Polyurethane is a general term for high-molecular polymers containing imidic acid groups (-NH-CO-O) in the molecular chain, referred to as PU (Polyurethane). It is usually prepared by reacting polyisocyanate with compounds or polymers containing polyhydroxyl groups. The polyurethane film used as packaging material is a thermoplastic polyurethane elastomer (abbreviated as TPU).

Polyurethane elastomer is a high-molecular synthetic material between rubber and plastic. Its molecular backbone is composed of flexible segments and rigid segments. The structure contains a large number of polar groups such as urethane groups and ester urea groups. The existence of these polar groups and their interactions give polyurethane elastomers a series of excellent properties. The use, diversification of functions and other reasons have led to the rapid development of polyurethane films, and have wide and unique applications in many fields.

What are the characteristics of polyurethane film are mainly reflected in:

1. Excellent wear resistance, good flexibility, especially high tear resistance, good elasticity, low temperature flexibility.

2. It has good characteristics in oil resistance, low temperature resistance, heat aging resistance, ozone resistance, radiation resistance, electrical insulation, adhesion, etc., excellent biocompatibility and resistance to various chemicals.

3. Polyurethane elastic material is synthesized from polyol, diisocyanate, etc. as raw materials. It has a unique block molecular structure, and its elasticity, hardness, hydrophilicity, etc. can be changed by adjusting the proportion of polyurethane soft and hard segments. New products. Its products have unparalleled characteristics: unique adhesion, wetting, flexibility, wear resistance, gloss, etc.

Polyurethane can be used well in waterproof and breathable membranes. There are two main types: microporous and hydrophilic.

1. The pore diameter of the microporous film is very small, only 10-50μm, between water vapor with a diameter of 4X10-4 μm and water droplets with a diameter of 100-300μm, the water vapor can penetrate the microporous film, and the water droplets Can not pass, so as to achieve the purpose of waterproof and breathable, under the electron microscope, can observe the obvious microporous structure, its breathability can be comparable to the respiration of human skin.

2. Hydrophilic type. The surface and body of the continuous non-porous film and coating material are uniform and dense structure. The water resistance is determined by the continuity of the material and the large surface tension. The breathability is determined by the type, proportion and relative molecular weight of the hydrophilic soft segment of the polyurethane. It is achieved by a complex molecular diffusion mechanism: polyurethane The micro-phase separation structure provides the possibility of complex molecular diffusion. Water molecules are transported along the dense molecular chain gaps, adsorbing moisture from the high humidity side, and passing through the hydrophilic groups on the polyurethane molecular chain to the low humidity side, but Its respiration is generally worse than that of microporous structures. A new type of polyurethane film and coating. By adjusting the proportion of hydrophilic soft segments and relative molecular mass, its water vapor transmission rate can reach the same level as microporous materials, thereby controlling the humidity and heat of the microenvironment in contact with the skin balance. In addition, its dense structure can play a role in blocking dust and bacteria.

Polyurethane film can be used in the medical industry and industry. Such as medical and health aspects: surgical coats, medical mattress pads, ice packs, bandages, plasma bags, etc. Industrial field: fire prevention, heat insulation, sound insulation materials, etc. In addition, it has a wide range of applications in footwear, sports goods, daily necessities, etc.