With the advent of readily available nonpaper substrates (plastics and foils) in the mid-to-late 1950’s, the requirement for a reliable production speed surface treatment process became apparent. Several different technologies have been tried, but one, corona treatment, has become, by far, the primary surface treatment technology used across the Extrusion and Converting Industries. We will touch on these various technologies, technically describe the need for surface treatment and how it is measured, trace the development of corona treatment as the leading surface treatment method, and detail the current state-of-the-art in equipment, control parameters and applications.

The measurement and interpretation of contact angles deceptively appear to be simple. This paper attempts to summarize the pitfalls in the field, and how to avoid them. First, the fundamental underlying theory that is necessary in order to properly measure and interpret contact angles is discussed, emphasizing recent developments. Then, the practical implications of these theoretical aspects are presented. In addition, the discussion highlights the missing pieces of the picture that need to be completed through future research.

Understanding, measuring, and interpreting equilibrium contact angles appear to be simple, but may actually be quite confusing. This paper is an attempt at a guide to the perplexed. First, a comprehensive, clearly defined terminology is suggested. Then, the theory of equilibrium contact angles on smooth, rough, or chemically heterogeneous surfaces is briefly discussed. Finally, the practical implications of the theory to contact angle measurement and interpretation are indicated and explained.

Improvement of paint adhesion to aluminium surfaces is one of the main challenges in many industrial applications. In this paper, we introduce the atmospheric pressure air plasma jet as an appropriate candidate for preparation of 5052 aluminium surface alloy to improve paint adhesion in the industrial level. The employed plasma jet can promote paint adhesion to aluminium surface at the treatment velocity of 2 m/min and plasma size of 10 mm. Based on the cross-cut test, adhesion of polyurethane paint to the surface greatly increases from 1B to 5B level due to the plasma treatment. According to the results, the surface wettability increases under the influence of the plasma treatment so that water droplet contact angle reduces from 79.0°±2.0°–27.5°±2.0° after the treatment. Dyne test ink also denotes the increment of surface energy to the greater than 72 mN/m. Besides, we employ various analytical methods to investigate the physical and chemical changes arise from the plasma processing to the surface. Atomic force microscopy (AFM) results show a twofold increase in the roughness parameters of plasma treated surface which can result in a stronger paint and surface interlocking. Chemical analysis of the surface reveals that plasma treatment of the aluminium surface leads to the surface cleaning and formation of hydrophilic functional groups that attract much more water towards the surface and improves the paint adhesion.

Metallized OPP (oriented polypropylene) film offers exceptional gas and water vapor barrier properties, making it one of the most cost-effective flexible protective packaging materials. Its barrier properties correlate with opacity, which, in turn, de pends on the degree of coverage by the metallization. Minor defects, such as scratches, will generally represent only a small percentage of the total coverage of a package and have a proportionally small effect on the barrier properties of the pack age. The high-energy metal surface is extremely active and will wet well and adhere strongly when clean. In fact, it is so active that it is easily coated with trace amounts of any low energy organic material with which it makes contact. For assurance of consistent wetting and bonding, metallized OPP surfaces should be cleaned in-line, such as by bare-roll corona treatment.

Four ethylene vinyl acetate (EVA) co-polymers with different vinyl acetate (VA) contents (9–20 wt%) were treated with corona discharge to improve their adhesion to polychloroprene (PCP) adhesive. The thermal properties of the EVAs decreased as their VA content increased, caused by a decrease in crystallinity. The elastic and viscous moduli of the EVAs decreased and the temperature and modulus at the cross-over between these moduli decreased with increasing VA content. Contact-angle measurements (water), infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to analyse the surface modifications produced in the corona-discharge-treated EVAs. The corona discharge treatment produced improved wettability and created roughness and oxygen moieties on the EVA surfaces. The higher the VA content and the higher the corona energy, the more significant modifications were produced on the EVA surface. The VA content also affected the T-peel strength values of treated EVA/polychloroprene + isocyanate adhesive joints, as the values increased with increasing VA content. Mixed failure modes (interfacial + cohesive failure in the EVA) were obtained in the adhesive joints produced with corona discharge treated EVAs containing more than 9 wt% VA. The accelerated ageing of the joints did not affect the T-peel strength values, but the locus of failure in most cases became fully cohesive in the EVA, likely due to the higher extent of curing of the adhesive.

Ethylene vinyl acetate (EVA) material containing 20 wt% vinyl acetate (EVA20) was treated with corona discharge to improve its adhesion to polychloroprene adhesive. Several experimental variables in the corona discharge treatment of EVA20 were considered: corona energy, type of electrode, and number of consecutive treatments. Advancing contact angle measurements (water, 25°C) showed an increase in the wettability of EVA20 after treatment with corona discharge, which corresponds to an increase in the O/C ratio on the treated surface. The higher the corona energy (i.e. the higher discharge power and longer treatment times), the greater the degree of surface oxidation. Peel strength values of the joints produced with EVA20 using a polychloroprene adhesive containing 5 wt% isocyanate increased from 1.5 kN/m (as-received EVA20) to 4.3 kN/m (corona-treated EVA20). A mixed (adhesional + cohesive in EVA20) locus of failure was obtained in all adhesive joints produced with corona discharge-treated EVA20. Finally, the number of consecutive corona discharge treatments and the surface area of the electrode (spherical versus hook-shaped electrode) did not greatly influence the adhesion of EVA20 to polychloroprene adhesive.

Low-pressure plasma was selected as a surface treatment to improve the painting properties of elastomeric polyethylene (PE). Several experimental variables in the low-pressure synthetic air plasma treatment were considered: time of the treatment, plasma power and pressure inside the chamber. The durability of the treatment effects was also studied. Contact-angle measurements (water, 25 C) showed an increase in the wettability of elastomeric PE after treatment with plasma, which corresponds to an increase in the O/C ratio on the treated surface. In fact, different oxygen-containing groups were created on the PE surface. The more intense and longer the plasma treatment, the greater the degree of surface oxidation, up to a certain value. The painting properties of the material were evaluated by joints produced with as-received and treated elastomeric PE and an acrylic paint and using T-peel tests. Peel strength values increased after low-pressure plasma treatment, especially after the first 3 s of treatment with a power of 200 W; and an adhesion failure between the paint and the adhesive tape was obtained. This failure was maintained during four hours after the treatment. For longer treatment times the paint does not adhere to the material, the peel-strength values decrease and the contact angles increase, indicating that the effects of the surface modifications are not maintained.