JP3471873B2 - Image forming method - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to an image forming how,
For more information about the image forming how using an electrophotographic photosensitive member containing a specific material in a high speed process.

[0002]

2. Description of the Related Art An electrophotographic photosensitive member using an organic photoconductive substance has extremely high productivity, its material design is easier than that of an inorganic substance, its sensitivity region is easy to control, and it is relatively inexpensive. And has been widely studied so far. In particular, an electrophotographic photosensitive member having a charge generating layer containing a so-called charge generating substance such as an organic photoconductive dye or pigment and a charge transporting layer containing a charge transporting substance has been regarded as a defect of the conventional electrophotographic photosensitive member. Many of them exhibit good characteristics in terms of sensitivity and durability, and have been put to practical use.

In recent years, oxytitanium phthalocyanine (hereinafter, also referred to as TiOPc) has attracted attention among the charge generating substances. Since TiOPc has a very high sensitivity to light with a long wavelength around 600 to 800 nm, the light source is LE
It is extremely useful as a charge generating substance used in electrophotographic photoconductors for electrophotographic printers and digital copying machines, such as D and semiconductor lasers.

On the other hand, the electrophotographic apparatus is required to have higher image quality, higher speed and higher durability.

[0005]

However, TiO 2
Although the electrophotographic photosensitive member using Pc has high sensitivity, when it is used in a high-speed process, fog, black streaks, density unevenness, etc. occur in the obtained image.

An object of the present invention, an image forming how that can be obtained repeatedly stably excellent image even when used at high speed
To provide.

[0007]

Means for Solving the Problems That is, the present invention provides a charging step of charging a cylindrical electrophotographic photosensitive member by charging it, and exposing the charged electrophotographic photosensitive member. And an image exposure step of forming an electrostatic latent image by the above, a developing step of forming a visible image by developing the electrostatic latent image, and a transfer step of transferring the visible image to a transfer target member, In the image forming method, wherein the step, the image exposing step, the developing step and the transferring step are performed while the electrophotographic photosensitive member makes one rotation, the electrophotographic photosensitive member has a photosensitive layer on a conductive support, and the photosensitive layer Contains oxytitanium phthalocyanine as a charge generating substance and a charge transporting substance, and the work function (W _F ^CG ) of the charge generating substance and the work function (W _F ^CT ) of the charge transporting substance are represented by the following formula −0.2 <W. _F ^CG -W _F Satisfies ^T ≦ 0 (eV), an image forming method, wherein the time the electrophotographic photosensitive member is required for one rotation is equal to or less than 1.5 seconds.

As described above, when the electrophotographic photoreceptor containing TiOPc is used in a high speed process, image defects such as fog, black streaks and uneven density are likely to occur. The reason is not clear, but it is considered as follows. Since TiOPc has extremely high sensitivity, it is estimated that the amount of photocarriers generated is very large. Therefore, in the high-speed process, the following electrophotographic process is applied before the injection, transport and recombination of the generated photocarriers with the charge transport material are sufficiently performed, that is, with the photocarriers accumulated in the photosensitive layer. Will be done. This residual carrier adversely affects the image obtained as a memory (falling of the surface potential). This tendency becomes more remarkable as the charge generating substance has higher sensitivity and as the process cycle becomes shorter.

Therefore, the present inventors have found that the work function of TiOPc (W _F ^CG ) and the work function of the charge transport material used (W _{F C).}
The electrophotographic photoreceptor as ^CT) satisfies the following expression ^{_{-0.2 <W F CG -W F CT}} ≦ 0 (eV), the photosensitive member is used in a high speed process of one revolution within 1.5 seconds As a result, it was found that the effect of the present invention, that is, high image quality, high speed, and high durability can be realized.

When W _F ^CG -W _F ^CT is -0.2 eV or less, the effect of the present invention is not sufficiently obtained, and when W _F ^CG -W _F ^CT is more than 0, injection of photocarriers is excessively promoted and the electrophotographic photoreceptor is exposed to the surface. It becomes impossible to sufficiently hold the electric charge of.

The work function in the present invention is measured by measuring photoelectrons excited by ultraviolet rays in the atmosphere using a surface analyzer AC-1 type (low energy photoelectron measuring device) manufactured by Riken Keiki Co., Ltd. This was done by analyzing the sample surface.

The photosensitive layer of the electrophotographic photosensitive member used in the present invention may be a so-called single layer type in which the charge generating substance and the charge transporting substance are contained in the same layer, but the charge generating layer containing the charge generating substance and the charge transporting layer are also included. A so-called laminated type having a charge transport layer containing a substance may be used. In the present invention, an electrophotographic photoreceptor having a conductive support, a charge generation layer and a charge transport layer in this order is preferable.

The charge generation layer is formed by applying a solution in which TiOPc is dispersed in a suitable binder resin using a suitable solvent, and drying the solution. The film thickness is preferably 5 μm or less, and particularly preferably 0.1 to 2 μm.

TiOPc used in the present invention is represented by the following formula.

[0015]

[Outer 1] (In the formula, X ₁ , X ₂ , X ₃ and X ₄ represent Cl or Br, and h, i, j and k represent an integer of 0 to _4. ) TiO
References relating to the Pc synthesizing method and electrophotographic characteristics include, for example, JP-A-57-148745 and 59-362.
54, 59-44054, and 59-31.
No. 965, No. 61-239248, and No. 62.
-67094 publication etc. are mentioned. There are various kinds of crystal forms of TiOPc, like other phthalocyanine compounds. For example, JP-A-59-49544 (USP 4,444,861), JP-A-59-16
6959, JP-A 61-239248 (U)
SP 4,728,592), JP-A-62-67094 (USP 4,664,997), JP-A-63-36.
6, JP-A-63-116158, JP-A-6-
3-198067 and Japanese Unexamined Patent Publication No. 64-17066 report TiOPc having different crystal forms.

Among them, the diffraction angle 2θ ± 0.2 ° in CuKα characteristic X-ray diffraction is 9.0 °, 14.2 °,
The crystalline form of TiOPc having strong peaks at 23.9 ° and 27.1 ° has high sensitivity, and the present invention works very effectively.

Although the work function of TiOPc varies depending on the crystal form, it shows a value of about 5.2 to 5.4 eV.

The charge-transporting layer is formed by applying a solution of a charge-transporting substance dissolved in a suitable binder resin using a suitable solvent and drying it. Preferred examples of the charge transporting substance that can be used are shown below.
_{^{<W F CG -W F CT ≦}} 0 (eV) is not limited as long as it satisfies the following substances. Further, in the present invention, if the work function of the mixture satisfies the above relationship, two or more kinds of charge transport materials may be used. In this case, it is preferable to measure the work function with the charge transport substance dispersed in the resin.

[0019]

[Outside 2]

[0020]

[Outside 3]

In the present invention, W _F ^CG −W _F ^CT ≧ −
It is preferably 0.1 (eV).

In the present invention, the compounding ratio of the charge transport material and the binder resin is preferably 1: 2 to 2: 1 by weight, and particularly preferably 4: 5 to 3: 2. . If the ratio of the charge transport material is too small, the mobility may be low, and the effect of the present invention may not be obtained. Conversely, if the ratio of the charge transport material is too large, the mechanical strength as a film of the charge transport layer may be low. It may pass.

The thickness of the charge transport layer is preferably 5 to 40 μm, and particularly preferably 15 to 30 μm.

Even when the photosensitive layer is of a single layer type, the same materials as described above can be used, and the film thickness is preferably 5 to 40 μm, and particularly preferably 15 to 30 μm.

Examples of the conductive support used in the present invention include aluminum, aluminum alloys, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, indium, gold and platinum. In addition, a plastic (for example, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, acrylic resin, etc.) formed by coating such a metal or alloy by a vacuum deposition method, and conductive particles (for example, carbon black and silver particles) are suitable. Examples thereof include a support coated on a plastic, metal or alloy substrate with a binder resin, or a support obtained by impregnating plastic or paper with conductive particles.

In the present invention, an undercoat layer having a barrier function and an adhesive function may be provided between the conductive support and the photosensitive layer. The subbing layer can be formed of casein, polyvinyl alcohol, nitrocellulose, polyamide (nylon 6, nylon 66, nylon 610, copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, aluminum oxide and the like. The thickness of the undercoat layer is 5μ
It is preferably m or less, and particularly preferably 0.1 to 3 μm.

Further, in the present invention, in order to protect the photosensitive layer from external mechanical and chemical adverse effects, a resin layer as a protective layer, a resin layer containing conductive particles or a charge transport substance, etc. is exposed. It can also be provided on a layer.

The electrophotographic photoreceptor of the present invention can be used not only in electrophotographic copying machines, but also in electrophotographic applications such as facsimiles, laser beam printers, CRT printers, LED printers, liquid crystal printers and laser plate making. You can

FIG. 1 shows a schematic structure of an electrophotographic apparatus using the image forming method of the present invention.

In the figure, reference numeral 1 denotes a drum-shaped electrophotographic photosensitive member of the present invention, which is rotationally driven around an axis 1a in a direction of an arrow at a predetermined peripheral speed. The photoconductor 1 is uniformly charged on its peripheral surface by a charging means 2 at a predetermined positive or negative potential in the course of rotation, and then an image exposure means (not shown) exposes an exposure image L (slit). Exposure and laser beam scanning exposure). In this way, electrostatic latent images corresponding to the exposed images are sequentially formed on the peripheral surface of the photoconductor.

The formed electrostatic latent image is then developed by the developing means 4.
The toner developed image is transferred to a transfer material P, which is fed from a sheet feeding unit (not shown) between the photoconductor 1 and the transfer unit 5 in synchronization with the rotation of the photoconductor 1. 5 are sequentially transferred.

The transfer material P that has undergone the image transfer is introduced into the image fixing means 8 separated from the surface of the photoconductor, undergoes the image fixing, and is printed out as a copy.

After the image transfer, the surface of the photoreceptor 1 is cleaned by the cleaning means 6 to remove the residual toner after transfer, and then the pre-exposure means 7 removes the charge to repeatedly use the image.

In the present invention, a plurality of constituent elements such as the electrophotographic photoreceptor 1, the charging means 2, the developing means 4 and the cleaning means 6 are integrally combined as an apparatus unit. May be detachably attached to the apparatus body. For example, at least one of the charging unit 2, the developing unit 4, and the cleaning unit 6 is integrally supported together with the photosensitive member to form a unit, and a unit that is detachably attached to the apparatus body by using a guide unit such as a rail of the apparatus body. Good as a unit.

Further, in the case of using the electrophotographic apparatus as a copying machine or a printer, the light image exposure L irradiates the photoconductor with reflected light or transmitted light from the original, or reads the original with a sensor. The signal is converted into a signal, and a laser beam is scanned, an LED array is driven, or a liquid crystal shutter array is driven in accordance with the signal to irradiate the photoconductor with light.

Next, the present invention will be described according to examples.

[0037]

【Example】

Example 1 A coating composed of the following materials was applied to a 30φ × 260 mm aluminum cylinder by a dipping method, and 140 ° C.
And heat-cured for 30 minutes to form a conductive layer having a thickness of 18 μm.・ Conductive pigment: Titanium oxide coated titanium oxide 10 parts (weight part, the same applies below) ・ Resistance adjustment pigment: Titanium oxide 10 parts ・ Binder resin: Phenol resin 10 parts ・ Leveling agent: Silicone oil 0.001 part ・ Solvent : Methanol / methyl cellosolve (weight ratio) = 1
/ 1 20 copies

Next, a solution prepared by dissolving 3 parts of N-methoxymethylated nylon and 3 parts of copolymerized nylon in a mixed solvent of 65 parts of methanol and 30 parts of n-butanol was dipped on the conductive layer. By applying and drying, an undercoat layer having a film thickness of 0.5 μm was formed.

Next, TiOPc crystal powder (the diffraction angle 2θ ± 0.2 ° in CuKα characteristic X-ray diffraction was 9.0 °, 1
Those having strong peaks at 4.2 °, 23.9 ° and 27.1 °, W _F ^CG = 5.3 eV) 3 parts, polyvinyl butyral resin 2 parts and cyclohexanone 80 parts φ1 mm
After dispersing for 6 hours by a sand mill using glass beads, 100 parts of ethyl acetate was added to this solution to obtain a charge generation layer dispersion liquid. This solution was applied onto the undercoat layer by a dipping method and dried to form a charge generation layer having a thickness of 0.2 μm.

Next, 10 parts of the charge transport material (W _F ^CT = 5.4 eV) of the compound (1) and 10 parts of the polycarbonate Z resin were dissolved in a mixed solvent of 50 parts of monochlorobenzene and 10 parts of dichloromethane. . This coating material was applied onto the above-mentioned charge generation layer by a dipping method and dried to form a charge transport layer having a thickness of 23 μm.

The stability of the potential of the obtained photoreceptor was evaluated by a latent image tester having the same structure as an actual electrophotographic apparatus. This tester is designed so that the diameter of the photosensitive member and the process speed can be arbitrarily set. In this embodiment, the process speed is 72 mm / second, that is, the time required for the photosensitive member to make one rotation is 1.3 seconds. And Regarding the stability of the potential, the initial dark portion potential Vd is set to −650 V, the light portion potential V1 is set to −150 V, and each potential is measured after repeating the charging and exposure process 1,000 times, and the change amount is measured. It was evaluated by determining.

Further, the photosensitive member was attached to a laser beam printer (LBP-NX, manufactured by Canon Inc.), the process speed was set to the above value, and a continuous image output durability test of 10,000 sheets was conducted to obtain the result. The obtained image was visually evaluated. The results are shown in Table 1.

Example 2 Photosensitization was carried out in the same manner as in Example 1 except that 9 parts of Compound Example (1) and 1 part of Compound Example (7) (W _F ^CT = 5.45 eV) were used as the charge transport material. The body was created and evaluated.
However, the process speed was set to 94 mm / sec (the time required for the photoconductor to make one rotation was 1.0 sec). The results are shown in Table 1.

Example 3 A conductive layer and an undercoat layer were formed in the same manner as in Example 1 except that an aluminum cylinder of 40φ × 260 mm was used as the support.

Next, TiOPc crystal powder (the diffraction angle 2θ ± 0.2 ° in CuKα characteristic X-ray diffraction was 9.5 °,
9.7 °, 11.7 °, 15.0 °, 23.5 °, 2
Having strong peaks at 4.1 ° and 27.3 °, W
_F ^CG = 5.2 eV) 3 parts, polyvinyl butyral resin 2
And 80 parts of cyclohexanone were dispersed in a sand mill using φ1 mm glass beads for 24 hours, and then 100 parts of methyl ethyl ketone was added to this solution to obtain a charge generation layer dispersion liquid. This solution was applied onto the undercoat layer by a dipping method and dried to form a charge generation layer having a thickness of 0.2 μm.

Next, 9 parts of the charge transport material (W _F ^CT = 5.35 eV) of the above compound example (2) and polycarbonate Z
10 parts of the resin was dissolved in a mixed solvent of 50 parts of monochlorobenzene and 10 parts of dichloromethane. This coating material was applied onto the above-mentioned charge generation layer by a dipping method and dried to form a charge transport layer having a film thickness of 25 μm.

The photoreceptor thus obtained was evaluated in the same manner as in Example 1. However, since the process speed was 90 mm / sec (the time required for the photoreceptor to make one rotation of 1.4 seconds) and the diameter of the photoreceptor was different, the continuous image output durability test was not performed. The results are shown in Table 1.

Example 4 Compound Example (3) (W _F ^CT = 5.3e) as a charge transport material
A photoreceptor was prepared and evaluated in the same manner as in Example 1 except that 12 parts of V) were used. However, the process speed is 120
mm / sec (0.79 time required for the photoreceptor to make one rotation)
Seconds). The results are shown in Table 1.

Example 5 Compound Example (4) (W _F ^CT = 5.35) as a charge transport material
eV) was used and a photoreceptor was prepared and evaluated in the same manner as in Example 1 except that the thickness of the charge transport layer was 25 μm. However, the process speed was set to 67 mm / sec (the time required for the photosensitive member to rotate once was 1.4 sec). The results are shown in Table 1.

Example 6 Compound Example (8) (W _F ^CT = 5.47) as a charge transport material
A photoconductor was prepared and evaluated in the same manner as in Example 1 except that eV) was used. However, the process speed is 63 mm /
Second (time required for one rotation of the photosensitive member is 1.5 seconds). The results are shown in Table 1.

Example 7 Compound Example (9) (W _F ^CG = 5.49) as a charge transport material
A photoconductor was prepared and evaluated in the same manner as in Example 6 except that eV) was used. The results are shown in Table 1.

Comparative Example 1 Comparative compound (A) represented by the following formula as a charge transport material
(W _F ^CT = 5.55eV) except for using creates a photoreceptor in the same manner as in Example 1 and evaluated.

[0053]

[Outside 4] The results are shown in Table 1.

Comparative Example 2 The same as Example 1 except that 4 parts of the compound example (1) as the charge transport material and 6 parts of the charge transport material (W _F ^CT = 5.52 eV) used in Comparative Example 1 were used. A photoconductor was prepared in this manner and evaluated. The results are shown in Table 1.

Experimental Example 1 An electrophotographic photosensitive member was prepared and evaluated in the same manner as in Comparative Example 2 except that the process speed was 24 mm / sec (the time required for the photosensitive member to make one rotation 3.9 seconds). The results are shown in Table 1.
Shown in.

[0056]

[Table 1]

[0057]

As is evident from the foregoing description, according to the present invention, it is possible to provide an image forming how that can repeating superior image be used at a high speed to stably obtain.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a schematic configuration of an electrophotographic apparatus using an image forming method of the present invention.

[Explanation of symbols]

1 Electrophotographic photoreceptor of the present invention 1a axis 2 charging means 3 exposure section 4 developing means 5 Transfer means 6 Cleaning means 7 Pre-exposure means 8 Image fixing means L light image exposure P transfer material

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideyuki Ainotani               3-30-2 Shimomaruko, Ota-ku, Tokyo               Non non corporation (72) Inventor Hidetoshi Hirano               3-30-2 Shimomaruko, Ota-ku, Tokyo               Non non corporation

Claims (4)

(57) [Claims] 1. A charging step of applying an electric charge to a cylindrical electrophotographic photosensitive member by charging it, and an image in which an electrostatic latent image is formed by exposing the electrophotographic photosensitive member to which the electric charge is applied. An exposing step, a developing step of forming a visible image by developing the electrostatic latent image, and a transferring step of transferring the visible image to a transfer target member, the charging step, the image exposing step, the developing step and the transferring step. In an image forming method in which the step is performed while the electrophotographic photosensitive member makes one revolution, the electrophotographic photosensitive member has a photosensitive layer on a conductive support, and the photosensitive layer has oxytitanium phthalocyanine as a charge generating substance, and It contains a charge transport material, electric work function of the load generating material (W F ^_CG) and a work function of the charge transport material (W
_F ^CT ) satisfies the following formula −0.2 <W _F ^CG −W _F ^CT ≦ 0 (eV), and the time required for the electrophotographic photosensitive member to rotate once is 1.5.
An image forming method characterized by being less than a second. 2. The crystal form of the oxytitanium phthalocyanine has a diffraction angle (2θ) in CuKα characteristic X-ray diffraction.
The image forming method according to claim 1, wherein (± 0.2 °) has strong peaks at 9.0 °, 14.2 °, 23.9 ° and 27.1 °. 3. The image forming method according to claim 1, wherein the W _F ^CG and W _F ^CT satisfy the following formula: −0.1 <W _F ^CG −W _F ^CT ≦ 0 (eV). 4. The image forming method according to claim 1, wherein the photosensitive layer has a charge generating layer containing a charge generating substance and a charge transporting layer containing a charge transporting substance.