1. Good liquidity
Good fluidity can make the film uniform the film thickness uniform. Because of the long coating die head, especially the long die head, double die head wide canvas die which are coated on both sides at one time, the melt flow distance in the die is longer, the passing time is longer, the resistance in the die is larger. If the resin with good fluidity is not selected, the film thickness will be uneven the flow rate will be unequal. The temperature of the moulding lip varies, there will be local first cooling loss of viscoelasticity, fastness of bonding with the woven fabric. The melting index M1 is used to measure the fluidity. Generally speaking, polyethylene is 4-15 g/10 min polypropylene is 7-30 g/10 min.
2. Certain Melt Strength
The melt flowing out of the die must have a certain viscoelasticity, that is, the melt strength should be high. Because the melt casting distance to the braided fabric is a traction drawing process has a certain traction ratio, the melt must have a certain strength in order not to be pulled or broken. Because of the inertia caused by die weight traction speed, the melt fluidity can not be too good in the distance from die to knitted fabric, so as to avoid the non-uniform stacking film or film thickness in the longitudinal direction, so the melting index of resin can not be too high. The melt index of PP raw material for flat filament is 2-6g/10min, which is not suitable for coating. The flow is too slow the film thickness is uneven.
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