Photoreactive titanium dioxide composition

SWEDEN

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PATENTS AND REGISTRATION OFFICE

PUBLISHING WRITING No. 355 253 intci G 03 c 1/72

Patent Application. No. 7167/69 Income 21 T 1969 Validity Day 21 V 1969

Ans. generally available on 25 X 1969

Ans. published and the pamphlet published on 9 TT 1973

Priority requested from 22 V 1968 (USA, 731 326)

KRONOS TITAN AS, FREDRIKSTAD, NORWAY

Inventor: HF Dantro, Sayreville, NJ USA

Agent: N Larfeldt

Photoreactive, powdery anatase-titanium dioxide material

The present invention relates generally to a titanium dioxide composition having photosensitive properties which can be used in technical systems designed to react to the effects of light, namely photographic emulsions, copy paper and the like.

Many types of photosensitive materials are used in photographic and copy paper systems. Among these are carbon black and zinc oxide. Although carbon black has excellent conductive properties, it has few or none of the photoreactive properties necessary for the use of in-copy paper systems, while zinc oxide, although used with limited success, has low opacity in copy paper. Although most technical grade titanium dioxide pigments have a weak photoreactivity, it is not sufficient for use in copy paper systems. However, the particular titanium composition obtained according to the present invention is not a pigment grade material, but is specifically intended to have a high degree of photoreactivity and opacity in paper systems and is thus suitable for the copy paper industry.

The present powder composition of photoreactive titanium dioxide has the crystal structure of the anatase and comprises finely divided particles having individual particle sizes of 100-500 angstroms, a sulfur content, count Dupl. kl. C 09 c 1/36 ρ

as a percentage of S, which is within 0.03-0.3%, an area of ​​60-250 m / g, a moisture content of 2-10 µm and a photoreactivity, measured by mandelic acid test, as a change in reflection of at least 5 units for 2 minutes when exposed to ultraviolet radiation, characterized by a metal oxide coating of one or more of the oxide PbO, Bi₂O, TiO₂, SiO₂, ZnO, Α1₂Or a mixture thereof in an amount of 0.2 µl - 2.0 µl metal oxide, based on the weight of the titanium dioxide composition.

This type of composition of photoreactive, powdered titanium dioxide is prepared by hydrolyzing a solution of titanium sulfate iron sulfate, obtaining aqueous titanium dioxide, filtering, bleaching and washing to remove soluble iron salts therefrom, the bleached aqueous oxide being substantially free of iron , but contains from 5 to 15 sulfuric acid joined to the aqueous oxide, forming an aqueous mass of the bleached aqueous oxide, treating the pulp with a sufficient amount of an ammoniacal compound consisting of ammonium hydroxide, ammonium carbonate or ammonia gas, to raise the pH of the pulp to at least 6.0, washing the neutralized aqueous oxide to remove substantially all the ammonium sulfate formed, of the washed aqueous oxide at 250-700 ° C, wherein soft aggregates of titanium dioxide crystals are formed with an individual particle size of 100-500 Å and grinding the aggregates to a fine powder which is slurried in water and added to a soluble metal salt of the metal lead, bismuth, titanium, zinc, silicon, aluminum or mixtures thereof , then t

the metal oxide or metal oxides are precipitated on the surface of the titanium dioxide composition in amounts of 0.2 µ - 2.0 µm of metal oxide, based on the weight of the titanium dioxide composition, after which the coated titanium dioxide composition is filtered, washed, dried and ground.

Before further describing the present invention, it is desirable that the term photoreactivity be defined. A photo-reactive material is one which reacts in a photosensitive system and especially in a copy paper system to produce an image when exposed to ultraviolet light.

The titanium compositions obtained according to the present invention were examined for photoreactivity and found to meet certain standards which have been selected as being technically suitable.

These tests and their standards are described below.

The almond acid test for the photoreactivity of the titanium dioxide g of the titanium composition is mixed with a sufficient amount of an aqueous solution of 0.5 mole of almond acid to form a soft paste. The paste is placed on a microscope slide (127 x 127 x 1 mm) of window glass, covered with a thick glass plate (127 x 127 mm double-thickness window glass) and pressed to distribute the paste over a surface of approximately 76 mm in diameter, slide (25). x 76 χ 1 mm) was used between the plates as dividers. The edges of the plates are bonded together with 25 mm strips to prevent evaporation. The initial reflection of the paste is measured through the slide using Colormaster

Differential Colorimeter with green filter. The plates are placed on a rotating disk, with the slide side up, and arranged below them in equilateral triangle 33 cm from center to center, about 33 cm above the three solar lamps (275 watts) of the turntable. Prior to each test, each lamp's ultraviolet radiation and weak lamps were exchanged. Measurements of reflection are made on the pastes at appropriate intervals and the change of reflection over time is determined. This value is a measure of the photoreactivity of the titanium composition. A change in reflection of at least 5 units for 10 minutes is required as a minimum to obtain acceptable images in copy paper systems, photographic emulsions and similar technical uses.

The aqueous oxide used can be prepared by any well known method of hydrolysis. In such processes, a solution of titanium sulphate iron sulphate is formed by dissolving titanium-containing iron ore in concentrated sulfuric acid to form so-called digestion cake, which is dissolved in water or weak acid. Such a solution is subjected to hydrolysis after clarification and concentration by diluting and boiling to precipitate the titanium content. The resulting aqueous titanium oxide is then washed and bleached to give ferrous sulfate and other staining

30 °. contaminants are removed. Such hydrolyzed titanium oxide also contains, after careful washing 5^-15 % combined or absorbed in the composition.

In order to obtain the present composition, it is necessary to reduce the content of H₂SO ^ present in the aqueous oxide.

Ammonia gas, ammonium hydroxide or ammonium carbonate is then added to a mass of aqueous titanium oxide to give ammonium sulfate, which can be easily removed by washing. The amount of ammonium compound added is the amount of. is required to raise the aqueous ammonium hydroxide mass to at least 6.0. Raising the pH above 8.0 does not further improve the product, but only increases the process costs.

After the appropriate amount of ammonium compound is added, liquid is removed from the aqueous titanium dioxide, which is washed until the content of sulfate in the dry product is reduced below 0.3 calculated as S on the dry weight of titanium dioxide. After washing, the neutralized aqueous titanium dioxide is dried at 250 ~ 700 ° C until the average particle size of the titanium dioxide crystal is 100-500 Å. The dry product is then ground to decompose the soft aggregates formed during the drying step, slurried in water and coated with various metal oxide compounds.

It has been found that coatings of one or more of the following metal oxides are particularly useful: lead oxide, bismuth oxide, zinc oxide, titanium oxide, silica and alumina.

The amount of metal coating of the powdered titanium dioxide composition should be 0.02 to 2.0 µm of metal oxide based on the weight of the TiCl 2 composition.

The metal oxide coating is applied by forming an aqueous slurry of the titanium dioxide composition, adding to the slurry a soluble metal salt and precipitating the aqueous oxide of the metal on the surface of the titanium dioxide composition. The coated composition is then dried and ground.

The dry product is then analyzed to determine the various properties.

The average particle size is determined by X-ray diffraction analysis. The moisture content of the product is determined by heating 1 g of sample of the product for 1 hour at 750 ° C and determining the weight loss.

The invention is further illustrated by the following examples.

Example 1. Aqueous titanium dioxide was prepared by adding a solution of titanium sulfate iron sulfate to hot water and boiling. The titanium sulfate solution used had the following composition:

Ten₂ 250 gpl

hrs₂S0 ^ 500 gpl

FeSOjj 169 gpl

hrs₂SE₄/Ten₂ 2,0

Spec. weight 1.675 at 60 ° C,

3000 ciP of this titanium solution heated to 96 ° G was added to 750 cn? water heated to 96 ° C within 16 minutes. The whole mixture was then heated to boiling and boiled for 3 hours to complete the hydrolysis. 790 cm 2 of hot water was added to the mixture to reduce the concentration to

165 gpl TiO₂.

The resulting aqueous titanium oxide was filtered, washed free of soluble iron salts, bleached with 10% sulfuric acid and 0.1% metallic aluminum for 1 hour at 80 ° C and 20% dry substance, then filtered and washed with water until iron-free. The washed filter cake contained 10% sulfuric acid, based on TiO₂. 2143 g of the filter cake containing 35 t of dry substance were mixed with 1,607 cm 2 of water to obtain a pulp containing 20 dry substance. 159 g of ammonium hydroxide diluted with stirring with 178 cm 2 of water were added to the aqueous oxide pulp at 60 ° C to raise the pH of the pulp to 7.1.

The neutralized solid was filtered and washed with 15 liters of water and dried at 350 ° C for 1 1/2 hours, thereby reducing the moisture content of the material to 6.2%. The dried material was lightly steamed then.

400 g of powdered titanium dioxide composition was slurried in water to 23 dry substance and to the slurry a lead acetate solution was added in sufficient quantity to obtain 0.2 PbO based on TiO₂After the mixture was thoroughly stirred, the slurry was treated with NH 3 OH in sufficient quantity to obtain pH 7 5 to precipitate the lead as aqueous oxide. The pH of the slurry was kept for one hour at 7.5. The pulp was then dewatered and the filter cake washed thoroughly with water to remove soluble salts. The washed cake was then dried and ground.

In order to show the coating's effectiveness on the present powdered titanium dioxide composition, images were prepared on a substrate using an uncoated product and the required coating. the product of Example 1.

The images were prepared by mixing the titanium dioxide composition with water and a polyacrylate and coating a substrate with the mixture. The coating on the substrate was then subjected to a redox reaction to develop the image. The details for producing the image are the same as those described in French Patent Specification 1,482,724.

Imaging properties were determined as maximum optical density and velocity using the method described in The American Standards Association in a publication entitled: American Standard Sensitometry of Photographic Papers, March 17, 1966.

When the uncoated composition was used, the image obtained had a maximum optical density of 0.8 at the rate of 16. When an image was made using the coated product of Example 1, the maximum optical density increased about 25 without decreasing the velocity.

Examples 2-7. The procedure of Example 1 was repeated using various agents to form the metal oxide coatings. Chlorides of bismuth, titanium, aluminum, silicon and zinc were added to form the respective metal coatings on the titanium dioxide composition. In Example 5, a mixture of bismuth and titanium chloride was used, while in Example 6 sodium metasilicate was added as a SiO₂-source. The agents used and their amounts are given below:

<td>Example</td><td>Salt used</td><td>Metal oxide obtained</td><td>Amount of oxide</td>

<td> 2</td><td>BiClj</td><td>Bi₂0,</td><td> 0,2</td>

<td> 3</td><td>TiCl₄</td><td>Ten₂</td><td> 0,2</td>

<td> 4</td><td>Zinc Carbon₂</td><td>ZnO</td><td> 0,2</td>

<td> 5</td><td>BiClj + TiCljj</td><td>Bi₂0J + Ti0₂</td><td> 0,2+0,2</td>

<td> 6</td><td>NapSiO ^</td><td>Si0₂</td><td> 0,2</td>

<td> 7</td><td>AICI</td><td>ai₂O₃</td><td> 0,2</td>

When the images were prepared using these coated compositions, the imaging intensity was increased from 10 Ά to 25% over the images obtained using uncoated product without decreasing the speed.