Low PVC matting paint formulation

Abstract

The present invention relates to (i) a low PVC paint formulation having excellent matting properties at high angles of incidence comprising at least one pigment and / or one filler, at least one binder and hydroxyapatite having a specific particle size as matting agent; and (ii) a method of imparting excellent matting properties to a high gloss paint coating comprising the use of the paint formulation.

Description

Technical Field

[0001] The present invention relates to low-PVC paint formulations having excellent matting properties at high angles of incidence, which comprise at least one pigment and / or at least one filler, at least one binder and hydroxyapatite with a specific particle size as matting agent.

[0002] The present invention relates to a method for imparting excellent matting properties to a coating obtained with a low-PVC paint, which comprises using said paint formulation. Background of the Invention

[0004] Lacquer is a surface coating that is applied to a substrate and dries to form a continuous film, used for decorative purposes and to protect the substrate. Consumer lacquers are air-dried and primarily decorative architectural paints applied to interior or exterior surfaces where the paint has sufficient fluidity to flow and form a continuous film and then dry at ambient temperature. Industrial maintenance lacquers are similar coatings applied to substrates in industrial settings, primarily to protect the substrate.

[0005] Latex paints, also known as emulsion paints and coatings, have captured a large portion of the interior and exterior paint market due to their many advantages over solvent-based products. They typically contain an organic polymer binder, pigments, and various paint additives. In the dried paint film, the polymer binder acts as a binder for the pigments and provides adhesion of the dried paint film to the substrate. The pigments can be organic or inorganic and functionally contribute to the opacity and color of the dried paint film in addition to durability and hardness.

[0006] In some cases, it is most desirable for the paint to have low gloss (matt) properties, which is usually achieved by adding matting agents to the paint formulation, which roughen or profile the film surface in the micrometer range. As a result, incident light is no longer reflected directionally but diffusely. The height, shape and number of surface structures determine the gloss of the paint film.

[0007] Examples of these matting agents are inorganic fine powders such as silica, alumina or calcium carbonate, or bead-like fine particles made of polyethylene resin, polyurethane resin, epoxy resin, polyamide resin, polyester resin or the like.

[0008] The gloss of a paint varies with the pigment volume concentration (PVC), i.e. the higher the PVC, the lower the gloss. Therefore, the addition of matting agents is particularly necessary in low-PVC paints (also called "high-gloss paints") (PVC < 50). These paints are considered high-quality products, contain a high content of binders and are known for being super glossy and reflective, especially at very low PVC values, giving the substrate an almost mirror-like appearance.

[0009] Unfortunately, many conventional matting agents used in such paints exhibit low gloss reduction at high angles of incidence. Low gloss at high angles of incidence is a very important requirement, especially for applications on large surfaces, as it ensures a uniform appearance across the entire coating area from all observation points.

[0010] Furthermore, these matting agents often impose significant disadvantages on the preparation, handling and performance of the paint formulation. Most importantly, the matting effect increases with the amount of matting agent used. When the matting efficiency is low, this can lead to a significant increase in the viscosity of the formulation, making it more difficult to manufacture, handle and process. Inorganic matting particles also tend to precipitate out of the formulation.

[0011] Furthermore, while effective in reducing gloss, matte particles often damage the integrity of the film and can lead to a loss of key film properties such as water resistance, abrasion resistance, and slip resistance. This results in a matte surface that wears quickly and has an unsightly appearance.

[0012] Furthermore, some matting agents gradually polish or buff after rubbing, causing the gloss to increase over time.

[0013] Finally, silica-based matting agents are dangerous to handle due to their health concerns and strong dusting tendency.

[0014] Therefore, there is still a need in the art to find a matting agent that can overcome all of the above problems.

[0015] We have now surprisingly found that hydroxyapatite (HAp) with a specific particle size shows advantageous properties as a matting agent when incorporated into low-PVC paints.

[0016] Compared to conventional matting agents, the hydroxyapatite of the invention exhibits particularly low gloss values ​​at all viewing angles, especially at high angles (i.e. 85°). This means that, in order to achieve a certain matting effect, less material is required than is the case with conventional matting agents, or a better effect can be achieved for a given amount of matting agent.

[0017] HAp is fully compatible with low PVC paint formulations and does not significantly increase their viscosity.

[0018] Finally, hydroxyapatite is biocompatible and poses no health concerns.

[0019] To the best of applicant's knowledge, the Hap of the present disclosure and its advantageous properties have not been described before.

[0020] The paint formulations of the present invention can be used, for example, as low PVC paints for architectural interior and exterior coatings, which are applied on-site to fixed structures (e.g., residential, commercial, institutional and industrial buildings and their appurtenances), portable buildings or sidewalks; the paint formulations can also be formulated to contain other conventional ingredients of low PVC paints.

[0021] In the present invention, all particle size parameters, ie, Dv10, Dv50, Dv90, Dv100 and mode, are derived from volume-based distributions as measured with a laser diffraction particle size analyzer (eg, Mastersizer 3000) (Malvern Panalytical).

[0022] A "paint formulation having excellent matting properties" is defined as a paint formulation having a gloss value of less than 20, preferably less than 15 at 85°.

[0023] "High gloss paint" is defined as a paint formulation having a PVC percentage of less than 50%.

[0024] In the present invention, unless otherwise specified, all weight percentages are based on the total weight of the preparation. Summary of the invention

[0025] Therefore, an object of the present invention is to provide a paint formulation having a pigment volume concentration (PVC) percentage of 5% to 50% and excellent matting properties, which comprises at least one pigment and / or one filler, at least one binder and as a matting agent between 0.5 and 15% by weight of hydroxyapatite (Hap), wherein the hydroxyapatite has a Dv50 between 10 and 50 μm, a Dv90 below 85 μm and a Dv10 above 3 μm, as determined by a laser diffraction particle size analyzer.

[0026] Another object of the present invention is to provide a method for imparting excellent matting properties to a coating obtained with a paint having a PVC percentage <50%, comprising the following steps:

[0027] i) preparing the paint formulation;

[0028] ii) optionally adding water or other conventional paint additives to the paint formulation;

[0029] iii) applying the resulting paint formulation having a PVC percentage < 50% to a substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 . SEM image of spray-dried Hap1.

[0031] Figure 2 . SEM image of ground Hap5. DETAILED DESCRIPTION

[0032] The paint formulations of the invention can be provided either as a dry mix paint formulation, which is usually dispersed in water before use, or preferably as a liquid waterborne paint formulation, in particular as a waterborne latex paint formulation.

[0033] Paints are usually characterized by their pigment volume concentration (PVC), which is the volume relationship of pigment / filler to total solids in the dry paint film. The PVC percentage is calculated using the following formula:

[0034]

[0035] in

[0036] V p is the total pigment volume,

[0037] V f is the total packing volume,

[0038] V b is the total adhesive volume.

[0039] The paint formulations of the present invention may have a PVC percentage value between 5 and 50%, preferably between 10 and 40%, more preferably between 10 and 30%.

[0040] Pigments suitable for realizing the present invention are those commonly used in water-based building paints. Specific examples of suitable pigments are inorganic white pigments, inorganic color pigments, organic pigments, carbon black and inorganic black pigments. Preferred pigments are inorganic metal oxides, hydroxides, sulfates, carbonates, organic pigments and mixtures thereof. As inorganic white pigments, oxides such as titanium dioxide, zinc oxide (ZnO), zirconium oxide, carbonates and sulfates (such as lead sulfate) should be mentioned in particular, and titanium dioxide is particularly preferred. As inorganic color pigments, those selected from oxides and hydroxides should be mentioned, which are in the form of separate inorganic compounds or mixed phases, especially iron oxide pigments, chromium oxide pigments and oxidized mixed phase pigments with rutile or spinel structures. Examples of iron oxide pigments are Color Index Pigment Yellow 42 and Pigment Red 101. Examples of chromium oxide pigments are Color Index Pigment Green 17 and Pigment Green 18. Examples of oxidized mixed phase pigments are nickel titanium yellow and chrome titanium yellow, cobalt green and cobalt blue. Examples of inorganic black pigments that should be mentioned include those already described above and inorganic colored pigments, in particular black iron oxide and black oxide mixed phase pigments. Preferred examples of organic pigments are those of the monoazo, disazo, azo lake, beta-naphthol, azo metal complex series, and polycyclic pigments such as those from phthalocyanine, quinacridone and thioindigo series. Also suitable as organic pigments are lake dyes, such as Ca, Mg and Al lake dyes containing sulfonic acid or carboxylic acid groups, and carbon black. Special mention should be made of the carbon black obtained by the furnace black process, and chemically surface modified carbon blacks, such as carbon blacks containing sulfonic or carboxyl groups.

[0041] In a preferred embodiment, the paint formulation of the present invention does not contain any metal powder-based pigments.

[0042] Fillers, also called extender pigments, comprise substances other than the pigments mentioned, which are mainly light-colored and inert to the binder components. Particularly preferably, the filler has an optical refractive index lower than the aforementioned white pigments. Examples of inorganic fillers that may be mentioned include carbonates, such as chalk, calcite or dolomite, silicon dioxide (quartz powder), natural or synthetic silicon dioxide, silicates, such as talc, kaolin or mica, and sulfates, such as barium sulfate. Examples of organic fillers include polymer powders and those organic fillers known as hollow spheres.

[0043] The adhesive suitable for the preparation of the paint formulation of the present invention can be any standard type and can include different adhesive materials. Suitable adhesives include organic and inorganic compounds. Preferred organic adhesives are water-soluble, water-dispersible or water-emulsifiable, natural, naturally modified or synthetic film-forming compounds. Examples of natural adhesives include natural resins, such as rosin or shellac, natural oils, especially oils containing saturated or fatty acids containing various unsaturations, if necessary, the oils can be oxidized and dried, such as linseed oil, castor oil, soybean oil, castor oil, etc. Modified natural adhesives are particularly chemically modified natural resins, such as rosin maleate resins, and modified oils, such as isomerized oils, styrenated and acrylated oils, and cellulose derivatives, such as nitrocellulose, organic acid cellulose esters. Examples of synthetic adhesives are saturated polyesters obtained by polyesterifying difunctional or higher polyfunctional alcohols with polyfunctional saturated aliphatic, cycloaliphatic or aromatic carboxylic acids and / or their anhydrides. Other synthetic organic binders are alkyd resins (polyesters modified with unsaturated fatty acids, fatty oils or higher synthetic carboxylic acids) and chemically modified alkyd resins, such as styrenated, acrylated or urethanized alkyd resins. Other suitable organic binders include acrylic resins (polyacrylates) in the form of homopolymers and copolymers, such as styrene acrylates and polyacrylic polyols.

[0044] Water-dilutable acrylic resins are particularly preferred as binders.

[0045] The paint formulation of the invention comprises as matting agent 0.5 to 15 wt %, preferably 3 to 10 wt % of HAp having a Dv50 between 10 and 50 μm, a Dv90 below 85 μm and a Dv10 above 3 μm.

[0046] Preferably, the Dv50 of the HAp of the present invention is between 15 and 45 μm, more preferably between 15 and 35 μm.

[0047] Preferably, the Dv90 of HAp is below 75 μm, more preferably below 65 μm.

[0048] Preferably, Dv10 is higher than 4 μm.

[0049] In a preferred embodiment, the mode of the particle size distribution of the Hap of the present invention is between 15 and 40 μm, more preferably between 17 and 35 μm.

[0050] In a particularly preferred embodiment, the Dv100 of Hap is below 150 μm, more preferably below 120 μm, most preferably below 100 μm.

[0051] Hydroxyapatite, Ca 10 (PO4)6(OH)2 is a compound present in the human body and is the main mineral component of bone tissue and tooth enamel. In fact, 99% of the calcium in the human body is stored in bone tissue in the form of hydroxyapatite. Due to its excellent biocompatibility, synthetic hydroxyapatite is used in artificial bones, artificial tooth roots, bone fillings, drug carriers, cosmetics such as toothpaste, sunscreen, etc.

[0052] The hydroxyapatite of the present invention may be of natural or synthetic origin.

[0053] In a preferred embodiment of the present invention, the hydroxyapatite is natural hydroxyapatite.

[0054] Stoichiometric HAp consists essentially of calcium and phosphorus, with a Ca / P ratio equal to 1.67. However, natural HAp is non-stoichiometric and lacks either calcium or phosphorus. The calcium position is the most common vacancy in natural HAp and is occupied by trace cations (e.g., Na + Mg 2+ and Al 3+ ), while carbonate anions can replace phosphate or hydroxide ions, and fluoride ions can replace hydroxide ions.

[0055] Natural hydroxyapatite can be extracted from biological sources or waste, such as mammalian bones (e.g., cow bones, camel bones, and horse bones), marine or aquatic sources (e.g., fish bones and fish scales), shell sources (e.g., clams, eggshells, etc.), plants and algae, and mineral sources (e.g., limestone).

[0056] Calcination and alkaline heat treatment are the most common methods for producing Hap from mammalian bones and marine or aquatic sources. Calcination is most preferred.

[0057] The calcination process removes the organic components of the bones through a thermal process. The organic matter is converted into carbon dioxide and ash (calcium phosphate compounds).

[0058] In alkaline heat treatment, an alkaline solution (usually NaOH) is used to remove organic matter from the bone. The NaOH solution hydrolyzes the organic components of the bone, and the remaining calcium phosphate is washed and separated using filtration.

[0059] The CaCO 3 -rich shells are typically calcined to form CaO, which, together with excess CaCO 3 , is used for further processing, such as sol-gel precipitation or wet chemical precipitation, to produce high-purity HAp.

[0060] After extraction, the resulting natural Hap can be ground and sieved to obtain the desired size value.

[0061] Preferably, the natural Hap suitable for implementing the present invention is obtained according to the method described in WO 2020 / 193750.

[0062] In another preferred embodiment of the present invention, the hydroxyapatite is synthetic hydroxyapatite.

[0063] According to a specific embodiment of the present invention, the synthetic hydroxyapatite is a hydroxyapatite in which calcium ions are partially substituted by various metal ions to form corresponding metal-substituted hydroxyapatites.

[0064] According to another specific embodiment of the present invention, the synthetic HAp is carbonate-hydroxyapatite (C-Hap). Carbonate-hydroxyapatite is HAp in which the hydroxyl or phosphate anions are partially replaced by carbonate anions. Synthetic C-HAp more closely mimics bone apatite crystals in composition, structure, size and morphology than "pure" synthetic Hap, so it is also defined as "bionic" hydroxyapatite.

[0065] In another specific embodiment of the present invention, the synthetic hydroxyapatite is Hap, wherein the hydroxyl anions are partially replaced by fluoride and / or chloride ions.

[0066] In another specific embodiment of the present invention, the synthetic hydroxyapatite is metal-substituted carbonate-hydroxyapatite.

[0067] Methods for preparing synthetic hydroxyapatite are well known in the art. Synthetic HAp can be made by various methods, such as dry methods (solid state and mechanochemical), wet methods (chemical precipitation, hydrolysis, sol-gel, hydrothermal, emulsion and sonochemical) and high temperature methods (calcination and pyrolysis). Preferably, the HAp of the present invention is obtained by chemical precipitation by contacting a calcium ion source with a phosphate anion source.

[0068] According to one embodiment of the present invention, the chemical precipitation method for preparing the synthetic HAp of the present invention comprises the following steps:

[0069] I. providing an aqueous solution or suspension comprising a Ca cation source;

[0070] II. The aqueous solution or suspension of step I) is mixed with an aqueous solution or suspension containing a phosphate anion source;

[0071] III. stirring the mixture to allow a suspension of HAp particles to form;

[0072] IV. Separating the hydroxyapatite particles from the suspension obtained in step III and drying the wet particles.

[0073] Suitable calcium cation sources are calcium fluoride, calcium chloride, calcium nitrate, calcium carbonate, calcium hydroxide, calcium acetate or a combination thereof. Preferably, the calcium cation source is calcium hydroxide or calcium chloride. More preferably, the calcium cation source is calcium hydroxide.

[0074] Preferably, the pH of the aqueous solution or suspension in step I) is between 7 and 13, more preferably between 8 and 12.

[0075] Suitable phosphate anion sources are disodium hydrogen phosphate, sodium dihydrogen phosphate, orthophosphoric acid, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, diammonium hydrogen phosphate or a combination thereof. Preferably, the phosphate anion source is orthophosphoric acid.

[0076] Step II) may be performed at a temperature below 60°C, preferably 30 to 50°C, for a period of 30 minutes to 2 hours.

[0077] In the method of the present invention, step III) allows the particles of hydroxyapatite to grow to the desired size and structure. Typically, step III) is performed at a temperature below 60°C for at least 6 hours. Preferably, step III) is performed at a temperature of 25 to 45°C for 6 to 36 hours, more preferably 12 to 24 hours.

[0078] The separation in step IV) is carried out using techniques well known to those skilled in the art, for example by decantation, centrifugation, filtration, spray drying, and the like.

[0079] The wet Hap particles may be dried, for example by freeze drying or drying in a ventilated or vacuum oven at 40-90°C.

[0080] If necessary, at the end of the process, the Hap particles can be ground and / or sieved to obtain Hap of an appropriate size suitable for use as a matting agent.

[0081] In a preferred embodiment, the suspension of Hap particles is spray dried to directly obtain the appropriate particle size suitable for use as a matting agent. Advantageously, the Hap obtained by spray drying exhibits a more uniform particle size distribution and a more spherical shape than the Hap obtained by grinding.

[0082] In a preferred embodiment, the method may also include an additional step of washing the separated particles with water or an alkaline solution before drying. If necessary, the washing operation may be repeated several times. Advantageously, the optional washing step is useful for removing any reagent residues that may be adsorbed or captured by the particle aggregates.

[0083] In order to obtain metal-substituted HAp, the aqueous solution or suspension of step I) may also include a suitable metal cation source. Examples of suitable metal cations are copper (Cu 2+ ), aluminum (Al 3+ ), magnesium (Mg 2+ )、Zn 2+ ), cobalt (Co 2+ ), iron (Fe 3+ and Fe 2+ ), silver (Ag + ), manganese (Mn 2+ ), Sr 2+ ), titanium (Ti 4+ ) or a combination thereof. Suitable sources are oxides or salts of these cations or mixtures thereof. Suitable metal cation salts are acetates, nitrates, citrates, fluorides, chlorides, hydroxides and carbonates of the above metals or a combination thereof. Preferably, the metal cation source is a carbonate.

[0084] According to a preferred embodiment of the present invention, the metal-substituted HAp contains cations selected from the group consisting of Mg, Cu, Zn, Ag cations and combinations of these cations.

[0085] According to a more preferred embodiment, the metal-substituted HAp contains Zn, Cu and Ag cations or a combination thereof.

[0086] By careful selection of operating conditions (temperature, concentration, etc.) and reagents, carbonate-hydroxyapatite can be successfully synthesized. C-HAp particles can be prepared simply by stirring a solution or suspension in the presence of carbon dioxide gas, for example by a mechanical stirrer, or by bubbling carbon dioxide gas into the liquid phase, or by combining mechanical stirring with gas bubbling.

[0087] The carbon dioxide gas may be a gas containing carbon dioxide. Pure carbon dioxide gas or air may be used as the carbon dioxide gas.

[0088] Alternatively, the carbonate may be added in advance to the aqueous solution or suspension of step I), or to the solution or suspension containing the phosphate source. Otherwise, the carbonate may be added to the mixture obtained in step II). In addition, step II) may be performed by simultaneously adding a solution or suspension containing carbonate and another solution or suspension containing phosphate anions to the aqueous solution or suspension of step II).

[0089] As the carbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate, potassium carbonate or potassium bicarbonate may be used. Alternatively, in the case of metal-substituted C-Hap, the carbonate source may be a carbonate of the substituted metal.

[0090] In addition to the above ingredients, the paint formulations of the present invention may optionally contain other conventional additives such as rheology modifiers (thickeners), surfactants and defoamers.

[0091] Thickeners are used for rheology control purposes, in particular for increasing viscosity and imparting desired rheological properties to paint formulations. Thickeners for latex paints can be inorganic thickeners, such as bentonite, natural polymers, such as guar gum, xanthan gum or microfibrillated cellulose, synthetic polymers, such as thickeners based on polyacrylates or polyurethanes, or semisynthetic polymers, or chemically modified natural polymers. Among chemically modified natural polymers, the thickener of choice can be a derivative of cellulose, including carboxymethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, methyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, hydrophobically modified hydroxyethyl cellulose and blends thereof. Polygalactomannan derivatives, such as hydroxyethyl or hydroxypropyl derivatives of guar gum or cassia, are other suitable thickeners for preparing paint formulations of the present invention.

[0092] The surfactant used is preferably a dispersant, wetting agent and emulsifier widely used in commercial paints and coatings. In particular, they can be nonionic, anionic, cationic or amphoteric in nature, and monomeric or polymeric. These paint formulations may also include some suitable thixotropic agents. These include but are not limited to multilayer silicates, pyrogenic silica and organic compounds based on, for example, high molecular weight polyolefins, hydrogenated castor oil, polyamides or polyacrylates.

[0093] Suitable defoamers include those based on natural or mineral oils, chemically modified silicones and silica materials.

[0094] In addition to the above-mentioned additives, the paint formulations of the present invention may include other standard paint additives and auxiliaries, such as water softeners, pH regulators, other film-forming and leveling aids, driers (driers), anti-skinning agents, antifouling agents, UV protectants and stabilizers, fungicides, etc. Solvents may also be present in these paint formulations. Preferred solvents include water-soluble solvents or water-miscible solvents. Solvent-free paint formulations are particularly preferred.

[0095] The paint formulation of the present invention can be used to prepare many different types of paints, such as dispersion paint, wall paint, interior paint, abrasion-resistant paint, washable paint, satin paint, exterior paint, facade paint, filling paint, silicate paint, single-layer paint, double-layer paint, structural paint, concrete paint, spray paint, etc.

[0096] Example

[0097] In the examples, the following ingredients were used:

[0098] Titanium dioxide R-HD2 = Titanium dioxide pigment, d50 0.24 μm [Huntsman]

[0099] PU1 = polyurethane beads, d50 5-8 μm;

[0100] PU2 = polyurethane beads, d50 22-30 μm;

[0101] PA1 = polyacrylate microspheres, d50 8-12 μm;

[0102] PA2 = polyacrylate microspheres, d50 18-22 μm;

[0103] Acematt OK607 = fine particle size wax-treated precipitated silica, d50 4.4 μm, [Evonik Industries AG];

[0104] Calcitec V 40S = 99.5% calcium carbonate; d50 6 μm, (Mineraria Sacilese Ltd.);

[0105] Byk 024 = VOC-free silicone defoamer (BYK-Chemie GmbH);

[0106] Reotan HS = polyacrylic acid dispersant [Lamberti Ltd.];

[0107] Crilat 4830 = acrylic emulsion adhesive [VINAVIL Ltd.];

[0108] Viscolam PS170AIR = Associative polyurethane thickener [Lamberti Ltd.].

[0109] The Hap reported in Table 1 were tested.

[0110] Table 1

[0111]

[0112]

[0113] *Used in comparative examples

[0114] The particle size was determined using a Mastersizer 3000 (Malvern Panalytical). The measurements were performed under ultrasound at 25° C. The particle size distribution was calculated based on the average of three replicate measurements.

[0115] Scanning electron microscopy characterization

[0116] Hap was further characterized by scanning electron microscopy (SEM).

[0117] SEM imaging highlights that, compared with the ground HAp5 ( Figure 2 ) compared to spray-dried HAp1( Figure 1 ) shows a more uniform granular structure.

[0118] This property allows for a more uniform composite surface, resulting in consistent gloss reduction and high polish resistance at different angles of incidence.

[0119] Examples 1-12

[0120] The performance of HAp as a matting agent was determined on a paint formulation with a PVC of 17 and prepared using the commercially available ingredients reported in Table 2.

[0121] Table 2

[0122]

[0123] *4.0 for Acematt OK 607

[0124] The paint formulations were prepared following a three-stage process:

[0125] - In the first stage, the liquid ingredients of stage 1 were mixed in a beaker with stirring (Cowles mixer at 800 rpm) for 10 minutes.

[0126] - Subsequently, titanium dioxide was gradually poured into the mixture and the stirring speed was increased to 1000 rpm for 20 minutes.

[0127] - In the third stage, the first aliquot of Crilat 4830 (binder) was introduced to obtain sufficient volume to ensure proper stirring. Subsequently, the matting agent was carefully added at 500 rpm and after 10 minutes, the remaining part of the binder and all other ingredients were added in the order reported in Table 2. Finally, the resulting paint formulation was homogenized at 1300-1500 rpm for 10 minutes.

[0128] A control paint formulation was also prepared using the same recipe and process with TiO2 as the matting agent (control).

[0129] The Brookfield viscosity (20 rpm at 20° C.) and the Stormer viscosity (200 rpm at 20° C.) of the paint formulations were measured after 24 hours.

[0130] Table 3

[0131]

[0132] *Comparative Example

[0133] The paint formulations containing Hap according to the present invention show very close performance to the control paint formulation at low (Brookfield, 20 rpm) and medium-high (Stormer) shear rates. This performance demonstrates the high compatibility of Hap according to the present invention with other paint ingredients. In contrast, Hap of Example 6 and other known matting agents show a strong influence on the rheology of the paint formulation.

[0134] Table 4 shows the viscosity (mPa*s) shortly after preparation and after 14 days at 50 °C, measured using an Anton Paar MCR 302 rheometer equipped with a cone-plate measuring system (CP-50) at 20 °C and a shear rate of 3.98 s -1 Measured under the circumstances.

[0135] Table 4

[0136]

[0137] *Comparative Example

[0138] The viscosity values ​​show that the HAp of the invention has no influence on the viscosity values ​​both soon after preparation and after storage for 14 days at 50° C., allowing the substitution of titanium dioxide (control) without any influence on the rheology of the paint.

[0139] This does not apply to other matting agents, in particular Acematt OK607, which showed a decrease in viscosity compared to the control soon after its introduction into the formulation.

[0140] Matting performance

[0141] The paint formulations of the examples were applied to Form 1B Penopac cardboard [Leneta] using a 120 μm rod coater. After curing for 5 days at 23° C. and 50% relative humidity, the gloss at different incident angles was measured. A micro-tri-gloss gloss meter (BYK) was used for measurement. The results are reported in Table 5.

[0142] Table 5

[0143] Gloss 20° Gloss 60° Glossiness 85° Control* 37 70.1 89.3 Example 1 2,1 10.4 7.1 Example 2 2,5 12 6.1 Example 3 2,2 10.3 5.8 Example 4 2,6 12 6.2 Example 5* 3,8 20.4 26.8 Example 6* 15,6 49.7 82.5 Example 7* 4,3 22.1 42.3 Example 8* 2,8 14.5 12.6 Example 9* 2,6 13.4 13.3 Example 10* 2,3 11.5 8.4 Example 11* 2 10.5 39.8 Example 12* 6,8 33.0 50.7

[0144] *Comparative Example

[0145] These gloss values ​​clearly demonstrate that the Hap of the present invention exhibits very high matting properties regardless of the incident angle. These properties are superior to those of commercial matting agents. In particular, Acematt OK607 exhibits high matting efficiency at 20°, but the performance drops sharply at high incident angles.

[0146] Polishing resistance

[0147] The polish resistance of the paint formulations was determined on painted PVC samples after curing for 11 days at 23°C and 50% relative humidity according to ASTM D 6736. To increase the accuracy of the results, each paint formulation was applied to two PVC samples with a wet thickness of 200 μm. The gloss values ​​at 85° were measured at 3 different points on each sample before and after rubbing. The Δ gloss value was calculated by subtracting the average gloss values ​​measured after 20, 40, 60, 80 and 100 rubbing cycles from the initial gloss value.

[0148] The average Δ value of two replicates for each example as well as the initial gloss value at 85° are reported in Table 6. The lower the Δ value, the better the performance.

[0149] Table 6

[0150]

[0151] *Comparative Example

[0152] The Hap of the present invention exhibits excellent polishing resistance, which is superior to that obtained by other commercial matting agents.

Claims

1. A paint formulation having a pigment volume concentration (PVC) percentage of between 5% and 50% and excellent matting properties, comprising at least one pigment and / or one filler, at least one binder and 0.5 to 15% by weight of hydroxyapatite (Hap) as a matting agent, wherein the Dv50 of the hydroxyapatite is between 10 and 50 μm, the Dv90 is lower than 85 μm and the Dv10 is higher than 3 μm, as determined by a laser diffraction particle size analyzer.

2. The paint formulation of claim 1, having a PVC percentage of between 10 and 40%.

3. The paint formulation of claim 1, comprising 3 to 10 wt% of the HAp.

4. The paint formulation of claim 1, wherein the Dv50 of the Hap is between 15 and 45 μm.

5. The paint formulation of claim 1, wherein the Hap has a Dv90 of less than 75 μm.

6. The paint formulation of claim 1, wherein the Hap has a Dv100 of less than 150 μm.

7. The paint formulation of any one of claims 1 to 6, wherein the Hap is a synthetic HAp.

8. The paint formulation of claim 7, wherein the synthetic Hap is a metal-substituted hydroxyapatite.

9. The paint formulation of claim 7, wherein the synthetic Hap is carbonate-hydroxyapatite.

10. A method for imparting excellent matting properties to a coating obtained with a paint having a PVC percentage <50%, comprising the following steps: i. preparing a paint formulation having a PVC percentage between 5 and 50%, the paint formulation comprising at least one pigment and / or one filler, at least one binder and 0.5 to 15 wt. % of hydroxyapatite as a matting agent, the hydroxyapatite having a Dv50 between 10 and 50 μm, a Dv90 below 85 μm and a Dv10 above 3 μm, as determined by a laser diffraction particle size analyzer; ii. optionally adding water or other conventional paint additives to the paint formulation; iii. Applying the resulting paint formulation having a PVC percentage < 50% to a substrate.

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