Coating composition for producing magnetically induced images

The present invention relates to coating compositions for producing magnetically induced images. More particularly, it relates to printing inks for the production of magnetically induced images for use on secure documents or securities or branded products in order to protect them against falsification and illegal reproduction.

Background of the invention [0002] Optically variable elements of different types are used as an effective security measure on secure documents and securities. Among them, optically variable printing inks (OVP®; EP-A-0227423) are particularly important optically variable copy protection means. Optically variable (OVI®) printing inks are used to print surfaces and / or signs that exhibit a color that varies depending on the viewing angle (= color shift).

[0003] Said copy protection paints are made based on optically variable pigments (OVP); preferred types are thin-film optically interference flake-shaped pigments described in US 4,705,300; US 4,705,356; US 4,721,271 and related disclosures.

[0004] Other useful OVP types for recipes of optically variable inks include coated interference pigments described in US 5,624,486 and US 5,607,504 and thin-film cholesterol (i.e., chiral-nematic) liquid crystal pigments described in US 5,807,497 and US 5,824,733.

[0005] Optically variable printing inks, coatings and varnish products are known in the art, e.g., from EP-A-0227423, US 5,279,657, or WO 95/29140. These optically variable printing inks can be used in many printing processes, such as printing with copper plates (intalgio printing), gravure printing, flexographic printing or screen printing.

[0006] As known to a person skilled in the art, the wet film thickness obtained in said printing processes can vary over a wide range, from about 2 μm to about 50 μm, depending on the method and conditions used.

[0007] In order to obtain a strong color shifting effect for a printing ink or an optically variable coating, the optically variable pigment (OVP) preferably has the shape of a plate or flake, as disclosed in the prior art.

[0008] Perceived optical properties and color purity depend on the final orientation of the pigment in the cured ink layer or the coating on the substrate. Randomly oriented flakes or optically variable pigment plates exhibit poor color shift and low color purity. The maximum color shift and color purity requires that the flakes or plates of the optically variable pigment in the ink or coating adopt the same particular orientation, e.g., coplanar to the surface of the substrate.

[0009] These optical effects are further enhanced when the surface of the substrate is pre-leveled by applying a primer. Optically variable pigment flakes can be easier to lay flat in this case, thereby increasing surface coverage, color purity and color shift.

[0010] In order to obtain coatings having optically variable pigment flakes arranged in the same flat position on the surface, typically a printing ink or a coating formulation is used that allows the wet film thickness to be reduced during the drying process to less than 10 μm. The gradual reduction of the thickness of the layer during the drying process forces the optically variable pigment flakes to settle in a single plane parallel to the surface of the substrate, ensuring maximum coverage and color shift on the substrate.

[0011] Magnetic optically variable pigments are disclosed in WO 02/073250; US 4,838,648; EP-A-686,675; WO 03/00801 and US 6,838,166 as an improvement of optically variable pigments for printing inks for security documents, securities and banknotes; these documents are incorporated herein by reference.

[0012] Magnetic optically variable pigments in printing inks or coatings make it possible to produce images, drawings and / or patterns magnetically produced by applying a suitable magnetic field, causing local orientation of the magnetic optically variable pigment in the coating, followed by drying / curing of the latter. The result is a fixed image, drawing or pattern induced magnetically in optically variable paint.

[0013] Materials and technologies for the orientation of magnetic molecules in coating compositions and printing processes are disclosed in US 2,418,479; US 2,570,856; US

3,791,864; DE 2006848-A; US 3,676,273; US 5,364,689; US 6,103,361; US 2004/0051297; US 2004/0009309; EP-A-710,508; WO 02/090002; WO 03/000801; WO 2005/002866 and US

2002/0160194; these documents are included herein as related material.

[0014] US 2,418,479 and US 2,570,856 disclose a method and coating composition for the magnetic orientation of metallic pigments in paint layers. Said layers exhibit a strong degree of orientation and a low degree of brightness as well as unusual properties of reflection and transparency. The metallic pigments include flakes of a ferromagnetic material, preferably nickel, in amounts ranging from 0.1% to 95% by weight relative to the film-forming binder; and organic volatile components are included in the composition in amounts ranging from 50% to 70% by weight relative to the total weight. A 25 mil (635 μm) wet coating is applied, and is subjected to a magnetic field to orientate the metallic flakes, keeping the field until the layer is dried. These documents do not apply to OVI® and mainly disclose paint compositions containing magnetic metallic pigments in the form of flakes and a coating with an effect based thereon. There are no recipe rules for recipe size, flake concentration and coating thickness for the best optical effect.

[0015] US 3,791,864 and DE 2006848-A relate to furnace enamel compositions, nitrocellulose compositions and two-component compositions containing magnetic components (e.g., lamellar-shaped iron pigments or rods) for producing magnetically oriented coatings. The documents relate to the method and process of magnetic orientation of pigments in a two-layer coating; the formulation aspects of the coating composition used are, however, not considered.

[0016] US 3,676,273 discloses magnetically oriented coatings containing high reflecting nickel flakes dispersed in an acrylic binder. The amount of magnetic pigment varies from 0.1% to 95% by weight relative to the film-forming material. Specific aspects of preparing recipes are not provided in this document.

[0017] US 5,364,689 discloses a painted product comprising magnetic particles having a non-spherical shape in a paint medium in which said magnetic particles are oriented to give a three-layer optical appearance pattern. Magnetic particles include one or more materials from nickel, cobalt, iron and their alloys. The particles have a thickness of 0.1 to 1.0 μm and a length of 10 to 100 μm. The base for the paint is selected from alkyl, polyester, acrylic, polyurethane and vinyl resins. The particles are in amounts between 1 and 60 parts per 100 parts by weight of the paint base. However, no specific rules regarding the paint base recipe are given.

[0018] US 6,103,361 relates to heat-resistant coating compositions comprising fluoro polymers, such as PFTE (polytetrafluoroethylene) and magnetizable flakes that allow the magnetic development of patterns in the coating on a frying pan.

[0019] US 2004/0051297 and US 2004/0009309 relate to a method and apparatus for orienting magnetic flakes during painting or printing processes. The particles of the magnetic optically variable pigment are dispersed in the liquid medium of the lacquer or ink. A typical petal is about 20 μm long and about one μm thick. The flakes typically contain a magnetic metal layer, such as a thin layer of ferromagnetic metal or an alloy such as cobalt, nickel or PERMALOY (typically 80% Ni, 20% Fe) and an optical interference structure, such as the absorber structure, the Fabry-Perot dielectric reflector on both sides of the metallic layer. US 2004/0051297 contains notes on the effect of the thickness of the layer and the type of organic carrier used on the magnetic orientation of the pigments. But,

[0020] WO 02/090002 relates to processes for the preparation of coated articles with the formulas by using a magnetic optically variable pigment and coated articles. The pigment consists of reflecting magnetic flakes (RMF) of the type described in WO 03/000801 "Multi-Layered Magnetic Pigments and Foils / Multilayer magnetic pigments and foils" and contains a magnetic core layer. However, no rules have been given for creating recipes for coating compositions that should be used.

[0021] WO 05/002866 relates to a method and means for producing a magnetically induced pattern in a coating comprising magnetic particles. Said coating preferably contains magnetic optically variable particles. The coating composition is preferably selected from the group of liquid inks including screen printing inks, intaglio printing inks and flexographic inks. Liquid inks have a low viscosity (in the range of 0.1 to 5 Pa * s in 20^aboutC) and allow easy orientation of the magnetic pigment. The drying / curing of the ink may be based on solvent or water evaporation, and UV crosslinking or hybrid curing mechanisms, including solvent evaporation, UV curing and other reticulation reactions, such by oxidation. None of the given paint formulations, however, were optimized for the magnetic pattern / imprinted effect in the coating.

[0022] US 2002/0160194 relates to multi-layered magnetic pigments and films. The disclosed pigment flakes may be spread in a binder medium to form a dyeing composition (printing ink) that can be applied to a wide range of objects or papers. The binding medium contains a resin or a mixture of resins, and a solvent (organic solvent or water) and can be dried / cured in heat processes such as heat-curing, heat-setting or solvent evaporation by means of heat or photochemical cross-linking.

[0023] The printing inks and optically variable coating compositions used in the prior art are directed to displaying a bright color, a strong color shift and providing a good coverage of the substrate when using as little as possible an amount of optically variable pigment. A low concentration of pigment is desirable to reduce raw material costs and to obtain good printing ink and print durability. These objectives have been achieved by providing printing inks with a relatively large amount of volatile components, such as organic solvents, water or mixtures thereof, of the order of 50% by weight or more, based on the weight of the composition and a relatively small amount of non-volatile components, i.e. binding and OVP, of the order of 50% by weight or less, based on the weight of the composition.

[0024] The specific formulation ensures a reduction in the volume of the coating layer during the drying process and proper orientation of the OVP particles in the plane of the printed substrate. This is why most OVI formulations or coating formulations containing pigments with an optical effect are based on solvents or water, with solids content not exceeding 50%. The solids content represents the proportion of non-volatile constituents in the printing ink or coating layer after the drying / curing processes.

[0025] However, in the case of magnetic optically variable pigments, it has been found that this type of paint formulas, when used to develop magnetic images, drawings or patterns in the printed ink layer, leads to poor visual effects.

Brief Description of the Invention The technical problem underlying the present invention was to find coating compositions and appropriate formulation principles that are particularly adapted to the magnetic orientation of a magnetic optically variable pigment (MOVP) in a printing ink or coating layer that gives an attractive visual effect. By using conventional formulations suitable for OVI® printing, magnetic images transferred to the wet ink layer are remarkably strongly reduced in terms of resolution and contrast during the drying / curing process, due to the shrinkage of the printed ink or coating layer in the vertical direction.

[0027] The resulting inks should comply with standard printing requirements, such as print speed and print resolution, and economic cost control restrictions by limiting the quantities applied. Printing technologies for use in MOVP particle printing should include flexographic printing, gravure printing, screen printing and roller coating.

[0028] According to the present invention, this problem has been solved by means of a coating composition as defined in the appended claims.

[0029] In particular, the present invention relates to a coating composition for producing magnetically inducable images according to the present invention consisting of volatile constituents (S) and non-volatile constituents, the latter consisting of a paint (I) adhesive and a solvent-dispersible adhesive. magnetically orientate the optically variable (P) interference pigment, characterized in that the ratio of the volume of the paint (V (I)) to the volume of the pigment (V (P)) is higher than 5.0, and in that the coating composition is a printing ink selected from the group consisting of flexographic printing inks, intaglio printing inks, printing inks for screen printing and printing inks by rollers.

[0030] The present invention also relates to a method of producing a coating composition for producing magnetically inducable images, which comprises the step of mixing together volatile components (S) and non-volatile components, the latter consisting of a paint adhesive (I) and orientable a magnetically variable optically variable (P) pigtail, characterized in that the ratio of the volume of the varnish binder (V (I)) to the volume of the pigment (V (P)) is higher than 5.0, and in that the coating composition is a printing ink chosen from the group consisting of flexographic printing inks, printing inks for intaglio printing, printing inks for screen printing and printing inks by rollers.

[0031] According to the present invention, the term "magnetic optically variable pigment (MOVP)" refers to magnetic particles in the form of platelets or flakes containing an optical interference coating, as is known in the art. A special property of MOVP in relation to OVP is that the MOVP particles can be orientated by applying a magnetic field. MOVPs are therefore "optically variable interfering pigments that can be magnetically oriented". The MOVP contained in the printing ink or coating composition of the present invention consist of flat plates or flake-shaped particles selected from the group of interference pigments with vacuum deposited magnetic thin film, coated interference metal pigments, coated non-metallic interference pigments, magnetic liquid crystal pigments as disclosed in PCT / EP2005 / 056260 and mixtures thereof. Particularly preferred are five-layer or seven-layer interference pigments with a vacuum-applied magnetic thin layer according to US 4,838,648 and WO 02/73250.

[0032] The MOVPs used in the present invention are also characterized by their average particle size. In order to obtain saturated colors and rapid color changes, the average particle diameter (d50) should be typically in the range of 5 to 40 μm, preferably 15 to 25 μm, and have a thickness of 0.1 to 6 μm, more preferably in the range of 0 , 5 to 3 μm.

[0033] According to the present invention, the term "volatile components" refers to ingredients having a boiling point below 300^aboutC under normal pressure, i.e., anything that evaporates after printing. The volatile components contained in the printing ink composition / coating composition can be selected from organic solvents, water and mixtures thereof, i.e. from solvents typically used in the preparation of printing inks.

[0034] According to the present invention, the term "non-volatile constituents" refers to ingredients having a boiling point of at least 300^aboutC under normal pressure, i.e. everything that remains after printing.

[0035] According to the present invention, the term "paint vehicle" refers to a non-volatile part of a printing ink or coating composition, with the exception of a magnetic optically variable interference pigment. The paint binder may, however, contain other pigments. Thus, the paint binder of the present invention may contain components from the group consisting of colorless varnishes / varnishes (i.e., binders), oligomers, fillers, pigments, dyes, leveling agents, wetting agents, surfactants, corrosion inhibitors, drying catalysts. , photoinitiators, waxes, cross-linking agents, non-volatile diluents or monomers.

[0036] According to the present invention, the term "volume of a paint binder" refers to the volume of the dried / cured paint binder.

[0037] According to the present invention, three different mechanisms are usually distinguished by the term "drying" in the art. Two, mainly physical, drying processes involve evaporating the volatile components of the printed ink or coating, leaving their solid constituents in the form of resin and pigment, and penetrating / absorbing non-volatile paint or coating solvent into the substrate. A third chemical drying process, also called curing or crosslinking, refers to converting a liquid composition into a solid composition by chemical polymerization, or a crosslinking reaction initiated by UV radiation, electron beam bombardment, or oxidative polymerization (oxidative crosslinking caused by a common oxygen and catalysts such as as Co and Mn catalysts). One or more of these drying processes may be involved in drying the same individual printing ink or coating. Thus, curing is a specific form of drying. "Double cure" means a combination of physical evaporation and / or penetration into the substrate of volatile components cured by UV radiation or by oxidation polymerization or chemical polymerisation initiated with a suitable additive; "UVOX" means a combination of UV curing and oxidation polymerization. "Double cure" means a combination of physical evaporation and / or penetration into the substrate of volatile components cured by UV radiation or by oxidation polymerization or chemical polymerisation initiated with a suitable additive; "UVOX" means a combination of UV curing and oxidation polymerization. "Double cure" means a combination of physical evaporation and / or penetration into the substrate of volatile components cured by UV radiation or by oxidation polymerization or chemical polymerisation initiated with a suitable additive; "UVOX" means a combination of UV curing and oxidation polymerization.

[0038] Printing technologies that are used to print MOVP particles include flexographic printing, concave printing, screen printing and roller coating.

[0039] In order to achieve printing requirements, suitable printing elements are selected to apply a typical average dry film thickness in the range of 2 to 50 μm, preferably 5 (flexographic printing) to 30 μm (screen printing).

[0040] The average diameter of the pigment is chosen depending on the thickness of the layer that can typically be obtained and the technical constraints associated with the use of a given type of printing. The selection of too small pigment particles will in all cases lead to poor color shifting, strong light scattering and low color saturation. This is well known to a person skilled in the art and will be taken into consideration by him in the selection of suitable pigments.

[0041] It has been found that the vertical shrinkage of the printing ink or coating layer must be avoided during the drying / curing process in order to prevent the position of the planar oriented pigment particles from being absorbed, which significantly reduces or even completely destroys the orientation effect produced by the magnetization. This is achieved by providing a suitably thick layer of non-volatile paint binder that remains after evaporation of volatiles.

[0042] Thus, the volumetric ratio V (I) / V (P) of the dried / cured paint binder (I) to the volume of the magnetic optically variable pigment (P) contained in the paint binder is of greatest importance. It was found that at a volume ratio V (I) / V (P) below 3.0 it was not possible to produce a satisfactory magnetic image in the coating of the present invention. According to the present invention, volumetric ratios are calculated based on experimental data and known product properties as disclosed in the detailed description.

[0043] What must be included is the thickness of the dried / cured ink layer. The inventors have found that the layer of dried / hardened solid ink should have a thickness of not less than d50 / 3, preferably not less than d50 / 2, in order to obtain a coating layer that is orientable giving a satisfactory magnetically oriented image. The size d 50 is the average diameter of the optically variable magnetic pigment and is determined in a manner known in the art.

[0044] In coatings that are much thinner than d50 / 2 the resulting orientation effect is poor.

[0045] The coating composition according to the present invention for the production of magnetic images may be a flexographic printing ink, a gravure printing ink, a silk-screen printing ink or a roll-printing ink and may be suitably used in flexographic printing, intaglio printing, screen printing processes or in a roll coating process.

Brief description of the drawings [0046]

Figures 1 to 3 show (a) the various optical effects obtained from the three example compositions and (b) the obtained pigment orientations within the paint layers.

Fig. 1 shows the results obtained with a UV-curable screen printing ink according to example 2a. Fig. 1a shows the obtained magnetized image. Fig. 1b shows a cross-section of a printing ink layer on a substrate from a scanning electron microscope (SEM).

Fig. 2 shows the results obtained with the UV-curable screen printing ink according to example 2b. Fig. 2a shows the obtained magnetized image. Fig. 2b shows a cross-section of the ink layer on the substrate from a scanning electron microscope (SEM).

Fig. 3 shows the results obtained with ultraviolet (UV) radiation-based screen printing ink according to example 2c (comparative example). Fig. 3a shows the obtained magnetized image. Fig. 3b shows a cross-section of a layer of ink on a substrate from a scanning electron microscope (SEM).

Detailed Description of the Invention [0047] Magnetic optically variable printing inks or coating compositions of the present invention are divided into three major components. Magnetic optically variable pigment (P), solvents or volatile components (S), (i.e., anything that eventually evaporates after printing: organic solvents, water or mixtures thereof) and a paint binder (I), (i.e. everything that remains printing, except for pigment: ie non-volatile constituents, such as varnishes (transparent) / varnishes, oligomers, fillers, pigments, dyes, leveling agents, wetting agents, surfactants, corrosion inhibitors, drying catalysts, photoinitiators, waxes, agents crosslinking, non-volatile diluents or monomers).

[0048] The magnetic pigment of the present invention is typically selected such that the platelet shaped particles have a median particle diameter (d50) in the range of 5 to 40 μm, more preferably a diameter in the range of 15 to 25 μm, and a thickness in the range of 0, 1 to 6 μm, more preferably in the range of 0.5 to 3 μm.

[0049] The diameter of the platelet-shaped particles should be understood as the average (d50) size, determined as known to a person skilled in the art. Likewise, the thickness of the platelet-shaped particles should be understood as the average distance between the upper and lower surfaces of the plate, as known to the skilled man.

It has been found by the inventors that irrespective of the process used to apply the magnetic ink to the substrate there is a lower limit of the volume ratio V (I) / V (P) of the paint adhesive (I) to the magnetic optically variable pigment (P) contained in the adhesive varnish, below which the visual effect of a magnetically oriented image, pattern or pattern disappears after drying the wet layer. This lower limit was found at a volume ratio V (I) / V (P) of 3.0. Good results are obtained at a volume ratio (V (I) / V (P) higher than 5.0 as claimed.

[0051] In other words, there must be a sufficient volume of the ink vehicle (I) per volume of pigment (P) in the dry paint layer to allow the pigment flakes to retain their orientation if it does not later fall into the plane of the substrate.

[0052] To calculate the volume ratio V (I) / V (P), the volume of the paint binder itself and the volume of the pigment in the ink vehicle must be known. This will then be outlined with reference to example 2.

[0053] Three ink formulations according to example 2a to 2c (UV-curable screen printing inks) served as a basis for correlation of recipe parameters with the obtained magnetic orientation effect. For the details of these examples, refer to the experimental section below. The formulation of example 2a shows excellent magnetic orientation; the formulation of example 2b shows slight degradation compared to example 2a, and the recipe of example 2c (comparative example) shows severe degradation compared to example 2a. It can be assumed that formulas with V (I) / V (P) ratios smaller than 3.0 no longer show any useful effect.

[0054] The experimental data determined for the basic recipe of example 2 (first column) showed that the specific gravity (density) of wet paint (Dmokrej paint) is 1.24 g / cm³, (for dry paint

Dsuchej paint 1.26 g / cm³). The density of the magnetic optically variable pigment was determined to be 2.82 g / cm³ (pigment density varies within certain limits, depending on the ratio of dielectric material (MgF2 (optical properties)) and magnetic material (Ni, Fe, Co or Ni alloy (magnetic properties)) in the pigment plate. The pigment used in this example has an experimental density 2.82 g / cm³and the density of the solvent (Dowanol) is 0.967 g / cm³. The experimental densities were determined using a pycnometer. The use of a pycnometer for density determination is well known to those skilled in the art and need not be discussed in detail here (see ISO 1183-1: 2004).

[0055] The base formulation of the wet ink can be approximated as follows (including W = mass, V = volume before mixing, I = paint binder, P = MOVP, S = solvent, D = density):

W (I) + W (S) + W (P) = Dmokrej paint (V (I) + V (S) + V (P)) = 1.241 [g / cm³] * (V (I) + V (S) + V (P)) [cm³] Given the weight ratio of the recipe W (I) + W (S) = 0.80 g / g and W (P) = 0.20 g / g and the pigment density D (P) = 2.82 g / cm³, the volume of pigment V (P) per gram of paint is calculated using the known relationship d = m / V as 0.071 cm³and the remaining volume of wet paint binder is 0.735 cm³.

[0057] The dried / cured ink formulation can be approximately described as follows:

W (I) + W (P) = Dsuchej paint (V (I) + V (P)) = 1.26 [g / cm³] * (V (I) + V (P)) [cm³] From the above data and the densities of solvent D (S) = 0.967 g / cm³ (Dowanol), the amount of solvent to be evaporated can be determined and the mass of the binder is as 0.747 g / g of the initial recipe of the ink; the corresponding volume V (I) is 0.68 cm³; this gives a density of the paint adhesive D (I) of 1.098 g / cm³. In the present example (basic recipe) the volume ratio V (I) / V (P) is thus determined to be 9.58.

[0059] Referring to examples of the magnetic orientation (recipes of Examples 2a to 2c), the respective volumetric ratios were calculated in the same way, using the determined specific weights of MOVP and the paint vehicle (I) and the respective weight percentages:

Table 1

<td>Recipe</td><td>Example 2a</td><td>Example 2b</td><td>Example 2c *</td>

<td>Paint binder</td><td>80</td><td>60</td><td>thirty</td>

<td>V (I)</td><td>0.637</td><td>0.729</td><td>0.273</td>

<td>Pigment</td><td>20</td><td>20</td><td>20</td>

<td>V (P)</td><td>0.071</td><td>0.071</td><td>0.071</td>

<td>Solid content</td><td>100</td><td>80</td><td>50</td>

<td>Volume ratio</td><td>10.27</td><td>7.69</td><td>3.85</td>

<td>V (I) / V (P)</td><td></td><td></td><td></td>

<td>Thickness of the dry layer</td><td>19</td><td>14</td><td>11</td>

comparative example [0060] Paint binder, pigment content and solids in%; V (I) and V (P) in cm³, dry film thickness in μm; the pigments used had d (50) of 22 μm.

Analogously the volumetric ratio V (I) / V (P) for example 1, which is not an example according to the invention, which concerns a gravure printing ink, was defined as 4.83. Densities of dried / hardened and wet ink for printing were marked as Dsuchej paint = 1.37 g / cm³, Dmokrej paint = 1.236 g / cm³. The pigment and solvent densities were determined as D (P) = 2.82 g / cm³, and D (S) = 0.805 g / cm³ (solvent for Ink solvent 27/29 from Shell Industrial Chemicals). 0.3 g / g of pigment (P) was mixed with 0.7 g / g (paint adhesive (I) + solvent for paint (S)). The density of the paint adhesive D (I) was determined as 1.066 g / cm³.

[0062] A further point to consider when effectively preparing a recipe for a printing ink is the thickness of the dried / hardened solid coating layer. The coating layer should be thicker than d50 / 3, preferably thicker than d50 / 2, where d50 is the average diameter of the flakes of the magnetic optically variable pigment, determined in a manner known in the art.

[0063] The solvent-containing coatings must be suitably thicker after application than the solvent-free coatings; considering that the thickness of the dry and solid layer after evaporation of the solvent must meet the criteria given above. In the examples underlying Fig. 1 to Fig. 3, the thickness of the dry solid layer satisfies the preferred criterion d50 / 2 in all cases.

[0064] The amount of non-volatile components in the coating composition of the present invention is selected between 50% and 100% by weight relative to the weight of the total composition, preferably between 80% and 100% by weight relative to the weight of the total composition.

[0065] Fig. 1 relates to a coating composition having a volume ratio V (I) / V (P) of 10.3 and a maximum solids content of 100% by weight (20% MOVP), which leads to optimal magnetically induced effects (images, patterns or drawings) in a corresponding coating layer, while Fig. 3 relates to a coating composition having a volume ratio V (I) / V (P) of 3.8 and a maximum solids content of 50% by weight (20% MOVP) which is still present. allows you to create magnetically generated images, patterns or drawings in the coating layer, albeit low quality.

The skilled person will know that the general idea described herein can be used for a series of ink formulas with different amounts of solids (with different amounts of MOVP) leading to different volumetric ratios V (I) / V (P).

[0067] Table 2 shows one of the possible compilations, in addition to many calculated formula matrices according to the inventive concept. The volume ratios are about 0.6 and about 23.

Table 2 (UV-curable screen printing ink according to example 2) _____

<td></td><td>SC 100%</td><td>SC 90%</td><td>SC 80%</td><td>SC 50%</td>

<td>And [%]</td><td>90</td><td>80</td><td>70</td><td>40</td>

<td>P [%]</td><td>10</td><td>10</td><td>10</td><td>10</td>

<td>V (I) [cm³/ cm³]</td><td>.8197</td><td>.7286</td><td>.6375</td><td>.3643</td>

<td>V (P) [cm³/ cm³]</td><td>0.0355</td><td>0.0355</td><td>0.0355</td><td>0.0355</td>

<td>V (I) / V (P)</td><td>23.1148</td><td>20.5464</td><td>17.9781</td><td>10.2732</td>

<td colspan="5">continued</td>

<td></td><td>SC 100%</td><td>SC 90%</td><td>SC 80%</td><td>SC 50%</td>

<td>And [%]</td><td>80</td><td>70</td><td>60</td><td>thirty</td>

<td>P [%]</td><td>20</td><td>20</td><td>20</td><td>20</td>

<td>V (I) [cm³/ cm³]</td><td>.7286</td><td>.6375</td><td>.5464</td><td>.2732</td>

<td>V (P) [cm³/ cm³]</td><td>0.0709</td><td>0.0709</td><td>0.0709</td><td>0.0709</td>

<td>V (I) / V (P)</td><td>10.2732</td><td>8.9891</td><td>7.7049</td><td>3.8525</td>

<td>And [%]</td><td>70</td><td>60</td><td>50</td><td>20</td>

<td>P [%]</td><td>thirty</td><td>thirty</td><td>thirty</td><td>thirty</td>

<td>V (I) [cm³/ cm³]</td><td>.6375</td><td>.5464</td><td>.4554</td><td>.1821</td>

<td>V (P) [cm³/ cm³]</td><td>.1064</td><td>.1064</td><td>.1064</td><td>.1064</td>

<td>V (I) / V (P)</td><td>5.9927</td><td>5.1366</td><td>4.2805</td><td>1.7122</td>

<td>And [%]</td><td>60</td><td>50</td><td>40</td><td>10</td>

<td>P [%]</td><td>40</td><td>40</td><td>40</td><td>40</td>

<td>V (I) [cm³/ cm³]</td><td>.5464</td><td>.4554</td><td>.3643</td><td>.0911</td>

<td>V (P) [cm³/ cm³]</td><td>.1418</td><td>.1418</td><td>.1418</td><td>.1418</td>

<td>V (I) / V (P)</td><td>3.8525</td><td>3.2104</td><td>2.5683</td><td>.6421</td>

<td colspan="5">SC solid content, I = mass fraction of the binder varnish, P = mass of the pigment fraction, V (I) / V (P) ratio volume</td>

[0068] Table 2 provides an arbitrary selection based on different amounts of total solids and their respective compositions. From a technical point of view, the skilled man will know that a minimum amount of pigment is required to obtain satisfactory results and that the large amount of pigment contained in the printing ink reduces the printability of the paint and increases the cost.

[0069] Thus, table 2 provides the selection of a suitable coating composition with respect to solid boundaries as well as the volume ratio V (I) / V (P) of the present invention. The indicated examples correspond to the claimed ratio V (I) / V (P) higher than 5.0 of examples 2a and 2b and serve only for purposes of illustration.

[0070] However, in printing inks with a volume ratio below 4.0, the amount of magnetic optically variable pigment increased relative to the printing ink liquid makes the magnetic orientation of the MOVP more difficult and may unnecessarily increase the cost of the magnetic optically variable ink if the printed layer paint will be thick.

The method for producing a printing ink or a coating composition according to the present invention for generating magnetically induced images comprises the step of mixing together volatile components (S) and non-volatile components, the latter consisting of a paint coat (I) and an optically variable interference optical pigment giving is oriented magnetically (P), characterized in that the ratio of the volume of the varnish binder (V (I)) to the volume of the pigment (V (P)) is higher than 5.0, and in that the coating composition is a printing ink selected from the group consisting of flexographic printing inks, printing inks for intaglio printing, inks for screen printing and printing inks by means of a printing roll chosen from the group of flexographic printing inks, printing inks for gravure printing,inks for screen printing and coating paints using rollers.

[0072] The volatile components for the method of making a printing ink or coating composition according to the present invention are selected from organic solvents, water and mixtures thereof.

The present invention further relates to a method for producing a magnetically induced image which comprises the steps of a) applying the coating composition of the present invention to the surface of the substrate, b) orienting the magnetic pigment particles in the applied coating composition of step a) by applying a magnetic field ic) curing / drying the oriented coating composition of step b) to fix the particles in an oriented position.

The coating method of step b) for applying the coating composition to the surface of the substrate is selected from flexographic printing, intaglio printing, roll coating and screen printing. These methods are well known to the expert.

[0075] Said printing processes allow the application of a wet film with a thickness of about 2 μm to about 50 μm. The preferred wet coating layer has a thickness ranging from about 5 Pm to about 30 Pm. The resulting coating on the substrate has an average dry thickness between 2 μm and less than or equal to 50 μm, preferably between 5 μm and less than or equal to 30 μm, more preferably between 10 μm and less than or equal to 20 μm.

[0076] The orientation step b) can be carried out either simultaneously with the coating step a) or after the coating step a). The magnetic orientation of magnetic particles is known and described in the state of the art. In relation to this, reference should be made to documents known in the art, cited in the introductory section of this application.

[0077] The curing / drying step c) may be carried out by physical evaporation of volatiles, UV curing, cross-linking by oxidation, chemical crosslinking, electron beam bombardment or any combination thereof. Also this step is known in the art and does not have to be described in detail here.

[0078] The present invention further relates to a magnetically induced coating on a substrate that comprises a magnetically oriented pigment (P) in a cured solid lacquer (I), characterized in that the ratio of the volume of a paint vehicle (V (I)) to the volume of the pigment (V (P)) is higher than 5.0, and in that the coating layer is thicker than d50 / 3, preferably thicker than d50 / 2, where d50 is the average diameter of the optically variable radiant optical flake flakes. The amount of magnetically oriented pigments in the solid cured paint (I) varies between 1% to 40% by weight, preferably between 5% and 30% by weight, more preferably between 10 and 20% by weight relative to the wet coating.

[0079] A printing ink or coating composition according to the present invention may be used to produce magnetically induced images. Said magnetically induced images can be used as security elements on, e.g., banknotes, credit cards, access cards, security signs, securities, legal documents or identity documents, means of transport, lottery tickets, event tickets, tax bands, threads safety labels, stickers, foils, security strips or products for security applications.

[0080] Said security element may additionally comprise additional marking means, such as infrared markers, fluorescent markers, UV markers, phosphorescent markers, magnetic markers, court markers and a mixture thereof.

[0081] The invention may be implemented on any type of material in the form of a printable sheet or tape, in particular on materials used for making banknotes, credit cards, access cards, security marks, securities, legal documents or identity documents, media tickets transport, lottery tickets, event tickets, tax bands, security threads, stickers, foils, security straps or products for security applications. The printable sheet or tape material may further comprise a single layer as well as a plurality of layers.

[0082] The present invention will now be further described with reference to non-limiting examples and drawings. Unless otherwise indicated, all amounts are given as weight percent.

Example 1 is not an example of the invention: A printing ink for intaglio printing on paper wipes [0083] In this example, a recipe for gravure printing on paper wipes is given.

<td>Product of the addition of tung oil and phenolic resin modified with maleic acid in high-boiling mineral oil (PKWF 28/31)</td><td>35%</td>

<td>Oily alkyd resin</td><td>7.50%</td>

<td>Alkylphenol resin modified with crude tung oil in paint solvent 27/29</td><td>16%</td>

<td>Polyethylene wax</td><td>3.30%</td>

<td>Aerosil 200 (Degussa-Huels)</td><td>2.00%</td>

<td>Magnetic optically variable pigment (7-layers)</td><td>thirty %</td>

<td>Solvent for printing inks 27/29 (Shell Industrial Chemicals)</td><td>6%</td>

<td>Cobalt octoate (11% metal)</td><td>0.10%</td>

<td>Manganese octanate (10% metal)</td><td>0.10%</td>

Example 2: Screen printing ink, UV curing [0084] In this example, a silk screen printing ink formulation according to the present invention is given.

<td></td><td>Recipe basic</td><td>Example 2a</td><td>Example 2b</td><td>Example 2c *</td>

<td>Paint binder (I) in total:</td><td>70%</td><td>80%</td><td>60%</td><td>thirty %</td>

<td>Oligomer of epoxidized acrylate</td><td>40</td><td>45.7</td><td>34.2</td><td>17.1</td>

<td>Trimethylolpropane triacrylate monomer</td><td>10</td><td>11.5</td><td>8.6</td><td>4.3</td>

<td colspan="5">(continued)</td>

<td></td><td>Recipe basic</td><td>Example 2a</td><td>Example 2b</td><td>Example 2c</td>

<td>Glycol diacrylate monomer tripropylene</td><td>10</td><td>11.5</td><td>8.6</td><td>4.3</td>

<td>Genorad 16 (Rahn)</td><td>1</td><td>1.1</td><td>0.9</td><td>0.4</td>

<td>Aerosil 200 (Degussa-Huels)</td><td>1</td><td>1.1</td><td>0.9</td><td>0.4</td>

<td>Irgacure 500 (CIBA)</td><td>6</td><td>6.8</td><td>5.1</td><td>2.6</td>

<td>Genocure EPD (Rahn)</td><td>2</td><td>2.3</td><td>1.7</td><td>0.9</td>

<td>Pigment (P) in total:</td><td>20%</td><td>20 %</td><td>20 %</td><td>20 %</td>

<td>Magnetic optically variable pigment (7 layers)</td><td>20</td><td>20</td><td>20</td><td>20</td>

<td>Solvent (S) in total:</td><td>10%</td><td>0%</td><td>20 %</td><td>50%</td>

<td>Dowanol PMA</td><td>10</td><td>0</td><td>20</td><td>50</td>

comparative example [0085] The formulation of example 2a was applied to security paper. Before drying, the wet printing ink was magnetized. The average dry film thickness was 19 μm. The solids content of the paint was 100%, wherein the magnetic optically variable (P) pigment was contained in an amount of 20% by weight and the paint adhesive (I) was contained in an amount of 80% by weight. The result is shown in Figs. 1a and 1b. In Fig. 1a, the obtained magnetic image is shown. Fig. 1b shows a cross-section of a printing ink layer on a substrate from a scanning electron microscope (SEM). The average angle of the petals is defined as 24^about ± 12^about in relation to the level.

[0086] In Fig. 1b, "matrix" refers to the fixing material that is needed to make the cross-section. The effect created by magnetization is a clearly defined image.

[0087] The formulation of example 2b was applied to security paper. Before drying, the wet printing ink was magnetized. The average dry film thickness was 14 μm. The solids content of the paint was 80%, the magnetic optically variable (P) pigment was included in the amount of 20% by weight, the paint vehicle (I) was contained in an amount of 60% by weight and the solvent (S) was contained in an amount of 20% by weight . The result is shown in Figs. 2a and 2b. In Fig. 2a, the obtained magnetic image is shown. Fig. 2b shows a cross-section of the ink layer on the substrate from a scanning electron microscope (SEM). The average angle of the petals is defined as 25^about ± 12^about in relation to the level. The effect created by the magnetization is a picture with reduced resolution but still clearly visible.

[0088] The formulation of example 2c (comparative example) was applied to security paper. Before drying, the wet printing ink was magnetized. The average dry film thickness was 11 μm. The solids content of the paint was 50%, the magnetic optically variable pigment (P) was contained in an amount of 20% by weight, the paint vehicle (I) was contained in an amount of 30% by weight and the solvent (S) was contained in an amount of 50% by weight . The result is shown in Figs. 3a and 3b. In Fig. 3a, the obtained magnetic image is shown. Fig. 3b shows a cross section of the ink layer on a scanning electron microscope (SEM) substrate. The average angle of the petals is defined as 10^about ± 9^about in relation to the level. The effect created by magnetization is a picture with a rather poor resolution.

[0089] The formulation of example 2a showed excellent susceptibility to magnetic orientation; the formulation of example 2b showed some degradation compared to example 2a, and the formulation of example 2c (comparative example) showed significant degradation compared to example 2a. It can be concluded that formulas with a ratio V (I) / V (P) of less than 3.0 will not show any useful effect.

[0090] It is evident from figures 1 to 3 and table 1 above that there is an excellent correlation between the susceptibility of the magnetic pigment and the volumetric ratio V (I) / V (P) on one side and between the pigment orientability and the dry film thickness On the other hand.

Example 3: Screen printing ink, UV drying [0091] In this example, a silk screen printing ink formulation according to the present invention is given .___

<td>Oligomer of epoxidized acrylate</td><td>40%</td><td rowspan="7">AND</td>

<td>Trimethylolpropane triacrylate monomer</td><td>10%</td>

<td>Tripropylene glycol diacrylate monomer</td><td>10%</td>

<td>Genorad 16 (Rahn)</td><td>1%</td>

<td>Aerosil 200 (Degussa-Huels)</td><td>1%</td>

<td>Irgacure 500 (CIBA)</td><td>6%</td>

<td>Genocure EPD (Rahn)</td><td>2%</td>

<td colspan="3"></td>

<td>Magnetic optically variable pigment (5</td><td>20</td><td></td>

<td>layer)</td><td></td><td></td>

<td colspan="3"></td>

<td>Dowanol PMA</td><td>10%</td><td>S</td>

Example 3: Printing ink for flexographic printing, UV curing. [0092] In this example, a flexographic printing ink formulation according to the present invention is given.

<td>Urethane acrylic oligomer</td><td>40%</td>

<td>Propoxylated tri-acrylate monomer glycerine</td><td>10%</td>

<td>Tripropylene glycol diacrylate monomer</td><td>15%</td>

<td>Florstab UV-1 (Kromachem)</td><td>1%</td>

<td>Magnetical optically variable pigment (7 layers)</td><td>25%</td>

<td>Aerosil 200 (Degussa-Huels)</td><td>1%</td>

<td>Irgacure 500 (CIBA)</td><td>6%</td>

<td>Genocure EPD (Rahn)</td><td>2%</td>