JP3141294B2 - Developer and image forming method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a developer for visualizing an electrostatic charge image in an image forming method such as electrophotography, electrostatic recording, and electrostatic printing, and an image forming method. About.

More specifically, the present invention relates to a developer and an image forming method used in an electrophotographic method, which has a charging step of charging by charging a charging member to which a voltage is externally applied to a member to be charged.

[Related Art] Conventionally, a corona discharger has been known as a charging unit in an electrophotographic apparatus or the like. However, corona dischargers have problems such as the need to apply a high voltage and the generation of a large amount of ozone.

Therefore, recently, the use of contact charging means without using a corona discharger has been studied. Specifically, a voltage is applied to a conductive roller serving as a charging member, and the roller is brought into contact with a photosensitive member serving as a member to be charged, thereby charging the surface of the photosensitive member to a predetermined potential. If such a contact charging means is used, the voltage can be reduced as compared with a corona discharger, and the amount of generated ozone can be reduced.

For example, in Japanese Patent Publication No. 50-13661, a low voltage can be applied when photosensitive paper is charged by using a roller having a core covered with a dielectric material made of nylon or polyurethane rubber.

However, in the above-mentioned conventional example, when the core metal is coated with nylon, there is no elasticity of rubber or the like, so that sufficient contact with the member to be charged cannot be maintained, resulting in poor charging.
On the other hand, when the core metal is coated with polyurethane rubber, the softening agent impregnated in the rubber-based material exudes, and when the photoreceptor is used as the charged body, the charging member sticks to the photoreceptor when the photoreceptor stops at the contact portion. Or the area may cause image blurring. Also, when the softener in the rubber material of the charging member seeps out and adheres to the surface of the photoreceptor,
When the resistance of the photoreceptor is reduced and image flow occurs, the use of the photoreceptor becomes unusable at times. In other cases, toner remaining on the surface of the photoreceptor adheres to the surface of the charging member, causing a filming phenomenon. When a large amount of developer adheres to the surface of the charging member, the surface of the charging member is insulated, the charging ability of the charging member is lost, and the charging of the surface of the photoreceptor becomes nonuniform, thereby affecting an image.

This is because the developer is strongly pressed against the surface of the photoreceptor by the charging member, so that the residual developer adheres to the charging member or the surface of the member to be charged, and furthermore, it is easy to cause scratches and scraping.

In the image forming method according to the present invention, a DC voltage or a DC voltage obtained by superimposing an AC voltage is applied to the charging member and used. At this time, particles around the contact portion between the charging member and the photosensitive drum are particularly damaged. Abnormal charging and flying movement of the residual developer having a small diameter and light overlap are repeated repeatedly, which makes it easy for the residual developer to be electrostatically attracted and embedded on the charging member and the surface of the photosensitive drum. This is very different from the case where non-contact charging means using a conventional corona discharger is used.

On the other hand, in recent years, small and inexpensive personal use copiers and laser printers have emerged. In these small machines, from a maintenance-free standpoint, a cartridge integrating a photoconductor, a developing device, a cleaning device, etc. It is desirable to use a magnetic one-component type developer because the system is used and the structure of the developing device can be simplified as the developer.

Such a developer has a strong polishing effect of the developer itself,
In an image forming process in which a photoconductor having a low surface hardness such as an organic photoconductor (OPC) is pressed against the photoconductor,
In particular, in the case of a developer to which inorganic fine powder is externally added, a whitening phenomenon caused by scraping the surface of the pressure-contact member and the photoreceptor, a fusion of the developer by scratching the pressure-contact member and the photoreceptor, and a photoreceptor such as filming Contamination is likely to occur, and in extreme cases, image loss will occur.

This problem is prominent when a contact member such as the charging member is in contact with the surface of the photoreceptor with a predetermined contact pressure.

[Problem to be Solved by the Invention] An object of the present invention is to prevent a developer from being fused on a photoreceptor,
It is an object of the present invention to provide a developer capable of obtaining an image having a high density and no fog and an image forming method.

More specifically, the present invention provides a developer which hardly contaminates a contact charging device with a developer and does not cause uneven charging even if contaminated, and an image forming method having a contact charging step and a developing step of developing the developer of the present invention. The purpose is to:

[Means and Actions for Solving the Problems] The present invention provides an image forming method including a charging step of charging a photosensitive member by bringing a charging member to which a voltage obtained by superimposing a DC voltage and an AC voltage is applied into contact with the OPC photosensitive member. Developer used in the method, the glass transition point (T
and g) a thermoplastic silicone resin having a temperature of 40 to 90 ° C. and a binder resin, a colorant or a magnetic material.

Further, the present invention includes a charging step of bringing the charging member into contact with the OPC photoreceptor, applying a voltage obtained by superimposing a DC voltage and an AC voltage from the outside to charge the photoreceptor, and a developing step using the developer. The present invention relates to an image forming method having the same.

In the present invention, the thermoplastic silicone resin has a glass transition point (Tg) of 40 ° C. to 90 ° C. measured according to the ASTM D3418-82 method using a differential thermal analyzer (DSC measuring device), DSC-7 (manufactured by PerkinElmer). It must be in ° C.

If the Tg of the thermoplastic silicone resin is lower than 40 ° C., the dispersion in the developer particles is poor, so that a fog image is liable to occur and the fluidity tends to deteriorate. If Tg is higher than 90 ° C., the effect of preventing fusion of the photoconductor is small.

The amount of the thermoplastic silicone resin contained in the developer is 0.05 to 20 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the binder resin of the developer. Dispersion of the agent worsens.

The softening point of the thermoplastic silicone resin according to the present invention by microscopic observation on a hot plate is 70 ° C. to 150 ° C. from the viewpoint of dispersibility in developer particles and the effect of preventing fusion of the photoconductor.
C is preferred.

The organic group contained in the thermoplastic silicone resin of the present invention is at least one selected from an alkyl group, an aryl group, a modified alkyl group, and a modified aryl group (A), and at least one selected from a phenyl group and a modified phenyl group (B ) Is preferable for obtaining a thermoplastic silicone resin having a relatively high affinity for the binder resin of the developer. More preferably, the number of organic groups with respect to the silicon atom is A <B.

External addition and mixing of a hydrophobic inorganic fine powder on the surface of the developer of the present invention is one of the preferred embodiments of the present invention, and more preferably, the inorganic fine powder is a fine silica powder.

Silicate fine powder used in the present invention is a dry method called so-called dry method or fumed silica produced by vapor phase oxidation of a silicon halide compound, and both so-called wet silica produced from water glass and the like. can be used but less silanol groups on the inner surface and fine silica powder, and Na ₂ O, who dry silica without producing residue of SO ₃ ^2-like.

In the case of fumed silica, for example,
By using another metal halide such as aluminum chloride or titanium chloride together with a silicon halide, a composite fine powder of silica and another metal oxide can be obtained, and these are also included.

The average particle diameter is preferably in the range of 0.001 to 2 μm, particularly preferably 0.002 to 0.2 μm.
It is preferable to use silica fine powder in the range of μ.

Examples of the binder resin of the developer according to the present invention include a homopolymer of styrene such as polystyrene and polyvinyltoluene and a substituted product thereof; a styrene-propylene copolymer, a styrene-vinyltoluene copolymer, and a styrene-vinylnaphthalene copolymer. Copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-dimethylaminoethyl acrylate copolymer, styrene -Methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-dimethylaminoethyl methacrylate copolymer, styrene-vinyl methyl ether copolymer, styrene -Vinyl ethyl ether copolymer, styrene Vinyl methyl ketone copolymer, styrene - butadiene copolymer, styrene - isoprene copolymer, styrene - maleic acid copolymer, styrene - styrene copolymer and maleic acid ester copolymers;
Polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene,
Polyvinyl butyral, polyacrylic resin, rosin,
Modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, paraffin wax, carnauba wax and the like can be used alone or in combination.

As the colorant of the developer according to the present invention, conventionally known carbon black, copper phthalocyanine, iron black and the like can be used.

Further, the developer of the present invention is preferably a magnetic toner. As the magnetic fine particles contained in the magnetic toner, a substance that is magnetized when placed in a magnetic field is used, and powder of a ferromagnetic metal such as iron, cobalt, nickel, or magnetite, γ-Fe ₂ O ₃ , ferrite Alloys and compounds such as can be used.

These magnetic fine particles preferably have a BET specific surface area of 1 to ²⁰ m ² / g, particularly 2.5 to 12 m ² / g, and more preferably a magnetic powder having a Mohs hardness of 5 to 7 by a nitrogen adsorption method. The content of the magnetic powder is preferably from 10 to 70% by weight based on the weight of the developer.

Further, the developer of the present invention is preferably negatively charged, and may contain a charge control agent, if necessary. Control agents are used. Further, the developer according to the present invention preferably has a volume resistivity of 10 ¹⁰ Ω · cm or more, particularly 10 ¹² Ω · cm or more, in view of triboelectric charge and electrostatic transferability. The volume resistivity referred to here is defined as a value obtained by molding a developer at a pressure of 100 kg / cm ² , applying an electric field of 100 V / cm thereto, and converting the current value one minute after the application. You.

The developer of the present invention may further contain other additives such as a fixing aid (eg, low-molecular-weight polyethylene, low-molecular-weight polypropylene, etc.) as long as they do not have a substantial adverse effect.
Alternatively, a metal oxide such as tin oxide may be added as a conductivity imparting agent.

In the production of the developer of the present invention, the constituent materials are kneaded well by a hot kneader such as a hot roll, a kneader, an extruder and the like, and then the material is obtained by mechanical pulverization and classification, or the material is added to a binder resin solution. After dispersion, a method obtained by spray drying, or a polymerization method of obtaining a developer by mixing a predetermined material with a monomer to constitute a binder resin to form an emulsion suspension and then polymerizing to obtain a developer, respectively. Method can be applied.

Hereinafter, the contact charging step of the present invention applicable to the developer and the image forming method of the present invention will be specifically described.

FIG. 1 is a schematic diagram showing an example of a contact charging device that can be used in the image forming method of the present invention. Reference numeral 1 denotes a photosensitive drum which is an object to be charged, and a drum base made of aluminum
An organic photoconductor (OPC) 1b as a photoreceptor layer is formed on the outer peripheral surface of 1a, and rotates at a predetermined speed in the direction of the arrow.
In this apparatus, the photosensitive drum 1 has an outer diameter of 30 mmφ.
Reference numeral 2 denotes a charging roller which is a charging member brought into contact with the photosensitive drum 1 with a predetermined pressure, and a conductive rubber layer 2b is provided on a metal core 2a, and a surface layer 2c which is a release coating on the peripheral surface thereof. Was provided. The surface layer of the present apparatus is a release film, and it is preferable to provide a release film in terms of matching with the developer and the image forming method according to the present invention. However, if the resistance is too high, the photoreceptor drum 1 is not charged. If the resistance is too low, a large voltage is applied to the photoreceptor drum 1, causing damage to the drum and generation of pinholes. The resistance, that is, the volume resistivity is preferably 10 ⁹ to 10 ¹⁴ Ωm, and the thickness of the release coating at this time is preferably within 3.0 μm. Further, the lower limit of the thickness of the coating is considered to be about 5 μm if there is no peeling or swelling of the coating.

In this apparatus, the outer diameter of the charging roller 2 is 12 mmφ, the conductive rubber layer 2b is made of EPDM, and the surface layer 2c is made of 10 μm thick nylon resin. The hardness of the charging roller 2 is 54.5 mm (ASKE
RC). E is a power supply unit that applies a voltage to the charging roller 2 and supplies a predetermined voltage to the metal core 2 a of the charging roller 2. In FIG. 1, E indicates a DC voltage,
It is preferable that an AC voltage is superimposed on a DC voltage.

 Preferred process conditions in this case are shown below.

Contact pressure 5 to 500 g / cm AC voltage 0.5 to 5 KV _pp AC frequency 50 to 3000 Hz DC voltage -200 to -900 V FIG. 2 is a schematic diagram showing another example of the contact charging device. The same reference numerals are given to the same members as those in the apparatus of FIG. 1 described above, and the description will not be repeated.

The contact charging member 2 'of this apparatus is in the form of a blade which is brought into contact with the photosensitive drum 1 in a forward direction at a predetermined pressure, and the blade 2' is electrically connected to a metal supporting member 2'a to which a voltage is supplied. Rubber 2'b is supported, and the photosensitive drum 1
Is provided with a surface layer 2'c to be a release coating. Nylon having a thickness of 10 μm was used as the surface layer 2′c. According to this embodiment, the same operation and effect as those of the apparatus shown in FIG. 1 can be obtained without any trouble such as adhesion between the blade and the photosensitive drum.

In the above two examples, a roller-shaped or blade-shaped charging member was used. However, the present invention is not limited to this, and the present invention can be applied to other shapes.

In addition, the charging member is composed of a conductive rubber layer and a release coating, but is not limited thereto. A high resistance layer between the conductive rubber layer and the release coating surface to prevent leakage to the photoreceptor, for example, an environment It is preferable to form a hydrin rubber layer having small fluctuation.

Also, PVDF is used as a release coating instead of nylon resin.
(Polyvinylidene fluoride) or PVDC (polyvinylidene chloride) may be used. As the photoconductor, amorphous silicon, selenium, ZnO or the like can be used. In particular, when amorphous silicon is used for the photoconductor, compared to the case where other materials are used, even if the softening agent of the conductive rubber layer adheres to the photoconductor even to a small extent, the image flow becomes severe, so The effect of the insulating coating is great.

In the cleaning step, the photosensitive drum after the transfer of the developer image is generally cleaned and cleaned by a cleaning member such as a blade or a roller of a cleaner, which is subjected to wiping and removal of the remaining developer and other contaminants. Provided for image formation.

In addition, such a cleaning process involves electrophotography,
It is also possible to carry out the charging step, the developing step, or the transferring step at the same time.

The present invention is particularly effective for an image forming apparatus in which the surface of a latent image carrier is an organic compound. When the organic compound forms the surface layer, it has good adhesion to the binder resin contained in the developer, and particularly when the same material is used, a chemical bond is generated at the contact point, and the This is for accelerating the agent fusion.

Examples of the surface material of the latent image carrier include silicone resin, vinylidene chloride, ethylene-vinyl chloride, styrene-acrylonitrile, styrene-methyl methacrylate, styrene, polyerythene terephthalate, and polycarbonate, but are not limited thereto. Other monomers or copolymerization or blending between the exemplified resins can also be used.

The present invention is particularly effective for an image forming apparatus in which the diameter of the latent image carrier is 50 mm or less. This is because, in the case of a small-diameter drum, even if the linear pressure is the same, the curvature is large, and the concentration of pressure tends to occur at the contact portion.

It is considered that the same phenomenon occurs in the belt photoreceptor, and the present invention is also effective for an image forming apparatus having a radius of curvature of 25 mm or less at the transfer section.

Embodiments The basic configuration and features of the present invention have been described above, but the present invention will be specifically described below based on embodiments. However, this does not limit the embodiment of the present invention at all. Parts in the examples are parts by weight.

Example 1 The above mixture is melt-kneaded with a twin-screw extruder heated to 120 ° C., the cooled kneaded material is coarsely pulverized by a hammer mill, the coarsely pulverized material is finely pulverized by a jet mill, and the obtained finely pulverized powder is The particles were classified to obtain a magnetic particle classified powder (Tg 60 ° C.) having a volume average particle diameter of 12 μm.

0.3% by weight of silica fine powder was added to the classified powder and mixed with a Henschel mixer to obtain a developer (I).

Next, the developer (I) was charged using a DC voltage and an AC voltage (150 Hz, 1500 V _pp ) to the charging device by using an image forming apparatus having a contact charging device shown in FIG.
Was applied, and a printing test was conducted at normal temperature and normal humidity (25 ° C., 60% RH) to form a developer image by a reversal developing method at a printing speed of 4 sheets (A4) / min. . At the same time, the appearance of the charging member (roller type) and the surface of the photosensitive drum were observed, and fusion was evaluated using a solid black image.

 Table 1 shows the evaluation results.

 However, the evaluation was performed according to the following criteria.

Fog ○: Almost none △: Fogged but practically acceptable ×… Not practically acceptable Photoreceptor fusion (evaluated by the number of white spots on A4 solid black image) ○: No fusion at all ○ △: 1 in A4 solid black 3 to 10 fusion points in A4 solid black × 10 or more fusion points in A4 solid black Example 2 Silicone resin II instead of silicone resin I
(Tg80 ° C.) Developer (II) was prepared and evaluated in the same manner as in Example 1 except that 1 part was used.

 Table 1 shows the evaluation results.

Example 3 Example 1 except that the amount of silicone resin I was changed to 5 parts.
A developer (III) was prepared in the same manner as described above, and evaluated using the blade-type charging member shown in FIG.

 Table 1 shows the evaluation results.

Comparative Example 1 A developer (IV) was prepared and evaluated in the same manner as in Example 1 except that the silicone resin I was not used.

 Table 1 shows the evaluation results.

Comparative Example 2 Silicone Resin III Instead of Silicone Resin I
A developer (V) was prepared and evaluated in the same manner as in Example 1 except that (Tg = 30 ° C.) was used.

 Table 1 shows the evaluation results.

[Effects of the Invention] According to the present invention, a specific silicone resin is contained in the developer particles to protect the surface of the photoreceptor, and high-quality images free from developer fusion and fogging can be obtained. Obtainable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are explanatory views schematically showing a contact charging device used in the image forming method of the present invention. 1 ... Photoreceptor drum, 2,2 '... Charging member E ... Power supply

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masayoshi Kato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Satoshi Matsunaga 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Hiroshi Yusa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Kiyoko Tsuchiya 3-30-2, Shimomaruko, Ota-ku, Tokyo Canon Inc. ( 56) References JP-A-58-38958 (JP, A) JP-A-56-123551 (JP, A) JP-A-53-130036 (JP, A) JP-A-56-1550757 (JP, A) Hei 4-142556 (JP, A) JP-A-1-267667 (JP, A)

Claims (4)

(57) [Claims] 1. A developer used in an image forming method having a charging step of charging a photoreceptor by bringing a charging member to which a voltage obtained by superimposing a DC voltage and an AC voltage applied thereon into contact with an OPC photoreceptor, Glass transition point (Tg) measured by thermal analyzer
A thermoplastic silicone resin having a temperature of 40 to 90 ° C. and a binder resin, a colorant or a magnetic substance. 2. A silicone resin comprising, as organic substituents, at least one substituent selected from an alkyl group, an aryl group, a modified alkyl group and a modified aryl group, and a phenyl group;
The developer according to claim 1, wherein the developer has one or more substituents selected from a modified phenyl group. 3. A charging step of bringing a charging member into contact with an OPC photoreceptor and applying a voltage obtained by superimposing a DC voltage and an AC voltage from the outside to charge the photoreceptor; and a glass transition measured by a differential thermal analyzer. Point (T
g) using a thermoplastic silicone resin having a temperature of 40 to 90 ° C. and a developer containing at least a binder resin, a colorant, or a magnetic substance. 4. A silicone resin comprising, as an organic substituent, at least one substituent selected from an alkyl group, an aryl group, a modified alkyl group and a modified aryl group, and a phenyl group;
The image forming method according to claim 3, wherein the image forming method has one or more substituents selected from a modified phenyl group.