WO1997001449A1

WO1997001449A1 - Post-printing treatment of ink-jet generated images

Info

Publication number: WO1997001449A1
Application number: PCT/GB1995/002517
Authority: WO
Inventors: Meinrad Schär; Fernand Gervais; Pierre Maudonnet
Original assignee: Ilford A.G.; Matthews, Richard, Nordan
Priority date: 1995-06-27
Filing date: 1995-10-24
Publication date: 1997-01-16
Also published as: GB9513096D0; AU3705195A

Abstract

There is described a method of treating a coated ink receiving sheet after it has been ink-printed which comprises directing on to the ink receiving sheet a stream of steam at a temperature of 100 °C or over and for between 0.1 to 100 seconds under such conditions that only minimum condensation of water occurs on the surface of the ink receiving sheet. In a preferred method, after the sheet has been steam-treated, there is directed on to it heat for between 0.1 and 100 seconds so that the surface temperature of the sheet is between 60 °C and 150 °C.

Description

Post-Printing Treatment of Ink-iet Generated Images The present invention relates to a post-printing treatment of ink-jet generated images. Ink-jet images generated at the present time have a particular need for improvement in their handling properties. They should be smear resistant. This means that the recorded image should remain intact after rubbing the surface with a slightly wet finger. The dyes should remain in their original positions. Very often a small quantity of dye does not penetrate into the ink receiving sheet but is deposited on the surface ofthe ink receiving sheet. This surface dye is easily displaced mechanically which results in a soiled image. The presence of surface due can in many cases be seen when looking at the image under a low angle. The surface dye may alter the reflection properties of the surface. Depending on the viewing angle the image colour may change.

The present invention provides a solution towards this problem of smudge resistance.

Ink-jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink-jet systems the continuously emitted ink droplets are charged in accordance with digital data signals and passed through a static electric field which adjusts the trajectory of each droplet in order to direct it to a gutter or to a specific location on a recording medium. In drop-on-demand systems a droplet is expelled from an orifice to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.

Although the main effort in this invention is directed towards images of high quality recorded by the continuous stream system it is not meant to be restricted to this method, but is applicable as well to images recorded by drop-on-demand systems (e.g. thermal ink-jet or piezo ink-jet). Ink-jet printers often use inks that contain water soluble dyes. Such dyes are often not very smear resistant when printed on ink receiving sheets. The smear resistance of water based inks may be improved by the addition of formamide (US 4,961,785), pyrrolidones (US 5,108,503), ammonium zirconium polymer salt (US 5,250,107), and the like.

Often such modifications of the inks have the tendency to give inks liable to show precipitates upon prolonged storage. Such precipitates subsequently tend to clog the nozzles of ink-jet printers.

Ecological and toxicological reasons also do not recommend the use of such modified inks: The solvents used in such modified inks increase the solvent content in the air near the ink-jet printer and therefore sophisticated and costly installations may be required to remove the solvent containing air in the ink-jet printer surroundings so as to stay within legal limits for the solvent content in the air.

The use of such solvents with a high boiling point also slows down the drying of the printed ink receiving sheets, eventually needing supplementary drying, for example microwave drying as described in EP 0,559,324.

Another attempt to improve smudge resistance has been the use of reactive dyes, as for instance in US 4,443,223, US 5,098,475, US 5,074,914, US 5,230,733, EP 0,429, 171 and references cited therein. These reactive dyes have a reactive moiety attached to the chromophore and are capable of forming a covalent bond to one or more of the components of the receiving layers of the ink receiving sheet. Although some improvement has been achieved by this technique no satisfactory results can in general be obtained due to the fact that the conditions which are possible in practice in a printing environment do not suffice to achieve reaction of these dyes with given binders.

There is a need to produce high quality ink-jet generated images and one method of achieving this is to use coated papers as the image receiving sheet and for example, gelatin is a useful coating for such sheets. However, it is difficult to get the dyes in the inks used to penetrate the surface of such coated papers and not to remain on the surface from which they are easily removed in smearing the image.

It would therefore be much preferred if the improved smudge resistance could be achieved by a modification of the ink receiving sheets or a post-treatment of already printed images.

Such a post-treatment would be the method of choice as it would be applicable to a wide variety of inks and ink receiving sheets and combinations thereof.

It is well known that even a gentle contact of the surface of a printed ink receiving sheet with water (for example with a wet finger) mobilises the dyes deposited at the surface. These dyes subsequently are easily moved mechanically to adjacent parts of the image. If water flows for a short time over the surface of a printed ink receiving sheet it carries the surface dye with it. This dye is later deposited at another place ofthe sheet.

It was therefore totally unexpected that the treatment of printed ink receiving sheets with steam should lead to a dramatic improvement in smudge resistance. Rubbing of such treated ink receiving sheets with a wet finger leaves the ink receiving sheets totally or nearly unaltered. Also water flowing over the surface no longer carries the surface dye with it. When looking under a low angle at the image no more surface dye is seen after the treatment. The resulting image looks much more pleasant.

An objective of this invention therefore is to provide a simple post-printing treatment of ink receiving sheets to improve smudge resistance.

According to the present invention there is provided a method of treating a coated ink receiving sheet after it has been ink printed which comprises directing on to the ink receiving sheet a stream of steam at a temperature of 100°C or over and for between 0.1 to 100 seconds under such conditions that only minimum condensation of water occurs on the surface of the ink receiving sheet.

Thus it is to be understood that the temperature of the steam, the length of time the steam is directed on to the printed ink receiving sheet and the distance of the means for directing the steam on to the printed ink receiving sheet must be arranged relative to each other so that only minimum condensation of water from the steam on the ink receiving sheet occurs.

Preferably in the method ofthe present invention the temperature ofthe steam is from 100 to 120°C.

Preferably in the method of the present invention the steam is directed on to the ink receiving sheet from 0.1 to 10 seconds.

In one method of the present invention the treatment with steam is carried out off-line. That is to say after the ink receiving sheet is ink printed and dried, the ink receiving sheet is treated with steam in a separate treating means. However, in another method of the present invention the treatment with steam is carried out on-line a short time after the ink receiving sheet has been ink printed and before the ink receiving sheet has dried completely.

Preferably the ink receiving sheet which comprises the image is heat-treated after the steam treatment.

Therefore in the preferred method of the present invention there is provided a method of treating a coated ink receiving sheet after it has been ink printed which comprises directing on to the ink receiving sheet a stream of steam at a temperature over 100°C and for between 0.1 and 100 seconds under such conditions that minimum condensation of water occurs on the surface of the ink receiving sheet and then directing heat on to the sheet for between 0.1 and 100 seconds so that the surface temperature of the sheet is between 60°C and 150°C.

Preferably the steam and the heat are directed on to the sheet for between 0.1 and 10 seconds.

Preferably the heating means is a convection heater or is a radiant heater for example an infra-red radiant-heater.

Preferably the sheet is subjected to two heaters each arranged over the path of the sheet.

Preferably in the method of the present invention the steam generating means comprises a steam inlet tube, the open end of which is located in an insulated steam jacket with a slot or arrangement of slots outlet. Most preferably a heater is provided in the steam jacket to eliminate the risk of water condensing from the steam prematurely. The temperature in the steam jacket can be raised so that super-heated steam is produced.

Preferably in the method of the present invention the chamber which comprises the heater or heaters also comprises a fan which directs air heated by the heater or heaters on to the sheet being conveyed beneath.

Most conveniently the first heater is located as close as is possible to the steam chamber so that after the sheet has been steam treated it is at once dried at an elevated temperature.

The method of the present invention can be used to treat sheets of paper or rolls of paper which have been ink-jet printed.

The following Example will serve to illustrate the method of the present invention.

Example

The coated ink receiving sheets were prepared according to Example 7 of our pending patent application PCT/GB 95/00784. The coated layers on a glossy RC paper support had the following compositions:

First coated layer on to resin coated paper (RC paper):

Gelatin with high isoelectric point 3.750 g/m²

Lanthanum nitrate 0.300 g/m²

Olin 10G (wetting agent) 0.125 g/m²

Second layer on top of the first layer:

Gelatin with high isoelectric point 3.750 g/m 2

Spacing agent 0.100 g/m 2

Olin 10G (wetting agent) 0.150 g/m

2-(4-dimethylcarbamoylpyridino)-ethanesulfonate 0.033 g/m (Cross linker)

Olin 10G is available from Olin Chemicals, USA.

Three series of sheets were ink printed in an Iris 3024 ink-jet printer with ID inks both available from Iris Graphics Inc, USA, and then treated as just described. These sheets were compared with similar sheets which after ink printing were cold air dried. In the series, steam when applied was applied for 2 seconds and heat when applied was for 2 seconds to yield a surface temperature of 120°C.

In the first series the sheets were treated to both steam and then heat.

In the second series the sheets were subjected to steam treatment and were then allowed to be cold air dried.

In the third series the sheets were heat treated only, that is to say no steam treatment was used.

The treated sheets of the first, second and third series and the untreated sheets were all tested for smudge resistance and for gloss.

For the smudge test maximum density dye patches on the sheets were gently rubbed with a wet finger and whether dye smudging occurred or not was noted.

Gloss measurements were done as specified in DIN norm 67,530 (January 1982) for the angles 20°, 60° and 85° on colour patches of 70% of maximum density or on white patches on the treated and on the non-treated sheets.

Table 1 shows the results of the smudge test

Table 1

Sheets tested Ink smudging

Series 1 sheets No

Untreated sheets Yes

Series 2 sheets No

Series 3 sheets Yes

This shows that steam treatment is required to obviate dye smudging. Table 2 shows the results of the gloss measurements.

Table 2

Sheets Tested Area Tested Gloss

20° 60° 85°

Untreated Black 32.1 61.9 38.0

White 36.3 38.8 24.6

Magenta 33.5 61.2 33.9

First Series Black 51.3 67.0 55.1

White 52.3 65.3 43.6

Magenta 40.8 62.2 53.8

Second Series Black 28.6 61.7 38.7

White 33.5 58.3 23.8

Magenta 30.5 60.7 34.9

Third Series Black 28.6 61.7 38.7

White 33.5 58.3 23.8

Magenta 30.0 60.7 34.9 These results show that when the sheets had been treated both with steam followed by heat (first series) a greatly improved gloss is obtained compared with the untreated sheets.

However, when the sheets had been steam treated only not followed by heat treatment (second series) no improvement in gloss was obtained.

The results also show that when the sheets were heat treated without the prior steam treatment (third series) no improvement in gloss was obtained.

Claims

Claims:-

1. A method of treating a coated ink receiving sheet after it has been ink printed which comprises directing on to the ink receiving sheet a stream of steam at a temperature of 100°C or over and for between 0.1 to 100 seconds under such conditions that only minimum condensation of water occurs on the surface of the ink receiving sheet.

2. A method according to claim 1 wherein the temperature of the steam is between 100 and 120°C.

3. A method according to claim 1 wherein the steam is directed on to the ink receiving sheet from 0.1 to 10 seconds.

4. A method according to claim 1 wherein the treatment with the steam is carried out off-line.

5. A method according to claim 1 wherein the treatment with the steam is carried out on-line a short time after the ink receiving sheet has been ink printed.

6. A method of treating a coated ink receiving sheet after it has been ink printed which comprises directing on to the ink receiving sheet a stream of steam at a temperature 100°C or over and for between 0.1 and 100 seconds under such conditions that only minimum condensation of water occurs on the surface of the ink receiving sheet and then directing heat on to the sheet for between 0.1 and 100 seconds so that the surface temperature of the sheet is between 60°C and 150°C.

7. A method according to claim 6 wherein both the steam and the heat are directed on to the receiving sheet for between 0.1 and 10 seconds.

8. A method according to claim 6 wherein the heating means is a convection heater or is a radiant heater.

9. A method according to claim 8 wherein the heater is an infra-red radiant heater.

10. A method according to claim 9 wherein the sheet is subjected to two infra-red heaters each arranged over the path of the sheet.

11. A method according to claim 10 wherein the first heater is located as close as is possible to the steam chamber so that after the sheet has been steam treated it is at once dried at an elevated temperature.