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US-12624217-B2 - Coated pigment and method of making

US12624217B2US 12624217 B2US12624217 B2US 12624217B2US-12624217-B2

Abstract

The invention provides a method for applying a new form of protective coating to substrates such as pigments, and also the coated substrates obtainable by this method. The coating are characterized by the fact that they impart good chemical resistivity to the substrate whilst also preserving its optical properties.

Inventors

  • Phu Qui Nguyen

Assignees

  • ECKART GMBH

Dates

Publication Date
20260512
Application Date
20200205
Priority Date
20190205

Claims (20)

  1. 1 . A method of coating a substrate, the method consisting of: (a) a step of reacting a mixture consisting of an inorganic network former and an organofunctional network former in a condensation-type reaction, optionally in the presence of a solvent, to form a reaction product on the substrate, and subsequently: (b) one or more further steps of reacting a mixture consisting of an inorganic network former and an organofunctional network former in a condensation-type reaction in the presence of the reaction product from step (a) and optionally in the presence of a solvent, wherein the organofunctional network former used in the method consists of one or more compounds of formula (II): R 1 i R 2 j R 3 k SiX (4-i-j-k) (II) wherein each of i, j and k is independently 0 or 1, provided that at least one of i, j and k is 1, each of R 1 , R 2 and R 3 is independently an organic group, provided that at least one of R 1 , R 2 and R 3 is a reactive organic group, and each X is independently an optionally hydrolyzable and/or condensable group selected from the group consisting of halogen, —OH, —OR′, or —Y, and/or one pair of X moieties together represent a divalent chelating ligand, wherein each R 7 is independently an organic group, and each Y is independently —(O—R 4 —O—Si(R 5 ) m (X′) 2-m —) n R 6 , wherein each R 4 is independently a divalent organic group, each R 5 is independently an organic group, each m is independently 0, 1 or 2 each X′ is independently an optionally hydrolyzable and/or condensable group selected from halogen, —OH, or —OR 7 , and/or one or more pairs of geminal X′ moieties together represent a divalent chelating ligand, wherein each R 7 is independently an organic group, n is 1 to 10, and R 6 is an organic group.
  2. 2 . A method according to claim 1 , wherein part (b) consists of one or two further steps in which an inorganic network former and an organofunctional network former are subjected to a condensation-type reaction.
  3. 3 . A method according to claim 1 , wherein the substrate is a metal or metal oxide.
  4. 4 . A method according to claim 1 , wherein the substrate is a metal pigment.
  5. 5 . A method according to claim 1 , wherein the substrate comprises, or is, an aluminium, bronze, copper or zinc pigment.
  6. 6 . A method according to claim 5 , wherein the substrate is an aluminium pigment and the proportion of aluminium is ≥99% by weight based on the total weight of the uncoated aluminium pigment.
  7. 7 . A method according to claim 1 , wherein the inorganic network former is a compound of formula (I): MX n (I) wherein M is Si, Al, Ti, Zr, B, Fe, Mg, Mn, Sb, Cr, Zn and/or Ce, each X is independently an optionally hydrolysable and/or condensable group selected from halogen, —OH, or —OR, and/or one, two or three pairs of X moieties together represent a divalent chelating ligand, wherein each R group is a C1-10 alkyl group in which the carbon chain is optionally interrupted by one or more heteroatoms selected from N, O and S, and n is an integer from 2 to 6 and corresponds to the oxidation state of M.
  8. 8 . A method according to claim 7 , wherein M is Si, Al, Ti, Zr or Fe, each X is C1-6 alkoxy, and n is 2, 3 or 4.
  9. 9 . A method according to claim 7 , wherein M is Si, X is methoxy or ethoxy, and n is 4.
  10. 10 . A method according to claim 1 , wherein each reactive organic group is, independently, a hydrocarbyl group having one or more substituents selected from epoxy, amino, hydroxyl, thiol, acrylate, methacrylate, vinyl, allyl, alkenyl, alkynyl, carboxyl, carboxylic anhydride, isocyanate, cyanate, ureido and carbamate.
  11. 11 . A method according to claim 1 , wherein the organofunctional network former is selected from: 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-(n-butyl)-3-amino- propyltrimethoxysilane, N-(n-butyl)-3- amino-propyltriethoxysilane, N-2-aminoethyl-3- aminopropyl(methyl)dimethoxysilane, N-2- aminoethyl-3-aminopropyl(methyl) diethoxysilane, N-2-aminoethyl-3- aminopropyltrimethoxysilane, N-2- aminoethyl-3-aminopropyltriethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-ureidopropyltrimethoxysilane, and 3-ureidopropyltriethoxysilane.
  12. 12 . A method according to claim 1 , wherein: the inorganic network former in each of step (a) and (b) is, independently, a tetraalkoxysilane, the organofunctional network former in step (a) is an epoxysilane or an aminosilane, and the organofunctional network former in step (b) is an epoxysilane.
  13. 13 . A method according to claim 1 , wherein the substrate is a metal pigment, and the coated metal pigment or coated metal oxide pigment has a value of at least 40 mJ·m 2 /g for MIE*surface area, wherein MIE is the minimum ignition energy and the surface area is the surface area as measured by the BET method.
  14. 14 . A method according to claim 1 , wherein the substrate is a pigment having (i) a d 50 value of ≤30 μm and (ii) an average aspect ratio of at least 100.
  15. 15 . A method comprising: applying one or more surface modifiers to the coated substrate produced by the method of claim 1 , wherein the substrate is a pigment.
  16. 16 . A method according to claim 15 , wherein said one or more surface modifiers include (a) both (i) an organophosphorous compound, and (ii) a compatibilizer having a molecular weight of 5,000 or less, and wherein the organophosphorous compound and compatibilizer are applied simultaneously, separately or sequentially; (b) both (i) a fatty acid, and (ii) a compatibilizer having a molecular weight of 5,000 or less, and wherein the fatty acid and compatibilizer are applied simultaneously, separately or sequentially; or (c) both (i) an organofunctional network former, and (ii) an organophosphorous compound and wherein the organofunctional network former and organophosphorous compound are applied simultaneously, separately or sequentially.
  17. 17 . A method according to claim 15 , wherein said one or more surface modifiers include both (i) an organophosphorous compound, and (ii) a compatibilizer having a molecular weight of 5,000 or less, and wherein the organophosphorous compound and compatibilizer are applied simultaneously, separately or sequentially.
  18. 18 . A method according to claim 17 , wherein the organophosphorus compound is a compound of formula (III): I-X-P (O)(OR 1 )(OR 2 ) (III) R 1 and R 2 are each independently H, optionally substituted hydrocarbyl, optionally substituted amine, polyether, an ammonium ion, an alkali metal, or an alkaline earth metal; X is divalent and is (a) a straight or branched hydrocarbon chain, said hydrocarbon chain being optionally interrupted by one or more heteroatoms selected from O, S and N, (b) an optionally substituted carbocyclic ring, wherein said ring is selected from cycloalkyl, cycloalkenyl, aryl and a fused carbocyclic group, or (c) an optionally substituted heterocyclic ring including one or more heteroatoms selected from O, S and N; and Iis H or an initiator moiety for polymerization.
  19. 19 . A method according to claim 18 , wherein R 1 and R 2 are H; X is C 4-14 alkylene; and I is H.
  20. 20 . A method according to claim 17 , wherein the compatibilizer is a melamine resin, an isocyanate resin, a polyurethane resin or an acrylic resin.

Description

The present invention relates to a new form of protective coating that can be applied to substrates such as pigments. It also relates to a new method of treating pigments, including in particular pigments to which the new protective coating of the invention has been applied, so as to provide them with improved properties. In particular, the invention enables the production of stabilized fine pigments (e.g. aluminium pigments) with a superior combination of optical properties (e.g. gloss and/or lightness) and chemical resistance. BACKGROUND TO THE INVENTION Protective coatings are known in the art. For instance, metallic effect pigments such as those based on aluminium, bronze, iron oxide or steel can react with water, acids or bases in coating or ink formulations, and so the addition of a protective coating to such pigments may therefore be used to improve their chemical resistance. One drawback associated with applying such protective coatings to pigments, though, is that it may generally be expected to impact negatively on their optical properties. So there is often a trade-off between the potentially competing aims of optimising the chemical resistance and also maintaining good optical properties with pigments. For instance, among known commercially available coated aluminium (Al) pigments, those sold by Eckart under the “PCU” trade name have been described as being the best Al pigment product in the market in terms of chemical resistance. However, this useful attribute comes at the expense of the optical properties of the pigment. This is illustrated, for instance, in FIG. 2, which is an image of two polymer powder coating samples. One of them features PCU1000 pigment, and the other features pigment particles having the same particle size (namely 15 μm) but sold by Schlenk under the trade name POWDAL 8500 and having a different protective coating. As explained in more detail below, the POWDAL 8500 product can be seen to have better optical properties, but inferior chemical resistivity. Other coated pigments that have been discussed in the art include those described in CN106317969, CN106700662, WO9638506 and US20110195244 and include coatings prepared using poly addition reactions. SUMMARY OF THE INVENTION The present invention is based on the finding that a particular method of coating a pigment leads to a product with a surprisingly advantageous combination of both chemical resistivity and optical properties. Thus, the present invention provides a method of coating a substrate, the method comprising (a) a step of subjecting an inorganic network former and an organofunctional network former to a condensation-type reaction, and subsequently (b) one or more further steps in which an inorganic network former and an organofunctional network former are subjected to a condensation-type reaction. The present invention also provides a method of preparing a coated substrate, the method comprising one or more steps in which an inorganic network former and an organofunctional network former are subjected to a condensation-type reaction in the presence of a product, wherein said product is obtainable by subjecting an inorganic network former and an organofunctional network former to a condensation-type reaction in the presence of the substrate. This aspect of the invention focuses on just step (b) of the method of the invention as defined above. The preferred aspects of the invention as outlined herein apply correspondingly to this embodiment. In this regard, coated substrates prepared by the above process have been found to enable a combination of high chemical resistivity and good optical properties that is believed to be unobtainable using previous coating methods. Also, the coating which results from the above process is believed to be more effective at reducing the likelihood of ignition during subsequent processing and handling as compared to coatings applied using previous coating methods. Also, the coating which results from the above process is believed to be more effective at improving gassing stability as compared to coatings applied using previous coating methods. However, the precise structural differences that result from using a method including the two steps (a) and (b) may not always be immediately susceptible to simple and immediate characterisation, and so the new products are most appropriately defined by reference to the particular combination of properties that they exhibit. Thus, the present invention also provides a coated substrate obtainable by the method of the invention as defined above. Also, the present invention provides a coated metal pigment or coated metal oxide pigment which (i) has a chemical resistivity score of no more than 12 in the “Test method for measuring chemical resistivity of coated pigments” set out further below, and (ii) has a gloss variance value (X) of ≤5.0, wherein: X=Y/(13−the chemical resistivity score of the coated pigment),Y is the percentage change in gloss