U.S. patent application number 11/063029 was filed with the patent office on 2005-10-27 for multilayer heat shrinkable film comprising styrene polymer or a blend of styrene polymers.
Invention is credited to Roussos, George.
Application Number | 20050235611 11/063029 |
Document ID | / |
Family ID | 34707354 |
Filed Date | 2005-10-27 |
United States Patent
Application |
20050235611 |
Kind Code |
A1 |
Roussos, George |
October 27, 2005 |
Multilayer heat shrinkable film comprising styrene polymer or a
blend of styrene polymers
Abstract
The present invention provides a multilayer heat shrinkable film
incorporating an oxygen barrier material and layer comprising a
styrene polymer or blend of styrene polymers, where the shrinkage
of the film in at least one of MD, TD is at least 30% at 90.degree.
C. The invention is further directed to a method of manufacturing a
bag from said multilayer heat shrinkable film.
Inventors: |
Roussos, George; (Athens,
GR) |
Correspondence
Address: |
MOORE & VAN ALLEN PLLC
P.O. BOX 13706
Research Triangle Park
NC
27709
US
|
Family ID: |
34707354 |
Appl. No.: |
11/063029 |
Filed: |
February 22, 2005 |
Current U.S.
Class: |
53/455 ; 428/335;
428/339; 428/347; 428/474.4; 428/500; 428/522; 428/523 |
Current CPC
Class: |
B29K 2025/00 20130101;
B32B 2250/05 20130101; B32B 2270/00 20130101; B32B 27/30 20130101;
B32B 2307/746 20130101; B32B 2333/08 20130101; B32B 2309/105
20130101; B32B 2250/24 20130101; Y10T 428/2826 20150115; B32B
2325/00 20130101; B32B 7/12 20130101; B65D 33/00 20130101; B32B
27/327 20130101; B32B 2307/31 20130101; B32B 27/302 20130101; Y10T
428/31855 20150401; Y10T 428/31935 20150401; B32B 2307/736
20130101; B32B 2323/046 20130101; B32B 27/308 20130101; B32B 27/304
20130101; B32B 2553/00 20130101; B32B 27/16 20130101; Y10T
428/31938 20150401; B65D 75/002 20130101; Y10T 428/31725 20150401;
B32B 27/34 20130101; Y10T 428/24975 20150115; Y10T 428/265
20150115; Y10T 428/2495 20150115; B32B 27/08 20130101; Y10T
428/24992 20150115; B32B 2439/70 20130101; B32B 27/32 20130101;
B32B 27/18 20130101; B32B 2307/7244 20130101; B32B 2377/00
20130101; Y10T 428/1328 20150115; B32B 2439/06 20130101; B29C
61/003 20130101; Y10T 428/269 20150115; B32B 27/306 20130101; B32B
2327/00 20130101; Y10T 428/264 20150115; B29L 2009/00 20130101;
Y10T 428/2817 20150115; B32B 2439/46 20130101; Y10T 428/31917
20150401 |
Class at
Publication: |
053/455 ;
428/500; 428/522; 428/523; 428/347; 428/474.4; 428/335;
428/339 |
International
Class: |
B65B 043/04; B32B
027/34; B32B 027/30; B32B 027/32 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2004 |
EP |
04 003 934.9 |
Claims
1. A multilayer heat shrinkable film comprising at least a) a layer
comprising an oxygen barrier material, and b) a layer comprising a
styrene polymer or a blend of styrene polymers, where the film has
a machine direction and a transverse direction and the shrinkage of
the film in at least one of the machine direction or the transverse
direction is at least 30% at 90.degree. C.
2. The multilayer heat shrinkable film of claim 1, wherein a layer
of the multilaver film is an outer layer and the layer comprising
the styrene polymer or the blend of styrene polymers is the outer
layer of the film.
3. The multilayer heat shrinkable film of claim 1, wherein between
the layer comprising the styrene polymer or blend of styrene
polymers and the barrier layer a bonding layer exists.
4. The multilayer heat shrinkable film of claim 3, wherein the
bonding layer contains ethylene ester copolymers or ethylene alpha
olefin copolymers.
5. The multilayer heat shrinkable film of claim 1, wherein the
styrene polymer or the blend of styrene polymers is chosen from one
or more of a styrene homopolymer or copolymer or terpolymer.
6. The multilayer heat shrinkable film of claim 1, wherein at least
one layer comprises a cycloolefin copolymer or a blend of
cycloolefin copolymer and alpha olefin copolymer.
7. The multilayer heat shrinkable film of claim 1, wherein the film
additionally contains a heat sealable inner layer.
8. The multilayer heat shrinkable film of claim 7, wherein the heat
sealable inner layer comprises a heat sealable thermoplastic
polymer or polymer blend.
9. The multilayer heat shrinkable film of claim 8, wherein the heat
sealable inner layer comprises alpha olefins.
10. The multilayer heat shrinkable film of claim 8, wherein the
heat sealable inner layer comprises a styrene copolymer or
polypropylene, ethylene-propylene copolymer or an ionomer.
11. The multilayer heat shrinkable film of claim 2, wherein the
outer layer comprises a styrene copolymer in a blend with a slip
agent.
12. The multilayer heat shrinkable film of claim 1, wherein the
styrene copolymer is one or more of SBC (styrene butadiene
copolymers), SBS copolymers, SIS copolymers, SEBS copolymers,
Ethylene Styrene interpolymers.
13. The multilayer heat shrinkable film of claim 1, wherein the
styrene content in one or more of the styrene polymer, copolymer or
terpolymer is more than 50% by weight.
14. The multilayer heat shrinkable film of claim 1, wherein the
oxygen transmission rate through the entire multilayer film is
below about 20 cc/l m.sup.2/24 hrs/atm.
15. The multilayer heat shrinkable film of claim 1, wherein the
oxygen barrier layer comprises polyamides (Nylon), hydrolyzed
ethylene vinyl acetate copolymer (EVOH) or a vinylidene
copolymer.
16. The multilayer heat shrinkable film of claim 7, wherein the
thickness of the heat sealable inner layer is between about 0.4
mils and about 2.0 mils.
17. The multilayer heat shrinkable film of claim 1, wherein the
barrier layer thickness is between about 0.1 mils to about 0.5
mils.
18. The multilayer heat shrinkable film of claim 1, wherein one or
more of the layers of the film additionally contain one or more
film additives.
19. The multilayer heat shrinkable film of claim 1, wherein the
heat shrinkable multilayer film is in the form of a tubular
article, flat sheets or bag.
20. The multilayer heat shrinkable film of claim 1, wherein the
multilayer heat shrinkable film is irradiated.
21. The multilayer heat shrinkable film of claim 1, which comprises
the following components: a) an outer layer of a styrene amorphous
copolymer; b) an adjacent layer of a blend of EMA copolymer, EVA
copolymer and metallocene LLDPE; c) a barrier core layer comprising
PVDC copolymer; d) an adjacent layer of EVA copolymer or EMA
copolymer, EVA copolymer and metallocene LLDPE; and e) an inner
sealing layer comprising EVA, VLDPE, or a plastomer or a blend
thereof.
22. The multilayer heat shrinkable film of claim 9, wherein the
alpha olefin is a member of the polyethylene family.
23. The multilayer heat shrinkable film of claim 9, wherein the
alpha olefin is selected from the group consisting of linear
low-density polyethylene (LLDPE), very low and ultra low density
polyethylene (VLDPE and ULDPE respectively), plastomers and blends
and copolymers thereof.
24. The multilayer heat shrinkable film of claim 8 wherein the heat
sealable inner layer comprises a cycloolefin copolymer or a blend
of a cycloolefin copolymer and alpha olefin copolymer, or ethylene
vinyl acetate, plastomers, copolymers or blends thereof.
25. A method for manufacturing a bag from a multilayer shrinkable
film of claim 1, comprising the steps of: a) forming a bag, in
which the inner layer of the film forms the inside portion of the
bag while the outer layer of the film forms the outside portion of
the bag, wherein said film is the multilayer heat shrinkable film
of claim 1; b) inserting a good to be packaged into the bag; and c)
sealing the bag by hot bar or impulse sealing.
26. The multilayer heat shrinkable film of claim 5, wherein the
styrene content in one or more of the styrene polymer, copolymer or
terpolymer is more than 50% by weight.
27. The multilayer heat shrinkable film of claim 15, wherein the
vinylidene copolymer comprises one or more of vinylidene
chloride-vinyl chloride (PVDC) or vinylidene chloride-methyl
acrylate copolymer (MA-VDC).
28. The multilayer heat shrinkable film of claim 18, wherein the
one or more film additives comprise one or more of slip agents,
antiblocking agents, colorants, odor inhibitors or oxygen
inhibitors.
Description
FIELD OF THE INVENTION
[0001] This invention relates to multilayer heat shrinkable
films.
[0002] This invention has particular application to such films for
use in packaging or foods such as meat, poultry and the like.
However, it is envisaged that films in accordance with the present
invention may find use in other packaging applications such as
packaging for curable putties and sealants and for various types of
respiring and non respiring cheese.
BACKGROUND OF THE INVENTION
[0003] Primal meat cuts are generally smaller than a side of beef,
but larger than the ultimate cut sold to the retail consumer.
Primal cuts are prepared at the slaughter house and shipped to
retail meat stores or restaurants where they are butchered into
smaller cuts of meat commonly referred to as sub-primal meat cuts.
Sub-primal cuts, however, may also be prepared at the
slaughterhouse.
[0004] Primal and sub-primal cuts are packaged to minimize air
(i.e. oxygen) exposure and prevent meat spoilage and discoloration
during shipping and handling. One common way to package primal and
sub-primal cuts and protect them from the adverse effects of air is
to shrink package the cuts in a film having good oxygen barrier
properties. For example, a multilayer film having a barrier layer
containing polyvinylidene chloride (PVDC) is a well-known packaging
material. PVDC is known to have excellent oxygen barrier
properties. The other layers of the multilayer film function to
protect the PVDC layer and provide the requisite low temperature
and abrasion resistance properties, which the PVDC layer lacks.
There are other types of biaxially oriented heat shrinkable
multilayer films, which do not require oxygen barrier properties,
for example films to be used for shrink wrapping poultry.
[0005] Shrinkage properties may be produced in a film by biaxially
stretching the film in the machine and transverse direction. The
resulting film will heat shrink within a specified range of
percentages such as from about 20 to about 50 percent at about
90.degree. C. Preferably the shrinkage should be more than 30
percent in at least one of machine and transverse directions at
90.degree. C.
[0006] A multilayer heat shrinkable film may also be formed into
packaging bags. Bags are generally made by transversely sealing a
tubular stock of multilayer film and cutting or splitting the tube,
or by superimposing flat sheets of multilayer film and sealing on
three sides, or by end folding flat sheets and sealing the two
sides. A common type of seal used in manufacturing bags is a hot
bar seal. The adjacent thermoplastic layers, referred to as the
inner layers, are sealed together by application of heat and
pressure across the area to be sealed, using contact with opposing
bars of which at least one is heated to cause the adjacent layers
to fusion bond. Bags manufactured from a tube stock generally
require one hot bar seal transverse to the tube. This seal is also
referred to as a bottom seal. Once the bottom seal is applied, the
tube stock is transversely cut to form the mouth of the bag. The
strength of seals may be measured by determining the time for a
seal to fail when under certain conditions. For example, the seal
is immersed in hot water at 95.degree. C. and the hot water seal
strength ("HWSS") may be measured by a test such as that described
as the "restrained shrinkage-seal strength test" in Funderburk et
al U.S. Pat. No. 3,900,635.
[0007] Once meat or poultry is inserted into the bag, the package
is evacuated and the bag mouth must be sealed. At one time, the
standard method for sealing a bag was to fasten a clip around the
mouth of the bag. Today, impulse heat sealing techniques are
employed to seal the bag mouth. In general, a bag mouth is impulse
sealed by application of heat and pressure using opposing bars. At
least one of the bars has a covered wire or ribbon through which
electric current is passed for a very brief time period (hence the
name "impulse") to cause the adjacent film layers to fusion bond.
Following the impulse of heat the bars are cooled while continuing
to hold the bag inner surfaces together to achieve adequate seal
strength.
[0008] Irradiation of a multilayer film causes the various
irradiated layers in the film to cross-link. Under controlled
conditions, cross-linking by irradiation not only provides a higher
temperature impulse heat sealing range, but also enhances the
puncture resistance of the film. Under controlled conditions,
polymeric multilayer films can be irradiated to produce a
cross-linked product having greater puncture resistance
characteristics and other enhancements.
[0009] Three basic requirements of a commercial shrinkable
multilayer film are as follows
[0010] 1. Excellent optical properties, such as low haze and high
gloss, both before and after shrinkage. This is important for the
better aesthetic presentation of the product.
[0011] 2. Shrinkage at least as high as 30 percent in at least one
direction at temperatures about 90.degree. C. This also contributes
to better presentation of the product to the consumer (in super
markets).
[0012] 3. Easy bag making of the product (reduced scrap during bag
making). This is more easily achievable when the film is
comparatively stiff.
[0013] Prior art films typically used may have low haze and high
gloss in unshrunk configuration, but much worse optical properties
after shrinking. Alternatively, they may keep their optical
properties after shrinkage, but do not shrink enough for an
acceptable product presentation.
[0014] Therefore, it is an object of the present invention to
provide a multilayer heat shrinkable film, which optimizes the
clarity-shrinkage behaviour. It is a further object of the present
invention to render the bag making process more efficient than with
existing films.
[0015] These objects are solved by the subject-matter of the
independent claims. Preferred embodiments are set forth in the
dependent claims.
SUMMARY OF THE INVENTION
[0016] This invention in one aspect resides broadly in a multilayer
heat shrinkable film including a layer of styrene polymer or a
blend of styrene polymers and an oxygen barrier polymer layer. The
film shrinks at least 30% in at least one of machine and transverse
directions by measuring unrestrained shrink of the stretched film
at 90.degree. C. for five seconds, or equivalent shrinkage
thereof.
[0017] As used herein, the term "polymer" refers to the product of
a polymerization reaction and is inclusive of homopolymers,
copolymers, terpolymers etc.
[0018] As used herein, the term "homopolymer" is used with
reference to a polymer resulting from the polymerization of a
single monomer.
[0019] As used herein the term "copolymer" refers to polymers
formed by the polymerization reaction of at least two different
monomers.
[0020] As used herein, the term "polypropylene" refers to any
polymer comprising propylene polymerization units regardless of
whether the polymer is a homopolymer or a copolymer and further
includes blends of such homopolymers and copolymers.
[0021] As used herein the term "ethylene propylene copolymer"
refers to polypropylene copolymerized with ethylene monomer.
[0022] As used herein the phrase "ethylene alpha-olefin copolymer"
refers to such heterogeneous materials as linear low density
polyethylene (LLDPE), linear medium density polyethylene (LMDPE)
and very low and ultra low density polyethylene (VLDPE and ULDPE),
as well as homogeneous polymers such as TAFMER.TM. supplied by
Mitsui Petrochemical corporation and metallocene catalysed polymers
such as Exact materials supplied by Exxon. Other ethylene alpha
olefin copolymers such as the long chain branched homogeneous alpha
olefin copolymers available from Dow Chemical Company, known as
Affinity resins, are also included in the present invention.
Homogeneous ethylene alpha olefin copolymers with a density less
than about 0.905 are generally called plastomers.
[0023] As used herein "EVOH" refers to ethylene vinyl alcohol
copolymer.
[0024] As used herein "PVDC" refers to vinylidene chloride
homopolyers and copolymers.
[0025] As used herein, the term "polyamide" refers to high
molecular weight polymers having amide linkages along the molecular
chain and refers more specifically to synthetic polyamides such as
nylons.
[0026] As used herein, the term "barrier" is used with reference to
the ability of films to serve as barrier to oxygen or other
gases.
[0027] As used herein, the term "oriented" refers to a polymer
containing material which has been stretched at an elevated
temperature, followed by being "set" in the stretched configuration
by cooling the material while substantially retaining the stretched
dimensions.
[0028] As used herein, the phrase "heat shrinkable", "heat shrink"
and the like, refer to the tendency of a film, especially an
oriented film, to shrink upon the application of heat.
[0029] As used herein, the phrase "ethylene vinyl acetate" or EVA,
refers to a copolymer formed from ethylene and vinyl acetate
monomers, wherein the ethylene derived units in the copolymer are
present in major amounts, preferably between about 60 to about 98
percent, while the vinyl acetate derived units in the copolymer are
present in minor amounts, preferably between about 2 and 40
percent.
[0030] As used herein, the phrase "ethylene methyl acrylate", or
EMA, refers to a copolymer formed from ethylene and methyl acrylate
monomers, wherein the ethylene derived units in the copolymer are
present in major amounts, preferably between about 60 to about 98
percent, while the methyl acrylate derived units in the copolymer
are present in minor amounts, preferably between about 2 and 40
percent.
[0031] As used herein, the phrase "cycloolefin copolymer" refers to
a copolymer composed of ethylene units and/or of units comprising
an alpha olefin with a cyclic, bicyclic or multicyclic olefin.
Preferably the COC is a copolymer of ethylene and norbornene.
[0032] The styrene content in the polymers used in the present
invention is preferably more than 50 wt. % of styrene in the
styrene copolymer. Preferably, more than 60 wt. %, further
preferably more than 70%, more than 80% or even more than 90% by
weight of styrene in the styrene copolymer is used. In another
preferred embodiment a styrene homopolymer is used.
[0033] As used herein the term "ionomer" is a copolymer of ethylene
with an ethylenically unsaturated acidic monomer, for instance
acrylic or methacrylic acid. The ionomer is preferably in its
ionised form, the neutralizing cation being any suitable metal. A
well known ionomer material is Surlyn from Dupont.
DETAILED DESCRIPTION OF THE INVENTION
[0034] According to a first and main aspect, the invention provides
a multilayer heat shrinkable film comprising at least
[0035] a) a layer comprising an oxygen barrier material,
[0036] b) a layer comprising a styrene polymer or a blend of
styrene polymers,
[0037] where the shrinkage of the film in at least one of MD, TD
(machine direction, transverse direction) is at least or more than
30% at 90.degree. C.
[0038] In one preferred embodiment of the invention, the layer of
the styrene polymer or blend of styrene polymers is the outer layer
of the structure, being exposed to the environment.
[0039] In a further embodiment, between the layer of the styrene
polymer or blend of styrene polymers and the barrier layer there is
a bonding layer which may include ethylene ester copolymers or
ethylene alpha olefin copolymers.
[0040] Additionally, the multilayer heat shrinkable film of the
invention may comprise a heat sealable inner layer. The inner layer
may be made of a heat sealable thermoplastic polymer or polymer
blend. The heat sealable inner layer may be of any material
conventionally used for its heat sealing capability. Heat sealable
thermoplastic polymers are recognized by those skilled in the art
as being capable of heat sealing to themselves at a variety of
time, pressure and temperature conditions. For example, at a given
pressure either a relatively high temperature may be applied
briefly or a lower temperature may be applied for a longer period
of time to obtain similarly suitable seals. It is to be appreciated
that persons skilled in the art will be able to select sealing
parameters such as temperature, pressure and time of application
that depend upon such factors as the type of heat sealing equipment
used. The term "inner layer" generally relates to that side of the
multilayer heat shrinkable film, which is not exposed to the
environment in a given product form (e.g. bag), but the good to be
packaged.
[0041] This inner sealing layer may for instance be an alpha olefin
copolymer or a blend of alpha olefin copolymers, e.g. a VLDPE, EVA,
plastomer or a blend thereof. Alternatively, a styrene polymer or a
blend of styrene polymers may also be used as the inner heat
sealing layer. In another embodiment, a cycloolefin copolymer or a
blend of cycloolefin copolymer and alpha olefin copolymer may be
the inner sealing layer.
[0042] Suitable polymers and copolymers may include alpha olefins
such as members of the polyethylene family such as linear
low-density polyethylene (LLDPE); very low-density polyethylene
sometimes referred to as ultra low-density polyethylene (VLDPE and
ULDPE respectively), plastomers or blends thereof. Still other
suitable thermoplastic polymers as the heat sealable inner layer
include polypropylene, ethylene-propylene copolymer or an ionomer.
It is to be understood however that the thermoplastic polymers
mentioned herein are not intended to be an exhaustive list, but
merely exemplary.
[0043] In a preferred embodiment of the invention, the outer layer
(directly exposed to the environment) comprises a styrene copolymer
in a blend with a slip agent.
[0044] Preferred styrene polymers are polystyrene homopolymer, SBC
(styrene butadiene copolymers), SBS copolymers, SIS copolymers,
SEBS copolymers, Ethylene Styrene interpolymers and blends thereof.
Suitable materials are K RESIN from Chevron Philips Chemical,
FINACLEAR from Atofina and Styrolux from BASF. A preferred styrene
homopolymer is STYRON from Dow. In one preferred embodiment, the
styrene content of the material is more than 50% by weight. This
increases the stiffness of the material, thus making it more easy
to convert.
[0045] One functional requirement of the barrier layer may be that
together with the other layers, the oxygen transmission rate
through the entire multilayer film may be below about 20 cc/l
m.sup.2/24 hrs/atm, measured at 23 C, 75% RH. This is to avoid
spoilage of certain food products, for example meat enclosed in the
multilayer film package due to oxygen passage from the environment
through the film wall. This requirement may be satisfied by
numerous well-known barrier layer materials. For example, these may
include certain of the polyamides (Nylon), hydrolyzed ethylene
vinyl acetate copolymer (EVOH) and preferably a vinylidene
copolymer. Vinylidene chloride-vinyl chloride (PVDC) is a commonly
used copolymer but vinylidene chloride-methyl acrylate copolymer
(MA-VDC) may also be used.
[0046] The thickness of the heat sealable inner thermoplastic first
layer may be between about 0.4 mils and about 2.0 mils. Thinner
layers may not perform the described functions while thicker layers
may not appreciably improve processability of the film and may
reduce total film performance.
[0047] The barrier layer thickness may be between about 0.1 mils to
about 0.5 mils. Thinner barrier layers may not perform the intended
functions and thicker layers do not appreciably improve
performance.
[0048] Regardless of the structure of the film, one or more film
additives may be incorporated, such as slip agents, antiblock
agents, colorants, odor inhibitors, oxygen inhibitors etc. The
skilled in the art technician can be well aware of these
additives.
[0049] While the composition of the film may eliminate the need for
irradiation of the multilayer film, it is to be understood that the
multilayer heat shrinkable film in accordance with the invention
may be irradiated to further enhance puncture and temperature
resistance.
[0050] According to a preferred embodiment, the multilayer heat
shrinkable film of the invention comprises the following
components:
[0051] a) an outer layer of a styrene amorphous copolymer
[0052] b) an adjacent (bonding) layer of a blend of EMA copolymer,
EVA copolymer and metallocene LLDPE
[0053] c) a barrier core layer comprising PVDC copolymer
[0054] d) an adjacent (bonding) layer of EVA copolymer or EMA
copolymer, EVA copolymer and metallocene LLDPE
[0055] e) an inner sealing layer comprising EVA, VLDPE, or a
plastomer or a blend thereof.
[0056] The heat shrinkable multilayer film in accordance with the
present invention may be in the form of a tubular article or flat
sheets. The multilayer film may be formed into bags useful for the
packaging of meats. The multilayer film may be especially useful
for those bags manufactured by hot bar or impulse sealing, and
after meat is inserted therein, impulse heat sealing may be used to
seal the mouth.
[0057] One end of the bag may be heat sealed by adhesion between
contiguous inner layer surfaces in a direction transverse to the
oppositely located sidewalls of the bag. The mouth end of the bag
may be impulse heat sealable by fusion bonding between contiguous
inner layer surfaces after filling the bag with food.
[0058] A bag from the multilayer film may be manufactured such that
the inner layer forms the inside portion of the bag while the outer
layer forms the outside portion of the bag. Accordingly, the inner
layer of the tubular multilayer film may be the heat sealable
layer, which is easily sealed by hot bar sealing. Moreover, because
of the latter, the mouth of the bag may be more easily sealed by
impulse heat sealing.
[0059] Thus, according to a second aspect, the invention is
directed to a method for manufacturing a bag from a multilayer
shrinkable film as defined above, comprising the steps of:
[0060] a) forming a bag, in which the inner layer of the multilayer
heatshrinkable film as defined herein forms the inside portion of
the bag while its outer layer forms the outside portion of the
bag,
[0061] b) inserting a good to be packaged into the bag, and
[0062] c) sealing the bag by hot bar or impulse sealing.
[0063] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention pertains. All
references mentioned herein are incorporated by reference in their
entirety. In case of conflict, the present specification, including
definitions, will control. In addition, the examples are
illustrative only and not intended to be limiting.
EXAMPLES
[0064] In this series of tests, bags of the same size (400 mm
long.times.230 mm wide) and of 60 micron thickness were fabricated
from films comprising a heat sealable thermoplastic inner layer, an
adjacent layer adhered on one side to the sealable inner layer, an
oxygen barrier layer, an adjacent layer and an outer layer. The
core layer in most tests was a vinylidene chloride copolymer type
oxygen barrier. The film was the biaxially oriented heat shrinkable
type, prepared by the double or trapped bubble method as broadly
described in the aforementioned Palkhe U.S. Pat. No. 3,456,044. In
particular, all layers were simultaneously coextruded.
[0065] Certain physical properties of bags were measured by either
of the test procedures discussed below.
[0066] Shrinkage values were obtained by measuring unrestrained
shrink of the stretched film at 90.degree. C. for five seconds.
Four test specimens were cut from a given sample of the oriented
film to be tested. The specimens were cut to 10 cm in the machine
direction by 10 cm. in the transverse direction. Each specimen was
completely immersed for 5 seconds in a 90.degree. C. water bath.
The distance between the ends of the shrunken specimen was
measured. The difference in the measured distance for the shrunken
specimen and the original 10 cm was multiplied by ten to obtain the
percent of shrinkage for the specimen. The shrinkage for the four
specimens was averaged for the MD shrinkage values of the given
film sample, and the shrinkage for the four specimens was averaged
for the TD shrinkage value.
[0067] The tensile modulus compared below has been measured
according to ASTM D 882 with an Instron testing device. The optical
properties were tested according to ASTM D1003(haze) and BS
2782(gloss).
[0068] The bag making testing was done with a use of a commercial
bag making machine.
Example 1
[0069] A heat shrinkable multilayer film was produced having:
[0070] a) an outer layer of a styrene amorphous copolymer
[0071] b) an adjacent layer of a blend of EMA copolymer, EVA
copolymer and metallocene LLDPE
[0072] c) a barrier core layer
[0073] d) an adjacent layer of EVA copolymer
[0074] e) an inner sealing layer
[0075] More specifically
[0076] Outer layer: 98% S1+2% slip masterbatch, 12% of the total
structure
[0077] Adjacent layer 15% M1+15% M2+45% E1+20% LL1+5% ADDITIVES,
19% of the total structure
[0078] Barrier layer: PVDC copolymer, 11% of the total
structure
[0079] Adjacent layer: 100% E1, 12% of the total structure
[0080] Inner sealing layer: 20% E1+10% E2+32% P1+30% V1+8%
ADDITIVES, 46% of the total structure.
Example 2
[0081] A heat shrinkable multilayer film was produced having:
[0082] a) an outer layer of a styrene amorphous copolymer
[0083] b) an adjacent layer of a blend of EMA copolymer, EVA
copolymer and metallocene LLDPE
[0084] c) a barrier core layer
[0085] d) an adjacent layer of EMA copolymer, EVA copolymer and
metallocene LLDPE
[0086] e) an inner sealing layer
[0087] More Specifically
[0088] Outer layer: 98% S1+2% slip masterbatch, 12% of the total
structure
[0089] Adjacent layer 15% M1+15% M2+45% E1+20% LL1+5% ADDITIVES,
19% of the total structure
[0090] Barrier layer: PVDC copolymer, 11% of the total
structure
[0091] Adjacent layer: 15% M1+15% M2+45% E1+20% LL1+5% ADDITIVES,
12% of the total structure
[0092] Inner sealing layer: 20% E1+10% E2+32% P1+30% V2+8%
ADDITIVES, 46% of the total structure
Comparative Example 3
[0093] As a comparative example, we use a commercial product of
FLEXOPACK under the name FMX containing no styrene.
Example 4
[0094] Outer layer: 98% S1+2% slip masterbatch, 12% of the total
structure
[0095] Adjacent layer 15% M1+15% M2+45% E1+20% LL1+5% ADDITIVES,
19% of the total structure
[0096] Barrier layer: PVDC copolymer, 11% of the total
structure
[0097] Adjacent layer: 15% M1+15% M2+45% E1+20% LL1+5% ADDITIVES,
12% of the total structure
[0098] Inner sealing layer: 20% E1+10% E2+32% P1+30% P2+8%
ADDITIVES, 46% of the total structure
Example 5
[0099] Outer layer: 98% S1+2% slip masterbatch, 12% of the total
structure
[0100] Adjacent layer 15% M1+15% M2+45% E1+20% LL1+5% ADDITIVES,
19% of the total structure
[0101] Barrier layer: PVDC copolymer, 11% of the total
structure
[0102] Adjacent layer:, 15% M1+15% M2+45% E1+20% LL1+5% ADDITIVES,
12% of the total structure
[0103] Inner sealing layer: 30% E1+62% P2+8% ADDITIVES, 46% of the
total structure
Example 6
[0104] Outer layer: 98% S1+2% slip masterbatch, 12% of the total
struct6ure
[0105] Adjacent layer 15% M1+15% M2+45% E1+20% LL1+5% ADDITIVES,
19% of the total structure
[0106] Barrier layer: PVDC copolymer, 11% of the total
structure
[0107] Adjacent layer: 15% M1+15% M2+45% E1+20% LL1+5% ADDITIVES,
12% of the total structure
[0108] Inner sealing layer: 30% E1+42% P2+20% C1+8% ADDITIVES, 46%
of the total structure
[0109] The films were e-beam radiated with a dose of 4 MRAD.
1TABLE 1 SHRINKAGE COMPARISONS SHRINK- SHRINK- SHRINK- SHRINK- AGE
AGE AGE AGE SAMPLE 80 C. 85 C. 90 C. 95 C. NOTES EXAMPLE 1 28/28
39/37 50/48 55/46 EXAMPLE 2 30/30 38/35 50/47 55/47 EXAMPLE 3 30/32
38/37 49/45 55/49 EXAMPLE 4 31/31 42/40 50/50 57/52 EXAMPLE 5 27/28
37/37 50/45 55/47 EXAMPLE 6 32/32 44/44 50/50 57/55
[0110] According to TABLE 1, there is practically no difference in
the comparison of shrinkage between the three different
materials.
[0111] In the following table the optical property comparisons are
explained.
2TABLE 2 HAZE AFTER SAMPLE HAZE GLOSS SHRINKAGE NOTES EXAMPLE 1 8.2
92 30 Excellent clarity after shrink onto product EXAMPLE 2 9 92 36
Excellent clarity after shrink onto product EXAMPLE 3 10.5 81 40
Good clarity after shrink onto product EXAMPLE 4 7.5 97 25
Excellent clarity after shrink onto product EXAMPLE 5 8 95 27
Excellent clarity after shrink onto product EXAMPLE 6 11.5 94 45
Excellent clarity after shrink onto product
[0112] Measurement of tensile modulus has been also carried out,
according to ASTM D 882.
3 TABLE 3 TENSILE NOTES MODULUS DURING BAG SAMPLE MD/TD NOTES
MAKING EXAMPLE 1 210/195 stiff Very easy to convert EXAMPLE 2
239/209 stiff Very easy to convert EXAMPLE 3 173/175 soft
Convertible only with reduced machine speed. Blocks during bag
making. EXAMPLE 4 205/190 Easy to convert EXAMPLE 5 230/225 Very
easy to convert EXAMPLE 6 250/250 Very easy to convert
[0113] The resins used are explained in table 4.
4TABLE 4 Melt Melting Index Density point Type Description
Manufacturer g/10 min g/cm.sup.3 .degree. C. E1 EVA Dupont 3135 X
0.35 0.93 95 E2 EVA 1005 VN2 0.40 0.928 102 V1 VLDPE Dow Attane
1.00 0.912 122 SL 4100 P1 Plastomer Dow Affinity 1.0 0.885 74 VP
8770 PB1 Polybutylene Shell 8640 2 118 LL1 LLDPE Atofina M3410 1
0.934 123 S1 SB DK13 10 1.01 COPOLYMER M1 EMA Atofina LOTRYL 2-3.5
0.95 61 copolymer 29MAO3 M2 EMA Atofina LOTRYL 0.5 0.94 70
copolymer 24MA005 P2 Plastomer Dow Affinity 1 0.902 100 PL 1880 C1
Cycloolefin Ticona Topas 1.02 copolymer 8007
* * * * *