JP3247779B2 - How to apply paint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a paint. More specifically, the surface of the coating film formed using a coating compounded with a volatile organic solvent is not whitened,
For example, the present invention relates to a method for applying a paint which can be suitably used in the production of an electrophotographic photosensitive member.

[0002]

2. Description of the Related Art Conventionally, for example, a charge transporting layer of an electrophotographic photosensitive member is manufactured by applying a coating material in which a binder resin and a charge transporting agent are dissolved in a volatile organic solvent to a base tube such as aluminum. When using such a paint, the volatile organic solvent removes the heat required for evaporation from the formed coating, so that when the temperature of the coating falls below the dew point, water vapor in the air condenses and the coating forms. The surface of the whitened. As described above, the whitening of the surface of the coating film is not only unfavorable in appearance, but also a fatal defect for, for example, an electrophotographic photoreceptor or the like whose optical characteristics greatly affect the performance of the product. There is a problem.

Therefore, as a method for preventing the whitening of the surface of the coating film, for example, a method of lowering the humidity at the time of applying a paint can be considered. However, it is not clear to what extent such humidity should be reduced, and therefore the running cost is increased by installing equipment having an excessive dehumidifying capacity, or conversely, it is formed due to insufficient dehumidification. There are problems such as insufficient prevention of whitening of the coating film surface.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present inventors have found that when coating is performed using a paint containing a volatile organic solvent, running costs are increased due to excessive dehumidification. We are keen to develop a coating method for paint that can completely prevent the whitening of the surface of the coating film without any problems such as insufficient whitening of the surface of the formed coating film due to insufficient dehumidification. As a result of repeated research, paying attention to the temperature decrease due to the evaporation of the volatile organic solvent when the coating film was formed, when painting at a lower humidity than the specific humidity based on such temperature decrease, The problem was solved, and it was found that the surface of the formed coating film was not whitened at all, and the present invention was completed.

[0005]

That is, the present invention relates to a method for coating a coating material to which a volatile organic solvent is blended on an object to be coated, wherein the saturated water vapor pressure P at the temperature of the coating material at the time of coating is applied.
_0, and the saturated water vapor pressure P _{1 at a} temperature lower than the temperature of the paint at the time of application by the temperature drop 20 seconds after the application due to the evaporation of the volatile organic solvent when the paint is applied to form a coating film. determined, the ratio between P ₀ and P ₁ ((P ₁ / P
_{The present} invention relates to a coating method of a paint, characterized in that the coating is performed at a humidity lower than the relative humidity represented by ₀ ) × 100).

[0006]

The coating method of the present invention takes into account that the volatile organic solvent which evaporates after coating has an effect on the whitening of the coating film. based cracking heat, and saturated water vapor pressure P ₁ in the temperature decline by low temperatures of the coating film after coating for 20 seconds to obtain the saturated vapor pressure P ₀ at the temperature of the paint during painting, the P ₀ and P ₁ and Is applied at a humidity lower than the relative humidity represented by the ratio ((P ₁ / P ₀ ) × 100).

First, a description will be given of a decrease in the temperature of a formed coating film due to evaporation of the volatile organic solvent when a coating material containing a volatile organic solvent is applied to form a coating film.

According to the study of the present inventors, when a paint containing a volatile organic solvent is used, the volatile organic solvent evaporates rapidly after the coating, and the film of the coating film is rapidly evaporated. The thickness decreases, and usually about 8 seconds after coating, about 8
0% evaporates rapidly, about 90 to 50 seconds after painting.
% Or more, it was found that the film thickness evaporated more slowly and the film thickness became almost constant about 90 seconds after coating. Here, the whitening of the surface of the coating film is caused by the volatile organic solvent in the coating film rapidly evaporating and removing heat, and the temperature of the coating film is rapidly lowered. It has been found that it is sufficient to consider the amount of heat taken in 20 seconds after coating, in which about 80% of the volatile organic solvent rapidly evaporates, which greatly affects the whitening of the surface. In addition, the evaporation rate may be low depending on the type of the volatile organic solvent incorporated, and about 80% of the volatile organic solvent evaporates even after 20 seconds or more after the coating, and the subsequent evaporation. Since the speed is usually even lower, there is no sharp drop in temperature of the coating which would cause whitening.

As described above, the amount of heat taken from the coating film when the volatile organic solvent evaporates for 20 seconds after the coating is deeply involved in lowering the temperature of the formed coating film.

First, the amount (dL (cm ³ )) of the volatile organic solvent that evaporates from the coating film for 20 seconds after coating is represented by the following formula: dL = LS × d (where L is the weight of the coated paint) The amount (cm ³ ), S is the coating area (cm ² ), and d is the film thickness (cm) of the coating film 20 seconds after the start of coating.)

Here, the amount (L) of the applied paint may be obtained from the coating area and the thickness of the coating film immediately after being formed, or the amount of the paint actually used may be measured. . Further, the measurement of the film thickness (d) takes into account the time-dependent change of the film thickness.
For example, a laser outer diameter measuring machine (KEYENCE LS-300) that can measure instantaneously without contacting a coating film.
2) Instantaneous multi-metering system (MCPD-1000)
It is preferable to use such as.

Then, the amount of heat (W ₁ (J · cm ³ / cm) taken from the coating film when the volatile organic solvent evaporates for 20 seconds after coating.
g)) uses the amount (dL) of the volatile organic solvent evaporating from the coating film, and is represented by the following formula: W ₁ = dL × m ₁ × y (where m ₁ is the volatility at the temperature of the paint at the time of coating) Specific gravity of organic solvent, y is latent heat of vaporization of volatile organic solvent (J / g)
Is shown).

Further, in order to determine the temperature reduction width of the formed coating film, it is sufficient to know the heat capacity of the object to be coated, and the heat capacity of the object to be coated (W ₂ (J · cm ³ / (g · ° C.)) )
Formula: W ₂ = V × m ₂ × h (where V is the volume of the object to be coated (cm ³ ), m ₂ is the specific gravity of the object at the temperature of the paint at the time of coating, and h is the unit of the object to be coated. Heat capacity (J / (g · ° C)).

Therefore, the temperature decrease width (ΔT (° C.)) 20 seconds after the application due to the evaporation of the volatile organic solvent when the paint is applied to form a coating film, is determined by the volatile organic solvent 20 seconds after the application. There heat depriving coating upon evaporation (W ₁₎
Value of the ratio (W ₁ / W ₂ ) of the heat capacity (W ₂ ) of the object to be coated,
That is, formula (I):

[0015]

(Equation 2)

(Where L, S, d, m ₁ , y, V, m ₂
And h are as defined above).

In determining the temperature decrease width (ΔT) 20 seconds after the coating, the volatile organic solvent remaining in the formed coating film and the heat capacity of the coating film are not taken into consideration. When the formed coating film is a thin film having a thickness of, for example, about 10 to 50 μm, which is usually formed when manufacturing a charge transporting layer of an electrophotographic photoreceptor, for example, these greatly affect the temperature drop. It is not considered to affect.

The volatile organic solvent to be added to the paint used in the present invention is, for example, chloroform, trichloroethylene, trichloroethane, tetrachloromethane, dichloromethane, acetone, toluene, etc.
The object to be coated is not particularly limited, and may be appropriately selected and used depending on the use and the like.

Next, the humidity at which the surface of the coating film starts to whiten is determined by using the thus obtained value of the temperature decrease width 20 seconds after the coating, and the coating is performed at a humidity lower than this humidity.

The humidity at which the surface of the coating film begins to whiten is
The saturated water vapor pressure P ₀ at the temperature of the paint during coating is determined from the ratio of the saturated vapor pressure P ₁ in the low as the temperature decreases in width than the temperature of the paint during coating temperature and humidity, i.e. (P ₁ / P ₀ ) × 100 is the relative humidity (%), and when the coating is performed at a humidity higher than the above humidity, moisture is condensed on the surface of the coating film to cause whitening. For example, a dehumidifier may be provided in the coating facility. In addition, it is necessary to adjust the temperature in the coating equipment so that the temperature of the paint at the time of painting and the environmental temperature at the time of painting are equal, and to carry out painting. This is preferable in that it can prevent

In the present invention, the humidity at which the paint is applied is set lower than the relative humidity. However, if the paint is applied at a humidity too close to the relative humidity, the surface of the coating film is In consideration of the fact that there is a tendency that moisture may be slightly condensed, and that the obtained relative humidity value may include an error, in order to eliminate the possibility of dew condensation at all, the relative It is preferable to adjust the humidity so that the humidity is lower than the humidity by about 2%.

In the coating method of the present invention, the coating method may be appropriately selected according to the kind of the target product and the like, and is not particularly limited. Examples thereof include a normal dipping method (dipping method) and roll coating. A method, a spray coating method, a flow coating method and the like can be employed. Among them, the immersion method is preferred because the temperature of the paint and the temperature of the object to be coated can be made the same.

Next, the coating method of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to only these Examples.

Example 1 80.36 parts by weight of chloroform was mixed with a binder resin (polycarbonate) and a compound represented by the following formula:

[0025]

Embedded image

A paint was obtained by dissolving 19.64 parts by weight of the charge transporting agent represented by the formula (1).

An aluminum tube (inner diameter: 3)
cm, thickness: 0.075 cm, length: 30.1 cm), and the length of the outer surface of the aluminum tube is 29.4 c.
The part m was coated with the paint by an immersion method so that the temperature of the paint (23 ° C.) became equal to the temperature of the aluminum tube under the condition of an environmental temperature of 23 ° C.

The amount (L) of the coating material applied to the aluminum pipe was determined by the coating area and the thickness of the coating film immediately after the coating (the instant multi-photometry system (MCPD-100)).
0, measured by Otsuka Electronics Co., Ltd.)
It was 2.88 cm ³ . When the thickness (d) of the formed coating film after 20 seconds from the start of coating was measured by the instantaneous multi-photometry system, it was 0.00365 cm.

The coating area (S) and the volume (V) of the aluminum tube are as follows.

[0030]

(Equation 3)

Further, the specific gravity of chloroform at 23 ° C. (m ₁ ) and latent heat of vaporization (y), and the specific gravity of aluminum at 23 ° C. (m ₂ ) and unit heat capacity (h)
Are as shown below.

M ₁ = 1.429 y (J / g) = 247.8 m ₂ = 2.7 h (J / (g · ° C.)) = 0.9349 From these values, first, 20 seconds after coating, The amount (dL) of chloroform evaporating from the coating film is dL (cm ³ ) = 2.88−276.95 × 0.00365, and the amount of heat (W ₁ ) taken from the coating film when chloroform evaporates for 20 seconds after coating is W ₁ (J · cm ³ _{/g)=(2.88-276.95×0.00365)}
× 1.429 × 247.8.

Further, the heat capacity of aluminum (W ₂ )
Is W ₂ (J · cm ³ / (g · ° C.)) = 20.8 × 2.7 × 0.9349.

From these, the temperature decrease width (ΔT) 20 seconds after the coating due to the evaporation of chloroform when the coating was applied to form a coating film was determined by the ratio of W ₁ to W ₂ (W ₁ / W).
₂ )) When calculated as the value of:

[0035]

(Equation 4)

As shown in the above, the temperature was about 12.61 ° C.

Therefore, the ratio of the saturated steam pressure (P ₁ ) at 10.39 ° C. which is 12.61 ° C. lower than 23 ° C. at the time of coating and the saturated steam pressure (P ₀ ) at 23 ° C. is 2813 Pa. ,formula:

[0038]

(Equation 5)

As shown in the above, the relative humidity is about 45.0%.
If the coating is performed under a lower humidity condition, it can be predicted that moisture does not condense on the surface of the coating film and whitening does not occur.
The film thickness (d) of the coating film after 20 seconds from the start of coating in Example 1 was about 5% with respect to the thickness of the aluminum tube, so that the relative humidity was 45.0%. Considering that some degree of error may be included,
The coating may be performed at a humidity of less than 2.8%.

Therefore, a paint was applied to the outer surface of the aluminum pipe by the dipping method in the same manner as described above, except that a dehumidifier was provided in the coating equipment and the humidity at the time of coating was maintained at 42.0% or 45.0%. did.

As a result, when the humidity was maintained at 42.0%, the surface of the coating film was not whitened at all. On the other hand, when the humidity was maintained at 45.0%, the coating film was not whitened. 2
After the elapse of 0 seconds, moisture started to form on the surface of the coating film and whitened.

For this reason, in order to perform coating using a paint containing a volatile organic solvent such as chloroform, for example, the temperature after 20 seconds of coating due to evaporation of the volatile organic solvent when the coating film is formed is considered. examine the decline, and saturated water vapor pressure P ₁ at a temperature lower than the temperature of the paint during application only takes temperature decline takes this seeking and saturated water vapor pressure P ₀ at the temperature of the paint during painting P ₀ and P ₁ And the relative humidity ((P ₁ / P ₀ ) × 100) is determined from the ratio, and it is understood that the coating may be performed at a humidity lower than the relative humidity.

[0043]

According to the method for coating a paint of the present invention, a paint containing a volatile organic solvent can be applied to an object without completely whitening the surface of the formed coating film. The effect that the increase in running cost resulting from the increase in power consumption due to the dehumidification can be sufficiently suppressed can be obtained.

Therefore, the coating method of the present invention is as follows.
For example, the present invention has an effect that it can be used particularly suitably in the production of an electrophotographic photosensitive member or the like whose optical characteristics greatly affect the performance of a product.

Continuation of the front page (56) References JP-A-5-27455 (JP, A) JP-A-5-277408 (JP, A) JP-A-6-148956 (JP, A) JP-A-3-118872 (JP) , A) (58) Fields studied (Int. Cl. ⁷ , DB name) B05D 3/00 B05D 1/18 B05D 5/00 G03G 5/05 102

Claims (3)

(57) [Claims] 1. A method for coating a coating material to which a volatile organic solvent is blended on an object to be coated, wherein a saturated water vapor pressure P _{0 at} the temperature of the coating material at the time of coating and a coating film are formed by coating the coating material. The saturated water vapor pressure P _{1 at a} temperature lower than the temperature of the paint at the time of coating by 20 seconds after the coating due to the evaporation of the volatile organic solvent at the time of coating is obtained, and the ratio of the above P ₀ and P ₁ ((( A method for coating a paint, wherein the coating is performed at a humidity lower than the relative humidity represented by (P ₁ / P ₀ ) × 100). 2. The temperature decrease width ΔT (° C.) after 20 seconds of application due to evaporation of a volatile organic solvent when a coating is applied to form a coating film is represented by the following formula (I): (Where L is the amount of paint applied (cm ³ ), S is the paint area (cm ² ), d is the thickness of the paint film after 20 seconds from the start of painting (cm), and m ₁ is the paint time , The specific gravity of the volatile organic solvent at the temperature of the paint, y is the latent heat of evaporation of the volatile organic solvent (J / g), V is the volume of the object to be coated (cm ³ ), and m ₂ is the temperature at the temperature of the paint at the time of coating. The specific gravity and h of the coating material are represented by a unit heat capacity (J / (g · ° C.)) of the coating material, and the temperature of the coating material at the time of coating is equal to the environmental temperature at the time of coating.
The method of applying the paint described. 3. The method according to claim 1, wherein the coating is performed by a dipping method.
The method of applying the paint described.