In extrusion coating, the inadequate adhesion between the polymer coating and the fiber-based paper substrate (paper and paperboard) is both a common and a constant problem. The lack of adhesion between the printing ink, or glue, and the polymer coating is another area where adhesion improvement is needed. The common means of improving adhesion are flame, corona, and ozone treatments. A modem extrusion coating line is equipped with both a pretreatment and a post-treatment unit. From the work presented here, the following observations were made. The higher the applied corona power and the thicker the coating, the higher the surface energy and polarity of the low density polyethylene (PE-LD) surface. When a high corona power was applied to the coating, only the polar component of the surface energy was increased. The surface energy decreased sharply as a function of aging, but remained more or less constant after about 2 weeks' storage time. The contact angles of water on paper correlated well with the oxygen contents (determined by ESCA) and with the applied corona power. The polarities of both paper and paperboard increased as a function of the applied corona power. Corona pretreatment of paper and paperboard improved their adhesion to PE-LD remarkably. The adhesion of the polypropylene (PP) homopolymer is based more on mechanical interlocking than on interfacial bonding. On the other hand, the oxidizing pretreatments of the paper substrates significantly promoted the adhesion of the PP copolymer.

One of the causes leading to low bond strength between a coating and a substrate (adhesion strength) - if coatings are formed at elevated temperatures in air - is assumed to be a weak boundary layer generated in the region of adhesional contact: the boundary layer consisting mostly of low-molecular-weight products resulting from thermal oxidative degradation of the polymer. It has been verified experimentally that products of oxidation diffuse from the coating surface layer to the contact area. The oxidation process is supposed to be localized within that surface layer. A method has been devised to determine the thickness of the layer, and model experiments have been conducted to show that low-molecular-weight products of oxidation deteriorate the adhesion strength. Ways have been found to increase the adhesion strength of coatings by means of modification of the coating applied in a layer-by-layer manner. The idea is to introduce separately such modifiers as antioxidants, inorganic fillers possessing high adsorption capacities, and crosslinking agents into the coating surface layer. This method of coating modification allows one to eliminate the negative effects of the low-molecular-weight products generated in the surface layers during the formation.

Surface modifications of polyetheretherketone (PEEK) made by chemical etching or oxygen plasma treatment were examined in this study. Chemical etching caused surface topography to become irregular with higher roughness values R_a and R_q. Oxygen plasma treatment also affected surface topography, unveiling the spherulitic structure of PEEK. R_a, R_q and surface area significantly increased after plasma treatment; topographical modifications were, nonetheless, moderate. Wetting angle measurements and surface energy calculations revealed an increase of wettability and surface polarity due to both treatments. XPS measurements showed an increase of surface oxygen concentration after both treatments. An O:C ratio of 3.10 for the plasma-treated PEEK surface and 4.41 for the chemically-etched surface were determined. The results indicate that surface activation by oxygen plasma treatment for subsequent coating processes in supersaturated physiological solutions to manufacture PEEK for biomedical appiications is preferable over the chemical etching treatment.

A theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday. Results are obtained, in concentric sphere geometry, for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions, negative ions and metastable oxygen molecules, coupled with Poisson's equation. A series of ‘saw-toothed’ current pulses of period about is predicted with a DC current level. Accompanying the current peaks are discrete pulses of light 30 ns wide. Successive ‘shells’ of positive ions, from successive current pulses, carry 96% of the mean current. The mean current - voltage relationship has the classic square-law form. The seed electrons required for successive pulses are detached from negative ions by metastable oxygen molecules. Photo-ionization is crucial for the discharge at the anode and for the formation of negative ions throughout the gap. The pulse frequency varies with applied voltage and is found to be approximately proportional to the positive-ion mobility. The surface electric field at the central electrode remains close to Peek's onset field. The origin of onset streamers is explained and sub-microsecond voltage pulses are found to produce streamers. The results for concentric-cylinder electrodes are described briefly.

Injection-moulded plates of ten polypropylene (PP) and thermoplastic polyolefin (TPO) materials with varying material composition (different type of rubber, varying degree of ethylene etc.) were characterized before and after oxygen plasma treatments. Untreated materials were studied by means of differential scanning calorimetry (d.s.c.), size exclusion chromatography (s.e.c.), Fourier-transform infrared spectroscopy (FTi.r.), attenuated total reflectance (ATR) and transmission measurements, and the effect of plasma treatment conditions was followed by X-ray photoelectron spectroscopy (X.p.s.) and contact angle measurements. S.e.c. analysis revealed only minor variations among the materials, while the d.s.c. and FTi.r. experiments confirmed that the differences were to be expected as a result of the variation in material composition. The FTi.r.-ATR results showed that all samples had a gradient in material composition. The materials were generally more rich in PP in the topmost ∼ 200 nm than in the first ∼800 nm, and a lesser extent of ethylene modification and/or rubber was observed in the topmost ∼ 200 nm. It was also shown that the degree of surface crystallinity was normally greater at ∼ 800 nm than at ∼ 200 nm, and that a higher mould temperature led to a higher degree of surface crystallinity. The water contact angles and the atomic composition showed that the materials were more oxidized after plasma treatment at high power-to-gas pressure (P/G) ratios than at low ratios. Moreover, the dependence on material composition was weak for samples that were plasma-treated at low P/G ratios whereas the materials that were least ethylene-modified were less oxidized than the others at high P/G ratios. © 1997 Elsevier Science Ltd.

Polypropylene sheets are treated with oxygen plasma for the interfacial control of GF/PP composites. The interfacial strength between glass fabric and PP resin is estimated by the T-peel test method. The evaluation of T-peel test data is done by both the T-peel strength method and the T-peel amplitude method. The T-peel strength value and T-peel amplitude value were respectively increased to about 50% and 120% compared with each value of non-treated specimens. The T-peel strength relates to the surface energy on the PP-sheet and the T-peel amplitude relates to the fracture pattern of the delamination surface. From SEM observations on the delamination surface, many voids in the space enclosed with fiber bundles are observed in the case of non-treated specimen and no void and fiber bridging are observed on the plasma treated specimens. It is found that interfacial properties between fiber and resin are improved by this plasma process.

Injection-moulded plates of four polypropylene-based copolymers with ethylene or an unconjugated diene as the comonomer were subjected to oxygen plasma treatments. The main objective was to investigate how the degree of wettability and the adhesion properties were influenced by the type and amount of comonomer and by selected plasma parameters. The change in wettability was monitored by static water contact angle measurements and the adhesion between plasma-treated polypropylene plates and a two-component polyurethane lacquer was evaluated by a 90° peel test. No significant difference in the degree of wettability depending on material composition or treatment conditions could be observed. However, the lacquer adhesion was shown to be a function of both material composition and discharge power, while the influence of gas pressure was less clear. For all procssing conditions used, the lacquer adhesion was distinctly improved as the diene content was increased. An increasing extent of crosslinking reactions combined with a reduction in the number of main chain scissions are proposed to account for the observed results.

The effects of solvents on the surface properties of oxygen plasma-treated polyethylene and polypropylene films have been studied by ESCA, contact angle measurement, and adhesion testing. The results show that oxygen plasma treatment produces some low molecular weight materials (LMWM) on the treated surfaces, which can be removed, to some extent, by solvents. It seems that the LMWM has different solubilities in different solvents. Among the solvents (water, acetone, and 2-propanol) used, acetone has the most significant effect. The removal of LMWM considerably reduces the wettability of the treated materials, but does not impair the adhesion increased by the plasma treatment.

The adhesion properties achieved after oxygen plasma treatments of ten polypropylene (PP) and thermoplastic polyolefin (TPO) materials of different compositions were studied. It is shown that the adhesion between a polyurethane (PUR) lacquer and plasma-treated materials was strongly influenced by the plasma treatment conditions and the chemical composition of the materials. Generally, a low power-to-gas pressure (P/G) ratio during the plasma treatment and a high ethylene content, preferably in the form of blocks, and/or the presence of double bonds in the matrix, are favourable for adhesion properties. Moreover, the TPOs were less sensitive towards the plasma treatment conditions than the corresponding PPs. The properties and the type of rubber may also be important for the adhesion properties. Furthermore, it was shown by X-ray photoelectron spectroscopy (X.p.s.) and Fourier transform infrared (FTi.r.) spectroscopy (using the attenuated total reflectance (ATR) technique) that all failures—even the apparently interfacial failures—were located in the substrate, below the oxidized surface layer, the only difference being the depth of failure. The fracture surfaces of samples showing low peel forces generally had a more PP-like composition than fracture surfaces that were clearly cohesive in the substrate. This observation offers evidence that the lacquer adhesion is determined by the extent to which chain scission reactions occur in the near-surface region of the substrate during the plasma treatment. © 1997 Elsevier Science Ltd.

Low density polyethylene (LDPE) and high density polyethylene (HDPE) were plasma-treated with N₂ and O₂ plasma. The wettability and polar component of surface free energy of plasma-treated polyethylene were investigated by contact angle measurement. The concentration of functional groups formed by plasma treatment such as hydroxyl and carbonyl groups was measured using attenuated total reflection Fourier transform infrared spectroscopy (ATR FTi.r.). The concentration of polar functional group increased rapidly with 5–10s of plasma treating time and then very slowly after that. The adhesion strength of epoxy resin/plasma-treated polyethylene joints was examined by a 90° peel test. The increase of the adhesion strength was similar to that of concentration of polar functional groups. The higher adhesion strength of epoxy resin/plasma-treated HDPE joints was observed than that of epoxy resin/plasma-treated LDPE joints since HDPE deformed more during the peel tests and had more polar functional groups on the surface.

The present invention is a polyester film base which has a surface approximately 5 nm thick. The surface of the film base has been altered to include about 6 to 15 atomic percent nitrogen in the form of imines, secondary amines and primary amines in the ratio of about 1:1:2. The invention also includes a film base whose surface includes oxygen in the form of hydroxyl, ether, epoxy, carbonyl or carboxyl groups wherein the oxygen is about 4 to 10 atomic percent above the original surface content of the base. The polyester film base can be either polyethylene terephthalate or polyethylene naphthalate.

Ion irradiation with various oxygen flow rates has been carried out to improve the wettability of polymethylmethacrylate (PMMA) to water and to enhance the adhesion between Al and the polymer. Ar+ ion and oxygen ion were irradiated on the polymer, and amounts of ions were changed from 5 × 1014 Ar+/cm2 to 5 × 1016 Ar+/cm2 by a broad ion beam source. Oxygen gas from 0 ml/min to 7 ml/min was flowed near the polymer surface during the ion irradiation, and the energy of ions was changed from 500 eV to 1500 eV. The wetting angle was reduced from 68° to 49° with the Ar+ ion irradiation only at 1 keV energy, to 43° with the oxygen ion irradiation, and dropped to 8° with Ar+ ion irradiation with flowing 4 ml/min oxygen gas near the polymer surface. Changes of wetting angle with oxygen gas and Ar+ ion irradiation were explained by a two-step chemical reaction among polymer matrix, energetic ions, and oxygen gas. The effects of Ar+ ion and oxygen ion irradiation were explained by considering formation of hydrophilic groups due to a reaction between irradiated polymer chain by energetic ion irradiation and blown oxygen gas, and enhanced adhesion between Al and PMMA was explained by the formation of electron acceptor groups in polymer and electron donors in metal, and by the chemical reaction in the interface between irradiated polymer surface and deposited metal.

Argon plasma-pretreated polytetrafluoroethylene (PTFE) films were subjected to further surface modification by near-UV light-induced graft copolymerization with acrylic acid (AAc), sodium salt of styrenesulfonic acid (NaSS), and N,N-dimethylacrylamide (DMAA). The surface compositions and microstructures of the modified films were characterized by angle-resolved X-ray photoelectron spectroscopy (XPS). A stratified surface microstructure with a significantly higher substrate-to-graft chain ratio in the top surface layer than in the subsurface layer was always obtained for PTFE surface with a substantial amount of the hydrophilic graft. The stratified surface microstructure was consistent with the observed hysteresis in advancing and receding water contact angles. The graft yield increased with Ar plasma pretreatment time and monomer concentration. Covalent immobilization of trypsin on the AAc polymer-grafted PTFE films was facilitated by water-soluble carbodiimide (WSC). The effective enzyme activities increased initially with increasing surface concentration of the grafted AAc polymer but became saturated at a moderate AAc polymer concentration. The immobilized enzyme could still retain close to 30% of its original activity. Solution-coating of the polymeric acid-modified PTFE films with the emeraldine (EM) base of polyaniline readily resulted in an interfacial charge transfer interaction and a semiconductive PTFE surface.

The treatment of surfaces by corona discharges is a well-established method to improve surface properties. The surface to be treated is moved continuously and is exposed to transient gas discharges, known as microdischarges, in air at atmospheric pressure between electrodes, where at least one electrode is covered with a dielectric barrier. Because of the short duration, only some 10 ns, the current through the microdischarges is predominantly carried by electrons. The ion temperature remains close to room temperature. Owing to these properties such discharges are qualified to treat surfaces which are sensitive to higher temperatures. For a large number of applications this treatment is adequate, but the adhesion of aqueous glues and inks to some plastic materials is insufficient if the surfaces are treated in this way. Furthermore, it is difficult to meet the requirements of surface properties of, for instance, polyolefine film (e.g. surface tension, adhesion). This material is not based on monomers containing chlorine or fluorine and is preferred for ecological reasons. This paper presents the results of experiments which demonstrate that in comparison to a common corona treatment significant improvements in surface properties of plastic materials can be achieved if repetitively generated pulse trains and reactive gases are used instead of air. If, for instance, the microdischarges are established in acetylene, thin films with a thickness of several namometres are formed on surfaces, which increase and stabilize the surface tension up to a level of 72 mN m−1. The state of the art of this new technology is discussed.

This study analyzes the combination of different tie layers with normal coextrusion and coating parameters: temperature, speed, and pretreatments. We wanted to determine the best combination possible and to issue recommendations for extrusion and coating. The typical structure was paper/tie layer/barrier layer/tie layer/LDPE (low-density polyethylene). When LDPE is coated on paper, pretreatments of the web are used (such as corona or flame). Sometimes ozone is sent onto the melt to increase natural oxidation. The same thinking could be applied to tie layers, but the trials showed that certain combinations lead to different conclusions. The effect of parameters such as corona or flame power, which were thought to depend only on the paper type, could also be influenced by the combination paper-tie layer. This could mean that web pretreatments are not always needed.

Polypropylene (PP) film was treated with radio-frequency-induced oxygen plasma, followed by the vacuum deposition of aluminum (Al) thin film, and the peel strength of the Al deposited PP film (Al/PP) was examined. The peel strength of plasma-treated PP film varied widely in the range of 6.7 to 157 N/m depending upon the plasma treatment conditions, whereas that of the untreated PP was 5.2 N/m. The peel strength was minimized at oxygen pressure near 13.3 Pa (0.1 Torr), and decreased with increasing discharge power. The peel strength rapidly increased at the initial stage of plasma treatment (∼ several seconds), decreased at the second stage, and slightly increased again at the third stage. A good agreement was found between the peel strength of Al/PP and the amounts of oxygen introduced onto the PP surface at the initial stage. A short-time treatment was very effective to improve the adhesion of Al/PP. At the end of the second stage, a large amount of carbon was detected by XPS on the Al layer of the peeled interface of Al/PP, which gave a minimum peel strength. Cohesive failure of PP film might have occurred. SEM photograph showed that PP surface was etched by oxygen plasma at the thrid stage. These peel behaviors of Al/PP were explained by the chemical and physical changes of the PP surface caused by oxygen plasma treatment: (1) introduction of O-functional groups onto the PP surface at the initial stage, (2) formation of weak booundary layers resulting from the partial scission of PP molecules at the second stage, and (3) plasma etching of the PP surface at the third stage.

The present invention is a polyester film base which has a surface approximately 5 nm thick. The surface of the film base has been altered to include about 6 to 15 atomic percent nitrogen in the form of imines, secondary amines and primary amines in the ratio of about 1:1:2. The invention also includes a film base whose surface includes oxygen in the form of hydroxyl, ether, epoxy, carbonyl or carboxyl groups wherein the oxygen is about 4 to 10 atomic percent above the original surface content of the base. The polyester film base can be either polyethylene terephthalate or polyethylene naphthalate.

The influence of film roughness on the wetting properties of vacuum-deposited polytetrafluorethylene (PTFE) thin films has been investigated using atomic force microscopy (AFM) and contact angle goniometry. Surface roughness has been characterized by atomic force microscopy in terms of RMS roughness (R_q) and fractal dimensions. A contact angle correlation with surface roughness, as determined by AFM, is evident from these results, which are discussed on the basis of wetting theory. The results also confirm that the high water contact angles (as high as 150°) recently observed at the surface of a new water repulsive coating material (mixture of PTFE and binder) are because of surface roughness. Such measurements clarify the effect of nanometer-size surface asperities on the wetting properties of hydrophobic coating.

Contact-angle measurements, the ASTM standard wetting test for polyolefin films, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated polypropylene (PP) films. Two combustion models, STANJAN and PREMIX, were then used to determine the chemical and physical properties of the flames used to treat the PP films. Both the flame equivalence ratio and the position of the PP film in the flame are important variables in determining the extent of oxidation and improvement in wettability obtained by flame treating. The optimal equivalence ratio for the flame treatment of PP is 0.93, while the optimal luminous flame-to-film distance is 0-2 mm. Modeling of the combustion processes occurring in the flame provides evidence that the extent of treatment correlates closely with the concentrations of H, O, and OH radicals present in the flame. The extent of surface modification of the flame-treated PP does not appear to correlate with either the flame temperature or the concentraion of oxygen molecules. The mechanism of surface oxidation by flame treatment probably involves polymer-radical formation by O and OH, followed by rapid reaction of the polymer radicals with O, OH, and O₂.