The present invention relates to polymer particles which can be used as matting agent in aqueous coating compositions to provide a coating that have a high matt (i.e. low gloss) finish and also have a smooth feel.

Coating compositions which give a substrate a matt surface are of considerable interest for aesthetic and other reasons. In comparison with a highly glossy surface, a matt surface is superior to hide surface imperfections and does not require to be cleaned very frequently since for example fingerprints are less visible. The most common method to reduce the gloss of a coating is to add matting agents. Typically, these matting agents are inorganic particles of calcium carbonate, silica, and the like, that lower the gloss by increasing the surface roughness of the coating. While effective at reducing the gloss, the inorganic particles compromise the durability and performance of the resulting coating.

Also, coatings with special tactile properties are more and more desired. Tactile impression and touching is a subconscious process that is regarded very important in the perception of materials. The industry wants their product to stand out and get noticed and in particular packaging with smooth feel surface are in high demand.

Aqueous acrylic copolymer coating compositions are widely used in the coating industry. However, usually upon drying of the aqueous coating composition glossy surfaces are obtained.

It is also known to use non-film-forming micron-sized acrylic copolymer particles for imparting gloss reduction to an acrylic latex coating composition. When applying non- film-forming micron-sized acrylic polymer particles to reduce the gloss, a key aspect to steer the smoothness of the feel and matting properties of a coating is the control of the particle size and the particle size distribution of the non-film-forming micron-sized particles. The presence of too many small, nano-sized particles (particle size less than 500 nm, in particular less than 100 nm) do not or hardly contribute to the reduction of gloss while micron-sized particles with a particle size greater than the thickness of the coating may result in a gritty feel of the coating. Thus preparing micron-sized particles with a narrow particle size distribution, in particular particles with a volume average particle size diameter dso of from 900 nanometre to 6 micrometre and a narrow particle size distribution which can be advantageously applied as matting agent for coatings with a dry thickness of preferably at most 6 micrometre (such as film packaging, varnishes, primers, inks or top coats to protect for example printed text or graphics) is highly desired.

US5,346,954 describes a process for preparing core-shell particles with an average diameter of from 2 to 15 pm and a particle size distribution such that at least 90% by weight of the particles fall within approx. 20% of the average particle diameter. The process comprises A) polymerizing a first aqueous emulsion to produce a particulate composition comprising polymer particles; B) performing one or more times the steps of 1) swelling the particles of the particulate composition produced in A), or if appropriate the particles of B), with one or more monomers, and 2) polymerizing the swelling monomer within the particles until all of the monomers have been polymerized; and c) polymerizing one or more monomers which are polymerizable to form a polymer compatible with the matrix polymer to produce the core-shell polymer particles. The monomer composition used for swelling the particles is free of monomers containing carboxylic acid groups and polymerizing the swelling monomer within the particles until all of the monomers have been polymerized is effected in the presence of an oil-soluble organic free radical initiator. The patent publication also describes the use of the micron sized particles to reduce the gloss of coating compositions comprising a matrix polymer. It has however been found that using the micron sized particles as described in this patent publication as matting additive for coating compositions comprising a matrix polymer may result in that the smoothness of the coating appearance is negatively affected.

The object of the present invention is to provide a process for preparing acrylic particles with a volume average particle size diameter dso of from 900 nanometre to 6 micrometre and with a narrow particle size distribution whereby the growing of the particles is effected in a controlled way, i.e. particles with the desired particle size and a small particle size distribution can be obtained (i.e. the measured particle size being close to the theoretically calculated particle size) resulting in that the particles can be used for efficiently reducing the gloss of the coatings and obtaining coatings with smooth feel, while preferably also the smoothness of the coating appearance is improved. It is believed that in the process of the invention secondary nucleation and agglomeration of particles does not occur to such extent that it would result in substantial deviations of the obtained particle size and/or in substantial broadening of the particle size distribution. The object has surprisingly been achieved by providing a process for preparing an aqueous particulate composition of particles with a volume average particle size diameter dso of from 900 nanometre to 6 micrometre comprising:

I. Preparing an aqueous seed particulate composition (I .A) of seed polymer particles with a volume average particle size diameter dso of lower than 700 nanometre by emulsion polymerising of a monomer composition (I) in water in the presence of a chain transfer agent, wherein the monomer composition (I) comprises

(I. a) from 0 to 20 wt.%, preferably from 0.1 to 20 wt.%, more preferably from 0.2 to 15 wt.%, more preferably from 0.5 to 8 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and

(I.b) from 80 to 100 wt.%, more preferably from 80 to 99.9 wt.%, more preferably from 85 to 99.8 wt.%, more preferably from 92 to 99.5 wt.%, of ethylenically unsaturated monomers different from monomers (I. a), wherein the amounts of (I. a) to (I.b) are given relative to the total weight amount of the monomer composition (I),

II. Polymerizing a monomer composition (II) in water in the presence of seed polymer particles, with a volume average particle size diameter dso of lower than 700 nanometre, of the seed particulate composition (I. A) and in the presence of an oil-soluble organic free radical initiator and/or a water-soluble ionic free radical initiator by starve feed adding at least the monomer composition (II) and the oil-soluble organic free radical initiator and/or the water-soluble ionic free radical initiator to seed particles of the seed particulate composition (I. A) to form first generation particles, wherein the monomer composition (II) comprises

(II. a) from 0.05 to 10 wt.%, preferably from 0.1 to 8 wt.%, more preferably from 0.15 to 6 wt.% and most preferably from 0.2 to 6 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and (II. b) from 90 to 99.95 wt.%, more preferably from 92 to 99.9 wt.%, more preferably from 94 to 99.85 wt.% and more preferably from 94 to 99.8 wt.% of ethylenically unsaturated monomers different from monomers (II. a); wherein the amounts of (II. a) to (II. b) is given relative to the total weight amount of the monomer composition (II), and III. Optional sequentially repeating step II. N times to obtain (N+1) ^th generation particles by starve feed adding at least monomer composition (II) and oil-soluble organic free radical initiator and/or water- soluble ionic free radical initiator to a mixture comprising water and particles generated in the previous step, where N is a number of 1 to 10, wherein the polymerisation to obtain the first generation particles and each subsequent polymerisation, if any, to obtain the N ^th generation particles are effected in the presence of a chain transfer agent, and wherein at least 80 wt.% of the ethylenically unsaturated monomers (I.b) and

(II.b) are ethylenically mono-unsaturated monomers selected from the group consisting of C alkyl (meth)acrylates, aryl alkylenes and any mixture thereof.

It has surprisingly been found that with the process of the invention particles with a volume average particle size diameter dso of from 900 nanometre to 6 micrometre and with a narrow particle size distribution can be obtained in a controlled way, and in addition the narrow particle size distribution can also be substantially maintained whereby the growing of the particles is effected in a controlled way. It has surprisingly been found that despite the use of carboxylic acid monomer in the polymerisation steps to grow the seed polymer particles a narrow particle size distribution of the particles can still be obtained. Without wishing to be bound to any theory, it was believed that the use of carboxylic acid monomer in the polymerisation steps to grow the seed particles would result in secondary nucleation and hence broadening of the particle size distribution. Narrow particle size distribution is advantageous since in terms of feel it will suppress the gritty feel sensation whereas for matting it will result in a higher efficient gloss control. Thus with the particles of the present invention matt coatings with a smooth feel surface can be obtained. It has furthermore surprisingly been found that the ability to use acid group containing monomers in the growth steps enables to improve the smoothness of the coating appearance. A further advantage of the present invention is that the ability to use acid group containing monomers in the growth steps may provide improved storage stability and/or may provide advantages with respect to interaction with pigments and adhesion to substrates like metals. It has also been found that the free radical initiation of the polymerisation steps to grow the seed polymer particles can also be effected by using water-soluble ionic free radical initiators, while a narrow particle size distribution of the particles can surprisingly still be obtained. Without wishing to be bound to any theory, it was believed that the use of water-soluble ionic free radical initiator in the polymerisation steps to grow the seed particles would result in secondary nucleation and hence broadening of the particle size distribution. It has furthermore surprisingly been found that using water-soluble ionic free radical initiators in the polymerisation steps to grow the seed polymer particles in step II. and, if present, in step III. results in improved in-process dispersion stability which results in less equipment fouling.

For all upper and/or lower boundaries of any range given herein, the boundary value is included in the range given, unless specifically indicated otherwise. Thus, when saying from x to y, means including x and y and also all intermediate values.

The term "coating composition" encompasses, in the present description, paint, film, varnish, primer, top coat and ink compositions, without this list being limiting.

Starve feed adding at least the monomer composition (II) and the oil-soluble organic free radical initiator and/or the water-soluble ionic free radical initiator to seed polymer particles of the seed particulate composition (I. A) produced in I. or to polymer particles generated in a previous step means charging seed polymer particles or polymer particles generated in the previous step to a reactor and continuously feeding to the reactor the monomer composition (II) and the free radical initiator (i.e. the oil-soluble free radical initiator and/or the water-soluble ionic free radical initiator) in precise quantities such that the reaction ensues nearly instantaneously and completely upon exposure to the reaction conditions (i.e. at a temperature preferably at least as high as that at which the initiator is activated), preferably a reaction temperature of from 70 to 95°C and at atmospheric pressure. A starved feed polymerization in the context of the present invention is regarded as being a polymerization in which the content of the unreacted monomers in the reaction solution is minimized over the duration of the reaction, meaning that the monomer composition and the free radical initiator are metered in in such a way that a concentration of unreacted monomer of preferably 12 wt.%, more preferably 10 wt.%, even more preferably 8 wt.%, even more preferably 5 wt.%, even more preferably 4 wt.%, even more preferably 3 wt.% and most preferably 2 wt.%. in the reaction solution, based in each case on the particle weight of the dispersion and preferably on the total amount of monomer composition, is not exceeded over the entire duration of the reaction.

The amount of unreacted monomer in the reaction solution at any time during step II. and, if present, during step III. is preferably at most 12 wt.%, more preferably at most 10 wt.%, more preferably at most 8 wt.%, even more preferably at most 5 wt.%, even more preferably at most 4 wt.%, even more preferably at most 3 wt.% and most preferably at most 2 wt.% of the particle weight of the dispersion and preferably on the total amount of monomer composition. The concentration of unreacted monomer in the reaction solution can be determined by gas chromatography.

The volume average particle size diameter dso of the final polymer particles obtained in the process according to the invention is from 900 nanometre to 6 micrometre, preferably from 1 pm to 6 pm, more preferably from 1 to 5 pm, even more preferably from 1 pm to 4 pm, even more preferably from 1 pm to 3.5 pm. In one embodiment of the invention, the volume average particle size diameter dso of the final polymer particles obtained in the process according to the invention is preferably from 2 pm to 4 pm, more preferably from 2 pm to 3.5 pm and even more preferably from 2.5 pm to 3.5 pm. In another embodiment of the invention, the volume average particle size diameter dso of the final polymer particles obtained in the process according to the invention is preferably from 1 pm to 2.5 pm, more preferably from 1.5 pm to 2 pm. The volume average particle size distribution (dgo-dio)/dso (span) of the final particles obtained in the process according to the invention is preferably from 0.2 to 0.9, more preferably from 0.25 to 0.8, more preferably from 0.3 to 0.7 and even more preferably from 0.3 to 0.5. With the process of the invention, particles can advantageously be obtained which are substantially spherical, which is in particular beneficial for the smoothness of the coating, and which are non-aggregated, which is in particular beneficial for the dispersion stability. Volume average particle size diameter (d50) and particle size distribution (defined as (d90-d10)/d50) are analyzed using laser diffraction with Malvern Mastersizer 3000 Particle Size Analyzer as described in ISO Standard 13320 (2009) equipped with a hydro LV sampler and demineralized water as dispersant (Refractive Index =1.33). Material settings: a refractive index of 1.35, an absorption index of 0.60 and a density of 1 g/cm3. Sample is measured 3 times using continuous ultrasonic (setting at 50%) having a measurement loop of 30sec using red light (630nm) and 30sec using blue light (470nm). Average result will be reported as volume average particle size diameter d50, d10 and d90. d50 is defined as the particle size for which 50 percent by volume of the particles has a diameter lower than the d50. d10 is defined as the particle size for which 10 percent by volume of the particles has a diameter lower than the d10. d90 is defined as the particle size for which 90 percent by volume of the particles has a diameter lower than the d90.

The process of the present invention for preparing an aqueous dispersion comprising particles with a volume average particle size diameter dso of from 900 nanometre to 6 micrometre comprises at least steps I. and II. and optionally step(s) III.:

I. Preparing an aqueous seed particulate composition of seed polymer particles with a volume average particle size diameter dso of lower than 700 nanometre and

II. Preparing an aqueous particulate composition of particles with a volume average particle size diameter dso of from 900 nanometre to 6 micrometre by polymerizing a monomer composition (II) comprising (II. a) ethylenically mono-unsaturated monomers containing carboxylic acid groups and (II. b) ethylenically unsaturated monomers different from monomers (I I. a) in water in the presence of the seed polymer particles with a volume average particle size diameter dso of lower than 700 nanometre, and in the presence of an oil-soluble organic free radical initiator and/or a water-soluble ionic free radical initiator by starve feed adding at least the monomer composition (II) and the oil-soluble organic free radical initiator and/or the water-soluble ionic free radical initiator to seed particles of the seed particulate composition, and

III. Optional sequentially repeating step II. N times to obtain (N+1) ^th generation particles by starve feed adding at least monomer composition (II) and oil-soluble organic free radical initiator and/or water-soluble ionic free radical initiator to a mixture of at least water and particles generated in the previous step, where N is a number of 1 to 10, preferably 1 to 5, more preferably 1 to 3, to obtain an aqueous particulate composition of particles with a volume average particle size diameter dso of from 900 nanometre to 6 micrometre.

The aqueous seed particulate composition of seed polymer particles with a volume average particle size diameter dso of lower than 700 nanometre is prepared by emulsion polymerising of a monomer composition (I) in water to prepare an aqueous particulate composition (I. A). The seed polymer particles with a volume average particle size diameter dso of lower than 700 nanometre used in step II. of the process of the invention is prepared by an emulsion polymerisation process known to those skilled in the art. Methods for preparing vinyl polymers by free-radically initiated emulsion polymerization in an aqueous medium are known in the art and are described in for example Handbook Emulsion Polymerization: Theory and Practice, 1975, by D.C. Blackley (ISBN 978-0- 85334-627-2). Emulsion polymerization can produce particles up to about 0.5-1.0 micrometre having a relatively narrow particle size distribution, but the size is limited by the nature of an emulsion. Suitable free-radical-yielding water-soluble initiators for the free-radically initiated emulsion polymerization I. include persulphates such as ammonium, K and Na salts of persulphate, or redox initiator systems; combinations such as t-butyl hydroperoxide or hydrogen peroxide or cumene hydroperoxide, with isoascorbic acid or sodium formaldehydesulphoxylate, and optionally FeEDTA are useful. The free-radical-yielding initiators for the emulsion polymerization I. is preferably a persulfate, more preferably ammonium persulfate. The amount of initiator or initiator system fed in step I. is generally from 0.05 to 3 wt.%, preferably from 0.1 to 1.5 wt.%, more preferably from 0.25 to 0.75 wt.%, relative to the monomer composition (I).

The volume average particle size diameter dso of the emulsion-polymer seed particles of the seed particulate composition (I. A) produced in I. is preferably from 200 nm to 700 nm, more preferably from 250 nm to 700 nm, even more preferably from 300 to 600 nm and even more preferably from 300 to 500 nm. Emulsion polymerisation process inherently produce particles of relatively narrow particle-size distribution. The volume average particle size distribution (dgo-dio)/dso (span) of the seed polymer particles of the seed particulate composition (I.A) produced in I. is usually from 0.1 to 0.7, preferably from 0.2 to 0.65, more preferably from 0.3 to 0.65 and even more preferably from 0.45 to 0.6. One skilled in the art will understand how to vary the emulsion polymerization conditions to produce particles having a volume average particle size diameter dso and a volume average particle size distribution as described above.

Surfactants can be utilized in the emulsion polymerization to prepare the aqueous seed particulate composition of seed polymer particles with a volume average particle size diameter dso of lower than 700 nanometre. Suitable surfactants include conventional anionic and/or non-ionic surfactants and mixtures thereof such as Na, K and NH4 salts of dialkylsulphosuccinates, Na, K and NH ₄ salts of sulphated oils, Na, K and NH ₄ salts of alkyl sulphonic acids, Na, K and NhU alkyl sulphates, alkali metal salts of sulphonic acids; fatty alcohols, ethoxylated fatty acids and/or fatty amides, and Na, K and NhU salts of fatty acids such as Na stearate and Na oleate. Other anionic surfactants include alkyl or (alk)aryl groups linked to sulphonic acid groups, sulphuric acid half ester groups (linked in turn to polyglycol ether groups), phosphonic acid groups, phosphoric acid analogues and phosphates or carboxylic acid groups. Non-ionic surfactants include polyglycol ether compounds and preferably polyethylene oxide compounds as disclosed in "Non-Ionic Surfactants - Physical Chemistry" edited by M.J. Schick, M. Decker 1987. Preferred surfactants are anionic surfactants. If surfactant is used, the amount of added surfactant used is preferably 0.03 to 3% by weight based on the weight of the monomer composition (I). Preferably the emulsion polymerization to prepare the aqueous seed particulate composition of seed polymer particles is effected in the absence of added surfactant. The polymerisation to obtain the seed polymer particles (I. A), the polymerisation to obtain the first generation particles, and the polymerisation in each subsequent growth step, if any, to obtain the N ^th generation particles are effected in the presence of a chain transfer agent in order to control the molecular weight of the polymer.

Accordingly, steps I., II. and each subsequent growth step (if any) of the process of the invention up to the final growth step are effected in the presence of a chain transfer agent. The final growth step (i.e. the polymerisation to obtain the (N+1) ^th generation particle) can be carried out in the absence of chain transfer agent, but is preferably also carried out in the presence of a chain transfer agent.

Accordingly, steps I., II. and, if present, step III. of the present invention are preferably effected in the presence of a chain transfer agent. Preferred chain transfer agents include alkyl mercaptanes and alkyl halogenides. More preferred, the chain transfer agent is selected from the group of lauryl mercaptane, 3-mercapto propionic acid, i- octyl thioglycolate, mercaptoethanol, tetrabromo methane, or tribromo methane. Most preferably the chain transfer agent is a mercaptane, selected from the group of lauryl mercaptane, 3-mercapto propionic acid, i-octyl thioglycolate, and mercaptoethanol.

The monomer composition (I) comprises

(I. a) from 0 to 20 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and (I.b) from 80 to 100 wt.% of ethylenically unsaturated monomers different from monomers (I. a).

Monomer (I. a) is preferably present in the monomer composition (I) because this advantageously results in increased compatibility of the monomer composition (II) and the seed particles of the seed particulate composition (I. A).

Preferably, the monomer composition (I) comprises

(I. a) from 0.1 to 20 wt.%, of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and

(I.b) from 80 to 99.9 wt.% of ethylenically unsaturated monomers different from monomers (I. a).

Preferably, the monomer composition (I) comprises

(I. a) from 0.2 to 15 wt.%, of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and

(I.b) from 85 to 99.8 wt.% of ethylenically unsaturated monomers different from monomers (I. a).

More preferably, the monomer composition (I) comprises

(I. a) from 0.5 to 8 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and

(I.b) from 92 to 99.5 wt.% of ethylenically unsaturated monomers different from monomers (I. a).

Even more preferably, the monomer composition (I) comprises (I. a) from 0.5 to 6 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and

(I.b) from 94 to 99.5 wt.% of ethylenically unsaturated monomers different from monomers (I. a).

The amounts of (I. a) to (I.b) are given relative to the total weight amount of the monomer composition (I). Preferably, the amounts of monomers (I. a) to (I.b) add up to 100 wt.%, i.e. the monomer composition (I) preferably consists of monomers (I. a) and (I.b).

The carboxylic acid functional ethylenically mono-unsaturated monomers (I. a) are preferably selected from the group consisting of acrylic acid, methacrylic acid, b- carboxyethyl acrylate, citraconic acid, crotonic acid, fumaric acid, itaconic acid, monoalkyl esters of itaconic acid such as for example monomethyl itaconate, maleic acid, and potentially carboxylic acid functional olefinically unsaturated monomers such as itaconic anhydride or maleic anhydride, and combinations thereof. Monomer (l.a) is more preferably selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, fumaric acid and mixtures thereof. Even more preferred monomers (l.a) are methacrylic acid and/or acrylic acid. Most preferred monomer (l.a) is methacrylic acid.

The monomers (I.b) are ethylenically unsaturated monomers which are different from monomers (l.a) and are amenable for copolymerization with monomers (l.a). At least 80 wt.%, preferably at least 90 wt.%, more preferably at least 92 wt.%, more preferably at least 94 wt.% and most preferably 100 wt.% of the total amount of monomers (I.b) are ethylenically mono-unsaturated monomers, and thus ethylenically mono- unsaturated monomers constitute the main monomers (I.b). The main monomers (I.b) are selected from the group consisting of C alkyl methacrylates, C alkyl acrylates, aryl alkylenes and any mixture thereof. Suitable aryl alkylene monomers may be selected from: styrene, a-methyl styrene, vinyl toluene, t-butyl styrene, di-methyl styrene and/or mixtures thereof, especially styrene and/or a-methyl styrene. Most preferred aryl alkylene monomer is styrene. Preferred (meth)acrylates are CMO alkyl (meth)acrylate(s), for example Ci-s alkyl (meth)acrylate(s). Suitable (meth)acrylate(s) may be selected from: methyl (meth)acrylate, ethyl (meth)acrylate, 4-methyl-2-pentyl (meth) acrylate, 2-methylbutyl (meth) acrylate, isoamyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-octyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and/or mixtures thereof. More preferably, the main monomers (I.b) are selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl methacrylate, n-butyl acrylate, sec-butyl methacrylate, sec-butyl acrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-octyl acrylate, 2-octyl methacrylate, styrene, and any mixture thereof. Even more preferably, the main monomers (I.b) are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-octyl acrylate, 2- octyl methacrylate or any mixture thereof.

Optionally crosslinking monomers (I.b) suitable for use as the crosslinker in the seed polymer particle are used which are generally ethylenically polyunsaturated monomers in which the ethylenically unsaturated groups have approximately equal reactivity, as for example divinylbenzene, glycol di- and trimethacrylates and glycol di- and triacrylates. Preferred crosslinking monomers (I.b) are butylene glycol diacrylates and propylene glycol diacrylates. Most preferred crosslinking monomers (I.b) are dipropyleneglycol diacrylate and dibutyleneglycol diacrylate. Optionally graftlinking monomers (I.b) are used which are generally ethylenically polyunsaturated monomers having two or more non-conjugated double ethylenically bonds of differing reactivity, as for example allyl methacrylate, diallyl maleate and allyl acryloxypropionate. Most preferred graftlinking monomer (I.b) is allyl methacrylate. If crosslinking and/or graftlinking monomers (I.b) are employed, it is preferably used in in an amount of from 0.5 to 10 wt.%, more preferably from 0.1 to 5 wt.%, and most preferably from 0.1 to 1 wt.%, based on the total amount of monomers (I.b).

However, in one embodiment of the present invention advantageously the polymer of the seed polymer particle is substantially free of, more advantageously have no crosslinking and graftlinking monomers. In this embodiment, the ethylenically unsaturated monomers (I.b) are ethylenically mono-unsaturated monomers selected from the group consisting of C alkyl (meth)acrylates, aryl alkylenes and any mixture thereof. Preferred aryl alkylenes are styrene and/or a-methyl styrene, most preferred aryl alkylene is styrene. Preferred (meth)acrylates are CMO alkyl (meth)acrylate(s), for example Ci-s alkyl (meth)acrylate(s). Preferably, the ethylenically unsaturated monomers (I.b) are selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl methacrylate, n-butyl acrylate, sec-butyl methacrylate, sec-butyl acrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-octyl acrylate, 2-octyl methacrylate, styrene and any mixture thereof. More preferably, the ethylenically unsaturated monomers (I.b) are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-octyl acrylate, 2-octyl methacrylate or any mixture thereof.

The glass transition temperature T _g of the polymer of the seed particles of the seed particulate composition (I. A) produced in I. is preferably in the range from 0 to 150°C, more preferably from 20 to 100°C, most preferably form 30 to 80°C. As used herein, the glass transition temperature is determined by calculation by means of the Fox equation. Thus, the T _g in Kelvin, of a copolymer having "n" copolymerized comonomers is given by the weight fractions W of each comonomer type and the T _g ’s of the homopolymers (in Kelvin) derived from each comonomer according to the equation: T _g = 1/(å(W _n /Tg _n )

The glass transition temperatures of homopolymers may be found, for example, in "Polymer Handbook", edited by J. Brandrup and E.H. Immergut.

The weight average molecular weight M _w of the polymer of the seed particles of the seed particulate composition (I. A) produced in I. is preferably in the range from 5 to 50 kDaltons. As used herein, the weight average molecular weight M _w is determined by Size Exclusion Chromatography (SEC) using a method which is a modification of ISO/FDIS 13885-1 and DIN 55672:

Weigh-in approximately 32 mg sample (re-calculated to 100% solids) into a 10ml culture tube with screw cap and PTFE inlay. Add approximately 8 ml Tetrahydrofuran (THF), 99.8%, stabilised with Bis Hydroxy Toluene (250 mg per liter) and mix regularly until completely dissolved. Accordingly, 1mI_ is injected on a SEC apparatus consisting of eluent reservoir, degasser, pump delivering a pulse free reproducible and constant flow (Flow rate 1.0 mL/min +/- 0.1%), injection system with no memory effects (Reproducibility 1% or better, carry over less than 0.1%), column(s) (1 x PLgel 5pm Guard 50x7.5mm + 3 x PLgel 5pm Mixed-C 300x7.5mm), differential refractometer (cell volume < 10mI) and data station with GPC software. Molecular weight is calculated from the resulting chromatogram using polystyrene Mp 160-10,000,000 Daltons (polymer standard service (PSS) DIN certified) standards.

The solid content of the particulate composition (I. A) produced in I. is preferably from 20 to 50 wt.%, more preferably from 25 to 45 wt.%.

In step II. and the optional step III., the process of the invention involves swelling emulsion seed polymer particles of the seed particulate composition produced in I. with monomer composition (II) and an oil-soluble organic free radical initiator and/or a water-soluble ionic free radical initiator and starve feed polymerizing the monomer composition (II) within the emulsion seed polymer particles, thereby becoming part of the emulsion seed polymer particles and permanently increasing their size. The swelling and polymerizing steps may be repeated until the particles have grown to the desired size. The monomer composition (II) and the oil-soluble organic free radical initiator and/or the water-soluble ionic free radical initiator are starve feed added to particles generated in the previous step. Accordingly, step II. and the optional step III. are starve feed polymerizations.

The process of the invention involves feeding into step II. at least a part of the aqueous emulsion (I .A) of the seed particles produced in I., optionally after dilution with water, but preferably without isolation of the seed polymer particles. The seed polymer particles are preferably not isolated from the seed particulate composition (I .A) produced in I. for further increasing the control of the growth of the particles in step II. and, if present, step III., i.e. to obtain even less broadening of the particle size distribution and/or to reduce reactor equipment fouling. Thus, preferably all of the seed polymer particles present in the seed particulate composition (I .A) or in a part of the seed particulate composition (I. A) are fed to the growth step II.

The initiator useful in step II. and, if present, in step III. is an oil-soluble organic free radical initiator and/or a water-soluble ionic free radical initiator, and preferably has a one-hour half-life temperature of from 60 to 100 °C. The one-hour half-life temperature is understood by those skilled in the art as that temperature at which one half of the initiator present at any given time will have decomposed, forming free radicals, within one hour.

Preferred oil-soluble organic free radical initiators are substantially completely dissolvable in hexane under standard conditions. Preferred oil-soluble organic free radical initiators are 2,2’-azobis(2,4-dimethylvaleronitrile) (ADVN), di-benzoyl peroxide (BPO), di-lauroyl peroxide (LPO), di-methylbenzoyl peroxide (MBPO), 2,2’-azobis(2- methylbutyronitrile) (AMBN), 2,2’-azobis(isobutyronitrile) (AIBN), tert.-butyl-2-ethyl- hexanoate, tert.-amyl-2-ethylhexanoate or a mixture of at least two of these compounds. More preferred oil-soluble organic free radical initiators are di-lauroyl peroxide (LPO), 2,2’-azobis(isobutyronitrile) (AIBN), 2,2’-azobis(2-methylbutyronitrile) (AMBN), tert.-butyl-2-ethyl-hexanoate and/or tert.-amyl-2-ethylhexanoate. Even more preferred oil-soluble organic free radical initiators are di-lauroyl peroxide (LPO), tert- butyl-2-ethyl-hexanoate and/or tert.-amyl-2-ethylhexanoate. Using oil-soluble organic free radical initiator in step II. and, if present, in step III. in the process of the present invention is advantageous for the smoothness of the coating appearance. It has been found that using oil-soluble organic free radical initiator in step II. and, if present, in step III. in the process of the present invention results in improved wetting of the substrate and/or improved film formation, resulting in improved smoothness of the coating appearance, which is shown, for example, by the reduced presence of fish-eyes in the coating. Figure 1 shows a coating with fish-eyes.

Preferred water-soluble ionic free radical initiators are persulfates. Preferred persulfates are ammonium, potassium and/or sodium persulfate. Most preferred persulfate is ammonium persulfate. It has surprisingly been found that a water-soluble ionic free radical initiator can be used in step II. and, if present, in step III., while a narrow particle size distribution of the particles can still be obtained. Without wishing to be bound to any theory, it was believed that the use of a water-soluble ionic free radical initiator in the polymerisation steps to grow the seed particles would result in formation of new particles and hence broadening of the particle size distribution, because it partitions into the aqueous phase and thus would tend to promote formation of new particles. Even more surprisingly, it has been found that both water-soluble ionic free radical initiator and carboxylic acid monomer can be used in step II. and, if present, in step III., while a narrow particle size distribution of the particles can still be obtained. Furthermore, it has surprisingly been found that the use of water-soluble ionic free radical initiator as free radical initiator in step II. and, if present, in step III. results in improved in-process dispersion stability which results in less equipment fouling. Accordingly, the free radical initiator applied in step II. and, if present, in step III. is preferably a water-soluble ionic free radical initiator. Preferably the water-soluble ionic free radical initiator is a persulfate, more preferably ammonium persulfate.

In step II. and, if present, in step III. of the present invention, the monomer composition (II) and the oil-soluble organic free radical initiator and/or the water-soluble ionic free radical initiator are starve feed added to the reactor at a temperature preferably at least as high as that at which the initiator is activated, until sufficient monomer composition (II) has been fed to grow the particles to a selected intermediate size. The temperature is maintained as high as that at which the initiator is activated until sufficient monomer composition (II) has been fed to grow the particles to a selected size and until all or nearly all the monomers present in the monomer composition (II) is polymerized. These steps being repeated until the selected intermediate size is equal to the selected final particle size.

Step I., II. and, if present, step III. of the present invention are preferably carried out at a temperature of from 70 to 95°C and preferably at atmospheric pressure.

The amount of oil-soluble organic free radical initiator and/or of water-soluble ionic free radical initiator fed that is starve feed added in step II. and, if present, in step III. is preferably from 0.01 to 2 wt.%, more preferably from 0.02 to 1 wt.% relative to the monomer composition (II). Preferably, oil-soluble organic free radical initiator and/or water-soluble ionic free radical initiator is also fed in an amount of preferably from 0.01 to 0.05 wt.%, relative to the monomer composition (II), to the reactor separately and prior to starve feed adding the monomer composition (II) and oil-soluble organic free radical initiator and/or of water-soluble ionic free radical initiator.

In an embodiment of the invention, step II. and, if present, step III. are effected in the presence of an added surfactant that is preferably present in an amount of at most the critical micelle concentration, more preferably in an amount below the critical micelle concentration. The critical micelle concentration CMC is given by the supplier of the surfactant. Suitable examples of surfactants and the critical micelle concentration CMC are given below:

Preferred surfactants are sodium-n-alkyl-benzene sulphonates, more preferably sodium dodecyl benzene sulphonate. The monomer composition (II) comprises

(II. a) from 0.05 to 10 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and (II.b) from 90 to 99.95 wt.% of ethylenically unsaturated monomers different from monomers (II. a).

Preferably, the monomer composition (II) comprises

(II. a) from 0.05 to 9 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and (II.b) from 91 to 99.95 wt.% of ethylenically unsaturated monomers different from monomers (II. a).

More preferably, the monomer composition (II) comprises

(II. a) from 0.1 to 8 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and (II.b) from 92 to 99.9 wt.% of ethylenically unsaturated monomers different from monomers (II. a).

Even more preferably, the monomer composition (II) comprises (II. a) from 0.15 to 6 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and (II.b) from 94 to 99.85 wt.% of ethylenically unsaturated monomers different from monomers (II. a).

Even more preferably, the monomer composition (II) comprises (II. a) from 0.2 to 6 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and (II.b) from 94 to 99.8 wt.% of ethylenically unsaturated monomers different from monomers (II. a).

The amounts of (I I. a) to (II.b) are given relative to the total weight amount of the monomer composition (II). Preferably, the amounts of monomers (II. a) to (II.b) add up to 100 wt.%, i.e. the monomer composition (II) preferably consists of monomers (II. a) to (II.b).

The total weight amount of monomer composition (I) relative to the total weight amount of monomer compositions (II) is preferably from 1:99 to 1:1, preferably from 2.5:97.5 to 30:70 and most preferably from 5:95 to 20:80. The carboxylic acid functional ethylenically mono-unsaturated monomers (II. a) are preferably selected from the list of monomers as described above for monomers (l.a). Monomer (I l.a) is more preferably selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, fumaric acid and mixtures thereof. Even more preferred monomers (I l.a) are methacrylic acid and/or acrylic acid. Most preferred monomer (I l.a) is methacrylic acid.

The monomers (II.b) are ethylenically unsaturated monomers which are different from monomers (I l.a) and are amenable for copolymerization with monomers (I l.a). Monomers (II.b) are preferably selected from the list of monomers as described above for monomers (I.b). At least 80 wt.%, preferably at least 90 wt.%, more preferably at least 92 wt.%, more preferably at least 94 wt.% and most preferably 100 wt.% of the total amount of monomers (II.b) are ethylenically mono-unsaturated monomers, and thus ethylenically mono-unsaturated monomers constitute the main monomers (II. b). The main monomers (II. b) are selected from the group consisting of C1-12 alkyl methacrylates, C1-12 alkyl acrylates, aryl alkylenes and any mixture thereof. Suitable arylalkylene monomers may be selected from: styrene, a-methyl styrene, vinyl toluene, t-butyl styrene, di-methyl styrene and/or mixtures thereof, especially styrene and/or a-methyl styrene. Most preferred aryl alkylene monomer is styrene. Preferred (meth) acrylates are C _MO alkyl (meth)acrylate(s), for example C1-8 alkyl

(meth)acrylate(s). Suitable (meth)acrylate(s) may be selected from: methyl (meth)acrylate, ethyl (meth)acrylate, 4-methyl-2-pentyl (meth) acrylate, 2-methylbutyl (meth) acrylate, isoamyl (meth)acrylate, sec-butyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate,2-ethylhexyl (meth)acrylate, 2-octyl (meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl

(meth)acrylate and/or mixtures thereof. More preferably, the main monomers (II. b) are selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl methacrylate, n-butyl acrylate, sec-butyl methacrylate, sec-butyl acrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-octyl acrylate, 2-octyl methacrylate, styrene and any mixture thereof. Even more preferably, the main monomers (II.b) are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-octyl acrylate, 2- octyl methacrylate or any mixture thereof. In an embodiment, the main monomers (II. b) are selected from n-butyl methacrylate, n- butyl acrylate, sec-butyl methacrylate, sec-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-octyl acrylate, 2-octyl methacrylate, styrene or any mixture thereof. In this embodiment, step II. and, if present, step III. can advantageously be effected in the absence of added surfactant.

Optionally crosslinking monomers (II. b) suitable for use as the crosslinker in the polymer particle are used which are generally ethylenically polyunsaturated monomers in which the ethylenically unsaturated groups have approximately equal reactivity, as for example divinylbenzene, glycol di- and trimethacrylates and glycol di- and triacrylates. Preferred crosslinking monomers (II. b) are butylene glycol diacrylates and propylene glycol diacrylates. Most preferred crosslinking monomers (II. b) are dipropyleneglycol diacrylate and dibutyleneglycol diacrylate.

Optionally graftlinking monomers (II. b) are used which are generally ethylenically polyunsaturated monomers having two or more non-conjugated double ethylenically bonds of differing reactivity, as for example allyl methacrylate, diallyl maleate and allyl acryloxypropionate. Most preferred graftlinking monomer (II. b) is allyl methacrylate. The polymer of the particles of the particulate composition obtained in the growth step II., or if present in the growth step III., may comprise crosslinking monomers and/or graftlinking monomers to further improve final resistance and mechanical properties. In particular in case the glass transition temperature of the polymer of the final particles is lower than 30 °C , the polymer of the particles of the particulate composition obtained in the growth step II., or if present in the growth step III., preferably comprises crosslinking monomers and/or graftlinking monomers. If crosslinking and/or graftlinking monomers (II. b) are employed, it is preferably used in in an amount of from 0.5 to 10 wt.%, more preferably from 0.1 to 5 wt.%, and most preferably from 0.1 to 1 wt.%, based on the total amount of monomers (II. b). Further, if crosslinking and/or graftlinking monomers are used in the process of the invention, they are preferably solely used in the final growth step. If crosslinking and/or graftlinking monomers (II.b) are employed in a growth step, the monomers (II. b) of the monomer composition (II) used in the growth step then preferably consists of from 0.5 to 10 wt.%, more preferably from 0.1 to 5 wt.%, and most preferably from 0.1 to 1 wt.% of crosslinking and/or graftlinking monomers and from 90 to 99.5 wt.%, more preferably from 95 to 99.9 wt.%, and most preferably from 99 to 99.9 wt.% of ethylenically mono-unsaturated monomers selected from the group consisting of C alkyl (meth)acrylates, aryl alkylenes and any mixture thereof, whereby the amounts are given relative to the total weight of the monomers

(N.b).

Preferably, the type and relative amounts of the monomers of monomer composition (I) are the same as for monomer composition (II), except for the final growth step. In the final growth step, the monomer composition (II) advantageously comprises the same monomers as present in the monomer composition (II) used in step I. and in the previous growth steps and preferably also comprises crosslinking and/or graftlinking monomers (II.b).

It has furthermore also been found that in case the growth step II., and if appropriate growth step III. (in case present) of the process of the invention are effected in the presence of a water-soluble ionic free radical initiator, the monomer composition (II) may also be free from ethylenically mono-unsaturated monomers containing carboxylic acid groups. The use of ethylenically mono-unsaturated monomers containing carboxylic acid groups (I I. a) in the growth step II. and, if appropriate, in the growth step III. (in case present) of the process of the invention is however advantageous since this enables to improve the smoothness of the coating appearance which is shown for example by reduced fish-eye forming tendency in the coating.

Accordingly, the present invention also relates to a process for preparing an aqueous dispersion comprising particles with a volume average particle size diameter dso of from 900 nanometre to 6 micrometre comprising:

I. Preparing an aqueous seed particulate composition (I. A) of seed polymer particles with a volume average particle size diameter dso of lower than 700 nanometre by emulsion polymerising of a monomer composition (I) in water, wherein the monomer composition (I) comprises

(I. a) from 0 to 20 wt.%, more preferably from 0.1 to 20 wt.%, more preferably from 0.2 to 15 wt.%, more preferably from 0.5 to 8 wt.%, more preferably from 0.5 to 6 wt.% of ethylenically mono- unsaturated monomers containing carboxylic acid groups, and (I.b) from 80 to 100 wt.%, more preferably from 80 to 99.9 wt.%, more preferably from 85 to 99.8 wt.%, more preferably from 92 to 99.5 wt.%, more preferably from 94 to 99.5 wt.% of ethylenically unsaturated monomers different from monomers (I. a), wherein the amounts of (I. a) to (I.b) are given relative to the total weight amount of the monomer composition (I),

II. Polymerizing a monomer composition (II) comprising monomers (II. b) in water in the presence of seed polymer particles of the seed particulate composition (I. A) and in the presence of an oil-soluble organic free radical initiator and/or a water-soluble ionic free radical initiator by starve feed adding at least the monomer composition (II) and the oil-soluble organic free radical initiator and/or the water-soluble ionic free radical initiator to seed particles of the seed particulate composition (I. A) to form first generation particles, and

III. Optional sequentially repeating step II. N times to obtain (N+1)th generation particles by starve feed adding at least monomer composition (II) comprising monomers (II. b) and oil-soluble organic free radical initiator and/or water-soluble ionic free radical initiator to a mixture comprising water and particles generated in the previous step, where N is a number of 1 to 10, to obtain an aqueous particulate composition of particles with a volume average particle size diameter dso of from 900 nanometre to 6 micrometre, with the proviso that in case the polymerizing of monomer composition (II) is effected in the presence of oil-soluble organic free radical initiator the monomer composition (II) comprises

(II. a) from 0.05 to 10 wt.%, more preferably from 0.05 to 9 wt.%, more preferably from 0.1 to 8 wt.%, more preferably from 0.15 to 6 wt.%, more preferably from 0.2 to 6 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and

(II. b) from 90 to 99.95 wt.%, more preferably from 91 to 99.95 wt.%, more preferably from 92 to 99.9 wt.%, more preferably from 94 to 99.85 wt.% and most preferably from 94 to 99.8 wt.% of ethylenically unsaturated monomers different from monomers (I I. a); wherein the amounts of (I I. a) to (II.b) is given relative to the total weight amount of the monomer composition (II), and with the proviso that in case the polymerizing of monomer composition (II) is effected in the presence of water-soluble ionic free radical initiator the monomer composition (II) comprises (II. a) from 0 to 10 wt.%, preferably at most 9 wt.%, more preferably at most 8 wt.%, more preferably at most 6 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and preferably at least 0.05 wt.%, more preferably at least 0.1 wt.%, more preferably at least 0.15 wt.%, most preferably at least 0.2 wt.% of ethylenically mono-unsaturated monomers containing carboxylic acid groups, and (II.b) from 90 to 100 wt.%, preferably at least 91 wt.%, more preferably at least 92 wt.%, more preferably at least 94 wt.% of ethylenically unsaturated monomers different from monomers (II. a), and preferably at most 99.95 wt.%, more preferably at most 99.9 wt.%, even more preferably at most 99.85 wt.%, most preferably at most 99.8 wt.% of ethylenically unsaturated monomers different from monomers (II. a); wherein the amounts of (II. a) to (II.b) is given relative to the total weight amount of the monomer composition (II).

The glass transition temperature T _g of the polymer of the final particles is preferably in the range from 0 to 150°C, more preferably from 20 to 100°C, most preferably form 30 to 80°C.

The weight average molecular weight M _w of the polymer of the final particles is preferably in the range from 20 to 200 kDaltons, more preferably from 50 to 500 kDaltons.

The solid content of the particulate composition obtained in step II. or, if present, obtained in step III. is preferably from 15 to 55 wt.%, more preferably from 20 to 50 wt.%, even more preferably from 25 to 45 wt.%.

The present invention also relates to an aqueous dispersion obtained or obtainable with the process of the present invention as described above.

The present invention further relates to the use of the aqueous dispersion as described above as matting agent in an aqueous coating composition comprising a latex polymer to obtain a matt coating with smooth feel when applied to a substrate . The dry thickness is preferably in the range from 0.5 pm to 6 pm, more preferably from 1 pm to 5 pm and even more preferably from 1 pm to 4 pm. As known by a skilled person, the thickness of the dry coating depends on the function of the coating, e.g film, varnish, primer, top coat or ink. The dry thickness of the coating is preferably at most 6 pm, more preferably at most 5 pm, more preferably at most 4 pm, even more preferably at most 3.5 pm. The dry thickness of the coating is preferably at least 0.1 pm, more preferably at least 0.2 pm, even more preferably at least 0.5 pm, even more preferably at least 1 pm. A matt coating preferably has < 40, more preferably < 20, even more preferably < 15, even more preferably < 10 gloss units at 60 degrees. The dry thickness is calculated by multiplying the percentage of solids by weight in the applied aqueous coating composition with the wet coating thickness applied. The aqueous coating composition may further comprise other ingredients like additives and/or auxiliaries, such as coalescents, levelling agents, waxes, thickeners, heat stabilisers, UV absorbers, antioxidants and fillers.

The present invention further relates to an aqueous coating composition comprising the aqueous dispersion as described above and further comprising an aqueous dispersion of particles of a latex polymer where the particles of the latex polymer has a volume average particle size diameter (dso) of less than 500 nanometres (nm) and preferably where at least 90% of the particles by weight of the total amount of the particles of the latex polymer has a size less than 200 nm, more preferably less than 150 nm. The latex polymer is preferably a carboxylic acid functional polymer, preferably selected from a vinyl polymer, a polyurethane, an alkyd polymer, any combination thereof or any mixture thereof. The aqueous dispersion of the latex polymer preferably forms a film having high gloss (> 60 gloss units at 60 degrees) and (i) where the weight ratio - calculated on solid polymers- of the polymer present in the aqueous dispersion obtained by the process of the invention to the latex polymer is preferably from 1/99 to 50/50 30/70 (preferred 15/85 to 45/55, more preferred 25/75 to 35/65) ; and (ii) where the aqueous coating composition forms a matt (in particular < 40 gloss units at 60 degrees) coat.

Although the advantages of the invention are apparent in coatings of normal thickness, the aqueous coating composition according to the invention is particularly suitable for making thin coatings, more particularly suitable for making films, varnishes, primers, top coats and inks and even more particularly suitable for making films, varnishes, top coats and inks. Thin coatings are considered to be coatings having a dry thickness of at most 6 pm, more preferably of at most 5 pm, more preferably of at most 4 pm, more preferably of at most 3.5 pm. The dry thickness is calculated by multiplying the solid content (wt.%) of the applied aqueous coating composition with the wet coating thickness applied. The term "coating " encompasses, in the present description, paint, film, varnish, primer, top coat and ink, without this list being limiting. Preferred coatings are films, varnishes, top coats and inks. The present invention further relates to a coating obtained by drying the aqueous coating composition as described above to obtain a coating with a dry thickness of preferably at most 6 pm, more preferably of at most 5 pm, more preferably of at most 4 pm, even more preferably of at most 3.5 pm. The carrier medium may be removed from the coating composition by natural drying or accelerated drying (by applying heat) to form a coating.

The present invention is now illustrated by reference to the following examples. Unless otherwise specified, all parts, percentages and ratios are on a weight basis. TEST METHODS AMD MEASUREMENTS

Unless otherwise indicated all the tests herein are carried out under standard conditions as also defined herein.

Gloss analysis Gloss is determined by casting 12pm wet film @35 wt.% solids which was force-dried for 30 minutes at 50° C and relatively humidity of 50% +/- 5%, resulting in a dry film thickness coating of 4.2 pm microns on a LENETA 2C Opacity Chart and determining gloss using a BYK-Gardner micro TRI-gloss analyser. Gloss is determined according to DIN67530 and reported in gloss units under 60° angle.

Particle size calculation

Particle number can, according to literature, be calculated using following equation: N _p

— 6M / TT . Ppolymer Dv ³ Wherein:

N _p = Number of particles per litre of aqueous phase

M = Grams of monomer per litre water [g/dm ³ ]

Pp _oiymer = Density of final polymer [g/ml]

D _v = Volume average diameter of the latex particles [cm] In absence of particle nucleation, the number of particles (Np) will not change from the prepared seeds to next stage particle populations.

If assumed that this condition is valid, no second population of particles will be formed which means that the seed/final polymer volume ratio is equal to the seed/final polymer weight fraction.

Based in this assumption particle growth can be described by: D _fP ³ / Di _S ³ = M _fP / Mi _S wherein:

D _fP Diameter final product particles [nm]

Di _s Diameter initial seed particles [nm]

M _fP Mass final polymer [gram]

Mi _s Mass initial seed polymer [gram]

With seed particle size being known and mass of both seed particles and final polymer known, the particle size of any following stage can be calculated. As long as the measured/calculated ratio is close to 1 this is indicative that no particle nucleation has taken place.

Zeta-potential The zeta potential is crucial in determining the stability of a colloidal suspension. When all the particles have a large negative or large positive charge they will repel each other, and so the suspension will be stable. In case the zeta potential is low the tendency for flocculation is increased. The zeta potential is used to indicate the electrostatic repulsions or potential stabilization of a colloidal system. The zeta potential is measured with Malvern Nano ZS and Flow through cell type DTS1070 as equipment and the following reagents:

Zeta potential Transfer standard: -42 mV +/- 4.2 mV reference liquid (DTS 1235 Malvern) for the transfer standard procedure.

Water 1 mM Potassium Chloride (KCI) : 0.0745 gram Potassium Chloride in 1 liter purified water for measuring the zeta potential of the sample. The sample is diluted with 1mM Potassium Chloride solution to a concentration about 0.01%. Solid content (solids) determination

Weigh empty aluminum dish (A). Weigh out about 1 g of sample to 4 decimal places (B); carry out the determination in triplicate. Transfer the dishes to the oven for 1 hour at 105°C followed by 1 hour at 150°C. Take the dishes out of the oven and let them cool down for about 5 minutes. Subsequently, weigh the dishes (C).

Calculation:

((C-A)/(B-A)) x 100% = . % solids

A= weight of empty aluminum dish

B= weight of empty aluminum dish + sample (before drying) C= weight of empty aluminum dish + sample (after drying)

Abbreviations used

DM denotes demineralised water Amm denotes ammonia (25wt%) TM denotes total monomers BA denotes n-butylacrylate BMA denotes n-butylmethacrylate MAA denotes methacrylic acid MMA denotes methylmethacrylate LMKT denotes dodecylmercaptane i-OMPA denotes iso-octylmercaptopropionate LDBS denotes sodium-n-alkylbenzenesulphonate (25wt% active) APS denotes ammoniumpersulphate AIBN denotes azo-bis-isobutyronitrile CMC denotes critical micelle concentration t-BHPO denotes tert-Butyl-hydroperoxide

Experiments 1-4 : Step I., Seed preparation

In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredient (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C. Ingredient ‘2’ till ‘5’ are charged to a stirred feed vessel.

Upon reaching reactor temperature of 80°C ingredient ‘6’ dissolved in 7’ is charged to the reactor and monomer feed vessel content is transferred to the reactor over a 210 minutes period. Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over 75micron filter cloth. The data and results are reported in Table 1 and 2.

Table 1 Experiment 1: Step I., Preparation of seed 1 in absence of acid-functional monomer Table 2 Experiments 2-4 : Step I., Preparation of seeds 2-4 using acid-functional monomer

Compared to preparation of seed 1, incorporation of acid functionality further lowers the zeta-potential and thus increases dispersion stability.

Growth step preparation Comparative Experiment 1

In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredient and ‘2’ (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C. Ingredient ‘3’ till ‘8’ are charged to a stirred feed vessel. Upon reaching reactor temperature of 80°C a slurry of Ί0’ in ‘9’ is charged to the reactor and monomer feed transferred to the reactor over a 210 minutes period. Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over a 75micron filter cloth. The data and results are reported in Table 3.

The 0.33pm seed polymer prepared in Experiment 1 has been grown in various stages to larger monomodal sizes. Table 3: Growth steps in the absence of acid-functional monomer and in the presence of oil-soluble organic free radical initiator As can be observed from above data, the initial obtained seed particles and any of the subsequent obtained dispersions can be grown in a controllable way with resulting in measured particle size being close to the theoretical calculated size. This means that secondary particle nucleation can be considered as close to negligible. Furthermore, particle size distribution is low and characteristic for mono-modality. Zeta-potential, i.e. charge difference between polymer particles and matrix, is typically below -30mV which is characteristic for good dispersion stability.

Example 1 In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredient and ‘2’ (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C.

Ingredient ‘3’ till ‘9’ are charged to a stirred feed vessel. Upon reaching reactor temperature of 80°C a slurry of Ί T in Ί0’ is charged to the reactor and monomer feed transferred to the reactor over a 210 minutes period. Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over a 75micron filter cloth. The data and results are reported in Table 4. The seed polymer prepared in Experiment 2-4 has been grown in various stages to larger monomodal sizes.

Table 4: Growth steps using acid-functional monomer and oil-soluble organic free radical initiator

Results of the growth steps surprisingly show that the ratio of measured (actual)/calculated particle size remains near to 1 which confirms that also in presence of acid functionality no secondary nucleation is taking place. Also, particle size distributions (span) remains surprisingly low and not showing broadening as would 5 have been expected by introducing acid functionality. Furthermore, within the acid range evaluated there are also no signs of decay in the actual versus calculated particle size. This confirms that acid functionality can be incorporated without loss of particle growth control.

Furthermore, data confirms that in presence of acid-functional monomer, the zeta- 0 potential of seed particles is lower opposite the non-acid functional seed. Visual observation of reduced particle sagging upon storage is aligning with zeta-potential.

Example 2-Growth steps in the presence of acid-functional monomer and water-soluble ionic free radical initiator 5 First a seed was prepared according to the process as described for the seeds as reported in Table 2: In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredient (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C. 0 Ingredient ‘3’ till ‘6’ are charged to a stirred feed vessel.

Upon reaching reactor temperature of 80°C ingredient ‘9’ dissolved in Ί0’ is charged to the reactor and monomer feed transferred to the reactor over a 210 minutes period. Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over 75micron filter 5 cloth. For the growth steps the procedure of Example 1 was repeated except that in the growth steps water-soluble ionic free radical initiator is applied instead of oil-soluble organic free radical initiator. In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredient and ‘2’ (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C.

Ingredient ‘3’ till ‘8’ are charged to a stirred feed vessel.

Upon reaching reactor temperature of 80°C a solution of ‘9’ in ‘10’ is charged to the reactor and monomer feed transferred to the reactor over a 210 minutes period. Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over a 75micron filter cloth. The data and results are reported in Table 5.

Table 5: Growth steps in the presence of acid-functional monomer and water-soluble ionic free radical initiator Reference Experiment 1 -Growth steps in the absence of acid-functional monomer and in the presence of water-soluble ionic free radical initiator First a seed was prepared according to the process as described for the seeds as reported in Table 2: In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredient (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C.

Ingredient ‘3’ till ‘5’ are charged to a stirred feed vessel. Upon reaching reactor temperature of 80°C ingredient ‘8’ dissolved in ‘9’ is charged to the reactor and monomer feed transferred to the reactor over a 210 minutes period. Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over 75micron filter cloth. For the growth steps the procedure of Comparative Experiment 1 was repeated except that in the growth steps water-soluble ionic free radical initiator is applied instead of oil- soluble organic free radical initiator. In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredient and ‘2’ (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C.

Ingredient ‘3’ till 7’ are charged to a stirred feed vessel.

Upon reaching reactor temperature of 80°C a solution of ‘8’ in ‘9’ is charged to the reactor and monomer feed transferred to the reactor over a 210 minutes period.

Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over a 75micron filter cloth. The data and results are reported in Table 6.

Table 6: Growth steps in the absence of acid-functional monomer and in the presence of water-soluble ionic free radical initiator.

As shown controlled growth with water soluble APS initiator is surprisingly similar to use of non-water soluble organic AIBN initiator, and controlled growth with water soluble APS initiator is feasible in the absence and also in the presence of acid- functional monomer. Compared to the use of AIBN, APS has the advantage of low equipment fouling. Low equipment fouling is observed when using APS in the absence as well as in the presence of acid functional monomer. This shows that surprisingly oil- soluble organic initiator like AIBN is not an absolute necessity to control particle size and for avoiding secondary nucleation as initially anticipated.

Reference Experiment 2-Growth steps in the absence of acid-functional monomer and in the presence of water-soluble ionic free radical initiator

First a seed was prepared according to the process as follows:

In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredient (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C. Ingredient ‘5’ till 7’ are charged to a stirred feed vessel.

Upon reaching reactor temperature of 80°C ingredient ‘8’ dissolved in ‘9’ is charged to the reactor and monomer feed transferred to the reactor over a 210 minutes period. Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over 75micron filter cloth.

For the growth steps the procedure following procedure was used:

In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredients and ‘2’ (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C.

Ingredient ‘3’ till 7’ are charged to a stirred feed vessel.

Upon reaching reactor temperature of 80°C ingredient ‘8’ dissolved in ‘9’ is charged to the reactor and initiator solution Ί0’ dissolved in Ί T and monomer feed transferred to the reactor over a 210 minutes period. Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over 75micron filter cloth.

The data and results are reported in Table 7. Table 7: Growth steps in the absence of acid-functional monomer and in the presence of water-soluble ionic free radical initiator. Comparative Experiment 2 and Example 3

The dispersion obtained in Growth 3 of Comparative Experiment 1 respectively the dispersion obtained in Growth 2B of Example 1 has been blended with NeoCryl ^® A- 2092, a glossy acrylic latex polymer dispersion obtainable from DSM, in amounts as shown in Table 8. The gloss at 60° has been measured as described above. The feel and film appearance have been assessed by the same person. Smooth feel is obtained when by passing with finger across the film surface no imperfections or particles can be detected. Smooth film appearance means that no imperfections can visually be detected.

Table 8

Of Example 3B, a photo of the coated Leneta chart has been taken. Figure 2 shows that for Example 3B using matting particles according to the invention a smooth film without fish-eyes was obtained. Figure 1 shows a coating with fish-eyes.

Example 4

First a seed was prepared according to the process as follows: In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredient (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C. Ingredient ‘5’ till ‘8’ are charged to a stirred feed vessel.

Upon reaching reactor temperature of 80°C ingredient ‘10’ dissolved in ΊT is charged to the reactor and monomer feed transferred to the reactor over a 210 minutes period. Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over 75micron filter cloth.

For the growth steps the following procedure was used: In a 2-liter glass 3-neck spherical reactor equipped with nitrogen inlet, Pt100, exhaust cooling and stirrer, ingredients and ‘2’ (see table below) is loaded to the reactor. Accordingly, stirrer, nitrogen purge and exhaust cooling started, and reactor content heated to 80°C.

Ingredient ‘3’ till ‘9’ are charged to a stirred feed vessel. Upon reaching reactor temperature of 80°C a slurry of Ί2’ in ‘13’ is charged to the reactor and monomer feed transferred to the reactor over a 210 minutes period.

Directly after the feed has been completed the temperature of 80°C is maintained for another 60 minutes. Next obtained dispersion is cooled and filtered over 75micron filter cloth. The data and results are reported in Table 9.

Table 9

When comparing first stage growth steps in presence of an increasing concentration of surfactant the particle size data remain which shows excellent particle size response opposite theoretical (calculated) values.