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EP-3935113-B1 - AQUEOUS COATING COMPOSITION

EP3935113B1EP 3935113 B1EP3935113 B1EP 3935113B1EP-3935113-B1

Inventors

  • MESTACH, DIRK EMIEL PAULA
  • VERHAGEN, Nicole Emile Maria
  • VAN GORKUM, Anne P.M.
  • ADOLPHS, Robert L.

Dates

Publication Date
20260506
Application Date
20200305

Claims (17)

  1. A crosslinkable aqueous vinyl polymer composition comprising: a) from 70 to 97.5 weight % of a crosslinkable oligomer stabilized dispersion PD1 of vinyl polymer P1, PD1 comprising, based on the polymer weight of vinyl polymer dispersion PD1: i) from 20 to 60 weight % on polymer solids in PD1 of a water-soluble or water-dispersible crosslinkable oligomer OL obtained by emulsion polymerizing a monomer mixture comprising : 1) at least one acid functional ethylenically unsaturated monomer M1, 2) at least one ethylenically unsaturated monomer M2 with functionality for crosslinking upon film-formation, other than M1, 3) at least one ethylenically unsaturated monomer M3 other than M1 and M2, 4) optionally, one or more multifunctional ethylenically unsaturated monomers M4 for pre-crosslinking, and ii) from 40 to 80 weight % on polymer solids in PD1 of at least one high molecular weight vinyl polymer P1 prepared by emulsion polymerizing, in the presence of the water-soluble or water-dispersible crosslinkable vinyl oligomer OL, a monomer mixture comprising: 1) optionally at least one acid functional ethylenically unsaturated monomer M1', 2) optionally one or more ethylenically unsaturated monomers M2' with functionality for crosslinking upon film-formation, other than M1', 3) at least one ethylenically unsaturated monomer M3' other than M1' and M2', and 4) optionally, one or more multifunctional ethylenically unsaturated monomers M4' for pre-crosslinking, preferably in an amount less than 5 weight %, wherein the sum of i) and ii) is 100 wt%, and wherein the solids content of the crosslinking oligomer stabilized dispersion PD1 is within the range of from 20 to 60 weight %, b) from 2 to 29.5 weight % of at least one non-oligomer stabilized dispersion PD2 of vinyl polymer P2, PD2 obtained by emulsion polymerizing a monomer mixture comprising: 1) at least one acid functional ethylenically unsaturated monomer M1", 2) optionally one or more ethylenically unsaturated monomers M2" with functionality for crosslinking upon film-formation, other than M1", 3) at least one ethylenically unsaturated monomer M3" other than M1" and M2", and 4) optionally, one or more multifunctional ethylenically unsaturated monomers M4" for pre-crosslinking, preferably in an amount less than 5 weight %, 5) optionally, in the presence of a conventional non-oligomeric, non-crosslinkable surfactant, optionally a copolymerizable surfactant, wherein the solids content of the non-oligomer stabilized dispersion PD2 is within the range of from 20 to 60 weight %, c) from 0.5 to 28 weight % of at least one crosslinker X reactive with the functional groups of monomers M2 of OL and optionally with the functional groups of monomers M2' of P1 and/or M2" of P2, based on the total weight of a), b) and c), wherein the total weight of a), b) and c) is 100 wt% of the crosslinkable aqueous vinyl polymer composition, wherein the crosslinkable aqueous vinyl polymer composition is prepared by blending the aqueous polymer dispersion PD1 comprising the oligomer stabilized vinyl polymer P1 with the aqueous dispersion PD2 comprising the vinyl polymer P2, and wherein the crosslinker X is added to PD1 and optionally PD2 prior to blending or after blending of PD1 with PD2.
  2. The composition according to claim 1, wherein the oligomer OL has an acid value of at least 45 mg KOH/g.
  3. The composition according to claim 1 or 2, wherein the oligomer OL has a number average molecular weight of from 500 to 50,000 g/mol, determined by using gel permeation chromatography (GPC) according to ISO 13885-1:2008, ASTM D3536 and ASTM D3593.
  4. The composition according to any of claims 1 to 3, wherein the oligomer OL is derived from a monomer system comprising 1-45 weight % of monomer(s) M1, 0.5 to 20 weight % of crosslinking monomer(s) M2, and 98.5-50 weight % of monomer(s) M3.
  5. The composition according to any of claims 1 to 4, wherein the number average molecular weight of vinyl polymer P1 is higher than 60,000 g/mole, determined according to ASTM D3536 and ASTM D3593.
  6. The composition according to any of claims 1 to 5, wherein vinyl polymer P1 is derived from a monomer system comprising 0 to 5 weight % of monomer(s) M1', 0 to 10 weight % of crosslinking monomer(s) M2', 80 to 100 weight % of monomer M3', and 0 to 5 weight % of monomer M4'.
  7. The composition according to any of claims 1 to 6, wherein the crosslinkable oligomer stabilized dispersion PD1 of vinyl polymer P1 comprises a high molecular weight vinyl polymer P1A and a high molecular weight vinyl polymer P1B different from polymer P1A.
  8. The composition according to claim 7, wherein the vinyl polymer P1A has a Tg which is different from the Tg of vinly polymer P1B by at least 40 °C, the Tg being calculated using the Fox equation.
  9. The composition according to any of claims 7 or 8, wherein vinyl polymer P1A is derived from a monomer system comprising 0 to 5 weight % of monomer(s) M1', 0 to 10 weight % of crosslinking monomer(s) M2', 80 to 100 weight % of non-acid functional, non-crosslinking monomer(s) M3' different from M1' and M2', and 0 to 5 weight % of monomer M4', and polymer P1B is derived from a monomer system comprising less than 1 weight % of monomer(s) M1', less than 1 weight % of monomer(s) M2', and 98 to 100 weight % of monomer M3', and 0 weight % of monomer M4'.
  10. The composition according to any of claims 1 to 9, wherein the vinyl polymer P2 contains more than 2.5 weight % of monomer M2", has a glass-transition temperature Tg between - 35 °C and 75 °C, calculated using the Fox equation, a particle size of at most 100 nm (Z-average mean according to ISO13321), a number average molecular weight of at least 100,000 g/mole, determined according to ASTM D3536 and ASTM D3593, and a MFFT below 10 °C, determined according to ASTM D2354-10.
  11. The composition according to any one of claims 1 to 9, wherein the vinyl polymer P2 has a glass-transition temperature of at least 80 °C, calculated using the Fox equation, a particle size of at most 100 nm (Z-average mean according to ISO13321), a number average molecular weight of at least 100,000 g/mole, determined according to ASTM D 3536 and ASTM D 3593, and is not film-forming at ambient temperature.
  12. The composition according to any one of claims 1 to 9, wherein the vinyl polymer P2 has a glass-transition temperature between 0 and 100 °C, a particle size between 100 and 200 nm (Z-average mean according to ISO13321), a number average molecular weight of 4,000 to 50,000 g/mole, determined according to ASTM D 3536 and ASTM D 3593, and contains 6 to 10 weight % of monomer M2".
  13. The composition according to any of claims 1 to 12, wherein the acid functional monomers M1, M1' and M1" are, each independently, selected from the group of acrylic acid and methacrylic acid, and mixtures thereof.
  14. The composition according to any of claims 1 to 13, wherein the monomers M2, M2' and, M2", are, each independently, selected from acetoacetoxyethyl methacrylate and diacetone acrylamide, and mixtures thereof.
  15. The composition according to any of claims 1 to 14, wherein the monomers M3, M3' and M3" are, each independently, selected from vinyl monomers and esters of acrylic acid and methacrylic acid of formula CH 2 =CR 1-C(O)OR2 wherein R1 is H or methyl and R2 is optionally substituted C1 to C20 alkyl, cycloalkyl, aryl or (alkyl)aryl; and mixtures thereof.
  16. The composition according to any of claims 1 to 15, wherein the crosslinker X is selected from diamines, polyamines, dihydrazides and polyhydrazides, and mixtures thereof.
  17. An aqueous coating composition comprising at least one aqueous composition according to any of claims 1 to 16 and at least one or more conventional ingredients selected from pigments, dyes, emulsifiers, surfactants, plasticizers, thickeners, heat stabilizers, levelling agents, anti-cratering agents, fillers, sedimentation inhibitors, UV absorbers, antioxidants, drier salts, organic co-solvents, wetting agents and the like, and mixtures thereof.

Description

The present invention pertains to crosslinkable aqueous vinyl polymer compositions, to a coating composition comprising said crosslinkable aqueous vinyl polymer compositions and to an article coated with the coating composition. DESCRIPTION OF THE RELATED ART Recent changes in the legislation concerning the emission of organic solvents have led to a growing interest in waterborne coating systems for industrial and decorative applications. Waterborne coating systems have been used already for a long time in applications where the decorative aspects of the coating are of more importance than the protective properties. The aqueous polymer dispersions that are used as binders in such coatings are often prepared by means of emulsion polymerization processes. Due to increasingly stringent laws concerning the allowable contents of volatile organic compounds in coatings, major efforts have been made to minimize the use of organic co-solvents in water borne coatings based on acrylic binders. However, in water borne coatings that use vinyl polymers as the main binder, the final hardness is affected by the reduction in the amount of organic co-solvents as the minimal film-formation temperature (MFFT) needs to be lowered. For some coating applications a minimum hardness is required, for example if a high blocking-resistance or mar-resistance is important. The hardness of a final coating can be increased by introducing a crosslinking mechanism into the coating composition. Introducing a crosslinking mechanism by provision of an oligomer with crosslinking groups and optionally crosslinking groups on the dispersed polymer is a well-known method to improve some of the properties (e.g. water and chemical resistance) of aqueous polymer dispersions when they are used in coating applications. Examples of these products can be found in US 5,859,112, US 5,962,571 and US 5,498,659. Waterborne ambient to medium temperature crosslinking coating compositions are commonly supplied as either one-package or two-package systems. In a one-package system, the polymer dispersion is pre-combined with a crosslinker, and is sealed in a single package for storage. In two-package systems, the binder and crosslinker are provided to the consumer in separate packets and are mixed by the consumer shortly before application to a substrate. Curing of one-package systems occurs when the coating composition is exposed to an external environment, at ambient temperature or by baking the coating after application at medium temperature, e.g. 50 - 60 °C. In two-package systems, curing occurs upon mixing and hence reaction of the binder and the crosslinker. Two-package systems suffer from the disadvantage that mixing of the components must be carried out by the consumer requiring accurate measurement and often specialized mixing equipment. One-package systems do not suffer from this disadvantage, but may suffer problems with shelf-life because the crosslinking reactants are in contact in the single package during storage. In order to be used as a one component coating, the composition must be stable, meaning that the reactive components must co-exist in a single composition that is shelf-stable. Often a one-package system makes use of the reaction between carbonyl-groups attached to the polymer with carbonyl-reactive crosslinkers. The carbonyl-groups can be introduced into the polymer by means of carbonyl-functional monomers. Carbonyl-reactive crosslinkers are usually poly-functional amines or amine derivatives such as di- or poly functional hydrazides. In case a hydrazide is used, the hydrazide groups react with carbonyl groups by a condensation reaction to form hydrazone linking bonds between the polymer chains. Water-borne polymer dispersions comprising a crosslinkable oligomer and a polymer based on such crosslinking systems possess a good combination of performance and application properties for use in aqueous coating compositions. In these coating compositions, crosslinking of the polymers takes place on drying through formation of a Schiff's base. Removal of water from the system, such as by evaporation during air drying, drives the reaction towards the crosslinked product. Since water evaporation drives the reaction, it is possible to cure such compositions at ambient or medium temperatures. However, the use of said coating compositions is sometimes limited because it is not uncommon for these one-package systems to show viscosity-instability upon storage or when formulating them into paint. The viscosity behavior of the formulated paint also affects the application properties of the coating, also referred to as the open time (OT). More particularly, a layer of a coating composition freshly applied to a substrate is said to be open when it is still in a state where it can be manipulated during the curing without leaving substantial visible defects in the cured coating. The open time is the period of time between the point of first application of a co