JPH07117769B2 - Dry developer and image forming method using the developer - Google Patents

Description

The present invention relates to a novel developer used for electrophotography, electrostatic recording, magnetic recording and the like, and an image forming method using the developer.

[Prior Art] In electrophotography, an electrostatic latent image is first formed by utilizing the properties of a photoconductor such as cadmium sulfide, polyvinylcarbazole, selenium, and zinc oxide. For example, generally, an electrical charge is uniformly applied to the photoconductor layer and imagewise exposed to form an electrostatic latent image. Then, it is developed with a toner powder charged in the opposite polarity to the charge of the electrostatic latent image, and further transferred and fixed on a transfer sheet if necessary.

For example, in a developing method using a two-component developer, when the image portion of the latent image is developed by the developer applied on the developing roller, the toner in the developer is the toner applied on the developing roller. Use less than a few percent of This is extremely inefficient considering the developing device configuration. This is because it is necessary to apply a large amount of developer on the developing roller with a constant amount and uniform toner concentration each time the developing roller rotates in order to obtain a predetermined sufficient developing concentration. Therefore, the size of the developing device is increased.
It was complicated. Of course, attempts have been made to improve the developing efficiency even in this type of developing method. For example, the present applicant has proposed JP-A-55-32060, 55-133058, 56-70560, and NP-8500
It has been put to practical use in copiers. According to this, although the development density can be increased and the development efficiency can be increased, the development efficiency close to 100% cannot be achieved in the image area, and this type of development method still has room for improvement. Is left.

The one-component developing method is superior to the two-component developing method in terms of improving the developing efficiency. Among them, in Japanese Patent Application Laid-Open No. 54-43037, which was previously filed by the applicant of the present invention, a toner thin layer of 200 μm or less is formed on the developing roller, and the toner applied on the sleeve is developed to almost 100% in the image area. Developing with efficiency. Therefore, it was possible to put the developing device into a compact and simple structure for practical use. This was achieved because a thin layer of 200 μm or less could be formed on the developing roller. However, it is extremely difficult to form a thin layer of a dry developer in either one-component development or two-component development. Therefore, even in the one-component development, a relatively thick layer is formed by a developer other than the applicant. Are configured. From the viewpoint of image quality, the sharpness of the developed image, the resolution,
Currently, the development of a thin layer forming method of a dry developer and its apparatus are indispensable.

By the way, the above-mentioned applicant's method relates to the formation of a thin layer of the magnetic toner. In order to give the magnetic toner magnetism, it is necessary to internally add a magnetic substance to the toner. This is because of poor fixability when thermally fixing a developed image transferred onto a transfer paper, and the magnetic substance is internally added to the toner itself. Therefore (the magnetic substance is usually black), there is a problem such as poor color when reproducing the color.

Therefore, as a method for forming a thin layer of non-magnetic toner, a soft brush like beaver's bristles is made into a cylindrical brush, and toner is adhered and applied to this, or a developing roller whose surface is made of fiber such as velvet is used. A method of applying with a doctor blade or the like has been proposed.

However, when an elastic blade is used as a doctor blade for the fiber brush, the amount of toner can be regulated, but uniform application is not performed, and the fiber of the brush is simply rubbed by rubbing the fiber brush on the developing roller. Since triboelectrification charges are not applied to the toner existing between them, there is a problem that fogging or the like is likely to occur.

Further, magnetic toners can easily prevent the toner from scattering by utilizing magnetic force, but non-magnetic toners cannot utilize magnetic force, and the toners are easily scattered inside the machine. The inconveniences described above occur not only during copying but also when vibration or shock is applied during transportation of the apparatus.

The applicant of the present invention uses a non-magnetic toner and magnetic particles as a developing device which is completely different from the above-mentioned conventional method, provides a magnetic particle restraining member facing the toner carrying member, and restrains the magnetic particle with respect to the moving direction of the surface of the holding member. A method has already been proposed in which a magnetic brush of magnetic particles is formed upstream of the member by the magnetic force of the magnetic field generating means, the magnetic brush is restricted by the magnetic particle restriction member, and a thin layer of non-magnetic toner is formed on the toner holding member. (JP-A-58-143360). According to this method, the gap between the latent image carrier and the toner carrier is set to be wider than the toner layer thickness in the developing section and a non-magnetic toner developed image is obtained on the surface of the latent image carrier by applying alternating electrolysis. It was put to practical use. As a result, it is possible to obtain a color developed image with extremely high developing efficiency and a small and simple developing device configuration. Particularly, in the two-component magnetic brush rubbing development, a good quality solid image was obtained without any rubbing marks generated in the solid image portion. However, with the diversification of the output information from the reader unit that reads the image of the document, the printer unit is also required to be able to respond to such diversification. Especially, as a digital printer, the spot diameter of laser light is 50
In order to develop a latent image formed to about 150 μm with high resolution, it has been desired to develop a developing system and a developer with further improved developed image quality.

On the other hand, in the case of an apparatus having a transfer step, it is usual to remove the residual toner on the latent image carrier that has not been transferred to the transfer sheet, and repeatedly use the latent image carrier.

As a method of removing the residual toner on the latent image carrier,
Generally, a cleaning member is brought into contact with the latent image holding member, such as a blade cleaning method, a fur brush cleaning method, or a magnetic brush cleaning method.
In this case, since the cleaning member is pressed against the latent image holding member with an appropriate pressure, the latent image holding member may be scratched or the toner may be fixed during repeated use. In order to avoid the phenomenon that the toner adheres to the latent image holding member, it has been proposed in JP-A-48-47345 to add both a friction reducing substance and an abrasive substance to the toner. This method is effective in avoiding the toner sticking phenomenon, but has the following drawbacks. That is, if a friction reducing substance is added to the extent that the toner sticking phenomenon can be avoided, it is difficult to remove low electric resistance substances such as paper dust and ozone adducts that are generated or adhered to the latent image carrier surface by repeated use. In particular, there is a drawback that the latent image on the latent image carrier is significantly impaired by the low electric resistance under a high temperature and high humidity environment.

The addition amount of each of the friction-reducing substance and the polishing substance is delicate, and if the polishing substance is added in an amount sufficient to remove the deposits on the stable photoreceptor, the latent image carrier may be damaged,
The phenomenon occurs that the cleaning blade is damaged and cleaning failure occurs.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above problems in an image forming method using a dry developer including at least magnetic particles and a non-magnetic toner.

That is, an object of the present invention is to provide a developer and an image forming method which are excellent in cleaning characteristics without filming or cleaning failure of the latent image carrier.

Another object of the present invention is to provide a developer and an image forming method capable of obtaining an excellent image of high density from the initial stage.

It is another object of the present invention to provide a developer and an image forming method which are free from fogging due to durability, sleeve contamination, and image deterioration.

[Means and Actions for Solving Problems] The present inventors have completed the present invention as a result of earnest researches for overcoming the above-mentioned problems in the prior art and achieving the above-mentioned object. It was

That is, according to the present invention, the surface potential data of the latent image carrier when the image of the original is converted into an electric signal, two kinds of different biases are applied to the latent image carrier, and the latent image carrier is exposed with two different intensities. An electrostatic latent image is formed on the latent image holding member according to the electric signal by a latent image forming device that controls the latent image formation based on the latent image forming device, and then the latent image holding member and the developer carrying member facing it are developed. In a region, a developer comprising at least a non-magnetic toner and magnetic particles, which is subjected to an image forming method in which a latent image is reversely developed with a non-magnetic toner while applying an alternating electric field between the latent image carrier and the developer carrier. The magnetic particles have a true specific gravity of 6 or less, a volume average particle diameter of 40 to 65 μm, a volume distribution of less than 35 μm is 5 to 25% by weight, and 35 to 40 μm is 35 μm.
It is less than less than, and is coated with an electrically insulating resin, and forms a magnetic brush of 5 to 80 mg / cm ^{2 in} the developing area of the developer carrier, and serves as a latent image carrier in the developing area. The dry developer is characterized in that the non-magnetic toner reciprocates between the surface of the developer carrying member and the surface of the magnetic brush to reversely develop the latent image.

In addition, the image of the original is converted into an electric signal, and the latent image holder 2
A latent image forming device that controls latent image formation based on the surface potential data of the latent image carrier when two kinds of different biases are applied and exposed with two different intensities for each, is generated according to the electric signal. An electrostatic latent image is formed on the latent image carrier, and then an alternating electric field is applied between the latent image carrier and the developer carrier in the development area of the latent image carrier and the developer carrier opposite thereto. However, it is an image forming method of reversal developing a latent image with a non-magnetic toner.
65μm, 5 ~ 25wt% less than 35μm in volume distribution 35
Magnetic particles with a particle size of ~ 40μm less than 35μm and coated with an electrically insulating resin are used to form a magnetic brush in the developing area of the developer carrier to 5-80mg / cm ² Non-magnetic toner is reciprocally developed between the image carrier and the surface of the developer carrier and the surface of the magnetic brush to perform reverse development, transfer this image to a transfer member, and then remove the residual developer on the latent image carrier. And an image forming method comprising the steps of:

In general, if toner adheres to the latent image holding member, cleaning failure or the like occurs, which causes deterioration of image quality. However, in the present invention, since the magnetic particles having a small particle diameter of less than 35 μm are contained in the developer, the small magnetic particles adhere to the latent image holding member and serve as a polishing effect to remove the toner. There is.

This point will be described in detail below.

Since the reversal development method in the present invention is, for example, ON-OFF development using laser light, a latent image is usually formed with only two values of a dark portion potential V _D and a light portion potential V _L. Here, when the bias potential on the developing sleeve is V _DC , the developing contrast is | V _L -V _DC | and the reverse contrast is | V _D -V _DC |. In the present invention, since latent image formation is controlled based on the surface potential data of the latent image carrier when different biases are applied to the latent image carrier for exposure, the surface of the latent image carrier is kept in a normal state. If so, the development contrast and the reversal contrast can take desired values, but if toner adheres to the latent image carrier, the potential on the latent image carrier will not be attenuated and proper control of latent image formation will be impossible. It will be possible. In addition, the toner adhered matter causes, for example, poor cleaning, resulting in image deterioration. Take several measurement points,
When a means for excluding abnormal values is incorporated, there is no practical effect on the above-described control of latent image formation at the initial stage of toner fixation.

According to the study by the present inventors, when the reverse contrast | V _D -V _DC | is about 100 V or less, the magnetic particles are not developed on the latent image carrier at all, but above 150 V, a small particle size of less than 35 μm is obtained. It was found that the magnetic particles of the above began to develop slightly.
For example, using negative charge toner, reverse contrast V _D
When -V _DC is set to -70 to -150V, the magnetic particles do not develop on the latent image carrier and no fog is observed. However, in the present invention, for example, when a latent image forming apparatus using a laser beam is used, the potential of the dark portion on the latent image holding member is controlled in the state of laser exposure because of the rise of the laser beam. Therefore, there is a difference of about 50 V between the dark portion potential V _{D2 of the} portion where the toner is fixed and the dark portion potential V _{D1 of the} portion where the laser is exposed. Therefore, the reversal contrast of the portion to which the toner is fixed becomes about 50 V higher than usual, and the magnetic particles, especially the magnetic particles having a small particle size, are developed on the latent image carrier.
As a result, the magnetic particles having a small particle size developed on the toner-fixed portion on the latent image holding member act to scrape off the toner-fixed matter, and the image deterioration is eliminated.

Any latent image carrier can be used in the present invention,
It is desirable not to have a charge generation layer on the surface. That is,
In the present invention, since the surface of the latent image carrier is inevitably scraped off at the same time when the toner adhered matter is scraped off, if the charge generation layer is exposed in the surface layer, the surface is scraped by repeated use. It is not preferable because the sensitivity is lowered.
Therefore, in the present invention, it is particularly preferable to use an organic photoconductor (OPC) latent image carrier having a charge transfer layer on its surface.

Examples of the organic photoconductor used in the present invention include those using an organic photoconductive polymer such as polyvinylcarbazole, and low molecular weight organic photoconductive substances using an insulating polymer as a binder. Among these, a laminated type photoreceptor comprising a charge transfer layer and a charge generation layer is preferably used in the present invention, and the charge generation layer includes azo pigments such as Sudan Red, Diane Blue and Genus Green B, Argol Yellow and Pyrenequinone. , Quinone pigments such as indanthrene brilliant violet RRP, quinocyanine pigments, perylene pigments, indigo pigments such as indigo and thioindigo, bisbenzimidazole pigments such as Indian fast orange toner, phthalocyanine pigments such as copper phthalocyanine, and charge generation of quinacridone pigments The functional substance is dispersed in a binder resin such as polyester, polystyrene, polyvinyl butyral, polyvinyl pyrrolidone, methyl cellulose, polyacrylic acid esters, and cellulose ester. Its thickness is 0.01
˜1 μm, preferably 0.05 to 0.5 μm.

Further, the charge transfer layer has a polycyclic aromatic structure such as anthracene, pyrene, phenanthrene, coronene in the main chain or side chain, or indole, carbazole, oxazole, isoxazole, thiazole, imidazole, pyrazole, oxadiazole, pyrazoline, thiadiazole. ,
It is formed by dissolving a compound having a nitrogen-containing cyclic structure such as triazole and a hole-transporting substance such as a hydrazone compound in a resin having film-forming properties. This is because the charge transfer material generally has a low molecular weight and is poor in film forming property by itself. Examples of such a resin include polycarbonate, polymethacrylic acid esters, polyarylate, polystyrene, polyester, polysulfone, styrene-acrylonitrile copolymer, styrene-methyl methacrylate copolymer and the like. The thickness of charge transfer layer is 5 ~ 20μ
m is preferred. As the resin that constitutes the surface layer of the photoreceptor such as the charge transfer layer, properties such as abrasion resistance and oil lubricity are also important, and from such a point, T _g at the peak position measured by DSC as a resin is important. Is preferably 60 ° C. or higher, particularly 80 ° C. or higher, and further preferably contains 30% by weight or more, particularly 70% by weight or more of a vinyl polymer.

As the transfer method used in the present invention, conventionally known methods such as an electrostatic transfer method, a bias roll method, a pressure path transfer method, and a magnetic transfer method are used. Further, as a method for cleaning the residual toner on the photoconductor, a blade cleaning method, a fur brush cleaning method, a magnetic brush cleaning method, etc. which are well known in the related art are used.
Immediately before reaching the cleaning step, a charge removing step or the like may be provided as necessary to facilitate toner cleaning.

In the image forming method of the present invention, the blade cleaning method is preferable as an excellent combination of the toner of the present invention and the photoconductor. In a particularly preferred embodiment of the present invention, the pressure w / a required for displacing a cleaning blade having an axial length acm of the photoconductor by 1 mm is 5 to 60 g / cm, preferably 8 to 50 g / c.
This is a method of using a counter blade cleaning method using an elastic blade in the range of m.

Further, for fixing the toner of the present invention to the transfer member, oven fixing, heat roll fixing, pressure fixing, flash fixing,
Well-known methods such as microwave fixing can be applied.

In the production of the toner of the present invention, after the constituent materials are well kneaded by a heat kneader such as a hot roll, a kneader or an extruder, mechanical pulverization or a method of obtaining by classification, or a magnetic powder in a binder resin solution, etc. The method of obtaining the toner by dispersing the above-mentioned material and then spray-drying or a method of mixing the monomer to form the binder resin with a predetermined material and then polymerizing this emulsion suspension to obtain a toner. Each method such as a toner manufacturing method can be applied.

The latent image forming method used in the present invention may be anything as long as the light source or the optical path is turned ON-OFF according to an electric signal, but generally a semiconductor laser light source or a liquid crystal shutter is often used. .

Hereinafter, a) the description of the developing method, b) the details of the developing mechanism, and c) the constitution of the materials will be described in this order.

a) Description of developing method Hereinafter, the main developing method will be described with reference to Examples. FIG. 1 shows an example of a developing device used in the present invention. In FIG. 1, 1 is a latent image holding member, 2 is a toner supply container, 3 is a non-magnetic sleeve, 4 is a fixed magnet, 5 is a magnetic or non-magnetic blade, 7 is a magnetic particle circulation region limiting member, and 8 is magnetic particles. ,
Reference numeral 9 is a non-magnetic toner, 10 is a developer collecting container portion, 11 is a scattering prevention member, 12 is a magnetic member, 13 is a developing area, and 14 is a bias power source. The sleeve 3 rotates in the b direction, and the magnetic particles 8 circulate in the c direction accordingly. This causes contact and rubbing between the sleeve surface and the magnetic particle layer to form a non-magnetic toner layer on the sleeve surface. Further, while the magnetic particles circulate in the c direction, a part of the magnetic particles is regulated to a predetermined amount by the gap between the magnetic or non-magnetic blade 5 and the sleeve 3, and is applied onto the non-magnetic toner layer. That is, the non-magnetic toner is applied on both the surface of the sleeve and the surface of the magnetic particles, and the same effect as that of substantially increasing the surface area of the sleeve is exhibited.

In the developing region 13, one of the magnetic poles of the fixed magnet 4 is opposed to the latent image surface to form a clear developing pole, and the alternating electric field causes the toner to fly and develop on the sleeve and from the magnetic particles. (This phenomenon will be described later.)
After development, the magnetic particles and the undeveloped toner are collected in the developing container as the sleeve rotates.

The sleeve 3 may be a paper cylinder or a synthetic resin cylinder, but if the surface of these cylinders is subjected to a conductive treatment or is made of a conductor such as aluminum, brass or stainless steel, it can be used as a developing electrode roller.

As the magnetic particles used in the present invention, in order to remove the discharge between the sleeve and the latent image carrier due to an alternating electric field, it is desirable that the magnetic particles have an electrically high resistance. It is preferably partially covered. The electrical insulating property referred to here means 10 ⁸ Ω · cm or more.

Further, the magnetic particles used in the present invention preferably have a low specific gravity so that the magnetic brush constituted by the magnetic particles can behave smoothly by an alternating electric field, and specifically, the true specific gravity is preferably 6 or less.

The coating amount of the magnetic particles on the downstream sleeve surface of the magnetic or non-magnetic blade 5 in the present invention is 5 to 80 mg / cm ² , preferably 10 to 10 in order to fully utilize both the magnetic brush and the surface of the sleeve 3. It is desirable that the amount is as small as 60 mg / cm ² . If the amount of the magnetic particles present on the surface of the sleeve is too large, the regulation force of the blade 5 is weakened, and the rubbing force between the sleeve and the magnetic particles is reduced, so that the toner cannot be charged smoothly. Further, there is a drawback that the magnetic particles also fly during the flight development of the toner and adhere to the latent image carrier 1. Further, as the sleeve peripheral speed becomes faster, the regulation by the fixed magnet becomes weaker and the scattering of the developer becomes remarkable. On the contrary, when the amount of the magnetic particles existing on the sleeve surface in the developing area 13 is too small, the amount of toner applied to the developing area is reduced, resulting in uneven density and image density. The amount of magnetic particles present on the surface of the sleeve can be adjusted mainly by the gap with the sleeve 3, the position of the N ₁ pole of the fixed magnet 4, the magnetic density of the S ₁ pole, and the like.

The method for measuring the abundance of magnetic particles in the present invention is described below. First, a magnetic brush made of only magnetic particles was formed on the sleeve, magnetic particles in a portion corresponding to the developing area were sucked using a cylindrical filter as a filter, and the weight M (mg) was measured. Next, the remaining magnetic particles on the sleeve after the magnetic particles were attracted were sampled with a transparent adhesive tape, and the occupied area S (cm ² ) of the attracted magnetic particles was determined. The abundance m (mg / cm ² ) of magnetic particles was calculated as follows.

m = M / S The developing area refers to an area of 10 mm in the sleeve circumferential direction with the closest part of the latent image carrier and the developer carrier as the center.

The tip of the blade 5 and the developing sleeve 3 at the point 6 position
The distance d between the surface and the surface is 50 to 650 μm, preferably 100 to
It is 600 μm. If the distance d is less than 50 μm, magnetic particles, which will be described later, will be clogged, and the sleeve will be damaged. On the other hand, if it is larger than 650 μm, a large amount of non-magnetic toner and magnetic particles, which will be described later, leak out and a thin layer cannot be formed.

In FIG. 1, 7 is a magnetic particle circulation region limiting member in which the lower surface is in contact with the upper surface side of the blade 5 and the front end surface is an undercut surface.

Reference numerals 8 and 9 denote magnetic particles and non-magnetic toner that are sequentially accommodated in the toner supply container 2.

The bottom plate of the toner supply container 2 is extended below the developing sleeve 3, which is a toner holding member, to prevent the toner from leaking to the outside. Further, in order to further prevent the leakage of this toner to the outside, a leaked toner collecting container portion 10 for receiving and restraining the leaked toner is scattered on the upper surface of the extension bottom plate, and scattered along the length of the tip edge of the extension bottom plate. Prevention member
11 are provided. A voltage described later is applied to this member 11.

The magnetic particles 8 generally have a volume average particle diameter of 40 to 65 μm, preferably 42 to 55 μm. If the particle size is smaller than 40 μm, the magnetic particles are likely to be developed on the latent image carrier, and the latent image carrier and the cleaning blade are easily damaged. on the other hand,
If the particle size is larger than 65 μm, the toner holding ability of the magnetic particles is lowered, resulting in non-uniformity of solid image, toner scattering, fog and the like. The non-uniformity of the solid image is a fatal defect because the digital printer is on-off development for the latent image.

In the present invention, the effect is remarkable when the magnetic particles have a volume particle size distribution of less than 35 μm of 5 to 25% by weight, preferably 7 to 20% by weight. That is, if less than 35 μm is less than 5% by weight, the polishing effect of the magnetic particles does not last long and image deterioration due to durability occurs, and if more than 25% by weight, scratches or excessive abrasion of the latent image holding member occur. Harm occurs. 35 μm
As a means for increasing the number of magnetic particles of less than 35 to 40 μm more than that of magnetic particles of 35 to 40 μm, it is preferable to adjust the particle size distribution in the step of firing the magnetic particles, but even if magnetic particles of less than 35 μm are separately added and uniformly mixed. good.

The particle size distribution in the present invention was measured according to JIS H2601 as follows.

1) Weigh about 100 g of sample to the order of 0.1 g.

2) Use a 100-500-mesh standard sieve (hereinafter referred to as a sieve) as the sieve, stack from the top in the order of 100,200,250,350,400,500, place a saucer on the bottom, put the sample on the top sieve and cover. .

3) This is oscillated by a vibrating machine to rotate horizontally at 285 ± 6 times per minute,
Sift for 15 minutes at 150 ± 10 impulses per minute.

4) After sieving, weigh out the magnetic particles in each sieve and the pan to the order of 0.1 g.

5) Calculate the weight percentage to the second decimal place, and round to the first decimal place according to JIS Z8401.

Remarks: The size of the frame of the sieve is such that the inner diameter above the sieve surface is 200 mm and the depth from the top surface to the sieve surface is 45 mm.

, The total weight of magnetic particles in each part must not be less than 99% of the weight of the sample initially taken.

Each magnetic particle may be composed of only a magnetic material, a combination of a magnetic material and a non-magnetic material, or a mixture of two or more kinds of magnetic particles. Then, by first introducing the magnetic particles 8 into the toner supply container 2, the magnetic particles 8 from the toner supply container 2 in which the sleeve surface region where the magnetic particles 8 face the inside of the container 2, that is, the sleeve 3 is disposed. Or a magnetic member 12 for preventing toner leakage.
To the tip of the blade 5 serving as the magnetic particle restraining member, the magnetic field generated by the magnet 4 in the sleeve 3 attracts and holds the sleeve surface area to cover the entire sleeve surface area. The non-magnetic toner 9 is stored in a large amount outside the magnetic particle layer as the first layer with respect to the sleeve 3 by being charged into the container 2 after the magnetic particles 8 are charged, and is present as the second layer.

The magnetic particles 8 to be initially charged preferably originally contain about 2 to 30% by weight of the non-magnetic toner 9 with respect to the magnetic particles, but may include only the magnetic particles. Further, once the magnetic particles 8 are adsorbed and held as a magnetic particle layer in the sleeve surface area, they do not substantially flow to one side even if the apparatus is vibrated or the apparatus is tilted to a large extent. The state of covering the whole is maintained.

Thus, in the state where the magnetic particles 8 and the non-magnetic toner 9 are sequentially charged and stored in the container 2 as described above, the magnetic particle layer portion near the sleeve surface corresponding to the magnetic pole S ₂ position of the magnet 4 has a strong magnetic pole. The magnetic field forms a magnetic brush of magnetic particles.

Further, the magnetic particle layer portion in the vicinity of the tip of the blade 5 serving as a magnetic particle regulating member has a regulating force based on the effect of gravity and magnetic force and the presence of the blade 5 even if the sleeve 3 is rotationally driven in the direction of the arrow b, and the sleeve. Due to the balance with the conveying force of 3 in the moving direction, it accumulates at the point 6 position on the surface of the sleeve 3 and forms a stationary layer which can move a little but is difficult to move.

When the sleeve 3 is rotated in the direction of the arrow b, the magnetic brush circulates in the direction of the arrow c near the magnetic pole S ₂ by appropriately selecting the position of the magnetic pole and the fluidity and magnetic characteristics of the magnetic particles 8. Form a circulating layer. In the circulation layer, the magnetic particles relatively close to the sleeve 3 rise up from the vicinity of the magnetic pole S ₂ onto the stationary layer on the downstream side of the rotation of the sleeve 3 by the rotation of the sleeve 3. That is, it receives the force of pushing it up. The magnetic particle portion pushed up by the magnetic particle circulation area limiting member 7 provided on the upper part of the blade 5,
Since the upper limit of the circulation area is determined, the blade 5
It does not climb up, falls by gravity, and returns to the vicinity of the magnetic pole S ₂ again. In this case, the magnetic particles having a small push-up force, such as being located far from the sleeve surface, may fall before reaching the magnetic particle circulation region limiting member 7. That is, in the circulation layer, the magnetic brush of magnetic particles is circulated as indicated by an arrow c due to the magnetic force and frictional force due to gravity and magnetic poles and the fluidity (viscosity) of the magnetic particles. The non-magnetic toner 9 is sequentially taken in from the toner layer on the upper side and returned to the lower portion in the developer supply container 2, and this circulation is repeated as the sleeve 3 is rotationally driven.

As the developing bias power source 14, an alternating voltage having the same peak voltage on the positive side and the negative side or a DC voltage superimposed on this alternating voltage can be used. For example, development contrast +300
V, reverse contrast -100V, and as an example, when the DC voltage + 450V was superimposed on the sleeve 3 and the AC component was developed by changing the frequency and the peak-to-peak voltage, the correlation diagram as shown in FIG. 5 was obtained. It was

When the frequency is less than 1000 Hz, the vibration and flight of the magnetic particles are not sufficient, and the magnetic brush marks appear on the developed image, which is not preferable. On the other hand, if it exceeds 3000 Hz, both the toner and the magnetic particles will not follow the electric field, resulting in a thin image and easy fog, which is not preferable. The area shaded by a vertical line is an area where discharge easily occurs between the sleeve and the photoconductor, and this value becomes even lower in the area where the high atmospheric pressure is low. The area shaded with a horizontal line is an area in which background fog is likely to occur in the background portion, and the area shaded with a diagonal line is an area in which magnetic particles do not fly sufficiently in the voids. Therefore, it is preferable to perform the development in the area surrounded by these lines. From the viewpoint of image density gradation (fogging, latitude, etc.), the frequency is more preferably 1.2 to 2 KHz, and V _PP is preferably in the range of 800 to 1500 V.

More preferably, the region of 1.4 to 1.8 KHz and 1000 to 1350V _PP is good. Similarly, the SD (sleeve-photoreceptor) interval is 25
When the development was carried out under the same setting by changing the thickness from 0 to 700 μm, the best image was obtained when the alternating electric field shown in Table 1 was applied.

Similar frequencies 1~2.2KHz in practice than experiment, V _PP 800 to
In the range of 2200 and S-Dgap 250 to 700 μm, almost good images were obtained. When S-Dgap is 800 μm or more,
Even if the alternating electric field voltage is increased, the reproduction of fine lines is deteriorated, which is not preferable.

In any case, the upper limit of V _PP is determined by the gap discharge limit value of the developing section, and the lower limit is determined by the toner flight limit value on the sleeve and magnetic particles.

Taking the above into consideration, the resistance of the entire developing magnetic brush is preferably 10 ⁸ Ωcm or more in the thickness direction of the developing brush when the latent image carrier 1 is in contact with the developing brush.

The resistance value of the magnetic particles and the magnetic brush described in the present invention means the developing sleeve 3 by the developing device shown in FIG.
A magnetic brush of 50 mg / cm ² magnetic particles is formed on the top, a developing sleeve and a metal drum with a gap of about 300 μm are provided opposite to this, and a circuit of about 1 MΩ resistance is connected in series to these circuits. This is calculated and obtained from the value of the current flowing when the voltage is applied.

b) Details of Development Mechanism The development in the development section 13 will be described below regarding the reversal development method according to the present invention.

2 and 3 are enlarged explanatory views of the developing section in the developing method according to the present invention. Reference numeral 21 is the latent image charge in the dark area on the latent image carrier. 9 is a non-magnetic toner. 14 is an alternating voltage power source on which a DC component is superimposed. FIG. 2 shows a case where a negative waveform component of the alternating voltage is applied to the sleeve 3, and FIG. 3 shows a case where a positive waveform component of the alternating voltage is added. The polarity of the latent image charge is shown as negative and the polarity of the developer is shown as negative.

Since the resistance of the developing brush 22 is relatively large (greater than about 10 ⁸ Ωcm), the developing brush 22 depends on the charging / discharging time constant of the electric charge due to the material of the developing brush 22 itself, etc. Alternatively, there is an electric charge injected by the mirror charge, the latent image electric field on the latent image carrier 1 and the alternating electric field between the latent image carrier 1 and the sleeve 3.

When the electric field due to the latent image charge 21 in the dark portion on the latent image carrier 1 and the electric field due to the alternating electric field do not match, the developing brush 22 is in the maximum sagging state in the sleeve 3 direction.

When the direction of the electric field due to the latent image charge on the latent image carrier 1 and the direction of the electric field due to the alternating electric field coincide with each other, the yield of the developing brush 22 becomes small and the developing brush 22 comes into contact with the latent image carrier.

In any case, as described above, the developing brush 22 is generated by the alternating electric field.
Becomes a fine but violent vibration state, and the fog toner excessively attached to the latent image holding member is rubbed by the developing brush to be removed from the latent image holding member 1 and pulled back onto the brush. Further, due to the above-mentioned vibration of the brush, the toner easily comes off from the brush 22 and is easily supplied to the latent image holding body 1, so that the image density also improves. Also a brush
The above vibration of 22 loosens the toner in the brush 22, which contributes to improvement of image density and prevention of ghost. Further, when this vibration state is severe, a part of the magnetic brush separates from the brush or the sleeve and reciprocates between the latent image carrier and the sleeve surface. The kinetic energy of this reciprocating brush is large and efficient, and the effect of the above-mentioned vibration is expected. The above behavior of the magnetic particles in the developing section is a phenomenon observed as a result of high-speed photography of 8000 frames per second with a high-speed camera.

c) Composition of Material As the magnetic particles for toner coating used in the present invention, any magnetic particles having a true specific gravity of 6 or less can be used, for example, surface-oxidized or unoxidized iron, nickel, cobalt, manganese, chromium. , Metals such as rare earths, and alloys or oxides thereof can be used, but preferably metal oxides, more preferably ferrite particles can be used. Moreover, there is no particular limitation in the manufacturing method.

Further, as a method of coating the surface of the magnetic particles with a resin, a conventionally known method such as a method of dissolving or suspending a resin in a solvent and applying it to adhere to the magnetic particles, a method of simply mixing with a powder, etc. Both are applicable.

The coating resin on the surface of the magnetic particles varies depending on the toner material, and examples thereof include polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, metal complex of di-t-butylsalicylic acid, and styrene-based resin. Resin, acrylic resin, polyacid, polyvinyl butyral, nigrosine, amino acrylate resin, basic dye and its lake, fine silica powder, fine alumina powder and the like are suitable, but not limited to these .

The treatment amount of the above resin may be appropriately determined so that the magnetic particles satisfy the above conditions, but in general, the total amount is preferably 0.1 to 30% by weight (preferably 0.5 to 20% by weight) based on the magnetic particles.

On the other hand, as the binder resin of the toner used in the present invention,
Polystyrene, homopolymers of styrene such as poly-p-chlorostyrene, polyvinyltoluene and the like and substituted products thereof; styrene-p-chlorostyrene copolymers, styrene-propylene copolymers, styrene-vinyltoluene copolymers, styrene-vinyl. Naphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, Styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-acryl-aminoacrylic copolymer, styrene-
Amino acrylic copolymer, styrene-α-methyl chloromethacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer Styrene-based copolymers such as polymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, styrene-maleic acid ester copolymer; poly Methyl methacrylate,
Polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenolic resin, aliphatic or alicyclic Hydrocarbon resins, aromatic petroleum resins, chlorinated paraffins, paraffin waxes, etc. can be used alone or in combination.

In the toner, any suitable pigment or dye can be used as a colorant. For example, there are known dyes and pigments such as carbon black, iron black, phthalocyanine blue, ultramarine blue, quinacridone, and benzidine yellow.

Further, as a charge control agent, an amino compound, a quaternary ammonium compound and an organic dye, particularly a basic dye and a salt thereof,
Benzyl dimethyl-hexadecyl ammonium chloride, decyl-trimethyl ammonium chloride, nigrosine base, nigrosine hydrochloride, safranine γ and crystal violet, metal-containing dyes, salicylic acid-containing metal compounds and the like may be added. Further, magnetic powder may be added to the extent that the effects of the present invention are not impaired.

EXAMPLES The present invention will be described in more detail with reference to examples. Parts given in the examples are parts by weight.

As the developing device, the one shown in FIG. 1 was used.

In the apparatus of the embodiment, the photosensitive drum 1 is 60 mm in the direction of arrow a.
Rotate at a peripheral speed of / second. 3 is stainless steel with an outer diameter of 32 mm and a thickness of 0.8 mm that rotates in the direction of arrow b at a peripheral speed of 66 mm / sec (SUS
304) sleeve, the surface of which was subjected to irregular sandblasting using # 600 alundum abrasive grains, and the circumferential surface roughness was set to 0.8 μm (R _Z =). On the other hand, a ferrite sintered type magnet 4 is fixedly arranged in the rotating sleeve 3, and the magnetic pole arrangement is such that the maximum value of the surface magnetic flux density is about 800 gauss as shown in FIG. The blade 5 used was 1.2 mm thick non-magnetic stainless steel. Blade-sleeve clearance is 200
μm. As the latent image carrier 1 facing the sleeve 3, a photosensitive drum having a surface layer having a charge transfer layer of 10 μm was used. Grid bias voltage 500V, 700V 2
By selecting the type, the surface state of the photosensitive drum is controlled by the potential attenuation according to the two types of exposure amounts at that time, and the development contrast is controlled to a desired value by the latent image forming device in FIG. An image was formed and the distance from the sleeve surface was set to 300 μm. Then, the power source 14 supplies the frequency 14 to the sleeve.
At 00 Hz, the peak-to-peak value was 1.4 kV, and DC / AC superposition voltage was applied for development.

The latent image forming device shown in FIG. 4 was used.

The laser light is turned on and off according to the electric signal sent from the reader, and the bright and dark parts of the original are reproduced on the latent image holding pair 1. The laser light emitted from the laser unit 51 is applied to a polygonal hiller (polygon mirror 53) that rotates at high speed by a scanner motor 52, and the reflected light passes through an imaging lens 54 and is reflected on the surface of the latent image holder 1. It is illuminated to form a latent image.

The residual toner on the latent image carrier was removed by using a counter blade cleaning method. The hardness w / a of the blade used was 25 g / cm.

Example 1 0.6% of colloidal silica was added to the above-mentioned red powder having a volume average particle diameter of 11 μm to obtain a toner. Ferrite particles whose surface is coated with silicone resin (average particle diameter 45 μm, true specific gravity 5.1, less than 35 μm 15%, 35 to 4)
0 μm 7%) was prepared.

The above toner and magnetic particles are mixed at a weight ratio of 10:90,
Used as a developer. By applying this to the developing device of FIG. 1, the amount of magnetic particles present on the sleeve in the developing portion m = 60 mg / cm ²
When the image was printed with setting so that a clear image with no fog was obtained. In addition, a running test of 10,000 sheets was performed at room temperature and normal humidity (23 ° C, 60%, development contrast
300V), low temperature and low humidity (15 ℃, 10%, development contrast 35
0V), high temperature and high humidity (30 ℃, 90%, development contrast 250
As a result of carrying out under each environment of V), good images were obtained in all cases, and toner adhesion to the surface of the latent image carrier and fogging due to scratches and the like did not occur.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the average particle size of the magnetic particles was 46 μm and the volume particle size distribution of less than 35 μm was 4% by weight. As a result, streaky image unevenness occurred after 3000 sheets under high temperature and high humidity. , 40
It was confirmed that the toner adhered to the latent image bearing member at 00 sheets.

Comparative Example 2 The procedure of Example 1 was repeated except that the average particle size of the magnetic particles was 43 μm and the volume particle size distribution of less than 35 μm was 27% by weight. The latent image carrier was scratched after 5000 sheets under low temperature and low humidity. It was

Example 2 Ferrite particles whose surface was coated with polymethylmethacrylate-polytetrafluoroethylene as magnetic particles (average particle size 43 μm, 12% less than 35 μm in volume particle size distribution, 35-
Image formation was performed in the same manner as in Example 1 except that 40 μm was 8%), and good results were obtained as in Example 1.

[Effects of the Invention] As described above, according to the present invention, an excellent image with high density can be obtained from the initial stage with a simple structure, and filming of the latent image carrier does not occur due to durability, and there is no cleaning failure. A developer having excellent characteristics and an image forming method can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view of a developing device according to the developing method according to the present invention, FIGS. 2 and 3 are enlarged explanatory views of a developing portion according to the developing method according to the present invention, and FIG. 4 is a latent image according to the present invention. FIG. 5 is a schematic view of the forming apparatus, and FIG. 5 is a view showing an example of the developing characteristic curve of the developing apparatus in the present invention. 1 ... Latent image holder, 2 ... Developer supply container, 3 ... Non-magnetic sleeve, 4 ... Fixed magnet, 5 ... Blade, 7 ...
Magnetic particle circulation region limiting member, 8 ... Magnetic particles, 9 ... Non-magnetic toner, 10 ... Developer collection container part, 11 ... Scatter prevention member, 12 ... Magnetic member, 13 ... Development area, 14 ...... Bias power supply, 21 …… Electrostatic latent image, 22 …… Magnetic brush, 51 …… Laser unit, 52 …… Scanner motor, 53 …… Polygon mirror, 54 …… Imaging lens, 55 …… Mirror.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location G03G 13/09 15/08 502 A 507 L G03G 9/10 351 (72) Inventor Mitsuru Uchida Tokyo 3-30-2 Shimomaruko, Ota-ku Canon Inc. (72) Inventor Hiroyuki Kobayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Canon Inc. (72) Ryoichi Fujita 3 Shimomaruko, Ota-ku, Tokyo Canon No. 30-2 Canon Inc. (56) Reference JP-A-59-67565 (JP, A) JP-A-60-131549 (JP, A)

Claims (4)

[Claims] 1. An image of a document is converted into an electric signal, and two kinds of different biases are applied to a latent image carrier, and two are applied to each of them.
An electrostatic latent image is formed on the latent image carrier according to the electric signal by a latent image forming device that controls latent image formation based on surface potential data of the latent image carrier when exposed with different intensities. Then, the latent image is reversely developed with a non-magnetic toner while applying an alternating electric field between the latent image carrier and the developer carrier in the development area of the latent image carrier and the developer carrier opposite thereto. A developer for use in an image forming method, comprising at least a non-magnetic toner and magnetic particles, wherein the magnetic particles have a true specific gravity of 6 or less, a volume average particle diameter of 40 to 65 μm, and a volume distribution of less than 35 μm of 5 to 25 weight. % And 35-40 μm is less than 35 μm and is coated with an electrically insulating resin, forming a magnetic brush of 5-80 mg / cm ^{2 in} the developing area of the developer carrier, In the developing area, the latent image carrier, the surface of the developer carrier and the surface of the magnetic brush A dry developer characterized in that a non-magnetic toner reciprocates between them to reversely develop a latent image. 2. A surface potential data of a latent image carrier when an image of a document is converted into an electric signal, two kinds of different biases are applied to the latent image carrier, and the latent image carrier is exposed with two different intensities. An electrostatic latent image is formed on the latent image holding member according to the electric signal by a latent image forming device that controls the latent image formation based on the latent image forming device, and then the latent image holding member and the developer carrying member facing it are developed. An image forming method of reversal developing a latent image with a non-magnetic toner while applying an alternating electric field between a latent image holding member and a developer carrying member in a region, the true specific gravity of which is 6 or less, and the volume average particle diameter.
40 to 65 μm, 5 to 25% by weight of less than 35 μm in volume distribution, 35 to 40 μm less than 35 μm, and magnetic particles coated with an electrically insulating resin to 5 to 5% in the developing area of the developer carrier. A magnetic brush is formed to 80 mg / cm ^2, and in the development area, non-magnetic toner is reciprocally developed between the latent image carrier and the surface of the developer carrier and the surface of the magnetic brush to perform reverse development, and this image is transferred. An image forming method comprising the steps of transferring to a member and then removing the residual developer on the latent image carrier. 3. The image forming method according to claim 2, wherein the latent image carrier contains an organic polymer having a charge transfer layer on its surface. 4. The image forming method according to claim 2, wherein the step of removing the residual developer on the latent image holding member is performed by a counter blade cleaning method.