U.S. patent application number 10/054620 was filed with the patent office on 2002-07-25 for halogen-free, printable, multilayered shrink films and articles encapsulated therein.
Invention is credited to Kovalchuk, John, Rackovan, Mitchell J..
Application Number | 20020098303 10/054620 |
Document ID | / |
Family ID | 22690166 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020098303 |
Kind Code |
A1 |
Rackovan, Mitchell J. ; et
al. |
July 25, 2002 |
Halogen-free, printable, multilayered shrink films and articles
encapsulated therein
Abstract
The present invention relates to a halogen-free, multilayered
heat shrink film comprising (A) a core layer comprising a copolymer
of ethylene or propylene with an alpha olefin and the core having
an upper and lower surface, (B) a skin layer on the upper surface
of the core layer, wherein the skin layer comprises a polyolefin or
polyolefin blend and (C) a printable layer on the lower surface of
the core layer, wherein the shrinkage of the film is at least about
30%. The invention also relates to articles, including cylindrical
articles such as batteries. The films have good shrinkage and
avoids end puckering. Additionally, the films are printable, even
with gravure printing. The films and labels produced thereform may
be applied at high speeds and have good heat stability.
Inventors: |
Rackovan, Mitchell J.;
(Madison, OH) ; Kovalchuk, John; (Painesville,
OH) |
Correspondence
Address: |
Heidi A. Boehlefeld
Renner, Otto, Boisselle & Sklar, LLP
1621 Euclid Avenue, Nineteenth Floor
Cleveland
OH
44115
US
|
Family ID: |
22690166 |
Appl. No.: |
10/054620 |
Filed: |
January 22, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10054620 |
Jan 22, 2002 |
|
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|
09187715 |
Nov 6, 1998 |
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Current U.S.
Class: |
428/34.9 ;
428/516; 428/520 |
Current CPC
Class: |
B32B 27/08 20130101;
B32B 2323/04 20130101; B32B 2323/10 20130101; Y10T 428/1341
20150115; B32B 2553/00 20130101; B32B 2581/00 20130101; Y10T
428/1476 20150115; B32B 2307/736 20130101; Y10T 428/1334 20150115;
Y10T 428/31928 20150401; H04L 43/10 20130101; Y10T 428/31913
20150401; B32B 2250/242 20130101; Y10T 428/14 20150115; B32B 27/32
20130101; Y10T 428/1452 20150115; Y10T 428/1328 20150115; B32B
2457/10 20130101 |
Class at
Publication: |
428/34.9 ;
428/516; 428/520 |
International
Class: |
B32B 001/08; B32B
027/08 |
Claims
1. A halogen-free, multilayered heat shrink film comprising (A) a
core layer comprising a copolymer of ethylene or propylene with an
alpha olefin and the core having an upper and lower surface, (B) a
skin layer on the upper surface of the core layer, wherein the skin
layer comprises a polyolefin or polyolefin blend and (C) a
printable layer on the lower surface of the core layer, wherein the
shrinkage of the film is at least about 30%.
2. The film of claim 1 wherein (A) is a copolymer of ethylene or
propylene and butene or hexene.
3. The film of claim 2 wherein the copolymer has a butene content
of about 3% to about 20%.
4. The film of claim 1 wherein the core layer further comprises an
olefin homopolymer.
5. The film of claim 4 wherein the olefin homopolymer is propylene
or butylene homopolymer.
6. The film of claim 1 wherein (B) is polypropylene, polybutene, or
a propylene and butene copolymer.
7. The film of claim 1 wherein (B) is a polyolefin blend of a
polyolefin homopolymer and a copolymer of ethylene or propylene and
an alpha-olefin.
8. The film of claim 1 wherein (B) is a polyolefin blend of a
propylene homopolymer and a copolymer of propylene and an alpha
olefin.
9. The film of claim 1 wherein (C) is blend of a polyolefin and a
soft polar additive.
10. The film of claim 9 wherein the polyolefin is an ethylene or
propylene homopolymer or a copolymer of ethylene and propylene.
11. A halogen-free, multilayered heat shrink film comprising (A) a
core layer comprising a blend of (1) a copolymer of ethylene or
propylene with an alpha olefin and (2) a homopolymer of an olefin,
and having an upper and lower surface, (B) a skin layer on the
upper surface of the core layer, wherein the skin layer comprises a
polyolefin homopolymer or a blend of a polyolefin homopolymer and a
copolymer of ethylene or propylene and an alpha olefin and (C) a
printable layer on the lower surface of the core layer, wherein the
printable layer comprises a blend of a polyolefin and a soft polar
additive, wherein the shrinkage of the film is at bast about
35%.
12. The film of claim 11 wherein the copolymer of (1) is a
propylene and butene copolymer.
13. The film of claim 11 wherein homopolymer of (2) is a
polybutene.
14. The film of claim 11 wherein the polyolefin homopolymer is
polypropylene or polybutene and the copolymer is a propylene butene
copolymer.
15. The film of claim 11 wherein the polyolefin is a polypropylene
or polyethylene and the soft polar additive is ethylene vinyl
acetate.
16. An article encapsulated with a multilayer heat shrink film of
claim 1.
17. A article encapsulated with a multilayer heat shrink film of
claim 10.
18. The article of claim 16, wherein the article is a battery.
19. The article of claim 17, wherein the article is a battery.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to a halogen-free multilayered shrink
films. More specifically, the invention relates to halogen-free
multilayered shrink films which are useful in encapsulating
cylindrical articles, such as batteries.
BACKGROUND OF THE INVENTION
[0002] Shrink film has been used for years to encapsulate articles.
The shrink film must be able to shrink sufficiently to provide a
smooth consistent coating. Previously, shrink films have been
polyolefins and polyolefin blends which were and are used
extensively in the food and packaging business to protect and
preserve articles, such as food. One problem with polyolefin and
polyolefin film blends is the difficulty of printing on the film.
For printing to be successful, the films must provide a surface
which will accept printing. Additionally the films must have
sufficient tensile modulus to withstand the rigors of the printing
process. Many polyolefin films do not have the tensile strength to
withstand gravure printing.
[0003] Shrink film has also been used for encapsulating cylindrical
articles such as batteries. Polyvinyl chloride (PVC) films provide
acceptable shrinkages of about 40%. However, PVC shrink films have
a problem with heat stability. After forming the shrink film, the
film should not shrink prematurely. Often, after formation, the
film may be exposed to temperatures, such as in transport. It is
desired that the shrink film does not shrink until desired. Another
problem with PVC shrink films is recent concerns over the
environmental impact of PVC film. Concern regarding potentially
adverse effect of halogens on the ozone layer has lead to efforts
to provide halogen free shrink films.
[0004] Batteries are typically encapsulated by shrink films. The
film must shrink sufficiently to encase the battery. A problem with
encapsulating batteries and any other cylindrical article is end
puckering. End puckering occurs when the shrink film does not
shrink sufficiently to provide a smooth encapsulating film at the
ends of the battery. This film folds over itself and forms a
"pucker." This puckering is unacceptable to consumers and therefore
the manufacturer.
[0005] Battery encapsulating is done at very high speeds. The speed
of the labelling is often more that 700 labels applied per minute.
It is difficult for typical shrink film labels to work under such
high speed conditions.
[0006] It is desirable to have a film which provides high
shrinkages, e.g. shrinkages of greater than 25%. It is also
desirable to have the films be halogen free. The desired film would
smoothly encapsulate the articles and avoid end puckering. Finally,
it is desirable to have of films which were printable and able to
be applied at high speeds.
[0007] U.S. Pat. No. 4,194,039, issued to Mueller, relates to a
multi-layered polyolefin shrink film. The film has three layers
comprising a core layer of a blend of ethylene-vinyl acetate
copolymer with ethylene-butylene copolymer and each skin layer of
ethylene-propylene copolymer.
[0008] U.S. Pat. No. 4,196,240, issued to Lustig et al, relates to
heat shrinkable multilayer packaging film of blended copolymers and
elastomers. The multilayer film includes a first outer layer
comprising a blend of propylene-ethylene copolymer having a high
isotactic molecular structure with less than about 6% by weight
being ethylene and having a melt flow of from about 1.5 to about 18
decigrams per minute; and (butene-1)-ethylene copolymer having a
high isotactic molecular structure with less than about 10% by
weight ethylene and having a melt flow of about 0.1 to about 5.0
decigrams per minute, and a thermoplastic elastomer selected from
the group consisting of ethylene-propylene copolymers and
ethylene-propylene diene terpolymers, the ratio of the weight of
the propylene-ethylene copolymer to the (butene-1)-ethylene
copolymer being from 2:1 to about 1:2 and the thermoplastic
elastomer being present from about 10% to about 50% by weight. The
multilayer film also has an outer layer comprising an
ethylene-(butene-1) copolymer having a melt flow of from about 0.1
to about 1 decigram per minute, having a density of from about
0.916 to about 0.920 gram per cubic centimeter, and being a linear
polymer. The multilayer film is also biaxially oriented.
[0009] U.S. Pat. No. 4,207,363, issued to Lustig et al, relates to
flexible heat-shrinkable multilayer film for packaging primal meat.
The multilayer film includes (1) a first outer layer comprising a
blend of a propylene-ethylene copolymer, a (butene-1)-ethylene
copolymer and a thermoplastic elastomer selected from the group
consisting of ethylene-propylene copolymers and ethylene-propylene
diene terpolymers; (2) a first core layer connected to the first
outer layer and being capable of being stretched during the biaxial
orientation of the multilayer film and comprising an extrudable
adhesive; (3) a second core layer connected to the first core layer
and serving as an oxygen barrier to prevent the meat cut from
spoilage and being compatible to the biaxial orientation and heat
shrinking of the film; and (4) a second outer layer comprising an
ethylene vinyl acetate copolymer. The multilayer film is biaxially
oriented.
[0010] U.S. Pat. No. 5,190,609, issued to Lin et al, relates to
stable pressure sensitive shrink label technique. The heat shrink
labels are formed from a polyolefin, such as a polypropylene, and
have a permanent acrylic pressure sensitive adhesive on one side
thereof and may be mounted on a release coated backing strip. A
metallized layer and open style graphics may be applied to the
labels and the graphics may be protected by varnish or a second
layer of heat shrinkable polyolefin material.
[0011] U.S. Pat. No. 5,443,895, issued to Peiffer et al, relates to
multilayer transparent polyolefin film for application in shrink
labeling. The heat shrinkable film comprises a base layer prepared
from a polypropylene-containing polymer and a hydrocarbon resin.
The base layer contains about 5 to 40% by weight of a polypropylene
homopolymer, 0 to about 30% by weight of a hydrogenated hydrocarbon
resin having a softening point in the range from about 80 to 125C.
and from about 30 to 95% by weight of a random ethylene-propylene
copolymer.
[0012] U.S. Pat. No. 5,494,717, issued to Peiffer et al, relates to
matte, biaxially oriented, multilayer polypropylene film of high
shrinkage, and processes of making the same. The multilayer
polypropylene film comprises at least onebase layer containing a
propylene polymer and a propylene polymer mixture in at least one
outer layer which comprises a mixture or a blend. The mixture
contains copolymers and terpolymers of alpha olefins containing 2
to about 10 carbon atoms and high density polyethylene.
[0013] U.S. Pat. No. 5,691,043, issued to Keller et al, relates to
uniaxially shrinkable biaxially oriented polypropylene film and it
method of preparation. The polypropylene film comprises a
polypropylene-containing core layer comprising at least 70% by
weight of said multilayer film and at least one
polyolefin-containing skin layer adjacent to the core layer. The
core layer is prepared by biaxially orienting a coextrudate and
thereafter orienting said coextrudate by stretching 10 to 40% in
the machine direction. The core layer contains isotactic
polypropylene and a modifier which reduces the crystallinity of the
polypropylene by increasing chain imperfections or reducing
isotacticity of the polypropylene containing core. The modifiers
include atactic polypropylene, syndiotactic polypropylene,
ethylene-propylene copolymer, propylene-butylene copolymer,
ethylene-propylene-butylene terpolymer and linear low density
polyethylene. The skin layers are selected from the group
consisting of polypropylene, ethylene-propylene copolymer,
polyethylene and ethylene-propylene-butylene terpolymer.
SUMMARY OF THE INVENTION
[0014] The present invention relates to a halogen-free,
multilayered heat shrink film comprising (A) a core layer
comprising a copolymer of ethylene or propylene with an alpha
olefin and the core having an upper and lower surface, (B) a skin
layer on the upper surface of the core layer, wherein the skin
layer comprises a polyolefin or polyolefin blend and (C) a
printable layer on the lower surface of the core layer, wherein the
shrinkage of the film is at least about 30%. The invention also
relates to articles, including cylindrical articles such as
batteries. The films have good shrinkage and avoid end puckering.
Additionally, the films are printable, even with gravure printing.
The films and labels produced therefrom may be applied at high
speeds and have good heat stability, e.g., they don't shrink
prematurely, even at temperatures approaching 170F.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present invention relates to the use of multilayer
shrink films and labels produced therefrom. The films and labels
have a shrinkage of greater than 30%, or greater than 35%, or even
greater than 40%. The shrinkage is determined at 270 degrees F. and
by ASTM D 1204. The preferred shrink temperature range is from 250
to 270 degrees F. These films also, in one aspect, may be oriented
in the machine direction, e.g. uniaxially oriented. The film
typically has a thickness from about 0.5 to about 12, or from about
1 to about 8, or from about 1.5 to about 5 mils. Here and elsewhere
in the specification and claims, the range and ratio limits may be
combined.
[0016] As described above, the multilayered shrink films have a
core layer which is comprised of a copolymer of ethylene or
propylene with an alpha-olefin. The core layer comprises a major
portion of the shrink film. Typically, the core layer has a
thickness from about 0.6 to about 4, or from about 0.8 to about 3,
or from about 1 to about 2.5, or from about 1.2 to about 2 mils
thick. The films have sufficient strength to be printed by
flexographic and gravure printing. These films generally have a
Young's modulus from about 150,000 to about 500,000, or from about
175, 000 to about 400,000, or from about 200,000 to about 300,000
psi. Young's modulus is determined by ASTM D 882. In one
embodiment, the core layer is free of vinyl acetate resins.
[0017] The core layer comprises at least one copolymer of ethylene
or propylene with an alpha-olefin. The copolymers generally have a
melt flow of about 2 to about 8, or from about 3 to about 5 g/10
min. The copolymer typically comprises from about 2% to about 30%,
or from about 5% to about 25%, or from about 10% to about 20% by
weight of the alpha-olefin. The alpha olefins have from about 3 to
about 12, or from about 4 to about 8 carbon atoms. The alpha
olefins include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene,
etc. Preferred alpha olefins are 1-butene and 1-hexene, with
1-butene more preferred.
[0018] For example, the copolymers may be obtained by
copolymerization of ethylene or propylene with an alpha olefin,
such as 1-butene, using single-site metallocene catalysts. Such
copolymers are available from Union Carbide. Polypropylene SRD4-127
is a random copolymer of propylene and 1-butene containing from
about 8% by weight of butene. This polymer is available from Union
Carbide and is characterized as having a melt flow of 8 g/10 min.
Similar copolymers include SRD4-126, SRD4-128, SRD4-130, and
SRD4-131. Polypropylene SRD4-104 is a random copolymer of propylene
and 1-butene containing about 11% butene. This polymer is available
from Union Carbide and is characterized as having a melt flow of
5.0 g/10 min. Another useful propylene and 1-butene copolymer is
available commercially from Union Carbide under the trade
designation DS4D05. This copolymer has 14% butylene and a melt flow
of about 5.5 g/10 min.
[0019] In another embodiment, the core layer comprises a blend of
one or more of the above copolymers with a polyolefin. The
polyolefin may be one of the above described copolymers, in which
case two or more of the above polymers are blended together. The
polyolefin may be a homopolymer or copolymer, preferably an olefin
homopolymer. The olefins used to make the polyolefins have from 2
to about 16, or from 3 to about 12, or from about 4 to about 8
carbon atoms. The olefins include ethylene, propylene, butylene,
pentene, hexene, heptene, octene, nonene, decene, etc. The
polyolefins typically have a melt flow from about 2 to about 10, or
from about 3 to about 8, or from about 4 to about 6 g/10 min.
[0020] In one embodiment, the polyolefin is a homopolymer of
propylene or butylene. Polypropylene and poly-1-butene may be used
as the polyolefin. An example of a propylene homopolymer useful in
the present invention is the homopolymer identified as 5C97/5A97
available from Union Carbide. This homopolymer is characterized as
having a melt flow of 3.9 g/10 min. Examples of a butylene
homopolymers are identified as 0200 (melt flow of 1.8 g/10 min) and
0300 (melt flow of 4.0 g/10 min) and available from Shell Chemical
Company.
[0021] In one embodiment, the polyolefin is a copolymer. The
copolymer may be a propylene-ethylene or a butylene-ethylene
copolymer. In one embodiment, the polyolefins are
propylene-ethylene copolymers containing up to about 10% or less of
ethylene and more often less than about 6% ethylenic content.
Ethylenic contents of from about 0.2% to about 10% are useful.
Preferably, the ethylene content is from about 3% to about 10% by
weight and more preferably from about 3% to about 6% by weight.
Examples of the types of propylene copolymers which are useful in
the present invention include Polypropylene DS 6D20, a propylene
random copolymer which contains about 3.2% by weight of ethylene
and is available from Union Carbide. This polymer has a melt flow
of 1.9 g/10 min. Polypropylene DS6D81 is a polypropylene random
copolymer available from Union Carbide which contains 5.5% by
weight of ethylene. This random copolymer is characterized as
having a melt flow of 4.5 g/10 min. When the copolymer is a
butylene copolymer, it typically includes ethylene at a level of
about 0.5% to about 12%, or of about 1% to about 10%, or from about
1.5% to about 8%. Examples of useful butylene-ethylene copolymers
are available from Shell Chemical Company as DP 8220, having an
ethylene content of 2% and a melt flow of 2.0 g/l 0 min, and DP
8310, having an ethylene content of 6% and a melt flow of 3.2 g/10
min.
[0022] When the core layer is a blend, the amount of the polyolefin
comprises from about 5% to about 55%, or from about 15% to about
50%, or from about 20% to about 45% by weight of the polymer of the
core layer. The copolymer of ethylene or propylene with an alpha
olefin makes up the balance of the polymers in the core layer. In
one embodiment, the core layer is free of ethylene homopolymer. In
another embodiment, the core layer is free of ethylene propylene
copolymers.
[0023] The following table contains examples of formlations for the
core layer of the present films and labels. Here and throughtout
the specification and claims the amounts are by weight, unless
clearly indicated otherwise.
1 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 Propylene- 100 -- 90 -- 75 -- 65
-- 55 80 butylene copolymer A.sup.1 Propylene- -- 100 -- 85 -- 70
-- 65 -- -- butylene copolymer B.sup.2 Polypropylene.sup.3 -- -- 10
-- -- -- -- -- -- 10 Polybutylene.sup.4 -- -- -- -- 25 10 -- 25 --
10 Butylene -- -- -- 15 -- 20 35 10 45 -- copolymer.sup.5
.sup.1DS4D05 (14% butylene) of Union Carbide .sup.2SRD4-127 (8%
butylene) of Union Carbide .sup.35A97 of Union Carbide .sup.40200
of Shell Chemical .sup.58220 of Shell Chemical
[0024] The following table contains further examples of core layer
formulations. In this table, DS4D05 refers to propylene-butylene
copolymer DS4D05 (14% butylene) of Union Carbide and 8220 refers to
butylene copolymer 8220 of Shell Chemical. The cores are extrusion
cast and uniaxially oriented at a ratio of 5.5:1.
2 C11 C12 C13 C14 C15 C16 C17 Core 100% 95% 90% 80% 70% 60% 55%
For- 4D05 4D05 4D05 4D05 4D05 4D05 4D05 mula 5% 10% 20% 30% 40% 45%
8220 8220 8220 8220 8220 8220 Ten- 321,000 287,000 247,000 225,000
198,000 185,000 169,000 sile psi psi psi psi psi psi Mod- ulus
[0025] The multilayer shrink film has a skin layer on the upper
surface of the core layer. The skin layer is composed of a
polyolefin or polyolefin blend. The melt index of the polyolefin or
blend is generally in the range of 4 to 12, or of about 5 to about
8 g/10 min. The polyolefin may be one or more of the above
described homopolymers or copolymers, such as ethylene-propylene
copolymers or the ethylene or propylene copolymers with an alpha
olefin. The copolymers have been described above.
[0026] When a polyolefin blend is used for the skin layer, in one
embodiment, the skin layer comprises a major amount of one or more
of the above described olefin homopolymer and a minor amount of one
or more of the above described copolymer of ethylene or propylene
with an alpha olefin. Typically the olefin homopolymer is present
in an amount from about 55% to about 95%, or from about 60% to
about 85%, or from about 80% by weight of the polymers of the skin
layer. The olefin copolymers make up the balance of the skin layer.
In one embodiment, the skin layer is free of ethylene homopolymers.
In another embodiment, the skin layer is free of ethylene propylene
copolymers.
[0027] The following table illustrates formulations for the skin
layer.
3 S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 Poly- 100 85 20 80 70 85 65 70
pro- pylene.sup.1 Poly- 100 60 70 butyl- ene.sup.2 Pro- 100 20 15
30 15 35 15 pylene- butyl- ene copoly- mer.sup.3 Ethyl- 15 5 30 15
ene- pro- pylene copoly- mer.sup.4 .sup.15A97 of Union Carbide
.sup.20200 of Shell Chemical .sup.3DS4D05 (14% butylene) of Union
Carbide .sup.4DS6D20 (3.2% ethylene) of Union Carbide
[0028] The multilayer shrink film has a printable layer on the
lower surface of the core layer. The printable layer may be
prepared by any printable material. In one embodiment, the
printable layer is a blend of a polyolefin and a soft polar
additive. The soft polar additives (SPA) of the olefin SPA blends
generally comprise random copolymers of an olefin and one or more
polar moiety. A presently preferred soft polar additive is ethylene
vinyl acetate copolymer (EVA). In particular, a commercially
available EVA which is useful contains 19% vinyl acetate and has
the following characteristics: tensile modulus (1% secant), 5300
psi; ultimate tensile strength, 2150 psi; ultimate elongation,
730%; hardness, 87 Shore A. Although EVA is presently most
preferred, alternative materials useful as soft polar additives in
the olefin-SPA blends include ethylene methyl acrylate (EMA) and
acrylonitrile butadiene rubber. These materials disclosed for use
in the printable layer comprise, in one embodiment, physical blends
of (1) polypropylene or copolymers of propylene and ethylene, as
described above, and (2) ethylene vinyl acetate (EVA) in weight
ratios ranging from 50/50 to 60/40. The soft polar additive and the
olefin blends are described in U.S. Pat. No. 5,709,937 issued to
Adams et al and U.S. Pat. No. 5,585,193 issued to Josephy et al,
the disclosure of which is incorporated by reference.
[0029] Examples of polymers which may be used to form the print
layer include the above polyolefins and polymers such as
polyethylene methyl acrylate, poly ethylene vinyl acetate,
polyethylene ethyl acrylate, polymethylmethacrylates, acrylonitrile
butadiene styrene polymer, nylon, polybutylene, polystyrene,
polyurethane, polysulfone, polyvinylidene chloride, polypropylene,
polypropylene copolymers, polycarbonate, polymethylpentene, styrene
maleic anhydride polymer, styrene acrylonitrile polymer, ionomers
based on sodium or zinc salts of ethylene/methylacrylic,
cellulosics, fluoroplastics, polyacrylonitriles, and thermoplastic
polyesters. In one embodiment, the third layer is a blend of about
25% to 75%, or about 50% of polyethylene vinyl acetate, such as UE
63104 available from Equistar, and blend of about 25% to 75%, or
about 50% of polypropylene homopolymer, such as Union Carbide 5A97
(4 melt flow).
[0030] As mentioned above, the composites of the present invention
comprise at least one print layer comprising an olefin-SPA blend
comprising from about 30% to about 60% by weight of SPA. In other
embodiments, the olefin-SPA blend used in the print layer will
contain from about 40% to about 60% by weight of SPA, and in
another embodiment, about 50% by weight of SPA.
[0031] The following table illustrates formulations for the
printable layer.
4 P1 P2 P3 P4 P5 P6 Polypropylene.sup.1 50 -- 60 40 -- 55 Ethylene-
-- 50 -- -- 55 -- propylene copolymer.sup.2 EVA.sup.3 50 50 40 60
45 45 .sup.15A97 of Shell Chemical .sup.2DS6D20 (3.2% ethylene) of
Union Carbide .sup.3ethylene vinyl acetate copolymer (18% vinyl
acetate) of AT Polymer of Toronto, Canada
[0032] As noted above, the core layer is relatively thick compared
to the outer, e.g. printable and skin layers. Thus, the core layer
may be about 2 to 20 times as thick as each of the outer layers.
Examples of thickness ratios of the core to the outer layers
combined include 90:10, 80:20, 70:30 etc. The thickness ratios of
the printable skin layer to the core and then to the outer skin
layer are 5-20:9060:20-5, or 10-15: 70-90:15-10. Thickness ratios
for the three layered films include 5:90:5, 10:80:10, 15:70:15,
20:60:20, etc. The two skin layers do not have to be of equal
thickness.
[0033] The films and labels of the present invention are further
illustrated in reference to the attached drawings. FIG. 1 is a
cross-sectional area of a label of the present invention. Label 10
is a coextrudate which comprises core layer 11, skin layer 12 and
print layer 13. Print layer 13 is adhered to pressure sensitive
adhesive 14. Pressure sensitive adhesive 14 is releasably bonded to
release liner 15.
[0034] It is also contemplated that the present film may have one
or more of the skin layers and one or more of the print layers.
These layers are attached by coextruding a tie layer between each
of the skins. The tie layers may be-any polymer which improves the
adhesion of the layers. Examples of suitable tie layers include
Platamid, available from Elf Atochem, and CXA, Bynel, or Plexar
series of tie layers available from DuPont Chemical.
[0035] The film with tie layers is further illustrated by FIG. 20.
Label 20 has core layer 21 attached to inner skin layer 23. Inner
skin layer 23 is attached to outer skin layer 22 by tie layer 24.
The opposite side of core layer 21 is attached to an inner print
layer 25. The inner print layer 25 is attached to tie layer 27 and
to outer print layer 26. Outer print layer 26 is bonded to pressure
sensitive adhesive 28 which in turn is releasably bonded to release
liner 29.
[0036] The following labels contain examples of multilayered films
of the present invention. These films are prepared by coextrusion
and uxiaxially oriented to a stretch ratio of 5.5:1.
5 L1 L2 L3 L4 L5 L6 L7 L8 L9 L10 Skin layer S1 S6 S1 S4 S1 S7 S8 S1
S6 S6 Core layer C1 C5 C7 C1 C5 C7 C1 C5 C7 C7 Printable layer P1
P1 P1 P1 P1 P1 P1 P1 P1 P1
[0037] The multilayer shrink film may be prepared by means known to
those in the art. The film may be prepared by co-extrusion,
extrusion coating or lamination. The following table contains
examples of multilayer shrink films which are useful in the present
invention. These films are generally prepared by coextrusion of the
three layers.
[0038] As discussed above the films may be directionally oriented.
This is accomplished by stretching the film as is known to those in
the art. The multilayer films of the present invention typically
hate a stretch ratio from about 2 to about 9, or from about 3.5 to
about 7, or from about 4 to about 6. The processes for extruding
films and orient them are described in U.S. Pat. No. 5,709,937,
issued to Adams et al, and U.S. Pat. No. 5,435,936, issued to
Rackovan et al, the disclosures of which are incorporated by
reference for these teachings.
[0039] As described above, the films are useful in many shrink film
applications. The films may be converted to a label by adding a
pressure sensitive adhesive to the printable side of the film,
e.g., the side with the soft polar additives. Print indicia may be
placed onto the film prior to adding a pressure sensitive adhesive.
The adhesive may be any of those known to those skilled in the
art.
[0040] The pressure sensitive adhesive may be any solvent or
emulsion based pressure sensitive adhesive such as acrylic or
rubber based pressure sensitive adhesives. Typically, the adhesive
is placed onto the film at a coat weight of about 10 to about 40,
or from about 20 to about 25 grams/m.sup.2. An example of a
particularly useful adhesive is S2001 available from Avery
Chemicals.
[0041] The labels of the present invention may be prepared by
coextruding a skin layer, core layer and print layer such as those
described above. This film is then printed by gavure printing and
transfer laminated to a pressure sensitive adhesive on a release
liner such as the silicone treated paper.
[0042] The labels are particularly useful in encapsulating articles
such as batteries. By way of illustration, the above film is
laminated to a pressure sensitive adhesive with liner. The film is
die cut to form individual labels and the matrix surrounding the
labels are removed. The resulting labels are then applied to a
battery and then shrink wrapped in a heat tunnel. The temperature
of the heat tunnel is approximately 250-260.degree. F. The labels
of the present invention encapsulate the battery as well without
end puckering. When using these labels to encapsulate batteries, it
is also understood that the labels may further include circuitry
such as that used to determine the strength of the battery charge.
Circuitry may be internal of the label, e.g., on the adhesive side
of the label or on the outer surface of the label such as circuitry
which would then be further covered with another film such as those
described above, or a varnish to protect it from damage.
Encapsulates for batteries and methods for encapsulating batteries
along with description of some circuitry for battery labels is
described in U.S. Pat. No. 5,190,609, issued to Lin et al. This
patent in incorporated by reference for those teachings.
[0043] While the invention has been explained in relation to its
preferred embodiments, it is to be understood that various
modifications thereof will become apparent to those skilled in the
art upon reading the specification. Therefore, it is to be
understood that the invention disclosed herein is intended to cover
such modifications as fall within the scope of the appended
claims.
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