Plasmavorbehandlung und Beschichtung von Kunststoffolien. Teil 1: Beschichtung von unbehandelten Kunststoffolien

Plasma Pretreatment and Coating of Polymer Films. Part 1: Coating of Non-treated Polymer Films The food packaging industry demands cheap polymer films possessing a high barrier against permeation of gases, moisture and flavor. Candidates for the most successful materials fulfilling these requirements are vacuum web coated biaxial oriented polypropylene (BOPP) films containing a thin inorganic barrier layer. For a good adhesion of the barrier layer on the BOPP films, the polymer film must be pretreated. The industry uses the Corona atmosphere plasma. This work is separated in three parts. The first part describes the experimental setup and the properties of vacuum web coated layers on polymer films. The next part contains the results of the systematic modification of polymer surfaces by atmosphere and low pressure plasmas. The influence of the surface properties on the final functionality of the coated films is given. In the last part, the discussion of the results of the first and second part reveals systematic relations between the production parameters of the high barrier films and their final functionality. These results firstly reveal the adhesion mechanism of the inorganic barrier layers of the polymer films and the necessary surface properties of the polymer films, in order to get cheap high barrier films by vacuum web coating.     

Plasmavorbehandlung und Beschichtung von Kunststoffolien. Teil 2: Experimentelle Ergebnisse der Plasmavorbehandlung von Kunststoffolien

Plasma Pretreatement and Coating of Polymer Films. Part 2: Experimental Results of the Plasma Pretreatment of Polymer Films The food packaging industry demands cheap polymer films possessing a high barrier against permeation of gases, moisture and flavor. Candidates for the most successful materials fulfilling these requirements are vacuum web coated b iaxial o riented p olypropylene (BOPP) films containing a thin inorganic barrier layer. For a good adhesion of the barrier layer on the BOPP films, the polymer film must be pretreated. The industry uses the Corona atmosphere plasma. This work is separated in three parts. The first part describes the experimental setup and the properties of vacuum web coated layers on polymer films [1]. The next part contains the results of the systematic modification of po } ymer surface by atmosphere and low pressure plasmas. The influence of the surface properties on the final functionality of the coated films is given. In the last part, the discussion of the results of the first and second part reveals systematic relations between the production parameters of the high barrier films and their final functionality. These results firstly reveal the adhesion mechanism of the inorganic barrier layers of the polymer films and the necessary surface properties of the polymer films, in order to get cheap high barrier films by vacuum web coating.     

Stofftransport durch Schichtsysteme aus Polymeren und dünnen anorganischen Schichten

Mass transport through layer systems consisting of polymers and thin inorganic layers Flexible layer systems from polymeric substrates, thin inorganic layers deposited by vacuum coating and additional polymeric layers are frequently in use to obtain high barrier properties, predominantly against oxygen and water vapour. Especially in cases where additional polymeric coatings are able to fill defects in the inorganic layers, barrier properties of the resulting layer systems show a stronger dependence on their thickness. For the transport of condensable substances, especially of water vapour, an additional porosity in the sub‐nm‐size can be assigned to the inorganic layers. This, however, has a negligible effect on gas permeation. Multilayer structures made from substrates and alternating polymeric and inorganic layers show much better barrier properties than single polymeric substrates coated with single inorganic layers. These improvements, however, are less than previously reported here. Moreover, also in these cases, the condensation of water vapour in sub‐nm pores gives much higher rates for the permeation of substances than expected from simple defect models.     

Stofftransport durch polymere und anorganische Schichten

Polymeric materials are to be found in an increasing number of applications. In many areas, however, their high permeability for substances such as gases or water vapour creates problems. Traditionally, additional barrier layers are deposited onto the polymeric substrates as a permeation barrier, i.e. as a barrier against the transport of substances. Typically, polymeric layers are deposited from solution in atmospheric pressure, inorganic layers in vacuum processes. Highest barrier properties can be achieved via multi layer systems from inorganic and organic layers. This article describes basic principles of the permeation of substances through layer systems, highlights the differences of the substance transport through polymeric materials and inorganic layers and gives consequences for the production of materials with high and ultra‐high barrier properties, on the basis of polymeric substrates     

Preparation of silica-based hybrid materials coated on polypropylene film

In this study, silica-based organic–inorganic hybrid coating materials were prepared by the sol–gel method. Tertaethoxysilane and polyvinyl alcohol were used as the inorganic and organic compounds, respectively. The substrate polypropylene film surface was modified by corona-plasma treatment to provide appropriate adhesion between the coating material and the polymer base film. A silane.coupling agent of vinyltriethoxysilane was also used to improve the adhesion between the base film and the coated layer. The effects of vinyltriethoxysilane in the hybrid materials were investigated using Fourier transform infrared analyses and X-ray diffraction. The vinyl group of vinyltriethoxysilane increased the hydrophobicity of the hybrid materials. The polypropylene films coated with the hybrid materials were characterized by examining their morphology, optical transparency and oxygen permeability. The results showed that the formation of hydrogen bonds between polyvinyl alcohol and the other compounds affected the microstructure of the coating solution and the final oxygen permeation property. Further, although the presence ofvinyltriethoxysilane in the hybrid coating solution could improve adhesion between the coated layer and the polymer base film, it deteriorates the effectiveness of the barrier to prevent of oxygen permeation through the coated film. However, the coated film maintained visible transparency and even enhanced the transmission of long wavelength visible-light owing to refractive index matching.     

Hochreflektierende Beschichtungen auf Kunststoffoptiken

Metallized polymer substrates offering highest reflectance are not yet state of the art. Coating organic substrate materials is still a task that is connected with multiple problems. Insufficient adhesion of coatings on polymer substrates represents one of the main difficulties. We could show by experiment that aluminium and silver layers indicate good coating adhesion on many different polymers if they are deposited by vacuum evaporation considering certain process parameters. High reflectance values and a good climatic stability of the metal coated polymer parts are other important challenges to plastic mirrors. By performing roughness measurements on the different polymer samples and by comparing reflection values obtained after coating these samples the impact of the polymers surface quality on the reflectance after metal coating has been investigated. Particularly high reflectance above 97% was realized with a protected silver mirror as well as with dielectric enhanced aluminium. Applying these layer systems excellent reflection properties has been obtained on several plastic substrates comparable to those on glass mirrors. Furthermore the dielectric layers used for reflection enhancement showed the ability to protect the aluminium coating against climatic influences.     

Mineral Oil Barrier Testing of Cellulose‐Based and Polypropylene‐Based Films

Recycled cardboard has been identified as a major source of mineral oil hydrocarbon (MOH) contamination of foods. Identifying and using appropriate functional barriers is a mechanism through which this problem can be addressed. A number of cellulose‐based and biaxially oriented polypropylene (BOPP) films were evaluated as potential functional MOH barriers. The films were tested using a donor material, a paper containing MOH placed on one side of the film barrier and a paper which acted as the receptor on the other. Testing was performed at accelerated conditions of 60°C, the receptor analysed periodically for MOH. The results demonstrated that the cellulose‐based film types provided an MOH barrier of >3.5 years. This contrasted with the BOPP selected films, for which only the proprietary acrylic‐coated BOPP film provided an effective barrier to MOH migration. Further investigation of the MOH barrier properties of the proprietary acrylic‐coated BOPP film was undertaken. Various coating strategies were employed including increasing the coating application weight, increasing the number of coating lay downs and coating one or both surfaces of the film. It was found that an MOH barrier of 1.5 years when tested at 40°C could be achieved for the proprietary acrylic‐coated BOPP film; however, barrier effectiveness was dependent on the coating integrity of the film. Further work with a vertical form filler packaging machine and the use of a staining technique with transmission microscopy proved effective at highlighting and assessing the coating integrity of packets during a typical packaging operation. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimizing the heat sealing parameters of multilayers polymeric films

Polymer–metal multilayers have been widely used for decades in packaging industry, and more recently for vacuum insulation panels for building application. In both cases, the seal zone could represent a weak area for mechanical and barrier properties. The aim of this report is to investigate the heat sealing properties of multilayers composed of one polyethylene layer and one or three polyethylene terephthalate layers coated with aluminum. The quality of seal was quantified by peeling test and the failure mechanisms. In order to optimize the set of heat sealing parameters, a series of mechanical and morphological relevant parameters were measured and compared to the failure modes. A comparison between the sole sealant film and multilayers was performed in terms of range of optimal heat sealing parameters and mechanical behavior of seals. Although they present a much narrower range of optimal properties, the multilayers films show a strong advantage over the single films.     

Crystalline structure and morphology of biaxially oriented polypropylene film under the coexistence of organic silica particles and its influence on the adsorption diffusion of polar solvent molecules

In this article, a silica/EVA/PP composite was prepared by melt‐blending nanosilica with polypropylene, and a surface‐modified BOPP film was prepared by using this as raw material. SEM studies have shown the special microscopic morphology of the surface and its cross section. X‐ray diffraction (XRD) characterized and analysed crystallinity, molecular orientation, and grain size in the modified film. Furthermore, the presence of microholes in the modified film was verified by positron annihilation spectroscopy. The results show that compared with the unmodified films, the modified BOPP films have higher crystallinity and smaller grain size. Its dense surface structure and reticular fibre bundle structure make the diffusion coefficient and solubility of ethyl acetate small in the film. The mechanical properties, barrier properties, heat resistance, and ink adhesion of this film have been significantly improved. Modified film can be used as the food packaging film which has high performance and low residue.     

Flexible Materialien mit ultrahohen Barriereeigenschaften

Flexible polymeric components are being increasingly sought after for applications in a variety of technical fields. Due to their relatively high permeability for various substances, such as gases or water vapor, the application of polymers remains limited. With particular regard for high added‐value areas, the required barrier properties are orders of magnitude higher than can be achieved by all available polymers. Therefore, additional barrier layers have to be deposited onto the polymeric substrates: inorganic and organic layers, via coating techniques in vacuum or atmospheric pressure. Highest barrier properties can be achieved via multi layer systems from inorganic and organic barrier layers. This article describes basic principles of the permeation of substances through such multi layer systems, approximations for predictive calculations of barrier properties, and the basic characteristics of the different materials and processes that are currently investigated in the Fraunhofer‐Alliance Polymer Surfaces.     

Raman spectroscopy and mechanical properties of multilayer tetrahedral amorphous carbon films

In order to take the tetrahedral amorphous carbon (ta-C) films as the high acoustic impedence layer in a Bragg reflector isolating acoustic wave from the substrate in solidly mounted resonator, the multilayer films consisting of sp2-rich layers and sp3-rich layers were deposited from a filtered cathodic vacuum arc by adjusting the substrate bias. The microstructure of the films was evaluated using a visible Raman spectroscopy. The stress was calculated according to the changed curvature of the coated and bare substrate. The hardness, modulus and scratching were measured using a nanoindenter. It has been shown that the multilayer structure maintaining high tetrahedral content, high hardness and high elastic modulus is still characterized with lower intrinsic stress and better adhesion.     

Atomic layer deposition on polymer based flexible packaging materials: Growth characteristics and diffusion barrier properties

One of the most promising areas for the industrial application of atomic layer deposition (ALD) is for gas barrier layers on polymers. In this work, a packaging material system with improved diffusion barrier properties has been developed and studied by applying ALD on flexible polymer based packaging materials. Nanometer scale metal oxide films have been applied to polymer-coated papers and their diffusion barrier properties have been studied by means of water vapor and oxygen transmission rates. The materials for the study were constructed in two stages: the paper was firstly extrusion coated with polymer film, which was then followed by the ALD deposition of oxide layer. The polymers used as extrusion coatings were polypropylene, low and high density polyethylene, polylactide and polyethylene terephthalate. Water vapor transmission rates (WVTRs) were measured according to method SCAN-P 22:68 and oxygen transmission rates (O₂TRs) according to a standard ASTM D 3985. According to the results a 10 nm oxide layer already decreased the oxygen transmission by a factor of 10 compared to uncoated material. WVTR with 40 nm ALD layer was better than the level currently required for most common dry flexible packaging applications. When the oxide layer thickness was increased to 100 nm and above, the measured WVTRs were limited by the measurement set up. Using an ALD layer allowed the polymer thickness on flexible packaging materials to be reduced. Once the ALD layer was 40 nm thick, WVTRs and O₂TRs were no longer dependent on polymer layer thickness. Thus, nanometer scale ALD oxide layers have shown their feasibility as high quality diffusion barriers on flexible packaging materials.     

Transparente Barriereschichten auf flexiblen Polymersubstraten

Transparent permeation barrier layers on flexible polymer substrates This paper reviews different vacuum based technologies for manufacturing transparent permeation barrier layers and layer stacks on flexible polymer substrates. With plasma assisted reactive evaporation, a cost‐efficient, highly productive process for food packaging applications is presented. Reactive dual magnetron sputtering is a technology for the deposition of oxide layers with a very low water vapor and oxygen transmission rate at a reasonable deposition rate. Many groups suggest multilayer stacks for the encapsulation of flexible electronic devices. In this paper, an all‐in‐vacuum inline concept for manufacturing such multilayers is presented. It is based on the combination of reactively sputtered barrier layers with interlayers grown by using a magnetron based PECVD process (Magnetron‐PECVD). Both, process parameters, such as deposition rate and process pressure, and important layer properties, such as morphology and the water vapor and oxygen transmission rate are compared for the different single and multi layer technologies.     

添加剂对BOPP薄膜光学性能的影响

目的研究常见类型添加剂对BOPP(双向拉伸聚丙烯)薄膜表面光泽度和雾度的影响。方法通过测试BOPP薄膜的表面光泽度、雾度,对比分析不同类型添加剂对BOPP薄膜光学性能的影响。结果氢化石油树脂与芯层PP有良好的相容性,有利于改善BOPP薄膜的表面光泽度和透明性,质量分数为5%～20%的氢化石油树脂可以使BOPP薄膜的光泽度由88%提高到95%,雾度由1.7%降至0.8%,增透效果明显。抗静电剂(烷基二乙醇胺、单甘酯)和爽滑剂(硅酮类、芥酸酰胺)与PP有部分相容性,在迁移过程中不同程度地影响了BOPP薄膜的光学性能。在烷基二乙醇胺与单甘酯复配的抗静电体系中,烷基二乙醇胺的添加有利于BOPP薄膜光学性能的提高,单甘酯含量的提高明显恶化了薄膜的光学性能,芥酸酰胺的添加造成BOPP薄膜光泽度下降,雾度增加,苯基改性硅酮比普通硅酮更有利于提高BOPP薄膜表面的光泽度与透明性。抗粘连剂二氧化硅与表层PP不相容,形成了界面,在二氧化硅含量大于0.15%(质量分数)时,雾度迅速提高,光泽度下降。结论薄膜生产配方中添加剂的选择与优化是开发高表面光泽度低雾度BOPP薄膜的关键。     

A Comparison of the Cell Compatibility of Poly(ethyleneimine) with that of other Cationic Biopolymers Used in Applications at Biointerfaces

Poly(ethyleneimine) (PEI) is used as an initiating base layer or intermediate layer for layer‐by‐layer (LBL) technology. Since PEI is potentially cytotoxic in solution, it is necessary to investigate the influence of the physical properties of PEI layers on osteoblast cells. Therefore, the first aim of this study was to test the hypothesis that there is no statistically significant difference of cell adhesion, proliferation, and viability in response to nanometer thin polymer layers of PEI compared to other well‐known polymers. The second aim of this study was to test the hypothesis that the amine‐substituted dextran (aminodextran (AMD)) adheres well on Ti and can be used as a polymer coating in biomaterials applications. Titanium samples were coated with PEI, poly‐L ‐lysine (PLL), or AMD using dip coating. The polymer films were investigated with ellipsometry, atomic force microscopy, contact angle measurements, and X‐ray‐photoelectron spectroscopy (XPS). Cell adhesion, proliferation, and viability tests were carried out using osteoblast‐like cells (CAL‐72). Thin polymer layers below 10 nm layer thickness were found on the Ti surfaces. It was shown for the first time that base layers of PEI with nanometer thickness do not affect the bone cell reaction negatively. PEI, therefore, can be used as a functional base layer for LBL functionalization of metallic implants. AMD can be used in biomedical applications but does not adhere on titanium without an adhesion promoter.     

Improvements in barrier performance of perfluorinated polymer films through suppression of instability during film formation

We present a general method for making thin and smooth films of a water-repelling perfluorinated polymer. These films function as encapsulation barrier layers against water and oxygen permeation. Based on a phenomenological analysis, we find that disturbances in flow due to the Rayleigh-Benard-Marangoni instability during drying of spin-cast perfluorinated polymer films cause high surface roughness and the formation of “pinholes”. Atomic force microscopy measurements show that this instability can increase the surface roughness by an order of magnitude. Casting films from solutions with higher polymer concentration and from solvents with higher viscosity suppress the instability and significantly reduce the roughness. Suppression of the instability results in improved barrier properties as indicated by the calcium thin film optical transmission test.     

Einfluss der chemischen Umgebung auf Morphologie und Struktur von Magnesiumhydroxid auf Magnesiumoberflächen

Influence of the Chemical Environment on the Morphology and Structure of Magnesium Hydroxide formed on Magnesium Surfaces Successful application of magnesium in metal construction is promoted by available methods for surface protection and, if needed, an electrical isolating layer between magnesium and other construction metals of composite materials [1]. Suitable materials for surface protection are polymer coatings, e. g. polymer paints. These coatings require a sufficiently corrosions resistant ground, which up to now normally is a environmentally dangerous, chromium‐containing conversion layer. In case of destruction of a conversion layer, caustic magnesium hydroxide is formed and responsible for a promoted delamination of various commercial polymer paints. Thus, development of a new magnesium – polymer – systems is of great interest. One probably successful possibility is a defined chemical attachment of molecular adhesion promoters to the magnesium conversion layers. These adhesion promoters should include a magnesium hydroxide specific group for a strong chemical attachment to magnesium conversion layer, which is hydrolytically stable in water, and additionally a second adhesive group at the other end of a hydrophobic spacer to ensure the attachment of a polymer. Direct attachment of these molecular adhesion promoters onto magnesium metal is not promising as all known magnesium organic compounds are hydrolytically instable [2]. As the hydroxide conversion coating is a substantial part of a magnesium‐polymer‐composite, the properties of the magnesium hydroxide layer have to be investigated and optimized depending on preparation conditions. In order to characterize the magnesium hydroxide conversion layer we use IR‐spectroscopy, quartz microbalance and Scanning Probe Microscopy. IR‐spectroscopic investigations show the presence of water in hydroxide conversion coatings formed at pH = 7–10. Conversion coatings prepared at pH > 12 are spectroscopically free of water. Taking into account the isoelectric point and the reactions resulting from a pH change, a model for the formation of the hydroxide layer is presented. This model explains the formation of a water free hydroxide layer at pH levels above 12 and the formation of water containing hydroxide layers below pH 12. The topography of the conversion layers is investigated by Scanning Probe Microscopy. If the conversion layer is formed in a solution with low pH a rough structure is built up compared to conversion layers, which are formed in solutions with high pH. These differences can be explained by taking into account the solubility of magnesium hydroxide and the change of OH⁻‐concentration in the solution due to different pH.     

Effects on Oxygen‐barrier Properties of Pretreating Paperboard with a Starch–Poly(Vinyl Alcohol) Blend before Polyethylene Extrusion

Polyethylene (PE) extrusion coating was performed on paperboard pre‐coated with water‐borne barrier coatings based on starch–poly(vinyl) (PVOH)–plasticizer blends in order to investigate that how the addition of a plasticizer to the pre‐coating affects the oxygen‐barrier properties of the board after PE extrusion coating. The plasticizers used were glycerol, polyethylene glycol (PEG) and citric acid (CA). Photomicrographs showed that the barrier coating layers were rather smooth, but defects were observed in the starch–PVOH layers when a plasticizer was added. Starch–PVOH layers had oxygen‐barrier properties similar to those of pure PVOH without plasticizers. When a sufficient number of layers (four layers) were applied to cover defects, the starch–PVOH layers containing CA showed oxygen transmission rate (OTR) values similar to those of starch–PVOH layers without plasticizer. The adhesion of PE to pre‐coated paperboard decreased when a plasticizer was added to the pre‐coating recipes. PE extrusion coating resulted in a reduction in the OTR in the case of pre‐coating formulations containing plasticizers. A lower OTR after polyethylene extrusion was observed with PEG as plasticizer than with CA as plasticizer. This could be explained by the increase in brittleness due to cross‐linking under the high temperature load during the extrusion process. Dynamic mechanical analysis of the films showed a substantial increase in storage modulus between 100°C and 200°C for CA‐containing starch–PVOH films. The contact angle of diiodomethane on the pre‐coating layer decreased when a plasticizer was added to the coating recipe indicating an increase in wetting of the PE melt. Addition of PEG to the pre‐coating led to a greater wetting than the addition of CA, and this may have sealed some defects in the pre‐coating leading to lower OTR values.     

Adhesion enhancement of sol-gel coating on polycarbonate by heated impregnation treatment

The main limitation in using coated plastics for optical components, electronic applications and display systems is the softness of the substrate surfaces, which is responsible for the low impact and abrasion resistance and weak adhesion between the coating and the substrate. In this paper, we report a new strategy for surface pre-treatment of plastics using heated vacuum equipment and sol-gel materials to provide both chemical bonds and penetrated hard layer into the plastic surface to increase the overall performance of the coated plastic components. The heated vacuum treatment process involves: (1) surface cleaning and pore opening by heating and vacuum conditions, (2) impregnation of hydrolyzed hybrid precursor into polymer substrate under pressure and elevated temperature, (3) aminolysis of diffused precursor with surface to form chemical bonds and hardened surface layer, (4) formation of chemical bonds at treated surface with sol-gel hard coating. An impregnation depth of 1.5 µm was detected. Water contact angle dropped to below 40° and roughness increased after treatment. These provided better adhesion by increased wettability and contact area. Much increased nanoindentation hardness and Young's modulus after impregnation provided a gradient in mechanical properties between soft substrate and hard sol-gel coating. The hardened substrate delays the plastic deformation in substrate during pencil scratch test, thereby preventing early gouge failure. Both the better adhesion and the delayed gouge failure contributed to the increased scratch resistance from 6B to 8H after sol-gel coating.     

Numerical simulation of permeation through vacuum‐coated laminate films

The material usage in the packaging market of Germany has decreased over the last few years. This trend results from the substitution of heavy packages with light‐weight, flexible materials. In this context, aluminium foil‐based multilayer films have been partly replaced by metallized laminates in food packaging technology. Other coating materials, such as Al₂O₃ or SiO_x, are used where transparent films are desired. The disadvantage of these vacuum‐coated layers is the existence of pinholes which allow diffusion processes, in contrast to aluminium foil‐based multilayer films. In this study the barrier behaviour of vacuum coated laminate films was predicted by numerical simulation. The results are presented in terms of dimensionless parameters so that they may be transferred to analogous problems. This model provides a method to calculate the oxygen permeation through coated laminates. However, it is invalid for condensable gases such as water vapour. The simulation is suited for characterizing the influence of the compound structure on the barrier properties of vacuum coated laminate films. The results are verified by comparing the calculated with measured values. Copyright © 2002 John Wiley & Sons, Ltd.