151
MARINELLI ET AL .
TABLE 1
Properties of the dispersion
Coating
Solid content [%]
T g [ C]
pH
Ford cup #4 viscosity [s]
coatings involved in this study.
0 a
8
12
H39K80
50
0 a
H39K60
50
8
11
SA-B
46
31.7
8
>60
SAP-H
51
12.1
7
18
a T g of HPH 39 (neat latex used in the coating formulation).
Before any use, experimental formulations were stirred with a magnetic anchor for at least 1 h to ensure proper homogeneity. H39K 80 and H39K 60 were applied wet-on-wet to prepare double-layer coated samples.
coated samples and the measured one of UC. The pinhole test was assessed according to the procedure defined in BS EN 13676:2001 41 with a 25 cm 2 testing apparatus. Five replicates were tested for each coating material. Additionally, Bendtsen roughness according to DIN 53108, and air permeability were measured using a Lorentzen & Wettre (Kista, Sweden) SE 114 Bendtsen Paper Roughness and Air Permeability Tester 10 measurements for each coating, as well as for UC. The pressure was 1.47 kPa for both roughness and air perme- ability tests; the latter was measured over an area of 10 cm 2 . A Biolin Scientific AB Attension Theta Optical Tensiometer (Göteborg, Sweden) was used to measure the sessile drop contact angle of both coated and uncoated substrates. A total of seven mea- surements were averaged for each sample. The deionized water drop- let volume was 3 μ l. The contact angle was measured 1 s after the application of the drop.
2.1.3 | Commercial aqueous dispersions
In this work, two commercial aqueous dispersions were investigated. Such dispersions were already part of previous research for single- layer coated paper packaging 22,24 . Adopting a previous nomenclature, the specific grades studied in this context were: • SA-B: styrene acrylate DC developed to provide barrier performance. Solid content is 46% (on a weight basis), whereas T g is31.7 C. • SAP-H: heat-sealable styrene acrylate-based DC with 6% pigment by weight. Solid content is 51% (on a weight basis), whereas T g is 12.1 C. Considering a wet-on-wet double-layer coating investigation, three distinct configurations were produced and tested: SA-B, SAP-H and SAP-H over SA-B to make the coated substrates heat-sealable. Table 1 reports the properties of both experimental and commercial DCs.
2.2.2 | Mechanical properties
A total of 20 samples (measuring 140 by 15 mm) – 10 alongside MD, and the same number alongside CD – were tensile tested according to BS ISO 1924-3:2005 42 using a Lorentzen & Wettre (Kista, Sweden) SE 064 Tensile tester. The testing length was 100 mm, whereas the crossheads speed was 100 mm/min. A total of 20 samples (100 by 38 mm) – 10 alongside machine direction and the same amount alongside cross direction (CD) – were bending tested using a Lorentzen & Wettre (Kista, Sweden) SE 160 Bending Tester. The bending resistance (0 – 15 ) and two-point bending stiffness (0 – 5 ) were measured according to BS ISO 2493-1:2010 43 and ISO 5628:2019 44 , respectively. For both tests, the bending length was 50 mm. Before their testing, both grammage (see Section 2.2.1) and thick- ness were determined for both tensile and bending tests; the thickness was obtained using a Messmer Büchel (The Netherlands) 49 – 56 Micrometer, averaging 20 measurements.
2.2
Methods
|
2.2.1 | Sample preparation and preliminary characterization
The top side of UC was double coated along the machine direction (MD) using a 20 μ m (wet film thickness) wire drawdown coater mounted on an Erichsen (Hemer, Germany) Coatmaster 510 auto- mated coater. The machine was equipped with a vacuum suction plate to improve UC flatness on the coating plane. The coating speed was 50 mm/s, and no additional mass weighed on the coating rod. The second coat layer was applied wet-on-wet over the first one, that is, without oven-drying the first layer. Drying occurred in a VWR (Leuven, Belgium) Venti-line 180 Prime oven at 120 C for 90 s. Unless elsewhere specified, coated samples were conditioned at 23±1 C and 50 ± 2% relative humidity for at least 24 h before any further characterization and tests. The average dry coat grammage was determined as the difference between the grammage of the
2.2.3 | Barrier properties
Conditioned samples were tested for water absorptiveness (Cobb test), Water Vapour Transmission Rate (WVTR) and Oil and Grease Resistance (OGR). Cobb 1800 (i.e., 30 min) test was performed according to the methodology defined in BS EN ISO 535:2014 45 on five samples over
Made with FlippingBook Online newsletter maker