Polyethylene blowing film material selection

  1. Raw materials

Grade of raw materials should be used for blown film of polyethylene resin particles, contain appropriate smooth agent, to ensure that the film began.

  1. Influence of raw material properties on processing

The melting index (MI) of resin particles is too large, the viscosity of the melt resin is too small, the processing range is narrow, the processing conditions are difficult to control, the resin film formation is poor, not easy to process into a film; In addition, the melt index (MI) is too large, the polymer relative molecular weight distribution is too narrow, the thin film strength is poor. Therefore, the melting index (MI) should be chosen to be smaller, and relatively wide molecular weight distribution of the numerical raw materials, which can meet the performance requirements of the film, and ensure the processing characteristics of resin. Blow molded polyethylene film generally choose the melting index (MI) in the range of 2-6g/10min quality of polyethylene raw materials.

Analyze and solve common problems of film blowing

  1. Lead membrane difficult

(1) improper head temperature control: the head temperature should be adjusted appropriately.

(2) uneven discharge of the die: adjust the gap of the die and adjust the temperature of the connector.

(3) the molten material contains coke impurities: purify the raw material and clean the machine head and screw.

(4) improper control of extrusion process conditions: appropriate adjustment of process conditions.

  1. Bubble tube skew

(1) fuselage and die temperature is too high: appropriate reduction.

(2) the temperature of the machine head connector is too high: reduce it appropriately.

(3) uneven discharge of the die and uneven thickness of the film: properly adjust the gap of the die and the temperature of the connector of the head.

  1. Bubble tube in reed

(1) the clamping force of the traction roller is too small, or the rotation speed of the traction roller is affected by the regular change of mechanical transmission resistance: appropriately increase the clamping force of the traction roller, overhaul the mechanical transmission part of the traction device, so that the rotation speed of the traction roller is stable.

(2) the traction speed is not stable, and the wind pressure of cooling air ring is too large: for this, the traction speed should be adjusted to make it run stably; The wind pressure of the air ring should be reduced appropriately.

  1. Bubble tube swing

(1) melt temperature is too high: appropriately reduce the fuselage and nose temperature.

(2) the cooling efficiency of the cooling air loop is too low: appropriately increase the wind pressure and air volume of the cooling air loop.

(3) the friction between the bubble tube and the miter plate is too large: appropriately increase the miter plate Angle, reduce the contact area between the bubble tube and the miter plate.

(4) the head temperature is too low, difficult to discharge, membrane bubble beating: appropriately increase the head temperature and increase the screw speed.

  1. Film surface hair flower

(1) the temperature of the fuselage or nose is low, and the melt is not plasticized well: appropriately raise the temperature of the fuselage or nose.

(2) screw speed is too fast: appropriately slow down.

(3) the screw temperature is too high or too low: control the screw temperature in an appropriate temperature range by adjusting the flow rate of cooling medium in the screw.

  1. Hanging line is obvious

(1) mold discharging mouth mouth has decomposition material or material adhesion: with copper shovel will impurities or focal shaving, serious when should be clean out mandrel.

(2) the mouth mould was bruised: shaping mould.

(3) too small pressure in the head: add filter.

(4) melt temperature is too high: appropriately reduce the fuselage and nose temperature.

  1. Poor transparency

(1) fuselage or nose temperature is too low: appropriately raised.

(2) insufficient cooling of the bubble tube: improve the cooling efficiency of the cooling system, increase the air pressure and air volume of the air ring, and reduce the extrusion speed appropriately.

  1. Film of colloidal particles or white dots

(1) mixed impurities in raw materials: screen out impurities and purify raw materials.

(2) broken filter: replace the filter.

(3) melting material overheating decomposition: clean the machine head and screw, and reduce the molding temperature appropriately.

  1. In the film a rigid block

(1) the filter is broken: replace the filter.

(2) improper control of molding temperature: in general, if the molding temperature is low and the molten material is not plasticized well, it is easy to produce cold material stiff block, so the temperature should be adjusted appropriately.

  1. Bubbles on the surface

(1) raw materials are not fully dried and the moisture content is too high: carry out pre-drying treatment.

(2) cooling water leakage in barrel or hopper: repair cooling pipes and devices to eliminate leakage.

  1. Film thickness uneven

(1) improper adjustment of die clearance, uneven discharge: adjust die clearance.

(2) uneven air output of cooling air loop: adjust and clean the air loop to make the air output even.

(3) eccentric deformation of mandrel: replace mandrel.

(4) uneven temperature around the nose: check the heating device of the nose.

(5) too large blowing ratio: appropriately reduce.

(6) unstable compressed air pressure: maintenance of air compressor.

(7) unreasonable head structure design: modify the process parameters of the head.

(8) too little output: appropriately improve the extruder speed to increase the output.

  1. Membrane folds

(1) uneven film thickness: adjust the film thickness.

(2) insufficient cooling or uneven cooling: strengthen the cooling efficiency or reduce the molding speed.

(3) herringbone splint or traction roller is not aligned with the center of the machine head: recalibrate the center line.

(4) the Angle of hermitage splint is too large: reduce the Angle appropriately, sometimes, the Angle of hermitage splint and the diameter of the bubble tube is not suitable, should be adjusted, the geometric shape of the splint should be symmetrical.

(5) the clamping force of the traction roller is uneven, with different tightness: adjust the clamping force appropriately to make the clamping force on the roller surface evenly distributed.

(6) winding tension is not constant: adjust the size of winding friction plate friction, to ensure the winding tension is constant.

(7) uneven head installation: correct the levelness of the head.

(8) the airflow outside the bubble tube is unstable: block a screen around the bubble tube to keep the airflow around the bubble tube stable.

  1. Winding rough

(1) uneven film thickness: adjust the film thickness.

(2) the traction officer clamping force is not uniform, film deviation: adjust the clamping force, so that the clamping force on the roller surface is uniform.

(3) air in the bubble tube is carried to the diaphragm, causing wrinkles: adjust the clamping force of the clamp, and eliminate the gas in the film tube.

  1. Film doesn’t open well

(1) fuselage and nose temperature is too high: appropriate reduction.

(2) traction roller clamping force is too large or traction speed is too fast, poor cooling: reduce the clamping force or reduce the traction speed.

(3) poor cooling: improve the cooling efficiency of the cooling system.

(4) too little amount of lubricant: add an appropriate amount of internal lubricant.

(5) plasticizer dosage is too much: reduce its dosage, as far as possible choose efficient plasticizer.

  1. Frost line is too high

(1) too high nose temperature: appropriate reduction.

(2) too much extrusion: appropriately reduce the screw speed.

(3) insufficient cooling: increase the air volume of the cooling air ring.

  1. The frost line is too low

(1) nose temperature is too low: appropriately raised.

(2) too little extrusion: properly improve the screw speed.

(3) excessive cooling: reduce the air volume of the cooling air ring.

  1. The seam line is well marked

(1) too high temperature of machine head or machine head connector: lower the temperature appropriately, but not too low, otherwise the seam line will still be generated.

(2) cokes adhere to the tip of the mandrel: the shape of the tip of the mandrel should be modified to make it smooth and transitional.

(3) unreasonable head mechanism design: the head design should be modified.