Method of printing and printed article

Abstract

Disclosed is a method of printing comprising: (i) applying an oil-based ink to a substrate by inkjet printing to form a printed substrate; and (ii) impregnating the printed substrate with an impregnating agent comprising a melamine component. Also disclosed are printed articles obtained or obtainable by the method of printing of the invention. Further disclosed are printed articles comprising: (i) a substrate; (ii) an oil-based ink; and (iii) a melamine resin.

Description

METHOD OF PRINTING AND PRINTED ARTICLE

[0001] The present invention relates to methods of inkjet printing using oil-based inks. The invention also relates to printed articles comprising a substrate, an oil-based ink, and a melamine resin. For instance, the invention relates to printed articles obtained or obtainable by the methods described herein.

[0002] A large printing industry exists concerned with producing decor papers, decorative board, and other decorative surfaces. Such printed articles are used in many contexts. For some purposes, it is desirable for these decorative printed articles to have hard-wearing qualities, for instance where the decorative article will be subject to heavy use or rough treatment.

[0003] A known way to improve the hard-wearing qualities of a printed article is to apply a protective layer. In one example, it is known to employ melamine resin impregnation in the field of decorative printing. Impregnation with melamine, typically melamine-formaldehyde resin, leads to decor papers with improved water, heat, and chemical resistances. This technique is described in EP 3415337 A1. In this method a water-based ink or UV curing ink is applied to a substrate before melamine resin impregnation.

[0004] However, there are drawbacks to the use of water-based inks for this purpose. Decor paper can be deformed on drying after printing with water-based ink as the water can swell the natural fibres causing dimensional change. Moreover, the water-based inks require a drying step after printing which can slow down the printing process and may incur energy costs if heat is applied.

[0005] Accordingly, it is desirable to provide a new printing method for producing hard-wearing decorative articles which can be faster and potentially more energy-efficient than the methods known in the art.

[0006] The inventors have found that decorative printing can be performed in conjunction with melamine resin impregnation using an oil-based ink. This eliminates the need for a drying step, as would be required with a water-based ink. However, substrates printed with oil-based ink may suffer from smearing and spreading when melamine impregnation is attempted. The inventors have found that good printing resolution is achieved when the oil-based ink is applied by inkjet printing.

[0007] Accordingly, the present invention provides a method of printing comprising: (i) applying an oil-based ink to a substrate by inkjet printing to form a printed substrate; and (ii) impregnating the printed substrate with an impregnating agent comprising a melamine component.

[0008] Further, printed patterns or images may feature inks of different colour adjacent to one another. In such applications, a high resolution of the pattern or image is desirable. Smearing of ink is undesirable as it can cause the unwanted mixing of printed colours, resulting in a lack of resolution of printed patterns and images and dulling of colours. In making the present invention, the inventors noted that some oil-based inks can smear and spread when applied in conjunction with melamine impregnation. However, the inventors identified particular plant-based inks highly suitable for inkjet printing which had a particularly low susceptibility to smearing or spreading when used in the methods described herein. Accordingly, in a preferred embodiment, the oil-based ink comprises: (a) a semi-drying solvent; (b) a pigment; (c) an amine-based polymeric dispersant in an amount greater than 0 wt％ based on the total weight of the oil-based ink; and (d) an alkyd resin in an amount of 0 wt％ or more based on the total weight of the oil-based ink. Particularly good results with respect to spreading and smearing were observed in another particularly preferred embodiment where the substrate is a treated substrate comprising an ink-receiving layer.

[0009] The present invention further provides a printed article obtained or obtainable by the above method of printing of the invention.

[0010] The present invention further provides a printed article comprising:

[0011] (i) a substrate;

[0012] (ii) an oil-based ink; and

[0013] (iii) a melamine resin.

[0014] Figure 1 shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 1. The darker (black) ink at the right-hand side of the image has not smeared into the paler (yellow) ink at the left-hand side of the image.Figure 2A shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 2. In Figure 2A the darker (black) ink at the right-hand side of the image has not smeared into the paler (yellow) ink at the left-hand side of the image.Figure 2B shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 2. In Figure 2B the ink (black) at the top left-hand side of the image has not smeared into the unprinted area at the bottom and right-hand sides of the image.Figure 2C shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 2. In Figure 2C the ink (black) at the top and bottom of the image has not smeared into the unprinted area in the centre of the image.Figure 2D shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 2. In Figure 2D the ink (black) at the top of the image has not smeared into the unprinted area at the bottom of the image.Figure 3 shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 3. The ink (black) at the top of the image has not smeared into the unprinted area at the bottom of the image.Figures 4A shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 4. In Figure 4A, the darker (black) ink at the right-hand side of the image has smeared into the paler (yellow) ink at the left-hand side of the image.Figure 4B shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 4. In Figure 4B, the ink (black) at the top of the image has smeared into the unprinted area at the bottom of the image.Figure 5 shows a substrate that has been treated with an ink-receiving layer, inkjet printed with an oil-based ink, and impregnated with melamine as per Example 5. The darker (black) ink at the right-hand side of the image has not smeared into the paler (yellow) ink at the right-hand side of the image.Figure 6 shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 6. The darker (black) ink at the right-hand side of the image has smeared into the paler (yellow) ink at the left-hand side of the image.Figure 7A shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 7. In Figure 7A the ink (black) at the top left-hand side of the image has smeared into the unprinted area at the bottom and right-hand sides of the image.Figure 7B shows a substrate that has been inkjet printed with an oil-based ink and impregnated with melamine as per Example 7. In Figure 7B the ink (black) at the top and bottom of the image has smeared into the unprinted area in the centre of the image.

[0015] The invention is described hereafter with reference to particular embodiments and figures. However, the invention is not limited to any specific embodiment, example or figure given herein. Those skilled in the art will be able to recognise many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the appended claims.

[0016] The following description refers to a method of printing, and to a printed article such as a printed article obtained or obtainable by the described method. It should be noted that, unless the context indicates otherwise, any aspect described in the context of the method applies equally to that aspect in the context of the products, and vice versa. For instance, the features of the “substrate” as described in the context of the method of printing are also features of the substrate present in the described products.Definitions

[0017] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of skill in the relevant art.

[0018] As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to “an oil-based ink” includes two or more oil-based inks.

[0019] Certain values herein are modified by the term “about”. It may be understood that the term “about” indicates that the indicated value may is within ±10％ of the stated value, preferably within ±5％ of the stated value, more preferably within ±1％ of the stated value.

[0020] The method and printed article described herein comprise one or more oil-based inks. For brevity, in places the term “ink” may be used. Unless the context implies otherwise, the term “ink” as used herein in the context of the invention should be understood to refer to an oil-based ink.Method of printing

[0021] The method of printing of the invention comprises: (i) applying an oil-based ink to a substrate by inkjet printing to form a printed substrate; and (ii) impregnating the printed substrate with an impregnating agent comprising a melamine component.

[0022] Steps (i) and (ii) may be performed in any order. Preferably, step (i) is performed before step (ii). Moreover, the steps of the method described herein may be performed once or more than once. For instance, step (i) and / or step (ii) may repeated. Typically, step (ii) is performed one, two, three or four times.

[0023] Step (i) comprises applying one or more oil-based inks. Where multiple oil-based inks are to be applied by inkjet printing, step (i) may be repeated such that each oil-based ink is applied sequentially. Alternatively or additionally, two or more oil-based inks may be applied simultaneously during step (i). The process is advantageous where two or more inks are used, as problems associated with smearing can be pronounced where two or more inks are present. The process is especially advantageous where two or more inks are used and one is darker in colour than another, because smearing causes more pronounced loss of image quality where a darker ink can smear into a lighter ink. Thus, step (i) may comprise applying a first oil-based ink and a second oil-based ink by inkjet printing, where the second oil-based ink is lighter or darker in colour than the first oil-based ink. However, it should be noted that smearing is not only problematic where two or more inks are present. Smearing can occur when only a single ink is present. Smearing is also particularly noticeable where the colour of the printed ink is markedly different to the colour of the substrate.

[0024] Alternatively or additionally, the method may comprise repeating step (i), such that the method comprises: applying a first oil-based ink to a substrate by inkjet printing to form a printed substrate; and applying a second oil-based ink to a substrate by inkjet printing to form a printed substrate, which second oil-based ink is lighter or darker in colour than the first oil-based ink.

[0025] Use of an oil-based ink is advantageous over the use of a water-based ink owing to the requirement of a drying step for water-based inks which can negatively affect the printed article, for instance by deforming the printed substrate. Moreover, such drying steps slow the printing process and may also increase the energy cost of the process if they involve applying heating the printed article. Such drying steps are advantageously avoided when using oil-based inks.

[0026] The method of printing of the invention therefore may not comprise a water evaporation step. Typically, the method of printing of the invention does not comprise a water evaporation step. Preferably, the method of printing of the invention does not comprise a water evaporation step between steps (i) and (ii) described above.

[0027] A water evaporation step is a step in which water is permitted or encouraged to evaporate from the printed substrate. A water evaporation step may comprise applying heat to the printed substrate, and / or providing a flow of gas such as air over the printed substrate. A water evaporation step may comprise heating the printed substrate to a temperature of 50℃ or higher, for instance by placing the printed substrate in an oven. Accordingly, in general the method of the invention does not comprise applying heat and / or a flow of gas such as air over the printed substrate between steps (i) and (ii). Typically the method does not comprise heating the printed substrate to a temperature of 50℃ or higher between steps (i) and (ii).

[0028] Step (ii) may directly follow step (i), without any other step inbetween.

[0029] Step (ii) comprises impregnating the printed substrate with an impregnating agent. Thus, step (ii) comprises exposing the printed substrate to said impregnating agent. Step (ii) may comprise allowing the impregnating agent to be absorbed into the substrate, for instance where the substrate comprises a porous material.

[0030] The method of impregnating the printed substrate with an impregnating agent is not particularly limited. For example, the impregnating agent may be introduced to the printed substrate by submerging the printed substrate in the impregnating agent, brush coating the printed substrate with the impregnating agent, or roller coating the printed substrate with the impregnating agent. Where the substrate has more than one surface (for instance where the substrate is in the form of a sheet) the impregnating agent can be applied to one or more surfaces of the substrate. Typically, at least the surface of the printed substrate to which the oil-based ink has been applied is exposed to the impregnating agent. Preferably, impregnating the printed substrate comprises submerging the printed substrate in the impregnating agent.

[0031] Impregnating the printed substrate with an impregnating agent may comprise exposing the substrate to the impregnating agent for at least about 5 seconds or at least about 20 seconds, and may comprise exposing the substrate to the impregnating agent for a longer period, for instance up to about one hour or up to about two hours. Inkjet printing

[0032] Step (i) involves applying an oil-based ink to a substrate by inkjet printing. Inkjet printing is a technique well-known in the art and does not require detailed description here. Briefly, inkjet printing involves applying droplets of the oil-based ink to the substrate. The ink is generally applied using an inkjet print head. The ink may be heated before or while it passes through the print head.

[0033] As has been noted above, a problem exists in that melamine resin impregnation of substrates printed with oil-based inks may cause smearing of the oil-based ink. “Smearing” occurs when ink spreads from the location to which it has been applied during the printing process. Smearing of a single ink is particularly problematic as the ink spreads beyond where it was intended to be printed, causing a loss of resolution of the printed image. Smearing is also particularly problematic where blocks of different colours are printed adjacent to one another, and the one or more inks forming each block bleed into the adjacent block. This changes the observed colour around the boundary between the two colour blocks and reduces image quality.

[0034] Whether or not smearing has occurred can straightforwardly be determined by eye. If, after printing, an ink is observed in a region of the printed substrate to which the ink was not applied during the printing process, smearing has occurred. The occurrence of smearing could alternatively be determined by performing a colorimetric measurement. A block of a first colour ink (e.g. a yellow ink) may be applied printed adjacent to a block of a second colour ink (e.g. a black ink). The colour of the yellow ink block adjacent to the boundary between the two ink blocks may be determined by colorimetry. The measurement can then be repeated on a second printed substrate to which only the first colour ink and not the second colour ink has applied. If the result differs, smearing has occurred.

[0035] However, in the inkjet printing method of the invention, it has been found that smearing of the oil-based ink can be reduced or avoided. In particular, it has been found that excellent results with low smearing or even no smearing at all can be achieved with particular plant-based inks suitable for inkjet printing. Accordingly, the method of printing of the invention may reduce or prevent smearing of the oil-based ink. Preferably, the method of printing of the invention reduces smearing of the oil-based ink. More preferably, the method of printing of the invention prevents smearing of the oil-based ink. For instance, in the method of the invention, smearing of the oil-based ink in the printed article is not observed after step (ii).Further method steps

[0036] The method of printing may or may not comprise one or more further steps in addition to (i) and (ii).

[0037] Optionally, the method may comprise removing any excess impregnating agent from the printed substrate after step (ii). This can be done by, for instance, passing the substrate through a set of rollers. For instance, where step (ii) involves submerging the printed article in the impregnating agent, the method may also comprise removing the printed article from the impregnating agent.

[0038] The impregnating agent is generally in the form of a flowable material such as a liquid or gel. Thus, the method may in some cases involve a drying step after step (ii).

[0039] Often, the method will additionally involve a curing step. As will be described in further detail below, the impregnating agent comprises a melamine component. This impregnating agent typically requires a further process to produce the hard-wearing melamine resin present in the ultimate product, typically by forming cross-links between the melamine component parts of the impregnating agent. This additional process is referred to as a curing process. Thus, the process may involve a curing step. In other words, the process may also involve curing the impregnating agent to form a melamine resin.

[0040] Curing the impregnating agent may simply involve leaving the impregnating agent for a period of time. Alternatively or additionally, curing the impregnating agent may require an active step.

[0041] For instance, some impregnating agents have thermosetting characteristics and require heat to form a melamine resin. Thus, curing the impregnating agent may involve heating the printed article after step (ii). For instance, curing may comprise raising the temperature of the printed article to a temperature above room temperature. Curing may comprise raising the temperature of the printed article to 30℃ or more, or 50℃ or more, or 100℃ or more, or 140℃ or more. Generally, if the curing process involves raising the temperature of the printed article, the maximum temperature to which the printed article is heated does not exceed 400℃. The curing process may comprise raising the temperature of the printed article for at least about one minute, or at least about five minutes, or at least about 30 minutes. Generally the curing process does not require raising the temperature of the printed article for more than three hours. Thus, curing the impregnating agent may comprise heating the printed article to a temperature of from 40℃ to 350℃ for a period of from one minute to three hours. Preferably, curing the impregnating agent may comprise heating the printed article to a temperature of from 100℃ to 300℃ for a period of from one minute to two hours.

[0042] Some impregnating agents may require exposure to a chemical agent (such as a cross-linking agent) to form a melamine resin. The curing step may therefore comprise applying a cross-linking agent to the printed article. A cross-linking agent may comprise a further resin such as an alkyd, epoxy, acrylic or polyester resin.

[0043] The process may or may not comprise other steps to produce a finished article, such as a further printing process. In addition, the process may or may not comprise a manual processing step such as a cutting or shaping operation to produce the final printed article.

[0044] Accordingly, the process may optionally comprise, after step (ii), one or more of the following steps: (iii) removing excess impregnating agent from the printed substrate; (iv) drying the printed substrate; (v) curing the impregnating agent to produce a melamine resin, typically by heating or applying a crosslinking agent; (vi) a further printing step; and (vii) a manual processing step such as a cutting or shaping step.

[0045] These steps may be performed in any order, although where step (iii) and step (v) are both performed step (iii) is generally performed before step (v). Typically, at least step (v) is performed.Oil-based ink

[0046] An oil-based ink comprises a non-aqueous solvent. Accordingly, an oil-based ink differs from an aqueous ink as an aqueous ink typically includes water as a primary ingredient. Non-limiting examples of such non-aqueous solvents include, for example, oils, alcohols, and semi-drying solvents.

[0047] Typically, the oil-based ink comprises no more than 10 wt％ water. Preferably, the oil-based ink comprises less than 10 wt％ water. More preferably, the oil-based ink comprises less than 5 wt％ water. Still more preferably, the oil-based ink comprises less than 1 wt％ water. For instance, the oil-based ink may not comprise water except as an unavoidable impurity. Preferably, the oil-based ink does not comprise water.

[0048] The oil-based ink should be suitable for inkjet printing. Suitability for inkjet printing can be readily determined by the skilled person, but in particular, properties such as the viscosity, optical density, and physical stability of the oil-based ink are preferably selected for suitability in inkjet printing.

[0049] The viscosity of the oil-based ink is such that the ink is suitable for inkjet printing. Viscosity of a fluid varies with temperature. In the context of the oil-based ink, the viscosity of the ink should be suitable for inkjet printing at the temperature at which the oil-based ink is applied to the substrate, otherwise known as the “jetting temperature”. The “jetting temperature” may be from 10℃ to 75℃ but is typically from about 40℃ to about 60℃, preferably from about 40℃ to about 50℃, and most preferably about 50℃.

[0050] However, it is often most convenient to measure the viscosity of an ink at room temperature (herein, “room temperature” is taken to mean 25℃). Accordingly, viscosity is discussed herein both at a jetting temperature and at room temperature.

[0051] Viscosity of the oil-based ink can be determined using a viscometer. For instance, the viscosity may be measured on a Brookfield DF3T viscometer.

[0052] Thus, oil-based inks having a wide range of viscosities are in principle applicable in the process of the invention as they can be heated, if needed, to ensure that a suitable viscosity is achieved at the temperature at which the ink is applied to the substrate. The viscosity of the oil-based ink as measured at room temperature may, for example, be in the range of about 1 to about 40 cP; about 5 to about 30 cP; or about 10 to about 25 cP.

[0053] The viscosity of the oil-based ink as measured at room temperature may, for example, be more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 cP. The viscosity of the oil-based ink as measured at room temperature may, for example, be less than about 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26 or 25 cP.

[0054] The viscosity of the oil-based ink as measured at room temperature may, for example, be about 10 cP; about 15 cP; about 20 cP; or about 25 cP; or about 30 cP.

[0055] The viscosity of the oil-based ink as measured at the jetting temperature is typically in the range of about 1 to about 30 cP; for example about 5 to about 25 cP; or about 7 to about 12 cP.

[0056] The viscosity of the oil-based ink as measured at the jetting temperature may, for example, be more than about 1 cP; more than about 2 cP; more than about 3 cP; more than about 4 cP; more than about 5 cP; more than about 6 cP; or more than about 7 cP.

[0057] The viscosity of the oil-based ink as measured at the jetting temperature may, for example, be less than about 30 cP; less than about 29 cP; less than about 28 cP; less than about 27 cP; less than about 26 cP; less than about 25 cP; less than about 24 cP; less than about 23 cP; less than about 22 cP; less than about 21 cP; less than about 20 cP; less than about 19 cP; less than about 18 cP; less than about 17 cP; less than about 16 cP; or less than about 15 cP.

[0058] The viscosity of the oil-based ink as measured at the jetting temperature may, for example, be about 5 cP; about 10 cP; about 15 cP; or about 20 cP. In particular, the viscosity of the oil-based ink at the jetting temperature may, for example, be about 5 cP; about 6 cP; about 7 cP; about 8 cP; about 9 cP; about 10 cP; about 11 cP; about 12 cP; about 13 cP; about 14 cP; or about 15cP.

[0059] Preferably, the viscosity of the oil-based ink as measured at the jetting temperature is from about 5 to about 25 cP. More preferably, the oil-based ink has a viscosity as measured at the jetting temperature in the range of about 7 to about 12 cP.

[0060] For optimal jettability, the viscosity of the oil-based ink as measured at the jetting temperature is preferably from about 1 to about 15 cP, and more preferably from about 4 to about 13 cP, and most preferably from about 7 to about 12 cP.

[0061] Viscosity may also depend on shear rate. Viscosity is preferably measured at a shear rate of 90 s-1.

[0062] The optical density of the oil-based ink is also not particularly limited, but should be suitable for inkjet printing. The optical density of the oil-based ink can, for example, be determined using a spectro-densitometer such as a Spectro Connect spectrometer, sold by Techkon under the product name SpectroDens. Typically, optical densities of 1.00-1.20 for Black are desirable.

[0063] The physical stability of the oil-based ink is not particularly limited, but should be suitable for inkjet printing. In particular, it is preferable that the oil-based ink is stable with respect to any significant change in viscosity over a long storage period. If the viscosity changes significantly on storage, it may clog an inkjet printing nozzle during use. Thus, it is preferred that the viscosity of the ink does not change by more than 10％ during storage, or more than 5％ during storage. For instance, it is preferred that the viscosity of the ink does not change by more than 10％, or more than 5％, during storage for six months at room temperature (typically 25℃) in a sealed container.

[0064] It is possible to test for physical stability during storage as follows. The viscosity of the oil-based ink is measured at room temperature (25℃). The oil-based ink is then stored for two weeks at 70℃, after which it is returned to room temperature and its viscosity is tested at 25℃ again. The oil-based ink is considered to have good stability if, during this test, the viscosity has changed by 10％ or less. Preferably, under such test conditions, the viscosity of the ink changes by 5％ or less. The inventors have found that plant-based inks can be used in the method of the invention to provide exceptionally good results with low or even no smearing of ink. Exemplary inks are described in WO 2021 / 106950 A1, which is incorporated herein by reference in its entirety. Such inks include a semi-drying solvent, a pigment, an amine-based polymeric dispersant, and optionally an alkyd resin. The quantity of pigment, amine-based polymeric dispersant and alkyd resin (where present) can be varied while achieving the above-discussed physical properties, particularly the discussed viscosities.

[0065] Typically, the oil-based ink comprises: (a) a semi-drying solvent; (b) a pigment; (c) an amine-based polymeric dispersant; and optionally: (d) an alkyd resin.

[0066] In particular, the oil-based ink typically comprises: (a) a semi-drying solvent; (b) a pigment; (c) an amine-based polymeric dispersant in an amount greater than 0wt％ based on the total weight of the oil-based ink; and (d) an alkyd resin in an amount of 0wt％ or more of based on the total weight of the oil-based ink.

[0067] The oil-based ink typically comprises a semi-drying solvent.

[0068] The term semi-drying solvent is a term of art and relates to the type of solvent present in the oil-based ink. It does not relate to the state or dryness of the oil-based ink. Semi-drying solvents are discussed in more detail in Surface Coatings Vol I - Raw Materials and Their Usage by the Oil and Colour Chemists Association of Australia (1983); § 3.2.4, which is incorporated herein by reference in its entirety.

[0069] As used herein, a semi-drying solvent may be a solvent with an iodine value of 120 to 150. The iodine value of a solvent is a parameter well understood in the field of ink raw materials and is defined as the number of grams of iodine absorbed by 100 grams of oil. The iodine value is determined by the chemical structure of the components of the solvent, and is a measure of unsaturation by determination of the amount of iodine absorbed or reacted at the double bonds. Iodine values are discussed in more detail in Surface Coatings Vol I - Raw Materials and Their Usage by the Oil and Colour Chemists Association of Australia (1983); §3.2.7. The iodine value of a solvent can be determined by well-known methods, such as those discussed in Surface Coatings Vol I - Raw Materials and Their Usage by the Oil and Colour Chemists Association of Australia (1983); §3.2.7.

[0070] The semi-drying solvent may comprise an ester (hereinafter referred to as a first ester). The first ester is derived from an acid (hereinafter the acid component of the first ester) and an alcohol (hereinafter the alcohol component of the first ester). Typically, the acid component of the first ester is an unsaturated fatty acid. Preferably the acid component of the first ester is a di-unsaturated fatty acid. Di-unsaturated fatty acids may be obtained, for example, by hydrolysis of vegetable oils (e.g. soy oil). Examples of suitable di-unsaturated fatty acids include linoleic acid, eicosadienoic acid, and docosadienoic acid. Linoleic acid is preferred as the acid component of the first ester. Linoleic acid can be obtained by hydrolysis of soy oil.

[0071] Typically, the alcohol component of the first ester is a monohydric alcohol. Examples of suitable monohydric alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, i-butanol and t-butanol. Methanol is preferred as the alcohol component of the first ester.

[0072] The first ester may be an ester of a di-unsaturated fatty acid and a monohydric alcohol, and examples of the first ester include methyl esters such as linoleic acid methyl ester, eicosadienoic acid methyl ester, docosadienoic acid methyl ester and and linolelaidic acid. Linoleic acid methyl ester is preferred as the first ester.

[0073] The semi-drying solvent may be a single substance, or a mixture of different substances. The one or more further substances may be other esters (e.g. other esters of fatty acids, including unsaturated and saturated fatty acids, and monohydric alcohols), or other substances of the types commonly found in solvents for inkjet inks. When the semi-drying solvent is a mixture of the first ester and one or more further substances, the first ester may be present in an amount of 50 wt％ or more of the semi-drying solvent, with reference to the amounts of the semi-drying solvent discussed above.

[0074] Typically, the semi-drying solvent is selected from the group consisting of linoleic acid methyl ester, eicosadienoic acid methyl ester, docosadienoic acid methyl ester and linolelaidic acid. Preferably, the semi-drying solvent is linoleic acid methyl ester.

[0075] The oil-based ink typically comprises a pigment. The pigment is not particularly limited.

[0076] The pigment may be a black pigment. The black pigment which may be used in the oil-based ink of the present invention is not particularly limited. The black pigment may for example be a carbon black pigment. Examples of carbon black pigments which can be used in the oil-based ink of the present invention include REGAL (registered trademark) series (e.g. REGAL (registered trademark) 400R, REGAL (registered trademark) 660R), EMPEROR (registered trademark) series (e.g. EMPEROR (registered trademark) 1600, EMPEROR (registered trademark) 1800), MONARCH (registered trademark) series (MONARCH (registered trademark) 800), VULCAN (registered trademark) series (e.g. VULCAN (registered trademark) XC72R) available from Cabot Corporation, Birla N330, available from Birla Carbon, and black pigments from the Raven range available from Columbian Chemicals Company.

[0077] The pigment may be a white pigment. Examples of white pigments which can be used in the oil-based ink of the present invention include Pigment White 7.

[0078] The pigment may be a coloured pigment. The coloured pigment may be a blue pigment, a green pigment, a violet pigment, a red pigment, a brown pigment, a yellow pigment, or a magenta pigment. Examples of coloured pigments which can be used in the oil-based ink of the present invention include Pigment Black 7, Pigment Blue 15:3, Pigment Blue 60, Pigment Green 7, Pigment Violet 37, Pigment Red 202, Pigment Red 144, Pigment Red 166, Pigment Red 185, Pigment Red 254, Pigment Brown 23, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 110, Pigment Yellow 151.

[0079] The oil-based ink may comprise more than one pigment. The oil-based ink may comprise a mixture of pigments.

[0080] As described above, the oil-based ink typically comprises an amine-based polymeric dispersant.

[0081] Suitable amine-based polymeric dispersants comprise an amine-based polymeric component.

[0082] Typically, the amine-based polymeric dispersant may consist of an amine-based polymeric component. Typically, the amine-based polymeric dispersant may comprise an amine-based polymeric component and may further comprise an organic medium. The amine-based polymeric dispersant may comprise the amine-based polymeric component in an amount of from 30 to 50 wt％, or about 40 wt％, of the dispersant. Such dispersants may, in addition to the 30 to 50 wt％ of the dispersant, comprise an organic medium (e.g. an aliphatic component with a boiling point of 220 to 280oC).

[0083] Suitable amine-based polymeric components are described in US Patent No. 8,167,992 B2, the content of which is incorporated herein by reference in its entirety. For example, the amine-based polymeric component may be a compound of formula (1), or a salt thereof: wherein U is independently R'-N-(G’)-T'-O-, or R-O-;

[0084] R or R' may be the same or different and are independently H or C1-50-optionally substituted hydrocarbyl, or hydrocarbonyl group (acyl group), or the residue of an epoxide, or the residue of an optionally substituted (meth) acrylic ester or amide group; Y is C2-4-alkyleneoxy; T or T' is independently C2-4alkylene; B is an alkylene group, such as, methylene; Z is an inorganic acidic polar head group, such as, a sulphur or phosphorus acidic polar head group;

[0085] G and G' may be the same or different and are independently H or C1-50-optionally substituted hydrocarbyl or C1-50-optionally substituted hydrocarbyl or hydrocarbonyl group or the residue of an epoxide, or the residue of an optionally substituted (meth) acrylic ester or amide group; r is zero or 1; q is 1 or 2, with the proviso that when q is 2, r is zero; and x is from 2 to 90.

[0086] Specific examples of suitable amine-based polymeric dispersants include: Solsperse 13940 available from Lubrizol, which is a 40％ active amine-based polymeric dispersant in a 240 / 260 (oC) aliphatic distillate; Solsperse J965 available from Lubrizol, which is a 100％ active polymeric dispersant Solsperse 11200 available from Lubrizol, which is a 50％ active polymeric dispersant in SHELLSOLTMD40; Solsperse 21000 available from Lubrizol, which is a 100％ active polymeric dispersant; Hypermer KD1 available from Croda, which is a 100％ active cationic polymeric dispersant; Hypermer KD4 available from Croda, which is a 100％ active anionic polymeric dispersant; and Hypermer KD9 available from Croda, which is a 100％ active anionic polymeric dispersant.

[0087] Solsperse 13940 is preferred as the amine-based polymeric dispersant.

[0088] The oil-based ink optionally comprises an alkyd resin.

[0089] As used herein, an amount of alkyd resin of 0wt％ in the oil-based ink indicates that the alkyd resin is absent.

[0090] As used herein, an alkyd resin comprises an ester (hereinafter referred to as a second ester). The second ester is derived from an acid (hereinafter the acid component of the second ester) and an alcohol (hereinafter the alcohol component of the second ester).

[0091] Typically, the acid component of the second ester is an unsaturated fatty acid.

[0092] Preferably the acid component of the second ester is a di-unsaturated fatty acid. Di-unsaturated fatty acids may be obtained, for example, by hydrolysis of vegetable oils (e.g. soy oil). Examples of suitable di-unsaturated fatty acids include linoleic acid, eicosadienoic acid, docosadienoic acid and linolelaidic acid. Linoleic acid is preferred as the acid component of the second ester. Linoleic acid can be obtained by hydrolysis of soy oil.

[0093] Typically, the alcohol component of the second ester is a polyhydric alcohol. Examples of suitable polyhydric alcohols include glycerol, trimethylolpropane, and pentaerythritol. Pentaerythritol is preferred as the alcohol component of the second ester.

[0094] The second ester may be an ester of a di-unsaturated fatty acid and a polyhydric alcohol, and examples of the second ester include glyceryl esters of linoleic acid (e.g. glyceryl monolinleaate, glyceryl dilonleate, glyceryl trilinoleate, or any mixture thereof) , glyceryl esters of eicosadienoic acid (e.g. glyceryl monoeicosadienoate, glyceryl dieicosadienoate, glyceryl trieicosadienoate or any mixture thereof), trimethylolpropyl esters of linoleic acid (e.g. trimethylolpropyl monolinoleate, trimethylolpropyl dilinoleate, trimethylolpropyl trilinoleate or any mixture thereof), trimethylolpropyl esters of eicosadienoic acid (e.g. trimethylolpropyl monoeicosadienoate, trimethylolpropyl dieicosadienoate, trimethylolpropyl trieicosadienoate or any mixture thereof), trimethylolpropyl esters of docosadienoic acid (e.g. trimethylolpropyl monodocosadienoate, trimethylolpropyl didocosadienoate, trimethylolpropyl tridocosadienoate or any mixture thereof), pentaerythrityl esters of linoleic acid (e.g. pentaerythrityl monolinoleate, pentaerythrityl dilinoleate, pentaerythrityl trilinoleate, pentaerythrityl tetralinoleate, or any mixture thereof), pentaerythrityl esters of eicosadienoic acid (e.g. pentaerythrityl monoeicosadienoate, pentaerythrityl dieicosadienoate, pentaerythrityl trieicosadienoate, pentaerythrityl tetraeicosadienoate, or any mixture thereof), and pentaerythrityl esters of docosadienoic acid (e.g. pentaerythrityl monodocosadienoate, pentaerythrityl didocosadienoate, pentaerythrityl tridocosadienoate, pentaerythrityl tetradocosadienoate, or any mixture thereof). Pentaerythrityl esters of tetralinoleic acid are preferred as the second ester. Mixtures comprising pentaerythrityl monolinoleate and pentaerythrityl dilinoleate are particularly preferred.

[0095] The alkyd resin may be a single substance, or a mixture of different substances. The one or more further substances may be other esters (e.g. other esters of unsaturated fatty acids and polyhydric alcohols), or other substances of the types commonly found in alkyd resins. When the alkyd resin is a mixture of the second ester and one or more further substances, the second ester may be present in an amount of 50 wt％ or more of the alkyd resin.

[0096] Typically, the oil-based ink comprises an ester in an amount of 40wt％ or more of based on the total weight of the oil-based ink. Preferably, the oil-based ink comprises an ester in an amount of 50wt％ or more of based on the total weight of the oil-based ink.

[0097] Typically, a solvent is present in an amount of 64 to 85 wt％, based on the total weight of the oil-based ink. Typically, the solvent is a semi-drying solvent.

[0098] Typically, the pigment is present in an amount of 4wt％ or more and 25wt％ or less, based on the total weight of the oil-based ink. Preferably, the pigment is present in an amount of 4wt％ or more and 16wt％ or less, based on the total weight of the oil-based ink. More preferably, the pigment is present in an amount of 6wt％ or more and 14wt％ or less, based on the total weight of the oil-based ink.

[0099] Typically, where present, the ratio of the weight of the pigment to the weight of the amine-based polymeric dispersant in the oil-based ink is 1.0 or more and 3.5 or less; and the ratio of the weight of the semi-drying solvent to the sum of the weights of the amine-based polymeric dispersant and, if present, the alkyd resin in the oil-based ink is 3.6 or more and 9.5 or less

[0100] In some suitable oil-based inks, each of the amine-based polymeric dispersant and alkyd resin may be present in an amount of 5wt％ or more based on the total weight of the oil-based ink. In such cases, each of the amine-based polymeric dispersant and alkyd resin is preferably present in an amount of 5 to 10 wt％ based on the total weight of the oil-based ink, for instance from 6 to 8 wt％ based on the total weight of the oil-based ink. Such oil-based inks typically contain pigment in an amount of 20 wt％ or less based on the total weight of the oil-based ink, preferably 10 to 18 wt％ based on the total weight of the oil-based ink, and particularly preferably 13 to 15 wt％ based on the total weight of the oil-based ink.

[0101] In some alternative suitable oil-based inks: (a) the amine-based polymeric dispersant is comprised in an amount of greater than 0wt％ based on the total weight of the oil-based ink, and less than 5wt％ based on the total weight of the oil-based ink; and (b) the alkyd resin is comprised an amount of 0wt％ based on the total weight of the oil-based ink, or is comprised in an amount of up to 15wt％ based on the total weight of the oil-based ink.

[0102] Such oil-based inks typically contain pigment in an amount of 25 wt％ or less based on the total weight of the oil-based ink, preferably 20 wt％ or less based on the total weight of the oil-based ink, and particularly preferably 4 to 16 wt％ based on the total weight of the oil-based ink. In such oil-based inks, typically, the ratio of the weight of the pigment to the weight of the amine-based polymeric dispersant in the oil-based ink is 1.0 or more and 3.5 or less; and the ratio of the weight of the semi-drying solvent to the sum of the weights of the amine-based polymeric dispersant and, if present, the alkyd resin in the oil-based ink is 3.6 or more and 9.5 or less.

[0103] Further alternative oil-based inks include those in which: (a) the alkyd resin is comprised an amount of 0wt％ based on the total weight of the oil-based ink, or is comprised in an amount less than 5wt％ based on the total weight of the oil-based ink; and (b) the amine-based polymeric dispersant is comprised in an amount of greater than 0wt％ based on the total weight of the oil-based ink, and up to 15wt％ based on the total weight of the oil-based ink.

[0104] Such oil-based inks typically contain pigment in an amount of 25 wt％ or less based on the total weight of the oil-based ink, preferably 20 wt％ or less based on the total weight of the oil-based ink, and particularly preferably 4 to 16 wt％ based on the total weight of the oil-based ink. In such oil-based inks, typically, the ratio of the weight of the pigment to the weight of the amine-based polymeric dispersant in the oil-based ink is 1.0 or more and 3.5 or less; and the ratio of the weight of the semi-drying solvent to the sum of the weights of the amine-based polymeric dispersant and, if present, the alkyd resin in the oil-based ink is 3.6 or more and 9.5 or less.

[0105] More alternative oil-based inks include those in which the amine-based polymeric dispersant is comprised in an amount of greater than 0wt％ based on the total weight of the oil-based ink, and less than 5wt％ based on the total weight of the oil-based ink, and the amount of alkyd resin in the oil-based ink is 0wt％ (i.e. the alkyd resin is absent).

[0106] Such oil-based inks typically contain pigment in an amount of 15 wt％ or more and 25 wt％ or less based on the total weight of the oil-based ink, preferably 16 to 25 wt％ based on the total weight of the oil-based ink. In such oil-based inks, typically, the ratio of the weight of the pigment to the weight of the amine-based polymeric dispersant in the oil-based ink is 1.0 or more and 3.5 or less; and the ratio of the weight of the semi-drying solvent to the amine-based polymeric dispersant in the oil-based ink is 3.6 or more and 9.5 or less.

[0106] Exemplary formulations of oil-based inks are described in the following Tables.

[0107]

[0108]

[0109] It will be understood by the skilled person that the compositions of the oil-based inks described herein reflect those at the time of printing onto the substrate within the method of the invention. The nature of some of the components comprised within the oil-based inks are such that changes in their composition may occur following their application to the substrate. Such changes may be resultant through evaporation, for example of an organic component, or curing under ambient conditions. Such variations of the oil-based ink following its application to the substrate are additionally contemplated within the scope of the invention.Substrate

[0110] The term “substrate” refers to the object to which ink is applied in the method and printed article. After printing, the substrate carries a printed ink and may be referred to as a “printed substrate”. As used herein, reference to a “substrate” includes reference to a printed substrate.

[0111] The substrate may be any substrate suitable for inkjet printing. The substrate has a surface suitable for receiving ink, which is usually a flat surface. Most typically the substrate is in the form of a sheet.

[0112] The substrate may comprise one or more materials. For instance, the substrate may comprise two or more layers of differing materials. Examples of suitable materials for the substrate include board, paper, foil, or plastic. However, as explained previously, the method described herein using an oil-based ink is particularly advantageous where the substrate is capable of absorbing liquid, and particularly water. Thus, in a preferred aspect, the substrate comprises or consists of a porous material. For instance, the substrate may be a porous substrate. Typically, the substrate comprises natural fibres and may consist of natural fibres. Preferably, the substrate comprises paper; for instance, the substrate may be a paper substrate. Particularly preferably, the substrate comprises or is decor paper.

[0113] The substrate may be a treated substrate comprising an ink-receiving layer. That is, a “treated substrate” comprises a substrate and an ink-receiving layer. A treated substrate may also comprise printed ink, after the printing process.

[0114] Ink-receiving layers are known in the art and may enhance the colour intensity of the oil-based ink when printed. An ink-receiving layer assists in reducing spreading of ink during or after printing. Thus, in the method and article of the invention, the effect of an ink-receiving layer can combine with the inkjet printing technique using the advantageous plant-based inks described to produce exceedingly good printing results with very low smearing.

[0115] An ink-receiving layer usually comprises a material capable of absorbing a liquid component of ink. Typically, an ink-receiving layer comprises silica and / or alumina. An ink-receiving layer may also comprise a polymer, such as poly(vinyl alcohol)-PVOH, poly(acrylic acid)-PAA, poly(acrylamide)-PAmd and their copolymers, poly(vinyl pyrrolidone)-PVP, or cellulose derivatives. Typically, the ink-receiving layer comprises silica and a polymer. Typically, the polymer is polyvinyl alcohol, a polyester such as polyethylene terephthalate, or polyvinyl chloride, and preferably the polymer is polyvinyl alcohol. Thus, in a preferred aspect, the ink-receiving layer may comprise or consist of (a) an inorganic component selected from silica and / or alumina, and (b) a polymer selected from poly(vinyl alcohol)-PVOH, poly(acrylic acid)-PAA, poly(acrylamide)-PAmd and their copolymers, poly(vinyl pyrrolidone)-PVP, or cellulose derivatives.

[0116] The ink-receiving layer may, for example, have a weight per unit area of about 5 to about 30 gsm (dry); about 5 to about 25 gsm (dry); about 5 to about 20 gsm (dry); about 5 to about 15 gsm (dry); about 10 to about 30 gsm (dry); about 10 to about 25 gsm (dry); about 10 to about 20 gsm (dry); about 10 to about 15 gsm (dry); about 15 to about 30 gsm (dry); about 15 to about 25 gsm (dry); or about 15 to about 20 gsm (dry).

[0117] The ink-receiving layer may, for example, have a weight per unit area of more than about 5 gsm (dry); more than about 10 gsm (dry); or more than about 15 gsm (dry).

[0118] The ink-receiving layer may, for example, have a weight per unit area of less than about 30 gsm (dry); less than about 25 gsm (dry); or less than about 20 gsm (dry).

[0119] The ink-receiving layer may, for example, have a weight per unit area of about 5 gsm (dry); about 10 gsm (dry); about 15 gsm (dry); about 20 gsm (dry); about 25 gsm (dry); or about 30 gsm (dry).

[0120] Preferably, the ink-receiving layer has a weight per unit area of about 10 to about 25 gsm (dry). More preferably, the ink-receiving layer has a weight per unit area of about 15 to about 20 gsm (dry). Most preferably, the ink-receiving layer has a weight per unit area of about 15 gsm (dry).

[0121] By “gsm (dry)” is meant the weight of the ink receiving layer in grams per square metre as measured under dry conditions and before application of ink. For instance, the weight may be measured after drying at a temperature exceeding 50℃, for instance for at least 60 seconds. The dry weight is the steady weight achieved under drying conditions.

[0122] The ink-receiving layer may be applied to the substrate at any suitable time prior to the application of the oil-based ink. Typically, the method of printing of the invention further comprises producing a treated substrate by applying the ink-receiving layer to the substrate prior to step (i). Thus, the term “substrate” as used herein includes a “treated substrate”.

[0123] The ink-receiving layer may be applied by any suitable method, such as those known in the art to the skilled person. The ink-receiving layer may, for example, be applied by using a bar coating method, a rod coating method, a reverse rolling method, an extrusion dye method, a curtain flow coating method, an air doctor coating method, a blade coating method, a knife coating method, a squeeze coating method. Typically, the ink-receiving layer is applied by using a bar coating method or a rod coating method. Preferably, the ink-receiving layer is applied by using a Meyer bar. More preferably, the ink-receiving layer is applied by using a closed wire Meyer bar. The closed-wire Meyer bar may be, for example, a horn coloured Meyer bar (No. 5).Impregnating agent

[0124] According to the present invention, the method of printing comprises impregnating a printed substrate with an impregnating agent comprising a melamine component. Impregnating agents comprising a melamine component are known in the art.

[0125] By “melamine component” is meant a precursor capable of forming a melamine resin. For instance, the “melamine component” is typically a component which can be cross-linked to form a melamine resin. The impregnating agent comprising a melamine component is cured to form a melamine resin.

[0126] The melamine component may be melamine. Alternatively, the melamine component is a chemical containing one or more structural units derived from melamine. For example, the melamine component usually comprises units of formula (I): in which formula a dashed line indicates a covalent bond. Thus, the melamine component may be a compound comprising a unit of formula (I).

[0127] The impregnating agent is typically a liquid. For instance the impregnating agent may be a solution or suspension comprising the melamine component and a solvent. The melamine component may be dissolved and / or suspended in the solvent. The solvent may comprise, for instance, water, an alcohol, an aldehyde, a ketone or an ester. Examples of suitable solvents include water, methanol, ethanol, propanol, butanol, formaldehyde, ethanal, propanal or butanal. The impregnating may comprise one or more solvents. The impregnating agent may comprise other additives such as a buffer component, urea, or xylene.

[0128] Preferably, the impregnating agent is a solution or suspension comprising (a) melamine or a compound comprising a unit of formula (I), and (b) formaldehyde. An exemplary impregnating agent comprises melamine and formaldehyde. Another exemplary impregnating agent comprises melamine, formaldehyde and water.

[0129] Within the impregnating agent, the melamine component may be partially condensed with another component such as an amide or aldehyde (such as formaldehyde). However, further curing is generally needed to produce the solid, hard-wearing melamine resin.

[0130] In step (ii), the impregnating agent impregnates the printed substrate. In this context is meant at least that the impregnating agent coats all or part of a surface of the printed substrate. Typically, the impregnating agent coats all or part of at least the surface of the printed substrate to which the oil-based ink has been applied. Preferably, the impregnating agent also penetrates into said surface of the substrate. Preferably, the impregnating agent may entirely permeate the substrate. Where the impregnating agent penetrates into the substrate, the substrate may be referred to as an “impregnated substrate”. The term “substrate” as used herein includes an “impregnated substrate”.Melamine resin

[0131] The melamine resin is obtainable from the impregnating agent. The impregnating agent can be cured as described above to produce a melamine resin. By “melamine resin” is meant a polymer comprising multiple units of formula (I). A “melamine resin” as used herein is a solid.

[0132] A melamine resin is typically colourless and transparent when in the form of a thin layer (such as a layer less than 500 μm thick).

[0133] The melamine resin is derived from the melamine component. Accordingly, the melamine resin comprises units of formula (I): in which formula a dashed line indicates a covalent bond.

[0134] Preferably, the melamine resin is a formaldehyde-melamine resin. A formaldehyde-melamine resin is a cross-linked product of formaldehyde and melamine. A formaldehyde-melamine resin generally comprises units of formula (I) linked by one or more -CH2-O-CH2- groups. Thus, a formaldehyde-melamine resin comprises units of formula (II): in which formula a dashed line indicates a covalent bond.

[0135] Impregnating agents which can be cured to produce formaldehyde-melamine resins, and formaldehyde-melamine resins, are commercially available. Formaldehyde-melamine resins may be obtained and combined with one or more solvents (and optionally other components) in order to produce an impregnating agent. Examples of such commercially available formaldehyde-melamine resins and impregnating agents include the Kauramin (registered trademark) range available from BASF. These may or may not need to be combined with a chemical agent (often referred to as a hardener) in order to cure and produce the final melamine resin.

[0136] A suitable example is Kauramin (registered trademark) 773 (available from BASF).

[0137] As explained above, the impregnating agent from which the melamine resin is formed coats all or part of a surface of the printed substrate (which is generally the surface of the printed substrate to which the oil-based ink has been applied). Preferably, the impregnating agent also penetrates into said surface of the substrate. Accordingly, the melamine resin may form a surface layer which does not penetrate the substrate. Alternatively, the melamine resin may at least partially extend into the substrate.Printed article

[0138] Provided herein is a printed article obtained or obtainable by the method of printing of the invention. The printed article comprises a substrate and an oil-based ink. The immediate product of steps (i) and (ii) also comprises an impregnating agent. The impregnating agent may be cured to form a melamine resin, and so the printed article also comprises an impregnating agent and / or a melamine resin. The ultimate product comprises a substrate, an oil-based ink, and a melamine resin.

[0139] Accordingly, the invention provides a printed article which is obtained or obtainable by a method of printing comprising: (i) applying an oil-based ink to a substrate by inkjet printing to form a printed substrate; (ii) impregnating the printed substrate with an impregnating agent comprising a melamine component; and subsequently curing the impregnating agent to form a melamine resin.

[0140] Thus, also provided herein is a printed article comprising: (i) a substrate; (ii) an oil-based ink; and (iii) a melamine resin.

[0141] Preferably, said printed article is obtained or obtainable by the method of printing of the invention. Hereafter, the term “printed article” refers to a printed article which may or may not be obtained by the method described herein.

[0142] The printed article may comprise one or more further components such as an ink receiving layer, a backing layer, and so on.

[0143] The printed article may comprise or consist of a substrate, an oil-based ink, a melamine resin, and optionally an ink-receiving layer.

[0144] Typically, the printed article of the invention comprises: (a) an oil-based ink as described herein; (b) a substrate as described herein; and (c) an impregnating agent and / or melamine resin as described herein.

[0145] The invention is illustrated below by means of the following non-limiting examples.

[0146] Cone and plate viscometers of the Brookfield type DV3T are suitable for determining viscosity of the oil-based ink. Viscosity was determined using a Brookfield DV3T viscometer with a CPA-40Z cone operating at 10 rpm. Viscosity stabilities were tested as follows. The viscosity of the oil-based ink was measured at room temperature (25℃). The oil-based ink was then stored for two weeks at 70℃, after which it was returned to room temperature and its viscosity was tested at 25℃ again. The oil-based ink was considered to have good stability if, during this test, the viscosity has changed by 10％ or less. If the viscosity of the ink had changed by more than 10％ under such conditions, its viscosity stability was considered to be poor. Inks of the invention were found to show minimal change in viscosity when measured under these conditions, and they were classed as having “good” viscosity stability.

[0147] Spectro-Densitometers of the Techkon SpectroDens type are suitable for determining optical density of the printed article. Optical densities were determined using a Techkon SpectroDens and applying a Techkon proprietary M0 method.Exemplary oil-based inks

[0148] Inks having the compositions set out in Table 3 (Inks 1 to 3) and Table 4 (Comparative Inks 1 to 3) below were prepared according to the following procedure.

[0149] Step 1: The liquid components, i.e. all components except pigment, which are listed in Table 3 or 4 below, were added to a mixing vessel and then blended together using a mechanical stirrer equipped with a toothed wheel mixing impeller, such as an Eiger Torrance HSD Lab mixer. Blend speed 1000rpm and time 5 minutes.

[0150] Step 2: The pigment was added to the blended oil phase mix and then wetted out under vacuum (Vacuum pressure less than -500mbar), using a mechanical stirrer as before, to disperse the pigment. Wetting removes air and moisture from the pigment surface ensuring uniform dispersion. Wetting speed 1000rpm and time 30 minutes.

[0151] Step 3: The wetted mix was then pre-mixed on a mechanical stirrer as before, to reduce and equalise the particle size of the dispersed pigment, so that the mix was suitable for milling. Premix time 30 minutes, premix vacuum less than -500mbar and premix speed 3000rpm.

[0152] Step 4: The premix was then transferred to a horizontal bead mill and milled to reduce the pigment particle size further. Mills of the Netzsch Minizeta type are suitable, using cerium stabilised zirconium beads with a size of 0.4 to 0.7mm. The loading of the beads in the mill chamber should be greater than 85％ by volume. The mill should be cooled with cold water to maintain a mix temperature of less than 50℃. Milling speed 3000rpm and time 2 hours.

[0153] Step 5: The resulting ink mix was then tested for viscosity and particle size. Cone and plate viscometers of the Brookfield type DV3T and Dynamic Light Scattering particle size instruments of the Malvern Zetasizer Nano-ZS types are suitable. Step 6: The ink was then filtered through a glass fibre filter system. A Pall vacuum filter system is suitable using Whatman GF / B filter discs. Pore size of the discs 1μ and vacuum pressure less than -800mbar.

[0154] Amounts of components shown in Tables 3 and 4 are weight percentages. The components used and analysis outcomes are as follows: Solvent (Methyl ester): Mosselman oil (Soy based oil) Solvent (Dioctyl adipate): Dioctyl adipate Pigment (Carbon black): Regal 400R Alkyd resin: Vilkyd 782 Saturated resin: Abitol E Amine-based polymeric dispersant: Solsperse 13940

[0155]

[0156]

[0157] The viscosity of Ink 2 was measured and found to be 17.87 cP. The viscosity of Ink 3 was measured and found to be 21.86 cP. These viscosity measurements were performed at room temperature. The viscosity of the oil-based inks decreases when the oil-based inks are heated to the jetting temperature.Application of ink-receiving layer

[0158] A paper substrate (TC9669-095) was coated with an ink receiving layer (PrintRite (trademark) DP 338E, available from Lubrizol) using a closed wire Meyer bar (Horn coloured Meyer bar (No. 5)). The coated substrate was placed in an oven at 100℃ for 90 seconds to dry the material thereby forming a treated substrate. The resulting ink-receiving layer of the treated substrate had a weight per unit area of 15 gsm (dry).Inkjet printing method

[0159] Inkjet printing was performed using a Ricoh Gen5 printhead (MH5420). Ink was delivered from a bottle with no back-channel flow through. A 5-10 pL droplet was used. Jetting frequency was 20 kHz.Melamine component preparation

[0160] A first mixture was formed by stirring together non-ionic alkylphenol ethoxylate (Kauropal (registered trademark) 931, available from BASF; 16.67 g) with water (83.17 g) for 15 minutes.

[0161] A second mixture was formed adding a melamine-formaldehyde resin (Kauramin (registered trademark) 773, available from BASF; 333 g) to water (267 g) at 60℃ with stirring. Heating was removed following addition of the resin. The components were stirred together for a further 15 minutes before cooling to room temperature.

[0162] A third mixture was formed by stirring together the first mixture (2.1 g) and the second mixture (600 g) for 10 minutes.

[0163] A final mixture was formed by stirring together the third mixture (602.1 g) and a hardener (Kauramin (registered trademark) Hardener 668f: Blend: formic acid, aqueous solution, available from BASF; 30.1 g) for at least 10 minutes or until the mixture was homogeneous.Melamine impregnation method

[0164] The final mixture described above was placed into a metal tray. The printed substrate was laid into the final mixture with the printed side facing upwards. The printed substrate was submerged in the final mixture for at least 10 seconds, ensuring that the mixture had completely penetrated the printed substrate. The impregnated printed substrate was checked for smearing, by observation of whether one printed ink had bled into another.

[0165] The impregnated printed substrate was removed from the final mixture and squeezed through metal rollers to remove excess liquid. The impregnated printed substrate was placed in a second metal tray and fixed in place using magnets. The impregnated printed substrate in the metal tray was placed in an oven set at 110℃ for at least 1 minute before being removed from the oven.

[0166] The impregnated printed substrate was submerged in the final mixture again for 30 seconds before being once more passed through metal rollers to remove excess liquid. The impregnated printed substrate was again fixed in a metal tray and placed in an oven set at 110℃ for at least 5 minutes before being removed from the oven. A final check for bleeding was performed.Assessment of smearing

[0167] Substrates were printed with oil-based inks and treated with melamine as described above. In some examples, an ink-receiving layer (IRL) was applied as described above. In some cases, a dark (black) ink was printed together with a pale (yellow) ink; in other cases, a single dark ink was printed. An assessment of smear was undertaken. Smear was assessed and graded as “good” or “poor”, with “good” being ascribed to no smearing or essentially no smearing, and “poor” being ascribed to substantial smearing.

[0168] The assessment outcomes are shown in Table 5. Figures 1 to 5 show photographs of the results of various examples. The test examples are described below; the substrate does not include an ink receiving layer except where mentioned.

[0169] In Example 1, Ink 1 (which is black in colour) was inkjet printed onto a substrate adjacent to a paler, yellow ink. The substrate was impregnated with melamine. The results are shown in Figure 1. The lower image shows the substrate after impregnation with melamine. The darker (black) ink at the right-hand side of the image has not smeared into the paler (yellow) ink at the left-hand side of the image.

[0170] In Example 2, Ink 2 (which is black in colour) was inkjet printed onto a substrate. In a first trial, Ink 2 was printed adjacent to a paler, yellow ink. The substrate was impregnated with melamine. The results are shown in Figure 2A. The darker (black) ink at the right-hand side of the image has not smeared into the paler (yellow) ink at the left-hand side of the image. In a second trial, Ink 2 was inkjet printed onto a substrate in the absence of other inks, and the substrate was again impregnated with melamine. The results are shown in Figures 2B, 2C, and 2D. It is clear from Figures 2B-2D that the ink (black) has not smeared into the unprinted area at the bottom of the image. The images of figures 2B-2D may be compared to those of figures 7A, 7B and 4B respectively, which relate to corresponding tests using the comparative inks. The tests using comparative inks show significant smearing.

[0171] In Example 3, Ink 3 (which is black in colour) was inkjet printed onto a substrate. The substrate was impregnated with melamine. The results are shown in Figure 3. The ink has not smeared into the unprinted area at the bottom of the image. This may be compared to the image in Figure 4B, wherein the same test was performed using comparative Ink 1, and significant smearing was observed.

[0172] In Example 4, Comparative Ink 1 (which is black in colour) was inkjet printed onto a substrate. In a first trial, this comparative ink was printed adjacent to a paler, yellow ink. The substrate was impregnated with melamine. The results are shown in Figure 4A. The darker (black) ink at the right-hand side of the image has smeared into the paler (yellow) ink at the left-hand side of the image. In a second trial, Comparative Ink 1 was inkjet printed onto a substrate in the absence of other inks, and the substrate was again impregnated with melamine. The results are shown in Figure 4B. The ink has smeared into the unprinted area at the bottom of the image.

[0173] In Example 5, Comparative Ink 1 was inkjet printed onto a substrate treated with an ink-receiving layer. The substrate was impregnated with melamine. The results are shown in Figure 5. The darker (black) ink at the right-hand side of the image has not smeared significantly into the paler (yellow) ink at the right-hand side of the image.

[0174] In Example 6, Comparative Ink 2 was inkjet printed onto a substrate. The substrate was impregnated with melamine. As is shown in Figure 6, in that case the black ink smeared very significantly into the paler, yellow ink. Thus, in the absence of an ink-receiving layer, the comparative ink is susceptible to smearing.

[0175] In Example 7, Comparative Ink 3 was inkjet printed onto a substrate in the absence of other inks, and the substrate was again impregnated with melamine. The results are shown in Figures 7A and 7B. In each case it is clear that the ink (black) has smeared into the unprinted area adjacent to the printed ink block(s).

[0176]

[0177] The invention is described above with reference to certain embodiments and typical features. However, those embodiments and typical features are merely illustrative and a skilled person will appreciate that various modifications are possible, including combinations of features which are described above with reference to separate embodiments and typical features, without departing from the scope of the invention as defined in the following claims (with due account being taken of equivalents thereto).

[0178] The present application is based on and claims priority of United Kingdom Patent Application No. 2418837.7 filed on 20 December 2024, the entire contents of which are hereby incorporated herein by reference.

Claims

1. A method of printing comprising: (i) applying an oil-based ink to a substrate by inkjet printing to form a printed substrate; and (ii) impregnating the printed substrate with an impregnating agent comprising a melamine component.

2. The method of claim 1, wherein the method does not comprise a water evaporation step between steps (i) and (ii).

3. The method of any preceding claim, wherein impregnating the printed substrate comprises submerging the printed substrate in the impregnating agent.

4. The method of any preceding claim, wherein the oil-based ink has a viscosity at the jetting temperature of about 4 to about 13 cP; most preferably, in the range of about 7 to about 12 cP.

5. The method of any preceding claim, wherein the oil-based ink comprises: (a) a semi-drying solvent; (b) a pigment; (c) an amine-based polymeric dispersant in an amount greater than 0wt％ based on the total weight of the oil-based ink; and (d) an alkyd resin in an amount of 0wt％ or more of based on the total weight of the oil-based ink.

6. The method of claim 5, wherein the pigment is present in an amount of 6wt％ or more and 14wt％ or less, based on the total weight of the oil-based ink.

7. The method of claim 5 or claim 6, wherein the ratio of the weight of the pigment to the weight of the amine-based polymeric dispersant in the oil-based ink is 1.0 or more and 3.5 or less; and wherein the ratio of the weight of the semi-drying solvent to the sum of the weights of the amine-based polymeric dispersant and, if present, the alkyd resin in the oil-based ink is 3.6 or more and 9.5 or less.

8. The method of any of claims 5 to 7, wherein the semi-drying solvent is selected from the group consisting of linoleic acid methyl ester, eicosadienoic acid methyl ester, docosadienoic acid methyl ester and linolelaidic acid, preferably wherein the semi-drying solvent is linoleic acid methyl ester.

9. The method of any preceding claim, wherein the melamine component comprises units of formula (I): in which formula a dashed line indicates a covalent bond; preferably wherein the melamine component is a formaldehyde-melamine resin.

10. The method of any preceding claim, wherein the substrate is a treated substrate comprising an ink-receiving layer.

11. The method of claim 10, wherein the ink-receiving layer comprises silica and a polymer, preferably wherein the polymer is polyvinyl alcohol.

12. The method of claim 10 or claim 11, wherein the ink-receiving layer has a weight per unit area of 5 to 30 gsm (dry).

13. The method of any of claims 10 to 12, wherein the method comprises producing the treated substrate by applying the ink-receiving layer to the substrate prior to step (i).

14. The method of any preceding claim, wherein the substrate is a porous substrate.

15. The method of any preceding claim, wherein the substrate comprises natural fibres, preferably wherein the substrate is paper, and more preferably wherein the substrate is decor paper.

16. The method of any preceding claim, wherein the method reduces or prevents smearing of the oil-based ink.

17. A printed article obtained or obtainable by the method of any one of claims 1 to 16.

18. A printed article comprising: (i) a substrate; (ii) an oil-based ink; and (iii) a melamine resin.

19. The printed article of claim 18 wherein: (a) the oil-based ink is defined as in any one of claims 4 to 8; and / or (b) the substrate is a treated substrate comprising an ink receiving layer, preferably wherein the ink receiving layer is as defined in claim 11 or claim 12; and / or (c) the substrate is as defined in claim 14 or claim 15.

20. The printed article of claim 18 or claim 19, wherein the melamine resin comprises units of formula (I): in which formula a dashed line indicates a covalent bond; preferably wherein the melamine resin is a formaldehyde-melamine resin.

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