Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2000-03-23
2002-08-13
Lovering, Richard D. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C427S096400, C523S459000, C524S406000
Reexamination Certificate
active
06432540
ABSTRACT:
TECHNICAL FIELD
This invention relates to flame retardant molding compositions.
BACKGROUND
Epoxy resin is a widely used molding compounds for coating electronic devices such as integrated circuits. For safety reasons, molding compositions containing epoxy resin often include flame retardants. A common flame retardant system is a combination of bromine containing flame retardants and antimony oxide flame retardant synergists. However, these compounds are pollutants of the environment. Some bromine containing flame retardants (especially brominated diphenyl ethers) are toxic and possibly carcinogenic. As to antimony trioxide, it is classified by the International Agency for Research on Cancer as a Class 2B carcinogen (i.e., antimony trioxide is a suspect carcinogen based mainly on animal studies). In addition, this compound is often used at relatively high level (2-4%) and is also slightly water-soluble, leading to further environmental concerns. This concern is highlighted by the fact that integrated circuit manufacturers currently discard up to one half of the total amount of molding compositions used as waste product in landfills.
Phosphorus-containing compounds have been proposed as flame retardants. Although they are less hazardous, molding compositions containing these compounds generally possess undesirable properties such as high moisture absorption rate. Thus, there exists a need to develop new flame retardant molding compositions that do not contain brominated flame retardants, phosphorus-containing compounds, or antimony oxide flame retardant synergists.
SUMMARY
In general, the invention relates to flame retardant molding compositions that are substantially free of halogen, phosphorus, and antimony. In addition to having good flame retarding properties, these compositions form good cull cure in short time periods and absorb low amount of moisture, and can be used to coat electronic or electrical devices such as semiconductors, diodes, and integrated circuits. Such coated devices demonstrate good electrical reliability at high temperature.
In one aspect, the invention features a flame retardant molding composition that is substantially free of halogen, phosphorus, and antimony. The molding composition includes an epoxy resin, a first transition metal oxide containing a refractory metal, and a second transition metal oxide containing an oxyanion of a Group VIA element.
In another aspect, the invention features a flame retardant molding composition substantially free of halogen, phosphorus, and antimony, including an epoxy resin, a phenol novalac hardener containing a biphenyl or naphthyl moiety, and a transition metal oxide of a Group VIA element.
In another aspect, the invention features a flame retardant molding composition that is substantially free of halogen, phosphorus, and antimony, including an epoxy resin containing a biphenyl or naphthyl moiety, a phenol novalac hardener, and a transition metal oxide of a Group VIA element.
The invention also features a method of preparing a flame retardant polymer composition that is free of halogen, phosphorus, and antimony. The method includes heating a molding composition to a temperature sufficient to cure the molding composition (e.g., about 150° C. to about 200° C., or about 165° C. to about 195° C.). The molding composition cures in about 1 minute to about 2 minutes, and contains an epoxy resin, a first transition metal oxide containing a refractory metal, and a second transition metal oxide containing an oxyanion of a Group VIA element. The invention also features polymer compositions formed by this method.
The invention also features a method of coating an electrical or electronic device such as an integrated circuit. The method includes heating a molding composition to a temperature sufficient to cure the molding composition (e.g., about 150° C. to about 200° C., or about 165° C. to about 195° C.). The polymer composition thus formed coats the surface of the device. The molding composition contains an epoxy resin, a first transition metal oxide containing a refractory metal, and a second transition metal oxide containing an oxyanion of a Group VIA element. The invention also features coated devices prepared by this method.
As used herein, a composition that is “substantially free” of a material means that the amount of the material is negligible in the composition, i.e., less than about 0.001 wt % of the total weight of the composition.
As used herein, a refractory metal is a metal having a melting point of around 2,000° C. or above. Some examples of a refractory metal are zirconium, niobium, molybdenum, ruthenium, iridium, hafnium, tantalum, tungsten, osmium, vanadium, chromium, rhenium, and rhodium.
As used herein, an oxyanion is a polyatomic anion containing oxygen, e.g., molybdate and chromate.
As used herein, a compound is water-insoluble when it has a solubility of less than 0.05 g in 100 mL of water at 25° C.
As used herein, a molding composition is cured when it forms a good cull cure (i.e., strong and not brittle).
Other features and advantages of the invention will be apparent from the description of the preferred embodiments thereof, and from the claims.
DETAILED DESCRIPTION
A preferred molding composition contains an epoxy resin, a hardener, and two transition metal oxides, and optionally a third transition metal oxide.
There is no restriction on the type of epoxy resin that can be used in the molding compositions so long as it contains two or more reactive oxirane groups. Some suitable epoxy resins are epoxy cresol novalac resin, biphenyl epoxy resin, hydroquinone epoxy resin, phenolic novalac epoxy resin, and stilbene epoxy resin. Epoxy cresol novalac resin is preferred. The molding compositions can include more than one epoxy resin, for example, a combination of epoxy cresol novalac resin and biphenyl epoxy resin. The preferred weight percent of the epoxy resin ranges from 4 wt % to about 12 wt %, and more preferably, from about 5.5 wt % to about 8.5 wt %, based on the total weight of the molding composition.
The hardener promotes crosslinking of the molding composition to form a polymer composition. Some suitable hardeners that can be included in the molding compositions are phenol novalac hardener, cresol novalac hardener, dicyclopentadiene phenol hardener, and limonene type hardener. Phenol novalac hardener is preferred. Similar to the epoxy resin component, more than one type of hardener can be included in the molding compositions. The preferred weight percent of the hardener ranges from 1 wt % to about 10 wt %, and more preferably, from about 1.5 wt % to about 6 wt %, based on the total weight of the molding composition.
As to the two transition metal oxides, the first transition metal oxide contains a refractory metal, e.g., chromium, molybdenum, and tungsten, and the second transition metal oxide contains an oxyanion of a Group VIA element, e.g., molydate and tungstate. While there is no particular restriction on the cation of the second transition metal oxide, it is preferred to be a Group IIB metal cation, e.g., zinc. Both the first and second transition metal oxides are preferred to be water-insoluble. A particularly preferred first and second transition metal oxides are tungsten trioxide and zinc molybdate, respectively. The transition metal oxides are preferred to be in their free form, i.e., they are not associated with materials such as silica or talc. The oxides are also preferred to be finely divided, e.g., having a diameter of about 0.1 &mgr;m to about 10 &mgr;m, preferably, about 0.5 &mgr;m to about 5 &mgr;m, or more preferably, about 0.5 &mgr;m to about 2 &mgr;m. The oxides can be obtained commercially, e.g., tungsten trioxide and zinc molybdate are available from Aldrich Chemical Company (Milwaukee, Wis.) and the Sherwin-Williams Company (Cleveland, Ohio), respectively. The molding composition can include, for example, about 0.25 wt % to about 2 wt %, preferably about 0.5 wt % to about 1 wt %, and more preferably about 0.75 wt % of the first transition metal oxide based on the tot
Loctite Corporation
Lovering Richard D.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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