JPH09127726A - Developer for electrostatic latent image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress decrease in the image density and production of irregular density by preventing melt sticking of a toner to a blade which forms a toner thin layer on a developer roller in an image forming device. SOLUTION: This developer is used for an image forming method to develop an electrostatic latent image formed on a photoreceptor 10 with a toner 26 to form an image on a recording medium 18. The developer for an electrostatic latent image contains elastic particles 34 having a larger particle size than the particle size of the toner 26, preferably >=1.5 times as large as the average particle size of the toner 26, or elastic particles 34 having >=1.5 times as large as the thickness of the toner layer formed on the photoreceptor 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic latent image developer used in an image forming apparatus adopting an image forming method of developing an electrostatic latent image with toner to form an image on a recording medium, and more particularly, to an electrostatic latent image developer. An electrostatic charge capable of suppressing a decrease in image density and the occurrence of density unevenness by preventing the toner from being fused to a blade that forms a thin layer of toner on a toner carrying roller provided in an image forming apparatus. The present invention relates to a latent image developer.

[0002]

2. Description of the Related Art Conventionally, electrophotographic developing systems are generally roughly classified into one-component developing systems and two-component developing systems. 1
The component developing method is composed only of toner for developing the electrostatic latent image formed on the photoconductor, while the two-component developing method efficiently charges the toner for developing the electrostatic latent image and the toner. And a carrier for.

Here, the two-component developing system is generally constituted by a mixture ratio of carrier 95 to 98% and toner 2 to 5% by weight. At this time, if the toner is a non-magnetic toner and the mixing ratio with respect to the carrier is 5% or more,
Toner fogging occurs in the non-printed portion, resulting in deterioration of image quality. Therefore, a method has been proposed in which the toner is a magnetic toner to increase the mixing ratio of the toner, and it is between the one-component developing method and the two-component developing method.
It is also called a five-component developing system. In the 1.5-component developing system, the developer is composed of a mixture ratio of 30 to 80% carrier and 20 to 70% toner.

In the two-component developing method and the 1.5-component developing method, the toner and the carrier are agitated and charged in the developing device, and the toner is conveyed through the carrier while the ears of the carrier are erected in the direction of the photoconductor by the electric field. Developing an electrostatic latent image on the photoconductor. For this reason, since the toner is not formed in a thin layer and a blade for charging the toner is not required, the phenomenon of fusion of the toner to the blade does not occur, and there is no problem in this respect.

Further, the one-component developing method is described in US Pat.
Nos. 909258 and 4121193, and the like using magnetic toners, and US Pat. 287
There is a type using a non-magnetic toner disclosed in Japanese Patent Publication No. 7 and Japanese Patent Publication No. 54-3824, and in any type, thin development is performed on a toner carrier that conveys toner to an electrostatic latent image on a photoconductor. It is configured to form an agent layer.

Specifically, in the developing method using the toner for the one-component developing method, a thin layer of toner is formed on the surface of the developing roller which conveys the toner to the photosensitive member on which the electrostatic latent image is formed. Then, the thin layer is brought into contact with the photoconductor to guide the toner to the electrostatic latent image for development, and at the same time, the toner is transferred to the recording medium. In this developing method, the toner is efficiently formed by a blade or the like on the developing roller that conveys the toner to the electrostatic latent image, and is formed into a thin layer and charged in an extremely short time. The image is developed and then developed on the recording medium by the transfer device.

[0007]

However, as described above, in the one-component developing system, since a thin layer of toner is formed and charged on the developing roller by using a blade, the toner by this blade is used. When the thin layer is formed, a large stress is applied to the toner via the blade, which causes the toner to be heated and fused to the blade.

Therefore, when the toner is fused to the blade when forming a thin layer of the toner on the developing roller, streaks may occur in the toner layer formed on the developing roller due to the fusion, or The toner layer may become extremely thin, and in some cases, the toner may not exist on the developing roller. As a result, there is a possibility that a uniform thin layer of toner may not always be formed on the developing roller, so that an image formed on the recording medium may have a portion having a low density and a portion having a high density. The unevenness and the image density are reduced as a whole, and the image density is lowered.

The present invention has been made to solve the above-mentioned conventional problems, and prevents fusion of toner to a blade that forms a thin layer of toner on a toner carrying roller provided in an image forming apparatus. By doing so, it is an object of the present invention to provide an electrostatic latent image developer capable of suppressing the decrease in image density and the occurrence of density unevenness.

[0010]

In order to achieve the above object, the electrostatic latent image developer according to claim 1 is used in an image forming method for developing an electrostatic latent image with toner to form an image on a recording medium. In the electrostatic latent image developer described above, the electrostatic latent image developer has a configuration in which elastic particles having a particle size larger than the particle size of the toner are contained in the toner.

According to the electrostatic latent image developer of the first aspect, the elastic particles are contained in the toner, and the particle size of the elastic particles is larger than the particle size of the toner. , The effect of alleviating the pressure exerted on the toner between the blade and the toner carrying roller to the extent that the charging of the toner is not affected. Due to the action of the elastic particles, the fusion of the toner on the blade can be prevented.

Here, when the toner is fused to the blade, the state of the toner carried on the toner carrying roller is caused by the large growth of the nuclei generated a little away from the contact point between the blade and the toner carrying roller. However, even in such a case, the elastic particles have a function of scraping and removing the small fusion cores generated in the blade. As a result, even when toner fusion starts to occur on the blade, the nucleus of the fusion is removed by the elastic particles, so that the density of the image formed on the recording medium and the density unevenness may occur. It is possible to reliably and effectively prevent this. If a physically and chemically stable material such as silicone rubber or urethane rubber is used as the material of the elastic particles, the elastic particles themselves will not stick to the blade.

The electrostatic latent image developer according to claim 2 is
The electrostatic latent image developer according to claim 1, wherein the particle size of the elastic particles is 1.5 times or more the particle size of the toner, or
The toner layer has a thickness of 1.5 times or more. When the elastic particles have a particle diameter of the toner or a toner layer thickness of 1.
When the particle size is 5 times or more, the action of the elastic particles can be more effectively exerted, and more effectively prevent density reduction and density unevenness of the image formed on the recording medium. It becomes possible. Regarding the external addition method of the elastic particles to the toner, the elastic particles may be stirred and mixed at the same time as the toner, but the elastic particles are added to the toner while stirring and mixed to uniformly and uniformly disperse the external particles. Sometimes you can get good results.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electrostatic latent image developer according to the present invention will be described based on an embodiment embodying the present invention. The electrostatic latent image developer according to the present embodiment is applied to an image forming method for developing an electrostatic latent image such as an electrophotographic system or an electrostatic recording system. A case in which an image is formed by using an electrostatic latent image developer in a laser beam printer will be described with reference to FIG.
FIG. 1 is an explanatory diagram schematically showing a main part of a laser beam printer. In the following, the electrostatic latent image developer is referred to as toner.

In FIG. 1, the laser beam printer is provided with a detachable developing device 2, and the developing device 2 has a functional portion for accumulating, charging, developing and transferring toner. Specifically, the developing device 2 is arranged around a photoconductor 10 in which a photoconductive layer is applied to an aluminum conductive cylinder, a charging roller 12 that applies a surface potential to the photoconductor 10, and a laser scanner 14 that provides image information. A developing roller 16 as a toner carrying roller for carrying the toner 26 and carrying it to the electrostatic latent image on the photoreceptor, a blade 4 for regulating the toner 26 on the developing roller 16 into a uniform thin layer, and a developing roller 16. A supply roller 8 for supplying the toner 26 to the roller 16; an agitator 6 for agitating the toner 26 stored in the toner storage portion 28 to keep the fluidity in a good state;
A transfer roller 20 that transfers the visible image of the toner 26 formed on the photoconductor 10 to the recording medium 18 such as paper, and a cleaning roller 22 that removes the toner 26 that is not transferred by the transfer roller 20 on the photoconductor 10. And and recording medium 1
Thermal fixing device 2 for fixing the toner image on 8 by heat fusion
4 (consisting of a pair of rollers with a built-in heater).

The toner 26 according to the present embodiment is filled in the toner storage portion 28 of the developing device 2, and is agitated by the agitator 6 and brought into contact with the supply roller 8. The supply roller 8 is biased at −400 V, and the developing roller 16 is at −30 V.
It is biased at 0 volts. Therefore, the negatively charged toner 26 is supplied from the supply roller 8 to the developing roller 16 in accordance with the rotational movement of the supply roller 8 and the developing roller 16 in the arrow direction, and is formed into a thin layer by the blade 4.

In the charging roller 12, about 1.
When a voltage of about 4 kV is applied, -90 is applied on the photoconductor 10.
A surface potential of about 0 to -1000 V is formed. The charging roller 12 may be in contact or non-contact with a shape other than a roller shape, for example, a scorotron which gives a predetermined surface potential to the photoconductor 10 by corona discharge, or a surface potential which is brought into contact with the photoconductor 10. It is possible to use a member such as a semi-conductive brush, a blade or the like which gives

The image information converted into an electric signal is supplied as an optical signal from the laser scanner 14 to the photoconductor 10 to which the surface potential is given by the charging roller 12, and the light of the photoconductor 10 is activated by the action of the photoconductive layer. The potential of the exposed portion is reduced, and an electrostatic latent image having a different potential distribution is formed. In addition to the laser scanner, an LED or the like can be used as a means for supplying image information to the photoconductor as an optical signal.

Here, the blade 4 is made of SUS having a length of 250 mm, a free length of 9 mm, and a tip bending angle R of 0.3 mm, and the bent portion is applied to the developing roller 16 by a linear pressure of 400 g. Pressed. The developing roller 16 is made of silicone rubber, and has a surface roughness of RZ 7 micrometers or less and a rubber hardness of 50 degrees (Asuka C).

The toner 26 formed into a thin layer by the blade 4 and conveyed by the developing roller 16 is the toner 26.
Is contacted with the photoconductor 10 and only the toner 26 is developed on the electrostatic latent image formed on the photoconductor 10. Photoconductor 1
The electrostatic latent image on 0 is in the state where the surface potential applied from the charging roller 12 is −900 to −1000 V.
It is formed when the potential of the exposed portion is lowered to −50 V by the exposure by the laser scanner 14. On the other hand, a potential of −300 V is applied to the developing roller 16 as a bias potential, and the negatively charged toner 26 is developed on the potential portion of −50 V on the photoconductor 10. The chargeability of the toner 26 used is
In the present embodiment, negative charging is used, but positive charging can also be applied if the potentials applied to the respective members are of opposite polarities.

The visible image of the toner 26 thus formed on the photoconductor 10 is controlled by a constant current of 3 microamperes (μA), and the transfer roller 20 whose polarity is controlled to be positive is used to record a recording medium 18 such as paper. The toner 26 is transferred onto the recording medium 18, and the toner 26 is fixed on the recording medium 18 by the thermal fixing device 24.
A desired recorded image can be obtained. This thermal fixing device uses a non-contact type electric field such as a scorotron, whether it is in contact or not, a roller, a brush,
There is a method of contacting with a blade. On the other hand, recording medium 1
The toner 26 that was not transferred to No. 8 and remained on the photoconductor is +4
Recovered through cleaning roller 22 biased at 00 volts.

Next, the toner 26 used in the laser beam printer constructed as described above will be described in detail. The toner 26 according to this embodiment is configured as a non-magnetic one-component developer. The toner 26 is basically composed of a binder resin, carbon black, a release agent, and a charge control agent.

Here, the binder resin acts as a binder, for example, polystyrene, polyacrylate, polymethacrylate, vinyl resin, polyester resin, polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, polyether. Polycarbonate, cellulosic resin, epoxy resin, polyamide and copolymers of monomers forming these resins can be used alone or in combination of two or more kinds. In the present embodiment, since a minus toner is used, a polyester resin having a carboxyl group as a terminal functional group and being rigid in strength is convenient.

Further, carbon black acts as a colorant, and examples of such carbon black include furnace black, ketjen black, lamp black, thermal black, channel black, and the like, and these may be used alone. , You can mix multiple types. Further, these carbon blacks are preferably those having a small specific surface area and a large oil absorption, and specifically, those obtained by dividing the specific surface area by the oil absorption are preferably 0.8 or less. In particular, furnace black satisfies the conditions described above and is suitable.

Further, as the release agent, polyalkylene or natural wax can be mixed, and specific examples thereof include polyethylene, polypropylene, carnauba wax, candelilla wax, rice wax and the like. be able to. Examples of charge control agents include
Examples thereof include nigrosine dyes, quaternary ammonium salts, alkoxylated amines, alkylamides, metal complexes of azo dyes, and metal salts of higher fatty acids.

Next, the elastic particles externally added to the toner basically composed of the above components will be described. The elastic particles used in the present embodiment include shearing action, rubbing action, friction, etc., like rubber elastic substances such as silicone rubber, urethane rubber, NBR, and resin elastic substances such as polyethylene terephthalate and high density ethylene. Particles having a tough elastic force with respect to the physical force of are suitable. Also,
It is further advantageous if the elastic particles also have the property of being chemically resistant.

The elastic particles have a particle size larger than the average particle size of the toner (generally, a particle size of about 10 μm). Specifically, the average particle size of the toner is 1. A particle size of about 5 to 10 times or a particle size of about 1.5 to 10 times the thickness of the toner carrying layer formed on the developing roller 16 can be preferably used.

Here, in the case of elastic particles having an average particle diameter of toner or a particle diameter smaller than 1.5 times the thickness of the toner carrying layer on the developing roller 16, a position slightly apart from the contact point between the blade and the developing roller 16 is used. It is extremely difficult to peel off the fused toner, and if the elastic particles have a particle size larger than 10 times the average particle size of the toner or 10 times the thickness of the toner carrying layer on the developing roller 16, the developing roller will be used. The blade 4 cannot pass through the gap formed between the blade 16 and the blade 4, and the blade 4 stops at the gap, so that the blade 4 does not sufficiently exert the peeling action of the fused toner, and the toner is thin. It also becomes an obstacle when forming a layer.

Even when the particle size of the elastic particles has the above-described relationship with the average particle size of the toner,
The amount of addition of the elastic particles was 0.
If it is 5 parts by weight or less, a sufficient effect of preventing sticking cannot be obtained. Further, the addition amount is 5 with respect to 100 parts by weight of the toner.
If the amount is more than the weight part, the frictional resistance between the blade and the elastic particles becomes large, the load on the motor for rotating the developing roller 16 increases, and the motor is frequently out of step. A toner having the above composition may be used in combination with a fluidity-imparting agent for improving the fluidity of the toner, an abrasive for preventing toner filming on the photoconductor, and the like.

Here, the function of preventing the toner from being fused by the elastic particles will be described with reference to FIG. FIG. 2 is an explanatory view schematically showing the toner fusion preventing action of the elastic particles. In FIG. 2A, the developing roller 16 is rotated in the direction of the arrow, and a thin layer 30 (two layers) of the toner 26 is formed on the surface of the developing roller 16 via the blade 4. . As the thin layer 30 is formed,
As shown in FIG. 2A, the toner 26 starts fusion at a position near the lower end portion 4A of the blade 4, and a fusion nucleus 32 begins to be formed.

At this time, the elastic particles 3 are contained in the toner 26.
4, the elastic particles 34 are moved to the blade 4 side in response to the rotation of the developing roller 16.
The elastic particles 34 are, as shown in FIG.
An attempt is made to pass through the gap between the developing roller 16 and the blade 4. Thus, when the elastic particles 34 pass through the gap, the elastic particles 34 pass through the gap while elastically deforming, and at this time, the elastic particles 34 are nuclei 32 of toner fusion.
Is removed from a position in the vicinity of the lower end 4A of the blade 4 and passes through the gap. As a result, the nuclei 32 for toner fusion adhere to the elastic particles 34 while passing through the gaps (see FIG. 2C). As a result, a uniform thin layer of toner is always formed on the developing roller 16, and it is possible to prevent a decrease in image density and uneven density.

[0032]

EXAMPLES Next, the toner according to the present exemplary embodiment will be described with reference to a plurality of examples. << Example 1 >> Polyester resin (Mitsubishi Rayon FC-701) 100 parts by weight Carbon black (Mitsubishi Chemical # 44) 13 parts by weight Wax (Sanyo Kasei VISCOL 660P) 5 parts by weight Charge control agent (Orient Chemical Co., Ltd. Bontron S-34) 2 Part by weight is mixed in the form of powder, and carbon black, wax, and a charge control agent are dispersed in the resin while heating with a kneading extruder. After cooling the heated and kneaded material, the material is coarsely pulverized and finely pulverized to obtain toner fine particles on the order of several μm. Furthermore, it was made into powder particles having a particle size of 10 μm with an air classifier.

3 parts by weight of silicone rubber elastic particles having an average particle diameter of 70 μm, and an average particle diameter of 10 to 20 parts by weight relative to 100 parts by weight of the toner particles having the above composition before external addition treatment
1 part by weight of finely divided hydrophobic silica powder having a particle size of 1 nm and mixed with a Henschel mixer to obtain a dry toner. The toner adjusted as described above was filled in the developing unit of the laser beam printer shown in FIG. For image output, an image was developed on a photosensitive member by a developing device, transferred to a recording medium paper by a transfer roller, and toner was fixed on plain paper by a heat fixing roller. The recording medium is XERO.
An image was formed and printed using 4024 20 pound paper manufactured by X company.

Under the above-mentioned image forming conditions, the image density was measured, and the presence or absence of toner fusion on the blade after image formation was observed. Here, regarding the image density, 3 is set every time the initial image and 1000 sheets of images are formed.
Up to 000 sheets, the transmission densities of the high density portion and the low density portion in the image formed on the recording medium were measured with a Macbeth transmission densitometer TD904. The allowable value of the image density is generally 1.7 or more. Regarding the presence / absence of toner fusion on the blade, the blade was visually observed after image formation to determine the presence / absence of toner fusion. The measurement results were as shown in Table 1 below.

[0035]

[Table 1]

As can be seen from Table 1, the initial image, 100
After forming 0 images, after forming 2000 images, and 3
It can be seen that the minimum density sufficiently satisfies the allowable value in any case after the image formation of 000 sheets. Also,
The density difference between the maximum density and the minimum density after the formation of 3000 images from the initial image is within 0.07. Furthermore,
When the blade was visually observed after forming 3000 sheets of images, no toner fusion phenomenon was found. This is because the action of the silicone rubber elastic particles contained in the toner and the action of the silica fine powder prevent the toner from being fused to the blade, effectively suppressing the decrease in image density and the occurrence of density unevenness. It is thought to be based on what was able to be done.

Example 2 With respect to 100 parts by weight of toner particles produced by the same composition and method as in Example 1, 3 parts by weight of silicone rubber elastic particles having an average particle diameter of 30 μm and an average particle diameter of 10 are used. 1 part by weight of hydrophobic silica fine powder having a particle size of up to 20 nm was mixed and stirred with a Henschel mixer to prepare a dry toner. When each measurement was performed under the above conditions, the measurement results were as shown in Table 2 below.

[0038]

[Table 2]

As can be seen from Table 2, the initial image, 100
It can be seen that the minimum density sufficiently satisfies the permissible value in any case after the formation of 0 image and the formation of 2000 images. The density difference between the maximum density and the minimum density after the formation of 2000 images from the initial image is 0.1.
It is within 4. On the other hand, the minimum density after image formation on 3000 sheets was 1.56, which was slightly less than the allowable value (1.7). Further, when the blade was visually observed after the image formation of 3,000 sheets, a toner fusion phenomenon was found and streaks were scattered on the toner layer on the developing roller 16. However, even in this case, it is understood that the image density sufficiently satisfies the allowable value until the image formation of 2000 sheets. As in the case of Example 1, this is because the action of the silicone rubber elastic particles contained in the toner and the action of the silica fine powder prevent the toner from being fused to the blade, thus lowering the image density, It is considered that this is based on the fact that the occurrence of density unevenness could be effectively suppressed.

Next, in order to confirm the quantitative effect of the elastic particles contained in the toner, a toner according to a comparative example was produced, and the measurement was carried out under the same conditions as above, and the measurement result was obtained for each. Hereinafter, the toner of the comparative example will be described.

Comparative Example 1 0.3 part by weight of silicone rubber elastic particles having an average particle diameter of 150 μm and an average particle diameter of 100 parts by weight of the toner particles produced by the same composition and the same method as those in Example 1 were used. 1 part by weight of hydrophobic silica fine powder having a particle size of 10 to 20 nm was mixed and stirred with a Henschel mixer to prepare a dry toner. When each measurement was performed under the above conditions, the measurement results were as shown in Table 3 below.

[0042]

[Table 3]

As is clear from Table 3, the initial image, 100
After the image formation of 0 sheets and the image formation of 2000 sheets, the minimum image density once satisfies the allowable value,
It is understood that the image density gradually decreases after the formation of the image of 00 sheets, and the minimum density as well as the maximum density does not satisfy the allowable value when the image of 3000 sheets is formed. Further, the density difference is 0.
While it is about 06, it increases from 0.12 to 0.15 when forming images of 2000 to 3000 sheets. Further, when the blade was visually observed after the image formation of 3,000 sheets, a remarkable toner fusion phenomenon was found.
This is because the addition amount of the silicone rubber elastic particles contained in the toner was small, and the effect of preventing the fusion of the toner by the silicone rubber elastic particles was insufficient. Conceivable.

Comparative Example 2 100 parts by weight of toner particles produced by the same composition and the same method as those in Example 1 were used, but without adding elastic particles such as silicone rubber, the average particle diameter was 10 to 20 nm. Hydrophobic silica fine powder 1
Only parts by weight were mixed and stirred with a Henschel mixer to obtain a dry toner. When each measurement was performed under the above conditions, the measurement results were as shown in Table 4 below.

[0045]

[Table 4]

As is clear from Table 4, the maximum density and the minimum density satisfy the permissible values in the initial image, and the density difference is 0.08, but the minimum density is 1 when forming 1000 images. .48, which does not already satisfy the allowable value,
The density difference is as large as 0.35. Also, 2000
At the time of image formation on one sheet, even the maximum density does not satisfy the allowable value, and at the time of image formation on 3000 sheets, this tendency becomes more remarkable. As a result of observing the fused state of the toner with respect to the blade, a streak where no toner is carried is found on the surface of the developing roller 16 at the time of image formation of 1000 sheets, and the developing roller 16 corresponding to this streak is detected. A toner fusion phenomenon was found on the blade corresponding to the portion where the toner carrying layer is thin. In particular, a larger toner fusion phenomenon occurred in the blade portion corresponding to the portion of the developing roller 16 on which the toner is not carried.

This is because the toner of Comparative Example 2 does not contain elastic particles such as silicone rubber, so that the toner fusion phenomenon to the blade occurs at a relatively early stage as described above. It is considered to be caused by this. The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various improvements and modifications can be made without departing from the spirit of the present invention.

[0048]

As described above, according to the present invention, the fusion of the toner to the blade for forming the thin layer of the toner on the toner carrying roller disposed in the image forming apparatus is prevented, so that the image density is reduced and the density is reduced. An electrostatic latent image developer capable of suppressing the occurrence of unevenness can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram schematically showing a main part of a laser beam printer.

FIG. 2 is an explanatory view schematically showing a toner fusion preventing action of elastic particles.

[Explanation of symbols]

 2 Developing Device 4 Blade 6 Agitator 8 Supply Roller 10 Photosensitive Member 12 Charging Roller 14 Laser Scanner 16 Developing Roller 18 Recording Medium 20 Transfer Roller 22 Cleaning Roller 24 Thermal Fixing Device 26 Electrostatic Latent Image Developer 30 Thin Layer of Toner 32 Toner Fusing Nucleus of arrival 34 Elastic particles

Claims (2)

[Claims] 1. An electrostatic latent image developer used in an image forming method for developing an electrostatic latent image with a toner to form an image on a recording medium, wherein the electrostatic latent image developer is applied to the toner. An electrostatic latent image developer containing elastic body particles having a particle size larger than that of the toner. 2. The particle size of the elastic particles is 1.5 times or more the particle size of the toner, or 1.5 times the toner layer thickness.
The electrostatic latent image developer according to claim 1, wherein the electrostatic latent image developer is at least double.