Opaque pearlescent films containing dispersed incompatible polymer and polymeric interfacial agent

Opaque pearlescent polymer films, e.g., polypropylene, containing finely dispersed particles of an incompatible polymer e.g., nylon, are improved by blending a polymeric interfacial agent with the film polymer and the incompatible polymer to give a film having the incompatible polymer dispersed in smaller spherical particles and reduced stringness.

CROSS-REFERENCE TO RELATED APPLICATIONS 
In my concurrently filed application entitled "OPAQUE PEARLESCENT FILM 
CONTAINING BLENDS OF POLYMERS FOR IMPROVED DISPERSION OF INCOMPATIBLE 
POLYMER PHASE" there are disclosed opaque polymeric films containing a 
dispersed phase of incompatible polymer as the opacifying agent. Improved 
opacity is obtained by virtue of finer dispersion of the incompatible 
polymer by the addition of a polymer to the continuous film phase to alter 
its melt rheology and to cause dispersion of the incompatible polymer in 
small spherical particles with reduced stringiness. 
BACKGROUND OF THE INVENTION 
Opaque polymeric films in which the opacifying agent is finely divided 
polymer dispersed in the continuous film polymer phase are described in 
U.S. Pat. Nos. 4,368,295 and 4,377,616, which are incorporated herein by 
reference in entirety. U.S. Pat. No. 4,368,295 discloses opaque polyester 
films containing dispersed polypropylene and a carboxylated polyethylene 
additive. 
In U.S. Pat. No. 4,377,616, a film is prepared by melting a mixture of a 
major proportion of a film forming polymer such as polypropylene and a 
minor proportion of an incompatible polymer which has a higher melting 
point, at a temperature sufficient to melt the incompatible polymer and to 
dispense it in the film forming polymer, extruding the mixture into a film 
and biaxially orienting the film. The dispersed incompatible polymer 
provides sites for the formation of voids surrounding the dispersed 
polymer particles. These voids provide opacity and give the film an 
attractive pearlescent sheen. Reduction of the size of the dispersed 
particles and reduction of the occurrence of stringiness in those 
particles, as sometimes occurs, results in a film having improved opacity 
and better appearance. Such improvements are provided in accordance with 
this invention. 
SUMMARY OF THE INVENTION 
This invention relates to improvements in opaque polymeric films containing 
finely dispersed incompatible polymer as the opacifying agent. Particle 
size and stringiness in the dispersed incompatible polymeric phase are 
reduced by incorporating a polymeric interfacial agent in the mixture of 
polymers. 
DETAILED DESCRIPTION OF THE INVENTION 
The opaque polymeric films of the invention containing finely dispersed 
incompatible polymer as the opacifying agent are improved by the 
incorporation into the polymeric blend prior to formation of the film of 
an interfacial polymeric additive. The interfacial additive generally has 
a polymeric moiety which is similar to the polyolefin film forming polymer 
and a moiety which is more compatible with the polymer of the dispersed 
phase. For example, the moiety which is compatible with the polyolefin 
film forming phase is advantageously a polyolefin moiety such as 
polyethylene or polypropylene. The moiety which is more compatible with 
the dispersed phase is advantageously a carboxylic acid, carboxylic salt, 
carboxylic acid ester or carboylic acid amide group. Preferably, 
carboxylic acid or carboxylic acid salt derivatives of ethylene or 
propylene copolymers are used. Such materials include copolymers of 
ethylene with the appropriate monomer such as acrylic acid, methacrylic 
acid, or esters such as acrylates, methacrylates and vinyl acetates. The 
carboxylic acid group can be introduced after formation of the polymer as 
disclosed in U.S. Pat. No. 4,368,295. Particularly suitable are the 
"Surlyn" ionomer resins available from DuPont which are believed to be 
certain salts of polymers of ethylene copolymerized with a carboxylic acid 
monomer. 
The polymeric interfacial agent is added in an amount which is effective to 
reduce the size of the dispersed polymer particles and to reduce the 
stringiness observed in the dispersed polymer. Particularly effective 
additives will result in a film in which the dispersant size is 8 microns 
or less and which has very few, if any, stringiness in the dispersed 
phase. It is preferred to include the additive in amounts sufficient to 
obtain a particle size of 5 microns or less and preferably 3 microns or 
less with no stringiness in the particles. Generally, levels of additives 
in the range of 0.5 to 10 weight percent can be used. However, excesses 
are to be avoided because the particle size becomes too small and opacity 
is reduced. Preferably, the additive is in an amount of ranging from about 
1 to about 4 weight percent. About 2 weight percent has been found 
suitable with particularly effective additives. 
The methods for preparing the films described in U.S. Pat. No. 4,377,616 
can be used herein. As described in the patent, the films can contain 
additional components such as inorganic fillers and the like. Similarly, 
the films can contain one or more additional layers to achieve high gloss, 
heat sealability or other desired characteristics. 
The invention is illustrated by the following non-limiting examples. All 
parts are by weight unless otherwise specified.

EXAMPLES 1-8 
A series of films from resin blends comprising 15 weight percent Nylon-6 
(Allied 8207F), the indicated amount of polymeric interfacial additive, 
the remainder being polypropylene, were prepared. 
Extrusion tests were conducted by dry blending resin mixtures and cast 
extruding the blends into 10 mil sheets using 3/4" Brabender extruder 
equipped with a two-stage mixing screw. The sheets were then biaxially 
oriented on a T.M. Long Orientor. 
The distribution of the resin components in the extrudate were examined 
optically. The surface and the cross-sections of the cast films were 
stained with aqueous iodine solution for one minute and then examined 
under an optical microscope. Polar components, such as Nylon, appeared as 
dark brown areas, while the polypropylene was not affected by the 
staining. 
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Dispersant Size 
Nylon 
Example % Additive (microns) Strings 
______________________________________ 
Control 0 7 Several 
1 2% Kenamide S-180 
7.5 Several 
2 2% Modic 300M 5 Some 
3 2% EMA 2207 5 Few 
4 2% PEOX 500 4 Some 
5 2% AC-400 3 Some 
6 2% Plexar 2511 
2.5 Few 
7 2% EAA-459 2.5 None 
8 2% Surlyn 1652 
2.5 None 
______________________________________ 
The interfacial additives listed above are identified in the Table below. 
TABLE I 
______________________________________ 
INTERFACIAL ADDITIVES FOR NYLON/PP 
RESIN BLENDS 
Product Chemical Description 
Producer 
______________________________________ 
EMA 2207 Ethylene Methylacrylate 
Gulf 
EAA-459 Ethylene Acrylic Acid 
Dow 
Surlyn 1652 Ionomer DuPont 
AC-400 Ethylene Vinyl Acetate 
Allied 
Plexar 2511 Anhydride Modified PP 
Chemplex 
Modic P-300M Anhydride Modified PP 
Mitsubishi 
PEOX 500 Polyethyloxazoline 
Dow 
Kenamide S-180 
Stearyl Stearamide 
Witco 
______________________________________ 
Although the present invention has been described with preferred 
embodiments, it is to be understood that modifications and variations may 
be restored to, without departing from the spirit and scope of this 
invention, as those skilled in the art will readily understand. Such 
modifications and variations are considered to be within the purview and 
scope of the appended claims.