Despite all the electronic production monitoring tools, minor deviations cannot be avoided. These are often caused by external temperature fluctuations during extrusion.
The permitted tolerances and test methods are specified in the GKV test and evaluation clauses for polyethylene films. These were set up by the IK Industrievereinigung Kundststoffverpackungen e.V.
© 2018 GKV
Here are some excerpts:
The thickness measurements are carried out evenly across the entire width of the production hose. At least 10 measurements are taken on a film width of 1 m.
The thickness measurement is to be carried out with a calibrated thickness gauge in accordance with DIN 55543 (packaging test - test methods for packaging films -).
The thickness measurement is generally carried out across the production of the film. The spread of the individual deviations from the nominal thickness (target thickness) may be:
|until 2500 mm||> 25 μm||± 13 %|
|from 2501 mm||> 25 ≤ 50 μm||± 20 %|
|from 6001 mm||≤ 50 μm||± 25 %|
|from 6001 mm||> 50 μm||± 20 %|
The following width tolerances apply to tubular, half-tubular, gusseted tubular with extended gusset and untrimmed flat film:
|Width in mm ||Deviation in mm |
|until 800 ||± 8|
|from 800||± 10|
|from 1.200 ||± 12|
|from 2.000||± 15|
|from 3.000||± 30|
|from 4.000||± 50|
|from 5.000||± 80|
For trimmed flat film, 50% of the specified width tolerance applies.
The following length tolerances apply to tubular, half-tubular, gusseted tubular with extended gusset and untrimmed flat film:
|Roll length in mm ||Deviation in % |
|until 100 ||± 3,0|
|from 100||± 2,5|
|from 500 ||± 2,0|
|from 1.000||± 1,5|
|from 2.000||± 1,2|
|from 5.000||± 0,8|
Maximum permissible width/length deviations (tolerances) from the dimensions resulting from the manufacturing process:
Bag/sack length +/- 3%
Bag/sack width +/- 3%