TITLE: Process for preparing a fibril-reinforced polyolefin film and olefin
polymer film so prepared.
European Patent Application EP0009300 A1

ABSTRACT:
A fibril reinforced olefin polymer is made of a web of
randomly-dispersed olefin polymer fibrils which are heated under an
applied pressure to form a fused polymer film having a small percentage
of unmelted fibrils therein. The film has a higher tensile strength
than a solvent cast film prepared from the same olefin polymer.

INVENTORS:
Murphy, Clarence R.
Boehme, Robert E.
Paviak, Stanley C.

APPLICATION NUMBER: EP19790301268
PUBLICATION DATE: 04/02/1980
FILING DATE: 06/29/1979

ASSIGNEE: GULF OIL CORP (US)
INTERNATIONAL CLASSES: B29C57/00; B29C43/00; B29C43/22; B29C61/00; B29D7/00; B29D7/01;
C08J5/18; (IPC1-7): D21H5/20; C08J5/18
EUROPEAN CLASSES: D21H5/20D

FOREIGN REFERENCES:
FR2128750A
FR2173928A
FR2265806A

CLAIMS:
CLAIMS:
1. A process for preparing a fibril-reinforced polyolefin compris-j.ng:
(a) forming ct web of randomly dispersed olef in polymer fibrils, (b)
heating the web to a temperature at which said fibrils melt, (c)
subjecting the web to pressure throughout step (b) so as to form a
compressed melted film, and (d) cooling the compressed melted film of
step (c) to form a self-supporting film; the olefin polymer included in
said fibrils having a weight average molecular weight of at least one
million; the duration of heating step (b) being such that a portion of
the fibrils are incompletely melted and retain their fibril identity in
the fused olefin polymer film.
2. A process according to claim l,in which the web is laid down from a
aqueous dispersion of the olefin polymer fibrils and the web is melted
by being passed through heated calender rolls.
3. A process according to claim 1 or claim 2, in which the olefin
polymer is an ethylene polymer.
4. A process according to claim 1 or claim 2, in which the olefin
polymer is a propylene polymer.
5. A process according to claim 1, substantially as hereinbefore
described.
6. An olefin polymer film whenever prepared by the process claimed in
any of clainis 1 to 5.

DESCRIPTION:
jyibri l-x' tn :o:Cc clc :£irr,oi'.er I In Olefin polymer films,
particularly ethylene polymer films, are used in commerce in large
volume. By reXsolJ O:£ their volume usage, the art is continuously
seeking (1) olefin polymer films having improved properties and (2)
more economical processes for the manufacture of olefin polymer films.
According to this invention there is provided a process for preparing a
fibril-reinforced polyolefin comprising: (a) forming a web of randomly
dispersed olefin polymer fibrils, (b) heating the web to a temperature
at which said fibrils melt, (c) subjecting the web to pressure
throughout step (b) ) so as to form a compressed melted film, and (d)
cooling the compressed melted film of step (c) to form a
self-supporting film; the olefin polymer included in said fibrils
having a weight average molecular weight of at least one million; the
duration of heating step (b) being such that a portion of the fibrils
are incompletely melted and retain their fibril identity in the fused
olefin polymer film.
Preferably the web is laid down from an aqueous dis- persion of the
olefin polymer fibrils and the web is melted by being passed through
heated calender rolls.
The olefin polymer may be a polymer of ethylene or propylene.
The olefin polymer fibrils employed in the practice of the invention
constitute a recognized class of materials knows and described in the
at. Such fibrils are prepared by precipitating an olefin polymer from
an organic solvent solutiofl thereof under conditions of high shear.
Representative U.S. patents diselasing the preparation of such fibrils
include the ol OVj f U.S. 2,933.782 U.S. 3,031,519 U.S. 3,341,242 U.S.
3,740,333 U.S. 3,743,272 U.S. 3,306,091 U.S. 3,335,014 U.S. 3,891.499
U.S. 4,010,229 U.S. 4,013,751 When examined with the nakcd eye, tho ol
ef- in polymer fibrils employed in the invention resemble In appearance
natural fibres such as cotton and. staple fibres of solution spun
polymers such as nylon and the like. When examined microscopically,
however, fibrils have grossly irregular shapes, including segments
which appear to l)e film-like in nature. See for example Fig. 4 of U.S.
3,391,499. It's believed possible that these particular physical
character- istics may play a role in the function of the olefin polymer
fibrils in the present invention.
The majority of the olefin polymer fibrils employed in the practice of
the invention are small in size, with the largest dimension not
exceeding about 10 mm. The fibrils have a large surface to weight ratio
of at least about 2 m2/gram as determined by nitrogen
absorpion/desorption methods.
The olefin polymer fibrils deployed in the invention are prepared from
an ethylene or propylene polymer having a weight average molecular
weight of at least about 1 million and preferably at least about 1.5
million. Sch polymers will have an intrinsic viscosity of at least 3.5
preferably at least 5.0, and most especially at least lC, O.
A listing of suitable olefin polymers and olefin polymer mixtures is
set forth in U.S. 4,013,751, which description is incorporated herein
by reference.
The web of randomly-dispersed olefir polymer fibrils employed in the
invention can be prepared by numerous techniques known and reported iii
t.llC art. The preferred method is to prepare a water-laid web by the
techniques knowe and used in the paper making al5t.S.
The fused film is piepaled by heating the web to a temperature above
the @el@ @ng peint of the olefin g@ly@ier and subj-'cting the veb to
pressure to compress the melted polymer to form a fused film. The
pressure required and the duration of the required heating cycle will
depend upon a multiplicity of factors including the thickness and bulk
density of the web, the melting point of the olefin polymer, and the
heat transfer charactclistics of the press surfaces.
The proper combination of t;emperature and pressure to be employed for
a given web in a particular press can be readily established through a
few routine experiments.
In pressing a given web at a fixed temperature and a fixed pressure, it
is noted that the fibrils at the surface of the web melt first. With
the passage of time, the fibrils in the interior of the web melt. If
the heating is continued for a sufficient period of time, all of the
fibrils melt and a homogeneous fused film is obtained. At intermediate
points in the heating cycle, it is noted that the film, while fused,
will contain thin fibre-like sections of unmelted fibrils. Film
containing such a structure has a tensile strength greater than solvent
cast film prepared from the olefin polymer from whIch the fibrils were
prepared.
Accordingly, the temperature, pressure and cycle time should be
controlled so that the fused film contains some incomplete- ly melted
fibrils.
A desirable feature of the invent ion is that the fused film can be
prepared at high rates of speed at low cost in a continuous process.
Tie random web of fibrils is laid down continuosly on a paper making
machine. The web then is passed over drying roll and passed through a
stack of heated calender rolls The following exarnplc is set forth to
illustrate more clearly the principles ad practice of this invention to
those skilled in the art.
Where parts or percentages are referred to, they are parts or
percentages by weight unless otherwise noted Example 1 Part A A lot of
fibrils was prepared following the procedure of Example 1 of U.S.
4,013,751. The ethylene polymer from which the fibrils were prepared
bad a weigh average molecular weight of about 1,500,000. The hydro
carbon-wet fibrils were refinc.d with 91% isopropanol to displace the
hydrocarbon. The fibrils then were filtered and pressed to expel the
maximum quantity of isopropanol.
Part B Water-laid sheets were prepared froze the fibrils of Part A
employing an experimental size paper aking machine The dried sheets had
a basis weight of about GO Ibs. per ream. An 8" x 8" sheet was pressed
for 5 minutes in a platen press under a pressure of 40,000 psig at a
plate temperature of 300 F (149 C). The resulting film was well fused
and generally transparent. When viewed in strong light, a few fine
fibres were noted in the film. The film had a tensile strength of 4203
psi..
Part C A hydrocarbon solution was prepared from the ethylene polymer
employed in Part A and a film was cast therefrom. The film had a
tensile strength of 2900 psi