JPS62182761A - Reversal developing method - Google Patents

Abstract

PURPOSE:To obtain a reversal image which has the especially high resolution and does not generate dust around the image, by giving a positive electrification characteristic to an image carrier and giving a negative electrification characteristic to a magnetic toner and applying a positive DC voltage to a sleeve. CONSTITUTION:Such characteristic is given to a toner 3 that it is electrified negatively with a polarity opposite to that of an electrostatic latent image formed on a photoconductive layer 1a, and the toner has a negative electric charge in the carrying stage by contacting between the toner 3 and a sleeve 4 or a doctor blade 6 and between toner particles. At the time of reaching the developing area, the toner 3 having the negative electric charge is stuck to the non-image part of the photoconductive layer 1a to form a toner image. This toner image reaches a transfer position by the rotation of a photosensitive drum 1, and a negative electric field having a polarity opposite to that of the electrostatic latent image is applied from the rear face of a transfer sheet to transfer the toner image onto the transfer sheet, and this image is fixed by a means using heat or pressure.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention involves attaching magnetic toner in a developer consisting of a magnetic carrier and magnetic toner to an uncharged area of an electrostatic latent image formed on the surface of an image carrier. The present invention relates to a reversal developing method for obtaining a reversal toner image.

[Conventional technology]

In recent years, with the increasing performance and diversification of information processing equipment,
Output formats are also becoming more diverse and faster speeds are required.

Non-impact electrophotographic printers have been developed. The recording principle of the above printer is similar to that of general electronic copying machines, in which an electrostatic latent image formed on the surface of an image carrier is developed, and then
It is used to transfer the image onto a passing sheet of paper.

In printers, it is necessary to write information from a computer onto the surface of a uniformly charged image carrier using a laser beam or the like, and to apply one reversal development to adhere toner to the written area, that is, the exposed area.

The developer used in the above reversal development is generally a two-component developer consisting of a magnetic carrier and a toner.

Although this method enables electrostatic transfer of toner images onto plain paper and provides high-quality printer images, it requires a means to maintain a constant mixing ratio of carrier and toner. Therefore, there is a drawback that the developing device becomes larger and more complicated, and the carrier needs to be replaced periodically.

In order to overcome these drawbacks, there is a method of developing an electrostatic latent image using a one-component developer consisting only of magnetic toner particles. In the above reversal development method using magnetic toner, a DC bias voltage of the same polarity as the electrostatic latent image is applied to a conductive sleeve holding magnetic toner having a charge of the same polarity as the electrostatic latent image. This causes the toner to adhere to the non-image area. Further, when a toner image obtained by development is electrostatically transferred onto a transfer sheet, an insulating magnetic toner with high electrical resistance is generally used.

[Problem that the invention seeks to solve]

The reality is that when a charged type insulating magnetic toner as described above is charged to the same polarity as the electrostatic latent image and reversal development is performed, the two-image quality is inferior to that using a two-component developer.

In other words, when using a magnetic toner that is charged to the same polarity as the electrostatic latent image, results equivalent to those using the two-component developer described above can be obtained in terms of single image density, but in terms of resolution. Furthermore, since the developing gap formed between the surface of the image carrier and the sleeve is narrow, dust tends to occur around the two images.

The present invention solves the above problems, has high resolution,
It is an object of the present invention to provide a reversal developing method that does not cause dust to occur around the image.

[Means for solving problems]

In order to solve the above problems, the following technical means were adopted in the present invention. Namely.

A developer that forms an electrostatic latent image on the surface of the image carrier and is made of a magnetic carrier and magnetic toner and is placed on a non-magnetic conductive sleeve that is disposed opposite to the surface of the image carrier and has a magnetic field generating member inside. supply.

The developer is conveyed toward the surface of the image carrier by the relative rotation of the sleeve and the magnetic field generating member, and a DC voltage is applied to the sleeve so that the non-image area of the electrostatic latent image is exposed to the developer in the developer. In a reversal development method that attaches magnetic toner.

B. The image carrier has positive charging characteristics.

C0 The magnetic toner has negative charging characteristics.

D. Applying a positive DC voltage to the sleeve.

This is a technical measure taken.

[Effect]

FIG. 1C is a sectional view of a main part showing an example of a developing device for carrying out the present invention. In the figure, l is a photoreceptor drum, which is composed of a photoconductive layer 1a holding an electrostatic latent image (indicated by a + symbol in the figure) and an electrically grounded exclusive substrate 1b, which is indicated by the arrow W. It is provided so that it can rotate freely in the direction. Next, reference numeral 2 denotes a toner tank, which stores toner 3 made of a mixture of a magnetic carrier such as ferrite and magnetic toner. One tank of tona 2
A sleeve 4 is provided at the bottom of the photoreceptor drum 1 so as to be independently rotatable in the direction of arrow Y, facing the photoreceptor drum 1.

A permanent magnet member 5 having a plurality of magnetic poles on its surface is provided in the sleeve 4 coaxially with the sleeve 4 and rotatable independently in the direction of arrow X. Reference numeral 6 denotes a doctor blade, which is provided facing the surface of the sleeve 4 so as to be able to move in and out, and regulates the thickness of the toner 3 moving on the sleeve 4. Next, the sleeve 4 is made of a non-magnetic and electrically conductive material such as austenitic stainless steel or aluminum alloy.

It is electrically connected to a DC power supply 7 having positive polarity.

A reversal development method using the above configuration will be described. First, by rotating the sleeve 4 and the permanent magnet member 5 relatively, the toner 3 contained in the toner tank 2 is pulled out onto the sleeve 4, and the doctor gap d is drawn out in the direction of the arrow Y.
from there toward the developing gap D. The toner 3 has a characteristic of being negatively charged with a polarity opposite to that of the electrostatic latent image formed on the photoconductive layer la, and is charged to the sleeve 4 in the B feeding process. When the doctor blade 6 or the toner 3 come into contact with each other, they become negatively charged. 1 with negative charge facing
When the toner 3 reaches the development area, it adheres to the non-image areas of the photoconductive layer 1a and forms an image. Next, this toner image reaches the transfer position by rotation of the photoreceptor drum 1,
By applying a negative electric field of opposite polarity to the electrostatic latent image from the back side of a transfer sheet (not shown), the image is transferred onto the transfer sheet and then fixed by means of heat or pressure.

Since the reversal development method of the present invention uses a magnetic toner that is charged with a polarity opposite to that of the electrostatic latent image,
It is thought that magnetic toner adheres to the image area of the electrostatic latent image, but according to experiments conducted by the present inventors, it does not clearly adhere to the non-image area of the electrostatic latent image as described above. Confirmation and reproducibility are also well present.

The magnetic toner used in the present invention has a triboelectric charge amount of -5 to -25 μc/cm when measured by a blow-off method.
g, and it is desirable that the charging voltage on the sleeve is -6 to -80V. That is, when the amount of triboelectric charge and the charging voltage are excessive, the image area density decreases, while when they are insufficient, there is an increase in fog, both of which are disadvantageous.

Next, the magnetic powder constituting the magnetic toner includes alloys or compounds containing ferromagnetic elements such as ferrite magnetite, iron, cobalt, and nickel, and various other materials that exhibit ferromagnetism through heat treatment or other treatments. Alloys etc. may be used. Since these ferromagnetic substances are contained in toner having a particle size of several μm to several tens of μm, it is desirable that the average particle size is 0.02 to 3 μm. Therefore, the amount to be contained in the toner is 30 to 30% based on the total amount of toner.
The content is preferably 70% by weight. If it is less than 30% by weight, the magnetic force of the toner will decrease and it will easily fly off from the sleeve, while if it exceeds 70% by weight, the resin content will be extremely low and the fixing performance will deteriorate, which is disadvantageous.

Next, the fixing resin can be appropriately selected depending on the fixing method. For example, in the case of using a heat fixing means such as oven heating or a hot roll, various thermoplastic resins such as those described below can be used. That is, styrenes, vinyl esters, esters of α-methylene aliphatic monocarboxylic acids, acrylonitrile, and methacrylate trile.

Acrylamide, vinyl ethers, vinyl ketones,
A homopolymer obtained by polymerizing monomers such as an N-vinyl compound, or a copolymer obtained by copolymerizing a combination of two or more of these monomers.

Mixtures thereof can be used. In addition, rosin-modified phenol-formalin resin, bisphenol-type epoxy resin, oil-modified epoxy resin, polyurethane resin, cellulose resin, and polyether resin.

Non-vinyl thermoplastic resins such as polyester resins or mixtures thereof with vinyl resins such as those described above can also be used.

In particular, when fixing is carried out by oven heating means, bisphenol-type epoxy resins and bisphenol-type polyester resins are preferable, and when fixing is carried out by hot rolls, styrene-based resins or polyester resins are preferable. In the styrene resin, the greater the styrene component, the better the mold releasability against hot rolls. In order to further improve the mold releasability against hot rolls, fatty acid metal salts, low molecular weight polyolefins, higher fatty acids having 28 or more carbon atoms, natural or synthetic paraffins, thermoplastic rubber, etc. may be added.

On the other hand, if the fixing means is a pressure fixing method using only pressure at room temperature, 1, for example, the following resins are used. That is, higher fatty acids, higher fatty acid metal salts, higher fatty acid derivatives, higher fatty acid amides, waxes, rosin derivatives, and alkyd resins.

Epoxy-modified phenolic resin, natural resin-modified phenolic resin, amino resin, silicone resin, polyurethane, urea resin, polyester resin, copolymerized oligomer of acrylic acid or methacrylic acid and long-chain alkyl acrylate, styrene and long-chain alkyl acrylate, long chain Examples include copolymerized oligomers with alkyl methacrylate, polyolefins, ethylene to t''A hl hinyl copolymers, ethylene to vinyl alkyl ether copolymers, maleic anhydride copolymers, 1 petroleum residues, gono, etc. It will be done.

Any of the above-mentioned resins can be freely migrated and mixed as desired, but in order not to reduce the fluidity when formed into a toner, those having a glass transition point exceeding 40° C. are effective.

In addition to the above, various pigments and/or additives used in general dry developers can be added. However, the content based on the total amount of toner is suitably less than 10% by weight, taking into consideration the electrical properties of the toner. Pigments that can be used include carbon blank, aniline blue, calco oil blue, and chrome yellow.

Cow 1-Lamaline Blue, DuPont Oil Red.

Quinoline yellow, methylene blue chloride.

Phthalocyanine blue, malachite green octylate. lamp black, rose bengal and mixtures thereof, etc. Note that if the magnetic powder itself is colored, such as magnetite, there is no need to add it. Further, when carbon black is used, it is preferably contained in a range of 0.01 to 5 parts by weight per 100 parts by weight of the resin component in the toner so as not to reduce the insulation properties of the toner.

Also, in order to give negative charging characteristics to the toner.

A dye having negative charge characteristics such as a metal-containing (Cr) azo dye or a negative charge control agent such as a resin having a group capable of controlling negative charge may be added.

The addition amount is generally desirably in the range of 0.1 to 5%.

Next, the magnetic toner used in the present invention can be manufactured from the above-mentioned materials by a known method such as a pulverization method or a spray drying method. The average particle size of the toner to be produced is preferably in the range of 5 to 30 μm, preferably 10 to 20 μm. The electrical resistance or fluidity can be adjusted by adding conductive particles such as carbon black or tin oxide or additives such as silica powder to the toner particle surface after classification.

The developer used in the present invention is prepared by mixing a magnetic carrier such as iron powder, magnetite, or ferrite with the above magnetic toner. However, from the viewpoint of image quality, it is preferable to use a ferrite carrier as described in Japanese Patent Application No. 182328/1983 filed by the present applicant. The mixing ratio of carrier and toner is 30 to 2 weight ratio.
A range of 0 to 10 near 90 is desirable. When the carrier content is less than 30% by weight, there is too much toner (■), which makes the toner easy to fly off and the amount of Sven+-1-ner increases.On the other hand, when the carrier content exceeds 90% by weight, the carrier aggregates. Both are disadvantageous because they become easy to use and cause carrier adhesion.

Next, in order to prevent magnetic agglomeration of carriers, it is preferable that the developer conveyance method be one in which at least the sleeve is rotated. good. Note that in order to convey the developer well, it is desirable to rotate the permanent magnet member in a direction opposite to that of the sleeve.

〔Example〕

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples.

First, the magnetic carrier and magnetic toner used for image evaluation will be described in detail.

Ferrite carrier 60% by weight (Hitachi Metals KBN-100 particle size 70-140μm) Magnetic 1st grade - 4
The 0 weight percent magnetic toner is prepared by dry mixing styrene acrylic resin (R520 manufactured by Segisui Kagaku Kogyo Co., Ltd.), magnetite (EPT500 manufactured by Toda Kogyo Co., Ltd.) and charge control agent (Bontron R81 manufactured by Orient Chemical Co., Ltd.) according to the composition shown in the table, and then mixed in a kneader. The mixture was heated and kneaded at a temperature of 200°C. After cooling and assimilating the resulting kneaded material, it is milled to 20 μm using a shet mill.
It was ground into particles less than m. Next, this pulverized powder was put into a super mixer, and 0.5 parts by weight of i-powdered silica (R972 manufactured by Nippon Aerosil Co., Ltd.) was added and mixed. The mixed powder was introduced into an air stream at 120°C, heat treated, and then classified using a Schiffzab classifier to give a 5 to 20
Magnetic 1-ner Nos. 1 to 4 having a particle size distribution of μm were obtained. The triboelectric charge amount (hereinafter referred to as TEC) and surface potential of these magnetic toners are as shown in the table. Note that no,
For comparison, Sample No. 5 used Bontron No. 3 manufactured by Orient Chemical Co., Ltd. as a charge control agent.

In the following, the TEC of the magnetic toner is a value measured under the following conditions using a commercially available blow-off powder charge measuring device (TB-200 manufactured by Toshiba Chemical).

Carrier (Japan Iron Powder Z-200) 10g and toner 0
Pour 65g into a plastic container with an outer diameter of 4Q+nφ,
The mixture was rotated for 10 minutes using a flow surface angle measuring device, and 200 square samples were taken from the resulting mixture and placed in a container using a 325 mesh sieve. /cut.

Measurement is performed under the condition of blowing for 1 hour and 40 seconds.

Further, the charging voltage, that is, the surface potential of the toner is measured by the apparatus shown in FIG. In the same figure.

8 is a non-magnetic sleeve (outer diameter 501@φ), 9 is a permanent magnet member (outer diameter 461 mφ, length 150 mm, 12-pole symmetrical magnetization, magnetic flux density on the sleeve 1000 G).

10 is a surface electrometer (TRESOK 344), and 11 is a measuring head. Therefore, the gap g between the sleeve 8 and the probe 11 is set to 51
After adjusting the temperature, 3g of toner was supplied onto the sleeve 8, and the permanent magnet member 9 was heated to 1000r, p.

The surface potential of the toner is measured when the toner is rotated for 1 minute at m.

Images were formed using the above magnetic toner under the following conditions and evaluated, and the results are shown in the table above.

Rotates at a circumferential speed of 150 mm/sec. After the PC drum was uniformly charged to +800 cm using a corona charger, an electrostatic latent image was formed by exposing it to light in sections using a commercially available semiconductor laser.

Next, development was carried out using the developing device shown in FIG.

For the sleeve 4, a cylinder made of 5US304 with an outer diameter of 32° is used, and the permanent magnet member 5 is symmetrically magnetized with 10 poles and has an outer diameter of 29° and 31φ. used.

Doctor gap d and development gap D are each 0.2
1 and 0.3 m-, with the sleeve 4 in the direction of arrow Y and the permanent magnet member 5 in the direction of arrow X, and 200 r each.
, p, m, and rotated by 1000 r, p, m.

The DC bias voltage was set to +700■. The obtained toner image is transferred to +IV paper and then fixed at a fixing temperature of 180°C.
Heat roll fixing was performed at a two-line pressure of 1 kg/cm.

As is clear from the table, toner Nos. and L to 4 not only show good values in both density and resolution.

A clear image with no dust generated around the image was obtained. On the other hand, toner Nos. 5 to 7 have dust around two images, especially toner No.

In the cases shown in No. 5, No. 7, and No. 7, both density and resolution remained at low values.

In this example, an example was shown in which a ferrite gear carrier was used as the magnetic carrier, but iron powder was used instead.

Other magnetic carriers such as iron oxide (Fez (14)) have the same effect.

〔Effect of the invention〕

Since the reversal developing method of the present invention has the structure and operation as described above, high-quality images can be obtained.

In particular, there is an effect that an inverted image with high resolution and no dust generated around the image can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a developing device for carrying out the present invention, and FIG. 2 is a sectional view showing a toner surface potential measuring device. ■=photosensitive drum, 3: toner, 4 sleeves. 5: Permanent magnet member.

Claims (2)

[Claims] (1) An electrostatic latent image is formed on the surface of the image carrier, and a development consisting of a magnetic carrier and magnetic toner is placed on a nonmagnetic conductive sleeve that is disposed opposite to the surface of the image carrier and has a magnetic field generating member inside. The developer is supplied toward the surface of the image carrier by relative rotation between the sleeve and the magnetic field generating member, and a DC voltage is applied to the sleeve to remove the non-image portion of the electrostatic latent image. In the reversal development method in which magnetic toner in a developer is attached to the image carrier, the image carrier has a positive charging characteristic, the magnetic toner has a negative charging characteristic, and a positive DC voltage is applied to the sleeve. Reversal development method. (2) The amount of triboelectric charge of the magnetic toner is -5 to -25 μc/g
The reversal developing method according to claim 1, wherein the charging voltage on the sleeve is -6 to -80V.