Through some typical application examples of polyphthalimide, the ways to utilize its unique properties to obtain practical and economical effects are expounded. A common application for adhesive polyimide films is the manufacture of mechanical moving parts such as bearings, piston rings, seals, wear plates, etc., rather than structural parts. These applications take advantage of properties of polyphthalimide resins not found in metals and most other engineering plastics
Taking bearings as an example, polyphthalimide resin bearings, with their excellent high temperature resistance, high pressure resistance, self-lubrication and chemical stability, can also operate normally when other materials are not competent. Therefore, the problems that were difficult to solve in the previous design were solved by using polyphthalimide parts. Polyimide bearings do not require additional protection measures such as vacuum, high or ultra-low temperature, atmospheric corrosion and radiation. In the past, special protective screens, seals, cooling baths and other expensive devices were often used.
The good chemical stability of polyphthalimide allows its products to be used in conditions where other bearing materials such as oil-impregnated bronze are damaged by chemical corrosion. Polyphthalimide has excellent radiation resistance, and bearings made from it can be used at high radiation densities.
When the inner surface temperature of a plastic bearing exceeds the critical limit of the bearing material, it is damaged by wear. The inner surface temperature of the bearing increases with increasing load and rotational speed. Bearings made of polyphthalimide can withstand higher speeds and higher loads than other plastic bearings due to their high temperature resistance and high load performance.
The tensile strength and burst strength of HDPE film are higher than those of LDPE film, but the impact strength and tear strength are lower than those of LDPE film. In addition, due to the linear structure of HDPE, users can easily orient in the flow direction during rolling, resulting in lower tear strength in this direction. HDPE film is harder and does not have a distinct waxy feel like LDPE film.
Due to the high softening point of HDPE, it can withstand cooking sterilization. The low temperature resistance is similar to that of low density polyethylene, and the air permeability of the latter is 5-6 times that of the former. The barrier to moisture is particularly good, but in fact, vinyl chloride/vinylidene oxide copolymers are often used when moisture barrier is required. HDPE films have better chemical resistance than LDPE films, especially oil and grease. Solubility in organic solvents decreases with increasing density. HDPE also suffers from environmental stress cracking, but to a lesser extent.
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