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LSC 5 |
Crease Height Measurement
The following documentation informs about:
The microscopic structure of coated paper used for liquid container blanks.
Methods to deal with this structures for evaluating crease heights.
The picture above is a Raster Electron Microscope (REM) image from a crease on a carton blank. To be able to get a REM image a carton piece was sputtered with some atomic layers of gold.
One clearly sees the structure of the PE coating. Mostly due to rolling and enrolling the carton from the coils. An Aluminium coated carton was used. All structures are due to PE coating. The paper structure is not visible.
Views from Microscope:
To get more quantitative documentations we prepared part of a carton into resin. We used epoxy for its low shrinkage. After hardening the specimen was grinded and polished.
Below a mikroskope one gets the following images.
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Microscopic image of Al-coated carton |
Detail from left picture, showing Al foil and PE coating above |
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Structure of PE – Coated carton seen from top |
Part of PE-Coated paper embedded in resin |
Another example of crease microstructure, which makes problems in height measurement.
Of course different parts of a carton exhibt different structures.
The general conclusion one can see from this microscopic images: PE as well as AL coated cartons have structures in heigt up to 20 µm (sometimes even more). The structrues in length are typical in a scale of 10-50 µm, sometimes up to 100µm.
Views from an autofocus measurement system:
Another very precise height measurement method is the optical autofocus principle.
This measurement principle is used e.g. in adjusting the reading head of a CD-player. Typical the measurement precision is about 1µm.
The measurement is independent of surface type, so it is not necessary to prepare the carton surface to measure crease heights.
We show here two crease scans, done with a UBM scanning system (height precision: 1 µm).
Above: Profile Scan of Al-coated carton
Above: Profile Scan of PE-coated carton
The overall result is consistent with microscopic results:
PE as well as AL coated cartons have structures in height up to 20 µm (sometimes even more). The structrues in length are typical in a scale of 10-50 µm, sometimes up to 100µm.
We emphasize again, that measurement results taken with the most precise systems (Microscope and autofocus) are variing from place to place of the same carton. They vary of course even more if one compares cartons of different manufacturers and production lines.
As result the following conclusions can be made:
· There are height variations in PE coating in the range of typical 20 µm, sometimes even more.
· These height structures vary on a length scale of 10 – 100µm.
· It is not possible to assign a height value of a crease without describing the way it is measured.
. It is not possible to compare crease height values from different measurement methods in a simple way.
