Ink for ink-jet printing and method of ink-jet printing

Abstract

A solvent type curable ink for ink-jet printing obtained by dissolving or dispersing, in a volatile organic solvent, polyesterpolyol having a molecular weight of not more than 8000, a hydroxyl value (KOH mg/g) of 17 to 50 and a glass transition point (Tg) of not higher than 70° C., and blocked polyisocyanate. The ink is capable of forming ink-jet-printed image on the surfaces of various kinds of formed articles without burring and maintaining close adhesion upon being heated at a low temperature for a short period of time.

Claims

1. An ink for ink-jet printing including a liquid obtained by dissolving or dispersing polyesterpolyol and blocked polyisocyanate in a volatile organic solvent, said polyesterpolyol having a number average molecular weight of not more than 8000, a hydroxyl value (KOH mg/g) in a range of 17 to 50 and a glass transition point (Tg) of not higher than 70° C.

2. The ink for ink-jet printing according to claim 1, wherein said polyisocyanate has not less than 3 functional groups.

3. The ink for ink-jet printing according to claim 1, wherein said blocked polyisocyanate includes at least one kind of a constituent unit selected from the group consisting of diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), hexamethylene diisocyanate (HDI), metaxylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, lizine isocyanate and isophorone diisocyanate (IPDI).

4. The ink for ink-jet printing according to claim 1, wherein said blocked polyisocyanate has its terminals blocked with an active methylene compound.

5. The ink for ink-jet printing according to claim 1, wherein diethylene glycol diethyl ether is used as said volatile solvent.

6. The ink for ink-jet printing according to claim 1, wherein a pigment is, further, contained.

7. A method of ink-jet-printing images on a surface of plastic or nonmetallic formed article, comprising: using the ink for ink-jet printing described in claim 1; forming a printed layer on the surface of the formed article by ink-jet-printing said ink thereon; and heating the surface of the formed article at a temperature of 70 to 130° C. to solidify said printed layer, wherein: (a) the formed article is a polyolefin cap, and ink-jet printing is performed on the outer surface of the top panel of the cap, and (b) said heating at a temperature of 70 to 130° C. for fixing the printed layer is carried out for 1 to 30 seconds.

Description

EXAMPLE

(1) The invention will now be described by way Experiment described below.

(2) <Preliminary Testing>

(3) Polyesterpolyols A to P shown in Table 1 were evaluated for their solubilities in an organic solvent to obtain the results as also shown in Table 1.

(4) Evaluating the Solubilities;

(5) The sample polyesterpolyols were each added in an amount of 25 parts by weight per 100 parts by weight of the diethylene diglycol (DEDG), and were heated in a hot bath maintained at 45° C. for 16 hours.

(6) After heated, the solutions were filtered to make sure the presence of aggregated matters with the naked eye, and the solubilities were judged on the following basis. X: Aggregated matters were confirmed indicating poor solubility. ◯: No aggregated matter was confirmed indicating good solubility.

(7) TABLE-US-00001 TABLE 1 Molecular Hydroxyl Polyester- weight Tg value polyol (Mn) × 10.sup.3 ° C. KOH mg/g Solubility A 23 47 5 X B 17 67 6 X C 19 60 6 X D 22 72 5 X E 23 7 5 X F 16 47 7 X G 15 68 3 X H 8 79 16 X I 10 60 11 X J 18 79 5 X K 14 71 7 X L 18 84 5 X M 8 65 20 ◯ N 6 46 19 ◯ O 5 53 50 ◯ P 3 60 37 ◯

(8) From the above preliminary testing, it was learned that M to P dissolved well. Therefore, these polyesterpolyols were used in the following Experiment.

Experiment 1

(9) After a high molecular activating agent was added to the diethylene glycol diethyl ether, carbon black was added thereto such that the amount thereof was 15 wt %. The mixture was dispersion-treated by using a stirrer and a bead mill. Thereafter, coarse particles were removed by centrifugation, and a dispersion solution was prepared.

(10) Further, a mixed solution was prepared by mixing together the polyesterpolyol M and the polyisocyanate at an NCO/OH mol ratio of 5.36.

(11) The polyesterpolyol was the one dissolved in the diethylene glycol diethyl ether. The polyisocyanate was the one blocked with the active methylene compound so as to have an average functional group number of 5.5 and an average molecular weight of 1500 which was being dissolved in a mixed solution of n-butyl acetate and n-butyl.

(12) The above dispersion solution, mixed solution and diethylene glycol diethyl ether were so mixed together that the concentration of the pigment was 9 wt %, the amount of the solid components (sum of the polyesterpolyol and polyisocyanate) was 14 wt % and the viscosity was 7 to 9 mPa.Math.s to prepare an ink for evaluation.

(13) By using a piezo system on-demand ink-jet head, the ink for evaluation was ejected onto the top panel of a polyethylene cap for a PET bottle, and was so heated, by using a drier, that the temperature of the top panel of the cap was about 70 to about 130° C. for 1 to 5 seconds so as to be dried and cured.

(14) The thus prepared sample was judged for its curing property. The curing property was evaluated as described below.

(15) Evaluating the Curing Property;

(16) The printed surface of a printed cap was brought into contact with a cardboard of a thickness of 4 mm manufactured by Oji Container Co. being pressed with a load weighing 1 kg. In this state, the printed cap was caused to slide thereon at a constant speed over a distance of 60 mm at a rate of 45 round trips a minute by using a slide testing machine manufactured by Toyo Seiki Mfg. Co. The testing was conducted up to 100 round trips and after that the printed surface was visually evaluated for peeling of the ink.

(17) ⊚: No peeling was recognized.

(18) ◯: Peeling was recognized but the peeled area was not more than 5% of the printed area.

(19) X: Peeling was recognized and the peeled area was not less than 6% of the printed area.

(20) ⊚ and ◯ represent allowable ranges and X represents a range which is not allowable.

(21) Next, inks for evaluation were prepared in the same manner as described above but using the polyesterpolyols N, O and P, and were judged for their curing properties.

(22) The curing properties were evaluated as follows depending on the polyesterpolyols:

(23) TABLE-US-00002 Polyesterpolyol Curing property evaluated to be M ◯ N ◯ O ⊚ P ⊚