EP1622775B1 - Method for improving printability on paper or paper products with the aid of ink-jet printing method - Google Patents

Abstract

A process for improving the printability of paper and paper products by enhancing the water resistance of ink-jet printed images, wherein the process comprises treating the paper or paper products with aqueous solutions of cationic polymers comprising vinylamine units and having a charge density of at least 3 meq/g as the sole treatment composition in aqueous solution, wherein the sole treatment composition is applied in an amount from 0.05 to 5 g/m2 to the surface of the paper or the surface of the paper product.

Description

The invention relates to a process for improving the printability of paper and paper products in printing by means of the inkjet printing process by treating the paper or paper products with aqueous solutions of cationic polymers.

The printing of paper, paper-like materials or textiles with so-called "digital printing processes" is becoming increasingly important in the printing industry. These digital printing processes also include the ink-jet printing process, which is also called ink-jet process.

In classical printing processes, a printing plate applied with ink is pressed onto the paper. The printing inks are in most cases not dissolved in water but in an organic solvent such as toluene. In contrast, in the ink-jet method, drops of a color usually dissolved in water are ejected from the nozzle onto the recording material according to the contours on the artwork. Therefore, the demands of the user and of the ink-jet printing technique on the recording material, eg paper, are of a completely different kind than in the classical printing methods. But as with all other printing methods, the requirements for the printed image and thus for the paper used vary greatly in quality, depending on the purpose for which the image is intended. For images that should have the quality of a photograph, a correspondingly high-quality paper must be used. For the simplest messages and designs on paper that are not kept, papers of a quality that allow reading or recognizing the message or image are sufficient. Between these two extremes there is a wide range of papers that must meet the requirements for inkjet printing. High quality papers suitable for this printing process are e.g. B. provided with a coating of a water-absorbent pigment, a hydrophilic binder and a cationic polymer (see. G. Morea-Swift, H. Jones, THE USE OF SYNTHETIC SILICAS IN COATED MEDIA FOR INK-JET PRINTING, 2000 TAPPI Coating Conference and Trade Fair Proceedings, 317-328 ). For very undemanding inkjet prints, plain papers are often used with a simple starch application.

In contrast to most other printing processes, the inkjet printing process has the principal drawback that the prints are water soluble or the water dispersibility of the inks used are water sensitive. This results in the contact of the printed image with water to a bleeding of the colors into each other and into the paper, both in the paper plane and perpendicular to the paper plane. In the worst case, a font is no longer readable, a picture blurred and the colors hit on the back of the paper. Of course, the waterfastness of the term is not of great importance to all users, but even users whose pictures do not normally come into contact with water are in great jeopardy when drops of water accidentally get on the picture and blur it, and if the spilled color is the cause Tablecloth soiled or the image shows the prints of damp fingers. For papers that have been printed using the inkjet printing process and that are exposed to rain, such as poster papers or packaging papers, or that may become moist due to condensation or filling liquids, such as bottle labels, waterfastness of the inkjet printout is essential. If z. B. the bar code on a package or on a label due to moisture is no longer sharp and is not read or wrong, the economic damage can be very high. High-quality expensive papers for inkjet printing, as z. B. for the segment photography, art print, etc., provide waterproof printed images. They are prepared by coating the base paper with a paint consisting of a water-absorbent pigment, preferably silica, a water-soluble binder, preferably polyvinyl alcohol, optionally further water-soluble binders, and cationic organic polymers (cf. G. Morea-Swift, H. Jones, THE USE OF SYNTHETIC SILICAS IN COATED MEDIA FOR INK-JET PRINTING ).

From the WO-A-03/021041 It is known that one can increase the whiteness of recording materials when applied to mixtures containing an optical brightener, a cationic polymer and a solvent. The recording materials thus obtainable can be printed by the ink-jet method. They deliver a much better color rendition and sharpness than conventional papers.

For the large amount of simpler papers, z. As office papers, such special coatings are too expensive, too expensive and often not suitable for conventional processing of papers such. For example, for printing by the offset method, for copying, for easy writing with ink or for drawing with pencil and erasing the drawing. The printing of daily newspapers from the Internet on an inkjet printer is becoming more and more fashionable. For the reasons mentioned above, one needs a simple paper that provides a waterproof inkjet printout.

The invention is therefore based on the object to improve the printability of paper and paper products that do not give sufficiently waterproof inkjet print images.

The object is achieved by a method for improving the printability of paper and paper products in printing by means of the ink jet printing process by treating the paper or paper products with aqueous solutions of cationic polymers, characterized in that as cationic polymers vinylamine units containing polymers having a charge density of at least 3 meq / g as the sole treating agent in aqueous solution and applying it in an amount of 0.05 to 5 g / m ² to the surface of the paper or paper products.

It was surprising that simply by treating a paper with solutions of suitable organic polycations without further additives, it is possible to waterproof the printed image obtained with an inkjet printer.

Particular preference is given to polymers containing cationic vinylamine units which are hydrolyzed homopolymers or copolymers of N-vinylformamide having a degree of hydrolysis of 20 to 100%.

The polyelectrolytes mentioned can be used according to the invention either individually or in any combination with one another. Optionally, they may also be mixed with nonionic water-soluble polymers.

The waterfastness of the printed images of the inkjet prints depends on various factors, for example the inks used and the paper treated with the polycations, as well as the density of the positive charges on the polycations and on the molecular weight of the polycations. With charge densities of at least 3 milliequivalents per gram (hereinafter always referred to as "mVal / g") polycation (without considering the anions) one can already observe a good water resistance. However, the water resistance increases with the charge density, so that charge densities of over 3.5 to 23 meq / g of polycation are preferred. Very particular preference is given to charge densities of from 8 to about 20 meq / g of polycation. The molecular weight of the polycations also has an influence on the water resistance. It is for example at least 10 000 daltons, wherein the polymers should preferably be selected so that the charge density is low at low molecular weights. Preference is given to molar masses of the polycations of more than 50,000 daltons, more preferably of more than 100,000 daltons.

The molecular weights of the cationic polyelectrolytes which can be used according to the invention can be, for example, up to 5 million daltons, preferably up to 2 million daltons. The viscosities of the aqueous solutions of the polyelectrolytes are adjusted so that a sufficient amount of polymer can penetrate into the paper. The viscosities of the aqueous solutions of the cationic polymers should not be higher than 3,000 mPas, preferably not higher than 2,000 mPas. They are usually in the range of 10 to 1,000 mPas, each measured at 20 ° C.

The treatment according to the invention with the solutions of the cationic polyelectrolytes can be carried out according to the methods customary for the surface treatment of paper in the paper industry. You can use known order aggregates, z. B..Filmpressen, size presses, different coating units with squeegees, scrapers (English blades) or air brushes, or spraying, as they eg for the application of starch in the EP-A-0 373 276 or for the application of coating compounds from V. Nissinen, Wochenblatt für Papierfabrikation, 2001, 11/12, pages 794-806 , to be discribed. However, the application of the aqueous solutions of the cationic polyelectrolytes can also take place in the calendering of paper via the moistening devices. It is important that the cationic polyelectrolyte at least partially penetrates into the paper and does not stick to the surface of the paper alone.

The amount of cationic polyelectrolyte which is applied to the paper according to the invention can vary within wide limits. In general, it is 0.05 g to 5 g, based on m ^{2 of} paper, and is preferably in the range of 0.1 g to 3 g and more preferably 0.5 g to 2 g per m ^{2 of} paper, based on the solvent-free cationic polyelectrolyte.

The invention also provides the use of aqueous solutions containing cationic vinylamine units containing polymers having a charge density of at least 3 meq / g as the sole treating agent for application to the surface of paper or paper products in an amount of 0.05 to 5 g cationic Polymer / m ² for improving the ink-jet printability of paper and paper products.

According to the invention, the printability of all recording materials such as graphic papers, natural paper or coated paper or of paper products such as cardboard and paperboard can be improved by applying aqueous solutions of the cationic polyelectrolytes to the surface of the papers or paper products. The application of the aqueous solutions of the cationic polymers can be carried out once or several times, for example once to three times, preferably once to twice. In most cases, a single order is enough. The job can only be done on one side or on both sides (front and back) of the paper. The aqueous solutions of the cationic polymers can also be applied simultaneously to the top and bottom of the paper.

In the case of a multiple application of the aqueous solution of the cationic polymers, this can be carried out, for example, on the top side of the paper or of the paper products, or also, for example in the case of coated paper, on the back side, for example once on the base paper, once before and once after End stroke, or once after the pre-coat, once after the middle stroke and once after the end stroke or once before and once after the end stroke.

The solution of the polyelectrolyte is preferably applied to a natural paper or to a coated paper after the end coating, particularly preferably once to twice and most preferably once. The aqueous solution of the cationic polymers can be applied to the paper or paper products, for example, by means of a size press, a film press, a spraying device, a coater or a paper calender.

After applying the aqueous polyelectrolyte solutions to the paper or paper products, the products are preferably dried to remove the water and optionally satinized. Drying of the treated papers is e.g. by drying cylinders, infrared radiators, hot air, etc .. The calendering (calendering) of the treated papers is usually carried out at a temperature between 15 and 100 ° C.

The papers, boards or cardboard treated according to the invention can be printed with the various variants of the inkjet printing process with the aid of the respective printing devices. However, they can also be used in conventional methods, e.g. Offset, gravure or gravure printing, flexographic printing or other digital printing processes, e.g. Laser printing process - or indigo printing process print. Even with these printing processes, waterproof printed images are obtained.

The method according to the invention makes it easier for a person skilled in the art to produce papers with very simple means and high flexibility, which produce waterproof printed images when printed by various inkjet methods and can also be printed using classical printing methods and other digital printing methods and optionally have further advantageous properties.

The percentages in the following examples are by weight. The charge density of the cationic polymers was determined by colloid titration, cf. D. Horn, Progr. Colloid & Polymer Sci., Vol. 65, 251-264 (1978) ,

The water sensitivity of printed images obtained with an ink jet printing process was particularly evident in multicolor prints. For the evaluation of black-and-white inkjet print images, there are quantitative measurement methods that evaluate so-called wicking, i. leakage of ink into the unprinted paper. The same method of measurement is sometimes used to assess bleeding. This is the process of passing two colors into each other. For multicolor print images, black leakage into a yellow printed area is measured.

In working out the method according to the invention, however, it has been shown that in many, but not all, inkjet printers the color black is relatively waterproof and even in a yellow printed area expires relatively little, while the colors blue, magenta and yellow so much leak into adjacent unprinted or differently colored areas that a quantitative measuring method is overwhelmed. Therefore, in the following examples, the water resistance was qualitatively judged by the gradients of the colors blue, magenta and yellow in unprinted area and in one another with subjective scores 1 for "very good waterproof" to 5 for "very little waterproof". For coated papers, the color grading was evaluated in the same way, with the decrease of the color intensity and the decrease of the acutance as "quality of the printed image" with the grades 1 for "very good waterproof" to 5 for "very little waterproof".

Similarly, the staining was evaluated on an underlayed filter paper with the grades 1 for "no staining" to 5 for "strong staining". In some cases, the penetration of the colors after the water treatment was also evaluated on the back of the paper with the ink jet 1 to 3 marks.

Used cationic organic polyelectrolytes:

Polyelectrolyte I: commercial polydiallyldimethylammonium (Catiofast® ^® CS from BASF Aktiengesellschaft). The charge density of the polycation measured at pH 4.5 was 7.9 meq / g.

Polyelectrolyte II: polyamidoamine of adipic acid and diethylenetriamine, which was grafted with ethyleneimine and crosslinked with polyethylene glycol dichlorohydrin ether with 34 ethylene oxide units, cf. Example 3 of DE-PS-2434816 , The charge density of the polycation measured at pH 4.5 was 10.2 meq / g.

Polyelectrolyte III: commercial Polyamidoaminepichlorhydrinharz (Luresin ^® KNU from BASF Aktiengesellschaft). The charge density of the polycation measured at pH 4.5 was 3.5 meq / g.

Polyelectrolyte IV (comparative): Polyvinylformamide with a molecular weight of about 300,000 daltons, were split off from the 10% of the formyl groups to form amino groups. The charge density of the polycation measured at pH 4.5 was 1.5 meq / g.

Polyelectrolyte V: polyvinylformamide with a molecular weight of about 300,000 daltons, from which 30% of the formyl groups are split off with the formation of amino groups. The charge density of the polycation measured at pH 4.5 was 4.8 meq / g.

Polyelectrolyte VI: Polyvinylformamide with a molecular weight of about 300,000 daltons, from which 50% of the formyl groups were split off. The charge density of the polycation measured at pH 4.5 was 8.8 meq / g.

Polyelectrolyte VII: Polyvinylformamide having a molecular weight of about 300,000 daltons, in which 75% of the formyl groups were cleaved to form amino groups. The charge density of the polycation measured at pH 4.5 was 14.4 meq / g.

Polyelectrolyte VIII: Polyvinylformamide having a molecular weight of about 300,000 daltons, were split off from the 90% of the formyl groups to form amino groups. The charge density of the polycation measured at pH 4.5 was 19.7 meq / g.

Polyelectrolyte IX: Polyvinylformamide with a molecular weight of about 30,000 Dalton, were split off from the 90% of the formyl groups to form amino groups. The charge density of the polycation measured at pH 4.5 was 20.4 meq / g.

Polyelectrolyte X: High molecular weight polyethylenimine, crosslinked with a Polyethylenglykoldichlorhydrinether and neutralized with formic acid (Catiofast SF ^® from BASF Aktiengesellschaft). The charge density of the polycation measured at pH 4.5 was 19.0 meq / g.

Polyelectrolyte XI: polyvinylformamide with a molecular weight of about 45,000 daltons, from which 23% of the formyl groups were cleaved to form amino groups. The charge density of the polycation measured at pH 4.5 was 3.6 meq / g.

Polyelectrolyte XII: High molecular weight polyethylenimine, neutralized with formic acid (Catiofast ^® PL BASF Aktiengesellschaft). The charge density of the polycation measured at pH 4.5 was 19.8 meq / g.

Examples 1

In a laboratory size press, sheets of a large-scale paper used as a base for a coated paper were treated at a basis weight of 68 g / m ² with aqueous solutions of various polyelectrolytes. The concentrations of polyelectrolyte in the size press liquors and the amount of solvent-free polyelectrolyte applied to the paper are shown in Table 1.

The papers were printed after drying with the inkjet printers also shown in Table 1 with a printed image, the black, white and colored Font and surfaces contained. From the printed papers smaller strips were cut out in the same places, which in turn contained black, white and colored writing and areas. These strips, two different per image, were held in a jar of tap water for 30 seconds, with slight agitation for 10 seconds. Then they were placed on a blotting paper of white untreated pulp and allowed to dry. The bleeding of the colors and the blotting on the blotter paper were evaluated with the grades 1 to 5 as described above. The results are listed in Table 1. Table 1 polyelectrolyte * I * II * III IV (comparison) V VI VII VIII IX Concentration of polyelectrolyte in the % - 10.0 9.1 10.0 6.3 6.3 5.3 5.8 5.0 10.0 size press liquor Viscosity of the size press liquor mPas - 30 94 60 80 84 88 82 70 14 Application to polyelectrolyte (solid) on the paper g / m ² 0 2.3 2.0 2.2 1.6 1.6 1.4 1.5 1.2 1.5 Assessment of the water resistance of the print Printer: Epson Stylus Color 980 1st strip color bleed grade 5 3 2 3 4 1 1 2 3 3 Dyeing on filter paper grade 5 5 4 3 4 1 1 2 3 3 2nd strip color bleed grade 5 4 1 3 2 1 1 3 3 2 Dyeing on filter paper grade 5 5 3 2 4 2 1 2 2 3 Printer: Hewlett Packard 895 Cxi 1st strip color bleed grade 5 2 1 2 3 1 1 1 1 1 Dyeing on filter paper grade 5 5 2 1 4 1 1 1 3 2nd strip color bleed grade 5 2 1 2 4 1 1 1 1 1 Dyeing on filter paper grade 5 4 1 1 3 1 1 1 1 2 * Reference example

Reference Example 2

On a paper, which was provided with 10 g / m ^{2 of} a prior art coating consisting of 100 parts of calcium carbonate, 6 parts of starch, 16 parts of a 50% polymer dispersion (Styronal ^® D 610 BASF Aktiengesellschaft) and smaller 10% aqueous solutions of cationic polyelectrolytes were applied by hand bar so that after drying 1.0 g / m ² of Polyelektolyten remained on the paper. The paper was dried and calendered according to the state of the art. Thereafter, the papers were printed with the ink jet printer shown in Table 2 with a printed image containing black, white and colored writing and areas. From the printed papers smaller strips were cut out in the same places, which in turn contained black, white and colored writing and areas. These strips were held in a jar of tap water for 30 seconds, with slight agitation for 10 seconds. Then they were placed on a blotting paper of white untreated pulp and allowed to dry. The quality of the printed image and the penetration of the colors on the back of the paper after the water treatment were evaluated as described above with the grades 1 to 5 and 1 to 3, respectively. The results are listed in Table 2. Table 2 polyelectrolyte I X Concentration of polyelectrolyte in the solution % - 10.0 10.0 Viscosity of the solution mPas - 35 105 Application to polyelectrolyte (solid) on the paper g / m ² 0 1 1 Assessment of the water resistance of the print Printer: Hewlett Packard 895 Cxi Quality of the printed image grade 5 3 1 Breakthrough on back grade 3 2 1

Example 3

On a paper, which was provided with 10 g / m ^{2 of} a prior art coating consisting of 100 parts of calcium carbonate, 6 parts of starch, 16 parts of a 50% polymer dispersion (Styronal ^® D 610 BASF Aktiengesellschaft) and smaller Quantities of auxiliaries were, as shown in Table 3, each 10 percent aqueous solutions of cationic polyelectrolytes applied with the hand blade so that after drying 1.0 g / m ^{2 of} the polyelectrolyte remained on the paper. The paper was dried and calendered according to the state of the art. Thereafter, the papers were printed with the ink jet printer shown in Table 3 with a printed image containing black, white and colored writing and areas. From the printed papers smaller strips were cut out in the same places, which in turn contained black, white and colored writing and areas. These strips were held in tap water for 30 seconds, lightly agitated for 10 seconds. Then they were placed on a blotting paper of white untreated pulp and allowed to dry. The quality of the printed image and the penetration of the colors on the back of the paper after the water treatment were evaluated as described above with the grades 1 to 5 and 1 to 3, respectively. The results are listed in Table 3. Table 3 polyelectrolyte * I * II V XI * XII Concentration of polyelectrolyte in the solution % - 10.0 10.0 10.0 10.0 10.0 Viscosity of the solution mPas - 28 55 1000 23 20 Application to polyelectrolyte (solid) on the paper g / m ² 0 1.0 1.0 1.0 1.0 1.0 Assessment of the water resistance of the print Printer: Hewlett Packard 2000 C Quality of the printed image grade 5 3 1 2 2 1 Breakthrough on back grade 3 2 1 2 2 2 * Reference example

Example 4

On a large scale manufactured paper with a grammage of 68 g / m ² , which was used as a basis for a coated paper, was applied 10 percent aqueous solutions of the cationic polyelectrolytes indicated in Table 4 with the squeegee so that after drying 2, 0 g / m ^{2 of} the polyelectrolyte remained on the paper. The paper was dried and calendered according to the state of the art.

Thereafter, the papers were printed with the ink jet printer shown in Table 4 with a printed image containing black, white and colored writing and areas. From the printed papers smaller strips were cut out in the same places, which in turn contained black, white and colored writing and areas. These strips were held in a jar of tap water for 30 seconds, with slight agitation for 10 seconds. Then they were placed on a blotting paper of white untreated pulp and allowed to dry. The bleeding of the colors and the penetration of the colors on the backside of the paper after the water treatment was evaluated as described above with the notes 1 to 5 and 1 to 3, respectively. The results are listed in Table 4. Table 4 polyelectrolyte * I * II IV (comparison) V XI Concentration of polyelectrolyte in the solution % - 10.0 10.0 10.0 10.0 10.0 Viscosity of the solution mPas - 28 55 1710 1000 23 Application to polyelectrolyte (solid) on the paper g / m ² 0 2 2 2 2 2 Assessment of the water resistance of the print Printer: Hewlett Packard 2000 C color bleed grade 5 2 1 5 4 2 Breakthrough on back grade 3 2 1 3 1 2 * Reference example

Claims (8)

1. A process for improving the printability of paper and paper products when printing with the aid of the ink-jet printing method by treating the paper or the paper products with aqueous solutions of cationic polymers, wherein cationic polymers comprising vinylamine units and having a charge density of at least 3 milliequivalents/g are used as the sole treatment composition in aqueous solution and said composition is applied in an amount of from 0.05 to 5 g/m² to the surface of the paper or of the paper product.
2. The process according to claim 1, wherein the charge density of the polycation in the polymer comprising vinylamine units is from 3.5 to 23 milliequivalents/g.
3. The process according to claim 1, wherein the charge density of the polycation in the polymer comprising vinylamine units is from 8 to 20 milliequivalents/g.
4. The process according to any of claims 1 to 3, wherein the polycation of the polymer comprising vinylamine units has a molar mass M_w of at least 10 000.
5. The process according to any of claims 1 to 4, wherein the polymers comprising vinylamine units used are hydrolyzed homo- or copolymers of N-vinylformamide having a degree of hydrolysis of from 20 to 100%.
6. The process according to any of claims 1 to 5, wherein the aqueous solution of the polymers comprising vinylamine units is applied to the paper with the aid of a size press, a film press, a spraying means, a coating unit or a paper calender.
7. A paper which is obtainable by the process according to claims 1 to 6.
8. The use of an aqueous solution which comprises, as cationic polymers, polymers comprising vinylamine units and having a charge density of at least 3 milliequivalents/g as the sole treatment composition, for application to the surface of paper or paper products in an amount of from 0.05 to 5 g of cationic polymer per m² for improving the ink-jet printability of paper and paper products.