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 and the amino-functional silicone resin is an alkoxy functional siloxane, which optionally is derived from sterically hindered alcohol-amine precursor moieties. 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 comprising in polymerized form, structural units of: (i) (R.sub.3SiO.sub.1/2).sub.a; (ii) (R.sub.2Si(OR′).sub.xO.sub.(2-x)/2).sub.b; (iii) (RSi(OR′).sub.y,O.sub.(3-y)/2).sub.c; and (iv) (Si(OR′).sub.zO.sub.(4-z)/2).sub.d wherein each R′ is hydrogen, an alkyl group or a functionalized alkyl group, provided that at least 5 mole percent of all R′ groups are amine containing groups of the formula: —R.sub.a—NHR.sub.b; wherein R.sub.a is an alkyl group or an aryl-containing group derived from an amino alcohol and R.sub.b is hydrogen, an alkyl group, or an aryl group; wherein a+b+c+d=1.00 (100 mole percent); x is either 0 or 1; y is either 0, 1 or 2; and z is either 0, 1, 2, or 3; wherein each R is independently hydrogen, an alkyl group, or an aryl group; and 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 at least 20 mole percent of all R′ groups of the amino-functional silicone resin are amine containing groups of the formula: —R.sub.a—NHR.sub.b.

4. The coating composition of claim 1 wherein from 5 to 42 mole percent of all R′ groups of the amino-functional silicone resin are amine containing groups of the formula: —R.sub.a—NHR.sub.b.

5. The coating composition of claim 1 wherein the amino alcohol is selected from the group which (a) has steric hindrance around the COH moiety; (b) is a secondary or tertiary alcohol; or (c) mixtures thereof.

6. The coating composition of claim 1 wherein the amino alcohol is 1-amino-2-propanol or 1-amino-2-methylpropan-2-ol.

7. 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.

8. 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.

9. 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.

10. 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.

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

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

Description

EXAMPLES AND EXPERIMENTAL METHODS

Acrylic Copolymers

[0048] 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 methacrylate (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.

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 50 10 30 10 75% −3 400 300 monomer composition grams 150 30 90 30 36 88 A2 Wt % of 50 15 35 0 72% −2 400 300 monomer composition grams 150 45 105 0 36 88

Acrylic Copolymer Characterization

GPC

[0049] 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 performed 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.

EEW

[0050] EEW is measured in accordance with ASTM D1652. The epoxy resin is dissolved in methylene chloride and titrated with standardized 0.1N perchloric acid (HClO4) 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.

Percent Solids

[0051] Label the bottom of a small aluminum pan, place the pan on a scale and record its weight to the closest 0.0001 gram. 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

[0052] 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° C./minute, isotherm for 5 minutes, Tg was analyzed with TA software.

Viscosity

[0053] 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 a torque of ˜25 Newton meters (N*m). Measurements were reported in unites of centipoises (cP).

Amino-Functional Silicone Resins

[0054] Amino-functional silicone resins 51 to S13 are shown in Table 2 and each is a reaction product of a silicone resin and an alcohol-amine Representative silicone resin 51 was prepared by reacting a silicone resin reagent/reactant with an NMR determined structure of D.sub.0.337T.sup.Cyclohexyl.sub.0.010T.sup.Ph.sub.0.653 (OZ=68.64 mol %, FW-126.5 g/mol Si) with 1-amino-2-propanol (Mw=75.11, TCI brand, bp=160° C.); according to the following procedure: A 250 mL 1-neck round bottom flask was loaded with the silicone resin reactant (94.19 g, 0.745 mols Si. 0.511 mols OZ) and 1-amino-2-propanol (16.52 g, 0.220 mols, 0.440 mols NH). The flask was equipped with a magnetic stir bar and a Dean Stark apparatus attached to a water-cooled condenser. The mixture was hazy at room temperature. The mixture was heated at an aluminum block temperature of 140° C. for 2 hours. The amount of volatiles collected in the first hour was 3.35 g and in the second hour was 0.31 g. The reaction mixture turned clear while heating to 140° C. The aluminum block temperature was increased to 180° C. and held at this temperature for 2 hours. The amount of volatiles collected in the first hour was 1.85 g and in the second hour was 0.13 g. The final product was stripped on a rotovapor at an oil bath temperature of 115° C. and at a pressure of ˜1 mm Hg.

[0055] The resulting product was a clear viscous liquid at room temperature. The isolated yield of the product was 100.9 g and it had a calculated amine hydrogen equivalent weight from .sup.13C NMR spectrum of 256 g/mol NH. NMR Analysis of product showed it to be: D.sub.0.333T.sup.Cyclohexyl.sub.0.007T.sup.Ph.sub.0.660 with an OZ content of 61.95 mol % (26.9 mol % OR and 33.5 mol % OMe). The OR and OMe values were calculated from 13C NMR by taking the ratio of the OR integral value and dividing that by the integral value of phenyl groups.

[0056] Representative silicone resin S6 was prepared by reacting a silicone resin reagent/reactant derived from alkoxysilanes with ethanolamine; according to the following procedure:

Reagents:

[0057] Phenyltrimethoxysilane—Dowsil™ Z-6124 silane (available from Dow, Inc. or an affiliated company)—

[0058] Methyltrimethoxysilane—Silastic™ Z-6070 silane (available from Dow, Inc. or an affiliated company), lab distilled; Mw=136.22

[0059] Ethanolamine, available from Acros Organics

[0060] A 250 mL 2-neck round bottom flask was loaded with Phenyltrimethoxysilane (106.28 g, 0.536 mols), Methyltrimethoxysilane (35.96 g, 0.264 mols) and Ethanolamine (12.91 g, 0.21 mols, 0.42 mols NH). A magnetic stir bar was used for mixing and the mixture was heated to an aluminum block temperature of 50° C. DI water (14.83 g, 0.823 mols) was added slowly and the mixture was heated at an aluminum block temperature of 70° C. for 1 hour. The aluminum block temperature was increased to 120° C. and then held at this temperature for 1 hour. The amount of volatiles removed was 55.8 g. The product was stripped on a rotovapor at an oil bath temperature of 80° C., ˜1.0 mm Hg, 45 min. The resulting product was a clear viscous liquid at room temperature with a calculated amine equivalent weight from 13C NMR spectrum of 304 g/mol NH. NMR Analysis of product showed it to be: T.sup.Me.sub.0.300T.sup.Cyclohexyl.sub.0.010T.sup.Ph.sub.0.690; with an OZ content of 83.4 mol %.

TABLE-US-00002 TABLE 2 Resulting Amino-functional Si Resin Si Resin and Alcohol- mol % mol amine Reactants OR % Ex Alkoxy Si Resin Mol Alcohol- (from OMe/ g/mol No. Composition % OZ amine Source Si molar fractions amine) OEt NH S1 D.sub.0.337T.sup.Cyclohexl.sub.0.010T.sup.Ph.sub.0.653 68.64 1-amino-2- D.sub.0.333T.sup.Cyclohexl.sub.0.007T.sup.Ph.sub.0.660 26.9 33.5 256 propanol S2 D.sub.0.337T.sup.Cyclohexl.sub.0.010T.sup.Ph.sub.0.653 68.64 Ethanolamine D.sub.0.326T.sup.Cyclohexl.sub.0.007T.sup.Ph.sub.0.664 23.5 34.3 280 S3 D.sub.0.654T.sup.Cyclohexl.sub.0.005T.sup.Ph.sub.0.341 61.99 Ethanolamine D.sub.0.642T.sup.Cyclohexl.sub.0.010T.sup.Ph.sub.0.354 22.2 32.4 255 S4 D.sub.0.654T.sup.Cyclohexl.sub.0.005T.sup.Ph.sub.0.341 61.99 Ethanolamine D.sub.0.635T.sup.Cyclohexl.sub.0.004T.sup.Ph.sub.0.361 18.7 18.1 289 S5 D.sub.0.654T.sup.Cyclohexl.sub.0.005T.sup.Ph.sub.0.341 61.99 Ethanolamine D.sub.0.640T.sup.Cyclohexl.sub.0.003T.sup.Ph.sub.0.357 36.1 17.4 162 S6 Started from alkoxysilanes — Ethanolamine T.sup.Me.sub.0.300T.sup.Cyclohexl.sub.0.010T.sup.Ph.sub.0.690 22.7 60.7 304 S7 D.sub.0.337T.sup.Cyclohexl.sub.0.010T.sup.Ph.sub.0.653 68.64 Ethanolamine D.sub.0.327T.sup.Cyclohexl.sub.0.007T.sup.Ph.sub.0.666 41.7 17.6 166 S8 Started from alkoxysilanes — Ethanolamine D.sub.0.003T.sup.Me.sub.0.638T.sup.Cyclohexl.sub.0.002.sup.Ph.sub.0.666T.sup.Ph.sub.0.357 18.1 53.2 316 S9 D.sub.0.337T.sup.Cyclohexl.sub.0.010T.sup.Ph.sub.0.653 68.64 2-amino-1- D.sub.0.321T.sup.Cyclohexl.sub.0.011T.sup.Ph.sub.0.673 27.3 29.7 260 butanol S10 Made from alkoxysilanes — 2-amino-1- T.sup.Me.sub.0.289T.sup.Cyclohexl.sub.0.01qT.sup.Ph.sub.0.700 27.6 53.6 266 butanol S11 D.sub.0.337T.sup.Cyclohexl.sub.0.010T.sup.Ph.sub.0.653 68.64 2-amino-2- D.sub.0.335T.sup.Cyclohexl.sub.0.010T.sup.Ph.sub.0.655 26.4 35.7 268 methyl-1- propanol S12 D.sub.0.337T.sup.Cyclohexl.sub.0.010T.sup.Ph.sub.0.653 68.64 1-amino-2- D.sub.0.338T.sup.Cyclohexl.sub.0.007T.sup.Ph.sub.0.655 25.7 34.6 266 propanol S13 D.sup.Me2.sub.0.010T.sup.Me.sub.0.990 71.77 1-amino-2- D.sub.0.011T.sup.Me.sub.0.989 17.9 32.5 297 propanol

Coating Formulation: Clear Coatings

[0061] The clear coating compositions of Table 3 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™. In formulating the coating compositions, the acrylic copolymer and amino-functional silicone resin are added in an amount to provide an epoxy/NH molar ratio of 1:1.

TABLE-US-00003 TABLE 3 Acrylic Amino-functional Coating Example Copolymer silicone resin CTG 1 A1 S1 CTG 2 A1 S2 CTG 3 A1 S3 CTG 4 A1 S4 CTG 5 A1 S5 CTG 6 A1 S6 CTG 7 A1 S7 CTG 8 A1 S8 CTG 9 A1 S9 CTG 10 A1 S10 CTG 11 A1 S11 CTG 12 A1 S12 CTG 13 A1 S13 CTG 14 A2 S12 CTG 15 A2 S13 CTG 16 A1 DOWSIL ™ 3055

[0062] DOWSIL™ 3055 is an amine-functional siloxane resin with SiC bonded amine functionality, in contrast to SiOC bonded amine functionality, and is available from Dow, Inc. or an affiliated company.

Draw Down Application Method for Clear Coat Applications

[0063] 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.

Coating Application and Test Methods

[0064] 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.

[0065] 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.

[0066] 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.

Pencil Hardness

[0067] The pencil hardness of a coating film is measured according to the ASTM D3363 method. A coating composition is applied on a glass panel to form a 120 micron thick wet film and cured at room temperature for 7 days. The resultant film is then tested by a Zhonghua pencil. The hardness of the pencil used is 9H, 8H, 7H, 6H, 5H, 4H, 3H, 2H, F, HB, B, 2B, 3B, 4B, 5B, 6B, where 9H is the hardest, 6B is the softest.

[0068] 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.

[0069] 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 micrometers on glass panel and measurements were taken over black Leneta chart. Measurements were logarithmic scaling with brightness compensation.

[0070] 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.

[0071] The performance characteristics of the coating compositions are shown in Tables 4 and 5. Ctg 12 and Ctg 13 as compared to Ctg 14 and Ctg 15 respectively, illustrate the importance of a cure compatibility group (e.g. HEMA) in the acrylic copolymer to provide improved pencil hardness, improved dry time, improved gloss readings, improved hardness and improved MEK Resistance. Tables 4 and 5 illustrate that coating compositions having multi-functionalized acrylic copolymer and amino-functional silicone resin curing agents improves the properties of the coating composition in a cost effective manner Coating properties are improved where the acrylic copolymer has, in polymerized form, epoxy functionalized groups and cure compatibility groups and the amino-functional silicone resin is an alkoxy functional siloxane. Moreover, coating properties are most improved where the amino-functional silicone resins have an alkoxy functional siloxane derived from sterically hindered alcohol-amine precursor moieties or where the alcohol-amine precursor is a secondary or tertiary alcohol.

TABLE-US-00004 TABLE 4 ctg 7 d MEK Ctg. Ex Clarity 20° 60° Thickness 1 d hardness hardness double No. (1-5) Gloss Gloss (mil) (Konig sec) (Konig sec) rubs Impact Ctg 1 4 96 102 3.21 33 94 >200 60 ctg 2 2 93 99 2.58 33 66 171 40 Ctg 3 5 85 99 2.29 9 17 74 140 Ctg 4 5 88 100 2.5 9 22 140 >160 Ctg 5 5 80 98 3.17 16 37 >200 80 Ctg 6 1 1 12 3.26 43 73 176 20 Ctg 7 3 70 90 3.59 30 58 >200 40 Ctg 8 3 34 55 4.32 39 65 >200 20 Ctg 9 1 98 100 3.71 8 78 >200 20 Ctg 10 1 80 92 3.55 12 100 >200 <20 Ctg 11 2 97 101 2.98 6 57 146 20 Ctg 12 5 100 105 3.0 34 99 >200 40 Ctg 13 5 74 95 3.1 28 87 >200 20 Ctg 14 1 88 94 2.6 10 44 107 Testing discontinued due to poor film quality. Ctg 15 2 10 37 2.4 14 30 198 Testing discontinued due to poor film quality. Ctg 16 5 102 108 2.76 37 84 >200 20

TABLE-US-00005 TABLE 5 Dry Times (hr) Pencil Set-To- Tack- Dry- Dry- Ctg. Ex No. Hardness Touch Free Hard Through Ctg 12 F 0.6 4 8 20 Ctg 13 F 0.4 1 2 9 Ctg 14 2B 1.0 20 >24 >24 Ctg 15 2B 0.5 6 18 >24