The present invention relates to a method for the provision of an epoxy paint coating on the surface of a cargo hold for carrying solid cargos.

Cargo holds are used to store and transport solid cargo from one place to another by land or by sea. Cargo holds come into contact with a wide variety of solid compounds/cargo. Cargo holds are frequently filled and emptied of the solid cargo, which means that the surfaces of cargo holds must be provided with a coating to protect the surface from abrasion and impact from the solid cargo.

Cargo holds are large. The volume of a cargo hold generally ranges from about 4,000 m ³ to about 25,000 m ³ Frequently encountered volumes of cargo holds are in the range of 10,000 m ³ to 15,000 m ³ . This is much larger than the maximum volume of a cargo tank, which is about 3,000 m ³ A cargo hold is different to a cargo tank. Firstly, cargo tanks carry liquid cargos whereas cargo holds carry solid cargos. Cargo hold coatings must provide good resistance to abrasion and impact caused by the solid cargo, but for cargo tank coatings impact resistance is not as important, as liquids are not abrasive. Cargo tank coatings must have a high chemical resistance in the sense that they are able to resist absorption of and can desorb a broad spectrum of chemical compounds, but for cargo holds which carry solid cargo, high chemical resistance is not so important. If a coating has good chemical resistance, it does not automatically have good abrasion resistance as well, and vice versa. In order to improve abrasion and impact resistance, typically the amounts and the types of components in the cargo hold coating compositions, such as fillers and pigments, are altered. The choice of pigments, fillers and loading will influence coating performance, including abrasion and impact resistance. The degree of curing of cargo hold coatings may increase over longer periods of time during the service life of the coating. While this may improve the impact and abrasion resistance of the coating over time, it has been found that significant damage to cargo hold coatings is often already caused during the first few loading cycles. Hence, there is a need for cargo hold coatings having improved impact and abrasion resistance in particular in the early phase of their service life.

The invention provides a new method for the provision of an epoxy paint coating on the surface of a cargo hold. The epoxy paint coating has an improved abrasion and impact resistance which is not primarily due to the variation in the components, such as fillers and pigments, in the coating composition. Rather, the improvement is due to the post cure step (c) of the method.

The present invention relates to a method for the provision of an epoxy paint coating on the surface of a cargo hold for carrying solid cargos, said method comprising

a. applying a coating composition onto said surface thereby forming a curable paint film on said surface, wherein the coating composition comprises

i. an epoxy resin and

ii. a curing agent having active hydrogen groups, for curing the epoxy resin;

b. allowing said coating composition to cure at ambient temperature thereby forming an epoxy paint coating; and then

c. curing the epoxy paint coating at a temperature in the range of from 50 ^° C to 130 ^° C

wherein the cargo hold has a volume in the range of from 4,000 m ³ to 25,000 m ³ .

Until now, post curing cargo hold coatings at a temperature of at least 50 ^° C has never been carried out in practice. The first reason for this is that it is relatively expensive to heat the very large volume of space inside the cargo hold to such a high temperature (in contrast, cargo tanks are significantly smaller, which makes a post curing practically and economically more viable). The second reason for this is that changing the curing temperature of epoxy-functional coatings to lower temperatures (by lower temperatures, we mean temperatures in the range of from 15 ^° C to 40 ^° C), was found to have very little effect on the impact or abrasion resistance. Therefore, it would not have been expected that post curing the coating at a temperature between 50 ^° C and 130 ^° C would result in a step-change improvement in impact and abrasion resistance. Further, it was expected that post curing the coating might result in an undesirable loss in elasticity of the coating and therefore undesirable cracking. Due to the difficulty and expense involved in heating the large volume inside a cargo hold to a temperature in the range of from 50 ^° C to 130 ^° C, no expectation that this would bring a significant improvement in impact and abrasion resistance, and the possibility that the coating would be more susceptible to cracking, people working in the coatings industry simply never considered post curing coatings in cargo holds. Instead, the skilled person looking to improve abrasion and impact resistance of cargo hold coatings simply concentrated on varying the formulation of the coating composition to achieve improved coating resistance.

In the method of the invention the cargo hold may have a volume of at least 10,000 m ³ For example, the volume of the cargo hold may range from 10,000 m ³ to 25,000 m ³ The surface of a cargo hold is typically metal such as mild steel or high tensile steel grades

Step (a) of the method requires applying a coating composition onto said surface thereby forming a curable paint film on said surface, wherein the coating composition comprises i. an epoxy resin and

ii. a curing agent having active hydrogen groups, for curing the epoxy resin.

The coating composition is generally applied directly to the metal surface of the cargo hold. Although not preferred, it is not excluded to apply a primer layer prior to the epoxy coating according to the invention. The amount of coating composition is selected to achieve the desired dry film layer thickness. The dry film layer thickness generally ranges from 100 to 600 micrometers. Typically, the dry film layer thickness is in the range of 250 to 450 micrometers. In order to achieve the required dry film layer thickness, one or more layers may be applied successively.

Curing agent(s) having active hydrogen groups and epoxy resins will be discussed in more detail below. The coating composition comprises an epoxy resin. The coating composition may alternatively comprise more than one epoxy resin. Suitable epoxy resins are known in the art. They encompass, for example, phenol novolac epoxy resins, bisphenol F epoxy resins and resorcinol diglycidyl ether (RDGE) epoxy resin. Other suitable epoxy resins include diglycidyl ether of bisphenol A, bisphenol A novolac resins, hydrogenated bisphenol A, or bisphenol S, condensed or extended glycidyl ethers of any of the above bisphenols, hydrogenated condensed glycidyl ethers of bisphenols, dicyclopentadiene based epoxy resins, polyglycidyl ethers of polyhydric alcohols such as trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, pentaerythritol tetraglycidyl ether, dipentaerythritol polyglycidyl ethers, butanediol diglycidyl ether, neopentylglycol diglycidyl ether, hexanediol diglycidyl ether and sorbitol glycidyl ether, epoxidized oils, epoxy compounds like di-epoxyoctane and epoxidized polybutadienes.

In a preferred embodiment, the epoxy resin comprises an aromatic epoxy resin, in particular a bisphenol A based epoxy resin. Examples of suitable commercially available bisphenol A epoxy resins are DER331 (Dow Chemicals), DER660X80 (Dow Chemicals) and Epikote 1001-X-75 (Momentive ).

Other suitable epoxy resins are phenol novolac epoxy resins. Examples of phenol novolac epoxy resins that can be used include DEN 425, DEN 431 and DEN 438 (ex. DOW Chemicals), Epon 154, Epon 160, Epon 161 and Epon 162 (ex. Momentive Performance Chemicals), and Epalloy 8250 (ex. Emerald Chemical Co.). Other epoxy resins which may be used comprise epoxy cresol novolac resins, such as Epon 164 and Epon 165 (ex Momentive Performance Chemicals), or bisphenol A epoxy novolac resins, such as the Epon SU range of resins. In other embodiments, the epoxy resin comprises a bisphenol F epoxy resin. Examples of bisphenol F epoxy resins that can be used include DER 354 (ex. DOW Chemicals) or Epikote 862 (ex. Momentive performance Chemicals). In one embodiment, the epoxy resin comprises a Resorcinol diglycidyl ether (RDGE) based epoxy resin. An RDGE epoxy resin that can be used in the composition in accordance with the present invention is normally a low viscosity epoxy compound with an epoxy equivalent weight of 1 10-140 g/eq., for example 120-135 g/eq.

Blends of any of the above epoxy resins may be used in combination with each other. In particular, in order to minimize the solvent content of any coating composition containing the epoxy resin, it is preferred that the epoxy resin has a low solvent content, e.g., below 30 wt.% , preferably below 25 wt.%, based on the weight of epoxy resin. Preferred epoxy resins include: Epikote 874L, EPON 828, DER3680, DER331 , DER660, DER664UE, DER671 , with the most preferred being DER664UE, DER331 and DER660. The curing agent(s) having active hydrogen groups may be amine-functional curing agent(s).

As epoxy resins are electrophilic in nature, they commonly react with nucleophiles. The curing agents used in this invention comprise nucleophilic functional groups, in the present case amine groups, that react with epoxy groups. During the ring-opening reaction of an epoxide with a nucleophile (nucleophilic functional groups), a hydrogen atom is transferred from the nucleophile to the oxygen atom of the epoxide. This transferred hydrogen atom is referred to as the "active hydrogen". The reaction is illustrated:

Nu-H + It is common therefore to quote the equivalent weight of the nucleophilic species in terms of the active hydrogen equivalent weight. This is simply the weight of nucleophilic species required to yield one mole (or one "equivalent") of hydrogen atoms transferable to the ring opened epoxy. In the case of an amine-functional curing agent, the active hydrogen equivalent weight of the amine-functional curing agent is therefore the weight of the curing agent to give one mole (or one "equivalent") of N-H groups. A primary amine-functional curing agent, for example, would have two active hydrogens as it can react with two epoxide groups. The amine-functional curing agent used in the present invention may have on average at least two active hydrogens per molecule. The amine groups can be primary and/or secondary amine groups. An amine-functional curing agent with more than one nitrogen atom may be termed a polyamine curing agent. Examples of suitable polyamine curing agents are ethylene diamine, N-(2- hydroxyethyl)ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, and the curing agents commonly manufactured by reacting these polyamine curing agents with fatty acids and dimer fatty acids, leading to amidoamines and amine- functional polyamide curing agents. Examples of such curing agents are described in "Protective Coatings, Fundamentals of Chemistry and Composition", by Clive H. Hare, published by the Society for Protective Coatings (ISBN 0-938477-90-0) and are hereby incorporated by reference. Further polyamine curing agents are dicyandiamide, isophorone diamine, m-xylylene diamine, m-phenylene diamine, 1 ,3- bis(aminomethyl)cyclohexane, bis(4-aminocyclohexyl) methane, bis(4-amino-3- methylcyclohexyl) methane, N-aminoethyl piperazine, 4,4'-diaminodiphenyl methane, 4,4'- diamino-3,3'-diethyl-diphenyl methane, diaminodiphenyl sulfone.

Phenalkamine and mannich base curing agents are preferred. Phenalkamines are obtained from cardanol, a major component of cashew nutshell liquid (CNSL). Phenalkamines contain aliphatic polyamine substituents attached to the aromatic ring. Phenalkamines are typically synthesized from ethylene diamine (EDA) and the final product is a complex blend of phenalkamine (ortho or para substituted), poly- phenalkamines, and EDA. Their composition can be tuned by the manufacturing process including purification, stripping, and reaction conditions and then be classed into different commercial grades. Examples of phenalkamines include Cardolite NC541 LV, Cardolite NX-4709E, Cardolite LX-5459, Docure KMH-151 (ex. Kukdo), Epoxy hardner AP1041 (ex. Admark Polycoat), and Hiescat Hi-51A (ex. Keumjung Co).

Polyamine curing agents may be used, for example Ancamine 2264 (ex. Air Products) is a commercial quality curing agent comprising mainly bis(4-aminocyclohexyl) methane. Examples of amine curing agents are described in "Protective Coatings, Fundamentals of Chemistry and Composition", by Clive H. Hare, published by the Society for Protective Coatings (ISBN 0-938477-90-0), "Epoxy Resins" by H Lee and K Neville, published by LLC (ISBN 978-1258243180), "Resins for Coatings", edited by D Stoye and W Freitag, published by Hanser (ISBN 978-1569902097) and are hereby incorporated by reference.

Amide containing curing agents can likewise be used, for example Crayamid 115 (ex. Arkema) or Crayamid 125 (ex. Arkema). Adducts of any of these amines can also be used. Such adducts can be prepared by reaction of the amine with a suitably reactive compound such as a silicon-free epoxy resin or an epoxy-functional reactive diluent, for example butyl glycidyl ether. This will reduce the free amine content of the curing agent, making it more suitable for use under conditions of low temperature and/or high humidity. Further examples of epoxy-functional reactive diluents are described in "Protective Coatings, Fundamentals of Chemistry and Composition", by Clive H. Hare, published by the Society for Protective Coatings (ISBN 0- 938477-90-0) and are hereby incorporated by reference. Adducts of any of these amines can also be prepared by reaction of the amine with a suitably reactive compound such as an acrylate, a maleate, a fumarate, a methacrylate, or even electrophilic vinyl compounds such as acrylonitrile. The amine curing agent should be capable of at least partially curing the epoxy resin at a temperature in the range of from 0 °C to 50 °C. Mixtures of amine curing agents can also be used.

The curing agent may alternatively comprise at least one phenol resin curing agent, polythiol curing agent, polyanhydride curing agent and/or polycarboxylic acid curing agent. Examples of phenol resin curing agents are phenol novolac resin, bisphenol novolac resin and poly p-vinylphenol. Examples of polycarboxylic acid curing agents include phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, 3,6- endomethylenetetrahydrophthalic anhydride, hexachloroendomethylenetetra- hydrophthalic anhydride and methyl-3,6-endomethylenetetrahydrophthalic anhydride. Examples of thiol curing agents include pentaerythritol tetramercapto propionate. Mixtures of curing agents can also be used, for example thiols and amines.

In the method of the invention, the relative proportions of epoxy resin and curing agent are typically selected so that the stoichiometry of epoxy groups to active hydrogen groups ranges from 1 :0.4 to 1 : 1.2.

Step b of the method requires "allowing said coating composition to cure at ambient temperature thereby forming an epoxy paint coating". This means that the coating composition is allowed to cure without applying any extra or artificial sources of heat over the heat that is already in the surroundings. Typically this means temperatures in the range of -10 ^° C to 40 ^° C. The duration of step b is not critical. Generally, in the method of the invention, step b may be carried out for a period ranging from 4 hours to 10 days, or from 8 hours to 6 days. If the coating is applied in more than one layer to achieve the required thickness, the aforementioned period relates to the period after the last coating layer is applied. In the method of the invention, step c may be carried out by exposing the coating to hot air at a temperature in the range of from 50 °C to 130 ^° C. This could be carried out by placing at least one high velocity combustion burner inside the cargo hold, sealing the cargo hold and allowing the air inside the cargo hold to heat up to the desired temperature range. A further way of applying or at least augmenting this process would be to empty the ballast tanks and apply hot air in the ballast tank

Step c may for example be carried out at a temperature in the range of from 60 ^° C to 100 ^° C, or from 65 ^° C to 85 ^° C. Step c may be carried out for at least 4 hours, for example for a time in the range of from 4 to 24 hours, 4 to 12 hours or 6 to 10 hours. Step c may be carried out by placing gas burners on the deck and having trunks transporting hot air to holds. Alternatively, the cargo holds may be heated by hot water.

The coating composition generally comprises one or more pigments and/or fillers. The one or more pigments may be colouring pigments, for example titanium dioxide (white pigment), coloured pigments such as yellow or red iron oxide or a phthalocyanine pigment.

The one or more pigments may be strengthening pigments such as micaceous iron oxide, crystalline silica and wollastonite. Preferred pigments include bauxite, aluminium flakes, silicon carbide, boron carbide, talc, china clay and nepheline syenite. The one or more pigments may be anticorrosive pigments such as zinc phosphate, zinc molybdate or zinc phosphonate. The one or more pigments may be a filler pigment such as barytes, talc, feldspar, or calcium carbonate.

The composition may contain one or more further ingredients, for example a thickening agent or thixotrope such as fine-particle silica, bentonite clay, hydrogenated castor oil, or a polyamide wax. The composition may also contain a plasticizer, for example a hydrocarbon resin, pigment dispersant, stabilizer, flow aid, wetting agent, defoamer, adhesion promotor, or thinning solvent. Preferably the coating composition comprises micaceous iron oxide and/or bauxite. Preferably both the micaceous iron oxide and the bauxite are present at ≥10% by volume in the wet coating composition (i.e. coating composition, including solvent).

The coating composition may optionally contain compounds known to accelerate the curing reaction of epoxy resins. Suitable accelerators are well known and include Lewis acids, such as calcium nitrate, thiocyanate salts, lithium and other tetrafluoroborates, hexafluorophosphates, zinc triflate, antimony triflate, ytterbium triflate, lithium or magnesium perchlorate, lithium bromide; alcohols, such as hydroxyamines, dihydroxyamines, furfuryl alcohol, benzyl alcohol, glycols, glycerol; phenols, such as phenol, halophenols, nitrophenols, alkylphenols, catechols, poly(catechol), poly(vinylphenol), calixarenes, naphthalenediols, anthracene diols, bisphenols, cyanophenols, 2,4,6 tris (dimethylaminomethyl phenol); and acids, such as oxalic acid, maleic acid, monoesters of these dibasic acids, sulphonic acids, salicylic acid, lactic acid, 3,5-dichlorosalicylic acid and benzoic acid.

The coating composition is typically provided as a two-pack coating composition wherein the first pack comprises the epoxy resin and the second pack comprises the curing agent having active hydrogen groups, for curing the epoxy resin. The invention will now be elucidated with reference to the following examples. These are intended to illustrate the invention but are not to be construed as limiting in any manner the scope thereof.

Examples

Coating Formulation A: Based on a bisphenol A semi solid epoxy resin having an epoxide equivalent weight of 325, a phenalkamine curing agent, accelerator Ancamine K54, and pigmented with bauxite and micaceous iron oxide. Coating Formulation B: Based on a bisphenol A semi solid epoxy resin having an epoxide equivalent weight of 325, phenalkamine curing agent, pigmented with talc, china clay, aluminium flake.

Coating Formulation C: Based on a bisphenol A solid epoxy resin having an epoxide equivalent weight of 895, hydrocarbon diluent, a bisphenol A liquid epoxy resin having an epoxide equivalent weight of 187, a bisphenol A semi solid epoxy resin having an epoxide equivalent weight of 325, curing agents phenalkamine and a mixture of polyamide curing agents, and pigmented with talc and nepheline syenite.

Two layers of Coating Formulation A, B or C, were applied to 10 mm thick steel at a total dry film thickness of 300 micrometers. The coatings were allowed to cure at 23 ^° C for 7 days, and then heated to 100 ^° C in an oven for 1 day.

Impact Resistance Testing

Testing followed ASTM D 2794. Coated steel panels were subjected to impact from a weight, the height from which the weight is dropped is progressively increased until the coating fractures under impact (coating damage is assessed visually). The weight of the impacting material and the height from which it is dropped make it possible to calculate the impact energy, which is shown in Figure 1. A high impact energy to coating failure means that the coating provides improved resistance to impact. The test is commonly referred to as Gardner Impact Testing

Abrasion Resistance Testing

Abrasion resistance was tested on 12 x12 inch coated steel panels, placed in a jig which holds the panel in a horizontal position. Cargo (typically coal or iron ore) was placed on the panel and subjected to a defined load. The cargo was then moved across the panel at a defined speed. After unloading the coating surface was analyzed using image analysis software to determine the extent of coating damage. This test very effectively reproduces both the comparative performance of different hold coatings and the mode of coating damage observed in cargo holds when the cargo settles in the hold at sea. Tensile Testing

Testing followed ASTM D 638. Free film samples of the coatings were tested. The tensile modulus, strain to break and tensile strength were measured. Results of Testing

The impact testing clearly shows the benefit of post curing the coating in that for all three coatings tested the impact energy required to cause coating failure increases significantly following post cure.

Benefit of post curing on abrasion resistance was determined for coating A. With 300 kPa Coal, the % coating damage was reduced from 5.05% (2 weeks cure under ambient conditions) to 1.3% (post cure).

The change in mechanical properties is demonstrated in the tensile testing for coatings A and B.

For coating A, post cure nearly doubles both the modulus and tensile strength but has little effect on the strain to break.

For coating B the results are summarized below:

On post cure modulus and tensile strength increase by a factor of -3.5, while the strain to break decreases from 1.09 to 0.7%. The strain of the post cured coating is still in the acceptable range for avoiding cracking.