Spray-dried dye compositions, process for the production and use thereof

Abstract

The invention relates to spray-dried, washfast dye compositions, preferably in the form of pigment powders, having a bleeding rate of 0.5% and consisting of water-soluble functional dyes, preferably food dyes, which are firmly incorporated in a silica matrix. Apart from low bleeding of dye, these compositions are remarkable for their high stability to pH changes and/or ascorbic acid. The invention is also directed to the production of the dye compositions and the use thereof. The dye compositions are preferably employed in coloring foods, cosmetics, pharmaceutical products, but also in other uses.

Claims

1. A process for the production of spray-dried dye compositions comprising water-soluble functional dyes incorporated in an organosilane-based silicon dioxide matrix with bleeding rates of 0.5%, comprising the steps of: a) producing a silicon dioxide sol by weak acid hydrolysis of alkoxysilanes (organosilanes) in an aqueous organic solvent mixture at a pH of 5 to 6.5, wherein hydrolysis is effected by an aqueous acidic ion exchanger and producing the silicon dioxide sol is performed for 48 hours; b) adding a water-soluble dye; c) gelling by spray-drying the dyed sol to provide resulting compositions, and d) temperature treating the resulting compositions for 5 to 48 hours at a temperature above 50 C., wherein the bleeding rate of the dye compositions is measured by contacting a 0.1% aqueous solution of nonylphenol ethoxylate for at least 1 hour with stirring at room temperature.

2. The process according to claim 1, wherein the temperature treatment is carried out at temperatures of from above 50 C. to 300 C.

3. The process according to claim 1, wherein the mixture fed into the spray-drying process contains no further additives.

4. The process according to claim 1, wherein the water-soluble functional dyes are natural or synthetic food dyes used in food products, oral pharmaceutical preparations or cosmetics.

5. The process according to claim 1, wherein the temperature treatment is carried out at temperatures of from 70 C. to 150 C.

6. The process according to claim 1, wherein the dye compositions are further coated with a dye-free SiO.sub.2 layer.

7. The process according to claim 1, wherein the temperature treatment is carried out for a time period of 24 hours.

Description

EXAMPLE 1

(1) Production of a Blue Color Pigment by Spray-drying a Dyed TEOS Hydrolyzate

(2) 20 g of tetraethoxysilane (TEOS) is mixed with 50 g of distilled water, 10 g of ethanol and 4.0 g of glacial acetic acid and stirred vigorously at room temperature using a magnetic stirrer. The TEOS in the liquid initially forms a separate phase (turbid emulsion), but after about 2 hours a clear solution is formed as a result of hydrolysis of TEOS into silicic acid and further condensation to form an SiO.sub.x sol.

(3) 0.6 g of FD&C Blue 1 (pure dye) is dissolved in the above solution.

(4) The resulting blue liquid is processed into a powder in a BCHI B290 Mini Spray Dryer (inlet temp.=140 C.).

(5) Residual solvents are removed from the powder by secondary drying at elevated temperature.

(6) A pigment with a bleeding rate of 0.01% is obtained.

EXAMPLE 2

(7) Production of a Purple Color Pigment by Spray-drying a Dyed TEOS Hydrolyzate

(8) 20 g of tetraethoxysilane (TEOS) is mixed with 4.5 g of distilled water, 10.5 g of ethanol and 5.0 g of 0.001 N HCl and stirred vigorously at room temperature for 48 hours using a magnetic stirrer.

(9) The resulting sol is dyed by adding 3.0 g of Purple Sweet Potato Powder E-500 (20% in maltodextrin), which dye must be completely dissolved by stirring at RT for at least 1 hour.

(10) The dyed sol is immediately processed into a powder in a BCHI B290 Mini Spray Dryer (inlet temp.=130 C.).

(11) Residual solvents are removed from the powder by secondary drying at elevated temperature.

(12) The bleeding rate of the obtained pigment is around 0.1%.

EXAMPLE 3

(13) Production of a Blue Color Pigment by Spray-drying a Dyed TEOS Hydrolyzate

(14) 20 g of tetraethoxysilane (TEOS) is mixed with 4.5 g of distilled water, 10.5 g of ethanol and 5.0 g of 0.001 N HCl and stirred vigorously at room temperature for 48 hours using a magnetic stirrer.

(15) The resulting sol is dyed by adding 0.6 g of FD&C Blue 1 with stirring and processed into a powder in a BCHI B290 Mini Spray Dryer (inlet temp.=130 C.).

(16) The powder is subjected to secondary drying at elevated temperature, thereby removing residual solvents.

(17) The bleeding rate of the obtained pigment is around 0.02%.

EXAMPLE 4

(18) Production of a Blue Color Pigment by Spray-drying a Dyed TEOS Hydrolyzate Produced by Heterogeneous Catalysis

(19) 20 g of tetraethoxysilane (TEOS) is mixed with 9.5 g of distilled water, 10.5 g of ethanol and 5.0 g of strongly acidic Dowex HCR-W2 ion exchanger and stirred vigorously at room temperature for 48 hours using a magnetic stirrer.

(20) The resulting sol is filtered from the ion exchanger, dyed by adding and admixing 0.6 g of FD&C Blue 1 and processed into a powder in a BCHI B290 Mini Spray Dryer (inlet temp.=130 C.).

(21) Residual solvents are removed from the powder by secondary drying at elevated temperature.

(22) The bleeding rate of the obtained pigment is around 0.01%.

EXAMPLE 5

(23) Production of a Blue Color Pigment by Spray-drying a Dyed TEOS Hydrolyzate and Subsequent Coating with a Dye-Free SiO.sub.2 Layer

(24) 20 g of tetraethoxysilane (TEOS) is mixed with 4.5 g of distilled water, 10.5 g of ethanol and 1.0 g of glacial acetic acid and stirred vigorously with a magnetic stirrer, starting with 50 C. for 8 hours, followed by room temperature for 96 hours. The resulting sol is dyed by adding and admixing 0.6 g of FD&C Blue 1 and processed into a dry powder in a BCHI 8290 Mini Spray Dryer (inlet temp.=140 C.).

(25) Residual solvents are removed from the powder by secondary drying.

(26) The bleeding rate of the obtained pigment is around 0.2%.

(27) 5 g of the obtained dry pigment is stirred in 30 g of tetraethoxysilane using a magnetic stirrer and added with 0.3 g of concentrated HCl. The mixture is stirred at RT for 24 hours. Thereafter, the pigment is filtered, washed with water and ethanol and dried.

(28) The bleeding rate is 0.005%.

EXAMPLE 6

(29) Production of a Blue Color Pigment by Spray-drying a Dyed TEOS Hydrolyzate

(30) 20 g of tetraethoxysilane (TEOS) is mixed with 50 g of distilled water, 10 g of ethanol and 4.0 g of glacial acetic acid and stirred vigorously at room temperature using a magnetic stirrer. The TEOS in the liquid initially forms a separate phase (turbid emulsion), but after about 2 hours a clear solution is formed as a result of hydrolysis of TEOS into silicic acid and further condensation to form an SIO.sub.x sol.

(31) 0.6 g of FD&C Blue 1 (pure dye) is dissolved in the above solution.

(32) The resulting blue liquid is processed into a powder in a BCHI B290 Mini Spray Dryer (inlet temp.=140 C.).

(33) The powder is heat-treated using temperature treatment in a drying oven at 110 C. for a time period of 15 hours.

(34) A pigment with a bleeding rate of 0.005% is obtained.

EXAMPLE 7

(35) Production of a Purple Color Pigment by Spray-drying a Dyed TEOS Hydrolyzate

(36) 20 g of tetraethoxysilane (TEOS) is mixed with 4.5 g of distilled water, 10.5 g of ethanol and 5.0 g of 0.001 N HCl and stirred vigorously at room temperature for 48 hours using a magnetic stirrer.

(37) The resulting sol is dyed by adding 1.2 g of aqueous elderberry extract (resin-purified, 50% dye content).

(38) The dyed sol is immediately processed into a powder in a BCHI B290 Mini Spray Dryer (inlet temp.=130 C.).

(39) The powder is heat-treated using temperature treatment in a drying oven at 140 C. for a time period of 24 hours.

(40) The bleeding rate of the obtained pigment is around 0.05%.

COMPARATIVE EXAMPLE 1

(41) Production of a Color Pigment by Spray-drying a Dyed Kstrosol Solution

(42) 45 g of Kostrosol 1520 (an aqueous liquid containing 20% SiO.sub.2, commercially available from Chemiewerk Bad Kstritz, Germany) is added with 50 g of distilled water and 0.9 g of FD&C Blue 1 (pure dye).

(43) The obtained blue liquid is immediately processed into a powder in a BCHI B290 Mini Spray Dryer.

(44) Residual solvents are removed from the powder by secondary drying at elevated temperature.

(45) A pigment with a bleeding rate of 7.3% is obtained.

COMPARATIVE EXAMPLE 2

(46) Production of a Color Pigment by Spray-drying a Dyed TEOS Hydrolyzate Obtained by Hydrolyzing with Strong Acid

(47) 20 g of tetraethoxysilane (TEOS) is mixed with 10.5 g of ethanol and 9.5 g of 0.1 N HCl and stirred vigorously at room temperature for 24 hours using a magnetic stirrer.

(48) The resulting sol is dyed by adding and admixing 0.6 g of FD&C Blue 1 and processed into a powder in a BCHI B290 Mini Spray Dryer (inlet temp.=130 C.).

(49) This powder is subjected to secondary drying at elevated temperature and made free of residual solvents in this way.

(50) The bleeding rate of the obtained pigment is around 0.01%.

(51) Instead of blue, as desired, the color of the powder is green.