Inkjet recording method and apparatus therefor

Abstract

A method of image recording, comprising following steps a. Providing a substrate (17); and b. Applying through a nozzle plate (16) of an ink jet head (11), drops of an aqueous pre-treatment liquid having an average drop mass equal to 6 ng / drop or less and equal to 1 ng / drop or more, onto at least a part of a recording region S of an upper surface of the substrate (17) with a drop density being equal to 55 drops / mm² or more and equal to 1600 drops / mm² or less, the aqueous pre-treatment liquid comprises a fixing agent, the distance between the nozzle plate (16) and the upper surface of the substrate (17) is equal to 2.5 mm or less; and c. Attaching an aqueous inkjet ink onto at least a part of the recording region S to form an image, the aqueous inkjet ink comprises a pigment and a water-soluble organic solvent. A recording apparatus for performing the method is also provided.

Description

PatXML 1 / 41 GN24010DescriptionInkjet recording method and apparatus therefor.Technical Field

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus in a two liquid type inkjet recording process, at least one liquid is a pre-treatment liquid. More specifically, the present invention relates to an inkjet recording method and an inkjet recording apparatus in which image quality is improved on a substrate, and more particularly a substrate to be used as packaging material.Background Art

[0002] Inkjet printing technology is a growing area of printing substrates for display purposes such as signs and posters, but also for packaging purposes such as plastic foils, liners for corrugated cardboards and liners for folding cardboards. In printing of liners for cardboards, usually flexographic printing or offset printing is performed.

[0003] Nowadays, there is a growing area of digital printing of liners for corrugated packaging, corrugated cardboards and folding cardboard. Primers or pre-treatment liquids improve the image quality of the printed image. The possibility to apply a pre-treatment liquid, only on the parts which will carry the image, e.g. by a jetting technique makes it possible to reduce the total consumption of the pre-treatment liquid in the printing job.

[0004] To obtain high quality images, the pre-treatment liquid is capable of receiving ink and holding or fixing colorants in the ink to a greater degree than a substrate not treated with a pre-treatment liquid. In particular, the pre-treatment liquid is capable of holding or fixing colorants at or near the surface of the substrate so that colour gamut of the printed image may be improved and bleeding and feathering of the coloured ink considerably reduced compared to a substrate that is not treated with the pre-treatment liquid.

[0005] In the packaging printing industry there is a tendency of increased productivity demanding high printing speeds and the use of single passPatXML 2 / 41 GN24010 printer equipment in combination with high conveying speeds of packaging material such as plastic foils and paper based substrates.

[0006] Due to this, it is observed that the pre-treatment liquid drops are hardly dried before the inkjet ink drops are adhered to the pre-treated substrate. This is even more pronounced when the substrate is a coated paper which shows a low ink absorbability leading to a reduced ink absorption speed or when the substrate is non-absorbing (e.g. a plastic foil) which does not show ink absorbability

[0007] One of the disadvantages of undried pre-treatment drops when adhering ink drops in printing an image containing solids, is the occurrence of unevenness and white stripes in the solid areas of the image. This is more pronounced in solid areas of composite colours (green, red, blue and black) which contain high ink loads.

[0008] To reduce the negative effect of undried pre-treatment drops in the image forming process, the amount of applied pre-treatment liquid must be reduced to a level which is insufficient to obtain an acceptable level of colour fixing. Due to the decreased amount of applied pre-treatment liquid an unacceptable bleeding and feathering in the printed image are observed.

[0009] US 1053085055 discloses a recording method wherein the inkjet ink is adhered within 30 seconds after the application of a pre-treatment liquid onto a coated paper substrate. The pre-treatment liquid drops are dried by heating the substrate before, during or after applying the pre-treatment liquid drops. However, to achieve still high printing speeds an extra heating equipment which increases cost and complexity of the printing equipment is then required.

[0010] US 2018 / 0244078 discloses a recording method wherein the drop mass of the pre-treatment liquid is 5 ng / dot and wherein a cyan ink is attached to the region wherein the pre-treatment liquid was attached. No combination of different inkjet inks to from secondary colors is reported.

[0011] EP3366486 discloses an inkjet recording method including a reaction liquid adhesion step of ejecting a reaction liquid in the form of liquid droplets containing an aggregating agent which aggregates an inkPatXML 3 / 41 GN24010 composition to a recording medium which is a non-absorptive or low- absorptive recording medium. To achieve high printing speeds, a reaction liquid drying step is included so that evaporation rates of water is at least 70 wt.% and of organic solvent contained in the reaction liquid is 60 wt.% or less.

[0012] There is still a need for a recording method which provides acceptable image quality of inkjet printed images onto substrates for packaging at high printing speeds without the need for drying the pre-treatment liquid prior to the inkjet printing of the image.Summary of invention

[0013] It is an objective of the present invention to provide a solution to the above stated problems. The objective has been achieved by providing an image recording method as defined in Claim 1.

[0014] It is another embodiment of the invention to provide an inkjet recording apparatus as defined in Claim 14.

[0015] Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention. Specific embodiments of the invention are also defined in the dependent claims.Brief description of drawings

[0016] Fig. 1 : Image recording apparatus according to the invention.

[0017] Fig. 2: Printed image with yellow pigment containing ink.

[0018] Fig. 3: Printed image with magenta pigment containing ink.

[0019] Fig. 4: Printed image obtained by combining image printed with yellow containing pigment ink and magenta containing pigment ink.Description of embodimentsA. Method of image recording.

[0020] The method of image recording according to the invention comprises following steps (see Fig. 1): a) Providing a substrate (17); and b) Applying through a nozzle plate (16) of an inkjet head (11), drops of an aqueous pre-treatment liquid having a drop mass equal to 6 ng / drop orPatXML 4 / 41 GN24010 less and equal to 1 ng / drop or more, onto at least a part of a recording region S of an upper surface of the substrate (17) with a drop density being equal to 55 drops / mm2or more and equal to 1600 drops / mm2or less, the aqueous pre-treatment liquid comprises a fixing agent, the distance between the nozzle plate and the upper surface of the substrate is equal to 2.5 mm or less; and c) Attaching an aqueous inkjet ink onto at least a part of the recording region S, the aqueous inkjet ink comprises a pigment and a water-soluble organic solvent.

[0021] In a preferred embodiment of the invention, after step c), a second aqueous inkjet ink is attached onto at least a part of the recording region S to form an image, the second aqueous inkjet ink comprises a second pigment and a water-soluble organic solvent, the second pigment is different from the pigment in the aqueous inkjet ink of step c) (= first pigment). In a more preferred embodiment of the invention, a third and a fourth aqueous inkjet ink comprising a third and a fourth pigment and a water-soluble organic solvent may be attached onto at least a part of the recording region S. The third and fourth pigment are different from each other and from the second and first pigment.

[0022] It has been found by thorough investigation that when applying the above described image recording method comprising the steps a), b) to c), wherein in step b) the drop mass of the pre-treatment liquid is equal to 6 ng / drop or less and equal to 1 ng / drop or more and the drop density is equal to 55 drops / mm2or more and equal to 1600 drops / mm2or less, unevenness of the solid areas of an inkjet printed image at high printing speed, is substantially reduced, while ink bleeding is kept at an excellent level. An optimal drop density within the above-mentioned range, can be observed wherein bleeding and solids unevenness are both minimal.A.1. Providing a substrate (17)

[0023] The first step of the recording method according to the invention is the provision of a substrate which can be i) ink absorbing such as plain paper, or textile fabrics; ii) low ink absorbing such as coated paper, coatedPatXML 5 / 41 GN24010 cardboard liners for corrugated cardboard or folding cardboard, wood, ceramics, leather, and iii) ink non-absorbing such as plastic film (e.g. PET film, polyethylene film, polypropylene film, metal, glass, polyvinylchloride, PMMA, polycarbonate, polyamide, polystyrene).

[0024] The pre-treatment composition according to the invention is particularly suited for being jetted onto cardboard liners used in the folding cardboard and corrugated cardboard printing industry. The term ‘cardboard liners’ refers to paper (as sheets or web), folding-carton board, the top-liner of corrugated-carton boards, and the top-liner of corrugated boards. The method according to the invention comprises the provision of a substrate as a web and / or as separate sheets. The image recording method seems to be particularly suitable if the substrate is a coated cardboard liner.

[0025] The coating provided on a coated cardboard liner reduces the ink absorption in the gaps between the cellulose fibres. A too high ink absorption by the gaps between the paper fibres results in an insufficient colour density due to insufficient colorants present at the surface of the paper liner and a too high absorption by the fibres leads to feathering of ink resulting in unsharp edges between printed areas and unprinted areas.

[0026] The coating applied on coated paper and coated cardboard liners to improve image quality comprises resins such as poly styrene acrylic binders or acrylonitrile-styrene-butadiene. One of the effects of these resins is to limit the absorption of the ink drops into the cardboard liner. This leads to low-absorbability coated papers and cardboard liners being a "recording medium of which the quantity of water absorption from the start of contact to 30 ms1 / 2is 10 ml / m2or less according to the Bristow method ". The Bristow method is widely used as a method for measuring the liquid absorption amount in a short period of time and has been adopted by Japan Technical Association of the Pulp and Paper Industry (Japan TAPPI). The details of the testing method are described in the standard No. 51 "Paper and Paperboard-liquid absorbability testing method-Bristow method" of the "JAPAN TAPPI paper and pulp testing method 2000 version".PatXML 6 / 41 GN24010

[0027] Another effect of binders present into the surface of coated paper and cardboard liners is that the surface energy can be relatively low, such as from 20 mJ / m2or more and 60 mJ / m2or less. This reduced surface energy hampers a good spreading of the aqueous inkjet ink drops. It is believed that also the relatively low surface energy of non-absorbing substrates comprising plastics, hampers the good spreading of the aqueous inkjet ink drops. The recording method according to the invention is particularly suitable to provide even and homogenous solids in the printed image on substrates having a low surface energy, at an excellent level of ink bleeding.A.2. Applying drops of an aqueous pre-treatment liquid

[0028] In step b) of the image recording method according to the invention, droplets of an aqueous pre-treatment liquid comprising a fixing agent are applied onto the substrate in a recording region S of the substrate (17). The pre-treatment liquid drops have an average drop mass equal to 6 ng / drop or less and equal to 1 ng / drop or more and the drop density is equal to 55 drops / mm2or more and equal to 1600 drops / mm2or less.

[0029] More preferably, the average drop mass is equal to 1 ng / drop or more and equal to 4.8 ng / drop or less, more preferably the average drop mass is equal to 2 ng / drop or more and equal to 4.8 ng / drop or less.

[0030] The droplets are preferably applied via a droplet discharge device such as an inkjet printhead (11) or a valve jet printhead, both having a nozzle plate (16), the distance between the nozzle plate and the upper surface of the substrate is equal to 2.5 mm or less, preferably equal to 2.5 mm or less and equal to 0.1 mm or more, more preferably equal to 2.5 mm or less and equal to 0.5 mm or more, most preferably equal to 2.5 mm or less and equal to 1.0 mm or more. When the distance is less than the above- mentioned lower values, there is a risk that the upper surface of the substrate may touch the nozzle plate of the printhead due to vibrations occurring at high printing speed of the printing equipment.

[0031] It has been observed that if the distance between the upper surface of the substrate and the nozzle plate of the printhead is more than 2.5 mm, thePatXML 7 / 41 GN24010 pre-treatment liquid drops having an average drop mass equal to 6 ng / drop or less and equal to 1 ng / drop or more do not land accurately and properly onto the surface of the substrate.

[0032] Without being bound by a theory, it is thought that at distances higher than 2.5 mm, drops of pre-treatment liquid having an average drop mass equal to 6 ng / drop or less and equal to 1 ng / drop will lose velocity to such an extent that they do not reach the surface of the substrate or at least not where they are supposed to land. One of the possible consequences is that mist formation will occur of pre-treatment drops. When mist formation occurs, drops of pre-treatment liquid will deposit onto the printing equipment such as the nozzle plate of the printheads. When these drops dry, they may clog the nozzles resulting in bad printing reliability. This is even more pronounced when the pre-treatment liquid contains a resin. Another consequence of a too high distance between upper surface of the substrate and nozzle plate of the printhead is that the pre-treatment drops will not be adhered homogenously leading to a reduced image quality such as unevenness in the solid parts of the printed image or poor text character sharpness.

[0033] In case of an ink jet printhead, it is possible to discharge the pre-treatment liquid from a nozzle of an inline head or a scanning head. In a system which uses an inline head (also called single pass system), it is possible to apply drops of pre-treatment liquid to the recording region S by fixing the head, moving the substrate in a sub-scanning direction, and operating during the movement to discharge pre-treatment liquid droplets. In addition, in a scanning system, it is possible to apply droplets of pretreatment liquid onto the recording region S of the substrate by moving the head in a main scanning direction and fixing the substrate.

[0034] When the pre-treatment liquid drops are applied to the recording region S by using an inkjet print head, the average mass of the pre-treatment liquid per droplet is equal to or smaller than 6 ng / drop and equal to 1 ng / drop or more.

[0035] If the mass of the pre-treatment liquid per droplet is below these limits, the amount of fixing agent deposited is insufficient to guarantee sufficientPatXML 8 / 41 GN24010 fixing of the colorants of the inkjet ink to be applied, leading to unacceptable bleeding and feathering at the edges of the printed image. It has also been observed that average drop mass below 1 ng result in less accurate landing of the drops onto the substrate further forming mist of pre-treatment liquid drops which may deposit onto the equipment negatively affecting the jetting reliability.

[0036] If the average mass of the pre-treatment liquid per droplet is above 6 ng, it is observed that unevenness of the solid areas (white stripes, white spots) of the printed image is increased to an unacceptable level, leading to a decrease in colour density and unacceptable image quality of printed text characters being blurred and showing low colour densities.

[0037] It is preferable to discharge the pre-treatment liquid as liquid droplets onto the recording region S of a surface treated substrate by means of an inkjet print head having a specific print resolution. The print resolution is determined by the nozzle density, the addressability of the nozzles and the conveying speed of the substrate (in the fixed inline head print mode) I scanning speed (in the fixed substrate line mode). Print resolution along the printhead = Slow scan resolution (= SLSC). Print resolution in the print direction = Fast scan resolution (=FS). The SLSC should be minimum 200 dpi, preferably 600 dpi, most preferably 1200 dpi. FS should be minimum 200 dpi, preferably 600 dpi, most preferably 1200 dpi.

[0038] The print resolution is preferably 200 dpi or more x 200 dpi or more, more preferably 600 dpi or more x 600 dpi or more, and even more preferably 1200 dpi or more x 1200 dpi or more.

[0039] The upper limit of the print resolution is not limited but is preferably 3600 dpi or less x 3600 dpi or less. Print resolutions above this upper limit would negatively impact the printing speed too much, resulting in a low productivity.

[0040] It has been observed that, when using an inkjet print head at a print resolution of 200 dpi x 200 dpi, more preferably of 600 dpi x 600 dpi, most preferably of 1200 dpi x 1200 dpi, the drop density of the pre-treatment liquid in the recording region S should be reduced by omitting the discharge of drops. In another embodiment, it is also possible, startingPatXML 9 / 41 GN24010 from a 600 dpi X 600 dpi pixel matrix or image, more preferably from a 1200 dpi x 800 dpi pixel matrix or image, most preferably from a 1200 dpi x 1200 dpi pixel matrix or image to selectively generate additional drops. In both embodiments, the drop density of pre-treatment liquid drops comprising a fixing agent is from 55 drops / mm2to 1600 drops / mm2, preferably from 110 drops / mm2to 1600 drops / mm2, more preferably from 220 drops / mm2to 1600 drops / mm2. The drop density is the number of pretreatment liquid droplets which are discharged in a predetermined area.

[0041] If the drop density of the pre-treatment liquid is lower than the above- mentioned lower limit, insufficient pre-treatment liquid is applied onto the recording region which will lead to insufficient fixing of the colorants of the coloured inkjet inks when they are adhered to the recording region. Insufficient fixing results in bleeding in the printed image. If the drop density (in liquid state) is higher than the above-mentioned upper limit, it is observed that unevenness of the solid areas (white stripes, white spots) of the printed image is increased to an unacceptable level and that the amount of adhered pre-treatment liquid is hampering high printing speeds due to the amount of liquid to be evaporated during the drying step. Drying of the pre-treatment liquid droplets after adhering the inkjet droplets is then a problem at printing speeds of 30 m / min or more

[0042] When applying inkjet ink onto at least a part of a recording region S comprising a fully uniform layer of pre-treatment liquid drops, or a liquid pre-treatment coating onto a substrate, unevenness of the solid areas of the image is being observed. This unevenness is even more pronounced at solid areas having high ink loads such as e.g. consisting of composite colours such as green, red, blue and black. It is thought that when the aqueous pre-treatment liquid is applied at a drop density above 1600 drops / mm2a uniform liquid coating is obtained due to the coalescence of the pre-treatment liquid drops following a spreading of these drops onto the substrate.

[0043] Without being bound by a theory, it is thought that spreading of aqueous inkjet drops onto a liquid pre-treatment coating or high density of pretreatment liquid drops which are still in a liquid state (because they werePatXML 10 / 41 GN24010 not yet absorbed by substrate, nor were the solvents in the drops evaporated before adhering inkjet drops), is insufficient due to the low surface energy of the pre-treatment liquid to assure homogenous spreading of the ink drops. By applying pre-treatment liquid drops onto a substrate with a drop density from 55 to 1600 drops I mm2, preferably 110 to 1600 drops / mm2, more preferably 220 to 1600 drops / mm2, with a drop mass from 1 to 6 ng / drop sufficient amount of surface of the substrate is available to guarantee sufficient spreading of the aqueous inkjet drops to obtain even and homogenous solids in the printed image at an acceptable level of ink bleeding.

[0044] In order to achieve a drop density within the above mentioned ranges, drops may be selectively generated according to an image (which may be a bitmap, a matrix or generated when sending the firing signals to the inkjet head) defined by the resolution of the print head used and its firing frequency or drops may be selectively omitted from an image generating drops according to an image (bitmap, matrix) defined by the resolution of the printhead used and its firing frequency.

[0045] The omission of the discharge of drops can be achieved by skipping the discharge of nozzles in a structured way (e.g. every xthpixel) or in a semirandom way via halftoning methods. In another embodiment the generation of discharge of drops can be done in a structured way (e.g. every xthpixel) via threshold tiles or in a semi-random way via halftoning methods. Dithering and error diffusion halftoning techniques can be used to achieve the semi-random way of generating drops or skipping the discharge of nozzles.

[0046] The composition of the aqueous pre-treatment liquid, comprising a fixing agent according to the invention is described in § B.1 .

[0047] A preferred ink jet print head (11 ) for the discharge of pre-treatment liquid drops is a piezoelectric inkjet head. Piezoelectric inkjet discharging is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of a voltage changes the shape of the piezoelectric ceramic transducer in the print head creating a void, which is then filled with aqueous pre-treatment liquid. When the voltage isPatXML 11 / 41 GN24010 again removed, the ceramic expands to its original shape, discharging a drop of pre-treatment liquid from the inkjet print head. However, the discharging of the pre-treatment liquid according to the present invention is not restricted to piezoelectric inkjet printing. Other inkjet print heads can be used and include various types, such as a continuous type, a thermal print head type, a Memjet-type of head and a valve jet type.

[0048] In a preferred embodiment, the discharging system of the pre-treatment liquid may be configured to recirculate the pre-treatment liquid prior to printing. A particularly useful inkjet head to discharge the pre-treatment liquid of the invention, is from the type that includes a recirculation of the liquid within the head such as through-flow heads as disclosed in WO 2006 / 030235 A2 and WO 2006 / 064036 A1 . This type of inkjet head is very suitable to be incorporated in a printing system comprising a through-flow print head having one or more nozzles for ejecting drops of a pretreatment liquid. There are many different recirculation systems which are suitable for the method of the invention. One particular system is the use of a buffer tank local to the print heads. From this buffer tank (1) the pretreatment liquid is pumped to another identical buffer tank (2) which then supplies the "feed" side of the print head via a manifold, the "return" side of the head then flows back to the first buffer tank (1) via another manifold. The system is closed loop locally to the print heads wherein the pretreatment liquid never returns back to the main tank.

[0049] After discharging the pre-treatment liquid drops onto the recording region S of the substrate, the drops may be partially dried before aqueous inkjet drops are adhered to at least the recording region S.

[0050] The drying of the pre-treatment liquid drops can be performed by applying an air flow and / or apply heating. The heating step is then performed by using heat sources; examples include equipment for forced-air heating, radiation heating such as IR-radiation, including NIR-, CIR- and SWIR radiation, conduction heating, high-frequency drying, RF, ultrasonic and microwave drying.A.3. Attaching a coloured aqueous inkjet inkPatXML 12 / 41 GN24010

[0051] After the application of pre-treatment liquid drops onto the recording region S of the substrate, an aqueous inkjet ink is attached onto at least a part of the recording region S such as to obtain a printed image. More preferably, the aqueous inkjet ink may be attached to the pre-treatment liquid drops already present onto the surface of the substrate.

[0052] The inkjet ink comprises a pigment and a water-soluble solvent. A preferred method of attaching the aqueous inkjet ink to a substrate is by means of an ink jetting technique. For preferred inkjet heads, see § A.2.

[0053] After attaching the inkjet ink comprising a pigment and a water-soluble solvent step, a second aqueous inkjet ink may be attached onto at least a part of the recording region S to form an image, the second aqueous inkjet ink comprises a second pigment and a water soluble organic solvent, the second pigment is different from the pigment in the aqueous inkjet ink of step c. (= first pigment). In a more preferred embodiment of the invention, a third and a fourth aqueous inkjet ink comprising a third and a fourth pigment and a water-soluble organic solvent may be attached onto at least a part of the recording region S. The third and fourth pigment are different from each other and from the second and first pigment. Typical pigments are yellow, magenta, cyan and black pigments for use in these above- mentioned inks.

[0054] After having attached one or more aqueous inkjet inks onto at least a part of the recording region S, such that an image is formed, the image may be dried.

[0055] The drying step of the image can be performed by applying an airflow and I or applying heating. The heating step must be performed by using heat sources; examples include equipment for forced-air heating, radiation heating such as IR-radiation, including NIR-, CIR- and SWIR radiation, conduction heating, high-frequency drying, RF, ultrasonic and microwave drying.

[0056] Examples of the heating process include, but are not limited to, heat press, atmospheric steaming, high-pressure steaming, and THERMOFIX. Any heat source can be used for the heating process; for example, an infrared ray lamp is employed.PatXML 13 / 41 GN24010A.4. Application of a varnish

[0057] After having attached the aqueous inkjet ink to at least a part of the recording region S, a varnish may be applied onto at least a part of the image obtained by the adhering of the aqueous inkjet ink.

[0058] All well-known conventional methods can be used for coating or printing the varnish onto at least a part of the image. Examples of the method include air knife coating, blade coating, roll coating, gravure coating and spraying. The advantage of the coating or printing technique is that thick varnish layers in one pass of the recording medium can be obtained to assure sufficient rub resistance of the image.

[0059] The varnish is preferably applied via a jetting technique which allows to apply the varnish selectively onto the image. This means of applying the varnish composition, which is preferably according to an image, has the advantage that the amount of required varnish material is substantially lower than with the other application methods. The jetting heads suitable for jetting the varnish are the same as described in § A.2.

[0060] Finally, the applied varnish is dried according to one of the ways described above for drying the pre-treatment liquid or the aqueous inkjet ink.B. Pre-treatment liquid, aqueous inkjet ink and varnish compositions B.1. Aqueous pre-treatment liquid

[0061] The aqueous pre-treatment liquid to be used in the method according to the invention comprises a fixing agent. The fixing agent serves to crash, precipitate or destabilize the ink colorants such as dyes or pigments and hence fix them to the substrate. This leads to an improved image quality due to less bleeding, less feathering and / or less coalescence.

[0062] The fixing agent is preferably a multivalent metal salt or a cationic polymer.

[0063] The multivalent metal salt may be present in the pre-treatment liquid to improve image quality of the inkjet printed image. Generally, the multivalent metal salt may be any water-soluble multivalent metal salt. In specific examples, the multivalent metal salt may include calcium chloride (CaCh), magnesium chloride (MgCh), magnesium sulfate (MgSC ),PatXML 14 / 41 GN24010 aluminium chloride (AICI3), calcium nitrate (Ca(NOs)2), magnesium nitrate (Mg(NO3)2), magnesium acetate (Mg(CH3COO)2), zinc acetate (Zn(CHsCOO)2) calcium propionate (Ca(C2H5COO)2), or a combination thereof. In further examples, the multivalent metal salt may include a metal cation selected from calcium, copper, nickel, magnesium, zinc, barium, iron, aluminium, chromium, or another multivalent metal.

[0064] Polymeric cationic polymers, suitable as fixing agent in the pre-treatment liquid contain either guanidinium or fully quaternized ammonium functionalities, such as quaternized polyamine copolymers. Generally, the weight average molecular weight (Mw) of the cationic polymer allows viscosity less than 25 cP at 25°C (measured on a Brookfield viscometer). Typical Mw are less than 500.000, and in one aspect, less than 50.000.

[0065] Suitable classes of cationic polymers that can be used include, but are not limited to, quaternized polyamines, dicyandiamide polycations, diallyldimethyl ammonium chloride copolymers, quaternized dimethylaminoethyl(meth)acrylate polymers, quaternized vinylimidizol polymers, alkyl guanidine polymers, alkoxylated polyethylene imines, and mixtures thereof.

[0066] The medium of the pre-treatment liquid according to the invention contains water as a vehicle but may include one or more water-soluble organic solvents.

[0067] The one or more organic solvents may be added for a variety of reasons. For example, it can be advantageous to add a small amount of an organic solvent to improve the dissolution of a compound in the pre-treatment liquid to be prepared, to obtain better penetration in porous substrates or to prevent fast drying of the pre-treatment liquid at the nozzle of the inkjet head. Preferable water-soluble organic solvents are polyols (e.g., ethylene glycol, glycerin, 2-ethyl-2-(hydroxymethyl)-1 ,3-propanediol, tetraethylene glycol, triethylene glycol, tripropylene glycol, 1 ,2,4-butanetriol, diethylene glycol, propylene glycol, dipropylene glycol, butyleneglycol, 1 ,6- hexanediol, 1 ,2-hexanediol, 1 ,5-pentanediol, 1 ,2-pentanediol, 2,2- dimethyl-1 ,3-prapanediol, 2-methyl-2,4-pentanediol, 3-methyl-1 ,5- pentanediol, 3-methyl-1 ,3-butanediol, and 2-methyl-1 ,3-propanediol), N-PatXML 15 / 41 GN24010 hydroxyethyl-pyrrolidon, N-butyl-pyrrolidon, amines (e.g., ethanolamine, and 2-(dimethylamino)ethanol), monohydric alcohols (e.g., methanol, ethanol, and butanol), alkyl ethers of polyhydric alcohols (e.g., diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether), 2,2'-thiodiethanol, amides such as N,N-dimethylformamide, heterocycles such as 2-pyrrolidone and N-methyl- 2-pyrrolidone, and acetonitrile. The humectant is preferably added to the pre-treatment liquid formulation in an amount of 0.1 to 35 wt.% based on the total weight of the liquid.

[0068] The pre-treatment liquid according to the invention may comprise a resin. The resin improves the mechanical and water resistance of the printed image. The resin is preferably selected from a group consisting of an aqueous soluble carboxylic acid containing polymer or salt thereof, a carboxylic acid anhydride containing polymer, a poly(urethane) or copolymer thereof, an acrylate or copolymer thereof, a poly(ester) or copolymer thereof and a poly(styrene) or copolymer thereof, with the proviso that if the resin is a resin particle in the aqueous pre-treatment liquid, it is stabilized by a non-ionic group or non-ionic or amphiphilic compound.

[0069] In a preferred embodiment of the invention, the pre-treatment liquid for inkjet printing according to the invention comprises a carboxylic acid containing polymer or salt thereof or a carboxylic acid anhydride containing polymer. It is believed that carboxylic acid anhydrides are at least partially hydrolysed upon dissolving in the aqueous vehicle of the pre-treatment liquid to a carboxylic acid or salt thereof.

[0070] The effect of the use of carboxylic acid containing polymer or salt thereof or a carboxylic acid anhydride containing polymer in the pre-treatment liquid on image quality might be related to the interaction of these polymers with the fixing agent being multi valent metal ions or cationic polymers present in the pre-treatment liquid. The function of these fixingPatXML 16 / 41 GN24010 agents is to interact with the dispersed colorants from the ink such as dyes or pigments that are negatively charged such as to fix the colorants and avoid image bleed.

[0071] Without being bound by a theory, it is believed that the activity of the fixing agent is better controlled when the carboxylic acid functionalized polymers are present and as such an optimum in image sharpness and ink spreading can be obtained.

[0072] The carboxylic acid containing polymer or salt thereof or the carboxylic acid anhydride containing polymer in the pre-treatment liquid, is not limited to a specific polymer, but should preferably have an acid value equal to 950 mg KOH / g of polymer or less and equal to 450 mg KOH / g of polymer or more, assuming that the carboxylic acid or salt thereof or carboxylic acid anhydride containing polymer is in its acid form. If the acid value is above this range, i.e. for maleic acid and fumaric acid based homopolymers the degree of polymerisation will be too low and consequently providing less interaction with the used multivalent salts leading to a poor ink spreading. If the acid value is below the above range, solubility of the polymer in the pre-treatment liquid may be too low to give sufficient image quality.

[0073] The acid number is defined in mg KOH / g polymer corresponding to the amount of carboxylic acid groups or carboxylate groups. The acid value can be determined either via titration or via calculation. An example of a titration method is described in ASTM D3644-06.

[0074] Preferable carboxylic acid containing polymers are homopolymers such as polyacrylic acid, poly itaconic acid, poly cratonic acid, polymethacrylic acid and, poly(N-(2-hydroxyethyl)maleamic acid), poly(3-(aminocarbonyl)-3- butenoic acid), poly(4-amino-2-methylene-4-oxobutanoic acid) and poly(maleamic acid) and salts of the corresponding homopolymers.

[0075] Other preferable carboxylic acid containing polymers are modified anhydride homopolymers which are hydrolysed by water or a base such as KOH, NaOH, or a water-soluble organic base such as a water soluble mono-amine such as ethanol amine, ammonia and amine terminated polyethylene glycol, e.g. CAS registry number 65421-52-5, 171863-88-0,PatXML 17 / 41 GN2401033881-50-4 and 176703-83-6. Typical anhydride homopolymers or copolymers which can be used for a hydrolysis or post-modification are based on maleic anhydride and itaconic anhydride. When hydrolysed using a base, the carboxylic acid can be present as a salt.

[0076] Other preferable carboxylic acid or carboxylic acid anhydride containing polymers are copolymers such as poly(ethylene-co-maleic anhydride), poly(isobutylene-co-maleic anhydride), poly(isobutene-co-anhydride), poly(vinyl methyl ether-co-maleic anhydride), poly(vinyl acetate-co-crotonic acid), poly(styrene-co-maleic anhydride), poly(acrylic acid-co-maleic acid) and maleic acid-methyl vinyl ether copolymer and salts of the corresponding copolymers.

[0077] Further other preferable carboxylic acid or carboxylic acid anhydride containing polymers are copolymers of anhydride monoamine monomers such as maleamic acid = maleic acid monoamide, fumaric acid monoamide, 3-(carbamoyl)acrylic acid, 3-(aminocarbonyl)-3-butenoic acid, 4-amino-2-methylene-4-oxobutanoic acid, N-(2- hydroxyethyl)maleamic acid and maleimide monomers such as 3- pyrroline-2, 5-dione, 3-maleimidopropionic acid, N-(2- hydroxyethyl)maleimide, N-(2-aminoethyl)maleimide or salts of the corresponding copolymers, or reaction products of anhydride copolymers (e.g. maleic anhydride or itaconic anhydride) and a water soluble monoamine such as ethanol amine, ammonia and amine terminated polyethylene glycol.

[0078] Preferably the carboxylic acid containing polymer or salts thereof or carboxylic acid anhydride containing polymers have an Mw equal to 2000 g / mol or more. The molecular weight is determined via GPC using universal calibration using polyethylene glycol standards. When the Mw is equal or higher that 2000 g / mol, a further improvement in image quality is observed, especially in the spreading of the ink in printing of solids.

[0079] The amount of the carboxylic acid containing polymer or salt thereof or carboxylic acid anhydride containing polymer is preferably from 0.1 to 5 wt.%, more preferably from 0.2 to 4 wt.% based on the total weight of the pre-treatment liquid. An amount below this range does show insufficientlyPatXML 18 / 41 GN24010 an improvement of the image quality and mechanical resistance. An amount above this range can lead to (i) a decrease in jetting performance as a too high polymer content is present in the liquid, (ii) solubility issues leading to sedimentation, (iii) a decrease in image sharpness and an increase in bleeding and feathering.

[0080] In another preferred embodiment of the invention, the resin in the pretreatment liquid may be a resin particle. The resin of the resin particle is preferably selected from the group consisting of poly(urethanes) and copolymers thereof, acrylics and copolymers thereof, poly(esters) and copolymers thereof, poly(styrenes) and copolymers thereof. The resin particle is preferably stabilized by a non-ionic group or a non-ionic or amphiphilic compound. Non-ionic groups are to be understood as groups which are covalently linked to the resin particle.

[0081] To be compatible with multivalent metal salts or cationic polymers, the resin particle is preferably non-ionically stabilized.

[0082] For poly(urethane) dispersions, a non-ionic stabilization can be accomplished by use of polyether diols in the preparation of the poly(urethane) resin. The polyether diol preferably used in the present invention, is Ymer N180, Ymer N120, Ymer N90 or Tegomer D 3403, i.e. a -[2,2-bis(hydroxymethyl)butyl]-u)-methoxy-Poly(oxy-1 ,2-ethanediyl). These diols can be prepared from trimethylol propane oxetane (TMPO). A possible synthesis procedure is described by Fock, J.; Mohring, V., Polyether-1 ,2- and -1 ,3-diols as macromonomers for the synthesis of graft copolymers, 1. Synthesis and characterization of the macromonomers. Die Makromolekulare Chemie 1990, 191 (12), 3045-3057. In general, also other polyether 1 ,2- or 1 ,3-diols can be used.

[0083] For addition polymerization, e.g. preparation of polyacrylates, monomethacrylate or mono-acrylate terminated polyethers can be used for the preparation of graft copolymers with polyether side chains. Examples of suitable macromers for addition polymerisations are listed [0022-0024] of W02023 / 001650A.

[0084] A preferred resin particle incorporated in the pre-treatment liquid, is based on polyurethane particle dispersions. In the polyurethane synthesis onePatXML 19 / 41 GN24010 can implement different polyols for obtaining suitable physical, mechanical or optical properties, such as adhesion towards the substrate used, water resistance, solvent resistance, weather resistance, scratch resistance, gloss or opacity, etc... Regularly used polyols are: polyether polyols, polyester polyols, polycarbonate polyols, polyamide polyol, polyacrylate polyols and polyolefine polyols.

[0085] The amount of the resin particle in the pre-treatment liquid is between 1 wt.%, and 50 wt.%, preferably between 5 wt.% and 45 wt.%, more preferably between 20 wt.% and 40 wt.% with respect to the total solids content of the pre-coat composition. An amount exceeding these values has a negative effect on the jetting reliability of the pre-coat composition if it is applied via a jetting technique.

[0086] Suitable commercially available Pll dispersions are e.g. Vondic 2220, Vondic 1980NE supplied by Toyobo, Printrite DP375 and Printrite PD379 supplied by Lubrizol, Esacote PLI3511 supplied by Lamberti, Neorez R9340 available from DSM and 2019WTT001-3 available from BASF.

[0087] The pre-treatment liquid of the invention may further include a dispersant to improve storage stability of the liquid, preferably a non-ionic dispersant, more preferably a non-ionic polymeric dispersing agent.

[0088] Suitable non-ionic dispersants are polymeric dispersing agents, non-ionic surfactants and segmented polymers, such as graft-, block-, star- branched, comb- or gradient copolymers. These polymeric dispersing agents are preferably amphiphilic structures having at least one segment which is soluble, dispersible or compatible in water-based media. The medium is not necessarily only water but can also be a mixture with other solvents. In water-based pre-treatment liquids and inkjet inks, other water- soluble solvents can be added such as propylene glycol, glycerol, dipropylene glycol monomethyl ether, 2-hydroxyethyl pyrolidone. At least one segment or part of the polymeric dispersing agent should be compatible with the solvent medium of the pre-treatment liquid and ink. Examples of suitable non-ionic surfactants as non-ionic dispersants are listed in [0033-0034] of W02023001650. Examples of suitable polymeric dispersants are listed in [0035-0039] of W02023001650.PatXML 20 / 41 GN24010

[0089] The pre-treatment liquid according to the invention may also contain humectants. Humectants are preferably incorporated in a pre-treatment liquid, especially if this liquid has to be applied by means of a jetting technique such as inkjet or valve jet. Humectants prevent the clogging of nozzles. The prevention is due to its ability to slow down the evaporation rate of the pre-treatment liquid and inkjet ink, especially the water in the liquid. The humectant is preferably an organic solvent having a higher boiling point than water. Suitable humectants include triacetin, N-methyl-2- pyrrolidone, glycerol, urea, thiourea, ethylene urea, alkyl urea, alkyl thiourea, dialkyl urea and dialkyl thiourea, diols, including ethanediols, propanediols, propanetriols, butanediols, pentanediols, and hexanediols; glycols, including propylene glycol, polypropylene glycol, ethylene glycol, polyethylene glycol, diethylene glycol, tetraethylene glycol, and mixtures and derivatives thereof. A preferred humectant is glycerol.

[0090] The humectant is preferably added to the pre-treatment liquid formulation in an amount of 0.1 to 40 wt.% based on the total weight of the liquid.

[0091] The pre-treatment liquid may contain a surfactant. Any known surfactant may be used but preferably a non-ionic oxirane, mono(2-propylheptyl) ether or fatty alcohol alkoxylate or a combination of both is used.

[0092] A biocide may be added to the pre-treatment liquid composition to prevent unwanted microbial growth, which may occur over time. The biocide may be used either singly or in combination. Suitable biocides include sodium dehydroacetate, 2-phenoxyethanol, sodium benzoate, sodium pyridinethion-1 -oxide, ethyl p-hydroxybenzoate and 1 ,2-benzisothiazolin-3- one and salts thereof.

[0093] Preferred biocides are Proxel™ GXL and Proxel™ Ultra 5 available from ARCH UK BIOCIDES and Bronidox™ available from COGNIS.

[0094] A biocide is preferably added to the aqueous medium in an amount of 0.001 to 3 wt.%, more preferably 0.01 to 1.0 wt. %, each based on the total weight of the liquid.

[0095] The pre-treatment liquid may further comprise at least one thickener for viscosity regulation in the liquid. Suitable thickeners are hydrophilicallyPatXML 21 / 41 GN24010 modified Pll thickeners (HELIR) like Thijet 170 from Lamberti and Polyacrylic esters like BYK LP-R21675 from BYK.

[0096] The thickener is added preferably in an amount of 0.01 to 20 wt.%, more preferably 0.1 to 10 wt.% based on the liquid.B.2. Aqueous inkjet ink

[0097] The aqueous inkjet ink as part of the method of the invention, comprise a pigment. The pigment is preferably stabilized by anionic dispersing groups. The pigment can also be additionally stabilised by polymeric dispersants, surfactants or a combination thereof to achieve extra colloidal stability.

[0098] The aqueous medium of the ink contains water and one or more water- soluble organic solvents. Suitable water-soluble organic solvents are described in § B.1.

[0099] In a preferred embodiment of the invention, the aqueous inkjet ink comprises a resin particle and / or a wax particle.

[0100] The aqueous inkjet ink may further comprise a surfactant, a humectant, a resin and a thickener as an additive. Suitable humectants and thickeners are listed in § B.1.

[0101] The pigments in the aqueous inkjet ink according to the invention may be black, white, cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixtures thereof, and the like. A colour pigment may be chosen from those disclosed by HERBST, Willy, et al. Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley - VCH, 2004. ISBN 3527305769.

[0102] Suitable pigments are disclosed in paragraphs

[0128] to

[0138] of WO 2008 / 074548.

[0103] The pigment particles are dispersed in an aqueous medium using a polymeric dispersant, a surfactant or a combination thereof. Self- dispersible pigments can also be used. The latter prevents interaction of the polymeric dispersant with the dispersing groups of binders or capsules which may be included in the inkjet ink (see below).

[0104] A self-dispersible pigment is a pigment having on its surface covalently bonded anionic hydrophilic groups or salt-forming groups, that allow thePatXML 22 / 41 GN24010 pigment to be dispersed in an aqueous medium without using a surfactant or a resin.

[0105] The technology for making self-dispersible pigments is well-known. For example, EP1220879A discloses pigments having attached a) at least one steric group and b) at least one organic ionic group and at least one amphiphilic counterion, wherein the amphiphilic counterion has a charge opposite to that of the organic ionic group that are suitable for inkjet inks. Also EP906371A discloses suitable surface-modified coloured pigments having attached hydrophilic organic groups containing one or more ionic groups or ionizable groups. Suitable commercially available self- dispersible colour pigments are, for example, the CAB-O-JETTM inkjet colorants from CABOT.

[0106] Pigment particles in inkjet inks should be sufficiently small to permit free flow of the ink through the inkjet-printing device, especially at the ejecting nozzles. It is also desirable to use small particles for maximum colour strength and to slow down sedimentation.

[0107] The average pigment particle size is preferably between 0.050 and 1 pm, more preferably between 0.070 and 0.300 pm and particularly preferably between 0.080 and 0.200 pm. Most preferably, the numeric average pigment particle size is no larger than 0.150 pm.

[0108] Also special colorants may be used, such as fluorescent pigments for special effects, and metallic pigments for printing a luxury look of silver and gold colours.

[0109] Suitable white pigments are given by Table 2 in

[0116] of WO 2008 / 074548. The white pigment is preferably a pigment with a refractive index greater than 1.60. The white pigments may be employed singly or in combination. Preferably titanium dioxide is used as pigment with a refractive index greater than 1.60. Suitable titanium dioxide pigments are those disclosed in

[0117] and in

[0118] of WO 2008 / 074548.

[0110] Suitable polymeric dispersants are copolymers of two monomers, but they may contain three, four, five or even more monomers. The properties of polymeric dispersants depend on both the nature of the monomers andPatXML 23 / 41 GN24010 their distribution in the polymer. Co-polymeric dispersants preferably have the following polymer compositions:• statistically polymerized monomers (e.g. monomers A and B polymerized into ABBAABAB);• alternating polymerized monomers (e.g. monomers A and B polymerized into ABABABAB);• gradient (tapered) polymerized monomers (e.g. monomers A and B polymerized into AAABAABBABBB);• block copolymers (e.g. monomers A and B polymerized into AAAAABBBBBB) wherein the block length of each of the blocks (2, 3, 4, 5 or even more) is important for the dispersion capability of the polymeric dispersant;• graft copolymers (graft copolymers consist of a polymeric backbone with polymeric side chains attached to the backbone); and• mixed forms of these polymers, e.g. blocky gradient copolymers.

[0111] Suitable dispersants are DISPERBYKTM dispersants available from BYK CHEMIE, JONCRYLTM dispersants available from BASF and SOLSPERSETM dispersants available from Lubrizol. Other suitable dispersants are Edaplan 482 from Miinzing. A detailed list of non- polymeric as well as some polymeric dispersants is disclosed by MC CUTCHEON. Functional Materials, North American Edition. Glen Rock, N. J.: Manufacturing Confectioner Publishing Co., 1990. p.110-129.

[0112] The polymeric dispersant has preferably a number average molecular weight Mn between 500 and 30000, more preferably between 1500 and 10000.

[0113] The polymeric dispersant has preferably a weight average molecular weight Mw smaller than 100,000, more preferably smaller than 50,000 and most preferably smaller than 30,000.

[0114] The pigments are preferably present in the range of 0.01 to 15 %, more preferably in the range of 0.05 to 10 % by weight and most preferably in the range of 0.1 to 5 % by weight, each based on the total weight of the inkjet ink. For white inkjet inks, the white pigment is preferably present in an amount of 3% to 40% by weight of the inkjet ink, and more preferablyPatXML 24 / 41 GN240105% to 35%. An amount of less than 0.01 % by weight cannot achieve sufficient covering power.

[0115] In a preferred embodiment of the invention the aqueous ink comprises a pigment which is encapsulated by means of a cross-linked polymeric shell. Encapsulated pigments provide printed images having improved physical properties such as water resistance and dry rub resistance with respect to pigments dispersed by means of un-cross-linked polymers.

[0116] Suitable encapsulated pigments are provided by Lubrizol as Diamond HSDX-dispersions and by Fujifilm as RxD pigment dispersions such as APD1000 and APD4000 premium dispersions.

[0117] The inkjet ink composition according to the invention may comprise a resin particle. The resin is often added to the inkjet ink formulation to achieve a good adhesion of the pigment to the substrate. The resin is preferably a polymer and suitable resins can be an acrylic based resin, urethane based or a wax.

[0118] The polyurethane resin is to be incorporated in the ink formulation as a dispersion and may be selected from the group consisting of aliphatic polyurethane dispersions, aromatic polyurethane dispersions, anionic polyurethane dispersions, non-ionic polyurethane dispersions, aliphatic polyester polyurethane dispersions, aliphatic polycarbonate polyurethane dispersions, aliphatic acrylic modified polyurethane dispersions, aromatic polyester polyurethane dispersions, aromatic polycarbonate polyurethane dispersions, aromatic acrylic modified polyurethane dispersions, or a combination of two or more of the above.

[0119] A preferred urethane resin to be used as dispersion in the ink of the invention is a polyester resin including a structural unit containing a urethane bond. Among such resins, a water-soluble or water-dispersible urethane-modified polyester resin is preferred. It is preferable that the urethane-modified polyester resin include at least one structural unit derived from a hydroxyl group-containing polyester resin (polyester polyol) and at least one structural unit derived from an organic polyisocyanate.

[0120] Furthermore, the hydroxyl group-containing polyester resin is a resin formed by an esterification reaction or transesterification reaction betweenPatXML 25 / 41 GN24010 at least one polybasic acid component and at least one polyhydric alcohol component.

[0121] A preferred polyurethane resin to be included in the ink of the invention is a polyurethane resin obtainable by reacting a polyester polyol, a polyether diol, a polyol containing an anionic group and a polyisocyanate. A particular preferred polyurethane resin is a polyurethane resin obtainable by reacting a polyester polyol, a polyether diol, a polyol containing an anionic group and a polyisocyanate, and wherein the polyester polyol is obtained by reacting an aromatic polycarboxylic acid and a polyol. Examples of suitable polyurethane resins and their preparations are disclosed in the patent application EP3532545A.

[0122] Some examples of suitable polyurethane dispersions are NEOREZ R-989, NEOREZ R-2005, and NEOREZ R-4000 (DSM NeoResins); BAYHYDROL UH 2606, BAYHYDROL UH XP 2719, BAYHYDROL UH XP 2648, and BAYHYDROL UA XP 2631 (Covestro); DAOTAN VTW 1262 / 35WA, DAOTAN VTW 1265 / 36WA, DAOTAN VTW 1267 / 36WA, DAOTAN VTW 6421 / 42WA, DAOTAN VTW 6462 / 36WA (Allnex); and SANCURE 2715, SANCURE 20041 , SANCURE 2725 (Lubrizol Corporation), for example, or a combination of two or more of the above.

[0123] Acrylic based resins include polymers of acrylic monomers, polymers of methacrylic monomers, and copolymers of the aforementioned monomers with other monomers. These resins are present as a suspension of particles having an average diameter of about 30 nm to about 300 nm. The acrylic latex polymer is formed from acrylic monomers or methacrylic monomer residues. Examples of monomers of the acrylic latex polymer include, by way of illustration, acrylic monomers, such as, for example, acrylate esters, acrylamides, and acrylic acids, and methacrylic monomers, such as, for example, methacrylate esters, methacrylamides, and methacrylic acids. The acrylic latex polymer may be a homopolymer or copolymer of an acrylic monomer and another monomer such as, for example, a vinyl aromatic monomer including, but not limited to, styrene, styrene butadiene, p-chloromethylstyrene, divinyl benzene, vinyl naphthalene and divinylnaphthalene.PatXML 26 / 41 GN24010

[0124] Some examples of suitable acrylic latex polymer suspensions are, JONCRYL 537 and JONCRYL 538 (BASF Corporation, Port ArthurTX); CARBOSET GA-2111 , CARBOSET CR-728, CARBOSET CR-785, CARBOSET CR-761 , CARBOSET CR-763, CARBOSET CR-765, CARBOSET CR-715, and CARBOSET GA-4028 (Lubrizol Corporation); NEOCRYL A-1110, NEOCRYL A-1131 , NEOCRYL A-2091 , NEOCRYL A- 1127, NEOCRYL XK-96, and NEOCRYL XK-14 (DSM); and BAYHYDROL AH XP 2754, BAYHYDROL AH XP 2741 , BAYHYDROL A 2427, and BAYHYDROL A2651 (Bayer), for example, or a combination of two or more of the above.

[0125] The concentration of the resin in the inkjet ink according to the invention is at least 1 wt.% and preferably lower than 30 wt.%, more preferably lower than 20 wt.% with respect to the total weight of the ink.

[0126] The aqueous inkjet ink of the invention may also comprise a wax. The wax in the ink improves wet rub or wet scratch resistance of the printed layer.

[0127] As such, the wax may be polyethylene waxes, petroleum waxes, paraffin waxes, carnauba waxes, polypropylene waxes, crystalline and microcrystalline waxes, amide waxes (oleamide, stearamide, erucamide, cyclic amide, etc... ), and combinations thereof. In an aspect of the invention, the wax may be a high-density polyethylene wax.

[0128] In an aspect of the invention, the wax may be a polyethylene wax or modified paraffin wax. An example of polyethylene wax includes high density polyethylene (HDPE) wax, which has a density ranging from about 0.93 g / ml to 0.97 g / ml.

[0129] Some specific examples of wax that may be used include those of the JONCRYL Wax series (such as JONCRYL Wax 22, JONCRYL Wax 26, and JONCRYL Wax 120 available from BASF Corp.), those of the AQUACER series (such as AQUACER 498, AQUACER 501 , AQUACER 505, AQUACER 513, AQUACER 530, AQUACER 531 , AQUACER 535, AQUACER 537, AQUACER 539, and AQUACER 552 available from BYK- Gardner, Columbia, Md. ) and Liquilube 404E from Lubrizol .PatXML 27 / 41 GN24010

[0130] The wax may be present in the ink in an amount ranging from 3 to 30 wt.%, more preferably from 5 to 25 wt.%, relative to the total solids weight of the ink.

[0131] The inkjet ink composition according to the invention may comprise a capsule. Capsules, more preferably, nanocapsules are often incorporated in inkjet ink formulations to encapsulate colouring agents (US2009227711A, JP2004075759) or to encapsulate reactive ingredients which can cross-link. Particularly useful are the nanocapsules disclosed in WO201 5158649 [0037-0110]: The nanocapsules have a polymeric shell surrounding a core containing reactive chemistry. The shell material includes polyureas, polyurethanes, polyesters, polycarbonates, polyamides, melamine based polymers and mixtures thereof, with polyureas and polyurethanes being especially preferred. Other particularly useful nanocapsules are disclosed in WO2016165970 [0051-0138]: the nanocapsules are self-dispersable and include a dispersing group covalently coupled to the shell polymers. The core of the nanocapsules in WO201 5158649 [0037-0110] and WO2016165970 [0051-0138] comprise reactive chemistry which is able to form a reaction product upon application of heat and / or light, allowing a wide variety of substrates to be addressed. Other suitable reactive chemistry is the one which is activated upon radiation as described in WO2015158649 [0068-0110],

[0132] The capsules are preferably present in the inkjet ink in an amount of no more than 30 wt.%, preferably between 5 and 25 wt.% based on the total weight of the ink.

[0133] The ink composition may contain a surfactant. Any known surfactant may be used but preferably a glycol surfactant and / or an acetylene alcohol surfactant and / or a polysiloxane surfactant is used. The use of the acetylene glycol surfactant and / or the acetylene alcohol surfactant and / or the polysiloxane surfactant further reduces bleeding to improve printing quality, and also improves the drying property in printing to allow highspeed printing.

[0134] The acetylene glycol surfactant and / or the acetylene alcohol surfactant is preferably one or more selected from 2, 4, 7, 9-tetramethyl-5-decine-4, 7-PatXML 28 / 41 GN24010 diol, alkylene oxide adducts of 2,4,7, 9-tetramethyl-5-decine-4, 7-diol, 2,4- dimethyl-5-decin-4-ol, and alkylene oxide adducts of 2,4-dimethyl-5-decin- 4-oL These are available, for example, from Air Products (GB) or from Nissin Chemical Industry, e.g Olfine series (registered trademark) such as Olfine E1010 and Surfynol (registered trademark) series, as Surfynol 465, Surfynol 104H and Surfynol 61.

[0135] A biocide may be added to the ink composition to prevent unwanted microbial growth, which may occur over time. Suitable biocides are listed in § B.1. The biocide is preferably added to the aqueous medium in an amount of 0.001 to 3 wt.%, more preferably 0.01 to 1.0 wt.%, each based on the total weight of the ink.B.3. Varnish

[0136] The varnish which may be used in the method according to the invention is used to protect the inkjet printed image against wet & dry rubbing, scratches and solvents. The varnish therefor, comprises water and resin particles.

[0137] Examples of the resin particles included in the varnish include well-known resins such as a urethane-based resin, an acrylic resin, a fluorene-based resin, a polyolefin-based resin, a rosin modified resin, a terpene-based resin, a poly-ester-based resin, a polyamide-based resin, an epoxy-based resin, and a vinyl chloride-based resin. The vinyl chloride-based resin includes a vinyl chloride copolymer such as a vinyl chloride-vinyl acetate copolymer. These resins may be used alone, or two or more thereof may be used in combination.

[0138] Among the aforementioned resin particles, the resin included in the varnish is preferably a urethane-based resin, an acrylic resin, a styrene- acrylic resin or a polyolefin-based resin.

[0139] As the urethane-based resin, commercially available products may be used, for example, commercially available products such as SUPER FLEX 460, 460s, 840, E-4000 (trade name, manufactured by DKS Co., Ltd.), RESAMINE D-1060, D-2020, D-4080, D-4200, D-6300, D-6455 (trade name, manufactured by Dainichiseika Color & Chemicals Mfg.Co., Ltd.),PatXML 29 / 41 GN24010TAKELAC WS-6021 , W-512-A-6 (trade name, manufactured by Mitsui Chemicals Polyurethanes INC.,), SUNCURE 2710 (trade name, manufactured by LUBRIZOL Corporation), and PermalinUA-150 (trade name, manufactured by Sanyo Chemical Industries, Ltd.) may be used.

[0140] The acrylic resin is a general name of a polymer obtained by polymerizing at least an acrylic monomer such as (meth)acrylic acid and (meth)acrylate, and the examples thereof include a (meth)acryl resin obtained from the acrylic monomer, and a copolymer of the acrylic monomer and monomers other than the acrylic monomer (for example, a vinyl based monomer such as styrene). Acrylamide and acrylonitrile can be also used as the acrylic monomer. The acrylic resin can be non-reactive or self-cross linking. As a resin emulsion using the acrylic resin as a raw material, commercially available products may be used, and the examples thereof include FK-854 (trade name, manufactured by CH I RIKA. Co., ltd.), Mowinyl 952B, 718A (trade name, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.), Nipol LX852, and LX874 (trade name, manufactured by ZEON Corporation).

[0141] Examples of styrene-acrylic resins include poly(styrene-alkyl acrylate), polystyrene-1 , 3-diene), poly(styrene-alkyl methacrylate), polystyrenealkyl acrylate-acrylic acid), poly(styrene-1 , 3-diene-acrylic acid), poly(styrene-alkyl methacrylate-acrylic acid), poly(styrene-alkylacrylate- acrylonitrile-acrylic acid), and poly(styrene-1 , 3-diene-acrylonitrile-acrylic acid). Other examples include poly(styrene-propyl acrylate), poly(styrene- butylacrylate), poly(styrene-butadiene-acrylic acid), poly(styrene- butadiene-methacrylic acid), poly(styrene-butadieneacrylonitrile-acrylic acid), poly(styrene-butyl acrylateacrylic acid), poly(styrene-butyl acrylatemethacrylic acid),poly(styrene-butyl acrylate-acrylononitrile), poly(styrenebutyl acrylate-acrylononitrile-acrylic acid). Commercial styrene-acrylic resins are Neocryl D2101 (Covestro) and Bonron PS001 and Bonron PS002 (Mitsui).

[0142] Other suitable resins include Esajet acrylic latices from Lamberti such as Esajet AC 20, Esajet AC22, Esajet AC 29, Esajet AC31 and Esajet AC03.PatXML 30 / 41 GN24010

[0143] The varnish contains the resin in an amount from 1 wt.% to 30 wt.% with respect to the total mass of the liquid. When the content of the resin in the varnish is within the aforementioned range, the effect of improving rub resistance of the image tends to become more excellent. More preferably the varnish contains the resin in an amount from 3 to 15 wt.% with respect to the weight of the liquid. Most preferably the varnish contains the resin in an amount from 5 wt.% to 12 wt.% with respect to the weight of the liquid.

[0144] The varnish as comprised in the liquid set according to the invention may comprise a wax. The wax may improve the durability of the printed image. Generally, any suitable wax may be used in the varnish composition. Suitable waxes are described in § B.2.

[0145] The varnish may contain a surfactant. Suitable surfactants are listed in §B.2., but polyether siloxane surfactants are preferable. Humectants and biocides may be added to the varnish. Suitable humectants and biocides are listed in §.B.1.

[0146] The varnish may further comprise a water-soluble polymer selected from the group of linear PPO-PEO copolymers and arylethylphenyl polyglycol ethers as described in unpublished patent application EP23161106.2 A.

[0147] The varnish may further comprise a crosslinking agent. Any water soluble or water dispersible crosslinking agent can be used, but preferably the crosslinking agent is a carbodiimide such as described in the unpublished patent application EP23164057.4 A.C. Image recording apparatus

[0148] One of the embodiments of the invention is the provision of an image recording apparatus for forming an image on a substrate.

[0149] The recording apparatus (see Fig. 1) comprises a conveyor mechanism (18) configured to convey a substrate in a conveyance direction; and an inkjet printing head (11) for applying pre-treatment liquid drops through a nozzle plate (16), having a drop mass equal to 6 ng / drop or less and equal to 1 ng / drop or more, onto at least a part of a recording region S of an upper surface of the substrate with a drop density being equal to 55 drops / mm2or more and equal to 1600 drops / mm2or less, the pre-PatXML 31 / 41 GN24010 treatment liquid contains a fixing agent; the distance between the nozzle plate of the print head and the upper surface of the substrate is equal to 2.5 mm or less; and an inkjet printing head (12) (13) (14) (15) for adhering an aqueous inkjet ink containing a pigment and a water-soluble organic solvent onto at least a part of the recording region S.

[0150] In a more preferred embodiment, the inkjet heads are fixed inline heads. This head configuration provides the highest achievable printing speeds.

[0151] The conveying mechanism is suitable for conveying substrates as sheet material and / or as web material.D. ExamplesD.1. Materials

[0152] All materials used in the following examples were readily available from standard sources such as Aldrich Chemical Co. (Belgium) and Acros (Belgium) unless otherwise specified. Where used, water is demineralised water (D.l. water). Where used, water is demineralised water (D.l. water).• Proxel is a 5 wt.% aqueous solution of 1 ,2-benzisothiazolin-3-one available as Proxel™ K from YDS CHEMICALS NV.• Surfynol 104PG50 is a 50 wt.% solution of 2,4,7,9-Tetramethyl-5- decyne-4,7-diol in propylene glycol from Evonik• Printrite DP379 is an aqueous 30 wt.% dispersion of a polyether based polyurethane from Lubrizol• Aquacer 530 is an aqueous dispersion containing 32 wt.% oxidized HDPE wax from BYK• Kauropal K933 is a non-ionic oxirane, mono(2-propylheptyl) ether from BASF• Pluronic PE10500 is a block copolymer of ethylene oxide and propylene oxide, with 50% EC and a Mw of 6500 from BASF• Pluronic PE10500 solution is an 18 wt.% in water of a block copolymer of ethylene oxide and propylene oxide, with 50% EC and a Mw of 6500 from BASF• Tego Foamex 822 is a polyether siloxan copolymer from Evonik• Mg(NOs)2.6H2O is Magnesium nitrate hexahydrate from Merck GroupPatXML 32 / 41 GN24010• PG is propane 1 ,2-diol from Merck• ZEMAC E60 is poly(ethylene-co-maleic anhydride) having a Mw from 60.000 g / mole a calculated acid value of 779 mg KOH / g of from Aurorium• Sokalan CP12S is a poly(acrylic acid-co-maleic acid) having a Mw of 3000 g / mole, a calculated acid value of 826 mg KOH / g from BASF• Ultralube GA1042 is an aqueous dispersion containing 35 wt% of HDPE wax from Keim additec surface GmbH• Hydropalat WE3120 is a fatty alcohol alkoxylate from BASF• Ensocoat is a coated cardboard liner from Stora Enzo, having an absorpability of 4.4 ml / m2according to the Bristow method and a surface energy of 37.6 mJ / m2• HSDCX1 is a 19.7 wt.% PB15:3 dispersion in water from Lubrizol Corp.• HSDYX1 is a 20 wt.% PY74 dispersion in water from Lubrizol Corp.• HSDKX1 is a 20 wt.% Pigment Black 7 dispersion in water from Lubrizol Corp.• HSDMX1 is a 19 wt.% PR122 dispersion in water from Lubrizol Corp.D.2. Evaluation methodsD.2.1. Determination of the optimal drop density of the pre-treatment liquid.

[0153] To determine the optimal drop density of a cardboard liner sheet as substrate, the card board liner sheet is introduced in a single pass printer (fixed inline head) equipment according to Fig. 1 at a conveying speed of 75 m / min.

[0154] The single pass printer equipment comprises an inkjet print head (11) being a Samba G3L from FujiFilm Dimatix having a nozzle density of 1200 dpi, for applying pre-treatment liquid drops onto a recording region S of the cardboard liner. The distance between the upper surface of the card board liner sheet and the nozzle plate of printhead (16) is 1.5 mm. Parallel to the printhead (11), the same type inkjet print heads (12) and (13) for applyingPatXML 33 / 41 GN24010 coloured inkjet ink drops are positioned. The distance between the printheads (11) and (12) is 300 mm.

[0155] In the single pass printer equipment, pre-treatment liquid drops are applied through the nozzle plate of print head (16) onto the recording region S of the cardboard liner in a single pass mode. The drop density of the pretreatment liquid was varied from 0 drops / mm2to 2232 drops / mm2and the average drop mass was varied from 2.0 ng / drop to 8.5 ng / drop.

[0156] The average drop mass of the pre-treatment liquid was measured by adhering a pre-determined amount of drops onto a Poly-Back Universal Mat from New Pig (Glasgow, UK) and determine the weight increase of the sheet after drying. The drop mass of the pre-treatment liquid as jetted through the nozzle plate of a G3L Samba Dimatix print head can be modified by means of varying the pressure wave form pulses driving the printhead (see How to Optimize a Waveform (imagexpert.com)

[0157] After the adhering of the pre-treatment liquid drops onto the recording region S of the cardboard liner, an image according to Fig. 2 is printed by adhering drops of a yellow pigment comprising aqueous inkjet ink to the recording region S with the inkjet print head (12). The drop mass of this inkjet ink is 5 ng / drop and is applied in a single pass mode at a resolution of 1200 dpi x 1200 dpi and a dot coverage of 95%.

[0158] Following to the printing of the image from Fig. 2, an image according to Fig.3 is then printed by adhering drops of a magenta pigment comprising aqueous inkjet ink onto the horizontal bar of the image from Fig. 2. with the inkjet print head (13) (also having a drop mass of 5 ng / drop) in a single pass mode at a resolution of 1200 dpi x 1200 dpi and a dot coverage of 100%).

[0159] The obtained image is according to Fig. 4 and is consequently dried at 200 °C during about 5 s.

[0160] The level of bleeding of the printed magenta ink into the printed yellow ink is evaluated visually through a microscope at a magnification of 50x and scored according to the criteria of Table 1 .Table 1 : Evaluation criteria of ink bleeding of magenta ink into yellow ink.PatXML 34 / 41 GN24010

[0161] A score of 3 and 4 is of practical use for printed images on packaging.D.2.2. Determination of the image quality of solid parts and text characters of a printed image

[0162] To determine the colour density of solid images of primary colours, a test image comprising separated CMYK bars with a colour density of 0 to 100% in steps of 5% was printed at the optimal drop density of the pretreatment liquid drops (see § D.5.). The colour density of the CMYK bars was determined using a 11 PRO3 X-RITE equipment.

[0163] Therefore, sheets of cardboard liners are introduced in the single pass printer (fixed inline head) equipment according to Fig. 1 at a conveying speed of 75 m / min. After having adhered pre-treatment liquid drops through the nozzle plate of print head (11) onto the recording region S of the cardboard liner at an optimal drop density (as determined in § D.2.2.), the image comprising separated CMYK bars were printed onto the recording region S of the cardboard liner by means of the printheads (12), (13), (14) and (15), respectively. The black text characters were also printed by means of printhead (15). The sharpness of text characters at the optimal drop density of the pre-treatment liquid drops was evaluated by printing black text characters at 2 to 8 pt onto the recording region S of the cardboard liner and visually evaluated by means of a microscope at a magnification of 50x.

[0164] The image quality of the black text characters was scored a value of 3 for excellent sharp and dense characters, a score of 2 for dense and sharp characters, while a score of 1 was used for blurred characters having a low black density.PatXML 35 / 41 GN24010D.2.3. Pre-treatment liquid recirculation test

[0165] A recirculation test is carried out to test the suitability of the pre-treatment liquid to be used in a printhead equipped with a recirculating ink system.

[0166] To conduct a recirculation test, a device constantly drives an amount of 3.5 - 4 L of pre-treatment liquid within a loop and through a filter mesh of 10 pm size at a flow rate of 1.0 - 1.3 L / min. at a temperature of 32 °C. The pressures of the pre-treatment liquid before and after the filter mesh are monitored throughout the complete testing period. The pressure drop across the filter is calculated according to following equation:Pressure drop=Pressure (before entering the filter) - Pressure (after exiting the filter)

[0167] Over time, an increase in pressure drop can be observed indicating the clogging of the filter mesh. A suitable pre-treatment liquid demonstrates no substantial pressure drop increase after 10000 minutes of recirculation.D.3. Preparation of aqueous pre-treatment liquids

[0168] Pre-treatment liquids were prepared by mixing the ingredients given in Table 2. The weight percentages are relative to the total weight of the pretreatment liquid. The raw materials were used as supplied without any further treatments.Table 2: Composition of pre-treatment liquids according to the inventionPatXML 36 / 41 GN24010D.4. Preparation of aqueous inkjet ink compositions

[0169] Aqueous inkjet inks were prepared by adding all ingredients as listed in Table 3. All ingredients are expressed in wt.% based on the total weight of the ink. Water was added to complete the ink to the desired pigment concentration.Table 3: Composition of aqueous inkjet inks according to the inventionD.5. Results of evaluation of image quality

[0170] Firstly, it was determined from which amount of drop density of the pretreatment liquid PL-1 on, the lowest level of ink bleeding is obtained. This value is defined as the optimal drop density of the pre-treatment liquid.

[0171] Indeed, a higher amount of adhered pre-treatment liquid will not bring additional benefits regarding image quality of the printed image such aPatXML 37 / 41 GN24010 bleeding, but will decrease printing speed as the amount of liquid to be dried increases. The evaluation of the ink bleeding is as described in § D.2.1.

[0172] Table 4 lists the bleeding levels of magenta ink INK-M into yellow ink INK- Y in function of the drop density and drop mass of the pre-treatment liquid PL-1.Table 4: Bleeding levels of magenta ink INK-M in yellow ink INK-Y in function of the drop density and the average drop mass of the pre-treatment liquid PL-1.

[0173] From Table 4 it follows that the optimal drop density of the pre-treatment liquid PL-1 is 670 drops / mm2for an average drop mass of 2.0 ng; 447 drops / mm2for an average drop mass of 4.8 ng and 335 drops I mm2for an average drop mass of 8.5 ng of the pre-treatment liquid.

[0174] At the optimal drop density of the pre-treatment liquid adhering, the optical density of the solid parts of the image and image quality of black text characters was then determined according to § D.2.2.

[0175] The most optimal drop density of the pre-treatment liquid PL-1 and corresponding optical density of solids (100 %) of yellow, magenta, cyan and black (printed with INK-Y, INK-M, INK-C INK-K respectively) together with the image quality of the black text characters (printed with INK-K) are listed in Table 5.PatXML 38 / 41 GN24010Table 5: Optical density of 100% solids and image quality of text characters in function of drop mass of pre-treatment liquid at the optimal drop density

[0176] It can be observed from Table 5that the colour density of the solids and the image quality of the black text characters are significantly higher when printed according to the recording method of the invention with pretreatment liquid drops having an average drop mass equal to or less than 6 ng / drop and equal to or more than 1 ng / drop than with the pre-treatment liquid drops having an average drop mass above 6 ng / drop.D.6. Results of evaluation of recirculation behaviour of pre-treatment liquid

[0177] The recirculation behaviours of the pre-treatment liquids PL-1 and PL-2 were tested for recirculation according to § D.2.3. After 10,000 minutes of recirculation, the wax containing pre-treatment liquid PL-2 showed a pressure drop increase of more than 15%; the pre-treatment liquid PL-1 containing an aqueous soluble carboxylic acid containing polymer or salt thereof, did not show any pressure drop increase throughout the 10,000 minutes of recirculation.

[0178] It can be concluded that pre-treatment liquids containing an aqueous soluble carboxylic acid containing polymer or salt thereof do show excellent image quality when combined with aqueous inkjet inks and at the same time do not result in filter clogging when used in recirculation type inkjet heads.

Claims

1.PatXML 39 / 41 GN24010ClaimsClaim 1 . A method of image recording, comprising following steps a) Providing a substrate (17); and b) Applying through a nozzle plate (16) of an inkjet head (11), drops of an aqueous pre-treatment liquid having an average drop mass equal to 6 ng / drop or less and equal to 1 ng / drop or more, onto at least a part of a recording region S of an upper surface of the substrate (17) with a drop density, the aqueous pre-treatment liquid comprises a fixing agent; and c) Attaching an aqueous inkjet ink onto at least a part of the recording region S to form an image, the aqueous inkjet ink comprises a pigment and a water- soluble organic solvent; characterized in that the drop density is equal to 55 drops / mm2or more and equal to 1600 drops / mm2or less and the distance between the nozzle plate (16) and the upper surface of the substrate (17) is equal to 2.5 mm or less.Claim 2. The method of image recording according to Claim 1 wherein after step c), a second aqueous inkjet ink is attached onto at least a part of the recording region S to form an image, the second aqueous inkjet ink comprises a second pigment and a water soluble organic solvent, the second pigment is different from the pigment in the aqueous inkjet ink of step c).Claim 3. The method of image recording according to any of the preceding claims wherein the fixing agent is a multivalent metal salt or a cationic polymer.Claim 4. The method of image recording according to any of the preceding claims wherein the average drop mass is equal to 4.8 ng / drop or less and equal to 1 ng / drop or more.Claim 5. The method of image recording according to any of the preceding claims wherein the inkjet head (11) is a through-flow head.Claim 6. The method of image recording according to any of the preceding claims wherein the pre-treatment liquid comprises further a resin.Claim 7. The method of image recording according to Claim 6 wherein the resin is selected from a group consisting of an aqueous soluble carboxylic acid containing polymer or salt thereof, a carboxylic acid anhydride containing polymer, a poly(urethane) or copolymer thereof, an acrylate or copolymer thereof, a poly(ester) or copolymer thereof and a poly(styrene) or copolymerPatXML 40 / 41 GN24010 thereof, with the proviso that if the resin is a resin particle in the aqueous pretreatment liquid, it is stabilized by a non-ionic group or non-ionic or amphiphilic compound.Claim 8. The method of image recording according to Claim 7 wherein the aqueous soluble carboxylic acid containing polymer or salt thereof or the carboxylic acid anhydride containing polymer have an acid value equal to 950 mg KOH / g of polymer or less and equal to 450 mg KOH / g of polymer or more.Claim 9. The method of image recording according to any of the preceding claims wherein the substrate has an absorbability of 10 ml / m2or less of water within a 30 ms1 / 2from the start of contacting the water according to Bristow method.Claim 10. The method of image recording according to any of the preceding claims wherein the substrate is a cardboard liner.Claim 11 . The method of image recording according to Claim 10 wherein the cardboard liner is a coated cardboard liner.Claim 12. The method of image recording according to any of the preceding claims and further applying a varnish onto at least a part of the image and applying an air flow and / or heat to dry the varnish.Claim 13. The method of image recording according to Claim 12 wherein the varnish comprises water and resin particles.Claim 14. A recording apparatus comprising:(i) a conveyor mechanism configured to convey a substrate in a conveyance direction (18); and(ii) inkjet printing head (11) for applying pre-treatment liquid drops through a nozzle plate (16), having a drop mass equal to 6 ng / drop or less and equal to 1 ng / drop or more, onto at least a part of a recording region S of an upper surface of the substrate with a drop density; and(iii) a distance between the nozzle plate (16) of the print head (11) and the upper surface of the substrate (17) is equal to 2.5 mm or less; and(iv) an inkjet printing head (12) for adhering an aqueous inkjet ink containing a pigment and a water-soluble organic solvent onto at least a part of the recording region S;PatXML 41 / 41 GN24010 characterized that the drop density is equal to 55 drops / mm2or more and equal to 1600 drops / mm2or less.Claim 15. The printing apparatus according to wherein the inkjet printing head (11) is a through-flow head.

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