Research Article – IJAAT – 2017 – 32

International Journal of Advances on Automotive and Technology http://dx.doi.org/10.15659/ijaat.17.09.524 Promech Corp. Press, Istanbul, Turkey Manuscript Received March 20, 2017; Accepted August 10, 2017

Vol.1, No. 4, pp. 212-216, October, 2017

This paper was recommended for publication in revised form by Co-Editor Yasin Karagoz

EFFECT OF PLASMA TREATMENT ON WETTABILITY PROPERTIES OF THE ELECTROPHORETIC COATING (E-COAT) ON STEEL AUTOMOTIVE PARTS

*Ekrem Altuncu Fatih Kurtuldu Sakarya University, Techonology Faculty, Sakarya University, Technology Faculty Dept. of Metallurgy and Materials Eng. Dept. of Metallurgy and Materials Eng. Serdivan, Sakarya, Turkey Serdivan, Sakarya, Turkey

Keywords: E-coat, Plasma Treatment, Surface, Contact Angle * Corresponding author: Phone: 0264 295 7217 E-mail address: [email protected]

ABSTRACT electrophoretic coating (e-coat) on steel automotive parts are investigated. Different plasma surface treatment parameters as Today, e-coatings or powder paintings are considered as an distance, velocity, pass number are employed on e-coated important market and play a major role in automotive industry. surfaces and measured their water contact angle. And also They not only impart decorative and a pleasant appeal to car experimental results are compared with properties of bodies, also protect them against degrading environmental the powder coated and plasma treated surfaces. effects. Their use extends from metallic parts to polymeric based vehicle components both as exterior and interior types. INTRODUCTION Two main goals are envisaged when coatings are applied to substrates. The first involves protecting the substrate against The automotive industry is one of the most important users various aggressive environmental agents (such as UV, humidity of modern surface technologies. Increasing demands on and corrosive gas/liquid products) and the second includes production processes lead to the need of continuous imparting color and aesthetic appeal to the substrate. In some improvement in surface technologies. The priming of a car body applications, these two are highly important such as in is carried out nearly completely with the electrophoretic coating automotive coatings. Extensive exposure to different permanent process [1]. Cathphoresis (terms such as: E-Coat, Electro environmental factors during service life as well as occasional painting, Electro deposition, Electrophoretic coat etc.) means makes the first goal highly prominent in automotive coating application of paint by an electro-phoretic method, whereby the industries. Automotive coatings are considered a multi-layer painted product becomes a cathode in the direct current anolyte system in which each layer has its own especial function. These (water solution of the epoxy paint) and thus attracts the colour make the whole system resist to various environmental factors. cations. Cataphoresis represents one of the most progressive Plasma surface treatment is the advanced and a new most production technologies of application of basic paints with a widely used surface pretreatment activations, cleaning and high degree of corrosion protection of metals. The cataphoresis etching process for the surface coating, painting and/or method of paint application is considered to belong among the finishing of ferrous, non-ferrous metals and polymers.In this most advanced technologies of metal products surface study; effect of plasma treatment on wettability properties of the treatments. Currently cataphoresis does not have comparable

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competition in series of production areas. The biggest contribution to the development of cataphoresis technology has automotive industry, where anti-corrosion resistance of bodyworks and other components is the focus of interest of all producers. High quality of surface treatment together with economic and environmental advantages predestined this technology to be used in other fields of engineering and consumer goods industry. The average thickness of standard e- coatings for automotive parts can vary from less than 25 µm up to 150 µm, according to the targeted corrosion performance [1- 4]. E-Coat ensures the even coating and of the desired thickness not only for geometrically complicated structures, but also for the inner cavities of the parts. The possible coating thickness of parts is from 15 to 35 µm.

Fig. 2 Typical automobile surface coating cross section (Basf), robotic painting

Plasma treatment for surface modification is also used to produce hydrophobic or hydrophilic surfaces on metals and polymers. Many studies have been performed to improve the wettability of polymers because forming hydrophilic surface can solve many problems induced by the hydrophobic nature of polymer. Therefore, the transformation of polymer surface properties by plasma treatment is more and more becoming a routine tool in obtaining materials for specific applications, for Fig 1. E-coat process scheme for car body [5]. it allows modification of the surface properties without

changing the characteristics of the bulk of the material [6,7]. In The dissolved positively charged polymer precipitate on this work, we have studied on e-coated surface modification the surface and form a dense, electrical insulating layer. The treated by air plasma activation method with/without plasma coating thickness of this process is very homogenous. E-coating treatment for enhancing their wettability and is possible on steel, zinc-plated steel, aluminium and properties between layer and e-coated metallic magnesium. The process is usually combined with inorganic substrates. Based on this work, we have suggested the e-coating conversion layers like zinc phosphate in order to improve the technology for automobile parts without adapting any or less adhesion. The process typically involves a number of stages primer coating. including a cleaning stage followed by a phosphate conversion coating which enhances the corrosion resistance of the metal EXPERİMENTAL DETAİLS and also provides an improved base for the subsequent coating.

After the metal is properly prepared the e-coating process can APP experiments are carried out using open air plasma take place. This is then followed by an oven curing stage. The system (Openair®) with rotary nozzle developed by Plasmatreat complete process stages are as follows: chemical degreasing, (Steinhagen, Germany). Figure 3 shows rotary nozzles images. rinsing, pickling, rinsing, activation, Zn phosphate, rinsing, The plasma source was dried air, plasma parameters were 280V passivation, rinsing, cataphoresis, rinsing, ultrafiltrate, blowing, / 16A, 21Hz and 4 bar air. The jet nozzle body is fixed on the curing, cooling [1-4]. frame of the X–Y-Z moving table equip with benchtops robot

Janome JR2300N. Atmospheric-pressure plasma jet used in

different control parameters such as velocity, gap distance and

the number of passes which means repeating the APP proses

multiple times. E-coated steels (S355) used for this experiments

were 10mm x 50mm x 0,5mm thick. Before plasma treatment,

the samples surface are cleaned in acetone, methyl alcohol, and

de-ionized water by ultrasonic cleaning method. All the

treatments carried out under the room temperatures. Surface wettability tests were performed on sample surfaces with 4 μL deionized (DI) water droplets, and static contact angles were measured with Krüss drop shape analyzer, and average contact

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angle determinate after three measurements. Also we perform increasing of number of passes resulted on effective decrease of aging test, it’s important to know how long the effect stand on contact angles at low gap distance, on the other hand at high the surface for industry applications. gap distance, increasing the number of passes didn’t effect contact angle too much. In this direction, its understood that in order to gain higher wettability, gap distance should be under 8mm.

Fig 3. Samples and Plasma surface activation set up (Plasma Treat Gmbh). Fig. 4 The effect of gap distance and number of passes on contact angle RESULTS AND DISCUSSION

Electrophoretic coatings have 78±3 contact angle which applied on steel substrates. In automotive industries after electrophoretic coatings there are painting steps which is consist a few layers as can see figure 2b. There are primer coatings which is improving of adhesion of painting on electrophoretic coatings. In this multilayer system strength, atmospherically strength and the quality of paintings depend on e-coat’s layer qualification such as thickness and adhesion performance. In today’s applications primer coatings, which are imported, are not long for their high cost, time consumption and environmental pollutant risks. Plasma technology offers innovative solutions for improving surface properties between e-coats and painting and this way primer coatings could be Fig. 5 The change of contact angle with plasma treatment. eliminated. Thereby plasma treatment on e-coats have great potential on automotive industries, but there’s not enough The effect of velocity of plasma nozzle. research on this subject in literature. So in this study, we tried to control wettability properties of e-coats with plasma treatment. Contact angles changes with different velocity at fixed gap The results and findings are reported in the following sections distance could be seen in figure 6. Contact angle dropped 50° to from experimental studies. 30° levels in single pass of plasma treatment with decreasing velocity of plasma nozzle. The scanning velocity’s decrease The effect of gap distance between plasma nozzle and surface effect the plasma time on per unit area. Then this change of velocity caused decreasing of contact angle. This effect give Contact angles changes with different gap distance and similar result with number of passes. So it is thought that slower number of sweeps in fixed velocity could be seen in figure 4. As velocity and closer gap distance could be resulted much lower can be seen contact angle dropped 78° to 50±5° level in one contact angles. pass of plasma treatment. Contact angle could be dropped under

40° levels in 3 pass of plasma treatment at 8mm gap distance. As for 6 pass of plasma treatment, it could be dropped under 30° levels. On the other hand, the results from 12mm and 16mm gap distances are give close contact angles measurements. Then

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Plasma treatments permanentness on the surface

Plasma interaction the surfaces coated with e-coat have obtained low contact angles. Then plasma treatment’s permanent stays on the e-coated surface in time determinant with aging test. In this context, best resulted plasma treatment’s parameters were performed at aging test as can be seen in figure 7. Thereby, we tried to evaluate when the plasma treatment become unfunctional. Contact angle change 15° to 55° level in 8 hours. Therefore, it’s recommended that e-coat surface should be painted within three to four hours after plasma treatment. Then plasma treatment is envisaged with different plasma gases for improve permanence effect of the plasma treatment. Fig. 6 The effect of scan velocity on contact angle

Dual interaction of velocity and gap distance

In contact angles measurements there is a significant difference in 6mm gap distance at different velocity. Table 1. shows the effect of gap distance, velocity and number of passes on contact angle and surface temperature. Contact angle dropped 25° levels with single pass in 6mm gap distance at 2,5mm/s velocity, and it’s dropped most desired contact angle values with three passes. In this sense, the surfaces temperature increased over 50°C with increasing the number of passes of plasma treatment. When the lowest contact angle (6mm – 2,5mm/s – 3 Pass) measured, the substrate surface temperature was measured 76°C. Thereby it is concluded that surface temperature is important parameter for changing of wettability.

Table 1. The effect of gap distance, velocity and number of Fig. 7 Aging test of plasma treatment. passes on contact angle and surface temperature CONCLUSION Gap Velocity Number Contact Temperature Distance (mm/s) of Angle (°C) (mm) Passes (θ) E-coated surface’s contact angle proven that it could be - - - 78,05° 25°C dropped 78° to 15° with plasma surface activation technique. 6 5 1 36,02° 45°C Therefore, it’s concluded that surface energy could be 6 2,5 1 24,63° 62°C increased. It has great benefits like economics perspective and 6 2,5 3 12° 76°C environmental perspective to use plasma surface activation 8 20 1 52,37° 29°C technique instead of primer coatings before painting for 8 20 3 34,16° 45°C companies. E-coated surface expected to be adequate contact 8 20 6 31,36° 48°C angles in three to four hours after plasma treatment. Optimum 8 10 1 41,48° 37°C experiment parameters concluded that 6mm gap distance, 8 5 1 31,05° 46°C 2,5mm/s velocity and 3 pass of plasma treatment and substrate 8 2,5 1 29,72° 55°C temperature measured 70±5°C which give needed wettability 12 20 1 43,76° 32°C properties. 12 20 3 46,93° 37°C 12 20 6 46,8° 40°C REFERENCES 16 20 1 44,73° 27°C 16 20 3 40,63° 34°C [1] K.Bewilogua, G. Brauer, A. Dietz, J. Gabler, G. Goch, 16 20 6 48,71° 46°C B. Karpuschewski, B. Szyszka Surface technology for automotive engineering CIRP Annals- Manufacturing Technology 58 (2009) 608–627. [2] E.Almeida, I. Alves, C. Brites, L. Fedrizzi, Cataphoretic and autophoretic automotive primers: A comparative study,

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Progress in Organic Coatings, Volume 46, Issue 1, January Evolution of the Automotive Body Coating Process—A Review, 2003, Pages 8-20. MDPI, Coatings 2016, 6, 24. [3] Nguyen Van Phuonga, Sungmo Moon, Deposition and [6] C.-K. Jung,, I.-S. Bae, S.-B. Lee, J.-H. Cho,E.-S. characterization of E-paint on magnesium alloys, Progress in Shin,S.-C. Choi, J.-H. Boo; Development of painting Organic Coatings 89 (2015) 91–99. technology using plasma surface technology for automobile [4] Hans-Joachim Streitberger (Editor), Karl-Friedrich parts,Thin Solid Films 506 – 507 (2006) 316 – 322 Dossel (Editor), Automotive Paints and Coatings, 2nd Edition [7] J. M. Shenton, M. C. Lovell-Hoare and G. C. Stevens, (2008). “Adhesion Enhancement of Polymer Surfaces by Atmospheric [5] Nelson K. Akafuah , Sadegh Poozesh , Ahmad Plasma Treatment,” Journal of Physics D: Applied Physics, Vol. Salaimeh, Gabriela Patrick, Kevin Lawler, Kozo Saito, 34, No. 18, 2001, pp. 2754-2760.

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