U.S. patent application number 10/141258 was filed with the patent office on 2003-11-13 for cold seal release film with improved scuff resistance.
Invention is credited to Longmoore, Kenneth J..
Application Number | 20030211349 10/141258 |
Document ID | / |
Family ID | 29399614 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030211349 |
Kind Code |
A1 |
Longmoore, Kenneth J. |
November 13, 2003 |
Cold seal release film with improved scuff resistance
Abstract
A cold seal release film in the form of a monolayer film or an
outer layer of a multilayer film. The cold seal release film
includes a nucleating agent and 10%-100% by weight of the polymer
composition of a polymer selected from the group consisting of
poly-1-butene homopolymers, poly-1-butene/ethylene random
copolymers having over 50% by weight poly-1-butene therein and a
blend of the poly-1-butene homopolymers and poly-1-butene/ethylene
random copolymers, and 90%-0% by weight of the polymer composition
of a polymer selected from the group consisting of ethylene random
copolymers of polypropylene, butene random copolymers of
polypropylene and ethylene-butene random terpolymers of
polypropylene.
Inventors: |
Longmoore, Kenneth J.;
(Newark, DE) |
Correspondence
Address: |
CAESAR, RIVISE, BERNSTEIN,
COHEN & POKOTILOW, LTD.
12TH FLOOR, SEVEN PENN CENTER
1635 MARKET STREET
PHILADELPHIA
PA
19103-2212
US
|
Family ID: |
29399614 |
Appl. No.: |
10/141258 |
Filed: |
May 8, 2002 |
Current U.S.
Class: |
428/515 ;
428/500 |
Current CPC
Class: |
C09J 2423/006 20130101;
B32B 2553/00 20130101; C08L 23/142 20130101; Y10T 428/31913
20150401; B32B 27/08 20130101; Y10T 428/31855 20150401; B32B 27/28
20130101; B32B 2307/748 20130101; Y10T 428/31938 20150401; B32B
27/18 20130101; C08J 2323/22 20130101; Y10T 428/31909 20150401;
C08L 23/22 20130101; C08J 5/18 20130101; C08L 23/22 20130101; C09J
2423/005 20130101; Y10T 428/2848 20150115; C09J 7/40 20180101; Y10T
428/28 20150115; C08L 2666/04 20130101 |
Class at
Publication: |
428/515 ;
428/500 |
International
Class: |
B32B 027/00 |
Claims
1. A cold seal release film in the form of a monolayer film or an
outer layer of a multilayer film, said cold seal release film
comprising a nucleating agent and 10%-100% by weight of the polymer
composition of a polymer selected from the group consisting of
poly-1-butene homopolymers, poly-1-butene/ethylene random
copolymers having over 50% by weight poly-1-butene therein and
blends of the poly-1-butene homopolymers and the
poly-1-butene/ethylene random copolymers, and 90%-0% by weight of
the polymer composition of a polymer selected from the group
consisting of ethylene random copolymers of polypropylene, butene
random copolymers of polypropylene and ethylene-butene random
terpolymers of polypropylene, said polypropylene being over 50% by
weight of the polymer composition in said ethylene random
copolymers of polypropylene and butene random copolymers of
polypropylene and being the major component by weight of the
ethylene-butene random terpolymers of polypropylene.
2. The cold seal release film of claim 1, wherein 100% of said
polymer composition is selected from the group consisting of
poly-1-butene homopolymers, poly-1-butene/ethylene random
copolymers having over 50% by weight poly-1-butene therein and
blends of the poly-1-butene homopolymers and the
poly-1-butene/ethylene random copolymers.
3. The cold seal release film of claim 1, wherein 100% of said
polymer composition is a poly-1-butene/ethylene random copolymer
having over 50% by weight poly-1-butene therein.
4. The cold seal release film of claim 1, wherein said nucleating
agent is 0.02% to 0.1% of sodium benzoate by weight based on the
weight of the polymer composition.
5. The cold seal release film of claim 2, wherein said nucleating
agent is 0.02% to 0.1% of sodium benzoate by weight based on the
weight of the polymer composition.
6. The cold seal release film of claim 3, wherein said nucleating
agent is 0.02% to 0.1% of sodium benzoate by weight based on the
weight of the polymer composition.
7. The cold seal release film of claim 1 being an outer layer of a
multilayer film.
8. The cold seal release film of claim 2 being an outer layer of a
multilayer film.
9. The cold seal release film of claim 3 being an outer layer of a
multilayer film.
10. The cold seal release film of claim 4 being an outer layer of a
multilayer film.
11. The cold seal release film of claim 5 being an outer layer of a
multilayer film.
12. The cold seal release film of claim 6 being an outer layer of a
multilayer film.
13. The cold seal release film of claim 1, wherein when said film
is a monolayer film one surface is a release surface and an opposed
surface is treated to receive either a cold seal adhesive or a
laminating adhesive thereon, and when said film is the outer layer
of a multilayer film an outer surface of said multilayer film
opposed to the outer surface of the layer constituting the cold
seal release film is treated to receive either a cold seal adhesive
or a laminating adhesive thereon.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to cold seal release films,
and more particularly to cold seal release films having improved
scuff resistance.
[0002] Cold seal release films are most commonly used as the
outside web or film of a multi-web packaging structure. In common
practice, the release film is a clear web that is reverse printed
and adhesive laminated to an inner web such as an opaque film (in a
candy bar wrap) or a metallized film (in a breakfast bar wrap).
After the two films are laminated a layer of cold seal adhesive is
applied to the inner web as the web is wound into a roll. The cold
seal release film serves the following functions: 1) it provides a
transparent web which can be reverse printed so that the decoration
is "buried" beneath the clear web to prevent the ink from being
worn away; 2) it provides the desired slip properties so that the
laminate will run effectively on packaging machines and 3) it
provides a surface with low adhesion to the cold seal adhesive so
that the laminate roll can be unwound during a packaging operation,
with the adhesive remaining on the desired surface of the
lamination.
[0003] The most successful prior art cold seal release film in the
market place today employs a polypropylene homopolymer as the cold
seal release surface. This prior art film provides good printing
characteristics, low coefficient of friction (COF) and a reasonably
low adhesive release force from the most common cold seal
adhesives; namely, acrylic/rubber latex adhesives. Moreover, prior
art cold release films employing a polypropylene homopolymer also
have reasonably good scuff resistence. However, the prior art films
employing polypropylene homopolymer have a major deficiency;
namely, they do not provide the desired low adhesive release force
from synthetic adhesives, e.g., ethylene vinyl acetate based
adhesives.
[0004] Other polymer films containing poly-1-butene homopolymer,
poly-1-butene/ethylene copolymers (collectively referred to as
polybutenes) and poly-1 butene copolymers blended with ethylene
and/or butene random polypropylene copolymers yield low adhesive
release force from both synthetic adhesives and acrylic/rubber
latex adhesives. However, these prior art films do not have desired
scuff resistence properties. Representative patents disclosing
these latter polymer compositions for cold release films are U.S.
Pat. Nos. 5,981,047; 5,798,174; 5,489,473 and 5,792,549, which are
all incorporated herein by reference.
[0005] As noted above, an important characteristic for cold seal
release films is good scuff resistence. This is an important
property because the film serves as the outside web or layer in a
monolayer or multilayer cold seal packaging application. Therefore,
scuffing, which can occur either during the printing/laminating
process or the packaging process, causes the finished product to
have a dull or shop-worn appearance, which is undesirable.
[0006] The following additional patents also disclose films
employing butene polymers:
[0007] U.S. Pat. No. 4,554,321 to Hwo et al. discloses heat
sealable films having improved seal impact strength comprising a
stereoregular, elastomeric polymer of butene-1 or blends thereof
with conventional butene-1-ethylene copolymers, optionally with
small amounts of polypropylene and/or crystallization nucleating
agents. The use of such stereoregular, elastomeric polymers is not
desirable for use in cold seal release films of this invention.
[0008] U.S. Pat. No. 5,998,039 to Tanizaki, et al. discloses a
polypropylene composite film comprising (1) a crystalline
polypropylene layer and (2) a layer formed from a blend of a
polypropylene homopolymer (5-95%) and a propylene 1-butene random
copolymer (95-5%), wherein the propylene component is greater than
50%, by weight, of the copolymer composition.
[0009] WO 00/32395 A1 to Chang et al. discloses a polypropylene
film containing a non-migratory slip and release additive package
of a synthetic or mineral wax, an aluminosilicate additive, and
optionally silicone oil and a cross-linked silicone polymer resin
to improve cold seal adhesive release properties. Although this
patent discloses adding nucleating agents to a polypropylene film
for improving the strength of the film, there is no disclosure or
suggestion that nucleating agents should or could be added to a
polymer composition including a poly-1 butene homopolymer or
copolymer composition.
[0010] Nucleating agents are known to increase the stiffness of
processed materials. Nucleating agents also are known to improve
the optical and barrier properties of the resulting materials.
Sodium benzoate is a desirable nucleating agent because, for among
other reasons, it is readily available and economically practical
to use.
[0011] However, the use of nucleating agents such as sodium
benzoate in the production of biaxially oriented polypropylene
films has been considered to be undesirable because, in the amounts
typically employed, it creates processing difficulties. U.S. Pat.
No. 5,837,177 to DiNardo et al. discloses a method of making a
polypropylene product for use in making biaxially oriented films.
The method includes the addition of an improved nucleating system
that allows for even distribution of a nucleating agent in a
polypropylene material. The improved nucleating system comprises a
nucleating agent such as sodium benzoate and a liquid miscible with
the nucleating agent. The solution is combined with the
polypropylene material, and the miscible liquid is removed during
processing.
[0012] There is a need in the packaging field for an improved cold
seal release film exhibiting both a low adhesion to cold seal
adhesives, including synthetic adhesives, and improved scuff
resistance. It is to such films that the present invention
relates.
[0013] All references cited herein are incorporated herein by
reference in their entireties.
SUMMARY OF THE INVENTION
[0014] A cold seal release film constituting either a monolayer
film or an outer layer of a multilayer film includes a nucleating
agent, such as sodium benzoate, provided in a polymer composition
comprising 10%-100% by weight of the polymer composition of a
polymer selected from the group consisting of poly-1-butene
homopolymers, ethylene random copolymers of poly-1-butene including
over 50% by weight poly-1-butene and blends of the poly-1-butene
homopolymers and the ethylene random copolymers of poly-1-butene,
and 90%-0% by weight of the polymer composition of a polymer
selected from the group consisting of ethylene random copolymers of
polypropylene, butene random copolymers of polypropylene and
ethylene-butene random terpolymers of polypropylene.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0015] A cold seal release film in accordance with this invention
includes a nucleating agent, preferably sodium benzoate, added to a
polymer composition comprising 10%-100% by weight of the polymer
composition of a polymer selected from the group consisting of
poly-1-butene homopolymers, poly-1-butene/ethylene random
copolymers having over 50% by weight poly-1-butene and blends of
the poly-1-butene homopolymers and ethylene random copolymers of
poly-1-butene, and 90%-0% by weight of the polymer composition of a
polymer selected from the group consisting of ethylene random
copolymers of polypropylene, butene random copolymers of
polypropylene and ethylene-butene random terpolymers of
polypropylene. These films have been determined to have excellent
cold seal release from a variety of adhesives, including
acrylic/rubber latex adhesives and synthetic adhesives, as well as
excellent scuff resistant properties. Most preferably, the cold
seal release from the synthetic adhesives is less than 50
grams/inch.
[0016] In accordance with this invention the poly-1-butene/ethylene
random copolymers include over 50% by weight of the 1-butene
monomer. Most preferably the poly-1-butene/ethylene random
copolymer includes less than 10% by weight of ethylene and more
preferably between 0.1% and 6% by weight of ethylene.
Representative poly-1-butene/ethylene random copolymers usable in
this invention are Basell DP8220 and Basell PB8340, which are
medium ethylene content and low ethylene content poly-1-butene
random copolymers, respectively. In particular, Basell DP8220
includes approximately 2.5% by weight ethylene and Basell PB 8340
includes approximately 0.2% by weight ethylene. It is believed,
based upon experience, that the poly-1-butene homopolymer will
perform in this invention the same as the poly-1-butene random
copolymer including 0.2% by weight ethylene. Both of the
above-identified poly-1-butene/ethylene random copolymers are
manufactured by Basell Polyolefins of Wilmington Del. 19808.
[0017] As noted above, the poly-1-butene homopolymers and
poly-1-butene/ethylene random copolymers can be employed alone, can
be blended together, or each can be employed in combination with
other copolymers and terpolymers, including ethylene/propylene
random copolymers, propylene/butene random copolymers and
propylene/ethylene/butene random terpolymers. The preferred
ethylene/propylene random copolymers are predominately propylene
monomers, by weight, including up to about 10% by weight ethylene.
More preferably the propylene/ethylene random copolymers include
less than 6% ethylene, by weight. A representative
propylene/ethylene random copolymer usable in this invention is
Fina 8573, which includes approximately 5% by weight ethylene
monomer in it. Fina 8573 is manufactured by ATO FINA
Petrochemicals, LaPorte Tex., 77571.
[0018] As noted above, another copolymer that can be employed in
combination with either poly-1-butene homopolymer or a
poly-1-butene/ethylene copolymer is a propylene/butene random
copolymer, wherein the propylene is the major component, by weight,
of the copolymer. Most preferably the propylene/butene random
copolymer includes less than 35% by weight butene and more
preferably 3% to 20% by weight butene. A representative
propylene/butene random copolymer usable in this invention is Union
Carbide DS4DO5, manufactured by DOW Plastics in Houston Tex. 77042.
This propylene/butene random copolymer includes approximately 14%
by weight butene in it.
[0019] A representative propylene/ethylene/butene random terpolymer
usable in this invention is Sumitomo SP88. This terpolymer includes
approximately 85% by weight polypropylene, based on the weight of
the polymer composition of the terpolymer, approximately 12% by
weight ethylene based on the weight of the polymer composition of
the terpolymer and approximately 3% by weight butene based on the
weight of the polymer composition of the terpolymer. This
terpolymer is manufactured by Phillips Sumika, Houston Tex.
77058
[0020] The preferred nucleating agent employed in this invention is
sodium benzoate; preferably in the range of 0.02-0.1% of the
overall polymer blend. It is considered to be within the scope of
this invention to employ other nucleating agents. Individuals
skilled in the art can test various nucleating agents to determine
whether they provide enhanced scuff resistance without adversely
affecting the cold seal release properties from the adhesive.
[0021] In the context of this invention a nucleating agent is one
that has the ability to raise the crystallization temperature of a
polyolefin as measured by Differential Scanning Calorimetry (DSC).
The quantity of the nucleating agent required to raise the
crystallization temperature will vary depending upon the specific
nucleating agent that is employed.
[0022] In accordance with this invention the cold seal release film
can be a monolayer web or film, or an outer layer of a multilayer,
coextruded film. In common packaging applications the monolayer or
multilayer, coextruded release films are adhered to yet another
film, which also can be a monolayer or multilayer film having
additional desired properties for specific packaging applications
and also receiving a cold seal adhesive on the outer exposed
surface thereof. For example, the other film can be a single layer
or multilayer white opaque film or a metallized film layer. In
these latter applications the surface of the monolayer or
multilayer, coextruded release film opposite the release surface,
which is the surface to be laminated to the other film, is treated,
preferably oxidatively treated by corona or flame treatment, to
make it receptive to laminating adhesives and, optionally, to
printing inks. Thus, this latter surface optionally can be reverse
printed so as to be viewable from the outer side of the release
layer and also is capable of receiving a laminating adhesive
thereon to bond the monolayer or multilayer release film to the
other film, as described above.
[0023] In other applications the monolayer or multilayer,
coextruded release film may be used by itself, without being
laminated to any other films. In this mode of operation, the
surface of the film opposite the surface that is intended to
function as the cold seal release surface preferably is treated,
preferably oxidatively treated by corona or flame treatment, to
make this opposite surface receptive to cold seal adhesives and,
optionally, to printing inks.
[0024] In accordance with the most preferred embodiments of this
invention, the cold seal release film is an outer layer of a
composite, multilayer, coextruded film including a central core, an
outer release layer including a nucleating agent combined with the
earlier-described polymer compositions and a skin layer on the side
opposite the release layer. As explained above, the outer surface
of this latter outer skin layer is treated, preferably oxidatively
treated by corona or flame treatment, to make the surface receptive
to printing inks and/or laminating adhesives and/or cold seal
adhesives, depending upon whether this outer surface is intended to
be reverse printed, laminated to an additional film that will
include the cold seal adhesive on the outer exposed surface
thereof, or intended to directly receive the cold seal
adhesive.
[0025] Preferably the skin layer opposite the release layer in the
multilayer, coextruded release film is a propylene/ethylene
copolymer including less than 10% ethylene, by weight, and more
preferably less than 7% ethylene by weight. A preferred
propylene/ethylene copolymer employed as the skin layer is Fina
8573, which, as noted earlier in this application, includes
approximately 5% by weight ethylene monomer in it.
[0026] In a preferred embodiment of this invention the core layer
is a polyolefin material, or a blend of polyolefin materials, and
most preferably is a polypropylene homopolymer. A representative
polypropylene homopolymer employed as the core layer is Fina
3371.
[0027] A preferred multilayer construction of this invention is a
three-layer structure including a release film or layer having a
thickness in the range of 0.25 to 20 microns; preferably 1 micron,
a 20-micron-thick core layer and 1-micron-thick skin layer.
[0028] It should be understood that the films of this invention may
include a variety of additives that are well known to those skilled
in the art. For example, antistatic additives, slip additives
(e.g., high molecular weight fatty acid amides), organic or
inorganic antiblocking additives (e.g., organic polymers such as
polyamides, polyesters, polycarbonates and inorganic materials such
as silicon dioxide and silicates) and antioxidants may be added to
one or more layers of the films of this invention, if desired.
[0029] Table 1, infra, more specifically describes the construction
and composition of seven sample multilayer, coextruded
constructions; samples 2, 5 and 6 being within the scope of the
present invention. The remaining samples were prepared for
comparison purposes.
[0030] Table 2, infra, shows the cold seal release properties and
the scuff resistence properties of the seven samples identified in
Table 1. It should be noted that in order to achieve the maximum
benefits of this invention, care should be taken to introduce the
nucleating agent uniformly throughout the composition. This can
best be achieved by grinding the sodium benzoate or other
nucleating agent to a very fine particle size, on the order of less
than 10 microns. Most preferably the nucleating agent employed in
this invention is sodium benzoate having 99.5%, by weight, of a
particle size of 10 microns or less.
1TABLE 1 Sample Descriptions Release skin Material Material
composition Description Core Composition Description Skin
composition -1 Fina 3371 homopolymer polypropylene Fina 3371
homopolymer Fina 8573 polypropylene -2 Basell DP8220 medium
ethylene content (2.5%) Fina 3371 homopolymer Fina 8573 0.05%
sodium benzoate poly-1-butene polypropylene -3 Basell DP8220 medium
ethylene content (2.5%) Fina 3371 homopolymer Fina 8573 0.0% sodium
benzoate poly-1-butene polypropylene -4 Fina 3571 homopolymer
polypropylene Fina 3371 homopolymer Fina 8573 0.3% Tospearl T-120
crosslinked polydialkyl siloxane 0.05% behenamide fatty acid amide
polypropylene (antiblock agent) (slip agent) -5 40% Basell DP8220
medium ethylene content poly-1-butene Fina 3371 homopolymer Fina
8573 60% Fina 8573 ethylene propylene random copolymer 0.05%
behenamide fatty acid amide polypropylene 0.1% sodium benzoate 0.3%
Tospearl T-120 crosslinked polydialkyl siloxane -6 40% Basell
PB8340 low ethylene (0.2 %) poly-1-butene Fina 3371 homopolymer
Fina 8573 60% Union Carbide DS4DO butene propylene random copolymer
0.05% behenamide fatty acid amide polypropylene 0.1% sodium
benzoate 0.3% Tospearl T-120 crosslinked polydialkyl siloxane -7
40% Basell DP8220 medium ethylene content poly-1-butene Fina 3371
homopolymer Fina 8573 60% Fina 8573 ethylene propylene random
copolymer 0.05% behenamide fatty acid amide polypropylene 0.0%
sodium benzoate 0.3% Tospearl T-1 20 crosslinked polydialkyl
siloxane note: all samples prepared with 1 micron release skin/20
micron core/1 micron print skin
[0031]
2TABLE 2 Cold Seal Adhesive Release Force g/in 16 hr @ 22 C, 100
psi Sutherland Rub test Release Skin Polymer ATOfindley ATOfindley
Technical Coatings Technical Coatings Initial Final or Polymer
Blend 1380 7114 339D 357D % Haze % Haze -1 Homopolymer PP 18 30 90
144 1.4 1.5* -2 Basell DP8220 + 10 20 35 54 5 6.3* Sodium Benzoate
-3 Basell DP8220 + 17 nm nm nm 4.5 22.7* NO Sodium Benzoate -4
Homopolymer PP 41 35 73 121 1.5 1.5** -5 40% DP8220 + 60% 42 30 35
64 1.2 1.2** Fina 8573 + Sodium Benzoate -6 40% PB8340 + 60% 38 24
36 63 1 1.2** DS4D05 + Sodium Benzoate -7 40% DP8220 + 60% 35 28 38
60 1.2 2.5** Fina 8573 + NO Sodium Benzoate Notes: Samples 1-3
prepared on laboratory TMLong Stretcher Samples 4-7 prepared on
pilot tenter line nm-not measured *Sutherland Rub test or 50 cycles
**Sutherland Rub test for 10 cycles
[0032] Film Testing Procedure to Determine the Cold Seal Adhesive
Release Force
[0033] A coating of the specified adhesive was applied via a Mayer
rod onto the designated film substrate to provide an adhesive
strength greater than 300 g/in. The coating was dried and then the
release film was placed against the adhesive. Next, the two films
were placed into a blocking jig where a contact force of 100 psi
was applied. The samples were held in the jig for 16 hours at
22.degree. C. The force to separate the release film from the
adhesive was then measured.
[0034] Film Testing Procedure to Determine Scuff Resistance
[0035] Two sheets of film with the release surfaces facing each
other were mounted on the base and sled of a Sutherland rub tester.
The two surfaces were then rubbed for the number of cycles
specified in Table 2. The percent of transmission haze was measured
before and after the Sutherland rub test, and the difference is the
measure of scuff resistance, i.e., the lower the difference the
better the scuff resistance.
[0036] The invention is illustrated in more detail with reference
to the following Examples, but it should be understood that the
present invention is not deemed to be limited thereto.
EXAMPLES
[0037] The test results reported in Table 2 demonstrate that the
addition of a nucleating agent, e.g., sodium benzoate, improves the
scuff resistance of the films of this invention, without adversely
affecting cold seal release from both acrylic/rubber latex
adhesives and synthetic adhesives.
[0038] Samples 1 through 3 were produced via a laboratory
co-extrusion die and then drawn 7.times. by 7.times. at a
temperature of 140.degree. C. to effect biaxial orientation. After
orientation, the films were heat set 10%. Simultaneously biaxial
orientation was carried out on a T. M. Long stretcher (T. M. Long
Corporation, Somerville, N.J.).
[0039] Samples 4 through 7 were produced by a co-extrusion process
on a pilot tenter machine, with the cross-direction orientation
step taking place after machine direction orientation, and with the
machine direction/cross-machine direction draw ratios being
5.times. by 10.times.
[0040] As noted above, samples 1-3 were prepared on the laboratory
extruder and T. M. Long stretcher. Samples 1 and 2 were evaluated
with one acrylic/rubber latex (ATOfindley 1380) and three synthetic
adhesives (ATOfindley 7114, Technical Coatings 339D and Technical
Coatings 357D). The comparative sample 3 was evaluated only with
the acrylic/rubber latex.
[0041] The ATO findley adhesives are manufactured by ATO Findley,
Wauwatosa Wis. 53226. The ATOfindley 1380 adhesive is an
acrylic/rubber latex adhesive. The ATOfindley 7114 adhesive is a
synthetic adhesive.
[0042] The Technical Coatings adhesives are manufactured by Rohm
& Haas, Woodstock Ill. 60098. Both the Technical Coatings 339D
adhesive and the Technical Coatings 357D adhesive are synthetic
adhesives.
[0043] The test results of sample 2 versus sample 1 demonstrate
that the poly-1-butene/ethylene copolymer surface has release
properties superior to homopolymer polypropylene for synthetic
adhesives, but has an inferior scuff resistance. However, a
comparison of sample 2 to comparative sample 3 demonstrates that
the scuff resistance of the nucleated polymer (sample 2) is
substantially superior to the non-nucleated polymer (comparative
sample 3).
[0044] Samples 4 through 7 were prepared in a separate set of
experiments on a pilot tenter machine, as described earlier herein.
In this sample set a polypropylene control, designated sample 4 was
compared to nucleated blends of poly-1-butene/ethylene copolymers
with an ethylene random polypropylene copolymer designated sample
5, and with a butene random polypropylene copolymer designated
sample 6. Comparative sample 7 is the same polymer blend as sample
5 but with no sodium benzoate nucleator added. Note that due to
differences in the manner of producing samples 1 and 4 the absolute
values of the adhesive release force are different. However, they
still are of the same order of magnitude; demonstrating poor
release from synthetic adhesives.
[0045] A comparison of sample 4 with samples 5 and 6 again
demonstrates that blends containing poly-1-butene/ethylene
copolymers yield superior cold seal release force for synthetic
adhesives. Comparison of sample 5 with comparative sample 7 again
demonstrates that the addition of sodium benzoate nucleator
improves the scuff resistance of the film (note that samples 1
through 3 were run for 50 cycles on the Sutherland rub tester and
samples 4 through 7 were run for only 10 cycles).
[0046] While the invention has been described in detail with
reference to specific examples thereof, it will be apparent to one
skilled in the art that various changes and modifications can be
made therein without departing from the spirit and scope
thereof.
* * * * *