JP2009008191A - Pipe joint for ultrapure water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pipe joint for ultrapure water and its piping system capable of preventing the elution of impurities from the pipe joint to ultrapure water, and capable of improving oxygen non-permeability and chemical resistance, in the pipe joint and its piping system capable of handling the ultrapure water. <P>SOLUTION: In the pipe joint for ultrapure water, at least a liquid contact part of the synthetic resin pipe joint is coated with a DLC film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is an ultrapure water pipe joint mainly used for piping equipment for supplying ultrapure water, and in particular, an ultrapure water pipe capable of preventing impurities from eluting into water from a pipe system such as a pipe joint. The present invention relates to a joint and its piping system.

Conventionally, ultrapure water has been required for cleaning and the like in IC manufacturing processes such as semiconductor wafers. In order to supply such ultrapure water, equipment such as pipes used for piping or the like is necessary.
Since the pipes used for this pipe do not affect the quality of ultrapure water, it is required to prevent elution of impurities such as metal ions and TOC (total organic carbon) from the pipe.

  As a method for preventing the elution of such impurities, the material used for the piping system should be a material with less elution such as impurities. Specifically, the glass transition temperature of the homopolymer is -140 to -20 ° C. Acrylic copolymer 1 to 10 weights obtained by copolymerizing 100 parts by weight of an acrylic monomer component containing 50% by weight or more of a certain alkyl (meth) acrylate monomer and 0.01 to 10 parts by weight of a polyfunctional monomer component. The main component is a composite vinyl chloride resin having an average polymerization degree of 600 to 3000 obtained by graft copolymerization of 99 to 90% by weight of a vinyl chloride monomer alone or a mixed monomer of vinyl chloride monomer and other copolymerizable monomer. An example using a certain hard vinyl chloride resin tube (see Patent Document 1) is known.

On the other hand, it is also known that the plastic material is a plastic container (see Patent Document 2) in which a DLC (diamond-reliable carbon) film is formed on the surface of the plastic container in view of the fact that the gas body is easily permeable. .
In this technology, when a plastic container is used as a filling container for carbonated drinks, wine, etc., oxygen permeates the plastic and oxidizes the drink over time, or carbon dioxide in the carbonated drink permeates the plastic. It is used to prevent the carbonated beverage from being exhausted because it is released to the outside, and utilizes the property that the permeability can be prevented by forming the above-described DLC film.
JP 2005-155901 A JP 2001-31045 A

In general, plastic materials have a drawback of low gas barrier properties. However, in the technique described in Patent Document 1, since a plastic tube made of vinyl chloride resin is used, oxygen or the like permeates the tube, and elution into ultrapure water occurs over time. There was a disadvantage that there is a possibility of adversely affecting the ultrapure water.
In addition, with the recent increase in the density of ICs and the like, the line width is becoming narrower. For this purpose, it is necessary to further increase the purity of the washing water.
Therefore, the present invention has been made to solve the above-mentioned conventional problems, and as an ultrapure water pipe joint capable of handling ultrapure water and a piping system therefor, 1 . 1. There is no elution of impurities from pipe fittings into ultrapure water. 2. can improve non-oxygen permeability; It is an object of the present invention to provide an ultrapure water pipe joint and its piping system capable of improving chemical resistance.

  As a result of intensive studies in order to solve the above problems, the present inventor has coated a diamond-like carbon (DLC) film excellent in non-oxygen permeability on at least the liquid contact portion of a synthetic resin pipe joint Thus, a practically highly desirable pure water pipe joint and its piping system capable of preventing the elution of impurities from the pipe joint into ultrapure water have been found, and the present invention has been completed.

That is, the present invention is an ultrapure water pipe joint in which a diamond-like carbon (hereinafter simply referred to as DLC) film is coated on at least a liquid contact part of a synthetic resin pipe joint for ultrapure water.
In addition, in a piping system composed of resin pipes, joints, valves, etc., it is also an ultrapure water piping system in which at least a liquid contact portion is coated with a DLC film.

  The ultrapure water pipe joint of the present invention can prevent elution of impurities from the pipe joint into the ultrapure water, so that it is a further excellent ultrapure water for cleaning wafers used in semiconductor devices. It is possible to provide an excellent ultrapure water pipe joint for water and its piping system.

Hereinafter, the form of the ultrapure water pipe joint of the present invention will be described in detail.
The pure water pipe joint of the present invention is made of a synthetic resin, and examples thereof include hard vinyl chloride resin, polyethylene, polypropylene resin, crosslinked polyethylene, polybutene, polyethylene terephthalate resin, and polycarbonate resin. Among these, hard vinyl chloride resin is preferably employed in terms of moldability and the like.

  The above-mentioned synthetic resin material is adopted for the pipe joint for ultrapure water of the present invention, but these resins may use a transparent or opaque resin material, and can be appropriately selected according to the application. .

  The shape and nominal diameter of the pipe joint for ultrapure water of the present invention are not particularly limited as long as they are normally used, but generally, those having a nominal diameter of about 13 to 300 mm are adopted, and the thickness Is, for example, about 2 to 20 mm, and can be appropriately selected as necessary.

The ultrapure water pipe joint of the present invention is technically characterized in that a DLC film is coated on at least a liquid contact portion of the pipe joint made of the above-described material.
The wetted part coated with the DLC film is a part where ultrapure water comes into contact with a synthetic resin pipe joint, and is usually the inner surface or outer surface of the pipe joint, or a connection part between the pipe joint and another pipe, etc. That is.
This DLC film is an amorphous carbon thin film with an intermediate structure between diamond and graphite, and has excellent properties such as high hardness, low coefficient of friction, high wear resistance, and high chemical stability. It can be suitably used as a membrane.

In the ultrapure water pipe joint of the present invention, a room temperature CVD plasma treatment method is employed as a method of coating the DLC film on the wetted part.
Conventionally, this method cannot be coated with a metal coating method unless the plasma temperature is 200 ° C. or higher. Therefore, this could not be applied to a synthetic resin pipe joint due to problems such as melting and thermal deterioration. By this method, the DLC film can be coated in a plasma temperature range of 50 to 60 ° C.

For example, in the present invention, the pipe joint can be cleaned (or etched) in advance by subjecting it to a low-temperature plasma treatment or the like. Further, if necessary, the base material may be degreased by alcohol washing or the like according to a conventional method prior to the cleaning treatment. The cleaning treatment by the low temperature plasma treatment can be performed by a known high frequency plasma treatment method or microwave plasma treatment method using at least one of Ar, H ₂ , N ₂ , He, CF ₄ and the like. That is, it is performed while maintaining the gas pressure at about 10 to 150 Pa (more preferably about 13 to 135 Pa) at a temperature at which the pipe joint is not thermally deteriorated (determined by the type of synthetic resin material). By this low-temperature plasma treatment, the pipe joint is highly purified and surface-modified.

  Next, the pipe joint that has been cleaned as necessary is subjected to a CVD plasma process using a methane-argon mixed gas. This step can be performed under similar temperature and pressure conditions using a plasma generator similar to that used above. The methane content in the methane-argon mixed gas in this step is usually about 10 to 80% by volume, more preferably about 20 to 50% by volume. By this step, a carbon intermediate layer having excellent adhesion to the base material is formed on the surface of the pipe joint. This carbon intermediate layer is mainly made of amorphous carbon. The thickness of the carbon intermediate layer varies depending on the use of the final product and the like, but is usually about 10 to 1000 nm, more preferably about 20 to 500 nm. The thickness of the carbon intermediate layer can be controlled by the methane content (methane partial pressure) in the mixed gas, the conditions (temperature, pressure, time) in the CVD plasma treatment, and the like.

  Next, the pipe joint in which the carbon intermediate layer is formed by this step is subjected to a CVD plasma processing step using a hydrocarbon gas or a mixed gas of hydrocarbon gas and hydrogen. This CVD plasma treatment step can be performed under the same temperature and pressure conditions using the same plasma generator as that used in the above step. Examples of the hydrocarbon include methane, ethane, ethylene, acetylene and the like. The transition from the above process to the plasma treatment process is continued without interrupting the plasma treatment operation by increasing the hydrogen content while decreasing the argon content while maintaining the atmospheric gas pressure at a predetermined value. Can be done automatically. In this case, it is possible to form a “gradient functional film” in which the structure and physical properties from the carbon intermediate layer to the DLC layer are continuously changed.

  In this functionally gradient film, there is no clear interface between the carbon intermediate layer (lower layer) and the DLC film (upper layer), so that the adhesion between the DLC film and the pipe joint is further improved. The hydrocarbon content in the hydrocarbon-containing gas at the final stage of the CVD plasma treatment process is about 10 to 100% by volume, more preferably about 25 to 100% by volume. By this CVD plasma processing step, a desired high hardness DLC film is formed on the outermost surface of the pipe joint. The thickness of the DLC film can be controlled by the hydrocarbon content (hydrocarbon gas partial pressure) in the hydrocarbon-containing gas, various conditions (temperature, pressure, time, etc.) in the CVD plasma treatment, and the like.

The thickness of the DLC film constituting the present invention is not particularly limited, but is preferably in the range of 50 to 500 mm, more preferably in the range of 200 to 400 mm.
If this thickness is less than 50 mm, there is a possibility that effects such as non-oxygen permeability cannot be exhibited sufficiently, and conversely if it exceeds 500 mm, there is a risk that it becomes economically disadvantageous.

In the present invention, it is preferable that the above-mentioned DLC film is formed at least on the liquid contact portion in a piping system including a resin pipe, a joint, a valve, and the like.
In this case, resin pipes, joints, valves, and the like may be used as usual.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited only to the following Example.

[Example 1]
An ultrapure water pipe joint in which a DLC film having an average thickness of 300 mm was formed on a wetted part of a pipe joint made of a hard polyvinyl chloride resin having a nominal diameter of 20 mm and a thickness of 3 mm was formed by room temperature plasma CVD.
Using this ultrapure water pipe joint, the ultrapure water was sealed, and the elution of impurities from the pipe joint after 30 days into the ultrapure water was examined. There wasn't.

[Comparative Example 1]
A pipe joint made of a hard vinyl chloride resin having a nominal diameter of 20 mm and a thickness of 3 mm, on which no DLC film was formed on the surface, was produced. Using this pipe joint, ultrapure water was sealed in this, and as a result of examining the elution of impurities from the pipe joint after 30 days into the ultrapure water, elution was observed as compared with the stock solution.

  Since the pipe joint for ultrapure water of the present invention can prevent the elution of impurities from the pipe joint into the ultrapure water, it is particularly intended for ultrapure water for wafer cleaning used in semiconductor devices. Therefore, an excellent ultrapure water pipe joint and its piping system can be provided, and its industrial utility value is extremely high.

Claims (2)

  A pipe joint for ultrapure water, wherein a diamond-like carbon (DLC) film is coated on at least a liquid contact portion of a pipe joint made of synthetic resin.   An ultrapure water piping system, wherein a diamond-like carbon (DLC) film is coated at least on a liquid contact portion in a piping system including a resin pipe, a joint, a valve, and the like.