HARDCOAT

Abstract

Display substrates having a hard coat layer on a colorless polyimide substrate are formed from hard coat compositions having certain organic solvents that do not substantially impact the optical and mechanical properties of the colorless polyimide substrate.

Claims

1. A method comprising: (a) providing a flexible substrate; and (b) disposing a layer of a coating composition on the flexible substrate; wherein the flexible substrate has a pencil hardness of 1H, a haze value of <2%, and a yellowness index of <6; and wherein the coating composition comprises: (1) one or more curable oligomers; and (2) at least one organic coating solvent chosen from: 2,6-dimethylcyclohexanone; 2,4-dimethyl-3-pentanone; 2,2,4,4-tetramethyl-3-pentanone; 2,4-dimethyl-3-pentanol; 2,6-dimethyl-4-heptanone; methyl 2-hydroxy-2-methylpropanoate; isopropyl acetate; and isoamyl acetate.

2. The method of claim 1 wherein the coating composition further comprises one or more secondary organic solvents different from the organic coating solvent in an amount of from 1 to 49.5 wt % based on the total weight of organic solvents.

3. The method of claim 1 wherein the curable oligomer is chosen from (meth)acrylate oligomers, urethane oligomers, (meth)acrylate-urethane oligomers, siloxane oligomers, and combinations thereof.

4. The method of claim 1 wherein the flexible substrate is polyimide.

5. The method of claim 1 wherein the coating composition further comprises one or more of: nanoparticles; a cationic photoinitiator; a reactive modifier comprising at least two epoxycyclohexane groups or at least two oxetane rings; leveling agents; and mixtures thereof.

6. A composition comprising: (1) one or more curable siloxane oligomers; and (2) at least one organic coating solvent chosen from: 2,6-dimethylcyclohexanone; 2,4-dimethyl-3-pentanone; 2,4-dimethyl-3-pentanol; 2,2,4,4-tetramethyl-3-pentanone; 2,6-dimethyl-4-heptanone; and methyl 2-hydroxy-2-methylpropanoate.

7. The composition of claim 6 further comprising one or more secondary organic solvents different from the organic coating solvent.

8. The composition of claim 6 wherein the curable siloxane oligomer comprises polymerized units of formula R.sup.1.sub.mR.sup.2.sub.nSi(OR.sup.3).sub.4-m-n, wherein: R.sup.1 is a C.sub.5-20 aliphatic group comprising an oxirane ring fused to an alicyclic ring; R.sup.2 is a C.sub.1-20 alkyl, C.sub.6-30 aryl group, or a C.sub.5-20 aliphatic group having one or more heteroatoms; R.sup.3 is a C.sub.1-4 alkyl group or a C.sub.1-4 acyl group; m is 0.1 to 2.0; and n is 0 to 2.0.

9. The composition of claim 6 further comprising one or more of: non-porous nanoparticles having an average particle diameter from 5 to 50 nm; a cationic photoinitiator; a reactive modifier comprising at least two epoxycyclohexane groups or at least two oxetane rings; leveling agents; and mixtures thereof.

Description

[0031] Example 1. On a level surface, a small, clean specimen of polyimide substrate was placed and subsequently each of the solvents reported in Table 1 was placed onto the substrate via pipette so that most of the surface of the specimen was covered with solvent. After being left undisturbed for three minutes at 90 C. on a hotplate, the solvent was removed from the substrate, and the substrate visually inspected for changes in haziness and curl. If no changes were detected, the compatibility of the solvent was rated Good. If slight or severe haze was detected, the compatibility of the solvent was rated Acceptable or Poor, respectively. The results are reported in Table 1.

TABLE-US-00003 TABLE 1 Solvent PI 1 Comparative PI Methyl iso-butyl ketone Poor Poor to Acceptable PGME Poor Acceptable to Good HBM Acceptable Acceptable 2,4-Dimethyl-3-pentanone Good Poor Toluene Good Good

[0032] Example 2. Samples of PI 1 substrate, each having a thickness of 50 m, were contacted with each of the solvents listed in Table 2 according to the procedure of Example 1. After the solvent was removed, the substrate was evaluated for changes in nanoindentation modulus and nanoindentation hardness. The results are reported in Table 2.

TABLE-US-00004 TABLE 2 Nanoindentation Nanoindentation Solvent Modulus (GPa) Hardness (GPa) None 5.58 0.53 2,6-Dimethylcyclohexanone 5.71 0.50 2,4-Dimethyl-3-pentanone 5.56 0.51 2,2,4,4-Tetramethyl-3-pentanone 5.52 0.52 HBM 5.49 0.53 2,6-Dimethyl-4-heptanone 5.40 0.51 2,4-Dimethyl-3-pentanol 5.37 0.50 Isopropyl acetate 5.37 0.5 Isoamyl acetate 5.37 0.5 Toluene 5.3 2-Hexanone 5.26 0.50 Isopropanol 5.21 2-Methylcyclohexanone 4.68 0.30 Methyl iso-butyl ketone 4.44 0.35 PGME 3.7 Cyclohexanone 3.27 0.20 2,4-Dimethyl-3-pentanone/HBM 5.30 (9/1, w/w) 2,4-Dimethyl-3-pentanone/PGME 5.25 (9/1, w/w)

[0033] As can be seen from the data in Table 2, many common solvents used in hardcoat compositions adversely impact the mechanical properties (nanoindentation modulus and hardness) of PI 1.

[0034] Example 3. The procedure of Example 2 was repeated except that samples of PI 2 having a thickness of 30 m were used in place of PI 1. The nanoindentation data and the solvents used are reported in Table 3. As can be seen from the data in Table 3, many common solvents used in hardcoat compositions adversely impact the mechanical properties (nanoindentation modulus and hardness) of PI 2.

TABLE-US-00005 TABLE 3 Nanoindentation Nanoindentation Solvent Modulus (GPa) Hardness (GPa) None 6.93 0.505 2,4-Dimethyl-3-pentanone 6.93 0.485 2,6-Dimethylcyclohexanone 6.91 0.475 Isopropyl acetate 6.89 0.493 Isoamyl acetate 6.83 0.498 2,6-Dimethyl-4-heptanone 6.82 0.483 2,2,4,4-Tetramethyl-3-pentanone 6.76 0.495 Cyclohexanone 6.7 0.462 Methyl iso-butyl ketone 6.58 0.479 2-Methylcyclohexanone 6.51 0.463

[0035] Example 4. Four formulations were prepared according to the general procedure using the components listed in Table 4, where 24 DP=2,4-dimethyl-3-pentanone, MIBK=methyl isobutyl ketone, and HBM=methyl 2-hydroxy-2-methylpropanoate. The siloxane resin used in each formulations was a commercially available epoxysiloxane (PC-2000HV, available from Polyset). Each formulation contained 1.2 wt % of a triarylsulfonium hexafluoroantimonate salt (50 wt % in propylene carbonate) as a photoactive curing agent. The nanoparticles used were SiO.sub.2 nanoparticles having an average particle size diameter of 25 m (available from Admatechs) as a suspension in the solvent reported in Table 4. The amount of the Each formulation was then coated on separate 50 m thick samples of PI 1 according to the general procedure described above. The pencil hardness of each coating was determined after curing and the data reported in Table 4.

TABLE-US-00006 TABLE 4 Film Pencil Formu- Siloxane Thick- Hard- lation resin Nanoparticles Solvent ness ness 1 30.7 wt % 30.7 wt % 24DP/ 10 m 4H toluene (1:1, w/w) 37.4 wt % 2 28.4 wt % 28.4 wt % HBM 7 m 4H 42 wt % 3 30.7 wt % 30.7 wt % 24DP/PGME 8 m 4H (1:9, w/w) 37.4 wt % Compar- 28.4 wt % 28.4 wt % MIBK 7 m 3H ative 42 wt %

[0036] Example 5. The procedure of Example 4 is repeated to prepare Formulations 2-5 using the components in the amounts shown in Table 5. PC-2003 is an epoxysiloxane oligomer available from Polyset. SR399 is dipentaerythritol pentaacrylate available from Sartomer. KTO46 is a photosensitizer available from Lamberti. The nanoparticles are SiO.sub.2 nanoparticles having an average particle size diameter of 25 m (as a suspension in methyl ethyl ketone (MEK), available from Admatechs. The abbreviation 26D refers to 2,6-dimethylcyclohexanone.

TABLE-US-00007 TABLE 5 Formulation Resin #1 Resin #2 PAG Nanoparticles Solvent 4 SR399: DM588: KTO46: 50 wt % in 24DP: 3.791 g 3.785 g 0.311 g 15.122 g 5 Acrylate- PAG: 1 wt 24DP: containing %/ 25 wt % silsesquioxane: KTO46: 70 wt % 4 wt % 6 Polyacrylate- PAG: 24DP: silsesquioxane 2 wt %, 25 wt % copolymer: 73 wt % 7 PC-2003: PAG: 1 wt % 50 wt % in 24DP: 26D 4.91 g 10.5 g 2.7 g