Weatherable and durable coating compositions

Abstract

A curable coating composition is provided having multi-functionalized acrylic copolymer and amino-functional silicone resin curing agents. The acrylic copolymer of the curable coating composition has, in polymerized form, epoxy functionalized groups and cure compatibility groups. The coating compositions are useful in the field of superior weatherable and durable coatings and are useful to replace isocyanate-containing polyurethane based coatings. Also provided are coated articles produced from the curable composition.

Claims

1. A curable coating composition comprising: (1) an amino-functional silicone resin of the fully condensed formula
R.sub.xSiO.sub.(4−x)/2 where (a) x is a number from 1.0 to 2.1; (b) the amino-functional silicone resin is comprised of the Si units R.sub.3SiO.sub.1/2, R.sub.2SiO.sub.2/2, RSiO.sub.3/2, and SiO.sub.4/2 in polymerized form, where at least 5 mole percent of the total amount of Si units of the amino-functional silicone resin comprise (i) RSiO.sub.3/2 groups, (ii) SiO.sub.4/2 groups or (iii) mixtures thereof; (c) each R is independently an alkyl group, an aryl group, or an amino-functional hydrocarbyl group, provided that the —NH— equivalent mass of the amino-functional silicone resin is from 50 to 750; and (2) an acrylic copolymer which has, in polymerized form, epoxy functionalized groups and cure compatibility groups; and wherein the coating composition has a molar ratio of amine NH functionality to epoxy functionality in the range of from 0.5 to 1.3.

2. The coating composition of claim 1 having a molar ratio of amine NH functionality to epoxy functionality in the range of from 0.8 to 1.

3. The coating composition of claim 1 wherein the amino-functional silicone resin has less than 30 mole percent of repeat units bearing OR′ groups bound to Si; wherein R′ is hydrogen or a hydrocarbon group.

4. The coating composition of claim 1 wherein the amino-functional silicone resin has at least 10 mole percent of the total amount of Si units of the amino-functional silicone resin comprise (1) RSiO.sub.3/2 groups, (2) SiO.sub.4/2 groups or (3) mixtures thereof.

5. The coating composition of claim 1 wherein the epoxy functionalized groups of the acrylic copolymer are derived from one or more monomers selected from the group of glycidyl methacrylate (GMA), glycidyl acrylate, and mixtures thereof; and wherein the acrylic copolymer has an epoxy equivalent weight (EEW) in the range of 200-600.

6. The coating composition of claim 4 wherein the acrylic copolymer comprises in polymerized form, 30-60% glycidyl(meth)acrylate monomer units by weight based on the weight of the total monomer units of the acrylic copolymer.

7. The coating composition of claim 1 wherein the acrylic copolymer comprises in polymerized form, from 2% to 20% cure compatibility group monomer units by weight based on the weight of the total monomer units of the acrylic copolymer.

8. The coating composition of claim 1 wherein the cure compatibility groups of the acrylic copolymer comprise monomer groups, in polymerized form, that contain one or more of alcohol (OH) functionality, a phenolic group, a tertiary amine or an acid group that is either pendant to the backbone or attached as an end group.

9. The coating composition of claim 1 wherein the cure compatibility group is derived from hydroxyethyl methacrylate (HEMA).

10. A coated article comprising one or more layers of a cured coating composition of claim 1.

Description

EXAMPLES AND EXPERIMENTAL METHODS

(1) Acrylic Copolymers

(2) Xylene was added to a 500 mL 4 neck round bottomed flask, equipped with stir shaft, condenser, thermocouple port and addition ports. A heating mantle was used to bring the temperature of the xylene up to reflux (140° C.). A monomer blend consisting of glycidyl methacrylate (GMA), methyl methacrylae (MMA), 2-ethylhexyl acrylate (EHA), and 2-hydroxyethyl methacrylate (HEMA) was weighed out and mixed in a 500 mL glass jar then divided equally into 50 mL plastic feed syringes with Luer Lock connectors. The initiator, tert-butylperoxyacetate (TBPA, 50% in mineral spirits) was added to a single 50 mL plastic syringe and connected to feed tubing via the Luer Lock connection with long feed needle attachment. A dual syringe pump was used to add monomer mix at a constant feed rate and a single feed syringe pump was used to feed the initiator. The feeds were initiated when the solvent was at reflux. The feed rate time and temperature are dependent on the solvent and the half-life of the initiator. Once feeds were depleted the lines were flushed with small amount of solvent. Run was continued for an additional hour to reduce residual monomer and initiator to acceptable levels. Table 1 shows the acrylic copolymers made.

(3) TABLE-US-00001 TABLE 1 Acrylic copolymers EEW g/mol EEW g/mol % Tg epoxy, as epoxy, on Acrylic GMA MMA EHA HEMA TBPA xylene solids ° C. measured solids A1 Wt % of  40 25    35 0   75% −2 535 400 monomer composition grams 400 250    350 0   120 293 A2 Wt % of  45 17.5   35 2.5 72% −4 456 330 monomer composition grams 450 175    350 25   120 293 A3 Wt % of  40 20    35 5   73% −2 520 380 monomer composition grams 400 200    350 50   120 293 A4 Wt % of  50 10    30 10   73% −3 400 300 monomer composition grams 150 30    90 30    36  88
Acrylic Copolymer Characterization
GPC

(4) Sample was dissolved 2 mg/mL in tetrahydrofuran (THF); solutions were filtered through 0.2 μm PTFE syringe filter prior to injection. Molecular weight measurements were performed with GPC measured on an Agilent 1100 series with MIXED-D columns (300×7.5 mm) at a flow rate of 1.0 mL/min at 35° C. Agilent refractive index detector is used by Agilent GPC/SEC software. Calibration is preformed using 17 narrow PS standards from Polymer labs, fit to a 3rd order polynomial curve over the range of 3,742 kg/mol to 0.580 kg/mol.

(5) EEW

(6) EEW is measured in accordance with ASTM D1652. The epoxy resin is dissolved in methylene chloride and titrated with standardized 0.1N perchloric acid (HC104) in glacial acetic acid in the presence of excess tetraethyl ammonium bromide (TEAB) in acetic acid. Measurements were performed using a Metrohm 905 titrator and the associated Tiamo titration software configured for EEW determinations.

(7) Percent Solids

(8) Label the bottom of a small aluminum pan, place the pan on a scale and record its weight to the closest 0.0000. Distribute approximately 0.5 g-1.5 g of sample evenly in the pan using a pipette. Record that weight as initial (pan+sample). Place on baking pan and clip down with a binder clip before putting sample in oven, cover resin with about 2 grams of toluene using pipette, then carefully place in pre-heated Class A oven. After 2 hours, remove baking pan and samples from the oven. Tare balance and place sample (and pan) on balance and record final weight, and calculate the solids content by the formula:
Solids %=(Final weight−pan weight)/(initial weight−pan weight)*100
Glass Transition Temperature

(9) The T.sub.g was measured with Differential Scanning calorimetry DSC Q2000 V24.10 in accordance with ASTM D7426 with a sample size of about 5-10 mg. The temperature profiles performed as followed: Isotherm at 10° C. for 5 minutes. Ramp to −50 C @ 10° C./minute, isotherm for 5 minutes, ramp to 150 C @ 10°/minute, isotherm for 5 minutes, Tg was analyzed with TA software

(10) Viscosity

(11) Viscosity measurements were taken using the Brookfield DV-III Ultra viscometer with the Small Sample Adapter (SSA). The Small Sample Adapter's rheologically correct cylindrical geometry provides extremely accurate viscosity measurements and shear rate determinations. For these samples 9 mL of material was deposited into the cylinder and spindles #31 or #34 were used and the speed was varied to achieve at torque of −25. Measurements were reported in unites of centipoises (cP).

(12) Amino-Functional Silicone Resins

(13) Amino-functional silicone resin SA1 is a reaction product of hydrolysis and condensation of the following mixture of silanes: phenyltrimethoxysilane (25 wt %), diphenyldimethoxysilane (31 wt %), and hexamethyldisiloxane (HMDS, 17 wt %), with water (1.2 mole/mole Si), catalyzed by trifluoromethanesulfonic acid (TFMSA, 750 ppm relative to the silanes mixture), followed by addition of γ-Aminopropyldiethoxymethylsilane (APDEMS, 27 wt %) to enable its hydrolysis and co-condensation into the silicone resin. Upon removal of by-product alcohols, n-heptane was added, water removed via azeotropic distillation, the reaction mixture filtered and solvent removed by distillation.

(14) Amino-functional silicone resins SB1-SB3 were prepared in the following manner. A mixture of phenyltrimethoxysilane, γ-aminopropyldiethoxymethylsilane (APDEMS), optionally phenylmethyldimethoxysilane, dimethyldimethoxysilane, and/or methyltrimethoxysilane, catalyzed by potassium hydroxide (45% KOH) was optionally dissolved in aromatic solvent (xylenes), hydrolyzed with water, and heated to reflux for three hours. The base catalyst was neutralized by addition of aqueous hydrochloric acid (37% HCl), by-product alcohol removed by distillation and the product filtered. The amount of each ingredient is shown in Table 2. The final amino-functional silicone resin composition and —NH— (amine H) equivalent weight are shown in Table 3.

(15) Amino-functional silicone resins SC1 and SC2 were prepared in the following manner A mixture of phenyltrimethoxysilane and γ-aminopropyldiethoxymethylsilane (APDEMS), xylenes, and catalytic potassium hydroxide (45% KOH) was hydrolyzed with water, followed by distillative removal of by-product alcohol. Additional water was added, and removed by azeotropic distillation. The base catalyst was neutralized with aqueous hydrochloric acid (37% HCl) and water removed via azeotropic distillation. The mixture was filtered and concentrated by distillative removal of a portion of solvent to yield the product amino-functional silicone resin. The amount of each ingredient is shown in Table 2. The final amino-functional silicone resin composition and —NH— (amine H) equivalent weight are shown in Table 3.

(16) Amino-functional silicone SD1 was prepared in the following manner: Aminoethylaminoisobutyldimethoxymethylsilane (AEAiBDMMS) was hydrolyzed with water (3.0 mole/mole Si), followed by distillative removal of by-product alcohol. The final amino-functional silicone resin composition and —NH— (amine H) equivalent weight is shown in Table 3.

(17) TABLE-US-00002 TABLE 2 Mass (g) Example Me.sub.2Si(OMe).sub.2 PhMeSi(OMe).sub.2 APDEMS PhSi(OMe).sub.3 MeSi(OMe).sub.3 Xylene Water 45% KOH 37% HCl SB1 95.0 224.3  180.8 51.8  1.1 0.9 SB2 220.9  229.0 49.5  0.5 0.4 SB3 177.5 565.5  146.6 302.0 561.3 150.3  2.6 2.1 SC1 48.5  451.6 324.5 65.0  1.1 0.9 SC2 665.0 106.8  805.0 199.9  1.8 1.4 Me refers to methyl and Ph refers to phenyl.

(18) TABLE-US-00003 TABLE 3 Mole fraction Mole fraction -NH- T + Q OH + OR′ Amino- Equivalent in amino- in amino- functional Mass functional functional Example silicone resin (g/mol NH) silicone resin silicone resin SA1 R.sub.2.05SiO.sub.0.975 257 0.234 0.038 SB1 R.sub.1.66SiO.sub.1.17 146 0.341 0.115 SB2 R.sub.1.51SiO.sub.1.25 83 0.492 0.148 SB3 R.sub.1.59SiO.sub.1.21 121 0.405 0.120 SC1 R.sub.1.10SiO.sub.1.45 626 0.900 0.018 SC2 R.sub.1.59SiO.sub.1.21 1,060 0.405 0.166 SD1 R.sub.1.99SiO.sub.1.00 58 0.009 0.079
Coating Formulation: Clear Coatings

(19) The clear coating compositions of Table 4 were prepared by the following manner: the acrylic copolymer was placed in a MAX 40 SpeedMixer™ cup and the amino-functional silicone resin was added and mixed for 2 minutes at 2000 rpm in FlackTek™ DAC150 SpeedMixer™.

(20) TABLE-US-00004 TABLE 4 g amino- % solids Molar ratio g Amino- functional of amino- of amine Acrylic functional silicone resin functional functionality Acrylic resin (in silicone (including silicone to epoxy Copolymer solvent) resin solvent) resin functionality Comparative A1 15 SB1 4.1 100% 1:1 Example 1 SE 1 A2 15 SB1 7.1 100% 1:1 SE 2 A3 15 SB1 4.2 100% 1:1 SE 3 A4 15 SA1 9.8 100% 1:1 SE 4 A4 15 SB2 6.4  49% 1:1 SE 5 A4  6 SC1 13.7   68% 1:1 SE 6 A4 15 SB3 6.8  61% 1:1 Comparative A4  5 SC2 16.7   79% 1:1 Example 2 Comparative A4 15 SD1 2.2 100% 1:1 Example 3
Draw Down Application Method for Clear Coat Applications

(21) A coating was applied to Q-Panel R-412-I (phosphate treated cold rolled steel) and AL 412 (chromate treated aluminum) panels according to ASTM D4147. The panel was secured on a firm horizontal surface using a magnetic chuck or clamp. A multiple clearance square applicator was used to apply coating to the panel, 5 to 6 mil wet thickness was targeted to achieve the desired dry film thickness of −2.5 mils.

(22) Coating Formulation: Pigmented Coatings

(23) The pigmented coating composition SE7 was prepared as follows: 30 g acrylic copolymer A4, 0.09 g Dow Corning Additive DC-7, 0.29 g BYK 118, and 29.4 g TS-6200 TiO.sub.2 pigment were measured into a MAX 100 SpeedMixer™ cup; the cup was mixed 5 minutes @ 3000 rpm with SpeedMixer™ model DAC150 FV2-K from FlackTek, Inc. Landrum, SC 29356; fineness of the grind was measured using a Hegman Gauge to assure a value of >6; 9.75 g N-Butyl acetate, 3.0 g Aromatic 100, 1.37 g HALS 292, and 0.09 g Dow Corning Additive DC-11 were added; the mixture was mixed 1 min @ 1500 rpm and allowed to rest overnight; the grind was then mixed for 1 minute @ 1500 rpm followed by adding 19.2 g of amino-functional silicone resin SA1; and the final mixture was mixed 2 minutes @ 1500 rpm, followed by adding about 7 g xylene to lower viscosity for spray, as needed. The molar ratio of amine functionality to epoxy functionality is 1:1.

(24) Comparative Example 4 was prepared in the same manner as coating composition SE7, except that Aradur® 2978-1 was used in place of amino-functional silicone resin SA1. The molar ratio of amine functionality to epoxy functionality is 1:1.

(25) Disperbyk 118, available from BYK Gardner is a wetting and dispersing additive for solvent-borne systems to stabilize acidic, neutral and basic titanium dioxides. DOW CORNING® 7 ADDITIVE, available from The Dow Chemical Company, provides foam prevention and defoaming plus leveling and wetting in solvent-borne systems. TS-6200, available from Chemours, is a TiO.sub.2 pigment. Butyl acetate, available from The Dow Chemical Company, is a solvent. Aromatic 100, available from The Dow Chemical Company, is a tail solvent. Tinuvin® 292, available from BASF Corporation, is a liquid hindered amine light stabilizer. DOW CORNING® 11 ADDITIVE, available from The Dow Chemical Company, provides slip, mar resistance and leveling in solvent-borne systems; also prevents pigment separation. Xylene, available from Fisher, is a thinner/solvent. Aradur® 2978-1, available from Huntsman Advanced Materials, is a low-color, ambient-cure, low-viscosity, cycloaliphatic amine.

(26) Coating Application and Test Methods

(27) Spray Application: Three types of panels were used in the studies (phosphate treated cold rolled steel (CRS), blasted steel, and chromate treated aluminum panels) the phosphate treated and blasted steel panels were cleaned with either a degreaser or shop solvent prior to being sprayed. Paints were put in disposable spray containers equipped with a 200 μm filter and either a 1.4 mm or a 1.8 mm atomizing head was used. The panels were place on a wire rack and sprayed using conventional, air assisted application with 3M™ Accuspray™ System industrial sprayer. Panels were allowed to cure in the lab at a controlled temperature and humidity of 72° F. and 50% relative humidity.

(28) Dry Time: Coatings were drawn down onto 1″×12″ glass substrates with a wet film thickness of 76 micrometers (μm) and set on a BYK drying time recorder. The set-to-touch, tack-free time, and dry hard were measured by dragging a needle through the coating using a BYK drying time recorder according to ASTM D5895-03.

(29) Pendulum Hardness: Pendulum hardness was measured using a Pendulum Hardness Tester from BYK Gardner equipped with a Konig pendulum. The tester was run according to ISO 1522 and set to measure hardness in seconds.

(30) Gloss: The 20°, 60°, and 85° gloss of the coatings were measured according to ASTM D-523-89 using a micro-TRI-gloss meter from BYK Gardner.

(31) Haze: Haze in a clear-coat formulation is measured in accordance with ASTM E430 Test Method B with the micro-haze plus meter from BYK. Coatings were drawn down at 76 um on glass panel and measurements were taken over black Lenta chart. Measurements were logarithmic scaling with brightness compensation.

(32) Methyl Ethyl Ketone Double Rub Test: The methyl ethyl ketone (MEK) double rub test was performed according to ASTM D5402 using the semi-automatic MEK Rub Test machine made by DJH DESIGNS INC. The testing continued until the coating was rubbed through to the substrate or a maximum of 200 double rubs were completed without breakthrough.

(33) Chemical Resistance: The chemical resistance testing was in accordance with ASTM D1308. A couple drops of specified chemicals (including Water, 3% Acetic acid in water, 10% sulfuric acid, 10% sodium hydroxide solution, 3% Sodium Chloride in Water, Toluene, Ethanol, and Methanol) were deposited onto coated panel. For those chemicals with low surface tension or quick evaporation, filter papers with (25 mm dia.) were put on the coatings prior to insulting with chemical. Plastic caps were then put on to cover the droplets or the saturated filter papers. Data were recorded after soaking for 24 hrs. The rating scale was as follows: 5 No visible affect 4 Slight blush 3 Major blush, Slight blister, change in touch 2 Major blisters 1 Coating failure

(34) Accelerated Weathering Using QUV: The weathering of the coatings was determined by monitoring the gloss retention over time as the panel were exposed to ultraviolet light. The test was carried out in accordance to ASTM G-53. Cured coating samples on aluminum panels were placed into a QUV unit (Q-Lab model QUV/se). The QUV chamber cycled between 60° C. at 0.89 W/m{circumflex over ( )}2 irradiance for 8 hours and a condensation cycle 50° C. for 4 hours.

(35) The performance characteristics of the coating compositions are shown in Tables 5 through 10. Table 5 illustrates the importance of a cure compatibility group (e.g. HEMA) in the acrylic copolymer, providing compatibility (higher HA reading), improved dry time and improved 20 degree gloss readings. Table 6 illustrates the compositional range of the amino-functional silicone resins and subsequent performance. Table 7 shows weatherability performance for coating compositions of the present invention. Tables 8 through 10 illustrate the ability to provide a pigmented coating and a comparative example of non-Si amine based coating.

(36) TABLE-US-00005 TABLE 5 7 day HA on Set-to- Tack- Dry- König glass Touch Free Hard Thick- hard- over Exam- Time Time Time 20° 60° ness ness black ples (hr) (hr) (hr) Gloss Gloss (mils) (sec) lenta Comp 0.16 10.3  >24    80  89 3.95 12 223 Ex 1 SE 1 0.48 2.6 3.4 89  98 4.50 45 414 SE 2 0.40 1.5 2.5 93 104 4.15 54 428

(37) TABLE-US-00006 TABLE 6 7 day Set-to- Tack- Dry- König Touch Free Hard Thick- hard- MEK Exam- Time Time Time 20° 60° ness ness double ples (hr) (hr) (hr) Gloss Gloss (mils) (sec) rubs SE 3 1.0 3.0 6.8 105 110 3.5  91 >200  SE 4 0.1 0.9 3.1  93 104 3.3  98 >200  SE 5 0.1 0.2 4.7  92 102 2.4 117 >200  SE 6 0.8 1.4 7    87 100 2.5  69 >200  Comp 5.1 9.5 >24     88 101 2.6  16 180 Ex 2 Comp — — — — — — — — Ex 3 Comparative Example 3 failed to form a continuous film and could not be tested.

(38) TABLE-US-00007 TABLE 7 500 hr % 1000 hr % 1500 hr % 2000 hr % gloss gloss gloss gloss Examples retention retention retention retention SE 3 100 100 100 97 SE 4 98 97 96 93 SE 5 100 100 100 100 SE 6 96 95 92 89

(39) TABLE-US-00008 TABLE 8 25% Set-to- Tack- Dry- Film Touch Free Hard Thick- 7 Day Loss Time Time Time 20° 60° ness hard- or 200 Examples (hr) (hr) (hr) Gloss Gloss (mils) ness rubs SE 7 1.3 4 7 93 97 2.8  82 >200 Comp 1.5 4 7 80 91 2   113 >200 Ex 4

(40) TABLE-US-00009 TABLE 9 24 hr 24 hr 10% 24 hr 10% 24 hr 24 hr Water H2SO4 NaOH Gasoline Antifreeze Examples Resistance Resistance Resistance Resistance Resistance SE 7 5 5 4 4 5 Comp Ex 5 2 4 4 4 4

(41) TABLE-US-00010 TABLE 10 500 hr gloss 1000 hr gloss 1500 hr gloss 2000 hr gloss Examples retention retention retention retention SE 7 100 98 95 94 Comp Ex 55 21 14 10 4