Plastic articles having multi-layer antireflection coatings, and sol-gel process for depositing such coatings

• US 5,856,018 A
• Filed: 06/17/1996
• Issued: 01/05/1999
• Est. Priority Date: 06/17/1996
• Status: Expired due to Term

• Current Assignee: Yazaki Corporation
• Original Assignee: Yazaki Corporation
• Inventors: Sarkar, Arnab, Chen, Din-Guo, Sato, Yoshitake, Yan, Yongan, Raychaudhuri, Satyabrata
• Primary Examiner(s): Pezzuto, Helen L.
• Application Number:
  US08/664,911
• Time in Patent Office: 932 Days
• Field of Search: 428/412, 428/446, 428/448, 428/480, 428/500, 427/162, 427/372.2, 427/380
• US Class Current: 428/448
• CPC Class Codes: C09D 183/02 Polysilicates
• CPC Class Codes: C09D 185/00 Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing atoms other than silicon, sulfur, nitrogen, oxygen, and carbon; Coating compositions based on derivatives of such polymers
• CPC Class Codes: G02B 1/115 Multilayers
• CPC Class Codes: Y10T 428/31507 Of polycarbonate
• CPC Class Codes: Y10T 428/31786 Of polyester [e.g., alkyd, etc.]
• CPC Class Codes: Y10T 428/31855 Of addition polymer from unsaturated monomers

Abstract

A sol-gel process is disclosed for depositing multi-layer antireflection coatings on plastic substrates. One or more polymerized, titanium-containing solutions are provided by mixing a titanium alkoxide, an alcohol, and water, and one or more polymerized, silicon-containing solutions are provided by mixing a silicon alkoxide, an alcohol, and water. These solutions are applied to the plastic substrate in an alternating fashion, to produce a succession of uniform layers of polymerized titanium dioxide and polymerized silicon dioxide. Each layer is individually cured before the next layer is applied. The resulting coating of multiple polymerized layers provides very low reflectance over the entire visible wavelength range, yet with excellent mechanical strength and durability.

Claims

1. A process for depositing a multi-layer antireflection coating on a plastic substrate, comprising the steps of:

providing one or more polymerized, non-organic, titanium-containing solutions consisting essentially of a titanium alkoxide, an alcohol, and water;

providing one or more polymerized, non-organic, silicon-containing solutions consisting essentially of a silicon alkoxide, an alcohol, and water;

applying a titanium-containing solution and applying a silicon-containing solution to the plastic substrate, in an alternating fashion, wherein a prescribed amount of the solution adheres to the substrate following each step of applying; and

following each step of applying, curing the adhered solution, before the next successive step of applying occurs, each such step of curing forming a separate, polymerized layer on the substrate, wherein the successive polymerized layers cooperate to form a multi-layer coating of at least four layers that provides substantially reduced reflectivity of visible light.

2. A process as defined in claim 1, wherein:

each layer of the multi-layer coating that is formed from a titanium-containing solution has an index of refraction in the range of 1.80 to 2.20; and

each layer of the multi-layer coating that is formed from a silicon-containing solution has an index of refraction in the range of 1.40 to 1.46.

3. A process as defined in claim 1, wherein:

a first layer of the multi-layer coating is formed from a titanium-containing solution and has a uniform thickness in the range of 10 to 30 nanometers;

a second layer of the multi-layer coating is formed from a silicon-containing solution and has a uniform thickness in the range of 20 to 40 nanometers;

a third layer of the multi-layer coating is formed from a titanium-containing solution and has a uniform thickness in the range of 70 to 100 nanometers; and

a fourth layer of the multi-layer coating is formed from a silicon-containing solution and has a uniform thickness in the range of 80 to 110 nanometers.

4. A process as defined in claim 3, wherein each step of applying includes a step of dipping the substrate into, and removing the substrate from, a titanium-containing solution or a silicon-containing solution, each successive removal occurring at a controlled rate, such that a prescribed amount of the solution adheres to the substrate.

5. A process as defined in claim 1, wherein each silicon-containing solution is prepared by mixing the following:

a silicon alkoxide selected from the group consisting of tetraethyl orthosilicate and tetramethyl orthosilicate;

ethyl alcohol;

deionized water; and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid.

6. A process as defined in claim 5, wherein a second layer of the multi-layer coating is formed from a solution that contains 70 to 90 moles of ethyl alcohol, 2 to 6 moles of deionized water, and 0.1 to 0.3 moles of the acidic catalyst for each mole of the silicon alkoxide.

7. A process as defined in claim 5, wherein a fourth layer of the multi-layer coating is formed from a solution that contains 25 to 35 moles of ethyl alcohol, 2 to 5 moles of deionized water, and 0.05 to 0.1 moles of the acidic catalyst for each mole of the silicon alkoxide.

8. A process as defined in claim 1, wherein each titanium-containing solution is prepared by mixing the following:

a titanium alkoxide selected from the group consisting of titanium isopropoxide, titanium propoxide, and titanium ethoxide;

ethyl alcohol;

deionized water; and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid.

9. A process as defined in claim 8, wherein a first layer of the multi-layer coating is formed from a solution that contains 80 to 120 moles of ethyl alcohol, 2 to 5 moles of deionized water, and 0.05 to 0.5 moles of the acidic catalyst for each mole of the titanium alkoxide.

10. A process as defined in claim 8, wherein a third layer of the multi-layer coating is formed from a solution that contains 35 to 55 moles of ethyl alcohol, 2 to 5 moles of deionized water, and 0.1 to 0.4 moles of the acidic catalyst for each mole of the titanium alkoxide.

11. A process as defined in claim 1, wherein:

each silicon-containing solution is prepared by mixing the following

a silicon alkoxide selected from the group consisting of tetraethyl orthosilicate and tetramethyl orthosilicate,

ethyl alcohol,

deionized water, and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid; and

each titanium-containing solution is prepared by mixing the following

a titanium alkoxide selected from the group consisting of titanium isopropoxide, titanium propoxide, and titanium ethoxide,

ethyl alcohol,

deionized water, and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid.

12. A process as defined in claim 11, wherein:

a first layer of the multi-layer coating is formed from a titanium-containing solution that contains 80 to 120 moles of ethyl alcohol, 2 to 5 moles of deionized water, and 0.05 to 0.5 moles of the acidic catalyst for each mole of the titanium alkoxide;

a second layer of the multi-layer coating is formed from a silicon-containing solution that contains 70 to 90 moles of ethyl alcohol, 2 to 6 moles of deionized water, and 0.1 to 0.3 moles of the acidic catalyst for each mole of the silicon alkoxide;

a third layer of the multi-layer coating is formed from a titanium-containing solution that contains 35 to 55 moles of ethyl alcohol, 2 to 5 moles of deionized water, and 0.1 to 0.4 moles of the acidic catalyst for each mole of the titanium alkoxide; and

a fourth layer of the multi-layer coating is formed from a silicon-containing solution that contains 25 to 35 moles of ethyl alcohol, 2 to 5 moles of deionized water, and 0.05 to 0.1 moles of the acidic catalyst for each mole of the silicon alkoxide.

13. A process as defined in claim 1, wherein the steps of providing one or more silicon-containing solutions and one or more titanium-containing solutions include mixing each solution at room temperature for at least four hours before being applied to the substrate.

14. A process as defined in claim 10, wherein the steps of providing one or more silicon-containing solutions and one or more titanium-containing solutions each include a step of filtering each solution through a filter having openings no larger than 5 microns in size.

15. A process as defined in claim 1, wherein the step of applying a titanium-containing solution to the plastic substrate occurs within a coating chamber in which the relative humidity is at least 40%.

16. A process as defined in claim 1, wherein the step of applying a silicon-containing solution to the plastic substrate occurs within a coating chamber in which the relative humidity is less than 40%.

17. A process as defined in claim 1, wherein the steps of curing the first, second, third and fourth layers of the multi-layer coating each occur at an elevated temperature for at least 10 minutes.

18. A process as defined in claim 17, wherein the elevated temperature of the successive steps of curing is less than the deformation temperature of the plastic substrate.

19. A process as defined in claim 18, wherein:

the plastic substrate is formed of polymethyl methacrylate; and

the elevated temperature of the successive steps of curing is less than 84°

C.

20. A process as defined in claim 18, wherein the successive steps of curing include:

raising the temperature of the substrate to the elevated temperature at a rate not exceeding 15°

C. per minute; and

reducing the temperature of the substrate from the elevated temperature to room temperature at a rate not exceeding 15°

C. per minute.

21. A process as defined in claim 1, wherein the multi-layer coating that is provided after the final step of curing exhibits an average reflectivity of less than or equal to 0.2% over the wavelength range of 450 nanometers to 650 nanometers and exhibits less than or equal to 0.9% over the wavelength range of 400 to 700 nanometers.

22. A process as defined in claim 1, wherein the multi-layer coating that is provided after the final step of curing withstands at least a 1H pencil scratch test without failure.

23. A process as defined in claim 1, wherein the multi-layer coating that is provided after the final step of curing withstands exposure to 95% relative humidity at 60°

C. for at least 192 hours, without significant degradation of optical and mechanical properties.

24. A process as defined in claim 1, wherein the multi-layer coating that is provided after the final step of curing withstands exposure to a temperature of 84°

C. for 192 hours and exposure to a temperature of -40°

C. for 192 hours, without significant degradation of optical and mechanical properties.

25. A process as defined in claim 1, wherein the multi-layer coating that is provided after the final step of curing withstands exposure to a temperature that cycles 200 times between 84°

C. and -30°

C., without significant degradation of optical and mechanical properties.

26. A process as defined in claim 1, wherein the plastic substrate is formed of a material selected from the group consisting of polymethyl methacrylate, polystyrene, polycarbonate, allyl diglycol carbonate, and polyethylene terephthalate.

27. A process as defined in claim 1, and further including a preliminary step of applying a base coat to the plastic substrate.

28. A process as defined in claim 1, wherein each step of applying includes a step of dipping the substrate into, and removing the substrate from, a titanium-containing solution or a silicon-containing solution, wherein each successive removal occurs at a controlled rate, such that a prescribed amount of the solution adheres to the substrate.

29. A process for depositing a multi-layer antireflection coating on a plastic substrate, comprising the steps of:

mixing one or more first polymerized, non-organic solutions consisting essentially of an alkoxide, an alcohol, and water, wherein the one or more first polymerized solutions are formulated to provide thin films having a refractive index of 1.80 or more;

mixing one or more second polymerized, non-organic solutions consisting essentially of an alkoxide, an alcohol, and water, wherein the one or more second polymerized solutions are formulated to provide thin films having a refractive index of 1.46 or less;

applying a first polymerized solution and a second polymerized solution to the plastic substrate, in an alternating fashion, wherein a prescribed amount of the solution adheres to the substrate following each step of applying; and

following each step of applying, curing the adhered solution, before the next successive step of applying occurs, each such step of curing forming a separate, polymerized layer on the substrate, wherein the successive polymerized layers cooperate to form a multi-layer coating of at least four layers that provides substantially reduced reflectivity of visible light.

30. A process as defined in claim 29, wherein:

the alkoxide mixed in the step of mixing to produce the one or more first polymerized solutions is selected from the group consisting of titanium isopropoxide, titanium propoxide, and titanium ethoxide, and the polymerized layers produced from such one or more first solutions include titanium dioxide; and

the alkoxide mixed in the step of mixing to produce the one or more second polymerized solutions is selected from the group consisting of tetraethyl orthosilicate and tetramethyl orthosilicate, and the polymerized layers produced from such one or more second solutions include silicon dioxide.

31. A process as defined in claim 30, wherein:

each layer of the multi-layer coating that is formed from a first solution has an index of refraction in the range of 1.80 to 2.20; and

each layer of the multi-layer coating that is formed from a second solution has an index of refraction in the range of 1.40 to 1.46.

32. A process as defined in claim 30, wherein:

a first layer of the multi-layer coating is formed from a first solution and has a thickness in the range of 10 to 30 nanometers;

a second layer of the multi-layer coating is formed from a second solution and has a thickness in the range of 20 to 40 nanometers;

a third layer of the multi-layer coating is formed from a first solution and has a thickness in the range of 70 to 100 nanometers; and

a fourth layer of the multi-layer coating is formed from a second solution and has a thickness in the range of 80 to 110 nanometers.

33. A process as defined in claim 30, wherein each of the one or more second solutions is prepared by mixing the following:

a silicon alkoxide selected from the group consisting of tetraethyl orthosilicate and tetramethyl orthosilicate;

ethyl alcohol;

deionized water; and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid.

34. A process as defined in claim 30, wherein each of the one or more first solutions is prepared by mixing the following:

a titanium alkoxide selected from the group consisting of titanium isopropoxide, titanium propoxide, and titanium ethoxide;

ethyl alcohol;

deionized water; and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid.

35. A process as defined in claim 30, wherein:

each silicon-containing solution is prepared by mixing the following

a silicon alkoxide selected from the group consisting of tetraethyl orthosilicate and tetramethyl orthosilicate,

ethyl alcohol,

deionized water, and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid; and

each titanium-containing solution is prepared by mixing the following

a titanium alkoxide selected from the group consisting of titanium isopropoxide, titanium propoxide, and titanium ethoxide,

ethyl alcohol,

deionized water, and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid.

36. A process as defined in claim 35, wherein:

a first layer of the multi-layer coating is formed from a titanium-containing solution that contains 80 to 120 moles of ethyl alcohol, 2 to 5 moles of deionized water, and 0.05 to 0.5 moles of the acidic catalyst for each mole of the titanium alkoxide;

a second layer of the multi-layer coating is formed from a silicon-containing solution that contains 70 to 90 moles of ethyl alcohol, 2 to 6 moles of deionized water, and 0.1 to 0.3 moles of the acidic catalyst for each mole of the silicon alkoxide;

a third layer of the multi-layer coating is formed from a titanium-containing solution that contains 35 to 55 moles of ethyl alcohol, 2 to 5 moles of deionized water, and 0.1 to 0.4 moles of the acidic catalyst for each mole of the titanium alkoxide; and

a fourth layer of the multi-layer coating is formed from a silicon-containing solution that contains 25 to 35 moles of ethyl alcohol, 2 to 5 moles of deionized water, and 0.05 to 0.1 moles of the acidic catalyst for each mole of the silicon alkoxide.

37. A process as defined in claim 29, and further including a preliminary step of applying a base coat to the plastic substrate.

38. A process as defined in claim 29, wherein each step of applying includes a step of dipping the substrate into, and removing the substrate from, a first solution or a second solution, wherein each successive removal occurs at a controlled rate, such that a prescribed amount of the solution adheres to the substrate.

39. A process for depositing a multi-layer antireflection coating on a plastic substrate, comprising the steps of:

providing a first polymerized, non-organic, titanium-containing solution consisting essentially of the following ingredients, in the indicated proportions

1.0 moles of a titanium alkoxide selected from the group consisting of titanium isopropoxide, titanium propoxide, and titanium ethoxide

80 to 120 moles of ethyl alcohol,

2 to 5 moles of deionized water, and

0.05 to 0.05 moles of an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid;

providing a second polymerized, non-organic, titanium-containing solution consisting essentially of the following ingredients, in the indicated proportions

1.0 moles of a titanium alkoxide selected from the group consisting of titanium isopropoxide, titanium propoxide, and titanium ethoxide

35 to 55 moles of ethyl alcohol,

2 to 5 moles of deionized water, and

0.1 to 0.4 moles of an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid;

providing a first polymerized, non-organic, silicon-containing solution consisting essentially of the following ingredients, in the indicated proportions

1.0 moles of a silicon alkoxide selected from the group consisting of tetraethyl orthosilicate and tetramethyl orthosilicate,

70 to 90 moles of ethyl alcohol,

2 to 6 moles of deionized water, and

0.1 to 0.3 moles of an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid;

providing a second polymerized, non-organic, silicon-containing solution consisting essentially of the following ingredients, in the indicated proportions

1.0 moles of a silicon alkoxide selected from the group consisting of tetraethyl orthosilicate and tetramethyl orthosilicate,

25 to 35 moles of ethyl alcohol,

2 to 5 moles of deionized water, and

0.05 to 0.1 moles of an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid;

applying the first polymerized, titanium-containing solution to a substrate formed of a material methacrylate, polystyrene, polycarbonate, allyl diglycol carbonate, and polyethylene terephthalate, wherein a prescribed amount of the solution adheres to the substrate;

curing the adhered solution to form a first polymerized layer, the layer including polymerized titanium dioxide and having a prescribed uniform thickness and an index of refraction in the range of 1.80 to 2.20;

applying the first polymerized, silicon-containing solution to the coated substrate, wherein a prescribed amount of the solution adheres to the coated substrate;

curing the adhered solution to form a second polymerized layer, the layer including polymerized silicon dioxide and having a prescribed uniform thickness and an index of refraction in the range of 1.40 to 1.46;

applying the second polymerized, titanium-containing solution to the coated substrate, wherein a prescribed amount of the solution adheres to the coated substrate;

wherein the first, second, third and fourth layers cooperate to form an antireflection coating that provides substantially reduced reflectivity of visible light.

40. A process as defined in claim 39, wherein:

the first layer has a thickness in the range of 10 to 30 nanometers;

the second layer has a thickness in the range of 20 to 40 nanometers;

the third layer has a thickness in the range of 70 to 100 nanometers; and

the fourth layer has a thickness in the range of 80 to 110 nanometers.

41. A process for depositing a polymerized titanium dioxide, thin-film optical coating on a plastic substrate, comprising:

providing a polymerized, non-organic, titanium-containing solution consisting essentially of a titanium alkoxide, an alcohol, and water;

applying the titanium-containing solution to the plastic substrate such that a prescribed amount of the solution adheres to the substrate, wherein applying occurs within a coating chamber in which the relative humidity is at least 40%; and

curing the adhered titanium-containing solution to form a polymerized titanium dioxide, thin-film optical coating on the substrate.

42. A process as defined in claim 41, wherein the titanium-containing solution is prepared by mixing the following:

a titanium alkoxide selected from the group consisting of titanium isopropoxide, titanium propoxide, and titanium ethoxide;

ethyl alcohol;

deionized water; and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid.

43. A process as defined in claim 41, wherein providing includes filtering the titanium-containing solution through a filter having openings no larger than 5 microns in size.

44. A process as defined in claim 41, wherein curing occurs at an elevated temperature for at least 10 minutes, the elevated temperature being less than the deformation temperature of the plastic substrate.

45. A process for depositing a polymerized silicon dioxide, thin-film optical coating on a plastic substrate, comprising:

providing a polymerized, non-organic, silicon-containing solution consisting essentially of a silicon alkoxide, an alcohol, and water;

applying the silicon-containing solution to the plastic substrate such that a prescribed amount of the solution adheres to the substrate, wherein applying occurs within a coating chamber in which the relative humidity is less than 40%; and

curing the adhered silicon-containing solution to from a polymerized silicon dioxide, thin-film optical coating on the substrate.

46. A process as defined in claim 45, wherein the silicon-containing solution is prepared by mixing the following:

a silicon alkoxide selected from the group consisting of tetraethyl orthosilicate and tetramethyl orthosilicate;

ethyl alcohol;

deionized water; and

an acidic catalyst selected from the group consisting of hydrochloric acid and nitric acid.

47. A process as defined in claim 45, wherein providing includes filtering the silicon-containing solution through a filter having openings no larger than 5 microns in size.

48. A process as defined in claim 45, wherein curing occurs at an elevated temperature for at least 10 minutes, the elevated temperature being less than the deformation temperature of the plastic substrate.