70 degree transparent TPU injection molding Dechuang Chemical
The main characteristics of TPU are:
Wide range of hardness: by changing the proportion of TPU reaction components, products with different hardness can be obtained, and with the increase of hardness, the products still maintain good elasticity and wear resistance.
TPU has high mechanical strength: TPU products have outstanding bearing capacity, impact resistance and shock absorption.
Outstanding cold resistance: TPU has a relatively low glass transition temperature and still maintains good elasticity, flexibility and other physical properties at minus 35 degrees.
Good processability: TPU can be processed by common processing methods of thermoplastic materials, such as injection molding, extrusion, calendering, etc. Meanwhile, TPU and some polymer materials can be processed together to obtain polymer alloy with complementary properties.
Oil, water and mould resistance. The recycling property is good.
TPU, as an elastomer, is a material between rubber and plastic. Judging from its rigidity, the rigidity of TPU can be measured by elastic modulus. The elastic modulus of rubber is usually 1-10 MPa, TPU is 10-1000 MPa, and plastic (nylon, ABS, PC, POM) is 1000-10000 MPa. TPU has a fairly wide hardness range, ranging from Shore A 60~Shore D 80 and has high elasticity throughout the hardness range. TPU has flexibility in a wide temperature range of-40-120 DEG C without plasticizer; TPU has good resistance to oils (mineral oil, animal and vegetable oils and lubricants) and many solvents; TPU also has good weather resistance and excellent high energy ray resistance. The well-known wear resistance, tear resistance and buckling strength are excellent. High tensile strength, high elongation and low permanent deformation rate under long-term compression are all the remarkable advantages of TPU.
The TPU properties introduced here include three aspects: mechanical properties, physical properties and environmental properties.
1. Mechanical properties: The mechanical properties of TPU elastomer mainly include: hardness, tensile strength, compression property, tear strength, rebound elasticity and wear resistance, buckling resistance, etc., while the mechanical properties of TPU elastic plastic include higher shear strength and impact power, etc. in addition to these properties.
(a) Hardness: Hardness is an indicator of a material's ability to resist deformation, scoring and scratching. The hardness of TPU is usually measured by Shore A and Shore D durometers. Shore A is used for softer TPU and Shore D is used for harder TPU. Hardness is mainly determined by the hard segment content in TPU structure. The higher the hard segment content, the higher the hardness of TPU will be. After hardness increases, other properties of TPU will also change, tensile modulus and tear strength increase, rigidity and compressive stress (load capacity) increase, elongation decrease, density and dynamic heat generation increase, and environmental resistance increase. The hardness of TPU is related to temperature. Cooling from room temperature to mutation temperature (-4~-12℃), hardness has no obvious change; At the abrupt temperature, TPU hardness suddenly increases and becomes very hard and loses elasticity, which is the result of soft segment crystallization.
(b) The relationship between hardness and tensile stress and elongation, and the relationship between hardness and tear strength. With the increase of TPU hardness, 100% constant tensile stress and 300% constant tensile stress increase rapidly and elongation decreases. This is mainly due to the increase of hard segment content: the higher the hard segment content is, the easier the hard segment phase formed is to form sub-crystal or crystalline structure, which increases the amount of physical crosslinking and limits the deformation of the material. If the material is deformed, the stress must be increased so as to increase the constant elongation stress and decrease the elongation. The relationship between TPU hardness and tear strength increases rapidly with the increase of hardness for the same reason as the explanation of modulus.
The formula and properties of TPU can be arranged and combined in many kinds. However, in the actual formulation design and industrial production, it is still very difficult to make the research and development that can really be used in very high-end applications due to the mutual restriction of raw materials (polyol and polyisocyanate and chain extender).
