UV-CURING ACRYLIC RESIN COMPOSITIONS FOR THERMOFORMABLE HARD COAT APPLICATIONS

Abstract

The present invention provides ultraviolet (UV) curing acrylic compositions for use in making thermoformable hard coats for curved optical displays comprising: (a) one or more multifunctional (meth)acrylate diluents chosen from (a1) an aliphatic trifunctional (meth)acrylate monomer; (a2) an aliphatic tetrafunctional (meth)acrylate monomer; or (a3) an aliphatic pentafunctional (meth)acrylate monomer; (b) from 3 to 30 wt. %, based on the total weight of monomer solids, of one or more one (meth)acrylate monomer containing an isocyanurate group; (c) from 5 to 40 wt. %, based on the total weight of monomer solids, of one or more aliphatic urethane (meth)acrylate functional oligomer having from 6 to 12 (meth)acrylate groups; (d) from 2 to 10 wt. %, based on total monomer solids, of one or more UV radical initiators; and (e) one or more organic solvents for the monomer composition. The composition has a viscosity measured by Anton Parr ASVM 3001 digital viscometer at 50 wt. % solids of from 10 to 200 centipoise (cPs).

Claims

1. An ultraviolet (UV) curing acrylic composition for use in making thermoformable hard coats for curved optical displays comprising: (a) one or more multifunctional (meth)acrylate diluents chosen from (a1) an aliphatic trifunctional (meth)acrylate monomer; (a2) an aliphatic tetrafunctional (meth)acrylate monomer or (a3) an aliphatic pentafunctional (meth)acrylate monomer; (b) from 3 to 30 wt. %, based on the total weight of monomer solids, of one or more (meth)acrylate monomer containing an isocyanurate group; (c) from 5 to 40 wt. %, based on the total weight of monomer solids, of one or more aliphatic urethane (meth)acrylate functional oligomer having from 6 to 12 (meth)acrylate groups; (d) from 2 to 10 wt. %, based on total monomer solids, of one or more UV radical initiators; (e) one or more organic solvents for the monomer composition, wherein the composition has a viscosity measured by Anton Parr ASVM 3001, at 50 wt. % solids of from 10 to 200 centipoise (cPs), wherein the total amount of monomer and functional oligomer solids amounts to 100%.

2. The composition as claimed in claim 1 comprising: from 3 to 25 wt. %, based on total monomer solids, of (a) the multifunctional (meth)acrylate diluent (a1) one or more aliphatic trifunctional (meth)acrylate monomer, wherein the total amount of monomer and functional oligomer solids amounts to 100%.

3. The composition as claimed in claim 1 comprising: from 3 to 25 wt. % or, based on total monomer solids, of (a) the multifunctional (meth)acrylate diluent (a2) one or more aliphatic tetrafunctional (meth)acrylate, monomer, wherein the total amount of monomer and functional oligomer solids amounts to 100%.

4. The composition as claimed in claim 1 comprising: from 3 to 25 wt. %, based on total monomer solids, of (a) the multifunctional (meth)acrylate diluent (a3) one or more aliphatic pentafunctional (meth)acrylate, monomer, wherein the total amount of monomer and functional oligomer solids amounts to 100%.

5. The composition as claimed in claim 1 comprising: from 9 to 70 wt. % in total, based on total monomer solids, of (a) two or more multifunctional (meth)acrylate diluent monomers chosen from the (a1) aliphatic trifunctional (meth)acrylate monomer, (a2) the aliphatic tetrafunctional (meth)acrylate monomer or (a3) the aliphatic pentafunctional (meth)acrylate monomer, wherein the total amount of monomer and functional oligomer solids amounts to 100%.

6. The composition as claimed in claim 1 comprising: (b) from 10 to 30, based on the total weight of monomer solids, of one or more one (meth)acrylate monomer containing an isocyanurate group, wherein the total amount of monomer and functional oligomer solids amounts to 100%.

7. The composition as claimed in claim 1 comprising: (c) from 10 to 40 wt. %, based on the total weight of monomer solids, of one or more aliphatic oligomer having from 6 to 12 (meth)acrylate groups, wherein the total amount of monomer and functional oligomer solids amounts to 100%.

8. The composition as claimed in claim 1, wherein the at least one (c) aliphatic urethane (meth)acrylate functional oligomer has a formula molecular weight of from 1,400 to 10,000.

9. The composition as claimed in claim 1 comprising: 20 wt. % or less in total of mono- and di-functional (meth)acrylates, based on total monomer solids, wherein the total amount of monomer and functional oligomer solids amounts to 100%.

10. The composition as claimed in claim 1, wherein the amount of the (e) one or more organic solvents ranges from 10 to 90 wt. %, based on the total weight of the composition.

Description

EXAMPLES

[0064] The following Examples seek to illustrate the present invention.

[0065] All materials including photoradical initiators, (meth)acrylate monomers, aliphatic urethane (meth)acrylate functional oligomers, solvents, polyethylene terephthalate (PET) (Mellinex 462 polyester, Tekra, a division of EIS, Inc., New Berlin, Wis.), were used as received unless specified otherwise.

[0066] The abbreviations or names given to materials used in the Examples below have the following meanings:

[0067] The following test methods were used in the following Examples:

[0068] Elongation-to-Break:

[0069] An Instron mechanical tester was used to measure the elongation-to-break of coatings. Cured coatings on PET substrates were cut to specimens in 15 mm wide and 100 mm long. Next, specimens with 60 mm gauge length were gripped by pneumatic grips and then preloaded to 1 MPa in tensile stress. Then, the specimens were loaded in tension at the loading rate of lmm/min until a vertical crack is observed. During the tensile test, the specimens were under a white LED light for easier crack detection. Once a crack was found in the specimens, the loading was immediately stopped and corresponding tensile strain was reported as elongation-to-break. A result of at least >2% is acceptable. >4% is preferred.

[0070] Haze:

[0071] A BYK haze measurement system (Byk Gardner, Geretsried, Del.) was used to measure the haze of the indicated coatings. The haze values were obtained based on ASTMD1003 standard (2013). A % transparency of >90% (550 nm) and a % haze<2 is acceptable. The same transparency and % Haze below 1 is preferred.

[0072] Indentation modulus (E, GPa) and hardness (H, GPa):

[0073] A Nanoindenter iMicro (Nanomechanics, Tenn.) was used to characterize the indentation modulus and hardness of cured hard coatings. The nanoindenter had load and displacement resolutions of 6 nN and 0.04 nm, respectively and was operated in continuous stiffness mode in which the indenter tip was continuously oscillated at a 2 nm amplitude for improved surface detection and extraction from a single measurement of mechanical properties as a function of indentation depth. A standard Berkovich tip whose projected contact area function was calibrated to an indentation depth of from 200 and 2000 nm was used by making 20-25 indentations on a fused silica specimen with an indentation modulus of 72 GPa1 GPa. The indicated cured hard coatings were mounted on sample holders using a hot melt adhesive with a melting point of circa 54 C. (Crystal Bond 555, TedPella, Inc., Redding, Calif.). Indentations to 2000 nm depth were made on each coating in at least 10 different locations once the test system had reached a thermal drift of <0.1 nm/sec. A Poisson's ratio of 0.3 was assumed. Subsequent to the measurement, 3 to 5 indentations were again made on the fused silica specimen to verify the previous calibration. Adequate hardness comprises a modulus greater than 4 GPa and a hardness at least >0.3 GPa.

[0074] Outward Bending Radius:

[0075] The outward bending radius of cured coatings was measured using a manual cylindrical bend tester (TQC). The tester is equipped with smooth metal mandrels having different diameters (32, 25, 20, 19, 16, 13, 12, 10, 8, 6, 5, 4, 3, and 2 mm) to apply discrete sets of strain to cured coatings. Cured coatings with a thickness 50 m on 50 m PET were used. One side of the cured film was fixed at the bottom of the equipment, and a smooth metal mandrel with a desired diameter was set in the tester. Note that for the initial test, mandrels with sufficiently large diameters were chosen not to cause cracking in cured coatings. Then, the cured coating was lightly sandwiched between the mandrel and plastic cylinders such that only tensile bending strain is applied to the top side of the coatings. Subsequently, the cured coating was bent to the radius of the metal mandrel. After the bending, the coating was detached from the tester for visual crack detection. This process was repeated until a crack was formed. Once a crack was detected, the smallest mandrel diameter without cracking was converted into an outward bending radius (dividing diameter by 2) and reported. Bending radius below and/or equal to 1.5 mm is acceptable; and below 1 mm is preferred. Pencil hardness: Pencil hardness (ASTM standard D3363 (2011) measurements of coatings cured as indicated were measured using an automatic pencil hardness tester (PPT-2016, Proyes International Corp., TaiChung, Taiwan). The test was performed at a 10 mm/min in speed and at a 0.75 kgf vertical load using UNI pencils (Mitsubishi, Japan). During testing, the cured coatings were placed on a flat, clean and 0.5 cm thick glass plate. An acceptable result is greater than or equal to 4H.

[0076] Hard Coating Thickness:

[0077] Coating thickness was measured by a micro-meter (Mitsutoyo, Japan). The micro-meter was re-zeroed before measurements, and subsequently multiple locations on a given hard coating were measured.

[0078] The UV curing acrylic compositions indicated in Tables 1 and 2, below, were prepared by mixing the indicated constituents using a vortex and optionally a speed mixer at room temperature. The final compositions were left on a slow rotary mixer for from 1 hour to 72 hours until all of the components were dissolved and become clear solution in an ambient lab environment to ensure homogenous mixing before film preparation. Preferably, the total mixing time is 1-24 hours. the solution can also be heated up to 60 C. during the mixing.

[0079] Film Casting:

[0080] PET substrates were cleaned with a jet of filtered laboratory air. An automatic draw-down coater (ElcometerUSA, Rochester Hills, Mich.) was used to cast the indicated compositions on PET substrates at room temperature. Draw-down bars with different gaps were used to obtain desired coatings at a thickness of 40 um. The films were then UV-cured using a Fusion 300 conveyor system (irradiance 3000 mW/cm.sup.2, Fusion Systems, Inc., Gaithersburg, Md.). Each film passed the lamp four times 0.24 m/s. The average values for energy density at 0.24 m/s are around 480, 120, 35, and 570 mJ/cm.sup.2 in the UVA, UVB, UVC, and UVV regimes, respectively.

[0081] In the Examples below, the following materials were used:

[0082] DPEPA: Dipentaerythritol pentaacrylate ester: (SR399 Sartomer, Exton, Pa.), CAS#60506-81-2<=100 wt. %; SR399 is a mixture of tetra-, penta-, and hexa-acrylate; Tentative molar ratio of acrylates is 25:50:25;

[0083] MEDA: 2-Propenoic acid, (5-ethyl-1,3-dioxan-5-yl)methyl ester: SR531 (Sartomer, f=1 CAS#66492-51-1, <=95%); also includes a) 2-Propenoic acid, 2-ethyl-2-[[(1-oxo-2-propenyl)oxy]methyl]-1,3-propanediyl ester, f=3 CAS#15625-89-5, <=5%; b) Phenol, 2,6-bis(1,1-dimethylethyl)-4-methyl-(aka BHT), CAS #128-37-0, <=1%; and c) 2-Propenoic acid (acrylic acid), f=1, CAS#79-10-7, <=0.1%;

[0084] Monomer 2: Isobornyl acrylate, SR506C (Sartomer, f=1 CAS#5888-33-5,);

[0085] THEIA: Tris (2-hydroxyethyl)isocyanurate triacrylate: Photomer 4356 (IGM, United States, f=3, Cas#40220-08-4, >98%; also includes acrylic acid, <1%;

[0086] Photoinitiator 1: Oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] (Esacure One, IGM Resins B. V., Waalwijk, NL. CAS#163702-01-0);

[0087] Photoinitiator 2: Omnipol BP (CAS 515136-48-8, -[(4-benzoylphenoxy)acetyl]-w-[[2-(4-benzoylphenoxy)acetyl]oxy]-poly(oxy-1,4-butanediyl))

[0088] HUA; Aliphatic urethane acrylate: CN9006 (Sartomer, f=6, CAS# proprietary, >=30-<60% (GPC analysis of main oligomer: Mw=1.5 kDa, Mn=1.3 kDa, PDI=1.20); also includes a) 2-Propenoic acid, 2-(hydroxymethyl)-2-[[(1-oxo-2-propenyl)oxy]methyl]-1,3-propanediyl ester, f=3; CAS#3524-68-3, >=10-<30%; b) 2-Propenoic acid, 2,2-bis[[(1-oxo-2-propenyl)oxy]methyl]-1,3-propanediyl ester, f=4; CAS#4986-89-4, >=10-<30%; other acrylates, f=unknown, >=10-<30%;

[0089] Urethane nonaacrylate: CN9013 (Sartomer, f=9, CAS proprietary, <=100%);

[0090] Silicone (non-reactive): BYK307 additive (BYK USA, Chester, Pa.);

[0091] Alumina oxide: BYK3601 (BYK);

[0092] HUA 2: Urethane acrylate CN9025 (Sartomer, CAS# Proprietary aliphatic, f=6, >=60-<=100%; also contains Proprietary Acrylic ester, f=6>=10-<30%);

[0093] TUA: urethane acrylate oligomer: Photomer 6008 (IGM, CAS proprietary, f=3); also contains tripropylene glycol diacrylate, CAS#42978-66-5, 15-25%; b) 2-hydroxyethyl acrylate, CAS#818-61-1, <2%;

[0094] Alicyclic TUA: Methylenedi-4,1-cyclohexyleneisocyanate, (2-hydroxyethyl)-2-propenoate, -hydro--hydroxypoly(oxy-1,4-butanediyl)polymer: Photomer 6010 (IGM, CAS#67599-25-1, f=3, >85%); also contains a) ethoxylated (3) trimethylolpropane triacrylate, CAS#28961-43-5, f=3, >10-<15%; b) 2-hydroxyethyl acrylate, <1%; c) hydroquinone<0.05%; and,

[0095] Silica: X12-2444 silica nanoparticles in multifunctional acrylate (Shin Etsu Chemical, Ltd., Tokyo, JP).

TABLE-US-00001 TABLE 1 Inventive Compositions and Performance Example.sup.1 1 2 3 MEDA 10 10 10 (acrylate monomer (f = 1)) DPEPA 20 20 10 Acrylate monomer f = 5 THEIA 20 20 30 Acrylate monomer with isocyanurate HUA: Urethane oligomer (f = 6) 45 20 35 Acrylate monomer (f = 3) Acrylate monomer (f = 4) Urethane nonaacrylate (f = 9) 25 Photoinitiator 2 2 2 2 Photoinitiator 1 3 3 3 Pencil hardness 7H 4H 7H (0.75 kg, thickness 50 m) Outward radius (mm); <1; <1; <1; Thickness (m) 13 9 9 .sup.1f represents functionality.
As shown in Examples 1 to 3, the inventive compositions provide hard coatings having both acceptable pencil hardness and flexibility, as shown in outward radius.

TABLE-US-00002 TABLE 2 Comparative Compositions and Performance Example.sup.1 4* 5* 6* 7* 8* 9* MEDA 10 10 10 10 10 10 (acrylate monomer (f = 1)) ??mer 2? 20 20 20 20 20 (acrylate monomer (f = 1)) DPEPA 20 Acrylate monomer f = 5 THEIA 30 25 20 Acrylate monomer with isocyanurate Silica 20 HUA: Urethane oligomer (f = 6) 65 45 35 50 Acrylate monomer (f = 3) Acrylate monomer (f = 4) TUA (f = 3) 65 Urethane nonaacrylate (f = 9) 45 Photoinitiator 2 2 2 2 2 2 2 Photoinitiator 1 3 3 3 3 3 3 Pencil hardness 2 H <6 B 2 H 3 H H 3 H (0.75 kg, thickness 50 m) Outward radius (mm); <1; <1; <1; Thickness (m) 10 7 9 .sup.1*Denotes Comparative Example; .sup.1f represents functionality.

[0096] As shown in Table 2, above, none of the Comparative Examples 4 to 9 gave the acceptable pencil hardness for a thermoformable coating in accordance with the present invention. All of Comparative Examples 4 to 8 contain too much mono (meth)acrylate monomer; this is so even when the example contains adequate aliphatic urethane (meth)acrylate functional oligomer and isocyanurate (meth)acrylate monomer, as in Comparative Examples 7, and 8. Comparative Example 9 fails to contain any aliphatic tetrafunctional (meth)acrylate. Comparative Example 6 contains too much silica or filler.