Process for producing a surface-functionalised pigment, surface-functionalised pigment

Abstract

The invention relates to a process for producing a surface-functionalised pigment, to a surface-functionalised pigment, and to a printing ink. The process for producing a surface-functionalised pigment, in particular a colourshift pigment, comprises providing at least one layer of a pigment material on a carrier material (S1); detaching the pigment material from the carrier material using a water-containing liquid (S2); reducing the proportion of liquid in the detached pigment material until a suspension of the pigment having a water content of 25 to 75 wt.% is obtained (S3); adding a silane, which has at least one surface-active or reactive group and at least one functional group that can be hydrolysed with water, to the suspension of the pigment (S4); and drying the silane-containing suspension of the pigment, wherein the pigment is silanised (S5).

Description

[0001] V method for the creation of a surface-functionalized pigment, surface-functionalized pigment

[0002] The invention relates to a method for producing a surface-functionalized pigment, a surface-functionalized pigment and a use of the surface-functionalized pigment.

[0003] Data carriers, such as valuables, identification documents, security documents, and even valuables like branded goods, are often enhanced with pigments, such as color-shifting pigments, pearlescent pigments, and / or metallic effect pigments, for security purposes. These pigments are often printed on the media to allow verification of its authenticity and simultaneously serve as protection against unauthorized reproduction. Such pigments can be integrated into the substrate of the data carrier or applied to it. Pigments can be produced, among other methods, by coating a substrate, such as a film, with a pigment material. The coating is then removed from the substrate and ground into small fragments, as described, for example, in WO 2019057321 Al. These fragments can be suspended as pigments in a binder and ultimately printed.

[0004] The functionalization of inorganic particles, e.g., made of metals such as aluminum (Al) and chromium (Cr), metal oxides such as Al₂O₃ and Cr₂Ü₃, or metal nitrides such as BN, with silanes is known. The silane molecules possess both an inorganic head and an organic residue. The inorganic part of the molecule allows the silane to bond covalently to the surface of the particle to be functionalized. The organic residue of the silane can interact with other organic materials or be available for chemical reactions. In this way, for example, hydrophilic inorganic pigments can be functionalized so that they can be incorporated into hydrophobic organic binders (e.g., intaglio binders) for a printing process without agglomerating. A process for the production of pigments is known, for example, from DE 102020006457 Al. Silanes exist with different chemical anchor groups.For a reaction with particles to be functionalized, the silanes are typically first hydrolyzed. This occurs through reaction with water and the elimination of a leaving group bound to the silane. The hydrolyzed silane can react in aqueous solution with reactive groups, such as hydroxyl (-OH) or carboxyl (-COOH) groups, on the surface of the particle to be modified, via groups formed during hydrolysis. The reaction type is typically a condensation and occurs with the elimination of water. Since this reaction is an equilibrium reaction, the presence of water, according to Le Chatelier's principle, shifts the equilibrium towards the reactants and thus prevents the reaction from proceeding to completion.

[0005] Silicon dioxide exhibits reactive OH groups on its surface. Both aluminum and chromium typically have reactive groups on their surfaces because both metals are passivated by the formation of oxide layers, such as layers of Al₂O₃ and Cr₂O₃, and reactive OH groups also exist on these surfaces. For other metals or materials that do not have sufficient reactive groups on their surface, these can be generated by pretreatment with acids (e.g., nitric acid), alkalis (e.g., sodium hydroxide), hydrogen peroxide (H₂O₂), ozone, corona, or plasma treatment.

[0006] Several methods for the silanization of inorganic materials are known, including:

[0007] • Reaction in aqueous solution or alcoholic (e.g. ethanol, isopropanol) aqueous solution, as explained above.

[0008] • Gas-phase reaction following activation of the silane by aqueous or alcoholic aqueous solution. The silane is deposited from the gas phase (CVD, Chemical Vapor Deposition) and then reacts with the material to be functionalized.

[0009] • Activation of the surface of the material first with silicon tetrachloride (SiCL), followed by hydrolysis with water and finally reaction with organolithium compounds (Grignard reagents).

[0010] Furthermore, there are known ways to influence the reaction rate and the reaction product: • Use of alcoholic solutions, e.g., ethanolic solutions: This shifts the hydrolysis equilibrium towards the reactants. This results in a stabilization of the solution, slower hydrolysis, and prevention of premature condensation of the silane molecules.

[0011] • Acid catalysis during the reaction: This leads to a rapid hydrolysis and a slow condensation reaction of the silane molecules among themselves.

[0012] • Base catalysis during the reaction: This results in a slow hydrolysis and a rapid condensation reaction between the silane molecules.

[0013] • Catalysis of the reaction using ammonia or other non-nucleophilic amines such as triethylamine or diazabicycloundecene.

[0014] Known methods for silanizing a pigment thus involve the use of a variety of chemicals and solvents that can damage the pigment and are detrimental to the environment or health. Furthermore, the chemicals and solvents used can remain in the pigment as unwanted residues and impair its applications.

[0015] The task is to specify a simple and cost-effective method for producing a surface-functionalized pigment and a pigment produced using this method.

[0016] The invention is defined in the independent claims. The dependent claims relate to preferred embodiments.

[0017] One embodiment relates to a method for producing a surface-functionalized pigment, in particular a ColourShift pigment, with

[0018] Providing at least one layer of at least one pigment material on a carrier material;

[0019] Detachment of the pigment material from the carrier material using a water-containing liquid;

[0020] Reducing the liquid content of the detached pigment material until a suspension of the pigment with a water content of 25 to 75 wt.%, preferably 30 to 70 wt.%, is obtained; adding a silane having at least one surfactant or reactive residue and at least one water-hydrolyzable functional group to the suspension of the pigment; and

[0021] Drying of the silane-containing suspension of the pigment, whereby the pigment is silanized.

[0022] The process of these embodiments enables drying and surface functionalization of the pigment in a single process step. In the same process step, the silane can be added to the pigment suspension and / or the silane can be activated by hydrolysis with water. The hydrolysis can occur at the water-hydrolyzable functional group. Thus, the steps of adding the silane to the pigment suspension and drying the silane-containing pigment suspension can be performed in one process step. The process can therefore be carried out with a reduced number of process steps. The aqueous pigment can be dehydrated to excess water immediately after the pigment material is detached from the support material, dried, and silanized during drying.

[0023] In all embodiments, the pigment can be selected from a color-shifting pigment, a pearlescent pigment, and / or a metallic effect pigment. These pigments can each be surface-functionalized using the process. The pigment can have particles with a size between 1 and 100 pm, preferably between 20 and 50 pm. The suspension can be a fine suspension, e.g., with particle sizes between 1 and 100 pm, preferably between 20 and 50 pm.

[0024] Using this method, even with an unexpected excess of water in a silanization process, ideal surface functionalization of inorganic pigments can be achieved. A self-organized monolayer of silane can be formed. The pigment suspension can be dried by vacuum drying. Furthermore, the process can be carried out without the use of aggressive chemicals. For example, it is not necessary to use environmentally and health-damaging amines, acids, or alkalis. Acids and alkalis can damage the product, for example, by undesirably oxidizing the aluminum in the pigment structure. The process can also be carried out without the use of organic solvents. In a modification of the process, the silane can be added only during drying. This allows the system in which the process is carried out to be sufficiently inerted with water before the silane is added.Therefore, the device for drying the silane-containing suspension of the pigment does not need to be explosion-proof.

[0025] Furthermore, the process can be carried out at low cost and with minimal environmental impact. Residues of excess and / or unused silane can be removed from the product during drying, e.g., in a vacuum and / or by increasing the temperature, and do not interfere with the potential applications of the pigments. During drying, e.g., by vacuum drying, increasing amounts of water are continuously removed. This shifts the reaction equilibrium of silane and pigment condensation further and further towards the products, i.e., towards the silanized pigment. This promotes silanization at the surface of the pigment. The pigment can thus be produced with high quality, e.g., with a low tendency to agglomerate when incorporated into a binder.

[0026] The pigment material can be inorganic and / or contain at least one element selected from Cr, Al, and SiCh. The pigment can be a color-shifting pigment (also called a CS pigment), a pearlescent pigment, and / or a metallic effect pigment. The pigment can exhibit and / or produce an effect, such as an optically variable effect. The pigment can be used for a security feature, for example, on a data carrier, security document, or valuable item. The color-shifting pigment can be used for a color-shifting element. By varying the viewing angle, the effect pigment, the color-shifting pigment, the color-shifting element, and / or the security feature can, for example, change its color. Metallic effect pigments, also called metallic luster pigments, can be used to manufacture optically variable devices (OVDs) as anti-copying protection, for example, in security documents.

[0027] The substrate can be covered with a release layer and / or a liquid-soluble, particularly water-soluble, release layer. In this case, the pigment layer is applied to the release layer of the substrate. The release layer can also be called a release liner. The water-soluble release layer may contain polypropylene (PVP). The release layer can be applied to the substrate to facilitate the release, i.e., separation, of the pigment layer from the substrate. The substrate can be a film. The substrate may contain, for example, polyethylene terephthalate (PET), polyethylene (PE), polymethyl methacrylate (PMMA), and / or polycarbonate (PC).

[0028] The pigment layer on the substrate can be provided and / or applied to the substrate or the substrate covered with the release layer by physical vapor deposition (PVD) and / or chemical vapor deposition (CVD). The pigment layer can be provided as a dry and / or solid layer. The pigment layer can also be referred to as the pigment material layer. The pigment layer can be provided and / or applied with a thickness of 0.1 to 4 pm, preferably 0.3 to 3 pm, more preferably 0.4 to 2 pm. The pigment layer can be provided and / or applied with multiple layers of the same and / or different pigment material composition, particularly as a thin-film system.The application of the pigment material to the substrate can be achieved by applying a finished layer of a release layer and / or a finished layer of the pigment material to the substrate. Applying the pigment material to the substrate can involve applying the release layer to the substrate and applying the layer of pigment material to the substrate or to the substrate covered by the release layer.

[0029] The pigment layer can be designed as a thin-film system exhibiting an optically variable effect. For example, the pigment layer can be a color-shifting thin-film system, also known as a color-shifting thin-film system, which presents a different color impression to the viewer at different viewing angles. Color-shifting thin-film systems are based, for example, on an absorbing layer (e.g., Cr) and a reflective layer (e.g., Al), with the two layers separated by an interposed dielectric spacer layer (e.g., SiCh, MgF2, or ZnS). Furthermore, the thin-film system exhibiting an optically variable effect can have a symmetrical structure, for example, with the layer sequence Cr / SiO2 / Al / SiO2 / Cr or the layer sequence Al / SiO2 / Al / SiO2 / Al.CS pigments can be magnetic or can be made magnetic, for example by incorporating an FeSi layer as a magnetic layer. A possible structure of the associated layer sequence is, for example...

[0030] Cr / SiO2 / Al / FeSi / Al / SiO2 / Cr.

[0031] The pigment material can be dissolved with water, especially deionized water, as the water-containing liquid. Deionized water can also be called demineralized water (DI water). If the carrier material has a release layer that is soluble in the liquid, this layer can be dissolved and / or removed, especially washed away, when the pigment material is dissolved in the liquid.

[0032] The reduction of the liquid content can be achieved by dewatering and / or pressing the detached pigment material. This dewatering and / or pressing can be performed once or several times. When reducing the liquid content, a water content of the pigment suspension of 25 to 75 wt.%, preferably 30 to 70 wt.%, more preferably 40 to 60 wt.%, and more preferably 45 to 55 wt.%, can be obtained, and in particular adjusted. The detached pigment material can be milled, e.g., by wet milling. The detached pigment material can be milled to a particle size distribution D90 of 1 to 100 µm, preferably 20 to 50 µm, more preferably 20 to 40 µm, and more preferably 30 to 40 µm. Milling of the detached pigment material can be carried out before, during, and / or after reducing the liquid content.

[0033] Drying and / or silanization can be carried out by vacuum drying and / or temperature increase. This shifts the reaction equilibrium towards the products, i.e., towards the silanized pigment. Silanization, particularly the condensation reaction of the hydrolyzed silane, at the pigment surface is thereby promoted, and more extensive silanization can occur. The yield of silanized pigment is increased. The boiling point of the silane can be in the range of 100°C to 300°C at 950 hPa to 1013 hPa, preferably 200°C to 270°C at 1013 hPa, and more preferably 60°C to 140°C at 100 to 300 mbar. This allows a sufficient temperature for silanization to be established before any excess silane is removed from the pigment. During drying, the liquid, water, excess silane and / or a byproduct formed during the hydrolysis of the silane, e.g.Ethanol or methanol can be removed. The silane can be activated by hydrolysis with water after its addition to the pigment suspension and / or during drying of the silane-containing pigment suspension. This process hydrolyzes the water-hydrolyzable functional group of the silane, releasing a residue product. The addition of the silane to the pigment suspension and the drying of the silane-containing pigment suspension can be performed in a single process step.

[0034] The surfactant moiety of the silane can be hydrophilic, hydrophobic, oleophilic, and / or oleophobic. For example, a hydrophilic, inorganic pigment can be functionalized so that it can be incorporated into a hydrophobic, organic binder, e.g., for a printing process, without agglomerating. The surfactant moiety of the silane can contain an alkyl group with at least 3 carbon atoms, preferably 3 to 20 carbon atoms, more preferably 6 to 10 carbon atoms, and further preferably 7 to 8 carbon atoms. The surfactant moiety of the silane can be long-chain and / or branched. This can result in hydrophobization of the pigment. For example, the silane can be a trimethoxyoctylsilane.

[0035] The reactive residue of the silane can include at least one reactive group selected from an amine group, a methacryloxy group, a thiol group, a carboxyl group, a hydroxy group, and any combination thereof.

[0036] The at least one hydrolyzable functional group of the silane can be selected from an alkoxy group, in particular a methoxy or ethoxy group, a chloro group, in particular a dichlor or trichloro group, a triacetoxy group, or any combination thereof. An alkoxy group advantageously allows the hydrolysis of the silane to produce an alcohol as a residue product that is easily removed and does not undesirably attack the pigment material, e.g., by causing undesirable corrosion. For example, the silane can be a triacetoxysilane.

[0037] An amount of 2 to 7 wt.%, preferably 3 to 6 wt.%, of silane can be added to the pigment suspension. This amount is sufficient for extensive silanization and surface functionalization of the pigment. The process may include further steps. For example, the process may include at least one step selected from: providing the support material covered with a release layer; mechanically fracturing the applied pigment layer at specific locations; soaking the fracturing pigment layer in the liquid; and applying mechanical force to the support material covered with the pigment layer, such that the pigment layer is released as a plurality of pigment particles corresponding to the fractures present at the specific locations.

[0038] One embodiment relates to a surface-functionalized pigment, in particular ColourShift pigment, produced by a method according to one of the foregoing embodiments or variations thereof.

[0039] An additional embodiment relates to the use of a surface-functionalized pigment according to the above embodiment in a printing ink.

[0040] Another embodiment relates to a surface-functionalized pigment, in particular a ColourShift pigment, especially for data carriers, security documents and / or valuables, obtained or obtainable by a process according to one of the preceding embodiments or variations thereof. Another embodiment relates to a printing ink, especially for data carriers, security documents and / or valuables, containing a pigment according to one of the preceding embodiments. A further embodiment relates to a data carrier, a security document and / or a valuable, containing a pigment or a printing ink according to one of the preceding embodiments.

[0041] The preferred embodiments and modifications presented with reference to the method according to the invention and their advantages apply accordingly to the pigment according to the invention.

[0042] Further features of the invention will become apparent from the claims, the figures, and the description of the figures. The invention is explained in more detail below with reference to exemplary embodiments and the accompanying schematic drawings, which also disclose essential features of the invention. These exemplary embodiments serve only for illustration and are not to be interpreted as limiting. For example, a description of an exemplary embodiment with a plurality of elements or components is not to be interpreted as meaning that all such elements or components are necessary for implementation. Rather, other exemplary embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components from different exemplary embodiments may be combined with one another unless otherwise specified.Modifications and variations described for one embodiment may also be applicable to other embodiments. To avoid repetition, identical or corresponding elements in different figures are designated with the same reference numerals and are not explained multiple times. The figures show:

[0043] Fig. 1 schematically shows the steps of an exemplary process for the production of a surface-functionalized pigment; and

[0044] Fig. 2 schematically shows reaction equations of reactions taking place in an exemplary process.

[0045] Examples

[0046] Pearlescent pigments can be understood as pigments that exhibit angle-dependent changes in hue and / or gloss based on reflection and / or interference. Pearlescent pigments can be platelet-like. Pearlescent pigments can, for example, contain mica coated with one or more layers of, for example, T₁O₂ and / or Fe₂O₃. Colour-shift (CS) pigments can be understood as color-shifting thin-film pigments. Colour-shift pigments can, for example, convey a different color impression to a viewer depending on the viewing angle. Metallic effect pigments can be understood as pigments with a viewing-angle-dependent brightness shift. The effect is based on the reflection of incident light on the surface of the effect pigment or scattering at the edges of the pigment. The shallower the viewing angle, the more the scattering effect predominates.At steeper viewing angles, reflection predominates, so that a paint containing the pigment, and thus the areas of the paint containing the metallic effect pigment, appear bright in this case. Metallic effect pigments can be based on aluminum, copper, or brass, in particular.

[0047] In Examples 1 to 5, ColourShift(CS) and / or metallic effect pigments or pearlescent pigments were prepared using various exemplary silanes according to the process for producing a surface-functionalized pigment. Exemplary steps S1 to S5 of the process for producing a surface-functionalized pigment are shown schematically in Fig. 1. For the silanization of the pigments, alkoxy silanes or chlorosilanes were used in Examples 1 to 5 and their variations, as specified in Table 1. The boiling point of OCTMO is approximately 246 °C at 1013 hPa (DIN 51751), the boiling point of OCTEO is approximately 265 °C at 1013 hPa (DIN 51751), and the boiling point of trichloro(octyl)silane is approximately 233 °C at 975 hPa. The boiling point of Dynasylan MTMS is 102 °C at 1013 hPa. Dynasylan 4148 can decompose at 1013 hPa before reaching its boiling point.In examples of the process, the initial pressure when using Dynasylan 4148 is chosen, e.g., approximately 200 mbar, such that the boiling point of Dynasylan 4148 is below its decomposition temperature. This allows Dynasylan 4148 to be used in this way.

[0048] In step S1 of Example 1, a pigment layer consisting of pure aluminum (Al) was vapor-deposited onto a substrate material in the form of an approximately 10 pm thick polyethylene terephthalate (PET) film, as described, for example, in DE102020006457 Al, to produce a surface-functionalized metallic effect pigment. The layer thickness can be in the range of 0.5–10 pm, preferably in the range of 1–5 pm. In the present example, a layer thickness of 1 pm was chosen. In a modification of this example, the substrate film was printed with a water-soluble release layer of polyvinylpyrrolidone (PVP), e.g., 1–2 pm thick, in this case 1.5 pm thick, using a printing process, e.g., gravure printing, before the aluminum was vapor-deposited.

[0049] In step S2, the pigment material was then stripped from the carrier material using a water-containing liquid, in this example deionized water (DI water). Subsequently, in step S3, the liquid content of the stripped pigment material was reduced in a chamber filter press KFP 500-30-25KGA0-MPN from MSE Filterpressen until a suspension of the aluminum pigment with a water content of 40 wt% was obtained. The pigment exhibited an APOa layer on its surface. In step S4, 3 wt% of Dynasylan OCTEO (octyltriethoxysilane; Evonik), based on the dry weight of the pigment, was added as a silane. With the octyl group, OCTEO possessed at least one surfactant, and with the ethoxy groups, OCTEO possessed at least one water-hydrolyzable functional group. In a step S5, at approximately...The silane-containing pigment suspension was dried at 140 °C in a Bolz Lab Dryer ML003 vacuum dryer at an initial pressure of 200 mbar. The water content of the pigment suspension hydrolyzed the silane, thus activating it as shown in the reaction equation of the first line of Fig. 2. The pigment was then silanized and activated in a condensation reaction by removing water during drying, as shown by the right-pointing arrow in the reaction equation of the second line of Fig. 2. With respect to silanization, the pigment suspension contained excess water at the beginning of the drying process. Drying resulted in a self-organized monolayer of the silane OCTEO, covalently bonded to the surface of the aluminum pigment. Steps S4 and S5 were carried out in a single process step by adding the silane to the dryer, in a modification of Example 1.

[0050] The process of Example 1 was carried out in a modified form to produce a ColourShift pigment. In step S1, several pigment materials were deposited on the support material, or in a further modification, on the support material covered with a release layer, in the form of a thin-film system with multiple layers in the sequence Cr-SiO₂-Al-SiO₂-Cr, e.g., by PVD. In this example, the Cr layers were produced with a thickness of 4 nm and can be applied with thicknesses ranging from 4 to 10 nm. The SiO₂ layers were produced with a thickness of 300 nm and can be applied with thicknesses ranging from 200 to 1000 nm. The Al layers were produced with a thickness of 40 nm and can be applied with thicknesses ranging from 40 to 50 nm.The CS pigments produced can therefore have thicknesses from 0.4 to 2 pm.

[0051] The process of Example 1 was carried out in additional exemplary modifications to produce a pearlescent pigment exhibiting angle-dependent hue and / or gloss changes based on reflection and / or interference. For this purpose, in step S1, a substrate material in the form of an approximately 10 pm thick polyethylene terephthalate (PET) film was coated with a thin-film system consisting of alternating layers of TiCh and SiCh. In one modification of step S1, the substrate material was first printed with a release layer (PVP) and then coated with the thin-film system. The number n of layers was chosen as n = 3 in this example, and the coated layer structure was TiCh-SiCh-TiCh. The layer thicknesses can be in the range of 50–250 nm for each individual layer; in this example, a layer thickness of 200 nm was chosen for each individual layer, and the individual layers were deposited using PVD technology.

[0052] In a further variation of Example 1, and in Examples 2 to 5, the respective metallic effect or CS pigment material, or pearlescent pigment material, was applied to a 15 pm thick PET film with a total layer thickness of approximately 0.7 pm, ranging from 0.5 pm to 1.3 pm in variations. Different layer thicknesses of the CS pigment material can produce different color changes. The pigment material was applied, for example, by PVD or CVD. PVD was used for the CS pigment with the Cr-SiCh-Al-SiCh-Cr layer structure. After applying the pigment material to the substrate, the pigment was stripped from the PET film by washing it off with water, breaking up the pigment layer and yielding pigment platelets. The resulting pigment-water mixture was placed in a first chamber filter press KFP 500-30-25KGA0-MPN and dewatered.The pigment was then milled in the pigment-water mixture to achieve the desired particle size distribution. This distribution was obtained by milling with the Malvern Panalytical Mastersizer 3000, equipped with a Hydro MV wet dispersion unit, and measured in degassed demineralized water. The pigment suspension was then dewatered a second time in the first chamber filter press or in a second chamber filter press of the same design. After this second treatment in the chamber filter press, the water content of the pigment mixture was approximately 40 to 60 wt.%, resulting in a water-moist pigment. This relatively high water content served to hydrolyze the silane in the subsequent process, thus activating it for the silanization reaction. The water-moist pigment in the examples had a D90 particle size distribution of 30 to 40 pm after milling, while a variation of the examples showed a distribution of 20 to 30 pm.In a further modification of Example 1 and in Examples 2 to 5, the surface functionalization of the water-moist pigment and the hydrolysis and activation of the silane were carried out in a single process step together with a drying process. For this purpose, the water-moist pigment from the second chamber filter press was transferred to a Bolz Lab Dryer ML003 vacuum dryer. Before evacuating the dryer and increasing the temperature, the silane of the respective example, as specified in Table 1, was added to the water-moist pigment in the dryer. In an alternative drying procedure, the dryer was first evacuated, and the silane of the respective example was drawn into the dryer from a container by the vacuum. The amount of silane added was approximately 5 wt.% based on the dry weight of the pigment.The dry weight of the pigment in the examples was determined using a residual moisture scale MA35M from the manufacturer Sartorius Weighing Technology GmbH.

[0053] After adding the silane, the vacuum dryer was evacuated and heated. In the alternative drying procedure, the vacuum dryer was already evacuated, as the silane had been introduced under vacuum. The temperature of the vacuum dryer's thermal oil was set to 140 °C, measured at the inner wall of the double-walled vacuum dryer. The outlet pressure and the pressure inside the vacuum dryer during the process were approximately 100 to 300 mbar. Towards the end of the process, once the product was dry, the pressure dropped to a minimum of approximately 50–60 mbar. As soon as this final pressure was reached in the vacuum dryer and no more condensate, such as methanol or ethanol from the hydrolysis of the silane, water, and / or excess silane, was collected in the vacuum dryer's condensate separator, the process was complete. The temperature in the vacuum dryer was then reduced, the pressure was brought down to atmospheric pressure with air, and the product was removed.

[0054] For the silanes OCTEO and OCTMO of Examples 1 and 2, the hydrolysis products of the silane upon reaction with water are identical, and thus these silanes also yield an identically silanized pigment. One difference in the hydrolysis is that methanol is released as a residue in OCTMO, while ethanol is released as a residue in OCTEO. Furthermore, the process with OCTMO proceeds somewhat faster, as OCTEO (265 °C at 1013 hPa) has a slightly higher boiling point than OCTMO (246 °C at 1013 hPa). The quality of the surface treatment of the pigment of each example was verified using a phase distribution test in water and n-octane CAS 111-65-9, purity for synthesis, manufacturer Sigma-Aldrich. For this purpose, approximately 3 ml of deionized water and 3 ml of n-octane (purity: for synthesis) were placed in a 10 ml roll-topped snap-on glass vial. A spatula of the surface-treated pigment was added and then the vial was shaken vigorously.Table 1 shows the observed phase distribution for each of Examples 1 to 5. The variations of Examples 1 to 5 resulted in the same phase distribution. As Examples 1, 2, and 5 and their variations demonstrate, treatment with a hydrophobic silane led to almost complete distribution (>99%) of the pigment in n-octane, and thus to extensive hydrophobization of the pigment. These pigments are therefore suitable, for example, for use in hydrophobic binders for a printing process. Treatment with the more hydrophilic silane of Examples 3 and 4 resulted in a distribution of the pigment in both phases, making these pigments suitable, for example, for applications in printing processes using more hydrophilic and / or aqueous binders. The surface-functionalized pearlescent pigments produced in variations of the examples also showed a phase distribution in the phase distribution test, either only in the n-octane or in both phases.

[0055] In further modifications of Examples 1 to 5, 2 to 7 wt% of the silane and / or a water content of the pigment suspension of 25 to 75 wt%, preferably 30 to 70 wt%, and particularly 40 to 60 wt%, were used. Drying was carried out at 120 to 160 °C and an initial pressure of 100 to 300 mbar. The support material had a layer thickness of 5 to 20 pm. The total layer thickness of the pigment material on the support material was 0.5 to 1.3 pm. In further modifications of the examples, a support film made of, for example, PET was used as the support material, which was or was covered with a water-soluble release layer, for example, made of PVP (polyvinylpyrrolidone), with a layer thickness of 0.05 to 20 pm, which dissolved upon stripping.

[0056] The process for producing a surface-functionalized pigment enables the drying and surface treatment of the pigments in a single step. Furthermore, the process allows for ideal surface functionalization of inorganic pigments with a self-organized monolayer of the silane, without the use of organic solvents and even with a surprisingly high excess of water for a silanization process. This has been demonstrated particularly for hydrophobic silanes, such as those in Examples 1 and 2, which are insoluble in aqueous solvents. Surface treatment with the silanes of Examples 1, 2, and 5 can be used not only to generate reactive groups but also to make inherently hydrophilic pigments compatible with hydrophobic binders. Additionally, an increase in the chemical resistance of the pigment, e.g., to aqueous acids or alkalis, can be achieved.

[0057] Figure 2 schematically shows, in the second row, the reaction equation for Example 1 of the silanization of the Al(aluminum) pigment particle coated with Al₂O₃ with the silane OCTEO during the drying of the pigment suspension. First, the silane OCTEO was hydrolyzed by the water content of the pigment suspension according to the reaction equation in row 1 of Figure 2. In the example of octyltriethoxysilane (OCTEO) shown, the ethoxy group (-OC₂H₅) was cleaved during the hydrolysis of the silane, forming ethanol. Subsequently, according to the reaction equation in row 2 of Figure 2, the condensation reaction of the silanol formed onto the Al₂O₃ on the surface of the pigment particle took place upon the removal of water.

[0058] Table 1

Claims

Patent claims 1. Method for producing a surface-functionalized pigment, in particular a ColourShift pigment, with Providing at least one layer of at least one pigment material on a carrier material (Sl); Detachment of the pigment material from the carrier material with a water-containing liquid (S2); Reducing the liquid content of the detached pigment material until a suspension of the pigment with a water content of 25 to 75 wt.%, preferably 30 to 70 wt.%, is obtained (S3); Addition of a silane having at least one surfactant or reactive residue and at least one water-hydrolyzable functional group to the suspension of the pigment (S4); and Drying of the silane-containing suspension of the pigment, whereby the pigment is silanized (S5).

2. The method of claim 1, wherein the pigment material is inorganic and / or contains at least one element selected from Gr, Al and S1O2; and / or wherein the pigment is a pearlescent pigment, a ColourShift pigment and / or a metallic effect pigment.

3. Method according to claim 1 or 2, wherein the carrier material is or is covered with a release layer and / or with a release layer soluble in the liquid, in particular water-soluble.

4. A method according to any of the preceding claims, wherein the layer of pigment material is provided on the substrate material or the substrate material covered with the release layer by means of physical vapor deposition (PVD) and / or chemical vapor deposition (CVD). and / or is applied or is applied; and / or wherein the layer of pigment material is provided and / or applied with a layer thickness of 0.1 to 4 pm, preferably 0.3 to 3 pm, more preferably 0.4 to 2 pm; and / or wherein the layer of pigment material is provided and / or applied with several layers of the same and / or different composition of the pigment material, in particular as a thin-film system.

5. Method according to any of the preceding claims, wherein the pigment material is dissolved with water, in particular deionized water, as the water-containing liquid; and / or wherein the release layer is dissolved and / or removed when the pigment material is dissolved in the liquid.

6. A method according to any one of the preceding claims, wherein the reduction of the liquid content is carried out by dewatering and / or pressing the detached pigment material; and / or wherein, upon reduction of the liquid content, a water content of the pigment suspension of 25 to 75 wt.%, preferably 30 to 70 wt.%, more preferably 40 to 60 wt.%, more preferably 45 to 55 wt.%, is obtained; and / or wherein the detached pigment material is ground; and / or wherein the detached pigment material is ground to a particle size distribution D90 of 1 to 100 pm, preferably 20 to 50 pm, more preferably 20 to 40 pm, more preferably 30 to 40 pm.

7. A method according to any of the preceding claims, wherein drying is carried out by means of vacuum drying and / or temperature increase; and / or wherein the boiling point of the silane is in the range of 100°C to 300°C at 950 hPa to 1013 hPa, preferably 200°C to 270°C at 1013 hPa, more preferably 60°C to 140°C at 100 to 300 mbar.

8. A method according to any of the preceding claims, wherein the silane is activated by hydrolysis with water after the addition of the silane to the suspension of the pigment and / or during the drying of the silane-containing suspension of the pigment; and / or wherein the addition of the silane to the suspension of the pigment and the drying of the silane-containing suspension of the pigment are carried out in a single process step.

9. A method according to any of the preceding claims, wherein the surfactant residue of the silane is hydrophilic, hydrophobic, oleophilic, and / or oleophobic; and / or wherein the surfactant residue of the silane contains an alkyl group with at least 3 carbon atoms, preferably 3 to 20 carbon atoms, more preferably 6 to 10 carbon atoms, and further preferably 7 to 8 carbon atoms.

10. A method according to any of the preceding claims, wherein the reactive residue of the silane comprises at least one reactive group selected from an amine group, a methacryloxy group, a thiol group, a carboxyl group, a hydroxy group and any combination thereof; and / or wherein the at least one hydrolyzable functional group of the silane is selected from an alkoxy group, in particular a methoxy group or an ethoxy group, a chloro group, in particular a dichlor group or a trichloro group, a triacetoxy group or any combination thereof.

11. Method according to one of the preceding claims, wherein an amount of 2 to 7 wt.%, preferably 3 to 6 wt.%, of the silane is added to the suspension of the pigment.

12. Surface-functionalized pigment, in particular ColourShift pigment, produced by a method according to one of the preceding claims.

13. Use of a surface-functionalized pigment according to claim 12 in a printing ink.

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