Note: Descriptions are shown in the official language in which they were submitted.
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. STABILIZED POLYCARBONATE-POLYESTER
, - COMPOSITIONS
This invention relates generally to polycarbon-
ate-polyester resin compositions, alone, or in further
combination with other resins, and more particularly to
methods f~r stabilizing blends of high molecular weight
linear thermoplastic polycarbonates and polyesters
against undesirable changes in melting point.
BACKGROUND OF THE INVENTION
10Polyester resins derived from terephthalic
acid and reactive derivatives thereof, such as dimethyl
terephthalate, and alkanediols of from e.g., 1 to 10
inclusive carbon atoms, e.g., ethylene glycol and 1,4-
butanediol, as well as related diols, such as 1,6-
cyclohexane dimethanol, and mixture-s of such resins
have been known for some time and have become impor~ant
constituents in iniection moldable compositions. Work-
pieces molded from such polyester resin compositions,
alone, or combined with reinforcements, offer a high
degree of surface hardness and abrasion resistance, high
gloss, and lower surface friction. More recently, blends
of such polyester resins with one or more second resins
have become of significant commercial interest because
such second resins, carefully selected, can greatly
improve impact strength, as well as tensile strength,
modulus and distortion temperature under load in parts
molded from such compositions. ~y way of illustration,
such second resins can comprise minor proportions aro-
matic polycarbonate resins, as described for example,
in ~awase et al, U.S. 3,953,539. Also known are such
blends in further combination with other resins, such
as polyacrylate resins. See, for example, Cohen and
Dieck, U.S. 4,257,937.
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All such polycarbonate-polyester resin compo-
sitions have, however, a tendency to-be unstable in the
molten states as evidenced by a change in melting point.
Especially troublesome in this respect are polycarbonate
resin compositions containing minor proportions of poly-
ester resins. Such compositions seem to undergo a
chemical reaction commonly referred to as "jumbling".
The "jumbling" reaction may be due to catalyst residues
remaining in the polyester resin because some success
has been achieved in using organic phosphites as melt
stabilizers, see, e.g., Hofrichter, Jr., U.S. 2,6~0,213;
and W. German Offen 2,710,729; and as color stabilizers
in polycarbonate resins, Fritz et al, U.S. 3,305,520.
However, considerable variability in the effectiveness
of jumbling suppression has been observed with such
phosphites, and more reliable melt stabilizers are
needed.
It has now been discovered that two specific
inorganic phosphorus reagents, monosodium phosphate and
monopotassium phosphate, alone, or in combination, are
highly effective to stabilize such polycarbonate-poly-
ester resin compositions containing, predominantly,
polycarbonate, especially if the polyester is made with
a titanium compound catalyst, e.g., tetra octyl titanate.
Monosodium phosphate and monopotassium phosphate, both
rather innocuous, mildly acidic reagents, are surpris-
ingly effective as stabilizers for polycarbonate-polyester
compositions. The stabilizers can be used in various
manners, including prior incorporation as a concentrate
in the polycarbonate resin, or in the polyester resin.
ln addition to the high degree of reliability as stabil-
izers in such compositions, monosodium phosphate andl
or monopotassium phosphate do notdetrimentally
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affect any of the resinous components in the composi-
tion, e. 9., the polycarbonates, or the polyesters,
because the prior art mono ammoni~m phosphates, as will
be shown later, at the same levels degrade the individual
polymers. In addition, monosodium phosphate appears to
be unique as a stabilizer for polycarbonate-polyester
blends comprising predominantly polycarbonate because it
is superior to the chemically closely related disodium
phosphate, as will be shown later.
Especially difficult to melt stabilize are
combinations of polycarbonates and polyester resins with
third resins such as polyacrylates, as well as flame
retarded blends of polycarbonates and polyesters. Such
formulations are rendered reliably melt stable with
monosodium phosphate and/or monopotassium phosphate,
according to the present invention.~ In addition to the
specific instances noted above, melt stabilization can
also be induced in other combinations of polycarbonates
with polyesters and other resins, especially those in
which an active catalyst was used to prepare one or all
of the polymers in the blend.
SUMMARY OF THE INVENTION
; According to the present invention, there are
provided thermoplastic compositions comprising predomi-
nantly a polycarbonate and at least one polyester resin
derived from terephthalic acid or a reactive derivative
thereof- and an alkanediol, alone, or in further combina-
tion with at least one additional resin, melt stabilized
with monosodium phosphate and/or monopotassium phosphate.
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DESCRIPTION OF THE INVENTION
Any amount of the monosodium and/or monopo-
tassium phosphate will melt stabilize a polycarbonate-
polyester resin blend. Preferably, however, from about
0.01 parts to about 7.5 parts by weight of the phosphate
should be used, and most preferably, from about O.l
parts to about 4.0 parts by weight should be used, based
on lO0 parts by weight of the total polyester resinous
component (b) in the composition. Although the phos-
10 phates are, as mentioned, relatively innocuous, amountslarger than about lO.O parts by weight should be used
with caution since such larger amounts will provide melt
stability, but might also deleteriously affect the
mechanical properties of one or more of the resins in
15 the composition.
The phosphate of the invention may be mixed
with the polymers by any suitable means. Since most
phosphates are solids, they can be most expeditiously
mixed with the resin either as a precompounded concen-
20 trate, or directly into the melt, e.g., in an extruder.
Generally, all thermoplastic resins made withactive catalysts, e.g., titanium catalysts, are melt
unstable, and all such resins can be treated with in-
organic phosphates according to this invention. The
25 polycarbonate resins can be produced from a diphenol and
phosgene or a phosgene precursor, such as from a dihydroxy
diaryl alkane, e.g., bisphenol-A and phosgene or a
diester of carbonic acid, see, e.g., Schnell et al,
Canadian Patent No. 578,585. As indicated above, the
30 polyester resins can be produced from terephthalic acid
or a reactive derivative thereof and an alkanediol or
cyclohexane dimethanol, such as, for example, processes
described in Whinfield and Dickson, U.S. 2,465,319.
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; The ratio of polycarbonate resin to polyester
resin is also important, if not critical to the present
invention. For every 100 parts of polycarbonate resin
component (a) there must be present no less than 5 and
no more than 95, and preferably between 10 and 70 parts
by weight of polyester resin component (b).
Those embodiments of the invention which are
melt-stabilized flame retardant thermoplastic polycar-
bonate-polyester resin compositions are made by including
10 the monosodium and/or monopotassium phosphate in composi-
tions rendered flame retardant with an effective amount
of one or more flame retardant additives, in conventional
ways. Such additives are, for example, bromine- or
chlorine-containing compounds, e.g., decabromodiphenyl
15 ether, a polycarbonate of tetrabromob~isphenol A
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- or a copolycarbonate of tetrabromobisphenol A and
bisphenol A, and the li~e, ~lone, or preferably,
combined with a synergist, such as antimDny trioxide.
The examples which follow will show melt stabilization
of a number of s~c~ compositions according to the
present invention.
DESCRIPTION O~ THE PREFERRED 1~K30DIME~T5
The following examples illustrate the present
invention, but are not intended to limit the scope-of
the claims in any manner whatsoever All parts are by
weiqht unless otherwise specified.
EX~HPLES 1-2
Compositions are prepared by co-extr~ding
poly(bisphenol A) carbonate (General Electric Com3any
LEXA~ 145) and poly~l,4-butylene terephthalate)~Gener21
Electric Company VALOX6 315) in a vacuum-vented 1-3/4 in.
Sterling extruder operated at 400D ~. ~zone 1); 425~.
zone 2); 450'~. ~zone 3); and 475~ (at the èie).
; 20 Helt viscositles were
measureo in a Tinlu5-~lsen E~rusion Plastomete.. ~or
control and comparison purposes, a composition omitting
stabilizing additives, and three containing additives
proposed by the prior art were also made and tested. The
~ormul~tions used, ~nd the re~sults obtaines are set forth
in Tabl e 1:
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The combination of high melting points and
high melt viscosities demonstrate the advantages of
monosodium phosphate and monopotassium phosphate (Examples
1 and 2). The lowering of melting point demonstrates
5 the jumbling effect (Control lA and Comparison Example
2A). The loss in melt viscosity aemonstrates degrada-
tion of at least one of the polymeric components by the
ammonium compounds (Comparison Examples 2~ and 2C).
EX~MPLE 3
The general procedure of Example 1 was used to
prepare and test a formulation of poly(bisphenol A
carbonate)/poly(1,4-butylene terephthalate) impact
15 modified with a polyacrylate resin (RDhm & Haas ACRYLOID
KM 653). The formulations used and the results obtained
are set forth in TABLE 2:
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TABLE 2: IMPACT-MODIFIED POLYCARBONATE
POLYESTER COMPOSI~IONS
EXAMPLE 3A* 3
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5 COMPOSITIO~ (parts)
Poly(bisphenol A carbonate) 2500 2500
Poly(1,4-butylene terephthalate) 1200 1200
Polyacrylate resin - 500 500
Antioxidant 40 40
10 Monosodium phosphate (NaH PO ) 0 20
PROPERTIES
Melting point, C. 210 219
* Control
The stabilizing effect of monosodium phosphate
is demonstrated by the higher melting point of Example 3
in comparison to the control.
EXAMPL~ 4
A flame retardant composition was prepared,
molded and tested by the general procedure of Examples
1-2. The $ormulation used and the properties obtained
25 were as set forth in Table 3:
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TABLE 3: FLAME-RETARDANT POLYCARBONATE-
- POLYESTER COMPOSITIONS
EXAMPLE 4A* 4
5 COMPOSITION (Parts)
Poly(bisphenol-A)carbonate` 700~ 700 ~
`974 ~974
Poly(tetrabromobisphe
carbonate 274 274
Poly(1,4-butylene terephthalate) 900 900
Antimony oxide 82 82
Ethylene/vinyl acetate copolymer 44 44
Poly~tetrafluoroethylene) 8 8
~onosodium phosphate (Na~2P04) 0 30
15 PROPERTIES
Melting p~int, C. 205 219
Flammability rating, Underwriters'
Bulletin Flame Test (UL-94), V-O V-O
60 mil sample
* Control
The high melting point demonstrates the
effectiveness of monosodium phosphate to melt stabilize
those normally difficult to stabilize flame-retardant
~ compositions, while maintaining the highest flammability
: rating.
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Obviously, many variations of the present
invention will suggest themselves to those skilled in
this art in light of the above, detailed description.
For example, instead of poly(l,4-butylene terephthalate)
there can be substituted poly(ethylene terephthalate)
alone or in a 50:50 admixture with poly(l,4-butylene
terephthalate). Conventional additives such as clay,
mica, pigments and colorants all can be added in
conventional amounts. All such obvious variations are
within the full intended scope of the appended claims.
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