Alkali or alkaline earth salts of sulfosuccinic acid esters as internal antistatic agents, take-off and winding aids for transparent polycarconate films

The invention relates to the use of salts of sulfosuccinic acid esters as internal antistatic agents, take-off and winding aids for transparent cast films of polycarbonates, to a process for the production of cast polycarbonate films and to the cast polycarbonate films themselves containing salts of sulfosuccinic acids and also to the use of the new cast polycarbonate films in the electrical field and optical field.

This invention relates to the use of alkali salts or alkaline earth salts 
of sulfosuccinic acid esters corresponding to the following formula 
##STR1## 
in which M is an alkali metal cation and n is 1 or 
M is an alkaline earth metal cation and n is 2 and 
R is a C.sub.4 -C.sub.20 alkyl, C.sub.4 -C.sub.20 alkenyl, C.sub.6 
-C.sub.20 cycloalkyl or C.sub.6 -C.sub.20 cycloalkenyl radical, 
as internal antistatic agents, take-off and winding aids for transparent 
cast films of high molecular weight, thermoplastic, aromatic 
polycarbonates in quantities of 0.01 to 2% by weight and preferably in 
quantities of 0.05 to 1% by weight, based on the total weight of 
polycarbonate and salt corresponding to formula 1. 
In addition, polycarbonate films containing salts of formula 1 in such 
quantities are hardly affected in their transparency, i.e. have a haze 
value of, for example, 0% to at most 2% (as measured in accordance with 
ASTM-D-1003). 
The antistatic properties are reflected in the fact that the surface 
resistance (as measured in accordance with DIN 53 482) is less than 
10.sup.14 ohm. 
Accordingly, the added salts act on the one hand as internal antistatic 
agents by lowering the surface resistance of the film without affecting 
the specific resistivity .rho..sub.D and without damaging the 
polycarbonate. 
On the other hand, the effect of the added salts is that the film can be 
taken more easily off the casting substrate, such as for example polished 
or roughened materials, such as steel or chromium, in the form of casting 
drums or belts, can be better guided over the rollers of subsequent dryers 
and can be better wound in conventional winding machines. 
The use of sulfonic acid esters as antistatic agents in polycarbonate films 
is known from DE-OS 29 31 172 and from DE-OS 30 04 017. However, films 
such as these generally have relatively high haze values. 
In addition, DE-OS 24 58 968 describes the addition of alkali or alkaline 
earth sulfonates of phenolsulfonic acid esters to polycarbonates, which 
provides the polycarbonates with flame-retarding properties. The 
sulfonates used include, in one Example, 
disodium-bis-(4-chlorophenyl)-2,2'in one Example, 
disodium-bis-(4-chlorophenyl)-2,2'-succinate disulfonate (page 11 of DE-OS 
24 58 968). 
Salts of this type also generally produce relatively high haze values in 
the polycarbonate. 
DE-OS 26 48 131 describes non-opaque flame-retarding polycarbonate 
compositions containing alkali and alkaline earth metal salts of phenol 
ester sulfonic acids, the polycarbonate and the salt having a refractive 
index of 1.54 to 1.65. There is no mention of succinates. 
In addition, DE-OS 24 60 052 describes the production of non-inflammable 
thermoplastic polycarbonates produced by the addition of soluble basic 
alkali salts. Suitable alkali salts are inter alia alkali salts of 
succinic acid (page 8 of DE-OS 24 60 052). These salts are incorporated at 
temperatures of 250.degree. to 400.degree. C. and bring about 
non-inflammability by partial crosslinking of the polycarbonates. 
From DE-OS 2 653 327 and from DE-OS 2 460 787 polycarbonate compositions 
are known containing alkali- or earthalkali-metal salts of aliphatic 
sulphonic acids. The purpose for the addition of these salts is the 
improvement of flame retardancy of the polycarbonates. 
In addition, it is known that films or moldings can be antistatically 
finished by subsequent treatment with an external antistatic agent, for 
example by coating a film with a solution of an antistatic chemical. It is 
possible in this way to reduce the surface resistance R.sub.OA of the film 
or molding and to prevent or completely avoid any electrostatic charging 
(cf. GB 852,923 or NE 6 411 681). 
However, films such as these show adequate antistatic behavior only briefly 
because the surface coating of antistatic agent can be rapidly removed 
again by weathering and external mechanical influences. 
Another method of antistatically finishing films or moldings is to apply a 
conductive layer of, for example, carbon black or metal. This reduces the 
transparency of the films and makes then susceptible to any external 
mechanical stressing which can easily cause flaking or tearing of the 
coating. 
It is also known that the surface resistance R.sub.OA of films can be 
reduced by incorporation of carbon black in quantities by weight of up to 
30%. 
Black-colored films such as these show a distinct deterioration in their 
mechanical properties. The reduction in the surface resistance R.sub.OA of 
the film is accompanied by a reduction in its volume resistivity 
.rho..sub.D, so that the film cannot be used, for example, as an 
electrical insulating material. 
In addition, it is known that the general tendency of polycarbonate films 
to stick to rollers and to block during winding can be reduced by 
incorporation of lubricants (antiblocking agents) in the films. 
Silica gels or talcum are examples of antiblocking agents which have been 
used in the past. These inorganic materials have two main disadvantages: 
firstly, they are not soluble in the polymer and, accordingly, lead to 
distinct hazing of the film; secondly, they are difficult to disperse 
uniformly in the polymer so that agglomerates of the salts are frequently 
formed and the film as a whole becomes inhomogeneous and shows 
deteriorated mechanical properties. 
It has surprisingly been found that, as mentioned at the beginning, 
polycarbonate films containing 0.01 to 2% by weight and preferably 0.05 to 
1% by weight, based on the total weight of polycarbonate and added salt, 
of an alkali or alkaline salt of a sulfosuccinic acid ester corresponding 
to formula 1 show a reduced surface resistance R.sub.OA, their volume 
resistivity .rho..sub.D corresponding to the values of the additive-free 
film. In addition, the films show distinctly better take-off and winding 
behavior than a pure polycarbonate film. At the same time, the haze of the 
films differs only negligibly from that of an additive-free film. 
In the context of the invention, aromatic polycarbonates are understood to 
be homopolycarbonates and copolycarbonates based, for example, on one or 
more of the following bisphenols: hydroquinone, resorcinol, 
dihydroxydiphenyls, bis(hydroxyphenyl)-alkanes, 
bis-(hydroxyphenyl)-cycloalkanes, bis-(hydroxyphenyl)-sulfides, 
bis-(hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones, 
bis-(hydroxyphenyl)-sulfoxides, bis-(hydroxyphenyl)-sulfones, 
.alpha.,.alpha.'-bis-(hydroxyphenyl)-diisopropylbenzenes and also 
nucleus-alkylated and nucleus-halogenated compounds thereof. These and 
other suitable aromatic dihydroxy compounds are described, for example, in 
U.S. Pat. Nos. 3,028,365, 2,999,835, 3,148,172, 3,275,601, 2,991,273, 
3,271,367, 3,062,781, 2,970,131 and 2,999,846, in DE-OSS 15 70 703, 20 63 
050, 20 63 052, 22 11 956, 22 11 977, in FR-PS 1 156 518 and the book by 
H. Schnell entitled "Chemistry and Physics of Polycarbonates", 
Interscience Publishers, New York, 1964.

Preferred bisphenols correspond to the following formula 
##STR2## 
in which the substituents R may be the same or different and represent H, 
C.sub.1 -C.sub.4 alkyl, Cl or Br and in which X is a bond, a C.sub.1 
-C.sub.8 alkylene radical, a C.sub.2 -C.sub.8 alkylidene radical, a 
C.sub.5 -C.sub.15 cycloalkylene radical, a C.sub.5 -C.sub.15 
cycloalkylidene radical, --SO.sub.2 or 
##STR3## 
Examples of these bisphenols are 4,4'-dihydroxydiphenyl, 
2,2-bis-(4-hydroxyphenyl)-propane, 
2,4-bis-(4-hydroxyphenyl)-2-methylbutane, 
1,1-bis-(4-hydroxyphenyl)-cyclohexane, 
.alpha.,.alpha.'-bis-(4-hydroxyphenyl)-p-diisopropylbenzene, 
2,2-bis-(3-methyl-4-hydroxyphenyl)-propane, 
2,2-bis-(3-chloro-4-hydroxyphenyl)-propane, 
bis-(3,5-dimethyl-4-hydroxyphenyl)-methane, 
2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, 
bis-(3,5-dimethyl-4-hydroxyphenyl)-sulfone, 
2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane, 
1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-cyclohexane, 
.alpha.,.alpha.'-bis-(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropylbenzene, 
2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane and 
2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane. 
Particularly preferred bisphenols are, for example, 
2,2-bis-(4-hydroxyphenyl)-propane, 
2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, 
2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane, 
2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane and 
1,1-bis-(4-hydroxyphenyl)-cyclohexane. 
Preferred aromatic polycarbonates are those based on one or more of the 
preferred bisphenols mentioned above. Particularly preferred 
copolycarbonates are based on 2,2-bis-(4-hydroxyphenyl)-propane and one of 
the other bisphenols mentioned is particularly preferred. Polycarbonates 
based solely on 2,2-bis-(4-hydroxyphenyl)-propane or 
2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane are also particularly 
preferred. 
The aromatic polycarbonates may be prepared by known methods, for example 
by transesterification in the melt from bisphenols and diphenylcarbonate 
and by the two-phase interfacial method from bisphenols and phosgene, as 
described in the literature mentioned above. 
The aromatic polycarbonates may also be branched through the incorporation 
of small quantities of polyhydroxy compounds, for example 0.05 to 2.0 
mol-% (based on the bisphenols used). Polycarbonates of this type are 
described, for example, in DE-OSS 15 70 533, 15 95 762, 21 16 974, 21 13 
347, in GB-PS 1,079,821 and in U.S. Pat. No. 3,544,514. Some of the 
polyhydroxy compounds which may be used are, for example, phloroglucinol, 
4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-2-heptene, 
4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane, 
1,3,5-tri-(4-hydroxyphenyl)-benzene, 1,1,1-tri-(4-hydroxyphenyl)-ethane, 
tri-(4-hydroxyphenyl)-phenyl methane, 
2,2-bis-[4,4-bis-(4-hydroxyphenylisopropyl)-phenol, 
2,6-bis-(2'-hydroxy-5'-methylbenzyl)-4-methylphenol, 2,4-dihydroxybenzoic 
acid, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane and 
1,4-bis-(4',4"-dihydroxytriphenylmethyl)-benzene. 
The aromatic polycarbonates should have molecular weights M.sub.w of 
generally from 10,000 to more than 200,000 and preferably from 20,000 to 
80,000. 
Alkali and alkaline earth salts suitable for the purposes of the invention 
are lithium, sodium, potassium, calcium, magnesium or barium salts 
corresponding to general formula 1 above. Sodium 
bis-(2-ethylhexyl)-sulfosuccinate 
##STR4## 
is particularly preferred. 
Where it is not known from the literature, the production of the salts of 
formula 1 suitable for use in accordance with the invention is carried out 
by neutralization of the corresponding free acids with the corresponding 
alkali or alkaline earth hydroxides in known manner, for example in 
H.sub.2 O or H.sub.2 O/alcohol mixtures. The salts are isolated in known 
manner. 
The salts corresponding to formula 1 are incorporated through the solutions 
of the thermoplastic polycarbonates in standard polycarbonate solvents, 
such as CH.sub.2 Cl.sub.2, chlorobenzene or mixtures of CH.sub.2 Cl.sub.2 
and chlorobenzene. 
Accordingly, the salt of formula 1 may also be dissolved in the 
polycarbonate solvent and then added in the necessary quantities to the 
separately prepared polycarbonate solution. 
The solutions of polycarbonates in standard organic polycarbonate solvents, 
which are directly obtainable in the production of the polycarbonates by 
the two-phase interfacial method and which are washed until neutral, may 
also be directly used, i.e. without isolation of the polycarbonate, for 
mixing with the solutions of the salts corresponding to formula 1. The 
salts of formula 1 may also be added to the polycarbonate solutions as 
such or in solution in solvents. 
Cast polycarbonate films may then be prepared in a certain way from the 
polycarbonate solutions (cf. for example DE-AS 12 74 274 and DE-OS 25 17 
032). 
Accordingly, the present invention also relates to a process for the 
production of cast polycarbonate films which is characterized in that 
solutions of thermoplastic aromatic polycarbonates in their standard 
solvents are mixed with salts of formula 1 in quantities of 0.01 to 2% by 
weight and preferably in quantities of 0.05 to 1% by weight, based on the 
total weight of polycarbonate plus salt of formula 1, either as such or in 
solution in polycarbonate solvents and the resulting mixture subsequently 
processed in known manner to cast films. 
The present invention also relates to cast polycarbonate films containing 
0.01 to 2% by weight and preferably 0.05 to 1% by weight of salts 
corresponding to formula 1, based on the total weight of polycarbonate 
plus salt. 
Suitable polycarbonate solutions for the production of the cast 
polycarbonate films should have a concentration of from about 10 to 15% by 
weight, based on polycarbonate plus solvent. 
The cast polycarbonate films according to the invention should preferably 
have a thickness of from about 10 .mu.m to 200 .mu.m. 
In addition to the salts of formula 1, other standard additives, such as UV 
stabilizers or heat stabilizers, may also be added to the polycarbonate 
solutions before production of the cast films. 
The cast polycarbonate films according to the invention are used in known 
fields of application for polycarbonates, but especially in the electrical 
field, the glazing field and, above all, in the optical field. 
The films of polycarbonate solution used in the Examples have layer 
thicknesses of 50 .mu.m to 100 .mu.m and consist of a homopolycarbonate 
based on 2,2-bis-(4-hydroxyphenyl)-propane with a weight average molecular 
weight Mw of 57,000 (PC calibration) and a relative solution viscosity 
n.sub.rel of 1.75, as measured on a 0.5% solution in methylene chloride, 
and were prepared by casting from a methylene chloride solution. Example 1 
is the pure PC film and is intended for comparison purposes. 
The additive according to the invention 
(Na-bis-(2-ethylhexyl)-sulfosuccinate) is known from the literature (Merck 
Index 10, 3409) and was dissolved in methylene chloride and added to the 
polycarbonate solution before casting. The surface resistance (R.sub.OA) 
tests described in the Examples were carried in accordance with DIN 53 482 
at 23.degree. C./50% relative air humidity. 
Haze values were measured in accordance with ASTM-D-1003. 
EXAMPLES 
______________________________________ 
Additive R.sub.OA .rho..sub.D 
Haze 
Example (% by weight) 
(ohms) (ohms) [%] 
______________________________________ 
1 -- .about.10.sup.15 
&gt;10.sup.16 
0-1 
2 0.1 3.0 .multidot. 10.sup.13 
2.3 .multidot. 10.sup.16 
1 
3 0.5 83 .multidot. 10.sup.12 
2.0 .multidot. 10.sup.15 
2 
______________________________________