JPH09136058A - Method for forming coating film on cylindrical body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stable formation of a uniform coating film in the case a coating film is formed on the surface of a cylindrical body by immersing the cylindrical body in a coating liquid and pulling up the body from the liquid. SOLUTION: A coating apparatus is provided with a liquid circulation system provided with an overflow pipe to gather a liquid which overflows out of a coating tank and sends it to a storage tank and a hood which cover an upper part of the coating tank to form a closed space and moreover the apparatus is so composed as to prevent a gas from flowing out and flowing in through the overflow pipe and while using the apparatus and keeping the saturation degree of a solvent vapor in the upper part of the coating tank at not less than 60%, coating is carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coating film on a tubular body, and in particular, in the production of an electrophotographic photoreceptor, a charge generation layer is formed on the tubular body such as an aluminum tube. The present invention relates to a suitable method.

[0002]

2. Description of the Related Art A method of immersing a tubular body in a coating solution and then pulling it up to form a coating film on the tubular body is widely used in the production of an electrophotographic photoreceptor using an organic photosensitive material. For example, in a commonly used laminated electrophotographic photoreceptor, an aluminum tube is first dipped in a coating solution containing a charge generating agent and then pulled up to form a charge generating layer having a dry thickness of submicron to several microns. . Then, this is immersed in a coating solution containing a charge transfer agent and then pulled up to form a charge transfer layer having a dry thickness of several microns to several tens of microns on the charge generation layer to obtain an electrophotographic photoreceptor.

In this method, when the solvent evaporates on the surface of the coating liquid contained in the coating tank, the concentration of the coating liquid on the surface becomes non-uniform, and as a result, the coating film formed on the aluminum tube is formed. Also has the problem of being non-uniform. There is also a problem that the coating film becomes non-uniform even if the evaporation of the solvent from the raw pipe pulled up from the coating liquid becomes non-uniform. In order to cope with this, it has been proposed to suppress the evaporation of the solvent by filling the solvent vapor with the upper space of the coating tank being a space substantially closed except for the inlet and outlet of the cylindrical body (Japanese Patent Publication No. 55-55-55).
33389). Further, it has been proposed that not only the upper space of the coating tank is closed, but also solvent vapor is positively supplied thereto (see Japanese Patent Publication No. 4-37750 and Japanese Patent Application Laid-Open No. 6-123989).

[0004]

Since these methods complicate the apparatus, the operation is complicated, and the effects are insufficient, it is easier and more reliable to form a uniform coating film. There is a need for a way to do it. There is a demand for a method applicable to a thin coating film having a dry film thickness of 5 μm or less, particularly 1 μm or less, which is difficult to form a uniform coating film. The present invention addresses this need.

[0005]

According to the present invention, when a coating film is formed on a tubular body by immersing the tubular body in a coating bath containing a coating liquid and then pulling it up, The upper part is a space that is almost closed except for the inlet and outlet of the cylindrical body, which prevents the free flow of solvent vapor generated from the coating tank, and the coating liquid overflows from the coating tank and is attached. Of the coating liquid storage tank and is circulated to the coating liquid tank by a pump, and an overflow pipe for guiding the overflowing coating liquid to the coating liquid storage tank has a gas between the closed space and the coating liquid storage tank. A uniform coating film is formed on a tubular body by using a coating device that does not flow and maintaining the solvent vapor concentration above the coating liquid at 60% or more of the saturation concentration to form a coating film. You can

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION To explain the present invention in more detail, the present invention was made by elucidating the relationship between the surface state of the coating liquid in the coating tank and the coating film formed. . That is, when the coating liquid was supplied to the coating tank from the lower side and the coating liquid was overflowed from the upper end of the tank to perform coating on the cylindrical body, a line pattern was generated in the overflowing coating liquid and flowed to the surroundings. It was observed that a net-like pattern might be generated in the central part of the coating tank when the process was performed or when the process was further advanced. This phenomenon is observed for the first time when the surface of the coating liquid is strongly illuminated, but it has been found that when this phenomenon occurs, the coating film formed on the tubular body tends to become non-uniform. Further, this phenomenon occurs at different frequencies depending on the type of the coating liquid, and is likely to occur when a charge generation layer having a small film thickness is applied during the production of a laminated electrophotographic photosensitive member.

According to the studies made by the present inventors, the cause of this phenomenon is that the solvent evaporates from the surface of the coating liquid and the coating liquid locally concentrates on the surface. It is conventionally known that the evaporation of the solvent causes the coating liquid to become non-uniform, and as a result, it hinders the formation of a good coating film. It is proposed to suppress the evaporation of the solvent as a space that is almost closed except for. Further, as another method, it is known that the coating liquid is circulated by overflowing the coating liquid from the coating tank and returning the overflowed coating liquid to the coating tank with a pump to make the coating liquid uniform ( See JP-A-6-262113). However,
According to the study by the present inventors, even when the upper space of the coating tank is closed and the coating solution is circulated, the coating failure is caused by the local concentration change of the coating solution due to the evaporation of the solvent from the coating solution as described above. It was difficult to completely prevent.

As a result of studying the cause, the inventors of the present invention have surprisingly made a great contribution that the solvent vapor flows out through the overflow pipe for returning the overflowed coating liquid to the attached coating liquid storage tank, and also the inflow of air. I found out that That is, it was found that the air flowing in from the overflow pipe lowered the concentration of the solvent vapor on the surface of the coating liquid and promoted the evaporation of the solvent. Although not yet proved, locally changing the concentration of the solvent vapor in the process in which the air flowing in from the overflow pipe diffuses to the upper surface of the coating liquid causes a local change in the solvent evaporation amount. there is a possibility.

According to the present invention, by preventing the outflow of solvent vapor and the inflow of air through the overflow pipe, the saturation of the solvent vapor on the upper surface of the coating liquid is kept high, and as a result, the solvent from the coating liquid is kept high. Since the evaporation of the coating liquid is suppressed and the nonuniformity of the coating liquid is avoided, a uniform coating film can be constantly formed on the cylindrical body. In order to prevent the outflow of solvent vapor and the inflow of air through the overflow pipe, a liquid reservoir such as a U-shaped part that blocks the flow of air is provided in the middle of the overflow pipe, or the end of the overflow pipe is filled with overflow liquid. It can be easily achieved by immersing the coating liquid in the coating liquid storage tank.

FIG. 1 shows an example of the influence of the outflow of solvent vapor and the inflow of air through the overflow pipe on the concentration of solvent vapor in the space above the coating tank. FIG. 1 shows a coating tank provided with a coating tank and a coating solution storage tank, and a gutter provided around the coating tank for collecting the overflowing coating solution, an overflow pipe for sending the coating solution collected in the gutter to the coating solution storage tank, and a coating solution storage tank. A coating liquid circulation system consisting of a coating liquid supply pipe having a pump in the middle of circulating the coating liquid to the bottom of the coating tank, and a space almost closed above the coating tank including the gutter except for the inlet and outlet of the cylindrical body. Using a coating device provided with a hood, a coating liquid for charge generation layer (viscosity 2.4 centipoise) having the following composition is applied to the cylindrical body by a dipping method so that the dry film thickness becomes 0.42 μm.
It is a figure which shows the density | concentration of the solvent vapor | steam of the coating liquid upper surface at the time of apply | coating at 5 degreeC.

Coating liquid for charge generating layer Bisazo compound (charge generating agent) 1 part by weight Polyvinyl butyral resin (binder resin) 0.5 part by weight Phenoxy resin (binder resin) 0.25 part by weight Dimethoxyethane (solvent) 31 .5 parts by weight Pentoxone 3.5 parts by weight (4-methoxy-4-methyl-pentanone-2) (solvent)

In the figure, the solid line shows the solvent vapor concentration when a U-shaped liquid reservoir is provided in the middle of the overflow pipe to interrupt the air flow, and a uniform coating film is constantly formed on the cylindrical body. The coating solution was formed, and the surface of the coating solution was uniform, and no streak pattern was observed. On the other hand, the dotted line is the solvent vapor concentration when the overflow pipe is not provided with a liquid reservoir and the end of the overflow pipe is opened to the air, and the coating film is nonuniform and streaky coating unevenness occurs. . A mesh pattern was observed on the surface of the coating solution. In all cases, the solvent vapor was only dimethoxyethane, and almost no pentoxone was present.

As is clear from this figure, the outflow of solvent vapor and the inflow of air through the overflow pipe have a great influence on the solvent concentration in the space above the coating tank, and the quality of the coating film formed on the tubular body is improved. Influences. In case of solvent vapor outflow and air inflow through the overflow pipe,
The concentration of the solvent vapor on the surface of the coating liquid drops sharply upward from the liquid surface. However, when there is no outflow of solvent vapor or inflow of air through the overflow pipe, the concentration of solvent vapor above the liquid surface 20
The concentration of solvent vapor is almost constant up to about mm, and the concentration of solvent vapor decreases rapidly above that (probably due to the inflow of air through the inlet and outlet of the tubular body). Therefore, in the present invention, 10 mm above the surface of the coating liquid.
The solvent vapor concentration at the position is used as an index of the solvent vapor concentration in the space.

In FIG. 1, the ratio of the concentration of the solvent vapor to the saturation concentration when there is no outflow of solvent vapor or inflow of air through the overflow pipe is as follows. The charge generating agent in the coating solution is almost insoluble in the solvent,
Since the molecular weight of the binder resin is sufficiently larger than that of the solvent, these can be ignored when calculating the saturated vapor pressure of the solvent. Then, the solution becomes dimethoxyethane (molecular weight 9
0) and pentoxone (molecular weight 130), and the molar ratio is 0.929 dimethoxyethane and 0.071 pentoxone. Since the vapor pressure of dimethoxymethane at 25 ° C is 68 mmHg and the vapor pressure of pentoxone is 2 mmHg, the saturation concentration is calculated from Raoul's law as an ideal solution.

[0015]

[Equation 1] (68 × 0.929 + 2 × 0.071) / 76
0 × 100 = 8.3 (%)

On the other hand, as shown in FIG. 1, the concentration of the solvent vapor at a point 10 mm above the coating liquid is 5.5%, and therefore the degree of saturation is 5.5.
/8.3×100=66%. On the other hand, when there is gas flow through the overflow pipe,
The concentration of the solvent vapor at the point of 0 mm is 1.1 from FIG.
%, The saturation is 1.1 / 8.3 × 100 = 13%.

Although there is no gas flow through the overflow pipe, a part of the sealing material between the coating tank and the hood that closes the space above the coating tank is removed so that air can flow in and out. When coating was performed using the same coating solution as described above using the same coating apparatus as described above except that the concentration of the solvent vapor was 4.5% at a position 10 mm above the surface of the coating solution. Therefore, the degree of saturation is 4.5 / 8.3 ×
It becomes 100 = 55%. In this case, the coating film formed on the tubular bodies was not so good, and streaky coating unevenness occurred on about half of the tubular bodies. In addition, it was occasionally observed that streak-like patterns were generated on the surface of the coating liquid and flowed around.

From these results, the flow of gas through the overflow pipe is blocked, and the hood above the coating tank is well sealed to maintain the concentration of solvent vapor in this space at 60% or more of the saturated concentration. It turned out to be necessary. In addition, in the coating device, from the simplest one in which the cylindrical bodies are immersed one by one, several coating tanks in which the cylindrical bodies are immersed one by one are arranged in parallel, and the upper part of these is covered with a common hood. Various types are known, such as one in which a plurality of cylindrical bodies are simultaneously immersed in one coating tank, and the present invention can be applied to any of these.

[0019]

According to the present invention, it is possible to form a uniform coating film on a cylindrical body without requiring a complicated coating device.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of changes in the concentration of solvent vapor on the surface of a coating liquid in the case where gas flows through an overflow pipe and the case where gas does not flow. In the figure, there is a measuring point where the position from the liquid surface is -10 mm. The gutter part where the overflowed coating liquid is collected (the bottom of the gutter is about 50 mm higher than the upper end of the coating tank (= overflow surface)).
mm lower position), minus 1 from the top of the coating tank
It is measured at a position of 0 mm.

Claims (4)

[Claims] 1. A method of forming a coating film on a tubular body by immersing the tubular body in a coating tank containing a coating liquid and then pulling it up. It is a space that is almost closed except for the free flow of solvent vapor generated from the coating tank.The coating solution overflows from the coating tank and flows into the attached coating solution storage tank. The pump is circulated to the coating liquid tank, and the overflow pipe for guiding the overflowing coating liquid to the coating liquid storage tank prevents gas from flowing between the closed space and the coating liquid storage tank. A method of forming a coating film by using a coating device while maintaining the solvent vapor concentration above the coating liquid at 60% or more of the saturation concentration. 2. The method according to claim 1, wherein the overflow pipe has a liquid reservoir partway or the end is immersed in the liquid in the coating liquid storage tank. 3. The method according to claim 1, wherein a coating film having a dry film thickness of 5 μm or less is formed on the cylindrical body. 4. The method according to claim 1, wherein the coating film is a photosensitive layer of an electrophotographic photosensitive member.