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Atomic and molecular layer deposition (ALD and MLD, respectively) are based on repeated cycles of gas-solid surface reactions. A monolayer of precursor molecules is chemisorbed onto the surface during a single deposition cycle, enabling control of thin film growth in principle down to sub-monolayer resolution. This level of control has made ALD and MLD interesting for various applications. This presentation shows that low-temperature ALD can also be used to adjust wetting characteristics of polymer webs with non-ideal surfaces. For example, print quality can be optimized by surface modification with just few ALD cycles. We have also developed inorganic-organic hybrid materials providing, for example, improved adhesion between an inorganic oxide surface and extrusion coatings. These open up new application areas for ALD and MLD. Due to e.g. the small amount of deposited materiaL/cycles needed this could also help to alleviate the challenges related to the limited speed of roll-to-roll ALD processes.

Atomic layer deposition (ALD) is a layer-by-layer deposition process based on repeated self-limiting gas-solid reactions by using volatile precursors. It is suited for producing dense and pinhole-free inorganic nanoscale coatings uniform in thickness at relatively low temperatures. The purpose of this presentation is to demonstrate the potential and the challenges of using ALD to create functional coatings for polymer films. ALD is an efficient tool for improving the barrier properties of polymer films. However, adequate barrier properties are only one of the key requirements set for the packaging materials. As far as safety issues are concerned, these coatings, for example, seem not to fall under the European definition of nanotechnology and migration is low enough to meet the requirements set by current European regulations. ALD can also be used to create antimicrobial coatings, and thin oxide coatings can be modified for improved mechanical and surface properties. It is recommended that ALD coatings are protected with an additional polymer layer providing also heat sealability. Although ALD is today carried out in batch mode, the development of roll-to-roll processes will enhance the feasibility of ALD for e.g. packaging materials

Atomic layer deposition (ALD) is a surface controlled layer-by-layer process based on self-limiting gas-solid reactions. Thin films are prepared using volatile precursors in repeating cycles until a preferred film thickness is obtained. ALD is suited for producing dense and pinhole-free inorganic films uniform in thickness. Most important commercial applications lies today in microelectronics, but they range from displays to protective coatings on silver jewellery. The purpose of this presentation is to demonstrate both the potential and the challenges of using ALD to create thin barrier layers for packaging materials. ALD can have a profound effect on the barrier values of various polymer films and polymer coated paperboards. As far as safety issues are concerned, these thin barrier films seem not to fall under the European definition of nanotechnology and migration is low enough to meet the requirements set by current European regulations. ALD can also be used to create antimicrobial thin films, and thin oxide films can be modified for improved mechanical and surface properties. It is recommended that ALD deposited thin films are protected with an additional polymer layer also providing heat sealability. Although ALD is today carried out in batch mode, the development of roll-to-roll processes will enhance the techno-economic feasibility of ALD, among others, for packaging materials.

Possibility to control the adhesion properties is important in various industrial applications. Since the topmost surface layers have the greatest role in adhesion thus making surface-controlled atomic layer deposition (ALD) reactions appealing method for tailoring surface adhesion properties. In this presentation we show that ALD and molecular-layer-deposition (MLD) can be used to adjust wetting characteristics of polymers and metals. Recently we have been modifying surface properties for various applica-tions including ink-jet printed films, adhesion promoting layers for extrusion coatings and anti-ice coatings. In addition to conventional inorganic metal oxides, such as Al2O3, we have tested also inorganic-organic hybrid MLD materials. Various tools, such as XPS, FT-IR and TOF-ERDA, were used to characterize these films, and wetting behavior was determined using contact angles measurements with the sessile drop method

Atomic layer deposition (ALD) is an efficient tool for improving the barrier properties of polymer films and polymer coated papers/paperboards. However, adequate barrier properties are only one of the key requirements set for food packaging materials, while other properties have only been studied to a limited extent. The main safety aspects related to polymer films with a thin ALD grown Al2O3 layer are presented in this paper. Although ALD methods for preparing thin films can be classified as part of nanotechnology, ALD grown Al2O3 thin layers do not fall under the European Commission's definition of nanomaterial, even though the thickness of the layer is in the nanoscale. Al2O3 is also accepted as an additive for plastics in contact with food. In abrasion tests ALD grown films did not increase the number of airborne particles in the surrounding air. ALD films on reference silicon wafers and oriented polymers were exposed directly to specific food simulants and the key material properties were evaluated. Finally, the films were also tested for migration. The Al2O3 layer was affected by the simulant exposure, and the degree of impact depended also on the base film. As a conclusion ALD grown Al2O3 thin layers require an additional protective layer.

Atomic and molecular layer deposition techniques have been successfully combined to produce inorganic-organic hybrid films with properties derived from both the inorganic and organic components. There are few reports dealing with further converting of ALD/MLD thin films. Typically inorganic oxide layers on polymer films in most cases require an additional top layer to enable heat sealing and to protect the thin film from mechanical stresses and defects. Adhesion of low-density polyethylene, polyethylene terephthalate and polylactic acid on ALD Al2O3 have been tested previously, where good adhesion was achieved in most cases only with the low-density polyethylene. In this study we report deposition of a hybrid ALD/MLD layer, its properties, as well as its use as adhesion layer for polyactic acid (PLA) extrusion coatings. A mixture of both lactic acid optical isomers, D- and L-lactic acids, was used as MLD precursor. 25 and 45 nm thick hybrid films were analyzed. XPS analyses gave a quite similar composition for both of these two coatings. FTIR analyses also indicated presence and bonding of hybrid components. The oxygen to carbon and oxygen to aluminum ratios were in line with theoretical calculations for such a hybrid. Deposition mechanism is expected to involve both hydroxyl groups of the lactic acid. However, the results indicated also other types of bonding between lactic acid and TMA or between the lactic acid molecules. The thickness of the hybrid remained the same for at least a week after the deposition indicating certain level of stability. In next step cellophane film deposited with 25 nm Al2O3 and 13 nm TMA-lactic acid hybrid was used as a substrate for PLA extrusion at different melt temperatures. Uncoated cellophane and BOPLA were used as reference substrates. PLA adhered only to itself and to the ALD/MLD hybrid with peel strength values exceeding 100 N/m, while PLA did not adhere to plain cellophane. Thickness of the MLD/ALD hybrid on ALD Al2O3 layer had no obvious effect on the adhesion properties at sealing temperature of 170 °C.

Atomic layer deposition (ALD) is an efficient tool for improving the barrier properties of polymer films and polymer-coated papers/paperboards. However, adequate barrier properties are only one of the key requirements set for the packaging materials. Purpose of this paper is to present the safety aspects related to polymer films with a thin ALD grown Al2O3 layer. Several approaches were tested. Based on our analyses ALD grown Al2O3 thin layers do not fall under the European Commission's definition of nanomaterial, and thus the limitations set in the Commission Regulation (EU) No 10/2011 on plastic materials would not be valid in this case. Al2O3 is also accepted as an additive for plastics in contact with food. Abrasive testing of polymer films, although detrimental in several cases to the film itself, did not increase the number of airborne particles. Coated silicon wafer and oriented polymer films were also exposed to specific simulants and key material properties were followed. Finally, we also tested the films for migration, although overall migration from a similar thin film has been regarded extremely low. Our tests were based on the worst case scenario, where the thin inorganic layer is exposed directly to the simulant. The Al2O3 coated films were affected by the simulant exposure, but the degree of impact depended also on the base film. This could indicate different thin layer growth on different polymer films. As a conclusion, such ALD grown Al2O3 thin layers require additional protective layers acting also as a sealant layer.

Atomic and molecular layer deposition (ALD and MLD, respectively) techniques are examples of self-assembly based on repeated cycles of self-limiting gas-solid reactions. The precursors are pulsed into a reactor alternately, separated by inert gas pulses. During a single cycle, only one molecular layer is deposited on the surface, enabling tailored film composition in principle down to molecular resolution on ideal surfaces. These cycles are repeated until a layer with a specific thickness is achieved. Few materials are, however, ideal. During the early film growth precursors adsorb onto the surface and absorb into the near-surface regions depending both on the substrate and the deposition parameters. These precursors can react with the substrate affecting e.g. mechanical, barrier and surface properties. The deposited material starts then to form clusters leading to nonuniform early film growth. The purpose of this presentation is to demonstrate that thin and non-uniform layers can be used to tailor the surface characteristics of different substrates. For example, print quality (ink spreading and penetration) of inkjet printing on polymer films can be adjusted with metal oxide. Secondly, this can be used to control water penetration into porous nonwovens. Third example demonstrates how adhesion of extrusion coated biopolymer to inorganic oxides can be improved with a novel hybrid layer based on lactic acid. As the amount of material to be deposited is small, this will help to increase the speed in ALD/MLD processes designed for moving webs.

The goal was to study polymer films and coated paperboard as base substrates for atomic layer deposition (ALD), to understand the parameters affecting layer growth and functional properties, to characterize thin layers, and to assess their safety and sustainability. Barrier properties of most polymer films studied were improved by Al2O3 thin layers. The relative improvement was the most significant with cellulose and polyester films, while certain plastic additives completely prevented thin layer growth. Polymer pre-coatings on fiber-webs have to be smooth and have good film forming properties. Layer growth starts by sorption of precursors onto and into the polymer surface followed by chemical reactions with the polar oxygen groups of the polymer and a possible formation of an interphase. This is followed by cluster formation and growth through clusters. The amount of oxide needed to cover the polymer depends on its' surface chemistry. Surface chemistry of polymer film has an impact on the layer growth and final functional properties. Polymer pretreatments prior to the ALD can be used to improve the barrier properties. Ozone can activate difficult surfaces, and the barrier properties can be adjusted by choosing the oxygen source. In addition, deposition temperature should be as high as possible. Mechanical properties of oxide layers were improved by combining thinner oxide and inorganic-organic hybrid layers into a nanolaminate. In addition, a contact between the oxide layers and the bacteria promoted antimicrobial activity. Uniform Al2O3 barrier layers do not seem to fall under the EU's definition of nanomaterial. Migration of Al2O3 to food simulants was low. However, ALD coated polymers require a top layer to protect the oxide layer from stresses, to prevent dissolution and to act as a sealant.

Atomic layer deposition (ALD) is an efficient tool for improving the barrier properties of polymer films and polymer-coated papers/paperboards. However, adequate barrier properties are only one of the requirements set for the packaging materials. The purpose here is to present the safety aspects related to polymer films with a thin ALD deposited oxide barrier layers, especially those with Al2O3. Several approaches for testing ALD material were utilized. Based on our analyses ALD grown uniform Al2O3 thin barrier layers do not fall under the European Commission's definition of nanomaterial and the related limitations in the Commission Regulation. Plastic food contact materials may also contain non-authorized substances provided that their migration to food do not exceed very low migration limit (0.01 mg/kg food) and they are not mutagenic, carcinogenic nor toxic for reproduction, or are in nanoform. However, functional barrier concept should not be used to separate food and nanomaterial. Meanwhile, U.S. Food and Drug Administration (FDA) has a more inclusive approach to identifying products of interest in context of nanotechnology including size and/or function. FDA does not categorically judge products containing nanomaterials to be inherently harmful. Al2O3 and organic compounds of interest, such as ethylene glycol and glycerol, are accepted in Europe as additives for plastics in contact with food. Likewise, in USA these are accepted as either as indirect additives used in food contact substances or generally regarded as safe. According to some producers AlOx coatings have also been approved in USA for indirect contact with food. In our experiments abrasive testing of polymer films, although detrimental in several cases to the film itself, did not increase the number of airborne particles. ALD Al2O3 deposited at 100 ºC onto silicon and commercial polymer films were also exposed to liquid food simulants while evaluating the change in surface and barrier properties. Finally, we also tested the films for migration, although overall migration from thin films has been previously regarded as extremely low. The Al2O3 coated films were affected by the simulant exposure, but the impact depended on the substrate material and the oxidizing precursor. This indicates different thin layer growth on different polymer films. As a conclusion, ALD grown Al2O3 thin layer requires an additional, for example, laminated or extrusion coated top layer to protect it from both mechanical and chemical stresses, to prevent migration to the food, and also to act as a sealant layer in food packaging.

In offset printing unit the interaction between ink, blanket and paper surface defines adhesion of the web on the blanket surface. After ink transfer paper web follows the blanket surface at the nip exit until it is released due web tension. The adhesion of the web depends on the surface properties of paper, printing material combinations, the layout and press settings. In general, shorter follow-up of the web on blanket surface predicts easier release thus longer follow-up can lead to higher release angle. The purpose of this study was to clarify the factors (material and process parameters) controlling paper web's release from the blanket. The release of six various paper grades was followed. Other studied variables were the release property of blankets and the influence of ink tack on web release. Furthermore, during printing the effect of fountain solution feed and nip pressure on web release was examined. The release force between printing materials was first studied in laboratory and the verification was carried out in full-scale heatset printings. On printing press the release of the web was measured using release angle measurement arrangements. Furthermore, an acoustic signal was gathered from ink film splitting to describe the web release. According to results, paper grade determines the level of web release angle. The results indicate that the smooth paper surface induces strong adhesion on the blanket which leads to higher release angle. Furthermore, the surface structure of the paper and the speed of ink absorption affect web release. In addition, it was noted that small amount of accumulated material on blanket surface easies the web release. According to studies, the release angle of the web can be lowered by selecting easy release blanket, lower ink tack, higher fountain solution feed and lower nip pressure.

Thin Al2O3 coatings were deposited at low temperatures of 80 or 100°C on various polymercoated boards and plain polymer fi lms using the atomic layer deposition (ALD) technique. The work demonstrated that such ALD-grown Al2O3 coatings signifi cantly enhance the barrier performance against oxygen and water vapour. Even extremely thin (25 nm) barrier coatings of Al2O3 could be suitable barrier layers for dry food and pharmaceutical packages made from temperature-sensitive fi bre-based materials. It was also demonstrated that these coatings may have relatively high seal strengths when sealed against LDPE coatings or themselves. In addition, ALD-grown Al2O3 coating did not significantly reduce the degradability of biopolymercoated boards in composting conditions.