In the process of production of composite membranes, it is likely to encounter problems such as how the heat sealing is not completely caused by the leakage or deterioration of the contents, how to deal with brittleness and brittle fracture, and what solution to the warpage of the package after heat sealing. Today, China Plastics Network - Jiuzhi Plastics Network will give a brief explanation for these issues.
The heat sealing uses external conditions (electric heating, high-frequency heating, ultrasonic waves, etc.) to make the sealing portion of the plastic substrate film into a viscous flow state and to fuse the upper and lower layers of the film together by means of the pressure of the heat sealing cutter, cooling After that, it can maintain a certain strength. The quality of the bag and the quality of the heat seal of the composite bag have a great influence on the packaging process, transportation, storage of contents and product distribution.
1. What if the heat seal does not completely cause the contents to leak or deteriorate?
the reason:
The anti-contamination heat-sealing property of the film is poor, and the resin used for the inner seal layer is not suitable.
Countermeasures:
It adopts anti-pollution heat sealing property and film. In general, LDPE has moderate anti-pollution heat sealability, EVE has good anti-pollution heat sealability when VA content is large, LLDPE also has good anti-pollution heat sealability, ionic resin and metallocene poly It has excellent anti-pollution heat sealability.
2. What should I do if the seal is brittle and brittle?
the reason:
(1) The heat sealing temperature is too high.
(2) The pressure is too large.
(3) The heat sealing time is too long.
(4) The edge of the upper sealer is too sharp or the wrapped Teflon cloth is damaged.
(5) The silicone rubber on the bottom sealer is too hard.
(6) During the compounding and ripening process, a part of the adhesive penetrates into the inside of the film. The substrate is affected by the penetration of the adhesive, the toughness (impact resistance) is reduced, and the brittleness is improved.
(7) After the cooling of the plastic composite packaging bag, the heat sealing strength is increased, and there is also a tendency to become brittle.
Countermeasures:
(1) According to the material of the inner sealing layer and the heat sealing property, a suitable processing temperature, pressure and heat sealing time are selected.
(2) Improve the surface condition of the upper heat-sealing knife and make the surface of the sealer flat.
(3) Wrap the sealer with Teflon cloth.
(4) Select a silicone rubber mat of suitable hardness.
3. What should I do if the bag is warped after heat sealing?
the reason:
(1) The thickness of the composite film is inconsistent.
(2) The heat sealing temperature is too high or the heat sealing time is too long.
(3) In the longitudinal heat sealing knife portion, the running track of the composite film is not straight.
(4) The cooling is insufficient.
(5) The curing time is not enough.
(6) The surface layer substrate film is inferior in heat resistance.
(7) The tension matching of the composite substrate during the compounding process is improperly controlled, resulting in residual stress after the ripening and setting, especially when the thickness of the composite film is thin.
Countermeasures:
(1) Adjust the tension roller tension.
(2) An inner sealing substrate having a low temperature heat sealability is selected.
(3) Adjust the heat sealing temperature to a suitable temperature.
(4) Fully cooled.
(5) Fully matured.
(6) Reselect the surface substrate film.
(7) Adjust the tension of each part of the composite processing equipment, and try to make the recombination rates of the two composite substrates equal.
4. What should I do if the outer contour of the heat seal is unclear?
the reason:
(1) The cooling time is short.
(2) Poor contact of the cooling plate.
(3) Since the rubber base is heated, the edge portion is melted.
(4) The longitudinal heat seal knife is unbalanced.
(5) The edge of the heat sealing knife is not neat and blunt.
5. What should I do if the heat seal strength is poor?
the reason:
(1) The adhesive in the composite film is not sufficiently hardened.
(2) The heat sealing conditions are not appropriate.
(3) The distance between the heat seal knife and the cooling plate is too long.
(4) There is a problem with the inner seal film.
(5) The heat resistance of the ink is poor, resulting in a decrease in the composite strength of the heat-sealed portion film.
(6) Dust, powder and other substances adhere to the hot cover.
(7) The composite strength is low or the composite strength at the heat seal is excessively decreased.
Countermeasures:
(1) The curing of the adhesive is promoted by curing (aging, curing), and the composite strength and heat resistance of the composite film are improved.
(2) According to the constitution of the composite membrane, the heat-sealing state, etc., the optimum heat sealing conditions (temperature, time and pressure) are selected, or the heat sealing method is improved, and cooling is performed immediately after heat sealing.
(3) Check the shelf life and storage conditions of the heat seal layer film. If the heat seal layer uses the old batch film and the heat treated film, special attention should be paid.
(4) Increasing the thickness of the heat seal layer film.
(5) The type and grade of the heat seal layer film are changed, and an inner seal film having anti-contamination heat sealability is used.
(6) Check whether the grade of the adhesive meets the requirements (the leakage of low molecular substances in the grease sometimes affects the composition of the adhesive).
(7) Improving the heat sealing property of the heat seal layer (substrate), controlling the content of the slip agent, and using a mLLDPE film.
(8) Control the content of MDI monomer in the composite adhesive.
(9) Check the degree of processing of the hot cover.
(10) Replace the ink (preferably two-liquid type ink).
(11) Change the printing pattern of the packaging bag so that the printed portion avoids the heat-sealed portion or changes the heat-sealing method (special attention should be paid not to the metal ink printed on the seal).
6. What should I do if the heat seal is bubbled or the surface is uneven?
the reason:
(1) When heat-sealing is performed on a material structure containing a hygroscopic film such as a nylon film, bubbles are generated when moisture-absorbing film absorbs moisture.
(2) The heat sealing knife or the heat sealing silicone pad is not flat.
(3) The heat sealing pressure is insufficient.
(4) Using a one-component adhesive, such as a neoprene adhesive, the heat cover is prone to irregularities and small pits when heat-sealed.
Countermeasures:
(1) Keep raw materials and semi-finished products in a safe place to avoid moisture absorption.
(2) Check or adjust the heat seal knife and heat seal silicone pad.
(3) Replace the adhesive.
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