JPH07239559A - Method for producing thick photosensitive layer of electrophotographic photoreceptor - Google Patents

Abstract

(57) [Abstract] [Purpose] When a thick electrophotographic photosensitive layer using an abrasion-resistant binder resin is formed by dip coating, the electrophotographic photosensitive layer is less likely to cause sagging of the coating at the coating start portion. To provide a manufacturing method of. [Structure] When a thick photosensitive layer is formed by a dip coating method,
Before the dip coating at the second stage coating speed (V ₂ ) for setting the speed of pulling up the coating object 1 from the coating liquid 2 at two stages, and making the entire film thickness a predetermined film thickness at this time In addition, there is a short-time (Tv ₁ ) dip coating with a first-step coating speed (V ₁ ) faster than the second-step coating speed (V ₂ ). Do it continuously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrophotographic photosensitive member used in a copying machine, a printer, a facsimile or the like, and more particularly to a method for manufacturing an electrophotographic photosensitive member by a dip coating method.

[0002]

2. Description of the Related Art In an electrophotographic process, a latent image is visualized by electrostatic force, and an electrophotographic photosensitive member used in the process requires good chargeability and rapid surface potential decay by light irradiation. Become. In order to satisfy these characteristics, a photoconductor composed of an inorganic compound such as selenium, selenium-tellurium alloy, and selenium arsenide has been adopted, and has been used in many copying machines and printers. However, these materials have some problems in terms of environmental safety, are difficult to handle because they are used in an amorphous state, and are expensive because they need to be vacuum-deposited to a thickness of several tens of μm. However, it cannot be said that the requirements for the electrophotographic photosensitive member are sufficiently satisfied.

In order to improve these drawbacks, electrophotographic photoreceptors using organic materials have been actively developed and put into practical use. One of the practically used organic material-based electrophotographic photoreceptors is a laminated-type electrophotographic photoreceptor comprising a charge generation layer (CGL) and a charge transport layer (CTL). It is actually used, but in recent years CG on CTL for positive charging process
There is also a proposal of a configuration in which L is provided.

Furthermore, since the coating process of the electrophotographic photosensitive member of the laminated type is complicated, the charge generating material and the charge transporting material are dispersed together in the binder resin to have both the charge generating function and the charge transporting function. There is also a proposal for a single-layer type electrophotographic photoreceptor. By the way, when an endless belt-shaped metal foil or metal cylinder is used as a conductive support of an electrophotographic photoreceptor and a photosensitive layer is provided thereon, a method of immersing the support in a coating liquid and pulling it up is generally adopted. . For example,
A cylindrical conductive support having CGL previously formed thereon is dipped in a thick film coating solution containing the above CTL, and by dip coating, a CTL is formed on the CGL and a laminated photoreceptor. Become. The photosensitive layer of such an electrophotographic photoreceptor is
In the case of a laminated type, a CTL of 10 μm or more is provided on a CGL of 1 μm or less, and in the case of a single layer type, one layer has a thickness of 10 μm.
It is necessary to apply a thick film of m or more. This dip coating method will be described with reference to the drawings. FIG. 4 is a diagram showing an outline of the dip coating method. FIG. 4 (a) shows a state in which the article to be coated 1 is immersed in the coating solution 2 in the coating tank 3, and FIG. 4 (b) shows that the entire article to be coated is pulled up from the coating solution to be coated. The state where the coating liquid layer 4 is attached to the surface of the work is shown. After this, the coating liquid layer 4 on the article to be coated
Is dried by heating in an oven or the like to obtain an object to be coated having a thick coating film. After this, again with the new support,
The steps of FIGS. 4A and 4B are repeated.

By the way, the life of the electrophotographic photosensitive member is largely attributed to the abrasion of the photosensitive layer in the cleaning step of the electrophotographic process, and studies are being made daily for higher durability. For example, various resins have been studied as a binder resin for an electrophotographic photosensitive member having this thick photosensitive layer, but so-called engineering plastics such as polycarbonate resin are often used.
In order to further improve the abrasion resistance of the photosensitive layer, development is progressing in the direction of increasing the molecular weight of a resin having high abrasion resistance, such as a polycarbonate resin, and increasing the thickness of the photosensitive layer. Thick film coating liquids containing these abrasion-resistant engineering plastics as binder resins have low solubility in general solvents and often use special solvents such as dichloromethane (hereinafter referred to as MDC) as solvents. .

[0006] The MDC has a good solubility in a resin having a high abrasion resistance, such as a polycarbonate resin, and has a low boiling point of about 40 ° C, so that evaporation at the time of coating is quick, and the coating film sag (predetermined film). It is a solvent that is safe for the production of electrophotographic photoconductors because it has a property that it does not easily form a thin portion until obtaining the thickness) and has low flammability even though it is a low boiling point solvent.

However, the problem here is MD.
Even if C is used, when the film thickness is increased by the dip coating method, the coating sag at the coating start portion (upper pulling portion) becomes long. FIG. 5 is a diagram for explaining the definitions of coating film sag and stable film thickness. In FIG. 4, when a thick film is formed on the surface of the object to be coated by the dip coating method, the film thickness of the coating film on the pulling up part of the material to be coated is the film thickness of the portion where the predetermined film thickness on the lower side The thin portion until D (called stable film thickness) is the sagging of the coating film. The film separation from the coating start position to the portion 1 μm thinner than the stable film thickness D is defined as the coating sag length L. The shorter the coating film sagging length L, the faster the film thickness rises and the smaller the sagging.

Further, if the binder resin is made to have a higher molecular weight aiming at abrasion resistance, the viscosity of the coating liquid with respect to the solid content increases, so that the solid content concentration must be lowered, and the coating film at the coating start portion is also required. There is a problem that the sauce becomes longer.

[0009] On the other hand, the influence of halogen-based solvents such as MDC on the environment has begun to be regarded as a problem, and regulation has recently started from some halogen-based solvents. For example, MDC standards were set in early 1993 for water quality regulations. Atmospheric emission regulations have not been listed yet, but it is possible that they will be subject to regulations in the future, and voluntary regulations have started in the industry. In the United States, MDC is classified as a substance suspected of being carcinogenic.
It is necessary to find an alternative solvent and change it aggressively before it is subject to usage restrictions. If a non-halogen solvent such as tetrahydrofuran (hereinafter referred to as THF) is used, the problem of sagging becomes more remarkable. THF has a strong dissolving power and can sufficiently dissolve a resin having high abrasion resistance, such as a polycarbonate resin and other photosensitive material components. However, since THF has a boiling point of 66 ° C and a boiling point that is about 26 ° C higher than that of MDC (about 40 ° C) and has a slow evaporation rate, the solvent of the dipping start portion is higher than that of the coating liquid using MDC. It has the drawback that the sauce becomes longer.

On the other hand, not from the solvent side of the dip coating solution,
Although it has been confirmed that the concentration of the solid content of the thick film coating liquid is high, the effect of suppressing the film sagging is confirmed, but since the liquid viscosity of the thick film coating liquid increases,
It becomes difficult to remove bubbles in the thick film coating liquid. There is also a method of partially (double) coating only the upper end (JP-A-59-80364 and JP-A-5-66854).
Gazette), the effect of suppressing coating film sag is small, and solvent MDC is used.
Even if the suppression effect is sufficient in the case of the coating liquid of No. 2, the effect is insufficient in the case of THF having a large coating sag, and it is difficult to increase the film thickness.

[0011]

SUMMARY OF THE INVENTION According to the present invention, when a thick electrophotographic photosensitive layer using a resin having high abrasion resistance as a binder resin is formed by a dip coating method, a problem of coating sagging at a coating start portion is a problem. An object of the present invention is to provide an industrially advantageous manufacturing method of an electrophotographic photosensitive member having a thick photosensitive layer suppressed to a level that does not exist.

[0012]

According to the present invention, in a method for producing a thick film photosensitive layer of an electrophotographic photoreceptor by a dip coating method, after dipping a coating object in a coating solution, The entire work is pulled up from the coating liquid at two speeds to perform dip coating, and at this time, the second coating speed (V ₂ ) is applied to make the overall film thickness a predetermined thickness. Before coating, there is a short-time (Tv ₁ ) dip coating with a _first coating speed (V ₁ ) faster than the _second coating speed (V ₂ ). Provided is a method for producing a thick photosensitive layer of an electrophotographic photosensitive member, characterized in that dip coating is continuously performed.

The present inventor has previously proposed a method for producing an electrophotographic photosensitive member in which a thick film is applied by dip coating when a thick photosensitive layer is provided by the dip coating method. And a method in which the coating film is pre-dried or heat-dried between the second immersion coating and the second immersion coating (JP-A-5-3448605).
issue). The present inventor has further studied the method for producing a thick film by dip coating, and does not perform dip coating in two steps, but in a single dip coating, the entire coating object is in the coating liquid. Immersion coating is carried out by pulling it up at a two-step speed, and at this time, two steps are performed before the second-step coating speed (V ₂ ) for achieving the predetermined overall film thickness. Shorter time (Tv ₁ ) due to the _first stage coating speed (V ₁ ) faster than the eye coating speed (V ₂ ).
It has been found that the problem can be more easily solved by continuously performing the first step and the second step.

In the production method of the present invention, in forming a thick electrophotographic photosensitive layer, a non-halogen solvent which has little influence on the environment is used, and a binder resin having a high molecular weight is used to form a thick photosensitive layer. Even if the film formation is advanced, it is possible to obtain an electrophotographic photosensitive member having a CTL in which sagging of the coating film at the coating start portion is suppressed to a problem-free level. The method of the present invention can also be applied to a thick film CTL of a laminated photosensitive layer composed of CGL and CTL, and a single-layer photosensitive layer having a charge generating function and a charge transporting function.

The present invention will be described in more detail below. Figure 1
FIG. 4 is a diagram for explaining film formation and development of dip coating. Figure 1
Compared to the case where the coating speed is high as in (c),
As shown in (b) to FIG. 1 (a), as the coating speed is gradually decreased, the stable film thickness becomes thinner and the coating film sag length becomes shorter. The rising state is shown by a similar curve regardless of whether the coating speed is high or low. That is, when the coating speed is slow, the film thickness rising state similar to that when the coating speed is high is taken up to near the stable film thickness in the middle of the film thickness rising curve.

The film thickness when the coating speed is changed even if the coating speed at the coating start portion is increased for the purpose of shortening the coating sag portion and thereafter the entire coating is performed at a predetermined speed. Since the rising curves are the same, as shown in FIG. 1D, the film thickness distribution is limited to the thick film portion before the stable film thickness. However, as a result of diligent study on the film-forming development of the dip coating, the present inventor found that
By making the coating speed (V ₁ ) in the _first step of the coating start portion faster than the coating speed (V ₂ ) in the second step and shortening the time (Tv ₁ ) in the V ₁ state, As shown in d ₁ ) to (d ₄ ), the thick film part before the stable film thickness moves to the coating start side, and in (d ₄ ) the thick film part supplements the rising part of the film thickness (the thick film part disappears. It looks like).

By utilizing this development, the film thickness is secured by applying the _first step coating speed (V ₁ ) for a short time, and then the predetermined film thickness is obtained by the second step coating speed (V ₂ ). By dip coating to obtain
It has become possible to compensate for the sagging portion of the coating film and accelerate the rise of the coating film thickness to shorten the sagging length of the coating film. The fast coating speed (V ₁ ) of the _first step of the present invention depends on the coating speed (V ₂ ) of the second step for a predetermined overall film thickness, but is twice to 4 times (V ₂ ).
Double speed is preferred. (V ₁₎ of the time (Tv ₁₎ also (V ₂₎
However, 0.1 to 1.0 second is preferable. The method of the present invention is an industrially advantageous manufacturing method in which the existing equipment can be used as it is without any new modification, the coating time is almost the same as that of the current method, and the length of coating film sag can be shortened.

In the present invention, although various chlorine-based solvents can be used as the paint solvent, it is preferable to use THF because it poses a problem of environmental pollution. When THF is used, if it is used in the form of a mixed solvent in which other solvent is used in combination with this instead of THF alone, the viscosity per solid content can be lowered, and therefore, the same viscosity can result in a high solid content concentration. preferable. As the solvent that can be mixed with THF, a solvent having a boiling point of 30 to 65 ° C is desirable, and for example, acetone (about 56 ° C), methyl acetate (about 57 ° C),
Methanol (65 ° C), n-pentane (about 36 ° C), t
Examples thereof include ert-butyl methyl ether (about 55 ° C.), and acetone is particularly desirable. However, the mixing ratio with THF needs to be appropriate. The binder resin that can be used in the present invention is preferably an engineering plastic having high abrasion resistance, such as a polyamide resin, a polycarbonate resin, a polysulfone resin, or a polyphenylene oxide, but other resins may be used together. As the polycarbonate resin, there are general C, A and Z types, but the Z type is preferable. The amount of these binder resins in the laminated CTL or single-layer type photosensitive layer is 30 to 90 wt%, preferably 40 to 70 wt%.

[0019]

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

Example 1 94 parts by weight of a charge transport material represented by the following formula (1) and a Z type polycarbonate resin (manufactured by Teijin Ltd .: Panlite TS-2)
050) 104 parts was dissolved in 802 parts by weight of the solvent THF, and a charge transport liquid (solid content 19.8 wt%, viscosity about 300) was obtained.
cPs).

[Chemical 1] A cylindrical substrate was dipped in this charge transporting liquid, the coating speed (V ₁ ) was 16.0 mm / sec, the time in the state of V ₁ (Tv ₁ ) was 0.3 seconds, and then the coating speed (V ₂ ) 6.0m
Slow down to m / sec to coat the whole, and dry for 30 minutes at 130 ° C with an open dryer to obtain a stable film thickness D of about 30.
An evaluation sample of μm was prepared.

Comparative Example 1 A cylindrical substrate was dipped in the charge transport liquid of Example 1, coated at a coating speed (V ₂ ) of 6.0 mm / sec, and dried at 130 ° C. for 30 minutes in an open dryer. Then, an evaluation sample having a stable film thickness D of about 30 μm was prepared. The film thickness of the CTL provided on the cylindrical substrates of the above Examples and Comparative Examples was measured with an eddy current film thickness meter in the axial direction of the cylindrical substrate from the coating start portion at a measurement interval of 5 mm. The results are shown in Table 1 and FIG.

[0022]

[Table 1] It can be seen from Table 1 and FIG. 3 that even with the same stable film thickness of 30 μm, the sag of the comparative example is 50 mm, whereas the sagging length of the coating is 50 mm in the comparative example. The length was 27 mm, and the effect of reducing the sagging of the coating film was observed. In the above Examples and Comparative Examples, THF was used as the coating liquid solvent.
However, when the environmental problem was tolerated and only the problem of thickening the film was taken into consideration, the same effect was observed with a chlorine-based solvent.

[0023]

According to the present invention, when a thick electrophotographic photosensitive layer is formed by the dip coating method, the speed of pulling up the coating object from the coating liquid is set to two stages, and the second stage coating speed ( V ₂ )
The coating speed (V ₁ ) is further increased to perform the first stage dip coating for a short time (Tv ₁ ), and then the second stage coating speed (V ₂ ).
It is possible to suppress sagging of the coating film by continuously performing the dip coating. Further, by using this method, it is possible to increase the film thickness while suppressing the coating film. Further, the effect can be obtained even if a non-halogen solvent that causes a large sagging of the coating film is used as the solvent of the coating liquid. Therefore, the method of the present invention is
It is a highly practical manufacturing method that can use the existing equipment as it is without any modification, the coating time is almost the same as the current one, and the coating sag length can be shortened.

[Brief description of drawings]

FIG. 1 is a diagram illustrating film formation and development in dip coating.

[FIG. 2] The coating speed (V ₁ ) in the _first step at the coating start portion is made faster than the coating speed (V ₂ ) in the second step, and the time in the state of V ₁ (T
v ₁₎ by a shorter, illustrates that the thick film portion before stable thickness is moved in the coating start side.

FIG. 3 is a diagram showing the CTL film thickness distribution in the axial direction of the cylindrical substrate in the photoconductors obtained in Examples and Comparative Examples.

FIG. 4 is a diagram showing an outline of a dip coating method.

FIG. 5 is a diagram for explaining the definition of coating film sag and stable film thickness, showing a typical example of axial film thickness distribution of a thick film provided on a cylindrical support by a dip coating method. Is.

[Explanation of symbols] 1 coating object 2 coating liquid 3 coating tank 4 coating liquid layer

Claims (1)

[Claims] 1. A method for producing a thick film photosensitive layer of an electrophotographic photosensitive member by a dip coating method, comprising dipping a coating object in a coating solution, and then dipping the entire coating object in the coating solution. Immersion coating is carried out by pulling up at a step speed, and at this time, before the dip coating at the second step coating speed (V ₂ ) to obtain a predetermined overall film thickness, the second step is performed. There is a short-time (Tv ₁ ) dip coating with a first-step coating speed (V ₁ ) that is faster than the coating speed (V ₂ ), and the first-step and second-step dip coatings are performed continuously. A method for producing a thick film photosensitive layer of an electrophotographic photosensitive member, comprising: