Aqueous pigment-based inkjet ink

Abstract

An aqueous inkjet ink for an inkjet printhead having a silicon-based material in contact with the aqueous inkjet ink wherein the aqueous inkjet ink has a pH of between 7.0 and 10.0 and comprises a color pigment selected from the group consisting of organic color pigments and carbon black pigments, and an anti-corrosion compound, the anti-corrosion compound is selected from a compound comprising a six-membered aromatic ring having two para-hydroxyl groups and a compound according to Formula 2: # imgabs0 # wherein R5 is selected from an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, and aryl and heteroaryl groups; r6 to R9 are independently selected from the group consisting of hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, and aryl and heteroaryl groups; or any R6 to R9 may represent the necessary atoms to form a five to eight membered ring.

Description

Technical Field

[0001] The present invention relates to an aqueous inkjet ink mainly developed to improve the printhead life of a silicon-based MEMS inkjet printhead. Background Art

[0002] Economies of scale, the availability of inexpensive high-quality materials, and the ability to incorporate electronic functionality have made silicon-based materials attractive for constructing microelectromechanical systems (MEMS) devices such as silicon-based MEMS inkjet printheads. However, it has been observed that aqueous chemical inkjet inks can cause corrosion by etching silicon-based materials (see Figure 1 ), resulting in a significant deterioration in the ejection performance of the printhead. Such corrosion can lead to a deterioration in the ejection and landing accuracy of ink droplets and is thus detrimental to printing reliability, which is an essential requirement in industrial inkjet environments along with cost-effectiveness.

[0003] One approach is to protect the MEMS and the circuitry included in a silicon-based MEMS inkjet printhead from exposure to the corrosive nature of the aqueous inkjet ink passing through and ejected therefrom by applying a sealing film to the MEMS and the circuitry. For example, EP3962793 A (HP) discloses an undoped dielectric film as a sealing film, while EP 1465773 A (XAAR TECHNOLOGY LTD) discloses depositing a parylene film to provide corrosion resistance. However, depositing thin films in a reproducible manner in this way will reduce the advantages of silicon-based materials in providing low-cost printheads.

[0004] Another approach is to adjust the aqueous inkjet ink such that the corrosiveness of the ink is reduced. WO 2010 / 138191A (EASTMAN KODAK CO) discloses an aqueous ink composition for an inkjet printer that contains a soluble organic aromatic azo compound in a concentration sufficient to inhibit the corrosion of silicon-based materials upon contact with the ink composition. However, it has been observed that in printed matter produced by printing decorative paper with an aqueous inkjet ink, the addition of these aromatic azo dyes can cause image bleeding during the impregnation process performed after printing. The dyes leach out in the impregnation bath and cause color contamination during this process.

[0005] Another approach, as disclosed in US2008129811 A (SONY CORP), uses a dispersion of alumina or ceria particles that are positively charged in the pH range of 4 to 6. It is believed that these positively charged particles will adhere to the negatively charged silicon-based surfaces in the printhead and thus prevent the ink from corroding these surfaces. These methods are limited to specific ink compositions and are not applicable to pigment-based inks, in which the negative charges on the pigment surface and the polymer are crucial for the stability of pigment-based inkjet inks. The latter pigment-based inkjet inks require an alkaline pH greater than 7.

[0006] In yet another method, US2012105553 A (EASTMAN KODAK CO) discloses the use of specific soluble metal ligand complexes in aqueous inkjet inks to inhibit the corrosion of silicon-based materials of printheads. However, pigmented aqueous inks typically contain organic polymer binders or dispersants, which are usually dissolved by the deprotonation of carboxylic acid groups at a weakly basic pH level. The resulting carboxylate ions may form complexes with the polyvalent metal ions of the soluble metal ligand complexes, where the polymers may further crosslink and become insoluble, leading to unreliable inkjet printing.

[0007] There is a need for pigmented aqueous inkjet inks that have improved corrosion resistance when used in silicon-based MEMS inkjet printheads without affecting ink performance, especially printing reliability. SUMMARY OF THE INVENTION

[0008] To overcome the above problems, a preferred embodiment of the present invention has been achieved with such an aqueous inkjet ink having a pH between 7.0 and 10.0 and comprising a color pigment and an anti-corrosion compound selected from compounds comprising a six-membered aromatic ring having two para-hydroxy groups and compounds according to Formula 2,

[0009] wherein R 5 is selected from alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, alkaryl groups, and aryl and heteroaryl groups; R 6 to R 9 are independently selected from hydrogen, alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, alkaryl groups, and aryl groups and heteroaryl groups; or any of R 6 to R 9 may represent the necessary atoms forming a five- to eight-membered ring.

[0010] Surprisingly, it has been found that the above specific compounds can be used as anti-corrosion compounds in silicon-based MEMS inkjet printheads. It has been observed that in the absence of such specific anti-corrosion compounds, when printing with an inkjet ink containing carbon black pigment, the acoustic period of the G3L printhead will increase significantly. Printheads with a larger acoustic period show a higher droplet volume. In addition, frequency scans show that printheads with a larger acoustic period have more unstable regions.

[0011] An object of the present invention is to provide a pigmented aqueous inkjet ink that exhibits improved corrosion resistance in an inkjet printhead having a silicon-based material in contact with the aqueous inkjet ink.

[0012] Another object of the present invention is to use a specific compound in a pigment-based aqueous inkjet ink having a pH between 7.0 and 10.0 to reduce corrosion in an inkjet printhead made of a silicon-based material that comes into contact with the aqueous inkjet ink.

[0013] Another object of the present invention is to provide an inkjet printing method with high printing reliability.

[0014] Further advantages and embodiments of the present invention will be apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A micrograph (magnified 3999 times) of the nozzle 2 in the nozzle plate 1 is shown, and corrosion has occurred at the nozzle edge 3 of the nozzle plate 1. DETAILED DESCRIPTION

[0016] Definition

[0017] The term "alkyl" refers to all possible variants of each number of carbon atoms in an alkyl group, namely: methyl; ethyl; for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl, and tert-butyl; for five carbon atoms: n-pentyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl, and 2-methylbutyl, etc.

[0018] Unless otherwise specified, a substituted or unsubstituted alkyl group is preferably a C 1 to C 6 -alkyl group.

[0019] Unless otherwise specified, a substituted or unsubstituted alkenyl group is preferably a C 2 to C 6 -alkenyl group.

[0020] Unless otherwise specified, a substituted or unsubstituted alkynyl group is preferably a C 2 to C 6 -alkynyl group.

[0021] Unless otherwise specified, a substituted or unsubstituted aralkyl group is preferably a phenyl or naphthyl group containing one, two, three, or more C 1 to C 6 -alkyl groups.

[0022] Unless otherwise specified, a substituted or unsubstituted alkaryl group is preferably a C 7 to C 20 -alkyl group containing a phenyl group or a naphthyl group.

[0023] Unless otherwise specified, a substituted or unsubstituted aryl group is preferably a phenyl group or a naphthyl group.

[0024] Unless otherwise specified, the substituted or unsubstituted heteroaryl group is preferably a five- or six-membered ring substituted by one, two or three oxygen atoms, nitrogen atoms, sulfur atoms, selenium atoms or combinations thereof.

[0025] The term "substituted" in, for example, a substituted alkyl group means that the alkyl group can be substituted by other atoms different from those normally present in such a group (i.e., carbon and hydrogen). For example, a substituted alkyl group can contain a halogen atom or a thiol group.

[0026] The term "unsubstituted" in, for example, an unsubstituted alkyl group means that the alkyl group contains only the atoms normally present in such a group, i.e., carbon and hydrogen.

[0027] Unless otherwise specified, the substituted alkyl group, substituted alkenyl group, substituted alkynyl group, substituted aralkyl group, substituted alkaryl group, substituted aryl and substituted heteroaryl group are preferably substituted by one or more substituents selected from: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl, ester group, amide group, ether group, thioether group, ketone group, aldehyde group, sulfoxide group, sulfone group, sulfonate group, sulfonamide group, -Cl, -Br, -I, -OH, -SH, -CN and -NO 2 。

[0028] Water-based inkjet ink

[0029] The aqueous inkjet ink according to a preferred embodiment of the present invention includes an aqueous inkjet ink for an inkjet printhead, the inkjet printhead having a silicon-based material in contact with the aqueous inkjet ink, wherein the aqueous inkjet ink has a pH between 7.0 and 10.0 and contains a color pigment and an anti-corrosion compound, the anti-corrosion compound being selected from compounds containing a six-membered aromatic ring with two para-hydroxy groups and compounds according to Formula 2,

[0030] wherein R 5 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted aralkyl groups, substituted or unsubstituted alkaryl groups, substituted or unsubstituted aryls and substituted or unsubstituted heteroaryls; R 6 to R 9Independently selected from hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl, and a substituted or unsubstituted heteroaryl group; or any of R 6 to R 9 may represent the necessary atoms to form a five- to eight-membered ring.

[0031] In a preferred embodiment, R 5 is selected from a substituted or unsubstituted alkyl group and a substituted or unsubstituted aryl group, particularly preferably a substituted or unsubstituted aryl group, and most preferably a substituted or unsubstituted phenyl group. A carboxylic acid group or its salt and a sulfonic acid group or its salt are particularly preferred substituents. The cation of the salt in the carboxylic acid and sulfonic acid groups or their salts is preferably monovalent and is preferably selected from Li + , K + , Na + , NH 4 + and a monovalent organic cation.

[0032] It has been observed that inkjet inks containing compounds according to formula 2 having a carboxylic acid group or its salt are often more efficient and effective in combating corrosion than other types of acid groups or their salts.

[0033] In another preferred embodiment, R 6 and R 7 represent hydrogen.

[0034] In another preferred embodiment, R 8 and R 9 are independently selected from hydrogen and a substituted or unsubstituted alkyl group.

[0035] Where possible, there is no limitation to the combination of the above preferred embodiments.

[0036] Typical examples of the components according to formula 2 are given in Table 1 but are not limited thereto. Table 1 In + , the compounds shown with an acid group may also be their salts, and the compounds disclosed as salts may also include any cation selected from Li + , Na + , K 4 + and a monovalent organic cation, or may be an acid group.

[0037] Table 1

[0038]

[0039]

[0040]

[0041] The corrosion-resistant compound can also be a compound containing a six-membered aromatic ring having two para-hydroxy groups.

[0042] In a preferred embodiment, the compound containing a six-membered aromatic ring having two para-hydroxy groups is a compound according to Formula 1:

[0043] wherein R 1 to R 4 are independently selected from hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl or heteroaryl group, a halogen, a hydroxy group, an ether group, an ester group, a carbonate group, an amide group, a carbamate group, a carboxylic acid group or a salt thereof, a nitrile group, a nitro group, an amine group, a thiol group, a thioether group, a sulfonic acid group or a salt thereof, a sulfonamide group, a sulfonate group, a sulfoxide group, a sulfone group, a phosphate group or a salt thereof, a phosphate ester group, a phosphonic acid group or a salt thereof, a phosphonate ester group, an aldehyde group and a ketone group, or wherein R 1 and R 2 and / or R 3 and R 4 may represent the necessary atoms to form a five- to eight-membered ring.

[0044] In a preferred embodiment, R 1 to R 4 are independently selected from hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a carboxylic acid group or a salt thereof and a sulfonic acid group or a salt thereof.

[0045] In an even more preferred embodiment, R 1 to R 4 are independently selected from hydrogen, a C1 to C4 alkyl group, a substituted or unsubstituted benzene ring, a carboxylic acid group or a salt thereof and a sulfonic acid group or a salt thereof.

[0046] The carboxylic acid group or a salt thereof and the sulfonic acid group or a salt thereof are particularly preferred substituents. The cation of the salt in the carboxylic acid and the sulfonic acid group or a salt thereof is preferably monovalent and is preferably selected from L i+ , K + , Na + , NH 4 + and a monovalent organic cation.

[0047] It has been observed that inkjet inks containing compounds according to Formula 1 having carboxylic acid groups or salts thereof tend to be more efficient and effective in combating corrosion than other types of acid groups or salts thereof.

[0048] In another preferred embodiment, R 1 and R 2 and R 3 and R 4 It represents the atoms necessary to form a six-membered ring, particularly preferably an aromatic six-membered ring.

[0049] Where possible, there is no restriction on the combinations of the above-described preferred embodiments.

[0050] Typical examples of compounds according to Formula 1 are Table 2 Given in, but not limited to. Table 2 The compounds shown as having an acid group may also be salts thereof, and the compounds disclosed as salts may also include compounds selected from Li + 、Na + , K + NH 4 + and any cation of a monovalent organic cation, or may be an acid group.

[0051] Table 2

[0052]

[0053]

[0054]

[0055]

[0056] The compounds in Table 1 and Table 2 are readily available from commercial sources such as MERCK, SIGMA-ALDRICH and ACROS.

[0057] In a preferred embodiment of the aqueous inkjet ink, the color pigment is a carbon black pigment. Although corrosion may occur with different types of color pigments, it has been observed that the advantages of the present invention are most clearly observed with carbon black pigments. The reason for this is that carbon black pigments appear to catalyze the corrosion of silicon-based MEMS inkjet print heads.

[0058] The anti-corrosion compound is preferably present in an amount of 0.01 wt % to 15 wt %, more preferably 0.05 wt % to 10 wt %, most preferably less than 5 wt %, or even 2 wt %, all weight percentages (wt %) being based on the total weight of the aqueous inkjet ink.

[0059] In a most preferred embodiment of the aqueous inkjet ink, the compound according to formula 1 or 2 is present in an amount of 0.01 to less than 2.0% by weight, based on the total weight of the aqueous inkjet ink. At such concentrations, no decrease in dispersion stability is observed.

[0060] The aqueous inkjet ink has a pH between 7.0 and 10.0. When the pH is below 7.0, the dispersion stability deteriorates and the anti-corrosion compound loses its effectiveness. When the pH is above 10.0, an accelerated corrosion process of silicon is observed. In a more preferred embodiment of the aqueous inkjet ink, the pH of the aqueous inkjet ink is between 7.5 and 9.0.

[0061] The static surface tension of the aqueous inkjet ink is preferably in the range of 18 mN / m to 40 mN / m at 25 °C, and more preferably in the range of about 19 mN / m to about 30 mN / m at 25 °C. Within these ranges, the ink spreading is optimal to obtain good image quality, for example, on decorative paper for manufacturing decorative panels.

[0062] For good jetting ability and fast inkjet printing, the viscosity of the one or more aqueous inkjet inks at a temperature of 32 °C is preferably less than 30 mPa·s, more preferably less than 15 mPa·s, and most preferably between 1 and 10 mPa·s, all at a shear rate of 1,000 s -1 The preferred jetting temperature is between 20 and 40 °C, more preferably between 25 and 45 °C, and most preferably below 35 °C.

[0063] The above-mentioned aqueous inkjet ink, more preferably a black aqueous inkjet ink containing carbon black pigment, is preferably part of an aqueous inkjet ink set. In a more preferred embodiment, all pigment-based aqueous inkjet inks contain the anti-corrosion compound as described above.

[0064] Color pigment

[0065] The colorants in the aqueous pigment-based inkjet ink include one or more colored pigments. Organic and / or inorganic pigments can be used, but organic colored pigments are preferably used because they allow maximizing the color gamut. A single colored pigment or a mixture of colored pigments can be used in the aqueous inkjet ink.

[0066] The pigments used in the pigment-based inkjet ink according to the present invention can be black, cyan, magenta, yellow, red, orange, purple, blue, green, brown, mixtures thereof, etc.

[0067] Suitable color pigments may be selected from those disclosed in HERBST, Willy et al., Industrial Organic Pigments, Production, Properties, Applications, 3rd Edition, Wiley-VCH, 2004, ISBN 3527305769.

[0068] The choice of color pigment is generally determined by the application. For example, if the image to be reproduced is a wood replica, a CRYK inkjet ink set is preferably used instead of a CMYK inkjet ink set.

[0069] The pigment used for the black ink is carbon black pigment (C.I. Pigment Black 7). Such pigments are readily available from commercial sources, such as Regal TM 400R, Mogul TM L, Elftex TM 320, or CarbonBlack FW18, Special Black TM 250, Special Black TM 350, Special Black TM 550, Printex TM 25, Printex TM 35, Printex TM 55, Printex TM 90, Printex TM 150T, MA8 from MITSUBISHI CHEMICAL Co.;

[0070] Mixed crystals can also be used as color pigments. Mixed crystals are also known as solid solutions. For example, under certain conditions, different quinacridones mix with each other to form solid solutions, which are quite different from both the physical mixtures of the compounds and the compounds themselves. In a solid solution, the molecules of each component enter the same crystal lattice, usually but not always the lattice of one of the components. The x-ray diffraction pattern of the resulting crystalline solid is characteristic of the solid and can be clearly distinguished from the pattern of a physical mixture of the same components in the same proportions. In such a physical mixture, the x-ray patterns of each component can be distinguished, and the disappearance of many of these lines is one of the criteria for the formation of a solid solution. One commercially available example is Magenta L 4540 from BASF. Magenta L 4540.

[0071] The pigment particles in the inkjet ink should be small enough to allow the ink to flow freely through the inkjet printing device, especially at the ejection nozzles. To achieve good ejection performance, the average particle size is preferably less than 300 nm, more preferably less than 200 nm. It is also desirable to filter the aqueous inkjet ink with a filter having a pore size of 1 μm, preferably 0.5 μm, to eliminate oversize particles.

[0072] The average pigment particle size of the pigment particles is preferably determined using a device based on the principle of dynamic light scattering. The ink is then usually diluted with water to a pigment concentration of 0.002 wt% for measurement.

[0073] The pigment is used in the pigment dispersion in an amount of 0.1 to 20 wt%, preferably 0.6 to 6 wt%, based on the total weight of the pigment dispersion.

[0074] If excellent quality granulation is required, one or more light inkjet inks can be added to the aqueous pigment-based inkjet ink set. The light inkjet ink preferably has the same pigment as the corresponding aqueous dark inkjet ink of the same color, but at a much lower concentration. The aqueous inkjet ink set preferably contains one or more aqueous light inkjet inks, the aqueous light inkjet inks containing a pigment in an amount of 0.1 to 1.2 wt% pigment, wherein the weight percentage (wt%) is based on the total weight of the aqueous light inkjet ink.

[0075] The inkjet ink can also contain a white pigment as a colorant, more preferably the white pigment is present in the inkjet ink in an amount of 15 to 25 wt% based on the total weight of the inkjet ink. Within the above range, a thin layer of white ink will obtain good opacity while the viscosity will not increase too much, thus not impairing the ejection performance. For this purpose, titanium dioxide pigment (preferably rutile) is particularly preferably used as the white pigment.

[0076] For the surface treatment of titanium dioxide, an aqueous treatment or a gas-phase treatment is applied, and an alumina-silica treatment agent is generally used. Untreated, alumina-treated or alumina-silica-treated titanium dioxide can be used. Organic surface treatment can be used alone or in addition to the aforementioned surface treatment.

[0077] Dispersant

[0078] The pigment-based aqueous inkjet ink preferably contains a polymeric dispersant for dispersing the color pigments. One or more aqueous inkjet inks can also contain a dispersion synergist to further improve the dispersion quality and stability of the ink.

[0079] Suitable polymeric dispersants are copolymers of two monomers, although they can contain three, four, five or even more monomers. The properties of the polymeric dispersant depend on both the nature of the monomers and their distribution in the polymer. The copolymeric dispersant preferably has the following polymeric composition:

[0080] · Statistically polymerized monomers (e.g., monomers A and B polymerized to ABBAABAB);

[0081] · Alternatingly polymerized monomers (e.g., monomers A and B polymerized to ABABABAB);

[0082] · Gradient (graded) polymerized monomers (e.g., monomers A and B polymerized to AAABAABBABBB);

[0083] · Block copolymers (e.g., monomers A and B polymerized to AAAAABBBBBB), where the block length of each block (2, 3, 4, 5 or even more) is important for the dispersing ability of the polymeric dispersant;

[0084] · Graft copolymers (graft copolymers consist of a polymer backbone and polymer side chains attached to the backbone); and

[0085] · Mixed forms of these polymers, such as block-gradient copolymers.

[0086] Suitable commercially available dispersants are DISPERBYK available from BYK CHEMIE TM dispersants, JONCRYL TM dispersants available from BASF and SOLSPERSE TM dispersants available from LUBRIZOL. MC CUTCHEON.Functional Materials, North American Edition.Glen Rock, N.J.:Manufacturing Confectioner Publishing Co., 1990.p.110 - 129 discloses non-polymeric dispersants and a detailed list of some polymeric dispersants.

[0087] The polymeric dispersant preferably has a number average molecular weight Mn between 500 and 30,000, more preferably between 1500 and 10,000 to obtain good spraying performance.

[0088] The polymeric dispersant preferably has a weight average molecular weight Mw less than 100,000, more preferably less than 50,000, most preferably less than 30,000 to obtain good spraying performance.

[0089] In a preferred embodiment, the polymeric dispersant used is a copolymer comprising between 3 and 11 mol% of a long aliphatic chain (meth)acrylate, wherein the long aliphatic chain contains at least 10 carbon atoms. The long aliphatic chain (meth)acrylate preferably contains from 10 to 18 carbon atoms. The long aliphatic chain (meth)acrylate is preferably decyl (meth)acrylate. The polymeric dispersant can be prepared by simple controlled polymerization of a mixture of monomers and / or oligomers comprising between 3 and 11 mol% of a long aliphatic chain (meth)acrylate, wherein the long aliphatic chain contains at least 10 carbon atoms. A commercially available polymeric dispersant which is a copolymer comprising between 3 and 11 mol% of a long aliphatic chain (meth)acrylate is Edaplan TM 482, which is a polymeric dispersant from MUNZING.

[0090] Surfactant

[0091] The aqueous inkjet ink may contain at least one surfactant. The surfactant can be anionic, cationic, nonionic or zwitterionic, and is generally added in a total amount of less than 1% by weight, particularly less than 0.3% by weight based on the total weight of the inkjet ink. The above total amount is expressed as dry solids.

[0092] Surfactants suitable for use in aqueous inkjet inks include fatty acid salts, ester salts of higher alcohols, alkylbenzene sulfonates of higher alcohols, sulfosuccinate salts and phosphate esters (e.g., sodium dodecylbenzene sulfonate and sodium dioctyl sulfosuccinate), ethylene oxide adducts of higher alcohols, ethylene oxide adducts of alkylphenols, ethylene oxide adducts of polyol fatty acid esters, and acetylene glycols and their ethylene oxide adducts (e.g., polyoxyethylene nonylphenyl ether, and SURFYNOL TM 104, 104H, 440, 465 and TG) available from AIR PRODUCTS & CHEMICALS INC.

[0093] Preferred surfactants are selected from fluorosurfactants, such as fluorinated hydrocarbons.

[0094] A particularly preferred commercially available fluorosurfactant is Capstone TM FS3100 from DU PONT.

[0095] In one embodiment of the aqueous inkjet ink, the surfactant is a fluorosurfactant, more preferably an alkoxylated fluorosurfactant, and most preferably an alkoxylated fluorosurfactant containing a sulfonic acid group or its salt.

[0096] In a preferred embodiment, the surfactant is a silicone surfactant, preferably a polyether-modified polydimethylsiloxane.

[0097] Biocide

[0098] Biocides suitable for use in the aqueous inkjet inks of the present invention include sodium dehydroacetate, 2-phenoxyethanol, sodium benzoate, sodium pyridinethion-1-oxide, ethyl p-hydroxybenzoate, and 1,2-benzisothiazolin-3-one and its salts.

[0099] Preferred biocides are Proxel available from ARCH UK BIOCIDES TM GXL, Proxel TM K and Proxel TM Ultra 5 and Bronidox available from COGNIS TM .

[0100] A particularly preferred biocide is a 1,2-benzisothiazolin-3-one based biocide.

[0101] The biocide is preferably added in an amount of 0.001 to 3.0% by weight, more preferably 0.01 to 1.0% by weight, based on the total weight of the pigmented inkjet ink.

[0102] Humectant

[0103] The aqueous inkjet ink preferably contains a humectant.

[0104] Suitable humectants include glyceryl triacetate, N-methyl-2-pyrrolidone, 2-pyrrolidone, glycerol, urea, thiourea, ethylene urea, alkyl ureas, alkyl thioureas, dialkyl ureas and dialkyl thioureas, diols including ethylene glycol, propylene glycol, glycerol, butylene glycol, pentylene glycol and hexylene glycol. Preferred humectants are 2-pyrrolidone, glycerol and 1,2-hexanediol, the latter having been found to be most effective in improving the reliability of inkjet printing in industrial environments.

[0105] The humectant is preferably added to the inkjet ink in an amount of 0.1 to 35% by weight of the formulation, more preferably 1 to 30% by weight of the formulation, and most preferably 2 to 25% by weight of the inkjet ink.

[0106] pH regulator

[0107] The aqueous inkjet ink may contain at least one pH regulator. Suitable pH regulators include NaOH, KOH, NEt 3 , NH 3 , HCl, HNO 3 , H 2 SO 4and (poly)alkanolamines such as triethanolamine and 2-amino-2-methyl-1-propanol. Preferred pH regulators are triethanolamine, NaOH, and H 2 SO 4 .

[0108] Preferably, the pH is adjusted to a value between 7.5 and 10.0, more preferably to a value between 8.0 and 9.0; it has been observed that the latter pH range results in improved ink stability.

[0109] Other additives

[0110] In addition to the above components, the ink may optionally contain other additives as needed.

[0111] Examples of other components include known additives such as decolorization inhibitors, emulsion stabilizers, penetration enhancers, UV absorbers, preservatives, antifungal agents, viscosity regulators, rust inhibitors, and chelating agents.

[0112] Preferred UV absorbers include benzophenone compounds, benzotriazole compounds, salicylate compounds, and hydroxyphenyltriazines.

[0113] Preparation of inkjet ink

[0114] An inkjet ink can be prepared by precipitating or grinding a color pigment in a dispersion medium in the presence of one or more polymeric dispersants.

[0115] Mixing equipment for preparing the pigment dispersion can include a pressure kneader, an open kneader, a planetary mixer, a dissolver, and a Dalton universal mixer. Suitable grinding and dispersing equipment are a ball mill, a pearl mill, a colloid mill, a high-speed disperser, a two-roll mill, a bead mill, a paint conditioner, and a three-roll mill. The dispersion can also be prepared using ultrasonic energy.

[0116] If the inkjet ink contains more than one pigment, separate dispersions of each pigment can be used to prepare the color ink, or alternatively, several pigments can be mixed and co-ground during the preparation of the dispersion.

[0117] The dispersion process can be carried out in a continuous, batch, or semi-batch mode.

[0118] The preferred amounts and ratios of the components of the mill grind will vary widely depending on the specific materials and the intended application. The contents of the grinding mixture include the mill grind and the grinding medium. The mill grind contains the pigment, the dispersant, and a liquid carrier such as water. For aqueous inkjet inks, the pigment is typically present in the mill grind at 1 to 50 wt%, preferably 10 to 25 wt%, excluding the grinding medium. The weight ratio of the pigment to the dispersant is preferably from 20:1 to 1:2.

[0119] The grinding time can vary greatly and depends on the pigment, the selected mechanical device and residence conditions, the initial and desired final particle sizes, etc.

[0120] After grinding is complete, the grinding medium is separated from the ground particulate product (in the form of a dry or liquid dispersion) using conventional separation techniques such as by filtration, screening through a sieve, etc. The sieve is usually built into the mill, for example in the case of a bead mill. The ground pigment concentrate is preferably separated from the grinding medium by filtration.

[0121] The pigment dispersion is preferably also filtered through a 1 μm, preferably 0.5 μm filter to remove so-called "oversize particles", i.e., pigment particles that have been inefficiently ground and have a much larger particle size of around 2 μm.

[0122] Generally, it is desirable to prepare the color ink in the form of a concentrated pigment dispersion, which is subsequently diluted to an appropriate concentration for use in an inkjet printing system. This technique allows for the preparation of a larger amount of pigment-based ink from the equipment. If the mill grind is made in a solvent, it is diluted with water and optionally other solvents to an appropriate concentration. If it is made in water, it is diluted with additional water or a water-miscible solvent to make a mill grind of the desired concentration. By dilution, the ink is adjusted to the viscosity, color, hue, saturation density, and print area coverage required for a specific application.

[0123] The viscosity can also be adjusted by using a low molecular weight polyethylene glycol (e.g., polyethylene glycol with a number average molecular weight between 200 and 800). An example is PEG 200 from CLARIANT.

[0124] Inkjet printing method

[0125] An inkjet printing method according to a preferred embodiment of the present invention includes the steps of: a) jetting one or more of the aqueous inkjet inks as described above onto a substrate; and b) drying the aqueous inkjet ink jetted onto the substrate. The substrate is preferably selected from decorative paper, paperboard boxes, corrugated cardboard, or the liner of corrugated cardboard. The substrate preferably has an ink-receiving layer to improve the image quality.

[0126] The inkjet printing in the manufacturing method is preferably carried out by a single-pass printing process.

[0127] The aqueous inkjet ink is preferably jetted at a jetting temperature in the range of 20 °C to 40 °C, preferably 25 °C to 38 °C, and most preferably not exceeding 35 °C. This will ensure good printing reliability. Using a higher temperature, such as 45 °C, will accelerate the evaporation of water at the nozzle, resulting in delay problems.

[0128] Inkjet printing system

[0129] An inkjet printing system according to a preferred embodiment of the present invention comprises: a) a silicon-based MEMS inkjet printhead and b) an aqueous inkjet ink as described above.

[0130] In a preferred embodiment of the inkjet printing system, the silicon-based MEMS inkjet printhead is a piezoelectric flow-through printhead. Commercially available examples of such silicon-based MEMS piezoelectric flow-through printheads are the G3L and G5L printheads from FUJIFILM DIMATIX.

[0131] The one or more aqueous inkjet inks are ejected by a printhead that ejects small droplets onto a substrate in a controlled manner, with the substrate moving relative to the printhead. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied to it. The application of the voltage changes the shape of the piezoelectric ceramic transducer in the printhead, creating a void that is then filled with ink. When the voltage is removed again, the ceramic expands back to its original shape, ejecting an ink droplet from the printhead. However, the inkjet printing method according to the present invention is not limited to piezoelectric inkjet printing. Other inkjet printheads can be used and include various types, such as silicon-based MEMS thermal printheads.

[0132] In a multi-pass inkjet printing method, the inkjet printhead scans back and forth in the lateral direction, across the surface of the moving substrate. Sometimes the inkjet printhead does not print on the return pass. To achieve high areal productivity, bi-directional printing is preferred.

[0133] Another preferred printing method is the "single-pass printing method", which can be carried out by using a page-width inkjet printhead or a plurality of staggered inkjet printheads that cover the entire width of the substrate surface. In the single-pass printing method, the inkjet printhead generally remains stationary while the substrate surface is conveyed beneath the inkjet printhead.

[0134] A dryer may be included in the inkjet printing apparatus to remove at least a portion of the aqueous medium. Suitable dryers include devices that circulate hot air, ovens, and devices that use air suction.

[0135] A preferred drying device uses carbon infrared radiation (CIR) to rapidly heat the exterior of the paper substrate.

[0136] Another preferred dryer is a NIR source that emits near-infrared radiation. The NIR radiation energy rapidly penetrates into the depth of the inkjet ink layer and removes water and solvents from the entire layer thickness, while conventional infrared and hot air energy is mainly absorbed at the surface and slowly conducted into the ink layer, which typically results in a slower removal of water and solvents.

[0137] An effective infrared radiation source preferably has a maximum emission between 0.8 and 1.5 μm. Such an infrared radiation source is sometimes referred to as a NIR dryer.

[0138] In a preferred form, the NIR radiation source is in the form of an NIR LED, which can be easily mounted on the shuttle system of a plurality of inkjet printheads in a multi-pass inkjet printing apparatus.

[0139] Industrial applicability

[0140] The above-described inkjet printing method can be used in many applications, but can be advantageously utilized in the manufacturing methods of decorative laminates, printed paper boxes, and printed corrugated cardboard. In these applications, the aqueous inkjet ink according to the present invention provides the printing reliability required in an industrial environment.

[0141] Manufacturing method of decorative laminate

[0142] A method for manufacturing a decorative laminate according to a preferred embodiment of the present invention includes the steps of: a) printing a decorative paper as a substrate using the inkjet printing method described above; b) impregnating the printed decorative paper with a thermosetting resin; and c) hot-pressing the printed decorative paper impregnated with the thermosetting resin into a decorative laminate.

[0143] The decorative laminate is then preferably cut into decorative panels selected from floors, kitchens, furniture, and wall panels.

[0144] A preferred aqueous pigment-based inkjet ink set comprises:

[0145] - a cyan aqueous inkjet ink containing a β-copper phthalocyanine pigment;

[0146] - a red aqueous inkjet ink containing a pigment selected from C.I. Pigment Red 57 / 1, C.I. Pigment Red 122, C.I. Pigment Red 170, C.I. Pigment Red 175, C.I. Pigment Red 176, C.I. Pigment Red 187, C.I. Pigment Red 188, C.I. Pigment Red 207, C.I. Pigment Red 242, C.I. Pigment Red 254, C.I. Pigment Red 272, and their mixed crystals;

[0147] - a yellow aqueous inkjet ink containing a pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Yellow 83, C.I. Pigment Yellow 97, C.I. Pigment Yellow 110, C.I. Pigment Yellow 120, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150, C.I. Pigment Yellow 151, C.I. Pigment Yellow 154, C.I. Pigment Yellow 155, C.I. Pigment Yellow 175, C.I. Pigment Yellow 180, C.I. Pigment Yellow 181, C.I. Pigment Yellow 194, C.I. Pigment Yellow 213, C.I. Pigment Yellow 214, and their mixed crystals; and

[0148] - A black aqueous inkjet ink containing carbon black pigment. Such an ink set allows for accurate reproduction of wood colors in decorative floor laminates.

[0149] Preferably, a printed decorative paper impregnated with a thermosetting resin is hot-pressed between a core layer and a protective layer and cut into a decorative panel, and the decorative panel is selected from floors, kitchens, furniture, and wall panels. The thermosetting resin used is preferably a melamine-based resin.

[0150] The decorative paper preferably includes a plurality of ink-receiving layers, and the outermost ink-receiving layer does not contain an inorganic pigment or the amount of its inorganic pigment is less than that of one or more ink-receiving layers located between the paper substrate and the outermost ink-receiving layer. The advantage is improved printing reliability. For rapid drying, the ink-receiving layers contain a large amount of inorganic pigments such as fumed silica, which can cause dust problems due to the conveyance of the paper substrate in an inkjet printer, especially in single-pass inkjet printing, where the paper substrate is conveyed at a very high speed under the print head. By making the outermost ink-receiving layer free of or containing only a small amount of inorganic pigment, such dust problems can be reduced.

[0151] The one or more ink-receiving layers preferably contain an inorganic pigment selected from aluminum hydrate, aluminum oxide, aluminum hydroxide, aluminum silicate, and silica. The one or more ink-receiving layers contain a polymer binder, which is preferably selected from polyvinyl alcohol, vinyl alcohol copolymer, or modified polyvinyl alcohol. Preferably, the one or more ink-receiving layers contain a breaking agent selected from cationic polymer binders, cationic inorganic pigments, and polyvalent salts.

[0152] In one embodiment, the paper substrate is a colored paper substrate, more preferably a bulk colored paper substrate. Using a colored paper substrate will reduce the amount of inkjet ink required to form a colored image.

[0153] It has been observed that improved image quality will be obtained when inkjet printing is performed in such a way that the extending direction of the wood grain in the colored image substantially corresponds to the inkjet printing direction. For the single-pass inkjet printing method, the inkjet printing direction is the conveyance direction of the paper substrate. In the multi-pass inkjet printing method, the inkjet printing direction is the scanning direction of the print head.

[0154] In a preferred embodiment, a grayscale inkjet printing method is used to manufacture a decorative panel including a tongue and a groove that can achieve a glue-free mechanical joint between decorative panels.

[0155] The inkjet printing method is preferably part of a DPL process, in which a decorative layer is added to the stack and pressed together with the core layer, the protective layer and preferably also a balancing layer. Of course, it is not excluded that the method according to the invention forms part of a CPL (compact laminate) or HPL (high-pressure laminate) process, in which the decorative layer is hot-pressed at least together with a plurality of resin-impregnated core paper layers (such as so-called kraft paper), thereby forming a substrate under the decorative layer, and in which the obtained pressed and cured laminate layer or laminate (in the case of HPL) is glued to another substrate, such as glued to a particle board or an MDF or HDF board.

[0156] In a preferred embodiment, a protective layer containing paper impregnated with a thermosetting resin is applied to the inkjet-printed color image. The thermosetting resin can be a colored thermosetting resin to reduce the amount of inkjet ink to be printed.

[0157] Manufacturing method of printed packaging

[0158] According to a preferred embodiment of the invention, a method for manufacturing a printed folding carton or a printed corrugated board comprises the steps of: a) providing an ink-receiving layer on the paper surface of a substrate; and b) inkjet-printing an image onto the ink-receiving layer with the aqueous inkjet ink as described above.

[0159] In a preferred embodiment of this manufacturing method, the inkjet printing is carried out according to the single-pass printing method. Single-pass inkjet machines run at very high speeds, some even up to 150 m / min.

[0160] Although inkjet printing can be carried out directly on a corrugated board having one or more ink-receiving layers, this manufacturing method preferably comprises step c) of laminating an inkjet-printed paper liner to the corrugated board of the corrugated board. The latter is beneficial to the image quality.

[0161] The method for manufacturing a printed folding carton or a printed corrugated board preferably further comprises the step of applying a protective varnish layer on the inkjet-printed image. Such a protective varnish layer generally also increases the gloss of the inkjet-printed image, which is beneficial to the image quality.

[0162] The ink-receiving layer and the varnish are preferably applied by spraying with an inkjet print head. In such a case, the ink-receiving layer is usually referred to as a sprayable primer.

[0163] In another particularly preferred embodiment of the manufacturing method, the ink-receiving layer and / or the protective varnish layer are applied by flexographic printing. This is beneficial for productivity. The ink-receiving layer and the protective varnish layer can also be applied by coating, for example using a rod coater or a knife coater. However, coating methods generally produce more waste because it takes some time to reach a stable coating state of good quality. Flexographic printing has the advantage that the flexographic printing roller can be easily incorporated into the inkjet printing system and run at the same printing speed.

[0164] The corrugated cardboard preferred in the present invention is single-wall or double-wall, more preferably single-wall corrugated cardboard, because this cardboard is strong enough and easy to fold. Single-sided corrugated cardboard is usually not strong enough to hold the merchandise, while triple-wall cardboard is usually more difficult to fold into a packaging box.

[0165] The cardboard used in the corrugated cardboard, such as kraft paper, is usually tan. In a preferred embodiment of the above manufacturing method, the paper liner has a white color. By having a white background, enhanced image quality will be obtained. The inkjet printing colors on the white paper liner have much higher vividness than the colors when printed on a tan kraft paper liner. The white background also helps to enhance the customer experience because customers consider this to be a more luxurious product. Alternatively, a white background can be applied as a layer by coating or printing before the inkjet printing. However, a white paper liner is preferred because this will enhance the reliability of the printing process by eliminating possible problems that may occur during the coating or printing of the white layer. Suitable paper liners with a white background include white top kraft paper and white coated kraft paper.

[0166] Examples

[0167] Materials

[0168] Unless otherwise specified, all materials used in the following examples can be easily obtained from standard sources, such as Sigma-Aldrich (MERCK, Belgium) and Acros (Belgium). The water used is demineralized water.

[0169] PBL7 is the abbreviation for Printex TM 90, which is a carbon black pigment from EVONIK.

[0170] ID-1 is the abbreviation for Edaplan TM 482, which is an acrylic polymer dispersant from MUNZING, containing about 6 mol% of long aliphatic chain (meth)acrylate and carboxylic acid groups. The acid value of ID-1 is 175 mg KOH / g.

[0171] Proxel is the abbreviation for ProxelTM Abbreviation for K (5% aqueous solution of 1,2-benzisothiazolin-3-one), available from YDS CHEMICALS NV.

[0172] PEG 200 is a polyethylene glycol from CLARIANT with an average molecular weight of 200.

[0173] NaOH-sol is an aqueous solution of 81 g of sodium hydroxide in water.

[0174] TEA is triethanolamine.

[0175] CAH-1 is a catechol compound represented by the following formula:

[0176]

[0177] (CASRN 29571-26-4, Preparation: Westervelt et al., Tappi, 65(5), 179-180 (1982))

[0178] CAH-2 is the sodium salt of 3,4-dihydroxybenzoic acid:

[0179]

[0180] (CASRN 24885-75-4, Preparation: Saito et al., Helvetica Chimica Acta, 89(7), 1395-1407 (2006))

[0181] CAH-3 is a catechol compound represented by the following formula:

[0182]

[0183] (CASRN 156245-29-3, Preparation: FR2902096 A1 (Rhodia Recherches et Technology))

[0184] CAP-1 is a compound represented by the following formula:

[0185]

[0186] CAP-1 is prepared according to the scheme given below:

[0187]

[0188] 76 g (0.5 mol) of 4-hydrazinobenzoic acid was added to 250 ml of acetonitrile, and then 62.5 g (1.15 mol) of formic acid (85%) was added. After the addition of formic acid, the temperature rose to 34 °C. The reaction mixture was heated to reflux and the reaction was allowed to continue under reflux for two hours. The mixture was cooled and CAP-1 was separated by filtration, washed with acetonitrile and dried. 83 g (yield: 92%) of CAP-1 was isolated (TLC analysis was performed on TLC silica gel 60F254 supplied by Merck, eluent dichloromethane / acetic acid / methanol 86 / 4 / 10, Rf = 0.26)

[0189] AH-1 is hydroquinone (supplied by TCI Europe), which is the compound HQ-1 in Table 2

[0190] AH-2 is the compound corresponding to Table 2 HQ-17 in

[0191] AH-3 is the compound corresponding to Table 2 HQ-2 in

[0192] AH-4 is the compound corresponding to Table 2 HQ-5 in

[0193] AP-1 is the compound corresponding to Table 1 Phen-2 in

[0194] The synthesis of AP-1 is given below:

[0195]

[0196] 92 g (4 mol) of sodium was added to 4 liters of isopropanol in portions. During the addition, the reaction mixture was gently refluxed. 405 g (2 mol) of methyl 4-hydrazinobenzoate hydrochloride was added. A thick suspension was formed after the addition. 172 g (181 ml, 2 mol) of acrylic acid was added and the reaction was allowed to continue refluxing for two hours. After two hours, 2 liters of isopropanol was removed by distillation and the mixture was cooled to room temperature. 2 liters of 5N H 2 SO 4 ​Solution. Add another one liter of water and then add 3 liters of dichloromethane. Separate the organic fraction, extract with 1 liter of water and 1 liter of saturated sodium chloride solution and dry. Remove the solvent under reduced pressure and recrystallize the crude isopropyl ester from 2 liters of isopropanol. Separate the isopropyl ester by filtration, wash twice with 150 ml of isopropanol and dry. 349 g (y: 79%) of isopropyl ester was separated out (TLC analysis was carried out on TLC silica gel 60F supplied by Merck 254 with eluent dichloromethane / acetic acid / methanol 95 / 2 / 3, R f = 0.4).

[0197] Add 340 g (1.37 mol) of isopropyl ester to 1545 ml of 5N NaOH solution. Add 1 liter of methanol. After adding methanol, the temperature rises to 40 °C. Heat the mixture to reflux and let the reaction continue under reflux for 3 hours. Based on TLC analysis (TLC analysis was carried out on TLC silica gel 60F supplied by Merck 254 with eluent dichloromethane / acetic acid / methanol 95 / 2 / 3), when no starting material can be detected any more, stop the reaction. Let the reaction mixture cool to room temperature and add 1.6 liters of 5N HCl solution. AP-1 precipitates out from the medium, is separated by filtration, washed twice with 100 ml of water and dried. 301 g of CAP-1 was separated out, which still contains a limited amount of salt. This CAP-1 is considered pure enough to be used in ink formulations, as confirmed by 1 1H-NMR analysis.

[0198] Measurement method

[0199] 1. Viscosity

[0200] The viscosity of the inkjet ink was measured using a Brookfield DV-II+ viscometer at a shear rate of 1,000 s -1 at 32 °C.

[0201] 2. Average particle size (concentrated pigment dispersion)

[0202] The average particle size of the pigment particles in the pigment dispersion was determined by photon correlation spectroscopy at a wavelength of 633 nm using a 4 mW HeNe laser on a diluted sample of the pigment-based inkjet ink. The particle size analyzer used was a Malvern TM nano-S available from Goffin-Meyvis.

[0203] The sample was prepared by adding a drop of ink to a cuvette containing 1.5 mL of water and mixing until a homogeneous sample was obtained. The measured particle size was the average of 3 consecutive measurements consisting of 6 runs of 20 seconds each.

[0204] 3. Average Particle Size (Inkjet Ink)

[0205] The ink sample was diluted with water to a pigment concentration of 0.002 wt%. The average particle size of the pigment particles was measured using a Nicomp TM 30 submicron particle analyzer based on the principle of dynamic light scattering.

[0206] To obtain good inkjet characteristics (jetting and printing quality), the average particle size of the dispersed particles is preferably below 250 nm.

[0207] 4. Corrosion Test

[0208] The corrosion inhibition was evaluated via an immersion test. An inkjet ink was filled into a 25 mL plastic container up to half of its volume. Then, a substrate was placed into the plastic container such that half of the substrate was exposed to the inkjet ink in the container. Then, the plastic container was closed and placed in an oven at 60 °C for a certain number of days. Visual evaluation was carried out according to Table 4 the standard.

[0209] Table 4

[0210] Score Standard (visual observation through human eyes) A No visible corrosion B Visible thin line at the air-ink interface on the substrate in the container C Discoloration of the part of the substrate immersed in the ink D Obvious corrosion of the part of the substrate immersed in the ink

[0211] The desired result of the corrosion test is a score of "A".

[0212] This immersion test uses two different substrates:[[]]

[0213] 1) Si<100>-wafer substrate; and

[0214] 2) NWC Si wafer substrate, where the Non Wetting Coating test piece is obtained from FUJIFILM DIMATIX, such as used for the G3L print head. NWC is a non-wetting coating present on the Si-wafer forming the nozzle plate. A durable non-wetting coating is applied to achieve high printing reliability and easy maintainability of the print head.

[0215] Example 1

[0216] This example illustrates how to prepare an inkjet ink containing carbon black pigment with good corrosion resistance.

[0217] Preparation of concentrated pigment dispersion CPK

[0218] Using a Disperlux TM mixer, the composition according to Table 5 was mixed for 30 minutes to prepare a concentrated aqueous pigment dispersion CPK.

[0219] Table 5

[0220] Weight % of components CPK PB7 15.00 ID-1 7.50 Proxel 0.02 Water 77.48

[0221] Then Dynomill is used TM RL is ground with 0.4 mm yttria-stabilized zirconia beads YTZ TM The concentrated aqueous pigment dispersion is ground with grinding media (obtainable from TOSOH Corp.). The grinding machine is charged with 41.9% of its volume of grinding beads and the dispersion is ground in a recirculation mode at a rotational speed of 4500 for 151 minutes. After grinding, the dispersion is separated from the beads. The concentrated aqueous pigment dispersion CPK is used as a basis for preparing black aqueous inkjet ink. The average particle size measured with Malvern TM nano-S is 131 nm.

[0222] Preparation of inkjet ink

[0223] By mixing the components in Table 6 in water in the amounts listed, inkjet inks INV-1 and INV-2 are prepared. Then the pH of the inkjet ink is adjusted to 8.5 by adding NaOH-sol. Then the concentrated aqueous pigment dispersion CPK is added. Then the pH of the inkjet ink is adjusted to 8.5 by adding NaOH-sol, and then the remaining water is added to bring the ink composition to 100% by weight.

[0224] Table 6

[0225] Weight %: INV-1 INV-2 Water 20.00 20.00 AH-2 0.10 0.10 1,2-Hexanediol 3.00 3.00 Glycerol 20.00 20.00 PEG200 19.00 19.00 Proxel 0.20 0.20 NaOH-sol Until pH = 8.5 Until pH = 8.5 CPK 16.65 25.35 NaOH-sol Until pH = 8.5 Until pH = 8.5 Water The rest The rest Total 100.00 100.00

[0226] Evaluation and results

[0227] The viscosity and average particle size (Nicomp) of the inkjet ink are measured. A corrosion test is carried out at 60 °C for 14 days. The results are shown in Table 7 .

[0228] Table 7

[0229]

[0230] It is observed that carbon black can catalyze the corrosion of (NWC) Si-wafers in some way. As can be seen from Table 7 , even a 50% increase in the carbon black pigment concentration (from 2.5% by weight in INV-1 to 3.8% by weight in INV-2) due to the presence of compound AH-2 does not reduce the corrosion resistance.

[0231] Example 2

[0232] This example illustrates the importance of suitable anti-corrosion compounds and hydroxyl groups in the para position on the aromatic ring for good corrosion resistance.

[0233] Preparation of inkjet ink

[0234] The comparative inkjet inks COMP-1 to COMP-9 were prepared to have a composition according to Table 8 whereas the inkjet inks INV-1 to INV-12 of the present invention were prepared to have a composition according to Table 9 and Table 10 . Styrene maleic anhydride salt was used as a dispersant in all the inkjet inks. By adding TEA (triethanolamine), the pH of the inkjet inks in Table 8 to Table 10 was adjusted to 8.5, and then a pigment dispersion was added. Thereafter, if necessary, the pH was adjusted to a value in the range of 8.0 to 9.0. Then the remaining water was added to bring the ink composition to 100% by weight.

[0235] The abbreviation "rem." represents the remainder. The pH was measured and shown in Table 8 to Table 10 .

[0236] Table 8

[0237]

[0238]

[0239] Table 9

[0240]

[0241]

[0242] Table 10

[0243]

[0244] Evaluation and results

[0245] A corrosion test was carried out at 60 °C for 14 days. The results are shown in Fig. 1.

[0246] Table 11

[0247]

[0248] From Table 11 it should be directly clearly visible that only the inkjet inks INV-1 to INV-12 of the present invention showed good results in terms of corrosion on both the NWC Si-wafer substrate and the Si<100>-wafer substrate from FUJIFILM DIMATIX.

[0249] It has also been observed that inkjet inks containing hydroquinone type compounds having a carboxylic acid or its salt (see AH-2 or AH-3) tend to be more efficient and effective against corrosion than hydroquinone type compounds or phenidone type compounds (see AP-1) or combinations thereof (see AP-1 / AH-1) that do not have a solubilizing group (see AH-1) or have a solubilizing group different from a carboxylic acid or its salt (see AH-4).

[0250] List of reference signs

[0251] Table 12

[0252] 1 Nozzle plate 2 Nozzle 3 Corrosion of the nozzle edge

Claims

1. An aqueous inkjet ink for an inkjet printhead, the inkjet printhead having a silicon-based material in contact with the aqueous inkjet ink, wherein the aqueous inkjet ink has a pH between 7.0 and 10.0 and contains a color pigment and an anti-corrosion compound, the color pigment being selected from organic color pigments and carbon black pigments, and the anti-corrosion compound being selected from compounds containing a six-membered aromatic ring having two para-hydroxy groups and compounds according to Formula 2, wherein R 5 is selected from alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, alkaryl groups, and aryl and heteroaryl groups; R 6 to R 9 are independently selected from hydrogen, alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, alkaryl groups, and aryl and heteroaryl groups; or any of R 6 to R 9 may represent the necessary atoms to form a five- to eight-membered ring.

2. The aqueous inkjet ink as claimed in claim 1, wherein the compound containing a six-membered aromatic ring having two para-hydroxy groups is a compound according to Formula 1: wherein R 1 to R 4 are independently selected from hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl group, a heteroaryl group, a halogen, a hydroxy group, an ether group, an ester group, a carbonate group, an amide group, a carbamate group, a carboxylic acid group or a salt thereof, a nitrile group, a nitro group, an amine group, a thiol group, a thioether group, a sulfonic acid group or a salt thereof, a sulfonamide group, a sulfonate group, a sulfoxide group, a sulfone group, a phosphate group or a salt thereof, a phosphate ester, a phosphonic acid group or a salt thereof, a phosphonate group, an aldehyde group and a ketone group, or wherein R 1 and R 2 and / or R 3 and R 4 may represent the necessary atoms to form a five- to eight-membered ring.

3. The aqueous inkjet ink as claimed in claim 1 or 2, wherein the color pigment is a carbon black pigment.

4. The aqueous inkjet ink as claimed in any one of claims 1 to 3, wherein the compound according to Formula 1 or 2 is present in an amount of 0.001 to less than 1.0% by weight based on the total weight of the aqueous inkjet ink.

5. The aqueous inkjet ink as claimed in any one of claims 1 to 4, wherein the pH of the aqueous inkjet ink is between 7.5 and 9.

0.

6. The aqueous inkjet ink according to any one of claims 1 to 5, wherein R 1 to R 4 are independently selected from hydrogen, C1 to C4 alkyl groups, substituted or unsubstituted benzene rings, carboxylic acid groups or their salts, and sulfonic acid groups or their salts; and / or wherein R 5 is a substituted or unsubstituted phenyl group having a carboxylic acid group or its salt and a sulfonic acid group or salt as substituents; and / or wherein R 6 and R 7 represent hydrogen; and / or wherein R 8 and R 9 are independently selected from hydrogen and alkyl groups.

7. The aqueous inkjet ink as claimed in any one of claims 1 to 6, wherein the compound according to Formula 1 or 2 is selected from: Provided that the above-mentioned compounds having an acid group may also be their salts; and provided that the above-mentioned compounds disclosed as salts may include any cation selected from Li + , Na + , K + , NH 4 + and monovalent organic cations.

8. An aqueous inkjet ink set, the aqueous inkjet ink set comprising a plurality of aqueous inkjet inks as claimed in any one of claims 1 to 7.

9. The aqueous inkjet ink set as claimed in claim 8, wherein the ink set comprises: - a cyan aqueous inkjet ink containing β-copper phthalocyanine pigment; - a magenta aqueous inkjet ink containing a pigment selected from C.I. Pigment Red 57 / 1, C.I. Pigment Red 122, C.I. Pigment Red 170, C.I. Pigment Red 175, C.I. Pigment Red 176, C.I. Pigment Red 187, C.I. Pigment Red 188, C.I. Pigment Red 207, C.I. Pigment Red 242, C.I. Pigment Red 254, C.I. Pigment Red 272 and their mixed crystals; - a yellow aqueous inkjet ink containing a pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Yellow 83, C.I. Pigment Yellow 97, C.I. Pigment Yellow 110, C.I. Pigment Yellow 120, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150, C.I. Pigment Yellow 151, C.I. Pigment Yellow 154, C.I. Pigment Yellow 155, C.I. Pigment Yellow 175, C.I. Pigment Yellow 180, C.I. Pigment Yellow 181, C.I. Pigment Yellow 194, C.I. Pigment Yellow 213, C.I. Pigment Yellow 214 and their mixed crystals; and - a black aqueous inkjet ink containing carbon black pigment.

10. An inkjet printing method, the method comprising the steps of: a) ejecting one or more aqueous inkjet inks as claimed in any one of claims 1 to 7 onto a substrate; and b) drying the aqueous inkjet ink ejected onto the substrate.

11. A method of manufacturing a decorative laminate, the method comprising the steps: a) Printing a decorative paper as a substrate using the inkjet printing method claimed in claim 10; b) Impregnating the printed decorative paper with a thermosetting resin; and c) Thermally pressing the printed decorative paper impregnated with the thermosetting resin into a decorative laminate.

12. A method for manufacturing a printed paper box or a printed corrugated cardboard, the method comprising the steps of: a) Providing an ink-receiving layer on the paper surface of a substrate; and b) Inkjet printing an image onto the ink-receiving layer using the inkjet printing method claimed in claim 10.

13. An inkjet printing system, the inkjet printing system comprising a) a silicon-based MEMS inkjet printhead and b) an aqueous inkjet ink claimed in any one of claims 1 to 7.

14. The inkjet printing system claimed in claim 13, wherein the silicon-based MEMS inkjet printhead is a piezoelectric through-flow printhead.

15. Use of a compound according to formula 1 and / or 2 in a pigmented aqueous inkjet ink having a pH between 7.0 and 10.0 for reducing corrosion in an inkjet printhead having a silicon-based material in contact with the aqueous inkjet ink, wherein the compound according to formula 1 and 2 is: wherein R 1 to R 4 are independently selected from hydrogen, alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, alkaryl groups, aryl groups, heteroaryl groups, halogens, hydroxy groups, ether groups, ester groups, carbonate groups, amide groups, carbamate groups, carboxylic acid groups or their salts, nitrile groups, nitro groups, amine groups, thiol groups, thioether groups, sulfonic acid groups or their salts, sulfonamide groups, sulfonate groups, sulfoxide groups, sulfone groups, phosphate or its salts, phosphate esters, phosphonic acid or its salts, phosphonate groups, aldehyde groups and ketone groups, or wherein R 1 and R 2 and / or R 3 and R 4 may represent the necessary atoms to form a five- to eight-membered ring; R 5 is selected from alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, alkaryl groups and aryl and heteroaryl groups; R 6 to R 9 are independently selected from hydrogen, alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, alkaryl groups and aryl groups and heteroaryl groups; or any of R 6 to R 9 may represent the necessary atoms to form a five- to eight-membered ring.

Images