WO2016156408A2

WO2016156408A2 - Metallic ink for printing

Info

Publication number: WO2016156408A2
Application number: PCT/EP2016/056931
Authority: WO
Inventors: Mauro ZEMIGNANI
Original assignee: Novachem S.R.L.
Priority date: 2015-04-02
Filing date: 2016-03-30
Publication date: 2016-10-06
Also published as: WO2016156408A3

Abstract

A metallic ink for printing which comprises: one or more vacuum metalized pigments, one or more polymers of ethyl cellulose with content ethoxy comprised between 48% and 50%, and one or more organic solvents selected from the group consisting of alcohols and esters of alkanes, which have from 2 to 6 carbon atoms, in defined quantities. The invention further relates to a method for preparing such ink and its use for printing materials for wrapping and/or packaging. The invention also relates to materials for wrapping and/or packaging which are printed with the ink described herein.

Description

METALLIC INK FOR PRINTING

The present invention relates to a printing ink for providing a metalized effect on substrates of different type; the invention also relates to the method for preparing such ink and its use for providing, by way of printing, completely or partially metalized substrates.

The films that are commonly used for wrapping and/or packaging a wide series of products are usually made with polymers such as for example polyester, polyethylene terephthalate (PET), polyethylene (PE), polyvinyl chloride (PVC), and polypropylene (PP). Sometimes, the polymeric films are bonded with a metallic layer, thus obtaining metalized films. The metallic layer is usually constituted by aluminum. The thickness of this metallic layer is on average comprised between 6 and 15 microns, but in some cases it can be less than 6 microns. The metallic layer is commonly applied to the polymeric medium by way of a method of "vacuum metalization", known and fully described in the current state of the art, in which the atoms of metal are evaporated under vacuum and made to adhere to the destination medium.

Other types of materials for wrapping or packaging, such as for example cardboard, usually glossy, can also be bonded with a metallic layer as described previously.

Both polymeric films and cardboards (especially if bonded with a metallic layer) offer the products that are packaged with them protection against atmospheric gases, water vapor, light, radiation etc; furthermore, such materials ensure a pleasing decorative effect, improving the appearance of the packaging and rendering the product more appealing to the end consumer. In fact, the metallic layer gives chromatic brilliance and intensity to any colors applied by printing. When the metallic layer is itself visible, furthermore, it indicates to the consumer that the product contained in such a package is of high quality and well protected. For this reason, metalized packaging, in particular metalized polymeric films, are widely used in the packaging of food products, after the interposition of a further protective lamination in order to prevent direct contact between the foods and the metallic layer.

The conventional metalization process, however, suffers a series of drawbacks, both from the technical point of view and from the practical point of view. First of all, conventional metalization can be carried out before or after complementary printing methods, but in any case it cannot be carried out "in-line". This entails that the step of printing and the step of metalization remain distinct and separate. Furthermore, since metalization is a complex procedure that requires special apparatuses, it is usually done by specialist companies, different from the printing companies. This implies a continual movement of material, which makes the method inefficient both economically and in terms of the timescales in play.

Another disadvantage of the metalization method is the fact that it is carried out on the entire width of the substrate to be processed, or at any rate on very wide bands. However, sometimes it is desired to metalize only small or irregular areas, such as designs or wordings, or to create areas free from metalization, in order to make the contents of the packaging visible (for example, in order to show the extent of cooking and the quality of oven- baked products or French fries). In these cases, therefore, it is necessary to metalize larger areas of substrate than desired, in order to then proceed to remove the metallic layer from the portions of the substrate where the metalization is not wanted. The "de-metalization" procedure requires the application of a protective lacquer on the portions of the substrate on which the metallic effect is to be retained, and a subsequent alkaline washing of the substrate with a solution containing soda, in order to remove the metalized layer from the portions that are not protected by the lacquer. The removed metal can no longer be used and its disposal entails considerable cost and a significant environmental impact.

Furthermore the metalization and de-metalization procedures, because of the apparatuses and the operating conditions that they require and because of the discarded material that they generate (for instance waste water, which has to be properly purified), are expensive and pollutant.

In brief therefore, the methods currently in use and based on conventional metalization and de-metalization suffer clear drawbacks in terms of logistics, because of the need to perform treatments in different and separate plants, because of the costs, which, being extremely high, limit the use of metallic substrates (which could be a lot more widespread on the end market), and because of the environmental impact.

As an alternative to the methods described above, some methods have likewise been developed in which conventional metalization is substituted by printing with inks containing metallic pigments; with these methods substrates are obtained that have a metalized appearance effect, the result of printing with ink. However, none of the printing inks containing metallic pigments which have been developed to date has made it possible to obtain aesthetic results comparable to those obtained by way of conventional metalization. In particular, it is not currently possible to obtain a high specularity of the metalized effect, i.e. the characteristic "mirror effect" of metallic materials. Conventional metalization therefore remains the method of choice in order to obtain materials with the best aesthetic effect of a metallic finish.

The aim of the present invention is therefore to provide a methodology for obtaining a metalized effect on substrates of various types, which solves the above mentioned technical problems, while removing the drawbacks and overcoming the limitations of the known art.

Within this aim, an object of the invention is to provide an ink for obtaining a metalized effect by way of printing. In particular, the present invention sets out to provide a printing ink for obtaining metalized-effect decorations with characteristics of higher specularity (in particular, with a "mirror effect") with respect to conventional metallic inks. Furthermore, the present invention sets out to provide an ink with which to obtain a metalized effect using conventional printing machines (of the rotogravure and flexographic type) directly, thus avoiding the conventional metalization process which must necessarily be carried out "off line".

Another object of the invention is to provide a method for preparing a printing ink for obtaining decorations with a metalized effect with high specularity.

The present invention also sets out to provide the use of an ink for obtaining decorations with a metalized effect with high specularity on different and varied types of substrates, by way of a printing process.

Another object of the invention is to provide a printing ink for obtaining decorations with a metalized effect which can be used for various types of printing (for example, flexographic printing and rotogravure printing), has good rheological characteristics, is easy to provide, and is low cost to prepare and use.

This aim and these and other objects which will become better apparent hereinafter are achieved by a metallic ink for printing, which comprises:

(a) 2.5% to 5.5% by weight on the total weight of the ink of one or more vacuum metalized pigments;

(b) from 1% to 3% by weight on the total weight of the ink of one or more polymers of ethyl cellulose with ethoxy content comprised between 48% and 50%;

(c) 91.5% to 96.5% by weight on the total weight of the ink of one or more organic solvents selected from the group consisting of alcohols and esters of alkanes, which have from 2 to 6 carbon atoms.

The aim and objects of the invention are also achieved by a method for preparing the metallic ink according to the invention, which comprises the steps of: (a) preparing a solution constituted by 5-15% by weight on the total weight of the solution of one or more polymers of ethyl cellulose with an ethoxy content comprised between 48% and 50% and by 85-95% by weight on the total weight of the solution of one or more organic solvents selected from the group consisting of alcohols and esters of alkanes which have from 2 to 6 carbon atoms;

(b) adding to the solution prepared in step (a) the one or more vacuum metalized pigments and the one or more organic solvents selected from the group consisting of alcohols and esters of alkanes which have from 2 to 6 carbon atoms, wherein said one or more organic solvents are the same one or more organic solvents used to prepare the solution in step (a).

Furthermore, the aim and objects of the invention are achieved by the use of the metallic ink according to the invention for printing materials for wrapping and/or packaging.

Further characteristics of the invention will become better apparent from the detailed description that follows. Furthermore, the ink according to the present invention, the method for its preparation and the its use offer a considerable series of advantages and benefits, which will become better apparent hereinafter.

The metalized pigments used in the ink according to the invention are known in the state of the art and are commonly indicated with the acronym VMP (Vacuum Metalized Pigments). Such pigments are usually in the form of non-leafing lamellar metal flakes, with a granulometry comprised between 8 and 13 μιη. Typically, these lamellar metal flakes are available on the market as a solvent-based slurry (the solvent being ethyl acetate) containing 10% metal. In a preferred embodiment of the invention, the vacuum metalized pigment can be metallic aluminum. Furthermore, the one or more metalized pigments present in the ink of the invention can preferably be selected from the pigments sold by BASF with the name Metasheen®, which are in the form of a slurry based on ethyl acetate and which contain 10% aluminum. The colorings of the Metasheen® pigments range from a whitish shade with a "liquid silver" effect to darker colors with a "chrome-like" effect. In a particularly preferred embodiment, the pigment can be Metasheen® 410410; this pigment gives a dark chrome-like effect, with high reflectance and specularity. In another particularly preferred embodiment, the pigment can be Metasheen® 710410; this pigment gives a typical aluminum effect, lighter in chromatic terms than that obtained with the Metasheen® 410410 pigment and usually considered the "standard degree" of the metallic effect. Furthermore, with the Metasheen® 710410 pigment a less reflective effect is obtained than that obtained with the Metasheen® 410410 pigment, but equally specular.

In the context of the present invention, the terms "reflectance" and "specularity" have the meanings that are commonly attributed to them in the sectors of metalization and metallic inks and which are well known to the person skilled in the art. In particular, "reflectance" is the ratio between the intensity of the reflected radiant flux and the intensity of the incident radiant flux, i.e. the proportion of incident light that a surface is capable of reflecting. The term "specularity" refers to a qualitative characteristic of a surface and indicates the fact that it has the "mirror effect" characteristic of metallic materials. If the substrates, besides being printed with the metallic ink of the invention, must also be colored by way of common colored printing inks, then preferably the Metasheen® 710410 pigment is used.

The function of the polymers of ethyl cellulose is to act as a binder in the formulation of the ink and make it possible to maintain an optimal formulation equilibrium between the components of the ink.

The polymers of ethyl cellulose used in the ink according to the invention have an ethoxy content comprised between 48% and 50%. Furthermore, the polymers of ethyl cellulose can preferably have a viscosity comprised between 3 mPa*s and 110 mPa*s; such viscosity values are measured at 20°C for a 5% solution of polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight.

In a particularly preferred embodiment, the polymers of ethyl cellulose can have a viscosity equal to 3 mPa*s, measured at 20°C for a 5% solution of polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight. In another particularly preferred embodiment, the polymers of ethyl cellulose can have a viscosity equal to 110 mPa*s, measured at 20°C for a 5% solution of polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight.

Preferably furthermore, the polymers of ethyl cellulose can have a specific weight comprised between 1.12 g/cm³ and 1.15 g/cm³.

The polymers of ethyl cellulose can preferably be selected from the polymers sold by DOW CHEMICAL under the trade name Ethocel™. In a particularly preferred embodiment, the polymers of ethyl cellulose can be of the Ethocel™ 4 type: such polymers have an ethoxy content of ethyl cellulose comprised between 48% and 50% and a viscosity equal to 3 mPa*s (measured at 20°C for a 5% solution of polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight, as indicated previously). Polymers of the Ethocel™ 4 type are mainly used for preparing metalized inks for flexographic printing. Flexographic printing is a method of direct rotary printing, in which the inked plates (made of rubber or of photopolymeric materials) use the relief printing principle; such plates are wrapped around a cylinder that, by exerting pressure, transfers the ink from the plate to the substrate to be printed. In another particularly preferred embodiment, the polymers of ethyl cellulose can be of the Ethocel™ 100 type: such polymers also have an ethoxy content of ethyl cellulose comprised between 48% and 50% but they have a viscosity equal to 110 mPa*s (measured at 20°C for a 5% solution of polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight, as indicated previously). Polymers of the Ethocel™ 100 type are mainly used for preparing metalized inks for rotogravure printing. Rotogravure printing is also a direct rotary method, but it uses intaglio printing plates, i.e. they are constituted by metallic cylinders covered by a layer on which the subject to be printed is engraved; the engraved areas are inked and during printing the ink is transferred by decalcomania directly onto the substrate to be printed. With respect to other methods of printing, rotogravure printing is the one that gives the best results in terms of specularity.

In the metallic ink according to the invention, the one or more organic solvents are alcohols or esters of alkanes, which have a number of carbon atoms comprised between 2 and 6. In a preferred embodiment, the organic solvent present in the ink can be ethanol. In another preferred embodiment, the organic solvent present in the ink can be ethyl acetate. In yet another preferred embodiment, the organic solvent present in the ink can be a mixture of ethanol and ethyl acetate.

In an more preferred embodiment, the polymers of ethyl cellulose can have a viscosity equal to 3 mPa*s, measured as indicated previously (for example Ethocel™ 4 polymers) and the organic solvent can be a mixture of ethanol and ethyl acetate. In another more preferred embodiment, the polymers of ethyl cellulose can have a viscosity equal to 110 mPa*s, measured as indicated previously (for example Ethocel™ 100 polymers) and the organic solvent can be ethyl acetate.

In an even more preferred embodiment, the metallic ink according to the invention can comprise:

(a) 5% by weight on the total weight of the ink of one or more vacuum metalized aluminum pigments;

(b) 2.5% by weight on the total weight of the ink of one or more polymers of ethyl cellulose with viscosity equal to 3 mPa*s, measured as indicated previously (for example Ethocel™ 4 polymers);

(c) 92.5% by weight on the total weight of the ink of a mixture of ethanol and ethyl acetate, in which 45% is ethyl acetate and 47.5% is ethanol. In another even more preferred embodiment, the metallic ink according to the invention can comprise:

(a) 3% by weight on the total weight of the ink of one or more vacuum metalized aluminum pigments;

(b) 1.5% by weight on the total weight of the ink of one or more polymers of ethyl cellulose with viscosity equal to 110 mPa*s, measured as indicated previously (for example Ethocel™ 100 polymers);

(c) 95.5% by weight on the total weight of the ink of ethyl acetate.

The type and quantity of the components of the metallic ink for printing according to the invention are calibrated on the basis of the type of application for which the ink is destined, i.e. according to whether the ink is used for flexographic printing or rotogravure printing. The main characteristics of the metallic ink which vary according to the type of application are its solvent state, the dry residue, and the final viscosity, as is known to the person skilled in the art.

The total dry residue of the ink, which is the most important characteristic, can vary between 4% and 8% by weight on the total weight of the ink, according to the type of application of the ink.

The final viscosity of the ink, i.e. the viscosity of the product ready for printing, measured in Ford Cup no. 4 at 20°C, can vary between 15 seconds and 19 seconds.

The equilibrium of the solvent state is a determining factor in maximizing the "mirror effect" of the resulting printed substrate.

In order to ensure excellent print performance, even more so when using the metallic ink of the present invention, it is important to apply the correct quantity of ink on the substrate to be printed. In order to apply the metallic ink in correct quantities using conventional printing machines, for example, cylinders with engraving of 65-70 lines per square centimeter can be used for rotogravure printing, and anilox cylinders can be used for flexographic printing. It is important to emphasize that the application of the metallic ink of the invention does not entail any alteration of the printing speeds commonly applied when using traditional printing inks. For example, excellent metalized-effect printing results are obtained using rotogravure machines with a printing speed even higher than 250 m/min.

Another aspect of the invention relates to a method for preparing the metallic ink for printing according to the present invention, which comprises the steps of (a) preparing a solution constituted by one or more polymers of ethyl cellulose and one or more organic solvents, as defined previously in more detail; and (b) adding to this solution the one or more vacuum metalized pigments and the one or more organic solvents, as defined previously in more detail, where the one or more organic solvents are the same ones used to prepare the solution in step (a).

The preparation of the solution of ethyl cellulose in solvent (step (a) of the method) occurs preferably in stainless steel basins provided with a Cowles stirrer with toothed impeller. The one or more solvents are placed in the basin and the polymers of ethyl cellulose are added by pouring, while stirring.

The preparation of the final ink (step (b) of the method) also occurs preferably in stainless steel basins provided with a Cowles stirrer with toothed impeller. The one or more metallic pigments and the solution prepared in step (a) are placed in the basin and stirring is begun. The speed of the stirring must be such as to obtain the "doughnut" effect in the basin. The one or more solvents are then added by pouring, again while stirring. Once the one or more solvents have been incorporated, stirring is kept at the same speed until the components are perfectly homogenized. Mixing by way of a mechanical stirrer (or mixer) is crucial in order to obtain a product in which the components are completely mutually homogenized. The time necessary to prepare the solution of ethyl cellulose in solvent (step (a)) and the time necessary to prepare the final ink (step (b)) are variable in relation to the quantity of product to be prepared, in relation to the ratio between the diameter of the impeller and the diameter of the basin, and in relation to the speed of the stirrer (RPM of the shaft). For example, in order to prepare 100 kg of ink in a stainless steel basin of 60 cm diameter and 200 1 capacity, equipped with a toothed impeller of 30 cm diameter with a top stirring speed of 800 RPM, it is necessary to mix the metallic pigments and the solution of ethyl cellulose for about 10-15 minutes. At the end of the addition by pouring of the solvent, the stirring must be maintained for a further 5-10 minutes without changing the speed. It should be understood that the above values are given exclusively by way of example and can easily be modified by a person skilled in the art according to the properties of the ink being prepared. For example, it is possible that during the preparation of the ink it is necessary to add extra solvent in order to adjust the viscosity and/or retard the product. As is known to the person skilled in the art, "retarding the product" consists of adding small quantities of solvents to the formulation which evaporate more slowly than the solvents already present in that formulation, in order to slow down the drying of the ink. In the present invention, to this end one or more organic solvents can be used which are selected from the group constituted by alcohols, glycols and esters of alkanes, which have from 4 to 6 carbon atoms. The quantity of solvent added in any case must not exceed 10% by weight of the total weight of the ink. Preferably, the solvent added to the mixture can be methoxypropanol.

It furthermore appears evident that, if the one or more vacuum metalized pigments are used in slurry form, the ink will contain, in addition to the one or more organic solvents used for the formulation of the ink, the solvent present in the slurry as well. In the current state of the art, the slurries that comprise the vacuum metalized pigments are based on ethyl acetate.

Another aspect of the invention relates to the use of the metallic ink according to the present invention for printing materials of various types, in common use in the sector of wrapping and/or of packaging. Preferably, materials for wrapping and/or packaging printed with the metallic ink of the present invention can be polymeric films, glossy cardboards, or bonded substrates which comprise at least one of these materials. More specifically, polymeric films can be transparent and flexible films such as, for example, polypropylene (PP), polyester, polyethylene terephthalate (PET), and polyethylene (PE).

Furthermore, the above mentioned materials for wrapping and/or packaging can preferably be printed with the metallic ink of the invention by rotogravure printing or flexographic printing.

Preferably, when the materials to be printed with the ink of the invention are transparent films, they can be "reverse" printed; as is known to the person skilled in the art, reverse printing is carried out on the opposite surface of a polymeric film from the surface already treated with an ink. Reverse printing is applied especially in rotogravure printing. Furthermore, reverse printing makes it possible to maximize the mirror effect.

Substrates printed with the metallic ink of the invention can also be colored, by way of one or more conventional printing passes using high- transparency colored inks. For example, it is possible to use inks prepared with metal-complex soluble dyes, which ensure the maximum degree of transparency.

When the substrates to be printed both with the metallic ink and with one or more colored inks are transparent films, the one or more colored inks can preferably be applied on the back of the film, which shows the "reverse" printing of the metalized mirror effect. When on the other hand the substrates to be printed are glossy cardboards (or in general non-transparent substrates), the one or more colored inks must necessarily be applied directly on the metalized mirror-effect printed surface.

Finally, another aspect of the invention is represented by materials for wrapping and/or packaging which are printed with the metallic ink according to the present invention. The materials for wrapping and/or packaging can preferably be polymeric films or glossy cardboards or bonded substrates which comprise at least one of these materials and they can preferably be printed by way of rotogravure printing or flexographic printing.

It should be understood that the characteristics of embodiments described with reference to an aspect of the present invention are to be considered valid also with reference to the other aspects of the invention described herein, even if they are not explicitly repeated.

EXAMPLES:

Example 1 : preparation of metallic ink for flexographic printing

Prepare a solution constituted by 10% by weight on the total weight of the solution of Ethocel™ 4 ethyl cellulose and 90% by weight on the total weight of the solution of ethanol. The solution is prepared in a stainless steel basin provided with a Cowles stirrer with toothed impeller. The polymers of ethyl cellulose are added by pouring, while stirring, to the solvent already in the basin.

Metasheen® 410410 or Metasheen® 710410 (slurry containing 10% metallic pigment and 90% ethyl acetate as solvent) and extra ethanol are added to the solution of Ethocel™ 4 in ethanol, thus obtaining an ink that has the following proportions between the ingredients:

25% by weight on the total weight of the ink of Ethocel™ 4 solution in ethanol (corresponding to 2.5% by weight on the total weight of the ink of Ethocel™ 4 and 22.5% by weight on the total weight of the ink of ethanol);

50% by weight on the total weight of the ink of Metasheen® (corresponding to 5% by weight on the total weight of the ink of metallic pigment);

25% by weight on the total weight of the ink of ethanol.

Therefore, the ink thus prepared contains: 5% by weight on the total weight of the ink of metallic pigment;

2.5% by weight on the total weight of the ink of Ethocel™ 4 polymers of ethyl cellulose;

47.5% by weight on the total weight of the ink of ethanol (22.5% contained in the solution of Ethocel™ 4 and 25% added during the formulation of the ink); and

45% ethyl acetate contained in the Metasheen® slurry,

for a total of 92.5% organic solvents.

The final ink is prepared in a stainless steel basin of 60 cm diameter and 200 1 capacity, equipped with a Cowles stirrer with a toothed impeller of 30 cm diameter. The Metasheen® slurry and the solution of Ethocel™ 4 in ethanol are introduced into the basin, in the correct quantities. Stirring is begun at 800 RPM (creating the "doughnut" effect in the basin) for 15 minutes. While stirring, the correct quantity of ethanol is added by pouring. Stirring is continued at the same speed for a further 10 minutes.

The metallic ink for flexographic printing thus obtained has the following physical properties:

- dry residue: 7.5%

- viscosity (Ford Cup no. 4 at 20°C): 17 seconds

- specific weight (at 20°C): 0.900 g/cm³.

Example 2: preparation of metallic ink for rotogravure printing

Prepare a solution constituted by 10% by weight on the total weight of the solution of Ethocel™ 100 polymers of ethyl cellulose and 90% by weight on the total weight of the solution of ethyl acetate. The solution is prepared in a stainless steel basin provided with a Cowles stirrer with toothed impeller. The polymers of ethyl cellulose are added by pouring, while stirring, to the solvent already in the basin.

Metasheen® 410410 or Metasheen® 710410 (slurry containing 10% metallic pigment and 90% ethyl acetate as solvent) and extra ethyl acetate are added to the solution of Ethocel™ 100 in ethyl acetate, thus obtaining an ink that has the following proportions between the ingredients:

15% by weight on the total weight of the ink of Ethocel™ 100 solution in ethyl acetate (corresponding to 1.5% by weight on the total weight of the ink of Ethocel™ 100 and 13.5% by weight on the total weight of the ink of ethyl acetate);

30% by weight on the total weight of the ink of Metasheen® (corresponding to 3% by weight on the total weight of the ink of metallic pigment);

55% by weight on the total weight of the ink of ethyl acetate.

Therefore, the ink thus prepared contains:

3% by weight on the total weight of the ink of metallic pigment;

1.5% by weight on the total weight of the ink of Ethocel™ 100 polymers of ethyl cellulose;

95.5% by weight on the total weight of the ink of ethyl acetate (27% contained in the Metasheen® slurry, 13.5% contained in the solution of Ethocel™ 100 and 55% added during the formulation of the ink).

The final ink is prepared in a stainless steel basin of 60 cm diameter and 200 1 capacity, equipped with a Cowles stirrer with a toothed impeller of 30 cm diameter. The Metasheen® slurry and the solution of Ethocel™ 100 in ethyl acetate are introduced into the basin, in the correct quantities. Stirring is begun at 800 RPM (creating the "doughnut" effect in the basin) for 15 minutes. While stirring, the correct quantity of ethyl acetate is added by pouring. Stirring is continued at the same speed for a further 10 minutes.

The metallic ink for rotogravure printing thus obtained has the following physical properties:

- dry residue: 4.5%

- viscosity (Ford Cup no. 4 at 20°C): 17 seconds

- specific weight (at 20°C): 0.950 g/cm³.

In practice it has been found that the ink according to the invention fully achieves the set aim in that it makes it possible to obtain, by printing, a metalized effect that is fully comparable to that obtained by way of conventional vacuum metalization methods. In particular, printing with the ink of the present invention ensures a specularity ("mirror effect") similar to the specularity conferred by the conventional metalization method.

Furthermore, the ink of the invention and its use in methods of printing materials with a metalized effect enable a considerable economic saving and make it possible to optimize timescales in that the metalized effect printing can occur "in-line" as part of the standard printing steps, using the same plant and the same tools and so avoiding the continuous movement of the material. The metalized ink of the invention can therefore be used as a supplement to the colored inks traditionally used in printing, in an entirely similar manner thereto. Also, the ink of the invention, the method for its preparation, and its use for printing have a considerably lower environmental impact than conventional metalization and de-metalization processes, thus avoiding the pollution resulting from production discards and the disposal of metals and the waste water from the apparatuses used.

The metallic ink for printing, conceived as described herein, is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other elements, the equivalence of which is known to the person skilled in the art.

The disclosures in Italian Patent Application No. MI2015A000475 (102015902342295) from which this application claims priority are incorporated herein by reference.

Claims

1. A metallic ink for printing, which comprises:

(b) 1% to 3% by weight on the total weight of the ink of one or more polymers of ethyl cellulose with ethoxy content comprised between 48% and 50%;

2. The metallic ink according to claim 1, wherein the vacuum metalized pigment is metallic aluminum.

3. The metallic ink according to claim 1 or 2, wherein the one or more polymers of ethyl cellulose have a viscosity comprised between 3 mPa*s and 110 mPa*s, measured at 20°C for a 5% solution of said one or more polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight.

4. The metallic ink according to claim 3, wherein the one or more polymers of ethyl cellulose have a viscosity equal to 3 mPa*s, measured at 20°C for a 5% solution of said one or more polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight.

5. The metallic ink according to claim 3, wherein the one or more polymers of ethyl cellulose have a viscosity equal to 110 mPa*s, measured at 20°C for a 5% solution of said one or more polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight.

6. The metallic ink according to one or more of the preceding claims, wherein the organic solvent is selected from the group consisting of ethyl acetate and a mixture of ethanol and ethyl acetate.

7. The metallic ink according to claim 4, wherein the organic solvent is a mixture of ethanol and ethyl acetate.

8. The metallic ink according to claim 5, wherein the organic solvent is ethyl acetate.

9. The metallic ink according to claim 7, wherein said ink comprises:

(b) 2.5% by weight on the total weight of the ink of one or more polymers of ethyl cellulose with a viscosity equal to 3 mPa*s, measured at 20°C for a 5% solution of said one or more polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight;

(c) 92.5% by weight on the total weight of the ink of a mixture of ethanol and ethyl acetate, in which 45% is ethyl acetate and 47.5% is ethanol.

10. The metallic ink according to claim 8, wherein said ink comprises:

(b) 1.5% by weight on the total weight of the ink of one or more polymers of ethyl cellulose with a viscosity equal to 110 mPa*s, measured at 20°C for a 5% solution of said one or more polymers of ethyl cellulose in a mixture of toluene and ethanol with a ratio of 8:2 by weight;

(c) 95.5% by weight on the total weight of the ink of ethyl acetate.

11. A method for preparing the metallic ink according to one or more of the preceding claims, which comprises the steps of:

(a) preparing a solution constituted by 5-15% by weight on the total weight of the solution of one or more polymers of ethyl cellulose with an ethoxy content comprised between 48% and 50% and by 85-95% by weight on the total weight of the solution of one or more organic solvents selected from the group consisting of alcohols and esters of alkanes which have from 2 to 6 carbon atoms;

12. Use of the metallic ink according to one or more of claims 1 to 10 for printing a material for wrapping and/or packaging.

13. The use according to claim 12, wherein the material for wrapping and/or packaging is selected from the group consisting of polymeric films, glossy cardboards and bonded substrates which comprise at least one of these materials.

14. The use according to claim 12 or claim 13, wherein the material for wrapping and/or packaging is printed by printing of the rotogravure or flexographic type.

15. A material for wrapping and/or packaging printed with the metallic ink according to one or more of claims 1 to 10.