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Novel green process to modify ABS surface before its metallization: optophysic treatment.

Abstract The preconditioning of an ABS surface prior to metallization was achieved by a new technique, here named "optophysic treatment." The dry procedure consists of alternating corona discharges and UV. The substrates are metallized by either the electroless or dynamic chemical plating (DCP) method. The surface modification is attributed to capture-release of charges, chemical modification on the surface, and a preferential removing of polybutadiene domains. Corona and UV cause superficial and depth ozonolysis, respectively, which increase oxygen content and propitiate a final hydrophilic surface. Corona acts by stripping more efficiently UV reticulated polymeric chains. Deposits with adhesions that surpass those of conventional electroless are obtained with optophysic treatment and a precoating by DCP.

Keywords Chromium (VI), Corona discharge, Electroless, Surface modification, UV irradiation

Introduction

The principal issue with metallization of nonconductive materials, particularly polymers, is concerned with adherence in the metal-substrate interface. Whichever the concerned industry (automobile, aeronautic, decoration), the interface between the thin metallic film and the substrate should be standardized, with the purpose of responding to different specifications. The adhesion of a metallic film to a substrate has different origins: mechanical anchorage due to the modification of roughness or porosity on the polymer surface or by chemical bonds due to the functionalization of the substrate surface. Acrylonitrile butadiene styrene (ABS) is broadly used with the aim of propitiating these conditions. ABS resins are thermoplastics comprised of an admixture of styreneacrylonitrile copolymer (SAN) and SAN-grafted butadiene rubber. They have high impact resistance, toughness, rigidity, and processability but low dielectric strength, continuous service temperature, and elongation. (1) It is possible to have a selective attack in polybutadiene (PB), allocated as spheres in the SAN (Fig. 1) during the etching step of the electroless process that confers the required physical and chemical characteristics.

The current procedure for metallization of polymers requires many stages (Fig. 2). After cleaning the surface, the polymer is attacked by a chemical solution known as sulfochromic admixture that increases significantly the surface roughness of the substrate. (2-9) The chemical oxidation, conducted with high Cr(VI) content at moderate temperatures (around 70[degrees]C), leads to the breakdown of PB chains on the surface of the treated object, leading to the loss of material in its corresponding spherical-shaped spaces and the formation of holes and interconnected cavities, typically in the order of 200-5000 nm. After the acidic chemical attack, the surface needs to be neutralized. By this means, it is possible to obtain an excellent adhesion between the polymer and the metal film. (2,10,11)

In order to proceed to the electroless deposition of nickel or copper, consisting of the reduction of a metallic salt by a reducer, it is necessary to effectuate an activation step using the colloidal catalyst Sn-Pd. The catalyst is adsorbed on the polymer surface, and the Sn is removed during the acceleration step. The palladium sites allow the autocatalytic reduction with the metal salt complexing on the polymer surface.

The electroless-deposited Cu or Ni film usually is around 0.5-1 [micro]m thick, which is not enough for most applications but makes the surface of ABS conductive. So, the object can be used as a cathode to deposit an electrolytic plating of Cu, Ni, or Cr with a total thickness in the range of 20-30 [micro]m. The plating process of polymers is lengthy and demands, along with the rinses, a total of 15 stages. The substrates are immersed in solutions, or electroless baths, which require control of temperature and concentration of electroactive species. The lifetime of these baths is short, with the risk of precipitation of the electroactive species. The use of complex or organic additives imposes a high cost of effluent treatment. Also, something to take into account is the uncertainty and increase in palladium prices. One crucial point in the classical metallization process of polymers is the use of sulfochromic admixture, which today must be substituted considering that new international regulations forbid the use of Cr(VI). Currently, there are reports that study the possibility of eliminating the sulfochromic admixture of the electroless process or even the activation stage. (3,6-16)

Another form of metallizing nonconductor substrates is the dynamical chemical plating (DCP) method, (17) which is a wet deposition technique that has been shown to be a good alternative for producing deposits of single metals such as Cu, Ni, and Ag. (18) This method consists of the projection of two aqueous solutions that contain the electroactive species (metallic salt and reducer) forming a liquid film on the surface, which react spontaneously through redox reactions. The rates of the resulting redox reactions must be controlled to insure the formation of a metallic deposit on the surface instead of a massive precipitation of the metal as a powder in the liquid film. (18) The DCP method has advantages over electroless; it is faster and cheaper because it does not need the activation step with palladium, unlike the autocatalytic process. (7,19-23) However, this process also needs surface preparation in order to have a good adherence between the metallic film and the surface substrate.

The necessity of developing new procedures to modify the ABS surface, which requires an excellent adhesion of the metallic film and avoidance of chemical carcinogenic compounds, had led us to study the corona method and UV radiation. Although these are well-established methods in the field of surface treatment, they are used independently. This work uses them to show that the characteristics of both in combination can provide significant results in preparing the ABS surface for metallization.

Experimental

Etching tests were performed with ABS sheets of Senosan AA50 White 1000 (containing as pigment 2% of TI[O.sub.2] in 100% rutile phase) with 15 min as treatment time. The sulfochromic admixture was used with a concentration of 350 g [L.sup.-1] Cr[O.sub.3] at 99.2% (J.T. Baker) and 22% (v/v) of [H.sub.2]S[O.sub.4] at 98.4% (J.T. Baker), which was stirred and heated at an average temperature of 75[degrees]C.

The optophysic treatment is a technique that involves exposing the ABS surface sequentially to a corona discharge electrode of 20 kV and to UV rays from a 125 W mercury lamp (Fig. 3). The corona discharges were applied with Corona JET equipment from the company DMG Sistemes de Traitement Corona, with a current application of 1.6 A. The distance between the corona electrode and the substrate was fixed at 0.5 cm. The substrate irradiation was done with a mercury vapor lamp of high-pressure type HPK 125 Philips of 125 W, which provides a maximum energy at 365 nm, with main peaks at 435,404, 313, and 253 nm. The distance between the UV lamp and the substrate was fixed at 5 cm. These conditions were specific for the lamp used. Before the treatment, the degreasing of ABS samples was performed with a neutral liquid soap, with a subsequent rinsing using any of the following alcohols: isopropanol, methanol, or ethanol.

The experimental methodology was based on the application of 1, 2, 6, or 12 sequences (corona-UV), with total treatment times of 12 or 24 min of corona and 30 min of UV (Table 1). The choice of these time intervals was a compromise between the time required under the experimental setup used to observe a significant change and a reasonable time for an industrial application.

The characterization of substrates was done using the following techniques: contact angle measurements with Digidrop GBX equipment produced by Scientific Instruments; infrared spectroscopy (FTIR) by reflection with a Spectrum One spectrometer produced by Perkin Elmer; X-ray photoelectron spectroscopy (XPS or ESCA) with a VG Scientific 220 I spectrometer with a monochromatic X-ray of A1 K[alpha] and employing the Scofield sensitive factor; scanning electron microscopy (SEM) with a JEOL model JSM-5400LV microscope and a Philips XL 20 microscope (in both cases, 20 kV was applied and the micrographs were obtained at 5000x); atomic force microscopy (AFM) and atomic force acoustic microscopy (AFAM) in a Dimension 3100 NANOSCOPE IV Digital Instruments microscope with an internal configuration for AFAM; mechanical profilometry with a Vecco profilometer, model Dektak[R] 6 M; optical interference profilometry with a Wyko interferometer; profilometry by AFM, resulting from AFM images; surface potential decay measurements with an apparatus made by the LAPLACE laboratory at the University Paul Sabatier in Toulouse. This device has a maximum detection of 2000 V, mapping the potential difference between the electrode and the surface in a path of an arithmetic spiral or spiral of Archimedes.

The metallization of ABS substrates, after optophysic treatment, was performed under two metallization procedures: (a) electroless process with a nickel film deposit and an electrolytic coating of Cu/Ni/Cr and (b) dynamic chemical process (DCP), applying 0.3 pm of NiB and an electrolytic coating of Cu using a current density of 0.5 A [cm.sup.-2] with a Potentiostat/Galvanostat/ZRA, Gamry, model Reference 600.

The coating adhesion characterizations were performed with the following techniques: (a) cross-cut tape test according to the ASTM D-3359 method, using a device manufactured by Precision Gage & Tool Co.; (b) pull-off test according to ASTM D4541-02, using a Elcometer[R] device; (c) cross-cut tape test according to ASTM D-3359, using a device manufactured by Precision Gage & Tool Co.; (d) cross-cut tape test according to the norm ISO 2409 at 5.5 N [cm.sup.-1]; (e) peel-off according to ASTM B533 method (A), made with an angle of 90[degrees], with a peeling rate of 25 mm [min.sup.-1]. These characterizations were performed on ABS substrates having optophysic treatment, coatings of NiB obtained with the DCP technique, and a Cu acid deposit of 30 [micro]m of thickness, aged at least 3 days after the plating process prior to characterization.

Results

The purpose of this investigation was to obtain an adherent metal film on a substrate of ABS. In this context, the adhesion is attributed to two factors: the functionalization of the surface that allows chemisorption and the roughness of the surface that allows a good mechanical anchoring of the metal film on the polymer matrix. In order to evaluate these two factors, different characterization techniques were used in ABS substrates with optophysic treatment.

In the case of chemical modification of the surface, measurements of wettability, FTIR, and XPS as a function of the optophysic treatment parameters were performed (Table 1). The morphological evolution of the ABS surface was observed at different scales by SEM, AFM, and AFAM. Also, the changes in roughness at different scales were evaluated using the mechanical, optical, and AFM profilometry techniques. Finally, we found that trapped electrical charges under the action of alternating UV-corona on ABS were assessable by the surface potential measuring technique.

Related to the surface potential measuring technique, there are some remarks to be addressed. It is important to observe the response of an insulator when it is subjected to different charge configurations and a low-frequency electric field. Some electrostatic measurement systems describe the phenomena; this is the case with the surface potential measuring technique. There are two classic situations for electrostatic type measurements. The first case is where the environment sets a constant potential, and where the response of the insulator determines the charge in the terminals. This includes capacitors and the majority of circuits where the insulation is used for separating the conductors. In this case, the current flowing into the circuit is measured depending on the accumulated charges. In the second case, the environment determines the amount of charge (or current) deposited on the surface, and the potential is determined by the properties of the insulation. This is the most common case when the insulator is not in an electrical circuit. In this case, a surface potential is measured by imposing a null field in the insulator surface.

The adherence achieved by ABS surfaces modified under optophysic treatment was quantitatively evaluated by the macroscopic adhesion techniques cross-cut tape test, pull-off and peel-off. In order to conduct these tests, metallic coatings were first deposited by electroless or DCP (around 0.3-1 [micro]m) with a subsequent electrochemical deposition with thicknesses around 30 pm.

Chemical modification of ABS surfaces

The wettabilities of ABS surfaces untreated and treated by corona and UV, alone and combined, were characterized with the measurement of the contact angles (Fig. 4). The contact angle of untreated ABS surfaces was around 78[degrees], nearly hydrophobic. The contact angles increased 8% (around 88[degrees]) after UV treatment and decreased 68% (around 25[degrees]) after corona treatment, tending to be hydrophilic. In the case of 12 sequences with 2.5 min of UV and 2 min of corona by alternation, the contact angle decreased by 53%. Through the following analysis, we intend to prove that alternation of both physical treatments is crucial, and the result is much better than simply the addition of the effect of each one.

The FTIR spectra of the untreated ABS surface, the surface exposed to UV for 30 min, and the surface exposed to corona discharge for 12 min are shown in Fig. 5. The results show that UV treatment modifies the group on the surface in the hydroperoxide (-COOH) band, which appears with a less intense signal with corona treatment. Also, for both treatments, it highlights the formation of carbonyl groups (C=0). The other infrared signals presented in these spectra show the characteristic ABS bands (corresponding to nitrile, butadiene, and styrene). In the case of the FTIR spectrum of an ABS surface treated with six sequences (2 min corona and 5 min UV) by optophysic treatment (Fig. 5), the presence of the -COOH band signal was found with an average intensity obtained with regard to UV treatment (alone) and corona (alone) while, similarly, the C=0 group is also present. Also, an increase in the bands of 912 [cm.sup.-1] (PB 1-2) and 970 [cm.sup.-1] (PB 1-4) can be seen. This is due to the selective removal of the PB with the optophysic treatment, which is purely superficial. Once the surface has been eroded, the equipment has a greater area of analysis and the PB spheres within the material will be present in greater proportion. Only the PB at the surface level is eliminated.

IR spectroscopy provides an indication of the surface modification reaching a depth of analysis around 5 pm, while X-ray photoemission spectroscopy (XPS) provides information on changes in the most superficial level (5 nm depth). This technique allowed quantification of the amount of oxygen present in the polymer surface after treatment. Compared with the reference (untreated ABS), the amount of oxygen was 320% higher with corona treatment (alone) and only 112% with UV treatment (Fig. 6). With optophysic treatment, the percentage of oxygen was 273% higher relative to the reference and 261 % higher than the UV treatment, but 85 % lower than with corona. The presence of oxygen favors the chemical adhesion of metallic coatings.

This high percentage of oxygen in the external surface, in the case of corona treatment, can be explained by the large amount of ozone created by the cold plasma due to corona discharge and, consequently, creating a polar surface functionalization. Therefore, the contact angle is much lower (24[degrees], Fig. 4).

Morphological evolution of ABS surface

It is important to show the microscopic appearance of untreated ABS (Fig. 7a) and, subsequently, that chemically attacked by the sulfochromic admixture (Fig. 7b) in order to appraise the morphological changes and surface roughness of ABS after optophysic treatment. The ABS surfaces in commercial objects are typically too smooth and hydrophobic, which thwarts the providing of a mechanical or chemical anchorage to the metallic deposit. The chemically treated ABS pieces have a high roughness with a density of 2-3 microholes pm . These holes have an average diameter of 1.5 pm. This refers to the density of microholes that exist in a given area. For this work, microhole denotes a hole that is in the range 100 nm-1 mm. The average roughness obtained by optical interference profilometry for chemically treated ABS pieces is greater than 130 nm, while that for the untreated ABS is 51 nm (Table 2). Figure 8 shows the AFM surface profile of ABS with a higher frequency in the number of peaks when optophysic treatment is used, contrary to what is observed with sulfochromic attack.

The morphological observation of the ABS surface under 30 min of UV treatment (alone) (Fig. 7c) shows no change compared to the reference (Fig. 7a). After 12 min of treatment of corona (alone), the micrograph (Fig. 7d) shows a morphological change with an increment of the average roughness by optical profilometry and the existence of microholes around 0.9 [micro]m in diameter with a density of 1 microhole [micro][m.sup.-2] (Table 2).

The average roughness after optophysic treatment, obtained by optical profilometry, ranged from 74 to 110 pm, depending on the number of sequences and the exposure time of corona and UV (Fig. 7e). The morphology showed a homogeneous texturing on the surface, with a particular increase in the density of microholes (4-5 microholes [micro][m.sup.-2]) with a maximum diameter of 1.2 [micro]m (Table 2). Profilometry by AFM analysis (Fig. 8) for ABS after optophysic treatment shows a regular attack with an average depth of 0.5 [micro]m.

AFAM is a modality of AFM, which allows differentiating domains on surfaces according to their elastic module. AFAM is based on a vibrating tip in an ultrasonic frequency range and moving this tip, as in AFM. A fixed sensor is in contact with the surface of the sample and resonates according to the nature of the material analyzed by the tip.

In Fig. 9a, an AFAM amplitude image of untreated ABS PB nodules was identified and their sizes measured up to a maximum diameter of 1 pm. After optophysic treatment, the AFAM image shows the disappearance of the nodules (Fig. 9b). However, they can still be identified, but at a level well below the surface. Also, the figure includes an SEM micrograph of the ABS surface after optophysic treatment (Fig. 9 c), which shows microholes with similar sizes to the polybutadiene nodules.

Trapping electrical charges

It is important to observe the response of an insulator when it is subjected to different charge configurations and a low-frequency electric field. Some electrostatic measurement systems described the phenomena; this is the case of the measuring surface potential technique. There are two classic situations for electrostatic type measurements. The first case is where the environment sets a constant potential, and where the response of the insulator determines the charge in the terminals. This includes capacitors and the majority of circuits where the insulation is used for separating the conductors. In this case, the current flowing into the circuit is measured depending on the accumulated charges. In the second case, where the environment determines the amount of charge (or current) deposited on the surface, and where the potential is determined by the properties of the insulation, is the most common case when the insulator is not in an electrical circuit. In this case, a surface potential is measured by imposing a null field in the insulator surface.

It was possible to obtain the cartography of potential changes on the ABS surface before and after optophysic treatment using the electrical potential measurements on the surface. (24-25) The role of different treatments on trapping charges in the material was evaluated. The variations of potentials on ABS surfaces are represented in Fig. 10 with a color scale, the brown color corresponding to 1200 V and the blue color to 0 V. Figure 10a shows a typical 40 [mm.sup.2] section of untreated ABS, which may display different levels of charge. After exposing the surface to UV radiation. Fig. 10b shows the polymer trap charges in a homogeneous and durable form (even some months) having a potential above 2000 V. In contrast, the ABS sample treated by corona (alone) had an opposite effect, a release of charges that led to a relatively homogenous potential of -400 V (Fig. 10c).

The results of surface potential measurements of a sample treated by optophysics depend on the number of sequences (corona-UV) and time of exposure in each of the treatments. Under the action of UV radiation, the material is charged; these charges probably come from the crosslinking and restructuring of PB chains. The application of corona treatment contributes to discharge of the material and creation of roughness on the surface, particularly by the ablation of PB nodules.

Figures 10d and 10e correspond to ABS with optophysic treatment in two different sequences of corona-UV. In Fig. lOd, the corona treatment was applied two times lower than in Fig. 10e. The surface potential of the sample in Fig. lOd had at most 200 V, while the potential was greater than 2000 V for the sample in Fig. 10e, which makes the graph completely saturated. In both cases, the time of exposure to UV radiation was the same (15 min per sequence).

The breaking of molecular bonds and dehydrogenation at surface occurs by placing the polymer in the path of the corona discharge. This creates very reactive free radicals which can react rapidly in the presence of oxygen to form various functional groups on the substrate surface. Functional groups resulting from these oxidation reactions (carbonyl -C=0-; carboxyl HOOC-; hydroperoxide HOO-; hydroxyl HO-) increase the surface energy and consequently promote adhesion. The polymer surface may be affected, while inserting these oxygen and nitrogen species, by the formation of ketone, amide, and nitrogen, and additionally by a crosslinking process. The crosslinking means formation of a three-dimensional network by covalent and/or ionic bonds linking one polymer chain to another to form a unit. This causes a greater stiffness.

The potential measurement and the results of morphological and physicochemical characterization, presented above, have helped explain the erosion mechanism of the ABS substrate with optophysic treatment and the usefulness of alternating corona-UV. The PB crosslinked by UV is not sufficiently eroded with a short exposure to corona. The reexposure to UV radiation does not charge the material, and the potential remains low. On the other hand, the crosslinked PB can be eroded with a longer corona treatment; a new layer of ABS is again exposed to UV radiation in the following sequence to be oxidized and crosslinked. Finally, corona and UV treatments complement each other. The latter crosslinks polymeric chains (more favorable in PB) and the former erodes the sensitized layer and charges the surface, converting it from hydrophobic to hydrophilic. This contributes to creating both roughness and a chemical compatibility for a better adhesion of the metallic deposit. It was estimated that the depth of treatment was less than 0.4 mm for the substrate with optophysic treatment (2-2.5) * 12 = 54 min, while the chemical treatment was about 3.7 mm. The material loss is considerably greater with the conventional chemical treatment.

Measuring adherence

Figures 11a and lib show two ABS substrates identically modified with optophysic treatment (12 sequences of corona-UV), both with a metallic deposit of 30 [micro]m. Figure 11a shows a sample with a first metallic coating of NiB achieved by DCP and an electrolytic deposit of Cu/Ni/Cr. In Fig. lib, the first deposit was achieved with Cu electroless and a final electrolytic deposit of Cu. Semiquantitative analysis, conducted with the cross-cut tape test, showed that the substrate with an NiB DCP deposit did not present any percentage of detachment (5B), while the detachment was less than 5% (4B) for an electroless nickel deposit. The optophysic treatment results were appropriate for preparing the surface prior to the application of either of the two techniques. Nonetheless, the optimal optophysic treatment parameters are not the same for DCP or electroless coating techniques.

Using sulfochromic admixture, the ABS modification has a greater depth, allowing electroless solutions to penetrate through the interconnected microholes, favoring the adhesion of metal deposition by mechanical anchorage (Fig. 12a). In the case of DCP, the solutions cannot penetrate through the microholes; therefore, there will be a porous surface below the metallic coating causing metal coating brittleness and poor adhesion (Fig. 12b). The characteristics of optophysic treatment allow the ABS surface modification, depending on the required surface conditions. A deep surface modification makes an electroless coating or a slight modification allows a DCP deposit without empty sites between the surface and the metallic coating.

Once the optophysic treatment was optimized, the adhesion values were obtained (validated by the company Atotech, Berlin) using the peel test technique. The adhesion of a metallic deposit on an ABS substrate with optophysic treatment of 12 sequences (1-1 min; UV-corona) was 0.81 N [mm.sup.-1]. For comparison, the adherence value for a treatment performed in a single application of UV-corona, with an exposure time of 30 min with UV and 12 min of corona, was 0.18 N [mm.sup.-1]. The standard for decorative coatings indicates 0.3 N [mm.sup.-1] as the minimum permissible adherence value, while for printed circuits it is 0.7 N [mm.sup.-1]. The adhesion value obtained by the pull-off test for the optophysic treatment was greater than 2 N [mm.sup.-2]. The rupture was observed at the epoxy resin used in the test and not at the interface of the metal-substrate.

Discussion

The ABS material is a copolymer with unsaturated PB, aromatic functions of styrene, and nitrile functions of acetonitrile. Like all polymers, ABS has a conduction and valence band separated by a band gap where electrons, among others, can be trapped. Under the action of UV photons, many effects are involved in parallel.

On the one hand, the photo-reticulation of PB leads to trap charges in depth energy levels (around 0.4 eV) below the conduction band. These trap levels are stable, which explains why the ABS under UV radiation remains charged for several months. On the other hand, crosslinking enhances the volume of electrical permittivity variation between PB, which lost unsaturated bonds, and delocalized orbitals from nitrile and styrene SAN. Finally, UV radiation creates oxidation by ozonolysis below the surface rather than barely on the outer surface.

Corona electrical discharges imply many effects in parallel as in UV radiation. The creation of a plasma between the electrodes charged to 20 kV leads to ozone formation over the surface of the material with an estimated concentration between 10 and 20 ppm. The ozonolysis leads to creation of superficial polar bonds, with a significant content of oxygen. On the other hand, corona charges the surface, but the energy of the trap is shallow, and the electrical effect does not last for long.

The combined action of sequences of UV treatment followed by corona treatment leads to the specific effect described above for each treatment. Moreover, approaching the corona electrode 1 or 2 mm to the surface, with an electric field of 20 kV, reduces the barrier height for electron capture from the UV treatment, which is known as the Frenkel-Poole effect. (26) Therefore, a release of energy and charges will be transformed into thermal agitation that can lead to dielectric and mechanical breakdowns, creating microholes in the higher insulating areas of the copolymer, the crosslinked PB nodules. A microhole morphology begins to appear on the surface of the ABS substrate. The following description outlines the proposed sequence of the optophysic treatment: the material is charged by UV exposure, and a release of charges by the corona effect contributes to increase the microhole density. Continuing with these sequences (UV-corona), the material is eroded layer by layer.

Conclusions

The ABS surfaces in commercial objects are typically too smooth and hydrophobic, which thwarts the providing of a mechanical or chemical anchorage to the metallic deposit. In this work, the usefulness of the named optophysic treatment, comprised of UV-corona consecutive alternating sequences, for preparing the ABS surface for metallization was presented. It was shown that alternating the application of both physical treatments and a series of sequences were crucial in order to achieve optimum modified surfaces.

The ABS surface modification was performed by applying corona discharge and UV radiation sequences by selectively removing the PB areas on the polymer surface. The combination of electronic and photonic UV irradiation in the ABS resulted essentially in two types of effects that led to the polymer surface modification: the capture-release of charges and the chemical modification of the surface. The former transforms into thermal agitation that can lead to dielectric and mechanical breakdowns, creating microholes in the higher insulating areas of the copolymer, the UV crosslinked PB nodules. Continuing with these sequences (UV-corona), the material is eroded layer by layer. Either treatment, UV or corona, causes depth and superficial ozonolysis, respectively, which leads to the creation of polar bonds with a significant content of oxygen.

The morphological and chemical changes caused by the optophysic treatment allowed metallic coatings with excellent adhesion results to be obtained. Nonetheless, the optimal optophysic treatment parameters are not the same for DCP or electroless as coating techniques. Therefore, parameters of time, intensity, and number of sequences required adjustments according to the specific deposition technique.

An industrial successful substitution of sulfochromic admixture in the electroless process by optophysic treatment may imply a great change in the safety of the process and in the amount and toxicity of effluents with environment repercussions. On the other hand, metallic coatings were obtained by DCP with similar characteristics and adherence like the conventional electroless and electrolytic processes. This technique may represent a turning point for some specific finishings, since not only the surface modification but also the expensive palladium activation stage are reduced to a single step of autocatalytic spraying over the surface.

DOI 10.1007/s11998-014-9632-5

L. Magallon Cacho, J. J. Perez Bueno ([mail]), Y. Meas Vong

Centro de Investigacion y Desarrollo Tecnologico en Electroquimica, S.C., Parque Tecnologico Queretaro Sanfandila, CP 76703 Pedro Escobedo, QRO, Mexico

e-mail: jperez@cideteq.mx

L. Magallon Cacho e-mail: lmagallonc@yahoo.com.mx

Y. Meas Vong e-mail: yunnymeas@cideteq.mx

L. Magallon Cacho, G. Stremsdoerfer

Laboratory of Tribology and Dynamics of the Systems, UMR 5513, Ecole Central de Lyon, 36 Avenue Guy de Collongue, BP 163, 69131 Ecully Cedex, France

G. Stremsdoerfer

e-mail: guy.stremsdoerfer@ec-lyon.fr

F. J. Espinoza Beltran

Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional (CINVESTAV), Unidad Queretaro, Libramiento Norponiente #2000, Fracc. Real de Juriquilla, Apartado Postal 1-798, CP 76230 Queretaro, QRO, Mexico

e-mail: fespinoza@qro.cinvestav.mx

J. Martinez Vega

Laboratoire Plasma et Conversion d'Energie (LAPLACE), Universite de Toulouse; UPS, 1NPT, 118 route de Narbonne, 31062 Toulouse Cedex 9, France e-mail: juan.martinez-vega@laplace.univ-tlse.fr

Acknowledgments The authors gratefully acknowledge CONACYT for financial support through the Project QRO-2101-C01-191210 and for the doctorate scholarship granted to L. Magallon-Cacho. Special thanks are dedicated to the PCP (Postgraduate Cooperation Program Mexico-France) and to the French company Jet Metal Technologies. The authors are especially grateful to Darlene Garey of the U.S. Peace Corps for her valuable suggestions for this work.

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Table 1: Experimental methodology for the optophysic treatment

UV      30                              xl   xl
(min)   15                         x2   x2
        5               x6    x6
        2.5       x12   xl2
        0
              0   1     2     4    6    12   24

                        Corona (min)

Table 2: Optical analysis and AFM profilometry on ABS substrates
with different surface treatments

                        Untreated             Etching (a)

Density-SEM                 0                     2-3
  (microcavities
  [micro][m.sup.-2])
Average optical            51       [greater than or equal to] 130
  roughness (nm), Ra
Maximum diameter            0                     1.5
  ([micro]m)
Depth of treatment          0                     3.5
  ([micro]m)

                        UV (30 min)   Corona (12 min)   Optophysic (b)

Density-SEM                  0              1               4.5
  (microcavities
  [micro][m.sup.-2])
Average optical             51              82              74-110
  roughness (nm), Ra
Maximum diameter             0              0.9             1.2
  ([micro]m)
Depth of treatment                                          0.4
  ([micro]m)

(a) Attack with sulfochromic admixture Cr(VI) 350 g [L.sup.-1]

(b) Optophysic treatment, six sequences (4 min Corona-5 min UV)

Fig. 6: Oxygen (01s) atomic percentage measured by XPS
on ABS surface with different surface treatments

                   Atomic %   Corona      UV      Optophysic
                    (O1s)     (alone)   (alone)

                               320%      112%        273%

Untreated ABS        6.12
Corona discharge    26.06
UV radiation        13.19
Optophysic          23.19
                                Reference (untreated ABS)


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Title Annotation:acrylonitrile butadiene styrene
Author:Cacho, L. Magallon; Bueno, J.J. Perez; Vong, Y. Meas; Stremsdoerfer, G.; Beltran, F.J. Espinoza; Veg
Publication:Journal of Coatings Technology and Research
Geographic Code:1USA
Date:Mar 1, 2015
Words:6112
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