ORIENTED HDPE LAMINATES FOR EASY DIRECTIONAL OPENING

STRATIFIES ORIENTES D'HDPE DONNANT UNE OUVERTURE DIRECTIONNELLE FACILE

English Abstract

This invention provides oriented plastics film packaging which has easy
directional control of opening and is reclosable. One aspect of the invention
is a laminate which comprises: (i) a film of high density polyethylene
laminated to (ii) an oriented web wherein (i) is biaxially oriented such that
the ratio of the deformation ratio in the transverse direction to the
deformation ratio in the machine direction is greater than 1.

French Abstract

L'invention concerne un emballage à couches plastiques orientées qui procure une bonne maîtrise directionnelle d'ouverture et peut se refermer. Un aspect de l'invention concerne un stratifié comprenant: (i) une couche d'un polyéthylène à haute densité (HPDE) laiminée sur (ii) une bande orientée. Cette couche présente une orientation biaxiale telle que le rapport entre le rapport de déformation transversale et celui de la déformation intervenant dans le sens de la machine dépasse 1.

Claims

Claims
1. A laminate which comprises:
(i) a film of high density polyethylene laminated to
(ii) an oriented web
wherein (i) is biaxially oriented such that the ratio
of the deformation ratio in the transverse direction to
the deformation ratio in the machine direction is greater
than 1.
2. A laminate according to claim 1 wherein the
deformation ratio in the transverse direction is from 6 to
12 while the deformation ratio in the machine direction is
from 1.1 to 2.
3. A laminate according to claim 1 wherein the high
density polyethylene has a density of at least 0.94 g/cm3.
4. A laminate according to claim 1 wherein the high
density polyethylene has a melt index from greater than
0.5 to 2Ø
5. A laminate according to claim 1 wherein (ii)
comprises a biaxially oriented plastic film.
6. A laminate according to claim 5 wherein the
oriented plastic film of (ii) comprises an olefin polymer.
7. A laminate according to claim 6 wherein the
olefin polymer is polypropylene.
8. A laminate according to claim 1 which is
fabricated into a bag.

9. Method for manufacturing a laminate film
comprising high density polyethylene film which comprises
biaxially orienting said high density polyethylene film
such that the ratio of the deformation ratio in the
transverse direction to the deformation ratio in the
machine direction is greater than 1, and laminating said
biaxially oriented high density polyethylene film to an
oriented web.
10. The method of claim 9 wherein the deformation
ratio in the transverse direction is from 6 to 12 while
the deformation ratio in the machine direction is from 1.1
to 2.
11. The method of claim 9 wherein the high density
polyethylene has a density of at least 0.94 g/cm3.
12. The method of claim 9 wherein the high density
polyethylene has a melt index from greater than 0.5 to
2Ø
13. The method of claim 9 wherein the oriented web
comprises a biaxially oriented plastic film.
14. The method of claim 13 wherein the oriented
plastic film of the oriented web comprises an olefin
polymer.
15. The method of claim 14 wherein the olefin
polymer of the oriented web is polypropylene.

Description

w 096/ososl 2 ! ~ 4 7 6 7 pcTrus9slloll3
"ORIENTED HDPE LAMINATES FOR EASY DIRECTIONAL OPENING"
This invention relates to oriented high density
; polyethylene ( HDPE ) laminates; more particularly, the
present invention relates to such laminates used to
fabricate bags which possess both easy directional opening
and reclosability.
Oriented plastics films currently enjoy a substantial
share of the packaging market, especially of perishable
goods such as comestibles. However, bags made with such
films on vertical form, fill and seal (VFFS) and
horizontal form, fill and seal (HFFS) packaging machines
have hermetic seals; and these seals often present the
consumer with difficulty of access to the product.
Attempts to overcome this difficulty include precut
systems at the top transverse direction ( TD ) seal which
allow the consumer to initiate a tear in the package; but
often with biaxially oriented film, the propagation of the
tear is uncontrolled and results in destruction of the
bag; jetti~on of product; and consumer dissatisfaction.
Other attempts include tear tape systems which can give a
measure of directional control to the propagation of the
tear but still result in bag destruction; furthermore, it
is often the consumer's experience that the tape itself
ruptures.
This invention seeks to provide oriented plastics
film packaging which not only provides the consumer with
easy directional control of opening but also is
reclosable.
Accordingly, therefore, to one aspect of the present
invention there is provided a laminate which comprises:
(i) a film of high density polyethylene laminated to
(ii) an oriented web
wherein (i) is bi A~i A lly oriented such that the ratio of
the deformation ratio in the transverse direction (DRTD)

WO96/05051 2 1 9 4 7 6 7 PCT~S95/10113
to the deformation ratio in the machine direction (DRMD)
is greater than l.
In accordance with a further aspect of this
invention, there is also provided the use of a film of
high density polyethylene which is biaxially oriented such
that the ratio of the deformation ratio in the transverse
direction (DRTD) to the deformation ratio in the machine
direction (DRMD) is greater than l, laminated to an
oriented web, to provide propagation control along the
transverse direction of the high density polyethylene.
The biaxially oriented high density polyethylene
films used in the laminates of this invention are prepared
using high density polyethylene (HDPE) having a density of
at least 0.94, preferably at least 0.96 g/cm3. The film
can be composed exclusively of a single HDPE resin, a
mixture of HDPE resins, or of HDPE cont~ining up to lO
weight percent microcrystalline wax. The mixture of HDPE
resins gives better processing characteristics in the
extruder by reducing extruder torque. Films made with
either a blend of HDPE resins or with microcrystalline wax
reduce splittiness of the film which manifests itself as
the tendency of the film to break in the TD during
operation on VFFS machinery.
The blends of HDPE polymers can comprise two or more
polymers all of which preferably have densities of at
least 0.96. Blends of HDPE polymers advantageously
comprise a major proportion of HDPE having a melt index of
0.6 to l.2 and one or more polymers having a different
melt index. Terblends have been found particularly
desirable. Suitable terblends generally comprise 50 to 98
weight percent, preferably 84 to 96 weight percent, of
HDPE having a density of 0.96 g/cm3 or higher and a melt
index of greater than 0.5 to 2.0; l to 25 weight percent,
preferably 3 to 8 weight percent, of HDPE having a density
of 0.96 g/cm3 or greater and a melt index of O.l to 0.5;
and l to 25 weight percent, preferably 3 to 8 weight

WO96/05051 ~ 9 4 1 61 PCT~S95/10113
percent, of HDPE having a density of 0.96 g/cm3 or higher
and a melt index of greater than 2 to 8. Preferably, the
~econd and third HDPE polymers (which are minor
components) are present in about equal amounts.
It is highly desirable that the biaxially oriented
HDPE films used in the laminates of this invention be
provided with a heat seal layer. The heat seal layer can
be applied in the known manner to the HDPE, for example by
coating or coextrusion before orientation or by coating
the HDPE after one or both of the biaxial orientation
operations.
The heat seal layer can be any of the conventional
material used for this purpose in conjunction with
polyolefin films particularly polyethylene films. For
example ethylene-vinyl acetate copolymers or ethylene-
methacrylic acid salt ionomers (available from DuPont as
~Surlyn") can be used. Films in which the heat seal layer
is an ethylene-methacrylic acid salt ionomer have been
found to be particularly useful in preparing films which
are suitable for VFFS applications. The heat seal layer
can comprise the heat seal resin as such or can include
small amounts of other materials. For example, the
relatively costly Surlyn ionomer can be mixed with small
amounts of less costly materials such as low density
polyethylene.
The HDPE films of this invention can include other
polymer layers in addition to or instead of the heat seal
layer, for example polymers having desirable barrier
properties for gases such as oxygen. Examples include
polymers of vinylidene chloride.
The degree of orientation of the HDPE films is an
important aspect of this invention inasmuch as the proper
degree of orientation provides desirable physical
properties, good water vapor transmission (WVTR)
characteristics and dead-fold. For example, it has been
determined that the films of this invention having a

W096/OS051 2 t ~ 4 7 6 7 PCT~S95/10113
thickness of 1.0 to 1.2 mils will have acceptable WVTR of
less than 0.28 g-mil/100 in2/24 hr/1 atm (less than 4.34 x
10-4 g-mil/cm2/24 hr/l atm).
In the usual manner the film is heated to its
orientation temperature and first subjected to MD
orientation between two sets of nip rolls, the second
rotating at a greater speed than the first in an amount
equal to the desired draw ratio. Then the film is TD
oriented by heating and subjected it to transverse
stretching in a tenter frame. Typically, MD orientation
is conducted at 60~ to 120~C and TD orientation at 100~ to
145~C. The preferred deformation ratios are from 1.1 to
2, suitably from 1.18 to 1.25 in the MD and from 6 to 12
in the TD.
The oriented web (ii) may comprise an oriented
plastics film or paper, preferably a biaxially oriented
plastics film. The film may suitably comprise an olefin
polymer, especially polypropylene.
The web may be formed and laminated to the biaxially
oriented film (ii) in any known manner. The laminate may
then be formed with a bag with conventional VFFS or HFFS
machinery.
It is found that when utilizing a laminate in
accordance with this invention in the fabrication of bags
then, whatever the present system used, the propagation of
the tear is always in the TD. This provides not only
control of opening but also enables the consumer to
utilize the lower tear edge as a pouring lip.
Furthermore, the dead-fold of the oriented HDPE enables,
simply by twisting or folding, the bag to be reclosed.
None of these advantages is present unless the HDPE is
laminated in accordance with this invention.
The following Examples illustrate the invention.
Laminates were made, both in accordance with the present
invention and by way of comparison, on a pilot coater.
Bags were then produced on a VFFS machine to evaluate the

WO 96/05051 2 1 9 4 7 6 7 PCT/US95/10113
directional tear and reclosability. The results are shown
in the following Table. The following ranking was used:
E : excellent
G : good
M : medium
F : fair
B : bad

Wos6/ososl 2 1 ~ 4 7 6 7 PCT~S95/10113
TABLE
Directional Reclosability
Laminates Tear TwistFolding
12 PET/30 HDPE E G M
12 Pet/30 LLDPE F F B
20 PP/30 HDPE~ E G M
20 PP/30 LLDPE B B B
30 PP/30 HDPE M M F
30 PP/30 LLDPE B B B
12 PA/30 HDPE E G M
12 PA/30 LLDPE M B B
40 g Paper/30 HDPE E E G
40 g Paper/30 LLDPE B G M
30 PP/ 30 PP B B B
40 PP B B B
where:
PET represents polyethylene terephthalate
HDPE represents biaxially oriented HDPE
PP represents biaxially oriented polypropylene
LLDPE represents linear low density polyethylene
PA represents oriented nylon
40g Paper represents paper having a weight of 40 g
per sq. metre
DRTD = 8.0 and DRMD = 1.18