U.S. patent application number 14/555096 was filed with the patent office on 2015-04-30 for non-chemical thermally printable film.
The applicant listed for this patent is Toray Plastics (America), Inc.. Invention is credited to Matthew H. BROWN, Emilio COLETTA, Harold E. KOEHN.
Application Number | 20150118459 14/555096 |
Document ID | / |
Family ID | 49301082 |
Filed Date | 2015-04-30 |
United States Patent
Application |
20150118459 |
Kind Code |
A1 |
BROWN; Matthew H. ; et
al. |
April 30, 2015 |
NON-CHEMICAL THERMALLY PRINTABLE FILM
Abstract
A two-layer mono-axially oriented film includes a first layer of
an opaque beta-nucleated microvoided propylene-based polymer; and a
second layer containing a dark pigment that is adapted for use in a
thermal printer in which the thermal print-head contacts the
exposed surface of the first layer. The dark pigment of the second
layer pigment has a color contrasting with the color of the first
layer and can contain a carbon black. The first layer includes
microvoids and may be made transparent upon the application of heat
by collapsing the voids of the first layer or upon the application
of ultra-sonic energy.
Inventors: |
BROWN; Matthew H.;
(Wakefield, RI) ; KOEHN; Harold E.; (North
Kingstown, RI) ; COLETTA; Emilio; (North Kingstown,
RI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Toray Plastics (America), Inc. |
North Kingstown |
RI |
US |
|
|
Family ID: |
49301082 |
Appl. No.: |
14/555096 |
Filed: |
November 26, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13857374 |
Apr 5, 2013 |
8968863 |
|
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14555096 |
|
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61621173 |
Apr 6, 2012 |
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Current U.S.
Class: |
428/207 ;
264/129; 264/173.16; 264/173.18; 428/315.5; 428/523 |
Current CPC
Class: |
B29C 71/02 20130101;
B32B 2307/41 20130101; Y10T 428/31938 20150401; Y10T 428/24998
20150401; B29K 2105/0005 20130101; B32B 27/205 20130101; B32B
2519/00 20130101; B29K 2023/12 20130101; B32B 2307/516 20130101;
Y10T 428/249958 20150401; B29C 48/17 20190201; B32B 27/20 20130101;
B29C 48/21 20190201; B32B 27/08 20130101; B32B 2307/518 20130101;
B32B 2250/02 20130101; B29K 2105/0032 20130101; B32B 2307/75
20130101; Y10T 428/24901 20150115; B29L 2009/00 20130101; B32B
2250/242 20130101; B32B 2307/4026 20130101; Y10T 428/249953
20150401; Y10T 428/249982 20150401; Y10T 428/249978 20150401; B32B
2307/412 20130101; B29L 2007/008 20130101; B32B 3/26 20130101; Y10T
428/24996 20150401; B32B 27/32 20130101 |
Class at
Publication: |
428/207 ;
264/129; 264/173.16; 264/173.18; 428/523; 428/315.5 |
International
Class: |
B32B 27/20 20060101
B32B027/20; B32B 27/32 20060101 B32B027/32; B29C 71/02 20060101
B29C071/02; B29C 47/04 20060101 B29C047/04; B29C 47/06 20060101
B29C047/06 |
Claims
1. A multilayer film comprising at least a two-layer film
comprising: a first layer comprising an opaque beta-nucleated
polypropylene-based polymer; and a second layer comprising a dark
pigment; wherein the multilayer film forms an image without using
an ink or a dye.
2. The multilayer film of claim 1, wherein the dark pigment of the
second layer pigment has a color contrasting with the color of the
first layer.
3. The multilayer film of claim 1, wherein the first layer
comprises a propylene-based polymer and an amount of a
beta-nucleating agent or beta-nucleated propylene polymer.
4. The multilayer film of claim 3, wherein the second layer
comprises a propylene-based polymer and an amount of carbon black
pigment in propylene-based polymer carrier resin.
5. The multilayer film of claim 1, wherein the dark pigment of the
second layer comprises a carbon black.
6. The multilayer film of claim 1, wherein the first layer
comprises micro-voids.
7. The multilayer film of claim 1, wherein the first layer
comprises a beta nucleating agent selected from the group
consisting of pimelic acid supported on nano-CaCO.sub.3; amides of
dicarboxylic acid including
N,N'-dicyclohexylnaphthalene-2,6-dicarboxamide and aryl
dicarboxylic acid amide, two-component beta nucleating agents of
organic dibasic acids selected from the group consisting of pimelic
acid, azelaic acid, o-phthalic acid, terephthalic acid and
isophthalic acid; oxide, hydroxide, or acid salts of Group II
metals; gamma-crystalline forms of quinacridone colorants; aluminum
salt of 6-quinizarin sulfonic acid; and bisodium salt of o-phthalic
acid.
8. The multilayer film of claim 1, wherein the first layer can be
made transparent upon the application of heat by collapsing the
voids in said first layer.
9. The multilayer film of claim 1, wherein the first layer can be
made transparent upon the application of ultrasonic energy.
10. The multilayer film of claim 1, wherein the first layer
comprises a transparent dye.
11. The multilayer film of claim 10, wherein the second layer
comprises a transparent dye that is of a different hue or color
than that of the first layer.
12. An imageable multilayer film comprising: a polypropylene first
layer that is clear or comprises a pigment or colorant; and an
image-side tie layer comprising a cavitating agent.
13. The multilayer film of claim 12, wherein colorants, pigments,
and opacifying agents are substantially absent from the image-side
tie layer.
14. The multilayer film of claim 12, wherein the image-side tie
layer has contacted to within the range of from 0.1% to 15% of its
original thickness upon collapse of the voids created by the
cavitating agent in the areas where an image is effected.
15. The multilayer film of claim 12, wherein the image-side tie
layer comprises a material having a density in the range of 0.9
g/cm.sup.3 to 1.13 g/cm.sup.3, a DSC melting point in the range of
40.degree. C. to 165.degree. C., and a melt flow rate in the range
of 1.6 dg/min to 4 dg/min.
16. The multilayer film of claim 12, wherein the film is treated
with a device that imparts selective physical or thermal treatment
to the image-side of the multi-layer film to affect an image.
17. The multilayer film of claim 12, wherein the multilayer film is
biaxially oriented.
18. A method of forming an image on a multilayer film comprising
the steps of: co-extruding at least a first layer, and an
image-side tie layer; orienting the multilayer film in at least one
direction; and imparting selective physical or thermal treatment to
the image-side of the multilayer film to effect an image
thereon.
19. The method of claim 18, wherein the first layer comprises a
colorant or pigment.
20. The method of claim 18, wherein colorants, pigments, and
opacifying agents are substantially absent from the image-side tie
layer.
21. The method of claim 18, wherein a colored coating or metal
coating is placed on the multilayered film surface opposite the
image-side tie layer.
22. The method of claim 18, wherein the imparting causes the
image-side tie layer to contract within the range of from 0.1% to
15% of its original thickness upon collapse of the voids created by
the cavitating agent in the areas where an image is effected.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of U.S. application
Ser. No. 13/857,374 filed Apr. 5, 2013, which claims priority of
U.S. Provisional Application No. 61/621,173, filed Apr. 6,
2012.
FIELD OF THE INVENTION
[0002] This invention relates to an oriented propylene-based film
which exhibits an appearance change when subjected to heat that
does not involve any chemical change. This film is well-suited as a
label film that can be activated by a thermal print-head to provide
custom information. This invention provides a visual change based
on a nonreversible physical change in the film, obviating the need
for chemical reactive coatings or at least minimizing the amount of
coating used. Another feature of this invention is that it is not
limited to a black-and-white color contrast for images or graphics.
Activation can also be accomplished by ultrasonic means.
[0003] This film is suitable as an "on-demand" label film for
custom labeling, bar-code printing, cash register receipts, for
consumer, industrial, and retail applications. It may be part of a
laminate structure involving multiple films, or as a single
laminate web for these applications.
BACKGROUND OF THE INVENTION
[0004] For creating custom information on labels, such as data or
bar codes, or even cash receipts, a common practice has been to
coat either paper or plastic substrates with a thermal reactive ink
that reacts to the heat from a thermal print-head to create a
visible contrast on the substrate material.
[0005] With the increasing scrutiny of Bisphenol-A--which is a
common ingredient or component of such thermal ink coatings--the
current thermal printable papers are under increasing pressure to
change the composition of the chemicals that create this color
contrast. The current approach with thermally reactive coated
papers or labels leaves unreacted chemicals on the substrate
surface which can expose the public consumer to doses of chemicals
that have been shown to have detrimental side effects particularly
in children but also in adults, even at low exposure dosages.
[0006] Another problem with thermal-change inks is that the image
is not stable. It is common knowledge that with time, faxes,
receipts, and labels that are printed with these thermal inks often
either fade or go completely dark with aging. This is particularly
true if exposed to higher temperatures or sunlight.
[0007] U.S. Pat. No. 4,004,065 describes a heat sensitive recording
member composed of a support and a heal sensitive layer overlying
the support. The heat sensitive layer contains an iron salt of a
higher fatty acid and gallic acid as color forming components, a
stilbene series fluorescent dye as an unusual color forming
inhibitor, and hydroxypropyl cellulose and hydroxypropyl methyl
cellulose.
[0008] U.S. Pat. No. 4,602,265 describes a heal sensitive
color-producing multilayer coating including a first coating layer
formed from a base polymeric coating composition comprising a
solution of film-forming polymer, a source of polyvalent metallic
ions, and at least one fatty add or derivative thereof; a second
coating layer, on the first coating layer, formed from a
sensitizing coating composition comprising a solution of organic
film-forming polymer, at least one fatty acid or derivative
thereof, and a reducing agent selected from catechol, pyrogallol,
hydroquinone, diphenyl carbazides, thereof; and a third coaling
layer, on the second coating layer formed from a base polymeric
coaling composition as defined above.
[0009] U.S. Pat. No. 5,863,859 describes a heat-sensitive recording
material suited for use in direct thermal imaging, wherein the
recording material includes: (i) a layer (1) uniformly distributed
in a film-forming water-insoluble resin binder a substantially
light-insensitive organic metal salt, preferably a silver salt, and
(ii) a layer (2) in direct contact with said layer (1) or in
thermal working relationship therewith through the intermediary of
a spacer layer (3), characterized in that the layer (2) contains,
uniformly distributed in a film-forming water-soluble hydrophilic
binder at least one organic reducing agent that is capable of
diffusing out of said layer (2) Into said layer (1) on heating said
recording material, and is coated from an aqueous solution.
[0010] U.S. Patent Publication No. 2008/0233290 A1 describes a
method of preparing a thermally printable sheet which includes
providing a substrate including a base sheet having at least one
surface coated with a layer containing a pigment in solid porous
particulate form, and, using a printer, printing onto the coated
surface of the substrate, a thermal ink which includes a color
former, a color developer, which can be bisphenol A., and a
sensitizer, characterized in that the sensitizer includes dimethyl
terephthalate and the ink also includes at least one pigment. This
publication also discloses a thermally printable sheet suitable for
use In such a method.
[0011] U.S. Patent Publication No 2009/0031921 A1 describes a
thermal ink which includes a color former, a color developer and a
sensitizer, in which the color former can be
3-dibutylamino-6-methyl-7-an.anilinofluoran; the color developer
can be bisphenol A; and the sensitizer can be dimethyl
terephthalate, and the ink also comprises at least one pigment This
ink may be used in thermal papers to reduce unwanted discoloration
during storage.
[0012] U.S. Pat. No. 6,104,422 describes a sublimation thermal
image transfer recording method for thermally forming images on an
image-receiving sheet prepared by forming a dye-receiving layer on
a substrate. The dye-receiving layer contains a subliminal
dye-containing ink, such as C. I. Disperse, Yellow, Red, Blue; and
a binder resin such as polyvinyl butyral or styrene-maleic acid
copolymer.
[0013] U.S. Pat. No. 4,415,615 describes a cellular
pressure-sensitive adhesive membrane including 15 to 85'% voids
that does not collapse after being briefly compressed, has
remarkably good adhesion on contact with rough surfaces and
remarkably good flexibility and conformability at sub-freezing
temperatures.
[0014] U.S. Pat. No. 5,134,174 describes biaxially oriented
microporous polypropylene films made using beta-nucleation and
specific processing temperatures. The micro porous films are
open-celled with a high porosity of 30-40% with average pore size
of 200-800 Angstroms.
[0015] U.S. Pat. No. 4,975,469 describes oriented porous
polypropylene-based films using beta-nucleating agents. The pores
have typical diameters ranging from 0.2 to 20 microns and
inter-connect with each other and are "open-celled" such that the
porous film exhibits a high moisture vapor transmission rate of
about 2500-7500 g/m.sup.2/day. The beta-crystalline portions are
extracted via a sol vent to form a porous film.
[0016] Canadian patent application No. CA02551526 describes a
biaxially oriented white polypropylene film for thermal transfer
recording including a polypropylene resin of 30% or higher beta
crystal ratio and 140-172.degree. C. melting temperature, in which
the biaxially oriented white polypropylene film has substantially
non-nucleated voids. A receiving layer is provided on one side of
the film for thermal transfer recording in which the receiving
layer includes at least one or more kinds of resin selected from
polyolefin, acryl-based resin, polyester-based resin, and
polyurethane based resin.
SUMMARY OF THE INVENTION
[0017] This invention addresses the issue of potential chemical
hazards used in thermally-reactive coated substrates by making a
label film that can create a distinct visual contrast via a
physical change to the film. The invention eliminates the need for
unreacted chemicals to create customizable labels. By using the
micro-voids formed by beta-nucleation of the propylene-based
substrate in the top visual layer and the selective application of
heat from a thermal print-head to specific portions of this
micro-voided top layer (i.e. in the shape of images or alphanumeric
characters), the beta-nucleated voids collapse and thus provide a
transparent film in the heated areas. This contrast between an
opaque, white microvoided area and a non-voided transparent area
allows the formation of discrete images and alphanumeric characters
as desired. In addition, since the temperature required to collapse
the microvoids is much higher than typical ambient conditions, such
images are expected to be more durable and resistant to fading over
time and ambient environmental exposure than the current art using
thermally-reactive coatings and inks.
[0018] The film of this invention works with a non-reversible
physical change in the structure of the film to go from an opaque
white or Light-colored appearance that is due to micro-voids in the
film, to selectively collapsing or eliminating the voids to provide
a transparent, clear film in the area where heat has been applied.
By laminating the film to a darker-colored or contrasting colored
substrate- or by coating one side of the film with a dark-colored
or contrasting colored ink or coating--such contrasting colors will
show through the clear or transparent areas of the inventive film.
As this visual change (from white to clear) requires enough heat to
change the structure of the film, i.e., a softening point of about
148.degree. C., it is not likely that the custom information would
fade or be converted over a wide area due to aging or ambient
environmental conditions, such as exposure to sunlight or other
outdoor weather conditions.
[0019] Polypropylene is not known for its resistance to sunlight
but a short exposure of a few days or even up to a year, would not
be expected to have any effect on the film's imagery after thermal
printing. Nevertheless, robustness to prolonged exposure, such as
is need for an agricultural plant tag, could be provided by
modifying the film to incorporate an UV stabilizer or blocker to
preserve the polypropylene and ensure durability in harsher
environmental conditions.
[0020] A dark background would be necessary to create a good
contrast where the "thermal print" is to occur, but the color does
not need to be restricted to black or white. The white surface,
while easiest to create with the micro-voids, may also be colored
or pigmented, as long as the color would consist of a transparent
pigment, which would still result in sufficient contrast against
the dark background. Similarly, the contrasting color need not be
black but any suitable color or shading that provides enough
contrast with the micro-voided film to distinguish the "printed"
information for the naked eye or machine readers.
[0021] The background on creating the micro-voided or cavitated
film was in the food packaging industry, so all the components of
the film can easily be made to comply with FDA packaging standards.
Specifically, the method to create this film utilizes a
beta-crystalline nucleating agent for polypropylene. Polypropylene
can exist in several crystalline forms: alpha, beta, gamma, delta,
and smectic crystal forms. Of interest in this invention are the
alpha and beta forms. The specific conditions to produce a
polypropylene article rich in beta-crystals is well-known in the
art, typically requiring specific processing conditions and usually
with a specific beta-nucleating agent. In this invention, it
requires a hot casting roll that, in conjunction with the nucleator
additive, causes the formation of a less dense beta crystalline
form for the crystal portions of the semicrystalline polypropylene
film. When this resulting film is stretched or oriented in the
machine direction, the beta crystal changes to the "preferred"
denser alpha crystal form for polypropylene. This change in density
creates small micro-voids that, with the orientation, are enlarged
enough such that the voids impart a white, opaque appearance to the
film. This cavitation is also shown by a reduced density in the
resulting film. Stretching the sheet either monoaxially or
biaxially produces opaque, cavitated film with lowered density,
high strength, and enhanced printability.
[0022] One embodiment is a two-layer mono-axially oriented
coextruded film (MOPP) including a microvoided main layer A of a
propylene-based polymer including an impact ethylene-propylene
copolymer and an amount of beta-crystalline nucleating agent; and a
second layer B of a propylene-based polymer including a crystalline
isotactic propylene homopolymer and an amount of pigment such as a
carbon block pigment; in which the second layer B is contiguously
attached to one side of layer A and is coextruded as a skin layer
or sublayer with the main layer A. This second layer B is not
required to be microvoided.
[0023] Another embodiment is as a two-layer laminate structure in
which one layer A is a microvoided mono-axially oriented extruded
film or sheet including an impact ethylene-propylene copolymer and
an amount of beta-crystalline nucleating agent; and a second layer
B is a pigmented sheet or film including a polymeric or paper sheet
containing a pigment, (preferably a color that is in contrast with
layer A's color or appearance). Layer B is laminated or adhered
contiguously to one side of layer A by various means well-known in
the art, such as adhesive lamination or extrusion lamination
processes. Layer B is not required to be microvoided.
[0024] In an another embodiment, it can also be contemplated to
coat the second layer B onto one side of main layer A (as described
in the previous embodiments) by various means well-known in the art
such as extrusion-coating or solution coating. For example, it can
be contemplated to extrusion-coat a polyethylene-including melt or
other polymeric coating such as polypropylene or other polymer
types (it may also be contemplated to use tie-resin materials,
layers, primers, discharge-treating, etc., as needed to improve
bonding between layers A and B), pigmented with carbon black (or
other color suitably contrasting with layer A), onto one side of
layer A.
[0025] In yet another embodiment, it can be contemplated to apply
layer B onto one side of layer A (as described in the previous
embodiments) in which layer B is comprised of an ink or inks which
provide a contrasting color to layer A. The inks may be
solvent-borne or aqueous (or UV or electron-beam curable ink
systems), and may be applied by various means well-known in the art
such as flexographic plates or rotogravure rolls; in addition, it
can be contemplated to use primers or other materials to improve
bonding of the inks to layer A. It can also be contemplated to
discharge-treat the side of layer A which is to receive layer B
printing inks by various means well-known in the art such as
corona, flame, or atmospheric plasma treating systems; as well as
using priming materials in combination with discharge-treatment
methods. It may also be contemplated to apply the layer B printing
inks as full coverage over the chosen side of layer A or as a
discrete pattern, preferably in alignment with the desired thermal
printing pattern applied to layer A by a thermal head printer. This
latter embodiment may be useful as a cost-savings method to reduce
the amount of ink coverage needed.
[0026] All these embodiments may also include additional additives
in layer A and/or B, such as antiblock particles, slip agents,
process aids, antistatic agents, defoamers, adhesion promoters,
etc., as needed to enhance processability and other film handling
properties. These additives may be added in quantities as described
later in the specification so as not to materially affect or
interfere with the basic properties of the film of this
invention.
[0027] This invention provides a method to impart thermal print
images and information via the application of heat only, or with
ultrasound, and without the need of a chemical change of a
thermally active compound. Additional advantages of this invention
will become readily apparent to those skilled in the art from the
following detailed description, wherein only the preferred
embodiments of this invention are shown and described, simply by
way of illustration of the best mode contemplated for carrying out
this invention. As will be realized, this invention is capable of
other and different embodiments, and its details are capable of
modifications in various obvious respects, all without departing
from this invention. Accordingly, the examples and description are
to be regarded as illustrative in nature and not as
restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a perspective view of a film according to an
embodiment of the invention. Shown is a mono-oriented polyolefinic
film 100, comprised of two layers. Layer 101 is a white or
light-colored/pigmented opaque beta-nucleated and micro-voided
polypropylene layer. Layer 102 is a black or dark-colored/pigmented
polypropylene layer upon one side of Layer 101. The side of 101
opposite to 102 is the thermal print side.
[0029] FIG. 2 is a top view of a thermally exposed 2-layer film
sheet 100 of the invention showing the change in appearance where a
heated platen was applied to white beta crystalline micro-voided
top layer 101, thus changing its appearance from white to clear in
that area, and allowing black pigmented bottom layer 102 to show
through the transparent portion of top layer 101.
DETAILED DESCRIPTION OF THE INVENTION
[0030] In one embodiment of the invention, the laminate film is a
two-layer mono-oriented coextruded film including a first layer A
of a polyolefin resin layer including a propylene-based polymer and
an amount of a beta-nucleating agent or beta-nucleated propylene
polymer; and a second layer B coextruded with layer A contiguously
upon one side of layer A. Layer B is comprised also of a
propylene-based polymer and an amount of carbon black pigment in
propylene-based polymer carrier resin. If desired, one or both
sides of the laminate film structure may be discharge-treated.
[0031] The coextruded polyolefin resin layers A and B were
uniaxially (or monoaxially) oriented. It can be contemplated to
biaxially orient the laminate film as well in both the machine (MD)
and transverse (TO) directions. The propylene-based polymer can be
an isotactic ethylene-propylene impact copolymer with an
ethylene-propylene rubber content of about 10-30 wt % of the
polymer wherein the ethylene content of the rubber is about 10-80
wt % of the rubber. Typically, the copolymer is an
ethylene-propylene copolymer, an ethylene-butene copolymer, a
propylene-butene copolymer, or an ethylene-propylene-butene
copolymer. Preferably, an ethylene-propylene or
ethylene-propylene-butene copolymer is used. The copolymer may be
an elastomer or plastomer. A thermoplastic elastomer can be
described as any of a family of polymers or polymer blends (e.g.
plastic and rubber mixtures) that resemble elastomers in that they
are highly resilient and can be repeatably stretched and, upon
removal of stress, return to close to its original shape; is
melt-processable at an elevated temperature (uncrosslinked); and
does not exhibit significant creep properties. Thermoplastic
elastomers typically have a density of between 0.860 and 0.890
g/cm3 and a molecular weight Mw of 100,000 or greater. Plastomers
differ from elastomers: a plastomer can be defined as any of a
family of ethylene-based copolymers (i.e. ethylene alpha-olefin
copolymer) which has properties generally intermediate to those of
thermoplastic materials and elastomeric materials (thus, the term
"plastomer") with a density of less than about 0.900 g/cm.sup.3
(down to about 0.865 g/cm.sup.3) at a molecular weight Mw between
about 5000 and 50,000, typically about 20,000 to 30,000. Plastomers
generally have an ethylene crystallinity between thermoplastics and
ethylene alpha-olefin elastomers and are generally of a higher
crystallinity than elastomers (which can generally be considered
amorphous). As such, plastomers generally have better tensile
properties than elastomers.
[0032] A suitable example of ethylene-propylene impact copolymer
for this invention is Total Petrochemical's 5571. This resin has a
melt flow rate of about 7 g/10 minutes at 230.degree. C., a melting
point of about 160-165.degree. C., a Vicat softening point of about
148.degree. C., and a density of about 0.905 g/cm.sup.3. Another
example of ethylene-propylene impact copolymer can be Total
Petrochemical's 4180 with a melt flow rate of about 0.7 g/10
minutes at 230.degree. C., a melting point of about 160-165.degree.
C., a Vicat softening point of about 150.degree. C., and a density
of about 0.905 g/cm.sup.3. Other suitable ethylene-propylene impact
copolymers can be Braskem's TI-4015-F with an ethylene-propylene
rubber of 10-30 wt %, a melt flow rate of 1.6 g/10 minutes at
230.degree. C., melting point of 160-165.degree. C., Vicat
softening point of 148.degree. C., and a density of about 0.901
g/cm.sup.3; and ExxonMobil Chemical's PP7033E2 with a melt flow
rate of about 8 g/10 minutes at 230.degree. C. and a density of
about 0.9 g/cm.sup.3.
[0033] Other suitable propylene-based polymers can be isotactic
crystalline propylene homopolymers and "mini-random" isotactic
crystalline ethylene-propylene copolymers. "Mini-random" propylene
homopolymers are those class of ethylene-propylene copolymers in
which the ethylene content is fractional, i.e. less than 1 wt %,
typically on the order of about 0.2-0.8 wt %, and preferably about
0.5-0.7 wt %. These crystalline isotactic polypropylenes are
generally described as having an isotactic content of about 90% or
greater as measured by C13 NMR. Suitable examples of crystalline
propylene homopolymers for this invention are Total Petrochemicals
3271 and 3373HA, Phillips CH016 and CR035, and Braskem FF018. These
resins also have melt flow rates of about 0.5 to 5 g/10 min at
230.degree., a melting point of about 163-167.degree. C., a
crystallization temperature of about 108-126.degree. C., a heat of
fusion of about 86-110 J/g, a heat of crystallization of about
105-111 J/g, and a density of about 0.90-0.91. Higher isotactic
content propylene homopolymers (i.e. "high crystalline"
homopolymers) may also be used. Suitable examples of these include
those made by Total Petrochemicals 3270 and 3273 grades, Braskem
grade HR020F3, and Phillips 66 CH020XK. These high crystalline
polypropylenes typically have an isotactic content of 93% or
greater as measured by 13C NMR spectra obtained in
1,2,4-trichlorobenzene solutions at 130.degree. C. The % percent
isotactic can be obtained by the intensity of the isotactic methyl
group at 21.7 ppm versus the total (isotactic and atactic) methyl
groups from 22 to 19.4 ppm. These resins also have melt flow rates
of about 0.5 to 5 g/10 min, a melting point of about
163-167.degree. C., a crystallization temperature of about
108-126.degree. C., a heat of fusion of about 86-110 J/g, a heat of
crystallization of about 105-111 J/g, and a density of about
0.90-0.91.
[0034] In the case of using high crystalline propylene
homopolymers, it may also be contemplated to employ processing aids
to help improve orientation, lowering orientation stresses, uneven
stretching marks, motor draw amps, etc. Examples of suitable
processing aids can be those based on hydrocarbon resins of various
types. In particular, polydicyclopentadiene hydrocarbon resins are
preferred processing aids as having good clarity, no smoking
issues, no odor issues, and good miscibility with propylene-based
resins. As a processing aid, inclusion of the hydrocarbon resin
allows a wider "processing window" in terms of processing
temperatures for machine direction (MD) and/or particularly,
transverse direction (TD) orientation. A suitable hydrocarbon resin
is of the polydicyclopentadiene type available in masterbatch form
from ExxonMobil as PA639A, which is a 40% masterbatch of
polypropylene carrier resin and 60% hydrocarbon resin. Suitable
amounts of the hydrocarbon masterbatch to use in Layer A and/or
Bare concentrations of up to 10% masterbatch or up to 5% of the
active hydrocarbon resin component. The pure hydrocarbon resin can
also be obtained (i.e. not as a masterbatch) as ExxonMobil
PR100A.
[0035] Suitable examples of propylene-based random copolymers for
this invention are: Total Petrochemicals Z9421 ethylene-propylene
random copolymer elastomer of about 5.0 g/10 min melt flow rate
(MFR) at 230.degree. C., melting point of about 120.degree. C.,
density 0.89 g/cm.sup.3, and ethylene content of about 7 wt % of
the polymer; Total Petrochemicals 8473 ethylene-propylene random
copolymer of about 4.0 MFR at 230.degree. C. and ethylene content
of about 4.5 wt % of the polymer; Sumitomo Chemical SPX78R1
ethylene-propylene-butene random copolymer of about 9.5 g/10 min
MFR at 23 0.degree. C., ethylene content of about 1.5 wt %, and
butene content of about 16 wt % of the polymer; or ExxonMobil
Chemical Vistamaxx.TM. ethylene-propylene random copolymer
elastomers such as grade 3980 FL with an MFR of about 8.3 g/10 min
at 230.degree. C., Vicat softening point of about 80.degree. C.,
melting point of about 79.degree. C., density of about 0.879
g/cm.sup.3, and ethylene content of about 8.5 wt %. Other suitable
propylene-based copolymers and elastomers may be contemplated
including but not Limited to: metallocene-catalyzed thermoplastic
elastomers like ExxonMobil's Vistamaxx.TM. 3000 grade, which is an
ethylene-propylene elastomer of about 11 wt % ethylene content, 8
g/10 min MFR at 230.degree. C., density of 0.871 g/cm.sup.3,
T.sub.g of -20 to -30.degree. C., and Vicat softening point of
64.degree. C.; or ethylene-propylene alpha-olefin copolymer
plastomers of Dow Chemical's Versify.TM. grades, such as grade
3300, which is an ethylene-propylene plastomer of about 12 wt %
ethylene content, 8 g/10 min MFR at 230.degree. C., density of
0.866 g/cm.sup.3, T.sub.g of -28.degree. C., and Vicat softening
point of 29.degree. C.; and Mitsui Chemicals Tafmer.TM. grades
XM7070 and XM7080 metallocene-catalyzed propylene-butene random
elastomers of about 22 and 26 wt % butene content, respectively.
They are characterized by a melting point of 75.degree. C. and
83.degree. C., respectively; a Vicat softening point of 67.degree.
C. and 74.degree. C., respectively; a density of 0.883-0.885
g/cm.sup.3; a T.sub.g of about -15.degree. C.; a melt flow rate at
230.degree. C. of 7.0 g/10 minutes; and a molecular weight of
190,000-192,000 g/mol.
[0036] Additionally, an amount of inorganic antiblocking agent may
be optionally added up to 5000 ppm to either or both resin Layers A
and B as desired for film-handling purposes, winding, antiblocking
properties, and control of coefficient of friction. Preferably
300-5000 ppm, and more preferably 500-1000 ppm, of antiblock may be
added. Suitable antiblock agents comprise those such as inorganic
silicas, sodium calcium aluminosilicates, crosslinked silicone
polymers such as polymethylsilsesquioxane, and
polymethylmethacrylate spheres. Typical useful particle sizes of
these antiblocks range from 1-12 urn, preferably in the range of
2-6 .mu.m.
[0037] Migratory slip agents such as fatty amides and/or silicone
oils can also be optionally employed in either or both film layers,
either with or without the inorganic antiblocking additives, to aid
further with controlling coefficient of friction and web handling
issues. Suitable types of fatty amides are those such as stearamide
or erucamide and similar types, in amounts of 100-5000 ppm of the
layer. Preferably, erucamide can be used at 500-1000 ppm of the
layer. A suitable silicone oil that can be used is a low molecular
weight oil of 350 centistokes which blooms to the surface readily
at a loading of 400-600 ppm of either or both layers.
[0038] The beta crystalline phase in polypropylene differs from the
alpha crystalline phase as mentioned previously. The alpha phase is
the most common crystalline phase and has a melting point typically
of about 164.degree. C. whereas the beta phase is less common and
has a melting point typically of about 150.degree. C. Microvoids
can form in the substrate during orientation when in the solid
state, due to the transformation of the beta crystals into alpha
crystals, and this accounts for the white opaque appearance of the
inventive film's layer A. These microvoids can collapse upon
melting and recooling of the substrate and the white opaque
appearance can turn transparent and clear; without being bound by
any theory, it is this property that gives the unique non-chemical
thermal print opportunities of the inventive film as a thermal
printing head is put in contact with the beta-nucleated and
microvoided layer A and is activated.
[0039] Beta nucleating agents are well-known and studied. Truly
effective beta nucleators are not common, but effective beta
nucleators have been found based on materials such as: pimelic acid
supported on nano-CaC0 3; amides of dicarboxylic acid (e.g.
N,N'-dicyclohexylnaphthalene-2,6-dicarboxamide; aryl dicarboxylic
acid amide); two-component beta nucleating agents of organic
dibasic acids (such as pimelic acid, azelaic acid, o-phthalic acid,
terephthalic acid, isophthalic acid) and oxide, hydroxide, or acid
salts of a Group II metals (e.g. magnesium, calcium, barium);
gamma-crystalline form of quinacridone colorant; aluminum salt of
6-quinizarin sulfonic acid; bisodium salt of o-phthalic acid. Beta
nucleating agents are conveniently obtained as a commercial
masterbatch in a polypropylene carrier resin; a suitable one for
use is Mayzo Corporation's BNX.RTM. MPM1112 grade beta nucleant
polypropylene masterbatch with melt flow rate of 12 g/10 min at
230.degree. C., dual melting point of 150-1 55.degree. C. for beta
crystal phase and 162-167.degree. C. for alpha crystal phase (as
measured on a 2 wt % letdown ratio of the masterbatch in propylene
homopolymer resin via second heat using a differential scanning
calorimeter), and specific gravity of 0.90 g/cm.sup.3. Suitable
amounts of this masterbatch to use in layer A of the inventive film
is from about 0.5 to 3.0 wt % of the layer, preferably about 1.0 to
2.0 wt %, and more preferably, about 1.1 wt % to 1.8 wt %.
[0040] For the contrasting color layer B of this coextruded
two-layer film embodiment, carbon black pigment may be used
(although other contrasting colors may also be used). Carbon blacks
are commonly and widely used as pigments, colorants, and fillers
for rubber and plastic products. Carbon blacks are typically
produced from the charring of organic materials such as wood or
bone; or the incomplete combustion of petroleum products and/or
vegetable oils. Carbon black pigments are most conveniently used
and handled in a masterbatch form and a suitable one for the
present invention can be obtained from Ampacet Corporation as grade
19114 FDA Black carbon black pigment in a polypropylene carrier.
This masterbatch has typical properties of a 4 g/10 min melt flow
rate at 230.degree. C., melting point of 160-165.degree. C., and
density of 1.13 g/cm.sup.3. Suitable amounts to use in layer B for
a suitable dark color is about 1-20 wt % of the layer, and
preferably, about 6-9 wt %.
[0041] The beta-nucleated resin layer A can be 20 .mu.m to 200
.mu.m in thickness after monoaxial orientation, preferably between
30 .mu.m and 150 .mu.m, and more preferably between 70 .mu.m and
100 .mu.m in thickness. The coextruded layer B of this embodiment
can be between 2-200 .mu.m in thickness, but any thickness may be
chosen that is suitable for the contrast ratio between the clear
and dark areas after thermal printing. The main criteria is to
ensure a thick enough coextruded layer B to reasonably and
sufficiently contain enough pigment to provide a good contrasting
color. Preferably, the thickness of both A and B layers combined
should be in the range of 25 to 200 .mu.m, more preferably, 100 to
200 .mu.m. The ratio of layer A to layer B thickness can be varied
and optimized to meet specific end-use applications for thermal
print substrates and labels.
[0042] The surface of layer A opposite layer B can also be surface
treated with either an electrical corona-discharge treatment
method, flame treatment, atmospheric plasma, or corona discharge in
a controlled atmosphere of nitrogen, carbon dioxide, or a mixture
thereof, with oxygen excluded and its presence minimized. The
latter method of corona treatment in a controlled atmosphere of a
mixture of nitrogen and carbon dioxide results in a treated surface
that comprises nitrogen-bearing functional groups, preferably at
least 0.3 atomic % or more, and more preferably, at least 0.5
atomic % or more.
[0043] In the above embodiment of a coextruded two-layer film, the
respective layers can be coextruded through a multi-layer
compositing die such as a 2-layer die, and cast onto a chill roll
to form a solid film suitable for further processing. In the case
of a single layer film, the respective layer can be extruded
through a single-layer die and cast onto a chill roll to form a
solid film suitable for further processing. Extrusion temperatures
are typically set at 235-275.degree. C. with a resulting melt
temperature at the die of about 230-250.degree. C. Preferably, the
extrusion profile of beta-nucleated layer A is a "reverse"
temperature profile in which the feed zones of the extruder are set
higher than the final zones. In this case, suitable extrusion
temperature settings are from about 271.degree. C. in the initial
feed zone, to about 240.degree. C. in the final zone. Filter and
melt pipe temperatures were set at about 240.degree. C.; die
temperature was about 232.degree. C.
[0044] The inventive laminate film was extruded into a sheet form
and cast onto a cooling drum at a speed of 6 to 15 mpm whose
surface temperature is controlled between 99.degree. C. and
104.degree. C. to solidify the non-oriented laminate sheet. These
higher casting temperature conditions are important to form and
favor beta crystal formation.
[0045] The laminate film was monoaxially oriented in the machine
direction (MD) to a certain amount. The amount of monoaxial machine
direction orientation should be about 2.5-7 times in the machine
direction, preferably 3-7 times, and more preferably 4.0 to 7.0
times. Above a 7:1 machine direction orientation ratio,
processability issues may result such as film breakage which can
affect the product cost and machine efficiency; below a 2.5:1
machine direction orientation ratio, processability issues such as
uneven film profile, gauge bands, and uneven stretch marks can
occur which also can result in higher product costs and lower
machine efficiencies. Once oriented at the appropriate stretch
ratio, the laminate film's layer A appears white and opaque due to
the formation of micro voids around the beta crystal sites. It
should be noted that that the microvoids of the inventive film were
closed-cell, and not open-cell, and thus, did not result in
continuous pores which made the microvoided film porous. The
density of the microvoided beta-crystalline layer A ranged from
about 0.77 to 0.80 g/cm.sup.3.
[0046] MD orientation temperatures were typically set at about:
113.degree. C. for preheat rolls; 93.degree. C. for stretching; and
126.degree. C. for annealing Annealing or heat-setting in the final
sections of the MD orientation unit was used to help reduce
internal stresses within the laminate film and minimize heat
shrinkage and maintain a dimensionally stable mono-axially oriented
film.
[0047] The uniaxially oriented sheet was then optionally passed
through a discharge-treatment process on one side of the film (i.e.
the side of layer A opposite layer B) such as an electrical corona
discharge treater at a watt density of about 2.4 watt/ft.sup.2. The
one-side treated film was then wound into roll form. The finished
article appeared as a film with one side white (layer A) and the
opposite side dark (layer B).
[0048] Further embodiments may be contemplated as well. In one
embodiment, it may be contemplated to produce at least a single
layer A only of the mono-axially oriented microvoided film
comprised of a propylene-based polymer and the betacrystalline
nucleating agent or masterbatch, and laminating film A to a second,
standalone, dark or contrasting colored or pigmented film or
substrate C by means well-known in the art with an adhesive. This
adhesive lamination may be accomplished by using any number of
aqueous or solvent-borne adhesives (e.g. 2-part urethane) via
well-known solution coating methods including, but not limited to,
gravure or rod coating methods; solventless-lamination methods
including, but not limited to, extrusion lamination using molten
solventless adhesives such as low density polyethylene, or hot melt
systems; solventless adhesive systems such as UV or electron beam
curable adhesives using application methods including, but not
limited to, gravure or rod coating methods. Such adhesives may be
applied to one side of the colored film C or to one side of the
opaque micro-voided beta-crystalline propylene-based polymer film
of layer A as desired for the lamination process.
[0049] The colored film or substrate C of the above embodiment may
be opaque or translucent, but should be a separate film from the
film made of layer A. It can be produced in a separate film-forming
process as the film of layer A. For example, one could extrude (or
coextrude a multi-layer film) film C as including a propylene-based
film and carbon black of the formulation described previously for
layer B. Film C could range in thickness including, but not limited
to, from 1 .mu.m to 100 .mu.m as desired. The contrasting colored
film C may be comprised (but not limited to) of: paper; paperboard;
cellulosic films; metal foils and films; polymeric film or films
including polypropylene, polyethylene, polyethylene terephthalate,
polyester, nylon, polylactic acid, polystyrene, other polymers;
metallized substrates (e.g. paper or polymeric films); or
combinations of substrates.
[0050] In another embodiment, it may be contemplated to apply a
contrasting colored ink or pigmented coating to one side of the
film of layer A. For printing an ink or applying a pigmented
coating to one side of the layer A film, it may be desirable to
discharge-treat the side of interest of the film, to help promote
wet-out and adhesion of the ink or coating. Primers or other
adhesion promotes may be used as well for this purpose. In the case
of printing, an ink--e.g. a black ink or other contrasting colored
ink could be applied to one side of the film of layer A by means
well-known in the art such as gravure roll or flexographic plates.
The ink may be water-based, solvent-based, or solventless type that
is cured by UV or electron beam. A contrasting colored coating may
also be applied to one side of the film including layer A. For
example, a carbon black containing polymeric coating may be
extrusion-coated on one side of the film including layer A;
alternatively, an aqueous or solvent-based coating may be applied
to one side of the film including layer A via gravure or rod
coating or other means well-known in the art; further, both an ink
and a coating may be applied together to one side of the film
including layer A, in which the ink is applied directly to the film
and the coating applied on top of the ink. The latter may be
advantageous in that the coating--being thicker than the ink--may
add additional opacity and contrast to support the ink pigment or
color, and need not be the same color as the ink. The coating may
be white opaque (same color as the film including layer A) for
example as long as the ink between the coating and layer A film is
of a contrasting color to the layer A film. In addition, the
coating may also be useful to help protect the ink layer from
scuffing or wear (and may also be transparent or unpigmented if
used for this purpose). It could also be contemplated to coat or
deposit a metallic layer (e.g. aluminum metallization) to provide a
suitable contrast.
[0051] In the above embodiments, it could further be contemplated
that the film including layer A could also be a coextruded
multi-layer film, for example, at least a 2-layer coextruded film,
in which both layers A and second coextruded layer B are both
comprised of the propylene-based polymer and the beta-crystalline
nucleating agent. This multi-layer film could then be laminated to
the separate contrasting colored layer C or printed on one side
with a contrasting colored pigment or ink.
[0052] In a typical thermal printing application, the thermal print
head (or heads) is used to transfer ink or dye from the ink or dye
donor elements (e.g. thermal transfer ink-containing film or
ribbon) to a receiving or recording element (e.g. print receiving
substrate). Alternatively, the thermal print head may contact a
substrate containing a thermally sensitive ink or dye that changes
color or becomes visible upon application of heat from the thermal
print head. Other known sources for transferring or activating
thermal inks or dyes, such as lasers, may be used. A thermal ink or
dye transfer assemblage may include 1) an ink or dye-donor element;
2) an ink or dye receiving or recording element, the ink or
dye-receiving element being in a superposed relationship with the
ink or dye-donor element such that the ink or dye layer of the
donor element may be in contact with the ink or dye-receiving layer
of the receiving element.
[0053] In the case of the present invention, as an example using
the embodiment including a coextruded 2-layer film of a
beta-crystalline nucleated white opaque propylene-based polymer
layer A and a contrasting colored propylene-based layer B, it is
contemplated that the laminate film structure of layers A and B are
fed into the thermal print head assembly such that the side of
layer A including the beta-nucleated and microvoided layer is
subjected to heat treatment from the thermal print head. Upon
activation of the thermal print head heating elements, sufficient
thermal energy is transferred into layer A to partially melt the
layer in the region of thermal contact, thus transforming the
micro-voided beta crystalline regions into alpha crystals. This
renders the appearance of the thermally-contacted areas from white
(or opaque) to clear (or transparent). Thus, the physical contrast
between the opaque portions and the transparent portions can be
visible by eye (looking through the film from the layer A side
wherein the contrasting layer B underneath shows through the clear
portions of Layer A) and information conveyed via thermal printing
head onto the inventive receiving substrate without the use of
chemical inks or dyes.
[0054] In yet another embodiment, it could be contemplated that the
nonchemical thermal print film of the invention could include only
a single layer A including a propylene-based polymer and an amount
of beta-nucleating agent. After orientation, the essentially
mono-Layer film has a micro-voided white opaque appearance and,
after passing through the thermal print head, the thermally
"printed" areas of layer A turn from white to clear, thus providing
enough contrast to discern information such as alphanumeric
lettering and/or barcodes or other information.
[0055] It can also be contemplated that in addition to thermal
print heads, ultrasonic energy may also be sufficient to collapse
the beta-crystalline micro-voids, thus converting the white opaque
regions into transparent regions where the ultra-sonic energy is
directed.
[0056] This invention will be better understood with reference to
the following examples, which are intended to illustrate specific
embodiments within the overall scope of the invention.
Example 1
[0057] A two-layer mono-axially oriented film (MOPP) was made using
a monoaxial orientation process with two distinct coextruded
layers. The two layers comprised a black pigmented layer B and a
white opaque beta-crystalline nucleated layer A and the laminate
film appeared dark colored on one side (layer A) and light colored
on the opposite side (layer A) after orientation. Layer A was
composed of about 98.2 wt % of an impact propylene copolymer
Braskem TI4015F and about 1.8 wt % of a betacrystalline nucleating
masterbatch Mayzo MPM1112. Layer B was composed of about 94 wt %
Braskem TI4015F and about 6 wt % of a carbon black pigment
masterbatch Ampacet 191114. The coextruded film substrate was made
via co-extrusion through a die, cast on a temperature controlled
drum at 104.degree. C., oriented in the machine direction through a
series of heated and differentially sped rolls at various
orientation draw ratios (MDX) of about 4:1. Once oriented the clear
layer B appeared whitish and opaque due to the formation of
microvoids from the beta-nucleation. Thus, the finished article
appeared as a film with a black side and a white side (Figure I).
The film was heat-set or annealed in the final zones of the MD
orientation section to reduce internal stresses and minimize heat
shrinkage of the film and maintain a dimensionally stable
mono-axially oriented film. After orientation, the finished
thickness of the 2-layer laminate coextruded film was nominal 150
.mu.m or 6000G. The thickness of the beta-nucleated layer A was
about 135 .mu.m; the thickness of the carbon black pigmented layer
B was about 15 .mu.m.
Example 2
[0058] Example 1 was substantially repeated except that the amount
of Mayzo MPMIII2 beta-nucleating masterbatch was about 2.2 wt % and
about 97.8 wt % Braskem TI4015F in layer A.
Example 3
[0059] Example 1 was substantially repeated except that the amount
of Mayzo MPMIII2 beta-nucleating masterbatch was about 1.2 wt % and
about 98.8 wt % Braskem TI4015F in layer A; the amount of carbon
black Ampacet 191114 was about 9 wt % and about 91 wt % Braskem
TI4015F in layer B; and the overall thickness was about 100 .mu.m
with the A layer about 90 .mu.m and the B layer about 10 .mu.m.
Example 4
[0060] A mono-axially oriented film was made as in the above
Example 1. However, in this case, both layers A and B were
comprised of the beta-nucleated impact copolymer of about 98.2 wt %
of Braskem TI4015F and about 1.8 wt % of Mayzo MPM III2,
effectively producing a single layer film of the same composition
throughout. A black pigmented film was obtained commercially from
an outside vendor and adhesively laminated with a 2-part urethane
adhesive to the beta-nucleated white opaque film.
[0061] In the Examples above, thermal printability was tested using
a laboratory heat sealing device Sentinel modell2ASL wherein the
beta-crystalline micro-voided white opaque side of the film (layer
A) was exposed to the heated platen (the other sealing platen or
jaw was unheated) of the heat sealer at 320.degree. F. (160.degree.
C.) at a dwell time of 0.8 and 20 psi pressure, whereupon that
portion of the white surface of layer A subjected to heat, turned
transparent and lost its opacity, allowing the darker layer B
beneath to show through (FIG. 2). A second test was also done at
the same temperature and pressure, except that the dwell time was
increased to 2.0 seconds (FIG. 2).
[0062] Basic properties of the Examples are shown in Table 1.
TABLE-US-00001 Density Light Gloss Gloss Color A-layer Blackness
A-layer Example Transm % A-side B-side L* a* b* B-layer g/in.sup.3
Ex 1 12.5 17 18 95.84 -0.35 0.17 1.39 0.79 Ex 2 14.6 19 16 94.36
-0.29 0.34 1.34 0.78 Ex 3 20.3 17 16 95.76 -0.32 0.23 1.46 0.78
Test Methods
[0063] The various properties in the above examples were measured
by the following methods:
[0064] Thermal Printability: Evaluated using a Sentinel sealer
model 12 ASL at about 20 psi, 0.5-2.0 second dwell time, with
heated flat upper seal jaw Teflon coated, and unheated lower seal
jaw, rubber with glass cloth covered. The film sample is placed 24
between the sealer jaws at the desired seal temperature(s) in the
Sentinel sealer (e.g. 320.degree. F. or 160.degree. C.).
Temperatures may be increased or decreased at desired intervals,
e.g. 10.degree. F. increments for further evaluation of determining
the clarity of the thermal "printability".
[0065] Light Transmission of the film was measured by measuring a
single sheet of film using a light transmission meter like a BYK
Gardner model "Haze-Gard Plus.RTM." substantially in accordance
with ASTM D 1003.
[0066] Gloss of the film was measured by measuring the desired side
of a single sheet of film via a surface reflectivity gloss meter
(BYK Gardner Micro-Gloss) substantially in accordance with ASTM 0
2457 at a 60.degree. angle.
[0067] Wetting tension of the surfaces of interest was measured
substantially in accordance with ASTM D2578-67.
[0068] Lightness L *a *b* was measured using a spectrodensitometer
such as X-Rite model 528.
[0069] Blackness was measured using an optical densitometer such as
Tobias Associates model TBX transmission densitometer.
[0070] Density of the film was calculated by taking a stack of 10
sheets (letter paper size e.g. 8.5 inches by 11 inches) of film and
cutting them via a die of area 33.69 cm.sup.2 and weighing the cut
sheets on an analytical scale. The 10 sheets are also measured for
thickness using a flat-head micrometer to get an average thickness
of the film. The measured weight and thickness is then used in a
calculation to obtain density:
Weight ( g ) Thickness ( cm ) .times. area ( cm 2 ) = Density ( g /
cm 3 ) ##EQU00001##
[0071] Film yield is calculated using film density and thickness by
the following formula:
453.59 Density ( g / cm 3 ) .times. ( 2.54 ) 3 .times. thickness (
inches ) = Yield ( in 2 / lb ) ##EQU00002##
[0072] Tensile properties such as Young's modulus, ultimate
strength, and elongation are measured substantially in accordance
with ASTM 0882.
[0073] This application discloses several numerical ranges in the
text and figures. The numerical ranges disclosed inherently support
any range or value within the disclosed numerical ranges even
though a precise range limitation is not stated verbatim in the
specification because this invention can be practiced throughout
the disclosed numerical ranges.
[0074] The above description is presented to enable a person
skilled in the art to make and use the invention, and is provided
in the context of a particular application and its requirements.
Various modifications to the preferred embodiments will be readily
apparent to those skilled in the art, and the generic principles
defined herein may be applied to other embodiments and applications
without departing from the spirit and scope of the invention. Thus,
this invention is not intended to be limited to the embodiments
shown, but is to be accorded the widest scope consistent with the
principles and features disclosed herein. Finally, the entire
disclosure of the patents and publications referred in this
application are hereby incorporated herein by reference.
* * * * *