Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-08-18
2001-08-14
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S114000, C525S119000
Reexamination Certificate
active
06274673
ABSTRACT:
The present invention relates to a reaction product of a microgel that contains carboxylic acid groups with a nitrogen-containing base (microgel amine salt or microgel imidazole salt), to a process for the preparation of such a reaction product, to a composition comprising such a reaction product and an epoxy resin, and also to cross-linked products obtainable by curing that composition.
Nitrogen-containing bases are well known to the person skilled in the art as hardeners or curing-accelerators for epoxy resins. However, such systems have only limited storage stability, since the bases react with epoxides even at relatively low temperature, in some cases even at room temperature, which manifests itself in an increase in the viscosity of the epoxy resin formulation and, in the case of a prolonged period of storage, results in gelling of the mixture. Increasing reactivity of the nitrogen-containing base reduces the storage stability of the epoxy resin mixture and shortens the usable life (pot life). For that reason, such systems are formulated in the form of two-component systems, that is to say the epoxy resin and the nitrogen-containing base are stored separately and are mixed together only shortly before processing.
Attempts have been made to improve the storage stability of such systems by developing curing systems that have a high latency. High latency means high stability at the storage temperature in question without there being any substantial reduction in the reactivity at the desired curing temperature.
EP-A-304 503 describes master batches comprising encapsulated materials and epoxides as latent hardeners for epoxy resins, the core material being a tertiary amine in the form of a powder, which is surrounded by a shell comprising a reaction product of the same amine with an epoxy resin.
A similar curing system, but having a core material comprising an amine and an anhydride, is disclosed in JP-A-Hei 02-191624.
Although such latent hardeners or accelerators based on encapsulated particles are suitable for the preparation of one-component systems that are stable to storage, they have the disadvantage of insufficient stability towards mechanical influences, such as, for example, shearing forces and compressive loads.
The problem underlying the present invention is to provide latent epoxy curing systems having an improved pot life that also have higher stability towards mechanical stress in the form of shearing forces.
It has now been found that salts of microgels that contain COOH groups with nitrogen bases have the required property profile.
The present invention relates to a reaction product of a microgel that contains carboxylic acid groups with a nitrogen-containing base.
Generally, microgels are understood to mean macromolecules, the chain segments of which are cross-linked in the region of the individual agglomerates by covalent bridges.
Microgels can be prepared in accordance with various known polymerisation methods. An advantageous method is the emulsion polymerisation of compounds having polymerisable C—C double bonds in the presence of so-called multifunctional cross-linkers, for example in accordance with the seeding technique. In that technique, after the polymerisation the microgel particles are in the form of an aqueous emulsion or suspension. The further reaction with the nitrogen-containing base can be carried out preferably using such an emulsion/suspension. It is, however, also possible first to isolate the microgel in the form of a solid powder, for example by means of spray-drying or freeze-drying, or to convert the aqueous emulsion into an organic phase by solvent exchange.
In principle, any compounds containing at least two polymerisable C—C double bonds may be used as multifunctional cross-linkers.
Intramolecularly cross-linked copolymers are formed, which generally have particle sizes in the nanometer range (approximately from 5 to 1000 nm).
A preferred microgel for the preparation of the reaction product according to the invention is a copolymer of at least one unsaturated carboxylic acid and at least one multifunctional cross-linker.
An especially preferred microgel is a copolymer of at least one unsaturated carboxylic acid, at least one vinyl monomer that contains no carboxylic acid groups and at least one multifunctional cross-linker.
In principle, any carboxylic acids that contain a polymerisable C—C double bond are suitable for the preparation of microgels that contain carboxylic acid groups.
Preferred unsaturated carboxylic acids are acrylic acid, methacrylic acid, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, phthalic acid mono(2-acryloylethyl) ester, phthalic acid mono(2-methacryloylethyl) ester, maleic acid, maleic acid monomethyl ester, maleic acid monoethyl ester, fumaric acid, fumaric acid monomethyl ester, fumaric acid monoethyl ester, itaconic acid, cinnamic acid, crotonic acid, 4-vinylcyclohexanecarboxylic acid, 4-vinylphenylacetic acid and p-vinylbenzoic acid.
Acrylic add and methacrylic acid are especially preferred.
In principle, any compounds containing at least two polymerisable C—C double bonds are suitable as multifunctional cross-linkers. Also suitable as multifunctional crosslinkers are mixtures of at least two vinyl monomers, for example methacrylic acid and glycidyl methacrylate, that are capable of reacting with one another by way of additional functional groups during or after the polymerisation reaction.
As a multifunctional cross-linker it is preferred to use a polyfunctional acrylic acid ester or methacrylic acid ester of an aliphatic, cycloaliphatic or aromatic polyol, an addition product of acrylic acid or methacrylic acid and a polyglycidyl compound, an addition product of acrylic acid or methacrylic acid and glycidyl acrylate or methacrylate, an acrylic acid alkenyl ester or methacrylic acid alkenyl ester, a dialkenylcyclohexane or a dialkenylbenzene.
Especially preferred multifunctional cross-linkers are ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol diacrylate, propylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, 1,1,1-trimethylolpropane triacrylate, 1,1,1 -trimethylolpropane trimethacrylate, diglycidyl ether diacrylate of bisphenol A, diglycidyl ether dimethacrylate of bisphenol A, acrylic acid allyl ester, methacrylic acid allyl ester, divinylcyclohexane and divinylbenzene.
The monomer mixture used for the preparation of the microgels may contain one or more vinyl monomers that contain no carboxylic acid groups, for example butadiene and butadiene derivatives, acrylonitrile, methacrylonitrile, acrylic acid esters and amides, methacrylic acid esters and amides, vinyl ethers and esters, allyl ethers and esters, styrene and styrene derivatives.
Preferred vinyl monomers that contain no carboxylic acid groups are alkyl esters, hydroxyalkyl esters and glycidyl esters of unsaturated carboxylic acids, and styrene derivatives.
Especially preferred vinyl monomers that-contain no carboxylic acid groups are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate and styrene.
The reaction product according to the invention is preferably prepared from a microgel that is a copolymer of from 2 to 70% by weight of at least one unsaturated carboxylic acid, from 0 to 96% by weight of at least one vinyl monomer that contains no carboxylic acid groups and from 2 to 70% by weight of at least one multifunctional cross-linker, the total of the percentages by weight always being 100.
Especially preferred microgels are copolymers of from 5 to 50% by weight, especially from 10 to 40% by weight, of at least one unsaturated carboxylic acid, from 0 to 90% by weight, especially from 30 to 85% by weight, of at least one vinyl monomer that contains no carboxylic acid groups
Eldin Sameer Hosam
Roth Martin
Tang Qian
Buttner David J.
Lyon & Lyon LLP
Vantico Inc.
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