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TPU coating processing technology

Update:29-09-2020
Summary:

TPU film has been widely used, and there are two new tr […]

TPU film has been widely used, and there are two new trends in the application of sports shoes: one is the popular wind blown by Nike sports shoes, that is, the TPU film is first screen-printed and colored, and then formed and glued with high frequency. Put it together on the upper for decoration to obtain a special decorative effect. The second is to use waterproof and moisture-permeable TPU film and shoe material cloth to be used together to achieve the effect of waterproof and moisture-permeable.

TPU extrusion coating is a production process in which molten TPU is attached to a substrate. The TPU pellets are squeezed and melted in the extruder barrel, and then pressed down and extruded between two rollers through a plate die. At the same time, the substrate is drawn between the molten plasticized material and the rubber pressure roller. The pressure of the pressure roller is controlled, and the plasticized TPU material is bonded to the base material. After the hot adhesive cloth is cooled by the metal roller, it is cut and wound.

The dies used for TPU extrusion coating are divided into flexible lip extrusion die and flexible extrusion die with restrictor. The die should make the melt have good melt coating fluidity and lateral dripping. The heatable connecting sleeve of the central feed port mold sends the melted and plasticized material from the extruder head to the die port. The die connecting sleeve and the die should be kept at the same temperature to ensure the best extrusion effect. The die is heated by a resistance wire heating cylinder, and the heater is placed in the air at the selected position to avoid local overheating, thereby ensuring good fluidity of the melt. The die lip is V-shaped to minimize the gap between the die and the roller.

Between uncoiling and coiling, a set of precise stretching, positioning and centering equipment is usually installed to ensure that the product can pass through the roller smoothly during high-speed production. The fast splicing device guarantees the long-term high-speed continuous operation of the production line.

The base material can be preheated with an open flame or a belt heater, but it is best to preheat with a metal heating drum. The inside of the drum is heated by electricity or steam, and the temperature reaches 177℃. General polyurethane adhesives can bond TPU coatings to various substrates. Preheating the substrate can improve the adhesion of the coating.

The preheated substrate is drawn onto the pressure roller to meet the molten material flowing down from the die, so that the substrate and the molten material are bonded in the nip, and the bonding state and appearance are controlled by the hardness of the rubber pressure roller. The pressure roller is driven by air pressure or hydraulic pressure. The inside of the roller is cooled by high-speed circulating water, and a water-cooled aluminum roller is installed on the rear edge of the roller as a heat sink. The cooling roller quickly cools the molten material on the substrate, and there is a set of precise water cooling system in the roller. The rotation speed of the cooling roller determines the thickness of the coating and the overall melting efficiency, and the smoothness of the roller surface determines the effect of the coating surface.

Process conditions-first adjust the position of the extruder, determine the extrusion conditions, adjust the die lip to give a constant melt under the specified output, and the lip and melt temperature is 188~204℃. Secondly, the base material moves at a low speed to adjust the extrusion line. Make the melt coating line quickly reach the predetermined line speed and melt coating quality. The cooling roll temperature is 27~38℃, and the preheating system temperature is 71-~93℃. Then adjust the preheating conditions, the gap between the die and the roll, and the pressure of the roll to adjust the adhesion of the substrate. The adjustment of the line speed can control the coating weight.

TPU film is mainly used in shoes, ready-to-wear, medical supplies, defense supplies, sports goods, industrial supplies, baby supplies and toys, people's livelihood supplies and daily necessities, etc. TPU film is widely used in sports shoes: trademark decoration on soles and uppers, airbags, air cushions, oil bags, etc. From this it seems extremely versatile.

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