Effects of Corrosion Inhibitors on Lubrication Performance of Rolling Oil for Copper Foil

Transcription

1 Lubrication Research China Petroleum Processing and Petrochemical Technology 2014, Vol. 16, No. 2, pp June 30, 2014 Effects of Corrosion Inhibitors on Lubrication Performance of Rolling Oil for Copper Foil Xiong Sang 1 ; Sun Jianlin 1 ; Zeng Yingfeng 2 ; Xu Yang 1 (1. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing ; 2. Research Institute of Petroleum Processing, Sinopec Corp., Beijing ) Abstract: The 2,5-bis(ethyldisulfanyl)-1,3,4-thiadiazole (T561), benzotriazole (BTA), 1-N, N-bis (2-ethylhexyl) aminomethyl-4-methyl-1h-benzotriazole (IRGAMET39) and 1-[N, N-bis (2-ethylhexyl) aminomethyl] methyl benzotriazole (TT- LX) have been evaluated as corrosion inhibitors used in rolling oil for cold rolling of copper foil. The MRS-10A four-ball friction and wear tests have been carried out to compare their tribological properties, and the lubricating performance of rolling oils has been studied through rolling experiments. The oil sample containing IRGAMET 39 has the same P B value as that one containing T561, with the coefficient of friction increased by 35.6% and wear scar diameter decreased by 4%. The minimum rolling gauge has been studied after rolling lubrication, but the results show that inhibitors have no effect on it. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses have indicated that the inhibitor is adsorbed on the copper surface to prevent copper from being corroded easily. In addition, the LEXT OLS4000 laser confocal microscopy has been used to observe the foil surface which shows that the streaks of foil surface are clear, the scratches are shallow and the surface failure is improved effectively. Key words: copper foil; corrosion inhibitor; cold rolling; surface topography; lubrication 1 Introduction Rolling of copper foil is an extremely complex production process, which covers the detection and control over precision, the lubrication and surface treatment, the heat treatment process and other procedures. High level of production equipment is needed during cold rolling of copper foil. Technological lubrication is one of the key factors to improve the technology for rolling of copper foil, in order to satisfy the market demand for high quality rolled copper foil, so that the research and development of efficient lubrication technology is required [1-2]. The lubricants for rolling of copper foil should meet the requirements for operating under extreme pressure along with possessing necessary abrasion resistance, antifriction, lubrication and cooling properties. Lubricating oil plays an important role in copper foil rolling process, which can reduce the minimum rolling gauge, and improve the surface quality of rolled copper foil. Brist [3] has shown that the surface roughness can reach up to 0.32 μm, which has been conducive to the high frequency signal transmission. During the cold rolling process, because the rollers and the workpiece are in close contact, friction and wear will inevitably occur and the energy loss will increase. Lubricants can be used to form a lubricating film on the workpiece, which can reduce the incidence of friction and wear during the rolling process [4-5]. Full film lubrication of smooth surfaces is accurately modelled by the Reynolds equation. Currently, cold rolling lubricating oil has been prepared to contain different types of additives, in which most additives usually comprise a high ratio of harmful elements such as sulfur and phosphorus [6-7]. And the existence of these elements can corrode the surface of rollers and workpiece, causing the shortening of roller life and the worsening of surface quality of workpiece during rolling operation [8]. At the same time, the rolling oil containing corrosion inhibitors can also be adsorbed on the copper strip surface to prevent it from being cor- Recieved date: ; Accepted date: Corresponding Author: Prof. Sun Jianlin, Telephone: ; address: sjl@ustb.edu.cn. 71

2 China Petroleum Processing and Petrochemical Technology 2014,16(2):71-78 roded easily and improve the surface quality of rolled copper foil [9-10]. Because benzotriazole, thiadiazole and their derivatives have a close and stable structure, a protective film can be formed on metal surface by physical adsorption or chemical reaction to avoid contact between the rollers and the workpiece, which plays a part in antiwear and extreme pressure resistance [10]. This environmentally friendly additive does not contain phosphorus, heavy metal elements and ashes. With the emergence of high-precision copper foil technology, an opportunity is provided to develop a new kind of cold rolling oil and to solve the above-mentioned problems. The reasonable selection of base oil and additives is crucial for rolling of copper foil under the same condition. The present work focuses on the assessment of 2,5-bis(ethyldisulfanyl)-1,3,4-thiadiazole (T561), benzotriazole (BTA), 1-N, N-bis (2-ethylhexyl) aminomethyl-4- methyl-1h-benzotriazole (IRGAMET 39) and 1-[N, N-bis (2-ethyl-hexyl) aminomethyl] methyl benzotriazole (TT- LX) as corrosion inhibition additives in rolling oil used for cold rolling of copper foil. Therefore, the tribological properties of rolling oils containing different inhibitors, the lubrication performance and the rolled copper foil surface quality were studied. Furthermore, this work can offer a reference for the development of high-precision copper foil technology in the future. 2 Experimental 2.1 Materials The copper foil coupon had a purity of %. The traditional benzotriazole (BTA), and the new chemicals 2,5-bis(ethyldisulfanyl) -1,3,4-thiadiazole (T561), 1-N, N-bis(2-ethylhexyl) aminomethyl-4-methyl-1h-benzotriazole (IRGAMET 39) and 1-[N, N-bis(2-ethyl-hexyl) aminomethyl] methyl-benzotriazole (TT-LX) were added to the same rolling oil under the same condition. Molecular structures and the specific parameters of these new inhibitors are given in Figure 1 and Table 1, respectively. A common oil for cold rolling of copper foil without addition of inhibitor was used in the comparison test (denoted as the BLANK ). The electrode was then washed with re-distilled water, degreased with acetone, then washed with re-distilled water again and finally dried in a pure nitrogen stream. Figure 1 Molecular structure of new inhibitors Table 1 Performance parameters of new inhibitors Parameter T561 IRGAMET39 TT-LX Appearance Brownish yellow transparent liquid Clear, yellow to brown liquid Clear, yellow to brown liquid Kinetic viscosity (40 ), mm 2 /s Density (20 ), g/cm Flash point, >120 > Solubility, % In mineral oil <0.01 <0.01 <0.01 In water >5 >5 >5 Nitrogen content, m% Test on tribological properties A MRS-10A four ball testing machine was used according to the national standard GB/T to measure the maximum non-seizure load (P B value) adopted for estimating the load carrying capacity of the rolling oil containing different inhibitors. The average coefficient of friction of different rolling oil samples was obtained from experiments conducted in 30 minutes of testing at room temperature under a loading force of 392 N, a rotational speed of revolutions per minute. 72

3 Xiong Sang, et al. Effects of Corrosion Inhibitors on Lubrication Performance of Rolling Oil for Copper Foil 2.3 Cold rolling test A four-high rolling mill of Φ95/200 mm 200 mm with a velocity of 60 r/min and a rolling power of 35 kw was used to evaluate the lubricity of the rolling oil containing different inhibitors. The workpiece thickness was 0.18 mm and the pass-reduction was 20%. The surface morphology analyses of rolled copper foil were conducted by a TR200 roughness instrument, a German model LEXT OLS4000 laser confocal microscope, a scanning electron microscope (SEM), and an energy dispersive spectrometric (EDS) analyzer. 3 Results and discussion 3.1 Tribological properties P B is an important parameter that reflects the load carrying capacity of rolling oil [5], which is determined by the rolling oil viscosity, the adsorption film toughness and the sliding speed. P B, the coefficient of friction, and the wear scar diameter are three important indexes of antiwear performance and friction-reducing properties of the rolling oil. The bigger the P B value is, the stronger oil film and better anti-wear and friction-reducing performance of the rolling oil will be. Similarly, the less the coefficient of friction is and the smaller the wear scar diameter is, the better the lubricity will be. However, the three factors are not always coincident. For the convenience of the analysis, we propose an extreme pressure anti-wear and friction reducing coefficient (ψ) that can combine the P B value, the wear scar diameter and the coefficient of friction with the same standards to reflect the tribological properties of rolling oil directly, as shown in Eq. (1). PB ψ = ln (1) µ D where ψ is the extreme pressure anti-wear and friction reducing coefficient, P B is the maximum non-seizure load, D is the wear scar diameter, and μ is the coefficient of friction. The values of P B, μ, D and ψ applicable to different rolling oils are given in Table 2. It can be seen that P B value of the rolling oil blended with T561 is equal to that of the oil with addition of IRGAMET 39 or the BLANK, and however, it is higher than that of oil samples with addition of BTA or LL-TX. The coefficient of friction of the oil with addition of T561 is lower than other oil samples and its wear scar diameter is larger than that of the oil containing IRGAMET 39. Compared to the BLANK, the conventional BTA inhibitor added to the rolling oil can effectively reduce the P B value by 10.5%, with the coefficient of friction decreased by 1.2% and the wear scar diameter increased by 1.9%. Although the oil containing IRGAMET 39 has the same P B value as that of the BLANK and the oil sample containing T561, its coefficient of friction increased by 26.5% and 35.6% and the wear scar diameter decreased by 5.9% and 4%, respectively, as compared to the corresponding values of the BLANK and the oil containing T561. It is shown that the ψ of rolling oil blended with different corrosion inhibitors increased in the following order: ψ IRGAMET 39 < ψ BTA <ψ BLANK = ψ LL-TX <ψ T561. The higher the value of ψ is, the better the extreme pressure anti-wear and friction reducing performance of rolling oil will be. Table 2 Tribological property parameters of different corrosion inhibitors added to rol Corrosion inhibitor P B, N µ, D 30 min, mm ψ BLANK T BTA IRGAMET TT-LX Figure 2 shows the wear scar diameter of the steel balls used in the four-ball tribological test under lubrication by rolling oil samples in 30 min of friction testing. Obviously, upon comparing the size and depth of wear scars, the steel balls lubricated by the BLANK oil showed larger wear scar diameter, rough edges and more defects. However, upon lubrication by the rolling oil containing IR- GAMET 39, the balls got the smallest wear scar diameter, shallower wear scar, less abrasion and full profile. The reason is that a kind of film has been formed and can efficiently adhere to the surface of the balls during the long process of friction. T561 inhibitor as an additive blended to the rolling oil can result in finer surface finish, regular and shallow wear scar gap, and larger wear scar diameter on steel balls. The relationship between the coefficient of friction and the operating time is shown in Figure 3. It can be seen 73

4 China Petroleum Processing and Petrochemical Technology 2014,16(2):71-78 Figure 2 Three lubrication conditions of wear scars (left) and 3D morphology (right) Figure 3 Coefficient of friction of rolling oil samples with blended additives during copper foil rolling BLANK; T561; BTA; IRGAMET 39; LL-TX that, within 3 minutes, the coefficient of friction of BLANK rose with an increasing operating time, then gradually decreased, and after 18 minutes it basically reached a relatively stable value of The coefficient of friction on steel balls lubricated by oil containing IR- GAMET 39 fluctuated heavily with the increase in operating time, and finally stabilized at In comparison with the performance of previous two oil samples, it can be found that the coefficient of friction on balls lubricated by two rolling oil samples containing T561 and LL-TX, respectively, can in six minutes reach and 0.061, respectively, and remain stable until the experiment is completed. It is shown that a stable film has been formed completely to prevent the rubbing surfaces from contacting each other directly and to reduce friction and wear during friction process. 3.2 Lubrication performance of rolling oil in the course of cold rolling Rolling force has been recorded by stress test sensors during cold rolling. The variation in average rolling force and rolling power with the rolling pass is given in Figure 4 (a) and (b). By comparing the six curves, it can be seen that the rolling force and rolling power gradually rise with the 74

5 Xiong Sang, et al. Effects of Corrosion Inhibitors on Lubrication Performance of Rolling Oil for Copper Foil increase of the rollling pass, and reach a maximum at the seventh rolling pass, prior to declining with the further increase of rolling passes. When cold rolling is carried out in the presence of lubricating oil, the rolling force and rolling power are significantly reduced. Especially, rollers under the lubrication of rolling oil containing T561 have the minimum rolling force and rolling power during rolling process, indicating to its best energy-saving performance. of BLANK, T561, BTA, IRGAMET 39 and LL-TX are overlapping. Thickness reduction indicates no obvious change after the seventh pass and the eighth pass of rolling, and the thickness of workpiece is equal to the minimum rolling gauge. Thus, the corrosion inhibitors have no effect on the minimum rolling gauge of copper foil during rolling operation. Figure 5 Thickness of copper foil under different lubrication conditions No lubrication; BLANK; T561; BTA; IRGAMET 39; LL-TX Figure 4 Variation of average rolling force (a) and rolling power with the rolling pass (b) No lubrication; BLANK; T561; BTA; IRGAMET 39; LL-TX It can be seen that the minimum rolling gauge is only associated with the coefficient of friction of the deformation zone in a direct proportional relationship [11], and the coefficient of friction can reflect the level of the quality of rolling lubrication directly, when the rolling parameters and the workpiece are the same, according to the minimum rolling gauge theory of Stone. The rolling thickness of copper foil with 20% reduction per pass using different lubricating oils are shown in Figure 5. The curves The parameter R a (mean height of profile irregularities) is used to characterized the surface roughness of rolled copper foil, which has been measured by a TR200 roughness instrument, with the results presented in Figure 6. The sample, which was made of copper foil after the eighth pass of rolling, was subjected to ultrasonic cleaning to remove the residual rolling oil on the surface. It is confirmed that the surface roughness of copper foil has been improved after adopting lubrication during cold rolling. The reason is that a good lubricating film has formed between the roller and the workpiece, which can avoid direct bumping of roller against the surface of copper foil when exercising rolling at high speed. It is also shown that there are slight changes of rolled copper foil when rolling oil contains inhibitors. The contact surfaces are covered with a molecular layer of a substance whose specific properties can significantly influence the friction and wear characteristics. The surface roughness of rolled copper foil is improved and the wear and tear phenomena are reduced. Because the greater the rolling oil viscosity is, the larger oil film thickness can be obtained, and the rolling force is reduced between the roller and the work- 75

6 China Petroleum Processing and Petrochemical Technology 2014,16(2):71-78 piece. The difference is inconspicuous among the rolling oil containing corrosion inhibitors, because the contacting time of the roller and the workpiece is short, and a severe corrosion between the copper foil and oil will not happen in a short period of time. on the copper foil surface and makes the copper foil surface brighter. Therefore, inhibitors added to the rolling oil with their high efficiency and high performance will have a good application prospect. In Figure 7(b), the surface of rolled copper foil is smooth with slight ups and downs and the rolling texture is clear when a rolling oil containing IRGAMET 39 is used. Figure 6 Rolled surface roughness curve of oil containing different inhibitor addtives The surface quality of rolled copper foils under different lubricating conditions has been checked by the LEXT OLS4000 laser confocal microscopy, with the 3D microphotographs shown in Figure 7. When the hard particles contact with each other directly without lubrication, many defects composed of pits and scratches have been formed during the rolling process. When a rolling oil containing inhibitors is used, the defects are obviously decreased. At the same time, the streaks of foil surface are clear, the scratches are shallow and the friction and wear resistance is improved effectively. The reasons are as follows. Firstly, deformation heating is caused by plastic deformation of the metal, and friction heating is generated in the contact surface between the roller and workpiece. It makes the surface temperature at the contacting position increase, which is conducive for the rolling oil spreading effectively to form boundary lubricating film. Boundary lubricating films are created from surface-active substances and their chemical reaction products. Adsorption, chemisorption, and tribochemical reactions also play significant roles. Secondly, the film-forming additives onto the metal surface can effectively reduce such phenomena as sticking and welding that take place during the rolling process. Thirdly, the addition of corrosion inhibitors can form a multilayer film which has a good protective effect Figure 7 3D morphology of rolled copper foil surface under different conditions In general, the adsorption of an inhibitor on the metal surface depends on the surface charges of the metal, the adsorption mode and its chemical structure. Benzotriazole and its derivatives contain nitrogen atoms, by which they coordinate with Cu (0), Cu (I) or Cu (II) through the lone pair electrons to form copper-azole complexes [12]. These complexes are generally believed to be polymeric in nature and form an adherent protective film on the copper surface [13]. And benzotriazole can build protective films by a strong triazolic ring metallic substrate bond on copper surface [14]. The additive T561 containing mercapto groups also has been used as the copper corrosion inhibitor for different industrial applications [15]. In order to see whether the inhibitor molecules are adsorbed on the copper foil surface, both SEM and EDS analyses have been carried out. The specimen has been washed with water, thoroughly dried, and mounted into the spectrometer without any further treatment. The SEM image and the corresponding 76

7 Xiong Sang, et al. Effects of Corrosion Inhibitors on Lubrication Performance of Rolling Oil for Copper Foil EDS profile analysis for the copper foil surface are shown in Figure 8. The element composition of the copper surface contains C, N, O and S. The existence of O element is ascribed to the partial surface oxidation of copper foil. Meanwhile, the existence of C and N elements is assigned to the surface adsorption, which has a certain amount of hydrocarbons and corrosion inhibitor existing on the copper foil. The corrosion on the surface of copper foil in the presence of cold rolling oil slows down, which is attributed to the adsorption of some IRGAMET 39 on the surface. This indicates that the IRGAMET 39 molecules can be effectively adsorbed on the copper foil surface forming a Cu-IRGAMET 39 bond that has a lubricating effect. In addition, it can be seen that the rolling oil can distribute uniformly during rolling operation, and a copper foil surface free from any macro-defects can be Figure 8 The SEM image of the rolled copper foil surface which is lubricated with rolling oil containing IRGAMET 39 or nothing (a) and the corresponding EDS profile analyses of the area shown in the image (b) obtained. 4 Conclusions (1) The tribological experiments showed that the P B value, the coefficient of friction and the wear scar diameter show micro-variation among the rolling oil samples containing different corrosion inhibitors. P B value of the rolling oil containing T561 is equal to that of the oil sample containing IRGAMET 39 or the BLANK, and is higher than that of oil samples containing BTA or LL-TX. Although the oil containing IRGAMET 39 has the same P B value as that of the BLANK and the oil sample containing T561, its coefficient of friction increased by 26.5% and 35.6% and its wear scar diameter decreased by 5.9% and 4%, respectively, as compared to the corresponding values of the BLANK and the oil containing T561. (2) The extreme pressure anti-wear and friction reducing coefficient (ψ) of rolling oil containing different corrosion inhibitors increases in the following order: ψ IRGAMET 39 <ψ BTA <ψ BLANK =ψ LL-TX <ψ T561. The higher the value of ψ is, the better the extreme pressure anti-wear and friction reducing performance of rolling oil will be. The T561 additive showed the most effective extreme pres- 77

8 China Petroleum Processing and Petrochemical Technology 2014,16(2):71-78 sure anti-wear and friction reducing property. (3) During the cold rolling experiments, rolling oil samples containing different inhibitors show no impact on the minimum rolling gauge of the workpiece. But the energy consumption of rolling process can be reduced effectively by using the rolling oil containing inhibitors. The corrosion inhibitors added into the rolling oil can be firmly adsorbed on the copper foil surface to form a multilayer film which has a good protective effect on the copper foil surface to make the copper foil surface brighter and smoother. Acknowledgments: The work is financially supported by the National Natural Science Foundation of China (No ), the Key Science and Technology Project of China (No.2011BAE23B00) and the Cooperation Program between USTB and SINOPEC (No ). References [1] Larsson R. Modeling the effect of surface roughness on lubrication in all regimes [J]. Tribology International, 2009, 42(4): [2] Lee C Y, Moon W C, Jung S B. Surface finishes of rolled copper foil for flexible printed circuit board [J]. Materials Science and Engineering A, 2008, : [3] Brist G, Hall S, Clouser S, Liang T. Non-classical conductor losses due to copper foil roughness and treatment [J]. Proc Electron Circuits World Conv, 2005, 10: [4] Sun J L, Wu X D, Kang Y L, et al. Experimental research and general evaluation of additives in rolling oil during aluminum cold rolling [J]. Lubrication Engineering, 2004, 28 (2): 5-8 (in Chinese) [5] Zhang X, Wang Y Z, Yao W J, et al. Development and lubricating properties of rolling oil for stainless steel cold rolling [J]. China Petroleum Processing and Petrochemical Technology, 2011, 13(2): [6] Liu N N, Sun J L, Wu D, et al. Research of tribological characteristics and lubrication performance of rolling oil for electronic copper foil [J]. Functional Materials, 2012, 20(43): (in Chinese) [7] Lin X Z, Gong M. Research progress of environmentally friendly copper corrosion inhibitor [J]. Journal of Corrosion and Protection, 2009, 30(5): [8] Wang B, Zhou G D. Photoelectric chemical research of the corrosion inhibition of copper from BTA derivatives [J]. Journal of Solar Energy, 2000, 21(1): [9] Zhang S T, Xue M Y, Wang Y B. Research of BTA corrosion inhibitors on copper surface cover behavior [J]. Journal of Corrosion Science and Protection Technology, 2006, 18(5): [10] Xu Q J, Zhou G D, Lu Z, et al. Benzene and triazolium nitrogen and 4-carboxyl of benzene and triazolium nitrogen on the corrosion inhibition of copper in NaCl solution [J]. Chinese Journal of Nonferrous Metals, 2001, 11(1): (in Chinese) [11] Hu Y, Man R L, Liu X F. Material composition and properties of stock oil used in aluminum foil rolling oil [J]. Acta Petrolei Sinica (Petroleum Processing Section), 2008, 24(3): (in Chinese) [12] Kovács K, Stampf G, Klebovich I, et al. Aqueous solvent system for the solubilization of azole compounds[j]. European Journal of Pharmaceutical Sciences, 2009, 36(2/3): [13] Gomma G K. Effect of azole compounds on corrosion of copper in acid medium[j]. Matrials Chemistry and Physics, 1998, 56(1): [14] Döner A, Solmaz R, Özcan M, et al. Experimental and theoretical studies of thiazoles as corrosion inhibitors for mild steel in sulphuric acid solutin[j]. Corrosion Science, 2011, 53(9): [15] Izquierdo J, Santana J J, González S, et al. Scanning microelectrochemical characterization of the anti-corrosion performance of inhibitor films formed by 2-mercaptobenzimidazole on copper[j]. Progress in Organic Coatings, 2012, 74(3):