Coating formulations with improved color retention

Abstract

The present invention is a coating formulation comprising water, a binder, a rheology modifier, and cerium (III) hydroxycarbonate. The coating formulations of the present invention exhibit improved color retention compared to coating formulations that do not contain cerium (III) hydroxycarbonate.

Description

Background Art

[0001] The present invention relates to coating formulations having improved color retention, and more particularly to paint formulations comprising a cerium (III) hydroxycarbonate additive.

[0002] Cerium (III) carbonate is an effective additive for improving color retention and reducing color change in paint coatings. (See US2021 / 1888227 A1 (Bohling), pages 7-9.) Bohling discloses that a 20 wt% aqueous wet paste of ligand-terminated cerium (III) carbonate particles having a z-average particle size of 110 nm ± 5 nm can be prepared by mixing a solution of ammonium cerium (III) nitrate with a chelating agent (EDTA) and ammonium carbonate, followed by centrifugation and removal of the supernatant. (Page 4, lines 4 to 6 and page 5, lines 1 to 6). Chelating agents are believed to "promote the formation of nano-dispersed particles while stabilizing the particles to prevent agglomeration." (Page 3, lines 27 to 29).

[0003] US 8,637,153 B2 (Cho) discloses (column 10, lines 5 to 29) a method for preparing crystalline cerium (III) carbonate by first contacting a hydrate of Ce (NO3)3 with urea at a temperature in the range of 80°C to 100°C and then adding 10 to 30% by weight of a polymer dispersant, such as polyethylene glycol or polyacrylic acid, to the mixture. (column 10, lines 22 to 24 and column 5, lines 61 to 65.) The water is then removed and the temperature is raised to 140°C. After the reaction is complete, the product can be washed with water to remove unreacted urea and polymer dispersant and then dried to isolate the crystalline solid. The volume average diameter of the experimentally prepared particles is reported to be in the range of 75nm to 90nm (column 12, Table 1); in general, Cho discloses that the particle size can be controlled by varying the amount and molecular weight of the polymer dispersant. (column 8, lines 19 to 30). Cerium (III) carbonate is then used as a precursor to prepare cerium oxide nanoparticles of uniform size. (Column 13, lines 3 to 8).

[0004] There is a need in the paint formulation art to design additives that provide better color retention in paints. Summary of the invention

[0005] The present invention meets the need in the art by providing a coating formulation comprising water, a binder, a rheology modifier, and cerium (III) hydroxycarbonate.The coating formulation of the present invention provides improved color retention and resists unwanted color change. DETAILED DESCRIPTION

[0006] The present invention is a coating formulation comprising water, a polymer binder, a rheology modifier and cerium (III) hydroxycarbonate.

[0007] As used herein, "polymer binder" refers to a polymeric material that forms a film on a desired substrate with or without a coalescing agent. Examples of polymer binders include acrylic, styrene-acrylic, urethane, alkyd, vinyl ester (e.g., vinyl acetate and versatate), and vinyl acetate-ethylene (VAE) polymer binders and combinations thereof.

[0008] Suitable rheology modifiers include hydrophobically modified ethylene oxide urethane polymers (HEUR), alkali swellable emulsions (ASE), hydrophobically modified alkali swellable emulsions (HASE), and hydroxyethyl cellulose (HEC).

[0009] In another aspect, the coating formulation is a paint formulation further comprising an opacifying pigment. Examples of suitable opacifying pigments include TiO2, ZnO and organic opacifying pigments such as opaque polymers.

[0010] In yet another aspect, the coating formulation is a colored formulation further comprising one or more colorants. Examples of suitable colorants include phthalocyanine blue, phthalocyanine green, monoarylate yellow, diarylate yellow, benzimidazolone yellow, heterocyclic yellow, DAN orange, quinacridone magenta, quinacridone violet, organic red (metallized azo red and non-metallized azo red), carbon black, lamp black, black iron oxide, yellow iron oxide, brown iron oxide, red iron oxide.

[0011] Cerium (III) hydroxycarbonate, preferably in the form of a high solids (25 to 75 wt %) aqueous dispersion of cerium (III) hydroxycarbonate, is mixed with one or more ingredients for preparing a paint or pre-paint formulation. The concentration of cerium (III) hydroxycarbonate is typically in the range of 0.2 wt % or 0.5 wt % or 1 wt % to 10 wt % or to 8 wt % or to 6 wt % based on the weight of the paint formulation.

[0012] The dispersion is advantageously prepared by mixing cerium (III) hydroxycarbonate powder with a premix of water and the conjugate base of an acid-functionalized dispersant. As used herein, "carboxylate" refers to a conjugate base (i.e., salt) of a carboxylic acid, wherein at least 90%, or at least 95%, or at least 99% of the carboxylic acid groups of the dispersant are in the form of a salt.

[0013] Suitable carboxylate-functional dispersants include salts of polyacrylic acid and polymethacrylic acid homopolymers and copolymers, such as the sodium salt of polyacrylic acid, which is available as TAMOL TM 963 dispersant (a trademark of The Dow Chemical Company or its affiliates) is commercially available. The pH of the premix is ​​advantageously raised using a suitable base such as ammonium hydroxide, preferably to a pH of ≥ 6.0.

[0014] Based on the weight of the composition, the concentration of water in the dispersion is 20 wt % or 25 wt % or 28 wt % to 70 wt % or to 55 wt % or to 40 wt % or to 35 wt %.Based on the weight of the composition, the concentration of hydroxy cerium carbonate (III) in the composition is generally in the range of 25 wt % or 40 wt % or 55 wt % or 60 wt % or 65 wt % to 75 wt % or to 72 wt % or to 70 wt %.Based on the weight of the composition, the concentration of carboxylate functionalized dispersant is generally in the range of 0.5 wt % or 1 wt % or 1.5 wt % to 5 wt % or to 3 wt % or to 2.5 wt %.

[0015] The cerium (III) hydroxycarbonate powder can be prepared by contacting cerium (III) nitrate and urea at a temperature in the range of 110° C. to 200° C. and in the substantial absence of a polymer dispersant. As used herein, the term "substantially absent a polymer dispersant" refers to less than 5 wt%, preferably less than 1 wt%, more preferably less than 0.1 wt%, and most preferably 0 wt% of a polymer dispersant in a polymer melt of cerium (III) nitrate and urea, based on the weight of cerium (III) nitrate. More specifically, the polymer dispersant refers to polyethylene glycol; a polymer functionalized with a carboxylic acid group, such as polyacrylic acid and polymethacrylic acid; polyvinyl alcohol; or polyvinyl pyrrolidone; or a combination thereof.

[0016] Preferably, the reaction is also carried out in the substantial absence of a chelating agent capable of forming a capping ligand with cerium (III) hydroxycarbonate. The term "substantially absent a chelating agent capable of forming a capping ligand with cerium (III) hydroxycarbonate" refers to less than 1 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt% and most preferably 0 wt% of a chelating agent based on the weight of cerium (III) nitrate, the chelating agent being a) an amine carboxylic acid or a salt thereof, such as ethylenediaminetetraacetic acid (EDTA), ethylenediaminediacetic acid (EDDA) and nitrotriacetic acid (NTA); and b) an amine phosphonic acid or a salt thereof, such as aminotrimethylphosphonic acid (ATMP), 6-amino-2-[bis(carboxymethyl)amino]hexanoic acid and N-(phosphonomethyl)iminodiacetic acid (PIDA).

[0017] As used herein, "cerium (III) nitrate" refers to anhydrous or hydrated cerium (III) nitrate. Cerium (III) nitrate is preferably used as a hydrate, more particularly as a hexahydrate. The reaction of cerium (III) nitrate and urea is most preferably carried out under a net condition (i.e., solvent-free and anhydrous) except the water produced by the hydrate. It is also preferred that the combination of cerium (III) nitrate and urea accounts for at least 95% by weight, or at least 98% by weight, or at least 99% by weight or 100% by weight of the components in the initial reaction mixture.

[0018] The molar ratio of cerium nitrate (III) and urea is preferably in the range of 1:3 or 1:4 or 1:5 to 1:20 or to 1:10 or to 1:8. The reaction is carried out at a temperature in the range of 110°C or 125°C or 140°C to 200°C or to 180°C or to 160°C, continuing the time for a satisfactory conversion rate sufficient to produce the desired product, usually in the range of 1 to 10 hours. It has been found that the particle size of the product can be controlled by adjusting the relative amount of cerium nitrate (III) and urea and by changing the temperature. Generally, it is found that higher temperatures and higher urea: cerium nitrate (III) ratio provide smaller particle size.

[0019] It has been found that the paint formulations of the invention exhibit improved color retention compared to formulations without cerium (III) hydroxycarbonate. The formulations advantageously contain other additives including preservatives, dispersants, surfactants, defoamers, extenders, solvents and coalescing agents.

[0020] Intermediate Example 1 - Preparation of cerium (III) hydroxycarbonate

[0021] Cerium (III) nitrate hexahydrate (30.0 g, 69.1 mmol, 1 eq) and urea (25.0 g, 416 mmol, 6 eq) were added to a round-bottom flask equipped with a stirring bar, a condenser, and a Dean-Stark trap. The solid mixture was heated to 150 ° C and stirred for 5 h. The mixture was cooled to less than 100 ° C, and then water (80 g) was added to wash the material. The aqueous slurry was centrifuged at 18,500 rpm for 5 minutes to separate the solids, followed by three more rounds of washing and centrifugation. The solids were collected and dried at room temperature to produce 13.7 g (91.3% yield) of white powder, which was identified as hexagonal cerium (III) hydroxycarbonate by X-ray powder diffraction. The material exhibited the same powder XRD pattern observed in Figure 7 of Cho.

[0022] Example 1 - Preparation of cerium (III) hydroxycarbonate composition

[0023] TAMOL TM A liquid premix of 963 dispersant (0.07 g), ammonium hydroxide (0.02 g, 28 wt % aqueous solution) and water (1.01 g) was added to a container containing dry cerium (III) hydroxycarbonate (2.33 g) as prepared in Intermediate Example 1. The mixture was pre-dispersed with a glass rod until a slurry of smooth texture was obtained. The slurry was blended for 3 to 5 minutes at 2900 rpm using a Flacktec twin-shaft mixer. The pH of the slurry was found to be 6.5.

[0024] Table 1 shows semi-gloss paint formulations for blue and red paints with and without cerium (III) hydroxycarbonate (Ce(OH)CO3). All values ​​are reported in parts by weight. In-can preservative refers to Kathon LX in-can preservative (1.5 wt% active); dry film preservative refers to Bioban dry film preservative; dispersant refers to TAMOL TM 165A dispersant; HW-1000 surfactant refers to TRITON TM HW-1000 surfactant; defoamer refers to DOWSIL TM 8590 defoamer; TiO2 refers to Ti-Pure R-706TiO2; extender refers to Minex 4 extender; light TiO2 refers to Aeroxide TiO2 P25 (22 wt% active matter); 15-S-12 surfactant refers to TERGITOL TM 15-S-12 surfactant; latex refers to RHOPLEX TM AC-261LF aqueous emulsion; coalescing agent refers to Optifilm Enhancer 400 coalescing agent; RM-3030 refers to ACRYSOL TM RM-3030 rheology modifier; RM-8W refers to ACRYSOL TM RM-8W rheology modifier; the red colorant refers to ColorTrend 808-0836 organic red; and the blue colorant refers to ColorTrend 808-7214 phthalocyanine blue. The light TiO2 is anatase TiO2 and effectively accelerates the paint deterioration process.

[0025] Table 1 - Semi-gloss paint formulations with Ce(OH)CO3

[0026] C Ex1 Ex 1 Ex 2 C Ex 2 Ex 3 Ex 4 Paint Color blue blue blue red red red <![CDATA[ Step 1: Cowles Grinding ]]> water 7.52 7.50 7.47 7.53 7.51 7.48 Preservatives in cans 0.16 0.16 0.16 0.16 0.16 0.16 Dry film preservative 0.53 0.53 0.53 0.53 0.53 0.53 Dispersants 0.80 0.80 0.80 0.80 0.80 0.80 HW-1000 surfactant 0.18 0.18 0.18 0.18 0.18 0.18 Defoaming agent 0.09 0.09 0.09 0.09 0.09 0.09 <![CDATA[TiO2]]> 22.12 22.05 21.98 22.15 22.08 22.01 Bulking Agent 4.42 4.41 4.40 4.43 4.42 4.40 <![CDATA[ Step 2: Flacktec Dispersion Addition ]]> <![CDATA[Ce(OH)CO3 (69 wt% aqueous solution)]]> 0.00 0.64 1.27 0.00 0.64 1.27 <![CDATA[Photonic TiO2]]> 7.94 7.91 7.89 7.95 7.92 7.90 <![CDATA[ Step 3: Unloading ]]> 15-S-12 surfactant 0.18 0.18 0.18 0.18 0.18 0.18 latex 40.35 40.21 40.08 40.40 40.26 40.13 Ammonia (28%) 0.09 0.09 0.09 0.09 0.09 0.09 Defoaming agent 0.05 0.05 0.05 0.05 0.05 0.05 Propylene glycol 0.19 0.19 0.19 0.19 0.19 0.19 Coagulant 1.99 1.99 1.98 2.00 1.99 1.98 RM-3030 0.58 0.59 0.57 0.58 0.59 0.57 RM-8W 0.19 0.22 0.21 0.19 0.22 0.21 water 9.40 9.02 8.70 9.41 9.03 8.71 <![CDATA[ Step 4: Colorant Addition ]]> Red colorant 0.00 0.00 0.00 3.10 3.09 3.08 Blue colorant 3.22 3.21 3.20 0.00 0.00 0.00 gross weight 100 100 100 100 100 100

[0027] Methods for measuring color retention

[0028] ASTM D4587-11 was used to simulate natural exterior weathering from sunlight and moisture cycles typical for exterior coatings. Cycle #4 in Table 1 of the ASTM method describes the conditions used. The weathering experiments were accelerated using a QUV accelerated weathering tester model QUV / se. Q-Panel (AL-363" x 6") chrome-treated aluminum panels were used as substrates for coating applications. A vacuum panel was used to hold the aluminum panels during application of the test paints. The coating was applied at a wet film thickness of approximately 5 mils using the 10-mil edge of a 2" wide multi-gap film applicator. The coated panels were dried in a controlled temperature laboratory (72°F (24°C) / 50% relative humidity) for 7 days prior to exposure to accelerated weathering. L*, a*, b* color values ​​were recorded using a BYK Specto-guide 45 / 0 spectrophotometer (approx. 6801). Color values ​​were recorded prior to exposure in the QUV unit (time = 0) and at approximate increments of 500 h total QUV unit operating time. The 500-h test increments lasted 1951 h, which was found to be sufficient to observe differential degradation between experimental samples. ΔL* was measured to compare test results from exposed panels. Higher ΔL* values ​​(L* f -L* o ) indicates that the color of the exposed paint is lighter, which is a typical characteristic of paint color fading. Table 2 shows the results of the exposure test.

[0029] Table 2 - Exposure test results

[0030] Paint ID ΔL* C Ex 1 3.84 Ex 1 1.82 Ex 2 1.44 C Ex 2 2.77 Ex 3 1.92 Ex 4 1.54

[0031] The ΔL* values ​​for the samples containing cerium (III) hydroxycarbonate show a significant improvement in maintaining hue relative to the control sample.

Claims

1. A coating formulation comprising water, a binder, a rheology modifier and cerium (III) hydroxycarbonate.

2. The coating formulation according to claim 1, which is a paint formulation further comprising an opacifying pigment.

3. The paint formulation of claim 2, further comprising a colorant.

4. The paint formulation of claim 3, wherein the binder is an acrylate or styrene-acrylate polymer binder and the opacifying pigment is TiO 2 , and the rheology modifier is a hydrophobically modified ethylene oxide urethane polymer.

5. The paint formulation of claim 2, wherein the concentration of cerium (III) hydroxycarbonate is in the range of 0.2 wt% to 10 wt% based on the weight of the paint formulation.

6. The paint formulation of claim 4, wherein the concentration of cerium (III) hydroxycarbonate is in the range of 0.5 wt% to 6 wt% based on the weight of the paint formulation.

7. The paint formulation according to any one of claims 2 to 6, further comprising one or more additives selected from the group consisting of preservatives, dispersants, surfactants, defoamers, extenders, solvents and coalescing agents.

8. The paint formulation according to any one of claims 2 to 6, further comprising a dispersant, a surfactant, an extender and a defoamer.

9. A method for preparing a coating composition, the method comprising the step of mixing an aqueous dispersion of cerium (III) hydroxycarbonate and a carboxylate functionalized dispersant with a material comprising a binder and a rheology modifier, wherein the concentration of cerium (III) hydroxycarbonate in the aqueous dispersion is in the range of 25 wt % to 75 wt % based on the weight of the dispersion, and the concentration of the carboxylate functionalized dispersant in the composition is in the range of 0.5 wt % to 8 wt % based on the weight of the dispersion.

10. The method of claim 9, wherein the aqueous dispersion of cerium (III) hydroxycarbonate is further mixed with an opacifying pigment and a colorant; wherein the concentration of cerium (III) hydroxycarbonate in the aqueous dispersion is in the range of 40 wt % to 72 wt % based on the weight of the dispersion, and the concentration of the carboxylate functionalized dispersant is in the range of 1 wt % to 5 wt % based on the weight of the dispersion; and wherein the concentration of cerium (III) carbonate in the composition is in the range of 0.2 wt % to 10 wt %.

11. The method of claim 10, wherein the concentration of cerium (III) hydroxycarbonate in the aqueous dispersion is in the range of 65 wt % to 70 wt % based on the weight of the dispersion, and the concentration of the carboxylate functionalized dispersant is in the range of 1.5 wt % to 3.5 wt % based on the weight of the dispersion, wherein the carboxylate functionalized dispersant is a salt of polyacrylic acid.