Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1995-01-19
1996-05-28
Johnson, Rachel
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525902, 523201, 524260, 521 54, 521 55, 521134, 521 70, 521 65, C08F26502
Patent
active
055212530
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to hollow polymer latex particles and a process for the production of the particles which are useful as opacifying plastic pigments for various coatings and particularly as gloss-enhancing plastic pigments for paper and paperboard coatings.
2. Prior Art
Hollow particles are known to be useful as opacifying agents in coating applications such as in paint or paper coating. They also improve paper coating gloss. The use of the hollow latex in such coatings reduces the need for expensive pigments, such as TiO.sub.2, without adding excessive and undesirable weight to the coating. The hollow latex particle provides opacity because the hollow structure in a latex particle scatters light more efficiently than a corresponding particle of uniform density. The light scattering properties are related to the difference in refractive index between the shell and the internal void. Such hollow latexes have additional utility in areas other than coatings such as in processes involving microencapsulations to prepare, for example, control release agents.
U.S. Pat. No. 4,427,836 and U.S. Pat. No. 4,594,363 disclose two different processes for making hollow latexes by swelling core-shell polymer particles having acid-containing cores with a volatile base or a permanent base. U.S. Pat. No. 4,880,842 describes several disadvantages of having high levels of copolymerized acid in the core polymer and discloses a process for making hollow latexes by introducing a non-polymeric acid to an early stage of the multi-stage polymer particles instead of copolymerizing acid to make swellable cores.
These known methods for preparing hollow latexes require cores containing acid or acidic monomers to enable swelling to occur at room temperature. The existence of acid in the polymer disadvantageously increases the polymer's affinity to water. The sensitivity to the effects of water undesirably renders the coating into which the latex is formulated sensitive to moisture as well; an undesirable property in coating applications. An acidic core is also thought to impart polarity to the polymer and because of such polarity the polymer is thought to not adsorb surfactants well rendering the polymer unstable or prone to coagulation or aggregation in larger particles. The water sensitivity of the core or high affinity for water by the core is thought to make it difficult to encapsulate the core with the shell polymer because the core tends to remain at the polymer-water interface on the surface of the particle rather than be encapsulated by the shell.
These known processes for preparing hollow polymer particles often also require a post-encapsulating step with crosslinked polymers, that is, the acid-containing cores are encapsulated with an uncrosslinked shell, the core is swelled, then the shell can be encapsulated with crosslinked polymers.
It would be desirable to have improved hollow polymer particles with acid-free hydrophilic cores and a process for their production.
SUMMARY OF THE INVENTION
The present invention relates to a hollow polymer particle derived from a polymer particle comprising
A. an acid-free hydrophilic core copolymer phase made of (meth)acrylate monomers, vinyl ester monomers of carboxylic acids or a mixture thereof, and one or more crosslinking monomers; the core copolymer being base-hydrolizable at temperatures greater than the T.sub.g of the copolymer; and
B. an intermediate shell copolymer phase which is compatible with the hydrophilic core copolymer phase, the intermediate shell copolymer made of (meth)acrylate monomers having a T.sub.g for their copolymer greater than 50.degree. C.; and one or more vinyl acid monomers; and, optionally, one or more monovinyl aromatic monomers; and, optionally, one or more crosslinking monomers; the intermediate shell copolymer also being compatible with
C. an outer rigid shell copolymer which is hydrophobic and crosslinked, the copolymer having a T.sub.g greater than about 80.degree. C., the outer shell copolym
REFERENCES:
patent: 4427836 (1984-01-01), Kowalski et al.
patent: 4594363 (1986-06-01), Blankenship et al.
patent: 4880842 (1989-11-01), Kowalski et al.
patent: 5157084 (1992-12-01), Lee et al.
J. W. Vanderhoff; Preparation of Soft Hydrophilic Polymer Core/Hard Hydrophobe Shell Particles; Polym. Mater. Sci. Eng.; 1991; Oct.; 64; pp. 345-346.
Leadbetter Arthur N.
Lee Do I.
Mulders Michael R.
Nicholson Dwayne J.
Johnson Rachel
The Dow Chemical Company
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