(description)
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
AND
THE PATENTS RULES, 2003
COMPLETE
SPECIFICATION

(See Section 10; rule 13)
TITLE OF THE INVENTION
“POLYMER FILMS AND THEIR PRODUCTION AND USE”
APPLICANT
The Supreme Industries Limited of Solitaire Corporate Park,
Building No. 11, 6th Floor, Chakala, Andheri East,
Mumbai 400 093, India; Indian

The following specification particularly describes
the invention and the manner
in which it is to be performed
The invention relates to a new use of embossment to improve the
stretchability of a polymer film.
Polymer film is very often used in a form, in which it has been subjected
5 to uniaxial or biaxial stretching carried out in solid state. The uniaxial stretching
may be in the machine direction (m.d.) or in the transverse direction (t.d.), and
the biaxial stretching may be by one or more steps of m.d. stretching and one or
more steps of t.d. stretching, or by combined m.d. and t.d. stretching. Such
oriented film is e.g. used for manufacture of garbage bags and shopping bags,
10 as a tarpaulin substitute and as roof cover. The film to become stretched may
be a blown extruded film, or may be formed from a flat extrusion die, in both
cases either while it is in molten or in dissolved state. If blown film is used, it is
flattened before the stretching. These processes are very well known. A
particular use of m.d. and/or t.d. oriented film is in the manufacture of "cross15 laminates", i.e. polymer laminates which in analogy with plywood exhibit crisscrossing molecular orientation. This important use shall be further explained in
connection with the description of a sub-claim. In existing technology, it has
always been necessary to carry out the said stretching at a temperature rather
close to the melting range of the polymer and in a stretch ratio quite close to the
20 point of rupture.
The inventor has found it interesting to explore if it would be possible to
modify the stretching technology in a way which would allow use of lower
stretching temperatures and/or lower stretch ratios, and thereby create different
and interesting properties for each end product. The example in the present
25 description indicates what has been achieved. It is also likely, although not yet
proven, that the present invention will permit stretching of film in higher gauges
than those which have been achieved before.
In mechanical technology, it is well known that a spot-formed defect in a
metal plate tends to develop linearly if the plate gets under a sufficient one30 directional stress. This development takes place under an angle of 45 degrees
to the direction of stress. Similarly, the inventor has found that a small defect in
2
a practically unoriented plastic film, e.g. a small air bubble, tends to develop into
a thin, short, angular line when the film comes under a sufficient tension.
In the present invention, this phenomenon is utilized for improved
orientation of a polymer film, formed form molten, dispersed or dissolved state.
5 As a start of this orientation process, the film becomes embossed in a pattern of
closely spaced dots or thin short lines to become oriented within these
embossments. Thereafter, the orientation process is continued in one or more
steps by m.d. stretching, t.d. stretching or combined m.d. and t.d. stretching,
such that the embossed and oriented dots or lines gradually grow. The
10 orientation process is carried out to the extent that essentially the entire film
becomes oriented.
For most applications, the high molecular weight polymer mainly
consists of polyolefin, polyamide, polyester, polyvinylidene chloride, or a
biodegradable polymer.
15 Depending on the application of the final product, the embossment may
be carried out in one, two or more steps.
Further re the embossment, the distance between any adjacent dots or
short lines is preferably shorter than 50 mm, more preferably shorter than 30
mm, and still more preferably shorter than 10 mm. This refers to a slack state
20 immediately prior to the continued stretching.
When two or more steps of embossment are carried out, it may be
advantageous to form a pattern, in which embossed lines cross each other or
form zig-zag.
Two films may become embossed simultaneously, while one is arranged
25 on top of the other.
The embossment and subsequent stretching may be carried out on a
lay-flat tube. In this case, and when two films are embossed simultaneously,
3
one on top of the other, the embossment is preferably carried out first from one
outer surface, and then from the other outer surface.
The film to become embossed and stretched, may have started as a
tubular film extruded from a circular die. Then the molten or semi-molten tubular
5 film in the state of draw-down is preferably blown in a ratio no less than 1,1:1,
preferably no less than 1,2:1, and more preferably no less than 1,3:1.
I also claim any set of apparatus, which is suitable for carrying out any
embodiment of the method described above, and any polymer product produced
by any of the embodiments. In this connection, a particular interesting product is
10 the so-called "cross-laminate", which is a film-analogy to plywood. It can be
defined as a film laminate comprising at least two films which each either is
uniaxially, or is unbalanced biaxially oriented, and are laminated in such manner,
that the uniaxial or unbalanced biaxial directions in different films cross each
other. Most practical, an m.d. oriented tubular film is cut on bias to form an
15 obliquely oriented film, which thereafter is continuously laminated with a similarly
made obliquely oriented film, turned such that the directions of orientation cross
each other. The first disclosure of such cross-lamination is GB816607A (OleBendt Rasmussen), which claims priority from 1954. A particularly practical way
of carrying out such process and apparatus for this are known from US5,248,366
20 and US5,361,469 (both Ole-Bendt Rasmussen and priority from 1988).
For some end-uses of the embossed and stretched film, a corrugated
look of the film may be advantageous, but for some uses a plain look may be
preferable. In such cases, the depth of the original embossment must be
carefully adapted such that the embossments in the final product become
25 practically invisible when the film is studied with the naked eye, at a distance of
about 100 cm.
The process, apparatus and product shall now be described in further
detail with references to the flow-sheet fig. 1 and the photo fig. 2, the latter
showing a film in relaxed state immediately after the embossment and directly
30 following m.d. stretching in ratio 1,5:1. The embossment was in the form of
4
round dots. The distance between adjacent dots on the roller was 20 mm in
both t.d. and m.d. When making the photo, the film was placed between
crossing polarization filters, and light was sent through the assemblage.
In fig. 1, the basically unoriented film (or assemblage of two, non5 bonded films) becomes pleated in a low ratio while kept under m.d. tension.
This step is optional, but preferable. In the next step, the film becomes
embossed between a he-shaped and a she-shaped embossment roller. While
the film leaves these rollers it is m.d. stretched in a low ratio. This stretching is
also optional, but preferable. After this follows a process of deeper pleating by
10 conventional means (known from conventional m.d. stretching processes) and
final m.d. stretching, or alternatively (without any pleating) either t.d. or biaxial
stretching. A biaxial stretching can take place in three different ways, namely a)
first m.d. stretching, then t.d. stretching in a tenter-frame; b) opposite of a); and
c) combined m.d. and t.d. stretching in a special tenter-frame. Finally, the
15 oriented film is brought to relax and to some extent contract in an oven heated to
a temperature near the melting range of the polymer, otherwise it will gradually
shrink during storage and use.
In fig. 2, the vertical direction represents the m.d. of the embossed and
directly thereafter mildly stretched film. The dots have developed and formed
20 lines, which in this experiment have become continuous. That is due to the short
distance between the dots. Such fine and even pattern facilitates the final
stretching, but makes the embossment rollers expensive, and as it appears from
the main claim, the invention has a broader scope re the form and distribution of
the embossments.
5
WE CLAIM
1. A process to orient a high molecular weight polymer film, formed from
molten, dispersed or dissolved state, characterised in that as a start of this
orientation process the film becomes embossed in a pattern of closely spaced
5 dots or thin short lines, thereby becoming oriented within these embossments,
whereafter the orientation process is continued in one or more steps by m.d.
stretching, t.d. stretching, or combined m.d. and t.d. stretching, whereby the
embossed and oriented dots or lines gradually grow and develop until essentially
the entire film has become oriented.
10 2. A process according to claim 1, characterised in that the high molecular
weight polymer mainly consists of polyolefin, polyamide, polyester,
polyvinylidene chloride, or a biodegradable polymer.
3. A process according to claim 1 or claim 2, characterised by at least two
such steps of embossment.
15 4. A process according to claim 1, 2 or 3, characterised in that as
measured in slack state immediately prior to the continued stretching, the
distance between any adjacent dots or short lines, is shorter than 50 mm.
5. A process according to claim 4, characterised in that these distances
are shorter than 30 mm, preferably shorter than 10 mm.
20 6. A process according to claim 3, characterised in that there is formed a pattern
of embossed lines, which cross each other, or form a zig-zag pattern.
7. A process according to any of the preceding claims, characterised in
that two films become embossed simultaneously, while one is arranged on top of
the other.
25 8. A process according to any of the claims 1-6, characterised in that the
process is carried out on a lay-flat tubular film.
6
9. A process according to claim 6, 7 or 8, characterised in that the
embossment is carried out, first from one outer surface, and then from the other
outer surface.
10. A process according to any of the preceding claims, characterised in
5 that the film originally was a tubular film extruded from a circular die, and during
draw-down the molten or semi-molten tubular film is blown in a ratio no less than
1,1:1, preferably no less than 1,2:1, and more preferably no less than 1,3:1.
11. Any set of apparatus suitable for carrying out any of the claims 1-10.
12. Any polymer film product, including cross-laminates, manufactured
10 under use of any of the claims 1-10