What's the Advantages and disadvantages of casting-type polyurethane prepolymers?
Casting-type polyurethane prepolymers, also known as liquid rubber, are products produced by pouring liquid reaction mixtures into molds. They are widely used and have high production yields.
Major Advantages of Casting-type Polyurethane Prepolymers:
1. Wide range of adjustable performance.
By selecting raw materials and adjusting formulations, various physical and mechanical performance indicators can be changed within a certain range to meet different user requirements for product performance. For example, hardness is often a critical indicator for product evaluation. Polyurethane prepolymers can be used to manufacture soft printing rolls with a Shore A hardness of about 20, as well as hard steel rolls with a Shore D hardness exceeding 70, which is difficult to achieve with common elastic materials. Polyurethane prepolymers are polar polymer materials composed of many flexible and rigid segments. As the proportion of rigid segments increases and the density of polar groups increases, the original strength and hardness of the elastomer will correspondingly increase.
2. Excellent wear resistance.
Especially under working conditions with wetting media such as water and oil, their wear resistance is often several to tens of times that of ordinary rubber materials. Even though metals like steel are very hard, they may not necessarily be wear-resistant. For instance, in large water pumps in the Yellow River irrigation area, metal wear rings and protector rings of the overflow components suffered severe wear and leakage after being washed by a large amount of sediment within a few hundred hours. In contrast, wear rings and protector rings coated with polyurethane prepolymers (cyclone separators) continued to operate for 1800 hours without wear. Other applications of polyurethane prepolymers include rice husk beds for rice milling, vibrating screen plates for coal selection, tracks for sports fields, dynamic oil seals for cranes and forklifts, elevator wheels and roller skate wheels, solid polyurethane tires, photocopier and screen printing doctor blades. It's worth mentioning that, to improve the friction coefficient of medium and low-hardness polyurethane prepolymers and enhance their wear resistance under load, a small amount of lubricants such as aluminum disulfide, graphite, or silicone oil can be added to these types of polyurethane prepolymers.
3. Versatile processing methods and wide applicability.
Casting-type polyurethane prepolymers can be formed using molding, mixing, and curing processes similar to ordinary rubber (referred to as MPU). They can also be made into liquid rubber, cast molding, sprayed, sealed, or centrifuged (referred to as CPU). They can also be made into granular materials, similar to common plastics, using processes such as injection molding, extrusion, rolling, and blow molding (referred to as TPU).
Molded or injection-molded parts can also be mechanically processed within a certain hardness range, such as cutting, grinding, and drilling. The diversity in processing makes polyurethane prepolymers highly versatile, and their application areas continue to expand.
4. Polyurethane prepolymers have advantages such as oil resistance, ozone resistance, aging resistance, radiation resistance, low-temperature resistance, good sound transmission, strong adhesion, strong biocompatibility, and strong blood compatibility. These advantages have led to the widespread application of polyurethane prepolymers in military, aerospace, acoustics, biology, and other fields.