DE1592976C3 - Process for the production of a photosensitive titanium dioxide with the crystal structure of anatase - Google Patents

Description

Various types of photosensitive materials have been used in systems that are sensitive to exposure of light address like soot and zinc oxide used. Carbon black has excellent photoconductive properties Properties, but little or no light-sensitive properties, which are suitable for use in Copier paper systems are necessary, while zinc oxide, although used with limited success, have a low opacity for copier papers.

From J. Barksdale and Titanium, 1949, pp. 382 and 385 and from French patent specification 12 31 998 are various types of titanium dioxides and their production known. According to the first-mentioned reference, a titanium dioxide pigment is specified, the predominant of which Part of the particles are from about 0.2 microns to about 7 microns in diameter.

The German patent specification 9 54 280 describes a process for the production of an anastitanium dioxide pigment with a particle size of 0.1-0.5 microns.

DT-AS 10 70 318 describes a process for the production of anatase with improved color strength known, in which phosphoric acid or phosphate is added as an antirutilizing agent before annealing. However, none of the cited references give any indication of the manufacture of a photosensitive Titanium dioxide, which can be used as a light-sensitive component in light-sensitive systems.

The object of the invention is to provide a photosensitive titanium dioxide, which due to its Photosensitivity or photoreactivity and due to its opacity for use in photosensitive Systems and especially in copy paper systems is particularly suitable.

This object is achieved by a method for producing a light-sensitive titanium dioxide with the crystal structure of anatase, in which aqueous titanium oxide is bleached, washed, optionally treated with a phosphorus and / or potassium compound, heated, ground and sifted, which is characterized in that the washed water-containing titanium oxide with a maximum of 0.3 wt .-% of a phosphorus and / or potassium compound, calculated as P2O5 or K2O and based on TiO ₂ , treated, heated to a temperature of 760-825 ⁰ C, up to an average Particle size of 0.05 to 0.15 μm is ground and sifted so that at least 70% of the particles have a diameter between 0.03 and 0.13 μm.

According to one embodiment of the invention, the heated TiO _{2 is} steam-milled at a steam / TiO 2 ratio of 5: 1.

An essential difference between the process according to the invention and known processes is that the titanium hydrate, which is essentially free of iron after its bleaching, without addition or after addition of only small amounts of a phosphorus and / or potassium compound of at most 0.3 wt. %, calculated as P ₂ O ₅ or K ₂ O, is calcined. In addition, the titanium hydrate is calcined at relatively low temperatures until the calcined anatase titanium dioxide contains no more than a maximum of 0.15% sulfur, calculated as S, based on TiO ₂ . This particular type of calcination results in a soft calcined product. A material calcined in this way would definitely be under-calcined, based on previous titanium dioxide pigment production processes, and consequently has lower pigment properties such as whitening power, hiding power, oil absorption and chalking resistance compared to the commercially available forms of T1O2 pigment.

In addition, the soft calcined product is subjected to a milling process to form a finely divided material subject. The following was found for the spectral characteristics of this ground material described test has a value of at least +4. In contrast, it has a commercially available TiO2 pigment usually a spectral characteristic of only + 2 to 0.

The invention also relates to a photosensitive titanium dioxide with the crystal structure of anatase, which has been obtained by the process according to the invention.
The anatase crystal structure obtainable according to the present invention is a non-pigment titanium dioxide and contains finely divided particles having an average individual particle size of 0.05 to 0.15 microns, of which at least 70% by weight of the particles are of one size which falls in the range of 0.03 microns to 0.13 microns; a spectral characteristic of at least +4; a sulfur content, calculated as% S, below 0.15; a surface area of 14 to 35 m² / g and a photoreactivity, measured according to the mandelic acid test, accordingly

a change in reflectance of at least 5 units in 10 minutes when there is ultraviolet radiation is exposed.

In the present case, light-sensitive or photoreactive titanium dioxide is understood to mean titanium dioxide, that in a photosensitive system and particularly in a copy paper system when exposed to ultraviolet exposure to produce an image.

The titanium dioxide obtained according to the invention was examined with regard to its photosensitivity, and it has been found to conform to certain standard values considered commercially available usefully selected.

These tests and their standard values are described as follows.

Mandelic acid test of photosensitivity

of titanium dioxide

10 g of titanium dioxide are mixed with a sufficient amount of aqueous 0.5 molar mandelic acid solution Mixed forming a soft paste. The paste is placed on a microscope slide glass plate

(12.7 cm 12.7 cm 1 mm) and with a thick glass plate (12.7 cm 12.7 cm; double the thickness of window glass) and pressed to make the paste Spread over an area approximately 3 inches in diameter. There will be microscope slides (2.5 cm 7.6 cm 1 mm) used as a spacer between the panels. The ends of the panels will be connected to each other with 1 inch (2.5 cm) adhesive tape to prevent evaporation. The initial reflection the paste through the microscope slide glass plate is measured using a differential colorimeter with a Green filter measured. The plates are placed on a rotating turntable with the microscope slide side brought up. Underneath are three sunlight lamps (275 watts) in one equilateral Triangle, 33 cm from center to center, placed about 33 cm above the turntable. Before each measurement, the Ultraviolet intensity of the lamp is measured and weak lamps are replaced.

Reflection measurements are carried out at suitable intervals and the change is shown in% Reflection per time determined. This quantity is a measure of the sensitivity of titanium dioxide to light. One Change in reflectance of at least 5 units in 10 min is considered acceptable for commercial applications Minimum required.

Test of the spectral characteristics of the T1O2

The titanium dioxide is mixed with a soy alkyd binder solution containing carbon black and the mixture is formed into a paste. The amounts of TiO ₂ and carbon black present in the paste are 3.3 and 0.1 g, respectively. The paste is then sprayed onto a sheet of lacquer and the wet film is immediately examined in a Colormaster colorimeter. The spectral characteristic of the TiO ₂ is measured by subtracting the red reflection from the blue reflection and comparing these results with the spectral characteristic of a previously determined TiO ₂ standard.

The invention is illustrated in the following examples.

example 1

A titanium hydrate is prepared by adding a titanium sulfate solution to hot water and the mixture is boiling. The titanium sulfate solution used has the following analytical data:

TiO ₂
H2SO4
FeSO ₄
H ₂ SO ₄ ZTiO ₂
Spec. Weight

250 g / l

500 g / l

169 g / l

2.0

1.675 at 6O ⁰ C

60

3000 ml of this titanium solution, heated to 96 ° C., are added to 750 ml of water heated to 96 ° C. over a period of 16 minutes. The entire mixture is heated to a boil and cooked for three hours to complete hydrolysis. 790 ml of hot water are added to the mixture in order to lower _{the concentration to 165 g / l TiO 2.}

The hydrate is filtered, washed free of soluble salts, containing 10% H ₂ SO ₄ and 0.1% aluminum metal for one hour at 8O ⁰ C bleached at a solids content of 20%, then filtered and washed with water free from iron. The filter cake is then treated with 0.1% phosphoric acid and 0.22% potassium hydroxide, calculated as P2O5 or K ₂ O, based on TiO ₂ weight, and the treated titanium hydrate is calcined at 780 ° C. for 1½ hours to give a soft calcined TiO ₂ material. The soft calcined material is then subjected to steam milling at a steam / pigment ratio of 5/1. After grinding, the calcined TiO ₂ material has the following properties:

1. An average particle size of 0.10 microns with 70% by weight of the particles from 0.04 to 0.11 microns.

2. A sulfur content of 0.09%, calculated as S, based on TiO ₂ weight.

3. A spectral characteristic of +4.4.

4. A surface area of 14 m ² / g.

5. Its photoreactivity in 0.5 molar mandelic acid solution, measured as reflection loss, is when exposed to ultraviolet radiation, 12.3 in 10 minutes.

Example 2

Another TiO ₂ material was prepared as described in Example 1, with the exception that the bleached hydrate was treated _{with 0.1% phosphoric acid and 0.1% potassium hydroxide, calculated as P2O5 and K 2} O, based on TiO _{2 weight} would. The hydrate is calcined at 800 ° C. for one hour and ground as described in Example 1.

The TiOrMaterial has the following properties:

1. An average particle size of 0.06 microns, with 70% by weight of the particles from 0.03 to 0.07 microns.

2. A spectral characteristic of +6.6.

3. A sulfur content of 0.1%, calculated as S.

4. A surface area of 29.1 m ² / g.

5. Its photoreactivity, measured as reflection loss in 0.5 molar mandelic acid solution, is 20.4 in 10 minutes if exposed to ultraviolet radiation.

Examples 3 and 4

The same procedure is used again in these examples with the exception that none Treatment of the hydrates is done prior to calcination. The calcination temperatures are 770 ° C or 820 ° C.

The results are shown together with those of Examples 1 and 2 in the table below listed.

In order to compare the products of the present invention with a TiO ₂ pigment of commercially available form, the following comparison pigment is prepared:

A titanium hydrate similar to that in the previous examples is treated with 0.25% phosphoric acid and 0.39% potassium hydroxide, calculated as P ₂ O ₅ or K ₂ O based on TiO _2. The treated hydrate is then for two hours at 985 ° C in the usual commercial forms of TiO ₂ -Pigmen-

tes used type calcined. The calcined TiO ₂ is then ground. The results are given in the table below.

You can see this in comparison with a TiO ₂ pigment in commercially available form or conventional forms of the

table

_{ZnO pigment that the TiO 2} obtainable according to the invention has both a superior photosensitivity and good opacity and it is therefore particularly well suited for use in photosensitive systems of the copy paper type.

Example no. 2 3 4th Comparison 1 pigment Pre-calcination treatment 0.1 - - 0/0 K2O 0.22 0.1 - - 0.39 % P2O5 0.1 0.25 Calcination 800 770 820 Temperature, ⁰ C 780 1.0 2.0 1.5 985 Time (hours) 1.5 2.0 Calcined pigment 0.10 0.14 0.035 % S 0.09 + 6.6 + 5.9 + 4.0 0.006 Spectral characteristics + 4.4 0.06 0.06 0.07 + 2.2 Average particle size, 0.1 0.22 micron 29 31 21 Surface area, m ² / g 14th -20.4 -20.1 -20.1 11.5 Photosensitivity -12.3 -3.0 Loss of reflection in 10 minutes

As can be seen from the above, there is a novel type of photosensitive titanium dioxide generated. This is finely divided and has slight differences in particle size. It has a high spectral characteristic, a large surface area and that necessary for use in the copy paper industry Photosensitivity.

Claims (3)

Patent claims: 1. A process for the production of a light-sensitive titanium dioxide with the crystal structure of anatase, in which the hydrous titanium oxide is bleached, washed, optionally treated with a phosphorus and / or potassium compound, heated, ground and sifted, characterized in that the washed hydrous titanium oxide with at most 0.3 wt .-% of a phosphorus and / or potassium compound, calculated as P2O5 or K2O and based on T1O2 treated, heated to a temperature of 760-825 ⁰ C, to an average particle size of 0.05 to 0 , 15 μπι is ground and sifted so that at least 70% of the particles have a diameter between 0.03 and 0.13 μπι. 2. The method according to claim 1, characterized in that the heated T1O2 at a ratio Steam / TiO2 how 5: 1 is steam milled. 3. Photosensitive titanium dioxide with the crystal structure of anatase, characterized in that it according to claim 1 has been obtained.