Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2002-03-05
2004-06-29
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S059000, C252S182220, C602S008000
Reexamination Certificate
active
06756467
ABSTRACT:
TECHNICAL FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to curable resin compositions and in particular to isocyanate based resin systems suitable for use in medical applications, such as orthopaedic casting and splinting.
A favored method for curing isocyanate resins is to use water curing. Water curing can be achieved by many means, for example the resin being immersed in water, contact with atmospheric moisture or by being sprayed with water after application.
As used herein, “water curable” means that the resin system is capable of hardening to a rigid or semi-rigid structure on exposure to water.
Any isocyanate based resin system depending on the reaction of an isocyanate with water, amine or alcohol group for curing may benefit from the use of catalysts to speed up the curing so that the resin sets in an acceptably short time.
The use of inorganic carbonate catalysts has been proposed with isocyanate resin systems, however the shelf life was affected in the presence of any moisture, as the catalyst is in direct contact with the resin and was set off in the presence of moisture. More recently different catalysts based on tertiary amines have been used with isocyanate functionalized resin systems.
The use of inorganic carbonate catalysts has been proposed with functionalized isocyanate resin systems in Patent Application WO 88/02636, U.S. Pat. Nos. 5,027,804 and 4,427,003; however the shelf life may be affected in the presence of any moisture, as the catalyst is in direct contact with the resin and would be set off in the presence of moisture. More recently, alternative catalysts based on tertiary amines have been used with isocyanate functionalized resin systems.
Reactive tertiary amines are rarely fully chemically incorporated into the polyurethane during the isocyanate-water reaction. In addition, such tertiary amines may be vaporised by the exotherm generated during the polyurethane reaction. Thus, there is the possibility that catalyst may leach or evaporate from the resin system during cure or after curing. Such amines may have a strong odor and the potential inhalation and absorption toxicity of tertiary amines is well known.
Patent Application WO 94/02525 partially addresses the problems encountered with tertiary amine catalysts by modifying reactive tertiary amine catalysts by mixing under reaction conditions a reactive tertiary amine, a polyol and an organic isocyanate compound to give a catalyst which has a higher molecular weight and may therefor be retained more.
Patent Application WO 94/05475 discloses a tertiary amine as a polyurethane reaction catalyst, where the catalyst is added to a binder containing isocyanate groups. Lignocellulose fibres are coated with the binder and then shaped into a mat which is pressed under the influence of heat to form a board, where the catalyst is subsequently built into the board.
However such catalysts may still be prone to leaching especially when used in a water curable isocyanate composition.
It may be possible to use a lower level of catalysts to reduce the problems discussed above, however such a catalyst is unlikely to be suitable for rapid cure systems, as would be required for a splinting material.
The present invention seeks to overcome these disadvantages by providing a curable resin composition with catalysts which are not a potential hazard due to leachable components.
The use of a chemically bound-in tertiary amine catalyst would overcome the problems associated with the leaching of catalyst. “Chemically bound-in” means the catalyst is ionically and/or covalently bound to the curable isocyanate functionalized prepolymer.
Furthermore the use of more than one catalyst may benefit the curing speed of isocyanate functionalized resin systems.
Surprisingly it was found that the curing reaction of a water curable isocyanate functionalized resin, when catalyzed by a first and a second catalyst resulted in a greatly increased curing rate of the resin as the two catalysts together showed a synergistic effect.
The synergistic effect described in this invention is the increase in the reaction rate between water and isocyanate functionalized prepolymers in polyurethane/urea synthesis.
Thus according to the present invention there is provided a resin system comprising at least a water curable, isocyanate functionalized prepolymer and a first and second catalyst component wherein the first catalyst is chemically bound-in to the prepolymer and the second catalyst is not chemically bound-in.
Chemically bound-in catalysts include catalysts bonded covalently and/or ionically to the isocyanate functionalized prepolymer.
Preferably the first chemically bound-in catalyst is covalently bound-in to the prepolymer.
Preferably the first catalyst is a tertiary amine catalyst.
Suitable tertiary amine catalysts comprise both a tertiary amine group and an isocyanate reactive group.
The term “isocyanate reactive group” refers to a group which forms a covalent bond when reacted with an isocyanate group (—NCO) under appropriate conditions, these include for example hydroxy and amine groups as well as carboxylic acids, thiols, anhydrides, urethanes, ureas and other such groups with an active hydrogen atom known to one skilled in the art.
Preferably the chemically bound-in tertiary amine catalyst is covalently bound-in to the prepolymer.
The bound-in tertiary amine group may be present at any appropriate location in the isocyanate prepolymer. For example they may be introduced at an end of the isocyanate prepolymer molecules via a capping reaction, they may be present on a side chain extending from the main polymer backbone, or may be part of the polymer backbone itself.
The tertiary amine group may be optionally substituted with substituents which do not substantially adversely affect the reaction of the tertiary amine group with isocyanate groups or the catalytic effect of the tertiary amine groups when present in the isocyanate prepolymers of the resin composition of the present invention.
Appropriate molecules for reacting with the polyisocyanates so as to form the prepolymers of the composition of the present invention may include but are not limited to the following molecules:
1-(2-Hydroxyethyl) pyrrolidine, 1-methyl piperazine,
1-methyl-2-piperidine methanol,
1,4-6is(2-hydroxyethyl) piperazine
2[2-(dimethylamino) ethyl]methyl amino ethanol,
gramine, 3-morpholino-1,2-propanediol,
1,4-bis(3-aminopropyl)piperazine, tropine,
3-aminopropyl morpholine, 4,2-hydroxyethyl morpholine,
3,3-diamino-N-methyl dipropylamine,
1,4-bis(2-hydroxypropyl)-2-piperazine,
1-(2-hydroxypropyl) imidazole, 3-dimethyl amino propanol and &bgr;-hydroxy-4-morpholine propane sulphonic acid.
The chemically bound-in tertiary amine catalyst may be a single species or mixture of species. Further, several species of such bound-in tertiary amines may be present within a prepolymer composition or within one isocyanate functionalized prepolymer molecule.
Any one of the prepolymer molecules may contain a single bound-in tertiary amine catalyst of a single species or more than one tertiary amine catalyst of a number of species.
In addition any one prepolymer molecule may include more than one tertiary amine catalyst either present on a side chain, as end groups or part of the polymer backbone, for example, when the tertiary amine catalysts include two or more isocyanate reactive catalysts and act as chain extenders.
The isocyanates used to react with the tertiary amine catalyst comprising both a tertiary amine group and an isocyanate reactive group may be any suitable isocyanates well known in the art, for example aliphatic, cycloaliphatic, aromatic or heterocyclic isocyanates. Preferably aliphatic isocyanates are used.
Whatever species of tertiary amine containing molecules are utilized to prepare a bound-in catalyst, it is preferred that they comprise less than 10% by weight more preferably from 0.1 to 5% by weight of the curable composition.
The second catalyst is preferably 0.05 to 10% and more preferably 0.1 to 5% by weight of the curable comp
Adams Evans P.A.
BSN Medical Inc.
Gorr Rachel
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