Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2002-07-15
2004-06-29
Robertson, Jeffrey B. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S028000, C528S033000, C528S038000, C525S474000, C525S476000, C525S523000
Reexamination Certificate
active
06756469
ABSTRACT:
TECHNICAL FIELD
This invention generally relates to improved hardeners or curing agents for thermosetting resins, and more specifically to a novel class of polysilazane-modified polyamine hardeners for epoxy resins, useful compositions, reaction mixtures and reaction products prepared therewith.
BACKGROUND OF THE INVENTION
Epoxy resin can be generally defined as containing a molecule with one or more epoxide, oxirane or ethoxylene groups. The resins may be classified as thermosetting polymers, and are widely used as adhesives, high performance coatings, potting and encapsulating materials, to name but a few applications. Epoxy resins possess excellent electrical properties, low shrinkage, good adhesion to many metals, resistance to moisture, and resistance to thermal and mechanical shock. Of the two main categories of epoxy resins, the glycidyl ether epoxy resins, such as the diglycidyl ether of bisphenol-A and the novolac epoxy resins are among the most commonly used epoxies.
Typical commercial epoxy resins of the diglycidyl ether of bisphenol-A type are synthesized by reacting bisphenol-A with epichlorohydrin in the presence of a basic catalyst. The properties of the resin will depend on the number of polymer repeat units, commonly referred to as the degree of polymerization, which is dependent on the stoichiometry of the synthesis reaction. In many commercial products of this type the repeating units can generally range from about 1 to about 25.
The novolac epoxy resins are glycidyl ethers of phenolic novolac resins. Phenols are reacted in excess, with formaldehyde in the presence of acidic catalyst to produce the phenolic novolac resin. Novolac epoxy resins are synthesized by reacting phenolic novolac resin with epichlorohydrin in the presence of sodium hydroxide catalyst.
The multiple epoxide groups usually present in novolac epoxy resins allow these resins to achieve high cross-link densities in formulating molding compounds for microelectronics packaging as a result of their superior performance at elevated temperatures, excellent moldability, and mechanical properties, superior electrical properties, and heat and humidity resistance.
In order to convert such epoxy resins into hard, infusible, and rigid materials without the use of a catalyst, it is necessary to cure the resins with hardener. The curing process is a chemical reaction characterized by the epoxide groups in the epoxy resin reacting with the curing agent, or hardener to form highly crosslinked, three-dimensional networks.
Amines are the most commonly used curing or hardening agents for epoxy resins. Primary and secondary amines are especially highly reactive with epoxies. Tertiary amines are also useful in catalyzing or accelerating the curing reaction.
To-date, the modification of nucleophilic, organic polyamines with polysilazanes for use as epoxy resin hardeners has not been demonstrated. Since the bulk of amine hardeners used to cure epoxy resins at room temperature comprise polyamines, the use of such polysilazane-modified polyamines to cure epoxy resins would have widespread utility.
Polysilazanes are polymers which contain repeat units wherein silicon and nitrogen atoms are bonded in alternating sequence. Polysilazanes all possess reactive Si—N functionality which enables co-reaction with various electrophilic organic materials, such as epoxy resins. The direct reaction of polysilazane with epoxy resins is known.
Heretofore, in reactions of a polysilazane with an epoxy resin as taught, for example, in U.S. Pat. No. 5,616,650, the methods were performed under conditions wherein the silicon-nitrogen bond of the polysilazane reacted directly with the oxirane groups of the epoxy resin to form the cured polymer. Heat, however, typically in excess of 100° C., was required to perform the reactions. Methods for incorporating polysilazanes into cured epoxy resins at room temperature, however, have not been described. By forming the reaction product of the immediate invention, the organic amine residues of the reaction product can be used to react directly with the oxirane rings of the epoxy resin at room temperature to effect epoxy resin cure. At these lower temperatures the silicon-nitrogen bonds of the polysilazanes, which are incorporated into the reaction product of the polyamine and the polysilazane, do not react with the oxirane rings of the epoxy resin. Instead, the organic amine groups of the reaction product initiate and propagate the cure. These novel cure reactions lead to hybrid polymer systems wherein the cured epoxy resins display increased thermal stability with retention of mechanical properties at higher temperatures, higher char yields, and better adhesion to inorganic fillers and substrates than epoxy resins cured with conventional polyamines.
Silazanes have also been shown to react with nucleophilic organic materials such as alcohols, amines and phenols.
For example, U.S. Pat. No. 5,089,552, to Myers teaches the in-situ polymerization of various silicon-nitrogen containing cyclic silazane monomers with phenolic resins to generate thermally stable high char yield polysilazoxane-modified phenolic resins. The reaction of polysilazanes with OH groups of polyphenols is thus known, but not the reaction of polysilazanes with the —NH
2
or NRH groups of polyamines.
U.S. Pat. No. 6,310,168 B1 to Shimizu et al teaches the reaction of various polysilazanes with amine residue-containing hydroxyl compounds to generate amine-appended polysilazanes in which the amine residue-containing hydroxyl compound reacts with the polysilazane at the hydroxyl group to generate a product which comprises a silicon-oxygen bond. The reaction with the less reactive —NH
2
or —NRH groups does not occur.
U.S. Pat. No. 4,975,512, on the other hand, teaches the reaction of various polysilazanes with monomeric primary and secondary amines or hydrazines to form “reformed” polysilazanes. The reaction disclosed involves compounds of the formula:
H—A—NR
3
R
7
wherein A is a direct bond or —NR
4
— where R
4
is hydrogen, an alkyl, an alkenyl, a cycloalkyl, an aryl, an aralkyl or a heterocyclic group, and R
3
and R
7
, are independently selected from hydrogen, an alkyl, an alkenyl, a cycloalkyl, an aryl, an aralkyl or a heterocyclic group. Thus, when A is a direct bond, the compound is either ammonia, or a simple primary or secondary amine comprising a single reactive nitrogen group. When A is a hydrocarbyl or heterocyclic group as defined, the compound is either a primary, secondary, or tertiary amine also comprising a single reactive nitrogen group. When A is —NR
4
— a hydrazine compound results, which is neither a simple monomeric amine, nor a polyamine. The reaction requires polysilazane comprising Si—H bonds, is performed in a solvent, and is said to proceed by dehydrogenative polycondensation with the in situ production of hydrogen gas.
U.S. Pat. No. 5,198,519 teaches the preparation of polysilazanes by reacting (A) with (B), wherein (A) is one or more silicon amide monomers represented by the general formula:
[(R
1
)
2
N]
a
SiR
b
wherein each R is independently selected from hydrogen or a hydrocarbon group, each R
1
is a saturated hydrocarbon group, a is an integer from 2 to 4, b is an integer from 0 to 2, and the sum of a and b equals 4, and (B) is one or more polyamines. (A) is never a polysilazane.
Although silazanes are formally disilylamines, their reactivity with epoxies does not parallel that of organic amines. Silazanes are not as basic as organic amines, and the reactivity of silazane-based polymers with epoxy resins stems primarily from the polarity of the Si—N bond and its oxophilic nature, allowing it to react with a variety of epoxy resins by Si—N bond addition across epoxy resin oxirane groups at elevated temperature, as taught in U.S. Pat. Nos. 5,616,650; 5,741,878; 5,637,641; 5,767,218; 5,807,954; 5,733,997; and 5,750,628. Typically, however, the reaction of the silicon-nitrogen bond of a polysilazane with an epoxy resin is rather sluggish, and high temperatures are normally required to effect
Ellis Howard M.
Kion Corporation
Robertson Jeffrey B.
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