Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-01-25
2002-07-16
Hoke, Veronica P. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S506000, C524S133000, C524S134000, C524S136000, C524S417000, C524S436000
Reexamination Certificate
active
06420459
ABSTRACT:
The invention relates to flame-retardant thermoset compositions, to a process for their preparation, and to their use.
BACKGROUND OF THE INVENTION
Components made from thermoset resins, in particular those which have glass-fiber reinforcement, feature good mechanical properties, low density, substantial chemical resistance and excellent surface quality. This and their low cost has led to their increasing use as replacements for metallic materials in the application sectors of rail vehicles, the construction of buildings and air travel.
Unsaturated polyester resins (UP resins), epoxy resins (EP resins) and polyurethanes (PU resins) are combustible and therefore need flame retardants in some applications. Increasing demands in the market for fire protection and for environmental compatibility in products are increasing interest in halogen-free flame retardants, for example in phosphorus compounds or metal hydroxides.
Depending on the application sector, there are different requirements in relation to mechanical, electrical and fire-protection properties. In the rail vehicle sector in particular, fire-protection requirements have recently been made more stringent.
It is known that bromine- or chlorine-containing acid and/or alcohol components are used to formulate flame-retardant unsaturated polyester resins. Examples of these components are hexachloroendomethylene tetrahydrophthalic acid (HET acid), tetrabromophthalic acid and dibromoneopentyl glycol. Antimony trioxide is often used as a synergist.
In JP 05245838 (CA 1993: 672700), aluminum hydroxide, red phosphorus and antimony trioxide are combined with a brominated resin to improve flame retardancy. A disadvantage of bromine- and chlorine-containing resins is that corrosive gases are produced in a fire, and this can result in considerable damage to electronic components, for example to relays in rail vehicles. Unfavorable conditions can also lead to the formation of polychlorinated or brominated dibenzodioxins and furans. There is therefore a requirement for unsaturated polyester resins and unsaturated polyester molding compositions which are flame-retardant and halogen-free.
It is known that unsaturated polyester resins and unsaturated polyester molding compositions may be provided with fillers, such as aluminum hydroxide. The elimination of water from aluminum hydroxide at elevated temperatures gives some degree of flame retardancy. At filler levels of from 150 to 200 parts of aluminum hydroxide per 100 parts of UP resin it is possible to achieve self-extinguishing properties and low smoke density. A disadvantage of systems of this type is their high specific gravity, and attempts are made to reduce this by adding, for example, hollow glass beads [Staufer, G., Sperl, M., Begemann, M., Buhl, D., Düll-Muhlbach, I., Kunststoffe 85 (1995), 4].
PL 159350 (CA 1995: 240054) describes laminates made from unsaturated polyester resins with up to 180 parts of magnesium hydroxide. However, injection processes, which are extremely important industrially, cannot be used with formulations of this type, due to the high viscosity of the uncured UP resin with the aluminum hydroxide or, respectively, magnesium hydroxide.
The processes described at a later stage below for formulating flame-retardant unsaturated polyester resins likewise have a large number of disadvantages, in particular the requirement for a very high filler content.
To reduce the total filler content, aluminum hydroxide can be combined with ammonium polyphosphate, as described in DE-A-37 28 629. JP 57016017 (CA96(22): 182248) describes the use of red phosphorus as a flame retardant for unsaturated polyester resins, and JP 55094918 (CA93(24): 22152t) describes the combination of aluminum hydroxide, red phosphorus and antimony trioxide.
PL 161333 (CA 1994: 632278) achieves low smoke density and low-toxicity decomposition products by using aluminum hydroxide, magnesium hydroxide or basic magnesium carbonate, red phosphorus and, if desired, finely dispersed silica. DE-A-2159757 moreover claims the use of melamine and aluminum hydroxide.
Since aluminum hydroxide on its own is not a very effective flame retardant for unsaturated polyester resins or for epoxy resins, combinations with red phosphorus are also proposed, in order to reduce the filler content. A disadvantage here, however, is the red intrinsic color of the product, limiting its use to components with dark pigmentation.
Unsaturated polyester resins are solutions, in copolymerizable monomers, preferably styrene or methyl methacrylate, of polycondensation products made from saturated and unsaturated dicarboxylic acids, or from anhydrides of these, together with diols. UP resins are cured by free-radical polymerization using initiators (e.g. peroxides) and accelerators. The double bonds in the polyester chain react with the double bond in the copolymerizable solvent monomer. The most important dicarboxylic acids for preparing the polyesters are maleic anhydride, fumaric acid and terephthalic acid. The diol most frequently used is 1,2-propanediol. Use is also made of ethylene glycol, diethylene glycol and neopentyl glycol, inter alia. The most suitable crosslinking monomer is styrene. Styrene is fully miscible with the resins and copolymerizes readily. The styrene content in unsaturated polyester resins is normally from 25 to 40%. A monomer which can be used instead of styrene is methyl methacrylate.
Another group of thermosets, epoxy resins, are nowadays used for preparing molding compositions and coatings with a high level of thermal, mechanical and electronic properties.
Epoxy resins are compounds prepared by a polyaddition reaction of an epoxy resin component with a crosslinking (hardener) component. The epoxy resin components used are aromatic polyglycidyl esters, such as bisphenol A diglycidyl ester, bisphenol F diglycidyl ester or polyglycidyl esters of phenol-formaldehyde resins or cresol-formaldehyde resins, or polyglycidyl esters of phthalic, isophthalic or terephthalic acid, or else of trimellitic acid, N-glycidyl compounds of aromatic amines or of heterocyclic nitrogen bases, or else di- or polyglycidyl compounds of polyhydric aliphatic alcohols. Hardeners which are used are polyamines, such as triethylene tetramine, aminoethylpiperazine or isophoronediamine, polyamidoamines, polybasic acids or anhydrides of these, e.g. phthalic anhydride, hexahydrophthalic anhydride or methyltetrahydrophthalic anhydride, or phenols. The crosslinking may also take place via polymerization using suitable catalysts.
Epoxy resins are suitable for the potting of electrical or electronic components, and for saturation and impregnation processes. The epoxy resins used in electrical engineering are predominantly flame-retardant and used for printed circuit boards or insulators.
In the prior art, epoxy resins for printed circuit boards are currently rendered flame-retardant by including bromine-containing aromatic compounds in the reaction, in particular tetrabromobisphenol A. A disadvantage is that brominated hydrocarbon (a dangerous substance) is liberated in a fire, and this can cause corrosion damage. Under unfavorable conditions, polybrominated dibenzodioxins and furans can also be produced. The use of aluminum hydroxide is completely excluded since it eliminates water when processed.
Fire-protection requirements for electrical and electronic equipment are laid down in specifications and standards for product safety. In the US, fire-protection testing and approval procedures are carried out by Underwriters Laboratories (UL), and UL specifications are nowadays accepted worldwide. The fire tests for plastics were developed in order to determine the resistance of the materials to ignition and flame spread.
The materials have to pass horizontal burning tests (Classification UL 94HB) or the more stringent vertical tests (UL 94V-2, V-1 or V-0), depending on the fire-protection requirements. These tests simulate low-energy ignition sources which occur in electrical devices and to which plastic parts in electrical modules can be
Clariant GmbH
Hanf Scott E.
Hoke Veronica P.
Jackson Susan S.
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