AQUEOUS DISPERSANT COMPOSITION

Abstract

The invention relates to aqueous composition having a continuous aqueous phase, wherein the composition comprises•a) a polymer having a polymer backbone having carboxylic acid groups covalently linked to the polymer backbone, dissolved in the continuous aqueous phase, wherein 10 to 100 mol-% of the acid groups are neutralized by a base selected from ammonia, and amines having 1 to 12 carbon atoms, and mixtures thereof, •b) a polyalkylene oxide terminated at one end by a hydrocarbyl group having 8 to 30 carbon atoms, and, •c) a compound according to formula (I) (Formula I)•wherein R.sup.1 is an aliphatic or aromatic hydrocarbon with 3 to 10 carbon atoms, R.sup.2 is H or CH.sub.3 and n is 1 or 2, •wherein components a), b), and c) together have an acid value in the range of 20 to 200 mg KOH/g, •and wherein the polymer has one or more pendant groups (A) connected to the polymer backbone by a covalent link, wherein the pendant group (A) comprises a polyalkylene oxide segment and a hydrocarbyl segment having 8 to 30 carbon atoms, and wherein the polyalkylene oxide segment is located between the hydrocarbyl segment and the covalent link.

##STR00001##

Claims

1. An aqueous composition comprising: a continuous aqueous phase, a polymer comprising a polymer backbone including carboxylic acid groups covalently linked to the polymer backbone, dissolved in the continuous aqueous phase, wherein 10 to 100 mol-% of the carboxylic acid groups are neutralized by a base including one or more of ammonia, an amine having 1 to 12 carbon atoms, and mixtures thereof, a polyalkylene oxide terminated at one end by an aliphatic hydrocarbyl group having 8 to 30 carbon atoms, and a compound according to formula (I) ##STR00006## wherein R.sup.1 is an aliphatic or aromatic hydrocarbon with 3 to 10 carbon atoms, R.sup.2 is H or CH.sub.3 and n is 1 or 2, wherein the polymer, the polyalkylene oxide, and the compound according to formula (I) together have an acid value in the range of 20 to 200 mg KOH/g, and wherein the polymer has one or more pendant groups (A) connected to the polymer backbone by a covalent link, wherein a pendant group of the one or more pendant groups (A) comprises a polyalkylene oxide segment and a hydrocarbyl segment having 8 to 30 carbon atoms, and wherein the polyalkylene oxide segment is located between the hydrocarbyl segment and the covalent link.

2. The composition according to claim 1, wherein the polymer has one or more pendant groups (B) connected to the polymer backbone by a covalent link, wherein a pendant group of the one or more pendant groups (B) comprises one aromatic or aliphatic group and 1 or 2 non-cyclic ether groups, and wherein the 1 or 2 non-cyclic ether groups are located between the aromatic or aliphatic group and the covalent link.

3. (canceled)

4. The composition according to claim 1, wherein the polymer comprises repeating units of polymerized ethylenically unsaturated monomers.

5. The composition according to claim 4, wherein the ethylenically unsaturated monomers comprise one or more of vinyl aromatic monomers, carboxylic acid-functional monomers, and carboxylic anhydride-functional monomers.

6. The composition according to claim 4, wherein the ethylenically unsaturated monomers include one or more of a combination of styrene and maleic anhydride, a combination of alpha-methylstyrene and maleic anhydride, and a combination of alpha-methyl styrene, styrene, and maleic anhydride.

7. The composition according to claim 1, wherein the base includes one or more of ammonia and an amine that has a boiling point of at most 100° C. at a pressure of 1000 mbar.

8. (canceled)

9. An aqueous coating composition comprising i) water, ii) a film-forming binder, and iii) the composition according to claim 1.

10. The aqueous coating composition according to claim 9, wherein the composition further comprises solid particles.

11. The aqueous coating composition according to claim 10, wherein the solid particles are selected from pigments and fillers.

12. A process for preparing an aqueous composition comprising a continuous aqueous phase, the process comprising: providing a copolymer comprising cyclic carboxylic anhydride groups, in the absence of water, reacting the cyclic carboxylic anhydride groups of the copolymer with a polyalkylene oxide and a compound and generating carboxylic acid groups, wherein the polyalkylene oxide is terminated at one end by an aliphatic hydrocarbyl group having 8 to 30 carbon atoms, and the compound is of the following formula (I): ##STR00007## wherein R.sup.1 is an aliphatic or aromatic hydrocarbon with 3 to 10 carbon atoms, R.sup.2 is H or CH.sub.3 and n is 1 or 2, wherein the copolymer comprising the carboxylic acid groups, the polyalkylene oxide, and the compound together have an acid value in the range of 20 to 200 mg KOH/g, neutralizing 10 to 100 mol-% of the carboxylic acid groups of the copolymer by adding a base including one or more of ammonia an amine having 1 to 12 carbon atoms, and mixtures thereof, diluting the mixture of the copolymer, the polyalkylene oxide, and the compound with water.

13. The process according to claim 12, said carboxylic acid groups being neutralized with an aqueous solution of said base.

14. A process of dispersing solid particles in an aqueous composition comprising combining the aqueous composition of claim 1 with solid particles.

Description

EXAMPLES

[0073] Methods of Analysis:

[0074] Acid and amine values may be calculated based on raw materials used or determined by titration.

[0075] Measurement of Acid Values

[0076] The acid value is the KOH quantity in mg that is required for neutralizing 1 g of substance. The acid values were determined by a neutralization reaction with a 0.1 N KOH in Ethanol according to DIN EN ISO 2114.

##STR00005##

[0077] Measurement of Amine Values

[0078] The amine number is the amount KOH in mg which corresponds to the amine content of 1 g of substance. The amine values were determined according to DIN 16945 by potentiometric titration with 0.1 N perchloric acid in acetic acid.

R—NH.sub.2+HClO.sub.4.fwdarw.R—NH.sub.3.sup.++ClO.sub.4.sup.−

TABLE-US-00001 Used (raw) materials: DISPERBYK P1* (comparative example); BYK-Chemie GmbH, Acidic 190 W&D additive with polyether side chains and without neutralization (acid value 10 mg KOH/g, 40% active substance) Lutensol C.sub.13-C.sub.15 Oxo alcohol ethoxylate with 11 ethylene oxide AO 11 units, purchased from BASF SE SMA 2000 Styrene maleic anhydride copolymer, ratio of styrene/maleic anhydride 2/1, acid value 355 mg KOH/g, purchased from Cray Valley SMA 3000 Styrene maleic anhydride copolymer, ratio of styrene/maleic anhydride 3/1, acid value 285 mg KOH/g, purchased from Cray Valley

[0079] Synthesis of Wetting and Dispersing Additives:

P2* (Comparative Example)

[0080] Preparation according to US 2010/0322879 A1, Examples Polymer 1, page 5, paragraph [0086] to [0090]. 50 g of the polymer solution 4 were mixed and homogenized with 50 g of ester 1. Acid value: <1.0 mg KOH/g, amine value: 72.8 mg KOH/g).

P3

[0081] Into a four-necked flask equipped with stirrer, thermometer, reflux condenser and nitrogen inlet tube 95.0 g of methoxypropyl acetate (PMA) were introduced. The solvent was heated up to 50° C. 95.0 g of SMA 2000 were added in portions. After the addition of one portion, the mixture was stirred until the solution got clear again, then the next portion was added. After complete addition, 0.16 g of potassium carbonate were added and the mixture was heated up to 145° C. When the temperature had reached 80° C. a mixture of 64.2 g Lutensol AO 11 and 29.9 g 2-(2-phenoxyethoxy)ethanol was metered in within 60 minutes. After complete addition, the reaction mixture was stirred at 145° C. for 3 hours. The solvent was distilled off under reduced pressure and the mixture was cooled down to 97° C. At this temperature, a diluted solution of ammonia (437.6 g water and 21.0 g ammonia (25%)) was metered in at a rate that the temperature did not fall below 80° C. After complete addition, the reaction mixture was stirred at 80° C. for 1 hour. (Acid value: 27.1 mg KOH/g, amine value: 26.2 mg KOH/g). Calculated on the sum of a), b) and c), the following acid- and amine values were determined: Acid value: 90.3 mg KOH/g, amine value: 87.3 mg KOH/g.

P4

[0082] Into a four-necked flask equipped with stirrer, thermometer, reflux condenser and nitrogen inlet tube 60 g of methoxypropyl acetate (PMA) were introduced. The solvent was heated up to 50° C. 60 g of SMA 3000 were added in portions. After the addition of one portion, the mixture was stirred until the solution got clear again, then the next portion was added. After complete addition, 0.15 g of potassium carbonate were added and the mixture was heated to 145° C. When the temperature had reached 80° C., a mixture of 29.5 g Lutensol AO 11 and 17.7 g 2-butoxyethanol was metered in within 60 minutes. After complete addition, the reaction mixture was stirred at 145° C. for 1 hour. The solvent was distilled off under reduced pressure and the mixture was cooled down to 97° C. At this temperature a slow addition of 183.8 g water was started and at 86° C. a slow addition of 15.4 g triethylamine was started additionally. The temperature was slowly reduced to 80° C. and the reaction mixture was stirred at this temperature for 3 hours. (Acid value: 44.0 mg KOH/g, amine value: 28.9 mg KOH/g). Calculated on the sum of a), b) and c), the following acid- and amine values were determined: Acid value: 110.0 mg KOH/g, amine value: 72.3 mg KOH/g.

P5

[0083] Into a four-necked flask equipped with stirrer, thermometer, reflux condenser and nitrogen inlet tube 60 g of methoxypropyl acetate (PMA) were introduced. The solvent was heated up to 50° C. 60 g of SMA 3000 was added in portions. After the addition of one portion, the mixture was stirred until the solution got clear again, then the next portion was added. After complete addition, 0.13 g of potassium carbonate were added and the mixture was heated to 145° C. When the temperature had reached 80° C., a mixture of 29.5 g Lutensol AO 11 and 13.7 g 2-phenoxyethanol was metered in within 60 minutes. After complete addition, the reaction mixture was stirred at 145° C. for 1 hour. The solvent was distilled off under reduced pressure. The mixture was cooled down to 97° C. A diluted solution of ammonia (150.8 g water and 10.3 g Ammonia (25%)) was metered in at a rate that the temperature did not fall below 80° C. After complete addition, the reaction mixture was stirred at 80° C. for 1 hour. (Acid value: 36.8 mg KOH/g, amine value: 29.0 mg KOH/g). Calculated on the sum of a), b) and c), the following acid- and amine values were determined: 92.0 mg KOH/g, amine value: 72.5 mg KOH/g.

P6

[0084] Into a four-necked flask equipped with stirrer, thermometer, reflux condenser and nitrogen inlet tube 47.5 g of methoxypropyl acetate (PMA) were introduced. The solvent was heated up to 50° C. 47.5 g of SMA 2000 was added in portions. After the addition of one portion, the mixture was stirred until the solution got clear again, then the next portion was added. After complete addition, 0.16 g of potassium carbonate were added and the mixture was heated to 145° C. When the temperature had reached 80° C., a mixture of 29.8 g Lutensol AO 11 and 18.3 g 2-(2-phenoxyethoxy)ethanol was metered in within 60 minutes. After complete addition, the reaction mixture was stirred at 145° C. for 3 hours. The solvent was distilled off under reduced pressure and the mixture was cooled down to 100° C. A diluted solution of ammonia (221.5 g water and 9.8 g Ammonia (25%)) was metered in at a rate that the temperature did not fall below 80° C. After complete addition, the reaction mixture was stirred at 80° C. for 1 hour. (Acid value: 27.4 mg KOH/g, amine value: 22.8 mg KOH/g). Calculated on the sum of a), b) and c), the following acid- and amine values were determined: Acid value: 91.3 mg KOH/g, amine value: 76.0 mg KOH/g.

APPLICATION TESTING

[0085]

TABLE-US-00002 Used raw materials Demineralized water BYK-024 BYK-Chemie GmbH, VOC-free silicone-containing defoamer for aqueous emulsion lacquers, printing inks, overprint varnishes, and emulsion adhesives Acticide MBS Thor Specialities Ltd., Mixture of 1,2-benzisothiazolin-3- one (2.5%) and 2-methyl-4-isothiazolin-3-one (2.5%). Industrial microbiocide, algicide & fungicide BYK-420 BYK-Chemie GmbH, Liquid rheology additive for aqueous and water-reducible coating systems Bayferrox micronized iron oxide red 130M Heliogen BASF, Alpha-modified phthalocyanine blue organic Blue L6900 pigment AMP 90 Angus Chemical Company, 2-amino-2-methyl-1-propanol containing 10% water Kronos 2190 Kronos International, Inc., Titanium dioxide, rutile type produced by the sulphate process Calcilit Alpha Calcit Fullstoff Gesellschaft mbH & Co. KG, Super G calcium carbonate Alberdingk Alberdingk Boley GmbH, self-crosslinking and adhesion AC 2403 promoted two phase acrylic dispersion BYK-349 BYK-Chemie GmbH, Silicone surfactant for aqueous coatings, adhesives and maintenance products Texanol Eastman Chemical Company, Co-Solvent, 2,2,4- Trimethyl-1,3-pentanediol Monoisobutyrate Nalzin Elementis Specialties, Inc., corrosion inhibitor for FA 179 aqueous paint systems to counteract the formation of flash-rust OPTIFLO-T BYK-Chemie GmbH, VOC-free associative thickener 1000 (HEUR) for aqueous systems to generate a Newtonian flow behavior

[0086] 1. Pigment Stabilization

[0087] 1.1. Production of Pigment Concentrates and White Base

[0088] According to the formulation below, pigment concentrates with Bayferrox 130 M and Heliogen Blue L6900 were prepared. For Bayferrox 130 M, the amount of dispersing agent, based on non-volatile content thereof, was 10% by weight, calculated on the weight of the pigment. For Heliogen Blue L 6900, the amount of dispersing agent, based on non-volatile content thereof, was 40% by weight, calculated on the weight of the pigment.

TABLE-US-00003 Pigment concentrate Bayferrox 130 M (Color Index PR 101) weight [g] Heliogen Blue L 6900 weight [g] Water 70.2  55.2  70.2  70.2  55.2  93.9  28.9  17.2  28.9  28.9  17.2  47.2   P1* 45.0  — — — — — 35.0  — — — — — P3 — 60.0  — — — — — 46.7  — — — — P4 — — 45.0  — — — — — 35.0  — — — P5 — — — 45.0  — — — — — 35.0  — — P6 — — — — 60.0  — — — — — 46.7  —  P2* — — — — — 21.3  — — — — — 16.7  BYK-024 3.0 3.0 3.0 3.0 3.0 3.0 1.0 1.0 1.0 1.0 1.0 1.0 Acticide MBS 0.3 0.3 0.3 0.3 0.3 0.3 0.1 0.1 0.1 0.1 0.1 0.1 BYK-420 1.5 1.5 1.5 1.5 1.5 1.5 — — — — — — Pigment 180.0  180.0  180.0  180.0  180.0  180.0  35.0  35.0  35.0  35.0  35.0  35.0  300.0  300.0  300.0  300.0  300.0  300.0  100.0  100.0  100.0  100.0  100.0  100.0 

[0089] All components from the table above were added in the same order as in the formulation into a temperature controlled grinding vessel. After addition of each component, the mixture was homogenized with a spatula. The dispersion was done with a vertical beadmill using a teflon disk, 4.5 cm 0 (Dispermat CV, Getzmann GmbH) with the following parameters:

[0090] Grinding Conditions: [0091] Grinding time: 30 min (Bayferrox 130 M)/40 min (Heliogen Blue L6900) [0092] Speed: 8000 rpm (Bayferrox 130 M)/10000 rpm (Heliogen Blue L6900) [0093] Grinding media: Glass beads (1.0-1.3 mm 0), removed after dispersion by filter (Glass beads: pigment concentrate 1:1 by weight) [0094] Temperature: 20° C.

[0095] White base was produced according to the following formulation:

TABLE-US-00004 Pos. Raw material weight [g] 1 Demin. Water 56.8 2 DISPERBYK-190 10.4 3 AMP 90 0.8 4 BYK-024 0.8 5 Kronos 2190 141.6 6 Calcilit Super G 60.0 7 Alberdingk AC 463.2 2403 8 Demin. Water 36.0 9 BYK-349 0.8 10 AMP 90 1.6 11 Texanol 17.6 12 Nalzin FA 179 4.0 13 OPTIFLO-T 1000 4.0 14 BYK-024 2.4 800.0

[0096] Therefore, component 5 and 6 were placed together in an 80 ml PE-cup and component 7 in a 175 ml PE-cup and put aside. In another 80 ml PE-cup, component 1-4 were added in the same order as in the table above and homogenized by using a Dispermat CV (Getzmann GmbH) with a Teflon disk, ø 2.0 cm, for 2 minutes at 4 m/s.

[0097] Then, component 5 and 6 were added to that preparation under stirring and dispersed for 10 minutes at 10 m/s. After finishing this preparation, so called slurry, it was put aside and the 175 ml PE cup, with component 7 in it, was placed under the Dispermat CV. The slurry was then added to component 7 under stirring at 4 m/s.

[0098] In a final step, component 8-14 were added under stirring one after the other and then dispersed for 3 minutes at 4 m/s.

[0099] White base and pigment concentrates were stored for 24 hours at room temperature before continuing.

[0100] 1.2. Testing of Pigment Stabilization Via White Reduction and Rub-Up Test

[0101] First, the white bases were blended with the pigment concentrates to form white reductions of the pigment concentrates. The blending rations are indicated in the table below.

TABLE-US-00005 White Reduction Bayferrox 130M Heliogen Blue L 6900 White Base [g] 36.0 36.5 Pigment concentrate [g] 4.0 3.5 40.0 40.0

[0102] Therefore, the white base was put into a Speedmixer cup (Hauschild Engineering) and the pigment concentrate was added on top. Then the samples were mixed for 1 minute at 2500 rpm with the Speedmixer (DAC 150.1 FVZ, Hauschild Engineering). Afterwards a draw down with a 200 μm wire bar coater was applied on contrast card (byko-chart 2851, BYK-Gardner GmbH). After application, the rub-up test was carried out by rubbing the finger on about ⅓ of the applied area. This was done when the paint got sticky or when there was a certain resistance to the rubbing. Rubbing was continued until the color difference between rubbed and non-rubbed area had reached the highest value and until this color difference remained constant.

[0103] After 24 hours, color difference was measured by measuring the ΔE-values between rubbed and non-rubbed areas with BYK spectro-guide sphere gloss (sample averaging: n=3, observer: D65/10°, geometry: d/8 spin, color system: CIELab; BYK-Gardner GmbH).

[0104] 1.3. Results

TABLE-US-00006 White Bayferrox 130 M Reduction P1* P2* P3 P4 P5 P6 Color 54.8 55.0 54.9 55.1 54.8 55.0 (L*a*b*) 23.5 23.1 23.5 23.2 23.7 23.4 9.1 8.1 8.8 8.4 9.1 8.5 Rub-Up 0.2 −0.1 0.0 −0.1 0.0 0.0 (ΔL*Δa*Δb*) 0.2 0.4 0.1 0.2 0.0 0.1 0.2 0.6 0.2 0.3 0.1 0.2 ΔE* 0.4 0.7 0.2 0.3 0.1 0.2

TABLE-US-00007 White Heliogen Blue L 6900 Reduction P1* P2* P3 P4 P5 P6 Color 52.4 54.1 53.7 54.8 53.1 55.6 (L*a*b*) −15.6 −15.8 −15.9 −16.1 −15.8 −16.6 −35.4 −33.6 −35.2 −33.7 −35.2 −33.3 Rub-Up 1.1 1.0 0.5 0.4 0.4 0.5 (ΔL*Δa*Δb*) 0.3 0.1 0.1 0.1 0.1 0.2 0.2 0.0 0.0 -0.1 0.1 0.1 ΔE* 1.2 1.0 0.5 0.5 0.5 0.5

[0105] White reduction in combination with rub-up is an established method to evaluate the quality of a pigment dispersion. Lower ΔE-values between rubbed and non-rubbed area indicate a better stabilization of the pigments.

[0106] With P3, P4, P5 and P6 an improved pigment stabilization in form of lower ΔE-values between rubbed and non-rubbed area for both tested pigments could be achieved in comparison to P1*, and P2*.

[0107] 2. Anti-Corrosive Performance

[0108] 2.1. Production of Samples According to Formulation

[0109] According to the table below, samples were prepared. The amount of dispersing agent, based on non-volatile content thereof, was 1.5% by weight, calculated on the combined weight of pigment and filler (components 5 and 6 in the table below).

TABLE-US-00008 W&D additive Control P1* P2* P3 P5 P6 active substance — 40 84 30 40 30 [% in water]  1 Demineralized water 7.1 7.1 7.1 7.1 7.1 7.1  2 Wetting and — 1.0 0.5 1.3 1.0 1.3 dispersing additive  3 AMP 90 0.1 0.1 0.1 0.1 0.1 0.1  4 BYK-024 0.1 0.1 0.1 0.1 0.1 0.1  5 Kronos 2190 17.7 17.7 17.7 17.7 17.7 17.7  6 Calcilit Super G 7.5 7.5 7.5 7.5 7.5 7.5  7 Alberdingk AC 2403 57.9 57.9 57.9 57.9 57.9 57.9  8 Demin. Water 5.8 4.8 5.3 4.5 4.8 4.5  9 BYK-349 0.1 0.1 0.1 0.1 0.1 0.1 10 AMP 90 0.2 0.2 0.2 0.2 0.2 0.2 11 Texanol 2.2 2.2 2.2 2.2 2.2 2.2 12 Nalzin FA 179 0.5 0.5 0.5 0.5 0.5 0.5 13 OPTIFLO-T 1000 0.5 0.5 0.5 0.5 0.5 0.5 14 BYK-024 0.3 0.3 0.3 0.3 0.3 0.3 100.0 100.0 100.0 100.0 100.0 100.0

[0110] Therefore, components 5 and 6 were placed together in an 80 ml PE-cup and component 7 in a 175 ml PE-cup and put aside. In another 80 ml PE-cup, component 1-4 were added in the same order as in the table above and homogenized by using a Dispermat CV (Getzmann GmbH) with a Teflon disk, Ø 2.0 cm, for 2 minutes at 4 m/s.

[0111] Then, component 5 and 6 were added to that preparation under stirring and dispersed for 10 minutes at 10 m/s. After finishing this preparation, so called slurry, it was put aside and the 175 ml PE cup, with component 7 in it, was placed under the Dispermat CV. The slurry was then added to component 7 under stirring at 4 m/s.

[0112] In a final step, component 8-14 were added under stirring one after the other and then dispersed for 3 minutes at 4 m/s.

[0113] The samples were stored for 24 h.

[0114] 2.2. Application

[0115] After 24 hours storage, all samples were homogenized by stirring with a spatula and then applied onto cold rolled steel (Gardobond OC panels, Chemetall) by using a 200 μm wire bar coater. Each sample was applied onto 3 panels. After application, the panels were stored for 7 days at room temperature.

[0116] 2.3. Neutral Salt Spray Test (NSS) According to ISO 9227

[0117] Neutral salt spray test was carried out according to DIN EN ISO 9227 after drying for 7 days at room temperature.

[0118] Before putting the panels into the salt spray tester (VLM), a scribe mark was applied in the middle of the coating of each panel (50 mm long, 1 mm wide) by using a scribing tool according to DIN EN ISO 17872, Annex A (e.g. Sikkens). Furthermore, the non-coated areas of the panels, reverse sides and edges, were protected against corrosion with an adhesive tape. After preparing the panels, they were exposed in the salt spray tester for 20 days.

[0119] After 20 days, the panels were removed, dried by paper and immediately evaluated. The loose or delaminated coating was removed along the scribe mark with a special knife (scraper). The scraper was held with its force perpendicular to the panel surface and parallel to the scribe, moving it back and forth across the scribe to remove the coating that suffered loss of adhesion. The coating that still has adhesion was not removed.

[0120] The following formula was used to measure the width of delamination:

[00001]$\mathrm{Wd}\left(\mathrm{mm}\right)=\frac{\mathrm{Average}\mathrm{of}\mathrm{delamination}\mathrm{measured}\mathrm{on}6\mathrm{diff}.Math.\mathrm{points}-1}{2}$

[0121] 2.4. Results

TABLE-US-00009 Neutral salt spray test (DIN EN ISO 9227)- Delamination 480h Panel [mm] Control 1 10 2 13 3 10 P1* 1 14 2 15 3 12 P2* 1 5 2 8 3 8 P3 1 2 2 5 3 5 P5 1 8 2 3 3 6 P6 1 7 2 7 3 3

[0122] The results of the salt spray test show that with the wetting- and dispersing additives P3, P5 and P6 less delamination than without any wetting- and dispersing additive (Control) or with the not inventive wetting- and dispersing additives P1* and P2* was achieved.

[0123] Less delamination means a better adhesion of the coating on the substrate, which correlates to an improvement of corrosion resistance.