Note: Descriptions are shown in the official language in which they were submitted.
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BACKING FOR ADHESIVE TAPE AND SUCH TAPE
TECHNICAL FIELD
The present invention relates generally to films useful as tape backings, and
more particularly to biaxially oriented polypropylene film backings and tapes
including such backings.
BACKGROUND OF THE INVENTION
Biaxially oriented polypropylene films are typically used in applications in
which the combination of low cost and excellent mechanical and optical
properties
are advantageous. Some applications for such films include packaging overwraps
and adhesive tape substrates.
An important factor determining the properties of a semi-crystalline
polymer, such as polypropylene, is the packing order of the polymer chains.
Crystallization is a means to control the degree and morphology of the packing
of
polymer chains. The degree and nature of this order has a tremendous influence
on
the final mechanical properties of the material.
The important parameters controlling crystallization in polypropylene are:
(1) the total crystallinity, (2) the number of crystalline entities per unit
volume,
2o also known as the nucleation density, (3) the average diameter or size of
the
crystallites or crystallite aggregates (called spherulites), and (4) the
average
distance between the crystalline entities. When extruding and quenching
polypropylene polymer from the melt, the polymer crystallizes into a lamellar
structure that will lead to a spherulitic macrostructure in the finished cast
sheet.
These lamellar and spherulitic structures are joined via tie molecules; tie
molecules
are the parts of polymer chains extending from one lamella to another. These
tie
molecules concentrate and distribute stresses throughout the finished
material.
The prior art suggests that it is advantageous for the spherulitic
macrostructure generated during the quenching of a polymer to be as small as
possible. To achieve this, it has been suggested that the number of
crystalline
entities per unit volume must be large and therefore the "undercooling" of the
cast
polymer by quenching must be high and rapid. In addition, it has been
suggested
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that it is desirable to maximize the rate of growth of the lamellar and
spherulitic
structures as well. D.W. van Krevelen, Chimia, 32 (8), August, 1978. Van
Krevelen has developed a universal master curve relating the rate-of growth of
spherulites as a function of the ratio of the crystallization temperature to
the
polymer melt-temperature. For polypropylene, Van Krevelen reports that the
maximum spherulitic growth-rate occurs at a crystallization temperature of
approximately 90°C.
Commercially available pressure sensitive adhesive tapes are usually
provided in a roll form on a tape dispenser (see, for example, U.S. Patent
Nos.
4,451,533 and 4,908,278). Tape dispensers typically have either a metal or a
plastic serrated cutting blade. "Severability" of adhesive tape is defined as
the
amount of energy or work required to cut or sever a length of tape by pulling
the
tape over the serrations on the cutting edge of a tape dispenser. Severability
is also
referred to as "dispensability."
It is desirable that the severed tape does not chip, sliver, fracture or break
in
an unpredictable manner (see U.S. Patent Nos. 4,451,533 and 4,908,278), so
that a
cleanly serrated cut edge is formed on the severed tape strip. Cleanly
serrated
edges are preferred for aesthetic reasons in applications such as gift
wrapping,
mending, and the like.
2o Severability is governed primarily by the mechanical properties of the
backing of the adhesive tape. The ease with which an adhesive tape can be
severed
depends on the deformation resistance (toughness) of the tape backing film,
also
referred to as the substrate. Typically, this backing is coated or laminated
with
surface layers to provide an adhesive surface and a release surface. In most
cases,
25 the energy required to sever the tape is governed primarily by the backing,
with
little contribution by the adhesive and other layers or coatings.
Several attempts at providing desirable biaxially oriented polypropylene
films are known from the art. See, for example, United States Patent Nos.
4,451,533; 5,252,389; and 5,366,796. Several attempts at providing tape
backings
3o that may be torn by hand (typically in the transverse direction of the
backing) are
known from the art. See, for example, United States Patent Nos. 3,491,877;
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3,853,598; 3,887,745; 4,045,515; 4,137,362; 4,139,669; 4,173,676; 4,393,115;
4,414,261; 4,447,485; 4,513,028; 4,563,441; 4,581,087; 5,374,482; and
5,795,834.
SUMMARY OF THE INVENTION
A brittle, biaxially oriented polypropylene film is provided by minimizing
the nucleation density in the extruded and quenched polypropylene polymer cast
sheet followed by maximizing the spherulitic growth rate of the resultant
quenched
polymer. In addition, it is preferred to stretch the cast sheet so formed at
higher-
than-normal temperatures in the subsequent orientation steps for producing the
biaxially oriented polypropylene film. This process produces a more brittle
film.
to The polypropylene composition, extrusion temperature, cast roll
temperature (i.e., quench temperature), and stretch temperature and other
parameters are selected in accordance with the teachings herein such that the
resulting film, backing, or tape has the following preferred properties, taken
individually or in any preferred combination:
15 A) an MD tensile energy-at-break of up to about 90 N-mm/mm3, more
preferably from about 30 to 90 N-mm/mm3, still more preferably up
to about 60 N-mm/mm3, and most preferably from about 30 to 60
N-mm/mm3;
B) an MD elongation to break of at least 70%, preferably from about 70 to
20 150%;
C) a puncture energy, when tested according to the Puncture Test described
below, of up to about 130 N-mm, more preferably up to about 70 N-
mm;
D) a dispense energy, when tested according to the Dispense Test described
25 below of up to about 350 N-cm/cm2; more preferably up to about
170 N-cm/cm2;
E) when dispensed on commercially available serrated plastic or metal
dispenser blades, the serrated edge of the tape or backing closely
follows the contour of the dispensing blade;
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F) an ability to be torn by hand in the TD, as defined by at least 50%
success as described below. More preferably the backing or tape
can be torn by hand with at least 90% success as described below,
and most preferably 100%; and
5 G) an ability to be torn by hand in the MD, as defined by at least
50°Io
success as described below. More preferably the backing or tape
can be torn by hand with at least 90% success as described below,
and most preferably 100%.
One aspect of the present invention provide an adhesive tape, comprising a
backing and a layer of adhesive on the backing. The backing comprises
polypropylene and has been biaxially oriented in the MD and TD of the backing.
The backing is hand-tearable in the TD, and when the backing is severed on a
serrated plastic cutting blade, the backing exhibits a serrated edge that
closely
corresponds to the contour of the blade.
15 In one preferred embodiment of the above tape, the backing comprises a
monolayer.
In another preferred embodiment of the above tape, when the backing is
severed according to the Dispense Test, the backing has an energy to sever in
the
MD of up to 350 N-cm/cm2. Still more preferrably, the backing has an energy to
2o sever in the MD of up to 170 N-cm/cm2.
In another preferred embodiment of the above tape, when the backing is
tested according to the Puncture Test, the backing has a puncture energy of up
to
130 N-mm. Still more preferably, the backing has a puncture energy of up to 70
N-mm.
25 In another preferred embodiment of the above tape, the backing has a
tensile energy to break in the MD of up to 90 N-mm/mm3.
In another preferred embodiment of the above tape, the backing has a
tensile elongation to break in the MD of at least 70%.
In another preferred embodiment of the above tape, the backing is hand-
30 tearable in the MD.
In another aspect, the present invention provides an alternative adhesive
tape comprising a backing and a layer of adhesive on the backing. The backing
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comprises polypropylene and has been biaxially stretched. The backing has a
tensile energy to break in a first direction of up to 90 N-mm/mm3, and when
the
backing is severed on a serrated plastic cutting blade, the backing exhibits a
serrated edge that closely corresponds to the contour of the blade.
On one preferred embodiment of the above tape, the backing comprises a
monolayer.
In another preferred embodiment of the above tape, the first direction is the
MD.
In another preferred embodiment of the above tape, the backing has a
1o tensile elongation to break in the MD of at least 70%.
In another preferred embodiment of the above tape, the backing is hand-
tearable in the TD. More preferably, the backing is also hand-tearable in the
MD.
In another preferred embodiment of the above tape, when the backing is
severed according to the Dispense Test, the backing has an energy to sever in
the
15 MD of up to 350 N-cm/cm2. More preferably, the backing has an energy to
sever
in the MD of up to 170 N-cm/cm2.
In another preferred embodiment of the above tape, when the backing is
tested according to the Puncture Test, the backing has a puncture energy of up
to
130 N-mm. More preferably, the backing has a puncture energy of up to 70 N-
20 mm.
In yet another aspect, the present invention provides another alternative
adhesive tape comprising a backing and a layer of adhesive on the backing. The
backing comprises polypropylene, and has been biaxially stretched in the MD
and
TD: The backing has a tensile elongation to break in the MD of from 70% to
25 150% and is hand-tearable in the TD.
In one preferred embodiment of the above tape, the backing comprises a
monolayer.
In another preferred embodiment of the above tape, when the backing is
tested according to the Puncture Test, the backing has a puncture energy of up
to
30 130 N-mm. More preferably, the backing has a puncture energy of up to 70 N-
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In another preferred embodiment of the above tape, when the backing is
severed on a serrated plastic cutting blade, the backing exhibits a serrated
edge that
closely corresponds to the contour of the blade.
In another preferred embodiment of the above tape, when the backing is
severed according to the Dispense Test, the backing has an energy to sever in
the
MD of up to 350 N-cm/cm2. More preferably, the backing has an energy to sever
in the MD of up to 170 N-cm/cm2.
In another preferred embodiment of the above tape, the backing has a
tensile energy to break in the MD of up to 90 N-mm/mm~.
l0 In another preferred embodiment of the above tape, the backing is hand-
tearable in the MD.
In still another aspect, the present invention provides another alternative
adhesive tape comprising a backing and a layer of adhesive on the backing. The
backing comprises polypropylene and has been biaxially stretched in the MD and
15 TD. The backing is hand-tearable in the TD and in the MD.
In one preferred embodiment of the above tape, the backing comprises a
monolayer.
In another preferred embodiment of the above tape, when the backing is
tested according to the Puncture Test, the backing has a puncture energy of up
to
20 130 N-mm. More preferably, the backing has a puncture energy of up to 70 N-
mm.
In another preferred embodiment of the above tape, when the backing is
severed on a serrated plastic cutting blade, the backing exhibits a serrated
edge that
closely corresponds to the contour of the blade.
25 In another preferred embodiment of the above tape, when the backing is
severed according to the Dispense Test, the backing has an energy to sever in
the
MD of up to 350 N-cm/cm2. More preferably, the backing has an energy to sever
in the MD of up to 170 N-ctn/cm'.
In another preferred embodiment of the above tape, the backing has a
3o tensile energy to break in the MD of up to 90 N-mm/mm3.
In another preferred embodiment of the above tape, the backing has a
tensile elongation to break in the MD of at least 70%.
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In any of the tapes described above, the backing preferably has an MD
stretch ratio of at least 4:1.
In any of the tapes described above, the backing preferably has a TD stretch
ratio of at least 7:1.
In any of the tapes described above, the backing preferably has an MD
stretch ratio of at least 4:1 and a TD stretch ratio of at least 7:1.
The present invention provides films described above, tape backings made
from such films, tapes including the backings, and methods of making the
films,
backings, and tapes.
l0 Certain terms are used in the description and the claims that, while for
the
most part are well known, may require some explanation. "Biaxially stretched,"
when used herein to describe a film, indicates that the film has been
stretched in
two different directions, a first direction and a second direction, in the
plane of the
film. Typically, but not always, the two directions are substantially
perpendicular
t5 and are in the machine direction ("MD") of the film (the direction in which
the film
is produced on a film-making machine) and the transverse direction ("TD") of
the
film (the direction perpendicular to the MD of the film). The MD is sometimes
referred to as the Longitudinal Direction ("LD"). Biaxially stretched films
may be
sequentially stretched, simultaneously stretched, or stretched by some
combination
20 of simultaneous and sequential stretching. "Simultaneously biaxially
stretched,"
when used herein to describe a film, indicates that significant portions of
the
stretching in each of the two directions are performed simultaneously. Unless
context requires otherwise, the terms "orient," "draw," and "stretch" are used
interchangeably throughout, as are the terms "oriented," "drawn," and
"stretched,"
25 and the terms "orienting," "drawing," and "stretching."
The term "stretch ratio," as used herein to describe a method of stretching
or a stretched film, indicates the ratio of a linear dimension of a given
portion of a
stretched film to the linear dimension of the same portion prior to
stretching. For
example, in a stretched film having an MD stretch ratio ("MDR") of 5:1, a
given
30 portion of unstretched film having a 1 cm linear measurement in the machine
direction would have 5 cm measurement in the machine direction after stretch.
In
a stretched film having a TD stretch ratio ("TDR") of 9:1, a given portion of
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unstretched film having a 1 cm linear measurement in the transverse direction
would have 9 cm measurement in the transverse direction after stretch.
"Area stretch ratio," as used herein, indicates the ratio of the area of a
given
portion of a stretched film to the area of the same portion prior to
stretching. For
example, in a biaxially stretched film having an overall area stretch ratio of
50:1, a
given I cm2 portion of unstretched film would have an area of 50 cm2 after
stretching.
The mechanical stretch ratio, also know as nominal stretch ratio, is
determined by the unstretched and stretched dimensions of the overall film,
and
to can typically be measured at the film grippers at the edges of the film
used to
stretch the film in the particular apparatus being used. Global stretch ratio
refers to
the overall draw ratio of the film after the portions that lie near the
grippers, and
thus are affected during stretching by the presence of the grippers, have been
removed from consideration. The global stretch ratio can be equivalent to the
15 mechanical stretch ratio when the input unstretched film has a constant
thickness
across its full width and when the effects of proximity to the grippers upon
stretching are small. More typically, however, the thickness of the input
unstretched film is adjusted so as to be thicker or thinner near the grippers
than at
the center of the film. When this is the case, the global stretch ratio will
differ
20 from the mechanical or nominal stretch ratio. These global or mechanical
ratios
are both to be distinguished from a local stretch ratio. The local stretch
ratio is
determined by measuring a particular portion of the film (for example a 1 cm
portion) before and after stretch. When stretch is not uniform over
substantially
the entire edge-trimmed film, then the local ratio can be different from the
global
25 ratio. When stretch is substantially uniform over substantially the entire
film
(excluding the area immediately near the edges and surrounding the grippers
along
the edges), then the local ratio will be substantially equal to the global
ratio.
Unless the context requires otherwise, the term stretch ratio is used herein
to
describe the global stretch ratio.
_g_
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BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be further explained with reference to the
appended Figures, wherein like structure is referred to by like numerals
throughout
the several views, and wherein:
Figure 1 is an isometric view of a length of tape according to the present
invention;
Figure 2 is a side view of a roll of adhesive tape according to the present
invention;
Figure 3 is an isometric view of a test fixture used to test the severing
characteristics of film according to the present invention;
Figure 4 is an isometric view of the metal dispenser blade useful in the test
fixture of Figure 3;
Figure 5 is a side view of the metal dispenser blade of Figure 4;
Figure 6 is a side view of a portion of the apparatus of Figure 3 and the
metal dispenser blade of Figure 6;
Figure 7 is an illustration of a typical severance or dispense testing curve
for a polypropylene tape backing of the present invention;
Figure 8 is an enlarged photograph of a polypropylene film according to the
present invention (Example ES) severed according to the test method described
2o herein; and
Figure 9 is an enlarged photograph of a prior art polypropylene film
(Example C 1 ) severed according to the test method described herein.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Figure 1, there is shown a length of tape 10 according to one
preferred embodiment of the present invention. Tape 10 comprises a biaxially
oriented polypropylene film backing 12 which includes first major surface 14
and
second major surface 16. Preferably, backing 12 has a thickness in the range
of
about 0.002 to about 0.006 centimeters. Backing 12 of tape 10 is coated on
first
major surface 14 with a layer of adhesive 18. Adhesive 18 may be any suitable
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adhesive as is known in the art. Backing 12 may have an optional release or
low
adhesion backsize layer 20 coated on the second major surface 16 as is known
in
the art.
The backing film 12 preferably comprises polypropylene. For the purposes
5 of the present invention, the term "polypropylene" is meant to include
copolymers
comprising at least about 90% propylene monomer units, by weight.
"Polypropylene" is also meant to include polymer mixtures comprising at least
about 75% polypropylene, by weight. Polypropylene for use in the present
invention is preferably predominantly isotactic. Isotactic polypropylene has a
io chain isotacticity index of at least about 80%, an n-heptane soluble
content of less
than about 1 S % by weight, and a density between about 0.86 and 0.92
grams/cm3
measured according to ASTM D1505-96 ("Density of Plastics by the Density-
Gradient Technique"). Typical polypropylenes for use in the present invention
have a melt flow index between about 0.1 and 15 grams/10 minutes according to
15 ASTM D1238-95 ("Flow Rates of Thermoplastics by Extrusion Plastometer") at
a
temperature of 230°C and force of 2160 g, a weight-average molecular
weight
between about 100,000 and 400,000, and a polydispersity index between about 2
and 15. Typical polypropylenes for use in the present invention have a peak
melting temperature as determined using differential scanning calorimetry of
2o greater than about 130° C, preferably greater than about 140°
C, and most
preferably greater than about 150° C. Further, the polypropylenes
useful in this
invention may be copolymers, terpolymers, etc., having ethylene monomer units
and/or alpha-olefin monomer units of between 4-8 carbon atoms, said
comonomer(s) being present in an amount so as not to adversely affect the
desired
25 properties and characteristics of the backing and tapes described herein,
typically
their content being less than 10 % by weight. One suitable polypropylene resin
is
an isotactic polypropylene homopolymer resin having a melt flow index of 2.5
g/10 minutes, commercially available under the product designation 3374 from
FINA Oil and Chemical Co., Dallas, TX.
30 Polypropylene for use in the present invention may optionally include, in
an amount so as not to adversely affect the desired characteristics and
properties
described herein, a resin of synthetic or natural origin having a molecular
weight
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between about 300 and 8000, and having a softening point between about
60° C
and 180° C. Typically, such a resin is chosen from one of four main
classes:
petroleum resins, styrene resins, cyclopentadiene resins, and terpene resins.
Optionally, resins from any of these classes may be partially or fully
hydrogenated.
Petroleum resins typically have, as monomeric constituents, styrene,
methylstyrene, vinyltoluene, indene, methylindene, butadiene, isoprene,
piperylene, and/or pentylene. Styrene resins typically have, as monomeric
constituents, styrene, methylstyrene, vinyltoluene, and/or butadiene.
Cyclopentadiene resins typically have, as monomeric constituents,
cyclopentadiene
and optionally other monomers. Terpene resins typically have, as monomeric
constitutents, pinene, alpha-pinene, dipentene, limonene, myrcene, and
camphene.
Polypropylene for use in the present invention may optionally include
additives and other components as is known in the art. For example, the films
of
the present invention may contain fillers, pigments and other colorants,
antiblocking agents, lubricants, plasticizers, processing aids, antistatic
agents,
antioxidants and heat stabilizing agents, ultraviolet-light stabilizing
agents, and
other property modifiers. Fillers and other additives are preferably added in
an
effective amount selected so as not to substantially affect the nucleation of
the cast
film and so as not to adversely affect the properties attained by the
preferred
embodiments described herein. Typically such materials are added to a polymer
before it is made into an oriented film (e.g., in the polymer melt before
extrusion
into a film).
The polypropylene can be cast into sheet form by apparatus known to those
of skill in the art, provided the polypropylene is cast in accordance with the
preferred temperatures and methods described herein. Such cast films are then
stretched to arrive at the preferred film described herein. When making
polypropylene films, a suitable method for casting a sheet is to feed the
resin into
the feed hopper of a single screw, twin screw, cascade, or other extruder
system
having an extruder barrel temperature adjusted to produce a stable homogeneous
melt. The polypropylene melt can be extruded through a sheet die onto a
rotating
cooled metal casting wheel. Optionally, the casting wheel can be partially
immersed in a fluid-filled cooling bath, or, also optionally, the cast sheet
can be
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passed through a fluid-filled cooling bath after removal from the casting
wheel. _
The temperatures of this operation can be chosen by those of skill in the art
with
the benefit of the teachings herein to provide the desired nucleation density,
size,
and growth rate such that the resulting stretched film has the desired
characteristics
and properties described herein. These temperatures will vary with the
material
used, and with the heat transfer characteristics of the particular apparatus
used. For
one particular arrangement, the following temperatures are preferred.
Preferably,
the polypropylene composition is extruded at a temperature of about 245-
250°C.
Preferably, the cast roll is at a temperature of at least 90°C, more
preferably
to approximately 90-94°C.
The sheet is then stretched to provide backing 12 having the desired
characteristics and properties described herein. Preferably, the backing is
biaxially
stretched.
In one preferred sequential stretch embodiment, the MD stretch ratio is
from about 4:1 to 6:1. More preferably, the MD stretch ratio is about 4.5:1 to
about 5.5:1. In another preferred sequential stretch embodiment, the TD
stretch
ratio is at least 7:1. More preferably, the TD stretch ratio is from about 7:1
to
about 12:1. In another preferred sequential stretch embodiment, the MD stretch
ratio is from about 4:1 to about 6:1 and the TD stretch ratio is at least 7:1.
More
preferably, the MD stretch ratio is from about 4.5:1 to about 5.5:1 and the TD
stretch ratio is from about 7:1 to about 11:1. One particularly preferred
backing is
one that is sequentially biaxially stretched having an MD stretch ratio of
about 5:1
and a TD stretch ratio of about 8:1 to 10:1.
In one preferred simultaneous biaxial stretch embodiment, the area stretch
ratio is from about 35:1 to about 108:1. More preferably, the area stretch
ratio is
from about 45:1 to about 60:1. The MD component and TD component of these
embodiments is chosen so as to provide the desired film properties and
characteristics described herein.
The preferred properties described herein may be obtained by any suitable
3o apparatus for biaxially orienting the backing 12 according to the preferred
methods
described herein. Of all stretching methods, the apparatus preferred for
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commercial manufacture of films for tape backings include: known sequential
biaxial stretching apparatus that typically stretches in the MD first by
passing the
film over a sequence of rotating rollers whose speed provides a higher output
film
line speed than input speed, followed by TD stretching in a tenter on
diverging
rails; simultaneous biaxial stretching by mechanical tenter such as the
apparatus
disclosed in U.S. Patent Nos. 4,330,499 and 4,595,738; and the tenter
apparatus for
simultaneous biaxial stretch disclosed in U.S. Patent Nos. 4,675,582;
4,825,111;
4,853,602; 5,036,262; 5,051,225; and 5,072,493. Although biaxially stretched
films can be made by tubular blown film or flat film tenter stretching
processes, it
to is preferable that the films of this invention, when used as tape backings;
be made
by a flat film stretching apparatus to avoid processing difficulties that may
arise
with tubular blown film processes.
The temperatures of the stretching operation can be chosen by those of skill
in the art with the benefit of the teachings herein to provide a film having
the
desired characteristics and properties described herein. These temperatures
will
vary with the material used, and with the heat transfer characteristics of the
particular apparatus used. For one preferred sequential stretch apparatus, it
is
preferred that the preheat roll and the stretch roll for the MD stretch be
maintained
at about 120-135°C. It is also preferred that for the TD stretch in the
tenter, the
2o preheat zone be maintained at about 180-190°C, and the stretch zone
be maintained
at about 160-177°C. For simultaneously stretched backings, it is
preferred that the
preheat and stretch be from approximately 170°C to 200°C.
The backing 12 useful in this invention, when used as a backing for a tape
10, preferably has a final thickness between about 0.002-0.006 cm. V
ariability in
film thickness is preferably less than about 5%. Thicker and thinner films may
be
used, with the understanding that the film should be thick enough to avoid
excessive flimsiness and difficulty in handling, while not being so thick so
as to be
undesirably rigid or stiff and difficult to handle or use.
The polypropylene composition, extrusion temperature, cast roll
temperature, and stretch temperature and other parameters are selected in
accordance with the teachings herein such that the resulting backing or tape
has the
following preferred properties, taken individually or in any preferred
combination:
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A) an MD tensile energy at break of up to about 90 N-mm/mm3, more
preferably from about 30 to 90 N-mm/mm3, still more preferably up
to about 60 N-mm/mm3, and most preferably from about 30 to 60
N-mm/mm3;
B) an MD elongation to break of at least 70%, preferably from about 70 to
150%;
C) a puncture energy, when tested according to the Puncture Test described
below, of up to about 130 N-mm, more preferably up to about 70 N-
mm;
l0 D) a dispense energy, when tested according to the Dispense Test described
below of up to about 350 N-cm/cm2; more preferably up to about
170 N-cm/cmz;
E) when dispensed on commercially available serrated plastic or metal
dispenser blades, the serrated edge of the tape or backing closely
follows the contour of the dispensing blade;
~ an ability to be torn by hand in the TD, as defined by at least 50%
success as described below. More preferably the backing or tape
can be torn by hand with at least 90% success as described below,
and most preferably 100%; and
G) an ability to be torn by hand in the MD, as defined by at least 50%
success as described below. More preferably the backing or tape
can be torn by hand with at least 90% success as described below,
and most preferably 100%.
The above properties and characteristics are described herein with respect
to the preferred embodiments, and reported herein with respect to the
examples, for
a film or backing 12 without adhesive 18 thereon. It is expected that in most
cases,
the characteristics and properties are governed primarily by the backing, with
little
affect by the adhesive or other layers or coatings. Therefore, the above
preferred
characteristics and properties also apply to the adhesive tapes of the present
invention.
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WO 00!31202 PCT/US98/24784
One preferred embodiment of the present invention comprises a monolayer
backing. As used herein, the term monolayer includes multiple layers of
substantially the same material.
The adhesive 18 coated on the first major surface 14 of tape backing 12
may be any suitable adhesive as is known in the art. Preferred adhesives are
those
activatable by pressure, heat or combinations thereof. Suitable adhesives
include
those based on acrylate, rubber resin, epoxies, urethanes or combinations
thereof.
The adhesive 18 may be applied by solution, water-based or hot-melt coating
methods. The adhesive can include hot melt-coated formulations, transfer-
coated
l0 formulations, solvent-coated formulations, and latex formulations, as well
as
laminating, thermally-activated, and water-activated adhesives. Useful
adhesives
according to the present invention include all pressure sensitive adhesives.
Pressure sensitive adhesives are well known to possess properties including:
aggressive and permanent tack, adherence with no more than finger pressure,
and
~5 sufficient ability to hold onto an adherend. Examples of adhesives useful
in the
invention include those based on general compositions of polyacrylate;
polyvinyl
ether; diene rubber such as natural rubber, polyisoprene, and polybutadiene;
polyisobutylene; polychloroprene; butyl rubber; butadiene-acrylonitrile
polymer;
thermoplastic elastomer; block copolymers such as styrene-isoprene and styrene-
20 isoprene-styrene (SIS) block copolymers, ethylene-propylene-diene polymers,
and
styrene-butadiene polymers; poly-alpha-olefin; amorphous polyolefin; silicone;
ethylene-containing copolymer such as ethylene vinyl acetate, ethyla~crylate,
and
ethyl methacrylate; polyurethane; polyamide; epoxy; polyvinylpyrrolidone and
vinylpyrrolidone copolymers; polyesters; and mixtures or blends (continuous or
25 discontinuous phases) of the above. Additionally, the adhesives can contain
additives such as tackifiers, plasticizers, fillers, antioxidants,
stabilizers, pigments,
diffusing materials, curatives, fibers, filaments, and solvents. Also, the
adhesive
optionally can be cured by any known method.
A general description of useful pressure sensitive adhesives may be found
3o in Encyclopedia of Polymer Science and Engineering, Vol. 13, Wiley-
Interscience
Publishers (New York, 1988). Additional description of useful pressure
sensitive
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adhesives may be found in Encyclopedia of Polymer Science and Technology,
Vol. 1, Interscience Publishers (New York, 1964). .
The film backing 12 of the tape 10 may optionally be treated by exposure
to flame or corona discharge or other surface treatments including chemical
priming to improve adhesion of subsequent coating layers. In addition, the
second
surface 16 of the film backing 12 may be coated with optional low adhesion
backsize materials 20 to restrict adhesion between the opposite surface
adhesive
layer 18 and the film 12, thereby allowing for production of adhesive tape
rolls
capable of easy unwinding, as is well known in the adhesive coated tape-making
i0 art. The tape 10 may be spirally wound to make a roll 22, optionally on
core 24, as
illustrated in Figure 2.
The backings described herein are well-suited for many adhesive tape
backing applications. Because the backing is conformable, it is useful as a
masking tape backing. The backings are also well-suited for other applications
including utility tapes and light duty box sealing tapes.
The operation of the present invention will be further described with regard
to the following detailed examples. These examples are offered to further
illustrate
the various specific and preferred embodiments and techniques. It should be
understood, however, that many variations and modifications may be made while
2o remaining within the scope of the present invention.
Test Methods
Film Tensile Pronerty Determinations
The machine direction (MD) tensile energy-at-break and the tensile
elongation-at-break of the films were measured according to the procedures
described in ASTM D-882, "Tensile Properties of Thin Plastic Sheeting," Method
A. The films were conditioned for 24 hours at 22°C (72°F) and 50
percent relative
humidity (RH) prior to testing. The tests were performed using a tensile
testing
machine commercially available as a Model No. Sintech 400/S from MTS Systems
Corporation, Eden Prairie, MN. Specimens for this test were 1.25 cm wide and
15
3o cm long. An initial jaw separation of 5 cm and a crosshead speed of 50.8
cm/min
were used. Ten specimens were tested for each sample in the MD.
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WO 00/31202 PCT/US98/24784 .
Puncture-energy Determination -
Puncture energy was determined using a Model No. Sintech 400/S tensile
testing machine manufactured by MTS Systems Corporation, Eden Prairie, MN. A
clamp assembly, consisting of two rigid plates having a 7.62-cm diameter hole
in
the center of each plate, was used. A plunger, consisting of a 0.318-cm
diameter
steel rod having a hemispherical tip, was utilized. Displacement of the
plunger
assembly was measured during loading and complete penetration of each test
specimen. Specimens for testing were cut parallel to the MD into 1.9 cm wide
strips. Specimens were 12.7 cm in length in order to be adequately gripped in
the
clamp assembly. Each test was performed at a speed of 254 cm/min. At least
five
specimens were tested for each determination.
For each test, the specimen was clamped into the assembly. Each specimen
was centered across the plate opening. A piece of pressure-sensitive adhesive
tape
was used to hold the sample onto one side of the bottom plate of the clamp
assembly while a weight (75 g) was hung on the other side of the specimen so
as to
ensure that the sample was loaded under constant tension. The clamping plate
was
then tightened using thumb screws so that the sample did not slip during the
test.
The clamp assembly was positioned under the plunger so that the path of the
plunger was through the center of the sample. The total energy required to
puncture the sample was determined.
As used herein, including the claims, the term "Puncture Test" refers to the
just-described test.
TD Hand-Tear Determination
Ten specimens of film were cut parallel to the MD to a width of 2.5 cm
using a razor cutter. Thus the samples had a smooth edge, that is one that
does not
include intentional irregularities, roughness, flaws, or other tear-initiation
sites.
Hand-tearing along the TD was attempted 10 times at 22°C. The
percentage of
successful tears is considered to indicate the TD tear property.
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WO OOI31202 PCT/US98124784
MD Hand-Tear Determination
Ten specimens of film were cut parallel to the TD to a width of 2.5 cm
using a razor cutter. Thus the samples had a smooth edge, that is one that
does not
include intentional irregularities, roughness, flaws, or other tear-initiation
sites.
Hand-tearing along the MD was attempted 10 times at 22°C. The
percentage of
successful tear initiation and propagation is considered to indicate the MD
tear
property.
Determination of Appearance of the Serrated Edge on a Film
to Films produced according to this invention and comparative films
described herein were dispensed on a serrated plastic blade (3M Catalog #105
available as of the filing date hereof from Minnesota Mining and Manufacturing
Company, St. Paul, Minnesota). Films dispensed against this blade were
photographed using a Model Laborlux 12 POL microscope manufactured by Leitz
of Wetzlar, Germany. The samples were examined between crossed polarizers
having a'/a-wavelength-shift plate and using a magnification of 50 times. It
was
observed that each of the inventive Examples E1 through ES had a serrated edge
that closely followed the contour of the plastic cutting blade. Each of the
comparative Examples C1 through C7 had a serrated edge that was irregular and
did not closely follow the contour of the cutting blade.
Figure 8 is a lOX enlarged photograph of a polypropylene film according to
the present invention, Example ES. It is seen that the serrated edge of the
severed
backing closely follows the contour of the plastic cutting blade. Figure 9 is
a lOX
enlarged photograph of a prior art polypropylene film Example C 1. It is seen
that
the serrated edge does not closely follow the contour of the cutting teeth of
the
plastic dispenser blade.
Severance Pronerties~ Dispense Testing of Films
Test specimens 1.91 cm wide and 15 cm long were slit from uncoated
sample films using a razor blade cutter equipped with new blades. Test
specimens
3o were conditioned for 24 hours at 25° C and 50% relative humidity
prior to testing.
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- WO 00/31202 PCTNS98/Z4784 ._
The test fixture used to measure severability is shown in Figure 3. The test -
fixture comprised a commercially available tape dispenser 100M (Scotches Cat.
H-127 two-piece polystyrene molded dispenser equipped with a metal cutting
blade, available as of the filing date hereof from Minnesota Mining &
Manufacturing Co., St. Paul, MN) mounted to a 15.2 cm x 15.2 cm x 1.1 cm
aluminum rear mounting plate 102. The dispenser was restricted from flexing
during the severing test by being placed between the rear mounting plate 102
and a
0.3 cm thick aluminum front mounting plate 104 milled to the contour of the
test
dispenser 100M. The test dispenser was firmly held in place between the front
104
and rear 102 mounting plates by a threaded thumbscrew 106. The rear mounting
plate 102 was affixed to a 2.4 cm diameter cylindrical base mounting stud 108
by
machine screws 110. The base mounting stud 108 was milled to include a
90°
angle cut-out so that the rear mounting plate 102 was held in the vertical
centerline
of the tensile testing machine, that is, the angle between the axis of the
rear
mounting plate 102 and test dispenser 100M was 0° with respect to the
machine
centerline. The base stud 108 was affixed to the testing machine deck by
locking
pins inserted into drillouts 109 in the base stud.
The test dispenser 100M was mounted onto the rear mounting plate 102 by
inserting the dispenser hub over an aluminum hub mounting shaft 112 which is
screwed into the rear mounting plate 102. The bottom of the dispenser rested
against seat 115 which prevented rotation of the dispenser during testing. The
test
dispenser was mounted so that the row of teeth of the dispenser cutting blade
was
perpendicular to the machine centerline. In this way, the film being tested
was
loaded substantially uniformly across its width when severed.
Dispenser 100M included a steel serrated cutting blade 120 illustrated in
Figures 4 and 5. Steel cutting blade 120 was formed of about 0.05 cm thick
nickel
plated steel and included a rectangular land portion 122 at least as wide as
the film
12 and about 0.3 cm long in the direction corresponding to the reference
direction
R of the film 12 extending across the blade. The land portion 122 defines a
3o generally planar surface to which the test sample is temporarily secured.
Blade
120 also included a blade support portion 126 at the rear edge of the land
portion
122, with the land portion forming an angle ~i of 80° with the support
126. Blade
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support 126 is about 1.32 cm long. Blade 120 further included a generally U-
shaped portion 128 at the edge of the land portion .opposite the support
portion
which has a row of teeth 130 along its distal edge. Each tooth 130 is
generally
triangular, has a tip in or slightly lower than the plane of the land 122 and
spaced
from the tips of adjacent teeth 130 by about 0.12 cm, is defined by a height
of
about 0.06 cm, a sharpness defined by a radius of curvature of about 0.003 cm,
and
the apex 132 of said teeth 130 form an included angle of 60°. The teeth
130
project outward from the plane of the blade support portion 126 at an angle a
of
about 50°. The sides of the generally U-shaped portion 128 are at an
angle y to one
l0 another of 72°.
A piece of double-coated adhesive tape (Scotches Cat. 665) was applied to
land area 122 and the test specimen was adhered firmly to the adhesive surface
of
the double-coated tape with finger pressure to prevent forward motion during
severance testing. The test specimen was aligned at an angle of 0° to
the machine
15 centerline so that the force of the dispenser was substantially evenly
distributed
across the width of the sample. The dispenser 100M was oriented such that the
tips of the cutting blade 120 were directly under the jaws 162. The dispenser
was
oriented at an angle such that the land 122 was at an angle al of 110°
relative to
the vertical direction of travel A of the tester (see Figure 6, which
illustrates only
2o the cutter blade 120 relative to the jaws 162, with the rest of the
dispenser and test
fixture removed for illustrative purposes only).
The free end of the test specimen was then gripped in the upper jaws 162 of
the tensile testing machine so that the distance between the upper jaws and
the
cutting blade 120 was 10.2 cm. The specimen was loaded with no tension so that
25 the cutting blade did not contact the specimen prior to the start of the
test. The
upper jaws were attached to the machine crosshead which traveled on support
rails
103. The test specimen was next pre-loaded in tension to a value of 0.9 N to
make
contact with the cutting blade I20. The backing 12 was then pulled in
direction A
by the jaws 162 at a rate of 30 cm/minute. The load and elongation of the
3o specimen were measured and recorded, and the energy to sever was calculated
from the area under the load/elongation, as illustrated in Figure 7, and
reported in
Table 2. In Figure 7, the load is indicated along the vertical axis, with the
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CA 02351432 2001-05-18
WO 00/31202 PCTNS98/24784
elongation indicated on the horizontal axis. The load and elongation increase
along portion 200 of the curve, until the peak load 202 is reached, where the
elongation is indicated by 204. The load then decreases as the elongation
continues along portion 206 of the curve. As reported herein, the energy is
calculated for that portion of the curve from zero elongation to the
elongation 204
at maximum load 202. It is believed that the teeth of the dispenser puncture
the
film at about the point of maximum load 202, at which time the load decreases
as
the punctures through the film propagate to complete severance.
As used herein, including the claims, the term "Dispense Test" refers to the
just described test.
Preparation of Examples
Examule E1
A single-layer film having a final thickness of 0.030 mm was prepared by
extruding a polypropylene homopolymer having a melt flow index of 2.8 grams
/10 minutes at 230°C and 2160 g loading (ASTM D1238) and having a
melting
temperature of 157.8°C. The extruded film was taken off onto a casting
roll and
cooled, longitudinally stretched, then transversely stretched, and heat set.
Example E2
A single-layer film having a final thickness of 0.033 mm was prepared by
extrusion of a polypropylene homopolymer having a melt flow index of 1.8 g/10
min at 230°C and 2160 g loading (ASTM D1238) and having a melting
temperature of 164.0°C. The extruded film was taken off onto a casting
roll and
cooled, longitudinally stretched, transversely stretched, and heat set.
Example E3
A single-layer film having a final thickness of 0.020 mm was prepared by
extrusion of a polypropylene homopolymer having a melt flow index of 2.5 g/10
min at 230°C and 2160 g loading and having a melting temperature of
161.5°C.
The extruded film was taken off onto a casting roll and cooled. The extruded
film
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- CA 02351432 2001-05-18
WO 00/31202 PCT/US98/Z4784
was then stretched simultaneously in both the longitudinal and transverse
directions.
Example E4
Example E4 was prepared as reported for Example E3, except for final
thickness which was 0.022 mm, and the stretch ratios.
Examule ES
A single-layer film having a final thickness of 0.036 mm was prepared by
extrusion of a polypropylene homopolymer having a melt flow index of 2.5 g/10
min at 230°C and 2160 g loading and having a melting temperature of
161.5°C.
to The extruded film was taken off onto a casting roll and cooled,
longitudinally
stretched, transversely stretched, and heat set.
Comparative Example C 1
A single-layer film having a final thickness of 0.030 mm was prepared by
extrusion of a polypropylene homopolymer having a melt flow index of 2.8 g/10
15 min at 230°C and 2160 g loading (ASTM D 1238) and having a melting
temperature of 157.8°C. The extruded film was taken off onto a casting
roll and
cooled, longitudinally stretched, transversely stretched, and heat set.
Comparative Example C2
A single-layer film having a final thickness of 0.039 mm was prepared by
2o extrusion of a polypropylene homopolymer having a melt flow index of 2.5
g/10
min at 230°C and 2160 g loading and having a melting temperature of
161.5°C.
The extruded film was taken off onto a casting roll and cooled, longitudinally
stretched, transversely stretched, and heat set.
Comparative Example C3
25 A single-layer film having a final thickness of 0.038 mm was prepared by
extrusion of a polypropylene homopolymer having a melt flow index of 2.5 g/10
min at 230°C and 2160 g loading and having a melting temperature of
161.5°C.
The extruded film was taken off onto a casting roll and cooled, longitudinally
stretched, transversely stretched, and heat set.
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WO 00/31202 PCTNS98/Z4784 -
Comparative Example C4
A single-layer film having a final thickness of 0.038 mm was prepared by
extrusion of a polypropylene homopolymer having a melt flow index of 2.5 g/10
min at 230°C and 2160 g loading and having a melting temperature of
161.5°C.
The extruded film was taken off onto a casting roll and cooled, longitudinally
stretched, transversely stretched, and heat set.
Comparative Example CS
A single-layer film having a final thickness of 0.038 mm was prepared by
extrusion of a polypropylene homopolymer having a melt flow index of 2.5 g/10
min at 230°C and 2160 g loading and having a melting temperature of
161.5°C.
The extruded film was taken off onto a casting roll and cooled, longitudinally
stretched, transversely stretched, and heat set.
Comparative Example C6
A single-layer film having a final thickness of 0.031 mm was prepared by
extrusion of a polypropylene homopolymer having a melt flow index of 2.5 g/10
min at 230°C and 2160 g loading and having a melting temperature of
161.5°C.
The extruded film was taken off onto a casting roll and cooled. The extruded
film
was then stretched simultaneously in both the longitudinal and transverse
directions.
2o Comparative Example C7
Comparative Example C7 was prepared as reported for C6, except for the
final thickness which was 0.028 mm and the stretch ratios.
The examples were prepared as set forth in Table 1 below. The stretch
ratios indicated are global stretch ratios. Certain of the Examples were
tested by
certain of the methods described above. Results of such testing are reported
in
Table 2 below.
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CA 02351432 2001-05-18
WO 00/31202 PCT/US98/24784
0 0
V ~ ~ ~ ~ ,
o ~
U
~ 0 0
~ .~U ~ o o
~
w
0
~,
. ~ .~. ~ ~ ~
. . . . .
x
..
~ ~ ~'c~ ~ ~
-...,.-.~ .~~
. .
U V7
.L N
~ Y
w
_
o ~ ~no ~no
ov~ ~ o ~ o
o o
~ ~
a~
..
V
v o "~ v~~ ~m m n
''' , t M M M M M M
v M M
y
H
a~
~
V ~
o "., ~n ~n~n~n~n
~ i
~ M M ~ ~ ~ tI1M,~ ~ ~
~., r..-. N ._
C~
~
.C .... --r "" ."''~~.,.-
O M I
O p~ ~ OvI
~ ~ ~
....~.-r.,.~.-.,.-.~..-1..-i.-r.-.r.-r...~
O
~V o o o o et~to o o o o 0
' O~
o O~CTGvOvO~M V ~ 0000O~
1
U
c
0
p ~nv ~ v ~ ~nv Wn~n~nv~
~n o t w r Wt
d
U ~n~ d wt~ ~n~ t N N N N
N ~
N
,.,,J N N N N N N
W
U U U
W W W W W U U U U
-24-
CA 02351432 2001-05-18
WO 00/31202 PCT/US98/24784
Table 2
MD Tensile MD TensilePunctureDispense
energy to elongationEnergy Energy TD Hand MD Hand
Ex. break to break (N-mm) (N-cm/cm2)Tear Tear (%)
(%)
(N-mm/mm3) (%)
E1 32 70 69 167 100 100
E2 62 I45 7 155 100 100
E3 57 74 - - 9p -
E4 62 73 - - - 100
ES 89 145 127 322 100 100
C1 130 136 719 519 30 10
C2 170 141 529 455 0 0
C3 160 138 542 360 0 0
C4 150 I37 565 355 0 0
CS 100 122 260 500 30 0
C6 120 104 - - - 0
1~ 95 _ _ - 0
The tests and test results described above are intended solely to be
illustrative,
rather than predictive, and variations in the testing procedure can be
expected to yield
different results.
The present invention has now been described with reference to several
embodiments thereof. The foregoing detailed description and examples have been
given for clarity of understanding only. No unnecessary limitations are to be
understood therefrom. All patents and patent applications cited herein are
hereby
incorporated by reference. It will be apparent to those skilled in the art
that many
changes can be made in the embodiments described without departing from the
scope
of the invention. Thus, the scope of the present invention should not be
limited to the
exact details and structures described herein, but rather by the structures
described by
the language of the claims, and the equivalents of those structures.
-25-
