Alkaline cerium-based Cr / P / F-free coating composition for metal surface pretreatment

Abstract

The invention relates to a basic cerium-based coating composition for the pretreatment of metal surfaces, said coating composition comprising a source of cerium cations and at least one water-soluble resin comprising at least poly (meth) acrylic acid, a derivative thereof, or a copolymer thereof, said coating composition having a pH of 8.0 to 12.0. A process for preparing such a basic cerium-based coating composition. A method for treating a metal substrate on the basis of such an alkaline cerium-based coating composition and its use for corrosion pretreatment.

Description

Technical Field

[0001] This invention relates to an alkaline, cerium-based, Cr / P / F-free coating composition for metal surface pretreatment, wherein the composition comprises a cerium cation source and a water-based resin. The invention also relates to a method for preparing a conversion coating based on such an alkaline, cerium-based, Cr / P / F-free coating composition. This alkaline, cerium-based, Cr / P / F-free coating composition is environmentally friendly and stable, and further eliminates the need for subsequent washing steps. The conversion coating exhibits good rust prevention, corrosion resistance, and coating adhesion. Background Technology

[0002] Chemical conversion coatings are generally considered an effective method for improving corrosion resistance and adhesion to adjacent layers. Conversion coatings are coatings composed of metal salts (such as chromates) that are formed during and after the dissolution of the metal element, or precipitated from the salt onto the substrate. Due to the health risks associated with the application and disposal of chromate materials, there has been a worldwide effort to develop technically equivalent alternative coatings that do not pose environmental risks.

[0003] Phosphate conversion coatings have demonstrated excellent results on steel and galvanized steel and are widely used in various industries. However, due to drawbacks such as eutrophication, the need for frequent slag removal, additional sealing steps to reduce porosity, and costly energy input, phosphate conversion coatings are not an environmentally friendly option.

[0004] Therefore, new Cr / P-free conversion coating technologies have been extensively studied in recent years. These studies offer corrosion resistance comparable to Cr(VI) systems, but rely on certain complex fluorides and typically a certain amount of free fluorine, especially when used to pretreat various metallic materials in the same pretreatment line. However, fluorine is harmful to the environment and health, and therefore additional occupational safety measures are required when operating such pretreatment baths.

[0005] For over a decade, cerium salts have attracted attention as effective corrosion inhibitors due to their non-toxicity and relative inexpensiveness. The degree of protection provided to aluminum largely depends on the immersion time in CeCl3 solution. Achieving significant protection typically requires long immersion times (e.g., at least 100 hours), making this method commercially unattractive. The possibility of obtaining suitable cerium dip-coatings more quickly using oxidants has been explored. These coatings exhibit good adhesion to the substrate and the film; however, they do not perform as well as films prepared by long-term immersion methods. Scanning electron microscopy characterization revealed the presence of severely cracked regions significantly larger than the average film thickness.

[0006] Silane-based metal surface pretreatment agents can react on metal surfaces to form an intermediate layer capable of connecting organic and inorganic combinations. Compared to traditional hexavalent chromium passivation agents, silane metal surface treatment agents do not contain heavy metal ions (such as Cr). 6+ Phosphate or fluoride ions. However, prolonged storage and / or excessive impurity ions can cause silane solutions to gel, especially cations (such as Fe2+, which is abundant in tap water). 3+ Ca 2+ or Mg 2+ The corrosion resistance of silane films is significantly affected by factors such as the presence of calcium in industrial tap water. 2+ or Mg 2+ When cationic (cationic) substances are unstable, the instability of silane-based metal surface pretreatment agents can lead to product quality errors.

[0007] Therefore, there remains a need to develop Cr-free, P-free, and F-free alternative coatings that are technically equivalent to conventional thin-film conversion coating compositions, are easily prepared with tap water, and maintain a safe and stable pretreatment agent with fewer processing steps on industrial pretreatment lines. Such alternatives to conventional thin-film conversion coating compositions impart significant corrosion resistance and paint adhesion to treated metal substrates. Summary of the Invention

[0008] The present invention relates to an alkaline cerium-based coating composition for metal surface pretreatment, the coating composition comprising: a) a cerium cation source; b) at least one water-soluble resin comprising at least poly(meth)acrylic acid, a poly(meth)acrylic acid derivative, or a poly(meth)acrylic acid copolymer, wherein the pH of the coating composition is from 8.0 to 12.0.

[0009] The present invention relates to a method for preparing a coating composition according to the invention, the method comprising the steps of: a) mixing a cerium cation source with a water-soluble resin to form a composition; and b) then adjusting the pH of the coating composition to 8.0 to 12.0.

[0010] The present invention also relates to a method for pretreating a metal substrate, the method comprising the following wet chemical treatment steps: contacting the metal substrate with the coating composition of the present invention, preferably by spraying and dipping.

[0011] The present invention also relates to an article having at least one portion comprising the treated metal substrate of the present invention. Detailed Implementation

[0012] The invention is described in more detail in the following paragraphs. Unless explicitly stated otherwise, each aspect thus described may be combined with one or more other aspects. In particular, any feature indicated as preferred or advantageous may be combined with one or more other features indicated as preferred or advantageous.

[0013] In the context of this invention, unless the context otherwise requires, the terminology used will be interpreted according to the following definitions.

[0014] Unless the context clearly specifies otherwise, the singular forms “a / an” and “the” as used herein include both the singular and plural references. For example, references to “ion” cover embodiments having one, two, or more ions. Unless the content clearly specifies otherwise, the term “or” as used in this specification and the appended claims is generally used in its meaning including “and / or”.

[0015] The term “comprising / comprises / comprised of” as used herein is synonymous with “including / includes” or “containing / contains”, and is inclusive or open-ended, and does not exclude additional unlisted members, elements, or method steps.

[0016] The definition of numerical endpoints includes all numbers and fractions falling into their respective ranges, as well as the listed endpoints.

[0017] Unless otherwise defined, all terms used in this disclosure (including technical and scientific terms) have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains. Further guidance includes terminology definitions to better understand the teachings of this invention.

[0018] In the context of this disclosure, several terms will be used.

[0019] The term "water-soluble" means that the relevant components or ingredients of a composition are miscible in water over a wide concentration range (e.g., 0-90% by weight or more of water in the total mass of the liquid (medium) portion) to form a single-phase binary aqueous solution. Water-soluble resins are substances that dissolve, disperse, or swell in water, thereby altering the physical properties of an aqueous system in the form of gelation, thickening, or emulsification / stabilization.

[0020] The term "resin" as used in this article is consistent with its common usage in chemistry. When mixed in water, these resins typically form dispersions of micelles rather than true solutions. The particle size ranges from 0.01 to 0.1 micrometers, and a clear mixture is produced without the addition of pigments.

[0021] As used herein, the term "cerium cation source" should refer to any cerium-containing compound that, when dissolved in water, releases cerium cations or counterions centered on cerium atoms.

[0022] Unless otherwise stated, any amount of a compound quantified in “weight %” in the context of this invention should mean an amount as a weight percentage relative to the corresponding total composition. When the amount of a compound is quantified in ppm, the amount refers to parts per million (ppm). -6 ) parts per million (10 -6 (parts by weight).

[0023] The alkalinity of any composition in this invention refers to a pH greater than 8.0, and pH refers to the negative logarithm of the activity of hydrated hydrogen ions at 20°C, base 10.0.

[0024] The description of materials in ionic form also implies the presence of counterions sufficient to produce overall electrical neutrality of the composition (therefore, any counterions implicitly described should preferably be selected from other components explicitly described in ionic form as much as possible; otherwise, such counterions may be freely selected except for those that avoid adverse effects on the purpose of the invention).

[0025] Compound a) Cerium cation source The cerium cation source in this invention is preferably a water-soluble cerium(III) and / or cerium(IV) salt. Furthermore, the water-soluble salts of cerium(III) and / or cerium(IV) are more preferably selected from ammonium cerium(IV) sulfate, ammonium cerium(IV) nitrate, cerium(IV) sulfate, cerium(III) nitrate, cerium(III) acetate, and cerium(III) acetate. The cerium cation source is even more preferably selected from cerium(III) salts, and most preferably from cerium(III) carbonate, cerium(III) nitrate, and cerium(III) acetate.

[0026] The term "water-soluble" as used in this article refers to water solubility in deionized water (κ < 1 μS / cm) at 20°C. -1 The ability to dissolve more than 5 g / L of cerium salt in a solution while maintaining a homogeneous solution for 24 hours without visible precipitate.

[0027] In the alkaline aqueous coating composition of the present invention, the amount of compound a) in terms of elemental cerium is preferably not less than 10 ppm, or not less than 100 ppm, or not less than 150 ppm. If the concentration of water-soluble salt in the coating composition to be applied to a metal substrate is less than 10 ppm, the content of active ingredient is too low to form a protective coating when conventional methods (such as spraying) are applied. On the other hand, the cerium source compound a) in the alkaline aqueous coating composition according to the present invention preferably does not exceed 20,000 ppm, because coating compositions with higher cerium content tend to aggregate or form precipitates. In another preferred embodiment, the aqueous coating composition can be used directly by conventional application methods, and therefore the aqueous coating composition contains compound a) in terms of cerium not exceeding 4,500 ppm, or not exceeding 3,000 ppm, or not exceeding 2,000 ppm, more preferably not exceeding 1,200 ppm, or even more preferably not exceeding 1,000 ppm to ensure optimal formation of a thin protective film.

[0028] Compound b) Water-soluble resin The coating composition of the present invention comprises at least one water-soluble resin having a weight-average molecular weight of 500 g / mol to 120,000 g / mol, and the water-soluble resin comprises at least poly(meth)acrylic acid or its derivatives / copolymers.

[0029] The water-soluble resin also includes one or more selected from the following: polyesters and their derivatives, polyurethanes and their derivatives, phenolic resins and their derivatives, urea resins and their derivatives, and epoxy resins. The above-mentioned water-soluble resins can be used alone or in any combination.

[0030] In some embodiments of the present invention, the concentration of the water-soluble resin in the coating composition is preferably from 10 ppm to 120,000 ppm (0.001 wt% to 12.0 wt%), or from 10 ppm to 20,000 ppm, or from 10 ppm to 10,000 ppm, or from 15 ppm to 2,000 ppm, or from 20 ppm to 1,600 ppm. The lower limit concentration of the water-soluble resin in the coating composition is 10 ppm, or 12 ppm, or 15 ppm, or 18 ppm, or 20 ppm, or 80 ppm, or 100 ppm, or 200 ppm, or 400 ppm, or 600 ppm, or 800 ppm. The upper limit concentration of water-soluble resins is 120,000 ppm, or 80,000 ppm, or 50,000 ppm, or 30,000 ppm, or 20,000 ppm, or 10,000 ppm, or 8,000 ppm, or 6,000 ppm, or 5,000 ppm, or 4,000 ppm, or 2,000 ppm, or 1,800 ppm, or 1,600 ppm.

[0031] The ratio of component a) to component b) (cerium / resin) affects the corrosion resistance of the coating composition according to the invention. In some embodiments, the mass ratio of cerium in the cerium cation source to the water-soluble resin (cerium / resin) is 1:1 to 1:25, or 1:1 to 1:20, or 1:1.5 to 1:15, or 1:2 to 1:10. Preferably, it is preferably in the range of 1:2 to 1:5. If the mass ratio of cerium in the cerium cation source to the water-soluble resin (cerium / resin) exceeds 1:1, the cerium cation source will lead to saturation of the anti-corrosion effect and become uneconomical; furthermore, the stability of the composition will decrease. On the other hand, if the mass ratio of cerium in the cerium cation source to the water-soluble resin (cerium / resin) is less than 1:25, the anti-corrosion effect produced by the cerium cation source is not preferred.

[0032] The term "poly(meth)acrylic acid" in this invention refers to polyacrylic acid and / or polymethacrylic acid. Poly(meth)acrylic acid derivatives refer to poly((meth)acrylic acid), sodium poly(acrylate), ammonium poly(methacrylic acid), poly(vinyl acetate), acrylate-2-acryloylamino-2-methylpropanesulfonic acid copolymer, and other acrylic polymers. The weight-average molecular weight of poly(meth)acrylic acid and its derivatives is from 500 g / mol to 120,000 g / mol, or from 5,000 g / mol to 100,000 g / mol.

[0033] In some embodiments, the content of poly(meth)acrylic acid and its derivatives / polymers thereof is 15% to 100% by weight, or 20% to 99% by weight, or 25% to 90% by weight, or 25% to 85% by weight, based on the total weight of the water-soluble resin.

[0034] Examples of commercially available water-soluble resins include, for example, Acumer 1510 from DOW and NeoRez R-2252 XP from DSM China.

[0035] pH value of high temperature sealing solution The coating composition has a pH value of 8.0 to 12.0, or greater than 8.0 to 12.0, or 8.1 to 12.0, or 8.5 to 12.0, or 9.5 to 11.5, or 9.5 to 11.0, or 10.0 to 11.0. The lower limit of the pH value is 8.0, 8.1, or 8.2, or 8.5, or 8.8, or 9.0, or 9.2, or 9.5, or 10.0; the upper limit of the pH value is 12.0, or 11.8, or 11.6, or 11.5, or 11.2, or 11.0. One or more optional pH adjusters (including a small amount of alkaline component) may be used to adjust the pH value to a higher than the desired operating pH value (if required).

[0036] Examples of pH adjusters include sodium bicarbonate, potassium carbonate, calcium carbonate, sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia, monoethanolamine, triethanolamine, n-butyldiethanolamine, and sodium citrate (disodium citrate, trisodium citrate). Preferred pH adjusters may be sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, and triethanolamine. pH adjusters may be used alone or in combination of two or more of them. The amount of the pH adjuster in the treatment agent only needs to be such that it can be used to adjust the pH of the treatment agent to the desired operating pH value (e.g., in the range of 8.0 to 12.0).

[0037] water The coating composition of the present invention contains water as a solvent to dissolve all components in order to form the coating composition. In some embodiments of the invention, ion-exchanged water, pure water, or industrial tap water is preferably used as a solvent to prepare the coating composition and bath solution therefrom. The amount of water to be added relative to the total amount of the coating composition (treatment agent) may be 80,000 to 99.999% by weight, or 88,000 to 99.999% by weight, or 95,000 to 99.999% by weight, or 97,000 to 99.999% by weight, for example, the balance of the treatment agent (excluding other components).

[0038] The coating composition can be provided in a concentrated form, and the concentrated coating composition can be diluted with deionized water or tap water to provide an operational coating composition having the preferred concentrations listed above.

[0039] Cr / P / F-free The present invention is characterized in that the coating formed by the alkaline aqueous composition substantially prevents corrosion of the metal substrate, especially when an additional organic coating is applied. Therefore, the present invention does not rely on the formation of a coating substantially composed of: chromates; phosphates; fluoride anions and fluorometallate anions; or hydroxides / oxides of elements Zr, Ti, and / or Hf. Thus, the content of each of elements Cr, P, or F in the alkaline aqueous composition of the present invention is less than 100 ppm, preferably less than 10 ppm, more preferably less than 1 ppm. It is also preferred that each of elements Zr, Ti, or Hf is present in the alkaline aqueous composition in an amount of less than 50 ppm, more preferably less than 10 ppm, and even more preferably less than 5 ppm. That is, the coating composition of the present invention has technically equivalent corrosion resistance and does not contain any fluorine-containing, phosphorus-containing, or chromium-containing raw materials.

[0040] Zinc cation source The coating composition of the present invention may further comprise a zinc cation source. Preferably, the zinc cation source in the present invention comprises a water-soluble zinc salt. The water-soluble zinc salt is selected from zinc sulfate, zinc nitrate, zinc acetate, zinc borate, zinc citrate, zinc gluconate, and zinc carbonate. More preferably, the water-soluble zinc salt comprises zinc carbonate, zinc nitrate, and zinc acetate.

[0041] The amount of water-soluble zinc salt to be added, based on elemental zinc, can be from 10 ppm to 1000 ppm, or more preferably from 50 ppm to 300 ppm, relative to the water-based coating composition.

[0042] Optional additives The coating compositions of the present invention may also contain optional additives. The selection of suitable additives for the coating composition depends on the specific intended use of the coating composition and can be determined by those skilled in the art in each case.

[0043] Preparation method of coating composition In some embodiments of the present invention, the coating composition is preferably prepared by the following steps: a) Dissolve a water-soluble resin with a weight-average molecular weight of 500 g / mol to 120,000 g / mol in water while stirring to obtain solution a), wherein the water-soluble resin comprises at least water-soluble polyacrylic acid, sodium poly(acrylate), or acrylate-2-acrylamido-2-methylpropanesulfonic acid copolymer. b) While stirring, add a water-soluble cerium cation source to solution a) obtained in step a) to obtain solution b), and c) Then adjust the pH of the solution obtained in step b) to achieve an appropriate pH value of 8.0 to 12.0.

[0044] The "M" used in this article w "" refers to the weight-average molecular weight and means the theoretical value determined by gel permeation chromatography (GPC) relative to linear polystyrene standards from 1.1 M to 580 Da, and can be performed using the Waters 2695 separation module with a Waters 2414 differential refractometer (RI detector).

[0045] In some embodiments of the present invention, the pH of the coating composition is preferably 8.0 to 12.0, or greater than 8.5 to 12.0, or 9.5 to 11.5, or 10.0 to 11.0. Within the above ranges, the higher the pH value of the pretreated coating composition, the better the corrosion resistance.

[0046] However, due to the instability of silane systems, the pH of silane-containing pretreatment compositions generally does not exceed 9.0 or 10.0, otherwise gelation will occur. However, for the present invention, the pH can exceed 9.5 or 10.0.

[0047] Surprisingly, water-soluble acrylic resins can form stable solutions with cerium salts, and the solutions do not precipitate when the pH is increased to 8.0, 10.0, or even higher. If the pH of the water-soluble resin solution is first adjusted to alkaline (e.g., pH 8.0 or 10.0), the addition of cerium salts readily leads to precipitation. The coating composition is then insufficiently stable for subsequent treatments.

[0048] In some embodiments of the invention, the coating composition is a clear and homogeneous solution without layering or gelation.

[0049] Methods for processing metal substrates A method for treating a metal substrate using a coating composition according to the present invention, the method comprising: a) Bringing the metal substrate into contact with the coating composition, preferably by spraying or dipping; b) After step a), but before any additional coating is applied, and without an intermediate cleaning step, allow the metal substrate to dry.

[0050] As non-limiting examples, the most common metal substrates are cold-rolled steel, hot-rolled steel, galvanized steel, galvanized steel, aluminum, and aluminum alloys.

[0051] The time gap between step a) and step b) should not exceed 24 hours, preferably in ascending order of 24, 12, 6.0, 5.0, 4.0, 3.0, 2.0, 1.0, 0.50, 0.33, 0.1, or 0.01 hours. Preferably, the time gap between step a) and step b) should not exceed 20 minutes, 10 minutes, 5 minutes, or 1 minute.

[0052] The surface of the metal substrate treated according to the two processing steps has good corrosion resistance and rust resistance.

[0053] List of Implementation Plans 1. An alkaline cerium-based coating composition for metal surface pretreatment, said coating composition comprising: a) Cerium cation source; b) At least one water-soluble resin, said water-soluble resin comprising at least poly(meth)acrylic acid, a poly(meth)acrylic acid derivative, or a poly(meth)acrylic acid copolymer. The pH value of the coating composition is 8.0 to 12.0.

[0054] 2. The coating composition according to embodiment 1, wherein the cerium cation source is a water-soluble salt of cerium and / or cerium(IV), preferably a water-soluble salt of cerium.

[0055] 3. The coating composition according to any one of the foregoing embodiments, wherein the water-soluble salt of cerium and / or cerium(IV) is selected from cerium(IV) ammonium sulfate, cerium(IV) ammonium nitrate, chloride, cerium carbonate, cerium nitrate, cerium acetate and cerium sulfide, and preferably selected from cerium nitrate and cerium acetate.

[0056] 4. The coating composition according to any one of the foregoing embodiments, wherein, based on the total weight of the coating composition, the content of the cerium cation source, calculated as cerium, is 10 to 20,000 ppm, preferably 10 to 4,500 ppm, more preferably 15 to 1,800 ppm.

[0057] 5. The coating composition according to any one of the foregoing embodiments, wherein the water-soluble resin further comprises one or more selected from the group consisting of polyester and its derivatives, polyurethane and its derivatives, phenolic resin and its derivatives, urea resin and its derivatives, and epoxy resin.

[0058] 6. The coating composition according to any one of the foregoing embodiments, wherein, based on the total weight of the coating composition, the content of the water-soluble resin is 10 to 120,000 ppm, preferably 15 to 20,000 ppm, more preferably 80 to 8,000 ppm.

[0059] 7. The coating composition according to any one of the foregoing embodiments, wherein, based on the total weight of the water-soluble resin, the content of the poly(meth)acrylic acid, its derivatives, and copolymers thereof is from 15% to 99% by weight, preferably from 25% to 85% by weight.

[0060] 8. The coating composition according to any one of the foregoing embodiments, wherein the coating composition comprises a content of less than 100 ppm, preferably less than 10 ppm, more preferably less than 1 ppm of Cr, P or F calculated as elements Cr, P or F.

[0061] 9. The coating composition according to any one of the foregoing embodiments, wherein the mass ratio of cerium in the cerium cation source to the water-soluble resin is 1:1 to 1:25, preferably 1:1 to 1:20, more preferably 1:1 to 1:5.

[0062] 10. The coating composition according to any one of the foregoing embodiments, wherein the coating composition further comprises a pH adjuster, the pH adjuster comprising one or more selected from sodium hydroxide, potassium hydroxide, ammonia, ammonium bicarbonate, ethanolamine, and triethanolamine.

[0063] 11. The coating composition according to any one of the foregoing embodiments, wherein the pH value of the coating composition is 8.0 to 12.0, preferably 9.0 to 11.5, more preferably 9.5 to 11.0.

[0064] 12. A method for preparing a coating composition according to any one of embodiments 1-11, the method comprising the following steps: a) Mixing the cerium cation source with the water-soluble resin to form a composition; and b) Then adjust the pH of the coating composition to 8.0 to 12.0.

[0065] 13. A method for pretreating a metal substrate, the method comprising the following wet chemical treatment steps: contacting the metal substrate with a coating composition according to any one of embodiments 1-11, preferably by spraying and dipping to contact the metal substrate with the coating composition according to any one of embodiments 1-11.

[0066] 14. The method according to embodiment 13, wherein the metal substrate is dried after the wet chemical treatment step, but before any additional coating is applied, and without an intermediate cleaning step.

[0067] 15. An article having at least one portion comprising a treated metal substrate as described in embodiment 13.

[0068] Example The invention will be further described and illustrated in detail below with reference to the embodiments. These embodiments are intended to help those skilled in the art better understand and practice the invention, but are not intended to limit the scope of the invention. Unless otherwise stated, all figures in the embodiments are based on weight.

[0069] It should be understood that, alternatively, the listed components need not all be provided by individual chemicals.

[0070] raw material

[0071] All raw materials are used directly without any special processing.

[0072] Example 1 <Cleansing / Degreasing> At room temperature, immerse the CRS steel sheet in a mixture of 3% by weight BONDERITE C-AK 1022R and 0.3% by weight BONDERITE C-AD 1023S diluted with deionized water for 5 minutes.

[0073] <Preparation of alkaline cerium-based coating compositions> The alkaline cerium-based coating composition was prepared by the following steps: a) All raw materials were used directly without any special treatment. 10.00 g of cerium nitrate hexahydrate (powder, commercially available from Sinopharm Chemical Reagent Co., Ltd.) and 80.00 g of Acumer 1510 (liquid, commercially available from DOW, manufacturer's indicated Mw = 60000 g / mol and solids content = 25%) were dissolved in deionized water.

[0074] b) Add monoethanolamine (liquid, commercially available from Sinopharm Chemical Reagent Co., Ltd.) to adjust the pH of the solution from step a) to 10.5.

[0075] c) Add deionized water to form a 1 L solution.

[0076] d) Dilute the solution from step c) with deionized water / tap water to obtain the alkaline cerium-based coating composition described in Example 1.

[0077] <Treatment of CRS Steel Plates> CRS steel plates are processed using the following steps: e) An alkaline cerium-based coating composition is applied to a cleaned CRS steel sheet by means of an immersion method in a 2 L plastic beaker for 3 minutes.

[0078] f) Rinse the CRS plate with deionized water (optional).

[0079] g) Dry the liquid layer formed in the previous operation to form the treated surface.

[0080] h) Apply a polyester and epoxy blend-based powder coating (EA067Z from Akzo) electrostatically to the CRS plate using a spray gun to produce a 60-80 μm thick coating.

[0081] Various tests were performed on the treated CRS steel plate samples.

[0082] Examples 2-26 and CE1-CE11 Alkaline cerium-based coating compositions for E2 to E26 and CE1 to CE11 were prepared according to Example 1. CRS steel sheet samples of E2 to E26 and CE1 to CE11 were treated according to Example 1. Further details are listed in the results section below.

[0083] Test methods <Neutral Salt Spray Test> The treated CRS panels were subjected to a neutral salt spray test (NSST according to ASTM B117-03-2019). Corrosion delamination of the powder coating was assessed by the maximum creep at the scribing point after 500 hours of exposure in the above test.

[0084] For performance testing, if the creep value at 500 h NSST does not exceed 2 mm, it is considered good (G); when the creep value at 500 h NSST does not exceed 1.5 mm, it is considered very good (VG).

[0085] <Impact Test> The treated CRS plates were also subjected to impact testing (according to ISO 6272-2-2011). The plates were tested at a 100 kg·cm level, and cracks were observed in the impact zone of the coating. If no cracks appeared on the coated plate, it was marked "OK". Otherwise, it was marked "NG".

[0086] Anti-flush-rust test For the flash rust prevention test, prepare another set of plates, performing only step e) and omitting steps f) through h) of rinsing, drying, and applying powder coating. If no visible red rust appears on the plates within 15 minutes after step e), the plates are considered to have not exhibited flash rust. Mark them as “OK” in Table 1-4. Otherwise, mark them as “NG”.

[0087] <Product Stability (Deionized Water)> For product stability testing, if the coating composition solution (diluted with deionized water) remains clear without the formation of visible precipitates for two weeks at both 0°C and 38°C, the solution is considered stable. Mark it "OK" in Table 1-4. Otherwise, mark it "NG".

[0088] <Product Stability (Tap Water)> For product stability testing, if the paint composition solution (diluted with tap water) remains clear without forming visible precipitates for two weeks at both 0°C and 38°C, the solution is considered stable. Mark it "OK" in Table 1-4. Otherwise, mark it "NG".

[0089] result Table 1 shows the formulations and properties of alkaline cerium-based coating compositions E1 to E10.

[0090] Table 1.

[0091] Table 2 shows the formulations and properties of alkaline cerium-based coating compositions E11 to E19.

[0092] Table 2.

[0093] Table 3 shows the formulations and properties of alkaline cerium-based coating compositions E20 to E26.

[0094] Table 3.

[0095] Table 4 shows the formulations and properties of the comparative coating compositions CE1 to CE11.

[0096] Table 4.

[0097] In Examples 1-26, coating compositions were prepared according to the formulations of alkaline cerium-based coating compositions provided by the present invention. These formulations particularly contain a cerium cation source and at least one water-soluble resin, said water-soluble resin comprising at least poly(meth)acrylic acid, a poly(meth)acrylic acid derivative, or a poly(meth)acrylic acid copolymer, and the pH of the coating composition is from 8.0 to 12.0. It can be seen that when the content of the claimed components of the present invention is within a certain range, they can work synergistically to produce a coating composition with technically equivalent corrosion resistance and paint adhesion, and without any fluorine-containing, phosphorus-containing, or chromium-containing raw materials. Simultaneously, the coating composition has long-term storage capability, is easily prepared with tap water, and remains a safe and stable pretreatment agent with fewer processing steps on industrial pretreatment lines.

[0098] In Comparative Examples 5-9, the coating compositions were prepared using comparative water-soluble resins. The prepared coating compositions did not exhibit the desired storage capacity and could not be prepared using tap water.

Claims

1. An alkaline cerium-based coating composition for metal surface pretreatment, said coating composition comprising: a) Cerium cation source; b) At least one water-soluble resin, said water-soluble resin comprising at least poly(meth)acrylic acid, a poly(meth)acrylic acid derivative, or a poly(meth)acrylic acid copolymer. The pH value of the coating composition is 8.0 to 12.

0.

2. The coating composition according to claim 1, wherein the cerium cation source is a water-soluble salt of cerium and / or cerium(IV), preferably a water-soluble salt of cerium.

3. The coating composition according to claim 2, wherein the water-soluble salt of cerium and / or cerium(IV) is selected from cerium(IV) ammonium sulfate, cerium(IV) ammonium nitrate, chloride, cerium carbonate, cerium nitrate, cerium acetate and cerium sulfide, and preferably selected from cerium nitrate and cerium acetate.

4. The coating composition according to claim 1, wherein, Based on the total weight of the coating composition, the cerium cation source has a content of 10 to 20,000 ppm, preferably 10 to 4,500 ppm, and more preferably 15 to 1,800 ppm, in terms of elemental cerium.

5. The coating composition according to claim 1, wherein the water-soluble resin further comprises one or more selected from the group consisting of polyester and its derivatives, polyurethane and its derivatives, phenolic resin and its derivatives, urea resin and its derivatives, and epoxy resin.

6. The coating composition according to claim 1, wherein, Based on the total weight of the coating composition, the content of the water-soluble resin is 10 to 120,000 ppm, preferably 15 to 20,000 ppm, and more preferably 80 to 8,000 ppm.

7. The coating composition according to claim 1, wherein, Based on the total weight of the water-soluble resin, the content of the poly(meth)acrylic acid, its derivatives, and copolymers thereof is from 15% to 99% by weight, preferably from 25% to 85% by weight.

8. The coating composition according to claim 1, wherein the coating composition comprises a content of less than 100 ppm, preferably less than 10 ppm, more preferably less than 1 ppm of Cr, P or F, calculated as elements Cr, P or F.

9. The coating composition according to claim 1, wherein the mass ratio of cerium in the cerium cation source to the water-soluble resin is 1:1 to 1:25, preferably 1:1 to 1:20, more preferably 1:1 to 1:

5.

10. The coating composition according to claim 1, wherein the coating composition further comprises a pH adjuster, the pH adjuster comprising one or more selected from sodium hydroxide, potassium hydroxide, ammonia, ammonium bicarbonate, ethanolamine, and triethanolamine.

11. The coating composition according to claim 1, wherein the pH value of the coating composition is 8.0 to 12.0, preferably 9.0 to 11.5, more preferably 9.5 to 11.

0.

12. A method for preparing a coating composition according to any one of claims 1-11, the method comprising the following steps: a) Mixing the cerium cation source with the water-soluble resin to form a composition; as well as b) Then adjust the pH of the coating composition to 8.0 to 12.

0.

13. A method for pretreating a metal substrate, the method comprising the following wet chemical treatment steps: contacting the metal substrate with a coating composition according to any one of claims 1-11, preferably by spraying or dipping the metal substrate with the coating composition according to any one of claims 1-11.

14. The method according to claim 13, wherein, The metal substrate is dried after the wet chemical treatment step, but before any additional coating is applied, and without an intermediate cleaning step.

15. An article having at least one portion comprising the treated metal substrate according to claim 13.

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