JP2769828B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention visualizes an electrostatic charge image, and continuously or superimposes or synthesizes an image twice on the front and back surfaces of a transfer material to form an image twice. The present invention relates to an image forming method for forming.

[Prior Art] A method of visualizing an electrostatic latent image using a toner is roughly classified into a liquid developing method using a developer in which various pigments and dyes are dispersed in an insulating organic liquid, and a resin developing method. There is a dry development method in which a toner in which a colorant or the like is dispersed is used alone or as a developer mixed with a carrier. The present invention relates to a method in which an image is formed on both sides of a transfer material by a dry development method, or an image is formed on one side of the transfer material by multiple copying.

Multiple copying in this case is a method in which a fixed image is formed by temporarily making a copy on one side of a transfer material, and then changing the original and copying again on the same transfer material to obtain a fixed image. This is used, for example, when it is desired to fit another document into a single sheet to obtain an image, or when it is desired to obtain a color image with color toner on the same copy surface.

When an image is formed by multiplex copying on both sides or one side of a transfer material according to a conventional technique, a toner image transferred onto the transfer material is once subjected to heat, pressure, etc., to obtain a fixed image once. Then, a new toner image is transferred to the back surface or the same surface of the fixed image, and fixing is performed again by applying heat and pressure.

For this reason, the first formed toner image is
Heat, pressure, and the like are applied, causing inconveniences such as crushing, scattering, and fogging of the line image.

When images are continuously formed on both sides of a transfer material or on one side by multiplex copying, a plurality of transfer materials having a toner image transferred on one side of the transfer material are placed on a refeeding table. ,
The transfer material is pressed by the re-feed roller, and the transfer material is sequentially sent out by the rotation of the re-feed roller.

In this case, the transfer material is contaminated due to friction between the toner-adhering surface and the transfer material due to pressure bonding by the re-feed roller.

Further, when the re-feeding roller comes into contact with the toner adhering surface, roller contamination occurs, which is transferred to the transfer material, and there is a disadvantage that the transfer material is contaminated.

On the other hand, conventionally, as a developing method using a magnetic toner, a developing method using a conductive magnetic toner disclosed in U.S. Pat. No. 3,909,258 and the like is known and widely used.

However, such a developing method requires that the toner is essentially conductive, and the conductive toner uses an electric field to transfer the toner image on the latent image holding member to the final image supporting member (for example, plain paper). It was difficult to perform transcription (although the cause has not been fully elucidated).

The present applicant has previously proposed a new developing method which solves such a problem of the conventional developing method using a one-component magnetic toner (for example, JP-A-55-18656 and JP-A-55-186).
No. 59). In this method, an insulating magnetic toner is uniformly applied on a cylindrical toner carrier having a magnet therein, and the applied toner is brought into contact with the latent image holding member without being brought into contact with the latent image holding member for development. As a method of forming a toner layer on a toner carrier, there is a method of using a coating blade at an outlet of a toner container, and a magnetic material is provided at a position facing one magnetic pole of a fixed magnet provided in the toner carrier. A toner blade along the line of magnetic force between the magnetic pole and the magnetic material blade, and cutting the toner at the edge of the blade tip to control the thickness of the toner layer using the action of magnetic force. (See, for example, JP-A-54-43037).

During development, a low-frequency alternating voltage is applied between the toner carrier and the base conductor of the latent image carrier, and the toner is reciprocated between the toner carrier and the latent image carrier to eliminate ground fog. In addition, it is excellent in reproduction of gradation and can perform favorable development without thinning of the image edge. In this developing method, electrostatic transfer is easy because the toner is an insulator.

In such an image forming process, factors that regulate the amount of the toner on the toner after the transfer and before the fixing are as follows: (1) The toner carrier facing the electrostatic latent image carrier in the development stage (2) Contrast between the potential of the latent image on the electrostatic latent image carrier and the potential of the toner carrier, (3) The electrostatic latent image carrier and the toner carrier during development In the developing process in which an oscillating electric field is applied during the development, the intensity, frequency and waveform of the oscillating electric field, (4) the distance between the electrostatic latent image carrier and the toner carrier, and (5) the electrostatic latent image carrier The ratio between the moving speed and the moving speed of the toner carrier can be considered.However, it is generally necessary to set these conditions so as to keep the amount of toner applied on the transfer material after transfer and before fixing low. It is difficult to obtain a high image density, which is inconvenient.

The amount of toner on the transfer material after transfer and before fixing
Although transfer conditions also contribute significantly, controlling the transfer efficiency and suppressing the amount of toner applied on the transfer material not only does not provide clear images and high-density images, but also reduces the electrostatic charge latency. This may cause inconvenience in the step of cleaning the image carrier.

As described above, in the conventional magnetic toner, even when the image forming process is selected, the applied amount of the toner on the transfer material is 1.2 m / cm ^2.
It has been difficult to obtain a sufficiently high image density and clear image quality while controlling to 0.3 mg or less at g or less.

[Problems to be Solved by the Invention] An object of the present invention is to solve problems such as line image collapse and transfer material contamination when an image is formed by multiplex copying on both sides or one side of a transfer material as described above. To provide an improved image forming method.

Another object of the present invention is to provide an image forming method capable of obtaining a high image density with a small amount of toner consumption while solving the above-mentioned problems.

It is a further object of the present invention to provide an image forming method which is excellent in fine line reproducibility and gradation reproducibility and can obtain sharp image quality while solving the above-mentioned problems.

Means and Action for Solving the Problems In order to obtain a high image density with a small amount of applied toner, the present inventors used a magnetic toner having a specific particle size distribution different from the conventional one, and The present invention has been accomplished after intensive studies, with a focus on the regulation of

That is, the present invention develops an electrostatic image carrier carrying an electrostatic latent image with magnetic toner, transfers the toner image on the electrostatic image carrier to a transfer material, and removes the toner image on the transfer material. After the fixing, the transfer material is multiplied on the surface of the transfer material with the toner image, or on the back surface of the transfer material with the toner image, by repeating the same process once or twice or more. In the image forming method of forming an image on one side of the transfer material or forming images on both sides of the transfer material, the magnetic toner contains 12 to 60% by number of toner particles having a particle diameter of 5 μm or less. Toner particles having a particle size of 16 μm or more.
0% by volume or less, the magnetic toner has a volume average particle size in the range of 5 to 10 μm, the particle size distribution of the magnetic toner satisfies the following general formula (1), and is obtained after transfer and before fixing. 0.3mg in toner amount on the transfer material is 1 cm ² per 1.2mg or less
The present invention relates to an image forming method characterized by the above.

According to the conventional magnetic toner, in order to obtain a high-density image, the overlapping of the toner on the transfer material is coarse, so that the amount of toner to be applied must be increased and the height must be increased. In general, in the latent image on the electrostatic latent image carrier, the electric field intensity at the edge around the latent image is higher than that at the center of the latent image, so that the amount of toner applied inside the latent image becomes thinner than at the edge. easy. For this reason, even if the toner developability is slightly reduced due to environmental fluctuations or long-term use, so-called hollowing in which the toner is slightly applied to the inside of the latent image may occur, and the image density may appear to be thin. In order to prevent this, the amount of toner applied on the transfer paper must be further increased.
Contamination due to crushing by the fixing roller, and poor fixing due to sublime, and particularly in the case of a positively charged toner, easily adhere to the negatively charged fixing roller and stain the roller.

In the present invention, the amount of applied toner on the transfer material is 1c.
m ² per 1.2mg or less 0.3mg or more, or less preferably 1.0mg
With 0.4 mg or more, more preferably 0.8 mg or less and 0.4 mg or more, it is possible to obtain an image with excellent line reproducibility, with extremely little line image collapse even after multiple fixings, and refeeding It is possible to improve the transfer paper stain and the re-feed roller stain at the time.

If the amount of toner on the transfer material exceeds 1.2 mg / cm ² , for example, in the case of double-sided copying, the first side is once fixed with a hot roll, then the second side is re-fed and the toner image is transferred to the second side In the heat roll fixing step, the first side undergoes the heat roll fixing twice, resulting in a marked collapse of the line image on the first side. When a plurality of double-sided or multiple copies are to be obtained continuously, the transfer material that has undergone the heat roll fixing on the first side is stocked on a re-feeding table, and pressed and rotated by a re-feeding roller. Although the sheet is fed again, the line image after the heat roll fixing on the first sheet causes remarkable toner irregularities on the transfer material due to the large amount of toner applied, and this causes the transfer material and the re-feeding during refeeding. This may cause the feed roller to become dirty.

If the amount of toner applied on the transfer material is less than 0.3 mg per 1 cm _2, it is difficult to obtain a high-density image.

In order to embody the present invention, it is important to cover the transfer material with the toner particles as uniformly and as possible in a single layer as possible and to prevent the transfer material from being disturbed or deformed by fixing. However, there has not been a toner and an image forming method that can achieve such an object. The present inventors have obtained a high image density while controlling the amount of toner applied on the transfer material to 1.2 mg / cm ² or less, and have achieved a higher image density than the magnetic toner that has been conventionally used in order to achieve the object of the present invention. As a result of intensive studies, the use of a magnetic toner having a small particle size is considered. As a result, 12 to 60% of toner particles having a particle size of 5 μm or less are contained, and 2.0% by volume or less of a toner particle having a particle size of 16 μm or more. The volume average particle diameter is in the range of 5 to 10 μm, and the particle size distribution is represented by the general formula 0.25 ≦ S / ▲ ▼ ≦ 0.45
(However, S: standard deviation of magnetic toner number distribution, ▲
▼: By using a magnetic toner that satisfies the number average particle diameter (μm) of the magnetic toner, line images are crushed and scattered even in multiplex / double-sided copying while exhibiting high image density, sharp image quality, and excellent transferability. It has been found that emphasis on fog and contamination of the transfer material during refeeding can be overcome.

The magnetic toner of the present invention having the above-mentioned particle size distribution provides an image with high density, sharpness, and excellent fine line reproducibility and gradation even though the amount of toner applied on the transfer paper is kept low. As to the reason, the present inventors have made the following studies after diligent research.

In the magnetic toner according to the present invention, the volume average particle diameter is 5 to 5.
One characteristic is that the particle diameter is 10 μm, which is smaller than many toners used so far. FIG. 1 and FIG. 2 show the comparison between the particle diameters of many conventional magnetic toners (volume average particle diameter of 10 to 15 μm) and the particle diameters of the magnetic toner in the present invention.
As shown in the figure, when trying to obtain the same image density, the toner 2 having a large particle diameter has to be placed bulky to fill the gap between the toner particles. While the amount becomes large (thickness W ₁ ),
With the toner 3 of the present invention having a small particle diameter, the toner particles form a thin and uniform toner layer (thickness W ₂ ) on the transfer material 4 with a small amount of applied toner and no gap.

Therefore, the magnetic toner in the present invention can be covered with a thinner layer on the transfer material, very densely and uniformly, and can obtain a high-density image as well as a fixing roller and an electrostatic roller. There is little disturbance of the toner layer due to external pressure such as force.

One feature of the toner of the present invention is that 12 to 60% by number of toner particles having a particle size of 5 μm or less are contained. Conventionally, it has been considered that toner particles having a particle size of 5 μm or less have difficulty in controlling the charge amount, impair the fluidity of the toner, and need to actively reduce the amount of the toner particles as a component that causes image fogging. However, according to the study of the present inventors, toner particles of 5 μm or less are very rich in developability, and the toner particles of 5 μm or less are smoothly supplied to the development of the latent image on the electrostatic latent image carrier. In this case, the image is faithful to the latent image, and an image with excellent reproducibility can be obtained without protruding from the latent image.

Here, when the number of toner particles having a particle diameter of 5 μm or less is 12% by number or less, the amount of toner particles effective for high image quality is small. In particular, as the toner is used by continuing copy or printout, the effective toner particles As the components decrease, the balance of the particle size distribution of the toner as shown in the present invention deteriorates, and the image quality gradually decreases. Also,
When the content is more than 60% by number, toner particles are likely to aggregate with each other, resulting in a toner mass larger than the original particle size, resulting in rough image quality, reduced resolution, or an edge portion between the latent image and the interior. And the density difference with the image becomes large, and the image tends to be slightly hollow.

On the other hand, when the amount of toner particles having a size of 16 μm or more is more than 2.0% by volume, not only does it hinder the reproduction of fine lines, but also in the transfer, the thin layer surface of the toner particles developed on the photoreceptor has
The presence of coarse toner particles of μm or more protrudes, causing the delicate state of contact between the photoconductor and the transfer paper via the toner layer to be irregular, causing fluctuations in the transfer conditions and causing poor transfer images. This is a factor that occurs. The volume average particle diameter of the toner is 5 to 10 μm, and this value cannot be considered separately from the above-mentioned respective constituent elements. If the volume average particle diameter is less than 5 μm, in applications having a high image area ratio such as a graphic image, a problem that the amount of toner applied on the transfer paper is small and the image density is low tends to occur. This is considered to be due to the same reason as described above for lowering the density inside the edge portion of the latent image. If the volume average particle size exceeds 10 μm, the resolution is not good, and if the use is continued at the beginning of copying, the image quality is likely to deteriorate, and the amount of toner on the transfer paper increases. After the heat roll fixing, the line image is crushed.

In the magnetic toner according to the present invention, the particle size distribution has a general formula of 0.25 ≦ S / ▲ ▼ ≦ 0.45 (where S represents the standard deviation of the number distribution of the magnetic toner, and ▲ represents the number average particle size (μm)). Is one feature. As described above, the magnetic toner in the present invention has a volume average particle diameter as small as 5 to 10 μm as compared with the magnetic toners which have been widely used in the past, and the toner particles having a volume average particle diameter of 5 μm or less are 12 to 60% by number. It is characterized by containing a lot, but also S / ▲ ▼
It has been found that better results can be obtained by regulating the particle size distribution and making the particle size distribution appropriate for each number average particle size. S / ▲ ▼ indicates the spread of the particle size distribution. The smaller, the sharper, the larger, the broader.

If the coefficient of variation of the number distribution of the magnetic toner containing 12 to 60% by number of toner particles having a volume average particle size in the range of 5 to 10 μm and 5 μm or less is 0.25 or less, the reason is not clear, The thickness of the toner coat layer on the toner carrier increases, and the thickness of the toner layer on the photoconductor and transfer paper increases, making it difficult to effectively form a uniform and thin layer.

When the coefficient of variation of the number distribution is 0.45 or more, the particle size distribution becomes broad, so that the chargeability of the toner particles is likely to be non-uniform, so that the toner particles at the developing position on the toner carrier are disturbed. Further, the toner layer on the photoreceptor and transfer paper is coarse and easily disturbed, and the object of the present invention cannot be sufficiently achieved.

The present invention achieves the object by appropriately regulating the magnetic toner having the above-described features, and further, it is possible that the magnetic toner in the present invention is combined with appropriate image forming process conditions. Is more preferable.

First, the strength of the magnetic pole of the toner carrier facing the electrostatic latent image carrier is preferably 600 to 1200 G, and more preferably 800 to 1000 G. It should be noted that the strength of the magnetic pole at the developing position changes the appropriate condition depending on the content ratio of the magnetic substance in the magnetic toner. If the magnetic force of the developing magnetic pole is too weak, the toner is excessively applied on the electrostatic latent image carrier, and not only the amount of applied toner on the transfer material is excessive, but also the fog toner is significantly increased. If the magnetic force is too strong, the magnetic attraction acting as a binding force for the development of the magnetic toner becomes large, so that enough toner to obtain a sufficient image density is supplied onto the latent image on the electrostatic latent image carrier. Not done. Further, the bonding force between the toner particles at the ears (magnetic brush) of the magnetic toner at the developing position becomes too strong, resulting in a rough image. Since the magnetic toner in the present invention contains a large amount of toner particles having a very large developing ability and a small particle size, the magnetic force of the developing magnetic pole is increased as compared with the conventional magnetic toner, and the developability is suppressed to some extent. However, in order to take advantage of the magnetic toner of the present invention such as line reproducibility faithful to a latent image and excellent fine line reproducibility and gradation reproducibility, the toner spike at the developing magnetic pole position must be used. It is preferable to select the strength of the magnetic pole so that the standing length is 70 to 150 μm.

Further, since the magnetic toner in the present invention has a relatively small particle size, even if the particle size distribution is defined as in the present invention, the charge amount of the toner particles tends to be excessive under a low humidity environment or the like. The toner coat on the carrier may become unstable. Therefore, as a means for stabilizing the toner coat on the toner carrying member, it is necessary to define a magnetic regulating force acting on the toner layer between the toner carrying member and the toner layer regulating member (blade). That is, it is necessary to appropriately select the gap distance between the toner carrier and the toner layer regulating member, the strength of the magnetic force at the position of the toner carrier opposite the toner layer regulating member, and the like. When the toner layer regulating member is a magnetic blade, the gap distance between the toner layer regulating member and the toner carrier is preferably 200 to 300 μm. When using a blade made of an elastic material or the like, the pressing pressure against the toner carrier may be appropriately selected.

Further, the surface property of the toner carrier also contributes to the stability of the toner coat. When a cylindrical sleeve made of stainless steel is used as the toner carrier, when the surface of the sleeve is mirror-finished, the amount of toner coating per unit area of the sleeve increases, and uneven charging of toner particles due to environmental conditions and the like increases. Accordingly, the toner coat unevenness of the sleeve is easily caused. In the case of a developing sleeve in which the sleeve surface is made into an irregular rough surface composed of countless fine cuts or random projections by sandblasting with irregular shaped particles, the reason is not necessarily clear, but the toner coat amount per sleeve unit area Is relatively low. That is, by providing appropriate irregularities on the surface of the toner carrier, the amount of toner coating on the toner carrier can be adjusted. However, depending on the unevenness of the surface of the toner carrier, the toner component may adhere to the surface of the toner carrier, thereby preventing the toner particles from being uniformly charged.

Next, the potential difference between the potential of the latent image on the electrostatic latent image carrier and the potential of the toner carrier is set. The magnetic toner in the present invention has extremely excellent developability, and the potential difference is 300 V or less. Although it is possible to obtain a clear image with high image density over a long period of use, the potential difference must be 350 V or more in order to obtain a clearer image by taking advantage of excellent gradation reproducibility. preferable.

Further, in the process of applying an oscillating electric field between the electrostatic latent image carrier and the toner carrier and performing development, when the oscillating electric field is given by a synergistic AC and DC bias,
The DC bias is related to the potential of the toner carrier and is selected so that the potential difference between the previous latent image and the toner carrier can be appropriately set. It is desirable that the AC bias has a higher frequency than that of the conventional magnetic toner. These developing bias conditions also vary in appropriate conditions depending on the magnetic substance content in the magnetic toner, but the magnetic substance content was selected so that a high image density was obtained, the fog toner was extremely small, and a sharp image was obtained. If the proper AC bias is 500-2000V
pp, frequency 1500 ~ 3000Hz (800 ~ 2 with conventional magnetic toner
200Hz is the appropriate range). As a waveform of the AC bias, a sine wave or a rectangular wave is preferable.

Next, the distance between the electrostatic latent image carrier and the toner carrier is too small. If the distance is too small, the charge on the latent image leaks onto the toner carrier, causing the latent image to be disturbed. It becomes an image. On the other hand, if the size is too large, the transfer of the toner particles from the toner carrier to the latent image is not performed smoothly, resulting in a rough image lacking sharpness. The distance is preferably from 200 to 500 µm, more preferably from 250 to 400 µm.

Further, it is preferable that the ratio of the moving speed of the toner carrier to the moving speed of the electrostatic latent image carrier is larger than that of the conventional magnetic toner. This is because the magnetic toner in the present invention has a relatively short spike of toner particles at the developing position magnetic pole of the toner carrier as described above, and the toner coat layer on the toner carrier has a smaller thickness than the conventional magnetic toner. Therefore, it is intended to supply a necessary amount of toner to the developing area, and the ratio is preferably 120 to 300%. If it is less than 120%, it is difficult to obtain a high image density, and if it is more than 300%, not only too much toner on the transfer material due to too much toner on the latent image and the thinning of the fine lines become a problem. Inconveniences such as an increase in fog toner and contamination of the developing system and the transfer material due to scattering of toner particles occur.

Of course, the above-mentioned various conditions of the development process should not be considered individually, but should be set in balance with each other. In the present invention, the amount of toner on the latent image is adjusted by matching the various conditions of the developing process with the magnetic toner, thereby regulating the amount of toner on the transfer material.

As described above, while the development process conditions ensure the high image density, the regulation of the amount of toner on the latent image has already been regulated in accordance with the regulation of the amount of toner on the transfer material. It is desired that the toner image is selected so as to exhibit good transfer efficiency so that the toner image on the latent electrostatic image bearing member can be reproduced as faithfully as possible.

For example, after developing an electrostatic latent image into a toner image, the transfer device applies a charge of the opposite polarity to the toner on the back surface of the transfer material that is in close contact with the toner image, and holds the toner image by electrostatic attraction. The toner image is transferred to a transfer material by a method of separating from the body, and immediately thereafter, an AC corona or the like is applied to the back surface of the transfer material by a separating device to remove the charge from the transfer material and separate the transfer material from the image carrier. When electrostatic separation is used, it is known to provide an AC corona or the like to a toner image on a latent image carrier and to provide an appropriate charge in order to improve transferability after development and before transfer. I have. However, even after the toner image has been transferred onto the transfer material, the toner particles continue to retain a high charge, which causes problems such as scattering at the time of fixing with the heat roll. Although the reason for the magnetic toner in the present invention is not clear, the charge amount of the toner particles on the latent image suitable for transfer and electrostatic separation is smaller than that of the conventional magnetic toner. It is not necessary or extremely small to apply a charge to toner particles on the latent image, so that scattering at the time of fixing with a hot roll is minimized,
In addition, it has sharp image quality and enables faithful transfer down to fine lines. Also, the transfer efficiency is very excellent.

Although the transfer efficiency varies a little depending on the electrical resistance of the transfer material, environmental conditions, etc., the transfer efficiency is very stable and gives a good value of 90% or more. The regulation of the amount is linked to the regulation of the amount of toner applied on the transfer material without being damaged by the transfer.

In the magnetic toner according to the present invention, a charge control agent is blended with toner particles (internal addition) or mixed with toner particles (external addition).
It is preferable to use them. The charge control agent makes it possible to control the amount of charge optimally according to the development system.

In particular, in the present invention, since a more uniform chargeability of the toner particles is required, the charge control agent may be used as fine particles to improve the dispersibility of the charge control agent in the toner particles or between the toner particles. preferable. In this case, the number average particle diameter of the charge control agent is specifically preferably 4 μm or less, more preferably 3 μm or less.

Examples of the positive charge controlling agent used in the present invention include denatured products such as nigrosine and fatty acid metal salts; and quaternary ammonium salts such as tributylbenzylammonium-1-hydroxy-4-naphthosulfonate and tetrabutylammonium tetrafluoroborate. Diorganotin oxides such as dibutyltin oxide, dioctyltin oxide and dicyclohexyltin oxide; diorganotin borates such as dibutyltin borate, dioctyltin borate and dicyclohexyltin borate can be used alone or in combination of two or more.
Among these, charge control agents such as nigrosine and quaternary ammonium salts are particularly preferably used.

Also, the general formula R ₁ : H, CH ₃ R ₂ , R ₃ : a substituted or unsubstituted alkyl group (preferably C ₁
To C ₄ ): A homopolymer of a monomer represented by the following formula: or a copolymer with a polymerizable monomer such as styrene, an acrylate or a methacrylate as described above can be used as a positive charge control agent. In these cases, these charge control agents also have an action as (all or part of) the binder resin.

As the negative charge controlling agent that can be used in the present invention, for example, organometallic complexes and chelating compounds are effective, and examples thereof include aluminum acetylacetonate, iron (II) acetylacetonate, and 3,5-ditert-butyl. There are chromium salicylate and the like, particularly preferably an acetylacetone metal complex, a salicylic acid-based metal complex or salt,
Particularly, a salicylic acid-based metal complex or a salicylic acid-based metal salt is preferable.

When internally added to the toner, such a charge control agent is used in an amount of 0.1 to 20 parts by weight (more preferably, 0.2 to 10 parts by weight) based on 100 parts by weight of the binder resin.
Parts by weight).

The magnetic toner in the present invention contains a magnetic material.
In the present invention, uniform chargeability of the magnetic toner is particularly required. The good dispersibility of the magnetic material in the magnetic toner contributes not less to the uniform chargeability of the toner. Therefore, it is desired that the magnetic material has an average particle size of about 0.1 to 1 μm, preferably about 0.1 to 0.5 μm.

Examples of the magnetic material contained in the magnetic toner according to the present invention include iron oxides such as magnetite, γ-iron oxide, ferrite, and iron-rich ferrite; metals such as iron, cobalt, and nickel; or these metals and aluminum; cobalt,
Examples include alloys with metals such as copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures thereof.

The amount contained in the magnetic toner of these ferromagnetic substances is 40 to 200 parts by weight, preferably 50 to 150 parts by weight relative to 100 parts by weight of the resin component, more preferably 100 parts by weight of the resin component. , 65 to 100 parts by weight. When the amount of the magnetic material is small, the thin lines are crushed and scattered due to excessively loaded toner particles, and the resolution is deteriorated. These problems become more remarkable after a plurality of heat roll fixings.

On the other hand, if the amount of the magnetic material is too large, the image lacks sharpness such as a low image density and breaks in fine lines.

As the binder resin used in the toner of the present invention, the following binder resins for toner can be used.

For example, polystyrene, poly-p-chlorostyrene,
Styrenes such as polyvinyltoluene and their substituted homopolymers; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, styrene -Methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone Styrene-based copolymers such as copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers; polyvinyl chloride, phenolic resins, naturally-modified phenolic resins, and natural-resin-modified malees Acid resin, Acrylic Resins, methacrylic resins, polyvinyl acetate, silicone resins, polyester resins, polyurethane, polyamide resins, furan resins, epoxy resins, xylene resins, polyvinyl butyral, terpene resin, coumarone-indene resins, and petroleum resins.

In the heat and pressure roller fixing method in which little oil is applied, so-called offset development in which a part of the toner image on the toner image support member is transferred to the roller, and adhesion of the toner to the toner image support member are important issues. is there. Toners that fix with less heat energy tend to block or cake during storage or in a developing unit, and these problems must also be considered at the same time. The physical properties of the binder resin in the toner are most greatly involved in these phenomena. However, according to the study of the present inventors, when the content of the magnetic substance in the toner is reduced, the toner image supporting member is fixed at the time of fixing. Although the adhesiveness of the toner to the toner is improved, offset tends to occur, and blocking or caking tends to occur. Therefore, in the present invention, when using the heating / pressing roller fixing method in which almost no oil is applied, the selection of the binder resin is more important. Preferred binders include crosslinked styrenic copolymers or crosslinked polyesters.

Examples of the comonomer for the styrene monomer of the styrene copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, and methacrylic. Acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, a monocarboxylic acid having a double bond such as acrylamide or a substituted product thereof; for example, maleic acid, butyl maleate, Dicarboxylic acids having a double bond such as methyl maleate, dimethyl maleate and the like and their substituted products; for example, vinyl chloride, vinyl acetate,
Vinyl esters such as vinyl benzoate; ethylene olefins such as ethylene, propylene, butylene; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone; vinyl methyl ether, vinyl ethyl ether; Vinyl monomers such as vinyl isobutyl ether and the like; alone or two or more vinyl monomers are used.

Here, as the cross-linking agent, a compound having two or more polymerizable double bonds is mainly used, for example, an aromatic divinyl compound such as divinylbenzene, divinylnaphthalene and the like; for example, ethylene glycol diacrylate, ethylene glycol dimethacrylate Double bonds such as 1,3-butanediol dimethacrylate, etc.
Carboxylic acid esters having two or more compounds; divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide and divinyl sulfone; and compounds having three or more vinyl groups are used alone or as a mixture.

When a pressure fixing method is used, a binder resin for a pressure fixing toner can be used. For example, polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer can be used. Coalescent, ionomer resin, styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturated polyester, paraffin and the like.

In particular, in the present invention, the molecular weight distribution of the soluble component of the binder resin has at least two peaks, and the peak molecular weight is 500 to 12000 and 15,000 to 3.5 million, preferably 1500 to
10,000 and 15,000 to 2.5 million, more preferably 2000 to 100
00 and 20,000 to 1.5 million are good.

Further, a component (A) having a peak molecular weight of 500 to 12000 and
The composition ratio of component (B) of 15,000 to 3.5 million is from 10:90 to 90:
10 is good. Preferably, 20:80 to 80:20 is good. More preferably, 30:70 to 70:30 is good.

When such a binder resin is used, in the fixing, the crushing and the binding to the transfer paper are performed in a well-balanced manner, and the toner particles may be crushed too much even after a large number of fixings as in the present invention, or the fixing failure may occur. Does not cause splatter or disturbance.

When the component having a peak molecular weight of the binder resin of 15,000 to 3.5 million is less than 10% by weight of the total binder resin, the above effect is small, and the image quality is disturbed by crushing deformation of toner particles and offset.

If the component having a peak molecular weight of 500 to 12000 is less than 10% by weight of the total binder resin, the fixability is deteriorated, and the toner particles having poor fixation are charged on the surface of the fixation roller by the charging of the fixation roller surface and the transfer paper. Disturbed by the generated electric field, image quality degradation such as jumping and tailing occurs, and further worsened by multiplex copying.

In addition, there are various methods for measuring the molecular weight distribution of the binder resin, and a slight difference is thereby caused. Therefore, it is measured by the following measurement method.

That is, by gel permeation chromatography (GPC), the temperature was 40 ° C., the solvent was tetrahydrofuran,
Inject 300μ of THF at a measurement flow rate of 1.0ml / min and a concentration of 0.1wt%. In measuring the molecular weight of the sample, a calibration curve created with a monodisperse polystyrene standard sample is used. The column is not limited to this, and examples thereof include KF-80M manufactured by Shodex, KF802, 803, 804, and 805. It is advisable to combine these columns for accurate measurement.

In the present invention, as a method of obtaining the component ratio from the molecular weight distribution, a peak having a peak in the molecular weight distribution is separated at a valley portion at the lowest point, and an integrated value of each peak is obtained. did.

The magnetic toner of the present invention may optionally contain additives. Dyes conventionally known as colorants,
Pigments can be used, and usually 0.5 to 20 parts by weight per 100 parts by weight of the binder resin may be used. As other additives, for example, a lubricant such as zinc stearate, or an abrasive such as cerium oxide or silicon carbide or a fluidity imparting agent such as colloidal silica or aluminum oxide;
Anti-caking agent, or for example carbon black,
There is a conductivity imparting agent such as tin oxide.

Further, in order to improve the releasability at the time of hot roll fixing, a wax-like substance such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, sasol wax, paraffin wax, etc.
Addition of about 5 wt% to the magnetic toner is also a preferred embodiment of the present invention.

To prepare the magnetic toner for electrostatic image development according to the present invention, a magnetic powder and a vinyl-based, non-vinyl-based thermoplastic resin,
If necessary, a pigment or dye as a coloring agent, a charge control agent, other additives, etc. are sufficiently mixed by a mixer such as a ball mill, and then heated rolls, a kneader, melted using a heat kneader such as an extruder, Pigments or dyes are dispersed or dissolved in the resin after kneading and kneading to make the resins compatible with each other, and after cooling and solidification, pulverization and strict classification are performed to obtain the magnetic toner according to the present invention. .

Further, it is preferable to add fine silica powder to the magnetic toner in the present invention. A magnetic toner having a particle size distribution as a feature of the present invention has a larger specific surface area than conventional toners. When magnetic toner particles are brought into contact with the surface of a cylindrical conductive sleeve having a magnetic field generating means inside due to triboelectric charging, the number of times of contact between the surface of the toner particles and the sleeve increases compared to conventional magnetic toner, and the toner Particle wear and contamination of the sleeve surface are likely to occur. When the magnetic toner according to the present invention is combined with silica fine powder, wear is significantly reduced because the silica fine powder is interposed between the toner particles and the sleeve surface. As a result, the life of the magnetic toner and the sleeve can be prolonged, and a stable chargeability can be maintained, and a developer having a magnetic toner that is more excellent for long-term use can be obtained.
Further, the magnetic toner particles having a particle diameter of 5 μm or less, which play a major role in the present invention, exhibit more effects in the presence of the silica fine powder, and can stably provide high-quality images.

Among the fine silica powders, those having a specific surface area of 30 m ² / g or more (particularly 50 to 400 m ² / g) obtained by nitrogen adsorption measured by the BET method give good results. 0.01 to 8 parts by weight of silica fine powder, preferably 100 parts by weight of magnetic toner, preferably
It is preferable to use 0.1 to 5 parts by weight.

When the magnetic toner of the present invention is used as a positively charged magnetic toner, the silica fine powder added for preventing the toner from being worn and preventing the sleeve surface from being stained is more positively charged than negatively charged. It is preferable to use fine silica powder without deteriorating the charging stability.

As a method for obtaining a positively chargeable silica fine powder, a method in which the untreated silica fine powder described above is treated with a silicon oil having an organo group having at least one nitrogen base paper in a side chain, or a nitrogen-containing silane cup There is a method of treating with a ring agent or a method of treating with both.

In the present invention, the positively-charged silica refers to a silica having a positive tribocharge with respect to the iron powder carrier when measured by a blow-off method.

The applied amount of these treated positively charged silica fine powders is 0.01 to 8 with respect to 100 parts by weight of the positively charged magnetic toner.
The effect is exhibited when the amount is by weight, and particularly preferably 0.1 to 5 parts by weight.
Positive chargeability with excellent stability when added in parts by weight. In a preferred embodiment, the addition form is such that 0.1 to 3 parts by weight of the treated silica fine powder is attached to the surface of the toner particles with respect to 100 parts by weight of the positively charged magnetic toner. The untreated silica fine powder described above can be used in the same application amount.

The silica fine powder used in the present invention may be treated with a silane coupling agent or a treating agent such as an organosilicon compound for the purpose of hydrophobizing, if necessary.

Further, in the present invention, fine powder of a fluorine-containing polymer,
For example, it is preferable to add fine powder of polytetrafluoroethylene, polyvinylidene fluoride or the like and a tetrafluoroethylene-vinylidene fluoride copolymer. In particular, polyvinylidene fluoride fine powder is preferred in terms of fluidity and abrasiveness. The amount added to the toner
0.01 to 2.0 wt%, particularly preferably 0.02 to 1.0 wt%.

In particular, in the magnetic toner in which the silica fine powder and the above fine powder are combined, the reason is not clear, but stabilizes the state of silica attached to the toner, for example, the attached silica is released from the toner, The effect on abrasion and sleeve fouling is not reduced, and the charging stability can be further increased.

Although the particle size distribution of the toner can be measured by various methods, in the present invention, the measurement was performed using a Coulter counter.

In other words, the Coulter Counter TA is used as a measuring device.
-Type II (manufactured by Coulter, Inc.) is connected to an interface (manufactured by Nikkaki) that outputs the number distribution and volume distribution, and a CX-1 personal computer (manufactured by Canon). Prepare a% NaCl aqueous solution. As a measuring method, 0.1 to 5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the aqueous electrolytic solution, and 2 to 20 mg of a measurement sample is further added. The electrolyte in which the sample was suspended was treated with an ultrasonic
After a dispersion treatment for minutes, the Coulter Counter TA-II
According to the mold, the particle size distribution of particles of 2 to 40 μ was measured on the basis of the number, using a 100 μ aperture as the aperture.

In the present invention, the collapse of the line image was measured by the following method. That is, line width 100
Using a Luzex 450 particle analyzer as a measuring device, a line width is measured from an enlarged monitor image by an indicator using an image obtained by copying a single-sided original of a μm original under appropriate copying conditions. At this time, since the line width measurement position has irregularities in the width direction of the thin line image of the toner, the average line width of the irregularities is used as the measurement point. next,
Using the same original, make 10 continuous single-sided copies under appropriate copying conditions, stack them on the refeeding table, change the original to blank paper, and print a solid white image on the toner-adhered surface.
The line width of a line image which has been continuously taken and fixed twice with a hot roll is measured in the same manner as described above. Thus, the value of the line image collapse is calculated by the following equation.

Further, in the present invention, the resolving power was used for evaluating the collapse of the fine line. The resolution was measured by the following method. That is, a pattern consisting of five fine lines with the same line width and spacing, and 2.8, 3.2, 3.6, 4.0, 4.5, 5.0, 5.6, 6.
Create an original image that is drawn as if there were 3,7.1 or 8.0 lines. Observe the image obtained by copying the original manuscript having these 10 types of line images under appropriate copying conditions with a magnifying glass, and find the number of images (lines / m) where fine lines are clearly separated.
m) is the value of the resolving power.

In the present invention, the amount of applied toner on the transfer material was determined by using a so-called absorption Faraday gauge method. An original black sheet is prepared, copied under appropriate copying conditions, and the transfer sheet is transferred from the copying machine and then extracted before fixing to obtain an unfixed image having a solid black image on the transfer sheet.
The Faraday gauge outer cylinder is pressed against this solid black unfixed image to absorb all the toner on a certain area on the transfer paper, collected by a cylindrical filter, and the unit area on the transfer material is calculated based on the weight increase of the filter. The weight of the toner layer per unit was calculated, and this was used as the amount of applied toner.

[Examples] Hereinafter, parts in the examples mean parts by weight.

Example 1 After the above materials were mixed well in a blender, they were kneaded with a biaxial kneading extruder set at 150 ° C. After cooling the obtained kneaded material and coarsely pulverizing with a cutter mill, finely pulverizing using a fine pulverizer using a jet stream, classifying the obtained finely pulverized powder by wind power, and further strictly setting the fine powder side To obtain a classified powder. Add 100 parts of the classified powder to hydrophobic dry silica 0.4
Parts were added and mixed with a Henschel mixer to obtain a one-component magnetic toner.

The particle size distribution of the magnetic toner was as shown in Table 1.

A commercially available copier NP-3725 (manufactured by Canon Inc.) was modified to make the peripheral speed of the developing sleeve variable, and set to 150% of the machine process speed (photoreceptor moving speed). DC bias applied from external power supply
250 V _DC , V _PP = 1500 V for AC bias, frequency f = 2,000
Using a sine wave of Hz, the toner coated in a thin layer on the sleeve was efficiently developed and transferred. When the applied amount of the toner on the transfer material in the solid black image of the magnetic toner was measured,
0.87 mg / cm ² .

Furthermore, the image density, the line width at the time of single-sided copy, the line width at the time of multiple copy according to the resolution and the evaluation method described above,
The resolving power was evaluated. As shown in Table 2, a sharp image with excellent fine line reproducibility and high image density was obtained without causing line image collapse even after multiple copying. In addition, no stain on the back side of the transfer paper, no stain on the re-feeding roller, or the like occurred.

Example 2 Using the above materials, a one-component magnetic toner was obtained in the same manner as in Example 1. The particle size distribution of this one-component magnetic toner is
As shown in the table.

A commercially available copier NP using this one-component magnetic toner
-7550 (manufactured by Canon Inc.) was modified to increase the peripheral speed of the developing sleeve.
25% faster, 600% of 150% of machine process speed
The surface roughness of the developing sleeve was changed to 1.5 μm / sec, and the surface roughness was changed to 1.5μ (using a fine surface roughness meter manufactured by Tiller Hopson Co., Ltd., JIS 10 point average roughness (RZ) “JIS B 060
Measured by 1 ". The evaluation was performed in the same manner as in Example 1. As a result, as shown in Table 2, there was no collapse of the line image, a high-density image was obtained, and no stain on the transfer paper occurred. Further, the amount of toner applied to the solid black image on the transfer paper after the transfer and before the fixing was 0.77 mg / cm ² .

Examples 3 to 6 Evaluations were carried out in the same manner as in Example 1 except that toner having a particle size distribution as shown in Table 1 was used instead of the toner used in Example 1.

As shown in Table 2, all of the above-mentioned examples showed little collapse of the line image, did not cause transfer paper stains, and obtained a high-density and sharp image. Table 1 shows the amount of applied toner on each transfer sheet.

Comparative Example 1 A toner having the particle size distribution shown in Table 1 was used in a modified copier NP-3725 (manufactured by Canon Inc.) with the peripheral speed of the developing sleeve set to 90% of the machine process speed. Evaluation was performed in the same manner as in Example 1. At this time, the applied amount of the toner in the solid black image on the transfer paper was 0.58 mg / cm ² .

The obtained image showed good values in the evaluation of the resolving power at the time of multiple copying and the evaluation of the line image collapse, but the image density was low, and the line image was also poor and lacked sharpness.

Comparative Examples 2 to 4 A commercially available copying machine NP-3725 (Canon Inc.) was used in the same manner as in Example 1 except that toner having a particle size distribution as shown in Table 1 was used instead of the toner used in Example 1. Was evaluated using a remodeled machine manufactured by Toshiba Corporation.

As a result, as shown in Table 2, the resolution was degraded at the time of multiple copying, which indicates the thinning of the thin line due to the multiple copying. In addition, the measurement of the line width revealed that the line image was crushed.

Further, in Comparative Example 4, transfer paper stains occurred due to friction between the transfer paper and the toner adhering surface due to the pressure of the re-feed roller during re-feeding in multiple copies.

[Effects of the Invention] The present invention uses a magnetic toner having a specific particle size distribution and selects image processing conditions suitable for the magnetic toner, so that the magnetic toner can be formed on both sides of the transfer material or on one side of the transfer material. In the image forming method for forming an image, (1) the line image is substantially free from deterioration such as crushing, scattering and fogging even after a plurality of heat roll fixings. (2) (3) It is possible to obtain an image with high image density, sharpness, and excellent fine line reproducibility and gradation reproducibility with less toner consumption without causing stains on the paper feed roller and transfer material. And

[Brief description of the drawings]

FIG. 1 is a view schematically showing how toner is placed on a transfer material in the case of the particle size of the toner according to the present invention, and FIG. FIGS. 1A and 2A schematically show the toner layer on the transfer material, and FIGS. 1B and 2B are cross-sectional views of the toner layer on the transfer material. It is the figure seen from the top. 1,4 ...... transfer material, 2,3 ...... toner W _1, W ₂ ...... toner layer thickness

Continuing on the front page (72) Inventor Masaji Fujiwara 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Kiichiro Sakashita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-58-117553 (JP, A) JP-A-61-275766 (JP, A) JP-A-2-151876 (JP, A) JP-A-2-61652 (JP, A) JP-A 1-219761 (JP, A) JP-A 60-162261 (JP, A) JP-A 63-301960 (JP, A) JP-A 2-284156 (JP, A) JP-A 1-295270 (JP, A) JP-A-2-284151 (JP, A) JP-A-2-101481 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 15/08 G03G 9 / 08

Claims (1)

(57) [Claims] An electrostatic image carrier carrying an electrostatic latent image is developed with magnetic toner, the toner image on the electrostatic image carrier is transferred to a transfer material, and the toner image on the transfer material is fixed. After that, the same steps as described above are repeated once or twice on the surface of the transfer material having the toner image or on the back of the surface of the transfer material having the toner image. In an image forming method for forming multiple images on one side or forming images on both sides of the transfer material, the magnetic toner may be 5
The toner contains 12 to 60% by number of toner particles having a particle diameter of not more than 2.0 μm, and the magnetic toner has a volume average particle diameter of 5 to 5%.
The particle size distribution of the magnetic toner satisfies the following general formula (1), and the amount of toner applied on the transfer material after transfer and before fixing is 1.2 mg or less per cm ² and 0.3 mg or more per 1 cm ^2. An image forming method, characterized in that: