JPH0116556B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to an ultrapure water production system for obtaining ultraclean water with even higher purity from primary pure water. [Background of the Invention] In the semiconductor industry, pharmaceutical industry, etc., extremely pure water, so-called ultrapure water, is used. The quality of this ultrapure water is becoming increasingly strict year by year, and in the field of semiconductor industry in particular, extremely small amounts of impurities, which were not a problem in the past, have become a problem as the degree of integration of devices has increased. However, in conventional ultrapure water production systems, as described in JP-A-58-220000, the impurities in ultrapure water include ionic impurities,
Only three items are listed: the number of microorganisms and the number of particulates, and there is no mention of the amount of organic carbon called Total Organic Carbon (TOC). When organic carbon, that is, organic matter in the ultra-pure water increases, the number of microorganisms that use this organic matter as a nutrient source increases, leading to a series of contaminations in which fine particles increase, significantly impairing water quality. The above-mentioned impurities may cause element defects in VLSI manufacturing, leading to a decrease in yield. [Object of the Invention] In view of the above, the present invention provides an ultrapure water production system that has extremely low elution of organic substances, excellent swelling resistance against water, and durable piping that does not peel or crack. This is a daily thing. [Summary of the Invention] In order to achieve the above object, the present invention provides an ultraviolet sterilization device, an ion exchange device, and an ultrafiltration device for primary pure water, and each piping between these devices and to the department where ultrapure water is used. In an ultrapure water production system consisting of, each of the pipes is made of a tubular molded product mainly composed of polyvinyl chloride containing no plasticizer (hereinafter abbreviated as hard vinyl chloride pipe),
It is also characterized in that a plasma polymerized layer of octafluorocyclobutane is formed on its inner surface. [Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of an ultrapure water production system according to the present invention. 1 is an ultraviolet sterilizer for sterilizing microorganisms in primary pure water Wa, 2 is an ion exchange device for removing ions in primary pure water Wa, and 3 is for removing fine particles in primary pure water Wa. Ultrafiltration device, 4A, 4
Reference numeral B designates piping that connects the devices 2, 1 and 3, respectively, and 4C designates piping that connects the device 3 and a department (not shown) that uses ultrapure water Wb. As shown in FIG. 2, the pipes 4A to 4C have an inner diameter of 40 mm and have a plasma polymerized layer 6 of octafluorocyclobutane formed on the inner surface of the pipe body 5.
This is a hard PVC pipe. An example of the plasma polymerization conditions for the octafluorocyclobutane is shown below. (a) Discharge frequency 13.56MHz (b) Discharge power 100W (c) Monomer flow rate 30ml/min (d) Discharge time 10min Octafluorocyclobutane can be made into a water-repellent and dense film by plasma polymerization. However, it has the following three advantages as a monomer. (i) It is chemically very stable and cannot be made into polymers except by plasma polymerization. (ii) It is a gas at room temperature and a sufficient flow rate (or pressure) can be secured in a vacuum container. (iii) Fast plasma polymerization rate. Therefore, it has the advantage that it is easy to handle during plasma polymerization and that a film can be formed in a practical polymerization time. The plasma polymerization used in the present invention can be performed by a known method. For example, when performing high-frequency discharge, a pipe is installed in a vacuum container with an external electrode, a monomer gas is introduced into the pipe, and the inside of the system is normally maintained at 10 ^-3 to 5 Torr. This can be done by applying a high frequency power of several watts to several kilowatts within a certain period of time. The frequency for generating plasma is usually from several KHz to several MHz.
It is possible to use all frequencies from direct current to microwaves. Although the plasma polymerization time varies depending on the applied power and the flow rate (or pressure) of the monomer, it may generally be set from several seconds to several hours. Note that this plasma polymerization can be carried out not only by the above-mentioned external electrode method but also by an internal electrode method. The adhesiveness of the octafluorocyclobutane thus formed was very good, and no cracking or peeling occurred even when it came into contact with running water. The reason for this is that the polyvinyl chloride base material and the plasma polymerized layer of octafluorocyclobutane are chemically bonded. FIG. 3 shows the elemental distribution in the depth direction of the x-ray photoelectron spectrum of the plasma polymerized layer of octafluorocyclobutane. As is clear from the figure, chlorine atoms that exist only in the base material are incorporated into the plasma polymerized layer. This suggests that the plasma polymerization reaction proceeds by decomposition of the base material polyvinyl chloride and recombination of octafluorocyclobutane (or its decomposition active species), forming a chemical bond between the base material and the plasma polymerized layer. In the ultrapure water production system described above, the supplied primary pure water Wa is first subjected to sterilization treatment by ultraviolet irradiation in the ultraviolet sterilizer 1, and then introduced into the ion exchange device 2 via the pipe 4A. Here primary pure water
Dissolved ions in Wa are removed. The primary pure water Wa from which the ions have been removed is introduced into the ultrafiltration device 3 via the pipe 4B, where the primary pure water
The fine particles contained in Wa are removed and ultrapure water is produced.
It becomes Wb. This ultrapure water Wb is fed to the department where it is used via piping 4C. The performance of the ultrapure water produced by the ultrapure water production system of Example 1 is as shown in the item of Example 1 in Table 1. Amount of organic matter eluted (TOC amount)
It is clear that the amount of TOC is 1/5 compared to the amount of TOC in Comparative Example 1 using the conventional manufacturing system described below, which is extremely low. The amount of organic matter eluted (TOC amount) is a value measured at room temperature at the point where ultrapure water is used during operation of the ultrapure water production system. Comparative Example 1 is an ultrapure water production system that has the same configuration as Example 1 except for the piping, and the piping in Comparative Example 1 uses hard vinyl chloride pipes that do not have a plasma polymerized layer. There is. The performance of the ultrapure water according to Comparative Example 1 is as shown in the item of Comparative Example 1 in Table 1, and its TOC amount is five times greater than that of Example 1. Next, using exactly the same piping as used in Example 1 and Comparative Example 1, we investigated the long-term changes in the amount of TOC eluted at room temperature over a period of approximately one year.
The results shown in the figure were obtained. It is clear that in Example 1, the elution prevention effect was maintained over a year. This shows that the plasma-polymerized layer of octafluorocyclobutane does not change even if it comes into contact with ultrapure water for a long period of time, and can be said to be a layer with excellent lifetime stability.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent the elution of low-molecular organic substances from piping, and to provide durable piping with excellent swelling resistance against water and without peeling or cracking. This has the effect of providing an ultrapure water production system.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an ultrapure water production system according to the present invention, and FIG.
Figure 3 is a diagram showing the elemental distribution in the depth direction based on the X-ray optoelectronic spectrum of octafluorocyclobutane, and Figure 4 explains the long-term elution prevention effect of the piping of the present invention. This is a diagram. 1... Ultraviolet sterilizer, 2... Ion exchange device, 3... Ultrafiltration device, 4A to 4C... Piping,
5... Piping body, 6... Plasma polymerized layer.

Claims (1)

[Claims] 1. An ultraviolet sterilizer for sterilizing microorganisms in the primary pure water, an ion exchange device for removing ions in the primary pure water, and an ultrafiltration device for removing particulates in the primary pure water. In an ultrapure water production system consisting of a pipe between each of these devices and a point where pure water is used, each pipe is made of a tubular molded product whose main component is polyvinyl chloride, which does not contain any plasticizer. , and a plasma polymerized layer of octafluorocyclobutane is formed on the inner surface thereof.