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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to coating paper for printers. The invention
particularly relates to coating paper for ion deposition printers which
employ dry magnetic toner.
2. Discussion of the Prior Art
A number of conventional printers and copiers employ dry magnetic toner.
Ion deposition high speed printers, for example; as disclosed in U.S. Pat.
No. 4,409,604, are in conventional use as computer mainframe printers or
in other service such as the printing of tags and labels.
These printers normally employ dry magnetic toner to form a toned latent
image transferrable from the printer's dielectric imaging cylinder to
receiving paper. In practice, in order to obtain the best print quality
and toned image density, heat fusing equipment is often employed within
the printer. The toned latent image on the dielectric imaging cylinder is
subjected to heat fusing immediately after transfer whereupon the toned
image is heat fused to the receiving paper. While the process of heat
fusing improves print quality, it involves expensive heating equipment
within the printer and added operational complexity. It has thus been an
objective in this art to eliminate the heat fusing equipment without
sacrifice in image density and print quality. In addition to eliminating
the heat fusing step, it has also been a long standing objective to
improve the smudge resistance of the transferred toned image on the
receiving paper.
Dry magnetic toners normally require heat and pressure to melt fuse the
particles to the substrate being printed. These toners comprise
thermoplastic resin binders, colored pigment and magnetic additives or
charge control agent. The toner described in U.S. Pat. No. 4,528,257 is
representative of this type which employs a crystalline resin with a glass
transition temperature (T.sub.G) of 45.degree. C. to 90.degree. C. and an
immiscible amorphous resin component with a T.sub.G of 10.degree. C.
higher than the crystalline resin. U.S. Pat. No. 4,508,257 represents an
attempt to improve print quality and to permit faster printing speeds with
reduced fusion temperatures. Heretofore, cold pressure fixing of a dry
magnetic toner image on plain, coated or impregnated papers does not fully
compare in print quality to that offered by heat fusion or alternate
printing means such as thermal. Cold pressure fixing systems were
developed to eliminate heat fusing and associated fire hazards, to reduce
warm up time and lower the system's overall energy requirements. However,
cold pressure fixing normally requires high nip pressures (well above 100
pounds/linear inch) which increases paper gloss and results in a glossy
black image.
SUMMARY OF THE INVENTION
It is the object of this invention to provide a nonblocking pressure
sensitive coating which can be applied economically in wide widths or in
line on a flexo press during the printing operation which overcomes the
limitations and drawbacks of heat fusion and very high pressure cold
fixing. We have discovered that a coating containing amorphous polymer
binders with low glass transition temperatures (T.sub.G) under 20.degree.
C., preferably between -10.degree. C. to +10.degree. C., coupled with
particulate mineral fillers above one (1) micron to provide "tooth" to
capture and secure dry magnetic toner particles will permit excellent cold
pressure fixing at nip roll pressures at about 100 lbs./linear inch as
well as at higher pressures. Preferred polymer binders are vinyl acrylic
copolymers or ethylene vinyl chloride. The invention is not intended to be
limited by these species. The filler particles typically contain a
polymeric filler and a mineral dispersant filler. The polymeric filler is
preferably a polyethylene and polytetrafluoroethylene wax blend or a
polyethylene wax. The mineral dispersant filler is typically silicon
dioxide particles. The invention is not intended to be limited to these
materials.
It is theorized that the toner receptive coatings of the invention possess
a viscoelastic response to point loading of the relatively large toner
particles (about 20 microns) during the roll nip process. It is believed
that the point loading creates bonding of the toner particles to the
coating by the frictional heat generated at the interface which thermally
softens the coating creating a surface wetting of the toner by the fluid
amorphous polymer. The particulate mineral filler minimizes the contact
area to prevent blocking or sticking of the coating to the back of the
paper in roll or sheet form.
The preferred coating formulations balance the smudge resistance, toner
adhesion and crease resistance properties. The coatings exhibit much
improved smudge resistance as measured by print and bar code legibility.
Bar code scanners typically require 65% reflection differential (50%
minimum) at 640 nanometers wave length between the printed and unprinted
areas. Smudges through handling or package abrasion during shipment
against printed labels will smear toner particles into unprinted areas
causing difficulty or errors in reading visually or with optical devices.
The toner receptive coatings of the invention maximize smudge resistance
as measured by retention of opacity in the printed areas or by minimizing
toner transfer to adjacent areas after rubbing.
The elimination of a heat fusion requirement in an ion deposition printer
or any conventional printers or photostatic copiers which employ dry
magnetic toner has significant advantages in cost reduction, durability
and performance. Heating of rollers or drums for fusion requires higher
power consumption which can result in special wall wiring for higher
amperage, restricting placement and unit mobility. Heating machines
requires larger envelopes to dissapate the heat to minimize fire hazards.
Internal heat present in a printer or copier dries up lubrication
requiring more frequent servicing and a reduction in component life. The
cost savings permitted by the elimination of the heaters themselves and
the downsizing of the envelope is additive with the lower nip roll
pressure permitted by the toner receptive coating of this invention which
allows downsizing of the pressure components providing a unit which is
smaller and lower cost to the end user.
The cost of this coating technology is surprisingly affordable, adding less
than 3% of the cost of light to medium weight paper for the materials and
it can be applied on a single station of a flexographic press in-line with
printing of graphics and bar codes. The coating has been applied to bare
and precoated papers and paperboard before and after printing. Applied
over small print (1/16" characters) at 150 feet/minute, a minimum loss of
detail in the print was observed at an application rate of 1.5 lbs./3000
square foot ream (2.4 grams/square meter) while being fully legible due to
the contact transparency of the coating. Overprinting at the subsequent
flexo station in line with a solvent based flexo ink produced sharp
printing with no evidence of solvent attack.
The coating also tends to fill in thinner areas of the paper being printed
for improved thickness uniformity resulting in more complete toner
transfer. The coating can also be spot applied where high gloss graphics
are printed in adjacent areas. The receptive coating of the invention can
also be used in a heat fusion system. The coating can also be applied to
polymeric films, e.g., polyester, nylon, cellulose, polyolefins, etc.
DETAILED DESCRIPTION
The toner receptive coating of the present invention when applied to
conventional plain copier weight paper provides improved smudge resistance
for transferred toned images, particularly when employing dry magnetic
toner. Dry magnetic toner typically contains magnetic iron oxide
particles, a polymeric binders, e.g., ethylene vinyl acetate and
polyamides, and a flow agent, e.g., zinc oxide, to keep the particles from
clumping. Conventional ion deposition printing employing dry magnetic
toner to which application of the toner receptive coating of the present
invention is particularly directed is described for example in U.S. Pat.
No. 4,365,549, herein incorporated by reference. Such apparatus forms the
toner image on a very hard, smooth image cylinder and transfers the toner
image to paper fed through a nip under high pressure between the image
cylinder and a relatively compliant transfer roller. In an improvement to
the apparatus of U.S. Pat. No. 4,365,549, it has been found desirable to
provide a non-parallel orientation, or skew, between the image cylinder
and transfer roller. The skewing of these rollers, advantageously by an
angle of around 0.5.degree.-1.5.degree., has been observed to improve
transfer efficiency and fusing of the toner image. However, in practice it
has been found desirable to provide subsequent heat fusing of the toner
image transferred to plain paper, to improve print tenacity.
The toner receptive coating herein has the important advantage that it
eliminates the need for heat fusing toner particles onto the receiving
paper after the toned image has been transferred to the paper. In the art
of ion deposition printing, it is possible to utilize post-transfer heat
fusing equipment within the ion deposition printer in order to improve
print tenacity. In the apparatus of U.S. Pat. No. 4,365,549 (with skewed
rollers) the toned image is transferred from the image cylinder to paper
by passing the paper between the image cylinder and a nip roller which
contacts the paper under applied pressure and at ambient temperatures up
to 130.degree. F. There is no heat fusing at such temperature levels and
such temperature levels are below the softening temperature of the toner.
A heat fusable toner containing substantially magnetic iron oxide
particles and heat fusable resin particles is employed. After the toner
image transfers to the paper using the nip roller, the applied heat in a
subsequent step fuses the magnetic toner onto the receiving paper. Such
heat fusion process has been known to improve print durability in ion
deposition printing. However, the heat fusing process requires expensive
additional heating and auxiliary control equipment within the body of the
ion deposition printer.
The toner receptive coating of the present invention when applied to
conventional weight plain copier paper eliminates the need for heat
fusing, since the transferred print quality is at least equal to that
obtained when heat fusing of toner to conventional plain and coated papers
is employed.
The toner receptive coating of the invention additionally has very good
adhesion to paper and most polymeric film substrates and importantly does
not flake, crack or peel when the printed substrate is creased. The
present receptive coating formulations are conveniently prepared under
ambient conditions by simple blending and mixing of the coating
constituents to form a homogeneous dispersion. The solvent employed in the
mixture is nontoxic and is not an environ-mental pollutant. The coating
mixture is conveniently applied to plain copier paper, typically 50
lb/ream white plain or prefinished paper, using conventional coating
techniques such as gravure or flexographic coating methods. The coating is
thus easily applied as a smooth continuous film in patterns or full
coverage. It is thereafter immediately subjected to convective hot air
drying in order to evaporate solvents resulting in a contiguous, dry
translucent coating. The receptive coating is typically applied to the
paper at a coating weight in a range between about 1.5 to 3.0 lbs. per
ream (3000 sq. ft.). If the coating weight is less than about 1.5
lbs./ream, the desirable toner receptive qualities aforementioned are not
optimized. For example, if the coating is too thin, then there will not be
enough coating for the transferred toner image to adhere. If the receptive
coating is excessive, then longer convective drying time is required to
evaporate all the vehicle/solvent in the coating. This is undesirable
since it increases the material cost and the processing expenses
associated with drying. From a commercial standpoint it has been found
desirable to dry the coating at processing speeds of about at least 150
ft./min. using conventional hot air drying methods to coincide with
flexographic printing speeds.
The receptive coating formulation of the invention preferably has a clear
or whitish translucent appearance after it is applied to the substrate and
subsequently dried. The receptive coating is also suitable for application
to either plain or prefinished paper that has been previously imprinted
with text or design. The receptive coating is preferably translucent with
contact clarity in this application as well so that the underlying
imprinted design and colors are not obscured. The principal substrates for
the toner receptive coating herein described is conventional plain copier
paper or label stock typically 50 lb./ream paper. The receptive coating of
the invention makes unnecessary the use of conventional prefinished or
precoated copier paper. Such paper has not been found to noticeably
improve transferred toned image quality or smudge resistance when ion
deposition printing is applied or to render unnecessary the heat fusing
step. However, the receptive coating of the present invention can be used
over such prefinished copier paper with improvements in smudge resistance
and transferred image quality with or without heat fusing.
A toner receptive coating having all of the properties and advantages
aforementioned is composed preferably of a polymeric filler, a mineral
filler, a binder, dispersing agents and vehicle/solvent. It has been
determined that preferred binders are polymeric resins having a glass
transition temperature, T.sub.g, less than about 20.degree. C.,
preferably, in the range between about -10.degree. C. to +10.degree. C. It
has been found that if the glass transition temperature, T.sub.g, of the
binder is too high then the dried receptive coating will tend to be
unresponsive to pressure applied thus not accepting the toner. On the
other hand if T.sub.g is too low, then the dried receptive coating tends
to be too tacky. A condition wherein the coating has excess tack is
undesirable because it in turn causes blocking; that is, sticking of the
paper coating to the opposite side of the paper. It has been found most
desirable to formulate the receptive coating so that the coating is soft
and flexible enough that the hard dry magnetic toner particles forming the
transferred image can create an impression in the receptive coating.
However, the coating as aforementioned, cannot be too soft or too tacky
that the problem of blocking, i.e., sticking occurs. The receptive coating
must possess sufficient cohesive strength to avoid contamination of the
dielectric imaging cylinder or other machine parts as the coated paper
passes through the ion deposition printer. This in turn could degrade
transfer image quality and increase equipment service frequency.
In addition to promoting adherence of the transferred toner particles to
the receptive coating, the binder importantly should exhibit adequate
adhesive properties for other solid particles in the coating formulation
to maintain this cohesive integrity. The binder also promotes adequate
adhesion of the receptive coating to the underlying paper substrate and/or
coatings and finishes thereon.
Although a number of different polymeric binders exhibiting the
aformentioned properties are believed possible, a preferred polymeric
binder is a vinyl acrylic ester copolymer available as a white water based
anionic emulsion sold under the trademark HYCAR 26368 from B.F. Goodrich
Co., Chemical Group, Cleveland, Ohio. The emulsion has a specific gravity
of 1.06. The copolymer has a glass transition temperature of +5.degree. C.
An alternative vinyl acrylic copolymer is available as a water based white
liquid emulsion under the tradename 76 RES 6930 from Unocal Chemicals
Division. The emulsion has a viscosity of about 1000 centipoise and the
copolymer has a glass transition temperature of -8.degree. C.
Another preferred binder is ethylene vinyl chloride available in a water
based dispersion under the trademark AIR FLEX 4514 dispersion from Air
Products, Inc.
In order to achieve the best characteristics of the receptive coating, it
has been found desirable to add filler materials to the formulation. The
filler materials are selected which tend to make the coating less tacky
and thereby avoid blocking but yet do not inhibit pressure bonding to the
toner particles. Two types of filler are preferentially added to the
formulation. The first is a polymeric filler and the second a mineral
dispersant filler. The polymeric filler imparts lubricity and a sealing
quality to the toned image transferred on the receptive coating. The
polymeric filler preferentially should have wax-like properties. A
preferred polymer filler has been determined to be a polyethylene and
polytetrafluoroethylene wax blend. This blend is available under the
tradename POLYBLEND 100 white powder from Micro Powders, Inc. of
Scarsdale, N.Y. The Polyblend white powder has an average particle size of
about 2 microns, a melting point of about 230.degree. F. (110.degree. C.)
and a specific gravity of 1.02. Another suitable polymer filler is a
polyethylene wax powder available under the trade designation S394N5
polyethylene wax powder from Shamrock Chemical Corp., Newark, N.J. The
S394N5 polyethylene wax powder is a medium density microcrystalline
polyethylene wax. It has an average particle size of about 12.5 microns
and a melting point of about 235.degree. F. (113.degree. C.). The
polymeric fillers aforementioned have been found to impart a smudge
resistant characteristic to the transferred toned image on the receptive
coating. All the phenomena involved in attainment of the smudge resistant
characteristic by employing the aforementioned polymer binder filler is
not fully understood. However, it has been found that the aforementioned
polyethylene/polytetrafluoroethylene wax blend or polyethylene
microcrystalline wax filler provides improved surface slippage when the
transferred toned image is rubbed manually or when it is rubbed with
another material. It is hypothesized that the rubbing smears a very thin
layer of the waxlike polymeric filler over the transferred image and the
coating. This imparts a greater degree of overall lubricity to the surface
and seals the surface of the printed and unprinted areas thereby
inhibiting toner particle movement and transfer to unprinted areas.
Surprisingly, the polymeric fillers do not inhibit anchorage of over
printing with standard flexographic images. The physical result gives the
coated paper a cleaner appearance after rubbing the exposed transferred
image than would be the case if the toner receptive coating of the
invention were not employed.
The mineral dispersant filler which applicant has found advantageous to
include is preferably silicon dioxide particles, such as amorphous silicon
dioxide white powder available under the trade mark SYLOID 244 from W. R.
Grace Co. The SYLOID 244 silicon dioxide powder has an average particle
size of about 3 microns and a surface area of about 310 sq. meters per
gram. The silicon dioxide filler appears to serve three important
functions in the preferred formulations. Firstly, it increases the surface
area providing a rougher topography to capture and secure particles and
restrain toner particle mobility. Secondly, it functions as a dispersant
to help keep all solid particles in the formulation dispersed. Thirdly, it
functions as an antiblocking agent that is, it appears to make the
receptive coating less tacky.
It has been found desirable to add a small amount of dispersing agent to
the preferred formulation. Dispersing agents are well known in the art and
are often used to attain high degree of dispersion of fine solid particles
in liquid mixture. A suitable dispersing agent for the present formulation
may typically be SOLSPERSE.RTM. 2000 liquid hyperdispersant from Imperial
Chemical Industries, PLC. SOLSPERSE.RTM. 2000 liquid hyperdispersant has a
specific gravity of about 0.90, a viscosity of about 200 to 300 centipoise
at 25.degree. C. and is solvent free. Only a small amount, typically less
than 1 percent by weight of the liquid SOLSPERSE need be added to the
preferred coating formulation. An alternative suitable dispersing agent
may be a mineral spirit/propylene glycol based dispersant such as
NUOSPERSE.RTM. 700 liquid dispersant from Nuodex, Inc.
An advantage of the preferred receptive coating formulations is that
suitable modifying solvents may be selected from a group of safe nontoxic
solvents that are nonenvironmental pollutants. A solvent which has these
attributes for use in the preferred coating formulation is simply
isopropanol which is premixed with water. Other solvents, for example
other lower alcohols and glycols, could also be employed to adjust the
drying and coalescing rates.
Specific preferred coating formulations having the aforementioned component
types are illustrated by Formulations A, B and C in respective Tables 1, 2
and 3. These formulations for the receptive coating exhibit all of the
aforementioned advantageous properties. In particular, when these
formulations are employed as the toner receptive coating on plain 50 lb.
(81 grams/square meter) copier paper, they give the transferred dry
magnetic toned image on the coating, improved image density and quality,
improved smudge resistance and inhibit the transferred toned image from
flaking or peeling when the coated substrate is creased.
The percent by weight of each component employed in formulations A to C is
shown in the respective Tables 1-3:
TABLE 1
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Toner Receptive Coating Formulation A (White Translucent)
% by
Weight
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Polymeric Filler
Polyethylene/ 5.
Polytetrafluoroethylene Wax Blend
(e.g., Polyblend 100 White Powder
from Micro Powders, Inc.)
Mineral Dispersant Filler
Silicon dioxide 5.
(e.g., amorphous Syloid 244
White Powder from W.R. Grace Co.)
Binder
Vinyl acrylic copolymer emulsion
25.
(e.g., liquid Hycar 26368
White resin from B. F. Goodrich Co.)
Dispersing Agent
(e.g., viscous clear liquid
1.
Solsperse 2000 from Imperial
Chemical Industries, PLC.)
Solvents
Isopropyl alcohol 32.
Water 32.
100.
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TABLE 2
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Toner Receptive Coating Formulation B (White Translucent)
% By
Weight
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Polymeric Filler
Polyethylene White Powder -
5.
microcrystalline wax
(e.g., S394N5 polyethylene
powder from Shamrock Co.)
Mineral Dispersant Filler
Silicon Dioxide 5.
(e.g., amorphous Syloid 244
white powder from W. R. Grace Co.)
Binder
Vinyl acrylic copolymer emulsion
25.
e.g., liquid Hycar 26368 white
resin from B. F. Goodrich Co.)
Dispersing Agent
(e.g., viscous clear liquid
1.
Solsperse 2000 from Imperial
Chemical Industries, PLC.)
Solvents
Isopropyl alcohol 32.
Water 32.
100.
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TABLE 3
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Toner Receptive Coating Formulation C
% By
Weight
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Polymer Filler
Polyethylene/Polytetra-
5.
fluoroethylene wax blend.
(e.g., Polyblend 100 white powder
from Micro Powders, Inc.)
Mineral Dispersant Filler
Silicon dioxide 5.
(e.g., amorphous Syloid
244 white powder from
W. R. Grace Co.)
Binder
Ethylene Vinyl Chloride
25.
water based dispersion
(e.g., Air Flex 4514
dispersion from Air Products, Inc.)
Dispersing Agent
Mineral Spirit/Propylene
1.
Glycol based dispersant
(e.g., Nuosperse 700
liquid from Nuodex, Inc.)
Solvents
Water 32.
Isopropyl 32.
alcohol
100.
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TABLE 4
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Toner Receptive Coating Formulation D (white opaque)
% By
Weight
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Mineral Fillers
(e.g., Ansilex clay 8.
from Englehard, Inc.
Mineral Dispersant Filler
Silicon Dioxide 10.
(e.g., amorphous Syloid 244
white powder from W. R. Grace Co.)
Binder
Vinyl acrylic copolymer emulsion
40.
(e.g., 76 RES 6930 liquid water
based emulsion from
Unocal Chemicals Division)
Defoaming Agent
(Silicone based liquid defoaming
0.5
agent Colloid 999 from
Colloids, Inc.)
Pigment
(Titanium dioxide-white)
1.5
e.g., Hiltasperse white from
Hilton-Davis Co.
Diluent
10% ammonia Solution in water
40.
100.
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The formulations A to C are similar except that a polymeric filler of
polyethylene microcrystalline wax is employed in Formulation B whereas the
polymeric filler in Formulation A and C is a
polyethylene/polytetrafluoroethylene wax blend. The preferred polymer
binder in Formulation A and B is the vinyl acrylic copolymer emulsion,
e.g., liquid HYCAR 26368 whereas the polymer binder employed in
Formulation C is the ethylene vinyl water based dispersion, e.g., AIR FLEX
4514 dispersion from Air Products, Inc. In each formulation A to C silicon
dioxide particles, e.g., SYLOID 244 white powder was employed. The
dispersing agent and modifying solvents for Formulations A to C. are shown
in the respective tables. These formulations (A to C) appeared as a
whitish translucent coat after they were applied to plain paper substrate
and subsequently dried, but have contact transparency.
Another formulation for the receptive coating is illustrated in Table 4.
This formulation differs somewhat from formulation A to C, particularly in
that a clay filler instead of a polymeric filler was employed. The other
components were substantially the same as those shown in Table I except
that white pigment was added and the diluent system employed was a 10%
ammonia solution to adjust the viscosity and stabilize the pH of the
dispersion.
The formulation D when coated on plain paper substrate left a smooth
whitish opaque coating on drying. The formulation D upon drying exhibited
all of the aforementioned improved properties that formulations A to C
showed except it did not notably improve the smudge resistant
characteristic of the transferred toned image. Importantly, however, it
improved the transferred image density and inhibit the toned image from
peeling or flaking after the substrate was creased. This formulation,
however, tended to foam somewhat during the coating step at higher coating
speeds and therefore from an application standpoint is not as desirable as
formulation A to C for high speed flexographic printing. Also since the
formulation D coating is opaque it is not intended for use over substrates
that have been previously preprinted with design or text. Other pigments
could be incorporated in like manner.
The coating formulations A to D as presented in Tables 1 to 4 respectively,
were all prepared under ambient conditions by simply blending the
formulation components by use of conventional stirring mixer. It was found
preferable to mix the components of formulation A to D by first adding all
of the filler components to a mixing container and then adding solvents
and dispersing or defoaming agents. The mix was then stirred for a few
minutes under ambient conditions until a homogeneous mixture was obtained.
At this point, the binder was added and the mix was continually stirred a
few minutes longer to obtain a homogeneous mixture. The constituents were
added for each Formulation A to D in the amounts indicated in the
respective Tables 1 to 4.
Each of the respective coating mixtures was then applied to plain 50
lbs./ream (81 gpsm=grams/square meter) paper at a coat weight of between
about 1.5 to 3.0 lbs. per ream (2.4 to 4.9 gpsm) using conventional
gravure or flexographic coating methods. Each coating was dried by passing
the coated substrate through conventional hot air convective driers. Each
one of the preferred coating formulations A to D upon drying produced a
smooth, flexible toner receptive coating on the paper substrate.
Qualitative tests were made in the laboratory to compare the properties of
the various receptive coated paper substrates coated with Formulations A
to D and bare or other coated paper substrates after dry magnetic toned
image had been transferred onto these substrates using unheated pressure
nip rollers at pressures of about 100 pli. Thus, five sample substrates,
four coated and one uncoated, all with transferred image thereon were
tested. In each sample, a plain 50 lbs./ream (81 gpsm) paper substrate was
employed. Four basic tests were performed. The first test measured the
resistance to flaking of the transferred toned image after the substrate
with transferred toned image thereon was creased one time. It was then
observed whether any of the toned image flaked along the crease line.
A second test was made to determine the smudging characteristic of the
transferred toned image on the various sample substrates. This test was
performed by using a standard Sutherland rub tester apparatus. Each of the
sample substrates containing transferred toned image was rubbed the same
number of cycles and the sample was then tested for smudge on areas
adjacent to the images.
A third test was performed on each of the sample substrates containing
transferred toned image to measure the degree to which the transferred
toned image adhered to the substrate.
A fourth test on the samples was made to evaluate the tendency , if any, of
the substrate to block, that is to stick together after the substrate had
been rolled up and subsequently unwound or stacked in sheet form.
When the crease test was performed, it was found that discernible flaking
of the transferred toned image on plain paper or papers with harder
coatings occurred along the crease line. By contrast, no discernible
flaking of the transferred toned image occurred on the crease line when
any of the receptive coating Formulations A to D were employed on the bare
or precoated papers, or film substrates.
Smudging of the toned image on uncoated paper samples as clearly visible
after the sample was subjected to 50 rubbing strokes on the Sutherland rub
tester. In comparison, the samples employing the toner receptive coating
Formulations A to C of the present invention showed resistance to smudging
when the toned image thereon was rubbed the same number of cycles, i.e.,
50 strokes, using the same equipment. Although there were some smudge
marks discernible when the coated Formulations A to C were employed, such
smudges were much reduced than when the uncoated reference sample was
employed. There was only slight improvements in smudge resistance when
formulation D was employed when compared with the uncoated sample.
The degree of adhesion of the toned image to the paper substrate for each
sample including the uncoated sample was determined qualitatively. The
test was accomplished by applying a strip of conventional 3M Brand Scotch
Tape to the exposed toned image on each sample. The tape was then peeled
back and the amount of toned image which adhered to the tape was
determined by making surface densitometer measurements of the toned image
on the paper substrate before and after stripping the tape from the
substrate. The results of these tests clearly indicated that much more
toned image, e.g., about 20% more toned image was stripped away from the
uncoated reference substrate than from the coated substrates in which
coating Formulations A to D were employed.
A final qualitative test was performed to determine if any of the five
above-mentioned samples showed any tendency to "block", i.e., stick
together when the respective substrate samples containing toned image
thereon were unwound from a roll. There was no blocking evident when the
toner receptive coating Formulations (A to D) were employed. There was
also no blocking indicated when the uncoated sample was used. These tests
were performed at elevated temperatures of 120.degree. F. to 140.degree.
F. under humid conditions to assure that the receptive coating formulation
of the invention would not cause blocking even if the substrate roll were
stored at such extreme conditions.
Although preferred formulations for the toner receptive coating of the
invention have been described, it should be appreciated that alternative
formulations are possible without departing from the scope and concept of
the present invention. For example, the various important properties of
each component in the preferred formulation has been described along with
the properties of the coating as a whole. Accordingly, it should be
appreciated that those skilled in the art could find alternatives to the
preferred components without departing from the scope and concept of the
present invention. Accordingly, the invention is not intended to be
limited by the specific embodiments described herein but rather is defined
by the claims and equivalents thereof.
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