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Effect of a mixed aqueous solution of HCl and CaCl2 on adhesion of coating to evaporated indium layer
Progress in Organic Coatings 53 (2005) 17–22
Effect of a mixed aqueous solution of HCl and CaCl2 on adhesion of coating to evaporated indium layer Kentaro Watanabe a,∗ , Masahiko Yamanaka a , Toshiyuki Mozawa b , Norihiko Kobayashi b a
Nissan Motor Co. Ltd., Materials Engineering Department, 560-2, Okatsukoku, Atsugi-shi, Kanagawa 243-0192, Japan b Hashimoto Forming Industry Co. Ltd., 320, Kamiyabe-cho, Totsuka-ku, Yokohama-shi, Kanagawa 245-8511, Japan Received 10 December 2003; accepted 1 December 2004
Abstract The effect of a mixed aqueous solution of HCl and CaCl2 on the adhesion of a coating with an evaporated indium layer was evaluated. Peeling was observed between the evaporated indium layer and the clear-coat after dipping a coated panel in the mixed aqueous solution, and the coating films were seen to lose their metal gloss. Observation of the evaporated indium layer with scanning electron microscope (SEM) revealed various particle sizes of indium. A higher area ratio of indium particles in the indium layer led to faster peeling after dipping the coated panels in the mixed aqueous solution. The effect of the cross-linking density of clear coating film on the peeling between the indium layer and the clear-coat was investigated. A clear coating film with a lower cross-linking density resulted in a shorter peeling time in the mixed aqueous solution. It was considered that the peeling was caused by condensation of water in the spaces where indium was dissolved by penetration of the HCl from the HCl/CaCl2 aqueous solution into the evaporated indium layer. © 2005 Elsevier B.V. All rights reserved. Keywords: Indium; Vacuum evaporation; Adhesion; Urethane coating; Viscoelasticity; Moisture permeability
1. Introduction The performance of automotive coatings is affected by various chemical substances such as acid rain, bird droppings, sap, iron powder and inorganic salts. In a previous paper, we reported that: (1) peeling occurred in adhesion tests of coated films after washing the chrome-plating substrate with water containing inorganic salts[1,2]; (2) iron powder adhesion occurred under high temperature and humidity, adhering easily to a coating film with high moisture permeability[3]; (3) whitening of melamine-cured coating film occurred by addition of inorganic acid and a light stabilizer[4]; and (4) cracking of melamine-cured coating film was affected by the affinity of the 2-methylheptane to the melamine resin and also cracking of the coating film occurred in a shorter time when there was a higher affinity [5]. ∗
Corresponding author. Tel.: +81 46 270 1518; fax: +81 46 270 1585. E-mail address: [email protected] (K. Watanabe).
0300-9440/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2004.12.003
Recently, soft plastic substrates are used as parts for items such as radiator grilles for more stylish automobile design. Surface treatment with evaporated indium is performed on these substrates, as properties such as impact resistance are not obtained in surface treatment with rigid chromium plating and evaporated aluminum. However, indium coatings have poor acid resistance and thus are not suitable for automobiles in contact with acid rain or CaCl2 snow-melt salts. This paper reports on the effect of a mixed aqueous solution of HCl and CaCl2 on the adhesion of coatings with an evaporated indium layer.
2. Experimental 2.1. Sample preparations Indium was evaporated onto an acrylate-isocyanate cured primer, and an acrylate-isocyanate cured clear-coat was
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K. Watanabe et al. / Progress in Organic Coatings 53 (2005) 17–22
applied and cured. The primer and clear-coat had dry film thicknesses of 20 and 30 m, respectively. Both the primer and the clear-coat were force dried for 60 min at 80 ◦ C. The evaporation occurred under conditions of 0.1, 0.2 and 0.3 g of applied evaporated indium and at vacuum pressures of 1.33 × 10−1 , 1.33 × 10−2 and 1.33 × 10−3 Pa.
dynamic viscoelasticity automatic measurement apparatus. Cross-linking density was obtained from the equation, E = 3nRT (E = Young’s modulus, n = cross-linking density, R = gas constant, T = absolute temperature) [6–8].
2.2. Dipping test in a mixed aqueous solution of HCl and CaCl2
A moisture permeability cup (JIS 0208 standardized) was kept for 0, 4, 8, 12 and 24 h under 50 ◦ C and 50% relative humidity. The moisture permeability weight was measured and plotted against time. The moisture permeability was calculated using the slope of the best-fit line and a free film thickness of 30 m.
A mixed aqueous solution of HCl and CaCl2 was prepared by mixing 30 mL of 12 N HCl and 55 g of CaCl2 in 1000 mL of distilled water. Crosscut test pieces were dipped in the solution of HCl and CaCl2 for 72, 168 and 240 h at 50 ◦ C. Peeling was investigated after drying at room temperature. The peeling test was performed by pulling off tape adhered to the crosscut section, and the width of peeling indicated by the distance from the crosscut line.
2.5. Measurement of moisture permeability
2.6. Analysis of dissolution of indium layer The solution of HCl and CaCl2 was analyzed after the dipping test using an ICP Optical Emission Spectrometer.
2.3. Observation of evaporated indium layer 3. Results and discussion Indium was evaporated from 0.1, 0.2 and 0.3 g of indium and at vacuum pressures of 1.33 × 10−1 , 1.33 × 10−2 and 1.33 × 10−3 Pa. The surface and cross-section of the evaporated indium layers were observed using a Hitachi S-4000 scanning electron microscope. The samples were prepared by platinum sputter with a 15-kV accelerating voltage. The area ratio of indium particles on the evaporated indium layer was determined by portrait analysis of an SEM micrograph focused on the indium evaporation layer. 2.4. Cross-linking density of clear coating film The free films, without the indium or primer layers, were prepared by peeling off the coating films after coating by drying forcedly at 80 ◦ C for 60 min on tin foil. The dry free films were 50 m thick. The viscoelasticity of the free films was measured using a Rheology DVE-V4
Adhesion testing of the coating evaporated was performed under various conditions after dipping in the HCl/CaCl2 solution. Table 1 shows the conditions and results of the coating system with the evaporated indium layer. The results revealed that both peeling and loss of metal gloss occurred, and that the degree of peeling varied. A higher weight of indium applied via evaporation and a lower vacuum pressure resulted in a longer width of peeling from the crosscut section. The longest width of peeling occurred under conditions of 0.3 g applied indium and at 1.33 × 10−1 Pa vacuum pressure. The evaporated indium layer on the primer was observed with SEM. The results of SEM observation are shown in Fig. 1a, b, d and e. It was found that various particle sizes of indium were deposited on the primer. Fig. 1c indicates that there were no particles but instead the indium had formed a film. A higher vacuum pressure led to smaller particle
Table 1 Results after dipping test in a mixed aqueous solution of HCl and CaCl2 a Substrate
Thermo-polyurethane
Primer
Indium evaporation conditions
Clear-coat
Paint
Film thickness (m)
Weight (g)b
Vacuum pressure (Pa)
Film thickness (m)
Paint
Film thickness (m)
Polyurethane
20
0.1
1.33 × 10−1 1.33 × 10−2 1.33 × 10−3 1.33 × 10−1 1.33 × 10−2 1.33 × 10−3 1.33 × 10−1 1.33 × 10−2 1.33 × 10−3
50 30 40 100 70 70 90 100 100
Polyurethane
30
0.2
0.3
a b c
Test time was 168 h. Weight applied via evaporation. Yes: metal gloss was partially lost (confirmed by visual inspection).
Width of peeling (mm)
Metal glossc
0.9 0.3 0.3 7.0 0.3 0.3 30 0.3 0.3
Yes Yes Yes Yes Yes Yes Yes Yes Yes
K. Watanabe et al. / Progress in Organic Coatings 53 (2005) 17–22
19
Fig. 1. SEM images of surface of evaporated indium layer. The quantity of indium applied via evaporation, and vacuum pressure were varied. (a) Indium applied, 0.1 g; vacuum pressure, 1.33 × 10−1 Pa; (b) indium applied, 0.2 g; vacuum pressure, 1.33 × 10−1 Pa; (c) indium applied, 0.3 g; vacuum pressure, 1.33 × 10−1 Pa; (d) indium applied, 0.2 g; vacuum pressure, 1.33 × 10−2 Pa; (e) indium applied, 0.2 g; vacuum pressure, 1.33 × 10−3 Pa
sizes of indium, and a higher weight of indium applied via evaporation led to larger particle sizes. The effect of the area ratio of indium particles upon adhesion of the evaporated indium layer to the cured primer was clarified by observation with SEM. The results, shown in Fig. 2, indicate that a smaller area ratio of indium particles led to higher adhesion. A cross-section of the evaporated indium layer was observed with SEM. The results are shown in Fig. 3a and b. Fig. 3a shows that the area not occupied with indium particles was the primer layer. Fig. 3b shows complete coverage of the surface of the primer with indium particles. The clear-coat directly applied over the primer did not peel off after dipping in the HCl/CaCl2 solution. From these results, it was
concluded that the coating over the indium evaporation layer was fixed by adhesion between the clear-coat and primer. The coated panel dipped in the HCl/CaCl2 solution resulted in a loss of metal gloss. The effect of HCl and CaCl2 concentration on the loss of metal gloss as well as on the dipping time required to produce peeling was evaluated. Table 2 shows the results of the loss of metal gloss and peeling over time. Table 2 indicates that a higher HCl concentration in the HCl/CaCl2 solution led to both a loss of metal gloss and a reduction in the dipping time required for peeling. Peeling did not occur with dipping in distilled water. In addition, the dipping time required to cause a loss of metal gloss was almost the same as the dipping time to produce peeling. It
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K. Watanabe et al. / Progress in Organic Coatings 53 (2005) 17–22
Fig. 2. Relation between area ratio of indium particles and width of peeling.
was thought that both the loss of metal gloss and the peeling were caused by dissolution of indium by the HCl in solution, and that the peeling was caused by condensation water in the spaces where indium had dissolved by penetration of the solution of HCl in the evaporated indium layer. The clearcoat was considered to result from the condensed water’s osmotic pressure producing a force to promote peeling. The dissolution of the indium layer is also discussed. The aqueous solution was analyzed after the dipping test. Indium was detected by an ICP Optical Emission Spectrometer. This result confirmed that indium was dissolved by the HCl/CaCl2 solution. Additionally, it was believed that the hydrogen generated when the indium dissolves was discharged outside the system through the clear-coat. The results shown in Table 2 indicate that the presence of CaCl2 affected the dipping time to produce peeling, and that peeling did not occur in CaCl2 aqueous solution. Peeling occurred easily with HCl/CaCl2
Fig. 3. SEM images of cross-section of evaporated indium layer; (a) indium applied, 0.3 g; vacuum pressure, 1.33 × 10−2 Pa; (b) indium applied, 0.3 g; vacuum pressure, 1.33 × 10−1 Pa.
solution compared to only HCl solution. The acceleration of peeling by CaCl2 was interpreted as enhancement of the rate of solution penetration. It was thought that CaCl2 penetrating into the coating film caused the high osmotic pressure. The relation between moisture permeability of the clear coating film and dipping time in HCl/CaCl2 solution to produce peeling was investigated, as shown in Fig. 4. Peeling was found to occur easily in the clear-coat having a higher moisture permeability. The relation between dipping time required for peeling and film thickness is shown in Fig. 5. A thinner clear-coat led to peeling in a shorter dipping time. Thus, the dipping time required for peeling was affected by the moisture permeability of the clear coating film. The relation between moisture permeability of the clear coating film and cross-linking density was evaluated for
Table 2 Results of adhesion test after dipping in aqueous solution Indium evaporation conditions Weight
0.1
a b
(g)a
Concentrations HCl (wt%)/CaCl2 (wt%)
Vacuum pressure (Pa) 1.33 × 10−3
0/0 0/2.5 1.0/0 1.0/2.5 1.0/5.0 2.0/0 2.0/2.5 2.0/5.0 4.0/0 4.0/2.5 4.0/5.0
Test time (h) Width of peeling (mm)
Metal glossb
72
168
240
72
168
240
0 0 0 0 0 0 0 0 0 0.3 0.3
0 0 0 0.3 0.3 0 0.3 0.3 0.3 0.5 0.5
0 0 0.3 0.6 0.6 0.3 0.6 0.6 0.5 0.9 0.9
No No No No No No No No No Yes Yes
No No No Yes Yes No Yes Yes Yes Yes Yes
No No Yes Yes Yes Yes Yes Yes Yes Yes Yes
Weight applied via evaporation. Yes: metal gloss was partially lost (confirmed by visual inspection). No: metal gloss was not lost.
K. Watanabe et al. / Progress in Organic Coatings 53 (2005) 17–22
Fig. 4. Relation between moisture permeability of clear coating film and dipping time to produce peeling in a mixed aqueous solution of HCl and CaCl2 .
various clear coating films. The results shown in Fig. 6 reveal that moisture permeability was affected by the cross-linking density of the clear coating film, and that a coating with a lower cross-linking density led to higher moisture permeability. Based on the described results, the indium is considered to be dissolved by the HCl from the HCl/CaCl2 solution which permeates the indium evaporation layer and seems to generate peeling by condensation of the water. The promotion of the peeling by CaCl2 seems to be because of an increase in the water penetration. In addition, it was considered that the higher permeability of clear coating films caused by lower cross-linking density led to peeling in a shorter dipping time in the HCl/CaCl2 solution.
Fig. 5. Relation between thickness of clear-coat and dipping time to produce peeling in a mixed aqueous solution of HCl and CaCl2 .
21
Fig. 6. Relation between cross-linking density and moisture permeability of clear coating film.
4. Conclusions The effects of a mixed aqueous HCl/CaCl2 solution on the coating above the evaporated indium layer can be summarized. (1) Adhesion was affected by the conditions of indium evaporation. More indium applied via evaporation or a lower vacuum pressure led to both reduction in adhesion and loss of metal gloss. (2) A smaller area ratio of indium particles on the evaporated indium layer led to higher adhesion. (3) Peeling was affected by the concentration of HCl. A higher concentration led to peeling in a shorter dipping time, and peeling occurred in a shorter dipping time in the presence of CaCl2 . (4) Peeling was affected by the moisture permeability of the clear coating film. A coating with a lower moisture permeability resulted in peeling after a shorter dipping time. (5) Moisture permeability was affected by the cross-linking density of the clear coating film. A coating with lower cross-linking density resulted in peeling after a shorter dipping time. The peeling was considered to be caused by the condensation of water in the spaces where indium was dissolved by penetration of HCl from the HCl/CaCl2 solution in the evaporated indium evaporation layer. The acceleration of peeling by CaCl2 was interpreted as enhancement in the water penetration rate. In addition, it was considered that a higher permeability of clear coating film caused by lower crosslinking density led to peeling in a shorter dipping time in the HCl/CaCl2 solution.
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Acknowledgement The authors wish to express their gratitude to Professor M. Takeishi of Yamagata University for valuable discussions. References [1] M. Yamanaka, T. Kikugawa, Y. Shichi, M. Arita, M. Ishiwata, M. Mikami, Chem. Express 5 (1990) 609. [2] M. Yamanaka, Nippon Kagaku Kaishi (1991) 999.
[3] M. Yamanaka, Y. Inoue, J. Chem. Soc. Jpn., Nippon Kagaku Kaishi (1991) 1219. [4] K. Watanabe, T. Ishihara, M. Yamanaka, Nippon Kagaku Kaishi (2002) 685. [5] K. Watanabe, T. Ishihara, M. Yamanaka, Nippon Kagaku Kaishi (2002) 165. [6] L.E. Nielsen, J. Macromol. Sci., Rev. Macromol. Chem. C3 (1) (1969) 69. [7] T. Nakamichi, J. Jpn. Soc. Colour Mater. (SHIKIZAI) 57 (1984) 643. [8] K. Kitaoka, Guide of Synthetic Resin for Paint, Kobunshi Kankokai, Japan, 1974, p. 74.
Effect of a mixed aqueous solution of HCl and CaCl2 on adhesion of coating to evaporated indium layer Kentaro Watanabe a,∗ , Masahiko Yamanaka a , Toshiyuki Mozawa b , Norihiko Kobayashi b a
Nissan Motor Co. Ltd., Materials Engineering Department, 560-2, Okatsukoku, Atsugi-shi, Kanagawa 243-0192, Japan b Hashimoto Forming Industry Co. Ltd., 320, Kamiyabe-cho, Totsuka-ku, Yokohama-shi, Kanagawa 245-8511, Japan Received 10 December 2003; accepted 1 December 2004
Abstract The effect of a mixed aqueous solution of HCl and CaCl2 on the adhesion of a coating with an evaporated indium layer was evaluated. Peeling was observed between the evaporated indium layer and the clear-coat after dipping a coated panel in the mixed aqueous solution, and the coating films were seen to lose their metal gloss. Observation of the evaporated indium layer with scanning electron microscope (SEM) revealed various particle sizes of indium. A higher area ratio of indium particles in the indium layer led to faster peeling after dipping the coated panels in the mixed aqueous solution. The effect of the cross-linking density of clear coating film on the peeling between the indium layer and the clear-coat was investigated. A clear coating film with a lower cross-linking density resulted in a shorter peeling time in the mixed aqueous solution. It was considered that the peeling was caused by condensation of water in the spaces where indium was dissolved by penetration of the HCl from the HCl/CaCl2 aqueous solution into the evaporated indium layer. © 2005 Elsevier B.V. All rights reserved. Keywords: Indium; Vacuum evaporation; Adhesion; Urethane coating; Viscoelasticity; Moisture permeability
1. Introduction The performance of automotive coatings is affected by various chemical substances such as acid rain, bird droppings, sap, iron powder and inorganic salts. In a previous paper, we reported that: (1) peeling occurred in adhesion tests of coated films after washing the chrome-plating substrate with water containing inorganic salts[1,2]; (2) iron powder adhesion occurred under high temperature and humidity, adhering easily to a coating film with high moisture permeability[3]; (3) whitening of melamine-cured coating film occurred by addition of inorganic acid and a light stabilizer[4]; and (4) cracking of melamine-cured coating film was affected by the affinity of the 2-methylheptane to the melamine resin and also cracking of the coating film occurred in a shorter time when there was a higher affinity [5]. ∗
Corresponding author. Tel.: +81 46 270 1518; fax: +81 46 270 1585. E-mail address: [email protected] (K. Watanabe).
0300-9440/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2004.12.003
Recently, soft plastic substrates are used as parts for items such as radiator grilles for more stylish automobile design. Surface treatment with evaporated indium is performed on these substrates, as properties such as impact resistance are not obtained in surface treatment with rigid chromium plating and evaporated aluminum. However, indium coatings have poor acid resistance and thus are not suitable for automobiles in contact with acid rain or CaCl2 snow-melt salts. This paper reports on the effect of a mixed aqueous solution of HCl and CaCl2 on the adhesion of coatings with an evaporated indium layer.
2. Experimental 2.1. Sample preparations Indium was evaporated onto an acrylate-isocyanate cured primer, and an acrylate-isocyanate cured clear-coat was
18
K. Watanabe et al. / Progress in Organic Coatings 53 (2005) 17–22
applied and cured. The primer and clear-coat had dry film thicknesses of 20 and 30 m, respectively. Both the primer and the clear-coat were force dried for 60 min at 80 ◦ C. The evaporation occurred under conditions of 0.1, 0.2 and 0.3 g of applied evaporated indium and at vacuum pressures of 1.33 × 10−1 , 1.33 × 10−2 and 1.33 × 10−3 Pa.
dynamic viscoelasticity automatic measurement apparatus. Cross-linking density was obtained from the equation, E = 3nRT (E = Young’s modulus, n = cross-linking density, R = gas constant, T = absolute temperature) [6–8].
2.2. Dipping test in a mixed aqueous solution of HCl and CaCl2
A moisture permeability cup (JIS 0208 standardized) was kept for 0, 4, 8, 12 and 24 h under 50 ◦ C and 50% relative humidity. The moisture permeability weight was measured and plotted against time. The moisture permeability was calculated using the slope of the best-fit line and a free film thickness of 30 m.
A mixed aqueous solution of HCl and CaCl2 was prepared by mixing 30 mL of 12 N HCl and 55 g of CaCl2 in 1000 mL of distilled water. Crosscut test pieces were dipped in the solution of HCl and CaCl2 for 72, 168 and 240 h at 50 ◦ C. Peeling was investigated after drying at room temperature. The peeling test was performed by pulling off tape adhered to the crosscut section, and the width of peeling indicated by the distance from the crosscut line.
2.5. Measurement of moisture permeability
2.6. Analysis of dissolution of indium layer The solution of HCl and CaCl2 was analyzed after the dipping test using an ICP Optical Emission Spectrometer.
2.3. Observation of evaporated indium layer 3. Results and discussion Indium was evaporated from 0.1, 0.2 and 0.3 g of indium and at vacuum pressures of 1.33 × 10−1 , 1.33 × 10−2 and 1.33 × 10−3 Pa. The surface and cross-section of the evaporated indium layers were observed using a Hitachi S-4000 scanning electron microscope. The samples were prepared by platinum sputter with a 15-kV accelerating voltage. The area ratio of indium particles on the evaporated indium layer was determined by portrait analysis of an SEM micrograph focused on the indium evaporation layer. 2.4. Cross-linking density of clear coating film The free films, without the indium or primer layers, were prepared by peeling off the coating films after coating by drying forcedly at 80 ◦ C for 60 min on tin foil. The dry free films were 50 m thick. The viscoelasticity of the free films was measured using a Rheology DVE-V4
Adhesion testing of the coating evaporated was performed under various conditions after dipping in the HCl/CaCl2 solution. Table 1 shows the conditions and results of the coating system with the evaporated indium layer. The results revealed that both peeling and loss of metal gloss occurred, and that the degree of peeling varied. A higher weight of indium applied via evaporation and a lower vacuum pressure resulted in a longer width of peeling from the crosscut section. The longest width of peeling occurred under conditions of 0.3 g applied indium and at 1.33 × 10−1 Pa vacuum pressure. The evaporated indium layer on the primer was observed with SEM. The results of SEM observation are shown in Fig. 1a, b, d and e. It was found that various particle sizes of indium were deposited on the primer. Fig. 1c indicates that there were no particles but instead the indium had formed a film. A higher vacuum pressure led to smaller particle
Table 1 Results after dipping test in a mixed aqueous solution of HCl and CaCl2 a Substrate
Thermo-polyurethane
Primer
Indium evaporation conditions
Clear-coat
Paint
Film thickness (m)
Weight (g)b
Vacuum pressure (Pa)
Film thickness (m)
Paint
Film thickness (m)
Polyurethane
20
0.1
1.33 × 10−1 1.33 × 10−2 1.33 × 10−3 1.33 × 10−1 1.33 × 10−2 1.33 × 10−3 1.33 × 10−1 1.33 × 10−2 1.33 × 10−3
50 30 40 100 70 70 90 100 100
Polyurethane
30
0.2
0.3
a b c
Test time was 168 h. Weight applied via evaporation. Yes: metal gloss was partially lost (confirmed by visual inspection).
Width of peeling (mm)
Metal glossc
0.9 0.3 0.3 7.0 0.3 0.3 30 0.3 0.3
Yes Yes Yes Yes Yes Yes Yes Yes Yes
K. Watanabe et al. / Progress in Organic Coatings 53 (2005) 17–22
19
Fig. 1. SEM images of surface of evaporated indium layer. The quantity of indium applied via evaporation, and vacuum pressure were varied. (a) Indium applied, 0.1 g; vacuum pressure, 1.33 × 10−1 Pa; (b) indium applied, 0.2 g; vacuum pressure, 1.33 × 10−1 Pa; (c) indium applied, 0.3 g; vacuum pressure, 1.33 × 10−1 Pa; (d) indium applied, 0.2 g; vacuum pressure, 1.33 × 10−2 Pa; (e) indium applied, 0.2 g; vacuum pressure, 1.33 × 10−3 Pa
sizes of indium, and a higher weight of indium applied via evaporation led to larger particle sizes. The effect of the area ratio of indium particles upon adhesion of the evaporated indium layer to the cured primer was clarified by observation with SEM. The results, shown in Fig. 2, indicate that a smaller area ratio of indium particles led to higher adhesion. A cross-section of the evaporated indium layer was observed with SEM. The results are shown in Fig. 3a and b. Fig. 3a shows that the area not occupied with indium particles was the primer layer. Fig. 3b shows complete coverage of the surface of the primer with indium particles. The clear-coat directly applied over the primer did not peel off after dipping in the HCl/CaCl2 solution. From these results, it was
concluded that the coating over the indium evaporation layer was fixed by adhesion between the clear-coat and primer. The coated panel dipped in the HCl/CaCl2 solution resulted in a loss of metal gloss. The effect of HCl and CaCl2 concentration on the loss of metal gloss as well as on the dipping time required to produce peeling was evaluated. Table 2 shows the results of the loss of metal gloss and peeling over time. Table 2 indicates that a higher HCl concentration in the HCl/CaCl2 solution led to both a loss of metal gloss and a reduction in the dipping time required for peeling. Peeling did not occur with dipping in distilled water. In addition, the dipping time required to cause a loss of metal gloss was almost the same as the dipping time to produce peeling. It
20
K. Watanabe et al. / Progress in Organic Coatings 53 (2005) 17–22
Fig. 2. Relation between area ratio of indium particles and width of peeling.
was thought that both the loss of metal gloss and the peeling were caused by dissolution of indium by the HCl in solution, and that the peeling was caused by condensation water in the spaces where indium had dissolved by penetration of the solution of HCl in the evaporated indium layer. The clearcoat was considered to result from the condensed water’s osmotic pressure producing a force to promote peeling. The dissolution of the indium layer is also discussed. The aqueous solution was analyzed after the dipping test. Indium was detected by an ICP Optical Emission Spectrometer. This result confirmed that indium was dissolved by the HCl/CaCl2 solution. Additionally, it was believed that the hydrogen generated when the indium dissolves was discharged outside the system through the clear-coat. The results shown in Table 2 indicate that the presence of CaCl2 affected the dipping time to produce peeling, and that peeling did not occur in CaCl2 aqueous solution. Peeling occurred easily with HCl/CaCl2
Fig. 3. SEM images of cross-section of evaporated indium layer; (a) indium applied, 0.3 g; vacuum pressure, 1.33 × 10−2 Pa; (b) indium applied, 0.3 g; vacuum pressure, 1.33 × 10−1 Pa.
solution compared to only HCl solution. The acceleration of peeling by CaCl2 was interpreted as enhancement of the rate of solution penetration. It was thought that CaCl2 penetrating into the coating film caused the high osmotic pressure. The relation between moisture permeability of the clear coating film and dipping time in HCl/CaCl2 solution to produce peeling was investigated, as shown in Fig. 4. Peeling was found to occur easily in the clear-coat having a higher moisture permeability. The relation between dipping time required for peeling and film thickness is shown in Fig. 5. A thinner clear-coat led to peeling in a shorter dipping time. Thus, the dipping time required for peeling was affected by the moisture permeability of the clear coating film. The relation between moisture permeability of the clear coating film and cross-linking density was evaluated for
Table 2 Results of adhesion test after dipping in aqueous solution Indium evaporation conditions Weight
0.1
a b
(g)a
Concentrations HCl (wt%)/CaCl2 (wt%)
Vacuum pressure (Pa) 1.33 × 10−3
0/0 0/2.5 1.0/0 1.0/2.5 1.0/5.0 2.0/0 2.0/2.5 2.0/5.0 4.0/0 4.0/2.5 4.0/5.0
Test time (h) Width of peeling (mm)
Metal glossb
72
168
240
72
168
240
0 0 0 0 0 0 0 0 0 0.3 0.3
0 0 0 0.3 0.3 0 0.3 0.3 0.3 0.5 0.5
0 0 0.3 0.6 0.6 0.3 0.6 0.6 0.5 0.9 0.9
No No No No No No No No No Yes Yes
No No No Yes Yes No Yes Yes Yes Yes Yes
No No Yes Yes Yes Yes Yes Yes Yes Yes Yes
Weight applied via evaporation. Yes: metal gloss was partially lost (confirmed by visual inspection). No: metal gloss was not lost.
K. Watanabe et al. / Progress in Organic Coatings 53 (2005) 17–22
Fig. 4. Relation between moisture permeability of clear coating film and dipping time to produce peeling in a mixed aqueous solution of HCl and CaCl2 .
various clear coating films. The results shown in Fig. 6 reveal that moisture permeability was affected by the cross-linking density of the clear coating film, and that a coating with a lower cross-linking density led to higher moisture permeability. Based on the described results, the indium is considered to be dissolved by the HCl from the HCl/CaCl2 solution which permeates the indium evaporation layer and seems to generate peeling by condensation of the water. The promotion of the peeling by CaCl2 seems to be because of an increase in the water penetration. In addition, it was considered that the higher permeability of clear coating films caused by lower cross-linking density led to peeling in a shorter dipping time in the HCl/CaCl2 solution.
Fig. 5. Relation between thickness of clear-coat and dipping time to produce peeling in a mixed aqueous solution of HCl and CaCl2 .
21
Fig. 6. Relation between cross-linking density and moisture permeability of clear coating film.
4. Conclusions The effects of a mixed aqueous HCl/CaCl2 solution on the coating above the evaporated indium layer can be summarized. (1) Adhesion was affected by the conditions of indium evaporation. More indium applied via evaporation or a lower vacuum pressure led to both reduction in adhesion and loss of metal gloss. (2) A smaller area ratio of indium particles on the evaporated indium layer led to higher adhesion. (3) Peeling was affected by the concentration of HCl. A higher concentration led to peeling in a shorter dipping time, and peeling occurred in a shorter dipping time in the presence of CaCl2 . (4) Peeling was affected by the moisture permeability of the clear coating film. A coating with a lower moisture permeability resulted in peeling after a shorter dipping time. (5) Moisture permeability was affected by the cross-linking density of the clear coating film. A coating with lower cross-linking density resulted in peeling after a shorter dipping time. The peeling was considered to be caused by the condensation of water in the spaces where indium was dissolved by penetration of HCl from the HCl/CaCl2 solution in the evaporated indium evaporation layer. The acceleration of peeling by CaCl2 was interpreted as enhancement in the water penetration rate. In addition, it was considered that a higher permeability of clear coating film caused by lower crosslinking density led to peeling in a shorter dipping time in the HCl/CaCl2 solution.
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