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
1999-01-27
2002-08-13
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S107000, C525S124000, C526S273000, C526S307700, C526S319000, C427S340000, C427S372200, C427S385500, C427S393500
Reexamination Certificate
active
06433097
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to curable polymer compositions such as coating, sealant or adhesive compositions and to their preparation.
There has been increased concern in recent years about the release of volatile solvents into the atmosphere, and there has been a consequent need to reduce the volatile organic solvent content of coating, sealant and adhesive compositions. This has not been easy for coating compositions, which require a relatively low viscosity of about 0.2-1 Pas (2-10 poise) for application by the usual methods of spray, roller or brush, and particularly not for coating compositions which have to be applied and cure rapidly at ambient temperature, for example coatings for large structures such as ships, bridges, buildings, industrial plant and oil rigs. Coating compositions generally need to contain a polymer to confer film-forming properties, but any polymer needs to be of low molecular weight to give the required low viscosity, particularly after pigmentation as a paint. Preparation of low molecular weight acrylic polymers uses substantial quantities of polymerisation initiator and/or chain transfer agent and is highly exothermic, necessitating polymerisation in a solvent to control the exotherm. Preparation in a volatile organic solvent followed by stripping of the solvent is possible but is economically unattractive.
BACKGROUND ART
EP-A-206072 describes a semi-continuous process for preparing a polymeric reaction product which comprises the vinyl addition polymerisation of a vinyl monomer component selected from alkyl acrylates, alkyl methacrylates, monoalkenyl aromatic vinyl monomers, functional vinyl monomers and mixtures thereof at a temperature of at least 150° C. in the presence of a diluent selected from polyester polyols, carboxyl-functional polyesters, polyester urethane polyols, polyester polyepoxides and polyether polyols and having a molecular weight of at least 200, resulting in an ungelled product.
EP-A-433711 describes a terpolymer of a monovinylic aromatic monomer, an acrylic monomer and maleic anhydride formed according to a polymerisation method in which the maleic anhydride is added to the reactor in a molten state, free of solvents and diluents, and the polymerisation reaction is conducted in bulk in the absence of solvents and diluents.
U.S. Pat. No. 4,652,605 describes a process for preparing a polymeric reaction product which comprises the vinyl addition polymerisation of a vinyl monomer component, of which at least 50% by weight is an active hydrogen-containing vinyl monomer, in the presence of a polymeric diluent, which may for example be a polyester polyol.
U.S. Pat. No. 4,629,764 describes a polymer-modified epoxy resin composition which results from dehydrohalogenating the reaction product of an epihalohydrin with a composition which comprises a polyphenol and a copolymer of an alkenylphenol and a polymerisable ethylenically unsaturated monomer.
EP-A-118478 describes photocopolymerisable compositions comprising an epoxide comprising two or more groups such as 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate and a cycloaliphatic epoxide such as vinylcyclohexane monoepoxide.
DISCLOSURE OF THE INVENTION
A process according to the present invention for the preparation of a curable polymer composition by the free radical polymerisation of a functional olefinically unsaturated monomer containing a functional group which is selected from epoxide groups, isocyanate groups, alkoxysilane groups, cyclic carboxylic anhydride groups and activated —CH— groups bonded to at least two electron-withdrawing groups and which is capable of reacting with a curing agent, and optionally one or more ethylenically unsaturated comonomers, is characterised in that the polymerisation is carried out in the presence of a reactive diluent which is a liquid organic compound of viscosity less than 2 Pas (20 poise) at 25° C. having at least one functional group which is substantially non-reactive with the functional olefinically unsaturated monomer and which is capable of reacting with a curing agent to form a polymer network. By “viscosity” we mean the high-shear viscosity as determined by an I.C.I. cone and plate viscometer.
The process of the invention can be used to prepare a curable addition polymer composition of viscosity less than 5 Pas (50 poise), for example of viscosity 0.1 to 0.2 Pas (1 to 2 poise) up to 3 or 4 Pas (30 or 40 poise). A polymer composition so prepared, when mixed with a curing agent which may be of lower viscosity, can form a coating composition having a viscosity up to 1 Pas (10 poise), for example 0.2 to 0.6 Pas (2 to 6 poise), so that it can be applied to a substrate by conventional spray, roller or brush, without dilution by a volatile organic solvent. The use of volatile solvent can thereby be avoided both during preparation of the curable addition polymer and during application of a coating or sealant or adhesive, or the amount of volatile solvent can be reduced to a very low level such as less than 20% or even less than 10% by weight of the composition. If a low level of non-reactive volatile solvent is present during the polymerisation it may either be retained in the coating composition or be stripped from the composition after polymerisation is completed.
The functional group of the reactive diluent is preferably capable of reacting with the same curing agent with which the functional group of the olefinically unsaturated monomer reacts, so that the curable addition polymer and the reactive diluent can be linked by the curing agent in the same polymer network. Most preferably, the functional group of the reactive diluent has the same functionality as the functional monomer. The reactive diluent should be substantially non-reactive both with the functional group of the monomer and with the olefinic double bond of the monomer and therefore should not contain a polymerisable olefinic double bond.
The functional olefinically unsaturated monomer is preferably an acrylic monomer, particularly an acrylic ester, such as an acrylate or methacrylate, substituted by a reactive functional group.
In most cases, at least some of the reactive diluent preferably contains at least two of the said functional groups, although reactive diluents having one functional group can be used, particularly when the curing agent has functionality greater than 2. All of the reactive diluent may be of functionality 2 or more, or the reactive diluent may comprise a mixture of a monofunctional compound with one or more compounds of higher functionality.
The invention includes a curable acrylic polymer composition comprising an acrylic polymer of number average molecular weight Mn (determined by gas permeation chromatography (GPC)) less than 5000 containing pendant functional groups selected from epoxide groups, isocyanate groups, alkoxysilane groups, cyclic carboxylic anhydride groups and activated —CH— groups bonded to at least two electron-withdrawing groups, the polymer being dissolved in an organic compound of viscosity less than 2 Pas (20 poise) at 25° C. containing at least two functional groups of the same functionality as that present in the acrylic polymer, and a curing agent which is reactive with the functional groups of the acrylic polymer and with the functional groups of the organic compound.
The invention is particularly useful in preparing curable acrylic polymer compositions which are epoxide-functional, that is which comprise an epoxide-functional acrylic polymer (formed from a corresponding monomer)in a reactive diluent containing at least one epoxide group. An epoxide-functional acrylic monomer can for example be glycidyl acrylate or methacrylate.
Examples of ethylenically unsaturated comonomers which can be copolymerised with such a functional acrylic monomer are acrylic esters such as butyl acrylate or methacrylate, methyl methacrylate or acrylate, ethyl acrylate or methacrylate, propyl acrylate or methacrylate, n-hexyl acrylate or methacrylate, isopropyl acrylate or methacrylate, t-butyl acrylate or methacryla
Kelly Sarah Anne Mackie
Nixon Steven Alistair
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
International Coatings Limited
Zalukaeva Tatyana
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