Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-11-04
2001-09-04
Medley, Margaret (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S268000, C525S393000
Reexamination Certificate
active
06284824
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a flame retardant polycarbonate resin composition having improved optical transparency.
2. Prior Art
Flame retardant resin compositions are often used in various products such as electric and electronic parts, building members, automotive parts, and daily goods. These resin compositions are generally made flame retardant by adding organic halogen compounds optionally in admixture with antimony trioxide. However, these flame retardant resin compositions have the drawback that harmful halogen gases evolve upon combustion.
It is also known that resin compositions can be made flame retardant by adding silicone resins which do not evolve harmful gases.
JP-B 60421/1987 discloses a flame retardant resin composition comprising an organic resin and a silicone resin containing at least 80% by weight of trifunctional siloxane units. In consideration of the melt processing with the organic resin, a silicone resin consisting essentially of trifunctional siloxane units is used. Since such a silicone resin imparts less flame retardance, more than 10% by weight of the silicone resin must be added in order to achieve a satisfactory flame retardant effect.
JP-B 31513/1988 discloses a thermal oxidation resistant resin composition in which an alkoxy-terminated silicone resin is added. A liquid low molecular weight silicone having a high alkoxy group content is used. The silicone of this type, even when added in a minor amount, can have substantial influence on the outer appearance and strength of molded resin parts and tends to bleed out of molded resin parts. The silicone of this type is susceptible to hydrolysis to form as by-products flammable low-melting compounds such as alcohols. Then, no satisfactory flame retardant effect is expected.
JP-B 48947/1991, 78171/1996, and 33971/1996 disclose flame retardant resin compositions in which silicone resins consisting of monofunctional and tetrafunctional siloxane units are added. JP-A 128434/1995 discloses a flame retardant resin composition in which a silicone resin containing vinyl-bearing siloxane units is added. However, in order for these compositions to exert satisfactory flame retardant effects, the amount of silicone resin must be increased, and inorganic fillers such as aluminum hydroxide must be used in admixture with halogen or phosphorus compounds.
As discussed above, the addition of silicone resins arises the problem that no satisfactory flame retardant effect is obtained unless the amount of silicone resin added is increased, whereas an increased amount of silicone resin can drastically exacerbate the moldability of resin compositions and the outer appearance and mechanical strength of molded resin parts. Efforts were made to develop silicone resin additives having more flame retardant effect or additives capable of cooperating with silicone resins to improve their flame retardant effect.
JP-A 176425/1996 discloses a flame retardant resin composition comprising a polycarbonate resin, an epoxybearing organopolysiloxane, and an alkali metal salt of an organic sulfonic acid. JP-A 176427/1996 discloses a flame retardant resin composition comprising a polycarbonate resin, a polycarbonate resin modified with a phenolic hydroxyl-bearing organopolysiloxane, and an organic alkali metal salt. Further, JP-A 169914/1997 discloses a composition wherein a petroleum heavy oil or pitch is combined with a silicone compound for improving flame retardance. These silicone resins having special organic functional groups are expensive because of the complication of their preparation process, but do not achieve a sufficient flame retardant effect to compensate for the increased cost. Also, the heavy oil and pitch have disadvantage on moldability of the plastic containing them. In this regard, a further improvement is desired.
The above-mentioned prior art silicone resins for imparting flame retardance are less dispersible in or less compatible with polycarbonate resins. As a result, there are obtained molded parts of the island-in-sea structure in which two components having different indexes of refraction are present as separate phases. These molded parts have a low transparency and are even opaque when large amounts of the silicone resins are blended.
It is thus desired to have a technique of imparting flame retardance to polycarbonate resins while maintaining the physical properties and optical transparency thereof.
SUMMARY OF THE INVENTION
We have found that when an organopolysiloxane having a high content of phenyl groups each directly attached to a silicon atom, a specific structure, and a specific molecular weight is added to and mixed with a polycarbonate resin, there is obtained a polycarbonate resin composition which can be molded and cured into a product having improved flame retardance while maintaining the physical properties, typically mechanical strength, and optical transparency inherent to the polycarbonate resin.
According to a first aspect, the invention provides a flame retardant polycarbonate composition comprising (a) 100 parts by weight of an aromatic polycarbonate resin and (b) 1 to 10 parts by weight of an organopolysiloxane consisting essentially of 50 to 90 mol % of siloxane units T represented by R
1
.SiO
3/2
and 10 to 50 mol % of siloxane units D represented by R
2
R
3
.SiO
2/2
wherein R
1
, R
2
, and R
3
are independently substituted or unsubstituted monovalent hydrocarbon groups having 1 to 10 carbon atoms, phenyl being contained in an amount of at least 80 mol % of the entire organic substituents.
According to a second aspect, the invention provides a flame retardant polycarbonate composition comprising (a) 100 parts by weight of an aromatic polycarbonate resin and (b′) 1 to 10 parts by weight of an organopolysiloxane consisting essentially of 0 to 89.99 mol % of siloxane units T represented by R
1
.SiO
3/2
, 10 to 50 mol % of siloxane units D represented by R
2
R
3
.SiO
2/2
, and 0.01 to 50 mol % of siloxane units Q represented by SiO
4/2
wherein R
1
, R
2
, and R
3
are independently substituted or unsubstituted monovalent hydrocarbon groups having 1 to 10 carbon atoms, phenyl being contained in an amount of at least 80 mol % of the entire organic substituents.
According to the invention, since an organopolysiloxane of the specific structure free of special organic functional groups is added to a polycarbonate resin, the resulting flame retardant resin composition does not evolve harmful gases when burned by a fire or incinerated for disposal and is thus safe and imposes a little burden to the environment. As a result of the selection of the organopolysiloxane of the specific structure free of special organic functional groups, small amounts of the organopolysiloxane added can achieve a satisfactory flame retardant effect, little affect the moldability of the resin composition and the outer appearance and physical properties (mechanical strength) of molded parts thereof, and are economically advantageous. Since the organopolysiloxane of the specific structure is well dispersible in and compatible with the polycarbonate resin and imparts a sufficient flame retardant effect even with small amounts, the flame retardant resin composition has a high optical transparency.
DETAILED DESCRIPTION OF THE INVENTION
Component (a) of the flame retardant resin composition according to the invention is an aromatic polycarbonate resin which may be prepared by reacting a dihydric phenol with phosgene or carbonate diester. The dihydric phenol is preferably selected from bisphenols such as 2,2-bis(4-hydroxyphenyl)propane. It is acceptable to partially or entirely replace 2,2-bis(4-hydroxyphenyl)propane by another dihydric phenol. The dihydric phenols other than 2,2-bis(4-hydroxyphenyl)propane include, for example, hydroquinone, 4,4-dihydroxyphenyl, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfone, and bis(4-hydroxyphenyl)ketone. There may be used homopolymers of these dihydric phenols alone or copolymers of two or more of these dihydric phenols or
Iji Masatoshi
Kobayashi Yoshiteru
Serizawa Shin
Yamamoto Akira
Yamamoto Kenji
Medley Margaret
Millen White Zelano & Branigan P.C.
NEC Corporation
Toomer Cephia D.
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