Pyrogenically produced aluminum oxide

320 kg/h of previously vaporized aluminum trichloride (AlCl 3 ) are burned together with 100 Nm 3 /h hydrogen and 450 Nm 3 /h air in a burner of a known design.

After the flame reaction the fine-particle high surface area aluminum oxide is separated in a filter or cyclone from the hydrochloric acid gases generated at the same time, whereby any HCl traces still adhering are then removed by treatment with moist air at elevated temperature.

The high surface area pyrogenic aluminum oxide produced exhibits the physicochemical properties indicated in Table 1. Data for the commercially available pyrogenic aluminum oxide produced by Degussa-Hüls AG in Frankfurt am Main is also included in Table 1 for the purposes of comparison. (Trade name Aluminumoxid C).

Measurement of the Sears index is described in EP 0 717 008 which is relied on and incorporated herein by reference.

Manufacture of the Coating Slip and Coating

30 parts by weight of polyvinyl alcohol Mowiol 28-99 (from the Clariant company), 80 parts by weight of Sipernat 310 (precipitated silicic acid, Degussa-Hüls AG) and in each case 20 parts by weight of the pyrogenically produced oxides described above are used. The solids content is adjusted to 18%. This aqueous dispersion is stirred for 30 min at 3000 rpm with a high-speed mixer. This coating slip is applied to a 70 g/m 2 base paper by means of a profiled doctor bar. The coating slip is dried with hot air. The rate of application in the dry state is 10 g/m 2 .

Manufacture of the Coating Slip

35 parts by weight of polyvinyl alcohol Mowiol 28-99 (Clariant) and in each case 100 parts by weight of the pyrogenically produced oxides described above are used. The solids content is adjusted to 15%. This dispersion is homogenized. This coating slip is applied to a 100 micrometer thick polyester film by means of a profiled doctor bar. The coating slip is dried with hot air. The wet film thickness is 120 micrometers.

Manufacture of the Coating Slip

70 parts by weight of polyvinyl alcohol Mowiol 5-88 (Clariant), 20 parts by weight of PVP/VA W-735 (polyvinyl pyrrolidone-polyvinyl acetate copolymer, from the ISP company), 10 parts of polyvinyl pyrrolidone K-30 (ISP) and in each case 50 parts by weight of the pyrogenically produced oxides described above are used.

The solids content is adjusted to 20%. The coating slip is applied by means of a profiled doctor bar to a 100 micrometer thick polyester film in a wet film thickness of 80 micrometers. The coating slip is dried with hot air.

These results illustrate the advantages for the utilization of the aluminum oxide Alu 130 according to the invention.

For the purposes of comparison, Aluminumoxid C and MOX 170 (both Degussa-Hüls AG Frankfurt) were used in addition to the high surface area aluminum oxide 130 according to the invention.

Manufacture of the Coating Slip and Coating

Solution A is a 10 percent (relative to PVA) aqueous solution of polyvinyl alcohol (solid, abbreviation PVA) Mowiol 28-99 from Clariant.

Distilled water is added to this solution to form a solution B. Sipernat 310 (precipitated silicic acid, Degussa-Hüls AG) and each of the pyrogenically produced oxides are added to this solution B to form the coating slip C. This coating slip exhibits a mass ratio of 80 parts Sipernat 310 to 20 parts pyrogenic oxide to 30 parts PVA, relative to the solids. The total solids content is 18%.

The coating slip C is dispersed for 30 minutes at 3000 rpm in a high-speed mixer. The coating slip is then applied to a 70 g/m 2 base paper by means of a profiled doctor bar and dried with hot air. The rate of application in the dry state is 10 g/m 2 .

The printing tests are performed on an Epson Stylus Color 800 at maximum resolution (1440*720 dpi).

Coating Slip Formulation

For the purposes of comparison, Aluminumoxid C and MOX 170 (both Degussa-Hüls AG Frankfurt) are used as additional oxides in addition to the high surface area aluminum oxide 130 according to the invention.

An aqueous dispersion is produced from these three different pyrogenic oxides using a rotor-stator system (Ultra-Turrax) for a dispersion period of 30 minutes in a double-walled vessel (with water cooling). A 25 percent dispersion (relative to the solid) (w=0.25) is produced containing a proportion by weight of 0.5% acetic acid.

Manufacture of the coating slip

Solution A is an 8 percent (relative to PVA) aqueous solution of polyvinyl alcohol (solid, abbreviation PVA) Mowiol 40-88 from Clariant.

This solution A is diluted with distilled water to produce a solution B. Each of the various metal oxide dispersions is added to solution B to form a coating slip C. The coating slip C exhibits a mass ratio of 100 parts pyrogenic oxide to 25 parts PVA, relative to the solid. The total solids content is 15%. This coating slip is applied by means of a profiled doctor bar to a 100 micrometer thick polyester film and dried with hot air. The wet film thickness is 120 micrometers.

It was not possible to manufacture an adhesive coating using Aerosil MOX 170.

For this mixed oxide the proportion had to be increased to a ratio of 100 parts Aerosil to 40 parts PVA, relative to the solids ratio.

Coating Slip Formulation

For the purposes of comparison, Aluminumoxid C and MOX 170 (both Degussa-Hüls AG Frankfurt) were used as additional oxides in addition to the high surface area aluminum oxide 130 according to the invention.

Solution A is a 20 percent (relative to PVA) aqueous solution of polyvinyl alcohol (solid, abbreviation PVA) 4-88 from the Clariant company.

Solution B is a 50 percent (relative to the copolymer) aqueous solution of a copolymer of vinyl pyrrolidone and vinyl acetate (abbreviation PVP/VA) W 735 from the ISP company.

Solution C is a 20 percent (relative to PVP) aqueous solution of polyvinyl pyrrolidone (abbreviation PVP) K−30 from ISP.

These three solutions are mixed in the above sequence and in the following ratio (70 parts by weight PVA: 20 parts PVP/VA: 10 parts PVP, relative to the solid) and diluted with water so that a coating slip with a total solids content of 20% is obtained by addition of 50 parts of each of the metal oxides. This dispersion is dispersed for 30 minutes at 10000 rpm in a suitable dispersion device such as an Ultra-Turrax apparatus from Janke & Kunkel company with a rotor-stator system. The coating slip is applied by means of a profiled doctor bar to a 100 micrometer thick polyester film in a wet film thickness of 80 micrometers and dried with hot air.

Advantages of the Present Invention

In comparison to the commercially available products (Aluminumoxid C and Aerosil MOX 170, both Degussa-Hüls AG) the aluminum oxide according to the invention exhibits very good properties in the manufacture of inkjet receiving layers both alone and in combination with other fillers. It is characterized by enhanced brilliance and depth of color. These properties are of particular benefit in ink-receiving layers that are used for photographic quality reproduction. It also demonstrates improved color stability in the presence of water and light, which is advantageous for outdoor applications.

Further variations and modifications will be apparent to those skilled in the art from the foregoing and are intended to be encompassed by the claim appended hereto.

German priority application 199 43 291.0 is relied on and incorporated herein by reference.