
For example, the three-layer co-extruded layer structure is: PA/AD/PE (PP).
Nylon is on the outer layer and is not protected. Nylon has poor impact
resistance, is easy to scratch, leaks, and is hydrophilic, easy to absorb
moisture, and reduces oxygen permeability.
If it is a five-layer structure, PP (PET)/PE, PA outer/Ad. PA outer/PA, PA
outer/Ad, PP/(PE). In this way, the nylon is protected on both sides and
prevents the nylon from absorbing moisture.
Seven layers and nine layers have been tested. If various resins are
arranged properly, the shelf life can reach more than 1 year, almost reaching
the effect of tinplate cans, such as PET/Ad/PA/EVOH/PA/Ad/PE (PP). Oxygen
barrier layer that is still in multi-layer film, the functions and functions of
each layer are different: According to the storage period of the package,
determine the corresponding barrier material (PVDC, EVOH) and layer thickness,
the thickness of nylon is generally 20% , EVOH is generally 10%~15%, and the
thickness deviation should not exceed 10%. Within this range, the impact on
packaging storage is very small.
Adhesive layer (AD): Although nylon and EVOH have good extrusion
moldability, they have no ability to bond with other layers (LDPE, PP, EVA)
during co-extrusion. Special junction resin must be used as the junction layer
to achieve Higher peel strength between layers.
Therefore, the choice of layer material is a very important factor.
Appropriate grades should be selected according to the structure, the thickness
is generally 5~15g/m2, the inner and outer layers: nylon, EVOH although the
oxygen transmission rate is small, but the water vapor transmission rate is very
large, therefore, when determining the inner and outer layer materials, should
be Fully consider the problem of water vapor barrier, and the inner layer
material must take into account the heat sealing performance and heat sealing
strength, such as LDPE, MLLDPE, EVA, PPO, etc.;
If necessary, it can be modified with Surlyn, PRIMCOR, POP. When used as a
composite substrate, the corona on the outer surface reaches 38~42 dynes.
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