Photocurable clear ink composition for inkjet printing

Abstract

Clear inks are prone to heat-induced micro-gelling that can cause their storage stability to drop, and micro-gelling may also occur in clear inks with the passage of time, in which case their inkjet discharge property may drop. As a solution, a photocurable clear ink composition for inkjet printing is provided, which contains a photopolymerizable compound, a photopolymerization initiator, and an inorganic filler of 1 to 200 nm in average grain size accounting for 0.05 to 5.0 percent by mass in the composition, and whose visible light transmission factor is 30% or higher.

Claims

1. A photocurable clear ink composition for inkjet printing which contains a photopolymerizable compound, a photopolymerization initiator, an amino and/or acid group-containing pigment dispersant, an inorganic filler of 1 to 200 nm in average grain size accounting for 0.05 to 3.0 percent by mass in the composition, and a ketone resin, and whose visible light transmission factor as measured at 680 nm is 30% or higher.

2. The photocurable clear ink composition for inkjet printing according to claim 1, wherein the inorganic filler is silica and/or aluminum oxide.

3. The photocurable clear ink composition for inkjet printing according to claim 1, wherein an amide group-containing monofunctional monomer and benzyl acrylate are contained, as the photopolymerizable compound, by 50 to 75 percent by mass in total quantity in the photocurable clear ink composition for inkjet printing.

4. The photocurable clear ink composition for inkjet printing according to claim 3, wherein the amide group-containing monofunctional monomer is N-vinyl caprolactam and/or acryloyl morpholine.

5. The photocurable clear ink composition for inkjet printing according to claim 1, wherein a viscosity at 25° C. is 10 mPa.Math.s or lower.

6. The photocurable clear ink composition for inkjet printing according to claim 2, wherein an amide group-containing monofunctional monomer and benzyl acrylate are contained, as the photopolymerizable compound, by 50 to 75 percent by mass in total quantity in the photocurable clear ink composition for inkjet printing.

7. The photocurable clear ink composition for inkjet printing according to claim 6, wherein the amide group-containing monofunctional monomer is N-vinyl caprolactam and/or acryloyl morpholine.

8. The photocurable clear ink composition for inkjet printing according to claim 2, wherein a viscosity at 25° C. is 10 mPa.Math.s or lower.

9. The photocurable clear ink composition for inkjet printing according to claim 3, wherein the amide group-containing monofunctional monomer is N-vinyl caprolactam and/or acryloyl morpholine.

10. The photocurable clear ink composition for inkjet printing according to claim 3, wherein a viscosity at 25° C. is 10 mPa.Math.s or lower.

11. The photocurable clear ink composition for inkjet printing according to claim 4, wherein a viscosity at 25° C. is 10 mPa.Math.s or lower.

12. The photocurable clear ink composition for inkjet printing according to claim 6, wherein the amide group-containing monofunctional monomer is N-vinyl caprolactam and/or acryloyl morpholine.

Description

EXAMPLES

(1) The present invention is explained below in further detail using examples; however, it should be noted that the present invention is not limited to these examples. It should also be noted that, unless otherwise specified, “%” indicates “percent by mass,” while “part” indicates “part by mass.”

(2) The following materials are used in the examples and comparative examples below.

(3) <Pigment Dispersant>

(4) Ajisper (registered trademark) PB821 (manufactured by Ajinomoto Fine-Techno)

(5) <Photopolymerizable Compounds>

(6) Benzyl acrylate (manufactured by Osaka Organic Chemical Industry)

(7) Vinyl caprolactam 1,6-hexane diol diacrylate

(8) <Photopolymerization Initiator>

(9) TPO: 2,4,6-trimethyl benzoyl diphenyl phosphine oxide (manufactured by LAMBERTI)

(10) <Additives>

(11) BYK-315 (silicone additive, manufactured by BYK Chemie)

(12) UV-5=dioctyl maleate (manufactured by Kromachem)

(13) UV-22=quinone polymerization inhibitor (manufactured by Kromachem)

(14) <Inorganic Oxides>

(15) Silica (20 nm in grain size, NANOCRYL C 140, manufactured by Evonik, dispersed in 1,6-hexane diol diacrylate, solids content 50%)

(16) Aluminum oxide (80 nm in grain size, AEROXIDE Alu-C, manufactured by Nippon Aerosil, dispersed in-house, solids content 10%)

(17) <Preparation of Aluminum Oxide Dispersion>

(18) 10 parts by mass of AEROXIDE Alu-C, 1 part by mass of PB-821 as a dispersant, and 89 parts by mass of benzyl acrylate, were kneaded for 60 minutes in a Ready Mill (bead diameter: 0.2 nm, filling rate: 50%), to obtain an aluminum oxide dispersion of 4.9 cps in viscosity, 80 nm in grain size distribution, and 10% in solids content.

Examples 1 to 8 and Comparative Examples 1 to 3

(19) [Preparation of Photocurable Clear Ink Compositions for Inkjet Printing]

(20) The components were blended according to the blending compositions (percent by mass) in Table 1 and mixed under agitation, to obtain the photocurable clear ink compositions for inkjet printing in Examples 1 to 8 and Comparative Examples 1 to 3.

(21) [Viscosity Measurement of Photocurable Clear Ink Compositions for Inkjet Printing]

(22) The photocurable clear ink compositions for inkjet printing obtained in Examples 1 to 8 and Comparative Examples 1 to 3 were measured for viscosity using a type-E viscometer (product name: RE100L Viscometer, manufactured by Toki Sangyo) under the conditions of 25° C. in temperature and 500 rpm in rotor speed.

(23) The photocurable clear ink compositions for inkjet printing in Examples 1 to 8 and Comparative Examples 1 to 3 had viscosities of approx. 7 mPa.Math.s.

(24) <Visible Light Transmission Factor>

(25) Visible light transmission factor was measured using a UV/visible spectrophotometer (product name: UV-Vis Recording Spectrophotometer, manufactured by Shimadzu Corporation).

(26) <Gravity Filtration Test>

(27) The photocurable clear ink compositions for inkjet printing in Examples 1 to 8 and Comparative Examples 1 to 3 were tested immediately after manufacture (initial state) and after one month of preservation at 60° C., where 40 g was sampled from each photocurable clear ink composition for inkjet printing and passed through a SPC filter holder (Φ25 mm, manufactured by Sibata Scientific Technology) over a 2600 mesh, to measure the passing-through level.

(28) TABLE-US-00001 TABLE 1 Comparative Example Example Composition 1 2 3 4 5 6 7 8 1 2 3 Inorganic Silica Silica 0.05 0.5 1.0 1.5 5.0 — — — — — — fillers (grain size 20 nm, 1,6-hexane 0.05 0.5 1.0 1.5 5.0 — — — — — — NANOCRYL C 140, diol manufactured by Evonik, diacrylate solids content 50%) Aluminum oxide Aluminum — — — — — 0.1 0.3 0.5 0.03 5.5 — (grain size 80 nm, oxide AEROXIDE Alu-C, Benzyl — — — — — 0.9 2.7 4.5 0.27 49.5 — manufactured by Nippon acrylate Aerosil, dispersed in-house, solids content 10%) Aluminum oxide Aluminum — — — — — — — — — — 0.2 (grain size over 200 nm, oxide AEROXIDE Alu-C, Benzyl — — — — — — — — — — 1.8 manufactured by Nippon acrylate Aerosil, dispersed in-house, solids content 10%) Photopoly- Vinyl caprolactam 9 9 9 9 9 9 9 9 9 9 9 merizable Benzyl acrylate 55 54.1 53.1 52.1 45.1 54.1 52.1 50.1 54.8 0.1 53.1 compounds Ketone SK resin/V#160 SK resin 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 resin (solids content 40%) Benzyl 12.6 12.6 12.6 12.6 12.6 12.6 12.6 12.6 12.6 12.6 12.6 acrylate Initiator TPO 12 12 12 12 12 12 12 12 12 12 12 Additives UV5 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 UV22 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 BYK-315 (solids content 25%) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Evaluation Gravity filtration test (initial state) 7′42″ 8′13″ 7′50″ 8′03″ 7′57″ 8′19″ 8′21″ 7′39″ 7′21″ x 13′35″ Gravity filtration test (after one 8′03″ 8′21″ 8′01″ 8′24″ 8′18″ 8′27″ 8′33″ 8′01″ x x x month of acceleration at 60° C.) Visible light transmission factor (680 nm) 95 98 94 95 98 91 90 78 97 8 45

(29) According to Examples 1 to 8, which are examples in line with the present invention, despite the fact that the clear inks were high in visible light transmission factor, their storage stability was almost unchanged as compared to that in initial state measured immediately after manufacture, even after one month of acceleration (preservation) at 60° C. In contrast, the clear ink in Comparative Example 1 containing an insufficient content of inorganic filler, to which, in Comparative Example 2, an inorganic filler was added excessively, and to which, in Comparative Example 3, an inorganic filler of larger average grain size was added, degraded after having been kept for one month at 60° C. The clear inks to which an inorganic filler was added excessively or whose inorganic filler was too large, already had poor storage stability immediately after manufacture.