COMPOSITE COATING FOR ELIMINATING POLLUTION BY HEAVY METAL CHROMIUM AND VOCS FROM SOURCE AND PREPARATION METHOD

Abstract

Disclosed is a composite coating for eliminating pollution by chromium and VOCs from a source, the coating comprising a conversion film layer and a coating surface layer. The conversion film layer is made of a surface pretreatment liquid, and the surface pretreatment liquid comprises the following components: an organic compound A having an aromatic ring and at least two phenolic hydroxyl groups in the molecule thereof, or a hydrate thereof; an ionic compound B containing zirconium and/or titanium and fluorine; a mixed solution C containing manganese fluoride; and an inorganic salt D containing potassium ions or sodium ions. The coating surface layer is an FEVE-type fluorocarbon powder coating layer. Also disclosed is a preparation method for the described composite coating.

Claims

1. A composite coating for eliminating pollution by chromium and VOCs from a source, comprising a conversion film layer and a coating surface layer, wherein: the conversion film layer is made from a surface pretreatment liquid, and the surface pretreatment liquid comprises the following components: an organic compound A having an aromatic ring and at least two phenolic hydroxyl groups in the molecule thereof or a hydrate of the organic compound A; an ionic compound B containing an element of zirconium and/or titanium and fluorine; a mixed solution C containing manganese fluoride; and an inorganic salt D containing potassium ions or sodium ions, wherein the coating surface layer is a FEVE-type fluorocarbon powder coating layer.

2. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 1, wherein the surface pretreatment liquid further comprises a fast penetrating agent E.

3. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 2, wherein the molar concentration of each component of the surface pretreatment liquid is: 0.2 mmol/L to 1.0 mmol/L of the organic compound A having an aromatic ring and at least two phenolic hydroxyl groups in the molecule thereof or the hydrate of the organic compound A; 0.1 mmol/L to 0.5 mmol/L of the ionic compound B containing an element of zirconium and/or titanium and fluorine; 0.1 mmol/L to 0.5 mmol/L of the mixed solution C containing manganese fluoride; and 0.1 mmol/L to 0.5 mmol/L of the inorganic salt D containing potassium ions or sodium ions; and 2×10.sup.−6 mmol/L to 6×10.sup.−6 mmol/L of the fast penetrating agent E, wherein the concentration of the mixed solution C is calculated based on the concentration of manganese ions therein.

4. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 3, wherein a molecular structure of the at least two phenolic hydroxyl groups in the molecule of the organic compound A is: ##STR00008## wherein R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are selected from H or OH, and at least two of R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are OH, and R.sub.1 is selected from an amide group, a carboxyl group, or an aldehyde group.

5. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 4, wherein the organic compound A is selected from one or more of 3,4,5-trihydroxybenzamide, 3,4,5-trihydroxybenzoic acid, 3,4,5-trihydroxybenzaldehyde, and 2,4,6-trihydroxybenzoic acid.

6. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 5, wherein the organic compound A is 3,4,5-trihydroxybenzoic acid.

7. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 3, wherein the ionic compound B is selected from fluozirconic acid and/or fluozirconate or from fluotitanic acid and/or fluotitanate.

8. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 7, wherein the ionic compound B is selected from one or more of potassium fluorozirconate, sodium fluorozirconate, and ammonium fluorozirconate or from one or more of potassium fluorotitanate, sodium fluorotitanate, and ammonium fluorotitanate.

9. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 3, wherein the mixed solution C is prepared by dissolving manganese fluoride dihydrate in dilute sulfuric acid.

10. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 3, wherein the inorganic salt D is one or more of sodium sulfate, potassium sulfate, sodium fluoride, potassium fluoride, sodium hexafluoroaluminate, and potassium hexafluorochlorate.

11. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 3, wherein the fast penetrating agent E is diisooctyl maleate sulfonate.

12. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 3, wherein the FEVE-type fluorocarbon powder coating layer is selected from a fluorocarbon type powder coating with a FEVE resin content of 40% to 100% and with no organic solvent.

13. The composite coating for eliminating pollution by chromium and VOCs from a source according to claim 12, wherein the FEVE-type fluorocarbon powder coating layer is selected from a fluorocarbon type powder coating with a FEVE resin content of 45% to 80% and with no organic solvent.

14. A preparation method of the composite coating for eliminating pollution by chromium and VOCs from the source according to claim 1, comprising: a step (1): forming a conversion film layer on a metal surface by using a surface pretreatment liquid; a step (2): treating the conversion film layer as a transition layer and coating a surface thereof with a FEVE-type fluorocarbon powder coating to form a coating surface layer; and a step (3): curing the coating surface layer to form a composite coating.

15. The preparation method of the composite coating for eliminating pollution by chromium and VOCs from the source according to claim 14, characterized in that, further comprising: before using the surface pretreatment liquid in the step (1), the metal surface is etched, and the etching amount is preferably not less than 1.2 g/m.sup.2.

16. The preparation method of the composite coating for eliminating pollution by chromium and VOCs from the source according to claim 15, characterized in that, wherein a manner of immersion, spraying, or coating is used in the step (1) to allow the surface pretreatment liquid covering the metal surface to form the conversion film layer.

17. The preparation method of the composite coating for eliminating pollution by chromium and VOCs from the source according to claim 16, wherein the pH value of the surface pretreatment liquid is adjusted to 2.6 to 4.2, and the treatment time is 2 minutes to 12 minutes when the manner of immersion is used; the treatment time is 20 seconds to 60 seconds and the spraying pressure is less than 0.05 MPa when the manner of spraying is used; the treatment time is 10 seconds to 20 seconds when the manner of coating is used.

18. The preparation method of the composite coating for eliminating pollution by chromium and VOCs from the source according to claim 17, further comprising: after the manner of immersion, spraying, or coating is performed, the conversion film layer is dried to speed up the forming of the conversion film layer, wherein the drying temperature is 80° C. to 120° C., and the drying time is 10 minutes to 20 minutes.

19. The preparation method of the composite coating for eliminating pollution by chromium and VOCs from the source according to claim 15, wherein the FEVE-type fluorocarbon powder coating is sprayed on the surface of the conversion film layer by means of electrostatic spraying in the step (2), the thickness of spraying is 45 μm to 100 μm when the FEVE resin content of the FEVE-type fluorocarbon powder coating is 40% to 100%; and the thickness of spraying is 45 to 90 μm when the FEVE resin content of the FEVE-type fluorocarbon powder coating is 45% to 80%, wherein in the process of electrostatic spraying, the electrostatic high voltage is 65 kV to 80 kV, the electrostatic current is 10 μA to 15 μA, and the atomization pressure is 0.4 MPa to 0.45 MPa.

20. The preparation method of the composite coating for eliminating pollution by chromium and VOCs from the source according to claim 15, wherein during the curing process in the step (3), the curing temperature is 200° C. to 240° C., and the curing time is 10 minutes to 30 minutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The disclosure is further described in detail through the accompanying figures.

[0074] FIG. 1 is a picture showing effects of a metal surface treated with a conversion film layer.

[0075] FIG. 2 is a SEM image of the conversion film layer.

[0076] FIG. 3 is a partial enlarged view of FIG. 2.

[0077] FIG. 4 is a comparison graph of polarization curves of metal surfaces treated with the conversion film layer and not treated with the conversion film layer.

[0078] FIG. 5 is a comparison graph of alternating current impedances of metal surfaces treated with the conversion film layer and not treated with the conversion film layer.

[0079] FIG. 6 is EDX mapping of FEVE type fluorocarbon resin of a composite coating.

[0080] FIG. 7 is an image of a test of impact resistance of the composite coating.

[0081] FIG. 8 is an image of a test of cupping performance of the composite coating.

[0082] FIG. 9 is an image of a test of flexural properties of the composite coating.

[0083] FIG. 10 is an image of a test of boiling water adhesion performance of the composite coating.

[0084] FIG. 11 is an image of a test of high pressure boiling water adhesion performance of the composite coating.

[0085] FIG. 12 is an image of 2, 000 hours of acetic acid salt spray testing of the composite coating.

[0086] FIG. 13 is a data plot of results of a Florida exposure test for 24 months of the composite coating.

DESCRIPTION OF THE EMBODIMENTS

[0087] The disclosure is further described in detail through the following specific embodiments.

Embodiment 1

[0088] A composite coating is prepared by the following method:

[0089] (1) A metal surface to be treated is etched, and the etching amount is 1.2 g/m.sup.2.

[0090] (2) A surface pretreatment liquid is evenly sprayed on the metal surface to be treated, the spray pressure is 0.03 MPa, and the treatment time is 20 seconds to form a conversion film layer. The surface pretreatment liquid includes the following components in percentage by weight: 0.3 mmol/L of 2,4,6-trihydroxybenzoic acid, 0.5 mmol/L of sodium fluorozirconate, 0.1 mmol/L of diluted sulfuric acid solution of manganese fluoride dihydrate, 0.1 mmol/L of potassium fluoride, and 6×10.sup.−6 mmol/L of sodium diisooctyl maleate sulfonate, and pH is adjusted to 4.2.

[0091] (3) The conversion film layer is dried for 20 minutes, and the temperature is controlled at 80° C.

[0092] (4) The conversion film layer is treated as a transition layer, and a fluorocarbon powder coating with 100% FEVE resin content is sprayed on a surface thereof by electrostatic spraying to form a coating surface layer. The spraying thickness is 45 μm, the high voltage of electrostatic spraying is 70 kV, the electrostatic current is 15 μA, and the atomization pressure is 0.4 Mpa.

[0093] (5) Under the condition of 200° C., the coating surface layer is cured for 30 minutes to form a composite coating.

Embodiment 2

[0094] A composite coating is prepared by the following method:

[0095] (1) A metal surface to be treated is etched, and the etching amount is 1.5 g/m.sup.2.

[0096] (2) A metal to be treated is placed in a surface pretreatment liquid and immersed for 12 minutes to form a conversion film layer. The surface pretreatment liquid includes the following components in percentage by weight: 1.0 mmol/L of 3,4,5-trihydroxybenzoic acid, 0.3 mmol/L of fluorotitanic acid, 0.5 mmol/L of diluted sulfuric acid solution of manganese fluoride dihydrate, 0.2 mmol/L of potassium sulfate, and 2×10.sup.−6 mmol/L of ammonium diisooctyl maleate sulfonate, and pH is adjusted to 2.6.

[0097] (3) The conversion film layer is dried for 10 minutes, and the temperature is controlled at 100° C.

[0098] (4) The conversion film layer is treated as a transition layer, and a fluorocarbon powder coating with 80% FEVE resin content is sprayed on a surface thereof by electrostatic spraying to form a coating surface layer. The spraying thickness is 90 μm, the high voltage of electrostatic spraying is 65 kV, the electrostatic current is 10 μA, and the atomization pressure is 0.45 Mpa.

[0099] (5) Under the condition of 240° C., the coating surface layer is cured for 10 minutes to form a composite coating.

Embodiment 3

[0100] A composite coating is prepared by the following method:

[0101] (1) A metal surface to be treated is etched, and the etching amount is 1.3 g/m.sup.2.

[0102] (2) A surface pretreatment liquid is evenly coated on the metal surface to be treated, and the treatment time is 20 seconds to form a conversion film layer. The surface pretreatment liquid includes the following components in percentage by weight: 0.2 mmol/L of 3,4,5-trihydroxybenzaldehyde, 0.1 mmol/L of ammonium fluozirconate, 0.3 mmol/L of diluted sulfuric acid solution of manganese fluoride dihydrate, 0.5 mmol/L of potassium hexafluorochlorate, and 4×10.sup.−6 mmol/L of sodium diisooctyl maleate sulfonate, and is pH adjusted to 3.0.

[0103] (3) The conversion film layer is dried for 15 minutes, and the temperature is controlled at 120° C.

[0104] (4) The conversion film layer is treated as a transition layer, and a fluorocarbon powder coating with 40% FEVE resin content is sprayed on a surface thereof by electrostatic spraying to form a coating surface layer. The spraying thickness is 100 μm, the high voltage of electrostatic spraying is 80 kV, the electrostatic current is 12 μA, and the atomization pressure is 0.42 Mpa.

[0105] (5) Under the condition of 220° C., the coating surface layer is cured for 20 minutes to form a composite coating.

Embodiment 4

[0106] A composite coating is prepared by the following method:

[0107] (1) A metal surface to be treated is etched, and the etching amount is 1.25 g/m.sup.2.

[0108] (2) A surface pretreatment liquid is evenly coated on the metal surface to be treated, and the treatment time is 10 seconds to form a conversion film layer. The surface pretreatment liquid includes the following components in percentage by weight: 0.5 mmol/L of 3,4,5-trihydroxybenzamide, 0.2 mmol/L of Sodium fluorotitanate, 0.25 mmol/L of diluted sulfuric acid solution of manganese fluoride dihydrate, 0.5 mmol/L of sodium sulfate, and 5×10.sup.−6 mmol/L of sodium diisooctyl maleate sulfonate, and pH is adjusted to 3.5.

[0109] (3) The conversion film layer is dried for 12 minutes, and the temperature is controlled at 85° C.

[0110] (4) The conversion film layer is treated as a transition layer, and a fluorocarbon powder coating with 45% FEVE resin content is sprayed on a surface thereof by electrostatic spraying to form a coating surface layer. The spraying thickness is 60 μm, the high voltage of electrostatic spraying is 70 kV, the electrostatic current is 10 μA, and the atomization pressure is 0.4 Mpa.

[0111] (5) Under the condition of 230° C., the coating surface layer is cured for 15 minutes to form a composite coating.

Embodiment 5

[0112] A composite coating is prepared by the following method:

[0113] (1) A metal surface to be treated is etched, and the etching amount is 1.6 g/m.sup.2.

[0114] (2) A surface pretreatment liquid is evenly sprayed on the metal surface to be treated, the spray pressure is 0.04 MPa, and the treatment time is 60 seconds to form a conversion film layer. The surface pretreatment liquid includes the following components in percentage by weight: 0.3 mmol/L of 2,4-dihydroxybenzoic acid, 0.4 mmol/L of fluozirconic acid, 0.4 mmol/L of diluted sulfuric acid solution of manganese fluoride dihydrate, 0.1 mmol/L of sodium hexafluoroaluminate, and 3×10.sup.−6 mmol/L of sodium diisooctyl maleate sulfonate, and pH is adjusted to 4.0.

[0115] (3) The conversion film layer is dried for 20 minutes, and the temperature is controlled at 80° C.

[0116] (4) The conversion film layer is treated as a transition layer, and a fluorocarbon powder coating with 70% FEVE resin content is sprayed on a surface thereof by electrostatic spraying to form a coating surface layer. The spraying thickness is 70 μm, the high voltage of electrostatic spraying is 75 kV, the electrostatic current is 15 μA, and the atomization pressure is 0.45 Mpa.

[0117] (5) Under the condition of 200° C., the coating surface layer is cured for 20 minutes to form a composite coating.

Embodiment 6

[0118] A composite coating is prepared by the following method:

[0119] (1) A metal surface to be treated is etched, and the etching amount is 1.7 g/m.sup.2.

[0120] (2) A metal to be treated is placed in a surface pretreatment liquid and immersed for 2 minutes to form a conversion film layer. The surface pretreatment liquid includes the following components in percentage by weight: 0.6 mmol/L of 3,4,5-trihydroxybenzoic acid, 0.2 mmol/L of potassium fluorotitanate, 0.25 mmol/L of diluted sulfuric acid solution of manganese fluoride dihydrate, 0.3 mmol/L of potassium sulfate, and 2.5×10.sup.−6 mmol/L of ammonium diisooctyl maleate sulfonate, and pH is adjusted to 3.2.

[0121] (3) The conversion film layer is dried for 15 minutes, and the temperature is controlled at 100° C.

[0122] (4) The conversion film layer is treated as a transition layer, and a fluorocarbon powder coating with 60% FEVE resin content is sprayed on a surface thereof by electrostatic spraying to form a coating surface layer. The spraying thickness is 60 μm, the high voltage of electrostatic spraying is 75 kV, the electrostatic current is 13 μA, and the atomization pressure is 0.45 Mpa.

[0123] (5) Under the condition of 240° C., the coating surface layer is cured for 25 minutes to form a composite coating.

Embodiment 7

[0124] Test of Morphology of Conversion Film Layer

[0125] A metal to be treated is placed and immersed in a surface pretreatment liquid to form a conversion film layer. As shown in FIG. 1, the formed conversion film layer is uniform and flat.

[0126] As shown in FIG. 2 and FIG. 3, it can be seen from the SEM images that the conversion film layer exhibits a honeycomb skeleton structure. This honeycomb skeleton structure provides a good attachment point for the fluorocarbon powder coating, and has a positive impact on the compatibility of the conversion film layer with the fluorocarbon powder coating.

Embodiment 8

[0127] Test of Corrosion Resistance of Conversion Film Layer

[0128] The corrosion resistance of the conversion film layer is evaluated by using the polarization curve graph and the alternating current impedance analysis of the conversion film layer.

[0129] As shown in the comparison graph of the polarization curves of aluminum surfaces treated with the conversion film layer and not treated with the conversion film layer treatment in FIG. 4, the corrosion current density of the samples is significantly reduced after conversion treatment, indicating that the conversion film layer itself has good corrosion resistance.

[0130] As shown in the comparison graph of the alternating current impedances treated with the conversion film layer and not treated with the conversion film layer treatment in FIG. 5, the impedance of the sample treated with the conversion film layer is significantly greater than that of the untreated sample, indicating that the corrosion resistance of the aluminum substrate is considerably improved through the conversion film layer prepared by the disclosure.

[0131] Therefore, it can be seen from the test results in FIG. 4 and FIG. 5 that the corrosion resistance of the metal treated with the conversion film layer is significantly improved compared with that before the treatment.

Embodiment 9

[0132] Test of Adhesion Rate of Composite Coating Fluorocarbon Resin

[0133] The composite coating is tested by EDX mapping, and the results are shown in FIG. 6. It can be seen from the figure that the surface coverage of the fluorocarbon resin is relatively high, indicating that the fluorocarbon resin has good adhesion on the conversion film layer.

Embodiment 10

[0134] Results of Mechanical Property Testing of Composite Coating

[0135] The methods of impact resistance test, cupping resistance test, and bending resistance test of the composite coating are all carried out in accordance with the standard methods of GB/T 5237.4-2017.

[0136] As shown in FIG. 7 to FIG. 9, after the metal treated by the composite coating is tested for impact resistance, cupping resistance, and bending resistance, the composite coating has no obvious cracks and can meet the requirements of the I-level film performance.

Embodiment 11

[0137] The adhesion performance test of the composite coating against boiling water and high pressure boiling water is carried out according to the standard method of GB/T 5237.4-2017.

[0138] As shown in FIG. 10 and FIG. 11, after the test, the composite coating has no color change or peeling off, and the test results are all grade 0.

Embodiment 12

[0139] Acetic Acid Salt Spray Testing and Filiform Corrosion Testing of Composite Coating

[0140] The methods of the acetic acid salt spray testing and the filiform corrosion testing are carried out according to the standard method of GB/T 5237.4-2017.

[0141] As shown in FIG. 12, after 2,000 hours of acetic acid salt spray (AASS) testing, the penetration area along the grid is ≤8 mm.sup.2/10 cm, and the maximum penetration length along the grid is ≤2 mm.

[0142] After 1,000 hours of filiform corrosion (FFC) testing, the maximum length of corrosion is ≤2 mm, the average length of corrosion is ≤2 mm, and the number of filiform corrosion is ≤15/10 cm.

Embodiment 13

[0143] Aging Resistance Testing of Composite Coating

[0144] As shown in FIG. 13, after Florida exposure is performed on the composite coating for 24 months, the coating gloss retention rate is greater than 98%, and after 4,000 hours of QV-B accelerated aging testing, the coating gloss retention rate is greater than 85%.

[0145] After comparative experiments, it is shown that when the abovementioned embodiments 1 to 6 are applied to various common metal materials, equivalent technical effects can be achieved. In the embodiments, the organic compound A having at least two phenolic hydroxyl groups is not limited to the mentioned 3,4,5-trihydroxybenzamide, 3,4,5-trihydroxybenzoic acid, 3,4,5-trihydroxybenzaldehyde, and 2,4,6-trihydroxybenzoic acid, and may also be other organic compounds having the following structure:

##STR00007##

where R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are selected from H (hydrogen) or OH (hydroxyl), and at least two of R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are OH. For instance, R.sub.2 and R.sub.3 are hydroxyl groups, R.sub.3 and R.sub.4 are hydroxyl groups, and R.sub.2 and R.sub.4 are hydroxyl groups, R.sub.2 and R.sub.5 are hydroxyl groups, R.sub.2 and R.sub.6 are hydroxyl groups, R.sub.3 and R.sub.5 are hydroxyl groups, R.sub.3 and R.sub.6 are hydroxyl groups, R.sub.2, R.sub.3, and R.sub.4 are hydroxyl groups, R.sub.2, R.sub.3, and R.sub.5 are hydroxyl groups, R.sub.2, R.sub.3, and R.sub.6 are hydroxyl groups, R.sub.3, R.sub.4, and R.sub.5 are hydroxyl groups, R.sub.2, R.sub.4, and R.sub.5 are hydroxyl groups, etc.; R.sub.1 can be selected from other substituents such as an amide group, a carboxyl group, and an aldehyde group.

[0146] In addition to the benzene ring, other condensed ring compounds may also be used without affecting the implementation of the objective of the disclosure, and similar technical effects may also be produced.

[0147] Similarly, the ionic compound B is selected from fluozirconic acid and fluozirconate or is selected from fluotitanic acid and fluotitanate and includes but not limited to one or more of potassium fluorozirconate, sodium fluorozirconate, ammonium fluorozirconate, potassium fluorotitanate, sodium fluorotitanate, and ammonium fluorotitanate. The cation in the ionic compound B does not affect the implementation of the objective of the disclosure.

[0148] The mixed solution C is prepared by dissolving manganese fluoride dihydrate in dilute sulfuric acid. The inorganic salt D may be various inorganic salts containing potassium ions or sodium ions. The type of the anion has no obvious effect on the formation and performance of the conversion film layer as well as the performance of the final composite coating. The inorganic salt D may be one or more of sodium sulfate, potassium sulfate, sodium fluoride, potassium fluoride, sodium hexafluoroaluminate, potassium hexafluorochlorate, etc.

[0149] The fast penetrating agent diisooctyl maleate sulfonate is an optional component, which accelerates the film-forming speed of the conversion film layer. Even if the fast penetrating agent is not included in the surface pretreatment liquid, it may not hinder the implementation of the objective of the disclosure.

[0150] The content of FEVE resin is selected to be 40% to 100%, and more preferably 45% to 80% for the FEVE type fluorocarbon powder coating, and the remaining components are other powder-type resins. FEVE type fluorocarbon powder coatings within the above content range may achieve similar technical effects.

[0151] It should be noted that the above embodiments are only further descriptions of the disclosure, rather than limitations. Any adjustments or changes made by a person having ordinary skill in the art within the meaning and scope equivalent to the technical solutions of the disclosure should be considered to be included in the protection scope of the disclosure.