POLYCARBONATE FILM OF LOW INFLAMMABILITY

PELLICULE DE POLYCARBONATE A FAIBLE COEFFICIENT D'INFLAMMABILITE

English Abstract

ABSTRACT OF THE DISCLOSURE
A polycarbonate film having improved flame resistance
and good stress-corrosion-cracking resistance and having a
total halogen content of at least about 5% by weight, is
prepared from a solution of a mixture of a halogen-containing
low molecular weight polycarbonate and a higher molecular
weight polycarbonate prepared from bisphenol containing at
least 90 mol percent bisphenol A. The novel film can be
used to advantage for self-supporting electrical insulating
films.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:-
1. A cast polycarbonate film of low inflammability,
having an oxygen index of ?26%, measured at a layer thickness
of 0.1 mm, and a total halogen content of at least about 5%
by weight, and containing from about 10% to about 30% by
weight of (1) a halogen-containing aromatic polycarbonate
of average molecular weight of ?n = 8,000 to 20,000 and from
about 90% to about 70% by weight of (2) a polycarbonate based
on bisphenols containing bisphenol A and up to 10 mol-%, re-
lative to the total bisphenol content, of other bisphenols,
said polycarbonate (2) having an average molecular weight of
between ?W = 70,000 and ?W = 120,000.
2. The cast film of Claim 1 wherein the lower
molecular halogen-containing polycarbonate is based on tetra-
bromobisphenol A and is of ?n between 8,000 and 12,000.
3. The cast film of Claim 1 wherein the lower
molecular halogen-containing polycarbonate is based on
tetrachlorobisphenol A and is of ?n between 8,000 and 12,000.
4. The cast film of Claim 1 wherein the high
molecular aromatic polycarbonate is a copolycarbonate of from
about 99 to about 90 mol % of bisphenol A and from about 1 to
about 10 mol % of 1,1-bis-(4-hydroxyphenyl)-cyclohexane,
having a molecular weight of ?w between about 70,000 and about
120,000.
5. The film of Claim 1 wherein the high molecular
polycarbonate comprises in addition to residues of bisphenol A,
up to 0.5 mol % based on bisphenol A of branching residues.
6. A self supporting polycarbonate plastic film
adapted for use as an electrical insulator, said film having
14

a total halogen content of at least about 5% by weight,
having an oxygen index of 26% or greater than 26% as de-
termined by ASTM test method D 2863-70 and having been pre-
pared by casting from a solution comprising a mixture of
(1) from about 10 wt-% to about 30 wt-% of an aromatic
halogen-containing polycarbonate having an average molecular
weight of from about 8,000 to about 20,000; and (2) from
about 90 wt-% to about 70 wt-% of a polycarbonate having
an average molecular weight of between about 70,000 and
about 120,000 prepared by phosgenation of bisphenols con-
taining at least 90 mol-% bisphenol A and up to 10 mol-%,
based on the total bisphenol content, of another bisphenol
substnatially free from halogen; in an organic solvent
therefor.
7. A method for making an electrical insulating
polycarbonate film of improved flame resistance which com-
prises casting a solution containing a mixture of (1) from
about 10 wt-% to about 30 wt-% of an aromatic halogen-
containing polycarbonate having an average molecular weight
of from about 8,000 to about 20,000; and (2) from about
90 wt-% to about 70 wt-% of a polycarbonate having an
average molecular weight of between about 70,000 and about
120,000, and prepared by phosgenation of bisphenols containing
at least 90 mol-% bisphenol A and up to 10 mol-%, based on
the total bisphenol content, of another bisphenol substan-
tially free from halogen, said mixture having a total
halogen content of at least about 5 % by weight; and re-
moving the solvent from the solution.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE
8. A cast polycarbonate film of low inflammability,
having an oxygen index of ? 26%, measured at a layer thick-
ness of 0.1 mm, and a total halogen content of at least
about 5% by weight, and containing from about 10% to about
30% by weight of
(1) a halogeno-bisphenol-polycarbonate of average molecular
weight of ?n between 8,000 and 12,000 obtained from the
halogenated bisphenols of the following formula
<IMG>
wherein X is C1 or Br, n is 1, 2, 3, or 4 and Z is C1-C8-
alkylene, C2-C8-alkylidene, C5-C12-cycloalkylene, C5-C12-
cycloalkylidene or the following radical
<IMG> ,
and from about 90% to about 70% by weight of (2) a polycar-
bonate based on bisphenols containing bisphenol A and up to
10 mol-%, relative to the total bisphenol content, of other
bisphenols, said polycarbonate (2) having an average
molecular weight of between ?w = 70,000 and ?w = 120,000.
16

Description

Mo-1453-~
LeA 15,318
839
POLYCARBONATE FILM
This invention relates generally to aromatic poly-
carbonate plastics and more particularly to a novel high
quality cast polycarbonate plastic film.
It has been disclosed that high molecular weight
aromatic polycarbonates based on bis-(hydroxyphenyl)-alkanes,
especially 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A),
can be converted into films which are adapted to be used as
electrical insulating film in the electrical industry (German
Patent No. 971,790; Angew. Chem. 74, 1962, pages 647 to 650).
Such films are as a rule prepared from solutions
of the polycarbonate by casting. However, they can also be
obtained by extrusion through slit dies. If such films are
exposed to organic non-solvents, for example, carbon tetra-
chloride, their mechanical properties can be impaired greatly,especially if the films are exposed to stresses while such
non-solvents are acting on them. This can even go so far that
after a relatively short time the films lose their mechanical
strength and break. This property is known to those skilled
in the art as "stress-corrosion-cracking".
Since, components insulated with a plastic film may
come into contact with non-solvents, for example to remove
remnants of fat and oil therefrom, it is only possible to
use electrical insulating films which have as little tendency
to stress-corrosion-cracking as possible.
As the viscosity of the polycarbonates increases, the
films prepared therefrom show a reduced tendency to stress corro-
sion cracking. At a relative viscosity of 1.70 (0.5 g in 100 ml
~. ~
LeA 15,318
~-B
. ~ ~.
.

of methylene chloride solution), corresponding to an average
molecular weight of about 70,000, the tendency to stress corrosion
cracking is so low that there is no longer any impairment of
the usability of the films.
However, a disadvantage of this film is its in-
flammability. This can, inter alia, have a very adverse
effect in the case of components exposed to severe temperature
conditions, such as, for example, line transformers of color
television sets.
It is known that the inflammability of normally
processable high molecular weight polycarbonates, for example
polycarbonates for injection molding, can be lowered by mixing
the polycarbonate with substances containing halogen, such as
halogenated aromatics, especially diphenylene, halogenated
norbornane derivatives and others, if appropriate with simul-
taneous addition of metal salts, phosphorus compounds and
other substances [see, for example, DOS (German Published
Specification 2,013,496; 2,122,300; 2,153,101 and 2,243,226
U.S. 3,357,942 and French 1,439,030]. When such substances
are used to lower the inflammability of polycarbonate films,
the latter lose their good mechanical properties and in par-
ticular the tendency to stress-corrosion-cracking is greatly
increased by these substances.
Another way of reducing the inflammability of a
high molecular weight polycarbonate is to use bisphenols con-
taining halogen, such as, for example, tetrachloro- and tetra-
bromo-bisphenol as co-condensable monomers in making the poly-
carbonate. However, this process, which has found successful
acceptance for thermoplastic polycarbonates for moldings,
cannot he used for making polycarbonate films. In order to
LeA 15,-~18 -2-

io~
guarantee sufficient flame-resistance with thin layers of poly-
carbonate, such a high proportion of the bisphenols containing
halogen has to be cocondensed in making the polycarbonate that
the mechanical properties of the high molecular polycarbonates,
especially the stress crack resistance which is reduced thereby,
no longer suffice for use in films.
It is therefore an object of this invention to pro-
vide cast polycarbonate films having improved flame-resistance and
resistance to stress-corrosion-cracking. Another ob~ect of the in-
vention is to provide cast polycarbonate films which are sub-
stantially flame-resistant and have mechanical properties which
adapt them for use as electrical insulators. A further object
of the invention is to provide a method for imparting flame-
resistance to a polycarbonate film without seriously affecting
the electrical and mechanical properties such as stress-
corrosion-cracking resistance of the film.
The foregoing objects and others are accomplished
in accordance with this invention, generally speaking, by pro-
` viding a polycarbonate film cast from a solution containing a
low molecular weight polycarbonate prepared from a halogeno-
bisphenol and a high molecular weight polycarbonate prepared
from bisphenol A.
It has now been found, surprisingly, that by addition
of low molecular weight halogeno-bisphenol-polycarbonates to
high molecular bisphenol-A-homopolycarbonates or copolycarbo-
nates the inflammability of the cast films prepared therefrom
can be greatly reduced without deterioration of the good
mechanical, electrical and aging properties required for an
electrical insulating film. In particular, it is surprising that
the tendency to stress-corrosion-cracking is not increased although
LeA 15,318 -3-

10~ 33
the added halogeno-bisphenol-polycarbonates are them~elves of
Quch low-molecular weight that by themqelves they are not film-
forming.
The present invention therefore provides high quality
cast polycarbonate filmQ of low inflammability, having an oxygen
index of ~26~, measured at a layer thickness of 0.1 mm, and
having a total halogen content of ~5~ by weight, and consiqting
of from about 10~ to about 30~ by weight of a low molecular
weight polycarbonate based on halogeno-bisphenols and from
about 90~ to about 70% by weight of a halogen free high molec-
ular weight homopolycarbonate or copolycarbonate based on bis-
phenol A.
Any suitable low molecular weight halogeno-bisphenol-
polycarbonate may be used but it is preferred to use tetra-
chloro- and tetrabromo-bisphenol-A-polycarbonates with molecu-
lar weights of ~ = approx. 8,000 - 20,000. A molecular
weight range of 8,000 - 12,000 is preferred. When using poly-
carbonates in the molecular weight range of 8,000 - 12,000 as
an additive to high molecular polycarbonates, a marked rise in
the heat resistance of cast polycarbonate films prepared there-
from is observed in addition, this being surprising for high
molecular polycarbonates in view of such low molecular admix-
tures. The molecular weight of the halogeno-bisphenol-polycar-
bonates may be limited in a known manner by using a mono-
phenol as a chain stopper. Examples of suitable monophenolsare alkylphenols, such as the methylphenols, the ethylphenols,
the propylphenols and the isopropylphenols, the butylphenols
and unsubstituted phenol ; halogenophenols, especially 2,4,6-
trichlorophenol and 2,4,6-tribromophenol, are also suitable.
Any suitable high molecular weight (Mw between 30,000
LeA 15,318 -4-

~ v~
and 200,000) polycarbonate based on bisphenol A can be used
for the preparation of the films according to the invention.
The polycarbonate can be prepared from a mixture of bisphenols
which contain up to 10 mol-%, based on the total bisphenol con-
tent, of other bisphenols, and/or up to 0.5 mol-%, based on
bisphenol A, of branching components such as triphenols or
tetraphenols. Preferably, high molecular weight copolycarbon-
ates based on 99-90 mol-~ of bisphenol A (2,2-bis-(4-hydroxy- -
phenyl)-propane) and 1-10 mol ~ of 1,1-bis-(4-hydroxyphenyl)-
cyclohexane, with molecular weights Mw between 70,000 and
120,000, are used.
Other bisphenols which can be used for the prepara-
tion of the high molecular weight copolycarbonates are the di-
hydroxydiarylcycloalkanes and also dihydroxydiarylalkanes, such
as for example, bisphenol F (bis-(4-hydroxyphenyl)-methane) and
tetramethylbisphenol A (2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-
propane).
These polycarbonates, when mixed with the above-men-
tioned low molecular weight halogen-containing polycarbonates,
prove particularly advantageous from the point of view of a
reduced tendency to crystallization. This effect is of deci-
sive importance particularly for cast films since even a
slight crystallization of the polycarbonate composition gives
unusable films which are prone to stress-corrosion-cracking.
25 Both the low molecular weight halogen-containing
the high molecular weight aromatic polycarbonates are prepared
according to customary processes known to those skilled in the
art, such as, for example, according to the phase boundary pro-
cess. A suitable process is disclosed in U. S. Patent 3,028,365.
B LeA 15,318 -5-

lV~
The ca~t films are prepared according to known film
forming techniques, for example by conjointly dissolving the
components of the mixture in a suitable solvent for polycarbo-
nate, such as methylene chloride, 1,2-dichloroethane or chloro-
form, to give 5-20% strength solutions, which are cast on belt
casting machines or drum casting machines. Any suitable sol-
vent for the polycarbonates may be used.
The term "of low inflammability" is here used in the
sense that the inflammability of the films is much less than
that of comparative control samples. A suitable direct measure-
ment of the inflammability is the oxygen index test. In this
test, the inflammability of a product is measured on the basis
of the oxygen content of the combustion atmosphere. Suitable
samples are placed in a combustion chimney and the oxygen con-
tent is reduced in steps until the material no longer burnswith a flame. The oxygen index is defined as the oxygen con-
tent in per cent, relative to the sum of the percentage pro-
portions of nitrogen and oxygen in the gas used for the com-
bustion of the material to be tested.
The films are tested by a method based on ASTM test
method D 2863-70. The samples used are strips of film of size
50 x 150 mm and of 0.1 mm thickness, which are clamped verti-
cally and ignited at the upper edge. The films according to
the invention, which contain the halogen-containing low molecu-
lar polycarbonates which impart low inflammability, have a sub-
stantially higher oxygen index and are therefore much less in-
flammable than the comparison samples. As set forth herein-
before, the oxygen index of the film provided by the invention
is 26% or greater than 26%.
LeA 15,318 -6-

1()44~3~
Anoth~r method which can be used to m~a~ur~ the
flame rep~llency i9 the ~mnll burner te~t ~ccording to DIN
51,438, provisional qtand~rd speclfication. With the film
vertical, either ~he ~dges or the surface~ ar~ exposed to the
fl~me and the results are cla~ified under thre~ classes (Kl
to K3 (edge treatment) and Fl to F3 (surface tr~atment)
respectively . The polycarbonate films of low in1~mmability,
according to the invention, at a thickness of o.1 mm give the
b~st possible ra~ing in thiq test, namely Kl/Fl, which i8
regarded as the condition for being rated as 'lof low inflam-
mability".
The small burner test (according to DIN 53 438)1s
performed as follows:
A test specimen vertically clamped in a frame, is
sub~ected to a 20 mm high propane gas flame from a Bunsen
burner (burner tube 0 4 mm) for 15 seconds; in process K the
flame is applied to the free edge at the bottom and in process
F to the area within the lower part of the surface. The size
of the test specimen K is 110 mm x 90 mm and that of the test
specimen F 230 mm x 90 mm. The evaluation in accordance with
DIN 53 438 is done in three classes: K1, K2, K3 and F1, F2,
F3, whilst indicating the thickness o~ the test specimen.
Class 1: the flame extinguishes before reachlng the
measuring mark;
Class 2: the tip of the flame reaches the measuring mark
after more than 20 seconds,
Class 3: the tip of the flame reaches the measuring mark
after less than 20 seconds.
Le A 15,~18 - 7 -

The films provided by the invention are distinguished by
greatly reduced lnflammability and low tendency to stress corrosion
cracking and show, in addition to their stability to unsatur-
ated polyester casting resins, the typical good mechanical and
dielectric properties typical of polycarbonate films. They are
therefore outstandingly suitable for use as electrical insulating
films such as, for example, as insulation in line transformers
of color television sets.
The examples which follow indicate the influence of
the halogen-containing low molecular polycarbonate on the prop-
erties of polycarbonate films. The relative viscosities quoted
relate to a concentration of 0.5 g of polycarbonate in 100 ml
of methylene chloride and to a temperature of measurement of
25C.
Le A 15,318 - 8 -

Examples 1-5 iV~8~
The following were used to prepare the polycarbonate
films subsequently investigated:
a) a copolycarbonate prepared by phosgenating a mix~ure of 97
mol ~ of bisphenol A and 3 mol ~ of 1,1-bis-(4-hydroxyphenyl)-
cyclohexane, having a relative viscosity Of nrel = 1.75 and an
average molecular weight of ~ = approx. 80,000,
b) a copolycarbonate from 97 mol ~ of bisphenol A and 3 mol
of l,l-bis-(4-hydroxyphenyl)-cyclohexane, having a relative
viscosity of nrel = 2.05 and an average molecular weight of
Mw = approx. 110,000,
c) an aromatic polycarbonate containing bromine, prepared by
phosgenating tetrabromobisphenol A and tribromophenol as the
chain stopper, and having a relative viscosity of nrel = 1.06,
an average molecular weight of Mn = approx. 8,500 and a bromine
content of 58~ by weight,
and
d) an aromatic polycarbonate containing chlorine, prepared by
phosgenating~tetrachlorobisphenol A and trichlorophenol as the
chain stopper, and having a relative viscosity of nrel = 1.10,
an average molecular weight of Mn = approx. 8,000 and a chlorine
content of 38~ by weight.
The components a) and b) are dissolved in methylene
chloride together with the components c) and d) to give a 10
per cent strength solution which is cast on a belt casting
machine to give films.
The composition of the films and some of their prop-
erties are listed in Table 1 which follows.
LeA 15,318 - 9 -

iO44B3~
o ,, o U~ C~
~ ~0 04 0 N _I ~ CO CO ~ ~1 o
In ~ I I~ O~ ~ O~ 0~ ~1 0 0 _~ O
:~ ~
~)
O ~ O o
r~o In o o o o ~ ~
~ ` ~ ~1
O _I O o
~ o ~ a~ ~ o ~
X ~
O _~ o U~ o
o o ~ 1~ o
K N
O O ~ O C)
o ~ ~ O U) U'lt`~ Il') O ~ --I
O ~ I¢
_l
~1
. a)
C ~ ~ O
C ` O O U~ O
Z ~
o ~ ~ a s
~ iu HX _~ N ~ ~ ~
i~} t~ U ~
^ ^ ^ -- ~ o
~U O ~ ~ tJ~ R R O ~q O C~
d~ ~O
~ aOa~ 0
.4 X ~ 1 ~ S l h
~ : : :o R ~~ ~ ~ ~ ~ o
p, N ~ ~ ~ O rAo o o ~
LeA 15, 318 -- 10 -

Notes on Table 1
1) from the tensile teQt according to DIN 53,455
2) to measure the stresq-corrosion-cr~cklng, 15 mm wlde te8t 8trip8
of the films were spirally wound around a glass rod of
8 mm diameter and then stored for 10 seconds in toluene/n-
propanol mixtures. After drying, the test strips were
subjected to the tensile test according to DIN 53,455.
Any other combination of low molecular weight and
high molecular weight polycarbonateQ disclosed as suitable
herein can be used to prepare films like those of the fore-
going examples.
Although the invention has been described in detail
for the purpose of illustration, it is to be understood that
such detail is solely for that purpose and that variations
can bemade therein by those skilled in the art without
departing from the spirit and scope of the invention except
as it may be limited by the claims.
LeA 15,318 - 11 -

1C)4483~
SUPPLEMæNTARY DISCLOSURE
This is a Supplementary Disclosure to Canadian
Patent Application Serial No. 211,122, filed October 8, 1974.
Suitable low molecular weight halogeno-bisphenol-
polycarbonates with molecular weights of Mn = approx. 8000 -
20,000, preferably between 8,000 and 12,000, are the homo-
polycarbonates or copolycarbonates obtained from the halo-
genated bisphenols o the following formula
HO- ~ -Z- ~ OH
Xn Xn
wherein X is Cl or Br, n is 1, 2, 3 or 4 and Z is Cl-C8-
alkylene, C2-C8-alkylidene, C5-C12-cycloalkylene, C5-C
cycloalkylidene or the following radical
CH~_,CH3
CH3 CH3
Suitable examples for the halogeno-bisphenols are bis-(3,5-
dibromo-4-hydroxyphenyl)-methane, 2,2-bis-(3-bromo-4-
hydroxyphenyl)-propane, 2,4-bis-(3-bromo-4-hydroxyphenyl)-
2-methylbutane, 2,4-bis-(3,5-dichloro-4-hydroxyphenyl)-
2-methylbutane, 2,4-bis-(3,5-dibromo-4-hydroxyphenyl)-2-
methylbutane, l,l-bis-(3-bromo-4-hydroxyphenyl)-cyclo-
hexane, 1,1-bis-(3,5-dichloro-4-hydroxyphenyl)-cyclohexane,
1,1-bis-(3,5-dibromo-4-hydroxyphenyl)-cyclohexane, ~
bis-(3,5-dibromo-4-hydroxyphenyl)-p-diisopropylbenzene and
a,'-bis-(3,5-dichloro-4-hydroxyphenyl)-p-diisopropylbenzene.
Preferred examples o~ the halogeno-bisphenols are 2,2-bis-
LeA 15,318 -12-
'.~
,

^~ -
iO~8~3
(3,5-dibromo-4-hydroxyphenyl)-propane (Tetrabrombisphenol-A)
and 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane (Tetra-
chlorobisphenol-A).
LeA 15,318 -13-
r~