JPH06100858B2 - Electrophotographic method using photoconductive toner - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrophotographic method using a photoconductive toner, and more specifically, it efficiently transfers and forms a photoconductive toner. An improvement for improving the contrast of an image.

(Prior Art) An electrophotographic method using a photoconductive toner has been known for a long time. In FIG. 4 for explaining the conventional electrophotography of this type, a layer of the photoconductive toner 2 charged with a constant polarity charge (for example, a negative charge) is formed on the surface of the conductive substrate 1 ( Charging step (A)). Then, image exposure is performed through the original 3, the charge of the toner disappears in the light portion L, and the charge of the toner remains in the dark portion D to form the electrostatic latent image 4 on the photoconductive toner layer (image. Exposure step (B)). Transfer medium 5 to toner layer
Are superposed on each other, and, for example, the charge having the opposite polarity to the charge of the photoconductive toner is charged from the back surface of the transfer medium 5 by the corona charger 6 (transfer step (C)).

As a result, the charged photosensitive toner image 4 is electrostatically transferred onto the transfer medium surface on the transfer medium 5, and the copy is obtained by applying the transfer to a fixing means known per se.

(Problems to be Solved by the Invention) According to the above-mentioned electrophotographic method, although the transfer of the charged toner particles to the transfer medium is possible, the charged toner particles are still strong against the conductive substrate. Adhesion remained and therefore transfer efficiency was still low, and it was difficult to form an image having sufficient contrast.

Therefore, it is an object of the present invention to eliminate the above-mentioned drawbacks, efficiently transfer charged photoconductive toner particles from a conductive substrate to a transfer medium, and improve the contrast of a toner image.

(Means for Solving Problems) According to the present invention, a layer of charged photoconductive toner is formed on a conductive substrate, and the photoconductive toner layer is imagewise exposed to charge the toner layer. A photoconductive toner is used which is characterized in that an image composed of toner particles is formed and the charged toner image in the toner layer is electrostatically transferred to a transfer medium while applying mechanical vibration of 100 KHz to 1 MHz to the substrate. Electrophotography is provided.

(Operation) In FIG. 1 for explaining the transfer process of the present invention, the conductive substrate 1 is connected to the inverse piezoelectric element 7, and the inverse piezoelectric element 7 is connected.
The electric signal from the oscillator 8 is supplied to the conductive substrate 1 by amplifying the electric signal from the amplifier 8 with the amplifier 9.
Gives mechanical vibration in the direction perpendicular to the plane. When the back surface of the transfer medium 5 is charged to the opposite polarity to the charge of the photoconductive toner 4 under the condition that the mechanical vibration is applied, the charged toner 4 is efficiently transferred to the surface of the transfer medium 5.

Generally, the adhesive force between powder and flat plate is calculated by the following formula Given by. In the above formula, F is adhesive force, A is Hama
ker constant, R is particle diameter, D is particle-plate distance, k is plate dielectric constant, and q is powder charge amount. Here, the first term on the right side of the above equation (1) represents the dispersion force (Van der Waals force), and the second term represents the image force (Coulomb force).

Now, using a conductor for the flat plate, D = 4A, R = 5 μm, q = −
At 3 × 10 ^-5 esu, the image force is -0.0009 dynes and the dispersive force is 0.05 dynes, which shows that the adhesive force due to the dispersive force is much larger than that due to the electrostatic force (image force).
This is the reason why the charged photoconductive toner cannot be transferred efficiently under normal electrostatic transfer conditions.

By the way, when the flat plate is a conductor (k → ∞) and the distance at which the image force and the dispersive force are equal to each other is obtained, the following formula is obtained from formula (1). Is obtained, and by substituting the above-mentioned parameters, a value of D = 30Å is obtained.

As shown in the explanatory view of FIG. 2, in this case, the dispersion force is dominant in the area A ₁ where the distance D from the flat plate is within 30 Å, and the charged toner particles 4 are attracted to the flat plate side, It is understood that in the area A ₂ where the distance D exceeds 30 Å, the electrostatic force is dominant and the charged toner particles 4 can be attracted in the direction of the external electric field E.

According to the present invention, charged photoconductive toner particles are separated from the dispersion force-dominated region to the electrostatic force-dominated region by the inertial force thereof by borrowing the force of mechanical vibration, so that they are exposed to the external electric field. It is possible to efficiently move to the transfer medium. Further, the frequency of mechanical vibration for moving the charged toner to the region where the electrostatic force is controlled is in the range of 100 KHz to 1 MHz.

(Effects of the Invention) FIG. 3 is a plot of the relationship between the electric field strength and the transfer amount of charged photoconductive toner particles. According to the present invention (curve A), mechanical vibration is caused. By utilizing the toner inertial force, it becomes possible to transfer a larger amount of toner with a lower electric field than the conventional method (curve B), and the contrast between the exposed portion (L) and the non-exposed portion (D) is remarkable. It became possible to raise it to.

(Explanation of preferred embodiments) In the present invention, as the conductive substrate, for example, a metal drum such as aluminum, tin plate, copper or the like, or a plastic film substrate such as a biaxially stretched polyester film is laminated with aluminum foil or metal Al is vapor-deposited. Any electrically conductive substrate such as a composite or an electrically conductive glass (NESA glass) is used.

As the photoconductive toner, a photoconductive pigment in an electrically insulating resin fixing medium, for example, zinc oxide, an inorganic photoconductor such as CdS, or a perylene pigment, a quinacridone pigment, a pyranthrone pigment, a phthalocyanine pigment, or a disazo pigment. Particles composed of a composition in which a photoconductive organic pigment such as a base pigment or a trisazo pigment is dispersed are used. The photoconductive pigment is preferably used in an amount of 3 to 50 parts by weight, particularly 5 to 30 parts by weight, per 100 parts by weight of the fixing medium. When the amount of the photoconductive pigment is less than the above range, the image density and toner sensitivity tend to decrease, and when it is more than the above range, the charge retention property tends to decrease.

As the fixing medium, an electrically insulating fixing resin known per se, such as polystyrene, styrene-acrylic copolymer, acrylic resin, polycarbonate, polyarylate (polyester of bisphenol A and iso or terephthalate acid), polyvinyl butyral, Polysulfones can be used, and photoconductive resins such as polyvinylcarbazole, alone or in combination with electrically insulating resins, are also used for the purposes of the present invention.

In a suitable photoconductive toner, a charge transport medium is used as a fixing medium, the above-mentioned photoconductive pigment is dispersed as a charge generating pigment in the charge transport medium, and this dispersion system is used as a photoconductive toner. As the charge transport medium, the above-described electrically insulating resin and charge transport material such as polyvinylcarbazole, phenanthrene, N-ethylcarbazole,
2,5-diphenyl-1,3,4-oxazole, 2,5-bis-
(4-Diethylaminophenyl) -1,3,4-oxadiazole, bis-diethylaminophenyl-1,3,6-oxadiazole, 4,4′-bis (diethylamino) -2,2 ′
-Dimethyltriphenylmethane, 2,4,5-triaminophenylimidazole, 2,5-bis (4-diethylaminophenyl) -1,3,4-triazole, 1-phenyl-3
Hole transporting substances such as-(4-diethylaminostil) -5- (4-diethylaminophenyl) -2-pyrazoline and p-diethylaminobenzaldehyde- (diphenylhydrazone), 2-nitro-9-fluorenone, 2,7-
Dinitro-9-fluorenone, 2,4,7, -trinitro-9
-At least one of electron transport substances such as fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2-nitrobenzothiophene, 2,4,8-trinitrothioxanthone, dinitroanthracene, dinitroacridine and dinitroanthraquinone Is used in combination. The charge transport material is generally 10 to 200 parts by weight per 100 parts by weight of resin.
It is advisable to use parts by weight, in particular 30 to 120 parts by weight.

The photoconductive toner used in the present invention may contain, in addition to the above-mentioned essential components, auxiliary agents known per se in accordance with a known formulation. Examples of such auxiliaries include offset preventive agents such as waxes and pressure fixability imparting agents.

The toner can be molded by a dry method such as kneading, pulverizing and sieving, or a wet method of spray granulating in the form of a dispersion, and the particle size of the toner particles is generally in the range of 5 to 30 microns. Is desirable.

Examples of suitable photoconductive toners include phthalocyanine = styrene-acrylic resin type and phthalocyanine = polyester resin type. These photoconductive toners have triboelectrification characteristics toward negative polarity. On the other hand, as the photoconductive toner having the triboelectric charging property to the positive polarity, a resin toner containing a nitrogen atom in the main chain or side chain such as polyamide resin may be used instead of the above-mentioned resin.

For coating the photoconductive toner on the conductive substrate, any coating method can be adopted as long as uniform coating and adhesion are possible. The photoconductive toner is charged by friction or the like, and a bias charge is applied between the photoconductive toner support and the conductive substrate to electrostatically adhere the photoconductive toner onto the conductive substrate. For example, a method in which a photoconductive toner is mixed with a carrier to prepare a two-component agent, and a two-component magnetic brush known per se is formed on a conductive sleeve and applied, or a triboelectric charge is obtained. A method in which the toner alone is held on a first brush or a roller and applied is adopted.

Of course, instead of applying the charged photoconductive toner to the substrate, the non-chargeable toner may be applied to the substrate and the formed toner layer may be charged on the entire surface by using a corona charger or the like.

Image exposure of the charged photoconductive toner layer can be performed by transmissive exposure through a transparent original or reflective exposure through an opaque original, as well as light exposure from laser diodes, light emitting diodes, liquid crystal diodes, etc. You can also do it.

The direction of mechanical vibration applied to the substrate during electrostatic transfer may be vertical to the photoconductive toner layer supporting surface, horizontal, or intermediate to these. The vibration intensity is such that the toner particles on the surface of the substrate are transferred from the dispersion force control region to the electrostatic force control region, so that strong vibration is not required. Generally, it is desirable that the output of vibration is in the range of 0.001 to 100 watts, particularly 0.1 to 10 watts per 1 cm ^{2 of} unit area. As the frequency of vibration, the range of 100 KHz to 1 MHz is adopted as described above.

To give vibration to a conductive substrate, a method of giving vibration by inputting an electric signal to an inverse piezoelectric element such as a crystal oscillator or PZT porcelain connected to the conductive substrate; by an electromagnet connected to an AC power source A method of applying vibration; a method of mechanically applying vibration by rotational movement by a cam; a method of irradiating ultrasonic waves, etc. are appropriately adopted.

The present invention is characterized in that the toner is transferred to the transfer medium in a relatively low electric field. Generally, the transfer electric field is formed by performing corona discharge from the back surface of the transfer medium, or This is done by bringing the back surface of the medium into contact with an electrode roller to which a voltage is applied.

As the transfer medium, ordinary paper, a transparent resin film for an overhead projector, or the like is used, and the image is easily fixed by heat or pressure.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining a transfer process of the present invention, FIG. 2 is an explanatory diagram of the principle of the present invention, and FIG. 3 is a relationship between an electric field intensity and a transfer amount of charged photoconductive toner particles. FIG. 4 is a graph diagram in which is plotted, and FIG. 4 is an explanatory diagram illustrating an electrophotographic method using a conventional photoconductive toner. 1 ... Conductive substrate, 2 ... Photoconductive toner, 4 ... Electrostatic latent image,
5 ... Transfer medium.

Claims (1)

[Claims] 1. A conductive photoconductive toner layer is formed on a conductive substrate, and the photoconductive toner layer is imagewise exposed to form an image composed of charged toner particles on the toner layer. An electrophotographic method using a photoconductive toner, characterized in that the charged toner image in the toner layer is electrostatically transferred to a transfer medium while applying mechanical vibration of 100 KHz to 1 MHz.