The quality of composite bag making and heat sealing has great influence on the process of packaging, transportation, storage of contents and distribution of products. This paper summarizes the causes and countermeasures of the five common problems in heat sealing and bag-making.

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1. How to deal with leakage or deterioration of contents caused by incomplete heat sealing?


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


It adopts the film with good anti-pollution heat sealing property. Generally, LDPE has moderate anti-pollution heat sealing, EVA has good anti-pollution heat sealing when VA content is large, LDPE also has good anti-pollution heat sealing, ionic resin and metallocene polymer have excellent anti-pollution heat sealing.

2. How to solve the brittle and broken seal


(1) the heat sealing temperature is too high.

(2) too much pressure.

(3) the heat sealing time is too long.

(4) the edge of the upper sealing device is too sharp or the coated ptfe is damaged.

(5) the silicone rubber of the bottom seal is excellent.

(6) in the process of compounding and curing, part of the adhesive into the film. Because the substrate is affected by the penetration of adhesive, toughness (impact resistance) has decreased, brittleness increased.

(7) after cooling and placing, the heat sealing strength of the plastic composite packaging bag increases somewhat, and it also tends to become brittle.


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

(2) improve the surface state of upper heat sealing knife to make the surface of sealing mouthpiece smooth.

(3) with teflon cloth wrapped intact.

(4) choose appropriate hardness of silicone rubber pad.

3. How to solve bag warping after heat sealing


(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) insufficient aging time.

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

(7) improper tension matching and control of composite substrate in the process of composite leads to residual stress after its maturation and finalization, especially when the composite film thickness is relatively thin.


(1) adjust the tension of the floating roller.

(2) select internal sealing substrate with low temperature heat sealing.

(3) adjust the heat sealing temperature to an appropriate temperature.

(4) sufficient cooling.

(5) fully mature.

(6) re-select the surface substrate film.

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

5. How to deal with insufficient heat seal strength?


(1) the adhesive in the composite film has not fully hardened.

(2) improper heat sealing conditions.

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

(4) there is something wrong with the inner seal film.

(5) inks of poor heat sealing, resulting in heat sealing parts of the film composite strength decreased.

(6) dust, dusting and other substances are attached to the hot surface.

(7) low composite strength or excessive decrease of composite strength at heat seal.


(1) promote the hardening of adhesives (curing, curing) through heat preservation aging, and improve the composite strength and heat resistance of the composite film.

(2) select the best thermal sealing conditions (temperature, time and pressure) according to the composition structure of the composite film and the thermal sealing state, or improve the thermal sealing method, and carry out cooling immediately after the thermal sealing.

(3) check the preservation period and preservation conditions of the thermal seal layer film. If the thermal seal layer USES the film of the old batch number and the film after thermal seal treatment, special attention should be paid.

(4) increase the thickness of the heat sealing film.

(5) change the type and grade of thermal seal film, and use the inner seal film with anti-pollution thermal seal.

(6) check whether the grade of adhesives meet the requirements (leakage of low molecular substances in the resin, sometimes affect the composition of adhesives).

(7) improve the heat-sealing performance of the thermal seal layer (substrate), control the content of the slippery agent, and adopt LLDPE film.

(8) control the MDI monomer content in the composite anti-blocking masterbatch.

(9) check the treatment degree of hot cover.

(10) replace the ink (preferably with two liquid ink).

(11) change the printing pattern of the packaging bag so that the printing ink part avoids the heat sealing part, or change the heat sealing method. Pay special attention to the metal ink does not print in the seal.