Method for producing an original for use in an overhead projector

Disclosed is a method for producing an original for use in an overhead projector through an electrophotographic process. The method comprises a process for applying a first light-transmissive toner onto a surface of a transparent film, a process for heat-fixing the first light-transmissive toner on the film so that particles of the first light-transmissive toner are not melted completely and such that a diffusive surface is formed, a process for applying a second light-transmissive toner onto the diffusive surface corresponding to a document image, and a process for heat-fixing the toner image on the diffusive surface so that particles of the second light-transmissive toner forming the toner image are melted completely and that a toner image having a smooth surface is formed. When such films carrying toner images having a smooth surface formed on the diffusive surface are piled one over another, the toner images on the lower films placed under the top film are invisible through the top film and hence the toner image on the top film is clearly visible.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for producing an original for use 
in an overhead projector (hereinafter abbreviated to "OHP") and, more 
specifically, to a method for producing an original directly from a 
document by using an electrophotographic copying machine. 
2. Description of the Prior Art 
Transparent films carrying positive images have generally been used for 
projection. When such transparent films are placed in a pile, it is 
difficult to read the positive image formed on the top transparent film 
because the contents of the lower transparent films are visible through 
the top transparent film. Opaque white papers and the transparent films 
are placed alternately one over another to enable reading the contents of 
the individual transparent films, which makes handling the transparent 
films very troublesome. 
A method has been proposed for preparing films carrying highly visible 
negative images for projection by using an electrophotographic copying 
machine. This known method, however, requires troublesome work to convert 
a positive image of an original document into a corresponding negative 
image and to transfer the negative image to a film for projection by an 
electrophotographic copying machine. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a simple 
method for producing an original for use in an OHP. 
It is another object of the present invention to provide a method for 
easily producing highly visible original for use in OHP by using an 
electrophotographic copying machine. 
In one aspect of the present invention, a method for producing an original 
for use in an OHP from a document through an electrophotographic process, 
comprising: a first process for applying a first light-transmissive toner 
onto one of surfaces of a transparent film; a second process for producing 
a diffusive surface on said one of surfaces of said transparent film by 
fixing the layer of the first light-transmissive toner to the transparent 
film; a third process for applying a second light-transmissive toner onto 
said diffusive surface corresponding to an image on the document; and a 
fourth process for forming an image portion having a smooth surface 
corresponding to said document image by fixing said second 
light-transmissive toner on said diffusive surface. 
The image portion having a smooth surface can be formed by an 
electrophotographic copying machine. However, the smooth image may be 
formed by any suitable method; for example, the smooth image may be formed 
by a writing tool for writing or drawing with an adhesive ink, by applying 
a fusible ink onto the diffusive surface and by heating the fusible ink to 
melt the fusible ink, by spraying an adhesive ink onto the diffusive, or 
by adhesively attaching transparent films or tapes onto the diffusive 
surface. 
In accordance with the present invention, a diffusive surface is formed on 
one of the surfaces of a transparent film for use in an OHP (hereinafter 
referred to as "OHP film"), and then a smooth image corresponding to an 
image to be projected is formed on the diffusive surface. When the 
transparent OHP film carrying the smooth image is illuminated by a 
projection light source to project the image on a screen, the light 
emitted from the light source and transmitted through the smooth image 
forms a highlighted image on the screen while the light emitted from the 
light source toward areas other than the smooth image is diffused to form 
shadows on the screen as a background for the highlighted image. 
According to the present invention, an original carrying a negative image 
can be formed directly from a positive image of a document, for example, 
by using an electrophotographic copying machine through a simple 
procedure. The film prepared through the present invention carries a image 
formed on a diffusive reflecting surface, and hence the image is clearly 
visible before the diffusive reflecting surface even if a plurality of 
such films are placed one over another. Thus, the present invention 
facilitates the OHP projection operation remarkably.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Prior to the description of an image forming, an electrophotographic 
copying machine employed in forming an image according to the present 
invention will be described with reference to FIG. 1 by way of an example. 
Referring to FIG. 1, the electrophotographic copying machine has a 
photosensitive drum 1 which rotates in the direction of an arrow "a", a 
first developing unit 4 disposed near the circumference of the 
photosensitive drum 1, and a second developing unit 5 disposed near the 
circumference of the photosensitive drum 1 and after the first developing 
unit 4. The first developing unit 4 forms a diffusive surface on an OHP 
film by using a first developer, namely, a mixture of a carrier and a 
light-transmissive toner having a high viscosity. The second developing 
unit 5 develops a latent image formed on the drum 1, by using a second 
developer, namely, a mixture of a carrier and a light-transmissive toner 
having a low viscosity, to form an image having a smooth surface 
(hereinafter referred to as "smooth image"). The rest of the components, 
including a charger 2, an exposure unit 3 having an exposure lamp 31, a 
transfer charger 6, a separator 7, a cleaning unit 8, a eraser lamp 9, a 
automatic film feed cassette 20, a feed roller 21, a pair of timing 
rollers 22, a guide plate 23, a fixing unit 24 of a heat-fixing type, a 
delivery guide 25, a tray 26, a refeed unit 27, a refeed roller 28, a 
contact glass 35 and a cover 37, are the same in construction and function 
as those of the conventional electrophotographic copying machine, and 
hence the description thereof will be omitted. 
The method embodying the present invention for producing an original for 
use in an OHP, comprises a diffusive surface forming process and a smooth 
image forming process. 
DIFFUSIVE LAYER FORMING PROCESS 
The electrophotographic copying machine is started to perform the diffusive 
surface forming process. The photosensitive drum 1 is rotated in the 
direction of the arrow "a" and the circumference of the photosensitive 
drum 1 is charged by the charger 2 at a fixed potential. 
The first developing unit 4 applies the first developer to the 
circumference of the drum 1. The first developer is prepared in the 
following manner. 
Composition of a high-viscosity light-transmissive toner T1: 
styrene-acrylate copolymer (45.times.10.sup.5 poise at 100.degree. C.) 100 
parts by weight 
Offset inhibitor 5 parts by weight 
Charge control agent 5 parts by weight 
A mixture of the foregoing materials is mixed well by a mixer, and then the 
mixture is kneaded and cooled to solidify the mixture. Then, the solid 
mixture is crushed by a crusher into coarse particles. Then, the coarse 
particles are pulverized by a jet pulverizer into fine particles. The fine 
particles are classified to select a particles having particle sizes in 
the range of 4 to 20 .mu.m to obtain a toner having an average particle 
size of 11 .mu.m. 
Then, the toner T1 and a carrier having an average particle size of 35 
.mu.m are mixed to obtain the first developer. The carrier is a binder 
type magnetic carrier in which a magnetic powder is dispersed in a 
stylene-acrylic resin. 
In the image forming cycle, the second developing unit 5 is held 
inoperative by a control unit, not shown, which is the same procedure as 
that used for forming a multicolor image with an ordinary multicolor 
copying machine, and the exposure lamp 31 is not lighted to hold the 
exposure unit 3 inoperative. Consequently, the high-viscosity 
light-transmissive toner T1 is applied onto the entire area on the 
circumference of the photosensitive drum 1. The high-viscosity toner T1 is 
transferred to a transparent OHP film 36 fed out of the automatic film 
feed cassette 20 by the agency of the transfer charger 6 as shown in FIG. 
2. 
Then, the high-viscosity toner T1 is fixed to the transparent film 36 by 
the fixing unit 24 including a teflon upper roller and a silicon rubber 
roller. The fixing conditions of the fixing unit 24 are determined so that 
the high-viscosity toner T1 will not be melted completely and a diffusive 
surface 38 of the high-viscosity toner T1 is formed as shown in FIG. 3. In 
this case, the fixing temperature is 180.degree. C. and the fixing speed 
is 100 mm/sec. The transparent film 36 carrying the diffusive surface 38 
of the high-viscosity toner T1 is delivered to the refeed unit 27 for 
temporary storage. The transparent film 36 is refed for the smooth image 
forming process to form a smooth image on the diffusive surface 38 of the 
high-viscosity toner T1 in the next image forming cycle. 
(SMOOTH IMAGE FORMING PROCESS) 
The circumference of the photosensitive drum 1 is charged at a 
predetermined potential by the charger 2, and is exposed with light to 
form an electrostatic latent image of a document placed on the contact 
glass 35. The electrostatic latent image is developed by the second 
developing unit 5 accommodating the second developer which includes a 
low-viscosity toner T2. During the second image forming cycle, the first 
developing unit 4 is held inoperative by the control unit. 
The second developer is prepared in the following manner. 
Composition of the low-viscosity light-transmissive toner T2. 
styrene-acrylate copolymer (0.4.times.10.sup.5 poise at 100.degree.C.) 100 
parts by weight 
Offset inhibitor 5 parts by weight 
Charge control agent 5 parts by weight 
A mixture of the foregoing materials is processed in the same process as 
that for preparing the high-viscosity toner T1 to obtain the solid 
low-viscosity toner T2, and then the solid low-viscosity toner T2 is 
pulverized into particles having particle sizes in the range of 4 to 20 
.mu.m. Then, the particles are classified to obtain the low-viscosity 
toner T2 having an average particle size of 11 .mu.m. Then, the pulverized 
low-viscosity toner T2 and a carrier having an average particle size of 35 
.mu.m are mixed to obtain the second developer. The carrier is a binder 
type magnetic carrier in which a magnetic powder is dispersed in a 
stylene-acrylic resin. 
The transparent film 36 carrying the diffusive surface 38 of the 
high-viscosity toner T1 and stored in the refeed unit 27 is fed to a 
transfer position between the photosensitive drum 1 and the transfer 
charger 6 by the refeed roller 28 and the pair of timing rollers 22 in 
timed relation with the photosensitive drum 1. The image formed by the 
low-viscosity toner T2 is transferred onto the diffusive surface 38 of the 
high-viscosity toner T1 by the agency of the transfer charger 6 as shown 
in FIG. 4. 
The low-viscosity toner image is fixed by the fixing unit 24 at a fixing 
temperature of 180.degree. C. and a fixing speed of 100 mm/sec., at which 
the low-viscosity toner T2 is melted completely, to form a smooth image 39 
as shown in FIG. 5. 
As shown in FIG. 5, light L projected from behind the transparent film 36 
travels straight through the smooth negative image 39 to reach a screen, 
while the light L is diffused by the diffusive surface 38 and is unable to 
reach the screen. 
When a positive image 37 of a document shown in FIG. 6 is copied on an OHP 
film 36 by the method of the present invention, a smooth image 43 formed 
of the low-viscosity toner T2 is formed on a background 44 formed of the 
diffusive surface 38 of the high-viscosity toner T1 as shown in FIG. 7. 
When the OHP film 36 carrying the smooth image 43 and the background 44 is 
mounted on an OHP and projected on a screen, the smooth image is displayed 
in a highlighted image 45 and the background 44 is displayed in a shaded 
background 46 on the screen 50 as shown in FIG. 8. Thus, the smooth image 
can be formed simply on the OHP film from a positive image of a document 
by using an electrophotographic copy machine. Since the smooth image is 
formed on the diffusive surface which intercepts the light, the image 
formed on the OHP film is visible, which facilitates the OHP operation 
remarkably. 
The smooth image 39 may not necessarily be formed through an 
electrophotographic copying process; the smooth image 39 may be formed by 
any suitable means such as a pen using an ink capable of forming a smooth 
image 39 on the diffusive surface 38. 
Although this embodiment uses different toners, namely, the high-viscosity 
toner and the low-viscosity toner, respectively for forming the diffusive 
surface and the smooth image, different toners differing from each other 
in particle size may be used instead of the high-viscosity toner and the 
low-viscosity toner. 
Furthermore, toners of the same properties may be used for forming the 
diffusive surface and the smooth image and fixing conditions, such as 
fixing temperature, fixing pressure and/or fixing time, may be varied for 
forming the diffusive layer and for forming the smooth image. 
A method for producing an original for use in an OHP, in a second 
embodiment, according to the present invention uses an OHP film originally 
having a diffusive surface. This method eliminates the diffusive surface 
forming process of the method in the first embodiment. 
Referring to FIG. 9, an OHP film 56 for use in the second embodiment of the 
present invention originally has a diffusive surface 58. One of the 
surfaces of the transparent OHP film 56 is sandblasted to form the 
diffusive surface 58 having roughness of 12.5 .mu.m in average pitch and 
5.8 .mu.m in average peak-to-valley height. It is preferable that the 
average pitch and the average peak-to-valley height be the half of the 
toner's average particle size or less to form the smooth image 39 
effectively. The diffusive surface 58 may be formed through any suitable 
process such as an etching process or an embossing process. 
A smooth negative image 59 is formed on the diffusive surface 58 of the OHP 
film 56 as shown in FIGS. 10 and 11 through the same process as that for 
forming the smooth image 39 in the first embodiment. However, it is done 
in this second embodiment in a single copying cycle with the same 
electrophotographic copying machine by using the developing unit 5 which 
develops an image by using the low-viscosity toner T2. 
Thus, the second embodiment further simplifies the preparation of an OHP 
film carrying the negative image. 
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 present 
invention may be practiced otherwise than specifically described herein 
without departing from the scope and spirit thereof.