EP1333989A1

EP1333989A1 - Ink jet printing material

Info

Publication number: EP1333989A1
Application number: EP01982037A
Authority: EP
Inventors: Gunter Wendler; Susanne Oste; Beat Unger
Original assignee: SIHL
Current assignee: SIHL
Priority date: 2000-11-17
Filing date: 2001-11-19
Publication date: 2003-08-13
Also published as: WO2002040288A1; AU2002213734A1

Abstract

The invention relates to ink jet printing material (1) comprising base paper (2) and an ink-receiving layer (3). The ability to receive dye inks and pigment inks in an abrasion-resistant, sharp-contoured precise manner is increased by the fact that the ink-receiving layer (3) applied in the form of an aqueous solution contains pigments, binding agents, ink fixing agents and at least one inorganic salt with a bivalent cation and an anion exhibiting a substantially pH-neutral behavior.

Description

An ink-jet recording material

TECHNICAL AREA

The invention relates to a recording medium as it is used in the inkjet field (inkjet technology). The invention also relates to a method for producing such an inkjet recording material.

STATE OF THE ART

The ink jet recording process is one of the electronic printing processes and has already been described in many places. It is used in a wide range of applications for the production of color graphics, color images and also text prints. High demands are placed on the recording materials used in this technology. These include, for example, high color density, high resolution, short ink drying times, light stability and dimensional stability. The color should produce color dots on the carrier, which are localized as precisely as possible and only run to the same extent in the transverse plane (x, y plane, paper plane) as is desired, ie to the extent that the between the dots is perfect Localization of the remaining paper-white surface sections should be covered by the run as far as possible. On the one hand, the dye must be absorbed by the carrier as quickly as possible and fixed on or in it, so that on the one hand the print head does not smear the fresh ink the next time it passes over the area to be printed, and on the other hand the ink on the finished one Pressure cannot be blurred when touched. Ren on the walls ^¬ side are necessary to ensure that the dye does not too much into seeps into the carrier, since otherwise, due to the then above the color remaining layers matt the color appearance and to some extent acts blunt. In principle, they can and should Solvents in which the dyes are dissolved are quickly transported downwards from the paper surface so that the color remains dry on the surface; on the other hand, it must be prevented that to some extent paper chromatographic effects occur and the paper warps (so-called Curl effect, ie rolling up the entire paper sheet, and Cockle effect, ie the formation of smaller waves in the sheet). Another important requirement for commercial applications is surface gloss. This is particularly important in the production of art graphics. But gloss is also an important requirement when creating images that require a photo-like impression.

Various fonts, such as EP 0 650 850 A, EP 0 967 087 A describe ink jet recording materials, which are usually based on the principle that a sealing layer is arranged between a base paper and an ink receiving layer, which prevents the solvent of the ink from seeping too much through to the base paper and thus faults occur.

In the context of today's ink-jet techniques, a distinction must be made between so-called dye inks and pigment inks. The dye inks, which make up the major part of the inks used today in the ink jet sector, are essentially a solution of mostly organic dyes such as azo dyes, possibly supplemented by other components. On the other hand, pigment inks are a suspension of pigment dyes, i.e. of organic or inorganic essentially insoluble solids. For example, the naturally occurring pigments such as chalk, ocher, umber, green earth, terra de sienna and graphite. Pigment dyes often have a lower luminosity than the soluble dyes of dye inks, but they are far superior to the soluble dyes, especially in terms of long-term stability, even when exposed to strong UV / VIS. This makes the pigment inks that are still rarely used in the ink-jet area extremely attractive, especially for outdoors and for high-quality graphics.

Record carriers for the use of dye inks are widely known. EP 1 036 666 e.g. describes such a carrier for dye inks. WO 96/39304 describes e.g. on the other hand an inkjet recording medium, which is suitable for the absorption of pigment dyes.

The problem with the recording media known from the prior art is that they are each suitable either for the absorption of dye inks or for the absorption of pigment inks. The use of carriers provided for the dye area for Printing with pigment inks usually leads to unsatisfactory results with regard to the above-mentioned requirements for ink-jet prints such as resolution, abrasion resistance, etc. The same applies if substrates intended for printing with pigment inks are printed with dye inks.

PRESENTATION OF THE INVENTION

It is therefore an object of the present invention to provide a recording material and a method for producing such a recording material for the inkjet area, which can be printed with both dye inks and pigment inks. The carrier, which is alternatively printed with dye or pigment ink, is intended to meet the current high demands in terms of abrasion resistance, sharpness of contours, resolution, point accuracy, etc. A carrier with such properties reduces the manufacturing costs and the storage costs on the part of the paper manufacturer, also the storage costs on the consumer side and in many cases the purchasing costs, and is therefore desirable for all those involved.

The invention achieves the stated object in that the ink-receiving layer applied as an aqueous solution contains pigments, binders, ink fixers, and at least one inorganic salt with a divalent cation and an anion, both of which show essentially pH-neutral behavior. The essence of the invention is therefore to enable both precise fixing of pigment and dye inks by means of an adapted formulation of the ink-receiving layer. The effect of classic ink fixers known from the dye technique is combined with the effect of inorganic divalent salts. The ink fixers, which mostly and essentially consist of cationic polymers which are able to bind the anionic soluble dyes, are not in a position to fix the colored bodies of the pigmented ink sufficiently. The divalent cations added, on the other hand, can obviously take on the function of binding the pigments. Care must be taken to ensure that the added inorganic salt is not capable of significantly influencing the pH value, since otherwise the color properties of the soluble dyes in dye inks may change. It can be seen that the presence of both ink fixer and inorganic salt with a divalent cation and an anion, both of which show essentially pH-neutral behavior, leads to a synergistically improved overall impression of the printed image in both areas, dye and pigment ink , In a first preferred embodiment of the invention, the ink-receiving layer additionally contains brighteners and / or wetting agents and / or plasticizers and / or color components. These additional components allow the ink-receiving layer to be adjusted, inter alia, to the requirements with regard to the color appearance of the unprinted paper, and with regard to the properties of the base support and the desired haptic quality of the finished support.

Advantageously, leveling agents are also added, which increase the runnability of the application during the coating process. Air pockets, which lead to bubbles and subsequently poor ink absorption, can become problematic. The leveling agent serves to reduce the surface tension during application.

A second embodiment is characterized in that the inorganic salt is a salt with a cation selected from the second main group (IIA), particularly preferably Mg ²⁺ or Ca ²⁺ , and an anion selected from the group CI ^" , SO ₄ ^{2 "} , NO ₃ ^" , or a mixture of such salts. It is precisely these salts, and in particular MgSO ₄ , that pH-neutral introduction of the necessary divalent cations, ie fixation of the pigment dyes without spectral shifts of the soluble dye dyes. The inorganic salt is preferably present in a concentration in the range from 0.5 to 10%, preferably in the range from 2 to 5% and particularly preferably in the range of 3%, based on the dry weight of the ink-receptive layer "Bleeding", ie the colors are increasingly distributed in the transverse paper plane, above which the drying time of the applied ink increases pleasant to. Furthermore, the pigments are preferably selected from the group SiO ₂ , CaCO ₃ , MgO, TiO ₂ , alumina, kaolin, bentonite or a mixture thereof, the pigment having an average grain size in the range from 5 to 20 μm, in particular from 8 to 15 μm having. The ink fixer is preferably polymer-bound quaternary amines, in particular polyacrylic-bound quaternary amines or polymer-bound cyclic quaternary amines with a neutral pKa value. Furthermore, the binder is preferably selected from the group consisting of polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, gelatin, starch and their derivatives, polyvinyl acetate, polyethylene glycol, alginates, polyacrylic acid, or a mixture thereof. The optional optical brightener can be anionic stilbene derivatives, the wetting agent can be non-ionic type wetting agent, and the plasticizer can be low molecular weight glycols. A further embodiment is characterized in that the base paper has a basis weight in the range from 50 to 200 g / m ^2, in particular from 100 to 150 g / m ² , and the ink receiving layer has a basis weight in the range from 8 to 15 g / m ² . particularly preferably from 8 to 10 g / m ² . The base paper can optionally also be a plastic film or a paper carrier having a sealing layer arranged in the direction of the ink-receiving layer, the basis weight of the ink-receiving layer in this case preferably being in the range from 14 to 20 g / m ² . Another embodiment of the invention is characterized in that the base paper is a paper with a low fiber content in relation to the filler content, in particular a paper in which the filler content is in the range from 15 to 25%, particularly preferably in the range around 20% , the total dry weight of the base paper. Furthermore, the filler is preferably a precipitated calcium carbonate with an average particle size of 0.2 μm. With such a base paper, an optimal, to some extent, synergetic behavior between the base paper and the base layer can be obtained, especially in the case of the above-mentioned layer thicknesses of the ink-receiving layer, because in this case the base paper can suck off dye solvent in just the right amount, so that rapid drying with a low curl and cockle behavior can be achieved. Further embodiments result from the dependent claims. Furthermore, the invention relates to a method for producing an ink jet recording material according to the above type, characterized in that the ink receiving layer on-line on the papermaking machine onto a paper web with a roughness in the range from 2.5 to 3.5 μm, particularly preferably from 3 μm (Ra Values, measured with a pertometer), is applied, an aqueous solution of the components of the ink-receiving layer (3) having a solids content of 15 to 17.5%, in particular in the range of 16.5%, being applied to the fresh paper carrier (2). It can be seen that the behavior with regard to drying and folding properties is unsatisfactory below these solid components, above that increasing bronzing effects are observed in areas printed in black. Here too, in particular when applying on-line, ie immediately after the paper has been produced on the same machine, it is very important that the ink-receiving layer solution is as pH-neutral as possible, since otherwise major corrosion problems have to be dealt with. For example, if an acidic pH is generated when using chloride-containing aluminum hydroxides. Particularly high quality recording layers are obtained if the pigment component continues to be mixed together is dispersed with the other constituents of the ink receiving layer to be applied using a dissolver or ground in a mill in such a way that pigment agglomerates are separated. For optimum control of the viscosity of the solution to be applied, it can be applied at a temperature in the range from 25 to 40 ° C., particularly preferably from 30 °.

Preferably, the on-line application is carried out on a paper web which has been "over-dried" to a certain extent in the machine, i.e. has a water content of less than 5%, preferably from 2 to 3%. The drying process can partly be taken from paper, i.e. the over-dried paper absorbs part of the water from the barrier line.

In a particularly preferred embodiment of the method, the solution is applied in degassed form, particularly preferably by vacuum degassing the solution before application. The ink-receiving layer solution located in the bath in which the application roller is immersed should preferably also be exchanged continuously for vacuum-degassed solution. In the entire manufacturing process of the solution, it is also advisable to keep the formation of bubbles as low as possible by stirring thoroughly. Especially when applying on-line, existing bubbles partially reduce the homogeneity of the applied layer.

BRIEF EXPLANATION OF THE FIGURES

The invention will be explained in more detail below using exemplary embodiments in conjunction with the drawings. Show it:

Fig. 1a) a section through a two-layer ink jet recording medium; and Fig. 1b) a section through a multi-layer ink jet recording medium.

WAYS OF CARRYING OUT THE INVENTION

Fig. 1a shows a section through an embodiment of a coated ink jet recording medium, consisting of a base paper 2 and an ink receiving layer 3 applied thereon. The base paper has a basis weight of 100 to 200 g / m ² , for many photorealistic papers there are typically basis weights of 150 g / m ² application. As already mentioned above, it is advantageous to use a paper with a high filler content as base paper so that, together with the effect of the ink, tenaufnahmeschicht 3, optimal behavior is achieved, ie curl and cockle effects are avoided with good color properties.

First embodiment:

To produce the base paper 2, 124 kg of Wisabetula ECF, 242 kg of Ceasa Green (ECF) eucalyptus and 200 kg of beechwood with 5 kg of Catsol 9566 and 200 kg of Socal NZ (Catsol and Socal are slowly sprinkled in water before adding the fiber components) mixed in water in such a way that a consistency of 4.8% results. In addition, there may be dyes for coloring the paper, as well as other additives such as deaerators / defoamers, wet strength agents based on e.g. Polyamidamine-epichlorohydrin resins (e.g. Giluton N 1100/28 from Giulini Chemie, Ludwigshafen, DE) and amphoteric sizing agents based on styrene-acrylate copolymers such as, for example, perglutin 450/280 (available from BK Giulini Chemie, Ludwigshafen, DE) in dosages such as these are known to the person skilled in the art and can be determined by the latter without undue effort, among others depending on the paper machine used.

Wisabetula ECF is a bleached hardwood pulp (birch) available from UPM-Kymmene, Wisaforest, with a density in the range of 750 kg / m ³ and a pH in the slightly acidic range.

Ceasa Green (ECF) eucalyptus is a bleached eucalyptus pulp with a density in the range of 500 - 700 kg / m ³ and a pH in a slightly acidic range and an average fiber length of 0.8 mm.

Attisholz beech is a bleached book sulfite pulp available from Cellulose Attisholz AG (CH).

Catsol 9566 is a cationic starch in the form of a white, coarse powder that is soluble in cold water and has a slightly basic pH (8.5 to 10.5 in 5% distilled water). Socal NZ is a precipitated calcium carbonate available from Solvay, AT, with an average particle diameter of 0.2 μm, a surface area of 11 m ³ / g and a gram volume of 7.6 ml.

The base paper is made in the paper machine in a conventional manner, starting from the above pulp. Then, on-line, ie on the same machine, the ink-receiving layer is applied on one side in a single coating process, in this case a back coating in the sense of an adhesive, antistatic or non-curl layer is not necessary but possible. The line solution for the ink-receiving layer is manufactured according to the following procedure, followed by a detailed description of the individual components: In 340 kg of water at an engine speed of 260 rpm (blistering must be avoided in the entire manufacturing and application process) with 5.08 kg of magnesium sulfate heptahydrate added and stirred for 2 min. 37.4 kg of Induquat ECR 69L are then added at an engine speed of 350 rpm and then stirred at 1400 rpm for 5 minutes (early addition of the quaternary cationic ink fixer is recommended, since the pigments can be better suspended on it). Then 91.5 kg of Gasil HP 39 and 10.2 kg of Syloid 622 are added, after which the container wall is rinsed with 33 kg of water. The mixture is then stirred for 30 minutes, then reduced to 300 rpm and stirring is continued for 5 minutes. Then 527 kg of binder batch are added, 0.021 kg of Surfadon LP-300 and finally stirred for a further 1/2 h. If necessary, a flow aid such as Surfynol 440 can also be added after the addition of Surfadon, typically in an amount of 0.005 to 0.1%, preferably from 0.01 to 0.04%, particularly preferably in an amount of in the range of 0.04%. The percentages relate to the weight of the total solution (??).

The finished functional coat thus has a solids content of 16.7% and a total weight of 1077 kg.

The binder batch comprises the following components: 508 kg of Mowiol 28-99 10% are added at 260 rpm with 9.5 kg of leukophore UO diluted with water in a 1: 1 ratio and stirred for 10 minutes, then 9.5 kg in a 1: 1 ratio dye solution diluted with water was added and the mixture was stirred for a further 20 min. The binder batch thus produced is added in the amount of 527 kg as described above.

Induquat ECR 69L is a cationic quaternary, polymeric compound based on acrylate (CAS No. 79-41-4, ink fixer), available from Indulor Chemie GmbH, Ankum, DE. It has a solids content of approx. 40% in aqueous solution, a viscosity of 1500 - 3000 mPa-s, a pH of 4.5, and a density of 1.08 g / ml.

Gasil HP39 is a synthetic amorphous silicon dioxide (SiO _2r pigment) without surface treatment, available from Crosfield Group, Cheshire, UK, which has a specified particle size in the range of 9.4-11.3 μm with a typical value of 10.3 μm (APS Mastersizer, 100mm lens ), a mass loss at 1000 ° C of maximum 7%, a pH of 6.0-8.0 (5% suspension in water), and a pore volume of 1.8 ml / g. Syloid 622 is an amorphous silica (pigment) in the form of a white, loose powder, with medium porosity and large particle size, available from Grace GmbH, Worms, DE. It has a water content of maximum 3%, an average particle size of 10.8-14.2 μm (Coulter Counter, 100 μm nozzle opening), a wet sieve residue of maximum 0.01% (> 100 μm) and a pH of 6.0 to 8.0 (5% suspension in water ) on. The pore volume is 1.2 ml / g and the oil number 180 g / 100g (DIN ISO 787-5) Surfadon LP-300 is a 1-dodecylpyrrolidin-2-one (N- (N-dodecyl-2-pyrrolidone), CAS Reg. No. 00002687-96-9), available from ISP Europe, Guildford, UK. It has a pH of 3.5 - 7 (in 10% aqueous solution).

Surfynol 440 surfactant is an ethoxylated tetramethyldecynediol and, if necessary, is also added as a leveling agent. It is available from Air Products Ltd., Utrecht, NL, and is a white, waxy, non-ionic acetylenic diol. It has a solubility in water of approx. 0.12% at 25 degrees Celsius and is a surfactant that prevents foaming.

Mowiol 28-99 is a fully saponified polyvinyl alcohol (binder, CAS No. 9002-89-5), containing <3% methanol, available from Clariant Chemie, Basel, CH. It has a degree of hydrolysis of 99.4 mol%, an ester number of 8 ± 5 mgKOH / g, and a residual acetyl content of 0.6 ± 0.4% by weight.

Leukophor UO liquid is a brilliant, urea-free optical stilbene brightener with four sulfo groups in neutral white tone, available from Clariant Chemie, Basel, CH. It has a density of 1.13 kg / l, a viscosity of 100mPa-s, and a pH of 8.9. The ink-receiving layer 3, if applied directly to the base paper, with a basis weight of 8-10 g / m ² , optimally with 10 g / m ² . If, as shown in FIG. 1b), a multilayer paper is to be produced in which the base paper 2 is coated on the back with an antistatic, anticurl, or other back layer 5, and in which one between base paper 2 and the ink receiving layer 3 Sealing layer 4 is arranged, the ink receiving layer should be chosen thicker, ie with a basis weight of 14-20 g / m ² . The same applies if the ink-receiving layer is to be applied to a film, ie generally whenever the layer immediately below the ink-receiving layer is unable to take up part of the solvent absorption, and the ink-receiving layer only for drying the color, ie the removal of the solvent of the pigmented or dye ink is responsible. As already mentioned, the application is preferably carried out online on a paper web, ie not on a coating machine connected downstream. This considerably simplifies and reduces the cost of the process. In addition, the paper web in the machine should advantageously be "over-dried" to a certain extent before the line, ie have a water content of less than 5%, preferably 2 to 3%, usually 2%. This means that the drying process can be partially carried out by the paper, ie the over-dried paper absorbs part of the water from the barrier line.

Further examples:

The following additional test papers were produced and printed to check the printing properties:

Table 1: Composition of the ink-receiving layer

The base papers were coated on-line with the ink absorption layer solution prepared according to the above instructions and then printed with dye and pigment inks. The results of the color density numbers (FD) (according to ISO 5 / 3-1984) of Examples 2 to 6 are summarized in Table 2 for various basis weights of the ink-receiving layer (TAS):

Examples 2 and 3, which use the pigment system HP39 / Syloid 622, serve to demonstrate the effect of the magnesium salt. It can be clearly seen that in Example 2, significantly sharper resolution and significantly less bleeding, i.e. run the ink in the transverse direction, occurs than in Example 3. However, it turns out that the drying properties of Example 3 are better, and the slightly better color densities are achieved. For this reason, a magnesium content in the range of Example 3 was also selected in the first exemplary embodiment.

Examples 4-6 serve to investigate the pigment system HP39 / Syloid 244 and to investigate the effect of large proportions of magnesium salt. Example 4 b) shows massive bleeding but poor drying and curl, 4 a) shows strong bleeding, strong curl. Example 6 shows great sharpness, no bleeding and little cockle and curl. The clear superiority of Example 6 with magnesium can thus be seen.

NAME LIST

1 inkjet recording material

2 base paper

3 ink receiving layer

4 sealing layer

5 back layer

Claims

1. ink jet recording material (1) with a base paper (2) and an ink-receiving layer (3), characterized in that the ink-receiving layer (3) applied as an aqueous solution, pigments, binders, ink fixers, and at least one inorganic salt with a divalent cation and an anion, both of which show essentially pH-neutral behavior.

2. Ink jet recording material (1) according to claim 1, characterized in that the ink receiving layer (3) additionally contains brighteners and / or wetting agents and / or plasticizers and / or color components and / or flow aids.

3. Inkjet recording material (1) according to any one of the above claims, characterized in that it is a salt with a cation selected from the second main group (IIA), particularly preferably Mg ²⁺ or Ca ²⁺ , and the inorganic salt Anion selected from the group CI ^" , SO ₄ ^2" , NO ₃ ^" , or a mixture of such salts.

4. Ink jet recording material (1) according to one of the above claims, characterized in that the inorganic salt in a concentration in the range from 0.5 to 10%, preferably in the range from 2 to 5% and particularly preferably in the range of 3%, based on the dry weight of the ink-receiving layer.

5. Ink jet recording material (1) according to one of the above claims, characterized in that the pigments are selected from the group consisting of SiO ₂ , CaCO ₃ , MgO, TiO ₂ , alumina, kaolin, bentonite or a mixture thereof, the pigment has an average grain size in the range from 5 to 20 μm, in particular from 8 to 15 μm, that the ink fixer is polymer-bound quaternary amines, in particular polyacrylic-bound quaternary amines or polymer-bound cyclic quaternary amines with a neutral pKa value, and that the binder is selected from the group consisting of polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, gelatin, starch and their derivatives, polyvinyl acetate, polyethylene glycol, alginates, polyacrylic acid, or a mixture thereof.

6. Ink jet recording material (1) according to one of the above claims and claim 2, characterized in that it is in the brightener to anionic stilbene derivatives, the wetting agent is a wetting agent of anionic type, and the plasticizer is low molecular weight glycols.

7. ink jet recording material (1) according to any one of the above claims, characterized in that the base paper (2) has a basis weight in the range of 50 to 200 g / m ^2, in particular 100-150 g / m ² , and the ink receiving layer (3) has a basis weight in the range from 8 to 15 g / m ² , particularly preferably from 8 to 10 g / m ² .

8. Inkjet recording material (1) according to one of the above claims, characterized in that the base paper (2) is a plastic film or a paper carrier (2) having a sealing layer (4) arranged in the direction of the ink-receiving layer, the basis weight the ink-receiving layer (3) in this case is preferably in the range from 14 to 20 g / m ² .

9. ink jet recording material (1) according to one of claims 1 to 7, characterized in that it is the base paper is a paper with a low fiber content in relation to the filler content, in particular a paper in which the filler content in the range of 15 to 25%, particularly preferably in the range of 20%, of the total dry weight of the base paper.

10. inkjet recording material (1) according to claim 9, characterized in that the filler is a precipitated calcium carbonate with an average particle size of 0.2 microns.

11. Ink jet recording material (1) according to one of the above claims, characterized in that the ink-receiving layer, based in each case on the dry weight of the ink-receiving layer, is composed essentially of brighteners and coloring additives of low mass fraction:

3% magnesium sulfate heptahydrate (MgSO ₄ ^■ 7 H ₂ O);

8% of a quaternary polymeric compound as an ink fixer;

60% of a synthetic amorphous silicon dioxide of large average particle size in the range from 9 to 15 μm as pigment component; 29% fully saponified polyvinyl alcohol as a binder.

12. A method for producing an ink jet recording material according to any one of claims 1 to 11, characterized in that the ink receiving layer (3) on-line on the paper manufacturing machine on a paper web with a roughness in the range of 2.5 to 3.5 microns, particularly preferably of 3 microns , is applied, an aqueous solution of the components of the ink-receiving layer (3) having a solids content of 15 to 17.5%, in particular in the range of 16.5%, being applied to the fresh paper carrier (2).

13. The method according to claim 12, characterized in that the pigment component is mixed with a dissolver or ground in a mill prior to mixing with the other constituents of the ink-receiving layer (3) to be applied, in such a way that pigment agglomerates are separated.

14. The method according to any one of claims 12 or 13, characterized in that the aqueous solution of the components of the ink-receiving layer is applied at a temperature in the range from 25 to 40 ° C, particularly preferably from 30 °.

15. The method according to any one of claims 12 to 14, characterized in that the solution is applied in degassed form, particularly preferably in that the solution is vacuum degassed before application.