Polycarbonate resin composition

1. A flame-retardant composition, comprising: (A) 100 parts by weight of a polycarbonate resin, (B) from 0.2 to 10 parts by weight of a core/shell grafted rubbery elastomer, (C) from 0.02 to 5 parts by weight of an organic alkali metal salt and/or an organic alkaline earth metal salt, and (D) from 0.02 to 3 parts by weight of a polyfluoro-olefin resin; and

wherein, the core of the grafted rubbery elastomer comprises a polymer prepared from alkyl acrylate or alkyl methacrylate monomers; or alkyl acrylate or alkyl methacrylate monomers, each with one or more additional monomers; or a polysiloxane rubber; and

wherein, the composition does not contain a phosphate-containing flame retardant and does not contain a halogen-containing flame retardant, other than component (D).

2. The flame-retardant composition of claim 1 , further containing (E), from 0.1 to 10 parts by weight, relative to 100 parts by weight of the polycarbonate resin (A), of a silicone compound.

3. The flame-retardant composition of claim 1 , wherein the core of the grafted rubbery elastomer is at least 40% by weight of the grafted rubbery elastomer.

4. The flame-retardant composition of claim 2 , wherein the silicone compound is an organopolysiloxane having a basic structure of a general formula (1):

R 1 a R 2 b SiO (4−a−b)/2   (1)

wherein R 1 indicates a functional group selected from hydroxyl group, alkoxyl group, epoxy group, vinyl group, aryloxy group, carboxyl group, silanol group, hydride group, polyoxyalkylene group, amino group, or mercapto group; R 2 indicates a hydrocarbon residue having from 1 to 12 carbon atoms; and a and b are numbers satisfying the relations of 0<a≦3, 0≦b<3, and 0<a+b≦3.

5. The flame-retardant composition of claim 1 , wherein the polyfluoro-olefin resin is a polytetrafluoroethylene having the ability to form fibrils and having a mean molecular weight of at least 500,000.

6. The flame-retardant composition of claim 1 , wherein the polycarbonate resin has a viscosity-average molecular weight of from 15,000 to 25,000.

7. The flame-retardant composition of claim 1 , which satisfies the standard of UL94/5VA (2.5 mm) or UL94/5VB (2.5 mm).

8. A housing or a part of an electric or electronic appliance, which comprises the flame-retardant composition of claim 1 .

9. The flame-retardant composition of claim 1 , wherein the polysiloxane rubber is in the form of a composite rubber.

10. The flame-retardant composition of claim 1 , wherein the polysiloxane rubber is combined with a polyacryl(meth)acrylate rubber to form a composite rubber.

11. The flame-retardant composition of claim 9 , wherein the polysiloxane rubber component comprises 5 to 95% by weight of the composite rubber.

12. The flame-retardant composition of claim 1 , wherein the alkyl acrylates are selected from ethylacrylate, butylacrylate or 2-ethylhexylacrylate.

13. The flame-retardant composition of claim 1 , wherein one or more vinylic monomers are polymerized in the presence of the core of the grafted rubbery elastomer.

14. The flame-retardant composition of claim 13 , wherein the vinylic monomers are selected from aromatic vinyl compounds, alkyl acrylates, alkyl methacrylates, vinyl cyanide compounds or vinyl esters.

15. The flame-retardant composition of claim 13 , wherein the vinylic monomers are selected from styrene, α-methyl styrene, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, methacrylonitrile, vinyl acetate or vinyl propionate.

16. The flame-retardant composition of claim 1 , wherein the core of the grafted rubbery elastomer is grafted with an acrylic polymer.

17. The flame-retardant composition of claim 1 , wherein the grafted rubbery elastomer comprises n-butylacrylate and graft copolymers of styrene and methylmethacrylate.

18. The flame-retardant composition of claim 1 , further comprising a crosslinking agent.

19. The flame-retardant composition of claim 18 , wherein the crosslinking agent is selected from divinylbenzene, ethylene dimethacrylate, triallyl cyanurate, or triallyl isocyanurate.

20. The flame-retardant composition of claim 1 , wherein the composition comprises an organic aliphatic alkali metal salt and/or an organic aliphatic alkaline earth metal salt.