Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-12-29
2002-07-16
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S501000, C524S506000, C524S804000, C524S806000, C526S279000, C528S025000, C528S026000
Reexamination Certificate
active
06420479
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a star polymer reactive colloidal composition, and to one part coating compositions containing the colloidal composition. The star polymer has latent cross-linkable functionality. Coating compositions containing the colloidal composition have improved mechanical properties, film strength, block resistance, wet adhesion, and abrasion resistance.
BACKGROUND OF THE INVENTION
Surface active agents, or surfactants are used to provide stability for emulsion polymer particles. These emulsions can then be used in the production of emulsion coatings. A problem with coatings produced with surfactants is that over time, the surfactants can migrate to the surface of the coating, producing detrimental effects on the surface properties. These detrimental effects are especially negative in mechanical properties related to hardness.
U.S. Pat. No. 5,605,952 describes a coating composition comprising polymers having acetoxy functionality and polymers having acid functionality, which can form a stable enamine structure by reacting with an amine. These polymers, however, produce a linear polymeric structure. An advantage of star polymers is that they have a lower viscosity than linear polymers.
U.S. Pat. No. 5,274,064 describes star polymers with reactive functional groups. The star polymers disclosed are backbone polymers to which alkoxy Si groups are attached as side chains. Such side chains are not highly sterically hindered, and therefore can react prematurely to form crosslinks prior to film formation, causing coagulum problems during manufacture and storage, or producing surface crosslinking between emulsion particles, rather than stronger crosslinking formed after particle coalescence. The radial star polymers described are the sole constituent of a coating composition, rather than an emulsifier useful in producing a coating composition.
U.S. patent application Ser. No. 09/227,756 describes coating compositions prepared with a sterically hindered alkoxylated silane. These coating compositions are formed from linear polymers, and lack a controlled architecture.
U.S. patent application Ser. No. 09/190,527 describes the use of amphiphilic heteroarm star polymers as emulsion stabilizers in emulsion polymerization.
A useful one-part reactive coating composition should be stable. It should not react during the polymerization process, during storage, nor during the liquid coating stage. Surprisingly, it has been found that star polymer colloids of the present invention, having potentially cross-linkable groups on the polymer backbone fulfill these requirements, providing excellent stability and also physical coating properties when used as stabilizers in emulsions used as part of a coating composition.
SUMMARY OF THE INVENTION
The present invention provides a colloid composition comprising an amphiphilic star polymer having potentially crosslinkable sites on the polymer backbone consisting of either a sterically hindered silane monomer and an internal catalyst, or an acetoacetoxy group and at least one non-polymeric polyfunctional amine.
The present invention also provides a means of producing an emulsion polymer using the novel colloidal composition of the invention as a replacement for surfactants for stabilization.
Further, the present invention provides a one-part coating composition comprising a radial or star polymer having cross-linkable functionality and an emulsion polymer.
While not being bound by any particular theory, it is believed that the colloids of the present invention react primarily after coalescence has occurred, due to the high level of steric hinderance provided. Because the reactive groups on the star-polymer colloid are so hindered, a reaction occurs only after the reactive groups are forced into very close proximity—a condition which occurs after coalescence of the emulsion particles. This mechanism is different than the prior art having polymer reactive groups which form surface cross-links between adjacent polymer chains, providing a weak bond and weak coating film. Ideally the colloids of the present invention migrate into and intermingle with other polymer chains, prior to the formation of crosslinks. The result is a much stronger, more cohesive bond and water resistant film.
DESCRIPTION OF THE INVENTION
The protective colloid composition of the present invention is an amphiphilic star polymer containing potentially crosslinkable sites on the polymer backbone. As used herein the term amphiphilic star polymer refers to a polymer having both hydrophilic and hydrophobic components.
Star or radial polymers, as used herein, is intended to describe polymers that have three or more polymeric arms emanating from a central core. These polymers can be prepared by various polymerization procedures such as anionic, cationic, and free radical mechanisms. The star polymers are usually formed by using either multifunctional initiators, multifunctional chain transfer agents, or multifunctional coupling agents. The star polymers have unique properties including low viscosities in solution due to their compact structure, and high melt viscosities due to extensive entanglements relative to their linear coatings.
Preferably, star polymers of the present invention comprise a polyvalent mercaptan core and three or more polymeric arms which extend radially from the core.
Preferably the core is a residue of a tri- to octafunctional thiol, and most preferably a residue of a tri-, tetra-, or hexafunctional thiol. The arms of the radial or star polymer may be of several types, including random or block copolymers, or homopolymers. The arms may be of the same or different compositions. A preferred composition is one in which the all of the arms are essentially the same. Other preferred star polymers are those which are heteroarm star polymers.
Said heteroarm star polymer has at least one arm with a Tg of at least 20° C. for a stable emulsion, preferably at least 25° C. and most preferably at least 50° C. If all arms of the star polymer are essentially the same, the Tg of the arms is at least 20° C. or greater.
Preferably, the arms of the star polymer contain 5-20% by weight of an anionic monomer such as methacrylic acid and 1 to 50% by weight of a cross linking functionality, based on the star polymer.
The star polymer useful in the present invention has a number average molecular weight of from 10,000 to 100,000; preferably 15,000 to 75,000; more preferably 30,000 to 75,000; and most preferably 30,000 to 50,000, based on a theoretical molecular weight calculated as
Mw=(grams of monomer/moles of chain transfer agent)*n,
where n equals the number of arm on the star polymer.
Potentially crosslinkable sites, as understood herein, relates to functional groups which can react to form crosslinks, primarily during film formation after the onset of coalescence. Examples of potentially crosslinkable systems useful in the invention include, but are not limited to, chemical crosslinking, ionic crosslinking, and oxidative crosslinking.
Chemical crosslinking of the amphiphilic star polymer can result from several co-reactive groups, including but not limited to, sterically hindered silane, and acetoacetoxy functional chemistries. Other means of crosslinking include ionic crosslinking, such as a post-addition of a zinc ammonium complex to the latex; and oxidative crosslinking, as with dicyclopentenyl acrylate and castor acrylated monomer.
A star polymer having sterically hindered silane, is the reaction product of a residue of a tri-to-octafunctional thiol, an ethylenically unsaturated non-carboxy functional monomer, from 1 to 20 and preferably 2 to 10 parts per hundred monomer (pphm) of a sterically hindered alkoxylated silane monomer, optionally from 0.1 to 5 pphm of an ethylenically unsaturated carboxy-functional monomer, optionally from 0.1 to 5 pphm of a wet adhesion promoter such as an ureido-functional monomer, and an anionic surfactant. The sterically hindered alkoxylated silane is incorporated in the backbone of the polymer. The steric hindran
Farwaha Rajeev
Mukherjee Apala
Phan Lein
Thomaides John S.
Dawson Robert
National Starch and Chemical Investment Holding Corporation
Roland, Esq. Thomas F.
Zimmer Marc S
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