(19)
(11)EP 3 670 740 A1

(12)EUROPEAN PATENT APPLICATION

(43)Date of publication:
24.06.2020 Bulletin 2020/26

(21)Application number: 18214805.6

(22)Date of filing:  20.12.2018
(51)International Patent Classification (IPC): 
D21H 17/11(2006.01)
B32B 29/06(2006.01)
D21H 17/67(2006.01)
D21H 19/82(2006.01)
B32B 29/00(2006.01)
B32B 33/00(2006.01)
D21H 19/66(2006.01)
(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
Designated Extension States:
BA ME
Designated Validation States:
KH MA MD TN

(71)Applicant: European Central Bank
60314 Frankfurt am Main (DE)

(72)Inventors:
  • RAIMONDO, Mariarosa
    47521 Cesena (IT)
  • BLOSI, Magda
    48026 Russi (IT)
  • VERONESI, Federico
    48022 Lugo (IT)
  • BOVERI, Giulio
    15067 Novi Ligure (IT)
  • MOSELE, Giuseppe
    60316 Frankfurt am Main (DE)

(74)Representative: Prinz & Partner mbB 
Patent- und Rechtsanwälte Rundfunkplatz 2
80335 München
80335 München (DE)

  


(54)AMPHIPHOBIC CELLULOSIC MATERIALS, PRODUCTION THEREOF AND USES


(57) The present invention relates to an amphiphobic cellulosic material, a process for its production and the use of an amphiphobic coating for increasing dirt resistance and/or lifetime of a cellulosic material.




Description

FIELD OF INVENTION



[0001] The present invention relates to an amphiphobic cellulosic material, a process for its production and the use of an amphiphobic coating for increasing dirt resistance and/or lifetime of a cellulosic material.

BACKGROUND



[0002] The functionalization of cellulosic materials is extremely appealing with the aim of modifying their properties, reactivity and, most notably, their interaction with substances in the environment.

[0003] Compositions for making cellulosic materials, such as paper, cardboards, textiles etc., exhibiting an oil and water rough surface repellent are known in the art. In case the water and oil repellency of textiles, such as apparel, papers or cardboards, such as printing papers, food packaging papers, packaging cardboards and security papers, e.g. banknotes, need to be improved, it is necessary to maintain the look and feel of the materials to comply with the customers' expectations and/or relevant properties of the materials.

[0004] In particular banknotes are subjected to mechanical and environmental stress after input of the banknotes in the exchange circuits. For banknotes, the increased and preferably simultaneous repellence to water (hydrophobicity, superhydrophobicity) and oils/fats (oleophobicity, superoleophobicity) leads to the ability to decrease - or at least significantly limit - the adhesion of dirt (sebum, various stains) during their circulation, a phenomenon that diminishes their average lifetime. As of today, the need to withdraw dirty or damaged (by mechanical stresses) banknotes from circulation and to print and emit new ones leads to additional costs. At the moment, the average lifetime of a circulating banknote is estimated to be about 1.5 years.

[0005] EP 2 681 347 B1 and EP 2 864 522 B1 respectively disclose a method for the treatment of ceramic or metal surfaces for bestowing thereon a high hydrophobicity and oleophobicity. Ceramic and metal surfaces differ from cellulosic material surfaces in that they originally exhibit smooth surfaces and non-flexible materials, into which liquids penetrate generally less when compared to cellulosic materials.

[0006] Thus, there is still a need to provide amphiphobic cellulosic material exhibiting a simultaneous repellence to water and oils / fats and maintaining the look and/or feel of the cellulosic material. Preferably, the amphiphobic cellulosic material should exhibit an increased resistance to mechanical stress and/or an increased resistance to chemical stress and/or an increased lifetime when compared to cellulosic material not comprising the amphiphobic property.

SUMMARY OF INVENTION



[0007] The problem of the present invention is solved by the subjects of the independent claims. Advantages (preferred embodiments) are set out in the detailed description hereinafter including the figures as well as in the dependent claims.

[0008] Accordingly, a first aspect of the present invention relates to a cellulosic material comprising a cellulosic substrate and an amphiphobic coating, wherein the amphiphobic coating comprises an inorganic material and an organic fluoro material and is arranged on at least part of a surface of the cellulosic substrate, characterized in that the inorganic material is configured as a layer having a nanostructured surface on at least part of the surface of the cellulosic substrate, wherein the nanostructured surface of the layer of the inorganic material is at least partly fluorinated with the organic fluoro material, wherein the amphiphobic coating exhibits a nanostructured surface having
  1. i. a static water contact angle > 110°, preferably ≥ 120°, more preferably ≥ 140° measured at room temperature with a sessile drop method using 1 µl per drop deionized water,
  2. ii. a static n-hexadecane contact angle ≥ 60°, preferably ≥ 80°, more preferably ≥ 100° measured at room temperature with a sessile drop method using 1 µl per drop n-hexadecane,
  3. iii. optionally a melted sebum contact angle ≥ 60°, preferably ≥ 80° measured at 50 °C with a sessile drop method using 1.8 to 2.8 µl per drop synthetic sebum, and
  4. iv. optionally a surface energy ≤ 20 mJ/m2, preferable ≤ 15 mJ/m2, more preferable ≤ 10 mJ/m2 determined with the Owens, Wendt, Rabel and Kaelble (OWRK) method.


[0009] A second aspect of the present invention relates to a process for preparing an inventive cellulosic material, characterized in that the process comprises or consists of the following steps:
  1. a. Providing a cellulosic material substrate having a surface,
  2. b. Providing an inorganic material,
  3. c. Providing an organic fluoro material,
  4. d. Coating at least part of the surface of the cellulosic material substrate with the inorganic material thereby forming an inorganic material layer exhibiting a nanostructured surface and
  5. e. Coating at least part of the surface of the inorganic material layer with the organic fluoro material thereby forming a fluorinated inorganic material layer exhibiting a nanostructured surface of an amphiphobic coating.


[0010] A third aspect of the present invention relates to a use of a nanostructued amphiphobic coating comprising an inorganic material and an organic fluoro material exhibiting a
  1. i. a static water contact angle > 110°, preferably ≥ 120°, preferably ≥ 140° measured at room temperature with a sessile drop method using 1 µl per drop deionized water,
  2. ii. a static n-hexadecane contact angle ≥ 60°, preferably ≥ 80°, more preferably ≥ 100° measured at room temperature with a sessile drop method using 1 µl per drop n-hexadecane,
  3. iii. optionally a melted sebum contact angle ≥ 60°, preferably ≥ 80° measured at 50 °C with a sessile drop method using 1.8 to 2.8 µl per drop synthetic sebum, and
  4. iv. optionally a surface energy ≤ 20 mJ/m2, preferable ≤ 15 mJ/m2, more preferable ≤ 10 mJ/m2 determined with the Owens, Wendt, Rabel and Kaelble (OWRK) method,
for increase of dirt resistance and/or lifetime of a cellulosic material, characterized in that the nanostructured amphiphobic coating is arranged on at least part of a surface of a cellulosic substrate and wherein the inorganic material is configured as a layer having a nanostructured surface on at least part of the surface of the cellulosic substrate, wherein the nanostructured surface of the inorganic material is fluorinated with the organic fluoro material.

[0011] The aspects of the present invention as set out hereinbefore can also comprise, if reasonable to a person skilled in the art, any possible combination of the preferred embodiments as set out in the dependent claims or disclosed in the following detailed description.

BRIEF DESCRIPTION OF DRAWINGS



[0012] Further aspects, characteristics and advantages of the invention will ensue from the following description of the embodiments with reference to the accompanying drawings, wherein
Fig. 1
is a simplified cross-sectional view on a cellulosic material of an embodiment of the present invention.
FIG. 2
is a simplified cross-sectional view on a cellulosic material of an alternative embodiment of the present invention.
FIG. 3A), 3B), 3C)
are simplified views of process steps of an embodiment of the present invention

DETAILLED DESCRIPTION OF EMBODIMENTS



[0013] The present inventors have found out that the inventive cellulosic material exhibits amphiphobic properties, as it exhibits
  1. i. a static water contact angle > 110°, preferably ≥ 120°, preferably ≥ 140° measured at room temperature with a sessile drop method using 1 µl per drop deionized water,
  2. ii. a static n-hexadecane contact angle ≥ 60°, preferably ≥ 80°, more preferably ≥ 100° measured at room temperature with a sessile drop method using 1 µl per drop n-hexadecane,
  3. iii. optionally a melted sebum contact angle ≥ 60°, preferably ≥ 80° measured at 50 °C with a sessile drop method using 1.8 to 2.8 µl per drop synthetic sebum, and
  4. iv. optionally a surface energy ≤ 20 mJ/m2, preferable ≤ 15 mJ/m2, more preferable ≤ 10 mJ/m2 determined with the Owens, Wendt, Rabel and Kaelble (OWRK) method.


[0014] In the context of the present invention, the melted sebum contact angle can be determined any suitable synthetic sebum. A suitable synthetic sebum is in particular the following composition or any equivalent thereof:
Synthetic sebum according to Bey comprising free fatty acids (preferably 18 wt.-%), beef tallow (preferably 32.8 wt.-%), fatty acid triglycerides (preferably 3.6 wt.-%), lanoline (preferably 18.3 wt.-%), cholesterol (preferably 3.8 wt.-%), hydrocarbon mixture (preferably 12 wt.-%) and cutina (preferably 11.6 wt.-%), wherein the wt.-% are based on the total weight of the synthetic sebum composition (wfk - Testgewebe GmbH, Brüggen-Bracht, Germany, order code 00612).

[0015] The surface energy determined in the context of the present invention with the Owens, Wendt, Rabel and Kaelble (OWRK) method can be measured with any suitable method, e.g. Fowkes method, van Oss-Chaudhury-Good method and Zisman method.

[0016] The simultaneous repellence to water and oils / fats is facilitated by use of the amphiphobic coating comprising an inorganic material and an organic fluoro material. The amphiphobic coating is arranged on at least part of a surface of the cellulosic substrate and the inorganic material is configured as a layer having a nanostructured surface on at least part of the surface of the cellulosic substrate and the organic fluoro material is configured as a layer on at least part of the inorganic material layer retaining at least in part the nanostructured surface provided by the inorganic material.

[0017] The present invention acts on the rough cellulosic material surface by modifying the material surface, in particular by morphologically structuring the cellulosic material surface with the inorganic material and further increasing the repellency by chemically modifying at least part of the inorganic surface with the organic fluoro material.

[0018] In other words, the amphiphobic coating according to the present invention improves the known repellency properties of an organic fluoro coating, which generally facilitates oil repellence, by morphologically structuring the organic fluoro material layer using an inorganic material layer and thereby increasing the water repellency.

[0019] Due to the amphiphobic properties of the inventive cellulosic material, an increased dirt resistance is also facilitated when compared to a cellulosic material not comprising the amphiphobic coating.

[0020] Alternatively or cumulatively, an increased lifetime of the inventive cellulosic material is facilitated when compared to a cellulosic material not comprising the amphiphobic coating. In particular with respect to security paper, preferably banknotes as inventive cellulosic material, the increased dirt resistance and lifetime remarkably reduces the costs related to the withdrawal from the market due to soiling of banknotes. Furthermore, the printed graphics (numbers, images, etc.), relief carrying structures (intaglio printing, etc.) in particular allowing impaired people to read and other security features (holograms, watermark, etc.) are not impaired by the amphiphobic coating of the present invention.

[0021] Although EP 2 681 347 B1 and EP 2 864 522 B1 disclose methods for the treatment of smooth, non-flexible ceramic or metal surfaces for bestowing thereon a high hydrophobicity and oleophobicity, such treatments were not regarded to be suitable for cellulosic material surfaces. In particular the fact that the cellulosic material already exhibits a rough surface on a flexible substrate in contrast to the smooth surface of solid ceramics and metals was regarded to counteract the formation of the inorganic nanostructured surface layer. Moreover, on ceramics and metals the sol comprising the inorganic material remains on the surface and ,thus, allows the rearrangement of the inorganic material to form the nanostructured surface. In contrast thereto the liquid of the sol comprising the inorganic material penetrates into the cellulosic material and by absorption of the liquid into the cellulosic fibers and interstitials the surface of the cellulosic material changes. Furthermore, it was regarded that due to the absorption of the liquid the inorganic material would not have sufficient time to rearrange and form the nanostructued layer surface. In addition, the high curing temperatures in the range of 150 °C to 900 °C, which were regarded to be necessary for curing the inorganic gel film to obtain the nanostructured surface, would damage the cellulosic material as such. Accordingly, it is surprising that the inventive method provides the nanostructured amphiphobic layer by arranging the inorganic material in a layer exhibiting a nanostructured surface and chemically modifying at least part of the inorganic nanostructured layer with an organic fluoro material. Moreover, it is surprising that the nanostructured, amphiphobic layer according to the present invention remains stable on the flexible surface upon treatment simulating usage, like abrasion or crumpling test, and the superior amphiphobic properties remain.

[0022] According to all different aspects of the present invention, the cellulosic material substrate may be selected from the group consisting of paper, cardboard, textile, more preferably selected from the group consisting of printing paper, food packaging paper, packaging cardboard and security paper, in particular banknote, passport, identity card, and check. In particular all embodiments of all different aspects of the present invention are disclosed with respect to a banknote as substrate.

[0023] In the context of the present invention, the term "banknote" refers to a so called finished banknote, which means that it comprises all security features within the substrate and applied on the surface of the substrate, such as, e.g., (partly) embedded features, security printing layer, optical feature, foil feature, magnetic feature, tactile feature, electronic feature, etc., as well as other printing layers, ect..

[0024] According to the present invention, the amphiphobic coating is arranged on at least part, preferably all of the surface of the cellulosic substrate, such as a security paper, in particular banknote. In case security inks are to be used in case of robbery, the inks may also adhere to the surface of the inventively coated cellulosic material, in particular the inventively coated banknote. As security inks may not spread out on the inventively coated surface, the security inks should be dispersed by, e.g. spraying, exploding etc. prior to adherence.

[0025] According to a further alternative or cumulative embodiment of the present invention, the inorganic material may be selected from the group consisting of ceramic oxides, preferably Al2O3, TiO2, SiO2, Y2O3, ZnO and ZrO2. The use of Al2O3, TiO2, and SiO2 as the ceramic oxides facilitates both the inertness of the inorganic material layer when in contact with the environment and the maintenance of the feel and look of the cellulosic material substrate. Furthermore, in case the cellulosic material substrate is a paper, preferably a security paper, e.g. banknote, the ceramic oxides also retain the authentification of one or more security features in particular selected from the group consisting of optical features (holograms, watermarks, foil or micro lens patch or structures etc.), magnetic features, luminescent features, e.g. UV feature, infrared (IR) absorbing or emitting features, and electroluminescent features.

[0026] According to the present invention, the inorganic material is configured as a layer having a nanostructured surface on at least part of the surface of the cellulosic substrate. The nanostructured surface of the layer of the inorganic material is at least partly fluorinated with the organic fluoro material, so that the amphiphobic coating exhibits a nanostructured surface having
  1. i. a static water contact angle > 110°, preferably ≥ 120°, preferably ≥ 140° measured at room temperature with a sessile drop method using 1 µl per drop deionized water,
  2. ii. a static n-hexadecane contact angle ≥ 60°, preferably ≥ 80°, more preferably ≥ 100° measured at room temperature with a sessile drop method using 1 µl per drop n-hexadecane,
  3. iii. optionally a melted sebum contact angle ≥ 60°, preferably ≥ 80° measured at 50°C with a sessile drop method using 1.8 to 2.8 µl per drop synthetic sebum, and
  4. iv. optionally a surface energy ≤ 20 mJ/m2, preferable ≤ 15 mJ/m2, more preferable ≤ 10 mJ/m2 determined with the Owens, Wendt, Rabel and Kaelble (OWRK) method.


[0027] According to an embodiment of all aspects of the present invention, the layer of inorganic material has advantageously a mean thickness of less than 1 µm, preferably ≤ 700 nm, more preferably has a mean thickness in the range of 100 nm to 500 nm, even more preferably 200 nm to 400 nm. Such a layer thickness facilitates the maintenance of the look and feel of the cellulosic material substrate. In particular, the inorganic material layer thickness may facilitate an increased resistance to mechanical stress and/or an increased resistance to chemical stress while maintaining the look and feel of the cellulosic material substrate, when compared to cellulosic material not comprising the amphiphobic coating. In particular in case a security paper, e.g. a banknote, is used as cellulosic material, the inorganic material has a mean thickness of less than 1 µm, preferably 200 to 400 nm, as it then does not interfere with the look and feel of security features, such as optically variable security features (micro lens patch or structures, hologram features, watermarks or foil features etc.), etc. Such a mean thickness of inorganic material layer is obtainable by using particles of inorganic material with a mean particle diameter in the range of 30 to 100 nm and a low concentrated coating solution to achieve a single to a few nanoparticle layers of inorganic material.

[0028] According to a further alternative or cumulative embodiment of the present invention, the organic fluoro material is configured as a molecular layer on at least part of the nanostructured surface of the inorganic material layer. The organic fluoro material may be applied by dip coating, roller coating, such as flexographic (FLEXO) printing, spin coating, spray coating or any other Molecular Layer Deposition techniques.

[0029] According to a further alternative or cumulative embodiment of the present invention, the organic fluoro material is selected from the group consisting of fluoroalkylsilane polymers (FAS), acrylic fluoropolymers, and perfluoropolyalkylether polymers. Suitable organic fluoro materials are readily commercially available, such as Krytox® 100, Krytox ® 103 and Krytox® 105 (DuPont) as examples for perfluoropolyalkylethers; AFW in water (CHEM SPEC/DuPont) as example for acrylic fluoropolymers, and Dynasylan® SIVO Clear EC in alcohol (EVONIK) as example for fluoroalkylsilane polymers. The organic fluoro materials mainly facilitate the oil repellence of the inventive amphiphobic cellulosic material. Furthermore, in case the cellulosic material substrate is a paper, preferably a security paper, e.g. banknote, the organic fluoro material retains the authentication of one or more security features in particular selected from the group consisting of optical features (hologram, watermark, micro-lens patch or structures or foil features etc.), magnetic features, luminescent features, e.g. UV feature, infrared (IR) absorbing or emitting features, and electroluminescent features.

[0030] According to a further alternative or cumulative embodiment of the present invention, the cellulosic material substrate comprises a printed layer and/or a foil layer arranged between the cellulosic material substrate and the layer of the inorganic material, wherein the printed layer extends over at least part of the surface of the cellulosic material substrate and/or wherein the foil layer extends over at least part of the surface of the cellulosic material substrate. In particular with respect to paper, preferably security paper, such as banknotes, as cellulosic material substrate comprises one or more prints, preferably security prints of the surface of the paper substrate. Alternatively or cumulatively, the paper substrate as cellulosic material substrate comprises tactile features or optical features. The amphiphobic coating essentially maintains the look and/or feel of the print layer and/or security features represented on the foil layer and/or tactile features and/or other optical features of the paper substrate, in particular banknote substrate.

[0031] According to the second aspect of the present invention, the process for preparing an inventive cellulosic material is provided. All embodiments of the first aspect of the present invention in any suitable combination are also applicable for the second aspect of the present invention.

[0032] According to step a) of the inventive process, a cellulosic material substrate having a surface is provided. As already set out hereinbefore, the cellulosic material substrate may be selected from the group consisting of paper, cardboard, textile, more preferably selected from the group consisting of printing paper, food packaging paper, packaging cardboard and security paper, in particular banknote, passport, identity card, and check. Preferably, a banknote comprising all security features, print layers, foil features, tactile features and/or optical features is provided in step a) of the inventive process.

[0033] According to step b) of the inventive process, inorganic material is provided. As already set out hereinbefore, the inorganic material may be selected from the group consisting of ceramic oxides, preferably Al2O3, TiO2, SiO2, Y2O3, ZnO and ZrO2, preferably Al2O3, TiO2 and SiO2, more preferably TiO2 and SiO2. Preferably the inorganic material is generally provided with a mean particle diameter of ≤ 200 nm, more preferably, ≤ 100 nm, even more preferred in the range from 1 to 80 nm, even more preferred in the range com 30 to 70 nm. Suitably, according to a further alternative or cumulative embodiment, the inorganic material may be provided as a sol in a suitable dispersing agent, preferably selected from the group of alcohol, water and water containing medium. The inorganic material may in particular be prepared by an in situ reaction such as described, e.g. in EP 2 681 347B1 and EP 2 864 522 B1. As the use of alcohol as dispersing agent may cause environmental and safety problems when scaling up the process, water is preferably used as dispersing agent. The sol comprising the inorganic material may facilitate wet application of the inorganic material onto the cellulose material substrate. In particular in case the inorganic material has a mean particle diameter of ≤ 100 nm a sol of the inorganic material in a suitable dispersing agent provides a prolonged stability for up to 18 months. Such low gelification and precipitation rate is adequate for the industrial application.

[0034] According to step c) of the inventive process, organic fluoro material is provided. As already set out hereinbefore, the organic fluoro material may be selected from the group consisting of fluoroalkylsilane polymers (FAS), acrylic fluoropolymers, and perfluoropolyalkylether polymers. Detailed information on suitable organic fluoro material is provided with respect to the first aspect of the present invention. Optionally one or more suitable solvent agents may be added to achieve a suitable viscosity for the coating step e).

[0035] According to step d) of the inventive process, at least part of the surface of the cellulosic material substrate is coated with the inorganic material, e.g. a sol of the inorganic material thereby forming an inorganic material layer exhibiting a nanostructured surface. Preferably, the inorganic material layer has one or more, more preferably one, two or three layers of inorganic material. Generally, the coating step d) may be conducted by wet application of the inorganic material. The cellulosic substrate may be coated by dip coating, roller coating, such as flexographic (FLEXO) printing, spray coating or spin coating, preferably by dip coating or flexographic printing. Furthermore, a suitable drying step may optionally be conducted to remove the solvent of the inorganic material and a curing step may optionally be conducted to fix the inorganic material location. The drying step and the curing step may be conducted separately or in combination. The drying and/or curing step may optionally be conducted by thermal treatment, in particular by heating the inorganic material layer to a temperature in the range of 60 °C to 140 °C, more preferably 80 °C to 120 °C. Alternatively, as the solvent penetrates into the cellulosic material, whereby the rearrangement of the inorganic material for building the nanostructured layer surface is facilitated, the drying and/or curing step may be postponed, i.e. may not be conducted after application of the inorganic material in step d), but may be conducted after application of the organic fluoro material in step e) to reduce and, thus, optimize production time and production costs. In case the surface of the inorganic material after optional drying does not exhibit a suitable nanostructure, a subsequent structuring step of the inorganic material layer may be conducted. As an example, the structuring step can be conducted by hydrolyzing the surface (inorganic material layer in contact with, e.g., boiling water) thereby creating hydroxy functional groups to increase surface reactivity and modify the surface texture.

[0036] According to step e) of the inventive process, at least part of the surface of the inorganic material layer is coated with the organic fluoro material thereby forming a fluorinated nanostructured surface of the layer of inorganic material. Generally, the coating step e) is conducted by applying one, two, or more, preferably one or two times the fluoro material in wet form and conducting a suitable curing step. The organic fluoro material may be applied by any suitable method, e.g. dip coating, roller coating, such as flexographic (FLEXO) printing, spin coating, spray coating or any other Molecular Layer Deposition technique, preferably dip coating. Preferably the organic fluoro material is applied in form of a molecular layer. Optionally a drying and/or curing step as already described with respect to step d) of the inventive preparation process can be generally performed after application of the organic fluoro material. The drying and/or curing step may optionally be conducted at a temperature in the range of 60 °C to 140 °C, preferably 80 °C to 120 °C. This drying and/or curing step may also facilitate drying the cellulosic material from the solvent used for application of the inorganic material in step d).

[0037] All embodiments disclosed with respect to the first and second aspect of the present invention in particular comprising all suitable combinations also apply with the third aspect of the present invention concerning the use of the amphiphobic coating as set out hereinbefore for increase of dirt resistance and/or lifetime of a cellulosic material.

[0038] FIG. 1 is a simplified cross-sectional view on a cellulosic material 1 of an embodiment of the present invention. The cellulosic material 1 comprises a cellulosic substrate 10 and an amphiphobic coating 2 comprising an inorganic material 21 and an organic fluoro material 22. The amphiphobic coating 2 is arranged on at least part of a surface S1 of the cellulosic substrate 10. Due to the exploded view, the amphiphobic coating is displayed not in contact with the cellulosic material substrate 10, however, the amphiphobic coating is in direct contact with the surface S1 of the cellulosic material substrate 10 including any items arranged on the surface S1 of the cellulosic material substrate 10 (see FIG. 2 below). The inorganic material 21 is configured as a layer L1 having a nanostructured surface S2 (not shown in FIG 1, see FIG 3B) on at least part of the surface S1 of the cellulosic substrate 10. The nanostructured surface S2 of the layer L1 of the inorganic material 21 is at least partly fluorinated with the organic fluoro material 22. The fluorination is schematically represented by the chemical sign "F". The dimensions are not in true relation with the manufactured embodiment. Preferably, the organic fluoro material 22 is applied to the layer L1 of the inorganic material as a molecular layer L2. Molecular layer L2 means that the organic fluoro material 22 is present in a mean thickness of one molecule of the organic fluoro material 22. The amphiphobic coating 2 exhibits a nanostructured surface S3 having
  1. i. a static water contact angle > 110°, preferably ≥ 120°, preferably ≥ 140° measured at room temperature with a sessile drop method using 1 µl per drop deionized water,
  2. ii. a static n-hexadecane contact angle ≥ 60°, preferably ≥ 80°, more preferably ≥ 100° measured at room temperature with a sessile drop method using 1 µl per drop n-hexadecane,
  3. iii. optionally a melted sebum contact angle ≥ 80° measured at 50 °C with a sessile drop method using 1 µl per drop synthetic sebum, and
  4. iv. optionally a surface energy ≤ 20 mJ/m2, preferable ≤ 15 mJ/m2, more preferable ≤ 10 mJ/m2 determined with the Owens, Wendt, Rabel and Kaelble (OWRK) method.


[0039] According to an embodiment of the present invention, the cellulosic material substrate 10 is selected from the group consisting of paper, cardboard, textile, more preferably selected from the group consisting of printing paper, food packaging paper, packaging cardboard and security paper, in particular banknote, passport, identity card, and check.

[0040] According to an embodiment of the present invention, the layer L1 of inorganic material 21 has generally a mean thickness of less than 1 µm, preferably ≤ 700 nm, more preferably has a mean thickness in the range of 50 nm to 500 nm, even more preferably 200 nm to 400 nm. The mean thickness of the inorganic material 21 facilitates the maintenance of the look and feel of the cellulosic material. Furthermore, it facilitates that security features on or in banknotes may still be authenticated.

[0041] According to an embodiment of the present invention, the inorganic material 21 is selected from the group consisting of ceramic oxides, preferably Al2O3, TiO2, SiO2, Y2O3, ZnO and ZrO2. Preferably Al2O3, TiO2 and SiO2 are used, as they do not negatively interfere with environment. According to an embodiment the inorganic material 21 is TiO2 or SiO2, as when using Al2O3 a nanostructuring step prior to the optional drying step or prior to the application of the organic fluoro material may be necessary.

[0042] According to an embodiment of the present invention, the organic fluoro material 22 is selected from the group consisting of fluoroalkylsilane polymers (FAS), acrylic fluoropolymers, and perfluoropolyalkylether polymers.

[0043] FIG. 2 is a simplified cross-sectional view on a cellulosic material of an alternative embodiment of the present invention. The cellulosic material 1 of FIG 2 only differs from the cellulosic material of FIG. 1 in that a printed layer L3 and a foil layer L4 is arranged between the cellulosic material 1 and the layer L1 of the inorganic material 21. In FIG. 3 the printed layer L3 and the foil layer L4 are arranged separately from each other and they respectively extend over part of the surface S1 of the cellulosic material substrate 10. Other overlapping arrangements are also possible. Due to the exploded view, the cellulosic material substrate 10, the printed layer L3, the foil layer L4 and the layer L1 of inorganic material are shown not in direct contact with each other. However, when manufactured, the cellulosic material substrate 10, the printed layer L3, the foil layer L4 and the layer L1 of inorganic material are respectively in direct contact with each other. The cellulosic material substrate of FIG. 2 is a banknote comprising one or more security prints and/or other print layers L3 and one or more foil layers L4, a so called final banknote.

[0044] As shown in the example section, the inventive amphiphobic banknotes show an improved repellence against water, oil/fats and sebum in comparison to the uncoated comparative banknote and real banknotes prior to circulation (see example section item 6), while maintaining the optical, tactile, aesthetical and colorimetric parameters unchanged with respect to the uncoated comparative banknote. In particular the results of a static water contact angle measurements show, that the inventive amphiphobic banknotes have a static water contact angle of > 110°, preferably ≥ 120°, more preferably ≥ 140°, whereas the water is absorbed by the comparative banknotes (see example section, item 6). Moreover, the static n-hexadecane contact angle of the inventive banknote is ≥ 60°, preferably ≥ 80°, more preferably ≥ 100°, whereas the comparative banknotes absorb the n-hexadecane (see example section, item 6). In addition the inventive amphiphobic banknotes exhibit at 50° C a melted sebum contact angle of ≥ 60°, more preferably ≥ 80°, whereas the comparative banknotes absorb the synthetic sebum at 50 °C (see example section, item 6). Furthermore, the inventive banknotes exhibit a surface ≤ 20 mJ/m2, preferable ≤ 15 mJ/m2, more preferable ≤ 10 mJ/m2 determined with the Owens, Wendt, Rabel and Kaelble (OWRK) method (see example section, item 6). Finally, the inventive amphiphobic banknotes fulfill further requirements concerning durability, in particular UV exposure, Abrasion (in particular using UNI EN 1096-2 standard for coated glass), Crumpling (using Giesecke & Devrient Balloon Tester so called G&D LTT-1 Life Time Circulation Tester) and Washing (washing test and washing machine test).

[0045] Figures 3A), 3B), and 3C) show simplified views of process steps of an embodiment of the present invention.

[0046] FIG. 3A schematically shows the process step a) of an embodiment of the invention, wherein a cellulosic material substrate 10 having a surface S1 is provided. According to an embodiment, the cellulosic material substrate 10 is a banknote, which comprises all security features and other print and foil layers (not separately viewed in FIG. 3A). In an embodiment the surface S1 of the cellulosic material substrate 10, in particular banknote, may be pre-treated by washing or plasma treatment to clean the surface S1 and enhance bonding of the inorganic material 21 after deposition in step d) of the invention. In order to optimize the production procedure no pre-treatments may be conducted.

[0047] FIG 3B schematically shows the result of process step d) of an embodiment of the invention, wherein at least part of the surface S1 of the cellulosic material substrate 10 is coated with the inorganic material 21 thereby forming an inorganic material layer L1 exhibiting a nanostructured surface S2.

[0048] FIG 3C schematically shows the result of process step e) of an embodiment of the invention, wherein at least part of the surface S2 of the inorganic material layer L1 is coated with the organic fluoro material 22 thereby forming a fluorinated inorganic material layer exhibiting a nanostructured surface S3 of the amphiphobic coating 2.

[0049] According to an embodiment of the invention, the inorganic material 21, in particular Al2O3, TiO2 and/or SiO2, preferably TiO2 and/or SiO2, has a mean particle diameter of ≤ 200 nm, more preferably, ≤ 100 nm, even more preferred in the range from 1 to 80 nm, even more preferred in the range com 30 to 70 nm. According to an embodiment of the invention, the inorganic material is provided dispersed in a dispersing agent forming a sol. According to an embodiment of the invention, the dispersing agent is isopropyl alcohol or water. Water is preferred as dispersing agent, as it does not cause environmental or production safety concern.

[0050] According to an embodiment of the invention, the coating step d) is performed by applying the sol of partially hydrolyzed Al2O3, TiO2 or SiO2 as the inorganic material 21 onto at least part of the surface S1 of the cellulosic material substrate 10 thereby forming a gel film of inorganic material 21. The wet application of the inorganic material 21 can be conducted by any suitable method, in particular including dip coating, roller coating, such as flexographic (FLEXO) printing, spray coating and spin coating etc.. According to an embodiment of the invention, the deposition of the sol film on the cellulosic material substrate 10, in particular banknote, is performed with a dip coater using a constant immersion and emersion speed of 120 mm/min and a static immersion (soak) time of 5 seconds in the sol (+/- 10 % deviation respectively). During withdrawal of the banknote from the coating suspension, evaporation of the dispersing medium at room temperature starts as well as penetration of the dispersing medium into the cellulosic material, thus leading to a rearrangement of the ceramic oxide nanoparticles, in particular Al2O3, TiO2 or SiO2 nanoparticles, to form the nanostructured layer surface. Such nanoscale coating is adhering to the banknote surface. The formation of the nanostructured surface S2 of the inorganic material layer L1 may be facilitated without even drying the wet cellulosic material, as the solvent also penetrates into the cellulosic material thereby rearranging the ceramic oxide nanoparticles. However, to reduce the drying time, the banknote may be dried by thermal application after application of the inorganic material layer L1 or after application of the organic fluoro material layer L2. However, in case a drying step may be conducted, then the coated banknote may preferably be dried in a static furnace in air at 120 °C for up to 10 minutes.

[0051] Alternatively, the inorganic material 21 may be applied to the surface of the cellulosic material substrate 10 by flexographic printing.

[0052] According to an alternative embodiment of the invention, in particular when Al2O3 is used as inorganic material 21, the cellulosic material substrate 10, in particular banknote, comprising the coated gel film of Al2O3 is nanostructured and then optionally dried and/or cured. Alternatively, the nanostructuring with Al2O3 can be performed by immersing the cellulosic material substrate 10, in particular banknote, comprising the coated sol film of Al2O3 in boiling water for up to 30 minutes to increase surface reactivity by creating hydroxy functional groups and by modifying the surface texture. Subsequently, the nanostructured sol film of Al2O3 is optionally dried and/or cured. Drying and/or curing is preferably performed at 120 °C for up to 10 minutes.

[0053] According to an embodiment of the invention, the coating step e) is performed by a suitable wet coating technique, such as dip coating, roller coating, such as flexographic (FLEXO) printing, spin coating, spray coating or any other Molecular Layer Deposition technique. As an example the cellulosic material substrate 10, in particular banknote, comprising the nanostructured layer L1 of inorganic material 21 is dip coated into a solution of organic fluoro materials, e.g., fluoroalkylsilanes or acrylic fluoropolymers with an immersion and emersion speed of 120 mm/min and immersion (soak) time of up to 2 minutes (+/- 10 % deviation respectively). The cellulosic material substrate 10, in particular banknote, comprising the organic fluoro material 22 is withdrawn from the solution. The organic fluoro material 22 is applied once or two times to form the molecular layer L2. In other words, the organic fluoro material layer L2 does not add substantial thickness to the thickness of the inorganic material layer L1. Thus, the thickness of the amphiphobic coating 2 essentially relates to the thickness of the inorganic material 21, which is ≤ 1 µm, preferably ≤ 700 nm, more preferably is in the range from 50 nm to 400 nm. Subsequently, the cellulosic material substrate 10, in particular banknote, comprising the organic fluoro material 22 is cured at a temperature in the range of 60 °C to 140 °C, preferably at 80 °C to 120 °C for up to 30 minutes to promote fluorination of the ceramic oxide layer.

[0054] The embodiments disclosed with respect to the FIG.1, FIG.2, FIG.3A, 3B and 3C may be combined separately or in any (sub)combination with the general disclosure of all aspects of the invention set out hereinbefore.

[0055] In order to facilitate the scale-up of the process, adjustments to the process described hereinbefore may be conducted.

[0056] As far as the deposition method of the inorganic material 21 or the organic fluoropolymer 22 is concerned, dip coating can be performed at different withdrawal speed to tune film thickness, to obtain different structures and to adapt the amphiphobic coating to the substrate. Dipcoating may also be replaced by different techniques, such as roller coating, such as flexographic (FLEXO) printing, spin coating or spray coating. In the specific case of banknotes as cellulosic material substrate 10, dip coating can be supported or replaced by techniques like roller printing to better simulate the current deposition processes of protective layers on banknotes.

EXAMPLES



[0057] The present invention is described in the following on the basis of exemplary embodiments, which merely serve as examples and which shall not limit the scope of the present protective right. The exemplified features may be combined separately or in any (sub)combination with the general disclosure of all aspects of the invention as set out hereinbefore.

1. Materials


1.1 Preparation of sol comprising Al2O3 nanoparticles


1.1a) Preparation of sol comprising Al2O3 nanoparticles in water (also referred to as "Al2O3-aqu")



[0058] A colloidal suspension of alumina was prepared by peptization of aluminum tri-sec butoxide 0.5 M in aqueous solution in the presence of nitric acid as the acidic catalyst. The reactions of hydrolysis and condensation which lead to the formation of the sol occur keeping the system under stirring at 80 °C. The molar ratios of the sol are as follows:
aluminum tri-sec-butoxide : water: nitric acid = 1 : 100 : 0.07

1.1b) Preparation of sol comprising Al2O3 nanoparticles in alcohol (also referred to as "Al2O3-IPA")



[0059] A colloidal suspension 0.5 M of aluminium tri-sec-butoxide (Al(O-sec-Bu)3) in isopropyl alcohol was prepared. Preferably the atmosphere exhibits a low relative humidity (RH), such as RH of 5 % or lower. The suspension was kept under stirring for one hour. Then, a chelating agent was added in order to prevent formation of undesirable precipitates and guarantee homogeneity of the final suspension. The suspension was kept under stirring for three hours. Finally, to promote hydrolysis of the alkoxide a calculated amount of water was added, with consequent variation of the colour of the suspension from colourless to yellow, corresponding to the formation of dispersed nanoparticles (sol). The molar ratios of the sol were the following:
aluminium tri-sec-butoxide : isopropyl alcohol: ethyl acetate : water = 1 : 20 : 1 : 4

1.1c) Provision of TiO2 sol 1.5% (also referred to as "TN1.5")



[0060] The suspension of TiO2 with a concentration of 1.5% in water is prepared using the commercially available suspension of titania 6% in H2O (Colorobbia Italia, product code PH 000026) and subsequent dilution with water (neutral pH).

1.1d) Provision of TiO2 sol 3% (also referred to as "TN3")



[0061] The suspension of TiO2 with a concentration of 3% in water is prepared using the commercially available suspension of titania 6% in H2O (Colorobbia Italia, product code PH 000026) and subsequent dilution with water (neutral pH).

1.1e) Provision of TiO2 sol 3% (also referred to as "TAC")



[0062] The suspension of TiO2 "TAC" with a concentration of 3% in water is prepared using the commercially available suspension of titania nanosol 6% in H2O (Colorobbia Italia, product code NAMA41) and subsequent dilution with water (neutral pH).

1.1f) Preparation of TiO2 sol 3% (also referred to as "TAC-R")



[0063] The suspension of TiO2 "TACR" with a concentration of 3% in water is prepared by treating a suspension of TiO2 sol "TAC" 3% (1.2c) with a weak anion exchange resin (Dowex 66 anion exchange from Sigma Aldrich). The anion exchange resin was added while monitoring the pH. The resin was able to sequester Cl- ions and release OH- ions with a consequent increase in pH. Once the required pH value of 4.5 is reached, the resin was removed by simple separation. The pH obtained in the purified sample (TAC-R) was 4.5.

1.1g) Preparation of SiO2 sol



[0064] The sol of SiO2 with a concentration of 4% in water is prepared using the commercially available suspension of colloidal silica 40 wt% in water LUDOX® HS-40 (from Sigma-Aldrich, product number 420816) and subsequent dilution with water (neutral pH).

1.2 Organic fluoro material


1.2a) Acrylic fluoropolymers: AFW in water (CHEM SPEC)



[0065] 10% AFW in water as delivered from supplier (CHEM SPEC)

1.2b) Perfluoropolyalkylethers: Krytox® 100, Krytox® 103 and Krytox® 105 (DuPont)



[0066] All Krytox® oils were obtained from supplier (DuPont)

1.3 Substrate


1.3a) Test Banknote



[0067] A test banknote is prepared to carry out the test for the inventive coating with the following characteristics.

[0068] Vellum banknote substrate paper comprises offset and intaglio print, foil element comprising micro lens security feature, watermark, window feature, graphics (inks do not comprise IR absorbing or emitting pigments, UV luminescent pigments and OVMI pigments).

1.3b) Calendered Vellum banknote paper



[0069] Vellum banknote substrate paper with size of 350 x 450 mm is calendered on a KBA Mini Orlof. The plate was intaglio printing plate without engraving 0,85 mm thickness. The approximately pressure was 45 t and the temperature 55° C.

2. Preparation of inventive amphiphobic coating on test banknote (Examples of 1 to 13)



[0070] 
ExampleSubstrateInorganic1st organic2nd organic
1 1.3a) 1.1f TAC_R 1.2a AFW  
2 1.3a) 1.1f TAC_R 1.2a AFW 1.2b Krytox
3 1.3a) 1.1d TN3 1.2a AFW  
4 1.3a) 1.1d TN3 1.2a AFW 1.2b Krytox
5 1.3a) 1.1c TN1.5 1.2a AFW  
6 1.3a) 1.1c TN1.5 1.2a AFW 1.2b Krytox
7 1.3a) 1.1e TAC 1.2a AFW  
8 1.3a) 1.1e TAC 1.2a AFW 1.2b Krytox
9 1.3a) 1.1g SiO2 1.2a AFW  
10 1.3a) 1.1g SiO2 1.2a AFW 1.2b Krytox
11 1.3a) 1.1b Al2O3-IPA 1.2a AFW 1.2b Krytox
12 1.3a) 1.1b Al2O3-IPA 1.2a AFW  
13 1.3a) 1.1a Al2O3-aqu 1.2a AFW  

2.1 Coating deposition of inorganic material



[0071] The Al2O3, TiO2 or SiO2 sols as prepared above under items 1.1a) to 1.1f) are deposited by dip-coating (AUREL Automation equipment) on the test banknote sample 1.3a) with an immersion and emersion speed of 120 mm/minute and a residence time of 5 seconds. During the deposition the suspension can be kept under stirring.

[0072] The beaker capacity and suspensions volumes are variable according to the size of coated samples to be produced. The following example can be considered a typical example: for a banknote sample having the size of about 7.5 x 6.5 cm, the typical size of a beaker is 600 ml, the amount of inorganic or organic suspensions is 500 ml.

[0073] After the deposition, the banknote is taken out and the remaining solution is removed by gently shaking. The note is stored at room temperature for 1 hour and afterwards optionally cured in an oven at 120°C for 10 minutes in order to optimize drying time.

2.2 Coating deposition of organic material



[0074] The organic layer 1.2a) (AFW 10% solution in water) is deposited on at least part of the inorganic layer coating (see item 2.1) above).

[0075] The deposition instrument (AUREL Automation equipment) is the same as disclosed under item 2.1) above, wherein the immersion and emersion speed is 120 mm/minute and the residence time is up to 2 minutes including the storing conditions and drying step as set out under item 2.1).

2.3 2nd Coating deposition of organic material (examples 2, 4, 6, 8, 10 and 11)



[0076] The second organic layer 1.2b (Krytox 100) is deposited on at least part of the inorganic and the first organic layer coating (see items 2.1 and 2.2 above).

[0077] The deposition instrument (AUREL Automation equipment) is the same as disclosed under item 2.1) above, wherein the immersion and emersion speed is 120 mm/minute and the residence time is up to 2 minutes the storing conditions and drying step as set out under item 2.1).

3. Preparation of inventive amphiphobic coating on calendered vellum banknote (Examples 14 and 15)



[0078] 
ExampleSubstrateInorganic layer Roller Printer1st organic
14 1.3b) 1.1g SiO2 AFW
15 1.3b) 1.1c TN1.5 AFW

3.1 Coating deposition of inorganic material



[0079] The TiO2 and SiO2 sols as prepared above under items 1.1a) to 1.1f) are deposited on calendered banknote paper (1.3b) by a roller coater with a roller height of 12.3-12.5mm, a roller speed of 15m/min, a tape speed of 16 m/min, a blade angle of -1 to 0 degree and a blade height of 261 mm.

[0080] The Anilox (company Cheshire, roller no. M482) used for the roller coater application has the following parameter: length 722 mm, finished diameter 229 mm line screening 30 L/cm, engraving angle 45°, engraving type TWINFLO and hexagonal holes with total opening > 280 µm, cell opening > 250 µm and cell wall > 35 µm.

[0081] After the deposition, the paper is collected, stored at room temperature for 1 hour and afterwards optionally cured in an oven at 120°C for 10 minutes.

3.2 Coating deposition of organic material



[0082] The organic layer 1.2a) (AFW 10% solution in water) is deposited on at least part of the inorganic layer coating on a 50 x 30 mm piece cut out of the banknote paper produced according to 3.1) by dip-coating (AUREL Automation equipment) with an immersion and emersion speed of 120 mm/minute and a residence time of 2 seconds. During the deposition the suspension can be kept under stirring.

[0083] The beaker capacity and suspensions volumes are variable according to the size of coated samples to be produced. The following example can be considered a typical example: for a banknote sample having the size of about 7.5 x 6.5 cm, the typical size of a beaker is 600 ml, the amount of organic suspensions is 500 ml.

[0084] After the deposition, the banknote is taken out and the remaining solution is removed by gently shaking. The note is stored at room temperature for 1 hour and afterwards optionally cured in an oven at 120°C for 10 minutes.

4. Preparation of inventive amphiphobic coating on calendered vellum banknote (Examples 16 and 17)



[0085] 
ExampleSubstrateInorganic layer Flexo Printing1st organic
16 1.3b) 1.1g SiO2 AFW
17 1.3b) 1.1c TN1.5 AFW

4.1. Coating deposition of inorganic material



[0086] The TiO2 and SiO2 sols as prepared above under items 1.1a) to f) are deposited on calendered banknote paper (1.3b) by flexographic printing step on a Heidelberg GTO with a customized plug-on flexographic unit. The machine speed was 3000 sheets per hour. The Anilox (company Zecher, number: KG20171000) used for flexographic application has the following parameter: screening 120 L/cm, engraving angle 45°, depth 22 µm, wall/cell ratio 1:12, volume 9.0 cm3/m2.

[0087] After the deposition, the paper is collected, stored at room temperature for 1 hour and afterwards optionally cured in an oven at 120°C for 10 minutes in order to optimize drying time.

4.2 Coating deposition of organic material



[0088] The organic layer 1.2a (AFW 10% solution in water) is deposited on at least part of the inorganic layer coating on a 50x30 mm piece cut out of the banknote paper produced according to 4.1 by dip-coating (AUREL Automation equipment) with an immersion and emersion speed of 120 mm/minute and a residence time of 2 seconds. During the deposition the suspension can be kept under stirring.

[0089] The beaker capacity and suspensions volumes are variable according to the size of coated samples to be produced. The following example can be considered a typical example: for a banknote sample having the size of about 7.5 x 6.5 cm, the typical size of a beaker is 600 ml, the amount of organic suspensions is 500 ml.

[0090] After the deposition, the banknote is taken out and the remaining solution is removed by gently shaking. The note is stored at room temperature for 1 hour and afterwards optionally cured in an oven at 120°C for 10 minutes in order to optimize drying time.

5. Comparative examples



[0091] For carrying out the wettability and durability tests, the following test banknotes are used:
  • Uncoated test banknotes as described under item 1.3a above (Comparative Example 1)
  • Uncoated pre-calendered banknote paper as described under 1.3b above (Comparative Example 2)
  • Real new banknotes (denomination 10 €,) prior to circulation in the public, wherein the real banknotes already comprise a coating, which shall prevent staining and increase lifetime of banknote in circulation while not impacting any of the desired banknote features like feel and look or machine readability (Comparative Example 3)

6. Comparison of results of surface properties of the inventive amphiphobic banknotes versus comparative banknote


6.1 Description of Test methods:


6.1.a) Water, n-hexadecane and sebum contact angle measurements



[0092] Contact angle measurements were performed by use of the optical tensiometer OCA 15 Plus (DataPhysic Instruments) equipped with a CCD camera.

[0093] Measurements of static contact angle with deionized water (WCA) and n-hexadecane (CAn-hexa) were carried out at room temperature with the sessile drop method (drop volume of 1 µl).

[0094] The contact angle between banknote surface (kept T at 50°C) and molten drops of synthetic sebum (volume drop 1.8 to 2.8 µl of synthetic sebum according to Bey, wfk - Testgewebe GmbH) was also determined by sessile drop method using the optical tensiometer OCA 15 Plus (DataPhysic Instruments) equipped with a CCD camera.

6.1.b) Surface energy determined with the OWRK method



[0095] Surface energy (SE) of paper surfaces was calculated with the Owens-Wendt-Rabel-Kaeble (OWRK) method. It is based on the measurement of contact angles with drops of two test liquids with known surface tension ST and surface tension components, namely the disperse component STd and the polar component STp. Water and n-hexadecane were used as test liquids and their surface tension components are reported in the following table:
LiquidST (mN/m) at 20°CSTd (mN/m)STp (mN/m)
water 72.8 21.8 50.0
n-hexadecane 27.6 27.6 0


[0096] For each test liquid, the contact angle CA is measured (in this case, WCA and CAn-hexa). Values for CA, ST, STd and STp for each liquid are inserted into the following linear equation:



[0097] The slope of this line is the square root of the polar surface energy SEp, while the intercept is the square root of the disperse surface energy SEd, respectively. For each test liquid, a point is identified on the

vs.

graph; the linear interpolation provides SEp and SEd values. Total surface energy SE is the sum of SEp and SEd.

6.1.c) UV Exposure test:



[0098] The resistance of a banknote against UV radiation may be checked keeping the inventively coated cellulosic substrates (having a typical size of 5 cm x 3 cm) under an Osram Ultra-Vitalux 300W lamp at an irradiation intensity of 5.0 ± 0.2 mW/cm2 for 8 hours. The wetting performances may subsequently be tested after cooling the samples for 10 min at room conditions.

6.1d) Washing Test:



[0099] The resistance of a banknote to washing may be tested by filling a bowl (min 5 L volume) with 4 liters warm water (40 +/- 2 deg.) and adding with a 5 ml lab plastic pipette 3 drops Tinopal (TINOPAL CBS SP Slurry 33, Ciba Chemicals 119877906) and subsequently mixing the solution. This mixture can be used for 10 banknotes.

[0100] The inventively coated banknotes are applied to the bowl and immersed for 10 minutes into the prepared water mixture. The inventively coated banknote is subsequently taken out from the water mixture and the liquid mixture is further removed by gentle shaking. The banknote is subsequently dried by using paper towels, whereby both sides of the inventively coated banknote is covered with 3 to 5 paper towels, a pressure (at least 500 g over the area of the banknotes) is applied and the banknote is subsequently dried for at least 1 hour. When dry, the quality of the banknote is checked with respective test methods, such as UV/light. Inventively coated banknotes fulfilling the washing test requirements shine brightly. In homogeneities in brightness correspond to a crumple pattern and indicate that the coating is destroyed during crumpling.

6.1e) Washing machine Test, hot (60°C):



[0101] The resistance of a banknote to washing may alternatively be tested with a washing machine having a spin drier (600 rpm) programmed for domestic use.

Materials:



[0102] 
  1. a) detergent for machine washing:
    • ECE non-phosphate reference detergent A as used in the ISO 105-C09 - Annex A.
  2. b) Quantity of detergent:
    • 4 g/1 for ECE non-phosphate reference
  3. c) deionised water
  4. d) 20 washing gloves + safety pins:
    The number of gloves in the machine must always be 20. In case fewer banknote samples are treated, empty gloves must be added.

Procedure:



[0103] 
  1. 1. Set the machine for half load - main wash (2.5 kg), without pre-wash.
  2. 2. Put one banknote in each washing glove and fix the unfolded banknote with 2 safety pins, maximum 20 banknotes, inside the glove, while taking care not to damage the foil.
  3. 3. Place the 20 washing gloves into the machine.
  4. 4. Add the detergents in the soap dispenser.
  5. 5. The selected washing program should have a duration between 60 and 90 minutes.
  6. 6. Start the washing program. At the end of the washing program (spin dry completed) extract the gloves from the machine, remove the safety pins and take out the banknote samples.
  7. 7. Straighten the banknotes I samples and examine for damage.
  8. 8. Report the result.

6.1f) Crumpling Test



[0104] The crumpling test is performed with the Giesecke & Devrient Balloon Tester (G&D LTT-1 Life Time Circulation Tester) according to the manual. The Balloon tester consists of a sample chamber made of thick rubber that is connected to compressed air. The sample is placed into the thick rubber balloon without creasing the sample, and the balloon was thereafter inflated and deflated rapidly in a controlled and automatic manner with custom-built apparatus to mimic hand crumpling. In order to mimic banknotes in circulation, different cycles of inflating/deflating have been established and tested earlier. 7 cycles in the balloon correspond to a banknote that is still fit for circulation. 3-time repetition of 15 cycles of inflating/deflating (45 cycles in total) corresponds to unfit banknote. Both protocols were executed on the test notes and the results are compared to uncoated notes. After carrying out the inflating / deflating cycles, the quality of the banknote is checked with UV/light. Inventively coated banknotes fulfilling the crumple test requirements shine brightly. In homogeneities in brightness correspond to a crumple pattern and indicate that the coating is destroyed during crumpling.

6.2 Comparative test results for contact angle and surface energy measurements


6.2a) Test results for inventive amphiphobic coating on test banknote substrates



[0105] 
ExampleInorganic1st organic2nd organicWCA (°)CAn-hex (°)SE (mN/m)CA (°) Sebum
1 1.1f TAC_R 1.2a AFW   133 ± 6 72 ± 5 12.1 ± 0.4 70 ± 7
2 1.1f TAC_R 1.2a AFW 1.2b Krytox 126 ± 5 65 ± 2 13.9 ± 0.9 63 ± 5
3 1.1d TN3 1.2a AFW   122 ± 4 85 ± 8 8.3 ± 0.4 86 ± 4
4 1.1d TN3 1.2a AFW 1.2b Krytox 117 ± 7 67 ± 3 13.3 ± 0.6 82 ± 10
5 1.1c TN1.5 1.2a AFW   128 ± 6 82 ± 5 8.7 ± 0.4  
6 1.1c TN1.5 1.2a AFW 1.2b Krytox 120 ± 2 69 ± 3 12.5 ± 0.4  
7 1.1e TAC 1.2a AFW   117 ± 3 71 ± 3 12.4 ± 0.5 75 ± 6
8 1.1e TAC 1.2a AFW 1.2b Krytox 121 ± 3 63 ± 3 14.7 ± 0.8 63 ± 5
9 1.1g SiO2 1.2a AFW   130 ± 5 77 ± 7 10.2 ± 0.5  
10 1.1g SiO2 1.2a AFW 1.2b Krytox 118 ± 3 65 ± 3 13.8 ± 0.4  
11 1.1b Al2O3-IPA 1.2a AFW 1.2b Krytox 125±3 68±5 13  
12 1.1b Al2O3-IPA 1.2a AFW   137±7 102±6 4.4 109 ± 14
13 1.1a Al2O3-aqu 1.2a AFW   123±6 70±6 12  

6.2b) Test results for inventive amphiphobic coating on calendered vellum banknote substrates



[0106] 
ExampleInorganic layer Roller Printer1st organicWCA (°)CAn- hex (°)SE (mN/m)
14 1.1g SiO2 AFW 135±2 86±5 8±1
15 1.1c TN1.5 AFW 140±5 96±7 6±2

6.2c) Test results for inventive amphiphobic coating on calendered vellum banknote substrates



[0107] 
ExampleInorganic layer Flexo Printing1st organicWCA (°)CAn-hex (°)SE (mN/m)CA (°) sebum
16 1.1g SiO2 AFW 139±1 94±1 6±1 111±5
17 1.1c TN1.5 AFW 140±1 95±2 7±1 112±4

6.2d) Comparative test results for inventive amphiphobic coating on test banknote substrates, pre-calendered banknote paper substrates and real banknotes prior to circulation



[0108] 
Comparative exampleWCA (°)CAn-hex (°)SE (mN/m)CA (°) sebum
1 absorption absorption n.a absorption
2 absorption absorption n.a absorption
3 absorption * absorption n.a absorption
* absorption delayed due to the varnish, 10 x slower than absorption of n-hexadecane



Claims

1. Cellulosic material (1) comprising a cellulosic substrate (10) and an amphiphobic coating (2), wherein the amphiphobic coating (2) comprises an inorganic material (21) and an organic fluoro material (22) and is arranged on at least part of a surface (S1) of the cellulosic substrate (10), characterized in that the inorganic material (21) is configured as a layer (L1) having a nanostructured surface (S2) on at least part of the surface (S1) of the cellulosic substrate (10), wherein the nanostructured surface (S2) of the layer (L1) of the inorganic material (21) is at least partly fluorinated with the organic fluoro material (22), wherein the amphiphobic coating (2) exhibits a nanostructured surface (S3) having

i. a static water contact angle > 110°, preferably ≥ 120°, preferably ≥ 140° measured at room temperature with a sessile drop method using 1 µl per drop deionized water,

ii. a static n-hexadecane contact angle ≥ 60°, preferably ≥ 80°, more preferably ≥ 100° measured at room temperature with a sessile drop method using 1 µl per drop n-hexadecane,

iii. optionally a melted sebum contact angle ≥ 60°, preferably ≥ 80° measured at 50 °C with a sessile drop method using 1 µl per drop synthetic sebum, and

iv. optionally a surface energy ≤ 20 mJ/m2, preferable ≤ 15 mJ/m2, more preferable ≤ 10 mJ/m2 determined with the Owens, Wendt, Rabel and Kaelble (OWRK) method.


 
2. Cellulosic material (1) according to claim 1, wherein the layer (L1) of inorganic material (21) has a mean thickness of less than 1 µm, preferably ≤ 700 nm, more preferably has a mean thickness in the range of 50 nm to 500 nm, even more preferably 200 nm to 400 nm.
 
3. Cellulosic material (1) according to claim 1 or 2, wherein the organic fluoro material (22) is applied to the layer (L1) of the inorganic material as a molecular layer (L2).
 
4. Cellulosic material (1) according to any one of the preceding claims, wherein the inorganic material (21) is selected from the group consisting of ceramic oxides, preferably Al2O3, TiO2, SiO2, Y2O3, ZnO and ZrO2.
 
5. Cellulosic material (1) according to any one of the preceding claims, wherein the organic fluoro material (22) is selected from the group consisting of fluoroalkylsilane polymers (FAS), acrylic fluoropolymers, and perfluoropolyalkylether polymers.
 
6. Cellulosic material (1) according to any one of the preceding claims, wherein a printed layer (L3) and/or a foil layer (L4) is arranged between the cellulosic material (1) and the layer (L1) of the inorganic material (21), wherein the printed layer (L3) extends over at least part of the surface (S1) of the cellulosic material substrate (10) and/or wherein the foil layer (L4) extends over at least part of the surface (S1) of the cellulosic material substrate (10).
 
7. Cellulosic material (1) according to any one of the preceding claims, wherein the cellulosic material substrate (10) is selected from the group consisting of paper, cardboard, textile, more preferably selected from the group consisting of printing paper, food packaging paper, packaging cardboard and security paper, in particular banknote, passport, identity card, and check.
 
8. Process for preparing a cellulosic material (1) according to any one of claims 1 to 7, characterized in that the process comprises or consists of the following steps:

a. Providing a cellulosic material substrate (10) having a surface (S1),

b. Providing an inorganic material (21),

c. Providing an organic fluoro material (22),

d. Coating at least part of the surface (S1) of the cellulosic material substrate (10) with the inorganic material (21) thereby forming an inorganic material layer (L1) exhibiting a nanostructured surface (S2) and

e. Coating at least part of the surface (S2) of the inorganic material layer (L1) with the organic fluoro material (22) thereby forming a fluorinated inorganic material layer exhibiting a nanostructured surface (S3) of the amphiphobic coating (2).


 
9. Process for preparing a cellulosic material (1) according to claim 8, wherein the cellulosic material substrate (10) is selected from the group consisting of paper, cardboard, textile, more preferably selected from the group consisting of printing paper, food packaging paper, packaging cardboard and security paper, in particular banknote, passport, identity card, and check.
 
10. Process for preparing a cellulosic material (1) according to claim 8 or 9, wherein the inorganic material (21) in step b) is selected from the group consisting of ceramic oxides, preferably Al2O3, TiO2, SiO2, Y2O3, ZnO and ZrO2.
 
11. Process for preparing a cellulosic material (1) according to any one of claims 8 to 10, wherein the inorganic material (21) has a mean particle diameter of ≤ 200 nm, more preferably, ≤ 100 nm, even more preferred in the range from 1 to 80 nm, even more preferred in the range com 30 to 70 nm.
 
12. Process for preparing a cellulosic material (1) according to any one of claims 8 to 11, wherein the inorganic material (21) in step b) is provided as a sol in a dispersing agent selected from the group of alcohol, water and water containing medium, preferably water.
 
13. Process for preparing a cellulosic material (1) according to claim 12, wherein the coating step d) is conducted by i) applying the sol of the inorganic material (21) onto at least part of the surface (S1) of the cellulosic material substrate (10) thereby arranging the inorganic material (21) in form of a gel film having a nanostructured surface (S2), ii) optionally further nanostructuring the gel film of inorganic material (21) to form the nanostructured surface (S2) of the inorganic material layer (L1) and iii) optionally drying and/or curing the cellulosic material (1) comprising the inorganic material (21) having a nanostructured surface (S2).
 
14. Process for preparing a cellulosic material (1) according to any one of claims 8 to 13, wherein the coating step e) is conducted by

i. applying the organic fluoro material (22) onto at least part of the surface (S2) of the inorganic material layer (L1) and optionally drying the organic fluoro coated cellulosic material (1), and

ii. curing the organic fluoro material (22) thereby forming the fluorinated nanostructured surface (S3) of the amphiphobic coating (2).


 
15. Use of a nanostructured amphiphobic coating (2) comprising an inorganic material (21) and an organic fluoro material (22) exhibiting a

i. a static water contact angle > 110°, preferably ≥ 120°, more preferably 140° measured at room temperature with a sessile drop method using 1 µl per drop deionized water,

ii. a static n-hexadecane contact angle ≥ 60°, preferably ≥ 80°, more preferably ≥ 100° measured at room temperature with a sessile drop method using 1 µl per drop n-hexadecane,

iii. optionally a melted sebum contact angle ≥ 60°, preferably ≥ 80° measured at 50 °C with a sessile drop method using 1 µl per drop synthetic sebum, and

iv. optionally a surface energy ≤ 20 mJ/m2, preferable ≤ 15 mJ/m2, more preferable ≤ 10 mJ/m2 determined with the Owens, Wendt, Rabel and Kaelble (OWRK) method,

for increase of dirt resistance and/or lifetime of a cellulosic material (1), characterized in that the nanostructured amphiphobic coating (2) is arranged on at least part of a surface (S1) of a cellulosic substrate (10) and wherein the inorganic material (21) is configured as a layer (L1) having a nanostructured surface (S2), wherein the nanostructured surface (S2) of the inorganic material (21) is fluorinated with the organic fluoro material (22).
 




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Cited references

REFERENCES CITED IN THE DESCRIPTION



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Patent documents cited in the description