Freshure Coatings: Environmentally Friendly Barrier Coatings.

Transcription

1 Coatings: Environmentally Friendly Coatings. Dr. S. Jahromi Knowfort Technologies BV Urmonderbaan 20a 6160MD Geleen The Netherlands Roll-to-Roll vapor deposition of inorganic materials, such as Al and AlOx, on plastic webs is a well known and matured technique for producing functional coatings on an industrial scale. Vapor deposition of organic materials on the other hand is a relatively new method which has the potential to providing similar functionalities, for example in terms of performance, but at much more favorable conditions. For instance as compared with deposition of hard inorganic materials, vapor deposition of soft organic materials occurs at significantly lower temperatures and moderate pressures offering both cost and environmental advantages (e.g. less expensive equipment, lower energy consumption etc). We introduced the concept of vapor deposition of organic based triazine compounds already back in late 90 s. 1 It was shown that vapor deposition of compounds such as 1,3,5-triazine-2,4,6-triamine on typical polymeric films such as biaxially oriented polypropylene (BOPP) and poly(ethyleneterephthalate) (PET) results in formation of transparent crystalline layers with high oxygen. The formation of uniform layers was attributed to supramolecular interactions between triazine molecules aided by hydrogen bonding. The high oxygen was attributed to the lowering of diffusion of gases through crystalline layers. Since then we have been working to develop this technology from a conceptual to industrial and commercial level. In cooperation with partners, such as Applied Materials, roll-to-roll deposition of 1,3,5- triazine-2,4,6-triamine can now be carried out at industrial scale. At the moment, a number of commercial production lines for such coatings are already operational and several new production lines are in preparation. In this presentation we will outline various aspects of these coatings, branded as, in terms of safety, performance and final applications. We will explore both variations of Coatings, i.e. as a Single Coat on plastic webs and as a Top Coat on metalized films. Since one of the most prominent applications of Coatings is in food packaging, safety aspects are of paramount importance. Base material for Coatings, i.e.1,3,5-triazine-2,4,6-triamine is already in use for decades in food related packaging applications such as dinnerware and inner coatings of soda cans. This traizine compound is produced from natural gas. Gas plus air produces ammonia. From ammonia urea is manufactured which is a well-known fertilizer. Urea is the only ingredient for the production of 1,3,5-triazine-2,4,6-triamine. In soil environment, this triazine compound breaks down and for this reason it is sometimes used as slow fertilizer. This triazine compound has a very low acute toxicity of LD50> 3000 mg/kg which is comparable with table salt. Specifically for Coatings applications we have carried out extensive series of migration tests for different laminate structures under different conditions. 1

2 Table 1 shows the migration results for a typical laminate structure used for example for Modified Atmosphere Packaging (MAP) applications (PET12µm- - PE50µm). Table 1. Migration tests results carried out according EN on a PET12µm- -PE50µm laminate. Test conditions: 10 days at 40ºC (triplicates). Component Simulant Specific migration individual results (mg/kg) Specific migration mean results (mg/kg) 1,3,5-triazine-2,4,6- triamine Water 3% acetic acid 10% ethanol 50% ethanol Olive Oil MPPO *) Detection limit in olive oil is 1 mg/kg which is higher than in other simulants (0.1 mg/kg) The results in Table 1 indicate that there is no measureable migration of triazine compound. Similar experiments have been conducted on various different laminate structures with similar outcomes. Based on these results DSM Safety and Regulatory affairs has issued Non-Migration Declarations stating that the use of Coatings for food packaging applications is compliant with both US and European regulations. In terms of performance and potential applications, Single Coat offers performance which is superior to PVdC and sometimes even EVOH based materials. Table 2 shows typical values for PET- and OPA- laminated against PE. Table 2. values of laminates based on Single Coat. The laminates are prepared with solvent less glue. Substrate WVTR (g/m 2.24h) 23ºC at 85% RH OTR (cm 3 /m2.24h) 23ºC at 0% RH PET12µ- -PE50µ 0,71 1,0 OPA15µ- -PE50µ 0,63 0,3 As a Single Coat, is applied at a coating weight of about 0.2 gram/m 2 which is a factor lower than other materials such as PVdC and EVOH. At a price of raw material below 2 USD/kg, Coatings offer a very significant 2

3 cost advantage with respect to current transparent solutions. Combination of Coatings with compostable materials such as PLA opens the possibility to manufacture a fully biodegradable high transparent polymer. Mainly because of the cost advantage, is probably the only vacuum processed transparent solution currently available with the potential to capture significant portion of transparent market. This market is now primarily dominated by materials such as EVOH and PVdC. In combination with other metalized films, Top Coat creates a number of applications for different types of polymers. First of all since is an in-line coating process with high, the of primary metalized films is improved dramatically up to a factor of 3 or more. The exact value depends on various factors such as type of base film and optical density. The general behavior is shown in Figure 1 indicating that Top Coat raises the bar and improves the performance of standard metalized films with metalized CPP entering the market for metalized OPP (e.g. confectionary, sacks etc), metalized OPP entering the high markets (e.g. gas flushed products) and metalized PET replacing some of the applications which is now dominated by aluminum foil. Low (OTR<300 cc) MetCPP Medium (OTR<50 cc) High (OTR0 cc) Ultra High (OTR cc) MetOPP MetPET Al Foil MetCPP MetOPP MetPET Al Foil Figure 1. Schematic representation of the effect of Top Coat on gas performance of standard metalized films. As a top coat, is applied at very low thicknesses without affecting the appearance of the metalized films. In addition to improvement, Top Coat has a dramatic effect on other performance characteristics of the metalized films such as scratch resistance, Dyne level and printability. Triazine forms a hard crystalline layer on top of the metalized film, thereby protecting the metalized layer 3

4 against the formation of scathes in the vacuum chamber, during slitting, and down stream processing. Contrary to metalized coatings, Top Coat does not age as a function of time and thus offers a high surface tension (> 50 dyn/cm) which is unaffected by the storage time. Because of this characteristic Top Coated metalized Films are now instantly printable. Normally metalized films should be coated with an off-line primer before printing. Theses primers add to the total cost structure and also take away the glossy appearance of metalized films. With Top Coat, printability is provided with minimum additional costs and without loss of shinny appearance. This key feature offers the possibility to replacing multi-layer structures such as metalized OPP laminated against reverse printed OPP (used for confectionery) with heat sealable mono-layer Coated metalized OPP. In addition to applications in food packaging, Coatings can be used in (pressure sensitive) labels, as an economic replacement for acrylic coatings. Table 3 shows an overview of potential applications of both Single Coat and Top Coat in the flexible packaging industry. This list is not meant to be exhaustive as other uses can be envisaged, but it does show the most prominent applications. Table 3. An overview of potential application of Coatings flexible packaging industry. Coating Type Substrate Functionality Filed of Applications Potential advantages Single Coat PET, OPA, OPP, CPP, PLA Transparent Modified Atmosphere Packaging. Gas flushed packaging - Significant cost advantage. - Environmentally friendly (Chlorine free, less packaging material) OPP Instant printability - Rap around and pressure sensitive labels - Lower cost with respect to off-line primers (e.g. acrylics). Top Coat metopp, OPP- AlOx metopp metopp metpet PET-AlOx Instant printability, scratch resistance, Protection Improved Improved Protection during retort & instant printability - General packaging applications e.g. snacks; from laminate to mono-web - Rap around and pressure sensitive labels - Because of better (< 10cc) use of metopp for some of metpet applications - Less packaging materials (laminate to mono-web), i.e. lower costs. - Shinny appearance otherwise not possible with off-line primers - Lower cost with respect to off-line primers (e.g. acrylics). - Shinny appearance otherwise not possible with off-line primers - metopp offers a\ cost advantage with respect to metpet - Because of better (< - metpet is 0.5cc) use of metpet for some environmentally friendly of aluminium foil applications with better economics with respect to Alu-foil - General packaging where direct printing on PET-AlOx is required. - Significant cost savings as opposed to off-line priming. Apart from flexible packaging, other potential fields of application for include as layer for rigid packaging, i.e. PET bottles, and (flexible) electronics. 4

5 1 S. Jahromi, U. Moosheimer, Oxygen coatings based on supramolecular assembly of melamine Macromolecules, 33, 7582,