The autohesion of polyethylene sheets was markedly improved by corona discharge treatments in oxygen, nitrogen, argon and helium. Equal bond strength was produced by an equal number of discharge cycles regardless of the time or frequency of application. At a given operating voltage the power consumed in a discharge rather than the chemical nature of a gas proved to be a factor controlling the enhancement of autohesion. The detrimental effect of the oxidation upon autohesion was noted after a prolonged treatment in an oxygen corona.

Low density polyethylene sheet was subjected to treatment by corona discharge in oxygen, nitrogen, helium and argon; in addition some sheets were treated with ozone gas. The bond strength between two similarly treated sheets was then measured using a commercial flexographic ink as an adhesive. The results showed that although surface oxidation improved both the ink adhesion and the wetting properties of polyethylene it is not a necessary prerequisite for good bonding. When the sheet was subjected to electrical discharge in nitrogen, argon or helium, considerable enhancement of ink adhesion was obtained without any detectable change in the surface chemistry of the polymer. The results indicate that ink adhesion after treatment in various gases follows closely the trends established previously in corona-induced autohesion of polyethylene. This suggests that the mechanism of bonding is similar in the two cases.

With increase in sample density, corona treatment was found to be decreasingly effective in enhancing the autohesion of polyethylene sheets. The effect of higher density could be offset in part by an increase in temperature of lamination. This parallel behaviour suggests that similar molecular mechanisms govern the phenomena of thermally-induced and corona-induced autohesion.

Untreated aluminium and aluminium hydrated for 60 s in boiling water have been extrusion-coated with low-density polyethylene (LDPE). The hydration transforms the oxide surface into a porous oxyhydroxide, known as pseudoboehmite. LDPE samples with different melt indices (4.5, 7.5, and 15) were used, which influence the ability to penetrate into the pores. Compared with untreated aluminium, a superior peel strength was obtained for the laminates with hydrated aluminium. In almost all cases, the peel strength for the laminates with hydrated aluminium could not be measured, due to rupture in the polymer film. This improvement is suggested to be due to stronger acid-base interactions, increased contact surface, and mechanical keying into the porous surface. The obtained peel strength and analysis by means of scanning electron microscopy indicated that the polymer with the highest melt index or lowest melt viscosity had the greatest ability to penetrate into the formed pores. After ageing up to 12 weeks in solutions with 1% and 3% acetic acid, the peel strength dropped rapidly for the untreated Al laminates, but remained constant for the hydrated Al laminates. This is explained by the fact that, besides the improved adhesion, the hydrated oxide prevents corrosive attack.

X-ray photoelectron spectroscopy (ESCA), wettability measurements, and an ink adhesion test were used to characterize changes in the surface properties of air-corona-treated polypropylene (PP) films upon aging under a variety of storage conditions. No changes in ESCA O/C atomic ratios as a function of aging were observed for corona-treated PP films. The wettability data indicated a slight decrease in wettability upon aging. Aging did not affect ink adhesion for the particular PP and ink studied. The responses obtained were independent of the various film storage conditions employed. The slight decrease in wettability observed upon aging was attributed to reorientation of oxidized functionalities within the surface region.

—ESCA, wettability measurements, SEM, weight-loss determinations, and an ink adhesion test were used to characterize low-molecular-weight oxidized materials (LMWOM) formed during the corona-discharge treatment of polypropylene film. Water-soluble LMWOM is readily formed by scission processes occurring during corona treatment. The presence of water-soluble LMWOM complicates the interpretation of wettability-based measurements of corona effectiveness. Surface roughening on corona-treated polypropylene is caused by the interaction of LMWOM and water in a high-relative-humidity environment. LMWOM does not necessarily form a weak boundary layer that hinders subsequent adhesion of ink to the corona-treated film.

Contact-angle measurements in air and water environments and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface properties of air-corona-treated polypropylene (PP) and poly(ethylene terephthalate) (PET) films. Surface properties were examined as a function of the storage time at various temperatures. Corona treatment forms water-soluble, low-molecular-weight oxidized materials on both polymer films. Corona-treated PP and corona-treated PET films have markedly different responses to aging. For corona-treated PP stored at ambient temperatures, only a slight decrease in wettability was observed. This decrease was attributed to the reorientation of oxidized functionalities within the surface region. At elevated storage temperatures, migration of oxidized species out of the surface region occurred under some conditions. For corona-treated PET, extensive migration and reorientation of oxidized groups occurred even at ambient temperatures, leading to significant decreases in wettability and a loss of surface oxidation. The contrasts in the responses of PP and PET to corona treatment are primarily due to differences in the properties of the base polymer resins.

A cross-web non-uniformity ('laning') in the flame surface modification of polypropylene (PP) film was investigated using flame temperature measurements and Wilhelmy plate force measurements. To associate the cross-web non-uniformity in the flame treatment with specific features of the flame supported on an industrial 4-port ribbon burner, the temperature and force measurements were registered to a specific burner port. The Wilhelmy force measurements show that the upstream pair of ribbon-burner ports causes a slightly greater treatment of the PP surface than the corresponding downstream pair of ports. The average temperature experienced by the PP as the film traverses through the flame is noticeably higher along the down-web line of the upstream burner ports as compared with a line passing through the downstream pair. This greater average temperature correlates to an exposure to a greater concentration of the active species, such as OH radicals, that cause the surface oxidation of the PP.

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.

Contact-angle measurements and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize polypropylene (PP) films that were exposed to laminar premixed air: natural gas flames containing small quantities of nitrous oxide. During combustion, the nitrous oxide generates gas-phase nitrogen oxides that lead to the affixation of nitrogen-containing functional groups to the PP surfaces. Treatment of PP in nitrous oxide-containing flames also leads to an increase in surface oxidation and markedly improves wettability when compared with standard flame treatments. The chemical form of the nitrogen affixed to the PP surface is strongly dependent on the flame equivalence ratio. Fuel-lean flames tend to affix highly oxidized forms of nitrogen such as nitrate and nitro groups, while fuel-rich flames tend to affix less-oxidized nitrogen groups such as nitroso, oxime, amide, and amine. A computational model, SPIN, was used to elucidate the chemistry of the flame as it impinges upon the cooled PP surface. The SPIN modeling indicates that the principal reactive gas-phase species at or near the PP surface are O₂, OH, H, NO, NO₂, HNO, and N₂O. A number of possible reactions between these species and the PP can account for the formation of the various nitrogen functional groups observed.

Contact-angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated biaxially oriented polypropylene (PP) films. While the surface of PP treated in a fuel-lean flame is highly oxidized, no watersoluble low-molecular-weight oxidized material (LMWOM) is formed by the flame treatment. A new computational model, SPIN, was used to determine the chemical composition of the impinging flames used to modify the PP. The SPIN model indicates that the species primarily responsible for the surface oxidation of the PP are OH, HO₂, H₂O₂, and O₂. Because the concentration of atomic O in the flame is low, there is little scission of the PP chains and no formation of LMWOM. AFM indicates that a 'nodular' surface topography is generated during the flame oxidation of the PP. The surface topographical features generated by flame treatment are probably the result of the agglomeration of intermediate-molecular-weight materials.

ESCA and contact-angle measurements were used to characterize the surfaces of polystyrene films exposed to SF₆, CF₄, and C₂F₆ plasmas. SF₆ plasmas cause loss of aromaticity in the polystyrene surface region via saturation of the phenyl ring and/or carbon-bond breakage and subsequent fluorination. C₂F₆ plasmas graft CF_x radicals directly to the polystyrene surface without necessarily destroying the aromaticity of the polymer. CF₄ plasmas appear to be intermediate in character between SF₆ and C₂F₆ plasmas.

ESCA and contact angle measurements were used to characterize the surfaces of polypropylene and glass substrates exposed to CF₄, CF₃H, CF₃Cl, and CF₃Br plasmas. The use of both organic and inorganic substrates allowed clear distinction between treatments which led to plasma polymerization and treatments which caused grafting of functional groups directly to the substrate surfaces. CF₄ plasmas were the only treatments studied which fluorinated polypropylene surfaces directly, without the deposition of a thin, plasma-polymerized film. CF₃H polymerized in a plasma, while CF₃Cl and CF₃Br plasmas caused chlorination and bromination of polypropylene surfaces, respectively. Correlations were made between the active species present in the plasmas and the surface chemistry observed on the treated polypropylene substrates.

ESCA and contact angle measurements were used to characterize the surfaces of Polyethylene and polypropylene films exposed to SF₆, CF₄, and C₂F₆ plasmas. None of these gases polymerized in the plasma. However, all plasma treatments grafted fluorinated functionalities directly to the polymer surfaces. SF₆ plasmas graft fluorine atoms to a polyolefin surface. CF₄ plasmas also react by a mechanism dominated by fluorine atoms, but with some contribution from CF_x-radical reactions. Although C₂F₆ does not polymerize, the mechanism of grafting is still dominated by the reactions of CF_x radicals. For all gases studied, the lack of polymerization is attributed to competitive ablation and polymerization reactions occurring under conditions of ion bombardment.

Advancing and receding contact angle measurements on polymer surfaces can be performed using a number of different methods. Ballistic deposition is a new method for both rapidly and accurately measuring the receding contact angle of water. In the ballistic deposition method, a pulsed stream of 0.15-μL water droplets is impinged upon a surface. The water spreads across the surface and then coalesces into a single 1.8-μL drop. High-speed video imaging shows that, on most surfaces, the water retracts from previously wetted material, thereby forming receding contact angles that agree with the receding angles measured by the Wilhelmy plate technique. The ballistic deposition method measures the receding angle within one second after the water first contacts the surface. This rapid measurement enables the investigation of polymer surface properties that are not easily probed by other wettability measurement methods. For example, meaningful contact angles of water can be obtained on the water-soluble low-molecular-weight oxidized materials (LMWOM) formed by the corona and flame treatment of polypropylene (PP) films. Use of the ballistic deposition method allows for a characterization of the wetting properties and an estimation of the surface energy components of LMWOM itself. Both corona- and flame-generated LMWOM have significant contact angle hysteresis, almost all of which is accounted for by the non-dispersive (polar) component of the surface rather than by the dispersive component. Surface heterogeneity is thus associated primarily with the oxidized functionalities added to the PP by the corona and flame treatments.

The comparison of corona-treated and flame-treated polypropylene (PP) films provides insight into the mechanism of these surface-oxidation processes. Atomic force microscopy (AFM), contact-angle measurements, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize surface-treated biaxially oriented PP. While both processes oxidize the PP surface, corona treatment leads to the formation of water-soluble low-molecular-weight oxidized materials (LMWOM), while flame treatment does not. Computational modeling of the gas-phase chemistry in an air corona was performed using a zero-dimensional plasma-chemistry model. The modeling results indicate that the ratio of O to OH is much higher in a corona discharge than in a flame. Chain scission and the formation of LMWOM are associated with reactions involving O atoms. The higher ratios of O to OH in a corona are more conducive to LMWOM production. Surface-oxidized PP exhibits considerable thermodynamic contact-angle hysteresis that is primarily caused by microscopic chemical heterogeneity.

The effects of low-molecular-weight oxidized materials generated by corona treatment on the adhesion properties of polypropylene (PP) film were investigated by adhering four different materials to the modified PP: a polyamide printing ink, vapor-coated aluminum, a synthetic-rubber pressure-sensitive adhesive, and an acrylate-based pressure-sensitive adhesive. The low-molecularweight materials enhanced the adhesion of the ink and acrylate-based material, but hindered the adhesion of the metal and the rubber-based adhesive. This seemingly contradictory adhesion behavior can be readily explained using the principles outlined by Brewis and Briggs in the 1980s.

The present invention provides a method of modifying the surface of a polymeric substrate, e.g., to improve the wettability of the polymer film surface and/or alter the metal adhesion properties of the surface of the substrate by exposing the substrate to a flame. The flame is supported by an oxidizer and fuel mixture that includes an effective amount, for modifying the polymeric substrate, of at least one sulfur-containing compound that functions as a fuel substitute. In addition, substrates are provided that have increased wettability or increased metal adhesion performance.

The present invention provides a method of modifying the surface of a polymeric substrate, e.g., to improve the wettability of the polymer film surface and/or alter the reactivity of the surface of the substrate by further oxidation or affixation of nitrogen, comprising exposing the substrate to a flame. The flame is supported by a fuel and oxidizer mixture that includes an effective amount, for modifying the polymeric substrate, of at least one compound that functions as a fuel or oxidizer substitute and is selected from an oxygen-containing compound, in which the oxygen comprises between about 10 and 50 atomic percent of the compound, a nitrogen-containing compound or an oxygen-nitrogen-containing compound. In a preferred embodiment, which affixes nitrogen or nitrogen-containing chemical groups onto the surface of the film, the flame is supported by a fuel and oxidizer mixture that includes ammonia, nitrous oxide, nitric oxide or a mixture thereof in an effective amount. Large increases in the ASTM wetting test, e.g., greater than 13 mJ/m² over that reported with conventional flame-treating processes, have been observed in films treated according to this invention. In addition, significant increases in polymer film surface oxidation levels, e.g., as much as 55 percent, have been observed, as have significant amounts of nitrogen and nitrogen-containing chemical groups affixed to film surfaces.

Oxidation is the most common surface modification of polymers. This paper presents a comparison of five gas-phase surface oxidation processes: corona discharge, flame, remote air plasma, ozone, and combined UV/ozone treatments. Well-characterized biaxially oriented films of polypropylene and poly(ethylene terephthalate) were treated by each of the five techniques. The surface-treated films were then analyzed by X-ray photoelectron spectroscopy (XPS or ESCA), contact-angle measurements, and Fourier-transform IR (FTIR) spectroscopy. Corona, flame, and remote-plasma processes rapidly oxidize polymer surfaces, attaining XPS O/C atomic ratios on polypropylene of greater than 0.10 in less than 0.5 s. In contrast, the various UV/ozone treatments require orders of magnitude greater exposure time to reach the same levels of surface oxidation. While corona treatment and flame treatment are well known as efficient means of oxidizing polymer surfaces, the ability of plasma treatments to rapidly oxidize polymers is not as widely appreciated. Of the treatments studied, flame treatment appears to be the ‘shallowest’; that is, the oxygen incorporated by the treatment is most concentrated near the outer surface of the film. Corona and plasma treatments appear to penetrate somewhat deeper into the polymers. At the other extreme, the UV/ozone treatments reach farther into the bulk of the polymers.

Contact angles are used to solve research and manufacturing problems in an industrial environment. Contact angle measurements are scientific, readily acquired using relatively low-cost instruments and simple procedures, are agreeable for use in environments from academic research laboratories to industrial manufacturing facilities, and are an extremely powerful method for characterizing surfaces. The measurement of dynamic contact angles is rate-dependent at high capillary numbers. Water is a preferred probe liquid for contact angle measurements not only because of the importance of aqueous systems in science and industry, but also because water has the highest surface tension of any commonly available probe liquid and therefore has measurable contact angles on most polymeric materials. Most theories of solid surface energy have a basis in Young's equation, which employs the equilibrium contact angle. If surface energy or surface energy component calculations are made, both the advancing and the receding contact angle data should be used in those calculations.

The present invention provides a method of modifying the surface of a polymeric substrate, e.g., to improve the wettability of the polymer film surface and/or alter the reactivity of the surface of the substrate by further oxidation, comprising exposing the substrate to a flame. The flame is supported by a fuel and oxidizer mixture that includes an effective amount, for modifying the polymeric substrate, of at least one oxygen-containing compound that functions as a fuel substitute. Oxygen comprises between about 10 and 50 atomic percent of the compound. Large increases in the ASTM wetting test over that reported with conventional flame-treating processes, have been observed in films treated according to this invention. In addition, significant increases in polymer film surface oxidation levels have been observed.

The wettability of aluminum foil is an important concern in many industrial converting processes. X-ray photoelectron spectroscopy (XPS or ESCA) and water contact angle results indicated that relatively mild (i.e. 250 W, 15 s) oxygen plasma treatments efficiently removed residual carbon contamination from cold-rolled foil surfaces. This resulted in a significant improvement in the foil wettability. It was also found that the wettability of plasma-treated foils degraded with time, apparently due to the adsorption of hydrophobic, airborne carbon species and other contaminants. Furthermore, oxygen plasma treatments caused additional aluminum oxide to grow on the metal surface. The composition of this additional oxide was found to be similar to that of the native passivation oxide. The thickness of the aluminum oxide layer increased with both the plasma RF power and the plasma exposure time.

The surface energetic properties of different areas of the offset printing plate are the key factors of this printing process, since they control the ink transfer during printing. The importance of these factors is discussed for both waterless offset and conventional offset. The printing process is highly dynamic. New surfaces are created and their lifetimes are short. From recent theories of dynamic wetting, it has been concluded that spontaneous removal of ink films from nonimage areas is a very slow due to the high ink viscosity and the low dynamic contact angle. Thus it is of less importance.

Polypropylene (PP) films have been widely used in many industrial areas, such as for protective overcoats and food packaging. However, PP film’s hydrophobic surface properties induce poor wettability and adhesion; these properties have restrained the application of these films. Many surface modification techniques like wet-chemical treatment, UV irradiation, and plasma (including the atmospheric-pressure plasma, APP) treatment have been applied to films to enhance their hydrophilic properties. Among these technologies, APP treatment has attracted much attention due to its dry process, low vacuum equipment cost, and high productivity. In this study, the influence of process parameters would be the reactive gas ratio of plasma. To enhance its surface characteristics, treatment of PP film’s surface by APP was investigated. The XPS, OES, contact angle analyzer, SEM and AFM were used to examine the effect of process variables on film surface characteristics. It was found that Ar plasma mixing with oxygen has a better lasting aging effect. Moreover, the roughness of films is slightly changed after treatment. Through XPS analysis, we observed that the O/C ratio of PP decreases with an increased exposure time in air. Finally, the relationship among the aging time, surface energy, and roughness of the film was also investigated.

Thin polymer films were irradiated with boron ions with energies from 50 to 180 keV and irradiation doses between 1013 and 1016 B+/cm2. For comparison, plasma modification was performed in NH3 and N2O low-pressure gas discharges. A complex investigation of chemical changes in the surface regions was carried out using attenuated total reflection (ATR)-FTIR spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Optical properties were probed by spectroscopic ellipsometry. Hardness and elastic modulus profiles have been measured by a depth-sensing low-load indentation technique. Additionally, the surface and bulk conductivities of modified polymer films were determined. It could be shown that the increase of ion fluence leads to a partial destruction of the imide, aromatic and sulfone groups. The effective modification depth estimated from the hardness, Young’s modulus and refractive index depth profiles was 250–300 nm at an ion energy of 50 keV and 400–450 nm at an ion energy of 180 keV. In the case of low-pressure plasma treatment, the chemical modification of the polymer bulk extends only a few monolayers and is determined by the electronicprocess-related linear energy transfer (LET). The destruction of chemical bonds under ion bombardment leads to the formation of new amorphous and graphitelike structures, which increase the modified surface film conductivity, the optical absorption index, the density, and the sensitivity of these polymer films to moisture uptake, and decrease the refractive index anisotropy and the Freundlich’s coefficient of the moisture-uptake behavior.

Effects of corona treatment and aging on commercially produced corona discharged polypropylene (PP) films were followed via surface sensitive roughness analysis by atomic force microscopy (AFM), water contact angle (WCA), and X-ray photoelectron spectroscopic (XPS) measurements. Roughness analysis by AFM gave similar results for both untreated and corona-treated samples. The measured water contact angle decreased after corona treatment but increased with aging. XPS findings revealed that corona treatment caused an increase in the O-containing species on the surface of the films, but the measured O/C atomic ratio decreased with aging. The angle dependence of the observed XPS O/C atomic ratio further revealed that surface modifications by the corona treatment were buried into the polymer away from the surface as a function of aging. This is attributed to a surface rearrangement of the macromolecules in agreement with the findings of Garbassi et al. on oxygen–plasma-treated polypropylene. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1846–1850, 1999
https://onlinelibrary.wiley.com/doi/abs/10.1002/%28SICI%291097-4628%2819991114%2974%3A7%3C1846%3A%3AAID-APP29%3E3.0.CO%3B2-B

In the case of the peeling of adhesive tapes from soft adherends, the contributions of the compressive force at the adhered portion as well as the larger deformation of adherend have essential roles in determining the peeling properties. In this paper, the peel force of an adhesive tape from a soft adherend has been measured to understand the peeling mechanism, which is greatly affected by the peel angle. A commercially available pressure-sensitive adhesive was used as the tape, and a cross-linked polydimethylsiloxane (PDMS) was used as the soft adherend. The purpose of this study is to clarify the effects of the peel angle on the peel behavior of this system at room temperature under different material specifications and different experimental conditions. The factors that affect the peel force of the PDMS adherend included the degree of cross-linking in PDMS, the thickness of PDMS, peel angle, and peel velocity. Two characteristic peel patterns were observed, which depended on the material specifications and different experimental conditions. The peel mechanism was discussed in terms of the deformation of the adherend.

This invention relates to an improved method for treating the surface of plastic materials to render them capable of adhering to subsequently applied coatings such as printing inks, paints, pigments, adhesives, and various other materials which it may be desired to coat, print or otherwise attach to the treated surfaces.

Corona discharge introduces polar groups into the polymeric surfaces and, as a consequence, improves the surface energy, wettability, and adhesion characteristics. The main chemical mechanism of corona treatment is oxidation. This article further discusses some special problems that are related to corona treatment of polyolefin films by reviewing the recent developments in this field, such as effect of corona treatment on adhesion, effect of resin additives on corona treatment, insufficient treatment and over-treatment of corona discharge, aging, and re-treatment. © 1999 John Wiley & Sons, Inc. Adv Polym Techn 18: 171–180, 1999
https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1098-2329(199922)18:2%3C171::AID-ADV6%3E3.0.CO;2-8

The changes induced on the surface of polypropylene homopolymer following flame treatment have been studied. Surface compositions were determined using x-ray photoelectron spectroscopy and compared to surface free energies estimated from contact angle measurements. The effect of air-to-gas ratio, total flow rate, contact time with the flame and the distance between the inner cone tip of the flame and the polymer have been investigated. Mild flame treatments were found to be effective in promoting the adhesion of polyurethane paints to the polypropylene. The adhesion between flame-treated polypropylene and the paint film was assessed using a composite butt test and the measured bond strengths were found to be well in excess of those obtained using solvent wiping or chlorinated polyolefin primers.

The effects of corona discharge treatment on polyethylene and polypropylene homopolymers have been studied. X-ray photoelectron spectroscopy was used to determine surface compositions which were related to surface free energy estimates from contact angle measurements. Changes in composition and surface free energy were measured as a function of treatment level. The work of adhesion was seen to increase with oxygen incorporation. The increase was not linear and this is attributed to an increase in the degree of sub-surface to near-surface oxidation at intense treatment levels. Aging of samples followed by XPS and contact angle measurement showed that surface wettability is reduced whereas a slight increase in surface oxygen was found. This phenomenon was attributed to the reorientation/migration of functional groups. Morphological examination by scanning electron microscopy indicated no surface roughening at any power level.

Devices are presented which allow determination of unknown surface properties through the creation of a channel capillary, comprised in part of the subject surface or surfaces, and measurement of the capillary pressure created by a test fluid within the resultant channel. In various embodiments of the invention, a channel is created in a reference material which is bonded, through some mechanism, to the test surface in order to create a narrow capillary channel. In other embodiments of the invention, the capillary channel is created with test surfaces on either side of standoff strips which space the surfaces a precise distance from one another. Methods are presented for using these capillaries through immersion, along their length, in a bath of test fluid, such that the resultant fluid level provides a measure of capillary pressure. Being, in part, a consequence of the contact angle between the test fluid and the surface or surfaces under consideration, the capillary pressure is a convenient measure of surface properties inherently related to printability, affinity for adhesives, surface contamination by foreign substances, surface roughness, and the like. Devices are presented which allow measurement of test fluid height within the capillary, both in situations where a static equilibrium is achieved, and in situations where a dynamic contact angle is operative as the fluid rises or falls within the capillary.

Effects of corona treatment and aging on commercially produced corona discharged polypropylene (PP) films were followed via surface sensitive roughness analysis by atomic force microscopy (AFM), water contact angle (WCA), and X-ray photoelectron spectroscopic (XPS) measurements. Roughness analysis by AFM gave similar results for both untreated and corona-treated samples. The measured water contact angle decreased after corona treatment but increased with aging. XPS findings revealed that corona treatment caused an increase in the O-containing species on the surface of the films, but the measured O/C atomic ratio decreased with aging. The angle dependence of the observed XPS O/C atomic ratio further revealed that surface modifications by the corona treatment were buried into the polymer away from the surface as a function of aging. This is attributed to a surface rearrangement of the macromolecules in agreement with the findings of Garbassi et al. on oxygen–plasma-treated polypropylene. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1846–1850, 1999