NO153972B - PROCEDURE FOR AA EXTEND THE LIFE AGE FOR AN MOVIE OF ANTIGROMALING. - Google Patents

Description

The invention relates to a method for extending the lifetime of a film of an antifouling paint for underwater constructions by applying a coating of a graft copolymer to said film.

The maintenance of the antifouling properties of a film of antifouling paint for structures submerged in the sea, e.g. movable structures, such as ships, and stationary structures,

such as wharves, (extensions and bridges), for a long time contribute greatly to the economic operation of the constructions and to the efficient utilization of natural resources. There has therefore been a constant need for the development of paints with superior antifouling properties and of methods for maintain the anti-fouling ability of the paint furnaces for a long time.

Antifouling paints to prevent the growth of aquatic organisms are classified into two groups. One group comprises the antifouling paints in which a hydrophilic, synthetic polymer is used as the main binder. The second group comprises anti-fouling paints in which rosin is used as the main binder. In a paint film formed from such a paint containing a rosin binder, an antifouling agent in the paint film will be leached from it together with the leaching of rosin. Most antigromalings belong to this group. However, the leaching of rosin causes the paint film itself to break down. A paint film formed by a paint belonging to the latter group actually erodes strongly, and the toughness of the paint film decreases when it is kept submerged in seawater for several months.

When an anti-fouling film for ship bottoms is allowed to remain in air

for several weeks, flaking or cracking will usually occur. In addition, the film's surface is gradually exposed to roughening, which is accelerated when the ship is in operation. The roughness when the ship is in operation causes turbulence to occur which leads to greatly accelerated erosion of the film. The turbulence also causes

that the speed becomes lower, and extra fuel is needed to keep the speed up. Although growth does not occur when a ship is in motion, growth will occur on the bottom of the ship when the ship reaches it

is anchored up. It is therefore necessary for a ship's bottom paint to produce a film that is both tough and has an antifouling effect.

The invention aims to provide a method for extending the life of a film of an anti-fouling paint for constructions that are submerged in seawater.

The invention thus relates to a method for extending the life of a film of anti-fouling paint by applying to it a material containing a hydrophilic copolymer to thereby form a protective coating with a water absorption of over 5% by weight and a moisture permeability of 45-480 g" 0.l mm/m 2 • 24 h • cmHg,

and the method is characterized by the fact that a graft copolymer is used as copolymer, which is produced by polymerization of at least one vinyl monomer selected from the group consisting of methacrylic acid esters, acrylic acid esters, acrylonitrile, styrene and α-methylstyrene, optionally together with a small amount of a hydrophilic vinyl monomer selected from the group consisting of acrylic acid, acrylamide, methacrylic acid, 2-hydroxyethyl methacrylate and vinyl ethers, in the presence of a hydrophilic polymer selected from the group consisting of polyethylene glycol/polypropylene glycol, polyvinylpyrrolidone, polyvinylamine and derivatives thereof.

According to the invention, the applied coating of the water-resistant, water-permeable copolymer prevents too strong a breakdown of the film of antifouling paint and contributes to the paint film having an increased toughness, whereby the antifouling property of the paint film is maintained for a long time.

A method for improving the toughness of a colored paint film by applying a clear coating to the paint film has previously been known. However, this method cannot be used in connection with a film of an antifouling paint because a normal clear coating only has a sufficient toughness, but not a sufficient permeability to water. For this reason, the antifouling effect of the paint film is greatly reduced even though the toughness is improved. A conventional coating that is permeable to water, on the other hand, has a poor resistance to water and cannot be used

as a protective coating on a film of an antifouling paint.

Of the protective coating that is applied to the film of the antifouling paint, both a sufficient resistance to water and a sufficient permeability to water are required. It is of essential importance that the coating has sufficient resistance to water in order to be able to maintain the protective coating's toughness in water for a long time. A poor resistance to water leads to the breakdown of the protective coating within a short time. A suitable permeability for water is of essential importance to achieve a regulated leaching of an antifouling agent in the film of antifouling paint.

Hydrophilic acrylic polymers, such as poly-2-hydroxyethyl acrylate or methacrylate and copolymers of 2-hydroxyethyl acrylate or

- methacrylate as the main component, this has permeability to water. When such a polymer is used alone as a protective coating, cross-linking is required as resistance

the skill towards water otherwise will not be sufficient. A water-resistant polymer such as an acrylic polymer can also be improved to provide a coating with the required water permeability by mixing it with a hydrophilic polymer. If, however, a coating of a water-resistant polymer is made permeable to water simply by mixing the polymer with a hydrophilic polymer, not only will the water resistance be greatly reduced, but the water permeability of a coating made from such a mixture will also become inadequate.

In fig. 1 and 2 show curves for comparing the moisture permeability of a film made from a protective coating composition containing an acrylic polymer grafted hydrophilic polymer used according to the invention with the water permeability of a film made from a material containing a mixture of an acrylic polymer and a hydrophilic polymer.

More specifically, fig. 1 and 2 show the moisture permeabilities, as defined below, of a film made of a protective coating material containing a methyl methacrylate/ethyl acrylate/acrylic acid copolymer grafted hydrophilic polymer, and of a film made of a material containing a mixture of a methyl methacrylate/ ethyl acrylate/acrylic acid copolymer and a hydrophilic polymer, the weight ratio between the acrylic monomers methyl methacrylate:ethyl acrylate:acrylic acid being 69:30:1 and the proportion of the hydrophilic polymer, i.e. polyvinylpyrrolidone according to fig. 1 and polypropylene glycol according to according to fig. 2, is indicated by a value calculated using the equation hydrophilic polymer x 100/dry matter in the material (% by weight). According to the invention, a water-resistant polymer can be given permeability to water without this often exceeding the polymer's resistance to water, by polymerization of one or more vinyl monomers in the presence of a hydrophilic polymer, and it is assumed that by such polymerization the water-resistant polymer of vinyl monomers on the hydrophilic polymer. The use of such a polymer which possesses

both a sufficient resistance to water and a sufficient permeability to water are an important feature

cen the present invention.

The hydrophilic polymers used in carrying out the present method are polymerization products of monomers with hydrophilic groups and polymers with a large number of hydrophilic groups. The hydrophilic polymer which

used for carrying out the present method is polyethylene glycol, polypropylene glycol, polyvinylpyrrolidone, polyvinylamine or derivatives thereof.

The polymers used in carrying out the present method as a binder for the protective coating material for a film of an antifouling paint can be prepared by polymerizing one or more vinyl monomers in the presence of the hydrophilic polymer in the usual way. The vinyl monomers that can

are used in the execution of the present method, are methacrylic acid esters such as methyl methacrvlate, ethyl methacrylate, butyl methacrylate and lauryl methacrylate, acrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, sec. butyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate, acrylonitrile, styrene or α-nnethyl styrene. These vinyl monomers can optionally be used together with a small amount of other hydrophilic vinyl monomers, consisting of acrylic acid, methacrylic acid, 2-hydroxyethyl methacrylate, acrylamide or vinyl ether. The polymers can also be modified into crosslinkable polymers by introducing a crosslinkable monomer unit into a polymer

chain.

The polymerization of the vinyl monomers can be carried out in the presence of the hydrophilic polymer in the usual manner. The hydrophilic polymer and part of a polymerization initiator can e.g. is dissolved in a solvent and the polymerization is carried out at an elevated temperature by dropwise addition of a vinyl monomer or vinyl monomers to the solution. The polymerization is preferably carried out in an organic solvent, such as toluene, xylene, butyl acetate, methyl isobutyl ketone or mixtures thereof. These organic solvents can be used together with an alcohol, such as isopropyl alcohol or butanol. When the polymerization is carried out in the organic solvent, the resulting reaction mixture, which is usually a colorless, transparent material or a tarnished material, can be used as such as a protective coating material.

The amounts of the hydrophilic polymer and of the vinyl monomers used can vary depending on the types of the hydrophilic polymer and the vinyl monomers used and should be adapted so that the polymerization product has a sufficient resistance to water and the correct permeability to water. It is of significant importance in the present invention that the film formed by the produced protective coating material has a moisture permeability of 45-480 g • 0.1 mm/m 2 • 24 h • cmHg- When a film of an anti-fouling paint is applied a protective coating

with a moisture permeability of less than 45, an antifouling agent will not leach sufficiently from the film of antifouling paint. When the permeability to moisture is higher than

480, the protective coating's resistance to water will decrease. It is also important that the film formed by the protective coating material has a water absorption, as defined below, of more than 5% by weight. The water absorption is related to the type and content of the hydrophilic polymer, and when the water absorption is less than 5% by weight, an antifouling agent will not leach sufficiently from a film of an antifouling paint.

Pigments and other additives can be added to the protective coating material.

The protective coating material is usually diluted until it has a dry matter content of 10-20% by weight and applied to a film of an antifouling paint in the usual way, such as by brushing, spraying and rolling. As a diluent, alcohols,

such as isopropyl alcohol and butanol, methyl-Cellosol®, ethyl-Cellosolve® or mixtures of the alcohol as the main component with other solvents, such as toluene, xylene, ethyl acetate, butyl acetate or methylisobutyl ketone, are advantageously used. These thinners are chosen in accordance with the properties of the undercoat of anti-fouling paint.

Other anti-rust paints and anti-fouling paints can also be applied to the protective coating applied by the present method.

When the protective coating material is applied to a known film of an antifouling paint by the method according to the invention, a transient rapid leaching of an antifouling agent from the paint film can be prevented and the antifouling property maintained for a longer time without this affecting the antifouling effect, as water will always reach the surface of the antifouling paint surface via the protective

tend coating so that an antifouling agent in the paint film will leach into water, while the protective coating can strengthen the paint film and inhibit its degradation because the protective coating has toughness and resistance to water.

Example 1

A coating agent was prepared using the following ingredients:

A 500 ml four-necked flask was filled with polypropylene glycol, toluene and a portion of benzoyl peroxide (0.2 g) and the temperature was raised to 90-5°C. The monomers were added dropwise to the flask over 1.5 hours in a stream of nitrogen, and the polymerization was then continued for 6 hours at the above temperature.

Example 2

The procedure according to example 1 was repeated, but with the change that the following quantities of the components were used:

Examples 3-5

Coating materials were prepared using the components listed in table 1 in the same way as in example 1.

Comparative example

A coating agent was prepared using the following ingredients in the same manner as in Example 1:

The obtained reaction mixtures were used as coating materials. From the coating materials thus obtained, coating films were prepared, and their moisture permeability and water absorption were measured as follows:

Permeability to moisture

Rooms that were divided by a film were kept at a relative humidity of 88% and 0%, and the amount of water vapor that penetrated the film at 20°C for 24 hours was measured. Based on the amount of water vapor that penetrated the film, the moisture permeability was calculated using the following equation:

Permeability for moisture ( g-0.lmm/m 2•24h-cmHg) =

Q: the amount of water vapor that penetrated

1: film thickness

a: film area

t: time

(p a -pKo): difference in water vapor pressure between both rooms Water absorption

A film was immersed in water for 72 hours, and the amount of water absorbed was measured. The water absorption was calculated using the following equation:

The results of the measurement of the permeability for moisture and water absorption are reproduced in table 2.

In 00? In d.

The coating material obtained in each example and in the comparative example was sprayed onto each sample panel which was coated with the following antifouling paint, to obtain a coating with a thickness of approx. 12 fam. The sample panels produced in this way were exposed to seawater at a depth of 1 m. As a control, the sample panels coated with the anti-fouling paint were also exposed for the same time.

The antifouling paints used included a resin binder

and an antifouling agent and had the following composition:

(a) Of the chlorinated rubber copper (I) oxide type (commercially available under the trade mark "TOA SR ANTI-EOULING EXTRA SUPER

TROPICAL"),

(b) of the polyvinyl chloride-copper (I) oxide type (available in

trading under the trademark "VINAL ANTI-FOULING SUPER"\,

(c) of the turpentine balsam-copper (I) oxide type (available in

trade under the trademark "TOA ANTI-FOULING SUPER"), and

(d) of the chlorinated rubber-organotin compound type (available

in the trade under the trademark "TOA ANTI-FOULING OG".

After 3, 6, 9, 12 and 18 months, the fouling became

which was due to marine organisms, such as marine algae, duck shells and barnacles, and the erosion of a film of an antifouling paint with the coating material applied was observed. The fouling due to organisms and the erosion of the film were judged according to the following numerical scales.

Fouling by organisms

0: No or very little fouling

1: Small fouling

2: Considerable fouling

3: Fouling within a wide area

4: Fouling over the entire surface

-: Dense and thick fouling over the entire surface Erosion of film

A: No or very little erosion

B: Considerable erosion

C: Very strong erosion

-: Difficult to assess due to fouling by organisms The results of the exposure tests in a sea are reproduced

in tables 3, 4, 5 and 6.

From the results reproduced in tables 3-6, it will be understood that the top layer of the coating material according to the comparative example (which shows poor permeability to moisture according to table 2) prevents antifouling paints from developing their antifouling effect, while on the other hand the coating material used according to the invention reinforces a coating of an antifouling paint without this

exceeds the antifouling effect.

Claims (1)

Process for extending the life of a film of antifouling paint by applying thereto a material containing a hydrophilic copolymer to thereby form a protective coating with a water absorption greater than 5% by weight and a moisture permeability of 45-480 g - 0.1 mm /m 2 r 24 h • cmHg, characterized in that the copolymer used is a graft copolymer which is produced by polymerization of at least one vinyl monomer selected from the group consisting of methacrylic acid esters, acrylic acid esters, acrylonitrile, styrene and ct-methylstyrene, optionally together with a small amount of a hydrophilic vinyl monomer selected from the group consisting of acrylic acid, acrylamide, methacyl acid, 2-hydroxyethyl methacrylate and vinyl ether, in the presence of a hydrophilic polymer selected from the group consisting of polyethylene glycol, polypropylene glycol, polyvinylpyrrolidone, polyvinylamine and derivatives thereof.