Transfer-type electrothermographic recording method and recording medium for use with the same

A transfer-type electrothermographic recording method comprising the steps of uniformly charging an electrothermographic recording layer which exhibits chargeability A at room temperature and chargeability B above room temperature, where the chargeabilities A and B are in the relationship of A>B.gtoreq.0, forming a latent electrostatic image by applying digital thermal signals which correspond to an original image, developing the latent electrostatic image with a toner of which polarity is the same as or opposite to the polarity of the electric charge of the latent electrostatic image to form a toner image, transferring the toner image to a receiving medium, and fixing the toner image transferred on the receiving medium; and a recording medium for use with the transfer-type electrothermographic recording method, comprising the above electrothermographic recording layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a transfer-type electrothermographic recording 
method and a recording mediun for use with the same. 
2. Discussion of Background 
The following methods have been conventionally known as 
electrothermographic recording methods: 
(a) A recording method using a recording medium composed of an 
electroconductive support and a resinous layer formed thereon as disclosed 
in Japanese Patent Publication 35-14722. A resin of which electrical 
resistance is decreased when heated, such as polyvinyl chloride, 
polyethylene, polyester, polystyrene or a styrene - maleic acid copolymer 
is used for the resinous layer. The resinous layer is electrostatically 
charged and then heated by applying heat rays thereto in accordance with 
analogue signals corresponding to an original image, thereby forming an 
electrostatic image on the resinous layer. 
(b) A recording method as disclosed in Japanese Patent Publication 
38-14347. An electrothermographic material which is sufficiently 
transparent to heat rays, such as polyester, chlorinated polyvinyl 
chloride or vinyl chloride, is superposed on an original image and 
electrostatically charged. A latent electrostatic image is formed on the 
electrothermographic material by application of heat rays thereto, and 
reversely developed with a dry toner to form a visible toner image. The 
toner image is then fixed. 
In the above methods, an infrared ray is applied to the recording medium 
which is placed in close contact with an original copy. Therefore, a large 
amount of energy is required for recording, and images with high 
resolution cannot be obtained. In addition, since these recording media 
are made of electrically chargeable materials, they are costly. 
There has also been proposed a recording method in which a latent 
electrostatic image is formed on a photoconductor by application of light 
or on a dielectric material by applying, from a pin electrode, a pulse 
voltage with a polarity opposite to that of the electric charge on the 
dielectric material, and is developed with a toner. The toner image is 
transferred to a sheet of transfer paper and then fixed. This method 
however has shortcomings in that the process is complicated and an 
apparatus for use with the method is expensive. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a 
transfer-type electrothermographic recording method which does not require 
complicated processes, by which digital information can be recorded on 
plain paper without causing deterioration of a recording medium used 
therewith. 
Another object of the present invention is to provide a recording medium 
for use with the above transfer-type electrothermographic recording 
method, which can be produced inexpensively and has high durability. 
The above objects of the present invention can be attained by a 
transfer-type electrothermographic recording method comprising the steps 
of uniformly charging an electrothermographic recording layer which 
exhibits chargeability A at room temperature and chargeability B above 
room temperature, where the chargeabilities A and B are in the 
relationship of A&gt;B.gtoreq.0, forming an electrostatic latent image by 
applying digital thermal signals which correspond to an original image, 
developing the latent electrostatic image with a toner of which polarity 
is the same as or opposite to the polarity of the electric charge of the 
latent electrostatic image to form a toner image, transferring the toner 
image to a receiving medium, and fixing the toner image transferred on the 
receiving medium; and a recording medium for use with the transfer-type 
electrothermographic recording method, comprising an electrothermographic 
recording layer which exhibits chargeability A at room temperature and 
chargeability B above room temperature, where the chargeabilities A and B 
are in the relationship of A&gt;B.gtoreq.0, preferably having a surface with 
a critical surface tension (.gamma.c) of 35 dynes/cm or less.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The recording layer of the recording medium for use with the transfer-type 
electrothermographic recording method according to the present invention 
can be prepared by a thermoplastic resin which exhibits chargeability A at 
room temperature and chargeability B when heated above room temperature, 
where the chargeabilities A and B are in the relationship of A&gt;B.gtoreq.0. 
In addition, it is preferable that the thermoplastic resin have a 
softening point of 30 to 200.degree. C., preferably 60 to 150.degree. C., 
and exhibit an electrical resistance of 1.times.10.sup.10 
.OMEGA..multidot.cm or more at room temperature and 1.times.10.sup.9 
.OMEGA..multidot.cm or less when heated above room temperature. 
Specific examples of the thermoplastic resin usable for the recording layer 
include polyvinyl chloride, polyvinylidene chloride, cellulose acetate, 
polyvinyl alcohol, polyacetal, polycarbonate, a vinyl chloride - vinyl 
acetate copolymer, an ethylene - vinyl acetate copolymer, an acrylic 
polymer, a styrene-based polymer, polyester, polyamide, polyimide, 
polyethylene, polypropylene, a polypropylene-based polymer, perfluoroalkyl 
acrylate, a fluorinated-acryl - acryl copolymer, a silicone polymer such 
as a silicone resin, a silicone rubber, a silicone wax or a silicone oil, 
and a styrene - acryl copolymer. Of these, perfluoroalkyl acrylate, a 
fluorinated-acryl - acryl copolymer, polypropylene, a polypropylene-based 
polymer and a silicone polymer are preferred. 
Examples of the above-mentioned polypropylene-based polymer include a 
polypropylene - ethylene copolymer, a polypropylene - butene copolymer, a 
polypropylene - ethylene - butene terpolymer, a polypropylene - 
vinylacetate copolymer, a polypropylene - ethylacrylate copolymer, and a 
polypropylene - ionomer copolymer. 
It is preferable that the thickness of the electrothermographic recording 
layer be in the range of 5 to 100 .mu.m, preferably 10 to 30 .mu.m. 
Referring now to the accompanying drawings, the present invention will be 
explained in more detail. 
FIGS. 1a and 1b are the schematical cross-sectional views of typical 
embodiments of transfer-type electrothermographic recording media 
according to the present invention. 
The recording medium shown in FIG. 1a is composed of a base layer 1, an 
electrothermographic recording layer 2 and an electroconductive layer 3. 
The electrothermographic recording layer 2 comprises a thermoplastic resin 
having a softening point of 30 to 200.degree. C., preferably 60 to 
150.degree. C., as mentioned previously. 
The base layer 1 which supports the electrothermographic recording layer 2 
comprises a material having filmforming properties, such as polyester, 
vinyl chloride or polyethylene. It is possible to eliminate the base layer 
1 when a material having film-forming or self-supporting properties is 
used for the recording layer 2. 
It is better to form the electroconductive layer 3 on the back surface 
(opposite to the surface on which is overlaid the recording layer 2) of 
the base layer 1 in order to uniformly charge the recording layer 2. 
However, in the case where the recording layer 2 is charged on a metallic 
roller or plate, the electroconductive layer 3 is not necessarily 
required. 
The recording medium shown in FIG. 1b is composed of an 
electrothermographic recording layer 2 provided with an electroconductive 
layer 3. An aluminum-deposition layer with a thickness of 100 to 2000 
.ANG. or a layer treated with an electroconductivity-imparting agent is 
used as the electroconductive layer 3. When a metallic drum or belt is 
used as the electroconductive layer 3, the recording medium can be 
prepared without using a base layer as shown in this figure. 
The transfer-type electrothermographic recordig method according to the 
present invention will now be explained by referring to FIGS. 2a to 2e. 
1. Charging Step (shown in FIG. 2a) 
Corona charging is considered to be the best way to uniformly charge a 
recording layer. However, the following methods are also acceptable in the 
present invention: a method of applying an electric potential to a 
recording medium placed on a metallic roller; and a method of 
triboelectrically charging a recording layer by a brush having an organic 
or inorganic surface, or by a spongy roller. 
In this figure, a recording layer 2 formed on an electroconductive layer 3 
is negatively charged by a negative corona charger 4. 
2. Heating Step (shown in FIG. 2b) 
The recording layer 2 is heated by a thermal head 5, for instance, with a 
heating dot density of 8 dots/mm to 16 dots/mm, controlled by digital 
signals corresponding to an original image. 
In the present invention, a serial or line thermal head of a floating type 
or a bias type which can avoid the reduction of the potential of the 
background of the recording medium when brought into contact therewith is 
used. A bias voltage may be applied to the thermal head, if necessary. 
3. Developing Step (shown in FIG. 2c) 
This step is the same as the conventional developing step which employs a 
dry-type toner or a wet-type developer. 
The development step shown in this figure is a reversal development 
utilizing a repelling electric field generated between the remaining 
charges on the recording layer 2 and a toner 6 having the same polarity as 
the polarity of the charges. 
4. Image Transfer and Fixing Steps (shown in FIG. 2d) 
These steps are also the same as in the ordinary electrography. Namely, the 
toner image is transferred to a receiving medium (transfer paper) 7 with 
application of positive charge to the receiving medium by a positive 
corona charger 12. 
In the case where a dry-type toner is employed for the development, the 
toner image is heated by a thermal roller for fixation. When a wet-type 
developer is used, it is enough to simply dry the existing liquid. 
5. Cleaning Step (shown in FIG. 2e) 
In order to obtain high quality images, the toner remaining on the surface 
of the recording layer 2 is cleaned by a cleaning roller 14. 
By repeating a series of the above steps, digital information can be 
recorded on ordinary paper. 
It is preferable that the surface of the electrothermographic recording 
layer have lubricating properties. When the recording layer has a surface 
which is deficient in lubricating properties, the thermal head cannot 
smoonthly move thereon. As a result, a latent electrostatic image cannot 
be accurately obtained, and the background of recorded images tends to be 
stained. 
The lubricating properties can be imparted to a recording layer by any of 
the following methods: 
(a) A lubricating layer made of a polymer with a critical surface tension 
(.gamma.c) of 35 dynes/cm or less, preferably 30 dynes/cm or less, such as 
a fluorinated-acryl - acryl copolymer, perfluoroalkyl acrylate, a silicone 
polymer or polyethylene, is formed on the recording layer, or these 
materials are employed in the recording layer; 
(b) A lubricating layer made of a material with a critical surface tension 
(.gamma.c) of 35 dynes/cm or less, such as a fatty acid amide, for 
instance, stearic amide or behenic amide, or a wax, for instance, a 
polyethylene wax, is provided on the surface of the recording layer; 
(c) A lubricant is incorporated into the recording layer to make the 
friction coefficient of the surface thereof 0.6 or less, preferably 0.5 or 
less. 
Examples of the lubricant include inorganic fine powders such as silica, 
calcium carbonate, graphite, molybdenum disulfide, tungsten disulfide, 
talc, alumina, kaolin, titanium dioxide, barium sulfate and zeolite, fine 
powders of organic materials such as polystyrene, polymethylmethacrylate, 
polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, a 
benzoguanamine resin, a silicone resin, carboxymethyl cellulose and 
starch, higher fatty acid amides such as oleic amide, stearic amide, 
behenic amide, erucinic amide and elaidic amide, natural waxes, synthetic 
waxes and phosphoric esters; and 
(d) A lubricating layer containing the lubricant mentioned in the above 
item (c), having a friction coefficient of 0.6 or less, preferably 0.5 or 
less, is provided on the surface of the recording layer. 
Specific examples of an electrothermographic recording medium having such 
lubricating properties are shown in FIGS. 3a-3c and FIGS. 4a-4d. 
FIG. 3a is a schematical cross-sectional view of a transfer-type 
electrothermographic recording medium in which a recording layer 15 having 
lubricating properties is formed on an electroconductive layer 3. 
More specifically, a recording layer with a critical surface tension 
(.gamma.c) of 35 dyne/cm or less preferably 30 dyne/cm or less, is formed 
on an electroconductive layer such as an aluminum plate. The 
electroconductive layer can be eliminated when the recording layer is 
charged on a metallic drum. 
FIG. 3b is a schematical cross-sectional view of a transfer-type 
electrothermographic recording medium which is composed of a recording 
layer 2 and a lubricating layer 16 formed thereon. 
More specifically, a lubricating layer comprising stearic amide, behenic 
amide or a polyethylene wax is formed on the surface of the recording 
layer 2, which also serves as a base layer, made of polyethylene, 
polypropylene, polyester, polyvinyl chloride, polyvinylidene chloride, 
cellulose acetate, polycarbonate, nylon, polyvinyl alcohol, polyimide or 
aromatic polyamide. 
FIG. 3c is a schematical cross-sectional view of a transfer-type 
electrothermographic recording medium in which a lubricating layer 16 is 
formed on a recording layer 2 backed with an electroconductive layer 3. 
The recording medium of this type can be prepared by providing an 
electroconductive layer 3, such as an aluminumdeposition layer or an 
ion-treated layer, on the back surface of the recording layer 2 of the 
recording medium as shown in FIG. 3b. 
FIGS. 4a to 4d are schematical cross-sectional views of transfer-type 
electrothermographic recording media comprising the previously-mentioned 
lubricant. 
FIG. 4a shows a recording medium which is composed of a single recording 
layer 17 comprising the lubricant; FIG. 4b shows a recording medium, in 
which a layer 18 comprising the lubricant is formed on a recording layer 
1,2 which also serves as a base layer; FIG. 4c shows a recording medium 
composed of a recording layer 17 comprising the lubricant and an 
electroconductive layer 3; and FIG. 4d shows a recording medium which is 
prepared by providing an electroconductive layer 3 on the back surface of 
the recording layer 1,2 of the recording medium as shown in FIG. 4b. 
Other features of this invention will become apparent in the course of the 
following description of exemplary embodiments, which are given for 
illustration of the invention and are not intended to be limiting thereof. 
EXAMPLE 1 
An electrothermographic recording layer with a thickness of 10 .mu.m and a 
critical surface tension (.gamma.c) of 15 dynes/cm, made of a copolymer of 
fluorinated-acrylate (50 wt. %) and methylmethacrylate (50 wt. %) having a 
softening point of 140.degree. C. was formed on an aluminum drum 9 in an 
apparatus as shown in FIG. 5. 
Thus, transfer-type electrothermographic recording medium No. 1 according 
to the present invention was obtained, which is shown as a recording 
medium 10 in FIG. 5. 
The recording medium 10 was charged by applying a voltage of -5 kV by a 
negative corona charger 4 to make the surface potential thereof -200 V. To 
the charged recording medium 10, a thermal signal (image signal) with a 
thermal energy of 0.5 mJ/dot was applied by a line-type thermal head 5 (8 
dots/mm) with a width of 220 mm to form a latent electrostatic image 
thereon. The latent electrostatic image was developed with a liquid toner 
having a negative polarity for a plain paper copier (hereinafter referred 
to as PPC) (made by Ricoh Company, Ltd.) in a wet-type developing area 8. 
The resulting toner image was transferred to a transfer paper 7 (Trademark 
"Ricoh Type 6000", made by Ricoh Company, Ltd.) for a PPC under 
application of positive charge to the paper by a positive corona charger 
12. The transferred image was thermally fixed by a hot-air fan 11. The 
toner remaining on the recording medium was cleaned by a cleaning roller 
14 made of an electroconductive rubber. 
The optical density of the image thus obtained was measured. The background 
of the recorded image was visually observed whether or not the background 
was stained. Furthermore, the cleanness of the reocrding medium after the 
cleaning was also observed. The results are shown in Table 1. 
EXAMPLE 2 
Transfer-type electrothermographic recording medium No. 1 prepared in 
Example 1 was evaluated by using an apparatus shown in FIG. 6 in the 
following manner: 
The recording medium 10 was charged by a charging roller 13 as the 
recording medium 10 was rotated. The charging roller 13 also served as a 
cleaning roller. An image signal with a thermal energy of of 0.5 mJ/dot 
was applied to the charged recording medium by a thermal head 5 (8 
dots/mm) with a width of 220 mm to form a latent electrostatic image 
thereon. The latent electrostatic image was developed with the same toner 
as used in Example 1 in a wet-type development unit 8 to form a toner 
image. The resulting toner image was transferred to a transfer paper 7 for 
a PPC under application of positive charge to the paper by a positive 
corona charger 12. The transferred image was thermally fixed by a hot-air 
fan 11. The toner remaining on the recording medium was cleaned by the 
roller 13 which was a spongy roller made of urethane, impregnated with a 
carrier liquid of the liquid developer (isoparaffin) used. The charging 
and the cleaning of the recording medium therefore can be conducted at the 
same time in the apparatus shown in FIG. 6. 
The optical density of the image thus obtained was measured. The background 
of the recorded image was visually observed whether or not the background 
was stained. Furthermore, the cleanness of the recording medium after the 
cleaning was also observed. The results are shown in Table 1. 
EXAMPLE 3-7 AND COMATIVE EXAMPLES 1-2 
The procedure for Example 2 was repeated except that the 
electrothermographic recording medium 10 employed in Example 2 was 
replaced by the recording media including the electrothermographic layers 
with the following formulations. 
______________________________________ 
Formulation of Electrothermo- 
Critical Surfac 
graphic Recording Layer 
Tension (.gamma.c) 
Examples 
[Softening Point] (dynes/cm) 
______________________________________ 
Example Fluorinated-acrylate (50 wt. %) 
14 
3 Hydroxyethylmethacrylate 
(50 wt. %) 
[100.degree. C.] 
Example Fluorinated-acrylate (25 wt. %) 
18 
4 Hydroxyethylmethacrylate 
(75 wt. %) 
[110.degree. C.] 
Example Fluorinated-acrylate (30 wt. %) 
20 
5 Methylmethacrylate (70 wt. %) 
[190.degree. C.] 
Example Fluorinated-acrylate (30 wt. %) 
22 
6 Isobutylmethacrylate (70 wt. %) 
[120.degree. C.] 
Example Fluorinated-acrylate (30 wt. %) 
24 
7 2-Ethylhexylmethacrylate 
(70 wt. %) 
[30.degree. C.] 
Compar- Polytetrafluoroethylene 
19 
ative (Teflon) (100 wt. %) 
Example [260.degree. C.] 
Compar- Polymethylmethacrylate 
39 
ative (100 wt. %) 
Example [170.degree. C.] 
2 
______________________________________ 
Thus, transfer-type electrothermographic recording media Nos, 3 to 7 
according to the present invention and comparative ones Nos, 1 and 2 were 
obtained. 
The above recording media were evaluated in the same manner as in Example 
2, The results are shown in Table 1. 
TABLE 1 
______________________________________ 
Optical Stain of Cleanness 
Example Density Background of Medium 
______________________________________ 
1 1.2 none good 
2 1.0 none good 
3 1.2 none good 
4 1.2 none good 
5 0.8 none good 
6 1.1 none good 
7 1.4 slightly practically 
stained acceptable 
Comp. 1 (*) none good 
Comp. 2 1.4 stained poor 
______________________________________ 
Note) *: Recorded image was so vague that the optical density of the imag 
was unmeasureable. 
EXAMPLE 8 
A polypropylene film with a thickness of 20 .mu.m, serving as an 
electrothermographic recording layer, was desposited with aluminum to form 
an electroconductive layer with a thickness of 500 .ANG.. 
Thus, transfer-type electrothermographic recording medium No. 7 according 
to the present invention was obtained. 
The recording medium thus obtained was superposed on the aluminum drum 9 of 
the apparatus shown in FIG. 5 and charged by applying a voltage of -7 kV 
by a negative corona charger 4 to make the surface potential thereof -800 
V. To the charged recording medium, a thermal signal (image signal) with a 
thermal energy of 0.5 mJ/dot was applied by a line-type thermal head 5 (8 
dots/mm) with a width of 220 mm to form a latent electrostatic image 
thereon. The latent electrostatic image was developed with a negative 
liquid toner for a commercially available PPC (made by Ricoh Company, 
Ltd.). The resulting toner image was transferred to a transfer paper 7 
(Trademark "Ricoh Type 6000", made by Ricoh Company, Ltd.) for the PPC 
under application of a voltage of +6 kV to the transfer paper by the 
positive corona charger 12. The transferred image was thermally fixed by 
the hot-air fan 11. The toner remaining on the recording medium was 
cleaned by a cleaning roller 14 made of an electroconductive rubber. 
The toner image thus obtained had an optical density of 1.3, and was sharp. 
The background of the image was not stained at all. The toner remaining on 
the recording medium was thoroughly cleaned by the cleaning roller 14, so 
that the recording medium could be used repeatedly. 
EXAMPLE 9 
An electrothermgraphic recording layer with a thickness of approximately 10 
.mu.m and a critical surface tension (.gamma.c) of 18 dynes/cm, made of a 
fluorinated-acryl - methylmethacrylate copolymer was prepared as 
transfer-type electrothermographic recording medium No. 8 according to the 
present invention, and was evaluated by using the apparatus shown in FIG. 
6 in the following manner: 
The recording medium was superposed on the aluminum drum 9 and was charged 
to make the surface potential thereof -300 V by a charging roller 13 made 
of a porous urethane rubber, which also served as a cleaning roller. An 
image signal with a thermal energy of 0.5 mJ/dot was applied to the 
charged recording layer by a thermal head 5 (8 dots/m) with a width of 220 
mm to form a latent electrostatic image thereon. The latent electrostatic 
image was developed with the same toner as used in Example 1 to form a 
toner image. The resulting toner image was transferred to a transfer paper 
7 for a PPC (made by Ricoh Company, Ltd.) under application of a voltage 
of +1.2 kV to the transfer paper by a positive corona charger 12. The 
transferred image was thermally fixed by the hot-air fan 11. The toner 
remaining on the recording medium was cleaned by the roller 13 which was a 
spongy roller made of urethane, impregnated with a carrier liquid of the 
liquid toner (isoparaffin). 
The toner image thus obtained had an optical density of 1.0, and was sharp. 
The background of the image was not stained at all. The toner remaining on 
the recording medium was thoroughly cleaned by the cleaning roller 13. 
EXAMPLE 10 
A lubricating layer, made of a polyethylene wax, with a thickness of 3 
.mu.m and a critical surface tension (.gamma.c) of 31 dynes/cm was formed 
on a polyester film with a thickness of 9 .mu.m, serving as an 
electrothermographic recording layer, backed with a 500 .ANG. 
electroconductive aluminum-deposition layer. 
Thus, transfer-type electrothermographic recording medium No. 9 according 
to the present invention was obtained. 
The recording medium thus obtained was evaluated by using an apparatus 
shown in FIG. 7 in the following manner: 
The recording medium was made in the form of a roll and wound around a feed 
roller 24. This recording medium was fed onto a platen drum 25 by the feed 
roller 24 and charged by applying a voltage of -7 kV by a negative corona 
charger 4 to make the surface potential thereof -500 V. To the charged 
recording medium, a thermal signal (image signal) with a thermal energy of 
0.5 mJ/dot was applied by a thermal head 5 (8 dots/mm) with a width of 220 
mm to form a latent electrostatic image thereon. The latent electrostatic 
image was developed with a dry toner containing a cyan powder having a 
negative polarity for a color copying machine (Trademark "Ricoh Color 
5000", made by Ricoh Company, Ltd.) by a brush developing roller 20. The 
resulting toner image was transferred to a transfer paper 7 (Trademark 
"Ricoh Type 6000", made by Ricoh Company, Ltd.) for a PPC under 
application of a voltage of +6 kV to the transfer paper by a positive 
corona charger 12. The transferred image was fixed by an image fixing 
roller 28. 
The toner image thus obtained had an optical density of 1.4, and was sharp. 
The background of the image was not stained at all. 
EXAMPLE 11 
A lubricating layer with a thickness of 2 .mu.m, made of behenic amide 
having a critical surface tension (.gamma.c) of 29 dynes/cm, was formed on 
a polypropylene film with a thickness of 20 .mu.m, serving as an 
electrothermographic recording layer. 
Thus, transfer-type electrothermographic recording medium No. 10 according 
to the present invention was obtained. 
This recording medium was made in the form of a roll and wound around the 
feed roller 24 in the apparatus shown in FIG. 7 and was evaluated in the 
same manner as in Example 10 by use of the apparatus except that image 
formation was performed with the surface potential of the recording medium 
was set at -600 V. 
The toner image obtained had an optical density of 1.5, and was sharp. The 
background of the image was not stained at all. 
EXAMPLE 12 
A lubricating layer with a thickness of 2 .mu.m, made of a stearic amide 
having a critical surface tension (.gamma.c) of 32 dynes/cm, was formed on 
a polypropylene film with a thickness of 20 .mu.m, serving as an 
electrothermographic recording layer. 
Thus, transfer-type electrothermographic recording medium No. 11 according 
to the present invention was obtained. 
The recording medium thus obtained was evaluated in the same manner as in 
Example 11. 
The toner image obtained had an optical density of 1.5, and was sharp. The 
background of the image was not stained at all. 
EXAMPLE 13 
A polypropylene film with a thickness of 20 .mu.m containing 0.15 wt. % of 
erucinic amide having a critical surface tension of 34 dynes/cm, serving 
as an electrothermographic recording layer, was prepared as transfer-type 
electrothermographic recording medium No. 12 according to the present 
invention. 
This recording medium was diretly wound around the aluminum drum 9 in the 
apparatus shown in FIG. 5. The recording layer was charged by applying a 
voltage of -6 kV by the negative corona charger 4 to make the surface 
potential thereof -500 V. To the charged recording layer, a thermal signal 
(image signal) with a thermal energy of 0.5 mJ/dot was applied by a 
line-type thermal head 5 (8 dots/mm) with a width of 220 mm to form a 
latent electrostatic image thereon. The latent electrostatic image was 
developed with a negative liquid toner for a commercially available PPC 
(made by Ricoh Company, Ltd.). The resulting toner image was transferred 
to a transfer paper 7 (Trademark "Ricoh Type 6000", made by Ricoh Company, 
Ltd.) for the PPC under application of a voltage of +6 kV to the transfer 
paper by the positive corona charger 12. The transferred image was 
thermally fixed by the hot-air fan 11. The toner remaining on the 
recording medium was cleaned by the cleaning roller 14 made of an 
electroconductive rubber. 
The toner image thus obtained had an optical density of 1.2, and was sharp. 
The background of the image was not stained at all. 
EXAMPLE 14 
A polyester resin film with a thickness of approximately 1 .mu.m containing 
5 wt. % of silica having a friction coefficient of 0.4, serving as an 
electrothermographic recording layer, was formed on a polyester film with 
a thickness of 50 .mu.m backed with a 500 .ANG. aluminum-deposition layer, 
serving as a base layer provided with an electroconductive layer. 
Thus, transfer-type electrothermographic recording medium No. 13 according 
to the present invention was obtained. 
The recording medium thus obtained was evaluated by using the apparatus 
shown in FIG. 5 in the same manner as in Example 13. 
The toner image obtained had an optical density of 1.3, and was sharp. The 
background of the image was not stained at all. 
EXAMPLE 15 
A low-density polyethylene film with a thickness of 25 .mu.m containing 
0.05 wt. % of oleic amide having a critical surface tension of 33 
dynes/cm, serving as an electrothermographic recording layer, was prepared 
as transfer-type electrothermographic recording medium No. 14 according to 
the present invention. 
The thus prepared recording medium was made in the form of a roll and 
evaluated by use of an apparatus as shown in FIG. 8. 
The recording medium was wound around a feed roller 24 and fed onto a 
platen drum 25 via a charging roller 19 made of an electroconductive 
rubber, a thermal head 5 (8 dots/mm) and a development roller 20, and 
transported up to a take-up roller 23 as shown in FIG. 8. A recording 
layer 10 of this recording medium was charged by applying a voltage of 
-1.2 kV by the charging roller 19 to make the surface potential thereof 
-700 V. To the charged recording layer, a thermal signal (image signal) 
with a thermal energy of 0.5 mJ/dot was applied by the thermal head 5 with 
a width of 220 mm to form a latent electrostatic image thereon. The latent 
electrostatic image was developed with a liquid toner by the development 
roller 20. The resulting toner image was transferred to a transfer paper 7 
(Trademark "Ricoh Type 6000", made by Ricoh Company, Ltd.) under 
application of a voltage of +1.0 kV to the transfer paper.degree. The 
transferred image was thermally fixed. 
The toner image thus obtained had an optical density of 1.2, and was sharp. 
The background of the image was not stained at all. 
EXAMPLE 16 
The procedure for Example 7 was repeated except that the surface potential 
of the recording medium was set at -600 V and a thermal signal (image 
signal) with a thermal energy of 0.5 mJ/dot was applied by a line-type 
thermal head 5 (8 dots/mm) with a width of 220 mm under application of a 
bias voltage of -600 V to the thermal head. The surface potential in the 
thermal-signal-applied area of the recording medium was about -50 V and 
the surface potential in the background thereof was maintained at -600 V 
without any decrease thereof during the recording process. 
The toner image thus obtained had an optical density of 1.3, and was sharp. 
The background of the image was not stained at all.