Influence factors and countermeasures of crystal point of TPU film

Date:Feb 11, 2020

    Thermoplastic polyurethane elastomer (TPU) is a special elastic material between rubber and plastic.It has high modulus, high strength, high elongation, high elasticity, and excellent abrasion resistance, oil resistance, low temperature resistance, and aging resistance. performance. TPU can be processed into products with different uses by extrusion, injection, blow molding, calendering, melt spinning and other methods, and has been widely used in many fields. TPU film is formed by extrusion processing of TPU particles. There are four processing methods: blow molding, casting, calendering or calendering sheet molding, and extrusion coating. Generally speaking, blown TPU film can be used in shoes, waterproof and breathable clothing fabrics, medical and defense supplies, weapon packaging, tents, sports and leisure equipment, sanitary napkins, toys, and civilian daily necessities packaging. TPU film can be used in shoes, waterproof and breathable clothing fabrics, weapon packaging, tents, sports clothing, daily necessities, etc .; calendering or calendering is mainly used to produce TPU sheet products, used to produce transparent shoulder straps, medical packaging materials, safety Bulletproof glass interlayer film, conveyor belt, interior materials, pads and other products; extrusion coating is generally used for the production of composite fabrics, TPU and non-woven fabrics, industrial fabrics, clothing fabrics are coated at one time and can be used for clothing fabrics, trademarks , Gloves, etc. In addition to film grade TPU, in addition to appropriate crystallization speed and melt viscosity, an important requirement is the control of the crystal point of the product. Due to the thin thickness of the blow molding process, usually within 0.1mm, thinner films require higher crystal points. In addition to the effects of film extrusion and blow molding processes, the reason for the crystal point is more important during the TPU synthesis manufacturing process due to the effects of raw material quality, process methods, machine structure, personnel control, and the environment. There are two main forms: one is physical impurities and the other is chemical excess polymer. Sort out the following table:


Raw   material standards for MDI, polyester polyols and BDO
ItemMDIPolyester polyolBDO
Chroma (APHA)103010
Purity / %99.599.5
Freezing point / 38
Hydrolyzed chlorine / %0.001
Cyclohexane does not melt /%0.1
Acid value /mgKOH·g-10.30
Water / %
Acetaldehyde dieethanol /%0.15

Main factors and solutions of TPU process and processing   affecting crystal point
Control   item Main influence factor Countermeasure
R value 1.   Raw material moisture
    2. Perfusion flow fluctuations
1.   Control the moisture content of raw materials within 0.03%, and monitor each   batch.
    2. Set the flow fluctuation range within ± 0.2%, and isolate it if it   exceeds the range.
MI valueR value changeSame as above
Reactivity1.   Type of catalyst
    2. Catalyst addition method
1.   Catalysts that are not easily hydrolyzed are preferred
    2. Add catalyst to the side to prevent the catalyst from hydrolyzing in   polyester or polyether polyol 
LubricantsThe type and amount of lubricantsSuitable   for internal and external lubricants and their added amounts, ensuring the   melt fluidity, the lubricating effect with the screw surface, and reducing   residual
Processing1. Filter
    2. Lubricant
1.1.   Increase the number of meshes, for example between 100 mesh and 200 mesh;  
    1.2. Filters must be replaced before starting
    2. Focus on external lubricants to prevent the melt from sticking inside   the screw or on the surface of the film equipment 

Effect of equipment   on crystal point and solution
Control   item Main influence factor Countermeasure
Filling   machine1.   Precision of mass flow meter
    2. Stability of perfusion flow
1.   Accuracy of mass flow meter should be within 0.2%
    2. The stability of perfusion flow should be within ± 0.2%, and the alarm   should be isolated if it exceeds the range. 
Extruder1.   Polyester polyol and chain extender pre-mixed
    2. Dispersion, distribution, mixing and degree of reaction
1.   Due to the viscosity difference of each component, increasing the mixing   temperature and mixing speed of each component will help the adequacy of   subsequent extrusion reactions
    2. The length of the reaction section is preferably more than 45%
Raw material   tanks and pipesImpurities   and other raw materials Clean   the tanks and pipes with new batches of raw materials before production
Drying system Moisture, impurities and high hardness TPU1.   Purge and clean the pipes of the drying system and the inside of the drying   system before feeding TPU to prevent impurities from mixing with the previous   batch of high hardness TPU particles
    2. TPU drying standard is the best control of water content within 0.03%

Employees and   Production environment affect on the crystal point 
Control   item Main influence factor Countermeasure
EmployeesProcess   standard and Equipment cleanliness1.Training   of producers and operators and online control and verification   mechanism
    2.The operators' strict implementation of the process standard, the   cleanliness of the equipment, and the thorough online isolation of   unqualified particles. 
Production environmentCleaning   and finishing, lighting, temperature and humidity, material piping sealing,   nitrogen protection and safety, etc




ConclusionTPU film point control is an important part of the TPU production synthesis stage, through to the raw materials, methods, machinery, equipment, personnel and environment and so on five big quality factor analysis and practice, to improve the crystal point on the TPU film level, product quality and stability has been significantly improved, can satisfy the film processing requirements: TPU film processing is to control the crystal point later, need to pay attention to clean up and melt filter for extruder, and the choice of processing temperature and speed.

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