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EP-4499761-B1 - PRINTING INK

EP4499761B1EP 4499761 B1EP4499761 B1EP 4499761B1EP-4499761-B1

Inventors

  • OSBORNE, Gemma

Dates

Publication Date
20260506
Application Date
20230324

Claims (14)

  1. An inkjet ink comprising benzyl acrylate, (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate, a di- and/or multifunctional (meth)acrylate monomer and an N-vinyl amide monomer and/or an N-(meth)acryloyl amine monomer, wherein the ink has a viscosity of less than 15 mPas at 25°C.
  2. An inkjet ink as claimed in claim 1, wherein benzyl acrylate is present in an amount from 25 to 70% by weight, based on the total weight of the ink.
  3. An inkjet ink as claimed in claim 1 or 2, wherein (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate is present in an amount from 1 to 30% by weight, based on the total weight of the ink.
  4. An inkjet ink as claimed in any preceding claim, wherein the N-vinyl amide monomer and/or the N-(meth)acryloyl amine monomer comprises N-vinyl caprolactam and/or N-acryloylmorpholine.
  5. An inkjet ink as claimed in any preceding claim, wherein the N-vinyl amide monomer and/or the N-(meth)acryloyl amine monomer is present in a total amount from 5 to 35% by weight, based on the total weight of the ink.
  6. An inkjet ink as claimed in any preceding claim, wherein the ink comprises 65 to 90% by weight in total of monofunctional monomers including benzyl acrylate, (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate, and an N-vinyl amide monomer and/or an N-(meth)acryloyl amine monomer, based on the total weight of the ink.
  7. An inkjet ink as claimed in any preceding claim, wherein the ink further comprises a difunctional monomer and the difunctional monomer comprises polyethylene glycol 600 diacrylate and/or tripropylene glycol diacrylate.
  8. An inkjet ink as claimed in any preceding claim, wherein the di- and/or multifunctional monomer is present in a total amount of 15% by weight or less, based on the total weight of the ink, preferably wherein the di- and/or multifunctional monomer is present in a total amount of 0.5 to 10.0% by weight, based on the total weight of the ink.
  9. An inkjet ink as claimed in any preceding claim, wherein the ink further comprises a photoinitiator, preferably phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide.
  10. An inkjet ink as claimed in any preceding claim, wherein the ink further comprises a surfactant, preferably present in 0.1 to 1.5% by weight, based on the total weight of the ink.
  11. An inkjet ink as claimed in any preceding claim, wherein the ink contains less than 2% by weight of THFA, based on the total weight of the ink.
  12. An inkjet ink as claimed in any preceding claim, wherein the ink contains less than 2% by weight in total of category 1A and 1B carcinogenic, mutagenic and reprotoxic substances, based on the total weight of the ink.
  13. A method of inkjet printing comprising inkjet printing the inkjet ink as claimed in any preceding claim onto a substrate and curing the inkjet ink by exposing the inkjet ink to a curing source.
  14. A method of inkjet printing as claimed in claim 13, wherein the curing source is a UV LED curing source.

Description

The present invention relates to a printing ink and, in particular, an inkjet ink which has a desirable balance of properties. The present invention also relates to a method of printing said ink. In inkjet printing, minute droplets of black, white or coloured ink are ejected in a controlled manner from one or more reservoirs or printing heads through narrow nozzles on to a substrate, which is moving relative to the reservoirs. The ejected ink forms an image on the substrate. For high-speed printing, the inks must flow rapidly from the printing heads, and, to ensure that this happens, they must have in use a low viscosity, typically 200 mPas or less at 25°C, although in most applications the viscosity should be 50 mPas or less, and often 25 mPas or less. Typically, when ejected through the nozzles, the ink has a viscosity of less than 25 mPas, preferably 5-15 mPas and most preferably between 7-11 mPas at the jetting temperature, which is often elevated to, but not limited to 40-50°C (the ink might have a much higher viscosity at ambient temperature). The inks must also be resistant to drying or crusting in the reservoirs or nozzles. For these reasons, inkjet inks for application at or near ambient temperatures are commonly formulated to contain a large proportion of a mobile liquid vehicle or solvent such as water or a low-boiling solvent or mixture of solvents. Another type of inkjet ink contains unsaturated organic compounds, termed monomers and/or oligomers, which polymerise when cured. This type of ink has the advantage that it is not necessary to evaporate the liquid phase to dry the print; instead the print is cured, a process which is more rapid than evaporation of solvent at moderate temperatures. It can be difficult to formulate inkjet inks with a low viscosity which also have a desirable balance of properties. For example, typical monofunctional monomers such as PEA, CTFA and IBOA provide inks with a high cure speed and resistant film properties but these monomers have a relatively high viscosity, which does not provide inks with the desired low viscosity. In contrast, low viscosity monofunctional monomers such as TMCHA and IDA provide inks with the desired low viscosity but these monomers often limit cure sensitivity and reduce flexibility of the cured film. Even THFA, which can provide inks with the desired viscosity and flexibility, is not desirable in terms of the safety profile of the ink. In this regard, THFA is a hazardous monomer and bears the GHS hazard statement H314 (causes severe skin burns and eye damage). There is also growing evidence that it may damage fertility or the unborn child. US 2017/137642 relates to an ultraviolet-curable composition containing a polymerizable compound, a metal powder and a dendritic polymer, which contains a fluorine atom. EP 3 067 396 relates to an ultraviolet curable composition containing a polymerizable compound and metal powder, in which the metal powder contains a material which is subjected to surface treatment as a constituting particle, and a volume average particle size of the metal powder is in a range of 0.2 µm to 0.64 µm. US 2017/137653 relates to an ultraviolet-curable composition, which is discharged with an ink jet method and includes a polymerizable compound, a metal powder and a thixotropy suppressing agent, in which a relationship of η2-η1≦3 is satisfied between a viscosity η1 [mPa s] at a shearing speed of 1000 sec-1 and a viscosity η2 [mPa s] which is determined by measuring in a state where the shearing speed is 10 sec-1 after continuing to add shearing stress for 10 minutes at the shearing speed of 1000 sec-1. WO 2022/234290 relates to a white inkjet ink comprising: tricyclodecane dimethanol diacrylate; at least one of a difunctional urethane (meth)acrylate oligomer, (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate and a polyethylene glycol diacrylate; a white pigment; and a monofunctional monomer, other than (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate. There is therefore a need in the art for an inkjet ink which has a suitably low viscosity and which has a desirable balance of properties such as cure speed, adhesion, elongation, flexibility, resistance and safety profile. Accordingly, the present invention provides an inkjet ink comprising benzyl acrylate, (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate, a di- and/or multifunctional (meth)acrylate monomer and an N-vinyl amide monomer and/or an N-(meth)acryloyl amine monomer, wherein the ink has a viscosity of less than 15 mPas at 25°C. The present invention will now be described with reference to the accompanying drawings, in which: Figs. 1-8 show the results of an adhesion test for inks of the present invention compared to comparative inks; andFigs. 9-12 show the results of an elongation test for inks of the present invention compared to comparative inks. The inventors have surprisingly found that the inclusion of benzyl acrylate in combination with (2-methyl-2-et