Platelet-shaped metal pigments at least partially coated with new lubricants based on fatty acid esters of saccharides and method of making

Abstract

Platelet-shaped metal pigment covered at least partially on its surface with a lubricant comprising or consisting of a fatty ester or a polyethoxylated fatty ester of a monosaccharide or a disaccharide. These platelet-shaped metal pigments are 5 manufactured by milling metal grit with fatty ester or a polyethoxylated fatty ester of a monosaccharide or a disaccharide as grinding aids.

Description

[0001] Platelet-shaped Metal Pigments at least partially coated with new Lubricants based on fatty acid esters of saccharides and Method of making

[0002] The present invention relates to the making of metallic effect pigments by milling metal grit with lubricants based on fatty acid ester or polyethoxylated fatty acid esters of saccharides. The metal effect pigments are at least partially coated with these lubricants.

[0003] Metallic effect pigments are platelet-shaped metallic pigments which are distinguished by metallic luster and color effects such as a lightness flop. The metallic effect pigments may be used in paints, varnishes, printing inks, plastics, cosmetics, etc., since they allow production of particular optical effects, especially color effects and luster effects.

[0004] The metallic effect pigments are produced conventionally from atomized metal powder by grinding in ball mills. The metal powder required for this operation can be obtained by atomization of molten metal. In the course of the deformative grinding of the atomized metal powder, it is common to add lubricants in order to prevent cold welding of the metal particles to one another. Lubricants or grinding aids commonly used include fatty acids like oleic acid or stearic acid. The choice of lubricants can affect the properties of the metallic effect pigment. For example, milling with oleic acid produces metallic effect pigments with non-leafing properties. Milling with stearic acid produces leafing properties for the ground metallic effect pigments. Instead of these fatty acids it is possible to use higher or lower homologs as lubricants, such as palmitic acid, for example. Technical-grade fatty acids regularly consist of a mixture of a wide variety of homologous fatty acids, with a saturated fatty acid also always containing certain fractions of unsaturated fatty acids, and vice versa. In the practice of producing metallic effect pigments it is also usual to deliberately use mixtures of saturated and unsaturated fatty acids, in other words, for example, a mixture of stearic acid and oleic acid.

[0005] In an application medium, such as paint or ink, for example, metallic effect pigments constitute an alien body or a disruption, which can lead to impaired mechanical properties, on the part of the dried ink or cured paint, for example. These impaired mechanical properties can be manifested, for example, in low abrasion resistance and / or low stability toward environmental effects such as heat, cold, moisture etc. Impaired mechanical properties also include a splitting of a printing-ink or paint film along the plane in which the metallic effect pigments are oriented, resulting in extensive delamination (poor cleavage resistance).

[0006] GB 1193149 A teaches grinding aluminum grit in the presence of anionic wetting agents like sulphated fatty acids, fatty alcohols, alkyl-, aryl-, aralkyl-sulphonates, alkane sulphonates, polysulphonates, polysulphonates linked with ester or amide radicals and condensates thereof with ethylene oxide or propylene oxide.

[0007] US 4484951 A teaches grinding aluminum granules with dimer acids and further, to prevent agglomeration, aliphatic amines. The aluminum flakes obtained have enhanced color purity, metallic lustre and certain anti corrosion properties. However, the obtained aluminum flakes have a poor cleavage resistance, especially in applied printing inks. Application in powder coatings is also not feasible. Further, aliphatic amines are problematic due to their toxicology.

[0008] WO 2009 / 144023 A1 teaches milling aluminum granules in the presence of an additive based on polyether units connected with dimer acids. The pastes having the obtained flaky aluminum effect pigments have an enhanced shelf life and coatings containing these metal effect pigments have an enhanced mechanical stability. These polyether additives, however, are difficult to manufacture and have limited commercial availability. Additionally the metal pigments obtained cannot be used in powder coating without further steps like bonding of the metal pigments with powder coating binders.

[0009] A further drawback of commonly used fatty acids is the use of such ground flaky metal pigments in powder coatings. For example, aluminum effect pigments which were obtained by milling with stearic or oleic acid as lubricants cannot be used in powder coatings because of a lack of electrical chargeability. Such pigments first have to be encapsulated with e.g. silica or polymer coatings. Such coatings enable safe application in powder coatings and also impart chemical stability of the aluminum flakes in the cured powder coating. In some applications leafing pigments (milled with stearic acid) may be used.

[0010] Fatty acid esters of sorbitan are well-known in the cement industry as additives for gasgenerating materials like aluminum or zinc particles as taught, for example, in US 2009071375 A1. There is a need for a metal effect pigment which has high luster and high flop and good adhesion in printing inks or other coatings. It should be usable without further coating in powder coatings. The additives like lubricants of these metal pigments should have no toxicological risks and should be easily commercially accessible.

[0011] This need is met, at least in part, by providing a platelet-shaped metal pigment covered at least partially on its surface with a lubricant comprising a fatty ester or a polyethoxylated fatty ester of a monosaccharide or a disaccharide or mixtures thereof.

[0012] Further embodiments are described in claims 2 to 11 .

[0013] Also described is a method of manufacture of these platelet-shaped metal pigments. The method comprises: a) provision of a metal grit, b) milling the metal grit in a solvent in a milling equipment comprising grinding balls using a fatty ester or a polyethoxylated fatty ester of a monosaccharide or disaccharide or mixtures thereof as a grinding aid to form platelet-shaped metal pigments, c) separating the platelet-shaped metal pigments and solvent from the milling equipment to obtain a platelet-shaped metal pigment filter cake and d) optionally sieving and / or exchanging solvent and e) forming a metal effect pigment paste by adjusting the solvent content to the desired value or drying the filter cake to form a powder of platelet-shaped metal effect pigments.

[0014] Metal effect pigments:

[0015] The metal effect pigments used in this invention are obtained by milling.

[0016] The metallic effect pigments are based on a platelet-shaped metal core. A metal core referred to as “platelet-shaped” here is a core whose aspect ratio, i.e., the ratio of median size dso to median thickness hso, is greater than 5. Further preferred are metal cores having an aspect ratio in a range of 10 to 500 or 40 to 150.

[0017] Metal cores with a higher aspect ratio typically have better metallic properties such as lightdark flop or luster. In accordance with the invention it is preferred for the platelet-shaped metal core to comprise or consist of metals selected from the group consisting of aluminum, copper, zinc, tin, gold bronze, brass, iron, titanium, chromium, nickel, silver, steel and alloys and mixtures thereof. According to a further variant in accordance with the invention, the platelet-shaped metal core is any of aluminum, zinc, copper, iron, zinc-copper alloys (gold bronze) and preferably any of aluminum, zinc or gold bronze. Aluminum pigments are particularly preferred.

[0018] All of these mentioned platelet-shaped metal cores are commonly named as “metal effect pigments”. This is true with the exception of zinc pigments which are used as corrosion protection pigments. Platelet-shaped zinc pigments made by milling in the presence of the lubricants exhibit better corrosion properties than those milled with conventional fatty acids. Within this invention the terms “platelet-shaped metal pigments”, “platelet-shaped metallic effect pigments” „metal effect pigment" and “metallic effect pigments” may be used interchangeably and zinc pigments are also included for convenience.

[0019] The metallic effect pigments are either platelet-shaped and substantially circular (of a type referred to as “silver dollar”), or platelet-shaped and substantially “cornflake like” (of the type referred to as “cornflake”).

[0020] The platelet-shaped metal core of the metallic effect pigments of the invention, preferably possesses a median thickness hso in a range of 20 nm to 2 pm, more preferably in a range of 50 nm to 1 pm, and most preferably in a range of 100 nm to 600 nm.

[0021] The hso value relates to the cumulative frequency distribution of the thickness distribution.

[0022] The thicknesses of the platelet shaped metallic pigments are determined by measurements on the basis of scanning electron microscope (SEM) images. The procedure is as follows: the metal effect pigments in powder form are dispersed in a lacquer based on nitrocellulose and applied to an aluminum foil. The mixing ratio between powder and lacquer in the liquid system is about 1 :10. A section of about 1 to 2 cm2of the aluminum foil thus lacquered is separated out by irradiation with high-energy Ar ions using a broad-beam ion source to create a cross-section. To ensure sufficient conductivity, the separated cross-section is sputtered with a 5 nm thin carbon layer. The metal effect pigments in the cross-section are then imaged using a scanning electron microscope at magnifications ranging from 10,000x to 30,000x. The pigment thickness of at least 25 different metal effect pigments is determined. For each platelet-shaped metal pigment visible in the SEM picture a value is determined which corresponds to the average thickness value of this flake to compensate different thicknesses within one flake. For example, the minimum thickness and the maximum thickness of a particular flake can be determined and averaged, thereby avoiding artifacts. The median pigment thickness hso then represents the 50%-quantil of the determined pigment thickness distribution function.

[0023] The size distribution of the metal effect pigments of the invention are determined customarily by means of laser granulometry. This analysis produces a cumulative frequency distribution of the volume-averaged size distribution function. In this context, the dso value indicates the size at which 50% of the measured effect pigments have a volumeaverage diameter which is the same as or less than the particular value indicated. The scattered light signals are evaluated according to the Fraunhofer approximation. The size distribution is measured preferably using the particle size analyzer manufactured by Sympatec GmbH (model: Helos / BR) and following the instructions of the manufacturer.

[0024] The dso values of the size distribution of the metal effect pigments of the invention are preferably in a range of 2.0 to 200 pm, more preferably in a range of 3.0 to 100 pm, furthermore preferably in a range of 4.0 to 90 pm and very preferably in a range of 5.0 to 40 pm.

[0025] Lubricants:

[0026] In a first embodiment, the lubricant comprises or consists of fatty acid esters of a monosaccharide or a disaccharide which can be represented by formula (I):

[0027] (RI-CO-O)P-R2(I) wherein Ri is a linear or branched saturated or unsaturated aliphatic moiety with 9 to 21 C- atoms and R2is an aliphatic moiety comprising or consisting of a monosaccharide or a disaccharide, p is an integer from 1 to 3 and is preferably 1 . The ester group -CO-O- evolved from the carboxylic acid group of the fatty acid and a hydroxyl group from the monosaccharide or disaccharide. Therefore the first oxygen group of the ester group(s) belonged to the monosaccharide or disaccharide.

[0028] In preferred embodiments Ri is a linear or branched, saturated or unsaturated aliphatic moiety with 11 to 19 C-atoms. In more preferred embodiments Ri is chosen from the group consisting of C15H31 , Ci5H29, C17H33, C17H31, Ci7H29, Ci7H27, Ci7H25, and mixtures thereof. In preferred embodiments Ri comprises or consists of lauryl, myristyl, oleoyl, palmityl, stearyl, isostearyl, behenyl, erucyl and mixtures thereof and further preferred is oleoyl and stearyl and most preferred is oleoyl. Usually Ri will have a main component with a certain number of carbon atoms as described above and in smaller amounts other aliphatic chains with lower or higher number of carbon atoms will be present in the lubricant.

[0029] The saccharide R2 may have an open structure or a ring structure or a mixture thereof. The first oxygen atom of the ester group(s) of formula (I) originally belonged to a hydroxyl group of the saccharide. The amount of open structured or ring structured saccharide forms depends on external parameters like the amount of water, pH, temperature and other parameters as is well known from carbohydrate chemistry. Preferred monosaccharides in ring form are sorbitan, isosorbide, galactofuranose, galctopyranose, and mixtures thereof. Preferred monosaccharides in open form are, for example, ribose, D- and L-arabinose, D-xylose, sorbitol, mannitol, fructose, D-glucose, D-galactose and mixtures thereof. More preferred monosaccharides are sorbitan or sorbitol and most preferred is sorbitan. Sorbitan commonly exists as more than 80 mol-% in the form of 1 ,4- sorbitan with smaller amounts of 2,5-sorbitan, isoboride or the ring-opened form D-sorbitol.

[0030] Preferred fatty esters of sorbitan are sorbitan monocaprylate, sorbitan dicaprylate, sorbitan monomyristate, sorbitan dimyristate, sorbitan monooleate, sorbitan dioleate, sorbitan monoelaideate, sorbitan dielaideate, sorbitan monolaurate, sorbitan dilaurate, sorbitan monopalmitate, sorbitan dipalmitate, sorbitan monostearate, sorbitan distearate, sorbitan monoisostearate, sorbitan diisostearate or mixtures thereof. More preferred fatty esters of sorbitan are sorbitan monooleate, sorbitan dioleate, sorbitan monoelaideate, sorbitan dielaideate, sorbitan monostearate, sorbitan distearate, sorbitan monopalmitate and sorbitan dipalmitate or mixtures thereof. Most preferred fatty esters of sorbitan are sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate or mixtures thereof and further most preferred is sorbitan monooleate.

[0031] Commercially available products are sold, for example, under the trade name Span®. Structures of some commercially available sorbitan fatty esters are depicted in Fig. 1.

[0032] Preferred disaccharides are sucrose, trehalose, lactose, maltose, cellobiose and mixtures thereof. The most preferred disaccharide is sucrose. Examples for commercially available products are Sisterna PS750, Sisterna SP70 or Sisterna SP50. In some embodiments the lubricant may be a mixture of a fatty ester of a monosaccharide and a fatty ester of a disaccharide. Particularly the lubricant may be a mixture of a sorbitan fatty ester and a sucrose fatty ester.

[0033] Generally the fatty acid esters of mono- or disaccharides exhibit a large range of hydrophilic to hydrophobic properties depending on the number of ester bonds per molecule and the hydrophobicity of the Ri moiety. When expressed as HLB values according to the Griffin scale the HLB values for sorbitan fatty acid esters are preferably in a range of 1 .5 to 9.0 and more preferably in a range of 2.0 to 8.0. The sucrose fatty acid esters have a much wider range of HLB values which is in the range of 1 .0 to 16 and preferably in a range of 2.0 to 16.

[0034] In another embodiment the lubricant comprises or consists of ethoxylated species of saccharide fatty esters which can be represented by formula (II): wherein w is an integer from 1 to 30, x, y and z, are integers which independently are in a range of 0 to 29, and x + y + z + w = 3 to 30. The ethoxylates termed with index “w” denote to the ethoxylates bonded to the most reactive hydroxyl group of the mono- or disaccharide. R3is independently any of C(O)-Ri, H or CH3and with the proviso that at least one R3is C(O)-Ri. Preferably R3is C(O)-Ri or OH. The moiety R4(O)4represents an aliphatic moiety comprising or consisting of a monosaccharide or a disaccharide. The four oxygen atoms denote to original hydroxy groups of the monosaccharide or the disaccharide molecule, preferably for a monosaccharide molecule which are capable to be ethoxylated. Most preferably R4(O)4is sorbitan.

[0035] Preferably w is an integer in a range from 2 to 25 and most preferably in a range of 3 to 20. Preferably here x, y and z are integers which independently are in a range of 1 to 28, more preferably in a range of 2 to 25 and most preferably in a range of 3 to 20. The sum x + y + z + w denotes to the total amount of ethoxylated species and preferably this sum is in a range of 4 to 25, more preferably in a range of 5 to 22 and most preferably in a range of 6 to 20. A range of 4 to 20 is also a suitable range for the total amount of ethoxylated species in the molecule.

[0036] Examples of commercially available ethoxylated fatty ester saccharides are (the E-number is given in cases of a registered food additive): (polyoxyethylene-(20)- sorbitanmonolaurate; E 432), Polysorbat 21 (polyoxyethylene-(4)-sorbitanmonolaurate), Polysorbat 40 (polyoxyethylene-(20)-sorbitanmonopalmitate; E 434), Polysorbat 60 (polyoxyethylene-(20)-sorbitanmonostearate; E 435), Polysorbat 61 (polyoxyethylen- (4)-sorbitanmonostearate), Polysorbat 65 (polyoxyethylene-(20)-sorbitantristearate;

[0037] E 436), Polysorbat 80 (polyoxyethylene-(20)-sorbitanmonooleate; E 433), Polysorbat 81 (polyoxyethylene-(5)-sorbitanmonooleate), Polysorbat 85 (polyoxyethylene-(20)- sorbitantrioleate) or Polysorbat 120 (polyoxyethylene-(20)-sorbitanmonoisostearate)

[0038] Such products are commercially available under the trademarks Tween® or Kolliphor®. In Fig. 2 structural formulas are depicted for some of the most common ethoxylated fatty ester saccharides which are commonly also called polysorbates.

[0039] The HLB values of this class of lubricants are preferably in a range of 9.0 to 17.0 and more preferably in a range of 10.0 to 16.8.

[0040] Forms of platelet-shaped metal pigments:

[0041] The platelet-shaped metal pigment may occur as a powder or a paste. In preferred embodiments the platelet-shaped metal pigment is available as a paste with organic solvent. The amount of the platelet-shaped metal pigment in the paste is preferably in a range of 50 to 80 wt.% and more preferably in a range of 55 to 70 wt.%, each based on the total amount of the metal pigment paste.

[0042] In preferred embodiments the organic solvent of the platelet-shaped metal pigment paste is any of isopropanol, mineral spirit, 1-methoxy-2-propanol, butylacetate, ethanol, ethylacetate, n-propyl acetate, 1-methoxy-2-propylacetate, isopropyl acetate, butyl glycol, fatty acid esters, polyethylene glycols such as PEG 100, PEG 200 and mixtures thereof. More preferred solvents are isopropanol, mineral spirit, 1-methoxy-2-propanol, ethylacetate, n-propyl acetate and mixtures thereof and most preferred is isopropanol or mineral spirit. An example for a solvent composed of fatty acid ester is Estisol 312 (Esti Chem).

[0043] In further embodiments the platelet-shaped metal effect pigments may come into contact with further additives, for example when the platelet-shaped metal pigment pastes or powders are pre-dispersed in a solvent by gentle agitation (such as stirring) before they are finally formulated in an application medium like an ink formulation or a paint formulation. Such pre-dispersion is well-known in the art for platelet-shaped metal effect pigments as these pigments should not be subjected to high shear forces and additionally, they tend to form aggregates or agglomerates due to their high specific surface. When pre-dispersed by gentle agitation aggregates or agglomerates may be broken up. Frequently additives like dispersing additives may be added in a pre-dispersing step. As the lubricants which at least partially cover the surface of the platelet-shaped metal effect pigments have very good lubricating properties no further additives or only very little amounts of such further additives may be added.

[0044] Therefore, in preferred embodiments pastes or dispersions of the platelet-shaped metal effect pigments do not contain further additives or the weight ratio of the lubricant described above to any of further additives in the metal pigment powder or metal pigment pastes is > 3.0, more preferred > 4.0, furthermore preferred > 5.0, most preferred > 10.0 and further most preferred > 12.

[0045] Such further additives could also be added if the platelet-shaped metal pigments were milled with further additives or grinding aids besides the lubricants consisting of fatty acid esters or polyethoxylated fatty acid ester of a monosaccharide or a disaccharide. Typically such further additives may be fatty acids (with > 8 C-atoms), fatty amines (with > 8 C-atoms), fatty amides (with > 8 C-atoms).

[0046] In most preferred embodiments the platelet-shaped metal effect pigment is not coated even partially with a fatty acid, a fatty amine or a fatty amide, because only the fatty ester and / or polyethoxylated fatty ester of a monosaccharide or a disaccharide is used as a lubricant or grinding aids during the milling process to manufacture the platelet-shaped metal pigments.

[0047] In further embodiments the platelet-shaped metal pigments have a concentration of respective metal salt molecules in the metal powder or metal pigment paste in a range of 0.00 to 0.05 wt.%, based on the metal pigment powder or paste. The reason for this low amount is the fact that the lubricant is in the form of esters of a fatty acid and / or a saccharose molecule. Pure fatty acids which are commonly used as grinding lubricant are known to form metal salts with the underlying metal, e.g. aluminum fatty acid salts.

[0048] In further embodiments platelet-shaped metal pigments are free from salts of the respective metal and a carboxylic acid and especially are free from salts of the respective metal and a fatty acid. Most preferred is that the platelet-shaped metal pigments, especially aluminum pigments are free from metal salts of saturated fatty acids, especially from aluminum salts of saturated fatty acids. With the expression “free from” it is meant that common analytics of metal pigment pastes which involve extraction steps of the metal pigment in a solvent like e.g. ethers, hexane, acetone, isopropanol, possibly combined with an acid digestion at elevated temperatures for at least 6 hours and characterisation of this extract by common analytical methods like IR-spectroscopy, coupled GC-mass spectroscopy or NMR spectroscopy the amount of metal salts of fatty acids is below 0.01 wt.%, based on the initial amount of metal pigment.

[0049] Like metal effect pigments obtained by milling with fatty acids as grinding aids the plateletshaped metal effect pigments of this invention may be used as substrates in a further encapsulation step with metal oxides, particularly with silica and / or organic polymers. Such encapsulated metal effect pigments are well-known in the art and are usually used for metal effect pigments in aggressive media like water-based coating formulations. The encapsulation protects the metal effect pigment against corrosion, particularly aluminum effect pigments against gassing or attack of aggressive chemicals. Typical grinding aids like oleic acid and especially saturated grinding aids like palmitic acid or stearic acid which are chemically bonded to the surface of the metal effect pigment act as a barrier for such further encapsulation process. Surprisingly the inventive platelet-shaped metal effect pigments can be easily further encapsulated and may show improved properties like gloss, flop or hiding power.

[0050] Method of manufacturing of platelet-shaped metal effect pigments:

[0051] The method of manufacturing platelet-shaped metal effect pigments comprises: a) provision of a metal grit, b) milling the metal grit of step in a solvent a milling eguipment comprising grinding balls using a fatty ester or a polyethoxylated fatty ester of a monosaccharide or disaccharide or mixtures thereof as grinding aid to form platelet-shaped metal pigments, c) separating the milled metal pigments and solvent from the milling eguipment to obtain a metal pigment filter cake and d) optionally sieving and / or exchanging solvent and e) forming a metal effect pigment paste by adjusting the solvent content to the desired value or drying the filter cake to form a powder of platelet-shaped metal effect pigments.

[0052] The metal grit used may have an irregular form, a spherical form or may be spheres. Irregular grit may be used when forming so called “cornflakes” and spherical grit is used for forming so-called “silver dollar” metal pigments. In certain embodiments the median particle size dso.g of the grit is in a range of 1 .0 to 30 pm, more preferred in a range of 2.0 to 20 pm and even more preferred in a range of 2.5 to 15 pm. In some embodiments a very fine aluminum grit is used as described in WO 2008 / 077612 A2.

[0053] The metal grit powder may be obtained by atomization or cutting out metal foils and preferably it is obtained by atomization processes.

[0054] When the metal grit is aluminum the purity of the aluminum used in the atomization process is preferably from 99.0% to more than 99.9% by weight. The aluminum can contain the usual alloy components (e.g. Mg, Si, Fe) in appropriately small amounts.

[0055] The milling step is performed in a suitable apparatus like a ball mill or an attritor mill.

[0056] Preferably the grinding balls used are made of steel, glass, zirconia and the like. Preferably, the size of the grinding balls is in a range of 0.2 mm to 15 mm and more preferably in a range of 0.4 to 5 mm. Most preferred are spherical steel balls with a diameter in a range of 0.4 to 5 mm.

[0057] The milling step may be conducted according to methods described in US 7,163,580 B2, EP 1080810 A1 , EP 1424371 A1 , US 2004 / 250731 A1 or WO 2004 / 087816 A2.

[0058] In this invention the lubricant used as a grinding aid for milling is a fatty ester or a polyethoxylated fatty ester of a monosaccharide or disaccharide. All embodiments and examples disclosed above can be used as the lubricant in the milling method to manufacture a platelet-shaped metal pigment.

[0059] For the milling method these substances are denoted as “grinding aids” which is the common term in the art. They adsorb on the metal surface and prevent cold welding during the milling process.

[0060] These grinding aids are at least partially bonded to the surface of the final platelet-shaped metal effect pigments and since they are known to act as lubricants in coatings they are called “lubricants” for the final metal effect pigments.

[0061] A further embodiment of this invention is also the use of a fatty ester or a polyethoxylated fatty ester of a monosaccharide or a disaccharide as a grinding aid in milling metal grit, preferably aluminum grit, to a platelet-shaped metal pigment, preferably an aluminum effect pigment in a mill.

[0062] Surprisingly such grinding aids enable a very efficient milling process of metal grits to platelet-shaped metal pigments. Especially for aluminum and for gold bronze the plateletshaped pigments obtained have a lower median or average thickness compared to conventional lubricants like oleic acid, stearic acid or mixtures thereof. Depending on the choice of a particular grinding aid metal pigments with leafing or non-leafing behaviour may be fabricated. For example, the use of sorbitan monooleate as lubricant leads to a non-leafing metal pigment. Also metal pigments with properties in between (“semi-leafing”) may be fabricated. Besides the particular choice of the grinding aid the “leafing” or “nonleafing” properties also depend on the choice of the binder medium in the final application medium.

[0063] Surprisingly the metal pigments may be used in powder coating without any further coating. They can be easily applied in a dry blend and surprisingly have a certain stability against chemical attack of acids or bases.

[0064] The grinding aid should be employed in a sufficient amount, since otherwise the vigorous transformation of the aluminum grit can lead to very large surface areas of the prepared platelet-like metal, that are only inadequately saturated by adsorbed grinding aid. In this case cold welding may occur. Typical amounts are therefore in a range of 0.5% to 20.0% by weight, preferably in a range of 1 .0% to 12.0% by weight, and very preferably in a range of 2.0% to 7.0% by weight of lubricant based on the weight of metal employed.

[0065] In preferred embodiments no further grinding aids (lubricants) are used other than the fatty ester or a polyethoxylated fatty ester of a monosaccharide or disaccharide or mixtures thereof. In other embodiments small amounts of further grinding aids are used. Typically such further grinding aids may be fatty acids (with > 8 C-atoms), fatty amines (with > 8 C- atoms), fatty amides (with > 8 C-atoms). Particularly such further grinding aids may be fatty acids like the commonly known oleic acid, palmitic acid, stearic acid and mixtures thereof. In some embodiments the weight ratio of fatty ester or a polyethoxylated fatty ester of a monosaccharide or disaccharide or mixtures thereof to the any of further grinding aid is > 3.0, more preferred > 4.0, furthermore preferred > 5.0, most preferred > 10.0 and further most preferred > 12.

[0066] In preferred embodiments the solvent used for milling is any of mineral spirit, isopropanol, 1 -methoxy propanol, ethyl acetate, ethanol, n-propyl acetate, i-propyl acetate and mixtures thereof. More preferably the solvent is isopropanol, ethanol, 1 -methoxy propanol, mineral spirit or mixtures thereof and most preferably the solvent is isopropanol or mineral spirit.

[0067] The critical speed of rotation nCrit in a ball mill is an important parameter which indicates when the balls begin to press against the mill wall due to centrifugal forces, at which point virtually no more grinding takes place: wherein

[0068] D is the diameter of the mill drum and g is the gravitational constant.

[0069] The speed of rotation of the ball mill is preferably in a range from 25% to 90%, more preferably in a range from 40% to 75% and most preferably in a range of 50% to 65% of the critical number of revolutions nCrit.

[0070] The grinding time is preferably in a range of 3h to 60 h, more preferably in a range of 5 to 40 h and most preferably in a range of 8h to 30h.

[0071] Due to the manufacturing method of the invention, the metal pigments and particularly aluminum pigments are free from adherent polymer films, which is a great advantage over metal pigments produced by PVD. The aluminum pigments of the invention therefore do not suffer from the disadvantages of aluminum pigments still encumbered with residues of the release coats, such as are prepared by PVD methods. Moreover, their manner of production is cheaper than the complicated PVD production methods.

[0072] The separation of the resulting metal pigments from the grinding media in step c), can be carried out in conventional manner by screening.

[0073] In a further method step d), the resulting metal pigments can be subjected to size classification. It may involve, for example, wet screening, decantation, or alternatively separation by sedimentation caused, for example, by the action of gravity or by centrifugation. In wet screening, the coarse fraction is usually screened off. In the other methods, the fines, in particular, can be separated. Subsequently, the suspension is freed from excess solvent, for example, with the aid of a filter press, centrifuge and / or filter to obtain a metal pigment filter cake.

[0074] Finally the metal pigment filter cake is separated and either dried to form a powder of platelet-shaped metal pigments or a paste of platelet-shaped metal pigments is formed. If the desired solvent of the metal pigment paste is the same solvent which was used for the milling step the solvent content of the metal pigment filter cake is simply adjusted to the desired final content. If a different solvent is needed a further solvent exchange may be necessary. Herein the metal pigment filter cake is subjected to heat and vacuum to remove as much of the milling solvent as possible and then the desired solvent is added in appropriate amount and mixed with the metal pigment in a suitable apparatus like a mixer.

[0075] The effect pigments coated in accordance with the invention find use in paints, powder coatings, printing inks, cosmetics, toners or plastics. Particularly preferred is their use in printing inks and powder coatings. The printings inks can be gravure printing inks, flexographic printing inks, screen printing inks, offset printing inks or ink jet printing inks. Another preferred use are applications with food contact of the platelet-shaped metal pigments or coatings containing these.

[0076] Aspects:

[0077] In further embodiments the invention is directed to a method of milling metal pigments and of platelet-shaped metal pigments obtained by this method. These embodiments are described by the following aspects. All embodiments disclosed beforehand also apply to these aspects.

[0078] A first aspect is directed to a method of manufacturing platelet-shaped metal effect pigments comprising the following steps: a) providing a metal grit, b) milling the metal grit of step a) in a solvent in a milling equipment comprising grinding balls using a grinding aid comprising or consisting of fatty ester or a polyethoxylated fatty ester of a monosaccharide or disaccharide to form platelet-shaped metal pigments, c) separating the milled metal pigments and solvent from the milling equipment to obtain a metal pigment filter cake and d) optionally further steps like sieving or solvent exchange and finally e) forming a metal effect pigment paste by adjusting the solvent content to the desired value and / or drying the filter cake to form a powder of platelet-shaped metal effect pigments.

[0079] A second aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to aspect 1 , wherein the solvent is mineral spirit, isopropanol, 2-methoxy propanol, ethyl acetate, ethanol, n-propyl acetate, i-propyl acetate and mixtures thereof and preferably isopropanol or white spirit.

[0080] A third aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to aspect 1 or 2, wherein the grinding aid can be described by formula (I):

[0081] (RI-CO-O)P-R2(I) wherein Ri is a linear or branched saturated or unsaturated aliphatic moiety with 9 to 21 C-atoms, R2is an aliphatic moiety comprising or consisting of a monosaccharide or a disaccharide and p is an integer from 1 to 3; or by formula (II): wherein w is an integer from 1 to 30, x, y and z, are integers which independently are in a range of 0 to 29, wherein x + y + z + w = 3 to 30 and R3is independently any of C(O)- Ri, OH or OCH3and with the proviso that at least one R3is C(O)- Ri and the moiety R4(O)4represents an aliphatic moiety comprising or consisting of a monosaccharide or a disaccharide.

[0082] A fourth aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to any of preceding aspects, wherein, Ri is chosen from the group consisting of CISH3I , CISH29, CI7H33, C HSI, Ci7H29, Ci7H27, Ci7H25, and mixtures thereof. A fifth aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to any of preceding aspects, wherein R2 is a monosaccharide from the group consisting of sorbitan, isosorbide, galactofuranose, galctopyranose, ribose, D- and L-arabinose, D-xylose, sorbitol, mannitol, fructose, glucose, D-galactose and mixtures thereof and preferably sorbitan or sorbitol and mixtures thereof.

[0083] A sixth aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to any of preceding aspects, wherein R2 is a disaccharide selected from the group consisting of sucrose, trehalose, lactose, maltose, cellobiose and mixtures thereof and preferably sucrose.

[0084] A seventh aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to any of preceding aspects 2 to 5, wherein for the grinding aids according to formula (II) w is an integer in a range from 2 to 25 and x, y and z are integers which independently are in a range of 1 to 28, more preferably in a range of 2 to 25 and x + y + z + w = 3 to 30.

[0085] An eight aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to any of preceding aspects, wherein the milling step b) is performed in a suitable apparatus like a ball mill or an attritor mill.

[0086] A ninth aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to any of preceding aspects, wherein the metal grit is chosen from the group consisting of aluminum, copper, zinc, tin, gold bronze, brass, iron, titanium, chromium, nickel, silver, steel and alloys and mixtures thereof and preferably from the group consisting of aluminum, zinc, copper, iron and zinccopper alloys (goldbronze).

[0087] A tenth aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to any of preceding aspects, wherein the metal grit is aluminum. An eleventh aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to any of preceding aspects, wherein no further grinding aids (lubricants) are used other than the fatty ester or polyethoxylated fatty ester of a monosaccharide or disaccharide or mixtures thereof or the weight ratio of the amount of the fatty ester or a polyethoxylated fatty ester of a monosaccharide or disaccharide or mixtures thereof to the any of further grinding aid is > 3.0, more preferred > 4.0, furthermore preferred > 5.0, most preferred > 10.0 and further most preferred > 12.

[0088] A twelfth aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to aspect 11 , wherein such further grinding aids may be fatty acids (with > 8 C-atoms), fatty amines (with > 8 C- atoms), fatty amides (with > 8 C-atoms) and particularly such further grinding aids may be fatty acids like oleic acid, palmitic acid, stearic acid and mixtures thereof.

[0089] A thirteenth aspect is directed to a method of manufacturing platelet-shaped metal effect pigments, particularly aluminum effect pigments, according to any of preceding aspects, wherein no further lubricants or grinding aids other than a fatty ester or a polyethoxylated fatty ester of a monosaccharide or disaccharide is used.

[0090] A fourteenth aspect is directed to platelet-shaped metal effect pigments particularly aluminum, manufactured by any of aspects 1 to 13.

[0091] A fifteenth aspect is directed to platelet-shaped metal pigment of aspect 14, wherein the platelet-shaped metal effect pigments are available as a paste with organic solvent.

[0092] A sixteenth aspect is directed to platelet-shaped metal pigments, particularly aluminum effect pigments, of aspect 15, wherein in the organic solvent is selected from the group consisting of isopropanol, mineral spirit, 1-methoxy-2-propanol, 2-methoxy-propanol, butylacetate, ethanol, ethylacetate, n-propyl acetate, 1-methoxy-2-propylacetate, isopropyl acetate, butyl glycol, fatty acid esters, polyethylene glycols and mixtures thereof.

[0093] A seventeenth aspect is directed to platelet-shaped metal pigments, particularly aluminum effect pigments .according to any of preceding aspects 14 to 16, wherein the surface of the platelet-shaped metal pigments is free from salts of the respective metal and a carboxylic acid and especially is free from salts of the respective metal and a fatty acid.

[0094] An eighteenth aspect is directed to platelet-shaped metal pigments, particularly aluminum effect pigments, by the use of the platelet-shaped metal pigment of aspects 14 to 17 in a further encapsulation step with silica and / or organic polymers.

[0095] A nineteenth aspect is directed to the use of the platelet-shaped metal pigments, particularly aluminum effect pigments, of any of aspects 14 to 18 in paints, powder coatings, printing inks, cosmetics, toners or plastics.

[0096] EXAMPLES

[0097] A Manufacture or listing of Examples and Comparative Examples

[0098] Example 1 : Milling in attritor mill

[0099] 300 g of fine Al grit (commercially available aluminum grit from Eckart GmbH; dso.g: 3.4 pm) was ground with 24 g sorbitol ester Span 80 as lubricant in 700 g isopropanol using 1 .2 kg of steel balls of a diameter of 1 .0 mm as grinding media for 12 h in an agitator bead mill using a rotation number of 800 rpm. The resulting product had a median particle size dso of 12 pm.

[0100] Example 2: Milling in ball mill

[0101] 15 kg of fine Al grit (commercially available aluminum grit of Eckart GmbH with a dso.g: 3.9 pm) were ground with 240 g of sorbitol ester Span 80 as lubricant in 35 kg of isopropanol using 800 kg of steel balls of a diameter of 1 .0 mm as grinding media for 15 h in a ball mill with a length of 1 .0 m and a diameter of 1 .0 m at 13 rpm. The resulting product had a median particle size dso of 12 pm.

[0102] Example 3:

[0103] 15 kg of fine Al grit (commercially available aluminum grit of Eckart GmbH; dso.g: 1 .4 pm) were ground according to Example 2 with 500 g of sorbitol ester Span 80 as lubricant in 50 I isopropanol for 15 h in a mill. The resulting product had a median particle size dso of 6 pm.

[0104] Comparative Example 1 : Commercially available Metabrite GFX 1100-EA (a conventionally water-milled aluminum flake from Metaflake Ltd.) with a dso of about 12 pm.

[0105] Comparative Example 2a:

[0106] Silvershine 412 (a conventionally ground aluminum pigment from Eckart GmbH using a mixture of stearic acid and oleic acid grinding aid and white spirit as solvent) having a dso of about 12 pm.

[0107] Comparative example 2b (according to Example 1 of WO 2009 / 144023 A1):

[0108] 50 g of Pripol 1009 (hydrogenated C36 dimer acid from Unichema) and 89 g of MPEG 750 (methoxypolyethylene glycol) were weighed into a glass reaction vessel and heated to 80 °C under N2 protective gas with stirring. Then 0.8 g of p-toluenesulfonic acid (catalyst) was added and heated to 180 °C. The resulting water of reaction was removed using a water separator. The progress of the reaction was monitored using the acid number. The acid number was determined in accordance with DIN 53402. The reaction was stopped after an acid number of about 24 mg KOH / g additive was reached. This corresponds to a degree of esterification of about 67%. The average molecular weight of the resulting ester was approximately 1 ,750 g / mol, with the ratio of ether units to C atoms being approximately 0.3.

[0109] 100 g of atomized aluminum grit with median particle size dso: g= 2.2 pm and 440 g of isopropyl acetate and 8 g of the additive from above were added to a pot mill (length: 32 cm, width: 19 cm) and the mill was closed. The mixture was then ground for 12 hours with 4.5 kg of steel balls (diameter: 1.8 mm) at 50 rpm. The material was then ground in a second grinding stage for 13 hours at 24 rpm. The ground product discharged from the mill was washed with isopropyl acetate and separated from the grinding balls using a sieve (24 pm). The sieved material was largely freed of isopropyl acetate using a suction filter and then made into a paste with isopropyl acetate in a laboratory mixer (approx. 65% by weight solids content).

[0110] Example 4:

[0111] 45 kg of fine Al grit (commercially available aluminum grit from Eckart GmbH; dso.g: 3.0 pm) was ground according to Example 2 with 900 g of sorbitol ester Span 80 as lubricant in 55 I of white spirit (D60) for 34 h in a mill. The resulting product had a median particle size dso of 12 pm.

[0112] Example 4a: Polymer coated aluminum pigment:

[0113] 80 g of the platelet-shaped aluminum pigment from Example 4 were dispersed in 350 g mineral spirit in a reactor and 2.0 g of Dynasylan MEMO were added. The dispersion was heated to 130 °C under continuous stirring. Then 13.0 g of trimethylol propane triacrylate (TMPTMA) dissolved in 50 g of mineral spirit were added within 30 min and the reaction mixture was held for a further 250 min at 130 °C. Then the mixture was cooled down to 50 °C and was filtered. The coated aluminum pigment was finally obtained as a paste with mineral spirit.

[0114] Comparative Example 3:

[0115] Commercially available Silvershine 408 (an aluminum effect pigment representing a fine and thin silverdollar aluminum pigment which was ground conventionally with an oleic / stearic acid mixture from Eckart GmbH) having a dso of 10.5 pm and a mean thickness of the aluminum substrate of about 100 nm. Comparative Example 3a:

[0116] 80 g of the aluminum effect pigment of Example 3 were coated with an acrylate polymer coat according to the procedure of Example 4a.

[0117] Example 5:

[0118] 25 kg of fine Al grit (commercially available aluminum grit of from Eckart GmbH; dso.g: 2.2 pm) was ground according to Example 2 with 500 g of sorbitol ester Span 80 as lubricant in 50 I isopropanol for 20 h in a mill. The resulting product had a median particle size in dso of 9 pm. For testing in a powder coating application, the product was dried and sieved to < 100 pm. The final aluminum pigment had a specific surface (BET) of 11 .8 m2 / g.

[0119] The visual evaluation of the samples obtained shows a very bright metallic impression.

[0120] Comparative Example 4:

[0121] A conventionally ground aluminum pigment according to Example 5, except that a mixture of stearic acid and oleic acid was used as grinding aid.

[0122] Comparative Example 5:

[0123] PCR 1 100 (a commercially available silica coated aluminum effect pigment for powder coating with a dso ~ 8 pm from Eckart GmbH).

[0124] Comparative Example 6:

[0125] Commercially available PC 100 (Eckart GmbH with dso = 8.6 pm) for powder coating. This aluminum pigment is milled with stearic acid in a wet-milling process and exhibits leafing properties.

[0126] Example 6: zinc

[0127] 0.3 kg of coarse Zn grit (Zn AS 100, Eckart Suisse) was ground with 15 g of sorbitol ester Span 80 as lubricant in 300 g white spirit and using steel balls of a diameter of 4.0 mm as grinding media for 15 h in a ball mill of laboratory size. The resulting product had a median particle size dso of 17.4 pm. The optical density was determined to be 0.77.

[0128] Comparative example 7:

[0129] A conventionally ground zinc pigment according to Example 6, except that stearic acid was used as grinding aid. An additional 2 h grinding time was necessary to get a pigment with a comparable brightness to example 6 and a fairly comparable dso of 14.8 pm). The optical density was measured to 0.62.

[0130] The pigment of Example 6 had a higher hiding power and could be manufactured with lesser grinding time. Therefore, the zinc pigment of Example 6 can be manufactured more economically.

[0131] Example 7: gold-bronze

[0132] 0.3 kg of fine brass powder (RG MSV, Eckart GmbH) was ground with 15 g of sorbitol ester Span 80 as lubricant in 700 g isopropanol for 20 h in a mill. The resulting product had a median particle size dso of 9.0 pm.

[0133] Example 8:

[0134] 1 .0 kg of fine Al grit (commercially available aluminum grit of Eckart GmbH with dso.g: 3.9 pm) was ground according to Example 1 using 5 kg of isopropanol as solvent and 75 g of Span 60 (sorbitan stearate) as lubricant. The mill had a rotation number of 800 rpm and the milling time was 8 h. After milling the suspension was removed from the mill and most of the solvent was removed by centrifugation. An aluminum pigment paste with ethyl acetate as solvent and a solid content of 61 wt.% was created. The resulting product had a median particle size dso of 14.0 pm.

[0135] In the gravure printing application the product had a semi-leafing behavior with a gloss of 85° and a bright visual impression.

[0136] Example 9:

[0137] 300 g of fine aluminum grit (d io,g = 2.0 pm, dso.g = 4.0 pm, dgo.g = 6.5 pm) from Eckart GmbH and 1 .6 % by weight, based on the weight of the aluminum grit, of Span 80 in 700 g of isopropanol as solvent was added to a ball mill with a diameter of 19 cm and a volume of 6.7 I charged with 8 kg of steel balls having a diameter of 1 .0 mm. The aluminum powder was milled for 10 h at 86 rotations per minute and then for 6 h at 65 rotations per minute. After milling the suspension was removed from the mill and most of the solvent was removed by centrifugation. An aluminum pigment paste with isopropanol as solvent and a solid content of 70 wt.% was obtained.

[0138] This gentle milling procedure is typical for a deformation milling leading to a “silverdollar” type of aluminum effect pigments. Examples 10 to Example 18 and Comparative Examples 9 to 14 were done analogously as Example 9, but with varying the kind and the amount of the grinding aid or the solvent. The specific surface area (BET) was determined by a three-point method, the dso values was determined with a Malvern granulometric apparatus and the median as well as the average thickness was determined by SEM counting according to page 24 of W02004 / 087816 A2 but counting 25 particles only. Furthermore, the binder that is usable for SEM was replaced by an adhesive tape. All parameters varied compared to Example 9 and the physical characterization of the resulting platelet-shaped aluminum pigments are depicted in table 1 .

[0139] Furthermore, additional samples were made by adding other additives in a mixer which can be used as lubricants to a distinct aluminum pastes of this series. These additional samples are depicted in table 6.

[0140] Example 19:

[0141] 200 g of a gold bronze grit which was manufactured according to Example 1 a) of EP 2285913 B1 and 1.6 % by weight, based on the weight of the gold bronze grit, of Span 80 in 750 g of isopropanol as solvent was added to a ball mill with a diameter of 19 cm and a volume of 6.7 I charged with 8 kg of steel balls having a diameter of 2.2 mm. The gold bronze powder was milled for 24 h at 86 rotations per minute. After milling the suspension was removed from the mill and most of the solvent was removed by centrifugation. A flaky gold bronze pigment paste with isopropanol as solvent and a solid content of 70 wt.% was obtained.

[0142] Comparative Examples 15 to 17:

[0143] Milling of gold bronze grit was done as in Example 19, but with different lubricants. The lubricants and results of flake characterization can be depicted from table 1 . Table 1 : Varied milling parameters and basic physical characteristic data for Examples and Comp. Examples depending on Example 9

[0144] * IL: Isopropanol

[0145] ** Concentration lubricant additive in wt.% to Aluminum or gold bronze grit

[0146] ***PM: 1-methoxy-2-propanol (Dowanol PM)

[0147] B Test Methods:

[0148] Gravure printing application:

[0149] A gravure printing ink was manufactured by utilizing a sample having 2.0 g of metal effect pigment which was diluted with 11 .2 g of a 1 :1 wt. mixture of ethyl acetate and ethanol. Then 2.5 g nitrocellulose binder (30 wt-% of NC-wool) in ethanol diluted in ethylacetate was added and stirred to obtain a homogeneous printing ink.

[0150] A gravure printing test was conducted on a WSHG 5 paper substrate. The printing apparatus was an Erichsen RK printing proofer.

[0151] From these applications the optical density (OD) was measured and the gloss at 60° using a micro-tri gloss apparatus from Byk-Gardner. The results displayed in table 1 are average values of 5 single values measured on the probe application.

[0152] Tesa test:

[0153] To test the splitting resistance between pigment and binder in the inventive and comparative examples, drawdowns were produced from the above-mentioned varnishes and inks. Following complete curing of the ink or paint coat, an adhesive strip was adhered, firmly and without bubbles, to the surface of the drawdowns. This adhesive strip was then peeled off so the substrate (e.g. paper) was not damaged. The splitting resistance was assessed visually on the basis of a rating system. A poor splitting resistance is reflected in a correspondingly severe extraction from the print or coating.

[0154] The rating system is based on a 3 note system: passed: essentially no pigments seen on adhesive strip semi: a few pigments seen on adhesive strip

[0155] Not passed: a lot of pigments seen on adhesive strip.

[0156] Cross-Cut test according to DIN EN ISO 2409:

[0157] Certain samples were dispersed into a solvent based testing lacquer having an acrylate basis using 3 wt.% of aluminum effect pigments. The lacquers were sprayed using a flow cup gun (SATA jet 3000 ROB LAB; 1 ,3 RP) and an automatic painting machine (OERTER APL 3.3) in a one-coat layer on steel panels and were dried for 30 min at 80 °C.

[0158] A cross cut was made and evaluated according to DIN EN ISO 2409. Furthermore the adhesive side of the tape used here for testing the adhesiveness was evaluated regarding possible aluminum pigment adhesions. Results are depicted in table 2.

[0159] Powder Coating testing:

[0160] Various pigment samples were dry-blended at a concentration of 1 wt% with a commercially available polyester RAL 9005. Test panels of aluminum were powder coated with this system and cured at 200 °C for 10 min.

[0161] The brightness L*15° was measured of each test panel using a Byk mac instrument. Results are reported in table 3.

[0162] Chemical drop test:

[0163] In a test for resistance to various acids and bases, the powder coated test panels were exposed to drops of 10% hydrochloric acid and 1 M sodium hydroxide. The drops were allowed to react for 5 minutes, 10 minutes and 30 min for 1 M NaOH solution and for 30 min of 10% HCI solution. After the acids or bases had been washed off, the degree of gray discoloration of each drop area was rated according to the following criteria:

[0164] 0 points=no corrosion

[0165] 1 point=barely discernible corrosion

[0166] 2 points=clearly discernible corrosion

[0167] 3 points=complete gray discoloration

[0168] A total rating ranging from 0-12 points was calculated from a total of 4 drop areas.

[0169] C Results and Discussion:

[0170] Table 2: Results for printing applications

[0171] All inventive Examples exhibited high optical densities and excellent adhesion in the applied printing ink (tesa test). Comparative Examples 1 and 2 showed poor adhesion. If directly compared with Examples 1 and 2 the gloss of Comparative Example 1 was outstanding but the hiding power (OD) was low. For Comparative Example 2b the tesa test was excellent, but the hiding power was rather low.

[0172] In the series of Examples 1 to 3 it was demonstrated that new aluminum effect pigments can be made which have different hiding properties and gloss. It is well known that gloss and hiding properties are often somehow conflicting properties for metal effect pigments obtained by milling.

[0173] Table 3: Results of cross-cut testing:

[0174] For Comparative Example 3 bad cross cut and large amounts of the pigments on the tape were found. For Example 4 the results were excellent. Apparently this aluminum pigment has very good adhesion in the binder system. Table 4: Results for polymer coated aluminum pigments:

[0175] The uncoated aluminum pigment of Example 4 was taken as a reference. This uncoated reference of course has the highest hiding power and highest flop and gloss. Compared to this uncoated effect pigment the losses in flop and gloss are much less for Example 4a than for Comparative Example 3a. Apparently the coating or the organic polymer of an aluminum pigment produced by milling with a sorbitan fatty acid ester results in aluminum effect pigment with better optical properties compared to a very similar effect pigment which was obtained by milling conventionally with a mixture of oleic and stearic acid.

[0176] Table 5: Results for powder coating: Most surprisingly the aluminum pigments of Example 5 were applicable in powder coating without any problems. They exhibited a chemical stability in the dried powder coating test panels comparable to PCR 1100 which represents a silica coated aluminum pigment of the first generation. The brightness of Example 5 was higher and Comparative Example 5 appeared much darker and less metallic. All Comparative Examples 2a, 3 and 4 which represent products which were milled in an oleic / stearic acid mixture were not applicable in powder coating. The pigment particles formed agglomerates when applied to the panel and thus they were not usable in powder coating at least in a dry blending application. The same result was obtained for Comparative Example 2b which was manufactured according to WO 2009 / 144023 A1 .

[0177] The aluminum pigments obtained by Comparative Example 6 were applicable in powder coating. Due to the leafing properties of the pigment the brightness was high, however not as high as Example 5. The chemical stability was very bad.

[0178] Results for series of milling aluminum pigments with same milling receipt but varying the kind and concentration of the lubricant and the solvent (Examples 9 to and Comparative Examples 10 to 14).

[0179] From table 1 it can be depicted that the use of fatty ester or a polyethoxylated fatty ester of a monosaccharide or a disaccharide as lubricant leads to thinner aluminum effect pigments compared to the use of oleic acid or a mixture of stearic and oleic acid. The median size of the platelet-shaped aluminum effect pigments of these experiments did not vary much indicating that no significant crushing occurred. The specific surface of the thinner aluminum effect pigments was higher than the thicker aluminum pigments obtained by the fatty acid lubricants.

[0180] Therefore, the fatty ester or polyethoxylated fatty ester of a monosaccharide or a disaccharide surprisingly enable a better deformation of aluminum grit in a milling process than conventional lubricants.

[0181] The same results were obtained for samples using the goldbronze grit. Example 19 using Span 80 as lubricant yielded the thinnest goldbronze effect pigments with the highest specific surface. Table 6: Results for sample variation series based on Example 9 and sample variation series based on Example 19:

[0182] * Supplemented additive: additive added after milling

[0183] ** 1 :1 mixture of stearic and oleic acid

[0184] *** when supplemented additive: second concentration csa

[0185] All Examples 9 to 18 with fatty acid ester (Span 80) or polyethoxylated fatty acid ester of sorbit (Tween 60, Tween 40) do pass the tesa test immediately after milling and later. Slightly lower adhesion showed Example 16 where 3.2 wt.% of Sisterna SP50-C (a sucrose stearate) was used as lubricant. Example 15 with lower content of this lubricant showed excellent adhesion.

[0186] All Comparative Examples using a mixture of stearic and oleic acid or pure oleic acid as lubricants showed a bad adhesion. This did not change when Span 80 was added later (Comp. Examples 9a-c, 10a-c, 12a-c, 13a-c and 14a-c). Only Comparative Examples 11a- c showed a slightly better behavior in that the tesa test was passed later.

[0187] In further samples the 1 :1 mixture of stearic and oleic acids was added later to Examples using Span 80 as lubricants during milling (further samples 8a-c, 10a-c and 17a-c). In all cases the adhesion became worse compared to the respective Examples without supplement of the fatty acids. This shows that the use of lubricant comprising or consisting of a fatty ester or a polyethoxylated fatty ester of a monosaccharide or a disaccharide as milling lubricants of aluminum lead to products having different properties compared to products obtained by milling with fatty acids and subsequent supplement of these lubricants.

Claims

32Claims:1 . Platelet-shaped metal pigment covered at least partially on its surface with a lubricant comprising or consisting of a fatty ester or a polyethoxylated fatty ester of a monosaccharide or a disaccharide or mixtures thereof.

2. Platelet-shaped metal pigment according to claim 1 , wherein the lubricant can be described by formula (I):(RI-CO-O)P-R2(I) wherein Ri is a linear or branched saturated or unsaturated aliphatic moiety with 9 to 21 C-atoms, R2is an aliphatic moiety comprising or consisting of a monosaccharide or a disaccharide and p is an integer from 1 to 3; or by formula (II):wherein w is an integer from 1 to 30, x, y and z, are integers which independently are in a range of 0 to 29, and x + y + z + w = 3 to 30 and R3is independently any of C(O)- Ri, OH or OCH3and with the proviso that at least one R3is C(O)- Ri, and the moiety R4(O)4represents an aliphatic moiety comprising or consisting of a monosaccharide or a disaccharide.

3. Platelet-shaped metal pigment according to claims 1 or 2, wherein Ri is chosen from the group consisting of CisH3i, CISH29, CI7H33, C HSI, CI?H29, Ci7H27, Ci7H2s, and mixtures thereof.

4. Platelet-shaped metal pigment according to any of preceding claims, wherein R2is a monosaccharide from the group consisting of sorbitan, isosorbide, galactofuranose, galctopyranose, ribose, D- and L-arabinose, D-xylose, sorbitol, mannitol, fructose, glucose, D-galactose and mixtures thereof and preferably sorbitan or sorbitol and mixtures thereof.

335. Platelet-shaped metal pigment according to any of claims 1 to 3, wherein R2 is a disaccharides taken from the group consisting of sucrose, trehalose, lactose, maltose, cellobiose and mixtures thereof and preferably sucrose.

6. Platelet-shaped metal pigment according to any of preceding claims 2 to 5, wherein for the lubricants according to formula (II) w is an integer in a range from 2 to 25 and x, y and z are integers which independently are in a range of 1 to 28, more preferably in a range of 2 to 25 and x + y + z + w = 3 to 30.

7. Platelet-shaped metal pigment according to any of preceding claims, wherein the platelet-shaped metal effect pigment is available as a paste with organic solvent.

8. Platelet-shaped metal pigment according to claim 7, wherein organic solvent is taken from the group consisting of isopropanol, mineral spirit, 1 -methoxylpropanol, butylacetate, ethanol, ethylacetate, n-propyl acetate, 1-methoxy-2- propylacetate, isopropyl acetate, butyl glycol, fatty acid esters, polyethylene glycols and mixtures thereof.

9. Platelet-shaped metal pigment according to any of preceding claims, wherein the platelet-shaped metal effect pigment is chosen from the group consisting of aluminum, copper, zinc, tin, gold bronze, brass, iron, titanium, chromium, nickel, silver, steel and alloys and mixtures thereof and preferably from the group consisting of aluminum, zinc, copper, iron and zinc-copper alloys (goldbronze).

10. Platelet-shaped metal pigment according to any of preceding claims, wherein the platelet-shaped metal effect pigment does not contain a further additive or the ratio of the amount of the lubricant to the amount of any of further additives is > 3.0, wherein the further additive is preferably any of fatty acids (with > 8 C-atoms), fatty amines (with > 8 C-atoms) or fatty amides (with > 8 C-atoms).11 . Platelet-shaped metal pigment according to any of preceding claims, wherein the surface of the platelet-shaped metal pigments is free from salts of the respective metal and a carboxylic acid and especially is free from salts of the respective metal and a fatty acid.

12. Use of the platelet-shaped metal pigment of claims 1 to 11 as substrates in a further encapsulation step with metal oxide, particularly with silica and / or organic polymers.

13. Method of manufacturing platelet-shaped metal effect pigments according to claims 1 to 11 comprising the following steps: a) provision of a metal grit, b) milling the metal grit of step a) in a solvent in presence of a milling equipment comprising grinding balls using a fatty ester or a polyethoxylated fatty ester of a monosaccharide or disaccharide or mixtures thereof as grinding aid to form platelet-shaped metal pigments, c) separating the milled metal pigments and solvent from the milling equipment to obtain a metal pigment filter cake and d) optionally further steps like sieving or solvent exchange and finally e1) forming a metal effect pigment paste by adjusting the solvent content to the desired value or e2) drying the filter cake to form a powder of platelet-shaped metal effect pigments.

14. Method of manufacturing platelet-shaped metal effect pigments according to claim 11 , wherein the solvent is mineral spirit, isopropanol, 1-methoxy propanol, ethyl acetate, ethanol, n-propyl acetate, i-propyl acetate and mixtures thereof and preferably isopropanol or white spirit.

15. Use of fatty ester or a polyethoxylated fatty ester of a monosaccharide or a disaccharide as grinding aid in milling metal grit, preferably aluminum grit to a platelet-shaped metal pigment, preferably an aluminum effect pigment in a mill.

16. Use of the platelet-shaped metal pigments of any of claims 1 to 11 in paints, powder coatings, printing inks, cosmetics, toners or plastics.

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