# Patent

## Title
Dispersion of aluminium oxide

## Abstract

A dispersion containing a high-surface-area, pyrogenically-produced aluminium oxide with a surface area and BET of more than 115 m2/g and a Sears number of more than 8 ml/2 g, is produced by mixing a high-surface-area, pyrogenically-produced aluminium oxide having a BET specific surface area of more than 115 m2/g and a Sears number of more than 8 ml/2 g, with water, setting a pH value of 2 to 11 (preferably 3 to 8) and dispersing the mixture by the introduction of controlled shearing forces.
It can be used for the production of Inkjet media, digital imaging products and other printing medium.

## Background
RELATED APPLICATION
This application is a divisional of U.S. application Ser. No. 10/277,130 filed Oct. 22, 2002 now U.S. Pat. No. 7,572,854 which claims priority to European Patent Application No. 101 52 745.4 filed Oct. 25, 2001 and which is being incorporated in its entirety herein by reference.


BACKGROUND OF THE INVENTION
The invention relates to a dispersion of pyrogenically-produced aluminium oxide, a process for its production and its use.
The invention provides a dispersion, which is characterised in that it contains a high-surface-area, pyrogenically-produced aluminium oxide, which has a BET specific surface area of more than 115 m2/g and a Sears number of more than 8 ml/2 g.
In one embodiment of the invention, the aluminium oxide can be characterised in that the dibutylphthalate absorption of the powder, measured on a 16 g portion, is not measurable (no end-point detection).
The pyrogenically-produced aluminium oxide that can be used according to the invention, can be produced by the flame oxidation, or preferably flame hydrolysis, method, an evaporable aluminium compound, preferably the chloride, being used as the starting material.
The content of aluminium oxide can be 25±15 wt. %.
The dispersion may contain the following additional constituents:
Organic or inorganic acids or bases, salts, additives such as ionic or non-ionic surfactants, polymers, polyelectrolytes or biocides as well as other auxiliary substances to stabilise the dispersion or to increase its quality or storage stability.
The dispersion according to the invention may also contain, in addition to aluminium oxide, inorganic acids (such as phosphoric acid, nitric acid, sulfuric acid, . . . ), organic acids (such as formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, . . . ), inorganic or organic bases (such as potassium hydroxide, organic amines, . . . ), salts, (such as sodium chloride, potassium formate, calcium nitrate), buffer systems (such as for example potassium dihydrogenphosphate/phosphoric acid buffer, acetic acid/sodium acetate buffer, . . . ) ionic, or non-ionic surfactants, polyelectrolytes, polymers or other dispersing agents or stabilisers, and also biocides.
The invention further provides a process for the production of the dispersion according to the invention, which is characterised in that a high-surface-area, pyrogenically-produced aluminium oxide, which has a BET specific surface area of more than 115 m2/g and a Sears number of more than 8 ml/2 g, is mixed with water, a pH value of 2 to 11, preferably 3 to 8, in particular 2 to 8, is set and the mixture is dispersed by the introduction of shearing forces.
The invention is formed by mixing a high-surface-area, pyrogenically-produced aluminium oxide, which has a BET specific surface area of more than 115 m2/g and a Sears number of more than 8 ml/2 g, with water and additives in accordance with claim 4, setting a pH value of 2 to 11 (preferably 3 to 8), and dispersing the mixture by the introduction of controlled shearing forces.
To disperse the high-surface-area, pyrogenically-produced aluminium oxide, shearing equipment such as rotor-stator-type machines (batch- or continuous in-line machines), ball mills, pearl mills, agitated ball mills or high-energy shearing processes (in which the dispersion is dispersed under high pressure at pressures of over 1000 bar) is used and the dispersions obtained have a mean particle size distribution of d50<150 nm (d50 less than 150 nm; measured by dynamic light scattering).
The dispersion according to the invention has the following advantages:
high cationic charge on the surface of the particles, as compared with dispersions produced from aluminium oxides (-oxide hydroxides) by the wet chemical method particle size distributions of the dispersion can be set in a defined way, in contrast to dispersions of other pyrogenic aluminium oxides or aluminium oxides (-oxide hydroxides) produced by the wet chemical method, which are produced by different dispersion processes high dispersion purity, as compared with dispersions produced with aluminium oxides (-oxide hydroxides) produced by the wet chemical method

    
    
        precisely-controllable electrolyte level within the dispersion, as compared with dispersions of other pyrogenic aluminium oxides or aluminium oxides (-oxide hydroxides) produced by the wet chemical method, the electrolyte concentration of which cannot be set precisely as a result of the starting powder or the dispersion process
        very high surface area of the pyrogenic aluminium oxide as compared with dispersions of other pyrogenic aluminium oxides or aluminium oxides (-oxide hydroxides) produced by the wet chemical method
        highly distinctive “structure/crosslinking” of the aluminium oxide primary particles within the dispersion, as compared with dispersions of other pyrogenic aluminium oxides or aluminium oxides (-oxide hydroxides) produced by the wet chemical method
        a high degree of hardness and abrasion resistance of the particles distributed in the dispersion, as compared with dispersions of aluminium oxides (-oxide hydroxides) produced by the wet chemical method, in which the primary particles are less hard.
    
    


The dispersion according to the invention is eminently suitable for further processing in Inkjet coating pigments. The invention further relates to a process for the production of Inkjet coating pigments that have been produced with the dispersions according to the invention and the glossy media produced from them. These media are characterised by a very high gloss value, very high colour densities when printing, large colour space, extremely low drying times, a high absorption capacity and (in comparison with other aluminium oxides) increased water resistance, all of which are desirable characteristics.
The following examples demonstrate that the dispersion according to the invention is superior to known dispersions with regard to its processability in a coating pigment and in the associated Inkjet medium.
The recipes used for Inkjet coating pigments are guide recipes. Thus binders other than polyvinylalcohol (with various saponification grades) can be used in combination or alone, such as for example polyvinylpyrrolidone, polyvinylacetate, silanised polyvinylalcohols, styrene-acrylate lattices, styrene-butadiene lattices, melamine resins, ethylene-vinylacetate copolymers, vinylpyrrolidone-dimethylaminopropylenemethacrylamide copolymers, polyurethane resins, synthetic resins such as polymethylmethacrylates, polyester resins (for example unsaturated polyester resins), polyacrylates, modified starch, casein, gelatines, cellulose derivatives (for example carboxymethylcellulose) and also in other quantity ratios to the pyrogenic aluminium oxide than those stated in the application example.
The coating according to the invention may also contain, in addition to the dispersion according to the invention, one or more other pigments, and/or dispersions. These may be: calcium carbonates, layered silicates, aluminium silicates, plastic pigments (for example polystyrene, polyethylene, polypropylene), silicas (for example colloidal silicas, precipitated silicas, silica gels, pyrogenic silicas, pyrogenic mixed oxides), cationised variants of the stated silica compounds, aluminium compounds (for example aluminium sols, colloidal aluminium oxides and their hydroxy compounds, such as pseudo-boehmite, boehmite, aluminium hydroxide), magnesium oxide, zinc oxide, zirconium oxide, magnesium carbonate, kaolin, clay, talc, calcium sulfate, zinc carbonate, satin white, lithopones, zeolites or dispersions of these compounds.
Both the solid content of the dispersion and also that of the coating pigment can be varied in comparison with the application examples. Further possible variations consist in changing the pH value, the dispersion method, the composition of the coating pigment formulation and the dispersion medium.
To increase the water-resistance of the binder system and thus the coating, crosslinkers may be used, such as: zirconium oxides, boric acid, melamine resins, glyoxal and isocyanates and other molecules that bind the molecule chains of the binder system with each other.
Furthermore, auxiliary agents such as optical brighteners, de-foaming agents, wetting agents, pH buffers, UV absorbers and viscosity improvers can also be used.
Examples of cationic substances for the cationising of the binder are: polyethyleneimine, polyallylamines, polyvinylamines, polymers consisting of cationic monomers such as primary, secondary and tertiary amines, which are located on the side-chains, and quarternary ammonium compounds.
The coating structure of the medium may also differ from the application examples, in that the coating may consist of several coating layers of the same type or other layers, and the coating that has been produced with the dispersion according to the invention is only located in one of the layers present. Thus, for example, further ink-absorptive coatings (for example precipitated silica coatings) may be applied under the Inkjet coating according to the invention. Furthermore, one or more polymer layers (e.g. polyethylene) can be applied to the substrate and/or to the coating according to the invention, in order to increase the mechanical stability and/or gloss of the coating (for example photographic base paper, lamination). Even if the Inkjet medium contains one or more of the layers described above, and is provided with the coating according to the invention, printability is improved for the majority of printing applications.
The coating pigment recipe can be applied to a substrate by all conventional application processes (alone or in combination). Conventional processes (which are not, however, restricted to the stated processes) are: rolling, blade application, airbrushing, doctor blade (profiled, smooth, split), the cast-coating process, film pressing, bonding-pressing, curtain-coating and slot-die application (for example coating blade). The processes allowing extremely homogeneous coating, for example cast-coating, curtain-coating and slot-die application, are preferred.
The coated substrate can be dried by all of the conventional processes (alone or in combination). Conventional processes (which, however, are not restricted to the stated processes) are: air- or convection drying (for example hot air channel), contact- or conduction drying, energy radiation drying (for example infra-red and microwave).
The invention further provides coatings, which have an aluminium oxide-binder weight ratio of 8:1 to 1:2. The coatings can be used for the production of Inkjet-media, digital imaging products and other printing media.
The invention further provides recording media consisting of aluminium oxide dispersions, which are characterised in that they consist of substrates with glossy coatings, in which the coatings contain VP Alu 130 dispersions and dispersion additives (such as acids, bases, surfactants, polymers, polyelectrolytes etc.) and a binder system, the aluminium oxide particles that build up the coating originating from a dispersion according to the invention, with an average particle size of d50<200 nm (d50 less than 200 nm; measured by dynamic light scattering).
The aluminium oxide dispersion can be used in coatings for materials such as paper, metals, glass, ceramics, plastics, polymers, rubbers and textiles. Furthermore, it can be used to polish or clean metals, semi-conductor elements in the electronics industry, glass, ceramics and other hard materials.
The coatings that have been produced from coating pigments, may have a solid matter content of 15%, and preferably of 18% and more.
The coatings may have a substrate with a substance weight of 80 to 250 g/m2. The substrate may have a Cobb10 value of 0 to 60.
A water-impermeable sealing coat may be applied to the substrate.
The substrate may be a polymer film.
The coatings may be used for the production of Inkjet media (such as paper, films, textiles, . . . ), digital imaging products and other printing media.
“The dispersions according to the invention may be used for the coating of fluorescent tubes, lightbulbs or other light sources.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows VP W 520 “F” shearing tests measured on Jan. 11, 2001.
FIG. 2 shows VP W 520 “F” shearing tests measured on Jan. 25, 2001.
FIG. 3 shows changes in the viscosity of W 520 “F” with increasing shearing time.



DETAILED DESCRIPTION OF THE INVENTION
Example 1
Production of the Aluminium Oxide that can be Used According to the Invention
320 kg/h previously-evaporated aluminium trichloride (AlCl3) is burned together with 100 Nm3/h hydrogen and 450 Nm3/h air in a burner of known construction.
After the flame reaction, the fine-particle, high-surface-area aluminium oxide is separated from the hydrochloric acid gases that have also formed, in a filter or cyclone, any HCl traces still adhering being then removed by treatment with moistened air at increased temperature.
The high-surface-area pyrogenic aluminium oxide formed has the physical/chemical reference data shown in Table 1. The data for the pyrogenic aluminium oxide that can be obtained commercially from Degussa-Huls AG/Frankfurt (commercial name Aluminiumoxid C) are also included in Table 1 for reference.











TABLE 1








High-surface-area





aluminium oxide




according to the




invention
Aluminium



Unit
Alu 130
oxide C



















BET
m2/g
121
100


Specific


Surface area


Sears number
ml/2 g
9.38
7.05


(pH 4 to 9)


PH
4% aqueous
4.93
4.5



dispersion


Drying loss
wt. %
3.3
3.0


Bulk density
g/l
55
48


Tamped density
g/l
63
57


DBP-Absorption
wt. %
Not measurable,
231




no detectable end




point.









DBP: Dibutylphthalate

The measurement of the Sears number is disclosed in EP 0 717 008.
Example 2
Production of the Dispersion According to the Invention
First, 280 liters de-ionised water are brought to pH 3.9 with a propionic acid in a receiving vessel.
80 kg of the powder described in example 1 with a surface area greater than 115 m2/g (equivalent to 20 wt.-% aluminium oxide) are then introduced into the water with a rotor-stator machine. After incorporating the whole quantity of the powder, the suspension obtained is intensively sheared for ca. 60 minutes.
Whilst the powder is being introduced, the pH value is maintained at pH=4.0 to 4.1 by adding 18 liters of semi-concentrated acid. After intake of the aluminium oxide and immediately before shearing, a sample of the suspension is taken and a d50 value of d50=160 nm is determined (measurement in dilution by means of dynamic light scattering). The subsequent shearing process is carried out with the rotor-stator machine at maximum shear energy and lasts for a total of 60 minutes.
After completion of the shearing process, the pH value is 4.1. After adding 2 kg of a biocide, the pH value was brought to the final pH of 3.9 with a further 6 liters of propionic acid. Once production of the dispersion is complete, the liquid volume is increased to 400 liters by adding 14 liters distilled water. The particle size set after the shearing process is d50=130 nm.
Properties of the dispersion according to example 2 of the invention (VP W 520).
During production of the dispersion the average particle size falls significantly as the shearing time continues (cf. FIG. 1): without shearing (0 min) the value is still d50=160 nm, but after 60 minutes' shearing it falls to d50=130 nm:







TABLE 2







Comparison of the samples of the dispersion according to


the invention immediately after production and two weeks


later














0 min
15 min
27 min
30 min
45 min
60 min



Shear.
Shear.
Shear.
Shear.
Shear.
Shear.

















d50 in (nm)
160
155
149
143
137
130


(day of


production)


d50 in (nm)
170
155
153
147
139
136


(control, 2


weeks)









During production of the dispersion according to the invention, the pH value does not depend on the shearing time (cf. Table 2). The change in pH within two weeks is also the same for all samples:







TABLE 3







pH-values of the samples of the dispersion according to the


invention (dependency on shearing and time)














0 min
9 min
15 min
30 min
45 min
60 min



Shear.
Shear.
Shear.
Shear.
Shear.
Shear.

















pH-value
3.9
4.0
4.0
4.1
4.0
3.9


(production)


pH-value
4.5
4.5
4.6
4.6
4.5
4.5


(control, 2


Weeks)









The gloss values are measured with a Byk-Gardner gloss meter using test card 2855 (black spectrum) as a basis.
The printing properties of the coating are evaluated by printing out a test image on the coating, using an HP 550 C printer and an Epson Stylus Colour 800 printer respectively and having these printed coatings evaluated by 3 independent persons on the basis of the attached scale of marks.
The colour densities are measured on the basis of the test image, which also contains full-area colours (black, magenta, cyan, yellow) using a GretagMacbeth (trademark) SpectroEye at an observation angle of 2° and a D50 light source.
Example 3
Production of an Inkjet Coating


    Educts: aluminium oxide dispersion according to example 2 polyvinyl alcohol Mowiol 40-88 (Clariant, D) polyester film


Recipe and method for the production of Inkjet coating pigments:
The aqueous polyvinyl alcohol solution (Mowiol 40-88, Clariant) with 12.14% solid content, is placed in a 400 ml beaker and a quantity of water is added to it, so that, together with the aluminium oxide dispersions according to example 2, a solid content of 18% is obtained. The relevant dispersion is slowly dropped into the polyvinyl alcohol solution using a pipette, within 5 minutes, whilst stirring at 500 rpm. Once it has been added, stirring continues for a further 30 minutes at 500 rpm to obtain a homogenous coating pigment. The coating pigments are then de-aerated using a dessicator and water-jet pump. As a control, the actual solid matter, pH value and viscosity are measured after mixing the coating pigments.
The parts in the table below are understood to mean parts by weight in relation to the solid matter.







TABLE 4





Coating pigment reference values




















Aluminium oxide
100 parts





dispersion, acc.



to example 2,



15 minutes'



dispersion time



Aluminium oxide

100 parts



dispersion, acc.



to example 2,



30 minutes'



dispersion time



Aluminium oxide


100 parts



dispersion, acc.



to example 2,



60 minutes'



dispersion time



PVA 40-88
 20 parts
 20 parts
 20 parts



Actual solid
18.03
18.01
18.00



content of the



coating pigments



in %



PH value
4.7
4.6
4.6











Viscosity, Brookfield in mPa s after 24 h














After
 5 rpm
920
824
748


stirring
10 rpm
840
716
664



20 rpm
715
608
534



50 rpm
560
512
462



100 rpm 
463
398
346












Comments on
good
good
good



production of



coating pigments










The viscosity data obtained show that the dispersion according to example 2, and the longest dispersion time, produce the lowest viscosities. This is desirable as the solid matter in the coating pigment can still be increased without obtaining viscosities that are too high to be applied.
Method for the production of an Inkjet coating from the Inkjet coating pigment referred to above
A 100 micron thick, un-treated polyester film is coated using an Erichsen Film Applicator device with a 120 micron wet film spiral applicator. The coating pigment applied is dried using a hot air dryer.
Data for the coatings obtained:

















Aluminium oxide
100 parts





dispersion acc. To






example 2,






15 minutes'






dispersion time






Aluminium oxide

100 parts




dispersion acc. to






example 2,






30 minutes'






dispersion time






Aluminium oxide


100 parts



dispersion acc. to






example 2,






60 minutes'






dispersion time






PVA 40-88
 20 parts
 20 parts
 20 parts



Application behaviour
good
good
good



Average application
26.1
25.9
26.2



weight in g/m2 and
s = 0.4
s = 0.2
s = 0.3



standard deviation*





*Note: the printing test is carried out with coatings of virtually the same coating weight.






Coating Properties
















Aluminium oxide
100 parts




dispersion acc.





to example 2,





15 minutes'





dispersion time





Aluminium oxide

100 parts



dispersion acc.





to example 2,





30 minutes'





dispersion time





Aluminium oxide


100 parts


dispersion acc.





to example 2,





60 minutes'





dispersion time





PVA 40-88
 20 parts
 20 parts
 20 parts


Adhesion, surface
Good
Very good
Very good


and smoothness of
adhesion to
adhesion to
adhesion to


the coating
the film,
the film,
the film,



homogeneous
homogeneous
homogeneous



surface
surface
surface


Gloss at 20°/
24.6
26.3
28.8


standard
s = 0.4
s = 0.1
s = 0.3


deviation at





n = 5





Gloss at 60°/
46.3
49.7
54.7


standard
s = 0.2
s = 0.3
s = 0.3


deviation at





n = 5









Discussion of the Gloss Values

It can clearly be seen from the gloss values, that the dispersion according to the invention produces higher gloss values in the Inkjet coating after 60 minutes' dispersion time, than the dispersions produced by other methods. With photo-realistic coatings, a high gloss is desirable, as already disclosed in EP 0 732 219. The gloss values are lower than those in EP 0 732 219, but this is due to the different processes for the production of the Inkjet medium and not to the coating pigment. A spiral applicator is consciously used in this test to determine the contribution of the dispersion in the Inkjet coating to the gloss. With the cast-coating process used in EP 0 732 219, the gloss is primarily determined by the process itself.
Printing test (determined by 3 independent persons)
Top mark: 0.75 bottom mark: 6














Aluminium
Aluminium
Aluminium



oxide
oxide
oxide



dispersion
dispersion
dispersion



acc. to
acc. to
acc. to



example 2,
example 2,
example 2,



15 minutes'
30 minutes'
60 minutes'



dispersion
dispersion
dispersion


Dispersion used
time
time
time

















Four colour print Hewlett-Packard 550 C











Colour
Magenta/
1.25
1
1


intensity
Yellow/Cyan






Black
1
1
1


dot sharpness
Black in
1.5
1.25
1.25



colour





transitions
Colour to
1
1
1



colour






Black to
1.25
1
1



colour





Contours

1
1
1


Print

1.25
1.25
1


Halftone

1
1
1


Photo quality

1.25
1.25
1










Total evaluation
10.5
9.75
9.25


Average marks
1.17
1.08
1.03









Four colour print Epson Stylus Color 800











Colour
Magenta/
1.25
1
0.75


intensity
Yellow/Cyan






Black
1
1
0.75


Dot sharpness
Black in
1.25
1
1



colour





Transitions
Colour to
1
1
1



colour






Black to
1
1
1



colour





Contours

1
1
1


Print

1
1
1


Halftone

1.25
1
1


Photo quality

1
1
0.75










Total evaluation
9.75
9
8.25


Average mark
1.08
1.00
0.92









When using two different types of printer, the coating containing the dispersion with the longest dispersion time, according to example 2, produces the best results.










Colour densities









DIN













HP 550 C
Pap Pol




Filter




selected

























Aluminium
Aluminium
Aluminium




oxide
oxide
oxide




dispersion
dispersion
dispersion




acc. to
acc. to
acc. to




example 2,
example 2,
example 2,




15 minutes'
30 minutes'
60 minutes'



Dispersion
dispersion
dispersion
dispersion



used
time
time
time


















Paper white
0
0
0


Mean black
2.33
2.36
2.42


Mean yellow
1.67
1.69
1.73


Mean cyan
2.33
2.35
2.39


Mean
1.39
1.42
1.46


magenta





Total
7.72
7.82
8





















DIN


















Epson Stylus
Pap Pol



Color 800
Filter




selected























Aluminium





oxide





dispersion





acc. to
Aluminium oxide
Aluminium oxide



example 2,
dispersion acc.
dispersion acc.



15 minutes'
to example 2,
to example 2,


Dispersion
dispersion
30 minutes'
60 minutes'


used
time
dispersion time
dispersion time


















Mean black
3.07
3.08
3.14


Mean yellow
2.15
2.17
2.21


Mean cyan
3.23
3.25
3.33


Mean magenta
2.34
2.35
2.42


Total
10.79
10.85
11.1









When examining the colour densities, it can be seen that the coating containing the dispersion according to example 2 of the invention, with the longest dispersion time, reproduces the highest colour densities. This is desirable to obtain the most photo-realistic reproduction possible.
Example 4
Production of an Inkjet Coating


    Educts: aluminium oxide dispersion according to example 2 polyvinyl alcohol Mowiol 40-88 (Clariant)


Recipe and method for the production of Inkjet coating pigments:
The aqueous polyvinyl alcohol solution (Mowiol 40-88, Clariant) containing 12.14% solid matter is placed into a 400 ml beaker and a quantity of water is added so that, together with the aluminium oxide dispersions according to example 2, a solid content of 18% is obtained. The relevant dispersion is slowly dropped into the polyvinyl alcohol solution using a pipette, within 5 minutes, whilst stirring at 500 rpm. Once it has been added, stirring continues for a further 30 minutes at 500 rpm, to obtain a homogeneous coating pigment. The coating pigments are then de-aerated using a dessicator and a water jet pump. As a control, the actual solid matter, pH value and viscosity are determined after mixing the coating pigments.
The parts in the table below are understood to mean parts by weight in relation to the solid matter.
Coating pigment reference values















Aluminium oxide dispersion
100 parts




acc. to example 2,





15 minutes' dispersion





time





Aluminium oxide dispersion

100 parts



acc. to example 2,





30 minutes' dispersion





time





Aluminium oxide dispersion


100 parts


acc. to example 2,





60 minutes' dispersion





time





PVA 40-88
 18 parts
 18 parts
 18 parts


Actual solid content of
18.01
18.04
18.02


the coating pigment in %





pH-value
4.7
4.6
4.6







Viscosity, Brookfield in mPa s after 24 h










 5 rpm
912
813
748


 10 rpm
846
697
664


 20 rpm
702
589
534


 50 rpm
535
496
462


100 rpm
443
378
346


Comments on production of
good
good
good


coating pigments









The viscosity data obtained show that the lowest viscosities are obtained with the dispersion according to example 2 and the longest dispersion time. This is desirable, as the solid matter in the coating pigment can be increased still further without obtaining viscosities that are too high for application.
Method for the production of an Inkjet coating from the Inkjet coating pigment referred to above.
Matt-coated 110 g/m2 Inkjet paper (Zweckform no. 2576) is coated using an Erichsen Film Applicator device with a 60 micron wet film spiral applicator. The coating pigment applied is dried with a hot air dryer.
The coatings are then calendered three times at 10 bar pressure and 50° C. with a Gradek Oy (Trademark) laboratory calender.
Data for the coatings obtained:















Aluminium oxide
100 parts




dispersion acc. to





example 2,





15 minutes' dispersion





time





Aluminium oxide

100 parts



dispersion acc. to





example 2,





30 minutes' dispersion





time





Aluminium oxide


100 parts


dispersion acc. to





example 2,





60 minutes' dispersion





time





PVA 40-88
 18 parts
 18 parts
 18 parts


Application behaviour
good
good
good


Average coating weight
12.0
11.9
12.1


in g/m2 and standard
s = 0.4
s = 0.2
s = 0.3


deviation*





*Note: The printing tests were carried out with coatings of virtually the same coating weight.






Coating Properties
















Aluminium oxide
100 parts




dispersion acc. to





example 2,





15 minutes'





dispersion time





Aluminium oxide

100 parts



dispersion acc. to





example 2,





30 minutes'





dispersion time





Aluminium oxide


100 parts


dispersion acc. to





example 2,





60 minutes'





dispersion time





PVA 40-88
 18 parts
 18 parts
 18 parts


Adhesion, surface and
Very good
Very good
Very good


smoothness of the
adhesion to
adhesion to
adhesion to


coating
the paper,
the paper,
the paper,



homogeneous
homogeneous
homogeneous



surface
surface
surface


Gloss at 20°/
 5.4
 5.9
 6.7


standard deviation at
s = 0.4
s = 0.1
s = 0.3


n = 5





Gloss at 60°/
24.6
25.7
26.2


standard deviation at
s = 0.2
s = 0.3
s = 0.3


n = 5









Discussion of the Gloss Values

The gloss values clearly show that, after 60 minutes' dispersion time, the dispersion according to the invention produces higher gloss values in the Inkjet coating than dispersions produced by other methods. For photo-realistic coatings, a high gloss is desirable as already disclosed in EP 0 732 219. The gloss values are lower than those in EP 0 732 219, but this is due to the different processes for the production of the Inkjet medium and not to the coating pigment. A spiral applicator is consciously used in this test, to determine the contribution of the dispersion in the Inkjet coating to the gloss. With the cast-coating process used in EP 0 732 219, the gloss is primarily determined by the process itself.
Printing test (determined by 3 independent persons)
Top mark: 0.75 Bottom mark: 6














Aluminium
Aluminium
Aluminium



oxide
oxide
oxide



dispersion
dispersion
dispersion



acc. to
acc. to
acc. to



example 2,
example 2,
example 2,



15 minutes'
30 minutes'
60 minutes'



dispersion
dispersion
dispersion


Dispersion used
time
time
time

















Four colour print Hewlett-Packard 550 C











Colour
Magenta/
1.25
1.25
1


intensity
Yellow/Cyan






Black
1.25
1.25
1


Dot
Black in
1.5
1.25
1.25


sharpness
colour





Transitions
Colour to
1
1
1



colour






Black to
1
1
1



colour





Contours

1
1
1


Print

1.25
1.25
1


Halftone

1.25
1
1


Photo

1.5
1.25
1.25


quality














Total evaluation
11
10.25
9.5


Average mark
1.22
1.08
1.06









Four colour print Epson Stylus Color 800











Colour
Magenta/
1.5
1.25
1


intensity
Yellow/Cyan






Black
1
1
1


Dot
Black in
1.5
1.25
1.25


sharpness
colour





Transitions
Colour to
1.25
1.25
1



colour






Black to
1
1
1



colour





Contours

1
1
1


Print

1
1
1


Halftone

1.25
1
1


Photo

1.5
1.25
1.25


quality














Total evaluation
11
10
9.5


Average mark
1.22
1.11
1.06









When using two different types of printer, the coating containing the dispersion with the longest dispersion time according to example 2, produces the best results.










Colour densities









DIN













HP 550 C
Pap Pol




Filter




selected

























Aluminium
Aluminium
Aluminium




oxide
oxide
oxide




dispersion
dispersion
dispersion




acc. to
acc. to
acc. to




example 2,
example 2,
example 2,




15 minutes'
30 minutes'
60 minutes'



Dispersion
dispersion
dispersion
dispersion



used
time
time
time


















Paper white
0
0
0


Mean black
2.05
2.10
2.13


Mean yellow
1.49
1.54
1.58


Mean cyan
2.04
2.07
2.11


Mean





magenta





Total
6.86
7.03
7.17





















DIN


















Epson Stylus Color 800
Pap Pol




Filter




selected

























Aluminium
Aluminium
Aluminium




oxide
oxide
oxide




dispersion
dispersion
dispersion




acc. to
acc. to
acc. to




example 2,
example 2,
example 2,




15 minutes'
30 minutes'
60 minutes'



Dispersion
dispersion
dispersion
dispersion



used
time
time
time


















Mean black
2.89
2.96
2.98


Mean yellow
1.92
1.97
2.04


Mean cyan
2.96
3.03
3.09


Mean magenta
2.13
2.25
2.31


Total
9.9
10.21
10.42









When examining the colour densities, it can be seen that the coating containing the dispersion according to example 2 of the invention with the longest dispersion time reproduces the highest colour densities. This is desirable to obtain the most photo-realistic reproduction possible.
The dispersion according to the invention is eminently suitable for the production of Inkjet coating pigments and their further processing to produce high-gloss printing media, as can be seen from the examples given. The Inkjet media produced in this way have a particularly good print and gloss quality.

## Claims

1. Coatings comprising an aluminium oxide dispersion, wherein the coating has an aluminium oxide—binder weight ratio of 8:1 to 1:2 and the aluminium oxide is a high-surface-area, pyrogenically-produced aluminium oxide, characterized by a BET specific surface area of more than 115 m2/g and a Sears number of more than 8 ml/2 g and the dispersion has a mean particle size distribution of d50<137 nm.

2. A recording media comprising an aluminium oxide dispersion and substrate, wherein the dispersion contains high-surface-area, pyrogenically-produced aluminium oxide, characterized by a BET specific surface area of more than 115 m2/g and a Sears number of more than 8 ml/2 g and the dispersion has a mean particle size distribution of d50<137 nm.

3. The coating according to claim 1, further comprising coating pigments, which have a solids content of 15% or more.

4. The recording media according to claim 2, wherein the substrate has a surface weight of 80 to 250 g/m2.

5. The recording media according to claim 2, wherein the substrate is paper.

6. The recording media according to claim 2, wherein the substrate has a Cobb10 value of 0 to 60.

7. The recording media according to claim 2, wherein a water-impermeable sealing layer has been applied to the substrate.

8. The recording media according to claim 2, wherein the substrate is a polymer film.

9. A recording media according to claim 2 wherein the coatings are glossy and contain VP Alu 130 aluminium oxide particles and are built up originating from a dispersion with a mean particle size of d50<137 nm (d50 less than 200 nm; measured by dynamic light scattering).