Polyurethane Adhesive (styrofoam) is divided into two categories according to the curing method: one-component and two-component. Different types will be applied to different scenes. Let's take a look at the performance of different types of polyurethane adhesive.
One-component type
One-component polyurethane adhesive can be used directly, without mixing, with almost no metering error and convenient operation. There are mainly solvent-based, wet curing, water-based and hot-melt types.
1. Solvent. Polyester thermoplastic polyurethane solution adhesive is the most typical solvent-based adhesive. The high polarity of ester group endows the adhesive with adhesiveness to various materials (especially to plastics), and the crystallinity of polyester segment and the formation of hydrogen bond between ester group and carbamate group can improve the adhesive strength to the adherend. Increasing the glass transition temperature of polyurethane can improve the heat resistance of adhesive. Improving the relative molecular weight of polymer (preferably 50,000 ~ 100,000) is also an effective way to improve the initial and final bonding strength of adhesive.
2. Wet curing type. Wet-curing polyurethane adhesive, also known as prepolymer polyurethane adhesive, is made by reacting excess diisocyanate with polypropylene glycol, polyglycerol or polyester. The content of-—NCO in general components is 5% ~ 10%, and it is mainly cured by moisture in the air when bonding. The disadvantage is that the curing is slow and the adhesive layer is easy to produce bubbles.
The bonding mechanism is that the isocyanate group in the adhesive reacts with moisture in the atmosphere to generate amine and carbon dioxide, and the amine continues to react with the isocyanate group to obtain a chain-extending polymer (curing). Polyurethane adhesive modified by epoxy belongs to one-component wet-curing polyurethane adhesive. The appearance of the adhesive is yellow viscous liquid, and the main component is epoxy prepolymer with isocyanate group at the end. When using it, it is necessary to pay attention to the gluing and leave it at room temperature for 30~40min before bonding the adhered objects. It takes 2 ~ 3 days at room temperature to achieve a high bonding strength. It can bond materials such as metal, nylon, fabric and plastic, and it is insoluble in polystyrene foam and easy to operate. It has the properties of oil resistance, temperature resistance (110℃), wear resistance, hydrolysis resistance, vibration resistance and solvent resistance, etc., and is often used in corrosion protection and seepage prevention of chemical equipment.
3. Water-based. The biggest advantage of water-based polyurethane adhesive is that it is not easy to be poisoned and caught fire, and it is suitable for substrates that are easily corroded by organic solvents. In addition, its viscosity is not obviously different with the change of the relative molecular weight of the polymer, which can make the polymer obtain high relative molecular weight and improve its cohesive strength. Under the same solid content, its viscosity is generally lower than that of solvent, and products with high solid content (50% ~ 60%) can be made.
Water-based polyurethane adhesive can be used for wood adhesive, which can bond wood at room temperature or higher temperature, and has the advantages of high initial viscosity, excellent bonding strength and can also be used for wet wood. The adhesive layer has the advantages of good heat resistance, hot water resistance and aging resistance, no release of free formaldehyde, no pollution to the environment, no pollution and corrosion of bonded materials, which are beyond the reach of traditional wood adhesives. Wood chips and broken wood can also be made into particleboard with different properties by using waterborne polyurethane adhesive, which has good mechanical properties and is a practical building material for heat insulation and noise elimination. When used as a fabric treatment agent, the fabric is breathable after being treated with waterborne polyurethane containing ionic groups. After crosslinking, it has waterproof function.
4. Hot melt molding. It is a kind of hot melt adhesive made of thermoplastic polyurethane. Polyurethane elastomer is usually a block polymer with soft and hard segments polymerized from hydroxyl-terminated polyester or polyether, low molecular weight diol and diisocyanate. Therefore, polyurethane hot melt adhesive has better strength than polyester and polyolefin through hot melt adhesive. It has a wide range of applications and can be used for bonding materials such as metal, glass, plastic, wood and fabric. For example, the polyurethane hot melt adhesive synthesized from a specific ethylene glycol mixture and polyester can be used to bond fabric sheets. This bonded fabric has good washing and dry cleaning resistance, and it is soft and feels good.
