A PRINTABLE ARTICLE FOR INKJET PRINTING

Abstract

 The present invention relates to a printable article for inkjet printing having a fibrous base substrate and a coating disposed thereon. The coating is being comprised of at least one inorganic pigment being zeolite, metallic salt based di- and/or multivalent metallic cations, and at least one binder. The zeolite is substantially saturated with the di- and/or multivalent metallic cations and the disposed coating forms an exterior layer of the printable article capable of interacting with an ink. The invention further relates to a method for producing such printable article and to the use of a coating color for a printable article.

Description

Technical field of invention

[0001] The present invention relates to printable article for inkjet printing, a method for producing such printable article, and to the use of a coating color for a printable article.

Background

[0002] More and more printing productions are made with short notice and in smaller editions; often the type of printing method is decided late in the process and different editions of the same job can be done in different printing equipments. This behavior has lead to increased demands on printable substrates and it is therefore getting more and more important that the printable substrates are suitable for several different types of printing methods. Most printable substrates of today have originally been developed for offset printing as well as flexographic processes. During the last decades they have in addition often been developed to work better in toner base printing equipments. This has created multifunctional printable substrates.

[0003] Inkjet printing, i.e. a digital printing method, has been a common printing technique for many decades but it is mainly used for smaller desktop printers and non-commercial printers. Most printable substrates are to some extent suitable for desktop inkjet printers but there are also printable substrates being specially adopted for more demanding inkjet print. However, the development of high-speed inkjet printing presses set new demands on the printable substrates. The aim with these printing presses is to have a productivity that can match offset printing and at the same time utilize the advantages of digital printing.

[0004] The ink used in inkjet printing differs from the ink used for other, more traditional printing techniques in the large amount of liquids that carries a relative small amount of color pigment. This ink is sprayed or injected from a small distance into the paper surface, at extreme high speed. One of the challenges with inkjet printing is to get the pigment to stay on top of the printable substrate. The printable substrate most often consist of a network of absorbent fibers and the large amount of liquid as well as the color pigments in the ink will be absorbed into the substrate. The effect is that the image reproduction will be less good and the color density will be low due to the color pigments are absorbed vertically down into the printable substrate. Moreover, there is a large risk for a bleeding effect when the ink is spread horizontally in the fibrous material. This bleeding can e.g. be that a single color that bleeds causing less defined lines or multi-color bleeding causing bad color reproducibility.

[0005] To be able to keep the color pigment as much as possible to the surface of the printable substrate, the substrate needs to have a treated surface that can interact with the ink. This can be done with different kind of surface treatment as coating or surface sizing. Coating means normally that some type of mineral coating pigment is present and then added on top of the fiber surface to create a smoother or glossier surface while surface sizing is only a sizing to strengthen the surface or create a certain print characteristic, but not to change or cover the paper surface in any other way. Both coated and sized substrates work with the same principal in order to keep the ink on top of the substrate; firstly the substrate needs the right level of liquid absorption and secondly there is a need for interaction between the color pigments in the ink and surface or coating of the substrate.

[0006] There is constantly a demand for improved printing quality and improved productivity in the inkjet technology and thus there is still a need in the art for inkjet technology providing high printing quality and high productivity.

Summary of the invention

[0007] It is an object of the present invention to improve the current state of the art and to mitigate at least some of the above mentioned problems. These and other objects are achieved by a printable article, a method for manufacturing a printable article and a use of a printable article.

[0008] According to a first aspect of the invention a printable article for inkjet printing is provided. The printable article has a fibrous base substrate and a coating disposed thereon, the coating being comprised of at least one inorganic pigment being zeolite, metallic salt based di- and/or multivalent metallic cations, and at least one binder,
wherein said zeolite is substantially saturated with said di- and/or multivalent metallic cations, and wherein the disposed coating forms an exterior layer of the printable article capable of interacting with an ink.

[0009] The present invention is based on the realization that a higher printing quality of the printable article can be achieved due to that the zeolite is saturated, or substantially saturated, with said metallic salt based di- and/or multivalent metallic cations. The saturated, or substantially saturated, zeolite will interact with the ink resulting in coagulation of the ink and hence a higher printing quality may be achieved. The metallic salt based di- and/or multivalent metallic cations in the saturated, or substantially saturated, zeolite takes part in the coagulation process. By coagulation, the ink pigments clot together creating larger cohesive ink areas of ink pigment avoiding e.g. bleeding.

[0010] Thus, in a simplified manner, the mechanism may be described as follows: when the printable article is immersed in water, or simply wetted with water based inks, which do not contain any or very few multivalent metal cations, the di- and/or multivalent metallic cations in the saturated, or substantially saturated, zeolite (i.e. the trapped or adsorbed di- and/or multivalent metallic cations in the zeolite), will depart from the zeolite and move into the coating. Hereby, the ink (or ink pigments) reacts with the departed di- and/or multivalent metallic cations (causing coagulation of the ink), whereby other di- and/or multivalent metallic cations depart from the zeolite and move into the coating in order to re-establish the equilibrium. The process is ongoing until either all the ink pigments have been precipitated (i.e. have taken part in the coagulation process) or no more di- and/or multivalent metallic cations are available in the zeolite. Thus, only the di- and/or multivalent metallic cations which are necessary for the process are being departed or extracted from the zeolite (and thus leaving any remaining di- and/or multivalent metallic cations trapped or adsorbed in the zeolite).

[0011] Thus the zeolite acts as storage and carrier of di- and/or multivalent metallic cations. Furthermore, the zeolite is preferred as its chemical structure (high surface area) enables it to absorb water contained in the ink.

[0012] It should be understood that the zeolite is saturated, or substantially saturated, with said di- and/or multivalent metallic cations originating from a metallic salt (i.e. the metallic salt based di- and/or multivalent metallic cations). Substantially saturated may according to at least one example embodiment refer to that the zeolite is at least 75 %, such as e.g. at least 80 %, or at least 85 %, or at least 90 % or at least 95 %, or at least 99 % saturated with said di- and/or multivalent metallic cations.

[0013] According to at least one example embodiment of the present invention the fibrous base substrate is made from natural and/or synthetic fibers. The natural fibers used for the fibrous base substrate may for example be cellulose based fibers. The fibrous base substrate may e.g. be paper or cardboard, made of either chemical pulp or mechanical pulp, or paper or cardboard made of a combination of chemical and mechanical pulp. The fibrous base substrate may e.g. be bleached paper and/or unbleached paper. Thus the coating may be disposed on a paper made of chemical pulp and/or mechanical pulp. The coating may be applied to the fibrous base substrate at anytime during the process of transforming pulp to paper in the form of a coating color (which forms the coating once being applied to the fibrous base substrate, this is further explained below).

[0014] According to at least one example embodiment of the present invention the fibrous base substrate may be of various thicknesses. The thickness of the fibrous base substrate is typically described as the basis weight or the grammage. These terms are used interchangeably throughout the application. The grammage of printable article is according to at least one example embodiment of the invention within the range of 60 g/m² to 350 g/m², or in the range of 70 g/m² to 300 g/m².

[0015] According to at least one example embodiment of the invention the moisture content of the fibrous base substrate is in the range of 2 wt% to 8 wt%, or in the range of 4 wt% to 6 wt%.

[0016] According to at least one example embodiment of the invention the zeolite used in the coating, or coating color (or zeolite dispersion forming at least a part of the coating color), is comprised of, or consist of, natural and/or synthetic zeolite. The natural zeolite may for example be analcime, chabazite, clinoptilolite, heulandites, natrolite, philipsite and/or stilbite. The synthetic zeolite may for example be a commercially available zeolite such as e.g. Advan, Zeoflair or Zeocros. The zeolites typically have a porous structure that can accommodate a wide variety of metallic cations, such as e.g. Na⁺ and K⁺.

[0017] According to at least one example embodiment of the present invention the metallic salt based di- and/or multivalent metallic cations originates from at least one metallic salt of di- and/or multivalent metallic cations in the form of a solid, such as a powder or granulates, or of an aqueous solution. The at least one metallic salt may be a salt based on calcium ions. Thus, the metallic salt based di- and/or multivalent metallic cations may be calcium ions. Moreover, and as explained further below, the calcium ions may substitute the originally present monovalent ions in the zeolite (i.e. the originally present monovalent ions are ion exchanged with the calcium ions).

[0018] According to at least one example embodiment of the invention said zeolite is a pre-treated zeolite which has been substantially saturated with said di- and/or multivalent metallic cations prior to being applied to the fibrous base substrate.

[0019] By pre-treating the zeolite, the zeolite may be substantially saturated with said di- and/or multivalent metallic cations in an advantageous manner relating to the process of producing the printable article.

[0020] According to at least one example embodiment of the invention, said zeolite has been substantially saturated with said di- and/or multivalent metallic cations in a coating color or zeolite dispersion in which the weight percentage of said di- and/or multivalent metallic cations to said zeolite is between 0.5 wt% and 15 wt%.

[0021] In other words, said zeolite has been mixed with 0.5 wt% - 15 wt% (compared to the weight of the original zeolite) of metallic salt based di- and/or multivalent metallic cations in the coating color or zeolite dispersion. Stated differently, the metallic salt based di- and/or multivalent metallic cations are present in the coating color or zeolite dispersion by between 0.5 % by weight and 15 % by weight based on the total weight of the original zeolite. For example, if the metallic salt based di- and/or multivalent metallic cations is calcium (and hence the metallic salt used is a calcium based salt, such as calcium acetate), the calcium ions are present in the coating color or zeolite dispersion by between 0.5 % by weight and 15 % by weight based on the total weight of the original zeolite.

[0022] According to at least one example embodiment, the weight percentage of said di- and/or multivalent metallic cations to said zeolite is between 1 wt% and 15 wt%, such as e.g. between 5 wt% and 15 wt%, or between 7 wt% and 15 wt%, or between 10 wt% and 15 wt%, or between 13 wt% and 15 wt%.

[0023] According to at least one example embodiment, the weight percentage of said di- and/or multivalent metallic cations to said zeolite is between 0.5 wt% and 13 wt%, such as e.g. between 0.5 wt% and 10 wt%, or between 0.5 wt% and 7 wt%, or between 0.5 wt% and 5 wt%, or between 0.5 wt% and 3 wt%.

[0024] It should be understood that the coating color is referring to the compound mixture (e.g. as a paste) comprising inter alia the zeolite, a binder and the metallic salt prior to being applied to the fibrous base substrate, and that the coating is referring to corresponding compounds in the coating color, but when being applied to the fibrous base substrate.

[0025] It should be noted that the zeolite dispersion (or zeolite slurry) is referring to a dispersion forming the basis of the coating color (but prior to adding the binder), the zeolite dispersion comprising inter alia the zeolite and the metallic salt. The zeolite dispersion may further comprise dispersion agents and water.

[0026] As mentioned above, the zeolite may be pre-treated to be substantially saturated with said di- and/or multivalent metallic cations in the coating color or zeolite dispersion. Hence, the chemical structure of the zeolite will change due to ion exchange between the monovalent ions originally present in the zeolite, and the metallic salt based di- and/or multivalent metallic cations. The zeolite may thus be referred to as an original zeolite (in which none of the originally presented monovalent ions has been ion exchanged with the metallic salt based di- and/or multivalent metallic cations) prior to being brought into contact with the metallic salt, and the zeolite may be reffered to a substantially saturated zeolite or a pre-treated zeolite (in which e.g. most of the originally presented monovalent ions have been ion exchanged with the metallic salt based di- and/or multivalent metallic cations) after being brought into contact with the metallic salt in the coating color or zeolite dispersion.

[0027] According to at least one example embodiment, at least 75 %, such as e.g. at least 80 %, or at least 85 %, or at least 90 % or at least 95 %, or at least 99 % of the originally presented monovalent ions in the original zeolite is (or have been) ion exchanged with said metallic salt based di- and/or multivalent metallic cations.

[0028] According to at least one example embodiment, at least 75 %, such as e.g. at least 80 %, or at least 85 %, or at least 90 % or at least 95 %, or at least 99 % of the sites in the zeolite, which in the original zeolite were accommodated by monovalent ions (e.g. Sodium ions), is accommodated by said metallic salt based di- and/or multivalent metallic cations (such as e.g. Calcium ions).

[0029] Thus, according to at least one example embodiment, the original zeolite used in the coating color or zeolite disperison comprises (or accommodates) monovalent cations, such as Na⁺ ions. These monovalent positive ions are rather loosely held in the original zeolite and can thus readily be ion-exchanged with other ions, such as the metallic salt based di- and/or multivalent metallic cations from the metallic salt in a contact solution (e.g. in a coating color as explained below). An example of a zeolite accommodating Na⁺ cations is natrolite: Na₂Al₂Si₃O₁₀·2H₂O, another example is analcime.

[0030] In other words, the coating, or coating color (or zeolite dispersion) is prepared in such a way that monovalent metallic ions, such as Na⁺, in the original zeolite have been ion exchanged with metallic salt based di- and/or multivalent metallic cations to such an extent that adding more di- and/or multivalent metallic cations to the coating or coating color (or zeolite dispersion) will not result in any (substantial) increase in the ion-exchange between the monovalent metallic ions in the zeolite and the di- and/or multivalent metallic ions from the metallic salt.

[0031] Thus, the coating may be referred to as a di- and/or multivalent metallic cations (substantially) saturated zeolite coating. As mentioned above, the saturation of the zeolite with the di- and/or multivalent metallic cations is typically carried out prior to applying the coating to the fibrous base substrate (i.e. in the coating color or zeolite dispersion).

[0032] Stated differently, there is an equilibrium stemming from the ion exchange between the monovalent metallic ions in the zeolite, and the di- and/or multivalent metallic cations from the metallic salt, which equilibrium is shifted in such a way that the zeolite is saturated, or substantially saturated, with di- and/or multivalent metallic cations. In other words, monovalent metallic ions, such as Na⁺, in the original zeolite is (or has been) ion exchanged with di- and/or multivalent metallic cations from the metallic salt such that said equilibrium is shifted towards a di- and/or multivalent metallic ions saturated, or substantially saturated, zeolite.

[0033] According to at least one example embodiment of the invention the fibrous base substrate has a first surface and a second surface, the first surface being arranged opposite to the second surface, and wherein said coating covers at least one of said first surface and said second surface.

[0034] Thus, the fibrous base substrate is arranged as a sheet having two parallel surfaces, i.e. the first surface and the second surface. Thus, the printable article is formed as a sheet with corresponding surfaces. Such sheet is advantageous to use in the industry for various applications, such as e.g. in forming printing paper e.g. advertising paper, book paper, receipt paper, etcetera. Such sheet arrangement facilitates printing on the printable article.

[0035] According to at least one example embodiment of the invention the coating covers both said first surface and said second surface.

[0036] Hereby, high speed inkjet printing may be carried out on both sides of the printable article.

[0037] According to at least one example embodiment of the invention the grammage of the coating on one of said first surface and said second surface is within the range of from 2 g /m² to 25 g /m², preferably in an amount within the range of from 10 g to 20 g /m².

[0038] Hereby, a sufficient amount of coating for having an advantageous printable article for inkjet printing is provided.

[0039] According to at least one example embodiment of the invention printable article further comprising at least one further inorganic pigment chosen from the list of: kaolin clay, silica, ground calcium carbonate, precipitated calcium carbonate, aluminum hydroxide, talc and titanium dioxide and combinations or mixtures thereof.

[0040] Such further inorganic pigment may further improve the printable properties of the printable article. For example, such further inorganic pigment forms a suitable mixture or surface of the printable article enabling absorption of water comprised in the ink.

[0041] According to at least one example embodiment of the invention, said further inorganic pigment comprises at least one of the following: Ground calcium carbonate (GCC) is commercially available, for example, under the trade names OMYAFIL, HYDROCARB, and OMYAPAQUE. Precipitated calcium carbonate (PCC) may be obtained by calcining crude calcium oxide. Water is added to obtain calcium hydroxide, and then carbon dioxide is passed through the solution to precipitate the desired calcium carbonate. Precipitated calcium carbonate (PCC) is also commercially available, for example, under the tradenames OPACARB A40 and ALBACAR HO DRY. Examples of commercially available clays are KAOCAL TM, EG-44, CAPIM SP, and B-80.

[0042] According to at least one example embodiment of the invention the binder is at least one of the following: SB latex, SA latex, PVAc, PVA, PVP, polyvinyl versatate, PU, starch and combinations or mixtures thereof.

[0043] The binder is advantageous to achieve a suitable coating. As further explained below, the binder may be added to the zeolite dispersion to form the coating color.

[0044] According to at least one example embodiment of the invention the zeolite is present in the coating within the range of from 5 % by weight to 50 % by weight based on the total weight of the coating, preferably within the range of from 10 % by weight to 40 % by weight based on the total weight of the coating.

[0045] Hereby, the desired amount of zeolite for the above mentioned improved printing quality of the printable article is provided.

[0046] According to a second aspect of the invention a method for producing a printable article for inkjet printing is provided. The method comprising the steps of:

a) providing a fibrous base substrate,

b) providing a zeolite dispersion created by mixing an inorganic pigment being zeolite, at least one metallic salt comprising di- and/or multivalent cations, dispersion agents and water whereby said zeolite is substantially saturated by said di- and/or multivalent cations from said at least one metallic salt;

c) providing a coating color by adding to the zeolite dispersion in b) at least a binder;

d) disposing said coating color on the fibrous base substrate, and thereby enabling the coating color to form a coating on an exterior layer of the printable article capable of interacting with an ink.

[0047] Effects and features of this second aspect of the present invention are largely analogous to those described above in connection with the first aspect of the inventive concept. Embodiments mentioned in relation to the first aspect of the present invention are largely compatible with the second aspect of the invention.

[0048] It should be understood that step b) above results in a pre-treated zeolite. In other words, in step b) the previously defined original zeolite (e.g. accomdating monovalent ions) is ion exchanged with the di- and/or multivalent cations from the metallic salt resulting in the substantially saturated zeolite.

[0049] According to at least one example embodiment, step b) and step c) are carried out subsequently in e.g. two different containers. According to at least one example embodiment, step b) and step c) are carried out simultaneously in a common container.

[0050] According to at least one example embodiment, said coating color in stepb c) is further created by adding at least one of the following: a further inorganic pigment, and any aiding chemicals.

[0051] According to at least one example embodiment, the weight percentage of said di- and/or multivalent metallic cations to said zeolite in said zeolite dispersion or coating color is between 0.5 wt% and 15 wt%. That is, the weight percentage of said di- and/or multivalent metallic cations to said original zeolite in said zeolite dispersion or coating color is between 0.5 wt% and 15 wt%.

[0052] According to at least one example embodiment of the invention the zeolite (i.e. the original zeolite) is present in the coating color within the range of from 5 % by weight to 50 % by weight based on the total weight of the coating color, preferably within the range of from 10 % by weight to 40 % by weight based on the total weight of the coating color; and
wherein said at least one metallic salt of a di- and/or multivalent metal cation is present in the coating color within the range of from 1 % by weight to 10 % by weight based on the total weight of the coating color, preferably within the range of from 2 % by weight to 5 % by weight based on the total weight of the coating color.

[0053] According to at least one example embodiment, said metallic salt comprising the di- and/or multivalent cations is present in the coating color within the range of from 1 % by weight to 10 % by weight based on the total weight of the coating color, preferably within the range of from 2 % by weight to 5 % by weight based on the total weight of the coating color.

[0054] According to at least one example embodiment of the invention said at least one metallic salt is substantially dissolved in said water. According to at least one example embodiment, the water-soluble metallic salt of a di- and/or multivalent metallic cations may be in the form of a solid, such as a powder or a granulate, or of an aqueous solution. According to at least one example embodiment, said at least one metallic salt is substantially dissolved in said water in said zeolite dispersion.

[0055] According to at least one example embodiment of the invention there are substantially no undissolved salts in the color coating when depositing the coating color on the fibrous base substrate.

[0056] According to at least one example embodiment, the coating color is deposited on the fibrous base substrate after the fibrous base substrate has dried to a moisture content of the fibrous base substrate in the range of 1 wt% to 8 wt%, or in the range of 2 wt% to 6 wt% based on the total weight of the fibrous base substrate.

[0057] According to at least one example embodiment of the invention the at least one metallic salt is added to the zeolite dispersion or coating color in an amount which is less than the solubility limit of said metallic salt. Hence, a substantial amount of the salt is dissolved.

[0058] According to at least one example embodiment of the present invention, said zeolite is mixed with 0.5 wt% - 15 wt% (compared to the weight of the original zeolite), or between 0.5 wt% and 13 wt%, or between 3 wt% and 15 wt%, such as e.g. between 2 wt% and 13 wt%, or between 5 wt% and 15 wt%, or between 7 wt% and 15 wt%, or between 10 wt% and 15 wt%, or between 13 wt% and 15 wt%, or alternatively between 0.5 wt% and 10 wt%, or between 0.5 wt% and 7 wt%, or between 0.5 wt% and 5 wt%, or between 0.5 wt% and 3 wt%. Stated differently, the metallic salt based di- and/or multivalent metallic cations is provided in the coating color by between 0.5 % by weight and 15 % by weight based on the total weight of the original zeolite.

[0059] According to at least one example embodiment of the invention the metallic salt of a di- and/or multivalent metal cation is present in the coating color within the range of from 1 % by weight to 10 % by weight based on the total weight of the coating color, preferably within the range of from 2 % by weight to 5 % by weight based on the total weight of the coating color.

[0060] According to at least one example embodiment, the zeolite is pre-treated in the zeolite dispersion.

[0061] The zeolite dispersion may e.g. be made by

i) mixing the metallic salt of di- and/or multivalent metallic cations (e.g. calcium acetate) with water, such as e.g. de-ionized water. Such mixing may e.g. be carried out in room temperature or process temperature. The step of forming the pre-treated zeolite may further comprise the step of stirring the metallic salt-water dispersion in for e.g. 10 minutes.

ii) adding the zeolite, such as a Sodium-based zeolite to the metallic salt-water dispersion to form said zeolite dispersion. The zeolite dispersion may be further stirred in e.g. 10 minutes at room temperature.

[0062] According to at least one example embodiment, an ion-exchange ratio (weight on weight) of the di- and/or multivalent metallic cations to the zeolite is within 10 % - 15 % in the zeolite dispersion.

[0063] According to a third aspect of the invention use of a coating color for a printable article is provided,
wherein said coating color comprising at least one metallic salt of a di- and/or multivalent metallic ion, at least one inorganic pigment being zeolite and at least one binder, wherein said zeolite is saturated with said di- and/or multivalent metallic cations; and
wherein the coating color forms an exterior layer of the printable article capable of interacting with an ink.

[0064] Effects and features of this third aspect of the present invention are largely analogous to those described above in connection with the first and/or second aspects of the inventive concept. Embodiments mentioned in relation to the first and/or second aspects of the present invention are largely compatible with the third aspect of the invention.

[0065] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, device, component, means, step, etc." are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise.

Brief description of the drawings

[0066] The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

Fig. 1 a shows a cross-sectional view of a printable article according to at least one example embodiment of the invention;

Fig. 1b shows a perspective view of a printable article according to at least one example embodiment of the invention;

Fig. 2a shows three exemplarily zeolites;

Fig. 2b shows the chemical reaction for zeolite saturation according to at least one example embodiment of the invention;

Fig. 3 shows a flow chart of a method for producing a printable article according to at least one example embodiment of the invention.

Detailed description of the invention

[0067] In the present detailed description, embodiments of a printable article and a method for producing the same are discussed. It should be noted that this by no means limits the scope of the invention, which is also applicable in other circumstances for instance with other types or variants of printable articles than the embodiments shown in the appended drawings. Further, that specific components are mentioned in connection to an embodiment of the invention does not mean that those components cannot be used to an advantage together with other embodiments of the invention.

[0068] The printable article according to the invention can advantageously be used for high-speed inkjet printing in order to enhance the printing quality. The printing quality is enhanced by coagulation of the ink due to that the zeolite in the coating color used in the production of the printable article is saturated, or substantially saturated with metallic based di- and/or multivalent metallic cations. This saturation of the zeolite is enhancing the coagulation of the ink and hence the printing quality if compared with usage of other coatings or coating colors in which the zeolite is not saturated.

[0069] Fig. 1 a illustrates in cross section, a printable article 100 for high-speed inkjet printing having a fibrous base substrate 110 and a coating 120. The coating 120 is comprised of at least one inorganic pigment being zeolite, metallic salt based di- and/or multivalent metallic cations, and at least one binder as previously described.

[0070] Fig. 1b illustrates the printable article 100 in Fig. 1a, with the coating 120 disposed thereon thereby forming an exterior layer of the printable article 100 capable of interacting with an ink. As seen in Fig. 1b, the fibrous base substrate 110 has a first surface 102 and a second surface 104, the first surface 102 being arranged opposite to the second surface 104. As seen in Fig. 1b, the coating 120 is disposed on at least said first surface 102.

[0071] Fig. 2a shows three exemplarily zeolites (i.e. aluminosilicate minerals) which may be used as original zeolites in the coating color or zeolite dispersion. That is, each one of the three exemplarily zeolites structures may be used when saturating, or at least partly saturating, the zeolite in the coating color or zeolite dispersion prior to disposing the coating color to the fibrous base substrate. The "z" in each of the chemical formulas for the zeolites depends on the amount of water present in the zeolite and may be e.g. between 1 and 10. As seen in Fig. 2a, each one of the zeolite is a sodium-based zeolite. That is, the zeolites have a chemical structure of a sodium-based aluminosilicate mineral (Zeolite-Na). Stated differently, each one of the zeolites in Fig. 2a accommodates, or comprises, monovalent cations in the form of sodium ions which are relatively loosely held in the zeolite structure. Thus, these sodium ions may be ion exchanged with other cations, such as the previously mentioned di- and/or multivalent metallic cations (e.g. Calcium ions) originating from a metallic salt.

[0072] Fig. 2b shows an example where the reaction mechanism for the saturation of zeolite (i.e. an original zeolite) in the form of a sodium-based zeolite (Zeolite-Na) with a metallic salt comprising divalent or trivalent metallic cations (Me^2+/3+) e.g. in the form of calcium ions, is presented (if the metallic salt comprises calcium ions, or if the cations in the metallic salt are calcium ions, the metallic salt may be referred to as a calcium salt). The metallic salt is divided into ions when dissolved in water (as occur in the coating color or zeolite dispersion) and the divalent or trivalent metallic cations will saturate the zeolite through the process of ion exchange. Typically, the ion exchange will result in that monovalent ions, such as e.g. Sodium (Na) ions, originally present in the zeolite (i.e. in the original zeolite), are exchanged with the divalent or trivalent cations from the metallic salt (such as e.g. calcium ions).

[0073] As shown in Fig. 2b, the double pointed arrow indicates that there is an equilibrium stemming from the ion exchange between the monovalent metallic ions in the original zeolite, and the di- and/or multivalent metallic cations (the multivalent cation is here embodied as a trivalent metallic cation) from the metallic salt. By e.g. controlling the mass ratio of the di- and/or multivalent cations and the zeolite (e.g. the original zeolite), the equilibrium of the reaction may be shifted in a desired way. Hence, by providing a sufficient amount of di- and/or multivalent cations in the coating color, the zeolite may be saturated, or substantially saturated, with the di- and/or multivalent cations. In other words, monovalent metallic ions, such as the Sodium ions, in the original zeolite are ion exchanged with di- and/or multivalent metallic cations from the metallic salt such that the equilibrium is shifted towards a di- and/or multivalent metallic ions saturated, or substantially saturated, zeolite. According to at least one example embodiment of the present invention, said zeolite is (in the coating color or zeolite dispersion) mixed with 0.5 wt% - 15 wt% (compared to the weight of the original zeolite), or between 3 wt% and 15 wt%, such as between 2 wt% and 13 wt%, or between 5 wt% and 15 wt%, or between 7 wt% and 15 wt%, or between 10 wt% and 15 wt%, or between 13 wt% and 15 wt%, or alternatively between 0.5 wt% and 10 wt%, or between 0.5 wt% and 7 wt%, or between 0.5 wt% and 5 wt%, or between 0.5 wt% and 3 wt%. Stated differently, the metallic salt based di- and/or multivalent metallic cations is provided in the coating color by between 0.5 % by weight and 15 % by weight based on the total weight of the original zeolite.

[0074] As previously mentioned, the saturation of zeolite is enhancing the coagulation of ink when the printable article is being used for high-speed inkjet printing.

[0075] Fig. 3 shows an exemplary method 300 for producing a printable article, such as e.g. the printable article 100 described with reference to Fig. 1 a and 1 b. Of course, other printable articles than those described with reference to Fig. 1 a and 1 b may be produced by this exemplary method 300.

[0076] The first step 302 comprises providing a fibrous base substrate. The fibrous base substrate may e.g. be provided by a paper machine and the fibrous base substrate may thus be paper. The coating color is in Fig. 3 illustrated as being produced in two steps, 304 and the step 306, which may be carried out subsequently as two separated steps, or simultaneously in one common step. Step 304 comprises mixing the inorganic pigment being zeolite (such as e.g. a Zeolite-Na as shown in Fig. 2a), the at least one metallic salt of di- and/or multivalent metallic cations (such as e.g. a calcium-based salt), dispersion agents and water together, thereby forming a zeolite dispersion or zeolite slurry. Thus, in step 304 the zeolite is saturated by the metallic cations from the metallic salt as described in relation to Fig. 2b. Step 304 further allows the metallic salt to substantially dissolve in the water. This secures that almost all of the metallic salt is dissolved, and thereby minimizing the amount of undissolved salt in the coating color.

[0077] Step 304 may include the step of adjusting the mass of the di- and/or multivalent metallic cations to the mass of the original zeolite (e.g. a Zeolite-Na) in the zeolite dispersion such that the weight percentage of the di- and/or multivalent metallic cations to the original zeolite is between 0.5 wt% and 15 wt%.

[0078] Step 304 may include the step of: (determining and) adjusting the mass of the zeolite to be within the range of from 5 % by weight to 50 % by weight based on the total weight of the coating color (formed in step 306), preferably within the range of from 10 % by weight to 40 % by weight based on the total weight of the coating color, and

[0079] Step 304 may include the step of adding water (and dispersion agents).

[0080] Alternatively, the metallic salt of the di- and/or multivalent metal cations may be adjusted to be present in the coating color within the range of from 1 % by weight to 10 % by weight based on the total weight of the coating color, preferably within the range of from 2 % by weight to 5 % by weight based on the total weight of the coating color.

[0081] Step 306 comprises adding a binder to the zeolite dispersion from step 304. Step 306 may optionally comprise adding at least one of the following: at least one further inorganic pigment, any aiding chemicals needed for later processing and/or printing.

[0082] Step 304 and or 306 may e.g. be carried out in one or more containers, such as e.g. tanks with sufficient stirring. Further, various types of mixers may be used in order to ensure a good degree of mixing. Step 304 and/or step 306 may be carried out at room temperature or process temperature (e.g. 15 °C - 50 °C, or 15 °C - 25 °C (i.e. room temperature), or 40 °C - 50 °C (process temperature)).

[0083] In a subsequent step 308 the coating color provided by the steps 304 and 306 is disposed onto the fibrous base substrate. After being disposed onto the fibrous base substrate the coating color forms a coating on an exterior layer of the printable article and is thus capable of interacting with an ink.

[0084] Step 308 may e.g. be carried out in the paper machine before the drying of the paper. The coating can be provided with various types of coating assemblies such as e.g. roll coating, blade coating and/or spraying.

[0085] In the method 300, the zeolite may be present in the coating color within the range of from 5 % by weight to 50 % by weight based on the total weight of the coating color. The coating color as produced by the method 300 may be disposed on a fibrous base substrate 110 as shown in Fig. 1a, and thereby form the coating 120 of the printable article 100 of Fig. 1 a.

Examples

[0086] The amount of the di- and/or multivalent metallic cations to said zeolite (as described above as the weight percentage of the di- and/or multivalent metallic cations to said original zeolite) required to provide (substantial) saturation of the zeolite with the di- and/or multivalent metallic cations is at least partly depending on the type of zeolite and the temperature in which the zeoltie dispersion and coating color is created. An examples of the preparation of the coating color with a Sodium-based zeolite is given below. Note, that the example by no way limits the scope of the invention as being defined by the accompanying claims, but the example is rather included to show one specific working embodiment.

[0087] First, a preparation of a test zeolite dispersion was carried out. This test zeolite dispersion was formed to investigate zeolite saturation and ion exchange ratio.

A. Preparation of test zeolite dispersion

[0088] 

A1) A water dispersion consisting of 0.71 % by weight of calcuim formiate was prepared in de-ionized water at room temperature. After 10 minutes of stirring, the concentration of Ca²⁺ ions was measured using an ion selective electrode, and found to be 2.16 g/l.

A2) A water dispersion according to A1) was prepared, and to that, 0.96 % calculated on the amount of water, of the sodium-based zeolite (such as e.g. Zeocros, or antother zeolite like Advan, Zeoflair) was added and stirred for 10 minutes. The Ca²⁺ concentration was measured and determined to 1.11 g/l.

[0089] The difference in calcium concentration between steps A1) and A2), is due to the ion-exchange process within the zeolite. In this case it was calculated that the ion-exchange ratio was 11% (w/w) calcium/zeolite.

[0090] According to at least one example embodiment, the ion-exchange ratio of the di- and/or multivalent metallic cations to the zeolite is within 10 % - 15 %.

[0091] Secondly, a preparation of a coating color in two steps (similar to step 304 and 306 of Fig. 3 previously described) was carried out.

B. Preparation of coating color

[0092] 

B1) A zeolite dispersion (or zeolite slurry) comprising the following components calculated as mass of the total coating color was prepared prior to mixing with further components: 4.6 % calcium acetate in water solution, 27.2 % zeolite (Sodium-based zeolite, like Zeocros, Advan, or Zeoflair) and 0.2 % dispersing agent were carefully mixed at room temperature and stirred to attain a homogenous dispersion.

B2) The following components was thereafter mixed to the zeolite dispersion according to B1) to form a coating color, calculated as mass of the total coating color: 1.3 % (as dry) of polyvinyl alcohol dispersion, 7.3 % SB-latex, 52.0 % of a coarse calcium carbonate slurry and 7.4 % of a fine calcium carbonate slurry.

[0093] A second coating color was prepared according to the above mentioned procedure, but excluding the calcium salt. The two described coating colors were applied to a base sheet (i.e. a fibrous base substrate) in a lab coater. The coated sheet was dried and printed in an Epson L355 Piezo printer.

[0094] Color densities were measured with X-Rite SpectroEye 60 min after printing with a commercial grade of pigmented inks. Show through is based on the comparison of Y tristimulus values between paper measured on black background and paper measured on the reverse side of the black printed paper, divided by the tristimulus value of the paper on white background, all as percentages, see Table 1.

Table 1: Color densities and show through for two samples with different coating colors.

Coating color	Color densities 10°, D65 with pol. Filter				Show through
	K	C	M	Y	(YpapBlack-YpapInk)/YpapWhite
Including calcium salt	236	211	150	199	2.90%
Without calcium salt	171	125	146	161	16.25%

[0095] The values in Table 1 show the importance of the presence of the metallic salt comprising di- and/or multivalent cations, here embodied as a calcium salt. As seen, the print result is much worse if no metallic salt is included in the preparation of the zeolite disperson. The values also support the above mentioned mechanism including precipitation of ink pigments vs penetration of these.

[0096] It is of course understood that variations to the shown example may be carried out and using other metallic salts comprising another type di- and/or multivalent metallic cation as compared to calcium ions, and another zeolite than those described are within the scope of the invention.

[0097] The skilled person realizes that a number of modifications of the embodiments described herein are possible without departing from the scope of the invention, which is defined in the appended claims.

Claims

1. A printable article for inkjet printing having a fibrous base substrate and a coating disposed thereon, the coating being comprised of at least one inorganic pigment being zeolite, metallic salt based di- and/or multivalent metallic cations, and at least one binder,
wherein said zeolite is substantially saturated with said di- and/or multivalent metallic cations and wherein the disposed coating forms an exterior layer of the printable article capable of interacting with an ink.

2. The printable article according to claim 1, wherein said zeolite is a pre-treated zeolite which has been substantially saturated with said di- and/or multivalent metallic cations prior to being applied to the fibrous base substrate.

3. The printable article according to claim 2, wherein said zeolite has been substantially saturated with said di- and/or multivalent metallic cations in a coating color or a zeolite dispersion in which the weight percentage of said di- and/or multivalent metallic cations to said zeolite is between 0.5 wt% and 15 wt%

4. The printable article according to any of the preceding claims,
wherein the fibrous base substrate has a first surface and a second surface, the first surface being arranged opposite to the second surface, and wherein said coating covers at least one of said first surface and said second surface.

5. A printable article according claim 4, wherein the grammage of the coating on one of said first surface and said second surface is within the range of from 2 g /m² to 25 g /m², preferably in an amount within the range of from 10 g to 20 g /m².

6. A printable article according to any of the claims 4-5, wherein said coating covers both said first surface and said second surface.

7. The printable article according to any one of the preceding claims, further comprising at least one further inorganic pigment chosen from the list of: kaolin clay, silica, ground calcium carbonate, precipitated calcium carbonate, aluminum hydroxide, talc and titanium dioxide and combinations or mixtures thereof

8. The printable article according to any one of the preceding claims, wherein said binder is at least one of the following: SB latex, SA latex, PVAc, PVA, PVP, polyvinyl versatate, PU, starch and combinations or mixtures thereof.

9. The printable article according to any one of the preceding claims, wherein said zeolite is present in the coating within the range of from 5 % by weight to 50 % by weight based on the total weight of the coating, preferably within the range of from 10 % by weight to 40 % by weight based on the total weight of the coating.

10. A method for producing a printable article for inkjet printing comprising the steps of:

a) providing a fibrous base substrate;

b) providing a zeolite dispersion created by mixing an inorganic pigment being zeolite, at least one metallic salt comprising di- and/or multivalent cations, dispersion agents and water whereby said zeolite is substantially saturated by said di- and/or multivalent cations from said at least one metallic salt;

c) providing a coating color by adding to the zeolite dispersion in b) at least a binder;

d) disposing said coating color on the fibrous base substrate; and

thereby enabling the coating color to form a coating on an exterior layer of the printable article capable of interacting with an ink.

11. The method according to claim 10, wherein said coating color in step c) is further created by adding at least one of the following: a further inorganic pigment, any aiding chemicals.

12. The method according to any one of claims 10-11, wherein the weight percentage of said di- and/or multivalent metallic cations to said zeolite in said zeolite dispersion or coating color is between 0.5 wt% and 15 wt%.

13. The method according to any one of claims 10-12,
wherein said zeolite is present in the coating color within the range of from 5 % by weight to 50 % by weight based on the total weight of the coating color, preferably within the range of from 10 % by weight to 40 % by weight based on the total weight of the coating color; and
wherein said at least one metallic salt of a di- and/or multivalent metal cation is present in the coating color within the range of from 1 % by weight to 10 % by weight based on the total weight of the coating color, preferably within the range of from 2 % by weight to 5 % by weight based on the total weight of the coating color.

14. The method according to any one of claims 10-13, wherein said at least one metallic salt is substantially dissolved in said water.

15. Use of a coating color for a printable article,
wherein said coating color is comprised of at least one metallic salt of a di- and/or multivalent metallic cations, at least one inorganic pigment being zeolite and at least one binder, wherein said zeolite is saturated with said di- and/or multivalent metallic cations; and
wherein the coating color forms an exterior layer of the printable article capable of interacting with an ink.

Drawing