JPH04282646A - Image forming method - Google Patents

Abstract

PURPOSE:To provide the image recording method high in image density and resolution not causing bleeding or fogging, and stabilized in a distribution of triboelectrification amount. CONSTITUTION:A recording electrode is arranged opposite to a recording body 1 provided with an insulating layer on the surface and movably set to form a recording zone between the insulating layer and the recording electrode 6. A magnetic toner 9 is prepared by fixing conductive particles to the surface of each toner particle containing a fixing resin, a magnetic powder, and a 0.5-2.0wt.% positively chargeable charge controller and further fixing fine silica particles onto the outside to control a bulk resistivity to <=10<6>OMEGA.cm and a surface resistivity to 10<5>-10<15>OMEGA.cm. The toner image is formed on the surface of the recording body 1 by feeding the magnetic toner 9 to the recording zone, applying recording signal voltage corresponding to an original image to the recording electrode 6.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention uses magnetic toner,
The present invention relates to a method of directly forming a visualized toner image on the surface of a recording member via a large number of needle electrodes in response to electrical signals on the image.

0002

2. Description of the Related Art Conventionally, as an image forming method in an electrophotographic apparatus, for example, a photoreceptor drum is used as an image carrier, the surface of the photoreceptor drum is uniformly charged by corona charging means, etc., and then the photoreceptor is exposed to light. The most common method is to form an electrostatic charge image on the drum surface, visualize it using a magnetic developer using a magnetic brush method, transfer it onto a recording member, and then fix it. However, in recent years, a method has been proposed in which a visible toner image is directly formed on a dielectric material made of alumite or other material using a plurality of needle electrodes without using the photoreceptor drum (for example, US Pat. 3,8
16,840).

That is, for example, an alumite layer of about 10 μm thick is coated on the outer circumferential surface of an aluminum drum, a permanent magnet is provided near the inner circumferential surface of the drum, and conductive magnetic toner is housed above the outer circumferential surface of the drum. A toner container is disposed facing the permanent magnet. A magnetic plate and a plurality of needle electrodes are provided in a part of the toner container so as to face the toner and the permanent magnet. A toner chain is formed between the alumite layer and the electrode by the magnetic field of the permanent magnet, and a portion of the toner chain is in contact with the alumite layer.

With the above configuration, if an electric signal corresponding to an image, for example, a pulse voltage of around 50 V, is selectively applied to the plurality of needle electrodes, a Coulomb force acts on the toner in contact with the alumite layer. When the drum is moved while this Coulomb force is acting, toner selectively adheres to the alumite layer constituting the outer peripheral surface of the drum, and development is performed. Therefore, a copy image can be obtained by electrostatically transferring the toner image onto plain paper or the like by conventional means and fixing the transferred toner image.

[0005]

Problems to be Solved by the Invention When a visible toner image is developed directly on a dielectric material as described above, various problems arise if conventional magnetic toner is used as is. That is, conductive magnetic toner (for example, U.S. Pat.
, No. 639,245, No. 4,189,390, No. 4,189,390, No.
4,482,623), the resistance value (bulk resistance) of this magnetic toner is low (10
(approximately 2 to 108 Ω·cm), there is a problem that the image bleeds during transfer.

On the other hand, when a semiconductive or insulating magnetic toner is used, the resistance value is high (109 to 10
(approximately 16 Ω·cm), and the image density during development is low. It is also possible to lower the internal resistance by incorporating conductive particles such as carbon black inside the toner particles of the above-mentioned high-resistance magnetic toner, but it is necessary to include a large amount of carbon black, which reduces fixing performance. There is a problem in that it is a significant hindrance.

[0007] In order to solve the above problems, as described in US Pat. No. 4,873,540, a magnetic toner in which conductive particles and an insulating material are added to the surface of the toner particles is used. It is also proposed that Although high-quality images can be obtained by such means, there are problems in that the distribution of the amount of triboelectric charge is not stable and fogging is likely to occur. On the other hand, in recent years, requirements in the field of image recording have become more severe, and it is also desired to stabilize the distribution of the amount of triboelectric charge.

The present invention solves the problems existing in the above-mentioned prior art, and provides image recording that has high image density and resolution, does not cause bleeding or fogging, and has a stable triboelectric charge distribution. The purpose is to provide a method.

[0009]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, an insulating layer is provided on the surface and a recording electrode is disposed facing a movably formed recording body. A recording area is formed between the recording electrode and the recording electrode, and this recording area is filled with a fixing resin and magnetic powder of 0.5~
It consists of toner particles containing 2.0 parts by weight of a positively chargeable charge control agent, and particles made of a conductive material are added and fixed on the surface of the toner particles, and further, fine granular silica powder is added to the outside of the toner particles. is added and fixed, and the bulk resistance is 106 Ω・
cm or less and surface resistance of 105 to 1015 Ω・cm
A technical means was adopted in which a magnetic toner of 10% was supplied, a signal voltage corresponding to an image was applied to the recording electrode, and a toner image was formed on the surface of the recording medium.

The reasons for limiting the values of the bulk resistance and surface resistance of the magnetic toner used in the present invention will be described.

During the development process, magnetic toner adheres to the recording member due to the flow of current through the toner chain formed by the magnetic field (which provides an electrical circuit), so the lower the bulk resistance, the better. Developability is improved. On the other hand, in the process of electrostatically transferring a toner image formed on a recording member, magnetic toner is attracted toward the transfer paper due to the electrical charge of the transfer paper. That is, during transfer, substantially only the chargeability of the surface of the magnetic toner particles contributes to the transferability. Note that this charging property largely depends on the surface resistance of the magnetic toner.

[0012] For these reasons, good transferability cannot be obtained unless the surface resistance is high to some extent. Therefore, considering both developability and transferability, the bulk resistance is 106
Ω・cm or less, surface resistance is 105 to 1015 Ω・cm
It needs to be within the range of A more preferable range of bulk resistance is 10 3 to 10 5 Ω·cm, and a more preferable range of surface resistance is 10 6 to 10 13 Ω·cm. The optimum range of surface resistance is 10 7 to 10 13 Ω·cm.

In order to obtain the above resistance value, the amount of conductive particles and silica powder added must be adjusted to 1% of the magnetic toner particles.
0.00 parts by weight, preferably 0.3 to 4.0 parts by weight and 0.3 to 2.0 parts by weight, respectively.

In this case, the conductive particles and silica powder may have a smaller particle size than the toner particles, but the average particle size should be 0.01 to 2.0 μm, preferably 0.03 to 2.0 μm.
It is preferable to set it to 1.0 μm. If the average particle size is too small, it is bulky and processing operations become complicated, which is inconvenient in production. On the other hand, if the average particle size is too large, it becomes difficult to uniformly add and fix the toner particles onto the surface of the toner particles, which is not preferable.

When the fixing method is a heat fixing method (oven or heated roll), the fixing resin may be, for example, the following thermoplastic resins, such as styrenes, vinyl esters, α-methylene aliphatic monocarboxylic acids, etc. esters, acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers, vinyl ketones, N-vinyl compounds, and other homopolymers, or copolymerization of two or more of these monomers in combination. copolymers or mixtures thereof can be used. In addition, non-vinyl resins such as non-vinyl thermoplastic resins such as bisphenol-type epoxy resins, oil-modified epoxy resins, polyurethane resins, cellulose resins, polyether resins, and polyester resins, or combinations thereof with vinyl resins such as those mentioned above, may be used. A mixture of can be used.

Next, when the fixing method is a pressure fixing method, for example, the following pressure-sensitive resins, ie, higher fatty acids, higher fatty acid derivatives, higher fatty acid amides, waxes, rosin derivatives, alkyd resins, etc. , epoxy-modified phenolic resin, natural resin-modified phenolic resin, amino resin, silicone resin, urea resin, copolymerized oligomer of acrylic acid or methacrylic acid and long-chain alkyl methacrylate, long-chain alkyl acrylate, polyolefin, ethylene/vinyl acetate copolymer Examples include ethylene/vinyl alkyl ether copolymers, maleic anhydride copolymers, 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 other than polyolefins must have a glass transition point of 40°C. Resins or resin mixtures exceeding 100% are effective.

Next, if the content of the positively chargeable charge control agent is less than 0.5 parts by weight per 100 parts by weight of toner particles, no effect of stabilizing the charge amount distribution can be expected;
On the other hand, if the amount exceeds 2.0 parts by weight, the entire toner particles will be positively charged, making it difficult to develop and reducing the image density, which is disadvantageous.

As the magnetic powder, compounds or alloys containing iron such as ferrite and magnetite, and ferromagnetic elements such as cobalt or nickel can be used. In order to uniformly disperse the magnetic powder in the magnetic toner, it is desirable to form the magnetic powder to have an average particle size of 0.01 to 3 .mu.m. The content may be in the range of 10 to 80% by weight, preferably 40 to 75% by weight.

[0020]Also, various additives such as pigments and dyes used in general dry developers may be included as components other than those mentioned above, but in order not to reduce fixing properties, the amount added should be 10% by weight or less. It is better to

The magnetic toner in the present invention is produced, for example, as follows. That is, first, the raw materials are heated and kneaded, cooled and solidified, then pulverized, and then classified to obtain magnetic toner particles of a predetermined particle size. Particles made of an electrically conductive material are externally added to the surface of the magnetic toner particles, and the particles made of the electrically conductive material are fixed by heat treatment. Furthermore, after silica powder is externally added, the particles are fixed by heat treatment.

[0022]

[Operation] With the above configuration, the bulk resistance and surface resistance of the toner particles can be set within a predetermined desired range,
Moreover, the distribution of the amount of charge is stabilized, and a clear image can be directly formed on the recording medium.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cross-sectional view showing an example of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a recording body, which is formed into a hollow cylindrical shape and is arranged to be rotatable in the direction of arrow A by a drive means (not shown). Note that the recording body 1 is constituted by a base body 2 made of a conductive material and an insulating layer 3 provided on the surface thereof. This insulating layer 3 can be formed by subjecting the surface of the base 2 to an alumite treatment when the base 2 is made of, for example, aluminum or an alloy thereof.

The thickness of the insulating layer 3 is generally 2 to 10
Formed to 0 μm. A hopper 4 is provided facing the surface of the recording medium 1 and stores magnetic toner 9 therein. Next 6
is a recording electrode, which is provided on the downstream side in the rotational direction of the recording body 1;
A recording area Z is formed between the tip of the recording electrode 6 and the surface of the recording body 1.
form. The recording electrodes 6 are formed by a thick film process on the substrate 5 made of an insulating material such as ceramics, and are arranged in rows in the axial direction of the recording medium 1.

The tip of the substrate 5 on the recording area Z side is formed into a knife edge shape, and a blade 7 made of a magnetic material such as an iron plate is fixed to this portion. The blade 7 is provided to concentrate the magnetic flux lines from the permanent magnet 10 fixed inside the recording medium 1 on the tip of the recording electrode 6.

Next, reference numeral 8 denotes a drive circuit, which is electrically connected between the recording electrode 6 and the substrate 2 so as to be able to apply a voltage corresponding to an image between them. 12 is a conductive rubber roller that transfers the toner image formed on the recording medium 1 to the recording sheet 1.
It is electrically connected to a bias voltage source 15 for transferring to 1. 13 and 14 are fixing rollers, respectively.

The operation of the above configuration will now be described. First, the magnetic toner 9 supplied from the hopper 4 to the recording area Z continues in a chain shape along the magnetic flux lines generated from the permanent magnet 10, and forms a chain between the tip of the recording electrode 6 and the surface of the recording medium 1, that is, the recording surface. A toner chain is formed so as to close an electrical gap formed therebetween.

Next, when a voltage is selectively applied to the recording electrode 6 via the drive circuit 8 in accordance with the image signal, the toner chain comes into contact with the recording surface of the toner chain that is in contact with the recording electrode 6 to which this voltage has been applied. Charge is injected into the magnetic toner 9 by a current flowing through the toner chain. At the same time, charges of opposite polarity to those injected into the magnetic toner 9 are induced at the boundary between the base 2 and the insulating layer 3 of the recording medium 1, and these two charges attract each other due to Coulomb force. Therefore, when the recording body 1 rotates in the direction of the arrow A, the magnetic toner injected with charge is separated from the toner chain, and a toner image is formed on the recording body 1 moving in the direction of the arrow A.

On the other hand, the remaining toner chain is formed again by the magnetic toner 9 supplied from the opposite side of the recording electrode 6 as the recording medium 1 rotates. Note that when the recording medium 1 is rotated, a part of the magnetic toner 9 adheres to the surface of the recording medium 1 even though no charge is injected therein.
The toner image may be conveyed to a transfer section, that is, a portion adjacent to the recording medium 1 and the conductive rubber roller 12. The magnetic toner that undesirably adheres to the surface of the recording medium 1 in this way is
Since no attraction occurs due to Coulomb force with the recording medium 1, it can be easily removed by providing an appropriate magnetic attraction means downstream of the recording area Z in the rotational movement direction of the recording medium 1.

Next, when the toner image on the recording medium 1 reaches the transfer section, a bias voltage source 1 is applied to the conductive rubber roller 12.
5, a voltage of opposite polarity to the charge of the magnetic toner is applied,
Due to the electric force and pressure generated thereby, the toner image is transferred onto the recording sheet 11 moving in the direction of arrow B. Then, the recording sheet 11 passes between fixing rollers 13 and 14 to fix the toner image.

In order to obtain a high-quality image in the image recording method described above, as a result of a study focusing on magnetic toner in particular, it was found that the surface resistance of the magnetic toner should be set within a specific range as well as the bulk resistance of the magnetic toner. It was found that good results could be obtained. The results are described below.

Styrene-n-butyl methacrylate copolymer
38 parts by weight (Mw=25×104, Mn=
3×104) Polypropylene

2 parts by weight (Viscol 550P manufactured by Sanyo Chemical) Magnetite
60 parts by weight (EPT500 manufactured by Toda Kogyo) Charge control agent (a) Oleic acid modified nigrosine dye
1 part by weight (Positively chargeable Orient Chemical Oil Black BY)
(b) Oleic acid modified nigrosine dye
2 parts by weight (Positively chargeable Orient Chemical Oil Black BY) (c)
Chromium-containing azo dye
1 part by weight (negatively chargeable
Orient Chemical Bontron S-31) (d
) The amount of the charge control agent blended is based on the total amount (100 parts by weight) of the styrene-n-butyl methacrylate copolymer, polypropylene, and magnetite.

The raw materials of the above composition were kneaded for 30 minutes in a kneader equipped with heating rollers, cooled and solidified, and then pulverized and classified to adjust the particle size to 10 to 44 μm. next
2 parts by weight of carbon black (#44 made by Mitsubishi Kasei) and 1 part by weight of silica (R972 made by Nippon Aerosil) were individually added and fixed on the surface of the above toner particles in a hot air flow at 120°C to produce four types of magnetic toner. I got it. The bulk resistance value and surface resistance value of these four types of magnetic toners A to D (corresponding to the charge control agents a to d) were measured and found to be 10 5 Ω·cm and 10 8 Ω·cm.

In this case, the bulk resistance value of the magnetic toner is determined by weighing an appropriate amount (10-odd mg) of the sample and filling it into a hollow cylinder made of Teflon (trade name) with an inner diameter of 3.05 mm and equipped with an improved dial gauge. .1kg load, DC40
The resistance value was calculated by applying an electric field of 0.00 V/cm and measuring. Yokogawa Hewlett-Packard 432 was used to measure resistance.
A Type 9 insulation resistance meter was used. In addition, the surface resistance value was determined by filling a container with a sample, inserting a pair of 1 cm2 electrode plates, facing each other with a 1 cm interval, and applying DC voltage with virtually no load.
The measurement was performed by applying a voltage of 10V.

Next, developing and fixing conditions will be described. A dielectric drum serving as a recording medium was formed by coating an alumite layer with a thickness of 10 μm on the outer surface of an aluminum pipe with an outer diameter of 40 mm. Note that a rare earth cobalt magnet (H18-B manufactured by Hitachi Metals) was installed in this dielectric drum. Next, the gap between the needle electrode serving as the recording electrode and the alumite layer was set to 0.1 mm, and a pulse voltage of +50 V was applied to the needle electrode to obtain a toner image. After that, transfer it to plain paper (
-100V applied to conductive rubber roller), 180°C 1.
Hot roll fixation was carried out with a linear pressure of 0 kg/cm.

FIGS. 2 to 5 are diagrams showing the distribution of the charge amount of toner in the embodiments of the present invention, and show the relationship between the charge amount per particle size and the frequency. Note that FIGS. 2 to 5 correspond to the magnetic toners A to D, respectively. in this case,
The amount of charge on the toner is measured using the laser Doppler method.
A yeast part analyzer (manufactured by Hosokawa Micron) was used.

FIGS. 2 and 3 correspond to magnetic toners A and B, respectively, both of which contain a positively chargeable charge control agent. In both figures, the distribution of the amount of charge is approximately balanced between positive and negative charges, with many cases being slightly on the positive side. In this case, it was confirmed that the image was free from fog and had high image density and resolution.

Next, FIG. 4 shows a sample containing a negatively chargeable charge control agent, and as is clear from FIG. 4, the distribution is slightly biased toward the negative charge side. In this case, although no fogging occurred in the obtained image, a phenomenon was observed in which the image density and resolution were slightly lower than those shown in FIGS. 2 and 3.

In contrast to the above-mentioned toner, the toner shown in FIG. 5 is a conventional toner in which no charge control agent is contained in the magnetic toner, and the charge amount distribution is largely biased toward the negative charge side. In addition, fogging was observed in the obtained images.

In the above embodiment, an example was described in which oleic acid-modified nigrosine was used as the positively chargeable charge control agent, but other nigrosine dyes such as oil black BY, SY, etc. may also be used. Furthermore, although an example in which carbon black is used as the conductive material constituting the magnetic toner is shown, the material is not limited to the above materials, and other conductive materials (for example, metal powders such as Ni and Al) can be used. Of course, it can be selected as appropriate as long as it does not cause a chemical reaction with the magnetic toner and does not inhibit the properties of other constituent materials.

[0041]

Effects of the Invention Since the present invention has the structure and operation as described above, both image density and resolution are high in a method of directly forming a toner image on a recording medium using a recording electrode. , and the charge amount distribution is stable,
This has the effect that it is possible to obtain high-quality images that are free from bleeding or fog and have good fixing properties.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the distribution of the amount of charge of toner in an example of the present invention.

FIG. 3 is a diagram showing the distribution of toner charge amount in an example of the present invention.

FIG. 4 is a diagram showing the distribution of the amount of charge of toner in an example of the present invention.

FIG. 5 is a diagram showing the distribution of the amount of charge of toner in an example of the present invention.

[Explanation of symbols]

1 Recording body 6 Recording electrode 9 Magnetic toner

Claims (1)

[Claims] 1. A recording area is formed between the insulating layer and the recording electrode by arranging a recording electrode facing a movably formed recording body with an insulating layer provided on the surface, and a recording area is formed between the insulating layer and the recording electrode. , fixing resin and magnetic powder 0.5 to 2.0
consisting of toner particles containing part by weight of a positively chargeable charge control agent, particles made of a conductive material are added and fixed on the surface of the toner particles, and further, fine granular silica powder is added and fixed on the outside of the toner particles. Then, a magnetic toner having a bulk resistance of 106 Ω·cm or less and a surface resistance of 105 to 1015 Ω·cm is supplied, and a signal voltage corresponding to an image is applied to the recording electrode to form a toner image on the surface of the recording medium. An image recording method characterized by forming an image.