Problems and Solutions of Heat Sealing of Bag Making Machines

Problems and solutions of heat sealing in bag making machine

Bag-making processing is a process in the production and processing of plastic flexible packaging. If the quality of bag-making is unqualified or the consumption is too high, it will be equivalent to the failure of the previous steps, and the claims of downstream customers will have a significant impact on the production and operation of the company.

Heat sealing is the result of the combined action of heat and force. On the one hand, on the sealing surface in the molten state, the macromolecules diffuse, penetrate, and intertwine with each other to achieve sealing; on the other hand, the polymer molecules in the molten state rely on heat The pressure of the sealing tool makes the upper and lower layers of the film fuse with each other, and can maintain a certain strength after cooling and shaping.

The bag-making quality and heat-sealing quality of composite packaging bags have a great impact on the packaging process, transportation, storage of contents, and product distribution. The following are the common problems and solutions in the process of bag making.

1. Incomplete heat sealing causes leakage or deterioration of the contents.

Reason: The anti-pollution heat sealing property of the film is poor, mainly because the resin used in the inner sealing layer is not suitable.

Countermeasures: Use a film with good anti-pollution heat sealability. Generally speaking, LDPE has moderate anti-pollution heat-sealing properties, EVA has good anti-pollution heat-sealing properties when the VA content is large, LDPE also has good anti-pollution heat-sealing properties, and ionic resins and metallocene polymers have good anti-pollution heat-sealing properties. Has good anti-pollution heat sealability.

2. The seal is brittle and brittle.

reason:

(1) The heat sealing temperature is too high.

(2) Excessive pressure.

(3) The heat sealing time is too long.

(4) The edge of the upper sealer is too sharp or the PTFE covered is damaged.

(5) The silicone rubber of the bottom seal is too hard.

(6) During the compounding and curing process, a part of the adhesive penetrates into the inside of the film. Due to the penetration of the adhesive, the toughness (impact resistance) of the substrate decreases and the brittleness increases.

(7) After the plastic composite packaging bag is cooled and placed, the heat sealing strength has increased, and it also has a tendency to become brittle.

Countermeasures:

(1) According to the heat sealing characteristics of the material of the inner sealing layer, select the appropriate processing temperature, pressure and heat sealing time.

(2) Improve the surface state of the upper heat sealing knife and make the surface of the sealer flat.

(3) It is well wrapped with PTFE cloth.

(4) Choose a silicone rubber pad with appropriate hardness.

3. The outer contour of the heat sealing surface is not clear. (The knife pattern is not clear)

reason:

(1) The cooling time is short.

(2) Poor contact of cooling plate.

(3) Since the silicone pad is heated, the edge part is melted.

(4) The longitudinal heat sealing force is uneven.

(5) The edge of the heat sealing knife is irregular and dull.

Countermeasures:

(1) Adjust the cooling time.

(2) Adjust the cooling plate.

(3) Replace or adjust the heat sealing knife.

(4) Prevent edge melting caused by overheating of the silicone pad.

4. The bag is warped after heat sealing.

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 part, the running track of the composite film is not straight.

(4) Insufficient cooling.

(5) The aging time is not enough.

(6) The heat resistance of the surface substrate film is poor.

(7) The tension matching of the composite substrate is not properly controlled during the composite process, resulting in residual stress after curing and shaping, especially when the thickness of the composite film is thin, such failures are more likely to occur.

Countermeasures:

(1) Adjust the tension of the floating roller.

(2) Select the inner sealing substrate with low temperature heat sealing.

(3) Adjust the heat sealing temperature to a suitable temperature.

(4) Fully cooled.

(5) Fully ripening.

(6) Reselect the surface substrate film.

(7) Adjust the tension of each part of the composite processing equipment, and try to make the retraction rate of the two composite substrates equal.

5. Poor heat sealing strength.

reason:

(1) The adhesive in the composite film has not been sufficiently hardened.

(2) Inappropriate heat sealing conditions.

(3) The distance between the heat sealing knife and the cooling knife is too long.

(4) There is a problem with the inner seal film.

(5) The heat-sealing resistance of the ink is poor, resulting in a decrease in the composite strength of the film at the heat-sealing part.

(6) Dust, dusting and other substances are attached to the heat cover.

(7) The composite strength is low or the composite strength of the heat seal is too much.

Countermeasures:

(1) Promote the hardening (curing, curing) of the adhesive through thermal aging and improve the composite strength and heat resistance of the composite film.

(2) Select good heat sealing conditions (temperature, time and pressure) according to the composition of the composite film, heat sealing state, etc., or improve the heat sealing method, and cool it immediately after heat sealing.

(3) Check the shelf life and storage conditions of the heat-sealing layer film. If the heat-sealing layer uses the old batch of film and the film that has been heat-sealed, pay special attention.

(4) Increase the thickness of the heat sealing layer film.

(5) Change the type and grade of the heat-sealing layer film, and use the inner-sealing layer film with anti-pollution heat-sealing properties.

(6) Check whether the grade of the adhesive meets the requirements (the exudation of low molecular substances in the resin may sometimes affect the composition of the adhesive).

(7) Improve the heat sealing performance of the heat sealing layer (substrate), control the content of the slip agent, and use mLLDPE film.

(8) Control the monomer content of MDI in the composite adhesive.

(9) Check the degree of treatment of the heat cover.

(10) Replace the ink (two-liquid type ink is used).

(11) Change the printing pattern of the packaging bag so that the part printed with ink avoids the heat sealing part, or change the heat sealing method. (Particular attention is paid to metallic ink not to be printed on the seal). (Source: China Printing and Packaging Network)