The basic properties of polyurethane coated magnets
The basic properties of polyurethane composition are isophthalate, polyol, catalyst and chain extender. (1) The isocyanate group is very active and can react with alcohol, glue, acid and water. Diisocyanates and diisocyanates are now mainly used diisocyanates and diisocyanates. TDI is mainly used for flexible foam; MDI can be used for adhesives such as semi-rigid and rigid foam. Because PAPI has three major functions, it can be used for polyurethane thermosetting rigid foam, mixed products and casting products.
(2) Polyol is the elastic part of the polyurethane structure and is often used in polyurethane. The content of polyol in polyurethane determines the hardness, softness and hardness of polyurethane resin. It has the advantages of polyols and low-viscosity polyols. Moreover, this type of polyol is more widely used, especially in repercussive injection molding products. Polyester polyols are made from various organic polybasic acid esterification. The branched polyurethane composed of dibasic acid is mainly used for soft polyurethane, and the branched polyurethane composed of terpolymer is mainly used for rigid polyurethane.
In general, aromatic diamines are used for diamines, such as diphenylmethane diamine, methane diamine, etc. The influence of structure on the function of any polymer material is determined by its structure. The structure of polyurethane contains two aspects: chemical structure and aggregation structure. The chemical structure is the structure of the molecular chain and is an important factor in the initial formulation plan.
Aggregation structure refers to the stacking state of macromolecular chain segments, which is affected by molecular chain structure, composition process and application conditions. The influence of the soft segment on the function of the soft segment is as follows: the influence of the soft segment on the function of the soft segment. Polyurethanes prepared from different polyols and diisocyanates have different functions.
Because polyurethane contains many polar groups, soft polar groups can be formed on the hard phase to form a more uniform polar group between the polyurethane and the hard segment. Some polyesters will form soft segment crystals at room temperature, thereby affecting the function of polyurethane.
The strength, oil resistance and thermal oxidation stability of polyester polyurethane are higher than that of PPG polyurethane, but its hydrolysis resistance is poor. Polyethylene terephthalate (PTMEG) has a regular structure, similar strength to polyester, and is easy to crystallize. Generally speaking, polyethylene terephthalate (PET) has good flexibility and excellent low temperature function because the soft segment of the chain base is easy to rotate.
In addition, because the polymer molecular sieve does not contain ester groups, its anti-hydrolysis function is better than polyethylene terephthalate. The α-carbon in the soft segment of the polyhedron is easily oxidized to form peroxide free radicals, causing a series of oxidative degradation reactions. Because of the influence of steric hindrance, the hydrogen bond of the soft side chain segment is weak, the crystallinity is poor, and the strength is worse than that of polyester without side groups.
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