Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2000-11-01
2002-12-31
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S901000, C523S451000, C525S327400, C525S385000
Reexamination Certificate
active
06500546
ABSTRACT:
1. FIELD OF THE INVENTION
The invention relates to halogen-free phosphorous-containing flame-retardant epoxy resin compositions, to prepregs derived by impregnation of porous webs, and to composites and in particular to laminates, derived from said prepregs and to be used in printed circuit boards.
2. BACKGROUND OF THE INVENTION
Composites based on epoxy resins and inorganic or organic reinforcing materials have become very important in many industrial fields and in everyday life. The reasons therefore are, on the one hand, the relatively simple and safe processing of epoxy resins and, on the other hand, the good mechanical and chemical properties of cured epoxy resin moulded materials, which allow adaptation to different applications and advantageous utilization of the properties of all the materials which are part of the composite.
Epoxy resins are advantageously processed into composites via preparation of prepregs. For this purpose inorganic or organic reinforcing materials or embedding components in the form of fibres, non-woven and woven fabrics, or of flat-shaped articles are impregnated with the resin. In most cases this is accomplished with a solution of the resin in an easy-to-evaporate or easy-to-volatilize solvent. The prepregs thus obtained after heating, must no longer be tacky, but must not yet be hardened after this process, but rather the resin matrix must be in a pre-polymerized state. In addition, the prepregs must have sufficiently long shelf life. Thus, for example, a shelf life of at least three months is required for circuit board manufacturing. When they are further processed into composites, the resin in the prepregs must also melt and flow on when the temperature is increased and must bond with the reinforcing materials or embedding components as well as with the materials provided for the composite as firmly and permanently as possible under pressure, i.e. the cross-linked epoxy resin matrix must have a high interfacial adhesion to the reinforcing materials, or embedding components, as well as to the materials to be bonded such as metals, ceramics, minerals, and organic materials.
In the cured state, composites are normally expected to have high mechanical strength and thermal stability, as well as chemical resistance, and heat distortion or resistance to ageing. For electrotechnical and electronic applications, the requirements also include permanently high electrical insulation capability and, for special applications, a plurality of other requirements. For use as circuit board material, for example, high dimensional stability over a broad temperature range, good adhesion to glass and copper, high surface resistivity, low dielectric loss factor, good machinability (punchability, drillability), low water absorption, and high corrosion resistance are required.
With increasing load and intensive use of the composites, in particular the requirement for heat distortion becomes especially important. This means that the materials must resist high temperatures without deformation or damage of the composite, for example by delamination, during processing and use. Circuit boards, for example, are exposed to temperatures of over 270° C. during flow soldering. Temperatures over 200° C. may also occur temporarily and in a limited area during cutting and drilling. Materials with a high glass transition temperature have advantageous characteristics in this respect. If the glass transition temperature is above the aforementioned values, dimensional stability in the temperature range prevailing during processing is generally ensured and damage such as warping and delamination are mostly avoided. The epoxy resin currently used worldwide for FR4 laminates has a glass transition temperature Tg of only 130° C. after curing. This results, however, in the above-mentioned type of damage and failure during manufacturing. Therefore, it is still desired to have comparatively easy-to-process and inexpensive materials with a glass transition temperature Tg of up to approximately 180° C., and more preferably in the range of from 140 to 180° C.
Another requirement that is becoming more and more important is that of flame resistance. In many areas this requirement has first priority due to possible hazards to people and property, for example, in construction materials for aircraft and automobile manufacturing, as wel as for vehicles in public transportation. Flame resistance of circuit board materials is essential in electrotechnical, but especially electronic, applications due to the high value of the electronic components mounted on the boards, and the risk of fire caused by a short circuit.
Therefore materials must pass one of the strictest tests and attain V-0 classification by UL 94 V, for evaluating their flammability. In this test, a test object is exposed to a well-defined flame positioned vertically under its lower edge. The sum of burning times in ten tests (5 samples, each sample of which is submitted to a standard flame twice) may not exceed 50 s. This requirement is difficult to meet, especially if the material is thin, as is the case in electronics. The epoxy resin industrially used worldwide for FR4 laminates only meets these requirements because it contains approximately 30% to 40% ring-brominated aromatic epoxy components, with reference to the resin, i.e. approximately 17%-21% bromine. For other applications, comparably high concentrations of halogen compounds are used, often also combined with antimony trioxide as a synergist. The problem with these compounds is that, while they are highly effective as fireproofing agents, they also have very objectionable properties. Thus, antimony trioxide is listed as a carcinogenic chemical, and aromatic bromine compounds, during thermal decomposition, not only split off bromine radicals and hydrogen bromide, which are highly corrosive, but, especially the highly brominated aromatic compounds may also form highly toxic polybromine benzofurans and polybromine benzodioxins upon decomposition in the presence of oxygen. The disposal of bromine-containing waste materials and toxic waste represents another problem.
Materials that partially or fully meet the heat distortion requirement include, for example, bismaleimide/triazine (BT)-based moulded materials with a Tg of approximately 200° C. or polyimide (PI) with a Tg of 260° C. to 270° C. Recently also BT/epoxy blends with a Tg of 180° C., as well as cyanate ester resins with a Tg>200° C., have also become available. Laminates manufactured with these resins systems exhibit, however, poorer processing and machining characteristics compared to epoxy resin-based laminates. Thus, for example, the production of PI-based laminates requires press temperatures of approximately 230° C. and considerably longer after-curing times (approx. 8 h) at temperatures of 230° C. Another disadvantage of these resin systems is their six to ten times higher material costs.
A comparatively expensive resin system is obtained if aromatic and/or heterocyclic polyepoxy resins, i.e. polyglycidyl compounds, are combined with aromatic polyamines acting as hardening agents. Such polyamines known, for example, from German Patent 2,743,680, result in network polymers that exhibit a particularly high heat distortion and resistance to ageing. European Patent No. 0,274,646B discloses that, using 1,3,5-tris(3-amino-4-alkylphenyl)-2,4,6-trioxohexahydrotriazines as hardening agents, laminates with a glass transition temperature of up to 245° C. and good processing and machining characteristics can be obtained.
Although the above-mentioned resin systems have a widely different flammability, they all share the disadvantage of being insufficiently flame-retardant. Therefore, in order to meet the requirement of passing the UL 94 V combustibility test via V-0 classification, which is essential for many applications, the use of highly effective bromine-containing fireproofing agents cannot be avoided. As a result, both the potential hazard associated with bromine compounds and the impaired thermal-mechanical characteris
De Velder Helga Leontina Andrea
Heine Francoise Marie Louise
Riviere Jean Andre Alfred
Stevens Philippe Eric
Aylward D.
Dawson Robert
Resolution Performance Products LLC
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