Note: Descriptions are shown in the official language in which they were submitted.
113;~;~Z3
- 1 - 30389
POLYOLEF IN E' ILMS
This invention relates to a polymeric film, and, in
particular, to an antistatic thermoplastic polymeric film
of high modulus.
Polymeric films are widely utilized in the packaging
industry, and to be acceptable in this field of activity
must satisfy numerous stringent criteria. In particular,
for use with mechanised packaging equipment, such as that
employed in overwrapping cigarette cartons, a packaging
film should possess a sufficiently high modulus, or
inherent stiffness, to enable continuous lengths of the
film to be fed smoothly and uniformly through the
equipment. Desirably, the film should also exhibit a high
degree of electrical conductivity so that the free
movement of film through the equipment is not impeded by
the accumulation of static electricity on the film or
equipment surfaces which may cause the film to adhere to
parts of the equipment - with consequent disruption of the
packaging operation.
Accordingly, the present invention provides a self-
supporting multiple-layer film comprising
a substrate layer of a polymer of a mono-alpha-olefin
containing from 2 to 8 carbon atoms in its molecule,
a modulus improver, as hereinafter defined,
incorporated in the substrate layer,
a polymeric heat-sealable layer adhered to at least
one surface of the substrate layer, and,
on the surface of the heat-sealable layer remote from
the substrate, an antistatic medium comprising a
quaternary ammonium compound of general formula
~4 O- Z--CH 2 -N ~ ¦ X
q~@
, ~
~3'~3'~;3
-
wherein each of Rl, R2, and R3, which may be the same
or different, is a hydrogen atom or a lower alkyl radical
containing from 1 to 6 carbon atoms, or Rl and ~2 are
each methylene groupings within a common five- or
six-membered saturated heterocyclic ring, R4 is a hydrogen
atom or an acyl radical containing up to 15 carbon atoms,
z is a methylene group or a carbonyl group when R4 is a
hydrogen atom, or Z is a methylene group when R4 is said
acyl radical, and X is a univalent anion or an equivalent
of a multivalent anion.
By a "self-supporting" film is meant a film capable of
independent existence in the absence of a supporting substrate.
By an "antistatic medium" is meant a treatment medium
which confers upon the film a reduced tendency to accumulate
static electricity compared with an untreated film.
By a "modulus improver" is meant a resin, of natural
or synthetic origin, which is amorphous, hard, brittle, and solid
at ambient temperature, has a softening range at elevated
temperature, has a drop softening point of at least 70C/ and is
sufficiently compatible with the film-forming olefin polymer to
yield a composition from which may be formed a drawn, self-
supporting transparent film exhibiting a modulus exceeding that
of a film formed from an identical olefin polymer in the absence
of the improver resin.
Suitable modulus improvers include naturally-occurring
rosin acids, such as dihydroabietic acid, and derivatives of rosin
formed, for example, by disproportionation at elevated temperatures
--2--
.: .,' ~ ;' ' ~ '
~13;Z~3~3
or by hydrogenation at high pressures. Other suitable,
commercially available, resins, include the IMPREZ* aliphatic
hydrocarbon resins derived by polymerisation o~ a petroleum
residue containing a blend of C4 and C5
*Trade mark
-2a-
~13~
_ 3 _ 30389
olefins, and supplied by Imperial Chemical Industries
Limited; the ESCOREZ petroleum hydrocarbon resins supplied
by Esso Chemical Limited; the ZONAREZ polyterpene resins
supplied by the Arizona Chemical Company; a completely
saturated and aromatic vinyl toluene-alpha-methyl styrene
copolymer - such as PICCOTEX, and a ierpene resin derived
from beta-pinene - such as PICCOLYTE~ supplied by the
Pennsylvania Industrial Chemical Company. Particularly
useful modulus improvers are obtained by hydrogenation of
a product formed by polymerising mixtures of unsaturated
monomers from cracked petroleum - for example, by
hydrogenation of an aliphatic PICCOPALE hydrocarbon resin
supplied by the Pennsylvania Industrial Chemical Company.
Desirably, the modulus improver is relatively free
from olefinic unsaturation, and preferably exhibits an
iodine value of less than 50.
To prevent leaching of the modulus improver from the
film structure it is preferred that the modulus improver
is of relatively high molecular weight (weight average) -
for example, at least 500 and preferably of the order of1000 .
Although the functional mechanism of the modulus
improver is not completely understood, it is postulated
that, as crystallisation of the polyolefin film occurs -
for example, in the course of conventional orientingand/or heat-setting treatments, the hard, amorphous
modulus improver, if homogeneously dispersed throughout
the polyolefin matrix, accumulates in the residual
amorphous regions of the polyolefin to form adherent
inclusions between the polyolefin crystallites, thereby
improving the stiffness of the film structure.
The modulus improver may be blended with the
substrate-forming polyolefin by conventional mixing
techniques. For example, the modulus improver may be dry
mixed with the polyolefin in a simple tumble blender, or
11~3232~
~ 4 ~ 30389
the components of the blend may be intimately mixed by
melt extrusion, the components being, if desired, fed
directly to the feed pocket of an extruder, and either
directly extruded to form film or comminuted to
particulate form suitable for subsequent re-extrusion.
The modulus improver is employed in an amount
sufficient to confer the required improvement in film
modulus without detriment to other desirable character-
istics of the polyolefin film - such as heat-seal
strength. In practice, the modulus improver suitably
constitutes from 1 to 50%, preferably from ~.S to 35%, and
particularly preferably from 5 to 20%, by weight of the
blend (polyolefin substrate and modulus improver).
Suitable thermoplastic polyolefins for forming a
substrate layer include polymers and copolymers of
l-olefins such as ethylene, propylene, butene-l, and
4-methylpentene-1, a particularly useful material being a
high molecular weight stereoregular predominantly
crystalline polymer of propylene, either in the form of a
homopolymer or copolymerised with minor quantities (e.g.
up to 20~ by weight of the copolymer) of other unsaturated
monomers, such as ethylene.
The polymeric heat-sealable layer may be formed from
any homo- or co-polymer which adheres well to the
substrate, and which can be melted in a temperature range
below the melting temperature of the substrate polymer to
yield seals of acceptable strength using standard heat-
sealing equipment. Conventional heat-sealable polymers
may therefore be employed. Preferably, the heat-sealable
polymer is a polyolefin, e.g. an olefin homopolymer such
as high density polyethylene or an olefin copolymer such
as a rzndom copolymer of ethylene with from 0.25 to 15,
preferably 2 to 6, % by weight of the copolymer of an
alpha-mono-olefin containing from 3 to 6 carbon atoms in
its molecule. Propylene and butene-1 are preferred
- , . ~.
~L3~3;23
- 5 - 30389
monomers for copolymerising with ethylene. A further
preferred heat-sealable polymer comprises a random
copolymer of propylene (80 to 95% by weigh.) with another
alpha-olefin containing from 4 to 10 carbon atoms, such as
butene-l, as described in British patent 1 452 424, or a
blend of said propylene-alpha-olefin copolymer with from
25 to 95~ by weight of the blend of a polymer of an alpha-
olefin containing from 4 to 10 carbon atoms in its
molecule, such as butene-l, copolymerised with from 0 to
10~ by weight of the copolymer of an alpha-olefin
containing from 2 to 10 carbon atoms in its molecule, as
described in British patent 1 495 776.
Multiple-layer films are suitably formed by combining
the components of the substrate and heat-sealable layer in
conventional manner, but most conveniently by a
simultaneous coextrusion technique. A coextrusion
technique is particularly suitable for the production of
multi-layer films the opposed surface layers of which are
of different composition, within the herein defined
limits, or exhibit different characteristics - selected in
accordance with the requirements of the application
envisaged for the resultant film and/or of the packaging
equipment employed. For example, the opposed surface
layers may be modified to exhibit different frictional
characteristics, so that the resultant differential slip
film runs well on packaging machinery and seals
effectively during package formation.
The lower alkyl radicals in the aforementioned
formula of the quaternary ammonium compound present in the
antistatic medium are preferably methyl or ethyl radicals,
while the anion X, which may be any anion, including a
divalent ion, such as tartrate, is suitably a nitrate or
chloride ion. A preferred quaternary compound is choline
chloride of formula
113'~323
- 6 - 30389
[HOCH2CH2N ( CH3 ) 3 ] Cl -
Choline chloride is a particularly advantageous agent
for use in packaging films in that it is colourless, non-
toxic, being an essential constituent of the mammalian
diet, substantially odourless, and an extremely effective
antistatic agent because its small molecule yields highly
mobile ions.
Choline ester salts of general formula
+
[RCO.OCH2CH2N(CH3)3]X
wherein R is a linear alkyl radical containing not more
than 15 carbon atoms, and X is as hereinbefore defined,
may also be employed. Suitable ester salts include
N-(hexanoyl-oxyethyl)-trimethyl ammonium chloride.
Betaine,
[HOOCCH2N(CH3)3]OH ,
is another suitable quaternary ammonium compound.
In a preferred embodiment of the invention the
antistatic medium includes a glyceride of a fatty acid
containing up to 22 carbon atoms in its molecule. The
glyceride may be a mono-, di- or tri-glyceride or a
mixture of two or more thereof. A simple glyceride
containing two or more identical fatty acid residues, or a
mixed glyceride containing different acid residues, may be
employed. The fatty acid, preferably containing from 8 to
22 carbon atoms, from which the glyceride is derived is
preferably a saturated fatty acid, such as stearic acid or
behenic acid. A particularly suitable component is
glyceryl monostearate containing at least 50 weight per
cent of the alpha form of the monoester.
~ . ' ~ ,' " ,
- ~ .
_ 7 _ 30389
In a further preferred embodiment of the invention
the antistatic medium additionally comprises an organic
polyol containing from 3 to 12 carb~n atoms and at least
two free hydroxyl groups in its molecule. The polyol is
suitably an aliphatic compound, including a
monosaccharide, such as glucose, and a disaccharide, such
as sucrose, but is preferably of the general formula
CH2R
I
(X-C-Y)
I
C 2 R
wherein each of R' and R", which may be the same or
different, is hydrogen or an acyl radical containing from
2 to 20 carbon atoms, X is -H or -CH2OR', Y is -OH or
-CH2OR', and n is an integer from 1 to 10, with the
proviso that at least two free hydroxyl groups are present
in the molecule. The polyol is preferably of relatively
low molecular weight to assist migration of the polyol in
or on the heat-sealable layer treated therewith, and of
low volatility to assist retention of the polyol in
association with that layer. Glycerol, HOCH2CH(OH)CH2OH,
is a preferred polyol, and, being a component of the human
diet, is non-toxic. Pentaerythritol and low molecular
weight polyethylene glycols, for example having a
molecular weight (weight average) of from 300 to 400, are
also of utility.
In a still further preferred embodiment of the
invention the antistatic medium includes, in addition to
the hereinbefore defined quaternary ammonium compound,
glyceride and organic polyol, an amine salt of general
formula
:
323~3
- 8 - 30389
~ ~ + ~( 2C 2)XH1
LA (cH2cH2o)yH~
wherein x is a positive integer, y is zero or a positive
integer, the sum of x and y is from 2 to 5, A is a
hydrogen atom and when y is zero A may also be a lower
alkyl group containing from 1 to 6 carbon atoms, R is a
univalent aliphatic radical containing from 8 to 22 carbon
atoms, and X is a univalent anion or an equivalent of a
multivalent anion.
Suitably, the amine ~alt is an amine sulphate, and it
is preferred to use amine sulphates of the aforementioned
general formula in which the sum of x and y is 2, A = H,
and R is a mixture of aliphatic hydrocarbon radicals
having 8 to 18, preferably 12 to 18, carbon atoms,
particularly those which are derived from tallow or soya
oil and are predominantly composed of hexadecyl, octadecyl
and octadec-9-enyl (oleyl) radicals or derived from
coconut oil and predominantly (e.g. ~50 wt %) composed of
dodecyl with a minor proportion (e.g. up to 20 wt %) of
tetradecyl radicals. Examples of suitable amines from
which amine sulphates may be prepared are sold as
'Ethomeen' T/12, 'Ethomeen' S/12, and 'Ethomeen' C/12
(Armour Hess Division of Akzo Chemie UK Limited).
The proportions of the quaternary ammonium compound,
and, optionally, of the glyceride, organic polyol and
amine salt, in the antistatic medium may vary within a
wide range, and desirably should be selected by simple
experimentation to provide a medium which when applied to
the film confers thereon a surface resistivity (measured
at 50% Relative Humidity and a temperature of 25C) not
exceeding 10, and preferably less than 5.0, gigohms per
square.
.
.. : -: ,
~3'~3'h3
- 9 - 30389
Desirably each of the components of the medium is
present in an amount which will provide at least a
monomolecular layer at the film surface. Conveniently,
therefore, the medium at the film surface comprises, based
on the total weight of the film (substrate plus heat-
sealable layer(s)J, from 0.001 to 0.5 wt % of the
quaternary ammonium compound, from 0 to 0.75 wt % of the
glyceride, from 0 to 0.75 wt % of the organic polyol, and
from 0 to 0.05 wt % of the amine salt. A preferred
composition range at the film surface comprises from 0.005
to 0.25 wt ~ of the quaternary ammonium compound, from
0.005 to 0.5 wt % of the glyceride, from 0.001 to 0.5 wt %
of the organic polyol, and from 0.0001 to 0.025 wt ~ of
the amine salt.
The antistatic medium may be associated with the film
surface by conventional blending techniques - for example,
by tumble blending the component(s) of the antistatic
medium which are thermally stable at the extrusion
temperature with the polymeric film-forming material, and
subsequently extruding and fabricating the blend by known
film-forming techniques, thereby enabling the antistatic
medium to migrate through the interior of the film and on
to a surface thereof. Alternatively, and preferably, the
antistatic medium may be deposited directly on to the
external surface of the heat-sealable layer remote from
the substrate layer, conveniently as a solution or
dispersion in a suitable vehicle - preferably, for economy
and ease of application, in an aqueous vehicle. In a
preferred embodiment of the invention a combination of
preblending and wash-coating is employed in which, for
example, the relatively insoluble glyceride is
incorporated into the polymeric film-forming blend and
allowed to migrate to the surface of the resultant film,
while the quaternary ammonium salt and, optionally, the
organic polyol and the amine salt, are subsequently
~3Z323
- 10 - 30389
applied to the external film surface in a suitable liquid
vehicle.
The concentration of the antistatic medium in the
liquid coating vehicle depends, inter alia, on the level
of antistatic properties required in the treated film, and
relatively high concentrations may be employed, provided
that the viscosity of the solution or dispersion is not
increased to a level which adversely affects the mobility
and spreadability thereof. In practice, the antistatic
medium is conveniently employed at a concentration of from
1 to 50 wt %, preferably from 2.5 to 35 wt %, and
particularly preferably from 5 to 15 wt %, based on the
weight of the solution or dispersion. It will be
appreciated that because of partitioning between the
substrate and heat-sealable layers the concentration of
any antistatic component(s) preblended into the film-
forming polymer must be increased to a level which, after
migration through the film structure, will provide an
adequate concentration of that component in the
electrically conductive ionic layer at the film surface.
For example, the glyceride, if preblended, desirably
constitutes from 0.1 to 2, and preferably from 0.4 to 1~0,
per cent by weight of the film-forming polymer.
~ultiple-layer films according to the invention may
be unoriented or uniaxially oriented, but are preferably
biaxially oriented by drawing in two mutually
perpendicular directions in the plane of the film to
impart strength thereto. Orientation of flat film may be
effected by a stenter technique, while oriented tubular
film is suitably produced by coextruding the polymeric
materials in the form of a multi-layer tube from an
annular die, cooling the extruded tube (the cast tube),
reheating and inflating the tube by the so-called "bubble"
process to introduce transverse orientation, and
simultaneously elongating the tube longitudinally to
113~3'~3
- 11 - 30389
orient the film in a lengthwise direction. The film is
then preferably "heat-set", i.e. dimensional stability of
the film is improved by heating the film, while restrained
against thermal shrinkage, to a temperature above the
glass transition temperature of the polymer from which the
film is formed but below the melting point thereof.
As hereinbefore described, the antistatic medium may
be blended with the polymeric material prior to formation
of a rilm therefrom, or by a combination of preblending
and subsequent wash-coating. However, the relatively
soluble components of the antistatic medium, such as the
quaternary ammonium compound and, optionally, the organic
polyol, are required in only relatively small amounts and
are preferably applied directly to the external surface
of the heat-sealable layer as a solution or dispersion.
While the solution or dispersion may be applied between
the orienting steps of a sequential drawing procedure, we
prefer to apply the solution or dispersion to the cast,
unoriented extrudate immediately prior to the reheating
and orienting stage of the film-forming process.
Evaporation of the volatile vehicle (water) is therefore
effected during the reheating operation, and the
antistatic medium becomes firmly bound to the film surface
during orientation.
The films of the invention may conveniently contain
any of the agents conventionally employed in the
manufacture of thermoplastic polymeric films. Thus,
agents such as dyes, pigments, lubricants, anti-oxidants,
anti-blocking agents, surface-active agents, slip aids,
gloss-improvers, prodegradants, and ultra-violet light
stabilisers may be employed. In particular, the
development of film surface conductivity may be assisted
by the presence in the substrate of low molecular weight
non-electrolytes added to promote properties other than
conductivity, typical non-electrolytic additives being
; ~ :
~3Z~23
- 12 - 30389
an anti-blocking aid, such as oleamide, and a surfactant,
such as a long chain amine of the kind defined in the
aforementioned general formula of the optional amine salt
component of the antistatic medium. These additional
additives are conveniently present in respective
concentra,ions of from 0.01 to 1% (preferably about 0.2%)
and from 0.01 to 1% (preferably about 0.15%) by weight of
the substrate, and may be incorporated into the polymeric
melt from which the substrate is formed, in which case
they migrate to the film surface where they induce
electrical continuity in the electrolyte layer, or they
may be applied directly to the exposed surface of the
heat-sealable layer. Application of these additional
additives directly to the exposed surface is less
desirable in that they are not readily soluble in the
preferred vehicle (water), and it is difficult to apply
them in amounts which are not excessive in relation to the
amount of the antistatic medium.
The films may vary in thickness depending on the
intended application, but usually we find that films
having a thickness of from 2 to 150 microns are of
general utility. Films intended for use in packaging
operations are suitably within a thickness range from 10
to 50 microns. The thickness of the heat-sealable layer
25 is desirably within a range of from 0.05 to 2.5 microns.
The films may be subjected to conventional after-
treatments - for example, a corona discharge treatment to
improve the bonding and print-receptive properties of the
f ilm surface.
The invention is illustrated by reference to the
following Examples.
EXAMPLES 1 TO 6
Examples 1 and 2 are comparative and not according
to the invention.
~ ~ .
1~L3Z323
- 13 - 30389
From an annular coextrusion die was extruded a
composite triple-layer tube, having a propylene
homopolymer core with a heat-sealable layer of a 60:40 by
weight blend of a propylene-butene-l copolymer (14 wt
butene-l) and a butene-l homopolymer on each surface
thereof. The core contained 0.6 per cent by weight of
glyceryl monostearate. The extrudate was cooled and,
externally coated with an aqueous solution comprising 3.2
wt % choline chloride, 4.2 wt % glycerol, 0.19 wt ~
'Ethomeen' T/12 sulphate (prepared by reacting an aqueous
solution of 'Ethomeen' T/12 with concentrated sulphuric
acid), and 92.41 wt % pure water. The coated tube was
heated and inflated to form a bubble, which was then
collapsed to yield a biaxially oriented tubular film
exhibiting a draw ratio of about 7:1 in each of the
longitudinal and transverse directions, and having a
thickness of about 20 ~um. The thickness of the heat-
sealable blend layer on each surface of the film was about
0.3 micron. The tubular film was then slit to form a flat
film which was heat-set, at a temperature of about 120C,
on a system of matt-surfaced, hot rollers of the kind
described in British patent 1 124 886.
The aforementioned procedure was then repeated save
that the thickness of the blend layer was increased to
about 0.5 ~m.
A similar procedure was employed to produce a series
of films containing, varying amounts of 'Picco' 1055, a
natural polyterpene, in the core layer.
The resultant films were assessed for s~iffness (1%
secant modulus) in accordance with the standard method of
ASTM D882-75b, for clarity (narrow angle haze), for heat
seal strength on seals formed on a Sentinel Heat Sealer,
Model No. 12 AS, operating at a jaw pressure of 15 psi
(0.1 MNm 2), jaw closure time of 2 seconds, and jaw
temperature of 120C, and for electrical surface
- ~ ~
- 14 - 30389
conductivity by means of a simple apparatus comprising a
DC power supply of 70 volts in series with an electronic
microammeter and with an electrode assembly comprising a
pair of knife-edged electrodes which, when placed on the
film at the desired position, thereby completed an
electrical circuit through the apparatus and enabled the
surface conductivity (in units of 10 12 mhos per square
at 50% Relative Humidity and 25C) to be recorded by the
microammeter.
Results are recorded in the following Table.
Table
Poly- Heat-seal 1% Narrow Seal Conduc-
Ex. terpene Layer Secant Angle Strength tivi~in core Thickness Modul~s Haze Ig/25 mm) (lo
(wt %) (~m) (kg/m ) (%) mhos/sq)
1 0 0.3 245 23 370 _
2 0 0.5 245 25 420 236
3 5 Q.3 310 15 330
4 5 0.5 310 18 420 227
0.3 330 11 415 _
6 15 0.5 330 14 500 233
These results demonstrate a surprising improvement in
film clarity (reduction in haze) with an improvement in
film stiffness as the polyterpene content in the core is
increased. Heat-seal strength likewise shows a tendency
to increase, while electrical surfàce conductivity is not
significantly reduced by the inclusion of polyterpenes.
EXAMPLES 7 TO 9
Example 7 is comparative and not according to the
invention.
~3i~ 3
- 15 - 30389
A procedure similar to that of Example 1 was repeated
to yield an identical antistatic-coated multi-layer film
save that the amount of glyceryl monostearate was
increased to a nominal 0.8 weight % of the propylene
homopolymer substrate, and that the thickness of the
propylene-butene copolymer/butene homopolymer heat-
sealable layer was increased to about 0.7 micron. This
procedure was then repeated to yield two films each
containing 15 weight % of 'Zonarez' 7115, a polymerised
dipentene resin, in the core layer, one of these films
being coated with an antistatic medium identical to that
of Example 1, and the other being coated with such a
medium from which the glycerol was omitted.
Xesults are recorded in the following Table.
Table
Po1y- Glycerol 1% Narrou Seal Conduc-
Ex. terpene in a/s Secant Angle Strength tivi~Xin core medium Modul~s Haze (g/25 mm) (10_1~
_ (wt %) ~wt %) (kg/m ) (%) mhos/sq)
70 4.2 211 20 302923
815 4.2 217 19 477506
915 0 217 18 418632
.._ __
These results show that inclusion of the polyterpene
in the core yields an improvement in stiffness, in clarity
and in seal strength, although the surface conductivity is
somewhat depressed. Omission of the glycerol from the
antistatic medium yields an improvement in clarity and
surface conductivity at the expense of seal strength. In
general, inclusion of an organic polyol, such as glycerol,
,:
113~ 3
- 16 - 30389
in the antistatic medium enabled acceptable surface
conductivity values to be achieved under conditions of low
Relative Humidity and reduced the incidence of surface
blemishes on the films.
The generally higher level of surface conductivity
compared to that observed in Examples 1 to 6 is attributed
to the increased content of the glyceride added to the
core layer.
EXAMPLE 10
The procedure of Example 9 was repeated (no glycerol
in the antistatic medium) save that the heat-sealable
layer of 0.7 micron thickness was formed from a random
propylene-ethylene copolymer containing about 6 weight %
of ethylene, and that heat-setting was effected at an
increased temperature (150C).
The resultant film exhibited good stiffness (220
kg/m ), seal strength (410 g/25 mm) and surface
conductivity (822 units) and was extremely clear (narrow
angle haze 13%).
EXAMPLE 11
The procedure of Example 8 was repeated (glycerol
present) save that the heat-sealable layer of 0.7 micron
thickness was formed from a random ethylene-butene-l
copolymer containing about 4 weight % of butene-l, and
25 having a density at 23C of 0.933 g/cc and a Melt Flow
Index (190C/2 kg) of 3.0 g/10 minutes.
The resultant film exhibited good stiffness
(220 kg/m2), seal strength (352 g/25 mm) and surface
conductivity (443 units) and was of extreme clarity
(narrow angle haze 11%).
EXAMPLES 12 AND 13
Example 12 is comparative and not according to the
invention.
The procedure of Example 1 was repeated save that the
film substrate was formed from a propylene-ethylene block
l~3æ~3
- 17 - 30389
copolymer containing about 6 weight % of ethylene. The
resultant film exhibited good clarity and a surface
conductivity of 171 units (Example 12). A similar
procedure was employed to yield a film containing 15
B 5 weight % of 'Picco' 1055 in the copolymer core. The
resultant film was of slightly inferior clarity to that of
Example 12, but exhibited superior stiffness and a greatly
increase surface conduct.ivity of 423 units (Example 13).
