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 is a colorless polyimide substrate and has a pencil hardness of >1H, a haze value of <2%, and a yellowness index of <6 before the disposition; and wherein the coating composition comprises: (1) siloxane 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; and 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 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.

Description

(1) 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.

(2) 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

(3) Example 2. Samples of PI 1 substrate, each having a thickness of 50 μm, 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.

(4) 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)

(5) 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.

(6) Example 3. The procedure of Example 2 was repeated except that samples of PI 2 having a thickness of 30 μm 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.

(7) 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

(8) 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 μm (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 μm 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.

(9) 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 μm  4H toluene (1:1, w/w) 37.4 wt % 2 28.4 wt % 28.4 wt % HBM 7 μm 4H 42 wt % 3 30.7 wt % 30.7 wt % 24DP/PGME 8 μm 4H (1:9, w/w) 37.4 wt % Compar- 28.4 wt % 28.4 wt % MIBK 7 μm 3H ative 42 wt %

(10) 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 μm (as a suspension in methyl ethyl ketone (MEK), available from Admatechs. The abbreviation 26D refers to 2,6-dimethylcyclohexanone.

(11) 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