EP0575644A1 - Recording medium for receiving dyeing materials - Google Patents

Abstract

The uppermost, porous layer (1) comprises a filler-free plastic whose particles have fused together at their points of mutual contact, forming capillaries through which the colouring substance is conveyed in a downward direction. Below this layer (1) is arranged a receiving layer (2) for the respective dye diffusing in through the capillaries. The two layers (1, 2) are on a substrate layer. Since the colouring substance is thus conveyed rapidly through the uppermost layer (1) to the central layer (2) through the capillaries during printing, immediate drying at the surface of the recording medium takes place. Lateral spreading, i.e. blurring of the dye does not take place. No blurred areas are therefore produced and the images are very bright. <IMAGE>

Description

The invention relates to a recording medium for receiving coloring substances for recording images and information, with a flat underlayer and a porous layer arranged on at least one side thereof.

Known recording media of the type mentioned at the outset, which have materials or are coated with such materials which enable recording by means of ink, toner, ink and similar coloring substances, are constructed in such a way that the coloring substances mentioned are in the case of inks and toners Adsorption on the surface or in the case of inks by diffusion, in the case of paper and nonwovens by the capillary effect into the material in question. Colorants in which the dye is not dissolved but is dispersed in the form of small solid particles in a solvent, e.g. in the case of toners and inks, remain on the surface of the record carrier and the abrasion resistance of the corresponding record is therefore poor.

A first prerequisite for liquid media, ie coloring substances, to be able to diffuse into a layer of a recording medium is that the material has good wettability. If this requirement is met, it must be noted that diffusion processes are slow processes, that is to say that the diffusion of inks into a surface layer of a recording medium requires a certain period of time during which the diffusing substance is obviously still or must be flowable. In other words, it takes a certain amount of time for the ink to dry completely so that it can be handled of such a record carrier, the record can be smeared. Furthermore, slow drying due to the correspondingly persistent diffusion in the surface layer in question also causes the diffusing liquid to spread out to the side, with the result that the recorded image or the recorded image points run and the point resolution of the respective print thus decreases rapidly.

In particular, the sheet-like recording media for xerographic black / white and also color copying machines often have greasy surface layers due to the silicone oils used as abhesive agents. The resulting copies are then unsightly and uncomfortable to use.

If the recording medium consists of paper or similar fibrous substances or contains such substances, the coloring substances, e.g. Inks, absorbed between the fibers by capillary effect and will dry there. On the one hand, this capillary effect ensures the rapid absorption of the liquid coloring substances, but on the other hand has the disadvantage that, due to the capillaries, which are also horizontal with respect to the sheet surface, the resolution is negatively affected by the ink flowing along the paper fibers.

The invention seeks to remedy this.

The invention, as characterized in the claims, solves the problem of creating a recording medium in which, using capillary forces, rapid drying takes place as in paper, in which capillaries, pore or cell structures running exactly to the free surface thereof determinable size an optimal, constant pixel resolution is guaranteed.

The advantages achieved by the invention are essentially to be seen in the fact that, due to the microcapillarity obtained, rapid drying, one selective wetting and the possibility of encapsulating the coloring material and thus permanent protection of the print in question or the information content is made possible.

Depending on the production process, layer thickness of the microporous layer and choice of the carrier layer, the recording medium can be opaque, semi-transparent or transparent.

The microporous layer allows discrimination between different liquids or gases used for the printing process due to a specifically set polarity, respectively. Surface tension on the surface of the microporous layer, namely a specific wettability or specific absorption and adsorption properties.

These properties result from the choice of the thermoplastic, i.e. Polymers for the porous layer, as will be explained further below.

The production of layers with a porous structure from filler-free polymers is known as such from the technology for the production of membranes. Surprisingly, and according to the invention, it has been found that layers with capillaries or cavities oriented perpendicular to the surface, as are known from membrane technology, are not only usable for printing and recording processes, but also have excellent drying properties and, moreover, a constant, very high level Pixel resolution result.

Depending on the choice of the polymer used, the solvents used and a manufacturing process known from membrane technology, the desired capillarity or microporosity of the microporous layer is achieved by growing together cavities, by forming an open-pore polymer matrix when the solubility limits of the selected one are exceeded Polymers in the solvent (mixture) or by sintering together of individual polymer particles respectively. other mechanisms.

In contrast to known products for this application, the microporous structure of the microporous layer ensures, on the one hand, a very rapid drying of coloring substances in which the dye is dissolved in a solvent, e.g. for inks, on the other hand also a significantly better fixation of inks and toners, in which the dyes are not dissolved, but are dispersed in the form of small solid particles in a solvent.

Furthermore, the microporous structure of the microporous layer according to the invention and the choice of the polymer used for it ensure optimal resolution of the pixels in every printing process. The occurrence of ink drops (= image points) along fibers or in the known recording media. due to the chromatography effect within dense, quasi-pore-free layers, the recording medium according to the invention cannot occur, since the microporous layer contains neither fillers nor fibers and the drying process of the coloring substances, in particular of the inks, does not take place by diffusion.

Opaque and semi-transparent microporous layers can also be converted into a transparent layer after printing. For this purpose, the phase boundaries are made to disappear by exposing the respective layer to the action of heat and / or a solvent and / or pressure, which causes the individual particles to melt or dissolve. Another possibility of converting it into a transparent layer is to fill the capillaries of the microporous layer with a suitable solvent. These measures are generally known to those skilled in the art. Obviously there is in In these cases, the carrier layer made of a transparent material.

Since these inks and toners are now encapsulated in the interior of the microporous layer and are not only adsorbed on their surface as in the case of the known recording media, this results in an increased durability of a corresponding image.

Next because e.g. Inks are fixed in the capillaries of the microporous layer, there is a good, permanent resolution of the recording medium.

The recording medium according to the invention can be used for all currently known recording technologies and regardless of the respective format (poster, slide, etc.). The record carrier can be used for example for manual drawing, e.g. with felt-tip pen, ballpoint pen, with plotter devices, such as pen plotters or inkjet plotters or printers, with CAD recording devices. The recording medium can also be used for copying processes (e.g. xerography), in black and white copiers and color copying. Furthermore, the recording medium can be used extremely well in printing technology, e.g. for thermal transfer, thermal diffusion, inkjet printing, matrix, offset and flexographic printing.

The subject matter of the invention is explained in more detail below with reference to the drawings.

• Fig. 1 einen Schnitt durch Papier, bzw. ein Vlies, um den Faserverlauf zu zeigen,
• Fig. 2 einen Schnitt durch eine porenfreie Schicht mit aufgedruckten Bildpunkten,
• Fig. 3 eine aus Partikeln gemäss der Erfindung aufgebaute mikroporöse Schicht,
• Fig. 4 eine schwammartig aufgebaute mikroporöse Schicht gemäss der Erfindung,
• Fig. 5 einen Schnitt durch einen Aufzeichnungsträger einer ersten Ausführung, mit einer mikroporösen Schicht auf einer Trägerschicht, und
• Fig. 6 einen Schnitt durch einen Aufzeichnungsträger einer zweiten Ausführung, mit einer mikroporösen Schicht, einer darunten angeordneten Aufnahmeschicht und einer Trägerschicht.

It shows:

• 1 shows a section through paper or a nonwoven to show the course of the fibers,
• 2 shows a section through a pore-free layer with printed pixels,
• 3 shows a microporous layer constructed from particles according to the invention,
• 4 shows a sponge-like microporous layer according to the invention,
• 5 shows a section through a record carrier of a first embodiment, with a microporous layer on a carrier layer, and
• 6 shows a section through a recording medium of a second embodiment, with a microporous layer, a receiving layer arranged underneath and a carrier layer.

FIG. 1 shows, on a greatly enlarged scale and schematically drawn, a section through paper, that is to say a sheet of paper, or a fleece, in order to explain the fiber course of a recording medium according to the prior art with its disadvantages.

Due to the processing during production, a large part of the fibers 4 lie horizontally, so that the capillaries run predominantly horizontally. The capillaries formed by the fibers 4 are much longer than the pixels that are created during printing. On the one hand, as mentioned at the beginning, the capillary effect ensures a quick absorption of the respective liquid coloring material, on the other hand, however, the coloring material flows predominantly along the horizontal paper fibers, so that the resolution of the print is adversely affected.

Another embodiment of a known, also prior art receiving carrier is shown in FIG. 2. The receiving carrier 6 is here e.g. coated paper or a coated film, a thick, non-porous layer. The individual pixels are indicated by reference number 5. For inks, i.e. for all coloring substances in which the dye is dissolved in a solvent, the coloring substance penetrates slowly into the layer by diffusion or chronomatographically.

If the dye is dispersed in a liquid, as is the case with toners and ink, it remains on the surface with the disadvantages mentioned at the beginning.

In one embodiment of the invention, which is shown in FIG. 3, the microporous layer now consists of individual particles which are arranged relative to one another in such a way that capillaries directed perpendicular to the free surface, that is to say to be printed, are present. The coloring substance 8 can thus quickly penetrate into the layer. It should also be noted that the capillaries through which the coloring substance penetrates the layer have a smaller diameter than the pixels.

Another embodiment of the invention, which is particularly clearly shown and is known from membrane technology, is shown in FIG. 4. The plastic layer 9 is penetrated by elongated capillaries 10, which again run perpendicular to the free surface of the layer 9.

Specific embodiments of the invention will now be described with reference to FIGS. 5 and 6.

The flat underlayer 3, on which the microporous layer 1 designed according to the invention is applied directly or indirectly, is, for example, a paper sheet or a polyester film, depending on the respective intended use. For example, it should be noted that paper for opaque images and polyester can be used for semi-transparent and transparent images as a flat base.

For the production of the porous layer 1 on the base layer 3, thermoplastic polymers are used which are in the form of aqueous or non-aqueous dispersions or suspensions, of colloidal solutions in solvents or water.

Examples of such thermoplastic polymers are: poly-acrylates, polymethacrylates, polyacrylamides, polyesters, polyamides, polyurethanes, olefin polymers, styrene (co) polymers, vinyl acetate (co) polymers, polyvinyl alcohols, polyvinyl ethers, polyvinyl pyrrolidones, Polyethylene oxides, vinyl chloride or. Vinylidene chloride (co) polymers and maleic anhydride-based and fluorine-containing polymers, acetal resins and polyoxymethylenes, cellulose ethers and esters.

Modifications of these polymers are also. Copolymers of the monomers used in these polymers are suitable.

Polymers which are soluble in water and / or in organic solvents are therefore also used for the production of the porous layer 1.

The choice of the polymer for the microporous layer influences the printability and printing result of the recording medium. In practice, depending on a particular recording method, e.g. Xerography, thermal transfer printing, thermal diffusion printing, inkjet printing, matrix printing etc. by the appropriate choice of a polymer, the chemical composition and thus the polarity of the porous layer, the hydrophilicity or hydrophobicity and thus the wettability of the porous layer 1 are selected in order to more or the final printing result to be able to influence less.

In recording processes such as dry toner xerography and thermal transfer printing, ie processes using "dry colors", the influence of the polymer chosen is relatively small.

However, in recording processes in which liquid toners and inks are used, for example in ink jet printing or in liquid toner xerography, the influence of the choice of the polymer is great. In these latter printing processes, the quality of the print is decisively influenced by the wetting properties of the layer surface by the respective inks and liquid toners.

This also results in the possibility of creating selectively wettable, writable and printable surfaces, so that embodiments of the invention are of particular interest in the field of security papers. It should also be noted that on a given A flat underlayer 3 can be applied to both sides of a porous layer 1.

In a first embodiment, the record carrier thus consists of a suitable flat underlayer 3, on which a porous layer 1 with a thickness of 0.1-150 μm, preferably 0.1-50 μm, is applied.

In a second embodiment, it consists of a flat underlayer 3, on which an ink-receiving layer 2 is arranged, on which in turn the porous layer 1 described is applied with a thickness of 0.1 to 50 μ, preferably 1 to 30 μ.

The second embodiment, which therefore has a two-layer structure on the base layer 3, is particularly suitable for recording processes with liquid recording media such as inks, liquid toners, etc.

Due to its capillary absorbency, the porous cover layer 1, that is to say the top layer, causes the applied ink or liquid toner to quickly knock away and thus quick surface drying, and further increases the opacity of this porous layer 1 after the ink or Toner dyes is diffused into the underlying receiving layer 2, the color brilliance and depth of color of the respective print, in particular if the print image is viewed through a transparent base layer 3.

The receiving layer 2 under the porous cover layer 1 significantly increases the total absorption capacity for inks, liquid toners, etc. After the ink, the liquid toner, after the surface has been printed, is immediately sucked into the capillaries of the porous cover layer 1, the dye present in ink and toner diffuses into the underlying receiving layer 2. As a result, the liquid absorbing capacity of the entire recording medium can be increased, which can porous cover layer 1 here in comparison with the first Execution should be dimensioned significantly thinner. Because the porous cover layer 1 of the second embodiment, which is opaque per se, can now be made thinner with the same absorption capacity of the recording medium, it is also possible to remove this porous layer 1 from an opaque one with a small amount of energy (heat, pressure) in accordance with known procedures Convert state to a transparent state.

It is also possible to encapsulate the respective recording material in the porous layer 1 by means of known methods and thus to protect it permanently.

In both versions, the flat underlayer 3 can in principle be made of any material.

Paper or opaque films or foils made of polyester, polycarbonate, polypropylene, triacetate, polyvinyl chloride, etc. can be used as the opaque material.

If the opaque, porous cover layer 1 is used to increase the color brilliance and color depth of the recording, e.g. of an image, if it is viewed through the underlayer 3, is changed from the opaque state to a transparent state, a transparent underlayer 3 is obviously to be selected. Depending on a particular application, films or foils made of polyester, polycarbonate, triacetate (triacetyl cellulose), polypropylene, polyvinyl chloride, cellophane, polyamide, polysulfone, polyphenylene sulfide, polyimide, etc. can be used for this purpose.

Some exemplary embodiments of the recording medium are now described below, in particular the production thereof.

Example 1 :

Record carrier with a base and a porous layer applied directly thereon, suitable for xerographic recordings:
10 g of a thermoplastic polyamide resin with a softening point of 105-110 ° C. were dissolved in 90 g of ethanol and 45 g of n-hexane with stirring at room temperature in a 3-necked flask of 250 ml content. After the dissolution process was complete, 100 ml of pure ethyl acetate were added dropwise to the solution with vigorous stirring within 10 minutes. This resulted in an almost quantitative precipitation of the polymer used and a suspension of microscopic polymer particles resulted.

This polymer suspension was applied by means of a doctor blade to an untreated polyester film as a flat base layer 3, so that after evaporation of the solvents at 100 ° C., a microporous, opaque layer with a thickness of 10 microns was formed.

This record carrier was printed using a xerographic process.

The image quality and toner adhesion were excellent. In particular, there were no problems with the greasy surface layer, which are usually caused by the silicone oil abhesives used in the corresponding copying machines. The reason for this positive result is that the silicone oil was drawn directly into the capillaries of the porous layer.

In the sense of an additional variant, the printed and opaque layer 1 was subjected to a heat treatment by being exposed to a temperature of 150 ° C. for 10 minutes, so that the porous layer 1 was made transparent. This made the entire printed sheet (with the polyester film base) transparent. In addition, this heat treatment irreversibly fixed the toner particles by melting them into the layer.

Example 2 :

Recording medium with a base layer 3 and a porous layer 1 applied directly thereon by means of a phase inversion process, suitable for xerographic recordings:
10 g of a thermoplastic copolymer resin with a T _g of 55 ° C. were dissolved in 57 g of a 1: 1 mixture of ethyl alcohol / water with vigorous stirring.

After the dissolution process had been completed, an untreated polyester film was coated with the lacquer described above by means of a doctor knife, so that a dry layer thickness of 1.2 microns resulted.

This record carrier was also printed using a xerographic process. The properties of the image were the same as those described in connection with Example 1.

Again, the printed, opaque recording medium was made transparent by means of a heat treatment, here 6 minutes at 170 ° C. without loss of quality.

The same example was repeated, but instead of the untreated polyester film, a commercially available paper sheet was used as the base layer 3. The result was also excellent. Obviously, conversion to a transparent state was not carried out here.

Example 3 :

Recording medium, in which a receiving layer 2 for a coloring material is arranged between the flat underlayer 3 and the porous layer 1, suitable for inkjet printing processes:
The polymer solution described in Example 2 was again chosen as the porous layer 1 to be applied. Instead of the untreated polyester film According to Example 2, a transparent, coated film material suitable for printing by means of inkjet printing was used. This consists of a flat underlayer 3 and a receiving layer 2 applied thereon. Such foil material is sold, for example, by the company Folex under the name BG 31.

This inkjet printer film material was coated with the polymer solution described in Example 2 in the same process, the porous layer 1 being an opaque layer with a dry layer thickness of 3.5 microns.

This record carrier, consisting of a flat underlayer 3 and two layers 1, 2 arranged thereon, was printed with a commercially available inkjet printer. The applied ink dried immediately because, due to the capillary absorbency of the upper, porous layer 1, it was immediately absorbed and diffused into the underlying receiving layer 2, so that, in contrast to currently known recording media, even if the surface was coated immediately after printing Fingers or rags did not smear the ink.

The examination of the resulting print showed that it corresponded to the maximum achievable resolution of the ink jet printing device used. The print image, viewed through the transparent base layer, was of exceptional brilliance. (It should be noted that the porous layer applied formed the white background.)

The printed recording medium was then subjected to a heat treatment again (15 minutes at 170 ° C.). The result was a completely transparent film with an unchanged image quality, which can be projected onto e.g. allowed a canvas with an excellent image reproduction.

Claims (4)

Flat recording medium for receiving coloring substances for recording images and information, with a flat carrier layer and a porous layer arranged on at least one side thereof with an exposed surface and an opposite surface facing the carrier layer, characterized in that the porous layer is a is microporous layer, which consists of a filler-free thermoplastic, which has at least approximately perpendicular to the exposed surface of the microporous layer directed capillaries or pores. Record carrier according to claim 1, characterized in that the plastic is a thermoplastic polymer. Record carrier according to claim 1, characterized in that between the flat carrier layer and the respective microporous layer, a recording layer of a material absorbing a respective coloring substance is arranged. A method for producing a transparent, flat product with recorded images and / or information from a printed, flat recording medium according to claim 1, the microporous layer of which is opaque or cloudy, characterized in that the plastic particles of the microporous layer by the action of heat and / or solvents and / or pressure is melted and / or dissolved, or the capillaries are filled with a binder in order to remove the phase boundaries between the plastic particles, so that a dense, non-porous plastic structure is formed, the respective coloring substances being permanently embedded and fixed in the layer.

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