JPH0230748B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a pretreatment method for applying an underwater curing paint to a steel structure. (Prior art) Paints for painting underwater (including on wet surfaces and under the sea) have traditionally had a hardening function due to resins such as epoxy and urethane, but water entrapped in the paint has an effect on underwater wettability. Curing agents containing amine groups, etc. are used to alleviate the effects of and deactivate. (Problem to be solved by the invention) However, on the other hand, when such a curing agent is used, there are side effects such as affecting the primary adhesion of the coating after coating film formation, and there is a natural limit to the amount added. . In addition, pre-painting treatment in seawater for repair work on offshore and underwater steel structures involves sandblasting the rusted surface under water, similar to work done on land, to achieve a SIS Sa of 2.5 or higher.
Alternatively, the rusted surface may be polished to ST-3 with a power brush to prepare the surface, or in some cases, further power brush adjustment may be performed after blasting, but the iron surface exposed at this time is an active surface. It is in an environment that is susceptible to rapid oxidation and is extremely susceptible to red rust.
As a result, red rust immediately forms on the active surface, and since this red rust is in seawater, it is not only hydrated iron oxide and colloidal in itself, but also contains inorganic, organic, and biological floating substances with amino groups in the sea. It reacts with the metal and forms a colloid, covering the surface of the steel object and significantly inhibiting its underwater wetting properties. As described above, in 3% saline artificial seawater, even underwater curing paints containing amino groups that can be easily wetted are significantly affected by the amount of inorganic, organic, and suspended organisms that have amino groups. As a countermeasure to this problem, it is possible to add a substance to the resin or curing agent that easily forms a complex salt with the iron ions generated from the surface to be coated and inactivates the iron ions, but these additions may damage the coating film. Since it affects other properties such as primary adhesion, there are limits to its addition. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a coating pretreatment method that does not affect coating performance and has good underwater wetting properties on steel structures. (Means for Solving the Problems) A feature of the present invention is that when repairing submersible steel structures by applying an underwater curing paint, during manual rust removal using sandblasting or abrasives (at the same time or immediately after) ), a metal that is electrochemically more base than iron or an alloy thereof is installed in the brush using the rough grooves created during this rust removal work, and the brush is used to fill the rough grooves with metals that are electrochemically more base than iron. It is the attachment of metal. Another feature of the present invention is that metals that are electrochemically less noble than iron or alloys thereof are used in the final stage of rust removal work by blasting when applying and repairing underwater curing paint to steel structures underwater. The purpose is to apply the foil to the active iron surface and use blasting to adhere the metal to the rust-removed rough surface. The metals or alloys that are electrochemically more base than iron as used in the present invention include magnesium, zinc, aluminum, and alloys of two or more of these metals. It is added to ensure a metal that is easier to handle as a material, such as potassium, calcium, sodium, etc., which is easier to oxidize and is difficult to obtain as a metal, and a material that is easier to handle as a material even though it is electrochemically nobler than iron. It is only necessary that the main components of these additive metals are included in the alloy. For example, iron
These include nickel, tin, lead, and copper. Here, the circumstances leading to the development of the present invention will be explained. As a result of examining underwater wettability in various sea areas using so-called underwater curing paints, we found that even though the seawater contains suspended matter containing inorganic, organic, and biological amino groups, the coating material is zinc, aluminum,
Metallic silicon exhibits good wettability in seawater, and it has been found that the phenomenon that significantly affects the wettability in seawater as described above is a unique phenomenon of iron or its structures. In other words, it was found that hydrated iron ions eluted due to initial corrosion are largely involved in inhibiting wetting properties. Therefore, in the case of stainless steel, it is thought that the degree of influence on underwater wettability due to its rust resistance is considerably smaller than that of iron, and this has also been experimentally proven. Therefore, one of the effective measures to prevent the deterioration of underwater wetness is when repairing underwater steel structures by applying underwater curing paint.
Rust is removed using underwater sandblasting and power brushing, but at this time it is necessary to prevent or inactivate the iron hydrate ions that are eluted from the activated surface immediately before being painted underwater. Therefore, as mentioned above, surfaces such as zinc and aluminum are not affected by underwater wettability, so by attaching metals or alloys that are electrochemically less base than iron to the activated iron surface, it is possible to remove these metals or alloys. It was thought that this would act as a sacrificial anode and prevent the elution of iron hydrated ions from the active iron surface. That is, the sacrificial electrode metal can be simply attached at the same time as the iron active surface is generated. In general, underwater painting takes approximately one hour in terms of curing time and workability, and it is possible to prevent the elution of iron hydrated ions from iron surfaces within that time by applying iron water using metals or alloys baser than iron. All that is required is to prevent the elution of ions. Therefore, to explain the content of the present invention in detail, after removing rust from underwater steel structures by underwater sandblasting, manual rust removal using a power brush is performed before underwater painting. This uses a power brush with chemically base metals or alloys installed inside the power brush, which slides on the blast active surface and causes the metals or alloys baser than iron to adhere to the rough iron surface. . Note that metals that are electrochemically less noble than iron are generally softer than iron, and in a power brush equipped with these metals, only rods made of these metals or alloys are consumed. Therefore, it goes without saying that this metal needs to be replenished. In addition, in the final stage of removing rust from a steel structure by underwater sandblasting, if a metal or alloy foil is applied to the active surface of the iron and then underwater sandblasting is applied, the metal or alloy foil may be partially removed. is transferred to the iron-active surface. The foil made of these deposited metals or alloys prevents the elution of hydrated iron ions from the active iron surface, allowing work to be performed with good applicability. This metal or alloy foil can be easily applied to the active surface by using a magnet. This method is extremely effective when it is considered that the amount of metal or alloy deposited is insufficient to prevent the elution of iron hydrated ions from the iron over time. Normally, the amount consumed by immersing a metal electrochemically less noble than iron, such as zinc, in seawater to prevent rusting in about 1 hour is about 0.12 g/m ² hr (about 1.0 g in the case of salt spray). On the other hand, as ^a result of experiments, it was found that the amount of the metals mentioned above, such as zinc, deposited on rough blasted surfaces by manual sliding in the sea can be up to about 15 g/m ² . Generally, if the area weight is 3g/ ^m2 by electroplating method, the zinc coverage will be approximately 100%.
However, in the case of this method, the situation is different. In addition, if a coating weight of 15 g/m ² or more is required, which is difficult to obtain by the present sliding method, the predetermined coating weight can be obtained by transferring zinc by the sandblasting method as described above. The amount of coating at this time can be freely selected depending on the thickness of the zinc foil and the shot processing time. In order to prevent the elution of hydrated iron oxides on the active surface for one hour, at least 1 g/m ² to 5 g/m ² is required, although it varies somewhat depending on the metal type. It is not necessary to cover 100%. It is necessary to secure a minimum amount of a metal that is electrochemically more base than iron on the surface of the iron to prevent rusting of the iron under the sea during the time of the underwater painting operation. (Effects of the Invention) Since the present invention has the above configuration, most of these deposited metal corrosion products are washed away in water from a certain environment, and even if they remain, they are hydrated oxides, which are not coated. It has almost no effect on the primary adhesion of the film. (Example) An example of the present invention will be described in a separate sheet.

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Claims (1)

[Scope of Claims] 1. When removing rust when repairing underwater curing paint on steel structures under water, the rough surface grooves created during the rust removal work are used to remove metals that are electrochemically more base than iron. Alternatively, a method for pre-painting a steel structure, characterized in that an alloy thereof is installed in a brush, and the brush adheres the metal to the rough surface grooves. 2. In the final stage of rust removal work by blasting when applying and repairing underwater curing paint to steel structures underwater, a foil made of a metal that is electrochemically less noble than iron or an alloy thereof is applied to the active surface of the iron. , a method for pre-painting a steel structure, characterized in that the metal is adhered to a rough rust-removed surface using blasting.