The wettability and adhesion of the coating and printing films on the polymer substrates depend on the surface properties of the formulation ingredients and polymer surface. In addition, the transfer of ink from flexographic printing plates to substrates depends on the surface properties of the printing plate, water-based ink and polymer substrate. Among several surface properties such as surface composition, surface roughness, surface tension/surface energies and surface defects, the surface energies: polar, nonpolar and total energies of the dried coating films, flexographic printing plates and polymer substrates were determined by measuring contact angles of water and methylene iodide. These results were used to understand the ink transfer from printing plates to substrates during flexographic printing process, and ink spreading, wetting as well as ink adhesion behavior of the coatings and inks on the polymer substrates. The data indicates that for good ink transfer and adhesion to occur, the surface energy of the water-based ink should be lower than that of the printing plates and substrates.

Water-based ink and coating use is reviewed with the emphasis on wetting and printing of film, metal, and metallized substrates. This paper addresses the effects of surface tension of water-based flexographic and rotogravure inks and coatings. The mode of drying in water-based technology is explored as well as static and dynamic surface tension of inks and coatings. Ink formulation and manufacturing considerations are reviewed to optimize surface tension effects for high speed presses. The role of substrate and ink transfer mediums are discussed relative to their impact on ink and coating drying rates. Corona treatment of film substrates is analyzed from the perspective of its effect on drying speed and ink adhesion. Suggestions are made to improve the quality performance of water-based ink and coatings through use of on-line surface tension equipment. Most importantly, the question “Why should I measure surface tension of my water-based ink?” is answered from the perspective of improving press productivity and ink performance.

The surface free energy of solids is a characteristic parameter that determines most of the surface properties such as adsorption, wetting, adhesion, etc. The surface energetics of solids may be characterized by measurement of contact angles of different liquids. Nevertheless, the calculation of surface free energy from contact angle measurements has been the subject of much controversy. Indeed, this characteristic of a solid cannot be measured directly because of elastic and viscous restraints of the bulk phase, which necessitate indirect methods.

This paper describes various aspects of water-based coatings and printing processes with special emphasis on the surface characteristics of coating/printing films. The film formation depends significantly on the surface properties of formulated coating/ink, and their interactions with substrates. Several surface parameters in relation to coating defects are briefly described. The mechanisms of printing processes and coating/ink film formation by water-based systems are presented. It has been shown that the formation of surface tension gradient during film curing determines the quality of the coating and printing films. Results demonstrate that the incorporation of suitable additives in the formulation can considerably minimize the crater formation. The hydrophilic-lipophilic balance (HLB) concept and the effect of surfactant concentration on pigment dispersion in an aqueous medium are discussed.

Striking a balance between applied and theoretical research, this work details many of the uses of wettability and interprets experimental data from a variety of viewpoints, including the ‘separation of forces’ and the ‘equation of state approaches.’

The donor—acceptor interaction(1,2) and the acid—base interaction(3) have been reviewed. On many occasions, the two terms, though different, have been used interchangeably to describe the interactions involving the exchange of electrons between a donor and an acceptor. For polymer adhesion, Fowkes(4,5) and Bolger et al. (6) have pointed out the important role of the acid-base interaction in the formation of an adhesive bond.

In 1967, Lee published two papers on adhesion of high polymers^(1,2) on the basis of the Buche—Cashin—Debye equation⁽³⁾

where D is the molecular diffusion constant, η the bulk viscosity, A Avogadro’s number, ρ the density, k Boltzmann’s constant, T the absolute temperature, M the molecular weight, and R ² the mean-square end-to-end distance of a single polymer chain. It was concluded that the physical state of the polymer determines the major adhesion mechanism involved. Polymer adhesion can be subdivided into rubbery polymer-rubbery polymer adhesion (R—R adhesion), rubbery polymer—glassy polymer adhesion (R—G adhesion), and rubbery polymer—nonpolymer—solid adhesion (R—S adhesion). Diffusion, which depends to a great extent on the physical state of a polymer, is actually a limited selective process. Thus, diffusion of rubbery polymers can take place at the interface, but diffusion of a glassy polymer at a viscosity of 10¹³ poise or a diffusion constant of 10^-21 cm²/sec appears to be nearly impossible. On the other hand, physical adsorption is common to all three types of the above adhesion systems.

Electron Spectroscopy for Chemical Analysis (ESCA) is generally considered to be a non-destructive analytical technique as compared to e.g., SIMS and Auger spectroscopy. In fact, there have appeared only a few reports in the literature where soft X-ray induced spectral changes were noted. These studies have recently been reviewed by Storp. Several of these studies have been carried out with non-monochromatic X-ray sources which typically expose a sample surface with a flux of high kinetic energy electrons and thermal radiation. As pointed out by Storp, it is not entirely clear whether or not the reported changes can be therefore considered as uniquely caused by X-ray photons. Wheeler and Pepper have published a detailed beam damage study on polytetrafluoroethylene (Teflon) using a non-monochromatic X-ray source. The authors provided convincing evidence that the detected fluorine depletion of the surface is indeed caused by X-rays rather than electron bombardment. We wish to report ESCA experiment on Teflon and several other polymeric materials using a spectrometer with a monochromatic Al Kα X-ray source. Due to the physical separation between source and sample an unambiguous differentiation between X-ray vs. electron induced damage can be obtained.

Low-pressure plasma-treatments aimed to selectively graft-NH2 groups onto the surface of conventional polymers such as polyethylene, polystyrene and polyethyleneterephtalate are described. The combined use of plasma and surface diagnostics allowed elucidation of the effect of the experimental parameters on the extent of the surface modifications and to understand chemical mechanisms involved in the surface processes. The diagnostic approach is essential for engineering polymer surfaces with a dosed relative density of-NH2 groups, for scale-up and process transfer.

Silicone polymers exhibit good mechanical properties for a variety of biomedical and industrial applications. For instance, silicone rubber has been used for voice prostheses, urinary catheters, contact lens material, and icing coating materials. However, their inherently high hydrophobicity limits certain applications of this material despite its favorable mechanical properties6. Plasma treatment of silicone polymers may affect their hydrophobicity and therewith their boundability to other materials without affecting the bulk properties. Plasma treatment often involves progressive oxidation of the surface and cross-linking of surface molecular groups which inhibits migration of low molecular weight oligomers to the surface. Various gases have been used to modify silicone polymers by plasma treatment, such as oxygen, helium, ammonia, carbon dioxide, nitrogen and argon. Frequently a thin cross-linked, sometimes water washable, silica-like surface layer was produced by plasma treatment, but there is no consensus about the nature of the chemical groups produced at the outermost surface. The surface hydrophilicity created by plasma treatment is often lost over time. This so-called hydrophobic recovery can be influenced by the storage conditions, whether in air or in liquid, temperature or subsequent adsorption of a surfactant.

The theory of wetting is reviewed with respect to ink transfer which is based upon measured dynamic surface tension and calculated dynamic spreading coefficient. Laboratory gravure ink transfer results are presented for model water based inks with and without isopropanol as the cosolvent on untreated and corona treated polyethylene film. A mechanism of surface tension driven convection is proposed which is consistent with experimental results. The conclusion, which is based upon the proposed mechanism, is that uniform coverage of a water based ink on a nonpermeable substrate is facilitated by the presence of a high vapor pressure low surface tension cosolvent such as isopropanol. When no cosolvent is present, de-wetting and degree of ink mottling appears to be controlled by dynamics longer than one second.

The previous chapter was largely theoretical, in that it dealt with the interpretation of contact angle results in terms of solid surface energies. It also delved into the question of how the structure of a solid surface affects the contact angle that a liquid forms on the solid. The level of structure considered there included features that are not macroscopically observed, such as microheterogeneities, or minute peaks, pits, hills, and grooves in various geometries. Their existence may be inferred from certain observations, such as contact angle hysteresis, and sometimes they can be observed directly, e.g., with the optical or electron microscope.

This chapter, and the following one by Neumann and Good, deal with the measurement of contact angles in three-phase systems. The contact angle is, intrinsically, a macroscopic property, and one that should be amenable to a phenomenological treatment, e.g., to measurement without regard to its thermodynamic or microscopic interpretation. But inevitably, the desire for a thermodynamic and molecular interpretation arises. In addition, some fundamental questions about solid surfaces come up, and the problem of hysteresis must be given explicit consideration. So there is a need to go beyond phenomenology.

The concept of critical surface tension is generalized and reinterpreted in terms of a proposed equation of state. The equation defines a spectrum of critical surface tensions for a given surface, and provides a method by which the surface tension can be accurately determined from the contact angles of a series of testing liquids. The surface tensions obtained for solid polymers, organic solids and monolayers by this method agree remarkably well with those obtained from melt data (temperature dependence), liquid homologs (molecular-weight dependence) and the harmonic-mean equation. In contrast, those obtained by the geometric-mean equation and Zisman’s critical surface tensions are often too low. These results also support the validity of the harmonic-mean equation.

Metallized polymer or polymer-based materials are used in a large range of electronics applications including the fabrication of ohmic contacts, chip-level interconnects, printed circuit boards and shielded materials.^1–7 For such technological applications, electroless deposition is the most widely used method in practice today.⁸ Basically, electroless plating is an autocatalytic redox process occurring in aqueous solution between ions of the metal to be deposited (generally Ni or Cu) and a strong reducer. Typical procedures involve a variety of multi-step sequences for the preparation of the surfaces to be coated. Conventionally, substrates are cleaned with solvents to remove surface contaminants, chemically etched to obtain a micro-roughened oxidized surface, and then seeded with a catalyst such as palladium. Chronologically, the seeding process was first accomplished by using a two-step procedure involving substrate treatment successively in dilute SnC1₂ (sensitization step) and PdC1₂ (activation step) acidic solutions. Further, a one-step procedure using a colloidal suspension containing both Sn and Pd species (a SnC1₂/PdC1₂ acidic solution) has been developed and is presently in common use in industrial environments. In this last case, the Pd/Sn colloidal particles adsorbed on the polymer surface must be exposed (acceleration step) to a solubilizer (a HCl or NaOH solution) to remove the excess of Sn⁺² species surrounding the catalytic Pd-based core of the colloidal particles. As can easily be inferred from the details of such multi-step procedures, it is today highly desirable to develop alternative approaches for making the insulating surfaces catalytically active. These approaches should require no chemical surface etching, reduce the number of process steps, and provide a highly selective, well-defined interaction between the catalytic species and the surface to be coated.⁹

Effects of the electron radiation generated by a high-voltage linear accelerator on wettability and surface free energy (SFE) of low-density polyethylene (PE-LD) film were studied. Radiation doses of 25, 50, 100, 250, and500 kGy were used. Water, glycerol, formamide, diiodomethane, and α-bromonaphthalene were applied as measuring liquids for contact angle measurements. The calculations of SFE were made by Owens-Wendt and van Oss-Chaudhury-Good methods, using the results of measurements of contact angle with various systems of the measuring liquids. Wettability tests were also performed. It was found that the contact angle decreased with the rising radiation dose for all the measuring liquids and the shapes of these dependences were similar. However, significant quantitative differences were observed. The largest changes in the contact angle were detected for the dose range of up to 50 kGy. SFE values when measured by different methods and various measuring liquids differed generally in the whole range of the doses applied. Therefore, the surface free energy cannot be accepted as an absolute measure of the thermodynamic state of the surface layer of radiation-modified PE-LD film. Its values can be compared with one another only when they were determined using the same method and the same measuring or standard liquids.

The effects of the electron radiation dose and of compatibilizers on the contact angle and surface free energy (SFE) of the composites made of low-density polyethylene (PE-LD), high-density polyethylene (PE-HD), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) were studied. Use of the high-energy electron radiation with doses up to 300kGy and of compatibilizers was done to reach better mechanical and adhesion properties of the composites studied and, at the same time, to investigate the possibility of applying of this technique in the processes of polymeric materials recycling. The compatibilizers were the styrene-ethylene/butylene-styrene elastomer grafted with maleic anhydride (SEBS-g-MA), added at the amounts of 5, 10 or 15 wt.%, and trimethylol propane trimethylacrylate (TMPTA), added at the amounts of 1, 2 or 3 wt.%. The effects, discussed in the present article, are: enhancement of wettability and increase in SFE of the composites studied. It was found that the contact angle steadily decreased and SFE of the composites increased with the rising dose of the electron radiation and that TMPTA intensified these tendencies.

The physical and chemical principles of the process of polymeric material surface layer (WW) modification using corona discharge (WK) in an air were discussed. The phenomenon of low temperature plasma formation and the way of its interaction with polymer surface were described. Basic aims of the process of modification with WK were presented as well as the results obtained this way for particular polymers, among others PE, PP, PVC, PET. In case of PE and PP also the composite materials with polyolefine matrix or fiber filler were considered. The possibilities of corona discharge use in graft polymerization were noticed. Also numerous directions of practical use of the changes of polymers' surface layers caused by corona discharge were marked.

The paper investigates the effect of corona discharge (CD) treatment on the properties of surface layer (SL) of polylactide (PLA) film. The modification of PLAwas carried out in the air and helium atmosphere and the results were compared on the basis of the assessment ofwettability, surface free energy (SFE) calculated using Owens-Wendt method aswell as the degree of oxidation (O/C) of the modified SL, determined by photoelectron spectroscopy.

A new method of analysis of differences in the surface free energy (SFE) values of a solid, calculated using the methods of Owens-Wendt (OW) and Neumann and two measuring liquids, water and diiodomethane, is presented. The concept of the analysis bases on the differences in SFE, which occur objectively and regardless of both the precision and the performing conditions of the contact angle (CA) measurements. These differences result from utilizing of different mathematical relations between CA and SFE in each of the methods. The results obtained with these two methods are compared with one another over the SFE range common for polymeric materials (20-50 mJ/m 2). It is calculated that the relative difference in SFE between the results from the OW and Neumann methods can reach 19.9 % over this range.

In the article the analysis of the main methods of calculations of interfacial free energy and surface free energy (SEP) values of solids, in which contact angle measurements' results play a key role, has been presented. The importance of Young's equation and Berthelot's hypothesis as the scientific basis of these methods has been indicated. Various methods of calculations of interfacial free energy values for solid-liquid systems, including calculations of this energy on the basis of state equations or SEP divide to independent components, (especially for polymers) were discussed. The most important methods of calculations of SEP values for polymeric materials on this basis were characterized. The methods of calculations of contact angle values for porous materials, granulated products, powders or fibers on the basis of Washburn equation, what is a base for calculations of SEP of these materials, were presented.