JPH0448394B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a reversal development method in which a one-component magnetic toner is attached to an uncharged area of an electrostatic latent image formed on the surface of an image carrier to obtain a reversal toner image. [Background Art] In recent years, with the spread of computers, printers have been actively developed as peripheral terminal devices that output information in the form of characters and figures and create hard copies. Conventionally, the mainstream printers have been impact printers, which print by colliding selected printed characters with paper via an ink ribbon. However, with the increasing performance of computers and the diversification of information processing, there is a need for rapid processing of large amounts of information and a variety of output formats such as kanji, graphics, and characters of arbitrary sizes.
It is difficult for conventional impact printers to meet this demand, and a new non-impact printer (electronic printer) has been developed. Non-impact printers are classified into electrophotographic, electrostatic, and inkjet printers in terms of recording methods, but the electrophotographic method is the most advantageous in responding to the recent high-speed and high-density recording. . The recording principle of printers using electrophotography is
The recording principle is essentially the same as that of general copying machines, and includes the following steps: forming an electrostatic latent image by uniformly charging the surface of the image carrier and exposing it to light, developing the electrostatic latent image, transferring the developed toner image to plain paper, and fixing it. It consists of a process. However,
In a printer, information from a computer is written on the surface of a uniformly charged image carrier using a laser beam, etc.
In order to cause toner to adhere to this written area, that is, the exposed area, it is necessary to perform reversal development. The dry developer used in the reversal development method is
As in the case of copying machines, a two-component developer consisting of a magnetic carrier and toner is common, and most current printers employ this developer. When a two-component developer is used, since the toner has a distinct electrostatic charge due to frictional charging with the carrier, it is possible to faithfully develop the uncharged portion of the electrostatic latent image. Furthermore, since the toner retains its electrostatic charge even after development, electrostatic transfer of the toner image onto general-purpose plain paper is possible, and a high-quality printer image can be obtained. However, when using a two-component developer, a means is required to maintain a constant mixing ratio of carrier and toner in order to maintain a constant image density, which has the disadvantage that the developing device becomes larger and more complex. There is. Also, if the carrier is mixed with toner and stirred for a long time, a toner film will be formed on the surface.
Another drawback is that the carrier must be replaced periodically due to changes in triboelectric charging properties. In order to overcome these drawbacks, a method of developing electrostatic latent images using a one-component developer (magnetic toner) consisting only of magnetic toner particles as a dry developer has been proposed and put into practical use. . In the reversal development method using magnetic toner,
Generally, a DC bias voltage of the same polarity as the electrostatic latent image is applied to a conductive sleeve that holds magnetic toner with a charge of the same polarity as the electrostatic latent image, thereby causing the toner to adhere to the uncharged area. It is. Here, in order to make the magnetic toner have a predetermined polarity of electrolysis, a charged magnetic toner (e.g., JP-A-55-1999) is prepared by adding a charge control agent inside and/or on the surface of the toner.
48754, 57-45555 to 45557, etc.) are used. This charged magnetic toner becomes electrically charged when it comes into contact with a sleeve or a doctor blade, or when the toners come into contact with each other. Furthermore, when the developed toner image is electrostatically transferred onto a transfer sheet, insulating magnetic toner with increased electrical resistance is generally used to prevent disturbances in the transferred image (for example, insulating magnetic toner with increased electrical resistance). (See Publication No. 53-31136). [Problems to be Solved by the Invention] When the above-mentioned charged type insulating magnetic toner is charged to the same polarity as the electrostatic latent image and reversal development is performed, the image quality is inferior to that of a two-component developer. was the reality. Specifically, when using magnetic toner that is charged to the same polarity as the electrostatic latent image, it is possible to obtain results equivalent to two-component developers in terms of image density, but the resolution is not sufficient and the character quality is There was a problem that dust was easily generated around it. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a reversal development method that uses magnetic toner and can produce images of higher quality than conventional methods. [Means for solving the problem] As mentioned above, when reversing an electrostatic latent image using magnetic toner, it is necessary to use a magnetic toner that has the property of being charged to the same polarity as the electrostatic latent image. This is common knowledge, and such magnetic toners are actually used. However, as a result of various studies conducted by the present inventor, surprisingly, by using a magnetic toner that has the property of being charged with the opposite polarity to the electrostatic latent image, resolution is improved and dust is extremely reduced compared to conventional methods. It was discovered that images with good sharpness can be obtained. Therefore, in the reversal development method of the present invention, an electrostatic latent image is formed on the surface of an image carrier having predetermined charging characteristics, and a non-magnetic latent image is placed facing the surface of the image carrier and equipped with a magnetic field generating member inside. Insulating magnetic toner mainly composed of resin and magnetic powder is supplied onto the conductive sleeve, and the magnetic toner charged to a predetermined polarity is transported toward the surface of the image carrier by relative movement between the sleeve and the magnetic field generating member, and is then transferred to the sleeve. It is a reversal development method in which magnetic toner is attached to the non-charged area of the image carrier surface by applying a DC voltage of the same polarity as the electrostatic latent image, and the magnetic toner has charging characteristics of the opposite polarity to the electrostatic latent image. , the amount of frictional electrification determined by the blow-off method is in the range of 1 to 20 μc/g in absolute value, and the voltage generated by the rotation of toner particles on the non-magnetic sleeve having an internal permanent magnet member is 10 to 90 V in absolute value. It is characterized by using a magnetic toner within a range. The details of the present invention will be explained below with reference to the drawings. FIG. 1 is a sectional view showing an example of a developing device for carrying out the present invention. The photosensitive drum 1 has a photoconductive layer 1a holding an electrostatic latent image (indicated by a + signal in the figure) and a conductive base 1b which is electrically grounded, and rotates in the direction of arrow W in the figure. The developing device 2 includes a sleeve 3 disposed facing the photosensitive drum 1, a permanent magnet member 4 disposed inside the sleeve 3 having a plurality of magnetic poles on its surface, a toner tank 5 containing magnetic toner 6, and a sleeve. The magnetic toner 3 is provided with a doctor blade 7 for regulating the thickness of the magnetic toner 6 conveyed thereon. Here, the sleeve 3 is made of a non-magnetic and conductive material such as austenitic stainless steel or aluminum alloy, and is electrically connected to a DC voltage source 8. The reversal development process using the above-mentioned development device is as follows. By relatively rotating the sleeve 3 and the permanent magnet member 4, the magnetic toner 6 contained in the toner tank 5 is pulled out onto the sleeve 3 and directed from the doctor gap d to the developing gap D as shown by the arrow Y in the figure. Once conveyed. Here, the magnetic toner has the property of being charged with a polarity opposite to that of the electrostatic latent image, and when it comes into contact with the sleeve, doctor blade, or toner particles during the above-mentioned conveyance process, it becomes charged with the opposite polarity of the electrostatic latent image. Become. When the charged magnetic toner 6 reaches the development area, it adheres to the non-charged portion of the electrostatic latent image to form a toner image. When this toner image reaches the transfer position by rotation of the photoreceptor drum 1, it is transferred onto the transfer sheet by applying an electric field of opposite polarity to the electrostatic latent image from the back side of the transfer sheet (not shown), and then fixed. be done. Unlike conventional methods, the present invention uses magnetic toner that has the property of being charged with a polarity opposite to that of the electrostatic latent image. Accordingly, from the conventional thinking, it seems that the magnetic toner adheres to the image area of the electrostatic latent image. However, according to experiments conducted by the present inventors, it was confirmed that it adheres to the non-charged portion of the electrostatic latent image. The reason why high quality images can be obtained by the present invention is as follows.
Although the details are unknown, it is assumed that the following is the case. In the process of conveying magnetic toner on the sleeve,
As described above, most toner particles are charged with a polarity opposite to that of the electrostatic latent image, and most of the toner particles come to have a charge with a polarity opposite to that of the electrostatic latent image. This magnetic toner reaches the development area,
When entering the electric field of the electrostatic latent image, the charge in the toner moves according to the direction of the electric field, and the toner particles near the interface with the photoreceptor, where the electrostatic latent image potential is low, have the same polarity as the electrostatic latent image. It will have a charge of . As a result, toner particles having a charge of the same polarity as the electrostatic latent image adhere to the uncharged portion of the electrostatic latent image, thereby obtaining a reversed image.
Therefore, in the past, magnetic toner charged to the same polarity as the electrostatic latent image was used, which caused overdevelopment, that is, too much toner adhered to the surface of the photoreceptor, causing dust. According to the present invention, only the toner near the interface with the photoreceptor has a charging polarity that contributes to development, so it is thought that overdevelopment can be suppressed and dust generation can be prevented. Furthermore, according to experiments conducted by the present inventors, the amount of triboelectric charge of the magnetic toner used in the present invention is in the range of 1 to 20 μc/g in absolute value when measured by the blow-off method, and moreover, the amount of triboelectric charge measured by the blow-off method is in the range of 1 to 20 μc/g. It has been found that it is desirable to have charging characteristics in which the generated surface potential is in the range of 10 to 90 V in absolute value. This is because when the amount of triboelectric charge and surface potential become excessive, the image density decreases, while when the amount of triboelectricity and surface potential are insufficient, fog increases. Further, the most preferable ranges for the amount of charge and the surface potential are 3 to 10 μc/g in absolute value and 30 to 60 V in absolute value, respectively. The magnetic toner in the present invention can be manufactured from various materials used in ordinary magnetic toners. Magnetic powders include alloys or compounds containing ferromagnetic elements such as iron, cobalt, and nickel, including ferrite and magnetite, as well as various alloys that exhibit ferromagnetism through some treatment such as heat treatment. Can be used. These ferromagnetic materials preferably have an average particle size of about 0.1 to 3 μm in order to be included in the toner having a particle size of several μm to several tens of μm. The amount contained in the toner is preferably 30 to 70% by weight based on the total weight of the toner. If it is less than 30% by weight, the magnetic force of the toner will decrease and the toner will scatter more easily than the sleeve.
On the other hand, if it exceeds 70% by weight, the resin content will be extremely small and the fixing performance will deteriorate. The fixing resin may be appropriately selected depending on the fixing method. For example, when the fixing method is oven heating or hot roll method, various thermoplastic resins such as those described below are used. That is, styrenes,
Homopolymers made by polymerizing monomers such as vinyl esters, esters of α-methylene aliphatic monocarboxylic acids, acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers, vinyl ketones, N-vinyl compounds, or monopolymers of these monomers. A copolymer obtained by copolymerizing a combination of two or more polymers or a mixture thereof may be used. In addition, non-vinyl thermoplastic resins such as rosin-modified phenol-formalin resin, bisphenol-type epoxy resin, oil-modified epoxy resin, polyurethane resin, cellulose resin, polyether resin, polyester resin, or the above-mentioned vinyl Mixtures with other resins may also be used. In particular, when fixing is performed by heating in an oven, bisphenol type epoxy resins and bisphenol type polyester resins are preferred, and when fixing is performed using a hot roll, styrene resins or polyester resins are preferred. The greater the styrene component in the styrene-based resin, the better the releasability from hot rolls. In addition, in order to further improve the releasability of hot rolled materials, 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, when the fixing method is a pressure fixing method using only pressure at room temperature, the following pressure-sensitive resin is used, for example. Namely, higher fatty acids, higher fatty acid metal salts, higher fatty acid derivatives, higher fatty acid amides, waxes, rosin derivatives, alkyd resins, epoxy-modified phenolic resins, natural resin-modified phenolic resins, amino resins, silicone resins, polyurethane, urea resins. , polyester resin, copolymerized oligomer of acrylic acid or methacrylic acid and long-chain alkyl methacrylate, long-chain alkyl acrylate, copolymerized oligomer of styrene and long-chain alkyl acrylate, long-chain alkyl methacrylate, polyolefin, ethylene-vinyl acetate copolymer Examples include polymers, ethylene-vinyl acetate copolymers, ethylene-vinyl alkyl ether copolymers, maleic anhydride copolymers, petroleum residues, rubbers, and the like. These resins can be arbitrarily selected and mixed as desired, but in order not to reduce the fluidity when used as a toner, resins with a glass transition point exceeding 40°C or resin mixtures are effective. used. In addition to the above, various pigments and/or additives used in general dry developers may be added. However, the content based on the total amount of toner is
Considering the electrical properties of the toner, etc., it is appropriate that the amount is less than 10% by weight. Pigments that can be used include, for example, carbon black, aniline blue, calco oil blue, chrome yellow, ultramarine blue, Dupont oil red, quinoline yellow,
Methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal and mixtures thereof are used. If the magnetic powder itself is colored, such as magnetite, there is no need to add it. When carbon black is used, it is preferably added in an amount of 0.01 to 1 part by weight per 100 parts by weight of the resin component of the toner so as not to reduce the insulation properties of the toner. In addition, as a charge control agent, for example, nigrosine dyes having positive triboelectric properties or nigrosine dyes modified with higher fatty acids, metal-containing (Cr) substances having negative triboelectric properties, etc.
Azo dyes and the like can be used. In addition, special public service No. 51-28232
As described in Japanese Patent Application Publication No. 53-13284, certain polymeric dyes have stable charges and can be used effectively. Furthermore, oxidized carbon black and resins having positive or negative charge control groups can be regarded as a type of charge control agent and can be used effectively. The amount of charge control agent added is
Generally, it is desirable to set it in the range of 0.1 to 5% by weight. The magnetic toner used in the present invention can be manufactured using the above-mentioned materials by a known method such as a pulverization method or a spray drying method. For example, in the case of a pulverization method, the raw materials may be dry premixed, heated and kneaded, cooled and solidified, and then the cooled and solidified product is pulverized and then classified. The average particle size of the obtained toner is 5 to 5.
The thickness is preferably 30 μm, preferably in the range of 10 to 20 μm. Further, various additives such as conductive particles (for example, carbon black, tin oxide) and fine silica powder may be added to the surface of the toner particles after classification to adjust the electrical resistance and fluidity. In the present invention, the method of conveying the magnetic toner to the developing area is not particularly limited, and it is sufficient to rotate at least one of the sleeve and the permanent magnet member. However, among the various toner transport methods, the method in which the sleeve and the permanent magnet member are both rotated in the same direction and the magnetic toner is transported as a whole in the opposite direction (for example, see Japanese Patent Publication No. 57-12148) is one that It is desirable from the point of view. In this toner transport method, the doctor gap and developer gap are each
A range of 0.1 to 0.8 mm and 0.15 to 0.7 mm is preferable. In the present invention, the triboelectric charge amount of the toner is measured using a commercially available blow-off powder charge measuring device (manufactured by Toshiba Chemical Co., Ltd.).
TB-200) under the following conditions.
Carrier (Japan Iron Powder Z200) 10g and toner 0.5g
was placed in a plastic container with an outer diameter of 40 mmφ, and rotated for 10 minutes using a flow surface angle measuring device. A 200 mg sample was taken from the resulting mixture and placed in a container using a 325 mesh sieve. The amount of charge was measured using the above measuring device under the conditions of a blow pressure of 1.0 Kg/cm ² and a blow time of 40 seconds. It is assumed that the surface potential of the toner is measured using the apparatus shown in FIG. In the same figure, 8 is a non-magnetic sleeve (outer diameter 50mmφ), 9 is a permanent magnet member (outer diameter 46mm).
mmφ, length 150mm, 12 poles symmetrical magnetization, magnetic flux density on the sleeve 1000G), 10 is a surface electrometer (trek
344). The measurement was performed by adjusting the gap between the sleeve 8 and the surface electrometer 10 to 5 mm, then supplying 3 g of toner onto the sleeve, and then turning the permanent magnet member 9 on.
Let us determine the surface potential of the toner when it is rotated at 1000 rpm for 1 minute. To measure the resistance of the toner, weigh an appropriate amount (10 mg) of the sample, fill it in a Teflon (trade name) hollow cylinder with an inner diameter of 3.05 mm and equipped with an improved dial gauge.
Under a load of 0.1Kg, an electric field of D.C4KV/cm is applied and measured, and the resistivity is calculated. To measure the resistance, a 4329 type insulation resistance meter manufactured by Yokogawa Hiretsupat Card was used. [Examples] The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples. Example 1 37 parts by weight of styrene-acrylic copolymer (P520 manufactured by Sekisui Chemical Co., Ltd.) and magnetite (manufactured by Toda Kogyo Co., Ltd.)
62 parts by weight of EPT500) and 1 part by weight of a negative charge control agent (Bontron E81 manufactured by Orient Chemical Co., Ltd.) were dry mixed and kneaded by heating at a temperature of 200° C. in a kneader. After cooling and solidifying the obtained kneaded material, use a jet mill.
Grinded into particles of 20 μm or less. This pulverized powder was put into a super mixer, and 0.5 parts by weight of finely powdered silica (R972 manufactured by Nippon Aerosil) was added and mixed. The mixed powder was heat-treated by introducing it into a hot air stream at 120°C, and then subjected to circumferential force classification using a zigzag classifier to obtain a magnetic toner (No. 1) having a particle size distribution of 5 to 20 μm. The amount of triboelectric charge (hereinafter referred to as TEC) of this magnetic toner is -5μc/g, and the surface potential is -
It was 31V. Image evaluation was performed using the above magnetic toner under the following conditions. An Se drum rotating at a circumferential speed of 150 mm/sec was uniformly charged to +800 V with corona charging, and then exposed in sections using a commercially available semiconductor laser to form an electrostatic latent image, and then developed using the developing device shown in Figure 1. . Here, the sleeve 2 was a cylinder made of SUS304 with an outer diameter of 32 mmφ, and the permanent magnet member 3 was a ferrite magnet with an outer diameter of 29.3 mmφ, symmetrically magnetized with 10 poles, and a magnetic flux density of 800 G on the sleeve. Set the doctor gap d and the developing gap D to 0.6 mm and 0.2 mm, respectively, and move the sleeve 2 and the permanent magnet material 3 both in the direction of the arrow
It was rotated at 50 rpm and 1200 rpm, and the bias voltage was set to +700V. The obtained toner image is transferred to plain paper (transfer voltage -
4.5 KV) and then passed between a heat roll whose surface was coated with PFA resin and an RTV silicone rubber roll for heat roll fixing. The fixing conditions are: the surface temperature of the heat roll is 180℃, and the pressure between the rolls is 1.0Kg/
cm, and the nip width was set to 4.0 mm. As a result, a good image without dust was obtained with an image density of 1.4 and a resolution of 10 lines/mm. Example 2 Three types (No. 2 to No. 4) of magnetic toners having different charging characteristics were manufactured under the same conditions as in Example 1 except that the blending ratio of raw materials was changed. No.2 toner has a TEC of -10μc/g and a surface potential of -50V, and No.3 toner has a TEC of -10μc/g and a surface potential of -50V.
TEC is -15μc/g, surface potential is -60V, and No. 4 toner has a TEC of -20μc/g and surface potential of -90V.
It was hot. Images were formed using these magnetic toners under the same conditions as in Example 1. Comparative Example 1 A magnetic toner (No. 5) was produced under the same conditions as in Example 1 except that a positive charge control agent (Bontron N.03 manufactured by Orient Chemical Co., Ltd.) was used as the charge control agent. This magnetic toner had a TEC of +5 μc/g and a surface potential of +30V. An image was formed using this magnetic toner under the same conditions as in Example 1. Example 3 Two types of magnetic toners (No.
6,7) were produced. No. 6 toner has a TEC of -
1μc/g, surface potential -5V, No.7 toner,
The TEC was -25 μc/g and the surface potential was -100V. Images were formed using these magnetic toners under the same conditions as in Example 1. Table 1 shows the compositions, charging characteristics, and image evaluation results of the toners of the above Examples and Comparative Examples.

[Table] From Table 1, compared to the case where positively charged magnetic toner (No. 5) was used, negatively charged magnetic toner (No. 1 to No. 5) was used.
4, 6, and 7), the image quality is improved. However, since the No. 6 toner has a slightly lower charge amount, the image density is somewhat lowered, and the No. 7 toner has a slightly higher charge amount, so some dusting occurs, but neither of them poses any practical problems. Example 4 Styrene acrylic copolymer (manufactured by Sanyo Chemical Co., Ltd.)
SBM-600) weight part and magnetite (manufactured by Toda Kogyo)
Magnetic toner (No. 8) was produced under the same conditions as in Example 1 except that parts by weight of EPT500) and parts by weight of a positive charge control agent (Bontron N.01 manufactured by Orient Chemical Co., Ltd.) were used. The TEC of this magnetic toner is +5μc/g,
The surface potential was +20V. Using the above magnetic toner, an OPC drum with negative charging characteristics was used instead of the Se drum,
Charge the surface to -800V and set the bias voltage to -
Example 1 except that the transfer voltage was 600V and +5KV.
Images were created under the same conditions as . As a result, the image density was 1.3 and the resolution was 10 lines/mm.
A good image without dust was obtained. Example 5 Three types of magnetic toners (Nos. 9 to 11) having different charging characteristics were manufactured under the same conditions as in Example 4 except that the blending ratio of raw materials was changed. No.9 toner has +TEC
8μc/g, surface potential +40V, No.10 toner:
TEC is +16μc/g, surface potential is +65V, No.11 toner has TEC +19μc/g, surface potential is +80V
It was hot. Images were formed using these magnetic toners under the same conditions as in Example 5. Comparative Example 2 Example 4 except that a negative charge control agent (Bontron E84 manufactured by Orient Chemical Co., Ltd.) was used as the charge control agent.
A magnetic toner (No. 12) was produced under the same conditions as above.
This magnetic toner had a TEC of -3 μc/g and a surface potential of -30V. An image was formed using this magnetic toner under the same conditions as in Example 4. Example 6 Two types of magnetic toners (No.
13, 14) were manufactured. No.13 toner has a TEC of +
2μc/g, surface potential +6V, No.14 toner:
The TEC was +27μc/g and the surface potential was +97V. Images were formed using these magnetic toners under the same conditions as in Example 4. The compositions, charging characteristics, and image evaluation results of the toners of Examples 4 to 6 and Comparative Example 2 are shown in Table 2.

〔Effect of the invention〕

As described above, according to the present invention, by using a charged magnetic toner having a charging characteristic with a polarity opposite to that of an electrostatic latent image, it is possible to obtain a reversed image of high quality, particularly high resolution, and without dust. Can be done.

[Brief explanation of the drawing]

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 of a toner surface potential measuring device. 1... Photosensitive drum, 3... Sleeve, 4...
Permanent magnet member, 6...Magnetic toner.

Claims (1)

[Claims] 1. An electrostatic latent image is formed on the surface of an image carrier having predetermined charging characteristics, and resin and magnetic powder are 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. Insulating magnetic toner is supplied as a main component, and by relative rotation between the sleeve and the magnetic field generating member, the magnetic toner charged to a predetermined polarity is conveyed to the gap between the image carrier surface and the sleeve, and the sleeve In a reversal development method in which a DC voltage of the same polarity as that of the electrostatic latent image is applied to cause the magnetic toner to adhere to an uncharged portion of the electrostatic latent image, the magnetic toner is a DC voltage of opposite polarity to that of the electrostatic latent image. In addition to having charging characteristics, the amount of frictional charging determined by the blow-off method is in the range of 1 to 20 μc/g in absolute value, and the absolute value of the voltage generated by the rotation of toner particles on a non-magnetic sleeve that has a permanent magnet member inside is A reversal development method characterized by using magnetic toner in the range of 10 to 90V.