Treating process

A method for treating an inorganic powder

The present invention relates to a treatment method according to claim 1, wherein the inorganic powder is treated with an organic substance. According to the present invention, a process for treating an inorganic powder comprises polymerizing a reaction mixture of an ethylenically unsaturated monomer in the presence of a dispersed inorganic powder having a cationic charge on the surface of the particles, up to 200% by weight of said monomer, and subjecting said monomer to said powder. the polymerization time of the monomer, to coat said particles with a polymerized monomer.

The present invention relates to a process for coating particles of an inorganic powder with an organic polymer. The method minimizes the free polymer formed, which is not part of the coating, and all in all, the coating obtained is thicker than that obtained by the method without the use of ultrasonic vibration. The products are well dispersed and aggregation is minimal.

In general, the process initially involves preparing a dispersion of an inorganic powder to be coated, usually an aqueous dispersion, and, if necessary, modifying its particles so that they have a cationic charge on their surface. An ethylenically unsaturated monomer is then usually added to the dispersion of the inorganic powder and the polymerization is initiated by any suitable technique. For at least part of the polymerization time, the dispersion of the inorganic powder is subjected to ultrasonic vibration, which has the beneficial effects defined above. To further reduce the formation of free polymer, the amount of monomer should not exceed 200% by weight of the inorganic powder.

The method of the present invention can be used to coat particles of any inorganic powder, but the most interesting are inorganic pigments, extenders and fillers. In particular, inorganic pigments have been found to be the most useful in the process, and such pigments include titanium dioxide pigments, alumina pigments, antimony oxides, barium pigments, calcium pigments, zirconium pigments, chromium pigments, iron pigments and magnesium pigments. Extensions and / or fillers, such as silica, silicates, aluminates and in particular clays, can also be treated by the process according to the invention. Mixtures of pigments and extenders can also be treated, as can non-pigment forms of inorganic powders referred to as pigments. In the preferred method, the inorganic powder is a titanium dioxide pigment, preferably rutile titanium dioxide. The inorganic powder is preferably in finely divided form before coating and, if necessary, may be ground by suitable equipment to bring it into such a state.

In the polymerization, the surface of the particles of inorganic powder dispersed has a cationic charge. Usually, the inorganic powder has to be treated with a suitable compound to effect such a cationic charge, but in some types of powder the cationic charge can be achieved by lowering the pH of the aqueous powder dispersion below pH 7 by adding an acid. However, in many inorganic powders, the actual treatment with a surface charge modifier is necessary.

Usually the dispersion of the inorganic powder is treated with a suitable cation and examples of such cations are Al⁺, Zn²⁺, Th ^⁺, UC ^²* and Pd²⁺. However, the use of aluminum salts has been found to be the best because of their low price and ion size. Preferably, the surface charge modifier is an aluminum salt of an inorganic acid such as aluminum sulfate or aluminum chloride, but more preferably the salt is aluminum nitrate. If desired, the inorganic surface charge modifier may be partially replaced by an organic compound or, in addition, an organic compound which is cationic in the dispersion in question may be used. If desired, the organic compound itself may be a polymerizable monomer, but non-polymerizable cationic compounds may also be used. Preferably, the organic compound is a polyelectrolyte and suitable compounds include protein colloids, cationic guar gum, certain polymers of methacrylates, vinylamine and vinylpyridine. Methacrylic acid can be added to the powder dispersion, usually before the surface charge modifier, as an additive if desired.

The amount of surface charge modifier need only be sufficient to achieve the desired cationic charge density and can be determined by electrophoresis or other means. Typical amounts of surface charge modifier are from 2.5 to 7.5% by weight, for example aluminum salt, based on the weight of the inorganic powder, depending on the inorganic powder in question and the cation charge desired.

As described, in the process of the present invention, an ethylenically unsaturated monomer is polymerized to coat the inorganic powder particles with a polymer or, if desired, a copolymer. Any ethylenically unsaturated monomer that polymerizes in an emulsion polymerization system can be used in the present invention. The polymer usually obtained is preferably water-insoluble and, if necessary, can be crosslinked with a suitable crosslinking agent. Typical ethylenically unsaturated monomers are aliphatic or aromatic compounds containing a polymerizable unsaturated group, such as unsaturated carboxylic acids or unsaturated carboxylic acid esters. Preferably, two hydrogen atoms may be attached to one double bond-forming carbon atom, and vinyl monomers could be mentioned as such compounds. Typical useful monomers are acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid or its anhydride, fumaric acid, crotonic acid. Esters of acid monomers can also be used, such as methyl acrylate, ethyl acrylate, methyl methacrylate, butyl acrylate and ethyl methacrylate. Other monomers that can be polymerized to form the coating include styrene, vinyltoluene, alpha-methylstyrene, ethylene, vinyl acetate, vinyl chloride, acrylic ion, and the like.

If desired, two or more polymerizable monomers can be copolymerized. A crosslinking agent may also be present, and typical agents include di- or polyfunctional ethylenically unsaturated monomers, for example, ethylene glycol dimethacrylate, ethylene glycol diacrylate, allyl methacrylate, allyl acrylate, 1,3-butanediol diacinate, 1,3-butanediol diacrylate, The amount of such a crosslinking agent may be 10-50% of the total weight of said monomer used.

As described above, the amount of said polymerizable ethylenically unsaturated monomer does not exceed 200% by weight of the inorganic powder, and preferably the amount does not exceed 100% by weight thereof. In the most preferred method, the amount of said polymerizable ethylenically unsaturated monomer is 2-25% by weight of the inorganic powder.

If necessary, the inorganic powder is first formed into an aqueous dispersion by means of a dispersing agent. This dispersion can be ground, if desired, and then any necessary change in surface charge is added to the dispersion, followed by or before any desired organic polyelectrolyte or other additive. When the additive is an organic acid such as methacrylic acid, an amount of a crosslinking agent such as ethylene glycol imetacrylate may also be added.

In the process of the invention, the selected monomer is usually formed, prior to mixing with the inorganic powder, into an aqueous emulsion using, if necessary, a nonionic or anionic emulsifier or a mixture thereof to promote emulsification. Typical emulsifiers are sodium dodecyl benzenesulfonate and ethoxylated alkyl phenols, such as those in which the alkyl group is a nonyl, octyl or decyl group. Other known emulsifiers may be used.

When the polymerization is to be carried out in the presence of a crosslinking agent for a selected ethylenically unsaturated monomer or monomers, it is usually, but not always, added to the inorganic powder separately from the monomer emulsion.

Usually the polymerization is initiated with a water-soluble initiator such as a peroxy compound, a persulfate, a peracetate or an oxidation-reduction initiator, for example a salt of peracetic acid or an organic hydroperoxide or peroxide combined with a hydroserite or peroxide to a sulfite, bisulfite, bisulfite, bisulfite. The initiator is added at any suitable stage, for example before the monomer is added to the inorganic powder. Initially, only a portion of the required amount of initiator may be added, with the required final amount or amounts being added at one or more subsequent stages.

The polymerization of the added monomers is usually carried out at an elevated temperature and, depending on the ambient temperature, in a temperature range of 25 to 80 ° C, usually 30 to 50 ° C. The polymerization is usually, but not always, carried out in an inert atmosphere, for example a protective atmosphere of a gas, for example nitrogen.

In the process of the present invention, at least a portion of the polymerization is performed by subjecting the mixture of monomer and inorganic powder to ultrasonic vibration. Usually this is done by immersing the ultrasonic source in an aqueous mixture to be polymerized, and preferably the mixture is treated with vibration at the beginning of the polymerization. Ultrasonic vibration is a vibration known as power ultrasound, which usually uses frequencies of 20-50 kHz. The actual power applied to the mixture depends on its desired intensity and the volume of the mixture to be treated, and it has been found that quite advantageous results are obtained by using relatively low ultrasonic vibration powers. The power used for the polymerization mixture is preferably 15-60 watts / liter of mixture and most preferably 20-30 watts per liter. Usually the amount of inorganic powder in the mixture is 150-300 grams per liter, preferably 200-240 grams per liter.

By using lower ultrasonic vibration powers, a more even coating is obtained, as far as the degree of coverage. Higher powers cause the inorganic powder particles to disperse better. The use of lower concentrations of inorganic powder in the aqueous dispersion also improves the thickness and uniformity of the coating.

The coated particles produced by the process of the invention can be used as opacifiers in paints and other materials such as plastics and inks. The coating improves the dispersion of the inorganic substance in the organic matter and also has the effect of reducing the abrasion of the powder when manufacturing devices for plastic materials containing powders.

The invention is illustrated by the following examples.

IttI Jilil I 1 i Ml

Es i me rkkil

A general method for preparing coated inorganic powders is described in the following numbered steps, during which a dry nitrogen atmosphere was maintained in the reaction vessel.

Phase 1

The inorganic powder (190 g) was weighed into a 1 liter pot and 750 mL of N 2 purified (30-60 minutes, dry N 2) distilled water was added. The slurry was mechanically stirred at 20 ° C for 5-10 minutes.

Step 2

Methacrylic acid (MA) (1.9 g) was added and stirring was continued for 15 minutes at 20 ° C.

Step 3

Al (NO3) 3 (2.8 g) (Al) was added and stirring was continued for 10 minutes.

Step 4

Ethylene glycol dimethacrylate (EDMA, 0.525 g) was added and the temperature was raised to 40 ° C (20-30 minutes). Stirring was continued at 40 ° C for 15 minutes.

Step 5

Fresh 1% potassium persulfate solutions (0.25 g / 25 ml, solution A) and 1% sodium bisulfite solutions (0.25 g / 25 ml, solution B) were prepared, 1.8 g of solution A and 0.9 g of solution B were added to the kettle and stirring was continued for 15 minutes.

Step 6

Methyl methacrylate (MMA, 7.5 g) was emulsified in water (100 ml) with emulsifier (EA) (0.38 g) using an ultrasonic stick (5 minutes). The emulsion was added (5 ml aliquots) with stirring over 15 minutes.

Step 7

Ethylene glycol dimethacrylate (0.41 g) was added and the temperature was raised to 70 ° C (45-65 minutes).

Step 8

Additional aliquots of Solution A (7.2 g) and Solution B (3.6 g) were added and the polymerization was allowed to proceed for 4 hours at 70 ° C.

Step After 9 hours, the product was filtered, washed with water and dried overnight at 70 ° C.

The emulsifier was isooctylphenoxypolyethoxyethanol and was commercially available under the tradename TritonX ”.

By performing special experiments, which will be explained in detail below, the reaction vessel was ultrasonically tested in 2 ultrasonic baths (10-15 / cm 2 watts) and in other experiments with ultrasonic needles of different basic power, one having a maximum power of 225 watts (stick X) and one having a maximum power of 37 watts. (stick Y). Ultrasound was used according to three different programs, i.e.

Program

<td>I -</td><td>stages of</td><td> 1-5</td>

<td>E -</td><td>stages of</td><td> 1-7</td>

<td>P -</td><td>stages of</td><td> 5-7 .</td>

Twenty-six experiments were performed as described below under the conditions shown in Table 1. The wattages shown refer to the actual power applied to the reactants during the use of the ultrasonic coupling rod. In experiments 3-8, 11-18 and 21-26, the selected rod was used at 30% of the rated power and in other experiments at 60% of the rated power.

The amount of reagent shown is given in the overview (i.e. 1 = same; 1/2 = 1/2 of the amount in the overview, etc.).

table 1

<td rowspan="2">Test</td><td colspan="2">Ultrasound tube i kko /</td>

<td>watts / Duration</td><td>Powder</td>

<td> 1</td><td>and Iman</td><td>1 Ba₂SO4</td>

<td> 2</td><td>bath / W / E</td><td>1 Ba₂SO4</td>

<td> 3</td><td>Y / 47 / P</td><td>1 TiO₂</td>

<td> 4</td><td>X / 28 / P</td><td>1 TiO₂</td>

<td> 5</td><td>Y / 47 / E</td><td>1 TiO₂</td>

<td> 6</td><td>X / 28 / E</td><td>1 TiO₂</td>

<td> 7</td><td>X / 28 / I</td><td>1 TiO₂</td>

<td> 8</td><td>Y / 47 / I</td><td>1 TiO₂</td>

<td> 9</td><td>X / 55 / E</td><td>1 TiO₂</td>

<td> 10</td><td>Y / 41 / E</td><td>1 TiO₂</td>

<td> 11</td><td>Y / 22 / E</td><td>1 TiO₂</td>

<td> 12</td><td>X / 28 / E</td><td>1 TiO₂</td>

<td> 13</td><td>Y / 22 / I</td><td>1/2 TiO₂</td>

<td> 14</td><td>X / 28 / I</td><td>1/2 TiO₂</td>

<td> 15</td><td>Y / 22 / I</td><td>1/2 TiO₂</td>

<td> 16</td><td>X / 28 / I</td><td>1/2 TiO₂</td>

<td> 17</td><td>Y / 22 / I</td><td>1 TiO₂</td>

<td> 18</td><td>X / 28 / I</td><td>1 TiO₂</td>

<td>MA</td><td>A1N</td><td>EDMA</td><td>EA</td><td>&gt; OCT</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1/2</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1/2</td><td> 1</td>

<td> 1/2</td><td> 1/2</td><td> 1/2</td><td> 1/2</td><td> 1/2</td>

<td> 1/2</td><td> 1/2</td><td> 1/2</td><td> 1/2</td><td> 1/2</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1/2</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1/2</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

Table 1 (continued)

Experience the UI trajectory of the week / '

<td></td><td>watts / Duration</td><td>Powder</td><td>MA</td><td>A1N</td><td>EDMA</td><td>EA</td><td>OCT</td>

<td> 19</td><td>Y / 41 / I</td><td>1/2 TiO₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1/2</td><td> 1</td>

<td> 20</td><td>X / 55 / I</td><td>1/2 TiO₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1/2</td><td> 1</td>

<td> 21</td><td>Y / 22 / I</td><td>1 TiO₂</td><td> 2</td><td> 2</td><td> 2</td><td> 1</td><td> 2</td>

<td> 22</td><td>X / 28 / I</td><td>1 TiO₂</td><td> 2</td><td> 2</td><td> 2</td><td> 1</td><td> 2</td>

<td> 23</td><td>Y / 22 / I</td><td>1 TiO₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 2</td>

<td> 24</td><td>X / 28 / I</td><td>1 TiO₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 2</td>

<td> 25</td><td>Y / 22 / I</td><td>1 TiO₂</td><td> 2</td><td> 1</td><td>l (DVB)</td><td> 1/2</td><td> 1</td>

<td> 26</td><td>X / 22 / I</td><td>1 TiO₂</td><td> 2</td><td> 1</td><td>l (DVB)</td><td> 1/2</td><td> 1</td>

<td>DVB</td><td colspan="2">= divinylbenzene EDMA</td><td>: n</td><td>sij as ta.</td><td></td><td></td><td></td>

The obtained products were examined by electron microscopy and evaluated visually from micrographs. Overall, the study showed that the use of ultrasound improved the coverage of the product of Experiment 2 compared to Experiment 1.

It was found that the most favorable effect was obtained when ultrasound was used only at the beginning of the reaction, i.e. I was better than P, which was better than E.

The use of lower power levels also improved coverage compared to higher power, but higher power levels resulted in better dispersion of the coated particles.

Increasing the emulsifier / powder ratio improved the coverage. Reducing the TiO 2 content slightly improved the thickness and evenness of the coating. Similarly, increasing the monomer content improved the coverage and evenness of the coating.

The titanium dioxide used in the experiments was the reactor decomposition product obtained from the vaporase oxidation of titanium tetrachloride.

...... Example 2

The general procedure detailed in Example 1 was repeated with certain modifications, which are explained below in the detailed description of the experiments. The connection rod was rod Y and the voltage power was 22 watts in stages 15, unless otherwise stated. The same titanium dioxide was used as the powder as in Experiments 3-26.

Experiment 27

In step 2, acrylic acid (1.9 g) was added instead of methacrylic acid. The product was a polymer coated titanium dioxide.

Test 2 8

The emulsifier (EA) was used in three different amounts, 5%, 3% and 12% by weight of the monomer.

Similar degrees of powder coating were obtained for all, but the optimum level was about 10% by weight of the monomer.

Test 29

Butyl acrylate was used instead of methyl methacrylate. The powder was coated with a polymer.

Test 3 0

Styrene was used instead of methyl methacrylate. The product had a flat polymer coating.

Test 31

Instead of methyl imacrylate alone, a mixture of equal parts by weight of methyl methacrylate and butyl acrylate was used. The product was uniformly coated with polymer.

Experiment 3 2

Methyl methacrylate was replaced by butyl methacrylate.

An encapsulated product was obtained.

Experiment 3 3

Sodium dodecylbenzenesulfonate was used as the emulsifier (EA). A supercoiled product was obtained, but the coating was not as thick as that obtained by using the substance used in Experiments 1-24 as an emulsifier.

Test 34

Cetyltrimethylammonium bromide was used as the emulsifier. A similar product to Example 33 was obtained.

Experiment 3 5

Sodium dodecylbenzene sulfonate was used as the emulsifier and butyl acrylate was used instead of methyl methacrylate. A uniformly over-product was obtained.

Test 3 6

Methyl methacrylate was used in amounts corresponding to%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%,%, 23% and 25% of the polymer by weight of the powder. All produced coated products.

Test 37

Potassium persulfate was used in amounts of 1%,%, 4%, 5%, 6% and 6.5% by weight of the powder, and sodium metabisulfur was used in amounts of 1%,%, 3% and 3.25% by weight of the powder in steps 5. and 8. All produced polymer-coated products, but the optimum coating was obtained when 1.44% and 6.5% of potassium persulfate was used in steps 5 and 8, respectively, and sodium metabisulfite 0.72% and 3.25% in steps 5 and 8, respectively.

• «

Experiment 3 8

Instead of methyl methacrylate, a mixture containing 2 parts by weight of styrene and one part by weight of methyl methacrylate was used. The product was a polymer coated powder.

Test 39

Ultrasonic vibration was used in all reaction steps, but in pulses (about every 30 seconds) instead of continuous vibration. Again, a polymer coated product was obtained.

Test 40

The process of Example 1 was performed except that the power in step 1 was 50 watts. A polymer-coated powder was obtained.

When in Experiments 27-49 a reactant (or mixture) replaced one of the reactants described in Example 1, the same amount of substitute was used unless otherwise noted.

All products were visually analyzed from electron micrographs.