Influence of substrate contamination, web handling, and pretreatments on the barrier performance of aluminum oxide atomic layer-deposited BOPP film.
Keywords Atomic layer deposition, Aluminum oxide, Surface contamination, Web handling, Polypropylene
In recent years, researchers have studied the possibilities of enhancing the barrier properties of flexible materials with atomic layer-deposited aluminum oxide ([Al.sub.2][O.sub.3]) surface coatings. (1-3) Typical barrier coatings deposited by atomic layer deposition (ALD) are extremely thin, dense, and pinhole-free because of the self-limiting sequential deposition process in which they have been produced. (4) In order to achieve cost-effective production, a roll-to-roll ALD process is needed, which is able to coat reels of materials in a high throughput process. The development of a spatial ALD process, which enables the roll-to-roll process, has been widely reported. (5-7) The barrier properties obtained for extrusion-coated papers with these coatings have been studied. (8) In addition, other characteristics that are detrimental to the use of spatial ALD process have been investigated. (9,10) The spatial ALD process has been demonstrated to enable accurate control and functionalization of nanoscale surface coatings on various continuous substrates. (6,7)
Biaxially oriented polypropylene (BOPP) films are commonly used in packaging because of their low price, high transparency, high flexibility, and thermal stability. (11,12) As a drawback, BOPP has only moderate barrier properties against oxygen despite its oriented structure. (13) In order to improve the oxygen barrier performance, BOPP films are typically converted into secondary products through, for example, laminating, metallizing, and coating processes. Del Nobile et al. (14) investigated the transport mechanism of gases through BOPP films and found a significant oxygen barrier improvement produced by metallization. Struller et al. (15) characterized the oxygen barrier properties of [Al.sub.2][O.sub.3]-coated BOPPs, finding that they show considerable variations that are greatly dependent on the surface and coating conditions. Vaha-Nissi et al. (16) studied the growth mechanisms of ALD-deposited [Al.sub.2][O.sub.3] films on BOPP, revealing that in the early stages of the deposition process, growth of [Al.sub.2][O.sub.3] clusters takes place partly because of the hydrophobic BOPP surface.
It is possible to reduce the hydrophobicity of BOPP surface by pretreatments, which could also enhance the thin film coatability of the surface. Tuominen et al. (17,18) studied the surface properties of polyolefin films and found significant increase in the surface energy of low-density polyethylene and polypropylene surfaces after atmospheric corona, plasma, and flame treatments performed in the middle of a roll-to-roll winding process.
Methods other than coating or laminating have also been used to improve the barrier properties of BOPP. Jang and Lee (19) improved the oxygen barrier by producing BOPP/polyvinyl alcohol blends. Lin et al. (20) managed to improve the barrier by incorporating nanoscale high barrier constituents into the BOPP film. In general, common to all the attempts is that the barrier properties of BOPP are quite easily improved. This opens up the interesting possibility of studying the thin film coatability of the BOPP surface as a function of different process functions. As the barrier coating has a significant effect on the substrate, easily observable differences are generated between individual barrier results and the influence of individual processes can be detected.
Nanocoatings are very thin and because of this they are typically very sensitive and susceptible to defects. Hanika et al. (21) studied and modeled the influence of defects on the barrier performance of inorganic layers on polymeric films and Leterrier (22) reviewed the durability of thin oxygen barrier coatings on polymer films. In this study, we have investigated the thin film (ALD) coatability of BOPP film by depositing [Al.sub.2][O.sub.3] coatings to improve the oxygen barrier properties of the material. The influence of surface contamination, pretreatments, and web handling of ALD-deposited BOPP film on the barrier performance was investigated in order to characterize the significance of the individual factors and to achieve a better understanding of the combination of the nanoscale barrier coating with the BOPP substrate in practical production.
Materials and methods
The substrate used in the study was Rayoface[TM] C58, which is a 58-pm thick BOPP film produced by Innovia Films Ltd. (23) It has a three-layer structure in which two polyolefin top layers cover the heat set laminated middle layer. The film has a low additive level and it is corona-treated from one side by the supplier. The nontreated side of the film was used as a target surface for investigations in the study.
Surface treatments of the film before and after the ALD-[Al.sub.2][O.sub.3] depositions were made at the pilot line of Tampere University of Technology (TUT). (24) Also, the winding tests causing mechanical stresses for the ALD coating were performed at the same line. The treatments selected for the study were atmospheric corona, plasma, and flame treatments prior to the deposition process, and an atmospheric corona treatment after the deposition process. Each sample of the study went through only one of these treatments. The purpose of the pretreatments was to modify the BOPP's surface chemistry and possibly cause cleaning effects on the substrate, which might improve the barrier effect of the ALD-[Al.sub.2][O.sub.3] coating to be deposited. The purpose of the corona treatment taking place after the ALD deposition was to clarify how well the barrier performance of the [Al.sub.2][O.sub.3] layer is retained in the treated structure compared to the untreated one.
The corona treatments were performed with the Vetaphone Corona Plus system, in which the plasma discharge is created between ceramic electrodes and a steel backing roll in ambient air. The system had eight electrodes, each having the length and width of 500 and 15 mm, respectively. The power density was adjusted by means of the power supply (1.0-3.4 kW) and line speed (15-80 m/min). The plasma treatment used had a multi-jet plasma system in which the plasma was produced by passing air through a high-voltage field. The power consumption was 8 kW. The length and width of the plasma treatment area was 55 and 400 mm, respectively, and the air gap between the jets and the backing roll was 2 mm. Flame treatments were performed using a Hill GmbH model EF 75-1 flame treatment unit. It had a 500-mm-wide water-cooled burner which provided the flame based on an air/ propane gas mixture. The distance of the burner from the substrate was 12 mm. More detailed parameters of the treatments used can be found from Table 1.
The ALD depositions of the study were performed with a 3D batch reactor Beneq TFS 500 in Lappeenranta University of Technology (LUT). The substrates for the process were directly drawn from a supplier's reel or from the reel which had experienced the pretreatment processes at TUT. Rectangular sheets of 13 cm x 13 cm were cut from the material for the batch ALD depositions. The ALD-[Al.sub.2][O.sub.3] depositions were made by using trimethylaluminum (TMA) and ozone ([O.sub.3]) as aluminum and oxygen precursors, respectively. The reactor temperature used in the thermal ALD process was 65[degrees]C. The samples were conditioned overnight at the elevated temperature before the deposition process started in order to avoid humidity at the reaction area. The chamber pressure used was approximately 2 mbar. One deposition cycle consisted of a 250 ms TMA pulse, 6 s purge, 3 s ozone pulse, and 6 s purge, respectively. Four hundred ALD cycles were performed to achieve approximately 30 nm [Al.sub.2][O.sub.3] coatings. This process has been previously shown to deposit [Al.sub.2][O.sub.3] coatings. (3,8,9) The existence of the coating and the thickness obtained were confirmed by using spectroscopic ellipsometry (J.A. Woollam M2000FI) on polished silicon pieces deposited in the same processes. This method has been frequently used in evaluating ALD-deposited polymer surfaces. (3,8,9,25)
After the ALD depositions, the sample sheets were shipped back to TUT for a new winding process and for barrier testing. Some of the sheets travelled to TUT in "no touch" boxes, enabling the coatings to be free of any mechanical contacts during shipment. Other samples faced a mechanical contact during shipping as they were packed in tight plastic pouches using Al-foil between the samples to protect the coatings. At TUT, some of the samples were barrier tested without further treatment and others faced a winding process to investigate the effect of mechanical stresses.
In order to test the influences of mechanical stresses, the samples were taped onto the surface of a separate paperboard reel ([Al.sub.2][O.sub.3] layer on the outer surface), which had the thickness and basis weight of 275 pm and 210 g/m, (2) respectively. This reel was then subject to a roll-to-roll winding process. During this process, the [Al.sub.2][O.sub.3] surface layer faced 11 contacts to steel rollers with a diameter of 155 mm. The contact distance with individual rollers varied across the line. The surfaces faced also two pressurized nips at the rewinding station, and during two different periods they had also a permanent contact to the reverse side of the paperboard surface inside the reels as they were rolled up. Some of the samples exposed to the winding process were also post-corona-treated to see the effect on the barrier properties. In addition, some of the samples were corona-treated without any roller contacts. In such case, the samples were taped onto the supportive web just before the corona station and removed directly after the station. With this procedure, it was possible to isolate the effect of the plain corona treatment on the barrier results.
The surface energies of the samples were measured with the sessile drop method by using a KSV CAM 200 optical contact angle analyzer. Two test liquids were used: water and ethylene glycol. For the surface-treated samples without an ALD coating, the surface energies were measured within 24 h of the treatments, and the ALD coatings were deposited within 20 days of them. The surface energy measurements of the ALD-coated materials took place within 14 days from the coating process. All mechanical contacts were avoided before the measurement except for the necessary reverse-side contact of the surface-treated samples at the BOPP reel.
The barrier properties of the samples were measured with an oxygen transmission rate ([O.sub.2]TR) measurement by using a Mocon Ox-Tran Model 2/21 according to a standard ASTM D 3985. In the method, the ALD-coated side of a sample is sealed against a test cell by using high-vacuum grease. The measurements took place at 23[degrees]C, 0% RH conditions and the active test area of the sample was 5 [cm.sup.2]. Nitrogen with 10% oxygen content was used as a test gas. Each barrier result tabulated is based on four parallel measurements whose average is expressed as a test result. The [O.sub.2]TR test had a key role in the study as the ALD coating was expected to have a high impact on the oxygen barrier properties of BOPP.
The influence of the various treatment factors was investigated in two stages. In the first stage, the factors active before the ALD coating process were investigated and in the second stage, those affecting the barrier after the ALD coating were studied. The first stage factors included surface cleanliness and chemical activity of the substrate. These were tested through different substrate handling and pretreatment procedures, namely reel-to-reel winding process and corona, flame, and plasma pretreatments. The second stage factors included the mechanical stresses to which the barrier layer was exposed after ALD coating. These mechanical stresses took place during shipment and a further roll-to-roll winding process. The effect of a post-corona treatment on the ALD coating was also investigated.
First stage: processes before the ALD coating
Surface energy test
Corona, flame, and plasma pretreatments were performed for a BOPP reel in a separate roll-to-roll process before the material was ALD-coated. The effect of these treatments was measured in a surface energy test and the results were compared to the untreated substrate and also to the ALD-coated BOPP. The dispersive and polar components of the surface energies measured for the samples after the stronger pretreatments are shown in Table 2 and further illustrated in Fig. 1. According to the results, the biggest difference in the surface energy results was caused by the [Al.sub.2][O.sub.3] coating itself. As an obvious consequence from the oxide coating, the polar component of the samples was significantly increased and the dispersive component decreased because the nonpolar PP surface was replaced by the polar one.
The surface energy results show that the pretreatments used caused a much smaller effect on the surface energy of BOPP than the [Al.sub.2][O.sub.3] coating. The corona and flame treatments were able to slightly increase the surface energy, whereas the plasma treatment was not. It was suggested that this difference was caused by the different power densities of the treatments. According to the results, the flame treatment underneath the ALD coating decreased the surface energy of the ALD-coated material. This deviation compared to the other ALD-coated surfaces may originate from a change in the surface roughness of the substrate. The flame treatment used was strong and the changes it caused for the BOPP surface could be observed visually. (26,27)
As a conclusion from the surface energy test, the results leave a question mark on the importance of the surface pretreatments. The surface treatments used did not have a significant influence on the surface energy levels of the samples even though it is well known that the surface energy of BOPP can be significantly modified. (28) We assume that the surface energy effect remained small because of the short and inefficient treatments. The explanation can also be sought from the mechanical contact of the treated surface with the reverse-side corona-treated surface inside the rewound reel. The influence of the increased surface energy on the ALD growth of [Al.sub.2][O.sub.3] layer has been discussed elsewhere. (16) It is obvious that the increased surface energy could have influenced the deposition process by avoiding the formation of clusters in the early stages. However, as the following "Oxygen transmission rate test" section shows, a continuous [Al.sub.2][O.sub.3] coating was also obtained for untreated substrates (e.g., the set point 1 in Table 3). Thus, the importance of the early deposition process clusters in the barrier effect can be considered minor compared to, for example, the importance of cleanliness before the ALD coating process.
Oxygen transmission rate test
The [O.sub.2]TR results obtained for the ALD-coated BOPP films are shown in Table 3. The results for the samples were measured with and without the ALD coating. According to the results, the pretreatment as such did not affect the [O.sub.2]TR of the sample, but the results for the ALD-coated sample varied significantly as a function of the pretreatment. Figure 2 shows a more illustrative comparison between the results together with standard deviations.
According to the results, the best oxygen barrier with a significant difference to the second best was measured for the untreated sample of which substrate was directly taken from the supplier's reel. As all the other samples were exposed to surface contamination during an extra roll-to-roll handling process, this indicates that the cleanliness of the sample demonstrating the best barrier value measured caused the difference to others. The strong plasma and moderate flame treatments caused also a slight improvement in the [O.sub.2]TR level when compared to the untreated sample, which was wound through the line. However, the improvement caused by them was not as significant as with the untreated sample, which had not experienced the winding process. In conclusion, the cleanliness of the substrate can be stated to have much greater importance in achieving a good barrier level for ALD-coated BOPP than the surface activation with the tested pretreatments.
Second stage: processes after the ALD coating
Once the ALD coating is made, the main threat compromising the barrier improvement caused by the ALD coating is the mechanical stress which the material is exposed to during further processing. In order to investigate the effects of these processing steps, seven set points were performed with individual post-ALD treatments. One set point refers to an uncoated reference film in the test. In general, the ALD coatings were exposed to three different mechanical stresses before the demonstrative [O.sub.2]TR test took place. These included the shipment of the samples between aluminum foils, winding through a pilot line with different line speeds and a post-corona treatment. The descriptions of these procedures and the effects of them on the [O.sub.2]TR values are shown in Table 4.
A diagram of the [O.sub.2]TR results obtained for the set points 2-8 is shown in Fig. 3. In the figure, dark gray (left) illustrates the effect of shipment, light gray the effect of a roll-to-roll winding process, and dark gray (right) the effect of corona treatment. Standard deviations of the results are also included in the figure. The results reveal the significant influence of the mechanical stresses on the barrier performance of the coating. The most significant effect was caused by the further winding process at the pilot line. For these samples, the [O.sub.2]TR increased from 2% to 3% of the basic BOPP with ALD coating to ~30% with winding. Both the shipment between aluminum foils and the corona treatment also reduced the barrier performance, but their effect was considerably smaller. For these samples, the [O.sub.2]TR stayed below 12% of the uncoated BOPP. When comparing the results of set points 3 and 7, it can be seen that the shipment between aluminum foils reduced the barrier level somewhat more than the corona treatment without any roller contacts. However, the combined effect of these two was greater than either of them individually, as can be seen from the set point 8.
Looking more closely at the mechanical stresses caused by the roll-to-roll winding process on the samples, the damage to the barrier properties of the ALD-coated BOPP could arise from several causes. Figure 4 introduces the critical process steps the ALD-coated BOPP samples faced in the further roll-to-roll web processing. These were (a) bending at the rollers, (b) line tension, and (c) nip work at the rewinding station. In general, all these processes are able to cause mechanical strain in the ALD layer, which may lead to cracks and allow easy diffusion pathways for [O.sub.2] to transport through the material. Eleven of the steel rollers causing bending had also a direct contact with the ALD coating. This may cause rubbing or fretting of the film and localized damage and penetration through the film by dust and debris particles between the coating and the roller.
The tensile strain in the coating can be calculated from the tension in the linear runs of the paperboard web. Its effect is obviously reduced because the BOPP samples were mounted by adhesive tape on a paperboard roll which will allow some strain relief. However, even allowing for a rigid attachment of the BOPP to the paperboard, the maximum strain to which it will be subject will depend on the Young's modulus of the paperboard and the web tension. The modulus in the machine direction of paperboard has been measured to be approximately 5.0 GPa. (29) The web tension during the process was 115 N. For the paperboard web width of 0.5 m and thickness of 275 pm this will give rise to a tensile strain of 1.7 x [10.sup.-4]. Tests on ALD coatings of [Al.sub.2][O.sub.3] on PEN polymer substrates have shown (30) that for 40 nm films there is no deterioration of the barrier properties due to cracking if the strain is less than 5 x [10.sup.-3]. Thus, the effect of line tension causing strain can be neglected from the results.
The strain due to bending of the film around the rollers can be calculated according to a composite model comprising paperboard, BOPP, and ALD coating layers, assumed to be bonded together. As for the case of the linear strain, the mounting of the polymer sheet with adhesive polymer tape will reduce the actual strain below this level because of its stretch. However, this calculation will give an absolute maximum level which cannot be exceeded. A model based on beam bending theory has been developed for this situation. (31,32) The strain during bending is given by equation (1) where Y, d, and v refer to the Young's modulus, thickness, and Poisson's ratio of the materials, respectively; i, o, and s refer to the ALD layer, the BOPP, and the paperboard, respectively; and R is the bending radius. Equations (2-4) are used to define the values of [bar.[omega]], [lambda], and [beta].
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Table 5 gives the parameters used in the calculation. (29,32,33) The minimum roller diameter is 155 mm, giving a minimum bending radius of 77.5 mm. Using these values, the tensile strain in the ALD layer due to bending round rollers is 4.9 x [10.sup.-4]. Thus, even in the worst case, this is a factor of 10 lower than the 0.5% necessary to cause cracking of an ALD-[Al.sub.2][O.sub.3] layer.
During a nip process, the surface of a planar paperboard web may be subject to tensile strain because the cylindrical roller will compress the material and it would take the same shape as the roller circumference rather than a linear shape. However, in the case here, the nip occurs as the web is transferred from one roller to another, as shown in Fig. 4c. The web is already contacting the circumference of either the paperboard take-up roller or the counter roller and will not be subject to any further deformation than is produced by its contact with these. Thus, any damage to the coating causing a deterioration in barrier properties must be caused by contact either between the ALD layer and the rollers during the web transport process or the ALD layer and the reverse side of the paperboard as it is collected by the take-up reel.
In conclusion, the effect of the pilot line winding was found to be the most detrimental mechanical stress for the barrier coating. The contacts to steel rollers, the nip rollers, and the reverse-side contact with paperboard caused the biggest decrease in the barrier performance as was demonstrated. The results also show that the lower 15 m/min line speed caused a stronger effect on the barrier than the 51 m/min line speed in the context of the mechanical contacts. With the slower line speed, the duration of the roll contacts onto the [Al.sub.2][O.sub.3] coatings of the samples was longer, which may have caused the difference. However, the friction behavior of the coating vs steel roller interface should be studied carefully in order to understand the mechanisms present in the roller contact event. The corona treatment, which was performed in the middle of the winding process, further reduced the barrier level obtained.
The study clearly shows that thin-film-deposited [Al.sub.2][O.sub.3] coatings at ALD scale are sensitive to different processing steps before and after the thin film deposition process. The barrier improvement caused by the barrier layer is significantly compromised by different processing factors. In general, mechanical contacts that take place during the winding process are found to be the most detrimental for the barrier coating. The effect of surface contamination of the substrate is also found significant, but not as significant as the mechanical contacts during winding. These results suggest that the substrate should be protected or repaired from contamination prior to the deposition process by, for example, employing clean room facilities or using a suitable cleaning method to clean the substrate. Also, the nanoscale coating should be protected from mechanical contacts by, for example, using a polymer laminate to cover the sensitive barrier layer. A further study is recommended to investigate the effect of line tension and strain on the barrier properties of ALD coating.
The shipment of the coated material between Al-foil and atmospheric post-corona treatment had only minor effect on the barrier value. The effect of shipment had slightly higher impact on the barrier than the corona treatment and it also showed more significant variation between individual results than corona. It was found that the samples that had been shipped in different occasions between Al-foils, but did not experience any other treatments, had different [O.sub.2]TR results. As regards the investigation of the factors before the deposition process, the measured [O.sub.2]TR value for the sample was 150 [cm.sup.3]/[m.sup.2]/24 h whereas in the second stage of the study it was 36 [cm.sup.3]/[m.sup.2]/24 h. Most likely this anomaly was caused by the differences in the shipment and sample handling processes; i.e., the factors such as how carefully the samples are packed between the Al-foils, how the package is handled, and how the samples are treated when removing them from the package and organizing the barrier test are considered critical for the barrier value.
As a final step. Table 6 collects together all the factors tested in the study and compares them in the same table. The individual factor in question is expressed as a percentage value showing how much it reduced the barrier of the coated structure compared to the result of the uncoated material. Each index value shown in the table is calculated according to equation (5), where subscripts 1, 0, and REF denote the cases where the factor observed influences the result, the factor is not influencing the result, and the result of the uncoated BOPP film, respectively.
Index = [O.sub.2][TR.sub.1] - [O.sub.2][TR.sub.0]/[O.sub.2][TR.sub.REF] - [O.sub.2][TR.sub.0] x 100% (5)
The functionality of a nanoscale [Al.sub.2][O.sub.3] barrier coating deposited on a polymer film is subject to various threats originating from material processing before and after the deposition process. The surface contamination of the substrate before the deposition process and the mechanical stresses faced by the already-deposited material in roll-to-roll winding are found to be the most detrimental factors affecting the barrier quality, as was demonstrated with ALD-[Al.sub.2][O.sub.3]-deposited BOPP film. The shipment of the coated material between aluminum foils and the post-corona treatment to which the coating was exposed also reduce the barrier performance, but the effect is significantly lower than in the case of substrate contamination and mechanical stresses. The barrier properties of the ALD-[Al.sub.2][O.sub.3]-deposited BOPP film were not improved by using atmospheric corona, plasma, or flame treatment prior to the ALD coating in this study.
Acknowledgments The authors wish to acknowledge the support from the EU's FP7 project NanoMend. The material support from Innovia Films Ltd. is also acknowledged with gratitude.
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K. Lahtinen ([mail]), T. Seppanen, D. C. Cameron
ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, 50130 Mikkeli, Finland
J. Lahti, P. Johansson
Paper Converting and Packaging Technology, Tampere University of Technology, P.O. Box 589, 33101 Tampere, Finland
Table 1: Atmospheric surface activation treatments used in the study Treatment Power (kW) Line speed (m/min) Order Corona (strong) 3.0 40 Before ALD Corona 3.0 80 Before ALD Plasma (strong) 8.0 90 Before ALD Plasma 8.0 180 Before ALD Flame (strong) -- 90 Before ALD Flame -- 180 Before ALD Post-corona 1.0 15 After ALD Post-corona 3.4 51 After ALD Treatment Comment Corona (strong) Applied to a BOPP reel Corona Plasma (strong) Plasma Flame (strong) Mixture 27:1, flow 750 L/min Flame Post-corona Sample sheets attached to a paperboard line Post-corona Table 2: Surface energies of BOPP and ALD-coated BOPP surfaces pretreated with the stronger corona, plasma, and flame treatments Dispersive Polar Total (mN/m) (mN/m) (mN/m) Untreated 16 10 26 Corona 16 14 30 Plasma 14 7 21 Flame 17 11 28 ALD coated, untreated 8 34 42 ALD coated, corona 10 31 41 ALD coated, plasma 9 40 49 ALD coated, flame 8 20 28 Table 3: [O.sub.2]TR results of pretreated BOPP samples with and without the ALD-[Al.sub.2][O.sub.3] coating Treatment O.sub.2]TR without [O.sub.2]TR with ALD ([cm.sup.3]/ ALD ([cm.sup.3]/ [m.sup.2]/24 h) [m.sup.2]/24 h) 1 Untreated 1100 150 2 Untreated, through line 1100 220 3 Corona (strong) 1100 250 4 Corona 1100 270 5 Plasma (strong) 1100 200 6 Plasma 1100 240 7 Flame (strong) 1000 230 8 Flame 1000 190 Table 4: Influence of different mechanical stresses on the 02TR of ALD-[Al.sub.2][O.sub.3]-deposited BOPP film Set Structure Shipment point 1 BOPP (58 pm) -- 2 B0PP/[Al.sub.2][O.sub.3] (30 nm) No touch box 3 B0PP/[Al.sub.2][O.sub.3] (30 nm) Between Al-foils 4 B0PP/[Al.sub.2][O.sub.3] (30 nm) Between Al-foils 5 B0PP/[Al.sub.2][O.sub.3] (30 nm) Between Al-foils 6 B0PP/[Al.sub.2][O.sub.3] (30 nm) Between Al-foils 7 B0PP/[Al.sub.2][O.sub.3] (30 nm) No touch box 8 B0PP/[Al.sub.2][O.sub.3] (30 nm) Between Al-foils Set Line speed Roll contacts Corona point (m/min) at the line (kW) 1 No winding -- -- 2 No winding -- -- 3 No winding -- -- 4 15 11 -- 5 15 11 1.0 6 51 11 3.4 7 15 -- 1.0 8 15 -- 1.0 Set [O.sub.2]TR point ([cm.sup.3]/[m.sup.2]/24 h) 1 1100 2 20 3 36 4 300 5 390 6 240 7 32 8 81 Table 5: Mechanical properties of materials used in calculation of strain due to bending ALD layer (i) BOPP (0) Paperboard (s) Young's modulus 180 GPa 2.4 Gpa * 5 GPa ([Y.sub.0]) Poisson's ratio (v) 0.3 0.3 0.24 Thickness (d) 30 nm 58 [micro]m 275 [micro]m Bending radius (R) 77.5 mm * Manufacturer's data
Please note: Some tables or figures were omitted from this article.
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|Author:||Lahtinen, Kimmo; Lahti, Johanna; Johansson, Petri; Seppanen, Tarja; Cameron, David C.|
|Publication:||Journal of Coatings Technology and Research|
|Date:||Sep 1, 2014|
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