U.S. patent application number 09/151129 was filed with the patent office on 2001-12-20 for ink receptive coextruded film.
Invention is credited to CLECKNER, MICHAEL DALE, LU, PANG-CHIA.
Application Number | 20010053434 09/151129 |
Document ID | / |
Family ID | 22537442 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053434 |
Kind Code |
A1 |
LU, PANG-CHIA ; et
al. |
December 20, 2001 |
INK RECEPTIVE COEXTRUDED FILM
Abstract
The invention discloses an ink-based-image-bearing substrate.
This substrate includes a coextruded thermoplastic film having at
least one layer made from a polymer derived from polypropylene and
another layer made from an acidic functional group-bearing polymer.
The layer which includes the polymer derived from the polypropylene
is oriented in at least the machine direction. The layer which
includes the acidic functional group-bearing polymer is the
print-receiving layer. The acidic functional group bearing-polymer
is preferably ethylene-acrylic acid or ethylene-methacrylic acid.
Liquid toner ink is electrostatically printed on the layer which
includes the acidic functional group-bearing polymer. Additionally,
the invention includes a method for providing the
ink-based-image-bearing substrate.
Inventors: |
LU, PANG-CHIA; (PITTSFORD,
NY) ; CLECKNER, MICHAEL DALE; (HONEOYE, NY) |
Correspondence
Address: |
EXXONMOBIL CHEMICAL COMPANY
P O BOX 2149
BAYTOWN
TX
775222149
|
Family ID: |
22537442 |
Appl. No.: |
09/151129 |
Filed: |
September 10, 1998 |
Current U.S.
Class: |
428/195.1 |
Current CPC
Class: |
B32B 25/08 20130101;
B32B 27/08 20130101; B32B 2323/10 20130101; B32B 2307/514 20130101;
Y10T 428/24802 20150115; A61P 31/04 20180101; B32B 27/32 20130101;
G03G 7/004 20130101; G03G 7/008 20130101; B32B 2307/75
20130101 |
Class at
Publication: |
428/195 |
International
Class: |
B41M 005/00 |
Claims
In the claims:
1. An ink-based-image-bearing substrate comprising a coextruded
polypropylene-containing layer which is oriented in at least the
machine direction, an acidic functional group-bearing
polymer-containing layer, and an ink image electrostatically
printed on said acidic functional group-bearing polymer-containing
layer by liquid toner.
2. The ink-based-image-bearing substrate according to claim 1, in
which said acidic functional group-bearing polymer is
ethylene-acrylic acid having an acrylic acid content from about 1.0
wt % to about 18.0 wt %.
3. The ink-based-image-bearing substrate according to claim 2, in
which said acrylic acid content is from about 2.0 wt % to about 6.0
wt %.
4. The ink-based-image-bearing substrate according to claim 1, in
which said acidic functional group-bearing polymer is
ethylene-methacrylic acid having a methacrylic acid content from
about 1.0 wt % to about 18.0 wt %.
5. The ink-based-image-bearing substrate according to claim 4, in
which said methacrylic acid content is from about 2.0 wt % to about
6.0 wt %.
6. The ink-based-image-bearing substrate according to claim 1, in
which said acidic functional group-bearing polymer layer has a
softening point which is lower than the polypropylene layer.
7. A method for providing the ink-based-image-bearing substrate of
claim 1, which comprises assembling said layers followed by
electrostatic printing.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to thermoplastic films which are
capable of receiving ink derived from liquid toner, especially
liquid toner employed in electrostatic printing.
[0002] Electrostatic printing is a very effective method of image
transfer commonly used in photocopying and photo printing.
Typically, in electrostatic printing, a potential electrostatic
image is formed on an imaging surface carrying a uniform
electrostatic charge. The uniform electrostatic charge can be
created by exposing the surface to corona discharge. The uniform
electrostatic charge is then selectively discharged by exposing it
to a modulated beam of light which corresponds to an image formed
from an original. The discharged surfaces form the background while
the charged surfaces form the print image. The print image is
developed by applying pigmented toner particles which adhere to the
charged "print" portions of the surface. The pigment is
subsequently transferred by various techniques to a copy sheet.
[0003] Dry toner is most commonly used in electrostatic printing.
The quality and clarity of the image and image resolution, is
related to the size of the toner particles. While it is thought
that very fine particles will produce a finer image, there is a
practical limitation on the size of toner particles which can be
used. Dry toner particles must be of sufficient weight and size to
be deposited onto the print surface without becoming airborne,
which is thought to lead to machinery fouling and, possibly,
environmental problems. Additionally, in fixing the image, the dry
toner particles are fused onto the paper by exposure to very high
temperatures, e.g. in excess of about 400.degree. F. (204.degree.
C.). This energy requirement is a significant drawback.
[0004] Paper is widely used as the image receiving element in
electrostatic imaging. It would be advantageous to use plastic as
the receiving element. Among other advantages over paper, plastic
is moisture resistant, flexible and heat sealable and plastic
substrates can be either clear or opaque. However, the high
temperatures necessary for imaging with the dry toners will melt
plastic films and the liquid toners do not transfer well and adhere
to uncoated plastic.
[0005] Plastic films which can receive printing inks have been
disclosed; however, these films require specialized treatment to
enable them to receive the dry toner. For example, a layer of
plastic film used as a laminate for corrugated paperboards is
disclosed in U.S. Pat. No. 4,871,406. The film is a thermoplastic
co-extruded polymeric film, such as, polypropylene with ethylene
acrylic acid. This film can receive printing inks only after being
treated with a corona discharge device or a high velocity flame.
Another example is U.S. Pat. No. 4,853,290 which discloses
laminates of polypropylene film prepared by coextruding a polymer
composition onto a polypropylene film. This polypropylene film
requires corona treatment after printing on its surface.
[0006] Corona and flame treatments oxidize a plastic surface in
order to enable the fixing of dry printing inks. Besides adding
time, money and inconvenience to the production process, these
treatments pose safety and environmental hazards. A corona
treatment process generates toxic ozone so the atmosphere in the
treating step must be contained and exhausted from the operating
area. At high film speeds, a layer of air that contains ozone
adheres to the film as it leaves the treating enclosure. This layer
must be removed from the film by close-fitting baffles or a vacuum
system. In some cases corona treatment requires special chambers
and needs to be carried out off-line. Flame treatment entails
impinging a flame directly onto a film surface as the film is moved
across a cooling roll. The complexity of controlling the
flame-treating process presents safety hazards.
[0007] To overcome these disadvantages, liquid toners have been
developed in which the toner is dispersed in a solvent. The solvent
is removed in the last printing step by the mechanism of the press.
Because of the liquid medium, very fine dye particles can be
employed without concern for the particles becoming airborne. Thus,
copies of very high resolution can be made and high temperatures
needed to fuse dry toners are not required. Liquid toners for
electrostatic imaging are described in U.S. Pat. Nos. 5,225306;
5,276,492; 5,346,769 and 5,407,771.
[0008] In order to enable plastic films to be printed upon with
liquid toner, coatings can be applied which are able to receive
inks (see U.S. Pat. No. 5,215,817). However, the use of coatings
presents difficulties. The coating process adds time, money and
inconvenience to the production process, and presents practical
limitations.
[0009] Typical systems used for coating plastic films are the
dispersion, solvent and extrusion coating processes.
[0010] The dispersion coating system is a multi-step, complex
process that requires vigilant monitoring.
[0011] The dispersion coating process involves unwinding the film,
applying the coating uniformly at the desired thickness, waiting
for the coating to dry and rewinding the film into a uniform roll.
Coating thickness should be measured across the film as part of the
coating sequence. This can be done using radiation absorption. As
the chemical nature of the coating more nearly approaches the
substrate, this measurement becomes increasingly difficult.
[0012] The conditions of the dispersion coating process must be
carefully monitored in order to ensure adequate coalescence of the
coating. The dispersion coating polymer is dispersed in water often
with a surfactant. Once the coating is applied, the water is
evaporated. In order for a film to form, conditions need to be
highly regulated. If evaporation occurs at room temperature, the
dried polymer usually forms a fragile, uncoalesced coating. The
particles need to make intimate contact with each other in order
for coalescence to occur. Then diffusion and interpenetration of
the polymer molecules must occur readily across the particle
interfaces. The effectiveness of this diffusion depends on the
mobility of the polymer molecules which in turn depends on the
temperature of and the viscosity of the liquefying particle, which
is a function of molecular weight. Therefore, a balance must be
reached between a molecular weight low enough for coalescence but
high enough for adequate toughness and flexibility of the coating
film. Moreover, the surfactant used to create a stable dispersion
can act as a barrier to interpenetration at the surface of the
particles. Therefore an optimum must be found in the concentration
of the surfactant.
[0013] The solvent coating system also entails a multi-step
process. This process involves unwinding the film, applying the
coating uniformly at the desired thickness, waiting for the coating
to dry and rewinding the film into a uniform roll. The desired film
thickness can be achieved by the use of radiation absorption.
[0014] An example of a solvent coating process for plastic films,
which provides a surface that will receive liquid toners, is a
polyamide solution sold under the name TOPAZ by Indigo Company.
[0015] In the solvent coating process, the coating polymer is
dissolved in a solvent. The solvent is evaporated once the coating
is applied leaving behind a coating film. However, as the coating
develops it acts as a solvent barrier which makes it difficult to
drive off the last traces of residual solvent. An additional
disadvantage in the solvent coating process is that the solution is
sensitive to ambient conditions. The solution is difficult to
handle at low temperatures (it tends to lose solubility) and the
coating absorbs atmospheric moisture which may make the film tacky
even after drying. Among others, this can pose blocking
problems.
[0016] Significantly, the polyamides used in the solvent coating
process can present environmental hazards. Disposal of the solvent
must be conducted in a proper manner. Moreover, recovery of
solvent, which has become airborne, is complex.
[0017] In the extrusion coating process, the substrate film must be
unwound, fed through a quench roll or between a quench roll and a
nip roll to receive the falling polymer melt, and then the film
must be rewound again onto a roll.
[0018] Additionally, practical considerations narrow down the field
where the extrusion coating process can be utilized. Given the high
temperature of the polymer melt, the substrate film must have high
thermal stability. Additionally, there is a limitation on what can
be used as a melt coating polymer. Very high melting polymers,
polymers with low melt strength, and heat sensitive polymers are
ruled out. Furthermore, coating thickness is limited at the low end
to about 0.2 mil under the best conditions. (More comprehensively
reviewed in Plastic Films by K.
[0019] R. Osborn and W. A. Jenkins 1992, incorporated herein by
reference.)
[0020] Thus, it is an object of the present invention to overcome
difficulties presently encountered in the art by providing a
coextruded thermoplastic film which is capable of receiving ink
derived from liquid toner without the need of, among other things,
coating(s) and/or post-extrusion or post-printing processes.
SUMMARY OF THE INVENTION
[0021] The present invention provides an ink-based-image-bearing
substrate. This substrate includes a coextruded thermoplastic film
having at least one layer made from a polymer derived from
polypropylene and another layer made from a polymer bearing an
acidic functional group. The layer which includes the polymer
derived from the polypropylene is oriented in at least the machine
direction. The layer which includes the polymer bearing an acidic
functional group is the print-receiving layer. Liquid toner ink is
electrostatically printed on the layer which includes the polymer
bearing an acidic functional group. The polymer bearing an acidic
functional group is preferably ethylene-acrylic acid or ethylene
methacrylic acid. Additionally, the invention includes a method for
providing the ink-based-image-bearing substrate.
[0022] The ethylene-acrylic acid copolymer layer of the film
preferably has an acrylic acid content in the range of 1.0 to 18.0
wt %, and the most preferred range is from 2.0 to 6.0 wt %.
[0023] The ethylene-methacrylic acid copolymer layer of the film
preferably has an methacrylic acid content in the range of 1.0 to
18.0 wt %, and the most preferred range is from 2.0 to 6.0 wt
%.
[0024] Furthermore, the print-receiving layer has a softening point
in a range of 180.degree.-220.degree. F., which is lower than the
orientation temperature for oriented polypropylene.
[0025] It is an advantage of this invention that when a
thermoplastic film has a layer made from a polymer bearing an
acidic functional group, especially with an optimal acid content,
liquid toner can be used in electrostatic imaging of the film
without the difficulties presented by coating processes.
[0026] The application of coatings to thermoplastic films adds
time, money and inconvenience to the production process. Coating
systems are multi-step, complex processes requiring extensive
physical manipulation of the substrate films. Such processes
include unwinding the substrate film, applying the coating,
allowing the coating to dry and rewinding the film into a uniform
roll. Achieving the desired thickness for a coating may involve the
use of radiation absorption.
[0027] Furthermore, the dispersion coating process requires
vigilant monitoring of process conditions, including the
temperature and viscosity of the liquefying particles.
[0028] The solvent-based coatings present the additional problems
of environmental hazards pertaining to solvent disposal.
Furthermore, solutions used in these solvent-based coatings are
sensitive to ambient conditions, such as temperature and
atmospheric moisture which further complicate the production
process
[0029] Extrusion coating systems further present limitations with
respect to the substrate films and polymer melts that can be
used.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The present invention provides an ink-based-image-bearing
substrate. This substrate includes a coextruded thermoplastic film
having at least one layer made from a polymer derived from
polypropylene and another layer made from a polymer bearing an
acidic functional group. The layer which includes the polymer
derived from polypropylene is oriented in at least the machine
direction. The layer which includes the polymer bearing an acidic
functional group does not undergo orientation since it has a lower
melting point than the layer which includes the polymer derived
from polypropylene. The layer which includes the polymer bearing an
acidic functional group is the print-receiving layer. Liquid toner
ink is electrostatically printed on this layer which includes the
polymer bearing an acidic functional group. This ink-receiving
layer should be substantially resistant to the hydrocarbon liquid
carrier used in liquid toner. The polymer bearing the acidic
functional group is preferably ethylene-acrylic acid or
ethylene-methacrylic acid. These films do not require oxidation
treatment or coating processes for electrostatic printing.
[0031] This invention significantly improves the known procedures
by utilizing a layer which includes a polymer bearing an acidic
functional group. A preferred range of acid content is from about
1.0 to about 18.0 wt %, and most preferably from about 2.0 to 6.0
wt %. The polymer bearing an acidic functional group is preferably
ethylene-acrylic acid or ethylene-methacrylic acid. The
ethylene-acrylic acid preferably has an acrylic acid content from a
range of 1.0 to 18.0 wt %, and most preferably having an acrylic
acid content of about 2.0 to 6.0 wt %. The ethylene-methacrylic
acid preferably has a methacrylic acid content from a range of 1.0
to 18.0 wt %, and most preferably having a methacrylic acid content
of about 2.0 to 6.0 wt %. The ethylene content of the copolymer can
be from about 82.0 to 99.0 wt .%, preferably 94.0 to 98.0 wt % of
ethylene, while from about 1 to 18.0 wt. % can be of acrylic acid
or methacrylic acid.
[0032] Ethylene acid copolymers belong to a family of ethylene
copolymers in which the polyethylene chain is modified by the
presence of pendant carboxyl groups. These copolymers are
characterized by good toughness and adhesion to a variety of
metallic and nonmetallic substrates. Ethylene acid copolymers are
produced by the high pressure free radical copolymerization of
acrylic acid or methacrylic acid with ethylene to form ethylene
acrylic acid or ethylene methacrylic acid. When ethylene is
copolymerized with acrylic acid or methacrylic acid, the molecular
structure is significantly altered by the random inclusion of bulky
carboxylic acid groups along the backbone and side chains of the
copolymer. The carboxyl groups are free to form bonds and interact
with any polar substrate. The carboxyl groups disrupt the linearity
of the polyethylene backbone and reduce the total crystallinity. A
commercially available ethylene-acrylic acid copolymer is Primacor
4983 sold by Dow Chemical Co. The ethylene-acrylic acid is often
supplied as a resin.
[0033] Polypropylenes commercially suitable for this invention
include Fina 3371 (available from Fina Oil and Chemical Co. of
Dallas, Tex.), Exxon 4612 and Exxon 4252 (available from Exxon
Chemical Co. of Houston, Tex.) and Amoco 6361 (available from Amoco
Chemical Co. of Chicago, Ill.).
[0034] The term "liquid toner" covers a composition in which toner
particles are dispersed in a liquid base. Typically the liquid base
is non-polar such as an aliphatic hydrocarbon fraction. Typical
toners of this kind, and processes for using them in imaging, are
described in U.S. Pat. Nos. 5,225,306; 5,276,492; 5,346,796 and
5,407,771. The coextruded films of this invention, surprisingly,
are capable of receiving toner derived from these liquid toner
compositions.
[0035] The ethylene-acrylic acid copolymer layer of the film has a
softening point in a range of 180.degree.-220.degree. F., which is
lower than the orientation temperature for oriented polypropylene.
This feature allows for additional smoothing of the
ethylene-acrylic acid surface which enhances the printability of
the surface.
[0036] Optionally, the films of this invention can contain a
relatively inert particulate filler additive. A filler which has
found specific utility in the coextruded film of this invention is
fumed silica. The fumed silica is composed of particles which are
agglomerations of smaller particles and which have an average
particle size of, for example, about 2 to 9 microns, preferably
about 3 to 5 microns. Generally any finely divided inorganic solid
materials such as silica is contemplated as a useful filler for
purposes of the present coextruded film. These include talc,
calcium carbonate, diatomaceous earth, calcium silicate, bentonite
and clay. The total amount of filler typically ranges from about
0.1% to about 80%, specifically from about 0.3% to 7.0% based on
the entire weight of the coextruded film. When a clear film is
needed the particulate concentration will be relatively low, for
example from about 0.1% to about 10%, specifically from about 0.3%
to about 7.0%. The particulates are generally small in size,
typically ranging from about 1 m to about 10 m specifically from
about 3 m to about 7 m. Further examples of fillers include kaolin,
silica, aluminum silicates, clay and talc. Pulp is also
contemplated.
[0037] Preferred among the foregoing fillers are those that
function as antiblock/slip agents. Silica is a specific example of
a filler which is found to function in this manner.
[0038] Opacity enhancing particulates may also be employed. These
are relatively inert substances. Calcium carbonate is extensively
used in thermoplastics since it is relatively inexpensive and easy
to use. It can be used in its natural form but "precipitated
calcium carbonate," which is prepared by chemical processes, can be
employed. Sometimes, particles of calcium carbonate are coated with
a resin to reduce plasticizer absorption and this form can also be
employed.
[0039] The filler can also include pigment-imparting particulates.
Pigments contemplated are organic or inorganic substances with
particle sizes which are rarely less than 1 micron in diameter.
Typical pigments include carbon black and titanium dioxide. Calcium
carbonate can also act as a pigment. Other pigments not to be
excluded by this invention are metallic pigments such as particles
of aluminum, copper, gold, bronze or zinc. These pigments are
usually flake shaped particles which reflect light when
incorporated into the coextruded film.
[0040] The fillers, including inert particulate slip/antiblock
agents, opacifying agents, and/or pigments can be used in
combination, depending upon the desired degree of translucency or
opacity. Typically when the opacifying particulates and/or pigments
are used, the concentration is less than about 70% of the total
particulate concentration of the film, specifically about 20% to
about 50% of the total particulate concentration of the film.
[0041] Further specific examples of particulates which may be
employed in addition to those noted above include acetylene black,
alpha cellulose, aluminum silicates, barium sulfate, calcium
silicate, calcium sulphate, cellulose, clays, diatomite, glass
flake, keratin, lignin, lithophone, mica, microballoons, molybdenum
disulfide, nepheline syenite, paper, pulp, quartz, shell flour,
talc, vermiculite and wood.
[0042] Additionally, the invention includes a method for providing
the ink-based-image-bearing substrate. In a preferred method, a
polypropylene resin and an ethylene-acrylic acid resin is
coextruded to form a film with two layers. The film is then
quenched by casting it onto a cooling drum. Upon reheating the
film, the film is stretched about 3 to 7 times in the machine
direction. Stretching allows for orientation of the
polypropylene-containing layer. The ethylene-acrylic
acid-containing layer does not orient during stretching due to it
having a lower melting temperature than the
polypropylene-containing layer. Next an image is formed on the
ethylene-acrylic acid layer of the film with an electrostatic
printing toner derived from a liquid toner composition.
* * * * *