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between 6 and 24 h. PET sample was the only material that did not show dye colour leftovers on the coat side, highlighting that – at least to some extent – the coating absorbs dyed grease. Such results are coherent with similar previous literature 29 . Generally, samples failed because of general permeation through the coatings (Figure 10.c), suggesting once again the possible pres- ence of pores that were filled by dyed grease. However, pores' dimen- sion might be small, since colour was homogeneous and coat porosity was not observed at high magnification scanning electron microscope 22 . Nevertheless, as a general statement, samples were not affected by stroke or fibre orientation apart from SA-B + SAP-H, which failed because of several crease defects as of Figure 10.a and Figure 10.b. Such behaviour underlines a multi-DCs coat that is more brittle com- pared with aqueous dispersions used on their own. Single aqueous dispersions behaved similarly to extrusion-coated and laminated materials rather than cracking 60 at the studied crease depths. Therefore, crease stroke should be further reduced for SA-B + SAP-H, limiting creasing-induced defects. However, stroke reduc- tion means – like increasing crease rule width – shallower creases, which are detrimental for leakproof seals 31,35 . Additionally, given the measured data, it seems that crease tip-related defects are more likely to be witnesses as against the ones along the crease line. The reason lies in crease rule tips, which generally undergo a filing process that might leave some dents that can damage thin coat layers more easily.
Overall, DCs achieved properties that were sometimes similar to PET, but at a reduced dry coat grammage. This means that, from a barrier point of view, dispersion-coated substrates might represent more sustainable solutions since they decrease the non-cellulosic content.
3.4
Creasing
|
Results for creased samples are reported in Table 5, which also spec- ifies failure mode. PET provided the best performance, alongside SAP- H; still, H39K 80 and H39K 60 showed interesting results, resisting
TABLE 4
Grease permeability of the investigated coatings. Unless
specified, the results unit is minutes.
Uncreased
UC
Test result
0
Min-Max [min]
All <1
PET
Test result
>24h
Min-Max [min]
All >1440
H39K80
Test result
6<X<24h
Min-Max [min]
All ≤ 1440
H39K60
Test result
6<X<24h
Min-Max [min]
All ≤ 1440
SA-B
Test result
240
240 – 270
Min-Max [min]
3.5
Heat-sealing
|
SAP-H
Test result
>24h
Min-Max [min]
All >1440
Peel test results of heat-sealed samples are shown in Figure 11. H39K 60 and SA-B + SAP-H coated substrates behaved following the same trend, whereas H39K 80 did not vary as much as the others did. This
SA-B + SAP-H
Test result
6<X<24h
Min-Max [min]
All ≤ 1440
TABLE 5
Grease permeability of the investigated coatings after creasing. Different strokes and fibre orientation were considered.
Additionally, failure modes are reported. Unless specified, the results unit is minutes.
Stroke
0.5
0.5
0.6
0.6
Orientation
MD
CD
MD
CD
Failure mode
PET
Test result
>24h
>24h
>24h
>24 h
n.a.
Min-Max [min]
All >1440 All >1440 All >1440
All >1440
H39K80
Test result
6<X<24h 6<X<24h 6<X<24h 6<X<24h Permeationthroughcoating
Min-Max [min]
All 1440
All 1440
All 1440
All 1440
H39K60
Test result
6 < X < 24 h 6 < X < 24 h 6 < X < 24 h 6 < X < 24 h Permeation through coating (rare crease tip damage) 150 – 1440 330 – 1440 All 1440 150 – 1440
Min-Max [min]
SA-B
Test result
180
180
150
180
Permeation through coating
180 – 210
70 – 210
130 – 180
Min-Max [min]
All 180
SAP-H
Test result
>24h
>24h
>24h
>24 h
n.a. (rare crease tip damage)
All >1440 All >1440 1440 – >1440
1440 –
Min-Max [min]
>1440
SA-B + SAP- H
Test result
6<X<24h 6<X<24h 360
360
Crease tip damage ( + some along crease)
180 – 1440 24 – 1440
30 – 1440
26 – 1440
Min-Max [min]
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