Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-08-17
2004-05-25
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S161000, C524S162000, C524S423000, C524S430000, C524S431000, C524S432000, C524S433000, C524S492000, C524S497000
Reexamination Certificate
active
06740697
ABSTRACT:
The invention relates to a flame-resistant thermoplastic moulding composition which comprises an amorphous thermoplastic polymer and a flame retardant, and flame-resistant moulded bodies produced therefrom.
The flame behaviour of amorphous thermoplastics such as polycarbonates plays an important role in particular in areas in which compliance with specific fire safety regulations is a requirement, such as in the electrical, automotive, construction and to aeronautical sectors. UL-94, the Underwriters Laboratories flammability test (Underwriters Laboratories, Northbrook, Ill., USA) which considers both the burning duration of the plastic following flame impingement and also the tendency to drip burning material, is the standard frequently applied to flammability of solid plastics. In accordance with the UL-94 regulation a flame impinges under specified conditions on plastic samples of variable thickness measuring 12.7×1.27 cm, and the burning duration is determined. The samples are classified into UL-94 flammability classes V0, V1 and V2, in order of decreasing flame resistance. In order to be classified into UL-94 flammability class V0 a sample must not exceed a specified burning duration, amid additionally a surgical cotton wad located beneath the sample must not be ignited by dripping burning particles.
Flame retardants are utilised for the preparation of flame-resistant amorphous thermoplastics such as polycarbonates. They are generally known and are described, for example, in B. J. Sutker “Flame Retardants”, Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, 1998.
There is a need for mouldings made of flame-resistant amorphous thermoplastics, which meet the requirements of UL-94 flammability class V0 even at relatively low wall thicknesses. Thus in the case of electrical equipment weight savings can be achieved by the use of polycarbonate housings having the thinnest possible walls, for instance. There is furthermore a need for thin-walled mouldings of amorphous thermoplastics which in addition to having excellent flame retardant properties are transparent. Transparent polycarbonate mouldings have a role in, for instance, housings and covering plates for electrical equipment as well as in the construction sector for sheets, windows and claddings of widely varying types.
EP 0 531 861 A1 discloses the equipping of polycarbonates with a halogen-free sulfonic acid salt of aromatic aldehydes or acetal derivatives thereof, optionally in combination with inorganic sulfates such as sodium or potassium sulfate as fire retardants. The use of these fire retardants enables UL-94 flammability class V0 to be achieved for 3.2 mm-thick polycarbonate test specimens. Test specimens having a lesser thickness do not achieve UL-94 flammability class V0.
BP 0 362 623 A2 further discloses flame-retarded polyethylene terephthalate moulding compositions achieving good crystallisation, which comprise from 1 to 25 wt. % polyalkyl phosphonates as flame retardants as well as from 0.01 to 10 wt. % ultra-fine barium sulfate in combination with from 0.01 to 5 wt. % fluorinated polyolefins as crystallisation promoters. The fluorinated polyolefin content enables only cloudy mouldings to be produced from the polyethylene terephthalate moulding compositions described.
A disadvantage of the known flame retardants is that UL-94 flammability class V0can be achieved in respect of polycarbonate only at moulding wall thicknesses of 3.2 mm or more. The known flame retardants furthermore tend to cloud the thermoplastic moulding compositions and/or they are subject to frequent fluctuations in their flame-retardant effect. A further disadvantage is the frequent marked impairment, caused by the recycling process, of the flame-retardant effect of mouldings equipped with known flame retardants. Mouldings processed by shredding and re-extrusion of scrap to form recycled mouldings therefore frequently have a substantially poorer flame behaviour than the original mouldings. What is more, a range of known flame retardants are sensitive to compromising of their effectiveness by the presence of mould release agents such as glycerol monostearate (GMS) or pentaerythritol tetrastearate (PETS). Known flame retardants frequently require the use of additional transesterification catalysts in order to deploy their effect, potentially leading to undesirable changes in the properties of the plastic.
The object of the invention is to provide amorphous thermoplastic moulding compositions, in particular those such as are of polycarbonate, having improved flame behaviour. The moulding compositions should still achieve UL-94 flammability class V0 even at wall thicknesses of less than 3.2 mm. This should occur if possible with no deterioration in the transparency and mechanical properties of the moulding compositions. The moulding compositions should furthermore also still afford the desired flame retardancy as a recycled product. The flame retardancy should not furthermore be impaired by the use of mould release agents such as GMS or PETS. The moulding compositions should furthermore be preparable without the use of additional transesterification catalysts which lead to undesirable changes in the properties.
This object is achieved according to the invention by a thermoplastic moulding composition which comprises an amorphous thermoplastic polymer and a flame retardant in combination with an alkaline earth metal sulfate and/or an oxide having di each case an average particle size of up to 400 nm. The alkaline earth al sulfates and oxides used according to the invention having an average particle size of up to 400 nm are also designated hereinbelow “nanoparticulate” or “ultra-fine” alkaline earth metal sulfates and oxides.
The moulding composition which comprises an amorphous thermoplastic polymer in particular includes as a flame retardant a mixture of a known flame retardant selected from among sulfonic acid salts, sulfonamide acid salts, organic phosphates and salts thereof, halogenated benzoic acid ester salts and hexafluoroaluminates and an alkaline earth metal sulfate and/or an oxide having in each case an average particle size of up to 400 nm.
According to an embodiment of the invention the moulding composition according to the invention further comprises a fluorinated hydrocarbon such as polytetrafluoroethylene.
It was here, surprisingly found that flame-resistant thermoplastic moulding compositions having an extremely favourable property profile can be prepared by the addition of nanoparticulate alkaline earth metal sulfates and/or oxides in addition to the known flame retardants. The mouldings according to the invention thus still achieve UL-94 flammability class V0 even at a wall thickness of 0.8 mm and, at a thickness of up to 2.8 mm, pass the Underwriters Laboratories UL-94 5V bar test
The use of nanoparticulate alkaline earth metal sulfates and/or oxides enables the quantity of known flame retardants which is required in order to achieve a specified flame-retardant effect to be reduced. This means that less flame retardant needs to be utilised as a result of the utilisation of nanoparticulate alkaline earth metal sulfates and/or oxides, with the same flame-retardant effect.
The addition of nanoparticulate alkaline earth metal sulfates and/or nanoparticulate oxides is able to improve markedly the flame-retardant effect of known flame retardants despite neither of the compound classes first named having alone any flame-retardant effect. This means that the combination of known flame retardant and nanoparticulate alkaline earth metal sulfatestoxides deploys a synergistic effect with respect to the flame-retardant properties of the thermoplastic moulding compositions.
The mechanical properties of the thermoplastic moulding compositions according to the invention are not influenced disadvantageously by the presence of nanoparticulate alkaline earth metal sulfates and/or oxides and are good even after recycling of the moulding compositions. Thus the moulding compositions according to the invention are distinguis
Brenner Axel
Döbler Martin
Köhler Walter
Bayer Aktiengesellschaft
Franks James R.
Gil Joseph C.
Preis Aron
Szekely Peter
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