Inkjet recording method and apparatus therefor

Abstract

An image recording method comprising the steps of: a. providing a substrate; b. applying to at least a portion of a recording area S of a surface of the substrate droplets of an aqueous pre-treatment fluid having a droplet mass equal to 15 ng / drop or less and equal to 1 ng / drop or more, wherein the droplet density is equal to 55 droplets / mm 2 or more and equal to 1600 droplets / mm 2 or less, the pre-treatment fluid comprising a fixative and a resin; c. affixing to at least a portion of the recording area S an aqueous inkjet ink comprising a pigment and a water-soluble organic solvent. An apparatus suitable for carrying out the recording method is also provided.

Description

Technical Field

[0001] This invention relates to an inkjet recording method and apparatus in a two-component inkjet recording system. More specifically, this invention relates to an inkjet recording method and apparatus in which image quality is improved on a substrate, and more particularly to a substrate used as packaging material. Background Technology

[0002] Inkjet printing technology is a growing field of application for printing substrates used for display purposes (such as signs and posters) but also for packaging purposes (such as plastic foil, corrugated cardboard liners, and folding cardboard liners). In printing on cardboard liners, flexographic or offset printing is typically used to apply a pre-coating or primer.

[0003] In recent years, inkjet recording methods using water-based inks have been used not only to record images on recording media with excellent ink absorption (e.g., plain paper), but also on recording media with less ink absorption (low absorbency) (e.g., art paper, coated paper, corrugated board lining, folded cardboard), or on recording media that absorb almost no ink (non-absorbent) (e.g., plastic film). Water-based inks, including water as a base, have advantages from a global environmental and safety perspective.

[0004] Compared to non-water-based inks, water-based inks tend to be repelled on recording media with low absorbency or non-absorbency. Therefore, color uniformity in recorded images is more likely to occur on recording media with low ink absorbency or non-absorbency.

[0005] From this perspective, attempts have been made to use primers or pretreatment solutions (sometimes called reaction solutions) to achieve reaction with water-based ink compositions on low-absorption or non-absorbent recording media.

[0006] To obtain high-quality images on ink-absorbing substrates, the pretreatment solution must also be able to receive the ink and retain or fix the colorants within it. Specifically, the pretreatment solution must be able to retain or fix the colorants on or near the surface of ink-permeable substrates (e.g., porous substrates), thereby improving the color gamut of the printed image and significantly reducing bleeding and feathering of colored inks compared to substrates not treated with the pretreatment solution.

[0007] The possibility of applying the pretreatment liquid only to the portion of the substrate that will bear the image makes it possible to reduce the total consumption of pretreatment liquid in the printing process.

[0008] Printing images on packaging materials such as plastic foil, corrugated cardboard liners, and folding cardboard requires high mechanical resistance to abrasion and scratches under both dry and wet conditions. To achieve this, resins are included in water-based inkjet inks. However, it is known that resins can negatively impact inkjet reliability, especially at high printing speeds, by altering the viscoelastic properties of the ink. It is also known that resins can negatively affect ink stability due to the interaction between the resin and the dispersed pigment particles.

[0009] Therefore, it is sometimes advantageous to incorporate resin into the pretreatment solution so that the amount of resin in the inkjet ink can be reduced or eliminated without negatively affecting the physical properties of the printed image, such as mechanical resistance, solvent resistance, and water resistance.

[0010] WO2018 / 017089A describes a sprayable pretreatment liquid as a packaging material for corrugated linerboard or containerboard packaging. The pretreatment liquid composition contains a polyvalent metal salt, wax, dispersant, latex, and water. The latex includes monomers such as styrene, 1,3-butadiene, acrylonitrile, or combinations thereof.

[0011] WO2023 / 001650 discloses a jettable pretreatment composition for corrugated printing, comprising a water-soluble polyvalent metal salt, wax, nonionic dispersant, and resin particles. While the pretreatment composition may be jettable, in a preferred embodiment, the pretreatment composition is applied at a layer thickness of 4 µm.

[0012] US 2018 / 0244078, EP 3366486A1 and US 2020 / 270473A1 disclose an inkjet recording method comprising a reactive liquid attachment step ejected from an inkjet head, the reactive liquid being in droplet form and containing an aggregating agent, which may be a polyvalent metal salt or a cationic resin, but without any other resin.

[0013] In the packaging materials printing industry, there is a trend toward increasing productivity, which requires high printing speeds and the combination of single-pass printing equipment with high conveying speeds of packaging materials such as plastic foil and substrates.

[0014] As a result, it was observed that the pretreated droplets barely dried before adhering to the pretreated substrate. This was even more pronounced when the substrate was coated paper exhibiting low ink absorbency (which resulted in a reduced ink absorption rate) or when the substrate was non-absorbent (e.g., plastic foil, which does not exhibit ink absorbency).

[0015] US 1053085055 discloses a recording method in which inkjet ink is applied within 30 seconds after a pretreatment liquid is applied to a coated paper substrate. The pretreatment droplets are dried by heating the substrate before, during, or after the application of the pretreatment droplets. However, this implies additional heating equipment, which increases the cost and complexity of the printing equipment.

[0016] One drawback of pre-treating droplets when attaching water-based ink droplets to images containing solid colored areas is the appearance of unevenness and white streaks in these solid areas. This is even more pronounced in solid areas composed of composite colors (green, red, blue, and black) with high ink loads.

[0017] There is still a need for a recording method that provides acceptable image quality for inkjet-printed images on various substrates used for packaging, including ink-absorbing substrates (e.g., paper, cardboard liners), low-ink-absorbing substrates (e.g., coated paper, coated cardboard liners), and non-absorbent substrates (e.g., plastic films), and exhibits excellent mechanical resistance in the dry state of the printed image and when water is applied to the image. Summary of the Invention

[0018] One object of the present invention is to provide a solution to the above-mentioned problems. This object has been achieved by providing an image recording method as defined in claim 1.

[0019] Another embodiment of the present invention is to provide an inkjet recording apparatus as defined in claim 15.

[0020] Other features, elements, steps, characteristics, and advantages of the invention will become more apparent from the following detailed description of preferred embodiments of the invention. Specific embodiments of the invention are also defined in the dependent claims. Brief description of the attached diagram Figure 1 A pattern used in inkjet printing to evaluate the image quality of the resulting image. The pattern consists of solid areas and negative text in varying sizes, ranging from 1 pt to 16 pt. Detailed Implementation

[0022] A. Image recording methods The image recording method according to the present invention includes the following steps: a. Providing base materials; and b. Applying aqueous pretreatment droplets with a droplet mass of 15 ng / drop or less and 1 ng / drop or greater to at least a portion of the recording area S on the substrate surface, wherein the droplet density is 55 drops / mm². 2 Or greater than or equal to 1600 drops / mm 2Or smaller, the pretreatment solution contains a fixative and a resin; and c. Attaching water-based inkjet ink to at least a portion of the recording area S, said water-based inkjet ink comprising pigments and water-soluble organic solvents.

[0023] In-depth research has revealed that when the above-described image recording method, which includes steps a), b), to c), is applied, the droplet density of the pretreatment liquid in step b) is 55 drops / mm. 2 Up to 1600 drops / mm 2 Within an even smaller range, the unevenness of solid areas in inkjet-printed images is significantly reduced, while ink bleeding remains at an excellent level. Sometimes, optimal droplet density can be observed within the ranges mentioned above, where both bleeding and solid unevenness are minimized.

[0024] Without theoretical constraints, it is considered that the spreading of water-based inkjet droplets on a liquid pretreatment coating or on high-density pretreatment droplets still in a liquid state (because they have not yet been absorbed by the paper, and the solvent in the droplets has not evaporated before adhering to the inkjet droplets) is insufficient to ensure uniform droplet spreading due to the low surface energy of the pretreatment liquid. This is achieved by spreading droplets at rates ranging from 55 to 1600 drops / mm. 2 The pretreated droplets are applied to the substrate at a droplet density of 1 to 15 ng / drop, with sufficient substrate surface area to ensure adequate spreading of the water-based inkjet droplets, so as to obtain a smooth and uniform solid in the printed image at an acceptable level of ink bleeding.

[0025] A.1. Provide substrate The first step of the recording method according to the invention is to provide a substrate, which may be: i) ink-absorbent, such as plain paper or textile fabric; ii) low ink-absorbent, such as coated paper, coated paperboard lining for corrugated or folded paperboard, wood, ceramic, leather; and iii) ink-non-absorbent, such as plastic film (e.g., PET film, polyethylene film, polypropylene film, metal, glass, polyvinyl chloride, PMMA, polycarbonate, polyamide, polystyrene).

[0026] The pretreatment composition is particularly suitable for spraying onto cardboard liners used in the folding and corrugated board printing industry. The term "cardboard liner" refers to the top liner of paper (as a sheet or roll), folding carton board, corrugated carton board, and corrugated board. The method according to the invention involves providing a substrate as a roll and / or as a separate sheet. This image recording method appears particularly suitable if the substrate is a coated cardboard liner.

[0027] The coating applied to the coated paperboard liner reduces ink absorption in the gaps between the cellulose fibers. Excessive ink absorption in the gaps between paper fibers can lead to insufficient color density due to insufficient colorant present on the surface of the paper liner, and excessive fiber absorption can cause ink feathering, resulting in blurry edges between printed and unprinted areas.

[0028] Coatings applied to coated paper and coated paperboard liners to improve image quality contain resins, such as polystyrene-acrylic adhesives. One effect of these resins is to limit ink droplet absorption into the paperboard liner. This results in paper and paperboard liners with low absorbency coatings becoming “according to the Bristow method, from initial contact to 30 ms”. 1 / 2 The water absorption capacity is 10ml / m 2 "or less recording medium." The Bristow method is widely used as a method for measuring liquid absorption over short periods of time and has been adopted by the Japan Pulp and Paper Industry Technical Association (Japan TAPPI). Details of this test method are described in Standard No. 51 of the "JAPAN TAPPI Paper and Pulp Test Methods 2000 Edition" entitled "Paper and Paperboard - Liquid Absorption Test Method - Bristow Method".

[0029] Another effect of the adhesive present on the surface of coated paper and paperboard linings is that the surface energy can be relatively low, for example, from 20 mJ / m 2 or greater and 60 mJ / m 2 Or even smaller. This reduced surface energy hinders the good spreading of water-based inkjet ink droplets. It is believed that the relatively low surface energy of non-absorbent substrates containing plastics also hinders the good spreading of water-based inkjet ink droplets. The recording method according to the invention is particularly suitable for providing smooth and uniform solid areas in printed images with excellent ink penetration levels on substrates with low surface energy.

[0030] A.2. Apply aqueous pretreatment droplets In step b) of the image recording method according to the invention, an aqueous pretreatment droplet comprising a fixative and a resin is applied to the recording area S of the substrate. The droplet is preferably applied via a droplet discharging device.

[0031] The means used to apply the pretreatment droplets are preferably selected from spray equipment, inkjet printheads, and valve jet printheads.

[0032] In the case of an inkjet printhead, the pretreatment liquid can be ejected from the nozzle of either the line head or the scanning head. In systems using a line head (also known as a single-pass system), pretreatment droplets can be applied to the recording area S by fixing the head, moving the substrate along the secondary scanning direction, and operating during the movement to eject the pretreatment droplets. Furthermore, in a scanning system, pretreatment droplets can be applied to the recording area S of the substrate by moving the head along the main scanning direction and fixing the substrate.

[0033] When pretreatment droplets are applied to the recording area S using an inkjet printhead, it is preferable that the mass of the pretreatment solution per drop is equal to or less than 15 ng / drop and equal to or greater than 1 ng / drop. Preferably, the mass of the pretreatment solution per drop is equal to or less than 10 ng / drop and equal to or greater than 1 ng / drop, and most preferably equal to or less than 7 ng / drop and equal to or greater than 1 ng / drop.

[0034] If the mass of the pretreatment solution per droplet is below these limits, the amount of deposited fixative will be insufficient to ensure adequate fixation of the colorant in the inkjet ink to be applied, resulting in unacceptable bleeding and feathering at the edges of the printed image. Simultaneously, the amount of resin applied will also be insufficient to guarantee acceptable physical properties of the printed image.

[0035] If the mass of the pretreatment solution per droplet exceeds these limits, drying the pretreatment droplets after they adhere to the inkjet droplets will be problematic at printing speeds of 30 m / min or higher.

[0036] Preferably, the pretreatment liquid is ejected as droplets onto the recording area S of the surface-treated substrate using an inkjet printhead with a specific printing resolution. The printing resolution is determined by the nozzle density, the addressability of the nozzles, and the substrate transport speed (in a fixed line head printing mode) / scan speed (in a fixed substrate line mode). The printing resolution is preferably 200 dpi or greater x 200 dpi or greater, more preferably 600 dpi or greater x 600 dpi or greater, and even more preferably 1200 dpi or greater x 1200 dpi or greater.

[0037] There is no upper limit to the printing resolution, but it is preferably 3600 dpi or lower x 3600 dpi or lower. Printing resolutions higher than this limit will have an excessively negative impact on printing speed, resulting in low productivity.

[0038] It has been observed that when using an inkjet printhead at a print resolution of 200 dpi x 200 dpi, more preferably 600 dpi x 600 dpi, and most preferably 1200 dpi x 1200 dpi, the droplet density of the pretreatment liquid in the recording area S should be reduced by omitting droplet ejection. In another embodiment, droplets can be selectively generated starting from a pixel matrix or image of 600 dpi x 600 dpi, more preferably from a pixel matrix or image of 1200 dpi x 800 dpi, and most preferably from a pixel matrix or image of 1200 dpi x 1200 dpi. In both embodiments, the droplet density of the pretreatment droplets containing the fixative and resin is 55 drops / mm. 2 Up to 1600 drops / mm 2 The preferred value is 110 drops / mm 2 Up to 1600 drops / mm 2 More preferably 220 drops / mm 2 Up to 1600 drops / mm 2 Droplet density is the number of pretreated droplets discharged within a predetermined area.

[0039] If the droplet density of the pretreatment solution is below the lower limit mentioned above, insufficient pretreatment solution will be applied to the recording area, resulting in inadequate fixation of the colorants in the colored inkjet inks (when they adhere to the recording area). Inadequate fixation leads to bleeding in the printed image. If the droplet density (in liquid state) is above the upper limit mentioned above, an unacceptable increase in unevenness (white streaks, white spots) in the solid areas of the printed image is observed.

[0040] When inkjet ink is applied to at least a portion of a recording area S comprising a liquid pretreatment coating on a substrate or a uniformly pretreated droplet layer, non-uniformity in the solid areas of the image is observed. This non-uniformity is even more pronounced in solid areas with high ink loads, such as those composed of composite colors (e.g., green, red, blue, and black). It is believed that when inkjet ink is applied at a rate higher than 1600 drops / mm, the non-uniformity is significantly increased. 2 When an aqueous pretreatment solution is applied at a droplet density of 1 to 10 ng / drop, a uniform liquid coating is obtained due to the aggregation of the pretreatment droplets after these droplets spread on the substrate.

[0041] Without theoretical constraints, it is considered insufficient for water-based inkjet droplets to spread on liquid pretreatment coatings or on high-density pretreatment droplets that are still in a liquid state (because they have not yet been absorbed by the substrate, and the solvent in the droplets has not evaporated before adhering to the inkjet droplets), due to the low surface energy of the pretreatment liquid that ensures uniform droplet spreading. This is achieved by spreading droplets at rates ranging from 55 to 1600 drops / mm. 2 Optimal concentration: 110 to 1600 drops / mm2 More preferably 220 to 1600 drops / mm 2 The pretreated droplets are applied to the substrate at a droplet density of 1 to 15 ng / drop, preferably 1 to 10 ng / drop, more preferably 1 to 7 ng / drop. Sufficient substrate surface area is available to ensure the full spread of the water-based inkjet droplets, so as to obtain a flat and uniform solid in the printed image at an acceptable level of ink bleeding.

[0042] To achieve the droplet density within the range mentioned above, droplets can be selectively generated from an image (which can be a bitmap, a matrix, or generated when the jet signal is sent to the inkjet head) defined by the resolution of the printhead used and its firing frequency, or droplets can be selectively omitted from the image and generated from an image (bitmap, matrix) defined by the resolution of the printhead used and its firing frequency.

[0043] Skipping droplet ejection can be achieved via a halftoning method by skipping nozzle ejection in a structured manner (e.g., every x pixels) or semi-randomly. In another embodiment, droplet ejection can be generated via threshold tiles in a structured manner (e.g., every x pixels) or semi-randomly via a halftoning method. Dithering and error diffusion halftoning techniques can be used to achieve a semi-random approach to generating droplets or skipping nozzle ejection.

[0044] Compositions containing aqueous pretreatment solutions of polyvalent metal salts and resins are described in §B.1.

[0045] The preferred inkjet printhead for ejecting pretreatment droplets is a piezoelectric printhead. Piezoelectric inkjet ejection is based on the movement of a piezoelectric ceramic transducer when a voltage is applied. The applied voltage changes the shape of the piezoelectric ceramic transducer in the printhead, creating a cavity that is subsequently filled with an aqueous pretreatment liquid. When the voltage is removed again, the ceramic expands back to its original shape, ejecting the pretreatment droplets from the inkjet printhead. However, the ejection of the pretreatment liquid according to the invention is not limited to piezoelectric inkjet printing. Other inkjet printheads can be used, and include various types such as continuous, thermal printhead, Memjet-type, and valve-jet types.

[0046] In a preferred embodiment, the pretreatment liquid discharge system may be configured to recirculate the pretreatment liquid prior to printing. Particularly useful inkjet heads for discharging the pretreatment liquid of the present invention are those that include liquid recirculation within the head, such as through-flow heads disclosed in WO2006 / 030235 A2 and WO 2006 / 064036 A1. Such inkjet heads are well-suited for integration into printing systems that include through-flow printheads with one or more nozzles for ejecting pretreatment liquid droplets. Many different recirculation systems are suitable for the method of the present invention. One particular system uses a buffer tank near the printhead. From this buffer tank (1), the pretreatment liquid is pumped to another identical buffer tank (2), which then supplies the “feed” side of the printhead via a manifold, and the “return” side of the printhead then flows back to the first buffer tank (1) via another manifold. This system is locally closed-loop at the printhead, where the pretreatment liquid is never returned to the main tank.

[0047] After the pretreated droplets are ejected onto the recording area S of the substrate, the droplets can be partially dried before the water-based inkjet droplets adhere to at least the recording area S.

[0048] Drying of pretreated droplets can be performed by applying an airflow and / or applying heat. A heating step is then performed using a heat source; examples include devices for forced air heating, radiant heating such as IR radiation (including NIR-, CIR-, and SWIR radiation), conductive heating, high-frequency drying, RF, ultrasonic, and microwave drying.

[0049] It has been observed that by using a substrate exhibiting high surface energy, the optimal droplet density of the pretreatment liquid increases compared to a substrate with low surface energy. This increase in optimal droplet density corresponds to an increase in fixative settling, leading to a further reduction in ink bleeding and improved image sharpness.

[0050] Without being bound by theory, it is believed that the higher the surface energy of the substrate not covered by the pretreatment liquid, the better the ink droplets spread, resulting in a more uniform solid in the printed image, and leading to a higher optimal droplet density of the pretreatment liquid.

[0051] A.3. Adhesive colored water-based inkjet ink After applying a pretreatment liquid to the recording area S of the substrate, aqueous inkjet ink is applied to at least a portion of the recording area S to obtain a printed image. More preferably, the aqueous inkjet ink can be adhered to pretreatment droplets already present on the substrate surface.

[0052] The inkjet ink comprises pigments and water-soluble solvents. A preferred method for applying water-based inkjet ink is by means of ink jetting technology. For preferred inkjet heads, see §A.2.

[0053] After water-based inkjet ink has been applied to at least a portion of the recording area S to form an image, the image can be dried.

[0054] The drying step of an image can be performed by applying airflow and / or applying heat. The heating step must be performed by using a heat source; examples include equipment for forced air heating, radiant heating such as IR radiation (including NIR-, CIR-, and SWIR radiation), conductive heating, high-frequency drying, RF, ultrasonic, and microwave drying.

[0055] Examples of the heating methods include, but are not limited to, hot pressing, atmospheric pressure steam, high pressure steam, and THERMOFIX. Any heat source can be used in the heating methods; for example, an infrared lamp.

[0056] A.4. Apply varnish After water-based inkjet ink has been applied to at least a portion of the recording area S, a varnish can be applied to at least a portion of the image obtained by attaching the water-based inkjet ink.

[0057] In one embodiment of the invention, varnish is applied to an area outside the recording area S, more specifically to a non-image area containing a pretreatment solution.

[0058] All well-known conventional methods can be used to apply or print varnish onto at least a portion of an image. Examples of such methods include air knife coating, doctor blade coating, roller coating, gravure coating, and spray coating. The advantage of these coating or printing techniques is that a thick varnish layer can be obtained in a single pass through the recording medium, ensuring sufficient abrasion resistance of the image.

[0059] Preferably, the varnish is applied via a spraying technique that allows for selective application of the varnish onto the image. This method of applying the varnish composition (preferably according to the image) has the advantage that the amount of varnish material required is significantly less than with other application methods. The spray head suitable for spraying the varnish is the same as described in §A.2.

[0060] Finally, the applied varnish is dried according to one of the methods described above for drying the pretreatment liquid or water-based inkjet ink.

[0061] B. Pretreatment solution, water-based inkjet ink and varnish composition B.1. Aqueous pretreatment solution The aqueous pretreatment solution used in the method according to the invention comprises a fixative. The fixative is used to cause ink colorants (e.g., dyes or pigments) to crash, precipitate, or destabilize, and thus fix them onto the substrate. This results in improved image quality (less bleeding, less feathering, less coalescence).

[0062] The fixative is preferably a polyvalent metal salt or a cationic polymer.

[0063] Polyvalent metal salts can be present in the pretreatment solution to improve the image quality of inkjet-printed images. Typically, the polyvalent metal salt can be any water-soluble polyvalent metal salt. In specific examples, the polyvalent metal salt may include calcium chloride (CaCl2), magnesium chloride (MgCl2), magnesium sulfate (MgSO4), aluminum chloride (AlCl3), calcium nitrate (Ca(NO3)2), magnesium nitrate (Mg(NO3)2), magnesium acetate (Mg(CH3COO)2), zinc acetate (Zn(CH3COO)2), calcium propionate (Ca(C2H5COO)2), or combinations thereof. In further examples, the polyvalent metal salt may include a metal cation selected from calcium, copper, nickel, magnesium, zinc, barium, iron, aluminum, chromium, or other polyvalent metals.

[0064] Suitable cationic polymers for use as fixatives in pretreatment solutions contain guanidinium or fully quaternized ammonium functional groups, such as quaternized polyamine copolymers. Typically, the weight-average molecular weight (Mw) of the cationic polymer allows for a viscosity of less than 25 cP at 25°C (measured on a Brookfield viscometer). Typical Mw is less than 500,000, and in one aspect less than 50,000.

[0065] Suitable cationic polymer classes that may be used include, but are not limited to: quaternized polyamines, dicyandiamide polycations, diallyl dimethyl ammonium chloride copolymers, quaternized dimethylaminoethyl (meth)acrylate polymers, quaternized vinylimidazolium polymers, alkylguanidine polymers, alkoxylated polyethyleneimine, and mixtures thereof.

[0066] The pretreatment liquid according to the present invention contains water as a carrier, but may include one or more water-soluble organic solvents.

[0067] One or more organic solvents may be added for a variety of reasons. For example, adding a small amount of organic solvent may be advantageous to improve the solubility of the compound in the pretreatment solution to be prepared, to obtain better permeability in porous substrates, or to prevent the pretreatment solution from drying rapidly at the inkjet nozzle. Preferred water-soluble organic solvents are polyols (e.g., ethylene glycol, glycerol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, tetraethylene glycol, triethylene glycol, tripropylene glycol, 1,2,4-butanetriol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,5-pentanediol, 1,2-pentanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 3-methyl-1,3-butanediol, and 2-methyl-1,3-propanediol), N-hydroxyl... Ethylpyrrolidone, N-butylpyrrolidone, amines (e.g., ethanolamine and 2-(dimethylamino)ethanol), monohydric alcohols (e.g., methanol, ethanol, and butanol), alkyl ethers of polyols (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 (e.g., N,N-dimethylformamide), heterocyclic compounds (e.g., 2-pyrrolidone and N-methyl-2-pyrrolidone), and acetonitrile. The wetting agent is preferably added to the pretreatment solution formulation in an amount of 0.1 to 35 wt.% based on the total weight of the liquid.

[0068] The pretreatment solution according to the invention comprises a resin. This resin improves the mechanical resistance and water resistance of the printed image. The resin is preferably selected from water-soluble carboxylic acid polymers or their salts, carboxylic anhydride polymers, polyurethanes or their copolymers, acrylates or their copolymers, polyesters or their copolymers, and polystyrene or its copolymers, provided that if the resin is resin particles in an aqueous pretreatment solution, it is stabilized by nonionic groups or nonionic or amphiphilic compounds.

[0069] In a preferred embodiment of the invention, the pretreatment solution for inkjet printing according to the invention comprises a carboxylic acid polymer or a salt thereof, or a carboxylic anhydride polymer. It is believed that the carboxylic anhydride, when dissolved in an aqueous carrier of the pretreatment solution, undergoes at least partial hydrolysis to a carboxylic acid or a salt thereof.

[0070] The impact of using carboxylic acid polymers or their salts, or carboxylic anhydride polymers, in the pretreatment solution on image quality may be related to the interaction of these polymers with fixatives present in the pretreatment solution as polyvalent metal ion or cationic polymers. These fixatives function to interact with negatively charged dispersing colorants (e.g., dyes or pigments) from the ink to fix the colorants and prevent image bleeding.

[0071] Without being limited to theory, it is believed that the activity of the fixative is better controlled in the presence of carboxylic acid-functionalized polymers, thereby achieving optimal image sharpness and ink spread.

[0072] The pretreatment solution contains a carboxylic acid-containing polymer or its salt, or a carboxylic anhydride-containing polymer, which is not limited to a specific polymer, but preferably has an acid value of 950 mg KOH / g polymer or less, and 450 mg KOH / g polymer or greater, assuming that the carboxylic acid-containing polymer or its salt or carboxylic anhydride is in its acidic form. If the acid value is higher than this range, i.e., for homopolymers based on maleic acid and fumaric acid, the degree of polymerization will be too low, and thus provide less interaction with the polyvalent salt used, resulting in poor ink spreading. If the acid value is lower than the above range, the solubility of the polymer in the pretreatment solution may be too low to provide sufficient image quality.

[0073] Acid value is defined in mg KOH / g polymer and corresponds to the amount of carboxylic acid groups or carboxylate groups. Acid value can be determined by titration or calculation. Examples of titration methods are described in ASTM D3644-06.

[0074] Preferred carboxylic acid-containing polymers are homopolymers, such as polyacrylic acid, polyitacrylic acid, polycrotonic acid, polymethacrylic acid, poly(N-(2-hydroxyethyl)maleamic acid), poly(3-(aminocarbonyl)-3-butenoic acid), poly(4-amino-2-methylene-4-oxobutyric acid), and poly(maleamic acid), as well as salts of the corresponding homopolymers.

[0075] Other preferred carboxylic acid-containing polymers are modified anhydride homopolymers hydrolyzed by water or alkalis (e.g., KOH, NaOH) or water-soluble organic bases (e.g., water-soluble monoamines, such as ethanolamine, ammonia, and amine-terminated polyethylene glycols, e.g., CAS Registry Nos. 65421-52-5, 171863-88-0, 33881-50-4, and 176703-83-6). Typical anhydride homopolymers or copolymers suitable for hydrolysis or post-modification are based on maleic anhydride and itaconic anhydride. When using alkaline hydrolysis, the carboxylic acid can exist in the form of a salt.

[0076] Other preferred polymers containing carboxylic acids or carboxylic anhydrides are copolymers, such as poly(ethylene-co-maleic anhydride), poly(isobutylene-co-maleic anhydride), poly(isobutylene-co-maleic 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 copolymers, as well as salts of the respective copolymers.

[0077] Further preferred carboxylic acid or carboxylic 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-oxobutyric acid, N-(2-hydroxyethyl)maleamic acid, and maleimide monomers, such as 3-pyrrolino-2,5-dione, 3-maleimide propionic 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) with water-soluble monoamines (e.g., ethanolamine, ammonia, and amine-terminated polyethylene glycol).

[0078] Preferably, the carboxylic acid-containing polymer or its salt, or the carboxylic anhydride-containing polymer, has a molecular weight (Mw) of 2000 g / mol or greater. This molecular weight is determined using a universally calibrated GPC with polyethylene glycol standards. When Mw is equal to or greater than 2000 g / mol, a further improvement in image quality is observed, particularly in ink spread in printed solids.

[0079] Based on the total weight of the pretreatment liquid, the amount of the carboxylic acid polymer or its salt or the carboxylic anhydride polymer is preferably 0.1 to 5 wt.%, more preferably 0.2 to 4 wt.%. Amounts below this range do show insufficient improvement in image quality and mechanical durability. Amounts above this range may lead to: (i) decreased jetting performance due to excessively high polymer content in the liquid; (ii) precipitation due to solubility problems; and (iii) decreased image sharpness and increased bleeding and feathering.

[0080] In another preferred embodiment of the invention, the resin in the pretreatment solution may be resin particles. The resin particles are preferably selected from polyurethanes and their copolymers, acrylics and their copolymers, polyesters and their copolymers, and polystyrene and its copolymers. The resin particles are preferably stabilized by nonionic groups or nonionic or amphiphilic compounds. Nonionic groups should be understood as groups covalently linked to the resin particles.

[0081] To ensure compatibility with polyvalent metal salts or cationic polymers, the resin particles are preferably nonionic and stable.

[0082] For polyurethane dispersions, nonionic stabilization can be achieved by using polyether diols in the preparation of the polyurethane resin. The preferred polyether diols used in this invention are Ymer N180, Ymer N120, Ymer N90, or Tegomer D 3403, i.e., α-[2,2-bis(hydroxymethyl)butyl]-ω-methoxy-poly(oxy-1,2-ethanediyl). These diols can be prepared from trimethylolpropaneoxetane (TMPO). Possible synthetic steps are described in Fock, J.; Möhring, 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. Other polyether 1,2- or 1,3-diols can also be used.

[0083] For addition polymerization, such as the preparation of polyacrylates, monomethacrylate or monoacrylate-terminated polyethers can be used to prepare graft copolymers with polyether side chains. Examples of suitable macromonomers for addition polymerization are listed in sections [0022-0024] of WO2023 / 001650A.

[0084] The preferred resin particles incorporated into the pretreatment solution are based on a polyurethane particle dispersion. In polyurethane synthesis, different polyols can be used to obtain suitable physical, mechanical, or optical properties, such as adhesion to the substrate, water resistance, solvent resistance, weather resistance, scratch resistance, gloss, or opacity. Commonly used polyols include: polyether polyols, polyester polyols, polycarbonate polyols, polyamide polyols, polyacrylate polyols, and polyolefin polyols.

[0085] The amount of resin particles in the pretreatment liquid is between 1% and 50% by weight, preferably between 5% and 45% by weight, and more preferably between 20% and 40% by weight, relative to the total solids content of the precoating composition. If applied via a spraying technique, amounts exceeding these values ​​negatively impact the spraying reliability of the precoating composition.

[0086] Suitable commercially available PU dispersions include, for example: Vondic 2220 and Vondic 1980NE supplied by Toyobo; Printrite DP375 and Printrite PD379 supplied by Lubrizol; Esacote PU3511 supplied by Lamberti; Neorez R9340 available from DSM; and 2019WTT001-3 available from BASF.

[0087] The pretreatment liquid of the present invention may further include a dispersant to improve the storage stability of the liquid, preferably a nonionic dispersant, and more preferably a nonionic polymeric dispersant.

[0088] Suitable nonionic dispersants are polymeric dispersants, nonionic surfactants, and segmental polymers, such as graft copolymers, block copolymers, star-branched copolymers, comb copolymers, or gradient copolymers. These polymeric dispersants are preferably amphiphilic, having at least one segment soluble in, dispersible in, or compatible with a water-based medium. The medium is not necessarily only water but can also be a mixture with other solvents. Other water-soluble solvents, such as propylene glycol, glycerol, dipropylene glycol monomethyl ether, and 2-hydroxyethylpyrrolidone, can be added to water-based pretreatment solutions and inkjet inks. At least one segment or portion of the polymeric dispersant should be compatible with the solvent medium of the pretreatment solution and the ink. Examples of suitable nonionic surfactants as nonionic dispersants are listed in paragraphs [0033-0034] of WO2023001650. Examples of suitable polymeric dispersants are listed in paragraphs [0035-0039] of WO2023001650.

[0089] The pretreatment solution according to the invention may also contain a wetting agent. The wetting agent is preferably incorporated into the pretreatment solution, especially if the liquid must be applied by jetting techniques such as inkjet or valve jetting. The wetting agent prevents nozzle clogging. This prevention is due to its ability to slow down the evaporation rate of the pretreatment solution and the inkjet ink (especially water in the liquid). The wetting agent is preferably an organic solvent with a higher boiling point than water. Suitable wetting agents include triacetin, N-methyl-2-pyrrolidone, glycerol, urea, thiourea, ethylene urea, alkyl urea, alkylthiourea, dialkyl urea and dialkylthiourea, diols (including ethylene glycol, propylene glycol, glycerol, butanediol, pentanediol and hexanediol); glycols (including propylene glycol, polypropylene glycol, ethylene glycol, polyethylene glycol, diethylene glycol, tetraethylene glycol) and mixtures and derivatives thereof. A preferred wetting agent is glycerol.

[0090] The humectant is preferably added to the pretreatment solution formulation in an amount of 0.1 to 40% by weight based on the total weight of the liquid.

[0091] The pretreatment solution may contain a surfactant. Any known surfactant may be used, but nonionic ethylene oxide, mono(2-propylheptyl) ether, or fatty alcohol alkoxylates or a combination thereof are preferred.

[0092] Biocides can be added to the pretreatment solution composition to prevent unwanted microbial growth that may occur over time. The biocides can be used alone 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 their salts.

[0093] The preferred biocide is Proxel, which is available from ARCH UK BIOCIDES. TM GXL and Proxel TM Ultra 5 and Bronidox available from COGNIS TM .

[0094] The biocides are preferably added to the aqueous medium in amounts from 0.001 to 3% by weight, more preferably from 0.01 to 1.0% by weight, based on the total weight of the liquid.

[0095] The pre-coating composition may further include at least one thickener for viscosity adjustment in the liquid. Suitable thickeners are hydrophilic modified PU thickeners (HEUR), such as Thijet 170 from Lamberti, and polyacrylates, such as BYK LP-R21675 from BYK.

[0096] The thickener is preferably added in an amount of 0.01 to 20% by weight, more preferably 0.1 to 10% by weight, based on the liquid content.

[0097] B.2. Water-based inkjet inks The aqueous inkjet ink, as part of the method of the present invention, comprises pigments. The pigments are preferably stabilized by anionic dispersing groups. The pigments may also be further stabilized by polymeric dispersants, surfactants, or combinations thereof to obtain additional colloidal stability.

[0098] The aqueous medium of this 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 present invention, the water-based inkjet ink comprises resin particles and / or wax particles.

[0100] Water-based inkjet inks may further include surfactants, wetting agents, resins, and thickeners as additives. Suitable wetting agents and thickeners are listed in §B.1.

[0101] The pigments in the water-based inkjet inks according to the present invention can be black, white, cyan, magenta, yellow, red, orange, purple, blue, green, brown, or mixtures thereof. The colored pigments are freely selectable from those disclosed in HERBST, Willy et al., Industrial Organic Pigments, Production, Properties, Applications. 3rd ed. Wiley - VCH, 2004. ISBN 3527305769.

[0102] Suitable pigments are disclosed in paragraphs

[0128] to

[0138] of WO 2008 / 074548.

[0103] Pigment particles are dispersed in an aqueous medium using polymeric dispersants, surfactants, or combinations thereof. Self-dispersing pigments may also be used. The latter prevents the polymeric dispersant from interacting with the dispersing groups of binders or capsules that may be included in inkjet inks (see below).

[0104] Self-dispersible pigments are pigments with anionic hydrophilic groups or salt-forming groups covalently bonded to their surface, which allows the pigment to be dispersed in an aqueous medium without the use of surfactants or resins.

[0105] Techniques for manufacturing self-dispersible pigments are well known. For example, EP1220879A discloses a pigment connected to a) at least one sterically hindered group and b) at least one organic ionic group and at least one amphiphilic counterion, wherein the amphiphilic counterion carries a charge opposite to that of the organic ionic group suitable for inkjet inks. EP906371A also discloses suitable surface-modified colored pigments connected to hydrophilic organic groups containing one or more ionic or ionizable groups. Suitable commercially available self-dispersible colored pigments include, for example, CAB-O-JET™ inkjet colorant from CABOT.

[0106] The pigment particles in inkjet inks should be small enough to allow the ink to flow freely through the inkjet printing apparatus, especially at the jet nozzles. It is also desirable to use small particles for maximum color intensity and to slow down settling.

[0107] The average pigment particle size is preferably between 0.050 and 1 μm, more preferably between 0.070 and 0.300 μm, and particularly preferably between 0.080 and 0.200 μm. Most preferably, the numerical average pigment particle size is not greater than 0.150 μm.

[0108] Special colorants can also be used, such as fluorescent pigments for special effects, and metallic pigments for printing a luxurious silver and gold look.

[0109] Suitable white pigments are given in Table 2 of paragraph

[0116] of WO 2008 / 074548. The white pigments are preferably pigments having a refractive index greater than 1.60. White pigments can be used alone or in combination. Preferably, titanium dioxide is used as the pigment having a refractive index greater than 1.60. Suitable titanium dioxide pigments are those disclosed in paragraphs

[0117] and

[0118] of WO 2008 / 074548.

[0110] Suitable polymer dispersants are copolymers of two monomers, but they can contain three, four, five, or even more monomers. The properties of a polymer dispersant depend on both the properties of the monomers and their distribution in the polymer. Copolymer dispersants preferably have the following polymer composition: ● Statistically polymerized monomers (e.g., monomers A and B polymerize to form ABBAABAB). ● Monomers that polymerize alternately (e.g., monomers A and B polymerize to form ABABABAB). ● Monomers that undergo gradient (gradual) polymerization (e.g., monomers A and B polymerize to form AAABAABBABBB). ● Block copolymers (e.g., monomers A and B polymerized to form AAAAABBBBBB), where the block length of each block (2, 3, 4, 5 or even more) is important for the dispersing ability of the polymer dispersant; ● Graft copolymers (graft copolymers consist of a polymer backbone and polymer side chains attached to that backbone); and ● These polymers can be in mixed forms, such as block gradient copolymers.

[0111] A suitable dispersant is DISPERBYK, which is available from BYK CHEMIE. TM Dispersant, JONCRYL available from BASF TM Dispersants and SOLSPERSE available from Lubrizol TM Dispersants. Other suitable dispersants are Edaplan 482 from Münzing. A detailed list of non-polymer and some polymeric dispersants is available from MC CUTCHEON. Functional Materials, North American Edition. Glen Rock, NJ: ManufacturingConfectioner Publishing Co., 1990, pp. 110-129.

[0112] The polymer dispersant preferably has a number average molecular weight Mn between 500 and 30,000, more preferably between 1,500 and 10,000.

[0113] The polymer dispersant preferably has a weight-average molecular weight (Mw) of less than 100,000, more preferably less than 50,000, and most preferably less than 30,000.

[0114] Based on the total weight of the inkjet ink, the pigment is preferably present in an amount ranging from 0.01% to 15% by weight, more preferably from 0.05% to 10% by weight, and most preferably from 0.1% to 5% by weight. For white inkjet ink, the white pigment is preferably present in an amount ranging from 3% to 40% by weight of the inkjet ink, and more preferably from 5% to 35%. An amount less than 0.01% by weight cannot achieve sufficient hiding power.

[0115] In a preferred embodiment of the invention, the water-based ink comprises pigment encapsulated by a cross-linked polymer shell. Compared to pigment dispersed by an uncross-linked polymer, the encapsulated pigment provides a printed image with improved physical properties, such as water resistance and dry rubbing resistance.

[0116] Suitable encapsulated pigments were supplied by Lubrizol in Diamond HSDX dispersions and by Fujifilm in RxD pigment dispersions (such as APD1000 and APD4000 high-quality dispersions).

[0117] The inkjet ink composition according to the invention may contain resin particles. Resin is typically added to inkjet ink formulations to achieve good pigment adhesion to a substrate. The resin is preferably a polymer, and suitable resins may be acrylic-based, urethane-based, or wax-based.

[0118] Polyurethane resin is incorporated into the ink formulation in the form of a dispersion, and can be selected from aliphatic polyurethane dispersion, aromatic polyurethane dispersion, anionic polyurethane dispersion, nonionic polyurethane dispersion, aliphatic polyester polyurethane dispersion, aliphatic polycarbonate polyurethane dispersion, aliphatic acrylic modified polyurethane dispersion, aromatic polyester polyurethane dispersion, aromatic polycarbonate polyurethane dispersion, aromatic acrylic modified polyurethane dispersion, or a combination of two or more of the above.

[0119] The preferred polyurethane resin used as a dispersion in the inks of the present invention is a polyester resin comprising structural units containing urethane bonds. Among these resins, water-soluble or water-dispersible polyurethane-modified polyester resins are preferred. Preferably, the polyurethane-modified polyester resin comprises at least one structural unit derived from a polyester resin (polyester polyol) containing hydroxyl groups and at least one structural unit derived from an organic polyisocyanate.

[0120] Furthermore, the hydroxyl-containing polyester resin is a resin formed by an esterification reaction or transesterification reaction between at least one polyacid component and at least one polyol component.

[0121] The preferred polyurethane resin included in the inks of the present invention is a polyurethane resin obtained by reacting a polyester polyol, a polyether glycol, an anionic polyol, and a polyisocyanate. Particularly preferred polyurethane resins are polyurethane resins obtained by reacting a polyester polyol, a polyether glycol, an anionic polyol, and a polyisocyanate, wherein the polyester polyol is obtained by reacting an aromatic polycarboxylic acid with the polyol. Suitable polyurethane resins and examples of their preparation are disclosed in patent application EP3532545A.

[0122] Examples of suitable polyurethane dispersions include, for example, NEOREZ R-989, NEOREZ R-2005, and NEOREZ R-4000 (DSM NeoResins); BAYHYDROL UH 2606, BAYHYDROL UH XP 2719, BAYHYDROL UHXP 2648, and BAYHYDROL UA XP 2631 (Covestro); DAOTAN VTW 1262 / 35WA, DAOTAN VTW1265 / 36WA, DAOTAN VTW 1267 / 36WA, DAOTAN VTW 6421 / 42WA, and DAOTAN VTW 6462 / 36WA (Allnex); and SANCURE 2715, SANCURE 20041, and SANCURE 2725 (Lubrizol), or combinations of two or more of the above.

[0123] Acrylic acid-based resins include polymers of acrylic acid monomers, polymers of methacrylic acid monomers, and copolymers of the aforementioned monomers with other monomers. These resins exist as particulate suspensions with an average diameter of about 30 nm to about 300 nm. The acrylic latex polymers are formed from acrylic acid monomer or methacrylic acid monomer residues. Examples of monomers for acrylic latex polymers are illustratively included by comprising acrylic acid monomers such as acrylates, acrylamides, and acrylic acid, and methacrylic acid monomers such as methacrylates, methacrylamides, and methacrylic acid. The acrylic latex polymers can be homopolymers or copolymers of acrylic acid monomers with another monomer (e.g., vinyl aromatic monomers, including but not limited to styrene, styrene-butadiene, p-chloromethylstyrene, divinylbenzene, vinylnaphthalene, and divinylnaphthalene).

[0124] Examples of suitable acrylic latex polymer suspensions include JONCRYL 537 and JONCRYL 538 (BASF, Port Arthur TX); 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); 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 AHXP 2741, BAYHYDROL A 2427, and BAYHYDROL... A2651 (Bayer), or a combination of two or more of the above.

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

[0126] The water-based inkjet ink of the present invention may also contain wax. The wax in the ink improves the wet rubbing resistance or wet scratch resistance of the printed layer.

[0127] Therefore, the wax can be polyethylene wax, petroleum wax, paraffin wax, carnauba wax, polypropylene wax, crystalline and microcrystalline wax, amide wax (oleamide, stearamide, erucamide, cycloamide, etc.), and combinations thereof. In one aspect of the invention, the wax can be high-density polyethylene wax.

[0128] In one aspect of the invention, the wax may be a polyethylene wax or a modified paraffin wax. Examples of polyethylene waxes include high-density polyethylene (HDPE) wax having a density ranging from about 0.93 g / ml to 0.97 g / ml.

[0129] Some specific examples of waxes that can be used include those from the JONCRYL Wax series (such as JONCRYL Wax 22, JONCRYL Wax 26, and JONCRYL Wax 120, available from BASF Corp.), those from 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.

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

[0131] The inkjet ink compositions according to the invention may comprise capsules. Capsules, more preferably nanocapsules, are typically incorporated into inkjet ink formulations to encapsulate colorants (US2009227711A, JP2004075759) or crosslinkable reactive components. Particularly useful are the nanocapsules disclosed in paragraphs [0037-0110] of WO2015158649: said nanocapsules have a polymer shell surrounding a core containing reactive chemicals. The shell material includes polyurea, polyurethane, polyester, polycarbonate, polyamide, melamine-based polymers, and mixtures thereof, wherein polyurea and polyurethane are particularly preferred. Other particularly useful nanocapsules are disclosed in paragraphs [0051-0138] of WO2016165970: said nanocapsules are self-dispersible and include dispersive groups covalently linked to the shell polymer. The core of the nanocapsules in paragraphs [0037-0110] of WO2015158649 and paragraphs [0051-0138] of WO2016165970 contains reactive chemistry capable of forming reaction products upon application of heat and / or light, allowing for the processing of a wide range of substrates. Other suitable reactive chemistry includes those that are activated under radiation, as described in paragraphs [0068-0110] of WO2015158649.

[0132] Based on the total weight of the ink, the capsules are preferably present in the inkjet ink in an amount not exceeding 30 wt.%, preferably between 5 and 25 wt.%.

[0133] The ink composition may contain surfactants. Any known surfactant can be used, but glycol surfactants and / or alkynyl alcohol surfactants and / or polysiloxane surfactants are preferred. The use of alkynyl glycol surfactants and / or alkynyl alcohol surfactants and / or polysiloxane surfactants further reduces bleeding to improve print quality and also improves drying properties during printing to allow for high-speed printing.

[0134] The alkynyldiol surfactant and / or alkynol surfactant are preferably one or more selected from 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,4,7,9-tetramethyl-5-decyn-4,7-diol alkyl oxide adducts, 2,4-dimethyl-5-decyn-4-ol, and 2,4-dimethyl-5-decyn-4-ol alkyl oxide adducts. These are available, for example, from Air Products (GB) or Nissin Chemical Industry, such as the Olfine series (registered trademarks) such as Olfine E1010, and the Surfynol series (registered trademarks), such as Surfynol 465, Surfynol 104H, and Surfynol 61.

[0135] Biocides can be added to ink compositions to prevent unwanted microbial growth that may occur over time. Suitable biocides are listed in §B.1. Preferably, the biocides are added to the aqueous medium in amounts of 0.001 to 3% by weight, more preferably 0.01 to 1.0% by weight, each based on the total weight of the ink.

[0136] B.3. Varnish A varnish that can be used in the method according to the invention is used to protect inkjet-printed images from wet and dry friction, scratching, and solvents. Therefore, the varnish comprises water and resin particles.

[0137] Examples of resin particles included in varnishes include well-known resins such as urethane-based resins, acrylic resins, fluorene-based resins, polyolefin-based resins, rosin-modified resins, terpene-based resins, polyester-based resins, polyamide-based resins, epoxy-based resins, and vinyl chloride-based resins. The vinyl chloride-based resins include vinyl chloride copolymers, such as vinyl chloride-vinyl acetate copolymers. These resins can be used alone, or in combination of two or more.

[0138] Among the resin particles mentioned above, 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 a urethane-based resin, commercially available products can be used, such as SUPERFLEX 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.), TAKELAC WS-6021, W-512-A-6 (trade name, manufactured by Mitsui Chemicals PolyurethanesINC.), SUNCURE 2710 (trade name, manufactured by LUBRIZOL), and PermalinUA-150 (trade name, manufactured by Sanyo Chemical Industries, Ltd.).

[0140] Acrylic resins are a general term for polymers obtained by polymerizing at least one acrylic monomer (e.g., (meth)acrylic acid and (meth)acrylate), and examples include (meth)acryloyl resins obtained from acrylic monomers, and copolymers of acrylic monomers with monomers other than acrylic monomers (e.g., ethylene-based monomers, such as styrene). Acrylamide and acrylonitrile can also be used as acrylic monomers. Acrylic resins can be non-reactive or self-crosslinking. As resin emulsions using acrylic resins as raw materials, commercially available products can be used, and examples include FK-854 (trade name, manufactured by CHIRIKA.Co., Itd.), Mowinyl 952B, 718A (trade name, manufactured by 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), poly(styrene-1,3-diene), poly(styrene-alkyl methacrylate), poly(styrene-alkyl acrylate-acrylic acid), poly(styrene-1,3-diene-acrylic acid), poly(styrene-alkyl methacrylate-acrylic acid), poly(styrene-alkyl acrylate-acrylonitrile-acrylic acid), and poly(styrene-1,3-diene-acrylonitrile-acrylic acid). Other examples include poly(styrene-propyl acrylate), poly(styrene-butyl acrylate), poly(styrene-butadiene-acrylic acid), poly(styrene-butadiene-methacrylic acid), poly(styrene-butadiene-acrylonitrile-acrylic acid), poly(styrene-butyl acrylate-acrylic acid), poly(styrene-butyl acrylate-methacrylic acid), poly(styrene-butyl acrylate-acrylonitrile), and poly(styrene-butyl acrylate-acrylonitrile-acrylic acid). Commercially available styrene-acrylic resins are Neocryl D2101 (Covestro) and Bonron PS001 and Bonron PS002 (Mitsui).

[0142] Other suitable resins include Esajet acrylic latexes from Lamberti, such as Esajet AC 20, Esajet AC22, Esajet AC 29, Esajet AC31 and Esajet AC03.

[0143] The varnish contains 1 wt.% to 30 wt.% of resin relative to the total mass of the liquid. When the resin content in the varnish is within the range mentioned above, the effect of improving the image's abrasion resistance tends to be more superior. More preferably, the varnish contains 3 wt.% to 15 wt.% of resin relative to the weight of the liquid. Most preferably, the varnish contains 5 wt.% to 12 wt.% of resin relative to the weight of the liquid.

[0144] The varnish contained in the liquid group according to the invention may contain wax. This wax can improve the durability of printed images. Generally, any suitable wax can be used in the varnish composition. Suitable waxes are described in §B.2.

[0145] Varnishes may contain surfactants. Suitable surfactants are listed in §B.2, but polyether siloxane surfactants are preferred. Wetting agents and biocides may be added to varnishes. Suitable wetting agents and biocides are listed in §B.1.

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

[0147] The varnish may further contain a crosslinking agent. Any water-soluble or water-dispersible crosslinking agent may be used, but preferably the crosslinking agent is a carbodiimide, such as that described in unpublished patent application EP23164057.4 A.

[0148] C. Image recording equipment One embodiment of the present invention provides an image recording apparatus for forming an image on a substrate.

[0149] The recording device includes: a conveyor mechanism configured to convey a substrate along a conveying direction; and an inkjet printhead for applying pre-treated droplets to at least a portion of a recording area S on the surface of the substrate, said pre-treated droplets having a droplet mass of 15 ng / drop or less and equal to or greater than 1 ng / drop, wherein the droplet density is equal to 55 drops / mm². 2 Or greater than or equal to 1600 drops / mm 2 Or smaller, the pretreatment liquid contains a fixative and a resin; and an inkjet printhead for adhering aqueous inkjet ink containing pigments and water-soluble organic solvents to at least a portion of the recording area S.

[0150] In a more preferred embodiment, the inkjet head is a fixed linear head. This head configuration provides the highest achievable printing speed.

[0151] D. Example D.1. Materials Unless otherwise stated, all materials used in the following examples are readily available from standard sources (e.g., Aldrich Chemical Co. (Belgium) and Acros (Belgium)). The water used is deionized water (DI water).

[0152] • Proxel is a 5 wt.% aqueous solution of 1,2-benzisothiazolin-3-one, which can be used as Proxel TM K is obtained from YDSCHEMICALS NV.

[0153] • Surfynol 104PG50 is a 50 wt.% solution of 2,4,7,9-tetramethyl-5-decyn-4,7-diol in propylene glycol, from Evonik.

[0154] • Printrite DP379 is a 30 wt.% aqueous dispersion of a polyether-based polyurethane from Lubrizol.

[0155] • Aquacer 530 is an aqueous dispersion containing 32 wt.% oxidized HDPE wax, from BYK.

[0156] • Kauropal K933 is a nonionic ethylene oxide mono(2-propylheptyl) ether from BASF.

[0157] • Pluronic PE10500 is a block copolymer of ethylene oxide and propylene oxide, with 50% EO and Mw of 6500, sourced from BASF.

[0158] • Pluronic PE10500 solution is an 18 wt.% aqueous solution of a block copolymer of ethylene oxide and propylene oxide, with 50% EO and Mw of 6500, sourced from BASF.

[0159] • Tego Foamex 822 is a polyether siloxane copolymer from Evonik.

[0160] • Mg(NO3)2.6H2O is magnesium nitrate hexahydrate, from Merck Group.

[0161] • PG is propane-1,2-diol, from Merck.

[0162] • ZEMAC E60 is a poly(ethylene-co-maleic anhydride) with a molecular weight of 60,000 g / mol and a calculated acid value of 779 mg KOH / g, derived from Aurorium.

[0163] • Sokalan CP12S is a poly(acrylic acid-co-maleic acid) with a molecular weight of 3000 g / mol and a calculated acid value of 826 mg KOH / g, sourced from BASF.

[0164] • Ultralube GA1042 is an aqueous dispersion containing 35 wt.% HDPE wax, from Keim additecsurface GmbH.

[0165] • Hydropalat WE3120 is a fatty alcohol alkoxylate from BASF.

[0166] • Ensocoat is a coated cardboard liner from Stora Enzo, with an absorbency of 4.4 ml / m³ according to the Bristow method. 2 It also has a surface energy of 37.6 mJ / m 2 .

[0167] • MMX is a coated cardboard liner from Stora Enzo, with an absorbency of 4.2 ml / m³ according to the Bristow method. 2 And its surface energy is 40.4 mJ / m 2 .

[0168] • Graph Plus is a coated cardboard liner from Metsaboard, with an absorbency of 7.4 ml / m³ according to the Bristow method. 2 And its surface energy is 56.2 mJ / m 2 .

[0169] • Fusion Topliner is a coated cardboard liner from Sappi with a surface energy of 50.2 mJ / m². 2 .

[0170] • HSDCX1 is an aqueous dispersion of HSDCX1 EXP IJ06, 19 wt.% PB15:3, derived from Lubrizol.

[0171] • HSDYX1 is HSDYX1 EXP IJ06, 19.2 wt.% PY74 dispersion, derived from Lubrizol.

[0172] D.2. Evaluation Methods D.2.1. Sample Preparation The cardboard liner was introduced into the experimental single-pass printing press (fixed line head) at a conveying speed of 30 m / min.

[0173] In this single-pass printing press, in single-pass mode, a pre-treatment droplet is applied to the recording area S of the cardboard liner using an inkjet printhead (Ricoh Gen 5S printhead, ejecting droplets of 3 ng / drop). The droplet density is 223 drops / mm². 2 Up to 2232 drops / mm 2 change.

[0174] Within 0.2 seconds after the pretreatment solution is applied, water-based inkjet ink is applied to the recording area S in single-pass mode at a resolution of 1200 dpi x 1200 dpi using an inkjet printhead (Ricoh Gen 5S printhead, ejecting 5 ng / droplet of liquid). Figure 1 The image.

[0175] To obtain an image with composite colors, first, a solid area of ​​yellow ink is printed onto the recording area S, and then cyan ink is used to... Figure 1 The image is printed onto a yellow solid. In monochrome cases, the print is evaluated using cyan ink.

[0176] Dry the printed image in an oven at 60°C for 2 minutes.

[0177] D.2.2. Image Quality Image quality of printed images is assessed based on droplet density values ​​by visually analyzing the following properties: 1) ink spreading; and 2) ink bleeding.

[0178] Ink spreading: The ink should completely cover the surface. Figure 1 Solid areas in a printed image. Insufficient ink spread manifests as white lines in solid areas. Evaluation is done by visually inspecting the solid areas and assigning a rating from 0 (excellent ink spread, complete coverage) to 3 (poor ink spread, more than 20 white lines visible in solid areas). From a practical standpoint, a rating of 0 to 1 is acceptable.

[0179] Ink bleeding: Insufficient ink fixation of polyvalent metal salt ink colorants manifests as uneven edges between printed image elements (text, lines, solids, etc.) and unprinted areas. Bleeding is assessed by visually observing the sharpness of the edges of solid cyan ink areas and assigning a rating from 0 (strong colorant fixation, sharp edges) to 3 (poor colorant fixation, strong bleeding is observed). Bleeding from cyan into unprinted substrate areas in monochrome printing, and cyan bleeding into yellow ink in the case of multicolor printing, are both evaluated. From a practical standpoint, a rating of 0 to 1 is acceptable.

[0180] D.2.3. Pretreatment solution recirculation test A recycling test was conducted to assess the suitability of the pretreatment solution for use in printheads equipped with a recycled ink system.

[0181] For recirculation testing, the device was operated at 32°C, with a continuous flow rate of 3.5–4 L of pretreatment solution passed through a 10 µm filter at a flow rate of 1.0–1.3 L / min in the loop. The pressure of the pretreatment solution before and after the filter was monitored throughout the test. The pressure drop across the filter was calculated using the following equation: Pressure drop = Pressure (before entering the filter) - Pressure (after leaving the filter) An increase in pressure drop can be observed over time, indicating filter clogging. A suitable pretreatment solution exhibits less than a 15% increase in pressure drop after 10,000 minutes of recirculation.

[0182] D.2.4. Surface Energy Measurement (SFE) The surface energy of the cardboard liner was measured by determining the contact angles of water and diiodomethane at room temperature using a Kruss DSA100 droplet shape analyzer.

[0183] The surface energy is calculated based on the Owens-Wendt model, using the average static contact angle.

[0184] D.3. Pretreatment solution and water-based inkjet ink composition D.3.1. Pretreatment solution The pretreatment solution of the present invention was prepared by mixing the components given in Table 1. Weight percentages are relative to the total weight of the pretreatment solution. Raw materials were used as supplied, without any further processing.

[0185] Table 1. Comparison and Pretreatment Liquids of the Present Invention compound PL-1 PL-2 PL-3 Printrite DP379 - 8.7 12.45 Sokalan CP12S 4.0 - - <![CDATA[Mg(NO3)2.6H2O]]> 15.00 9.82 7.88 Aquacer 530 - - 5.6 Pluronic PE10500 - - 0.7 Pluronic PE10500 solution - 3.89 - Kauropal K933 0.04 0.03 0.03 TegoFoamex 822 0.04 0.03 0.03 Hydropalat WE3120 1.00 - - PG 32.00 32.00 25.00 n-Butanol 2.85 2.85 - ZEMAC E60 - 0.35 - 1,2-Hexanediol - - 2.85 Proxel K 0.2 0.2 - Acetic acid 0.03 0.04 - Sodium acetate trihydrate 1.28 0.05 - DI water Up to 100 wt.% Up to 100 wt.% Up to 100 wt.%

[0186] D.3.2. Water-based inkjet ink composition Water-based cyan inks INKC-1 and INKC-3, and water-based yellow inks INKY-2 and INKY-4, were prepared by adding all the ingredients mentioned in Table 2. All ingredients in Table 2 are expressed in wt.% based on the total weight of the inks. Water was added to achieve the desired pigment concentration.

[0187] Table 2. Water-based inkjet ink compositions compound INKC-1 INKY-2 INKC-3 INKY-4 Ultralube GA1042 - - 1.43 1.43 PG 43 37.5 42 36 n-Butanol 2.95 2.95 2.95 2.95 Surfynol 104PG50 0.4 0.4 0.4 0.4 Proxel 0.2 0.2 0.2 0.2 HSDCX1 13.16 - 13.16 - HSDYX1 - 19.79 - 19.79 DI water Up to 100 wt.% Up to 100 wt.% Up to 100 wt.% Up to 100 wt.%

[0188] D.4. Image quality assessment results First, the optimal image quality regarding ink bleeding and ink spreading was determined at which droplet density of the pretreatment solution was lowest. This value was defined as the optimal droplet density. The evaluation of ink bleeding and ink spreading is as described in § D.2.2.

[0189] At optimal image quality, the ink bleeding and ink spreading values ​​for different pretreatment liquid / ink combinations are listed in Tables 3, 4, 5, and 6 (for four different coated paperboard liners).

[0190] Table 3: Ink bleeding and ink spreading of different pretreatment liquid / ink combinations on Ensocoat cardboard lining

[0191] Table 4: Ink bleeding and ink spreading of different pretreatment liquid / ink combinations on MMX-coated cardboard liners.

[0192] Table 5: Ink bleeding and ink spreading of different pretreatment liquid / ink combinations on Fusion Topliner coated paperboard liners.

[0193] Table 6: Ink bleeding and ink spreading of different pretreatment liquid / ink combinations on Graph Plus coated paperboard liners.

[0194] As can be seen from Tables 3, 4, 5, and 6, if the droplet density of the pretreatment solution is between 55 and 1600 drops / mm², which is within the required protection range... 2 Within the acceptable range, the image quality of cyan and green printed images (obtained by combining yellow and cyan inks) exhibits values ​​within an acceptable range.

[0195] D.5. Evaluation results of the recirculation behavior of the pretreatment solution The recirculation behavior of pretreatment solutions PL-1 and PL-3 was tested according to § D.2.3. After 10,000 minutes of recirculation, the wax-containing pretreatment solution PL-3 showed an increase in pressure drop of more than 15%; while the pretreatment solution PL-1 of the present invention did not show any increase in pressure drop during the 10,000-minute recirculation.

[0196] It can be concluded that when combined with water-based inkjet inks, pretreatment solutions containing water-soluble carboxylic acid polymers with an acid value of 950 mg KOH / g or less do indeed exhibit excellent image quality, and at the same time do not cause filter clogging when used in recirculating inkjet heads.

Claims

1. An image recording method, comprising the following steps: a. Provide the base material; and b. Applying aqueous pretreatment droplets with a droplet mass of 15 ng / drop or less and 1 ng / drop or greater to at least a portion of the recording area S on the substrate surface, wherein the droplet density is 55 drops / mm². 2 Or greater than or equal to 1600 drops / mm 2 or smaller; and c. Adhere water-based inkjet ink to at least a portion of the recording area S, said water-based inkjet ink comprising pigments and water-soluble organic solvents. The aqueous pretreatment solution is characterized by comprising a fixative and a resin.

2. The image recording method according to claim 1, wherein the resin is selected from water-soluble carboxylic acid polymers or their salts, carboxylic anhydride polymers, polyurethanes or their copolymers, acrylates or their copolymers, polyesters or their copolymers, and polystyrene or its copolymers, provided that if the resin is resin particles in an aqueous pretreatment solution, it is stabilized by nonionic groups or nonionic or amphiphilic compounds.

3. The image recording method according to claim 2, wherein the water-soluble carboxylic acid polymer or its salt or the carboxylic anhydride polymer has an acid value equal to or less than 950 mg KOH / g polymer and equal to or greater than 450 mg KOH / g polymer.

4. The image recording method according to any one of the preceding claims, wherein, according to the Bristow method, 30 ms from the start of contact with water... 1 / 2 Inside, the substrate has 10 ml / m 2 Or even less water absorption.

5. The image recording method according to any one of the preceding claims, wherein the substrate is a cardboard pad.

6. The image recording method according to claim 5, wherein the cardboard liner is a coated cardboard liner.

7. The image recording method according to any one of the preceding claims, wherein the fixative is a polyvalent metal salt or a cationic polymer.

8. The image recording method according to any one of the preceding claims, wherein the attached aqueous inkjet ink is at least partially dried, and then an aqueous varnish is applied to at least a portion of the recording area S, the aqueous varnish comprising resin particles, the resin particles comprising a resin selected from polyacrylates and polyurethanes.

9. The image recording method according to any one of the preceding claims, wherein the application of preprocessing droplets is performed via an image of 200 dpi or larger × 200 dpi or larger, and wherein the droplets are generated in a structured manner or in a semi-random manner via a halftone method.

10. The image recording method of claim 3, wherein the carboxylic acid polymer or its salt, or the carboxylic anhydride polymer, has a molecular weight equal to or greater than 2000 g / mol, the molecular weight being measured relative to a polyethylene standard using a universally calibrated GPC method with a polyethylene glycol standard.

11. The image recording method according to claim 2, wherein the nonionic group is selected from polyethylene glycol grafts, cellulose, dextran, sugar derivatives and grafted polyvinyl alcohol.

12. The image recording method according to claim 2, wherein the nonionic or amphiphilic compound is selected from polyvinyl alcohol copolymers, cellulose derivatives, dextrin derivatives, polysaccharide derivatives, and cyclodextrins.

13. The image recording method according to any one of the preceding claims, wherein the substrate is conveyed at a conveying speed of 30 m / min or greater, and the time between the adhesion of the pretreatment droplets and the water-based inkjet droplets is 30 s or less.

14. The recording method according to any one of the preceding claims, wherein the application of the pretreatment liquid is performed by means of an inkjet head, and the pretreatment liquid is recycled in the head or the pretreatment liquid supply system of the inkjet head.

15. An inkjet recording apparatus for forming an image on a substrate, comprising: - A conveyor mechanism configured to convey a substrate along the conveying direction; as well as - An inkjet printhead for applying pre-treated droplets to at least a portion of a recording area S on a substrate surface, said pre-treated droplets having a droplet mass of 15 ng / drop or less and equal to or greater than 1 ng / drop, wherein the droplet density is equal to 55 drops / mm². 2 Or greater than or equal to 1600 drops / mm 2 or smaller, and - An inkjet printhead for adhering water-based inkjet ink containing pigments and water-soluble organic solvents to at least a portion of a recording area S; The pretreatment solution is characterized by containing a fixative and a resin.

Images