JPH04331956A - Substrate drying method - Google Patents

Abstract

PURPOSE:To dry a substrate surface without nonuniformly deteriorating its property by washing the substrate with ordinary-temp. pure water, then drying the substrate by a freeze drying method. CONSTITUTION:After the cylindrical substrate consisting of aluminum is immersed into a neutral detergent, the substrate is washed with the pure water at 23 deg.C (point a) under atm. pressure. The substrate is in succession cooled rapidly down to -20 deg.C (point b) under atm. pressure to freeze the pure water remaining on the surface. The pressure is then reduced down to 3Torr (point c) at this temp. and the substrate is heated up to 23 deg.C (point d) under the same pressure to sublimate the pure water remaining on the surface; thereafter, the pressure is restored to the atm. pressure (point a) and the dried substrate is obtd. The substrate is rapidly cooled down to the temp. below the triple point to freeze the moisture on the substrate surface and thereafter, the pure water is sublimated at ordinary temp. or below under the reduced pressure, by which the substrate surface is uniformly dried.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drying a substrate used in an electrophotographic photoreceptor, a magnetic recording medium, or various semiconductor products after cleaning with pure water.

0002

2. Description of the Related Art Various substrates are used in electrophotographic photoreceptors, magnetic recording media, and various semiconductor products. Electrophotographic photoreceptors are usually obtained by forming a photosensitive layer on a cylindrical substrate made of an aluminum alloy by vapor depositing or coating a photoconductive material such as a selenium/tellurium alloy, a selenium/arsenic alloy, or an organic pigment. . A magnetic recording medium is obtained by forming a magnetic layer or the like by sputtering on a non-magnetic substrate, such as a nickel/phosphorus alloy layer provided on an aluminum alloy plate. Furthermore, in various semiconductor products, semiconductor elements, electronic components, etc. are fixed onto a substrate made of copper, aluminum, ceramics, or the like.

[0003] When these substrates are used, their surfaces must be sufficiently cleaned, and they are degreased and washed. Traditionally, in this degreasing and cleaning process, chlorinated solvents with strong degreasing power such as Trichlorene and Freon have been used, but in recent years, environmental issues have become a hot topic, and detergents have been used instead of these chlorinated solvents. Water-soluble surfactants such as

However, when using chlorinated solvents,
Originally, there was no need for a drying process after washing because of its strong volatility, but when using a water-soluble surfactant, rinsing with pure water is required after degreasing and washing to remove the water-soluble surfactant. and a subsequent drying step. For this purpose, a drying method is used in which the substrate is degreased with a water-soluble surfactant, rinsed with pure water at room temperature, and then immersed in pure water at a temperature of approximately 70°C or higher and pulled up.
A so-called pure water drying method has been adopted.

[0005]

However, the above-mentioned pure water drying has the disadvantage that drying tends to be uneven and the surface quality of the substrate tends to vary.

Furthermore, when the substrate is made of aluminum or an aluminum alloy, there is a problem in that the surface of the substrate changes in quality before and after drying. That is, aluminum easily reacts with water, and its surface is oxidized, especially when it comes into contact with high-temperature water or steam. Moreover, since this oxidation state differs depending on the temperature, variations are likely to occur, and the substrate surface changes in quality before and after drying, resulting in variations in quality.

[0007] If such a substrate with uneven surface quality is used, the characteristics of the electrophotographic photoreceptor or magnetic recording medium will vary, and in the case of semiconductor products, the adhesion of semiconductor elements, electronic parts, etc. will vary. This is not desirable.

The present invention has been made in view of the above points, and provides a method for drying a substrate after cleaning with pure water in a manner that minimizes surface deterioration and prevents variations in surface quality. Make providing the problem the problem you are trying to solve.

[0009]

[Means for Solving the Problem] According to the present invention, the above problem is solved by cleaning the substrate with pure water at room temperature and then rapidly cooling it to a temperature below the triple point to freeze the remaining pure water on the surface of the substrate. Then, the pressure is reduced to below the triple point in the solid phase (ice) region, and then heated to a temperature below room temperature in the gas phase (steam) region to sublimate and dry the remaining pure water. This is solved by In addition, after washing the substrate with pure water at room temperature, it is rapidly cooled to a temperature below the triple point to freeze the remaining pure water on the substrate surface, and then the pressure is reduced to the gas phase (water vapor) region to remove the residual pure water. This problem can also be solved by sublimating pure water and drying it.

0010

[Operation] As mentioned above, after cleaning the substrate with pure water at room temperature, it is rapidly cooled to a temperature below the triple point to freeze the remaining pure water on the surface of the substrate, and then sublimated and dried under reduced pressure at below room temperature. By drying using the so-called freeze-drying method, the substrate can be dried evenly, and even in the case of substrates made of aluminum or aluminum alloy, surface deterioration (oxidation) can be kept to a minimum, and the surface can be dried evenly. It becomes possible to dry without deteriorating the quality.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of an example of the drying method of the present invention using a phase diagram of water. In Figure 1, T indicates the triple point, line AT indicates the sublimation curve, line TBC indicates the evaporation curve, and line TD indicates the melting curve.
The water phase (water) and gas phase (water vapor) are separated. B is the boiling point and C is the critical point. First, the state where water is pulled up from pure water at room temperature and adheres to the substrate surface is point a in the liquid phase region. This substrate is rapidly cooled to reduce b within the solid phase region.
The temperature is lowered to a point where the water on the surface freezes. Next, the pressure is reduced to point c in the same solid phase region while keeping the temperature constant, and then the temperature is raised to point d in the gas phase region while keeping the pressure constant.The frozen water immediately turns into gas. Become and sublimate. Finally, by increasing the pressure and returning to point a, a dry substrate can be obtained. A dry substrate can also be obtained by reducing the pressure from point b to point c1 in the gas phase region while keeping the temperature constant, immediately sublimating the frozen water, and then increasing the temperature and pressure to return to point a. be able to.

[0012] In the above example, point b and point c are at the same temperature, but this is not necessary as long as point c is within the solid phase region. Further, although the pressure at point c and point d is the same, it is not necessary as long as point d is within the gas phase region.

Example 1 A cylindrical substrate made of aluminum alloy and subjected to required machining was immersed in a neutral detergent for about 5 minutes, and then rinsed with pure water at a temperature of 23° C. under atmospheric pressure (a point). Subsequently, it was rapidly cooled to −20° C. under atmospheric pressure to freeze the remaining pure water on the surface (point b). Next, at that temperature, the pressure is 3T.
The pressure was reduced to orr (point c), and the temperature was 23°C under the same pressure.
(point d) to sublimate residual pure water on the surface, and then returned to atmospheric pressure (point a) to obtain a dry substrate.

Comparative Example 1 A cylindrical substrate made of an aluminum alloy and subjected to the required machining was immersed in a neutral detergent for about 5 minutes, and then rinsed with pure water at a temperature of 23° C. under atmospheric pressure. Temperature 7
A dried substrate was prepared by the conventional method of immersing it in pure water at 0° C. or higher and then pulling it up.

Electrophotographic photoreceptors of Example 1 and Comparative Example 1 were prepared by vacuum-depositing a selenium/arsenic alloy on each of these substrates to form a photosensitive layer.

It is known that in an electrophotographic photoreceptor using a substrate made of an aluminum alloy, the more the substrate surface is oxidized, the higher the surface potential after exposure, so-called residual potential. When the residual potential of the photoreceptor obtained as described above was measured, the results shown in FIG. 2 were obtained. In FIG. 2, the solid line shows the results for the photoreceptor of the example, and the dashed line shows the results for the photoreceptor of the comparative example. From FIG. 2, the photoreceptor of the example has a lower residual potential than the photoreceptor of the comparative example.
It was found that oxidation (surface alteration) on the surface of the substrate was suppressed to a low level, and it is clear that the drying method of the example is superior.

[0017]

According to the present invention, after cleaning a substrate used for an electrophotographic photoreceptor, magnetic recording medium, or semiconductor product with pure water at room temperature, the substrate surface is rapidly cooled to a temperature below the triple point. The residual pure water is frozen and dried by a so-called freeze-drying method, in which it is sublimated and dried under reduced pressure at room temperature or below. By adopting such a drying method, it is possible to dry the substrate evenly even if a water-soluble surfactant such as a detergent is used instead of a chlorine-based solvent for degreasing or cleaning the substrate. Even in the case of substrates, it is possible to minimize surface deterioration (oxidation) and dry without unevenly deteriorating the surface.
It becomes possible to avoid environmental pollution.

[Brief explanation of the drawing]

[Fig. 1] An explanatory diagram of an example of the drying method of the present invention using a state diagram of water.

[Figure 2] Diagram showing the residual potential of photoreceptors in Examples and Comparative Examples

Claims (3)

[Claims] Claim 1: After washing the substrate with pure water at room temperature, the remaining pure water on the surface of the substrate is frozen by rapidly cooling it to a temperature below the triple point, and then the pure water remaining on the substrate surface is frozen in the solid phase (ice) region. A method for drying a substrate, comprising: reducing the pressure to a certain pressure, and then heating the remaining pure water to a temperature below room temperature in a gas phase (steam) region to sublimate and dry the remaining pure water. Claim 2: After washing the substrate with pure water at room temperature, it is rapidly cooled to a temperature below the triple point to freeze the remaining pure water on the surface of the substrate, and then the pressure is reduced to the gas phase (water vapor) region. A method for drying a substrate, characterized in that the residual pure water is sublimated and dried. 3. The method for drying a substrate according to claim 1, wherein the substrate is made of aluminum or an aluminum alloy.