Expandable microspheres and methods of making and using the same

• US 8,679,294 B2
• Filed: 02/07/2013
• Issued: 03/25/2014
• Est. Priority Date: 08/28/2008
• Status: Active Grant

• Current Assignee: International Paper Company
• Original Assignee: International Paper Company
• Inventors: Hong, Yaoliang, Mohan, Kosaraju Krishna, Dimonie, Victoria Laurentia, Klein, Andrew, Daniels, Eric Scott, Boyars, Brian, Froass, Peter M., Anderson, Christopher D., Sudol, Edward David, Fagan, Mark Edward
• Primary Examiner(s): Halpern, Mark
• Application Number:
  US13/761,620
• Publication Number:
  US 20130146241A1
• Time in Patent Office: 411 Days
• Field of Search: 162/158, 162/164.1, 162/103, 521/56, 521/57, 524/27, 524/35, 428/402
• US Class Current: 162/103
• CPC Class Codes: B01J 13/14 Polymerisation; cross-linking
• CPC Class Codes: C08L 27/08 Homopolymers or copolymers of vinylidene chloride
• CPC Class Codes: C08L 33/20 Homopolymers or copolymers of acrylonitrile C08L55/02 takes precedence
• CPC Class Codes: D21H 21/54 being spherical, e.g. microcapsules, beads
• CPC Class Codes: Y10T 428/2982 Particulate matter [e.g., sphere, flake, etc.]

Abstract

Expandable microspheres formed by suspension polymerization using a shot growth method are provided. The microspheres are formed of a continuous, gas impermeable shell surrounding a blowing agent. The shell includes a first polymer layer formed from primary monomers and a second layer that includes a chemically reactive monomer or a high Tg monomer. To form the microspheres, the primary monomers are polymerized in a reaction vessel to an approximate 90% polymerization, at which time a secondary monomer that is either a monomer having a Tg of at least 85° C. or a chemically reactive monomer, is added to the reaction vessel to drive the polymerization reaction to completion. The outer layer thus contains either a larger amount of the high Tg monomer or a chemically reactive monomer that possesses the ability to covalently bond a cationic species. The microspheres may be used in papermaking processes to increase the paper bulk.

Claims

1. A method of forming an expandable microsphere comprising:

mixing primary monomers selected from nitrile containing monomers, acrylic ester monomers, methacrylic ester monomers, vinyl esters, vinyl halide monomers and combinations thereof, at least one blowing agent, a crosslinking monomer, a polymerization initiator, and a stabilizer system in a reaction vessel for a period of time sufficient to achieve an approximate 90% polymerization of said primary monomers and form a first polymeric layer surrounding said blowing agent; and

adding a secondary monomer selected from monomers having a Tg of at least 85°

C. and chemically reactive monomers to said reaction vessel to form a second polymeric layer at least substantially surrounding said first polymeric layer and forming an expandable microsphere.

2. The method of claim 1, wherein said reaction vessel further includes at least one member selected from a salt, a phase partitioner, an inhibitor an acid and water.

3. The method of claim 1, further comprising:

purging said reaction vessel to remove oxygen.

4. The method of claim 1, further comprising:

adding a cationic species to said microsphere such that said cationic species covalently bonds to said second polymeric layer.

5. The method of claim 1, wherein the secondary monomer is selected from monomers having a Tg of at least 85°

C. which are;

acrylonitrile (AN) monomers;

vinylidene chloride (VDC);

methyl methacrylate (MMA) monomers;

tetraethylene glycol dimethacrylate monomers (TEGDMA);

2,3-epoxypropyl acrylate monomers (EPA);

or methacrylonitrile monomers (MAN).

6. The method of claim 1, wherein the secondary monomer is selected from chemically reactive monomers which are:

glycidyl methacrylate (GMA);

methacrylic acid (MAA);

vinyl benzyl chloride (VBC);

or combinations thereof.