NL1038105A - Heat-resistant, chemical resistant, room temperature curable, solvent-free resin compositions to apply as protective coating. - Google Patents

Description

Title: Heat-resistant, chemical resistant, room temperature curable, solvent-free resin compositions to apply as protective coating

Introduction

Iron is a crucial raw material for human beings for a long time. Owing to its mechanical properties it has become an indispensable part of human society. Iron is the main compound in steel (a carbon alloy of iron), and is produced in amounts of 900 million tons annually. Steel is applied in a wide variety of tools and constructions.

Though the mechanical properties as such are excellent, a protection against corrosion is required. Owing to time, temperature, influence of chemicals, oxygen, moisture and possibly mechanical stress, abrasion and erosion, the surface area will be damaged irreparably. The function of the steel fades away, making e.g. constructions significantly weaker. Consequently, severe damage may occur.

Studies from the United States of America have shown that corrosion causes an annual damage of approximately 300 billion US dollars, being 4% of the Gross National Product. It basically means that a small improvement towards corrosion prevention can give a big economic advantage.

Currently, replacement of metal parts becomes more and more expensive owing to metal scarcity, increased demand of the world market, higher labor costs as well as to stricter laws and regulations.

A widely applied method either to prevent or strongly inhibit corrosion is to use a coating. Often they contain a wide range of chemicals to obtain the right properties, e.g.

binders, fillers, solvents, catalysts, biocides and pigments. These coatings are complex systems, being hardly compatible with other coatings and/or chemicals. Moreover, a good craftsmanship is required to obtain the desired performance. Nowadays anti-corrosion coatings comprise anti-corrosive pigments, such as zinc phosphate or calcium phosphate, alkyd resin binder and a proper organic solvent.

Although a wide range of protective coating products is known, there is still a need for a product/technology meeting the following criteria: • Well-available raw materials • Comparable or better performance with currently available coatings • Economically affordable, preferably strongly cost reducing • Easily applicable and implementable on existing systems • Preferably surface protection with one layer • Thin layers (<50 μ) effective • Robust • Solvent free • Low toxic • Controlled curing time • No primer required • Strong adhesion to the surface • Adjustable flexibility • Sustainable: long performance time • Repaintable • Non-flammable • Scratch resistant • High heat resistance • Good resistance against chemicals • Preferably gas and/or vapor tight • Tunable system ·=> tailor-made systems • Custom-made colorable • Compatible with other chemicals

In fact these requirements are valid for the protection of all kind of hard surfaces, such as glass, concrete, stone, rock, wood, material (cotton, polyester etc.), plastics and ceramics .

In nature, usually metals, in particular iron, corrode under acidic conditions by the formation of the Fenton's reagent, a mixture of hydrogen peroxide and iron salts. This mixture as such is highly corrosive and acts as strongly oxidizing agent. As a result, even high performing coating systems can be damaged in time. Hence, a strong loss of performance is observed.

So far, this problem could not be solved properly. This means there is a demand for an inorganic acid and/or oxidizing agent resistant coating.

Background

The requirements mentioned above cannot be sufficiently met upon applying the conventional techniques. A different approach is necessary to fulfill tomorrows' wishes.

Polyimides are known for their high thermal stability, good chemical resistance and excellent mechanical properties. In addition, thermoset polyimides exhibit very low creep and good tensile strength. These properties are maintained during continuous use to temperatures up to 380°C and for short excursions, as high as 500+°C. Moreover, imides are not much affected by common organic solvents. Some imides, such as the citraconimide group, appeared to be less stable in alkaline environment. Owing to all these characteristics, polyamides are often applied in the electronics industry on computer circuit boards as well as for insulating cables. Some polyimides are even used as an alternative for glass. The special features of polyimides are even recognized by the NASA (see e.g. US 4,564,663 and US 4,568,733).

The unique properties of polyimides are ascribed to the specific interaction between the electron acceptor (carbonyl group) and the electron donor (nitrogen), a so-called charge transfer complex. This effect is not only valid intramolecularly, but does intermolecularly as well. For the latter, polyimide chains will stack closely together, being arranged comparable with an inorganic crystal lattice. This makes polyimides impermeable for most gasses and hence, they can be suitable for applications where gas and/or vapor tightness is necessary.

Unfortunately, polyimides materials are in general brittle, making it very sensitive for abrasion and mechanical cracking. In addition, for several applications the heat resistance at high temperatures should be maintained continuously. Moreover, adhesion of solely polyimides to a hard surface, in particular metal, is not that straightforward. Reviewing these issues, polyimides posses several very attractive properties, but they need to be adjusted/processed/formulated further on before they can meet the desired criteria for full protection of hard surfaces.

Many patents have been filed either to improve or to adjust the properties of polyimides. The adhesion can be improved by admixing the imide with an epoxy resin and an organic solvent (WO 2005/006826). US patent 2007/0158869 describes the invention of adhesive films comprising polyimides and a imidazole or quinoline catalyst prepared via extrusion. A more advanced approach has been reported in WO 2008/018399, comprising plasma treatment of polyimide, followed by addition of an amine solution and drying/heating.

Those skilled-in-the-arts know that the brittleness of polyimides can be overcome by addition of an epoxy resin, e.g. a bisphenol-A derivative. Epoxy resins improve the adhesive properties as well. Alternatively, low viscous polysulfides,' such as polysulfide diepoxides, can be admixed with the imide polymers. These products have lower softening and curing temperature than the polyimides. The resulting cured resins show improved toughness, good chemical resistance, good thermal properties and excellent adhesion. Unfortunately, the compounds have to be dissolved in an organic solvent before a proper application is possible, due to high viscosity issues. Moreover, these compositions have shown a very limited shelf life, making it unfavorable for commercial purposes.

Bismaleimide polymer resins can be prepared in an elegant way, as for example reported in EP 2009058. Although they are often too brittle due to the high cross-link density, the physical properties meet most of the criteria. However, several maleimides were found to be highly toxic, mutagenic and/or carcinogenic. As a consequence these product compositions are often not suitable.

Biscitraconimides do not possess carcinogenic properties, making them more attractive/favorable for a wide range of applications. However, these compounds should be modified/adjusted/formulated in a distinctive matter to achieve a useful end product.

Although bismaleimides and biscitraconimides show at first sight very strong resemblance, the presence of the methyl-group at the 2-position of the imide ring can give rise to completely different reaction routes (see e.g. US 5,221,717)! Upon applying biscitraconimides in an alkaline environment, a pseudo Michael addition via the tautomeric form of biscitraconimide can occur, leading to completely different coating characteristics. In a curing system, chain extension occurs via allylic H-abstraction (of both tautomers), whereas a maleimide reacts via vinylic route. Moreover, due to the tautomeric equilibrium a biscitraconimide possesses much less aromatic character compared to the bismaleimide analogue. This means that the chemistry of bismaleimides is not representative for biscitraconimides and vice versa. One can clearly speak about a different class of compounds.

Citraconimide has formula (I), citraconimide tautomer has formula (II), and maleimide has formula (III) of the formula sheet.

Curable biscitraconimide polymers and copolymers with olefinically unsaturated materials, preferably styrene, were found to exhibit high glass temperatures, improved thermostability and solvent resistance, as reported in US 5,198,515. Moreover, in most cases no additional solvents apart from the olefin have to be applied to realize efficient curing. A drawback is the necessity to use olefins, such as styrene, making it unattractive for large applications owing to the volatility and toxicity.

The curing of citraconic (co)polymers can be enhanced by the addition of an anionic catalyst, preferably diazobicycloalkanes and substituted imidazoles (US 5,221,717). Nevertheless the high melting points of the citraconic (co)polymers hamper easy application and implementation on currently used systems.

Prepolymerization of biscitraconimide, bisitaconimide and/or citraconimido-itaconimide by an anionic catalyst leads to a good viscosity and solubility properties, as taught in WO 2007/134948. The resulting products can be admixed with a proper reagent to establish the desired polymer curing. The prepolymers as such are stable for several days up to weeks. However, for a smooth process throughout the whole production/application chain, it is absolutely necessary to increase the shelf-life for more than months.

Patent WO2009/077420 claims to circumvent almost every mentioned drawback on polyimides by applying an anionic curing system comprising an epoxy compound, a polyamine and a biscitraconimide co-curing agent, preferably 1,3-bis(citraconimidomethylene)benzene . The curing time, flexibility as well as adhesion of this 2K system can be tuned at wish. The coatings obtained show good chemical and scratch resistance and even auto repairing properties. In addition, upon admixing nano particles auto-topographic landscape formation can be created in the coatings.

However, Applicant has demonstrated that such 2K systems based on commercially available biscitraconimides, in particular 1,3-bis(citraconimidomethylene)benzene, can take on every color between light yellowish and very intense dark purple presumably due to the presence of stabilizers and/or tracers. This effect is clearly visible even at layer thicknesses of 100 micron. Owing to this color changes, the 2K system described in W02009/077420 is not suitable for many applications, e.g. protection of stainless steel whilst maintaining the typical original steel color. Moreover, the presence of stabilizers and/or stabilizers in commercially available biscitraconimides, leads to an almost random curing time. To ensure proper and reliable handling, i.e. shelf life and pot life) it is absolutely necessary to improve the coating formulations. This phenomenon can be circumvented by addition of specific acidic compounds.

In addition, 2K curing systems according to W02009/077420 do not always provide the demanded resistance against oxidizing agents and/or inorganic acids apparently due to the presence of the flexibilizers and several curing routes. Applicant has found that upon applying radical initiators, an excellent inorganic acid/oxidizing agent resistant coating system can be obtained.

Description of the invention

The present invention is intended to ensure a well-controlled curing time by the application of a radical curing 2K system instead of an anionic curing 2K system described in W02009/077420. As a result coatings can be obtained with optimal properties towards inorganic acids, oxidizing agents, chemical resistance, heat resistance and/or toughness, by selecting a polycitraconimide (An) having formula (IV) and/or its tautomeric forms (A'n and A"n) having formula (V) and (VI) respectively, of the formulasheet, preferably biscitraconimide types.

The products are obtained via a reaction of an amine, preferably a diamine (with the formulae N-X-N), with a citraconic anhydride, following the procedures as described in US 5,329,022.

R and R' are chosen from the groups: H, alkyl, poly(alkyl), aryl, poly(aryl), alkylene, poly(alkylene), alcohol, ester, halide, amine or sulfur.

R and R' can be equal, but not necessarily n = 1 - 20 X = linear alkyl ((CH2)m), branched alkyl ((CH2)m), alkylaryl ((CH2)m(Aryl), poly(aryl), alkylene, poly(alkylene) Aryl = benzene, naphthalene, anthracene, bis(phenyl) compounds, bis(naphtyl) compounds, bis (anthracyl) compounds m = 0 - 20 admixed with an organic peroxide, preferably a hydroperoxide, epoxy resin, polysulfide, fillers (e.g. silica) and/or catalysts, all coating properties can be obtained at wish. Moreover, the coatings can even be easily applied without the use of a solvent.

and a second component polyamine (B), e.g. ethylene diamine (EDA), triethylenetetramine, EDA homologues or a mixture thereof. Polyoxyalkyleneamines (Jeffamines), dendrimers and/or polyamino amides might be applied as well.

To ensure controlled curing reactions either for high temperature curing, organoperoxide, or in case of room temperature curing, organohydroperoxide towards a 2K system A

and B has to be admixed. The organo hydroperoxide can be selected, but not limited, from the of t-butyl hydroperoxide (TBH), cumyl hydroperoxide, p-isopropyl cumyl hydroperoxide, methyl ethyl ketone hydroperoxide, 1,1,3,3,-tetramethyl butyl hydroperoxide and cyclohexane hydroperoxide.

Upon applying hydroperoxides, a suitable catalyst/accelerator should be used (as for example described in US 6,770,716). The catalyst can be selected, but not limited, from a soluble copper catalyst e.g. dipyridyl, 2-ethyl hexanoate, naphthenate and tertiary amines copper complexes. Other metallic salts can be applied as well, e.g. cobalt naphthenate, cobalt acetoacetonate, cobalt octoate (2-ethyl hexanoate), iron octoate (2-ethyl hexanoate), and iron naphthenate; and mixtures thereof. Those skilled-in-the-arts know how and which catalysts and possibly inhibitors to apply.

Example

Component A: A 250 ml beaker is charged with 50 grams 1,3-bis(citraconimidomethylene)benzene (Flexsys) pellets and gently warmed up to 120 °C until the pellets are completely melted. A clear yellowish liquid is obtained and the temperature is maintained at 90 °C. 50 grams Epicote 828 (Hexion) is added and thoroughly stirred until a clear homogeneous yellow liquid is obtained. The mixture is allowed to cool down to room temperature. Finally 1 gram cumyl hydroperoxide is slowly added and the mixture is homogenized well.

Component B: A 250 ml beaker is charged with 50 grams Triethylenetetraamine (technical grade, Aldrich) and 75 grams Duomeen CD (Akzo Nobel) and mixed at 25 °C, until a transparent , clear liquid is obtained. Finally 0,5 mg copper naphthenate is added and the mixture is homogenized well.

Components A and B are mixed together in a 1:5 stoichiometry. The viscosity drastically lowered within several seconds. The mixture was poured onto an aluminum cup for analyses and surface tests (Q-panel, 90 micron polymer layer). Gel time was approximately 20 minutes and full cure into a solid polymer film was established after 4 hours.

The radical initiated polymer film treated Q-panel has been subjected to additional surface tests. This has been performed as follows. One glass flask of 20 ml has been charged with 10 ml 20% hydrochloric acid solution and one glass flask of 20 ml has been charged with a 10 ml 15% hydrogen peroxide solution. Both Flasks have been attached to the film by a silicone adhesive and allowed to dry. After 4 hours the adhered flasks were positioned in such matter that fluid and film are in contact. After 36 hours, the adhered flasks have been removed by cutting the silicone adhesive. The surface of the Q-panel has been examined for film damage and defects, using a digital microscope (200 x magnifications). Neither chlorine attack nor any form of oxidation of the film on the metal surface has been observed. Experiment above has successfully been performed for several concentrations of hydrochloric acid and hydrogen peroxide solutions using several radical polymerized biscitraconimide-based films.

Claims (15)

An inorganic acid and / or oxidant resistant coating composition to be tailored to requirements obtained via a synergistic radical and anionic curing process, comprising 0.01-20% by weight of an organic peroxide, 0.01-10% by weight of a catalyst , 0.1-40% by weight of a polyamine, 15-90% by weight of a compound that has at least one epoxide group, and 1-60% by weight of a co-curing agent, wherein the co-curing agent is polycitraconimide An, of formula ( IV) of the formula sheet, and / or the tautomeric forms (A'n and A "n), having formulas (V) and (VI) respectively of the formula sheet. Chain extension mainly takes place via an allylic H-abstraction route. R and R 'are selected from the group consisting of H, alkyl, poly (alkyl), aryl, poly (aryl), alkylene, poly (alkylene), alcohol, ester, halide, amine or sulfur, R and R' can are the same or different, η = 1 - 20, X = linear alkyl ((CH2) m), branched alkyl ((CH2) m), alkylaryl ((CH2) m (aryl), poly (aryl), alkylene, poly (alkylene), Aryl = benzene, naphthalene, anthracene, bis (phenyl) compounds, bis (naphthyl) compounds, bis (anthracyl) compounds, m = 0-20. The composition of claim 1, wherein the co-curing agent is a biscitraconimide or the isomeric / tautomeric form thereof bisitaconimide. The composition of claims 1 or 2, wherein the co-curing agent is 1,3-bis (citraconimidomethylene) benzene. The composition of any one of claims 1-3, wherein the organic peroxide is bisorganic peroxide or organic hydroperoxide. A composition according to any one of claims 1-4, wherein the organic hydroperoxide is selected from t-butyl hydroperoxide (TBH), cumyl hydroperoxide, p-isopropyl cumyl hydroperoxide, methyl ethyl ketone hydroperoxide, 1,1,3,3, -tetramethylbutyl hydroperoxide or cyclohexane hydroperoxide. The composition of any one of claims 1-5, wherein the organic hydroperoxide is cumyl hydroperoxide. The composition of any one of claims 1-6, wherein the catalyst is a metal salt. The composition of any one of claims 1-7, wherein the catalyst is selected from the group consisting of cobalt naphthenate, cobalt acetoacetonate, cobalt octoate (2-ethyl hexanoate), copper naphthenate, iron octoate (2-ethyl hexanoate), and iron naphthenate; and mixtures thereof. The composition of any one of claims 1-8, wherein the polyamine (polydiamine or EDA homologues) ethylene diamine (EDA), diethylene triamine (DETA), triethylenetetramine (TETA), tetraethylene pentamine (amineΑ), pentaethylene hexamine (PEHA), fatty (poly) amines, tripropylene tetramines, ethoxylated amines, propoxylated amines, dendrimers or polyaminoamides. The composition of any one of claims 1-9, wherein the compound having at least one epoxide group is a reactive epoxide, glycidyl ether, or glycidyl ester. Composition according to one or more of claims 1-10, further comprising coloring agents, in particular pigments. A composition according to any one of claims 1 to 11, further comprising fillers, especially nanoparticles or modified nanoparticles, in particular silica. A method for curing the coating composition according to one or more of claims 1 to 12, by heating the composition to a temperature and for a time sufficient for the co-curing agent, the compound having at least one organic peroxide, a catalyst, an epoxide group, and a polyamine, to be cured simultaneously. The method of claim 13, wherein the curing is carried out at a temperature of less than 130 ° C. The method of claims 13-14, wherein the curing is carried out at room temperature.