1. Material structure, especially the use of homopolymer CPP film:

    Under the condition that the material and process parameters of the BOPP/CPP structure composite bag are basically unchanged, the seal becomes brittle after the bag is made, and the sealing strength decreases.

    1) The "culprit" comes from the material. In the composite bag of this type of structure, the customer chooses CPP film as the inner layer functional film and heat sealing film, and CPP film as the inner layer composite film, with its good transparency, stiffness, The negative barrier and heat sealing properties have indeed been widely used. However, there is another feature of CPP film that we may ignore, that is, poor cold resistance, homopolypropylene film is brittle at 10 degrees, if not adjusted accordingly, after entering winter, the temperature drops and the seal becomes brittle. The phenomenon is common .

    Homopolypropylene thin film has poor cold resistance, we can choose to use cast copolymer polypropylene film (CCPP). As the ethylene content in the copolymer increases, the coldness of the copolymerized polypropylene film will also increase. Generally speaking, the film containing 5% to 7% ethylene can withstand -5 degrees to -10 degrees. At the same time, there is also a high-transparency, ultra-flexible and toughened cast polypropylene film on the market. Ultra-low density polyethylene (VLDPE) and ethylene and ethylene copolymer (polyolefin elastomer) POE are used to modify CPP for co-extrusion. , It also has a good effect on toughening and cold resistance of CPP film.

    2) As a CPP that is resistant to high temperature cooking, it should not be manufactured with homopolypropylene (polymer PPH of a single propylene monomer) but with copolymerized polypropylene (block copolymerized polypropylene PP--B) or blended modified Polypropylene pellets to manufacture. Because CPP made of homopolypropylene will become embrittled after being cooked at high temperature, it is easy to rupture from the seal, causing leakage of the contents, and the sedimentation marks at the vacuuming place are prone to air leakage, and the oil resistance is extremely poor. The copolymerized or blended CPP, because of its high crystallinity, low temperature resistance and impact resistance are better than the homopolymeric CPP.

2. The seal is brittle or easy to break due to the operation process:

    1) The most common plastic composite packaging bags increase the strength of the heat seal after cooling and placement, but also tend to become brittle.

    2) The edge of the upper sealer is too sharp or the PTFE covered is damaged,

    3) The heat sealing time is too long. In addition, there are reasons such as excessive pressure, excessively hard silicone rubber on the bottom seal, or excessive heat sealing temperature.
Countermeasures:
1) Improve the state of the upper surface of the heat sealing knife to make the surface of the sealer flat.
2) Use Teflon coating to improve the surface condition of the upper heat sealing knife and make the surface of the sealer flat.
3) According to the material of the inner sealing layer and the heat sealing characteristics, etc., the appropriate processing temperature, pressure and heat sealing time should be selected to improve this situation.

3. The aging of the film or the addition of a large amount of recycled materials and additives will seriously reduce the tensile strength and elongation at break of the film:

    It can be judged by detecting the change of the friction coefficient of the material or whether the tensile strength and elongation at break meet the standards.

4. During the compounding and curing process, a part of the adhesive enters the inside of the film:

    Because the substrate is affected by the penetration of the adhesive, the resistance (impact resistance) is reduced and the brittleness is improved; after the plastic composite packaging bag is cooled and placed, the heat sealing strength is increased, and at the same time, it also tends to become brittle.

5. In use, the sensitivity of the glue to moisture exceeds the range, which makes the glue harden and become brittle:

    Each adhesive has a certain sensitivity to moisture. If this sensitivity is exceeded, the adhesive will become hard and brittle. At this time, the composite film will become hard and brittle, and easily broken. (Glue sensitivity varies from glue to glue).