Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-08-02
2003-04-01
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S267000, C524S268000, C524S269000, C525S101000, C525S464000, C525S067000
Reexamination Certificate
active
06541548
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flame retardant aromatic polycarbonate resin composition. More particularly, the present invention is concerned with an aromatic polycarbonate resin composition imparted with flame retardancy by an organopolysiloxane having a specific structure.
2. Background Art
Aromatic polycarbonates are known engineering plastics which have excellent impact resistance, heat resistance and transparency, and have been widely used in various fields, especially in the fields of office automation machines, household electric appliances and data communication equipment. In these fields, there has been a demand for mechanical parts having a thin section as well as a complicated structure. To meet these demands, the melt fluidity of aromatic polycarbonates has been increased to achieve high injection moldability by adding a styrene resin to the polycarbonate. A rubber-modified styrene resin is generally used for this purpose to achieve desired properties such as impact resistance of the resultant aromatic polycarbonate resin composition.
An aromatic polycarbonate has a limiting oxygen index (which is a criterion for the flame retardancy) of from 26 to 27, and is known as a resin having a self-extinguishing property. However, in many electric/electronic devices, a higher level of flame retardancy is strictly required to assure the high safety of products.
As a technique for imparting a high level of flame retardancy to a resin, it is known to incorporate therein flame retardants, for example halogen-containing flame retardants, phosphorus-containing flame retardants, and auxiliary flame retardants such as antimony oxide. However, in recent years, due to the growing interest in the environment, attempts are being made to change the above-mentioned flame retardants to flame retardants having less environmental impact, for example organopolysiloxanes. The use of organopolysiloxanes as flame retardants is known in the art.
In general, an organopolysiloxane is a polymer comprising recurring units of at least one type of unit selected from the group consisting of the following formulae (1) to (4):
monofunctional structure (M structure);
bifunctional structure (D structure);
trifunctional structure (T structure)
(in formulae (1) to (3), R is a monovalent hydrocarbon group); and
tetrafunctional structure (Q structure)
See the SILICONE HANDBOOK, edited by Kunio Ito and published by The Nikkan Kogyo Shimbun Ltd., Japan (1990)).
The effect of conventional organopolysiloxanes to impart flame retardancy to a resin is not totally satisfactory, however, and, therefore organopolysiloxanes have generally been used in combination with other flame retardants. For example, unexamined Japanese Laid-Open Patent Application Nos. 51-45160 and 56-100853, Japanese Published Application (Kohyo) No. 59-500099, and unexamined Japanese Laid-Open Patent Application Nos. 61-241344, 6-306265 and 6-336547 disclose the use of an organic alkali or alkaline earth metal salt in combination with an organopolysiloxane.
Further, unexamined Japanese Laid-Open Patent Application Nos. 3-143951, 10-139964, 11-140294, 11-217494 and 11-222559 each disclose a method of improving the flame retardancy of a resin by using an organopolysiloxane having an appropriately branched structure as a flame retardant.
An organopolysiloxane having a branched structure, hereinafter, simply referred to as a “branched organopolysiloxane” mainly comprises trifunctional (i.e., T structure, RSiO
3/2
) and/or tetrafunctional structures (i.e., Q structure, SiO
4/2
) of the four types of units mentioned above. However, the flame retarding effect of the branched organopolysiloxane is still unsatisfactory. The branched organopolysiloxane, in general, is resinous and has a high silicon atom content and, therefore, when such a branched organopolysiloxane is incorporated into a resin such as an aromatic polycarbonate, it lowers the fluidity of the resin.
Due to the branched structure, branched organopolysiloxanes have a high content of reactive terminal groups, such as silanol groups i.e., a hydroxyl group directly bonded to a silicon atom, or an alkoxysilyl group. For this reason, the organopolysiloxane per se is not only unstable at high temperatures, but also is likely to decompose the aromatic polycarbonate when kneaded therewith. The occurrence of these disadvantageous phenomena is markedly increased when a low molecular weight organopolysiloxane is used so as to improve kneadability with the aromatic polycarbonate. This is because the terminal group content of the organopolysiloxane molecules is increased due to the use of the low molecular weight organopolysiloxane molecules.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide an aromatic polycarbonate resin composition which exhibits high flame retardancy without sacrificing the melt stability or the melt fluidity in molding the resin composition. The present inventors have made extensive studies with a view toward attaining the object of the present invention by using an organopolysiloxane comprising substantially bifunctional moieties (i.e., D structure, R
2
SiO
1/2
). As a result, it has unexpectedly been found that a resin composition may be prepared comprising an aromatic polycarbonate, and incorporated therein, organopolysiloxanes comprising in combination a linear organopolysiloxane comprised of recurring D units and a cyclic organopolysiloxane comprised of recurring D units. In such compositions, not only can the dispersibility of the organopolysiloxanes in the resin be improved, but also the resin composition exhibits excellent flame retardancy. In particular, the dripping of flaming particles is prevented when the resin composition burns. The present invention has been completed, based on this novel finding.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the present invention, there are provided flame retardant aromatic polycarbonate resin compositions comprising 100 parts by weight of a resin component (a) containing an aromatic polycarbonate and optionally a styrene polymer, wherein the resin mixture has an aromatic polycarbonate content of 20% by weight or more, and 0.1 to 50 parts by weight of an organopolysiloxane (b) comprising at least one linear organopolysiloxane (b)i and at least one cyclic organopolysiloxane (b)ii wherein the organopolysiloxane (b) contains component (b)ii in an amount of from 5 to 95% by weight, based on the total weight of components (b)i and (b)ii,
the at least one linear organopolysiloxane (b)i being represented by the following formula (5):
wherein:
n represents an integer of 2 or more;
each R
1
independently represents a monovalent C
6
-C
20
hydrocarbon group containing an aromatic group;
each R
2
independently represents a monovalent C
1
-C
20
hydrocarbon group containing no aromatic group; and
each of R
3
and R
4
independently represents a hydrogen atom or a triorganosilyl group SiR
5
3
, wherein each R
5
independently represents a monovalent C
1
-C
20
hydrocarbon group; and
the at least one cyclic organopolysiloxane (b)ii being represented by the following formula (6):
wherein m represents an integer of 3 or more; and
R
1
and R
2
are as defined for formula (1) above.
The invention further provides further compositions according to those just described, wherein each R
1
in formulae (5) and (6) is a phenyl group and each R
2
in formulae (5) and (6) is a methyl group.
Resin component (a) used in the present invention comprises an aromatic polycarbonate optionally containing a styrene polymer.
In the present invention, the aromatic polycarbonate used as resin component (a) is an aromatic polycarbonate having a main chain comprising recurring units represented by the following formula (7):
(wherein Ar is the residue of a bifunctional phenolic compound). Such aromatic polycarbonates can be produced, for example, by a reaction between a bifunctional phenolic compound and a carbonate precursor; a reaction between a bifuncti
Oda Hiroji
Weidner Richard
Brooks & Kushman P.C.
Buttner David J.
Wacker-Chemie GmbH
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