JPH1124405A - Method and device for forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an image obtained in an electrophotographic process, specially to improve the reproducibility of a highlight part of image information by using a toner having a low-concentration colorant and low in a charge quantity for the highlight part and using a toner having a high-concentration colorant and high in a charge quantity for a high-concentration part. SOLUTION: Two kinds of toners are used as for respective colors each as cyan, magenta, yellow and black by a developing unit. That is, an electrostatic latent image corresponding to a highlight part is developed by the low- concentration toner whose the charge quantity is low and an electrostatic latent image corresponding to a high-concentration part is developed by the high- concentration toner whose the charge quantity is high. The content of the colorant included in the toner having the low-concentration colorant and whose the charge quantity is low is preferably adjusted so as to become coloring ability within the range of 30 to 70 when the coloring ability of the toner which includes the high-concentration colorant and whose the charge quantity is high is made to 100. Besides, the charge quantity of the toner whose the charge quantity is low is preferably 10-90, more preferably 30-70 when the charge quantity of the toner whose the charge quantity is high is made to 100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic process.
The present invention relates to an image forming method for recording and visualizing image information on a transfer material such as paper.

[0002]

2. Description of the Related Art An image forming apparatus for forming a full-color image by using an electrophotographic process usually includes cyan, magenta,
An image is formed using four color toners of yellow and black. However, the image quality obtained by the electrophotographic process is lower than that of photographs and prints. When trying to express highlight areas (light density image areas) in the electrophotographic process, uneven image density (unevenness, roughness)
Occurs. The non-uniformity of the image density occurs because it is very difficult to uniformly arrange a small number of toners. In order to solve the above problems, Japanese Patent Laid-Open
JP-A-35038 proposes producing an image using a plurality of types of toners having different coloring densities for each of cyan, magenta, yellow, and black toners. In other words, by using two types of toner of each color for each color, using a light toner for the highlight part and further increasing the pixel unit of the highlight part,
This is to improve the reproducibility of the highlight portion.
However, although the image density non-uniformity is improved to some extent, in this method, the graininess decreases because the area of the highlight portion is increased. As a result, the image quality of the highlight part is hardly improved.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to improve an image obtained by an electrophotographic process, and in particular, to improve reproducibility of a highlight portion.

[0004]

The above object is achieved by the image forming method according to the present invention. In summary, the present invention makes an electrostatic latent image formed on an image carrier in accordance with image information visible by toner stored in a developing unit, transfers the visualized toner image to a transfer material, and prints the image. In the obtained image forming method, the toner separately includes a toner having a low concentration of a colorant and a low charge amount, and a toner having a high concentration of a colorant and a high charge amount, The toner having the low-concentration colorant and having a low charge amount is used for the highlight portion, and the toner having the high-concentration colorant and having a high charge amount is used for the high-density portion. An image forming method characterized by the following.

Further, the present invention provides a means for forming an electrostatic latent image on an image carrier in accordance with image information, a plurality of developing means for performing development with toner, and transferring a toner image which has been revealed to a transfer material. In an image forming apparatus having a transfer unit, a plurality of developing units include a toner having a low concentration of a colorant and a low charge amount, and a toner having a high concentration of a colorant and a high charge amount. An image forming apparatus that is housed individually. (Hereinafter, "toner having a low concentration and low charge amount" and "toner having a low concentration and low charge amount" are referred to as "toner having a high concentration of the colorant and high charge amount." Is sometimes referred to as “high-density and high-charge amount toner”.)

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The image forming method of the present invention is obtained by, for example, uniformly charging a photosensitive drum with a charger to make the surface of the photosensitive drum a uniform potential, and then performing color separation on the photosensitive drum. When forming an electrostatic latent image by exposing with a laser beam or the like based on the image information, the image information is divided into a highlight portion and a high-density portion, and based on the image information of each of the highlight portion and the high-density portion. To expose the photoconductors separately to form respective electrostatic latent images.

When the image information is divided into a highlight portion and a high-density portion, for example, in the case of a halftone image or a line image for each color, the image area per unit area is 3
It is preferred to split between 0% and 70%.

The developing device includes, for each of the colors such as cyan, magenta, yellow, and black, the low-density and low-charge amount toner used for the highlight portion and the high-density and high-charge amount toner used for the high-density portion. Two types of toners are used. As a developing method, a non-magnetic one-component or two-component developing method is used. As for black, one magnetic component can be further used. Here, the electrostatic latent image corresponding to the highlight portion is developed with low-density and low-charge amount toner, and the electrostatic latent image corresponding to high-density is developed with high-density and high-charge amount toner. When two developing devices are used, one each for cyan, magenta, yellow, and black, eight times of electrostatic latent image formation and development are required to obtain a full-color image.

The colorant content of a toner having a low concentration of a colorant and having a low charge amount is defined assuming that the coloring power of a toner having a high concentration of a colorant and having a high charge amount is 100. 3
It is desirable to adjust the coloring power in the range of 0 to 70.

The charge amount of a toner having a low concentration of a colorant and having a low charge amount is defined as follows: when the charge amount of a toner having a high concentration of a colorant and having a high charge amount is 100, 1
It is preferably 0 to 90, more preferably 3
Desirably, it is 0 to 70.

In the present invention, when the average particle diameter of the low-density and low-charge toner is equal to that of the high-density and high-charge toner, the low-density and low-charge toner is colored with respect to the high-density and high-charge toner. The power ratio is set to be between 30% and 70%, and the ratio of the charge amount of the low-density and low-charge toner to the high-density and high-charge toner is the value of the set coloring power ratio. It is desirable to set so as to be approximately the same. That is, it is desirable to set the value of the charge amount ratio to about ± 20% of the set value of the coloring power ratio. For example, the coloring power of the low-density and low-charge amount toner with respect to the high-density and high-charge amount toner is 5%.
When set to 0%, the low-density and low-charge amount toner is 50% more charged than the high-density and high-charge amount toner.
It is preferable to set to about ± 20%. As described above, when the coloring power and the charge amount of the low-density and low-charge amount toner with respect to the high-density and high-charge amount toner are both reduced by the same ratio, when developed, both the highlight portion and the high-density portion are developed. As a result, a uniform toner thickness can be obtained as a whole, and as a result, an effect of obtaining a uniform gloss can be obtained.

The charge amount (charge amount per unit weight) can be measured by a blow-off tribo apparatus or the like.

In the present invention, known toner binders, colorants and the like can be used. As the toner binder, styrene acrylic resin, polyester resin,
Epoxy resins and the like are preferably used. As the secondary binder, waxes, petroleum resins, and the like are used.
Known coloring agents such as pigments and dyes can be used. If necessary, a charge control agent or the like may be used.
As the external additive, silica, alumina, titania, inorganic oxide fine particles such as magnesia and the like can be used,
A hydrophobic treatment may be performed as necessary. Further, organic fine particles and the like can also be used. If necessary, a lubricant such as zinc stearate and polyvinylidene fluoride can be used. As the carrier core, ferrite, magnetite, iron powder and the like can be preferably used, and as the core coating resin, a fluorine-containing resin, a silicone resin, a nitrogen-containing resin, a polymethyl methacrylate resin,
Known ones can be used.

The adjustment of the toner density, that is, the adjustment of the coloring power,
Usually, it is carried out by adjusting the content ratio of dyes and pigments contained in the toner. In the present invention, the coloring power of the low-density and low-charge amount toner is preferably adjusted such that the coloring power of the high-density and high-charge amount toner is in the range of 30 to 70 when the coloring power of the toner is 100. .

The charge amount of the toner is controlled as follows.
There are various factors that control the charge amount of the toner.
That is, the toner contains a charge control agent, a dye,
Pigment, release agent and the like are dispersed and an external additive is further added. These binder resin, charge control agent, dye / pigment, external additive and the like greatly affect the charge amount of the toner. Therefore, when adjusting the charge amount, it is necessary to sufficiently consider these factors. Charge (charge) control agents are effective substances for controlling the amount of charge. Examples of charge control agents include metal salts of aromatic carboxylic acids such as benzoic acid, salicylic acid and alkyl salicylic acid, and quaternary ammonium salts. Commonly used charge control agents such as azo metal-containing dyes are exemplified. The charge amount can also be adjusted by an external additive. For example, when hydrophobic silica particles are used as an external additive, the toner can have a high charge amount.
Further, the charge amount of the toner can be adjusted by selecting a coating material that covers the carrier.Furthermore, the coating resin is used as a matrix resin, and a conductive agent and a charge-imparting agent are contained in the matrix resin. It may be dispersed. In this case, the charge amount can be controlled by changing the amounts of the conductive agent and the charge imparting agent.

As a method of controlling the charge amount, not only the selection of the above-described materials but also the adjustment of the particle diameter of the carrier particles is possible. That is, when the carrier particle diameter is reduced, the carrier surface area per unit weight is increased, and it is relatively easy to increase the toner charge amount. Therefore, even when the toner particle diameter is small, a high charge amount can be obtained relatively easily.

In the present invention, when the average particle diameter of the low-density and low-charge amount toner is smaller than that of the high-density and high-charge toner, the reproducibility of the highlight portion is further improved. I can do it. Also in this case, the coloring power and the charge amount can be set in the same manner.

Further, according to the present invention, the average particle diameter of the high-density and high-charge toner used in the high-density part is larger than the average particle diameter of the low-density and low-charge toner used in the highlight part of the image information. The carrier that charges the high-density and high-charge toner used in the high-density portion has a larger average particle diameter than the carrier that charges the low-density and low-charge toner used in the highlight portion of the image information. Includes an image forming method characterized by being large. By considering the particle size of the toner and the particle size of the carrier in this way, the reproducibility of the image is improved. The reason is that by reducing the diameter of the carrier, the number of contact points between the carriers increases, the number of conductive paths can be formed, and as a result, the developer resistance can be reduced, so that the reproduction of the highlight portion becomes good. . On the other hand, the developer used for the high density part is
A large amount of toner is consumed, and the charging speed of the additional toner needs to be high and the fluidity needs to be good. It is considered that the transport amount and the charging speed can be improved by increasing the carrier diameter.

The present invention also provides an electrostatic latent image formed on an image carrier in accordance with image information, which is made visible by toner contained in a developing means, and the developed toner image is transferred to an intermediate transfer member. Further, in an image forming apparatus that transfers the toner image to a transfer material to obtain an image, the toner separately includes a low-density and low-charge amount toner and a high-density and high-charge toner, and highlights image information. Wherein the low density and low charge amount toner is used, and the high density and high charge toner is used in a high density portion.
As described above, by using the intermediate transfer member in the present invention, scattering of the toner can be prevented, and the reproducibility of the highlight portion is improved.

Next, the image forming apparatus of the present invention will be described. FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus according to the present invention. Reference numeral 1 denotes a photoreceptor drum, the surface of which is uniformly charged by a charging device 4 and then exposed by a light beam scanning device (not shown) based on image information to form an electrostatic latent image. The electrostatic latent image formed on the photoconductor 1 is developed by a developing device. 5 is a developing device for black, 6 is a developing device for yellow, 7 is a developing device for magenta, and 8 is a developing device for Sian.
The toners 7 and 8 contain two types of toner, low density and low charge amount toner used for the highlight portion and high density and high charge amount toner used for the high density portion. The toner image on the photoconductor 1 is temporarily transferred to a belt of an intermediate transfer member indicated by reference numeral 2. 9 is a corona discharger for transfer. The intermediate transfer body 2 to which the toner image has been transferred is driven by a drive system including a drive roller 21, a tension roller 23, a backup roller 22, and a driven roller 24. The recording medium 3 passes between the intermediate transfer body belt 2 and the transfer roll 10, and the toner image on the intermediate transfer body is transferred to the recording medium 3 during the passage. The recording medium 3 onto which the toner image has been transferred is conveyed to a fixing device 15 by a conveying belt 14 and is fixed by the fixing device 15. Reference numeral 11 is a recording medium feed roller, 12 is a recording medium tray, 16 is a belt cleaner, 17 is a belt position sensor, 25 is a cleaning blade, and 26 is a metal roller. The image forming apparatus shown here is an example using an intermediate transfer body,
An image forming apparatus having a structure in which a toner image formed on a photoreceptor is directly transferred to a recording medium without using an intermediate transfer body is, of course, included in the image forming apparatus of the present invention.

Example 1 Preparation of Low Concentration / Low Charge Toner and Developer Polyester resin having Mn = 5000 and Mw = 11,000 (trade name: bisphenol A ethylene oxide / polycondensate containing terephthalic acid as a main component, Tg = 60) ° C, Tm
= 110 ° C) 100 parts by weight of Sian (CI Pigment Blue 15: 3), Magenta (CI Pigment Red 57: 1), Yellow (CI Pigment Yellow 97), Black ( 2 parts by weight of each of the carbon black) pigments, melt-kneaded, pulverized and classified,
Colored particles having an average particle diameter of 7 μm were prepared, and 30 parts of hydrophobic titanium oxide was mixed with 1 part by weight of a Henschel mixer to obtain each toner. Fuji Xerox Acolor
When the charge amount was evaluated in combination with a carrier used in a 635 copying machine, the charge amounts of the developers having the above-mentioned pigments were respectively -15, -16, -18, and -14 .mu.C.
/ G.

Preparation of High Concentration / Highly Charged Toner and Developer Polyester resin having Mn = 5000 and Mw = 11,000 (trade name: bisphenol A ethylene oxide / polycondensate containing terephthalic acid as a main component, Tg = 60 ° C., Tm
= 110 ° C) 100 parts by weight of Sian (CI Pigment Blue 15: 3), Magenta (CI Pigment Red 57: 1), Yellow (CI Pigment Yellow 97), Black ( 5 parts by weight of each of the carbon black) pigments, melt-kneaded, pulverized and classified,
Colored particles having an average particle diameter of 7 μm were prepared, and 1 part by weight of hydrophobic silica having a thickness of 16 nm was mixed with a Henschel mixer (manufactured by Nippon Aerosil Co., Ltd.) to obtain each toner. When the charge amount was evaluated in combination with the carrier used in the Fuji Xerox Acolor 635 copier, the charge amount of the developer having each of the pigments was -31, -34,
−38 and −30 μC / g.

Image Production and Evaluation Low density halftone images (image area ratio from 10% to 50% in 10% increments) by replacing the developer of Acolor 635 copier manufactured by Fuji Xerox Co. with four colors of low density and low charge toner. (Between primary and tertiary colors). Next, a high-density halftone dot image (with an image area ratio of 60% to 100% in increments of 10%, between primary and tertiary colors) was obtained by replacing the high-density and high-charge toner. For comparison, copies of the low-density halftone image and the high-density halftone image were similarly obtained using the developer of the Acolor 635 copying machine.
Low density halftone image using low density low charge toner is Acol
or635 is excellent in granularity as compared with a low-density halftone image obtained by using a developer of a copying machine, and has no gloss difference from a high-density halftone image obtained with high-density and high-charge toner. Image.

Example 2 Preparation of Low Concentration / Low Charge Toner and Developer Polyester resin having Mn = 5000 and Mw = 11000 (trade name: bisphenol A ethylene oxide / polycondensate containing terephthalic acid as a main component, Tg = 60) ° C, Tm
= 110 ° C) 100 parts by weight of Sian (CI Pigment Blue 15: 3), Magenta (CI Pigment Red 57: 1), Yellow (CI Pigment Yellow 97), Black ( 2 parts by weight of each of the carbon black) pigments, melt-kneaded, pulverized and classified,
Colored particles having an average particle diameter of 7 μm were prepared, and 30 parts of hydrophobic titanium oxide was mixed with 1 part by weight of a Henschel mixer to obtain each toner. Cu-Zn with an average particle size of 50 μm
Ferrite (saturated magnetization of 64 emu) with an average particle size of 0.3
A polymethyl methacrylate resin (solvent toluene) in which μm melamine beads (Nippon Shokubai Co., Ltd. Eposter S) was dispersed was coated with a kneader to obtain a carrier. The ratio of melamine beads to polymethyl methacrylate resin is 0.1% by weight. When 8% by weight of each toner was added to the obtained carrier and the charge amount was evaluated, the charge amount of the developer having each pigment was -1.
5, -14, -18 and -14 [mu] C / g.

Preparation of High Concentration / Highly Charged Toner and Developer A polyester resin having Mn = 5000 and Mw = 11,000 (trade name: bisphenol A ethylene oxide / polycondensate containing terephthalic acid as a main component, Tg = 60 ° C., Tm
= 110 ° C) 100 parts by weight of Sian (CI Pigment Blue 15: 3), Magenta (CI Pigment Red 57: 1), Yellow (CI Pigment Yellow 97), Black ( 4 parts by weight of each of the carbon black) pigments, melt-kneaded, pulverized and classified,
Colored particles having an average particle diameter of 9 μm were prepared, and 1 part by weight of 16 nm of hydrophobic silica was mixed with a Henschel mixer.
Each toner was obtained. Cu-Zn ferrite with an average particle diameter of 35 μm (saturation magnetization 65 emu) and an average particle diameter of 0.3 μm
Was coated with a polymethyl methacrylate resin (solvent toluene) in which melamine beads (Nippon Shokubai Co., Ltd. Eposter S) were dispersed to obtain a carrier. The ratio of melamine beads to polymethyl methacrylate resin is
0.2% by weight. When the amount of charge was evaluated by adding 8% by weight of each toner to the obtained carrier, the amount of charge of the developer having each pigment was -2.
8, -26, -30, and -26 µC / g.

Image Production and Evaluation Low density halftone image (image area ratio 10% to 50% in 10% increments) by replacing the developer of Acolor 635 copier manufactured by Fuji Xerox Co. with four color low density / low charge toner. (Between primary and tertiary colors). Next, a high-density halftone dot image (with an image area ratio of 60% to 100% in increments of 10%, between primary and tertiary colors) was obtained by replacing the high-density and high-charge toner. For comparison, copies of the low-density halftone image and the high-density halftone image were similarly obtained using the developer of the Acolor 635 copying machine.
Low-density halftone image using low-density, low-charge toner is Aco
lor635, which is much better in granularity than low-density halftone images obtained by using a developer of a copying machine, and has good gloss without difference in gloss from high-density halftone images obtained with high-density and high-charge toner. It was an image.

[0027]

[Brief description of the drawings]

FIG. 1 shows an example of an image forming apparatus using an intermediate transfer member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Intermediate transfer belt 3 Recording medium 4 Charging device 5 Black developing device 6 Yellow developing device 7 Magenta developing device 8 Sian developing device 9 Transfer corona discharger 10 Transfer roller 11 Feed roller 12 Tray 14 Conveyor belt 15 Fixer 16 Belt cleaner 17 Belt position sensor 21 Drive roller 22 Backup roller 23 Tension roller 24 Follower roller 25 Cleaning blade 26 Metal roller

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Akihiro Iizuka 1600 Takematsu, Minamiashigara-shi, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd.

Claims (16)

[Claims] A step of exposing an electrostatic latent image formed on an image carrier in accordance with image information by toner stored in a developing means; transferring the actualized toner image to a transfer material to form an image; In the image forming method including the step of obtaining, the toner separately includes a toner having a low-density colorant and having a low charge amount, and a toner having a high-density colorant and having a high charge amount. An image forming method, wherein the low density and low charge amount toner is used for a highlight portion of image information, and the high density and high charge amount toner is used for a high density portion. 2. A process for transferring an exposed toner image to a transfer material to obtain an image, wherein the revealed toner image is transferred to an intermediate transfer member, and the toner image is further transferred to a transfer material. The image forming method according to claim 1. 3. The image forming method according to claim 1, wherein the image information is digital information. 4. When the colorant content of a toner having a low concentration of a colorant and a low charge amount is set to 100, and the coloring power of a toner having a high concentration of a colorant and a high charge amount is set to 100. To
2. The image forming method according to claim 1, wherein the coloring power is adjusted to fall within a range of 30 to 70. 5. When the charge amount of a toner having a low concentration of a colorant and a low charge amount is set to 100, and the charge amount of a toner having a high concentration of a colorant and a high charge amount is set to 100, 2. The image forming method according to claim 1, wherein the charge amount is adjusted to fall within a range of 10 to 90. 6. When the charge amount of a toner having a low concentration of a colorant and a low charge amount is set to 100, and the charge amount of a toner having a high concentration of a colorant and a high charge amount is set to 100, The image forming method according to claim 1, wherein the charge amount is adjusted to be in a range of 30 to 70. 7. When the average particle diameter of a toner having a low concentration of a colorant and having a low charge amount is equal to that of a toner having a high concentration of a colorant and having a high charge amount, said low concentration and low charge amount The low-charge amount toner is set so that the ratio of the coloring power to the high-density and high-charge amount toner is between 30% and 70%, and the low-density and low-charge amount toner is a high-density and high-charge amount toner. 2. The image forming method according to claim 1, wherein the ratio of the amount of charge to the toner is set to be substantially equal to the value of the set ratio of the coloring power. 8. A volume average particle diameter of a toner having a low concentration of a colorant and having a low charge amount is smaller than a volume average particle diameter of a toner having a high concentration of a colorant and having a high charge amount. The image forming method according to claim 1, wherein: 9. The image forming method according to claim 1, wherein the toner is frictionally charged by a carrier. 10. The image forming method according to claim 9, wherein the carrier is coated with a resin. 11. An average particle diameter of a toner having a low concentration of a colorant and having a low charge amount is smaller than an average particle diameter of a toner having a high concentration of a colorant and having a high charge amount, and The average particle size of the toner carrier having a low concentration of the colorant and having a low charge amount is smaller than the average particle size of the toner carrier having a high concentration of the colorant and having a high charge amount. The image forming method according to claim 9, wherein: 12. The image forming method according to claim 1, wherein the toner has an external additive. 13. The image forming method according to claim 1, wherein a cyan toner, a magenta toner, a yellow toner, and a black toner are used as the toner. 14. A means for forming an electrostatic latent image on an image carrier according to image information, a plurality of developing means for performing development with toner, and a transfer means for transferring an exposed toner image to a transfer material. In an image forming apparatus having a plurality of developing units, a plurality of developing units separately store a toner having a low concentration of a colorant and a low charge amount and a toner having a high concentration of a colorant and a high charge amount An image forming apparatus, comprising: 15. A developing means comprising, for each toner including cyan toner, magenta toner, yellow toner, and black toner, a low-density colorant and a low-charge amount toner and a high-density colorant. The image forming apparatus according to claim 14, wherein the toner and the toner having a high charge amount are individually stored. 16. A transfer means for transferring an exposed toner image to a transfer material has an intermediate transfer member.
An image forming apparatus according to claim 14.