Image forming apparatus

An image supporting medium coated with microcapsule toner particles is exposed according to an image pattern, and then a latent image is formed thereon. The image supporting medium on which the latent image is formed and the image recording paper are superposed and pressurized, and the microcapsule toner particles are ruptured and the contents included therein are released. During this process, hardened microcapsule toner particles and wall material of the ruptured microcapsule toner particles from which the contents flowed remain on the image supporting medium by a keying effect, and only the contents, i.e. the toner, are transferred onto the image recording paper. Moreover, the critical surface tension of the wall material of the microcapsule toner particles is smaller than the surface tension of the contents of the microcapsule toner particles. Further, the surface tension of the contents of the microcapsule toner particles is smaller than the critical surface tension of the image recording paper confronting with the image supporting medium. Thus, only the contents of the microcapsules, i.e. the toner, are transferred to the image recording paper. Therefore, a clear and accurate image is formed thereon.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image forming apparatus, and more 
particularly to an image forming apparatus which uses photosensitive 
microcapsule toner particles. 
2. Description of Related Art 
It is well known to provide an image forming apparatus which uses a 
photosensitive medium coated with microcapsules comprising a dyeprecursor 
and a photo hardening material, etc. For example, such an image forming 
apparatus is disclosed in U.S. Pat. No. 4,399,209 in which the 
photosensitive medium is exposed based on image information, the 
microcapsules coated thereon are hardened, and then a latent image is 
formed on the photosensitive medium. Afterwards, an image forming paper 
coated with developer, which reacts with the dyeprecursor and makes color, 
is overlapped with the photosensitive medium and pressure is applied. The 
latent image is developed by applying such pressure, and an image is fixed 
on the image forming paper. 
Further, U.S. Pat. No. 4,943,509 discloses another image forming apparatus 
using the above photosensitive medium. In the apparatus, a photosensitive 
medium on which a latent image is formed and an image forming paper which 
is an ordinary paper are overlapped putting a developer layer between 
them, and are pressurized, so that an image is formed on the ordinary 
paper. U.S. Pat. No. 5,060,011 shows a similar apparatus. 
Furthermore, another image forming apparatus which uses a photosensitive 
medium which supports the microcapsules utilizes a coloring agent instead 
of the dyeprecursor discussed above, as disclosed in U.S. Pat. No. 
4,783,683 (Japanese Laid-Open Patent Publication No. 62-232652). A 
recording material including a coloring agent is disclosed in detail in 
U.S. Pat. No. 4,912,011. 
However, each photosensitive medium used in the above image forming 
apparatuses includes a plastic film layer such as PET (polyethylene 
terephthalate) film as a supporting layer with photosensitive 
microcapsules provided thereon. This kind of photosensitive medium is used 
as a member for aiding image formation and is disposed after use. 
Therefore, in conventional image forming apparatuses, the plastic film 
used as the supporting layer, which is not essential to form the image, is 
consumed in each use. Therefore, the cost for disposable photosensitive 
medium supplies is high. Thus, the whole cost for forming the image is 
increased. 
Ideally, a reusable photosensitive supporting medium from which the 
photosensitive microcapsules could easily separate would be desirable in 
order to reduce costs. However, a clear and accurate image must still be 
formed. If the microcapsules easily separate from the supporting medium, a 
blurred image will occur since all of the microcapsule material, including 
the ruptured walls and hardened microcapsules along with the toner, will 
transfer to the image recording medium. Thus, it has not been possible to 
provide a reusable photosensitive supporting medium which creates a clear 
and accurate image. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention is to provide an image 
forming apparatus which will transfer only the contents of the 
microcapsules to an image recording medium and which will form a clear and 
accurate printed image thereon. 
In order to attain the above and other objects, an image forming apparatus 
according to the present invention comprises an image supporting medium 
having microcapsule toner particles coated thereon, each said microcapsule 
toner particle comprising a microcapsule wall and flowable contents 
contained therein; an image recording medium; exposure means for forming a 
latent image of an original on the image supporting medium by hardening 
selected microcapsule toner particles corresponding to the latent image; 
and pressure developing means for applying pressure to the image 
supporting medium to rupture non-hardened microcapsule toner particles and 
for transferring the flowable contents to the image recording medium; 
wherein the hardened microcapsules and the ruptured microcapsule walls 
remain on the image supporting medium while the flowable contents are 
transferred to the image recording medium. 
In the image forming apparatus of the present invention thus constructed, 
when pressure is added to the supporting member on which the microcapsule 
toner particles are supported based on an original image, the contents, 
i.e. toner, flow out from the microcapsule toner particles which 
correspond to the area where the image will be formed. Then, the 
supporting member and the image recording medium are superposed with each 
other in the transferring means, so that only the contents are transferred 
to the image recording paper. Thus, the visible image is formed. 
During this process, the wall material of the microcapsules from which the 
contents flowed adheres onto the supporting member by a keying effect, and 
only the contents are transferred to the image recording paper. Thus, an 
excellent image is formed thereon. Further, at this time, the contents, 
i.e. the toner, do not adhere to the microcapsule wall because the 
critical surface tension of the wall material of the microcapsules is 
smaller than the surface tension of the toner. Therefore, the contents 
separate from the microcapsule wall easily, and are easily transferred to 
the image recording medium. Moreover, the contents adhere easily to the 
image recording medium since the surface tension of the contents of the 
microcapsule toner particles is smaller than the critical surface tension 
of the image recording medium which confronts the supporting member in the 
transferring means. Therefore, the toner is easily transferred to the 
image recording medium. Thus, an excellent image is formed thereon. 
As explained above, in the image forming apparatus of the present 
invention, the wall material of the capsule toner particles from which the 
contents flowed are adhered on the supporting member by a keying effect, 
and only the toner is transferred to the image recording paper. Moreover, 
only the contents are transferred to the image recording medium because 
the critical surface tension of the wall material of the microcapsule 
toner particles is smaller than the surface tension of the contents, and 
the surface tension of the contents is smaller than the critical surface 
tension of the image recording medium which confronts the supporting 
member in the transferring means. Therefore, an excellent image can be 
obtained.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the accompanying drawings, preferred embodiments of the 
present invention will be described in detail. 
FIG. 1 is a cross-sectional view of the microcapsule toner particle used 
for an image forming apparatus according to embodiments of the present 
invention. As shown in FIG. 1, a photosensitive microcapsule toner 
particle 1 includes an outer wall 2 and contents 3. The contents 3 are a 
photocurable composition in which acrylic monomer, photopolymerization 
initiator, sensitizing dye, and coloring agents such as pigment and dye 
are mixed. The surface tension of the contents 3 is about 34 dyne/cm. The 
wall 2 is constructed from material whose critical surface tension is 
smaller than the surface tension of the contents 3, such as polyethylene. 
The surface tension of the wall material 2 is, for example, about 31 
dyne/cm. 
Next, an image forming apparatus of a first embodiment will be explained 
with reference to FIG. 2. An exposure unit 10, a microcapsule toner 
particle coating unit 20, a pressure developing unit 40, and an image 
transferring unit 50 are installed in an image forming apparatus 5. Each 
unit is arranged so that an image supporting medium 44 of an endless belt 
type can be moved therethrough. The image supporting medium 44 has 
microcapsule toner particles supported thereon as described below. 
The exposure unit 10 includes an exposure lamp 11 which exposes an 
original, a support stand glass 15 on which the original is placed, an 
original cover 13 which covers the original, a scanner 14 for inputting a 
reflection light from the original and reading an image thereon, a 
controller C for controlling an image signal read by the scanner 14, and 
an exposure head 19 including a lamp and a liquid crystal shutter for 
exposing microcapsules supported on the image supporting medium 44 based 
on the signal from the controller C. 
The microcapsule toner particle coating unit 20 includes microcapsule toner 
particles 1, a toner particle casing 21 which stores the toner particles 1 
therein, an agitator 23 for stirring the toner particles 1 stored in the 
toner particle casing 21, a carrying roller 25 for carrying the toner 
particles 1, and a supplying roller 24 for supplying the toner particles 1 
to the carrying roller 25. This microcapsule toner particle coating unit 
20 is arranged adjacent the image supporting medium 44. 
In the pressure developing unit 40, a pair of pressure rollers 41A, 41B are 
arranged so that the image supporting medium 44 on which the microcapsule 
toner particles 1 are coated can pass therebetween. The pressure roller 
41B which touches the surface of the coated image supporting medium 44 is 
formed of material having small critical surface tension, for instance, 
Teflon. 
The image supporting medium 44, which is preferably made of a film sheet of 
synthetic resin, is extended through a driving roller 28 driven by a 
well-known motor, a confronting roller 27, a following roller 29, a 
pressure roller 41A, and a transferring roller 54A. 
The confronting roller 27 is connected to a power supply 26 through the 
controller C, so that an electric field is selectively formed in the area 
between the confronting roller 27 and the carrying roller 25. 
In the image transferring unit 50, a pair of transferring rollers 54A, 54B 
are arranged to pass the image supporting medium 44, on which the image is 
formed, and an image recording paper 52 therebetween. 
Beneath the toner particle coating unit 20, a cleaning unit 30 having a 
cleaning blade 31 is arranged adjacent to the image supporting medium 44. 
The cleaning unit 30 collects hardened microcapsule toner particles 32 
scraped from the image supporting medium 44. 
The surface of the image supporting medium 44 is rougher than that of the 
image recording paper 52. In general, the surface roughness of the image 
recording paper 52 is about Rz15 .mu.m. Therefore, it is preferable that 
the surface roughness of the image supporting medium 44 is more than about 
Rz20 .mu.m. (Rz is a unit expressing the average surface roughness of an 
object.) If the image recording paper 52 is more smooth, the image 
supporting medium 44 also can be made more smooth. In this case, the 
surface of the output image also becomes more smooth. 
A description will now be provided of the operation of the above described 
device. The driving roller 28 rotates when the start switch (not shown) is 
turned on and drives the image supporting medium 44. In the microcapsule 
toner particle coating unit 20, the toner particles 1 are 
electrostatically charged by the rotation of the agitator 23 and the 
supplying roller 24 and are supported on the carrying roller 25. The toner 
particles 1 supported by the carrying roller 25 are electrostatically 
attracted in the direction of the confronting roller 27 by the electric 
field formed between the confronting roller 27 and the carrying roller 25. 
As a result, the toner particles 1 are uniformly coated over the surface 
of the image supporting medium 44. 
Next, the photosensitive microcapsule toner particles are transported 
beneath the exposure unit 10. The exposure lamp 11, preferably a halogen 
lamp, is lit and the support stand glass 15 on which an original 12 is 
placed moves. An exposure operation is performed according to the original 
12. The light reflected by the original 12 is read by the scanner 14. The 
controller C controls the exposure head 19 based on the image signal read 
by the scanner 14. The surface of the image supporting medium 44, on which 
the microcapsule toner particles 1 are coated, is then exposed to the 
light based on an original image pattern. Thereby, a latent image is 
formed onto the image supporting medium 44. Then the image supporting 
medium 44 is further transported to the pressure developing unit 40. 
In the pressure developing unit 40, the image supporting medium 44, which 
supports the toner particles 1 thereon and on which the latent image is 
formed, passes between the pressure rollers 41A and 41B, and pressure is 
applied. The microcapsule toner particles which are not hardened by the 
exposure operation in the exposure unit 10 are ruptured and the contents 
3, i.e. toner, flow out from the ruptured microcapsules. 
The pressure roller 41B is formed with a material having a small critical 
surface tension such as Teflon. Therefore, when the image supporting 
medium 44 passes over the pressure roller 41B, the hardened microcapsule 
toner particles 32, the contents 3, and the wall material 2 will remain on 
the surface of the image supporting medium 44. Further, the hardened 
microcapsule toner particles 32 and the wall material 2 of the ruptured 
microcapsules are adhered to the image supporting medium 44 by a keying 
effect. The keying effect is caused when some objects, such as the 
hardened microcapsule toner particles and the microcapsule walls, enter a 
space of irregularity in the surface of the image recording paper and act 
as a keystone, causing mechanical adhesion. Afterwards, the image 
supporting medium 44 is transported to the image transferring unit 50. 
During the pressure operation, the image recording paper 52, which is an 
ordinary paper, is removed from a sheet cassette 51 and is sent to the 
image transferring unit 50. 
In the image transferring unit 50, the image supporting medium 44 on which 
the image is formed and the image recording paper 52 are fed between a 
pair of transferring rollers 54A, 54B, and are pressurized. Therefore, the 
toner 3 is transferred onto the image recording paper 52, and the image is 
formed thereon. Afterwards, the image formed on the image recording paper 
52 is fixed by a thermal fixing unit (not shown), and the image recording 
paper 52 is discharged onto a discharge tray. During this process, the 
hardened microcapsule toner particles 32 and the wall material 2 of the 
ruptured microcapsules remain on the image supporting medium 44 by the 
keying effect, because the surface of the image supporting medium 44 is 
rougher than that of the image recording paper 52. 
Moreover, the microcapsules rupture and adhere to the image supporting 
medium 44 because the wall material has a critical surface tension which 
is smaller than the surface tension of the contents 3. Therefore, the 
contents 3 are easily separated from the wall material 2 and are easily 
transferred to the image recording paper 52. Moreover, if the image 
recording paper 52 itself or the surface of the image recording paper 52 
is formed with a material having a critical surface tension which is much 
larger than the surface tension of the contents 3, for example, nylon 
(whose critical surface tension is about 42-46 dyne/cm), the contents 3 
adhere easily to the image recording paper 52 and transfer more easily to 
it. 
Afterwards, the hardened microcapsule toner particles 32 and the wall 
material 2 of the ruptured microcapsules remaining on the image supporting 
medium 44 are removed therefrom by being scraped by the blade 31 in the 
cleaning unit 30. Then, the microcapsule toner particles 1 are coated 
again onto the image supporting medium 44 which passes from the cleaning 
unit 30. 
As discussed above, the hardened microcapsule toner particle 32 and the 
wall material 2 of the ruptured microcapsules from which the contents 3 
flowed remain on the image supporting medium 44 through the keying effect, 
with only the contents 3 being transferred onto the image recording paper 
52, because the surface of image supporting medium 44 is rougher than that 
of image recording paper 52. Moreover, only the contents 3 are transferred 
to the image recording paper 52 because the critical surface tension of 
the wall material 2 of the microcapsule toner particles is smaller than 
the surface tension of the contents 3, and the surface tension of the 
contents 3 is smaller than the critical surface tension of the image 
recording paper 52 which confronts the image supporting medium 44 in the 
transferring unit 50. Therefore, an excellent image is formed on the image 
recording paper 52. 
Further, as explained above, the pressure developing unit 40 and the 
transferring unit 50 are separately provided, so that the developing 
operation can be performed firmly with high pressure in an instant, and 
then the transferring operation can be performed carefully. Therefore, the 
image recording paper 52 is not damaged and an excellent image can be 
formed. 
In should be noted that the invention is not limited to the above preferred 
embodiment, but may be embodied in various modes without departing from 
the scope of the invention. For instance, it is possible to easily clean 
the remaining microcapsule toner particles 32 and the wall material 2 in 
the cleaning unit 30 by applying light to the image supporting medium 44 
after pressure developing. 
Moreover, the photosensitive material contained in each microcapsule may be 
of the type which is hardened upon exposure to radiation, or alternatively 
of the type which is softened upon such exposure. 
Furthermore, in the present embodiment, the microcapsule toner particles 
are coated onto the whole surface of the image supporting medium, and then 
the image supporting medium is exposed to the light based on the original 
image. However, the microcapsule toner particles can be previously 
selected and coated onto the image supporting medium based on the original 
image. 
A second embodiment will be described with reference to FIG. 3. Because the 
construction of the image forming apparatus of the second embodiment is 
similar to that of the image forming apparatus of the first embodiment, 
only the differences will be described in detail. 
The main difference between the first embodiment and the second embodiment 
is that the mechanical structure of the pressure developing unit 40 of the 
first embodiment has been modified. 
As shown in FIG. 3, in a pressure developing unit 140, a pressure roller 
141 and a pressure developing and transferring roller 142 are arranged so 
that an image supporting medium 44 coated with microcapsule toner 
particles is passed therebetween. Also, beneath the pressure developing 
and transferring roller 142, a transferring roller 143 is arranged in 
order to pass an image recording paper therebetween. The surface of the 
pressure developing and transferring roller 142 is formed with a material 
having a critical surface tension which is larger than the surface tension 
of contents 3, such as nylon (whose critical surface tension is about 
42-46 dyne/cm). 
The image supporting medium 44 on which the toner particles are coated and 
a latent image is formed passes between the pressure roller 141 and the 
pressure developing and transferring roller 142 in the pressure developing 
unit 140. The contents 3 of the microcapsule toner particles flow out from 
the toner particles which did not harden in the exposure unit 10 when the 
toner particles are pressurized in the above pressure developing unit 140. 
At this time, the hardened microcapsule toner particles 32 and the wall 
material 2 of the ruptured microcapsules remain on the image supporting 
medium 44 by the keying effect because the surface of the image supporting 
medium 44 is rougher than that of the pressure developing and transferring 
roller 142. 
Moreover, only the contents 3 are transferred onto the pressure developing 
and transferring roller 142 because the roller 142 is formed with a 
material having a critical surface tension which is larger than the 
surface tension of the contents 3. 
On the other hand, the image recording paper 52, which is an ordinary 
paper, is supplied from the sheet cassette 51 and is fed and pressurized 
between the pressure developing and transferring roller 142, on which the 
contents 3 are supported, and the transferring roller 143. Then, the 
contents 3 are transferred to the image recording paper 52 by capillarity, 
and the image is formed on the image recording paper 52. Afterwards, the 
image is fixed by a thermal fixing unit (not shown), and the image 
recording paper 52 with the fixed image is discharged onto a discharge 
tray. 
Finally, the image supporting medium 44 with the remaining hardened 
microcapsule toner particles 32 and the wall material 2 of the ruptured 
microcapsules from which the contents 3 flowed is transferred to a 
cleaning unit 30. The hardened microcapsule toner particles 32 and the 
wall material 2 are scraped by a blade 31 in the cleaning unit 30 and 
removed from the image supporting medium 44. Then, microcapsule toner 
particles 1 are again coated onto the image supporting medium 44 which has 
been cleaned in the cleaning unit 30. 
Accordingly, in the second embodiment, it is not necessary to provide a 
separate image transferring part, so that the image forming apparatus of 
the second embodiment has a simple construction. 
Further, according to this second embodiment, it is possible to prevent the 
toner from changing in quality which can happen in a long feeding path 
because the feeding path of the contents flowing from the ruptured 
microcapsules is shortened. 
A third embodiment will be described with reference to FIG. 4. Because the 
construction of the image forming apparatus of the third embodiment is 
similar to that of the image forming apparatus of the first embodiment, 
only the differences will be described in detail. 
The main difference between the first embodiment and the third embodiment 
is that the mechanical structure of the pressure developing unit 40 of the 
first embodiment has been modified. 
As shown in FIG. 4, in a pressure developing unit 240, a pair of pressure 
rollers 241A, 241B are arranged to pass an image supporting medium 44, 
with microcapsule toner particles coated thereon and the latent image 
formed thereon, and an image recording paper 52 therethrough. 
The image supporting medium 44 on which a latent image is formed is 
transferred to the pressure developing unit 240. The image recording paper 
52, which is an ordinary paper, is supplied from a sheet cassette 51 and 
is fed into the pressure developing unit 240. In the pressure developing 
unit 240, the image supporting medium 44 on which the toner particles are 
coated and the latent image is formed, and the image recording paper 52 
are superposed and pass between the pressure rollers 241A and 241B. The 
contents 3 of the microcapsule toner particles flow from the microcapsules 
which do not harden when the microcapsule toner particles are pressurized 
in the above pressure developing unit 140. Therefore, only the contents, 
i.e. toner, are transferred to the image recording paper 52, and the image 
is formed on the image recording paper 52. Afterwards, the image recording 
paper 52 upon which the image is fixed by a thermal fixing unit (not 
shown) is discharged onto a discharge tray. At this time, the hardened 
microcapsule toner particles 32 and the wall material 2 of the ruptured 
microcapsules from which the contents 3 flowed remain on the image 
supporting medium 44 by a keying effect, because the surface of the image 
supporting medium 44 is rougher than that of the image recording paper 52. 
The hardened microcapsule toner particles 32 and the wall material 2 of 
the ruptured microcapsules remaining on the image supporting medium 44 are 
then transferred to the cleaning unit 30 and are scraped by the blade 31 
in the cleaning unit 30, thereby removing them from the image supporting 
medium 44. Then, the microcapsule toner particles 1 are again coated onto 
the image supporting medium 44 which has passed from the cleaning unit 30. 
Accordingly, in the third embodiment, an image can be transferred to the 
image recording paper in the pressure developing part, so that it is not 
necessary to provide an image transferring part in the image forming 
apparatus of the third embodiment. Therefore, the construction of the 
image forming apparatus of the third embodiment becomes more simple. 
Although the invention has been described in its preferred forms with a 
certain degree of particularity, obviously many changes and variations are 
possible therein. It is therefore to be understood that the invention may 
be practiced otherwise than as specifically described herein without 
departing from the scope and spirit of the invention.