Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1996-11-13
2001-11-06
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S333000, C526S334000, C528S322000
Reexamination Certificate
active
06313248
ABSTRACT:
TECHNICAL FIELD
This invention relates to heat curable bismaleimide resin systems and the preparation thereof. More particularly, the subject invention relates to the preparation of bismaleimide resins in which the bismaleimide reactants are slurry mixed at relatively low temperature into the remaining resin system components.
The subject Invention further relates to specific, solid diamine bismaleimide resin reactants reacted with a liquid propenyl benzophenone co-reactant to produce a thermosetting polymer. The resulting polymer has an unusually low weight loss during thermal treatment at high temperature.
BACKGROUND OF THE INVENTION
Bismaleimide resins are important resins in commerce for various uses, including fiber reinforced composite and structural adhesives. However, bismaleimide resins, while possessing high strength at elevated temperatures, tend to be somewhat brittle. Accordingly, it is common to modify the bismaleimides with additional comonomers to improve impact resistance.
Curable mixtures based on aromatic bismaleimides and propenyl compounds are known, for example, from H. D. Stenzenberger et al. (“Stenzenberger”), relating to various curable resins from bismaleimide and alkenyl phenyl hydroxy ether, and laminated articles produced from said resin as disclosed in U.S. Pat. Nos. 4,871,821, 4,917,954, 4,789,704, 4,939,305 and 5,120,824. The combination of a bismaleimide and a propenyl compound by slurry mixing Is not disclosed in any of the Stenzenberger patents.
Certain curable mixtures containing a bismaleimide and a propenyl compound are disclosed In A. Kramer, U.S. Pat. No. 5,013,804 (“Kramer”). Although various aromatic bismaleimides are contemplated, no disclosure, either as teaching or suggestion using methylenedianiline bismaleimide, is provided. Additionally, Kramer discloses a fusion process for bringing together a bismaleimide compound and a propenyl compound. Kramer does not teach or suggest the thermosetting polymer made, and the making thereof, using slurry mixing.
The process of slurry mixing bismaleimide resins is disclosed in L. Repecka, U.S. Pat. No. 5,003,018 (“Repecka”). Certain aromatic bismaleimides in combination with liquid co-reactants, like o,o′-diallylbisphenol A, are disclosed. All of the above mentioned patents are incorporated herein by reference.
Many comonomers are physically incompatible with the bismaleimide resins because following initial formulation at elevated temperatures, the bismaleimide component may crystallize during processing. The large crystals which then form result in a resin system which is heterogeneous, difficult to process and which may be prone to microcracking when used to prepare carbon fiber reinforced composites. In such a resin system, wherein the bismaleimide components are physically incompatible, adhesives and prepregs prepared therefrom by the conventionally prepared systems often do not have the drape and tack desired of them.
As a result, there is a need in this technical area for a bismaleimide resin that has a high temperature capability, superior oxidative stability, and acceptable tack and drape to make composite parts.
SUMMARY OF THE INVENTION
It has been surprisingly discovered that bismaleimide polymer systems made using specific bismaleimide components, specific co-reactant components as curing agents in an optimized formula and a slurry mixing technology, have unexpectedly improved thermal and oxidative stability when formed into composites adhesives, etc. Specifically, the novel formulation of the present Invention comprises a thermosettable curable resin composition prepared by slurry mixing a composition comprising a solid diamine bismaleimide resin reactant and a liquid propenyl benzophenone co-reactant in which the reactant and co-reactant are present in a weight ratio of substantially about 1:1. This particular composition has a decreased weight loss upon thermal aging and the tack and drape necessary to make composite parts.
This invention also relates to a process for preparing a thermosettable curable resin composition by slurry mixing a powdered bismaleimide resin reactant into a liquid co-reactant which has been heated to between 50° C. and 150° C.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process of the subject invention involves the slurry mixing of one or more solid bismaleimide monomers with the other resin system components. After cooling the bismaleimide resin systems thus obtained, very fine bismaleimide particles in the form of a stable dispersion are present. Upon standing, substantial crystallization of additional bismaleimide will not occur. The resulting heat-curable resin system is thus uniform and homogeneous.
In this application, the solid bismaleimide monomers may alternatively be described as a “specific bismaleimide component,” “a solid reactant” and “solid aromatic diamine bismaleimide resin reactant.”
The liquid co-reactant may be described to include a “curing agent”, a “propenyl compound”, a “liquid homogeneous benzophenone co-reactant” and an “incompatible comonomer(s).”
The term “resin composition” as used herein refers to a heat-curable resin composition in its final form. The composition may contain one or more reactive monomers and/or comonomers, curing agents, any necessary catalysts, and optionally filler, rheology control agents, tackifiers, tougheners, diluents, dyes, and pigments, but exclusive of fiber reinforcement.
The term “incompatible comonomer(s)” as used herein refers to comonomers and other ingredients which, when present, would allow crystallization of a particular bismaleimide component upon cooling a melt of such components. The incompatible comonomer may thus comprise one or more additional components having chemical functionalities other than maleimide, as well as other bismaleimide comonomers.
For example, it might be found that homogeneous melt of specific quantities of a particular bismaleimide monomer and a comonomer, might not present a problem with regard to crystallization of the bismaleimide on cooling. However, when a second bismaleimide, or when more of the first bismaleimide are added to the melt, substantial crystallization might occur under the same conditions. The resulting crystallization indicates incompatibility, in the sense used by the inventor, between the added bismaleimide and the other ingredients. Such incompatibility is most likely to result when high concentrations of bismaleimides are utilized, particularly when high concentrations of a single or limited number of bismaleimides are utilized.
The use of slurry mixing in the preparation of bismaleimide resin systems containing incompatible components is but one mode of practicing the subject invention. This mode is important when large quantities of crystalline bismaleimides are contained in the resin formulation, as such formulations, when prepared by fully dissolving, are frequently very difficult to process. The slurry mixing process has been found to be useful whether or not the overall resin system components are compatible. Such resin system may result when a compatible rather than an incompatible comonomer is utilized. An example of the latter might be the use of a bismaleimide monomer and a cyanate-functional comonomer.
Slurry mixing is merely an aid in preparing the resin of the invention. It should be noted that slurry mixing is not required for good resistance to oxidation. Good resistance to oxidation is a function of the monomers, not the process for preparation. However, for prepreg and adhesive applications, the invention will most likely be practical using slurry mixing. In other applications, for example, resin transfer molding (RTM), slurry mixing may not be needed.
The resin system, upon cooling, will generally not show the presence of large or substantial amounts of crystals. In some cases, the resin system may have the appearance of a solid solution or glass. Yet despite the uniform appearance, these uncured resin systems frequently possess virtually no tack, and often are highly brittle. Surprisingly, when the same components
Boyd Jack Douglas
Kuo Albert
Cytec Technology Corp.
Fitzpatrick ,Cella, Harper & Scinto
Lipman Bernard
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