WO2008035975A2 - Paint additive - Google Patents

Paint additive Download PDF

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Publication number
WO2008035975A2
WO2008035975A2 PCT/NL2007/050465 NL2007050465W WO2008035975A2 WO 2008035975 A2 WO2008035975 A2 WO 2008035975A2 NL 2007050465 W NL2007050465 W NL 2007050465W WO 2008035975 A2 WO2008035975 A2 WO 2008035975A2
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WO
WIPO (PCT)
Prior art keywords
kda
groups
modified
glucan
weight
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PCT/NL2007/050465
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French (fr)
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WO2008035975A3 (en
Inventor
Theodoor Maximiliaan Slaghek
Johannes Wilhelmus Timmermans
Ingrid Karin Haaksman
Hendrik Jacobus Arie Breur
Jurgen Scheerder
Gerritdina Hendrika Van Geel-Schutten
Original Assignee
Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno
Materials Innovation Centre B.V.
Dsm Ip Assets B.V.
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Application filed by Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno, Materials Innovation Centre B.V., Dsm Ip Assets B.V. filed Critical Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno
Priority to EP07808589A priority Critical patent/EP2064294A2/en
Publication of WO2008035975A2 publication Critical patent/WO2008035975A2/en
Publication of WO2008035975A3 publication Critical patent/WO2008035975A3/en

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    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08BPOLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B37/00Preparation of polysaccharides not provided for in groups C08B1/00 - C08B35/00; Derivatives thereof
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08BPOLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B11/00Preparation of cellulose ethers
    • C08B11/20Post-etherification treatments of chemical or physical type, e.g. mixed etherification in two steps, including purification
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08BPOLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B13/00Preparation of cellulose ether-esters
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08BPOLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B15/00Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08BPOLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B15/00Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
    • C08B15/02Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
    • C08B15/04Carboxycellulose, e.g. prepared by oxidation with nitrogen dioxide
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08BPOLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B31/00Preparation of derivatives of starch
    • C08B31/18Oxidised starch
    • C08B31/185Derivatives of oxidised starch, e.g. crosslinked oxidised starch
    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09DCOATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D101/00Coating compositions based on cellulose, modified cellulose, or cellulose derivatives
    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09DCOATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D5/00Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • C09D5/08Anti-corrosive paints

Definitions

  • the invention relates to the use of chemically modified carbohydrates as corrosion inhibitors and/or preservatives, especially in coatings, and to a composition suitable for coating solid surfaces, in particular metals, for the purpose of enhancing resistance to degradation of the surfaces.
  • Coatings based on vinyl chloride polymer binders show, when properly formulated, excellent anti-corrosive performance, which is due to their high barrier against oxygen. However, for many applications and for environmental reasons, the presence of chloride is not preferred.
  • Coatings based on styrene-acrylic or acrylic polymer binders have a much lower barrier against oxygen and therefore their anticorrosive performance is often inferior to that of the vinyl chloride based binders. Therefore, even more of the anti-corrosive performance relies on using anti-corrosive pigments and flash rust inhibitors.
  • the use of zinc and flash rust inhibitors like sodium nitrite is not preferred from an environmental point of view. Therefore, there is a need for additives that can partially or completely replace anti-corrosive pigments and/or flash rust inhibitors and which do not have the same negative environmental impact as metals or nitrite.
  • WO 03/008618 discloses certain high molecular weight bacterial ⁇ -glucans, some of which have anti-corrosive properties, e.g. for ship hulls. These are a 8 MDa highly branched ⁇ -l,3-glucan and a 36 MDa branched alternan-type ( ⁇ -l,3/ ⁇ -l,6) glucan.
  • the modified polysaccharide contains anionic groups.
  • a part of the hydroxyl groups may be blocked by hydrophobic alkyl or alkanoyl groups.
  • the coating compositions of the invention are water-based and contain conventional components such as pigments, binders, etc. and are characterised by containing 0.1-5 wt.% of the modified polysaccharide.
  • the polysaccharide to be used according to the invention can be any polysaccharide having repeating anhydroglycose units or their derivatives such as deoxyanhydroglycose or anhydroglycuronic acid units.
  • the polysaccharide preferably contains at least 30% of monosaccharide units having a hydroxymethyl group (-CH 2 OH), either as such, or as its oxidised form (uronic acid).
  • the polysaccharide is a glucan, which may be either an ⁇ -glucan (starch family etc.), or a ⁇ -glucan or xyloglucan (cellulose and chitin, tamarind kernel, ⁇ -1,3 and/or ⁇ -1,6 glucans, e.g (hetero)glucans in which at least 30% of the units are ⁇ -1,3, such as curdlan and scleroglucan).
  • ⁇ -glucan starch family etc.
  • xyloglucan cellulose and chitin, tamarind kernel, ⁇ -1,3 and/or ⁇ -1,6 glucans, e.g (hetero)glucans in which at least 30% of the units are ⁇ -1,3, such as curdlan and scleroglucan.
  • the polysaccharide is of the starch group, which may be from any source, including potato, corn, rice, tapioca, etc.
  • the starch Prior to its oxidation, the starch may be gelatinised in a manner known per se, such as heat treatment in water at 60°C, or treatment with alkali or the starch is modified via a granular process.
  • the starch may be derivatised in its granular form, e.g. using extrusion techniques.
  • the polysaccharide is a glucan having both ⁇ -1,3 and ⁇ -1,6 links, for example having between 10 and 50%, preferably between 20 and 40% of ⁇ -1,3 links, and between 20 and 70%, preferably between 30 and 60% of ⁇ -1,6 links, together with e.g. 5-20% of branching.
  • Examples include the alternan-type glucans from Leuconostoc mesenteroid.es, such as e.g.
  • the modified polysaccharide should have a molecular weight of at least 10 kDa (degree of polymerisation (DP) of about 60), and the molecular weight may be as high as 10,000 kDa (DP about 60,000) or even higher.
  • the average molecular weight is at least 15 kDa or even 20 kDa, up to 3000 kDa, or especially 1000 kDa; the most preferred molecular weight is between 20 and 800 kDa (DP between about 120 and 5,000).
  • a first fraction has an average molecular weight between 20 and 160 kDa, especially between 20 and 60 kDa, and/or at least 20% (by weight, up to e.g. 50% by weight) of the polysaccharide has a molecular weight between 20 and 160 kDa, especially between 20 and 60 kDa, while a second fraction having an average molecular weight between 200 and 800 kDa, e.g. accounting for 10-60% by weight, may also be present.
  • Average molecular weights as used herein are to be understood as weight-average. Molecular weights can be determined as described in the Example section below.
  • the molecular weight of a polysaccharide can be reduced to the desired values by chemical treatment, such as hydrolysis, prior to or after modification, or even during modification by adapting the modification conditions (e.g. the temperature and/or pH during oxidation).
  • the modified polysaccharide contains from 0.1 to 0.9 anionic groups per monosaccharide unit, preferably between 0.2 and 0.6 anionic groups per unit.
  • the anionic groups may be derived from carboxylic, phosphoric, sulphuric acid, and the like groups.
  • the acid groups can be present as a result of substitution or addition of suitable acid-containing reagents.
  • carboxylic groups may result from carboxyalkylation, in particular carboxymethylation, or from reaction with an anhydride such as maleic or succinic anhydride.
  • Phosphonic groups may be present as phosphate groups, resulting e.g. from reaction with phosphorylating agents (see e.g.
  • WO 97/28298 or as phosphonic or phosphinic acid groups, resulting e.g. from reaction with halomethyl phosphonic acids.
  • Sulphonic acids may be present e.g. as sulphate groups or as a result of sulphite addition to polysaccharide aldehydes (see e.g. WO 99/29354) or to maleic anhydride adducts (products with -0-CO-CH 2 - CH(COOH)-SO 3 H groups).
  • the anionic groups are carboxylic groups resulting from oxidation, e.g.
  • a (primary) hydroxymethyl group (-CH 2 OH, usually at C6 of a monosaccharide unit, but also optionally of hydroxymethyl groups in substituents, such as hydroxyethyl or hydroxypropyl groups), or of a bis(hydroxymethylene) group (-CHOH- CHOH-, usually at C2-C3 of a monosaccharide unit).
  • the anionic groups stem from TEMPO-mediated oxidation of hydroxymethyl groups.
  • TEMPO-mediated oxidation is well documented in the art, see e.g. De Nooy, Synthesis 1996, 1153-1174, WO 95/07303, WO 00/50388, WO 00/50621, WO 01/00681, WO 02/48197 and EP 1149846.
  • oxidising agent such as hypochlorite, hypobromite, hydrogen peroxide, or a peracid, or even oxygen
  • TEMPO 2,2,6,6-tetramethylpiperidine-N-oxyl
  • mediators such as halide ions, metal complexes or oxidative enzymes (e.g. peroxidase or phenol oxidase or laccase), leading to 6-carboxylic acid derivatives (uronic acids) in glucans and other aldohexose polymers.
  • a catalytic amount of nitroxyl is preferably 0.05-5% by weight, based on dry starch, or 0.05-5 mol% with respect to dry starch. Most preferably, these catalytic amounts are between 0.1 and 1 %.
  • the oxidation can be performed in aqueous solution or dispersion, e.g. by first adding TEMPO and optionally further catalysts or mediators, and then gradually or at once adding the oxidising agent, such a sodium hypochlorite solution, and reacting at temperatures between 0 and 50°C, preferably between 10 and 30°C, while maintaining neutral to mildly alkaline conditions, especially at a pH between 6 and 11, depending on the particular oxidising agent, preferably between 8 and 9.5.
  • the degree of oxidation determines the proportion of carboxyl groups in the modified polysaccharide, and can be varied by adapting the amount of oxidising agent. Any aldehyde groups remaining after oxidation may be further oxidised to carboxyl groups using additional of other oxidising agents, such as chlorite.
  • Oxidation of bis(hydroxymethylene) groups which produces two carboxyl groups in the same monosaccharide unit with ring opening, can be performed as well-known on the art, e.g. in a two-step process using periodate followed by e.g. chlorite oxidation, or in a one-step process using e.g. hypochlorite, with or without bromide.
  • the hypochlorite oxidation is usually accompanied with some chain length reduction.
  • the carboxyl groups may already be present in the native polysaccharide, such as in glycuronans.
  • Combinations of different anionic groups are also well suited for the invention. It is preferred that the anionic groups are in the ionised (salt) form, e.g. as alkali metal, alkaline earth metal, other metal, or ammonium salts.
  • Esterification can be done with activated Ci-Cs monocarboxylic acids, such as acid halides or anhydrides of Q-C O alkanoic, C 3 -C 8 cycloalkanoic or C 7 -C 8 benzoic or substituted benzoic acids.
  • C 2 -C 4 acyl groups are preferred.
  • the total degree of substitution (DS) of alkyl and acyl groups, preferably with acyl groups is from 0.01 to 2.2 per monosaccharide unit.
  • the DS is from 0.025 to 0.05 groups per unit, or between about 1 and 2% of the available hydroxyl groups being etherified or esterified.
  • the content of alkyl and acyl groups mentioned herein refers to those groups when attached to oxygen atoms of original hydroxyl groups of the parent polysaccharide, even though a minor substitution of anionic groups with such alkyl or acyl groups - resulting in partial esters and anhydrides respectively - is not detrimental to the effectiveness of the derivatives, as long as a major part of anionic groups is still anionic (including the neutral acid form).
  • Effective derivatives include those which contain two different types of groups on the hydroxyl positions, at least one of the two being an alkanoyl group.
  • the other may be another alkanoyl or other acyl group or an alkyl group.
  • a combination may e.g. be a methyl or ethyl group and an acetyl or propionyl group, an acetyl group and a propionyl or buryryl group, or a propionyl group and a butyryl group.
  • the degree of substitution is preferably between 0.01 to 1.1, especially from 0.02 to 0.1 group per monosaccharide unit.
  • the etherification and/or esterification can be carried out before or after the introduction of anionic groups.
  • the alkylation or acylation can be performed at the same conditions as most oxidation reactions, i.e. ambient temperature, a pH between 7 and 10, and in aqueous solution, preferably at relatively high concentration (e.g. between 5 and 75% dry substance of the reaction mixture).
  • the invention furthermore relates to modified glucans as such, which are modified in such a manner to contain from 0.1 to 0.6, preferably and from 0.2 to 0.5 carboxyl groups per monosaccharide, and from 0.01 to 0.2, preferably from 0.02 to 0.1 C2-C4 alkanoyl groups per monosaccharide unit.
  • the modified glucan has an average molecular weight between 20 kDa and 800 kDa, especially between 20 kDa and 500 kDa.
  • the glucan has a bimodal molecular weight distribution, e.g.
  • a glucan is defined herein as a polysaccharide containing at least 50% of optionally modified anhydroglucose units.
  • the invention also pertains to an aqueous coating composition
  • a polymeric binder and 0.1-10 wt.%, on polymeric binder weight, preferably 0.25-5 wt% and in particular 0.35-2 wt.%, of a modified polysaccharide as described above.
  • Any polymer can be used, but particularly useful are polymers that are suitable for anti-corrosive applications.
  • the polymeric binder can be waterborne or solvent-borne or can be prepared in a solvent which is O
  • the polymeric binders employed in the invention are vinyl polymers.
  • a vinyl polymer herein is meant a homo- or copolymer derived from the addition polymerisation (using a free radical process) of at least one olefinically unsaturated monomer which are also known as vinyl monomers.
  • the polymeric binder can be, but is not limited to, a polyacrylic, styrene-acrylic, epoxy, epoxy-acrylic, urethane, urethane-acrylic, polyester, polyamide, alkyd, chlorinated polymers, fluorinated polymers, or mixtures thereof.
  • the vinyl polymers may contain vinyl monomers which provide an adhesion and/or crosslinking functionality to the resulting polymer coating. Examples of these include (meth)acrylic monomers having at least one free carbonyl, hydroxyl, epoxy, aceto acetoxy, or amino group; allyl methacrylate, tetraethylene glycol methacrylate, and divinyl benzene. Adhesion promoting monomers include amino, urea, or N-heterocyclic groups.
  • the vinyl monomers bearing ionic or potentially ionic water- dispersing groups are vinyl monomers bearing anionic or potentially anionic water- dispersing groups, more preferably vinyl monomers bearing carboxylic acid groups and most preferably (meth)acrylic acid.
  • Especially preferred polymeric binder materials include styrene acrylic copolymers.
  • the styrene acrylic copolymers comprise monomers selected from i) styrenic monomers (such as for example styrene, alpha-methyl styrene); ii) Cl to C8 alkyl (meth)acrylates; iii) monomers carrying water-dispersing or potentially water-dispersing groups; and iv) other monomers.
  • the monomers carrying water-dispersing or potentially water-dispersing groups are preferably anionic or potentially anionic groups (e.g. (meth)acrylic acid).
  • the polymeric binder materials preferably comprise less than 10 wt% of functionalised monomers (e.g. carbonyl functional).
  • the polymeric binder materials, especially when they are styrene acrylic copolymers, preferably have an acid value in the range of from 3 to 80 mg KOH/g.
  • the polymeric binder materials have a weight-average molecular weight in the range of from 1,000 to 200,000, more preferably 1,000 to 100,000 g/mol as measured by GPC.
  • Molecular weights of polymers may be determined by using gel permeation chromatography using a polymer, such as polystyrene, of known molecular weight as a standard.
  • the polymeric binder materials have a Tg (glass transition temperature as calculated using the Fox equation) in the range of from 0 to 100 0 C, more preferably 0 to 60 0 C.
  • Tg glass transition temperature
  • the Tg of a polymer herein stands for the glass transition temperature and is well known to be the temperature at which a polymer changes from a glassy, brittle state to a rubbery state.
  • Tg values of polymers may be calculated using the well-known Fox equation.
  • Tg in Kelvin, of a copolymer having "n" copoly- merised comonomers is given by the weight fractions W of each comonomer type and the Tg' s of the homopolymers (in Kelvin) derived from each comonomer according to the equation:
  • the calculated Tg in Kelvin may be readily converted to 0 C.
  • the polymeric binders can optionally be crosslinked.
  • This can be a self-crosslinking system, i.e. a coating that crosslinks without the need for the addition of a compound that reacts with the polymeric binder, examples of which are Schiff-base, auto -oxidative or silane crosslinking.
  • Crosslinking may also be achieved by adding reagents that react with the binders, such as a (poly)amine compounds that react with epoxy-based polymeric binders, melamine or isocyanate compounds that react with OH or acid functional binders at ambient or elevated temperatures, and if required in the presence of a catalyst.
  • the vinyl polymers are normally made using free radical addition polymerisation o
  • the pH of the composition containing the vinyl polymer may be raised to neutralise sufficiently any acidic groups (i.e. render them sufficiently ionised) to allow the preparation of an aqueous composition by the addition of a base, such as an organic or inorganic base, examples of which include organic amines such as trialkylamines (e.g. triethylamine, tributylamine), morpholine and alkanolamines, and inorganic bases such as ammonia, NaOH, KOH and LiOH.
  • a base such as an organic or inorganic base, examples of which include organic amines such as trialkylamines (e.g. triethylamine, tributylamine), morpholine and alkanolamines, and inorganic bases such as ammonia, NaOH, KOH and LiOH.
  • Average molecular weight of polysaccharides can be determined by Size Exclusion Chromatography (HPLC) using a Waters Associates (Etten-Leur, NL) series liquid chromatography system with a refractive index (RI 410 nm) detector, a guard column (7.5 mm ID * 7.5 cm, particles size 12 ⁇ m) and two size exclusion columns (7.5 mm ID * 30 cm, particles size 17 ⁇ m). The temperature of the columns is maintained at 35°C. A phosphate buffer (100 mM sodium phosphate with 0.02% sodium azide, pH 7) is used as a mobile phase (flow 1 mL/min).
  • HPLC Size Exclusion Chromatography
  • the columns are calibrated with dextran standards with a molecular weight of 5,000, 10,000 and 500,000 (Pharmacia, Sweden), respectively.
  • a 100 mg sample is diluted with 10 mL phosphate buffer.
  • the solid content of the coating composition is 30-70 wt%, preferably 35-60 wt% and more preferably 40-55 wt%.
  • the polysaccharide can be added during any stage during the preparation of the polymer binders, or it can be added after completion of the polymeric binder, or it can be added during any stage during the paint preparation. Preferably the polysaccharide is added directly after completion of the polymeric binders.
  • the polysaccharide can be added as a solid component or it can first be dispersed or dissolved in water or a suitable solvent. If needed a surfactant can be used to aid dispersion of the polysaccharide in water. Preferably the polysaccharide is added as a solid or dissolved in water.
  • the polysaccharide can be applied first onto the substrate that needs to be protected followed by the application of an anti-corrosive polymer. The polysaccharide is then preferably applied as a solution in water. However preferably the polysaccharide is applied together with the polymeric binder.
  • the combination of polysaccharide and polymeric binder can be used as a primer, a topcoat or both.
  • the coating composition according to the invention further contains usual components for coating surfaces, such as extenders (e.g. calcium carbonate and china clay), pigments, dispersants such as pigment dispersion aids, fillers, binders, lubricants, surfactants, wetting agents, rheology modifiers, levelling agents, anti-cratering agents, biocides, antifoam agents, sedimentation inhibitors, UV absorbers, heat stabilisers, and antioxidants, solvents, other anti-corrosive agents, etc.
  • extenders e.g. calcium carbonate and china clay
  • dispersants such as pigment dispersion aids
  • fillers e.g. calcium carbonate and china clay
  • binders e.g. calcium carbonate and china clay
  • lubricants e.g. calcium carbonate and china clay
  • surfactants e.g. calcium carbonate and china clay
  • the composition is essentially free of heavy metals, meaning that the weight ratio between any heavy metals and modified polysaccharide is below 0.1, preferably below 0.02.
  • the modified polysaccharides and the coating compositions containing them can be used for coating metal like iron, steel like Cold Rolled Steel (CRS), galvanised steel, aluminium and other surfaces so as to provide them with an anti-corrosive coating. Such coatings are used to protect metals from corrosion.
  • the coatings can be applied by conventional coating applications techniques such as spraying or roll coating. The coatings are typically allowed to dry at ambient temperatures or dried at elevated temperatures depending on the application.
  • the surface Prior to applying the coatings, the surface may be prepared in conventional ways, for example, by cleaning (with for example a solvent or a water-based alkaline cleaner or an acidic solution), by mechanically treatment (for example abrasion), and/or conversion coating (phosphodising).
  • cleaning with for example a solvent or a water-based alkaline cleaner or an acidic solution
  • mechanically treatment for example abrasion
  • conversion coating phosphodising
  • the degree of substitution was determined by pretreating a sample by dissolving in water for free acid and in 0.5 M NaOH for total acid analysis.
  • the sample was analysed using HPLC (column Aminex HPX-87H 300 mm x 7.8 mm, eluent 0.01 M sulphuric acid, and PJ detection) and the analysis showed a degree of acetyl substitution of 0.03.
  • the degree of substitution was determined by pretreating a sample by dissolving in water for free acid and in 0.5 M NaOH for total acid analysis.
  • the sample was analysed using HPLC (column Aminex HPX-87H 300 mm x 7.8 mm, eluent 0.01 M sulphuric acid, and PJ detection) and the analysis showed a degree of acetyl substitution of 0.03.
  • the molecular weight measurements showed two peaks which correspond to MW's of 310 kDa and 33 kDa respectively.
  • Example 3 Example 2 was repeated with 41 % oxidised EPS LB 180.
  • Example 5 Carboxymethyl starch having a degree of carboxymethyl substitution of 0.20 (20%), obtained by reaction Paselli SA-2 with sodium monochloroacetate, was acetylated as described in Example 1.
  • 2,3-Dicarboxy starch having a DO of 24% obtained by hypochlorite oxidation of Paselli SA-2 in the presence of sodium bromide, was acetylated as described in Example 1.
  • 2,3-Dicarboxy starch having a DO of 22% obtained by hypochlorite oxidation of Paselli SA-2 in the absence of sodium bromide, was acetylated as described in Example 1.
  • a pigment paste was prepared by mixing under high shear demineralised water (21.6 gram), 2-aminopropanol (0.30 gram, as a 90% solution), Disperse-Ayd W-33 (3.60 gram) (a pigment dispersant commercially available from Sasol Servo), Butyl glycol (13.50 gram), Kronos 2190 (33,90 gram, TiC>2 available from Kronos), MicroTalc it extra (24,00 gram, a filler available from Mondo Minerals Oy), Heucophos ZPO (32.10 gram, Zinc Phosphate available from Heubach) and Hostaint Black (3.60 gram, black pigment available from Clarant).
  • NeoCryl XK-87 160.50 gram, a styrene- acrylic dispersion polymer commercially available from DSM NeoResins
  • Texanol 5.10 gram
  • Drew 210 693 (0.90 gram, a defoamer available from Ashland
  • Viscoatex 46 (0.15 gram, an acrylic thickener available from Codex)
  • Ser-AD FA179 (0.90 gram, a flash rust inhibitor available from Sasol Servo
  • the C6- oxidised carbohydrate from Example 1 or 2 was added (1.60 gram).
  • the same formulation was used without the C6-oxidised starch from Example 1 or 2.

Abstract

The invention provides a coating composition containing a modified polysaccharide, especially an α-glucan, containing from 0.1 to 0.9 anionic groups per monosaccharide unit and from 0.01 to 1.0 C1-C6 alkyl or alkanoyl groups per monosaccharide unit. The modified polysaccharide has a relatively high molecular weight of between 20 kDa and 3000 kDa.

Description

PAINT ADDITIVE
[0001] The invention relates to the use of chemically modified carbohydrates as corrosion inhibitors and/or preservatives, especially in coatings, and to a composition suitable for coating solid surfaces, in particular metals, for the purpose of enhancing resistance to degradation of the surfaces.
BACKGROUND
[0002] Current waterborne anti-corrosive primers are often styrene-acrylics, acrylics, epoxy or vinyl chloride based polymer binders. The anti-corrosive and other preservation properties of the coatings containing these binders are based on the barrier against water and oxygen. Therefore, in addition to the selection of the right polymer, the selection of ingredients that make up the total paint formulation is very important. Typical ingredients that are used in anti-corrosive formulations are anti-corrosive pigments like zinc phosphate and flash rust inhibitors like sodium nitrite and the like. Both zinc and nitrite are not preferred from an environmental point of view.
[0003] Coatings based on vinyl chloride polymer binders show, when properly formulated, excellent anti-corrosive performance, which is due to their high barrier against oxygen. However, for many applications and for environmental reasons, the presence of chloride is not preferred. [0004] Coatings based on styrene-acrylic or acrylic polymer binders have a much lower barrier against oxygen and therefore their anticorrosive performance is often inferior to that of the vinyl chloride based binders. Therefore, even more of the anti-corrosive performance relies on using anti-corrosive pigments and flash rust inhibitors. However, the use of zinc and flash rust inhibitors like sodium nitrite is not preferred from an environmental point of view. Therefore, there is a need for additives that can partially or completely replace anti-corrosive pigments and/or flash rust inhibitors and which do not have the same negative environmental impact as metals or nitrite.
[0005] WO 03/008618 discloses certain high molecular weight bacterial α-glucans, some of which have anti-corrosive properties, e.g. for ship hulls. These are a 8 MDa highly branched α-l,3-glucan and a 36 MDa branched alternan-type (α-l,3/α-l,6) glucan.
[0006] The technologies summarised above have not shown to be satisfactory in terms of both anticorrosive performance, acceptable cost and health and environmental safety for anticorrosive treatment of metal surfaces. Hence, there is still a strong need for novel and improved means and methods for anticorrosive agents for application in coatings. DESCRIPTION OF THE INVENTION
[0007] It has been found now that corrosion resistance of surfaces, in particular metal surfaces, can be improved by incorporating a modified polysaccharide into coating compositions. The modified polysaccharide contains anionic groups. In addition, a part of the hydroxyl groups may be blocked by hydrophobic alkyl or alkanoyl groups. The coating compositions of the invention are water-based and contain conventional components such as pigments, binders, etc. and are characterised by containing 0.1-5 wt.% of the modified polysaccharide. [0008] The polysaccharide to be used according to the invention can be any polysaccharide having repeating anhydroglycose units or their derivatives such as deoxyanhydroglycose or anhydroglycuronic acid units. Examples are glucans, galactans, mannans, glucomannans, galactomannans, fructans, arabans, xylans, arabinoxylans, arabinogalactans, galacturonans (including pectins, especially low-methoxyl and partially deacetylated pectins), (hetero)glucuronans (including gellan, especially partially deacetylated gellan, xanthan, and the like) etc., as well as combinations thereof. The polysaccharide preferably contains at least 30% of monosaccharide units having a hydroxymethyl group (-CH2OH), either as such, or as its oxidised form (uronic acid). Preferably, the polysaccharide is a glucan, which may be either an α-glucan (starch family etc.), or a β-glucan or xyloglucan (cellulose and chitin, tamarind kernel, β-1,3 and/or β-1,6 glucans, e.g (hetero)glucans in which at least 30% of the units are β-1,3, such as curdlan and scleroglucan). Most preferred, for reasons of economic accessibility are α-glucans, including starch, amylose, amylopectin, pullulan, nigeran, alternan, reuteran, and other α-1,3-, α-1,4- and/or α-l,6-linked glucans, and mixtures thereof. [0009] In one particular embodiment, the polysaccharide is of the starch group, which may be from any source, including potato, corn, rice, tapioca, etc. Prior to its oxidation, the starch may be gelatinised in a manner known per se, such as heat treatment in water at 60°C, or treatment with alkali or the starch is modified via a granular process. Alternatively, and preferably from an economic point of view, the starch may be derivatised in its granular form, e.g. using extrusion techniques. [0010] In another preferred embodiment, the polysaccharide is a glucan having both α-1,3 and α-1,6 links, for example having between 10 and 50%, preferably between 20 and 40% of α-1,3 links, and between 20 and 70%, preferably between 30 and 60% of α-1,6 links, together with e.g. 5-20% of branching. Examples include the alternan-type glucans from Leuconostoc mesenteroid.es, such as e.g. described in US 5,789,209, and the Lactobacillus reuteή 180 glucan described in WO 03/008618. [0011] The modified polysaccharide should have a molecular weight of at least 10 kDa (degree of polymerisation (DP) of about 60), and the molecular weight may be as high as 10,000 kDa (DP about 60,000) or even higher. Preferably, the average molecular weight is at least 15 kDa or even 20 kDa, up to 3000 kDa, or especially 1000 kDa; the most preferred molecular weight is between 20 and 800 kDa (DP between about 120 and 5,000). In an especially preferred embodiment, a first fraction has an average molecular weight between 20 and 160 kDa, especially between 20 and 60 kDa, and/or at least 20% (by weight, up to e.g. 50% by weight) of the polysaccharide has a molecular weight between 20 and 160 kDa, especially between 20 and 60 kDa, while a second fraction having an average molecular weight between 200 and 800 kDa, e.g. accounting for 10-60% by weight, may also be present. Average molecular weights as used herein are to be understood as weight-average. Molecular weights can be determined as described in the Example section below. If necessary, the molecular weight of a polysaccharide can be reduced to the desired values by chemical treatment, such as hydrolysis, prior to or after modification, or even during modification by adapting the modification conditions (e.g. the temperature and/or pH during oxidation).
[0012] The modified polysaccharide contains from 0.1 to 0.9 anionic groups per monosaccharide unit, preferably between 0.2 and 0.6 anionic groups per unit. The anionic groups may be derived from carboxylic, phosphoric, sulphuric acid, and the like groups. The acid groups can be present as a result of substitution or addition of suitable acid-containing reagents. For example, carboxylic groups may result from carboxyalkylation, in particular carboxymethylation, or from reaction with an anhydride such as maleic or succinic anhydride. Phosphonic groups may be present as phosphate groups, resulting e.g. from reaction with phosphorylating agents (see e.g. WO 97/28298), or as phosphonic or phosphinic acid groups, resulting e.g. from reaction with halomethyl phosphonic acids. Sulphonic acids may be present e.g. as sulphate groups or as a result of sulphite addition to polysaccharide aldehydes (see e.g. WO 99/29354) or to maleic anhydride adducts (products with -0-CO-CH2- CH(COOH)-SO3H groups). Preferably, the anionic groups are carboxylic groups resulting from oxidation, e.g. of a (primary) hydroxymethyl group (-CH2OH, usually at C6 of a monosaccharide unit, but also optionally of hydroxymethyl groups in substituents, such as hydroxyethyl or hydroxypropyl groups), or of a bis(hydroxymethylene) group (-CHOH- CHOH-, usually at C2-C3 of a monosaccharide unit).
[0013] Most preferably, the anionic groups stem from TEMPO-mediated oxidation of hydroxymethyl groups. Such TEMPO-mediated oxidation is well documented in the art, see e.g. De Nooy, Synthesis 1996, 1153-1174, WO 95/07303, WO 00/50388, WO 00/50621, WO 01/00681, WO 02/48197 and EP 1149846. It involves the use of an oxidising agent such as hypochlorite, hypobromite, hydrogen peroxide, or a peracid, or even oxygen, with a catalytic amount of TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) or an analogue or derivative thereof, optionally with further mediators, such as halide ions, metal complexes or oxidative enzymes (e.g. peroxidase or phenol oxidase or laccase), leading to 6-carboxylic acid derivatives (uronic acids) in glucans and other aldohexose polymers. A catalytic amount of nitroxyl is preferably 0.05-5% by weight, based on dry starch, or 0.05-5 mol% with respect to dry starch. Most preferably, these catalytic amounts are between 0.1 and 1 %. [0014] The oxidation can be performed in aqueous solution or dispersion, e.g. by first adding TEMPO and optionally further catalysts or mediators, and then gradually or at once adding the oxidising agent, such a sodium hypochlorite solution, and reacting at temperatures between 0 and 50°C, preferably between 10 and 30°C, while maintaining neutral to mildly alkaline conditions, especially at a pH between 6 and 11, depending on the particular oxidising agent, preferably between 8 and 9.5. The degree of oxidation (DO) determines the proportion of carboxyl groups in the modified polysaccharide, and can be varied by adapting the amount of oxidising agent. Any aldehyde groups remaining after oxidation may be further oxidised to carboxyl groups using additional of other oxidising agents, such as chlorite. [0015] Oxidation of bis(hydroxymethylene) groups, which produces two carboxyl groups in the same monosaccharide unit with ring opening, can be performed as well-known on the art, e.g. in a two-step process using periodate followed by e.g. chlorite oxidation, or in a one-step process using e.g. hypochlorite, with or without bromide. The hypochlorite oxidation is usually accompanied with some chain length reduction.
[0016] Alternatively, the carboxyl groups may already be present in the native polysaccharide, such as in glycuronans. Combinations of different anionic groups are also well suited for the invention. It is preferred that the anionic groups are in the ionised (salt) form, e.g. as alkali metal, alkaline earth metal, other metal, or ammonium salts.
[0017] It was found that improved efficacy is achieved when a part of the remaining hydroxyl groups of the anionic polysaccharide is capped with hydrophobic groups, e.g. by etherification or esterification. Etherification can be effected in a manner known per se, e.g. with Ci -CO alkyl groups by reaction of the polysaccharide with the appropriate alkyl halide, sulphate or sulphonate, for example methyl iodide or diethyl sulphate. Esterification can be done with activated Ci-Cs monocarboxylic acids, such as acid halides or anhydrides of Q-CO alkanoic, C3-C8 cycloalkanoic or C7-C8 benzoic or substituted benzoic acids. C2-C4 acyl groups are preferred. The total degree of substitution (DS) of alkyl and acyl groups, preferably with acyl groups, is from 0.01 to 2.2 per monosaccharide unit. Preferably this DS is from 0.02 to 1.0 groups, especially from 0.02 to 0.2 groups per monosaccharide unit (= 2- 20%), which corresponds to a percentage of substitution of all available hydroxyl groups of between about 0.8 and 8%. Most preferably, the DS is from 0.025 to 0.05 groups per unit, or between about 1 and 2% of the available hydroxyl groups being etherified or esterified. The content of alkyl and acyl groups mentioned herein refers to those groups when attached to oxygen atoms of original hydroxyl groups of the parent polysaccharide, even though a minor substitution of anionic groups with such alkyl or acyl groups - resulting in partial esters and anhydrides respectively - is not detrimental to the effectiveness of the derivatives, as long as a major part of anionic groups is still anionic (including the neutral acid form). [0018] Effective derivatives include those which contain two different types of groups on the hydroxyl positions, at least one of the two being an alkanoyl group. The other may be another alkanoyl or other acyl group or an alkyl group. Such a combination may e.g. be a methyl or ethyl group and an acetyl or propionyl group, an acetyl group and a propionyl or buryryl group, or a propionyl group and a butyryl group. The degree of substitution is preferably between 0.01 to 1.1, especially from 0.02 to 0.1 group per monosaccharide unit. [0019] The etherification and/or esterification can be carried out before or after the introduction of anionic groups. For practical reasons, in particular in case of introduction of anions by oxidation of the polysaccharide, it may be advantageous to first introduce the anionic groups, and then carry out the alkylation or acylation. The alkylation or acylation can be performed at the same conditions as most oxidation reactions, i.e. ambient temperature, a pH between 7 and 10, and in aqueous solution, preferably at relatively high concentration (e.g. between 5 and 75% dry substance of the reaction mixture).
[0020] The invention furthermore relates to modified glucans as such, which are modified in such a manner to contain from 0.1 to 0.6, preferably and from 0.2 to 0.5 carboxyl groups per monosaccharide, and from 0.01 to 0.2, preferably from 0.02 to 0.1 C2-C4 alkanoyl groups per monosaccharide unit. In particular, the modified glucan has an average molecular weight between 20 kDa and 800 kDa, especially between 20 kDa and 500 kDa. In a particular embodiment, the glucan has a bimodal molecular weight distribution, e.g. having 15-75%, especially 20-50 wt.% with an MW between 20 and 60 kDa, especially between 20 and 60 kDa, and 10-60 wt.% with an MW between 200 and 800 MDa. A glucan is defined herein as a polysaccharide containing at least 50% of optionally modified anhydroglucose units.
[0021] The invention also pertains to an aqueous coating composition comprising a polymeric binder and 0.1-10 wt.%, on polymeric binder weight, preferably 0.25-5 wt% and in particular 0.35-2 wt.%, of a modified polysaccharide as described above. Any polymer can be used, but particularly useful are polymers that are suitable for anti-corrosive applications. The polymeric binder can be waterborne or solvent-borne or can be prepared in a solvent which is O
removed afterwards. Waterborne polymeric binders are preferred.
[0022] Preferably the polymeric binders employed in the invention are vinyl polymers. By a vinyl polymer herein is meant a homo- or copolymer derived from the addition polymerisation (using a free radical process) of at least one olefinically unsaturated monomer which are also known as vinyl monomers.
[0023] The polymeric binder can be, but is not limited to, a polyacrylic, styrene-acrylic, epoxy, epoxy-acrylic, urethane, urethane-acrylic, polyester, polyamide, alkyd, chlorinated polymers, fluorinated polymers, or mixtures thereof. Examples of vinyl monomers which may be used to form the vinyl polymer include 1,3 -butadiene, isoprene, styrene, α-methyl styrene, divinyl benzene, acrylonitrile, methacrylonitrile, vinyl halides such as vinyl chloride, vinyl esters such as vinyl acetate, vinyl propionate, vinyl laurate, and vinyl esters of versatic acid such as VeoVa 9 and VeoVa 10 (VeoVa is a trademark of Shell), heterocyclic vinyl compounds, alkyl esters of mono-olefinically unsaturated dicarboxylic acids (such as di-n-butyl maleate and di-n-butyl fumarate) and, in particular, esters of (meth)acrylic acid of formula CH2=CR1COOR2 wherein R1 is H or methyl and R2 is optionally substituted alkyl or cycloalkyl of 1 to 20 carbon atoms (more preferably 1 to 8 carbon atoms) examples of which are methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate (all isomers), isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isopropyl (meth)acrylate, propyl (meth)acrylate (all isomers), and hydroxyalkyl (meth)acrylates such as hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate and their modified analogues like Tone M-IOO. (Tone is a trademark of Union Carbide Corporation). Olefinically unsaturated monocarboxylic and/or dicarboxylic acids, such as (meth)acrylic acid, beta-carboxyethyl acrylate, fumaric acid, and itaconic acid, are other examples which can be used. [0024] The vinyl polymers may contain vinyl monomers which provide an adhesion and/or crosslinking functionality to the resulting polymer coating. Examples of these include (meth)acrylic monomers having at least one free carbonyl, hydroxyl, epoxy, aceto acetoxy, or amino group; allyl methacrylate, tetraethylene glycol methacrylate, and divinyl benzene. Adhesion promoting monomers include amino, urea, or N-heterocyclic groups.
[0025] Preferably the vinyl monomers bearing ionic or potentially ionic water- dispersing groups are vinyl monomers bearing anionic or potentially anionic water- dispersing groups, more preferably vinyl monomers bearing carboxylic acid groups and most preferably (meth)acrylic acid. [0026] Especially preferred polymeric binder materials include styrene acrylic copolymers. Preferably the styrene acrylic copolymers comprise monomers selected from i) styrenic monomers (such as for example styrene, alpha-methyl styrene); ii) Cl to C8 alkyl (meth)acrylates; iii) monomers carrying water-dispersing or potentially water-dispersing groups; and iv) other monomers.
[0027] The monomers carrying water-dispersing or potentially water-dispersing groups are preferably anionic or potentially anionic groups (e.g. (meth)acrylic acid). The polymeric binder materials preferably comprise less than 10 wt% of functionalised monomers (e.g. carbonyl functional). The polymeric binder materials, especially when they are styrene acrylic copolymers, preferably have an acid value in the range of from 3 to 80 mg KOH/g.
[0028] Preferably the polymeric binder materials have a weight-average molecular weight in the range of from 1,000 to 200,000, more preferably 1,000 to 100,000 g/mol as measured by GPC. Molecular weights of polymers may be determined by using gel permeation chromatography using a polymer, such as polystyrene, of known molecular weight as a standard.
[0029] Preferably the polymeric binder materials have a Tg (glass transition temperature as calculated using the Fox equation) in the range of from 0 to 100 0C, more preferably 0 to 60 0C. The Tg of a polymer herein stands for the glass transition temperature and is well known to be the temperature at which a polymer changes from a glassy, brittle state to a rubbery state. Tg values of polymers may be calculated using the well-known Fox equation. Thus the Tg, in Kelvin, of a copolymer having "n" copoly- merised comonomers is given by the weight fractions W of each comonomer type and the Tg' s of the homopolymers (in Kelvin) derived from each comonomer according to the equation:
1/Tg = Wi / Tgi + W2 / Tg2 + Wn / Tgn
The calculated Tg in Kelvin may be readily converted to 0C.
[0030] The polymeric binders can optionally be crosslinked. This can be a self-crosslinking system, i.e. a coating that crosslinks without the need for the addition of a compound that reacts with the polymeric binder, examples of which are Schiff-base, auto -oxidative or silane crosslinking. Crosslinking may also be achieved by adding reagents that react with the binders, such as a (poly)amine compounds that react with epoxy-based polymeric binders, melamine or isocyanate compounds that react with OH or acid functional binders at ambient or elevated temperatures, and if required in the presence of a catalyst. [0031] The vinyl polymers are normally made using free radical addition polymerisation o
in an aqueous emulsion polymerisation process to form an aqueous polymer emulsion. Such an aqueous emulsion polymerisation process, and alternative processes for producing vinyl polymers, are well known in the art
[0032] The pH of the composition containing the vinyl polymer may be raised to neutralise sufficiently any acidic groups (i.e. render them sufficiently ionised) to allow the preparation of an aqueous composition by the addition of a base, such as an organic or inorganic base, examples of which include organic amines such as trialkylamines (e.g. triethylamine, tributylamine), morpholine and alkanolamines, and inorganic bases such as ammonia, NaOH, KOH and LiOH. [0033] Average molecular weight of polysaccharides can be determined by Size Exclusion Chromatography (HPLC) using a Waters Associates (Etten-Leur, NL) series liquid chromatography system with a refractive index (RI 410 nm) detector, a guard column (7.5 mm ID * 7.5 cm, particles size 12 μm) and two size exclusion columns (7.5 mm ID * 30 cm, particles size 17 μm). The temperature of the columns is maintained at 35°C. A phosphate buffer (100 mM sodium phosphate with 0.02% sodium azide, pH 7) is used as a mobile phase (flow 1 mL/min). The columns are calibrated with dextran standards with a molecular weight of 5,000, 10,000 and 500,000 (Pharmacia, Sweden), respectively. Before injection (20 μl), a 100 mg sample is diluted with 10 mL phosphate buffer. [0034] The solid content of the coating composition is 30-70 wt%, preferably 35-60 wt% and more preferably 40-55 wt%. The polysaccharide can be added during any stage during the preparation of the polymer binders, or it can be added after completion of the polymeric binder, or it can be added during any stage during the paint preparation. Preferably the polysaccharide is added directly after completion of the polymeric binders. [0035] The polysaccharide can be added as a solid component or it can first be dispersed or dissolved in water or a suitable solvent. If needed a surfactant can be used to aid dispersion of the polysaccharide in water. Preferably the polysaccharide is added as a solid or dissolved in water. The polysaccharide can be applied first onto the substrate that needs to be protected followed by the application of an anti-corrosive polymer. The polysaccharide is then preferably applied as a solution in water. However preferably the polysaccharide is applied together with the polymeric binder. The combination of polysaccharide and polymeric binder can be used as a primer, a topcoat or both.
[0036] The coating composition according to the invention further contains usual components for coating surfaces, such as extenders (e.g. calcium carbonate and china clay), pigments, dispersants such as pigment dispersion aids, fillers, binders, lubricants, surfactants, wetting agents, rheology modifiers, levelling agents, anti-cratering agents, biocides, antifoam agents, sedimentation inhibitors, UV absorbers, heat stabilisers, and antioxidants, solvents, other anti-corrosive agents, etc. Although metal-containing anticorrosive agents may additionally be present, it is preferred that the pre-treatment solution of the invention has low levels of heavy metals (heavy meaning atomically heavier than calcium). In particular, the composition is essentially free of heavy metals, meaning that the weight ratio between any heavy metals and modified polysaccharide is below 0.1, preferably below 0.02. [0037] The modified polysaccharides and the coating compositions containing them can be used for coating metal like iron, steel like Cold Rolled Steel (CRS), galvanised steel, aluminium and other surfaces so as to provide them with an anti-corrosive coating. Such coatings are used to protect metals from corrosion. The coatings can be applied by conventional coating applications techniques such as spraying or roll coating. The coatings are typically allowed to dry at ambient temperatures or dried at elevated temperatures depending on the application.
[0038] Prior to applying the coatings, the surface may be prepared in conventional ways, for example, by cleaning (with for example a solvent or a water-based alkaline cleaner or an acidic solution), by mechanically treatment (for example abrasion), and/or conversion coating (phosphodising).
EXAMPLES:
Preparation examples 1-9
Various carboxylated and acetylated polysaccharides were prepared as described below.
The product data are summarised in Table 1.
Example 1
22 gram (0.11 mol) of partly (45%) C6-oxidised starch (obtained by TEMPO-mediated hypochlorite oxidation of Paselli SA-2, a water-soluble potato starch) was dissolved in 100 ml of demineralised water. 0.53 ml of acetic anhydride was added in 1 minute. During the reaction, the pH was maintained at 8 by using a pH stat and 2 M NaOH, and the temperature was 20-220C. After 1 hour reaction time, the solution was desalted using a membrane filter (MWCO 3500). Finally, the solution was freeze-dried and the product was analysed for its composition. The degree of substitution was determined by pretreating a sample by dissolving in water for free acid and in 0.5 M NaOH for total acid analysis. The sample was analysed using HPLC (column Aminex HPX-87H 300 mm x 7.8 mm, eluent 0.01 M sulphuric acid, and PJ detection) and the analysis showed a degree of acetyl substitution of 0.03.
The molecular weight measurements showed two peaks which correspond to MWs of 480 kDa and 43 kDa respectively. Example 2
22 gram (0.11 mol) of partly (39%) oxidised EPS LB 180 (obtained by TEMPO- mediated hypochlorite oxidation of EPS LB 180, an α- 1,3/1, 6 glucan described in WO 03/008618) was dissolved in 100 ml of demineralised water. 0.53 ml of acetic anhydride was added in 1 minute. During the reaction, the pH was maintained at 8 by using a pH stat and 2 M NaOH, and the temperature was 20-220C. After 1 hour reaction time, the solution was desalted using a membrane filter (MWCO 3500). Finally, the solution was freeze-dried and the product was analysed for its composition. The degree of substitution was determined by pretreating a sample by dissolving in water for free acid and in 0.5 M NaOH for total acid analysis. The sample was analysed using HPLC (column Aminex HPX-87H 300 mm x 7.8 mm, eluent 0.01 M sulphuric acid, and PJ detection) and the analysis showed a degree of acetyl substitution of 0.03.
The molecular weight measurements showed two peaks which correspond to MW's of 310 kDa and 33 kDa respectively.
Example 3 Example 2 was repeated with 41 % oxidised EPS LB 180.
Example 4
Carboxymethyl starch having a degree of carboxymethyl substitution of 0.20 (20%), obtained by reaction Paselli SA-2 with sodium monochloroacetate, was acetylated as described in Example 1. Example 5
2,3-Dicarboxy starch having a degree of oxidation DO of 28% (i.e. 0.56 carboxyl groups per monosaccharide unit), obtained by periodate oxidation of Paselli SA-2 followed by oxidation with sodium chlorite, was acetylated as described in Example 1. Example 6
2,3-Dicarboxy starch having a DO of 24%, obtained by hypochlorite oxidation of Paselli SA-2 in the presence of sodium bromide, was acetylated as described in Example 1.
Example 7
2,3-Dicarboxy starch having a DO of 22%, obtained by hypochlorite oxidation of Paselli SA-2 in the absence of sodium bromide, was acetylated as described in Example 1.
Example 8
Dicarboxy EPS LB 180 (vicinal: 2,3 and 3,4) having a DO of 26%, obtained by hypochlorite oxidation of EPS LB 180 in the presence of sodium bromide, was acetylated as described in Example 1. Example 9
Dicarboxy EPS LB 180 having a DO of 15%, obtained by hypochlorite oxidation of in the absence of sodium bromide, was acetylated as described in Example 1.
Table 1: carboxylated and acetylated polysaccharides (degree of substitution - DS - per anhydroglucose unit)
Figure imgf000012_0001
Example 10
A pigment paste was prepared by mixing under high shear demineralised water (21.6 gram), 2-aminopropanol (0.30 gram, as a 90% solution), Disperse-Ayd W-33 (3.60 gram) (a pigment dispersant commercially available from Sasol Servo), Butyl glycol (13.50 gram), Kronos 2190 (33,90 gram, TiC>2 available from Kronos), MicroTalc it extra (24,00 gram, a filler available from Mondo Minerals Oy), Heucophos ZPO (32.10 gram, Zinc Phosphate available from Heubach) and Hostaint Black (3.60 gram, black pigment available from Clarant). To this paste, NeoCryl XK-87 (160.50 gram, a styrene- acrylic dispersion polymer commercially available from DSM NeoResins) was added, followed by Texanol (5.10 gram), Drew 210 693 (0.90 gram, a defoamer available from Ashland), Viscoatex 46 (0.15 gram, an acrylic thickener available from Codex), Ser-AD FA179 (0.90 gram, a flash rust inhibitor available from Sasol Servo) and finally the C6- oxidised carbohydrate from Example 1 or 2 was added (1.60 gram). For the reference, the same formulation was used without the C6-oxidised starch from Example 1 or 2. This gives a paint with a solids content of 57.8 % (w/w) and a Pigment Volume Concentration of 26.6%. Of the paints, 30-40 μm dry films were applied onto Q-panels (R-46) using a spray gun. After application the coatings were allowed to dry for 6 hours at room temperature followed by ageing during 16 hours at 50 0C. These panels were subjected to a salt-spray test according to ASTM B-117-73 and DIN 50021. The coatings prepared with the paints containing the C6-oxidised carbohydrate from Example 1 or 2 showed smaller and fewer blisters in the field, smaller and fewer blisters closer to the scribe and less corrosion products near the scribe throughout time of the salt-spray test.

Claims

1. A coating composition containing a polymeric binder, characterised by comprising 0.1- 10 wt.%, on the basis of dry the polymeric binder weight, of a modified α-glucan containing from 0.1 to 0.9 anionic groups per monosaccharide unit, the modified polysaccharide having a weight-average molecular weight of between 15 kDa and 3000 kDa.
2. A coating composition according to claim 1, in which the α-glucan is an α- 1,4- or α-1, 3/1, 6-glucan.
3. A coating composition according to claim 1 or 2, in which the modified α-glucan has a weight-average molecular weight of between 20 kDa and 1000 kDa.
4. A coating composition according to any one of claims 1-3, in which at least 20 wt% of the modified α-glucan has a molecular weight between 20 and 60 kDa.
5. A coating composition according to any one of claims 1-4, in which the anionic groups comprise 0.2-0.6 uronic carboxylate groups per monosaccharide unit.
6. A coating composition according to any one of claims 1-5, in which the α-glucan further contains from 0.01 to 1.0 CI-CO alkyl or alkanoyl groups per monosaccharide unit.
7. A coating composition according to claim 6, in which the modified α-glucan contains from 0.02 to 0.2 C2-C4 alkanoyl groups per monosaccharide unit.
8. A coating composition containing a polymeric binder, characterised by comprising 0.1- 10 wt.%, on the basis of the dry polymeric binder weight, of a modified polysaccharide containing from 0.1 to 0.9 anionic groups and from 0.02 to 0.2 CI-CO alkyl or alkanoyl groups per monosaccharide unit, the modified polysaccharide having a weight-average molecular weight of between 15 kDa and 3000 kDa.
9. A coating composition according to any one of claims 1-8, which is substantially free of heavy metals.
10. Use of a modified α-glucan containing from 0.1 to 0.9 anionic groups per monosaccharide unit, the modified polysaccharide having a weight -average molecular weight of between 20 kDa and 3000 kDa, as an anticorrosion agent.
11. Use of a modified polysaccharide containing from 0.1 to 0.9 anionic groups and from 0.01 to 1.0 Ci -CO alkyl or alkanoyl groups per monosaccharide unit, the modified polysaccharide having a weight-average molecular weight of between 20 kDa and 3000 kDa, as an anticorrosion agent.
12. A modified polysaccharide, which contains from 0.1 to 0.6 carboxyl groups per monosaccharide unit, and from 0.01 to 0.2 CI-CO alkanoyl groups per monosaccharide unit, the modified polysaccharide having a weight -average molecular weight between 20 kDa and 1000 kDa.
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