U.S. patent application number 10/735092 was filed with the patent office on 2005-06-16 for paired bags and method of making same.
Invention is credited to Mize, James A..
Application Number | 20050129885 10/735092 |
Document ID | / |
Family ID | 34523092 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050129885 |
Kind Code |
A1 |
Mize, James A. |
June 16, 2005 |
Paired bags and method of making same
Abstract
A set of bags comprises a first lay-flat bag and a second
lay-flat bag joined along their respective lengths. An end seal
extending across both the first bag and the second bag. The first
bag has a first side seal extending the length of the first bag,
and the second bag has a second side-seal extending the length of
the second bag. The first bag is connected with the second bag in
an area between the first side-seal and the second side-sea. Both
the first bag and the second bag having a total free shrink at
185.degree. F. of at least 10 percent and a transverse free shrink
at 185.degree. F. which is greater than a longitudinal free shrink
at 185.degree. F.
Inventors: |
Mize, James A.;
(Simpsonville, SC) |
Correspondence
Address: |
Sealed Air Corporation
P.O. Box 464
Duncan
SC
29334
US
|
Family ID: |
34523092 |
Appl. No.: |
10/735092 |
Filed: |
December 12, 2003 |
Current U.S.
Class: |
428/35.2 ;
428/43 |
Current CPC
Class: |
B65D 75/46 20130101;
B65D 2275/02 20130101; B65D 75/42 20130101; B65D 75/002 20130101;
Y10T 428/1334 20150115; Y10T 428/15 20150115 |
Class at
Publication: |
428/035.2 ;
428/043 |
International
Class: |
B65D 001/00 |
Claims
What is claimed is:
1. A set of bags made from a film, the set of bags comprising a
first lay-flat bag and a second lay-flat bag joined along their
respective lengths, an end seal extending across both the first bag
and the second bag, the first bag having a first side seal
extending the length of the first bag, and the second bag having a
second side-seal extending the length of the second bag, with the
first bag being connected with the second bag in an area between
the first side-seal and the second side-seal, with both the first
bag and the second bag having a total free shrink at 185.degree. F.
of at least 10 percent and a transverse free shrink at 185.degree.
F. which is greater than a longitudinal free shrink at 185.degree.
F.
2. The set of bags according to claim 1, wherein the set of bags
has a first outer side edge and a second outer side edge, and at
least one of the first outer side edge and the second outer side
edge is a folded edge.
3. The set of bags according to claim 1, wherein the film has a
total free shrink, at 185.degree. F., of at least 15 percent.
4. The set of bags according to claim 1, wherein the end-seal, the
first side-seal, and the second side-seal are heat seals.
5. The set of bags according to claim 1, wherein the end seal, the
first side-seal, and the second side-seal are each a seal of an
inside surface of a seamless tubing to itself.
6. The set of bags according to claim 1, further comprising a line
of weakness between the first bag and the second bag, the line of
weakness being between the first side seal and the second side
seal.
7. The set of bags according to claim 6, wherein the line of
weakness between the first bag and the second bag comprises
perforations.
8. The set of bags according to claim 1, wherein a patch is adhered
to at least one member selected from the group consisting of the
first bag and the second bag.
9. The set of bags according to claim 8, wherein the first bag has
a first patch adhered thereto, and the second bag has a second
patch adhered thereto.
10. The set of bags according to claim 9, wherein the first bag and
the second bag are both made from a film having a total free shrink
at 185.degree. F. of at least 15 percent, and the first patch and
the second patch are made from a film having a total free shrink at
185.degree. F. of at least 15 percent.
11. The set of bags according to claim 1, further comprising a
third bag between the first bag and the second bag, the third bag
having two side seals and an end seal.
12. The set of bags according to claim 1, wherein the set is a pair
of bags.
13. The set of bags according to claim 1, wherein the film is a
multilayer film comprising a first outer film layer, a second outer
film layer, and an inner O.sub.2-barrier layer comprising at least
one polymer selected from the group consisting of vinylidene
chloride/methyl acrylate copolymer, vinylidene chloride/vinyl
chloride copolymer, ethylene/vinyl alcohol copolymer, polyamide,
and polyethylene carbonate.
14. The set of bags according to claim 13, wherein the multilayer
film further comprises a fourth layer which serves as a tie layer
between the barrier layer and the first outer film layer, and a
fifth layer which serves as a tie layer between the barrier layer
and the second outer layer.
15. The set of bags according to claim 1, wherein both the first
bag and the second bag have printing thereon.
16. A plurality of sets of bags, comprising: (A) a first set of
bags comprising a first bag and a second bag joined along their
respective lengths, the first pair of bags having a first end-seal
extending across both the first bag and the second bag, the first
bag having a first side-seal extending the length of the first bag,
and the second bag having a second side-seal extending the length
of the second bag, the first bag being connected with the second
bag in an area between the first side-seal and the second side
seal, (B) a second set of bags comprising a third bag and a fourth
bag, the second set of bags having a second end-seal extending
across both the third bag and the fourth bag, the third bag having
a third side-seal extending the length of the third bag and the
fourth bag having a fourth side seal extending the length of the
fourth bag, the third bag being connected with the fourth bag in an
area between the third side-seal and the fourth side seal; and
wherein the second set of bags is joined to the first set of bags
in an area below the first end seal.
17. The plurality of sets of bags according to claim 16, wherein
the second set of bags is joined to the first set of bags along a
transverse line of weakness.
18. The plurality of sets of bags according to claim 17, wherein
the line of weakness between the first set of bags and the second
set of bags comprises perforations.
19. The plurality of sets of bags according to claim 16, further
comprising a third set of bags which is joined to the second set of
bags below the second end seal, and a fourth set of bags joined to
the third set of bags below a third end seal, with the plurality of
sets of bags being a portion of a strand of sets of bags, the
strand being of indeterminate length.
20. A set of bags made from a film, the set of bags comprising a
first lay=flat bag and a second lay-flat bag joined along their
respective lengths, an end seal extending across both the first bag
and the second bag, with the first bag connecting with the second
bag at a heat seal between the first bag and the second bag, the
heat seal extending the length of the first bag and the second bag,
with both the first bag and the second bag having a total free
shrink at 185.degree. F. of at least 10 percent and a transverse
free shrink at 185.degree. F. which is greater than a longitudinal
free shrink at 185.degree. F.
21. A process for converting a lay-flat film tubing to a plurality
of sets of bags, comprising: A. making a plurality of transverse
seals across the lay-flat film tubing, the transverse seals being
spaced apart from one another by a distance corresponding with the
length of each of the sets bags, each of the transverse seals
providing an end-seal across a bottom of each bag of each of the
sets of bags; B. making first and second longitudinal seals along
the length of the lay-flat film tubing, the longitudinal seals
providing a seal along an interior side edge of each of the sets of
bags; wherein the bags of each set of bags have a total free shrink
at 185.degree. F. of at least 10 percent and a transverse free
shrink at 185.degree. F. which is greater than a longitudinal free
shrink at 185.degree. F.
22. The process according to claim 21, wherein the lay-flat film
tubing is a seamless tubing, and after forming a set of bags from
the lay-flat tubing by making the transverse and longitudinal
seals, the set of bags is separated from a remainder of the
lay-flat tubing.
23. The process according to claims 22, further comprising making a
transverse line of weakness below each of the transverse seals.
24. The process according to claim 23, further comprising making a
longitudinal line of weakness between the first and second
longitudinal seals.
25. A process for converting a flat film tubing to a plurality of
sets of bags, comprising: A. center folding the flat film along its
length, to form a centerfolded film; B. making a plurality of
transverse seals across the centerfolded film, the seals being
spaced apart from one another by a distance corresponding with the
length of the sets of bags, each of the transverse seals serving as
end-seals across the bottom of each of the sets of bags; C. making
first, second, and third longitudinal seals along the length of the
centerfolded film, the first longitudinal seal providing a seal
along and second longitudinal seals providing a seal along an
interior side edge of each of the bags sets of bags.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to sets of bags made from a
heat-shrinkable flexible packaging film.
BACKGROUND OF THE INVENTION
[0002] Heat-shrinkable bags made from flexible thermoplastic film
have for some time been used for the packaging of various products,
such as food products, especially meat. An "end-seal" bag is one
such bag. In the making of heat-shrinkable end-seal bags,
thermoplastic material is extruded from an annular die, in the form
of a seamless tubing, with the extrudate (known as a "tape") being
relatively thick and relatively narrow. The annular extrudate is
then quenched. Optionally, the tape can then be irradiated and/or
coated with one or more additional layers containing thermoplastic
polymer. The tape is then reheated to its softening point by
exposure to hot water or steam (or other heating means) and is
stretched in its longitudinal and transverse directions while the
polymer remains in the solid state, resulting in heat-shrinkable
film in the form of a seamless tubing. The heat-shrinkable film
tubing is then converted into end-seal bags by placing the tubing
into a lay-flat configuration and heat-sealing across the tubing to
heat-seal the inside surface of the tubing to itself. The seals
across the tubing are made at intervals along the length of the
tubing, these intervals corresponding with the desired bag
length(s). The resulting sealed tubing is then converted into a
plurality of heat-shrinkable bags by cutting across the tubing a
short distance downstream of each of the transverse heat-seals,
resulting in a plurality of lay-flat bags having an open top, two
seamless side edges, a heat seal across the bag near the bottom
edge of the bag, and a short section of tubing (commonly referred
to as a "skirt") below the transverse heat seal.
[0003] Because end-seal bags extend across the entire width of the
lay-flat tubing, end-seal bags come off of the production line one
at a time, with each bag requiring a separate sealing cycle, a
separate printing cycle, and with each bag coming off the line as a
single bag. It would be desirable to reduce the number of sealing
cycles, printing cycles, and cutting cycles, to increase throughput
of the process, and in some cases to provide bags of reduced
width.
[0004] In addition, most meat processing plants have packaging
equipment with large vacuum chambers for the evacuation of
atmosphere and sealing of a bag containing a meat product. If two
small bags are loaded into the same vacuum chamber at the same
time, they may overlap and have weak seals. However, if a single
small bag is loaded into the large chamber, capacity is
under-utilized and additional labor is required. It would be
desirable to be able to place more than one small bag into the
chamber without having weak seals from bag overlap.
[0005] Side seal bags are also made by sealing across a seamless
tubing. Whereas end-seal bags have a width corresponding with the
lay-flat width of the seamless tubing, side-seal bags have a length
corresponding to the width of the seamless tubing, and have a width
corresponding to the selected distance between transverse seals
which run along the side edges of side-seal bags. In the production
of side-seal bags, two or more side-seal bags have been kept
together and cut free of the remainder of the tubing, and used as a
bag pair. However, side-seal bags have a disadvantage of having a
free shrink along the length of the side-seal bag (i.e., in the
transverse direction of the length of the seamless tubing) which is
higher than the free shrink across the width of the side-seal bag
(i.e., corresponding with the length of the tubing). Having a
higher shrink across the tubing is detrimental to the packaging of
relatively long, flat, flexible products in side-seal bags, as
during subsequent bag-length shrinkage of a side-seal bag, the
product can become distorted, i.e., "curved", which lowers the
appearance of the package to a consumer, and which is more
difficult to box because of the curve in the package. Moreover,
paired side-seal bags cannot be provided as a continuous string of
connected pairs, as to make the "pair" requires that the pair be
separated from the remainder of side-seal bags formed from the
tubing.
SUMMARY OF THE INVENTION
[0006] The present invention provides a set of heat-shrinkable bags
and a process for making sets of such bags. In the process, the
number of printing cycles, as well as the number of cycles used to
make the transverse seals, can be cut in half, thirds, etc., while
making the same total number of bags, thereby enabling a doubling,
tripling, etc., of the number of bags per extrusion die, as well as
per print cycle and per transverse seal cycle. In addition, the
sets of heat-shrinkable bags have a lengthwise free shrink (i.e.,
shrink in the machine direction) which is less than the transverse
free shrink (i.e., shrink across the width of the bags), so that
during shrinking the heat-shrinkable bags have less tendency to
distort flat, flexible, elongate products packaged in the bag.
[0007] The process can be used to produce sets of bags in which the
bags of each set are connected with one another across the machine
direction of the film being used to make the bags. Optionally, each
set of bags can be provided with an appropriate number of
longitudinal tear lines (i.e., tear lines running the length of the
bags, i.e., in the machine direction) for ease in separating the
bags from one another. In addition, because the bags are connected
to one another, like a single bag the connected series of bags can
be stretched out across the opening of a vacuum chamber without
risk of overlap during sealing.
[0008] Moreover, the invention can be carried out so that each set
of bags is connected to at least one other set of bags in a line of
succession, e.g., resulting in a strand of paired bags, which can
be of indeterminate length as it comes off of a production line.
Optionally, this strand of sets of bags can be provided with
transverse tear lines (i.e., a weakened region between the sets of
bags, such as a line of perforations, etc.) so that each set of
bags can be easily torn free of the strand of bags, as well as
lengthwise (i.e., machine direction) tear lines between the bags of
each set, so that the packaged product can be offered as singlets
or any subset of the original set of bags.
[0009] In the sets of bags of the invention, the bag length of each
of the bags in the set runs in the machine direction of the tubing.
Likewise, the bag width of each of the bags in the set runs in the
transverse direction, i.e., across the tubing. A greater free
shrink in the transverse direction is desirable for the packaging
of a wide variety of products, particularly food products which
tend to distort by bending along the length of the bag in which
they are packaged. Various meat products, such as small beef and
pork cuts, for example, beef and pork tenderloin, eye of round,
single ribs, beef spare ribs, split beef back ribs, and various
lamb cuts, tend to distort (i.e., bend) if packaged in a shrink bag
having a higher shrink along the length of the bag than across the
width of the bag. Such package distortion is reduced or eliminated
in the sets of bags of the invention, which have have greater free
shrink across the bag than along the length of the bag.
[0010] As a first aspect, the present invention is directed to a
set of bags made from a film. The set of bags comprises a first
lay-flat bag and a second lay-flat bag joined along their
respective lengths, with an end seal extending across both the
first bag and the second bag. The first bag has a first side seal
extending the length of the first bag, and the second bag has a
second side-seal extending the length of the second bag. The first
bag is connected with the second bag in an area between the first
side-seal and the second side-seal. Both the first bag and the
second bag having a total free shrink at 185.degree. F. of at least
10 percent, and both the first bag and the second bag have a
transverse free shrink at 185.degree. F. which is greater than a
longitudinal free shrink at 185.degree. F.
[0011] In one preferred embodiment, the set of bags has a first
outer side edge and a second outer side edge, and at least one of
the first outer side edge and the second outer side edge is a
folded edge.
[0012] Preferably, the film has a total free shrink, at 185.degree.
F., of at least 15 percent; more preferably, at least 20 percent,
more preferably, at least 25 percent; more preferably, at least 30
percent; more preferably, at least 35 percent; more preferably, at
least 40 percent; more preferably, at least 45 percent. Preferably,
the film has a total free shrink at 185.degree. F. of from 15 to
150 percent; more preferably, from 20 to 140 percent; more
preferably, from 25 to 130 percent; more preferably, from 30 to 120
percent; more preferably, from 35 to 110 percent; more preferably,
from 40 to 100 percent; and, more preferably, from 45 to 90
percent.
[0013] Preferably, the end-seal, the first side-seal, and the
second side-seal are heat seals. Preferably, the end seal, the
first side-seal, and the second side-seal are each a seal of an
inside surface of a seamless tubing to itself. The end-seal can be
a straight seal or can be curved or have at least one curved
region. If curved, preferably the end-seal is curved so that the
bottom of the lay-flat set of bags is convex.
[0014] Preferably, the set of bags further comprises a line of
weakness between the first bag and the second bag, the line of
weakness being between the first side seal and the second side
seal. Preferably, the line of weakness between the first bag and
the second bag comprises perforations.
[0015] Optionally, a patch is adhered to the first bag and/or the
second bag. Preferably, the first bag has a first patch adhered
thereto, and the second bag has a second patch adhered thereto.
Preferably, the first bag and the second bag are both made from a
film having a total free shrink at 185.degree. F. of at least 15
percent, and the first patch and the second patch are made from a
film having a total free shrink at 185.degree. F. of at least 15
percent.
[0016] Although the set of bags can be just a pair of bags, the set
of bags can further comprise a third bag between the first bag and
the second bag, the third bag having two side seals and an end
seal. If the set of bags is a pair of bags, the first bag is
preferably a mirror image of the second bag. Preferably, the first
bag has a length equal to the length of the second bag. Preferably,
first side-seal is parallel to the second side-seal.
[0017] Preferably, the film from which the set of bags is made is a
multilayer film comprising a first outer film layer, a second outer
film layer, and an inner O.sub.2-barrier layer comprising at least
one polymer selected from the group consisting of vinylidene
chloride/methyl acrylate copolymer, vinylidene chloride/vinyl
chloride copolymer, ethylene/vinyl alcohol copolymer, polyamide,
and polyethylene carbonate. Preferably, the multilayer film further
comprises a fourth layer which serves as a tie layer between the
barrier layer and the first outer film layer, and a fifth layer
which serves as a tie layer between the barrier layer and the
second outer layer.
[0018] Optionally, the first bag and the second bag have printing
thereon.
[0019] As a second aspect, the present invention pertains to a
plurality of sets of bags, with each set being in accordance with
the first aspect of the invention (described above). The first set
of bags comprises a first bag and a second bag joined along their
respective lengths, the first pair of bags having a first end-seal
extending across both the first bag and the second bag, the first
bag having a first side-seal extending the length of the first bag,
and the second bag having a second side-seal extending the length
of the second bag, the first bag being connected with the second
bag in an area between the first side-seal and the second side
seal. The second set of bags comprises a third bag and a fourth
bag, the second set of bags having a second end-seal extending
across both the third bag and the fourth bag, the third bag having
a third side-seal extending the length of the third bag and the
fourth bag having a fourth side seal extending the length of the
fourth bag. The third bag is connected with the fourth bag in an
area between the third side-seal and the fourth side seal. The
second set of bags is joined to the first set of bags in an area
below the first end seal. Preferably, the third side seal is a
continuation of the first side seal, and the fourth side seal is a
continuation of the second side seal. Preferably, the second set of
bags is joined to the first set of bags along a transverse line of
weakness. Preferably, the line of weakness between the first set of
bags and the second set of bags comprises perforations. Optionally,
the set of bags further comprises a third set of bags which is
joined to the second set of bags below the second end seal, and a
fourth set of bags joined to the third set of bags below a third
end seal, with the plurality of sets of bags being a portion of a
strand of sets of bags, the strand being of indeterminate length.
Unless inconsistent therewith, preferred embodiments of the second
aspect of the invention correspond with preferred features of the
first aspect of the present invention.
[0020] As a third aspect, the present invention pertains to a set
of bags made from a film. The set of bags comprises a first
lay-flat bag and a second lay-flat bag joined along their
respective lengths, and an end seal extending across both the first
bag and the second bag, with the first bag connecting with the
second bag at a heat seal between the first bag and the second bag,
the heat seal extending the length of the first bag and the second
bag, with both the first bag and the second bag having a total free
shrink at 185.degree. F. of at least 10 percent and a transverse
free shrink at 185.degree. F. which is greater than a longitudinal
free shrink at 185.degree. F. Unless inconsistent therewith,
preferred embodiments of the third aspect of the invention
correspond with preferred features of the first aspect of the
present invention.
[0021] As a fourth aspect, the present invention pertains to a
process for converting a lay-flat film tubing to a plurality of
sets of bags. The process comprises making a plurality of
transverse seals across the lay-flat film tubing, with the
transverse seals being spaced apart from one another by a distance
corresponding with the length of each of the sets bags. Each of the
transverse seals providing an end-seal across a bottom of each bag
of each of the sets of bags. Then first and second longitudinal
seals are made along the length of the lay-flat film tubing, the
longitudinal seals providing a seal along an interior side edge of
each of the sets of bags. The bags of each set of bags have a total
free shrink at 185.degree. F. of at least 10 percent and a
transverse free shrink at 185.degree. F. which is greater than a
longitudinal free shrink at 185.degree. F. Preferably, the lay-flat
film tubing is a seamless tubing which is converted to the sets of
bags by making transverse and longitudinal seals through the
tubing, with each set of bags being separated from a remainder of
the lay-flat tubing. Preferably, a the process further comprises
making a line of weakness below each of the transverse seals.
Preferably, the line of weakness is between the first and second
longitudinal seals. Preferably, the line of weakness is below each
of the transverse seals. Optionally, the process can be carried out
by making one longitudinal seal down the length of the tubing, to
produce a set of bags in accordance with the third aspect of the
invention.
[0022] As a fifth aspect, the present invention pertains to a
process for converting a flat film tubing to a plurality of sets of
bags. The process is carried out by (A) center-folding the flat
film along its length, to form a centerfolded film; (B) making a
plurality of transverse seals across the centerfolded film, the
seals being spaced apart from one another by a distance
corresponding with the length of the sets of bags, each of the
transverse seals serving as end-seals across the bottom of each of
the sets of bags; (C) making first, second, and third longitudinal
seals along the length of the centerfolded film, the first
longitudinal seal providing a seal along and second longitudinal
seals providing a seal along an interior side edge of each of the
bags sets of bags. Unless inconsistent therewith, preferred
embodiments of this fifth aspect of the invention correspond with
preferred features of the fourth aspect of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 illustrates a lay-flat view of a set (in this
illustration, a pair) of L-seal bags made from a seamless
tubing.
[0024] FIG. 2 illustrates a lay-flat view of a pair of L-seal bags
made from a seamless tubing, with the pair of bags being connected
to one another along a longitudinal line of weakness (e.g.,
perforations).
[0025] FIG. 3 illustrates a portion of a continuous string of
L-seal bag pairs made from a seamless tubing with a longitudinal
line of weakness between the bags of each pair, with each pair of
bags being connected to the next successive pair of bags with a
transverse line of weakness which is a short distance downstream of
the transverse seal across the bags.
[0026] FIG. 4 illustrates a lay-flat view of a set (e.g., pair) of
alternative L-seal bags made from a seamless tubing, each of the
bags of each set having a curved end seal.
[0027] FIG. 5 illustrates a lay-flat view of an alternative pair of
bags made by folding a flat film over on itself and sealing it to
form a pair of bags.
[0028] FIG. 6 illustrates a lay-flat view of an alternative set of
lay-flat bags which is made up of three bags across a seamless
lay-flat tubing.
[0029] FIG. 7 illustrates a lay-flat view of a set of L-seal patch
bags made from a seamless tubing to which a pair of patches are
adhered.
[0030] FIG. 8 illustrates a schematic of a preferred process for
producing the multilayer films for use in the sets of bags of the
present invention.
[0031] FIG. 9 illustrates a lay-flat view of an alternative pair of
L-seal bags in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] As used herein, the term "bag" is inclusive of L-seal bags,
side-seal bags, backseamed bags, and pouches (i.e., "U-sealed"
bags). An L-seal bag has an open top, a bottom seal, one side-seal
along a first side edge, and a seamless (i.e., folded, unsealed)
second side edge. A side-seal bag has an open top, a seamless
bottom edge, with each of its two side edges having a seal
therealong. Although seals along the side and/or bottom edges can
be at the very edge itself, (i.e., seals of a type commonly
referred to as "trim seals"), preferably the seals are spaced
inward (preferably 1/4 to 1/2 inch, more or less) from the bag side
edges, and preferably are made using a impulse-type heat sealing
apparatus, which utilizes a bar which is quickly heated and then
quickly cooled. A backseamed bag is a bag having an open top, a
seal running the length of the bag in which the bag film is either
fin-sealed or lap-sealed, two seamless side edges, and a bottom
seal along a bottom edge of the bag.
[0033] As used herein, the phrase "set of bags" refers to two or
more bags which are connected with one another in a side-by-side
relationship, with the bags extending across a tubing (seamed or
seamless). The set of bags preferably comprises from 2 to 20 bags
across the tubing, more preferably from 2 to 5 bags, more
preferably 2 to 3 bags. Each bag preferably has a length of at
least twice its width, more preferably three to ten times its
width, with bag length and bag width being measured based on inside
the bag dimensions while the bag is in a lay-flat position. The
phrase "connected with", as applied to the bags of a single set of
bags, refers to the side-by-side relationship of the bags to one
another, and does not require that the bags be directly adhered to
one another. That is, two bags are connected with one another even
if a third bag is between them or even if a section of waste film
is between them. Likewise, two bags are connected with one another
if they share as common side seal, as illustrated in FIG. 9,
described below.
[0034] The phrases "lay-flat film tubing", "lay-flat bag", and
"lay-flat width" are known to those of skill in the flexible film
art. A lay-flat film tubing is extruded through an annular die,
with the extrudate being cooled and gathered by converging sets of
rollers and wound up in flattened form. A lay-flat bag includes
end-seal, side-seal, L-seal, etc. bags which can be made by sealing
the inside of a lay-flat film tubing to itself, following by
cutting across the tubing to convert the tubing into, for example,
an end-seal bag. A side seal bag requires slitting one side edge of
the tubing in addition to cutting across the tubing. Side-seal and
L-seal lay-flat bags can also be made by folding a flat film and
sealing the inside surface of the folded film to itself. A pouch s
often made by sealing two separate pieces of flat film to one
another, with the seals extending up the sides of the pouch and
across the bottom of the pouch, leaving the top of the bag open for
the insertion of the product to be packaged.
[0035] As used herein, the phrase "line of weakness" refers to any
line, whether straight or curved, whether wide or narrow, in which
the film has been weakened by any means so that the film can
readily be torn apart along the line. Preferably the line of
weakness is formed by perforating the film.
[0036] As used herein, the phrases "heat-shrinkable film,"
"heat-shrink film" and the like refers to a film which has been
oriented while in the solid state (as opposed to a blown film,
which is oriented at, above, or near the melting point of the
polymer). The tension on a heat-shrinkable film increases upon the
application of heat if the film is restrained from shrinking. As a
corollary, the phrase "heat-contracted" refers to a heat-shrinkable
film, or a portion thereof, which has been exposed to heat such
that the film or portion thereof is in a heat-shrunken state, i.e.,
reduced in size (unrestrained) or under increased tension
(restrained). Preferably, the heat shrinkable film has a total free
shrink (i.e., machine direction plus transverse direction), with
the free shrink in each direction (measured in accordance with ASTM
D 2732) of at least as 5 percent at 185.degree. C., more preferably
at least 7 percent, still more preferably, at least 10 percent,
still more preferably, at least 15 percent, and, yet still more
preferably, at least 20 percent. The total free shrink at
185.degree. F. can be from 10 to 150 percent, more preferably from
20 to 120 percent, more preferably from 40 to 100 percent.
[0037] As used herein, the phrases "inner layer" and "internal
layer" refer to any layer, of a multilayer film, having both of its
principal surfaces directly adhered to another layer of the
film.
[0038] As used herein, the phrase "outer layer" refers to any film
layer of film having less than two of its principal surfaces
directly adhered to another layer of the film. The phrase is
inclusive of monolayer and multilayer films. In multilayer films,
there are two outer layers, each of which has a principal surface
adhered to only one other layer of the multilayer film. In
monolayer films, there is only one layer, which, of course, is an
outer layer in that neither of its two principal surfaces are
adhered to another layer of the film.
[0039] As used herein, the phrase "inside layer" refers to the
outer layer of a multilayer film packaging a product, which is
closest to the product, relative to the other layers of the
multilayer film.
[0040] As used herein, the phrase "outside layer" refers to the
outer layer, of a multilayer film packaging a product, which is
furthest from the product relative to the other layers of the
multilayer film. Likewise, the "outside surface" of a bag is the
surface away from the product being packaged within the bag.
[0041] As used herein, the term "adhered" is inclusive of films
which are directly adhered to one another using a heat seal or
other means, as well as films which are adhered to one another
using an adhesive which is between the two films.
[0042] Although the films used in the patch bag according to the
present invention can be monolayer films or multilayer films, the
patch bag comprises at least two films laminated together.
Preferably, the patch bag is comprised of films which together
comprise a total of from 2 to 20 layers; more preferably, from 2 to
12 layers; and still more preferably, from 4 to 12 layers. In
general, the multilayer film(s) used in the present invention can
have any total thickness desired, so long as the film provides the
desired properties for the particular packaging operation in which
the film is used, e.g. abuse-resistance (especially
puncture-resistance), modulus, seal strength, optics, etc.
[0043] FIG. 1 is a lay-flat view of a pair of L-seal bags 10 which
have been made by sealing the inside layer of a flexible,
thermoplastic seamless tubing to itself. Pair of bags 10 comprises
first bag 12 and second bag 14, which in turn have open tops 16 and
18, respectively, and transverse seal 20, with end seal portion 22
serving as the end seal for first bag 12 and end seal portion 24
serving as the end seal for second bag 14. First bag 12 has inner
longitudinal seal 13 and second bag 14 has inner longitudinal seal
15. Together end seal portion 22 and inner longitudinal seal 13
make up a so-called "L-seal" of first bag 12, with the same being
present for the combination of end seal portion 24 and inner
longitudinal seal 15 for second bag 14. First bag 12 and second bag
14 share central region 34, which as illustrated has no weakened
line, so that products packaged in first bag 12 and second bag 14
are paired with one another unless cut apart along the length of
central region 34. Side edge 28 of first bag 12 is a folded edge
(which usually is creased during processing of the seamless tubing
from which the bags are formed), as is side edge 30 of second bag
14. Skirt region 32 is below transverse seal 20, with skirt region
32 extending all the way across both first bag 12 and second bag
14, i.e., from side edge 28 to side edge 30, with skirt region 32
extending from immediately below transverse seal 20 to bottom edge
36.
[0044] FIG. 2 is a lay-flat view of a L-seal bag pair 40 having
features which correspond with the features of the pair of bags
illustrated in FIG. 1, except that L-seal bag pair 40 additionally
has a longitudinal line of weakness 42 running the length of
central region 34. Line of weakness 42 is preferably a set of
perforations aligned along a straight line which is located in the
middle of central region 34, and which runs the entire length of
central region 34.
[0045] FIG. 3 illustrates continuous string 50 of L-seal bag pairs
40 having all of the feature as illustrated in FIG. 2. However, in
continuous string 50, immediately beneath skirt 32 of each bag pair
40, is transverse line of weakness 52. Line of weakness 52 is
preferably a set of perforations aligned along a straight line
located far enough below transverse seal 32 to provide skirt 32
with adequate width.
[0046] FIG. 4 is a lay-flat view of alternative L-seal bag pair 80
having features which largely correspond with the features of the
pair of bags illustrated in FIG. 2, except that transverse seal 82
has curved sections 84 and 86, which provide end-seals across the
bottom of first bag 88 and second bag 90, respectively. Likewise,
matching curved sections are present at open top 92 and 94 of first
bag 88 and second bag 90, respectively.
[0047] FIG. 5 is an illustration of an alternative pair of bags 60
comprising first bag 62 and second bag 64 which can be made by
centerfolding a flat film (or slitting a seamless tubing). First
bag 62 and second bag 64 have open tops 16 and 18, respectively.
Pair of bags 60 has transverse seal 20, with seal sections 22 and
24 serving as the end seal for first bag 62 and second bag 64,
respectively. In addition, first bag 62 has outer folded edge 28
and inner longitudinal seal 13 (i.e., first bag 62 being an L-seal
bag). In addition to end seal section 24, second bag 64 has both
inner longitudinal seal 15 and outer longitudinal seal 66 (i.e.,
second bag 64 being a U-seal bag). Second bag 64 also has skirt 68
running the length of the bag, between outer longitudinal seal 66
and outer edge 70. As in FIG. 1, pair of bags 60 share central
region 34, which as illustrated has no weakened line, so that
products packaged in first bag 62 and second bag 64 are paired with
one another unless cut apart along the length of central region
34.
[0048] FIG. 6 illustrates a lay-flat view of an alternative set of
lay-flat bags (100) including first bag 102 along a first folded
side edge of the seamless tubing, second bag 104 along a second
folded side edge of the seamless tubing, and third bag 106
positioned between first bag 102 and second bag 104. Each of bags
102, 104, and 106 shares transverse end seal 108, and first bag 102
is an L-seal bag utilizing a portion of end seal 108 in combination
with first side seal 110. Second bag 104 is also an L-seal bag,
also utilizing a portion of end seal 108, but in combination with
second side seal 112. Third bag 106 is a U-seal bag utilizing yet
another portion of end seal 108, together with third side seal 114
and fourth side seal 116. While side seals 110, 112, 114, and 116
are termed side seals because they each run along a side edge of
respective bags 102, 104, and 106, they each run in the machine
direction. First bag 102 is joined to third bag 106 along line of
weakness 118 (preferably a line of perforations), and second bag
104 is joined to third bag 106 along line of weakness 120
(preferably also a line of perforations).
[0049] FIG. 7 illustrates a lay-flat view of a pair of bags 122
which correspond with pair of bags 40 illustrated in FIG. 2, except
that first bag 124 has patch 128 adhered thereto, and second bag
126 has patch 130 adhered thereto.
[0050] Preferably, the film stock film from which the bag is formed
has a total thickness of from about 1.5 to 5 mils; more preferably,
1.5 to 4 mils; more preferably, 2 to 3. mils; more preferably, 2 to
2.5 mils. Preferably the stock film from which the bag is formed is
a multilayer film having from 1 to 20 layers; more preferably, 3 to
10 layers; more preferably, 4 to 8 layers.
[0051] Preferably, the bag film, present in the form of a seamless
tubing, backseamed tubing (lap seal, fin seal, or butt sealed
backseamed tubing with butt seal tape) or as a flat film, has a
total (i.e., L+T) free shrink at 185.degree. F. of from about 45 to
125 percent, with a free shrink in the longitudinal (i.e., machine)
direction of from 20 to 50 percent, and a free shrink in the
transverse direction of from 25 to 75 percent, with the transverse
free shrink being greater than the longitudinal free shrink. More
preferably, the bag film has a total free shrink at 185.degree. F.
of from about 55 to 110 percent, with a free shrink in the
longitudinal direction of from 25 to 45 percent, and a free shrink
in the transverse direction of from 30 to 65 percent, again with
the transverse free shrink being greater than the longitudinal free
shrink. More preferably, the bag film has a total free shrink at
185.degree. F. of from about 65 to 95 percent, with a free shrink
in the longitudinal direction of from 30 to 40 percent, and a free
shrink in the transverse direction of from 35 to 55 percent, again
with the transverse free shrink being greater than the longitudinal
free shrink.
[0052] Preferably, the transverse free shrink at 185.degree. F. is
higher than the longitudinal free shrink at 185.degree. F. by an
amount of from about 5 to 30 percent, more preferably from 8 to 20
percent higher. Preferably, the transverse free shrink is from 1.1
times to 1.8 times as high as the longitudinal free shrink, more
preferably from 1.2 to 1.7 times as high, more preferably from 1.25
to 1.65 times as high.
[0053] Table I, below, provides a preferred multilayer film
structure for making a set of bags in accordance with the present
invention, including the composition, thickness, and general
function of each of the film layers. This film, extruded from an
annular die and thereafter extrusion coated, was in the form of a
seamless tubing and had a total thickness of approximately 2.4
mils, and exhibited a total free shrink at 185.degree. F. of 20% in
the machine direction and 33% in the transverse direction.
1TABLE I Layer Thickness Layer Function Layer Chemical Identity
(mils) Outside and abuse 90% EVA #1 0.58 layer 10% HDPE #1
O.sub.2-Barrier layer 96% VDC/MA #1; 0.19 2% epoxidized soybean
oil; and 2% bu-A/MA/bu-MA terpolymer Puncture-resistant 85% LLDPE
#1 & 15% EBA #1 1.15 Sealant and inside 80% SSPE#1 0.48 layer
20% LLDPE #2
[0054] In Table I, LLDPE #1 was DOWLEX.RTM. 2045 linear low density
polyethylene, obtained from the Dow Chemical Company of Midland,
Mich. LLDPE #2 was ESCORENE.RTM. LL3003.32 linear low density
polyethylene, obtained from Exxon Chemical Company of Baytown, Tex.
SSPE#1 was AFFINITY.RTM. Pl1280 metallocene-catalyzed
ethylene/octene copolymer, having a density of 0.900 g/cc and a
melt index of 6 g/10 min, obtained from The Dow Chemical Company,
of Midland, Mich. HDPE #1 was Fortiflex.RTM. T60-500-119 high
density polyethylene, obtained from Solvay Polymers, of Deer Park,
Tex. EVA No. 1 was ESCORENE.RTM. LD318.92 ethylene/vinyl acetate
copolymer having a melt index of 2.0, a density of 0.930 g/cc, and
a vinyl acetate mer content of 9 percent, this resin being obtained
from the Exxon Chemical Company. EBA No. 1 was SP1802
ethylene/butyl acrylate copolymer containing 18% butyl acrylate,
obtained from Chevron Chemical Company, of Houston, Tex.
[0055] Table II, below, provides another preferred multilayer film
structure for making the sets of bags in accordance with the
present invention, the film having a total thickness of 3 mils and
a free shrink at 185.degree. F. of 28 percent in the machine
direction and 36 percent in the transverse direction.
2TABLE II Layer Thickness Layer Function Layer Chemical Identity
(mils) Outside and abuse 80% SSPE2 0.21 layer 20% LLDPE3 Core Layer
100% LLDPE2 0.32 Tie Layer 100% EMA 0.11 O.sub.2-Barrier layer 96%
VDC/MA #1; 0.21 2% epoxidized soybean oil; and 2% bu-A/MA/bu-MA
terpolymer Tie Layer 100% EVA1 0.11 Substrate Core Layer 60% LLDPE2
1.5 40% LLDPE3 Seal Layer 60% SSPE1 0.56 40% LLDPE 1
[0056] Table III, below, provides another preferred multilayer film
structure for making the sets of bags in accordance with the
present invention, the film having a total thickness of about 2.2
mils and a free shrink at 185.degree. F. of about 31% in the
machine direction and about 44% in the transverse direction.
3TABLE III Layer Thickness Layer Function Layer Chemical Identity
(mils) Outside and abuse 85% SSPE2 0.19 layer 15% LLDPE3 Core Layer
100% LLDPE2 0.29 Tie Layer 100% EMA 0.1 O.sub.2-Barrier layer 96%
VDC/MA; 0.19 2% epoxidized soybean oil; and 2% bu-A/MA/bu-MA
terpolymer Tie Layer 100% EVA1 0.1 Substrate Core Layer 80% LLDPE2
0.86 20% LLDPE3 Seal Layer 80% SSPE1 0.48 20% LLDPE 1
[0057] Table IV, below, provides another preferred multilayer film
structure for making the sets of bags in accordance with the
present invention, the film having a total thickness of 2.3 mils
and a free shrink at 185.degree. F. of 25 in the machine direction
and 41 in the transverse direction.
4TABLE IV Layer Thickness Layer Function Layer Chemical Identity
(mils) Outside and abuse 100% EVA4 0.6 layer O2-Barrier layer 96%
VDC/MA #1; 0.17 2% epoxidized soybean oil; and 2% bu-A/MA/bu-MA
terpolymer Substrate Core Layer 100% EVA4 1.28 Seal Layer 100% LDPE
0.26
[0058] Table V, below, provides another preferred multilayer film
structure for making the sets of bags in accordance with the
present invention, the film having a total thickness of 2 mils and
a free shrink at 185.degree. F. of 31 in the machine direction and
46 in the transverse direction.
5TABLE V Layer Thickness Layer Function Layer Chemical Identity
(mils) Outside and abuse 85% SSPE2 0.18 layer 15% LLDPE3 Core Layer
100% LLDPE2 0.27 Tie Layer 100% EMA 0.09 O2-Barrier layer 96%
VDC/MA #1; 0.18 2% epoxidized soybean oil; and 2% bu-A/MA/bu-MA
terpolymer Tie Layer 100% EVA1 0.09 Substrate Core Layer 80% LLDPE2
0.73 20% LLDPE3 Seal Layer 90% SSPE1 0.45 10% MB1
[0059] Table VI, below, provides another preferred multilayer film
structure for making the sets of bags in accordance with the
present invention, the film having a total thickness of 2 mils and
a free shrink at 185.degree. F. of 26 in the machine direction and
42 in the transverse direction.
6 TABLE VI Layer Thickness Layer Function Layer Chemical Identity
(mils) Outside and abuse 85% EVA3 0.27 layer 15% LLDPE3 Core Layer
100% LLDPE2 0.4 Core Layer 100% EVA3 .13 Core Layer 100% EVA3 0.09
Substrate Core Layer 76% LLDPE2 0.8 24% MB2 Seal Layer 100% LLDPE4
0.31
[0060] Table VII, below, provides another preferred multilayer film
structure for making the sets of bags in accordance with the
present invention, the film having a total thickness of 2.2 mils
and a free shrink at 185.degree. F. of 36 in the machine direction
and 51 in the transverse direction.
7TABLE VII Layer Thickness Layer Function Layer Chemical Identity
(mils) Outside and abuse 100% SSPE2 0.19 layer Core Layer 100%
SSCPE3 0.29 Tie Layer 100% EVA2 0.10 O2-Barrier layer 96% VDC/MA
#1; 0.19 2% epoxidized soybean oil; and 2% bu-A/MA/bu-MA terpolymer
Tie Layer 100% EVA1 0.10 Substrate Core Layer 90% SSCPE3 0.86 10%
EPD Seal Layer 100% SSPE1 0.48
[0061] In Tables II through VII, SSPE1 was Dow Affinity.RTM. PL
1280 ethylene/octene copolymer, having a density of 0.900 g/cc and
a melt index of 6 g/10min. SSPE2 was Dow Affinity.RTM. PL 1850,
having a density of 0.902 g/cc and a melt index of 3 g/10 min.
SSCPE3 was DPF 1150.01 single site catalyzed ethylene/octene
copolymer having a density of 0.901 g/cc and a melt index of 0.9
g/10 min, obtained from Dow. LLDPE1 was Exxon Escorene.RTM.
LL3003.32 linear low density polyethylene having a density of
0.9175 g/cc and a melt index of 3.2 g/10 min. LLDPE2 was Dow
Attane.RTM. 4203, having a density of 0.905 g/cc and a melt index
of 0.8 g/10 min. LLDPE3 is Dow Dowlex.RTM. 2045.03 linear low
density polyethylene, having a density of 0.92 g/cc and a melt
index of 1.1 g/10 min. LLDPE4 was Exceed.RTM. 4518PA
ethylene/hexene copolymer having a density of 0.918 and a melt
index of 4.5 g/10 min. LDPE was Ruxell.RTM. V3401 ethylene/octene
copolymer having a density of 0.911 g/cc and a melt index of 5.7 to
7.5 g/10 min, obtained from Huntsman. EVA1 was LD-713.93
ethylene/vinyl acetate copolymer, having a vinyl acetate content of
15 percent, a density of 0.933 g/cc and a melt index of 3.5 g/10
min, and was obtained from Exxon. EVA2 was Escorene.RTM. LD 761.36
ethylene/vinyl acetate copolymer having a density of 0.95 g/cc, a
melt index of 5.7 g/10 min, and a vinyl acetate content of 28
percent, obtained from ExxonMobil. EVA3 was Escorene.RTM. LD 318.92
ethylene/vinyl acetate copolymer having a density of 0.93 g/cc, a
melt index of 2 g/10 min, and a vinyl acetate content of 9 percent,
obtained from ExxonMobil. EVA4 was Elvax.RTM. 3128 ethylene/vinyl
acetate copolymer having a density of 0.928 g/cc, a melt index of 2
g/10 min, and a vinyl acetate content of 8.9%, obtained from
DuPont. EMA was EMAC SP 1305 ethylene/methyl acrylate copolymer,
having a methyl acrylate content of 20 percent, a density of 0.944
g/cc and a melt index of 2 g/10 min, also obtained from Exxon. EPD
was Vistalon.RTM. 7800 ethylene/propylene/diene terpolymer, having
a density of 0.87 g/cc and a melt index of 1.5 g/10 min, obtained
from Exxon. VDC/MA was SARAN.RTM. MA-134 vinylidene chloride/methyl
acrylate copolymer, obtained from the Dow Chemical Company. The
epoxidized soybean oil was PLAS-CHEK.RTM. 775 epoxidized soybean
oil, obtained from the Bedford Chemical Division of Ferro
Corporation, of Walton Hills, Ohio. Bu-A/MA/bu-MA terpolymer was
METABLEN.RTM. L-1000 butyl acrylate/methyl methacrylate/butyl
methacrylate terpolymer, obtained from Elf Atochem North America,
Inc., of 2000 Market Street, Philadelphia, Pa. 19103. MB1 was FSU
93E polyethylene masterbatch with slip and antiblock, having a
density of 0.975 g/cc and a melt index of 7.5 g/10 min, obtained
from A. Schulman. MB2 was 180637 light cream masterbatch having a
density of 1.25 g/cc, obtained from Ampacet.
[0062] FIG. 8 illustrates a schematic of a preferred process for
producing the multilayer films described in Tables I, II, and III,
above. In the process illustrated in FIG. 8, solid polymer beads
(not illustrated) are fed to a plurality of extruders 140 (for
simplicity, only one extruder is illustrated). Inside extruders
140, the polymer beads are forwarded, melted, and degassed,
following which the resulting bubble-free melt is forwarded into
die head 142, and extruded through an annular die, resulting in
tubing 144 which is 10 to 30 mils thick, more preferably 15 to 25
mils thick.
[0063] After cooling or quenching by water spray from cooling ring
146, tubing 144 is collapsed by pinch rolls 148, and is thereafter
fed through irradiation vault 150 surrounded by shielding 152,
where tubing 144 is irradiated with high energy electrons (i.e.,
ionizing radiation) from iron core transformer accelerator 154.
Tubing 144 is guided through irradiation vault 150 on rolls 156.
Preferably, tubing 144 is irradiated to a level of about 4.5
MR.
[0064] After irradiation, irradiated tubing 158 is directed through
nip rolls 160, following which tubing 158 is slightly inflated,
resulting in trapped bubble 162. However, at trapped bubble 162,
the tubing is not significantly drawn longitudinally, as the
surface speed of nip rolls 164 are about the same speed as nip
rolls 160. Furthermore, irradiated tubing 158 is inflated only
enough to provide a substantially circular tubing without
significant transverse orientation, i.e., without stretching.
[0065] Slightly inflated, irradiated tubing 158 is passed through
vacuum chamber 166, and thereafter forwarded through coating die
168. Second tubular film 170 is melt extruded from coating die 168
and coated onto slightly inflated, irradiated tube 158, to form
two-ply tubular film 172. Second tubular film 170 preferably
comprises an O.sub.2-barrier layer, which does not pass through the
ionizing radiation. Further details of the above-described coating
step are generally as set forth in U.S. Pat. No. 4,278,738, to BRAX
et. al., which is hereby incorporated by reference thereto, in its
entirety.
[0066] After irradiation and coating, two-ply tubing film 172 is
wound up onto windup roll 174. Thereafter, windup roll 174 is
removed and installed as unwind roll 176, on a second stage in the
process of making the tubing film as ultimately desired. Two-ply
tubular film 172, from unwind roll 176, is unwound and passed over
guide roll 178, after which two-ply tubular film 172 passes into
hot water bath tank 180 containing hot water 182. The now
collapsed, irradiated, coated tubular film 172 is submersed in hot
water 182 (having a temperature of about 210.degree. F.) for a
retention time of at least about 5 seconds, i.e., for a time period
in order to bring the film up to the desired temperature for
biaxial orientation. Thereafter, irradiated tubular film 172 is
directed through nip rolls 184, and bubble 186 is blown, thereby
transversely stretching tubular film 172. Furthermore, while being
blown, i.e., transversely stretched, nip rolls 188 draw tubular
film 172 in the longitudinal direction, as nip rolls 188 have a
surface speed higher than the surface speed of nip rolls 184. As a
result of the transverse stretching and longitudinal drawing,
irradiated, coated biaxially-oriented blown tubing film 190 is
produced, this blown tubing preferably having been both stretched
in a ratio of from about 1:1.5-1:6, and drawn in a ratio of from
about 1:1.5-1:6. More preferably, the stretching and drawing are
each performed a ratio of from about 1:2-1:4. The result is a
biaxial orientation of from about 1:2.25-1:36, more preferably,
1:4-1:16. While bubble 186 is maintained between pinch rolls 184
and 188, blown tubing film 190 is collapsed by rolls 192, and
thereafter conveyed through nip rolls 188 and across guide roll
194, and then rolled onto wind-up roll 196. Idler roll 198 assures
a good wind-up.
[0067] FIG. 9 illustrates a lay-flat view of an alternative set of
lay-flat L-seal bags 200, also in accordance with the present
invention. Set of bags 200 has been made by sealing the inside
layer of a flexible, thermoplastic seamless tubing to itself. Pair
of bags 200 comprises first bag 202 and second bag 204, which in
turn have open tops 206 and 208, respectively, and transverse seal
210, with end seal portion 212 serving as the end seal for first
bag 202 and end seal portion 214 serving as the end seal for second
bag 204. First bag 202 is connected with second bag 204
longitudinal seal 216. First bag 202 and second bag 204 share seal
216, so that products packaged in first bag 12 and second bag 14
are paired with one another. Side edge 218 of first bag 202 is a
folded edge (which usually is creased during processing of the
seamless tubing from which the bags are formed), as is side edge
220 of second bag 204. Skirt region 222 is below transverse seal
210, with skirt region 222 extending all the way across both first
bag 202 and second bag 204, i.e., from side edge 218 to side edge
220, with skirt region 222 extending from immediately below
transverse seal 210 to bottom edge 224.
[0068] The polymer components used to fabricate multilayer films
for use in making the bags of the present invention may also
contain appropriate amounts of other additives normally included in
such compositions. These include antiblocking agents (such as
talc), slip agents (such as fatty acid amides), fillers, pigments
and dyes, radiation stabilizers (including antioxidants),
fluorescence additives (including a material which fluoresces under
ultraviolet radiation), antistatic agents, elastomers,
viscosity-modifying substances (such as fluoropolymer processing
aids) and the like additives known to those of skill in the art of
packaging films.
[0069] The multilayer films used to make the bags of the present
invention are preferably irradiated to induce crosslinking, as well
as corona treated to roughen the surface of the films which are to
be adhered to one another. In the irradiation process, the film is
subjected to an energetic radiation treatment, such as corona
discharge, plasma, flame, ultraviolet, X-ray, gamma ray, beta ray,
and high energy electron treatment, which induce cross-linking
between molecules of the irradiated material. The irradiation of
polymeric films is disclosed in U.S. Pat. No. 4,064,296, to
BORNSTEIN, et. al., which is hereby incorporated in its entirety,
by reference thereto. BORNSTEIN, et. al. Discloses the use of
ionizing radiation for crosslinking the polymer present in the
film.
[0070] Radiation dosages are referred to herein in terms of the
radiation unit "RAD", with one million RADS, also known as a
megarad, being designated as "MR", or, in terms of the radiation
unit kiloGray (kGy), with 10 kiloGray representing 1 MR, as is
known to those of skill in the art. A suitable radiation dosage of
high energy electrons is in the range of up to about 16 to 166 kGy,
more preferably about 40 to 90 kGy, and still more preferably, 55
to 75 kGy. Preferably, irradiation is carried out by an electron
accelerator and the dosage level is determined by standard
dosimetry processes. Other accelerators such as a van der Graaf or
resonating transformer may be used. The radiation is not limited to
electrons from an accelerator since any ionizing radiation may be
used.
[0071] As used herein, the phrases "corona treatment" and "corona
discharge treatment" refer to subjecting the surfaces of
thermoplastic materials, such as polyolefins, to corona discharge,
i.e., the ionization of a gas such as air in close proximity to a
film surface, the ionization initiated by a high voltage passed
through a nearby electrode, and causing oxidation and other changes
to the film surface, such as surface roughness.
[0072] Corona treatment of polymeric materials is disclosed in U.S.
Pat. No. 4,120,716, to BONET, issued Oct. 17, 1978, herein
incorporated in its entirety by reference thereto, discloses
improved adherence characteristics of the surface of polyethylene
by corona treatment, to oxidize the polyethylene surface. U.S. Pat.
No. 4,879,430, to HOFFMAN, also hereby incorporated in its entirety
by reference thereto, discloses the use of corona discharge for the
treatment of plastic webs for use in meat cook-in packaging, with
the corona treatment of the inside surface of the web to increase
the adhesion of the meat to the adhesion of the meat to the
proteinaceous material. Although corona treatment is a preferred
treatment of the multilayer films used to make the patch bag of the
present invention, plasma treatment of the film may also be
used.
[0073] A multilayer film is preferably converted to the bags of the
present invention by heat sealing both across the film (i.e., a
transverse heat seal) as well as heat sealing in the machine
direction along the length of the film (i.e., a machine direction
seal). The transverse seal is preferably made using a heat sealing
method known as "impulse sealing", which is carried out by placing
a seal bar across the film and thereafter momentarily passing
current through a heat seal wire on the seal bar. The seal wire
heats up, transferring heat through a first side of the film tubing
(or folded film) to the other side, causing the film to be sealed
to itself. This sealing method is well known to those of skill in
the art.
[0074] The lengthwise heat sealing (i.e., machine direction heat
sealing) can be carried out using a seal bar and impulse sealing,
i.e., in the same manner that the transverse seals are made.
However, impulse heat sealing is generally carried out by
forwarding the film intermittently in a direction along the length
of the film tubing or sheet. If continuous forwarding of the film
is desired during lengthwise heat sealing, a continuous band sealer
can be used. Such continuous band heat sealers are described in
U.S. Pat. No. 5,858,153, to Mack, entitled "Method for Making
Tubular Containers", as well as U.S. Pat. No. 6,344,258 B1, to
Rasmussen, entitled "Heat-Sealing Polymer Films", and U.S. Pat. No.
5,034,088, to Denker, entitled "Band Wheel and Tension Control",
each of which is hereby incorporated, in its entirety, by reference
thereto. Continuous band sealers are available from, for example,
Lamination Plus, 1142 West Flint Meadow Drive, P.O. Box 121,
Kaysville, Utah, 84037, and Pierce Packaging Equipment, Inc., 217
South Claremont Street, San Mateo, Calif., 94401.
[0075] Although the present invention has been described in
connection with the preferred embodiments, it is to be understood
that modifications and variations may be utilized without departing
from the principles and scope of the invention, as those skilled in
the art will readily understand. Accordingly, such modifications
may be practiced within the scope of the following claims.
* * * * *