Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-12-01
2002-03-05
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of metal
C428S457000, C428S458000, C525S391000, C528S205000
Reexamination Certificate
active
06352782
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
None.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
The present invention is related to polymerizable compositions with excellent thermal and dielectric properties suited for applications such as molding, laminating, encapsulation, coating or potting. A desired application of the present invention is in molding compositions where excellent dielectric and thermal properties, solvent resistance and low coefficients of thermal expansion are required. Another desired application is in laminating products that are useful for composites and dielectrics as for example in printed circuit boards. Further, the present invention relates to a process for making thermoset polymer resins and laminates, and to products characterized by excellent dielectric and thermal properties that can be made to exhibit excellent solvent resistance and flame resistance. More particularly, the present invention relates to reactively end capped poly(phenylene ether) compounds and to their cure with certain unsaturated compounds for synthesizing resins ideally adapted for impregnating fibrous reinforcement in the manufacture of circuit boards.
Thermoset molding compositions known in the art, are generally thermosetting resins containing inorganic fillers and/or fibers. Upon heating these materials initially exhibit viscosities low enough to allow for melt processing and molding of an article from the filled thermoset monomer composition. Upon further heating the thermosetting monomers react and cure to form hard resins with high modulus.
Metal-clad boards, particularly such boards for use in fabricating printed circuits, are also well-known in the art. The simplest of such boards generally comprises a resinous plastic (polymeric) substrate to which is bonded at least one thin sheet (foil) of an electrically conductive material, preferably copper. The resinous plastic substrate can be clad with the metal foil on one or both sides, depending upon the desired use, and can be rigid or flexible depending upon the composition of the resinous plastic substrate, the choice of reinforcement (if any), and the intended use of the board.
A number of polyphenylene ether compositions having favorable dielectric properties and utility in circuit board manufacture are known. However, due to deficiencies in one or more properties, many such compositions have not attained wide commercial use. Specifically, while polyphenylene ethers exhibit excellent dielectric properties, deficiencies often are found in areas such as, inter alia, solvent resistance, flammability, solderability, and resistance to high temperatures. Moreover, times required for curing such compositions typically are too long for effective manufacture of circuit boards in large volume.
In addition to excellent dielectric properties, resinous compositions to be used for printed circuit board manufacture should be highly flame-retardant. A V-1 rating, as determined by Underwriters Laboratories test procedure UL-94, is universally required, with V-0 usually being preferred. The V-0 rating requires a flame-out time (FOT) of not more than 10 seconds in any trial and a cumulative FOT of not more than 50 seconds for five samples. As a practical matter, purchasers often mandate a maximum cumulative FOT of 35 seconds.
The fabricated board should not lose substantial weight and its surface should not be appreciably marred by contact with methylene chloride, a solvent commonly used for cleaning. Since conductive connections with the printed circuit typically are made by soldering, the board must be solder-resistant as evidenced by the lowest possible percent increase in thickness (Z-axis expansion) when exposed to liquid solder at 288° C. In addition to all these properties of the cured material, a relatively short curing time is highly desirable. In preparing rigid metal-clad boards, it is common to form individual lamina, commonly called prepregs, by formulating a resinous binder composition made from epoxy, modified styrene, or the like. A liquid resin or solvent solution of the resin is placed impregnated into continuous webs of reinforcement and then dried and or partially cured in a vertical or horizontal treating tower or oven. Normally, the resin is partially cured or B-staged after exiting the treater tower or oven. The copper foil, optionally coated with an adhesive, is placed on one side of the prepreg and subjected to heating under pressure to effect a bond between the metal foil and the substrate. Multiple prepregs can be used in forming a single composite board.
Additionally, multilayer printed wiring boards will have a number of interposed laminae and copper sheets.
Pressing of the boards can be effected in a press by placing the foil/substrate structure between the platens and closing the press, or a continuous belt can be used. The curing cycle in the press will depend upon the nature and thickness of the laminate, the time and temperature of the cycle being those required to cure the substrate, and the bonding adhesive layer, if present. Sufficient pressure is required to effect adequate flow of the adhesive and/or substrate resins in order to wet-out and bond adequately. The pressure must be sufficient to prevent blistering which is due to the release of gases resulting either from retained volatiles in the substrate or adhesive layers, or resulting from by-products of the curing process.
Heretofore, Fox (U.S. Pat. No. 3,356,761) describes blends of high molecular weight, uncapped PPE (molecular weight 10,000 and preferably 50,000) with a liquid unsaturated vinyl monomer selected from the group consisting of styrenics, divinylbenzene, vinylpyridines, and alkylated and halogenated derivatives useful for film and fiber applications. Fox does not teach the advantages of capped PPE and said blends of capped PPE with allylic monomers, blend thereof, or blends of allylic monomers with styrenic monomers. Further he does not teach the advantages of alkylated styrenes, such a t-butyl styrene, in enhancing the thermal performance of the blend. He also does not demonstrate the significant thermal advantages of using a butylated styrene.
Wright, et al. (U.S. Pat. No. 3,557,045) disclose a thermosetting resin composition comprising (i) a polymerizable material containing a carbon-carbon double bonds, at least 5% of which is a liquid monomer, (ii) a poly(phenylene ether) resin, and (iii) a radical initiator. In particular the Wright, et al. teach compositions comprising a diallyl phthalate prepolymer, a poly(phenylene ether) resin, and a radical initiator, in which the composition is described as having improved electrical and mechanical properties.
Wright, et al. (U.S. Pat. No. 3,637,578) disclose a thermosetting resin composition comprising (i) a mixture of a liquid monomer containing carbon-carbon double bonds in an amount of at least 5% and having boiling point of 70° C. or higher with a reactive polyester resin, (ii) a poly(phenylene ether) resin, and (iii) a radical initiator. It is described that the thermosetting resin composition can be cured to obtain a thermoset resin having improved electrical and mechanical properties. Examples 3-2 and 3-4 of this Wright, et al. patent disclose compositions comprising a poly(phenylene ether) resin, a polyester resin, triallyl cyanurate, and diallyl phthalate. The poly(phenylene ether) content of the composition is 20% and the balance is comprised of crosslinking components (i.e. polyester resin, triallylcyanurate, and diallyl phthalate).
Wright, et al. (U.S. Pat. No. 3,936,414) describe flame retardant compositions comprising (i) 10-50 parts by weight of a polyunsaturated monomer, (ii) 5-30 parts by weight of a polychlorinated or polybrominated aromatic hydrocarbon having a molecular weight of at least 200 and a chlorine or bromine content of at least 50% by weight, (iii) 20-60 parts by weight of a poly(phenylene ether), (iv) 0-30 parts by weight of a polyunsaturated polymer having unsaturated carbon-carbon bonds, and (v) 2-10 parts b
Colborn Robert E.
Yeager Gary W.
General Electric Company
Short Patricia A.
LandOfFree
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