PRINTING INK

Abstract

The present invention provides an inkjet ink comprising: 10-50% by weight of one or more monomers each having a log P.sub.octanol/water value of 5.0 or more, based on the total weight of the ink; a photoinitiator package comprising one or more photoinitiators each having a log P.sub.octanol/water value of less than 4.0, and one or more photoinitiators selected from (I) and mixtures thereof, wherein n is a value from 1 to 10 and a+b+c is a value from 1 to 20; and wherein the one or more photoinitiators each having a log P.sub.octanol/water value of less than 4.0 are present in the ink in an amount of 0.5-4.5% by weight, based on the total weight of the ink. The present invention also provides a method of printing the inkjet ink of the present invention.

Claims

1. An inkjet ink comprising: 10-50% by weight of one or more monomers each having a log P.sub.octanol/water value of 5.0 or more, based on the total weight of the ink; a photoinitiator package comprising one or more photoinitiators each having a log P.sub.octanol/water value of less than 4.0, and one or more photoinitiators selected from ##STR00017## and mixtures thereof, wherein n is a value from 1 to 10 and a+b+c is a value from 1 to 20; and wherein the one or more photoinitiators each having a log P.sub.octanol/water value of less than 4.0 are present in the ink in an amount of 0.5-4.5% by weight, based on the total weight of the ink.

2. An inkjet ink as claimed in claim 1, wherein the ink comprises ##STR00018## wherein n is a value from 1 to 10.

3. An inkjet ink as claimed in claim 1, wherein the one or more one or more photoinitiators selected from ##STR00019## and mixtures thereof, wherein n is a value from 1 to 10 and a+b+c is a value from 1 to 20, are present in the ink in 1-10% by weight, preferably 1-5% by weight, based on the total weight of the ink.

4. An inkjet ink as claimed in claim 1, wherein the one or more photoinitiators each having a log P.sub.octanol/water value of less than 4.0 are present in the ink in an amount of 1.0-4.0% by weight, preferably in an amount of 1.5-3.5% by weight, based on the total weight of the ink.

5. An inkjet ink as claimed in claim 1 wherein the photoinitiator package is present in the ink in 10-30% by weight, preferably 15-20% by weight, based on the total weight of the ink.

6. An inkjet ink as claimed in claim 1, wherein the photoinitiator package comprises one or more additional photoinitiators.

7. An inkjet ink as claimed in claim 6, wherein the one or more additional photoinitiators are selected from ##STR00020## and mixtures thereof, wherein d+e+f+g is a value from 1 to 20.

8. An inkjet ink as claimed in claim 1, wherein the one or more monomers each having a log P.sub.octanol/water value of 5.0 or more comprise one or more monofunctional monomers, preferably one or more monofunctional (meth)acrylate monomers.

9. An inkjet ink as claimed in claim 91, wherein the ink comprises lauryl acrylate.

10. An inkjet ink as claimed in claim 1, wherein the one or more monomers each having a log P.sub.octanol/water value of 5.0 or more are present in the ink in 15-40% by weight, based on the total weight of the ink.

11. An inkjet ink as claimed in claim 1, wherein the ink further comprises one or more additional monomers, preferably wherein the one or more additional monomers are selected from 1,10-decanediol diacrylate (DDDA), hexanediol diacrylate (HDDA), polyethylene glycol diacrylate, tripropylene glycol diacrylate (TPGDA), 3-methyl 1,5-pentanediol diacrylate (3-MPDDA), dipropylene glycol diacrylate (DPGDA), tricyclodecane dimethanol diacrylate (TCDDMDA), propoxylated neopentyl glycol diacrylate (NPGPODA), trimethylolpropane triacrylate (TMPTA), di-trimethylolpropane tetraacrylate (DiTMPTA), di-pentaerythritol hexaacrylate (DPHA), ethoxylated trimethylolpropane triacrylate (EOTMPTA), ethoxylated pentaerythritol tetraacrylate (EOPETTA), triethylene glycol divinyl ether (DVE-3) and mixtures thereof.

12. An inkjet ink as claimed in claim 11, wherein the one or more additional monomers are present in the ink in 20-80% by weight, based on the total weight of the ink.

13. A method of inkjet printing comprising inkjet printing the inkjet ink as claimed in claim 1, 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 curing the ink by exposing the printed ink to a curing source comprises the following steps in order: (i) partially curing the inkjet ink by exposing the inkjet ink to a first curing source; and (ii) fully curing the inkjet ink by exposing the inkjet ink to a second curing source.

15. A method of inkjet printing as claimed in claim 14, wherein the first curing source is a UV LED lamp and the second curing source is a source of low-energy electron beam radiation.

Description

EXAMPLES

Example 1

[0191] Inkjet inks were prepared according to the formulations set out in Table 1. The inkjet ink formulations were prepared by mixing the components in the given amounts. Amounts are given as weight percentages based on the total weight of the ink.

TABLE-US-00001 TABLE 1 Ink 1 Ink 2 Ink 3 Component (invention) (comparative) (comparative) 3-MPDDA (difunctional 45.62 45.62 45.62 monomer) DVE-3 (difunctional 4.80 4.80 4.80 monomer) Lauryl acrylate (mono- 24.04 24.04 24.04 functional monomer) Irgastab UV22 0.20 0.20 0.20 (stabiliser) Cyan pigment dispersion 7.84 7.84 7.84 Omnirad 9210 3.00 (photoinitiator) Speedcure 7010L 6.50 8.00 9.50 (photoinitiator) Esacure KIP 160 3.50 5.00 3.50 (photoinitiator) Omnirad 819 3.50 3.50 3.50 (photoinitiator) Byk 307 (surfactant) 1.00 1.00 1.00 Total 100.00 100.00 100.00 Viscosity at 25° C. 11.16 9.81 11.22 (mPa .Math. s) UV dose required for 525 525 871 cure before freezer storage (mJ/cm.sup.2) UV dose required for 525 655 871 cure after freezer storage (mJ/cm.sup.2) Precipitated photo- No Yes No initiator after freezer storage?

[0192] 3-MPDDA, DVE-3 and lauryl acrylate are monomers, as defined herein. Lauryl acrylate is the only monomer present that has a log P.sub.octanol/water value of 5.0 or more, namely 5.8.

[0193] The cyan pigment dispersion A contains 30% pigment, 20% polymeric dispersing aid and 50% DVE-3. The dispersion was prepared by mixing the components in the given amounts and passing the mixture through a bead mill until the dispersion had a particle size of less than 0.3 microns. Amounts are given as weight percentages based on the total weight of the dispersion.

[0194] Omnipol 9210, Speedcure 7010L, Esacure KIP 160 and Omnirad 819 are photoinitiators, as defined herein. Esacure KIP 160 is the only photoinitiator present that has a log P.sub.octanol/water value of less than 4.0, namely 3.0.

[0195] The viscosity of the ink was measured using an ARG2 rheometer manufactured by T.A. Instruments, which uses a 40 mm oblique/2° steel cone at 25° C. with a shear rate of 25 s.sup.−1. All of the inkjet inks have a viscosity of less than 20 mPa.Math.s and so have an ink-jettable viscosity.

[0196] The cure speed of the inks of Table 1 was assessed both before and after freezer storage. The presence of any precipitated photoinitiator was also assessed after freezer storage.

[0197] Before freezer storage, the inks were drawn down in a 12 μm film using a 12 μm wire wound K-bar onto a 220 μm PVC from Genotherm. The inks were then cured using a medium pressure Hg Heraeus Noblelight UV lamp of power rating 180 W/cm. The UV doses required for cure before freezer storage are shown in Table 1.

[0198] The inks were then stored at −15° C. for one week and before testing, transferred to a water bath at 25° C.

[0199] The inks were printed and cured in the same way as before freezer storage. The UV doses required for cure after freezer storage are shown in Table 1.

[0200] 15 mL of each of the inks was also filtered through a 1.5 μm filter paper and the paper was visually inspected for any filtrate. The results are shown in Table 1.

[0201] As can be seen from Table 1, Ink 1 of the invention required the same low dose of UV radiation for cure before and after freezer storage and no photoinitiator precipitated after freezer storage. As such, Ink 1 has a high cure speed and excellent solubility stability.

[0202] In contrast to Ink 1 of the invention, comparative Ink 2 contained the same total amount of photoinitiators as Ink 1 but Esacure KIP 160 was present in an amount of 5.00% by weight, based on the total weight of the ink, and Omnipol 9210 was absent.

[0203] The presence of one or more photoinitiators each having a log P.sub.octanol/water value of less than 4.0 in more than 4.5% by weight, based on the total weight of the ink, means that although comparative Ink 2 required a low dose of UV radiation for cure before freezer storage, a higher dose of UV radiation for cure was required after freezer storage. Precipitated photoinitiator was observed after freezer storage, explaining the increase in dose of UV radiation required for cure. Therefore, comparative Ink 2 has a high cure speed but poor solubility stability.

[0204] In contrast to Ink 1 of the invention, comparative Ink 3 contained the same total amount of photoinitiators as Ink 1 and Esacure KIP 160 was present in the same amount as Ink 1, but Omnipol 9210 was absent.

[0205] Without the presence of at least one of Omnipol 910, Omnirad TPO-L, Omnipol BP, Omnipol 2702, Omnipol TX and/or Omnipol TP, comparative Ink 3 required a higher dose of UV radiation for cure than Ink 1. However, the dose of UV radiation for cure remained the same before and after curing and no photoinitiator precipitated after freezer storage because the ink contained no more than 4.5% by weight of one or more photoinitiators each having a log P.sub.octanol/water value of less than 4.0, based on the total weight of the ink. Comparative Ink 3 therefore has a low cure speed but excellent solubility stability.

[0206] Therefore, the examples show that the addition of at least one of Omnipol 910, Omnirad TPO-L, Omnipol BP, Omnipol 2702, Omnipol TX and/or Omnipol TP whilst restricting the amount of photoinitiators having a log P.sub.octanol/water value of less than 4.0 to 0.5-4.5% by weight, based on the total weight of the ink, increases the cure speed of the ink whilst maintaining the solubility stability.

[0207] Owing to the presence of 10-50% by weight of one or more monomers each having a log P.sub.octanol/water value of 5.0 or more, based on the total weight of the ink, the inks would also have good film properties such as water resistance.