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METHOD AND APPARATUS FOR FORMING
AN IMAGE HAVING UNIFORM
BACKGROUND OF THE INVENTION 5
This invention relates to an image forming method and apparatus for forming a toner image at the interface of a transparent substrate and a light reflecting material.
An image having uniform glossiness such as silver halide photographic image is difficultly obtained by electrophoto- 15 graphic method since the image is formed by granule toner particles, consequently, the image surface becomes irregular and uniform glossiness cannot be formed.
Therefore, a method for forming the uniform glossiness
similar to the silver halide photograph has been investigated.
For forming a glossy image, there is a means by improving the fixing process for thermally fixing the toner image. However, the problem of difference in the glossiness between the portion of the toner image and the portion where 25 no or small amount of toner exists cannot be completely solved by such the method.
A problem that the portion of the toner image is protruded as relief is not solved also.
Tokkai Hei 7-56409 proposes a method in which a mirror 30 image of the original image is transferred and fixed on a transparent film and a light reflecting material is laminated on the toner image carrying surface of the transparent film.
In the image formed by such the method, the surface of the transparent film opposite to the toner image carrying 35 surface becomes as the outermost surface of the finished image and the toner image is sandwiched by the transparent film and the light reflecting material. Therefore, an image having high and uniform glossiness can be obtained since the surface of the image is mirror surface with no toner 40 image.
However, the following problem remains in the above method which is basically superior for obtaining a photograph with high glossiness. ^
In the fixing process of toner image, the fixation is performed while coating a releasing agent (for example offset preventing oil) onto the heating member since offset phenomenon is caused by that a part of the toner constituting the image adheres to the heating member. However, the releasing agent tends to hinder the adhesion between the transparent film and the light reflecting material since the releasing agent is principally composed of oil. When such the releasing agent is employed, the oil adheres on the entire surface of the transparent film so that the light reflecting 55 material laminated on the transparent substrate tends to be easily peeled and problems of peeling off and slipping are caused.
SUMMARY OF THE INVENTION 60
An object of the invention is to solve the above-described problems and to provide an image forming method and an image forming apparatus by which an image having uniform glossiness is formed and the transparent substrate and the 65 light reflecting material are difficultly peeled off so that a durable print of photograph can be obtained.
The above objects can be the following constitutions.
1. An image forming method comprising the steps of
a) forming a mirror image by a toner on a transparent substrate, and
b) laminating a light reflecting material onto the toner carrying surface of the transparent substrate by putting an adhering layer or a tacking layer between the light reflecting material and the transparent substrate.
2. An image forming apparatus for forming a toner image by electrophotographic process comprising
an image forming section for forming a mirror image by a toner containing a wax on a transparent substrate,
a fixing means for fixing the toner image to the transparent substrate, and
a laminating section for laminating a light reflecting material onto the toner carrying surface of the transparent substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a mirror image formed on the transparent substrate.
FIG. 2 shows the cross section of a toner particle.
FIG. 3 shows an example of the fixing means.
FIG. 4 shows the laminating process.
FIG. 5 shows a color image forming apparatus as the first example of the embodiment of the invention.
FIG. 6 shows a block drawing of an image processing means.
FIG. 7 shows a drawing describing the reading out of image data from an image memory.
FIG. 8 shows a color image forming apparatus as the second example of the embodiment of the invention.
FIG. 9 shows a color image forming apparatus as the third example of the embodiment of the invention.
DETAILED DESCRIPTION OF THE
The invention is described bellow referring embodiments thereof, but the invention is not limited to the embodiments.
An embodiment of the image forming method of the invention includes the following image forming process, fixing process and laminating process.
(1) Image Forming Process
The image forming process is a process for forming a mirror toner image on the transparent substrate; particularly the toner image is formed by electrophotographic method.
Namely, an electrostatic latent image is formed on a photoreceptor by charging and light exposing the photoreceptor, and developing the electrostatic latent image.
The toner image on the photoreceptor is transferred onto a transparent substrate.
The transfer of the toner image from the photoreceptor to the transparent substrate is carried out by a direct transfer or an indirect transfer through an intermediate transfer member.
The toner image formed on the transparent substrate is a mirror image of an original image reversed in vertical or horizontal direction.
The photoreceptor is imagewise exposed by a light source such as a laser or a LED according to the image data in the course of the image formation; the imagewise exposure is carried out by image processing corresponding to the number of times of transfer in the course of the direct transfer or the indirect transfer so as to form the mirror image.
(2) Fixing Process
The fixing process for fixing the toner image to the transparent substrate is carried out by inserting the transparent substrate carrying the unfixed toner image into a nipping portion formed by a heating member and a pressing 5 member and conveying by nipping.
A roller fixing device having a heating roller as the heating member and a pressing roller as the pressing member in which the recording medium is nipped and conveyed by the pair of the rollers, and a belt fixing device having a 10 belt or a roller as the heating member and a belt or a roller in which the recording medium is nipped and conveyed by them, are preferably employed as the fixing means.
Hitherto, the fixation of a multi-color toner image has been performed while coating offset preventing oil such as 15 silicone oil. However, the offset preventing oil reduces the adhering force between the transparent substrate and the reflection material so that the durability of the obtained photograph is degraded and the transparent substrate is easily peeled off from the reflection material. 20
In the invention, the fixation is carried out without the use of the offset preventing oil for solving the above problems, and the later-mentioned toner of the invention, namely, a toner prepared by a wet method in which wax is substantially not exposed to the surface of the toner particle is 25 employed.
The content of the wax can be made higher in such the toner, and the offset and winding of the recording medium can be easily prevented since the wax is molten and oozed out to the particle surface at the portion for contacting the 30 toner with the heating member even though the oil is not coated on the heating member in the fixing process. As a result of that, the bonding force between the transparent substrate and the light reflecting material laminated with the substrate is strengthen so that the problems of peeling and 35 slipping can be solved.
Moreover, in the toner of the invention, the wax is difficultly oozed out between the transparent substrate and the toner image as described later since the wax is substantially not exposed to the surface of the toner particle as 40 shown in FIGS. 2a and 2b. As a result of that, a merit can be obtained that the transparent substrate is difficultly peeled from the light reflecting material.
Contrary, when the toner image is developed by a crushed toner as shown in FIG. 2c, the wax content in the crushed 45 toner itself is difficultly increased and the oil for preventing offset is difficultly eliminated. Therefore, the bonding force between the transparent substrate and the light reflecting material laminated with the substrate is reduced and the problems of peeling and slipping tend to be caused. 50
Furthermore, the wax is transferred from the toner to the heating member and easily retransferred from the heating member to the transparent substrate since the major portion of the toner particle surface is covered by the wax. As a result of that, the bonding force between the transparent 55 substrate and the light reflecting material laminated with the substrate is reduced and the problems of peeling and slipping tend to be caused as described later in detail.
FIG. 3 shows a preferable example of the fixing means.
In FIG. 3, a fixing belt 11a is laid with strain by support- 60 ing rollers 11c and lid and contacted by pressing to a pressing roller lib. A heater lie is provided in the supporting roller lid, and the heater lie heats the supporting roller lid and the fixing belt 11a so as to raise the temperature of the fixing belt by a fixing temperature. 65
The surface temperature of the fixing belt 11a is detected by a thermal sensor Ilk and the temperature of the fixing belt
lla is controlled according to the detected temperature so as to hold the temperature at a constant level.
A transparent substrate F carrying a unfixed toner image is nipped and conveyed by the fixing belt by lla and the pressing roller lib in the direction of the arrow sign and heated at the time of passing the nipping potion between the fixing belt lla and lib so as to fixing the toner image to the transparent substrate F.
Members ll/through 11/ is a cleaning means for cleaning the fixing belt lla, in which a cleaning web llf laid by stretching between a bulk roll Uh and a taking out roller Hi is contacted to the fixing belt lla by a pressing roller llg and cleans the fixing belt lla for removing the wax adhering on the fixing belt lla. The cleaning web 11/ is renewed for every designated working time of the fixing means.
The adhering amount of the wax contained in the toner to the fixing belt lla is insufficient for reducing the adhering force between the transparent substrate and the light reflecting material in the similar degree to that caused by the offset preventing oil coated to the heating member, and a print in which the transparent film F and the paper P are more strongly bonded is formed by cleaning by the cleaning web 11/
(3) Laminating Process
In the laminating process, the transparent substrate carrying is laminated with the light reflecting material and the toner image carrying surface of the transparent substrate is contacted to the light reflecting material. The toner image is sandwiched by the transparent substrate and the light reflecting material, therefore the mirror image appears as a right image since the image is observed from the side of the transparent substrate carrying no toner image.
FIG. 4 shows an example of the laminating process.
As is shown in FIG. 4, a toner image T is formed on a transparent substrate Bl. The toner image viewed from the side of the arrow Wl is a mirror image reversed in the vertical or horizontal direction.
After that, a light reflecting material B2 is laminated by adhering or tacking onto the toner image carrying surface of the transparent substrate Bl as shown in FIG. 4b.
The photograph completed by the laminating is viewed in the direction of the arrow sign W2. As a result of that, a right image is observed.
The lamination is performed by adhering or tacking. The adhering layer or a tacking layer is on the light reflecting material which is previously provided or formed by coating in the course of laminating process.
Known adhering agents, for example, a hot-melt adhering agent principally composed of an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer or a modified polyolefin, and a thermal hardening type adhering agent such as an epoxy type, can be employable as the adhering agent.
Known tacking agents such as a solvent type acryl tacking agent and an emulsion type tacking agent are usable.
(4) Transparent substrate and light reflecting material
A PET (polyethylene terephthalate) film is preferable and the thickness thereof is preferably from 50 to 500 urn.
A thickness of smaller than 50 urn causes appearance of irregularity caused by the toner image on the surface of the print of photograph in some cases. When the thickness exceeds 500 urn, the treatment in a usual electrophotographic image forming apparatus is hindered in some cases.
The light reflecting material is a white, milk-white or silver reflective sheet, and coated paper for printing, a
synthesized paper such as one having commercial name of Yupo, resin-coated paper and resin film are preferable.
When the coating layer of the coated paper contains a polyolefin such as paraffin, polyethylene and polypropylene, such the component dissolves with the wax and functions as 5 an adhesive. Therefore, the transparent substrate and the light reflecting material can be more strongly bonded by heating adhesion by the use of the coated paper containing a substance capable of dissolving with the wax for acting the coated layer as the adhering layer or the tacking layer. 10
(5) Developer and Wax-Containing Toner
The development is performed by the use of a doublecomponent developer. For a magnetic carrier particle of carrier constituting the double-component developer, known materials such as a metal such as iron, ferrite and magnetite, an alloy of the metal and another metal such as aluminum or lead can be employed. Particularly, ferrite is preferable. The volume average diameter of the magnetic particles is preferably from 15 to 100 um, and more preferably from 25 to 80 um. 20
The volume average diameter of the carrier particles can be typically measured by a laser diffraction particle size distribution measuring apparatus having a wet type dispersing machine HELOS, manufactured by Sympatec Co., Ltd.
A carrier comprising a magnetic particle coated by a resin or a magnetic particle dispersed in a resin so called as a resin dispersion type carrier is preferably employed as the carrier. Though the resin for coating the magnetic particle is not specifically limited for example, an olefin resin, a styrene 3Q type resin, a styrene-acryl type resin an ester type resin and a fluororesin are employable. As the resin for constituting the resin dispersion type carrier, know resins can be employed without any limitation, for example, a styreneacryl type resin, a polyester resin, a fluororesin and a phenol resin are employable.
A toner containing a wax is employed as the toner. As the wax-containing toner, one from which the wax is difficultly oozed to the surface thereof is employed.
By the use of such the toner, the adhesion or tack between the transparent substrate and the light reflecting material is made uniform and strong, and a durable printed image can be formed in which the peel off or the slip of the transparent substrate and the light reflecting material is little.
One of such the toner is a toner produced by a wet process.
The toner produced by the wet process is a toner produced by a process in which the toner particles are formed in a liquid such as an aqueous medium, for example, a toner produced by an emulsion polymerization method, a suspension polymerization method, an emulsifying dispersion method, a dispersion polymerization method or a seed polymerization method.
The polymerized toner is preferable, in which the toner particle is prepared by polymerization or fusion of plural particles formed by polymerization. Particularly, the toner produced by the suspension polymerization method or emulsion polymerization method is preferable and the toner produced by the emulsion polymerization method is most preferable. ^
<Suspension Polymerization Method>
An example of the suspension polymerization method is as follows.
In a polymerizable monomer, a charge controlling resin is dissolved and various constituting materials such as a colo- 65 rant, a wax and an additive such as a polymerization initiator are added, and then the constituting materials are dissolved
or dispersed in the polymerizable monomer by a homogenizer, a sand mill, a sand grinder or an ultrasonic disperser. The polymerizable monomer in which the constituting materials are dissolved or dispersed is dispersed in an aqueous medium containing a dispersion stabilizer using a homomixer or a homogenizer so that the polymerizable monomer is made to a state of oil droplet having a desired size for the toner. After that, the dispersion is poured into a reaction vessel (stirring vessel) having a stirring wings as latermentioned, and heated for progressing the polymerization reaction. After completion of the reaction, the dispersion stabilizer is removed and the particles are filtered, washed and dried to prepare the toner.
<Emulsion Polymerization Method>
As the emulsion polymerization method, those disclosed in Tokkai Hei 5-256252 and 9-96919 can be applied. Namely, a method in which an emulsion of a polymerizable monomer with necessary additives is prepared and polymerized to form resin particles, and the resin particles are salted out, coagulated and fused with dispersed particles of the constituting materials such as the colorant, and these particles are dispersed by using a emulsifying agent and salted out by adding a coagulating agent in an amount of not less than the critical coagulation concentration and fused particles are simultaneously formed and gradually grown by heating at a temperature not less that the glass transition point of the formed polymer for fusion of the coagulated particles. The growing of the particles is stopped by adding a lot of water at the time when the diameter of the particles is attained at the objective size, and then further heated and stirred for controlling the shape of the particle by smoothing the particle surface. And then the particles are dried by heating in a fluid state containing moisture. Thus a toner suitable for the invention can be obtained. In the prepared toner particles, wax can be uniformly dispersed and the offset preventing effect at the fixing time can be raised compared with the toner particles prepared by the suspension polymerization. The cross section of the toner particle prepared by the emulsion polymerization is shown in FIG. 2a and that prepared by the suspension polymerization is shown in FIG. 2b. A solvent capable of freely mixing with water such as alcohol may be simultaneously added with the coagulating agent.
In the toner formed by the above-described polymerization method, the amount of the wax can be made larger than that in a usual toner prepared by crushing method. Therefore, the offset onto the heating roller in the fixing process can be prevented by the wax without the coating of the oil.
The toner produced by the wet process differs as follows from the toner produced by the crushing method.
The cross section of the toner produced by the wet process is displayed in FIG. 2 comparing with that of the toner produced by the crushing method.
As examples of the toner produced by the wet process, the cross section of the toner particle produced by the emulsion polymerization method is shown in FIG. 2a and that of the toner particle produced by the suspension polymerization method is shown in FIG. 2b, and the cross section of an example of the toner particle produced by the crushing method is shown in FIG. 2c.
In the toner particle produced by the emulsion polymerization method or that produced by the suspension polymerization method, the surface SF thereof is almost covered by the binder resin BR, and the wax is substantially not exposed on the surface SF.