JP2632337B2 - For electrostatic image development-Component-based magnetic developer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a one-component magnetic developer for developing an electrostatic image for developing an electrostatic image in electrophotography, electrostatic recording, electrostatic printing and the like.

[Prior Art] Conventionally, as electrophotography, U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910 (U.S. Pat.No. 3,666,363), and Japanese Patent Publication No. 43-24748 (U.S. Pat. Three
Many methods are known, for example, a photoconductive substance is used to form an electric latent image on a photoreceptor by various means, and then the latent image is developed. (Hereinafter referred to as "toner"), and if necessary, a toner image is transferred to a transfer material such as paper, and then fixed by heating, pressure, pressurized heat or a solvent vapor to obtain a copy. Things. In the case where a step of transferring a toner image is provided, a step for removing residual toner on the photoconductor is usually provided.

A developing method for visualizing an electric latent image using toner is as follows.
For example, the magnetic brush method described in U.S. Pat.No. 2,874,063, the cascade developing method described in U.S. Pat.No. 2,618,552 and the powder cloud method described in U.S. Pat.No. 2,221,776, U.S. Pat. A method using a conductive magnetic toner described in the specification is known.

Conventionally, fine powders obtained by dispersing dyes and pigments in natural or synthetic resins have been used as toners applied to these developing methods. For example, particles obtained by finely dispersing a colorant in a binder resin such as polystyrene to about 1 to 30 μm are used as toner. A magnetic toner containing magnetic particles such as magnetite is used. In the case of a system using a so-called two-component developer, the toner is usually used by being mixed with carrier particles such as glass beads and iron powder. Further, the toner has positive or negative charges depending on the polarity of the electrostatic latent image to be developed.

In order to retain charge in the toner, it is possible to use the triboelectricity of the resin which is a component of the toner.However, in this method, since the toner has a small chargeability, an image obtained by development is easily fogged and unclear. It will be. Therefore, in order to impart a desired triboelectric charging property to the toner, a dye, a pigment for imparting the charging property, and a charge control agent are added.

Today, as charge control agents known in the art, there are nigrosine and quaternary ammonium salts for controlling the toner to be positively charged, and monoazo dyes for controlling the toner to be negatively charged. And metal complex salts of salicylic acid and naphthoic acid.

These are usually added to a thermoplastic resin, melt-dispersed under heat, finely pulverized, and adjusted to an appropriate particle size as required before use.

After development using the toner as described above and transfer to a transfer material, the toner is permanently fixed by heat, pressure, or the like. Conventionally, this fixing step has often been performed by heat.

In addition, the fixing method by heating has been replaced with the open fixing method, which has been around for a long time. In recent years, a heat roll type fixing method with good thermal efficiency has been introduced with the efficiency of copying work, energy saving, miniaturization, high speed and high performance of the copying machine. Occupy a large part of the population. This is to fix the toner on the paper by thermocompression bonding with a heating roller, and the heating body can obtain a satisfactory fixed image at a lower temperature and a higher speed than the non-contact type heating method using a hot wire. There are many advantages such as being possible.

Generally, a toner used for a specific fixing method cannot be used for another fixing method, and various toner materials suitable for heat-pressure fixing by a heating roller have been proposed with the change of the fixing method. In these proposals, a fairly wide range of technical contrivances such as the molecular weight distribution of the binder resin, the degree of cross-linking, the mixing of different resins, or the addition of a releasable substance have been made.

In particular, many proposals have been made regarding the molecular weight distribution of the binder resin, for example, using a broad distribution,
Alternatively, various improvements have been made, such as using a plurality of peaks instead of a single peak, and satisfactory fixed images have been obtained.

However, recently, the reliability of the copying machine has been improved, and a copying machine having a longer life has been developed and manufactured. Under these circumstances, a review of various characteristics of the toner, particularly the durability characteristics, revealed that the conventional toner was insufficient. That is, when development is performed using a conventional toner, as the number of copies increases, the image density gradually decreases, and at the same time, the fogging phenomenon on the white portion tends to increase, which has a problem in durability characteristics. Was.

[Problems to be Solved by the Invention] An object of the present invention is to provide a developer which has solved the above-mentioned problems.

That is, an object of the present invention is to provide a one-component magnetic developer for developing an electrostatic image having high image density and excellent durability.

Another object of the present invention is to provide a one-component magnetic developer for developing an electrostatic image having excellent fixability and anti-offset property.

Still another object is to provide a one-component magnetic developer for developing electrostatic images having clear image characteristics without fog.

Still another object is to provide a one-component magnetic developer for developing an electrostatic charge image which prevents contamination of the developer bearing member or the photoreceptor.

Means for Solving the Problems The present invention develops an electrostatic charge image held on an electrostatic image holding member with a one-component magnetic developer held on a developer holding member having a magnet inside. A one-component magnetic developer for developing an electrostatic image used in a developing method, wherein the one-component magnetic developer contains, as a magnetic toner, particles (A) containing at least a binder resin and a magnetic powder, and at least a resin And a magnetic toner having the particles (B) fixed or embedded by mechanical impact near the surface of the particles (A). The binder resin has a peak or shoulder at a molecular weight of 10,000 or less in the molecular weight distribution by GPC (gel permeation chromatography), and the resin of the particles (B) has a molecular weight of 1 in the molecular weight distribution by GPC.
The present invention relates to a one-component magnetic developer for developing an electrostatic image, characterized by having neither a peak nor a shoulder below 10,000.

The inventor of the present invention has studied to solve the above problems, and as a result of measuring the charge amount of the developer whose image density has decreased, it has been found that the charge amount is significantly lower than the value in the early days. As a result of further study of the cause, it was found that the developer carrying member was contaminated by the binder resin.

That is, to explain this, when the image density is lowered, the developer and the developer carrier are separated, and the developer is developed using a new carrier. As a result, the image density is high and the charge amount is the initial value. Was equivalent to On the other hand, when the developer carrying member after the endurance was developed using a new developer, the image density was low and the charge amount was equivalent to the value when the endurance decreased.

Then, the carrier was washed with a solvent, dried sufficiently, and developed again using a new developer. As a result, the image density was high and the charge amount was equal to the initial value. As a result of analyzing the solvent used for washing, it was found that the solvent was a low molecular weight component of the binder resin. On the other hand, as described above, since a low molecular weight component is necessary for improving the fixing property, the present inventor requires that the low molecular weight component of the binder resin be contained in the toner particles while being present inside the toner. The present inventors have found that the above-mentioned problems can be solved, and have reached the present invention.

In the present invention, as the binder resin used for the particles (A), homopolymers of styrene such as polystyrene, poly p-chlorostyrene, polyvinyl toluene and the like; styrene-p-chlorostyrene copolymer, styrene -Propylene copolymer, styrene-vinyl toluene copolymer, styrene-vinyl naphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer,
Styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer Styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-
Styrene-based copolymers such as isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, styrene-maleic acid ester copolymer; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, Polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane,
Polyamide, epoxy resin, polyvinyl butyral, polyamide, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, etc. can be used alone or in combination. .

Examples of the coloring material used for the particles (A) of the present invention include conventionally known carbon black, copper phthalocyanine, and the like.
Iron black, nigrosine, benzidine yellow, quinacridone, rhodamine B and the like can be used.

The particles (A) of the present invention may also serve as a colorant, but contain magnetic powder. As the magnetic powder, a substance that is magnetized when placed in a magnetic field is used, and there are ferromagnetic metal powders such as iron, cobalt, and nickel, or alloys and compounds such as magnetite, γ-Fe ₂ O ₃ , and ferrite. .

In particular, in order to exert the above-mentioned effect, the BET specific surface area by the nitrogen adsorption method is preferably ² to 20 m ² / g, particularly 2.5 to 12
Magnetic powder having m ² / g and Mohs hardness of 5 to 7 is preferred.
The content of this magnetic powder is 10 to 70% by weight based on the toner weight
Is good.

The particles (A) and (B) of the present invention may optionally contain a charge control agent. Nigrosine, a quaternary ammonium salt, etc. are used to control the chargeability of the toner. Metal complex salts of monoazo dyes, and metal complex salts of salicylic acid and naphthoic acid can be used to control the properties.

The resin used for the particles (B) of the present invention is the same as the above-mentioned resin group used for the particles (A), but it is desirable that the content of the low molecular weight component in the GPC of the resin used is small, and the molecular weight is 10,000. Those having neither a peak nor a shoulder in the following regions are used. If it has a peak or a shoulder, the blocking resistance is deteriorated, and the contamination of the developer carrying member cannot be prevented.

The molecular weight distribution by GPC in the present invention was measured by the following method. Measurement conditions were as follows: tetrahydrofuran was flowed as a solvent at a temperature of 25 ° C at a flow rate of 1 ml per minute, and the sample concentration was 8 mg / ml.
0.5 ml of a sample solution of tetrahydrofuran is injected and measured. In addition, as a column, in order to accurately measure the molecular weight region of 10 ³ to 2 × 10 ⁶ , it is preferable to combine a plurality of commercially available polystyrene gel columns, for example, μ-styragel 500, 10 manufactured by waters. Combinations of ³ , 10 ⁴ and 10 ⁵ and combinations of Shodex A-802, 803, 804 and 805 manufactured by Showa Denko KK are good. When measuring the molecular weight of a sample, the molecular weight distribution of the sample
It was calculated from the relationship between the logarithmic value of the calibration curve prepared from several types of monodisperse polystyrene standard samples and the count number. As a standard polystyrene sample for preparing a calibration curve, for example, Pr
essure Chemical Co. or Toyo Soda Kogyo Co., Ltd. has a molecular weight of 6 × 10 ² , 2.1 × 10 ³ , 4 × 10 ³ , 1.75 × 10 ⁴ , 5.1 × 10 ⁴ ,
It is appropriate to use a sample of 1.1 × 10 ⁵ , 3.9 × 10 ⁵ , 8.6 × 10 ⁵ , 2 × 10 ⁶ , 4.48 × 10 ⁶ and at least about 10 standard polystyrene samples. The detector uses RI (refractive index)
Use a detector.

In producing the particles (A) and (B) of the present invention,
A method in which the constituent materials are thoroughly kneaded with a hot kneader such as a hot roll, kneader, extruder, etc., and then obtained by mechanical pulverization and classification, or obtained by dispersing the materials in a binder resin solution and then spray drying. Each method can be applied, for example, a polymerization method in which a predetermined material is mixed with a monomer to constitute a binder resin to emulsify and form a suspension, and then polymerized to obtain a toner.

The volume average particle diameter of the particles (A) is 30 μm or less, preferably 5 to 20 μm. The particles (B) have a volume average diameter of 5 μm or less, preferably 2 μm or less.

The method for producing the toner according to the present invention is described below,
It is not limited to these.

As a pretreatment for embedding the particles (B) in the vicinity of the surface of the particles (A) in the present invention, the particles (B) are dispersed and rubbed with the colored particles (A) to form particles (E) by electrostatic force and van der Waals force. A). Generally, a mixer with a high-speed stirring blade is used, but any mixer having a mixing function and a dispersing function may be used. Further, a pulverizer, a vibration mill or the like may be used with a reduced impact force.

At this time, in order to make the pretreatment dispersion more uniform, a fluidity-imparting agent, a lubricant, a conductivity-imparting agent, or the like may be added as a dispersing aid, if necessary. For example, fine silica powder, polytetrafluoroethylene powder, polyvinylidene fluoride powder, metal salts of higher fatty acids, carbon black, conductive tin oxide and the like are used, and particularly preferably fine silica powder is used.

The silicic acid fine powder used in the present invention is a fine powder having a Si—O—Si bond, and includes both a powder produced by a dry method and a powder produced by a wet method.

Various conventionally known methods can be applied to the method for producing the fine silica powder used in the present invention by a wet method. For example, decomposition of sodium silicate by acid, as shown by the general reaction formula (hereinafter, the reaction formula is abbreviated), Na ₂ O.xSiO ₂ + HCl + H ₂ O → SiO ₂ .nH ₂ + NaCl In addition, ammonium silicate or alkali of sodium silicate Decomposition with salts, after producing an alkaline earth metal silicate from sodium silicate, a method of decomposing with an acid to produce silicic acid, a method of transforming sodium silicate solution into silicic acid with ion exchange resin, natural silicic acid or There is a method using a silicate.

Silicic acid fine powder referred to here includes anhydrous silicon dioxide (silica), aluminum silicate, sodium silicate,
Silicates such as calcium silicate, magnesium silicate and zinc silicate can all be applied.

The effect is exhibited when the addition amount of the dispersing aid is 5 parts by weight or less, preferably 3 parts by weight or less based on 100 parts by weight of the particles (A). The ratio of the particles (A) and (B) is 0.1 to 20 parts by weight for the particles (B) with respect to 100 parts by weight of the particles (A).
The pretreatment is preferably performed in the range of 0.5 to 15 parts by weight.

The mixture of the particles (A) and (B) obtained in this manner was mixed with the apparatus shown in FIG.
The toner was processed for 3 minutes at / sec, and the toner was observed with an electron microscope. As a result, it was observed that the toner was partially fixed. In addition, the sticking rate was determined to be 96% by the following method.
Met.

The ratio of the particles (B) fixed to the particles (A) was determined as follows.

First, the particles (A), the mixture of the particles (A) and (B), and the processed product thereof are respectively dispersed in water containing a surfactant in the same amount, and further dispersed in an ultrasonic disperser for 5 minutes. Thereafter, suction is immediately performed. At this time, the size of the opening of the filter is slightly larger than the diameter of the particles (B). Next, after further dispersing the obtained liquid with ultrasonic waves,
The transmittance T% of the liquid is measured using a spectrophotometer.
At that time, the equipment is adjusted with the liquid containing only the particles (A) as 100%. The values measured as described above were determined by defining the sticking rate using the following formula.

Permeability of liquid of processed material of particles (A) and (B): T _AB % Permeability of liquid of mixture of particles (A) and (B): T _{A + B} % As conditions for the fixation and burying treatment, it is important to control the impact force in a range where the particles (A) are not pulverized and the temperature control in a range where no fusion aggregation occurs. As an example of a fixing device for carrying out the method, a pin mill having a recycle function and having a large number of rotating pins, or applying an impact between a rotating blade or hammer (rotating piece) and a liner (fixing piece), and A crusher having a recycling mechanism is effective.

The peripheral speed of the tip of the rotary piece in the device is preferably 30 to 150 m / sec. The temperature varies depending on the physical properties of the particles (A) and the particles (B), but is preferably 20 to 90 ° C, preferably 30 to 70 ° C, and the residence time of the impact portion is preferably 0.2 to 12 seconds. In the case of a pin mill, it is necessary to increase the powder concentration. In the apparatus of the type shown in FIG. 1, the powder to be processed by the centrifugal force is collected near the liner 7, so that the latitude of the powder concentration is wide. The shortest gap between the pin mills or between the blade 4 or the hammer and the liner is preferably about 0.5 to 5 mm, and more preferably a good result is obtained when adjusted to 1 to 3 mm.

If necessary, the toner of the present invention may contain, for example, silica fine powder, polytetrafluoroethylene powder, polyvinylidene fluoride powder, metal of higher fatty acid such as a fluidity-imparting agent, a lubricant, a conductivity-imparting agent, and a fixing aid. Salt, carbon black, conductive tin oxide and the like may be added.

Further, the toner of the present invention preferably has a volume resistivity of 10 ¹⁰ Ωcm or more, particularly 10 ¹² Ωcm or more. The volume resistivity referred to herein, by molding the toner in pressure of 100 Kg / cm ^2, this 1
An electric field of 00 V / cm is applied, and is defined as a value converted from a current value one minute after the application.

The toner of the present invention may be mixed with carrier particles such as iron powder, glass beads, nickel powder, and ferrite powder, if necessary, and used as a developer for an electric latent image.

The developing method using the one-component magnetic developer of the present invention will be described. FIG. 2 is a sectional view showing one embodiment of the developing step. In the figure, the electrostatic image holder 16 moves in the direction of the arrow. The non-magnetic cylinder 17, which is a developer carrier, rotates in the developing section so as to advance in the same direction as the surface of the electrostatic image carrier. Inside the non-magnetic cylinder 17, a multi-pole permanent magnet 18 is arranged so as not to rotate. The one-component insulating magnetic developer 21 sent from the developer container 19 is applied on the non-magnetic cylindrical surface, and the toner particles are charged by the friction between the cylindrical surface and the toner particles with a polarity opposite to the electrostatic image charge. give. In addition, close the iron doctor blade 20 close to the cylinder surface (interval 50μ ~ 500μ
m), the thickness of the toner layer is regulated to be thin (30 μm to 300 μm) and uniformly by arranging the multipole permanent magnet 18 so as to face one magnetic pole (S pole in the drawing). This cylinder 1
By adjusting the rotation speed of 7, the surface speed and preferably the internal speed of the developer layer are set to be substantially equal to or close to the speed of the electrostatic image holding surface.
The opposite magnetic pole may be formed by using a permanent magnet instead of iron as the doctor blade 20. Further, an AC bias may be applied between the developer carrier and the electrostatic image holding surface in the developing section. This AC bias is f 200-4000Hz, Vpp
Should be 500-3000V.

As described above, in this developing step, the non-magnetic cylinder 17 containing the multi-pole permanent magnet 18 was used in order to stably hold the one-component magnetic developer on the developer carrier. Further, in order to form the developer layer thinly and uniformly, a doctor blade 20 made of a magnetic thin plate or a permanent magnet is provided near the surface of the cylinder 2.
Was placed. When a magnetic doctor blade is used in this way, an opposing magnetic pole is formed between the magnetic pole of the permanent magnet included in the developer carrier and the toner particle chains are forcibly formed between the doctor blade and the developer carrier. This causes the developer layer to rise, which is advantageous for regulating the thickness of the developer layer at another portion on the developer carrier, for example, at the developing portion facing the electrostatic image surface. Further, by applying such a forced movement to the developer, the developer layer becomes more uniform, and a thin and uniform toner layer can be formed. In addition, since the distance between the doctor blade and the sleeve can be set wider, there is also an effect of preventing destruction and aggregation of toner particles. When the toner particles are transferred in the developing portion, the toner particles are transferred to the electrostatic image side by the action of attracting the electrostatic image or the action of the AC bias.

[Examples] Parts in Examples are parts by weight.

Example 1 100 parts of styrene-2-ethylhexyl acrylate-divinylbenzene copolymer (Mw = 290,000, peak in a region of molecular weight of 10,000 or less (7000)), BET specific surface area: 8 m ² / g
Are mixed and melt-kneaded at 160 ° C. for 7 in a roll mill. After cooling, the mixture was roughly pulverized with a hammer mill, finely pulverized with a jet mill pulverizer, and then separated using an air classifier to obtain fine black powder particles (A) having a volume average diameter of 12 μm.

On the other hand, 100 parts of a styrene-butyl acrylate-divinylbenzene copolymer (Mw = 330,000, no peak in a molecular weight of 10,000 or less) and 6 parts of nigrosine were mixed, and the volume average diameter was determined in the same procedure as for the particles (A). Was obtained as black fine powder particles (B) having a particle size of 1.2 μm. Further, 1 part of silica fine powder was added to 100 parts of the particles (B) and mixed with a Henschel mixer. Then, 10 parts of the mixture and 100 parts of the particles (A) were further mixed with a Henschel mixer to perform pretreatment.

Next, using the apparatus shown in FIG. 1, processing was performed under the conditions of a minimum gap of 1 mm, a peripheral speed of the blade of 60 m / sec, and a processing time of 3 minutes. When the processed product was observed with an electron microscope, it was observed that the product was partially fixed and embedded, and the triboelectric charge was measured to be +13 μC / g. 0.4 part of silica fine powder was added to 100 parts of the toner to obtain a developer.

Using the above-mentioned developer, image formation was performed with a Canon copier NP-3525. The obtained image had a high density of 1.31 and was clear without any fog. Thereafter, 30,000 copies were made, and the samples during that time were all 1.30 densities.
It was stable at ~ 1.35, and fog and sharpness were equivalent to those at the initial stage. On the other hand, good fixability was obtained.

Comparative Example 1 A toner was obtained in the same manner as in Example 1 except that the binder resin used for the particles (A) in Example 1 was also used for the particles (B), and the amount of triboelectric charge was measured to be +13 μC / g. Met.
A developer was obtained from the above toner in the same procedure as in Example 1. Further, when an image was formed using this developer in the same manner as in Example 1, the initial image was at the same level.
The image density decreases as copying continues, the image density decreases to 0.5 to 0.7 at the time of 2000 sheets, there are many fogs,
Copying was stopped because an offset occurred on the image.

Comparative Example 2 One part of nigrosine was added to the same amount of the material used for the particles (A) in Example 1, and the particles (A) were produced in the same manner as in Example 1.
I got The measured triboelectric charge of the particles (A) was +14 μC / g. To 100 parts of the particles (A), 0.4 part of fine silica powder was added and mixed to obtain a developer.

Next, when an image was formed using this developer in the same manner as in Example 1, the initial image was at the same level, but the image density decreased as copying continued, and the image The density decreased to 1.0 and fog increased slightly. Copying was further continued. However, at 5000 sheets, the image density was reduced to 0.6 to 0.7, fog increased, and image smearing due to offset occurred, so copying was stopped.

[Effects of the Invention] As described above, by separating resins having different contents of low molecular weight components into the inside and the surface of the toner and blending them into the developer particles, concentration deterioration and fog due to contamination of the developer carrying member are achieved. There is an advantage that the durability can be improved by preventing the increase, and an image having good fixability and anti-offset property can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an example of an apparatus for fixing and embedding particles (B) on particles (A), and FIG. 2 shows an embodiment of a developing step to which the present invention can be applied. FIG. DESCRIPTION OF SYMBOLS 1 ... Rotating shaft 2 ... Rotor 3 ... Dispersion blade 4 ... Rotating piece (blade) 5 ... Partition disk, 6 ... Casing 7 ... Liner, 8 ... Impact part 9 ... Inlet chamber , 10 outlet chamber 11 return path 12 product take-out section 13 material feed valve 14 blower 15 jacket 16 electrostatic image holder 17 developer carrier 18 Permanent magnet 19 Developer container 20 Doctor blade 21 Developer

Claims (3)

(57) [Claims] An electrostatic image used in a developing method for developing an electrostatic image held on an electrostatic image holding member with a one-component magnetic developer held on a developer holding member having a magnet therein. In the one-component magnetic developer for development, the one-component magnetic developer includes, as a magnetic toner, particles (A) containing at least a binder resin and a magnetic powder, and particles (B) containing at least a resin. And a magnetic toner having the particles (B) fixed or embedded by mechanical impact near the surface of the particles (A), and the binder resin of the particles (A) is GPC (gel / gel). In the molecular weight distribution by permeation chromatography), the quantum (B) resin has a peak or shoulder at a molecular weight of 10,000 or less, and the resin of quantum (B) has a molecular weight of 1 in the molecular weight distribution by GPC.
A one-component magnetic developer for electrostatic image development, characterized by having neither a peak nor a shoulder below 10,000. 2. The magnetic toner is subjected to a pretreatment of mixing and dispersing the particles (A) and the particles (B) using a dispersing aid, and then mechanically adhering to the vicinity of the surface of the particles (A). 2. The one-component magnetic developer according to claim 1, wherein the particles (B) are fixed or embedded by a strong impact. 3. The ratio between the particles (A) and the particles (B) is as follows:
0.1 to 20 parts by weight of the particles (B) based on 100 parts by weight of the particles (A)
3. The method according to claim 1, wherein the amount is within a range of parts by weight.
5. The one-component magnetic developer for developing an electrostatic image according to claim 1.