Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-11-27
2004-02-10
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S094000, C524S127000, C524S141000, C524S142000, C524S175000, C524S200000, C524S204000, C524S399000, C252S609000, C252S400210, C252S400530
Reexamination Certificate
active
06689825
ABSTRACT:
BACKGROUND
The present disclosure relates to an additive for thermoplastic resins and to resin compositions containing such additives. In particular, the present disclosure relates to additives which enable improved flame retardant characteristics, heat deflection temperatures and flow rates of thermoplastic resins such resin compositions containing polyphenylene ether (PPE), high impact polystyrene (HIPS) and the like. The present disclosure also relates to a process for the preparation of a thermoplastic resin composition containing such additives and with improved flame retardant, heat deflection temperature and flow properties.
Thermoplastic resins have use in different industries such as materials for parts of electric and electronic appliances and also for parts of automobiles. Thermoplastic resin compositions such as high impact polystyrene (HIPS) and polyphenylene ether (PPE) resin compositions are also useful as adhesives, sealants, gels, automotives, cabling, electrical applications, aerospace, sporting equipment, electrical laminates and IC encapsulation materials. Polyphenylene ether resins are also useful as additives for various thermoplastic and thermoset materials. The physical, electrical and chemical properties of polyphenylene ether resin compositions make them ideal for a wide variety of industrial applications.
U.S. Pat. Nos. 3,383,435; 4,128,602 and 4,128,603 disclose thermoplastic polymer blends comprising polyphenylene ether (PPE) and vinylaromatic polymers, such as styrene polymers which are useful as molding materials. An important advantage of the polymer blends comprising polyphenylene ethers and styrene polymers is that, by admixing halogen-free additives, in particular phosphorus-containing compounds, it is possible to obtain molding materials which are flame-retardant and can therefore be used for many applications in the electrical industry. In particular, the test for flame retardancy according to UL 94 is critical for use in the electrical industry. In this test, a flame is applied repeatedly to vertically fastened test specimens. The test specimen heats up to a very great extent. In some cases, this leads to the dripping of flaming polymer material and ignition of the cotton wool mounted below the rod. This undesirable behavior is observed in particular when large amounts of flameproofing agents must be used in order to achieve short combustion times.
Styrenic polymer compositions such as HIPS, containing various polymeric additives such as rubbers to improve mechanical properties, acrylonitrile/butadiene/styrene (ABS) type compositions are widely used because of their mechanical properties. HIPS for example is widely used in the production of molded consumer goods, such as in the production of parts of television cabinets. ABS is used in production of parts that require higher toughness and chemical resistance. However, styrenic type polymers suffer from relatively high flammability, thereby limiting their applications involving subjection of the molded parts to high temperatures.
Several attempts have been made in the art to improve the flame retardancy of thermoplastic resins such as PPE and HIPS compositions. However, most of the solutions offered suffer from one disadvantage of the other.
Resorcinol bis(diphenyl phosphate) (also referred herein as “RDP”) has been used as a flame retardant aid in PPE/PPO/HIPS formulations to give effective flame retardance performance. It is also an effective plasticizer, which provides desirable mechanical and chemical properties to the polymer resin. In the art, it is also known that the amount of RDP in the thermoplastic resin should preferably be at a minimum both from the point of view of the cost of the additive and also since it has been that large amounts of RDP (greater than about 16-20 parts of RDP) result in reduction of the modulus of the resin formulation as well as impairs the heat deflection temperature properties of the resin formulation. Several compounds have been tried in the art as co-additives with RDP that would enable the reduction of RDP in the resin formulation. For example, both ferrocene and melamine polyphosphate have been tried individually as co-additives for RDP to be used in resin formulations. However, a problem faced in the use of either ferrocene or melamine polyphosphate as a co-additive with RDP is that while it is possible to reduce the amount of RDP and retain the flame retardance performance of the resin formulation, other properties of the resin such as flowability and Izod impact are impaired. In particular, for example, when melamine polyphosphate is used as a co-additive, to obtain effective flame retardance, large quantities thereof have to be used. This often results in bleeding of the melamine polyphosphate from the resin at high temperatures during processing.
It is also known in the art for example that addition of a halogen flame retardant imparts flame retardancy to thermoplastic polyester resins. However, the use of halogen flame retardants results in the formation of halogen compounds which act as impurities in the resin compositions. It is also observed that halogen products are sometimes formed as thermal decomposition products and result in corrosion of the kneader, molding machine, mold, and other equipment used in the kneading and molding steps. The use of halogen based flame retardants also suffers from the added disadvantage of formation of poisonous gas due to decomposition thereof.
Attempts have been made to avoid the use of halogen based flame retardants by using phosphorous based compounds. For example, Japanese published application JP-A 55-82149 discloses a method for improving flame retardancy of thermoplastic polyester compositions comprising addition of red phosphorus or a phosphoric acid compound thereto. However, it is observed that the addition of red phosphorous while avoiding the disadvantages of use of halogen based flame retardants does not improve the flame retardancy. This problem is sought to be overcome in the process disclosed in Japanese published application JP A 8-73720. The process disclosed herein comprises the addition of a calcium or aluminum salt of phosphinic acid to the polyester. The disadvantage of this process however is that in order to enhance the flame retardancy, the additive has to be added in large quantities, as a result of which the moldability of the polyester is impaired.
JP-A-5-179123 discloses a composition which is made flame-retardant by addition of an organic phosphorus flame retardant. The flame-retardant resin composition of this disclosure comprises inter alia, a polycarbonate resin and contains an organic phosphorus flame retardant, a boron compound, organopolysiloxane, and a fluororesin. The flame-retardant resin composition of JP-A-6-192553 comprises a polycarbonate resin and a polyalkylene terephthalate resin and contains a graft copolymer, an oligomeric organic phosphorus flame retardant, and a fluorinated polyolefin.
However, the use of red phosphorus poses several handling problems. Red phosphorous poses the danger of dust explosion and also may emit smell or gas when processed in high temperature. It is also observed that red phosphorus alone does not provide the desired flame retardance and requires to be used in either large quantities or in combination with another flame retardant or a flame retardation aid. Attempts have been made to overcome these problems by coating the surface of red phosphorus for stabilization. For example, JP-A-52-142751, JP-B-5-18356, and JP-A-5-239260 disclose red phosphorus coated with a thermosetting resin, aluminum hydroxide, and the like. JP-B-2-37370 proposes a flame-retardant resin composition comprising a polyester resin and thermosetting resin-coated red phosphorus and, if desired, a reinforcing filler. JP-A-5-239260 and JP-A-5-247264 disclose a flame-retardant resin composition comprising a thermoplastic resin such as polycarbonate, polyester resin, and the like, and electrolessly plated red phosphorus.
In the fields where such flame-retardant resin
Arakali Radhakrishna
Bajgur Chandra S.
Pecak William
General Electric Company
Sanders Kriellion A.
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