Patent Application
20230183515
The present invention relates to the field of coating composition and methods for making a substrate frost resistant.
Frosting happens when the surface temperature is below both water freezing temperature and air dew point temperature. In other words, the frost starts to form when the contact happens between the cold surface and the near water vapor in the air due to the temperature difference. Frosting is a common natural phenomenon on cold surface. Ice formation on surfaces is responsible for economic losses in many fields such as aviation, ground transportation, power transmission, communication and refrigeration. In our daily life, frosting on cold surface lowers the operating efficiency of refrigerating equipment and causes huge energy waste e.g.—frosting of heat exchangers of air conditionings,—frosting of refrigerators . . . . Because frost layer has thermal isolating properties, frost layer on a surface of refrigerating equipment impairs the heat transfer efficiency of the equipment and narrows or even blocks the airflow channel, thereby resulting in important energy waste.
Current anti-frosting surface modification technologies proceed in three general directions: superhydrophobic hydrophilic slippery surfaces and polymeric hydrophilic coatings. Superhydrophobic coating, typically nanocomposite coatings, usually suffers durability problem. Therefore, it is still technically challenging for the industry to produce superhydrophobic coatings with long-lasting frost-resisting performance. In recent years hydrophilic slippery surfaces also emerge as a new type of anti-frosting technology with increasing attention from researchers worldwide. With this technology, water drops spread and remove from the hydrophilic slippery surface. While promising, the technology is expensive and durability is still to be improved. Development of polymeric hydrophilic coating, typically containing hydroxyl acrylates, is the priority for the industry now, due to its facile fabrication process and easy access to hydrophilic resins. However frost-resisting performance remains unsatisfying and some improvement are still highly desirable.
Among hydrophilic polar chemical groups, zwitterions are known to be highly hygroscopic. U.S. Pat. No. 4,328,143 discloses an aqueous coating composition for formation of a coating film having high corrosion-resistance on a metal substrate which comprises (a) a film-forming polymeric material having at least one hydroxyl group and/or at least one carboxyl group, (b) a zwitter-ion compound and (c) an aminoplast resin and/or an epoxy resin with or without (d) a surface active agent having a hydrophilic functional group and at least one hydroxyl group and/or at least one carboxyl group. The role of such zwitter-ion compound may be considered to be as (1) serving as an acid catalyst in the crosslinking reaction; and (2) improving the hydrophilic property. However, the coating composition described showed limited improvement of initial surface wettability and the stability of resulting films was low. Nothing is said about frost resistance of the coated surface.
Thus, there is an ongoing need for new or improved coating compositions for making frost resistant a substrate. There is also a need for these coating compositions to provide durable coatings that are resistant to weathering and to scratch. There is a need for the coating compositions to provide coatings that make substrates resistant to corrosion when said substrates are submitted to corrosive environments. Finally, there is a need for these coating compositions to durably guaranty the heat transfer efficiency of coated equipment, e.g. heating or refrigerating equipment, resulting in important energy saving.
All these needs and others are fulfilled by the different aspects of the present invention.
In a first aspect, the present disclosure relates to a coating composition (C) comprising:
In a second aspect, the present disclosure relates to the use of the coating composition (C) as previously described for making frost resistant a substrate.
In a third aspect, the present disclosure relates to a method for making frost resistant a substrate, the method comprising processing a composition (C) as previously described onto the substrate thereby providing a top coating layer (TL) effective to make said substrate frost resistant.
In a fourth aspect, the present disclosure relates to an article comprising a metal or metal-containing surface, wherein the metal or metal-containing surface is coated with the coating composition (C) thereby providing the top coating layer (TL) previously described.
In a fifth aspect, the present disclosure relates to an article comprising a metal or metal-containing surface coated with the top coating layer (TL), wherein a base coating layer (BL) is sandwiched between the metal or metal-containing surface and the top coating layer (TL).
As used herein, the terms “a”, “an”, or “the” means “one or more” or “at least one” unless otherwise stated.
As used herein, the term “comprises” includes “consists essentially of” and “consists of.” The term “comprising” includes “consisting essentially of” and “consisting of.”
Throughout the present disclosure, various publications may be incorporated by reference. Should the meaning of any language in such publications incorporated by reference conflict with the meaning of the language of the present disclosure, the meaning of the language of the present disclosure shall take precedence, unless otherwise indicated.
The present disclosure discloses a coating composition (C) comprising:
The polymer (ZW) of the present disclosure comprises repeating units (RZW) derived from at least one zwitterionic monomer (A). As used herein, zwitterionic monomer (A) refers to monomer capable of polymerization. Generally, zwitterionic repeating units (RZW) are derived from at least one zwitterionic monomer (A) that is neutral in overall charge but contains a number of group (C+) equal to the number of group (A−). The cationic charge(s) may be contributed by at least one onium or inium cation of nitrogen, such as ammonium, pyridinium and imidazolinium cation; phosphorus, such as phosphonium; and/or sulfur, such as sulfonium. The anionic charge(s) may be contributed by at least one carbonate, sulfonate, phosphate, phosphonate, phosphinate or ethenolate anion, and the like. Suitable zwitterionic monomers include, but are not limited to, betaine monomers, which are zwitterionic and comprise an onium atom that bears no hydrogen atoms and that is not adjacent to the anionic atom. Suitable zwitterionic monomers include, but are not limited to ethylenically unsaturated monomer having at least two ionic groups, at least one of them being a cationic group [group (C+)] and at least one of them being an anionic group [group (A−)].
In some embodiments, units (RZW) are derived from at least one monomer (A) selected from the list consisting of
and
In some preferred embodiments, units (RZW) are derived from at least one monomer (A) selected from the list consisting of
In some more preferred embodiments, units (RZW) are derived from at least one monomer (A) selected from the list consisting of
In some even more preferred embodiments, units (RZW) are derived from sulfopropyldimethylammonioethyl methacrylate (SPE).
In some embodiments, polymer (ZW) according to the disclosure further comprises repeating units [units (RN)], different from units (RZW), derived from at least one monomer [monomer (D)], different from monomer A. Generally, monomer (D) is an ethylenically unsaturated monomer different from monomer A. Monomer (D) can be selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, acrylic acid, methacrylic acid, maleic acid, maleic acid anhydride, itaconic acid, crotonic acid, fumaric acid, 4-methacryloxyethyltrimellitic acid, 4-methacryloxyethyltrimellitic acid anhydride, methacryloyl-L-Lysine, 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, poly(ethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate and poly(ethylene glycol) ethyl ether acrylate.
In some embodiments, monomer (D) is 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate (HEA) or mixtures thereof. Typically, monomer (D) is 2-hydroxyethyl methacrylate (HEMA).
In some other embodiments, monomer (D) is acrylic acid, methacrylic acid, maleic acid, maleic acid anhydride or mixtures thereof. Typically, monomer (D) is acrylic acid.
The polymer (ZW) of the composition (C) according to the present disclosure generally comprises 50 wt. % or more, preferably 70 wt. % or more, more preferably 80 wt. % or more and even more preferably 90 wt. % or more of units (RZW), with respect to the total weight of polymer (ZW).
In some embodiments, the polymer (ZW) of the present disclosure substantially comprises, substantially consists of, or consists of repeating units (RZW) derived from monomer A. Typically, the polymer (ZW) of the present disclosure substantially comprises, substantially consists or consists of repeating units (RZW) derived from sulfopropyldimethylammonioethyl methacrylate (SPE).
When repeating units (RN) are present, polymer (ZW) generally comprises from 0.5 to 50 wt. %, preferably from 0.5 to 30 wt. %, more preferably from 0.5 to 20 wt. % and even more preferably from 0.5 to 10 wt. % of repeating units (RN), with respect to the total weight of polymer (ZW).
The polymer (CA) according to the present invention comprises repeating units (RCA) derived from at least one carboxylic acid and/or carboxylic anhydride containing monomer (B).
Generally, monomer (B) is selected from the list consisting of acrylic acid, methacrylic acid, maleic acid, maleic acid anhydride, itaconic acid, crotonic acid, fumaric acid, 4-methacryloxyethyltrimellitic acid, 4-methacryloxyethyltrimellitic acid anhydride and methacryloyl-L-Lysine. Preferably, monomer (B) is selected from the list consisting of acrylic acid, methacrylic acid, maleic acid and maleic acid anhydride. More preferably, monomer (B) is selected from the list consisting of acrylic acid, methacrylic acid and maleic acid; more preferably monomer (B) is acrylic acid or methacrylic acid.
In some embodiments, polymer (CA) according to the disclosure further comprises repeating units [units (RM)], different from units (RCA), derived from at least one monomer [monomer (E)], different from monomers A and B.
Generally, monomer (E) is an ethylenically unsaturated monomer different from monomers A and B. Monomer (E) can be selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, poly(ethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate and poly(ethylene glycol) ethyl ether acrylate.
In some embodiments, monomer (E) is 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate (HEA) or mixtures thereof. Typically, monomer (E) is 2-hydroxyethyl methacrylate (HEMA).
The polymer (CA) of the composition (C) according to the present disclosure generally comprises 50 wt. % or more, preferably 70 wt. % or more, more preferably 80 wt. % or more and even more preferably 90 wt. % or more of units (RCA), with respect to the total weight of polymer (CA).
In some embodiments, the polymer (CA) of the present disclosure substantially comprises, substantially consists of, or consists of repeating units (RCA) derived from monomer B. Typically, the polymer (CA) of the present disclosure substantially comprises, substantially consists or consists of repeating units (RCA) derived from acrylic acid.
When repeating units (RM) are present, polymer (CA) generally comprises from 0.5 to 50 wt. %, preferably from 0.5 to 30 wt. %, more preferably from 0.5 to 20 wt. % and even more preferably from 0.5 to 10 wt. % of repeating units (RM), with respect to the total weight of polymer (CA).
In some preferred embodiments, the composition (C) according to the invention comprises polymer (ZW) substantially comprising, substantially consisting or consisting of repeating units (RZW) derived from sulfopropyldimethylammonioethyl methacrylate (SPE) and polymer (CA) substantially comprising, substantially consisting or consisting of repeating units (RCA) derived from acrylic acid.
Substantially comprising or substantially consisting of as used herein means at least 90%, preferably at least 95%, more preferably at least 97%, e.g. at least 98%. Percentages given herein are % by weight, based on the total weight of the polymer (ZW) respectively on the total weight of the polymer (CA).
Polymer (ZW) according to the invention is linear or branched; it is a homopolymer or a copolymer such as a block copolymer, a statistical copolymer, an alternating copolymer or a grafted copolymer. Good results are obtained with polymer (ZW) being a homopolymer.
Polymer (CA) according to the invention is linear or branched; it is a homopolymer or a copolymer such as a block copolymer, a statistical copolymer, an alternating copolymer or a grafted copolymer. Good results were obtained with polymer (CA) being a homopolymer.
Unless otherwise indicated, when molar mass is referred to, the reference will be to the weight-average molar mass, expressed in g/mol. The latter can be determined by gel permeation chromatography (GPC) with light scattering detection (DLS or alternatively MALLS) or refractive index detection, with an aqueous eluent, an organic eluent or mixture thereof, depending on the polymer (ZW), respectively depending on the polymer (CA). There is no particular limitation to the molar mass of the polymer (ZW) (respectively polymer (CA)). However, the weight-average molar mass (Mw) of the polymer (ZW) (respectively polymer (CA)) is in the range of from about 500 to about 3,000,000 g/mol, typically from about 1,000 to about 1,000,000, g/mol, more typically from about 2,000 to 500,000 g/mol, even more typically 3,000 to 200,000 g/mol.
The copolymer (ZW) (respectively polymer (CA)) of the present disclosure may be obtained by any polymerization process known to those of ordinary skill. For example, the copolymer (ZW) (respectively polymer (CA)) may be obtained by radical polymerization or controlled radical polymerization in aqueous solution, in dispersed media, in organic solution or in organic/water solution (miscible phase). Just for the sake of example poly sulfopropyldimethylammonioethyl methacrylate homopolymer (polySPE) can be prepared by free radical copolymerization of sulfopropyldimethylammonioethyl methacrylate in water initiated by sodium or ammonium persulfate.
Still for the sake of example poly(acrylic acid) homopolymer (PAA) can be prepared by free radical copolymerization of acrylic acid in water initiated by sodium or ammonium persulfate.
The monomer (B) from which can be derived units (RCA) may be obtained from commercial sources.
The monomer (D) from which can be derived units (RN) may be obtained from commercial sources.
The monomer (E) from which can be derived units (RM) may be obtained from commercial sources.
The zwitterionic monomer (A) from which are derived units (RZW) may be obtained from commercial sources or synthesized according to methods known to those of ordinary skill in the art.
Suitable zwitterionic monomers (A) from which can be derived units (RZW) include, but are not limited to monomers selected from the list consisting of:
the synthesis of which is described in the paper “Sulfobetaine zwitterionomers based on n-butyl acrylate and 2-ethoxyethyl acrylate: monomer synthesis and copolymerization behavior”, Journal of Polymer Science, 40, 511-523 (2002),
and other hydroxyalkyl sulfonates of dialkylammonium alkyl acrylates or methacrylates, acrylamido or methacrylamido of formulae below
the synthesis of which is described in the paper “Synthesis and solubility of the poly(sulfobetaine)s and the corresponding cationic polymers: 1. Synthesis and characterization of sulfobetaines and the corresponding cationic monomers by nuclear magnetic resonance spectra”, Wen-Fu Lee and Chan-Chang Tsai, Polymer, 35 (10), 2210-2217 (1994),
the synthesis of which is described in the paper “Poly(sulphopropylbetaines): 1. Synthesis and characterization”, V. M. Monroy Soto and J. C. Galin, Polymer, 1984, Vol. 25, 121-128;
the synthesis of which is described in the paper “Hydrophobically Modified Zwitterionic Polymers: Synthesis, Bulk Properties, and Miscibility with Inorganic Salts”, P. Koberle and A. Laschewsky, Macromolecules, 27, 2165-2173 (1994), and other hydroxyalkyl sulfonates derived from piperazine of formulae below
the synthesis of which is disclosed in the paper “Evidence of ionic aggregates in some ampholytic polymers by transmission electron microscopy”, V. M. Castaño and A. E. Gonzalez, J. Cardoso, O. Manero and V. M. Monroy, J. Mater. Res., 5 (3), 654-657 (1990), and other hydroxyalkyl sulfonates derived from 2-vinylpyridine and 4vinylpyridine of formulae below
the synthesis of which is described in the paper “Aqueous solution properties of a poly(vinyl imidazolium sulphobetaine)”, J. C. Salamone, W. Volkson, A. P. Oison, S. C. Israel, Polymer, 19, 1157-1162 (1978), and corresponding hydroxyalkylsulfonate of formula below
the synthesis of which is described in the paper “New poly(carbobetaine)s made from zwitterionic diallylammonium monomers”, Favresse, Philippe; Laschewsky, Andre, Macromolecular Chemistry and Physics, 200(4), 887-895 (1999),
the synthesis of which is described in the paper “Hydrophobically Modified Zwitterionic Polymers: Synthesis, Bulk Properties, and Miscibility with Inorganic Salts”, P. Koberle and A. Laschewsky, Macromolecules, 27, 2165-2173 (1994), and other hydroxyalkyl sulfonates of dialkylammonium alkyl styrenes of formulae below
the synthesis of which is described in the paper “Hydrophobically Modified Zwitterionic Polymers: Synthesis, Bulk Properties, and Miscibility with Inorganic Salts”, P. Koberle and A. Laschewsky, Macromolecules, 27, 2165-2173 (1994),
the synthesis of which are disclosed in EP 810 239 B1 (Biocompatibles, Alister et al.);
the synthesis of which is described by M-L. Pujol-Fortin et al. in the paper entitled “Poly(ammonium alkoxydicyanatoethenolates) as new hydrophobic and highly dipolar poly(zwitterions). 1. Synthesis”, Macromolecules, 24, 4523-4530 (1991).
Suitable monomers comprising hydroxyalkyl sulfonate moieties from which can be derived units (RZW) can be obtained by reaction of sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa) with monomer bearing tertiary amino group, as described in US20080045420 for the synthesis of SHPP, starting from dimethylaminopropylmethacrylamide according to the reaction scheme:
Other monomers bearing tertiary amino group may be involved in reaction with CHPSNa to obtain suitable monomers from which are derived units (RZW)
Suitable monomers from which are derived units (RZW) may be also obtained by reaction of sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa) with monomer bearing pyridine or imidazole group:
The expression “derived from” which puts repeating units (RZW) in connection with a monomer is intended to define both repeating units (RZW) directly obtained from polymerizing the said monomer, and the same repeating units (RZW) obtained by modification of an existing polymer.
Accordingly, repeating units (RZW) may be obtained by modification of a polymer referred to as a precursor polymer comprising repeating units bearing tertiary amino groups through the reaction with sodium 3-chloro hydroxypropane-1-sulfonate (CHPSNa). Similar modification was described in WO2008125512 with sodium 3-chloropropane-1-sulfonate in place of CHPSNa:
Finally, repeating units (RZW) may be obtained by chemical modification of a polymer referred to as a precursor polymer with a sultone, such as propane sultone or butane sultone, a haloalkylsulfonate or any other sulfonated electrophilic compound known to those of ordinary skill in the art. Exemplary synthetic steps are shown below:
Similarly, repeating units (RZW) may be obtained by modification of a polymer referred to as a precursor polymer comprising repeating units bearing tertiary amino groups, pyridine groups, imidazole group or mixtures thereof through the reaction with sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa), a sultone, such as propane sultone or butane sultone, or a haloalkylsulfonate.
Generally in the composition (C) of the disclosure, the weight ratio of polymer (ZW) with polymer (CA) ranges typically from 0.01 to 1.0, more typically from 0.05 to 0.5 and even more typically from 0.05 to 0.15.
The composition (C) according to the present disclosure also comprises at least one crosslinking agent (CL).
Crosslinking agent (CL) may be polymeric compound or small molecule. Suitable crosslinking agent is generally a molecular structure comprising 2 or more functional groups, said functional groups being capable to react with carboxylic acid groups of the polymer (CA). Generally the crosslinking agent (CL) is selected from the list consisting of polyols, polyamines, polyepoxides, polyisocyanates, blocked polyisocyanates, polycarbodiimides and mixtures thereof.
By polyol crosslinking agent suitable for the invention is meant molecular structure comprising 2 or more hydroxyl groups. Generally, polyol is selected from the list consisting of polyvinyl alcohol polymers i.e. homopolymers or copolymers, ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, neopentyl glycol hydroxypivalate, cyclohexanedimethanol, butane-1,4-diol, pentane-1,5-diol, pentane-1,2-diol, hexane-1,6-diol, nonane-1,9-diol, glycerol, polyglycerol, trimethylolpropane, trimethylolpropane dimer, pentaerythritol, di pentaerythritol, xylitol, sorbitol, hydroxyalkylamides such as N,N,N′,N′-tetrakis(2-hydroxyethyl)hexanediamide, N,N,N′,N′-tetrakis(2-hydroxypropyl)hexanediamide, N,N,N′,N′-tetrakis(2-hydroxyethyl)butanediamide, N,N,N′,N′-tetrakis(2-hydroxypropyl)butanediamide, triethanolamine, triisopropanolamine, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine, N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine, trimethylol melamine, dimethylolurea, 1,1,3-tris(hydroxymethyl)urea, 1,1,3,3-tetrakis(hydroxymethyl)urea, alkoxylated polyols such as pentaerythritol ethoxylate, pentaerythritol propoxylate, and mixtures thereof. Good results were obtained using N,N,N′,N′-tetrakis(2-hydroxyethyl)hexanediamide. Just for the sake of example, a suitable commercially available polyol is VESTAGON® EP-HA320 available from Evonik.
By polyamine crosslinking agent suitable for the invention is meant molecular structure comprising 2 or more amine groups. Generally polyamine is selected from the list consisting of polyoxypropylene diamine, 1,2-ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, 1,2-butylenediamine, 1,3-butylenediamine, 1,4-butylenediamine, 2-(ethylamino)ethylamine, 3-(methylamino)propylamine, 3-(cyclohexylamino)propylamine, 4, 4′-diaminodicyclohexylmethane, hexamethylenediamines, trimethylhexamethylenediamine, 4,7-dioxadecane-1,10-diamine, N-(2-aminoethyl)-1,2-ethanediamine, N-(3-aminopropyl)-1,3-propanediamine, N, N′-1,2-ethanediylbis(1, 3-propanediamine), diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, 4-aminomethyl-1,8-octanediamine, 4,4-diaminodicyclohexylmethane (PACM), 4,4′-methylenedianiline (MDA), m-xylenediamine, isophorone diamine (IPD), 4,4′-diaminodiphenyl sulfone, 4,4′-diaminodiphenyl ether, melamine, 4,4′-methylenebis(cyclohexylamine)carbamate, and mixtures thereof.
By polyepoxide crosslinking agent suitable for the invention is meant molecular structure comprising 2 or more epoxide groups. Suitable polyepoxide can be selected from the list consisting of 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, resorcinol diglycidyl ether, trimethylolpropane triglycidyl ether, tris(4-hydroxyphenyl)methane triglycidyl ether, bisphenol A diglycidyl ether, bis[4-(glycidyloxy)phenyl]methane, bis[4-(diglycidylamino)phenyl]methane and mixtures thereof.
By polyisocyanate crosslinking agent suitable for the invention is meant molecular structure comprising 2 or more isocyanate groups. Generally polyisocyanate is selected from the list consisting of isophorone diisocyanate (IPDI), 1,4-phenylenedisocyanate, 1,4-diisocyanatobutane, hexane diisocyanates such as 1,6-diisocyanatohexane (HDI) and 1,5-diisocyanato-2-methylpentane (MPDI), 4,4′-methylenebis(cyclohexylisocyanate) (HMDI), heptane diisocyanates, octane diisocyanates, nonane diisocyanates such as 1,6-diisocyanato-2,4,4-trimethylhexane and 1,6-diisocyanato-2,2,4-trimethylhexane (TMDI), decane diisocyanates, undecane diisocyanates, dodecane diisocyanates, 4,4′-methylenebis(phenylisocyanate) (4,4′-MDI), 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), 2,5(2,6)-bis(isocyanatomethyl)bicyclo[2.2.1] heptane (NBDI), 1,3-bis(isocyanatomethyl)cyclohexane (1,3-H6-XDI), 1,4-bis(isocyanatomethyl)cyclo-hexane (1,4-H6-XDI), nonane triisocyanates such as 4-isocyanatomethyl-1,8-octane diisocyanate (TIN), decane triisocyanates, undecane triisocyanates, dodecane triisocyanates and mixtures thereof.
In some embodiments, polyisocyanate suitable for the invention is blocked. The term block isocyanate group refers to a functional group that breaks down to form an isocyanate group and a blocking compound. Examples of blocking compounds that may be used to prepare blocked isocyanates include, but are not limited to, phenols, alcohols, oximes such as, but not limited to, those obtained from methyl ethyl ketone, acetone and didisopropyl ketone, imidazole, 1,2-pyrazole, 3,5-dimethyl pyrazole (DMP), 1,2,4-triazole, benzotriazole, ε-caprolactam, ethyl acetoacetate and diethyl malonate. Upon heating blocked isocyanate group is unblocked to produce reactive isocyanate group that will react with carboxylic acid functionality on the polymeric backbone to give amide bound after CO2 elimination. Because the rate at which unblocked isocyanate crosslinking agents unblock to produce reactive isocyanate varies depending on the reactivity and steric factors associated with the blocking group and the isocyanate group, curing temperatures should be adjusted based upon the particular type of isocyanate group (e.g. aliphatic or aromatic) and blocking group. Some catalysts such as dibutyltin dilaurate (DBTL), cobalt or zinc acetylacetonate, diazabicyclo [2,2,2] octane (DABCO) or tetrabutylphosphonium bicarbonate can be added for accelerating the curing rate. By suitable blocked polyisocyanate is meant molecular structure comprising 2 or more blocked isocyanate groups. Suitable blocked polyisocyanate can be obtained from polyisocyanate selected from the list previously disclosed. Just for the sake of example, a suitable commercially available blocked polyisocyanate is Bayhydur® BL XP 2706 available from Covestro, Imprafix® 2794 available from Covestro, Trixene® Aqua BI 200, Trixene® Aqua BI 201 and Trixene® Aqua BI 220 available from Lanxess, Aqualink® X, Aqualink® U and Aqualink® D-HT available from Aquaspersions, KL-1202, KL-1204, KL-1205 and KL-1206 available from Holdenchem.
By polycarbodiimide crosslinking agent suitable for the invention is meant molecular structure comprising 2 or more carbodiimide moieties. Polycarbodiimides are generally synthesized through the reaction of polyisocyanates especially aliphatic or cycloaliphatic diisocyanates in the presence of a catalyst well known by the skilled person. In the catalytic cycle, the catalyst first reacts with an isocyanate, upon which a rearrangement occurs and carbon dioxide is liberated with formation of intermediate specie. This intermediate specie can subsequently react with another isocyanate group to give a carbodiimide moiety while the catalyst is regenerated. Examples of polyisocyanates that may be used to prepare polycarbodiimides include, but are not limited to, isophorone diisocyanate (IPDI), 1,4-phenylenedisocyanate, 1,4-diisocyanatobutane, hexane diisocyanates such as 1,6-diisocyanatohexane (HDI) and 1,5-diisocyanato-2-methylpentane (MPDI), 4,4′-methylenebis(cyclohexylisocyanate) (HMDI), heptane diisocyanates, octane diisocyanates, nonane diisocyanates such as 1,6-diisocyanato-2,4,4-trimethylhexane and 1,6-diisocyanato-2,2,4-trimethylhexane (TMDI), decane diisocyanates, undecane diisocyanates, dodecane diisocyanates, 4,4′-methylenebis(phenylisocyanate) (4,4′-MDI), 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), 2,5(2,6)-bis(isocyanatomethyl)bicyclo[2.2.1]heptane (NBDI), 1,3-bis(isocyanatomethyl)cyclohexane (1,3-H6-XDI), 1,4-bis(isocyanatomethyl)cyclo-hexane (1,4-H6-XDI), nonane triisocyanates such as 4-isocyanatomethyl-1,8-octane diisocyanate (TIN), decane triisocyanates, undecane triisocyanates, dodecane triisocyanates and mixtures thereof. The chain extending polycarbodiimides can be terminated e.g. by reacting with a monoisocyanate which may be alkyl, cycloalkyl, alkyl-aryl, or arylalkyl functional isocyanate, such as butylisocyanate, hexylisocyanate, octylisocyanate, undecylisocyanate, dodecylisocyanate, hexadecylisocyanate, octadecylisocyanate, cyclohexylisocyanate, phenylisocyanate, tolylisocyanate, 2-heptyl-3, 4-bis(9-isocyanatononyl)-1-pentylcyclohexane or may be further functionalized by methods well known by the skilled person. Convenient catalysts for preparing polycarbodiimides from polyisocyanates are 1-ethyl-3-methyl-3-phospholene-1-oxide, 1-phenyl-3-methyl-3-phospholene 1-oxide and 1-methylphospholene-oxide. Just for the sake of example, a suitable commercially available polycarbodiimide is Picassian®XL-702, Picassian®XL-721, Picassian®XL-732 and Picassian®XL-752 available from Stahl; Permutex® XR-13-554, Permutex® XR-5508, Permutex® XR-5577 and Permutex® XR-5580 also available from Stahl.
In some preferred embodiments, the crosslinking agent (CL) is selected from polyol crosslinking agents and mixtures thereof. Preferably polyol crosslinking agent is selected from the list consisting of N,N,N′,N′-tetrakis(2-hydroxyethyl)hexanediamide, N,N,N′,N′-tetrakis(2-hydroxypropyl)hexanediamide, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine, N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine and mixtures thereof. More preferably polyol crosslinking agent is N,N,N′,N′-tetrakis(2-hydroxyethyl)hexanediamide. Generally the weight ratio of crosslinking agent (CL) with polymer (CA) ranges typically from 0.01 to 0.5, more typically from 0.05 to 0.25.
In some embodiments, the composition (C) according to the invention comprises water in an amount of at least 5 wt. % of the total weight of said composition (C); preferably of at least 10 wt. %; more preferably of at least 15 wt. % and even more preferably of at least 20 wt. %. Besides, the composition (C) according to the invention comprises water in an amount of at most 90 wt. % of the total weight of said composition (C); preferably of at most 85 wt. %; more preferably of at most 80 wt. % and even more preferably of at most 75 wt. %.
In some embodiments, the composition according to the invention comprises water in an amount ranging from 5 wt. % to 90 wt. % of the total weight of said composition (C); preferably ranging from 10 wt. % to 85 wt. %; more preferably ranging from 15 wt. % to 80 wt. % and even more preferably ranging from 20 wt. % to 75 wt. % of the total weight of said composition (C).
In some embodiments, the composition (C) comprises an overall amount of polymer (ZW), polymer (CA) and crosslinking agent (CL) of at least 5 wt. %, more preferably of at least 10 wt. % and even more preferably of at least 15 wt. %, based on the total weight of water, polymer (ZW), polymer (CA) and crosslinking agent (CL). Besides, the composition (C) comprises an overall amount of polymer (ZW), polymer (CA) and crosslinking agent (CL) of at most 95 wt. %, preferably of at most 90 wt. %, more preferably at most 85 wt. % even more preferably of at most 80 wt. %, based on the total weight of water, polymer (ZW), polymer (CA) and crosslinking agent (CL).
In some embodiments, the composition (C) comprises an overall amount of polymer (ZW), polymer (CA) and crosslinking agent (CL) ranging from 5 wt. % to 95 wt. %; preferably ranging from 10 wt. % to 85 wt. % and more preferably ranging from 15 wt. % to 80 wt. %, based on the total weight of water, copolymer (ZW-CA) and crosslinking agent (CL).
The composition according to the present disclosure may comprise additional components to facilitate application of the composition onto the substrate and/or to provide additional benefits. Additional components include, but are not limited to crosslinking catalysts, chelating agents, fillers, pH adjusting agents, viscosity modifiers, wetting agents, water, co-solvents, antifoaming agents, leveling agents, colorants, pigments, anti-corrosion agents, preservatives, optical brighteners, opacifying or pearlescent agents, and the like.
In some embodiments, the composition according to the invention comprises water, wetting agents and co-solvents.
The co-solvent is generally selected from the list consisting of methanol, alcohol, isopropanol, ethylene glycol methyl ether, ethylene glycol ether, ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol ether, diethylene glycol ether and diethylene glycol butyl ether and mixtures thereof. Preferably the co-solvent is ethylene glycol butyl ether.
Wetting agent fort coating formulations is generally a surfactant having a hydrophilic and a hydrophobic part that would self-orientates at the surface of the substrate, reducing the surface tension of the liquid composition. Just as matter of example wetting agent can be chosen from sodium dodecylbenzenesulfonate, 4-octylbenzenesulfonic acid sodium salt, dodecane-1-sulfonic acid sodium salt and polyoxyethylene nonylphenyl ether.
Mixing of the polymer (ZW), the polymer (CA), the crosslinking agent (CL), water and optionally, but preferably, additional components may be accomplished using any method well known to those skilled in the art. In a second aspect, the present disclosure relates to the use of the coating composition (C) comprising:
for making frost resistant a substrate.
The composition (C) can have all the features previously disclosed in the description.
The substrate is typically in need of being made frost resistant.
In accordance with the present disclosure, generally a substrate in need of being made frost resistant is a substrate in contact with a gas medium comprising or consisting of water, typically moisture in the humid air, and whose surface temperature is below freezing point of water thus resulting in frost formation on said surface due to a phase change from water vapor (a gas) to ice (a solid) as the water vapor reaches the freezing point.
In accordance with the present disclosure, a substrate resisting the frost refers to partial or complete inhibition of the frost on a surface of said substrate. Resistance also includes slowing down frosting on a surface.
As used herein, the term “frost” is a thin layer of ice on a solid surface, which forms from water vapor in an above freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) to ice (a solid) as the water vapor reaches the freezing point.
Without wishing to be bound to theory, the formation of frost is believed to be delayed by the disrupted water crystallization on charged surfaces. Frosting, occurred on foreign hygroscopic surfaces, is described as heterogeneous ice nucleation (HIN). HIN on charged surfaces is believed to be affected by the interfacial water structure, and is also dependent on the amount of surface charges.
In a third aspect, the present disclosure relates to a method for making frost resistant a substrate, the method comprising processing the coating composition (C), having all the possible features previously described, onto the substrate thereby providing a top coating layer (TL) effective to make said substrate frost resistant.
In some embodiments, the present disclosure relates to a method for making frost resistant a substrate in need thereof, the method comprising:
The composition (C) can have all the features previously disclosed in the description.
As used herein, the top coating layer (TL) effective to make frost resistant a substrate depends on factors including the nature of the surface of the substrate; whether the aim is frost prevention, frost reduction or frost formation slow down; the contact time between the composition (C) and the surface; the curing temperature and the curing time; other additional components present in composition (C), and also the surface environment in question.
Generally step (i) is achieved using any method known to those of ordinary skill in the art. For example, the composition (C) can be applied by spray coating, spin coating, gravure coating, curtain coating, dip coating, slot-die coating, rod or bar coating, doctor-blade coating, flowcoating, which involves controlled gravity flow of a coating over the substrate, or the like.
Generally in step (ii) the coating composition (C) is allowed to dry at room temperature or may be dried at elevated temperature. A coated substrate having a top coating layer (TL) is typically prepared by curing the coating layer at a temperature of greater than 100° C., preferably at a temperature greater than 150° C. and more preferably greater than 200° C. Besides, the coating composition (C) is generally cured at less than 350° C., preferably less than 300° C. and more preferably less than 275° C.
In some embodiments, the coated substrate having a top coating layer (TL) is typically prepared by curing the coating layer at a temperature of greater than 100° C. and less than 350° C.; preferably of greater than 150° C. and less than 300° C. and more preferably of greater than 200° C. and less than 275° C.
As noted above, however, the curing temperature should be varied to suit the crosslinking agent included in the composition (C).
In some embodiments, the curing temperature as mentioned above represents the peak metal temperature (PMT). By peak metal temperature is meant the maximum temperature achieved by the metal substrate during the drying/curing process in a coil coating line.
Generally the curing time is greater than 2 seconds, preferably greater than 5 seconds and more preferably greater than 10 seconds. Besides, the curing time is generally less than 15 minutes, preferably less than 10 minutes and more preferably less than 5 minutes.
Generally the curing time ranges from 2 seconds to 15 minutes, preferably from 5 seconds to 10 minutes and more preferably from 10 seconds to 5 minutes.
In some embodiments, at least one curing catalyst is added to lower the curing temperature and/or to lower the curing time.
Without being bonded to any theory during curing the coating composition (C) is dried i.e. water, when present, is removed at least partially from the composition and crosslinking reaction occurs thus leading to a top coating layer (TL) which is hardened and crosslinked.
In some embodiments, the top coating layer (TL) effective to make frost resistant a substrate is such that it is deposited on the substrate in an amount ranging from 0.001 to 100 g/m2, typically from 0.01 to 50 g/m2, of the surface applied.
In some other embodiments, the top coating layer (TL) effective to make frost resistant a substrate is such that said top coating layer (TL) has a thickness ranging from 0.005 to 10 μm, typically from 0.01 to 5 μm.
Various substrates may be coated with the coating composition (C) of the invention. In some preferred embodiments, the substrate is a metal or metal-containing substrate, typically the metal is selected from the group consisting of iron, cast iron, copper, brass, aluminum, titanium, tin, carbon steel, stainless steel, and alloys thereof. Particularly preferred substrates are aluminum and steel. Most preferred substrate is aluminum.
In some other embodiments, the substrates that may be coated include plastic and paper.
Preferably, the substrate is pre-treated before coating to remove impurities and enhance the adhesion of coating compositions. For example, an aluminum substrate can be pre-treated by a degreasing agent, which has a concentration from 1% to 10% and pH from 11 to 13 for 30 seconds to 10 mins and then rinsed by water. The aluminum substrate is then dried under proper temperature, such as ambient temperature
In some preferred embodiments the substrate to be made frost resistant is coated with a base coating layer (BL) before processing the composition (C) to form the top coating layer (TL) effective to make said substrate frost resistant. Accordingly, the resulting substrate is coated with double layer coating consisting of a base coating layer (BL) and a top coating layer (TL), wherein base coating layer (BL) is sandwiched between the substrate and the top coating layer (TL).
Generally, the base coating layer (BL) is obtained by processing a based coating composition (BC) onto the substrate.
Processing a composition (BC) onto a substrate to form base coating layer (BL) generally comprises:
In some embodiments, the method for making frost resistant a substrate comprises:
Generally steps (i) and (iii) are achieved using any method known to those of ordinary skill in the art previously described for composition (C).
Generally steps (ii) and (iv) are achieved using conditions described for top coating layer formed with composition (C).
In some preferred embodiments, the substrate to be made frost resistant is a metal or metal-containing substrate, typically wherein the metal is selected from the group consisting of iron, cast iron, copper, brass, aluminum, titanium, carbon steel, stainless steel, and alloys thereof coated with a base coating layer (BL).
In some more preferred embodiments, the substrate to be made frost resistant is a steel or aluminum substrate coated with a base coating layer (BL).
In some even more preferred embodiments, the substrate to be made frost resistant is an aluminum substrate coated with a base coating layer (BL).
Generally, the base coating composition (BC) comprises at least one polymer, the nature of which is not particularly limited as long as the base coating layer (BL) formed has anti-corrosion function. Anti-corrosion refers to the protection of substrates from corroding in high-risk (corrosive) environments.
The base coating composition (BC) may further comprise a catalyst, water, a cosolvent, a leveling agent, a lubricant, an aqueous toughening resin, a defoamer or a thickener.
For example, the base coating composition (BC) may comprise a water-borne resin, an aqueous crosslinking agent, a catalyst, a co-solvent, a leveling agent, a lubricant, an aqueous toughening resin, a defoamer, a thickener and water.
Preferably, the water-borne resin is selected from a group consisting of a water-borne acrylic resin, a water-borne modified acrylic resin, a water-borne epoxy resin, a water-borne modified epoxy resin and a water-borne polyester resin. Preferably, the aqueous crosslinking agent is selected from a group consisting of an amino resin, an isocyanate, a silane coupling agent, a titanium coupling agent, a polycarboxylic acid and a polyamine.
Preferably, the catalyst is selected from a group consisting of p-toluenesulfonic acid, dodecylbenzenesulfonic acid, sulfamic acid, dinonylnaphthalene disulfonic acid and dinonylnaphthalenesulfonic acid.
Preferably, the co-solvent is selected from a group consisting of ethanol, n-butanol, tert-butanol, isobutanol, n-propanol, isopropanol, propylene glycol methyl ether, propylene glycol butyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether and dipropylene glycol methyl ether acetates. Preferably, the leveling agent is selected from a group consisting of an acrylate leveling agent, an organic fluorocarbon leveling agent, an ether bond-containing compound capable of reducing surface tension and an amphiphilic group-containing compound capable of reducing surface tension.
Preferably, the lubricant is selected from a group consisting of a silicone emulsion, an organic fluorine emulsion, a wax emulsion, an aqueous fatty acid, an aqueous fatty acid amide, an aqueous fatty acid ester and an aqueous fatty acid metal soap. The lubricant can also be an organic silicone, organic fluorine, or a fatty acid modified water-borne resin.
Preferably, the aqueous toughening resin is selected from a group consisting of an aqueous polyester polyol, an aqueous polyamide, an aqueous styrene-butadiene emulsion, an aqueous polyethersulfone resin and an aqueous polyurethane.
Preferably, the defoaming agent is selected from a group consisting of a mineral oil defoaming agent, a polyether antifoaming agent, an organosiloxane defoaming agent and a polyether modified organosiloxane defoaming agent. Preferably, the thickener is selected from a group consisting of a cellulose ether and a derivative thickener thereof, a polyacrylate thickener, a polyurethane thickener and a natural polymer and a derivative thereof.
It is also an object of the present invention to disclose an article comprising a metal or metal-containing surface, wherein the metal or metal-containing surface is coated with the coating composition (C) as previously described thereby providing a top coating layer (TL) effective to make the metal or metal-containing surface frost resistant.
It is still an object of the present invention to disclose an article comprising a metal or metal-containing surface coated with the top coating layer (TL), wherein a base coating layer (BL) is comprised between the metal or metal-containing surface and the top coating layer (TL).
In an embodiment, the article is a part of a heating and/or cooling system, typically heat exchanger of air conditionings, refrigerators and other refrigerating plants.
The article of the present disclosure is prepared by the methods described herein. The features of the methods described herein apply to the article, mutatis mutandis.
The applicants have surprisingly found that the coating composition (C) as previously described was suitable to prepare a top coating layer (TL) effective to delay frost formation on aluminum heat exchanger coated with a base coating layer (BL) having anti-corrosion function. Moreover they have found that surprisingly the top coating layer (TL) made from the coating composition (C) had very good adhesion onto the base coating layer (BL) and that the overall coating i.e. the double layer coating showed good resistance to corrosion and to scratch.
The methods and processes, including materials useful therefor, according to the present disclosure are further illustrated by the following non-limiting examples.
Poly(sodium-p-styrenesulfonate), M.W. 70,000, 20 wt. % solution in H2O and N,N,N′,N′-tetrakis(2-hydroxyethyl)hexanediamide were purchased from J&K Scientific, China. Sodium persulfate, sodium bisulfite, sodium dodecyl benzene sulfonate (SDBS), and ethylene glycol monobutylether (EGBE) were obtained from Sinopharm, China. Basecoat HD2805 was obtained from Guangzhou Human Chemicals Co. Ltd., China. Distilled water was used throughout the experiment.
Gel permeation chromatography was performed at 35° C. using Malvern GPCmax with RID & SEC-MALS 20 equipped with columns (Waters Ultrahydrogel 120 and 120, 250 in series). The mobile phase was composed of 80% 0.1 M NaNO3(aq) and 20% ACN, filtered with 0.22 μm filtration membrane, and the flow rate was of 0.8 mL/min. 1004, samples were injected, and calibration was obtained with PEO standard solutions.
Poly(acrylic acid) homopolymer (PAA) can be prepared by free radical copolymerization of acrylic acid in water initiated by e.g. sodium or ammonium persulfate according to a process well known by the skilled person.
In a reactor equipped with a condenser were added 190 g of water which were then heated and maintained at 85° C. under stirring. Then, were concomitantly added in the reactor within a duration of 3 hours—a solution A comprising 425 g of acrylic acid in 173 g of water—a solution B comprising 9.3 g of sodium persulfate in 173.2 g of water—a solution C comprising 70.3 g of sodium bisulfite in 131.7 g of water while maintaining the temperature at 85° C. and with stirring. After addition, the reaction medium was stirred for 1 more hour at 85° C. and then cooled to 50° C.
Conversion≥97%.
Mw (determined by GPC)=3200 g/mol.
Solid content: 42.55 wt. %.
Synthesis of Poly(Sulfopropyldimethylammonioethyl Methacrylate) (pSPE)
Synthesis of pSPE in the present invention by conventional radical polymerization (initiator: 2,2′-Azobis(2-methylpropionamidine)dihydrochloride V50).
In a 500 mL three-neck round-bottom flask equipped with a water condenser and a mechanical agitation, are introduced, at room temperature (22° C.), 1.1 g (1.18 mmol) of an aqueous solution of monomer SPE at 30 wt %, 32.04 g (5.91 mmol) of an aqueous V50 solution at 5 wt % and 30.97 g of MilliQ water. The mixture is purged with nitrogen for 30 minutes and then immersed in an oil bath preheated at 71° C. After stabilizing the temperature at 65° C. in the mass, 108.9 g (0.117 mol) of an aqueous solution of monomer SPE at 30 wt % is added to the reaction mixture over 10 hours using a syringe pump. After completion of the addition, the reaction is let stirring for an additional time of 2 hours. After this final ageing step, the mixture was cooled down to ambient temperature.
A sample is taken for 1H NMR analysis to determine the SPE monomer conversion. A sample was also taken for size exclusion chromatography analysis to determine the weight average molar mass Mw.
SPE monomer conversion (1H RMN)>99.9% Size exclusion chromatography (SEC) samples were diluted in a mobile phase (1M NH4NO3, 100 ppm of NaN3) and filtered (on 0.45 μm Millipore) before analyzing.
The samples were analyzed by SEC equipped with a Multi-Angle Laser Light Scattering (MALLS) detector accordingly to the conditions below:
w(SEC-MALS)=30,700 kg·mol−1
D=3.4
Solid content: 23.7 wt. %
Preparation of Topcoat Formulations (with pSPE)
Topcoat formulations can be prepared by mixing in the presence of water: PAA, Pspe, a crosslinking agent such as N,N,N′,N′-tetrakis(2-hydroxyethyl)hexanediamide (Vestagon®EP-HA320), a wetting agent such as Sodium dodecyl benzene sulfonate (SDBS) and co-solvents such as ethyleneglycol monobutylether (EGBE) and/or propylene glycol.
Comparative Topcoat Formulations (without pSPE)
Comparative topcoat formulations can be prepared by mixing in the presence of water: PAA, a crosslinking agent such as N,N,N′,N′-tetrakis(2-hydroxyethyl)hexanediamide (Vestagon®EP-HA320), a wetting agent such as Sodium dodecyl benzene sulfonate (SDBS) and co-solvents such as ethyleneglycol monobutylether (EGBE) and/or propylene glycol.
Comparative Topcoat Formulations (with PSS)
Topcoat formulations can be prepared by mixing in the presence of water: PAA, PSS, a crosslinking agent such as N,N,N′,N′-tetrakis(2-hydroxyethyl)hexanediamide (Vestagon®EP-HA320), a wetting agent such as Sodium dodecyl benzene sulfonate (SDBS) and co-solvents such as ethyleneglycol monobutylether (EGBE) and/or propylene glycol.
Four compositions of the topcoat formulations without pSPE, with pSPE (6 wt. %, 12 wt. %) and with PSS are reported in Table 1.
PAA solid content=42.55 wt. %
pSPE solid content=23.7 wt. %
PSS solid content=20 wt. %
If the mass of PAA aqueous solution is X and the mass of pSPE aqueous solution is Y:
6% was the mass ratio, which means:
At the same time, resin mass remains almost constant:
X+Y=22 Eq (2)
By solving Eq (1) & Eq (2), X=19.86 g and Y=2.14 g.
If the mass of PAA aqueous solution is X and the mass of pSPE aqueous solution is Y:
12% was the mass ratio, which means:
At the same time, resin mass remains almost constant:
X+Y=22 Eq (4)
By solving Eq (3) & Eq (4), X=18.10 g and Y=3.90 g.
If the mass of PAA aqueous solution is X and the mass of PSS aqueous solution is Y:
6% was the mass ratio, which means:
In Eq (5), X=22 g and Y=2.98 g.
All coatings were double layer coatings.
Basecoat formulation HD2805 available from Guangzhou Human Chemicals Co. Ltd., China is casted onto aluminum sheet surface using a 10 μm rod. Then, the resulting wet film is dried at 250° C. for 2 minutes, cooled up to ambient temperature to give aluminum sheet coated with basecoat layer having anti-corrosion function. Topcoat formulations are then casted onto aluminum sheet coated with basecoat layer using a 10 μm rod and the resulting wet films are dried at 250° C. for 2 minutes to give aluminum sheet double coated with basecoat and topcoat layers.
A degreased heat exchanger can be obtained by immersing Aluminum fin-tube heat exchanger into a 5% wt solution of degreasing agent for 5 minutes and then rinsing with deionised water for another 5 minutes before drying at room temperature. Said degreased heat exchanger is further dipped into the formulation of basecoat for 5 minutes lifted out the bath and dried at 250° C. during 2 minutes. Resulting heat exchanger coated with basecoat layer is then dipped into the formulation of topcoat for 5 minutes, lifted out the bath and dried at 250° C. during 2 minutes to obtain aluminum heat exchanger double coated with basecoat and topcoat layers.
A qualified coating should be kept intact i.e. without being swelled and/or detached and should keep its superhydrophilicity (SHL) in the long term especially in wet environment. Therefore, water dropping and soaking-in-water tests, the descriptions of which are described below, can be conducted for quick evaluation of the hydrophilicity and durability of the potential candidates.
Hydrophilicity of the coatings can be quickly evaluated by visual observation of water droplet of ˜0.02 ml spreading on the surface. Indeed it is conceptualized that surfaces with outstanding water spreading ability bring about frost delaying performances. Water droplet spreading is generally observed for coated surfaces obtained from formulations according to the invention giving evidence of hydrophilicity of the coatings.
This test can be conducted by immersing half of the coated aluminum sheet in distilled water for 100 h to visually assess the water resistance i.e. durability of the coating. Coated aluminum sheets obtained from formulations according to the invention are generally exempt of swelling, shrinkage or detachment.
Neutral salt spray test can be performed to give corrosion resistance information for samples of aluminum coated with topcoat layer according to the invention in a standardized corrosive environment. For this purpose, samples are submitted to the fog generated by a 5% NaCl aqueous solution at 37° C. for 1000 h in a salt spray chamber. Examination of the samples after test generally reveals that between 0.02% and 0.05% of the coated aluminum area are covered by impurities (corrosion), this level of contamination corresponding to Grade 9.5 according to Japanese Standard Association JIS Z 2371, method of salt spray testing (Feb. 20, 2000). Samples of aluminum coated with basecoat layer only reveals a similar level of contamination corresponding to Grade 9.5.
Cross-cut test method can be used to determine the resistance of the coatings to separation to the aluminum substrate using ASTM D3359 test Method B (2017). A cross-hatch pattern is made through the film to the aluminum sheet. Pressure sensitive tape is applied over the crosshatch cut after removal of detached flakes by brushing with a soft brush. Tape is then pulled off rapidly from the surface and adhesion of the coating is assessed by determination of the area of coating which was removed. The scale for this test ranges from 0 to 5, where 0 is when more than 65% area is removed and 5 is when 0% area is removed. The coatings according to the invention generally obtain evaluations ASTM D3359 Class 5B. Very good adhesion is observed for base coating layer onto aluminum substrate with class 5B obtained. Adding a PAA topcoat to this base coating layer result in an overall coating having still very good adhesion onto said substrate. Surprisingly, replacing PAA topcoat with a combination of PAA and pSPE is not detrimental to the overall coating adhesion which remains class 5B.
To evaluate the frost-resisting performance, a fin-tube heat exchanger, assembled from aluminum fins installed on copper tubes and coated with base coat and top coat, was set up to measure its heat exchange capacity (Q).
The facility employed to measure Q is shown in
In the equations, T is the temperature measured in Celsius degrees.
Ps is the saturated pressure of water vapor in kPa.
ϕ is relative humidity.
d is moisture content with the unit of kg/kg.
hs represents the enthalpy of moist air with the unit of kJ/kg.
{dot over (m)}, ρ and {dot over (V)} are respectively air mass flow rate, air density and air volume flow rate, with unit of kg/h, kg/m3 and m3/h respectively.
The temperature of fin-tube heat exchanger is controlled to be −10° C. by cold fluid in copper tube. As real air-conditioners will automatically start defrosting when Q decreases to 80% Qmax, the key indicator of the frost-resisting performance is Δt, i.e. the duration time between arriving and leaving 80% of Qmax.
Frost-resisting performance of base coated aluminum surface top coated with a combination of crosslinked PAA and pSPE is generally better than the frost-resisting performance of base coated aluminum surface top coated with crosslinked PAA when comparing their respective Δt values.
Fin-tube heat exchanger top coated with a combination of crosslinked PAA and pSPE are more resistant to frost formation than fin-tube heat exchanger top coated with crosslinked PAA. Accordingly, the beneficial effect of adding some amount of polymer containing zwitterionic moieties in the top coating composition is demonstrated.
The inventors have surprisingly found that replacing a top coat comprising crosslinked PAA by a top coat comprising crosslinked PAA and pSPE is not only effective to improve the frost resistance of fin-tube heat exchanger coated with a base coating layer having anti-corrosion function, but is also surprisingly effective to maintain a high level of adhesion of the overall coating onto the aluminum substrate while maintaining a high level of resistance to corrosive environment.
In other terms, the inventors have found that, replacing a top coat comprising crosslinked PAA by a top coat comprising crosslinked PAA and pSPE is not only surprisingly effective to improve the durability of the heat transfer efficiency of the coated equipment, i.e. fin-tube heat exchanger, resulting in important energy saving, but is also surprisingly effective to maintain a high level of adhesion of the overall coating onto the aluminum substrate while maintaining a high level of resistance to corrosive environment.
Furthermore, it was also found that a top coat comprising crosslinked PAA and pSPE has better anti-frosting performance than a top coat comprising crosslinked PAA and PSS.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/CN2020/084851 | Apr 2020 | WO | international |
This application claims priority to International Application. No. PCT/CN2020/084851 filed on Apr. 15, 2020, the whole content of this application being incorporated herein by reference for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2021/087224 | 4/14/2021 | WO |
