EXTRUDABLE BLENDS OF POLYETHYLENE AND FILMS THEREOF

MELANGES EXTRUDABLES DE POLYETHYLENE ET PELLICULES FAITES A PARTIR DE CEUX-CI

English Abstract

F-4092-L
EXTRUDABLE BLENDS OF POLYETHYLENE
AND FILMS THEREOF

ABSTRACT

The extrudability of linear polymers of ethylene such as
low density copolymers of ethylene and C4 to C10 olefins (LLDPE)
into thin films is improved by adding small amounts, e.g., 0.02 to 2
weight percent polyvinylidene fluoride to reduce melt fracture, head
pressure and to obtain films having excellent anti-blocking
characteristics.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An extruded film comprising:
(1) a linear low density polyethylene, viz, a
linear copolymer of ethylene and a higher olefin
containing 4 to 10 carbon atoms, having a density of 0.90
to 0.94; and
(2) 0.02 to 2 weight percent of polyvinylidene
fluoride homopolymer.

2. The film of claim 1 in which said linear low
density polyethylene is a copolymer of ethylene and
butene.

3. The film of claim 1 in which said linear low
density polyethylene is a copolymer of ethylene and
hexene.

4. The film of claim 1 in which said linear low
density polyethylene is a copolymer of ethylene and
octene.

5. An extruded film according to claim 1 in which
the polyvinylidene fluoride homopolymer has a weight
average molecular weight of from 20,000 to 1,000,000.

6. An extruded film according to claim 1 in which
the polyvinylidene fluoride homopolymer has a weight
average molecular weight of from 40,000 to 500,000.

7. An extruded film according to any one of claims
1-6 wherein the linear low density polyethylene has a
density of from 0.91 to 0.93.

8. An extruded film according to claim 1 or claim
2 wherein said linear low density polyethylene is an
ethylene-butene copolymer having a density of 0.918 and a

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melt index of 1, and wherein said polyvinylidene fluoride
has a weight average molecular weight of about 50,000.

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Description

E~iRDnPlLE ELEND6 OF P3IYE3NYIENE
AND FIINS T9EREOF
Linear ethylene polymers such a linear low density
polyethylenes (LLDPE) are widely used in the extrusion of
films because of their superior properties when ccmpqred
with high pressure polyethylene (LDPE). However, there are
persistent prcblems in the ocmmercial exploitation of mTnpE
resins due to difficulties in extrusion. For example, high
back pressure and torque due to extremely high shear
viscosity of the linear ethylene polymer axe encountered.
rurthermore, the extruded films exhibit surface distortion
relatj~d to m~lt fracture. Accordingly, much effort has
been devoted to finding additives, modifying extrusion
conditions and changing die materials in order to alleviate
some of the problems. For example, U.S. Patent 3,125,547
discloses the use of, i r alia, hexafluoropropylene-
vinylidene fluoride oopolymer as a film processing aid.
m is invention relates to the use of a semi-
crys~alline polymer of vinylidene fluoride, for example,
polyvinylidene fluoride, which impruves the extrusion
characteristics of linear ethylene polymers by reducing
melt fracture and head pressure, and results in a film
thereof having exoellent anti-blocking characteristics.
According to the present invention, there is prcvided
an extruded film ocmprising:
(1) a linear low density polyethylene, viz, a linear
oopolymer of ethylene and a higher olefin oontain mg 4 to
10 carbon atoms, having a density of 0.90 to 0.94; and
(2) 0.02 to 2 weight percent of polyvinylidene
fluoride hamopolymer. & id film has reduoed blocXing
oompqred to a film of the same oopolymer of ethylene
containing the same weiqht of hexafluoropropylene-
vinylidene fluoride copolymer.
m e linear ethylene polymers (i) which are suitable
for use in this invention are kncwn materials which are
widely commercially available. me preparation of suitable
polymers is described in U.S. Patent 4,076,698. Suitable
polymers are generally prepared
,

lZ~3a1~i7

F-4092-L 2

under low pressure conditions using Ziegler-Natta catalysts or
chromium oxide catalysts. The linear polymers are either
homopolymers of ethylene or copolymers of ethylene and alpha-olefins
containing from 4 to lO carbon atoms such as butene, hexene or
octene. This invention is particularly concerned with linear low
density polyethylenes which are copolymers as aforesaid and having a
density between 0.90 and 0.94, preferably between O.9l and 0.93.
The semicrystalline polymer of vinylidene fluoride (ii) is
preferably polyvinylidene fluoride homopolymer and should have melt
flow characteristics similar to that of the linear polyethylene
polymer so that it can be easily dispersed in the polyethylene. The
weight average molecular weight of (ii) should be in the range of
20,000 to l,000,000, preferably between 40,000 to 500,000.
Desirably, (ii) should be present in an amount from 0.02 to 2
percent by weight.
The semicrystalline polymer (ii) can be blended with the
linear ethylene polymer in any suitable manner. It has been found
to be advantageous to prepare a masterbatch containing the linear
ethylene polymer (i) which is rich in the semicrystalline polymer
(ii) for blending with additional ethylene polymer to achieve the
desired concentration of the additives.
This invention also provides an extruded film comprlsing a
composition as herein defined.
The following non-limiting Examples illustrate the
invention.

EXAMPLES 1 to 6

The linear low density polyethylene (LLDPE) used in all of
the Examples was an ethylene-butene copolymer having a density of
O.9l~ and a melt index of l which exhibits severe melt fracture
under commercial narrow die gap extrusion conditions. The
polyvinylidene fluoride used in the examples had a weight average
molecular weight of about 50,000 (Kynar 720 obtained from the
~.

3(~77

F-4092-L

Pennwalt Corporation). The hexafluoropropylene-vinylidene fluoride
polymer used in the control examples was Viton A from E.I. du Pont
de Nemours and Company.
Blocking force of the films containing various amounts of
the fluoropolymer was measured according to the ASTM method (D-3354)
on five samples of each film, averaged and reported in the Table
below.

T _
(Control)
lo Grams Grams
Blocking Force Blocking Force
Example Wt. % (KYNAR) (VITO~ A)
1 2.0 27.9 94.7
2 1.0 55.9 101
3 0.5 85.5 108
4 .25 115 120
0.1 119 130
6 0.04 130 133

All samples exhibited the absence of melt fracture which is
obtained when the same polymer is extruded under the same conditions
without fluorocarbon polymer but the"Kynar"(polyvinylidene fluoride)
examples give films having less blocking than the Viton counterparts.


("KYNAR" and "VITON" are registered Trademarks.)



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