U.S. patent application number 10/274389 was filed with the patent office on 2003-02-20 for novel slip agents and polypropylene films prepared therefrom.
This patent application is currently assigned to Applied Extrusion Technologies, Inc.. Invention is credited to Bullock, Edward K., Longmoore, Kenneth J..
Application Number | 20030036592 10/274389 |
Document ID | / |
Family ID | 25486916 |
Filed Date | 2003-02-20 |
United States Patent
Application |
20030036592 |
Kind Code |
A1 |
Longmoore, Kenneth J. ; et
al. |
February 20, 2003 |
Novel slip agents and polypropylene films prepared therefrom
Abstract
Novel polypropylene films are prepared from a composition
comprising polypropylene and an N,N--N,N'-bis-alkylene fatty amide
having the general structural formula
R--CO--NH--(CH.sub.2).sub.n--NH--CO--R.sup.1 wherein R and R.sup.1
are the same or different alkyl or alkenyl groups having about 15
to 21 carbon atoms, n is an integer from 2 to 4 and --CO-- is a
carbonyl group. Such films are found to have improved utility for
gravure printing applications.
Inventors: |
Longmoore, Kenneth J.;
(Newark, DE) ; Bullock, Edward K.; (Landenberg,
PA) |
Correspondence
Address: |
CAESAR, RIVISE, BERNSTEIN,
COHEN & POKOTILOW, LTD.
12TH FLOOR, SEVEN PENN CENTER
1635 MARKET STREET
PHILADELPHIA
PA
19103-2212
US
|
Assignee: |
Applied Extrusion Technologies,
Inc.
New Castle
DE
|
Family ID: |
25486916 |
Appl. No.: |
10/274389 |
Filed: |
October 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10274389 |
Oct 18, 2002 |
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08947869 |
Oct 9, 1997 |
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6497965 |
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Current U.S.
Class: |
524/229 ;
524/583 |
Current CPC
Class: |
B32B 27/32 20130101;
B32B 2323/10 20130101; C08K 5/20 20130101; Y10T 428/31913 20150401;
C08K 5/20 20130101; B32B 2250/40 20130101; Y10T 428/31909 20150401;
C08L 23/10 20130101 |
Class at
Publication: |
524/229 ;
524/583 |
International
Class: |
C08K 005/20 |
Claims
What is claimed is:
1. A composition comprised of polypropylene and an
N,N'-bis-alkylene fatty acid amide having the general structural
formula R--CO--NH--(CH.sub.2).su- b.n--NH--CO--R.sup.1 wherein R
and R.sup.1 are the same or different alkyl or alkenyl groups
having about 15 to 21 carbon atoms --CO-- is a carbonyl group and n
is an integer from 2 to 4, said N,N'-bis alkylene fatty acid amide
being present in an amount from about 0.05 to about 0.5% by weight
based on the combined weight of said amide and the
polypropylene.
2. The composition according to claim 1 wherein the polypropylene
is a copolymer of ethylene and propylene containing up to about 6%
by weight of ethylene.
3. The composition according to claim 2 wherein the
N,N'-bis-alkylene fatty acid amide is N,N'-bis-ethylene
oleamide.
4. A polypropylene film comprised of a composition comprising
polypropylene and an N,N'-bis-alkylene fatty acid amide, having the
general structural formula
R--CO--NH(CH.sub.2).sub.n--NH--CO--R.sup.1 wherein R and R.sup.1
are the same or different alkyl or alkenyl groups having about 15
to 21 carbon atoms --CO--is a carbonyl group and n is an integer
from 2 to 4, said N,N'-bis alkylene fatty acid amide being present
in an amount from about 0.05 to 0.25% by weight based on the
combined weight of said amide and the polypropylene.
5. A film according to claim 4 wherein the polypropylene component
is a copolymer of ethylene and propylene containing up to about 6%
by weight of ethylene.
6. A film according to claim 5 wherein the N,N'-bis-alkylene fatty
acid amide is N,N'-bis-ethylene oleamide.
7. A composite film comprised of a core layer of polypropylene
having one or more functional layers on its surfaces, at least one
functional layer being a layer comprising polypropylene and an
N,N'-bis-alkylene fatty acid amide having the general structural
formula R--CO--NH--(CH.sub.2).su- b.n--NH--CO--R.sup.1 wherein R
and R.sup.1 are the same or different alkyl or alkenyl groups
having about 15 to 21 carbon atoms --CO-- is a carbonyl group and n
is an integer from 2 to 4, said N,N'-bis alkylene fatty acid amide
being present in an amount from about 0.05 to 0.25% by weight based
on the combined weight of said amide and the polypropylene:
8. A composite film according to claim 7 wherein the polypropylene
component of the said at least one functional layer is a copolymer
of ethylene and propylene containing up to about 6% by weight of
ethylene.
9. A composite film according to claim 8 wherein the
N,N'-bis-alkylene fatty acid amide is N,N'-bis-ethylene oleamide.
Description
[0001] This invention relates to a novel polypropylene composition
having specific utility in the manufacture of oriented
polypropylene films and to polypropylene films prepared therewith.
More specifically, it relates to polypropylene compositions
containing certain fatty acid amides not heretofore known to be
useful as components in polypropylene compositions.
BACKGROUND INFORMATION
[0002] In the manufacture of polypropylene films, it is common
practice to include, in the polymer formulation, additives referred
to as slip agents. These additives migrate to the surface of the
film and decrease the coefficient of friction between the film and
the metal rollers over which it is passed during processing, thus
facilitating the processing of the film. They also decrease the
coefficient of friction between layers of the film when it is wound
into rolls thereby facilitating unwinding of the rolls for further
processing.
[0003] The slip additives employed in most commercial polypropylene
films are relatively high molecular weight fatty acid amides. The
most widely used fatty acid amides are erucamide, an unsaturated 22
carbon amide (13-docosenamide) and behenamide (docosanamide), the
saturated analogue of erucamide. Both of these compounds are
readily available, naturally occurring materials. They are normally
provided as mixtures containing a small amount of other amides
containing about 18 to 20 carbons.
[0004] Erucamide works quite well as a slip agent, but it is not
favored by some producers and converters as it is relatively
volatile and extra care is required during film manufacture and
conversion to avoid having quantities of the additive escape from
the film and plate out on processing equipment, thereby causing a
clean-up problem. For this reason, some producers prefer to use
behenamide as the slip agent. As slip agents, erucamide and
behenamide appear to perform substantially equally well but
behenamide is less volatile and therefore films containing
behenamide are easier to handle during processing since the
behenamide does not escape and plate out on the processing
equipment.
[0005] Despite the inconveniences encountered with
erucamide-containing film, erucamide is the fatty acid amide slip
agent of choice for those who wish to print the film using the well
known rotogravure printing technique. In the rotogravure process,
ink is applied to the print surface from a gravure cylinder
containing the desired image as depressions on its surface. Ink is
applied to the cylinder and the surface of the cylinder is wiped by
a doctor blade to remove excess ink. The film to be printed is then
contacted by the gravure cylinder and the image is thus transferred
from the cylinder to the film. While the film is in contact with
the cylinder, a small amount of erucamide is deposited on the
raised portion of the cylinder. Since erucamide is soluble in the
alcohol or ketone ink solvent, it is dissolved by the solvent in
the next application of ink and is removed by the next swipe of the
doctor blade. Thus, no build-up of erucamide occurs on the doctor
blade or on the gravure cylinder.
[0006] Behenamide, on the other hand, lacking the carbon-carbon
unsaturation found in erucamide, is substantially less soluble in
the alcohols and ketones found in printing inks. Thus, when, in the
course of rotogravure printing, some of the behenamide is deposited
on the printing cylinder, it is not dissolved in the printing ink
and wiped off when the next application of ink and wiping by the
doctor blade takes place. As a result, the behenamide is merely
wiped off by the next swipe of the doctor blade and substantially
all of it remains on the blade. After multiple swipes of the blade,
a behenamide build-up forms on the doctor blade and on the printing
cylinder, eventually reaching a point at which the blade is
prevented from wiping the surface of the printing cylinder clean.
This build-up causes streaks to form on the printed film, requiring
an interruption of the job in order to clean the doctor blade.
[0007] It will be immediately apparent that a slip additive that
does not cause the film processing problems associated with
erucamide but which allows the film to be rotogravure printed
without causing the problems associated with behenamide would be a
welcome contribution to the polypropylene film art. In accordance
with this invention, there has been discovered a slip additive that
accomplishes this objective.
[0008] It is an objective of this invention to provide oriented
polypropylene films that exhibit improved properties in rotogravure
printing as compared to films presently known to the art. it is
likewise an objective of this invention to provide film-forming
compositions for preparing such films.
BRIEF DESCRIPTION OF THE INVENTION
[0009] In accordance with this invention, it has been found that
certain bis-fatty acid amides exhibit a combination of properties
that makes them highly satisfactory as slip agents in oriented
polypropylene films. In particular, this combination of properties
make them highly satisfactory as slip agents in films that are to
be printed in rotogravure printing operations.
[0010] Briefly stated, the invention is a composition comprised of
a polymer or copolymer of propylene and an N,N'-bis-alkylene fatty
acid amide having the general structural formula
R--CO--NH--(CH.sub.2).sub.n--- NH--CO--R.sup.1 wherein R and
R.sup.1 are the same or different alkyl or alkenyl groups having
about 15 to 21 carbon atoms --CO-- is a carbonyl group and n is an
integer from 2 to 4 said N,N'-bis alkylene fatty acid amide being
present in an amount from about 0.05 to about 0.5% by weight based
on the combined weight of said amide and the polypropylene.
[0011] In another aspect, the invention contemplates an oriented
film comprised of a polymer or copolymer of propylene and an
N,N'-bis-alkylene fatty amide having the general structural formula
R--CO--NH--(CH.sub.2).s- ub.n--NH--CO--R.sup.1 wherein R and
R.sup.1 are the same or different alkyl or alkenyl groups having
about 15 to 21 carbon atoms, n is an integer from 2 to 4 and --CO--
is a carbonyl group said N,N'-bis alkylene fatty acid amide being
present in an amount from about 0.05 to about 0.5% by weight based
on the combined weight of said amide and the polypropylene.
[0012] A preferred embodiment of the invention is a composite film
comprised of a polypropylene core having, on at least one of its
surfaces, a film layer comprised of a composition comprising
polypropylene and up to about 0.5% of an N,N'-bis-alkylene fatty
amide having the general structural formula
R--CO--NH--(CH.sub.2).sub.n--NH--CO- --R.sup.1 wherein R and
R.sup.1 are the same or different alkyl or alkenyl groups having
about 15 to 21 carbon atoms, n is an integer from 2 to 4 and --CO--
is a carbonyl group, said N,N'-bis alkylene fatty acid amide being
present in an amount from about 0.05 to about 0.5% by weight based
on the combined weight of said amide and the polypropylene.
DETAILED DESCRIPTION OF THE INVENTION
[0013] As used in the description of this invention and in the
attached claims, the term "film" refers to a stand-alone film, i.e.
a film of a sufficient thickness to have the strength and other
characteristics required to have utility in packaging and other
applications without having to be united with another film to
support it. Stand-alone monolayer films are seldom seen in
commerce. However, the compositions of the invention are suitable
for use in such films.
[0014] Oriented polypropylene films of commerce are usually
composite, i.e. multilayer, structures in which a core layer of a
thickness sufficient to impart stand-alone properties to the
overall structure carries one or more thin functional layers on its
surface(s). The term "film" will also be used to refer to these
thin functional layer films although they do not have sufficient
thickness to stand alone.
[0015] Composite polypropylene films are typically comprised of a
homopolypropylene core having one or more functional layers on its
surfaces. Functional layers can act, e.g., as heat or cold seal
layers, as receiving layers for printing or other decorative
material or as barrier coating receiving layers. In these cases, it
is not required that the polymer in the surface layer be the same
as that employed in the core, although it may be the same polymer
formulated differently to serve the functional role that it is to
serve in the completed film. Frequently, the surface layer will be
of a different polymer that has been found to perform the desired
function more satisfactorily than would the polymer employed in the
core.
[0016] When reference is made herein to polypropylene, it is
intended to indicate a crystalline (isotactic) propylene
homopolymer or a copolymer of propylene with ethylene or an
.alpha.-olefin having 2 to 5 carbon atoms in an amount insufficient
to have a significant effect on the crystallinity of the
polypropylene. Typically, the comonomer will be ethylene in an
amount of 6% or less.
[0017] Suitable polypropylenes are the commercially available
isotactic polypropylenes having a melt flow rate between about 2
and about 10 dg/10 min at 230.degree. C. and 2.16 Kg. load and a
DSC melting point of about 160 to 166.degree. C. One polypropylene
that can be used is the isotactic homopolymer having a melt flow
rate of about 3.5 dg/10 min at 230.degree. C. and 2.16 Kg. load,
available from Aristech Chemical Corporation, Pittsburgh, Pa..
Suitable polypropylenes are also available from Montell, Inc.
Wilmington, Del., Exxon Chemical Company, Baytown, Tex., and Fina
Oil and Chemical Co., Deer Park, Tex.
[0018] Since different layers are formulated differently, it is
possible that different slip agents may be used in the different
layers or that some layers contain no slip agent. Thus, it is
possible and desirable, in cases where problems are encountered
when using conventional slip agents, e.g. in the rotogravure
printing process as described above, to limit the use of the
bis-amides of the invention to the functional layer where its
presence yields the desired advantage. In such cases, where in the
past the conventional slip agents have been added to the core layer
and allowed or forced to migrate into the functional layers, it is
found that the presence of the bis amides almost completely
prevents the migration of the conventional slip agent, e.g.
erucamide or behenamide from the core to the functional layer where
it can cause a problem.
[0019] The slip additives employed in the compositions and oriented
films according to this invention are N,N'-bis- fatty acid amides
having the general structural formula
R--CONH--(CH.sub.2).sub.n--NH--CO--R.sup.1 wherein R and R.sup.1
are the same or different alkyl or alkenyl groups having about 15
to 21 carbon atoms, n an integer from 2 to 4 and --CO-- is a
carbonyl group. The compounds employed in the compositions of this
invention are characterized by having a relatively low degree of
volatility and a relatively high degree of solubility in alcohols,
ketones and esters.
[0020] Compounds meeting the above definition and description
include, by way of example, N, N' bis-ethylene stearamide, N,N'-bis
ethylene oleamide, N,N'-bis ethylene behenamide, N,N'-bis ethylene
erucamide, N,N'-bis propylene stearamide, N,N'-bis butylene
oleamide.
[0021] The N,N'-bis-alkylene fatty acid amide is present in the
compositions of the invention in a concentration of about 0.05 to
about 0.5% by weight based on the total weight of the composition.
Preferably, the concentration of the slip additive is between about
0.05 and about 0.25% and most preferably between about 0.5 and
about 0.2%.
[0022] The slip agents of the prior art such as erucamide or
behenamide are sufficiently volatile that a measurable portion of
them always migrates from the interior of the film and forms a
layer of slip agent on the film's surface, whether the film is a
composite or a monolayer. The amount present on the surface can be
measured by a technique referred to as Attenuated Total Reflectance
Infra-Red Spectroscopy (ATRIR). When the ATRIR spectrum of a film
sample stored at room temperature is compared to that of a film
stored for 16 hours at 55.degree. C., an increase in the amount of
a prior art slip agent is detected. (Such heat aging is commonly
applied to simulate film aging conditions.) The amount of the slip
agents of this invention that migrates to the surface of a film
cannot be measured by ATRIR. Their presence on the film surface is
demonstrated only by their efficacy as slip agents.
[0023] The presence of conventional slip agents on the surface of a
film can also be detected by rinsing the film surface with a
solvent and testing for the slip agent by High Pressure Liquid
Chromatography. Similarly, no accumulation of the slip agent of the
invention can measured on the film surface by this technique,
whereas it is readily detected in the solvent employed to wash the
surface of a prior art film.
[0024] In prior art practice, slip agent is frequently incorporated
into the core layer of composite films, which are then heat treated
to force it to migrate to the surface layers. In other cases, if
the slip agent is present only in a surface layer, it tends to
migrate into the core layer although, as a rule, it is not needed
there. In either case, this migratory tendency results in slip
agent being present in locations where it is not needed. Moreover,
it also requires the use of greater quantities of slip agent than
are needed in order to assure that sufficient quantities are
present in the area where the real need exists.
[0025] It has been found that the slip agents of this invention
exhibit a very low tendency to migrate between layers or even
within a layer of the film. Thus, a slip agent incorporated in a
surface layer does not migrate into the core layer, nor does it
migrate and accumulate on the surface of a layer as do the slip
agents of the prior art. When tested by the ATRIR test or the
surface rinse procedure mentioned above no accumulation of the slip
agent is detected on the surfaces. The low migratory character of
these slip agents causes them to remain in the layer into which
they are incorporated.
[0026] Despite the absence of measurable amounts of the slip agent
on the film surface, the slip agents of the invention are
substantially equal to those of the prior art in decreasing the
coefficient of friction (COF) of the film surface. Thus, the COF
measured on the surface of a prior art film containing erucamide as
the slip agent is about 0.15 to 0.35. That measured on a prior art
film containing behenamide is about 0.15 to 0.35. The COF measured
on the surface of a film of this invention is generally between
about 0.15 and about 0.45.
[0027] The low migratory character of the slip agents of the
invention also leads to other favorable effects on film processing.
For example, the problem of vaporization encountered with erucamide
and to a lesser extent with behenamide is eliminated. Also, as will
be apparent from the above, in the preparation of composite films,
it is not always necessary to have a slip agent in the core layer.
Since the slip agent of the invention will not migrate into the
core layer, one can put only the amount actually needed to give the
desired slip properties in the surface layer and it will not
migrate into the core layer and reduce the level in the surface
layer below that required to give the surface of the film the
proper slip quality.
[0028] As indicated hereinabove, the compositions of the invention
have particular utility in the manufacture of rotogravure printable
oriented polypropylene film thanks to the unique combination of
good alcohol, ketone and ester solubility and low volatility
exhibited by the N,N'-bis-alkylene fatty acid amides. Due to their
low degree of volatility, these compounds do not vaporize from the
surface of the film during manufacturing and conversion. Due to
their relatively high degree of solubility in the solvents that are
normally employed as solvents for printing inks, whatever small
amounts these compounds that might be on the film surface does not
form a build-up on the doctor blade during rotogravure printing.
Films prepared using these compositions thus combine the favorable
properties of conventional films containing behenamide during the
manufacture and conversion of the film with the favorable
properties of those containing erucamide for use in rotogravure
printing.
[0029] In yet another aspect, the slip agents employed in the films
of the invention are found to be improved candidates for use as
cold seal films. Cold seal films are prepared by treating the films
with a cold sealable adhesive such as a rubber cement and many
applications for printed films are applications in which cold seals
are preferred over more conventional heat seals. In prior art
usage, particularly when erucamide is employed as the slip agent,
it is found that the high level of the slip agent on the film
surface weakens or even, in extreme cases, destroys cold
sealability. Using the slip agents of this invention at the levels
specified, very little or no harmful effect on cold seal is
seen.
[0030] In addition to the slip agents of this invention,
conventional additives, in conventional amounts, can also be
included in the films. Suitable conventional additives include, by
way of example, antioxidants, pigments, orientation stress
modifiers, flame retardants, antistatic agents, antiblocking
agents, and antifoggants. Any such additives that do not interfere
with the functioning of the slip agent can be present.
[0031] In any embodiment of the films of the invention, the film
can be either clear and transparent or it can be opaque. Typically,
polypropylene films are rendered opaque by loading the core layer
with a void forming opacifier such as calcium carbonate. Such
opacifiers cause opacity by forming microvoids in the polymer
matrix during the drawing operation. Other types of opacifiers
which cause opacity simply by increasing the optical density
without voiding can also be employed. Typical of such an opacifier
is titanium dioxide.
[0032] The total film thickness, for either the single or multiple
layer films, is preferably in the range of about 0.25 to about 1.5
mil, i.e. about 25 to about 150 gauge. In the multilayer
embodiment, the core layer preferably has a thickness of about 23
to about 40 gauge, while the other layers preferably each have a
thickness of about 2 to about 10 gauge.
[0033] To prepare a printable surface, the surface of the film that
is to be printed is subjected to an oxidation treatment to impart a
degree of polarity to the surface, which ensures good adhesion of
the printed information to the film. Suitable oxidation treatments
include, by way of example, corona discharge, flame and acid
etching. The preferred treatment is with corona discharge or with
flame. The use of flame and corona, seriatim, is also known and
frequently employed.
[0034] The oxidation treatment is preferably carried out to a
degree sufficient to create a surface tension on the film surface
equal to about 35 to about 60 dynes/cm. A preferred surface tension
is about 35 to about 40 dynes/cm.
[0035] As stated hereinabove, composite films can have, in addition
to the printable surface, other functional layers on the surface
opposite the print layer. If the layer on the side opposite the
print layer is a barrier coating receiving layer, that layer will
also be subjected to an oxidation treatment to approximately the
same degree as is applied to the print layer.
[0036] While the invention has been described with emphasis on its
utility in rotogravure printing, it will be apparent that other
types of films, including functional layers, can also benefit from
the low volatility and the lower degree of migratory tendency of
the slip agents of the invention. One type of such film is
metallizable film where the greater migratory tendency and
volatility of conventional slip agents tends to result in a greater
amount of slip agent on the film surface, which can sometimes
interfere with bonding of the metal coating to the film surface.
The same effect is also noted with cold seal coatings applied to
the film surface.
[0037] Polypropylene films according to the invention can be
prepared using film forming and orientation methods and techniques
well known to the plastic film art. Thus the films can be prepared
using the tubular or bubble process wherein a tube of film is
extruded through a circular die and is drawn and inflated
simultaneously to effect biaxial orientation. Likewise, they can be
prepared by the tenter process in which a flat sheet of the film is
drawn from the die at a multiple of the lineal rate of extrusion to
effect longitudinal orientation and is thereafter drawn laterally
by a preselected multiple of its original width to effect lateral
orientation. As a rule, films prepared by the bubble process are
drawn uniformly 6.times. by 6.times. or 7.times. by 7.times.. When
the tenter process is employed, the draw is usually carried out to
5.times. in the machine direction and 10.times. in the cross
direction. These draw ratios are also suitable for the films of the
invention, although other ratios can be employed if desired.
[0038] In the examples that follow, a series of biaxially drawn
three layer composite films were prepared on a 2.5 meter tenter.
The films were cast from a three layer die at 265.degree. C. onto a
chill roll maintained at 40.degree. C. The cast films were drawn
4.8.times. in the machine direction at 120.degree. C. and then
10.4.times. in the cross direction at 120.degree. C. Finally, they
were heat set at 160.degree. C. to a relaxation of about 8%. All
samples were then corona treated on a covered roll corona treater
at 35.degree. C. and 20 amps.
EXAMPLE 1
[0039] A three layer composite film comprised of a homopolymer core
of 0.69 mil thickness containing 0.07% by weight behenamide, a 0.02
mil homopolymer layer on one surface containing 0.25% crosslinked
methyl sesquioxide particles and, on the other surface, a 0.04 mil
layer of a copolymer of polypropylene and 4.5% ethylene (Fina 8573
from Fina Oil and Chemical Co., Deer Park, Tex.). This latter
layer, intended to serve as a print layer, contained 0.10% by
weight of N,N'-ethylenebis oleamide.
EXAMPLE 2
[0040] Example 1 was repeated except that the concentration of N,N'
ethylenebis oleamide was 0.05% by weight.
EXAMPLE 3
[0041] Example 1 was repeated except that the concentration of N,N'
ethylenebis oleamide was 0.20%. 11 color Cerutti press (North
American Cerutti Corporation, Pittsburgh, Pa.) Examples 1 to 6 were
printed with Manders inks (Manders Premium, Inc., Niles, Ill.)
thinned to a #22 Zahn cup with a 1:1 ethyl alcohol/n-propyl acetate
solvent. Examples 7 and 8 were printed with Sun NULAM and Sun
SUNPLI inks thinned with Sun SL02 and SL05 solvent systems. (Here
again we should have more informative descriptions).
[0042] All samples were evaluated on commercial quality print jobs
and evaluated against commercially accepted controls as standards.
In both evaluations, Examples 5 and 8, which contained no
N,N'-ethylenebis oleamide, exhibited unacceptable streaking and/or
ghosting. The films of Examples 1,2,3,4,6 and 7 which contained the
N,N'-ethylenebis oleamide, exhibited no streaking or ghosting.
[0043] Two aspects of the cold seal properties of the film samples
were examined. In order for the film to be able to be unwound from
a roll where the cold seal layer is in contact with the other
surface of the film on which no such adhesive is present, it must
release readily from that layer. Then, when a cold seal is formed
by bringing two areas of the cold seal layer together, it must not
separate without application of a significant pulling force. These
two aspects are referred to as release strength, which must be low,
and the cold seal strength, which must be high.
[0044] To test these two parameters, a typical commercially
available adhesive, Findlay C1099 (Findlay Adhesives, Wawatosa,
Wis.) was applied to the print layer of a specimen of the film
using a #7 Meyer rod. The coated film was then dried at 93.degree.
C. for 30 seconds. The dried film was then covered with a release
film and cut into six individual samples. These were placed in a
blocking jig at 100 psi and blocked at 100 psi for 16 hours at
50.degree. C.
[0045] To test cold seal release strength, the release film was
pulled from the specimen in an Instron tensile tester and the force
to required to remove the film was measured.
[0046] To test cold seal adhesion strength, a specimen was cut in
two along its longitudinal axis and the two halves were brought
together, coating to coating, and pressed together at 80 psi for
1/2 second. Within one minute following sealing, the two pieces of
film were pulled apart on the Instron tensile tester. Triplicate
measurements were made for each specimen.
[0047] The cold seal release strength and the cold seal adhesion
are both found to be comparable to that of conventional commercial
films prepared with behenamide and erucamide slip agents.
* * * * *