U.S. patent number RE30,726 [Application Number 06/082,992] was granted by the patent office on 1981-09-01 for polymer film having linear tear properties.
This patent grant is currently assigned to Tower Products, Inc.. Invention is credited to Norman J. Otten, Eldrige H. Presnell.
United States Patent |
RE30,726 |
Otten , et al. |
September 1, 1981 |
Polymer film having linear tear properties
Abstract
Certain blends or mixtures of polyethylene and ionomer resins
are blow extruded to make a film having excellent linear tear
properties in the direction of extrusion, which property is not
found in films of either of the resins alone.
Inventors: |
Otten; Norman J. (Prospect
Heights, IL), Presnell; Eldrige H. (Round Lake, IL) |
Assignee: |
Tower Products, Inc.
(Mundelein, IL)
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Family
ID: |
27374382 |
Appl.
No.: |
06/082,992 |
Filed: |
October 9, 1979 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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486082 |
Jul 5, 1974 |
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Reissue of: |
713703 |
Aug 12, 1976 |
04098406 |
Jul 4, 1978 |
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Current U.S.
Class: |
229/205;
428/35.2; 428/516; 229/940; 264/210.1; 428/515; 428/523;
264/171.28 |
Current CPC
Class: |
B32B
27/08 (20130101); B29C 48/10 (20190201); B29C
48/21 (20190201); B29C 48/335 (20190201); B29C
48/09 (20190201); Y10T 428/31938 (20150401); Y10T
428/31909 (20150401); Y10T 428/1334 (20150115); B29C
48/08 (20190201); B29C 48/0018 (20190201); Y10T
428/31913 (20150401) |
Current International
Class: |
B29C
47/06 (20060101); B29C 47/00 (20060101); B32B
27/08 (20060101); B65D 033/00 (); B29C 017/06 ();
B32B 027/08 () |
Field of
Search: |
;525/221,201,196
;428/35,515,516,523 ;264/171,176R,512,563 ;229/DIG.5
;206/601,604 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Dixon, Jr.; William R.
Attorney, Agent or Firm: Lee, Smith & Jager
Parent Case Text
CROSS REFERENCE
This is a continuation-in-part of our copending application Ser.
No. 486,082, filed July 5, 1974 now abandoned.
Claims
What is claimed is:
1. A method of imparting linear tear properties in the direction of
extrusion to a polymer film comprising the steps of preparing a
blend of resins consisting essentially of from about 12% to about
95% ionomer resin and from about 5% to about 88% low density
polyethylene resin, and extruding said blend of resins .Iadd.at a
stretch ratio of approximately 1.5 to 1 .Iaddend.into a film.[.,.].
whereby said film exhibits linear tear properties in a direction
parallel to the direction of extrusion .Iadd.and an Elmendorf tear
strength of from 30 to 125 g. .Iaddend.
2. The method of claim 1 wherein said polyethylene resin contains
up to about 7.5% of ethylene-vinyl acetate copolymer.
3. The method of claim 1 wherein said blend of resins is blow
extruded in the form of a tube.
4. The method of claim 1 wherein the density of said polyethylene
resin is in the range of from about 0.910 to about 0.960.
5. The method of claim 1 wherein .Iadd.a polymer .Iaddend.lacking
linear tear properties selected from the group consisting of
polyethylene, polyethylene modified with vinyl acetate,
polyethylene modified with isobutylene, ionomer and an
ionomerpolyethylene blend, is coextruded with said blend of resins
to provide a coextruded film having linear tear properties in the
direction of extrusion.
6. An extruded polymer film consisting essentially of from about
12% to about 95% of ionomer and the remainder as polyethylene
having a density of from about 0.910 to about 0.960, said film
being .Iadd.extruded at a stretch ratio of approximately 1.5 to 1
and being .Iaddend.capable of being torn in substantially a
straight line in the direction of extrusion at a deviation of less
than 20.degree. from said straight line, .Iadd.said film having an
Elmendorf tear strength of from 30 to 125 g. .Iaddend. .[.
7. The film of claim 6 wherein the Elmendorf tear strength of said
film is less than 125 g..].
8. The film of claim .[.7.]. .Iadd.6 .Iaddend.wherein the Elmendorf
tear strength of said film is from about 30 to about 125 g.
9. The film of claim 6 wherein said polyethylene contains up to
about 7.5% vinyl acetate.
10. The film of claim 6 wherein said film is blow extruded.
11. The film of claim 6 wherein said film is coextruded with a
second polymer film selected from the group consisting of
polyethylene, polyethylene modified with vinyl acetate,
polyethylene modified with isobutylene, ionomer and an
ionomer-polyethylene blend.
12. A pouch composed of an extruded polymer film, said pouch having
a top edge, bottom edge and side edges, said top and bottom edges
being substantially parallel with the direction of extrusion of
said film, the film of said pouch consisting essentially of from
about 12% to about 95% ionomer with the remainder as polyethylene
having a density of 0.910 to about 0.960 and containing from about
zero to 7.5% vinyl acetate, .Iadd.the film of said pouch being
extruded at a stretch ratio of approximately 1.5 to 1 and having an
Elmendorf tear strength of from 30 to 125 g, .Iaddend.said pouch
being capable of being torn from side to side in substantially a
straight line parallel with the direction of extrusion.
13. The pouch of claim 12 wherein said film is coextruded with a
second polymer, said second polymer being selected from the group
consisting of polyethylene, polyethylene modified with vinyl
acetate, polyethylene modified with isobutylene, ionomer, and an
ionomer-polyethylene blend.
14. A pouch comprising a blow extruded polymer tube section having
open ends, said tube being heat sealed adjacent each open end to
form an enclosure, said tube consisting essentially of from about
12% to about 95% ionomer with the remainder as polyethylene and
zero to about 71/2% vinyl acetate, the heat sealed edges of said
tube being perpendicular to the direction of extrusion, .Iadd.said
tube being extruded at a stretch ratio of approximately 1.5 to 1
and having an Elmendorf tear strength of from 30 to 125 g,
.Iaddend.said pouch being capable of being torn in substantially a
straight line between the sealed edges thereof.
15. The pouch of claim 14 comprising a notch in one of the sealed
edges thereof.
Description
BACKGROUND OF THE INVENTION
Various polymer films are used to make bags, pouches, packages and
the like. A common practice is to join opposed polymer sheets
together along a common line by heat sealing, wherein the sheets
are pressed together between heated bars for a sufficient length of
time and with sufficient pressure to cause fusion therebetween.
If a bag or package composed of a polymer film is heat sealed
together on all sides, difficulties are frequently encountered in
tearing the bag open. Many polymer films tend to stretch before
tearing. Moreover, most films will not tear along a straight line,
which presents a problem in opening of a bag or package.
A conventional method of forming polymer films is by blow
extrusion, wherein the polymer is melted and forced through a
circular die to produce a thin tube, which is inflated with a gas
in the vicinity of the die and drawn away in a continuous process.
Widely used polymers include low density polyethylene, usually
modified with vinyl acetate, as well as ionomers, both of which
provide a film having good heat sealing properties and excellent
strength. Films composed entirely of either an ionomer or low
density polyethylene, however, made by normal blow or other
extrusion methods, cannot be torn along a straight line in the
direction of extrusion. The film can be torn in such direction only
with great difficulty and not in a straight line.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that a film made
from certain blends of polyethylene and an ionomer, containing a
particular minimum amount of either, unexpectedly exhibits
excellent linear tear properties in the direction of extrusion. The
polyethylene-ionomer film contains from about 12 to about 95%
ionomer and from about 5 to about 88% polyethylene, the blends in
such ranges providing films having excellent properties as well as
excellent linear tear qualities in the direction of extrusion.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In accordance with the preferred embodiment, ionomer resin and
polyethylene resin are mixed together in dry form in the desired
proportions, melted, and then extruded through die in the form of a
tubing or sheet, which in the case of a tubing, is inflated with a
gas in the area of extrusion.
The term "ionomer" as used herein is characterized as a
metal-containing ionic copolymer obtained by the reaction between
ethylene or an alpha-olefin with an ethylenically unsaturated
monocarboxylic acid such as acrylic or methacrylic acid wherein at
least 10% of said carboxylic acid groups are neutralized by an
alkali metal ion, and having a melting point range of from about
370.degree. to 450.degree. F. A suitable ionomer for making films
is "SURLYN 1601" sold by E. I. DuPont De Nemours & Company.
U.S. Pat. No. 3,264,272 of record herein describes the types of
ionomer resins that may be used in the practice of the present
invention, and as used herein, the term "ionomer" shall be defined
as the class of copolymers described in said patent. Such
copolymers are more fully defined as ionic copolymers of a-olefins
having the formula R--CH--CH.sub.2, where R is a radical selected
from the class consisting of hydrogen and alkyl radicals having
from 1 to 8 carbon atoms, and a,B-ethylenically unsaturated
carboxylic acids having from 3 to 8 carbon atoms, said copolymers
having from 10% to 90% of the carboxylic acid groups ionized by
neutralization with metal ions uniformly distributed throughout the
copolymer, said copolymer being a direct copolymer of the a-olefins
and the unsaturated carboxylic acid in which the carboxylic acid
groups are randomly distributed over all molecules and in which (1)
the a-olefin content of the copolymer is at least 50 mol percent,
based on the a-olefin-acid copolymer, (2) the unsaturated
carboxylic acid content of the copolymer is from 0.2 to 25 mol
percent, based on the a-olefin-acid copolymer, and (3) any other
monomer component optionally copolymerized in said copolymer is
monoethylenically unsaturated, and said metal ions having an
ionized valence of from one to three inclusive when the unsaturated
acid is a monocarboxylic acid and an ionized valence of one when
the unsaturated acid is a dicarboxylic acid and said metal ions
being selected from the group consisting of uncomplexed and
complexed metal ions.
The term "polyethylene resin" includes polyethylene resins having a
density in the range of from about 0.910 to about 0.960. The
polyethylene may be modified to include from zero up to about 7.5%
vinyl acetate as a copolymer, without adverse effect on the tear
qualities of the resulting sheet. A suitable material is "Chemplex
3041" made by the Chemplex Corporation.
It has been found that either the ionomer or polyethylene may be
used as a base, and beyond a particular minimum amount of the other
polymer must be added to impart the desired tear qualities to the
resulting film. If polyethylene is the base, a minimum of at least
about 12% by weight of ionomer resin may be blended therewith to
impart linear tear qualities. If ionomer resin is used as the base,
a minimum of at least about 5% by weight polyethylene must be
added. Since all intermediate levels result in the desired
characteristic, the polymer blend may contain from about 12% to
about 95% ionomer and from about 5% to about 88% polyethylene,
although up to about 7.5% of the polyethylene contribution may
comprise vinyl acetate to improve puncture resistance.
The term "linear tear property" as used herein means the inherent
property or ability of the film to tear by hand along substantially
a straight line, with less than about a 20.degree., and preferably
less than 5.degree. to 10.degree. angle of deviation from said line
after initiation of the tear. The tear is made by a normal shearing
or parting motion without the necessity to guide or manipulate the
direction of the tear along the line and without using guides or
other external aids. The films of the present invention have the
inherent quality of easily tearing in or parallel to the machine
direction of the film in substantially a straight line. Once the
tear has been initiated, preferably by slitting or nicking the film
at one edge, continued tearing will result in a straight line tear,
without stretching or distortion of the film, as if the material
had been perforated or weakened along the line. This result is
totally unexpected, since neither the pure polyethylene or ionomer
films alone exhibit this property.
The degree of force required to make the tear is also a
contributing factor of the present invention. If the tear strength,
measured by the Elmendorf procedure, is substantially greater than
125 g, the film will offer excessive resistance to tearing, whereas
too low a tear strength will result in a film that could too easily
be torn accidentally during normal handling or use. The film of the
present invention will exhibit a tear strength or a resistance to
propagation of tear in the order of from about 30 g to about 125 g
and preferably in the order of about 40 to about 100 grams, which
is an ideal tear strength without encountering undue weakness or
resistance to propagation of tear in the film.
After the polymers have been blended in the desired proportions,
the mixture is preferably melted and blow extruded by conventional
methods and at temperatures in the order of about 300.degree. to
about 425.degree. F. The procedure results in the continuous
production of tubular film, which may thereafter be slit
longitudinally, cut into transverse sections, and heat sealed
adjacent the transverse cuts to form an open end bag or pouch.
Thereafter, any desired contents may be filled into the bag through
the open end, and such end is then heat sealed.
In the alternative, the film of the present invention may be cast
in the form of a sheet by convention methods, and the linear tear
property will still be exhibited in the machine direction.
In the conventional fabrication of bags or pouches, the side seams
run perpendicular to the direction of extrusion, and the remaining
open end of the pouch is considered as the top, with the printing,
labels, etc., being applied in the same orientation, i.e., along
lines parallel with the direction of extrusion. Thus, the product
of the present invention lends itself to the production of a pouch
having a linear tear property across the top or bottom of the
pouch. The finished pouch may also be provided with a notch at
either side to facilitate initiation of the tear, corresponding to
the direction of extrusion.
From the foregoing, the importance of providing a linear tear
property in the machine direction can be readily appreciated since
this is the direction from side to side of a conventionally
fabricated pouch. Thus, the pouch may be grasped at a top corner
and easily torn open. A notch is typically provided on one or both
sides of the pouch whereby the tear may be conveniently initiated
from either side.
It has also been found that polymers or blends that do not possess
the linear tear property can be coextruded with the blends
described herein, and the resulting multi-ply film will exhibit the
desired linear tear property in the machine direction. For example,
if one ply of the coextrusion comprises a linear tear blend, the
second ply may be composed of low density polyethylene,
polyethylene modified with vinyl acetate or polyisobutylene, or
ionomer, or a blend of ionomer and polyethylene falling outside of
the linear tear range described herein. As an example of the
latter, the second ply may comprise a blend containing polyethylene
and less than 12% ionomer.
A further benefit of the polymer composition of the present
invention is that while the linear tear feature is exhibited, there
is no detraction from the other properties that would normally be
expected from the individual components. Thus, there is no loss of
such properties such as stiffness modulus, impact strength or
elongation, but rather an average of the properties of the
individual components is realized.
In further illustration of the present invention, the following
examples are given.
EXAMPLE I
Four batches of identical low density polyethylene containing 0,
2%, 4.5% and 7.5% vinyl acetate were dry blended with varying
amounts of DuPont film grade Surlyn. The blends were each extruded
through a 4 inch die at a 1.5 to 1 blow-up ratio under the
following extrusion conditions: extruder L/D, 24 to 1; gauge, 3
mil., temperature at feed section of extruder, about 300.degree.
F.; temperature in extruder, from 320.degree. to 360.degree.;
average temperature at front and die of extruder, about 400.degree.
F. The tube for each batch was flattened, and notched specimens
tested for Elmendorf tear strength in the machine direction (ASTM D
1922-67, propagation tear resistance). The tear strength for each
sample was measured as follows:
TABLE I ______________________________________ Elmendorf Tear (gm.)
(Remainder Poly- ethylene). % Vinyl % Surlyn Acetate 0 10 25 50 75
100 ______________________________________ Homo- --(P) 120(G) 64(E)
68(E) 82(E) 189(P) polymer 2% Vinyl 630(P) 130(G) 59(E) 71(E)
100(E) --(P) Acetate 4.5% Vinyl 300(P) 255(P) 76(G) 79(E) 88(E)
--(P) Acetate 7.5% Vinyl --(P) 194(P) 67.6(P) 62(P) 84(G) --(P)
Acetate ______________________________________
EXAMPLE II
Each of the samples of Example I was also tested for linear tear
properties in machine direction based on the following criteria:
less than 5.degree. angular deviation from a straight line from
side to side of the film, excellent (E); less than 20.degree.
deviation, good (G); and more than 30.degree., poor (P). The
ratings for each sample are indicated adjacent the Elmendorf values
in Table I.
EXAMPLE III
Several of the blends exhibiting excellent linearity were
coextruded with a blend containing 5% ionomer and 95% low density
polyethylene. The resultant multi-ply film exhibited excellent
linear tear properties in accordance with the criteria of Example
II.
EXAMPLE IV
Samples containing various mixtures of Chemplex L.D. 3041
polyethylene containing 31/2% vinyl acetate and DuPont "surlyn"
1601 were blow extruded to determine the minimum amount of either
resin required to achieve linear tear properties in accordance with
the criteria of Example II. The tests included runs of 5%, 71/2%,
10%, 121/2% and 15% ionomer with the remainder as Chemplex, and 5%,
71/2%, 10%, 121/2% and 15% Chemplex with the remainder as ionomer.
It was found that the linear tear property was attained at a
minimum of 121/2% ionomer level with the remainder as polyethylene
and at a minimum of 5% polyethylene with the remainder as
ionomer.
* * * * *