SILICA COATING FOR ENHANCED HYDROPHILICITY

• US 20100092765A1
• Filed: 10/06/2009
• Published: 04/15/2010
• Est. Priority Date: 10/10/2008
• Status: Abandoned Application

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Schlechte, Jay S., Hager, Patrick J., Yorkgitis, Elaine M., Jing, Naiyong
• Application Number:
  US12/573,925
• Publication Number:
  US 20100092765A1
• Time in Patent Office: Days
• US Class Current: 428/331
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2006/12 Surface area
• CPC Class Codes: C01P 2006/22 Rheological behaviour as dispersion, e.g. viscosity, sedimentation stability
• CPC Class Codes: C08K 3/36 Silica
• CPC Class Codes: C08K 5/0091 Complexes with metal-heteroatom-bonds
• CPC Class Codes: C08K 5/5419 containing at least one Si—C bond
• CPC Class Codes: C08K 5/5425 containing at least one C=C bond
• CPC Class Codes: C08K 5/5435 containing oxygen in a ring
• CPC Class Codes: C08K 5/548 containing sulfur C08K5/5477 takes precedence
• CPC Class Codes: C08K 9/06 with silicon-containing compounds
• CPC Class Codes: C09C 1/0009 Pigments for ceramics C09C1/0015, C09C1/0078 take precedence
• CPC Class Codes: C09C 1/3081 Treatment with organo-silicon compounds
• CPC Class Codes: C09C 1/309 Combinations of treatments provided for in groups C09C1/3009 - C09C1/3081
• CPC Class Codes: C09D 183/02 Polysilicates
• CPC Class Codes: C09D 183/04 Polysiloxanes
• CPC Class Codes: C09D 7/62 modified by treatment with other compounds
• CPC Class Codes: C09D 7/67 Particle size smaller than 100 nm
• CPC Class Codes: Y10T 428/259 Silicic material

Abstract

A coating composition is provided comprising a) an aqueous dispersion, having a pH of less than 7.5, of silica nanoparticles having average particle diameters of 40 nanometers or less, b) an alkoxysilane oligomer; c) a silane coupling agent, and d) optionally a metal β-diketone complexing agent. The compositions may be used to prepare coated articles wherein the coating is substantially uniform in thickness, durably adheres to the substrate, and provides hydrophilic and/or antireflection surface properties to the substrate.

Claims

1. A coating composition comprising:

a) an aqueous dispersion, having a pH of less than 7.5 of silica nanoparticles having average particle diameters of 40 nanometers or less,

b) an alkoxysilane oligomer;

c) a silane coupling agent, and

d) optionally a metal β

-diketone complexing agent.

2. The coating composition of claim 1 comprising:

1. 30 to 95 wt. % of said silica nanoparticles,

2. 1 to 55 wt % of said an alkoxysilane oligomer;

3. 0.25 to 35 wt. % of said silane coupling agent; and

4. 0 to 10 wt. % of said metal β

-diketone complexing agent.

3. The coating composition of claim 1 wherein said alkoxysilane oligomer is of the formula:

where

each R¹ is individually H, C₁ to C₄ alkyl, an alkali metal, and alkali earth metal or ammonium;

each R² is independently C₁ to C₄ alkyl,

x is 2 to 100,

y and z may be zero,

x is greater than y+z; and

x+y+z is 2 to 100.

4. The coating composition of claim 1 wherein said silane coupling agent is of the formula:

[(Y)_c—

R³]_d—

Si—

(OR⁴)_b(R⁴)<sub>4−

(b+d)</sub>,

where

Y is a non-basic group that may bond to, or associate with, the surface of a preselected substrate,

R³ is a covalent bond or a di- or trivalent hydrocarbon bridging group,

R⁴ is independently an alkyl, aryl, or aralkyl group of 1 to 8 carbon atoms optionally substituted in available positions by oxygen, nitrogen and/or sulfur atoms;

c is 1 or 2, b is 1 to 3 and d is 1 or 2 and (b+d)≦

4.

5. The coating composition of claim 4, wherein the Y is an ethylenically unsaturated group Y².

6. The coating composition of claim 4, wherein the Y is a non-basic organic functional group Y¹, which may be selected from an epoxy group, an acid group, an ester group, a hydroxy group and a mercapto group.

7. The coating composition of claim 4, wherein Y is a non-functional hydrocarbyl group Y³, selected from alkyl groups an aryl groups.

8. The coating composition of claim 1 wherein the silica nanoparticles have average particle diameters of 20 nanometers or less.

9. The coating composition of claim 1 wherein the silica nanoparticles have average particle diameters of 10 nanometers or less.

10. The coating composition of claim 2 wherein the β

-diketone complexing agent is used in amounts of 0.1 to 5 wt. %.

11. The coating composition of claim 1 further comprising less than 20 wt. %, of a water-soluble or water-miscible organic solvent.

12. The coating composition of claim 1, wherein the silica nanoparticle content comprises surface modified nanoparticles having from 1 to 90% surface coverage of the modifier group.

13. The coating composition of claim 1 having a pH value of less than 4.

14. The coating composition of claim 13 wherein the composition is acidified to a pH value of less than 4 with an acid having a pKa of less than 5.

15. The coating composition of claim 14 wherein said acid is selected from oxalic acid, propionic acid, formic acid, citric acid, benzoic acid, acetic acid, benzenesulfonic acid, H₂SO₃, H₃PO₄, CF₃CO₂H, HCl, HBr, HI, HBrO₃, HNO₃, HClO₄, H₂SO₄, CH₃SO₃H, CF₃SO₃H, CF₃CO₂H, and CH₃OSO₂OH.

16. The coating composition of claim 1 wherein said alkoxysilane oligomer is represented by the unit cell formula represented by the unit cell of the formula Si(O)_o(OR¹)_p, where o is greater than zero and less than 1.2 and p is greater than 1.4 and less than 4.

17. The coating composition of claim 1, wherein said composition comprises the reaction product of the alkoxysilane oligomer, the silane coupling agent and optionally the metal β

-diketone complexing agent.

18. The coating composition of claim 1, wherein the silica nanoparticles are not surface modified.

24. A hydrophilic article prepared from the method of claim 1.

28. A coated article comprising a substrate having a dried coating of the coating composition of claim 1 thereon.

29. The coated article of claim 28 having a water contact angle of less than 50°

.

30. The coated article of claim 28 wherein said coating is less than about 1000 angstroms thick.

31. The coated article of claim 28 wherein said substrate is a glass, ceramic, cement, stone, painted or clearcoated surfaces, metal, paper, thermoset polymers and thermoplastic polymers.

19. A method of providing a coating to a substrate comprising providing a substrate;

contacting a substrate with a coating composition comprising;

a) an aqueous dispersion having a pH of less than 7.5 of silica nanoparticles having average particle diameters of 40 nanometers or less, and

b) an alkoxysilane oligomer,

c) silane coupling agent, and

d) optionally a metal β

-diketone complexing agent;

and drying to provide a silica nanoparticle coating.

20. The method of claim 19 wherein the substrate is a hydrophobic substrate having a water contact angle of greater than 50°

.

21. The method of claim 19 wherein the pH of the aqueous dispersion is less than 4.

22. The method of claim 21 wherein is aqueous dispersion is acidified to a pH of less than 4 with an acid having a pKa of less than 5.

23. The method of claim 22 wherein the acid is selected from oxalic acid, propionic acid, formic acid, citric acid, H₃PO₄, HCl, HBr, HI, HBrO₃, HNO₃, HClO₄, H₂SO₄, CH₃SO₃H, CF₃SO₃H, CF₃CO₂H, and CH₃SO₂OH.

25. The method of claim 19, wherein the substrate has a water contact angle of less than 50°

after coating.

26. The method of claim 19 wherein the pH of the coating composition is less than 4.

27. The method of claim 19 further comprising rinsing the excess wet coating composition with water prior to drying.