JPH07241550A - Antifouling method of underwater structure - Google Patents

Abstract

PURPOSE:To effectively prevent fouling of an underwater structure by a simple device without using a chemical substance by applying specific negative potential to a structure containing a conductive material in at least a part thereof in water. CONSTITUTION:When negative voltage is applied to a conductive substrate of a gass substrate 2 being a structure, for example, the conductive resin plate electrode 3 thereof in water containing bacteria, bacteria approaching the plate electrode 3 becomes impossible to adhere to the electrode 3 by electrical repulsion. Since the adhesion of bacteria is the initial stage of fouling of an underwater structure due to adhesion of organisms, the fouling due to the adhesion of organisms can be prevented finally. Negative potential to be applied is set to -0.4-below 0Vvs.SCE. When applied potential becomes 0Vvs.SCE or more, the attraction action of adhesive bacteria is developed contrarily and, in the case of below -0.4Vvs.SCE, pH rises and no pref. result is obtained because adverse effect is exerted on the peripheral environment of the electrode 3 or the electrode 3 itself.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for antifouling a surface of a structure in water.

[0002]

2. Description of the Related Art In an oligotrophic environment such as distilled water, seawater or tap water, microorganisms are aggregated and increase at the interface between a liquid phase and a solid phase. This is because the dilute organic matter existing in water is adsorbed and concentrated on such an interface, so that the microorganisms use the organic matter as a nutrient source. Microorganisms grown on the solid surface diffuse into water again to cause water pollution, or secrete slime-like substances while adsorbed on the solid surface to stain the surface. In particular, a large number of microorganisms are present in seawater, causing problems such as showing pathogenicity and adhering to undersea structures. Further, since the undersea structure is constantly in contact with a huge amount of seawater, the propagation of various marine organisms starting from the attachment of microorganisms becomes a problem on its surface. The mechanism of occurrence of these problems is as follows. First, adherent Gram-negative bacteria adsorb on the surface and secrete a large amount of slime-like substances. Subsequently, other microorganisms collect in the slime layer and proliferate to form a microbial film. Further, large organisms will propagate one after another on this microbial layer, and eventually the large organisms will cover the surface.

Conventionally, as an antifouling treatment against the adhesion and growth of microorganisms on the surface of such an underwater structure, for example, a sterilizing agent such as chlorine gas or hypochlorous acid is injected, or an organic tin compound or the like is coated on the surface. As described above, a method of treating using a chemical substance has been performed. However, these methods have a problem of residual toxicity because the used chemical substances are diffused and remain in water. In water, (1) a step of applying a positive potential to the conductive substrate to adsorb microorganisms in water to the surface of the conductive substrate to sterilize, and (2) applying a negative potential to the conductive substrate. There is also known a method of controlling the adherence and growth of microorganisms in the initial stage by carrying out a step of desorbing sterilized microorganisms adsorbed on the surface of the conductive substrate (Japanese Patent Laid-Open No. Hei 4 (1999) -411). -341392). This method is preferable in that it exerts a sufficient effect even in a place where microorganisms are heavily attached to the sea, but on the other hand, a device for alternately applying positive and negative potentials (for example, a pulse generator) is required. Therefore, the types of conductive materials that can be preferably used are practically limited.

[0004]

DISCLOSURE OF THE INVENTION The inventor of the present invention does not use a chemical substance that causes residual toxicity, uses a simple device, can effectively use an inexpensive metal material, and can prevent biological pollution. As a result of diligent research to develop a means, it was surprisingly found that it is possible to prevent the attachment of microorganisms approaching the surface of an underwater structure at the initial stage by simply applying a negative potential. The present invention is based on these findings.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a structure containing -0.4Vvs. SCE or more 0 V vs. The present invention relates to an antifouling method for an underwater structure, which is characterized by applying a negative potential lower than SCE.

The structure which can be treated by the method according to the invention, which may be wholly formed from a conductive material, is at least immersed in water and the surface (or part of the surface) which is to be protected from microbial contamination. It suffices that it has a structure capable of being charged with a negative charge, as long as it includes a conductive substrate made of a conductive material on the entire surface or a part of the surface or inside thereof. This is because the method of the present invention utilizes the repulsion between the surface negative charge of the adherent microorganism and the negative charge of the structure surface, so long as the repulsive force is sufficiently transmitted to the adherent microorganism, the surface This is because a non-conductive film may be present in the.

The shape of the conductive substrate is not particularly limited. For example, a conductive film provided on the surface of the structure, a conductive plate forming the surface of the structure or a part of the inside thereof, or the inside of the structure. The conductive regions may be arranged discontinuously (for example, in a mesh shape, a lattice shape, or a stripe shape).

The conductive material is also not particularly limited, but has good plasticity and moldability capable of forming a conductive surface layer on the above-mentioned conductive substrate, for example, a wide surface of an underwater structure or a ship. It is preferable to have Examples of conductive materials include graphite, carbon, oxide semiconductors, metals, and conductive polymer compounds. For _{example, In 2 O 3 -SnO 2,} SnO 2 -Sb
Oxide semiconductor such as ₂ O ₃ , CdO, CdSnO ₄ or ZnO, gold, silver, copper, palladium, platinum, aluminum,
Examples thereof include metals such as chromium, rhodium, titanium, stainless steel and tungsten, alloys of these metals, and conductive polymer compounds such as polypyrrole. Further, these conductive materials may be mixed with a binder polymer to form a conductive plate as it is, or a conductive film may be formed on the surface of an underwater structure using the conductive material-containing coating composition.

Examples of the binder polymer include polyurethane resin, silicone resin, vinyl acetate resin, a mixture of vinyl chloride resin and polyurethane resin, styrene butadiene rubber, chloroprene rubber, epoxy resin and the like. A conductive polymer (for example, polyaniline) may be added together with the binder polymer to reduce the resistance value.

In the present specification, the term "water" is not limited as long as it is water in which adherent microorganisms are present.
This includes river water, lake water, irrigation water, pool water, drinking water (in tanks). Further, the structure means any structure having a portion which is permanently or temporarily immersed in the above-mentioned water, and which may be undesirably contaminated by aquatic microorganisms. Examples include pipes and fishing gear.

In the method of the present invention, when a negative potential is applied to the conductive substrate of the structure in water containing microorganisms, microorganisms approaching the conductive substrate cannot attach due to electrical repulsion. Since this microbial adhesion is the initial stage of the biofouling of the aquatic structure, the biofouling can be finally prevented.

The negative potential applied is -0.4 Vvs. SCE
0 V vs. It is less than SCE. Applied potential is 0Vv
s. On the other hand, when it is more than SCE, it has an effect of adsorbing adherent microorganisms, and it has an effect of -0.4 Vvs. PH below SCE
Is increased, which adversely affects the environment around the electrode and the electrode itself, which is not preferable. Furthermore, the negative potential is -0.25Vv
s. The SCE or less is preferable because the antifouling effect is improved. Potentials within said range can be applied varyingly or preferably substantially constant, and intermittently or preferably continuously.

In Example 6 of the above-mentioned Japanese Patent Laid-Open No. 4-341392, the results of microbial control when a negative potential is applied to the microbial dispersion in a closed system are shown. It is shown that no difference was observed in the control effect between the case and the case where no potential was applied and the case where only a positive potential was applied. However, this result shows the control effect on the microorganisms in the water to be treated, and there is no description about the effect of the negative potential applied to the surface of the underwater structure.

In the method of the present invention, a conductive substrate is used as a working electrode, and a potential in the above range is applied to the conductive substrate by using a suitable counter electrode and a DC power supply (rectifier) to the working substrate. It is necessary to control so that The potential may be controlled using the reference electrode. The DC power supply (rectifier) is not particularly limited as long as it can apply a desired potential to the conductive substrate. In addition, a film containing a repellent (for example, an organotin-based, silicon-based, or copper-based repellent) may be formed on the surface of the structure to be treated by the method of the present invention.

[0015]

The antifouling effect by the negative potential of the method of the present invention utilizes electrostatic repulsion, so that the viable cell density near the conductive substrate is reduced, and even if some biological attachment occurs, electrostatic It is considered that the antifouling effect is maintained for a long time because the specific repulsion extends to the outside of the biofouling layer.

[0016]

The present invention will be described in detail below with reference to examples, but these do not limit the scope of the present invention. In the following examples, the device shown in FIG. 1 was used as the antifouling effect test device. In this apparatus, a conductive resin plate electrode 3 formed on a glass substrate 2 is arranged in an antifouling effect test tank 1, and the plate electrode 3 communicates with a potentiostat 4. Potentiostat 4
Is a reference electrode 6 and a counter electrode 7 arranged in the control tank 5.
I have contacted each other. The antifouling effect test tank 1 and the control tank 5 are connected by a salt bridge 8, and a stirrer 9 and a stirring rod 10 are arranged at the bottom of the antifouling effect test tank 1. As the conductive resin plate electrode 3, a material obtained by adding 50% by weight of graphite (Fluka company) to silicone resin was applied on the glass substrate 2 on the plate (2.6 mm).
X 2.6 mm x 1.5 mm), the counter electrode 7 is platinum, and the reference electrode 6 is a saturated sweet koh electrode (S
CE) was used. The test was carried out by putting the sample water 11 in the antifouling effect test tank 1.

Example 1: Effect of applied potential on seawater The effect of applied potential on seawater was investigated using the apparatus shown in FIG. 50m of seawater (pH 8.0) collected from Miura Beach
1 was put in the antifouling effect test tank 1, and a negative potential was applied to the plate electrode 3 for 30 minutes at room temperature while stirring at 350 rpm, and changes in current density, residual chlorine concentration and pH were measured. As is clear from FIG. 2 showing the measurement result, −0.4
V to 0 V vs. In the SCE range, the pH value was within the range of about 7.5 to 8 (■ in Fig. 2), and no pH change was observed. Therefore, −0.4 V to 0 V vs. In the SCE range, the antifouling effect due to pH change does not occur. Also, residual chlorine was not detected. Note that FIG. 2 also shows the result when a positive potential is applied.

Example 2: Antifouling effect test in a test tank Vibrio arginolyticus (Vibri)
o alginolyticus: ATCC 1774
9), and marine broth (Marine broth) 2
2 in 216 (DIFCO Laboratory Co.)
The cells were cultured aerobically at 5 ° C for 10 hours. The cultured cells were collected by centrifugation (10 minutes; 2000 × g) and then thoroughly washed with sterilized seawater. Then, 10 ⁵ cells / ml sample water was prepared using a hemacytometer. 150 ml of this sample water was put in the antifouling effect test tank 1 of FIG. 1, the plate electrode 3 was dipped, and treated at the following potential setting for 12 hours while gently stirring at 350 rpm. The potential setting is
(1) +1.0 Vvs. SCE constant potential, (2) -0.
3V vs. SCE constant potential, (3) +1.0 Vvs. S
CE 30 min / -0.2 Vvs. SCE 10mi
n pulse potential, (4) no potential is applied, (5) -0.
1 V vs. SCE constant potential, (6) -0.2 Vvs. S
CE constant potential, (7) -0.25 V vs. SCE constant potential, (8) -0.4V vs. Eight constant potentials of SCE were used. After 12 hours, the bacterial cells attached to the surface of each electrode were treated with propidium iodide (PI; propidium).
iodide), 4 ', 6-diamino-2-phenylindole dihydrochloride (DAPI; 4', 6-diami)
no-2-phenylindole dihydro
Chloride), and the number of cells adhering to the electrode 3 and the number of viable cells among the adhering cells were counted by a fluorescence microscope. The results are shown in Table 1.

[Table 1] Potential setting Number of adherent bacteria Number of viable cells Viability (1) 6.6 × 10 ⁶ 7.3 × 10 ² 0.01% (2) 8.4 × 10 ² 7.2 × 10 ² 85 .7% (3) 1.8 × 10 6 0 0% (4) 7.7 × 10 9 7.1 × 10 7 92.2% (5) 6.6 × 10 5 5.9 × 10 5 89 .3% (6) 8.4 × 10 ⁵ 7.2 × 10 ⁵ 85.7% (7) 6.7 × 10 ² 6.1 × 10 ² 91.0% (8) 7.7 × 10 ² 7.1 x 10 ² 92.2%

Example 3: Antifouling effect test in sea As shown in FIG. 3, carbon plate 13 [400 mm × 100 m
m × 10 mm; Toho Rayon Co., Ltd.], counter electrode 14
[200 mm x 150 mm; Vesfight W6101 /
Toho Rayon Co., Ltd.] and a reference electrode 15 [saturated silver chloride electrode, GST304AQ; Toa Denpa Kogyo Co., Ltd.] are fixed to a vinyl chloride plate 16 (500 mm × 700 mm × 10 mm), and potentiostat 17 [HA] is fixed to them. -15
1; Hokuto Denko Co., Ltd.] was connected. Carbon plate 13, counter electrode 1
Support plate 16 made of vinyl chloride to which 4 and reference electrode 15 are fixed
Submerged in seawater 19 (depth of about 1 m) at Tateyama Port, Chiba Prefecture,
-0.3Vv from potentiostat 17 to carbon plate 13
s. Adjust so that the potential of SCE is applied, 1993
The weight of the deposit on the carbon plate 13 was measured for about three months from September 3, 2013 to December 16, 1993. As a comparative example, vinyl chloride plate 18 (500 mm x 700 mm
X 10 mm) was fixed on a vinyl chloride plate 16, fixed without applying an electric potential and submerged, and the weight change was measured. The result is shown in FIG. In FIG. 4, ◯ indicates the weight change of the carbon plate 13 to which a negative potential is applied, and ● indicates the weight change of the vinyl chloride test plate 18 to which no potential is applied.

[0020]

EFFECTS OF THE INVENTION According to the method of the present invention, a chemical substance that causes residual toxicity is not used, a simple device is used, and an inexpensive metal material is used. Can be prevented. Further, in the method of the present invention, since only a negative potential is applied, unlike the conventional method in which positive and negative potentials are alternately applied, it is not necessary to use a device such as a pulse generator, and furthermore, when a positive potential is applied, corrosion easily occurs. Metal can also be used as the conductive material.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing the structure of an antifouling effect test tank used in Examples.

FIG. 2 is a graph showing the effect of applying a negative potential to seawater.

FIG. 3 is an explanatory view schematically showing the structure of an antifouling effect test plate used in Examples.

FIG. 4 is a graph showing changes in weight when a negative potential is applied to an electrode plate immersed in seawater.

[Explanation of symbols]

1 ・ ・ Antifouling effect test tank; 2 ・ ・ Glass substrate; 3 ・ ・ Conductive resin plate electrode; 4,17 ・ ・ Potentiostat; 5 ・ ・ Control tank; 6,15 ・ ・ Reference electrode;
14 ... Counter electrode; 8 ... Salt bridge; 9 ... Stirrer; 10 ...
Stirring bar; 11 ... Sample water; 13 ... Carbon plate; 16 ... Vinyl chloride support plate; 18 ... Vinyl chloride test plate; 19
..Seawater

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenji Ikeda 7-35 Higashiohisa, Arakawa-ku, Tokyo Within Asahi Denka Co., Ltd. (72) Inventor Hiroshi Sugiyama 7-35 Higashiohisa, Arakawa-ku, Tokyo Asahi Denka Kogyo Co., Ltd. (72) Inventor Hiroshi Edo 7-35 Higashiohisa Arakawa-ku Tokyo Tokyo Asahi Denka Kogyo Co., Ltd.

Claims (2)

[Claims] 1. A structure containing a conductive material in at least a part thereof in water is -0.4 Vvs. 0V above SCE
vs. An antifouling method for an underwater structure, which comprises applying a negative potential lower than SCE. 2. The negative potential is -0.4 Vvs. SCE or more −0.25 Vvs. The method according to claim 1, which has a SCE or less.