Solvent-free PU conductive coating

Abstract

The present invention relates to a solvent-free polyurethane coating composition comprising A) a polyisocyanate having a low viscosity of less than 800 mPa.s, B) single-walled carbon nanotubes (SWCNT) in the range of 0.012-0.04 wt%, based on the total weight of the composition, and C) carbon fibers having a length of less than 0.2 mm, in the range of 1.0-2.4 wt%, based on the total weight of the composition. The invention further relates to a coating system on a substrate for preventing electrostatic discharges, comprising the solvent-free polyurethane coating composition according to the invention.

Description

Technical Field

[0001] The present invention relates to a conductive solvent-free polyurethane coating, a method for preparing a dissipative coating using the conductive solvent-free polyurethane coating, an electrostatic conductive or dissipative coating system, and use of the polyurethane coating for forming a dissipative layer. Prior art

[0002] Many sectors of industry today place stringent demands on optimum environmental conditions. Particularly important in this regard is the protection against uncontrolled electrostatic charging and discharging.

[0003] Electrostatic charging and discharging is caused by the contact, friction or separation of two materials. In the process, one material becomes positively charged and the other negatively charged. In the case of floor coatings, this charge is generated by foot traffic or wheel traffic, for example using rubber soles or rubber wheels. Charging can also be caused by blowing air over an insulating surface, such as paint or coating.

[0004] Therefore, in sensitive areas, floors and walls with low ground resistance are required, which dissipate electrostatic charges immediately and in a controlled manner.

[0005] The grounding resistance and system resistance can be determined according to DIN EN 61340-4-1. For example, a dissipative coating or sealing coating according to DIN EN61340 series can be used if its grounding resistance is less than 10 9 ohms, then it is considered dissipative or electrostatically dissipative. Coatings with a larger resistance to ground are not dissipative. However, in order to have an adequate safety margin, especially for environmental conditions with very low absolute humidity, less than 10 7 A ground resistance of ohms is desired.

[0006] Coating systems are known which have ESD protection (ESD = “electrostatic discharge”), ie which have protection against electrostatic discharge. Dissipative systems based on epoxy resins or polyurethanes are usually used.

[0007] However, most of the epoxy resin or polyurethane dissipative systems on the market are solvent-based polyurethane systems or solvent-free epoxy systems. Although solvent-based polyurethane products have sufficient conductive properties or dissipative properties, they contain a certain amount of VOC content, which imposes a significant burden on the environment. Solvent-free epoxy products are environmentally friendly, but their weather resistance and wear resistance are poor.

[0008] Some water-based epoxy or PU products have also been developed. They can be applied as a thin top coat, but the hardness and abrasion resistance of the coating are poor. SUMMARY OF THE INVENTION

[0010] Therefore, the object of the present invention is to provide a solvent-free polyurethane coating composition for preparing a dissipative coating system, more particularly a floor coating system, which can exhibit 10 6 -10 9 ohm static dissipative resistance or 10 4 -10 6 ohm's electrostatic conductive resistance while producing a cured coating with high abrasion resistance, good weathering properties, good mechanical properties and excellent chemical resistance.

[0011] In particular, the composition of the present invention is suitable for use as a thin top coat for dissipative floor coatings, and is also suitable for use as a renovation material for repairing static conductive floors.

[0012] Therefore, in a first aspect, the present invention relates to a solvent-free polyurethane coating composition comprising:

[0013] A) polyisocyanates having a low viscosity of less than 800 mPa.s, preferably less than 500 mPa.s,

[0014] B) single-walled carbon nanotubes (SWCNTs) in the range of 0.012-0.04 wt %, such as 0.016-0.035 wt %, based on the total weight of the composition,

[0015] C) Carbon fibers having a length below 0.2 mm, preferably below 0.15 mm, more preferably 0.05-0.12 mm, in the range of 1.0-2.4 wt%, such as 1.2-2.3 wt%, based on the total weight of the composition.

[0016] It has been surprisingly found that the polyurethane coating composition as described above can be applied as a thin coating in a solvent-free manner and that the addition of specified amounts of single-walled carbon nanotubes (SWCNTs) and short carbon fibers can simultaneously produce the desired dissipative or conductive properties and good weathering and mechanical properties such as abrasion resistance. In addition, the polyurethane coating of the present invention has very low VOCs (volatile organic compounds).

[0017] In a second aspect, the present invention relates to a coating system for preventing electrostatic discharge on a substrate, comprising in the following order:

[0018] a) a primer layer on said substrate,

[0019] b) optionally a layer of dissipative synthetic resin, and

[0020] c) A top coating layer formed from the solvent-free polyurethane coating composition according to the present invention.

[0021] Preferred embodiments of the composition are reproduced in the dependent claims. DETAILED DESCRIPTION

[0022] Compound names beginning with "poly" denote substances that formally contain two or more of the functional groups that appear in their names per molecule. The compounds may be monomeric, oligomeric or polymeric. Polyamines, for example, are compounds having two or more amino groups. Polyepoxides are compounds having two or more epoxy groups.

[0023] "Molecular weight" refers to the molar mass of a molecule (g / mol). "Average molecular weight" refers to the number average Mn of a polydisperse mixture of oligomeric or polymeric molecules, which is usually determined by gel permeation chromatography (GPC) using polystyrene standards.

[0024] "Room temperature" refers to a temperature of 23°C.

[0025] "Aromatic isocyanate" refers to an isocyanate in which the isocyanate group is directly bonded to an aromatic carbon atom. Therefore, such an isocyanate group is called an "aromatic isocyanate group".

[0026] "Aliphatic isocyanate" refers to an isocyanate in which the isocyanate group is directly bonded to an aliphatic carbon atom. Therefore, such an isocyanate group is called an "aliphatic isocyanate group".

[0027] A composition is said to be "storage stable" if it can be stored in a suitable container at room temperature for extended periods of time, generally at least 3 months to 6 months and longer, without its application properties being altered by storage to an extent relevant to its use.

[0028] The term "solvent-free" means here that the coating composition contains less than 1.0 wt.-%, for example 0.5 wt.-%, preferably less than 0.1 wt.-%, more preferably less than 0.05 wt.-% of organic solvents, or most preferably contains no organic solvents, in particular no volatile organic compounds, based on the total weight of the composition. The solvent-free coating composition according to the invention is preferably prepared and formulated without volatile organic compounds and contains only water as a volatile carrier or liquid phase.

[0029] The term "volatile organic compound" (VOC) refers herein to an organic compound having a boiling point below 250° C. at a standard pressure of 101.3 kPa. The normal boiling point can be determined, for example, using an ebulliometer.

[0030] “Carbon nanotubes” are carbon tubes with a diameter in the nanometer range, in particular in the range from 1 nm to 50 nm, and with a wall made of one or more layers of graphene (ie carbon with carbon atoms arranged in a ring).

[0031] Carbon nanotubes are industrially produced and commercially available in various qualities. They are electrically conductive. Single-walled carbon nanotubes, so-called "SWCNTs", are particularly suitable for the present invention. They all consist of carbon atoms and their geometric structure can be considered to be a curled-up monolayer of graphene. They are preferably used as a dispersion in a liquid carrier material, in particular in a liquid that is highly compatible with epoxy resin compositions, in particular alkyl glycidyl ethers, fatty acid esters or ethoxylated alcohols.

[0032] Preference is given to dispersions with 10% by weight of carbon nanotubes, in particular in alkyl glycidyl ethers, in particular C12-C14 alkyl glycidyl ethers, such as are also used as reactive diluents for epoxy resins. Such dispersions are commercially available, for example Matrix 301 (from OCSIAl).

[0033] Carbon fiber is a high-strength and high-modulus fiber that is essentially composed of carbon, such as more than 90% carbon. Carbon fiber is made of fine and strong crystalline carbon fibers used to reinforce materials. It can generally be made of polyacrylonitrile and viscose fibers as raw materials, which are carbonized by high-temperature oxidation.

[0034] In the present invention, short carbon fibers must be used in the polyurethane coating composition of the present invention. It has been found that short carbon fibers below 0.2 mm, preferably below 0.15 mm, more preferably 0.05-0.12 mm as defined above can make Rs and Rg readings lower and more stable for a longer time, and also lead to the best surface effect, especially in combination with single-walled carbon nanotubes (SWCNTs).

[0035] The present inventors have discovered that the desired combination of single-walled carbon nanotubes and carbon fibers in a specified weight ratio or amount can enable the solvent-free coating composition of the present invention to be formulated into an electrostatic conductive system or an electrostatic dissipative system having desired properties.

[0036] In the coating composition according to the invention, an amount of SWCNTs higher than 0.04 wt. % makes it possible to obtain an Rs / Rg in the range of 1.0*10 6 Up to 1.0*10 9 Ω and an electrostatic dissipative system with good surface quality, while less than 0.012 wt% SWCNTs would result in such high Rs and Rg resistances that the coating composition is not suitable for an electrostatic conductive system.

[0037] For carbon fiber, less than 1.0 wt% will likely result in a higher Rg resistance required for the electrostatic conductive system and is also not conducive to the long-term use of the electrostatic dissipative system. Above 2.4 wt% will likely result in too low Rg in the electrostatic dissipative system and also result in difficulty in applying or processing the coating composition.

[0038] The polyisocyanates used in the present invention have a low viscosity of less than 800 mPa.s, preferably less than 500 mPa.s. It has been found that higher viscosities of the polyisocyanates can lead to much higher Rs or Rg values ​​and also to poor solvent-free applicability of the coating composition.

[0039] Preferably, the polyisocyanate contains 18% by weight or more free NCO groups, for example 20-30% by weight.

[0040] Suitable polyisocyanates are especially commercially available polyisocyanates, in particular:

[0041] - aromatic diisocyanates or triisocyanates, preferably diphenylmethane 4,4'- or 2,4'- or 2,2'-diisocyanate or any mixture of these isomers (MDI), toluene 2,4- or 2,6-diisocyanate or any mixture of these isomers (TDI), mixtures of MDI and MDI homologues (polymeric MDI or PMDI), benzene 1,3- or 1,4-diisocyanate, 2,3,5,6-tetramethyl-1,4-diisocyanatobenzene, naphthalene 1,5-diisocyanate (NDI), 3,3'-dimethyl-4,4'-diisocyanatobiphenyl (TODI), dianisidine diisocyanate (DADI), tris(4-isocyanatophenyl)methane or tris(4-isocyanatophenyl)phosphorothioate; preferably MDI or TDI;

[0042] aliphatic, cycloaliphatic or arylaliphatic diisocyanates or triisocyanates, preferably tetramethylene 1,4-diisocyanate, 2-methylpentamethylene 1,5-diisocyanate, hexamethylene 1,6-diisocyanate (HDI), 2,2,4- and / or 2,4,4-trimethylhexamethylene 1,6-diisocyanate (TMDI), decamethylene 1,10-diisocyanate, dodecamethylene 1,12-diisocyanate, lysine diisocyanate or lysine ester diisocyanate, cyclohexane 1,3- or 1,4-diisocyanate, 1-methyl-2,4- and / or-2,6-diisocyanatocyclohexane (HDI). 6 TDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), perhydrodiphenylmethane 2,4'- and / or 4,4'-diisocyanate (H 12 MDI), 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane, m- or p-xylylene diisocyanate, tetramethylxylylene 1,3 or 1,4-diisocyanate, 1,3,5-tris(isocyanatomethyl)benzene, di(1-isocyanato-1-methylethyl)naphthalene, dimer or trimer fatty acid isocyanates, such as, in particular, 3,6-bis(9-isocyanatononyl)-4,5-di(1-heptenyl)cyclohexene (dimer diisocyanate); preferably H 12MDI or HDI or IPDI;

[0043] - oligomers or derivatives of the diisocyanates or triisocyanates mentioned, in particular oligomers or derivatives derived from HDI, IPDI, MDI or TDI, in particular oligomers containing uretdione or isocyanurate or iminooxadiazinedione groups or different groups therein; or difunctional or polyfunctional derivatives containing ester or urea or carbamate or biuret or allophanate or carbodiimide or uretonimine or oxadiazinedione groups or different groups therein. In practice, such polyisocyanates are usually mixtures of substances with different degrees of oligomerization and / or chemical structures. They have in particular an average NCO functionality of 2.1 to 4.0.

[0044] Preferred polyisocyanates are aliphatic, cycloaliphatic or aromatic diisocyanates, in particular HDI, TMDI, cyclohexane 1,3- or 1,4-diisocyanate, IPDI, H 12 MDI, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane, XDI, TDI, MDI, benzene 1,3- or 1,4-diisocyanate or naphthalene 1,5-diisocyanate (NDI).

[0045] Particularly preferred polyisocyanates are HDI, IPDI, H 12 MDI, TDI, MDI or a form of MDI which is liquid at room temperature, in particular HDI, IPDI, TDI or an HDI trimer.

[0046] The polyurethane binder upon which the polyurethane coating composition is based can be formed by reacting a polyisocyanate with a polyol (examples of which are described below) or with water (which can be intentionally added or contained in the components or even originate from the atmosphere, such as moisture or humidity from the air).

[0047] In an advantageous embodiment, the polyurethane coating composition of the present invention may be free of polyols that react with polyisocyanates.

[0048] Suitable polyols for reaction with the polyisocyanates are the commercial polyols or mixtures thereof, in particular:

[0049] - polyether polyols, in particular polyoxyalkylene diols and / or polyoxyalkylene triols, in particular polymerization products of ethylene oxide or 1,2-propylene oxide or 1,2- or 2,3-butylene oxide or oxetane or tetrahydrofuran or mixtures thereof, where these can be polymerized with the aid of starter molecules having two or more active hydrogen atoms, in particular starter molecules such as, for example, water, ammonia or compounds having a plurality of OH or NH groups, for example ethane-1,2- -diol, propane-1,2- or -1,3-diol, neopentyl glycol, diethylene glycol, triethylene glycol, isomeric dipropylene glycol or tripropylene glycol, isomeric butanediols, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, cyclohexane-1,3- or -1,4-dimethanol, bisphenol A, hydrogenated bisphenol A, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, glycerol or aniline, or mixtures of the above compounds. Also suitable are polyether polyols in which polymer particles are dispersed, in particular polyether polyols with styrene / acrylonitrile (SAN) particles or polyurea or polyhydrazodicarbonamide (PHD) particles.

[0050] Preferred polyether polyols are polyoxypropylene diols or polyoxypropylene triols, or so-called ethylene oxide-terminated (EO-terminated) polyoxypropylene diols or triols. The latter are mixed polyoxyethylene / polyoxypropylene polyols, which are obtained in particular when the polyoxypropylene diol or triol is further alkoxylated with ethylene oxide at the end of the polypropoxylation reaction, so that it ultimately has primary hydroxyl groups.

[0051] Preferred polyether polyols have an unsaturation of less than 0.02 meq / g, especially less than 0.01 meq / g.

[0052] - Polyester polyols, also called oligoesterols, prepared by known methods, in particular polycondensation of hydroxycarboxylic acids or lactones or polycondensation of aliphatic and / or aromatic polycarboxylic acids with diols or polyols. Preference is given to polyester diols from the reaction of diols, such as in particular 1,2-ethanediol, diethylene glycol, 1,2-propylene glycol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, glycerol, 1,1,1-trimethylolpropane or mixtures of the above alcohols, with organic dicarboxylic acids or their anhydrides or esters, such as in particular succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid or hexahydrophthalic acid or mixtures of the above acids, or polyester polyols obtained from lactones, such as in particular ε-caprolactone. Particular preference is given to polyester polyols obtained from adipic acid or sebacic acid or dodecanedicarboxylic acid and hexanediol or neopentyl glycol.

[0053] - Polycarbonate polyols obtainable, for example, by reaction of the abovementioned alcohols for forming the polyester polyols with dialkyl carbonates, diaryl carbonates or phosgene.

[0054] - Block copolymers which carry at least two hydroxyl groups and have at least two different blocks having a polyether, polyester and / or polycarbonate structure of the abovementioned type, in particular polyether polyester polyols.

[0055] – Polyacrylate polyols and polymethacrylate polyols.

[0056] - polyhydroxy-functional fats and oils, for example natural fats and oils, in particular castor oil; or polyols obtained by chemical modification of natural fats and oils - so-called oleochemical polyols - for example epoxy polyesters or epoxy polyethers obtained by epoxidation of unsaturated oils and subsequent ring opening with carboxylic acids or alcohols, or polyols obtained by hydroformylation and hydrogenation of unsaturated oils; or polyols obtained from natural fats and oils by degradation processes such as alcoholysis or ozonolysis and subsequent chemical linking, for example by transesterification or dimerization of the degradation products, or derivatives thereof obtained therefrom. Suitable degradation products of natural fats and oils are in particular fatty acids and fatty alcohols and fatty acid esters, in particular methyl esters (FAME), which can be derivatized to hydroxy fatty acid esters, for example by hydroformylation and hydrogenation.

[0057] - Polyolefin polyols, also called oligoolefins, such as polyhydroxy-functional polyolefins, polyisobutylenes, polyisoprenes; polyhydroxy-functional ethylene / propylene, ethylene / butylene or ethylene / propylene / diene copolymers, such as those produced, for example, by Kraton Polymers; polyhydroxy-functional polymers of dienes, in particular 1,3-butadiene, which can also be prepared, in particular, by anionic polymerization; polyhydroxy-functional copolymers of dienes, for example 1,3-butadiene or diene mixtures and vinyl monomers, such as styrene, acrylonitrile, vinyl chloride, vinyl acetate, vinyl alcohol, isobutylene and isoprene, such as polyhydroxy-functional acrylonitrile / butadiene copolymers, which can be prepared, for example, from epoxides or amino alcohols and carboxyl-terminated acrylonitrile / butadiene copolymers (for example, can be prepared as CTBN or CTBNX or ETBN designations are commercially available from Emerald Performance Materials); and hydrogenated polyhydroxy-functional polymers or diene copolymers.

[0058] Also particularly suitable are mixtures of polyols.

[0059] Preference is given to polyether polyols, polyester polyols, polycarbonate polyols, poly(meth)acrylate polyols or polyhydroxy-functional fats and oils.

[0060] Particular preference is given to polyester polyols, especially aliphatic polyester polyols, or polyhydroxy-functional fats and oils, especially castor oil.

[0061] Preference is given to polyols having an average molecular weight of 400 to 20 000 g / mol, preferably 1000 to 10 000 g / mol.

[0062] Preference is given to polyols having an average OH functionality in the range from 1.6 to 3.

[0063] Preferably, in addition to the above-mentioned components A) to C), the composition additionally comprises one or more further ingredients, in particular selected from catalysts, fillers, plasticizers and additives for setting the electrical properties.

[0064] Suitable catalysts are those which serve to accelerate the reaction of isocyanate groups, in particular organotin(IV) compounds, such as, in particular, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dichloride, dibutyltin diacetylacetonate, dimethyltin dilaurate, dioctyltin diacetate, dioctyltin dilaurate or dioctyltin diacetylacetonate, complexes of bismuth(III) or zirconium(IV), in particular with a ligand selected from the group consisting of alkoxides, carboxylates, 1,3-diketonates, hydroxyquinolinates, 1,3-ketoesters and 1,3-ketoamidates, or compounds containing tertiary amino groups, such as, in particular, 2,2′-dimorpholinodiethyl ether (DMDEE).

[0065] Also particularly suitable are combinations of different catalysts.

[0066] Suitable fillers are, in particular, ground or precipitated calcium carbonate, optionally coated with fatty acids, in particular stearates, barite, quartz powder, quartz sand, white corundum of the corundum type, dolomite, wollastonite, kaolin, calcined kaolin, sheet silicates, for example mica or talc, zeolites, aluminum hydroxide, magnesium hydroxide, silicon dioxide, including finely divided silicon dioxide from pyrogenic processes, cement, gypsum, fly ash, graphite, metal powders, for example of aluminum, copper, iron, silver or steel, PVC powder or hollow beads.

[0067] Preferably, the polyurethane composition of the present invention contains wear particles as fillers, such as corundum, ceramics, silicon carbide, and the like.

[0068] Suitable plasticizers are, in particular, carboxylic acid esters, for example phthalates, in particular diisononyl phthalate (DINP), diisodecyl phthalate (DIDP) or di(2-propylheptyl) phthalate (DPHP), hydrogenated phthalates, in particular hydrogenated diisononyl phthalate or diisononyl cyclohexane-1,2-dicarboxylate (DINCH), terephthalates, in particular dioctyl terephthalate, trimellitates, adipates, in particular dioctyl adipate, azelates, sebacates, benzoates, glycol ethers, glycol esters, organic phosphates or sulfonates, polybutenes, polyisobutenes or plasticizers derived from natural fats or oils, in particular epoxidized soybean oil or linseed oil.

[0069] Suitable additives for setting the electrical properties are conductive additives, for example conductive fillers, such as conductive pigments or conductive fibers, salts, ionic liquids, ionic and nonionic surfactants and combinations thereof. Specific conductive additives for setting the electrical properties are, for example, carbon fibers, carbon black, graphite, silicon carbide, metal oxides, metals (such as iron), ammonium salts, metal-containing or heavy metal-containing fillers, especially antimony- and tin-containing fillers based on titanium dioxide or mica, ionic liquids, ionic and nonionic surfactants, melamine sulfonates and polycarboxylate ethers and combinations thereof. For example, the conductive additive for setting the electrical properties can be added in the form of powders, fibers, crumbs, liquids, flakes or particles. Conductive salts can also optionally be added as solutions.

[0070] The composition may contain other additives commonly used in polyurethane compositions. More particularly, the following auxiliaries and additives may be present:

[0071] – Colorants, such as colored quartz, dyes, pigments and color chips;

[0072] - drying agents, in particular molecular sieve powder, calcium oxide, highly reactive isocyanates such as p-toluenesulfonyl isocyanate, monomeric diisocyanates or orthoformates;

[0073] - adhesion promoters, in particular organoalkoxysilanes, in particular epoxysilanes, such as, in particular, 3-glycidoxypropyltrimethoxysilane or 3-glycidoxypropyltriethoxysilane, (meth)acryloylsilanes, anhydridesilanes, carbamatesilanes, alkylsilanes or iminosilanes, or oligomeric forms of these silanes, or titanates;

[0074] - latent curing agents or crosslinking agents, in particular aldimines, ketimines, enamines or oxazolidines;

[0075] - catalysts which promote the reaction of isocyanate groups, in particular salts, soaps or complexes of tin, zinc, bismuth, iron, aluminium, molybdenum, dioxomolybdenum, titanium, zirconium or potassium, in particular tin(II) 2-ethylhexanoate, tin(II) neodecanoate, zinc(II) acetate, zinc(II) 2-ethylhexanoate, zinc(II) laurate, zinc(II) acetylacetonate, aluminium lactate, aluminium oleate, diisopropoxytitanium bis(ethylacetoacetate) or potassium acetate; compounds containing tertiary amino groups, in particular N-ethyldiisopropylamine, N,N,N',N'-tetramethylalkylenediamine, pentamethylalkylenetriamine and their higher homologues, bis(N,N-diethylaminoethyl)adipate esters, tris(3-dimethylaminopropyl)amine, 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), N-alkylmorpholines, N,N'-dimethylpiperazine; aromatic nitrogen compounds, such as 4-dimethylaminopyridine, N-methylimidazole, N-vinylimidazole or 1,2-dimethylimidazole; organic ammonium compounds, such as benzyltrimethylammonium hydroxide or alkoxylated tertiary amines; so-called "delayed action" catalysts, which are modified forms of known metal or amine catalysts;

[0076] - rheology modifiers, in particular thickeners, in particular sheet silicates, for example bentonites, castor oil derivatives, hydrogenated castor oil, polyamides, polyamide waxes, polyurethanes, urea compounds, pyrogenic silicas, cellulose ethers or hydrophobically modified polyoxyethylenes;

[0077] - non-reactive polymers, in particular homopolymers or copolymers of unsaturated monomers, in particular selected from ethylene, propylene, butylene, isobutylene, isoprene, vinyl acetate or alkyl (meth)acrylates, in particular polyethylene (PE), polypropylene (PP), polyisobutylene, ethylene / vinyl acetate copolymers (EVA) or atactic poly-α-olefins (APAO);

[0078] - flame retardant substances, in particular the aluminum hydroxide or magnesium hydroxide fillers already mentioned, and also in particular organic phosphates, such as, in particular, triethyl phosphate, tricresyl phosphate, triphenyl phosphate, diphenylcresyl phosphate, isodecyl diphenyl phosphate, tris(1,3-dichloro-2-propyl) phosphate, tris(2-chloroethyl) phosphate, tris(2-ethylhexyl) phosphate, tris(chloroisopropyl) phosphate, tris(chloropropyl) phosphate, isopropylated triphenyl phosphate, mono-, di- or tris(isopropylphenyl) phosphates of varying degrees of isopropylation, resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate) or ammonium polyphosphate;

[0079] – additives, in particular wetting agents, leveling agents, defoamers, deaerators, stabilizers against oxidation, heat, light or UV radiation, or biocides;

[0080] or other substances commonly used in moisture-curing compositions.

[0081] It may be advisable to chemically or physically dry certain substances before mixing them into a composition.

[0082] The compositions are produced in particular under exclusion of moisture and stored at ambient temperature in moisture-proof containers. Suitable moisture-proof containers consist in particular of optionally coated metal and / or plastic and are in particular drums, transport boxes, pails, barrels, cans, bladders, bags, tubular bags, cartridges or tubes.

[0083] The composition may be in the form of a one-component composition or in the form of a multi-component (especially two-component) composition.

[0084] A composition referred to as a "one-component" composition is one in which all ingredients of the composition are in the same container and which is inherently storage stable.

[0085] Compositions referred to as "two-component" compositions are compositions in which the ingredients of the composition are in two different components that are stored in separate containers and are not mixed with one another until shortly before or during application of the composition.

[0086] When the composition is applied, the curing process begins. This produces a cured composition.

[0087] In the case of a two-component or multi-component composition, it is applied after the two or more components have been mixed and curing begins by internal reaction, which can be completed by the action of external moisture. The two or more components can be mixed continuously or batchwise using a dynamic mixer or a static mixer.

[0088] The composition is preferably applied at ambient temperature, especially in the range of about 0 to 50°C, preferably in the range of 5 to 40°C.

[0089] The composition preferably also cures at ambient temperature.

[0090] In a second aspect, the present invention relates to a coating system for preventing electrostatic discharge on a substrate, comprising in the following order:

[0091] a) a primer layer on said substrate,

[0092] b) optionally a layer of dissipative synthetic resin, and

[0093] c) A top coating layer formed from the solvent-free polyurethane coating composition according to the present invention.

[0094] An electrostatic conductive system or an electrostatic dissipative system can be obtained after curing the coating composition according to the invention. Therefore, the coating system of the invention can be obtained in the form of the above two systems, which can generally be distinguished from each other in view of the different requirements for the resistance Rs or Rg. In general, the Rs or Rg in the electrostatic dissipative resistance is 10 6 -10 9 The range of ohms, while the Rs or Rg in the electrostatic conductive resistance is 10 4 -10 6 Ohm, for example 5.0 * 10 4 -1.0 * 10 6 For more details of the two systems, technicians can refer to, for example, standard GB / T 22374-2018.

[0095] In the coating system of the present invention, the primer layer applied to the substrate may also optionally contain a leveling agent on the substrate, and the primer layer may preferably be conductive itself or have no conductive or dissipative function. In an exemplary embodiment of the present invention, the dissipative synthetic resin layer (4) applied between the primer layer and the top coat is conductive and therefore may preferably have a ground resistance of at least 100 kΩ according to VDE-0100-410. It goes without saying that the dissipative synthetic resin layer is different from the top coat formed by the solvent-free polyurethane coating composition of the present invention and may be any kind of dissipative synthetic resin layer of the prior art.

[0096] Dissipative layers can also be called electrostatic conductive layers or electrostatic dissipative layers. In contrast to non-dissipative or insulating layers, they allow the accumulated electrostatic charge to dissipate. For this purpose, the dissipative layer has a certain conductivity.

[0097] The coating system according to the invention can be a floor coating system or a wall coating system, wherein it is preferably a floor coating system. The coating system has wide commercial applicability and exhibits many advantages over systems according to the prior art. The system architecture is suitable for converting existing purely insulating coatings into ESD-capable systems in a simple, cost-effective and rapid manner.

[0098] The coating system according to the invention is suitable for all floors, industrial floors and walls, in particular floors, which require ESD protection. Areas where such floors or walls are required are, for example, the electrical and electronics industry, microelectronics, high-precision optics, biotechnology, photolithography, pharmaceuticals, life sciences, the automotive industry or the manufacture of data carriers. The coating system according to the invention is suitable, for example, for clean rooms, production facilities, assembly facilities, laboratories, etc., where electrostatic charges should or must be avoided.

[0099] The dissipation capacity can be determined, for example, by the ground resistance of the layer. As used herein and if not otherwise specified, the ground resistance of the layer can be determined according to the standard IEC 61340-4-1. Here and according to the IEC 61340-4-1 and IEC 61340-5-1 standards, if the layer has a ground resistance of not more than 10 9 ohms of ground resistance, the layer is considered conductive or electrostatically conductive. Layers with higher ground resistance are non-dissipative.

[0100] The dissipative synthetic resin layer 4 and, when the preferred synthetic resin basecoat is used as basecoat, the basecoat is also based on a synthetic resin. The optional scratch coating can be based on a synthetic resin. Synthetic resin layers as floor coverings or wall coverings are well known to the person skilled in the art and are widely used in this field. If not otherwise stated, the following statements apply equally to the synthetic resin layer, the synthetic resin basecoat and the optional scratch coating.

[0101] The synthetic resin layer is produced from a cured reaction resin or reaction resin compound, wherein a reaction resin compound is generally understood to mean a reaction resin containing one or more additives, such as fillers and / or solvents.

[0102] All conventional reactive resins known to the person skilled in the art can be used for preparing the dissipative synthetic resin layer, and the synthetic resin basecoat and the optional scratch coating. The same or different reactive resins can be used for the individual layers. Reactive resins, in particular those mentioned below, can be used in solvent-free or water-based form.

[0103] The reactive resins used for the individual layers or the optional basecoat or scratch coat are preferably selected independently of one another from epoxy resins, polyurethanes, polyureas, mixtures of polyurethanes and polyureas, poly(meth)acrylates, cementitious hybrid systems and polymer-modified cementitious mixtures (PCC “polymer cement concrete”).

[0104] The additives may already be present in the reaction resin or may be mixed into the reaction resin prior to processing. Examples of possible additives, besides solvents and water, are colorants, such as colored quartz, dyes, pigments and color flakes; fillers, such as quartz sand, ceramic powder, sand, chalk, fibers, hollow spheres and glass beads; emulsifiers, thixotropic agents and film-forming aids and also suitable additives for setting the electrical properties as described above.

[0105] In principle, all substrates present in large buildings are suitable as substrates for coatings, in particular floors or floor coatings. Examples of suitable substrates are concrete, cement screeds, magnesium oxide screeds, tiles, asphalt and any synthetic resin coatings that are optionally already present.

[0106] To prepare the coating system of the invention, the primer is first applied to the substrate, optionally after conventional substrate pretreatment, such as grinding, sandblasting, shot blasting or stripping with solvents or acids. For the primer, conventional primer compositions are applied, such as reaction resins or reaction resin compounds, or water-based synthetic resin dispersions, and cured. This is preferably a synthetic resin primer based on a cured reaction resin.

[0107] A grounding device for grounding the coating system can be installed in the coating system. In the case of a non-conductive primer, the grounding device can be arranged on top of it or directly between the primer and the top coating. In the case of a conductive primer, the grounding device can be arranged below the primer or between the primer and the substrate. In order to electrically connect the static dissipative coating, the grounding device is connected to the equipotential junction. Such grounding devices are known to those skilled in the art and such personnel can easily implement them. The grounding device can be formed, for example, by a ground conductor or an arrangement of ground conductors, which are connected to the equipotential junction. The connection to the equipotential junction or the ground potential can be made by one or more ground connections.

[0108] Suitable grounding conductors include, for example, copper tape and / or so-called conductor assemblies, which are mounted to dissipate the electrical potential. Self-adhesive copper tape may be used. Conductor assemblies are commercially available; for example Conductor assembly. This conductor assembly consists of stakes with copper tape, washers and threaded rods. In this way a so-called earth point is established which can subsequently be earthed by a skilled electrician.

[0109] General processing methods and processing equipment which can be used to produce the individual layers are known to the person skilled in the art. Specific recommendations for processing certain commercially available reaction resin products can also generally be found in the relevant product data sheets.

[0110] It is also possible to design the layers as double or multilayers, but this is generally not preferred. Further intermediate layers may also be optionally arranged in the coating system. Examples of such intermediate layers are those which also have crack bridging properties (e.g. 350 or 390).

[0111] BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Figure 1 : A solution of the coating system according to the present invention; and

[0113] Figure 2 : Another embodiment of the coating system according to the present invention.

[0114] exist Figure 1In the present invention, the coating system consists of (1) a substrate, (2) a grounding means such as a copper tape, (4) a dissipative synthetic resin layer and (5) a top coating layer formed from the coating composition of the present invention.

[0115] exist Figure 2 In the figure, the coating system consists of (3) a primer layer without a conductive function, (2) a grounding device such as a copper tape, and (5) a top coating layer formed from the coating composition of the present invention. The substrate below the primer layer is not shown in the figure.

[0116] Reference numerals list

[0117] 1. Substrate

[0118] 2 Grounding device

[0119] 3. Base coat

[0120] 4 Dissipative synthetic resin layer

[0121] 5 Top coating

[0122] The following examples illustrate the present invention but are not intended to limit the scope of the invention in any way.

[0123] Example

[0124] 1. The main commercial products used are as follows:

[0125]

[0126]

[0127] 2. Preparation of coating composition:

[0128] The coating composition was prepared by mixing four components (ie, component A, component B, component C and component D) in a weight ratio of A:B:C:D of 2.83:0.75:2.13:0.62 in a suitable container under stirring until a homogeneous mixture was obtained.

[0129] Component A was formulated based on two HDI trimers with different viscosities. In Example 4, component A was based on 100 wt. % Tolonate HDT LV, whereas in the remaining examples, component A was based on 100 wt. % DESMODUR N 31000.

[0130] In each example, Component B was formulated by mixing the individual ingredients in the amounts specified in the table below.

[0131] Component C consisted of 100% by weight of white corundum having a particle size of 220 mesh (70-75 μm).

[0132] Component D was formulated by mixing 36.7 wt% CFAME (chlorinated fatty acid methyl ester), 6.8 wt% K-Flex DP, 2 wt% Uniq 680U and the remainder of green filler to form a green slurry.

[0133] Table 1. Composition of component B in the examples

[0134]

[0135]

[0136] 3. Resistance measurement method:

[0137] An electrostatic conductive system was prepared by sequentially coating a primer Sikafloor-220W, an intermediate coating Sikafloor-206W and the coating composition of each example on a substrate (non-asbestos fiber cement board).

[0138] Accordingly, a static dissipative system was also prepared by sequentially coating the primer Sikafloor-220W, the middle coating Sikafloor-237EDF and the coating composition of each example on a substrate (non-asbestos fiber cement board).

[0139] According to SJT 11294-2018 General Specification for Floor Coatings for Electrostatic Protection, the resistance Rs and Rg of the two systems were tested using the device Metr iso3000. The results are recorded in the table below.

[0140] 4. VOC content measurement method:

[0141] The VOC content was measured according to the standard GBT 23985-2009. In the measurement, a test mixture was prepared by mixing components A, B, C and D under stirring, and then placed in a test oven at 105±2°C for 1 hour after conditioning at 23±2°C and 50±5% humidity for 24 hours.

[0142] The VOC contents measured for Examples 2, 3 and 4 were 42.4 g / l, 48.3 g / l and 40.9 g / l, respectively, all lower than 60 g / l, which is the allowable limit according to national standards.

[0143]

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150] As can be seen from Example 5, when the amount of carbon fiber is low (0.8 wt%), the Rg value of the electrostatic conductive system is higher in many cases. At the same time, some resistances Rs of the electrostatic dissipative system are also much higher, which may deteriorate the electrostatic dissipative effect of the system in the long term.

[0151] Regarding Example 6, when the amount of carbon fiber was as high as 2.5 wt%, the resistance Rg of the static dissipative system was excessively lower than the requirement for static dissipative resistance. In addition, due to the high amount of carbon fiber, it was found that the surface quality of the coating was poor and it was difficult to obtain a uniform coating film.

[0152] Regarding Example 7, using a high amount (0.05 wt%) of SWCNTs, a satisfactory static dissipative system could hardly be obtained due to too low resistances Rs and Rg. In addition, the surface quality of the film was also questionable, and it was difficult to obtain a uniform coating film.

[0153] Regarding Example 8, a smaller amount of SWCNTs was used, and although a significant improvement in surface quality was found, the resistance Rs / Rg of the electrostatic conductive system was much higher.

Claims

1. A solvent-free polyurethane coating composition comprising: A) polyisocyanates having a low viscosity of less than 800 mPa.s, preferably less than 500 mPa.s, B) single-walled carbon nanotubes (SWCNTs) in the range of 0.012-0.04 wt %, such as 0.016-0.035 wt %, based on the total weight of the composition, C) Carbon fibers having a length below 0.2 mm, preferably below 0.15 mm, more preferably 0.05-0.12 mm, and in the range of 1.0-2.4 wt%, such as 1.2-2.3 wt%, based on the total weight of the composition.

2. The coating composition according to claim 1, characterized in that The polyisocyanate is selected from aliphatic, cycloaliphatic or aromatic diisocyanates, in particular HDI, TMDI, cyclohexane 1,3- or 1,4-diisocyanate, IPDI, H 12 MDI, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane, XDI, TDI, MDI, benzene 1,3- or 1,4-diisocyanate or naphthalene 1,5-diisocyanate (NDI), more preferably selected from HDI, IPDI, H 12 MDI, TDI, MDI or a form of MDI which is liquid at room temperature, in particular HDI, IPDI, TDI or an HDI trimer.

3. A coating composition as claimed in any one of the preceding claims, characterised in that The coating composition contains a further polyol for reaction with the polyisocyanate, the further polyol being selected from polyester polyols, especially aliphatic polyester polyols, or polyhydroxy-functional fats and oils, especially castor oil.

4. A coating composition as claimed in any one of the preceding claims, characterised in that The polyisocyanate contains 18% by weight or more, for example 20-30% by weight, of free NCO groups.

5. A coating composition as claimed in any one of the preceding claims, characterized in that The coating composition further contains wear particles as fillers, such as corundum, ceramics, silicon carbide, etc., preferably corundum.

6. A coating system on a substrate for preventing electrostatic discharge, comprising in the following order: a) a primer layer on said substrate, b) optionally a layer of dissipative synthetic resin, and c) A top coating layer formed from the solvent-free polyurethane coating composition according to any one of the preceding claims.

7. The coating system according to claim 5, wherein the coating system comprises a grounding device for grounding the coating system.

8. The coating system according to claim 7, wherein the grounding device is arranged on top of the primer layer or directly between the primer layer and the top layer, in particular in case of a non-conductive primer layer.

9. The coating system according to claim 7, wherein the grounding device is arranged below the primer layer or between the primer layer and the substrate, in particular in the case of a conductive primer layer.

10. The coating system of claim 7, wherein the primer layer is electrically conductive.

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