JPH09258476A - Electrostatic latent image developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fogging due to decrease in the surface potential of a photoreceptor when a positive charge toner touches the photoreceptor to move electrons from the toner to be charged into positive to the photoreceptor. SOLUTION: Electron withdrawing groups are introduced to a one component positive charge toner binder so as to suppress electrons released from the toner as much as possible and to prevent decrease in the surface potential of a photoreceptor when an electrostatic latent image developer is charged by triboelectrification with the photoreceptor. Thus, an image with little fog can be obtd. Further, the electron withdrawing groups are included by between >=0.3mol and <=1.0mol per 1mol of the toner binder.

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 used in an image forming apparatus employing an image forming method for developing an electrostatic latent image formed on a photoreceptor to form an image on a recording medium. The present invention relates to a novel electrostatic latent image developer mainly applied to electrophotography and electrostatic recording of printers, facsimiles, copiers, plotters, and the like.

[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 electrostatic latent image developer used in the component developing system is composed of only a toner developed into an electrostatic latent image on a photoconductor. The electrostatic latent image developer used in the two-component developing system is composed of toner to be developed and a carrier for efficiently charging the toner.

Here, the two-component developing type electrostatic latent image developer is generally composed of a carrier of 95 to 98% by weight and a toner of 2 to 5% by weight. The toner at this time is a non-magnetic toner, and if the mixing ratio 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 spikes of the carrier are erected by the electric field toward the photosensitive member. Is being developed into an electrostatic latent image. With such a developing method, it is difficult to reduce the size and simplification of the apparatus, and recently, the one-component developing method has been actively developed. Since the electrostatic latent image developer used in the one-component developing system is composed of only toner, the electrostatic latent image developer is hereinafter referred to as toner.

The one-component developing system includes a type using a magnetic toner and a non-magnetic toner. In either type, a thin developer layer is formed on a toner carrier that conveys toner to an electrostatic latent image on a photoconductor. Are configured to form.

Specifically, in the developing method using the toner for positively charged one-component developing method, the surface of the photoconductor is charged to about + 700V by a charger, and the exposed partial potential is lowered to about + 100V by laser light or the like. Form a latent image.
A potential (development bias) lower than the photoconductor surface potential and higher than the exposure portion potential is applied to the surface of the developing roller that carries and conveys the toner, and generally +300 V to +500 V is applied. Here, it is assumed to be + 400V. The toner is formed as a thin layer on the developing roller by the blade and charged, and the toner is guided to the electrostatic latent image by bringing the thin layer into contact with the photoconductor. When the positively charged toner comes into contact with the latent image on the photoreceptor, +400 V
Of the developing roller of + 400V and the surface potential of the photosensitive member of + 700V, that is,
The developing gap of 300 V controls the toner so that the toner does not move from the developing roller to the photoconductor, and this principle visualizes and develops the electrostatic latent image on the photoconductor.

[0006]

However, in the above-described developing method, when the rotation direction of the developing roller and the photosensitive member is the same, that is, the photosensitive member is exposed at the nip portion (the contact portion between the developing roller and the photosensitive member). If the movement directions of the body and the developing roller are opposite to each other, that is, in a counter contact relationship, the insufficiently charged toner by the blade is now frictionally charged again. That is, when the positively charged toner is used, the insufficiently charged toner tends to positively charge by emitting electrons upon contact with the photoconductor. At this time, as shown in FIG. 3, the emitted electrons are likely to be emitted from the developing roller side of about +400 V to the non-printed portion of the photosensitive member surface potential of about +700 V, so that the electrons are emitted to the non-printed portion of the photosensitive member. As a result, the potential of the surface of the photoconductor is lowered.

As shown in FIG. 2, the portion where the surface potential is lowered in the nip portion is carried to the toner pool P generated by the counter contact between the developing roller and the photosensitive member as the photosensitive member rotates. In the toner pool P, charging by the blade is insufficient, and a relatively large amount of poorly charged toner having poor controllability exists. Therefore, the uncontrollable charging failure toner and the toner controllability significantly deteriorated due to the decrease in the development gap due to the decrease in the surface potential of the photoconductor, so that the toner is developed on the non-printed portion of the photoconductor. The toner was transferred to the paper, causing a so-called fog phenomenon.

Such a phenomenon is remarkable when the photoconductor and the developing roller are in contact with each other at the counter, but the photoconductor and the developing roller are rotating in the same moving direction at their contact portions. It is a phenomenon that occurs even in a state, a so-called accompanying state.

[0009]

To achieve the above object, an electrostatic latent image developer according to claim 1 develops an electrostatic latent image formed on a photoconductor to form an image on a recording medium. A positively charged electrostatic latent image developer used in an image forming apparatus is characterized in that the electrostatic latent image developer contains an electron withdrawing group. By using the electrostatic latent image developer according to claim 1, an electron withdrawing group is used to attract electrons that move to a non-printed portion of the photoconductor, thereby preventing a decrease in the surface potential of the photoconductor and fogging. It is possible to reduce the phenomenon. Examples of the electron-withdrawing group include a carbonyl group including a carboxyl group, a nitro group including a nitrile group, a sulfonyl group including a sulfonic acid group, a nitroso group, a trifluoroethyl group, a trichloroethyl group, and the like.

The electrostatic latent image developer according to claim 2 is
The electrostatic latent image developer according to claim 1 is characterized in that it has at least a toner binder as a binder and a charge control agent, and that the toner binder contains an electron withdrawing group. This electrostatic latent image developer is present on the surface of the electrostatic latent image developer and contributes significantly to charging by incorporating an electron-withdrawing group into the toner binder that plays a role as a binder resin that occupies most of it. It is possible to attract the electrons emitted by the charge control agent to the inside of the electrostatic latent image developer and positively charge the surface of the electrostatic latent image developer without releasing the electrons.

The electrostatic latent image developer according to claim 3 is
It is characterized in that the electron withdrawing group contained in the electrostatic latent image developer is contained in an amount of 0.3 mol or more and 1.0 mol or less in 1 mol of the toner binder. The presence of 0.3 mol or more of electron withdrawing groups in 1 mol of the toner binder makes it possible to effectively attract the electrons to be released to the outside of the toner. However, if more than 1.0 mol of electron-withdrawing groups are present in 1 mol of the toner binder, it is extremely difficult to control the electrostatic latent image developer such as generation of an electrostatic latent image developer of opposite charging, and the fog phenomenon occurs. May be noticeable.

The electrostatic latent image developer according to claim 4 is
2. The image forming apparatus according to claim 1, wherein the photosensitive member and the developer conveying roller are used in an image forming apparatus in which the photosensitive member and the developer conveying roller are in contact with each other and rotated so as to move in opposite directions at the contact position.
The electrostatic latent image developer according to any one of claims 1 to 3. The decrease in the surface potential of the photoconductor is remarkable when the photoconductor and the developing roller are in contact with each other by the counter, and the electrostatic latent image developer according to any one of claims 1 to 3 is used in such a system. Then, even if there is a so-called toner pool in which a slightly insufficiently charged electrostatic latent image developer exists in the nip portion between the photoconductor and the developing roller, the photoconductor surface potential in the non-printed portion does not decrease, and the development gap This makes it possible to control the electrostatic latent image developer and is extremely effective in suppressing fog.

[0013]

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 developing device 2. The developing device 2 has a detachable process unit 34 having a functional portion for accumulating, charging, supplying and developing toner, and a developing device. , A fixed drum unit 32 having a transfer function unit.

Specifically, the drum unit 32 is arranged around a photoconductor 10 in which a photoconductive layer is applied to an aluminum conductive cylinder, and a charger 12 for applying a surface potential to the photoconductor 10.
A laser scanner 14 that performs optical operations according to image information;
The toner 26 developed on the photoconductor is used as a recording medium 18 such as paper.
And a cleaning roller 22 for removing the toner 26 on the photoconductor 10 not transferred by the transfer roller 20.

The process unit 34 carries the toner 26 and a developing roller 16 as a developer carrying roller for carrying the electrostatic latent image on the photosensitive member, and the toner 26 on the developing roller 16 in a uniform thin layer. Toner 2 is attached to the developing roller 16 and the blade 4 for regulating and positively charging the toner 26.
The supply roller 8 supplies the toner 6 and the agitator 6 for stirring the toner 26 stored in the toner storage unit 28 and keeping the fluidity in a good state.

Drum unit 32 and process unit 3
Reference numeral 4 is in contact with the photoconductor 10 and the developing roller 16 by the pressure of the tension spring 30 of 500 g.

Further, adjacent to the developing device 2, a heat fixing device 24 for fixing the toner image on the recording medium 18 by heat melting.
(Comprising a pair of rollers incorporating a 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. In accordance with the rotational movement of the supply roller 8 and the developing roller 16 in the direction of the arrow, the toner 26 is supplied from the supply roller 8 to the developing roller 16, is formed into a thin layer by the blade 4, and is positively charged.

In the charger 12, about 1.4k
A voltage of about V is applied, and +600 to
A surface potential of about +700 V is formed. In addition, this charger 12 can be used regardless of contact or non-contact.
Any shape may be used. For example, a scorotron that gives a predetermined surface potential to the photoconductor 10 by corona discharge, a semiconductive brush that gives a surface potential by contacting the photoconductor 10,
Members such as blades and rollers can be used.

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 charger 12, and the photoconductive layer acts as an optical signal by the action of the photoconductive layer. The electric potential of the portion exposed by is lowered to about +100 V, and an electrostatic latent image having a different electric 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. As shown in FIG. 1, since the photoconductor 10 and the developing roller 16 are rotating in the direction of the arrow, the nip portions in contact with each other are moving so as to move in opposite directions.

The toner 26, which is formed into a thin layer by the blade 4 and is positively charged, and is conveyed by the developing roller 16 controlled to the developing bias of +400 V, contacts the photosensitive member 10 with the thin layer of the toner 26. Photoconductor 1
The toner 26 is developed only on the electrostatic latent image formed on the zero. The electrostatic latent image on the photoreceptor 10 is exposed by the laser scanner 14 in a state where the surface potential applied from the charger 12 is +600 to +700 V, and the potential of the exposed portion is reduced to +100 V by the exposure. It is formed by having. On the other hand, a potential of +400 V is applied to the developing roller 16 as a bias potential, so that the positively charged toner 26 is developed at a potential portion of +100 V on the photoconductor 10 and is not developed at a potential portion of +600 to +700 V. A visual image will be formed.

The visible image of the toner 26 thus formed on the photoconductor 10 is controlled to a constant current of 3 microamperes,
The toner is transferred onto the recording medium 18 such as paper by using the transfer roller 20 whose polarity is controlled to be negative, and the toner 26 is fixed on the recording medium 18 by the heat fixing device 24 to obtain a target recorded image. it can. On the other hand, the recording medium 18
The toner 26 remaining on the photoreceptor without being transferred to
0 volt biased cleaning roller 2
2 recovered.

Next, the toner 26 used in the laser beam printer constructed as described above will be described in detail. The toner 26 according to the exemplary embodiment is configured as a non-magnetic one-component positively charged 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 and occupies most of the toner. As the resin for the toner binder, polystyrene resin, polyacrylate resin, polymethacrylate resin, polyvinyl resin, polyester resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyether resin, polycarbonate resin , Polycellulose-based resins, polyamide-based resins, and copolymers forming these resins can be used. Generally for positive charging,
Polystyrene-based resin, acrylic-based resin, etc. are used as a binder because they show good charging. Examples of the electron-withdrawing group include a carbonyl group including a carboxyl group, a nitro group including a nitrile group, a sulfonyl group including a sulfonic acid group, a nitroso group, a trifluoroethyl group, a trichloroethyl group, and the like. . In this embodiment, a binder containing a carboxyl group or a sulfonic acid group is used.

In addition to the polystyrene-based binder, polyester-based binder was made into a toner and an experiment was conducted. For comparison, an experiment was conducted using a styrene-based binder containing no electron-withdrawing group.

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.

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. You can

Examples of charge control agents include nigrosine-based compounds,
Examples thereof include triphenylmethane-based, quaternary ammonium salts, alkoxylated amines, alkylamides and the like.

As an external additive added to the toner, hydrophobic silica fine powder is used as a fluidity-imparting agent to impart fluidity to the toner, or a deposit on a blade or a photoconductor is used. As an abrasive for polishing, an external additive such as aluminum fine powder is used in a necessary amount according to various purposes.

[0032]

EXAMPLES Next, the toner according to the present exemplary embodiment will be described with reference to a plurality of examples. First, the compounding ratio and the like of each material in forming the toner will be described below.

Carbon black (Mitsubishi Chemical # 260) 5 parts by weight Wax (Sanyo Kasei VISCOL 660P) 5 parts by weight Charge control agent (Orient Chemistry N-04) 4 parts by weight to 100 parts by weight of various kinds of binder resin Are mixed in the form of powder, and carbon black, wax, and a charge control agent are dispersed in the binder 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. Further, powder particles having a particle diameter of 3 to 20 μm were obtained using an air classifier.

100 parts by weight of the toner particles of the above composition before external addition treatment are mixed with 1 part by weight of a hydrophobic silica fine powder having a BET specific surface area of 300 square centimeters / milligram, and 2000 rpm with a Henschel mixer.
The toner was agitated for a minute 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. 1 to output an image. The image quality was evaluated not for what was printed on the recording medium but for what was developed on the photoreceptor. First, in the white printing portion where nothing is printed, the toner developed as fog on the photoconductor is printed by 3M Scotch.
Transferred to mending tape. Next, the whiteness of the tape to which nothing was transferred and the whiteness of the tape to which the fog toner was transferred were measured, and the difference between these two whitenesses was obtained. The magnitude of this value was used to distinguish the degree of the fog phenomenon. did. If the permissible value of the fog phenomenon is within 6.0 due to the difference in whiteness, it is not noticeable even when it is transferred to a recording medium, so that it is set within 6.0. The smaller the difference in whiteness, the less the degree of fog,
The larger the value, the more severe the fog. REF manufactured by Tokyo Denshoku Co., Ltd. for whiteness measurement
LECT METER MODEL TC-6MC was used.

Further, the surface potential of the photoconductor was measured for each toner, and its change was examined. To measure the surface potential of the photoreceptor, use a Trek model
344 was used.

For reference, the surface potential of the photoconductor was 700 V when the toner was not brought into contact with the photoconductor.

Example 1 A resin containing 0.35 mol of a carboxyl group in 1 mol of polystyrene binder resin was made into a toner under the above-mentioned conditions, and the image quality was evaluated.

The whiteness difference at this time was 2.3, which was a very satisfactory value.

Although the surface potential on the photoconductor is lowered, 6
Since it is 50 V, which is not so severe, it is considered that proper development was performed and good image quality was achieved.

Example 2 A resin containing 0.7 mol of carboxyl groups in 1 mol of polystyrene binder resin was prepared.
Under the above conditions, the toner was formed and the image quality was evaluated.

The whiteness difference at this time was 1.0, which was a very satisfactory value.

The surface potential on the photoconductor did not almost drop, and it is considered that proper development was performed and good image quality was achieved. Further, it is considered that the decrease in the surface potential of the photoconductor and the fog can be reduced by increasing the number of the carboxyl groups which are electron withdrawing groups, as compared with those shown in Example 1.

Example 3 A resin containing 0.4 mol of sulfonic acid groups in 1 mol of polystyrene binder resin was made into a toner under the above-mentioned conditions, and the image quality was evaluated.

The difference in whiteness at this time was 2.5, which was a very satisfactory value.

Although the surface potential on the photoconductor is lowered, 6
Since it is 60 V, which is not so terrible, it is considered that proper development was performed and good image quality was achieved.

Example 4 A resin containing 0.8 mol of sulfonic acid groups in 1 mol of polystyrene binder resin was made into a toner under the above-mentioned conditions, and the image quality was evaluated.

The difference in whiteness at this time was 3.8, which was a satisfactory value.

Although the surface potential on the photosensitive member was hardly lowered, the fog value was deteriorated because the amount of toner with poor controllability increased, which was within the permissible range as compared with Example 3. Seem.

Example 5 A resin in which 1 mol of a carboxyl group was contained in 1 mol of a polyester binder resin and the carboxyl group was capped was used. That is, a toner was experimentally manufactured and the image quality was evaluated for the resin containing 1 mol of carbonyl groups under the conditions described above.

At this time, the difference in whiteness was 5.5, which was a value within the allowable range.

Although the surface potential of the photosensitive member hardly decreased, the reason why the difference in whiteness barely fell within the permissible range is considered to be that the amount of uncontrolled toner increased.

Next, in order to confirm the quantitative effect of the electron-withdrawing group contained in the toner binder, the toner according to the comparative example was produced, and the measurement was carried out under the same conditions as above, and the measurement results were obtained for each. . Hereinafter, the toner of the comparative example will be described.

Comparative Example 1 Using a polystyrene binder resin containing no electron-withdrawing group, a toner was experimentally manufactured under the above conditions and the image quality was evaluated.

The whiteness difference at this time was 9.7, which was not a value within the allowable range.

The surface potential of the photoconductor is considerably lowered.
It was 0V. The surface potential of the photoreceptor is reduced by electrons emitted from the toner that is going to be positively charged. Normally, the toner should be controlled by a force of 300 V, which is a difference between the photoreceptor surface potential and the developing bias.
It is considered that the toner control could not be performed sufficiently.

Comparative Example 2 Using a resin containing 0.1 mol of carboxyl groups in 1 mol of polystyrene binder resin, a toner was experimentally manufactured under the above conditions and the image quality was evaluated.

The difference in whiteness at this time was 9.7, which was not a value within the allowable range.

The surface potential of the photoconductor is considerably lowered.
It was 0V. It is considered that electrons emitted from the toner to be positively charged lower the surface potential of the photoreceptor and the toner could not be sufficiently controlled.

Comparative Example 3 A toner was trial-produced under the above conditions using a polyester binder resin containing 1.3 mol of a carboxyl group in 1 mol of binder resin, and the image quality was evaluated.

The difference in whiteness at this time was 14.2, which was not a value within the allowable range.

The surface potential of the photoconductor did not almost decrease, and it is considered that the fog increased due to the increase in the amount of the toner which is insufficiently controlled such as reverse charging due to the large amount of the electron-withdrawing group contained in the binder resin.

From the above, by incorporating an electron-withdrawing group into the toner binder, it is possible to prevent a decrease in the surface potential of the photoconductor in the non-printed portion, and this electron-withdrawing group is contained in 1 mol of the toner binder. 0.3 mol or more,
It can be understood that the fog phenomenon can be effectively reduced by containing 1.0 mol or less.

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 gist of the present invention.

[0065]

As described above, according to the present invention, since the electrostatic latent image developer according to claim 1 contains the electron-withdrawing group, the electrons that move to the non-printed portion of the photoconductor are converted into electrons. Since the attracting group attracts, it has the effect of preventing the movement of electrons, preventing the decrease of the surface potential of the non-printed portion of the photoconductor, and reducing the fog phenomenon.

Further, in the electrostatic latent image developer of the second aspect, since the toner binder contains an electron-withdrawing group, the electron emitted by the charge control agent which is present on the surface of the developer and greatly contributes to charging is released. Is attracted to the inside of the toner, and the surface of the developer can be positively charged without releasing electrons.

In the electrostatic latent image developer of claim 3, the electron withdrawing group contained in the electrostatic latent image developer is contained in an amount of 0.3 mol or more and 1.0 mol or less in 1 mol of the toner binder. Therefore, there is an effect that it is possible to more effectively attract the electrons trying to go out of the developer and reduce the fog.

According to the electrostatic latent image developer of claim 4, even if a so-called toner pool is formed in the vicinity of the nip portion between the photosensitive member and the developer conveying roller, the surface potential of the photosensitive member in the non-printed portion is Since the developer can be controlled by the developing gap without lowering, it is possible to reliably prevent fog even in a so-called counter-contact image forming apparatus.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing a toner accumulation caused by contact between a photosensitive member of a laser beam printer and a developing roller.

FIG. 3 is an explanatory view schematically showing electrons emitted from positively charged toner due to a potential difference between a surface of a photoconductor and a developing roller.

[Explanation of symbols]

 2 Developing device 4 Blade 10 Photoconductor 12 Charging device 16 Developing roller 18 Recording medium 26 Electrostatic latent image developer 32 Drum unit 34 Process unit

Claims (4)

[Claims] 1. A positively charged electrostatic latent image developer used in an image forming apparatus for developing an electrostatic latent image formed on a photoconductor to form an image on a recording medium, wherein the electrostatic latent image developer is used. An electrostatic latent image developer containing an electron-withdrawing group in the image developer. 2. The electrostatic latent image developer has at least a toner binder, which is a binder, and a charge control agent, and the toner binder contains an electron-withdrawing group. The electrostatic latent image developer according to claim 1. 3. The electron withdrawing group contained in the electrostatic latent image developer is 0.3 mol or more in 1 mol of the toner binder,
The electrostatic latent image developer according to claim 2, which is contained in an amount of 1.0 mol or less. 4. The electrostatic latent image developer is used in an image forming apparatus in which a photoconductor and a developer transport roller are in contact with each other and are rotated so as to move in opposite directions at the contact position. Claim 1 thru | or Claim 3 characterized by the above-mentioned.
The electrostatic latent image developer according to any one of 1.