Background of the Invention
This invention relates to thermal mass transfer printing, and, in
particular, to a novel receptor sheet for such printing.
In thermal mass transfer printing, an image is formed on a receptor
sheet by selectively transferring image-forming material thereto from a donor sheet.
Material to be transferred from the donor sheet is selected by a thermal printhead,
which consists of small, electrically heated elements which are operated by signals
from a computer in order to transfer image-forming material from the donor sheet
to areas of the receptor sheet in an image-wise manner.
There are essentially two broad classes of donor sheet-receptor sheet
systems - (1) chemical reaction systems and (2) mass transfer systems.
In chemical reaction systems, the image is formed upon the receptor
sheet as a result of the imagewise transfer of some chemical reactant from the
donor sheet. An example is the transfer of a mobile molecule, such as a phenol,
to the receptor sheet, which bears a leuco compound thereon. The phenol is transferred
by being volatilized by the heat from the thermal printhead, and, upon reaching
the receptor sheet, reacts with the leuco compound to convert it from the colorless
to the colored form. Alternatively, the phenol can be on the receptor sheet and
the leuco compound can be on the donor sheet.
In mass transfer systems, no color-forming chemical reaction takes
place. Instead, the image is formed simply by the transfer of the coloring material
In U.S. Patent No. 3,898,086, a wax composition is transferred imagewise
to a receptor film by means of heat which melts the wax and allows it to readhere,
upon cooling, to the receptor film. The final step in this process is the separation
of the donor sheet and receptor film by pulling them apart. The donor sheet, which
bears a negative image, is then used as a visual transparency. The receptor film
used in this process is not of sufficient transparency to be useful for projection.
In another wax transfer process described in DE 3,143,320, pressure, rather than
heat, is used to effect the transfer. Such pressure can come from a pen, pencil,
or typwriter, or other pressure-applying device. This system is not adaptable
to thermal printing processes with the type of apparatus currently in use.
A typical donor sheet that is useful with thermal printers currently
on the market comprises a paper or film backing having a layer of a pigmented wax
coated thereon. such a sheet is described in Seto, et al., U.K. Patent Application
GB 2,069,160 A. The layer of transfer material comprises 1 to 20% by weight coloring
agent, 20 to 80% by weight binder, and 3 to 25% by weight softening agent. A solid
wax having a penetration of 10 to 30 is preferred as the binder. The softening
agent is an easily meltable material such as polyvinyl acetate, polystyrene, etc.
In order for image transfer to occur in such a system, the wax must soften sufficiently
so that it can be released from its backing, and transfer to the receptor sheet
in imagewise manner, but it should not become so soft as to run or move about
on the receptor sheet. At the instant of transfer, the pigmented wax is held between
the competing forces of the backing of the donor sheet and the image receptive
surface of the receptor sheet. If the receptor sheet is paper, the transfer occurs
by a combination of adhesion, capillary action, and mechanical intermingling of
wax and paper fibers. Because the porosity of paper makes the adhesion area of
the poper receptor sheet much greater than the surface area occupied by the image
on the donor sheet, release from the backing of the donor sheet and transfer to
and adhesion on the paper receptor sheet is favored.
If the receptor sheet is polymeric film, transfer depends entirely
upon the adhesion of the softened pigmented wax to the relatively smooth film surface.
In the absence of the mechanical coupling of pigmented wax to the receptor sheet,
such as is provided by the pores of a paper surface, the adhesive properties of
the polymeric film surface become critical. Adequate imaging will occur only if
the adhesion between the pigmented wax and the film surface of the receptor sheet
overcomes the adhesion of the wax to the backing of the donor sheet. It has been
found that pigmented wax from a donor sheet does not reliably adhere to bare,
untreated polyethylene terephthalate film because lack of compliance of the surfaces
of the donor sheet and receptor sheet makes contact between pigmented wax of the
donor sheet and image receptive surface of the receptor sheet difficult. Corona
treatment of the polyethylene terephthalate film just prior to imaging improves
wax transfer, but this is not a practical alternative for use in an office setting.
A further difficulty in the use of bare, untreated polyethylene terephthalate
film for thermal transfer imaging is the heat capacity of this material, which
limits the range of useable calipers to a maximum of approximately 2 mils (50.8
micrometers). Films having calipers greater than this cannot be heated sufficiently
to achieve the temperature needed for imaging.
Ideally, a receptor sheet made of polymeric film should have the
characteristics of high clarity, reliable feedability in conventional thermal mass
transfer printers, good handleability, and good adhesion of image-forming material.
Haze should be below 15% as measured on the Gardner hazemeter, a level of 10% or
less being preferred. The receptor sheet should preferably add no detectable color
to the printed image. The receptor sheet should preferably feed reliably through
the printer without sticking or jamming and without the need for any modification
to printers originally designed to make paper copies. The receptor sheet should
preferably be capable of being easily handled, without stickiness or susceptibility
to excessive fingerprinting, which would add visible defects to the sheet noticeable
upon projection. This is particularly important with respect to transparencies
made from the receptor sheet. Transfer of pigmented wax from the donor sheet to
the receptor sheet should preferably be complete in the areas to be imaged, and
there should not be excessive wax transfer in areas to be free of the printed
image. Sensitivity to small dots and thin lines is a desired feature and solid
dark areas should appear solid when projected. Tile receptor sheet should also
provide acceptable images for any caliper of film in the range of 38 to 178 µm
(1.5 to 7.0 mils).
Summary of the Invention
This invention is a receptor sheet suitable for receiving donor material
in an imagewise manner from a donor sheet by means of thermal mass transfer printing
comprising a transparent backing having on at least one major surface thereof
a transparent image receptive layer comprising a wax-compatible material having
a softening temperature of about 30°C to about 90°C and a critical surface tension
exceeding that of the donor material of the donor sheet, said image receptive
layer being sufficiently anchored to said backing to allow the image receptive
layer to remain on the backing upon transfer of said donor material from said donor
sheet to said image receptive layer, said receptor sheet having a haze value of
less than 15%, the critical surface tension of the image receptive layer being
equal to or greater than 31mN per m (31 dynes per centimeter), the coefficient
of static friction of the image receptive layer as measured against aluminum according
to ASTM D 1894 (1978) being less than about 0.50.
The backing can be made of any flexible, polymeric material to which
an image receptive layer can be adhered. A preferred backing material is polyethylene
terephthalate. A preferred image receptive layer can be formed from on ethylene
vinyl acetate copolymer blended with a paraffin wax, a microcrystalllne wax, or
mixture of both. Antioxidants, tackifiers, and other additives may also be contained
in the image receptive layer.
The receptor sheet of this invention is suitable for use in commercially
available thermal mass transfer printers.
Brief Description of the Drawings
The invention is described in detail hereinafter with reference to
the accompanying drawings wherein like reference characters refer to the same parts
throughout the views and in which:
- FIG. 1 is a cross-sectional view of the receptor sheet of this invention.
- FIG. 2 shows one method by which the recepteor sheet is imaged.
Referring to FIG. 1, there is shown a receptor sheet 10 comprising
a backing 12 and an image receptive layer 14.
The backing 12 should be sufficiently flexible in order to be able
to travel through conventional thermal mass transfer printers. Whenever the receptor
sheet 10 is to be used for preparing transparencies for overhead projection, the
backing 12 must be transparent to visible light. Representative examples of materials
that are suitable for the backing 12 include polyesters, polysulfones, polycarbonates,
polyolefins, such as polypropylene, polystyrenes, cellulose esters, such as cellulose
acetate and cellulose acetate butyrate. A preferred backing material is polyethylene
The image receptive layer 14 must be compatible with wax, since most
commercially available donor sheets are wax-based. Because different manufacturers
generally use different wax formulations in their donor sheets, the image receptive
layer 14 should preferably have an affinity for several different waxes, such as
beeswax, carnauba wax, paraffin wax, microcrystalline wax, and other synthetic
A simple, useful test for determining whether a material for the
image receptive layer is compatible with wax consists of dissolving 20 grams of
wax in 80 grams of hot toluene. In a second container, 20 grams of the material
being tested is dissolved in 180 grams of toluene. The two solutions are then mixed
and coated onto polyester film at 16µm (.63 mils) wet thickness with a wirewound
coating rod, then dried with hot forced air at about 82°C. The haze of the coating
resulting therefrom must be less than 15% for the material being tested to be considered
compatible with wax. Haze can be measured using a Gardner Model HG 1200 pivoting
sphere hazemeter or equivalent instrument according to ASTM D1003 (1977). If toluene
is not a suitable solvent for the test, other solvents may be used as long as
the dried coating weight is comparable to that described above.
The critical surface tension of the surface of the image receptive
layer 14 must be sufficiently high to assure that the image receptive layer 14
of the receptor sheet 10 is wet by the wax of the donor sheet when the wax is
in the molten state. Wetting will occur only if the surface tension of the donor
material is below that of the surface of the image receptive layer 14. Since most
waxes, particularly in the molten state, have values of surface tension of 31
dynes per centimeter or less, this condition can usually be met by choosing for
the image receptive layer 14 polymers having a critical surface tension of at
least 31 dynes per centimeter.
Critical surface tension is a measure of the "wettability" of a solid
surface, and surfaces having higher wettability exhibit higher values of critical
surface tension. Calculation of the critical surface tension of a material consists
of recording contact angles of drops of various liquids on the surface of a layer
of material being evaluated, plotting a curve of contact angle against surface
tension of the liquid, and extrapolating to a contact angle of zero. The critical
surface tension is the surface tension which a liquid would have to have in order
to just form a droplet with zero contact angle with the surface under consideration.
Surface tension of liquids can be measured by means of a du Nouy tensiometer,
using adaptations of methods given in ASTM D1331 (1980). Materials suitable for
image receptive layers should preferably have a critical surface tension above
31 dynes per centimeter, more preferably above 35 dynes per centimeter.
Because the transfer of donor material to the receptor sheet 10 is
essentially an adhesion process, it is important that there be intimate contact
between donor sheet and receptor sheet 10 at the instant of imaging, and that
during the period of contact, the image receptive layer 14 be in a softened condition.
The image receptive layer 14 should soften at a temperature below the imaging
temperature, more specifically, between about 30°C and about 90°C., and preferably
between about 60°C and about 80°C. The imaging temperature is normally 90°C or
higher. Softening temperature, as used herein, means Vicat softening temperature
determined in accordance with ASTM D1525 (1982) for polymers with no sharp melting
point, or, for polymers which do exhibit a sharp melting point, the melting point
itself. A softening temperature below about 30°C is not desirable, since the layer
14 is then likely to become tacky and soft at normal room temperatures. This would
lead to fingerprinting, blocking of stacked film, and other undesirable handling
characteristics. In some cases, the softening temperature of image receptive layers
formed from certain polymers can be raised by blending wax with the polymer. However,
this technique may introduce haze, unless the polymer and wax have a relatively
high degree of compatibility. A softening temperature above about 90°C is not
desirable, since the image receptive layer 14 is unlikely to soften sufficiently
to receive wax from the donor sheet at the imaging temperature.
The proper selection of critical surface tension and softening temperature,
as described above, are necessary conditions for a useful receptor sheet 10 for
thermal mass transfer printing. In addition, in order for the receptor sheet 10
to be useful in a commercial setting, the receptor sheet is preferably non-tacky
and handleable under the conditions to which overhead transparencies are normally
subjected; it is preferably capable of being fed reliably in conventional thermal
mass transfer printers; and it is preferably of sufficient durability so that it
will remain useable after such handling and feeding. If the receptor sheet is
to be used for preparing transparencies, such as for overhead projection, the image
receptive layer should be transparent to visible light.
A useful measure of how well a particular receptor sheet 10 and image
receptive layer 14 thereof meets the commercial requirement of reliable feeding
in a conventional thermal mass transfer printer is the coefficient of static friction
measured against aluminum according to ASTM D1894 (1970). Aluminum was chosen as
the reference surface because tests on a variety of receptor sheet samples have
shown aluminum to be a reliable indicator of those properties which have been found
important in the general handling and feeding of transparency films. For example,
coefficients of static friction greater than 1.0 indicate rubbery or tacky surfaces.
Coefficients of static friction above 0.6 indicate, for smooth, non-abraisive surfaces,
that the surface may be somewhat soft, but still useable for thermal mass transfer
printing. An image receptive layer 14 having a coefficient of static friction below
0.5 should handle well and feed reliably in must commercially available thermal
mass transfer printers, though the exact coefficient of friction which can be tolerated
is dependent upon the mechanical details of a given thermal printer, and upon
such features of the backing 12 as beam strength, and hence caliper. For a particular
make and model of thermal mass transfer printer, the acceptable range of coefficient
of static friction can be determined by feeding sample receptor sheets through
It has been found that the addition of suitable additives, such as
wax, to the composition for preparing the image receptive layer can have a beneficial
effect in reducing coefficient of static friction without adversely affecting
imageability. However, such additions may produce the detrimental side effect of
increasing haze. If, for example, wax is to be used for friction reduction or
other property improvements, it is desireable to add only a small amount thereof,
so as to keep haze to a minimum. The formulations described herein allow coefficients
of static friction as low as about 0.25, without exceeding a haze level of 15%.
In some cases, the surface of the image receptive layer 14 may tend
to be tacky, and consequently, the receptor sheet 10 may be difficult to feed into
the printer. This tackiness may also result in unwanted pigment transfer in the
unimaged background areas. By incorporating certain waxes, at an appropriate level,
into the composition from which the image receptive layer is formed, it has been
found that, at room temperature, such waxes prevent adjacent sheets from sticking
together or single sheets from jamming in the printer. During the printing process,
such waxes prevent pigmented wax from the donor sheet from sticking to the image
receptive layer 14 in the unimaged background areas. However, at imaging temperatures,
which are well above the melting point of the wax, the wax can combine with the
softened, pigmented wax of the donor sheet and promote bonding between the pigmented
wax and the image receptive layer 14 of the receptor sheet.
Adhesion of the image receptive layer 14 to the backing 12 is vital
to receptor sheet performance. transfer of the pigmented wax from the donor sheet
to the image receptive layer 14 is useful only if the anchoring of the image receptive
layer 14 to the backing 12 is sufficiently strong to allow the image receptive
layer to remain on the backing. In some cases, adhesion of the image receptive
layer to the backing can be improved by incorporation of adhesion promoters into
the composition from which the image receptive layer is formed. It is also possible,
in some cases, that adhesion promoters may also serve a second function of improving
the adhesion of the pigmented wax to the image receptive layer.
Materials that have been found to be useful for forming the image
receptive layer 14 include chlorinated polyolefins, polycaprolactones, blends of
chlorinated polyolefin and polymethyl methacrylate, block copolymers of styrene-ethylene/butylene-styrene,
and copolymers of ethylene and vinyl acetate. Preferably, copolymers of ethylene
and vinyl acetate should contain from about 10% to about 40% vinyl acetate units,
and blends of chlorinated polyolefins and polymethyl methacrylate should contain
no more than about 50% by weight polymethyl methacrylate. Waxes that have been
found to be useful for incorporation into the composition for forming the image
receptive layer 14 include paraffin wax, microcrystalline wax, beeswax, carnauba
wax, and synthetic hydrocarbon waxes. The amount of wax used should not exceed
50% by weight of the image receptive layer. Preferably, the amount of wax may
comprise up to 20% by weight of the image receptive layer; more preferably, the
amount of wax may comprise up to 12% by weight of the image receptive layer.
Various additives or modifying agents such as antioxidants and tackifiers
may also be included in the image receptive layer.
The caliper of the receptor sheet 10 can range from about 1.5 to
about 178 µm (1.5 mils to about 7 mils). A preferred caliper is about 76 to about
127 µm (3 mils about 5 mils). Typical coating weights for the image receptive
layer 14 range from about 0.54 to about 21.5 gramms per square meter (0.05 to about
2.0 grams per square foot).
An opaque sheet may also be adhered to the side of the backing 12
opposite the side bearing the image receptive layer 14 in order to facilitate feeding
of the receptor sheet 10 into the thermal mass transfer printing apparatus.
The receptor sheet 10 can be prepared by introducing the ingredients
for making the image receptive layer 14 into suitable solvents, mixing the resulting
solutions at ambient temperature, e.g,. 25°C, then coating the resulting mixture
onto the backing 12, and drying the resulting coating, preferably in a forced air
oven. Suitable coating techniques include knife coating, roll coating, air knife
coating, curtain coating, etc. While the technique described above makes use of
coating solutions, other methods of blending or coating may be used. Other possible
techniques include latex suspensions and hot melt systems.
The resulting receptor sheet 10 is useful for thermal mass transfer
imaging processes with conventional thermal mass transfer printing apparatus, e.g.,
"Fuji Xerox Diablo" Model XJ-284 and "Okimate" Models 10 and 20 and conventional
thermal mass transfer donor sheets, e.g., "Diablo" T052 Donor and "Okimate" donor
In Fig. 2, the receptor sheet 10 of this invention can be imaged
in a thermal mass transfer printer (not shown) wherein the printing is conducted
by a thermal head 20 which heats the donor sheet 22 in an imagewise manner. The
donor sheet 22 comprises a backing 24 and a layer of donor material 26. A useful
donor sheet is described in UK Patent Application GB 2,069,160 A, incorporated
herein by reference. The backing 24 is generally a plastic film or paper, e.g.
polyethylene film, polystyrene film, polypropylene film, glassine paper, synthetic
paper, laminated paper. The donor material 26 is formed from a composition containing
1 to 20% by weight of a coloring agent, 20 to 80% by weight of a binder, and 3
to 25% by weight of a softening agent. The binder is normally a wax, e.g. haze
wax, beeswax, ceresine wax, spermaceti. The softening agent is normally an easily
heat meltable material, e.g. polyvinyl acetate, polystyrene, styrene-butadiene
copolymer. The coloring agent is normally a conventional pigment. The thermal head
20 generates heat by pulse signals from a signalling device (not shown) so as
to melt the donor material 26 and allow transfer thereof from the donor sheet 22
to the image receptive layer 14 of the recePtor sheet 10. The image receptive
layer 14 is softened by heat from the thermal head 20 that is conducted through
the donor sheet 22. The thermal mass transfer printer is typically constructed
so that pressure-applying means induces intimate contact between the donor sheet
22 and receptor sheet 10 to allow effective transfer of the donor material 26 to
the image receptive layer 14.
In order to more clearly point out the advantages of the invention,
the following non-limiting examples are provided. In these examples, haze was measured
in accordance with ASTM D1003, and critical surace tension was calculated as described
previously through the employment of ASTM D1331.
A 20% by weight solution of ethylene vinyl acetate copolymer ("Elvax"
310, 25% by weight vinyl acetate, E. I. DuPont de Nemours) was prepared by dissolving
20 grams of solid copolymer in 80 grams of toluene. A 20% by weight paraffin wax
solution was prepared by dissolving 20 grams of paraffin wax ("Histowax" HX0482-5,
EM Science, melting point 56°C) in 80 grams of toluene. A wax/copolymer blend was
then formed by mixing the foregoing solutions together. The resulting solution
was coated onto a 4 mil polyethylene terephthalate (PET) backing using an #7 RDS
wirewound coating rod at a coating weight of about 0.54 to about 0.75 grams per
square meter (0.05 to about 0.07 gram per square foot). Drying was conducted in
a forced air oven at 82°C for two minutes. The dried coating consisted of 50% by
weight wax and 50% by weight ethylene vinyl acetate copolymer. Haze was less than
15%. The coefficient of static friction of the image receptive layer against aluminum
was 0.2. The critical surface tension of ethylene vinyl acetate is approximately
32 mN per m (32 dynes per centimeter). The softening temperature of "Elvax" 310
copolymer is 88°C, as measured by the ring and ball method (ASTM E28-67 (1982)),
which corresponds to a Vicat softening temperature of approximately 32°C. The sheet
fed reliably in a Fuji-Xerox Diablo printer and provided a satisfactory printed
Example I was repeated, the only exception being that the coating
solution was applied at a coating weight of 21.5 grams per square meter (2.0 grams
per square foot), instead of 0.54 to 0.75 grams per square meter (.05 to .07 grams
per square foot). The characteristics of the resulting film were similar to those
of the film in Example I, and images formed thereon were also of excellent quality.
This illustrates that the performance of the film is relatively insensitive to
the coating weight of the image receptive layer over a relatively wide range.
Example A (Comparative)
A solution of 5 grams styrene-butadiene-styrene copolymer ("Kraton"
1101, Shell Chemical Company) and 5 grams paraffin wax ("Histowax" HX0482-5) in
90 grams of toluene was coated onto a 102 µm (4 mil) PET backing and dried at
82°C in a forced air oven for three minutes. The resulting image receptive layer
had a coefficient of static friction against aluminum of 0.30. Haze was less than
10%. The softening temperature of the elastomeric moiety of "Kraton" 1101 copolymer
is approximately 20°C, which is outside the prescribed range of 30-90°C. Although
the film fed reliably through the printer, the resulting copy showed incomplete
fill of solid areas and failure to print solid lines. This example illustrates
the criticality of the range of softening temperature.
Example B (Comparative)
A 10% by weight solution of polymethyl methacrylate ("Elvacite" 2041,
E.I. DuPont de Nemours) in a solvent containing 50% toluene and 50% methyl ethyl
ketone was coated onto a 102 µm (4 mil) PET backing with a #7 wirewound rod and
dried at 82°C for two minutes in a forced air oven. The softening temperature of
polymethyl methacrylate is approximately 107°C, which is outside the prescribed
range of 30-90°C. The critical surface tension of polymethyl methacrylate is 39
mN per m (39 dynes per centimeter). Although the film fed reliably through the
printer, only about 30% of the image was transferred to the receptor sheet. The
characters were not completely filled in and had blank spaces where small dots
should have appeared.
A 25% by weight solution of chlorinated polyolefin (CP153-2, Eastman
Chemical Products, Kingsport, Tennessee) in xylene was blended with a 20% by weight
solution of paraffin wax ("Histowax" HX0482-5) in toluene to form a solution which,
when dried, would form a solid coating consisting of 12.5% by weight wax and 87.5%
by weight chlorinated polyolefin. This solution was coated onto a 102 µm (4 mil)
PET backing at coating weights of 3.8, 7.6, 11.9, and 22.6 grams per square meter
(.35, .71, 1.1, and 2.1 grams per square foot) and dried in a forced air oven
at 82°C. for three minutes. Chlorinated polyolefin has a critical surface tension
of approximately 38 mN per m (38 dynes per centimeter), and a Vicat softening temperature
of 57°C. The coefficients of static friction of the coatings against aluminum
were in the range of .33 to .40.
Feeding into the printer was acceptable regardless of coating weigiit.
All of the image receptive layers provided acceptable printed images, but the samples
having lower coating weights showed slight pinholing in the larger solid fill
areas. This pinholing was progressively reduced by going to higher coating weights,
until at a coating weight of 22.6 grams per square meter (2.1 grams per square
foot), there were almost no pinholes. This illustrates that even though acceptable
copies can be produced over a wide range of coating weights, there can still exist
a narrower range of optimum coating weights within the wide range.
A coating composition consisting of equal parts ethylene vinyl acetate
copolymer ("Elvax" 410, 18% vinyl acetate, E. I. DuPont de Nemours) and paraffin
wax ("Histowax" HX0482-5) dissolved in toluene was applied to a 102 µm (4 mil)PET
backing and dried at 82°C. for three minutes. When the thus-formed receptor sheet
was run in the Fuji-Xerox Diablo printer, image quality was very poor. Examination
of the copies showed that the entire image receptive layer was detaching from the
backing and sticking to the donor sheet.
In a second run, a coating of the type described above was subjected
to a 15 J per sec (15 watt)ultraviolet light for 24 hours. This treatment, which
was similar to the treatment described in U.S. Patents 3,188,265 and 3,188,266,
resulted in greatly improved adhesion between the backing and image receptive
layer, and the receptor sheet derived from this treatment yielded an acceptable
printed image. This illustrates the importance of providing good adhesion of the
image receptive layer to the backing, and that the range of useful image receptive
layers can be extended by the use of special treatments such as ultraviolet radiation.
A 20% by weight solution of polycaprolactone (Union Carbide PCL700)
in toluene was coated onto a 102 µm (4 mil) PET backing with a #7 RDS wire wound
rod. Polycaprolactone has a melting point of 60°C and a critical surface tension
of approximately 40 mN per m (40 dynes per centimeter). The resulting coating
was dried at 82°C fur five minutes in a forced air oven. The image receptive layer
had a coefficient of static friction against aluminum of 0.30. The receptor sheet
fed reliably through the Fuji Xerox Diablo printer and the resulting image exhibited
good optical density with no backgrounding.
A 25% by weight solution of equal parts chlorinated polyolefin (PC153-2,
Eastman Chemical Corp.) and polymethyl methacrylate ("Elvacite" 2041) in toluene
was coated onto a 102 µm (4 mil)PET backing with a #7 RDS wire wound rod. The
resulting coating was dried at 82°C for five minutes in a forced air oven. Haze
was less than 10%, the coefficient of static friction was about .3, and feeding
and imaging were acceptable. This illustrates that a polymer such as polymethyl
methacrylate which was unsatisfactory in Comparative Example C, when used alone,
can be made to work by blending it with another polymer, such as chlorinated polyolefin,
which was shown to work well in Example III.
A solution prepared by dissolving 17.5 grams of a block copolymer
made up of styrene/ethylenebutylene/styrene chains ("Kraton" G-1652, Shell Chemical
Company) and 2.5 grams of paraffin wax ("Histowax" HX0482-5) in 80 grams of toluene
was coated onto a 102 µm (4 mil) PET backing using a #7 RDS wirewound coating rod.
The critical surface tension of "Kraton" G-1652 copolymer is estimated to be just
over 31 mN per m (31 dynes per centimeter), and the Vicat softening temperature
this block copolymer is within the prescribed range of 30-90°C. The coefficient
of static friction of the coating was .26, feeding into the printer was reliable,
and image quality was acceptable.
A 102 µm (4 mil)PET backing was coated as in Example I with a 20%
by weight solution of ethylene vinyl acetate copolymer ("Elvax" 310) in toluene,
but without any added wax. The image receptive layer had a coefficient of static
friction against aluminum of 1.50 and a softening temperature of about 88°C. Haze
was less than 4%. When fed through the Fuji-Xerox Diablo printer used in Example
I, the film jammed and the machine had to be opened to remove the crumpled film.
However, images of excellent quality can be formed on the image receptive layer.