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CROSS REFERENCE TO RELATED APPLICATIONS
Reference is made to co-pending, commonly assigned U.S. Ser. No. 457,894,
filed Dec. 27, 1989, entitled "Shaped Articles From Orientable Polymers
and Polymer Microbeads," the disclosure of which is incorporated by
reference, now U.S. Pat. No. 4,994,312.
TECHNICAL FIELD
This invention relates to dye-receiving elements used in thermal dye
transfer, and more particularly to receiving elements having microvoided
supports.
BACKGROUND
In recent years, thermal transfer systems have been developed to obtain
prints from pictures which have been generated electronically from a color
video camera. According to one way of obtaining such prints, an electronic
picture is first subjected to color separation by color filters. The
respective color-separated images are then converted into electrical
signals. These signals are then operated on to produce cyan, magenta and
yellow electrical signals. These signals are then transmitted to a thermal
printer. To obtain the print, a cyan, magenta or yellow dye-donor element
is placed face-to-face with a dye-receiving element. The two are then
inserted between a thermal printing head and a platen roller. A line-type
thermal printing head is used to apply heat from the back of the dye-donor
sheet. The thermal printing head has many heating elements and is heated
up sequentially in response to the cyan, magenta and yellow signals. The
process is then repeated for the other two colors. A color hard copy is
thus obtained which corresponds to the original picture viewed on a
screen. Further details of this process and an apparatus for carrying it
out are contained in U.S. Pat. No. 4,621,271 by Brownstein entitled
"Apparatus and Method For Controlling A Thermal Printer Apparatus," issued
Nov. 4, 1986, the disclosure of which is hereby incorporated by reference.
Dye-receiving elements used in thermal dye transfer generally comprise a
polymeric dye image-receiving layer coated on a support. Supports are
required to have, among other properties, adequate strength, dimensional
stability, and heat resistance. For reflective viewing, supports are also
desired to be as white as possible. Cellulose paper, synthetic paper, and
plastic films have all been proposed for use as dye-receiving element
supports in efforts to meet these requirements. Recently, microvoided
films formed by stretching an orientable polymer containing an
incompatible organic or inorganic material have been suggested for use in
dye-receiving elements. U.S. Pat. No. 4,778,782 of Ito et al., for
example, discloses supports comprising a microvoided film obtained by
stretching a translucent plastic film containing fine fillers such as clay
or talc. By this stretching, bonds between the polymers and fillers in the
film are destroyed, whereby microvoids are considered to be formed in the
film. The microvoids lower the density of the film and also make it appear
white and opaque. European Patent Application 0 322 771 discloses
dye-receiving element supports comprising a polyester film containing
polypropylene and minute closed cells within the film formed upon
stretching.
A problem exists with the microvoided supports discussed above, however, in
that it is difficult to manufacture films with a high degree of
microvoiding. A high degree of microvoiding is desirable as this increases
the heat insulating property of the support, and thereby the thermal
efficiency of the dye transfer. EP 0 322 771 Comparative Example 4, for
example, shows that a high degree of microvoiding in
polyester/polypropylene stretched films, as evidenced by a relatively low
specific gravity, results in poor mechanical strength and frequent
breakage of the film during stretching. The lowest apparent specific
gravity for an operable film in EP 0 322 771 is 0.71 (Example 2).
It would be desirable to provide a dye image-receiving element for thermal
dye transfer with a manufacturable microvoided support which would provide
superior thermal efficiency.
SUMMARY OF THE INVENTION
These and other objects of the invention are achieved in accordance with
this invention which comprises a dye-receiving element for thermal dye
transfer comprising a support having thereon a polymeric dye
image-receiving layer wherein the support comprises a continuous oriented
polymer matrix having dispersed therein microbeads of a cross-linked
polymer coated with a slip agent and which are at least partially bordered
by void space.
The combination of cross-linked microbeads and a slip agent coating allows
supports with a relatively high degree of microvoiding to be manufactured.
The cross-linking of the microbead polymer provides resiliency and
elasticity while the slip agent permits easier sliding between the
microbeads and the matrix polymer to result in more effective
microvoiding. This allows films with a higher void percentage and thereby
greater insulating effect to be manufactured. Such films have been found
to be particularly advantageous for thermal dye transfer applications as
the greater insulating effect results in greater dye transfer efficiency.
DETAILED DESCRIPTION
The receiving elements of the invention use supports comprising a
continuous thermoplastic polymer phase having dispersed therein microbeads
of polymer which are at least partially bordered by voids. The microbeads
of polymer have a size of about 2 microns to about 30 microns, preferably
about 5 to about 20 microns, and are present in an amount of about 5% to
about 50% by weight based on the weight of continuous phase polymer. The
voids occupy up to about 60% by volume of the support, preferably from
about 30% to about 60% by volume. Larger beads generate a greater amount
of void space upon stretching of the supports, but result in a rougher
support surface. The use of smaller beads results in a smoother support
surface, but they do not generate as much void volume. To obtain a support
with both a high void volume and a smooth surface, a dual layer support
may be made. The bulk of such a support comprises a layer made with
relatively large beads in order to generate a large void volume, and this
layer is coated with a smoothing layer containing relatively small beads
or no beads at all.
The matrix polymer contains the generally spherical polymer microbeads
which, according to one aspect of the invention, are cross-linked to the
extent of having a resiliency or elasticity at orientation temperatures of
the matrix polymer such that a generally spherical shape of the
cross-linked polymer is maintained after orientation of the matrix
polymer. The supports according to this invention in the absence of
additives or colorants are very white, and are very resistant to wear,
moisture, oil, tearing, etc.
The supports are preferably in the form of a paper like sheet having a
thickness of about 50 to about 300 microns. Preferably, the supports are
made by biaxial orientation using procedures well known in the art.
The continuous phase polymer may be any article-forming polymer such as a
polyester capable of being cast into a film or sheet. The polyesters
should have a glass transition temperature between about 50.degree. C. and
about 150.degree. C., preferably about 60.degree.-100.degree. C., should
be orientable, and have an intrinsic viscosity of at least 0.5, preferably
0.6 to 0.9. Suitable polyesters include those produced from aromatic,
aliphatic or cyclo-aliphatic dicarboxylic acids of 4-20 carbon atoms and
aliphatic or alicyclic glycols having from 2-24 carbon atoms. Examples of
suitable dicarboxylic acids include terephthalic, isophthalic, phthalic,
naphthalene dicarboxylic acid, succinic, glutaric, adipic, azelaic,
sebacic, fumaric, maleic, itaconic, 1,4-cyclohexane-dicarboxylic,
sodiosulfoisophthalic and mixtures thereof. Examples of suitable glycols
include ethylene glycol, propylene glycol, butanediol, pentanediol,
hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, other
polyethylene glycols and mixtures thereof. Such polyesters are well known
in the art and may be produced by well-known techniques, e.g., those
described in U.S. Pat. Nos. 2,465,319 and 2,901,466. Preferred continuous
matrix polymers are those having repeat units from terephthalic acid or
naphthalene dicarboxylic acid and at least one glycol selected from
ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol.
Poly(ethylene terephthalate), which may be modified by small amounts of
other monomers, is especially preferred. Polypropylene is also useful.
Other suitable polyesters include liquid crystal copolyesters formed by
the inclusion of a suitable amount of a co-acid component such as stilbene
dicarboxylic acid. Examples of such liquid crystal copolyesters are those
disclosed in U.S. Pat. Nos. 4,420,607, 4,459,402 and 4,468,510.
Suitable cross-linked polymers for the microbeads are polymerizable organic
materials which are members selected from the group consisting of an
alkenyl aromatic compound having the general formula
##STR1##
wherein Ar represents an aromatic hydrocarbon radical, or an aromatic
halohydrocarbon radical of the benzene series and R is hydrogen or the
methyl radical; acrylate-type monomers including monomers of the formula
##STR2##
wherein R is selected from the group consisting of hydrogen and an alkyl
radical containing from about 1 to 12 carbon atoms and R' is selected from
the group consisting of hydrogen and methyl; copolymers of vinyl chloride
and vinylidene chloride, acrylonitrile and vinyl chloride, vinyl bromide,
vinyl esters having the formula
##STR3##
wherein R is an alkyl radical containing from 2 to 18 carbon atoms;
acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic
acid, fumaric acid, oleic acid, vinylbenzoic acid; the synthetic polyester
resins which are prepared by reacting terephthalic acid and dialkyl
terephthalics or ester-forming derivatives thereof, with a glycol of the
series HO(CH.sub.2).sub.n OH, wherein n is a whole number within the range
of 2-10 and having reactive olefinic linkages within the polymer molecule,
the hereinabove described polyesters which include copolymerized therein
up to 20 percent by weight of a second acid or ester thereof having
reactive olefinic unsaturation and mixtures thereof, and a cross-linking
agent selected from the group consisting of divinylbenzene, diethylene
glycol dimethacrylate, diallyl fumarate, diallyl phthalate and mixtures
thereof.
Examples of typical monomers for making the cross-linked polymer include
styrene, butyl acrylate, acrylamide, acrylonitrile, methyl methacrylate,
ethylene glycol dimethacrylate, vinyl pyridine, vinyl acetate, methyl
acrylate, vinylbenzyl chloride, vinylidene chloride, acrylic acid,
divinylbenzene, arylamidomethylpropane sulfonic acid, vinyl toluene, etc.
Preferably, the cross-linked polymer is polystyrene or poly(methyl
methacrylate). Most preferably, it is polystyrene and the cross-linking
agent is divinylbenzene.
Processes well known in the art yield non-uniformly sized particles,
characterized by broad particle size distributions. The resulting beads
can be classified by screening to produce beads spanning the range of the
original distribution of sizes. Other processes such as suspension
polymerization, limited coalescence, directly yield very uniformly sized
particles. Suitable slip agents or lubricants include colloidal silica,
colloidal alumina, and metal oxides such as tin oxide and aluminum oxide.
The preferred slip agents are colloidal silica and alumina, most
preferably, silica. The cross-linked polymer having a coating of slip
agent may be prepared by procedures well known in the art. For example,
conventional suspension polymerization processes wherein the slip agent is
added to the suspension is preferred. As the slip agent, colloidal silica
is preferred.
It is preferred to use the "limited coalescance" technique for producing
the coated, cross-linked polymer microbeads. This process is described in
detail in U.S. Pat. No. 3,615,972, incorporated herein by reference.
Preparation of the coated microbeads for use in the present invention does
not utilize a blowing agent as described in this patent, however.
The following is an example illustrating a procedure for preparing the
cross-linked polymeric microbeads coated with slip agent. In this example,
the polymer is polystyrene cross-linked with divinylbenzene. The
microbeads have a coating of silica. The microbeads are prepared by a
procedure in which monomer droplets containing an initiator are sized and
heated to give solid polymer spheres of the same size as the monomer
droplets. A water phase is prepared by combining 7 liters of distilled
water, 1.5 g potassium dichromate (polymerization inhibitor for the
aqueous phase), 250 g polymethylaminoethanol adipate (promoter), and 350 g
LUDOX.RTM. (a colloidal suspension containing 50% silica sold by DuPont).
A monomer phase is prepared by combining 3317 g styrene, 1421 g
divinylbenzene (55% active crosslinking agent, the other 45% is ethyl
vinyl benzene which forms part of the styrene polymer chain) and 45 g VAZO
52.RTM. (a monomer-soluble initiator sold by DuPont). The mixture is
passed through a homogenizer to obtain 5 micron droplets. The suspension
is heated overnight at 52.degree. C. to give 4.3 kg of generally spherical
microbeads having an average diameter of about 5 microns with narrow size
distribution (about 2-10 microns size distribution). The mol proportion of
styrene and ethyl vinyl benzene to divinylbenzene is about 6.1%. The
concentration of divinylbenzene can be adjusted up or down to result in
about 2.5-50% (preferably 10-40%) crosslinking by the active cross-linker.
Of course, monomers other than styrene and divinylbenzene can be used in
similar suspension polymerization processes known in the art. Also, other
initiators and promoters may be used as known in the art. Also, slip
agents other than silica may also be used. For example, a number of
LUDOX.RTM. colloidal silicas are available from DuPont. LEPANDIN.RTM.
colloidal alumina is available from Degussa. NALCOAG.RTM. colloidal
silicas are available from Nalco and tin oxide and titanium oxide are also
available from Nalco. Normally, for the polymer to have suitable physical
properties such as resiliency, the polymer is crosslinked. In the case of
styrene crosslinked with divinylbenzene, the polymer is about 2.5-50%
cross-linked, preferably about 20-40% cross-linked. By percent
cross-linked, it is meant the mol % of crosslinking agent based on the
amount of primary monomer. Such limited crosslinking produces microbeads
which are sufficiently coherent to remain intact during orientation of the
continuous polymer. Beads of such crosslinking are also resilient, so that
when they are deformed (flattened) during orientation by pressure from the
matrix polymer on opposite sides of the microbeads, they subsequently
resume their normal spherical shape to produce the largest possible voids
around the microbeads to thereby produce articles with less density.
The microbeads are referred to herein as having a coating of a "slip
agent". By this term it is meant that the friction at the surface of the
microbeads is greatly reduced. Actually, it is believed this is caused by
the silica acting as miniature ball bearings at the surface. Slip agent
may be formed on the surface of the microbeads during their formation by
including it in the suspension polymerization mix.
Microbead size is regulated by the ratio of silica to monomer. For example,
the following ratios produce the indicated size microbead:
______________________________________
Slip Agent
Microbead Monomer, (Silica)
Size, Microns Parts by Wt.
Parts by Wt.
______________________________________
2 10.4 1
5 27.0 1
20 42.4 1
______________________________________
The supports according to this invention are prepared by:
(a) forming a mixture of molten continuous matrix polymer and cross-linked
polymer wherein the cross-linked polymer is a multiplicity of microbeads
uniformly dispersed throughout the matrix polymer, the matrix polymer
being as described hereinbefore, the cross-linked polymer microbeads being
as described hereinbefore,
(b) forming a shaped article from the mixture by extrusion, casting or
molding,
(c) orienting the article by stretching to form microbeads of cross-linked
polymer uniformly distributed throughout the article and voids at least
partially bordering the microbeads on sides thereof in the direction, or
directions of orientation.
The mixture may be formed by forming a melt of the matrix polymer and
mixing therein the cross-linked polymer. The cross-linked polymer may be
in the form of solid or semi-solid microbeads. Due to the incompatibility
between the matrix polymer and cross-linked polymer, there is no
attraction or adhesion between them, and they become uniformly dispersed
in the matrix polymer upon mixing.
When the microbeads have become uniformly dispersed in the matrix polymer,
a shaped article is formed by processes such as extrusion, casting or
molding. Examples of extrusion or casting would be extruding or casting a
film or sheet, and an example of molding would be injection or reheat
blow-molding a bottle. Such forming methods are well known in the art. If
sheets or film material are cast or extruded, it is important that such
article be oriented by stretching, at least in one direction. Methods of
unilaterally or bilaterally orienting sheet or film material are well
known in the art. Basically, such methods comprise stretching the sheet or
film at least in the machine or longitudinal direction after it is cast or
extruded an amount of about 1.5-10 times its original dimension. Such
sheet or film may also be stretched in the transverse or cross-machine
direction by apparatus and methods well known in the art, in amounts of
generally 1.5-10 (usually 3-4 for polyesters and 6-10 for polypropylene)
times the original dimension. Such apparatus and methods are well known in
the art and are described in such U.S. Pat. No. 3,903,234, incorporated
herein by reference.
The voids, or void spaces, referred to herein surrounding the microbeads
are formed as the continuous matrix polymer is stretched at a temperature
above the Tg of the matrix polymer. The microbeads of cross-linked polymer
are relatively hard compared to the continuous matrix polymer. Also, due
to the incompatibility and immiscibility between the microbead and the
matrix polymer, the continuous matrix polymer slides over the microbeads
as it is stretched, causing voids to be formed at the sides in the
direction or directions of stretch, which voids elongate as the matrix
polymer continues to be stretched. Thus, the final size and shape of the
voids depends on the direction(s) and amount of stretching. If stretching
is only in one direction, microvoids will form at the sides of the
microbeads in the direction of stretching. If stretching is in two
directions (bidirectional stretching), in effect such stretching has
vector components extending radially from any given position to result in
a doughnut-shaped void surrounding each microbead.
The dye image-receiving layer of the receiving elements of the invention
may comprise, for example, a polycarbonate, a polyurethane, a polyester,
polyvinyl chloride, poly(styrene-co-acrylonitrile), poly(caprolactone) or
mixtures thereof. The dye image-receiving layer may be present in any
amount which is effective for the intended purpose. In general, good
results have been obtained at a concentration of from about 1 to about 5
g/m.sup.2. In a preferred embodiment of the invention, the dye
image-receiving layer is a polycarbonate. The term "polycarbonate" as used
herein means a polyester of carbonic acid and a glycol or a dihydric
phenol. Examples of such glycols or dihydric phenols are p-xylylene
glycol, 2,2-bis(4-oxyphenyl)propane, bis(4-oxyphenyl)methane,
1,1-bis(4-oxyphenyl)ethane, 1,1-bis(oxyphenyl)butane,
1,1-bis(oxyphenyl)cyclohexane, 2,2-bis(oxyphenyl)butane, etc. In a
particularly preferred embodiment, a bisphenol-A polycarbonate having a
number average molecular weight of at least about 25,000 is used. Examples
of preferred polycarbonates include General Electric LEXAN.RTM.
Polycarbonate Resin and Bayer AG MACROLON 5700.RTM..
A dye-donor element that is used with the dye-receiving element of the
invention comprises a support having theron a dye containing layer. Any
dye can be used in the dye-donor employed in the invention provided it is
transferable to the dye-receiving layer by the action of heat. Especially
good results have been obtained with sublimable dyes such as anthraquinone
dyes, e.g., Sumikalon Violet RS.RTM. (product of Sumitomo Chemical Co.,
Ltd.), Dianix Fast Violet 3RFS.RTM. (product of Mitsubishi Chemical
Industries, Ltd.), and Kayalon Polyol Brilliant Blue N-BGM.RTM. and KST
Black 146.RTM. (products of Nippon Kayaku Co., Ltd.); azo dyes such as
Kayalon Polyol Brilliant Blue BM.RTM., Kayalon Polyol Dark Blue 2BM.RTM.,
and KST Black KR.RTM. (products of Nippon Kayaku Co., Ltd.), Sumickaron
Diazo Black 5G.RTM. (product of Sumitomo Chemical Co., Ltd.), and Miktazol
Black 5GH.RTM. (product of Mitsui Toatsu Chemicals, Inc.); direct dyes
such as Direct Dark Green B.RTM. (product of Mitsubishi Chemical
Industries, Ltd.) and Direct Brown M.RTM. and Direct Fast Black D.RTM.
(products of Nippon Kayaku Co. Ltd.); acid dyes such as Kayanol Milling
Cyanine 5R.RTM. (product of Nippon Kayaku Co. Ltd.); basic dyes such as
Sumicacryl Blue 6G.RTM. (product of Sumitomo Chemical Co., Ltd.), and
Aizen Malachite Green.RTM. (product of Hodogaya Chemical Co., Ltd.);
##STR4##
or any of the dyes disclosed in U.S. Pat. No. 4,541,830, the disclosure of
which is hereby incorporated by reference. The above dyes may be employed
singly or in combination to obtain a monochrome. The dyes may be used at a
coverage of from about 0.05 to about 1 g/m.sup.2 and are preferably
hydrophobic.
The dye in the dye-donor element is dispersed in a polymeric binder such as
a cellulose derivative, e.g., cellulose acetate hydrogenphthatate,
cellulose acetate, cellulose acetate propionate, cellulose acetate
butyrate, cellulose triacetate; a polycarbonate;
poly(styrene-co-acrylonitrile), a poly(sulfone) or a poly(phenylene
oxide). The binder may be used at a coverage of from about 0.1 to about 5
g/m.sup.2.
The dye layer of the dye-donor element may be coated on the support or
printed thereon by a printing technique such as a gravure process.
The reverse side of the dye-donor element can be coated with a slipping
layer to prevent the printing head from sticking to the dye-donor element.
Such a slipping layer would comprise a lubricating material such as a
surface active agent, a liquid lubricant, a solid lubricant or mixtures
thereof, with or without a polymeric binder. Preferred lubricating
materials include oils or semi-crystalline organic solids that melt below
100.degree. C. such as poly(vinyl stearate), beeswax, perfluorinated alkyl
ester polyethers, poly(caprolactone), carbowax or poly(ethylene glycols).
Suitable polymeric binders for the slipping layer include poly(vinyl
alcohol-co-butyral), poly(vinyl alcohol-co-acetal), poly(styrene),
poly(vinyl acetate), cellulose acetate butyrate, cellulose acetate, or
ethyl cellulose.
The amount of the lubricating material to be used in the slipping layer
depends largely on the type of lubricating material, but is generally in
the range of from about 0.001 to about 2 g/m.sup.2. If a polymeric binder
is employed, the lubricating material is present in the range of 0.1 to 50
weight %, preferable 0.5 to 40, of the polymeric binder employed.
As noted above, the dye-donor elements and receiving elements of the
invention are used to form a dye transfer image. Such a process comprises
imagewise-heating a dye-donor element as described above and transferring
a dye image to a dye-receiving element to form the dye transfer image.
The dye-donor element may be used in sheet form or in a continuous roll or
ribbon. If a continuous roll or ribbon is employed, it may have only one
dye thereon or may have alternating areas of different dyes, such as
sublimable cyan, magenta, yellow, black, etc., as described in U.S. Pat.
No. 4,541,830. Thus, one-, two- three- or four-color elements (or higher
numbers also) are included within the scope of the invention.
In a preferred embodiment, the dye-donor element comprises a poly(ethylene
terephthalate) support coated with sequential repeating areas of cyan,
magenta and yellow dye, and the above process steps are sequentially
performed for each color to obtain a three-color dye transfer image. Of
course, when the process is only performed for a single color, then a
monochrome dye transfer image is obtained.
Thermal printing heads which can be used to transfer dye from the dye-donor
elements to the receiving elements are available commercially. There can
be employed, for example, a Fujitsu Thermal Head (FTP-040 MCS001), a TDK
Thermal Head F415 HH7-1089 or a Rohm Thermal Head KE 2008-F3.
A thermal dye transfer assemblage of the invention comprises:
a) a dye-donor element as described above, and
b) a dye-receiving element as described above,
the dye-receiving element being in a superposed relationship with the
dye-donor element so that the dye layer of the donor element is in contact
with the dye image-receiving layer of the receiving element.
The above assemblage comprising these two elements may be preassembled as
an integral unit when a monochrome image is to be obtained. This may be
done by temporarily adhering the two elements together at their margins.
After transfer, the dye-receiving element is then peeled apart to reveal
the dye transfer image.
When a three-color image is to be obtained, the above assemblage is formed
on three occasions during the time when heat is applied by the thermal
printing head. After the first dye is transferred, the elements are peeled
apart. A second dye-donor element (or another area of the donor element
with a different dye area) is then brought in register with the
dye-receiving element and the process repeated. The third color is
obtained in the same manner.
The following examples are provided to illustrate the invention.
Preparation of Microvoided Supports
A Welders Engineering Twin Screw Compounding Extruder heated to 282.degree.
C. was used to mix polystyrene microbeads (sizes, crosslinking %, and slip
agent coatings as indicated in the table below) and poly(ethylene
terephthalate)("PET", commercially available as #7352 from Eastman
Chemicals). Both components were metered into the compounder and one pass
was sufficient for dispersion of the beads into the PET matrix.
Cast sheets of the above bead/PET dispersion with a poly(ethylene
terephthalate) smoothing layer were coextruded using a Killion Sample
Coextruder System (a 1.5 inch Killion Extruder was used to produce the
bead/PET melt stream, and a 1 inch Killion Extruder was used for the PET
smoothing layer meltstream). The two meltstreams at 282.degree. C. were
fed into a 7 inch "coat-hanger" type single manifold die also heated at
282.degree. C. As the coextruded sheet emerged from the die, it was cast
onto a quenching roll set at 55.degree.C. The final dimensions of the
continuous cast sheet were 18 cm wide and 1270 microns thick. The bead/PET
layer was 1016 microns thick and the PET smoothing layer was 254 microns
thick.
The cast sheets (18 cm.times.18 cm) were then stretched at 110.degree. C.
and 50 mm/sec using an Iwamoto Seisakusho Co. LTD Model BIX7025 Sample
stretcher first 3.75 times in the X-direction and then 3.5 times in the
Y-direction. The stretched sheets were annealed at 117.degree.-122.degree.
C. for 90 sec and were allowed to cool at room temperature, and were then
removed from the stretcher.
The following microvoided supports each with the indicated composite
densities were produced. Each support had the same PET smoothing layer of
approximately 20 microns thickness after stretching.
______________________________________
% Slip Bead
Wt. % Cross- Agent Size,
Beads linking Coating
Microns
______________________________________
E-1 17 30 Silica 2
E-2 20 5 Alumina
2
E-3 5 30 Silica 5
E-4 20 30 Silica 10
E-5 25 30 Silica 10
______________________________________
Support Support Approx.
Thickness Density Void %
(Microns) (g/cm.sup.3)
(Voided layer)
______________________________________
E-1 144 1.03 25
E-2 158 1.01 27
E-3 177 0.84 43
E-4 230 0.67 54
E-5 297 0.59 59
______________________________________
The void percentages were calculated using approximate densities of 1.4
g/cm.sup.3 for PET and 1 g/cm.sup.3 for polystyrene.
Three control supports were also evaluated:
C-1 Eastman Radiographic Intensifying Screen
(A non-microvoided support of poly(ethylene terephthalate) of 180 microns
thickness, 1.41 g/cm.sup.3 density, containing approximately 8% titanium
dioxide.)
C-2 ICI Corp. MELINEX 571.RTM.
(A non-microvoided support of poly(ethylene terephthalate) of 180 microns
thickness, 1.35 g/cm.sup.3 density, containing approximately 18% barium
sulfate.)
C-3 Oji Yuka Goseishi YUPO FPG150.RTM.
(A microvoided support of polypropylene of 150 microns thickness, 0.78
g/cm.sup.3 density, containing calcium carbonate.)
Preparation of Dye-Receiving Elements
The smooth side of the microvoided supports were first coated with a
subbing layer of poly(acrylonitrile-co-vinylidene chloride-co-acrylic
acid) (14:80:6 wt. ratio) (0.11 g/m.sup.2) from butanone. On top of this
layer, a dye receiving layer of Bayer AG MAKROLON 5700.RTM. (a bis-phenol
A polycarbonate) (2.9 g/m.sup.2), 3M Corp. FLUORAD FC-431.RTM. (a
fluorinated surfactant) (0.02 g/m.sup.2), and Dow Corning DC-510.RTM.
Silicone Fluid (0.01 g/m.sup.2) was coated from dichloromethane. Each
control support was coated with the same dye-receiving layer.
Preparation of Dye-Donor Elements
Cyan dye-donor elements were prepared by coating the following layers in
the order recited on a 6 .mu.m poly(ethylene terephthalate) support:
1) A subbing layer of duPont TYZOR TBT.RTM. titanium tetra-n-butoxide (0.12
g/m.sup.2) from 1-butanol; and
2) A layer containing the cyan dye
##STR5##
and Shamrock Tech. S-363.RTM. (a micronized blend of hydrocarbon wax
particles) (0.016 g/m.sup.2) in a cellulose acetate butyrate (17% acetyl
and 28% butyryl) binder (0.66 g/m.sup.2) coated from a cyclopentanone,
toluene and methanol solvent mixture.
Magenta dye-donor elements were prepared by coating the following layers in
the order recited on a 6 .mu.m poly(ethylene terephthalate) support:
1) A subbing layer of duPont TYZOR TBT.RTM. (0.12 g/m.sup.2) from
1-butanol; and
2) A layer containing the magenta dyes
##STR6##
and Shamrock Tech. S-363.RTM. (a micronized blend of hydrocarbon wax
particles) (0.016 g/m.sup.2) in a cellulose acetate butyrate (17% acetyl
and 28% butyryl) binder (0.40 g/m.sup.2) coated from a cyclopentanone,
toluene and methanol solvent mixture.
On the back sides of the cyan and magenta dye-donor elements was coated:
1) A subbing layer of duPont TYZOR TBT.RTM. (0.12 g/m.sup.2) from
1-butanol; and
2) A slipping layer of Acheson Colloids EMRALON 329.RTM.
polytetrafluoroethylene dry film lubricant (0.59 g/m.sup.2), Petrarch
Systems PS-513.RTM. (an amino terminated polydimethyl siloxane) (0.005
g/m.sup.2), BYK-Chemie BYK-320.RTM. (a polyoxyalkylene siloxane) (0.005
g/m.sup.2), and Shamrock Tech. S-232.RTM. (a micronized blend of
polyethylene and carnauba wax particles) (0.016 g/m.sup.2) coated from a
n-propyl acetate, toluene, 2-propanol, and 1-butanol solvent mixture.
Evaluation of Dye-Transfer
The dye layer sides of cyan and magenta donor element strips of
approximately 9 cm.times.12 cm in area were placed in contact with the
image-receiving layer of receiving elements of the same area. Each
assemblage was fastened in the jaws of a stepper motor driven pulling
device, and laid on top of a 14 mm diameter rubber roller. A TDK Thermal
Head L-133 (No. 6-2R16-1) was pressed with a spring at a force of 3.6 kg
against the donor element side of the contacted pair pushing it against
the rubber roller.
The imaging electronics were activated causing the pulling device to draw
the assemblage between the printing head and roller at 3.1 mm/sec.
Coincidentally the resistive elements in the thermal print head were
pulsed at a per pixel pulse width of 8 msec to generate a maximum density
image. The voltage supplied to the print-head was approximately 25 V
representing approximately 1.6 watts/dot (13. mjoules/dot).
After printing the dye images to maximum density, the receivers were
separated from the donors. The Status A Green transmission density of the
magenta donors and the Status A Red transmission density of the cyan
donors were measured both before and after dye transfer. The greater the
change in transmission density, the greater the amount of dye transferred
to the receiver, demonstrating greater thermal efficiency.
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Magenta Donor Density
Cyan Donor Density
Sup- After After
port Initial Transfer Change Initial
Transfer
Change
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C-1 1.7 1.1 0.6 2.0 1.4 0.6
C-2 1.7 0.9 0.8 2.0 1.2 0.8
C-3 1.7 0.7 1.0 2.0 1.0 1.0
E-1 1.7 0.7 1.0 2.0 0.8 1.2
E-2 1.7 0.7 1.0 2.0 0.9 1.1
E-3 1.7 0.6 1.1 2.0 0.7 1.3
E-4 1.7 0.6 1.1 2.0 0.6 1.4
E-5 1.7 0.6 1.1 2.0 0.6 1.4
______________________________________
The above data demonstrates that the use of the thermal dye transfer
receiving elements of the invention results in improved transfer
efficiency as a greater amount of dye is transferred from dye donor
elements used with such receiving elements.
The invention has been described in detail with particular reference to
preferred embodiments thereof, but it will be understood that variations
and modifications can be effected within the spirit and scope of the
invention.
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