Hydrophilic-core microcapsules and their formation

• US 9,227,221 B2
• Filed: 08/16/2010
• Issued: 01/05/2016
• Est. Priority Date: 09/19/2005
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Calle, Luz M., Li, Wenyan, Buhrow, Jerry W., Jolley, Scott T.
• Primary Examiner(s): LOUIE, MANDY C
• Application Number:
  US12/856,849
• Publication Number:
  US 20100320421A1
• Time in Patent Office: 1,968 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: B01J 13/14 Polymerisation; cross-linking
• CPC Class Codes: B01J 13/16 Interfacial polymerisation
• CPC Class Codes: B05D 2202/00 Metallic substrate
• CPC Class Codes: B05D 5/00 Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
• CPC Class Codes: B05D 5/06 to obtain multicolour or other optical effects B05D5/02 takes precedence
• CPC Class Codes: C04B 20/1029 Macromolecular compounds
• CPC Class Codes: C04B 2103/54 Pigments; Dyes
• CPC Class Codes: C04B 2103/61 Corrosion inhibitors
• CPC Class Codes: C04B 40/0641 Mechanical separation of ingredients, e.g. accelerator in breakable microcapsules
• CPC Class Codes: C08K 9/10 Encapsulated ingredients
• CPC Class Codes: C09B 67/0097 Dye preparations of special physical nature; Tablets, films, extrusion, microcapsules, sheets, pads, bags with dyes
• CPC Class Codes: C09D 5/082 characterised by the anti-corrosive pigment
• CPC Class Codes: C09D 7/41 Organic pigments; Organic dyes
• CPC Class Codes: C09D 7/48 Stabilisers against degradation by oxygen, light or heat
• CPC Class Codes: C09D 7/65 macromolecular C09D7/41-C09D7/48 take precedence
• CPC Class Codes: C09D 7/70 characterised by shape, e.g. fibres, flakes or microspheres

Abstract

Hydrophilic-core microcapsules and methods of their formation are provided. A hydrophilic-core microcapsule may include a shell that encapsulates water with the core substance dissolved or dispersed therein. The hydrophilic-core microcapsules may be formed from an emulsion having hydrophilic-phase droplets dispersed in a hydrophobic phase, with shell-forming compound contained in the hydrophilic phase or the hydrophobic phase and the core substance contained in the hydrophilic phase. The shells of the microcapsules may be capable of being broken down in response to being contacted by an alkali, e.g., produced during corrosion, contacting the shell.

Claims

1. A method of forming hydrophilic-core microcapsules comprising:

forming a single hydrophilic phase including at least one pre-polymer or monomer, a cross-linking agent, at least one active substance, an optional co-solvent, and water;

forming a single hydrophobic phase including a hydrophobic substance and optionally at least one surfactant in the absence of any pre-polymer or monomer and in the absence of any cross-linking agent;

mixing the hydrophobic phase with the hydrophilic phase to create and disperse droplets of the hydrophilic phase within the hydrophobic phase to form an emulsion; and

initiating a reaction at an interface of the hydrophilic phase and the hydrophobic phase to form a solid shell encapsulating the hydrophilic phase forming hydrophilic-core microcapsules, wherein said solid shell includes a shell wall comprising a compound having one or more chemical bonds that are broken down when contacted with an alkali produced during a corrosion reaction causing the release of the hydrophilic phase, wherein said alkali has a pH above about 8.

2. The method of claim 1, wherein said at least one active substance is a corrosion indicator, a corrosion inhibitor, a film-forming compound, or combinations thereof.

3. The method of claim 1, including the further step of adding a surfactant to the emulsion.

4. The method of claim 3, wherein the surfactant comprises alkyl anhydride.

5. The method of claim 3, wherein the hydrophobic substance comprises methyl myristate.

6. The method of claim 1, wherein said cross-linking agent includes one or more ester groups.

7. The method of claim 6, wherein the cross-linking agent is selected from fully esterified monomers comprising ethyleneglycol di-2-mercapto acetate, ethyleneglycol di-2-hydroxyacetate, pentaerythritol tetrakis(2-hydroxyacetate), pentaerythritol tetrakis(3-hydroxypropionate) (PTT), pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), or from any number of partially esterified polyols comprising glycerol monoacetate, neopentylglycol monopropionate, or trimethylolpropane diacetate.

8. The method of claim 1, wherein said at least one pre-polymer or monomer is selected from the group consisting of urea formaldehyde, melamine formaldehyde and other amine formaldehyde prepolymers, polyurethane prepolymers, polyols, isocyanates, urea and formaldehyde solution, melamine and formaldehyde solution, and other amine formaldehyde solutions.

9. The method of claim 1, including the further step of adding a catalyst to the emulsion.

10. The method of claim 9, wherein the catalyst is an acid.

11. The method of claim 10, including the further step of adding the acid catalyst until the emulsion has a pH in the range of about 2 to 5.

12. The method of claim 1, including the further step of heating the emulsion.

20. The method of claim 1, wherein said shell wall includes about 20 percent to about 50 percent, by mass, cross-linking agent and about 50 percent to about 80 percent, by mass, pre-polymer.

21. The method of claim 1 wherein said hydrophilic phase consists of formaldehyde, melamine, a cross-linking agent, at least one active substance, an optional co-solvent, and optional surfactant and water.

22. The method of claim 1, wherein said cross-linking agent is pentaerythritol tetrakis (3-mercaptopropionate).

23. The method of claim 1, wherein said hydrophilic phase is formed including the steps of:

mixing water and said at least one pre-polymer to form a first mixture, and then heating said first mixture to about 70°

C. with stirring;

adding said cross-linking agent to said first mixture forming a second mixture; and

adding said at least one active substance to said second mixture.

13. A method of forming hydrophilic-core microcapsules comprising:

forming a hydrophilic phase including at least one active substance, a catalyst and water in the absence of any pre-polymer or monomer and in the absence of any cross-linking agent, wherein said catalyst is added until a pH of about 2 to about 4 is achieved;

forming a first hydrophobic phase including at least one surfactant and a first hydrophobic substance in the absence of any pre-polymer or monomer and in the absence of any cross-linking agent;

mixing the first hydrophobic phase with the hydrophilic phase to form an emulsion comprising droplets of the hydrophilic-phase dispersed in the first hydrophobic phase;

forming a second hydrophobic phase including a cross-linking agent comprising one or more ester groups, a pre-polymer or monomer, and a second hydrophobic substance;

mixing the second hydrophobic phase to said emulsion; and

initiating a reaction at an interface of the hydrophobic phase and droplets to form a single solid shell encapsulating the hydrophilic phase forming hydrophilic-core microcapsules, wherein said single solid shell includes a shell wall comprising a compound having one or more chemical bonds that are broken down when contacted with an alkali produced during a corrosion reaction causing the release of at least the first hydrophilic phase, wherein said alkali has a pH above about 8.

14. The method of claim 13 wherein said at least one active substance is a corrosion indicator or a corrosion inhibitor.

15. The method of claim 14, wherein said at least one active substance is a corrosion inhibitor and said hydrophilic phase includes about zero to about 10 percent, by mass, corrosion inhibitor and about 90 to about 100 percent, by mass, water.

16. The method of claim 13, wherein said first hydrophobic phase includes about 70 to about 90 percent, by mass, oil and about 10 to about 30 percent, by mass, surfactant.

17. The method of claim 13, wherein said second hydrophobic phase includes about 88 to about 92 percent, by mass, oil;

about 4 to about 7 percent, by mass, pre-polymer; and

about 4 to about 5 percent, by mass, cross-linking agent.

18. The method of claim 13, wherein said emulsion including said second hydrophobic phase includes about 40 to about 55 percent, by mass, the first hydrophobic phase;

about 30 to about 35 percent, by mass, the second hydrophobic phase; and

about 10 to about 30 percent, by mass water.

19. The method of claim 13, wherein said reaction proceeds for about 3 to about 5 hours.

24. The method of claim 13 wherein

said hydrophilic phase consists of at least one active substance, a catalyst, and water;

said first hydrophobic phase consists of at least one surfactant and a first hydrophobic substance; and

said second hydrophobic phase consists of a cross-linking agent comprising one or more ester groups, a pre-polymer, and a second hydrophobic substance.