Self-coalescing latex

Patent metadata

Field	Value
Publication number	US-9505922-B2
Application number	US-201214009295-A
Country	US
Kind code	B2
Filing date	May 15, 2012
Priority date	May 17, 2011
Publication date	Nov 29, 2016
Grant date	Nov 29, 2016

Abstract

The present invention relates to self-coalescing latexes that incorporate film fat ing polymers that are low molecular weight polymers that are compatible with the latex and act as thin plasticizers penetrating through the remainder of the latex particle and aiding in the coalescence of the remaining polymers. In a preferred embodiment, the self-coalescing latex is a sequentially polymerized polymer having at least a core, a shell and a skin. The film forming polymers are formed of monomers substantially the same as the monomers of the shell but having average weighted molecular weights substantially less than the polymers of the shell. The present invention also relates to the method of polymerizing the self-coalescing latex of the current invention, which largely results from the addition of a substantial amount of chain transfer agent to a remaining portion, about 15% or less, of the monomer pre-emulsion prior to polymerization. Lastly, the invention relates to paint compositions incorporating the self-coalescing latexes that are substantially free of coalescing agents or aids.

First claim

The invention claimed is:

1. A self-coalescing latex comprising a sequentially designed polymer comprised of at least
from about 10 to about 50% by weight of hard monomers forming a first stage of the latex having a glass transition temperature from about 50° C. to about 130° C.,
from about 10 to about 60% by weight of soft monomers forming a second stage of the latex having a glass transition temperature from about −10° C. to about 50° C., and
from about 0 to about 10% by weight of hydrophilic, hydrophobic or functional monomers
wherein the polymer further comprises a film forming polymer having a weighted average molecular weight of less than about 40,000 Daltons and is present in about 0.5% by weight to less than about 10% by weight of the polymer.

2. The self-coalescing latex of claim 1 , wherein the film forming polymer forms a third stage of the sequentially designed polymer.

3. The self-coalescing latex of claim 2 , the first stage comprises a core of the sequentially designed polymer, the second stage comprises a shell of the sequentially designed polymer, and the third stage comprises a skin of the sequentially designed polymer.

4. The self-coalescing latex of claim 3 , wherein the core has a weighted average molecular weight between about 175,000 to about 250,000 Daltons.

5. The self-coalescing latex of claim 4 , wherein the core has a weighted average molecular weight of between about 190,000 to about 240,000 Daltons.

6. The self-coalescing latex of claim 3 , wherein the core has a glass transition temperature of about 70 to about 110° C.

7. The self-coalescing latex of claim 1 , wherein the hard monomers comprise at least one of methacrylic monomers, acrylonitrile monomers, styrene monomers, vinyl halide monomers, and vinyl acetate monomers.

8. The self-coalescing latex of claim 1 , wherein the hard monomer comprises methyl methacrylate.

9. The self-coalescing latex of claim 3 , wherein the core is further comprised of hydrophobic monomers.

10. The self-coalescing latex of claim 3 , wherein the core comprises about 10 to 50% of the latex.

11. The self-coalescing latex of claim 3 , wherein the shell has a weighted average molecular weight between about 75,000 to about 175,000 Daltons.

12. The self-coalescing latex of claim 11 , wherein the shell has a weighted average molecular weight between about 90,000 to about 150,000 Daltons.

13. The self-coalescing latex of claim 3 , wherein the shell has a glass transition temperature in the range of about 10 to about 40° C.

14. The self-coalescing latex of claim 1 , wherein the soft monomers comprise at least one of acrylic monomers, vinyldiene halide monomers, alkylene monomers, and glycidyl acrylate monomers.

15. The self-coalescing latex of claim 1 , wherein the soft monomers comprise at least one of ethyl acrylate, butyl acrylate, butyl methacrylate, and 2-ethylhexy acrylate.

16. The self-coalescing latex of claim 3 , wherein the shell is further comprised of hydrophilic monomers and functional monomers.

17. The self-coalescing latex of claim 16 , wherein the functional monomers comprise crosslinking or wet adhesion monomers.

18. The self-coalescing latex of claim 3 , wherein the shell comprises about 20 to about 60% of the latex.

19. The self-coalescing latex of claim 3 , wherein the skin has a weighted average molecular weight that is less than about 25% of the weighted average molecular weight of the shell.

20. The self-coalescing latex of claim 3 , wherein the skin has a weighted average molecular weight of about 10,000 to about 40,000 Daltons.

21. The self-coalescing latex of claim 20 , wherein the skin has a weighted average molecular weight of about 15,000 to about 35,000 Daltons.

22. The self-coalescing latex of claim 3 , wherein the skin comprises about 0.5 to about 10% of the latex.

23. The self-coalescing latex of claim 1 , wherein the sequentially designed polymer has a minimum film forming temperature between about −5° C. to about 5° C.

24. A sequential emulsion polymerization method for the self-coalescing latex of claim 1 comprising the steps of:
preparing a monomer pre-emulsion mixture for the first stage,
preparing a monomer pre-emulsion mixture for the second stage,
initiating polymerization of the monomer pre-emulsion mixture for the first stage to form the first stage,
treating the first stage with a substantial portion of the monomer pre-emulsion for the second stage to form the second stage,
charging a remaining portion of the monomer pre-emulsion for the second stage with a chain transfer agent, and
treating the second stage with the remaining portion of the monomer pre-emulsion for the second stage to form a third stage, wherein the weighted average molecular weight of a polymer of the third stage is substantially less than the weighted average molecular weight of a polymer of the second stage.

25. The sequential emulsion polymerization method of claim 24 , wherein the remaining portion of the second stage monomer pre-emulsion for the third stage is about 10% of the monomer pre-emulsion for second stage.

26. The sequential emulsion polymerization method of claim 24 , wherein the chain transfer agent is selected from halomethanes, chloroform, carbon tetrachloride, carbon tetrabromide, bromotrichloromethane, mercaptol, methylthioglycol, isooctyl 2-mercaptopropionate, isooctylmercaptopropionate, aromatic mercaptans, or disulfides.

27. The sequential emulsion polymerization method of claim 24 , wherein the chain transfer agent is isooctylmercaptopropionate.

28. The sequential emulsion method of claim 24 , wherein about 2-about 3% by weight of the chain transfer agent is added to the monomer pre-emulsion for shell.

29. A paint composition comprising the self-coalescing latex of claim 1 that is substantially free of coalescing agents.

30. The paint composition of claim 29 , wherein the paint composition has a volatile organic compound content of less than about 50 g/L.

Assignees

• Gharapetian Hrire
• Tilara Navin
• Sheerin Robert
• Columbia Insurance Co

Inventors

• Gharapetian Hrire
• Tilara Navin
• Sheerin Robert

Classifications

• C09D133/00 Primary

  Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers · CPC title

• C08L33/12 Primary

  Homopolymers or copolymers of methyl methacrylate · CPC title

• C09D133/12

  Homopolymers or copolymers of methyl methacrylate · CPC title