Ink jet recording material

Abstract

Ink jet images are produced by spraying the recording substrate with a fine jet of a coloured liquid which is mudulated according to the image. The new type of recording material consists of a transparent or opaque substrate and an image receiving layer is formed by a molecular disperse or colloidal disperse substance. It is important that the image receiving layer should be wetted by the coloured liquid and that, after spraying, the coloured liquid should penetrate the layer to a depth of at least several microns. Ink jet images of high quality can be obtained with such a recording material.

Description

This invention relates to a recording material for ink-jet images which are produced by spraying a fine jet of a coloured liquid which is modulated according to the image. The recording material basically comprises a transparent or opaque substrate and an image receiving layer on this substrate.

A recording technique has recently become known by the term ink-jet process, in which technique a very fine jet of coloured liquid sprayed from a capillary tube is modulated in density according to the image by an electric field. The jet of coloured liquid from the capillary impinges on the substrate at a high velocity (approximately 20 m/sec). The ink jet process has been described, for example, in German Auslegeschrift DT-AS No. 1,271,754 and in British Patent Specification No. 1,123,587.

It has now been found that the quality of the image depends to a large extent on the properties of the recording material. The materials used for recording substrates have previously been paper or synthetic resin materials resembling paper in consistency or transparent foils, depending on whether the image to be produced is a transparency or an image viewed by reflected light.

The practice has already been adopted of improving the quality of the images viewed by reflected light by adding white or tinted pigments to the paper. In the case of paper which has not been coated, however, it is observed that the droplets of coloured liquid break on the surface of the paper or the ink solution spreads out so that the quality of the image is deleteriously affected as regards its resolution and visual density and the colours are matt and dull. If for the production of colour images, several different dye solutions are sprayed simultaneously or at short intervals onto the substrate, there is the added risk that the solutions will not dry or be absorbed by the surface sufficiently rapidly but will intermingle. In that case, cloudy irregularities are observed, especially in the case of large coloured or black areas. In addition, the colours sprayed on uncoated surfaces are generally not smudge-proof.

The substrates used for the production of transparencies by the ink-jet process are generally transparent foils (e.g. Cellite or polyester) but these foils generally have the disadvantage that their surfaces repel dye solutions, and the ink droplets coalesce to larger drops on the surface. Continuous colour surfaces are therefore not obtained.

It is an object of this invention to find an improved recording material for reflection copies and for transparencies. The individual properties in which improvement is required are:

1. The power of resolution should be increased.

2. The dye solution should not run after it has been sprayed on the surface and it should be fixed as quickly as possible on, or also in, the image receptor layer.

3. The smudge resistance should be increased.

4. A gloss effect is desired in order to achieve high visual density of reflection and high colour brilliance in reflection copies.

5. Uniform optical densities should be achieved in transparencies.

In a recording material which comprises a transparent or opaque substrate and an image receiving layer on this substrate, these conditions are substantially fulfilled if the image receiving layer comprises, according to the invention, of a moleculae disperse or colloidal disperse substance which is wetted by the coloured liquid and into which the sprayed coloured liquid preferably penetrates to a depth of at least several microns.

The image receiving layer preferably consists of a protein, polysaccharide, cellulose or cellulose derivative, polyvinyl alcohol or a copolymer of vinyl alcohols. Image receiving layers of gelatine, albumen or casein are found to be particularly suitable. Very good results have also been obtained with an image receiving layer consisting of a hydrophilic silica gel.

For reflection copies, it is advantageous to add dyes and/or white toners to the image receiving layer to increase the degree of whiteness.

For reflection copies, the recording material may be further improved by treating the image receiving layer with substances which produce a directional reflection in the optically visible wavelength range. Such a gloss effect can advantageously be produced by casting the image receiving layer on a layer of a polyolefine such as polyethylene or a polypropylene. An alternative method of producing a glass effect consists of pouring a layer of polyolefin or polypropylene on the image receiving layer after the recording has been made. A glossy surface on the image receiving layer can also be produced by heating in a glazing press or by calendering.

The new recording material fulfils the above mentioned requirements very satisfactorily and in particular the resolution and brilliance can be substantially increased.

To test the image quality of the recording material, an ink (aqueous solution of a cyan, magenta or yellow dye) which has a viscosity of 1.2 cp at room temperature is sprayed at a pressure of 40 excess atmospheres through a glass capillary which has an opening of 7 .mu.m. The scanning velocity, i.e. the relative velocity between the recording substrate and the ink-jet, is 5 m/sec. With scan line densities of 10 lines per mm, viewing densities on reflection copies of between 1.0 and 1.3 are obtained in the case of a single colour. Reflection copies of very high quality were obtained under these conditions in the following image receiving layers:

EXAMPLE 1

A suitably pigmented paper (e.g. the photographic raw paper weighing 90 g/m.sup.2 manufactured by Schoeller, Burg Gretesch) was coated with a gelatine layer with the addition of AGEPON as wetting agent and chrome alum as hardener. The layer had a thickness of 10 .mu.m when dry. The dye penetrated the layer to a depth of about 4 .mu.m, as shown by a thin layer section under the microscope. The depth of penetration of the dye could be adjusted by varying the quantity of hardener added. In the case of the reflection copies, it was seen under the microscope that the track of a single scan line had a width of less than 50 .mu.m whereas in uncoated paper this track spread to a width of about 100 .mu.m. When the ink was sprayed under the conditions defined above, viewing densities obtained on reflection copies were 1.1 for a single colour as compared with 0.7 in the case of an uncoated paper surface.

EXAMPLE 2

The pigmented paper was coated with a 5 .mu.m thick layer of silicic acid sol (K100, Farbenfabriken Bayer) with the addition of AGEPON as wetting agent. The depth of penetration of the dye solution was approximately equal to the thickness of the layer. The viewing density under reflected light was about 1.2 for one colour.

EXAMPLE 3

Gelatine and barium sulphate (ratio: 1:10) were mixed with water to form a spread coating suspension (temperature 50.degree. to 60.degree.C). Hardener (chrome alum) were added to this supsension and in addition white toner and pigment dyes were added to adjust the suspension to the optimum degree of whiteness. The suspension was then applied to the raw paper to produce a layer which has a thickness of 10 .mu.m when dry. The dye penetrated the layer to a depth of about 6 .mu.m. The viewing densities under reflected light were in the region of 1.1.

EXAMPLE 4

The pigmented paper was first covered with a coating of polyethylene as gloss layer. Over this, a layer of gelatine was cast as described in Example 1. Brilliant colours were obtained and the viewing density was increased to 1.3.

EXAMPLE 5

An image was produced by spraying on a material which had been prepared as described in Example 2. This image was then coated with a layer of clear lacquer. Viewing densities of 1.3 were obtained for each colour under reflected light and at the same time the lightfastness and smudge resistance of the image were increased.

EXAMPLE 6

Before application of the ink-jet image, the layer prepared according to Example 3 was passed over a calendering press in which the rollers were heated to about 80.degree.C. A glazing effect was thereby obtained and the viewing densities under reflected light were increased to 1.3 as in Example 3.

Claims

What we claim is:

1. In a process for information recording comprising producing a fine jet of colored liquid, directing the jet of colored liquid onto a recording medium, modulating the density of the applied jet by an electric field in accordance with the information to be recorded, the improvement comprising the recording medium consisting of a support with an image-receiving layer, wherein the image-receiving layer is a molecular or colloidal disperse substance, which is wetted by the colored liquid and into which the colored liquid penetrates to a depth in the order of a few microns.

2. A process according to claim 1 wherein the image receiving layer comprises a protein, a polysaccharide, cellulose, a cellulose derivative, a polyvinyl alcohol, a copolymer of vinyl alcohols or a hydrophilic silica gel.

3. A process according to claim 2 wherein the image receiving layer comprises gelatin, albumen or casein.

4. A process according to claim 1 wherein a white toner is added to the image receiving layer.

5. A process according to claim 1 wherein the image receiving layer is treated with a substance which produces a directional reflection in the optically visible wave-length range.

6. A process according to claim 5 wherein the image receiving layer is cast on a polyolefine layer.

7. A process according to claim 5 wherein a layer of polyolefine is cast on the image receiving layer after the recording has been made.

8. A process according to claim 5 wherein a glossy surface is imparted to the image receiving layer by heating in a glazing press or by calendering.