Slipping layer binder for dye-donor element used in thermal dye transfer

A dye-donor element for thermal dye transfer comprising a support having on one side thereof a dye layer and on the other side a slipping layer comprising an aminoalkyl(dialkylsilyl)-terminated poly(dialkyl siloxane) in a polymeric binder, the improvement wherein said polymeric binder comprises a poly(vinyl acetal) having more than 60 mole % acetal units which is formed from poly(vinylalcohol) and acetaldehyde or formaldehyde.

This invention relates to dye donor elements used in thermal dye transfer, 
and more particularly to the use of a certain poly(vinyl acetal) binder 
for silicone-containing slipping layers on the back side thereof. 
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. 
A problem has existed with the use of dye-donor elements for thermal 
dye-transfer printing because a thin support is required in order to 
provide effective heat transfer. For example, when a thin polyester film 
is employed, it softens when heated during the printing operation and then 
sticks to the thermal printing head, preventing donor transport. A 
slipping layer is typically provided to facilitate passage of the 
dye-donor under the thermal printing head. A defect in the performance of 
that layer causes intermittent rather than continuous transport across the 
thermal head. The dye transferred thus does not appear as a uniform area, 
but rather as a series of alternating light and dark bands (chatter 
marks). 
U.S. Pat. No. 4,753,920 discloses certain polymeric binders, such as 
cellulose acetate propionate, for use with amino-modified silicones as a 
slipping layer for a thermal dye transfer element. While this slipping 
layer has been useful in a number of applications, some problems have 
developed with this slipping layer when it is used with certain newer 
thermal print heads such as TDK thermal Head LV5404A 1A0008, which employ 
an inexpensive, acid-sensitive, soft ceramic glaze over the heating 
elements of the heat. Such a ceramic glaze may contain lanthanum and 
nitrogen in addition to silicon and oxygen. One problem with the prior art 
slipping layers when used with these newer thermal print heads is a 
permanent build-up of debris on the head that cannot be removed by 
cleaning with organic solvents and which causes scratches in the printed 
copy. In addition, without frequent cleaning of the heating line, these 
slipping layers can cause corrosion of the glaze by producing acidic 
products on heating which can attack the ceramic glaze and can also lead 
to build-up of debris on the head. 
It is an object of this invention to eliminate or reduce the above 
problems. It is another object of this invention to provide a slipping 
layer which has lower friction when compared to other prior art slipping 
layers. 
These and other objects are achieved in accordance with this invention 
which comprises a dye-donor element for thermal dye transfer comprising a 
support having on one side thereof a dye layer and on the other side a 
slipping layer comprising an aminoalkyl(dialkylsilyl)-terminated 
poly(dialkyl siloxane) in a polymeric binder, the improvement wherein the 
polymeric binder comprises a poly(vinyl acetal) having more than 60 mole % 
acetal units which is formed from poly(vinylalcohol) and acetaldehyde or 
formaldehyde. 
In a preferred embodiment of the invention, the 
aminoalkyl(dialkylsilyl)-terminated poly(dialkyl siloxane) has the 
following formula: 
##STR1## 
where m is from 3 to 6, n is from 10 to 2,000, p is from 0 to about 2,000 
and R.sub.1 -R.sub.6 are alkyl groups having from 1 to about 6 carbon 
atoms. In another preferred embodiment, R.sub.1 -R.sub.6 are each methyl, 
m is 3 and p is 0. This material is supplied commercially from Petrarch 
Systems, Inc. as PS513. 
In another preferred embodiment of the invention, the 
aminoalkyl(dialkylsilyl)-terminated poly(dialkyl siloxane) is a 
T-structure poly(dimethyl siloxane) with an aminoalkyl functionality at 
the branchpoint, such as one having the following formula: 
##STR2## 
where m is from 1 to 10 and n is from 10 to 1000. This material is 
supplied commercially from Petrarch Systems, Inc. as PS054. 
In another preferred embodiment of the invention, the slipping layer also 
contains another siloxane which is a copolymer of a polyalkylene oxide and 
a methylalkylsiloxane, such as a copolymer of polypropylene oxide and 
poly(methyl octyl siloxane), such as BYK 320 (50% in Stoddard solvent) or 
BYK S732 (98% in Stoddard solvent) from BYK Chemie, USA. 
The poly(vinyl acetal) employed in this invention is composed of at least 
60 mole % acetal units with the balance being predominantly vinyl alcohol 
units. Poly(vinyl acetal) has the following structure: 
##STR3## 
wherein x + y + z =100 (mole %). 
The component mers can be varied widely to give a polymer termed a 
poly(vinyl acetal). The optimal material is high in acetal units and low 
in vinyl acetate units. Useful compositions for this invention would have 
at least 60 mole % acetal units and no more than 20 mole % of acetate 
units. The optimal composition would have at least 70 mole % acetal units 
with the balance being vinyl alcohol units. The glass transition 
temperature of the optimal polymer would be about 110.degree. C. 
Poly(vinyl acetal) may be synthesized by reaction of acetaldehyde with 
poly(vinyl alcohol) such as Vinol 107.RTM. (Air Products and Chemicals 
Inc.). 
The siloxanes defined above can be employed in the invention herein at any 
concentration useful for the intended purpose. In general, good results 
have been obtained at a concentration of about 0.05 to about 1.0 
g/m.sup.2, preferably about 0.3 to about 0.6 g/m.sup.2, with or without a 
binder. 
Any dye can be used in the dye layer of the dye-donor element of 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. Examples of sublimable dyes include anthraquinone dyes, e.g., 
Sumikalon Violet RS.RTM. (Sumitomo Chemical Co., Ltd.), Dianix Fast Violet 
3R FS.RTM. (Mitsubishi Chemical Industries, Ltd.), and Kayalon Polyol 
Brilliant Blue N BGM.RTM. and KST Black 146.RTM. (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. (Nippon Kayaku Co., 
Ltd.), Sumickaron Diazo Black 5G.RTM. (Sumitomo Chemical Co., Ltd.), and 
Miktazol Black 5GH.RTM. (Mitsui Toatsu Chemicals, Inc.); direct dyes such 
as Direct Dark Green B.RTM. (Mitsubishi Chemical Industries, Ltd.) and 
Direct Brown M.RTM. and Direct Fast Black D.RTM. (Nippon Kayaku Co. Ltd.); 
acid dyes such as Kayanol Milling Cyanine 5R.RTM. (Nippon Kayaku Co. 
Ltd.); basic dyes such as Sumicacryl Blue 6G.RTM. (Sumitomo Chemical Co., 
Ltd.), and Aizen Malachite Green.RTM. (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. 
A dye-barrier layer may be employed in the dye-donor elements of the 
invention to improve the density of the transferred dye. Such dye-barrier 
layer materials include hydrophilic materials such as those described and 
claimed in U.S. Pat. No. 4,716,144 by Vanier, Lum and Bowman. 
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. 
Any material can be used as the support for the dye-donor element of the 
invention provided it is dimensionally stable and can withstand the heat 
of the thermal printing heads. Such materials include polyesters such as 
poly(ethylene terephthalate); polyamides; polycarbonates; glassine paper; 
condenser paper; cellulose esters such as cellulose acetate; fluorine 
polymers such as poly(vinylidene fluoride) or 
poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as 
polyoxymethylene; polyacetals; polyolefins such as polystyrene, 
polyethylene, polypropylene or methylpentene polymers; and polyimides such 
as polyimide amides and polyetherimides. The support generally has a 
thickness of from about 2 to about 30 .mu.m. It may also be coated with a 
subbing layer, if desired, such as those materials described in U.S. Pat. 
No. 4,695,288 or U.S. Pat. No. 4,737,486. 
The dye-receiving element that is used with the dye-donor element of the 
invention usually comprises a support having thereon a dye image receiving 
layer. The support may be a transparent film such as a poly(ether 
sulfone), a polyimide, a cellulose ester such as cellulose acetate, a 
poly(vinyl alcohol-co-acetal) or a poly(ethylene terephthalate). The 
support for the dye-receiving element may also be reflective such as 
baryta-coated paper, polyethylene-coated paper, white polyester (polyester 
with white pigment incorporated therein), an ivory paper, a condenser 
paper or a synthetic paper such as duPont Tyvek.RTM.. 
The dye image-receiving layer may comprise, for example, a polycarbonate, a 
polyurethane, a polyester, poly(vinyl 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. 
As noted above, the dye donor 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 of the invention 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 or may have alternating areas of other different 
dyes, such as sublimable cyan and/or magenta and/or yellow and/or black or 
other dyes. Such dyes are disclosed in U.S. Pat. Nos. 4,541,830; 
4,698,651; 4,695,287; 4,701,439; 4,757,046; 4,743,582; 4,769,360 and 
4,753,922, the disclosures of which are hereby incorporated by reference. 
Thus, one-, two-, three- or four-color elements (or higher numbers also) 
are included within the scope of the invention. 
In a preferred embodiment of the invention, the dye-donor element comprises 
a poly(ethylene terephthalate) support coated with sequential repeating 
areas of yellow, cyan and magenta 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. 
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 is repeated. The third color is 
obtained in the same manner. 
The following examples are provided to illustrate the invention.

EXAMPLE 1 
Preparation of Poly(vinyl acetal) 
440 g of VINOL 107.RTM. were added to 5580 g of distilled water and heated 
to 90.degree. C. for one hour to give a clear solution. The solution was 
cooled to 10.degree. C., 1300 g of 36% hydrochloric acid was added, and 
the mixture cooled to 10.degree. C. Acetaldehyde (274 g) was added with 
vigorous stirring. The mixture was stirred at 10.degree. C. for 10 minutes 
and became milky; a finely divided precipitate began to be formed. The 
mixture was stirred at 10.degree. C. for an additional 15 minutes and then 
warmed and kept 4 hrs. at a temperature of 30.degree. C. The finely 
divided white solid was filtered off and washed twice for 30 minutes with 
4L. of distilled water. The solid was washed a third time with 4L. of 
distilled water and the pH of the wash was adjusted with 10% sodium 
hydroxide until a constant pH of 7 was obtained. The solid was collected 
by filtration and dried in a vacuum oven at 40.degree. C. to give 487 g of 
a white product. NMR analysis showed the composition to be 75 mole % 
acetal and 25 mole % vinyl alcohol units. 
EXAMPLE 2 
Comparison of Slip Layers For Debris Transferred to Thermal Head and 
Propensity to Produce Scratches in the Printed Copy 
Poly(vinyl acetal) was compared to cellulose acetate propionate as a binder 
for the slip layer in the following experiment. 
A multicolor dye-donor was prepared by gravure coating on a 6 .mu.m 
poly(ethylene terephthalate) support: 
(1) a subbing layer of titanium alkoxide (DuPont Tyzor TBT).RTM.(0.13 
g/m.sup.2) from n-propyl acetate and n-butyl alcohol mixture, and 
(2) a dye layer containing the first yellow dye illustrated above (0.26 
g/m.sup.2) and Shamrock S363 N-1.RTM. polypropylene wax micronized powder 
(Shamrock Chemicals Corporation) (0.011 g/m.sup.2) in a cellulose acetate 
propionate (2.5% acetyl, 45% propionyl) binder (0.34 g/m.sup.2) coated 
from a toluene, methanol and cyclopentanone solvent mixture. 
(3) a dye layer containing the magenta dyes illustrated above (0.15 and 
0.14 g/m.sup.2 respectively) and Shamrock S363 N-1.RTM. polypropylene wax 
micronized powder (Shamrock Chemicals Corporation)(0.11 g/m.sup.2) in a 
cellulose acetate propionate (2.5% acetyl, 45% propionyl) binder (0.26 
g/m.sup.2) coated from the same solvent mixture as for the yellow dye. 
(4) a dye layer containing the cyan dyes illustrated above (0.37 and 0.11 
g/m.sup.2 respectively) and Shamrock S363 N-1.RTM. polypropylene wax 
micronized powder (Shamrock Chemicals Corporation)(0.021 g/m.sup.2) in a 
cellulose acetate propionate (2.5% acetyl, 45% propionyl) binder as above 
(0.35 g/m.sup.2) coated from the same solvent mixture as for the yellow 
dye above. 
On the back side of the dye-donor was coated: 
(1) a subbing layer of titanium alkoxide (DuPont Tyzor TBT).RTM.(0.13 
g/m.sup.2) from n-propyl acetate and n-butyl alcohol mixture, and 
(2) a slipping layer containing the amino-propylsilyl-terminated 
polysiloxane described below (0.011 g/m.sup.2) neutralized with 0.0003 
g/m.sup.2 p-toluenesulfonic acid and the poly(propylene oxide methyl octyl 
siloxane copolymer BYK 320 (from BYK 
Chemie, USA) (0.0054-0.0081 g/m.sup.2) in the binders each at 0.54 
g/m.sup.2 indicated below. 
PS 513 [aminopropyl-dimethyl-terminated poly(dimethyl siloxane)]is 
available commercially from Huls America Inc. (27000 molecular weight and 
2000 viscosity). 
Control Binder-- Cellulose acetate propionate (2.5% acetyl, 45% propionyl) 
was coated from a toluene, methanol and cyclopentanone mixture. 
Invention Binder-- Poly(vinyl acetal), 75 mole % acetal and 25 mole % vinyl 
alcohol units coated using the same solvent mixture as for the control. 
A dye-receiving element was prepared by coating the following layers in the 
order recited on a titanium dioxide-pigmented polyethylene-overcoated 
paper stock which was subbed with a layer of Dow Z6020.RTM., (an 
aminoalkyl alkoxy silane from Dow Chemical USA) (0.11 g/m.sup.2) coated 
from ethyl alcohol: 
(1) a dye-receiving layer of Makrolon 5700.RTM. (Bayer AG Corporation) 
polycarbonate resin (1.6 g/m.sup.2), a bisphenol A polycarbonate as 
described in U.S. Pat. No. 4,927,803 (1.6 g/m.sup.2), diphenyl phthalate 
(0.32 g/m.sup.2), dibutyl phthalate (0.32 g/m.sup.2) and surfactant 
FC-431.RTM. (3M Corp.) (0.011 g/m.sup.2) coated from methylene chloride. 
(2) overcoat layer of a polycarbonate of diethylene glycol (49.7 mole %), 
bisphenol A (49.8 mole %) and a bis(aminopropyl-terminated)-poly(dimethyl 
siloxane) (0.5 mole-%) (0.22 g/m.sup.2), FC431.RTM. surfactant (3M Corp.) 
(0.032 g/m.sup.2) and DC-510.RTM. surfactant (Dow Corning) (0.016 
g/m.sup.2) coated from methylene chloride. 
The dye side of the dye-donor element strip, approximately 13 cm .times.21 
cm in area, was placed in contact with the dye image-receiving layer of 
the dye-receiver element of the same area. The assemblage was suitably 
positioned between a 19.8 mm diameter rubber roller and a TDK Thermal Head 
(No. LV 540A, 1A0008). The head (thermostatted at 30.degree. C) was 
pressed with a force of 36 N against the dye-donor element side of the 
assemblage pushing the latter against the rubber roller. 
The imaging electronics were activated causing the donor/receiver 
assemblage to be advanced between the printing head and the roller at 5.0 
mm/sec. Coincidentally the resistive elements in the thermal print head 
were pulsed for 128 msec/pulse at 133 msec intervals during the 17 
msec/dot printing time. The voltage supplied to the print head was 13.3 
volts, resulting in an instantaneous peak power of 0.047 watts/dot and a 
maximum total energy of 0.33 mjoules/dot. The printed area was divided 
into two images approximately equal in size. One was a low-density, 
continuous tone portrait of an individual, the other image was a stepped 
density chart consisting of eleven 0.9.times.1.1 mm steps repeated eight 
times in a particular pattern. 
For the control and for the invention, 25 three-color prints were made. The 
condition of the heating line of the thermal head was documented by making 
photomicrographs at 78.times. magnification at specific points before and 
after printing the 25 prints. The amount of debris was noted as well as 
the condition of the surface at the heating line. Next, the effectiveness 
of cleaning the heating line to remove any debris was assessed. Cleaning 
was done alternately with acetone and water using a Kimwipe 
(Kimberly-Clark Corp.) to wipe the heating line. The prints were also 
visually examined for scratches. The following results were obtained. 
TABLE 1 
______________________________________ 
Amount of Result of 
Debris on Cleaning 
Heating Line 
Heating Line 
After 25 After 25 Scratches 
Slip Layer Prints prints Print 25 
______________________________________ 
CONTROL heavy; residue 34 
corrosion persisted 
appeared 
INVENTION light; no debris 0 
corrosion removed 
______________________________________ 
The above results indicate that the slipping layer according to the 
invention sharply reduced head debris and print scratches in the printing 
format employed. The slip layer of the invention also did not corrode the 
head glaze and allowed one to easily clean off the minimal debris found on 
the heating line. 
EXAMPLE 3 
Silicone variations, Force Measurement 
Three-color dye-donors with poly(vinyl acetal) slipping layers were 
prepared as described in Example 2 as follows: 
______________________________________ 
a) Invention A slipping layer 
PS513 at 0.008 g/m.sup.2 as only siloxane 
lubricant present. 
b) Invention B slipping layer 
PS513 at 0.011 g/m.sup.2 and BYK S732 at 
0.0008 g/m.sup.2. 
______________________________________ 
In the comparative examples (Comparisons 1-6), various silicones were used 
in place of PS513 in the slipping layer. The slipping layers were coated 
from 3-pentanone/methanol at 75/25 weight %. BYK S732 was used instead of 
BYK 320. Only the cyan areas were used for this evaluation. A dye receiver 
identical to the one described above was also used. 
The dye side of the dye-donor element strip, approximately 12.7 cm 
.times.21.6 cm was placed in contact with the dye image receiving layer of 
the dye receiver element of the same area. The assemblage was placed 
between a stepper-motor-driven 19.8mm diameter rubber roller and a TDK 
Thermal Head (LV540A) (thermostatted at 45.degree. C.). The head was 
pressed with a force of 5.0 kg against the dye-donor element side of the 
assemblage pushing it against the rubber roller. 
The imaging electronics were activated causing the donor-receiver 
assemblage to be drawn between the printing head and roller at 5 mm/sec. 
Coincidentally, the resistive elements in the thermal print head were 
pulsed for 29 g/m.sup.2 msec/pulse at 133 msec intervals during the 17 
msec/dot printing time. A stepped density image was generated by 
incrementally increasing the number of pulses/dot from 0 to 128. The 
voltage supplied to the print head was approximately 13.3 volts, resulting 
in an instantaneous peak power of 0.047 watts/dot and a maximum total 
energy of 0.33 mjoules/dot. 
As each "area test pattern" of given density was being generated, the force 
required to move the assemblage between the print head and the roller was 
measured using an S. Himmelstein Corp. 3-08TL(16-1) Torquemeter R (11.5 
cm-kg range and a Model 6-488B Conditioning Module R. Data were obtained 
at minimum density (0 pulses) (D-min) and at maximum density (128 
pulses)(D-max). The following results were obtained: 
TABLE 2 
______________________________________ 
RELATIVE FORCE 
SLIPPING (Kg) 
LAYER D-min D-max 
______________________________________ 
Invention A 0.50 0.86 
Invention B 0.45 0.68 
Comparison 1 2.54 2.09 
Comparison 2 1.82 2.04 
Comparison 3 stuck to head at Dmax 
Comparison 4 stuck to head at Dmax 
Comparison 5 1.73 1.32 
Comparison 6 2.45 2.36 
Comparison 7 0.59 1.41 
______________________________________ 
The polysiloxanes used in conjunction with BYK S732 in Comparisons 1-6 
were: 
Comparison 1. PS 043 (Huls America), trimethoxysiloxy-terminated 
polydimethylsiloxane. 
Comparison 2. PSW2804 (Huls America), aminopropyldimethyl-terminated 
poly(methyl phenyl siloxane). 
Comparison 3. PS342.5 (Huls America), silanol terminated 
polydimethylsiloxane. 
Comparison 4. PS130 (Huls America), polymethyloctadecylsiloxane. 
Comparison 5. PS137 (Huls America), copolymer of (48-58%) methyl phenethyl 
siloxane and (52-42%) methyl hexyl siloxane. 
Comparison 6. PS096.5 (Huls America), 
dimethylsiloxane-.alpha.-methylstyrene block copolymer. 
The above materials were coated at 0.011 g/m.sup.2 with 0.008 g/m.sup.2 BYK 
S732 (BYK Chemie Corp.) in the slipping layer. 
Comparison 7. BYK S732 only at 0.008 g/m.sup.2. 
The data in Table 2 show the uniqueness of Inventions A and B in that 
exceptionally low friction was observed with these slipping layers. A 
number of other polysiloxanes used with BYK S732 showed high friction or 
simply stuck to the printing head. Comparison 2 showed that not all 
aminopropyl-terminated polysiloxanes produce low friction like that of the 
invention. The data also showed that BYK S732 alone did not yield the low 
friction of the invention particularly when Dmax was printed. 
EXAMPLE 4 
Variations in Binder Composition 
A three-color donor was coated as in Example 2. A receiver was coated as 
described in Example 1 of U.S. Pat. No. 4,782,041. The friction force of 
the donor against the printing head was measured as described in Example 1 
of U.S. Pat. No. 4,782,041. Slipping layers were coated with poly(vinyl 
acetal) variations at 0.54 g/m.sup.2, PS513 at 0.011 g/m.sup.2 and BYK 
S732 at 0.0081 g/m.sup.2 on a Tyzor TBT.RTM. (DuPont Corp.) subbing layer 
opposite from the dye side of the donor. 
Binders A-J are poly(vinyl acetals). A-G were coated from ethyl 
acetate/methanol (85/15 wt.-%) so were K-M. H-J were coated from 
methanol/water (95/5 wt. %). K and L were poly(vinyl butyrals) (Butvar-76 
and Butvar-98 respectively). Binder M was a poly(vinyl propional). Binder 
N was Formvar 5/95E poly(vinyl formal) (Monsanto Co.) and was coated from 
toluene/methanol/water to produce a very hazy nonuniform coating. The cyan 
dye transfer to the slip layer was measured after heating the dye-donor 
wound on a 21 mm diameter wooden dowel for 3 days at 60.degree. C. and 70% 
R.H. The cyan dye transferred to the back of the yellow dye patch was 
determined by measurement of the total red transmission density and 
subtracting the red density of the yellow patch. The following results 
were obtained: 
TABLE 3 
______________________________________ 
Composition Mole % Retransfer 
Friction 
Binder 
Acetal Alcohol Acetate Density force (kg) 
______________________________________ 
A 75 25 0 0.11 0.39 
B 84 16 0 0.04 0.38 
C 77 15 8 0.13 0.38 
D 64 18 18 0.08 0.43 
E 50 22 28 0.32 0.37 
F 37 29 34 0.68 0.33 
G 65 0 35 0.14 0.58 
H 44 56 0 0.04 1.95 
I 43 44 13 0.18 1.45 
J 31 53 16 0.27 1.54 
K 69 31 0 0.66 0.36 
L 55 45 0 1.11 0.36 
M 63 37 0 0.60 0.36 
N 76 11 14 0.07 0.43 
______________________________________ 
The data in Table 3 show that the best compositions for the poly(vinyl 
acetal) are those high in acetal units and low in acetate. Such a binder 
provides a slip layer which shows low friction and minimizes transfer of 
dye from the dye side to the slip layer during storage at an elevated 
temperature (60.degree. C.). The data also show that poly(vinyl acetal) is 
superior to the higher aliphatic polymeric acetals which have much lower 
glass transition temperatures. Formvar (Monsanto) was inferior to 
poly(vinyl acetal) because of its limited solubility in organic solvents 
suitable for gravure coating and its tendency to give hazy nonuniform 
coatings with the addenda and solvents used here. 
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.