JPH11231604A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a stable and high transfer efficiency over a long period of time even by so called a cleanerless method by making it compatible to improve an efficiency of transferring a toner image from an image carrier to a transfer medium and to re-transfer it from the transfer medium to the image carrier, and making it possible to reduce toner for collection or waste to nil or almost to non-existent over a long period of time. SOLUTION: In a color image forming device which successively transfers toner images of each color element formed on an image carrier 1 by plural development means 3 (for example, 3a-3d) in transcript medium 5, a relation of W(1)<W(2)... W(N-1)<W(N) is satisfied when the number of the plural development means 3 is expressed by N, and a toner weight of a toner image formed on the image carrier I by the I-th development means 3 of the sequence of the image-forming processes is expressed by W(I).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotography in which a latent image formed on an indirect image carrier is visualized with toner, and the toner image is transferred to a transfer medium such as a recording material or an intermediate transfer member. The present invention relates to an indirect transfer type color image forming apparatus using recording technology, electrostatic recording technology, ionography, magnetography, etc., and particularly, does not install a cleaner that scrapes transfer residual toner transferred from an image carrier to a transfer medium. The present invention relates to improvement of a color image forming apparatus effective for a so-called cleanerless system.

[0002]

2. Description of the Related Art In an indirect transfer type image recording technique, a toner image formed on an image carrier is transferred to a transfer medium such as a recording material, and the like.
A fixed image is obtained by fixing. After the transfer of the toner image, the toner remaining on the image carrier is generally collected and discarded. For example, in an electrophotographic color image forming apparatus, a charging step for uniformly charging the surface of an image carrier prepared for each color of one or cyan, magenta, yellow and black having a photoconductor layer on the surface,
An exposure step of forming a latent image by irradiating the charged image carrier surface with image light, and developing a toner image by attaching toner of each color of cyan, magenta, yellow and black to the electrostatic latent image. Process, one or cyan, magenta,
A transfer step of sequentially and repeatedly transferring the toner image formed on the image carrier prepared for each color of yellow and black to a recording material, a fixing step of fixing a plurality of color toner images on the recording material, And one or cyan in the transfer step,
An image is formed by a cleaning step of removing toner remaining on the image carrier prepared for each of the colors magenta, yellow, and black.

In this cleaning step, the residual toner is collected by pressing an elastic rubber blade or brush against the surface of the image carrier, and the collected toner is accumulated in a collection container and periodically collected. Discarded. In such an apparatus, the amount of collected toner accumulated in the collection container must be constantly detected or measured, and the toner must be discarded or the collection container must be replaced before the collection container becomes full. In addition, when the apparatus is downsized, a large space cannot be secured for installing the collection container, and the inside of the drum-shaped image carrier is used. For this reason, it may be necessary to set the replacement time of the image carrier depending on the amount of collected toner. Furthermore, the recovered toner is being reused from the viewpoint of environmental protection, but in the case of color in particular, it is difficult to separate the toner for each color, and the energy generated for transportation and regeneration is low. It involves many technical issues, such as being large, collecting methods and securing collection sites.

As a means for solving such a technical problem, a color image forming apparatus in which a cleaning step is omitted has been proposed. Generally, if the image carrier after transfer is not cleaned, the toner (residual toner) remaining on the image carrier is printed out in the next image forming process, or the image light is blocked by the residual toner in the exposure process. There is a technical problem that a negative ghost occurs. For this reason, the transfer efficiency must be improved to such an extent that image defects such as ghosts and fogging do not occur even if the residual toner after transfer is not cleaned. Further, in the electrophotographic color image forming apparatus as described above, a color image is formed by a transfer process in which cyan, magenta, yellow, and black toner images are formed on an image carrier, and sequentially and repeatedly transferred onto a recording material. An image is formed. In this transfer step, a part of the toner image already transferred on the recording material is re-transferred onto the image carrier, and the above-mentioned ghost or fog occurs, or the re-transferred toner is transferred into the developing device of another color. , The chargeability of the toner in the developing device changes, it becomes difficult to accurately reproduce the color tone, and the developer and the image quality are significantly deteriorated.

The technical problem that a part of the already transferred toner image is re-transferred onto the image carrier is that a discharge occurs due to a transfer electric field between the image carrier and the recording material, and the polarity is reversed. It is considered that charged toner is generated, and the toner charged to the opposite polarity is re-transferred to the image carrier side by the transfer electric field. Discharge due to the transfer electric field can be prevented by reducing the voltage applied between the image carrier and the recording material, but on the contrary, there is a technical problem that the transfer efficiency is reduced. Under such circumstances, the color image forming apparatus in which the cleaning step is omitted has a larger problem than the conventional technology in terms of improving transfer efficiency and preventing retransfer.

Some means for solving such technical problems have already been proposed (for example, Japanese Patent Publication No.
No. 32981, Japanese Unexamined Patent Publication No. Hei 7-146597, Japanese Unexamined Patent Publication No. Hei 8-137174, Japanese Unexamined Patent Publication No. Hei 9-212010
Reference). For example, the first technique described in Japanese Patent Publication No. 1-32981 discloses that the toner transferred to the second color is more than the toner transferred to the first color, and that the toner transferred to the second color is three times. By controlling the charge amount of the toner in the developer so that the toner transferred to the color has a larger charge amount, the transfer electric field is weakened by the charge of each toner of the toner image already transferred. And to improve transfer efficiency.

A second technique described in, for example, JP-A-7-146597 has an image forming carrier and a plurality of developing devices for forming toner images on the image forming carrier. The surface potential of the toner layer after transferring the toner image excluding the toner image to the intermediate transfer medium is set to 560 V or less, or the absolute value of the charge amount of the toner is 11.0 μC /
g or less, or the thickness of the toner layer is 80 μm or less, or the toner filling rate is 9% or more, so that the charge of the toner in the toner layer is reduced, and the toner image to which the transfer electric field has already been transferred. Are prevented from being weakened by the charge of each toner, and the transfer efficiency is improved.

Further, for example, a third technique described in Japanese Patent Application Laid-Open No. 8-137174 discloses a method in which magenta, cyan, yellow, and black image forming units are arranged in line along a transfer material conveying member. In the color image forming apparatus in which the toner is superimposed by passing the transfer material sequentially to form a toner image, and the developing unit of the image forming unit also serves as a cleaning unit, the first yellow and the second Magenta, cyan at the third, and black at the end take the chromaticity change characteristics due to the mixture of the developers of each color into consideration to minimize the chromaticity change in each image forming unit, Is to prevent the deterioration.

Further, for example, Japanese Patent Application Laid-Open No. 9-212010
In the fourth technique described in Japanese Patent Application Laid-Open Publication No. H10-157, the toner is selectively transferred onto an image carrier having fine particles having a smaller particle diameter than the toner adhered to the surface substantially uniformly, and formed on the image carrier. The latent image is visualized and formed on the fine particle layer to form a toner image, so that there is a gap between the toner particles and the image carrier, or the contact area between the toner particles and the image carrier is small. In this state, the transfer efficiency is improved by reducing the adhesive force between the toner particles and the image carrier.

[0010]

However, in the above-described color image forming apparatus, the following technical problems are found. In the color image forming apparatus according to the first technique, the amount of charge of the toner of the toner image already transferred is made smaller than the amount of charge of the toner of the toner image to be transferred next, thereby reducing the effective transfer electric field. However, the technical problem that the transfer electric field cannot be reduced enough to prevent the discharge due to the transfer electric field and retransfer occurs still remains.

Further, in the color image forming apparatus according to the second technique, as in the first technique, the amount of charge of the toner layer can be reduced to prevent a reduction in the effective transfer electric field. The technical problem that the transfer electric field cannot be reduced to the extent that the discharge due to the transfer electric field is prevented, and retransfer occurs, still remains.

Further, in the color image forming apparatus according to the third technique, an image carrier is arranged for each color without a cleaning device, and after a toner image is transferred, when a next image is developed. The effect of the residual toner is reduced by transferring the residual toner to the developing roll within the electric field in the developing area and collecting the residual toner. However, as described above, due to the occurrence of retransfer, the residual toner is developed in a different color. There is a technical problem that the color mixture is mixed in the container (color mixture), and the color mixture progresses with each image formation, and it is difficult to reproduce an accurate color tone. Although the arrangement takes into account the chromaticity change characteristics due to the mixing of the developer of each color, the effect is limited, and the toner of different colors is charged mutually due to the change of the color tone and the progress of the mixing, and the development is performed. There is also a technical problem that the chargeability of the agent changes and the stability of the image density is impaired.

Further, in the color image forming apparatus according to the fourth technique, by attaching fine particles smaller than the toner particles to the surface of the image carrier, the adhesive force between the toner particles and the image carrier is reduced, and the transfer is performed. The transfer efficiency is improved while reducing the electric field. However, if the transfer electric field is reduced to a level at which discharge is prevented and sufficient transfer efficiency is to be obtained, the adhesion between the toner particles and the image carrier must be extremely reduced. This causes technical problems such as fogging of the background portion and dirt in the image forming apparatus.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems. The present invention has improved the transfer efficiency of a toner image from an image carrier to a transfer medium and improved the efficiency of transfer from the transfer medium to the image carrier. It is possible to prevent the occurrence of re-transfer of the toner image at the same time, and it is possible to eliminate or remarkably reduce the amount of toner to be collected and discarded. Therefore, it is possible to stably maintain a high transfer efficiency for a long time even in a so-called cleanerless system. A color image forming apparatus is provided.

[0015]

That is, as shown in FIG. 1, the present invention provides a latent image forming means 2 for sequentially forming an electrostatic latent image of each color component on an image carrier 1; A plurality of developing means 3 (for example, 3a to 3d) for selectively developing an electrostatic latent image of each color component on the image carrier 1 with a toner of a corresponding color; A color image forming apparatus having a transfer means 4 for sequentially transferring the color image to
When the number of the plurality of developing units 3 is N and the toner weight of the toner image formed on the image carrier 1 by the I-th developing unit 3 in the image forming process is W (I), W (I) 1) <W (2)... W (N−1) <W (N).

This conditional expression is, for example, the developing means 3a to 3b
Is one using any one of magenta, cyan, yellow and black toners, the toner weight of the first formed toner image is A, and the toner weight of the second formed toner image is B A means that the conditions of A <B and C <D are satisfied, where C is the toner weight of the third formed toner image and D is the toner weight of the fourth formed toner image. It is.

In such a technical means, the color image forming apparatus to which the present invention is applied forms, for example, a plurality of color component toner images on one image carrier 1 and transfers each color component toner image to a recording material or an intermediate material. As appropriate, such as a mode of sequentially transferring to a transfer medium 5 such as a transfer body, or a mode of forming one or a plurality of color component toner images on a plurality of image carriers 1 and sequentially transferring each color component toner image to the transfer medium 5 You can choose it. Here, the color image forming apparatus according to the present application may be provided with a cleaner 6 for collecting the residual toner on the image carrier 1, but from the viewpoint of the solution, a so-called cleaner excluding the cleaner 6 is used. The color image forming apparatus according to the present invention is particularly effective in the wireless system.

The image carrier 1 may be appropriately selected from a photoreceptor, a dielectric and the like, and the form thereof is not particularly limited, such as a drum shape and a belt shape. Further, the latent image forming means 2 may be appropriately selected as long as it forms an electrostatic latent image, such as an electrophotographic method through a charging and exposure step, or a method including a latent image writing step by an ion flow. Absent. Furthermore, regarding the transfer means 4,
As long as the toner image on the image carrier 1 is electrostatically transferred to the transfer medium 5 side, both the mode in which the transfer member is arranged in contact with the transfer medium 5 and the mode in which the transfer member is arranged in non-contact manner are included. Here, as the contact type transfer member, a roll shape,
A blade-shaped or brush-shaped transfer member may be appropriately selected, but a roll-shaped transfer member is preferably used because a predetermined transfer pressure can be applied. On the other hand, as the non-contact transfer member, a corona discharger such as a corotron can be used.

As for the plurality of developing means 3, if each developing means 3 is selectively arranged at a developing position,
A rotary developing unit in which a plurality of developing units 3 are mounted on a rotary holder may be used, or each developing unit 3 may be arranged in parallel with the image carrier 1. The developing method of each developing means 3 can be appropriately selected, such as one-component development, two-component development, contact development, and non-contact development.

The relationship between the toner weights is as follows.
The relationship described above may be satisfied, and the weights of the toners W (2)... W formed on the image carrier 1 in the order excluding the first and Nth orders
The magnitude relationship between (N-1) is not particularly limited. Therefore, W (2)... W (N-1) may be equal to each other, or may be appropriately selected such as a mode in which the toner weight is sequentially reduced according to the development order. From the viewpoint of minimizing retransfer, W (1) <W (2) <... <W (N-1) <W
(N) is satisfied (specifically, A <B <C
It is preferable to adopt the <D) mode.

Here, the reason why the weight between the second to (N-1) th toners does not matter is as follows. In the transfer step, the re-transfer property of the transferred toner image becomes a problem particularly in a portion of the transferred toner image where the toner weight is large, specifically, a toner image in which a plurality of color toners are superimposedly transferred. Part. For this reason, as will be apparent from the operation described later, if the toner weight of the entire superimposed toner image is small, the retransfer amount of the already transferred toner image is reduced. For example, in the second transfer step, the toner weight of the toner image already transferred is W
In the third transfer step, the toner weight of the toner image already transferred becomes W (1) + W (2), and in the fourth transfer step, the toner weight of the toner image already transferred in the fourth transfer step Is W (1) + W (2) + W (3).
Therefore, the toner weight to be reduced to reduce retransfer is W (1), W (1) + W (2), or W (1) + W (2) + W (3), and W (2) ) And W
The magnitude relation of (3) does not matter. That is, if the weight of the toner image formed first is smaller than the weight of the toner of the next and subsequent stages, even if the weight between the second to (N-1) th toners is arbitrarily set, for example, 1
By setting the weight of the toner formed first to be sufficiently small, it is possible to reduce the toner weight of the second and subsequent superimposed toner images.

Further, in the above-described color image forming apparatus, from the viewpoint of obtaining a good image, the number of the plurality of developing units 3 is N, and the developing order of the image forming process is I-th. When the pigment content of the toner image formed on the image carrier 1 is m (I), m (1)>
It is preferable that the relationship m (2)... m (N-1)> m (N) be satisfied. This conditional expression is, for example, the developing means 3a-3
In the embodiment in which b uses any one of the toners of magenta, cyan, yellow, and black, the pigment content of the toner image formed first and the pigment content of the toner image formed second When the quantity is b, the pigment content of the third toner image formed is c, and the pigment content of the fourth toner image is d, the conditions of a> b and c> d are satisfied. Means

Generally, the gloss of an image can be improved by increasing the amount of pigment contained in the toner.
In the present invention, by increasing the pigment content of the toner image, good image quality can be obtained even when the toner weight of the toner image formed on the image carrier 1 is reduced.

Further, the toner used in the above-described color image forming apparatus has a higher surface area than a so-called pulverized toner obtained by melting, kneading, pulverizing and classifying conventionally used toner raw materials. By using a spherical toner having a spherical shape or a spherical shape close to a spherical shape, it is possible to suppress the occurrence of retransfer, which is particularly preferable as described in the operation description below. As a method for producing such a spherical or nearly spherical spherical toner, various methods can be mentioned, and for example, it is preferable to produce the toner by an emulsion polymerization method. At this time, it is preferable to satisfy the following conditions. MI ≦ Mw / 1000 + 115 MI: Shape factor of toner (true sphere is 100) π × (toner maximum diameter) 2 / (4 × toner sectional area) × 10
0 Mw: weight average molecular weight of the toner

The weight average molecular weight Mw of the toner is preferably from 20,000 to 30,000.

Further, in the present invention, it is preferable to employ various means for improving the transfer efficiency of the toner image on the image carrier 1. For example, in a mode in which the latent image forming unit 2 forms a latent image by exposure, the transfer unit 4 exposes and irradiates the toner remaining on the image carrier 1 after passing through a portion facing the transfer unit 4. When the light transmittance is 90%
It is preferable to set so as to maintain the above-described transfer rate. Further, it is preferable that a release layer for reducing the adhesive force with the fine particles formed on the image carrier 1 is provided on the surface of the image carrier 1.

Next, the operation of the above technical means will be described. In the color image forming apparatus shown in FIG. 1, retransfer does not occur by making the toner weight of the toner image formed first smaller than the toner weight of the toner image transferred in the subsequent stage. . The occurrence of retransfer occurs when the toner image that has already been transferred onto the transfer medium 5 passes through the transfer area without the toner image being overlaid and transferred in the next transfer step. The larger the weight of the toner image transferred onto the transfer medium 5, the larger the amount of toner to be retransferred.

First, in the re-transfer, the toner image already transferred onto the recording material is not transferred in the next transfer step.
The reason (dot) occurring when passing through the transfer area is considered as follows. The toner image formed on the image carrier 1 is brought into close contact with the transfer medium 5 and, at the same time, a transfer blade or a transfer as a contact-type transfer means 4 abutting from the back surface thereof to transfer the toner image. The transfer charge is supplied to the transfer medium 5 by the roll. The polarity of the transfer charge is determined by the polarity of the toner. For example, when a negatively charged toner is used, a positive transfer charge is given. As a result, the toner image is electrostatically attracted to the toner image, and the toner image is attracted to the transfer medium 5.

Then, the transferred toner image on the transfer medium 5 is peeled off from the image carrier 1. By this peeling, an air gap is formed between the image carrier 1 and the toner image. A peeling discharge occurs due to an abrupt decrease in the capacitance and an increase in the potential difference. Most of the positive and negative electric charges generated by this peeling discharge are generated in a slight air gap surrounded by the image carrier 1 and the toner image, and a part of the positive electric charge jumps into the toner image,
The toner whose charging polarity is inverted by the positive charge is formed. At this time, since the negative charge also jumps into the toner image, the toner image on the transfer medium 5 is given a negative charge, and the charge amount increases. However, since the amount of the positive charge or the negative charge that jumps into the toner image changes depending on the layer state of the toner image on the transfer medium 5, the charge distribution of the toner image on the transfer medium 5 is very irregular and broad. And it is very difficult to control the charge distribution. Further, by repeating the transfer process, the amount of toner whose charge polarity is inverted increases, and the charge distribution of the toner layer on the transfer medium 5 becomes more irregular and broad.

The toner image on the transfer medium 5 whose charge polarity has been inverted is transferred to the image carrier 1 by a transfer electric field formed between the image carrier 1 and the transfer medium in the next transfer step. Retransfer occurs. However, in a region where the toner image on the image carrier 1 is transferred to be superimposed on the toner image on the transfer medium 5, there is a toner whose charge polarity is inverted in the toner image on the transfer medium 5. Also, the re-transfer does not occur because of the hindrance of the toner image on the image carrier 1. That is, 1
First, in the toner image formed on the transfer medium 5, retransfer occurs remarkably in a region where there is no toner image to be overlaid and transferred.

Next, the reason why the amount of toner to be retransferred is increased as the toner weight of the toner image transferred onto the recording material is increased is considered as follows. When the toner weight of the toner image formed on the image carrier 1 increases, it is necessary to increase the transfer charge supplied to the transfer medium 5 in order to increase the transfer efficiency. As a result, the electrostatic attraction for attracting the toner image can be increased, and a sufficient amount of the toner image is attracted to the transfer medium 5.

When the transferred toner image on the transfer medium 5 is separated from the image carrier 1, the increase in the potential difference due to the decrease in the capacitance is further increased by the transfer charge, and the separation discharge causes The amount of generated positive charges increases. Furthermore, when the toner image formed on the image carrier 1 in the transfer step is brought into close contact with the transfer medium 5, the larger the toner weight of the toner image on the transfer medium 5, the more the toner image between the image carrier 1 and the transfer medium 5 becomes. During this time, the toner in contact with the image carrier 1 is pressed against the image carrier 1 by strong pressure, and retransfer increases. As described above, by making the toner weight of the first toner image, in which retransfer is likely to occur, smaller than in the subsequent stage, retransfer is prevented from occurring.

In the present invention, the reason why the transfer efficiency is improved and the occurrence of retransfer can be more reliably suppressed by using the spherical toner will be described from the viewpoint of the adhesive force between the toner and the image carrier 1. Main forces acting on the toner in contact with the surface of the image carrier 1 include a mirror force and a Van der Waals force. The mirror power greatly depends on the amount of charge and its distance. The surface shape of the pulverized toner generated by general pulverization is uneven, and the convex portions are intensively charged by frictional charging. On the other hand, for example, a spherical polymerized toner formed by a polymerization method has a spherical or nearly spherical surface, so that the surface is uniformly charged. Therefore, in the pulverized toner, since the convex portions come into contact with each other and a lot of electric charges exist in a very close area, the mirroring power increases. On the other hand, when the toner is spherical, as in the case of the polymerized toner, the contact state becomes almost dot-like, the amount of charge in the proximity area is small, and the mirroring power is small as compared with the above.

The Van der Waals force is affected by the closest region, and becomes very large in a state where the contact occurs in a plane. Here, in the case of using a toner having an uneven surface, the number of portions that come into contact with the image carrier 1 increases,
The contact area increases, and the van der Waals force becomes very large. On the other hand, since the spherical toner has a spherical surface shape, the toner contacts the image carrier 1 at almost all points.
Therefore, the van der Waals force is also smaller for the spherical toner.

For the above reasons, in the case of a spherical or nearly spherical toner whose surface shape is spherical, the mirroring force and van der Waals force, that is, the adhesion force on the image carrier 1 are small, and as described above, the image carrier 1 And the toner adhesion is reduced,
If it is easy to peel off from the image carrier 1, the transfer charge supplied to the transfer medium 5 can be reduced in the transfer step, and the occurrence of peeling discharge can be suppressed while maintaining good transfer efficiency. . Such a spherical toner having a weak adhesive force can perform transfer with an efficiency close to 100%, and retransfer is unlikely to occur.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. FIG. 2 is a schematic configuration diagram showing one embodiment of a color image forming apparatus to which the present invention is applied. Referring to FIG. 1, a color image forming apparatus includes a drum-shaped image carrier 101 having a photosensitive layer on a surface.
And a charger 102 for uniformly charging the image carrier 101
And an image writing device 104 for irradiating the uniformly charged image carrier 101 with image light to form an electrostatic latent image, and 4 containing yellow, magenta, cyan, and black developers, respectively.
Developing units 105Y, 105M, 105C, 105BK
Is rotatably mounted on a rotary holder, and the image carrier 10
1 at predetermined developing units 105Y to 105Y.
An endless belt-shaped intermediate transfer body 111 in which one of the BKs intermittently moves and is in contact with the image carrier 101 and is stretched around a plurality of rolls 112, 113, 114 so as to be able to rotate. And the image carrier 1
And a primary transfer roll 106 for transferring the toner image formed on the image carrier 101 to the intermediate transfer member 111 and a recording sheet 116 conveyed along a paper guide (not shown). And a secondary transfer roll 115 for transferring the toner image on the transfer roller 111.

In the present embodiment, the image bearing member 101 has a release layer (for example, a thin layer of silica particles treated with silicon oil) having a reduced adhesion to the fine particles added to the toner on the surface of the photosensitive layer. Layer) is used. The intermediate transfer member 111 is, for example, an endless belt having a predetermined thickness (135 μm in this example) obtained by dispersing carbon black in a polycarbonate resin, and has an electric resistance value of 10 ⁸ to 10 ¹⁰ Ω ·. cm. The intermediate transfer member 111 and the image carrier 101 move at a predetermined process speed (in this example) in a direction indicated by an arrow in FIG.
It is driven at a peripheral speed of 160 mm / s, and these members are not provided with a cleaner.

The developer used in each of the developing units 105Y to 105BK of the color image forming apparatus will be described. In this embodiment, a two-component developer composed of a toner and a carrier is used as each developer. Here, the toner is manufactured by an emulsion polymerization method, and the shape can be controlled from a raspberry shape having large irregularities to a potato shape having small irregularities, and further to a spherical shape. The shape factor MI is spherical at 120 or less, approximately 120 to 125 is slightly distorted sphere, approximately 130 to 135 is potato shape, 138 to 150
The degree is a Raspberry shape. Normal kneaded and ground toner is 1
It is about 38 to 145. The weight average molecular weight Mw of the toner is preferably 20,000 to 30,000, and the relationship between the shape factor MI and the weight average molecular weight Mw of the toner preferably satisfies the following conditions. . MI ≦ Mw / 1000 + 115 MI: Shape factor of toner (true sphere is 100) π × (toner maximum diameter) 2 / (4 × toner sectional area) × 10
0 Mw: weight average molecular weight of the toner

In the emulsion polymerization method, a resin dispersion liquid containing an ionic surfactant is mixed with a pigment dispersed with an ionic surfactant having an opposite polarity, and hetero-aggregation is caused to form aggregated particles having a toner diameter. Then, the aggregates are coalesced and coalesced by heating above the glass transition point of the resin, followed by washing and drying. By selecting the heating temperature condition, the toner shape can be controlled from an irregular shape to a spherical shape. Normally, this process is performed by mixing a resin dispersion, a pigment dispersion, a release material dispersion, and the like as needed, and aggregating the aggregates in a uniform mixed state because the aggregation is performed. It is possible to make the toner composition uniform, and it is possible to easily control the molecular weight distribution by using a plurality of resin dispersions having different molecular weights.

Here, examples of the polymer used as the thermoplastic binder resin used in the present embodiment include styrenes such as styrene, parachlorostyrene and α-methylstyrene;
Methyl acrylate, ethyl acrylate, acrylic acid n-
Propyl, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate,
Esters having a vinyl group such as n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, vinyl nitriles such as acrylonitrile and methacrylonitrile, vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether, and vinyl methyl ketone , Vinyl ethyl ketone, vinyl ketones such as vinyl isopropenyl ketone, ethylene, propylene, copolymers such as monomers such as polyolefins such as butadiene or copolymers obtained by combining two or more thereof, or mixtures thereof, Further, a non-vinyl condensation resin such as an epoxy resin, a polyester resin, a polyurethane resin, a polyamide resin, a cellulose resin, a polyether resin, or a mixture of these with the vinyl resin, or a vinyl monomer in the presence of these. And the like graft polymer obtained in the polymerization. In the case of a vinyl monomer, a resin particle dispersion can be prepared by performing emulsion polymerization or seed polymerization using an ionic surfactant or the like,
In the case of other resins, if they are soluble in oily solvents with relatively low solubility in water, dissolve the resins in those solvents and disperse them in water with ionic surfactants and polymer electrolytes such as homogenizers. Disperse fine particles in water by
Thereafter, by heating or evaporating the solvent to evaporate the solvent, a resin dispersion can be prepared.

Examples of colorants and internal additives include carbon black, chrome yellow, Hansa yellow, benzidine yellow, slen yellow, quinoline yellow, permenet orange GTR, pyrazolone orange, vulcan orange, watchchang red, and permanent red. ,
Brilliantamine 3B, Brilliantamine 6B, Dupont Oil Red, Pyrazolone Red, Risor Red, Rhodamine B Lake, Lake Red C, Rose Bengal, Aniline Blue, Ultramarine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Phthalocyanine Green, Various pigments such as malachite green oxalerate, acridine-based,
Xanthene, azo, penzoquinone, azine, anthraquinone, thioindico, dioxazine, thiazine, azomethine, indico, thioindico, phthalocyanine, aniline black, polymethine, triphenylmethane, diphenylmethane One or more colorants such as various dyes such as thiazine, thiazole and xanthene can be used alone or in combination.

Further, as an internal additive, a magnetic substance such as a metal such as ferrite, magnetite, reduced iron, cobalt, nickel, and manganese, an alloy, or a compound containing these metals, or a quaternary ammonium salt as a charge controlling agent is used. Various commonly used charge control agents such as compounds, nigrosine-based compounds, dyes composed of complexes of aluminum, iron, chromium, etc. and triphenylmethane-based pigments can be used, but they affect aggregation and stability at the time of aggregation. From the viewpoint of controlling the ionic strength and reducing the pollution of wastewater, a material that is difficult to dissolve in water is preferable.
Examples of the inorganic fine particles to be added by wet method include silica, alumina, titania, calcium carbonate, magnesium carbonate, tricalcium phosphate, etc. which are all commonly used as external additives on the toner surface, such as ionic surfactants and polymer acids, It can be used by dispersing in a polymer base. Also,
After drying in the same manner as ordinary toner, inorganic particles such as silica, alumina, titania, calcium carbonate, etc. and resin fine particles such as vinyl resin, polyester, and silicone are added to the surface in a dry state by shearing to add fluidity. It can also be used as an agent or a cleaning aid.

Examples of surfactants used for emulsion polymerization, seed polymerization, pigment dispersion, resin particles, release agent dispersion, aggregation, or stabilization thereof include potassium laurate, sodium oleate, castor oil sodium and the like. Fatty acid soaps, octyl sulfate, lauryl sulfate, sulfate esters such as lauryl ether sulfate, nonylphenyl ether sulfate, lauryl sulfonate, dodecylbenzene sulfonate, triisopropyl naphthalene sulfonate, dibutyl naphthalene sulfonate, naphthalene sulfonate formalin condensate, monooctyl Sulfonates such as sulfosuccinate, dioctyl sulfosuccinate, lauric amide sulfonate, oleic amide sulfonate, lauryl phosphate, isopro Ruhosufeto, phosphoric acid esters such as nonyl phenyl ether phosphate, sodium dioctyl sulfosuccinate, lauryl sulfosuccinate 2
Sodium, anionic surfactants such as sulfosuccinates such as disodium lauryl polyoxyethylene sulfosuccinate, amines such as laurylamine hydrochloride, stearylamine hydrochloride, oleylamine acetate, stearylamine acetate, stearylaminopropylamine acetate Salts, lauryltrimethylammonium chloride, dilauryldimethylammonium chloride, distearyldimethylammonium chloride, lauryldihydroxyethylmethylammonium chloride, oleylbispolyoxyethylenemethylammonium chloride,
Cationic surfactants such as quaternary ammonium salts such as lauroylaminopropyldimethylethylammonium ethosulfate and lauroylaminopropyldimethylhydroxyethylammonium perchlorate; polyoxyethylene octyl ether; polyoxyethylene lauryl ether; polyoxyethylene stearyl ether , Alkyl ethers such as polyoxyethylene oleyl ether, alkyl phenyl ethers such as polyoxyethylene octyl phenyl ether and polyoxyethylene nonyl phenyl ether, polyoxyethylene laurate, polyoxyethylene stearate, and polyoxyethylene oleate. Alkyl esters, polyoxyethylene lauryl amino ether, polyoxyethylene stearylamino Ether, polyoxyethylene oleyl amino ether, polyoxyethylene soybean amino ether, alkyl amines, polyoxyethylene beef tallow amino ether, polyoxyethylene lauric acid amide,
Alkyl amides such as polyoxyethylene stearamide, polyoxyethylene oleic acid amide, vegetable oil ethers such as polyoxyethylene castor oil ether, polyoxyethylene rapeseed oil ether, lauric diethanolamide, stearic diethanolamide, oleic acid Nonionics such as alkanolamides such as diethanolamide, sorbitan ester ethers such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, etc. A non-ionic surfactant can be used. These may be used alone, or two or more kinds may be used at the same time.Anionic surfactants and nonionic surfactants, or cationic surfactants and nonionic surfactants may be used in combination. It is effective, and as a means for dispersion, a general one such as a rotary shearing homogenizer or a ball mill having a medium, a sand mill, a dyno mill or the like can be used.

As the carrier, a ferrite particle coated with a resin and having a controlled resistance value is used. In addition, a so-called polymer carrier obtained by mixing magnetic fine powder with a polymer can be used. Since the polymer carrier generally has lower magnetization than the magnetic particle carrier, a soft and high-density magnetic brush can be formed, and a high-quality image can be obtained. In addition, there is an advantage that the possibility of damaging the surface of the image carrier when adhered to the image carrier is reduced. Further, since the specific gravity is small, the mass of the carrier is also small, so that the stress applied to the toner when the developer is mixed in the developing device is reduced, and there is an advantage that a developer having a long life can be provided.
On the other hand, a magnetic particle carrier composed of metal particles such as iron, ferrite, and magnetite has a large carrier mass due to a large specific gravity of the carrier, and the stress on the toner increases when the developer is mixed in the developing device. There is an advantage that the charge of the developer rises quickly, and the carrier can be used properly depending on the required performance.

Regarding the particle size of the carrier, the smaller the particles, the denser the magnetic brush. Average particle size is 60μ
When it is less than m, the effect starts to appear. However, when the carrier has a small particle diameter such that the average particle diameter is less than 5 μm, the magnetic binding force of the carrier is weakened, so that the carrier adheres to the image carrier. from these things,
The average particle size of the carrier particles is preferably 20 μm or more and 60 μm or less.

As the developer in which the toner and the carrier are mixed, for example, a toner concentration (TC: Toner Concentr
ation) at a predetermined level (for example, 5 wt%) and the charge amount of the toner in the developer at a predetermined level (for example, -20 μC / g).
Can be used. Here, TC is expressed by equation (1) in FIG. Also, when the toner charge amount is too high when the toner and the carrier are mixed to form a developer, a phenomenon that the toner is not developed because the adhesion of the toner to the carrier becomes too strong. On the other hand, if the charge amount is too low, the adhesion of the toner to the carrier is weakened, and a toner cloud due to free toner is generated, which causes fogging in printing. From the viewpoint of transferring the toner and performing good development, it is desirable that the charge amount of the toner in the developer is in an absolute value of 5 to 80 μC / g, preferably 10 to 60 μC / g.

Particularly, in the present embodiment, for example, the developing order of the image forming process is yellow (1), cyan (2), magenta (3), black (4), and each color toner formed in the developing order The toner weight of the image is represented by W (1) to W (4)
Then, the weight of each toner becomes W (1) <W (2), W
(3) <W (4). In the present embodiment, for example, W (1) is set to 5.0 g / m ² or less, preferably 4.0 g / m ² or less.
In this embodiment, W (2) is 4.3 g / m ² ,
(3) is set to 4.3 g / m ² , and W (4) is set to about 4.5 g / m ² .

Next, the operation of the color image forming apparatus according to this embodiment will be described. In FIG. 2, the color image forming apparatus sequentially forms toner images of respective colors on the image carrier 101 and transfers the toner images in a superimposed manner on the intermediate transfer member 111, and operates as follows. After the image carrier 101 is driven to rotate and is uniformly charged by the charger 102, image light is emitted to form a latent image. This latent image is visualized by the yellow developing device 105Y, and the toner image is transferred onto the intermediate transfer member 111 by the primary transfer roll 106. Since the toner surface of the toner image formed in this manner has a spherical shape or a shape close to a spherical shape, the contact area with the image carrier 101 is very small, and there is van der Waals between the toner and the image carrier 101. Non-electrical adhesion such as force is reduced. Therefore, the toner is easily separated by the transfer electric field formed by the primary transfer roll 106 and is transferred to the intermediate transfer member 111. At this time, the toner image is 100
%.

In this color image forming apparatus, no cleaner is provided, and the image carrier 101 enters the next color image forming step after the transfer. That is, the image carrier 101 is further charged in the charger 102, irradiated with image light, and formed into a cyan toner image, and then transferred to the intermediate transfer member 111 in order to form a cyan toner image of the next color. enter. At this time, the yellow toner image formed in the previous step is formed on the intermediate transfer member 111, and the cyan toner image is transferred onto the yellow toner image or an area other than the yellow toner image.

Next, the respective colors of magenta and black are subjected to the steps of charging by the charger 102, irradiating the image light, forming the toner image, and transferring to the intermediate transfer member 111, and then the four colors are transferred onto the intermediate transfer member 111. A full-color image on which the toner images are superimposed is formed. This full-color toner image is collectively transferred to the recording paper 116 by the secondary transfer roll 115, and a full-color recorded image is obtained.

In such an image forming process, for example, in the cyan transfer step, the yellow toner image has already been transferred onto the intermediate transfer body 111, but the toner weight of the yellow toner image is, for example, 4 in a solid image. 0.0 g / m ² , almost no toner whose charge polarity was inverted due to peeling discharge was generated, and the transferred toner image and the image carrier 1
It was confirmed that the retransfer hardly occurred because the contact pressure between the film and the film No. 01 was not so large. Further, it was confirmed that almost no retransfer occurred in the magenta and black transfer steps. Therefore, in such a color image forming apparatus, a good full-color image could be formed without providing a cleaner and without collecting the residual toner on the image carrier 101.

In this embodiment, one image carrier 1
Although yellow, cyan, magenta, and black toner images were formed on the image No. 01, a so-called tandem type color image forming apparatus in which an image carrier, a charger, an image writing device, a developing device, and a transfer device were arranged for each color was also used. Is adaptable. Although the present embodiment has been described with reference to the electrophotographic recording method, the present invention is applicable to any indirect recording method such as a chargeless method and a backside exposure method that performs transfer to a transfer medium (intermediate transfer member 111 or recording paper 116). It is possible. On the other hand, the so-called electrostatic recording method, ionography method, and the like are also effective when a dielectric is used as the image carrier 101 instead of a photoconductor, and an electrostatic latent image is directly written, developed, and transferred. It is.

[0053]

Next, in order to evaluate the performance of the color image forming apparatus according to the present embodiment, various experiments were performed on the following examples. Specific conditions of the toner used in the present embodiment will be described. In this example, "parts" means parts by weight. Regarding the particle size, a Coulter Counter TA2 (manufactured by Coulter Inc.) was used for the particle size of the toner.
The particle size of the resin, the release agent and the pigment was LA-700 (manufactured by Horiba Ltd.), and the molecular weight of the resin fine particles and the toner was measured by gel permeation chromatography HLC-8.
120GPC (manufactured by Tosoh Corporation) was used to measure the glass transition point of the resin fine particles and the toner at a heating rate of 3 C / min using DSC-50 (manufactured by Shimadzu Corporation).

A resin dispersion 1 was prepared by mixing and dissolving 350 parts of styrene, 42 parts of butyl acrylate, 8 parts of acrylic acid, 16 parts of dodecyl mercaptan, 16 parts of carbon tetrabromide, and 4 parts of each of the above (all manufactured by Wako Pure Chemical Industries, Ltd.). 8 parts of a nonionic surfactant (manufactured by Sanyo Chemical Co., Noniball 85) and 10 parts of an anionic surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Neogen SC) were dissolved in 582 parts of ion-exchanged water in a flask. While emulsifying and slowly mixing for 10 minutes, ion-exchanged water 5 in which 3.5 g of ammonium persulfate (manufactured by Tokai Denka) was dissolved.
Then, 0 g was charged and the atmosphere was replaced with nitrogen. Thereafter, the contents were heated to 70 ° C. in an oil bath while stirring the flask, emulsion polymerization was continued for 6 hours, and then cooled to room temperature to obtain a resin dispersion. From the obtained resin dispersion, the solvent was left in an oven at 80 ° C. to remove water. Central particle size 130 nm, glass transition point 56 ° C, Mw 21,000
Was obtained.

60 parts of a pigment for each color toner were added to and mixed with 300 parts of ion-exchanged water together with 2 parts of an anionic surfactant (Ionnet D-2, manufactured by Sanyo Kasei Co., Ltd.), and dispersed with Ultra Turrax T50 manufactured by IKA. Processed, center diameter 160n
m of pigment dispersion liquid 1 was obtained.

Next, the above-mentioned resin dispersion 1 and pigment dispersion 1 were mixed in the following proportions: 300 parts of ion-exchanged water 240 parts of resin dispersion 1 40 parts of pigment dispersion 1 2 parts of cationic surfactant 2 parts (manufactured by Kao Corporation) , Sanisol B50) Ultra Turrax T5 in a round stainless steel flask
After mixing and dispersing at 0, the flask was heated to 47 ° C. with stirring in an oil bath for heating. After maintaining at 47 ° C. for 2.5 hours, observation with an optical microscope confirmed that aggregated particles of about 6.9 μm had been formed. Thereafter, 6 parts of Neogen SC was additionally added, and 9
Heated to 4 ° C and held for 8 hours. After this, the flask
After cooling to room temperature at 0 ° C./min, further filtering, washing sufficiently with ion-exchanged water, and keeping at 40 ° C. for 10 hours in a vacuum dryer, the central particle size is 7.0 μm, and the molecular weight Mw is 21,000.
Thus, magenta, cyan, yellow, and black toners having a shape factor MI of 119 were obtained. One part of colloidal silica (R972 manufactured by Nippon Aerosil Co., Ltd.) was added to 100 parts of the toner and mixed with a Henschel mixer.

Further, as the carrier used in this embodiment, 100 parts of ferrite particles having an average particle size of 35 μm,
1 part of a methacrylate resin having a molecular weight of 95,000 was put into a pressurized kneader together with 500 parts of toluene.
After mixing, the temperature was raised to 70 ° C. while mixing under reduced pressure, the solvent was distilled off, and the mixture was cooled and decorated with a 105 μm sieve to obtain a carrier for evaluation. The developer in which the toner and the carrier are mixed has, for example, a toner concentration TC of 5 wt%.
The toner charge amount in the developer at that time is-
The range was 20 μC / g to −30 μC / g.

An experiment for evaluating the retransfer property of the color image forming apparatus was conducted by storing the developers of the respective colors described above in the developing units 105Y to 105BK of the color image forming apparatus shown in FIG. In this experiment, in the color image forming apparatus, a cyan toner image was first formed on the intermediate transfer member 111, and the transfer process was repeated three times.
The re-transfer rate was measured for each transfer count by varying the weight of the cyan toner above. Here, the retransfer rate is calculated by equation (2) in FIG.

The results are shown in FIG. 4 and FIG. FIG. 5 shows the relationship between the toner weight and the retransfer rate, and FIG. 5 shows the relationship between the number of transfer cycles and the retransfer rate. As shown in these figures, as the toner weight of the toner image on the intermediate transfer body 111 is larger, the amount of toner to be retransferred is larger, and as the number of times the toner image on the intermediate transfer body 111 passes through the transfer process is larger, The amount of toner to be retransferred increases. From this, it is understood that retransfer is prevented by minimizing the toner weight of the toner image formed first, which has the largest number of passes through the transfer process. Specifically, by setting the toner weight of the first toner image to be formed to be 5.0 g / m ² or less, preferably 4.0 g / m ² or less, occurrence of retransfer can be prevented. It was confirmed that.

FIG. 6 shows the relationship between the weight of the solid image toner image having a sufficient image density and the content of the pigment contained in the toner calculated. Here, the content of the pigment contained in the toner when the weight of the toner image is 5.0 g / m ² is 4 wt% or more, and the content of the pigment contained in the toner when the weight of the toner image is 4.0 g / m ² is It was confirmed that by setting the content to 5.5 wt% or more, a sufficient image density can be obtained even with a small toner weight of the toner image. That is, in this embodiment, if the pigment content is increased for a toner having a small toner weight, a sufficient image density can be obtained, and good color image quality can be obtained.

Further, in the above embodiment, 20,000
When an image was formed on a sheet, a positive ghost in which the residual toner appeared in the next image did not occur.

In the transfer device (primary transfer roll 106 in this embodiment) of the color image forming apparatus according to the present embodiment, for example, even if toner remains after transfer, the image light transmittance is required to be 90% or more. It is preferable to set so that This is a condition for preventing the occurrence of a so-called negative ghost, and is based on the data shown in FIG. FIG. 7 shows the result of an experiment in which the relationship between the transmittance of the image light and the generation level of the negative ghost was examined, and the result is shown. It is shown that when the ratio becomes 90% or less, the ratio becomes higher than the allowable level.
In general, the transmittance decreases as the residual toner amount increases. However, the transmittance greatly differs depending on the type of toner as shown in FIG. 8, and the effective value is determined by determining the setting of the transfer device based on the transmittance instead of the residual toner amount. The negative ghost can be prevented.

As described above, in the color image recording apparatus of this embodiment, image defects such as a positive ghost and a negative ghost, and accumulation of toner on the image carrier 101 are prevented, and the residual toner is developed by the developing units 105Y to 105BK. Therefore, foreign matter such as paper dust does not enter the developing units 105Y to 105BK, and there is no need to periodically replace the developer.

[0064]

As described above, according to the present invention,
In an indirect transfer type color image forming apparatus that sequentially transfers each color toner image formed on an image carrier by a plurality of developing means to a transfer medium, the toner weight of a toner image formed first in an image forming process is minimized. Thus, by taking various known measures for improving the transfer efficiency, it is possible to achieve both the improvement of the transfer efficiency and the prevention of the re-transfer of the existing toner image. For this reason, it is possible to eliminate or significantly reduce the toner collected from the image carrier after the transfer, without collecting the residual toner,
By setting so that the toner is transferred together with the formed image, a so-called cleanerless type indirect transfer type color image forming apparatus which does not generate toner to be collected and discarded can be easily realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an outline of a color image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing one embodiment of a color image forming apparatus to which the present invention is applied.

FIG. 3 is an explanatory diagram of a toner density (TC) and a retransfer rate.

FIG. 4 is a graph illustrating the relationship between the toner weight of the toner image on the intermediate transfer member and the retransfer rate from the toner image on the intermediate transfer member to the image carrier in the color image forming apparatus according to the embodiment.

FIG. 5 is a graph showing the relationship between the number of times the toner image on the intermediate transfer member passes through the transfer step and the retransfer rate from the toner image on the intermediate transfer member to the image carrier in the color image forming apparatus according to the embodiment. is there.

FIG. 6 is a graph showing the relationship between the toner weight and the content of the pigment contained in the toner of the color image forming apparatus according to the embodiment.

FIG. 7 is a graph showing the relationship between the transmittance of image light with respect to transfer residual toner and the generation level of a negative ghost in the color image forming apparatus according to the embodiment.

FIG. 8 is a graph showing the relationship between the amount of transfer residual toner and the transmittance of image light in the color image forming apparatus according to the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Latent image forming means, 3 (3a-3d) ...
Developing unit, 4 Transfer unit, 5 Transfer medium, 6 Cleaner, 101 Image carrier, 102 Charger, 104 Image writing device, 105 Developing device, 106 Primary transfer roll, 111 Intermediate transfer member , 112, 113, 114: support roll, 115: secondary transfer roll, 116: recording paper

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Koide 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd.

Claims (6)

[Claims] 1. A latent image forming means for sequentially forming an electrostatic latent image of each color component on an image carrier, and selectively forming an electrostatic latent image of each color component on the image carrier by a toner of a corresponding color. A color image forming apparatus comprising: a plurality of developing means for developing; and a transfer means for sequentially transferring a toner image of each color component on an image carrier to a transfer medium. W (1) <W (2)... W (N−1) <W where W (I) is the toner weight of the toner image formed on the image carrier by the I-th developing means in the developing order of (N) a color image forming apparatus satisfying the following relationship: 2. The color image forming apparatus according to claim 1, wherein the number of the plurality of developing means is N, and the developing order of the image forming process is the I-th developing means. A color image forming apparatus which satisfies the relationship of m (1)> m (2)... M (N-1)> m (N), where the pigment content is m (I). 3. The color image forming apparatus according to claim 1, wherein the latent image forming means forms a latent image by exposure, wherein the transfer means carries an image after passing through a portion facing the transfer means. A color image forming apparatus, wherein a transfer rate at which a light transmittance is 90% or more is maintained when exposure and irradiation are performed while overlapping toner remaining on a body. 4. The color image forming apparatus according to claim 1, wherein a release layer is provided on the surface of the image carrier to reduce an adhesive force with fine particles formed on the image carrier. A color image forming apparatus. 5. The color image forming apparatus according to claim 1, wherein each color toner is manufactured by an emulsion polymerization method, and satisfies the following conditions. MI ≦ Mw / 1000 + 115 MI: Shape factor of toner (true sphere is 100) π × (toner maximum diameter) 2 / (4 × toner sectional area) × 10
0 Mw: weight average molecular weight of the toner 6. The color image forming apparatus according to claim 1, wherein the toner has a weight average molecular weight Mw of 20,000 to 30,
000.