Uv-curable inkjet ink and inkjet printing method

Abstract

A UV-curable inkjet ink comprising a) 20-45 wt% of a monofunctional monomer or oligomer comprising a monofunctional acrylate, a methacrylate; b) 5-55 wt% of an ethoxylated multifunctional acrylate monomer or oligomer; c) 12.0 wt% or more of an acylphosphine oxide photoinitiator and optionally an amine synergist; wherein the ratio R1 of the wt% of ethoxylated multifunctional acrylate monomer or oligomer to the wt% of non-ethoxylated multifunctional acrylate monomer or oligomer is between 0.1-4.0; wherein the ratio R2 of the wt% of monofunctional methacrylate to the wt% of monofunctional acrylate is not more than 1.2; and wherein all wt% are based on the total weight of the UV-curable inkjet ink. Also disclosed is an inkjet printing method using the UV-curable inkjet ink.

Description

Technical Field

[0001] This invention relates to UV-curable inkjet inks for manufacturing corrugated cardboard for inkjet printing, and more particularly UV-curable varnish inkjet inks. Background Technology

[0002] Corrugated cardboard is a preferred packaging material because it is inexpensive and lightweight. Lightweight packaging reduces transportation costs and facilitates handling during delivery to customers. Another benefit is that corrugated cardboard boxes are recyclable and stackable, making them easy to store and transport.

[0003] It has been observed that when inkjet-printed cardboard boxes are stacked in transport vehicles or on storage racks, they sometimes fail to slide well on each other. And when they do slide well, cracks are frequently observed when the corrugated cardboard used to make the boxes is bent.

[0004] UV-curable inkjet inks for printing on corrugated cardboard are known. For example, EP 4286483A (AGFANV) discloses an inkjet printing method comprising spraying a UV-curable varnish onto a substrate such as corrugated cardboard, wherein the static surface tension of the varnish is 28 mN / m or greater; and wherein the varnish contains more than 12% by weight of an acylphosphine oxide photoinitiator based on the total weight of the varnish.

[0005] Inkjet varnishes are also disclosed in, for example, US 2013286095 (SEIKO EPSON), EP 2657037A (SEIKO EPSON), US 2014370214 (FUJIFILM) and US 2015091217 (FUJIFILM).

[0006] However, there is still a need for improved UV-curable inkjet inks, especially varnishes that exhibit good sliding properties, no cracking when bent, and good UV curability. Summary of the Invention

[0007] To overcome the above problems, a preferred embodiment of the present invention has been implemented using a UV-curable inkjet as defined in claim 1.

[0008] Surprisingly, it was found that by controlling the specific ratio of monofunctional and polyfunctional monomers and oligomers in the ink composition, good flexural and sliding properties can be obtained while maintaining good UV curability.

[0009] The object of this invention is to provide an improved inkjet printing method, particularly for manufacturing printed corrugated cardboard.

[0010] Another object of the present invention is the use of UV-curable colorless inkjet ink as a varnish on (printed) corrugated cardboard.

[0011] These and other purposes will become apparent from the following detailed description. Attached Figure Description

[0012] Figure 1 This describes the structure of corrugated cardboard formed by gluing a grooved cardboard (1) to paper facing cardboard (2) and paper facing cardboard (3) with glue (4). The groove direction (5) and the vertical direction (6) are indicated to illustrate the bending test. Detailed Implementation

[0013] definition The term "monofunctional" in the context of monofunctional monomers or oligomers refers to compounds that contain a single polymerizable group.

[0014] The term "monofunctional acrylate" refers to a compound that contains a polymerizable group, more specifically a polymerizable acrylate group.

[0015] The term "monofunctional methacrylate" refers to a compound containing a polymerizable group, more specifically a polymerizable methacrylate group.

[0016] The term "multifunctional" in the context of multifunctional acrylate monomers or oligomers means that these compounds contain two or more polymerizable groups, including at least one polymerizable acrylate group.

[0017] The term "polyacrylate" refers to a compound having two or more polymerizable acrylate groups.

[0018] The term "ethoxylated" refers to two, three or more ethoxy groups linked together.

[0019] UV-curable inkjet ink The UV-curable inkjet ink according to the present invention comprises a) 20-45% by weight of a monofunctional monomer or oligomer comprising a monofunctional acrylate and 0-20% by weight of a monofunctional methacrylate; b) 5-55% by weight of an ethoxylated polyfunctional acrylate monomer or oligomer; c) 12.0% by weight or more of an acylphosphine oxide photoinitiator and optionally an amine synergist; wherein the ratio R1 of the weight percentage of the ethoxylated polyfunctional acrylate monomer or oligomer to the weight percentage of the non-ethoxylated polyfunctional acrylate monomer or oligomer is between 0.1 and 4.0; The ratio R2 of the weight percentage of monofunctional methacrylate to the weight percentage of monofunctional acrylate does not exceed 1.2; and all weight percentages are based on the total weight of the UV-curable inkjet ink.

[0020] In a preferred embodiment, the ratio R1 is between 0.2 and 2, for which particularly improved bending properties are observed.

[0021] In a preferred embodiment, the ratio R2 is no more than 1.0, more preferably no more than 0.8.

[0022] The UV-curable inkjet ink is preferably a UV-curable colorless inkjet ink, which can be applied to the substrate as a primer or varnish. The primer forms a first layer on the substrate and can improve adhesion or prevent absorption of subsequent ink layers. The varnish is the outermost layer on the substrate and can provide a glossy or matte finish to the (printed) substrate, and can form a protective layer for the underlying ink image. In this invention, the advantages of colorless UV-curable inkjet inks are most evident in UV-curable varnish inkjet inks, because the outermost layer is generally most susceptible to bending and also responsible for sliding properties.

[0023] UV-curable varnish inkjet inks can be used as the sole inkjet ink in inkjet printing on substrates such as corrugated cardboard, but are preferably used in combination with a UV-curable inkjet ink kit. Such a UV-curable inkjet ink kit further includes one or more colored UV-curable inkjet inks, wherein at least the UV-curable varnish inkjet ink is an inkjet ink according to the invention.

[0024] However, the UV-curable inkjet ink of the present invention can also be a colored inkjet ink, more preferably as part of a UV-curable inkjet ink kit. In such cases, it is preferable that multiple, and more preferably all, UV-curable inkjet inks are UV-curable inkjet inks according to the present invention.

[0025] The aforementioned UV-curable inkjet ink kit preferably includes at least one cyan curable ink (C), at least one magenta curable ink (M), and at least one yellow curable ink (Y), and more preferably includes at least one black curable ink (K). Such a CMYK ink kit can also be extended with additional inks, such as red, green, blue, purple, and / or orange, to further expand the color gamut of the image. The CMYK ink kit can also be extended by combining full-density inkjet inks with light-density inkjet inks. These combinations of dark and light inks and / or black and gray inks improve image quality by reducing graininess.

[0026] The viscosity of the UV-curable inkjet ink according to the present invention is preferably at 45°C and 1,000 s. -1The shear rate is less than 20 mPa·s, more preferably at 45°C and 1,000 s. -1 The shear rate is between 2-15 mPa·s. The viscosity of the inkjet ink can be obtained from Rotovisco by HAAKE. TM The RV1 viscometer operates at 45°C and 1,000 s⁻¹. -1 Measured at the shear rate.

[0027] The surface tension of the UV-curable inkjet ink according to the present invention is preferably in the range of about 20 mN / m to about 40 mN / m at 25°C, and more preferably in the range of about 22 mN / m to about 30 mN / m at 25°C.

[0028] The UV-curable inkjet ink is preferably a free radical curable inkjet ink, more preferably a UV LED free radical curable inkjet ink. Preferably, no secondary curing mechanism (such as cationic curing or thermal curing) is used for polymerization.

[0029] Monofunctional monomers and oligomers Monofunctional monomers and oligomers are polymerizable compounds having a single polymerizable group. Any monofunctional monomer and oligomer capable of free radical polymerization can be used. Suitable monofunctional monomers and oligomers can be found in Polymer Handbook Vol. 1+2, 4th Edition, edited by J. BRANDRUP et al., Wiley-Interscience, 1999.

[0030] Monofunctional monomers and oligomers include monofunctional acrylates, and preferably also include methacrylates as polymerizable compounds, but may also include other types of monofunctional monomers and oligomers, including olefinically unsaturated polymerizable groups selected from acrylamide, methacrylamide, styrene groups, maleate esters, fumarate esters, itaconic acid esters, vinyl ethers, vinyl esters, allyl ethers, and allyl esters. Preferred monomers include N-vinylcaprolactam, and more preferably vinylmethyloxazolidinone.

[0031] The monofunctional acrylates are preferably selected from isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isodecyl acrylate, isostearyl acrylate, 2-ethylhexyl-diethylene glycol acrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethylhexahydrophthalic acid, butoxyethyl acrylate, ethoxydiethylene acrylate, methoxydiethylene acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, and cyclic trimethylolpropane-formaldehyde acrylate. 3,3,5-Trimethylcyclohexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid, lactone-modified flexible acrylate, ethoxyethoxyethyl acrylate, tert-butylcyclohexyl acrylate and tricyclodecane methanol acrylate, (3-ethyl-3-oxetane)methyl acrylate and (2-methyl-2-ethyl-1,3-dioxolanecyclo-4-yl)methyl acrylate. Preferably, at least one monofunctional acrylate is derived from the above groups.

[0032] The monofunctional acrylate is preferably present in an amount of 10-45% by weight, more preferably in an amount of 15-30% by weight, wherein all weight percentages are based on the total weight of the UV-curable inkjet ink.

[0033] Suitable monofunctional methacrylates include methacrylic acid, alkyl methacrylates (straight-chain, branched and cycloalkyl) such as methyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate and isotridecyl methacrylate; aryl methacrylates such as benzyl methacrylate and phenyl methacrylate; and hydroxyalkyl methacrylates such as hydroxyethyl methacrylate and hydroxypropyl methacrylate.

[0034] Preferred monofunctional methacrylates are tetrahydrofurfuryl methacrylate and alkyl methacrylates (preferably C4 methacrylate). 12 -C 15 Alkyl esters), ethoxy ethoxy ethyl methacrylate, 2-phenoxy ethyl methacrylate, ethoxylated 4-phenyl methacrylate, urea methacrylate, behenyl methacrylate and 3,3,5-trimethylcyclohexanol methoxy polyethylene glycol (350) ester.

[0035] The most preferred monofunctional methacrylates include isobornyl methacrylate.

[0036] The monofunctional methacrylate is present in an amount of 0-20% by weight, preferably 0-10% by weight, and more preferably 0-8% by weight, wherein all weight percentages are based on the total weight of the UV-curable inkjet ink. Improvements in sliding properties are typically observed when no monofunctional methacrylate is used or when a smaller amount is used.

[0037] Ethoxylated polyfunctional acrylate monomers and oligomers The ethoxylated polyfunctional acrylate monomer or oligomer is preferably an ethoxylated polyacrylate monomer or oligomer. Therefore, the ratio R1 is preferably the ratio of the weight percentage of the ethoxylated polyacrylate monomer or oligomer to the weight percentage of the non-ethoxylated polyfunctional acrylate monomer or oligomer, and R1 is between 0.1 and 4.0.

[0038] VEEA is a preferred ethoxylated polyfunctional acrylate monomer or oligomer of the present invention, and is not an ethoxylated polyacrylate monomer or oligomer. VEEA is 2-(2-ethoxyethoxy)ethyl acrylate, which is available from NIPPONSHOKUBAI.

[0039] Based on the total weight of the UV-curable inkjet ink, the UV-curable inkjet ink includes 5-55% by weight, more preferably 10-35% by weight, of an ethoxylated polyfunctional acrylate monomer or oligomer, wherein all weight percentages are based on the total weight of the UV-curable inkjet ink.

[0040] The ethoxylated polyfunctional acrylate monomer or oligomer preferably comprises two or three acrylate groups, most preferably two acrylate groups. It has been observed that if a high content of ethoxylated polyfunctional acrylates having more than two acrylate groups is used, the bending properties decrease.

[0041] Ethoxylated polyfunctional acrylate monomers or oligomers comprise at least two ethoxy groups, but preferably three or more, as this particularly improves bending properties. In a preferred embodiment of the UV-curable inkjet ink according to the invention, the ethoxylated polyacrylate comprises 5-20 ethoxy units.

[0042] In a preferred embodiment of the UV-curable inkjet ink according to the present invention, the ethoxylated polyfunctional acrylate monomer or oligomer includes compounds selected from triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, ethoxylated (3EO) hexanediol diacrylate, ethoxylated (5EO) hexanediol diacrylate, ethoxylated trimethylolpropane triacrylate, and bisphenol A EO (ethylene oxide) adduct diacrylate.

[0043] Non-ethoxylated polyfunctional acrylate monomers and oligomers Non-ethoxylated polyfunctional acrylate monomers and oligomers are polymerizable compounds, including all polyfunctional acrylate monomers and oligomers that are not ethoxylated polyfunctional acrylate monomers and oligomers, and therefore include, for example, hexanediol diacrylate or propoxylated polyacrylates, such as dipropylene glycol diacrylate.

[0044] Suitable non-ethoxylated polyfunctional acrylate monomers and oligomers include dipropylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dimethyloltricyclodecane diacrylate, bisphenol APO (epoxypropylene) adduct diacrylate, hydroxypentyl ester neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, trimethylolpropane triacrylate, tri(propylene glycol) triacrylate, caprolactone-modified trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxytetraacrylate, dipentaerythritol hexaacrylate, di(trimethylolpropane) tetraacrylate, glycerol propoxytetraacrylate, and caprolactam-modified dipentaerythritol hexaacrylate.

[0045] In a preferred embodiment of the UV-curable inkjet ink according to the present invention, the non-ethoxylated polyfunctional acrylate monomer or oligomer includes at least one compound selected from 1,6-hexanediol diacrylate and dipropylene glycol diacrylate.

[0046] The non-ethoxylated polyfunctional acrylate monomers or oligomers preferably comprise two or three acrylate groups, most preferably two acrylate groups. It has been observed that if a high content of non-ethoxylated polyfunctional acrylates with more than two acrylate groups is used, the bending properties decrease.

[0047] The amount of nonethoxylated polyfunctional acrylate monomers and oligomers is preferably 14-50% by weight, more preferably 20-45% by weight, wherein all weight % is based on the total weight of the UV-curable inkjet ink.

[0048] Acylphosphine oxide photoinitiator The UV-curable inkjet ink according to the invention comprises at least 12.0% by weight or more, preferably greater than 12.5% ​​by weight, more preferably greater than 13.5% by weight, and most preferably 14.0-25.0% by weight or even 15.0-20.0% by weight of an acylphosphine oxide photoinitiator, wherein all weight percentages are based on the total weight of the UV-curable inkjet ink.

[0049] In a particularly preferred embodiment of the UV-curable inkjet ink, the acylphosphine oxide photoinitiator comprises or is composed of (2,4,6-trimethylbenzoyl) ethyl phenyl hypophosphite (commonly known as TPO-L). This acylphosphine oxide photoinitiator is commercially available, for example as Omnirad. TM TPO-L is derived from IGM Resins.

[0050] Other acylphosphine oxide photoinitiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and 2,4,6-trimethylbenzoyldiphenylphosphine oxide. However, these are less preferred than ethylphenyl(2,4,6-trimethylbenzoyl)phosphine hypophosphite. Although bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide has solubility issues, 2,4,6-trimethylbenzoyldiphenylphosphine oxide is considered carcinogenic, mutagenic, or toxic to reproduction. Such acylphosphine oxide photoinitiators are commercially available, for example as Omnirad. TM 819 and Omnirad TM TPO is derived from IGM Resins.

[0051] Acylphosphine oxides can also be polymer compounds, such as Omnipol derived from IGM Resins. TM TP.

[0052] In a preferred embodiment, the acylphosphine oxide photoinitiator comprises an acyl group containing a polymerizable group or an acyl group selected from: benzoyl group substituted with urea or oxalamido; 2,6-dimethylbenzoyl group substituted with urea or oxalamido at the 3-position; 2,6-dimethoxybenzoyl group substituted with urea or oxalamido at the 3-position; 2,4,6-trimethylbenzoyl group substituted with urea or oxalamido at the 3-position; and 2,4,6-trimethoxybenzoyl group substituted with urea or oxalamido at the 3-position. By using such an acylphosphine oxide photoinitiator, trimethylbenzaldehyde, which causes unpleasant odors on the printed substrate, is not released after UV curing.

[0053] Suitable acylphosphine oxide photoinitiators having acyl groups substituted with urea or oxalamide groups are disclosed in WO 2019 / 243039 (AGFA).

[0054] WO 2014 / 051026 (FUJIFILM) discloses suitable acylphosphine oxide photoinitiators comprising acyl groups containing polymerizable groups.

[0055] Combinations of different acylphosphine oxide photoinitiators can also be used. For example, combinations of monofunctional acylphosphine oxide photoinitiators (e.g., TPO and TPO-L) and polyfunctional acylphosphine oxide photoinitiators (e.g., bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide). Preferably, such combinations contain more monofunctional acylphosphine oxide photoinitiators than polyfunctional acylphosphine oxide photoinitiators. Combinations containing at least 70% by weight of monofunctional acylphosphine oxide photoinitiators in the acylphosphine oxide mixture generally exhibit higher curing efficiency.

[0056] Alternatively, acylphosphine oxide is a polymer compound in which the acylphosphine oxide structure is bonded to the polymer chain on its acyl side. Suitable compounds are disclosed in WO 2014 / 129213 (FUJIFILM). By bonding the acyl group to the polymer chain, the odor of printed materials is also suppressed.

[0057] Amine synergists To further increase photosensitivity, UV-curable inkjet inks may additionally contain one or more co-initiators, also known as polymerization synergists, preferably amine synergists.

[0058] Suitable examples of amine synergists can be classified into three groups: 1) Tertiary fatty amines, such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine, and N-methylmorpholine; (2) Aromatic amines, such as amyl p-dimethylaminobenzoate, 2-n-butoxyethyl 4-(dimethylamino)benzoate, ethyl 2-(dimethylamino)benzoate, ethyl 4-(dimethylamino)benzoate, and 2-ethylhexyl 4-(dimethylamino)benzoate; and (3) Amines esterified with (meth)acrylate, such as dialkylaminoalkyl esters of (meth)acrylate (e.g., diethylaminoethyl acrylate) or N-morpholinoalkyl esters of (meth)acrylate (e.g., N-morpholinoethyl acrylate).

[0059] UV-curable inkjet inks preferably include amine synergists, and more preferably polymerizable amine synergists.

[0060] In a preferred embodiment of the UV-curable inkjet ink, the polymerization synergist is an acrylated amine synergist. Preferred acrylated amine synergists include Sartomer from ARKEMA. TM CN3705, CN3715 and CN3755.

[0061] Suitable amine co-activators are commercially available, as in Omnipol. TM ASA, Omnipol TM 894 and Esacure TMA198 is from IGM Resins.

[0062] Preferred commercial amine synergists for acrylate esterification include Photomer from IGM Resins. TM 4068, 4250, 4771, 4775, 4780, 4967 and 5006.

[0063] Other photoinitiators Other photoinitiators can be present in UV-curable inkjet inks, with Norrish Type I or Norrish Type II initiators being preferred. Norrish Type I initiators are photoinitiators that split upon excitation, immediately generating initiating radicals. Norrish Type II initiators are photoinitiators activated by photochemical radiation and form radicals by abstracting hydrogen from a second compound, which then becomes the actual initiating radical. This second compound is called a polymerization synergist or co-initiator.

[0064] Other suitable photoinitiators are disclosed in CRIVELLO, JV et al., VOLUME III: Photoinitiators for Free Radical Cationic, 2nd ed., edited by BRADLEY, G., London, UK: John Wiley and Sons Ltd, 1998, pp. 287-294.

[0065] Norrish Type I photoinitiator In addition to acylphosphine oxide photoinitiators as Norrish type I photoinitiators, a second Norrish type I photoinitiator is preferably selected from benzoin ether, benzoyl ketal, α-haloketone, α,α-dialkoxyacetylphenyl ketone, α-hydroxyalkylphenyl ketone, α-halosulfone, α-aminoalkylphenyl ketone, acylphosphine sulfide, and phenyl glyoxylate.

[0066] In a preferred embodiment, the other photoinitiator is an α-hydroxyketone photoinitiator.

[0067] Suitable examples of α-hydroxy ketone photoinitiators include, but are not particularly limited to, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenylpropane-1-one and 1-[4-(2-hydroxyethoxy)-phenyl]2-hydroxy-2-methyl-1-propane-1-one.

[0068] Commercial examples of α-hydroxyketone photoinitiators include, but are not limited to, Omnirad derived from IGM RESINS. M 1173, Omnirad TM 184 and Omnirad TM127 and Omnirad TM 4817.

[0069] Based on the total weight of the UV-curable inkjet ink, the content of α-hydroxy ketone is preferably 1-10% by weight, more preferably 2-8% by weight, and even more preferably 3-6% by weight.

[0070] In a particularly preferred embodiment, the α-hydroxyketone photoinitiator is a polymer or a polymerizable photoinitiator.

[0071] Examples of suitable polymeric α-hydroxyketone photoinitiators include Esacure. TM KIP150 is available from IGM RESINS.

[0072] Suitable polymerizable α-hydroxy ketone photoinitiators are disclosed in US 4922004 (MERCK), such as 4-(2-acryloyloxyethoxy)-phenyl-2-acryloyloxy-2-propyl ketone prepared in Example 3 of that patent.

[0073] Norrish type II photoinitiator UV-curable inkjet inks preferably contain Norrish type II photoinitiators, which include photoinitiating moieties selected from thioxanthone, carbazole, and benzophenone groups. Norrish type II photoinitiators containing thioxanthone or carbazole groups are particularly preferred because they are beneficial for UV LED curing, especially for UV LEDs with emission wavelengths greater than 360 nm or even greater than 370 nm.

[0074] Suitable examples of Norrish type II photoinitiators containing a thioxanthone group include, but are not particularly limited to, thioxanthone; diethylthioxanthone, such as 2,4-diethylthioxanthone; isopropylthioxanthone, such as 2-isopropylthioxanthone and 4-isopropylthioxanthone; and chlorothioxanthone, such as 2-chlorothioxanthone.

[0075] A specific example of a commercially available Norrish type II photoinitiator containing a thioxanthone group is Speedcure from Lambson. TM DETX (2,4-diethylthioxanone) and Speedcure TM ITX (2-isopropylthioxanthione) and Kayacure from Nippon Kayaku Co. TM DETX-S (2,4-diethylthioxanone).

[0076] Preferred carbazole photoinitiators are disclosed in EP 2509948A (AGFA). These carbazole photoinitiators have advantages over thioxanone photoinitiators, exhibiting less photo-yellowing.

[0077] Suitable examples of Norrish type II photoinitiators containing a benzophenone group include, but are not particularly limited to, benzophenone; methyl benzophenone; methyl 2-benzoylbenzoate; phenyl benzophenone, such as 4-phenyl benzophenone; trimethyl benzophenone; bis(alkylamino)benzophenone; and 4-(dialkylamino)benzophenone.

[0078] A specific example of a commercially available Norrish type II photoinitiator containing a benzophenone group is Omnirad from IGMRESINS. TM 4MBZ and Omnirad TM BP, derived from Lambson's Speedcure TM PBZ and Speedcure TM 5040. The latter is a mixture of benzophenone and thioxanone.

[0079] Preferred examples of polymerizable Norrish type II photoinitiators, including photoinitiating moieties selected from thioxanone or benzophenone groups, are disclosed in EP 2161264A (AGFA), EP 2199273A (AGFA) and EP 2684876A (AGFA).

[0080] Preferred examples of polymeric Norrish type II photoinitiators, including photoinitiating moieties selected from thioxanone or benzophenone groups, are disclosed in EP 1616920A (AGFA) and EP 1616899A (AGFA).

[0081] Commercial examples of polymers such as thioxanone and benzophenone include Omnipol from IGM RESINS. TM BP, Omnipol TM TX and Omnipol TM 2702.

[0082] Based on the total weight of the free radical curable inkjet ink, the content of the Norrish II type photoinitiator, including the photoinitiating portion selected from thioxanthone, carbazole, and benzophenone groups, is preferably 0.5-7.5% by weight, more preferably 1-5% by weight. However, if the Norrish II type photoinitiator is a polymerizable or polymeric thioxanthone compound, the content can be higher, preferably up to 20% by weight, more preferably up to 15% by weight, based on the total weight of the UV-curable inkjet ink.

[0083] Colored pigments UV-curable inkjet inks can contain colored pigments, preferably organic colored pigments. Organic colored pigments offer a much larger color gamut than inorganic colored pigments, but are more prone to light fading. Color gamut represents the number of different colors that can be produced by an ink kit.

[0084] Colored pigments can be black, cyan, magenta, yellow, red, orange, purple, blue, green, brown, or mixtures thereof. Colored pigments can be selected from those disclosed in HERBST, Willy et al., Industrial Organic Pigments, Production, Properties, Applications. 3rd ed. Wiley-VCH, 2004. ISBN 3527305769.

[0085] The particularly preferred pigment for cyan UV-curable inkjet inks is CI Pigment Blue 60 or preferably β-copper phthalocyanine pigment, more preferably CI Pigment Blue 15:3 or CI Pigment Blue 15:4.

[0086] The magenta or red UV-curable inkjet ink preferably contains quinacridone pigments, diketolpyrrolopyrrole pigments, or mixtures thereof. In a preferred embodiment, the magenta or red UV-curable inkjet ink preferably contains pigments selected from CI Pigment Violet 19, CI Pigment Red 122, CI Pigment Red 144, CI Pigment Red 176, CI Pigment Red 188, CI Pigment Red 207, CI Pigment Red 242, CI Pigment Red 254, CI Pigment Red 272, and mixtures thereof.

[0087] The yellow UV-curable inkjet ink preferably contains a yellow pigment selected from CI Pigment Yellow 83, CI Pigment Yellow 93, CI Pigment Yellow 97, CI Pigment Yellow 110, CI Pigment Yellow 120, CI Pigment Yellow 138, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 175, CI Pigment Yellow 180, CI Pigment Yellow 181, CI Pigment Yellow 185, CI Pigment Yellow 194, CI Pigment Yellow 213, CI Pigment Yellow 214 and their mixtures.

[0088] The organic colored pigments selected above for use in cyan, magenta, red, or yellow inkjet inks exhibit minimal light fading when combined with polymerizable compositions as described above.

[0089] For black, UV-curable inks, suitable pigment materials include carbon black, such as Regal from Cabot Co. TM 400R, MogulTM L, Elftex TM 320, or Carbon Black FW18 or Special Black from DEGUSSA Co. 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, obtained from MITSUBISHI CHEMICAL Co. MA8, and CI Pigment Black 7 and CI Pigment Black 11.

[0090] Mixed crystals can also be used. Mixed crystals are also called solid solutions. For example, under certain conditions, different quinacridones are mixed together to form a solid solution, which is very different from both a physical mixture of compounds and the compounds themselves. In a solid solution, the molecules of the components enter the same crystal lattice, usually but not always into 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 proportion. 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. A commercially available example is Cinquasia from Ciba Specialty Chemicals. TM Magenta RT-355-D.

[0091] Mixtures of pigments can also be used. For example, a black UV-curable inkjet ink may contain carbon black pigment and at least one pigment selected from blue, cyan, magenta, and red pigments. Such black inkjet inks are found to allow for easier and better color management due to their more neutral nature.

[0092] The pigment particles in colored inkjet inks should be small enough to allow the ink to flow freely through the inkjet printing apparatus, especially at the nozzle. It is also desirable to use small particles to maximize color intensity and slow down sedimentation.

[0093] The average particle size of the pigment in the colored inkjet ink should preferably be between 50 nm and 300 nm, more preferably between 80 and 200 nm, and most preferably between 90 and 150 nm.

[0094] Based on the total weight of the UV-curable inkjet ink, the amount of pigment in the inkjet ink is 0.1-20% by weight, preferably 1-10% by weight, and most preferably 2-6% by weight. A pigment concentration of at least 2% by weight is preferred to reduce the amount of inkjet ink required to produce colored patterns, while a pigment concentration higher than 5% by weight reduces the color gamut and increases the graininess of the printed colored patterns. The ink kit may also contain low-density inkjet ink. In such cases, based on the total weight of the UV-curable inkjet ink, the low-density inkjet ink contains preferably 0.1-1.0% by weight, more preferably 0.5-0.8% by weight of pigment.

[0095] The average particle size is best determined by photon correlation spectroscopy using a 4mW HeNe laser at a wavelength of 633 nm on diluted samples of colored inkjet ink. A suitable particle size analyzer is a Malvern. TM Nano-S is available from Goffin-Meyvis. For example, a sample can be prepared by adding a drop of ink to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample is obtained. The particle size measured is the average of three consecutive measurements consisting of six 20-second runs.

[0096] However, for white UV-curable inkjet inks, the number-average particle size of the white pigment is preferably 50-500 nm, more preferably 200-400 nm, and most preferably 250-350 nm. When the average diameter is less than 50 nm, sufficient hiding power cannot be obtained, and when the average diameter exceeds 500 nm, the ink's storage capacity and ejection suitability tend to deteriorate. The number-average particle size is best determined by photon correlation spectroscopy using a 4 mW HeNe laser at a wavelength of 633 nm on diluted samples of the colored inkjet ink. A suitable particle size analyzer used is a Malvern. TM Nano-S is available from Goffin-Meyvis. For example, a sample can be prepared by adding a drop of ink to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample is obtained. The particle size measured is the average of three consecutive measurements consisting of six 20-second runs.

[0097] Suitable white pigments are given in Table 2 of WO 2008 / 074548 (AGFA GRAPHICS)

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

[0117] and

[0118] .

[0098] The white pigment is preferably present in an amount of 10% to 30% by weight, and more preferably 15% to 25% by weight, of the UV-curable inkjet ink. Amounts below 3% by weight cannot achieve sufficient hiding power and generally exhibit very poor storage stability and jetting properties.

[0099] polymer dispersants Colored, UV-curable inkjet inks contain dispersants to further improve pigment dispersion properties. For high printing reliability, polymeric dispersants are preferred. Such dispersants improve the reliability of inkjet printing methods due to their typically lower settling velocities, especially when they contain secondary or tertiary amine groups.

[0100] Typical polymer dispersants are copolymers of two monomers, but 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 polymerization (e.g., monomers A and B polymerize into AAABAABBABBBB); • Block copolymers (e.g., monomers A and B polymerized into AAAAABBBBBB), in which 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 • Mixed forms of these polymers, such as block gradient copolymers.

[0101] The polymer dispersant preferably has a number average molecular weight Mn between 500 and 30,000, and more preferably between 1,500 and 10,000.

[0102] 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.

[0103] The polymer dispersant preferably has a polydispersity PD of less than 2, more preferably less than 1.75, and most preferably less than 1.5.

[0104] Commercial examples of polymer dispersants are as follows: ·DISPERBYK TM The dispersant is available from BYK CHEMIE GMBH; SOLSPERSE TM The dispersant is available from LUBRIZOL; ·TEGO TM DISPERS TM Dispersant, obtained from EVONIK; ·EDAPLAN TM Dispersant, obtained from MÜNZING CHEMIE; ·ETHACRYL TM Dispersant, obtained from LYONDELL; ·GANEX TM Dispersant, obtained from ISP; DISPEX TM and EFKA TM Dispersant, obtained from BASF; ·DISPONER TM Dispersant, derived from DEUCHEM.

[0105] Particularly preferred polymer dispersants include Solsperse from LUBRIZOL. TM Dispersant, Efka from BASF TM Dispersant, Disperbyk, obtained from BYK CHEMIE GMBH TM Dispersant and Ajisper from AJINOMOTO FINE-TECHNOCo TM Dispersant. A particularly preferred dispersant is Solsperse from LUBRIZOL. TM Dispersants 32000, 35000 and 39000 and Disperbyk from BYK CHEMIE GMBH TM 162.

[0106] Dispersants can be used alone or in combination of two or more.

[0107] Based on the weight of the pigment, the polymer dispersant is preferably used in an amount of 2-600% by weight, more preferably 5-200% by weight, and most preferably 50-90% by weight.

[0108] Dispersing synergists Colored, UV-curable inkjet inks may include dispersing synergists to further improve dispersion stability via polymeric dispersants, and thus also improve printing reliability, as less pigment may deposit in the nozzles of the printhead when the inkjet unit is in standby mode.

[0109] Dispersing synergists typically consist of anionic and cationic moieties. The anionic moieties of dispersing synergists exhibit some molecular similarity to colored pigments, while the cationic moieties consist of one or more protons and / or cations to compensate for the charge of the anionic moieties.

[0110] The dispersing synergist is preferably added in a smaller amount than one or more polymeric dispersants. The ratio of polymeric dispersant to dispersing synergist depends on the pigment and should be determined experimentally. Typically, the ratio of polymeric dispersant by weight % to dispersing synergist by weight % is between 2:1 and 100:1, preferably between 2:1 and 20:1.

[0111] Commercially available suitable dispersants include Solsperse from LUBRIZOL. TM 5000 and Solsperse TM 22000.

[0112] Particularly preferred pigments for use in magenta inks are diketopyrrolo-pyrrole pigments or quinacridone pigments. Suitable dispersing synergists include those disclosed in EP 1790698A (AGFA GRAPHICS), EP 1790696A (AGFA GRAPHICS), WO 2007 / 060255 (AGFA GRAPHICS) and EP 1790695A (AGFA GRAPHICS).

[0113] When dispersing CI pigment blue at a ratio of 15:3, it is preferable to use a sulfonated Cu phthalocyanine dispersing synergist, such as Solsperse from LUBRIZOL. TM 5000. Suitable dispersants for yellow inkjet inks include those disclosed in EP 1790697A (AGFA GRAPHICS).

[0114] surfactants UV-curable inkjet inks may contain surfactants. Surfactants can be anionic, cationic, nonionic, or amphoteric surfactants. Based on the total weight of the UV-curable inkjet ink, the surfactant is preferably present in an amount of 0.1-3% by weight. At concentrations above 3% by weight, adhesion may deteriorate rapidly, while at concentrations below 0.1% by weight, insufficient ink spreading is typically observed.

[0115] Based on the total weight of the ink, the total amount of surfactant is preferably less than 3% by weight, and more preferably less than 1.5% by weight based on the total weight of the free radical curable inkjet ink, to prevent the ink from foaming in its container. Such foaming has a negative impact on printing reliability.

[0116] Preferred surfactants are selected from fluorinated surfactants (e.g., fluorinated hydrocarbons) and silicone surfactants. Silicone surfactants are preferably siloxanes and may be alkoxylated, polyester-modified, polyether-modified, polyether-modified hydroxyl-functionalized, amine-modified, epoxy-modified, and other modified or combinations thereof. Preferred siloxanes are polymers, such as polydimethylsiloxane.

[0117] Preferred commercial silicone surfactants include BYK from BYK Chemie. TM 333, BYK TM UV3510 and BYK TM UV3511 and Tegoglide obtained from EVONIK TM 410.

[0118] In a preferred embodiment, the surfactant is a polymerizable compound.

[0119] Preferred polymerizable silicone surfactants include (meth)acrylated silicone surfactants. Most preferably, (meth)acrylated silicone surfactants are acrylated silicone surfactants because acrylates are more reactive than methacrylates.

[0120] In a preferred embodiment, the (meth)acrylated silicone surfactant is a polyether-modified (meth)acrylated polydimethylsiloxane or a polyester-modified (meth)acrylated polydimethylsiloxane.

[0121] Preferred commercially available (meth)acrylated silicone surfactants include: Ebecryl TM 350, an organosilicon diacrylate derived from Cytec; polyether-modified acrylated polydimethylsiloxane BYK TM UV3500, BYK TM UV3510 and BYK TM UV3530, polyester-modified acrylated polydimethylsiloxane BYK TM UV3570, all manufactured by BYK Chemie; Tego TM Rad 2100, Tego TM Rad 2200N, Tego TM Rad 2250N, Tego TMRad 2300, Tego TM Rad 2500, Tego TM Rad 2550, Tego TM Rad 2600, Tego TM Rad 2700 and Tego TM RC711 is manufactured by EVONIK. Another preferred silicone is Silwet. TM L7500, derived from OSI SPECIALITIES BENELUX NV; Silaplane TM FM7711, Silaplane TM FM7721, Silaplane TM FM7731, Silaplane TM FM0711, Silaplane TM FM0721, Silaplane TM FM0725, Silaplane TM TM0701, Silaplane TM TM0701T, all manufactured by CHISSO Corporation; and DMS-R05, DMS-R11, DMS-R18, DMS-R22, DMS-R31, DMS-U21, DBE-U22, SIB1400, RMS-044, RMS-033, RMS-083, UMS-182, UMS-992, UCS-052, RTT-1011 and UTT-1012, all manufactured by GELEST Inc.

[0122] The preferred surfactant for free radical inkjet inks is Silmer, derived from the SILTECH CORPORATION. ® Surfactants, such as Silmer ® ACR Di-1508.

[0123] Polymer inhibitors UV-curable inkjet inks can also contain polymerization inhibitors. The presence of polymerization inhibitors prevents polymerization reactions before curing, such as during storage or transportation. This also improves printing reliability because the UV-curable inkjet ink in the printhead of the inkjet unit is maintained at a higher temperature, such as 45-55°C.

[0124] Suitable polymerization inhibitors include phenolic antioxidants, hindered amine light stabilizers, phosphorus antioxidants, benzoquinone, hydroquinone and its derivatives, such as hydroquinone monomethyl ether commonly used in (meth)acrylate monomers.

[0125] Examples of phenolic polymerization inhibitors include, but are not limited to, the following substances: p-methoxyphenol, cresol, tert-butylcatechol, di-tert-butyl-p-cresol, hydroquinone monomethyl ether, α-naphthol, 3,5-di-tert-butyl-4-hydroxytoluene, 2,6-di-tert-butyl-4-methylphenol, 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), 2,2'-methylene-bis(4-ethyl-6-butylphenol), and 4,4'-thio-bis(3-methyl-6-tert-butylphenol) and pyrogallol.

[0126] Suitable commercial inhibitors include, for example, Sumilizer. TM GA-80, Sumilizer TM GM and Sumilizer TM GS, manufactured by Sumitomo Chemical Co. Ltd.; Genorad TM 16. Genorad TM 18 and Genorad TM 20, derived from RahnAG; Irgastab TM UV10 and Irgastab TM UV22, Tinuvin TM 460 and CGS20, from Ciba Specialty Chemicals; Floorstab TM UV series (UV-1, UV-2, UV-5, and UV-8), obtained from Kromachem Ltd; Additol TM The S series (S100, S110, S120 and S130) are from Cytec Surface Specialties.

[0127] The preferred polymerization inhibitor is Irgastab, obtained from BASF. TM UV10. Other examples of polymerization inhibitors include TEMPO, TEMPOL, and the Al copper-iron reagent.

[0128] Polymerization inhibitors can be used alone or in combination of two or more of them.

[0129] In a preferred embodiment, the polymerization inhibitor is a mixture of different types of polymerization inhibitors. Preferred polymerization inhibitors are mixtures of alkyl radical-based polymerization inhibitors, phenol-based polymerization inhibitors, and amine-based polymerization inhibitors. Suitable examples are given in EP 2851402A (FUJIFILM).

[0130] Based on the total weight of the UV-curable inkjet ink, the polymerization inhibitor is preferably present in an amount of 0.1-5% by weight. Below 0.1% by weight, undesirable polymerization cannot be adequately suppressed, while above 5% by weight, the curing rate is significantly reduced.

[0131] Other ink components Other components of the types known in the art may be present in the ink to improve its properties or performance. These components may include, for example, defoamers, water, organic solvents, UV stabilizers, deodorizers, flow aids or slip agents, passivating resins, fillers such as silica or alumina, biocides, and identifying tracers. However, the UV-curable inkjet ink of the present invention preferably does not include organic solvents or water.

[0132] Preparation of UV-curable inkjet ink The preparation of UV-curable inkjet inks is well known to those skilled in the art. Preferred preparation methods are disclosed in paragraphs

[0076] to

[0085] of WO2011 / 069943 (AGFA).

[0133] Inkjet printing method The inkjet printing method according to the present invention includes the following steps: a) spraying a UV-curable inkjet ink as described above onto a substrate; and b) UV curing the sprayed UV-curable inkjet ink using a UV LED having an emission wavelength greater than 360 nm.

[0134] In a preferred embodiment of the inkjet printing method, the substrate is a packaging material, particularly corrugated cardboard.

[0135] In a preferred embodiment of the inkjet printing method, a UV-curable colorless inkjet ink is used as a varnish on corrugated cardboard.

[0136] UV curing is preferably performed using a UV LED with an emission wavelength greater than 360 nm, preferably greater than 370 nm.

[0137] Any suitable inkjet device can be used for inkjet printing methods. The inkjet device preferably includes the above-mentioned UV-curable inkjet ink (kit) and a UV LED source having spectral emission in the range of 360-420 nm.

[0138] UV-curable inkjet ink is ejected in a controlled manner through nozzles from a printhead that ejects small droplets onto a substrate that moves relative to one or more printheads. A piezoelectric printhead is the preferred printhead for inkjet printing systems. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied. The application of voltage alters the shape of the piezoelectric ceramic transducer in the printhead, creating a void, which is then filled with inkjet ink or liquid. When the voltage is removed again, the ceramic expands back to its original shape, ejecting ink droplets from the printhead. In industrial printing, piezoelectric printheads have proven to be the most reliable printheads.

[0139] The preferred piezoelectric printhead is the so-called push-type piezoelectric printhead, which has a relatively large piezoelectric element that is also capable of ejecting more viscous ink droplets. Such printheads are available from RICOH as part of the GEN5 series printheads.

[0140] Another preferred piezoelectric printhead is the so-called drop-on-demand piezoelectric printhead. Such printheads are available from TOSHIBA TEC as CF1ou printheads or from FUJIFILM as Samba printheads. TM The G3L printhead is obtained. Since ink flows continuously through the printhead, flow-through printheads are preferred because they enhance the reliability of inkjet printing.

[0141] In multi-pass inkjet printing, the inkjet printhead typically scans back and forth multiple times across a stationary or moving ink-receiving surface in the lateral direction. Multi-pass printing facilitates the concealment of individual nozzle malfunctions. Sometimes the printhead may not print on its return journey; however, bidirectional printing is preferred for achieving high area throughput.

[0142] Another preferred inkjet apparatus uses a "single-pass printing method," which can be performed by using a page-width inkjet printhead or multiple staggered inkjet printheads covering the entire width of the substrate surface, wherein the image is printed in a single pass. In the single-pass printing method, the inkjet printhead typically remains stationary while the substrate is conveyed below the inkjet printhead, thus allowing for increased production capacity through high printing speeds.

[0143] The advantage of using multi-pass UV curing is that the UV-curable inkjet ink is cured in a continuous pass, rather than in a single pass requiring high UV output from the curing unit. Printhead life is also longer with multi-pass printing. While a single side ejector is sufficient for the entire printhead in single-pass printing, multiple side ejectors and even failures can be tolerated in multi-pass printing. Furthermore, multi-pass printers are generally much less expensive, especially for wide-format substrates.

[0144] In a preferred embodiment, the number of passes used is 2-6, more preferably no more than 4. Multi-pass printing has higher printing reliability than single-pass inkjet printing.

[0145] To facilitate curing, inkjet printers may include one or more oxygen-consuming units. These units contain a cover of nitrogen or other relatively inert gases (such as CO2) with adjustable position and concentration to reduce the oxygen concentration in the curing environment. Residual oxygen levels are typically maintained as low as 200 ppm, but are generally in the range of 200 ppm to 1200 ppm.

[0146] substrate There are no limitations on the type of substrate for the UV-curable ink of this invention. The substrate can be transparent, translucent, or opaque. Preferred opaque substrates include so-called synthetic paper, such as Synaps from Agfa-Gevaert. TM Grade A, it is an opaque polyethylene terephthalate sheet.

[0147] Suitable substrates include those with the following surfaces: metals (such as aluminum); polyethylene; polypropylene; polystyrene; polycarbonate; polyvinyl chloride; polyesters such as polyethylene terephthalate (PET), glycol-modified polyethylene terephthalate (PETG), polyethylene naphthalate (PEN), and polylactide (PLA); and polyimide.

[0148] However, in a preferred embodiment of the invention, the substrate is packaging material, preferably a folded cardboard box or corrugated cardboard.

[0149] Corrugated cardboard is a packaging material formed by gluing one or more grooved sheets of cardboard (called corrugated base paper) onto one or more flat sheets of facing paper (called facing layers). There are four common types: (1) Single-sided: one grooved sheet is glued to one facing layer (two sheets in total); (2) Single-walled: one grooved sheet is sandwiched between two facing layers (three sheets in total), also known as double-sided or single-layer; (3) Double-walled: one single-sided sheet is glued to one single-walled sheet, such that two grooved sheets are alternately sandwiched between three flat sheets (five sheets in total), also known as double-layered or double-walled; and (4) Triple-walled: two single-sided sheets are glued to one single-walled sheet, such that three grooved sheets are alternately sandwiched between four flat sheets (seven sheets in total), also known as triple-layered.

[0150] Printed products In this invention, the printed article includes a substrate (preferably corrugated cardboard) and a cured layer of UV-curable inkjet ink as described above.

[0151] There are no restrictions on the shape of the substrate. It can be a flat substrate, or it can be a three-dimensional object, such as a bottle or furniture. Example

[0152] Material Unless otherwise specified, all materials used in the examples are readily available from standard sources such as Sigma-Aldrich Corporation and Thermo Scientific Chemicals (formerly Acros Organics).

[0153] 15EO-TMPTA is an ethoxylated (15)trimethylolpropane triacrylate containing 15 ethoxy units, with a molecular weight of 956, and is used as a sartomer. TM SR9035 is available from ARKEMA.

[0154] Ethoxylated (5) HDDA as Sartoromer TM SR561 is available from ARKEMA.

[0155] PEG400DA as a Sartamomer TM SR344 is available from ARKEMA.

[0156] Ethoxylated (3) HDDA-1 as Miramer TM M202 is available from Miwon Specialty Chemical.

[0157] Ethoxylated (3) HDDA-2 as Photomer TM 4361 is available from IGM Resins.

[0158] HDDA is 1,6-hexanediol diacrylate, used as a sartomer. TM SR238 is available from ARKEMA.

[0159] DPGDA as Sartomer TM SR508 is available from ARKEMA.

[0160] IDA as Sartomer TM SR395 is available from ARKEMA.

[0161] EOEOEA as Sartomer TM SR256 is available from ARKEMA.

[0162] Lauryl acrylate as a sartomerTM SR335 is available from ARKEMA.

[0163] IBOA is isobornyl acrylate, used as a sartomer. TM The SR506D is available from ARKEMA.

[0164] IBOMA is isobornyl methacrylate, used as a photomer TM 2012 is available from IGM Resins.

[0165] TPO-L is an acylphosphine oxide photoinitiator (MW=316), used as an Omnirad... ® TPO-L is available from IGM RESINS.

[0166] CN3755 is a diacrylated amine co-activator, serving as a sartomer. TM CN3755 is available from ARKEMA.

[0167] BYK UV 3511 is a silicone surfactant, as BYK... TM UV 3511 is available from BYK CHEMIE GMBH.

[0168] UV10 is 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxysepiacetate, available from Shanghai FINC Chemical Technology Co., Ltd.

[0169] MD5 is a polyvinyl chloride material, used as a metamark. TM MD5-100 is available from METAMARK.

[0170] MF is single-wall corrugated cardboard, available from MOONFOX CK NV.

[0171] MA-Paper is MultiArt TM Digital Gloss 170 g / m² paper, sourced from PAPYRUS Belgium NV.

[0172] Measurement methods 1. Viscosity Uses Rotovisco obtained from HAAKE TM The RV1 viscometer operates at 45°C and 1,000 s⁻¹. -1 The viscosity of the UV-curable composition was measured at a shear rate.

[0173] 2. Surface tension The static surface tension of UV-curable ink was measured using a KRÜSS K9 tensiometer from KRÜSS GmbH, Germany, after 60 seconds at 25°C.

[0174] 3. Bending test ANUVIA coated with AGFA NV in magenta using 10 µm wire rod. TM The ink-coated MF corrugated cardboard was subjected to a bending test. The ink-coated MF corrugated cardboard was placed on a conveyor belt and cured in six passes at full power and a linear conveyor speed of 20 m / min using an LED curing station from UVio equipped with a 12W UV LED emitting at 395 nm. Then, a 10 µm coating of the ink-coated ink from Example 1 was applied and cured in the same manner as the ink layer.

[0175] To test the bending of these samples, creases must be applied to facilitate the folding process of the corrugated cardboard. To create these creases, the sample is placed on a cutting mat with the coated side down, where the push rod is parallel to the groove of the corrugated cardboard. Figure 1 The groove direction is 5). On the resulting creases, the corrugated cardboard is bent at angles of 90° and 180°. The cardboard is then fully unfolded again and folded again at angles of 90° and 180°. After each degree of bending, a score between 0 and 5 is recorded. Therefore, for a sample, for... Figure 1 The groove bending in direction 5 will give 4 points. Then... Figure 1 The same crease and bending process was performed on the vertical direction 6 (perpendicular to the groove direction 5). The same evaluation was performed to obtain another 4 scores for the sample.

[0176] Add the 8 scores together to get the total score for the curve. For a good result, the total score should not exceed 20.

[0177] The criteria for assigning scores after a certain angle (90° or 180°) are given in Table 1.

[0178] Table 1 Fraction standard 0 No visible cracks 1 A crack is visible across the entire sample. 2 A small number of small cracks are visible throughout the sample. 3 Numerous thin and short cracks are visible throughout the sample. 4 A small number of deep or large cracks are visible throughout the sample. 5 Deep cracks are visible throughout the sample. 4. Sliding properties The slip properties of UV-curable inkjet inks were determined by coating on MA-paper. Coating was performed using a doctor blade coater and a 10µm wire bar. Samples were placed on a conveyor belt and cured at full power and a linear conveyor speed of 20 m / min using an LED curing station from UVio equipped with a 12W UV LED emitting at 395 nm. Six passes were performed under the LED curing station.

[0179] The sample was cut to a size of 350 × 35 mm to assemble around the aluminum slider of the static friction tester. The aluminum slider and sample were placed on the upper side of an inclined plane with the smaller side (35 mm) facing down. This inclined plane was made of particleboard with a sliding mechanism underneath to control the angle starting from 0° (horizontal). The angle was increased continuously in 1° increments, and the angle at which the aluminum block began to slide was recorded. This procedure was repeated three times. The average angle represents the degree of sliding of the UV-curable inkjet ink.

[0180] For good sliding, this value should not exceed 20 degrees.

[0181] 5. Curing properties Inkjet ink was applied to white MD5 PVC substrate using a doctor blade coater and a 10 µm wire bar. The sample was placed on a conveyor belt and cured at full power and a linear conveyor speed of 20 m / min using an LED curing station from UVio equipped with a 12W UV LED emitting at 395 nm. The number of passes for surface curing was obtained as a measure of curing speed; a maximum of 6 passes was acceptable. For excellent curability, no more than 3-4 passes were preferred.

[0182] According to Table 2, surface curing is checked by wiping the surface of the cured sample five times with a cotton swab.

[0183] Table 2 Surface curing fraction observe 0 No visual impairment 1 Changes in surface gloss 2 Clear surface damage 3 The coating was severely damaged. 4 Almost completely removed coating 5 The coating was completely removed during wiping. Example 1 This example illustrates how to achieve good flexural and sliding properties while maintaining good UV curability by controlling the ratio of certain components in the ink composition.

[0184] Preparation of UV-curable inkjet ink All UV-curable inkjet inks COMP-1 to COMP-14 and INV-1 to INV-30 were prepared in the same manner by mixing the components according to Tables 3 and 8. The weight percentage (wt%) of each component is based on the total weight of the UV-curable inkjet inks. The viscosity and static surface tension of each UV-curable inkjet ink were measured, and it was found that the viscosity at 45°C was between 7 and 10 mPa·s, and the static surface tension at 25°C was between 22 and 25 mN / m.

[0185] Table 3 Ethoxylated (5) HDDA 10.00 20.00 20.00 20.00 20.00 25.00 25.00 HDDA 47.40 43.40 49.40 30.40 30.40 28.40 28.40 IDA 13.00 13.00 EOEOEA 10.00 Lauryl acrylate 10.00 IBOA IBOMA 17.75 17.75 11.75 17.75 17.75 17.75 17.75 TPO-L 12.00 12.00 12.00 12.00 12.00 12.00 12.00 CN3755 12.00 6.00 6.00 6.00 6.00 6.00 6.00 BYK UV 3511 0.35 0.35 0.35 0.35 0.35 0.35 0.35 UV10 0.50 0.50 0.50 0.50 0.50 0.50 0.50 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Table 4 Ethoxylated (5) HDDA 25.00 25.00 25.00 50.00 HDDA 31.40 36.40 28.40 0.40 50.40 EOEOEA 5.00 Lauryl acrylate 10.00 10.00 11.00 11.00 IBOA 6.00 6.00 IBOMA 17.75 17.75 17.75 9.75 9.75 TPO-L 12.00 12.00 12.00 16.00 16.00 CN3755 3.00 3.00 6.00 6.00 6.00 BYK UV 3511 0.35 0.35 0.35 0.35 0.35 UV10 0.50 0.50 0.50 0.50 0.50 total 100.00 100.00 100.00 100.00 100.00 Table 5 Ethoxylated (5) HDDA 23.00 25.00 23.00 25.00 25.00 23.00 23.00 HDDA 7.40 27.40 28.40 27.40 27.40 28.40 27.40 27.40 DPGDA 23.00 Lauryl acrylate 11.00 11.00 10.00 11.00 11.00 10.00 11.00 11.00 IBOA 26.00 6.00 2.00 2.00 8.00 6.00 6.00 10.75 IBOMA 9.75 9.75 13.75 13.75 9.75 9.75 9.75 5.00 TPO-L 16.00 16.00 14.00 16.00 12.00 14.00 16.00 16.00 CN3755 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 BYK UV 3511 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 UV10 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Table 6 Ethoxylated (5) HDDA 23.00 23.00 23.00 23.00 30.00 15.00 10.00 5.00 HDDA 27.40 27.55 27.65 27.40 20.40 35.40 40.40 45.40 Lauryl acrylate 11.00 11.00 11.00 11.00 11.00 11.00 11.00 11.00 IBOA 15.75 6.00 6.00 6.00 6.00 6.00 6.00 6.00 IBOMA 9.75 9.75 9.75 9.75 9.75 9.75 9.75 TPO-L 16.00 16.00 16.00 16.00 16.00 16.00 16.00 16.00 CN3755 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 BYK UV 3511 0.35 0.2 0.1 0.35 0.35 0.35 0.35 0.35 UV10 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Table 7 15EO-TMPTA 23.00 Ethoxylated (5) HDDA 23.00 23.00 23.00 23.00 PEG400DA 23.00 Ethoxylated (3) HDDA-1 23.00 Ethoxylated (3) HDDA-2 23.00 HDDA 27.40 27.40 27.40 27.40 31.40 29.40 25.40 23.40 Lauryl acrylate 11.00 11.00 11.00 11.00 11.00 11.00 11.00 11.00 IBOA 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 IBOMA 9.75 9.75 9.75 9.75 9.75 9.75 9.75 9.75 TPO-L 16.00 16.00 16.00 16.00 12.00 14.00 18.00 20.00 CN3755 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 BYK UV 3511 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 UV10 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Table 8 Ethoxylated (5) HDDA 23.00 23.00 23.00 23.00 23.00 23.00 23.00 23.00 HDDA 29.40 27.40 25.40 23.40 17.40 27.40 27.40 27.40 Lauryl acrylate 11.00 11.00 11.00 11.00 11.00 5.00 15.00 IBOA 15.75 15.75 15.75 15.75 16.00 17.00 12.00 2.00 IBOMA 9.75 9.75 9.75 9.75 TPO-L 14.00 16.00 18.00 20.00 16.00 16.00 16.00 16.00 CN3755 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 BYK UV 3511 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 UV10 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Results and Evaluation The cureability (#number of cures), sliding properties, and flexural properties of UV-curable inkjet inks COMP-1 to COMP-14 and INV-1 to INV-30 were evaluated, and the results are shown in the columns titled "#number of cures," "Sliding test," and "Flexural test" in Table 9, respectively. For ease of comparison, the following headings have been added to the columns: The column titled “wt% MMO” displays the weight of monofunctional monomers and oligomers in the ink.

[0186] The column titled “wt% MA” displays the weight of monofunctional acrylates in the ink.

[0187] The column titled “wt% MMA” displays the weight of monofunctional methacrylates in the ink.

[0188] The column titled “wt% EP” shows the weight of ethoxylated polyfunctional acrylate monomers and oligomers in the ink.

[0189] The column titled "wt% AP" shows the weight of the acylphosphine oxide photoinitiator in the ink.

[0190] All weight percentages in these columns are based on the total weight of UV-curable inkjet ink.

[0191] The ratio of R1 to R2 is defined above.

[0192] Table 9 The results in Table 9 clearly show that only UV-curable inkjet inks INV-1 to INV-30 exhibit good flexural and sliding properties while maintaining good UV curability.

[0193] Reference tag list The reference numerals used in the attached figures are listed in Table 10.

[0194] Table 10

Claims

1. A UV-curable inkjet ink, comprising: a) 20-45% by weight of monofunctional monomers or oligomers including monofunctional acrylates and 0-20% by weight of monofunctional methacrylates. b) 5-55% by weight of ethoxylated polyfunctional acrylate monomers or oligomers; c) 12.0% by weight or more of an acylphosphine oxide photoinitiator and optional amine synergist; The ratio R1 of the weight percentage of ethoxylated polyfunctional acrylate monomers or oligomers to the weight percentage of non-ethoxylated polyfunctional acrylate monomers or oligomers is between 0.1 and 4.

0. The ratio (R²) of the weight percentage of monofunctional methacrylates to the weight percentage of monofunctional acrylates does not exceed 1.2; and All weight percentages are based on the total weight of the UV-curable inkjet ink.

2. The UV-curable inkjet ink according to claim 1, wherein the UV-curable inkjet ink is a UV-curable colorless inkjet ink.

3. The UV-curable inkjet ink according to claim 1 or 2, wherein the ethoxylated polyfunctional acrylate monomer or oligomer is present in an amount of 5-35% by weight.

4. The UV-curable inkjet ink according to any one of claims 1-3, wherein the ratio R1 is between 0.2 and 2.

5. The UV-curable inkjet ink according to any one of claims 1-4, wherein the UV-curable inkjet ink comprises a polymerizable amine synergist.

6. The UV-curable inkjet ink according to any one of claims 1-5, wherein the acylphosphine oxide photoinitiator comprises (2,4,6-trimethylbenzoyl) ethyl phenyl hypophosphite.

7. The UV-curable inkjet ink according to any one of claims 1-6, wherein the acylphosphine oxide photoinitiator is present in an amount of 15% by weight or more.

8. The UV-curable inkjet ink according to any one of claims 1-7, wherein the ethoxylated polyfunctional acrylate monomer or oligomer comprises two or three acrylate groups.

9. The UV-curable inkjet ink according to any one of claims 1-8, wherein the ethoxylated polyfunctional acrylate monomer or oligomer comprises a compound selected from polyethylene glycol diacrylate, ethoxylated hexanediol diacrylate, and ethoxylated trimethylolpropane triacrylate.

10. The UV-curable inkjet ink according to any one of claims 1-9, wherein the ethoxylated polyfunctional acrylate monomer or oligomer comprises three or more ethoxy groups.

11. A UV-curable inkjet ink kit comprising the UV-curable inkjet ink according to any one of claims 1-10.

12. A corrugated cardboard comprising a UV-curable inkjet ink layer according to any one of claims 1-10.

13. An inkjet printing method comprising the following steps: a) Spraying the UV-curable inkjet ink according to any one of claims 1-10 onto a substrate; and b) UV-curable inkjet inks that are UV-cured by using a UV LED with an emission wavelength greater than 360 nm.

14. The inkjet printing method according to claim 11, wherein the substrate is corrugated cardboard.

15. Use of the UV-curable colorless inkjet ink according to any one of claims 2-10 as a varnish on corrugated cardboard.

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