the rheological and mechanical properties of polyurethane sealants. Some scientists have also found that the use of calcite calcium carbonate fillers in polyurethane sealants will have good thixotropy and high tensile strength.
Compared with ordinary calcium carbonate, nano-calcium carbonate has a smaller particle size and a larger specific surface area. Because its particle surface is organically modified, when it is used as a polyurethane sealant filler, its particles are more likely to be in the polyurethane sealant. Medium dispersion, good compatibility with polyurethane prepolymer, which is beneficial to improve the reinforcing effect and sag resistance of the polyurethane sealant system.
application
achitechive
In the field of construction, polyurethane sealants are widely used for the sealing of construction joints such as concrete slab curtain walls, reinforced concrete and slate, thin plates, and glass fiber reinforced concrete. At the same time, polyurethane sealant is also widely used in the caulking of roads and runways and the bonding and sealing of various pipes and bridges, especially the joints subject to dynamic stress and thermal contraction and expansion.
Aerospace
Due to advances in sealing technology, polyurethane sealants have also opened up new markets in the aerospace field. In the mid-20th century, sealants have been used in the aerospace field, and there have been reports of the development of an Low-volatility high-grade sealants, and with the tremendous progress in aerospace technology, the demand for this new type of sealant will continue to grow.
Automobile industry
As far as the automotive industry is concerned, in recent decades, due to the development of the automotive industry requiring lightweight automotive components, a large number of plastic parts have been used, especially high-strength ERP (glass fiber reinforced plastic) and SMC (sheet molding material). , is used in automobile manufacturing. The polyurethane sealant not only has a good bonding and sealing effect on traditional metal materials, but also has a very good bonding effect on thermoplastics and new composite materials. Compared with traditional mechanical welding and riveting technology, polyurethane sealant has very obvious advantages, such as: able to bond substrates with different thermal expansion coefficients, firm bonding, high mechanical strength, good weather resistance, better insulation and Less corrosion, etc., and reduce vibration with screw and rivet assemblies, and improve efficiency in bonding of automotive assemblies.
At present, moisture-curing polyurethane sealant is the best bonding and sealing material for installing automotive windshields, and 95% of the world’s automotive windshields use one-component moisture-curing polyurethane sealants. More importantly, the outstanding feature of lightweight, green and environmentally friendly polyurethane sealant is to meet the requirements of policies and regulations such as environmental protection, industrial hygiene, and resources.
Analysis of Polyurethane Sealants
At present, the development of polyurethane sealants has been relatively mature, and with the development of science and technology, many fields have put forward higher requirements for the performance of polyurethane sealants, which requires us to continuously improve the formulation system to achieve product performance upgrades.
Microspectrometric analysis technology service can determine the types of isocyanates, macromolecular polyols, solvents and additives in polyurethane sealants through analysis and testing; at the same time, it can also analyze the types and functionalities of synthetic monomers and polyethers of polyester polyols. It is very convenient for us to find the corresponding raw materials. In terms of product development and design, it can also greatly help the research and development of new products, shorten the development time and improve the performance of products.