Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROTECTIVE PATCH FOR ~HRINKABLE BAG
FIELD OF THE INVENTION
This invention relates to the packaging of bone-in cuts
of meat. In particular, this invention relates to a protective
patch which prevents or reduces the likelihood that a bone will
completely puncture and rupture a thermoplastic vacuum bag and
patch combination.
BACKGROUND OF THE INVENTION
The use of heat shrinkable thermoplastics as flexible
packaging materials for vacuum packaging various foodstuffs
including meat is well-known. Such plastic materials, however,
while in general quite successful for packaging meat understand-
ably have difficulties in successfully packaging sharp or bony
products. For example, attempts to package bone-in primal cuts of
meat usually result in an unsatisfactorily large number of bag
failures due to bone punctures The use of cushioning materials
such as paper, paper laminates, wax impregnated cloth, and various
types of plastic inserts have proved to be less than totally
satisfactory in solving the problem. The preparation of special
cuts of meat or close bone trim with removal of offending bones
has also been attempted. However, this is at best only a limited
solution to the problem since it does not offer the positive
protection necessary for a wide variety of commercial bone-in
types of meat. Furthermore, removal of the bone is a relatively
expensive and time consuming procedure.
Accordingly, it is one object of the present invention
to provide a patch material and method for making the patch which
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will minimize or elimina-te the puncturing of flexible, heat
shrinkable vacuum bags by sharp bones.
An example of a prior art method of protecting a
thermoplastic bag from puncture is shown in United States Patent
No. 2,891,870 which issued on June 23, 1959 to Meyer S. Selby et
al. In the Selby patent the exposed bone in a bone-in cut of meat
is covered with a wax impregnated cloth and the thus protected
meat is placed in a heat shrinkable plastic bag. Accordingly, it
is another object of the present invention to eliminate the neces-
sity for having a separate packaging item such as a wax impregnat-
ed cloth which must be carefully positioned over the bone and
provide a protective patch which will not be as sensitive to or
dependent upon the position of the bone within a vacuum bag.
Another object of the present invention is to provide a
patch for a thermoplastic vacuum bag which is relatively strong
and tough and which can be readily adhered to -the outer surface of
a thermoplastic vacuum bag.
These and other objects of the present invention will be
more readily understood from the summary of the invention, the
drawings, and the description of the preferred embodiment which
follow:
SUMMARY OF THE INVENTION
In one aspect, the subject invention is a method of
making a multi-layer protective patch for a biaxially heat shrink-
able thermoplastic bag comprising the steps of:
a) coextruding a multi-layer, thermoplastic tube, the inner
wall of said tube comprising an ethylene vinyl acetate copolymer
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and the outer wall comprising linear low density polyethylene;
b) applying a sufficient amount cf an inert dust or powder
to the interior tube walls so that upon collapsing, the tube will
not self adhere;
c) collapsing the tube;
d) opening, inflating, heating, and stretching the tube to
biaxially orient the tube material;
e) simultaneously cooling, collapsing and flattening the
tube whereupon the tube adheres to itsel-f; and
f) cutting the tube into at least one patch.
In another aspect, the present invention provides a
protective multi-layer patch in combination with a biaxially heat
shrinkable bag, wherein said patch comprises:
I) an o~ter layer comprising a linear low density poly-
ethylene;
II) an inner layer comprising an ethylene-vinyl acetate
copolymer;
wherein said patch is biaxially heat shrinkable, and is adhered to
said bag; and wherein said patch will shrink with the bag, thereby
reducing the tendency of the patch to delaminate from the bag.
In another aspect, the present invention is a protec-
tive, biaxially heat shrinkable multi-layer patch for a biaxially
heat shrinkable bag comprising: (I) an outer layer comprising (a)
80% to 100~ by weight linear low density polyethylene, and (b) 20%
to 0% by weight ethylene-vinyl acetate copolymer having a vinyl
acetate content in the range of 7% to 12%; and (II) an inner layer
comprising an ethylene vinyl ace-tate copolymer, preferably having
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20% to 35% vinyl acetate content. In a particularly preferred
embodiment the patch material has been cross-linked to the
equivalent of a dosage level in the range between 4.5 and 13 MR.
The things or combinations that the applicant regards as
new and in which an exclusive property or privilege is claimed are
defined in the numbered claims forming part of this specification~
The claims also include some further and more particular embodi-
ments of the invention.
DESCRIPTION OF THE D~AWINGS
In the drawings which are appended hereto and made a
part of this disclosure,
Figure 1 is a perspective view of meat enclosed in a
heat shrunk bag with a patch of the present invention on the
exterior thereof;
Figure 2 is a perspective view similar to that in Figure
1, but showing meat with a prior art patch in position;
Figure 3 is a sectional view taken along lines 3-3 of
Figure 1;
Figure 4 is a fragmentary view showing the patch of the
2~ present invention adhered to a thermoplastic vacuum bag;
Figure 5 i6 a sectional view along lines 5-5 of Figure
4; and
Figure 6 is an exaggerated sectional view of the patch
material of the present invention showing a preferred arrangement
of the layers.
DETAI~ED DESCRIPTION
Referring more specifically to the drawings and to Figs.
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1-6, there is provided a bone-in cut of meat 2, for example, a leg
of lamb, having exposed bone portion 6. There is also provided
patch 8 on bag 12 covering a substantial portion of the visible
side of the package. Having the patch on the outside of the bag
facilitates the step of loading the bag by eliminating the concern
over dislodging a manually laid on cloth patch or a patch adhered
to the inside of the bag. Loading can, therefore, take place more
readily and easily. After a bone-in cut is loaded into the bag
air is evacuated from the package and the bag neck 10 is gathered
having the appearance as shown in Figure 1 and thereafter a clip 4
is applied to securely seal the bag. The bag can then be immersed
in hot water and shrunken tightly against the meat thus providing
a meat product in an evacuated atmosphere or aging and preserva-
tion. The patch 8 shrinks with the bag thus reducing the tendenc~
to delaminate when the patch is not shrinkable in the same manner
as the bag.
Figure 2 shows a prior art bag 12 and covering cloth
patch 8 which requires careful positioning of the cloth 8 over the
bone 6 and also requires care in positioning the bone within the
bag so that the cloth 8 is not pushed out of position or dis-
lodged.
Figure 3 shows t~e exposed bone portion 6 covered by bag
12 with the preferred pouch 8 adhered to the outside of the bag
over the bone protrusion.
In Figure 4 patch 8 is shown adhered to one side of a
wall of bag 12. Preferably patch 8 will cover substantially one
side of a bag in its flattened,
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lay-flat position. In many applications it is desirable to adhere
a patch to both sides o~ a bag.
Figure 5 is a cross-section view of Figure 4 showing
patch 8 adhered to the one wall of bag 12.
Figure 6 shows a cross-section, in an exaggerated form,
of patch 8 with outer layers 14 and 16 and inner layers 18 and 20.
In a preferred embodimen-t the composition of outer layers 14 and
16 comprises 87% by weight of linear low density pol~ethylene, 10%
by weight of e-thylene-vinyl acetate copolymer having 9~ vinyl
acetate and 3% pigments and additives to aid in extrusion. The
preferred linear low density polyethylene is Dowlex 2045* from Dow
Chemical Company of Midland, Michigan and the preferred ethylene-
vinyl acetate copolymer is ELVAX 3128* from the DuPont Company of
Wilmington, Delware. The inner layers 18 and 20 comprise
ethylene-vinyl acetate copolymer having 28~ vinyl acetate from the
U.S.I. Division of National Distillers of New York, N.Y. All
layers have been cross-linked by irradiation to the dosage level
which is equivalent to 7 MR.
In one test bags were made with a 17.5 inches wide and
2Q 18 inches long patch of the protective material of the present
invention on one side and a 17.5 inch wide and 10 inch long patch
on the other. The lay flat dimensions of these bags were 18
inches wide by 30 inches long. In a larger bag (22" x 34") for
blades a patch of 21.5 inches by 24 inches on one side and a patch
of 21.5 inches by 8 inches on the other was used~ Various bone-in
beef products were put up in bags with both the patch of the
present invention as described and with cloth covered bones. The
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products ranged from rib ends -to blades and arms. Of the total
of 1173 packages which used cloth to cover the protruding bones
therewere a total of 55 bone punctures whereas in 2097 packages
using the patches of the present invention as described there were
only 18 bone punctures.
The embodiment as described is a preferred one but a
satisfactory pouch can be made where the oute~ layers 14 and 16
comprise 15~ ethylene-vinyl acetate copolymer having 9~ vinyl
acetate and 83.3~ linear low density polyethylene with the balance
of 1.7% being a pigment. In addition, satisfactory pouches can be
made with the outer layers comprising a blend of 90% linear low
density polyethylene with 10~ vinyl acetate copolymer. Based on
experience it is believed that the desirable composition range for
the outer layer is 80% to 100% linear low density polyethylene and
20% to 0~ ethylene-vinyl acetate copolymer with the vinyl acetate
content having a range from 7% to 12% vinyl acetate. The inner
layer preferably comprises an ethylene-vinyl acetate copolymer
having 20 to 35% vinyl acetate content.
It has been surprisingly found tha-t the increased
strength and toughness of the patch according to the present
invention is greatly enhanced by the use of linear low density
polyethylene. The copolymers referred to as linear low density
polyethylene generally have a density of 0.900 to 0.935 grams per
cubic centimeter and a crystalline melting point in the range of
110C to 125C. These linear low density polyethylenes are not
homopolymers although they are referred to generally as "poly-
ethylene". In fact, they are copolymers of ethylene and an alpha-
olefin having a carbon number less than 18, for instance, butene-
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1, pentene-l, hexene-l, octene-l, etc. In the Dowlex* brand of
linear low density polyethylene used in the above preferred
embodiment it is understood that the alpha-olefin is octene-l.
Examples of patents showing the use of such polymers are U.S.
Patent No. 4,425,268 which issued on January 8, 1984 to Barry A.
Cooper; United States Paten-t No. 4,456,646 which issued on
June 26, 1984 to ~ishimoto et al United Statés Patent
No. 4,399,180 which issued on August 16, 1983 to William F. Briggs
et al; and United States Patent No. 4,457,960 which issued on
July 3, 1984 to David L. Newsome.
Typical vacuum bags and the vacuum bag of the type used
in the test and example set forth above are made according to the
process shown in United States Patent ~o. 3,741,253 which issued
on June 26, 1973 to Harri J. Brax et al. The method of the Brax
et al patent provides background for the description which follows
for the method of making the patch of the present invention.
To make the patch of the present invention, a first
ethylene-vinyl acetate copolymer having a vinyl-acetate content o~
approximately 28~ by weight is sent to a first extruder. This
material forms layer 18 and 20. (Fig. 6). Also, a blend having a
major proportion of linear low density polyethylene and a minor
proportion of a second ethylene-vinyl acetate copolymer, one hav-
ing a vinyl acetate content in the range of 7~ to 12%, is fed into
a second extruder. This material forms layers 14 and 16. Both
extruders feed a common coextrusion die of the type which is well-
known in the art. The extrudate which issues from the die has an
inner wall of the first ethylene-vinyl acetate copolymer and an
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outer wall of the blend. This type of coextrusion essentially
coextrudes two concentric tubes, one inside the other, and in this
case the first vinyl acetate copolymer is the inner tube~
As the tube is extruded downwardly it is closed off and
flattened by pinch rollers, but in order to keep the first vinyl
acetate copolymer from adhering to itself the interior of the tube
is coated with an inert dust or powder, preferably powdered corn-
starch, in a surface concentration sufficient to prevent self-
adherence. This flattened tubing is then fed through an irradia-
tion vault where it will preferably receive a dosage of approx-
imately 7 MR to cross-link the polymeric materials which comprise
the tube. The preferred range is 4.5 MR to 13 MR with the most
suitable range being between 6 and 8 MR. Chemical cross-linking
using an organic peroxide is thought to be an alternate cross-
linking method but irradiation cross-linking is preferred. After
receiving the cross-linking dosage the tube is opened, inflated,
heated, and stretched by the well-known bubble technique which is
described in the above mentioned Brax et al patent. The biaxially
stretching orients the tube material. After the material has been
stretched to the desired diameter and wall thickness, it is then
rapidly cooled and collapsed. This process results in a biaxially
oriented patch material which is heat shrinkable at approximately
the temperature at which it was oriented. When collapsed and
flattened the tubing will now tend to adhere to itself as the
stretching decreases the concentration of the cornstarch on the
inner surface of the bubble or stretched tubing. This concentra-
tion of the cornstarch now is low enough to permit self-
adherence. The vinyl acetate content of the inner wall is approx-
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6~536-569(S)
imately 28~ by weight. This is an ethylene-vinyl acetate copoly-
mer in the range where the ethylene-vinyl acetate copolymer acts
as an adhesive. Thus, a multi-layer tubular material is produced,
in this instance, a four layer material as shown in Figure 6 is
produced. This material can be cut into patches and adhered to
one or both sides of the heat shrinkable bag to produce a protec-
tive material which will greatly diminish the occurrence of bone
punctures.
Many suitable adhesives to adhere the patch to the bag
are available and can readily be selected by those skilled in the
art, the tendency to delaminate having been greatly reduced as the
patch shrinks biaxially as does the bag.
Having thus described my invention,
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