WO2006035004A1

WO2006035004A1 - Substrate having an outer layer of anionic clay, process for preparing the substrate, and use of the substrate

Info

Publication number: WO2006035004A1
Application number: PCT/EP2005/054800
Authority: WO
Inventors: Holger Ebbighausen; Aaldert Johannes De Jong; Ralf KRÜCKEL; Johannes Petrus Jozef Verlaan
Original assignee: Akzo Nobel N.V.
Priority date: 2004-09-27
Filing date: 2005-09-26
Publication date: 2006-04-06

Abstract

The invention relates to a substrate, e.g. paper, having an outer layer comprising a Mg-Al anionic clay having 3R2 or 3R1 stacking with in its interlayer a charge-balancing anion selected from the group consisting of OH-, NO3-, Cl-, Br-, and l-. This outer layer provides several advantages, such as improved inkjet printability properties. The invention also relates to the preparation of this substrate and its use in printing processes.

Description

SUBSTRATE HAVING AN OUTER LAYER OF ANIONIC CLAY, PROCESS FORPREPARINGTHE SUBSTRATE,AND USE OFTHE SUBSTRATE

The invention relates to a substrate having an outer layer comprising a Mg-Al anionic clay.

Such substrates are known from US 4,613,525. This reference describes an ink-jet recording medium which contains a hydrotalcite compound. The ink-jet recording medium may be prepared either by forming a wet web on a paper making machine from a slurry of disintegrated pulp fibre and a hydrotalcite compound, or by impregnating or coating a formed paper sheet, by means of a size press, with a coating composition containing the hydrotalcite compound. The hydrotalcite compound is defined as being a compound having a chemical composition of magnesium aluminium hydroxyl carbonate hydrate having a crystal structure such that the d values of the highest peak, the second highest peak, and the third highest peak are 7.89, 3.91 , and 2.60, respectively, as determined using X-ray diffraction. This hydrotalcite compound has carbonate ions in the interlayer.

EP 0 847 867 discloses recording media, i.e. materials which are printed or written on, comprising a substrate and a surface layer thereon, wherein the surface layer comprises a hydrotalcite-type compound. The surface layer may be applied in the form of a solution using a conventional coater.

EP 1 153 886 relates to an ink-jet recording medium having a water-colour ink accepting layer containing a hydrotalcite compound having silicic acid anions in the interlayer. A coating solution comprising the hydrotalcite compound, which serves as a dye-fixing agent, is applied onto paper using common substrate coating methods, for which conventional coaters can be used. The use of the hydrotalcite compounds in accordance with the prior art causes the coated substrate, particularly the coated paper, to have poor dye adhesion properties, a low water fastness, and a poor colour intensity.

It is therefore an object of the present invention to provide a substrate having an outer layer which has improved ink-jet printability properties. In this context the term "ink-jet printing" refers to any printing technology using water or solvent-based inks which contain dyes and/or pigments to generate a print-out on an ink-receiving substrate. "Ink-jet printing" includes continuous and drop- on-demand printing processes.

This object is achieved with a substrate having an outer layer comprising a Mg- Al anionic clay having 3R2 or 3Ri stacking with in its interlayer a charge- balancing anion selected from the group consisting of OH^", NO₃ ^", Cl^", Br^", and I^". A substrate having an outer layer in accordance with the invention has improved printability properties over substrates according to the prior art. In particular, such a substrate shows improved colour intensity, reduced mottling, and improved water fastness. If the substrate is paper, the outer layer will also show improved adhesion to the substrate. In some cases, a binder may even be omitted from the coating.

The substrate may be any type of paper, glass, fabrics including non-woven fabrics or synthetic resin film. Preferably, the substrate is a paper.

Examples of papers are tissue paper and paper toweling, newsprint, grocery bags, fine papers, kraft linerboard, and folding boxboards, papers for posters and wallpapers, or any coated form thereof.

Examples of preferred substrates according to the invention are papers having an outer layer comprising the Al-Mg anionic clay of the present invention, such as ink-jet office paper, ink-jet production paper (wide, standard, and narrow formats often used for continuous ink-jet printing), and photographic paper. In the context of the present application the term "outer layer" refers to a layer applied onto the substrate as well as to a layer applied onto precursors of the substrate, such as single fibres used in textile or non-woven fabrics.

The anionic clay of the present invention has brucite-like main layers built up of octahedra alternating with interlayers in which water molecules and charge- balancing anions are distributed. The charge-balancing anions are selected from the group consisting of OH^", NO₃ ^", Cl^", Br^", I^", and combinations thereof. Preferably, the charge-balancing anion is OH^". If desired, the interlayers may further contain other anions - such as CO₃ ^2", SO₄ ^2", SiO₃ ^2", BO₃ ^2", HGaO₃ ^2", HVO₄ ^2", BO₃ ^2"' phosphates, pillaring anions such as Vi₀O₂8^6" and Mo₇O₂₄ ^6", monocarboxylates such as acetate, dicarboxylates such as oxalate, and alkyl sulphonates such as lauryl sulphonate - although this is less preferred.

These anionic clays have a layered structure corresponding to the general formula

[Mg_m ²⁺ Al_n ³⁺ (OH)_2m+2n.] Xn/z^Z".bH₂O

wherein m and n have a value such that m/n=1 to 10, preferably 1 to 6, and b has a value in the range of from O to 10, generally a value of 2 to 6, and often a value of about 4. X represents the charge-balancing anion with valence z that is normally present in the interlayers of anionic clays. It is more preferred that m/n should have a value of 2 to 4, more particularly a value close to 3. Hydrotalcite is an example of a natural Mg-Al anionic clay with CO₃ ^2" anions in the interlayer; meixnerite is an example of a natural anionic clay with OH^" anions in the interlayer.

In one preferred embodiment, the Mg-Al anionic clay of the present invention has 3R₂ stacking. This anionic clay provides improved printability properties over anionic clays with other stacking sequences. This polytype of anionic clay has a three-layer repeat similar to hydrotalcite and meixnerite, which both have having 3Ri stacking, but it has a different interlayer arrangement. The 3R2 polytypes can be distinguished from the 3Ri polytype by the intensities of the 107 and 108 reflections, as predicted and explained by Bookin and Drits in Clays and Clay Minerals, Vol. 41 (1993) 551-557. The 3R₂-type anionic clay has a strong 107 reflection close to a d value of 2.05 A (about 45° 2-theta when using Cu kα X-ray source), whereas the 3R_rtype has a strong reflection (the 108 reflection) close to a d value of 1.93 A (about 47° 2-theta when using Cu kα X-ray source). It is understood that the precise d values for the 107 and 108 reflections will depend on the lattice a and c parameters for the Mg-Al anionic clay. Of course, there are more differences in the X-ray diffraction pattern, but this is the best range of reflection to make a distinction because it has hardly any other reflections from other compounds which are likely to be present in anionic clay-like material as well.

Further, the Mg-Al anionic clay having 3R2 stacking has a different morphology from the conventional 3Rrtype anionic clay, as can be seen by SEM (scanning electron microscopy) examination. The 3R2-type anionic clay generally has a structure with irregular flake-like platelets randomly agglomerated. Conventional 3Ri anionic clay has regular well-formed layers of platelets, which are arranged in the usual bookstack form.

The Mg-Al anionic clay having 3R2 stacking may be prepared by hydrothermally treating a slurry containing an aluminium source and a magnesium source to form a Mg-Al anionic clay having 3R2 stacking. Suitable preparation methods are described in EP 1 204 595.

The amount of Mg-Al anionic clay on the substrate preferably is at least 0.1 wt%, more preferably at least 0.5 wt%, and most preferably at least 1 wt%, calculated on the dry weight of the substrate having the outer layer, and generally at most 30 wt%, preferably at most 25 wt%, and most preferably at most 20 wt%, calculated on the dry weight of the substrate having the outer layer.

If the substrate is paper and the paper is coated on one side, the amount of Mg-Al anionic clay of the present invention generally is at least 0.1 wt%, preferably at least 0.5 wt%, and most preferably at least 1 wt%, calculated on the dry weight of the substrate having the outer layer, and generally at most 5 wt%, preferably at most 4 wt%, and most preferably at most 2 wt%, calculated on the dry weight of the substrate having the outer layer. If the paper is coated on both sides, the Mg-Al clay according to the invention is present in twice the amounts given above.

On a paper substrate, the amount of Mg-Al anionic clay preferably is at least 0.1 g/m², more preferably at least 0.25 g/m², and most preferably at least 0.5 g/m². Preferably, this amount is not more than 20 g/m², more preferably not more than 10 g/m², and most preferably not more than 5 g/m².

The outer layer may further comprise compounds conventionally used in such outer layers. Such compounds may be binders, fillers or pigments, cationic resins or any other additive known to the man skilled in the art. Examples of conventionally used compounds can be found in Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, Inc. 1996 (online posting date of December 4, 2000), in Papermaking Additives by M.A. Dulaney et al., and in Paper Chemistry by D. Eklund and T. Lindstrόm, 1991 , DT Paper Science Publications, Grankulla, Finland.

The substrate comprises an outer layer on at least one side of the substrate. If the substrate is a paper sheet, the outer layer is applied onto one or both sides of the paper sheet. If two or more sides of the substrate are coated, the outer layers on the different sides may be identical, or they may differ in composition and/or thickness.

It is also envisaged to apply a plurality of outer layers onto the substrate, wherein each layer may be the same or different in terms of thickness and/or composition.

The outer layer can be applied onto the substrate using any method known in the art. In one such method a molten resin, in which the anionic clay of the invention is dispersed, is applied onto the substrate and cooled afterwards. In a more preferred method, a coating medium comprising a liquid and the anionic clay of the invention is applied onto the substrate, after which the liquid is removed at least partially. The term "coating medium" refers to a coating emulsion or suspension containing at least the anionic clay and the liquid. The coating medium can be applied using conventional coaters such as a bar coater, a roll coater, an air-knife coater, a blade coater or a rod coater. If the substrate is paper, the coating medium can also be applied in a size or film press in the papermaking process. The advantage of using a size or film press is that two coatings having the same thickness and the same composition can be applied at the same time. However, as is shown in the Examples below, the colour stability and visibility may be higher using a conventional coater. The resulting paper is also referred to in the art as "pigmented paper" and can be used for several applications, in particular in printing processes, such as ink-jet printing.

The present invention is further illustrated in the Examples below. Examples

The Mq-Al anionic clays

An Mg-Al anionic clay having 3R2 stacking and OH^" anions in the interlayer was prepared according to the preparation process described in Example 3 of EP 1 204 595. In the present application the resulting clay is also referred to as "3R₂-OH".

A Mg-Al anionic clay having 3Ri stacking and OH^" anions in the interlayer ("3R-I-OH") was prepared according to the same method, with the proviso that the temperature at which the preparation was carried out was 9O⁰C. The 3Ri and 3R₂ anionic clays were characterized and distinguished from each other by the presence of the 47°and the absence of the 45° 2-theta reflection for 3Ri and vice versa for 3R₂.

Preparation of the ink-jet recording medium

The Mg-Al anionic clays were used to prepare ink-jet recording media according to the following method:

A suspension of the Mg-Al anionic clay with a concentration of 16.7% (w/v) was prepared by dilution of the original aqueous slurry. This suspension was applied to paper either by using a semi-automated bar coater (K Control Coater) or by passing the paper through a lab-size size press. The suspension temperature was 20-25⁰C and the suspension was circulated before and during application. The treated paper was dried at 115⁰C for 3 minutes.

The anionic clay concentration in the outer layer was determined gravimetrically by determining the difference in weight of the dry paper before and after surface treatment, using a lab balance. Ink-jet printing

Using various commercially available office ink-jet printer models, block areas of the base colours (cyan, magenta, yellow) were printed on the ink-jet medium prepared as described.

Evaluation of ink-iet properties

The ink-jet properties evaluated in these Examples were colour intensity and water fastness.

The colour intensity was measured using a densitometer (Gretag MacBeth). The water fastness was measured by comparing the print density before and after keeping the ink-jet recording medium - onto which block areas of the base colours were printed - in distilled water for 5 minutes while gently stirring using a magnetic stirrer. After drying in air the retained colour density was measured.

Example 1

Using a lab-size size press, a commercially available high-quality office paper (Clairalfa ex Papeterie Clairefontaine) was coated with varying amounts of the anionic clay having 3R2 stacking ranging from 0.1 to 2 g/m². On the samples, block areas of the three base colours were printed using four different, commercially available office ink-jet printers, i.e. Lexmark P707, HP Deskjet 970 Cxi, Epson Stylus C84, and Canon BJC 620.

In Tables 1-4, the colour intensities of the four samples are shown. It is noted that an increase in colour intensity of around 0.1 already results in a visible improvement of the print-out. Tables 1-4: Effect of the amount of Mg-Al anionic clay in the outer layer of paper on the colour intensity

Table 1 : Lexmark P 707

Colour without 0.1 g/m² 0.25 g/m² 0.5 g/m² 1 g/m² 2 g/m²

Cyan 0.74 0.82 0.83 0.86 0.92 0.94

Magenta 0.76 0.84 0.86 0.89 0.92 0.93

Yellow 0.66 0.72 0.73 0.72 0.72 0.69

Table 2: HP Deskjet 970 Cxi

Colour without 0.1 g/m² 0.25 g/m² 0.5 g/m² 1 g/m² 2 g/m²

Cyan 1 .24 1 .32 1 .32 1 .36 1 .44 1 .57

Magenta 1 .15 1 .20 1 .20 1 .23 1 .26 1 .35

Yellow 1 .02 1 .06 1 .06 1 .08 1 .12 1 .16

Table 3: Epson Stylus C84

Colour without 0.1 g/m² 0.25 g/m² 0.5 g/m² 1 g/m² 2 g/m²

Cyan 0.64 0.68 0.68 0.66 0.72 0.72

Magenta 0.85 0.89 0.91 0.91 0.91 0.94

Yellow 1.19 1.22 1.21 1.23 1.24 1.27

Table 4: Canon BJC 620

Colour without 0.1 g/m² 0.25 g/m² 0.5 g/m² 1 g/m² 2 g/m²

Cyan 1 .20 1 .37 1 .41 1.46 1 ,53 1 .63

Magenta 1 .17 1 .30 1 .37 1.42 1 .44 1 .50

Yellow 1 .04 1 .16 1 .17 1.25 1 .31 1 .36

In the above Tables 1-4, it is shown that the use of Mg-Al anionic clay having 3R2 stacking and OH^" anions in the interlayer improves the colour intensity and the visibility of the print-out. The colour intensity and the visibility are improved further when higher amounts of this anionic clay are used.

Example 2 A commercially available high-quality office paper (Stora Enso Berghuizer Superior) was coated with 1 g/m² of the Mg-Al anionic clay having 3R2 stacking, either on a lab-size size press or by using a rod coater. Block areas of the three base colours were printed on the samples using an Epson Stylus Color 860. The colour intensities of the base colours of each sample and of a coated paper wherein no anionic clay is present were determined and are shown in the Table below.

Table 5: Effect of coating method on the ink-jet printing quality

Coating Cyan Magenta Yellow (1 g/m² 3R₂-OH)

Without 1 .25 1. 03 0 .95 size press 1 .55 1. 21 1 .21

Rod coater 1 .64 1. 25 1 .25

From Table 5, it can be deduced that the coated substrates according to the present invention have improved colour stability and visibility. Coating with a rod coater appears to improve the colour intensity even further than coating with a size press.

Example 3

A commercially available high-quality office paper (Stora Enso Berghuizer Superior) was coated with 1 g/m² of the Mg-Al anionic clay having 3R₂ stacking using a rod coater. Block areas of the three base colours were printed on coated paper samples using a HP 2000 C and an Epson Stylus Color 860. The water fastness of the print-out was determined by cutting out the printed areas and immersing these samples in a beaker filled with distilled water for about 5 minutes while gently stirring using a magnetic stirrer. After removal of the samples from water, they were dried in air and the colour intensity of the base colours was determined. The water fastness values (expressed as a percentage) are shown in Tables 6 and 7.

Tables 6-7: Effect of coating on residual colour intensity after rinsing ("water fastness")

Table 6: HP 2000 C

Coating Cyan (%) Magenta (%) Yellow (%)

None 47 40 58 1 g/m² 3R₂-OH 72 59 86

Table 7: Epson Stylus 860

Coating Cyan (%) Magenta (%) Yellow (%)

None 64 47 85 1 g/m² 3R₂-OH 87 79 100

In Tables 6 and 7 it is illustrated that the water fastness of the coated paper according to the present invention is improved for all base colours.

Example 4

A commercially available high-quality office paper (Stora Enso Berghuizer

Superior) was coated with 2 g/m² of Mg-Al anionic clay using a rod coater.

Three types of anionic clays were used: a) a Mg-Al anionic clay having 3R₂ stacking having OH^" anions in the interlayer

(3R₂-OH), b) a Mg-Al anionic clay having 3Ri stacking having OH^" anions in the interlayer

(3RrOH), c) a commercially available Mg-Al anionic clay with 3Ri stacking and carbonate ions in the interlayer - type DHT-6, ex Kyowa Kisuma (3RrCO₃).

Block areas of the three base colours were printed on coated paper samples using three different office jet printers, i.e. HP Deskjet 970 Cxi, Epson Stylus C84, and Canon BJC 620. The colour intensities of the three samples are shown in Tables 8-10.

Tables 8-10: Effect of the type of anionic clay on the colour intensity

Table 8: HP Deskjet 970 Cxi

Colour without 3R₂-OH 3R_rOH 3R_rCO₃

Cyan 1 .27 1 .8 1 .62 1 .51

Magenta 1 .18 1. 56 1 .43 1 .16

Yellow 1 .04 1. 25 1 .17 0 .95

Table 9: Epson Stylus C84

Colour without 3R₂-OH 3R_rOH 3R_rCO₃

Cyan 0.65 0 .78 0.77 0.98

Magenta 0.87 1 .08 1.06 0.98

Yellow 1.3 1 .73 1.6 1.48

Table 10: Canon BJC 620

Colour without 3R₂-OH 3R_rOH 3R_rCO₃

Cyan 1 .15 1 .84 1.69 1 .62

Magenta 1 .24 1 .74 1.66 1 .01

Yellow 1 .04 1 .61 1.53 1 .17 Example 5

A commercially available high-quality office paper (Stora Enso Berghuizer Superior) was coated with 2 g/m² of Mg-Al anionic clay using a rod coater. Three types of anionic clays were used: a) a Mg-Al anionic clay having 3R₂ stacking having OH^" anions in the interlayer (3R₂-OH), b) a Mg-Al anionic clay having 3Ri stacking having OH^" anions in the interlayer (3RrOH), c) a commercially available Mg-Al anionic clay with 3Ri stacking and carbonate ions in the interlayer - type DHT-6, ex Kyowa Kisuma (3RrCO₃).

Block areas of the three base colours were printed on coated paper samples using two different office jet printers, i.e. HP Deskjet 5150 and Canon BJC 620. The water fastness of the printout was determined according to the method of Example 3. Water fastness values (expressed as percentage of original colour intensity) are shown in Tables 11 and 12.

Tables 11-12: Effect of the type of anionic clay on the residual colour intensity after rinsing ("water fastness")

Table 11 : HP Deskjet 5150

Colour without 3R₂-OH 3RrOH 3RrCO₃

Cyan 61 100 100 59

Magenta 43 94 82 47

Yellow 39 86 83 44 Table 12: Canon BJC 620

Colour without 3R₂-OH 3RrOH 3RrCO₃

Cyan 76 96 88 59

Magenta 36 59 51 37

Yellow 85 93 89 70

Claims

1. A substrate having an outer layer comprising a Mg-Al anionic clay having 3R₂ or 3Ri stacking with in its interlayer a charge-balancing anion selected from the group consisting of OH^", NO₃ ^", Cl^", Br^", and I^".

2. Substrate according to claim 1 wherein the anionic clay has 3R2 stacking.

3. Substrate according to claim 1 or 2 wherein the charge-balancing anion is OH^".

4. Substrate according to any one of the preceding claims wherein the substrate is paper.

5. Substrate according to any one of the preceding claims wherein the anionic clay content is 0.1-30 wt%, calculated on dry weight of the substrate containing the outer layer.

6. Substrate according to claim 5 wherein the anionic clay is present on the paper in an amount of 0.1-10 wt%, calculated on dry weight of the paper containing the outer layer.

7. A process for preparing a substrate according to any one of the preceding claims comprising the steps of: - applying onto the substrate a coating medium comprising a liquid and the Mg-Al anionic clay having 3R₂ or 3Ri stacking with in its interlayer a charge-balancing anion selected from the group consisting of OH^", NO₃ ^", Cl^", Br^", and I^", and - removing the liquid at least partially.

8. Use of a substrate according to claim 5 of 6 in an ink-jet printer.

9. Printing process using a substrate according to claim 5 or 6.