JPH04219169A - Coating method and device - Google Patents

Abstract

PURPOSE:To stably form a uniform coating film by dip coating by blowing flows of air in a specified way. CONSTITUTION:When a substrate as a body to be coated is dipped in a coating liq. in a dipping tank to form a coating film on the surface of the body, rising flows of air are blown on the coating film on the surface of the body at the time of pulling up the body. By the rising flows of air, negative pressure is produced on the surface of the coating liq., the open air is sucked into the space on the surface of the coating liq. under the negative pressure and the sucked open air is blown on the coating film on the surface of the body to be coated immediately after emerging from the dipping tank.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dip coating method for electrophotographic photoreceptors and an apparatus therefor. For more details,
The present invention relates to a dip coating method for forming a coating film with a uniform constant thickness on the surface of a substrate by controlling dryness to the touch, and an apparatus therefor.

0002

BACKGROUND OF THE INVENTION Conventionally, various methods have been proposed in the dip coating method for the purpose of preventing so-called sagging, which is the thinning of the coating film near the upper end. For example, by applying an air flow to the outside of a cylindrical object to be coated, an air doctor effect or a drying effect can be exerted, preventing the upper end of the coating film from sagging and forming a uniform coating film (for example, Showa 59
-225771) etc. have been attempted.

0003

In this method, the flow velocity of the blown air may be uneven in the circumferential direction due to manufacturing errors of the air blowing device. Even if the blowing unevenness is minute, it has the disadvantage that it causes unevenness in the thickness of the coating film. The various dip coating methods that have been proposed so far to prevent sagging by air blowing have the above-mentioned drawbacks, and lack stability against uneven film thickness, making it difficult to use equipment for producing large quantities. The problem was that it was difficult to introduce.

The present invention has been made in view of the above-mentioned problems in the prior art. That is, an object of the present invention is to provide a dip coating method that improves the drawback of the conventional air jet spray coating method, which is that it cannot form a stable and uniform coating film. ,
Another object is to provide a device for that purpose.

[0005]

[Means for Solving the Problems] The present invention provides an object to be coated with
A dip coating method in which a coating film is formed on the surface of a substrate by immersing it in a coating solution in a dipping tank and then pulling it up, and when pulling it up, a rising air flow is applied to the coating film on the surface of the substrate. In the dip coating method, the rising air flow generates negative pressure around the coating liquid surface, and based on the negative pressure, outside air is sucked around the coating liquid surface, and the sucked outside air exits the immersion tank. It is characterized in that it hits the coating film on the peripheral surface of the object to be coated immediately after it has been applied.

[0006] The dip coating apparatus used in the dip coating method of the present invention is equipped with a dipping tank and means for vertically movably supporting the object to be coated. The upper part of the rising air flow blowing means has an air blowing slit, and the lower part of the rising air blowing means has an air intake opening. Air is taken in from the air intake opening by the air blowout.

According to the present invention, in addition to the conventional technique of creating a coating film with less sagging by applying an air flow in the direction of pulling up the object to be coated immediately after the object is pulled up from the dipping tank, This technology has been improved in that when disturbances such as minute fluctuations in the blowing air flow occur, uneven film thickness occurs, making it difficult to form a stable and uniform coating film. This makes it possible to stably form a uniform coating film with little sagging.

The present invention differs greatly from the prior art in that, before the rising air stream hits the coating surface, that is, immediately after the object to be coated is lifted out of the dipping tank, the rising air stream is used as a primary touch drying means. It incorporates a means to reduce the direct effect of air flow on the paint film. By adopting the above-mentioned primary touch drying means, even if minute fluctuations occur in the rising air flow, the fluctuations will not affect the coating film due to the touch drying effect of the above-mentioned primary touch drying means. It is possible to stably obtain a coating film with less sagging, which is the original objective, without causing unevenness in film thickness.

The above-mentioned primary touch drying means and its effects will be explained in detail along with the mechanism. FIG. 1 is an explanatory diagram showing the concept of application by air blowing in the present invention. The dry-to-the-touch mechanism that prevents sagging by blowing upward airflow will be explained with reference to FIG. Negative pressure is generated in region C by the air (primary air) blown out from the air blowing device in drying zone B (secondary touch drying means) and the ejector effect caused by the primary air blowing. If an optimal gap is provided between the immersion tank lid 3 and the immersion tank 1, external air will be sucked in in a direction that cancels out the generated negative pressure. This suction air will be referred to as secondary air, and this secondary air performs the primary touch drying in the drying zone A by the primary touch drying means. This one
In the second drying to the touch, before the blowing air (primary air) with a relatively high flow rate from the blowing device, which is used to prevent sagging, hits the coating surface, the suction air (secondary air) from the outside is
This has the effect of promoting dryness to the touch to the extent that even if air with minute flow velocity unevenness hits the wet film immediately after leaving the dipping tank, there will be no unevenness. Due to this effect, even if the aforementioned minute primary air unevenness occurs (for example, circumferential direction blowing unevenness of about ±5% due to dimensional errors in device manufacturing), film thickness unevenness will not occur. You can live without it.

FIG. 2 shows the concept. Figure 2(a) shows 2
This shows the case where there is no drying immediately after the coating film is formed by air.
FIG. 2(b) shows the case where there is drying immediately after the coating film is formed by secondary air. If the coating film is not dried immediately after it is formed by secondary air, it will be subject to dynamic pressure fluctuations due to minute variations in the flow velocity of the primary air, causing unevenness on the wet film surface and causing shaft muscle failure. On the other hand, when the coating film is dried by secondary air immediately after it is formed, the coating surface becomes hard due to the drying of the secondary air and is less susceptible to the influence of dynamic pressure fluctuations of the air flow. That is, according to the present invention, when preventing sagging at the edges by applying an upward air flow, even if the air blown from the blowing device has minute unevenness as described above, the unevenness in film thickness can be prevented. Occurrence can be prevented.

In the coating device of the present invention, when a certain amount of primary air is blown out in region C shown in FIG.
An opening through which secondary air is sucked from the outside is required to prevent negative pressure in region C. The opening portion does not need to be particularly uniform in the circumferential direction of the base material, and it is sufficient that the secondary air can be sucked in without resistance.

As a result of studies by the present inventors, the primary air flow rate blown out from the nozzle and the suctioned secondary air flow rate are correlated when the shape of the blowing device is constant. It was found that the area where this occurs can be limited to some extent. The concept is shown in FIG. What is important here is that, as can be seen from Fig. 5, the flow rate of the secondary air sucked in by the flow rate of air blown out from the blowing device (primary air) must be determined appropriately when the shape of the blowing device is constant. This is something that can be done. In order to suction a sufficient amount of this secondary air, the opening area becomes a dominant factor. Preferably, the opening area is variable in accordance with the primary air flow rate. Note that FIG. 5 is a graph showing the relationship between the primary air flow rate and the secondary air flow rate, and has an air blow device having the structure shown in FIG. 4 described later, a=10 mm, θ=60 degrees,
The relationship is shown when d=1.0mm.

[0013] Even if the opening area of the opening part such as a slit is made too large, it will not affect the uneven drying, but it will cause adverse effects such as increased solvent evaporation, so the optimum value should be selected. It is preferable.

In the present invention, the blowing speed of the air stream from the slit may be arbitrarily set depending on the physical properties of the coating liquid used. Usually, a range of 3 to 20 m/sec is adopted. Further, the drawing speed (coating speed) of the object to be coated is arbitrarily set depending on the physical properties and film thickness of the coating liquid used, and is usually set in the range of 50 mm/min to 400 mm/min.

The coating material used in the present invention is not particularly limited, and known photoconductive materials, insulating materials, electrical materials, etc. can be coated. Examples of photoconductive materials include phthalocyanine, ZnO, CdS, TiO2
, polyvinylcarbazole, trinitrofluorenone, azo pigments, etc. are used. Examples of insulating materials used in combination with them or alone include thermoplastic resins such as polystyrene, polyvinyl chloride, and polycarbonate, and thermosetting resins such as polyurethane, epoxy resins, and phenolic resins.

[0016]

EXAMPLES The method of the present invention will be explained by examples and comparative examples. An electrophotographic photoreceptor having a 0.1μ charge injection blocking layer made of a zirconium compound and a 0.1μ charge generation layer containing 65% by volume of trigonal selenium on an 84mmφ×340mmL aluminum pipe as a cylindrical body. An intermediate product was used.

The coating solution was prepared as follows. 4 parts of a charge transport material having the structure shown below

[0018]

A coating solution was obtained by dissolving 6 parts of polycarbonate resin having a viscosity average molecular weight of 39,000 in 47 parts of monochlorobenzene. Monochlorobenzene is a solvent that does not easily evaporate. A coating operation was performed using the above coating liquid using the apparatus shown in FIG. 1 to form a charge transport layer, which required the thickest film among organic photoconductive films.

Example 1 and Comparative Example 1 Coating operations were carried out using a coating apparatus having the structure shown in FIGS. 3 and 4. Note that FIG. 3 is a schematic configuration diagram of an example of a dip coating apparatus used in the present invention, and FIG. 4 is a sectional view of the main parts thereof. Reference numeral 1 denotes an immersion tank, which is provided with an overflow receiver 2 at the top, and a coating liquid is held inside. An immersion tank lid 3 having an opening in the center is placed on top of the overflow receiver 2, and a ring-shaped air blowing device 4 is placed on top of the immersion tank lid 3. This dipping tank lid is further provided with an opening 31 around the periphery thereof. The coating liquid circulation means includes pipes 5 and 6, a circulation tank 7, and a circulation pump 8. The object supporting means for supporting the object 9 is composed of a motor 10, a support 12 that moves up and down by a ball screw 11, and a chuck device 13.

As shown in FIG. 4, the air blowing device 4 includes a hollow air jacket 4 having a slit 41.
2, and the slit 41 has a slit angle θ such that the airflow is ejected in a ring shape on the surface facing the object to be coated 9 and in an upward direction of 30 to 80 degrees with respect to the horizontal plane. = Open at an angle of 30 to 80 degrees. In this dip coating apparatus, the coating liquid is supplied from the circulation tank 7 through the piping 6 to the lower part of the dipping tank 1 by the circulation pump 8, and the coating liquid overflowing from the upper part is passed from the overflow receiver 2 through the piping 5 to the circulation tank. Return to 7.

When applying the coating liquid to the object to be coated, the object 9 to be coated is lowered by driving the motor 10 and immersed in the coating liquid in the dipping tank. Next, coating is performed by pulling up the object to be coated at a predetermined speed, and at this time, the surface of the coating film is exposed to the slit 41 of the air blowing device 4.
It will be exposed to the airflow coming out of it. Since the immersion tank lid is provided with an opening 31 around the periphery thereof, negative pressure is generated within the lid when the air flow is ejected from the slit 41, so that external air flows into the periphery of the immersion tank lid. opening 31
It is taken into the interior of the lid through the coating, hits the object to be coated immediately after coating, and dries the coating film by primary drying to the touch.

An example of the coating conditions for the above case is air amount: V=16Nm3/Hr (dew point at normal pressure -
Air at 17℃), angle θ between cylinder and slit = 60, slit interval: d = 1.0 mm (variation in slit interval in circumferential direction = 5%), distance between cylinder and slit (a = 10
mm), opening area: S = 3000 mm2, distance between liquid level and slit: b = 25 mm, straight body dimension c = 30 mm,
Pulling speed (coating speed): 110 mm/min, air flow speed on the coating surface: 12 m/sec. As a comparative example, a coating operation was performed using the same coating apparatus as used in Example 1 above, except that the opening area S was set to 0. In this case, the suction of secondary air is not sufficiently performed, and when the primary air is blown out, the area C in Fig. 1 becomes negative pressure (Comparative Example 1)
.

[0023] For Example 1 and Comparative Example 1, 10
Dip coating on aluminum drum, 135℃, 43℃
After drying for several minutes, an electrophotographic photoreceptor was prepared, and the stability against the occurrence of film thickness unevenness was compared. Film thickness unevenness occurs as density unevenness in copy image quality, so it was detected based on this. The results are shown in Table 1. The shape of the film thickness due to the defect was confirmed to be as shown in FIG. 7 as a result of measurement using an interference film thickness meter.

[0024]

[Table 1]

From the results shown in Table 1, in the present invention, by making it possible to suction secondary air, it is possible to prevent the above-mentioned uneven film thickness that tends to occur with the coating method that applies an upward air flow to prevent sagging, and to stabilize the film. We were able to develop a coating method with low sag and excellent film thickness uniformity.

Example 2 and Comparative Example 2 As Example 2, dip coating was carried out on eight objects to be coated using the dip coating apparatus shown in FIG. Note that FIG. 6 shows a schematic cross-sectional view of the same, and the immersion tank lid 3 is placed on the overflow receiver 2 provided at the upper part of the plurality of immersion tanks 1. An opening 15 is provided at a predetermined slit interval between the overflow receiver and the dipping tank lid.
It can be adjusted so that it occurs. Note that the other symbols are the same as those shown in FIG. 3 above. The details of the coating conditions for each tube were the same as in Example 1. Further, each blowing device was manufactured with the same specifications.

As Comparative Example 2, in FIG.
Coating was carried out under the same conditions as in Example 2 except that the secondary air suction was set to 0 and secondary air suction was eliminated.

In both Example 2 and Comparative Example 2, continuous coating was performed 100 times. (800 pieces each), and the results of whether or not film thickness unevenness occurred were examined. The results are shown in Table 2.

[0029]

[Table 2]

From these results, it was confirmed that Example 2 was a coating method with little sag at the edges and no unevenness in film thickness.

[0031] In the above example, the test was carried out using an apparatus in which the slit spacing had a variation of about ±5%, but this was due to variation in the blowing air flow velocity. appear. Practically speaking, there are not only manufacturing variations but also variations in the amount of air supplied, and this method is effective for these as well.

Comparative Example 3 Regarding the case where the opening area was set to 0 using the same device and the same conditions as in Example 1, but instead of secondary air being sucked,
The coating operation was performed by forcibly introducing secondary air from the outside. FIG. 8 shows a coating device in that case. In the figure,
81 is a secondary air supply device, 82 is a secondary air blowing surface, 83 is a secondary air supply pipe, 84 is an air jacket, 85 is an overflow surface adjustment tube, and other symbols have the same meanings as above. has.

The conditions for this device are as follows. Secondary air supply source: compressor air (dew point -17°C at normal pressure), secondary air flow rate: 12Nm3/Hr (Figure 5
(Set from the secondary air flow rate corresponding to the primary air flow rate), Secondary air blowing surface 82: 135 mmφ x 30 m
Use mH stainless steel sintered mesh (5μ, manufactured by Kansai Kinami Co., Ltd.).

In Comparative Example 3, as in Example 1, 1
0 drums were coated. Regarding the presence or absence of film thickness unevenness,
A similar investigation was conducted, but as in Example 1, no occurrence was found. From the results of Comparative Example 3, the importance of the presence of secondary air is clear, but in the case of this device, a device for forcibly introducing air is required, so the ejector effect in the present invention is It can be seen that suction from the outside is preferable.

[0035]

Effects of the Invention: In addition to the conventional technique of blowing an air stream onto the outside of the object to prevent sagging at the upper end immediately after pulling it out of the dipping tank, the coating method of the present invention also uses a fine blow-out air flow rate. Even if turbulence occurs, film thickness unevenness can be prevented, and flexibility can be provided with respect to errors in the production of the air blowing device, which is effective for mass production of organic photoreceptors. In addition, in order to increase coating production capacity, in the case of the dip coating method, it is necessary to increase the speed at which the object to be coated is pulled out. For close-ups, air blow application is very effective. Furthermore, when applied to a production line, there is an advantage of stability, that is, the ability to stably manufacture products without defects.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the concept of coating by air blowing in the present invention.

[Figure 2] An explanatory diagram illustrating the state of the coating film formed. (a) shows the case where there is no drying immediately after the coating film is formed by secondary air, and (b) shows the case where the coating film is formed by secondary air. Indicates the case where there is immediate dryness.

FIG. 3 is a schematic configuration diagram of a dip coating apparatus for carrying out the present invention.

FIG. 4 is a cross-sectional view of the main parts of the dip coating device shown in FIG. 3.

FIG. 5 is a graph showing the relationship between primary air flow rate and secondary air flow rate.

FIG. 6 is a schematic cross-sectional view of a dipping tank and an air blow device when coating a large number of objects at the same time.

FIG. 7 is a diagram showing the shape of film thickness unevenness of a charge transport layer in an example.

FIG. 8 is a cross-sectional view of the main parts of the dip coating device used in Comparative Example 3.

[Explanation of symbols]

1. ．． ．． ．． Immersion tank, 2. ．． ．． ．． Overflow receiver, 3
．． ．． ．． ．． Immersion tank lid, 31. ．． ．． ．． aperture, 4. ．． ．． ．． Air blow device, 41. ．． ．． ．． Slit, 42. ．． ．． ．． Air jacket, 5, 6. ．． ．． ．． Piping, 7. ．． ．． ．． Circulation tank, 8. ．． ．． ．． Circulation pump, 9. ．． ．． ．． object to be coated,
10. ．． ．． ．． Motors 10, 11. ．． ．． ．． ball screw,
12. ．． ．． ．． Support, 13. ．． ．． ．． Chuck device, 14
．． ．． ．． ．． Opening adjustment screw.

Claims (2)

[Claims] 1. A dip coating method in which a coating film is formed on the surface of the substrate by immersing the substrate in a coating liquid in a dipping tank and then pulling it up. In the dip coating method, which involves applying a rising air flow to the coating film, the rising air flow generates negative pressure around the coating liquid surface, and based on the negative pressure, outside air is sucked around the coating liquid surface. A dip coating method characterized in that the drawn outside air hits the coating film on the circumferential surface of the object to be coated immediately after leaving the dipping tank. 2. A dip coating apparatus comprising a dipping tank and means for vertically movably supporting the object to be coated, wherein an upward air flow blowing means having an air blowing slit is provided at the upper part of the dipping tank, An air flow intake means having an air intake opening is provided at a lower part of the ascending air flow blowing means,
A dip coating device characterized in that air is taken in from the air intake opening by blowing air from the air blowing slit.