JP2001109208A - Image forming method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method by which a high quality image having less density irregularity and less transfer omission are formed without being influenced by the surface condition of a recording medium, and to provide an image forming device forming an image by the same method. SOLUTION: As to this image forming method; the toner adhering area of a toner image by each pixel is found on the basis of image information carried by a toner image carrier, transparent toner is selectively applied to a pixel which is found to have small toner adhering area then the toner image carrier is superposed on the recording medium, and the toner image is transferred and fixed to the recording medium with the transparent toner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming method for forming an image on a recording medium using toner and an image forming apparatus for forming an image by the image forming method.

[0002]

2. Description of the Related Art Conventionally, as a typical image forming method for forming an image on a recording medium using a toner, there is an image forming method of an electrophotographic system. An electrophotographic image forming method forms an electrostatic latent image based on image information on a photoconductor,
After electrostatically developing the electrostatic latent image with toner, which is a fine thermoplastic colored particle, to form a toner image on the photoreceptor,
The toner image is electrostatically transferred to a desired image recording material, for example, a recording sheet, and then the toner image on the recording sheet is heated and fixed to the recording sheet to finally form an image on the recording sheet. Things.

In recent years, with the development of computers, the spread of color displays, the development of communication networks, the emergence of large-capacity storage media, and the spread of scanners and digital cameras, expectations for high-quality color image output devices have increased. Also in the field of photographic image forming apparatuses, development of high quality color image forming apparatuses has been actively carried out.

An electrophotographic color image forming apparatus independently forms toner images of each color such as black, yellow, magenta, and cyan on a photoreceptor, and superimposes the toner images of each color on recording paper sequentially. To form a color image by electrostatic transfer.

In a color image forming apparatus, compared to a conventional monochromatic image forming apparatus mainly for character information and a line image, a plane image mainly for shading is mainly used. Will be very severe. However, in the color image forming apparatus, the toner layer thickness is increased in order to superimpose the toner images of the respective colors, and as a result, toner scattering and transfer unevenness occur in the transfer portion where the toner image is transferred, and the image quality is deteriorated. There is a problem that deterioration is easily caused.

In the electrostatic transfer system, the transfer efficiency of the toner image increases in proportion to the strength of the electric field applied to the toner layer. If the strength of the electric field fluctuates due to unevenness or the like, the transfer efficiency also fluctuates, and transfer unevenness tends to occur. Also, if the transfer electric field is simply increased, a so-called Paschen discharge occurs and the intensity of the electric field applied to the toner layer is reduced, or a portion of the toner is charged to the opposite polarity, thereby decreasing the transfer efficiency. Resulting in. Accordingly, the transfer efficiency shows a peak at a certain electric field value. In general, the peak value of the transfer efficiency in electrostatic transfer does not reach 100%, and is at most 95%.
%.

As described above, in the method in which the toner image formed on the toner image carrier is directly transferred to the recording paper, the strength of the electric field fluctuates mainly due to surface properties such as unevenness of the recording paper and unevenness in electric properties. Transfer unevenness occurs. Recording paper not only has unevenness in its own electrical properties, but also has high hygroscopicity, so the electrical resistance value fluctuates greatly due to moisture absorption.
Further, transfer unevenness is likely to occur. In addition, there are various types of recording paper used in the image forming apparatus, and in particular, plain paper and rough paper having large surface irregularities are often used in offices and personal use, and fluctuations in transfer efficiency due to the surface irregularities also occur. This has a large effect on transfer unevenness. further,
When the toner images of each color independently formed on the toner image carrier are overlaid and transferred on the recording paper, the transfer unevenness occurs as described above every time the toner image of each color is transferred, and the transfer unevenness is accumulated. Since the density unevenness becomes more remarkable, it is difficult to stably form a high quality image.

On the other hand, the toner images of each color formed on the toner image carrier are primarily transferred so as to be superimposed on an intermediate transfer member whose surface properties and electrical properties are sufficiently controlled, so as to be multicolored. In a so-called intermediate transfer type image forming apparatus that forms a toner image and secondary-transfers the multicolor toner image formed on the intermediate transfer body onto recording paper, the transfer efficiency at the time of primary transfer is small, On the intermediate transfer member, it is possible to obtain an image in which transfer unevenness is extremely small as compared with an image obtained by direct transfer onto a recording sheet.

However, when an intermediate transfer member is used, transfer efficiency at the time of secondary transfer for transferring a multicolor toner image formed on the intermediate transfer member to recording paper becomes a major problem. Secondary transfer is susceptible to the effects of surface irregularities of the recording paper and unevenness of electrical properties as described above. Further, the multicolor toner image formed on the intermediate transfer member has a large variation in the thickness of the toner layer, such as three or more layers in a large area and one layer or less in a small area. Therefore, a constant electric field is applied to the toner image. It is extremely difficult. Therefore, in an image forming apparatus using an intermediate transfer member, a multicolor toner image formed on the intermediate transfer member and having low density unevenness cannot be secondarily transferred to recording paper as it is. It is not possible to obtain a high-quality color image with few images. In particular, since transfer unevenness in the secondary transfer is strongly affected by the thickness of the toner layer on the intermediate transfer member, the color balance of the color image transferred on the recording paper is greatly shifted, and a high-quality color image is obtained. There is also a problem that is difficult.

To solve these problems, Japanese Patent Publication No. 46-41
No. 679 discloses that a toner image formed on a photoreceptor is adhesively transferred to an elastic intermediate transfer member surface, and then the recording paper and the intermediate transfer member are heated using a heating roller to thereby form an intermediate transfer member. There is disclosed an image forming method in which the above toner image is heated and melted and thermally transferred onto recording paper. In this method, since the transfer of the toner image from the intermediate transfer member to the recording paper is performed in a non-electrostatic manner, the deterioration of the image quality in the electrostatic transfer method as described above hardly occurs.

Japanese Patent Application Laid-Open No. 51-94939 discloses a multicolor toner formed on an intermediate transfer member by primary transferring a plurality of color toner images so as to be electrostatically superimposed on the intermediate transfer member. A so-called simultaneous transfer fixing type image forming method is disclosed in which a multi-toner image is transferred and fixed on a recording paper by heating and melting the image to obtain a color image. Also in this simultaneous transfer fixing method, since the toner image is transferred to the recording paper in a non-electrostatic manner, the deterioration of the image quality in the above-mentioned electrostatic transfer method rarely occurs.

Further, as an improvement of the simultaneous transfer fixing method, US Pat. No. 2,990,278, JP-A-5-19642 and JP-A-5-24979 have been proposed.
No. 8 publication. In these publications, in order to completely transfer the toner image from the intermediate transfer body to the recording paper, the intermediate transfer body and the recording paper are heated and pressed to transfer the toner image to the recording paper, and the toner An image forming method is disclosed in which the sheet is conveyed in a contact state until the cohesive force becomes larger than the adhesive force between the toner and the intermediate transfer body, and after cooling, the recording paper is separated from the intermediate transfer body.

FIG. 10 is a schematic diagram of a conventional image forming apparatus employing the simultaneous transfer and fixing method.

In this image forming apparatus, photosensitive drums 31a, 31b, 31c, 31d corresponding to respective colors of black, yellow, magenta, and cyan, on each of which an electrostatic latent image is formed, are provided.
Chargers 32a for uniformly charging these photosensitive drums,
32b, 32c, and 32d; an image exposure device 33 that irradiates exposure light corresponding to each of the above-described color images onto the surface of each of the photosensitive drums to form an electrostatic latent image on each of the photosensitive drums; The developing devices 34a, 34b, 34c, and 34d for developing the formed electrostatic latent images with the toners of the respective colors to form toner images corresponding to the respective colors, and transfer the toner images formed on the respective photosensitive drums. , A transfer corotron 36a, 36b, 36c, which electrostatically transfers the toner images on the respective photosensitive drums to the intermediate transfer belt 35 so as to overlap each other.
36d, a heating / pressing roll 37 that heats and presses while superimposing the recording paper P so as to sandwich the multicolor toner image formed by being superimposedly transferred onto the intermediate transfer belt 35
a, 37b, a recording paper tray 38 for storing the recording paper P, and a cooling device 39 for cooling the toner image on the heated and pressurized recording paper P. In this image forming apparatus, the intermediate transfer belt 35 on which the toner image has been formed is brought into close contact with the recording paper P and heated and pressed by the heating / pressing rolls 37a and 37b, so that the heating and melting on the intermediate transfer belt 35 are performed. The toner image adhered to the recording paper P is cooled by the cooling device 39 until the toner image is sufficiently adhered to the recording paper P, so that the toner image can be fixed to the recording paper P.

[0015]

However, the image forming method employing the above-mentioned non-electrostatic transfer method has the following problems.

In a conventional electrophotographic image forming apparatus,
There are two types, an analog type and a digital type. Recently, digital type image forming apparatuses capable of stably obtaining high-speed and high-quality images have been increasingly used. In a digital image forming apparatus, on / off binary information is given as two-dimensional information for a predetermined location on a toner image carrier based on character data or image data. As a method of recording a halftone image using this binary information, a halftone dot structure that changes the size of a dot to express a gradation and a line structure that changes the thickness of a line to express a gradation are available. is there. These gradation expression methods have relatively simple algorithms and low cost, and are therefore adopted in many digital image forming apparatuses.

The present inventors combine a digital image forming apparatus for forming a halftone image by an area modulation method using a halftone dot structure or a line structure with the above-described simultaneous transfer and fixing method using heat. As a result of repeated formation tests, it has been confirmed that there is a problem that an image in a low density portion and fine lines and fine details of characters are dropped without being transferred. This is due to the state of contact between the toner image and the surface of the recording paper, and is due to the structure of the toner image formed on the toner image carrier and the surface properties of the recording paper.

In the conventional transfer simultaneous fixing method using heat, the toner image carrier and the recording paper are brought into close contact with each other so as to sandwich the toner image, heated, and the hot-melted toner image is adhered to the recording paper. After cooling, the recording paper is peeled off from the toner image carrier.

FIG. 11 is a diagram showing a transfer state of a toner image in a conventional transfer simultaneous fixing method using heat.

FIGS. 11A to 11D show the adhesive force between the toner T and the recording paper P as Fp, the cohesive force between the toners T as Ft, and the adhesive force between the toner T and the toner image carrier R. This shows the transfer state of the toner image according to the magnitude relationship of the respective forces when Fr is set. As shown in FIG. 11B, only when the force relations of Fr <Fp and Fr <F are established, the toner image T
Is detached from the toner image carrier R while adhering to the recording paper P, and transfer and fixing are simultaneously achieved.

Generally, the cohesive force Ft of the heat-fused toner
Is large, and Fr <F if cooled to a desired temperature.
t, Fp <Ft holds. Further, Fr can be reduced by performing processing to enhance the releasability of the toner image carrier surface from the toner, so that Fr <F
The relationship p can be realized relatively easily. However, the toner image carrier R is sandwiched between the toner images T.
When the recording paper P is brought into close contact with the recording paper P, if the toner image T and the recording paper P are not sufficiently contacted, Fr> Fp, and
The toner image T is not transferred to the recording paper P and remains on the toner image carrier R (FIG. 11D). Also, Ft <Fr
If Ft <Fp, only a part of the toner image T is transferred to the recording paper P, and a part of the toner image T remains on the toner image carrier R as shown in FIG. I will.

Here, the relationship between the structure of the toner image formed on the intermediate transfer member and the surface properties of the recording paper will be considered.
In digital image forming technology in recent years, higher resolution has been promoted for higher image quality.
/ Inch) and 1200 dpi (dot / inch) are becoming mainstream. In order to form such a high-resolution image, the minimum dot diameter is 20 μm for a halftone image.
~ 30μm or less, line width of 20μ even for line image
It is necessary to form very fine pixels of m to 30 μm or less.

Further, in order to realize such high-resolution pixel formation, the particle size of the toner has been reduced.
The toner image height is about 10 μm to 20 μm for a single color and about 30 μm for three colors.
It is about 60 μm. On the other hand, the unevenness of the surface of the recording paper is such that the depth of the concave is
The depth of the concave portion is about 5 to 20 μm in what is generally called plain paper, and the depth of the concave portion exceeds 30 μm in the case of recycled paper or rough paper. The size of the concave portion ranges from a small size of about several μm to a size exceeding 100 μm.

FIG. 12 is a schematic diagram showing the relationship between minute pixels of the toner image formed on the toner image carrier and the surface properties of the recording paper.

As shown in FIG. 12A, when smooth paper having a small surface irregularity is used as the recording paper P, the entire toner image T on the toner image carrier R can be transferred to the recording paper P. However, as shown in FIG. 12C, when rough paper having a large surface unevenness is used as the recording paper P, the toner image is not formed at a portion corresponding to a low density portion of a monochromatic image, a fine line, and a fine character. Pixels in which T and the recording paper P only partially contact each other, or pixels in which the recording paper P does not contact at all occur. Therefore,
The force relationship of Fr <Fp described with reference to FIG. 11 cannot be satisfied, and the toner image T is not transferred to the recording paper P, and the transfer is omitted.

As a method for solving this problem, an elastic layer is formed on the surface of the toner image carrier, and the elastic layer is pressed to be deformed along the surface irregularities of the recording paper so that the adhesion between the toner image and the recording paper is improved. However, it is necessary to form an elastic layer having a thickness of several tens μm or more on the toner image carrier. However, when such a thick toner image carrier is used, a large amount of energy is required to heat the toner image carrier, resulting in an image forming apparatus having extremely large energy consumption. Also, in general, the thermal conductivity of the elastic member is low, and it takes time to heat the toner image via the toner image carrier with the heat from the heat source, so that an image cannot be continuously formed at high speed. There are also problems.

In view of the above circumstances, the present invention provides an image forming method capable of forming a high-quality image with less density unevenness and transfer omission without being affected by the surface properties of a recording medium, and an image forming method using the image forming method. It is an object of the present invention to provide an image forming apparatus for forming an image.

[0028]

In order to achieve the above object, an image forming method according to the present invention has a toner image based on image information carried on a predetermined toner image carrier, and the toner image carried on the toner image carrier. Is heated, and the toner image carrier and the recording medium are superposed and pressed so that the toner image is sandwiched between the toner image carrier and a predetermined recording medium. In the image forming method of forming an image on a recording medium by transferring and fixing the image on the recording medium, the image forming method includes a toner attachment area of each pixel of the toner image based on the image information or a plurality of pixels carried on the toner image carrier. The average toner adhesion area for each area is determined, and a transparent toner is selectively applied to the pixel or the area having the small toner adhesion area. Characterized by transferring and fixing the toner image with a transparent toner on a recording medium by superposing the above recording medium.

Here, the criterion for judging whether or not to apply the transparent toner in accordance with the size of the obtained toner adhesion area is changed in accordance with the surface properties of the recording medium on which the toner image is transferred and fixed. It is preferable that

In applying the transparent toner to a pixel or an area having a small toner adhesion area, it is preferable to apply the transparent toner so as to be vertically overlapped with the toner constituting the toner image.

In applying the transparent toner to a pixel or a region having a small toner attachment area, it is also a preferable embodiment to apply the transparent toner so as to surround the toner of each pixel forming a toner image.

When applying the transparent toner to a pixel or a region having a small toner adhesion area, the transparent toner is applied in a shape which overlaps with the toner constituting the toner image and which is wider than the spread of the toner for each pixel. Is also one of the preferred embodiments.

It is also a preferable embodiment to change the amount of the transparent toner applied according to the surface properties of the recording medium on which the toner image is transferred and fixed.

As the transparent toner, it is preferable to use a transparent toner having substantially the same optical characteristics as those of a thermoplastic resin which is a constituent material of the toner used for forming the toner image.

It is also preferable to use a transparent toner having a melting point lower than the melting point of the toner used for forming the toner image as the transparent toner.

Further, it is a preferable embodiment to use a transparent toner having a lower melt viscosity than the toner used for forming the toner image as the transparent toner.

Further, according to the image forming apparatus of the present invention which achieves the above object, a toner image based on image information is carried on a predetermined toner image carrier, and the toner image carried on the toner image carrier is heated. The toner image carrier and the recording medium are overlapped and pressed so that the toner image is sandwiched between the toner image carrier and a predetermined recording medium, so that the toner image is transferred onto the recording medium and fixed. In the image forming apparatus for forming an image on a recording medium, the toner adhesion area of each pixel of the toner image based on the image information, which is carried on the toner image carrier, or the average area of each area composed of a plurality of pixels. Pixel area detecting means for obtaining a proper toner adhesion area, and transparent toner is selectively applied to pixels or regions having a small toner adhesion area obtained by the pixel area detecting means. A transparent toner applying means that, characterized in that a transfer fixing means for transferring and fixing the toner image with a transparent toner in conjunction with the recording medium overlapped and the toner image bearing member and the recording medium.

Here, the image forming apparatus measures the surface property of the recording medium before receiving the transfer of the toner image, and the surface property of the recording medium measured by the surface property measuring means. It is preferable to include a transparent toner application amount changing unit that changes the application amount of the transparent toner applied by the transparent toner application unit based on the above.

In the image forming method and the image forming apparatus of the present invention, "transfer and fix" means that heating and pressurizing are performed simultaneously while the toner image carrier and the recording medium are superposed. , And a method of performing heating after performing heating in advance.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples.

[0041]

Embodiment 1 FIG. 1 is a schematic structural view showing a first embodiment in which the image forming method of the present invention is applied to a color copying machine.

The color copying machine shown in FIG. 1 has a photoreceptor belt 1 having a photoconductive layer on the surface, a charger 2 for uniformly charging the surface of the photoreceptor belt 1, and a black belt based on image information on the photoreceptor belt 1. And irradiating a minute spot light corresponding to an image signal for forming a toner image of each color of yellow, magenta, and cyan, and a transparent toner application signal for applying a transparent toner on the photosensitive belt 1 to these signals. An image exposure device 3 for forming a corresponding electrostatic latent image, and developing the electrostatic latent image formed on the photoreceptor belt 1 with a toner of a corresponding color and a transparent toner to form a transparent toner on the photoreceptor belt 1 Developing units 4a, 4b, 4c, which form a multicolor toner image including
4d, 4e, photoconductor belt 1 on which multicolor toner image is formed
And recording paper P are superimposed on each other, and heating / pressing rolls 5a and 5b for heating and pressurizing, rollers 6 for stretching the photosensitive belt 1, a recording paper tray 7 for accommodating the recording paper P, and conveying the recording paper P Image signal processing for processing an image signal input from an image input device (not shown) and outputting a color-separated image signal for each color and a transparent toner application signal for applying a transparent toner. Device 9
It has. Further, a cooling device 10 for cooling the heated and pressurized photosensitive belt 1 and the recording paper P is provided as needed.

The photoreceptor belt 1 in this embodiment corresponds to the toner image carrier of the present invention, and the developing devices 4a, 4b, 4c, and 4d correspond to the toner image forming means and the developing device of the present invention. Reference numeral 4e corresponds to the transparent toner applying means according to the present invention, and includes heating and pressing rolls 5a, 5b.
Corresponds to the transfer fixing means in the present invention.

The photoreceptor belt 1 is formed by forming a photoconductive layer on a conductive endless belt such as aluminum.
Arrow A stretched by the heating roll 5a and the roller 6
Circular movement in the direction. Since the photoconductive layer is heated to at least the melting temperature of the toner, α
An inorganic photoconductive material such as -Si, α-SiC, Se, and CdS is used.

As the toner of each color, a toner composed of a transparent thermoplastic resin containing a dye of each color can be used. In this color copying machine, a colored toner using a polyester having the following melt viscosity characteristics as a binder was used. The average particle size of the toner was set to about 7 μm in consideration of image quality and handling.

FIG. 2 is a graph showing temperature-viscosity characteristics of the toner used in the first embodiment.

As shown in FIG. 2, as the transparent toner,
A transparent thermoplastic resin containing no dye and having a lower melting point and lower viscosity than the colored toner is used. For example, styrene,
Homopolymer or copolymer of styrene such as vinyltoluene, α-methyltoluene, chlorostyrene, aminostyrene or a derivative or substituted product thereof, or methacrylic acid ester such as methacrylic acid, methyl methacrylate or ethyl methacrylate Homopolymers or copolymers, or homopolymers or copolymers of acrylic acid esters such as acrylic acid, methyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; or dienes such as butadiene and isoprene; acrylonitrile, or vinyl ether Kind,
Homopolymers of vinyl monomers, such as maleic anhydride, vinyl chloride, and vinyl acetate, or copolymers with other monomers, polyamides, polyesters, polyurethanes, etc. may be used alone or mixed. Can be used.

In this embodiment, a polyester transparent toner is used as the transparent toner in consideration of the compatibility with the colored toner when melted by heating and the optical characteristics after heat fusion with the colored toner. The average particle size and melt viscosity characteristics of the transparent toner were also set to be the same as those of the colored toner.

In the present invention, the optical properties of the thermoplastic resin used as a binder for each toner are important. Even if it is a colorless and transparent thermoplastic resin, the refractive index of light, the reflectance,
The transmittance is slightly different. If there is a difference between the optical properties of the binder of the colored toner and the binder of the transparent toner, when they are heated and melted and then cooled and integrated, turbidity occurs at the fusion interface, resulting in reduced transparency and degraded image quality. Let me do it. In the present embodiment, polyester was used as the transparent toner, and the same polyester was used as the thermoplastic resin as a constituent material of the colored toner used for forming the toner image. No such problems occurred.

The polyester can be produced by reacting a polyhydric alcohol with a polybasic carboxylic acid. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butanediol, and cyclohexane. Diols such as dimethanol, bisphenol A alkylene oxide adducts such as hydrogenated bisphenol A, and polyoxypropylene bisphenol A, and other dihydric alcohols can be used. Examples of polybasic carboxylic acids include, for example, maleic acid, fumaric acid, metaconic acid, citraconic acid, itaconic acid, terephthalic acid, isophthalic acid, cyclohexanedicarnbonic acid, succinic acid, acid anhydrides, alkyl esters, and others of these. 2
Basic carboxylic acids can be used.

As the heating roll 5a, a metal roll in which a heat source such as a halogen lamp is disposed, or a metal roll whose surface is coated with a heat-resistant elastic layer such as silicon rubber can be used. The heating temperature of the heating roll 5a is desirably set to a temperature at which the colored toner and the transparent toner in the heating and pressurizing section are necessary and sufficiently softened. In this embodiment, the temperature of the heating roll 5a is set to about 120 ° C. to 200 ° C. Set to. Further, the pressure roll 5b may have the same configuration as the heating roll 5a, and may be supplementarily heated from the back surface of the recording paper P.

In this embodiment, a recording paper is applied to the pressure roll 5b.
P and the photosensitive belt 1 are pressed against the heating roll 5a.
Pressure mechanism (not shown) is provided. Heating
The nip pressure of the heating / pressing unit by the pressure rolls 5a and 5b is 1k
g / cm^TwoIn the following cases, the photosensitive belt 1 and the recording paper P
Insufficient adhesion and insufficient contact between recording paper and toner
In this case, transfer omission occurs remarkably. In addition, the nip
Pressure is 10kg / cm ^TwoThe photoreceptor
Recording due to excessive stress on belt 1 and recording paper P
The paper P becomes wrinkled. Also high nip pressure
The support mechanism for supporting the robot becomes complicated, and the device becomes larger.
Nip pressure of the heating and pressurizing section is 1
kg / cm^TwoMore than 10kg / cm^TwoHope to be
Good.

Further, the pressing mechanism of the pressing roll 5b in the present embodiment is configured to be retractable, and while the toner image of each color is being formed on the photoreceptor belt 1, the pressing roll 5b is operated. The heating / pressing rolls 5a and 5b are separated from each other while being retracted to the retract position. Then, the formation of the multicolor toner image on the photoreceptor belt 1 is completed, and the heating / pressing rolls 5 a and 5 are synchronized with the timing at which the recording paper P is supplied from the recording paper tray 7 to the heating / pressing unit.
b are set at positions where they are pressed against each other.

FIG. 3 is a schematic diagram of an image signal processing device in the color copying machine shown in FIG.

The image signal processing device 9 converts the RGB data input from the image input device 11 into colors and outputs a toner image forming signal for each color.
1. A pixel area detection circuit 9_2 for calculating a toner adhesion area of each pixel of a toner image based on image information or an average toner adhesion area for each region including a plurality of pixels, and a pixel having a small toner adhesion area obtained. Alternatively, it is constituted by a transparent toner applying signal forming circuit 9_3 for forming a transparent toner applying signal for selectively applying a transparent toner to an area.

The pixel area detection circuit 9_2 in the present embodiment.
Corresponds to the pixel area detecting means according to the present invention, and the transparent toner applying signal forming circuit 9_3 in the present embodiment corresponds to the transparent toner applying signal forming means according to the present invention.

The image input device 11 takes in color images of various formats from the outside, and for example, 8 bits, 25 bits for each color of RGB (red, green, blue).
A total of 24 bits of RGB data of 6 gradations are output to the image signal processing device 9. The image signal processing circuit 9_1 performs color conversion of the input RGB data from the image input device 11, and converts the data into four colors of YMCK, which is the color space of the image forming apparatus of the present embodiment. If necessary, UCR (Under
Color Removal: MTF (M
Odulation Transfer Function
on) A process such as correction and output gradation correction is performed, and a toner image forming signal for each color is formed and output to the image exposure device 3 (see FIG. 1). Note that RGB data is generally used as an input color image signal from the image input device 11, but the Y color used in the YMC color space or Photo-CD is used.
Data in another color space such as the CC color space may be used. The color space of the image forming apparatus is not limited to the YMCK color space,
Other color spaces such as a color space and an RGB color space may be used.

The image data for each color processed by the image signal processing circuit 9_1 is converted into a transparent toner application signal forming circuit 9_3.
A transparent toner application signal for controlling the application of the transparent toner is formed based on the image data, and is output to the image exposure device 3.

FIG. 4 is a flowchart of the processing by the pixel area detecting circuit and the transparent toner applying signal forming circuit of the image signal processing apparatus shown in FIG.

In this pixel area detection circuit, as shown in FIG. 4, the size of the toner image for each pixel, that is, the toner adhesion area of each pixel is calculated based on the image data of each color (step S1). . The size of the toner image of each pixel is calculated based on the output resolution of the image forming apparatus and the density level signal of the pixel. When a plurality of color toner images overlap the same pixel, the largest value among them is set as the size of the pixel.

Next, the value of the size of the toner image calculated for each pixel is compared with a "predetermined value" set in advance (step S2), and the value of the size of each pixel is set to "predetermined value". The value of the"
If it is smaller than 0 and the value of the size of each pixel is not zero (step S3), a transparent toner application signal is output (step S4). If the determination conditions in steps S2 and S3 are not satisfied, no transparent toner application signal is output. In other words, if the toner image has a halftone dot structure that reproduces the gradation by changing the size of the dots, a pixel in which the dot diameter of each pixel of the output image is smaller than a predetermined diameter is searched, and the transparent toner is found there. Is given. If the toner image has a line structure in which the gradation is reproduced by changing the line thickness, the pixel width of each pixel of the output image is searched for a pixel smaller than a predetermined width, and a transparent pixel is found there. Apply toner. Also, when the toner image is a line image or a character image with a plain background, the transparent toner is applied to a position where the line width is smaller than a predetermined width. That is, the toner adhesion area of each pixel or the average toner adhesion area of each region including a plurality of pixels is obtained, and the transparent toner is selectively applied to the pixel or the area having the small toner adhesion area.

Various methods can be used for applying the transparent toner as described below.

FIG. 5 is a schematic diagram showing the state of application of the transparent toner in the present embodiment.

FIG. 5A shows a state in which the transparent toner G is applied so as to be superimposed on the toner constituting the toner image T on the toner image carrier R, and FIG. 3) shows a state in which the transparent toner G is applied so as to be superimposed below the toner constituting the toner image T on the toner image carrier R.

FIG. 5C shows the toner image carrier R
The state where the transparent toner G is applied so as to surround the toner of each pixel forming the toner image T is shown.

FIG. 5D and FIG. 5E show
The state in which the transparent toner G is applied in a shape that overlaps with the toner forming the toner image T on the toner image carrier R vertically and that is wider than the spread of the toner for each pixel is shown.

FIG. 6 is a schematic view showing the effect of applying a transparent toner to a toner image on a toner image carrier.

FIG. 6A shows a state of a transfer section in a conventional image forming apparatus to which no transparent toner is applied. As shown in FIG. 6A, when the minute pixels of the toner image T formed on the toner image carrier R overlap with the concave portions H of the recording paper P, the toner that does not come into contact with the recording paper P at all. This toner image T is not transferred to the recording paper P.

On the other hand, FIG. 6B shows the state shown in FIG.
This shows a state in which the transparent toner G is applied so as to be superimposed on the toner image T as shown in FIG. 3, whereby the height of the toner image T is increased and the upper part of the transparent toner G is recorded. The toner image T can be brought into contact with the concave portion H of the paper P, and the toner image T is transferred to the recording paper P.

FIG. 6C shows a state in which the transparent toner G is applied so as to surround the toner image T as shown in FIG. 5C. The total area of the toner image T increases, and the transparent toner G and the toner image T can be brought into contact with the concave portion H of the recording paper.

Further, FIG. 6D shows that the toner forming the toner image T on the toner image carrier R vertically overlaps with the toner as shown in FIG. This shows a state in which the transparent toner G is applied in a widened shape, and both the height and the area of the toner image T are increased by doing so, so that the toner image T is more reliably brought into contact with the recording paper P. be able to.

As described above, by applying the transparent toner to the pixels where the toner adhesion area of each pixel of the toner image is smaller than the "predetermined value", the minute toner image forming a high-resolution image is provided. Can be sufficiently brought into contact with the recording paper, so that a high-quality image without transfer omission can be formed.

Further, in the present embodiment, the criteria for judging whether or not to apply the transparent toner, which is to be compared with the value of the size of the toner image calculated for each pixel, is “ The "predetermined value" can be changed to three levels of smooth paper, plain paper, and rough paper according to the surface properties of the recording paper.

This determination is not limited to only the surface irregularities of the recording paper, and may be set more finely than the above three steps even when the surface irregularities of the recording paper are used as a criterion. The surface properties of the recording paper are as follows: smooth paper such as art paper has a concave portion having a depth of about 2 μm to 5 μm, and commonly used plain paper has a concave portion having a depth of 5 μm to 5 μm.
Approximately 20 μm, the depth of the concave portion is 30 μm for recycled paper or rough paper.
Some parts exceed m. The size of the concave portion ranges from a small size of about several μm to a size exceeding 100 μm, but most of the size is about 50 μm or less.

In this embodiment, the smooth paper has a concave portion having a depth of 2 μm.
m to about 5 μm, and the toner adhesion area of the pixel of the toner image can be sufficiently contacted with the recording paper even in the minimum case. Therefore, in the case of smooth paper, the “predetermined value” is set to zero and transparent. It was set not to apply toner. In the case of plain paper, the “predetermined value” was set to 30 μm to 50 μm. In the case of rough paper, the “predetermined value” is set to 50 μm to 80 μm.
It was set to μm. In the present embodiment, the above-mentioned "predetermined value" is manually input. However, it is also possible to measure the surface properties of the recording paper and automatically set the "predetermined value". Details of the automation will be described later.

Returning to FIG. 1, the image forming method in this embodiment will be described.

First, the surface of the photoreceptor belt 1 circulating in the direction of arrow A is uniformly charged by the charger 2, and then the first color (black) toner image output from the image signal processing device 9. In accordance with the formation signal, the surface of the photoreceptor belt 1 is optically scanned by the image exposure device 3 to form an electrostatic latent image. Next, the electrostatic latent image is developed with black toner by the developing device 4a to form a black toner image on the photoreceptor belt 1. The photoreceptor belt 1 on which the black toner image is formed circulates in the direction of arrow A, and the second point in time when the toner image formation start point of the photoreceptor belt 1 returns to the position facing the charger 2 again.
The color (yellow) image forming cycle is started. Similar to the first color, uniform charging by the charger 2, the image exposure device 3
, And toner image formation by the developing device 4b (yellow). Subsequently, toner images of the third color (magenta) and the fourth color (cyan) are formed.

Next, a transparent toner is applied to form the fifth color toner image. Transparent toner is applied from the first color
As in the case of forming the toner image of the fourth color, the surface of the photoreceptor belt 1 is uniformly charged by the charger 2, and then the exposure light corresponding to the transparent toner application signal output from the image signal processing device 9 is subjected to image exposure. The surface of the photoreceptor belt 1 is irradiated by the device 3,
An electrostatic latent image for applying a transparent toner is formed. Next, the electrostatic latent image is developed with a transparent toner by the developing device 4e to provide a transparent toner image on the multicolor toner image on the photoreceptor belt 1.

In the color copying machine of the present embodiment shown in FIG. 1, the developing unit 4e for the transparent toner is disposed downstream of the developing units 4a, 4b, 4c, 4d for the respective color toners in the photosensitive belt moving direction. In this case, the transparent toner is applied after the toner image of each color is formed on the surface of the photoreceptor belt 1. However, the arrangement of the developing unit 4e for the transparent toner and the order of development are limited to this. Instead, for example, the developing unit 4e using the transparent toner may be disposed upstream of the developing unit for each color toner in the moving direction of the photoconductor belt, and the application of the transparent toner may be performed before forming the toner image of each color.

After the black, yellow, magenta, and cyan toner images and the transparent toner image are superimposed on the photosensitive belt 1 to form a multicolor toner image, the photosensitive belt 1 further circulates and moves. When the head of the multicolor toner image reaches the heating / pressing unit sandwiched between the heating / pressing rolls 5a and 5b, the recording paper P is supplied from the recording paper tray 7 to the heating / pressing unit at the same time. Come. Since the photoreceptor belt 1 on which the multicolor toner image has been formed reaches the heating and pressing unit while being heated by the heating roll 5a, the toner image is sufficiently heated when reaching the heating and pressing unit. In this state, the photosensitive belt 1 and the recording paper P are overlapped and heated and pressed by the heating / pressing rolls 5a and 5b, so that the multicolor toner image is transferred and fixed onto the recording paper P, and the photosensitive belt is 1 and the recording paper P are crosslinked.

The multicolor toner image may be heated only by the heating / pressing unit without heating the multicolor toner image before the heating / pressing unit. In order to heat the toner image, a sufficient heating time is required, and for that purpose, it is necessary to increase the contact area with the heating / pressing unit. However, in the heating / pressing unit, it is necessary to apply a high pressure in order to bring the toner image and the recording paper P into sufficient contact, and a complex mechanism that supports a very high pressure is required to realize these. Inevitably increase the size and cost of the device. Therefore, it is desirable to heat the toner image before the heating and pressurizing unit as in this embodiment.

The photosensitive belt 1 and the recording paper P are heated and
After being heated and pressurized by the pressure rolls 5a and 5b, when the recording paper P is conveyed in a state of close contact and reaches the roller 6 having a small curvature, the recording paper P is sensitized by the stiffness of the recording paper itself. Peeled off from If the toner image sandwiched between the photosensitive belt 1 and the recording paper P is not sufficiently cooled by the time the toner image reaches the separation portion, the cohesive force Ft of the toner image and the adhesive force between the toner and the photosensitive belt 1 Since a force relationship of Ft> Fr cannot be obtained with respect to Fr, in this embodiment, the cooling device 10 is used to cool the toner image until the above-mentioned force relationship is established. As the cooling means, a simple air cooling fan or the like can be used.

The image output by the color copying machine of this embodiment has almost no density unevenness. Even when a high-resolution digital image is formed, a low-density portion of a single-color image, fine lines and fine character details, etc. In the conventional method, the portion where the transfer omission was remarkable is also well transferred,
A high quality image without density unevenness and transfer omission was formed.

Further, by controlling the application of the transparent toner in accordance with the surface texture of the recording paper, a high quality image can be stably formed even when various recording papers having different surface textures are used. Was. Since it is not necessary to form an elastic layer or the like on the photoreceptor belt 1, a reduction in image forming speed and an increase in energy consumption did not occur. <Embodiment 2> FIG. 7 is a schematic diagram showing a second embodiment in which the image forming method of the present invention is applied to a color copying machine.

The color copying machine shown in the second embodiment differs from the color copying machine shown in the first embodiment shown in FIG. 1 in that it rotates in the direction of arrow B as a first toner image carrier. A photoconductor drum 14 having a photoconductive layer formed on the surface of a drum-shaped conductive substrate is used, and an endless belt-shaped intermediate transfer belt 15 circulating in the direction of arrow C as a second toner image carrier is used. This is a so-called intermediate transfer type image forming apparatus.

In the second embodiment, the toner image carrier is
Except for the difference from the toner image carrier in the first embodiment shown in FIG. 1, the charger 2, the image exposure device 3, the developing device 4a,
4b, 4c, 4d, 4e, heating / pressing rolls 5a, 5
b, roller 6 for stretching intermediate transfer belt 15, recording paper P
The recording paper tray (not shown) for accommodating the recording paper, the recording paper transport means (not shown) for transporting the recording paper P, the image signal processing device 9, the cooling device 10, and the like are the same as those in the first embodiment shown in FIG. The description is omitted because it is almost the same.

The intermediate transfer belt 15 in this embodiment is
It corresponds to the toner image carrier according to the present invention.

In addition, in addition to the above-described components, this color copying machine has a primary transfer copying unit 16 and a cleaning device 1.
7 are provided. As the primary transfer means 16, a high voltage is applied to the electrode wire to generate a corona discharge to give a charge of the opposite polarity to the toner on the back surface of the intermediate transfer belt 15,
A corotron for forming a transfer electric field between the photosensitive drum 14 and the intermediate transfer belt 15 was used.

The primary transfer in this embodiment is the transfer of the toner image from the photosensitive drum 14 to the intermediate transfer belt 15, and the surface properties and electrical characteristics of both can be controlled as described above. Since the surface properties and the electrical characteristics of the recording paper are stable, electrostatic transfer with very little unevenness can be performed. The primary transfer unit 16
Alternatively, a conductive roll or conductive brush may be disposed on the back surface of the intermediate transfer belt and a bias voltage may be applied thereto.

As the cleaning device 17, a cleaning device of a type in which a blade is brought into contact with the photosensitive drum 14 to scrape off residual toner was used.

As the intermediate transfer belt 15 in this embodiment, a belt having a two-layer structure including a base layer and a surface layer was used. For the base layer, a polyimide film having a thickness of 70 μm and having an electric resistance adjusted to 10 ⁷ Ω to ^{10 10} Ω by adding carbon black was used. As the base layer, it is possible to use a sheet having high heat resistance in addition to the above,
For example, polyester, polyethylene terephthalate,
A polymer sheet such as polyethersulfone, polyetherketone, polysulfone, polyimide, polyimideamide, or polyamide can be used. For the surface layer, a silicon copolymer having a thickness of 5 μm was used.
Since the silicone copolymer has a property of easily separating from the toner that has been melted and fluidized by heat, it is an optimal material for efficiently transferring the toner image from the intermediate transfer belt 14 to the recording paper P. In addition, a resin layer having a high releasability can be applied to the surface layer in addition to the silicon copolymer. For example, a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, polytetrafluoroethylene, or the like can be used. .

Next, an image forming method using this color copying machine will be described.

First, the surface of the photosensitive drum 14 rotating in the direction of arrow B is uniformly charged by the charger 2, and then the first color (black) toner image output from the image signal processing device 9 is formed. In response to the signal, the surface of the photosensitive drum 13 is optically scanned by the image exposure device 3 to form an electrostatic latent image. Then
The electrostatic latent image is developed with black toner by the developing device 4a to form a black toner image on the photosensitive drum 14. next,
The first color (black) toner image formed on the photosensitive drum 14 is transferred to the intermediate transfer belt 1 by the transfer corotron 16.
5 is primarily transferred onto the photosensitive drum 5 and is not transferred.
The unnecessary toner is scraped off by the cleaning device 17. The second color (yellow) image forming cycle is started at the timing when the photosensitive drum 14 further rotates and the toner image formation start point on the photosensitive drum 14 returns to the position facing the charger 2 again. . The circumferential length of the intermediate transfer belt 15 is an integral multiple of the outer circumference of the photosensitive drum 14, particularly, is equal in this embodiment, and the toner images formed on the photosensitive drum 14 are sequentially superimposed by the transfer corotron 16. Is transcribed. In this manner, the multicolor toner image is formed by superimposing the toner image of each color and the transparent toner on the intermediate transfer belt 15. In the present embodiment, the application of the transparent toner to the intermediate transfer belt 15 is performed after the image formation with the toner of each color. However, the application of the transparent toner is not limited to this order. It may be performed before.

Next, the intermediate transfer belt 15 carrying the multicolor toner image to which the transparent toner is applied is supplied to the heating / pressing unit at the same timing as the recording paper P conveyed from the recording paper tray, and the Heating and pressurization by the pressure rolls 5a and 5b. The heating and pressing conditions at this time are the same as in the first embodiment.

The intermediate transfer belt 15 and the recording paper P heated and pressed by the heating / pressing rolls 5a and 5b are conveyed in a state of close contact, and when they reach the roller 6 having a small curvature, the recording paper P becomes the recording paper itself. Is peeled off from the intermediate transfer belt 15 by the strength of the waist. If the toner image sandwiched between the intermediate transfer belt 15 and the recording paper P is not sufficiently cooled by the time it reaches the separation portion, a cooling device 10 such as a simple air cooling fan is disposed to sufficiently cool the toner image. Cooling.

The image output by the image forming apparatus of the present embodiment has almost no density unevenness. Even when a high-resolution digital image is formed, a low-density portion of a single-color image, fine lines and fine character details, etc. According to the conventional method, a portion where transfer omission is remarkable is also transferred well, and a high-quality image without density unevenness and transfer omission can be formed. <Embodiment 3> FIG. 8 is a schematic structural view showing a third embodiment in which the image forming method of the present invention is applied to a color copying machine.

The color copying machine shown in the third embodiment is different from the color copying machine shown in the first embodiment shown in FIG. 1 in that black, yellow,
Photoconductor drums 14 corresponding to each color of magenta and cyan
a, 14b, 14c, 14d, and a photosensitive drum 14e for applying a transparent toner, and an endless belt-shaped intermediate transfer belt 15 circulating in the direction of arrow E as a second toner image carrier. This is a so-called intermediate transfer type image forming apparatus.

The intermediate transfer belt 1 in this embodiment is
Reference numeral 5 corresponds to the toner image carrier according to the present invention.

The color copying machine rotates in the direction of arrow D, and includes photosensitive drums 14a, 14b, 14c, and 14d corresponding to black, yellow, magenta, and cyan, and photosensitive drums for applying transparent toner. 14e, and chargers 2a, 2b, 2 for uniformly charging each photosensitive drum.
c, 2d, and 2e; an image exposure device 3 that irradiates the surface of each photosensitive drum with exposure light corresponding to an image of each color to form an electrostatic latent image on each photosensitive drum; Toner developing units 4a, 4b, 4c, 4d of each color for developing the electrostatic latent image formed thereon, and a developing unit 4e for transparent toner for forming a transparent toner image, and a toner image formed on each photosensitive drum An intermediate transfer belt 15 on which is primarily transferred,
Transfer rolls 18a, 1 for electrostatically transferring toner images on the respective photosensitive drums so as to be superimposed on the intermediate transfer belt 15.
8b, 18c, 18d, 18e and the intermediate transfer belt 15
A heating roll 5a for heating the transparent toner multicolor toner image transferred thereon, and pressing rolls 5b and 5c for overlapping and pressing the intermediate transfer belt 15 and the recording paper P so as to sandwich the heated toner image therebetween. Recording paper tray 7 for accommodating recording paper P, recording paper transport means 8 for transporting recording paper P,
A cooling device 10 for cooling the heated and pressurized toner image on the recording paper P, and an image signal input from an image input device (not shown) are processed, and an image signal and a transparent toner that have been separated for each color are processed. An image signal processing device 9 for outputting a transparent toner application signal for application is provided.

Each of the above chargers, image exposure device 3, developing devices 4a, 4b, 4c, 4d, 4e, roller 6 for stretching intermediate transfer belt 15, recording paper tray 7 for accommodating recording paper P, recording paper The recording paper conveying means 8 for conveying P, the image signal processing device 9, the cooling device 10 and the like are almost the same as those in the first embodiment shown in FIG.

Next, an image forming method using the color copying machine will be described.

First, the photosensitive drum 1 corresponding to each color of black, yellow, magenta, and cyan rotating in the direction of arrow D
A toner image of each color and a transparent toner image are formed on 4a, 14b, 14c, 14d, and 14e, and then, a toner image of each color formed on each photosensitive drum by transfer rolls 18a, 18b, 18c, 18d, and 18e. The transparent toner images are sequentially transferred onto the intermediate transfer belt 15 in a superimposed manner. At this time, the intermediate transfer belt 1 circulating in the direction of arrow E in FIG.
5, it is necessary to adjust the timing so that the toner image of each color and the transparent toner image are accurately overlapped. The multicolor toner image formed on the intermediate transfer belt 15 is
After being heated sufficiently, the recording paper P is conveyed to the portions of the pressure rolls 5b and 5c, where it is pressed while being superposed on the recording paper P conveyed from the recording paper tray 7.

Transfer Roll 1 in Primary Transfer of this Example
As 8a, 18b, 18c, 18d, and 18e, metal rolls coated with polyurethane rubber whose electric resistance was controlled to 10 ⁶ to 10 ⁸ Ω were used. The intermediate transfer belt 15 used in this embodiment is the same as that used in the second embodiment.

The primary transfer in this embodiment is also similar to that of the second embodiment, and each of the photosensitive drums 14a, 14b, 14c, 14
d, 14e to transfer the toner image from the intermediate transfer belt 15 to the intermediate transfer belt 15. Since the surface properties and the electrical properties of the two can be controlled as described above, and are stable compared to the properties of the recording paper. Thus, electrostatic transfer with very little unevenness can be performed.

In the secondary transfer of the present embodiment, unlike the first and second embodiments, the heating of the toner image formed on the intermediate transfer belt 15 and the pressing of the recording paper P are performed separately. Done. The temperature setting of the heating roll 5a was set in a range from 160 ° C. to 240 ° C., which was higher than the temperature setting in Examples 1 and 2 in which pressure was applied simultaneously with heating. The pressing conditions by the pressing rolls 5b and 5c were the same as those in the first and second embodiments.

In the image forming method of the present embodiment, when the intermediate transfer belt 15 on which the multicolor toner image is formed and the recording paper P are overlaid and pressed, no heating source is provided.
The temperature of the toner image drops sharply, and a sufficient adhesive force Fp with the recording paper P cannot be obtained. Therefore, as described above, it is necessary to heat the toner image on the intermediate transfer belt 15 to a higher temperature than in the first and second embodiments by the heating roll 5a. However, the recording paper P and the heating roll 5a do not come into indirect contact with each other, and unnecessary heat is not deprived by the recording paper P, so that the total energy may be reduced. Also, the recording paper P
Since it is not heated, it has the advantage that the temperature of the toner image after passing through the pressurizing section is rapidly lowered, and the advantage that the safety in the event of paper jam is high.

The intermediate transfer belt 15 and the recording paper P pressed by the pressure rolls 5b and 5c are conveyed in a state of being in close contact with each other.
Is separated from the intermediate transfer belt 1 by the stiffness of the recording paper itself. If the toner image sandwiched between the intermediate transfer belt 15 and the recording paper P is not sufficiently cooled before reaching the separation portion, the cooling device 10 such as an air-cooling fan cools the toner image sufficiently. Can be.

In this embodiment, the intermediate transfer belt 15
Although the application of the transparent toner to the toner is performed after the image formation by the toner of each color, the present invention is not limited to this order, and the application of the transparent toner may be performed first.
The pressing mechanism using the pressing rolls 5 b and 5 c is configured to be retractable, and while forming the toner images of each color on the intermediate transfer belt 15, the pressing rolls 5 b and 5 c are used.
c to the retracted position, and the heating / pressing roll 5
a and 5b are separated from each other.

The image output by the color copying machine of the present embodiment has almost no density unevenness, and even if a high-resolution digital image is formed, the density of a low-density portion of a single-color image, fine lines and fine character details, etc. In the conventional method, the portion where the transfer omission was remarkable is also well transferred,
A high quality image without density unevenness and transfer omission was formed. <Embodiment 4> Next, a description will be given of an embodiment in which a surface texture measuring device for measuring the surface texture of the recording paper P is provided on the recording paper tray or the recording paper transport path in each of the above-described embodiments.

FIG. 9 is a schematic diagram of a recording paper surface texture measuring device used in each embodiment of the present invention.

The surface texture measuring device 19 shown in FIG. 9 includes an LED lamp 20 for irradiating the surface of the recording paper P with light for measurement.
And a two-dimensional CCD sensor 22 that receives light reflected from the surface of the recording paper P via a lens 21, and measures the surface properties of the recording paper P from output data of the CCD sensor 22. In addition to this method, various types of displacement meters such as a stylus type shape measuring device and a laser displacement meter may be used for measuring the surface texture.

The two-dimensional data taken in from the CCD sensor 22 is limited in spatial frequency band by a band-pass filter, and the surface roughness of the recording paper P is calculated using the two-dimensional data in which the spatial frequency band is limited. The calculated surface roughness data of the recording paper P is input to the image signal processing device 9 (see FIG. 1), and based on the surface roughness data, a criterion for determining whether or not to apply the transparent toner is determined. Is set.

In this embodiment, as in the first embodiment, the types of recording paper are set in three stages: smooth paper, plain paper, and rough paper. Ten-point average roughness is used as an index of surface roughness, and when the value of ten-point average roughness is 10 μm or less, smooth paper, 10 μm to
When it was 20 μm, it was determined as plain paper, and when it was 20 μm or more, it was determined as rough paper.

Note that the criterion is not limited to the above example, and may be set in more detail than the above three steps. Further, the surface property of the recording paper P may be determined based on the center surface roughness or the area average roughness which is another index of the surface roughness. The “predetermined value” corresponding to each type of recording paper was the same as in the first embodiment.

Such a surface texture measuring device 19 is disposed on the recording paper tray 7 (or the periphery of the recording paper transport path 8) as shown in FIG. 1, for example.
The measurement data measured by the above is used in the transparent toner application signal forming circuit 9_3 (see FIG. 3) to change the amount of transparent toner application in accordance with the surface texture of the recording paper, thereby using various recording papers having different surface properties. However, a high-quality image can be stably formed.

The surface texture measuring device 19 corresponds to the surface texture measurement according to the present invention, and the transparent toner applying signal forming circuit 9_3 (see FIG. 3) used in this embodiment is a It also serves as the transparent toner application amount changing means according to the invention.

Further, according to the data of the surface roughness of the recording paper P, the application amount and application range of the transparent toner can be changed. When changing the application range of the transparent toner,
The processing can be performed by the transparent toner application signal processing circuit 9_3. The amount of the transparent toner to be applied can be changed by changing the value of the current flowing through the wire of the charger 2, the amount of light of the image exposure device 3, or the developing bias of the developing device 4e.

As described above, by changing the application amount and the application range of the transparent toner in accordance with the surface properties of the recording paper, the application of the transparent toner is optimized. A high-quality image could be formed stably. <Embodiment 5> In each embodiment described above, an example will be described in which a transparent toner having a lower melting point or melt viscosity than a colored toner is used as the transparent toner.

As shown in FIG. 2, in the first embodiment,
As the transparent toner, a toner composed of a transparent thermoplastic resin having a lower melting point and a lower viscosity than a colored toner and containing no pigment is used. The same applies to the transparent toner used in the fifth embodiment. The transparent toner of the fifth embodiment is made of polyester, and the melting point of the polyester resin is controlled mainly by controlling the molecular weight. The average particle size of the transparent toner was about 7 μm, which is equivalent to that of the colored toner, and an external additive such as a conventionally known charge control agent was used as needed.

By doing so, when the multicolor toner image formed on the toner image carrier is heated, the transparent toner is reliably heated and melted, and the fluidity is increased. Since the heat fusion is performed, the toner image can be transferred more reliably. Therefore, a high-quality image with less transfer omission can be formed.

However, if the melting point of the transparent toner is too low, the transparent toner may agglomerate in the developing device, or if the output image is exposed to a high temperature, the adhesiveness of the image may increase and the contact object may be damaged. Or stick to it. If the melt viscosity of the transparent toner is too low, the image will flow when the multicolor toner on the toner image carrier is heated, or the transparent toner will adhere to the recording paper when heated in close contact with the recording paper. This causes a problem that the transparent toner does not exhibit sufficient transfer force. Therefore, it is necessary to set the melting point of the transparent toner so that the above-described problem does not occur. The melt viscosity is at least 100 Pa · s or more, preferably 1000 Pa · s or more.
Desirably, it is Pa · s or more.

In each of the embodiments described above, an apparatus provided with an electrophotographic toner image forming means has been described. However, the present invention is not limited to this. A toner image may be formed by directly flying toner based on digitally processed image data, and a magnetic latent image based on digitally processed image data may be formed on a predetermined toner image carrier. An image may be formed and a toner image corresponding to the magnetic latent image may be formed. Alternatively, a charge image based on digitally processed image data is directly written on a predetermined toner image carrier, and the image is statically formed. After forming an electrostatic latent image, a method of forming a toner image based on the electrostatic latent image may be used.

[0123]

As described above, according to the image forming method of the present invention, the toner adhering area of each pixel of the toner image based on the image information, which is carried on the toner image carrier, or is composed of a plurality of pixels. The average toner adhesion area for each area is determined, and the transparent toner is selectively applied to the pixel or the area having the small toner adhesion area, and then the toner image carrier and the recording medium are superposed on each other. Since the toner image is transferred and fixed together with the transparent toner at the same time, even when a high-resolution digital image is formed, transfer omissions occur remarkably in the conventional method such as a low-density portion of a single-color image and fine lines and fine character details. Since the transparent toner is applied to the portion where the toner image has been applied, the toner image and the recording paper come into sufficient contact, and the toner image can be reliably transferred to the recording paper. An image forming method capable of forming a low-quality image density unevenness or transfer void without receiving Jo effects can be achieved.

Further, according to the image forming apparatus employing the image forming method of the present invention, since the above-described image forming method is employed, the density non-uniformity and the transfer loss can be reduced without being affected by the surface properties of the recording medium. An image forming method capable of forming a high-quality image and an image forming apparatus for forming an image by the image forming method can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment in which the image forming method of the present invention is applied to a color copying machine.

FIG. 2 is a graph showing temperature-viscosity characteristics of the toner used in the first embodiment.

FIG. 3 is a schematic diagram of an image signal processing device in the color copying machine shown in FIG.

FIG. 4 is a flowchart of a process performed by a pixel area detecting unit and a transparent toner applying signal forming unit of the image signal processing apparatus shown in FIG. 3;

FIG. 5 is a schematic diagram illustrating a state of applying a transparent toner according to the exemplary embodiment.

FIG. 6 is a schematic diagram illustrating an effect of applying a transparent toner to a toner image on a toner image carrier.

FIG. 7 is a schematic configuration diagram showing a second embodiment in which the image forming method of the present invention is applied to a color copying machine.

FIG. 8 is a schematic configuration diagram showing a third embodiment in which the image forming method of the present invention is applied to a color copying machine.

FIG. 9 is a schematic diagram of a recording paper surface texture measuring device used in each embodiment of the present invention.

FIG. 10 is a schematic configuration diagram of a conventional image forming apparatus employing a simultaneous transfer and fixing method.

FIG. 11 is a diagram illustrating a transfer state of a toner image in a conventional transfer simultaneous fixing method using heat.

FIG. 12 is a schematic diagram illustrating a relationship between minute pixels of a toner image formed on a toner image carrier and surface properties of a recording sheet.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 photoreceptor belt 2, 2 a, 2 b, 2 c, 2 d, 2 e charger 3 image exposure device 4 a, 4 b, 4 c, 4 d, 4 e developing device 5 a, 5 b heating / pressure roll 5 c pressure roll 6 roller 7 recording paper tray Reference Signs List 8 recording paper conveying means 9 image signal processing device 9_1 image signal processing circuit 9_2 pixel area detection circuit 9_3 transparent toner applying signal forming circuit 10 cooling device 11 image input device 14, 14a, 14b, 14c, 14d, 14e photosensitive drum 15 intermediate Transfer belt 16 Primary transfer copying means 17 Cleaning device 18a, 18b, 18c, 18d, 18e Transfer roll 19 Surface texture measuring device 20 LED lamp 21 Lens 22 Two-dimensional CCD sensor

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G03G 15/24 G03G 15/24 2H078 (72) Inventor Hirokazu Mukai 430 Nakaicho Sakai, Ashigara-gun, Kanagawa Prefecture Green Tech Nakai Fuji Xerox Co., Ltd. Inside the company (72) Inventor Yu Ichime 430 Nakai-cho, Ashigami-gun, Kanagawa Prefecture Green Tech Nakai Fuji Xerox Co., Ltd.F-term (reference) 2H032 AA02 AA15 BA05 BA09 BA18 DA13 2H033 AA11 BB01 BB28 2H078 CC06 DD52 DD57 DD73

Claims (11)

[Claims] 1. A toner image carrier based on image information is carried on a predetermined toner image carrier, the toner image carried on the toner image carrier is heated, and the toner image is recorded on the toner image carrier by a predetermined recording method. The toner image carrier and the recording medium are superposed and pressed so as to be sandwiched between the recording medium and the toner image, so that the toner image is transferred onto the recording medium and fixed to form an image on the recording medium. In the image forming method for forming, the toner adhesion area of each pixel of the toner image based on the image information carried on the toner image carrier or the average toner adhesion area of each region including a plurality of pixels is obtained and calculated. The transparent toner is selectively applied to the pixels or areas having a small toner adhesion area, and then the toner image carrier and the recording medium are superposed on each other to form a transparent toner image on the recording medium. Image forming method characterized by transferring and fixing together over. 2. A criterion for determining whether or not to apply a transparent toner in accordance with the size of the obtained toner adhesion area is changed in accordance with the surface properties of a recording medium on which a toner image is transferred and fixed. The image forming method according to claim 1, wherein: 3. The method according to claim 1, wherein when the transparent toner is applied to a pixel or an area having a small toner adhesion area, the transparent toner is applied so as to be vertically overlapped with the toner constituting the toner image. Image forming method. 4. The method according to claim 1, wherein the transparent toner is applied to a pixel or a region having a small toner adhesion area so as to surround the toner of each pixel forming a toner image. Image forming method. 5. When applying a transparent toner to a pixel or an area having a small toner adhesion area, the transparent toner is applied in a shape that vertically overlaps a toner constituting a toner image and is wider than a spread of the toner of each pixel. The image forming method according to claim 1, wherein: 6. The image forming apparatus according to claim 3, wherein the amount of the transparent toner to be applied is changed in accordance with the surface properties of the recording medium on which the toner image is transferred and fixed. Method. 7. The method according to claim 1, wherein the transparent toner is a transparent toner having substantially the same optical characteristics as those of a thermoplastic resin which is a constituent material of the toner used for forming the toner image. 7. The image forming method according to any one of 6. 8. The image according to claim 1, wherein a transparent toner having a melting point lower than a melting point of the toner used for forming the toner image is used as the transparent toner. Forming method. 9. The toner according to claim 1, wherein a transparent toner having a lower melt viscosity than a toner used for forming the toner image is used as the transparent toner. Image forming method. 10. A toner image carrier based on image information is carried on a predetermined toner image carrier, and the toner image carried on the toner image carrier is heated and the toner image is recorded on the toner image carrier in a predetermined manner. The toner image carrier and the recording medium are overlapped and pressed so as to be sandwiched between the recording medium and the toner image carrier, and the toner image is transferred onto the recording medium and fixed to form an image on the recording medium. In the image forming apparatus for forming, a pixel area for obtaining a toner adhesion area of each pixel of a toner image based on image information, or an average toner adhesion area for each region including a plurality of pixels, carried on the toner image carrier. Detecting means; transparent toner applying means for selectively applying transparent toner to pixels or areas having a small toner adhesion area determined by the pixel area detecting means; An image forming apparatus comprising: a transfer / fixing unit that transfers a toner image onto a recording medium together with a transparent toner and fixes the toner image on the recording medium by superposing a holding body and the recording medium. 11. A surface property measuring means for measuring the surface property of the recording medium before receiving the transfer of the toner image, and the transparent toner applying means based on the surface property of the recording medium measured by the surface property measuring means. The image forming apparatus according to claim 10, further comprising: a transparent toner application amount changing unit configured to change an application amount of the transparent toner provided by the control unit.